Lee, Charles A. (Knoxville, TN)
Granberg, Frederick M. (Knoxville, TN)

05/188872

04/09/1974

10/13/1971

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International Paper Company (New York, NY)

241/18

241/152.100, 241/260, 241/29, 241/28

D21B1/06; D21B1/00; B02C13/14; B02C13/00; B02C13/20

162/4,191,28,261,264,100 241/14,26,28,138,18,19,115,161,260,257R,29,152R

3692246

FLUFF PREPARATION SYSTEM AND APPARATUS

September 1972

Law et al.

Bashore, Leon S.

Tushin, Richard H.

Fitch, Even, Tabin & Luedeka

We claim

1. A process for utilizing substantially dry sheet pulp having a density of greater than about 40 pounds per cubic foot in fluff comprising the steps of pretreating said pulp in its substantially dry state, said pretreatment including reducing said pulp to pieces, layering said pieces between opposing relatively movable surfaces to a thickness of not less than about 1/4 inch, working said pieces substantially against themselves while so layered for a time sufficient to reduce at least about 50 percent of said pulp to free fibers and bundles of fibers only a minor portion of which have a major dimension greater than about 11/2 inches, and flowing air past said pieces during said pretreatment, conveying said pretreated pulp to a refining stage, and thereafter, refining said pretreated pulp to a fluff.

2. The process of claim 1 wherein said sheet pulp has a density of at least about 55 pounds per cubic foot.

3. The process of claim 1 wherein said pulp is layered in an annular layer between opposed working surfaces disposed in generally concentric rings.

4. The process of claim 1 wherein the thickness of said layer of sheet pulp is reduced as said pretreatment progresses.

5. The process of claim 4 wherein the thickness of said layer of pulp initially is about two inches and is gradually reduced to about 1/4 inch.

6. The process of claim 1 and including the step of introducing said refined fluff to a production line as a controlled quantity.

7. The process of claim 6 wherein said fluff is introduced to said production line as a weighed stream.

8. The process of claim 6 wherein said process steps are performed continuously.

9. A continuous process for utilizing substantially dry sheet pulp having a density of greater than about 40 pounds per cubic foot in fluff comprising the steps of

This invention relates to fluff-producing processes and particularly to a process for utilizing high density pulp in fluff.

Defibrated cellulosic material, commonly referred to as fluff, is employed in disposable absorbent products such as diapers and sanitary napkins because of its ability to rapidly absorb and retain liquids. Conventionally, fluff is obtained through a process involving defibration of cellulose pulp which has been shipped to the converting facility from a paper mill.

Due in large part to the absence of an economically feasible process for utilizing other and less costly forms of pulp, the prior art fluff making procedures have employed pulp in roll form, referred to in the art as roll pulp. This type of pulp is one of the more expensive types of available pulp in terms of its cost of manufacture. Roll pulp is also less dense than certain other types of pulp such as pulp in sheet form known in the art as high density sheet pulp (referred to hereinafter at times as "sheet pulp"). Being less dense, a given weight (ton, for example) of roll pulp occupies more space than an equal weight of sheet pulp so that the cost of shipping roll pulp is greater, per unit of weight, than the cost of shipping sheet pulp. In general, sheet pulp costs about $20.00 per ton less than roll pulp as delivered to the converting facility.

Fluff, as an absorbent element in a disposable product commonly is incorporated into the product in a measured amount depending upon the anticipated absorptive capacity to be required of the product. About 20 grams of fluff may be included in a disposable diaper, for example. More than the necessary amount of fluff unnecessarily increases the cost of the diaper whereas too little fluff produces a faulty diaper. Heretofore, no known process was capable of economically converting sheet pulp to fluff in a manner such that the fluff could be incorporated into disposable products in measured amounts at an acceptable cost.

