JP7527278B2 - Lubrication Method - Google Patents

Description

The present invention relates to a lubrication method.

In machinery and devices that use metal materials as sliding members, various lubricants are used to lubricate the sliding members. Lubricants used include lubricating oils and greases, which contain various additives as necessary.

In recent years, the use of resin materials as sliding components has been considered for many applications from the standpoint of reducing the weight of parts and ease of processing due to the need for fuel saving. However, resin materials have inferior mechanical strength compared to metal materials, and may be subject to wear, breakage, etc.

For example, Cited Document 1 discloses that a lubricant (refrigeration oil) containing a base oil having at least one selected from mineral oil, synthetic alicyclic hydrocarbon compounds, and synthetic aromatic hydrocarbon compounds as a main component and having a kinetic viscosity of 1 to 8 mm ² /s at 40°C is applied to sliding parts made of polyphenylene sulfide or the like, or sliding parts having a polymer coating film or an inorganic coating film.

International Publication No. 2007/058072

When using resin materials (particularly materials containing engineering plastics) as sliding members, it is essential to improve the sliding properties more than when using metal materials. However, conventional lubrication methods are not necessarily sufficient in terms of improving sliding properties, and there is room for improvement.

The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a lubrication method capable of improving the sliding properties when a resin material is used as the sliding member.

The present invention provides a lubrication method for lubricating a pair of sliding members with a lubricating oil composition. In the lubrication method, at least one of the pair of sliding members is a member containing engineering plastic, and the lubricating oil composition contains a lubricating oil base oil and at least one anti-wear agent selected from the group consisting of anti-wear agents containing phosphorus as a constituent element and not containing sulfur, anti-wear agents containing sulfur as a constituent element and not containing phosphorus, and anti-wear agents containing phosphorus and sulfur as constituent elements. According to such a lubrication method, when a resin material is used as the sliding members from the viewpoint of weight reduction, it is possible to improve the wear resistance while reducing the friction coefficient between the sliding members, and to improve the slidability.

Of the pair of sliding members, preferably one is a member containing engineering plastic and the other is a member containing iron-based material.

According to the present invention, a lubrication method is provided that can improve the sliding properties when a resin material is used as a sliding member.

The following describes in detail the form for implementing the present invention. However, the present invention is not limited to the following embodiment.

One embodiment of the lubrication method is a method of lubricating a pair of sliding members (which move relative to each other in an opposing relationship) with a lubricating oil composition.

In the lubrication method of this embodiment, at least one of the pair of sliding members is a member containing engineering plastics (hereinafter, sometimes referred to as "engineering plastics"). Engineering plastics generally mean plastics with a heat resistance of 100°C or more, a strength of 50 MPa or more, and a flexural modulus of 2.4 GPa or more. Engineering plastics also include super engineering plastics (hereinafter, sometimes referred to as "super engineering plastics") that have a heat resistance of 150°C or more.

The engineering plastic is not particularly limited, but examples thereof include amorphous resins such as polycarbonate (PC) and modified polyphenylene ether (m-PPE), and (semi-)crystalline resins such as polyacetal (POM), polyamide (PA), polybutylene terephthalate (PBT), and polyethylene terephthalate (PET). Among these, the engineering plastic may be polyacetal (POM) or polyamide (PA).

The engineering plastic may be a super engineering plastic. The super engineering plastic is not particularly limited, but examples thereof include amorphous resins such as polyphenylsulfone (PPSU), polysulfone (PSF), polyarylate (PAR), polyetherimide (PEI), and polyamideimide (PAI), and (semi) crystalline resins such as polyetheretherketone (PEEK), polyphenylene sulfide (PPS), polyethersulfone (PES), liquid crystal polymer (LCP), polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE). Among these, the super engineering plastic may be polyetheretherketone (PEEK).

PEEK is a type of semi-crystalline polymer in which benzene rings are linked together by ether bonds or carbonyl groups. PEEK is, for example, a polymer having a structural unit represented by the following formula (A):

The number average molecular weight Mn of PEEK may be, for example, 20,000 to 50,000, and the weight average molecular weight Mw of PEEK may be, for example, 60,000 to 150,000. The molecular weight distribution, Mw/Mn, may be 2 to 4. The number average molecular weight Mn and weight average molecular weight Mw refer to values measured by the GPC method, and are relative values based on polystyrene.

