Lubricant composition

Abstract

To provide a lubricant composition excellent in shear stability and emulsion formation inhibition after mixing with water.SOLUTION: A lubricant composition includes at least one base oil selected from mineral oil base lubrication oil and synthetic oil base lubrication oil, a predetermined weight average molecular weight of polyalkyl methacrylate base viscosity index improver, dialkyl zinc thiophosphate x1 represented by formula (1), dialkyl zinc thiophosphate x2 represented by formula (2), and acidic phosphate ester amine salt Y, and satisfies formula (a): 1.0≤PX1 / PX2≤10.5. In the formula (a), PX1 and PX2 represent the amount of X1, X2 in terms of phosphorus concentration relative to the total mass of each lubricant composition. R1 to R4 independently represent a linear or branched C10-20 primary alkyl group, and R5 to R8 independently represent a linear or branched C3-6 primary or secondary alkyl group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to lubricating oil compositions. [Background technology]

[0002] Agricultural machinery includes tractors used for leveling the ground, rice transplanters used for cultivation and management, and binders or combines used for harvesting, with tractors being the most widely used.

[0003] In recent years, as the power output of agricultural machinery such as tractors has increased, the load on gears and the like has increased, and therefore it is desirable for lubricating oil compositions used in agricultural machinery to have high shear stability.With this demand as a background, for example, Patent Document 1 describes a lubricating oil composition for agricultural machinery that contains at least one base oil selected from the group consisting of mineral oil-based base oils and synthetic oil-based base oils, and a polyalkyl methacrylate-based viscosity index improver having a specific molecular weight, and that has a kinematic viscosity at 100°C, a kinematic viscosity reduction rate at 100°C in an ultrasonic shear stability test, and a Brookfield viscosity at -40°C within specified ranges. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2021 / 210068 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, lubricating oil compositions used in agricultural machinery are desired to have high shear stability. On the other hand, agricultural machinery is sometimes used in environments prone to contact with water, such as rice paddies, and water contamination into lubricating oil compositions is often observed during use. Therefore, it is necessary for agricultural machinery to maintain its functionality even in water-contaminated environments. In particular, agricultural machinery is prone to water contamination in its oil tank when used in rice paddies or during machine cleaning. Water contamination can cause emulsion formation in the lubricating oil composition, leading to filter clogging. Therefore, lubricating oil compositions are desired to have excellent emulsion formation suppression properties after water contamination. For example, the lubricating oil composition for agricultural machinery disclosed in Patent Document 1 contains a polyalkyl methacrylate-based viscosity index improver having a specific molecular weight, achieving excellent shear stability. However, further improvements are required to achieve both suppression of emulsion formation after water contamination and shear stability.

[0006] In view of the above circumstances, an object of one embodiment of the present disclosure is to provide a lubricating oil composition that has excellent shear stability and excellent emulsion formation suppression properties after water is mixed in. [Means for solving the problem]

[0007] The present disclosure includes the following aspects.

[0008] <1> At least one base oil selected from mineral oil-based lubricating oils and synthetic oil-based lubricating oils; a polyalkyl methacrylate-based viscosity index improver having a weight average molecular weight of 20,000 to 8,0000; Zinc dialkylthiophosphate X1 represented by the following formula (1), Zinc dialkylthiophosphate X2 represented by the following formula (2), an acidic phosphate amine salt Y represented by the following formula (3); Contains A lubricating oil composition that satisfies the relationship represented by the following formula (a):

[0009] [ka]

[0010] In formula (1), R 1 , R 2 , R 3 and R 4 each independently represents a linear or branched primary alkyl group having 10 to 20 carbon atoms.

[0011] [ka]

[0012] In formula (2), R 5 , R 6 , R 7 and R 8 each independently represents a linear or branched primary or secondary alkyl group having 3 to 6 carbon atoms.

[0013] [ka]

[0014] In formula (3), R, R 5 and R 6 each independently represents a hydrogen atom or a hydrocarbon group having 3 to 30 carbon atoms, and R 5 and R 6 At least one of these represents a hydrocarbon group.

[0015] 1.0≦P X1 / P X2 ≦10.5(a) In formula (a), P X1 represents the content of zinc dialkylthiophosphate X1 represented by formula (1) in terms of phosphorus concentration relative to the total mass of the lubricating oil composition, and P X2 represents the content of zinc dialkylthiophosphate X2 represented by formula (2) converted into a phosphorus concentration relative to the total mass of the lubricating oil composition.

[0016] <2> R in Equation (1) 1 , R2 , R 3 and R 4 are each independently a linear primary alkyl group having 10 to 12 carbon atoms, <1> The lubricating oil composition according to claim 1. <3> R in Equation (2) 5 , R 6 , R 7 and R 8 are each independently a primary alkyl group having 4 or 5 carbon atoms, <1> or <2> The lubricating oil composition according to claim 1. <4> R in Equation (3) 9 and R 10 are each independently at least one hydrocarbon group having 3 to 30 carbon atoms selected from the group consisting of an alkyl group, an aryl group, an alkenyl group, an alkylaryl group, and an arylalkyl group, <1> ~ <3> 1. The lubricating oil composition according to claim 1 .

[0017] <5> The polyalkyl methacrylate-based viscosity index improver contains a polyalkyl methacrylate having a structural unit represented by the following formula (1a) and a structural unit represented by the following formula (1b): <1> ~ <4> 1. The lubricating oil composition according to claim 1 .

