Lubricity improvers, sliding members and devices

Abstract

To provide a lubricity improver that can improve the lubricity of sliding members.SOLUTION: A lubricity improver contains an unsaturated fluorohydrocarbon. A sliding member comprises a metal member and a coating film that covers the metal member and is derived from an unsaturated fluorocarbon.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a lubricity improver, a sliding member, and a device.

Background Art

[0002] Devices such as transportation machines, machine tools, industrial machines, household electrical appliances, and precision machines mainly have sliding members composed of metal members. In order to reduce friction, wear, seizure, etc. associated with the sliding of the sliding member, generally, a lubricating oil for lubricating the sliding member is used.

[0003] <​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​

[0006] The inventors have found that unsaturated fluorinated hydrocarbons have the function of improving the lubricity of sliding members. In other words, one aspect of the present invention is a lubricity enhancer containing unsaturated fluorinated hydrocarbons.

[0007] Furthermore, the inventors have found that unsaturated fluorinated hydrocarbons can form a coating that improves the lubricity of sliding members. That is, one aspect of the present invention is a sliding member comprising a metal member and a coating derived from unsaturated fluorinated hydrocarbons that covers the metal member.

[0008] In each of the above aspects, the number of carbon atoms in the unsaturated fluorinated hydrocarbon may be 2 to 4, and the number of fluorine atoms may be 1 to 6.

[0009] Another aspect of the present invention is an apparatus including the above-described sliding member. This apparatus may further include a lubricating oil and may further include a refrigerant. [Effects of the Invention]

[0010] According to one aspect of the present invention, the lubricity of the sliding member can be improved. [Brief explanation of the drawing]

[0011] [Figure 1] This graph shows the measurement results of the coefficient of friction under conditions of 25℃ and 0.05MPa. [Figure 2] This graph shows the dependence of the friction coefficient on the introduced pressure. [Figure 3] This graph shows the temperature and introduction pressure dependence of the coefficient of friction. [Figure 4] This graph shows the temperature and introduction pressure dependence of wear amount. [Figure 5] This graph shows the fluorine concentration profile in the depth direction of the sliding member. [Figure 6] This graph shows the measurement results of the coefficient of friction for different load magnitudes. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described in detail below. One embodiment of the present invention is a lubricity enhancer containing an unsaturated fluorinated hydrocarbon. This lubricity enhancer can improve the lubricity of a sliding member by forming a film on a metal member constituting the sliding member. More specifically, this lubricity enhancer makes it possible to reduce the coefficient of friction of the sliding member, reduce the amount of wear of the sliding member (improve wear resistance), and improve the load-bearing capacity of the sliding member. Therefore, the lubricity enhancer can also be referred to as a coefficient of friction reducer, a wear reducer (wear resistance enhancer), or a load-bearing capacity enhancer.

[0013] Unsaturated fluorinated hydrocarbons (also called hydrofluoroolefins (HFOs)) have at least one carbon atom, one hydrogen atom, and one fluorine atom. Unsaturated fluorinated hydrocarbons may have one carbon-carbon unsaturated bond. The number of carbon atoms in an unsaturated fluorinated hydrocarbon may be 2 to 4 or 2 to 3, and the number of fluorine atoms may be 1 to 6 or 1 to 5.

[0014] The unsaturated fluorinated hydrocarbon is preferably a fluoropropene, and more preferably a fluoropropene having 3 to 5 fluorines. The fluoropropene may be at least one selected from the group consisting of 1,2,3,3,3-pentafluoropropene (HFO-1225ye), 1,3,3,3-tetrafluoropropene (HFO-1234ze), 2,3,3,3-tetrafluoropropene (HFO-1234yf), 1,2,3,3-tetrafluoropropene (HFO-1234ye), and 3,3,3-trifluoropropene (HFO-1243zf), and is preferably 2,3,3,3-tetrafluoropropene (HFO-1234yf).

[0015] The unsaturated fluorinated hydrocarbon may be fluoroethylene, preferably fluoroethylene having 1 to 3 fluorine atoms, more preferably 2 to 3 fluorine atoms. The fluoroethylene may be monofluoroethylene, difluoroethylene (HFO-1132), or trifluoroethylene (HFO-1123). The unsaturated fluorinated hydrocarbon may be fluorobutene, for example, (Z)-1,1,1,4,4,4-hexafluorobutene (HFO-1336mzz(Z)).

