JP5265996B2 - Lubricating oil composition - Google Patents

Description

  The present invention relates to a lubricating oil composition having basic performance (lubricity, oxidation stability) as a bearing oil while enhancing rust prevention ability by using synthetic calcium sulfonate and synthetic zinc sulfonate together in a lubricating base oil. Relates to a lubricating oil composition for iron bearings used as a lubricating oil for bearings mainly composed of iron.

  In recent years, various lubrication systems have been advanced, enhanced in performance, and multifunctional, and cost reduction and high reliability have been demanded. A bearing is used in many mechanical systems as a basic mechanical element for controlling rotational motion smoothly and accurately. There are various types of bearings, which are roughly classified into rolling bearings, slide bearings, sintered metal oil-impregnated bearings, and the like. In particular, sintered metal oil-impregnated bearings are manufactured through processes such as molding, sintering, and sizing fine metal powder, and are applied to a wide range of applications as inexpensive bearings compared to rolling bearings. Since the sintered metal oil-impregnated bearing itself is a porous body, it is usually used by being vacuum impregnated with lubricating oil and containing about 20% in volume in the bearing. The impregnating lubricating oil is required to have an appropriate viscosity and have basic performance as a bearing oil such as lubricity, rust prevention, and oxidation stability. In the old days, general-purpose lubricating oils such as turbine oil, hydraulic oil, and engine oil have been impregnated, but recently, oils dedicated to oil-impregnated bearings have been used in accordance with applications and lubricating conditions. Synthetic oil is used as a base oil especially in low temperature operating conditions such as refrigerators, applications that require stable operating characteristics over a wide range of temperatures, such as automotive electrical components, or applications that require low viscosity for high speed. A special oil for high performance oil-impregnated bearings has been developed (see Patent Document 1).

  At present, the materials of sintered metal oil-impregnated bearings are roughly classified into copper and iron. Specifically, pure iron, iron-copper, iron-carbon, iron-carbon-copper, bronze, and lead bronze are standardized. The proper use of these depends on the application, use conditions and environment, and iron is used for high load and low speed conditions, and copper is used for low load and high speed conditions (see Non-Patent Document 1).

Iron is relatively inexpensive among metal materials, has abundant resources, has high mechanical strength, but has problems such as poor corrosion resistance. In particular, Japan is in a high humidity environment, and lubricating oils used for iron bearings are required to have high rust prevention ability. Conventional lubricating oils are blended with rust inhibitors such as carboxylic acids and metal sulfonates for the purpose of imparting rust prevention properties. However, the conventional lubricating oil has a problem that rust is generated in a short period of time in a harsh environment such as being soaked in extremely high humidity and water. Therefore, a lubricating oil composition containing an organic sulfonic acid zinc salt as a rust preventive has also been proposed (see Patent Document 2). However, in a severe rust prevention test assuming a very severe use environment, a sufficient rust prevention effect was not obtained.
Japanese Patent Laid-Open No. 2003-261892 Tribology Handbook (published by Yokendo), P438 Japanese Patent No. 4008992

    This invention makes it a subject to provide the lubricating oil composition for iron-type bearings which was excellent in lubricity and oxidation stability while having high antirust ability.

  As a result of conducting extensive research to solve the above problems, the present inventor has a very high rust prevention ability by blending a specific amount of both a specific Ca sulfonate and a zinc sulfonate into a lubricating base oil. It has been found that a lubricating oil composition can be obtained.

The present invention has been made based on such findings and is as follows.
(1) Mineral oil or synthetic oil base lubricant base oil of synthetic calcium sulfonate and synthetic zinc sulfonate having a base number of 1 to 100 mgKOH / g is 3 to 30 mass as the total amount of the sulfonate based on the total amount of the composition. %, And a lubricating oil composition comprising an element ratio of calcium and zinc of 2: 8 to 8: 2.
(2) The lubricating oil composition according to the above (1), wherein the calcium sulfonate and zinc sulfonate have a base number of 2 to 50 mgKOH / g.

(3) A lubricating oil composition for an iron-based bearing comprising using the lubricating oil composition according to (1) or (2) above as a lubricating oil for a bearing containing iron as a main component.
(4) The lubricating oil composition for iron bearings according to (3), wherein the bearing containing iron as a main component is a sintered metal oil-impregnated bearing, a rolling bearing, or a sliding bearing.

  The lubricating oil composition of the present invention has a high rust prevention ability and is excellent in lubricity and oxidation stability. Therefore, when used in a bearing mainly composed of iron, for example, it is in contact with moisture and water. Even in a severe corrosive environment, rusting of the bearing can be prevented, and stability and reliability can be ensured for a long time with respect to the bearing and its mounting device.

