Method for producing acrylic polymer fine particles

1. A method for producing acrylic polymer fine particles, comprising:

(1) (a) polymerizing a monomer with a radical polymerization initiator in a medium consisting essentially of water and a monomer, wherein the monomer has a solubility of not less than 0.02 mass % in water at 20° C. and wherein a polymer of the monomer is insoluble in said medium, thereby obtaining a polymer dispersion;

(b) adding dropwise a monomer mixture into said polymer dispersion to obtain a coated polymer dispersion; and

(2) spray drying the polymer dispersion to recover the acrylic polymer fine particles.

2. The method of claim 1 , wherein the acrylic polymer fine particles comprise primary particles P having a core-shell structure comprising a core polymer C and a shell polymer S, in which the average particle diameter of the primary particles P is not less than 250 nm, the core polymer C and the shell polymer S are copolymers of the following monomer mixtures Mc and Ms, respectively, and the weight ratio of Mc and Ms is 10/90-90/10:

Mc:

methyl methacrylate

20-85 mol %,

(meth)acrylic ester of C 2 -C 8 aliphatic alcohol or aromatic alcohol or both

15-80 mol %,

other copolymerizable monomers

not more than 30 mol %,

wherein the total amount of monomers Mc is 100 mol %;

Ms:

methyl methacrylate

20-79.5 mol %,

(meth)acrylic ester of C 2 -C 8 aliphatic alcohol or aromatic alcohol or both

5-40 mol %,

monomer containing carboxyl group or sulfonic acid group

0.5-10 mol %, and

other copolymerizable monomers

not more than 30 mol %,

wherein the total amount of monomers Ms is 100 mol %.

3. The method of claim 2 , wherein the core polymer C and the shell polymer S are copolymers of the following monomer mixtures Mc and Ms, respectively, and the weight ratio of Mc and Ms is 30/70-70/30;

Mc:

methyl methacrylate

20-70 mol %,

at least one (meth)acrylic ester selected from the group consisting of n-butyl(meth)acrylate, iso-butyl(meth)acrylate and t-butyl(meth)acrylate

30-80 mol %, and

other copolymerizable monomers

not more than 20 mol %,

wherein the total amount of monomers Mc is 100 mol %;

Ms:

methyl methacrylate

30-79.5 mol %,

at least one (meth)acrylic ester selected from the group consisting of n-butyl (meth)acrylate, iso-butyl (meth)acrylate and t-butyl (meth)acrylate

5-40 mol %,

acrylic monomer containing carboxyl group

0.5-10 mol %, and

other copolymerizable monomers

not more than 20 mol %,

wherein the total amount of monomers Ms is 100 mol %.

4. The method of claim 2 , wherein the core polymer C and the shell polymer S are copolymers of the following monomer mixtures Mc, and Ms, respectively, and the weight ratio of Mc and Ms is 30/70-70/30;

Mc:

methyl methacrylate

20-70 mol %,

at least one (meth)acrylic ester selected from the group consisting of n-butyl (meth)acrylate, iso-butyl (meth)acrylate and t-butyl (meth)acrylate

30-80mol %, and

other copolymerizable monomers

not more than 10 mol %

wherein the total amount of monomers Mc is 100 mol %;

Ms:

methyl methacrylate

55-79.5 mol %,

at least one (meth)acrylic ester selected from the group consisting of n-butyl (meth)acrylate, iso-butyl (meth)acrylate and t-butyl (meth)acrylate

20-40 mol %,

acrylic monomer containing carboxyl group

0.5-5 mol %, and

other copolymerizable monomers

not more than 10 mol %,

wherein the total amount of monomers Ms is 100 mol %.

5. The method of claim 1 , wherein the acrylic polymer particles have a primary particle diameter of not less than 250 nm.

6. The method of claim 5 , wherein the acrylic polymer particles have a primary particle diameter of from 340 to 1,460 nm.

