US3719976A

US3719976A - Process for producing crimped polyester filaments

Info

Publication number: US3719976A
Application number: US00140209A
Authority: US
Inventors: Y Murase; H Toyoshima; R Yamamoto; N Izawa; M Kikuyama
Original assignee: Teijin Ltd
Current assignee: Teijin Ltd
Priority date: 1971-05-04
Filing date: 1971-05-04
Publication date: 1973-03-13
Anticipated expiration: 1990-03-13

Abstract

A process for producing polyester filaments having high Young''s modulus and excellent crimps, which comprises heat-treating a bundle of drawn filaments of linear polyester in which at least 85 mole percent of the recurring units consist of ethylene terephthalate, at a temperature of 135* to 240*C. under a tension of at least 0.3 g/denier, feeding the filaments to the nip rollers of a stuffer box while maintaining the filaments at a temperature at least 10*C. lower than the heat-treating temperature and between 100* and 140*C. under a tension of at least 0.1 g/denier, crimping the filaments in the stuffer box, and then with-drawing the filaments from the stuffer box.

Description

United States Patent [19 1 Izawa et al.

[ 1March 13, 1973 PROCESS FOR PRODUCING CRIMPED POLYESTER FILAMENTS Inventors: Nobuharu Izawa; Munetsugu Kikuyama; Hiroshi Toyoshima; Ryuji Yamamoto, Yasuhiro Murase; all of Matsuyama, Japan [73] Assignee: Teijin Limited, Osaka, Japan [22] Filed: May 4, 1971 [21] Appl. No.: 140,209

UNITED STATES PATENTS l/l97l Buschmann et al. ..28/l .6

Primary Examiner-Louis K. Rimrodt Attorney-Sherman & Shalloway [57] ABSTRACT A process for producing polyester filaments having high Youngs modulus and excellent crimps, which comprises heat-treating a bundle of drawn filaments of linear polyester in which at least mole percent of the recurring units consist of ethylene terephthalate, at a temperature of to 240C. under a tension of at least 0.3 g/denier, feeding the filaments to the nip rollers of a stuffer box while maintaining the filaments at a temperature at least 10C. lower than the heattreating temperature and between 100 and C. under a tension of at least 0.1 g/denier, crimping the filaments in the stuffer box, and then with-drawing the filaments from the stuffer box.

8 Claims, 1 Drawing Figure PROCESS FOR PRODUCING CRIMPED POLYESTER FILAMENTS This invention relates to a process for producing polyester filaments having both high Youngs modulus and excellent crimps.

Previously, polyester type fibers have been widely utilized in the form of staple fibers after being given mechanical crimps. Usually, after melt spinning, the polyester fibers obtained are drawn, and then subjected to heat-treatment while allowing shrinkage to take place in order to improve their dimensional stability, but the Youngs modulus of the polyester fibers thus obtained is considerably lower than that of natural cotton fibers. Therefore, there has been a demand for excellently crimped polyester fibers still having a Youngs modulus equal to, or higher than, natural cotton fibers. In an attempt to produce such polyester fibers, a method has been developed in which after melt spinning, the resulting filaments are drawn in multistages at the highest possible draw ratios to form polyester filaments having a high Youngs modulus, and then the filaments are subjected to a crimping treatment. However, when such filaments are crimped, for instance, by a stuffer crimper, there is the defect that the filaments are more difficult to crimp with increasing Youngs modulus. This is due to the fact that the deformation of the filaments is difficult to cause because of the high Youngs modulus, and the filaments are not sufficiently bent. One method of removing this defect is proposed in Japanese Patent Publication No. 22028/64 which discloses a method wherein the filaments are preheated before the crimping operation so as to reduce the Youngs modulus and accordingly to make them easy to crimp. Another method of this kind is disclosed in Japanese Patent Publication No. 14017/64, in which after heat-treatment under tension, the filaments are cooled to below the minimum crystallization temperature (usually 90-95C. for polyester fibers) to retard crystallization. These methods have contributed to some extent to the improvement of the crimpability of the polyester fibers of high Youngs modulus. But the crimpability is still inferior to that of polyester filaments having low Youngs modulus, and improvement is still required.

