Wet-formed non-woven fabric having good drape characteristics

Abstract

 A wet non-woven fabric having excellent drape characteristics, which is formed from a mixture of (A) a polyester short fiber in which a shrinkage factor in the direction of the fiber axis at a temperature not lower than 90°C is negative and (B) a short fiber showing a fusion-bondability at a temperature lower by at least 50°C than a temperature at which the short fiber (A) has a fusion bondability or (C) a polyester short fiber having a birefringence of 0.006 to 0.03, according to a wet paper-forming method.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates to a novel non-woven fabric composed of polyester short fibers, which fabric is very soft and has excellent practical properties. The wet non-woven fabric according to the present invention has excellent drape characteristics and strength, and accordingly, this wet non-woven fabric can be used for disposable clothing, surface materials of paper diapers and sanitary napkins, disposable operating gowns, covering cloths, operating room clothing, sheets, tablecloths, curtains, paddings, and base cloths for artificial leather.

2. Description of the Related Art

[0002] A non-woven fabric formed from a polyester short fiber and a short fiber composed at least partially of a polymer having a melting point lower than that of the polyester short fiber or an undrawn polyester short fiber according to the wet paper-forming method is known in the art. Also known is a non-woven fabric formed from a polyester short fiber having a birefringence of not less than 0.05 and a polyester short fiber having a birefringence of 0.006 to 0.03 according to the wet paper-forming method.

[0003] Furthermore, a product somewhat softened by subjecting this non-woven fabric to an embossing or creping treatment is known.

[0004] These non-woven fabrics, however, are defective in that because of the rigidity of the polyester fiber per se, and also the effects of bonding of fibers by the heat-fusion treatment, they have a very hard and paper-like touch. As means for obtaining a soft touch, there can be mentioned a method in which the titre of a constituent fiber is made finer and a method in which the basic weight of a non-woven fabric is reduced. However, if these methods are adopted, the strength is reduced and a practical product cannot be obtained. It may be expected that if the elongation is increased, the softness will be improved. However, even though a polyester fiber in a substantially undrawn state has a high elongation, if this polyester fiber is formed into a non-woven fabric, the product has a hard touch and is not preferred from the practical viewpoint. These defects are due substantially to the essential properties of polyester fibers and it has been difficult to obtain a wet non-woven fabric having a very soft touch and excellent drape characteristics.

[0005] A non-woven fabric formed from a highly shrinkable polyester fiber having a latent spontaneous elongation is known from Japanese Unexamined Patent Publication (Kokai) 53-58074. The fabric disclosed therein is dense and has excellent drape characteristics. However, the fabric has a drawback in that the production procedures thereof are both complex and troublesome.

SUMMARY OF THE INVENTION

[0006] It is a primary object of the present invention to overcome the foregoing defects by providing a wet non-woven fabric having excellent drape characteristics and a practical strength and also having a good tactility.

[0007] In accordance with the present invention, there is provided a wet non-woven fabric having excellent drape characteristics, which is formed from a mixture of (A) a polyester short fiber in which a shrinkage factor in the direction of the fiber axis at a temperature not lower than 90°C is negative, and (B) a short fiber showing a fusion-bondability at a temperature lower by at least 50°C than a temperature at which the short fiber (A) has a fusion bondability, or (C) a polyester short fiber having a birefringence of 0.006 to 0.03, according to a wet paper-forming method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The short fiber (B) referred to in the present invention is a fiber capable of fusion-bonding the short fiber (A) or the short fibers (A) and (B) at a temperature lower by at least 50°C than the melting temperature of the fiber (A). As this fusion-bonding short fiber, there can be mentioned short fibers composed of synthetic polymers such as an ethylene/vinyl acetate copolymer, an ethylene/propylene copolymer, polyethylene, polypropylene, a copolyester, nylon-6, and nylon-66. Moreover, a core-sheath type composite fiber or a side-by-side type composite fiber may be used as the short fiber (B). Such a composite fiber may be preferably composed of a polymer having a melting point lower by at least 50°C than the melting point of the short fiber (A) and a polymer having a melting point close to the melting point of the short fiber (A). In connection with the shape of the short fiber (B), a fiber length of 3 to 5 mm and a titre of 2 to 10 deniers are preferred. Where the short fiber (B) is employed for the formation of the non-woven fabric of the present invention, there may be incorporated in the non-woven fabric a third component short fiber selected from wood pulp, cellulosic regenerated fiber such as viscose rayon or cuprammonium rayon, protein regenerated fiber, and polyester fiber having a birefringence of not higher than 0.03.

