JP5538044B2 - Lubricating oil composition with excellent wear resistance - Google Patents

Description

  The present invention relates to a lubricating oil composition having excellent wear resistance based on an oxygen-containing compound such as ester, ether, animal or vegetable oil.

In recent years, environmental measures are required in various fields. In particular, the reduction of carbon dioxide is an urgent issue, and energy saving has been achieved in various domestic industrial fields, transportation fields including automobiles, and general consumer life.
For example, among industrial equipment machines, hydraulic systems that can convert the pressurization energy of hydraulic pumps into kinetic energy are often used in systems that require large work energy such as injection molding machines, machine tools, and press machines. . Even in this hydraulic system, energy saving needs are increasing, and energy saving measures are also required for hydraulic oil that is the pressure medium of the hydraulic system, and low viscosity and high viscosity index are being achieved. Due to the low viscosity, there have been problems such as a decrease in wear resistance and seizure of sliding parts.
Recently, the load on the sliding portion has increased due to the downsizing, speeding up, and fuel and energy savings of mechanical systems, and there has been a demand for lubricating oils that are more excellent in lubricity such as wear resistance. In response to this, the use of oxygen-containing synthetic oils such as esters and ethers is spreading.
On the other hand, biodegradable lubricating oils such as animal and vegetable oils and esters having a specific structure are considered to be increasingly used as environmentally friendly base materials from the viewpoint of dealing with environmental pollution. In other words, it is estimated that the number of lubricating oils based on oxygen-containing compounds that have characteristics not found in hydrocarbon oils such as mineral oil will increase significantly in the future.

The ideal characteristic of the lubricating oil is that there is little friction loss at high speeds and low speeds, and there is little wear such as fretting wear. That is, the lubricating oil is required to reduce friction loss and reduce wear. Therefore, it is desired that the friction loss is small and the wear is small even when the contact surface speed is high, such as when rotating at high speed, or when high torque is applied at low speed.
However, in the case of polar oxygenated compound lubricants, the antiwear agents used in hydrocarbon lubricants such as general mineral oils have an affinity for polar base oils, so they are resistant to sliding parts. Since the concentration of the wear agent is reduced and the effect of improving the lubricity is reduced, it is desired to develop an antiwear agent that is effective for oxygen-containing compound-based lubricants such as esters and has little adverse effect on stability.

Examples of the antiwear agent include (dithio) phosphate esters of fluoroalkyl ether alcohols and salts thereof (Patent Document 1), heterocyclic compounds having a heterocyclic skeleton derived from pyridines, and / or the heterocyclic compounds Reaction products with boron compounds and the like (Patent Document 2), mercaptoalkanecarboxylic acid ester zinc salts (Patent Document 3), triazole compounds and reaction products of the triazole compounds with boric acid compounds (Patent Document 4) are proposed. In the field of refrigerating machine oils where oxygen-containing compounds are most frequently used as base oils, phosphorus compounds other than phosphate esters (Patent Document 5) have been proposed.
However, these are a series of sulfur-based, nitrogen-based, and phosphorus-based additives that have been studied in the past, and are difficult to stabilize because they become strongly polar compounds after being decomposed by sliding or heat. Its wear resistance effect is also limited.
On the other hand, for example, it is known to add polyoxyalkylene-modified silicone oil or polyether-modified silicone oil to a lubricating oil to suppress foaming (for example, Patent Documents 6 and 7). It has not yet been known to add to lubricating oils to improve wear resistance.

JP 2005-154759 A JP 2009-40869 A JP 2009-84263 A JP 2009-235252 A JP 2009-263666 A JP 11-209778 A JP 2005-162883 A

In order to develop an oxygen-containing compound lubricant that has low friction loss at low speeds and low wear, such as fretting wear, and good stability, the present inventors have conducted intensive research. As a result of the advancement, the inventors have found that a specific modified silicone oil can significantly suppress wear by adding a small amount to the base oil, and has almost no adverse effect on the stability, and have arrived at the present invention.
The problem to be solved by the present invention is to solve various problems in the sliding part, which is more severe due to downsizing, high speed, fuel saving and energy saving, using an oxygen-containing compound type lubricating oil, and wear. In the field of lubricants that greatly reduce and stably exhibit a low coefficient of friction, especially in the field of refrigeration oils that are often used maintenance-free, good stability as well as high electrical insulation are required. Therefore, it is to provide a lubricating oil composition that also satisfies those required characteristics.

