| 摘要 |
A curable composition comprises an epoxy resin, a boron-trifluoride-amine complex curing agent having a decomposition temperature above 130 DEG C., finely divided silica and/or fume silica and a polyvinylal resin. Curing agents specified are BF3-piperidine complex, and BF3-triethanolamine complex. The polyvinylal resin may be prepared by combining formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde or benzaldehyde with partially or completely hydrolyzed polyvinyl esters, e.g. the acetate, propionate or butyrate. The compositions may be prepared by adding the fillers and polyvinylal resin to the heated epoxy resin, cooling to 90-130 DEG C. and adding the curing agent, which may be partially reacted to a stage short of gelation. The mixture may be cooled in liquid nitrogen and pulverized in a hammer mill. In Example 3, the composition contains 100 grams of "Araldite" 6060 (Registered Trade Mark), 40 grams of polyvinylal resin "Formvar" (Registered Trade Mark), 4 grams of BF3-piperidine complex, 70 grams of 200-mesh silica, and 3 grams of fume silica. Example 6 is similar but uses a BF3-triethanolamin complex as curing agent. The compositions may be used for coating steel panels by the fluidized bed method. Specifications 518,057 and 579,698 are referred to. |
