Silicone grease composition

Abstract

To provide a silicone grease composition which has an improved high friction property without reduction in wear resistance and has good storage stability.SOLUTION: A silicone grease composition includes (A) 55 to 95 mass% of a silicone oil as a base oil, (B) 2 to 35 mass% of a lithium soap-based thickener, (C) 0.1 to 10 mass% of zinc oxide powder, and (D) 0.1 to 10 mass% of surface-treated silica.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a silicone grease composition, and more particularly to a silicone grease composition that can be suitably used for lubricating parts that require a high coefficient of friction and excellent wear resistance, specifically lubricating parts of clutches and torque limiter mechanisms. [Background technology]

[0002] In consideration of global environmental issues, efforts to reduce the weight of automobiles have been made, and as a result, clutches and torque limiter mechanisms have been applied to a wider variety of locations than before. Of the clutches and torque limiter mechanisms in which grease compositions are used, the location with the greatest torque and strictest operating conditions is the clutch of an automobile engine starter.

[0003] An engine starter clutch is composed of a clutch outer, a clutch inner, a roller positioned in a wedge-shaped space formed between the clutch outer and the clutch inner to transmit the rotation of the clutch outer to the clutch inner, and a spring to bias the roller toward the narrower side of the wedge-shaped space. When the clutch outer rotates, the roller moves toward the narrower side of the wedge-shaped space and is sandwiched between the clutch outer and the clutch inner, transmitting the rotation to the clutch inner (torque transmission state). Therefore, the grease composition used in this area must have a high coefficient of friction to prevent slippage between the clutch outer, clutch inner, and roller.

[0004] Known greases include an overrunning clutch grease containing silicone oil as a base oil with a friction coefficient of 0.18 or higher (Patent Document 1), a grease composition using organopolysiloxane with a specified proportion of phenyl or methyl groups as a base oil (Patent Documents 2 and 3), and a traction grease composition containing a base oil containing 1 to 40% by weight of dimethylsilicone base oil with a specified kinematic viscosity, metal oxide particles, and a thickener (Patent Document 4). Silicone oil has a high friction coefficient and a surface tension of 20 to 25 dyn / cm. 2Because it is smaller than other oils, it is difficult to form a lubricating film and is prone to boundary lubrication.

[0005] Furthermore, when the rotational speed of the clutch inner becomes higher than that of the clutch outer, the roller automatically moves toward the wider wedge-shaped space while compressing the spring, and rotation is no longer transmitted (torque non-transmitting state). At this time, relative rotation occurs between the clutch outer, clutch inner, and roller, resulting in a slip state. Therefore, the grease composition used in this area must also have wear resistance.

[0006] Furthermore, in a silicone composition containing silicone oil, a diurea thickener, and a metal oxide (Patent Document 5), the diurea thickener is obtained by reaction in the base oil, but it is difficult to adjust the mixture to the desired consistency and it is prone to separation. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 3-004036 [Patent Document 2] Japanese Patent Application Publication No. 5-230486 [Patent Document 3] Japanese Patent Application Publication No. 6-279777 [Patent Document 4] Japanese Patent Application Laid-Open No. 2003-176489 [Patent Document 5] Japanese Patent Application Laid-Open No. 2015-151516 Summary of the Invention [Problem to be solved by the invention]

[0008] As mentioned above, with the recent trend toward lighter automobiles, clutches and torque limiter mechanisms are also required to be smaller and lighter, and their operating conditions are becoming more severe. In particular, with regard to torque transmission, grease compositions are required to have a higher friction coefficient in order to be able to transmit torque sufficiently even under more severe operating conditions. At the same time, clutches and torque limiter mechanisms are also required to have wear resistance. Furthermore, grease compositions are also required to have storage stability that prevents separation. The present invention has been made in order to solve the above problems, and an object of the present invention is to provide a silicone grease composition that has improved high friction properties without reducing wear resistance and that also has good storage stability. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides a silicone grease composition having the following characteristics. That is, in the present invention, (A) Silicone oil as base oil: 55 to 95% by mass (B) Lithium soap thickener: 2 to 35% by mass (C) Zinc oxide powder: 0.1 to 10% by mass (D) Surface-treated silica: 0.1 to 10% by mass The present invention provides a silicone grease composition comprising:

[0010] Such a silicone grease composition has improved high friction properties without reducing wear resistance, and also has good storage stability.

