JP2003261892A - Lubricating oil composition for sintered oil-impregnated bearings - Google Patents

Abstract

(57) [Problem] To provide a lubricating oil composition which provides stable operating characteristics over a wide temperature range from low temperature to high temperature, and is excellent in lubricity and volatility resistance. The following general formula (1): [Wherein, R ¹ and R ² are an alkyl group or an aryl group, and the substituent ratio of the aryl group in the molecule is at least 1%.
As mentioned above, it is less than 20%. And a kinematic viscosity at 40 ° C. of 10 to 3000 mm ² / s containing an aryl group represented by the formula:
A lubricating oil composition for a sintered oil-impregnated bearing, comprising 20 to 90% by weight of the polyorganosiloxane and 80 to 10% by weight of a carboxylic acid ester.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lubricating oil composition for a sintered oil-impregnated bearing, and in particular, it has a very high viscosity index of 250 or more, excellent low temperature fluidity, almost no viscosity change due to shearing, and a wide temperature range. The present invention relates to a lubricating oil composition that exhibits stable lubricating performance over a long period of time.

[0002]

2. Description of the Related Art In recent years, metal powder sintered oil-impregnated bearings have been widely used as bearings for multimedia such as automobile electrical equipment, home appliances, audio / visual equipment, and OA office equipment.
By using copper / iron-based metal powder and devising the shape of the bearing, it is possible to realize high speed, durability, and rigidity, and there is an advantage that the production cost can be kept low as compared with the conventional ball bearing. Sintered oil-impregnated bearings are manufactured by vacuum impregnating a lubricating oil according to the application and performance in an impregnating device through steps of mixing metal powder, molding, sintering, and sizing. As the lubricating oil to be impregnated, conventionally, mineral oil-based, poly α-olefin (PA
O), alkylated diphenyl ether, fatty acid ester, fluorinated oil, silicone oil and the like are known. A mixture of these base oils with various additives such as an antioxidant, a rust preventive, and an antiwear agent is used. The required performance of a lubricating oil for a sintered oil-impregnated bearing is that it has excellent viscosity characteristics, lubricity, long-term stability, volatility resistance, material compatibility (metal, resin, etc.). These performance requirements depend largely on the properties of the base oil itself, some of which can be improved by additives.
However, the viscosity characteristics, in particular the viscosity index (change in viscosity with temperature) and the volatility resistance are greatly affected by the characteristics of the base oil itself.

Recent technological changes have become more sophisticated, faster, smaller and lighter, and usage conditions have become more severe. The sintered oil-impregnated bearings used in the above-mentioned equipment are also required to have high performance, and low friction of sliding parts, long-term stability, and stable sliding characteristics over a wide temperature range are required. It was However, conventional lubricating oils have the above-mentioned required characteristics (appropriate viscosity characteristics, lubricity, long-term stability, volatility resistance,
Material compatibility) and cost are not satisfied, and the one suitable for the application has been appropriately used depending on the advantages and disadvantages of the characteristics of the base oil and the lubricating oil. Specifically, silicone oil is known as a base oil with a high viscosity index, but it has low lubricity, and it is difficult to dissolve commonly known additives such as antiwear agents, and it is difficult to improve lubricity. there were. Fluorine-based oil has the drawback of being extremely expensive. Other, mineral oil,
The viscosity index of poly-α-olefins, fatty acid esters, diphenyl ether, etc. is about 90 to 150, and the operating temperature range is limited.

[0004]

SUMMARY OF THE INVENTION The present invention has been made based on such a need for a sintered oil-impregnated bearing, that is, the present invention relates to a sintered oil-impregnated bearing oil, which can be used from low temperature to high temperature. It is an object of the present invention to provide a lubricating oil composition which brings stable operating characteristics over a wide temperature range, and is excellent in lubricity and volatility resistance.

[0005]

Means for Solving the Problems As a result of intensive studies by the present inventors, by blending a specific fatty acid ester with a specific polyorganosiloxane, a high viscosity index is ensured and lubricity is also improved. It was found that it is possible. As a result, by using these lubricating oil compositions in the sintered oil-impregnated bearing, stable sliding characteristics can be obtained in a wide temperature range.

