Method for producing drawn conjugated fiber, and drawn conjugated fiber

Abstract

Provided are a method for producing a drawn conjugated fiber, capable of producing a conjugated fiber having a high strength and a thin fineness, and a drawn conjugated fiber. A drawn conjugated fiber is produced by performing a spinning step of obtaining an undrawn fiber having a core-sheath structure in which a core material is a resin containing, as a main component, a crystalline propylene polymer and a sheath material is a resin containing, as a main component, an olefin polymer having a melting point lower than that of the core material, by means of melt-spinning (step S 1 ); and a drawing step of drawing the undrawn fiber (step S 2 ). During the production, a fineness of the undrawn fiber is adjusted to 1.5 dTex or less, and, in the spinning step, a melt flow rate of the core material discharged from the spinneret is adjusted to 70 to 170 g/10 minutes at 230° C. and a load of 21.18 N, and a ratio (=a core material MFR/a sheath material MFR) of the melt flow rate of the core material discharged from the spinneret at 230° C. and a load of 21.18 N to a melt flow rate of the sheath material discharged from the spinneret at 230° C. and a load of 21.18 N is adjusted to 1 to 2.2.

1 . A method for producing a drawn conjugated fiber comprising:
 a spinning step of obtaining an undrawn fiber having a core-sheath structure in which a core material is a resin containing, as a main component, a crystalline propylene polymer and a sheath material is a resin containing, as a main component, an olefin polymer having a melting point lower than that of the core material, by means of melt-spinning; and   a drawing step of drawing the undrawn fiber, wherein   the undrawn fiber has a fineness of 1.5 dTex or less, and   in the spinning step, the core material discharged from a spinneret has a melt flow rate of 70 to 170 g/10 minutes at 230° C. and a load of 21.18 N, and a ratio of the melt flow rate of the core material discharged from the spinneret at 230° C. and a load of 21.18 N to a melt flow rate of the sheath material discharged from the spinneret at 230° C. and a load of 21.18 N is from 1 to 2.2.   
     
     
         2 . The method for producing a drawn conjugated fiber according to  claim 1 , wherein at least one of a hydroxyamine ester, an isotactic polypropylene having a melt flow rate of 700 to 1550 g/10 minutes at 230° C. and a load of 21.18 N, and a metallocene polypropylene is added to the resin containing, as the main component, the crystalline propylene polymer, thereby adjusting the melt flow rate of the core material discharged from the spinneret at 230° C. and a load of 21.18 N. 
     
     
         3 . The method for producing a drawn conjugated fiber according to  claim 1  or  2 , wherein, in the spinning step, the sheath material discharged from the spinneret has a melt flow rate within a range of 60 to 90 g/10 minutes at 230° C. and a load of 21.18 N. 
     
     
         4 . The method for producing a drawn conjugated fiber according to any one of  claims 1  to  3 , wherein the crystalline propylene polymer, which is the main component of the core material, is an isotactic polypropylene. 
     
     
         5 . The method for producing a drawn conjugated fiber according to any one of  claims 1  to  4 , wherein a nucleating agent is added to the resin containing, as the main component, the crystalline propylene polymer. 
     
     
         6 . The method for producing a drawn conjugated fiber according to  claim 5 , wherein the nucleating agent is an organic nucleus-creating agent. 
     
     
         7 . The method for producing a drawn conjugated fiber according to  claim 6 , wherein the organic nucleus-creating agent is a metal salt of phosphate ester or a dibenzylidene sorbitol. 
     
     
         8 . The method for producing a drawn conjugated fiber according to any one of  claims 1  to  7 , wherein the olefin polymer, which is the main component of the sheath material, is a high density polyethylene. 
     
     
         9 . The method for producing a drawn conjugated fiber according to any one of  claims 1  to  8 , wherein the drawing step is continuously performed after the spinning step. 
     
     
         10 . The method for producing a drawn conjugated fiber according to any one of  claims 1  to  9 , wherein the drawing step is performed in pressurized saturated steam. 
     
     
         11 . A drawn conjugated fiber obtained by drawing an undrawn fiber having a core-sheath structure in which a core material is a resin containing, as a main component, a crystalline propylene polymer and a sheath material is a resin containing, as a main component, an olefin polymer having a melting point lower than that of the core material, wherein
 the undrawn fiber has a fineness of 1.5 dTex or less, and   the core material has a degree of crystallinity of 35% or more, measured according to a heat of fusion method at a temperature elevation rate of 30° C./minute using a differential scanning calorimeter.   
     
     
         12 . The drawn conjugated fiber according to  claim 11 , wherein a nucleating agent is added to the resin containing, as the main component, the crystalline propylene polymer, and
 the core material has a degree of crystallinity of 40% or more, measured according to a heat of fusion method at a temperature elevation rate of 30° C./minute using a differential scanning calorimeter.   
     
     
         13 . The drawn conjugated fiber according to  claim 11  or  12 , wherein, when the undrawn fiber is spun, the core material discharged from a spinneret has a melt flow rate within a range of 70 to 170 g/10 minutes at 230° C. and a load of 21.18 N, and a ratio of the melt flow rate of the core material discharged from the spinneret at 230° C. and a load of 21.18 N to a melt flow rate of the sheath material discharged from the spinneret at 230° C. and a load of 21.18 N is from 1 to 2.2.