Title:
APPARATUS FOR FORMING AIRLAID WEBS
United States Patent 3825381
Abstract:
An apparatus for forming airlaid wood fiber webs at high speeds, which webs may be used for sanitary wipe and toweling applications, comprises a means for air laying a wood fiber continuum on to a foraminous carrier, a water spray for wetting the continuum, a transfer roll positioned to accept the wetted continuum surface to strip it from the carrier and a patterned roll with land areas and relieved areas on the roll surface and held in pressure engagement with the transfer roll to compress the continuum to form a closely spaced pattern of deep indentations or bonded zones with fluffy mounds of fibers therebetween.


Inventors:
Dunning, Charles E. (Neenah, WI)
Kellenberger, Stanley R. (Appleton, WI)
Application Number:
05/384705
Publication Date:
07/23/1974
Filing Date:
08/01/1973
Assignee:
Kimberly-Clark Corporation (Neenah, WI)
Primary Class:
Other Classes:
19/161.1, 19/302, 19/303, 19/305, 162/290, 162/299, 162/315, 162/348, 425/82.1, 425/101, 425/115
International Classes:
B27N3/10; D04H1/02; D21F2/00; (IPC1-7): B29C13/00
Field of Search:
425/83,91 83
View Patent Images:
Primary Examiner:
Spicer Jr., Robert L.
Attorney, Agent or Firm:
Wolfe, Hubbard, Leydig, Voit & Osann, Ltd.
Parent Case Data:


RELATED U.S. APPLICATIONS

This is a continuation of U.S. Pat. application Ser. No. 145,452, now abandoned, filed May 20, 1971, entitled "Apparatus for Forming Airlaid Webs"; Charles E. Dunning, U.S. Pat. Ser. No. 783,877, filed Dec. 16, 1968, for: Air-Formed Web and Method for Making Such Webs, now abandoned; Charles E. Dunning, U.S. Pat. Ser. No. 882,257, filed Dec. 4, 1969, now U.S. Pat. No. 3,692,622 for: Air-Formed Web and Method for Making Such Webs, a continuation-in-part of U.S. Pat. Ser. No. 783,877;

Charles E. Dunning and Stanley R. Kellenberger application entitled "High Speed Method for Forming an Airlaid Web," U.S. Pat. Ser. No. 145,546, filed May 20, 1971.
Claims:
We claim as our invention

1. In a machine for manufacturing a lightweight cellulosic web characterized by a three-dimensional continuum of fibers interrupted by a pattern of bonded fiber areas, in combination, a movable foraminous carrier, means for air laying a continuum of fibers on said carrier, a spray apparatus mounted downstream of said airlaying means for spraying water on to and moisturizing the continuum, a transfer roll mounted adjacent the carrier and presenting a moving surface diverging from the carrier, said roll being positioned to accept the wetted surface of the continuum and effect stripping of the continuum from the carrier, and a pressure bonding roll having a pattern of land areas, the rolls forming a nip through which the moisturized continuum is passed after separation from the carrier and being adapted to compress the continuum in the nip into a pattern of thin localized bonded fiber zones with zones of substantially unbonded fibers therebetween.

2. The apparatus of claim 1 in which said air laying means includes a plurality of rotary pickers mounted in series along and above the foraminous carrier, a plurality of positively driven fiber sheet feed means adapted to feed a fiber sheet into each of the pickers, drive means for imparting movement to the carrier and means for connecting said drive means and said fiber sheet feed means such that the speed of the fiber sheet feed means is directly proportional to the speed of the carrier.

3. The apparatus of claim 1 wherein said airlaying means includes at least one picker, and each of said pickers comprises a rotatable cylindrical drum having a plurality of picking teeth positioned circumferentially and laterally on the surface thereof, and an enclosure for the drum having its interior surface closely spaced relative to the picker teeth, a sheet feed guide for the fiber sheet, a forming duct operably connecting the picker with the carrier, a primary air passage for supplying air to transport fibers through the forming duct to the carrier, and a secondary air supply including a passage positioned to supply a sufficient amount of air to the picker teeth to substantially prevent fibers from remaining on the teeth.

4. The apparatus of claim 3 wherein the fiber sheet feed guide surface extends circumferentially adjacent the picking teeth and gradually curves to a point of substantially zero clearance relative to the tips of the picking teeth, said surface of the feed guide being not greater than a 10° angle when measured in relation to a line tangent to the picking teeth.

5. The apparatus of claim 4 wherein said feed guide separates the primary air passage from said sheet feed guide surface, said guide surface having a removable insert adjacent the area of zero clearance with the picking teeth, said insert being made of a material which will wear in perference to said teeth and means for adjusting the feed guide to compensate for the wear of said insert.

6. The apparatus of claim 5 which includes means in the primary air passage for constricting the flow therethrough to provide substantially uniform flow across the transverse width of the primary air passage.

7. The apparatus of claim 1 wherein the spray means includes a plurality of spray heads positioned laterally across the carrier, said spray heads being positioned in such a fashion that the spray patterns resulting therefrom provide substantially uniform application across the lateral dimension of the continuum.

8. The apparatus of claim 7 which includes baffle means for preventing the spray from reaching the lateral edges of the continuum and means for separating and removing the unsprayed edges from the rest of the continuum.

9. The apparatus of claim 8 wherein said means for separating and removing the edge portions comprises an air jet for cutting said edge portions of said continuum, an air knife for at least partially lifting said cut edge portions from said carrier and a suction pickup assembly for removing said edge portions from said carrier.

10. The apparatus of claim 7 which includes suction means located below the carrier and the spray heads, said suction means having a suction area generally coincident with the wetted area of the continuum and being sufficient to draw water into the continuum.

11. The apparatus of claim 1 which includes suction means mounted above the carrier and capable of substantially separating and accepting the entire width of the continuum from the carrier and means for moving the suction means transversely across the carrier and out of operative contact with the continuum.

12. The apparatus of claim 11 which includes an air knife positioned below said carrier and adapted to cooperate with the suction means to separate the continuum from the carrier.

13. A machine for producing a lightweight, bonded web of wood fibers, comprising in combination an endless foraminous movable belt having a longitudinally extending upper source and a lower return course, means for air laying a continuum of wood fibers on the upper course of said belt, a spray apparatus mounted downstream of the airlaying means for spraying water on to the surface of the continuum opposite the belt such that the continuum is moisturized and free water remains on the surface thereof, a transfer roll mounted adjacent the downstream end of the upper source of the belt, said transfer roll presenting a moving transfer surface diverging from the belt, said roll being positioned to accept the wetted surface of the continuum and effect the stripping of the continuum from the belt, and a pressure bonding roll having a surface with a pattern of land areas thereon and held in pressure engagement with said transfer roll, thereby forming a pressure bonding nip through which said moisturized continuum passes, the pressure being sufficient to compress the fibers of the moisturized continuum in said pattern of land areas into localized bonded zones with zones of substantially unbonded fibers therebetween.

14. The apparatus of claim 13 wherein the transfer roll and the downstream end of the upper course of said belt are spatially positioned so that at the closest point therebetween the continuum is in substantial contact with both the belt and the transfer roll.

15. The apparatus of claim 13 which includes adjustable support means for the downstream end of the belt capable of moving the belt into position to cause adherence of the moisturized continuum to the transfer roll.

16. The apparatus of claim 13 wherein the transfer roll is positioned adjacent the belt at a position where the belt is unsupported.

17. The apparatus of claim 16 wherein the distance between the belt and the transfer roll is less than the uncompressed thickness of the moisturized continuum and the belt is partially wrapped about the transfer roll.

18. The apparatus of claim 13 wherein said bonding roller has a steel surface and which includes a means for heating said bonding roller to provide a surface temperature of at least about 150° F.

19. The apparatus of claim 13 wherein said transfer roll has a steel surface and which includes means for heating the surface of said transfer roll to a temperature of at least about 200° F.

20. The apparatus of claim 13 wherein said transfer roll has a nylon surface and which includes a means for removing indentations in the surface of said transfer roll.

21. The apparatus of claim 20 wherein said means for removing indentations comprises a roll contacting said nylon surface transfer roll.

22. The apparatus of claim 13 which includes means for conveying the coherent structure away from said nip.

23. The apparatus of claim 22 which includes a doctor blade adjacent the transfer roll and positioned downstream of the nip, said doctor blade being adapted to remove the coherent structure from the transfer roll and to substantially prohibit wrapping around said transfer roll and means for applying air between the surface of the transfer roll and the doctor blade to assist in removal of the coherent structure from the transfer roll surface.

24. The apparatus of claim 22 wherein said means for conveying the coherent structure away from the transfer surface includes a second foraminous belt positioned downstream and adjacent said transfer roll and a suction means for removing the coherent structure from the transfer roll and to retain it on the belt.

25. The apparatus of claim 24 which includes means for drying said coherent structure.

26. The apparatus of claim 25 wherein the means for drying the coherent structure includes means for passing heated air through the structure.

27. The apparatus of claim 26 which includes means for passing heated air through the coherent structure while it is retained on the second foraminous belt to effect drying of the structure.

