Grease composition having low power consumption and excellent self-locking property

Abstract

A grease composition for lubricating a resin member and a metal member, the grease composition containing a base oil, a calcium sulfonate complex as a thickener, and 5-20% by mass of powdered metal soap as an additive based on the total mass of the composition.

Description

Technical Field

[0001] This invention relates to a grease composition that has low power consumption and excellent self-locking properties (i.e., the property of suppressing gear reversal caused by slippage in the reducer). Background Technology

[0002] In automotive parts and similar applications, resin components are often used instead of metal components for the purpose of weight reduction. For example, the gearbox of the electric window motor in a car uses both resin (polyacetal) and steel worm gears.

[0003] The grease used in the lubrication parts of these speed reducers requires high self-locking properties to prevent reverse rotation. To achieve high self-locking properties, the static friction coefficient needs to be increased.

[0004] As a prior art for reducing the static friction coefficient, Patent Document 1 discloses a grease composition comprising a urea compound as a thickener and at least one additive selected from metal soaps (lithium stearate, lithium 12-hydroxystearate, calcium stearate, calcium 12-hydroxystearate, aluminum stearate, aluminum 12-hydroxystearate, barium stearate, barium 12-hydroxystearate, sodium stearate, sodium 12-hydroxystearate, etc.). The aforementioned grease composition can reduce the static friction coefficient of the lubricated portion and lower the starting voltage.

[0005] Patent document 2 discloses a grease composition containing 0.5 to 40% by mass of a polyolefin wax with an average molecular weight of 900 to 10,000.

[0006] Patent document 3 discloses a resin lubricating grease composition, characterized in that the grease containing a thickener and a base oil contains lignite wax.

[0007] Patent document 4 discloses a resin lubricating grease composition for use in the part where resin comes into contact with metal. It is characterized by containing a base oil containing at least one of polyalphaolefin oil, mineral oil and highly refined mineral oil in a specific proportion, a thickener containing at least one of metal soap and metal complex soap in a specific proportion, and at least one of non-polar wax and polar wax.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2004-314916

[0011] Patent Document 2: Japanese Patent Application Publication No. 9-194867

[0012] Patent Document 3: Japanese Patent Application Publication No. 2002-371290

[0013] Patent Document 4: Japanese Patent Application Publication No. 2005-054024 Summary of the Invention

[0014] The problem that the invention aims to solve

[0015] However, simply increasing the static friction coefficient cannot improve self-locking performance. On the other hand, to meet recent demands for reduced power consumption, it is necessary to reduce the static friction coefficient and lower the starting voltage. Therefore, the objective of this invention is to provide a grease composition that balances high self-locking performance and excellent starting performance.

[0016] Methods for solving problems

[0017] This invention relates to a grease composition, characterized in that it contains a calcium sulfonate complex in the thickener and a metal soap in the additive. Specifically, according to this invention, the following grease composition is provided.

[0018] 1. A grease composition for lubricating resin-made and metal-made components, the grease composition comprising a base oil, a calcium sulfonate complex as a thickener, and 5 to 20% by weight of powdered metal soap as an additive based on the total mass of the composition.

[0019] 2. The grease composition as described in 1 above, wherein the metal soap is lithium soap, calcium soap, magnesium soap, zinc soap, or a mixture thereof.

[0020] 3. A speed reducer in which the grease composition described in 1 or 2 above is incorporated.

[0021] Invention Effects

[0022] As described above, in order to balance high self-locking performance and excellent starting performance, it is necessary to increase the coefficient of dynamic friction without excessively reducing the static friction coefficient. According to the present invention, by combining a metal soap and a calcium sulfonate complex, a coefficient of friction that balances high self-locking performance and excellent starting performance can be obtained. Detailed Implementation

[0023] [Base oil]

[0024] As the base oil for the lubricating grease composition of the present invention, mineral-based lubricating oils and synthetic lubricating oils can be used. There are no particular limitations on the type. As a mineral-based lubricating oil, paraffinic mineral oils, cycloalkane-based mineral oils, and mixtures thereof can be used. As a synthetic lubricating oil, synthetic hydrocarbon oils, ether oils, ester oils, and fluorinated oils can be used. Synthetic oils are preferred, synthetic hydrocarbon oils are more preferred, and polyalphaolefins are even more preferred. It should be noted that the synthetic oil can be a so-called biomass oil manufactured from biological resources produced by animals and plants. For example, biomass ester oils synthesized from various fatty acids and alcohols derived from vegetable oils, and biomass hydrocarbon oils using vegetable oils such as palm oil, corn oil, and soybean oil can also be used.

[0025] From the viewpoint of low-temperature performance and durability, the kinematic viscosity of the base oil of this invention at 40°C is 15~450 mmHg. 2 / s, preferably 15~200mm 2 / s, further preferably 15~70mm 2 / s.