7. The method of claim 1 , wherein the acrylic polymer particles have a secondary or higher order structure.

8. The method of claim 1 , wherein the acrylic polymer particles have a primary particle diameter of more than 1,000 nm.

9. A method for producing acrylic polymer fine particles, comprising:

(1) (a) polymerizing a monomer with a radical polymerization initiator in the absence of an emulsifier micelle in a medium mainly comprising water, wherein the monomer has a solubility of not less than 0.02 mass % in the medium at 20° C. and a polymer of the monomer is insoluble in the medium, thereby obtaining a polymer dispersion;

(b) adding dropwise a monomer mixture into the polymer dispersion to obtain a coated polymer dispersion; and

(2) spray drying the polymer dispersion to recover acrylic polymer fine particles consisting essentially of primary particles P having a core-shell structure that further consist essentially of a core polymer C and a shell polymer S,

wherein the average particle diameter of the primary particles P is not less than 250 nm, the core polymer C and the shell polymer S are copolymers of the following monomer mixtures Mc and Ms, respectively, and wherein the weight ratio of Mc and Ms is 10/90-90/10:

Mc:

methyl methacrylate

20-85 mol %,

(meth)acrylic ester of C 2 -C 8 aliphatic alcohol or aromatic alcohol or both

15-80 mol %, and

other copolymerizable monomers

not more than 30 mol %,

wherein the total amount of monomers Mc is 100 mol %;

Ms:

methyl methacrylate

20-79.5 mol %,

(meth)acrylic ester of C 2 -C 8 aliphatic alcohol or aromatic alcohol or both

5-40 mol %,

monomer containing carboxyl group or sulfonic acid group

0.5-10 mol %, and

other copolymerizable monomers

not more than 30 mol %,

wherein the total amount of monomers Ms is 100 mol %.

10. The method of claim 9 , wherein the core polymer C and the shell polymer S are copolymers of the following monomer mixtures Mc and Ms, respectively, and the weight ratio of Mc and Ms is 30/70-70/30;

Mc:

methyl methacrylate

20-70 mol %,

at least one (meth)acrylic ester selected from the group consisting of n-butyl (meth)acrylate, iso-butyl (meth)acrylate and t-butyl (meth)acrylate

30-80 mol %, and

other copolymerizable monomers

not more than 20 mol %,

wherein the total amount of monomers Mc is 100 mol %;

Ms:

methyl methacrylate

30-79.5 mol %,

at least one (meth)acrylic ester selected from the group consisting of n-butyl (meth)acrylate, iso-butyl (meth)acrylate and t-butyl (meth)acrylate

5-40 mol %,

acrylic monomer containing carboxyl group

0.5-10 mol %, and

other copolymerizable monomers

not more than 20 mol %,

wherein the total amount of monomers Ms is 100 mol %.

11. The method of claim 9 , wherein the core polymer C and the shell polymer S are copolymers of the following monomer mixtures Mc, and Ms, respectively, and the weight ratio of Mc and Ms is 30/70-70/30;

Mc:

methyl methacrylate

20-70 mol %,

at least one (meth)acrylic ester selected from the group consisting of n-butyl (meth)acrylate, iso-butyl (meth)acrylate and t-butyl (meth)acrylate

30-80 mol %, and

other copolymerizable monomers

not more than 10 mol %,

wherein the total amount of monomers Mc is 100 mol %;

Ms:

methyl methacrylate

55-79.5 mol %,

at least one (meth)acrylic ester selected from the group consisting of n-butyl (meth)acrylate, iso-butyl (meth)acrylate and t-butyl (meth)acrylate

20-40 mol %,

acrylic monomer containing carboxyl group

0.5-5 mol %, and

other copolymerizable monomers

not more than 10 mol %,

wherein the total amount of monomers Ms is 100 mol %.

12. The method of claim 9 , wherein the acrylic polymer fine particles have a primary particle diameter of from 340 to 1,460 nm.

13. The method of claim 9 , wherein the acrylic polymer fine particles have a secondary or higher order structure.

14. The method of claim 9 , wherein the acrylic polymer fine particles have a primary particle diameter of more than 1,000 nm.

