Lubricating oil composition for transmission

Abstract

To provide a lubricant composition for a transmission capable of obtaining excellent performance.SOLUTION: The lubricant composition for a transmission comprises: a base oil; and a poly (meth) acrylate and an olefin copolymer as a viscosity modifier. A ratio of the poly (meth) acrylate to the olefin copolymer in the viscosity modifier is 100:0 to 20:80 in mass%. A kinematic viscosity of the composition at 100°C is 5.5 mm2 / s or less, a viscosity index is 160 or more, a rate of decrease in 100°C kinematic viscosity after a KRL shear stability test (60°C, after 20 hr) is 2% or less, and a deposit amount in a panel caulking test is 120 mg or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a lubricating oil composition that can be suitably used in transmissions, primarily automobile transmissions, and particularly manual transmissions. [Background technology]

[0002] Conventionally, when considering a lubricating oil composition for an automobile transmission, it has been extremely difficult to achieve all of the desired properties for that application, namely improved fuel economy, load resistance, and good low-temperature viscosity characteristics. In view of the above, the applicant has discovered that a GTL low-viscosity base oil containing a prescribed amount of Group 1 high-viscosity base oil, preferably containing no viscosity index improver, has the desired physical properties as a transmission oil, and has provided this (Patent Document 1).

[0003] The viscosity index of the above-mentioned lubricating oil composition depends largely on the base oil to be blended. In particular, in environments where the oil temperature is kept relatively low, such as when driving in urban areas with repeated starts and stops as seen in recent years, the viscosity becomes high, and further improvement in fuel economy is also desired. If a viscosity index improver is simply added to remedy this, it can cause a decrease in oxidation stability against heat and a decrease in viscosity due to shear, which can lead to early deterioration of the lubricating oil and trouble with the transmission. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6284865 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention is an improvement over the above-mentioned conventional lubricating oils, and aims to provide a lubricating oil which has a low viscosity, a high viscosity index, excellent viscosity characteristics at low temperatures, and high stability at high temperatures, and which can be suitably used over a wide temperature range as a lubricating oil composition for transmissions, and which has good load-bearing capacity, shear stability, and oxidation stability, as well as excellent high-temperature detergency, and which can also improve fuel economy. [Means for solving the problem]

[0006] The present invention contains a base oil and a poly(meth)acrylate and an olefin copolymer as a viscosity modifier, and the ratio of the poly(meth)acrylate and the olefin copolymer in the viscosity modifier is 100:0 to 20:80 in mass %, and the kinematic viscosity at 100°C is 5.5 mm 2 The lubricating oil composition for transmissions has a viscosity of 160 or more, a viscosity index of 160 or more, a decrease in kinetic viscosity at 100°C after a KRL shear stability test (60°C, 20 hours) of 2% or less, and a deposit amount of 120 mg or less in a panel coking test.

[0007] The base oil has a kinetic viscosity of 1 to 5 mm at 100°C. 2 A low-viscosity base oil of 0.1 to 1.0 kPa (1.0 / s) or less can be used, and a GTL (gas-to-liquid) base oil can be suitably used as such a low-viscosity base oil. The poly(meth)acrylate in the viscosity modifier may be a dispersion type poly(meth)acrylate or a non-dispersion type poly(meth)acrylate. Effect of the Invention

[0008] The lubricating oil composition of the present invention has low viscosity, high viscosity index, excellent viscosity characteristics at low temperature, and good shear stability.In addition, the amount of evaporation at high temperature is low, and the lubricating oil composition can be made to have good oxidation stability while maintaining friction characteristics, and even during high-temperature oxidation, the variation range of the kinematic viscosity and viscosity index is small, and the lubricating oil composition has various functions in a well-balanced manner, such as a power transmission medium, lubrication of gears, a heat transfer medium, and maintaining certain friction characteristics.Therefore, the lubricating oil composition can be suitably used as a transmission lubricating oil composition that is excellent in fuel efficiency and has excellent durability that allows it to be used for a long time under the same conditions at any time.