[0009] The polyester short fiber (C) preferably has a titre of 1 to 10 deniers and a fiber length of 3 to 5 mm. Where the polyester short fiber (C) is employed for the formation of the non-woven fabric, there may be incorporated in the fabric a third component short fiber selected from fibers made of polypropylene, polyethylene, polytetrafluoroethylene, polycarbonate, poly(2,6-diphenyl-para-phenylene oxide), polyamide including aromatic polyamide, polyacrylonitrile, polyvinyl alcohol, aromatic polyamide-imide, aromatic polyimide, polyvinyl chloride, glass, slag, asbestos, metal and potassium titanate, cellulosic regenerated fiber such as viscose rayon or cuprammonium rayon, wood pulp, and protein regenerated fiber.

[0010] The mixing ratio of the short fiber (B) or (C) is determined according to the required strength and the mixing ratio of the short fiber (A). However, if the mixing ratio of the short fiber (B) or (C) is lower than 5% by weight, the strength of the non-woven fabric is insufficient, and if the mixing ratio of the short fiber (B) or (C) exceeds 50% by weight, the touch becomes hard. Accordingly, it is preferred that the mixing ratio of the short fiber (B) or (C) be 5 to 50% by weight based on the entire non-woven fabric.

[0011] The short fiber (A) referred to in the present invention can be obtained by spinning and drawing a polyester under conditions such that a high crystallinity is not produced, to obtain a filament having a crystallinity lower than about 35%, heating and shrinking the filament for a certain time under conditions such that a crystallinity exceeding about 35% is not produced and the filament is allowed to shrink by at least 20% in the direction of the axis, and cutting the resulting polyester filament. This short fiber (A) is characterized in that the shrinkage factor in the direction of the fiber axis at a temperature higher than 90°C is negative, that is, irreversible spontaneous elongation is manifested.

[0012] In connection with the shape of the short fiber (A), a fiber length of 5 to 20 mm and a titre of 0.5 to 3 deniers are preferred. It is also preferred that the mixing ratio of the short fiber (A) be 50 to 95% by weight based on all the constituent fibers.

[0013] A dispersion to be subjected to the paper-forming operation can be obtained by dispersing the short fibers (A) and (B) in water. It is preferred that anionic polyacrylamide (marketed under the tradename of "Maypum" by Meisei Kagaku K.K.) be added as a thickener to the dispersion.

[0014] The paper-forming operation may be carried out by using an ordinary short-wire paper-making machine, a long-wire paper-making machine, or a cylinder paper-making machine. The obtained non-woven fabric is heated, for example, by a Yankee drier, to simultaneously effect drying and heat fusion-bonding of the fibers. Where a non-woven fabric having a much enhanced strength is required, it is preferred that the number of fusion bonds among the fibers be increased by the calender or embossing treatment. In this case, the strength of the non-woven fabric is enhanced by increasing the number of fusion bonds among the fibers but the drape characteristics are degraded.

[0015] To prevent the degradation of the drape characteristics by the embossing treatment, it is preferred that the ratio (area ratio) of the partially heat-pressed portion to the entire surface of the non-woven fabric be reduced as much as possible, the distance between the partially heat-pressed points be broadened, or the embossing pattern be selected in such a manner that the depth of the non-pressing portion (the concave portion of the embossing pattern) is increased.

