Aqueous coating composition and process for its production, and process for forming coating film

1. An aqueous coating composition comprising a fluoro-olefin copolymer, a pigment, the following copolymer (1) and an aqueous medium:

Copolymer (1): an A-B type block copolymer which is a copolymer having no fluorine atoms or ionic groups and which comprises hydrophilic blocks (A) having repeating units (a) having a polyoxyethylene chain in the side chain, and hydrophobic blocks (B) having repeating units (b) having a hydrocarbon chain in the side chain.

2. The aqueous coating composition according to claim 1 , wherein the copolymer (1) contains, based on all repeating units, from 20 to 80 mol % of the repeating units (a) and from 80 to 20 mol % of the repeating units (b), and from 80 to 100 mol % of such repeating units (a) are present in the hydrophilic blocks (A).

3. The aqueous coating composition according to claim 1 , wherein the repeating units (a) have, in the side chain, —(OC 2 H 4 ) n OR 1 [wherein n is an integer of from 2 to 30, and R 1 is a hydrogen atom or a C 1-3 monovalent hydrocarbon group].

4. The aqueous coating composition according to claim 3 , wherein the repeating units (a) are polymerized units based on CH 2 ═C(X)-Q 1 -(OC 2 H 4 ) n OR 1

[wherein n and R 1 are as defined above, X is a hydrogen atom or a methyl group, and Q 1 is a carbonyl group, —COOR 3 — (provided that the carbonyl group in —COOR 3 — is bonded to the carbon atom to which X is bonded, and R 3 is a C 3-6 alkylene group) or a single bond].

5. The aqueous coating composition according to claim 1 , wherein the repeating units (b) are polymerized units based on CH 2 ═C(X)-Q 2 -R 2

[wherein R 2 is a C 1-20 hydrocarbon group, X is a hydrogen atom or a methyl group, and Q 2 is —COO— (provided that the carbonyl group in —COO— is bonded to the carbon atom to which X is bonded), a single bond or an oxygen atom].

6. The aqueous coating composition according to claim 1 , wherein the content of the copolymer (1) is from 2 to 20 parts by mass per 100 parts by mass of the pigment contained in the aqueous coating composition.

7. The aqueous coating composition according to claim 1 , wherein the fluoro-olefin copolymer has an acid group which may form a salt.

8. The aqueous coating composition according to claim 7 , wherein the acid group is a carboxy group and/or a carboxylate group.

9. The aqueous coating composition according to claim 1 , wherein the amount of an organic solvent is not higher than 1 mass % based on the total mass of the aqueous coating composition.

10. The aqueous coating composition according to claim 1 , which contains no emulsifier.

11. The aqueous coating composition according to claim 1 , which is for top coating.

12. The aqueous coating composition according to claim 1 , wherein the content of the pigment is from 20 to 200 parts by mass per 100 parts by mass of the fluoro-olefin copolymer.

13. The aqueous coating composition according to claim 1 , wherein the fluoro-olefin copolymer is a copolymer having the following units (f), the following units (g), the following units (h) and the following units (i):

Units (f): repeating units based on a fluoro-olefin,

Units (g): repeating units based on a vinyl monomer, an allyl monomer or an isopropenyl monomer and having, bonded thereto, carboxylate groups, some of which may be in the form of carboxy groups,

Units (h): repeating units based on a vinyl monomer, an allyl monomer or an isopropenyl monomer and having, bonded thereto, no carboxy groups which may form hydroxy groups or salts,

Units (i): repeating units based on a vinyl monomer having a hydroxy group bonded thereto, an allyl monomer having a hydroxy group bonded thereto or an isopropenyl monomer having a hydroxy group bonded thereto and having, bonded thereto, no carboxy groups which may form salts.

14. A process for producing the aqueous coating composition as defined in claim 1 , which comprises a step of producing a fluoro-olefin copolymer aqueous dispersion by obtaining the fluoro-olefin copolymer by a solution polymerization using an organic solvent, and dissolving and/or dispersing the fluoro-olefin copolymer in an aqueous medium; a step of producing a pigment aqueous dispersion by dissolving and/or dispersing a pigment and the copolymer (1) in an aqueous medium; and a step of mixing the fluoro-olefin copolymer aqueous dispersion and the pigment aqueous dispersion.

15. A process for forming a coating film, which comprises a step of blending the aqueous coating composition as defined in claim 1 with a water-soluble or water-dispersible curing agent to obtain an aqueous coating material, and a step of applying the aqueous coating material to a surface of a substrate.