[0016] The unsaturated fluorinated hydrocarbon may further have a chlorine atom, for example, 1-chloro-2,3,3,3-tetrafluoropropene (HCFO-1224yd). 1-chloro-2,3,3,3-tetrafluoropropene (HCFO-1224yd) may be cis-1-chloro-2,3,3,3-tetrafluoropropene (HCFO-1224yd(Z)), trans-1-chloro-2,3,3,3-tetrafluoropropene (HCFO-1224yd(E)), or any mixture thereof.

[0017] The lubricity improver may consist only of the unsaturated fluorinated hydrocarbon or may consist of the unsaturated fluorinated hydrocarbon and other components. Examples of the other components include known compounds used as refrigerants such as saturated fluorinated hydrocarbons, hydrocarbons, fluorinated ethers, bis(trifluoromethyl)sulfide, methyl iodide trifluoride, ammonia, and carbon dioxide. In this case, the proportion of the unsaturated fluorinated hydrocarbon in the lubricity improver is preferably 50% by mass or more, and may be 70% by mass or more, 90% by mass or more, 95% by mass or more, or 99% by mass or more based on the total amount of the lubricity improver because a film derived from the unsaturated fluorinated hydrocarbon can be advantageously formed.

[0018] Another embodiment of the present invention is a sliding member including a metal member and a film derived from an unsaturated fluorinated hydrocarbon that coats the metal member.

[0019] The metal member may be a metal member commonly used for a sliding member. Examples of the metal constituting the metal member include steel, iron (cast iron), copper, aluminum, copper alloy (copper - tin, copper - zinc, etc.), aluminum alloy (aluminum - silicon, etc.), molybdenum steel, white metal (tin, lead, zinc, antimony, etc.), and the like. From the viewpoint that the effect of improving the lubricity by the film derived from unsaturated fluorinated hydrocarbon is more significantly obtained, the metal is preferably steel, iron (cast iron), or copper, and more preferably steel or copper.

[0020] The film derived from unsaturated fluorinated hydrocarbon may contain, for example, a fluorine - containing organic compound which is an unsaturated fluorinated hydrocarbon or its modified product, and may also contain a fluoride of the metal constituting the metal member. The components (fluorine - containing organic compound, fluoride of the metal) contained in the film can be identified, for example, by XPS (X - ray Photoelectron Spectroscopy).

[0021] The above - mentioned film covers at least the sliding surface of the metal member, and may cover the entire surface of the metal member. The thickness of the film may be, for example, 0.1 nm or more, 1 nm or more, or 5 nm or more, and may be 10000 nm or less, 1000 nm or less, or 500 nm or less.

[0022] The above - mentioned film can be formed by exposing the metal member to an atmosphere of unsaturated fluorinated hydrocarbon contained in the above - mentioned lubricity improver at the temperature and pressure described later. The atmosphere of unsaturated fluorinated hydrocarbon may further contain the other components described above, but preferably contains only unsaturated fluorinated hydrocarbon.

[0023] From the viewpoint of more suitably forming the above - mentioned film, the temperature of the metal member when exposing it to the atmosphere of unsaturated fluorinated hydrocarbon is preferably 0 °C or more, more preferably 25 °C or more, still more preferably 40 °C or more, and may be 70 °C or more or 90 °C or more. The temperature may be, for example, 500 °C or less, 200 °C or less, or 150 °C or less.

[0024] The pressure used when exposing the metal member to an unsaturated fluorinated hydrocarbon atmosphere (introduction pressure of unsaturated fluorinated hydrocarbon) is preferably 0.0001 MPa or higher, more preferably 0.001 MPa or higher, and even more preferably 0.01 MPa or higher, and may also be 0.04 MPa or higher or 0.07 MPa or higher, from the viewpoint of more favorably forming the above-mentioned coating. This pressure may also be, for example, 20 MPa or less, 10 MPa or less, or 5 MPa or less.

