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EP-4098725-B1 - RESIN LUBRICATION GREASE COMPOSITION

EP4098725B1EP 4098725 B1EP4098725 B1EP 4098725B1EP-4098725-B1

Inventors

  • SOMA Minami
  • TSUTSUI DAISUKE
  • SHIBATA RYO

Dates

Publication Date
20260506
Application Date
20210322

Claims (8)

  1. Use of a grease composition in lubrication between a resin-made member and a resin-made member or lubrication between a resin-made member and a member made from another material, wherein the resin-made member to be lubricated is of a polyamide and said grease composition comprises: a solid organic molybdenum compound in an amount of more than 0.5% by mass and less than 7.5% by mass relative to a total mass of the composition, 4 to 17% by mass relative to a total mass of the composition of a thickener which includes a lithium soap thickener, and a synthesized hydrocarbon oil as a base oil.
  2. The use according to claim 1, wherein the content of the solid organic molybdenum compound is 1 to 5% by mass.
  3. The use according to claim 1 or 2, wherein the thickener is lithium stearate, lithium 12-hydroxystearate, or lithium complex soap.
  4. The use according to any one of claims 1 to 3, wherein the base oil of the grease composition further contains a mineral oil.
  5. The use according to claim 4, wherein the proportion of the mineral oil in the base oil is 20 to 50% by mass.
  6. The use according to any one of claims 1 to 5, wherein the member made from another material other than the resin-made member to be lubricated is a metal-made member.
  7. The use according to any one of claims 1 to 6, wherein the thickener consists of the lithium soap thickener as a sole thickener.
  8. A reducer for an electric power steering, including a member made of resin together with a further member made of either resin or another material and filled with a grease composition, characterized in that the grease composition is the one used according to any one of claims 1 to 7 and is filled to provide lubrication between said member and said further member.

Description

Technical Field The present invention relates to a use of resin lubrication grease composition, more specifically, a resin lubrication grease composition for lubrication between resin-made members or between a resin-made member and a member made from another material, for example, a metal-made member. Background Art Various metal-made members have conventionally been used as automobile components and the like, but these days, resin-made members are increasingly being used instead of metal-made members for the purpose of reducing the weights. For this reason, both resin-made members and metal-made members are currently used. For example, a resin (polyamide)-made worm wheel gear and a steel-made worm gear are used in a reducer part of electric power steering of automobiles. As a grease composition to be used for lubrication between resin-made members and between a resin-made member and a metal-made member, Patent Literature 1 describes a lubrication grease composition containing a polyolefin wax. When used for resin lubrication parts, this grease composition can achieve low friction and can meet the demand for improvements in efficiency of components having resin lubrication parts. Patent Literature 2 describes a resin lubrication grease composition characterized in that the grease containing a thickener and a base oil is made contain a montan wax. This grease composition is excellent in that the grease composition can reduce the coefficient of static friction of a lubrication part to extend the durability life of the lubrication part. However, in the case where these grease compositions are applied to a reducer part of electric power steering, when the steering wheel is slightly turned while the steering is not assisted by a motor, like during the driving on a highway, for example, the lubrication part of the reducer slides, causing a problem that the steering wheel is displaced from the center in some cases, due to the low coefficient of static friction. Citation List Patent Literatures Patent Literature 1: Japanese Patent Application Publication No. Hei 9-194867Patent Literature 2: Japanese Patent Application Publication No. 2002-371290 Each of US 6 444 621 B1, WO 2009/121378 A1, WO 2016/155754 A1, and JP 2006 292083 A shows a resin grease composition with a solid organic molybdenum compound. A grease composition for lubricating resins of EP 3 239 281 A1 contains a base oil, a diurea compound represented by formula (I) as a thickener: R1 - NHCONH - R2 - NHCONH - R3 (I) (wherein R2 represents a bivalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R1 and R3 each independently represent a straight-chain or branched alkyl group having 8 to 22 carbon atoms), and a chained hydrocarbon polymer. JP 2006 194279 A shows a low noise reduction gear provided with a drive gear and a driven gear, each supported by a bearing, and a lubricant composition which includes lubricant and shock absorbing material particles of average particle diameter D1 of 50µm< D1 ≤300µm. Summary of Invention Problems to be solved by the invention Therefore, an object of the present invention is to provide a lubrication that can increase the coefficient of static friction of a lubrication part, and suppress an increase in the coefficient of dynamic friction associated with the increased coefficient of static friction and maintain the coefficient of dynamic friction at a certain low level, thus suppressing sliding of the lubrication part of a reducer when no assistance is provided by a motor and maintaining a lubrication efficiency when assistance is provided by the motor. Means for solution of the problems The present invention is defined in the claims. Advantageous Effects of Invention The present invention makes it possible to provide a resin lubrication that can increase the coefficient of static friction of a lubrication part and maintain the coefficient of dynamic friction at a certain low level, thus suppressing sliding of the lubrication part of the reducer when no assistance is provided by a motor and maintaining the lubrication efficiency when assistance is provided by the motor. Description of Embodiments [Thickener] The thickener to be used in the grease composition used in the present invention includes a lithium soap thickener. Lithium soap thickeners are e.g. represented by a Li soap and a Li complex soap, urea thickeners represented by diurea, inorganic thickeners represented by organoclay and silica, and organic thickeners represented by PTFE. Since soap thickeners themselves have low coefficients of dynamic friction, an excellent lubrication efficiency can be achieved by using a soap thickener. Lithium 12-hydroxystearate, lithium stearate, and a Li complex soap (for example, a Li complex soap formed from 12-hydroxystearic acid and azelaic acid) are more preferable, and lithium 12-hydroxystearate and a Li complex soap are particularly preferable. Since thickening can be made with a small amount of the thickener