Title:
METHOD OF TEXTURIZING THERMOPLASTIC YARN
United States Patent 3868749
Abstract:
The problem of nesting of yarns of continuous thermoplastic filaments when crimped after edge-drawing can be substantially eliminated by reheating the yarn, cooled to set the strain imparted by edge-drawing, to a crimping temperature while maintaining the yarn under sufficient tension to prevent crimping from occurring. Then, upon release of tension from the yarn at crimping temperature, the yarn will immediately balloon and retract to form crimps in the individual filaments independent of one another, thus substantially eliminating nesting.
US Patent References:
Process and apparatus for making crimped filaments
Speakman et al. - March 1961 - 2974391
Apparatus for processing thermoplastic yarns
Klein et al. - April 1961 - 2977746
Textile materials and method of making the same
Pittman - January 1962 - 3017684
Apparatus and method for debundlizing filter tow
Agett - November 1965 - 3220060
APPARATUS FOR STRAND TREATMENT
McClure - August 1971 - 3600774
Process and apparatus for making crimped filaments
Speakman et al. - March 1961 - 2974391
Apparatus for processing thermoplastic yarns
Klein et al. - April 1961 - 2977746
Textile materials and method of making the same
Pittman - January 1962 - 3017684
Apparatus and method for debundlizing filter tow
Agett - November 1965 - 3220060
APPARATUS FOR STRAND TREATMENT
McClure - August 1971 - 3600774
Application Number:
05/428173
Publication Date:
03/04/1975
Filing Date:
02/06/1974
View Patent Images:
Export Citation:
Assignee:
American Cyanamid Co. (Stamford, CT)
Primary Class:
Other Classes:
28/246, 28/261, 28/281, 57/351
International Classes:
D02G1/10; D02G1/14
Field of Search:
28/1.2,1.3,1.5,72.1,72.11,72.13,72.17,1CF 57/157R,157S,157MS
US Patent References:
| 3619874 | November 1971 | Li et al. |
Primary Examiner:
Rimrodt, Louis K.
Attorney, Agent or Firm:
Van Loo, William J.
Claims:
I claim
1. A process for texturizing untwisted yarn consisting of continuous thermoplastic filaments which comprises: heating the yarn to a temperature above its glass transition temperature but below its sticking temperature; drawing the yarn at such temperature over a sharp edge at an acute angle to induce a strain along one side of each filament length making up said yarn; cooling the yarn thus edge-drawn so as to set the strain and relax the yarn; reheating the yarn to a temperature sufficient to cause crimping while maintaining sufficient tension on the yarn to prevent crimp development from occurring during said reheating, said reheating temperature being below the edge-drawing temperature; immediately releasing the tension on the yarn when it is at the crimping temperature so as to cause the yarn to balloon and the individual filament to retract and develop crimp independently of and thereafter advancing the yarn under sufficient tension to remove temporarily the crimp thus developed.
2. The process of claim 1 wherein the yarn is heated and drawn for orientation prior to edge-drawing.
3. The process of claim 1 including the step of drawing the yarn prior to processing for orientation.
4. The process of claim 1 including the step of advancing the yarn to winding.
5. The process of claim 1 including the step of advancing the yarn to twisting and winding.
6. The process of claim 1 wherein the reheated yarn is allowed to retract 5 to 20 percent in crimping.
7. The process of claim 1 wherein the yarn after edge-crimping is cooled to a temperature at least 50°F. below its glass transition temperature.
8. The process of claim 1 wherein the yarn consists of polyethylene terephthalate filaments and is of carpet denier.
1. A process for texturizing untwisted yarn consisting of continuous thermoplastic filaments which comprises: heating the yarn to a temperature above its glass transition temperature but below its sticking temperature; drawing the yarn at such temperature over a sharp edge at an acute angle to induce a strain along one side of each filament length making up said yarn; cooling the yarn thus edge-drawn so as to set the strain and relax the yarn; reheating the yarn to a temperature sufficient to cause crimping while maintaining sufficient tension on the yarn to prevent crimp development from occurring during said reheating, said reheating temperature being below the edge-drawing temperature; immediately releasing the tension on the yarn when it is at the crimping temperature so as to cause the yarn to balloon and the individual filament to retract and develop crimp independently of and thereafter advancing the yarn under sufficient tension to remove temporarily the crimp thus developed.
