JPH09132790A - Gear oil composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a gear oil composition excellent in pitching resistance, extreme pressure characteristics, oxidation stability, sludge resistance, etc., further improved in synchronizing characteristics and useful for automobiles, etc., by blending a specific amount of a sulfur-phosphorous-based extreme pressure agent, an alkali metal borate hydrate, etc., to a base oil. SOLUTION: This gear oil contains (A) 2-10mass% sulfur-phosphorus-based extreme pressure agent, (B) 0.05-0.5mass% alkali metal borate hydrate, e.g. potassium borate hydrate, (C) 0.1-1mass% zinc alkyldithiophosphate, and further preferably (D) 0.1-3mass% alkenylsuccinimide or its derivative in 100mass% base oil having 2-50mm<2> /s dynamic viscosity and preferably reduced in sulfur content to <=1500ppm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gear oil composition, and more particularly, it has excellent extreme pressure resistance, pitting resistance, synchro characteristics, oxidation stability, sludge resistance and storage stability, and a manual transmission. The present invention relates to a so-called dual-purpose gear oil composition for automobiles, which can be commonly lubricated with the final reduction gear.

[0002]

2. Description of the Related Art Since gears for automobiles are used under high speed and high load conditions, the gear oil used for them must have excellent anti-seizure properties and abrasion resistance. Therefore, conventional gear oils contain sulfur-based additives represented by sulfurized olefins and sulfurized fats and oils in order to enhance anti-seizure property, and phosphoric acid ester or phosphoric acid ester in order to enhance anti-wear property. Gear oil added with a phosphorus-based additive such as an amine salt (that is, a sulfur-phosphorus extreme pressure agent (hereinafter,
Gear oil) added with (also sometimes referred to as SP-based extreme pressure agent) is used. For example, a manual speed reducer uses a multi-grade gear oil containing a mild sulfur-phosphorus extreme pressure agent with an extreme pressure level of GL-3 to GL-4, and a final reducer requires high extreme pressure characteristics. Therefore, a gear oil containing a highly active sulfur-phosphorus extreme pressure agent and having an extreme pressure level of GL-5 or higher is used. Therefore, the gear oils used for the manual transmission and the final reduction gear have different required characteristics, so that the manual transmission oil is used for the manual transmission and the final reduction gear oil is used for the final reduction gear. In recent years, due to the development of expressways, the nationwide expansion of courier services, and the rapid increase in demand for high-speed transportation, the proportion of high-speed operation has increased, and the gear part has been shielded from the viewpoint of higher engine output and improved aerodynamic characteristics. Due to downsizing of the gear unit from the viewpoint of improving fuel efficiency, the gear oil temperature of the manual transmission and the final reduction gear has been remarkably increased.

[0003]

From such a background,
Conventionally used sulfur-phosphorus extreme pressure agents cause problems such as oil deterioration due to insufficient heat resistance, metal corrosion, sludge formation, etc., and in manual transmissions, the synchronizer ring and gear cone part in the synchromesh mechanism are used. In some cases, a friction coefficient may be reduced or abnormal wear may occur, synchronization may not be successful, a shift force may increase, and gears may not be able to be shifted. Furthermore, in recent years, among the problems in the market relating to automotive gear oils, there are more machine troubles due to metal fatigue, so-called pitting, as compared with wear, seizure, etc., and therefore higher fatigue resistance ( (Pitching resistance) is required. On the other hand, in recent years, there has been a strong demand for maintenance-free operation and rationalization of oil management, and there is a demand for one that can be lubricated with one type of gear oil. The present invention has excellent extreme pressure characteristics, synchro characteristics, pitting resistance, oxidation stability, sludge resistance, and storage stability in consideration of the above circumstances, and has a common manual transmission and final reduction gear. An object of the present invention is to provide a dual-purpose gear oil composition for automobiles.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to achieve the above-mentioned object, and as a result, 2-5 at 100 ° C.
A base oil having a kinematic viscosity of 0 mm ² / s, a sulfur-phosphorus extreme pressure agent as a component (A), an alkali metal borate hydrate as a component (B), and a zinc alkyldithiophosphate as a component (C). The compositions in which the respective specific amounts are mixed show excellent extreme pressure properties, synchro characteristics, and pitting resistance due to the interaction of these compounding agents.
When a specific amount of the alkenyl succinimide or its derivative is blended as the component (D) together with the component (C), the sludge resistance and the storage stability are improved, and further, ² to 50 mm ² at 100 ° C. instead of the above base oil. Has a kinematic viscosity of / s,
It was found that heat resistance is improved by adding a base oil having a sulfur content reduced to 1500 ppm or less,
The present invention has been completed.

