JP2021130759A - Grease - Google Patents

Abstract

To provide grease which can suppress occurrence of a stick-slip phenomenon in a slide part.SOLUTION: Grease comprises: an ethylene polymer particle (A) having a median diameter (D50) of 1 μm or more and less than 20 μm; a base oil; and a thickener. A content percentage of the ethylene polymer particle (A) is 1 to 20 mass%.SELECTED DRAWING: None

Description

The present invention relates to grease.

Grease is widely used for lubricating sliding parts of various machines such as machine tools, precision machines, and steelmaking machines (see, for example, Patent Document 1). The sliding characteristics of the sliding portion are important. Further, smooth sliding motion in the sliding portion greatly contributes to extension of the life of the machine and reduction of running cost.

Japanese Unexamined Patent Publication No. 8-020787

In general, it is known that friction or wear in a sliding portion can be reduced by adding a small amount of solid lubricant to general-purpose grease. However, according to the study by the present inventors, for example, grease using an ultra-high molecular weight polyethylene powder having a large median diameter (D50) as a solid lubricant is used for lubrication of sliding parts of machine tools and the like whose accuracy is increasing year by year. It was found that the stick-slip phenomenon required for the oil composition was not sufficiently prevented. Here, the stick-slip phenomenon is a vibration phenomenon in which a stick (fixed) state in which a static friction force acts and a slip (slip) state in which a dynamic friction force acts alternately appear on the sliding portion, and sometimes an abnormal sound is generated. Accompanied by. For example, in a machine tool, the stick-slip phenomenon may cause a decrease in machining accuracy or adversely affect the life of the machine.

An object of the present invention is to provide a grease capable of suppressing the occurrence of a stick-slip phenomenon in a sliding portion.

As a result of studies to solve the above problems, the present inventors have found that the above problems can be solved by the grease described below, and have completed the present invention. The present invention relates to, for example, the following [1] to [5].
[1] Ethylene polymer particles (A) having a median diameter (D50) of 1 μm or more and less than 20 μm, a base oil, and a thickener are contained, and the content ratio of the ethylene polymer particles (A) is 1 to 1. Grease, which is 20% by mass.
[2] The grease according to the above [1], wherein the ethylene polymer particles (A) have an ultimate viscosity [η] of 5 to 50 dl / g.
[3] The ethylene polymer particles (A) have an aspect ratio of 1.0 to 1.2, a proportion of particles passing through a mesh sieve having a mesh size of 37 μm or more, and a particle diameter of 1 μm or less. The grease according to the above [1] or [2], which is a particle having a particle ratio of 5% by mass or less.
[4] The grease according to any one of the above [1] to [3], wherein a part or all of the base oil is a poly-α-olefin.
[5] The grease according to any one of [1] to [4] above, wherein the thickener is a metal soap or a urea compound.

According to the present invention, it is possible to provide a grease capable of suppressing the occurrence of a stick-slip phenomenon in a sliding portion. If the occurrence of the stick-slip phenomenon can be suppressed, the generation of abnormal noise can also be suppressed.

The numerical range represented by using "~" in the present specification means a range including the numerical values before and after "~" as the lower limit value and the upper limit value.
The grease of the present embodiment contains ethylene polymer particles (A) having a median diameter (D50) of 1 μm or more and less than 20 μm, a base oil, and a thickener. The content ratio of the ethylene polymer particles (A) is 1 to 20% by mass with respect to the mass of the grease.

<Ethylene polymer particles (A)>
The ethylene polymer particles (A) have a median diameter (D50) of 1 μm or more and less than 20 μm. The median diameter of the ethylene polymer particles (A) is preferably 3 μm or more, more preferably 4 μm or more, still more preferably 5 μm or more, preferably 18 μm or less, and more preferably 15 μm or less. The median diameter is a value at which the integrated value of the grain shape distribution is 50% by weight as measured by the weight-based particle size distribution by the Coulter counter method.

When the median diameter of the ethylene polymer particles (A) is within the above range, the occurrence of the stick-slip phenomenon can be suppressed, the frictional noise at the sliding portion can be suppressed, and the wear resistance can be improved. When the median diameter is 20 μm or more, the occurrence of the stick slip phenomenon tends to be insufficiently suppressed.