[0018] [ka]

[0019] In formula (la) and formula (lb), R 11 represents a hydrogen atom or an alkyl group having 1 to 24 carbon atoms, and R 12 represents a hydrogen atom or a methyl group, and R 13 represents an alkyl group having 1 to 24 carbon atoms substituted with an amino group, and m and n each independently represent an integer of 1 or more.

[0020] <7> It is a lubricant for agricultural machinery. <1> ~ <5> 1. The lubricating oil composition according to claim 1 . [Effects of the Invention]

[0021] According to one embodiment of the present disclosure, it is possible to provide a lubricating oil composition that has excellent shear stability and excellent ability to inhibit emulsion formation after water is mixed in. DETAILED DESCRIPTION OF THE INVENTION

[0022] The lubricating oil composition according to the present disclosure will be described in detail below. The following description may be based on representative embodiments, but the lubricating oil composition according to the present disclosure is not limited to such embodiments.

[0023] In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In the present disclosure, when a plurality of substances corresponding to each component are present in the composition, the amount of each component in the composition means the total amount of the corresponding substances present in the composition, unless otherwise specified. In the present disclosure, "mass %" and "weight %" are synonymous. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

[0024] In the present disclosure, the term "polyalkyl methacrylate-based" means that it contains structural units derived from alkyl esters of methacrylic acid.

[0025] In this disclosure, "JIS" is used as an abbreviation for Japanese Industrial Standards.

[0026] In this disclosure, "at least one base oil selected from mineral oil-based lubricating oils and synthetic oil-based lubricating oils," "a polyalkyl methacrylate-based viscosity index improver having a weight-average molecular weight of 20,000 to 80,000," "zinc dialkylthiophosphate X1 represented by formula (1)," "zinc dialkylthiophosphate X2 represented by formula (2)," and "acidic phosphate amine salt Y represented by formula (3)" may be abbreviated as "specific base oil," "specific viscosity index improver," "zinc dialkylthiophosphate X1," "zinc dialkylthiophosphate X2," and "acidic phosphate amine salt Y," respectively.

[0027] The lubricating oil composition according to the present disclosure contains a specific base oil, a specific viscosity index improver, a zinc dialkylthiophosphate X1, a zinc dialkylthiophosphate X2, and an acidic phosphate amine salt Y, and satisfies the relationship represented by the following formula (a): 1.0≦P X1 / P X2 ≦10.5(a) In formula (a), P X1 represents the content of zinc dialkylthiophosphate X1 in terms of phosphorus concentration relative to the total mass of the lubricating oil composition, and P X2 represents the content of zinc dialkylthiophosphate X2 converted into phosphorus concentration relative to the total mass of the lubricating oil composition.

[0028] The lubricating oil composition according to the present disclosure inhibits emulsion formation after water is mixed in and has excellent shear stability. The reason for this is unclear, but is speculated as follows. However, the speculation below is not intended to limit the lubricating oil composition according to the present disclosure, but is provided as an example.

[0029] It has been found that the inclusion of a polyalkyl methacrylate-based viscosity index improver (specific viscosity index improver) having a weight-average molecular weight of 20,000 to 80,000 is an effective method for improving the shear stability of a lubricating oil composition (see Patent Document 1). However, it has also been found that lubricating oil compositions containing specific viscosity index improvers tend to easily form emulsions when they come into contact with water. In contrast, the lubricating oil composition according to the present disclosure contains a specific base oil that has good compatibility with various additive components, a specific viscosity index improver, two types of zinc dialkyldithiophosphates having specific structures (i.e., zinc dialkylthiophosphates X1 and X2), and an acidic phosphate amine salt Y, and the contents of zinc dialkylthiophosphates X1 and X2 satisfy the relationship represented by formula (a), thereby providing excellent shear stability and excellent suppression of emulsion formation after the addition of water.

[0030] Each component contained in the lubricating oil composition according to the present disclosure will be described in detail below.

[0031] <Base oil> The lubricating oil composition according to the present disclosure contains at least one base oil (specific base oil) selected from the group consisting of mineral base oils and synthetic base oils. From the viewpoint of solubility of additives, the lubricating oil composition according to the present disclosure contains at least one specific base oil.

[0032] The lubricating oil composition according to the present disclosure may contain, as the specific base oil, a single type selected from mineral oil-based base oils or synthetic oil-based base oils, or may contain a mixed oil of a combination of two or more types selected from mineral oil-based base oils and synthetic oil-based base oils.

[0033] The specific base oil is not particularly limited as long as it is included in either a mineral base oil or a synthetic base oil, and can be selected from mineral base oils and synthetic base oils obtained by various production methods. From the viewpoint of additive solubility, the specific base oil is preferably one or more types selected from mineral base oils.

[0034] Mineral base oils include those obtained by various production methods. For example, preferred examples include paraffinic mineral oils that are highly refined by subjecting hydrorefined oil, catalytic isomerized oil, etc. to solvent dewaxing or hydrodewaxing treatment.

[0035] Examples of hydrorefined oils include raffinates obtained by solvent refining a base oil raw material using an aromatic extraction solvent such as phenol or furfural, and hydrotreated oils obtained by hydrotreating a silica-alumina-supported hydrotreating catalyst such as cobalt or molybdenum. In particular, hydrorefined oils obtained by a hydrocracking process or an isomerization process and exhibiting a high viscosity index (specifically, 110 or more) are suitable as mineral oil-based base oils in the present disclosure.

