JP4017639B2 - Grease base oil for bearings - Google Patents

Description

  The present invention relates to a grease base oil for bearings. More specifically, it is not only used as a lubricating oil such as machine oil, electrical insulating oil, refrigeration oil, hydraulic oil, compressor oil, etc., used in situations where temperature changes are severe, but also as a heat medium, plasticizer for plastics, lubricant, The present invention relates to a grease base oil for bearings that can be suitably used as a mold agent, a crystallization accelerator and the like.

Grease base oil is widely used as a lubricating oil mainly in various machines.
Conventionally, mineral oil has been widely used as the lubricating oil, and such mineral oil has an advantage that it is inexpensive, but has a drawback that lubricity is extremely poor when used at low temperatures.

  As a grease base oil that eliminates the above disadvantages, an ester grease base oil composed of an ester of neopentyl polyol and a fatty acid containing a tertiary fatty acid having 1 to 8 carbon atoms in the alkyl group is known. (See Patent Document 1).

  When the ester grease base oil is used, the lubricity at a low temperature is certainly improved, but there is a disadvantage that the lubricity is remarkably lowered during a long period of use at a high temperature.

Therefore, in recent years, with the improvement in performance of machinery, in addition to excellent lubricity at low temperatures, a wide range of operating temperatures that can maintain excellent lubricity even when used for a long time at high temperatures. Development of a grease base oil for bearings that exhibits excellent lubricity over a long period of time is awaited.
JP-A-1-139298

  The present invention has been made in view of the prior art, in addition to excellent lubricity at low temperatures, it can maintain excellent lubricity even when used for a long time at high temperatures, An object of the present invention is to provide a grease base oil for bearings that exhibits excellent lubricity over a long period of time in a wide range of operating temperatures.

  That is, the gist of the present invention consists of an esterified product obtained by an esterification reaction of pentaerythritol and carboxylic acid, and the carboxylic acid contains (A) n-heptanoic acid and (B) 2-ethylhexanoic acid, A) The present invention relates to a grease base oil for bearings having a molar ratio of n-heptanoic acid / (B) 2-ethylhexanoic acid of 20/80 to 42.2 / 48.9.

The grease base oil for bearings of the present invention has excellent lubricity at low temperatures, and can maintain excellent lubricity even when used for a long time at high temperatures. It exhibits excellent lubricity over a long period of time.
Therefore, the grease base oil for bearings of the present invention can be suitably used for machinery and the like used under conditions where the temperature change is severe.

  As described above, the bearing grease base oil of the present invention has a volatilization amount of 35% by weight or less when heated in a constant temperature bath at 180 ° C. for 500 hours and a pour point of −20 ° C. or less. is there.

  Surprisingly, the bearing grease base oil of the present invention has excellent lubricity at low temperatures as well as excellent lubricity even when used at high temperatures for a long time. In addition, an exceptionally excellent effect is exhibited in that excellent lubricity can be maintained over a long period of time in a wide range of operating temperatures.

  The reason why the grease base oil for bearings of the present invention exhibits such an excellent effect is not yet clarified at present, but the pour point of the bearing grease base oil of the present invention is probably −20 ° C. or lower. Based on the above, the bearing grease base oil of the present invention has an appropriate fluidity when used at a low temperature, and thus exhibits excellent lubricity, and when heated in a constant temperature bath at 180 ° C. for 500 hours. Based on the fact that the volatilization amount is 35% by weight or less, it is difficult to volatilize even when used for a long time at a high temperature, and it is considered that excellent fluidity is expressed over a long period of time.

  Thus, the bearing grease base oil of the present invention has a volatilization amount of 35% by weight or less and a pour point of −20 ° C. or less when heated in a constant temperature bath at 180 ° C. for 500 hours. Based on this, it has excellent lubricity at low temperatures and can maintain excellent lubricity even when used for a long time at a high temperature. For example, a wide temperature range from a low temperature of about −40 ° C. to a high temperature of about 150 ° C. It is an epoch-making invention that expresses excellent lubricity in a range.

  In addition, the said volatilization amount is a volatilization amount at the time of heating for 500 hours in a constant temperature bath whose atmospheric temperature is 180 degreeC based on JISK22205.6. The volatilization amount is 35% by weight or less, preferably 30% by weight so that excellent lubricity can be maintained for a long time even when the bearing grease base oil of the present invention is used at a high temperature for a long time. % Or less, more preferably 25% by weight or less.

