JP2008001734A - Lubricating oil composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a lubricating oil composition which is obtained by mixing a lubricant base oil with a primary antioxidant and a secondary antioxidant, suppresses abrupt decomposition and evaporation of lubricating oil even in the presence of a bearing metal and is used as a sintered metal bearing oil stably for a long period of time without corroding and degenerating a bearing material or forming a sludge. <P>SOLUTION: The lubricating oil composition is obtained by mixing a lubricant base oil with a diphenylamine-based antioxidant and a phosphite containing at least one phenylester group. The lubricating oil composition not only effectively achieves corrosion prevention of bearing material and formation prevention of sludge but also suppresses abrupt decomposition and evaporation of lubricating oil even in the presence of a bearing metal and is stably usable even under a high-temperature condition for a long period of time when used as a sintered metal bearing oil. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lubricating oil composition. More specifically, the present invention relates to a lubricating oil composition suitably used for sintered oil-impregnated bearings and the like.

  Sintered oil-impregnated bearings are used in a self-lubricated state by impregnating a porous body obtained by pressing and compacting metal powder typified by Cu, Fe, Sn, Zn, etc., and sintering the powder. Is a kind of plain bearing. Sintered oil-impregnated bearings are low-cost, relatively low-friction, high-accuracy, self-lubricating systems, so they drive automotive electrical components, audiovisual equipment, office supplies, household electrical equipment, and auxiliary storage devices for computers. It is widely used as a motor bearing in each part leading to the part.

  In recent years, with the improvement in performance of these devices, the performance required for sintered oil-impregnated bearings has become very severe, such as downsizing, high speed, low current and low power consumption. In order to meet these requirements, bearing manufacturers have examined the bearing materials, etc., but the performance of several milligrams of bearing oil impregnated in the bearing has a great influence on the characteristics and life of the motor. Therefore, it has become particularly important.

  The properties required for sintered oil-impregnated bearing oils are good compatibility with bearing materials, do not generate corrosion and sludge, can be used in a wide temperature range, have low evaporation loss at high temperatures, Good stability, low fluidity at low temperatures, good rust prevention, good resin resistance and low coefficient of friction to meet recent demands as mentioned above. Also, it is required to have excellent wear resistance.

  In order to meet these strict requirements, synthetic hydrocarbon oils, ester oils, silicone oils, fluorine oils, etc. are used as base oils, which have better temperature / viscosity characteristics, heat resistance, and low temperature characteristics than mineral oils. Furthermore, in order to further improve the properties of these synthetic oils, addition of an additive effective for conventional mineral oil has been studied.

  However, the characteristics of sintered oil-impregnated bearings that are inherently self-lubricating and maintenance-free are not exhibited when exposed to various types of metals with a very large surface area, which is unique to sintered oil-impregnated bearings. There are some cases where this occurs. For example, bearing metal becomes a catalyst and oxidation deterioration progresses at a very early stage, resulting in drastic reduction of bearing residual oil due to decomposition and evaporation of the lubricating oil, and corrosion of the metal due to additives contained in the lubricating oil or The generated sludge closes the hole in the bearing, and sufficient lubricant is not supplied to the sliding part, causing oil film shortage and poor lubrication. Finally, the motor stops with a much shorter life than expected. It leads to a situation that will end up.

  Therefore, an antioxidant, more specifically, at least one of various amine-based antioxidants and phenol-based antioxidants is often added to the lubricating oil. Although improvement is observed, the oxidative deterioration life of the sintered oil-impregnated bearing oil cannot be fully satisfied. In addition to such primary antioxidants (radical scavengers), the addition of secondary antioxidants that act as hydroperoxide degrading agents also widely prevents oxidation mechanisms that are said to proceed in a chain. Although it is carried out, not all the so-called secondary antioxidants affect the sintered oil-impregnated bearing material and cannot be used stably.