That is, the present invention provides the following lubricating oil composition for sintered oil-impregnated bearings. 1. The following general formula (1)

[Chemical 2] [Wherein R ¹ and R ² are an alkyl group or an aryl group, and the substituent ratio of the aryl group in the molecule is at least 1].
% Or more and less than 20%. ] The kinematic viscosity at 40 degreeC containing the aryl group represented by 10-3000 mm < ² > /
s, preferably 20 to 500 mm ² / s of polyorganosiloxane 20 to 90% by weight and carboxylic acid ester 8
A lubricating oil composition for a sintered oil-impregnated bearing, which comprises 0 to 10% by weight.

2. The lubricating oil composition according to the above item 1, wherein an antiwear agent and / or an antioxidant is added.

3. The lubricating oil composition according to the above item 1 or 2, which has a viscosity index of 250 or more.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The silicone oil used as the base material in the present invention is a polyorganosiloxane containing an aryl group, as shown in the general formula (1).

[0010]

[Chemical 3]

In the above formula, R ¹ and R ² are alkyl groups,
Or an aryl group, which may be the same or different from each other, examples of the alkyl group include a methyl group and an ethyl group. The aryl group represents a substituent containing at least one benzene ring, and examples thereof include a phenyl group, a tolyl group in which an alkyl group having 1 to 4 carbon atoms is added to a phenyl group, a xylyl group, and the like. preferable. R ¹ and R ² may be different for each siloxane unit. n is an integer that changes depending on the degree of polymerization, and if the degree of polymerization is too large, the desired performance may not be obtained in some cases, such as increased kinematic viscosity at low temperatures and poor fluidity. For the purpose of the present invention, the kinematic viscosity at 40 ° C. is 10 to 10.
3000 mm ² / s, particularly preferably a polymerization degree to be 20 to 500 mm ² / s. Therefore, it is preferable to adjust or select n so that the kinematic viscosity of the silicone oil falls within the above viscosity range. At the end of the polyorganosiloxane molecule, a maximum of three hydrocarbon groups will be attached to the Si element, but these substituents may be either alkyl groups or aryl groups. Typically, the alkyl group is a methyl group,
It is preferable that the aryl group is a phenyl group.

The substituent ratio (substitution ratio) of the aryl group in the polyorganosiloxane molecule is at least 1 of the total number of substituents.
% Or more, preferably 3% or more. If the substitution rate of the aryl group is less than 1%, the characteristics of the aryl group will not be exhibited.
In particular, the solubility with the carboxylic acid ester becomes insufficient.

Since the carboxylic acid ester to be mixed has a viscosity index of about 100 to 180, among these polyorganosiloxanes containing aryl groups, those having a viscosity index of 300 or more, preferably 400 or more, are used. Is preferred. The viscosity index depends on the substituent ratio of the aryl group, and the viscosity index of 300 or more can be secured when the substituent ratio is less than 20%. From this, the substituent ratio of the aryl group in the polyorganosiloxane molecule is at least 1
% And less than 20%, and 3 to 10% is particularly preferable.

Further, the above polyorganosiloxane containing an aryl group is highly purified by distillation to remove low molecular impurities of D10 component or less which are likely to be volatilized, so that the poor conductivity due to the formation of a silicic acid film can be prevented. It can also be applied to applications such as electronic equipment.

10% to 80% of a carboxylic acid ester is added to the above polyorganosiloxane containing an aryl group.
Specific examples of the carboxylic acid ester include a dibasic acid ester of an alcohol and a dibasic acid and / or a polyhydric alcohol fatty acid ester of a polyhydric alcohol and a fatty acid.

As the dibasic acid ester, an ester composed of a monohydric alcohol having 8 to 18 carbon atoms and a dicarboxylic acid having 6 to 15 carbon atoms (dibasic acid) represented by the following general formula (2) is used. preferable.

[Chemical 4] In the formula, R ³ and R ⁴ represent an alkyl group having 8 to 18 carbon atoms,
R ³ and R ⁴ may be the same or different, and m represents an integer of 4 to 13. Dibasic acid esters other than the above are volatile,
It is not suitable because it is inferior in low temperature fluidity, viscosity index and solubility. Specific examples include sebacic acid ester, adipic acid ester, azelaic acid ester, and dodecanedioic acid ester. In particular, adipic acid-di-
2-ethylhexyl, adipic acid-di-isononyl, adipic acid-di-isodecyl, sebacic acid-di-2-ethylhexyl, azelaic acid-di-2-ethylhexyl,
Dodecanedioate-di-2-ethylhexyl and the like are preferable.