The sliding member may be made of engineering plastics, but from the viewpoint of further improving the sliding properties, the sliding member may be a member containing other components in addition to the engineering plastics, such as solid lubricants, reinforcing fibers, fillers, additives, etc.

Examples of solid lubricants include boron nitride, molybdenum disulfide, fluororesin, and carbon-based solid lubricants (graphite, carbon black, etc.).

When the sliding member contains a solid lubricant, the content may be 0.1 to 30 mass % or 0.5 to 20 mass % based on the total amount of the sliding member. If the content of the solid lubricant is 30 mass % or less based on the total amount of the sliding member, defects are unlikely to occur in the process of producing pellets by compounding, and a significant decrease in the mechanical properties such as impact strength of the sliding member can be prevented. If the content of the solid lubricant is 0.1 mass % or more based on the total amount of the sliding member, the effect of including the solid lubricant can be fully obtained.

Examples of reinforcing fibers include glass fibers, carbon fibers, aramid fibers, and fibrous materials such as various whiskers. Among these, the reinforcing fibers are preferably glass fibers, carbon fibers, or aramid fibers, because they can further improve the sliding properties, and more preferably carbon fibers or aramid fibers, because they can further suppress wear of the sliding members during sliding.

When the sliding member contains reinforcing fibers, the content may be 0.1 to 80 mass% or less, or 0.5 to 70 mass% or less, based on the total amount of the sliding member. When the reinforcing fiber content is 80 mass% or less, based on the total amount of the member, defects are unlikely to occur in the process of producing pellets by compounding, and a significant decrease in the mechanical properties such as impact strength of the sliding member can be prevented. When the reinforcing fiber content is 0.1 mass% or more, based on the total amount of the sliding member, the effect of including reinforcing fibers can be fully obtained.

Examples of fillers include talc, mica, glass flakes, clay, sericite, calcium carbonate, calcium sulfate, calcium silicate, silica, alumina, aluminum hydroxide, calcium hydroxide, potassium titanate, titanium oxide, fluorocarbon resin fibers, fluorocarbon resin, barium sulfate, and various whiskers.

Additives include, for example, colorants, dispersants, plasticizers, antioxidants, curing agents, flame retardants, heat stabilizers, UV absorbers, antistatic agents, surfactants, etc.

The total content of the filler and additives is not particularly limited, but may be 10 mass% or less or 5 mass% or less based on the total amount of the sliding member.

The sliding member may contain polymers other than engineering plastics as long as the effects of the present invention are not significantly impaired. Examples of polymers other than engineering plastics include polyethylene, polystyrene, polypropylene, polyvinyl chloride, phenolic resins, and epoxy resins.

In a pair of sliding members that move relative to each other in opposition to each other, both sliding members may be members containing engineering plastics, but if one of the sliding members is a member containing engineering plastics, the other may be a member other than a member containing engineering plastics. Examples of such members include metal-based materials such as iron-based materials, aluminum-based materials, and magnesium-based materials, and non-metal-based materials such as polymers other than engineering plastics, plastics, and carbon. Among these, the other sliding member is preferably a member containing a metal-based material, and more preferably a member containing an iron-based material, since this can further improve the sliding properties.

When one of the sliding members is a member containing an engineering plastic and the other is a member containing a metal-based material, the lubrication method of this embodiment makes it possible to improve the sliding properties even in a member containing a metal-based material with a large surface roughness (arithmetic mean roughness Ra). The surface roughness (arithmetic mean roughness Ra) of the member containing a metal-based material may be, for example, 0.05 μm or more, 0.1 μm or more, or 0.3 μm or more.

The lubrication method of this embodiment lubricates the above-mentioned sliding members using a lubricating oil composition. The lubricating oil composition contains a lubricating base oil and a specified wear inhibitor.