That is, the present invention is 2 to 50 at 100 ° C.
In a base oil having a kinematic viscosity of mm ² / s, (A) 2 to 10% by mass of a sulfur-phosphorus extreme pressure agent, (B) 0.05 to 0.5% by mass of an alkali metal borate hydrate, and (C) A gear oil composition characterized by containing 0.1 to 1% by mass of zinc alkyldithiophosphate. Further, the present invention provides a base oil having a kinematic viscosity of ² to 50 mm ² / s at 100 ° C. and a sulfur content reduced to 1500 ppm or less,
(A) 2 to 10 mass% of sulfur-phosphorus extreme pressure agent, (B) 0.05 to 0.5 mass% of alkali metal borate hydrate,
A gist oil composition comprising (C) 0.1 to 1% by weight of zinc alkyldithiophosphate and (D) 0.1 to 3% by weight of alkenylsuccinimide or a derivative thereof. To do.

The gear oil composition of the present invention comprising the above components has the performance to be provided as a manual transmission oil, that is, 1) has an appropriate friction coefficient in the synchronizer ring and the gear cone portion. 2) Maintain this friction coefficient for a long time. 3) Excellent in pitting resistance. 4) Excellent in oxidative stability. 5) Excellent sludge resistance. 6) Excellent in storage stability. And the like, and the performance that the final reduction gear oil should have, that is, 1) It is excellent in extreme pressure. 2) Excellent in pitting resistance. 3) Excellent in oxidative stability. 4) Excellent sludge resistance. 5) It has excellent storage stability. With such performances, the manual transmission and the final reduction gear can be commonly lubricated. Hereinafter, the present invention will be described in detail.

As the sulfur-phosphorus extreme pressure agent of the component (A), one containing sulfur and phosphorus in one compound may be used, or a so-called sulfur extreme pressure agent and phosphorus type containing either one of them. It can also be used as a mixture with an extreme pressure agent. As the sulfur-based extreme pressure agent, a hydrocarbon sulfide represented by the general formula of Chemical formula 1, a terpene sulfide, a sulfurized fat and oil which is a reaction product of fat and sulfur, and the like can be used.

[0008]

## STR00001 ## R ¹ --S _x- (R ² --S _x ) _n --R ¹

In the general formula of Chemical formula ¹ , R ¹ is a monovalent hydrocarbon group and R ² is a divalent hydrocarbon group. x is an integer of 1 or more, preferably 1 to 8, and each x in the repeating unit may be the same or a different number. n
Is 0 or an integer of 1 or more. In the hydrocarbon sulfide represented by the general formula of Chemical formula ¹ , R ¹ has 2 to 2 carbon atoms.
20 straight or branched, saturated or unsaturated aliphatic hydrocarbon groups (eg, alkyl groups, alkenyl groups) having 6 carbon atoms
To 26 aromatic hydrocarbon groups, specifically, ethyl group, propyl group, butyl group, nonyl group, dodecyl group, propenyl group, butenyl group, benzyl group, phenyl group, tolyl group, hexylphenyl group. And so on.

Examples of R ² include a linear or branched saturated or unsaturated aliphatic hydrocarbon group having 2 to 20 carbon atoms and an aromatic hydrocarbon group having 6 to 26 carbon atoms.
Examples thereof include an ethylene group, a propylene group, a butylene group, and a phenylene group. Typical examples of the hydrocarbon sulfide represented by the general formula of Chemical formula 1 are sulfur olefin and general formula R ¹
-S _x -R ¹ _(x is an integer of 2 or more) is a polysulfide compound represented by the. Specifically, diisobutyl disulfide, dioctyl polysulfide, ditersharinonyl polysulfide, ditertiary butyl polysulfide, ditertiary benzyl polysulfide, and olefins obtained by sulfurizing olefins such as polyisobutylene and terpenes with a sulfur and other sulfiding agents. Is mentioned. Sulfurized fats and oils, which are reaction products of fats and oils, use animal and vegetable fats and oils such as lard, beef fat, whale oil, palm oil, coconut oil, and rapeseed oil as fats and oils. It is not one but various mixtures, and the chemical structure itself is not clear. As the phosphorus-based extreme pressure agent or the sulfur-phosphorus-based extreme pressure agent, a phosphoric acid ester, a phosphorous acid ester, a thiophosphoric acid ester, a dithiophosphoric acid ester or the like represented by the general formula of Chemical formula 2 is used.