28. The apparatus of claim 13 wherein said transfer roll has a steel surface and said bonding roll has a pattern of raised surfaces which comprises a multiplicity of generally circular surfaces arranged in rows generally parallel to the axis of the transfer roll, said circular surfaces in one of said rows being laterally offset relative to surfaces in adjacent rows.

29. The apparatus of claim 28 wherein the rows of raised surfaces are each canted within the range of about 1/2° to about 3° relative to a line on the circumference parallel to the axis of the bonding roll, a line through an edge portion of the circular surfaces in one row intersecting an edge of the circular surface in an adjacent row.

30. The apparatus of claim 13 which includes means for cleaning the foraminous belt, said means being positioned upstream of the means for air laying the continuum so as to present a substantially clean surface for the formation of the continuum on the belt.

31. The apparatus of claim 13 in which said airlaying means includes a plurality of rotary pickers each having a forming duct for guiding fibers to the belt, and further including suction boxes positioned between the rotary pickers, the capacity of said suction boxes being sufficient to hold the continuum on the belt.

32. The apparatus of claim 31 which includes second suction boxes below the belt opposite the forming ducts to remove the air transporting the fibers to the belt and wherein adjacent suction boxes have a mutual wall separating said boxes and means for adjusting the position of the mutual wall to thereby vary the effective area of said boxes.

33. A machine for producing a lightweight, bonded web of wood fibers comprising in combination a first endless foraminous movable belt having a longitudinally extending upper course and a lower return course, means for air laying a continuum of wood fibers on the upper course of said belt including a plurality of rotary separators mounted in series along and above the belt for separating fibers from relatively dry pulp supplied to said separators and a forming duct associated with each separator through which the fibers pass to the belt, a first spray means mounted downstream of the plurality of separators for spraying water on to the surface of the continuum opposite the belt in such a fashion that the continuum is moisturized and free water remains on the surface thereof, a second foraminous belt positioned above and partially overlapping the first foraminous belt downstream of the first spray means, suction means adapted to remove the moisturized continuum from the first foraminous belt and retain the continuum on the second belt with the unsprayed continuum surface exposed, second spray means for wetting the exposed surface of the continuum, a transfer roll mounted adjacent the downstream end of the second foraminous belt, said transfer roll presenting a moving transfer surface which diverges from the belt and being positioned to accept the wetted surface of the continuum upon the stripping of the continuum from the belt, said second foraminous belt having a surface allowing preferential adherence to the transfer roll, and a pressure bonding roll having a surface with a pattern of land areas thereon and held in pressure engagement with said transfer roll to form a nip through which said moisturized continuum passes, said pressure engagement being sufficient to compress the fibers of the moisturized continuum in the nip into localized bonded zones with zones of substantially unbonded fibers therebetween.

34. The apparatus of claim 33 wherein the suction means includes a section having a suction area generally coincident with the wetted area of the continuum derived from the second spray means.

35. In a machine for manufacturing a soft absorbent, pattern pressure-bonded-web from air laid wood pulp fibers in combination, a movable endless foraminous belt having a longitudinally extending upper course and a lower return course, a plurality of power driven rotary separators arranged in a series along and above the belt and adapted to separate fibers from dry pulp supplied to said separators, a plurality of forming ducts for guiding said fibers to said belt, one of said ducts extending toward said belt from each of said separators, an air system comprising a number of blowers for supplying air to transport the fibers through said forming ducts to the belt to form a fiber continuum thereon, a number of suction boxes, one for each separator and positioned below the belt opposite each forming duct, air tubes connected to said suction boxes, and power driven fans for moving air through said tubes to create suction in the suction boxes, the capacity of said fans being sufficient to pull substantially all air transporting the fibers to the belt through the belt, water spray apparatus mounted over the belt downstream of the forming ducts for spraying water on to the exposed top surface of the continuum so the continuum is moisturized and free water remains on the surface thereof, a transfer roll adjacent the downstream end of the upper course of the belt presenting a moving transfer surface which diverges from the belt and receives the wetted surface of the continuum upon stripping from the belt, and a pressure bonding roll having a patterned surface of land areas and held against and forming a nip with said transfer roll through which said continuum passes, said pressure roll being adapted to compress the fibers in said areas into relatively thin, localized hydrogen-bonded zones with zones of substantially unbonded fibers therebetween.

36. A machine for producing on a continuous basis a sheet of wood fibers suitable for tissue and toweling applications comprising a continuous screen trained around upstream and downstream screen support rolls to provide a longitudinally moving main course and a return course, roll supports for a plurality of rolls of wood pulp sheet adjacent the upstream end of said screen main course and individual sheet supports for supporting pulp sheet fed from each of the rolls toward the upstream end of the main course of said screen, a series of air layers each including a fiber separator and a moving air fiber laydown device spaced along and above the screen main course starting at the upstream end, each air layer being supplied with at least one pulp sheet from a roll on one of said roll supports, the web from each successive air layer being superimposed on webs from the air layers located upstream thereof to build an uncompacted, fluffy multi-layer fiber web having a basis weight of about 5 to 50 lbs./2,880 ft.2, a water spray device for applying water droplets on the top surface of the multi-layer web as it approaches the downstream end of the main course of the screen, and a power driven transfer and bonding roll assembly with the screen and the transfer roll defining a nip immediately adjacent the turn of the wire around the downstream wire support roll for transferring the multi-layer web from the main course of the wire, and the bonding roll having a patterned surface forming a nip with the transfer roll, the assembly forcing the transfer and bonding rolls against each other with high pressure sufficient to compact the multi-layer web and integrate it into a single ply sheet and pattern-hydrogen-bond the wood fibers therein to form a lightweight sheet having properties suitable for tissue and toweling applications.

37. The apparatus of claim 3 which includes suction means below the carrier opposite each forming duct for removing the air transporting the fibers to the carrier and baffles in the suction means having a configuration designed to produce uniform air flow through the carrier in the cross direction.

38. In a machine for manufacturing a light-weight cellulosic web characterized by a three-dimensional continuum of fibers of paper making length interrupted by a pattern of bonded fiber zones, in combination, a movable foraminous carrier, means for air laying a continuum of fibers on said carrier including at least one separator mounted along said carrier for separating fibers from a fiber source supplied to the separator, a spray apparatus mounted downstream of the air laying means for spraying water onto the surface of the continuum, and means for separating the continuum from the carrier and for pressure bonding the fibers therein including a moving transfer surface diverging from the carrier and accepting the wetted surface of the continuum which preferentially adheres to said transfer surface to strip the continuum from the carrier, and means forming a nip through which the continuum is passed, said nip forming means providing a pattern of similarly shaped high pressure areas acting on the continuum to press and compact the fibers in said areas, spaced by uniformly relieved low pressure areas, the combination of said high pressure areas and relieved areas and moisture which penetrates the continuum from the wetted surface producing thin, localized, compacted bonded fiber zones in the continuum spaced by uncompacted fluffy mounds of fibers of substantially uniform height some of the fibers in the continuum being rearranged into at least partially a Z-direction orientation is a result of the action of the high pressure areas in the nip of engaging and pressing the fibers and producing the compacted zones, together with other fibers having a Z-direction orientation in their airliad state, providing a significant Z-direction fiber component in the mound areas and a web of overall substantially uniform thickness, said compacted and bonded zones providing coherency and strength.

39. The apparatus of claim 1 in which said means for airlaying includes a plurality of rotary pickers mounted in series along and above the foraminous carrier, a plurality of positively driven fiber sheet feed means adapted to feed a fiber sheet into each of the pickers, each succeeding picker in said series being operable to pick fibers from the fiber sheet fed thereto for addition to the fibers from the preceding pickers airlaid on the carrier, drive means for imparting movement to the carrier, and means for operating said drive means and said fiber sheet feed means such that the speed of the fiber sheet feed means is proportional to the speed of the carrier and the basis weight of the continuum airlaid on the carrier with fibers from said series of pickers is maintained substantially constant despite changes in speed of the carrier.

Description:
BACKGROUND OF THE INVENTION

This invention relates to a method and apparatus for manufacturing cellulosic sheet materials and, more particularly, to a method and apparatus for air forming and thereafter bonding to form webs from wood pulp fibers characterized by a desirable combination of strength, absorbency, and tactile properties and suitable for uses such as, for example, sanitary wipes and toweling.

Conventionally, materials suitable for use as disposable tissue and towel products have been formed on paper-making equipment by water laying a wood pulp fibrous sheet. Conceptually, this equipment is designed so that the configuration of the resulting sheet approaches a two-dimensional structure. This allows continuous operation at high speeds, and such sheets may be formed at speeds of 3,000 to 4,000 feet per minute. Indeed, recent developments have allowed sustained production at speeds of up to 5,000 feet per minute.

Following formation of the sheet, the water is removed either by drying or by a combination of pressing and drying. As water is removed during formation, surface tension forces of very great magnitude develop which press the fibers into contact, resulting in overall hydrogen bonding at substantially all the intersections of the fibers; and a thin, essentially two-dimensional sheet is formed. It is the hydrogen bonds between fibers which provide the sheet strength, and such bonds are produced even in the absence of extensive additional pressing. Due to this overall bonding phenomenon, cellulosic sheets prepared by water-laid methods inherently possess very unfavorable tactile properties (e.g. -- harshness, stiffness, low bulk, and and poor overall softness) and absorbency for use as sanitary wipes and toweling.

