sliding member

Abstract

Technical problem The object of the present application is to maintain a low coefficient of friction between a resin coating layer and a sliding member even when the adhesive resin of the resin coating layer has fluidity due to an increase in temperature. Solution The sliding member of the present application has a resin coating layer containing an additive, the additive containing an oleophobic resin composed of a fluororesin and / or a silicon resin, and the appropriate amount of the oleophobic resin is uniformly dispersed in the sliding surface of the resin coating layer. According to the above sliding member, the sliding surface of the resin coating layer can be given oleophobicity.

Description

Technical Field

[0001] This invention relates to improvements in sliding components. Background Technology

[0002] Sliding components typically have a substrate layer and a surface layer, with the surface layer supporting the component being slidable. This surface layer is formed of a soft metal material, and its surface is sometimes covered with a resin coating.

[0003] This resin coating is formed by dispersing various additives in an adhesive resin. Solid lubricants are a representative example of such additives.

[0004] In order to reduce the frictional resistance with the sliding component, the solid lubricant is mostly a lubricant with cleavage properties (see Patent Documents 1 and 2).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. WO2011 / 111668

[0008] Patent Document 2: Japanese Patent Application Publication No. 2003-156045 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] When observing the coefficient of friction between the resin coating and the sliding component, cleavage-prone solid lubricants specifically function at the onset of sliding. This is because solid lubricants can cleave when the resin coating and the sliding component are in solid contact. However, in recent years, there has been a demand for lower coefficients of friction with fluid lubrication. With fluid lubrication, the shaft and bearing are completely separated by the lubricating oil, making cleavage by solid lubricants less likely.

[0011] Of course, the application of cleavage-based solid lubricants will undoubtedly reduce the coefficient of friction of the resin coating, but in order to meet the recent requirements for sliding components, it is necessary to select lubricants from a new perspective.

[0012] One of the objectives of this invention is to maintain a low coefficient of friction between the resin coating and the sliding component, even under fluid lubrication.

[0013] Technical solution

[0014] To achieve the above-mentioned objective, the inventors conducted repeated and in-depth research and discovered that it is sufficient to make the sliding surface of the resin coating oleophobic. If the oleophobicity of the sliding surface is insufficient, the lubricating oil between the sliding surface and the slidable component will wet and spread on the sliding surface and easily adhere to it.

[0015] In other words, when a speed difference is generated between the sliding surface and the sliding component, a shearing force is required to shear the lubricating oil film attached to the sliding surface.

[0016] Conversely, if the sliding surface has suitable oleophobicity, when a velocity difference occurs between the sliding surface and the slidable component, the lubricating oil does not adhere to the sliding surface but moves along it by sliding. It can be assumed that the force required to separate the lubricating oil from the sliding surface is less than the force required to shear the lubricating oil film. Therefore, the coefficient of friction between the sliding surface and the slidable component decreases.

[0017] Based on the above insights, the inventors conducted repeated studies on imparting oleophobicity to the sliding surface of the resin coating, and as a result, they came up with one aspect of the present invention.

[0018] That is, a sliding member having a resin coating layer comprising additives, wherein the additives comprise an oleophobic resin composed of fluoropolymer and / or silicone resin.

[0019] The oleophobic resin is dispersed in the sliding surface of the resin coating under the following conditions.

[0020] U=s / (S*0.2)≤1(1)

[0021] Of which 6% ≤ S ≤ 30%.

[0022] s is the standard deviation of the area of ​​the Voronoi polygon, and S is the area ratio exposed by the oleophobic resin.

[0023] According to the sliding member based on the dispersion of oleophobic resin in the sliding surface of the resin coating satisfying the above formula (1), an appropriate amount of oleophobic resin is appropriately dispersed to the sliding surface, and the area of ​​insufficient oleophobic resin is reduced. As a result, the entire surface of the sliding surface has appropriate oleophobicity. As a result, a preferred coefficient of friction can be maintained on the entire surface of the sliding surface.

[0024] The amount of oleophobic resin incorporated is specified by the area ratio S. That is, by setting the area ratio of the oleophobic resin incorporated in the resin coating layer to the area exposed on its surface to be 6% or more, sufficient oleophobicity of the sliding surface of the resin coating layer can be ensured. Furthermore, by setting the area ratio to 30% or less, excessive oleophobicity of the sliding surface of the resin coating layer can be prevented.

