Method for producing spherical polysilsesquioxane particles
Spherical silsesquioxane particles are formed by controlled hydrolysis of trialkoxysilane(s) in acidic media, followed by addition of base, storage for at least 2 hours, and spray drying. Essentially non-agglomerated spherical particles are produced without milling.
1. A process for producing spherical polysilsesquioxane particles, comprising:
in a first step, reacting trialkoxysilane(s) of formula (I)
RSi(OR 1 ) 3 (I),
in which
R represents a hydrocarbon radical having 1 to 16 carbon atoms whose carbon chain is optionally interrupted by nonadjacent —O— groups,
R 1 represents a C 1 - to C 4 -alkyl radical,
with acidified water having a pH of not more than 6 to form a hydrolysate;
in a second step, mixing the hydrolyzate with a solution of a base in water or in C 1 - to C 4 -alkanol;
in a third step, storing the mixture of the second step for at least 2 h without substantial agitation, forming polysilsesquioxane particles;
and in a fourth step, spray drying the polysilsesquioxane particles in the mixture or recovered therefrom.
2. The process of claim 1 , in which R represents an ethyl radical or a methyl radical.
3. The process of claim 1 , in which R 1 represents an ethyl radical or a methyl radical.
4. The process of claim 1 , in which in the first step, 5 to 43 parts by weight of trialkoxysilane are added per 100 parts by weight of water.
5. The process of claim 1 , in which in the second step, a solution of ammonia in water or alkali metal hydroxide in an alkanol having 1 to 3 carbon atoms is employed.
6. The process of claim 1 , in which sufficient solution of base is added to ensure that a pH of 6.5 to 9.5 is achieved, measured immediately after addition of base.
7. The process of claim 5 , in which sufficient solution of base is added to ensure that a pH of 6.5 to 9.5 is achieved, measured immediately after addition of base.
8. The process of claim 1 , in which the temperature of the addition of base in the second step is 10° C. to 40° C.
9. The process of claim 1 , in which in the third step, the mixture is stored for at least 7 h prior to spray drying.
10. The process of claim 1 , in which after the third step the mixture is neutralized by addition of an acid.
11. The process of claim 9 , in which after the third step the mixture is neutralized by addition of an acid.
12. The process of claim 1 , in which after the third step the particles are isolated and washed with a washing liquid, and the washed particles are redispersed with a liquid, prior to spray drying.
13. The process of claim 1 , in which an entry temperature of a dry gas stream into a spray-drying apparatus used for spray drying in the fourth step is 110° C. to 350° C.
14. The process of claim 1 , wherein step b) immediately follows step a).
15. The process of claim 1 , wherein an exit temperature from a spray dryer employed in step d) is at least 110° C.
16. The process of claim 1 , wherein an exit temperature from a spray dryer employed in step d) is at least 140° C.
17. The process of claim 1 , wherein an exit temperature from a spray dryer employed in step d) is at least 160° C.
18. The process of claim 1 , further comprising after-drying the polysilsesquioxane particles obtained from step d).
19. The process of claim 18 , wherein the step of after-drying takes place in at least one of a paddle dryer, fluidized bed dryer, tray drier, flow drier, or drum drier.