To improve these unfavorable properties, water-laid sheets are typically creped from the dryer roll; i.e., -- the paper is scraped from a dryer roll with a doctor blade. Creping reforms the flat sheet into a corrugated-like structure thereby increasing its bulk and simultaneously breaking a significant portion of the fiber bonds, thus artificially improving the tactile and absorbency properties of the material. But creping raises several problems. It is only effective on low (e.g., less than about 15 lbs./2,800ft.2) basis weight webs, and higher basis weight webs after creping remain quite stiff and are generally unsatisfactory for uses such as quality facial tissues. Because of this, it is conventional practice to employ at least two plies of creped low basis weight paper sheets for such uses. Only by doing this can a sufficiently bulky product with acceptable softness be prepared. Still further, the detrimental effects of the initial overall bonding in a water-laid paper sheet are not completely overcome.

Sanford et al. (U.S. Pat. No. 3,301,246) propose to improve the tactile properties of water-laid sheets by thermally pre-drying a sheet to a fiber consistency substantially in excess of that normally applied to the dryer surface of a paper machine and then imprinting the partially dryed sheet with a knuckle pattern of an imprinting fabric. The sheet is thereafter dryed without disturbing the imprinted knuckle-pattern bonds. While this method may somewhat improve the softness, bulk and absorbency of the resulting sheet, the spaces between the knuckle bonds are still appreciably compacted by the surface-tension forces developed during water removal and considerable fiber bonding occurs. Creping is still essential in order to realize the maximum advantage of the proposed process; and, for many uses, two plies are still necessary.

As will be apparent from the foregoing discussion, conventional paper-making methods utilizing water are geared towards the high speed formation of essentially two-dimensional sheets which inherently possess the inefficient attribute of initial "overbonding," which then necessitates a creping step to partially "debond" the sheet to enhance the tactile properties. Also, the extreme water requirements limit the locations where paper-making operations may be carried out. Such operations require removing a large quantity of the water used as the carrier, and the used process water can create an associated water pollution problem.

Air forming of wood pulp fibrous webs has been carried out for many years; however, the resulting webs have been used for applications where either little strength is required, such as for absorbent products, i.e., pads, or applications where a certain minimum strength is required but the tactile and absorbency properties are unimportant; i.e., various specialty papers. U.S. Pat. No. 2,447,161 to Coghill and U.S. Pat. No. 2,810,940 to Mills and British Pat. No. 1,088,991 illustrate air-forming techniques for such applications.

Indeed, heretofore, it has not been believed that air forming techniques could be advantageously used to prepare cellulosic sheet material that would be sufficiently thin and yet have adequate strength, together with softness and absorbency to serve in applications such as sanitary wipes and toweling.

The Dunning U.S. Pat. No. 3,692,622 discloses an aesthetically pleasing web having a combination of strength, absorbency and tactile properties suitable for such applications. This novel product is made by air forming wood pulp fibers to provide a three-dimensional continum of such fibers and thereafter pattern bonding the fibers by applying a limited amount of moisture and high pressure in a spaced pattern of small areas in the web.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to provide a method and apparatus for the manufacturing of such cellulosic webs. A related object is to provide a machine capable of making wide webs at speeds in excess of 1,000 feet per minute.

Another object lies in the provision of a machine which can make a product having the above identified properties with a capital investment considerably less than that required for cylinder or Fourdrinier machines for making water-laid products.

A still further object of the present invention is to provide a method and apparatus for the high speed formation of such a web with superior uniformity in the three dimensions of the web. A related and more specific object is to minimize the formation of visual irregularities in the web caused by clumps of fibers.

Yet another object is to provide a method and apparatus for forming such webs which minimizes fiber loss. A related and more specific aspect of this invention is to employ air recycling to minimize fiber loss in the formation of these webs.

A further object lies in the provision of a machine in which periodic replenishing of the fiber source can be made without interruption of continuous operation.

A more specific aspect of the present invention is to provide a machine wherein uniformity of the basis weight of the web may be readily maintained regardless of variations in the speed of the machine.

Yet another object of the present invention lies in the provision of a method and apparatus for transferring an air-laid substantially unbonded continuum from the surface on which it is formed into and then out of a bonding station wherein the continuum is transformed into a coherent structure.

Another and more specific object is to reduce the moisture content of the coherent structure in such a fashion as to retain, and even enhance, the soft texture of the coherent structure. A related object is to reduce the moisture content by employing through-drying.

Still another object provides a method and apparatus which minimizes the potentially disturbing effects of ambient air on the continuum during the manufacture of the web.

A still further object of the present invention is to provide a ready means of starting up the equipment.

Other objects and advantages of the present invention will be apparent as the following description proceeds, taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view illustrating an exemplary apparatus embodying the present invention;

FIG. 2 is a top plan view of the exemplary apparatus shown in FIG. 1;

FIG. 3 is a side elevation of a portion of the apparatus shown in FIG. 1, taken generally in the direction of the line 3--3 of FIG. 2, and showing the spatial relationship of the pulp feed, picker and forming duct at one of the four picking locations shown in FIG. 1;

FIG. 4 is a side view of a portion of the apparatus shown in FIG. 1 and particularly illustrates a portion of the drive assembly of the apparatus;

FIG. 5 is a top plan view taken generally in the direction of the line 5--5 of FIG. 4 and further illustrating the drive assembly;

FIG. 6 is a partial section of the view shown in FIG. 3 and showing the internal construction of the apparatus for picking and forming the continuum;

FIG. 7 is a sectional view taken generally along line 7--7 of FIG. 6, partly in cross-section, and illustrating the apparatus for providing substantially uniform flow in the cross machine direction and for removing the air used in transporting the fibers to the forming surface;

FIG. 8 is a cross-sectional view taken substantially along lines 8--8 of FIG. 6 and showing the internal surfaces of the forming duct;

FIG. 9 is a side elevation taken generally along line 9--9 of FIG. 2 and showing the moisture-increasing station;

FIG. 10 is a view taken generally along line 10--10 of FIG. 9 and further illustrating the moisture station;

FIG. 11 is a side elevation taken generally along line 11--11 of FIG. 2 and showing the apparatus for separating the trim from the wetted continuum and for removing the continuum from the forming wire prior to stabilized operation during startup;

FIG. 12 is another view taken generally along the line 12--12 of FIG. 11 and further showing the trim pickup and the continuum pickup;

FIG. 13 is a side elevation view taken generally along line 13--13 of FIG. 2 and illustrating one embodiment of the transfer and bonding station;

FIG. 14 is a view taken generally along the line 14--14 of FIG. 13 and further illustrating the transfer and bonding station;

FIG. 15 is an enlarged fragmentary view and showing one embodiment of the configuration and pattern of raised surfaces of a roller which may suitably be used for the bonding;

FIG. 16 is a schematic side view and illustrating another embodiment that may be used for the transfer and bonding station;

FIG. 17 is a schematic side view and illustrating yet another embodiment of a portion which may be utilized to carry out the transfer and bonding functions;

FIG. 18 is a schematic view and showing the air supply system for the apparatus of the present invention; and

FIGS. 19a and 19b are perspective views, enlarged and partially in section, illustrating the internal construction of a portion of the apparatus for picking and forming the continuum.

While the invention is susceptible of various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will hereafter be described in detail. It should be understood, however, that it is not intended to limit the invention to the particular form disclosed, but, on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as expressed in the appended claims.

DETAILED DESCRIPTION

Briefly, the machine shown in the drawings is capable, on a continuous, high speed production basis, of air laying wood pulp fibers and bonding such fibers into a web material suitable for sanitary wipes and toweling as disclosed in the Dunning U.S. Pat. No. 3,692,622 hereinbefore identified. Referring to FIG. 1, the machine in general comprises a pulp sheet feeding section 20, a fiber lay-down section 22, and a bonding section 24. The pulp sheet feeding section feeds one or more pulp sheets into the fiber lay-down section 22 in which the pulp sheets are separated into their component fibers and the fibers carried in an air stream to a moving belt to form a uniform continuum of unbonded fibers. The moving belt transports the fiber continuum to the bonding section wherein the continuum is transferred from the belt and a combination of pressure, water and heat is utilized to produce a plurality of spaced bond areas which transform the fiber continuum into a coherent structure that, after drying in a downstream portion of the bonding section, results in the soft absorbent web described in the herein-identified Dunning application.

Turning now to a more specific description of the apparatus of the present invention, the following detailed description is broken into subheadings generally corresponding to the foregoing sections of the apparatus.