[0025] The surface or cross-section of the oleophobic resin is photographed. The obtained images are processed to calculate the exposed area of ​​the oleophobic resin and other areas, and the area ratio S is determined.

[0026] The dispersibility of oleophobic resins is defined by the standard deviation *s* of the area of ​​the Thiessen polygons. A smaller standard deviation *s* means a more uniform area of ​​the Thiessen polygons, indicating a more even dispersion of the oleophobic resin.

[0027] Here, the area of ​​the Thiessen polygon can be obtained as follows: The surface of the coating layer is photographed. The resulting image is processed by connecting the centers of the exposed oleophobic resin to each other with straight lines. Connecting the perpendicular bisectors of the sides of the triangle thus formed, and eliminating the initially connecting lines, yields the Thiessen polygon. Its area is obtained through image processing using common image processing software.

[0028] The standard deviation s is calculated based on the distribution of the areas of all Thiessen polygons contained within a specified area of ​​the photographic image.

[0029] By adjusting the amount of oleophobic compound in the resin coating, it is easy to ensure the desired standard deviation s for the exposed oleophobic resin area. Therefore, the standard deviation s is correlated with the area ratio S as described in Equation (1). U in Equation (1) is an index representing the balance between the amount of oleophobic resin compounded and its dispersibility.

[0030] The preferred oleophobicity of the resin coating of the sliding member can also be specified as follows: when 10 μL of oil droplet is dropped onto the resin coating, the diameter of the oil droplet is less than 10.0 mm after 2 seconds.

[0031] Here, the method for evaluating oleophobicity by adding specified oil droplets to a resin coating layer and using the spread of the oil droplets after a specified time as an indicator is called the droplet addition method.

[0032] The expansion diameter of an oil droplet is the diameter of a circle with the same area as the droplet after 2 seconds of observation from a vertically above the dropping surface. It should be noted that an oil droplet equivalent to 0W-8 was used, and the ambient temperature during measurement was set to 20℃~30℃.

[0033] The amount of oil droplets (10 μL) and the elapsed time (2 seconds) used above are indicators assuming that the sliding component is commonly used in industry and that its resin coating is flat or has a curved surface with a radius of curvature of 40 mm or more.

[0034] If the radius of curvature becomes smaller, it is preferable to reduce the amount of oil droplets added accordingly, so that the height of the sliding surface and the apex of the oil droplets are the same as the above-mentioned indicators. In addition, the expanded diameter to be measured will also be adjusted accordingly.

[0035] Preferably, the oleophobic resin has a particle size of less than 1 μm and an aspect ratio of 1.0 to 1.4.

[0036] By setting the particle size of the oleophobic resin to below 1 μm and its aspect ratio to 1.0–1.4, the smoothness of the sliding surface of the resin coating is ensured. The Wenzel formula shows that when the contact angle of the sliding surface is less than 90 degrees, if the sliding surface is made rough, the lubricating oil can easily wet it. Therefore, by setting the oleophobic resin to the fine and nearly spherical shape described above, the smoothness of the sliding surface exposed by the oleophobic resin is ensured, without hindering the oleophobicity of the sliding surface.

[0037] Here, the particle size and aspect ratio are defined as follows. Images obtained by microscopic photography of the resin coating cross-section are processed, and the regions corresponding to the oleophobic resin particles are approximated as circles and ellipses, with the particle size using the equivalent circle diameter. Furthermore, the aspect ratio is determined by the major axis / minor axis of the approximate ellipse.

[0038] Preferably, the amount of additive in the resin coating is 30 vol% or more.

[0039] Here, the amount of additive can be specified by the volume ratio of the raw materials when manufacturing the resin coating. As mentioned above, the ratio of the area of ​​the additive to the resin coating in a cross-sectional image of the resin coating can also be set as the amount of additive.

[0040] Preferably, the amount of oleophobic resin in the resin coating layer is 20 vol% or more. In other words, it is preferably set that the exposed area S of the oleophobic resin is 6% or more. This ensures oleophobicity suitable for the sliding surface of the resin coating layer. Consequently, the coefficient of friction of the resin coating layer in a fluid-lubricated state is reduced.

