Patent ID: 6221288
Filing Date: 2001-04-24
Classification: B29C,B32B,Y10S,Y10T

Abstract:
A method of producing a composite stratiform material by co-extrusion of at least three layers, each comprising polypropylene and at least one filler, said co-extrusion being effected by means of at least one extruder having a pair of co-rotating screws; said method comprising the step of co-extruding:(I) a carrier layer formed of a mixture containing polypropylene and a particulate organic filler;(II) a first outer layer consisting essentially of a mixture containing polypropylene and an inorganic filler; and(III) a second outer layer consisting essentially of a mixture containing polypropylene and an inorganic filler;said co-extrusion providing for interfusion of said carrier layer with each of said first and said second outer layers at mutually opposite interfaces between said carrier layer and said outer layers; wherein said particulate organic filler for said carrier layer is selected from the group consisting of a vegetabilic nature and wood which is extruded by a co-rotational first extruder; and wherein said inorganic filler is introduced into at least one second extruder for extruding at least one of said outer layers;wherein said carrier layer includes comminuted articles made by thermal molding of said composite stratiform material, or of production scrap,whereby the material is repeatedly recyclable.