[0026] The base oil content in the grease composition of the present invention is the amount usually used in the manufacture of grease, for example, 45 to 90% by mass, preferably 47.5 to 87% by mass from the viewpoint of low temperature performance, and more preferably 50 to 82% by mass.

[0027] [Calcium sulfonate complex thickener]

[0028] The calcium sulfonate complex of the present invention is a complex (complex soap) containing calcium sulfonate and calcium salts of acids other than sulfonic acid.

[0029] Examples of sulfonic acids that constitute calcium sulfonate include dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, and petroleum sulfonic acid. Dodecylbenzenesulfonic acid is preferred as a sulfonic acid.

[0030] Examples of acids other than sulfonic acids include 12-hydroxystearic acid, acetic acid, carbonic acid, and boric acid.

[0031] The calcium sulfonate complex used in this invention is particularly preferably a complex formed from calcium dodecylbenzenesulfonate, calcium 12-hydroxystearate, calcium carbonate, and / or calcium acetate. More particularly preferably, it is a complex formed from calcium dodecylbenzenesulfonate, calcium 12-hydroxystearate, calcium carbonate, and calcium acetate. The complex of this invention may also contain calcium borate and calcium carbonate.

[0032] The content of the calcium sulfonate complex thickener in the composition of the present invention is an amount that can adjust the consistency of the grease composition of the present invention to, for example, the range of 235 to 415, typically 5 to 40% by mass based on the total mass of the composition, preferably 8 to 35% by mass, and more preferably 10 to 33% by mass.

[0033] It should be noted that the calcium sulfonate complex can also function as a wear-resistant agent and rust inhibitor in this invention.

[0034] In this specification, the term "consistency" refers to the consistency after 60 mixing cycles, which can be measured according to JIS K2220 7. From the viewpoint of low-temperature performance, the consistency of the grease composition of the present invention is preferably 235 to 415, more preferably 280 to 415.

[0035] [Metallic Soap]

[0036] The grease composition of the present invention includes a powdered metal soap as an additive. Examples of metal soaps include lithium soap, calcium soap, magnesium soap, zinc soap, or mixtures thereof. From the viewpoint of starting properties, lithium soap and zinc soap further reduce the static coefficient of friction and are therefore preferred. It should be noted that metal soaps are also commonly used as thickeners in greases. Generally, thickeners form a network structure in the base oil, enabling the base oil to remain liquid while forming a solid or semi-solid (i.e., grease). Since the metal soap used in the present invention is in powder form, it does not form a network structure and therefore does not function as a thickener.

[0037] The content of metallic soap in the grease composition of the present invention is 5 to 20% by mass, preferably 8 to 20% by mass from the viewpoint of starting performance, and more preferably 13 to 20% by mass.

[0038] [Any additives]

[0039] The grease composition of the present invention may further contain additives commonly used in greases. Examples of such additives include antioxidants, metal corrosion inhibitors, oiliness agents, and solid lubricants.

[0040] Examples of antioxidants include amine antioxidants and phenolic antioxidants.

[0041] Examples of metal corrosion inhibitors include benzotriazole.

[0042] Examples of oil-reducing agents include fatty acids, fatty acid esters, and phosphate esters.

[0043] Examples of solid lubricants include metal oxides such as CaO, ZnO, and MgO, carbonates such as CaCO3 or ZnCO3, molybdenum disulfide, graphite, PTFE, and MCA. Among these, CaCO3 is preferred from the viewpoint of extending bearing life.

[0044] It should be noted that the amount of these additives added is not particularly limited as long as it does not impair the purpose of the present invention. For example, it is 0 to 15% by mass based on the total mass of the composition, preferably 0 to 12% by mass.

[0045] The grease composition of the present invention preferably does not contain thickeners other than calcium sulfonate complexes.

[0046] The grease composition of the present invention preferably does not contain wax as an additive.

[0047] The grease composition of the present invention can be used for the lubrication of resin-made components and metal-made components, such as the lubrication of resin (polyacetal, polyamide) worm gears and steel worm gears in the reducers of electric window motors in automobiles, as well as the reducers of electric seat motors and sunroof motors.

[0048] Example

[0049] <Raw materials for the test grease composition>

[0050] (Thickener)

[0051] Dodecylbenzenesulfonic acid, 12-hydroxystearic acid, acetic acid, boric acid, calcium carbonate, calcium hydroxide

[0052] (Base oil)

[0053] • Poly-α-olefin (kinematic viscosity at 40°C: 38.7 mm) 2 / s)

[0054] (additive)

[0055] • Li soap

[0056] Lithium stearate (powder)

[0057] • Ca soap

[0058] Calcium stearate (powder)

[0059] • Zn soap

[0060] Zinc stearate (powder)

[0061] • PE wax

[0062] Molecular weight: 17,500 (weight average)

[0063] Physical properties: dropping point 132~138℃, acid value 0mgKOH / g, melt viscosity approximately 25,000mPa·s (140℃).