That is, the present invention is as follows.
(1) A lubricating oil composition in which 0.001 to 5.0 mass% of a carboxyl-modified silicone oil is added to a lubricating base oil composed of an oxygen-containing compound based on the total amount of the lubricating oil composition.
(2) The lubricating oil composition according to (1), wherein a phosphate ester is added in an amount of 0.3 to 3.0% by mass based on the total amount of the lubricating oil composition.
(3) The lubricating base oil comprising an oxygen-containing compound is at least one selected from animal and vegetable oils, esters and ethers, and the kinematic viscosity at 40 ° C. is ² to 1000 mm ² / s (1) or ( The lubricating oil composition according to 2).
(4) The lubricating oil composition according to any one of (1) to (3) above, wherein the biodegradable lubricating oil has a degree of biodegradation of 60% or more.
(5) The lubricating oil composition for a refrigerator according to any one of (1) to (4) above.

  The lubricating oil composition of the present invention exhibits a characteristic that the wear is remarkably reduced and the coefficient of friction is low and stable, and the stability is hardly adversely affected. Therefore, the lubricating oil composition of the present invention is suitable for long-term use and has a remarkable effect on energy saving due to the low and stable characteristic of the friction coefficient.

The lubricating oil composition of the present invention is based on animal and vegetable oils and / or synthetic oil-based oxygen-containing compounds such as esters and ethers, and 0.001 to 5.0% by mass of carboxyl-modified silicone oil is added thereto. Is.
By the way, since carboxyl-modified silicone oil has low solubility in hydrocarbon base oils such as mineral oils, it cannot be added to such a concentration that it can improve lubricity by itself. By using a certain oxygen-containing compound, it can be used at a concentration that improves lubricity. Among them, the carboxyl-modified silicone oil having a good balance between solubility and lubricity improvement effect exhibits a remarkable lubricity improvement effect.

[Lubricant base oil]
In the present invention, oxygen-containing compounds such as animal and vegetable oils and synthetic oils can be used as the lubricating base oil. Furthermore, these lubricating base oils can be used in combination of two or more.
The physical properties of the lubricating base oil used in the present invention are not particularly limited, but those having a kinematic viscosity at 40 ° C. of ² to 1000 mm ² / s are preferable, and energy saving can be achieved by lowering the viscosity. ˜500 mm ² / s, more preferably 5 to 100 mm ² / s. However, it is preferable to use a high viscosity base oil for high load applications.
The viscosity index is preferably 50 or more, more preferably 100 to 250. Moreover, the pour point which is a low temperature characteristic is preferably −10 ° C. or lower, more preferably −15 ° C. or lower. Furthermore, from the viewpoint of safety, the flash point is preferably 70 ° C. or higher, and more preferably 150 ° C. or higher.

  Animal and vegetable oil-based lubricating base oils include milk fat, beef tallow, lard (pig tallow), sheep fat, whale oil, coconut oil, bonito oil, herring oil, coconut oil, and soybean oil, rapeseed oil, sunflower oil, Saflower oil, peanut oil, corn oil, cottonseed oil, rice bran oil, sesame oil, olive oil, flaxseed oil, castor oil, cacao butter, palm oil, coconut oil, hemp seed oil, rice oil, tea seed oil can be suitably used. However, it is not limited to these.

Synthetic oil base oils include esters, ethers, glycols and the like. Of these, esters and ethers can be preferably used.
Esters are commercially available as compounds having various molecular structures, each having unique characteristics and having a high flash point as compared with hydrocarbon base oils having the same viscosity. Esters can be obtained by dehydration condensation polymerization reaction of alcohol and fatty acid. In the present invention, however, in terms of chemical stability, diester of dibasic acid and monohydric alcohol, polyol of polyol and monohydric fatty acid. Esters may be mentioned as suitable base oil components.

The ether includes various compounds such as polyalkylene glycol and polyvinyl ether, and a compound represented by the following general formula (1) is preferable.
X [-O- (AO) n-R ^1] m (1)
In the above formula (1), X is a hydrocarbon group obtained by removing a hydroxyl group from a monool or polyol, A is an alkylene group having 2 to 4 carbon atoms, R ¹ is hydrogen or an alkyl group having 1 to 10 carbon atoms, m Is a compound represented by a valence of X, and n is a positive number of 2 or more.

