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  Staple fiber non-woven fabric and process for producing the sameUSPTO Application #: 20060030230Title: Staple fiber non-woven fabric and process for producing the same Abstract: A staple fiber non-woven fabric is provided which comprises, as constituent fibers, first and second split staple fibers composed of first and second fiber formable polymers, respectively, and water-absorptive staple fibers. The first and second split staple fibers have a fineness of not greater than 0.5 denier per fiber. The first and second fiber formable polymers are different polymers selected from the group consisting of a polyamide, a polyester and a polyethylene which are incompatible with each other. The fiber split degree of the first and second split staple fibers is not lower than 85%. The constituent fibers are three-dimensionally entangled with each other. (end of abstract) Agent: Harness, Dickey & Pierce, P.L.C - Bloomfield Hills, MI, US Inventors: Kouichi Nagaoka, Atsushi Matsunaga, Noriko Yoshida USPTO Applicaton #: 20060030230 - Class: 442327000 (USPTO) Related Patent Categories: Fabric (woven, Knitted, Or Nonwoven Textile Or Cloth, Etc.), Nonwoven Fabric (i.e., Nonwoven Strand Or Fiber Material) The Patent Description & Claims data below is from USPTO Patent Application 20060030230. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention relates to a staple fiber non-woven fabric and a process for producing the same. BACKGROUND OF THE INVENTION [0002] Spunlaced non-woven fabrics produced by three-dimensionally entangling constituent fibers by the action of high pressure liquid streams are used for a variety of applications because of their excellent softness. Used as materials for such non-woven fabrics are natural fibers and synthetic fibers, depending on the applications thereof. [0003] For example, JP-A-62-268861 (1987) discloses a non-woven fabric produced by such a method that conjugate filaments are partially fibrillated when crimps are imparted to the filaments in a drawing process and liquid streams are applied to constituent fibers for promotion of the fibrillation and for entanglement of the constituent fibers. The resulting non-woven fabric is highly soft because it is composed of micro-denier fibers. However, the non-woven fabric is not suitable for use in a wet or moistened state, since the constituent fibers are made of a polymer having a poor water absorbing property. [0004] To overcome this drawback, JP-A-6-101148 (1994) discloses a spunlaced non-woven fabric for a wiper which comprises micro-denier split staple fibers of not greater than 0.5 denier and cotton or rayon fibers as a hydrophilic fibrous constituent. The non-woven fabric is highly soft with draping property and, therefore, suitable for cleaning precision instruments and the like without any damages thereto. In addition, the non-woven fabric has wiping and water absorbing properties. [0005] One fibrous component of the split staple fibers in the non-woven fabric disclosed in JP-A-6-101148 is composed of polypropylene. Since a polypropylene-containing filament cannot satisfactorily be quenched at melt-spinning thereof, the filament is likely to be sticky before drawing thereof. As a result, the drawability of the filament is impaired, making it difficult to obtain the intended split staple fibers. Further, the water absorbing property of the fibers is not satisfactory. In addition, a difference incompatibility index between the polypropylene fibrous component and another fibrous component of polyester is relatively great, so that the filament is liable to be fibrillated before a splitting process. This presents a problem in card passage, resulting in an unsatisfactory operability. SUMMARY OF THE INVENTION [0006] It is an object of the present invention to solve the aforesaid problems and to provide a non-woven fabric which is superior in water absorbing property, mechanical properties, softness, air permeation resistant property and operability, and can be used for wiping, filtering and the like in a wide variety of application fields. [0007] In accordance with one aspect of the present invention for achievement of the aforesaid object, there is provided a staple fiber non-woven fabric which comprises, as constituent fibers, first and second split staple fibers composed of first and second fiber formable polymers, respectively, and obtained by splitting splittable bicomponent conjugate staple fibers composed of the first and second fiber formable polymers, and water-absorptive staple fibers, wherein the first and second split staple fibers have a fineness of not greater than 0.5 denier per fiber, wherein the first and second fiber formable polymers are different polymers selected from the group consisting of a polyamide, a polyester and a polyethylene which are incompatible with each other, wherein a fiber split degree of the first and second split staple fibers is not lower than 85%, wherein the constituent fibers are three-dimensionally entangled with each other. [0008] In accordance with another aspect of the present invention, there is provided a process for producing a staple fiber non-woven fabric, which comprises the steps of: spinning splittable bicomponent conjugate staple fibers composed of first and second fiber formable polymers which are different polymers selected from the group consisting of a polyamide, a polyester and a polyethylene which are incompatible with each other; forming a non-woven web by blending the splittable bicomponent conjugate staple fibers with water-absorptive staple fibers; and subjecting the non-woven web to a high pressure liquid stream treatment, whereby the conjugate staple fibers are split at a fiber split degree of not lower than 85% into first split staple fibers composed of the first fiber formable polymer and having a fineness of not greater than 0.5 denier per fiber and second split staple fibers composed of the second fiber formable polymer and having a fineness of not greater than 0.5 denier per fiber, and the first and second split staple fibers and the water-absorptive staple fibers are three-dimensionally entangled with each other. [0009] In accordance with the present invention, the first and second split staple fibers are composed of different polymers selected from the group consisting of a polyamide, a polyester or a polyethylene, so that the quenching at the melt spinning is satisfactory and the split staple fibers are superior in heat stability. Since the non-woven fabric contains the water-absorptive staple fibers and the first and second split staple fibers having a fineness of not greater than 0.5 denier per fiber with a fiber split degree of not lower than 85%, the non-woven fabric is superior in softness and water absorbing property. In addition, the constituent fibers of the non-woven fabric are three-dimensionally and densely entangled