Bearing with coating and slide coating agent used therefor

Abstract

To provide a slide coating agent achieving sliding property, wear resistance approximately equal to a slide coating consisting of a slide coating agent including the fluorine containing organic component and further wear resistance of a mating material by finding a component, with which the fluorine containing organic component is replaced, the slide coating agent not including a fluorine containing organic compound, and a bearing, to which the slide coating is applied, and provide a slide coating agent achieving high temperature resistance that is difficult by using a fluorine containing organic compound as a lubricant, and a bearing to which the slide coating is applied.SOLUTION: Provided is a bearing with a coating comprising an inner ring, an outer ring and a ball or a roller disposed so as to be rolled while being interposed between both the rings. In the bearing, a slide coating formed from a slide coating agent is included in a slide surface of the bearing, and the slide coating agent includes potassium titanate and an organic resin as a solid-state lubricant and substantially does not include a fluorine containing organic compound.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a bearing with a film and a lubricating film agent used therefor.

Background Art

[0002] There are devices or parts having surfaces that move in a mechanism, such as bearings. The surfaces of such moving surfaces or mating materials wear depending on use, and their performance deteriorates. In order to suppress such deterioration, a lubricating film containing a solid lubricant may be formed on the moving surface. For example, a lubricating film obtained by baking a lubricating film agent may be applied to the outer diameter surface of the outer ring of a bearing. As such solid lubricant components, there are those containing molybdenum disulfide, graphite, and fluororesin (Non-Patent Document 1). On the other hand, as a movement including Europe and Japan, it has been discussed to regulate the use of about 10,000 fluorinated organic compounds included in PFAS (Non-Patent Document 2). This is because fluorinated organic compounds are not decomposed in nature due to their high durability, and there are concerns about their accumulation in living organisms. Therefore, for bearings as well, a lubricating film agent that does not use fluorinated organic compounds such as PTFE is desired, and the development of alternative materials has become an urgent task.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In view of the above technical and social trends, the present invention provides a sliding film agent that does not contain a fluorine-containing organic compound, finds a component to replace the fluorine-containing organic compound, and has a sliding property and wear resistance substantially equivalent to those of a sliding film formed of a sliding film agent containing a fluorine-containing organic compound, and further aims to provide a sliding film agent that realizes the wear resistance of a mating material and a bearing to which the sliding film is applied. Further, an object is to provide a sliding film agent that realizes high heat resistance, which is difficult to achieve when using a fluorine-containing organic compound as a lubricant, and a bearing to which the sliding film is applied.

Means for Solving the Problems

[0005] In response to the above object, the present inventors have intensively studied and confirmed the performance of various compounds as sliding film agents. As a result, it has been found that by using potassium titanate instead of a fluorine-containing organic compound, it is possible to maintain the characteristics of the sliding film agent as a sliding film. It has also been found that potassium titanate is thermally stable and excellent in high heat resistance. The present invention has been completed based on these findings. That is, the present invention provides the following means. (1) A film-bearing comprising an inner ring, an outer ring, and balls or rollers disposed between the two and arranged to be rotatable, having a sliding film formed from a sliding film agent on the sliding surface of the bearing, wherein the sliding film agent contains potassium titanate as a solid lubricant and an organic resin and substantially does not contain a fluorine-containing organic compound. (2) The film-bearing according to claim 1, wherein the solid lubricant contains molybdenum disulfide and / or graphite, and the organic resin contains a base resin and a curing agent. (3) The film-bearing according to (1), wherein the sliding surface is the outer diameter surface of the bearing outer ring. (4) The film-bearing according to any one of (1) to (3), wherein the sliding film is formed by firing the sliding film agent. (5) A rubbing film agent for forming a rubbing film applied to the outer diameter surface of the outer ring of a bearing, which contains a solid lubricant containing potassium titanate and an organic resin, and substantially does not contain a fluorine-containing organic compound. (6) The rubbing film agent according to (5), wherein the rubbing film agent further contains molybdenum disulfide and graphite as solid lubricants. (7) The rubbing film agent according to any one of (5) and (6), wherein the rubbing film is formed by firing the rubbing film agent.