It is therefore an object of this invention to provide a process for producing polyester filaments having high Youngs modulus and excellent crimps which properties have been somewhat inconsistent with each other.

According to this invention, a process is provided for producing polyester filaments having high Youngs modulus and excellent crimps, which comprises heattreating a bundle of drawn filaments of a substantially linear, fiber-forming, high-molecular-weight polyester having at least 85 mole percent of the recurring units consisting of ethylene terephthalate, at a temperature of 135 to 240C. under a tension of at least 0.3 g/denier, feeding the filaments to nip rollers of a stuffer crimper while maintaining the filaments at a temperature at least C. lower than the heat-treating temperature and between 100 and 140C. under a tension of 0.1 g/denier or more, crimping the filaments in the stuffer box and then withdrawing the filaments therefrom.

The invention will be described in greater detail below with reference to the accompanying drawing which is a schematic side elevation of an apparatus for performing one embodiment of the process of the present invention.

The polyester filaments used in the invention are those obtained from a substantially linear, fibenforming, high-molecular-weight polyester in which at least mole percent of the recurring units consist of ethylene terephthalate. The polyester polymer may contain less than 15 mole percent of an acid component such as isophthalic acid or adipic acid, an alcohol component such as propylene glycol, or a branching agent as a copolymerzable component.

. According to the process of the present invention, the polyester described above is melt-spun by an ordinary method to form undrawn filaments and then the undrawn filaments are hot drawn by a known method to form drawn filaments. Preferably, the drawing is carried out in multi-stages, and by this method highly oriented filaments can be obtained. The preferred total draw ratio used at this time is 3.5 to 6.0. The drawn filaments so obtained are heat treated at a temperature of to 240C. under a tension of at least 0.3 g/denier to produce polyester filaments having high Youngs modulus which are highly oriented and crystallized. 1f the heat-treatment temperature is lower than 135C, the Youngs modulus of the resulting crimped filaments is not sufficiently high. On the other hand, heat-treating temperatures above 240C. cause localized melting of the filaments, and result in the melt-adhesion of the filaments with one another. Such filaments are of course not viable for practical purposes.

The preferred heat-treating temperature is from 150 to 230C. The tension to be exerted on the filaments at the time of heat-treatment should be at least 0.3 g/denier. If the tension is lower than 0.3 g/denier, even heattreatment at temperatures within the above-specified range does not give filaments of sufficiently high Youngs modulus, and there is the accompanying defeet of the difficulty of crimping such filaments. The preferred lower limit of the tension is 0.5 gldenier, and the preferred upper limit is 3.5 g/denier.

The heat-treated polyester filaments are then cooled, and then fed to nip rollers of a stuffer box while the filaments immediately before entry into the nip rollers are maintained at a temperature at least 10C, preferably at least 20C. lower than the heat-treatment temperature and between 100 and C. and under a tension of at least 0.1 g/denier. Within the stuffer box, the filaments are crimped in a manner known per se. The crimped filaments are withdrawn from the stuffer box in accordance with a customary method. Coveniently, the temperature adjustment of the filaments is accomplished by using conventional heating rollers. The temperature of the filaments generally drops to some extent during the travelling of the filaments between the last heating roller and the nip rollers of the stuffer crimper. In the process of the present invention, therefore, it is necessary to set the temperature of the heating rollers so that the temperature of the filaments immediately before entry into the nip rollers is within the range specified above. The extent of temperature drop of the filaments travelling between the last heating roller and the nip rollers depends upon such factors as the difference between the temperature of the last heating roller and the ambient temperature or the travelling time (usually less than several seconds), but once the operational conditions are set at constant values, the extent of the temperature drop also becomes substantially constant. Therefore, in actual operation, the temperature of the filaments immediately before entry into the nip rollers is measured by a proper surface temperature measuring device, and the tempreature of the heating roller is set so that this measured temperature is within the temperature specified in the present invention.

The critical point of the process of the invention is that the polyester filaments heat-treated under tension are cooled to a temparature at least C. lower than the heat-treating temperature and between 100 and 140C. and placed under a tension of at least 0.1 g/denier, and in this state the filaments are fed to the nip rollers of the stuffer crimper. In particular, the novel feature of the invention consists in the employment of the above-described feed conditions in relation to the condition of heat treatment under tension mentioned above.

