JP4197407B2 - Lubricating oil composition for bearings - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lubricating oil composition for bearings, and more particularly to a low-viscosity lubricating oil composition for bearings suitable for jet lubrication systems such as machine tool main shafts.
[0002]
[Prior art]
In recent years, machine tools have been demanded to increase the spindle spindle speed and to perform high-precision machining with aluminum alloys used for aircraft parts and electronic parts in order to increase efficiency. Grease lubrication, oil-air lubrication, oil mist lubrication, and jet lubrication are the main spindle spindle lubrication methods. Of these, the jet lubrication method in which a large amount of lubricating oil is injected onto the bearing to lubricate and cool the bearing is the main spindle. It is said to be optimal for speeding up. In order to suppress the thermal deformation of the main shaft accompanying the increase in speed and improve the machining accuracy of the workpiece, it is necessary to reduce the stirring resistance of the lubricating oil as much as possible. Therefore, the bearing lubricating oil used in jet lubrication is 40 ° C. A kinematic viscosity having a low viscosity of 1 to 22 mm ² / s is used. However, low viscosity lubricating oil is difficult to form an oil film, and the addition of additives is indispensable for imparting high wear resistance and load resistance. Among these, zinc dialkyldithiophosphate (ZnDTP) is widely used because it exhibits low cost, excellent wear resistance, and load resistance.
[0003]
By the way, cutting oils according to the processing method and material of the workpiece are used in machine tools, but in recent years, as the speed of the spindle has increased, it has become an environment where cutting oil is likely to be mixed in the lubrication system. Yes. On the other hand, recently, water-soluble cutting oil has been widely used, and compatibility with the bearing oil has become important. In particular, deterioration and consumption of additives in bearing oil due to water-soluble cutting oil with high alkalinity are important. As a result, the initial performance of the bearing oil cannot be sufficiently maintained, and sludge generation and corrosion problems have arisen.
[0004]
[Problems to be solved by the invention]
The present invention solves the above problems, and the object of the present invention is to have high wear resistance and load resistance even when an ultra-low viscosity base oil is used, and to deteriorate additives even if water-soluble cutting oil is mixed. Another object of the present invention is to provide a lubricating oil composition for low viscosity bearings which does not cause sludge generation and corrosion problems.
[0005]
[Means for Solving the Problems]
That is, according to the present invention, a base oil having a kinematic viscosity at 40 ° C. of 1 to 25 mm ² / s is represented by the following general formula (1) based on the total amount of lubricating oil.
[0006]
[Chemical 1]
[(R ¹ O—) _m P (OH) _n (═O)] [NH (—R ² ) ₂ ] _n (1)
[0007]
(In the above formula, R ¹ and R ² represent a linear or branched alkyl group having 3 to 25 carbon atoms, an alkenyl group, or an alkyl-substituted or unsubstituted aromatic group, m and n are integers, and m + n = 3 , N is 1 or 2.) A lubricating oil composition for bearings containing 0.1 to 5% by mass of the acidic phosphate ester amine salt shown in (2), more preferably, based on the total amount of lubricating oil, The present invention relates to a bearing lubricating oil composition containing 0.05 to 2% by mass of a thiophosphate and / or 0.05 to 2% by mass of a thiadiazole compound.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The base oil of the present invention has a kinematic viscosity at 40 ° C. (according to the method defined in JIS K 2283) of 1 to 25 mm ² / s, particularly preferably 1 to 5 mm ² / s. Either of these or a mixture of both can be used.
[0009]
Mineral oil base oils are obtained by hydrorefining, solvent removal, solvent extraction, solvent dewaxing, hydrodewaxing, catalytic dewaxing of lubricating fractions obtained by distilling crude oil, especially lubricating light fractions, A suitable lubricating base oil can be obtained by performing purification by combining any one or more of hydrocracking, alkali distillation, sulfuric acid washing, clay treatment, and the like. Further, normal paraffins and isoparaffins having 11 to 15 carbon atoms can be suitably used. In the present invention, a mineral oil base oil obtained by refining a lubricating oil fraction having a boiling range such that the predetermined kinematic viscosity is obtained may be used alone, but a plurality of refined lubricating oil fractions may be used. The components may be mixed to prepare a predetermined kinematic viscosity.
[0010]
As the synthetic base oil, poly-α-olefin, fatty acid ester, phosphate ester, polyalkylene glycol and the like are suitable. These synthetic base oils may be used alone or in combination.