In general, the prior art process involved feeding roll pulp into a defibrator at a controlled rate so that the output of the defibrator was similarly controlled at a value which resulted in the proper amount of fluff being incorporated into the disposable product, i.e., a diaper. Because of the relatively high density and highly compacted state of sheet pulp, known defibrators are incapable of accepting sheet pulp directly and converting it to fluff on a continuous basis at a rate economically acceptable without scorching the cellulosic material which reduces its absorptivity and makes it unsightly in a product such as a diaper or sanitary product. In the prior art, even though the sheet pulp was fed relatively slowly to a defibrator so that scorching does not occur, fiber bundles appeared in the fluff in a quantity and of a size that reduced the absorptive capacity of the fluff below an acceptable limit. The low through-put rates obtainable were economically undesirable. Moreover, sheet pulp is adversely affected by gross shredding or fragmentation procedures and apparatus, known in the prior art, such as through the severe pounding and grinding of a hammer mill. Such severe prior art treatment steps produce broken fibers, referred to as fines, which also adversely affect the absorptivity of the fluff. Accordingly, heretofore there has been no known process which economically permitted the utilization of sheet pulp in fluff.

It is therefore an object of the present invention to provide a process for economically utilizing high density sheet pulp in fluff. It is a further object to provide a process wherein sheet pulp is converted to fluff and incorporated into a disposable product in a weighed amount. Other objects and advantages will be apparent from the following description including the drawings in which:

FIG. 1 is a representation of a process as disclosed herein;

FIG. 2 is a representation of an apparatus for carrying out a part of the disclosed process;

FIG. 3 is a fragmentary view, part cut-away, of the apparatus of FIG. 2.

In the disclosed process, high density sheet is initially broken into pieces and worked upon itself, preferably in a layer between working faces of a reducer apparatus, to provide an intermediate product wherein at least about 50 percent of the fibers of the pulp are freed as individual fibers or small bundles of fibers. This intermediate product is thereafter fed as a measured, preferably weighed, quantity to a refiner and refined to form a cellulosic fluff. The process preferably is carried out in a continuous fashion and combined with one or more production lines for the manufacture of disposable products.

In the illustrated embodiment of the disclosed process, depicted in FIG. 1, high density pulp 10, in sheet form, is pretreated to reduce the sheets 12 to small pieces as will be specifically described hereinafter. The output from the reducer step is conveyed, preferably pneumatically through a separator 14 to a storage chest 16 where the pieces are held for discharge, as by means of a false bottom conveyor 18, through an opening 20 in the chest to a flow divertor 22. The stream of pulp pieces admitted to the flow divertor is directed to one or more of a plurality of refining stations 24 (only one refining station is shown). At a refining station, the pulp pieces are detrained from the stream as by a separator 26 which in turn dumps the pieces onto a conveyor 28 which is reversible as to its direction of movement so as to feed pulp upon demand to each of two spaced apart refiners 30 and 32. As depicted in FIG. 1, the pulp pieces are caused to fall from the conveyor 28 through a compartmented chute 34 to a weigh belt 36 from which the pieces are discharged into the refiner 30. Within the refiner, the pulp is reduced to individual fibers or very small bundles of fibers to define a fluff which is admitted to a production line. Similarly, when the conveyor belt 28 is reversed in direction, pieces of pulp are discharged through chute 34 onto a second weigh belt 38 from which they are conveyed into the second refiner 32 wherein they are converted to a fluff and admitted to a second production line.

More specifically, and with particular reference to FIGS. 2 and 3, dry high-density sheet pulp 10 is pretreated in a material reducer 40 to which the pulp is admitted as loose sheets, untied bundles or other suitable form. As used herein, the term "high-density sheet pulp" refers to pulp in sheet form and/or pulp which is made as a continuous web and folded, as by festooning, for example, into a stack or bundle. It will be recognized that in the art "dry" paper or pulp includes about 6-10 percent by weight of moisture and the term is so used in the present disclosure. In general, high-density sheet pulp has a density greater than about 40 pounds per cubic foot.

During pretreatment in the reducer the action upon the pulp includes a reduction of the sheet material so that the major portion of it is less than a preselected size. Larger pieces are initially formed but these are further reduced in size as the pretreatment progresses so that eventually substantially all the pieces have a major dimension of less than about one and one-half inches and are suitable for refining.

