| 摘要 |
1,125,666. Foamed polyvinyl formals. KURASHIKI RAYON K.K. 24 Aug., 1966 [25 Aug., 1966], No. 38049/66. Headings C3C and C3P. Foamed polyvinyl formals are prepared by a process comprising the steps of (i) reacting polyvinyl alcohol with a formalizing agent in an aqueous solution containing a formalization catalyst and zinc chloride or acetic acid; (ii) before, during or after the reaction, introducing a foaming agent; and (iii) coagulating the resulting polyvinyl formal foam with an aqueous coagulating liquid. The expression " polyvinyl alcohol " includes completely and partially saponified polyvinyl esters and also saponified polyvinyl esters which are slightly acetalized, etherified or urethanized, and saponified products of copolymers of vinyl esters and copolymerizable monomers. Formalizing agents for use in step (i) can be formaldehyde and formaldehyde-forming substances and suitable formalization catalysts are inorganic and organic acids. Step (ii) may be accomplished by introducing into the viscous solution from step (i) a gas under high pressure and then decreasing the pressure; a substance having a low boiling point under pressure, followed by heating or reducing the pressure; a surfaceactive agent, if necessary, with air or other gas with agitation; a substance which evolves a gas by the action of acid; or a foaming agent which evolves a gas by heating or by the action of a promoter. The coagulating liquid for step (iii) is water, steam or an aqueous solution composed essentially of water; water containing less than 20% of zinc chloride or acetic acid being preferred. Various fillers, such as plasticizers, celluloses, synthetic fibres and inorganic materials, may be added to the polyvinyl formal solution and the foams may be shaped into many forms and subjected to colouring, coating, embossing, waterproofing, laminating, printing, compounding or softening. |
