EP1039005A1

EP1039005A1 - Nonwoven fabric and artificial leather using the same

Info

Publication number: EP1039005A1
Application number: EP99970436A
Authority: EP
Inventors: Masahisa Cordley Chemicals Ltd MIMURA; Shigeki Cordley Chemicals Ltd YAMAUCHI; Hideki Teijin Limited Mihara Factory NITTA
Original assignee: Teijin Ltd
Current assignee: Teijin Ltd
Priority date: 1998-10-14
Filing date: 1999-10-12
Publication date: 2000-09-27
Also published as: EP1039005A4; KR20010032960A; WO2000022217A1; ID26559A; CN1290313A

Abstract

A non-woven fabric prepared by thermally shrinking a web comprising 30 to 100 wt% of a hollow fiber (A) having a shrinkage factor in 70°C warm water of at least 35 % and 0 to 70 wt% of other fiber to an area shrinkage factor of at least 15 %, wherein

the hollowness of a hollow fiber (A') contained in the non-woven fabric after shrinkage is 30 to 70 %, the apparent density of the non-woven fabric is 0.12 to 0.20 g/cm³, and the tensile strength per unit area·unit weight of the non-woven fabric is 270 (kg/cm)/(g/cm²) or more.

Artificial leather obtained by impregnating this non-woven fabric with an elastic polymer.

The non-woven fabric of the present invention is light in weight and excellent in flexibility and buckling resistance. The artificial leather of the present invention is light in weight, strong, flexible and tight, rarely buckles and is useful as a shoe material.

Description

Field of the Invention

The present invention relates to a non-woven fabric which is light in weight, excellent in flexibility and rarely buckles and, more specifically, to a non-woven fabric especially suitable for use in artificial leather and to artificial leather which comprises the non-woven fabric, is light in weight, strong, flexible and tight, and rarely buckles.

Prior Art

The development and improvement of artificial leather as a substitute material for natural leather have been carried out heretofore. For example, a non-woven fabric which is formed by needle punching a web formed out of a highly shrinkable fiber or a combination of a highly shrinkable fiber and other fiber, for example, a self-extensible fiber, shrinking and heating the web under such conditions that develop extensibility when the self-extensible fiber is used to highly shrink the web and artificial leather prepared by impregnating the above non-woven fabric with a polyurethane resin and coagulating the resin are proposed as a non-woven fabric and artificial leather which are soft and rarely buckle (JP-B 62-46662) (the term "JP-B" as used herein means an "examined Japanese patent publication"). This artificial leather is tight, rarely buckles, has excellent flexibility and is excellent as a substitute material for leather. However, when a high-density non-woven fabric which has been highly shrunk is used for such an application purpose that keenly requires lightweight as sports shoes, it has such a problem that they easily become heavy.
Other artificial leather which comprises as a base a substrate formed out of an extremely fine fiber prepared by forming a non-woven fabric out of a multi-component fiber comprising polymers which differ in solvent solubility, impregnating the non-woven fabric with a polyurethane resin, and extracting and removing one component of the fiber has been developed. This artificial leather is excellent in quality but it involves such financial problems that it requires a solvent extraction step, its production process is complicated and its production cost is high.
Thus, artificial leather which is sufficiently light in weight, strong, flexible and tight, and rarely buckles is yet not to be obtained.

Summary of the Invention

It is an object of the present invention to provide a non-woven fabric which is light in weight and excellent in flexibility and rarely buckles as well as artificial leather which comprises the non-woven fabric, is sufficiently light in weight, strong, flexible and tight, and rarely buckles.

Means for solving problem

That is, according to the present invention, there is provided a non-woven fabric prepared by thermally shrinking a web which comprises 30 to 100 wt% of a hollow fiber (A) having a shrinkage factor in 70°C hot water of at least 35 % and 0 to 70 wt% of other fiber to an area shrinkage factor of at least 15 %, wherein the hollowness of a hollow fiber (A') contained in the non-woven fabric after shrinkage is 30 to 70 %, the apparent density of the non-woven fabric is 0.12 to 0.20 g/cm³, and the tensile strength per unit area·unit weight of the non-woven fabric is 270 (kg/cm)/(g/cm²) or more.
According to the present invention, there are further provided artificial leather prepared by impregnating the above non-woven fabric with an elastic polymer (C) and artificial leather having a porous cover layer or non-porous cover layer made from an elastic polymer on at least one side.

