Silsesquioxane mold release coating for unsaturated polyester thermoset molding compounds
View Patent ↗The process for molding a thermoset sheet-molding composition or bulk-molding composition is provided that includes the exposure of a mold surface to a silsesquioxane monomer or pre-polymer material under conditions to induce polymerization of said material or said monomer to form a mold release coating on the surface. The thermoset sheet-molding composition or bulk-molding composition is then injected into the mold and into contact with said coating under conditions to cure the composition to form an article.
1. A process for molding a thermoset sheet molding composition comprising:
applying a silsesquioxane monomer of RSi(OH) 3 , where R is the moiety is C 1-3 alkyl, vinyl, γ-glycidoxypropyl, or γ-methacryloxypropyl to a mold surface;
curing via condensation silanol functionality in said silsesquioxane monomer to form Si—O—Si bonds and form a silsesquioxane polymer mold release coating on the mold surface that is stable to SMC molding conditions;
introducing the thermoset sheet molding composition into the mold, the thermoset sheet molding composition containing monomers and fibers, and into contact with said mold release coating under conditions to cure the thermoset sheet molding composition to form a molded article, the fibers being glass, carbon, or a combination thereof;
removing the molded article from the mold and
introducing another thermoset sheet molding composition into the mold to form another article without the addition of more silsesquioxane monomer to the mold surface;
wherein said silsesquioxane monomer is a mixture of 5 to 40 percent by weight of silsesquioxane monomers having an average molecular weight of between 55 and 700 and a remainder of coating precursors have a molecular weight in the range of between 200 and 4000.
2. The process of claim 1 wherein the mold surface is formed of steel.
3. The process of claim 1 wherein the mold surface is formed of aluminum, or alloys thereof.
4. The process of claim 1 wherein the mold surface is formed of ceramic.
5. The process of claim 1 wherein said silsesquioxane polymer comprises RSiO 3/2 where R is C 1 -C 3 alkyl, vinyl, glycidoxypropyl, or methacryloxypropyl.
6. The process of claim 1 wherein said silsesquioxane polymer comprises a polycyclic octasilsesquioxane.
7. The process of claim 1 wherein said silsesquioxane polymer comprises a triethoxy silylethyl methyl siloxy silsesquioxane.
8. The process of claim 1 wherein said silsesquioxane polymer comprises a tetrahydridodimethylsiloxyoctasil.
9. The process of claim 1 wherein said silsesquioxane polymer comprises a tetraoxyethanoltetratriethoxysilylethane silsesquioxane.
10. The process of claim 1 wherein said silsesquioxane polymer comprises (tetratriethoxysilylethyldimethylsiloxy)(tetraglycidyldimethylsiloxy)octa-silsesquioxane.
11. The process of claim 1 further comprising removing said article from contact with said coating.
12. The process of claim 1 wherein repeating the injecting to form another article occurs at least 10 times.
13. The process of claim 1 wherein repeating the injecting to form another article occurs at least 30 times.
14. The process of claim 1 wherein repeating the injecting to form another article occurs at least 50 times.
15. The process of claim 1 wherein repeating the injecting to form another article occurs at least 70 times.
16. The process of claim 1 wherein repeating the injecting to form another article occurs at least 100 times.
17. The process of claim 1 further comprising suspending colloidal silica or glass fibers in the silsesquioxane monomer.