US3677880A - Synthetic conjugate filament fibers and a process for the manufacture of the same - Google Patents

Abstract

A SYNTHETIC CONJUGATED COMPOSITE FILAMENT FIBER, CONSITING OF TWO CONJUGATED POLYESTER FILAMENTARY COMPONENTS, ONE OF SAID COMPONENTS BEING POLYTHYLENE TEREPHTHALATE AND THE OTHER OF SAID COMPONENTS BEING POLYETHYLENE DIPHENOXYETHANE-4,4''-DICARBOXYLATE, SAID POLYETHYLENE TEREPHTHALATE BEING THE LOAD-BEARING COMPONENT.

Description

July 18, 1972 NOBQRU FUKUMA ETAL 3,677,880

SYNTHETIC CONJUGATE FILAMENT FIBERS AND A PROCESS FOR THE MANUFACTURE OF THE SAME Filed April 16, 1968 United States Patent US. Cl. 161-173 14 Claims ABSTRACT OF THE DISCLOSURE A synthetic conjugated composite filament fiber, con- 15 sisting of two conjugated polyester filamentary components, one of said components being polyethylene terephthalate and the other of said components being polyethylene diphenoxyethane-4,4'-dicarboxylate, said polyethylene terephthalate being the load-bearing component.

This invention relates to improved conjugated synthetic filament yarns and the like and a process for the manufacture of the same.

In the past, polyethylene phenoxyethane 4,4 dicarboxylate, hereinafter referred briefiy as PSEE which means poly symmetrical ether ester was known to have melt-spinnability. This fact was hidden behind the background where grave development efforts were made in the spinning technique of polyethylene terephthalate, hereinafter referred briefly as PET. Therefore, necessary spinning conditions, the nature and performance of the fiber manufactured therefrom, and the like specific data concerning PSEE have been difiicult to ascertain in the literature and almost unknown to those skilled in the art.

On the other hand, conjugated and crimpable fibers composed of PET as its one component have long been known and investigated to a substantial degree. In this advanced technique for the manufacture of conjugated filament fibers, the opposite conjugating partner has been exclusively polyamide the representative of which is nylon 66, as revealed, for instance, in prior published specifications of US. Pats. 2,931,091; 2,987,797 and 3,118,011.

A considerable difiiculty met with the above-mentioned known conjugated fibers resides in impracticability of forming side-by-side type conjugated filaments, on account of poor conjugation between the both components. Therefore, these conjugated filaments have been manufactured exclusively in the form of eccentric sheath core types which result naturally in considerable difiiculty in the formation of fine crimps on the filament fiber.

Therefore, it is the main object of the invention to provide a conjugated fiber capable of taking the form of sideby-side type having as its main component, a polyester polymer, yet capable of developing fine crimps on the fiber.

In the aforementioned known type conjugated filament, the more heavily load-carrying component which occupies the inner side position when the developed crimps are tensioned by being subjected to the action of an external tensile force, said component to be referred to as LB- component hereinafter throughout this specification, is composed exclusively of polyamide and therefore the crimp elongation resistance, crimp recovery performance and the like important factor of the conjugatedly spun product will naturally and substantially depend upon the kind and nature of the polyamide component employed. Therefore, it can be said that these known kind of fibers, when after-treated as conventionally into crimped yarns, are substantially similar to bulky nylon yarns in their fiber p CC characteristics, which represent however a comparatively poor crimp recovery performance.

A further object of the invention is to povide a conjugated fiber yarn which has a considerably improved crimp recovery performance relative to the bulky nylon yarns.

The aforementioned known type of conjugated filament with its main conjugated component being composed of polyamide has a further disadvantage of difliculty in the manufacture of pure white products, in that the fiber whiteness deteriorates upon exposure to light.

A still further object of the invention is to provide an improved conjugated fiber of the kind referred to above which is capable of obviating said conventional disadvantages.

The conventional conjugated filament fiber represents a further disadvantage with respect to dying, especially even dying thereof, on account of the presence of the PET-component.

It is a still further object of the invention to provide a synthetic conjugated fiber which has a superior dying characteristic.