Detailed Description of the Embodiment

The present invention will be described in detail hereinunder.
It is important to use a fiber having a small apparent density to reduce weight as the fiber constituting the non-woven fabric. Stated more specifically, a single-pore or multi-pore hollow fiber having a round or other shape and having a hollowness of 30 to 70 % is suitable. However, since a hollow fiber having a large hollowness is more difficult to obtain higher strength than a non-hollow fiber, various measures are required to improve the strength of the obtained non-woven fabric.
The following methods are generally conceivable to enhance the strength of a non-woven fabric: one in which a high-strength fiber is mixed in an appropriate amount for reinforcement, one in which the fineness of a fiber used is reduced to increase the degree of entanglement between fibers, and one in which the weight of the fiber of a non-woven fabric is increased. However, when only the weight of the fiber of the non-woven fabric or the hollowness of the fiber is changed in limits that satisfy the required strength of the non-woven fabric to reduce weight, the non-woven fabric and artificial leather obtained therefrom buckle like a folded corrugated paperboard and are not suitable for such application as shoes. The present invention is predicated upon the finding that a non-woven fabric which has solved the above problems is obtained by shrinking a web comprising a fiber having a large hollowness and high shrinkage as a constituent fiber.
That is, the constituent fiber of a web used to produce the non-woven fabric of the present invention is a shrinkable hollow fiber (A) having a shrinkage factor of at least 35 %, preferably 40 to 60 % when it is immersed in 70°C hot water for 2 minutes. The term "shrinkage factor" as used herein means the proportion (%) of the shrinked length of a fiber after shrinkage (the length of fiber before shrinkage-the length of fiber after shrinkage) to the length of the fiber before shrinkage. The proportion of the shrinkable hollow fiber (A) in the web of the present invention is 30 to 100 wt%, preferably 30 to 95 wt%, particularly preferably 40 to 90 wt%. A fiber other than the above shrinkable fiber (A) may be contained in the web in an amount of 70 to 0 wt%, preferably 70 to 5 wt%, particularly preferably 60 to 10 wt%.
The shrinkage factor of the shrinkable hollow fiber (A) contained in the web must be at least 35 %. When this shrinkage factor is smaller than 35 %, it is difficult to attain a surface shrinkage factor of 15 % or more after the web is shrunk and the non-woven fabric of interest cannot be obtained. When the proportion of the shrinkable hollow fiber in the web is smaller than 30 wt%, it is difficult to obtain a non-woven fabric which is light in weight and excellent in flexibility and strength.
The hollowness of the hollow fiber (A) must be 30 to 70 %, preferably 45 to 70 % after shrinkage which will be described hereinafter. When the hollowness is less than 30%, the obtained non-woven fabric cannot be light in weight and tight at the same time. When the hollowness is more than 70 %, strength cannot be retained disadvantageously. The fineness of the hollow fiber is advantageously 0.8 to 6.0 denier from the view point of its passing through non-woven fabric production equipment such as a card and a fiber entangling process. The strength of the hollow fiber (A) after shrinkage is generally 2 to 4.8 g/de, preferably 2.2 to 3.8 g/de. The polymer forming the hollow fiber (A) is any fiber formable polymer such as a polyester, polyamide or polyolefin. But from the view points of the characteristics of non-woven fabric or artificial leather, and easy production of a fiber having the above shrinkage in warm water, it is preferably a polyester such as polyethylene terephthalate, polytrimethylene terephthalate or polytetramethylene terephthalate or a modified polyester obtained by copolymerizing one of the polyesters with isophthalic acid, adipic acid, a sulfonic acid metal base such as 5-sodium sulfoisophthalic acid or isophthalic acid having a phosphonium base.
The method of producing the hollow fiber (A) when polyethylene terephthalate is used, for example, may be a method proposed by JP-A 10-292222 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). Stated more specifically, a spinneret having a very small slit width of 0.03 to 0.05 mm is used and the inner diameter of a hollow shape formed by the slit is increased as much as possible to obtain the hollow fiber (A) having a large hollowness with ease. The polymer has an intrinsic viscosity of 0.45 or more, preferably 0.55 to 0.70 and is molten and discharged from the above spinneret for forming hollow fiber. Fiber discharged is quenched by spraying 20 to 35°C cold wind right below the spinneret at a wind speed of 0.2 to 4.0 m/min and taken up at a spinning speed of 1,000 to 2,000 m/min. The obtained hollow unstretched fiber is stretched to 1.5 to 4.5 times in a warm water bath heated at 50 to 75°C according to required performance in limits that ensure that the shrinkage factor in warm water of the obtained fiber should be 35 % or more. Thus, a shrinkable hollow fiber of a polyester is obtained.
A hollow fiber having a low shrinkage factor can be obtained by heat setting the above fiber with a heating roller or heating plate after stretching and a hollow fiber having self-extensibility can be obtained by relaxing the above fiber by heating while it is overfed after stretching. These fibers may be used as other constituent fiber of the web used in the present invention as will be described hereinafter.