[0011]

[Chemical Formula 2] (R ³ ) _a H _3-a —X ₃ PX _b

In the general formula of Chemical formula 2, R ³ is a monovalent hydrocarbon group, and X is an oxygen atom or a sulfur atom. a is 1,
2 or 3, and b is 0 or 1. R ³ is a linear or branched saturated or unsaturated aliphatic hydrocarbon group having 5 to 20 carbon atoms (for example, an alkyl group or an alkenyl group), an aromatic hydrocarbon group having 6 to 26 carbon atoms, or a cycloalkyl group. Is mentioned. Specific examples of the ester compound represented by the above chemical formula 2 include, for example, monooctyl phosphate, dioctyl phosphate, trioctyl phosphate, dioctyl phosphite, trioctyl phosphite, dioctyl thiophosphate,
Trioctyl thiophosphate, didecyl phosphate, didecyl phosphite, didodecyl phosphate, tridodecyl phosphate, didodecyl phosphite, tridodecyl phosphite, tridecyl thiophosphate, trihexadecyl phosphate, trihexadecyl phosphite, thiophosphate Trihexadecyl, trioctadecenyl phosphate, trioctadecenyl phosphite, trioctadecenyl thiophosphate, tri (octylphenyl) phosphate, tri (octylcyclohexyl) phosphate, tridecyl dithiophosphate, etc. Can be mentioned.

Further, as the phosphorus-based extreme pressure agent, an acid phosphoric acid ester represented by the general formula of Chemical formula 2, an acidic phosphorous acid ester, an acidic thiophosphoric acid ester, an alkylamine salt of an acidic dithiophosphoric acid ester, or the like may also be used. You can Specific examples of these amine salts include acidic phosphoric acid esters,
Butyl acid phosphate, 2-ethylhexyl acid phosphate, octyl acid phosphate, lauryl acid phosphate, oleyl acid phosphate, tolyl acid phosphate and the like can be mentioned. Alkylamines for neutralizing these are represented by the general formula NR ⁴ R ⁵ R ⁶ (wherein R ⁴ , R ⁵ and R ⁶ are monovalent hydrocarbon groups or hydrogen atoms, and at least one of them is Hydrocarbon group), and specific examples of these compounds are:
Dibutylamine, octylamine, dioctylamine,
Examples include laurylamine, dilaurylamine, coconut amine, tallow amine, and the like. (A) component sulfur
The phosphorus-based extreme pressure agents may be used alone or in combination of two or more.

The alkali metal borate hydrate as the component (B) is lithium borate hydrate, sodium borate hydrate, potassium borate hydrate, rubidium borate hydrate, boric acid. Cesium hydrate and the like can be mentioned, and potassium borate hydrate and sodium borate hydrate are preferable, and potassium borate hydrate is particularly preferable.
Alkali metal borate hydrates include, for example, Japanese Patent Publication No. 53-
It can be produced by the method disclosed in Japanese Patent Publication No. 9763 or US Pat. No. 3,929,650. That is, an aqueous solution of potassium hydroxide and boric acid is added so that the atomic ratio of boron / potassium is 2.5 to 4.5.
Potassium borate hydrate obtained by adding water to an oil solution containing a neutral alkaline earth metal sulfonate or succinimide ashless dispersant and stirring vigorously to dehydrate it. The fine particle dispersion of can be used.

Further, as another production method, an alkali metal or alkaline earth metal neutral sulfonate is carbonated in the presence of an alkali metal hydroxide to obtain a superbasic sulfonate, which is reacted with boric acid. The resulting fine particle dispersion of alkali metal borate can be used. In this case, the carbonation reaction may be carried out in the presence of an ashless dispersant such as succinimide. The alkali metal borate hydrate which is the component (B) is more preferably potassium borate or boric acid produced by using an ashless dispersant such as neutral calcium sulfonate or succinimide. Mention may be made of sodium dispersions. Alkali metal borate hydrates obtained by these methods have, for example, the formula K ₂ O.3B ₂ O ₃ .3H ₂ O or N.
It is represented by a ₂ O · 2H ₂ O. As the alkali metal borate hydrate as the component (B), one type may be used alone, or two or more types may be used in combination. Further, zinc alkyldithiophosphate as the component (C) is represented by Chemical formula 3.