15. A method for producing acrylic polymer fine particles, comprising:

(1) (a) polymerizing a monomer with a radical initiator in a medium comprising mainly water, wherein the monomer has a solubility of not less than 0.02 mass % in the medium at 20° C. and a polymer of the monomer is insoluble in the medium, thereby forming a polymer dispersion;

(b) adding a monomer mixture dropwise into the polymer dispersion to obtain a dispersion of a coated polymer; and

(2) spray drying the dispersion of a coated polymer to recover particles that consist essentially of acrylic polymer fine particles.

16. The method of claim 15 , wherein the acrylic polymer fine particles comprise primary particles P having a core-shell structure comprising a core polymer C and a shell polymer S, in which the average particle diameter of the primary particles P is not less than 250 nm, the core polymer C and the shell polymer S are copolymers of the following monomer mixtures Mc and Ms, respectively, and the weight ratio of Mc and Ms is 10/90-90/10:

Mc:

methyl methacrylate

20-79.5 mol %,

(meth)acrylic ester of C 2 -C 8 aliphatic alcohol or aromatic alcohol or both

5-40 mol %,

monomer containing carboxyl group or sulfonic acid group

0.5-10 mol %, and

other copolymerizable monomers

not more than 30 mol %,

wherein the total amount of monomers Mc is 100 mol %;

Ms:

methyl methacrylate

20-79.5 mol %,

(meth)acrylic ester of C 2 -C 8 aliphatic alcohol or aromatic alcohol or both

5-40 mol %,

monomer containing carboxyl group or sulfonic acid group,

0.5-10 mol %, and

other copolymerizable monomers

not more than 30 mol %,

wherein the total amount of monomers Ms is 100 mol %.

17. The method of claim 15 , wherein the core polymer C and the shell polymer S are copolymers of the following monomer mixtures Mc and Ms, respectively, and the weight ratio of Mc and Ms is 30/70-70/30;

Mc:

methyl methacrylate

20-70 mol %,

at least one (meth)acrylic ester selected from the group consisting of n-butyl (meth)acrylate, iso-butyl (meth)acrylate and t-butyl (meth)acrylate

30-80 mol %, and

other copolymerizable monomers

not more than 20 mol %,

wherein the total amount of monomers Mc is 100 mol %;

Ms:

methyl methacrylate

30-79.5 mol %,

at least one (meth)acrylic ester selected from the group consisting of n-butyl (meth)acrylate, iso-butyl (meth)acrylate and t-butyl (meth)acrylate

5-40 mol %,

acrylic monomer containing carboxyl group

0.5-10 mol %, and

other copolymeiizable monomers

not more than 20 mol %,

wherein the total amount of monomers Ms is 100 mol %.

18. The method of claim 15 , wherein the core polymer C and the shell polymer S are copolymers of the following monomer mixtures Mc, and Ms, respectively, and the weight ratio of Mc and Ms is 30/70-70/30;

Mc:

methyl methacrylate

20-70 mol %,

at least one (meth)acrylic ester selected from the group consisting of n-butyl (meth)acrylate, iso-butyl (meth)acrylate and t-butyl (meth)acrylate

30-80 mol %, and

other copolymerizable monomers

not more than 10 mol %,

wherein the total amount of monomers Mc is 100 mol %;

Ms:

methyl methacrylate

55-79.5 mol %,

at least one (meth)acrylic ester selected from the group consisting of n-butyl (meth)acrylate, iso-butyl (meth)acrylate and t-butyl (meth)acrylate

20-40 mol %,

acrylic monomer containing carboxyl group

0.5-5 mol %, and

other copolymerizable monomers

not more than 10 mol %1

wherein the total amount of monomers Ms is 100 mol %.

19. The method of claim 15 , wherein the acrylic polymer fine particles have a primary particle diameter of not less than 250 nm.

20. The method of claim 15 , wherein the acrylic polymer fine particles have a primary particle diameter of from 340 to 1,460 nm.

21. The method of claim 15 , wherein the acrylic polymer fine particles have a secondary or higher order structure.

22. The method of claim 15 , wherein the acrylic polymer fine particles have a primary particle diameter of more than 1,000 nm.

23. Acrylic polymer fine particles produced by the method claimed in claim 1 .

24. Acrylic polymer fine particles produced by the method claimed in claim 9 .

25. Acrylic polymer fine particles produced by the method claimed in claim 15 .