Examples of lubricating base oils include hydrocarbon oils and oxygen-containing oils. Examples of hydrocarbon oils include mineral oil-based hydrocarbon oils and synthetic hydrocarbon oils. Examples of oxygen-containing oils include esters, ethers, carbonates, ketones, silicones, polysiloxanes, etc. One type of lubricating base oil may be used alone, or two or more types may be used in any combination in any ratio. It is preferable that the lubricating base oil contains a hydrocarbon oil (mineral oil-based hydrocarbon oil or synthetic hydrocarbon oil).

Examples of mineral oil-based hydrocarbon oils include paraffinic mineral oils (normal paraffin, isoparaffin, etc.), naphthenic mineral oils, aromatic mineral oils, etc., which are obtained by refining the lubricating oil fraction obtained by atmospheric and/or reduced pressure distillation of crude oil through a suitable combination of two or more refining processes such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid washing, and clay treatment.

Examples of synthetic hydrocarbon oils include alkylbenzenes, alkylnaphthalenes, poly-α-olefins (PAOs), polybutenes, ethylene-α-olefin copolymers, etc.

From the viewpoint of sliding properties, the 40°C kinematic viscosity of the lubricating base oil may be, for example, ¹ mm2/s or more, 5 ^mm2 /s or more, or ¹⁰ mm2/s or more, and may be ^{1000 mm2} /s or less, 600 mm2/s or less, 200 ^mm2 /s or less, ¹⁰⁰ mm2/s or less, or 50 ^mm2 /s or less. In this specification, the 40°C kinematic viscosity means the kinematic viscosity at 40°C measured in accordance with JIS K 2283:2000.

Other physical properties such as 100°C kinematic viscosity, viscosity index, NOACK evaporation amount, flash point, pour point, etc. of the lubricating base oil used in the lubrication method of this embodiment can be set appropriately.

The content of the lubricating base oil may be, for example, 70 mass% or more, 80 mass% or more, 85 mass% or more, 90 mass% or more, 95 mass% or more, or 97 mass% or more, and may be 99.9 mass% or less, 99.7 mass% or less, or 99.5 mass% or less, based on the total amount of the lubricating oil composition.

The anti-wear agent is at least one selected from the group consisting of an anti-wear agent that contains phosphorus as a constituent element but does not contain sulfur (hereinafter sometimes referred to as the "first anti-wear agent"), an anti-wear agent that contains sulfur as a constituent element but does not contain phosphorus (hereinafter sometimes referred to as the "second anti-wear agent"), and an anti-wear agent that contains phosphorus and sulfur as constituent elements (hereinafter sometimes referred to as the "third anti-wear agent").

Examples of the first antiwear agent include dialkyl zinc phosphate; phosphite esters (mono(alkyl or aryl) phosphite, di(alkyl or aryl) phosphite, tri(alkyl or aryl) phosphite, etc.) (phosphites); phosphate esters (mono(alkyl or aryl) phosphate, di(alkyl or aryl) phosphate, tri(alkyl or aryl) phosphate, etc.) (phosphates); amine salts, metal salts, and derivatives of phosphate esters or phosphite esters; condensed phosphate esters; phosphonate esters, etc. The first antiwear agent may be, for example, a phosphate ester (phosphate) or a metal salt thereof.

The zinc salt of a dialkyl phosphate (zinc dialkyl phosphate) may be, for example, a compound represented by the following formula (C):

In formula (C), R ²¹ to R ²⁴ each independently represent a linear or branched alkyl group. The number of carbon atoms in the alkyl group may be 1 or more or 3 or more, and may be 24 or less, 12 or less, or 8 or less.

Examples of phosphites include di(alkyl or aryl) phosphites such as dibutyl phosphite, dipentyl phosphite, dihexyl phosphite, diheptyl phosphite, dioctyl phosphite, dinonyl phosphite, didecyl phosphite, diundecyl phosphite, didodecyl phosphite, dioleyl phosphite, diphenyl phosphite, and dicresyl phosphite; and tri(alkyl or aryl) phosphites such as tributyl phosphite, tripentyl phosphite, trihexyl phosphite, triheptyl phosphite, trioctyl phosphite, trinonyl phosphite, tridecyl phosphite, triundecyl phosphite, tridodecyl phosphite, trioleyl phosphite, triphenyl phosphite, and tricresyl phosphite. The alkyl group may be linear or branched, and may have an unsaturated bond.