2. The process of claim 1 wherein the yarn is heated and drawn for orientation prior to edge-drawing.
3. The process of claim 1 including the step of drawing the yarn prior to processing for orientation.
4. The process of claim 1 including the step of advancing the yarn to winding.
5. The process of claim 1 including the step of advancing the yarn to twisting and winding.
6. The process of claim 1 wherein the reheated yarn is allowed to retract 5 to 20 percent in crimping.
7. The process of claim 1 wherein the yarn after edge-crimping is cooled to a temperature at least 50°F. below its glass transition temperature.
8. The process of claim 1 wherein the yarn consists of polyethylene terephthalate filaments and is of carpet denier.
Description:
This invention relates to an improved process for texturizing thermoplastic yarns consisting of continuous filaments. More particularly, the invention relates to such a process wherein such a yarn after edge-drawing and cooling is reheated under tension to a temperature sufficient to cause crimping, then allowed to balloon and crimp by release of tension on the reheated yarn, and finally advanced to further processing under sufficient temperature to remove temporarily the crimp thus developed.
It has long been known that the drawing of a filamentary over a sharp edge will induce curl or crimp in the filamentary material. This is disclosed, for example, in U.S. Pat. No. 1,959,104, issued May 15, 1934 to L. D. Mahan, wherein the filamentary material is metal. In U.S. Pat. No. 2,245,874, issued June 14, 1941 to W. S. Robinson, the same basic procedure is employed to provide a cushioning material composed of vegetable fibers. In British Pat. Specification No. 558,297, accepted Dec. 30, 1943 to Imperial Chemicals Industries, Ltd., the same basic procedure is employed on nylon fibers to provide crimped threads or filaments for use in textile applications. U.S. Pat. No. 2,919,534 issued Jan. 5, 1960 to E. D. Bolinger et al., discloses the same basic procedure modified to heat the filaments prior to contact with the sharp edge. U.S. Pat. No. 3,136,111, issued June 9, 1964 to E. H. Pittman, discloses essentially the same process as that of the Bolinger et al., reference except that the drawing tension is intermittently varied to provide an intermittent crimp. Numerous other modifications and extensions of the basic principle of edge-crimping are disclosed in a great number of additional patents, none of which are considered of any particular pertinency to the present application.
Basically, the object of edge-crimping is to impart a strain along one side of each filament length so that when the filaments are subjected to relaxation upon further heat treatment, one side retracts to a different extent then the other thus causing the filament to curl, crimp, or coil. Current practice is to draw the filaments heated to a temperature just below their sticking temperature over the sharp edge. After drawing has been effected as described, the yarn is cooled under tension to prevent premature crimping while setting the latent crimpability to provide for subsequent crimping when desired. The latent crimpability may be developed when desired by applying sufficient heat to the yarn in untensioned state so that it may retract for full crimp development. Often crimp development may be in stages, allowing a first partial retraction followed by a second retraction for full crimp development.
There are numerous methods by which the degree of retraction may be controlled, thereby controlling the degree of crimpiness developed. Usually the yarn is continuously overfed to a heated zone under controlled conditions so that the filaments are restrained from contracting to the maximum extent possible. For example, in U.S. Pat. No. 3,439,391, issued Apr. 22, 1969 to B. M. De Vore et al., the drawn filaments are transferred through narrow tubes containing a gas. The gas is heated by external means and the filaments are allowed to crimp under such influence. In U.S. Pat. No. 3,241,212, issued Mar. 22, 1966 to C. G. Evans et al., a modification of the procedure of De Vore et al., is disclosed. In U.S. Pat. No. 3,478,401, issued Nov. 18, 1969 to J. W. Whitworth et al., the drawn filaments are overfed to a perforated roll and the filaments are heated with a hot gas. In U.S. Pat. No. 3,102,321, issued Sept. 3, 1963 to N. E. Klein et al., the filaments are overfed to a heated roll. Each of these methods has certain advantages and disadvantages which are mentioned in one or another of the references cited.
All of the methods of controlling retracting mentioned above, however, have one common processing feature, that of overfeeding the drawn yarn into a heated zone. With particular reference to the Klein et al., citation wherein over-feeding is to a heated roll, the method can only be used for specific thermoplastic filaments such as nylon and very low denier filaments. Due to short residence time on the roll, heat transfer is insufficient to cause retraction of high-melting polyester filaments or heavy denier filaments used in carpet yarns. As a result, insufficient tension develops on the yarn which slides off the roll and the process becomes inoperative.