In order to realize the aforementioned objects, this invention resides in its broadest aspect, in a synthetic conjugated fiber consisting of two elemental filaments, one of which is com-posed of a polyethylene terephthalate polymer, and the other of which is composed of polyethylene diphenoxyethane-4,4'-dicarboxylate.

The invention in another aspect concerns a process for the manufacture of the same.

A preferred embodiment of the process according to this invention is carried out in such a way that PET-polymer and PSEE are melt-spun conjugatingly in the sideby-side mode or in the eccentric sheath core mode, and then stretched under tension at 140 C. The thus prepared filament fiber exhibits a remarkable and sensibly crimping performance which means it has a nature to develop crimps on the filament upon being only loosened from its tensioned and stretched state. When the thus loosened and crimped fiber filament is subjected to a heat treatment under its loosened state, the crimp characteristic is further improved, the LB-component thereof being exclusively composed of the PET-polymer.

The above embodiment of the process may be so additionally modified in such a way that the thermally stretched fiber at 70-140 C. is further thermally processed under tension at l00-l80 C. The thus developed crimps on the conjugated composite fiber are substantially finer than the case where the additional and final heat treatment has been dispensed with. When the conjugatedly spun filament be only kept loosened from its tensioned state, without being subjected to heat treatment step or steps as aforementioned, the crimps will have been too roughly developed to produce a bulky yarn.

PET-polymers employed in this invention as one of the conjugating components to be united into a single filament may be used either in its pure state or in its modified state. For the latter purpose, a third constituent may be included less than 20% in the main polymer PET, so as to form a copolymerized polyethylene terephthalate. When such modified PET-polymer is spun, stretched and then preferably heat treated, it provides fiber filaments having substantially the same as or an even greater thermal shrinkage coeflicient than the pure PET-polymer and being thus utilizable as LB-component of the filament fiber of the present invention.

The modified PET-polymer as the conjugated component has a rather improved drying characteristic in comparison with the pure PET-component, thus showing a corresponding advantage in this respect. However, the former shows an increased stiifness of the crimps in comparison with those on the pure PET-filament which is a corresponding drawback.

As the third constituent suitable for the preparation of said copolymer or modified PET, any one of the following compounds may be advantageously employed by way of example:

HOOC COOH or its ester HO-CHz-O-CHzOH no c C o 0 on or its ester HOOCCHzCHzC 0 OH or its ester These above mentioned compounds may be easily produced in the manner as disclosed in Japanese patent publication No. 4,639/53, now U.S. Pat. 2,465,150. By employing an Sb-catalyst well known the preparation of PET by polycondensation, the preparation of PSEE may be still further simplified and accelerated.

The polymer usable in the preparation of the conjugated filament fiber according to this invention may include a small amount of delustering agent such as TiO and/or the like conventional additives, without any appreciable adverse effect.

In the manufacture of the novel filament fiber, careful caution must be paid so as to keep the material polymers dry as possible. It is necessary to maintain the aqueous content of either polymer less than 0.05%, preferably 0.01 or less.

In the manufacture of the side-by-side conjugated filament fiber according to the inventive technique, the polymerization degree of the material polymer should preferably be so selected that both polymers measured at the outlet of the spinneret have substantially a common viscosity, so as to provide a possibility for easy spinning of straight-lined spun products. A considerable dilference in the viscosities of the polymers to be spinningly conjugated will result in the formation of wavy filaments.

As the spinning apparatus usable in this invention, any conventional one hitherto commonly used for the manufacture of conjugated composite filaments may be empolyed without hindrance. When the spinning velocity is adjusted to 300 m./min. or higher, the stretchability of the spun filaments may become more advantageous than otherwise.

A preferable stretching step employable in this invention will be briefly described hereinbelow by reference to the drawing, illustrating in a highly simplified and schematic way an apparatus designed for this purpose.