Patent Document 1 describes an impregnated bearing oil composition to which a specific structure phosphite (dihydrocarbyl hydrogen phosphite) and phosphate (trihydrocarbyl phosphate) are added, which improves friction and wear characteristics. It is aimed, and there is no mention of antioxidant performance. Further, although the bearing compatibility is improved, it is insufficient in terms of preventing corrosion of the bearing material and preventing generation of sludge. As for sludge, a method for preventing the formation thereof by adding alkylnaphthalene or the like has been proposed, but it is not sufficient.
Japanese Patent No. 3,433,402

Further, Patent Document 2 proposes a lubricating oil composition using a specific phosphate ester (considered as an acid phosphate) or its amine salt and various antioxidants, which also prevents bearing corrosion. And it is insufficient in terms of preventing sludge formation.
Japanese Patent Laid-Open No. 2002-180078

  An object of the present invention is to provide a lubricating oil composition in which a primary antioxidant and a secondary antioxidant are added to a lubricating base oil, to suppress rapid decomposition and evaporation of the lubricating oil even in the presence of a bearing metal, and to An object of the present invention is to provide a sintered metal bearing oil or the like that can be stably used for a long period of time without being corroded or altered, or without generating sludge.

  The object of the present invention is achieved by a lubricating oil composition obtained by adding a diphenylamine antioxidant and a phosphite having at least one phenyl ester group to a lubricating base oil.

  The lubricating oil composition according to the present invention comprises a diphenylamine antioxidant as a primary antioxidant and a phosphite having at least one phenyl ester group as a secondary antioxidant added to the lubricating base oil. When used as a sintered metal bearing oil, it not only effectively prevents the bearing material from being corroded and sludge produced, but also rapidly decomposes the lubricating oil even in the presence of the bearing metal. Evaporation is suppressed and it can be used stably for a long time even under high temperature conditions.

  The lubricating oil composition of the present invention having such effects is provided for gears, chains, bushes, hydraulic parts, automatic transmissions, contacts, resins, compressors, rolling bearings, sintered oil-impregnated bearings. It can be effectively used as a lubricating oil for bearings such as hydrodynamic bearings.

  The type of the lubricating base oil is not particularly limited, but an ester oil or a hydrocarbon synthetic oil having excellent heat resistance is preferably used. Examples of ester oils include diesters such as di (2-ethylhexyl) sebacate, fatty acid esters of polyols such as neopentyl glycol, trimethylolpropane, pentaerythritol, and dipentaerythritol, complex esters, carbonate esters, and aromatic esters. It is done. Examples of the hydrocarbon-based synthetic oil include poly α-olefin, ethylene / α-olefin copolymer oligomer, polybutene, alkylbenzene, and alkylnaphthalene. In addition, ether synthetic oils such as alkyl diphenyl ether and polypropylene glycol, various silicone oils, synthetic oils such as various fluorine oils, paraffinic mineral oils, naphthenic mineral oils, or these solvents are refined in combination as appropriate. Mineral oil is used. These lubricating base oils are used alone or in admixture of two or more.

These base oils have a kinematic viscosity at 40 ° C. of about ^{2 to} 1000 mm ² / sec, preferably about 5 to 500 mm ² / sec. Using a kinematic viscosity lower than this may cause a decrease in life, wear, and seizure, such as increased evaporation loss and reduced oil film strength, while using a kinematic viscosity higher than this May cause problems such as an increase in viscous resistance such as increased power consumption and torque.

  In the lubricating base oil, a viscosity index improver such as ethylene / propylene copolymer, styrene-isoprene copolymer, polystyrene, polyisobutylene, polyacrylate, polymethacrylate, etc. is used, preferably polymethacrylate. Is used. The molecular weights of these polymers are not particularly limited, but those having a number average molecular weight Mn in the range of about 3,000 to 1,000,000, preferably about 3,000 to 300,000, are used to sufficiently improve the viscosity index.

  The blending of polymethacrylate not only gives the desired viscosity characteristics (generally about 120-350, preferably about 150-250 as a viscosity index), but can simultaneously satisfy both low temperature characteristics and heat resistance. As the methacrylate for forming polymethacrylate, benzyl methacrylate, cyclohexyl methacrylate, or methacrylate having a linear or branched alkyl group having 1 to 22 carbon atoms, specifically methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, Pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, decyl methacrylate, lauryl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, cetyl methacrylate, heptadecyl methacrylate, octadecyl methacrylate, nonadecyl methacrylate, eicosyl methacrylate, etc. Preferably, Methacrylate is used. These may be used alone or in combination.