[0011] The surface-treated silica (D) is preferably silica surface-treated with (C6H5)2Si(OH)2.

[0012] Such surface-treated silica (D) is preferred because it results in a silicone grease composition with more stable worked penetration and less susceptible to changes over time.

[0013] In addition, it is preferable that the silicone oil (A) has 4 to 6 mol % of phenyl groups among all organic groups.

[0014] Such a silicone grease composition is preferable because it has excellent cold resistance.

[0015] The silicone grease composition preferably has a worked penetration at 25°C in the range of 290 to 380.

[0016] Such a silicone grease composition is preferable because it has better abrasion resistance.

[0017] The present invention also provides a method for producing the silicone grease composition, which method comprises the step of applying shearing force using at least a three-roll mill.

[0018] This method of producing a silicone grease composition is preferable because it makes it less likely that aggregates of the zinc oxide powder or surface-treated silica will remain in the silicone grease composition. [Effects of the Invention]

[0019] As described above, the silicone grease composition of the present invention improves high friction properties and has good storage stability without reducing wear resistance. DETAILED DESCRIPTION OF THE INVENTION

[0020] As described above, there has been a need for the development of a silicone grease composition that has improved high friction properties without reducing wear resistance and that also has good storage stability.

[0021] As a result of extensive research into the above-mentioned problems, the present inventors discovered that by using a silicone grease composition containing zinc oxide powder and surface-treated silica as friction modifiers, it is possible to provide a silicone grease composition that has good storage stability and increases the coefficient of friction without reducing wear resistance, and thus completed the present invention.

[0022] That is, the present invention provides: (A) Silicone oil as base oil: 55 to 95% by mass (B) Lithium soap thickener: 2 to 35% by mass (C) Zinc oxide powder: 0.1 to 10% by mass (D) Surface-treated silica: 0.1 to 10% by mass The silicone grease composition is characterized by comprising:

[0023] The present invention will be described in detail below, but the present invention is not limited thereto.

[0024] [Component (A)] The base oil used in the grease composition of the present invention is a silicone oil. Specific examples of silicone oils include dimethyl silicone oil, diphenyl silicone oil, methylphenyl silicone oil (phenyl-modified silicone oil), methylhydrogen silicone oil, polyether-modified silicone oil, aralkyl-modified silicone oil, fluoroalkyl-modified silicone oil, alkyl-modified silicone oil, and fatty acid ester-modified silicone oil. Preferred are dimethyl silicone oil, diphenyl silicone oil, and methylphenyl silicone oil. Particularly preferred is a silicone oil represented by the following general formula (1): (CH3)3SiO-[-Si(R 1 )(R 2 )-O-] n Si(CH3)3(1) (R in the formula 1 , R 2 each independently represents a methyl group or a phenyl group. It is preferable that 4 to 6 mol % of all organic groups are phenyl groups, and the remainder are methyl groups.

[0025] The kinematic viscosity of the silicone oil is not particularly limited, but is preferably 20 to 10,000 mm at 25°C. 2 / s, more preferably 50 to 2,000 mm 2 / s range is appropriate. 2 At 10,000mm / s or more, the base oil and grease are well mixed. 2 / s or less is practically preferable because torque is unlikely to increase even at low temperatures. The kinematic viscosity of the silicone oil mentioned above is the value measured at 25°C using a Cannon-Fenske viscometer.

[0026] In addition, R in the above general formula (1) 1 , R 2 each independently represents a methyl group or a phenyl group. Of all organic groups, it is preferable that 4 to 6 mol % are phenyl groups, with the remainder being methyl groups. This is because 4 to 6 mol % of phenyl groups can improve the cold resistance of the composition.