THE PULP FEED SECTION

In this section, a source of fibers in combined form is provided and is forwarded to the fiber lay-down section. As shown in the illustrative embodiment, and referring to FIGS. 1 and 2, the pulp feed section 20 of the machine comprises a pair of similar A-frame structures 26 and 28, each of which carry or support a number of pulp rolls 30, typically relatively dry (e.g. -- 7 or 8 percent moisture by weight) pulp sheets having a basis weight of 200 to 300 lbs./2,800 ft.2 and lightly bonded. The pulp rolls 30 supply plies of pulp that are selectively combined to form multi-ply sheets 34 for feeding into the fiber lay-down section 22. As shown, each of the A-frame structures 26 and 28 carries six pulp rolls 30, the plies 32 of which are combined to form four multi-ply sheets 34. Thus, in the particular embodiment illustrated, the multi-ply pulp sheets 34 have a three-ply configuration, but it is to be realized that a greater or lesser number of plies may be used if desired, provided that the thickness of the pulp sheets 34 is within acceptable limits for use in the fiber lay-down section 22. The pulp sheets 34 are passed around rolls 35, 36, 37 and 38 to place them in the proper elevation for feeding into the fiber lay-down section 22 and for achieving coincidence or alignment of the plies. Desirably, rolls 35, 36 and 37 are provided with guide flanges (not shown) that insure the proper lateral alignment of individual plies being combined as well as of the multi-ply sheets 34. The sheets are carried by sloping trays or chutes 39 into the fiber lay-down section 22.

It should be appreciated that fluff-pulp batts may also be used as the fiber source in place of the multi-ply pulp sheets 34. However, since such batts are quite loose and may have considerably less integrity or strength than the lightly bonded pulp sheets of the exemplary embodiment, the pulp feed section used for such batts should be structurally different from that shown in FIG. 1. Apparatus for forwarding pulp batts to a picker are well known in the art.

THE FIBER LAY-DOWN SECTION

In this section, the fiber sheets are separated into their component fibers by picking and are then transported to a foraminous moving surface to form a fluffy, unbonded fiber continuum thereon. The divellication of the pulp sheet into its individual fibers should be carried out in such a fashion as to minimize fiber breakage and/or fiber degradation (e.g. -- caused by development of heat). Also, while the picking could be carried out at a single location, it is advantageous to use a number of locations in series with the basis weight of the continuum being thereby sequentially built up. In this manner, the speed of the unit can be increased without sacrificing uniformity of the continuum or the quality of the picking. To this end, and as shown in FIG. 1, the multi-ply pulp sheets 34 are fed to multiple picking assemblies or pickers, herein shown as four pickers, including an upstream picker 40 and downstream pickers 42, 44 and 46, each of which is adapted to separate fibers from the pulp sheets 34 fed to them and carry the individual fibers to a foraminous forming surface, depicted as an endless foraminous flexible screen, wire or belt 48 having a longitudinally extending upper course and a lower return course and adapted to convey the fibers downstream to the bonding section 24. The pickers 40-46, identical in construction, each divellicate one of the multi-ply pulp sheets 34 into its component fibers and carry them to the belt to form a composite continuum of unbonded fibers thereon.

To feed the multi-ply pulp sheets into a picker (considering as exemplary the upstream picker 40), there is provided (FIG. 3) a sheet-feeding assembly 50 which includes feed assembly roll pairs 52, 52' and 54, 54' having transversely ribbed surfaces (not shown) for positively gripping the multi-ply sheet 34. Rolls 52 and 54 are journaled in assembly frame section 56 while rolls 52' and 54' are journaled in assembly frame section 58. The rolls are driven by a gear train which includes a drive gear 60 for positively advancing the sheet into the picker 40. Downstream roll pair 54, 54' may desirably be provided with a slightly larger diameter (e.g. -- 0.01 inch) to insure that a positive pulling force is maintained on the pulp sheet.

The sheet-feed assembly 50 comprises the sole advancing force on the plies being drawn from the rolls 30, although other advancing means within the pulp sheet feed section 20 may be provided. In this connection, it should be noted that during operation of the picker 40, forces acting on the multi-ply sheet 34 during divellication tend to advance the sheet; and the sheet-feed assembly roll pairs 52, 52' and 54, 54' may in fact exert forces that positively restrain the advancing movement of the sheet 34 to insure a proper rate of feed into the picker 40.

To initially thread the sheet 34 into the sheet-feed assembly during start-up or when an expended roll 30 is replaced or when a pulp jam-up occurs, the upper frame section 58 of the sheet-feed assembly is pivotable about an axis 62 of the drive gear 60. Thus, rolls 52', 54' may be pivoted away from their respective roll pair 52, 54 to allow ready access to the interior of the assembly. To accomplish the pivoting, a hydraulic or air cylinder 64 is connected to the upper frame section 58 and to a fixed portion of the structure of the fiber lay-down section 22.

In keeping with the invention, the pulp sheet 34 is positively driven down a passage 66 (FIG. 6) to the picker 40 which includes a rotatable cylindrical drum 68 flange a plurality of picking teeth 70 positioned circumferentially and laterally along its surface. The picker teeth may suitably have a height of about three-eighths inch, a pitch of about three-eighths inch and number about 16 to 24 per square inch of circumferential surface area of the drum. As illustrated, the picker is of the type described in the copending U.S. Pat. application of Appel and Sanford, Ser. No. 882,258. The drum has an axis 72 journaled in bearing blocks 74 on opposite sides of the picker. The pulp sheet travels downwardly in the passage 66 in a direction generally circumferential to the surface of the drum 68 and is urged into contact with the picking teeth 70 by a pulp-sheet feed guide 76 having a surface 78 which gradually curves to a point 80 of approximately zero clearance relative to the tips of the picking teeth 70. As shown in FIG. 3, the clearance between the feed guide 76 and the picking teeth can be adjusted by changing the setting on a micrometer adjusting screw 81. This allows an adjustment to be made when operation results in excessive wear on the feed guide. Also, the pulp sheet feed guide 76 is securely held in place during normal operation but is attached to a member 82 of the picker frame structure by a spring 84 or the like which provides a safety release enabling the point of minimum clearance 80 to widen in the event the pulp sheet becomes jammed between the guide and the drum or, more remotely, when a hard foreign object enters the picker.

The feed guide 76 (FIG. 6) is preferably made of a hard metal such as steel and has a section 86 including the guide surface 78. The section 86 should desirably comprise a heat conducting material such as aluminum to dissipate heat generated at the point of approximately zero clearance 80 during rotation of the drum 68. Section 86 may include a removable insert 87 preferably made of a resilient material and used to allow maintainenance of approximately zero clearance at the point 80 while avoiding excessive wear on the picker teeth. The material should not cause excessive wear on the picker teeth yet should be sufficiently durable to provide a reasonable operational life for the insert. In addition, the material used should be readily machineable, have a moderately high softening point (e.g. -- above about 280° F.) and should not cause sparks during operation. While any material meeting the above criteria may be used, it has been found desirable to form the insert from a "Delrin" acetal resin (E. I. du Pont de Nemours & Co., Wilmington, Delaware).

As the pulp sheet 34 is urged toward the picker teeth, individual fibers are separated from the multi-ply sheet and are driven past the point of approximately zero clearance into a forming duct 88 generally constructed in accordance with the forming duct set forth in Appel U.S. Pat. No. 3,606,175.

In brief, the forming duct 88 has an upstream wall 89 and a downstream wall 90 connected by side walls 91 (FIG. 8) to form a completely enclosed duct. The cut is angularly disposed relative to the belt 48 with the downstream wall 90 diverging from the upstream wall 89 at an angle of 5°, perhaps up to about 12°, to produce a forming duct with a larger cross-sectional area near the belt is compared with the area adjacent the point where the fibers enter the duct. The lateral end walls of the duct may desirably slightly converge (e.g. -- from about 49 inch width to 48 inch width for the exemplary apparatus). As shown in FIG. 8, all of the internal corners of the duct are curved with a definite radius of curvature to substantially prohibit the formation of low velocity stagnant areas in the corners that would enable fiber buildup. Such buildup could produce fiber clumps which would eventually drop onto the belt and detract from the uniform appearance of the continuum. A radius of curvature of about 5/16 inches has been found to be suitable.

It is desirable for the walls of the duct to be made of an electrically conducting material such as aluminum or steel so that any electrostatic field present will be substantially uniform across the interior surface of the duct. The substantial uniformity of such field minimizes the possibility of any isolated areas with increased electrostatic potential that would exert a force on the fibers and in turn steer the fibers passing through the areas to cause nonuniform formation of the fiber continuum. Although the walls may be made of a nonconducting material, it would be necessary to control the static electricity of the fibers themselves.

The individual fibers, separated from the pulp sheet and directed into the forming duct, are transported onto the wire to form a fiber continuum thereon. In accordance with one aspect of this invention, an air system and controls are employed to provide a controlled air movement which enhances separation of the picked fibers from the picker teeth, minimizes the development of secondary flow or vortices that could result in fiber clumping, achieves substantially uniform flow in the cross direction and transports the individual fibers through the forming duct to the wire 48 with the substantial avoidance of fiber clumping or fiber buildup on the walls of the duct.

To this end, and referring to FIGS. 1, 6 and 18, fans 92 supply air through ducts 93 to each of the pickers. The air flow is divided by adjustable flow splitters 94 into primary air ducts or passages 96 and secondary air ducts or passages 98. The flow splitters 94 are adjustable to control the ratio of air volume passing into the primary and secondary passages; and it has been found suitable to have the primary passages carry approximately twice the air volume as the secondary passages 98.