  The viscosity index improver can be obtained by polymerizing a methacrylate polymer in the same synthetic oil as the base oil, and the synthetic oil obtained by polymerizing in another polymerization solvent is a base oil. Diluted and dispersed may be used. These viscosity index improvers are a synthetic polymer base oil composed of a synthetic hydrocarbon oil, ester oil or a mixture thereof as a solvent for the methacrylate polymer, and a methacrylate polymer in a total amount with the synthetic oil base oil. About 0.5 to 40% by weight, preferably about 1.5 to 30% by weight.

  The diphenylamine antioxidant which is a primary antioxidant includes diphenylamine and one or both of its phenyl groups having 1 to 30, preferably 3 to 18 carbon atoms such as propyl, isopropyl, butyl, octyl, nonyl, etc. It may be substituted with a chain or branched alkyl group or alkenyl group, an aryl group having 6 to 30 carbon atoms, an aralkyl group having 7 to 30 carbon atoms, or the like. Specifically, for example, phenyl-propylphenylamine, Phenyl isopropylphenylamine, phenyl butylphenylamine, di (n-butylphenyl) amine, di (tertiary butylphenyl) amine, phenyl octylphenylamine, octylphenyl butylphenylamine, di (octylphenyl) amine, Phenyl nonylphenylamine, di (nonylphenyl) amine, 4,4-bis (α, α- And dimethyl) diphenylamine.

  One or more of these primary antioxidants are used at a ratio of about 0.01 to 5 parts by weight, preferably about 0.5 to 3 parts by weight per 100 parts by weight of the base oil, A sufficient anti-oxidation effect cannot be obtained, while it is economically disadvantageous if it is used in a larger proportion.

Secondary antioxidants include phosphites having at least one phenyl ester group, such as the general formula
(R ¹ R ² C ₆ H ₃ O) _n POR ³ _3-n
R ¹ and R ² : hydrogen atom, linear or branched alkyl group or alkenyl group having 1 to 30 carbon atoms
R ³ is the same as R ¹ or R ² or an aryl group having 6 to 30 carbon atoms and an aralkyl group having 7 to 30 carbon atoms.
n: 1 or 2
Specifically, for example, triphenyl phosphite, tricresyl phosphite, tris (2,4-di-tert-butylphenyl) phosphite, tris (monononylphenyl) phosphite, tris (di- Nonylphenyl) phosphite, tris (mono- and di-mixed nonylphenyl) phosphite, diphenyl hydrogen phosphite, diphenyl mono (2-ethylhexyl) phosphite, diphenyl monodecyl phosphite, diphenyl mono (tridecyl) phosphite, And dinonylphenyl mono (2-ethylhexyl) phosphite.

  One or two or more of these secondary antioxidants are used in a ratio of about 0.01 to 5 parts by weight, preferably about 0.5 to 3 parts by weight, based on 100 parts by weight of the base oil, and a lower use ratio In this case, a sufficient antioxidant effect cannot be obtained. On the other hand, if it is used in a larger proportion, it is economically disadvantageous.

  In addition to the above components, a pour point depressant, an ashless dispersant, a metal-based agent used in lubricating oils based on general synthetic oils as necessary, as long as the object of the present invention is not impaired. Known additives such as detergents, other antioxidants, rust inhibitors, corrosion inhibitors, antifoaming agents, antiwear agents, and oiliness agents can be added depending on the intended use. In addition, in order not to inhibit the low-temperature fluidity, heat resistance, and compatibility with the bearing material of the final product, it is preferable that the additive to be added is the minimum necessary amount.

  Examples of the pour point depressant include di (tetraparaffin phenol) phthalate, a condensation product of tetraparaffin phenol, a condensation product of alkylnaphthalene, a chlorinated paraffin-naphthalene condensate, and an alkylated polystyrene.

