Polyamide fiber for uncoated airbags

Abstract

The present invention relates to a polyamide fiber for uncoated airbags, the fineness and stress-strain curve of the monofilaments of which were controlled such that the polyamide fiber can absorb impact energy which occurs instantaneously when the airbags operate. More particularly, the present invention relates to a high strength polyamide fiber consisting of polyamide monofilaments each having a fineness of less than 4 denier and a stress-strain curve where (a) the monofilament elongates less than 5% when subjected to an initial stress of 1.0 g/d, (b) it elongates less than 12% when subjected to a middle stress of 4.5 g/d, and (c) it elongates more than 3% over a tensile strength range from a tensile strength of at least 9.0 d/g to the tensile strength at break of the monofilament, the elongation values being measured at ambient temperature. A fabric produced using the inventive polyamide fiber has high tensile strength and high tear strength, so that it will be useful as an uncoated fabric for airbags.

1 . A polyamide monofilament for uncoated airbags, which has a fineness of less than 4 denier and a stress-strain curve where (a) the polyamide monofilament elongates less than 5% when subjected to an initial stress of 1.0 g/d, (b) it elongates less than 12% when subjected to a middle stress of 4.5 g/d, and (c) it elongates more than 3% over a tensile strength range from a tensile strength of at least 9.0 g/d to the tensile strength at break of the monofilament yarn, the elongation values being measured at ambient temperature.  
     
     
         2 . The polyamide monofilament of  claim 1 , which has a tensile strength at break of 9.0-11 g/d.  
     
     
         3 . The polyamide monofilament of  claim 1 , which has a fineness of 2-3.5 denier.  
     
     
         4 . A polyamide multifilament for uncoated airbags, which consists of a assembly of the polyamide monofilaments of  claim 1 .  
     
     
         5 . The polyamide multifilament of  claim 4 , wherein the number of the polyamide monofilaments in the polyamide monofilament assembly is 50-500.  
     
     
         6 . The polyamide multifilament of  claim 4 , wherein the number of the polyamide monofilaments in the polyamide monofilament assembly is 136.  
     
     
         7 . The polyamide multifilament of  claim 4 , which has a total fineness of 200-800 denier.  
     
     
         8 . A fabric for uncoated airbags, which is produced by the steps: 
 (A) weaving the polyamide multifilament of  claim 4  into a grey fabric for airbags;    (B) heat-shrinking the grey fabric by successively passing it through 3-10 aqueous bath in which the temperature of each of the aqueous baths is 5-20° C. higher than that of the preceding aqueous bath; and    (C) drying the heat-shrunk fabric by passing it through a hot air drier.    
     
     
         9 . The fabric of  claim 8 , wherein the step (B) is performed by passing the grey fabric through an aqueous bath with a temperature of 50° C. and successively passing the grey fabric through five aqueous baths in which the temperature of each of the aqueous bath is 10° C. higher than that of the preceding aqueous bath.  
     
     
         10 . The fabric of  claim 8 , wherein the fabric passed through the aqueous baths is additionally heat-shrunk by successively passing it through a steam heater.  
     
     
         11 . The fabric of  claim 10 , wherein the temperature of the steam heater is 150-220° C.  
     
     
         12 . The fabric of  claim 8 , wherein a fabric inlet of the hot air drier in the step (C) is set to a temperature of 140-160° C., and a fabric outlet of the hot air drier is set to about 30-70° C. higher temperature than that of the fabric inlet.  
     
     
         13 . The fabric of  claim 8 , wherein the fabric for uncoated airbags has a tensile strength of 200-300 kg.  
     
     
         14 . The fabric of  claim 8 , wherein the fabric for uncoated airbags has a tear strength of 25-40 kg.  
     
     
         15 . The fabric of  claim 8 , wherein the fabric for uncoated airbags has an air permeability of less than 1.0 cm 3 /cm 2 /sec.