In keeping with the invention, a primary air flow of substantially uniform cross direction flow with a minimum of secondary flow or vortices is provided. Thus, as shown in FIG. 7, air flows to the left in the primary air passage 96 with the top wall of the passage sloping downwardly across the cross direction width of the pickers as indicated at 97 and downward through baffle plates 99. Also, the tapered shape across the passage 96 (FIG. 1) should compensate for friction in the flow and should be dimensioned to provide substantially uniform flow across the cross machine direction. The baffles should be sized and spaced to first eliminate any component of flow or velocity transverse to the lengthwise dimension of the baffles and then to smoothly bring the separate flows together quickly enough to prevent significant head losses from taking place but not so rapidly that separation of flow takes place. This can be achieved, for example, by forming the baffles 99 with a uniform thickness preferably about three times the distance between adjacent baffle plates throughout about approximately one-half of their length and with a taper to a point with an angle not greater than about 10° relative to the direction of flow (substantially vertical as shown in FIG. 7).

The primary air passage 96 (FIG. 6) exiting from the baffle plates curves inwardly toward the picker teeth and then turns generally tangent to the rotating drum at the point the air enters the forming duct 88. To provide the feed guide 76 with a geometrical configuration having the requisite strength requirements for the typical operating conditions, the primary air passage 96 must undergo a number of turns. Also, it is desirable to restrict the flow of air through the primary air passage to increase its velocity and to provide an evening effect across the cross direction of the wire. It is preferred to make this restriction (FIG. 6) after the turns in the primary air passage so that such turns are made with a minimum air velocity since increasing air velocity in turn increases the likelihood of creating secondary air currents.

The air flow through the primary air passage (termed the "primary air") joins with the "process air" from the picker to transport the fibers to the wire. As shown in FIG. 6, the cylindrical drum 68 is substantially completely enclosed by an enclosure 100. The picker drum (e.g. -- about 18 inches in diameter) is generally rotated at a relatively high speed (e.g., from 1,700 to 3,000 rpm) and thus creates an appreciable pumping action, which creates the "process air" referred to that tends to carry air as well as fibers around the drum as it rotates. Desirably, and in accordance with the herein identified Appel application, the air velocity carrying the fibers away from the teeth is coordinated with that of the primary air flow to provide a smooth merger and with minimal development of secondary flow or vortices.

In keeping with the present invention, a source of secondary air is provided which functions to aid in separation of the fibers from the picker teeth and to minimize flow disturbence which would be otherwise created by the "process air." Also, the secondary air source supplies the air that becomes the "process air." Thus, as seen in FIG. 6, a secondary air passage 98 extends through a flow evener 101 and terminates in a cross direction opening 102. The secondary air passing through the opening 102 should be directed to oppose the pumping action of the drum 68 and should create a sufficient pressure to effectively deflect the "process air" into the forming duct. This tends to strip or "doctor" the fibers from the picker teeth. Thus, the secondary air substantially limits the passing of primary air as well as "process air" from following around the rotating drum and collecting on the leading edge 104 of the wall 89. Although there may be a small amount of fibers continuing around the drum, the proper balancing of the secondary air substantially reduces the number of fibers following around the drum to a minimum.

The volume of secondary air required is dependent upon the picker geometry, the rotational velocity of the drum 68, and the volume of air flowing through the primary air passage 96. The flow splitter 94 may be adjusted so that the secondary air is balanced relative to the primary air; and, when such condition is reached, substantially all of the fibers properly separate from the picker teeth and do not continue around the drum or collect on the leading edge. One practical method of determining the balance is to provide a small window 103 (covered by any suitable transparent material) in downstream wall 90. Fiber collection on the leading edge can then be visually determined. Proper balance is achieved when substantially no fibers are collecting at the leading edge 104.

Pursuant to one aspect of the present invention, the enclosure 100 is closely spaced in relation to the outer tips of the teeth 70 to allow the teeth to sweep fibers from the surface so as to avoid fiber hangup or buildup thereon. If the space between the enclosure and the picker teeth were of a greater distance, the possibility of the generation of secondary currents would thereby be increased which could produce secondary flow defects or vortices at the point the primary air and "process air" merge to possibly detrimentally affect the uniform formation of the fiber continuum.

Provision is also made for the prevention of secondary air currents or vortices passing around the ends of the drum 68 and onto the drum surface by providing a flange 105 (FIG. 6) at each end of the picker drum, the flange 105 having a height substantially equal to the height of the picker teeth and extending completely around the circumference of the drum. Referring to FIGS. 19a and 19b, recess 106 is provided at opposite ends adjacent the leading edge 104 for receiving the flange 105 in close spaced relation. Thus, the end of the rotating drum is effectively sealed from the forming duct 88 to substantially prohibit undesirable secondary air currents from entering the forming duct and disrupting the uniform flow of fibers.

With the individual fibers being transported in an air stream to the wire, suction means are provided to insure proper lay-down and formation. Each of the pickers 40-46 thus have a primary partial vacuum system immediately below the wire and positioned opposite the respective forming duct 88 to accept the air flow passage through the duct. The amount of suction is controlled so that there is substantially no flow parallel to the wire which would disrupt the continuum being formed. Practically speaking, this means that the suction should be sufficient to remove all the air used to transport the fibers to the wire and yet not be so excessive as to pull in any significant quantity of outside air. As seen in FIGS. 6, 7 and 18, at each picker location, a duct 108 is connected to a fan 110 which is operable to pull the air through the belt 48. In keeping with the invention, the machine direction width of the suction opening can be readily varied. Thus, immediately adjacent the underside of the belt, a pair of transverse movable walls 112 (FIGS. 6 and 7) are provided to adjust the effective area of the primary suction. Each of the walls 112 has a keyed slide 114 movable relative to a guide member 116 that is attached to each of the sides. A rack 118, having a number of teeth on its upper surface, is attached to the wall 112 with the teeth of the rack 118 engaging a rotatable gear 120 attached to a shaft 122 which may be rotated by an operator. Rotation of the shaft 122 moves one of the walls 112 longitudinally with respect to the forming duct 88 to gain the desired machine direction width for optimum operation.

To provide uniform suction or vacuum across the full width of the belt, a number of baffles 124 (FIG. 7) are located within the duct 108 and are fixed to the sides of the duct near its upper opening. The baffles are adjustable downstream within the duct by means of threaded nuts 126 located on opposite sides of each of the baffles on a fixed threaded shaft 128.

In accordance with a further aspect of the present invention, uniformity of the basis weight of the continuum being formed is provided regardless of variations in machine speed. To this end, the pulp feed and the wire are commonly driven so that a variation in wire speed will automatically vary the pulp feed speed. Turning to FIGS. 4 and 5, each of the sheet feed assemblies 50 is driven by a common shaft 140 that extends longitudinally adjacent each of the feed assemblies 50. The longitudinal shaft 140 is rotatably journaled in a number of bearing blocks 142 positioned adjacent each of the feed assemblies. The sheet feed assemblies 50 are driven by a timing belt 144 or the like engaging a pulley 146 secured to a right angle gear reducer 148 having a shaft connected directly to the drive axle 62 of the sheet feed assembly (See FIG. 3). The timing belt provides a positive drive without slippage to coordinate the speed of pulp sheet feed with the speed of the belt 48. In addition to passing around the pulley 146, the belt 144 also passes around a pulley of clutch assembly 150 which may be disengaged from the shaft 140 to permit shutdown of any or a combination of the sheet-feed assemblies 50. A conventional tensioning roller 152 is positioned to provide proper tension to the belt 144 intermediate the clutch 150 and the pulley 146. The longitudinal shaft 140 itself is driven by a main shaft 154 which provides the primary drive for the apparatus including the foraminous wire 48. The main shaft 154 terminates at an infinitely variable speed regulator 155, the output of which is connected to the longitudinal shaft 140 by means of timing belts 156 and 158 or the like carried by pulleys 160 and a pair of conventional tensioning rollers 162 provided for the belts 156, 158. The speed of the pulp feed assemblies is proportional to the output speed of the speed regulator 155; and, therefore, the basis weight of the continuum of fibers being formed on the belt may be maintained substantially constant even though the belt speed may vary between speeds well below 1,000 ft./min. up to the optimum speed in excess of 1,000 ft./min.

By providing the capability of isolating any of the pulp sheet feed assemblies, continued operation of the apparatus is possible in the event that one of the picker assemblies or sheet feed assemblies is malfunctioning. Additionally, by selectively staggering the depletion of the pulp rolls 30, that is, by having the three rolls 30 making up one of the pulp sheets 34 running out at times different from other rolls, it is seen that continued operation of the apparatus may be performed by shutting down the pulp sheet feed assembly 50 associated with the sheet 34 being depleted, supplying new rolls 30 in their place, while increasing the speed of the pulp sheet assemblies to compensate for the one shutdown, and thereby continue forming a continuum of fibers having substantially the same basis weight as that being produced prior to shutdown. Thus, by selectively staggering the sources of the multi-ply sheets 34, continued operation may be achieved.

THE BONDING SECTION

In this section, water is sprayed onto the fluffy, unbonded continuum; the unusable edges are trimmed off; the continuum is removed from the wire during startup and then transfer of the wetted continuum off the forming wire is effected; bonding of the continuum is carried out; and the coherent web is then dried to remove excess water.

