Fiber-containing polymeric materials and methods thereof

Abstract

The present invention relates to light weight composite materials which comprise a metallic layer and a polymeric layer, the polymeric layer containing a filled thermoplastic polymer which includes a thermoplastic polymer and a metallic fiber. The composite materials of the present invention may be formed using conventional stamping equipment at ambient temperatures. Composite materials of the present invention may also be capable of being welded to other metal materials using a resistance welding process such as resistance spot welding. The invention also relates to methods for producing a sheet of the polymeric layer.

I claim: 
     
         1 . A method for making a sheet for a core layer of a weldable sandwich composite comprising steps of:
 feeding into an extruder, as separate materials or as a blend:
 i) metal fibers having a weight average length of about 5 μm to about 25 mm; and 
 ii) one or more polymers including a synthetic elastomer; and 
   extruding a sheet including the one or more polymers and the metal fibers;   wherein   the synthetic elastomer has a tensile strength at 100% elongation of less than about 3 MPa and a tensile elongation at break greater than about 110%, both measured according to ASTM D638-08 at a nominal strain rate of about 0.1;   the metal fibers are present in an amount from about 3 volume percent to less than about 30 volume percent, based on the total volume of the sheet.   
     
     
         2 . The method of  claim 1 , wherein the concentration of pores and voids in the polymeric core layer is from 0 to about 10 volume percent, based on the total volume of the sheet. 
     
     
         3 . The method of  claim 2 , wherein the metal fibers have an average length of about 5 μm to 8 mm and are present in an amount from about 5 volume percent to 20 volume percent, based on the total volume of the sheet. 
     
     
         4 . The method of  claim 3 , wherein the metal fibers are chopped fibers. 
     
     
         5 . The method of  claim 3 , wherein the one or more polymers includes a thermoplastic polymer having a melting temperature, and the method includes extruding the sheet at an extrusion temperature greater than the melting temperature. 
     
     
         6 . The method of  claim 5 , wherein the metal fibers and the one or more polymers are fed into different locations of the extruder. 
     
     
         7 . The method of  claim 5 , wherein the one or more polymer includes a thermoplastic polymer including a polyethylene copolymer of one or more α-olefins and optionally one or more additives, wherein the polyethylene copolymer includes at least about 80 weight percent ethylene and has a peak melting temperature as measured according to ASTM D3418-08 above 80° and below 250° C.;
 wherein the thermoplastic polymer has a number average molecular weight greater than about 20,000; and a crystallinity of about 10% or more. 
 
     
     
         8 . The method of  claim 5 , wherein the metal fibers are distributed and used in a sufficient amount so that a conductive network across the thickness of the sheet is formed. 
     
     
         9 . The method of  claim 8 , wherein the one or more polymers are not conductive. 
     
     
         10 . A method for making a sheet for a core layer of a weldable sandwich composite comprising steps of:
 pultruding a plurality of continuous fibers through a container including one or more polymers in a molten state;   coating the fibers with the one or more polymers;   chopping the coated fibers into pellets or granules, so that the metal fibers have a weight average length of less than 25 mm;   wherein the pellets or granules includes 3 volume percent or more of the metal fibers.   
     
     
         11 . The method of  claim 10 , wherein the method includes steps of:
 feeding the pellets or granules into an extruder;   heating the one or more polymers to an extrusion temperature greater than a melting temperature of the one or more polymers; and   extruding a sheet including the one or more polymers and the metal fibers.   
     
     
         12 . The method of  claim 11 , wherein the metal fibers having a weight average length of about 5 μm to about 25 mm; and the one or more polymers including a synthetic elastomer. 
     
     
         13 . The method of  claim 12 , wherein the synthetic elastomer has a tensile strength at 100% elongation of less than about 3 MPa and a tensile elongation at break greater than about 110%, both measured according to ASTM D638-08 at a nominal strain rate of about 0.1;
 the metal fibers are present in an amount from about 3 volume percent to less than about 30 volume percent, based on the total volume of the sheet.   
     
     
         14 . The method of  claim 11 , wherein additional polymers are fed into the extruder. 
     
     
         15 . The method of  claim 11 , wherein the additional polymers are optionally fed into the extruder and the volume ratio of the polymer (including the one or more polymers and any additional polymer) in the sheet to the metal fiber in the sheet is greater than about 3:1. 
     
     
         16 . The method of  claim 15 , wherein the concentration of pores and voids in the polymeric core layer is from 0 to about 10 volume percent, based on the total volume of the sheet. 
     
     
         17 . The method of  claim 16 , wherein the metal fibers have an average length of about 5 μm to 8 mm and are present in an amount from about 5 volume percent to 20 volume percent, based on the total volume of the sheet. 
     
     
         18 . The method of  claim 17 , wherein the one or more polymer includes a thermoplastic polymer including a polyethylene copolymer of one or more α-olefins and optionally one or more additives, wherein the polyethylene copolymer includes at least about 80 weight percent ethylene and has a peak melting temperature as measured according to ASTM D3418-08 above 80° and below 250° C.;
 wherein the thermoplastic polymer has a number average molecular weight greater than about 20,000; and a crystallinity of about 10% or more. 
 
     
     
         19 . The method of  claim 10 , wherein the metal fibers are distributed and used in a sufficient amount so that a conductive network across the thickness of the sheet is formed. 
     
     
         20 . A method for making a sheet for a core layer of a weldable sandwich composite comprising steps of:
 calendaring a polymeric composition including:
 i) metal fibers having a weight average length of about 5 μm to about 25 mm; and 
 ii) one or more polymers including a synthetic elastomer; and 
   rolling the polymeric composition into a sheet including the one or more polymers and the metal fibers;   wherein   the synthetic elastomer has a tensile strength at 100% elongation of less than about 3 MPa and a tensile elongation at break greater than about 110%, both measured according to ASTM D638-08 at a nominal strain rate of about 0.1;   
       the metal fibers are present in an amount from about 3 volume percent to less than about 30 volume percent, based on the total volume of the sheet.