Examples of phosphate esters include di(alkyl or aryl) phosphates such as diethyl phosphate, dibutyl phosphate, dipentyl phosphate, dihexyl phosphate, diheptyl phosphate, dioctyl phosphate, dinonyl phosphate, didecyl phosphate, diundecyl phosphate, didodecyl phosphate, dioleyl phosphate, diphenyl phosphate, and dicresyl phosphate; tri(alkyl or aryl) phosphates such as tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate, trinonyl phosphate, tridecyl phosphate, triundecyl phosphate, tridodecyl phosphate, tritridecyl phosphate, tritetradecyl phosphate, tripentadecyl phosphate, trihexadecyl phosphate, triheptadecyl phosphate, trioctadecyl phosphate, trioleyl phosphate, triphenyl phosphate, tricresyl phosphate, tri(ethylphenyl) phosphate, tri(propylphenyl) phosphate, tri(butylphenyl) phosphate, trixylenyl phosphate, cresyldiphenyl phosphate, and xylenyldiphenyl phosphate. The alkyl group may be linear or branched, and may have an unsaturated bond.

Examples of condensed phosphate esters include resorcinol bis(diphenyl phosphate), resorcinol bis(dixylenyl phosphate), bisphenol A bis(diphenyl phosphate), etc.

Examples of phosphonate esters include dialkyl phosphonoacetic acid, dialkyl hydroxymethyl phosphonate, dialkyl hydroxyethyl phosphonate, dialkyl hydroxyundecyl phosphonate, etc. The alkyl group of these phosphonate esters may be, for example, a linear or branched aliphatic group having 1 to 20 carbon atoms.

Examples of the second antiwear agent include dithiocarbamates, zinc dithiocarbamates, molybdenum dithiocarbamates (MoDTC), disulfides, sulfurized olefins, sulfurized oils and fats, etc. The second antiwear agent may be, for example, a sulfurized olefin.

The third antiwear agent may be, for example, zinc dialkyldithiophosphate (ZnDTP); thiophosphites; dithiophosphites; trithiophosphites; thiophosphates; dithiophosphates: trithiophosphates; amine salts, metal salts, and derivatives of thiophosphites, dithiophosphites, trithiophosphites, thiophosphates, dithiophosphates, or trithiophosphates. The third antiwear agent may be, for example, zinc dialkyldithiophosphate (ZnDTP).

Zinc dialkyldithiophosphate (ZnDTP) may be, for example, a compound represented by the following formula (B):

In formula (B), R ¹¹ to R ¹⁴ each independently represent a linear or branched alkyl group. The number of carbon atoms in the alkyl group may be 1 or more or 3 or more, and may be 24 or less, 12 or less, or 8 or less.

The antiwear agent is at least one selected from the group consisting of a first antiwear agent, a second antiwear agent, and a third antiwear agent. The antiwear agent is preferably the first antiwear agent or the third antiwear agent.

The content of the anti-wear agent may be, for example, 0.01 mass% or more, 0.05 mass% or more, 0.1 mass% or more, 0.3 mass% or more, or 0.5 mass% or more, and may be 20 mass% or less, 15 mass% or less, 10 mass% or less, 5 mass% or less, or 3 mass% or less, based on the total amount of the lubricating oil composition.

The lubricating oil composition may further contain any commonly used lubricating oil additives depending on the purpose. Examples of such lubricating oil additives include antioxidants, antifoaming agents, metal deactivators, viscosity index improvers, pour point depressants, detergent dispersants, acid scavengers, and rust inhibitors. The content of these lubricating oil additives may be, for example, 0.1 to 20 mass% based on the total amount of the lubricating oil composition.

From the viewpoint of sliding properties, the 40°C kinematic viscosity of the lubricating oil composition may be, for example, ¹ mm2/s or more, 5 ^mm2 /s or more, or ¹⁰ mm2/s or more, and may be ^{1000 mm2} /s or less, 600 mm2/s or less, 200 ^mm2 /s or less, ¹⁰⁰ mm2/s or less, or ⁵⁰ mm2/s or less.

