Process for producing nonwoven fabric

Abstract

A nonwoven fabric having an enhanced bulkiness and uniformity is produced by forming a nonwoven fabric, by an air-laid method, from machine-crimped synthetic fibers having a thickness of 0.5 to 200 dtex and a length of 3 to 30 mm, each fiber being constituted from two portions disproportional in thermal shrinkability from each other and located on both respective sides with respect to an imaginary interface extending along the longitudinal axis of each fiber, to thereby exhibit a latent crimpability upon being heated to manifest three-dimensional crimps and each fiber having mechanical crimps at the number of crimps of 1 to 13 crimps/25 mm and a crimp ratio of 2 to 20%; and heat-treating the resultant air-laid nonwoven fabric to manifest the three dimensional crimps on each fiber in the fabric.

1 - 30 . (canceled)  
   
   
       31 . A process for producing a nonwoven fabric comprising 
 forming a nonwoven fabric, by an air-laid method, from machine-crimped synthetic fibers comprising, as a major component, at least one type of thermoplastic synthetic resin, and having an individual fiber thickness of from 0.5 to 200 dtex and an individual fiber length of from 3 to 20 mm, wherein (1) the individual fibers are each constituted from two portions disproportional in thermal shrinkability from each other and located on both respective sides with respect to an imaginary interface extending along the longitudinal axis of each individual fiber, whereby the individual fibers exhibit a latent crimpability to manifest three-dimensional crimps upon being heat treated, and (2) the individual fibers have crimps formed by a mechanical crimping treatment and having the number of crimps of from 1 to 13 crimps/25 mm and a crimp ratio of from 2 to 20%; and    heat-treating the resultant air-laid nonwoven fabric to thereby manifest the three-dimensional crimps on the individual fibers in the nonwoven fabric.    
   
   
       32 . The process for producing a nonwoven fabric as claimed in  claim 31 , wherein the machine-crimped fibers has a peak of thermal shrinkage stress at a temperature in the range of from 60 to 180° C.  
   
   
       33 . The process for producing a nonwoven fabric as claimed in  claim 31 , wherein the machine-crimped fibers each have at least one hollow portion continuously extending along the longitudinal direction thereof.  
   
   
       34 . The process for producing a nonwoven fabric as claimed in  claim 31 , wherein the machine-crimped fibers each comprising, as a major component, a single type of thermoplastic synthetic resin and having two side portions located on both respective sides of the imaginary interface and disproportional in orientation degree and/or crystallinity degree of the resin.  
   
   
       35 . The process for producing a nonwoven fabric as claimed in  claim 31 , wherein the thermoplastic synthetic resin contains, as a major component, a single type of polyester that contains alkylene terephthalate units as major repeating units.  
   
   
       36 . The process for producing a nonwoven fabric as claimed in  claim 31 , wherein the machine-crimped fibers each comprises two fibrous segments comprising, as major components, thermoplastic synthetic resins different in thermal shrinkability from each other, the two fibrous segments extending along the longitudinal axis of the fiber and being bonded together to form a conjugate structure which is asymmetrical with respect to the imaginary interface.  
   
   
       37 . The process for producing a nonwoven fabric as claimed in  claim 31 , wherein the machine-crimped fibers each comprises two fibrous segments comprising, as major components, thermoplastic synthetic resins different in thermal shrinkability from each other, the two fibrous segments extending along the longitudinal axis of the fiber and being bonded together at a bonding interface corresponding to the imaginary interface to form a conjugate fiber having a side-by-side conjugate structure.  
   
   
       38 . The process for producing a nonwoven fabric as claimed in  claim 36 , wherein the two types of synthetic resins are each selected from polyester resins having alkylene phthalate units as major repeating units and exhibiting a melting point of 200° C. or more.  
   
   
       39 . The process for producing a nonwoven fabric as claimed in  claim 36 , wherein the two types of fibrous segments are arranged to form an eccentric core-in-sheath conjugate structure, and are composed of a low-melting point synthetic resin and a high-melting point synthetic resin different from each other in the melting point by 20° C. or more, the fibrous segment composed of the low-melting point synthetic resin forms the sheath portion of the eccentric core-sheath conjugate structure, and the fibrous segment composed of the high-melting point synthetic resin forms the core portion thereof.  
   