  Examples of the ashless dispersant include succinimides, succinamides, benzylamines, and ester ashless dispersants.

  Examples of the metal detergent include a sulfonic acid metal salt represented by dinonylnaphthalene sulfonic acid metal salt, a metal salt of alkylphenol, and a salicylic acid metal salt.

  Examples of other antioxidants include phenolic antioxidants such as 2,6-ditertiarybutyl-4-methylphenol and 4,4′-methylenebis (2,6-ditertiarybutylphenol), phenothiazine, Examples include amine-based antioxidants such as phenothiazine and alkylated phenothiazine, other phosphorus-based antioxidants, and sulfur-based antioxidants. These can be used alone or in admixture of two or more.

  Examples of the rust inhibitor include fatty acids, fatty acid soaps, alkyl sulfonates, fatty acid amines, paraffin oxides, and alkyl polyoxyethylene ethers. Examples of corrosion inhibitors include benzotriazole, benzimidazole, thiadiazole, and the like. Can be mentioned.

  Examples of the antifoaming agent include dimethylpolysiloxane, polyacrylic acid, metal soap, fatty acid ester, and phosphate ester.

  Examples of the antiwear agent include phosphorus compounds such as phosphate esters, phosphite esters and phosphate ester amine salts, sulfur compounds such as sulfides and disulfides, and chlorine compounds such as chlorinated paraffin and chlorinated diphenyl. And organometallic compounds such as zinc dialkyldithiophosphate and molybdenum dialkyldithiocarbamate.

  Examples of the oily agent include fatty acids, higher alcohols, polyhydric alcohols, polyhydric alcohol esters, aliphatic esters, aliphatic amines, and aliphatic monoglycerides.

  The composition is prepared by a method of adding a predetermined amount of each of the above components and sufficiently kneading with a three-roll or high-pressure homogenizer.

  Next, the present invention will be described with reference to examples.

Example 1
Trimethylolpropane trioctanoic acid ester (40 ° C. kinematic viscosity: 15-30 mm ² / sec) is blended with a polymethacrylate viscosity index improver (Mn: about 100000) to give a 40 ° C. kinematic viscosity of about 45-60 mm ² / 100 parts of a polyester base oil adjusted so as to be within the range of seconds (weight, the same applies hereinafter) 0.5 parts of phyto was added to prepare a lubricating oil composition having a kinematic viscosity at 40 ° C. of 56.4 mm ² / sec and a viscosity index of 210. The 40 ° C. kinematic viscosity and the viscosity index were both measured and calculated according to JIS K2283.

For this lubricating oil composition, the following items were measured or evaluated.
Change in air permeability: An iron-based sintered oil-impregnated bearing (outer diameter 18 mm, inner diameter 8 mm, length 5 mm) was immersed in 8 g of lubricating oil composition at 170 ° C. for 300 hours, and the air permeability of the oil-impregnated bearing before and after immersion was measured. The difference was defined as a change in air permeability. The air permeability was measured by measuring the pressure when an inert gas flowed at a constant flow rate on the inner diameter side of the oil-impregnated bearing. Presence or absence of sludge: The state of the lubricating oil composition was visually observed during the change in air permeability, and insoluble sludge was observed. No, ○, and “No” was evaluated. Thermal degradation test in the presence of bearing (solidification time): Immerse two iron-based sintered oil-impregnated bearings (outer diameter 18 mm, inner diameter 8 mm, length 5 mm) in 10 g of lubricating oil composition. Then, it was left in a constant temperature bath at 180 ° C., the viscosity was measured at regular intervals, and the solidification time until solidification was measured.

Example 2
In Example 1, 1.0 part of di (nonylphenyl) amine was used as the primary antioxidant, and the amount of secondary antioxidant was changed to 1.5 parts.

Example 3
In Example 1, 1.5 parts of dimethylbenzyldiphenylamine was used as the primary antioxidant, and the amount of secondary antioxidant was changed to 0.5 parts.

Comparative Example 1
In Example 1, the amount of primary antioxidant was changed to 1.5 parts and no secondary antioxidant was used.