[0025] The time for exposing the metal component to an unsaturated fluorinated hydrocarbon atmosphere is appropriately selected according to the desired film thickness, and may be, for example, 0.1 minutes or more, 1 minute or more, or 10 minutes or more, or 1440 minutes or less, 720 minutes or less, or 360 minutes or less.

[0026] The above-described sliding member is suitably used as a sliding part in devices such as transport machinery, machine tools, industrial machinery, household electrical appliances, and precision machinery. That is, another embodiment of the present invention is a device including the above-described sliding member. More specifically, the function of the sliding member can be utilized by first applying a lubricating film derived from unsaturated fluorinated hydrocarbons to the surface of sliding parts such as bearings, gears, pistons, vanes, cams, and rings using the above-described method, and then assembling them into a device.

[0027] More specifically, examples of devices include transportation machinery such as (electric) automobiles, railways, and aircraft; industrial machinery such as machine tools and robots; household electrical appliances such as washing machines, refrigerators, room air conditioners, and vacuum cleaners; and precision machinery such as clocks and cameras.

[0028] The apparatus may further contain a lubricating oil for lubricating the sliding members. Since the sliding members having a coating derived from unsaturated fluorinated hydrocarbons have excellent lubricity, only a very small amount of lubricating oil may be used in the apparatus, and the apparatus may not contain any lubricating oil at all (so-called semi-dry lubrication or dry lubrication may be used).

[0029] Lubricating oils contain a base oil. Hydrocarbon oils and oxygenated oils can be used as the base oil. Examples of hydrocarbon oils include mineral oil-based hydrocarbon oils and synthetic hydrocarbon oils. Examples of oxygenated oils include esters, ethers, carbonates, ketones, silicones, and polysiloxanes.

[0030] The ester may be, for example, an aromatic ester, a dibasic acid ester, a polyol ester, a complex ester, a carbonate ester, etc., and is preferably selected from polyol esters and complex esters. The ether may be a polyvinyl ether, a polyalkylene glycol, a polyphenyl ether, a perfluoroether, etc., and is preferably selected from polyvinyl ether and polyalkyne glycol, and more preferably polyvinyl ether.

[0031] The base oil content may be 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more, based on the total amount of lubricating oil, and may also be 99% by mass or less.

[0032] The lubricating oil may further contain additives (lubricating oil additives). The additives may be at least one selected from the group consisting of, for example, anti-wear agents, antioxidants, acid scavengers, oiliness agents, metal deactivators, viscosity index improvers, pour point depressants, and detergent dispersants. The total content of additives may be, for example, 0.1% by mass or more, 0.5% by mass or more, 1% by mass or more, or 2% by mass or more, and 5% by mass or less, 4% by mass or less, or 3% by mass or less, based on the total amount of lubricating oil.

[0033] If the device is a cooling device (also called a refrigeration unit) such as a refrigerator or room air conditioner, the device may further contain a refrigerant. Examples of refrigerants include saturated fluorinated hydrocarbons, unsaturated fluorinated hydrocarbons, hydrocarbons, fluorinated ethers, bis(trifluoromethyl) sulfide, methane trifluoride iodide, ammonia, and carbon dioxide. The refrigerant may be one of these refrigerants alone, or a mixture of two or more refrigerants.

[0034] When a device (refrigeration unit or refrigerant compressor) contains unsaturated fluorinated hydrocarbons as a refrigerant, a coating derived from unsaturated fluorinated hydrocarbons can be formed on sliding members (metal members) within the device (refrigeration unit or refrigerant compressor). Specifically, for example, by filling the device (refrigeration unit or refrigerant compressor) with refrigerant before filling with lubricating oil, and then test-running the refrigerant compressor under the aforementioned temperature and pressure conditions using semi-dry or dry lubrication, a coating derived from unsaturated fluorinated hydrocarbons can be formed on the sliding members within the refrigerant compressor. As a result, during subsequent normal operation (main operation), the coating is formed on the sliding members, providing excellent lubrication. [Examples]