[0016] This partial heat-pressing can be accomplished by subjecting the non-woven fabric to a heat-pressing treatment under the conditions wherein the non-woven fabric is inserted between an embossing roll having convexities and concavities on the surface and a metal roll having a smooth surface, between metal rolls, each having convexities and concavities on the surface, or between hot plates having convexities and concavities on the surface. Furthermore, the partial heat-pressing can be accomplished by an ultrasonic or high frequency welder or the like. The pattern of the partially heat-pressed portion is not particularly critical. For example, a pattern of parallel short lines or crossing zigzag-arranged short lines, a discontinuous pattern such as a polka-dotted pattern or a continuous pattern such as a hexagonal pattern, or a weave pattern or a lattice pattern may be adopted.

[0017] The area ratio of the partially heat-pressed portion to the entire surface of the non-woven fabric is preferably 5 to 60%. The heat-pressing temperature may be selected in the range between the melting point of the short fiber (A) and the closest point to the melting point of the short fiber (B), but it is ordinarily preferred that the heat-pressing temperature be selected in the range of from 120°C to 230°C.

[0018] The present invention will now be described in detail with reference to the following examples. Note, in the examples, the strength and elongation and the rigidity and softness were determined according to the following methods.

(1) Strength and elongation

[0019] The strength and elongation were determined by using a constant-speed stretching tensile tester according to the method of JIS P-8113.

(2) Rigidity and softness

[0020] The rigidity and softness were determined according to the cantilever method (JIS L-1074-A).

Examples 1 and 2

[0021] A spontaneously stretching polyethylene terephthalate short fiber (Al) having a titre of 1.47 denier, a fiber length of 5 mm, a strength of 3.3 g/d, and an elongation of 129%, _and also_having dry-heat shrinkage factor of 5% at 20 minutes' heat treatment at 180°C, was mixed at a mixing ratio shown in Table 1 with a one- component type polyethylene terephthalate copolyester short fiber (80; terephthalate/isophthalate weight ratio = 60/40 and ethylene glycol/diethylene glycol weight ratio = 95/5) having a melting temperature of 120°C, a titre of 4.0 denier, a fiber length of 5 mm, a strength of 3.0 g/d, and an elongation of 42%, and 3 g of the mixture was thrown into 5 A of water and sufficiently stirred to form a dispersion. Anionic polyacrylamide (marketed under the registered tradename of "Maypum" by Meisei Kagaku K.K.) was added as a thickener to the dispersion in an amount of 200 cc in the form of an aqueous solution having a concentration of 0.1 g/i.

[0022] The dispersion was formed into a sheet by using a square paper-making machine and the sheet was dried at 100°C for 1 minute on a drum type rotary drier to obtain a wet non-woven fabric having a basic weight of 50 g/m². This non-woven fabric had very excellent drape characteristics and a soft touch (Example 1).

[0023] To further enhance the strength, the non-woven fabric was subjected to a heat-pressing treatment between a convex embossing roll having a pattern of crossing zigzag-arranged short lines (short line length = 0.8 mm, short line width = 0.2 mm, trough depth = 0.19 mm, and area ratio of partially heat-pressed portion to entire surface of roll = 40%) and having the surface temperature adjusted to 150°C, and a smooth metal roll.

[0024] The obtained non-woven fabric had particularly excellent drape characteristics and had a practical strength and good touch (Example 2).

[0025] With respect to each of the non-woven fabrics obtained in Examples 1 and 2, the strength and elongation and the rigidity and softness were determined. The obtained results are shown in Table 2.

Examples 3 and 4

[0026] A spontaneously stretching polyethylene terephthalate short fiber (Al) having a titre of 1.47 denier, a fiber length of 5 mm, a strength of 3.3 g/d, and an elongation of 129%, and also having a dry-heat shrinkage factor of -5.0% at 20 minutes' heat treatment at 180°C, was mixed at a mixing ratio shown in Table 3 with a core-sheath type polyethylene terephthalate short fiber (Bl) (marketed under the registered tradename of "Melty" by Unitica) composed of a sheath component of a polyethylene terephtalate copolyester having a melting temperature of 110°C and a core component of polyethylene terephthalate having a melting point of 280°C, which had a titre of 4.0 denier, a fiber length of 5 mm, a strength of 3.2 g/d, and an elongation of 45%. Then, 3 g of the mixture was thrown into 5 t of water and sufficiently stirred to form a dispersion. Anionic polyacrylamide (marketed under the registered tradename of "Maypum" by Meisei Kagaku K.K.) was added as a thickener to the dispersion in an amount of 220 cc in the form of an aqueous solution having a concentration of 0.1 g/1.