[0027] The content of silicone oil is 55 to 95% by mass, preferably 55 to 90% by mass, and more preferably 60 to 85% by mass, based on the total mass of the composition. When silicone oil is contained in such an amount, a high coefficient of friction is exhibited, which is preferable. Furthermore, two or more types of component (A) with different viscosities may be used.

[0028] Silicone oil may also be mixed with other base oils. Examples of other base oils include one or more selected from the group consisting of mineral oil, poly-α-olefin, polybutene, alkylbenzene, animal and vegetable oils, organic acid esters, diesters, polyol esters, polyalkylene glycols, polyvinyl ethers, polyphenyl ethers, and alkylphenyl ethers. The amount of other base oil used in combination is preferably 0 to 50% by mass relative to the silicone oil base oil of the present invention, and more preferably 0 to 20% by mass, since this allows a high coefficient of friction to be maintained. 0 to 10% by mass is particularly preferred. It is most preferred that no other base oil is used.

[0029] [(B) Component] Examples of the lithium soap-based thickener used in the grease composition of the present invention include lithium salts of aliphatic carboxylic acids having a hydroxyl group, such as lithium-12-hydroxystearate, lithium salts of aliphatic carboxylic acids, such as lithium stearate, and mixtures thereof, with lithium stearate being particularly preferred from the viewpoint of durability. The content of the lithium soap thickener is 2 to 35% by mass relative to the total mass of the composition, and is appropriately determined depending on the target worked penetration, preferably 5 to 30% by mass, and more preferably 10 to 25% by mass. If it is less than 2% by mass, the grease will be liquid and cannot be used as a grease. If it exceeds 35% by mass, the resulting grease will be too hard and difficult to apply.

[0030] [(C) component] The zinc oxide powder used in the present invention is used as a friction modifier. Any of the commercially available JIS standard types 1, 2, and 3 may be used, but type 1 or 2 is preferred from the viewpoint of purity. Type 2 is even more preferred from an economic viewpoint. The particle size of the zinc oxide powder is preferably 0.1 to 1.5 μm, and more preferably 0.3 to 1.2 μm. The particle size refers to the particle size at 50% of the integrated value in the volume-based particle size distribution determined by a laser diffraction / scattering method. The average particle size and particle size distribution of the aluminum powder can be measured by the laser diffraction / scattering method using, for example, a Microtrac particle size analyzer MT3300EX (manufactured by Nikkiso Co., Ltd.). The amount of zinc oxide powder is 0.1 to 10% by mass, and preferably 1.0 to 5.0% by mass, relative to the total mass of the composition. If it is less than 0.1% by mass, no friction effect can be expected, and if it is more than 10% by mass, the friction effect is too great, causing wear of the contacting members.

[0031] [(D) component] The surface-treated silica used in the present invention functions as a friction modifier and is a component that imparts worked penetration. Surface-treated fumed silica is preferably used as the silica fine powder. Surface treatment stabilizes the worked penetration and makes it less susceptible to changes over time.

[0032] While (C6H5)2Si(OH)2, chlorosilane, silazane, siloxane, etc. are effective surface treatment agents, surface treatment with (C6H5)2Si(OH)2 is most preferred from the viewpoint of imparting worked penetration. When the amount of (C6H5)2Si(OH)2 added is 5 parts or more per 100 parts by weight of silica, it becomes easier to impart worked penetration, and when it is 50 parts or less by weight, it is economically preferable, so the range of 5 to 50 parts by weight is preferred. The range of 10 to 40 parts by weight is more preferred, and the range of 15 to 35 parts by weight is even more preferred.

[0033] For example, silica and (C6H5)2Si(OH)2 are mixed in toluene at 100-110°C under a nitrogen atmosphere, and after 1-4 hours, the toluene is removed by heating under reduced pressure to obtain surface-treated silica. The specific surface area of ​​the silica powder (BET method) is 50m 2 / g or more is preferable, and 100m 2 / g or more. 2 At a specific surface area (BET method) of 500 m / g or more, the composition is not too soft and is easy to handle, which is preferable. 2 / g or less, especially 300m 2 / g or less is preferable from the viewpoint of handling of the present composition.