[0036] Examples of synthetic base oils include base oils synthesized by the Fischer-Tropsch reaction using gases such as methane as a raw material, poly-α-olefin oligomers, polybutene, alkylbenzene, polyol esters, polyglycol esters, polyethylene propylenes, hindered esters, and dibasic acid esters.

[0037] The lubricating oil composition according to the present disclosure preferably contains only a specific base oil as the base oil.

[0038] The content of the specific base oil is not particularly limited as long as it is an amount that functions as a base oil, and can be, for example, 30 to 99.9 mass % relative to the total amount of the lubricating oil composition.

[0039] The kinematic viscosity of the base oil at 100°C is 1.00mm 2 / s~10.00mm 2 / s, and 2.00 mm 2 / s~8.00mm 2 / s is more preferable, and 2.00 mm 2 / s~7.00mm 2 It is more preferable that the ratio is / s.

[0040] The viscosity index of the base oil is preferably 110 or greater, and more preferably 120 or greater.

[0041] In the present disclosure, the kinematic viscosity of the base oil is a value measured according to JIS K2283 (2000). Even if the base oil is a mixed oil, the kinematic viscosity at 100°C should be confirmed according to JIS K2283 (2000). In the present disclosure, the viscosity index of a base oil is a value measured according to JIS K2283 (2000). When the base oil is a mixed oil, the viscosity index is also confirmed according to JIS K2283 (2000). If catalog values ​​for the kinematic viscosity and / or viscosity index of the base oil can be confirmed, the catalog values ​​shall be used.

[0042] <Viscosity index improver> The lubricating oil composition according to the present disclosure contains a polyalkyl methacrylate-based viscosity index improver (specific viscosity index improver) having a weight average molecular weight (polystyrene equivalent: Mw) of 20,000 to 80,000.

[0043] In the present disclosure, the weight average molecular weight is a molecular weight measured by gel permeation chromatography (GPC) and converted into a standard polystyrene for molecular weight calculation.

[0044] The specific viscosity index improver has a weight average molecular weight (polystyrene equivalent: Mw) of 20,000 to 80,000, preferably 25,000 to 75,000, and more preferably 30,000 to 70,000.

[0045] By setting the weight-average molecular weight (polystyrene equivalent: Mw) of the specific viscosity index improver to 20,000 or more, the viscosity index improving effect required for the lubricating oil composition can be obtained, and by setting the weight-average molecular weight (polystyrene equivalent: Mw) to 80,000 or less, the lubricating oil composition can be stabilized against mechanical shear stress both initially and over the long term.

[0046] The specific viscosity index improver may be a dispersant type viscosity index improver or a non-dispersant type viscosity index improver. In this disclosure, a viscosity index improver being "dispersant" means that it has a polar group such as an amino group or an amide group (preferably on a side chain), and being "non-dispersant" means that it does not have a polar group. Here, the main chain refers to the relatively longest connecting chain among the chain portions in the polymer, and the side chain refers to the chain connected to the main chain of the polymer.

[0047] One suitable embodiment of the specific viscosity index improver is a polyalkyl methacrylate (hereinafter also referred to as "polyalkyl methacrylate (1)") having a structural unit represented by the following formula (Ia) and a structural unit represented by the following formula (Ib):

[0048] The polyalkyl methacrylate (1) has a weight average molecular weight (polystyrene equivalent: Mw) in the range of 20,000 to 80,000, and is one embodiment of a dispersant-type specific viscosity index improver.

[0049] [ka]

[0050] In formulas (Ia) and (Ib), R 11 represents a hydrogen atom or an alkyl group having 1 to 24 carbon atoms, and R 12 represents a hydrogen atom or a methyl group, and R 13 represents an alkyl group having 1 to 24 carbon atoms substituted with an amino group, and m and n each independently represent an integer of 1 or more.

[0051] The polyalkyl methacrylate (1) may be a random copolymer or a block copolymer.

[0052] In formula (Ib), R 13 In the formula (I), the amino group substituting the alkyl group having 1 to 24 carbon atoms is not particularly limited and may be any of a primary amino group, a secondary amino group, and a tertiary amino group. Suitable examples of the amino group include tertiary amino groups such as a dimethylamino group and a diethylamino group.

[0053] One suitable embodiment of the specific viscosity index improver is a polyalkyl methacrylate (hereinafter also referred to as polyalkyl methacrylate (2)) that has a structural unit represented by the following formula (Ic) and has no polar group. Polyalkyl methacrylate (2) has a weight average molecular weight (polystyrene equivalent: Mw) in the range of 20,000 to 80,000, and is one embodiment of a non-dispersant specific viscosity index improver.

[0054] [ka]

[0055] In formula (Ic), R 14 represents a hydrogen atom or a methyl group, and R 15 represents a hydrogen atom or an alkyl group having 1 to 24 carbon atoms, and o is an integer of 1 or more.

[0056] The content of the specific viscosity index improver is preferably 5 to 17 mass %, more preferably 6 to 15 mass %, and even more preferably 6.5 to 14 mass %, relative to the total mass of the lubricating oil composition. When the content of the specific viscosity index improver is within the above range, the shear stability tends to be more excellent.

[0057] The specific viscosity index improver may be a synthetic product or a commercially available product.

[0058] The lubricating oil composition according to the present disclosure may contain only one type of specific viscosity index improver, or may contain two or more types.