Comparative Example 2
In Example 1, the amount of primary antioxidant was changed to 1.5 parts, and 1.0 part of dilauryl hydrogen phosphite was used as a secondary antioxidant.

Comparative Example 3
In Example 1, 1.0 part of di (nonylphenyl) amine was used as the primary antioxidant, and 1.0 part of dilauryl 3,3′-thiodipropionate was used as the secondary antioxidant.

Comparative Example 4
In Example 1, 0.5 part of di (nonylphenyl) amine was used as a primary antioxidant and 0.5 part of trilauryl trithiophosphite was used as a secondary antioxidant.

Comparative Example 5
In Example 1, 1.0 part of dimethylbenzyldiphenylamine was used as the primary antioxidant, and 0.5 g of dilauryl 3,3′-thiodipropionate was used as the secondary antioxidant.

Comparative Example 6
In Example 1, 1.0 part of phenyl-α-naphthylamine was used as the primary antioxidant, and 1.0 part of diphenyl monotridecyl phosphite was used as the secondary antioxidant.

Comparative Example 7
In Example 1, 1.5 parts of phenyl-α-naphthylamine was used as the primary antioxidant, and 1.5 parts of dilauryl 3,3′-thiodipropionate was used as the secondary antioxidant.

Comparative Example 8
In Example 1, 0.5 part of di (octylphenyl) amine was used as the primary antioxidant, and 1.5 parts of triisododecyl phosphite was used as the secondary antioxidant.

The results obtained in the above examples and comparative examples are shown in the following table.
table
Example Comparative Example
Measurement / Evaluation Items 1 2 3 1 2 3 4 5 6 7 8
40 ° C kinematic viscosity (mm ² / sec) 56.4 48.2 53.9 61.0 56.8 52.6 47.8 46.8 54.9 51.7 59.1
Viscosity index 210 213 209 201 206 211 216 214 208 209 203
Air permeability change (mPas) 0.0 -3.9 0.0 2.3 9.3 8.4 200 12.8 13.2 7.5 12.3
Presence or absence of sludge ○ ○ ○ ○ × ○ ○ × × × ×
Solidification time (hrs) 816 960 816 526 720 624 480 816 720 624 480

Example 4
The structure of one aspect of a vehicle fan motor using a sintered oil-impregnated bearing impregnated with the lubricating oil composition according to the present invention is shown as a longitudinal sectional view in FIG. In the vehicle fan motor 1, the motor casing 2 includes a casing 2a and an end cover 2b. A sintered oil-impregnated bearing 4 and a rolling bearing 5 are rotatably supported on the motor shaft 3 respectively. It is press-fitted. The sintered oil-impregnated bearing 4 is impregnated with the lubricating oil composition of Example 1.

  An endurance test was performed on the bearing impregnated with the lubricating oil composition of Example 1 and the bearing impregnated with the lubricating oil composition of Comparative Example 1. In the durability test, the shaft is inserted into each of these two types of bearings, and the shaft is rotated and paused every 15 seconds at a bearing temperature of 140 ° C. The time until the sludge-like deterioration can be visually confirmed is repeated. Measurements yielded values of 826 hours and 540 hours, respectively.

It is a longitudinal section of one mode of a fan motor using a sintered oil impregnated bearing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vehicle fan motor 2 Motor casing 2a Casing 2b End cover 3 Motor shaft 4 Sintered oil-impregnated bearing 5 Rolling bearing

Claims (5)

  A lubricating oil composition comprising a lubricating base oil added with a diphenylamine antioxidant and a phosphite having at least one phenyl ester group.   The lubricating oil composition according to claim 1, wherein diphenylamine antioxidant and at least one phosphite ester having at least one phenyl ester group are added in an amount of 0.01 to 5 parts by weight per 100 parts by weight of the lubricating base oil. .   The lubricating oil composition according to claim 1 or 2, wherein a lubricating base oil containing a polymethacrylate viscosity index improver is used.   A sintered oil-impregnated bearing impregnated with the lubricating oil composition according to claim 1, 2 or 3. A motor using the sintered oil-impregnated bearing according to claim 4.

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