[Lubricating base oil]
The lubricating base oil used in the present invention may be either a mineral base lubricating base oil used as a normal lubricating base oil or a synthetic base lubricating base oil. Also, a mineral base lubricant base oil and a synthetic base lubricant base oil can be mixed and used.

  In general, the mineral base lubricant base oil is a base oil obtained by subjecting a distillate obtained by subjecting crude oil to atmospheric distillation or further distillation under reduced pressure by various purification processes as a base oil. Alternatively, it is adjusted by mixing various additives. Examples of the purification process include hydrorefining, solvent extraction, solvent dewaxing, hydrodewaxing, sulfuric acid washing, and clay treatment. These processes can be combined and processed in an appropriate order to obtain a mineral oil-based lubricating base oil suitable for the present invention. A mixed oil of a plurality of refined oils having different properties obtained by combining different crude oils or distillate oils in different processes and sequences can be used as a suitable base oil.

  As the synthetic base oil, it is preferable to use a base material having excellent hydrolysis stability. For example, polyolefins such as poly-α-olefin, polybutene and copolymers of two or more kinds of olefins, and polyester , Polyalkylene glycol, alkylbenzene, alkylnaphthalene and the like. Among these, poly-α-olefin and polyester are preferable in terms of availability, cost, viscosity characteristics, oxidation stability, and compatibility with system members. These synthetic base oils can be used alone or in admixture of two or more.

The physical properties of these lubricating base oils are appropriately selected depending on the application, but in general, the kinematic viscosity at 40 ° C. is 5 to 600 mm ² / s, particularly 10 to 580 mm ² / s, and the viscosity index is 80. -150 and a pour point of -10 degrees C or less are suitable.

  When using a mixture of a plurality of lubricating base oils, including mineral oil-based and synthetic oil-based lubricating base oils, if the base oil mixture satisfies the above physical properties, the individual base oils before mixing are applied. It can be used even if out of the range of physical properties. Accordingly, the individual mineral oil-based and synthetic oil-based lubricating base oils do not necessarily satisfy the above-mentioned physical properties, but are preferably within the above-mentioned physical properties.

[Sulfonate]
In the lubricating oil composition of the present invention, the synthetic calcium sulfonate and the synthetic zinc sulfonate need to be used in combination, and these can be mixed at an arbitrary ratio. The ratio needs to be in the range of 2: 8 to 8: 2 in terms of element ratio of calcium and zinc.

  Further, among these synthetic calcium sulfonates and synthetic zinc sulfonates, those having a base number of 1 to 100 mgKOH / g and those having a low base number among those added as a rust preventive agent to lubricating oils have high rust prevention. The effect cannot be obtained. Preferably, it is 2 to 50 mg KOH / g. In addition, as for this sulfonate, it is necessary to use the synthetic sulfonate using synthetic sulfonic acid like dinonyl naphthalene sulfonic acid and heavy alkylbenzene sulfonic acid as a sulfonic acid. Petroleum sulfonates obtained by using petroleum sulfonic acid obtained by sulfonating aromatic hydrocarbon components in the lubricating oil fraction have a poor antirust effect and cannot be used. In addition, a highly basic sulfonate having a base number of 200 to 300 mgKOH / g in which calcium carbonate or the like is colloidally dispersed is not preferable because the calcium carbonate colloid coarsens in the presence of water and precipitates as sludge.

  Although the mechanism of the combined effect of these low basic synthetic calcium sulfonates and synthetic zinc sulfonates is not clear, it is thought that the adsorption activity to the metal surface and the strength of the rust-preventive coating formed are optimized. . According to these optimized formulations, a sufficient rust prevention effect can be obtained even in a very severe environment.

  The blending amount is 3 to 30% by mass in terms of the total amount of the calcium sulfonate and zinc sulfonate, based on the total amount of the composition. If the content is greater than or equal to mass%, the rust prevention effect corresponding to the cost cannot be expected.

[Other additives]
In addition, in order to impart performance as a normal lubricating oil to the lubricating oil composition of the present invention, a phenol-based or amine-based antioxidant, a phosphate ester, an anti-wear agent such as an organic sulfur compound, a phosphorus-based In addition, an extreme pressure agent of sulfur compound, an oily agent such as alcohol and higher fatty acids, an antifoaming agent such as silicone oil, a metal deactivator such as benzotriazole derivative, and the like can be appropriately blended. These additives are preferably added in an amount of 0.1 to 10 parts by mass, particularly 0.2 to 5 parts by mass with respect to 100 parts by mass of the lubricating base oil.

[bearing]
The lubricating oil composition of the present invention comprises a hydraulic oil, a compressor oil, a machine tool oil, a metalworking oil, a bearing oil, a gear oil, a refrigerator oil, a turbine oil, and other industrial lubricating oils, as well as automotive lubricating oils and marine oils. Although it can be used for various applications such as lubricating oil, the effect of the present invention can be most exerted when applied to bearings mainly composed of iron, particularly sintered metal oil-impregnated bearings, rolling bearings, and sliding bearings.