with each other, because the first and second split staple fibers have a fineness of not greater than 0.5 denier per fiber with a fiber split degree of not lower than 85%. Therefore, the non-woven fabric is soft and superior in mechanical properties. Accordingly, the non-woven fabric provided by the present invention can be used for wipers, filters, hygienic products such as sanitary napkins and disposable diapers, and the like in a wide variety of application fields. Particularly where the non-woven fabric is used for the hygienic products, superior liquid absorbing properties can be ensured by synergy of the water absorbing effects offered by the hydrophilic nature of the water-absorptive staple fibers and by the three-dimensional entanglement of the split staple fibers of not greater than 0.5 denier. In addition, the split staple fibers are effective to rapidly diffuse liquid hydrophilically absorbed by the water-absorptive staple fibers within the non-woven fabric. Therefore, the non-woven fabric is capable of absorbing a greater amount of liquid when used for the hygienic products. BRIEF DESCRIPTION OF THE DRAWING [0010] FIG. 1 is a diagram illustrating one exemplary cross-sectional configuration of each splittable bicomponent conjugate fiber constituting a non-woven fabric of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS [0011] Splittable bicomponent conjugate staple fibers constituting a non-woven fabric of the present invention are composed of first and second fiber formable polymers which are incompatible with each other. The incompatibility of the first and second fiber formable polymers allows the conjugate staple fibers to easily split when a high pressure liquid stream treatment is performed to apply impacts to the conjugate staple fibers. [0012] The splittable bicomponent conjugate staple fibers each have a cross-sectional configuration as shown in FIG. 1, for example, and include plural segments 10 of the first fiber formable polymer and plural segments 20 of the second fiber formable polymer which are circumferentially arranged in an alternating relation. The splittable bicomponent conjugate staple fibers having such a configuration are split at interfaces of the polymeric segments 10 and 20 into split staple fibers comprised of the polymeric segments 10 and 20 and having a fineness of not greater than 0.5 denier per fiber, when impacts are applied to the conjugate staple fibers during a fiber splitting process after spinning. [0013] For formation of the staple fibers of not greater than 0.5 denier per fiber, it is preferred that the number of the circumferentially arranged splittable segments be 4 to 24 on the precondition that the conjugate staple fibers having the cross-sectional configuration shown in FIG. 1 have a fineness of 2 to 12 denier per fiber. If the number of the circumferentially arranged segments is increased, smaller-denier split staple fibers can be formed. However, an upper limit of the number of the splittable segments is about 36 because of limitations on spinneret design and the like. [0014] If the single fiber fineness of the conjugate staple fibers is smaller than 2 denier, the productivity tends to be reduced. The productivity may be improved by using a greater number of spinnerets, but an unstable spinning process may result. On the other hand, if the single fiber fineness is greater than 12 denier, a melt-spun filament cannot sufficiently be quenched. This makes it difficult to take up the filament at the spinning. The quenching of the filament may be promoted by using a smaller number of spinnerets, but the productivity is reduced. [0015] If the single fiber fineness of the split staple fibers is greater than 0.5 denier, it is difficult to three-dimensionally and densely entangle the constituent fibers for non-woven fabric formation, thereby failing to obtain the non-woven fabric intended by the present invention. Therefore, it is particularly preferred that the single fiber fineness is not greater than 0.3 denier. [0016] The first and second fiber formable polymers constituting the splittable bicomponent conjugate staple fibers are different polymers selected from the group consisting of a polyamide, a polyester and a polyethylene which are incompatible with each other. Three combinations of the first and second fiber formable polymers are possible, i.e., a polyamide and a polyester, a polyamide and a polyethylene, and a polyester and a polyethylene. [0017] Examples of specific polyamides include polyimino-1-oxotetramethyle- ne (nylon 4), polytetramethylene adipamide (nylon 46), polycapramide (nylon 6), polyhexamethylene adipamide (nylon 66), polyundecanamide (nylon 11), polylaurolactamide (nylon 12), poly-m-xylene adipamide, poly-p-xylylene decanamide and polybiscyclohexylmethane decanamide, and polyamide copolymers containing a monomer of any of these polymers as a monomeric unit. Particularly, a copolymer of polytetramethylene adipamide (nylon 46) may be employed which is obtained by copolymerizing polytetramethylene adipamide (nylon 46) with not greater than 30 mol% of another polyamide component such as polycapramide, polyhexamethylene adipamide or polyundecamethylene terephthalamide. [0018] Examples of specific polyesters include homopolymers and copolymers of esters comprised of acid components of aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid and naphthalene-2,6-dicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid and sebacic acid, and esters of these acids, and alcohol components of diols such as ethylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol and cyclohexane-1,4-dimethanol. Further, p-hydroxybenzoic acid, 5-sodiumsulfoisophthalic acid, polyalkylene glycol, pentaerythritol, bisphenol A or the like may be added to or copolymerized with any of these polyesters. [0019] Examples of specific polyethylenes include linear low-density polyethylenes, medium-density polyethylenes and high-density polyethylenes. These polyethylenes preferably have melt index values of 10 to 80 g/10 minutes as measured in conformity with the method of ASTM-D-1238E. If the melt index value is lower than 10 g/10 minutes, the melt viscosity is too high, resulting in an inferior spinnability. If the melt index value exceeds 80 g/10 minutes, the melt viscosity is too low, resulting in slipperiness of the resulting fibers. In addition, the quenching of a spun filament is unsatisfactory, resulting in stickiness of the filament. These polyethylenes may be copolymerized with not greater than 10 wt % of any of various similar unsaturated ethylene-type monomers such as butadiene, isoprene, 1,3-pentadiene, styrene and .alpha.-methylstyrene, or copolymerized with not greater than 10 wt % of propylene, 1-butene, 1-octene, 1-hexene or a similar higher .alpha.-olefin, based on the amount of ethylene. Continue reading... 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