  The pour point is a value when measured according to a method defined in JIS K2269. When the pour point of the bearing grease base oil of the present invention is −20 ° C. or lower, for example, the bearing grease base oil of the present invention is used for an air conditioner fan motor bearing, automobile bearing, acoustic equipment bearing, computer bearing, etc. When used in the above, the low temperature starting torque can be drastically reduced. The pour point is preferably −30 ° C. or less, more preferably −40 ° C. or less, and particularly preferably −50 ° C. or less from the viewpoint of further improving the lubricity at low temperatures.

Furthermore, when the kinematic viscosity at 40 ° C. of the grease base oil for bearings of the present invention is 20 mm ² / sec or more, preferably 25 mm ² / sec or more, the volatilization amount of the bearing grease base oil at high temperatures is Further reduction can be achieved, and when it is 100 mm ² / sec or less, preferably 75 mm ² / sec or less, more preferably 65 mm ² / sec or less, the fluidity in a low temperature state can be enhanced.

  In the present invention, the bearing grease base oil is preferably an ester in which pentaerythritol is used as a constituent component from the viewpoint of excellent thermal stability, low volatility, suitable viscosity, and the like. From the viewpoint of oxidation stability and the like, it is preferable that a carboxylic acid is used as the acid component constituting the ester.

  The specific composition of the ester of pentaerythritol and carboxylic acid is not particularly limited as long as it satisfies the volatilization amount and the pour point. As typical examples of such esters, for example, the carboxylic acid is composed of (A) n-heptane and (B) at least one branched chain-containing fatty acid selected from 2-ethylhexanoic acid and i-nonanoic acid. These esters are particularly suitable for use in the present invention because of their low volatilization amount and low pour point.

  Examples of the i-nonanoic acid used for the branched chain-containing fatty acid include 3,5,5-trimethylhexanoic acid, 2-methyloctanoic acid, 2,2-dimethylheptanoic acid, and the like. Among these i-nonanoic acids, 3,5,5-trimethylhexanoic acid can be suitably used in the present invention because it is easily available.

  The molar ratio of the (A) n-heptanoic acid / (B) branched chain-containing fatty acid is 20/80 or more, preferably 25 / from the viewpoint of expressing low volatility at high temperature and improving fluidity at low temperature. It is desirably 75 or more, and from the viewpoint of increasing fluidity at a low temperature and obtaining an optimum viscosity, it is desirably 80/20 or less, preferably 75/25 or less.

  In addition, the carboxylic acid contains other carboxylic acids other than (A) n-heptanoic acid and (B) branched chain-containing fatty acid within a range in which the object of the present invention is not inhibited, for example, contained in the carboxylic acid. You may mix | blend so that the quantity may be 50 mol% or less, Preferably it is 40 mol% or less, More preferably, it is 30 mol% or less, Most preferably, it is 20 mol%. Examples of such other carboxylic acids include linear carboxylic acids such as n-pentanoic acid, n-hexanoic acid, n-octanoic acid, n-nonanoic acid and lauric acid, 2-methylbutanoic acid, 3-methylbutanoic acid, 2 -Branched chain carboxylic acids such as ethylbutanoic acid, 2-ethylpentanoic acid, 2-methylhexanoic acid, 2,2-dimethylhexanoic acid and 2,2-dimethylheptanoic acid.

  In the reaction of pentaerythritol and carboxylic acid, the equivalent ratio of the two is not particularly limited, but usually the carboxyl group of the fatty acid is 1.0 to 1.3 equivalents relative to 1 equivalent of the hydroxyl group of pentaerythritol. It is preferable to adjust to. In addition, when the ratio of the carboxyl group of the fatty acid is increased, the reactivity between pentaerythritol and the fatty acid is improved, but it is necessary to remove excess fatty acid after the reaction is completed. Thus, when a large amount of fatty acid is used, excess fatty acid can be removed by methods such as distillation under reduced pressure, steaming, adsorption using an adsorbent, and removal.

  The acid value of the ester is 1.0 mgKOH / g or less, preferably 0.5 mgKOH / g or less, more preferably from the viewpoints of flash point, oxidation stability, thermal stability, hydrolysis stability, metal corrosiveness, etc. It is desirable that it is 0.1 mgKOH / g or less. Further, the hydroxyl value of the ester is 10.0 mgKOH / g or less, preferably 7.0 mgKOH / g or less, more preferably 5, from the viewpoints of flash point, low temperature fluidity, thermal stability, hydrolysis stability and the like. It is desirable that it is 0 mgKOH / g or less.

