EP0056907A1

EP0056907A1 - Process for the preparation of suède-like raised fabrics

Info

Publication number: EP0056907A1
Application number: EP81306092A
Authority: EP
Inventors: Norihiro Minemura; Shigeru Ito; Kiyotaka Ozaki; Akihiro Terano
Original assignee: Teijin Ltd
Current assignee: Teijin Ltd
Priority date: 1980-12-26
Filing date: 1981-12-23
Publication date: 1982-08-04

Abstract

A process to prepare a suede-like raised fabric having extra fine naps, wherein the process comprises producing a raised fabric of a polyester composite fiber which consists of constituents hardly soluble in an alkali solution and constituents easily soluble in an alkali solution containing 3 to 12% polyalkylene glycol and/or anionic surfactant by weight and removing by solution the constituents easily soluble in an alkali solution contained in the composite fiber by treating the raised fabric in an aqueous alkali solution at 110 to 150°C.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a process for the preparation of suede-like raised fabrics having extra fine naps. More particularly, the present invention relates to a process for the preparation of suede-like raised fabrics from a polyester composite fiber which consists of constituents easily soluble in an alkali solution and constituents hardly soluble in an alkali solution.

Description of the Prior Art

Polyester composite fibers having polyester constituents containing polyalkylene glycol and/or anionic surfactant as constituents easily soluble in an alkali solution have hitherto been publicly known (See Japanese Patent Application Publication Nos.47532/72, 47533/72 and 13169/73).
Also raised fabrics having extra fine naps obtained with the use of polyester composite fibers containing constituents eassily soluble in an alkali solution have been publicly known (See Japanese Patent Application Laid-Opten Nos.6965/79 and 27058/79). For instarice, Japanese Patent Applicatin Laid-Open No.6955/79 discloses that a raised woven fabric is obtained according to the method in which a raised woven fabric is first woven of fibers of islands-in-sea type which consist of polyester (polyethylene terephthalate) copolymerized by 9 mole % 3,5-di(carbomethoxy)sodium benzenesulfonate as sea constituents and another polyester, which is not copolymerized by any other components, as island constituents, and this fabric is then treated continuously in the alkali bath containing alkali of 10 to 20 g/l at 90°C to dissolve the copolymerized polyester constituents to give a raised woven fabric having extra fine naps and consisting of polyester which is not copolymerized by other components.
Also in Japanese Patent Application Laid-Open No.27058/79, it is disclosed that a raised woven fabric having extra fine naps and comprising polyester not copolymerized by other components was obtained by first weaving a fabric of fibers of islands-in-sea type which consist of a mixture of polyethylene glycol and polyethylene terephthalate as sea constituents and polyethylene terephthalate not copolymerized by any other components as island constituents, then treating this woven fabric with an alkali solution having concentration of 20 g/l of alkali at 98°C for 20 minutes and further with an alkali solution having concentration of 5 g/l at 90°C for 60 minutes, and finally raising the surface of the woven fabric.
In removing the constituents easily soluble in an alkali solution by subjecting a polyester fabric, which is woven of polyester composite fibers comprising constituents easily soluble in an alkali solution and constituents hardly soluble in an alkali solution, to alkali treatment, it is desirable to follow a method which can minimize both the treatment time and the weight loss of polyester which forms constituents hardly soluble in an alkali solution; however, the old arts in which the alkali treatment is conducted in an alkali solution at 100°C or less, can not achieve such bifunctional effect at a time. An experiment was made with polyester yarns (75 denier/24 filaments), which consisted of constituents easily soluble in an alkali solution and was obtained by melt-spinning and drawing polyethylene terephthalate which contains 4% by weight of polyethylene glycol having molecular weight of 20,000 and 2% by weight of sodium lauryl sulfonate according to the ordinary method, and another polyester yarns (75 denier/24 filaments), which consisted of constituents hardly soluble in an alkali solution and was obtained by melt-spinning and drawing ordinary polyethylene terephthalate. Both yarns were treated in the same manner in an aqueous solution of caustic soda in a bath ratio of 1:50 at 100°C and the experiment was carried out to obtain the time required for almost completely dissolving the constituents easily soluble in an alkali solution and the percentage of weight loss caused to the constituents hardly soluble in an alkali solution during the same period of time at the respective concentrations of caustic soda. The results are shown in Table 1.
It would be clearly ascertained from Table 1 that the old arts have a disadvantage that comparatively long time is required to dissolve and remove the constituents easily soluble in an alkali solution when the alkali concentration is low, and when the alkali solution is high, the constituents easily soluble in an alkali solution can be dissolved and removed in considerably short time while the percentage of weight loss of the constituents hardly soluble in an alkali solution is high.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a process for the preparation of a suede-like raised fabric having extra fine naps, in which comparatively low alkali concentration and compar- tively short time can be accepted as conditions of treatment.
The present invention is directed to a process for the preparation of a suede-like raised fabric having extra fine naps which comprises (1) producing a polyester composite fiber which consists of constituents easily soluble in an alkali solution and constituents hardly soluble in an alkali solution, said constituents easily soluble in an alkali solution containing 3 to 12% by weight of polyalkylene glycol and/or anionic surfactant and at least 70% by weight of ethylene terephthalate units and said constituents hardly soluble in an alkali solution containing not less than 80% by weight of ethylene terephthalate and/or butylene terephthalate units, (2) preparing a raised fabric by using said polyester composite fibers, and (3) dissolving said constituents easily soluble in an alkali solution from the polyester composite fibers in the raised fabric by treating the raised fabric in an aqueous alkali solution at a temperature of 110°C to 150°C.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