[0011]
In the acidic phosphate ester salt represented by the general formula (1), R ¹ is a linear or branched alkyl group having 3 to 25 carbon atoms, an alkenyl group, or an alkyl-substituted or unsubstituted aromatic group. Among them, those having 5 to 20 carbon atoms are more preferable, and those having a hexyl group, an octyl group, an oleyl group, and a tolyl group are particularly preferable because they are easily available.
Further, R ² in the above formula is a linear or branched alkyl group having 1 to 25 carbon atoms, and particularly preferably one having 5 to 20 carbon atoms.
[0012]
In the present invention, instead of adding the acidic phosphate amine salt of the general formula (1), an ester corresponding to the acidic phosphate ester portion on the left side of the general formula (1) and the equivalent thereof Alternatively, the amine corresponding to the right amine part of the general formula (1) below is added separately to form an acidic phosphate amine salt of the general formula (1) in the lubricating oil. Also good.
These acidic phosphate ester amine salts may be contained in an amount of 0.1 to 5% by mass, preferably 0.2 to 1% by mass, based on the total amount of the lubricating oil.
[0013]
A thiophosphate ester can also be blended in the bearing lubricating oil composition of the present invention. As this thiophosphate ester, those generally used as extreme pressure agents for lubricating oils can be used. In particular, the use of a compound represented by the following general formula (2) is preferable from the viewpoint of corrosion resistance. preferable.
[0014]
[Chemical 2]
(R ³ —O—) ₃ P = S (2)
[0015]
In the above formula, R ³ represents a substituted or unsubstituted aromatic. R ³ is particularly preferably a phenyl group or a t-butylphenyl group.
These thiophosphates may be contained in an amount of 0.05 to 2% by mass, preferably 0.1 to 1% by mass, based on the total amount of the lubricating oil.
[0016]
The thiadiazole compound used in the present invention can be used without any problem as long as it has a thiadiazole skeleton, and in particular, a compound in which a sulfide group or a polysulfide group is substituted on the carbon in the thiadiazole skeleton, for example, 1, 3, In the compound having a 4-thiadiazole skeleton, a compound represented by the following general formula (3) is preferable.
[Chemical 3]
[0017]
R ⁴ and R ⁵ in the above formula are each independently a hydrocarbon group having 5 to 30 carbon atoms, and m and n are each independently an integer of 1 to 4.
In addition, this skeleton portion can be used in the same manner as the 1,2,3-isomer, 1,2,4-isomer other than the 1,3,4-isomer, and two or more kinds of thiadiazole compounds. Even if they are mixed, there is no problem for the purpose of the present invention. The hydrocarbon group of R ⁴ and R ^{5 in} the general formula (3) may be linear and / or branched, saturated and / or unsaturated, particularly an alkyl group having 5 to 15 carbon atoms. Is preferred.
The thiadiazole compound used in the present invention may be contained in an amount of 0.01-2% by mass, preferably 0.03-1% by mass, based on the total amount of the lubricating oil.
[0018]
The bearing lubricating oil composition of the present invention contains other commonly used lubricating oil additives such as antioxidants, rust inhibitors, viscosity index improvers, pour point depressants, antifoaming agents, metal An activator or the like can be appropriately added.
Examples of the antioxidant include phenol compounds such as di-t-butylparacresol, amine compounds such as alkylated diphenylamine and α-naphthylamine, and phosphorus compounds such as phosphite.
Examples of the rust inhibitor include alkenyl succinic acid esters, alkenyl succinic acid partial esters, sorbitan esters, and sulfonic acid metal salts.
Examples of the viscosity index improver and the pour point depressant include polymethacrylate polymers and olefin copolymers.
Examples of antifoaming agents include silicone polymers and polymethacrylate polymers.
Examples of the metal deactivator include benzotriazole and benzotriazole derivatives.
[0019]
【Example】
Hereinafter, although the lubricating oil composition for bearings of the present invention will be described in more detail with reference to Examples, the present invention is not limited thereto.
In preparing the bearing lubricating oil compositions of Examples and Comparative Examples, the following base materials were used. The following base oil and additive were stirred and heated at 60 ° C. for 1 hour, and the dissolution of the additive was confirmed and subjected to the test.
[0020]
(1) Lubricating base oil A mixture of normal paraffins having 12 and 13 carbon atoms in a mass ratio of 60:40 was used as the base oil. The kinematic viscosity at 40 ° C. is 1.5 mm ² / s.