  Sintered oil-impregnated bearings are porous sintered oil-impregnated bearings manufactured by mixing, forming, sintering, and sizing metal powders such as copper, bronze, brass, iron, and zinc. Generally, 5-30% There are gaps. In the present invention, among these materials, it is particularly preferable to apply to an iron-based sintered oil-impregnated bearing that requires a rust prevention effect.

  The rolling bearing is composed of two race rings (inner and outer rings), rolling elements (balls or rollers) and a cage, and the rolling elements between the inner ring and the outer ring are fixed by the cage so that they do not contact each other. It is a structure which is kept at the interval and performs a rolling motion, and is roughly classified into a radial bearing and a thrust bearing. Some of these rolling bearings are also made of a material such as iron or ceramics. However, in the present invention, it is preferable to apply to rolling bearings mainly composed of iron for which a rust prevention effect is particularly required.

  Sliding bearings are called differently depending on the direction in which the load is applied and the time variation, but they are broadly classified into journal bearings, thrust bearings, hydrostatic bearings, hydrodynamic bearings, etc., specifically round bearings, partial arc bearings, Examples include tilting pad bearings. Examples of materials constituting these bearings include various plastics, bronze, aluminum alloys, cast iron and the like. Among these, in the present invention, it is preferable to apply to an iron-based slide bearing that requires rust prevention.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to an Example.

[Lubricating base oil]
As the lubricating base oil, the following four types were used.
(1) Mineral oil (VG32): paraffinic mineral oil, kinematic viscosity (40 ° C) 32mm ² / s, viscosity index 100, pour point -12.5 ° C
(2) PAO (VG32): poly-α-olefin polymer, kinematic viscosity (40 ° C.) 32 mm ² / s, viscosity index 130, pour point −60 ° C.
(3) PAO (VG100): poly-α-olefin polymer, kinematic viscosity (40 ° C.) 100 mm ² / s, viscosity index 130, pour point −60 ° C.
(4) Ester (VG32): pentaerythritol fatty acid polyol ester, kinematic viscosity (40 ° C.) 32 mm ² / s, viscosity index 140, pour point −30 ° C.

[Additive]
The following were used as additives.
A. Antirust agent Synthetic Ca sulfonate [25]: Heavy alkyl benzene sulfonate calcium, base number 25mgKOH / g
Synthetic Zn sulfonate [28]: zinc dinonylnaphthalenesulfonate, base number 28 mgKOH / g
Synthetic Basulfonate [25]: Barium dinonylnaphthalenesulfonate, base number 25mgKOH / g
Synthetic Ca sulfonate [200]: calcium dinonylnaphthalenesulfonate, base number 200 mgKOH / g
Petroleum Ca sulfonate [20]: Calcium petroleum sulfonate, base number 20mgKOH / g
Succinic acid partial ester: acid value 160mgKOH / g

B. Other additives Amine-based antioxidants: alkylated phenyl-α-naphthylamine Phosphorus-based antiwear agents: tricresyl phosphate

[Test method]
The above base oils and additives were blended in the proportions shown in the upper part of Tables 1 and 2 to prepare lubricating oil compositions of Examples and Comparative Examples. These lubricating oil compositions were subjected to the following tests for evaluating practical performance.

(appearance)
Each lubricating oil composition was placed in a glass 110 ml screw bottle and the appearance was visually observed. When turbidity is observed, it indicates that the blended additives and their reactants are not uniformly dissolved, and therefore it is not preferred as a lubricating oil composition. On the other hand, if it is transparent, it can be used as a lubricating oil composition without problems.

(Kinematic viscosity, viscosity index)
According to the method prescribed | regulated to JISK2283, kinematic viscosity in 40 degreeC and 100 degreeC was measured using the Canon-Fenske viscometer. Moreover, the viscosity index was calculated by the method prescribed | regulated to JISK2283: 6.4B method.

(Acid value)
The acid value (mgKOH / g) of each lubricating oil composition was measured by potentiometric titration in accordance with the method defined in JIS K2501.

(Rust prevention test)
The following method evaluated as a rust prevention screening.
Immerse the iron-based sintered bearing parts that have been cleaned and degreased in each lubricating oil composition, impregnate them for 25 minutes in a vacuumed state, take out the bearing parts on a paper waste or the like, and leave it for 15 minutes to stand. It is removed by absorbing natural excess oil. Next, the bearing part is placed on a Petri dish, filled with water in an amount so that the bearing is half-immersed, and the upper part is not sealed, but is left in a room / room temperature environment in contact with air. At this time, the evaporated water is replenished in a timely manner. The state was observed each time, and the number of days from when the test was started until rusting was observed on the bearing parts was counted, and this was defined as the number of rusting days.