A particular deficiency in methods which develop the crimp by heating the yarns in a relaxed condition is a phenomenon known as "nesting." Nesting is a term applied when all adjacent filaments in the yarn bundle develop their crimps in phase. That is to say, the crimped yarn will appear to be a singular coil spring of many filaments rather than a series of coil springs of individual filaments. Yarn composed of nested crimped filaments results in poor yarn bulk. The Klein et al., reference discusses the problem of nesting and apparently is effective in overcoming the problem with respect to those yarns processable therein. However, as previously noted, the process of Klein et al., is not applicable to most yarns because upon overfeeding to a heated roll they would fall off the roll and curtail processing. The De Vore et al., and Whitworth et al., references also discuss the nesting problem which is overcome by passing the yarn through an aspiraor to open same prior to crimp development. Such a provision, however, necessitates a continuous expenditure of high pressure air, which complicates processing and increases costs.
Thus, there continues to exist the need for improved edge-crimping processes for thermoplastic yarns of continuous filaments which overcome the deficiencies of the prior processes. Polyester yarns of carpet denier are not edge crimped because of the lack of an economical commercially acceptable process that provides the necessary product control and acceptability.
In accordance with the present invention, there is provided a process for texturizing untwisted yarn consisting of continuous thermoplastic filaments which comprises: heating the yarn to a temperature above its glass transition temperature but below its sticking temperature; drawing the yarn at such temperature over a sharp edge at an acute angle to induce a strain along one side of each filament length making up said yarn; cooling the yarn thus drawn so as to set the strain and relax the yarn; reheating the yarn to a temperature sufficient to cause crimping while maintaining sufficient tension on the yarn to prevent crimp development from occuring during said reheating, said reheating temperature being below the edge-drawing temperature; immediately releasing the tension on the yarn when it is at the crimping temperature so as to cause the yarn to ballon and the individual filaments to retract and develop crimp independently of one another; and thereafter advancing the yarn under sufficient tension to remove temporarily the crimp thus developed.
By carrying out the process in the manner described, the yarn obtained possesses highly desirable bulk, the degree of crimpiness developed is readily controlled, the problem of nesting is substantially eliminated and the deficiencies of the prior processes are overcome.
Useful thermoplastic yarns are those composed of filaments of fibrous textile materials that normally respond to edge crimping. The yarn is essentially free of twist and may be pre-drawn for orientation purposes or not. It is preferable that the yarn be undrawn since such drawing can be carried out in conjunction with edge drawing and thus save processing steps. Although not limited thereto, the present process is particularly adaptable to edge drawing polyester yarns of carpet denier.
The present proceds includes the steps of heating the yarn for edge crimpings and of cooling after edge crimping as these steps are employed in conjunction with conventional processes. Subsequent steps, however depart markedly from conventional processing and are responsible for the distinct results. In the present process, after the yarn is cooled following edge crimping to set the strain and relax the yarn, it is then reheated to a crimping temperature without allowing the yarn to crimp. This is a distinct departure from prior procedures wherein such reheating is carried out under conditions which allow the yarn to crimp as it is reheated. In the present process only after the yarn has reached the crimping temperature is it allowed to develop crimp. The reheated yarn, at the crimping temperature, suddenly is relieved of the tension that restrains it from crimping and immediately balloons as a result and crimping begins. That is to say, the individual filaments of the yarn upon removal of the tension immediately separate from one another as crimping begins and crimping of the individual filaments proceeds independently of one another. This is an entirely unexpected phenomenon and is responsible for the substantial absence of nesting exhibited by the present process. This absence of nesting is thus accomplished without the need for special provisions such as compressed gas to prevent nesting. After the yarn has developed its crimp as described, it then advanced under sufficient tension to remove temporarily the crimp thus developed. Advancement is generally to winding or packaging which may include a twisting operation in conjunction with winding.
Although the present inventor does not know the mechanism by which the ballooning phenomenon occurs in the present process and does not wish to be bound by any theory, he is of the opinion that the one-sided strain induced by edge drawing the filaments is of sufficient magnitude to cause the filaments to snap-retract when released from restraining tension while at crimping temperature. By "snap-retract" is meant that the filaments retract so rapidly as to generate lateral motion which causes ballooning or opening up of the untwisted yarn bundle.
Reference will now be made to the accompanying drawings in which
FIG. 1 is a schematic plan for carrying out a preferred embodiment of the invention.
FIG. 2 is an enlarged view of the section of FIG. 1 enclosed in the dashed line are an ABCD.
FIG. 3 is a photograph of an edge crimped yarn exhibiting nesting and not obtained by the process of the present invention.
FIG. 4 is a photograph of an edge crimped yarn obtained by the process of the present process and exhibiting the substantial absence of nesting characteristic of the present invention.