The web in the present invention may contain the above shrinkable hollow fiber (A) in the above proportion and may further contain a fiber other than the above hollow fiber (A). The other fiber is a non-hollow fiber, hollow high-strength fiber or hollow self-extensible fiber. Other preferred examples of the fiber include a non-hollow fiber (B) having a strength of 4 to 30 g/de, a hollow fiber (G) having a strength of 4 to 8 g/de and a self-extensible hollow fiber (H) having a strength of 2.5 to 4 g/de. They may be used alone or in admixture of two or more. These fibers will be described hereinunder.
Illustrative examples of the preferably used non-hollow fiber (B) include polyester fibers, aliphatic polyamide fibers, aromatic polyamide fibers, polyimide fibers and polyolefin fibers having a strength of 4 to 30 g/de. Out of these, aromatic polyamide fibers, polyimide fibers and aromatic polyester fibers are preferred, and fibers having a strength of 10 g/de or more are particularly preferred because a non-woven fabric having excellent impact strength can be obtained. When the fineness of the fiber is too small, process stability during the production of a non-woven fabric using a card lowers significantly and when the fineness is too large, the stiffness of the fiber becomes too large, thereby deteriorating a feel such as flexibility or the like. Therefore, the fineness is preferably 0.3 to 10.0 denier, particularly preferably 0.5 to 5 denier.
Illustrative examples of the other preferably used hollow fiber (G) include polyester fibers, aliphatic polyamide fibers and polyolefin fibers having a strength of 4.0 to 8.0 g/de and a hollowness of 30 to 70 % from the viewpoint of the lightweight of the non-woven fiber. The fineness of the fiber is preferably 0.5 to 6.0 denier, particularly preferably 0.8 to 3.0 denier so as to increase the strength of the obtained non-woven fabric as much as possible. The hollow fiber (G) has a shrinkage factor in 70°C warm water of 30 % or less, preferably 20 % or less, particularly preferably 10 % or less.
When the hollow fiber (G) having the above large hollowness and high strength is used in combination with the hollow fiber (A), a non-woven fabric mainly formed out of the hollow fiber having a large hollowness is obtained. The hollow fiber of this non-woven fabric has a bending rigidity of 0.938 at a hollowness of 25 %, 0.750 at a hollowness of 50 % and 0.490 at a hollowness of 70 % when the bending rigidity of a round non-hollow fiber having the same cross section is 1. Therefore, since the hollow fiber has smaller bending rigidity than the non-hollow fiber, it is very flexible. When the proportion of the above highly shrinkable hollow fiber (A) to the fiber having a large hollowness is large, as the orientation degree of a hollow fiber (A') after shrinkage is low, the obtained non-woven fabric and artificial leather have excellent flexibility but their flexing resistance is liable to lower due to a reduction in folding resistance.
To further improve the flexing resistance, the above non-hollow fiber (B) or the hollow fiber (G) is preferably used in combination. Particularly when a non-hollow fiber having small fineness is used, its effect becomes large advantageously. The mixing weight ratio of the highly shrinkable hollow fiber (A) and non-hollow fiber (B) and/or hollow fiber (G) is preferably 95:5 to 30:70, particularly preferably 80:20 to 40:60 in terms of the hollow fiber (A): {non-hollow fiber (B) + hollow fiber (G)} as the mixing weight ratio when the web is mainly composed of these fibers. When the proportion of the non-hollow fiber (B) and/or hollow fiber (G) is smaller than 5 wt%, the effect of increasing strength becomes unsatisfactory and when the proportion is larger than 70 %, the feel of the non-woven fabric becomes hard.
Illustrative examples of the other preferably used hollow self-extensible fiber (H) include polyester fibers and aliphatic polyamide fibers having a strength of 2.5 to 4.0 g/de and a self extensibility of 3 % or more, particularly preferably 5 to 15 % when treated with dry heat at 150°C for 5 minutes. The hollowness of the fiber (H) is preferably 30 to 70 % from the viewpoint of the lightweight of the obtained non-woven fabric and the fineness thereof is preferably 0.5 to 6.0 denier. The mixing weight ratio of the hollow fiber (A) to the hollow self-extensible fiber (H) is 95:5 to 30:70, particularly preferably 80:20 to 30:70 from the viewpoint of the flexibility and buckling resistance of the obtained non-woven fabric and artificial leather.
To produce the non-woven fabric of the present invention, the above shrinkable hollow fiber (A) or a combination of the hollow fiber (A) and other fiber are blended together in predetermined amounts, a web (entangled non-woven fabric) is formed using equipment used for the production of a non-woven fabric, such as a card, random webber, cross lapper and needle locker which are known per se, and then the web must be thermally shrunk in warm water or hot wind to at least 15 %, preferably 20 % or more, particularly preferably 25 % or more of its original area. When the area shrinkage factor is less than 15 %, the buckling resistance and feel of the obtained non-woven fabric and artificial leather become unsatisfactory. The area shrinkage factor is preferably 65 % or less, more preferably 60 % or less. The term "area shrinkage factor (%)" as used herein means the proportion of reduced area after shrinkage (area before shrinkage-area after shrinkage) to area before shrinkage. The weight of the web (gram per one cm²) and the entangling degree of fibers may be suitably changed to ensure that the apparent density of the obtained non-woven fabric and the tensile strength per unit area·unit weight thereof should become values which will be given hereinafter. They can be determined by simple experiments.