Other physical properties such as 100°C kinematic viscosity, viscosity index, NOACK evaporation amount, flash point, pour point, etc. of the lubricating oil composition used in the lubrication method of this embodiment can be set appropriately.

The lubrication method according to the present embodiment can be applied to the lubrication systems of various devices. Examples of such lubrication systems include lubrication systems for lubricating parts that require lubrication in mechanical devices such as (electric) automobiles, railways, and aircraft, industrial machines such as machine tools and robots, household appliances such as washing machines, refrigerators, room air conditioners, and vacuum cleaners, and precision machines such as watches and cameras. Examples of parts that require lubrication include parts (sliding parts) where parts such as gears, bearings, pumps, vanes/rotors, and piston rings come into contact and slide against each other. Examples of mechanical devices that include such sliding parts include engines, gearboxes, compressors, hydraulic units, and motors. Other examples of mechanical devices that include such sliding parts include compressor systems that use various refrigerants.

In the lubrication system, the method of supplying the lubricating oil composition to the sliding member is not particularly limited. The lubrication system may be, for example, a system including a storage unit that stores the lubricating oil composition and a supply unit that supplies the lubricating oil composition from the storage unit to the sliding member. The supply unit may be a circulating supply unit that supplies the lubricating oil composition to the sliding member by a supply means such as a pump. The lubrication system may be a system that impregnates the sliding member with the lubricating oil composition. The lubrication system may be a system in which the lubricating oil composition is filled in a container equipped with a sliding member, such as a compressor in a refrigerant circulation system such as a refrigerator or room air conditioner.

The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples.

(Examples 1-1 and 1-2 and Comparative Examples 1-1 and 1-2)
(Examples 2-1 to 2-4 and Comparative Example 2-1)
(Examples 3-1 to 3-3 and Comparative Examples 3-1 and 3-2)
<Preparation of Lubricating Oil Composition>
Lubricating oil compositions were prepared by mixing the lubricating base oils and antiwear agents shown in Tables 1, 2, and 3. The numerical values shown in Tables 1, 2, and 3 refer to parts by mass.

Details of each component are as follows:
[Lubricant base oil]
Lubricating base oil 1: Poly-α-olefin (PAO, product name: Durasyn-164, manufactured by INEOS, 40° C. kinetic viscosity: 17.5 mm ² /s, 100° C. kinetic viscosity: 4.0 mm ² /s)
Lubricating base oil 2: Poly-α-olefin (PAO, product name: Durasyn-168, manufactured by INEOS, 40° C. kinetic viscosity: 46.0 mm ² /s, 100° C. kinetic viscosity: 8.0 mm ² /s)
Lubricant base oil 3: Mineral hydrocarbon oil (base oil classification according to API 1509, Appendix E: Group III, kinematic viscosity at 40°C: 20.3 mm ² /s, kinematic viscosity at 100°C: 4.3 mm ² /s, viscosity index: 121, density at 15°C: 0.836 g/cm ³ )
Lubricant base oil 4: Mineral hydrocarbon oil (base oil classification according to API 1509, Appendix E: Group I, kinematic viscosity at 40°C: 3.4 mm ² /s, kinematic viscosity at 100°C: 1.3 mm ² /s, viscosity index: 84, density at 15°C: 0.830 g/cm ³ )
[Anti-wear agent]
Comparative anti-wear agent: N-oleoyl sarcosine (product name: Sarkosyl O, manufactured by BASF)
Antiwear agent 1-1: Tricresyl phosphate (product name: TCP, manufactured by Daihachi Chemical Industry Co., Ltd., first antiwear agent)
Antiwear agent 1-2: Dioleyl phosphite (product name: JP-218-OR, manufactured by Johoku Chemical Industry Co., Ltd., first antiwear agent)
Antiwear agent 1-3: di-n-butyl zinc phosphate (phosphorus content: 13.2% by mass, sulfur content: 0% by mass, zinc content: 13% by mass, first antiwear agent)
Antiwear agent 2-1: Sulfurized olefin (product name: GS-440L, manufactured by DIC Corporation, second antiwear agent)
Antiwear agent 3-1: Zinc dialkyldithiophosphate (ZnDTP, product name: HiTEC 653, manufactured by Afton Chemical Japan Co., Ltd., third antiwear agent)

