Unsaturated ester resin composition, unsaturated ester-cured product, and manufacturing method therefor

1. An unsaturated ester resin composition comprising

60 to 99 parts by mass of an unsaturated ester resin, wherein the unsaturated ester resin comprises (1) a vinyl ester obtained from an unsaturated monocarboxylic acid and a polyvalent epoxide, and an ethylenically unsaturated monomer, or (2) an unsaturated polyester obtained from a polyhydric alcohol and an unsaturated polyvalent carboxylic acid or an anhydride thereof, and the ethylenically unsaturated monomer,

0.5 to 20 parts by mass of an epoxy resin,

0.1 to 20 parts by mass of crosslinked rubber particles having a number average particle diameter of 20 nm to 600 nm, wherein the crosslinked rubber particles are obtained by polymerizing a vinyl monomer in the presence of one or more rubber polymers selected from the group consisting of a butadiene rubber, a butadiene-styrene rubber, a butadiene-butyl acrylate rubber, a butyl acrylate rubber, and an organosiloxane rubber, and

the unsaturated ester resin composition is produced by a method comprising:

mixing an aqueous medium containing crosslinked rubber particles dispersed therein with an organic solvent having a solubility in water of not lower than 5% by mass and not higher than 40% by mass at 20° C.,

mixing excess water with the resulting mixture to extract the crosslinked rubber particles in an organic solvent phase,

removing a water phase not containing the crosslinked rubber particles to obtain a loose aggregate of crosslinked rubber particles containing an organic solvent,

adding an epoxy resin to the loose aggregate to give a crosslinked rubber particles-dispersed epoxy resin,

removing the organic solvent from the crosslinked rubber particles-dispersed epoxy resin to obtain the crosslinked rubber particles-containing epoxy resin, and

mixing the crosslinked rubber particles-containing epoxy resin with the unsaturated ester resin.

2. The unsaturated ester resin composition according to claim 1 , wherein the crosslinked rubber particles are dispersed in the state of primary particles.

3. The unsaturated ester resin composition according to claim 1 , wherein the crosslinked rubber particles are dispersed in the state of primary particles in the epoxy resin after the curing of the unsaturated ester resin composition.

4. The unsaturated ester resin composition according to claim 1 , which has a sea-island structure including the epoxy resin as an island part and the unsaturated ester resin as a sea part after the curing of the unsaturated ester resin composition.

5. The unsaturated ester resin composition according to claim 1 , wherein the unsaturated ester resin is composed of 51% to 80% by mass of (1) the vinyl ester obtained from an unsaturated monocarboxylic acid and a polyvalent epoxide, or (2) the unsaturated polyester obtained from a polyhydric alcohol and an unsaturated polyvalent carboxylic acid or an anhydride thereof, and 20% to 49% by mass of the ethylenically unsaturated monomer.

6. A method for producing an unsaturated ester cured product, comprising:

adding 0.1 to 5 parts by mass of a radical initiator to 100 parts by mass of the unsaturated ester resin composition according to claim 1 and curing the resulting mixture.

7. An unsaturated ester cured product obtained by adding 0.1 to 5 parts by mass of a radical initiator to 100 parts by mass of the unsaturated ester resin composition according to claim 1 , and curing the resulting mixture.

8. The unsaturated ester cured product according to claim 7 , wherein the crosslinked rubber particles are dispersed in the state of primary particles.

9. The unsaturated ester cured product according to claim 7 , wherein the crosslinked rubber particles are dispersed in the state of primary particles in the epoxy resin.

10. The unsaturated ester cured product according to claim 7 , which has a sea-island structure including the epoxy resin as an island part and the unsaturated ester resin as a sea part.

11. The unsaturated ester resin composition according to claim 1 , which consists of the unsaturated ester resin, the epoxy resin, the crosslinked rubber particles, and a radical initiator and/or a curing accelerator.