[0009] Furthermore, when the oil is used as a lubricant for a manual transmission, it can effectively prevent deposits from becoming caught in the synchronizer ring of the manual transmission, thereby preventing poor synchronization. Furthermore, this lubricant composition can be widely and effectively used as an industrial lubricant oil, such as automotive gear oil, AT oil, MT oil, CVT oil and other transmission oils, industrial gear oil, hydraulic oil, compressor oil and other industrial lubricants. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] As the base oil, mineral oil, synthetic oil, etc. are used. A preferred base oil is GTL (Gas to Liquid) base oil synthesized by the Fischer-Tropsch process, a technology for converting natural gas into liquid fuel. Compared with mineral oil base oils refined from crude oil, this GTL base oil has an extremely low sulfur content and aromatic content and an extremely high paraffin composition ratio, so it has excellent oxidation stability, a high flash point, and very small evaporation loss, and can be suitably used as the base oil of the present invention.

[0011] Such a base oil has a kinematic viscosity of 5mm at 100°C. 2 / s or less is preferable, and 1 mm 2 It is preferable that the kinetic viscosity is 1mm / s or more. 2 If the oil pressure is less than 5 mm / s, evaporation will be significant and there is a concern that a sufficient oil film will not be secured. 2 If it exceeds this limit, the viscosity at low temperatures will increase and stirring resistance may increase.

[0012] The GTL base oils generally have a total sulfur content of less than 1 ppm and a total nitrogen content of less than 1 ppm. The aniline point of these base oils is 90° C. or higher and 110° C. or lower, more preferably 95° C. or higher and 107° C. or lower, and the refractive index is 1.42 or higher and 1.46 or lower, more preferably 1.43 or higher and 1.45 or lower. Shell GTL is an example of such a GTL low-viscosity base oil.

[0013] The GTL base oil is used in an amount of 75 to 85 mass %, preferably 80 to 84 mass %. If the amount is less than 75 mass %, problems may occur in properties such as low-temperature fluidity, and the desired effects may not be obtained.

[0014] A viscosity modifier is used with the base oil to adjust its viscosity. Viscosity modifiers include poly(meth)acrylates (PMA) and olefin copolymers (OCP). The viscosity modifier has a number average molecular weight of 5,000 or more and 30,000 or less, preferably 5,000 or more and 20,000 or less, and more preferably 5,000 or more and 12,000 or less.

[0015] The viscosity modifier may be blended in an amount of about 2% by mass to 20% by mass, preferably 5% by mass to 15% by mass, based on the total amount of the composition. If the blending amount is too small, the high temperature viscosity of the composition may decrease, and wear of mechanical parts may increase when used in a transmission, whereas if the blending amount is too large, the viscosity of the lubricating oil composition may increase, resulting in an inconvenience of increased friction loss.

[0016] The above-mentioned poly(meth)acrylates include non-dispersed poly(meth)acrylates and dispersed poly(meth)acrylates, and either type can be used. In some cases, both types may be used in combination.

[0017] As the viscosity modifier, it is preferable to basically use poly(meth)acrylate (PMA) and olefin copolymer (OCP) in combination. The ratio of poly(meth)acrylate to olefin copolymer (OCP) in the viscosity modifier is in the range of 100:0 to 20:80, preferably 100:0 to 25:75, and more preferably 100:0 to 30:70, by mass. This provides an appropriate viscosity index and high temperature detergency.

[0018] Such a lubricating oil composition has a kinematic viscosity of 5.5 mm at 100°C. 2 / s or less, preferably 5.2 mm 2 / s or less, preferably 5.1 mm 2 Make sure it is less than or equal to / s. If the viscosity is higher than this, the stirring resistance increases, which affects fuel economy. The kinetic viscosity at 40°C is 25mm 2 / s or less, preferably 22 mm 2 Make sure it is less than or equal to / s.

[0019] The viscosity index must be at least 160, preferably at least 165, and more preferably at least 170. If it is lower than this, the viscosity will be high at low temperatures, increasing the resistance to stirring, and it will be difficult to maintain an oil film at high temperatures, increasing the possibility of increased wear.

[0020] Furthermore, in the KRL shear stability test measured under conditions of 60°C for 20 hours (hr), the rate of decrease in kinetic viscosity at 100°C after the test must be 2.0% or less, preferably 1.5% or less, and more preferably 1.0% or less. If this shear stability is poor, the viscosity of the composition will decrease significantly, which will affect the oil film retention at high temperatures.

[0021] In addition, the amount of deposit in the panel coking test described below shall be 120 mg or less. If the amount of deposits increases, this indicates that the cleaning performance at high temperatures is deteriorating.