[0064] Distributor: Clariant Chemicals Co., Ltd.

[0065] Product Name: LICOWAX PE190 P

[0066] • PP wax

[0067] Molecular weight: 28,200 (weight average)

[0068] Physical properties: softening point 112℃, melt viscosity approximately 9,300 mPa·s (170℃).

[0069] Distributor: Clariant Chemicals Co., Ltd.

[0070] Product Name: LICOCENE PP 3602

[0071] • Lignite wax

[0072] Physical properties: dropping point 96~102℃, acid value 9~14mgKOH / g, saponification value 102~122mgKOH / g

[0073] Distributor: Clariant Chemicals Co., Ltd.

[0074] Product name: LICOWAX OP FL

[0075] <Preparation of Experimental Grease Compositions>

[0076] In a base oil, dodecylbenzenesulfonic acid, 12-hydroxystearic acid, acetic acid, calcium carbonate, and calcium hydroxide were stirred and heated to 72°C. Then, boric acid and calcium hydroxide were added and stirred further, heating to 163°C. The mixture was then cooled to below 100°C while stirring to obtain a base grease. Metal soaps or waxes were then mixed in the proportions shown in Table 1 and dispersed using a three-roll mill to prepare the test grease compositions. The consistency of the test grease compositions was uniformly 350. Consistency was determined according to JIS K2220 7.

[0077] <Experimental Methods>

[0078] If the static friction coefficient is high during motor startup, a large force is required, resulting in higher power consumption. By using grease to reduce the maximum static friction coefficient, starting with less force is possible, power consumption is suppressed, and thus good starting performance (low starting voltage) is achieved. In other words, starting performance can be evaluated by the maximum static friction coefficient. The motor with the lower maximum static friction coefficient has better starting performance.

[0079] On the other hand, by increasing the maximum static friction coefficient, gear reversal caused by sliding is suppressed, and by increasing the maximum dynamic friction coefficient, even if gear reversal occurs, it can be suppressed to a minimum. In other words, the self-locking property can be evaluated by the maximum dynamic friction coefficient. The larger the maximum dynamic friction coefficient, the better the self-locking property.

[0080] Therefore, the maximum static friction coefficient and maximum dynamic friction coefficient were determined through the Bowden test, thereby evaluating the starting performance and self-locking properties. Specifically, a test grease composition was applied to the lower test piece, a specified load was applied to the upper test piece, and after a specified period of rest, the lower test piece was slid to determine the maximum static friction coefficient and maximum dynamic friction coefficient. The results are shown in Table 1.

[0081] [Experimental Conditions]

[0082] Upper test piece: POM

[0083] Lower test piece: S45C steel

[0084] Test speed: 0.06 mm / s

[0085] Test load: 39.2N

[0086] Test temperature: 80℃

[0087] Let stand time: 5 minutes

[0088] [Pass / Fail Criteria]

[0089] Maximum static friction coefficient: below 0.083

[0090] Maximum coefficient of kinetic friction: 0.043 or higher

[0091] [Table 1]

[0092]

[0093] • The maximum static friction coefficients of Examples 1, 2, 3, and 4, which contain 5-20% Li soap, are 0.083, 0.074, 0.060, and 0.048, respectively. These are lower than those of Comparative Example 1, indicating a reduction in starting voltage. The maximum dynamic friction coefficients are not too low, at 0.093, 0.081, 0.060, and 0.043, respectively, and the self-locking properties are also good.

[0094] • Examples 5 and 6, which are mixed with 5% Ca soap and Zn soap, have a maximum static friction coefficient of 0.08 and 0.067, and a maximum dynamic friction coefficient of 0.080 and 0.081, respectively, achieving the same effect as Example 1, which is mixed with 5% Li soap.

[0095] • Comparative Example 2, which was mixed with 4% Li soap, had a maximum static friction coefficient of 0.093, which was higher than that of Examples 1 to 4, indicating that the reduction in starting voltage was insufficient.

[0096] • The maximum coefficient of kinetic friction of Comparative Example 3, which was mixed with 25% Li soap, was 0.035, which was lower than that of Examples 1 to 4, indicating insufficient self-locking properties.

[0097] • The maximum static friction coefficients of Comparative Examples 4, 5, and 6, which were mixed with 5% PE wax, PP wax, and lignite wax, were 0.092, 0.106, and 0.102, respectively, which were higher than those of Examples 1 to 4, indicating that the reduction in starting voltage was insufficient.

Claims

1. A grease composition for lubricating resin components and metal components. The grease composition contains a base oil, a calcium sulfonate complex as a thickener, and 5-20% by weight of powdered metallic soap as an additive, based on the total mass of the composition.

2. The grease composition according to claim 1, wherein, Metallic soaps are lithium soaps, calcium soaps, magnesium soaps, zinc soaps, or mixtures thereof.

3. A speed reducer, wherein the grease composition of claim 1 or 2 is contained therein.

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