   
       40 . The process for producing a nonwoven fabric as claimed in  claim 37 , wherein the two types of fibrous segments forming the side-by-side conjugate structure are composed of a low-melting point synthetic resin and a high-melting point synthetic resin differing from each other in the melting point by 20° C. or more.  
   
   
       41 . The process for producing a nonwoven fabric as claimed in  claim 39 , wherein the low-melting point synthetic resin is selected from polyolefins, and the highmelting point synthetic resin is selected from polyesters containing alkylene phthalate units as major repeating units.  
   
   
       42 . The process for producing a nonwoven fabric as claimed in  claim 40 , wherein the low-melting point synthetic resin is selected from polyolefins, and the highmelting point synthetic resin is selected from polyesters containing alkylene phthalate units as major repeating units.  
   
   
       43 . The process for producing a nonwoven fabric as claimed in  claim 39 , wherein an isophthalic acidcopolymerized poly(alkylene terephthalate) having a melting point of from 50 to 200° C. is used as the low-melting point synthetic resin, and a poly(alkylene terephthalate) having a melting point higher than that of the low-melting point synthetic resin by 20° C. or more is used as the high-melting point synthetic resin.  
   
   
       44 . The process for producing a nonwoven fabric as claimed in  claim 40 , wherein an isophthalic acidcopolymerized poly(alkylene terephthalate) having a melting point of from 50 to 200° C. is used as the low-melting point synthetic resin, and a poly(alkylene terephthalate) having a melting point higher than that of the low-melting point synthetic resin by 20° C. or more is used as the high-melting point synthetic resin.  
   
   
       45 . The process for producing a nonwoven fabric as claimed in  claim 39 , wherein the low-melting point synthetic resin is selected from thermoplastic elastomers having a melting point of from 80 to 200° C.  
   
   
       46 . The process for producing a nonwoven fabric as claimed in  claim 40 , wherein the low-melting point synthetic resin is selected from thermoplastic elastomers having a melting point of from 80 to 200° C.  
   
   
       47 . The process for producing a nonwoven fabric as claimed in  claim 39 , wherein the low-melting point synthetic resin is selected from modified polyolefin resins obtained by graft polymerizing a polyolefin with a graft agent containing at least one substance selected from ethylenic unsaturated carboxylic acids and anhydrides thereof.  
   
   
       48 . The process for producing a nonwoven fabric as claimed in  claim 40 , wherein the low-melting point synthetic resin is selected from modified polyolefin resins obtained by graft polymerizing a polyolefin with a graft agent containing at least one substance selected from ethylenic unsaturated carboxylic acids and anhydrides thereof.  
   
   
       49 . The process for producing a nonwoven fabric as claimed in  claim 31 , wherein after the heat treating step is applied at temperature of from 60 to 200° C., the resultant three-dimensionally crimped individual fibers have a number of crimps of from 15 to 80/25 mm and a cramp ratio of from 25 to 90%.  
   
   
       50 . The process for producing a nonwoven fabric as claimed in  claim 31 , wherein the machine-crimped fibers are produced by a process comprising: 
 a melt spinning stage for producing undrawn synthetic resin filaments that comprises, during cooling and solidifying under a draft a filamentary synthetic resin molten flow prepared by melting a single type of thermoplastic synthetic resin and extruding the molten body through a spinneret into a filamentary flow, blowing a cold wind toward the one side of the filamentary synthetic resin molten flow in the direction transverse to the molten flow, whereby both sides of the imaginary interface of each filament along the longitudinal axis and transverse to the blowing direction of the cold wind are made disproportional in an orientation degree and/or a crystalline degree;    a drawing stage for producing drawn synthetic resin filaments having a thickness of from 0.5 to 200 dtex that comprises drawing the undrawn synthetic resin filaments at temperatures lower than the heat treatment temperatures for manifesting the crimps;    a machine crimping stage that comprises machine crimping the drawn synthetic resin filaments to impart a number of crimps of from 1 to 13/25 mm and a crimp ratio of from 2 to 20% to the drawn synthetic resin filaments; and    a cutting stage that comprises cutting the machine-crimped synthetic resin filaments into fiber pieces having a fiber length of from 3 to 20 mm.    
   
   
       51 . The process for producing a nonwoven fabric as claimed in  claim 46 , wherein the synthetic resin molten body in the melt spinning stage is extruded through a spinneret for forming hollow filaments into a hollow filamentary form.  
   