[0027] The dispersion was formed into a sheet by using a square paper-making machine and the sheet was dried at 100°C for 1 minute on a drum type rotary drier to obtain a wet non-woven fabric having a basic weight of 50 g/m². This non-woven fabric had very excellent drape characteristics and a soft touch (Example 3).

[0028] To further enhance the strength, the non-woven fabric was heat-pressed between a convex type embossing roll having a pattern of crossing zigzag-arranged short lines (short line length = 0.8 mm, short line width = 0.2 mm, trough depth = 0.19 mm, and area ratio of partially heat-pressed portion to entire roll surface = 40%) and having the surface temperature adjusted to l50°C, and a smooth metal roll.

[0029] The obtained non-woven fabric had particularly excellent drape characteristics and had a practical strength and a good touch (Example 4).

[0030] With respect to each of the non-woven fabrics obtained in Examples 3 and 4, the strength and elongation and the rigidity and softness were determined. The obtained results are shown in Table 4.

Comparative Examples 1 and 2

[0031] Non-woven fabrics of Comparative Examples 1 and 2 were prepared in the same manner as described in Examples 1 and 2 except that a polyethylene terephthalate fiber (A2) having a titre of 1.5 denier, a fiber length of 5 mm, a strength of 5.0 g/d, and an elongation of 48%, and also having a dry-heat shrinkage factor of +5.5% at 20 minutes' heat treatment at 180°C, was mixed at a mixing ratio shown in Table 5 with the same sheath-core polyethylene terephthalate short fiber (Bl) as used in Examples 3 and 4. Each of the obtained fabrics had a paper-like touch, and the drape characteristics of the non-woven fabrics of Comparative Examples 1 and 2 were much inferior to those of the non-woven fabrics of Examples 1 and 3 and Examples 2 and 4. With respect to each of the non-woven fabrics obtained in Comparative Examples 1 and 2, the strength and elongation and the rigidity and softness were determined. The obtained results are shown in Table 6.

[0032] 

Comparative Examples 3 and 4

[0033] Non-woven fabrics of Comparative Examples 3 and 4 were obtained in the same manner as described in Examples 1 and 2 except that a low oriented polyethylene terephthalate short fiber (A3) having a birefringence of 0.15, a titre of 1.5 denier, a fiber length of 5 mm, a strength of 1.15 g/d, and an elongation of 312%, and also having a dry-heat shrinkage factor of +80.5% at 20 minutes' heat treatment at 180°C, was mixed at a mixing ratio shown in Table 7 with the same sheath-core polyethylene terephthalate short fiber (Bl) as used in Examples 3 and 4. Each of the non-woven fabrics obtained in Comparative Examples 3 and 4 had a paper-like touch and had much inferior drape characteristics to the non-woven fabrics obtained in Examples 1 and 3 and Examples 2 and 4. With respect to each of the non-woven fabrics obtained in Comparative Examples 3 and 4, the strength and elongation and the rigidity and softness were determined. The obtained results are shown in Table 8.

Examples 5 and 6

[0034] A spontaneously stretching polyethylene terephthalate short fiber (Al) having a titre of 1.47 denier, a fiber length of 5 mm, a strength of 3.3 g/d, an elongation of 129%, and a dry-heat shrinkage factor of -5.0% at 20 minutes' heat treatment at 180°C, was mixed at a mixing ratio shown in Tale 1 with a low oriented polyethylene terephthalate short fiber (Bl) having a birefringence of 0.01, a titre of 1.1 denier, and a fiber length of 5 mm, and 3 g of the mixture was thrown into 5 1 of water and sufficiently stirred to obtain a dispersion. Then, anionic polyacrylamide (marketed under the registered tradename of Maypum" by Meisei Kagaku K.K.) was added as a thickener to the dispersion in an amount of 200 cc in the form of an aqueous solution having a concentration of 0.1 g/t.