[0016]

Embedded image

(In the formula, R ⁷ , R ⁸ , R ⁹ and R ¹⁰ are alkyl groups, preferably alkyl groups having 1 to 20 carbon atoms.) In the general formula of Chemical formula 3, R ⁷ , R ⁸ and R ⁹ and R ¹⁰ are particularly preferably alkyl groups having 5 or more carbon atoms, and are alkyl groups such as octyl group, decyl group, dodecyl group, tetradecyl group and hexadecyl group. Also, R ⁷ ,
R ⁸ , R ⁹ and R ¹⁰ are preferably primary alkyl groups. R
⁷ , R ⁸ , R ⁹ and R ¹⁰ may be the same or different. As the zinc alkyldithiophosphate as the component (C), one type may be used alone, or two or more types may be used in combination.

The alkenyl succinimide or its derivative as the component (D) is not particularly limited, and various ones which can be usually used as an ashless dispersant for lubricating oil can be used. Specific examples of the alkenyl succinimide or its derivative include, for example, a polyolefin having a molecular weight of 300 to 3000 such as polybutene is reacted with maleic anhydride to form a monoalkenyl succinic acid, and then ethylenediamine, diethylenetriamine, dipropylenetriamine, triethylene. Imidized with polyamines such as tetramine and tetraethylenepentamine, and various alkenyl succinimides such as monoimide, diimide, and triimide, or the resulting imides are left with aromatic polycarboxylic acids. A part of the amino group of amidated (for example, polybutene having a molecular weight of 900 is reacted with maleic anhydride and then imidized with tetraethylenepentamine, or one treated with trimellitic acid). .), Also, JP-B 42-8013, JP-Sho 42-801
4, JP-A-51-52381, JP-A-51-52381
-130408, boron compound derivative of alkenyl succinimide, organic phosphonate derivative and the like or alkenyl obtained by reacting alkenyl succinimide with aldehyde, ketone, carboxylic acid, sulfonic acid, alkylene oxide, sulfur and the like. Examples thereof include derivatives of succinimide. Among these alkenyl succinimides or derivatives thereof, preferred is alkenyl succinic acid monoimide obtained by reacting polybutene having a molecular weight of 600 to 1000 as polybutene with maleic anhydride and then imidized with tetraethylenepentamine. In addition, these alkenyl succinimide or its derivative may be used individually by 1 type, and may be used in combination of 2 or more type.

The base oil used in the gear oil composition of the present invention has a kinematic viscosity of ² to 50 mm ² / s at 100 ° C., and a mineral oil type, a synthetic type or a mixed type thereof is used. it can. The preferable range of the kinematic viscosity of the base oil is 1
It is 5 to 50 mm ² / s at 00 ° C, and a particularly preferable range is 7 to 50 mm ² / s at 100 ° C. In the case of a mineral oil-based lubricating oil, those refined by solvent refining, hydrorefining, etc. may be used. Examples of synthetic lubricating oils include α-olefin oligomers, which are polymers of α-olefins having 3 to 12 carbon atoms, dialkyl diesters having 4 to 12 carbon atoms such as sebacate including dioctyl sebacate, azelate and adipate. , 1-trimethylolpropane, pentaerythritol and 3 carbon atoms
Examples thereof include polyol esters such as esters obtained from monobasic acids of .about.12, alkylbenzenes having an alkyl group having 9 to 40 carbon atoms, and the like. The mineral oil-based lubricating oil and the synthetic lubricating oil may be used alone or in combination of two or more.

In the gear oil composition of the present invention, (A)-
When the component (D) is included, the base oil used is 2 at 100 ° C.
It has a kinematic viscosity of ~ 50mm ² / s and has a sulfur content of 1500p.
Base oils reduced to pm or less are preferred. A preferred range of kinematic viscosity of the base oil, 5 to 50 mm ² at 100 ° C. /
s, and a particularly preferable range is 7 to 50 m at 100 ° C.
m ² / s. Moreover, the preferable range of the sulfur content of this base oil is 1000 ppm or less, and the particularly preferable range is 800 ppm or less. Sulfur content is 15
If it exceeds 00 ppm, the oxidation stability tends to decrease. A base oil having a kinematic viscosity of ² to 50 mm ² / s at 100 ° C. and a sulfur content reduced to 1500 ppm or less is a highly refined base oil, a high viscosity index base oil, among the usual lubricating base oils. It is called low pour point base oil.