Thereafter, the thermally shrunk non-woven fabric is thermally pressed by a belt press, calender roll press or the like to adjust the thickness and apparent density of the non-woven fabric. To prepare a non-woven fabric suitable for use in lightweight artificial leather in the present invention, the apparent density of the non-woven fabric must be adjusted to a range of 0.12 to 0.20 g/cm³, preferably 0.14 to 0.19 g/cm³. When the apparent density is less than 0.12 g/cm³, the buckling resistance of the non-woven fabric and artificial leather obtained therefrom become unsatisfactory and when the apparent density is more than 0.20 g/cm³, lightweight is lost.
Further, to meet requirements for lightweight artificial leather from the field of shoes or the like, the artificial leather must have excellent strength even though it is light in weight. To this end, the tencil strength per unit area·unit weight must be 270 (kg/cm)/(g/cm²) or more, particularly 300 (kg/cm)/(g/cm²) or more. To obtain a non-woven fabric having the above properties, the constituent fiber must be adjusted to the above ranges and the entangling degree of fibers is suitably adjusted by needling punching or contact with a jet liquid flow. This tensile strength is 500 (kg/cm)/(g/cm²) or less, preferably 450 (kg/cm)/(g/cm²) or less for practical application.
The apparent density is obtained by measuring the weight and volume of the obtained non-woven fabric and calculating weight (g) per 1 cm² from the obtained value. The thickness of the non-woven fabric is measured under a load of 100 g/cm². The tensile strength per unit area·unit weight is a value obtained by dividing the tensile strength of the non-woven fabric per 1 cm in width by the unit weight (g/cm²) of the non-woven fabric.
When a web obtained by mixing the shrinkable hollow fiber (A) with a low-shrinkable fiber of small denier out of the non-hollow fibers (B) is thermally shrunk, the shrinkable fiber (A) gets into the inner layer of the non-woven fabric and the low-shrinkable fiber of small denier is mainly existent on the surface of the non-woven fabric. Therefore, as for artificial leather obtained by impregnating the non-woven fabric with the elastic polymer (C) which will be described hereinafter and further artificial leather having a porous or non-porous cover layer made from an elastic polymer, the high-strength fiber (B) is existent in the surface layer or the interface between the surface layer and the cover layer in large quantities and the effect of increasing flexing resistance becomes especially large.
The non-woven fabric of the present invention which has been described above is impregnated with the elastic polymer (C) to obtain artificial leather. The elastic polymer (C) preferably used is a polyurethane-based elastomer such as a polyurethane elastomer or polyurethane/urea elastomer, acrylic elastomer showing rubber-like elasticity, acrylonitrile-butadiene copolymer or styrene-butadiene copolymer. The elastic polymer is dissolved in an organic solvent solution or dispersion in water, impregnated into the non-woven fabric, coagulated and dried to obtain artificial leather.
In the present invention, to well balance between the flexibility and strength of the obtained artificial leather and achieve lightweight, the amount of the elastic polymer (C) impregnated must be adjusted to 25 to 95 wt%, especially 35 to 65 wt% based on the weight of the fiber. When the amount of impregnation is smaller than 25 wt%, the amount of the elastic polymer which functions as a binder in the non-woven fabric becomes too small and the strength of artificial leather becomes unsatisfactory. When the amount is larger than 95 wt%, the feel of artificial leather becomes too hard disadvantageously. To satisfy requirements for artificial leather, the modulus of the elastic polymer (C), the coagulation state of the elastic polymer (C) in the non-woven fabric, and the binding state of the elastic polymer (C) to the non-woven fabric fiber are preferably adjusted by conventionally known means, in addition to the amount of impregnation.
Further, the artificial leather of the present invention may have a porous or non-porous surface cover layer on at least one side. An elastic polymer (E) forming a porous cover layer or non-porous cover layer and an elastic polymer (F) forming a non-porous cover layer are both preferably a polyurethane-based elastomer such as a polyurethane elastomer or polyurethane/urea elastomer. A cover layer can be formed by coating an organic solvent solution of the above elastic polymer or a W/O dispersion prepared by dispersing the above elastic polymers in a non-solvent such as water on the above artificial leather and removing the solvent by a wet coagulation method or dry coagulation method known per se.
The thus obtained artificial leather of the present invention has an apparent density of 0.3 to 0.38 g/cm³, particularly preferably 0.31 to 0.36 g/cm³ and a thickness (T) of 0.06 to 0.16 cm, particularly preferably 0.065 to 0.14 cm, and the relationship between the weight (W: g/cm³) and thickness (T) of the artificial leather preferably satisfies 0.30T ≦ W ≦ 0.38T to well balance lightweight, strength, flexibility and buckling resistance.

