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  Dry-process nonwoven pulp fabric composed of united layer structuresUSPTO Application #: 20060194498Title: Dry-process nonwoven pulp fabric composed of united layer structures Abstract: Disclosed is a dry-process nonwoven pulp fabric composed of united layer structures, which contains heat-bondable synthetic fibers and comprises surface layer portions on both sides in which the synthetic fibers are heat bonded to one another and which has a basis weight of more than 5 g/m2 to 12 g/m2, and an internal layer portion in which heat-bondable synthetic fibers and pulp fibers are mixed at a ratio of 20/80 to 60/40% by weight and the synthetic fibers and/or the synthetic fibers and pulp fibers are heat bonded to one another and which has a basis weight of 8 to 240 g/m2, wherein the front and back surface layers and the internal layer portion are united as a whole by heat bonding of the synthetic fibers to one another, the ratio of a strength in a lengthwise direction to that in a crosswise direction is from 0.8 to 1.2 in both dry and wet states, the ratio of a strength in a dry state to that in a wet state is from 0.6 to 1.1, the water absorption is from 8 to 20 g/g, and the total basis weight is from 20 to 250 g/m2. The resulting dry-process nonwoven pulp fabric is free from the shedding of fibers, sufficient in water absorption properties and high in wet strength, and therefore suitable for wipers, kitchen sheets and the like used in a wet state. (end of abstract) Agent: Sughrue Mion, PLLC - Washington, DC, US Inventors: Yasuji Yasumitsu, Yasuyuki Yamazaki, Shoji Nishigawa USPTO Applicaton #: 20060194498 - Class: 442409000 (USPTO) Related Patent Categories: Fabric (woven, Knitted, Or Nonwoven Textile Or Cloth, Etc.), Nonwoven Fabric (i.e., Nonwoven Strand Or Fiber Material), Autogenously Bonded Nonwoven Fabric The Patent Description & Claims data below is from USPTO Patent Application 20060194498. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention relates to a dry-process nonwoven pulp fabric which is strong even when it is wetted. More particularly, the present invention relates to a nonwoven fabric used in a wet state, which is suitable for wipers for material use such as floor use, kitchen use or automobile use, for kitchen sheets for cleaning of cooking utensils, wiping of foodstuffs, drip absorption and the like, or for wipers for human use such as face use, hand use or body use. Further, in the present invention, even when the nonwoven fabric is used in a dry state, water exists in these uses in many cases, so that similar effects can be expected. Furthermore, the present invention relates to a nonwoven fabric similarly suitable for hygienic materials such as sanitary goods and diapers, or for medical use. BACKGROUND ART [0002] In a dry-process nonwoven pulp fabric which has hitherto been known, a pulp fiber layer is used as a base, and a chemical binder resin such as a polyacrylic ester-based or polyvinyl acetate-based resin is sprayed or applied on a surface layer thereof or impregnated throughout the whole thereof to form interfiber bonds. [0003] In such a nonwoven fabric, when the binder amount is increased, the resin forms a film to become hard, which causes a reduction in water absorption ability. On the other hand, when it is decreased, not only shedding of pulp fibers increases, but also a decrease in strength, particularly in wet strength, is unavoidable. [0004] Further, a method of imparting a powdery binder resin is conceivable. In this case, however, the number of adhesion points between the pulp fibers and the binder decreases to cause a tendency to increase shedding fibers, although the film is difficult to be formed. It is therefore difficult to produce a dry-process nonwoven pulp fabric excellent in wet strength while securing moderate water absorption properties, decreased shedding of fibers, strength available for practical use and the like. [0005] As a dry-process nonwoven pulp fabric used for absorption insert material use of sanitary goods or for domestic or industrial washing use, there has been proposed a dry-process nonwoven pulp fabric in which the basis weight (METSUKE) of a surface layer composed of only a binder fiber is from 1 to 5 g/m.sup.2, and the amount of the binder fiber contained in an internal layer portion is from 2 to 10% by weight (Published Japanese Translation of PCT Patent Application 2000-504792). [0006] The strength of this nonwoven fabric is sufficient with respect to ordinary strength for hygienic good use such as absorption insert material use of sanitary goods. However, it is not mentioned at all whether the nonwoven fabric is "strong even when wetted" or not, which is an important point of the present invention. The nonwoven fabric having a technical content within the scope of this published patent is as small as 2 to 10% by weight in the amount of the binder fiber contained in the