Conjugate fiber for air-laid nonwoven fabric manufacture and method for manufacturing a high-density air-laid nonwoven fabric

Abstract

Provided is a conjugate fiber for air-laid nonwoven fabric manufacture having a planar zig-zag crimp shape before a thermal treatment, such that a uniform web is obtained by air laying with high processability and productivity, and the conjugate fiber develops a spiral crimp when the web is subjected to a thermal treatment to thereby enable the web to shrink significantly, as a result of which a nonwoven fabric can be obtained in which fibers are amassed to a high density. The conjugate fiber for air-laid nonwoven fabric manufacture is a heat-fusible conjugate fiber in which a first component comprising an olefinic thermoplastic resin is conjugated with a second component comprising an olefinic thermoplastic resin having a melting point higher than that of the first component. The conjugate form is such that the centers of gravity of the conjugate components are mutually different in the fiber cross section, the fiber has a single-yarn fineness of 1 to 10 dtex, a fiber length of 3 to 20 mm, and a planar zig-zag crimp whose crimp shape index (actual length of short fiber/distance between both ends of short fiber) ranges from 1.05 to 1.60, and the web shrinkage upon thermal treatment at 145° C. of a web obtained by an air-laid method is not lower than 40%.

1 . A conjugate fiber for air-laid nonwoven fabric manufacture, being a heat-fusible conjugate fiber in which a first component comprising an olefinic thermoplastic resin is conjugated with a second component comprising an olefinic thermoplastic resin having a melting point higher than that of the first component, wherein the conjugate form is such that the centers of gravity of the conjugate components are mutually different in the fiber cross section, the fiber has a single-yarn fineness of 1 to 10 dtex, a fiber length of 3 to 20 mm, and a planar zig-zag crimp whose crimp shape index (actual length of short fiber/distance between both ends of short fiber) ranges from 1.05 to 1.60, and the web shrinkage upon thermal treatment at 145° C. of a web obtained by an air-laid method is not lower than 40%. 
     
     
         2 . The conjugate fiber for air-laid nonwoven fabric manufacture according to  claim 1 , wherein the conjugate form in the fiber cross section is a side-by-side shape in which a half-moon-shaped first component and a half-moon-shaped second component are bonded together. 
     
     
         3 . The conjugate fiber for air-laid nonwoven fabric manufacture according to  claim 1 , wherein the first component is a polypropylene copolymer and the second component is homopolypropylene. 
     
     
         4 . The conjugate fiber for air-laid nonwoven fabric manufacture according to  claim 3 , wherein the molecular weight distribution (weight-average molecular weight/number-average molecular weight) of the homopolypropylene of the second component is not smaller than 3.5. 
     
     
         5 . The conjugate fiber for air-laid nonwoven fabric manufacture according to  claim 1 , wherein short fiber bulkiness is no greater than 250 cm3/2 g. 
     
     
         6 . The conjugate fiber for air-laid nonwoven fabric manufacture according to  claim 1 , wherein a discharge efficiency during forming in an air-laying machine is not lower than 80%, and the number of defects in the web obtained by forming is no greater than 3/m2. 
     
     
         7 . A method for manufacturing a nonwoven fabric, comprising: thermally treating a web obtained through an air laying process of a heat-fusible conjugate fiber in which a first component comprising an olefinic thermoplastic resin is conjugated with a second component comprising an olefinic thermoplastic resin having a melting point higher than that of the first component, the conjugate form being such that the centers of gravity of the conjugate components are mutually different in the fiber cross section, the fiber having a single-yarn fineness of 1 to 10 dtex, a fiber length of 3 to 20 mm, a planar zig-zag crimp whose crimp shape index (actual length of short fiber/distance between both ends of short fiber) ranges from 1.05 to 1.60, and a crimp count ranging from 6 to 14 crimps/2.54 cm.