  In addition, the grease base oil for bearings of the present invention does not impair the purpose of the present invention with lubricating oil additives such as antioxidants, extreme pressure agents, rust inhibitors, antifoaming agents, and demulsifiers that are commonly used. It can be used if necessary in an amount within the range.

  Examples of the antioxidant include phenols such as 2,6-di-t-butyl-4-methylphenol and 4,4′-methylenebis (2,6-di-t-butyl-4-methylphenol). Antioxidant; p, p'-dioctylphenylamine, monooctyldiphenylamine, phenothiazine, 3,7-dioctylphenothiazine, phenyl-1-naphthylamine, phenyl-2-naphthylamine, alkylphenyl-1-naphthylamine, alkylphenyl-2- Examples thereof include amine-based antioxidants such as naphthylamine; sulfur-based antioxidants such as alkyl disulfide, thiodipropionic acid ester and benzothiazole; zinc dialkyldithiophosphate and zinc diallyldithiophosphate. These antioxidants can be used alone or in admixture of two or more.

  Examples of the extreme pressure agent include zinc dialkyldithiophosphate, zinc diallyldithiophosphate, dialkyl polysulfide, triallyl phosphate, and trialkyl phosphate. These extreme pressure agents can be used alone or in admixture of two or more.

  Examples of the rust preventive include alkenyl succinic acid, alkenyl succinic acid derivative, sorbitan monooleate, pentaerythritol monooleate, glycerin monooleate, and amine phosphate. These rust inhibitors can be used alone or in admixture of two or more.

   Examples of the antifoaming agent include silicone oils such as dimethylpolysiloxane and organosilicates such as diethyl silicate. These antifoaming agents can be used alone or in admixture of two or more.

  Examples of the demulsifier include polyoxyalkylene glycol, polyoxyalkylene alkyl ether, polyoxyalkylene alkylamide, polyoxyalkylene fatty acid ester, and the like, but the present invention is not limited to such examples. These demulsifiers can be used alone or in admixture of two or more.

  In addition, what is necessary is just to mix a thickener, when preparing grease using the grease base oil for bearings of this invention. Examples of the thickening agent include soaps such as calcium soap, sodium soap, and lithium soap; complex soaps such as calcium complex soap, aluminum complex soap, and lithium complex soap; terephthalamidate, urea, silica airgel, and the like. It is done.

  The grease base oil for bearings of the present invention has excellent lubricity at low temperatures, and can maintain excellent lubricity even when used for a long time at high temperatures. It exhibits excellent lubricity over a long period of time.

  Therefore, the grease base oil for bearings of the present invention is not only used as a lubricating oil such as machine oil, electrical insulating oil, refrigeration oil, hydraulic oil, compressor oil, etc. used under conditions where temperature changes are severe, but also as a heat medium. It can also be suitably used as a plasticizer for synthetic resins, a lubricant, a mold release agent, a crystallization accelerator and the like.

  Next, the present invention will be described in more detail based on examples, but the present invention is not limited to such examples.

Production Example 1
A 2 liter four-necked flask was equipped with a stirrer, thermometer, nitrogen gas blowing tube and dehydration tube with a cooling tube. To this flask, 75.4 moles of n-heptanoic acid and 24.6 moles of 3,5,5-trimethylhexanoic acid were added, and the carboxyl group of the carboxylic acid was 1. Pentaerythritol was added so as to be 25 equivalents.

  Next, it was made to react at 230 degreeC for 14 hours, blowing in nitrogen gas in the flask, and the distilled water was removed.

  After completion of the reaction, excess fatty acid was deoxidized for 1 hour under a reduced pressure of 5 mmHg, steamed for 1 hour under a reduced pressure of 5 mmHg, and remained with an adsorbent (Kyowa Chemical Industry Co., Ltd., trade name: KYOWADO 500SH). After adsorbing the fatty acid, filtration was performed to obtain an ester.

  Next, the volatilization amount, pour point, kinematic viscosity at 40 ° C., acid value, hydroxyl value and viscosity index of the obtained ester were examined according to the following method. The results are shown in Table 1.

(1) Volatilization amount The obtained ester is put in a constant temperature bath at 180 ° C. and heated in the atmosphere for 500 hours, and then the volatilization amount is obtained in accordance with JIS K2220 5.6.

(2) Pour point The pour point is determined according to JIS K2269.