In the drawing, numerical 1 denotes a positively driven feed roll which frictionally cooperates with a free-rotatable pressure roll 2 covered, as shown, with a rubber lining layer. Numeral 3 denotes a guide roll which is again of the positively driven type and fitted within its inside space With an electric heating coil, although the details thereof have been omitted for simplicity. 4 represents an elongated spacer roll, while 5 denotes a stationary heater plate fitted within its inside space with an electric heating coil, although not shown. 6 denotes a stretcher roll fitted equally with an inside heating coil, although not shown. 7 represents a second spacer roll, equally being heatable.

The multi-filament bundle 8 to be stretched is represented in a simplified form by a single line, the threading mode thereof being easily understood by a glance at the drawing.

Rolls 1 and 3 are driven substantially at a common peripheral speed, while roll 6 is driven at a higher-peripheral speed than roll 3, in order to provide a predetermined stretching ratio.

As a standard measure for carrying out the process according to this invention, the roll 3 is heated up to 70- 140 C. while heater plate 5 is removed and stretcher roll 6 is kept cold.

The introduced and thus non-stretched part of the multi-filament strand or bundle 8 is heated by contact with roll 3 and stretched during passage between rolls 3 and 6, thereby providing the stretched part at 9 of the bundle, which is then wound around a conventional bobbin, not shown. The temperature of roll 3 should be kept between 70-140 0, because at a certain lower temperature, say 60 C. or less, the stretching degree will be far less than desired for marketable products. With certain higher temperature, say 150 C. or higher, the resulted stretching will become uneven. The preferable and advantageous temperature range for said roll 3 extends normally from C. to C.

When a plurality of continuous filaments are spun from the aforementioned specific polymers and from a conventional conjngatingly spinning spinneret employed for extruding conjugated filaments of the side-by-side type or eccentric sheath core type, and then subjected under tension to a thermal stretching step as referred to above by reference to the drawing, the desired bundle of conjugated and composite filaments can be easily prepared.

In the modified manufacturing mode briefly referred to hereinbefore, the stretching step may be carried out in the following manner.

The roll 3 is kept at 70-l40 C. and the heater plate, kept at l00-l80 C., is inserted in position as illustrated. In this way, the first thermal stretching step is achieved. In order to carry out the second stretching step under tension, the roll 6 is also kept at 100480 C. If necessary, this second stretching step may be separately carried into effect.

In either case, each single filament represents the conjugated and composite, side-by-side type or eccentric sheath core type construction, as easily and clearly supposed from the foregoing.

The stretching ratio to be employed in this invention may vary to any desired degree upon consideration of the occasionally employed stretching speed and the desired performance of the produced filaments. As an example, a range of 2-5 times, preferably 3-4.5 times, may be recommended. It should be noted that for practice of the invention, there is no limitation in the selection of stretching speed which depends only upon the performance of the machine used in practice for this purpose.

The inventive process can be practiced in the form of a single continuous step. It is naturally conceivable that staple fibers can be easily produced from the continuous conjugated filaments prepared by the inventive process.

In the arrangement shown in the drawing, the heatable roll 3 may be replaced by a heatable pin. The heatable roll may be under circumstances dispensed with, if the heater plate 3 is inserted in its operating position. It should be noted further, the invention may be practiced in the production of the concentric sheath core type filaments, although the foregoing description has been directed substantially to the manufacture of other rather conventional conjugated types of filaments.

The process according to this invention is characterized by its simplicity in practice. Another considerable advantage resides in superior performance of the produced fiber. In the following, six representative types of the filament fiber prepared as so far briefly described will be mentioned below more specifically:

First type A filament fiber with its concentric core being composed of pure PET and with its sheath consisting of PSEE. In this conjugated concentric sheath core type filament,

the superior characteristics of pure PET-fibers are substantially maintained and the dyeing performance is highly improved in comparison with PET-fibers on account of the presence of PSEE-sheath.

Second type Concentric sheath-core type conjugated filament fiber, using modified PET and PSEE.

This fiber possesses a superior dyeing characteristic, while otherwise weak nerveness and disadvantageous dimensional stability by the existence of modified PET are improved by the PSEE-component.

Third-type Concentric sheath core type conjugated fiber, with its core consisting of pure PET and with its sheath being composed of PSEE, or side-by-side type conjugated fiber with both components being composed of said both polymers, respectively.