[0035] The dispersion was formed into a sheet by a square paper-making machine and dried at 100°C for 1 minute on a drum type rotary drier to obtain a non-woven fabric having a basic weight of 50 g/m². This non-woven fabric had very excellent drape characteristics and had a soft touch (Example 5).

[0036] To further enhance the strength, the non-woven fabric was heat-pressed between a convex embossing roll having a pattern of crossing zigzag-arranged short lines (short line length = 0.80 mm), short line width = 0.20 mm, trough depth = 0.19 mm, and area ratio of partially pressed portion to entire roll surface = 40%) and having the surface temperature maintained at 220°C and a smooth metal roll.

[0037] The obtained non-woven fabric had very excellent drape characteristics and had a practical strength and a good touch (Example 6).

[0038] With respect to each of the non-woven fabrics obtained in Examples 5 and 6, the strength and elongation and the rigidity and softness were determined. The obtained results are shown in Table 2.

Comparative Examples 5 and 6

[0039] Non-woven fabrics of Comparative Examples 5 and 6 were obtained in the same manner as described in Example 5 except that a polyethylene terephthalate short fiber (A2) having a titre of 1.5 denier, a fiber length of 5 mm, a strength of 5.0 g/d, an elongation of 48%, and a dry-heat shrinkage factor of +5.5% at 20 minutes' heat treatment at 180°C, was mixed at a mixing ratio shown in Table 3 with a low oriented polyethylene terephthalate short fiber (B2) having a birefringence of 0.015, a titre of l.l denier, and a fiber length of 5 mm. The non-woven fabrics obtained in Comparative Examples 1 and 2 had a paper-like touch and had much inferior drape characteristics to the non-woven fabrics obtained in Examples 5 and 6.

[0040] With respect to each of the non-woven fabrics obtained in Comparative Examples 5 and 6, the strength and elongation and the rigidity and softness were determined. The obtained results are shown in Table 4.

Claims

1. A wet non-woven fabric having excellent drape characteristics, which is formed from a mixture of (A) a polyester short fiber in which a shrinkage factor in the direction of the fiber axis at a temperature not lower than 90°C is negative and (B) a short fiber showing a fusion-bondability at a temperature lower by at least 50°C than a temperature at which the short fiber (A) has a fusion bondability, or (C) a polyester short fiber having a birefringence of 0.006 to 0.03, according to a wet paper-forming method.

2. A non-woven fabric as set forth in claim 1, wherein the short fiber (B) is a composite fiber composed of a polymer having a melting point lower by at least 50°C than the melting point of the short fiber (A) and a polymer having a melting point close to the melting point of the short fiber (A).

3. A non-woven fabric as set forth in claim 1, wherein the short fiber (B) has a fiber length of 3 to 5 mm and a titre of 2 to 10 deniers.

4. A non-woven fabric as set forth in claim 1, wherein the short fiber (C) has a fiber length of 3 to 5 mm and a titre of 1 to 10 deniers.

5. A non-woven fabric as set forth in claiml, wherein the mixing ratio of the short fiber (B) or (C) is 5 to 50% by weight based on the weight of the non-woven fabric.

6. A non-woven fabric as set forth in claim 1, wherein the short fiber (A) has a fiber length of 5 to 20 mm and a titre of 0.5 to 3 deniers.

7. A non-woven fabric as set forth in claim 1, wherein the mixing ratio of the short fiber (A) is 50 to 95% by weight based on the weight of the non-woven fabric.

8. A non-woven fabric as set forth in claim 1, wherein the surface has convexities and concavities formed by partial heat-pressing.

9. A non-woven fabric as set forth in claim 8, wherein the area ratio of the partially heat-pressed portion to the entire surface of the non-woven fabric is 5 to 60%.