[0059] The lubricating oil composition according to the present disclosure may further contain a viscosity index improver other than the specified viscosity index improver (hereinafter referred to as "other viscosity index improver"), as long as the effects of the present disclosure can be obtained. The lubricating oil composition according to the present disclosure may contain only the specified viscosity index improver as a viscosity index improver. From the viewpoint of viscosity adjustment, the other viscosity index improver may be a polyalkyl methacrylate-based viscosity index improver having a weight average molecular weight (polystyrene equivalent: Mw) of more than 80,000.

[0060] When other specific viscosity index improvers are contained, the content of the other specific viscosity index improvers is preferably 5 mass % or less, more preferably 4 mass % or less, and even more preferably 3 mass % or less, based on the total mass of the lubricating oil composition.

[0061] When the specific viscosity index improver and other viscosity index improvers are mixed with the base oil, they may be mixed as they are, or may be mixed as a diluent contained in diluent oil.

[0062] <Zinc dialkylthiophosphate x1> The lubricating oil composition according to the present disclosure contains zinc dialkylthiophosphate X1 (zinc dialkylthiophosphate X1) represented by the following formula (1).

[0063] [ka]

[0064] In formula (1), R 1 , R 2 , R 3 and R 4 each independently represents a linear or branched primary alkyl group having 10 to 20 carbon atoms. When the primary alkyl group has 10 to 20 carbon atoms, emulsion formation in the lubricating oil composition tends to be inhibited and the lubricating oil composition also tends to have excellent thermal stability, even when the lubricating oil composition is exposed to a high-temperature environment after water is mixed into the lubricating oil composition.

[0065] From the viewpoint of stability against hydrolysis, R 1 , R 2 , R 3 and R 4 The number of carbon atoms in the primary alkyl groups represented by the following formula (I) is preferably 10 to 16, more preferably 10 to 14, even more preferably 10 to 12, and particularly preferably 12.

[0066] In addition, from the viewpoint of suppressing emulsion formation when water is mixed, R1 , R 2 , R 3 and R 4 It is preferable that all of the primary alkyl groups represented by the following formula are linear.

[0067] In this specification, a primary alkyl group means that in the zinc dialkyldithiophosphate, the carbon atom at the α-position adjacent to the oxygen atom bonded to the phosphorus atom is a primary carbon (i.e., -CH2-O-), and a secondary alkyl group means that in the zinc dialkyldithiophosphate, the carbon atom at the α-position adjacent to the oxygen atom bonded to the phosphorus atom is a secondary carbon (i.e., >CH-O-).

[0068] From the viewpoint of maintaining stability to water and extreme pressure properties in a high-temperature environment, the content of zinc dialkylthiophosphate X1, calculated as phosphorus concentration, is preferably 0.045 to 0.09 mass%, more preferably 0.05 to 0.085 mass%, and even more preferably 0.055 to 0.08 mass%, based on the total mass of the lubricating oil composition.

[0069] <Zinc dialkylthiophosphate x2> The lubricating oil composition according to the present disclosure contains zinc dialkylthiophosphate X2 (zinc dialkylthiophosphate X2) represented by the following formula (2).

[0070] [ka]

[0071] In formula (2), R 5 , R 6 , R 7 and R 8 R each independently represents a linear or branched primary or secondary alkyl group having 3 to 6 carbon atoms. 5 , R 6 , R 7 and R 8However, when each of the groups is independently a primary or secondary alkyl group having 3 to 6 carbon atoms, the anti-wear properties tend to be excellent, and when the lubricating oil composition is exposed to an ambient temperature environment of about 25°C after water is mixed into the lubricating oil composition, the lubricating oil composition is even more effective in suppressing the formation of emulsion.

[0072] From the above perspective, R 5 , R 6 , R 7 and R 8 is preferably a primary alkyl group having 4 to 6 carbon atoms, and more preferably a primary alkyl group having 4 or 5 carbon atoms.

[0073] The zinc dialkylthiophosphate X2 preferably has at least one of the above-mentioned preferred alkyl groups in its structure, more preferably two or more, even more preferably three or more, and particularly preferably four. 5 , R 6 , R 7 and R 8 are each independently a primary alkyl group, and the primary alkyl group preferably has 4 or 5 carbon atoms.

[0074] From the viewpoint of stability to water in a room temperature environment and suitability for sealing materials, the content of zinc dialkylthiophosphate X2 is preferably 0.005 to 0.045 mass %, more preferably 0.006 to 0.040 mass %, and even more preferably 0.008 to 0.035 mass %, calculated as a phosphorus concentration relative to the total mass of the lubricating oil composition.

[0075] The total content of the zinc dialkylthiophosphate X1 and the zinc dialkylthiophosphate X2 is preferably 0.05% by mass to 0.14% by mass, more preferably 0.055% by mass to 0.13% by mass, and even more preferably 0.06% by mass to 0.12% by mass, calculated as a phosphorus concentration, relative to the total mass of the composition.

[0076] In the present disclosure, the content of zinc dialkyldithiophosphate can be confirmed, for example, by subjecting the lubricating oil composition to inductively coupled plasma (ICP) emission spectroscopy or the like. The content of zinc dialkylthiophosphate converted into phosphorus concentration can be calculated by dividing the content (mass %) confirmed by the above method by the atomic weight of phosphorus (=30.97).

[0077] <<Relationship expressed by formula (a)>> The lubricating oil composition according to the present disclosure satisfies the relationship represented by the following formula (a): 1.0≦P X1 / P X2 ≦10.5(a) In formula (a), P X1 represents the content of zinc dialkylthiophosphate X1 in terms of phosphorus concentration relative to the total mass of the lubricating oil composition, and P X2 represents the content of zinc dialkylthiophosphate X2 converted into phosphorus concentration relative to the total mass of the lubricating oil composition.