When the polyester filaments are stuffed into the stuffer box via the nip rollers, they are inevitably released from tension within the stuffer box. As is generally known, when filaments are placed under tension, free shrinkage is restrained by the tension, but when the filaments are placed in a tension free state, free shrinkage develops abruptly and easily; consequently, the orientation of the filaments is relaxed and their Youngs modulus is reduced. Such a relaxation of the orientation which occurs within the stuffer box is supposed to be higher with increasing temperature of the filaments fed into the stuffer box. It has been found that in order to prevent the high Youngs modulus of the polyester filaments attained by the heat-treatment specified in the present invention, from being reduced by the relaxation of the orientation described above, it is very effective to feed the filaments to the nip rollers of a stuffer box while maintaining the filaments at a temperature at least 10C., preferably at least C., lower than the heattreatment temperature.

For the same reason as mentioned above, too high a temperature of the filaments at the entry into the stuffer box is undesirable for maintaining a high' Youngs modulus. It is therefore necessary to adjust the temperature of the filaments to be fed to the nip rollers by the process of the invention to 140C. or below. On the other hand, from the standpoint of the ease of crimping, filaments to be crimped should convenietly have the highest possible temperature and be softened. Since the filaments to be crimped in the invention have high Youngs modulus and are highly oriented and crystallized, the softening of the filaments plays an especially important role for imparting good crimps to the filaments. Therefore, in the process of the invention, the temperature of the filaments to be fed to the nip rollers should be adjusted to 100C. or above, preferably 1 10C. or above.

It is further very important in the process of the present invention that the polyester filaments heattreated under tension should be fed to the nip rollers of the stuffer box while maintaining them under a tension of at least 0.1 g/denier without releasing the tension. In the conventional methods, it was common practice to release the tension offilaments and place them in a tension-free state or place them under a slight tension, and feed the filament into the stuffer box in such a tensionfree state. According to these methods, the fiber-structure of the filaments is stabilized incident to their shrinkage in a state of low tension. On the other hand, the degree of orientation is reduced, and the Youngs modulus of the filaments is decreased. It is due to this structural stabilization by the shrinkage that the filaments become difficult to crimp. The novel feature of the process of the present invention is that the filaments can be given both excellent crimps and a high level of Youngs modulus by placing the heat-treated filaments under tension until they are fed into the stuffer box and at the same time maintaining the filaments immediately before entry into the nip rollers at the specific temperature described above. In the process of the present invention, the preferredtension to be exerted on the filaments to be fed to the nip rollers is at least 0.2 g/denier. The upper limit of the tension is difficult to set, but can be defined as the tension such that the nip rollers of the stuffer box can grip the filaments sufficiently without slippage. Usually, the upper limit of the tension is about 1.0 g/denier. The stuffer crimper used in the invention may be of any type known and used in theart.

Referring to the accompanying drawing, undrawn filaments extruded from a melt-spinning apparatusof the conventional type (not shown) are drawn by feed rollers (not shown), a heating device (not shown) such as hot pin, hot plate, or hot bath and a pair of draw rollers l and 1' to produce drawn filaments 2. The drawn filaments 2 which have left a pair of draw rollers l and l, are heat-treated under tension by

rollers

3,4,5,6 and 7 heated at 240C. The filaments are then passed over

heating rollers

8 and 9 the temperature of which is set so that the temperature of the filaments immediately before entryinto between nip rollers 11 and 11' is at least 10C. lower than the heat-treating temperature and between 100 and C., and cooled to some extent. The filaments are then passed over a guide roller 10, and then fed between a pair of nip rollers 11 and 11' and then stuffed into a stuffer box 12 and crimped therein. Thereafter, the crimped filaments are withdrawn from the stuffer box 12, and fed onto a net conveyor 13. If desired, the filaments are subjected to heat-treatment in a relaxed state. Then the filaments are transferred to a cutter (not shown), and cut to staple fibers. It is preferred that the draw rollers l and l and the heating rollers 3 to 9 are alldriven at the same peripheral speed. The peripheral speed of the nip rollers 11 and 11' may be 95-105 percent of that of the heating roller 9 so that the tension on the filaments between the guide roller 10 and the nip rollers is 0.1 g/denier or above.