The formed fiber continuum is thus first carried on wire 48 to a moisturizing station, indicated generally at 176 (FIGS. 9 and 10). A number of spray nozzles 178 are secured to a transverse bar 180 above the plane of the continuum. The height of the nozzles above the continuum should desirably be adjusted to provide maximum penetration of the water to the interior of the continuum, and the cross-direction spacing should be such that the spray patterns from the nozzles achieve a substantially uniform cross-directional water application. For high speed operation, it is generally desirable to apply water in an amount from 20 to 60 percent by weight of the wetted continuum.

In keeping with the present invention, baffles are provided which serve to prevent water from contacting the wire and the extreme edges of the continuum, which edges are typically ragged or fuzzy (and often of different basis weight from the rest of the continuum) and must be trimmed from the useful portion of the continuum. To this end, a pair of baffle plates 182 are provided along each edge of the continuum to effectively limit application of water to such edges. Below each of the baffle plates 182 are curved troughs 184 which collect water run off and carry it to a drain or the like (not shown).

Pursuant to a further aspect of the present invention, suction means are provided to enhance penetration of the sprayed water into the continuum and to minimize the amount of water which deflects off the continuum surface (commonly termed "overspray"). Thus, as seen in FIGS. 9, 10 and 18, a moisture penetration suction box 240 is located below the spray nozzles 178 under the belt 48. A fan 242 produces the suction for box 240. A partial vacuum of from 2 to 10 inches water will be suitable for most purposes. The machine direction dimension of the box must be carefully coordinated with the spray patterns of the nozzles 178 since an insufficient length will result in overspray while too long a dimension or length will tend to undesirably dry out the continuum. Typically, the lengthwise dimension may vary from about 8 to 24 inches. Similarly, the cross-direction dimension of the box should extend desirably only out to the top edges of the baffle plates 182 to minimize or eliminate air flow under the plates which would tend to carry water droplets with it.

Subsequent to being wetted at the moisturizing station the fiber continuum is conveyed to a trim and pickup station indicated generally at 190 (FIGS. 11, 12 and 18). Since the outer edges of the fiber continuum may be somewhat ragged, uneven and thinner, such edges may be trimmed to form a continuum having substantially even edges and basis weight. To trim the edges, a pair of air jets 192 are positioned to cleanly cut the edges, the unusable edges perhaps amounting to about 1/2 to 1 inch from each side. Immediately adjacent and downstream of the air jets 192 are a pair of suction heads 194 having a width generally corresponding to the width of the trimmed edges. Immediately under each of the heads 194 is an air knife 195 also having a width corresponding to the width of the trimmed edges; the knives 195 being adapted to supply air upwardly through the wire 48 to aid the heads 194 in removing the trimmed edges. The suction heads 194 merge into a duct 196 which is connected to a fan 198 providing air movement therein which produces a partial vacuum pickup which literally sucks up the trimmed outer edges.

Following trimming, and in accordance with a still further aspect of the present invention, a continuum pickup assembly is provided to automatically strip the continuum from the wire until equilibrium operation is achieved, i.e. -- the fiber continuum reaches the desired basis weight and uniformity. The assembly may then be moved out of its operative position so as to allow the continuum to pass and transfer into the bonding station. As seen in FIGS. 11, 12 and 18, the continuum pickup assembly includes a fan 200 connected to a duct 201 and a movable duct 202 dividing into two ducts 204, each having a canopy 206 terminating in a slot 208 extending transversely across the entire width of the continuum. The fan provides a vacuum in the slot 208 of sufficient magnitude to pickup the complete continuum during startup or threading which are normally conducted at speeds of about 100 ft./min. or less. To assist in the pickup, it may be desirable to use an air-knife, such as is shown at 209.

The duct 202, the ducts 204, and the canopies 206 form a unitary structure that is suspended on slide brackets 210 movable on a support rod 212. A chain 214 or the like is carried by two sprockets 216 and 218, with the sprocket 216 having a handle 220. The chain is connected to one of the canopies 206 as is shown at 222 and rotation of the handle 220 is operable to move the continuum pickup assembly to the left as shown in the dash lines of FIG. 12. Thus, in keeping with the present invention, when the startup has produced a suitable continuum, an operator can turn the handle 220 and move the assembly transversely across the wire. Progressively less of the continuum is exposed to the vacuum, and the increasing unexposed portion remains on the wire and automatically transfers to the bonding section. This allows initiation of the transfer operation with less than the entire width of the continuum, perhaps only a few inches as opposed to a full width of 46 inches or so. To insure a uniform edge as the width of the fiber continuum increases, an air jet 224 may be provided at the end of the slot 208 as viewed in FIGS. 11 and 12.

In accordance with an important aspect of the present invention, means are provided to allow stripping of the wetted, unbonded fiber continuum from the wire and entry into the bonding section so that a coherent web can be formed from the flimsy continuum. To this end, stripping is effected by bringing the wetted surface of the continuum into sufficiently close proximit to a moving transfer surface diverging from the wire that adherence to the transfer surface results. It is critical to the transfer step, as will hereinafter be detailed, that a certain amount of "free water" be present on the surface of the continuum.

As shown in FIG. 13, the belt 48 carrying the fiber continuum is passed around a horizontally adjustable belt-support roll 232 which may have a perforated surface and a suction box 233 for holding the continuum on the roll as the direction of the continuum is changed. A transfer roll 234 is positioned downstream and adjacent to roll 232 and presents a moving surface diverging away from the belt. The transfer roll may be made of a hard material such as steel or a softer material having some resilience such nylon, for example. The specific requirements will be further amplified in connection with the discussion of the bonding step.

The gap can be varied within certain limits to effect transfer in one of two different modes, termed the "rolling mode" and the "stretch mode." In the rolling mode, the gap should be less than the uncompressed thickness of the continuum. As an example, for a web of about 14 lbs./2,800 ft.2, the gap should be about 0.015 inches, but not less than about 0.005 inches. While transfer can take place with smaller gaps, care must be taken to preclude substantial compressing of the continuum, as compressing may detrimentally affect the bulk and softness of the resulting web. Under conditions of the rolling mode transfer, the capillary attraction forces act substantially normal to the plane of the web, and therefore only small tension forces are present in the transfer which would tend to stretch or elongate the continuum. Sufficient free water (i.e., -- unabsorbed by the fibers) for the transfer will be present on the continuum surface when the amount of water added is within the range herein set forth and the suction below the spray is as has been set forth. This will also provide free water within the continuum which will add integrity for the continuum to allow transfer without significant disruption of the continuum.

In the stretch mode transfer, the clearance or gap between the belt 48 and the transfer roll 234 is of sufficient size so that there is no simultaneous contact of the continuum with both the belt and the transfer roll, even at the point of closest clearance. Due to this lack of contact, the continuum is pulled off the belt by tension forces created by the transfer roll. Since these forces are in the plane of the continuum, the continuum may be stretched somewhat more than in the rolling mode of transfer.

It should be appreciated that some fiber buildup may occur on the wire 48, particularly after sustained operation for a period of time. Any buildup is undesirable, and it may be necessary to include some means for cleaning the wire. As shown in FIG. 1, an air knife 235 may be positioned on the return course of the wire to carry out removal of fiber buildup. Additionally, a brush roll 235a may be positioned opposite the air knife and be rotated, preferably in a direction opposite the movement of the belt, for assisting the air knife in cleaning the belt.

Having now been transferred to the transfer surface, the wetted fiber continuum is bonded in accordance with the present invention by selectively applying pressure in predetermined areas to form a coherent web as disclosed in copending U.S. Pat. application Ser. No. 882,257. As shown in the embodiment of FIGS. 13 and 14, the continuum is passed around the transfer roll 234 and into a nip formed between the transfer roll which serves as an anvil or backup roll and a bonding roll 236 having a pattern of raised surfaces thereon. The bonding roll has its axis journaled in vertically adjustable bearing blocks 237, located at opposite ends thereof and vertically controlled by a pair of hydraulic cylinders 238, which are in turn suitably controlled by conventional apparatus (not shown). Elongation of the cylinders moves the bonding roll nto contact with the transfer roll to form a nip. The roll should suitably be provided with a means of internal heating, such as by internal passages (not shown), to allow the surface of the bonding roll to be heated by passing any conventional heating medium, such as oil, through the passages.

To achieve proper bonding at the bond areas, the cylinders 238 should urge the bonding roll into contact with the transfer roll at the raised surfaces under point pressure that is sufficient to cause the fibers in these points or areas to be completely bonded. The exact pressure required will vary and will depend, in part, on the machine speed. With a nylon backup roll and with machine speeds approaching 1,000 ft./min., the pressure on the raised surfaces should be at least about 5,000 p.s.i. A steel anvil roll allows development of higher pressures (up to about 70,000 p.s.i. for soft steel); but it may be desirable in some intances to use a resilient transfer and backup roll to minimize wear on the raised surfaces. It is not desired to employ passing through the nip and retain their substantially unbonded airlaid state. Thus, for a web of 14 lbs./2,880 ft.2, the heights of the raised surfaces may vary from about 0.010 to 0.030 inches, while the land areas may vary from about 0.000024 to 0.003 square inches. an anvil roll as hard as the bonding roll because of wear problems. Similarly, the use of an anvil roll much more resilient than a nylon roll (e.g. -- Young's Modulus -- 3.5 × 105 p.s.i. and Poisson's ratio -- 0.4) is not preferred since the increased deformation will now allow the development of the pressures in the high pressure areas provided by the raised surfaces necessary for the bonding operation.