As the glycol, a polyoxyalkylene glycol compound represented by the following general formula (2) is suitable.
R ² - [(OR ³⁾ f-OR ^4] g (2)
In the above formula (2), R ² represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an acyl group having 2 to 10 carbon atoms, or a residue of a compound having 2 to 8 hydroxyl groups, and R ³ represents the number of carbon atoms. R ⁴ represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or an acyl group having 2 to 10 carbon atoms, f is an integer of 1 to 80, and g is an integer of 1 to 8. It is a compound.
Usually, these lubricating base oils such as synthetic oils and animal and vegetable oils can be appropriately combined and blended at an appropriate ratio so as to satisfy various performances required for each application. At this time, a plurality of lubricating oil base oils of synthetic oil and animal and vegetable oils may be used.

[Carboxyl-modified silicone oil]
Specific examples of the carboxyl-modified silicone oil include those represented by the following general formula (3): side chain type (Y ² is —R ¹² COOH), both terminal types (Y ¹ and Y ³ are —R ¹² COOH), single-end type (Y ³ is —R ¹² COOH), side chain double-end type (Y ¹ , Y ² , Y ³ is —R ¹² COOH), and any of them may be used.

In the above general formula (3), R ⁵ , R ⁶ , R ⁷ , R ⁸ , R ⁹ , R ¹⁰ , R ¹¹ are each independently an alkyl group having 1 to 3 carbon atoms, Y ¹ , Y ² , Y ³ is at least one —R ¹² COOH, the rest independently represents an alkyl group having 1 to 3 carbon atoms, and h and i each represents an integer of 1 to 40. R ¹² represents a single bond or an alkylene group having 1 to 3 carbon atoms.
The carboxyl-modified silicone oil may be a random polymer or a block polymer. The compound is preferably a side chain type, more preferably a compound having a viscosity at 25 ° C. of 1000 to 8000 mm ² / s and a functional group equivalent of 2000 to 6000 g / mol.
The addition amount is 0.001 to 5.0% by mass based on the total amount of the lubricating oil composition, preferably 0.01 to 2.0% by mass, more preferably 0.02 to 1.0% by mass. is there. If the addition amount is less than 0.001% by mass, the effect of improving the lubricity is not obtained, and if it exceeds 5.0% by mass, the acid value is excessively increased and the stability of the lubricating oil is lowered. Particularly in the case of refrigeration oil applications, the amount added is preferably 0.5% by mass or less in order to keep the acid value low.

[Phosphate ester]
There are various types of phosphate esters such as alkyl type, aryl type, alkyl / aryl type, and acidic phosphate ester. Among them, aryl type such as triphenyl phosphate (TPP) and tricresyl phosphate (TCP) are stable. The addition amount is preferably from 0.3 to 3.0% by weight, and preferably from 0.5 to 2.0% by weight, based on the total amount of the lubricating oil composition. When the amount is less than 0.3% by mass, there is almost no effect of improving the lubricity, and when the amount exceeds 3.0% by mass, phosphoric acid is easily formed and stability is lowered.

[Other additives]
In the lubricating oil composition of the present invention, friction modifiers, antiwear agents, extreme pressure agents, antioxidants, which are conventionally used in lubricating oils, greases, etc., as long as the object of the present invention is not impaired. Additives such as a rust preventive, a metal deactivator, a cleaning dispersant, and an antifoaming agent can be included to further improve the performance.
As friction modifiers, molybdenum dithiocarbamate and molybdenum dithiophosphate, which are organic molybdenum compounds, aliphatic amines, aliphatic amides, aliphatic imides and alcohols, nitrogen compounds, esters, phosphate ester amine salts, phosphite amines Salts, antiwear agents such as phosphate esters and zinc dialkyldithiophosphates, extreme pressure agents such as sulfurized olefins and sulfurized fats and oils, and antioxidants such as amine and phenolic antioxidants. Examples of rusting agents include alkenyl succinic acid esters or partial esters, metal deactivators include benzotriazole and benzotriazole derivatives, and cleaning dispersants include alkaline earth metal sulfonates, alkaline earth metal phenates, and alkaline earths. Metal salicylate, etc. Metallic detergents or polyalkenyl succinimide,, ashless dispersants such as polyalkenyl succinic acid esters, as the defoaming agent silicone compounds, such as ester-based defoaming agents, respectively.