[0021]
(2) Additive (a) Antiwear Agent As the antiwear agent, the following acidic phosphate amine salts, thiophosphate esters, and thiadiazoles were used. For comparison, ZnDTP (zinc dialkyldithiophosphate) was also used.
a-1: Acid phosphate ester amine salt [R ^{1 in} formula (1): n-hexyl, R ² : C11-C14 alkyl group]
a-2: Acid phosphate ester amine salt [R ^{1 in} formula (1): oleyl, R ² : alkyl group of C8]
a-3: thiophosphate [R ^{3 in} formula (2): t-butylphenyl]
a-4: thiadiazole [R ⁴ + R ^{5 in} formula (3): alkyl group, total carbon number 22, m, n: 3]
a-5: ZnDTP
[Sec. C6 alkyl group type]
(B) Antioxidant b-1: Phenolic antioxidant [di-t-butylparacresol]
b-2: Amine-based antioxidant [dioctyldiphenylamine]
[0022]
(3) Evaluation of lubricity The wear resistance and load bearing capacity of the test oil were evaluated. The abrasion resistance was measured by a wear mark (mm) according to a shell 4-ball abrasion resistance test method (according to ASTM D2260, 1400 rpm, 15 kgf / cm ² , 30 min, room temperature). The load bearing capacity was measured by the seizure load (MPa) according to the Kamata type 4-ball method load bearing capacity test method (JIS K 2519, Shock method).
[0023]
(4) Evaluation of mixing stability with water-soluble cutting oil Copper corrosivity and sludge precipitation due to mixing of the test oil and water-soluble cutting oil were evaluated by the following methods. To 200 ml of the test oil, 20 ml of 20-fold diluted water-soluble cutting oil [A1 type (emulsion type) or A2 type (soluble type)] with purified water is added, and in the presence of a copper plate catalyst, the number of revolutions is 1500 rpm, The mixture was stirred at a temperature of 60 ° C. for 168 hours (using a device of JIS K 2510). For the sample oil after stirring, the discoloration of the copper plate catalyst (score according to the provisions of JIS K 2513) was observed, and the degree of contamination (JIS B 9931) was measured.
The above results of Examples and Comparative Examples are summarized in Table 1.
[0024]
[Table 1]
[0025]
In Examples 1 to 5 in which acidic phosphate ester was blended as an antiwear agent, the discoloration of copper was good at the 1b level in both the water-soluble cutting oils A1 and A2. Further, the degree of contamination is 11 mg / 100 ml or less, which is significantly smaller than the comparative example shown later. Lubricating property showed the comparative example level, while maintaining abrasion resistance by mix | blending a predetermined amount of thiophosphate ester and / or thiadiazole with acidic phosphate ester amine salt. From this, in order to have excellent mixing stability with water-soluble cutting oil and excellent wear resistance, the compounding of acidic phosphate amine salt is effective, and further to impart load bearing capacity It has been confirmed that it is promising to mix a predetermined amount of thiophosphate and / or thiadiazole.
The comparative example 1 which mix | blended ZnDTP as an antiwear agent showed the outstanding abrasion resistance and load bearing capacity. However, in the mixing test with the water-soluble cutting oil A1 type, the degree of contamination was high, and with the A2 type, the discoloration of copper was large.
[0026]
【The invention's effect】
The bearing lubricating oil composition of the present invention has high wear resistance and load resistance, and exhibits a special effect that sludge generation and corrosion problems hardly occur even when a water-soluble cutting oil is mixed.

Claims (2)

To a base oil having a kinematic viscosity at 40 ° C. of 1 to 5 mm ² / s composed of normal paraffin and / or isoparaffin having 11 to 15 carbon atoms, the following general formula (1)
(In the above formula, R ¹ is a linear or branched alkyl group, alkenyl group, or alkyl-substituted or unsubstituted aromatic group having 3 to 25 carbon atoms, and R ² is a linear or branched chain having 1 to 25 carbon atoms. represents an alkyl group, m and n are integers, m + n = 3, n is a jet which is characterized in that it contains 0.1 to 5 wt% of acidic phosphoric acid ester amine salt shown in 1 or 2.) Lubricating oil composition for bearings of lubrication system . Furthermore , the lubricating oil composition for bearings of Claim 1 which contains 0.05-2 mass% of thiophosphate ester and / or 0.05-2 mass% of thiadiazole compounds on the basis of the total amount of lubricating oil.