A particularly suitable pattern for the land areas providing the raised surfaces of the bonding roll is shown in FIG. 15. The land areas 320 have a generally similar shape herein shown as circular and are arranged in adjacent rows, each of which may be canted at an angle α within the range of about 0.5 to 3° relative to a line on the circumference of the roll 296 which is parallel to its axis. The circular surfaces within each of the rows are slightly overlapping with surfaces in adjacent rows so that a line 322 will intersect surfaces 320 in adjacent rows. Canting of the rows reduces the wear taking place on the raised surfaces 320 and also minimizes the unit pressure variation in the nip. Canting is accordingly more desirable when a steel transfer roll is employed since tolerances are more critical in such instance.

While a circular shape for the land areas is desirable because this may minimize wear on the points any other geometrical shape may also be used such as, for example a diamond shape. The points should have a smooth surface and be raised above the overall surface of the bonding roll and have a minimum taper, consistent with the requirements that the points should be able to withstand breakage or undue wear under the pressure conditions involved. Stated another way, in keeping with the present invention, it is preferred to provide uniformly relieved areas on the roll surface around the land areas, which exert low pressure on the continuum such that in these low pressure areas the fibers are compressed and forced together by the rolls but the compaction is minimized leaving zones in which the fibers are not bonded after.

Further, to produce a web having the desirable properties of that disclosed in the Dunning U.S. Pat. application, Ser. No. 882,257, the area of the continuum which is bonded and the spacing of the raised surfaces is important. Typically, the pattern of raised surfaces should provide a total bonded area for the resultant web of about 5 to 40 percent of the surface area. A higher percentage of bonded area may detrimentally affect absorbency and tactile properties while a lower percent of bonded area generally produces a web of insufficient strength. Strength is also somewhat dependent upon machine speed, and higher machine speeds desirably have a higher percentage of bonded area. For example, with a 14 lb./2,800 ft.2 sheet at a speed of 1,000 ft.min., it is preferred to employ a pattern such that the total bonded area will be about 25-30 percent. The individual bond areas should also be preferably spaced apart from one another a distance that is less than the average fiber length, which is typically of the order of about 0.1 inches for many types of cellulosic fibers. This can be accomplished by locating the raised surfaces along the bonding roll surface at a frequency of from about 10 to 40 (across both dimensions).

Another parameter which must be considered in achieving bonds of acceptable strength fashion the amount of water in the wetted continuum and its location therein. Because the moisture is generally sprayed only on the upper surface of the continuum, as in the illustrative embodiment of FIGS. 10 and 11, the water is not located uniformly throughout the thickness of the continuum. While penetration through the continuum to the wire can and does take place, the greater concentration, whether it is absorbed into the fibers or remains as unabsorbed "free" water, will be in the upper area of the continuum. The bonding operation must accordingly be carried out in such a fashion that sufficient pressure is exerted to bond the dryer fibers in the continuum. If sufficient bonding is not effected, the results are readily apparent since the dryer part of the web can be readily separated from the wetted, bonded portion.

A further aspect of the bonding operation is the employment of a bonding roll that is heated. With a steel transfer roll, the temperature of the bonding roll may be maintained at about 200° to 250° F. for a 14 lb./2,800 ft.2 sheet whereas, with a nylon transfer roll, the bonding roll should preferably be heated up to a generally higher temperature of about 250°-300° F. The minimum temperature utilized should be that which prevents the coherent, wetted web from sticking to the bonding roll. Temperatures above such minimum may be advantageously employed to aid in the bonding, particularly with a resilient transfer roll (e.g. -- nylon) where the additional heat can compensate for the inability to develop high unit pressures on the points.

Referring again to FIG. 13, when the transfer roll 234 has a resilient surface such as nylon, there may be some flexibility in terms of tolerances and uniform pressure across the width of the nip. However, when a steel transfer roll is utilized, a variation of 0.0002 inch in nip clearance across the width of the nip may detrimentally affect bonding of the continuum. A nylon surface would of course permit such variation due to its resilient nature and; accordingly, such close tolerances are not required. At high speeds however, the nylon surface may not have a sufficiently small recovery time to enable the removal during a single revolution of indentations caused by the raised surfaces of the bonding roll 236. In accordance with the subject invention, a smoothing roll 244 is preferably placed in contact with the nylon transfer roll 234 by cylinders 245 and is run in contact therewith to smooth the indentations formed by the raised surfaces of the bonding roll.

The thus-formed coherent web must then be separated from the transfer roll without damaging the structure. Although the coherent web downstream of the bonding nip is significantly stronger than the continuum entering the nip, the ultimate strength is not achieved until the moisture content is reduced to the desired level. Accordingly, care must be taken in transferring the formed web off the transfer roll surface. In the exemplary embodiment of FIG. 13, a foraminous belt 246 is passed around a rotatable support roll 248, which has a plurality of perforations in its surface and is provided with a stationary suction box 250 connected to a duct 252. A fan 253 (FIG. 18) provides the suction force for the box 250. The suction which is required is that which is adequate to remove the web from the transfer roll surface and cause adherence to the support roller 248.

Removal of the coherent web from the transfer roll 234 is not, however, solely a function of the amount of suction produced. Adherence of the continuum to the transfer roll is a function of the capillary attraction of the free water on the surface of the continuum; and the suction force, while sufficient to remove the web from the transfer roll surface, could degrade, disrupt or otherwise damage the web. Accordingly, when the transfer roll has a steel surface and the machine is operating at speeds in excess of 100 to 200 ft./min., the transfer roll should be heated to provide a surface temperature of at least about 150° F. The exact upper limit is determined by whether transfer from the belt 48 to the transfer roll can be carried out at such temperature. The roll may be internally heated by any conventional means (not shown). Without the employment of a heated transfer roll surface, adequate release of the coherent structure is often prohibited. It is believed that the heated surface reduces the extent of the capillary attraction for the transfer roll so that removal therefrom can take place.

To promote initial release during startup through the transfer and bonding station 230 as well as to prevent wrap of the web on the transfer roll in the event that structure ruptures, a doctor blade 254 is provided. The blade is closely spaced from the surface of the transfer roll, for example, about 0.01 inch, and is located after the area in which the web is normally removed from the roll. An air knife 256, integral with the blade 254, is provided to direct an air stream towards the gap between the knife and the transfer roll surface so as to assist in separation of the web from the roll.

The bonded web is then treated to reduce its moisture content to about 7 or 8 percent by weight. While any conventional method of drying could be utilized it is preferred, in accordance with one aspect of the present invention, to employ a means of drying which retains, and perhaps even enhances, the desirable aesthetics of the web. To this end, and as is shown in FIG. 1, the coherent structure is carried on the foraminous belt 246 through a through-dryer 247. This, as is known, utilizes heated air passing through the web to remove the moisture. There are no internal rollers or other devices contacting the coherent structure which would tend to compress it. The air passing through the web dries the fibers in such a fashion as to retain the desirable softness characteristic of the web and does not collapse its three-dimensional structure. Any suitable means of heating the air may be employed; and, at high speeds of operation, a steam-heated through-dryer having the air maintained within the range of from about 250° F. to about 320° F. has been found to produce acceptable results. The dryed web may then be wound up on any conventional windup mechanism.

THE AIR SUPPLY SYSTEM

An important feature of the machine of the present invention is the air supply system which enables the high web manufacturing speeds attainable on the subject apparatus. Referring to FIG. 18, the primary vacuum duct 108 of the upstream picker 40 may be connected through a duct 330 to the inlet side of each of the downstream supply fans associated with pickers 42-46. The duct 332 includes adjustable flow regulators or dampers 334 enabling the balancing of the air flow to the inlet of the three downstream supply fans 92. Also, inlets 333 permit the addition of fresh air in the system. In keeping with the present invention, the fibers passing through the belt 48 in the upstream vacuum duct 108, which may be about 2 to 4 percent of the fiber output of the picker 40, are recirculated to pickers 42-46. While the fibers from the other pickers could also be recirculated, the fibers being transported to the wire from pickers 42-46 have increasing difficulty in passing through the belt because of the partial buildup of fibers thereon. The primary vacuum of such downstream pickers will generally contain only minimal amounts of fibers and may be exhausted through a duct 336 connected to a high volume dynamic precipitator 338. While the percentage of the fibers being recirculated is slight, such recirculation may cumulatively represent significant amounts during continuous high speed operation. An adjustable duct 339 may be provided to connect the output of fan 242 to the inlet of the precipitator 338 so that the air volume in duct 332 can be controlled without reducing the operative level of the fan 242.