internal layer portion, so that it can not be said to be strong even when wetted. This brings about a significant decrease in strength in a wet state to be unsuitable for wiping, and therefore is completely different from the intension of the present invention. [0007] Further, there has also been proposed an air-laid nonwoven fabric having a specified tearing strength, which is formed by heat bonding intersecting points of binder fibers (JP-A-2000-345454). However, wet strength in compounding with pulp and water absorption properties are not mentioned at all, and there is utterly no description which suggests the technique as a layer structure of the present invention. [0008] Conventional nonwoven fabrics have the problems as described above. DISCLOSURE OF THE INVENTION [0009] The present inventors have made intensive studies in view of the present state as described above. As a result, the present inventors have discovered that a dry-process nonwoven fabric which is free from the shedding of fibers, sufficient in water absorption properties and strong, particularly sufficient in wet strength, can be obtained by making proper the basis weight (METSUKE) of heat-bondable synthetic fiber-containing front and back surface layers and increasing the amount of the heat-bondable synthetic fibers contained in an internal layer, thus completing the present invention. Best Mode for Carrying Out the Invention The present invention relates to a dry-process nonwoven pulp fabric (hereinafter also briefly referred to as a "dry-process nonwoven fabric") composing united layer structures, which contains heat-bondable synthetic fibers and comprises surface layer portions on both sides in which the synthetic fibers are heat bonded to one another and which has a basis weight of more than 5 g/m.sup.2 to 12 g/m.sup.2, and an internal layer portion in which heat-bondable synthetic fibers and pulp fibers are mixed at a ratio of 20/80 to 60/40% by weight and the synthetic fibers and/or the synthetic fibers and pulp fibers are heat bonded to one another and which has a basis weight of 8 to 240 g/m.sup.2, wherein the front and back surface layers and the internal layer portion are united as a whole by heat bonding of the synthetic fibers to one another, the ratio of a strength in a lengthwise direction to that in a crosswise direction is from 0.8 to 1.2 in both dry and wet states, the ratio of a strength in a dry state to that in a wet state is from 0.6 to 1.1, the water absorption is from 8 to 20 g/g, and the total basis weight is from 20 to 250 g/m.sup.2. [0010] Embodiments of the present invention are illustrated below. [0011] The nonwoven fabric of the present invention composed of a three-layer structure comprising an internal layer containing heat-bondable synthetic fibers and pulp fibers and surface layers containing heat-bondable synthetic fibers, between which the internal layer is sandwiched, and is united by heat bonding. [0012] In the present invention, the heat-bondable synthetic fibers which are a main component forming the surface layers or mixed with pulp may be any, as long as they are melted by heat and bonded to one another, and the pulp is fixed by a network structure caused by these interfiber bonds. Accordingly, the fibers using a polymer having high affinity with the pulp fibers are particularly preferred. Examples thereof include a polyolefin, a polyolefin grafted with an unsaturated carboxylic acid, a polyester, polyvinyl alcohol and the like. [0013] Of these, as the polyolefinic heat-bondable synthetic fibers, there are suitable sheath-core type or eccentric side-by-side type conjugate fibers. The polyolefins constituting the sheath or a peripheral portion of the fiber include polyethylene and polypropylene. The polymers constituting the core or an internal portion of the fiber are preferably polymers having a melting point higher than that of the sheath and unchangeable at a heat bonding treatment temperature. Such combinations include, for example, polyethylene/polypropylene, polyethylene/polyester, polypropylene/polyester and the like. These polymers may be modified within the range that the operation and effect of the present invention are not impaired. Further, they may be fibrillated fibers. Examples thereof include SWP supplied from Mitsui Chemicals, Inc. [0014] When the heat-bondable synthetic fibers are fine in size, the number of constituent fibers increases. Accordingly, shedding fibers decrease, and the hand feeling also becomes soft. When they are heavy in size, spaces among fibers become large to form a bulky nonwoven fabric, and the scraping effect is also expected. Accordingly, the size of the fibers may be selected depending on their use. However, the fineness thereof is preferably from 0.5 dt to 50 dt, and more preferably from 0.8 dt to 30 dt. Exceeding 50 dt unfavorably results in uncontrollable shedding of the pulp. On the other hand, less than 0.5 dt is unpractical because of poor