What is referred to as a polyester composite fiber in the present invention is a so-called islands-in-sea type composite fiber, segmental multilayer type composite fiber, etc. in which each of the constituents easily soluble in an alkali solution and each of the constituents hardly soluble in an alkali solution are arranged and distributed independently in the same fiber. And this constituent easily soluble in an alkali solution contains polyalkylene glycol and/or anion active agent equal to 3 to 12% of the whole constituent by weight and at least 70% by weight of the whole constituent consists of ethylene terephthalate units.
As concrete example of polyalkylene glycol to be used in the present invention, polyoxyethylene glycol, polypropylene glycol, polytetramethylene glycol, and a copolymer of propylene glycol and tetramethylene glycol may be mentioned but not to be limited to them.
Said anionic surfactant is a surfactant which contains at least one of the alkaline metal salts of any of sulfonic acid, carboxylic acid, and phosphonic acid as a hydrophilic group and has a hydrophobic group of appropriate size in the same molecule. More concretely, such ones as those having the following chemical structures, for instance, may be mentioned but are not limited to them. In the following formulas, M indicates an alkali metal salt.

(c) Alkaline metal salt of randomly sulfonated compounds represented by C₁₂H₂₆ to C₁₈H₃₈.

In the present invention, when the quantity of polyalkylene glycol and/or anionic surfactant contained in the constituents easily soluble in an alkali solution is small, the substantially complete removal by solution of the constituent in the alkali treatment increases the percentage of weight loss of the constituents hardly soluble in an alkali solution. On the contrary, when the quantity of polyalkylene glycol and/or anionic surfactant contained in the constituents easily soluble in an alkali solution is large, the spinnability and drawability of the polyester fiber are degraded. Therefore, it is desirable to keep the content of polyalkylene glycol and/or anionic surfactant in the range of 3 to 12% by weight, perferably in.the range of 4 to 6% by weight.
Polyester to be used in the constituents easily soluble in an alkali solution should necessarily contain at least 70% by weight of ethylene terephthalate units to maintain adequate strength required for the meet-spinning, weaving, and knitting processes. In addition to polyalkylene glycol and/or anionic surfactant, the constituents easily soluble in an alkali solution may contain one or two kinds of publicly known third constituent such as isophthalic acid, adipic acid, cebacic acid, diethylene glycol, and 1,4-butanediol. Also well-known titanium oxide, antioxidant, etc. may be added thereto.
In the present invention, it is indisputably necessary for the constituents hardly soluble in an alkalin solution, which consist of polyester containing 80% by weight or more ethylene terephthalate units and/or butylene terephthalate units, should not contain any component that will make the constituents more soluble in the alkali treatment than the constituents easily soluble in an alkali solution, but may contain such alkali-resistant polymers as polycarbonate, poly c-capramide, etc. and inactive titanium oxide. When the content of ethylene terephthalate units and/or butylene terephthalates units is below 80% by weight, the physical properties such as Young's modulus, strength, melting point, become degraded.