This is a most representative fiber according to this invention. Although both filament components have highly difierent crystalline structures from each other, as ascertained by microscopic observation, it was surprisingly found that the conjugating power relative to each other-is highly efi'icient so that side-by-side type conjugated fibers have been provided for the first time in the art, when employing PET as its one of the conjugating elements.

These components have naturally, considerably different thermo-setting performances and further, highly different heat shrinkage coefiicients to appear later and relative to each other. Therefore, when this kind of conjugated and composite filament fiber is stretched under tension and then loosened, the PET-component, having naturally an inferior heat-setting ability, will behave to restore its original configuration on account of its inherent rather higher elasticity, showing therefore a tendency of creating crimps on the fiber component only. When this conjugated fiber is thermally treated at the boiling point of water or still higher under loose condition, the PET- component, having a comparatively high heat shrinkage coefiicient, will contract still further, thereby creating finer crimps on the fiber, with its LB-component being occupied by PET.

Since the thus crimped filament fiber, having as its LB- component the PET-constituent element, has naturally a high performance in the crimp recovery upon tension, the fiber shows a tough stifiness as a whole. This fiber possesses a specific feeling which may be attributed to its rapid crimp recovery tendency. The formed crimps will recover rapidly its shaped configuration against any disturbing outside force. In addition, as ascertained by experiments, this conjugated fiber exhibits a high crimp developing power under light loads, as appearing when subjected to a heat treatment under load. That is to say, it is insensible to variable load conditions in the course of the thermally crimp developing stage, as will be later described more fully hereinafter, which meanns a considerable progress in the art. Such an improved fiber performance is not in any way obvious to those skilled in the art, when only observing the chemical structure of these constituent polymers.

The filament fibers prepared according to this invention are highly suitable for the manufacture of outer wear fabrics, carpets and the like flexible, yet tough nature of the formed crimps.

Fourth type Side-by-side type or eccentric sheath core type conjugated fiber, having conjugating components of modified- PET and PSEE.

This kind of conjugated fiber has similar crimp characteristics as those of the third mode. The desirous crimps may develop by subjecting the conjugatedly spun filaments to a heat treatment under loose condition of the fiber bundle, the thus developed crimps having its LB-component being occupied by the modified PET.

In comparison with the third mode fiber, the PET- component has been replaced by the corresponding modified one, thus the crimp recovery rate and performance being somewhat inferior in this case, but the dyeing characteristics are correspondingly superior than the third mode fiber.

In the following, the invention will be described more in detail by reference to several numerical examples which will be given however for illustrating purpose only, and thus in no way be intended to limit the invention.

In these examples, the term intrinsic viscosity used for demonstrating the characteristic of PET and modified PET, means that expressed in terms of asp/c and measured with a solvent mixture, consisting of phenol and trichlorophenol, 2:1 by weight. Similar values were measured concerning PSEE with a solvent mixture of phenol and titanium or tetrachloroethane tetrachloride, 1:2 by weight, and expressed in terms of nsp/c (reduced viscosity). The term 0, in both cases, the polymer concentration in the respective solvent mixture being taken as 1.0% and the measuring temperature was 25 C.

The crimp extension percentage and the crimp recovering percentage were determined by the following respective formulae:

Crimp extension percentage Z X LL Crimp recovery pereentage= La X 100 where EXAMPLE 1 PSEE-chips, reduced viscosity: 0.75, and PET-chips, intrinsic viscosity: 0.5 8, were combinedly melt-spun into a bundle of side-by-side type conjugated filaments. The spinning machine used for this purpose comprised two sets of extruders, two respective spinning gear pumps and a composite spinneret. The extruded melt filaments from the spinneret were cooled conventionally by artificial lateral cooling air-streams. The spinneret was of IO-orifices and 0.3 mm. bore diameter. The spinning temperature was 275 C., while the cooling air of 20 C., was fed at a rate of 0.1 m./sec. The spinning velocity was set at 300 m./min.