Also, in accordance with the present invention, suction means may be employed to assist in holding the fluffy continuum on the wire and to prevent ambient conditions and air currents caused by the movement in the apparatus from disturbing the continuum. Thus, as shown in FIGS. 1, 6 and 18, intermediate each of the primary vacuum ducts 108 and also downstream of the picker 46 and the continuum pickup station, a number of supplementary suction boxes 340 are provided. These are connected through ducts 342 and 344 to another high volume dynamic precipitator 346 which creates a partial vacuum acting on the continuum in the areas between and downstream of the primary vacuum ducts. The supplementary suction boxes are intended to hold the substantially unbonded fiber continuum on the left prior to its being bonded into a coherent web in the bonding section 24. Also connected to the duct 344 is a duct 347 terminating at a suction box 349 located beneath the belt 246. The partial vacuum in suction box 349 is adapted to keep the web on the belt until it enters the dryer 247. Precipitator 346 is suitably of a type which is capable of removing the fine fibers in the stream and exhausting the air to the atmosphere.

The ducts 195 and 202 are from the trim and web pickup stations, respectively, each connect to the duct 201 which terminates at the inlet of the fan 200. The outlet from the fan passes through duct 348 to a filter 350 where most of the larger fibers are trapped. The air exits the filter through duct 352 and passes through precipitator 346 where the finer fibers are removed and the air is passed to the atmosphere.

OTHER EMBODIMENTS FOR THE TRANSFER AND BONDING STATIONS

In addition to the embodiment herein described, varying conditions may make applicable other embodiments for carrying out the transfer and bonding functions. Thus, in some situations, it may be desirable to minimize compression which may take place during the transfer step. To achieve this result, the transfer step is carried out with the same structure as the initial embodiment; but the positioning of the elements is different so that there is no support provided for the continuum carrier at the point of transfer. An "open wire" transfer is thus achieved. As seen in FIG. 16, the transfer and bonding station of this embodiment comprises a transfer roll 262, a bonding roll 264, a smoothing roll 266 (where the transfer roll has a resilient surface), a foraminous belt 268, a support roll 270 with a suction duct 272, a doctor blade 274 and integral therewith, an air knife 276, all of which are constructed and function substantially similar to the corresponding components of the transfer and bonding station 230. However, in this embodiment, the belt 48 carrying the continuum is passed around a pair of belt support rollers 278 and 280, which are vertically spaced from transfer roll 262.

Transfer is effected intermediate the support rollers 278, 280 as is generally indicated at 282. With the transfer occurring intermediate the support rolls, the belt or wire is free at this point in that there is no backup or support. This is believed to minimize the slight compaction which can take place in the transfer operation. Although the rolling mode as well as the stretch mode of transfer is theoretically possible with this embodiment, it has been found in practice that acceptable transfer is desirably effected only when the wire 48 is partially wrapped around the transfer roll 262. The wrap provides good contact of the continuum with the transfer roll and should be generally in the range of about 0.5 to 2 inches. In the absence of such a wrap, vibrational movement normal to the plane of the belt can break the continuum, particularly at higher running speeds. Such open belt transfer may also reduce the tendency for the fibers to adhere to the belt when the continuum is transferred.

FIG. 7 illustrates a still further embodiment for the transfer and bonding station. This embodiment is useful when it is necessary to have apparatus that can accomplish spraying of the continuum on both surfaces. In this embodiment, an inverted section is employed to separate the wetted continuum following the first spray application from its carrier and to hold the wetted continuum while exposing its dry surface to a second spray application. The twice-sprayed continuum is then transferred into the bonding station.

To this end, the inverted section includes a second foraminous belt 290 which partially overlies the first belt 48 and is adapted to retain the fiber continuum from above and convey it to the transfer and bonding station 292. Transfer is accomplished by maintaining a gap between foraminous belts 290 and 48 less than the uncompressed thickness of the continuum as in the previous rolling mode embodiments. A vacuum box 294 is provided with sections 295 and 297 which assist transfer from the belt 48 to belt 290 as well as hold the transferred continuum against gravity upon the belt 290 so the unsprayed side may be wetted. Section 295 is also sized to accommodate the spray pattern from an additional moisturizing station 296 positioned downstream of the belt 48 and below the belt 290. The machine direction dimension of section 295 should be determined as has herein been described in connection with the suction box 240. For a 14 lbs./2,880 ft.2 web, the vacuum for section 295 may be between 2 to 10 inches of water, while section 297 may suitably have a vacuum of 1/2 inch water or more. Roller 299 may require internal vacuum to hold the continuum until it is transferred to the bonding station.

The transfer into the bonding station 292 is substantially similar to the transfer into station 230 illustrated in FIG. 13, except that since the operation is inverted, the continuum is traveling upwardly when transfer is effected rather than generally downwardly as in the embodiment shown in FIG. 13. As illustrated, a transfer roll 298, a bonding roll 300, a smoothing roll 302 are provided for the bonding station and are substantially similar to the corresponding components of the embodiment illustrated in FIG. 13. Since both sides of the continuum have been sprayed, care must be exercised in selecting the material for the foraminous belt 290. The surface must be such that the wetted surface will transfer to transfer roll 298 rather than continue adherence to foraminous belt 290. It is preferably to employ a belt having a "Teflon" polytetrafluoroethylene resin coating (E. I. Du Pont de Nemours & Co., Wilmington, Delaware). The belt itself may be formed of, for example, bronze. Also, as in the FIG. 13 embodiment, an air knife 304 integral with a doctor blade 306 are provided to assist in removing the web from the transfer roll. Also, to remove the bonded web from a surface of the transfer roll, a belt 308 with a support roll 310 and an intermediate roll 312 with a suction segment 314 are provided.

The application of water to both sides of the continuum by the moisturizing stations 176 and 296 achieves more uniformity of the water throughout the thickness of the continuum so as to allow an adequate bond to be more readily formed and to substantially reduce the possibility that the formed web will have one surface with loosely adherent fibers as could occur when only one side of the continuum is moisturized. It is particularly desirable to employ this inverted section embodiment when the transfer roll in the bonding station has a resilient surface. In such situations, the double application of moisture compensates for the inability to develop the high unit pressures on the bonding roll raised surfaces which can be achieved with a steel transfer roll.

Thus, as has been seen, the present invention provides a machine which is capable of manufacturing at speeds in excess of 1,000 ft./min. wide cellulosic webs (e.g. -- 46 inches or even wider) which have adequate strength, softness and absorbency to be used in sanitary wipes and toweling applications. The products formed have superior uniformity in the three dimensions, and the apparatus minimizes the formation of visual irregularities in the web that may be caused by clumps of fibers. Continuous operation can be achieved by suitably phasing the supply to the picking operation, and the machine drive is coordinated with the machine speed so that a web with uniform basis weight will be formed regardless of variations in machine speed. The basis weight of the web will vary with the intended application and will generally be in the range of about 5 to 50 lbs./2,880 ft.2, preferably about 10 to 30. An important feature of the subject invention allows the transfer of the flimsy fiber continuum into and out of the bonding station in such a fashion that high speed orientation can be accomplished without the continuum being disrupted.

The apparatus of the present invention thus provides an integrated unit for forming an airlaid, pattern-hydrogen-bonded web having the desirable aesthetics and absorbency described in the copending Dunning U.S. Pat. application Ser. No. 882,257. From the initial formation of the three-dimensional fiber continuum on the moving wire, the present invention provides a machine that forms a product which retains, to the extent possible, the loft or three-dimensional character of the continuum while interrupting the continuum with a pattern of closely spaced, deep indentations wherein the fibers are highly compacted and thereby bonded, to provide the desired coherency. A cross-sectional view of the web shows it to have a series of fluffy mounds wherein the fibers are in their substantially unbonded airlaid condition periodically interrupted by the highly compacted bonded areas.

This unique structural organization of the fibers within the web results in certain product attributes. More particularly, and as has been herein noted, the bonded areas are typically less than about 40 percent or even 20 percent of the height of the fluffy, mound regions. The airlaid continuum before compaction in the nip of the bonding rolls is a loose, unbonded array of dry, relatively stiff fibers in random orientation and which have a Z-direction component, the continuum being so highly compressible as to make mechanical measurement of the thickness extremely difficult. This unbonded airlaid state of the fibers is substantially retained in the mound areas, but is interrupted by the compacted areas wherein the fibers are bonded. This structure may be visualized as a "spring" structure. A considerable number of fibers may be viewed as starting in the bonded area, emerging out of such areas into the mound regions with a significant Z-direction component and then returning to the plane of the web in an adjacent bonded area. Individual fibers can be visualized as anchored at spaced points along the fiber length in one plane and therebetween being bent considerably out of the plane. When it is appreciated that a multiplicity of such individual fibers are present in the web, it can be seen that the action of the high pressure areas of the bonding rolls of engaging and pressing the fibers to produce the compacted zones rearrange both those fibers that are contacted and those entangled with the contacted fibers such that a large proportion of the variously straight and bent fibers packed within the mounds have a significant Z-direction component throughout at least some part of the fiber length. The mounds thus provide a fluffy structure which has spring or resilience when compressive force is applied in a direction perpendicular to the plane of the web. It is believed that this structure contributes significantly "the desirable tactile properties of the web. Further, the "spring" structure is believed to be at least partially responsible for the surprisingly high rate at which the webs are able to absorb liquids due to the existence of a capillary network between the fibers of fluffy mound regions. Thus, the highly compacted bonded areas apparently serve to at least delay disintegration of the web on contact with liquid so that the spring-like mound structure of the web does not collapse on initial web wetting.