[0034] The amount of surface-treated silica added is 0.1 to 10% by mass, preferably 1.0 to 5.0% by mass, based on the total mass of the composition. If it is less than 0.1% by mass, the friction effect and the effect of imparting worked penetration cannot be expected, and if it is more than 10% by mass, the composition becomes too hard, making application difficult.

[0035] [Other additives] Other additives include those typically used in grease compositions, such as antioxidants, rust inhibitors, metal deactivators, detergents and dispersants, extreme-pressure additives, antifoaming agents, demulsifiers, oiliness improvers, and solid lubricants. These additives can be used alone or in combination of two or more. These additives are added as needed, and the amount added is generally 0.01 to 10 mass %, but is not particularly limited.

[0036] [Worked penetration] The worked penetration of the grease composition of the present invention is preferably 290-380, more preferably 300-370, and most preferably 310-360.

[0037] Furthermore, it is preferable to finally shear the silicone grease composition of the present invention using a three-roll mill. If the composition is not sheared using a three-roll mill, aggregates of the zinc oxide powder and surface-treated silica may remain in the composition, potentially causing greater wear than expected on components that come into contact with them. There is no particular limit to the number of times the composition should be sheared using a three-roll mill, but it is preferable to shear the composition three to five times. If the shearing is done three to five times, the aggregates will be sufficiently removed, which is economical.

[0038] The silicone grease composition of the present invention is suitable for use in lubricated parts that require a high coefficient of friction and excellent wear resistance, specifically lubricated parts of clutches and torque limiter mechanisms. More specifically, it is suitable for use in overrunning clutches in automobile starters, one-way clutches in office equipment, and various traction drive mechanisms. In particular, it is preferred for the lubricated parts to be components with steel surfaces. [Example]

[0039] EXAMPLES The present invention will be specifically explained below using examples and comparative examples, but the present invention is not limited to these.

[0040] [Production of Silicone Grease Composition] (A)Ingredients A-1; Viscosity at 25°C is 100mm2 / s, and in formula (1), R 1 and R 2 are methyl or phenyl groups, and the proportion of phenyl groups in all organic groups is 5 mol %, and the proportion of methyl groups is 95 mol %. A-2; Viscosity at 25°C is 1000mm 2 / s, and in formula (1), R 1 and R 2 are methyl or phenyl groups, and the proportion of phenyl groups in all organic groups is 5 mol %, and the proportion of methyl groups is 95 mol %. (CH3)3SiO-[-Si(R 1 )(R 2 )-O-] n -Si(CH3)3(1)

[0041] (B) Ingredients B-1; Lithium Stearate

[0042] (C) Components C-1; Zinc oxide powder (average particle size 0.9 μm)

[0043] (D) Components D-1; Specific surface area (BET method) 200m 2 Surface-treated silica in which 25 parts by weight of (C6H5)2Si(OH)2 was surface-treated per 100 parts by weight of silica.

[0044] The base oil and lithium stearate were mixed at 190°C for 1 hour, then cooled. After that, zinc oxide powder and surface-treated silica were added and mixed for another 30 minutes. The paste was passed through a triple roll mill three times to obtain the target product.

[0045] [Test method] Low speed, high load friction test This test simulates the lubrication conditions under which the clutch transmits torque. The test was carried out using a Falex testing machine specified in ASTM D 2670. Test grease was applied to the journal and block, which were then clamped together with a predetermined load, and the journal was rotated for approximately 1 second. The generated friction force was recorded, from which the initial coefficient of friction 0.001 seconds after starting was calculated. The test specimen and test conditions were as follows: Journal: Outer diameter φ1 / 4n, SAE3135STEEL, Rb87~91 Block: AISI1137STEEL, Rc20-24 Surface pressure: 200kgf / mm 2 Circumferential speed: 0.096m / sec

