Rubber-containing graft polymer powder, and laminated-glass interlayer and solar-cell sealing material including same

The purpose of the present invention is to provide a rubber-containing graft polymer powder in which 1, 3-butadiene is used, and with which a solar-cell sealing material and a laminated-glass interlayer which exhibit excellent corrosion resistance, impact resistance, transparency, weather resistance, heat resistance, and economical efficiency can be achieved. Provided is a rubber-containing graft polymer powder for a polyvinyl acetal used for a solar-cell sealing material or a laminated-glass interlayer, said rubber-containing graft polymer powder having an acidic-constituent elution amount after hydrothermal testing of not more than 0.10 KOHmg/g. The rubber-containing graft polymer powder is preferably obtained by subjecting a vinyl monomer to graft polymerization in the presence of a rubber-like polymer, and subsequently solidifying the resultant substance, said rubber-like polymer being obtained by polymerizing a monomer (x) including a conjugated diene (x1) and an acrylic acid alkyl ester (x2) having a C2-8 alkyl group.