With reference to FIG. 1, an undrawn, untwisted, multifilament, thermoplastic yarn 10 is continuously fed from supply package 11 over tension bars 12 to a draw feeding roll 13. Roll 13 is preferably heated. After several wraps about roll 13 and idler rolls 14, the yarn is passed over heater plate 15 and makes surface contact therewith so as to heat the yarn to its draw temperature. The yarn is drawn by passing to draw roll 16, the peripheral speed is sufficiently greater than that of roll 13 to effect the desired draw ratio. Several wraps of yarn are taken about roll 16 and idler roll 17. Roll 16 is heated so that yarn 10 is hotter than its draw temperature but below its sticking temperature. The draw ratio may be up to about 6. The yarn 10 is then passed at an acute angle over a sharp edge 18 to roll 19 and idler 20. Roll 19 is significantly colder than roll 16 and serves to cool the yarn and set the strain imposed by edge 18. The surface speed of roll 19 is slightly less than that of roll 16, thereby allowing the yarn to shrink slightly after it passes over edge 18 and thus relax. Several wraps of yarn are taken about roll 19 and idler 20. The yarn is then advanced to roll 21 and idler 22, about which several wraps of yarn are taken. Roll 21 is heated to a temperature at which the yarn will crimp, which is below the temperature of roll 16 but above the temperature of roll 19. The tension on the yarn on roll 21 is sufficient to prevent the yarn from crimping even though it reaches crimping temperature. The yarn advances from roll 21 to idler 22 to a pair of nip rolls 23, 24, the surface speed of which is 5 to 20 percent less than that of roll 21. Thus, rolls 23 and 24 serve to rapidly release the tension restraining yarn 10 from crimping. As a result, yarn 10 as it leaves roll 21 and idler 22 immediately balloons and the individual filaments crimp independently of one another to form crimped yarn substantially free of nesting. The yarn 10 proceeds from nip rolls 23, 24, over guide rolls 25 to a winder 26 under tension sufficient to remove temporarily the crimp that has thus been imparted thereto.
In the above description of FIG. 1, actual temperatures, tensions, and roll speeds have not been given because these conditions will be dependent upon the particular type of thermoplastic yarn being processed, its chemical composition, molecular weight, denier of individual filaments and yarn, degree of drawing to be effected, the degree of crimp development desired, etc. Several essential requirements may be stated, however, which can readily be adapted to use. The temperature of the yarn on the draw roll 16 must be higher than the temperature of the yarn as it leaves the reheating roll 21. The yarn on roll 19 should be at a temperature which is lower than when the yarn is on either roll 16 or roll 21 and should reach a temperature below the glass transition temperature to set the strain. Preferably, a temperature well below the glass transition temperature will be reached, such as about 50°F. or more below the glass transition temperature, if possible. The temperature of the yarn as it leaves roll 21 should be sufficient to cause crimping as the tension is released. The temperature of the yarn as it is taken up on roll 16 must be above the glass transition temperature but below the sticking temperature. The temperature of the yarn as it leaves roll 21 is above the glass transition temperature but below the temperature reached on roll 16.
With reference to FIG. 2, the reheating roll 21 and idler 22 upon which the cooled drawn yarn is reheated is shown in conjunction with nip rolls 23 and 24 which operate at room temperature. The nip rolls run at a slower linear speed than that of roll 21 so that the tension on the yarn wrapped about roll 21 is immediately released as the yarn 10 leaves roll 21. In the space between roll 21 and nip roll 23, therefore, the yarn ballons and snap-retracts so that the individual filaments crimp independently of one another as shown. The nip rolls serve to control the amount of crimp developed by their linear speed but also enable tension to be reintroduced on the fiber without interfering with ballooning and snap-retraction thereof. Tension is necessary as the yarn advances from the nip rolls in order to remove temporarily the crimp obtained so that the yarn can properly be packaged or twisted and packaged. While the extent to which yarn retraction occurs in the space between roll 21 and nip roll 23 may vary widely, it is generally, preferable to control the retraction to between about 5 and 20 percent based on the drawn yarn length. When retraction is in the range stated, no true yarn shrinkage will occur, that is, the yarn upon subjection to tension just sufficient to be straightened from its crimped state will be substantially as long as it was prior to crimping. If retraction is less than about 5 percent, the yarn bulk is generally insufficient. If retraction is greater than about 20 percent, the yarn bulk is generally greater than desired.
The invention is more fully illustrated by the examples which follow employing polyester yarn of carpet denier. It is to be understood that the invention is readily carried out with other thermoplastic yarns of a wide range of deniers without departing from the scope of the appended claims.