Examples of the ethylene polymer constituting the ethylene polymer particles (A) include an ethylene homopolymer and a copolymer of ethylene and an α-olefin having 3 or more carbon atoms. Examples of the α-olefin having 3 or more carbon atoms include propylene, 1-butene, 4-methyl-1-pentene, 1-pentene, 1-hexene, 1-octene, 1-decene and the like having 3 to 20 carbon atoms. Examples include α-olefins. Among these, ethylene homopolymers are preferable from the viewpoint of wear resistance. Even an ethylene homopolymer may have a branched structure depending on the olefin polymerization catalyst used, but it is preferable that the ethylene polymer used in the present invention does not have such a branched structure.

The content ratio of the ethylene-derived structural unit in the above-mentioned copolymer is preferably 97 mol% or more, more preferably 98 mol% or more, and further preferably 99 mol% or more. The above content ratio ^{can be measured by the 13} C-NMR measurement method.

The method for producing the ethylene polymer particles (A) is not limited in any way. The ethylene polymer particles (A) can be obtained, for example, by homopolymerizing ethylene using a known catalyst for olefin polymerization, or by copolymerizing ethylene with an α-olefin having 3 or more carbon atoms. For example, the ethylene polymer particles (A) can be produced by the production methods described in International Publication No. 2009/011231 and International Publication No. 2006/054696.

The ethylene polymer particles (A) preferably have an intrinsic viscosity [η] of 5 to 50 dl / g. The ultimate viscosity [η] of the ethylene polymer particles (A) is more preferably 8 dl / g or more, further preferably 10 dl / g or more, more preferably 40 dl / g or less, still more preferably 30 dl / g or less. .. The ultimate viscosity [η] is a value measured at 135 ° C. in a decalin solvent. The ethylene polymer particles having the ultimate viscosity [η] within the above range are ultra-high molecular weight ethylene polymers, and when such ethylene polymer particles are used, the obtained grease suppresses the stick-slip phenomenon and has abrasion resistance. It is preferable because it has excellent properties.

The ethylene polymer particles (A) preferably have an aspect ratio of 1.0 to 1.2. The aspect ratio of the ethylene polymer particles (A) is preferably 1.05 or more, and preferably 1.15 or less.

The aspect ratio is measured by image analysis of the ethylene polymer particles (A). The aspect ratio is expressed by the ratio of the length and width of the smallest rectangle (extrinsic rectangle) when the figure on which the particles are projected is surrounded by a rectangle. It indicates that it is close to a sphere.

When the aspect ratio of the ethylene polymer particles (A) is within the above range, the ethylene polymer particles (A) can be densely packed, and coupled with the effect based on the above range of median diameter, the ethylene polymer particles (A) are dispersed in the base oil. It is preferable in terms of noise reduction because it is excellent in properties and the ethylene polymer particles (A) can effectively suppress the occurrence of the stick-slip phenomenon by effectively playing a role like a roller.

In the ethylene polymer particles (A), the proportion of the particles passing through the mesh sieve having a mesh size of 37 μm is preferably 95% by mass or more, more preferably 96% by mass or more of the whole particles (A). The proportion of particles that pass through the 37 μm mesh sieve is a numerical value calculated from the mass of the particles that have passed through the 37 μm mesh sieve or ultrasonic vibration sieve. Is.

When the proportion of particles passing through the 37 μm mesh sieve having a mesh size in the ethylene polymer particles (A) is 95% by mass or more, it means that the abundance of coarse particles is small. It is considered preferable to have ethylene polymer particles having few coarse particles present in the grease because the particles efficiently contribute to the improvement of sliding characteristics.

In order to keep the proportion of particles passing through the 37 μm mesh sieve in the above range, the reaction conditions and the type of polymerization catalyst used in the production stage (polymerization stage) of the ethylene polymer particles (A) are adjusted. It is also possible to use only particles that have passed through a 37 μm mesh sieve with a mesh size.

In the ethylene polymer particles (A), the proportion of particles having a particle diameter of 1 μm or less is preferably 5% by mass or less, more preferably 3% by mass or less, still more preferably 1% by mass or less of the total particles (A). Is.

