| 摘要 |
PURPOSE:To obtain the titled composition which hardly gels and has good miscibility with (NH4)2SO4, by mixing a specified polyvinyl acetate emulsion and (NH4)2SO4. CONSTITUTION:50-60pts.wt. water and 3-5pts.wt. CMC as protective colloid are fed into a polymerizer and are heated at 75-80 deg.C for 1-5hr to dissolve the CMC. After cooling this solution to about 60 deg.C, 1-10% solution comprising 30-40pts.wt. vinyl acetate monomer and 5-7pts.wt. plasticizer (e.g., dibutyl phthalate) and a polymerization catalyst are added thereto, and the temperature is raised to about 80 deg.C. The remaining solution of vinyl acetate monomer and a plasticizer is then added thereto, and the mixture is allowed to undergo polymerization for 2-4hr and to age at 80-90 deg.C for 1-2hr. Thereafter, the pH is adjusted to 4-5, thus giving a polyvinyl acetate emulsion having a nonvolatile content of 40-50%, a viscosity of 1,000-2,000cP (30 deg.C, Brookfield BL viscometer 3/30), and a particle diameter of 1-2mum. 100pts.wt. (in terms of resin content) of this emulsion is mixed with 100pts.wt. or less (NH4)2SO4 to give a binder composition for a mat for raising seedling having a solid content of 70% or less.
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