| 摘要 |
An object of the invention is to provide a polyvinyl acetal resin for thermoforming that allows providing a molded product that is excellent in thermal stability, and excellent in the heat resistance without harming the properties of the polyvinyl acetal resin, and the invention relates to a polyvinyl acetal resin for thermoforming, which is obtained by acetalization of a polyvinyl alcohol resin having a viscosity average polymerization degree of 500 to 2000 and a saponification degree of 99.5 mol % or more with aldehyde, wherein the sum of vinyl alcohol units acetalized with the aldehyde is 65 to 88 mol % with respect to the total repeating units, and the content of alkali metal or alkali earth metal is 0.1 to 50 ppm. The molar ratio of a vinyl alcohol unit acetalized with an aldehyde having four or more carbon atoms/a vinyl alcohol unit acetalized with an aldehyde having three or less carbon atoms is preferably 90/10 to 0/100.
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