[0041] Here, the amount of oleophobic resin in the additive can be specified by the volume ratio of the raw materials when manufacturing the resin coating. As mentioned above, the ratio of the area of ​​the additive appearing in the cross-sectional image of the resin coating to the area of ​​the oleophobic resin can also be set as the amount of additive.

[0042] It should be noted that by setting the area ratio to below 30%, excessive oleophobicity of the sliding surface is prevented. Excessive oleophobicity of the sliding surface may adversely affect the formation of the lubricating oil film between the sliding surface and the slidable surface.

[0043] Preferably, the ratio of Rp (maximum peak height) to Rv (maximum valley height) on the surface of the resin coating is Rp / Rv = 0.7 to 1.8.

[0044] More preferably, Rp / Rv = 0.8 to 1.6. By setting Rp / Rv = 0.8 to 1.6, the surface smoothness of the resin coating is ensured, and the oleophobicity is improved. As a result, the coefficient of friction of the resin coating in a fluid lubrication state is reduced. Attached Figure Description

[0045] Figure 1 This is a cross-sectional view showing the configuration of the sliding member according to an embodiment of the present invention. Detailed Implementation

[0046] The present invention will now be described in further detail based on the embodiments.

[0047] The substrate layer 2 constituting the sliding member 1 is usually made of a metallic material.

[0048] In a bearing, one example of a sliding component, the base layer 2 is a structure in which an aluminum-based bearing alloy layer 4 is laminated onto a metal backing layer 3 made of steel.

[0049] A resin covering layer 5 is laminated on the substrate layer 2.

[0050] The resin coating layer 5 is composed of a composition incorporating various additives into the adhesive resin.

[0051] The adhesive resin can be appropriately selected according to the application of the sliding component 1. For example, it can be one or more of polyimide resin, polyamide-imide resin, epoxy resin, phenolic resin, polyamide resin, and elastomer, or it can be a polymer alloy.

[0052] Oleophobic resins can be used as additives.

[0053] The material of the oleophobic resin can be appropriately selected according to the application of the sliding component 1.

[0054] In this invention, resins composed of fluororesins and resins composed of silicone resins are of interest as oleophobic resins.

[0055] Examples of oleophobic resins composed of fluoropolymers include PTFE, PFA, FEP, ETFE, and PVDF.

[0056] Examples of oleophobic resins composed of silicone include organosilicon powder and silicone rubber powder.

[0057] Preferably, an appropriate amount of these oleophobic resins is uniformly dispersed in the sliding surface of the resin coating. More preferably, they are also uniformly dispersed in the thickness direction.

[0058] In this invention, the dispersion of the oleophobic resin in the sliding surface of the resin coating is specified as follows.

[0059] U=s / (S*0.2)≤1 (1)

[0060] Of which 6% ≤ S ≤ 30%.

[0061] s is the standard deviation of the area of ​​the Thiessen polygon, and S is the area ratio exposed by the oleophobic resin.

[0062] To ensure that the oleophobic resin is evenly dispersed in the resin coating layer, the particle size of the oleophobic resin, the selection of the adhesive resin, and the stirring method should be adjusted appropriately.

[0063] There is no particular limitation on the ratio of fluoropolymer to silicone resin; it can be the former alone, the latter alone, or a mixture of the former and the latter.

[0064] For oleophobic resins, the particle size is set to 1.0 μm or less, and the aspect ratio is set to 1.0 to 1.4. More preferably, the particle size is 0.8 μm or less, and more preferably, the aspect ratio is 1.0 to 1.1. The lower limit of the particle size is not particularly limited, but as an industrially available oleophobic resin, 0.2 μm can be considered as the lower limit.

[0065] The methods for determining particle size and aspect ratio are as described above.

[0066] In addition to the aforementioned oleophobic resins, general-purpose solid lubricants, hard particles, etc., can also be used as additives.

[0067] Examples of solid lubricants include: molybdenum disulfide, tungsten disulfide, h-BN (h-boron nitride), graphite, melamine cyanurate, carbon fluoride, phthalocyanine, graphene nanoplatelets, fullerene, ultra-high molecular weight polyethylene (Mitsui Chemicals, trademark "MIPELON"), and Nε-lauroyl-L-lysine (Ajinomoto, trademark "Amihope").