A polyester composite fiber of the present invention consists of two kinds of fiber forming polymer components, each of which has a different hydrosis rate, i.e. constituents easily soluble in an alkali solution and constituents hardly soluble in an alkali solution, and these two different polymer components are arranged and distributed independently from each other in the same fiber. More particularly, these polymer components are substantially arranged extending along the longitudinal axis of the fiber continuously and present themselves distributed independently from each other when the fiber is viewed cross-sectionally. What is referred to as the presence of two or more polymer components distributed independently from each other on the cross-sectional view of the composite fiber means that the polymer components are so distributed that, when one kind of the polymer component, or the constituents easily soluble in an alkali solution, is removed by solution in the alkali treatment of a composite fiber, extra fine filaments comprising other kind of the polymer component, or the constituents hardly soluble in an alkali solution, are formed plurally. Of such composite fibers, an islands-in-sea type composite fiber, hollow type or solid type segmental multilayer composite fiber, and sandwich type composite fiber are desirably used in the present invention. In the case where an islands-in-sea type composite fiber is used, the sea component should necessarily be the constituents easily soluble in an alkali solution. It is desirable to set the size of a composite fiber in the range of 1 to 10 denier so that the formed extra fine filament resulting from a single constituent hardly soluble in an alkali solution may be 0.01 to 0.5 denier, preferably 0.05 to 0.3 denier. From the viewpoint of spinnability, drawability, and workability for making extra fine filaments, a hollow type segmental multilayer composite fiber is especially desirable for use. In this case, it is preferable to keep the hollow ratio in the range of 1 to 30%.
In the present invention, a fabric is next prepared by use of polyester composite fibers obtained in the procedure mentioned above. What is referred to as a fabric in the present invention means a nonwoven fabric, woven fabric, knitted fabric or a combination thereof.
Nonwoven fabrics may include all those prepared according to any known methods. A raised fabric having extra fine naps of the present invention can be obtained by raising one or both surfaces of a nonwoven fabric with the use of such a raising machine as roller sander machine with sand paper or emery cloth.
The woven fabric is woven of multifilament yarns or spun yarns, which are prepared from the composite yarns of the present invention, used as warps and/or wefts by use of an ordinary weaving machine. One or both surfaces of thus obtained woven fabric may be raised by using a conventional raising machine such as emery raising machine, teazel raising machine, wire raising machine, and roller sander machine with sand paper or emery cloth, to give a raised fabric of the present invention. As for the woven fabric, it is preferable to use a satin fabric, which is composed of a multifilament yarn or spun yarn having a yarn size of 50 to 500 denier consisting of the composite fibers as the weft and a multifilament yarn, mixed filament yarn, spun yarn, or mixed spun yarn having a yarn size of 50 to 300 denier consisting of ordinary fibers as the warp. When it is desired to raise both surfaces of a fabric, it is perferable to use a double faced woven fabric having a satin structure on both surfaces. Among the satin fabrics, 3- to 5-shaft satin fabrics are especially desirable. As for the warp, a crimped textured yarn consisting of such polyester as polyethylene terephthalate or such polyamide as nylon 6 and nylon 66 is particularly preferable.
The knitted fabric is prepared from a multi- filament yarn or a spun yarn consisting of the composite fibers of the present invention by using a conventional knitting machine. In the case of a warp knitted fabric, it is preferable to use a multi- filament yarn or a spun yarn consisting of the composite fibers as the front yarn and a spun yarn or a mixed spun yarn consisting of the ordinary fibers as the back yarn. In the case of a circular knitted fabric, it is preferable to use a multi- filament yarn or a spun yarn consisting of the composite fibers as yarns for the front portion and back portion or only for the front portion. One or both surfaces of the knitted fabric are raised as in the case of the woven fabric to obtain a raised fabric of the present invention.