As the polyhydric alcohol fatty acid ester,
Polyhydric alcohol having 2 to 6 valences of 3 to 10 carbon atoms and 6 carbon atoms
It is preferable to use an ester composed of -18 monovalent carboxylic acids (fatty acids). Among them, an ester with glycerin or neopentyl polyol is preferable, and an ester having no hydroxyl group residue between trimethylolethane, trimethylolpropane and pentaerythritol represented by the following general formula (3) and carboxylic acid is particularly preferable.

[Chemical 5] In the formula, R ⁵ represents a carbon atom, a carbon atom having a methyl group or an ethyl group, R ⁶ represents an alkyl group having ^{5 to 17} carbon atoms, and p represents an integer of 3 or 4. The three to four R ⁶ may be the same or different.

The fatty acid ester of trimethylolpropane is particularly preferably used because it is excellent in volatility, low temperature fluidity, viscosity index and solubility. Specific examples include trimethylolpropane trihexyl, trimethylolpropane trioctyl, trimethylolpropane trinonyl, trimethylolpropane tridecyl, and trimethylolpropane tritridecyl. Particularly, trimethylolpropane trihexyl, trimethylolpropane trioctyl, trimethylolpropane trinonyl and the like are preferable. Regarding fatty acid esters of pentaerythritol, pentaerythritol tetraheptyl, pentaerythritol tetraoctyl,
Pentaerythritol tetradecyl, pentaerythritol tetratridecyl and the like are also mentioned as preferable esters.

The mixing ratio of the above polyorganosiloxane and the carboxylic acid ester of dibasic acid ester and / or polyhydric alcohol fatty acid ester is 90/10 to 20/80.
(Weight ratio). 1 carboxylic ester
When it is less than 0%, the viscosity index is high, but sufficient lubricity and solubility of additives cannot be expected. On the other hand, when it exceeds 80%, the viscosity index becomes 250 or less, which is not preferable for the purpose of the present invention.

A base material prepared by blending the above polyorganosiloxane containing an aryl group with a dibasic acid ester and / or a polyhydric alcohol fatty acid ester is used as an antiwear agent and / or
Alternatively, various additives may be added as antioxidants.

For example, as the antiwear agent, a fatty acid type,
Additives such as sulfur-based, phosphorus-based, zinc dialkyldithiophosphate, etc., preferably fatty acids such as oleic acid, dibenzyl sulfide, thiadiazole, sulfurized fats and oils, phosphoric acid esters, thiophosphoric acid esters,
Examples thereof include phosphate amine salts, dithiophosphates, zinc dialkyldithiophosphates, and the like.

As antioxidants, phenolic antioxidants (di-t-butyl paracresol, (3,5-di-
t-butyl-4-hydroxyphenyl) -propionic acid ester type, bisphenol type, etc.), amine type (alkylated diphenylamine, phenyl α-naphthylamine,
Examples include additives such as alkylated phenyl α-naphthylamine) and phosphorus-based (phosphorous acid ester).

The lubricating oil composition of the present invention described above is characterized by having a very high viscosity index of 250 or more, and therefore can be stably used in a wide temperature range. Particularly in the low temperature range, the increase in viscosity is small, which is effective for energy saving and power saving, and in the high temperature range, there is little decrease in viscosity and an oil film is easily formed, so that excellent lubricity is exhibited. Further, additives such as antiwear agents and antioxidants are dissolved, and by adding these various additives, it is possible to further improve properties such as lubricity and oxidative stability. Further, the base material in which a polyorganosiloxane containing an aryl group is mixed with a dibasic acid ester and / or a polyhydric alcohol fatty acid ester is different from a high-viscosity index base oil in which a high molecular polymer as a viscosity index improver is mixed, Almost no decrease in viscosity and viscosity index due to shearing. Therefore, the sintered oil-impregnated bearing lubricating oil of the present invention is stable against shearing of each sliding portion in actual use, and has a small change in viscosity and viscosity index over time, and can exhibit stable performance over a long period of time.

[0024]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited thereto.