EXAMPLE 1
A supply of 2250 denier polyethylene terephthalate yarn composed of 140 continuous filaments was employed. The polymer used to form the filaments had an intrinsic viscosity of 0.6. The yarn was advanced from the supply roll to a heated draw feed roll at 108 feet per minute (f/m). Five wraps of yarn were wound on the feed roll and idlers associated therewith, the feed roll being at 200°F. The yarn was then advanced to contact a heater plate having a surface temperature of 250°F. and taken up by a draw roll at a temperature of 430°F. The linear speed of the draw roll was 538 f/m thus drawing the yarn to a length that was 500 percent greater than its original length, i.e., a draw ratio of 5. Five wraps of yarn were taken about the draw roll and idler. The yarn was then guided under a sharp blade to a cooling roll at a temperature of 210°F. and having a linear speed of 508 f/m., thus allowing a relaxation of 5.6 percent. The angular path of the yarn with respect to the blade edge was about 30°. Five wraps of the strained yarn were taken about the cooling roll and idler so as to cool the yarn.
Up to this point, the process steps are conventional and well known in the art. The next series of steps depart from conventional procedures and constitute the distinguishing features of the present process which reflect the improved process and product therefrom.
The cooled yarn was fed to a heated roll at a temperature of 360°F. and having a linear speed of 510 f/m, which represents a slight underfeed. Five wraps of yarn were taken about the roll and idler so as to reheat the yarn under tension to a crimping temperature without enabling the yarn to retract and crimp. The yarn was then overfed to a pair of nip rolls having a linear speed of 450 f/m. As the yarn came off the roll at its reheated temperature it was free of tension because of the overfeed to the nip rolls. The yarn upon the release of tension immediately ballooned and retracted to form crimps in the individual yarns independently of one another i.e., with substantial absence of nesting. The nip rolls were at room temperature. From the nip rolls the yarn was guided to a winder at a tension of 55 grams so as to remove temporarily the crimp imparted.
COMPARATIVE EXAMPLE A
The procedure of Example 1 was repeated up to and including winding on the cooling roll. A yarn sample was taken as the yarn came off the cooling roll and placed in an oven at 300°F. to retract and crimp. A photograph of the yarn obtained after crimping is shown in FIG. 3, which is typical of yarn crimped by prior art procedures where nesting occurs.
EXAMPLE 2
A sample of the yarn produced was taken from the package wound. The sample was placed in an oven at 300°F. to retract and crimp. A photograph of the yarn obtained after crimping is shown in FIG. 4. The photograph demonstrates that the process of this invention produces a yarn having latent crimps which, when developed, develop "out of phase," i.e., are substantially free of the nesting problem shown in FIG. 3.
It has long been known that the drawing of a filamentary over a sharp edge will induce curl or crimp in the filamentary material. This is disclosed, for example, in U.S. Pat. No. 1,959,104, issued May 15, 1934 to L. D. Mahan, wherein the filamentary material is metal. In U.S. Pat. No. 2,245,874, issued June 14, 1941 to W. S. Robinson, the same basic procedure is employed to provide a cushioning material composed of vegetable fibers. In British Pat. Specification No. 558,297, accepted Dec. 30, 1943 to Imperial Chemicals Industries, Ltd., the same basic procedure is employed on nylon fibers to provide crimped threads or filaments for use in textile applications. U.S. Pat. No. 2,919,534 issued Jan. 5, 1960 to E. D. Bolinger et al., discloses the same basic procedure modified to heat the filaments prior to contact with the sharp edge. U.S. Pat. No. 3,136,111, issued June 9, 1964 to E. H. Pittman, discloses essentially the same process as that of the Bolinger et al., reference except that the drawing tension is intermittently varied to provide an intermittent crimp. Numerous other modifications and extensions of the basic principle of edge-crimping are disclosed in a great number of additional patents, none of which are considered of any particular pertinency to the present application.
Basically, the object of edge-crimping is to impart a strain along one side of each filament length so that when the filaments are subjected to relaxation upon further heat treatment, one side retracts to a different extent then the other thus causing the filament to curl, crimp, or coil. Current practice is to draw the filaments heated to a temperature just below their sticking temperature over the sharp edge. After drawing has been effected as described, the yarn is cooled under tension to prevent premature crimping while setting the latent crimpability to provide for subsequent crimping when desired. The latent crimpability may be developed when desired by applying sufficient heat to the yarn in untensioned state so that it may retract for full crimp development. Often crimp development may be in stages, allowing a first partial retraction followed by a second retraction for full crimp development.