Examples

The following examples are given to further illustrate the present invention. The evaluation items in the examples are measured in accordance with the following methods.

〈weight〉

This is measured in accordance with the JIS K 6505 method.

〈thickness〉

This is measured in accordance with the JIS K 6505 method. The measurement load is 100 g/cm².

〈apparent density〉

This is calculated from the above measurement values of weight and thickness.

〈tensile strength〉

This is measured in accordance with the JIS K 6505 method.

〈tear strength〉

This is measured in accordance with the JIS K 6505 method.

〈flexing resistance〉

This is measured in accordance with the JIS K 6505 method.

〈buckling resistance〉

The palms of both hands are turned up with the small fingers of both hands facing each other and both 10 cm end portions in a transverse direction of a non-woven fabric or artificial leather sample measuring about 10 cm x 20 cm are held between the thumbs and forefingers of both hands. Then, the sample held by both hands is bent at an angle of about 45° by moving the palms of both hands toward each other. The buckling resistance is evaluated based on bending lines (bending wrinkles) on the surface of the non-woven fabric or artificial leather sample.
As for the sample having excellent buckling resistance, fine bending wrinkles are formed and the bent portion is rounded. As for the sample having poor buckling resistance, bending wrinkles are large and linear and the bent portion makes an acute angle like a bent corrugated paperboard.

〈flexibility〉

The flexibility of a non-woven fabric is evaluated based on softness when it is grasped by hand. The flexibility of artificial leather is evaluated based on bending rigidity measured in accordance with the following method. The smaller the value of bending rigidity the softer the sample becomes.
A sample piece measuring 2.5 cm x 9.0 cm is fixed to a fixing tool at a position 2.0 cm from one end portion. Reactive force generated when it is bent at 90° at a curvature radius of 2 cm is measured at a position 2.0 cm from the other end of the sample and bending rigidity (g/cm) per 1 cm in width of the sample piece is calculated from this measurement value.

Example 1

Polyethylene terephthalate having an intrinsic viscosity measured at 30°C in orthochlorophenol of 0.60 was spun into fiber using a spinneret for hollow fibers at 290°C. Thereafter, the obtained unstretched fiber was stretched to 2.7 times in 58°C warm water, dried by exposure to dry cold air, treated with a fiber lubricant and cut to a fiber length of 64 mm. This fiber was a hollow fiber (A) having a shrinkage factor in 70°C warm water of 56 %, a hollowness of 52 %, a single filament fineness of 1.0 denier (substantially equivalent to an outer diameter of about 2 denier) and a single filament strength of 2.8 g/de.
Similar polyethylene terephthalate was spun into fiber likewise which was then stretched to 3.5 times to obtain a non-hollow fiber (B) having a single filament fineness of 1.2 denier, a single filament strength of 4.5 g/de and a fiber length of 50 mm. The above hollow fiber (A) and the above non-hollow fiber (B) were blended together in weight ratios of (1) 100/0, (2) 80/20, (3) 50/50 and (4) 35/65 to obtain webs with a card and cross lapper and the webs were subjected to needle punching at a rate of 800 penetrations/cm² to obtain non-woven fabrics (entangled non-woven fabrics). These non-woven fabrics had shrinkage factors in 70°C warm water shown in Table 1.
The webs were adjusted in weight as shown in Table 1 based on the above shrinkage factors, subjected to needle punching at a rate of 1,000 penetrations/cm² and immersed in 70°C warm water for 2 minutes to be shrunk at area shrinkage factors shown in Table 1. The non-woven fabrics after thermal shrinkage were adjusted to a water content of 50 % with a suction dehydroextractor, impregnated with a 0.3 % solution of a non-woven fabric treating agent which contained organic silicone as the main ingredient and squeezed to a liquid content of 150 %. These non-woven fabrics were let pass through a belt press having a drum surface temperature of 110°C to be dry pressed at a surface pressure of 0.08 to 0.12 kg/cm² to ensure that the non-woven fabrics have an apparent density of about 0.14 g/cm³. As a result, the non-woven fabrics shown in Table 1 were obtained.

The obtained non-woven fabrics were excellent in buckling resistance and tight, had a soft feel and was useful as a non-woven fabric for artificial leather.

item	Ex.1-a	Ex.1-b	Ex.1-c	Ex.1-d
hollow fiber (A)/non-hollow fiber (B)	100/0	80/20	50/50	35/65
weight of web (g/cm²)	0.0063	0.0072	0.0082	0.0102
area shrinkage factor	58	52	45	32
non-woven fabric
weight (g/cm²)	0.014	0.014	0.014	0.014
thickness (mm)	1.00	1.00	1.00	1.00
apparent density (g/cm³)	0.14	0.14	0.14	0.14
tensile strength (kg/cm)L/C(TS)	5.0/4.6	5.2/4.8	5.5/5.1	5.8/5.3
TS/weight of non-woven fabric L/C (kg/cm) / (g/cm²)	357/328	371/343	393/364	414/378
buckling resistance	satisfactory	satisfactory	satisfactory	satisfactory
flexibility	satisfactory	satisfactory	satisfactory	satisfactory
light weight	satisfactory	satisfactory	satisfactory	satisfactory
Ex.: Example

Example 2

An impregnation solution was prepared by adding a porosity controlling agent and a colorant to a dimethyl formamide solution (concentration of 10 %) of a polyurethane elastomer having a nitrogen content of 3.5 wt% based on diisocyanate obtained by reacting a 1:1 mixed polymer diol of polytetramethylene glycol (molecular weight of 2,040) and polyhexamethylene adipate (molecular weight of 2,000) with 4,4'-diphenylmethane diisocyanate and ethylene glycol. This impregnation solution was impregnated into the non-woven fabrics prepared in Example 1 which were then squeezed to ensure that the amount of the impregnation solution became 900 g/m², and a polyurethane elastomer solution having the same composition (except concentration of 20 %) was coated on the drum contact surface sides of the non-woven fabrics in an amount of 900 g/m².
The non-woven fabrics were immersed in a coagulation water bath to coagulate the polyurethane elastomer, washed repeatedly to remove the solvent and then dried. The polyurethane covered surface of the obtained artificial leather was buffed with a buffing machine equipped with 240-mesh sandpaper to obtain nubuck-like artificial leather having polyurethane fine pores on the surface thereof.