[0035] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0036] (Example 1) In Example 1, a ball-on-disk reciprocating sliding lubrication tester with controllable atmosphere was used. The test disc was reciprocated by a crank mechanism with a sliding width of ±20 mm and an average sliding speed of 10 mm / s. The test ball was adjusted to balance with a balance weight via a pivot point, and then a load weight was placed on top of the test ball to apply the test load. The coefficient of friction was calculated using a load cell on the test ball side. A steel (SUJ-2) ball was used as the test ball, and the test disc was made of steel (SUJ-2), cast iron (FC250), pure copper (99.9%), or pure aluminum (99.5%). The lubrication section was sealed with a steel plate and an acrylic plate with compressive strength (sealed space volume: approximately 0.08 m³). 3After evacuating the system using a vacuum pump, 2,3,3,3-tetrafluoropropene was introduced into a sealed space from a cylinder through piping at four different pressures: 0.0125 MPa, 0.025 MPa, 0.05 MPa, and 0.08 MPa. After introducing 2,3,3,3-tetrafluoropropene (HFO-1234yf), a 10-minute standing period was observed before starting the sliding friction test. The test was conducted under dry lubrication (no lubricant, surface pressure 0.7 GPa) and boundary lubrication conditions. A heater was also provided at the bottom of the test disc, and the temperature at the bottom center of the disc was measured using a thermocouple. The test was conducted at two temperatures: 100°C and 25°C.

[0037] (Comparative Example 1) A sliding friction test was conducted in the same manner as in Example 1, except that 2,3,3,3-tetrafluoropropene was replaced with difluoromethane.

[0038] [Evaluation of friction coefficient and wear amount under conditions of 25℃ and 0.05MPa] In a sliding friction test conducted for 10 minutes under the conditions of a test temperature of 25°C and an introduction pressure of 0.05 MPa, the coefficient of friction was measured every 5 seconds. In addition, the amount of wear of the sliding members (wear mark diameter on the steel ball and wear mark width on the steel disc) after the test was measured. The results of the friction coefficient measurement are shown in Figure 1. The results of the wear measurement are shown in Table 1. As can be seen from Figure 1 and Table 1, in Example 1, which used unsaturated fluorinated hydrocarbons, the coefficient of friction was lower and the amount of wear of the sliding members (wear mark diameter and wear mark width) was also smaller compared to Comparative Example 1, which used saturated fluorinated hydrocarbons.

[0039] [Table 1]

[0040] [Temperature and introduction pressure dependence of friction coefficient] In Example 1, the coefficient of friction was measured every 5 seconds during a sliding friction test conducted for 10 minutes under the two test temperature conditions and the four introduction pressure conditions described above. The measurement results for each introduction pressure (four conditions) at a test temperature of 25°C are shown in Figure 2. The measurement results for a test temperature of 25°C or 100°C and an introduction pressure of 0.05 MPa or 0.08 MPa are shown in Figure 3. As can be seen from Figure 2, the coefficient of friction tended to be lower in the initial stages of sliding as the introduction pressure increased, and the coefficient of friction tended to be higher as the introduction pressure decreased. Also, as can be seen from Figure 3, a lower coefficient of friction was observed at a higher test temperature, and a lower coefficient of friction was observed in the steady state (a state in which the value of the coefficient of friction is stable) at a higher introduction pressure.

[0041] [Temperature and introduction pressure dependence of wear amount] In both Example 1 and Comparative Example 1, the diameter of the wear marks on the steel balls was measured after a sliding friction test conducted for 10 minutes under the two test temperature conditions and the four introduction pressure conditions described above. The results are shown in Figure 4. As can be seen from Figure 4, in Example 1, the amount of wear tended to decrease as the test temperature and introduction pressure increased. On the other hand, in Comparative Example 1, the dependence of the amount of wear on the introduction pressure was relatively small.

[0042] [Dependence on the type of metal used in sliding members] In both Example 1 and Comparative Example 1, a steel (SUJ-2) disc, an iron (cast iron, FC250) disc, a pure copper (99.9%) disc, or a pure aluminum (99.5%) disc was used as the test disc. After a sliding friction test conducted for 10 minutes at a test temperature of 25°C and an introduction pressure of 0.05 MPa, the wear mark width on each test disc was measured. The results are shown in Table 2. As can be seen from Table 2, for all types of metal discs, Example 1 showed a smaller wear mark width than Comparative Example 1, but in particular, for steel and copper discs, Example 1 showed a significantly smaller wear mark width than Comparative Example 1.

