Biaxially stretched five-layer film and method for manufacture thereof

Claim 1

A method for the manufacture of a biaxially stretched five-layer laminate resin film which comprises use of a three-layer tubular molding die provided with three resin flow paths respectively for an outermost resin layer, an intermediate resin layer and an innermost resin layer, each of said three resin flow paths being provided with a torpedo which serves in modifying a solid resin flow into a tubular flow, characterized in that, (a) two resin-feed ducts are installed respectively into the path for the outermost resin layer and in the path for the intermediate resin layer so as to have each of the end portions of the installed resin-feed ducts inserted into each of said paths for the outermost and the intermediate resin layers with each of said paths and extended short of direct contact with each of said torpedoes; (b) an olefine polymer resin selected from the group consisting of an ionomer, a homopolymer and a copolymer of an olefine and a mixture of said homopolymer and said copolymer of an olefin is fed from outside of said die in a melt state and is extruded through said resin flow path for said outermost resin layer; a copolymer of vinylidene chloride is fed from outside of said die in a melt state and is extruded through said resin flow path for said intermediate resin layer; an ionomer is fed from outside of said die in a melt state and is extruded through said resin flow path for said innermost resin layer and, at the same time, a copolymer of ethylene having a crystal-melting point of 5° to 30° C. lower than that of said ionomer is fed from outside of said die and is extruded through both of said feed ducts, thereby producing a five-layered laminate resin tube at the outlet of said die; (c) the resultant five-layered laminate resin tube is rapidly cooled by quenching so as to cause said copolymer of vinylidene chloride in said laminate tube to assume an amorphous state; and (d) the thus quenched laminate resin tube is biaxially stretched at a temperature lower than the crystal-melting point of said olefine polymer resin in said outmost resin layer and that of said ionomer in said innermost resin layer and at least 4° C. higher than that of said copolymer of ethylene, thereby yielding a biaxially stretched five-layered laminate resin film having a first resin layer of 7 to 25μ, a second resin layer of 0.2 to 3μ, a third resin layer of 5 to 15μ, a fourth resin layer of 0.2 to 3μ and a fifth resin layer of 20 to 50μ in thickness, the ratio of thickness of said first resin layer to that of said fifth resin layer being in the range of from 0.4 to 0.6 and the total thickness of said five-layered laminate resin film being in the range of from 35 to 90μ.

Claim 2

A method for the manufacture of a biaxially stretched five-layer laminate resin film which comprises use of a three-layer tubular molding die provided with three resin flow paths respectively for an outermost resin layer, an intermediate resin layer and an innermost resin layer, each of said three resin flow paths being provided with a torpedo which serves in modifying a solid resin flow into a tubular flow, characterized in that, (a) two resin-feed ducts are installed respectively into the path for the outermost resin layer and in the path for the intermediate resin layer so as to have each of the end portions of the installed resin-feed ducts inserted into each of said paths for the outermost and the intermediate resin layers with each of said paths and extended short of direct contact with each of said torpedoes; (b) an olefine polymer resin selected from the group consisting of an ionomer, a homopolymer and a copolymer of an olefine and a mixture of said homopolymer and said copolymer of an olefin is fed from outside of said die in a melt state and is extruded through said resin flow path for said outermost resin layer; a copolymer of vinylidene chloride is fed from outside of said die in a melt state and is extruded through said resin flow path for said intermediate resin layer; an ionomer is fed from outside of said die in a melt state and is extruded through said resin flow path for said innermost resin layer and, at the same time, a copolymer of ethylene having a crystal-melting point of 5° to 30° C. lower than that of said ionomer is fed from outside of said die and is extruded through both of said feed ducts, thereby producing a five-layered laminate resin tube at the outlet of said die; (c) the resultant five-layered laminate resin tube is rapidly cooled by quenching so as to cause said copolymer of vinylidene chloride in said laminate tube to assume an amorphous state; and (d) the thus quenched laminate resin tube is biaxially stretched at a temperature lower than the crystal-melting point of said olefine polymer resin in said outmost resin layer and that of said ionomer in said innermost resin layer and at least 4° C. higher than that of said copolymer of ethylene, thereby yielding a biaxially stretched five-layered laminate resin film having a first resin layer of 7 to 25μ, a second resin layer of 0.2 to 3μ, a third resin layer of 5 to 15μ, a fourth resin layer of 0.2 to 3μ and a fifth resin layer of 20 to 50μ in thickness, the ratio of thickness of said first resin layer to that of said fifth resin layer being in the range of from 0.4 to 0.6 and the total thickness of said five-layered laminate resin film being in the range of from 35 to 90μ.