[0068] Examples of hard particles include: metal particles, metal oxide particles, metal nitride particles, and carbides. By incorporating hard particles, the wear resistance of the resin coating is maintained.

[0069] In addition, pigments can be added as additives.

[0070] There is no particular limitation on the lower limit of the amount of additive, but it is preferably 30 vol% or more in the resin coating. A further preferred amount is 40 vol% or more. There is no particular limitation on the upper limit of the amount, but from the viewpoint of ensuring other properties of the resin coating (such as abrasion resistance), it can be set to 60 vol%.

[0071] The method for specifying the amount of this mixture is as described above.

[0072] Of all the additives incorporated into the resin coating, the lower limit of the amount of oleophobic resin is not particularly limited, but it is preferable to set this amount to 20% or more. A further preferred amount is 30% or more. The upper limit of this amount is not particularly limited, but from the viewpoint of ensuring other properties of the resin coating (anti-galling, etc.), it can be set to 50%. A further preferred upper limit is 40%.

[0073] The method for specifying this quantity is also as described above.

[0074] The additives are selected such that the ratio of Rp (maximum peak height) to Rv (maximum valley height) in the sliding surface of the resin coating is Rp / Rv = 0.7 to 1.8. A further preferred range is Rp / Rv = 0.8 to 1.6.

[0075] Here, Rp and Rv depend on the specifications of JIS B 0601.

[0076] The resin coating layer 5 is formed as described below.

[0077] To dissolve the resin materials used in adhesive resins, specific solvents such as NMP (N-methyl-2-pyrrolidone), isophorone, GBL (gamma-butyrolactone), DMSO (dimethyl sulfoxide), and DAM (dimethylacetamide) can be used. These solvents typically have high boiling points (above 150°C) and are expensive. A solid lubricant must also be dispersed in this solvent. Therefore, after dissolving the adhesive resin in a first solvent such as NMP, a second solvent is added, and various additives containing oleophobic resins are added sequentially while stirring to adjust the viscosity to achieve a easily dispersible state. This second solvent can be a solvent with a lower boiling point (below 150°C) compared to the first solvent, such as ethanol, butyl acetate, cyclohexane, methyl ethyl ketone, MIBK (methyl isobutyl ketone), toluene, xylene, or ethylbenzene.

[0078] The resulting liquid composition is coated onto the surface of the bearing alloy layer 4, dried to allow the solvent to evaporate, and then thermoset. Known methods such as spraying, roller coating, pad printing, and screen printing can be used for coating.

[0079] Example

[0080] The embodiments of the present invention will be described below.

[0081] The sliding member 1 in the embodiment is, for example, set as Figure 1The cross-sectional structure is shown. More specifically, a bimetallic material is manufactured by lining an aluminum-based bearing alloy layer 4 onto a steel metal backing layer 3, and shaping the bimetallic material into a semi-cylindrical shape. Then, the surface of the bearing alloy layer 4 is bored and polished. This forms the substrate layer 2 (thickness: 1.5 mm). Next, the surface of the semi-cylindrical molded part is cleaned (cleaned to roughen the surface).

[0082] A resin capping layer 5 (3–10 μm) containing an oleophobic resin is laminated onto the upper surface of the substrate layer 2 thus obtained. The lamination conditions are as follows.

[0083] (1) Mixing method

[0084] Solvent 1: NMP.

[0085] Solvent 2: Xylene.

[0086] (2) Coating method: Spray coating at a preheated temperature (80℃~100℃).

[0087] (3) Drying conditions: Dry in an oven (140℃~180℃) for about 5 minutes.

[0088] Friction tests were conducted on the sliding components of the obtained embodiments and comparative examples under the following conditions at room temperature.

[0089]

[0090] The area ratio S and standard deviation s are calculated by image processing of the cross-section of the resin coating.

[0091] The imaging device used was an electron microanalyzer JXA-8530F.

[0092] The area calculation of oleophobic resins, etc., and the determination of the area and standard deviation s of the Thiessen polygon were performed using standard image processing software (WinROOF2021).

[0093] The combination of Examples 1-3 and Comparative Examples 1-6 and the measurement results are shown in Table 1.

