| 摘要 |
<p>PURPOSE:To improve transparency, coloring property, printability and assembling property to a box and to facilitate secondary fabrication by consisting an external case of a styrene/butabiene block copolymer or a resin compsn. of said copolymer and a styrene resin and/or styrene copolymer resin and incorporating the butadiene into the copolymer at 10-35wt% by the total weight. CONSTITUTION:This external case for a video cassette consists essentially of a styrene/butadiene block copolymer. The styrene/butadiene copolymer (SB coalescence) refers to the block copolymer in which the content of polybutadiene is 10-80wt% and which can be manufactured by a method of using anion polymn. initiator and above all an org. lithium compd. and polymerizing stepwise both styrene and butadiene monomers, a method of copolymerizing the mixture composed of both monomers in an inert solvent or a method of making adequately combination use thereof. The resin to be mixed with the SB polymer is required to maintain the initial transparency without spoiling the same. The content of the polybutadiene in the SB polymer is 10-35wt%, more preferably 12-30wt%. If the content is <10wt%, the part bent in the stage of forming a box is whitened or cracked. If the content exceeds 35wt%, the stiffness of the sheet after forming decreases.</p> |