In addition to the initial break-up of the sheets, during pretreatment the pulp is caused to accumulate in a layer or layers between opposed working surfaces at least one of which is movable relative to the other. While so layered, the material is worked upon itself with a substantial portion of the reducing action being accomplished by action of the pulp upon itself. The action of the pulp upon itself while layered between opposing working surfaces may be visualized as similar to "hydraulic shear" wherein two spaced apart working surfaces which move relative to one another set up shear forces in the liquid between the surfaces. Thus in the present process the faces of the body of pulp are worked by moving work surfaces so that pieces of pulp are moved relative to one another and the pieces themselves rub and shear pieces and fibers from one another. This action is to be distinguished from a grinding and tearing action which tends to break individual fibers and form substantial quantities of fines. The working of applicant's method frees substanial quantities of individual cellulose fibers and small bundles of fibers and reduces the pulp to small pieces so as to reduce the work necessary in a subsequent refining step to accomplish relatively complete defibration of the pulp to a fluff. In a preferred pretreatment of the pulp, of the order of at least 50 percent of the cellulose fibers are separated into individual fibers and/or small bundles of fibers. Many pieces are much smaller. Pretreating the pulp to bring about greater reduction in the size of the pieces or more extensive defibration has been found unnecessary for successful subsequent refining, hence wasteful. Substantially less pretreatment, however, fails to provide a product suitable for refining in that larger pieces and less defibration during pretreatment require greater working of the pulp in the refining step and the resultant fluff is scorched and/or contains an unacceptable percentage of fiber bundles. The reducer product, i.e., the pieces of pulp and free fibers and fiber bundles, is characterized also by its bulky state wherein the pieces appear crumpled and larger and smaller pieces are mixed with separated fibers and small bundles of fibers making the reducer product suitable for subsequent refining.

The pretreatment of the pulp is enhanced by removing heat as it is generated within the reducer apparatus and thereby increasing the through-put capability of the process. The degree of cooling is adjusted to prevent such heat build-up as will result in scorching of the pulp under the conditions of work being done on it by the reducer.

A suitable reducer apparatus is identified as Model 100, available from the Eidal International Corporation, Albuquerque, New Mexico. This apparatus is depicted in FIGS. 2 and 3 and includes a plurality of sets 42 of freely rotatable toothed gears 44 whose peripheries are disposed in regulated proximity to a plurality of bar elements 46 disposed on the inner wall 48 of a housing 50 which circumscribes the several gears. The tips 52 of the teeth on the gears 44 are generally flat. Similarly, the bars 46 are provided with generally flat surfaces 54 facing the flat gear teeth tips to define a generally annular space or gap 56 therebetween. The gears 44 in each set 42 are disposed in a stack with several sets being mounted between horizontal platforms 58 and 60 which are rotated by a shaft 62 turned by a motor 64 connected to the shaft 62 through a belt drive 66 to carry the sets of toothed gears about the inner circumference of the housing 50. Each gear is independently rotatable about a shaft 68 relative to its mates and is caused to turn about shaft 68 incident to contact with pulp disposed in the space 56 between the gear teeth and the bars 46. The shaft 68 of each set of toothed gears 44 resides in a radial notch 70 provided in each gear to provide a degree of freedom of movement to the gear in a radial direction, depending upon the material disposed in the space between the gear teeth and the bars 46 on the housing wall 50. Hard clumps of material in the space thus force the gears radially inwardly temporarily until the clump is broken down.

Material to be acted upon by the apparatus is fed into the top 72 of the reducer 40 and is subjected to a reducing action as the material passes to the bottom 74 and out of the apparatus. The apparatus also includes a massive breaker arm 76 near the infeed thereof to initially contact and break down large pieces or quantities of material. Reduction of the pulp sheet is effected initially by the breaker bar and subsequently by action of the pulp pieces upon themselves as they pass between the gears 44 and the bars 46. The outer wall 50 of the reducer is tapered inwardly to a lesser diameter adjacent the bottom of the upright reducer causing the pulp to be progressively urged toward the gears 44 and accumulated in a layer in the annular space 56 between the gears 44 and bars 46 thereby keeping the pulp working upon itself as it is further reduced to smaller pieces.

