| 摘要 |
PURPOSE:To widen a heat shrinkage packing temp. range, in a coextrusion shrink film wherein both outer layers are composed of a crystalline polypropylene resin and a core layer is composed of an ethylene/methyl methacrylate copolymer, by specifying the melting points and melt flow index(MI) of both resins. CONSTITUTION:A crystalline polypropylene resin has an m.p. of 135 -150 deg.C and MI of 1-7 and a resin prepared by copolymerizing about 2-4wt.% of ethylene or 3-8wt.% of ethylene and butene with propylene is used preferably EMMA used in a core layer has an m.p. of 90-102 deg.C and MI 1/3-2 times that of the aforementioned crystalline polypropylene resin. This film is prepared by coextruding a multilayer non-stretched original film and re-heating said film to stretch the same by at least 3.0 times or more in longitudinal and lateral direction and subsequently cooling the stretched film. Further, an m.p. is measured by a differential scanning heat analysis method and MI is a value measured under a condition of temp. 230 deg.C and load 2160g in the crystalline polypropylene resin and a value measured under a condition of temp. 190 deg.C and load 2160g according to the A-method of JIS-E-71210. |