Advantages of the Invention

[0006] According to the rubbing film agent of the present invention, while not containing a fluorine-containing organic compound, when it is incorporated into the rubbing surface of a bearing as a rubbing film obtained by firing it, it has substantially the same rubbing performance and wear resistance as a rubbing film containing a fluorine-containing organic compound, and further realizes the wear resistance of the mating material. Furthermore, potassium titanate is stable even at high temperatures, is excellent in high temperature resistance when used as a rubbing film, which is difficult to achieve with fluorine-containing organic compounds, and exhibits an effect different from that of conventional examples. The bearing of the present invention in which the rubbing film formed by firing from the above-mentioned rubbing film agent of the present invention is incorporated into the rubbing surface exhibits high performance and high durability.

Brief Description of the Drawings

[0007]

Figure 1

Modes for Carrying Out the Invention

[0008] The bearing of the present invention has a hydrodynamic film agent or a hydrodynamic film formed thereby, and the hydrodynamic film agent substantially does not contain a fluorine-containing organic compound. Currently, in the Stockholm Convention on Persistent Organic Pollutants (POPs Convention), among the aforementioned PFAS (Per and Polyfluoroalkylsubstances), perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are listed as regulated substances. Furthermore, in the EU, a regulatory proposal targeting all PFAS is being considered. From March to September 2023, public comments have been solicited, and the adoption of the regulation is expected around 2025. In Japan, manufacturing and importing are also prohibited in principle based on this convention. The current regulatory proposal in the EU greatly exceeds the scope of the regulations stipulated in the POPs Convention and extensively expands the scope of application. In such a social environment, it is an essential requirement for the present invention that the hydrodynamic film or its composition of the bearing substantially does not contain a fluorine-containing organic compound. Stating that it "substantially" does not contain a fluorine-containing organic compound means not excluding what may be contained in the system as inevitable impurities. That is, it is allowed to contain a fluorine-containing organic compound as an inevitable impurity, for example, in an amount of about 0.1%.

[0009] The hydrodynamic film agent of the present invention contains an organic resin and a solid lubricant. Hereinafter, each component will be described. The organic resin preferably contains a base resin and a curing agent. The base resin is not particularly limited, and a polymer can be selected and used according to needs. From the viewpoints of wear resistance and curability by the curing agent, for example, polyamide-imide or polyamide (PA66: 66 nylon, etc.) can be used. As the curing agent, an epoxy-based curing agent can be used. There is no limitation on the epoxy-based curing agent, and examples thereof include bisphenol A type, cresol novolak type, biphenyl type, brominated epoxy resin, alicyclic epoxy resin, etc. Further, aliphatic polyamine, polyaminoamide, polymercaptans, aromatic polyamine, acid anhydride, dicyandiamide, etc. can be mentioned. In order to enhance the reactivity of the epoxy-based curing agent, a curing accelerator can also be used in combination, and tertiary amine, tertiary amine salt, imidazole, phosphine, phosphonium salt, sulfonium salt, etc. can be used. By using an organic resin as the base resin and the curing agent of this combination, the curing temperature can be lowered. As a result, the firing temperature of the rust preventive film agent can be reduced. Consequently, it becomes possible to perform the treatment at a temperature below the tempering temperature of the bearing, and it is possible to avoid the dimensional change due to the deformation of the bearing and the decrease in hardness due to softening.