(3) Kinematic viscosity at 40 ° C. or 100 ° C. The kinematic viscosity at 40 ° C. is determined according to JIS K2283.

(4) Viscosity index After determining the viscosity at 100 ° C. according to JIS K2283, JIS K2283
Viscosity index is determined according to K2283.

(5) Acid value An acid value is calculated | required based on KSTM20045.

(6) Hydroxyl value The hydroxyl value is determined according to KSTM 20046.

Production Examples 2-5
In Production Example 1, the composition of pentaerythritol and carboxylic acid was changed as shown in Table 1 and adjusted such that the carboxyl group of the carboxylic acid was 1.25 equivalents relative to 1 equivalent of the hydroxyl group of pentaerythritol. The ester was prepared in the same manner as in Production Example 1.

The properties of the resulting ester are shown in Table 1.
In Table 1, iC9 acid represents 3,3,5-trimethylhexanoic acid.

Comparative Production Examples 1-8
In Production Example 1, the composition of pentaerythritol and carboxylic acid was changed as shown in Table 2, and the carboxyl group of the carboxylic acid was adjusted to 1.25 equivalents relative to 1 equivalent of the hydroxyl group of pentaerythritol. The ester was prepared in the same manner as in Production Example 1. The properties of the obtained ester are shown in Table 2.

  In addition, iC7 acid described in Table 2 is i-heptanoic acid [manufactured by Kyowa Hakko Co., Ltd., trade name: Kyowanoic GH], iC8 acid is i-octanoic acid [manufactured by Exxon Chemical Co., Ltd., trade name: Secanoic C8 acid], iC9 acid represents 3,3,5-trimethylhexanoic acid.

Examples 1 to 5 and Comparative Examples 1 to 8 (Examples 1, 2 and 5 are reference examples)
The esters obtained in Production Examples 1 to 5 and Comparative Production Examples 1 to 8 are used as bearing grease base oils, and the lubricity at low temperatures and the lubricity after long time use at high temperatures are as follows. It investigated according to the method of. The results are shown in Table 3.

[Lubricity of grease base oil for bearings]
(A) Lubricity at low temperatures (starting torque and rotational torque at low temperatures)
The obtained grease base oil for bearings is used for a low temperature torque test in accordance with JIS K2220 5.14, and the starting torque and the rotational torque are measured in an atmosphere of −40 ° C. to examine the lubricity.

(B) Lubricity when used for a long time at high temperature (operating time at high temperature)
The obtained grease base oil for bearings was used for CRC lubrication life test in accordance with ASTM D 3336, and the torque was increased by repeating the operations of rotating at 10000 rpm, 150 ° C. for 21.5 hours, and resting for 2.5 hours. Measure the operation time until it stops due to heat generation.
In addition, it means that it is excellent in the lubricity at high temperature, so that operation time is long.

  From the results shown in Table 3, the grease base oils for bearings obtained in Examples 1 to 5 all have a volatilization amount of 35% by weight or less when heated in a thermostat at 180 ° C. for 500 hours, Also, since the pour point is -20 ° C or lower, the starting torque and rotational torque at low temperatures are low, the lubricity at low temperatures is excellent, and the operating time at high temperatures is long, so it is used at high temperatures for a long time. It turns out that it is excellent in the lubricity at the time.

Claims (1)

A esterification bearing grease base oil ing from esterification product obtained by the pentaerythritol with a carboxylic acid, and (1) a carboxylic acid and (A) n-heptanoic acid (B) 2-ethylhexanoate Or (2) in addition to (A) n-heptanoic acid and (B) 2-ethylhexanoic acid, i-nonanoic acid, n-pentanoic acid, n-hexanoic acid, n-octanoic acid, n- From nonanoic acid, lauric acid, 2-methylbutanoic acid, 3-methylbutanoic acid, 2-ethylbutanoic acid, 2-ethylpentanoic acid, 2-methylhexanoic acid, 2,2-dimethylhexanoic acid, and 2,2-dimethylheptanoic acid consisting consist least one member selected from the group, (a) n-molar ratio of heptanoic acid / (B) 2-ethylhexanoate Ri 20/80 to 42.2 / 48.9 der in the carboxylic acid 2-D A grease base oil for bearings , wherein the content of tilhexanoic acid is 48.9 mol% or more, the kinematic viscosity of the esterified product at 40 ° C is 25 to 33.64 mm ² / sec, and the pour point is -45 ° C or less .