The blending ratio of each component of the present invention is such that the component (A) is 2 to 10% by mass, preferably 6 to 9% by mass, and the component (B) is 0.05 to 0.5% by mass, preferably 0. 2 to 0.
4% by mass, component (C) is 0.1 to 1% by mass, preferably 0.3 to 0.7% by mass. In addition, these (A) ~
When the component (D) is added to the component (C),
Component (D) is 0.1 to 3% by mass, preferably 0.5 to
It is 1.5% by mass. If the amount of the component (A) is less than the above range, the gear performance (extreme pressure property) is lowered, and if it is too large, this effect is saturated, which is economically disadvantageous. If the amount of the component (B) is less than the above range, the oxidation stability and the synchro performance are lowered, and if it is too much, the pitting resistance and the sludge resistance are lowered. If the amount of the component (C) is less than the above range, the pitching resistance and synchro performance are lowered, and if it is too much, the sludge resistance is lowered. If the amount of component (D) is less than the above range, the oxidation stability, sludge resistance, and storage stability are reduced, and if it is too large, the effect is saturated and it is economically disadvantageous.

In the gear oil composition of the present invention, in addition to the above-mentioned components, known additives which are usually used as required, for example, friction modifiers, antioxidants, corrosion inhibitors, viscosity index improvers, A pour point depressant, a defoaming agent and the like can be added. As the friction modifier, fatty acids, organic molybdenum compounds and the like, as antioxidants, amine-based and phenol-based antioxidants, etc., as corrosion inhibitors, benzotriazole, alkenyl succinic acid ester, etc.
Examples of the viscosity index improver include polymethacrylate and olefin copolymer, examples of the pour point depressant include polymethacrylate, and examples of the defoaming agent include silicone compound and ester defoaming agent. In addition to these, various additives can be appropriately blended.

The gear oil composition of the present invention may be prepared by appropriately mixing the base oil, the above-mentioned essential components and, if necessary, various additives, and the mixing order is not particularly limited, and the base oil is not limited. The essential components may be sequentially mixed, or the essential components may be mixed in advance and then mixed with the base oil. Furthermore, various additives may be added to the base oil in advance or may be added to the essential components.

[0024]

Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples. The base oil used for the preparation of the gear oil composition of each Example and each Comparative Example, the essential components, the types of additives, and each evaluation test are as follows.

1. Base oil Base oil A: Neutral base oil having a kinematic viscosity of 12 mm ² / s at 100 ° C. Base oil B: Synthetic base oil (polyalphaolefin) having a kinematic viscosity of 10 mm ² / s at 100 ° C. Base oil C: 100 1. Hydrorefined base oil having a kinematic viscosity of 12 mm ² / s at ℃ and a sulfur content of 700 ppm. Additives and Gear Oils Sulfur-Phosphorus Extreme Pressure Agent: Sulfur-Phosphorus Extreme Pressure Agent Package Type Additive (Sulfur Content: 22.9% by Mass, Phosphorus Content: 1.4% by Mass) Boric Acid Potassium: An aqueous solution of potassium hydroxide and boric acid is added to an oil solution containing a neutral alkaline earth metal sulfonate or succinimide ashless dispersant, and vigorously stirred to form a water-in-oil emulsion. Fine particle dispersion of hydrated potassium borate hydrate (boron content: 7.6% by mass) Zinc dialkyldithiophosphate (ZnDTP): C8, C8, C8, C8 primary Zinc primary dialkyldithiophosphate with alkyl group

Alkenyl succinimide: alkenyl succinic acid monoimide imidized with tetraethylenepentamine after polybutene having a molecular weight of 700 as polybutene is reacted with maleic anhydride, and other additives: viscosity index improver, antifoaming agent, etc. All commercial products Commercial gear oil D: Commercial transmission gear oil containing sulfur-phosphorus extreme pressure agent (GL-390) Commercial gear oil E: Commercial differential gear oil containing sulfur-phosphorus extreme pressure agent (GL- 590) Commercially available gear oil F: Gear oil for transmission / differential containing sulfur-phosphorus extreme pressure agent

3. Evaluation test (1) Pitching resistance test A four-cylinder test was performed as an evaluation of pitching resistance. The test conditions of the four-cylinder test and the method of judging the fatigue life are as follows. B) Test conditions Rotational speed: 1000 rpm Sliding ratio: 30% Contact pressure: 65 kg / mm ² Oil temperature: 80 ° C b) Fatigue life determination method The test machine is stopped every 50,000 cycles from the start of operation and can be visually observed. The number of cycles until damage occurred was defined as the fatigue life. That is, the longer the number of cycles, the longer the fatigue life. In this test result, a fatigue life of 300,000 cycles was passed.