[0010] As the solid lubricant, the present invention uses potassium titanate as an essential component. In addition, molybdenum disulfide, graphite, etc. can be mentioned. Preferably, potassium titanate, molybdenum disulfide and graphite are used in combination. The blending amount of the solid lubricant can be determined as appropriate, but when the above organic resin is 100 parts by mass, potassium titanate is preferably 20 parts by mass or more and 60 parts by mass or less, more preferably 30 parts by mass or more and 50 parts by mass or less, and still more preferably 35 parts by mass or more and 45 parts by mass or less. Molybdenum disulfide is preferably 30 parts by mass or more and 70 parts by mass or less, more preferably 40 parts by mass or more and 60 parts by mass or less, and still more preferably 45 parts by mass or more and 55 parts by mass or less. The blending amount of graphite is preferably 3 parts by mass or more and 30 parts by mass or less, more preferably 5 parts by mass or more and 20 parts by mass or less, and still more preferably 7 parts by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the organic resin. In addition, as the solid lubricant, it may further contain antimony oxide (Sb2O3) etc.

[0011] In the present invention, the essential solid lubricant is potassium titanate as described above. Regarding potassium titanate, potassium dititanate (K2Ti2O5), potassium tetra titanate (K2Ti4O9), potassium hexatitanate (K2Ti6O 13 )(pH 7 - 8), potassium octatitanate (K2Ti8O 17 )(pH 9 - 10) can be mentioned, and it can be used without particular restrictions. Potassium titanate is preferably in the form of whiskers, that is, preferably needle-shaped powder. As a specific product, there is the composite material "Poticon" containing the ultrafine potassium titanate fiber "Tismo" manufactured by Otsuka Chemical Co., Ltd.

[0012] Potassium titanate is preferably in the form of whiskers (needle-shaped particles) as described above. Therefore, its size can be defined by the width (cross-sectional diameter) of the short side and the length instead of the general average particle size. The width (cross-sectional diameter) is preferably 0.1 or more and 2 μm or less, more preferably 0.2 or more and 1 μm or less, even more preferably 0.25 or more and 0.7 μm or less, and particularly preferably 0.3 or more and 0.6 μm or less. The length of the needle-shaped particles is preferably 1 μm or more and 50 μm or less, more preferably 3 μm or more and 40 μm or less, even more preferably 5 or more and 20 μm or less, and particularly preferably 10 or more and 20 μm or less. The cross-sectional diameter (width) and length of the needle-shaped particles are obtained by microscopic observation, and the average value of any 50 values is adopted. Alternatively, as the average particle size measured by JIS Z8825:2022 "Particle Size Analysis - Laser Diffraction / Scattering Method", it is preferably 5 - 500 μm, more preferably 10 - 300 μm, and even more preferably 15 - 150 μm. In this specification, unless otherwise specified, the average particle size refers to the value measured based on JIS Z8825:2022 described above.

[0013] The average particle size of molybdenum disulfide powder is preferably 0.1 to 10 μm, more preferably 0.2 to 6 μm, and even more preferably 0.5 to 3.5 μm. Regarding further specifications of molybdenum disulfide, as an example, the friction coefficient is 0.04, and the pressure resistance load is about 30,000 kg / cm 2 , and those with a service temperature range of -180°C to 400°C can be cited.

[0014] The average particle size of graphite powder is preferably 1 to 700 μm, more preferably 3 to 500 μm, and even more preferably 5 to 350 μm in the case of flake graphite. Regarding an example of the specifications of graphite, the fixed carbon content is 97.0 to 98.0% for general products. For high-purity products, it is over 99.0%. The apparent density is 0.05 to 0.6 g / cm 3 . The volatile content is less than 1.0%. In addition, earthy graphite powder, artificial graphite powder, exfoliated graphite, spherical graphite, acid-treated graphite, high specific surface area products, and surface-treated graphite powder can be cited, and the preferred average particle size is substantially the same as that described above.

[0015] Regarding the lubricating film-forming agent according to a preferred embodiment of the present invention, a product in which an organic resin and a solid lubricant are dissolved, dispersed, or mixed in a solvent can be used. Examples of the solvent include N-methyl-2-pyrrolidone (NMP) and xylene.