1. Base oil As the base oil, the following polyorganosiloxane and ester were used. (Polyorganosiloxane) Silicone A-1: Methylphenylpolysiloxane Phenyl group content: 5% Viscosity index: 391 Kinematic viscosity (40 ° C.): 71.23 mm ² / s Kinematic viscosity (100 ° C.): 26.67 mm ² / s (Comparative polyorganosiloxane) Silicone A-2: Dimethylpolysiloxane Phenyl group content: 0% Viscosity index: 431 Kinematic viscosity (40 ° C.): 37.93 mm ² / s Kinematic viscosity (100 ° C.): 15.90 mm ² / S

(Ester) Ester B-1: dodecanedioic acid-di-2-ethylhexyl ester B-2: adipic acid-di-iso-decyl ester C-1: trimethylolpropane trioctyl ester C-2: Trimethylolpropane tridecyl (comparative base oil) Poly α-olefin kinematic viscosity (40 ° C.): 29.51 mm ² / s

2. Additive (antiwear agent) As antiwear agent A, phosphorus-based tricresyl phosphate was used. (Antioxidant) The following phenolic and amine compounds were used as antioxidants. Antioxidant A: (3,5-di-t-butyl-4-hydroxyphenyl) -propionate antioxidant B: alkylated diphenylamine

3. Test method The above-mentioned base oil and additives were blended in the proportions shown in the upper part of the table below to prepare lubricating oil compositions of Examples and Comparative Examples. The prepared lubricating oil compositions were tested for viscosity characteristics, dissolution stability, lubricity, oxidation stability, and thermal stability, and practical performance evaluation was performed using sintered oil-impregnated bearings.

(Viscosity characteristics) Kinematic viscosity and viscosity index are JIS
It was measured and calculated according to K2283.

(Solubility Stability (Compatibility)) The solubility of the polyorganosiloxane and the fatty acid ester was evaluated by the following procedure. The polyorganosiloxane and the fatty acid ester were weighed out and mixed with stirring at room temperature (25 ° C.). The mixed solution was transferred to a test tube and allowed to stand in a low temperature bath at -20 ° C for 1 day. Regarding the solubility, immediately after stirring at room temperature and after standing still, it was visually observed whether or not it was uniformly dissolved, whether there were two-layer separation or turbidity. When there were no two-layer separation or turbidity, "○" was given, and when two-layer separation or turbidity was observed, "X" was given.

(Pour Point) Pour point (JIS)
K2269).

(Lubricity) As a desk lubrication test, a shell 4-ball abrasion resistance test (ASTM D4172) was conducted.
The test conditions are 1200 rpm, 40 kgf / cm ² , 5
At 0 ° C. for 60 minutes, the wear scar diameter after the test was measured.

(Oxidation stability) Oxidation stability is measured by rotary cylinder type oxidation stability (RBOT, JIS K2514).
The oxidation induction period (min) was measured.

(Thermal Stability / Evaporation Resistance) The thermal stability was evaluated by a lubricating oil thermal stability test (JIS K2540). 20 g of the sample oil was placed in a glass container having an inner diameter of 51 mm and a height of 56 mm, kept at 160 ° C., and the evaporation loss (%) was calculated from the weight change after 504 hours for the evaluation of evaporation resistance. Also, the presence or absence of sludge was observed from the outside.

(Evaluation of Practical Performance) A copper-based sintered oil-impregnated bearing (inner diameter 4 mm, outer diameter 7 mm, height 3 mm) having an oil content of 20% was prototyped and a shaft (SUS420J2) was incorporated (clearance: 13 μm). The sliding characteristics were evaluated under the conditions. Load: 100 gf (0.9 kgf / cm ² ) Rotation speed: 3000 rpm (37.6 m / min) Temperature: -30 ° C, 25 ° C, and 80 ° C Time: 1 hr at each temperature Measurement item: Friction coefficient after 1 hour of startup Comparative oil: poly-α-olefin kinematic viscosity (40 ° C.): 29.2 mm ² / s kinematic viscosity (100 ° C.): 5.7 mm ² / s Viscosity index: 138

4. Test results The composition of each sample and the test results are shown in Tables 1 to 4.

[0037]

[Table 1]

Examples 1 to 8 are shown in Table 1, and when methylphenylpolysiloxane (silicone A-1) was mixed with four kinds of carboxylic acid esters and when the mixing ratio was changed, additives (antioxidants) were used. , Anti-wear agent) are added, the compatibility, viscosity characteristics and lubricity are shown. Dodecanedioate-di-2-ethylhexyl (ester B-1), adipate-di-2-ethylhexyl (ester B-2), trimethylolpropane trioctyl (ester C-1), trimethylolpropane The mixed solution of tridecyl (ester C-2) and methylphenyl silicone does not separate even at low temperature, has a viscosity index of 250 or more, and is excellent in lubricity. By adding an antiwear agent to methylphenylpolysiloxane and a carboxylic acid ester (such as dodecanedioic acid-di-2-ethylhexyl or trimethylolpropane trioctyl), lubricity can be further improved (implementation). Examples 7 and 8).