[0043] [Table 2]

[0044] [Surface analysis] XPS (X-ray Photoelectron Spectroscopy) analysis was performed on the surface of a steel disc after a sliding friction test conducted for 10 minutes under the conditions of a test temperature of 25°C and an introduction pressure of 0.05 MPa. Three locations (from the ends to the center) of the linear sliding marks were selected, and elemental analysis was performed on the outermost surface, followed by depth analysis by argon sputtering. Figure 5 shows the depth profile of the measured fluorine element / iron element ratio. As can be seen from Figure 5, in Example 1, the fluorine concentration was more than twice as high as in Comparative Example 1, and high fluorine concentration was detected even at depths (for example, the fluorine element / iron element ratio was 0.01 to 0.03 at depths of 10 to 60 nm (in SiO2 equivalent)). In other words, it was found that in Example 1, which used unsaturated fluorinated hydrocarbons, a thicker coating (e.g., an iron fluoride coating) was formed compared to Comparative Example 1, which used saturated fluorinated hydrocarbons.

[0045] [Evaluation of load-bearing capacity] A steel disc was exposed to 2,3,3,3-tetrafluoropropene for 10 minutes at a temperature of 100°C and an introduction pressure of 0.08 MPa to form a coating derived from 2,3,3,3-tetrafluoropropene on the steel disc. Using the steel disc with this coating, the coefficient of friction was measured every 5 seconds when dry lubrication (without lubricant) was performed for 10 minutes in an air atmosphere at a test temperature of 100°C and loads of 4.9 N, 9.8 N, or 14.7 N. The results are shown in Figure 6. As can be seen from Figure 6, the steel disc with the 2,3,3,3-tetrafluoropropene coating maintained a significantly lower coefficient of friction compared to the steel disc without the coating at loads of 4.9 N and 9.8 N. Even when the load increased to 14.7 N, although there was a slight increase in the coefficient of friction, a lower coefficient of friction was obtained compared to the steel disc without the coating.

[0046] (Example 2) A steel disc was exposed to 2,3,3,3-tetrafluoropropene for 10 minutes at a temperature of 100°C and an introduction pressure of 0.08 MPa to form a coating derived from 2,3,3,3-tetrafluoropropene on the steel disc. A lubricating oil (polyol ester VG68) was applied to the steel disc with this coating, and a sliding friction test was conducted for 10 minutes in an air atmosphere at a test temperature of 25°C and a load of 19.6 N. The amount of wear of the sliding member (width of wear marks on the steel disc) was measured after the test.

[0047] (Comparative Example 2) Except for using an untreated steel disc without a coating instead of a coated steel disc, the sliding friction test was conducted in the same manner as in Example 2, and then the amount of wear of the sliding member (width of wear marks on the steel disc) was measured.

[0048] Table 3 shows the measurement results of the amount of wear (wear mark width on steel discs) of the sliding members in Example 2 and Comparative Example 2. As can be seen from Table 3, the steel discs with a coating derived from 2,3,3,3-tetrafluoropropene showed a smaller wear mark width compared to steel discs without this coating. [Table 3]

Claims

1. A lubricity enhancer for forming a film on a sliding member in dry lubrication or semi-dry lubrication, comprising an unsaturated fluorinated hydrocarbon.

2. The lubricity enhancer according to claim 1, wherein the unsaturated fluorinated hydrocarbon has 2 to 4 carbon atoms and 1 to 6 fluorine atoms.

3. A sliding member comprising a metal member and a coating derived from an unsaturated fluorinated hydrocarbon that covers the metal member.

4. The sliding member according to claim 3, wherein the unsaturated fluorinated hydrocarbon has 2 to 4 carbon atoms and 1 to 6 fluorine atoms.

5. An apparatus including the sliding member described in claim 3 or 4.

6. The apparatus according to claim 5, further comprising lubricating oil.

7. The apparatus according to claim 5, further comprising a refrigerant.

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