[0046] High-speed, low-load wear testing This test simulates the lubricated conditions when the clutch is not transmitting torque. The LFW#1 testing machine specified in ASTM D 2714 was used. A roller was placed on the ring, a load was applied, and the ring was rotated to measure the wear on the roller with a micrometer. The test specimen and test conditions were as follows: Ring: Outer diameter φ35mm x width 8.7mm, SAE4620STEEL, Rc58~63, RMS6~12 Roller: Cylindrical roller for roller bearing, φ6mm x 6mm, SUJ-2 Surface pressure: 10kgf / mm 2 Circumferential speed: 12.8m / sec

[0047] [Evaluation criteria] Low speed, high load friction test Friction coefficient ◎: 0.030≦μ ○: 0.025≦μ<0.030 △: 0.020≦μ<0.025 ×: μ<0.020

[0048] High-speed, low-load wear test: Wear depth ○:<6mm ×:≧6mm

[0049] Worked consistency Measurement was carried out at 25°C according to JIS K2220.

[0050] The results are shown in Tables 1 to 3. In the tables, the mass percentages of the silicone oil as the base oil, the lithium soap-based thickener, and the zinc oxide powder and surface-treated silica as friction modifiers are values ​​relative to the total mass of the grease composition. [Table 1]

[0051] [Table 2]

[0052] [Table 3]

[0053] Examples 1 to 4 were prepared in accordance with the components defined in the present invention, and silicone grease compositions were obtained that had desirable worked penetration, a high coefficient of friction of 0.025 or greater, and a wear depth of less than 6 mm. In Comparative Example 1, the amount of component (C) exceeded the specified range, resulting in a worked penetration of 280 and a wear depth of more than 6 mm; in Comparative Example 2, the amount of component (D) exceeded the specified range, resulting in a too hard and inconsistent grease-like consistency; in Comparative Example 3, the amount of component (C) did not meet the specified range, resulting in a low friction coefficient of 0.017; in Comparative Example 4, the amount of component (D) did not meet the specified range, resulting in immediate separation; in Comparative Example 5, the amount of component (B) did not meet the specified range, resulting in immediate separation; and in Comparative Example 6, the amount of component (B) exceeded the specified range, resulting in a too hard and inconsistent grease-like consistency. None of the comparative examples yielded a satisfactory silicone grease composition.

[0054] The present specification includes the following aspects. [1]: (A) Silicone oil as base oil: 55 to 95% by mass (B) Lithium soap thickener: 2 to 35% by mass (C) Zinc oxide powder: 0.1 to 10% by mass (D) Surface-treated silica: 0.1 to 10% by mass 1. A silicone grease composition comprising: [2]: The silicone grease composition according to [1] above, wherein the surface-treated silica (D) is silica surface-treated with (C6H5)2Si(OH)2. [3]: The silicone grease composition of the above [1] or [2], wherein the silicone oil (A) contains 4 to 6 mol % of phenyl groups among all organic groups. [4]: The silicone grease composition according to [1], [2] or [3] above, wherein the silicone grease composition has a worked penetration at 25°C in the range of 290 to 380. [5]: A method for producing the silicone grease composition according to any one of [1], [2], [3], or [4] above, which method comprises a step of shearing the composition using at least a three-roll mill.

[0055] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention.

Claims

1. (A) Silicone oil as base oil: 55 to 95% by mass (B) Lithium soap-based thickener: 2 to 35% by mass (C) Zinc oxide powder: 0.1 to 10% by mass (D) Surface-treated silica: 0.1 to 10% by mass 1. A silicone grease composition comprising:

2. The surface-treated silica (D) is ６ H ５ ) ２ Si(OH) ２ 2. The silicone grease composition according to claim 1, wherein the silica is surface-treated with a hydroxypropyl methylsilyl group.

3. 2. The silicone grease composition according to claim 1, wherein the silicone oil (A) contains 4 to 6 mol % of phenyl groups as a proportion of all organic groups.

4. 2. The silicone grease composition according to claim 1, wherein the silicone grease composition has a worked penetration at 25°C in the range of 290 to 380.

5. 5. A method for producing the silicone grease composition according to claim 1, comprising the step of shearing the composition using at least a three-roll mill.

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