The extruded filament bundle was subjected to hotstretching by passing through a drawing apparatus schematically shown in FIG. 1. Rolls 3 and 6 were kept cold, while heater plate 5 was kept at C. The ratio of stretching was 4.0. The stretching speed was 250 m./ min. In this way, a stretched multi-filament yarn: 50 d./ 10 f. was obtained.

The thus stretched multi-filament yarn was taken out from a yarn package and processed on a reeling machine into a hank, for bringing the yarn into loose state so as to develop crimps thereon. When the bank was processed at 130 C. for 30 minutes, the developed crimps became still finer. The crimp characteristics are enumerated briefly hereinbelow:

Number of developed crimps: 34/25 mm.

Mean loop diameter of crimps: 0.4 mm.

Crimp extension percentage: 185% Crimp recovery percentage: 92%

Tensile force for elongation of crimp to length:

9 mg./denier For comparison, a nylon 6-false twisted yarn prepared under similar denier and crimping conditions were tested,

resulting in a large rate of crimp elongation: 250% which means a considerable reduction in the stiffness of the created crimps.

On the other hand, several yarn samples were taken from a relaxed skein composed of the yarn according to this invention and tested under various different loads for crimp developing performance by subjecting to a heat treatment at 30 C. for 30 minutes. The results were such that the respective number of crimps per 25 mm. of the yarn amounted respectively to 35, 38, 29 and 25 under 0.6 mg, 1.2 mg., 1.8 mg. and 3.0 mg. per denier, which means a superior performance substantially irrespective of load variation.

20 g. of the strand were taken from a relaxed skein and treated at 100 C. for 60 minutes in a l-lit. padding bath, containing 0.6 g. of Cl. Disperse Orange, 3, 11005 and then soaped at 60 C. for 30 minutes with a solution, 1 lit., containing 2 g. of SCORERO-LL (non-ionic surfactant of polyoxyethylene alkyl ester type, manufactured by Kao Soap Company Limited, Osaka, Japan). The dyed product, dye exhaustion percentage: 75%, showed an apparently dark orange tone. When more precisely observed, it was found that convex loops of the crimps were composed by PSEE which represented a darker orange tone, resulting in a orange colored tone as a whole.

In comparison, PET-strands, prepared under similar conditions, each being 50 d./ 10 f., were dyed with the same dye-stuff. The exhaustion of dye in this case amounted only to 50%.

EXAMPLE 2 The procedures were substantially the same as before, exclusive of the following.

The spinneret was formed with 24 orifices, each bore 0.5 mm. The spinning velocity was 900 m./ min. Hot plate was removed. Roll 3 was kept at 90 C. Stretch ratio 3.0. Stretching velocity 400 m./min. In this way, a strand of multifilament, 50 d./ 24 f., was obtained.

When this strand was packaged on a bobbin and then skeined in a loosened state, considerable crimps were developed.

This skein was dyed in the similar manner as in Example 1, a beautiful dark orange colored, crimped yarn was obtained. The crimps became still finer in the course of the dying operation. The dyed product showed a crimp extension percentage: 160%; and a crimp recovering percentage: 95%.

EXAMPLE 3 PSEE-chips, reduced viscosity: 0.85, and PET-chips, intrinsic viscosity: 0.60, were jointly spun into side-by-side type conjugated filament bundle. The operational conditions were similar to those as set forth in Example 2, excepting the following:

Spinning temperature: 285 C.

Roll temperature at 3: 80 C.

Heater plate temperature at 5: 140 C. Stretching ratio: 4.0

In this way, a multi-filament strand, 100 d./24 f., was obtained. This multi-filament strand was kept in its loosened state in the form of a skein, resulting in developed course and rough crimps. By drying this skein in a drier machine at 150 C. for minutes, highly fine crimps were developed. Rate of crimp extension percentage: 160%; crimp recovering percentage: 94%.

EXAMPLE 4 The operating conditions were substantially the same as in Example 3, excepting the following:

Roll temperature at 3: 90 C. Hot plate temperature at 5: 150 C. Roll temperature at 6: 160 C.

The thus obtained stretched strand was kept in its loosened state in the form of a skein, but no appreciable crimps were observed. When, however, this skein was dried at 140 C. for 15 minutes in a drier, considerably fine crimps were developed.