[0078] That is, the lubricating oil composition according to the present disclosure contains a specific base oil, a specific viscosity index improver, zinc dialkylthiophosphate X1, zinc dialkylthiophosphate X2, and an acidic phosphate amine salt Y, and by satisfying the relationship represented by formula (a), the lubricating oil composition has excellent shear stability and suppresses the formation of emulsion after mixing with water.

[0079] On the other hand, P X1 / P X2 If P is less than 1.0, the lubricating oil composition is likely to become cloudy due to emulsification, X1 / P X2 If the ratio exceeds 10.5, emulsion will be generated after mixing with water, causing clogging of the filter.

[0080] The lubricating oil composition according to the present disclosure preferably satisfies the relationship represented by the following formula (a1), and more preferably satisfies the relationship represented by the following formula (a2). 1.5≦P X1 / P X2 ≦10.0 (a1) 2.0≦P X1 / P X2 ≦9.8 (a2)

[0081] <<Other zinc dialkyldithiophosphates>> The lubricating oil composition according to the present disclosure may contain zinc dialkyldithiophosphates other than zinc dialkyldithiophosphates X1 and X2 (hereinafter referred to as "other zinc dialkyldithiophosphates") as long as the effects of the present disclosure can be obtained, but it is preferable that the lubricating oil composition contain only zinc dialkyldithiophosphates X1 and X2.

[0082] When the lubricating oil composition according to the present disclosure contains other zinc dialkyldithiophosphates, from the viewpoints of suppressing emulsion formation and improving the friction characteristics of a wet clutch, the content of the other zinc dialkyldithiophosphates is preferably 0.05% by mass or less, more preferably 0.03% by mass or less, and even more preferably 0.01% by mass or less, calculated as phosphorus concentration, relative to the total mass of the lubricating oil composition.

[0083] <Amine salt of acidic phosphate ester> The lubricating oil composition according to the present disclosure contains an acidic phosphate amine salt Y (acidic phosphate amine salt Y) represented by the following formula (3).

[0084] [ka]

[0085] In formula (3), R, R 9 and R 10 each independently represents a hydrogen atom or a hydrocarbon group having 3 to 30 carbon atoms, and R 9 and R 10 At least one of these represents a hydrocarbon group.

[0086] R 9 or R 10Examples of the hydrocarbon group having 3 to 30 carbon atoms represented by the formula (I) include an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group. The aliphatic hydrocarbon group may be saturated or unsaturated, and may be linear or branched. The alicyclic hydrocarbon group may be saturated or unsaturated. The aromatic hydrocarbon group may have a substituent. The hydrocarbon group having 3 to 30 carbon atoms may be a hydrocarbon group containing a halogen atom.

[0087] R 9 and R 10 From the viewpoints of suppressing the formation of an emulsion after mixing with water and achieving excellent filterability and extreme pressure properties, the hydrocarbon groups having 3 to 30 carbon atoms represented by the following formula (I) are each independently preferably a hydrocarbon group having 3 to 30 carbon atoms selected from an alkyl group, an aryl group, an alkenyl group, an alkylaryl group, and an arylalkyl group, and more preferably an alkyl group having 3 to 30 carbon atoms.

[0088] The hydrocarbon group having 3 to 30 carbon atoms represented by R includes the above-mentioned R 9 or R 10 Examples of the hydrocarbon groups include those having 3 to 30 carbon atoms and represented by the following formula: Among these, the hydrocarbon group having 3 to 30 carbon atoms represented by R is preferably an aliphatic hydrocarbon group, more preferably an aliphatic hydrocarbon group having 6 to 20 carbon atoms, still more preferably an aliphatic hydrocarbon group having 12 to 14 carbon atoms, and particularly preferably a branched aliphatic hydrocarbon group having 12 to 14 carbon atoms.

[0089] In one embodiment, the acidic phosphate amine salt Y is represented by the formula (3): 9 and R 10 Preferably, each of R independently represents an alkyl group having 8 or 10 carbon atoms, and R represents a branched alkyl group having 12 or 14 carbon atoms.

[0090] Examples of the acidic phosphate amine salt Y include di-2-ethylhexyl acid phosphate amine salt, diisodecyl acid phosphate amine salt, dilauryl acid phosphate amine salt, dioleyl acid phosphate amine salt, diphenyl acid phosphate amine salt, dicresyl acid phosphate amine salt, S-octylthioethyl acid phosphate amine salt, and S-dodecylthioethyl acid phosphate amine salt. Among these, di-2-ethylhexyl acid phosphate amine salt and diisodecyl acid phosphate amine salt are preferred.

[0091] From the viewpoint of extreme pressure properties, the acidic phosphate amine salt Y is preferably di-2-ethylhexyl acid phosphate oleylamine salt or diisodecyl acid phosphate oleylamine salt.

[0092] Acidic phosphate ester amine salt Y content P Y is preferably 0.014 to 0.025 mass %, more preferably 0.015 to 0.024 mass %, and even more preferably 0.016 to 0.022 mass %, calculated as a phosphorus concentration, relative to the total amount of the lubricating oil composition. Acidic phosphate ester amine salt Y content P Y However, if the phosphorus concentration is 0.014% by mass to 0.025% by mass relative to the total mass of the composition, anti-wear properties and anti-oxidation properties are sufficiently ensured, and the emulsion formation suppression properties are excellent. The acidic phosphate amine salt Y may contain one kind alone or two or more kinds in combination. In addition, when the acidic phosphate ester amine salt Y contains two or more kinds of acidic phosphate ester amine salts Y, the content P Y means the total content.