The proportion of particles having a particle size of 1 μm or less is a value calculated from the result of particle size distribution analysis measured by the Coulter counter method.
When the proportion of particles having a particle diameter of 1 μm or less is within the above range, the grease obtained by using the ethylene polymer particles (A) has the ethylene polymer particles (A) having excellent dispersibility in the base oil and the ethylene weight. Since the coalesced particles (A) can effectively suppress the occurrence of the stick-slip phenomenon by effectively playing a role like a roller, it is preferable in terms of noise reduction.

In order to adjust the proportion of particles having a particle size of 1 μm or less within the above range, the reaction conditions and the type of polymerization catalyst used are appropriately adjusted in the production stage (polymerization stage) of the ethylene polymer particles (A). It is also possible to use only the particles remaining on the sieve through a 1 μm mesh sieve with a mesh opening.

The ethylene polymer particles (A) may be those in which the ethylene polymer particles having a median diameter (D50) of 1 μm or more and less than 20 μm are irradiated, or may not be irradiated.

Irradiation of the ethylene polymer particles causes cleavage and cross-linking of the molecular chains, resulting in the molecular chains being joined at the cross-linking points. As a result, the molecular chain cannot flow freely even at the glass transition temperature or above the melting point, and the high temperature characteristics tend to be improved. Further, the particles can maintain their morphology even when subjected to stress, and can retain their mechanical properties.

Examples of radiation include α-rays, β-rays, γ-rays, electron beams, and ions, all of which can be used, but electron beams or γ-rays are suitable.
The irradiation dose of radiation varies depending on the monomer species constituting the ethylene polymer particles, but is preferably 50 kGy or more, more preferably 100 kGy or more, preferably 700 kGy or less, and more preferably 500 kGy or less. At such an irradiation dose, the cross-linking reaction of the ethylene polymer proceeds efficiently, and when the obtained cross-linked ethylene polymer particles are used, the sliding characteristics of the lubricant are maintained even at high temperatures, and the durability of the grease is further maintained. Is preferable because it can improve.

One kind or two or more kinds of ethylene polymer particles (A) can be used.
In the grease of the present embodiment, the content ratio of the ethylene polymer particles (A) is 1% by mass or more, preferably 1.5% by mass or more, more preferably 3% by mass or more, and 20% by mass. It is preferably 15% by mass or less, and more preferably 10% by mass or less. Such an embodiment is preferable because the occurrence of the stick-slip phenomenon can be suppressed more satisfactorily.

<Base oil>
The base oil contained in the grease is not particularly limited as long as it is an ordinary base oil used for grease, and examples thereof include synthetic oils, mineral oils, animal and vegetable oils, and gas liquefied oils. These base oils can be used over a wide viscosity range, a wide temperature range, and the like.

Examples of the base oil include normal paraffin, isoparaffin, polybutene, polyisobutylene, 1-decene oligomer, and ethylene / α-olefin copolymer (eg, co-oligocarbonate of ethylene and α-olefin such as propylene and 1-decene). Synthetic hydrocarbon oils such as poly-α-olefins or hydrides thereof; silicone-based synthetic oils such as dimethylpolysiloxane, diphenylpolysiloxane, alkyl-modified polysiloxane; dibutyl sebacate, di-2-ethylhexyl sebacate, etc. Diester synthetic oils such as dioctyl adipate, diisodecyl adipate, ditridecyl adipate, ditridecyl glutarate, methylacetylsinolate, and aromatic ester synthetic oils such as trioctyl remeritate, tridecyl trimerite, and tetraoctyl pyromerite. Oils, polyol ester synthetic oils such as trimethylolpropane caprilate, trimethylolpropane pelargonate, pentaerythritol-2-ethylhexanoate, pentaerythritol verargonate, polyhydric alcohol mixed with dibasic acid and monobasic acid Ester-based synthetic oils such as complex ester oils that are oligoesters with fatty acids; Polyglycol-based synthetic oils such as polyethylene glycol, polypropylene glycol, polyethylene glycol monoethers, and polypropylene glycol monoethers; monoalkyltriphenyl ethers, alkyldiphenyl ethers, and dialkyls. Phenyl ether synthetic oils such as diphenyl ethers, pentaphenyl ethers, tetraphenyl ethers, monoalkyl tetraphenyl ethers and dialkyl tetraphenyl ethers; fluorosynthetic oils such as perfluoropolyethers; paraffin mineral oils, naphthenic mineral oils, aromas Mineral oils such as system mineral oils; animal and vegetable oils such as castor oil, rapeseed oil, wax (wax), whale oil; gas liquefied oil synthesized by the Fisher Tropsch method from natural gas and the like can be mentioned.