There are numerous methods by which the degree of retraction may be controlled, thereby controlling the degree of crimpiness developed. Usually the yarn is continuously overfed to a heated zone under controlled conditions so that the filaments are restrained from contracting to the maximum extent possible. For example, in U.S. Pat. No. 3,439,391, issued Apr. 22, 1969 to B. M. De Vore et al., the drawn filaments are transferred through narrow tubes containing a gas. The gas is heated by external means and the filaments are allowed to crimp under such influence. In U.S. Pat. No. 3,241,212, issued Mar. 22, 1966 to C. G. Evans et al., a modification of the procedure of De Vore et al., is disclosed. In U.S. Pat. No. 3,478,401, issued Nov. 18, 1969 to J. W. Whitworth et al., the drawn filaments are overfed to a perforated roll and the filaments are heated with a hot gas. In U.S. Pat. No. 3,102,321, issued Sept. 3, 1963 to N. E. Klein et al., the filaments are overfed to a heated roll. Each of these methods has certain advantages and disadvantages which are mentioned in one or another of the references cited.
All of the methods of controlling retracting mentioned above, however, have one common processing feature, that of overfeeding the drawn yarn into a heated zone. With particular reference to the Klein et al., citation wherein over-feeding is to a heated roll, the method can only be used for specific thermoplastic filaments such as nylon and very low denier filaments. Due to short residence time on the roll, heat transfer is insufficient to cause retraction of high-melting polyester filaments or heavy denier filaments used in carpet yarns. As a result, insufficient tension develops on the yarn which slides off the roll and the process becomes inoperative.
A particular deficiency in methods which develop the crimp by heating the yarns in a relaxed condition is a phenomenon known as "nesting." Nesting is a term applied when all adjacent filaments in the yarn bundle develop their crimps in phase. That is to say, the crimped yarn will appear to be a singular coil spring of many filaments rather than a series of coil springs of individual filaments. Yarn composed of nested crimped filaments results in poor yarn bulk. The Klein et al., reference discusses the problem of nesting and apparently is effective in overcoming the problem with respect to those yarns processable therein. However, as previously noted, the process of Klein et al., is not applicable to most yarns because upon overfeeding to a heated roll they would fall off the roll and curtail processing. The De Vore et al., and Whitworth et al., references also discuss the nesting problem which is overcome by passing the yarn through an aspiraor to open same prior to crimp development. Such a provision, however, necessitates a continuous expenditure of high pressure air, which complicates processing and increases costs.
Thus, there continues to exist the need for improved edge-crimping processes for thermoplastic yarns of continuous filaments which overcome the deficiencies of the prior processes. Polyester yarns of carpet denier are not edge crimped because of the lack of an economical commercially acceptable process that provides the necessary product control and acceptability.
In accordance with the present invention, there is provided a process for texturizing untwisted yarn consisting of continuous thermoplastic filaments which comprises: heating the yarn to a temperature above its glass transition temperature but below its sticking temperature; drawing the yarn at such temperature over a sharp edge at an acute angle to induce a strain along one side of each filament length making up said yarn; cooling the yarn thus drawn so as to set the strain and relax the yarn; reheating the yarn to a temperature sufficient to cause crimping while maintaining sufficient tension on the yarn to prevent crimp development from occuring during said reheating, said reheating temperature being below the edge-drawing temperature; immediately releasing the tension on the yarn when it is at the crimping temperature so as to cause the yarn to ballon and the individual filaments to retract and develop crimp independently of one another; and thereafter advancing the yarn under sufficient tension to remove temporarily the crimp thus developed.
By carrying out the process in the manner described, the yarn obtained possesses highly desirable bulk, the degree of crimpiness developed is readily controlled, the problem of nesting is substantially eliminated and the deficiencies of the prior processes are overcome.
Useful thermoplastic yarns are those composed of filaments of fibrous textile materials that normally respond to edge crimping. The yarn is essentially free of twist and may be pre-drawn for orientation purposes or not. It is preferable that the yarn be undrawn since such drawing can be carried out in conjunction with edge drawing and thus save processing steps. Although not limited thereto, the present process is particularly adaptable to edge drawing polyester yarns of carpet denier.
