Textured Polyethylene Terephthalate Yarns

Abstract

Textile articles comprise yarns of a synthetic thermoplastic material, especially polyethylene terephthalate, in which the individual filaments comprise alternating zones of increasing and decreasing thickness, the thinner zones having the higher crystallinity index and vica versa; the filaments have a non-spiral three-dimensional crimp, and both they, and the yarn comprising them, have a high apparent volume. The yarn is made by only partially stretching the initial yarn in contact with a crack promoting agent such as an aqueous alcohol, and subsequently giving the yarn, before or after it is made up, a heat treatment while it is in a relaxed state.

Parent Case Text

CROSS REFERENCE TO RELATED APPLICATIONS

This is a division of copending application Ser. No. 799,795 filed Feb. 17, 1969.

Description

This invention relates to new textile articles comprising textured yarns of high apparent volume having a three-dimensional non-spiral crimp and to a process and a device for the manufacture of such yarns.

A large variety of so-called textured yarns already exists, and these can be schematically classified into spirally crimped yarns and non-spirally crimped yarns. The former are obtained by twisting, setting and untwisting, generally by means of a continuous false twist process. These yarns are noteworthy for a high elasticity which must for certain applications be reduced by means of a supplementary setting treatment.

The non-spirally crimped yarns have crimps of various configurations and are generally much less elastic, which is usually not undesirable. They are obtained by various processes using mechanical, pneumatic or mechanical-pneumatic devices. These processes suffer from the disadvantage of a relatively limited production speed as a result of the fact that moving elements are used.

Chemical processes have also been used to texture yarns. In fact it appears logical a priori to hope to obtain reproducible results more easily by chemical means.

However this method of texturizing has hitherto remained little developed because the processes which have been discovered have not given industrial results comparable to those obtained by mechanical means such as for example by false twist.

It was observed a long time ago that polyamide yarns can be cold-drawn more easily if they are moistened with water or with a hydroxylated non-solvent such as a lower aliphatic alcohol, a glycol or a hydroxy ester,

It has been proposed to manufacture a crimped yarn by moistening an unstretched or partially stretched polyamide yarn with water, stretching it in the cold, drying it in the untensioned state and subjecting it to a heat treatment before or after the cold drawing but before the untensioned drying.

It was later shown that stretching synthetic yarns in such baths causes the formation of cracks or surface crazing. Starting from this observation, a process for the manufacture of slub yarns has been proposed in which the filaments are tensioned whilst they are in contact with an agent which causes crazing, stretched to at least 1.01 times, and in general to approximately 2.5 times, their initial length, withdrawn from the influence of the crazing agent and stretched to produce a slub yarn having an oriented structure.

It has also been proposed to manufacture textured yarns from a yarn whose structure has been rendered asymmetric during spinning by the action of a cooling agent by tensioning it while it is in contact with a crazing bath, moistening it with a liquid medium which is free from crazing agents and stretching it in the moistened state. Yarns of a cracked structure have also been manufactured by maturing in a cracking bath with gentle stretching and then withdrawing the yarns from the bath and stretching them strongly. However, apart from the fact that this process does not produce textured yarns but yarns having a ribbed surface, it requires several days to carry out.

All these methods either produce a product such as a slub yarn which cannot pretend to replace a textured yarn, or provide a textured yarn but using, at some stage, another conventional process for obtaining a textured yarn such as asymmetric cooling of the yarn during spinning which is an operation which is delicate to carry out.

The present invention provides a new textured yarn of synthetic thermoplastic material, which can be obtained in a simple manner, the texturizing being effected either continuously on the yarn itself with orientation stretching of the yarn or, as is industrially an advantage, by pretreating the yarn and bringing out the texture during a subsequent treatment stage of the finished product, e.g., a knitted or woven fabric or similar material.

In one aspect the invention consists in a new textile article which comprises continuous multifilament yarns, and staple fibers obtained from such yarns, of a synthetic thermoplastic material, in which each filament comprises alternating zones in which its diameter increases and decreases progressively between at least two different mean values, the zones of lowest diameter corresponding to the zones having highest crystallinity index and a higher molecular orientation, each filament furthermore having a non-spiral three-dimensional crimp and a high apparent volume. The textile article is preferably made of a polyester.

In the case of polyethylene terephthalate, the thick zones are practically totally amorphous and unoriented and the thin zones have a crystallinity index exceeding 15 percent and in practice between 20 and 50 percent, the difference in the crystallinity indices of the different zones generally being of the order of 10 to 30 percent. Of course these figures are approximate, because the crystallinity indices depend on the degree of the stretching and of the subsequent heat treatment employed in the production of the yarn.