[0093] Acidic phosphate ester amine salt Y content P Y is the content P of zinc dialkyldithiophosphate X mentioned above. X It can be measured by the same method as above.

[0094] In the lubricating oil composition according to the present disclosure, the total content P of zinc dialkylthiophosphates X1 and X2 X1+X2 and the content P of acidic phosphate ester amine salt Y Y From the viewpoint of shear stability and suppressing the formation of an emulsion after water is mixed, it is preferable that the relationship of the following formula (b) be satisfied. 3.0≦P X1+X2 / P Y ≦6.0 Formula (b)

[0095] The lubricating oil composition according to the present disclosure more preferably satisfies the relationship represented by the following formula (b1), and even more preferably satisfies the relationship represented by the following formula (b2). 3.5≦P X1+X2 / P Y ≦5.8 (b1) 3.8≦P X1+X2 / P Y ≦5.5 (b2)

[0096] <Other additives> In addition to the components described above, the lubricating oil composition according to the present disclosure may contain known additives as needed, such as metal detergents, friction modifiers, antiwear agents, oiliness agents, extreme pressure agents, rust inhibitors, ashless dispersants, antioxidants, pour point depressants, antifoaming agents, colorants, agricultural machinery hydraulic oil additive packages, and various lubricating oil additive packages containing at least one of these additives. Furthermore, one additive may perform two or more functions. A package additive refers to a mixture of two or more additives.

[0097] Metallic detergents include alkaline earth metal salts such as alkaline earth metal sulfonates, alkaline earth metal phenates, and alkaline earth metal salicylates.

[0098] Examples of the friction modifier include organic molybdenum compounds, polyhydric alcohol partial ester compounds, amine compounds, amide compounds, ether compounds, sulfurized esters, phosphate esters, and diol compounds.

[0099] Examples of the anti-wear agent include metal dithiophosphates, metal thiophosphates, sulfur compounds, phosphates, phosphites, acid phosphates, and amine salts thereof.

[0100] Examples of oily agents include oleic acid, stearic acid, higher alcohols, amine compounds, amide compounds, sulfurized oils and fats, acid phosphates, and acid phosphites.

[0101] Examples of extreme pressure agents include hydrocarbon sulfides, sulfurized oils and fats, phosphates, phosphites, chlorinated paraffins, and chlorinated diphenyls.

[0102] Examples of the rust inhibitor include carboxylic acids and their amine salts, ester compounds, sulfonates, and boron compounds.

[0103] Ashless dispersants include succinimides having polyalkenyl groups and their boron derivatives.

[0104] Examples of the antioxidant include amine compounds, phenol compounds, and sulfur compounds.

[0105] Metal deactivators include benzotriazole, thiadiazole, alkenyl succinate, and the like.

[0106] Pour point depressants include chlorinated paraffin-naphthalene condensates, alkylated polystyrenes, and the like.

[0107] Examples of the antifoaming agent include silicone compounds such as dimethylpolysiloxane, fluorosilicone compounds, and ester compounds.

[0108] <Physical properties of lubricating oil composition> <<Kinematic viscosity and viscosity index>> The lubricating oil composition of the present disclosure has a kinematic viscosity at 100°C of 6.0 mm 2 / s~15.0mm 2 / s, and 7.0 mm 2 / s~13.0mm 2 / s is more preferable, and 7.5 mm 2 / s~11.0mm 2 / s, more preferably 7.5 mm / s to 9.0 mm2 / s is particularly preferable.

[0109] The viscosity index of the lubricating oil composition is preferably 150 or greater, more preferably 170 or greater, and even more preferably 190 or greater.

[0110] When the kinematic viscosity at 100°C and viscosity index of the lubricating oil composition fall within the above ranges, the lubricity is maintained and the low-temperature startability is also excellent.

[0111] The kinematic viscosity and viscosity index at 100°C are values ​​measured in accordance with JIS K 2283 (2000) (ASTM D445).

[0112] <<Kinematic viscosity reduction rate>> The lubricating oil composition according to the present disclosure preferably has a kinematic viscosity reduction rate at 100°C in an ultrasonic shear stability test (hereinafter also simply referred to as "kinematic viscosity reduction rate") of 10% or less, more preferably 6% or less. A smaller value of the kinematic viscosity reduction rate means better shear stability. The lower limit of the kinematic viscosity reduction rate is not particularly limited and may be 0%. The kinematic viscosity reduction rate of the lubricating oil composition according to the present disclosure is, for example, 1.0% to 6.0%.

[0113] In the present disclosure, the kinematic viscosity reduction rate of a lubricating oil composition at 100°C is measured by the following method in accordance with JPI-5S-29-88.