[0039]

[Table 2]

Table 2 shows various performances of Comparative Examples 1-8. When methyl phenyl polysiloxane (silicone A-1) and dimethyl polysiloxane (silicone A-2) were used alone, the viscosity index was high at around 400,
In the 4-ball shell wear resistance test, seizure occurred, and problems occurred in lubricity (Comparative Examples 1 and 2). Further, dibasic acid esters (esters B-1 and B-2) and trimethylolpropane esters (esters C-1 and C-2) have excellent lubricity, but have a viscosity index of about 130 to 170, which is from low temperature to high temperature. The stable sliding performance of the sintered oil-impregnated bearing cannot be obtained in a wide temperature range up to (Comparative Examples 3 to 6). Furthermore, dimethyl polysiloxane (silicone A-2) could not dissolve the carboxylic acid ester (Comparative Examples 7 and 8).

[0041]

[Table 3]

Table 3 shows the thermal stability, oxidative stability and lubricity of Examples 7 and 8. In addition, Comparative Example 9 using a base oil of poly α-olefin as a comparative oil is also shown. In Examples 7 and 8,
It has a high viscosity index of 300 or more and is expected to be applied in a wide temperature range. The RBOT value showing the oxidation stability is also 1500
It is as high as min or more, and shows excellent oxidation stability as compared with Comparative Example 9. Further, the evaporation characteristics of Examples 7 and 8 are superior to those of Comparative Example 9, and the insufficient lubrication of the oil-impregnated bearing due to the evaporation loss of oil can be reduced even in a high temperature range.

[0043]

[Table 4]

Table 4 shows the practical performance evaluation results according to the eighth embodiment. In addition, as Comparative Example 10, the result of the poly-α-olefin oil is also shown. In Example 8, from -30 ° C to 80
Up to ° C, the change in friction coefficient was smaller than in Comparative Example 10, and stable sliding characteristics were obtained. Particularly at low temperatures, the friction coefficient is low, and the characteristics of the high viscosity index of Example 8 are exhibited.

[0045]

The lubricating oil composition of the present invention has a high viscosity index, is excellent in lubricity, and can be further improved in lubricity and oxidation stability by the addition of additives.
In particular, by impregnating a sintered oil-impregnated bearing with these lubricating oil compositions, stable sliding characteristics can be expected over a wide temperature range from low temperatures to high temperatures.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C10M 137/04 C10M 137/04 // C10N 20:02 C10N 20:02 40:02 40:02 (72) Inventor Seijiro Antomi 3-17-35, Shinzonan, Toda City, Saitama Prefecture Japan Energy Co., Ltd. (72) Inventor Yoji Takezaki 2-121 Nisshin-cho, Saitama City, Saitama Prefecture (72) Inventor Sanpei Seki 2-121, Nisshin-cho, Saitama-shi, Saitama F-term in POLYITE Co., Ltd. (reference) 4H104 BB05C BB31A BB33A BB34A BB35C BE07C BH03C CJ06A EA02A LA04 PA01 PA04 RA03

Claims (3)

[Claims] 1. The following general formula (1): [Wherein R ¹ and R ² are an alkyl group or an aryl group, and the ratio of the substituent of the aryl group in the molecule is at least 1%.
As described above, it is less than 20%. ] The kinematic viscosity at 40 degreeC containing the aryl group represented by is 10-3000 mm < ² > / s.
20 to 90% by weight of the polyorganosiloxane and 80 to 10% by weight of a carboxylic acid ester, and a lubricating oil composition for a sintered oil-impregnated bearing. 2. The lubricating oil composition for a sintered oil-impregnated bearing according to claim 1, further comprising an antiwear agent and / or an antioxidant. 3. The lubricating oil composition for a sintered oil-impregnated bearing according to claim 1, which has a viscosity index of 250 or more.