  The lubricating oil composition of the present invention is suitable for lubrication of sliding parts made of iron, iron alloys, and aluminum, and is used as hydraulic oil, refrigeration oil, air compressor oil, lubricating oil for internal combustion engines, or biodegradation Suitable as a functional lubricant. Among them, it is suitable for biodegradable lubricating oil and ester-based or ether-based refrigerating machine oil whose viscosity has been reduced for power saving and whose lubricity is a problem.

EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example and a comparative example, this invention is not limited to this Example.
(Preparation of lubricating oil composition)
Using the following carboxyl-modified silicone oil, phosphate ester, zinc thiophosphate, lubricating base oil, and other additives, the blending ratio shown in the upper part of Table 1 (addition amount is mass% based on the total amount of the composition) The lubricating oil compositions of Examples and Comparative Examples were prepared by blending with JIS K2283, the viscosity index was measured according to JIS K2269, the pour point was measured according to JIS K2269, and the acid value was measured according to the method defined in JIS K2501. . The measurement results are also shown in Table 1.

(A) Antiwear additive (A1) Carboxyl-modified silicone oil, X-22-3701E (side chain type, 25 ° C. kinematic viscosity: 2000 mm ² / s, functional group equivalent: 4000 g / mol) [manufactured by Shin-Etsu Chemical Co., Ltd.]
(A2) Carboxyl-modified silicone oil, X-22-162C (both ends, 25 ° C. kinematic viscosity: 220 mm ² / s, functional group equivalent: 2300 g / mol) [manufactured by Shin-Etsu Chemical Co., Ltd.]
(A3) tricresyl phosphate (TCP) [Wako Pure Chemical Industries, Ltd.]
(A4) Zinc dialkyldithiophosphate (ZnDTP), Lubrizol 1375 (manufactured by Nippon Lubrizol)

(B) Lubricating base oil (B1) Polyol ester oil (neopentyl glycol and n-nonanoic acid ester, 40 ° C. kinematic viscosity: 8.4 mm ² / s, viscosity index: 134, pour point: −37.5 ° C. Flash point: 180 ° C)
(B2) Polyalkylene glycol (PAG, PAG whose terminal is a butyl group and a hydroxyl group and skeleton is oxypropylene, 40 ° C. kinematic viscosity: 56 mm ² / s, viscosity index: 187, pour point: −42.5 ° C., flash point : 220 ° C)
(B3) Rapeseed oil (vegetable oil), (40 ° C. kinematic viscosity: 35.6 mm ² / s, viscosity index: 210, pour point: −27.5 ° C., flash point: 334 ° C.)
(C) Other additives Antioxidant: Di-t.-butyl-p.-cresol (DBPC)

[Evaluation of lubricating oil composition]
With respect to each of the lubricant compositions of Examples 1 to 7 and Comparative Examples 1 to 4 thus obtained, the lubricating performance (wear resistance; friction coefficient, Depth of wear), refrigeration oil, lubricating oil for internal combustion engines, biodegradable lubricating oil, and hydraulic oil characteristics were evaluated. The obtained evaluation results are summarized in the lower part of Table 1.
(Abrasion resistance test)
The wear resistance was measured using a ball / disk type reciprocating friction tester.
The test conditions were such that the oil film was less likely to be produced and the sliding speed was low (1 cm / s), high load (2200 gf), the amplitude was 20 mm, and the test was started at room temperature for 2 hours reciprocation so that the strict lubrication conditions were obtained. Friction was performed. In addition, the bearing carbon steel (SUJ-2) was used for the test piece of a ball | bowl and a disk. The friction coefficient after 2 hours and the disc wear depth after the test were measured with a stylus type surface roughness meter.

(Evaluation as refrigeration oil)
For thermal stability, in accordance with ANSI / ASHRAE 97-1983, 20 g of test oil, 5 g of refrigerant (R134a) and catalyst (iron, copper, and aluminum wires) are sealed in a stainless steel cylinder (100 ml) and kept at 175 ° C. After heating and holding for 10 days, the hue (ASTM display) and acid value of the test oil were measured. Moreover, about the electrical insulation, the volume resistivity in 80 degreeC was calculated | required based on JISC2101.