[0016] FIG. 1 is a cross-sectional view schematically showing a part of a ball bearing and a part of a housing according to an embodiment of the present invention. The bearing 10 of the present embodiment has an outer ring 1, an inner ring 2, and balls 3 interposed between recesses of both of them. The balls 3 are arranged to be rollable and are configured to move in contact with the inner diameter surface 1a of the recess of the outer ring and the outer diameter surface 2a of the recess of the inner ring. Thereby, the outer ring 1 and the inner ring 2 are configured to be rotatable. A housing 6 is arranged outside the outer ring 1 and is configured to move in contact with a sliding film 5 provided on the outer diameter surface 1b of the outer ring. In the bearing of the present embodiment, the sliding film 5 formed by firing the above-described sliding film agent is provided on a sliding surface (in this specification, a surface that moves in contact with a member or another member as a part of the bearing is defined as a sliding surface). More specifically, the sliding film 5 is arranged between the outer diameter surface 1b of the outer ring and the inner surface 6a of the housing. The housing 6 is often made of, for example, aluminum or its alloy, but since the sliding film 5 is softer than that, it is preferable because it does not damage the housing even when it moves in contact. Alternatively, the sliding surface of the housing may be made of carbon steel, but as described above, since the sliding film 5 is sufficiently soft, it does not damage the housing side. Further, the sliding film itself is also difficult to wear due to the effect of potassium titanate, and the effect is made to last for a long time. Furthermore, although fluorine-containing organic compounds are organic compounds and often lack high-temperature durability, potassium titanate is an inorganic compound and is stable even at high temperatures, and exhibits high heat resistance at a higher level than when a fluorine-containing organic compound is blended even when used as a sliding film.

[0017] The firing temperature for firing the sliding film agent of the present invention into a sliding film is not particularly limited, but is preferably 70 to 150°C, more preferably 80 to 130°C, and even more preferably 90°C or higher and less than 120°C. The firing time is preferably 10 to 100 hours, more preferably 20 to 70 hours, and even more preferably 30 to 60 hours. The film thickness of the sliding film is preferably 3 to 100 μm, more preferably 5 to 50 μm, and even more preferably 10 to 30 μm. Although a ball bearing has been exemplified and described in the present embodiment, the present invention is not limited thereto, and for example, it may be applied to other rolling bearings such as a cylindrical roller bearing or a tapered roller bearing. For any bearing, a sliding film can be provided on the outer diameter surface of the outer ring, and thus the effects of the present invention can be achieved.

Example

[0018] Based on Transactions of the Japan Society of Mechanical Engineers, Series C, Vol. 70, No. 689 (2004-1), Paper No. 03-0252, pp. 283-290 (hereinafter referred to as the "paper"), the performance of the sliding film containing PTFE was confirmed. The outline is as follows. The composition contained PTFE (polytetrafluoroethylene) as a solid lubricant in the range of 5% to 50% by weight in a binder polyamideimide (PAI). Next, a mixed solution of the solid lubricant, the binder polyamideimide resin, and a solvent was applied by the spray method. Since the film thickness that can adhere at one time is several μm, the application was repeated until the film thickness reached 25 μm. The measurement was performed using a ring-on-disk type friction and wear test apparatus prepared by modifying a commercially available ball disk. The frictional force was obtained from the torque value of a cutting dynamometer, and the friction coefficient was calculated. Further, the measurement of the wear scar shape was performed by incorporating a surface shape measuring device into the friction and wear test apparatus, interrupting the friction experiment at regular intervals, and raising the ring. The results are shown in Test Specimens 3, 4, and 5 in Table 1 below.