[0114] After irradiating 30 mL of standard oil with ultrasonic waves for 10 minutes, the output voltage at which the rate of decrease in kinematic viscosity at 40°C becomes 15% is determined. For 30 mL of the sample to be measured, the kinematic viscosity at 100°C is measured before ultrasonic irradiation (i.e., before the test). Under the conditions of the output voltage obtained above, 30 mL of the sample to be measured is irradiated with ultrasonic waves for 30 minutes, and the kinematic viscosity at 100°C of the sample after ultrasonic irradiation (i.e., after the test) is measured. The kinematic viscosity at 100°C measured for the sample before and after the test is applied to the following formula X to calculate the value, which is rounded off to two decimal places to obtain the kinematic viscosity reduction rate (%). Formula (X): Kinematic viscosity reduction rate (%) = [100°C kinematic viscosity before test - 100°C kinematic viscosity after test] / 100°C kinematic viscosity before test × 100

[0115] Preparation of Lubricating Oil Composition The lubricating oil composition according to the present disclosure can be prepared by appropriately mixing a specific base oil, a specific viscosity index improver, zinc dialkylthiophosphate X1, zinc dialkylthiophosphate X2, an acidic phosphate amine salt Y, and, as necessary, various additives. The order in which these components are mixed is not particularly limited, and they may be mixed into the base oil sequentially, or various additives may be added to the base oil in advance.

[0116] ~Applications~ The lubricating oil compositions according to the present disclosure are preferably used in agricultural machinery. Examples of agricultural machinery include, but are not limited to, tractors as land leveling machines, rice transplanters as cultivation and management machines, and harvesting machines such as binders and combines. The lubricating oil composition according to the present disclosure can be suitably used in tractors, and can be used as a universal lubricating oil for hydraulic pumps, transmissions, PTO clutches, differential gear units, wet brakes, etc. [Example]

[0117] Next, the lubricating oil composition according to the present disclosure will be explained in more detail using examples, but the lubricating oil composition according to the present disclosure is not limited in any way by these examples.

[0118] The lubricating oil compositions of the Examples and Comparative Examples were prepared by mixing the base oil, viscosity index improver, zinc dialkylthiophosphate, acidic phosphate ester amine salt, and other additives to the contents shown in Tables 1 and 2.

[0119] Details of the components shown in Tables 1 and 2 are as follows:

[0120] [Ingredients included] (1) Base oil Base oil A: kinematic viscosity at 100°C is 6.50mm 2 / s and a hydrotreated refined oil (mineral base oil) with a viscosity index of 131 Base oil B: kinematic viscosity at 100°C is 3.10mm 2 / s and a hydrotreated refined oil (mineral base oil) with a viscosity index of 102 Base oil C: kinematic viscosity at 100°C is 5.60mm 2 / s and a hydrotreated refined oil (mineral base oil) with a viscosity index of 109

[0121] (2) Viscosity index improver Viscosity index improver A: Non-dispersant polyalkyl methacrylate, weight average molecular weight (Mw): 150,000, active ingredient amount excluding diluent oil: 50% by mass Viscosity index improver B: Non-dispersant polyalkyl methacrylate (weight average molecular weight (Mw): 47,000, active ingredient amount excluding diluent oil: 68% by mass) Viscosity index improver B is a specific viscosity index improver that falls within the category of non-dispersant polyalkyl methacrylate (1). Viscosity index improver C: Dispersion-type polyalkyl methacrylate (weight average molecular weight (Mw) 58,000, product name: Amount of active ingredients excluding diluent oil: 65% by mass) Viscosity index improver C is a specific viscosity index improver that falls within the category of dispersant-type polyalkyl methacrylate (2). Viscosity index improver D: Non-dispersant polyalkyl methacrylate (weight average molecular weight (Mw) 55,000, active ingredient amount excluding diluent oil: 72% by mass) Viscosity index improver D is a specific viscosity index improver that falls within the category of non-dispersant polyalkyl methacrylate (1).

[0122] (3) Zinc dialkylthiophosphate x1 R in Equation (1) 1 , R 2 , R 3 and R 4 All of the alkyl groups are primary alkyl groups with 12 carbon atoms. Phosphorus concentration: 6.1% by mass. (4) Zinc dialkylthiophosphate x2 In equation (2), 5 , R 6 , R 7 and R 8 are all primary alkyl groups, and the alkyl groups have 4 or 4 carbon atoms. Phosphorus concentration: 8.3% by mass

[0123] (5) Acidic phosphate ester amine salt Y R in Equation (3) 9 and R 10 is an alkyl group having 8 carbon atoms, or 10 carbon atoms, or a combination of 8 and 10 carbon atoms, and R is a branched alkyl group having 12 or 14 carbon atoms. Phosphorus concentration: 8.2% by mass

[0124] (6) Package additives (mixture of the following additives) Metallic detergents (overbased calcium sulfonates) Friction modifiers Silicone antifoaming agent The amounts of the main elements in the package additives were as follows: Calcium: 7.3% by mass, sulfur: 1.4% by mass, nitrogen: 0.035% by mass, silicone: 80 ppm by mass

[0125] (7) Other additives (mixtures of the following additives) Silicone-based defoaming agent Metal deactivators or rust inhibitors Coloring agents

[0126] 〔evaluation〕 (1) Emulsion formation suppression After water was mixed into the lubricating oil composition, the state of the oil layer was checked and the amount of emulsion was measured to evaluate the emulsion formation inhibiting ability of the lubricating oil composition. The occurrence of turbidity in the oil layer means that emulsion has occurred in the lubricating oil composition due to the inclusion of water. In this evaluation, when the oil layer was not cloudy and the amount of emulsion was 1.8 mL or less, it was determined that the emulsion formation inhibitory effect was excellent.

[0127] (1-1) Oil reservoir condition 1 mL of water was mixed into 99 mL of the lubricating oil composition and stirred for 10 minutes. After stirring, the lubricating oil composition was allowed to stand for 168 hours, and the presence or absence of turbidity in the oil layer was visually confirmed to evaluate the state of the oil layer.