[0022] The transmission lubricating oil composition of the present invention may contain, as necessary, known additives, such as extreme pressure agents, dispersants, metal detergents, friction modifiers, antioxidants, corrosion inhibitors, rust inhibitors, demulsifiers, metal deactivators, pour point depressants, seal swelling agents, antifoaming agents, colorants, and the like, either alone or in combination. In such cases, it is often sufficient to use commercially available transmission additive packages, either alone or in combination. EXAMPLES

[0023] EXAMPLES The lubricating oil composition for transmissions of the present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited thereto in any way. In order to prepare the examples and comparative examples, the following materials were prepared.

[0024] (1) Base oil (Base oil A-1): GTL (Gas-to-Liquid) base oil (Properties: Kinematic viscosity at 40°C is 9.7mm) 2 / s, kinetic viscosity at 100°C is 2.7mm 2 / s) (Base oil A-2): GTL (Gas-to-Liquid) base oil (Properties: Kinematic viscosity at 40°C is 5.4mm 2 / s, kinetic viscosity at 100°C is 1.8mm 2 / s)

[0025] (2) Additives (Additive B-1): Viscosity modifier, non-dispersed poly(meth)acrylate (number average molecular weight 8400) (Additive B-2): Viscosity modifier, dispersant poly(meth)acrylate (number average molecular weight is 12,000) (Additive B-3): Viscosity modifier, olefin copolymer (number average molecular weight 8700)

[0026] (Additive C): Additive package (Zn-based GL-4 additive package for commercial manual transmissions) (Additive D): Pour point depressant (Additive E-1): Defoamer (commercially available silicone-based defoamer) (Additive E-2): Defoamer (commercially available silicone-based defoamer)

[0027] Example 1 To 80.64 mass% of GTL base oil (base oil A-1), 11.5 mass% of dispersant poly(meth)acrylate (additive B-2), 7.8 mass% of additive package (additive C), and 0.06 mass% of antifoaming agent (additive E-2) were added and thoroughly mixed to obtain the transmission lubricant composition of Example 1. Furthermore, the ratio (mass %) of Additive B-3 in Additive B in the above composition was calculated and is shown in Tables 1 and 2. In Example 1, it is 0 mass %.

[0028] (Examples 2 to 6) Using the compositions shown in Table 1 and following the procedure of Example 1, transmission lubricant oil compositions of Examples 2 to 6 were obtained.

[0029] (Comparative Examples 1 to 3) Using the compositions shown in Table 2 and otherwise following the same procedure as in Example 1, lubricating oil compositions of Comparative Examples 1 to 3 were obtained.

[0030] 〔test〕 In order to examine the properties and performance of the above-mentioned Examples and Comparative Examples, the following tests were carried out as appropriate. (Kinematic viscosity at 40℃) Based on JIS K2283, kinematic viscosity at 40°C (mm 2 / s) was measured. (Kinematic viscosity at 100℃) Based on JIS K2283, 100℃ kinematic viscosity (mm 2 / s) was measured. (viscosity index) Calculations were based on JIS K2283. Evaluation criteria: 160 or above: Good (○) Less than 160: Defective (×)

[0031] (KRL shear stability test) Based on CEC-L-45-A-99, the material was treated at 60° C. for 20 hours, and the kinetic viscosity at 100° C. after the treatment was measured, and the rate of decrease (%) in the kinetic viscosity at 100° C. after the treatment compared to before the treatment was calculated. Evaluation criteria The decrease in kinetic viscosity at 100°C is 2.0% or less. Good (○) The decrease in kinetic viscosity at 100°C exceeds 2.0%: poor (×).

[0032] (Panel caulking test) In accordance with the US Federal Test Method Standard 791-3462, a test was conducted in which test oil at a temperature of 90°C was splashed onto an aluminum panel heated and set to the specified temperature of 290°C with a rotating splasher for 2 hours at intervals of 15 seconds rotation time and 45 seconds rest time, and the test oil's ability to inhibit deposit formation, i.e., cleanliness, was evaluated based on the increase in weight of the panel before and after the test. The test results are shown in terms of the weight increase (mg) of the aluminum panel, and the evaluation indexes showing high-temperature cleanliness are as follows: Evaluation criteria: 0mg~80.0mg ···Excellent (◎) Over 80.0mg to 120.0mg or less: Good (○) More than 120.0 mg...Not possible (×)

[0033] (comprehensive evaluation) The results of the above tests were taken together and an overall evaluation was made of the transmission lubricating oil composition according to the following criteria. Particularly suitable as a lubricating oil composition for transmissions: Excellent (◎) Lubricating oil composition suitable for transmissions: Good (〇) Unsuitable as a transmission lubricant composition: Not acceptable (×)

[0034] (result) The results of the above tests are shown in Tables 1 and 2. In the tables, the blanks for the results of the KRL shear test indicate that the test was omitted based on the results of the other tests.