   
       52 . The process for producing a nonwoven fabric as claimed in  claim 46 , wherein the thermoplastic synthetic resin provided to the melt spinning stage comprises as a major component a polyester containing alkylene terephthalate units as major repeating units.  
   
   
       53 . The process for producing a nonwoven fabric as claimed in  claim 31 , wherein the machine-crimped fibers are produced by a process comprising: 
 resin provided to the melt spinning stage comprises major component a polyester containing alkylene terephthalate units as major repeating units.    as a melt spinning stage for producing undrawn synthetic resin eccentric core-in-sheath type conjugate filaments that comprises separately melting two types of thermoplastic synthetic resins differing from each other in thermal shrinkability, extruding the two molten bodies through a spinneret for forming eccentric core-in-sheath type conjugate fibers into a conjugate filamentary form, and cooling and solidifying under a draft the extruded conjugate filamentary synthetic resin melt flow;    a drawing stage for producing drawn synthetic resin conjugate filaments having a thickness of from 0.5 to 200 dtex that comprises drawing the undrawn synthetic resin conjugate filaments at temperatures lower than the heat treatment temperatures for manifesting the crimps;    a machine crimping stage that comprises machine crimping the drawn synthetic resin filaments to impart a number of crimps of from 1 to 13/25 mm and a crimp ratio of from 2 to 20% to the drawn synthetic resin filaments; and    a cutting stage that comprises cutting the machine-crimped synthetic resin conjugate filaments into fiber pieces having a fiber length of from 3 to 20 mm.    
   
   
       54 . The process for producing a nonwoven fabric as claimed in  claim 31 , wherein the machine-crimped fibers are produced by a process comprising: 
 a melt spinning stage for producing undrawn synthetic resin side-by-side type conjugate filaments that comprises separately melting two types of thermoplastic synthetic resins differing from each other in thermal shrinkability, extruding the two molten bodies through a spinneret for forming side-by-side type conjugate fibers into a conjugate filamentary form, and cooling and solidifying under a draft the extruded conjugate filamentary synthetic resin molten flow;    a drawing stage for producing drawn synthetic resin conjugate filaments having a thickness of from 0.5 to 200 dtex that comprises drawing the undrawn synthetic resin conjugate filaments at temperatures lower than the heat treatment temperatures for manifesting the crimps;    a machine crimping stage that comprises machine crimping the drawn synthetic resin filaments to impart a number of crimps of from 1 to 13/25 mm and a crimp ratio of from 2 to 20% to the drawn synthetic resin filaments; and    a cutting stage that comprises cutting the machine-crimped synthetic resin conjugate filaments into fiber pieces having a fiber length of from 3 to 20 mm.    
   
   
       55 . The process for producing a nonwoven fabric as claimed in  claim 49 , wherein, in the melt spinning stage, a poly(ethylene terephthalate) resin melt is fed to the spinneret for forming the eccentric core-sheath type conjugate fibers as a synthetic resin for forming the core portion, at temperatures of from 265 to 280° C., an isophthalic acid-copolymerized poly(alkylene terephthalate) resin melt having a melting or softening point of from 50 to 220° C. is fed thereto as a synthetic resin for forming the sheath portion, at temperatures of from 180 to 230° C., and the conjugate filamentary melt flow thus extruded is uniformly cooled and solidified with cooling air adjusted to temperatures of from 15 to 40° C.  
   
   
       56 . The process for producing a nonwoven fabric as claimed in  claim 49 , wherein the core portion of the undrawn eccentric core-sheath conjugate filaments is formed from a poly(ethylene terephthalate) resin, the sheath portion is formed from an isophthalic acid-copolymerized poly(alkylene terephthalate) resin having a melting or softening point of from 50 to 220° C., the total draw ratio to be applied to the undrawn conjugate filaments in the undrawing stage is set at from 0.70 to 0.95 times the maximum draw ratio of the undrawn conjugate filaments in hot water at 45° C., the undrawn conjugate filaments are first drawn until the draw ratio reaches from 0.60 to 0.90 times the total draw ratio in hot water at temperatures of from 70 to 80° C., and then the filaments are drawn in hot water at temperatures of from 60 to 80° C. until the draw ratio reaches the total draw ratio designed.  
   
   
       57 . The process for producing a nonwoven fabric as claimed in  claim 31 , whereinthe heat-treating step is applied to the air-laid nonwoven fabric under relaxation.