nonwoven fabric productivity. [0015] Further, the length of the heat-bondable synthetic fibers is preferably from 1 to 15 mm. The shorter fibers result in better mixing properties with pulp, which causes a tendency to form the more uniform nonwoven fabric. However, less than 1 mm results in an approach to a powdery state, so that it is difficult to form the network structure caused by the interfiber bonds. Accordingly, not only shedding of the pulp becomes uncontrollable, but also the strength as the nonwoven fabric decreases. This is therefore unfavorable because of lack of practicability. On the other hand, longer than 15 mm results in an increase in the strength of the nonwoven fabric, but fibers become liable to be entangled with one another during pneumatic transportation of the fibers in the production of the nonwoven fabric, which unfavorably increases fiber agglomerate defects. Particularly preferred is from 3 to 10 mm. [0016] The surface layer may contain other fibers such as regenerated fibers such as rayon, semi-synthetic fibers such as acetate, synthetic fibers such as polyester, polypropylene, polyamide and Vinylon, and natural fibers such as pulp, cotton and hemp, as well as the above-mentioned heat-bondable synthetic fibers. In this case, the ratio of the heat-bondable synthetic fibers in the surface layer is preferably from 70 to 100% by weight, and more preferably from 85 to 100% by weight. In the case of less than 70% by weight, the possibility that shedding of the above-mentioned other fibers occurs increases, and not only the effect of inhibiting shedding of the pulp in the internal layer portion is reduced, but also the wet strength decreases, which causes a practical problem. [0017] These fibers forming the surface layer are heat bonded, and the pulp is fixed by the network structure caused by these interfiber bonds. The basis weight must be more than 5 g/m.sup.2 to 12 g/m.sup.2. Less than 5 g/m.sup.2 results in the decreased amount of synthetic fibers having water resistance and the decreased number of interfiber bonds. Accordingly, not only sufficient wet strength sustainable for wiping can not be secured, but also an increase in shedding fibers is liable to be brought about. Different from an application in which importance is attached to absorptivity, such as hygienic materials, such a nonwoven fabric is unpractical to use for wipers, kitchen sheets and the like, because of its easy fiber shedding when used for wiping. On the other hand, exceeding 12 g/m.sup.2 results in too thick a heat-bonded layer having water resistance, leading to insufficient water absorption to the internal layer and hard hand feeling. This is also unpractical. An increase in basis weight results in an increase in strength, but in a reduction in water absorption properties. However, the nonwoven fabric having sufficient water absorption properties, sufficient strength even in a wet state, no shedding of fibers and soft hand feeling can be obtained within the range of the present invention. [0018] Further, the synthetic fibers are contained in large amounts, so that oil is well absorbed and compatibility with oil is good. Accordingly, there is also the advantage that stains are easily removed. [0019] In the internal layer portion, the heat-bondable synthetic fibers and the pulp fibers are united by heat bonding. The heat-bondable synthetic fibers may be the same as or different from those used in the surface layer. As the pulp fibers, pulverized pulp having a length of 0.2 mm to 5 mm is preferred. [0020] As for the mixing ratio of the heat-bondable synthetic fibers and the pulp fibers in the internal layer portion, when the ratio of the heat-bondable synthetic fibers is less than 20% by weight based on the total of the heat-bondable synthetic fibers and the pulp fibers, shedding fibers increase and strength, particularly strength in a wet state, decreases. Such a nonwoven fabric can be used in an application in which importance is attached to water absorption properties and softness, such as a hygienic material, even when low in strength. However, it is unsustainable for use as a nonwoven fabric for wiping which is an object of the present invention. On the other hand, exceeding 60% by weight results in a decrease in the amount of the pulp fibers contributing to absorptivity, which causes not only lack of water wiping properties and absorptivity, but also hard hand feeling. This is therefore unpractical. [0021] An increase in the ratio of the heat-bondable synthetic fibers results in an increase in strength, but in a reduction in water absorption properties. Continue reading... Full patent description for Dry-process nonwoven pulp fabric composed of united layer structures Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Dry-process nonwoven pulp fabric composed of united layer structures patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. 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