[0094] [Table 1]

[0095]

[0096]

[0097] The PAI (polyamide-imide) used in the examples and comparative examples was a product manufactured by Solvay. The PTFE (polytetrafluoroethylene) used in the examples and comparative examples was a product manufactured by Chemours-Mitsui Fluoroproducts. The oleophobic resin had a particle size of 1 μm or less. Furthermore, its aspect ratio was 1.0 to 1.4. The silicone resin used in Example 4 was a product manufactured by Shin-Etsu Chemical Industry Co., Ltd. The oleophobic resin had a particle size of 1 μm or less. Furthermore, its aspect ratio was 1.0 to 1.4.

[0098] As can be seen from the friction values ​​of the embodiments and comparative examples in Table 1, it is preferable to set the value of U specified in formula (1) to be less than 1.

[0099] It is known that the amount of additives in the total complex (②+③ / ①+②+③) is preferably set to 30 vol% or more.

[0100] Furthermore, it is known that the amount of oleophobic resin (PTFE or silicone resin) in the additives (② / ②+③) is preferably 20 vol% or more.

[0101] Next, under the condition that U<1 in Equation (1), the relationship between the roughness of the sliding surface of the resin coating and the friction value is shown in Table 2.

[0102] [Table 2]

[0103]

[0104] In Table 2, the particle size of the oleophobic resin (PTEF) is less than 1 μm. Furthermore, its aspect ratio is 1.0–1.4.

[0105] According to the results in Table 2, the ratio of Rp (maximum peak height) to Rv (maximum valley height) of the sliding surface of the resin coating is preferably set to Rp / Rv = 0.7 to 1.8. More preferably, Rp / Rv = 0.8 to 1.6.

[0106] Here, Rp and Rv depend on the specifications of JIS B 0601. Surface measurements were performed using a Surfcorder SE3500.

[0107] Surface roughness is adjusted by sandblasting.

[0108] A drop-addition test was performed on the sliding surface of the resin coating as described below.

[0109] At room temperature, using a microsyringe, bring the needle of the microsyringe into contact with or slightly separate from the sliding surface of the resin coating of the stationary sliding component, and add 10 μL of oil (specific name: HONDA ULTRANEXT).

[0110] With the sliding component kept stationary, photograph the state of the sliding surface 2 seconds after the oil is applied, taken from a vertically above it. Process the obtained image to obtain the area of ​​the oil. Calculate the diameter (expansion value) of the circle with the same area as the obtained area.

[0111] The images were captured using a VHX-6000 microscope. Area calculations were performed using standard image processing software (VHX-6000 microscope).

[0112] The results of the droplet addition tests for the examples and comparative examples are shown in Table 3.

[0113] [Table 3]

[0114]

[0115] According to the results in Table 3, it is preferable to set the expansion diameter of the oil droplets to less than 10.0 mm.

[0116] This invention is not limited in any way by the description of the embodiments described above. Various modifications that can be readily conceived by those skilled in the art without departing from the scope of the claims are also included in this invention. Bearing mechanisms such as internal combustion engines using the sliding member of this invention exhibit excellent sliding characteristics.

[0117] Symbol Explanation

[0118] 1: Sliding component

[0119] 2: Substrate layer

[0120] 3: Metal backing layer

[0121] 4: Bearing alloy layer

[0122] 5: Resin coating layer

Claims

1. A sliding member comprising a resin coating layer including additives, wherein the sliding member, The additive comprises an oleophobic resin composed of fluoropolymers and / or silicone resins. The oleophobic resin is dispersed in the sliding surface of the resin coating under the following conditions: U=s / (S 0.2)≤1, where 6%≤S≤30%, in, s is the standard deviation of the area of ​​the Thiessen polygon. S represents the area ratio of the exposed oleophobic resin.

2. The sliding member according to claim 1, wherein, The oleophobic resin has a particle size of less than 1.0 µm and an aspect ratio of 1.0 to 1.

4. The particle size of the oleophobic resin is the equivalent circle diameter of the oleophobic resin particles.

3. The sliding member according to claim 1, wherein, The amount of the additive in the resin coating is 30 vol% or more.

4. The sliding member according to claim 1, wherein, The amount of the oleophobic resin in the additives contained in the resin coating is 20 vol% or more.

5. The sliding member according to claim 1, wherein, The ratio of Rp (maximum peak height) to Rv (maximum valley height) in the sliding surface of the resin coating is Rp / Rv = 0.7 to 1.8.

Images