In the present invention, the raised fabric obtained in the above is then treated in an aqueous alkali solution under high temperature and high pressure to dissolve and remove the constituents easily soluble in an alkali solution in the polyester composite fibers woven into the raised fabric.
An explanation will next be made hereunder as to the functional effect of the treatment with an aqueous alkali solution under high temperature and pressure which is a distinct feature of the present invention.
Polyester yarns (75 denier/24 filaments), which consisted of constituents easily soluble in an alkali solution and was obtained by melt-spinning and drawing polyethylene terephthalate which contained 4% by weight of polyethylene glycol having molecular weight of 20,000 and 2% by weight of sodium lauryl sulfonate according to the ordinary method, and another polyester yarns (75 denier/24 filaments), which consisted of constituents hardly soluble in an alkali solution and was obtained by melt-spinning and drawing ordinary polyethylene terephthalate, were treated in an aqueous solution of caustic soda in a bath ratio of 1:50 at 130°C. It took 15 minutes to raise the temperature of the solution from 100°C to 130°C and 10 minutes to lower the temperature from 130°C to 100°C. The time required for almost completely dissolving the constituents easily soluble in an alkali solution and the percentage of weight loss caused to the constituents hardly soluble in an alkali solution during the same period of time at the respective concentrations of caustic soda are shown in Table 2.
It will be clear from the comparison between Table 2 and the aforementioned Table 1 that, as compared with the alkali treatment carried out at 100°C, the alkali treatment carried out at 130°C not only required lower alkali concentration and shorter time for the treatment but also lowered the percentage of weight loss of the constituents hardly soluble in an alkali solution during the period of time required for substantially dissolving the whole constituents easily soluble in an alkali solution.
As the alkalis to be used in the present invention, caustic soda, caustic potash, sodium carbonate, and potassium carbonate may be mentioned but not limited to them; however, caustic soda is most preferable from the functional as well as economical viewpoint. It is desirable to maintain the alkali concentration in the range of 3 g/£ to 30 g/i. When such a quanternary ammonium salt as lauryl dimethylbenzyl ammonium chloride, cetyl dimethylbenzyl ammonium chloride, etc. is used together with alkali, the hydrolysis of the polymer component is accelerated.
As for the temperature of the treatment by aqueous alkali solution proposed in the present invention, at least 110°C is necessary. It is unadvisable to try the treatment at the temperature below 110°C since the alkali consumption and the percentage of weight loss of the constituents hardly soluble in an alkali solution increases. If the treatment temperature is too high, the constituents hardly soluble in an alkali solution become brittle. Therefore, it is advisable to keep the temperature at 150°C at the highest. The temperature, therefore, should preferably be kept in the range of 115 to 140°C. The use of an ordinary high temperature and pressure dyeing machine is advisable for this treatment.
In the present invention, such a method as to first apply an aqueous alkali solution to the fabric with the use of pads and then treat the fabric with high pressure steam should be avoided. In such a method, the aqueous alkali solution is hardly allowed to move about in the texture of fabric to exercise its function effectively. Accordingly, if the treatment conditions are made satisfactorily enough to remove the constituents easily soluble in an alkali solution, the weight loss of the constituents hardly soluble in an alkali solution would be very great. Therefore, the alkali treatment in the present invention must be carried out in an aqueous alkali solution and it is preferable for the treatment to be accompanied by stirring. It does not matter at all whether the fabric may be pushed out of the aqueous solution (exposed to the atmosphere) once in a while due.to the stirring:

The present invention offers a suede-like raised fabric having naps of extra fine fibers of monofilaments each of which having a size of 0.01 to 0.5 denier by subjecting the fabric to the alkali treatment as mentioned above. The aforementioned process of raising the fabric may be practiced after the alkali treatment of the fabric. Conventional methods of dyeing and finishing can be applied to the raised fabric.

Further, the application of an elastic polymer to the suede-like raised fabric obtained according to the present invention is an especially preferable mode of treatment, because it remarkably improves the resiliency of the naps and crease resistance of the fabric. As elastic polymers, natural rubber and synthetic elastic polymers such as acrylonitrile-butadiene copolymer, polychloroprene, styrene-butadiene copolymer, polybutadiene, polyisoprene, ethylene-propylene copolymer, acrylate type copolymers, silicone, polyurethane, polyacrylate, polyvinyl chloride, polyvinyl acetate, ethylene-vinyl acetate copolymer, etc. can be used. Polyurethane is especially preferable among them all. The method which comprises applying an urethane prepolymer, in which a free isocyanate group is blocked, to the fabric and then heating the applied fabric to form polyurethane in the fabric is also preferably employed in the present invention. The elastic polymer is applied to the fabric in the form of a solution such as an organic solvent solution, aqueous solution or emulsion of the elastic polymer. For applying a solution of the elastic polymer, there are a method of impregnating the raised fabric with the solution, a method of coating the raised fabric with the solution and a method of spraying the raised fabric with the solution. After the application of the elastic polymer, the raised fabric may be sheared, brushed'or buffed.
A suede-like raised fabric obtained according to the present invention has very soft, mellow hand and also has a lustrous and beautiful surface and an excellent writing effect similar to natural suede products. The fabric has the outstanding resiliency and crease resistance, too. Accordingly, the fabric has a wide variety of uses as clothings such as jackets, jumpers, blazers, skirts, trousers, shorts, slacks, dresses, suits, vests, coats and gloves, or bags, boots, chair covers, etc.
The following examples are illustrative of the present invention. Parts and % in the examples are all by weight.

Example 1

(1) Preparation of polyester composite fiber.

An undrawn hollow composite fiber having a 3% hollow ratio and a total denier size of 205 denier and a single yarn denier size of 6.8 denier was obtained by composite melt spinning 70 parts of polyethylene terephthalate having the intrinsic viscosity of 0.64 determined at 25°C in orthochlorophenol (as constituents hardly soluble in an alkali solution) and 30 parts of mixed polyethylene terephthalate, having the intrinsic viscosity of 0.64 determined at 25°C in orthochlorophenol, prepared by adding 2 parts of sodium alkyl sulfonate having 15 carbon atoms and 2 parts of polyethylene glycol having molecular weight of about 15,000 to 96 parts of polyethylene terephthalate at the time of its polymerization (as constituents easily soluble in an alkali solution). The composite melt spinning was carried out at the discharge temperature of 285°C and withdrawing rate of 1100 m/min. in such a way as to form a composite fiber of hollow, segmental multilayer type, in which said two constituents were distributed alternately side by side in 32 segments arranged radially on a cross-sectional view of the fiber according to the method disclosed in U.S. Patent 4,109,038. This undrawn hollow composite fiber was drawn at a drawing ratio of 3.35 with a heating roller at 80°C, made to go through a slit heater kept at 210°C, and wound up to give a drawn fiber of total denier size of 61 denier, having 0.09-denier polyethylene terephthalate components (constituents hardly soluble in an alkalin solution) and 2.04-denier single yarns. Three composite fibers thus obtained were then folded into a multifilament yarn of 183 denier/90 filaments.

(2) Preparation of raised fabric.

A single twist yarn obtained by giving 120 turns per meter "S" twist to a paralleled yarn (366 denier/180 filaments) consisting of two composite multifilament yarns was used as a weft. A two folded polyethylene terephthalate yarn (200 denier) of 150 turns per meter "S" twist, consisting of wooly yarns (false twisted) of 100 denier/24 filaments, was used as a warp.
A 4-shaft satin fabric having the density of 70 warp ends per inch and 50 filling picks per inch was made of the abovementioned weft yarn and warp yarn. The weight of the composite fiber was 56.7% of the whole fabric and the weight of the constituents easily soluble in an alkalin solution was 17%.
The obtained fabric was made to relax in a hot bath at 98°C for 30 minutes, dried at 120°C for 3 minutes, and treated with an oil mainly consisting of a mineral oil. Thereafter, the fabric had its surface raised fifteen times at a running speed of 30 meters per minute by use of a wire raising machine equipped with a 33-gauge wire fillet. The raised fabric was then preheated at 170°C for 30 seconds with a heat setter of the pin tenter type.
The raised fabric thus obtained was treated in an aqueous solution of caustic soda (concentration 8 g/£) at 130°C for 20 minutes by using a high pressure jet dyeing machine (Circular VII type: manufactured by Nichiban Seisakusho Co.). The temperature was raised to 100°C in 25 minutes, from 100°C to 130°C in 15 minutes and lowered from 130°C to 100°C in 10 minutes. After the fabric was washed thoroughly with water, the percentage of weight loss was determined to be 20.7% as a whole, from which the percentage of weight loss of the constituents hardly soluble in an alkali solution was calculated at 45% (
x 100). A suede-like raised fabric having extra fine naps (0.09 denier) was thus obtained.
After that, the pre-heat set raised fabric was dyed in a water dye bath containing 4% Duranol Brilliant Blue G (C.I.No.63305, trade name for a disperse dye manufactured by I.C.I.) (based on the weight of the fabric), 0.2 mℓ/ℓ, density of acetic acid, and 1 g/k density of a dispersing agent mainly consisting of a condensation product of naphthalane- sulfonic acid and formamido at 130°C for 60 minutes, subjected to soaping in an aqueous solution of nonionic detergent at 80°C for 20 minutes, and dried at 120°C for 3 minutes.