In one embodiment, among the base oils, synthetic oils are preferable, synthetic hydrocarbon oils and silicone-based synthetic oils are preferable, and poly-α-olefins are more preferable.
The kinematic viscosity of the base oil at 40 ° C. is preferably 10000 mm ² / s or less, more preferably 1000 mm ² / s or less, still more preferably 500 mm ² / s or less, and preferably 10 mm ² / s or more. The kinematic viscosity is measured according to JIS K2283.

One type or two or more types of base oil can be used.
In the grease of the present embodiment, the content ratio of the base oil is preferably 60% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, preferably 98% by mass or less, more preferably 96% by mass or more. It is 5.5% by mass or less, more preferably 94% by mass or less.

<Thickener>
The thickener contained in the grease can be roughly classified into a soap-based thickener and a non-soap-based thickener. Examples of the soap-based thickener include metal soaps such as lithium soap, lithium composite soap, calcium soap, calcium composite soap, sodium soap, sodium composite soap, aluminum soap, and aluminum composite soap. Examples of the non-soap-based thickener include urea compounds, organic bentonite, and silica gel.

Among the thickeners, lithium soap is preferable. Lithium soap is a saponification reaction product of fatty acid or a derivative thereof and lithium hydroxide. Examples of fatty acids include saturated or unsaturated fatty acids having 2 to 22 carbon atoms.

One or more thickeners can be used.
In the grease of the present embodiment, the content ratio of the thickener is preferably 1% by mass or more, more preferably 2% by mass or more, still more preferably 3% by mass or more, preferably 30% by mass or less, more preferably. It is 20% by mass or less, more preferably 10% by mass or less.

<Additives>
The grease of the present embodiment may further contain additives as long as the effects of the present invention are not impaired. Examples of the additive include antioxidants, rust inhibitors, corrosion inhibitors, extreme pressure agents, oily agents, viscosity index improvers, and solid lubricants (excluding ethylene polymer particles (A)). ..

Examples of the antioxidant include 2,6-dit-butyl-4-methylphenol, 4,4'-methylenebis (2,6-dit-butylphenol), and benzenepropanoic acid 3,5-bis (1, 1-Dimethylethyl) -4-hydroxy C _7-9 Side chain alkyl ester and other phenolic antioxidants, alkyldiphenylamine, triphenylamine, phenyl-α-naphthylamine, phenothiazine, alkylated phenyl-α-naphthylamine, phenithiazine , Alkylated phenylithazine and other amine-based antioxidants, as well as phosphoric acid-based antioxidants and sulfur-based antioxidants.

Examples of the rust preventive include fatty acids, fatty acid amines, alkyl sulfonic acid metal salts, alkyl sulfonic acid amine salts, paraffin oxide, and polyoxyethylene alkyl ether, and examples of corrosion inhibitors include benzotriazole and benzo. Examples include imidazole and thiadiazol.

Examples of extreme pressure agents include phosphorus compounds such as phosphate esters, phosphite esters, and phosphate ester amine salts, sulfur compounds such as sulfides and disulfides, dialkyl dithiophosphate metal salts, and dialkyl dithiocarbamic acid metal salts. Sulfur-based compounds such as metal salts, chlorinated paraffins, chlorinated diphenyl and other chlorinated compounds can be mentioned.

Examples of the oily agent include fatty acids or esters thereof, higher alcohols, polyhydric alcohols or esters thereof, aliphatic amines, fatty acid monoglyceride, montan wax, and amide waxes.