The extent of the size reduction accomplished in the reducer is adjusted by choice of the proximity of the toothed gear elements 44 to the bars 46 on the outer housing 50 of the apparatus and the residence time of the material within the reducer. The space or gap 56 between the gear tooth faces 52 and the faces 54 of the bars 46 at the bottom of the space suitably is between about 11/2 and 1/4 inches, with a 1/4 inch space being preferred. When the pulp layer is reduced to less than about 1/4 inch thickness, insufficient pulp remains in the layer to bring about the desired working of the pulp upon itself and the dominant size-reduction action becomes a severe pounding and grinding which breaks unacceptably large members of fibers. Gap distances, hence pulp layer thicknesses, greater than about 11/2 inches reduce the effectiveness of the shearing action within the layer so that greater residence times within the reducer are required to obtain equivalent results. The gap distance at the top of the space 56 depends in part upon the material being processed and the gap distance at the bottom but usually is less than about 2 inches. Adjustment of the residence time of the pulp within the reducer is suitably made by providing a radially adjustable restrictor 78 immediately upstream of the outlet 80 of the reducer, the radial position of the restricter being changed to permit more or less outflow of material from the reducer per unit of time. A suitable restrictor comprises a flat annular ring divided into sections 82 and 84 which are adjustably held in a selected radial position by means of bolts 86.

As previously noted, greater through-put of material through the pretreatment step is made possible by cooling the material in the reducer sufficiently to keep the temperature of the material below that temperature at which scorching of the cellulose occurs. One suitable means for controlling the temperature of the material within the reducer is to flow air through the interior of the reducer while it is in operation. The quantity of air flow employed depends in large part upon the desired degree of cooling. Other means for controlling the temperature of the material within the reducer will be apparent.

In the illustrated process, the product from the reducer 40 is conveyed, preferably by pneumatic means, from the reducer to a storage chest 16 for retention and subsequent feeding to one or more refining stations 24. When employing the preferred pneumatic conveying means, the reducer product is entrained in air at the outlet of the reducer and fed through a separator, such as a cyclone separator 14, which collects the product from the air stream and dumps it into the storage chest while diverting the air through a filter system (not shown) to the atmosphere. The reducer product is held in the storage chest for dispensing and conveying, as by an air stream, on demand to one or more refining stations 24 through a flow diverter 22 thereby providing for the supplying of reducer product to several refining stations from a single storage unit and resultant efficient marriage of the disclosed process to one or more production lines where the refined fluff product is incorporated into an absorbent product such as a disposable diaper. In the preferred air conveyor, considerable mixing occurs to aid in dispersing the pulp pieces so that a substantially uniform mixture of sizes with free moisture removed is fed to the refiner and a uniform fluff is formed.

At the refining station, the reducer product, which comprises pulp pieces, is defibrated, the cellulosic fibers being generally separated one from another to form a fluff containing randomly oriented separated fibers, and delivered to a production line as a weighed stream. In the illustrated method, the pulp reducer product is air conveyed from the storage chest 16, through the flow diverter 22, to the cyclone separator 26 where the reducer product is detrained from the air stream and dumped onto the conveyor 28 disposed above the chute 34 having compartments 87 and 89 which empty onto separate weigh belts 36 and 38. The conveyor 28 is reversible in direction of travel thereby providing for the transfer of pulp pieces to either of the compartments 87 and 89 of the chute 34 in response to a control signal. Each weigh belt is controlled to deliver pulp pieces in a weighed stream to a refiner 30 which defibrates the pulp to convert it to fluff that is delivered from the refiner to a production line. The fluff demand of the production line serves as the basis from which appropriate control signals are developed by a controller 90 to effect coordinated functioning of the several units of apparatus which are employed to carry out the steps of the disclosed process. Specifically, appropriate signals are developed to (1 ) control a motor 92 which drives the conveyor 18 in the storage chest 16 to insure adequate delivery of pulp to the refining station or stations, (2) control a motor 94 which drives the reversible conveyor 28, both the speed and direction of travel of which are controlled to deliver pulp alternately to the separate weigh belts 36 and 38, and (3) control motors 96 and 98 which move the weigh belts 36 and 38, respectively, at proper speeds to deliver the measured amount of pulp to each refiner 30 and 32, respectively, which will satisfy the demand of the production line associated with a particular refiner.