[0035] (Consideration) Example 1 uses A-1 GTL low viscosity base oil as base oil and Additive B-2 as Additive B (the ratio of Additive B-3 is 0% by mass), and has appropriate values ​​for 40°C kinematic viscosity and 100°C kinematic viscosity, and also has a passing viscosity index of 165. In addition, the amount of deposits in the panel coking test was small at 31.1 mg, and the overall evaluation was excellent (◎). In Example 2, the amount of additive B-2 was increased compared to Example 1, and the viscosity index was improved to 174. The 100°C kinematic viscosity reduction rate of the KRL shear stability was very small at 0.9%, but the amount of deposits in the panel coking test was slightly high at 109.2 mg, and the overall evaluation was slightly inferior to Example 1, being good (◯).

[0036] In Example 3, the amount of additive B was approximately the same as in Example 1, and additives B-2 and B-3 were used in combination, with the ratio of B-3 being 21 mass %.The viscosity index and KRL shear stability were good, and the amount of deposits in the panel coking test was small at 72.2 mg, so the overall evaluation was excellent (◎), just like in Example 1. In Example 4, additive B was used in combination with additives B-2 and B-3, with the ratio of B-3 being 51% by mass. The viscosity index and KRL shear stability were both good, and the amount of deposits in the panel coking test was slightly high at 103.2 mg, resulting in an overall evaluation of good (◯).

[0037] In Example 5, additive B-1 was used instead of additive B-2 in Example 4, and B-3 was used in the same ratio of 51 mass%, and the viscosity index and the values ​​in the panel caulking test were almost the same, and the overall evaluation was good (◯). Thus, it can be seen that almost the same results can be obtained even if the dispersant poly(meth)acrylate of B-2 used in combination with additive B-3 is replaced with the non-dispersant poly(meth)acrylate of B-1. In Example 6, the amount of additive B-2 used was reduced and the amount of B-3 used was increased, making the ratio of B-3 65% by mass. However, the results of the viscosity index and panel coking test were almost the same as those of Example 4 above, and the overall evaluation was also good (◯).

[0038] On the other hand, Comparative Example 1 uses additives B-2 and B-3 in combination, but the proportion of additive B-3 is increased to 81 mass %. The 40°C kinematic viscosity, 100°C kinematic viscosity, and viscosity index are similar to those of Example 6, but the result of the panel coking test is a large value of 141.1 mg, and the overall evaluation results are poor (×).

[0039] In Comparative Example 2, additive B was used so that the ratio of additive B-3 was 100% by mass, and the antifoaming agent was changed from E-2 to E-1. The viscosity index was almost the same as in each of the Examples, and better results were obtained in the KRL shear stability than in each of the Examples. However, the result in the panel coking test was 143 mg, which was a large value like in Comparative Example 1, and the overall evaluation was poor (×). In addition, in Comparative Example 3, A-2 was used as the base oil, the amount of additive B-3 was increased from that in Comparative Example 2 to 100% by mass, and a small amount of additive D, a pour point depressant, and additive E-1, an antifoaming agent, were used. Although the viscosity index was significantly improved to 207, the result in the panel coking test was deteriorated to 171.8 mg, and the overall evaluation was unacceptable (×).

[0040] [Table 1]

[0041]

Table 2

Claims

1. The viscosity modifier contains at least one of a poly(meth)acrylate and an olefin copolymer, the ratio of the poly(meth)acrylate to the olefin copolymer being 100:0 to 20:80 in mass %, and the kinetic viscosity at 100° C. is 5.5 mm ２ / s or less, a viscosity index of 171 or more, a decrease in kinetic viscosity at 100°C after a KRL shear stability test (60°C, 20 hr) of 2% or less, and a deposit amount in a panel coking test of 120 mg or less, The above base oil has a kinematic viscosity of 1 to 5 mm at 100°C. ２ / s low viscosity base oil, and also contains GTL (gas to liquid) base oil, The content of the GTL base oil is 80.4 to 84% by mass, The content of the viscosity modifier in the lubricating oil composition for transmissions is 2 to 20 mass % based on the total amount of the composition.

2. 2. The transmission lubricating oil composition according to claim 1, wherein the poly(meth)acrylate in the viscosity modifier is a dispersant type poly(meth)acrylate and / or a non-dispersant type poly(meth)acrylate.

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