Examples of the viscosity index improver include polymethacrylate, ethylene-propylene copolymer, polyisobutylene, polyalkylstyrene, and styrene-isoprene copolymer hydride.

Examples of the solid lubricant include molybdenum disulfide, graphite, polyethylene tetrafluoride, polyimide resin, antimony sulfide, boron nitride, silane nitride, and borates of alkali metals and alkaline earth metals.

One kind or two or more kinds of additives can be used.
When the grease of the present embodiment contains an additive, the total content ratio of the additive is preferably 20% by mass or less, more preferably 10% by mass or less.

[Grease manufacturing and application]
The grease of the present embodiment is obtained by mixing ethylene polymer particles (A) with, for example, a base grease obtained by mixing a thickener with a base oil. The grease of this embodiment is, in one embodiment, a semi-solid or solid composition at room temperature.

Specifically, the grease of the present embodiment is obtained by mixing the above-mentioned ethylene polymer particles (A), a base oil, a thickener, and various additives as needed in a predetermined ratio. Be done. The mixing method can be any of the general solid-liquid mixing methods such as a kneader, a planetary mixer, three rolls, a mechanical stirrer, a self-revolving mixer, a homomixer, a homogenizer, a ball mill, and a bead mill. You may combine the methods of. In addition, heating or depressurization may be performed as needed.

The grease of the present embodiment can be widely used for lubrication of sliding portions of various machines such as transportation machines such as automobiles, general machines, machine tools, precision machines, and steelmaking machines. The sliding portion is a concept that includes all the portions where the target components slide with each other and may cause wear or abnormal noise.

Specifically, the grease of the present embodiment includes power transmission devices such as speed reducers / accelerators, gears, chains, and motors, traveling system parts, control system parts such as anti-lock / brake systems (ABS), and steering. System parts, drive system parts such as transmissions, automobile reinforcement parts such as power window motors, power seat motors, sun roof motors, electronic information equipment, hinge parts such as mobile phones, food / pharmaceutical industry, steel, construction, glass industry, It can be widely applied to various parts in the cement industry, chemical / rubber / resin industry such as film tenter, environment / power equipment, paper / printing industry, wood industry, textile / apparel industry, and machine parts that move relative to each other. It can also be applied to rolling bearings, thrust bearings, dynamic pressure bearings, resin bearings, bearings for linear motion devices, and the like.

Hereinafter, the present invention will be described in more detail based on Examples, but the present invention is not limited to these Examples. In the description of the following examples and the like, "parts" means "parts by mass" unless otherwise specified.

The method for measuring the physical properties is as follows.
<Median diameter (D50) and proportion of particles with a particle size of 1 μm or less>
The median diameter (D50) and the proportion of particles having a particle diameter of 1 μm or less were measured by a precision particle size distribution measuring device (“Coulter Counter Multisizer III”, manufactured by Beckman).

<Percentage of particles passing through a 37 μm mesh sieve>
The proportion of particles passing through the 37 μm mesh sieve was measured by determining the mass of the particles that passed through the 37 μm mesh sieve (Typer # 400).

<Aspect ratio>
The aspect ratio was measured by image analysis using a particle size / shape distribution measuring device (“PITA-3”, manufactured by Seishin Enterprise Co., Ltd.).

<Extreme viscosity [η]>
The ultimate viscosity [η] was measured at 135 ° C. by dissolving ethylene polymer particles in decalin.
<Dynamic coefficient, stick slip index>
Grease was applied between the test pieces using a Haydon reciprocating friction tester, and the number of dynamic friction coefficients and resistances exceeding the threshold was confirmed under the following conditions.
Specimen: SPCC-SB steel plate / SPCC-SB steel plate Load: 200 g
Test temperature: Room temperature Travel distance: 20 mm
Speed: 20 mm / sec Number of reciprocations: 100 reciprocations Threshold of resistance: | 35 gf | (If the resistance is 35 gf or more or -35 gf or less, it is judged that the resistance exceeds the threshold)

The stick-slip index can be expressed by the following formula, where X is the number exceeding the resistance threshold value of each test example and Y is the number exceeding the resistance threshold value in Comparative Example 1 below. The smaller the stick-slip index, the less the stick-slip phenomenon occurs.
Stick slip index = X / Y