[0019]

Table 1

[0020] Test specimens 3, 4, and 5 are the results disclosed in the above-mentioned paper. The friction coefficient was 0.1 or 0.2, and the specific wear rate with respect to S45C (carbon steel for machine structures) was 0.001 and 0.002. In contrast, test specimen 1 such as potassium titanate confirmed by the inventor had a friction coefficient of 0.15 and had the same performance as test specimens 3, 4, and 5 (0.1, 0.2) using PTFE. Also, it can be seen that the specific wear rate of the sliding film itself is much lower than that of test specimen 2 using glass fiber, indicating excellent wear resistance. Furthermore, in terms of the specific wear rate with S45C as the counter material, test specimen 1 using potassium titanate or the like had a result of 0.000, which was lower than that of test specimens 4 and 5 (0.001, 0.002) using PTFE. Furthermore, regarding test specimens 1 and 2, their performance with respect to AL5052 (aluminum-magnesium alloy) was also confirmed. The specific wear rate of the sliding film was 0.708 for test specimen 2 using glass fiber, but for test specimen 1 with potassium titanate and others, it was 0.026, showing a significantly better improvement by orders of magnitude. Also, the specific wear rate of the sliding film of the counter material was 0.020 for glass fiber, but it can be seen that it was greatly improved to 0.000 for potassium titanate and the like.

[0021] PTFE is an organic compound, and its upper use temperature limit is set at 260°C (http: / / www.jfia.gr.jp / pdf / Fluororesin_handling_manual_11.pdf). On the other hand, potassium titanate is an inorganic compound, and its melting point is about 1300°C or higher (https: / / www.otsukac.co.jp / advanced / tis-poti-develop / what-is-tismo / ). Bearings may be exposed to high-temperature environments, such as when the ambient temperature is high or when they rotate and become hot due to frictional heat. In contrast, according to the sliding film agent of the present invention and the bearing with a film applied with the film, potassium titanate as a lubricant is sufficiently stable within the temperature range assumed in the use of the bearing, and the performance can be guaranteed even for high-temperature use.

[0022] From the above results, it can be seen that the test specimen 1 of the example containing potassium titanate as a lubricant has substantially the same basic properties as the test specimens 3, 4, and 5 of the reference examples containing PTFE, that is, sliding properties (low friction coefficient) and wear resistance, and further has the wear resistance of the mating material. Therefore, it can be understood that even when a sliding film containing potassium titanate is applied to the outer diameter surface of the outer ring of the bearing, it can exhibit the same performance as that containing PTFE. In addition, the bearing to which the sliding film containing potassium titanate as a lubricant of the test specimen 1 is applied exhibits excellent high temperature resistance as a different and unique effect, which is different from the bearing using PTFE.

Explanation of Signs

[0023] 1 Outer ring 1a Inner diameter surface of outer ring 1b Outer diameter surface of outer ring 2 Inner ring 2a Inner diameter surface of inner ring 3 Ball 5 Sliding film 6 Housing 10 Bearing

Claims

1. A bearing with a film, comprising an inner ring, an outer ring, and balls or rollers disposed between the two and arranged to be rotatable, having a sliding film formed from a sliding film agent on the sliding surface of the bearing, wherein the sliding film agent contains potassium titanate as a solid lubricant and an organic resin, and substantially does not contain a fluorine-containing organic compound.

2. The bearing with a film according to Claim 1, wherein the solid lubricant contains molybdenum disulfide and / or graphite, and the organic resin contains a base resin and a curing agent.

3. The bearing with a film according to Claim 1, wherein the sliding surface is the outer diameter surface of the bearing outer ring.

4. The bearing with a film according to any one of Claims 1 to 3, wherein the sliding film is formed by firing the sliding film agent.

5. A sliding film agent for forming a sliding film applied to the outer diameter surface of the outer ring of a bearing, containing a solid lubricant containing potassium titanate and an organic resin, and substantially not containing a fluorine-containing organic compound.

6. The sliding film agent according to Claim 5, wherein the sliding film agent further contains molybdenum disulfide and graphite as solid lubricants.

7. The sliding film agent according to any one of Claims 5 and 6, wherein the sliding film is formed by firing the sliding film agent.

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