The obtained artificial leather was very flexible, excellent in buckling resistance, tight, lighter in weight than conventional leather sheets and excellent as a shoe material.

	Ex.2-a	Ex.2-b	Ex.2-c	Ex.2-d
non-woven fabric	Ex.1-a	Ex.1-b	Ex.1-c	Ex.1-d
artificial leather
Weight (g/cm²)	0.0365	0.0370	0.0365	0.0363
Thickness (mm)	1.10	1.10	1.09	1.10
apparent density (g/cm³)	0.335	0.336	0.335	0.330
tensile strength (kg/cm)L/C	8.0/7.6	8.2/7.8	8.5/8.1	8.8/8.3
tear strength (kg)L/C	2.00/2.15	2.65/2.55	2.85/2.65	2.80/2.70
flexibility
bending rigidity (g/cm)	0.8	0.8	0.9	1.1
flexing resistance
200,000 times	4	5	5	5
400,000 times	3	4	5	5
Ex.: Example

Example 3

Polyethylene terephthalate having an intrinsic viscosity measured at 30°C in orthochlorophenol of 0.60 was spun into fiber using a spinneret for hollow fibers at 290°C. Thereafter, the obtained unstretched fiber was stretched to 3.5 times in 58°C warm water, dried by exposure to dry cold air, treated with a fiber lubricant and cut to a fiber length of 64mm. This fiber had a shrinkage factor in 70°C warm water of 0 %, a hollowness of 48 %, a single filament fineness of 1.0 denier and a single filament strength of 4.2 g/de.
This hollow fiber (G) having high strength and the above highly shrinkable non-hollow fiber (A) prepared in Example 1 were blended together in ratios shown in Table 3 to obtain webs having a weight of 100 g/m² with a random webber and then the webs were subjected to needle punching at a rate of 800 penetrations/cm² to obtain a web (entangled non-woven fabrics). The shrinkage factors of these non-woven fabrics when they were immersed in 70°C warm water for 2 minutes are shown in Table 3.
The webs were adjusted in weight based on the above shrinkage factors to ensure that the weights of the non-woven fabrics after shrinkage should become 210 g/m², subjected to needle punching at a rate of 1,000 penetrations /cm² and immersed in 70°C warm water for 2 minutes to be shrunk at area shrinkage factors shown in Table 3. The non-woven fabrics after thermal shrinkage were adjusted to a water content of 50 % with a suction dehydroextractor, impregnated with a 0.3 % solution of a non-woven fabric treating agent which contained organic silicone as the main ingredient and squeezed to a liquid content of 150 %. These non-woven fabrics were let pass through a belt press having a drum surf ace temperature of 110° C to be dry pressed at a surface pressure of 0.08 to 0.12 kg/cm² to ensure that the non-woven fabrics have an apparent density of about 0.16 g/cm³. As a result, the non-woven fabrics shown in Table 3 were obtained.
An impregnation solution was prepared by adding a porosity controlling agent and a colorant to a dimethyl formamide solution (concentration of 8 %) of a polyurethane elastomer having a nitrogen content of 3.3 wt% based on diisocyanate obtained by reacting a 1:1 mixed polymer diol of polytetramethylene glycol (molecular weight of 2,040) and polyhexamethylene carbonate (molecular weight of 1,800) with 4,4'-diphenylmethane diisocyanate and ethylene glycol. This impregnation solution was impregnated into the above non-woven fabrics which were then squeezed to ensure that the amount of the impregnation solution became 1,100 g/m², and a polyurethane elastomer solution having the same composition (except concentration of 20 %) was coated on the drum contact surface sides of the non-woven fabrics in an amount of 900 g/m².
The non-woven fabrics were immersed in a coagulation water bath to coagulate the polyurethane elastomer, washed repeatedly to remove the solvent and then dried. Dimethyl formamide was applied to the polyurethane covered surface of the obtained artificial leather with a 100-mesh gravure roll to prepare a substrate having polyurethane fine pores in the surface, and then a polyurethane resin coating containing titanium oxide was coated to a solid weight of about 10 g/m² in such a manner that the fine pores were not smashed. The obtained artificial leather was light in weight, strong, very flexible and excellent as a material for the insteps of sport shoes which were hardly wrinkled by buckling.