Example 2

This example shows how an elastic polymer was applied to the raised fabric obtained in Example 1.

(1) Preparation of urethane pre-polymer.

An urethane pre-polymer having free isocyanate groups was prepared by allowing the following mixture (the mole ratio between isocyanate groups and active hydrogen atoms was 2.06) at 100 to 105°C for 1 hour in a stream of nitrogen gas. The mixture consisted of (1) 21 parts of a block-copolymerized polyether diol having a number average molecular weight of 2,400 which was obtained by reacting polypropylene glycol having a number average molecular weight of about 1,200 with ethylene oxide, (2) 56 parts of a polyester diol which was obtained by reacting adipic acid, 1,6-hexane diol and neopentyl glycol in a mole ratio of 10:7:4 respectively, (3) 3 parts of 1,6-hexane diol, and (4) 20 parts of hexamethylene diisocyanate. The contents of the isocyanate groups and oxyethylene groups in the resultant urethane pre- polymer were 5.02% and 10.2% respectively.
The resultant urethane pre-polymer was cooled to 40°C and diluted by adding 20 parts of dioxane. 65 parts of an aqueous solution of sodium bisulfate having a concentration of 25% by weight was further added to the diluted urethane prepolymer and mixed thoroughly at 40°C for 30 minutes. After that, 202 parts of water and a proper amount of hydrogen peroxide were added to the reaction system to obtain an aqueous solution of urethane pre-polymer (pH 3) having a concentration of about 30% by weight.

(2) Application of urethane pre-polymer.

The raised woven fabric obtained in Example 1 was immersed in an 8% aqueous solution (whose pH value was adjusted to 6.0 with sodium bicarbonate) of the abovementioned urethane pre-polymer and then squeezed to a pick-up ratio of 70% based on the weight of the fabric. The fabric was dried at 100°C for 3 minutes and heat-treated at 140°C for 30 seconds. The raised surface of the heat-treated raised woven fabric was then fuffed one time by use of a roller sander having 100-mesh sand paper and further brushed.
The raised woven fabric thus obtained had a beautiful lustrous surface look and excellent resiliency and crease resistance similar to natural suede.

Example 3

Polyethylene terephthalate chip was prepared after the polymerization of polyethylene terephthalate was carried out according to the ordinary method with addition of 3 parts of polyoxyethylene glycol having molecular weight of 20,000 and 1.5 parts of sodium lauryl sulfonate before starting polymerization. Then a composite fiber of hollow, segmental multilayer type, in which two constituents, i.e. 30 parts of said chip (constituents easily soluble in an alkali solution) and 70 parts of polyethylene terephthalate (constituents hardly soluble in an alkali solution), were distributed alternately in 16 segments arranged radially on a cross-sectional view of the fiber, was melt-spun and drawn according to the known method to obtain a filament yarn of total denier size of 45 denier, consisting of 3.75-denier single yarns and having a hollow percentage of 4.8%.
A satin tricot fabric of 36 gauge, back 01/21 and front 10/34, was prepared by using thus prepared 45-denier filament yarn as a front yarn and a polyethylene terephthalate filament yarn (30 denier/10 filaments) as a back yarn (the weight of the composite fiber was 77% of the whole fabric and the weight of the constituents easily soluble in an alkali solution was 23.1%). The obtained knitted fabric was relaxed in a hot water bath for 10 seconds, dried and raised 15 times with a wire raising machine. The raised knitted fabric was heat set at 170°C for 30 seconds on the pin tenter. The knitted fabric was then treated with an aqueous solution of caustic soda having the concentration of 7.5 g/ℓ at 130°C for 30 minutes with the use of a jet dyeing machine (Uniace, made by Japan Dyeing Machine Co.), in which treatment the temperature of the solution was first raised to 130°C and then lowered after the treatment was over according to the same way as described in Example 1, and washed with water after having been cooled. The percentage of weight loss of the whole treated knitted fabric was 28.5%. The weight loss of the constituents hardly soluble in an alkali solution was 7.0%. The knitted fabric was further dyed, heat set, and brushed to give a suede-like fabric having densely raised extra fine naps with very soft_ hand on the surface.

