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

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 into 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 100 to 50,000 mass ppm in terms of silicon;
• and
• (ii) adding the dilution obtained in the (i) into a lubricating oil,
• wherein the (A) first defoaming agent is (A1) a first polymer, or (A2) a second polymer, or any combination thereof;
• the (A1) first polymer comprises:
• at least one first polymer chain comprising a polysiloxane structure, wherein the polysiloxane structure has a polymerization degree of 5 to 2000 and is represented by the following general formula (1);
• and
• at least one second polymer chain bonded with the first polymer chain, wherein the second polymer chain comprises a repeating unit represented by the following general formula (2);
• the (A2) second polymer is a copolymer of a first monomer component and a second monomer component, wherein the first monomer component is at least one polysiloxane macromonomer selected from compounds represented by the following general formula (7) or (8), and wherein the second monomer component is at least one monomer represented by the following general formula (9);
• and
• the (B) second defoaming agent is a silicone defoaming agent:
• wherein in the general formula (1), polysiloxane repeating units may be in any order;
• R1 and R2 are each independently a C1-18 organic group comprising no fluorine atom;
• R3 and R4 are each independently an organic group comprising at least three fluorine atoms, or a C1-18 organic group comprising no fluorine atom, wherein at least one of R3 and R4 is the organic group comprising at least three fluorine atoms;
• n is an integer of 0 or more;
• m is an integer of 1 or more;
• and n+m is 5 to 2000;
• wherein in the general formula (2), X1 is a repeating unit obtainable by polymerization of an ethylenically unsaturated group;
• Y1 is a side chain consisting of a substituted or unsubstituted C1-40 hydrocarbyl group;
• Z1 is a linking group linking the repeating unit X1 and the side chain Y1;
• wherein in the general formulae (7) and (8), polysiloxane repeating units may be in any order;
• R5 and R6 are each independently a C1-18 organic group comprising no fluorine atom;
• R7 and R8 are each independently an organic group comprising at least three fluorine atoms, or a C1-18 organic group comprising no fluorine atom, wherein at least one of R7 and R8 is the organic group comprising at least three fluorine atoms;
• Q5, Q6, and Q7 are each independently a polymerizable functional group comprising an ethylenically unsaturated group;
• Z5 is a linking group linking the polymerizable functional group Q5 and the polysiloxane moiety;
• Z6 is a linking group linking the polymerizable functional group Q6 and the polysiloxane moiety;
• Z7 is a linking group linking the polymerizable functional group Q7 and the polysiloxane moiety;
• T5 is a non-polymerizable organic group;
• g is an integer of 0 or more;
• h is an integer of 1 or more;
• and g+h is 5 to 2000;
• and
• Q8-Z8—Y8 (9)
• wherein in the general formula (9), Q8 is a polymerizable functional group comprising an ethylenically unsaturated group;
• Y8 is a substituted or unsubstituted C1-40 hydrocarbyl group;
• and Z8 is a linking group linking Q8 and Y8.

A defoaming agent composition comprising:

• (A) a first defoaming agent, the first defoaming agent being (A1) a first polymer, or (A2) a second polymer, or any combination thereof;
• and
• (B) a second defoaming agent being a silicone defoaming agent,
• the (A1) first polymer comprising:
• at least one first polymer chain comprising a polysiloxane structure, the polysiloxane structure having a polymerization degree of 5 to 2000 and being represented by the following general formula (1);
• and
• at least one second polymer chain bonded with the first polymer chain, the second polymer chain comprising a repeating unit represented by the following general formula (2),
• the (A2) second polymer being a copolymer of a first monomer component and a second monomer component, the first monomer component being at least one polysiloxane macromonomer selected from compounds represented by the following general formula (7) or (8), the second monomer component being at least one monomer represented by the following general formula (9):
• wherein in the general formula (1), polysiloxane repeating units may be in any order;
• R1 and R2 are each independently a C1-18 organic group comprising no fluorine atom;
• R3 and R4 are each independently an organic group comprising at least three fluorine atoms, or a C1-18 organic group comprising no fluorine atom, wherein at least one of R3 and R4 is the organic group comprising at least three fluorine atoms;
• n is an integer of 0 or more;
• m is an integer of 1 or more;
• and n+m is 5 to 2000;
• wherein in the general formula (2), X1 is a repeating unit obtainable by polymerization of an ethylenically unsaturated group;
• Y1 is a side chain consisting of a substituted or unsubstituted C1-40 hydrocarbyl group;
• Z1 is a linking group linking the repeating unit X1 and the side chain Y1;
• wherein in the general formulae (7) and (8), polysiloxane repeating units may be in any order;
• R5 and R6 are each independently a C1-18 organic group comprising no fluorine atom;
• R7 and R8 are each independently an organic group comprising at least three fluorine atoms, or a C1-18 organic group comprising no fluorine atom, wherein at least one of R7 and R8 is the organic group comprising at least three fluorine atoms;
• Q5, Q6, and Q7 are each independently a polymerizable functional group comprising an ethylenically unsaturated group;
• Z5 is a linking group linking the polymerizable functional group Q5 and the polysiloxane moiety;
• Z6 is a linking group linking the polymerizable functional group Q6 and the polysiloxane moiety;
• Z7 is a linking group linking the polymerizable functional group Q7 and the polysiloxane moiety;
• T5 is a non-polymerizable organic group;
• g is an integer of 1 or more;
• h is an integer of 1 or more;
• and g+h is 5 to 2000;
• and
• Q8-Z8—Y8 (9)
• wherein in the general formula (9), Q8 is a polymerizable functional group comprising an ethylenically unsaturated group;
• Y8 is a substituted or unsubstituted C1-40 hydrocarbyl group;
• and Z8 is a linking group linking Q8 and Y8.