The total crystallinity index of this yarn is low. The crystallization and molecular orientation phenomena observed are reversible in character, in that if the yarn obtained according to the invention is again stretched to a total degree less than is required to orient it completely and this yarn is then treated thermally in the relaxed state, it re-assumes the appearance of the yarn of the invention before this additional stretching.

The overall crystallinity index value is determined by the method of W.O. Statton [Journal of Applied Polymer Science, Vol 7, Pages 803- 815-(1963) ] and the angle of orientation by the method of W. A. Sisson [Journal of Textile Research, Vol 7, Page 425 (1937)]. The values of the crystallinity indices and of the orientation angles for the various zones are determined taking into account the crystallinity indices and the overall orientation of the yarn, the proportions by volume of the various zones, the appearance of X-ray crystallographs, fluoresence comparisons after dyeing the various zones of a given yarn or of several yarns, and the morphology of these zones.

The differences in thickness of the yarn between the various zones and the number of different zones observed depend also on the working conditions. New zones are considered to have appeared if the appearance of sequences is observed wherein the variation from the mean diameter is at least equal to one tenth thereof. The yarn of the invention shows an alternation of at least two different zones having a random statistical distribution of their dimensions. It goes without saying that the values of the crystallinity index given above to characterize these zones are also statistical, but that they correspond to an acceptable probability factor.

The yarn of the invention is noteworthy for its microporosity and its very good dyeing affinity.

The invention also consists in a new process for the texturization of a yarn of a synthetic thermoplastic material, especially of a polyester which comprises partially stretching the yarn in contact with a crazing agent, and heat treating the partially stretched yarn in the relaxed state.

The heat treatment which may be termed "development," causes the structure of the yarn described above to appear.

The degree of stretching must always be partial, i.e., less than would cause a complete orientation of the yarn.

In practice, in the case of polyethylene terephthalate yarns of usual filament deniers, such as those employed in knitting or weaving, that is to say with filament deniers of less than 12, the degree of stretching is between 2 and 3.5 times and advantageously between 2.5 and 3 times. For yarns of filament denier exceeding 12 the degree of stretching should be between 3 and 4.5. This stretching is advantageously carried out at or near ambient temperature.

The thermal treatment can be carried out continuously with the stretching or can be given during a subsequent treatment of the yarn or, in the piece, during any stage of manufacture of a finished product, such as a dyeing treatment, or on the finished product itself. The time between this heat treatment and the stretching in a crazing bath can be of any length without causing problems with the resulting product and can be determined by considerations outside the purview of the invention, such as storage or handling times or requirements.

The heat treatment can be effected in any known manner, such as by steam, with hot air, or by contact with or by immersion in a bath of a liquid at a high temperature.

Known crazing agents can be used, e.g., alcohols, glycols, dimethylformamide, kerosene, perchlorethylene, polyoxyethylenic liquids of the "Carbowax" type, pyridine, etc. Such compounds have frequently been described in the literature. Preferably, relatively cheap agents are employed, such as lower alcohols.

The present invention consists further in a device for the continuous manufacture of a textured yarn which in sequence comprises yarn feeding means, means for immersing the yarn in a crazing agent, means for continuously stretching the yarn in contact with the crazing agent, a heat relaxation element consisting of a heating means combined with means of relaxing the yarn, and winding up means. It can also comprise means for controlling the temperature of the crazing bath.

This device advantageously also comprises a device for interlacing the constituent filaments of the yarn, arranged upstream from the heat relaxation element. Such a device can be used to increase the bulk of the yarn. An advantageous interlacing device is described in French Pat. No. 1,492,945.

The heat relaxation element can be of a type which is in itself known. It can for example consist of a mechanism for forwarding the yarn, especially by means of rollers, combined with a heating box. It can also comprise a device which serves also for the application of another treatment for example a dyeing vat.

The invention is illustrated in the accompanying drawing, in which

FIG. 1 is a schematic view of a device according to the invention.

FIG. 2 is a representation of the filament obtained, and

FIG. 3 is a representation of a multifilament yarn of the invention.

The device shown in FIG. 1 consists of a creel 1 carrying spools 2 which deliver an unstretched yarn 3 which is drawn off, over a wire thread guide 4, by means of a system of feed rollers 5 and 6, and then passes into a vat 7 containing a crazing bath. From this it passes to a set of stretching rollers 8 and 9, set to run at a higher peripheral speed than the feed rollers 5 and 6.

The yarn then passes to a heat relaxation element consisting of a heating box 12 arranged downstream from the stretching rollers 8 and 9 and a set of relaxing rollers 13 and 14 arranged downstream from the heating box and upstream from a wind-up device, for example comprising a spindle. The relaxing rollers 13 and 14 are arranged to run at a lower peripheral speed than the stretching rollers 8 and 9.

This device can furthermore comprise a heating plate 11 located just downstream from the vat 7.