<Evaluation of friction characteristics>
The lubricating oil compositions prepared above were subjected to a friction characteristic test under the following conditions using an MTM (Mini Traction Machine) tester (manufactured by PCS Instruments), and the average friction coefficient (μ) for the last 10 minutes was determined. The balls used were commercially available steel balls of ½ inch, high carbon chromium bearing steel (AISI52100), hardness 800-920HV, and surface roughness <0.02μm, which had been shot blasted to adjust the surface to an arithmetic mean roughness (Ra) of 0.5μm. The disks were prepared by injection molding polyetheretherketone (PEEK, super engineering plastic, KetaSpire (registered trademark) KT-820NT manufactured by Solvay) containing no filler, and preparing PEEK sheets with dimensions of 40 mm length x 40 mm width x 2 mm thickness (PEEK disks). The results are shown in Tables 1, 2, and 3. The smaller the friction coefficient, the better the friction characteristics.
Oil temperature: 25℃
Load: 50N
Circumferential speed: 0.5 m/s
Slip rate: 50%
Test duration: 60 minutes

<Evaluation of wear characteristics>
The depth of the wear mark on the disk after the friction property test was measured to determine the volumetric wear amount. The results are shown in Tables 1, 2, and 3. The smaller the volumetric wear amount, the more excellent the wear property.

(Comparative Examples 4-1 and 4-2)
<Preparation of Lubricating Oil Composition>
Lubricating oil compositions were prepared by mixing the lubricating base oils and antiwear agents shown in Table 4. The values shown in Table 4 are in parts by mass. The details of each component are the same as above.

<Evaluation of friction characteristics and evaluation of wear characteristics>
The lubricating oil compositions prepared above were subjected to evaluation of friction properties and wear properties in the same manner as above, except that the PEEK disk was replaced with a steel disk (PCS standard steel disk, material: AISI52100). The results are shown in Table 4. For comparison, data from Comparative Example 2-1 and Example 2-3 are also shown.

As shown in Tables 1, 2, and 3, the examples using the lubricating oil composition containing a specific antiwear agent were able to reduce the friction coefficient between the sliding members and the volumetric wear amount compared to the comparative examples using only the lubricating oil base oil and the comparative examples using the lubricating oil composition not containing the specific antiwear agent. Also, as shown in Table 4, when the pair of sliding members is a steel ball and a steel disk, Comparative Example 4-2, in which a specific antiwear agent was added, was inferior in terms of friction characteristics and wear characteristics to Comparative Example 4-1, in which a specific antiwear agent was not added. On the other hand, when the pair of sliding members is a steel ball and a PEEK disk, although there is a difference between Comparative Example 4-1 and Comparative Example 4-2 and the absolute value of the volumetric wear amount due to the type of disk, Example 2-3, in which a specific antiwear agent was added, was superior in terms of friction characteristics and wear characteristics to Comparative Example 2-1, in which a specific antiwear agent was not added. From this, it was found that the improvement in sliding properties by using a specific antiwear agent is an effect that is specifically expressed when at least one of the pair of sliding members is a member containing engineering plastic. From the above, it was confirmed that the lubrication method of the present invention can improve the sliding properties when a resin material is used as the sliding member.

Claims (1)

A method for lubricating a pair of sliding members with a lubricating oil composition (excluding lubricating oil compositions containing an aromatic ester and a polyalphaolefin having a viscosity index of 140 or more), comprising the steps of:
one of the pair of sliding members is a member containing engineering plastic, and the other is a member containing an iron-based material;
The lubricating oil composition contains a lubricating base oil and at least one antiwear agent selected from the group consisting of antiwear agents containing phosphorus as a constituent element and not containing sulfur, antiwear agents containing sulfur as a constituent element and not containing phosphorus, and antiwear agents containing phosphorus and sulfur as constituent elements,
The lubricating base oil comprises a hydrocarbon oil or an oxygen-containing oil,
The oxygen-containing oil is at least one selected from the group consisting of esters (excluding aromatic esters), ethers, carbonates, and ketones,
A lubricating method, wherein the content of the lubricating base oil is 70 mass% or more based on the total amount of the lubricating oil composition.