The present proceds includes the steps of heating the yarn for edge crimpings and of cooling after edge crimping as these steps are employed in conjunction with conventional processes. Subsequent steps, however depart markedly from conventional processing and are responsible for the distinct results. In the present process, after the yarn is cooled following edge crimping to set the strain and relax the yarn, it is then reheated to a crimping temperature without allowing the yarn to crimp. This is a distinct departure from prior procedures wherein such reheating is carried out under conditions which allow the yarn to crimp as it is reheated. In the present process only after the yarn has reached the crimping temperature is it allowed to develop crimp. The reheated yarn, at the crimping temperature, suddenly is relieved of the tension that restrains it from crimping and immediately balloons as a result and crimping begins. That is to say, the individual filaments of the yarn upon removal of the tension immediately separate from one another as crimping begins and crimping of the individual filaments proceeds independently of one another. This is an entirely unexpected phenomenon and is responsible for the substantial absence of nesting exhibited by the present process. This absence of nesting is thus accomplished without the need for special provisions such as compressed gas to prevent nesting. After the yarn has developed its crimp as described, it then advanced under sufficient tension to remove temporarily the crimp thus developed. Advancement is generally to winding or packaging which may include a twisting operation in conjunction with winding.
Although the present inventor does not know the mechanism by which the ballooning phenomenon occurs in the present process and does not wish to be bound by any theory, he is of the opinion that the one-sided strain induced by edge drawing the filaments is of sufficient magnitude to cause the filaments to snap-retract when released from restraining tension while at crimping temperature. By "snap-retract" is meant that the filaments retract so rapidly as to generate lateral motion which causes ballooning or opening up of the untwisted yarn bundle.
Reference will now be made to the accompanying drawings in which
FIG. 1 is a schematic plan for carrying out a preferred embodiment of the invention.
FIG. 2 is an enlarged view of the section of FIG. 1 enclosed in the dashed line are an ABCD.
FIG. 3 is a photograph of an edge crimped yarn exhibiting nesting and not obtained by the process of the present invention.
FIG. 4 is a photograph of an edge crimped yarn obtained by the process of the present process and exhibiting the substantial absence of nesting characteristic of the present invention.
With reference to FIG. 1, an undrawn, untwisted, multifilament, thermoplastic yarn 10 is continuously fed from supply package 11 over tension bars 12 to a draw feeding roll 13. Roll 13 is preferably heated. After several wraps about roll 13 and idler rolls 14, the yarn is passed over heater plate 15 and makes surface contact therewith so as to heat the yarn to its draw temperature. The yarn is drawn by passing to draw roll 16, the peripheral speed is sufficiently greater than that of roll 13 to effect the desired draw ratio. Several wraps of yarn are taken about roll 16 and idler roll 17. Roll 16 is heated so that yarn 10 is hotter than its draw temperature but below its sticking temperature. The draw ratio may be up to about 6. The yarn 10 is then passed at an acute angle over a sharp edge 18 to roll 19 and idler 20. Roll 19 is significantly colder than roll 16 and serves to cool the yarn and set the strain imposed by edge 18. The surface speed of roll 19 is slightly less than that of roll 16, thereby allowing the yarn to shrink slightly after it passes over edge 18 and thus relax. Several wraps of yarn are taken about roll 19 and idler 20. The yarn is then advanced to roll 21 and idler 22, about which several wraps of yarn are taken. Roll 21 is heated to a temperature at which the yarn will crimp, which is below the temperature of roll 16 but above the temperature of roll 19. The tension on the yarn on roll 21 is sufficient to prevent the yarn from crimping even though it reaches crimping temperature. The yarn advances from roll 21 to idler 22 to a pair of nip rolls 23, 24, the surface speed of which is 5 to 20 percent less than that of roll 21. Thus, rolls 23 and 24 serve to rapidly release the tension restraining yarn 10 from crimping. As a result, yarn 10 as it leaves roll 21 and idler 22 immediately balloons and the individual filaments crimp independently of one another to form crimped yarn substantially free of nesting. The yarn 10 proceeds from nip rolls 23, 24, over guide rolls 25 to a winder 26 under tension sufficient to remove temporarily the crimp that has thus been imparted thereto.
In the above description of FIG. 1, actual temperatures, tensions, and roll speeds have not been given because these conditions will be dependent upon the particular type of thermoplastic yarn being processed, its chemical composition, molecular weight, denier of individual filaments and yarn, degree of drawing to be effected, the degree of crimp development desired, etc. Several essential requirements may be stated, however, which can readily be adapted to use. The temperature of the yarn on the draw roll 16 must be higher than the temperature of the yarn as it leaves the reheating roll 21. The yarn on roll 19 should be at a temperature which is lower than when the yarn is on either roll 16 or roll 21 and should reach a temperature below the glass transition temperature to set the strain. Preferably, a temperature well below the glass transition temperature will be reached, such as about 50°F. or more below the glass transition temperature, if possible. The temperature of the yarn as it leaves roll 21 should be sufficient to cause crimping as the tension is released. The temperature of the yarn as it is taken up on roll 16 must be above the glass transition temperature but below the sticking temperature. The temperature of the yarn as it leaves roll 21 is above the glass transition temperature but below the temperature reached on roll 16.