It is preferred that one or more of the heating rollers 3 to 9 should be used for cooling purposes. The number of the cooing rollers is properly chosen. Hot plates or hot vapor may also be used as the heating or cooling medium. The use of rollers is advantageous in that a larger length of contact between the roller and the filaments can be obtained with the need for a smaller space.

The following Examples will illustrate the present invention.

EXAMPLE 1 A 500,000 denier undrawn polyethylene terephthalate tow was drawn at a draw ratio of 3.80 at 70C. in a It is clear from the results given in Table l that polyester filaments having sufficiently high Youngs modulus cannot be obtained at temperatures below 135C., and when the heat-treatment temperature is first stage, and at a draw ratio of at in 5 250C, the undesirable melt-adhesion of the individual a second stage The tow was then passed over heating filaments occurs. The results of the

comparison

2, 3 rollers of the type shown in the accompanying dra g, and 4 show that unless the temperature of the filaments and then fed into a stuffer crimpe Wher t as immediately before entry into the crimper is kept at crimped. The heating rollers 3 to 7 were used for heatleast C. lower than the heat-treating temperature treating purposes, and the

heating rollers

8 and 9, for 10 and between 100C. and 140C., both the crimpability cooling purposes. The experiments were performed at and Youngs modulus cannot be improved at the same varying roller temperatures. The tension of the tow was time. 1.5 g/denier between the roller 3 and the cooling roller 9, and 1.0 g/denier between the guide roller 10 and the EXAMPLE 2 nip rollers 11 and 11'. The results are shown in Table 1. C im ed l e ter filaments were produced under The percentage crimp, the number of-crimps, and the same conditions as used in the preparation of the Youngs modulus were measured by the following filaments in Run 5 of Example 1 except that the tension methods. of the yarn was the same both at the time of the heattreatment under tension and at the time of cooling PERCENTAGE CRIMP treatment, and this tension was varied as shown in Table 2 below. The properties of the filaments obtained The specimen filament ofa given length (a) is placed are shown in Table 2 below. under an initial load of 2 mg/denier. Then, a load of 50 mg/denier is exerted on the filament, and the length (b) T bl 2 of the filament is measured after the lapse of P seconds. The percentage crlmp 1s expressed by: Tension of Number of gg Young,s Run Nos. the yarn crimps per camp lrtntlxduh s d 25 m X 100 (Percent) s-1 e) l5. 6 g 731i 30 5-2 0.6 12.6 14,2 680 54 0.4 13.0 13.3 600 NUMBER OF CRIMPS Comparison 0.25 12.8 11.6 510 The g i a g 3 It is seen from the results shown in Table 2 that the i 5. 2 emler s 5 tension of the yarn at the time of the heat-treatment Va 9 y 6 Va 0 gwes t e must be at least 0.3 g/denier, preferably at least 0.5 number of cr1mps per 25 mm smce the number of g/denier, and when the tension is reduced to 0.25 g/debuckllng pomts 1s tw1ce as great as that ofcrlmps. flier the Youngis modulus decreases, and filaments having high Youngs modulus cannot be obtained. YOUNG S MODULUS EXAMPLE 3 The stress-strain curve of the specimen filament is Crimped polyester filaments were produced under recorded by an lnstron tensile tester, and the Youngs the Same conditions as Shown in Runs NOS. 1 and 7 in modulus is calculated from the inclination of the tan- Example 1 except that the tension f the yam between gem which Provides the maximum gradient oh the the heating roll 9 and the nip rollers of the crimper was curvechanged as follows: (a) reduced to 0.5 g/denier, (b) The temperature of the filaments at the inlet of the reduced to 2 g/denier, (c) reduced to 1 g/denier, crimper as shown in Table l was obtained by measuring 1) d d to 0 05 /d nier, nd (e) reduced to 0.05 the temperature of the filaments immediately before g/denier and the elevated to 5 g/denieL The entry to the nip rollers of the crimper using a surface cemage rimp and the number of crimps of each of the temperature measuring instrument type PIP-4F filaments obtained were measured and shown in Table produced by Anritsu Meter Mfg., Co. 3