Example 4

An undrawn hollow composite fiber having a 4% hollow ratio and a total denier size of 190 denier and a single yarn denier size of 6.3 denier was obtained by composite melt spinning 70 parts of polybutylene terephthalate having the intrinsic viscosity of 0.85 determined at 25°C in orthochlorophenol (as constituents hardly soluble in an alkali solution) and 30 parts of mixed polyethene terephthalate, having the intrinsic viscosity of 0.64 determined at 25°C in orthochlorophenol, prepared by adding 2 parts of sodium alkyl sulfonate having 15 carbon atoms and 2 parts of polyethylene glycol having molecular weight of about 15,000 to 96 parts of polyethylene terephthalate at the time of its polymerization (as constituents easily soluble in an alkali solution). The composite melt spinning was carried out at the discharge temperature of 286°C and withdrawing rate of 1200 m/min. in such a way as to form a composite fiber of hollow, segmental multilayer type, in which said two constituents were distributed alternately side by side in 32 segments arranged radially on a cross-sectional view of the fiber according to the method disclosed in U.S. Patent 4,109,038. This undrawn hollow composite fiber was drawn at a drawing ratio of 3.1 with a heating roller at 80°C, made to go through a slit heater kept at 210°C, and wound up to give a drawn fiber of total denier size of 61 denier, having 0.09-denier polyethylene terephthalate components (constituents hardly soluble in an alkali solution) and 2.04-denier single yarns. Three composite fibers thus obtained were then folded into a multi-filament yarn of 183 denier/90 filaments.
.-Thereafter a raised woven fabric was obtained according to the same method as described in Example 1, dyed and treated with an alkali solution to give a suede-like raised woven fabric having extra fine naps (0.09 denier) comprising polybutylene terephthalate.

Claims

1. A process for the preparation of a suede-like raised fabric having extra fine naps which comprises (1) producing a polyester composite fiber which consists of constituents easily soluble in an alkali solution and constituents hardly soluble in an alkali solution, said constituents easily soluble in an alkali solution containing 3 to 12% by weight of polyalkylene glycol and/or anionic surfactant and at least 70% by weight of ethylene terephthalate units and said constituents hardly soluble in an alkali solution containing not less than 80% by weight of ethylene terephthalate and/or butylene terephthalate units, (2) preparing a raised fabric by using said polyester composite fibers, and (3) dissolving said constituents easily soluble in an alkali solution from the polyester composite fibers in the raised fabric by treating the raised fabric in an aqueous alkali solution at a temperature of 110°C to 150°C.

2. The process according to Claim 1, wherein the composite fiber is obtained by composite-spinning the constituents easily soluble in an alkali solution and the constituents hardly soluble in an alkali solution into a composite fiber of islands-in-sea type or multilayer type.

3. The process according to Claim 1 or 2, wherein the constituents easily soluble in an alkalin solution of the composite fiber is polyethylene terephthalate which contains a total of 3 to 12% polyalkylene glycol and/or anionic surfactant by weight and the constituents hardly soluble in an alkali solution is polyethylene terephthalate.

4. The process according to Claim 1, wherein an aqueous alkali solution has the concentration of caustic soda in the range of 3 to 30 g/£.

5. The process according to Claim 1, wherein the process for raising a fabric is conducted after the alkali treatment of the fabric.