Example 4

Polyethylene terephthalate having an intrinsic viscosity measured at 30°C in orthochlorophenol of 0.60 was spun into fiber using a spinneret for hollow fibers at 290°C. Thereafter, the obtained unstretched fiber was stretched to 2.5 times in 58°C warm water and dried by exposure to dry cold air to obtain a fiber having a shrinkage factor in 70°C warm water of 58 %, a hollowness of 50 % and a single filament fineness of 1.0 denier. This shrunk fiber was heated in 68°C warm water in constant length to obtain a fiber having a hollowness of 48 %, a single-filament fineness of 1.0 denier, a single-filament strength of 3.0 g/de and a self extensibility of 6 % at 150°C.
A non-woven fabric and artificial leather were prepared under the same conditions as in Example 3-b except that this self-extensible fiber was used in place of the high-strength hollow fiber.

The obtained artificial leather was slightly inferior to that of Example 3-b in flexing resistance but very flexible, light in weight and extremely useful as a shoe material.

	Ex.3-a	Ex.3-b	Ex.3-c	Ex.4
hollow fiber (A)/hollow fiber (G)	70/30	55/45	40/60	55/45
weight of web (g/cm²)	0.0105	0.0111	0.0130	0.0113
area shrinkage factor (%)	50	47	38	46
non-woven fabric
weight (g/cm²)	0.021	0.021	0.021	0.021
thickness (mm)	1.30	1.30	1.30	1.30
apparent density (g/cm³)	0.161	0.161	0.161	0.165
tensile strength (kg/cm)L/C(TS)	6.8/6.6	7.1/6.9	7.3/7.1	6.6/6.4
TS/weight of non-woven fabric L/C (kg/cm) / (g/cm²)	324/314	338/328	348/338	314/305
Artificial leather
weight (g/cm²)	0.0453	0.0452	0.0445	0.0453
thickness (mm)	1.35	1.35	1.35	1.35
apparent density (g/cm³)	0.336	0.335	0.330	0.330
tensile strength (kg/cm)L/C	10.9/10.6	11.4/11.0	11.7/11.4	10.2/9.9
tear strength (kg)L/C	2.30/2.25	2.55/2.50	2.65/2.60	2.10/2.10
Flexibility
bending rigidity (g/cm)	1.8	1.9	2.0	1.6
flexing resistance
200,000 times	5	5	5	5
400,000 times	5	5	5	4
Ex.: Example

Example 5

A polyurethane resin film (thickness of 30 µm) colored with carbon black and formed on calf-like releasing paper was laminated on a side having a porous cover layer of the artificial leather prepared in Example 3-b with a polyurethane adhesive to obtain artificial leather having a non-porous cover layer.
The obtained artificial leather was light in weight, had strength and high surface abrasion resistance, and was excellent as a sport shoe upper material.

Comparative Example 1

Polyethylene terephthalate having an intrinsic viscosity measured at 30°C in orthochlorophenol of 0.60 was spun at 290°C to obtain unstretched non-hollow fiber having a round cross section. The obtained unstretched fiber was stretched to 2.7 times in 58°C warm water and dried by exposure to dry cold air to obtain a fiber having a shrinkage factor in 70°C warm water of 56 % and a single-filament fineness of 2.0 denier.
A non-woven fabric and artificial leather were prepared under the same conditions as in Example 1-c except that the above highly shrinkable fiber having a round cross section and the high-strength non-hollow fiber (B) were mixed together in a ratio of 100/50 so that they could have the same pore volume as that of the non-hollow fiber (B) prepared in Example 1.
The obtained non-woven fabric had higher strength than that of Example 1-c but it had low strength per unit area·unit weight and high apparent density and was unsatisfactory in terms of lightweight.

Comparative Example 2

A non-woven fabric and artificial leather were formed to have the same fiber constitution as in Example 1-c except that the non-woven fabric was adjusted to a weight of 0.025 g/cm² and an apparent density of 0.25 g/cm³. The obtained non-woven fabric and artificial leather had high strength according to the weight of the fiber but were unsatisfactory in terms of lightweight and not suitable for use as a shoe material.

Comparative Example 3

A non-woven fabric and artificial leather were formed to have the same fiber constitution as in Example 1-c except that the non-woven fabric was adjusted to a weight of 0.010 g/cm² and an apparent density of 0.10 g/cm³. The obtained non-woven fabric and artificial leather had insufficient strength, and was inferior in buckling resistance and not suitable for use as a shoe material.

Comparative Example 4

The mixing weight ratio of the highly shrinkable hollow fiber (A) to the non-hollow fiber (B) in Example 1 was changed to 15:85. Since the obtained web had an area shrinkage factor of less than 10 %, the obtained non-woven fabric and artificial leather were satisfactory in tens of lightweight but was inferior in buckling resistance. Therefore, they were easily wrinkled and not suitable for use as a shoe material.