[0128] (1-2) Amount of emulsion The water mixing method was carried out as described in the filterability evaluation described in SAE (SOCIETY of Automotive Engineers) Paper 972788. Specifically, the amount of emulsion was measured for the lubricating oil composition mixed with water using the measurement method described below.

[0129] (Method for measuring emulsion amount) 1 mL of water and 99 mL of the lubricating oil composition were added to a centrifuge tube and stirred to prepare a test oil, which was then left to stand in a thermostatic bath maintained at 10°C for one week, and the amount of emulsion formed was measured.

[0130] (2) Shear stability The shear stability was evaluated based on the rate of decrease in kinematic viscosity at 100°C (%) calculated for each lubricating oil composition by the method shown below. A value of the 100°C kinematic viscosity reduction rate (%) of 10.0% or less was determined to be excellent in shear stability.

[0131] (Calculation method for 100°C kinematic viscosity decrease rate (%)) The shear stability test (ultrasonic shear stability test) was carried out in accordance with JPI-5S-29-88 using the following evaluation method, and the kinematic viscosity was calculated from the kinematic viscosity at 100°C. After irradiating 30 mL of standard oil with ultrasonic waves for 10 minutes, the output voltage at which the kinematic viscosity reduction rate at 40°C was 15% was determined. The kinematic viscosity of 30 mL of the sample to be measured at 100°C was measured before ultrasonic irradiation (i.e., before the test). Under the conditions of the output voltage obtained above, 30 mL of the sample to be measured was irradiated with ultrasonic waves for 30 minutes, and the kinematic viscosity at 100°C of the sample after ultrasonic irradiation (that is, after the test) was measured. The measured values ​​of the kinematic viscosity at 100°C of the sample before and after the test were applied to the following formula X to calculate the value, which was rounded off to two decimal places to obtain the kinematic viscosity reduction rate (%). Formula (X): 100°C kinematic viscosity decrease rate (%) = [100°C kinematic viscosity before test - 100°C kinematic viscosity after test] / 100°C kinematic viscosity before test × 100

[0132] The evaluation results are shown in Tables 1 and 2 below.

[0133] In Tables 1 and 2 below, blank spaces in the composition columns mean that the corresponding component is not contained. In Table 1 below, P X1 / P X2 Ratio and P X1+X2 / P Y A "-" in the ratio column means that the corresponding value cannot be calculated.

[0134] [Table 1]

[0135] [Table 2]

[0136] The results shown in Tables 1 and 2 show that the lubricating oil compositions of the Examples are superior in shear stability and in suppressing emulsion formation after water is mixed in, compared to the lubricating oil compositions of the Comparative Examples.

Claims

1. At least one base oil selected from mineral oil-based lubricating oils and synthetic oil-based lubricating oils; a polyalkyl methacrylate-based viscosity index improver having a weight average molecular weight of 20,000 to 8,0000; Zinc dialkylthiophosphate X represented by the following formula (1) １ and, Zinc dialkylthiophosphate X represented by the following formula (2) ２ and, an acidic phosphate amine salt Y represented by the following formula (3); Contains A lubricating oil composition that satisfies the relationship represented by the following formula (a): 【Chemical 1】 In formula (1), R １ , R ２ , R ３ and R ４ each independently represents a linear or branched primary alkyl group having 10 to 20 carbon atoms. 【Chemistry 2】 In formula (2), R ５ , R ６ , R ７ and R ８ each independently represents a linear or branched primary or secondary alkyl group having 3 to 6 carbon atoms. 【Chemistry 3】 In formula (3), R, R ５ and R ６ each independently represents a hydrogen atom or a hydrocarbon group having 3 to 30 carbon atoms; R ５ and R ６ At least one of these represents a hydrocarbon group. 1.0≦P Ｘ１ / P Ｘ２ ≦10.5 (a) In formula (a), P Ｘ１ is the amount of zinc dialkylthiophosphate X represented by the formula (1) relative to the total mass of the lubricating oil composition. １ represents the content in terms of phosphorus concentration, and P Ｘ２ is the amount of zinc dialkylthiophosphate X represented by the formula (2) relative to the total mass of the lubricating oil composition. ２ The phosphorus content is expressed as a phosphorus concentration.

2. R in the formula (1) １ , R ２ , R ３ and R ４ and each independently represent a linear primary alkyl group having 10 to 12 carbon atoms.

3. R in the formula (2) ５ , R ６ , R ７ and R ８ The lubricating oil composition according to claim 1, wherein each independently represents a primary alkyl group having 4 or 5 carbon atoms.

4. R in the formula (3) ９ and R １０ and each independently represent a hydrocarbon group having 3 to 30 carbon atoms selected from the group consisting of an alkyl group, an aryl group, an alkenyl group, an alkylaryl group, and an arylalkyl group.

5. 2. The lubricating oil composition according to claim 1, wherein the polyalkyl methacrylate-based viscosity index improver comprises a polyalkyl methacrylate having a structural unit represented by the following formula (1a) and a structural unit represented by the following formula (1b): 【Chemistry 4】 In formula (1a) and formula (1b), R １１ represents a hydrogen atom or an alkyl group having 1 to 24 carbon atoms, R １２ represents a hydrogen atom or a methyl group, R １３ represents an alkyl group having 1 to 24 carbon atoms substituted with an amino group, and m and n each independently represent an integer of 1 or more.

6. The lubricating oil composition according to any one of claims 1 to 5, which is a lubricating oil for agricultural machinery.

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