(Evaluation as lubricating oil for internal combustion engines)
For evaluation as a lubricating oil for an internal combustion engine, a cylinder / disk type SRV friction tester was used, the temperature was set at a high temperature of 100 ° C., and the disk wear scar diameter and the friction coefficient were measured.
Conditions were as follows: load: 200 N, frequency: 300 Hz, amplitude: 1.0 mm, test time: 1 hour, the disk was subjected to reciprocating friction on the disk, and the wear scar diameter generated on the disk was measured with a microscope. The coefficient of friction was measured with a strain gauge provided in advance in the friction tester.

(Evaluation as a biodegradable lubricant)
The biodegradable lubricant is evaluated by the OECD method (OECD301B), which is an accreditation standard for obtaining the “Eco Mark” certified by the Japan Environment Association, and is difficult to produce high degradation rates. It was measured. A biodegradability of 60% or more is certified as a biodegradable lubricant.

(Evaluation as hydraulic oil)
The hydraulic oil was evaluated by a high pressure vane pump test. The test conforms to ASTM D2882 and circulates 56.8 liters of oil in a pump tester, pressure: 140 kg / cm ² , pump speed: 1200 rpm, inlet oil temperature: 65.5 ° C., after 100 hours of test time The total weight loss of vanes and cam rings was measured and used as the amount of wear.

The friction coefficient in the friction test of the lubricating oil compositions of Examples 1 to 7 is 0.10 to 0.11, and is low and stable. Further, the disc wear depth after the friction test is 0.08 to 0.15 μm, which is a level with almost no wear.
On the other hand, in Comparative Example 1 using only the base oil, the friction coefficient is high and the disk wear depth is also large. Moreover, in Comparative Examples 2-4 which mix | blended antiwear agents other than carboxyl modification silicone oil, a friction coefficient is high and the wear depth is also much larger than an Example.
Among them, Comparative Examples 3 and 4 blended with ZnDTP, which is a commonly used antiwear agent, have slightly improved lubricity, but are not as good as the examples, and have poor stability and volume resistance. The rate is also low. On the other hand, Comparative Examples 1 and 2 have good stability and volume resistivity, but no improvement in lubricity, which is a point, has been made.
Thus, by blending the carboxyl-modified silicone oil with the lubricating base oil, the lubricity can be greatly improved while maintaining the stability level of the lubricating oil composition.
In addition, it can be seen that the lubricating oil compositions of Examples 1 to 7 are all excellent in characteristics as lubricating oils and hydraulic oils for internal combustion engines. In particular, Examples 1 to 3, 6 and 7 are biodegradable. is there.

  Since the lubricating oil composition of the present invention exhibits a characteristic that the wear is remarkably reduced and the coefficient of friction is low and stable, the lubricating oil for sliding parts of various machines and devices, particularly refrigerator oil, hydraulic oil It is useful as a lubricating oil such as a lubricating oil for internal combustion engines, and further as a biodegradable lubricating oil.

Claims (5)

A carboxyl-modified silicone oil represented by the following general formula (3) is added to a lubricating base oil composed of an oxygen-containing compound in an amount of 0.001 to 5.0% by mass based on the total amount of the lubricating oil composition. Lubricating oil composition ( excluding aqueous cutting oil and aqueous cutting agent ).

(In the above general formula (3), R ⁵ , R ⁶ , R ⁷ , R ⁸ , R ⁹ , R ¹⁰ , R ¹¹ are each independently an alkyl group having 1 to 3 carbon atoms, Y ¹ , Y ² , Y ³ is at least one —R ¹² COOH, the rest independently represents an alkyl group having 1 to 3 carbon atoms, h and i each represents an integer of 1 to 40, and R ¹² is a single bond, An alkylene group having 1 to 3 carbon atoms is shown.)   The lubricating oil composition according to claim 1, wherein the phosphate ester is added in an amount of 0.3 to 3.0 mass% based on the total amount of the lubricating oil composition. The lubricating oil according to claim 2, wherein the lubricating base oil composed of an oxygen-containing compound is at least one selected from animal and vegetable oils, esters and ethers, and has a kinematic viscosity at 40 ° C. of ² to 1000 mm ² / s. Composition. The biodegradable lubricating oil according to any one of claims 1 to 3, wherein the biodegradable lubricating oil has a degree of biodegradation of 60% or more. The lubricating oil composition for refrigerators in any one of Claims 1-4.