In another variant, the last traces of crazing agent are removed in the cold by passing the yarn into a strand interlacing device 15, such as for example that described in the above mentioned French Pat. No. 1,492,945, which is advantageously situated between the stretching rollers 8 and 9 and the heating box 12.

The yarns used in the following illustrative Examples consist of polyethylene terephthalate having an intrinsic viscosity, in o-chlorophenol, of a value which is usual for textile yarns, of the order of 0.065.

EXAMPLE 1

A 33 filament polyethylene terephthalate yarn of filament denier 7 is stretched by a factor of 3 in an aqueous bath containing 25 percent per weight of ethanol and kept at 40.degree.C. From this bath it passes into a strand interlacing device 15 and it is then treated in the completely relaxed state in a steam oven 12 at a temperature of 126.degree. C. The stretching rollers 8 and 9 run at a peripheral speed of 250 m/minute and the relaxing rollers 13 and 14 at 81 m/minute.

The yarn obtained has a bulkiness, as measured by the Konigh method, of 2.5 cm.sup.3 g, a crimp of about 25 waves per cm and a tensile strength of 3.5 g/denier.

For purposes of comparison, certain characteristic properties were measured on each elementary filament before and after the heat treatment in the relaxed state.

Before the heat treatment it is found that, if the diameter of each elementary filament is irregular at all, the difference between the swollen parts and the thin parts is relatively slight, their respective diameters being 16.7 and 15.6 microns (.mu.). The overall crystallinity index is about 3 percent. The thin parts have a crystallinity index of about 15 while the crystallinity of the thick parts is essentially zero, both parts being fairly well oriented. On microscopic examination the filament shows surface crazing or cracks.

After it has been developed by heat treatment in the completely relaxed state, it is found that the yarn has shrunk considerably by at least 25 percent of its initial length and usually between 50 and 80 percent of its initial length.

Microscopic observations shows the presence of narrow zones and swollen zones very closely packed, giving the filament the appearance of a string of slubs as illustrated in FIG. 2.

The diameter of the swollen parts has changed from 16.7 to 28 .mu., while that of the thin parts remains essentially unchanged.

It is furthermore observed that the crystallinity index of the thin parts is now about 25 percent whilst that of the thick parts has remained about zero. This difference in crystallinity is also determined by observing the fluorescence with Rhodamine B (C.I. 45,170 ).

On the other hand the orientation is very slight, the angle of molecular orientation p is about 75.degree. for the thin parts and 90.degree. for the thick parts.

Furthermore this yarn shows good dyeing affinity. This latter property is demonstrated in the following manner.

The yarn is continuously dyed by passing it, after the heat treatment in the relaxed state and before winding-up, over a dyeing device comprising a porous partition having an essentially plane smooth surface such as is described in French Pat. No. 1,502,746, the said surface being impregnated with an aqueous dyeing bath containing 15 g/l of the dispersed dyestuff Disperse Yellow 7 (C.I.26,090).

A yarn dyed yellow is obtained, though under the same conditions a standard polyethylene terephthalate yarn does not accept the dye.

EXAMPLE 2

The procedure of Example 1 is followed, except that the yarn is interlaced after stretching and before the winding-up and heat treatment. The yarn then has a bulk of 3 cm.sup.3 /g.

EXAMPLE 3

In this Example the yarn is stretched in the same way, but is developed in a Venturi type of nozzle fed with air heated to 200.degree. C.

The yarn then has a bulk of 2.5 cm.sup.3 /g.

It is thus seen that this new texturizing process makes it possible continuously to obtain closely reproducable yarns of high apparent volume in the course of very simple operations using a device that has a minimum of moving elements and chemical baths of constant concentration. Furthermore this process makes it possible to texture yarns at high speeds, comparable to the speeds achieved during winding-up after spinning and stretching.

Furthermore, by virtue of the shrinkage of these yarns, it is possible, by heat-treating in the piece, to achieve effects comparable to those given by other shrinkable yarns.

The yarns of the invention may be used, by themselves or in mixtures, in the form of continuous lengths or of cut fibers, in the majority of textile applications and can in particular be converted into woven or knitted fabrics.

Claims

We claim:

1. Textile articles comprising multi-filament polyethylene terephthalate yarns, in which each filament consists of alternating zones whose diameter progressively increases and decreases respectively between at least two different mean values, the parts of lowest diameter having the highest crystallinity index and molecular orientation, the crystallinity index in the thinner parts of the filaments being at least 15% and the thicker parts being substantially wholly unoriented and amorphous, each filament having a non-spiral three-dimensional structure and a high apparent volume.

2. Textile articles according to claim 1, in which the crystallinity index of the thinner parts of the filaments is between 20 and 50.