TABLEI Temperature Temperature Temperature of heating eating ofthe tow Number 01 Percentage Youngs rollers 3 to 7 rollersBand 9 at the inlet crlmps per crimp modulus Run numbers 0.) C.) of crimper .5 cm. (percent) (kg/mm?) Comparison 1. 125 115 111 13. 0 13. 0 550 1 135 115 110 12. s 14. 3 710 2 135 125 119 13.1 12.3- 660 Comparison 2 135 135 129 12.9 12.1 530 com arisons 150 87 13.2 10.3 720 3 150 102 13.1 12.9 750 4" 150 104 12. 9 1a. 9 150 5. 150 113 1:1. 3 15.8 780 a... 170 130 121 13.0 15.4 860 1 170 13s 13. 1 14. 0 s50 Cmnparison 4 170 147 13. 0 12.4 570 a 230 130 120 12.8 12. 4 s30 Comparison 5 250 130 118 Melt adhesion occurred partly TABLE 3 Run No. 1 Run N0. 2

Heat-treating temperature Cooling temperature Number Percentage Young's Number Percentage Youngs of crimps crimp modulus of crimps crimps modulus Properties per 2.5 cm. (percent) (kgJmmfl) per 2.6 cm. (percent) (kg/mm!) The results shown, in Table deinh'iihTtFafiwfieh I ff'ififii's"tfciafih'i, wherein the upper limit of the tension of the yarn is once reduced as in (d) and (e), the relaxation of the strain of the filaments rapidly proceeds, and it becomes difficult to impart good crimps to the filaments and at the same time, the Youngs modulus is reduced.

What we claim is:

l. A process for producing polyester filaments hav- 7 ing high Youngs modulus and excellent crimps, which comprises heat-treating a bundle of drawn filaments of a substantially linear, fiber-forming, high-molecularweight polyester in which at least 85 mole percent of the recurring units consist of ethylene terephthalate, at a temperature of 135 to 240C. under a tension of at least 0.3 g/denier; feeding the filaments to the nip rollers of a stuffer box while maintaining the filaments at a temperature at least 10C. lower than the heat-treating temperature and between 100 and 140C. under a tension of at least 0.1 g/denier; crimping the filaments in the stuffer box; and then withdrawing the filaments from the stuffer box.

the tension during the heat-treatment is 3.5 g/denier.

3. A process of claim 1, wherein the lower limit of the tension during the heat-treatment is 0.5 g/denier.

4. A process of claim 1, wherein the treating temperature in the heat-treatment step is to 230C.

5. A process of claim 1, wherein the filaments heattreated under tension are fed to the nip rollers with the temperature of the filaments maintained at at least 20C. lower than the heat-treating temperature.

6. A process of claim 1, wherein the lower limit of the temperature of the filaments fed to the nip rollers is 1 10C.

7. A process of claim 1, wherein the upper limit of the tension of the filaments fed to the nip rollers is 1.0 1

g/deier.

8. A process of claim 1, wherein the lower limit of the tension of the filaments fed to the nip rollers is 0.2 g/denier.

Claims

1. A process for producing polyester filaments having high Young''s modulus and excellent crimps, which comprises heat-treating a bundle of drawn filaments of a substantially linear, fiber-forming, high-molecular-weight polyester in which at least 85 mole percent of the recurring units consist of ethylene terephthalate, at a temperature of 135* to 240*C. under a tension of at least 0.3 g/denier; feeding the filaments to the nip rollers of a stuffer box while maintaining the filaments at a temperature at least 10*C. lower than the heat-treating temperature and between 100* and 140*C. under a tension of at least 0.1 g/denier; crimping the filaments in the stuffer box; and then withdrawing the filaments from the stuffer box.

2. A process of claim 1, wherein the upper limit of the tension during the heat-treatment is 3.5 g/denier.

4. A process of claim 1, wherein the treating temperature in the heat-treatment step is 150* to 230*C.

5. A process of claim 1, wherein the filaments heat-treated under tension are fed to the nip rollers with the temperature of the filaments maintained at at least 20*C. lower than the heat-treating temperature.

6. A process of claim 1, wherein the lower limit of the temperature of the filaments fed to the nip rollers is 110*C.

7. A process of claim 1, wherein the upper limit of the tension of the filaments fed to the nip rollers is 1.0 g/deier.