Method for producing silica composite particle

1. A method for producing a silica composite particle, the method comprising:

(i) providing a silica particle dispersion liquid having a silica particle content of about 20 mass % or more;

(ii) mixing and reacting a compound represented by formula (Si) and the silica particle dispersion liquid to obtain a slurry, where the compound represented by formula (S1) is:

Si(R 1 ) n (OR 2 ) 4-n   Formula (S1)

where R 1 and R 2 each independently represent an alkyl group or an aryl group, and n represents an integer of 1 or more and 3 or less;

(iii) providing at least one compound in which an aluminum atom bonds to an organic group through oxygen; and

(iv) then mixing and reacting the slurry with the at least one compound to form the silica composite particle in which a coverage X of a surface of the silica composite particle with the aluminum atoms of the at least one compound is about 0.01 at % or more and about 30 at % or less,

where the coverage X is calculated from a ratio of the aluminum Al/Si detected by X-ray photoelectron spectroscopy.

2. The method of claim 1 , wherein the step of providing the silica particle dispersion liquid having a silica particle content of about 20 mass % or more includes:

(i) providing an aqueous silica particle dispersion liquid; and

(ii) concentrating the aqueous silica particle dispersion liquid by removing water from the liquid so that the concentrated liquid has an amount of silica particles in the range of 25 mass % or more and 60 mass % or less.

3. The method of claim 1 , wherein the aluminum atom of the at least one compound is bonded to at least one of an acyloxy group, an alkyl acetoacetate group, and an acetylacetonate group.

4. The method of claim 1 , wherein the at least one compound is selected from the group consisting of aluminum alkoxides, aluminum chelates, aluminum oxide acylates, aluminum complexes of β-diketone, aluminum complexes of β-ketoester, and aluminum complexes of carboxylic acid.

5. The method of claim 1 , wherein the at least one compound is an aluminum alkoxide selected from the group consisting of aluminum methoxide, aluminum ethoxide, aluminum n-propoxide, aluminum i-propoxide, aluminum n-butoxide, aluminum i-butoxide, aluminum sec-butoxide, and aluminum tert-butoxide.

6. The method of claim 1 , wherein the silica composite particle has an average particle size of about 10 nm or more and about 300 nm or less.

7. The method of claim 1 , wherein the silica composite particle has an average circularity of about 0.5 or more and about 0.99 or less.

8. The method of claim 1 , wherein the silica composite particle has a particle size distribution index of about 1.1 or more and about 1.5 or less.

9. The method of claim 1 , wherein:

when a binding energy peak of O1s in an oxide of the aluminum atoms is assumed to be MO1s, a binding energy peak of O1s in SiO 2 is assumed to be SO1s, and a binding energy peak of O1s in the silica composite particle is assumed to be MSO1s, the binding energy peaks being detected by X-ray photoelectron spectroscopy, formula (1) below is satisfied,

0.000452× X 2 −0.059117× X+SO 1 s<MSO 1 s ≤( SO 1 s−MO 1 s )/100× X+SO 1 s   (1).

10. The method of claim 9 , wherein formula (2) below is satisfied,

0.000452× X 2 −0.059117×0.9 X+SO 1 s<MSO 1 s ≤( SO 1 s−MO 1 s )/100× X+SO 1 s   (2).

11. The method of claim 9 , wherein formula (3) below is satisfied,

0.000452× X 2 −0.059117×0.7× X+SO 1 s<MSO 1 s ≤( SO 1 s MO 1 s )/100× X+SO 1 s   (3).

12. The method of claim 1 , wherein the silica composite particle has an average circularity of more than 0.85 and about 0.99 or less.

13. The method of claim 1 , wherein the coverage X is about 0.05 at % or more and about 20 at % or less.

14. The method of claim 1 , wherein:

an addition amount of the compound represented by the formula (Si) in step (ii) is 0.01 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the silica particles; and

an addition amount of the at least one compound in step (iv) is 0.01 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the silica particles.

15. The method of claim 1 , wherein steps (ii)-(iv) are continuous processes.

16. The method of claim 1 , wherein the compound represented by formula (S1) is selected from the group consisting of methyltrimethoxysilane, dimethyldimethoxysilane, propyl-trimethoxysilane, octadecyl-trimethoxysilane, and phenyl-trimethoxysilane.

17. The method of claim 1 , further comprising:

(v) subjecting the silica composite particle to hydrophobization with hexamethyldisilazane.