A preferred refiner comprises a disc refiner of the type generally known in the art as a Bauer refiner. The refiner preferably employs a pair of opposed and oppositely rotating discs whose opposed faces are provided with radial bars having a minimum of rough edges which tend to snag and accumulate fibers. The faces of the bars on the opposed discs normally are spaced apart by a few thousandths of an inch to define a refining region therebetween. The discs, which conventionally are each about 24 inches in diameter, normally are rotated at respective speeds of about 1,750 revolutions per minute. The pulp pieces are received between the opposed faces of the discs, which are spaced apart between about 0.040 and 0.120 inch, preferably about 0.040 inch, and reduced to a fluff by the action of the counter-rotating discs on the pretreated material.

A generally uniform and constant output from a refiner 30 is obtained when the weigh belt 36 which feeds reducer product to the refiner in a measured stream is operated at a substantially constant forward rate of travel. Intermittent movement of the weigh belt has been found useful to provide intermittent delivery of fluff to a production line to form spaced apart units of fluff on a component of the production line moved in a continuous fashion beneath the outlet of the refiner. The refiner 30 thus is provided with a controlled input with the result that the output thereof is maintained suitable to satisfy the fluff demand of the production line. The fluff is particularly useful in forming the absorbent pad of a disposable diaper or sanitary napkin and is made a part of the product by production line means known in the art.

As noted hereinbefore, it has been found that the pretreatment of the sheet pulp which is carried out in the reducing apparatus provides a feed material which can be processed successfully through a refiner of the type described. Considerable variance in the degree of such preliminary treatment is permissible but when at least about 50 percent of the fibers have been freed as individual fibers or small bundles of fibers and most of the pieces are of less than about 11/2 inches in their major dimension satisfactory results are obtained in the refining step. Substantially less preliminary treatment increases the work required of the refiner to produce an acceptable fluff and increases the occurrence of heat build-up in the refiner with the accompanying undesirable results. Substantially more preliminary treatment appears to provide little increased benefit in the refiner, hence is economically wasteful.

EXAMPLE

Sheet pulp having a density of 55 lbs. per cubic foot in bundle form, was fed through a reducer 40 and initially broken into relatively large pieces of the breaker bar 76 of the reducer. These pieces then passed into the annular space 56 between the opposed faces 52 and 54 of the teeth of the gears 44 and the bars 46 on the inner wall 48 of the reducer housing 50. The gap spacing between these opposing faces 52 and 54 varied from 2 inches nearest the top 99 of the reducer to 1/4 inch at the outlet of the reducer. The residence time of the pulp within the reducer was chosen so that the reducer product comprised a mixture of pulp pieces, only a small portion of which had a dimension greater than about 11/2 inches, and free fibers and small fiber bundles. More than 50 percent of the mixture comprised free fibers and bundles containing only a few fibers.

The toothed gears 44 of the reducer measured 121/2 inches in diameter and were carried along their circular paths by rotating their supporting platforms 58 and 60, at a rotational speed of 450 revolutions per minute (rpm). Each of the platforms 58 and 60 were of 39 inches diameter and each gear 44 extended about 11/2 inches beyond the circumferential edge of the platform when the gear was in its most radial position. The height of the annular space 56, i.e., the distance between the top 99 and the bottom 74, was 91/2 inches. About 1,000 cubic feet of air was flowed through the reducer per each minute to effect the desired heat removal.

This pretreated pulp was conveyed pneumatically to a storage chest 16 from which it was dispensed to a refining station 24. At the refining station the pulp was measured into a stream on a weigh belt 36 which discharged the pulp at the rate of about 7,300 grams per minute into a Bauer refiner 30 which is equivalent to a usual rate employed in producing a disposable diaper. Within the refiner the pulp was passed between counter-rotating discs each having a diameter of 24 inches, which were rotated at 1,750 rpm. The opposed refining faces of the discs were spaced apart about 0.070 inch at their closest point.

The fluff product from the refiner comprised substantially free fibers with a minor portion of fiber bundle comprising a few unseparated fibers. No scorching of the fibers or similar adverse qualities of the fluff were noted upon visual observation.

Diapers made up from fluff product according to this Example were tested for absorptive capacity and rate of absorption. Both these characteristics were found to be well within acceptable limits.