Rate of crimp extension percentage: 130%; and rate of crimp recovering percentage: 96%.

EXAMPLE 5 Chips of modified-PET, having a copolymer component, succinic acid dimethyl ester, 10 mol percent, having intrinsic viscosity: 0.58, and PSEE-chips, reduced viscosity: 0.75, were jointedly spun, with the latter as core, into eccentric sheath core type conjugated filaments.

Further operating conditions were similar to those set forth in Example 2, excepting:

Roll temperature at 3: C. Hot plate temperature at 5: 130 C. Stretching ratio: 3.5

In this way, a multi-filament strand, 75 d./ 24 f., was obtained.

When this strand was kept in its loosened state in the form of a skein, rough crimps were only developed. When this skein was dyed in the similar manner as set forth in Example 1, considerably fine crimps were developed, and the crimped strand represented a dark orange color tone. Rate of crimp extension percentage: 185%; crimp recovering percentage: 87%

EXAMPLE 6 PSEE-chips, reduced viscosity: 0.85; and PET-chips, intrinsic viscosity: 0.60, were conjugatedly spun, with the former polymer as core, resulting in concentric sheath core type conjugated multi-filament strand. The operational conditions were substantially the same as set forth in Example 3.

Even when the strand was kept in its loose state in the form of a skein, no remarkable crimps were observed. Then, this strand was subjected to a dyeing step, as was set forth in Example 1. Dye exhaustion percentage: 58%. This strand was woven into a plain fabric and then the produced fabric was treated at 90 C. for 30 minutes, resulting in a 5%-weight reduction and showing a silk-like feeling. The wash-and-wear resistance was measured in accordance of the standards of A.A.T.C.C. (American Association of Textile Chemists and Colorists), and found to correspond to 88A1964-Class 5.

EXAMPLE 7 The core and sheath material selection was reversed in Example 6, thus PET being the core in this example. Under similar other conditions, a concentric sheath type conjugated multi-filament strand was spun out.

This strand was loosened, but it did not develop any appreciable crimp. It was subjected to a dyeing step as was disclosed in Example 1, the dye exhaustion percent 79%. This strand was twisted, woven into a plain fabric, and treated with a NaOH solution as set forth in the same example, resulting in no appreciable weight reduction. The feeling was too hard to be acceptable.

EXAMPLE 8 The multi-filament strand which was obtained in Example 3 and stretched as mentioned therein, was cut into short lengths, about 30 mm., and carded. The only roughly crimped fibers were processed on a conventional spinning machine. This spun yarn was wound into a skein which was then subjected to a dry heat treatment at 150 C. for 10 minutes, thereby improving the crimps and inviting a corresponding reduction in the overall skein sizes. The rate of crimp extension percentage: 60%; the rate of crimp recovering percentage: 98%.

EXAMPLE 9 The spun and stretched strain obtained in Example 3 was cut into staple fibers of 400 mm.-length, and then steamed at C. for 10 minutes. These staples had fine crimps formed thereon. They were processed on a cardmg machine, and spun conventionally, yielding bulky yarns of the least stretchability.

EXAMPLE 10 PSEE-chips, reduced viscosity: 0.85, and PET-chips, intrinsic viscosity: 0.60, were conjugatedly spun into a side-by-side type conjugated multi-filament strand. The operating conditions were substantially the same as set forth in Example 3, excepting:

Orifice dia.: 0.5 mm.

Number of orifices: 100 Spinning velocity: 400 m./min. Stretching speed: 80 m./min.

In this way, a roughly crimped, 2000 d./ 100 f.-multifilament yarn was obtained. Two of such yarns were twisted together, forming a thread of 4000 d./200 f., and fabricated on a tufting machine into a carpet which showed elastic, yet highly tough and well set crimps.

EXAMPLE 1 l PSEE-chips, reduced viscosity: 0.85, and PET-chips, intrinsic viscosity: 0.60, were conjugatedly spun, the latter being taken as core element, into an eccentric sheath core type conjugated multi-filament strand, as before. The operating conditions were substantially similar to those as set forth in Example 3. The strand was kept in its loose state in the form of a skein, thereby developing crimps.

