Lubricating oil composition, method for defoaming lubricating oil, and defoaming agent composition

1. A lubricating oil composition comprising:

a lubricant base oil;

(A) a first defoaming agent obtained by polymerizing

(b) at least one defoaming agent monomer in

(a) a polymerization solvent under coexistence of

(c) a polymer soluble in the polymerization solvent; and

(B) a second defoaming agent being a silicone defoaming agent.

2. The lubricating oil composition according to claim 1 ,

the (b) at least one defoaming agent monomer comprising a first monomer, the first monomer giving a repeating unit represented by the following general formula (1) upon polymerization:

wherein in the general formula (1), X 1 is a repeating unit obtained by polymerization of an ethylenic unsaturated group; Y 1 is a side chain comprising a linear or branched polysiloxane structure, the polysiloxane structure comprising a repeating unit represented by the following general formula (2) and having a polymerization degree of 5 to 300; and Z 1 is a linking group linking the repeating unit X 1 and the side chain Y 1 ;

wherein in the general formula (2), R 1 and R 2 are each independently a C 1-18 organic group or combination of two or more C 1-18 organic groups.

3. The lubricating oil composition according to claim 1 ,

wherein a ratio of a content of the (A) first defoaming agent in terms of silicon to a content of the (B) second defoaming agent in terms of silicon is 0.01 to 100.

4. The lubricating oil composition according to claim 1 , wherein

the polymerizing is carried out by dispersion polymerization; and

the (c) polymer soluble in the polymerization solvent is (c1) a polymer dispersant.

5. The lubricating oil composition according to claim 4 ,

the (a) polymerization solvent comprising a hydrocarbon solvent having 6 or more carbons, a mineral oil, a synthetic oil, or an ester oil, or combination thereof.

6. The lubricating oil composition according to claim 4 ,

the (c1) polymer dispersant comprising a polyalkyl (meth)acrylate having a weight average molecular weight of 10,000 to 1,000,000.

7. The lubricating oil composition according to claim 1 ,

wherein the polymerizing is carried out by solution polymerization.

8. The lubricating oil composition according to claim 7 ,

the (c) polymer soluble in the polymerization solvent comprising a polyalkyl (meth)acrylate having a weight average molecular weight of 10,000 to 1,000,000.

9. A method for defoaming a lubricating oil, the method comprising:

(i) dissolving or finely dispersing (A) a first defoaming agent and (B) a second defoaming agent in a diluting solvent, to obtain a dilution, such that a total concentration of the (A) first defoaming agent and the (B) second defoaming agent in the dilution is 500 to 50,000 mass ppm in terms of silicon; and

(ii) adding the dilution obtained in the step (i) to a lubricating oil,

the (A) first defoaming agent being obtained by a process, the process comprising:

polymerizing (b) at least one defoaming agent monomer in (a) a polymerization solvent under coexistence of (c) a polymer soluble in the polymerization solvent; and

the (B) second defoaming agent being a silicone defoaming agent.

10. The method according to claim 9 ,

the diluting solvent comprising a hydrocarbon solvent having 6 or more carbons, a mineral oil, a synthetic oil, an ester oil, an aliphatic ether having 4 or more carbons, an ester of an aliphatic monocarboxylic acid having 2 or more carbons and a monoalcohol having 1 to 5 carbons, an aliphatic ketone having 3 or more carbons, an aliphatic alcohol having 4 or more carbons, or a halogenated hydrocarbon, or combination thereof.

11. The method according to claim 9 ,

wherein the polymerizing is carried out by dispersion polymerization; and

the (c) polymer soluble in the polymerization solvent is (c1) a polymer dispersant.

12. The method according to claim 9 ,

wherein the polymerizing is carried out by solution polymerization.

13. A defoaming agent composition comprising:

(A) a first defoaming agent obtained by polymerizing (b) at least one defoaming agent monomer in (a) a polymerization solvent under coexistence of (c) a polymer soluble in the polymerization solvent; and

(B) a second defoaming agent being a silicone defoaming agent.

14. The defoaming agent composition according to claim 13 , further comprising:

a diluting solvent, the diluting solvent comprising a hydrocarbon solvent having 6 or more carbons, a mineral oil, a synthetic oil, an ester oil, an aliphatic ether having 4 or more carbons, an ester of an aliphatic monocarboxylic acid having 2 or more carbons and a monoalcohol having 1 to 5 carbons, an aliphatic ketone having 3 or more carbons, an aliphatic alcohol having 4 or more carbons, or a halogenated hydrocarbon, or combination thereof.

15. The defoaming agent composition according to claim 13 ,

wherein the polymerization is carried out by dispersion polymerization; and

the (c) polymer soluble in the polymerization solvent is (c1) a polymer dispersant.

16. The defoaming agent composition according to claim 13 ,

wherein the polymerization is carried out by solution polymerization.