[Comparative Example 1]
92.85 parts of hydrocarbon-based synthetic oil (Lucant (registered trademark) HC-20, manufactured by Mitsui Chemicals Co., Ltd., the same applies hereinafter) as the base oil, 6.65 parts of lithium soap as a thickener, and antioxidants. As a result, 0.5 part of benzenepropanoic acid 3,5-bis (1,1-dimethylethyl) -4-hydroxy C _7-9 side chain alkyl ester (IrganoxL135, manufactured by BASF Japan Ltd.) is mixed and greased. Then, grease was prepared. The number of greases obtained in which the dynamic friction coefficient and the resistance force exceeded the threshold value was measured. The measurement results are shown in Table 1.

[Example 1]
91.04 parts of hydrocarbon-based synthetic oil as the base oil, 6.46 parts of lithium soap as the thickener, and 3,5-bis (1,1-dimethylethyl) -4 of benzenepropanoate as the antioxidant. -Hydroxy C _7-9 side chain alkyl ester (IrganoxL135, BASF Japan Ltd.) 0.5 part was mixed and greased, and this was used as a base grease. In 98 parts of the obtained base grease, a median diameter of 11 μm, an aspect ratio of 1.1, an ultimate viscosity [η] of 13 dl / g, a proportion of particles passing through a mesh sieve with an opening of 37 μm, 97% by mass, and particles having a particle diameter of 1 μm or less. Two parts of ethylene polymer particles (“MIPERON® PM-200”, manufactured by Mitsui Kagaku Co., Ltd.) having a ratio of 0.1% by mass were added and uniformly stirred to prepare a grease. The coefficient of dynamic friction and the stick slip index of the obtained grease were measured. The measurement results are shown in Table 1.

[Example 2]
88.23 parts of hydrocarbon-based synthetic oil as a base oil, 6.27 parts of lithium soap as a thickener, and 3,5-bis (1,1-dimethylethyl) -4 of benzenepropanoate as an antioxidant. -Hydroxy C _7-9 side chain alkyl ester (IrganoxL135, manufactured by BASF Japan Ltd.) was mixed with 0.5 part and greased, and this was used as a base grease. To 95 parts of the obtained base grease, 5 parts of the ethylene polymer particles used in Example 1 were added and uniformly stirred to prepare a grease. The coefficient of dynamic friction and the stick slip index of the obtained grease were measured. The measurement results are shown in Table 1.

[Comparative Example 2]
As the ethylene polymer particles, instead of the ethylene polymer particles used in Example 1, two parts of ethylene polymer particles having a median diameter of 30 μm, an aspect ratio of 1.1, and an extreme viscosity [η] of 13 dl / g were added. , A grease was obtained in the same manner as in Example 1. The coefficient of dynamic friction and the stick slip index of the obtained grease were measured. The measurement results are shown in Table 1.

[Comparative Example 3]
As the ethylene polymer particles, grease was obtained in the same manner as in Example 2 except that 5 parts of the ethylene polymer particles used in Comparative Example 2 were added instead of the ethylene polymer particles used in Example 1. The coefficient of dynamic friction and the stick slip index of the obtained grease were measured. The measurement results are shown in Table 1.

Claims (5)

Ethylene polymer particles (A) having a median diameter (D50) of 1 μm or more and less than 20 μm,
Base oil and
Including thickener
The content ratio of the ethylene polymer particles (A) is 1 to 20% by mass.
Grease. The grease according to claim 1, wherein the ethylene polymer particles (A) have an ultimate viscosity [η] of 5 to 50 dl / g. The ethylene polymer particles (A) are
The aspect ratio is 1.0 to 1.2,
The proportion of particles passing through the 37 μm mesh sieve with a mesh size is 95% by mass or more.
The proportion of particles having a particle size of 1 μm or less is 5% by mass or less.
The grease according to claim 1 or 2. The grease according to any one of claims 1 to 3, wherein a part or all of the base oil is a poly-α-olefin. The grease according to any one of claims 1 to 4, wherein the thickener is a metal soap or a urea compound.