With reference to FIG. 2, the reheating roll 21 and idler 22 upon which the cooled drawn yarn is reheated is shown in conjunction with nip rolls 23 and 24 which operate at room temperature. The nip rolls run at a slower linear speed than that of roll 21 so that the tension on the yarn wrapped about roll 21 is immediately released as the yarn 10 leaves roll 21. In the space between roll 21 and nip roll 23, therefore, the yarn ballons and snap-retracts so that the individual filaments crimp independently of one another as shown. The nip rolls serve to control the amount of crimp developed by their linear speed but also enable tension to be reintroduced on the fiber without interfering with ballooning and snap-retraction thereof. Tension is necessary as the yarn advances from the nip rolls in order to remove temporarily the crimp obtained so that the yarn can properly be packaged or twisted and packaged. While the extent to which yarn retraction occurs in the space between roll 21 and nip roll 23 may vary widely, it is generally, preferable to control the retraction to between about 5 and 20 percent based on the drawn yarn length. When retraction is in the range stated, no true yarn shrinkage will occur, that is, the yarn upon subjection to tension just sufficient to be straightened from its crimped state will be substantially as long as it was prior to crimping. If retraction is less than about 5 percent, the yarn bulk is generally insufficient. If retraction is greater than about 20 percent, the yarn bulk is generally greater than desired.
The invention is more fully illustrated by the examples which follow employing polyester yarn of carpet denier. It is to be understood that the invention is readily carried out with other thermoplastic yarns of a wide range of deniers without departing from the scope of the appended claims.
EXAMPLE 1
A supply of 2250 denier polyethylene terephthalate yarn composed of 140 continuous filaments was employed. The polymer used to form the filaments had an intrinsic viscosity of 0.6. The yarn was advanced from the supply roll to a heated draw feed roll at 108 feet per minute (f/m). Five wraps of yarn were wound on the feed roll and idlers associated therewith, the feed roll being at 200°F. The yarn was then advanced to contact a heater plate having a surface temperature of 250°F. and taken up by a draw roll at a temperature of 430°F. The linear speed of the draw roll was 538 f/m thus drawing the yarn to a length that was 500 percent greater than its original length, i.e., a draw ratio of 5. Five wraps of yarn were taken about the draw roll and idler. The yarn was then guided under a sharp blade to a cooling roll at a temperature of 210°F. and having a linear speed of 508 f/m., thus allowing a relaxation of 5.6 percent. The angular path of the yarn with respect to the blade edge was about 30°. Five wraps of the strained yarn were taken about the cooling roll and idler so as to cool the yarn.
Up to this point, the process steps are conventional and well known in the art. The next series of steps depart from conventional procedures and constitute the distinguishing features of the present process which reflect the improved process and product therefrom.
The cooled yarn was fed to a heated roll at a temperature of 360°F. and having a linear speed of 510 f/m, which represents a slight underfeed. Five wraps of yarn were taken about the roll and idler so as to reheat the yarn under tension to a crimping temperature without enabling the yarn to retract and crimp. The yarn was then overfed to a pair of nip rolls having a linear speed of 450 f/m. As the yarn came off the roll at its reheated temperature it was free of tension because of the overfeed to the nip rolls. The yarn upon the release of tension immediately ballooned and retracted to form crimps in the individual yarns independently of one another i.e., with substantial absence of nesting. The nip rolls were at room temperature. From the nip rolls the yarn was guided to a winder at a tension of 55 grams so as to remove temporarily the crimp imparted.
COMPARATIVE EXAMPLE A
The procedure of Example 1 was repeated up to and including winding on the cooling roll. A yarn sample was taken as the yarn came off the cooling roll and placed in an oven at 300°F. to retract and crimp. A photograph of the yarn obtained after crimping is shown in FIG. 3, which is typical of yarn crimped by prior art procedures where nesting occurs.
EXAMPLE 2
A sample of the yarn produced was taken from the package wound. The sample was placed in an oven at 300°F. to retract and crimp. A photograph of the yarn obtained after crimping is shown in FIG. 4. The photograph demonstrates that the process of this invention produces a yarn having latent crimps which, when developed, develop "out of phase," i.e., are substantially free of the nesting problem shown in FIG. 3.