	C.Ex.1	C.Ex.2	C.Ex.3	C.Ex.4
hollow fiber (A)/non-hollow fiber (B)	100/50	50/50	50/50	15/85
weight of web (g/cm²)	0.0123	0.0138	0.0055	0.0156
area shrinkage factor (%)	45	45	45	10
non-woven fabric
weight (g/cm²)	0.0224	0.0250	0.0100	0.0140
thickness (mm)	1.00	1.00	1.00	1.00
apparent density (g/cm³)	0.224	0.250	0.101	0.140
tensile strength (kg/cm)L/C(TS)	7.5/7.8	8.2/8.4	2.6/2.5	5.3/4.8
TS/weight of non-woven fabric L/C (kg/cm) / (g/cm²)	334/348	328/336	260/250	378/343
Artificial leather
weight (g/cm²)	0.0453	0.0475	0.0345	0.0370
thickness (mm)	1.10	1.13	1.05	1.03
apparent density (g/cm³)	0.336	0.420	0.330	0.359
tensile strength (kg/cm)L/C	11.9/11.6	11.4/11.0	4.7/4.5	8.2/7.9
tear strength (kg)L/C	2.50/2.35	3.05/2.85	1.65/1.60	2.10/2.10
flexibility
bending rigidity (g/cm)	1.8	1.9	2.0	1.6
flexing resistance
200,000 times	5	5	5	5
400,000 times	5	5	5	4
buckling resistance	-	-	insufficient	insufficient
C.Ex.: Comparative Example

Effect of the Invention

The non-woven fabric of the present invention is light in weight and excellent in terms of flexibility and buckling resistance, and the artificial leather of the present invention produced from the non-woven fabric is light in weight, strong, flexible and tight, rarely buckles and is especially useful as a shoe material.

Claims

A non-woven fabric prepared by thermally shrinking a web which comprises 30 to 100 wt% of a hollow fiber (A) having a shrinkage factor in 70°C warm water of at least 35 % and 0 to 70 wt% of other fiber to an area shrinkage factor of at least 15 %, wherein

the hollowness of a hollow fiber (A') contained in the non-woven fabric after shrinkage is 30 to 70 %, the apparent density of the non-woven fabric is 0.12 to 0.20 g/cm³, and the tensile strength per unit area·unit weight of the non-woven fabric is 270 (kg/cm)/(g/cm²) or more.
The non-woven fabric of claim 1, wherein the web comprises 30 to 95 wt% of the hollow fiber (A) and 5 to 70 wt% of other fiber.
The non-woven fabric of claim 1 or 2, wherein the other fiber is at least one selected from the group consisting of a non-hollow fiber (B) having a strength of 4 to 30 g/de, a hollow fiber (G) having a strength of 4 to 8 g/de and a self-extensible hollow fiber (H) having a strength of 2.5 to 4 g/de.
The non-woven fabric of claim 1, wherein the hollow fiber (A) is formed from an aromatic polyester.
The non-woven fabric of claim 1, wherein the web comprises 30 to 95 wt% of the hollow fiber (A) and 70 to 5 wt% of the non-hollow fiber (B) having a strength of 4 to 30 g/de.
The non-woven fabric of claim 5, wherein the non-hollow fiber (B) is formed from an aromatic polyester, aliphatic polyamide, aromatic polyamide or polyimide.
The non-woven fabric of claim 1, wherein the web comprises 30 to 95 wt% of the hollow fiber (A) and 70 to 5 wt% of a hollow fiber (G) having a strength of 4 to 8 g/de.
The non-woven fabric of claim 7, wherein the hollow fiber (G) is formed from an aromatic polyester, aliphatic polyamide or polyolefin.
The non-woven fabric of claim 1, wherein the web comprises 30 to 95 wt% of the hollow fiber (A) and 70 to 5 wt% of a self-extensible hollow fiber (H) having a strength of 2.5 to 4 g/de.
The non-woven fabric of claim 9, wherein the self-extensible hollow fiber (H) is formed from an aromatic polyester or aliphatic polyamide.
Artificial leather prepared by impregnating the non-woven fabric of claim 1 with an elastic polymer.
The artificial leather of claim 11, wherein the elastic polymer is impregnated in an amount of 25 to 95 wt% based on the non-woven fabric.
The artificial leather of claim 11 which has an apparent density of 0.3 to 0.38 g/cm³, a thickness (T cm) of 0.06 to 0.16 cm and a weight (W g/cm²) which satisfies 0.3T ≦ W ≦ 0.38T.
The artificial leather of claim 11 which has a porous cover layer or non-porous cover layer made from an elastic polymer (E) on at least one side.
The artificial leather of claim 14 which has an apparent density of 0.3 to 0.38 g/cm³, a thickness (T cm) of 0.06 to 0.16 cm and a weight (W g/cm²) which satisfies 0.3T ≦ W ≦ 0.38T.
A process for producing a non-woven fabric comprising a shrunk hollow fiber (A') having a hollowness of 30 to 70 % and having an apparent density of 0.12 to 0.20 g/cm³ and a tensile strength per unit area·unit weight of 270 (kg/cm)/(g/cm²) or more, the process comprising shrinking a web comprising 30 to 100 wt% of a hollow fiber (A) having a shrinkage factor in 70°C warm water of at least 35 % and 0 to 70 wt% of other fiber to an area shrinkage factor of at least 15 % by heating.