  This rusting days is the “rust prevention ability” of each lubricating oil composition, and the longer the rusting days, the better the performance. This test simulates an environment where rust is very likely to occur because the oil-impregnated iron bearing is exposed to both water and air (oxygen). In general turbine oil and hydraulic oil, rusting is observed after one day. Moreover, in general antirust oil, rusting occurs in about 40 days. In the present invention, a case where the life is twice as long as that of a general rust preventive oil is defined as “extremely high rust preventive ability”.

(Oxidation degradation test)
The oxidation stability was evaluated by the following method.
Weigh 80 g of each lubricating oil composition into a glass 100 ml screw bottle, immerse the washed and degreased metal catalyst (copper and iron, rod-shaped), cover the screw bottle with aluminum foil, and bring it to 140 ° C. It left still in the set air bathtub, and it heated for 240 hours, and forcedly deteriorated each lubricating oil composition. The amount of sludge generated contained in each forcedly deteriorated oil was measured according to the method specified in JIS B9931, and the oxidation stability of each lubricating oil composition was evaluated. The smaller the value, the better the oxidation stability. If it is substantially 5 mg / 100 ml or less, it can be used as a lubricating oil without any problem.

(Shell 4-ball wear test)
According to the method prescribed | regulated to ASTMD4172-94, it performed using ROXANA MACHINE WORKS shell 4 ball | bowl abrasion tester. In this test, JIS B1501 ball bearing steel balls (20 grade, 1/2 inch) were used, and the conditions were as follows.
Rotation speed: 1200rpm
Load: 30kgf / cm ²
Temperature: Start at room temperature, subsequent time: 30 minutes The wear resistance of each lubricating oil composition is evaluated based on the size of the wear scar diameter after the test. The smaller the value, the better. It can be said that the property is good.

  The above results are shown in Tables 1 and 2.

In the lubricating oil compositions of Examples 1 to 8 in Table 1, the appearance after oil production is all transparent, and there is no problem due to the additive formulation. Viscosity characteristics and acid value are improved depending on the kind and blending amount of the blended rust inhibitor.
As for the rust prevention test, Examples 1 to 8 all have rusting days exceeding 80 days, showing rusting on the 95th day at the longest, and have extremely high rust prevention ability in actual use. I understand that.
In the oxidation degradation test, all of Examples 1 to 8 have a sludge generation amount of 5 mg / 100 ml or less, and are excellent in sludge resistance.
In the wear resistance test, the wear marks are on the order of 0.3 mm and the lubricity is good in any of the examples.

On the other hand, among the lubricating oil compositions of Comparative Examples 1 to 8 in Table 2, Comparative Examples 7 and 8 had turbidity after oil production and had problems with the reaction and solubility of the rust inhibitor. Viscosity characteristics and acid value were values depending on the blended additive composition, as in the examples.
Rust prevention property was comparative examples 1-6, showed rusting days 15-45 days, and stayed at the rust prevention level of general rust prevention oil. Comparative Examples 7 and 8 rusted within 5 days.
In the oxidation deterioration test, only Comparative Examples 1 and 2 showed a sludge amount of 5 mg / 100 ml or less, and Comparative Examples 3 to 8 were at a level that could not be used practically.
Regarding the lubricity, all of the comparative examples 7 and 8, except for the large wear marks, were at a level with no problem.

From the evaluation of the above Examples and Comparative Examples, the combination of the low basic synthetic calcium sulfonate and the synthetic zinc sulfonate satisfies both extremely high antirust performance, oxidation stability, and lubricity. I understood that.
On the other hand, in the comparative example, although it was excellent in oxidation stability and lubricity depending on the composition, the rust prevention property under the test conditions was insufficient with the level of a general rust prevention oil.

The lubricating oil composition of the present invention has a high anti-corrosion ability, and is excellent in lubricity and oxidation stability. Therefore, hydraulic oil, compressor oil, machine tool oil, metal working oil, bearing oil, gear oil, It can be used for various applications such as industrial lubricants such as refrigeration oil and turbine oil, automobile lubricants and marine lubricants, bearings mainly composed of iron, especially sintered metal oil-impregnated bearings, It is suitable as a lubricating oil for rolling bearings and sliding bearings.

Claims (2)

Synthetic calcium sulfonate and synthetic zinc sulfonate having a base number of 2 to 50 mgKOH / g in a mineral or synthetic oil-based lubricating base oil, 3 to 30% by mass as a total amount of the sulfonate based on the total amount of the composition, And the lubricating oil composition for iron-type bearings characterized by mix | blending the element ratio of calcium and zinc by 2: 8-8: 2. Wherein the iron-based bearing, sintered metal oil-impregnated bearings, roller bearings, or iron bearing lubricating oil composition of claim 1 which is a sliding bearing.