This skein was dyed under similar conditions as set forth in Example 1, thereby the crimps becoming still further finer in the course of the dyeing step. The rate of crimp extension percentage 120%; and the rate of crimp recovering percentage was 95%. Dye exhaustion percentage: 75%.

As Will be clear from the foregoing disclosure, the multifilament yarns prepared according to the novel teaching of the present invention and further dyed in the aforementioned way set forth only by way of example will develop fine elastic and tough crimps on the colored yarns of the conjugated and composite filament. Therefore, with such improved bulky yarns, a nerve fabric may be fabricated therefrom and the fabricated products can be advantageously utilized for the manufacture of outer wear clothes and further even for carpets and the like.

If the present conjugated multi-filament yarns were spun into those of the concentric sheath core type, remarkable crimps cannot be produced if not otherwise heat-treated, but highly improved yarns having superior wash and wear resistance performance, as well as superior dyeing characteristics may easily be provided which means also a remarkable progress in the art.

Although, in the foregoing, only a limited number of specific embodiments have been described, many and various changes and modifications may easily occur to those skilled in the art without departing from the scope and spirit of the invention to be set forth in the appended claims.

What we claim is:

1. A synthetic conjugated composite filament fiber consisting of two conjugated polyester filamentary components, one of said components being polyethylene terephthalate and the other of said components being polyethylene diphenoxyethane-4,4-dicarboxylate, said polyethylene terephthalate being of load-bearing component.

2. A process for the manufacture of a synthetic conjugated composite filament fiber, consisting of two conjugated polyester filamentary components, which comprises melt-spinning in a side-by-side manner or in an eccentric sheath-core manner, polyethylene terephthalate, and polyethylene diphenoxyethane-4,4'-dicarboxylate, and thermally stretching the resulting composite filament at a temperature of from -140 C., said polyethylene terephthalate being the load-bearing component.

3. The process of claim 2 wherein the thermal stretching is carried out at a temperature ranging from C. to C.

4. The process of claim 2 wherein said resulting composite filament is further subjected to a thermal stretching step under tension at a temperature ranging from 100- C.

5. The process of claim 2 wherein the spinning velocity is at least 300 meters per minute.

6. The process of claim 4 wherein the stretching ratio varies from 2 to 5.

7. The process of claim 6 wherein the stretching ratio varies from 3 to 4.5.

8. A composite filament fiber as set forth in claim 1 wherein said fiber is a sheath-core type fiber, the core being composed of a polyethylene terephthalate and the sheath being composed of polyethylene diphenoxyethane- 4,4'-dicarboxylate.

9. A conjugated filament fiber as set forth in claim 1 wherein said components are arranged into a sheath-core type filament, the core being composed of polyethylene terephthalate, and the sheath being composed of polyethylene diphenoxyethane-4,4'-dicarboxylate.

10. A conjugated filament fiber as set forth in claim 1 wherein said components are arranged in a side-by-side manner.

11. The crimped conjugated filament fiber as set forth in claim 9.

12. The crimped conjugated filament fiber as set forth in claim 10.

13. The synthetic conjugated composite filament fiber of claim 1, wherein the aqueous content of either polymer is 0.05 percent or less.

14. The synthetic conjugated composite filament fiber of claim 13, wherein the aqueous content of either polymer is 0.01 percent or less.

References Cited UNITED STATES PATENTS 3,118,011 1/1964 Breen 264-171 3,400,194 9/ 1968- Boone et al 264-210 F 3,454,460 7/1969 Bosley 264-168 3,458,390 7/1969 Ando et al 161-173 3,500,498 3/ 1970 Fukuma et al. 18-8 3,454,460 7/ 1969 Bosley 161-173 3,489,641 1/ 1970 Harcolinski et al 161-173 3,520,770 7/ 1970 Shima et al. 161-173 ROBERT F. BURNETT, Primary Examiner L. KOECKERT, Assistant Examiner v U.S. Cl. X.R.

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