(2) Synchronous characteristic evaluation test First, a synchronizer ring and a gear cone are set on a table, and the rotation speed of the gear cone is set to 1200 r by a motor.
Keep at pm. Then 4 synchronizer rings
Press with a load of 0 kgf. Then remove the load on the synchronizer ring and disconnect the synchronizer ring from the gear cone. The pattern consisting of pressing and separating this synchronizer ring is 100
Repeat 00 cycles. In this repetition, the torque generated when the synchronizer ring was pressed was measured to determine the friction coefficient. This friction coefficient was compared between 100 cycles and 10,000 cycles, and evaluated based on the level of the friction coefficient. That is, those having a high friction coefficient and being able to maintain this high friction coefficient even after the endurance were regarded as having excellent synchro characteristics. In this test result, those having a friction coefficient μ after 10,000 cycles of 0.100 or more were accepted.

(3) Extreme Pressure Test An IAE gear test was conducted under the conditions shown in Table 1. Note that I
The EA gear test is based on IP (English Petroleum Institute) I
It carried out according to P166 / 68, and measured the seizure limit load.

[0030]

[Table 1] (The operation was started with a load of 10 pounds and the load was increased by 5 pounds every 5 minutes.)

(4) Oxidation stability test Method for lubricating oil stability test for internal combustion engine (JIS K 251)
According to 4), it was carried out under the conditions of 135 ° C. and 96 hours. The evaluation was performed by increasing the viscosity, increasing the total acid value, and the presence or absence of sludge. (5) Sludge resistance test Based on the lubricating oil thermal stability test method (JIS K 2540), the sludge resistance test was performed under the conditions of 160 ° C and 24 hours. The evaluation was performed by the presence or absence of sludge after the test. (6) Storage stability test Put 150 cc of oil in a 300 cc beaker and
It was left for one day at room temperature (open state). The evaluation was performed based on the presence or absence of turbidity and precipitation of oil.

Examples and Comparative Examples Various base oils and various additives shown in Tables 2 and 3 were blended in the proportions shown in Tables 2 and 3 to prepare gear oil compositions, and these gear oil compositions were described above. A performance test was conducted. The performance test was also performed on the commercially available gear oils shown in Table 4. The results of these evaluation tests are shown in Tables 2-4.

[0033]

[Table 2]

[0034]

[Table 3]

[0035]

[Table 4]

[0036]

The gear oil composition of the present invention has excellent pitting resistance, extreme pressure resistance, oxidation stability, sludge resistance, and storage stability, and at the same time, can improve synchro characteristics. Thereby, it is possible to provide gear oil that can lubricate the manual transmission and the final reduction gear in common, contribute to longer drainage, and contribute to labor saving by simplifying inventory management.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C10M 137: 10 135: 06 135: 20 137: 02 125: 26 133: 56) C10N 10:02 20 : 02 30:06 30:10 40:04 (72) Inventor Yukio Okano 1134-2 Gongendo, Satte City, Saitama Prefecture, inside the Research and Development Center, Cosmo Research Institute Co., Ltd. (72) Kazuyoshi Mise, Satte City, Saitama Prefecture 1134-2 Gongendo Co., Ltd. Research & Development Center, Cosmo Research Institute Co., Ltd. (72) Ikuo Fukuhara, Ikio Fukuhara Saitama Prefecture Gongendo 1134-2 Cosmo Research Institute Co., Ltd. Research & Development Center

Claims (3)

[Claims] 1. A base oil having a kinematic viscosity of ² to 50 mm ² / s at 100 ° C., (A) 2 to 10% by mass of a sulfur-phosphorus extreme pressure agent, and (B) an alkali metal borate hydrate 0 .05 to 0.
5% by mass, and (C) zinc alkyldithiophosphate 0.1
The gear oil composition is characterized by containing 1 to 1% by mass. 2. The gear oil composition according to claim 1, further comprising 0.1 to 3 mass% of alkenyl succinimide or its derivative. 3. A base oil having a kinematic viscosity of ² to 50 mm ² / s at 100 ° C. and a sulfur content reduced to 1500 ppm or less, and (A) 2 to 10% by mass of a sulfur-phosphorus extreme pressure agent. ,
(B) 0.05 to 0.5% by mass of alkali metal borate hydrate, 0.1 to 1% by mass of (C) zinc alkyldithiophosphate, and (D) 0.1 to alkenylsuccinimide or its derivative. A gear oil composition comprising 3% by weight.