Patent Application
20180216608
The present invention relates to a sliding member that has a resin coating layer in which a solid lubricant is dispersed.
A sliding member is known which has a resin coating layer in which a solid lubricant is dispersed. Patent Document 1 discloses a sliding member in which a resin film layer (a resin coating layer) that has a thickness of 3 μm or less and includes a solid lubricant with a relative c-axis intensity ratio of 90% is formed in order to realize a decrease in the friction coefficient and an improvement in seizure resistance.
Patent Document 1: JP 5391327B
For example, with a sliding member that is used in an environment with relatively little lubricant, such as a swash plate for a swash plate compressor, wear is likely to progress, and in the technique disclosed in Patent Document 1, there has been a possibility that the coating layer will wear out due to initial run-in.
On the contrary, the present invention provides a technique for achieving both the prevention of wearout of the coating layer due to initial run-in and an improvement in seizure resistance.
The present invention provides A sliding member including: a base material; and a coating layer formed on the base material, having a thickness of 10 μm or more, wherein the coating layer includes: a binder resin; and a solid lubricant that is dispersed in the binder resin and has a c-axis orientation, and a relative c-axis intensity ratio of the solid lubricant in the coating layer is 80% or more.
The binder resin may include at least one of polyamide imide, polyamide, and polyimide.
The solid lubricant material may include at least one of MoS2, graphite, WS2, and h-BN.
Also, the present invention provides a swash plate compressor in which one of the above-described sliding members is used as a swash plate.
According to the present invention, it is possible to achieve both prevention of wearout of the coating layer due to initial run-in and an improvement in seizure resistance.
1 Compressor
2 Shaft
3 Swash plate
31 Base material
32 Coating layer
321 Binder resin
322 Solid lubricant
33 Coating layer
4 Piston
5 Shoe
From the viewpoint of preventing wearout of coating layer 32, the thickness of coating layer 32 is preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 20 μm or more. For example, if the thickness of coating layer 32 is less than 5 μm, coating layer 32 will wear and base layer 31 will be exposed in some cases. If base layer 31 is exposed, the friction coefficient will increase and adhesion with shoes 5 will occur, which is problematic. Also, if the film thickness of the coating layer 32 is excessively large, the seizure resistance will decrease in some cases, and therefore the film thickness is preferably 50 μm or less.
Also, from the viewpoint of improving seizure resistance, the relative c-axis intensity ratio of solid lubricant 322 in coating layer 32 is preferably 80% or more, and more preferably 85% or more. Here, the relative c-axis intensity ratio refers to the ratio of the diffraction peak intensities from cleavage planes, with respect to all diffraction peak intensities in X-ray diffraction. More specifically, the relative c-axis intensity ratio is defined as the ratio of the integrated value of diffraction peak intensities from the (002), (004), and (008) planes with respect to the integrated value of diffraction peak intensities from the (002), (004), (100), (101), (102), (103), (105), (110), and (008) planes. Although diffraction peaks from crystal planes other than the above-described nine crystal planes appear in some cases, since their peak intensities are weak, they are ignored in the calculation of the relative c-axis intensity ratio.
A state in which the relative c-axis intensity ratio is 80% or more, or in other words, in which the relative c-axis intensity ratio is high, means a state in which the crystal orientations of solid lubricant 322 are aligned in coating layer 32. The relative c-axis intensity ratio is hereinafter referred to as the “orientation ratio”, which indicates the degree to which the crystal orientations are aligned. In general, a solid lubricant has a low friction coefficient due to inter-layer sliding in the crystals, which have layer structures. The crystal orientations being aligned means that the directions in which the inter-layer sliding occurs are aligned.
The average particle diameter of solid lubricant 322 is 1 to 6 μm, for example. The average particle diameter is measured using a laser diffraction method, for example.
Coating layer 33 is formed similarly to coating layer 32.
In step S3, coating material for forming the coating layers is prepared. First, the binder resin and the solid lubricant are mixed using a known method. The resulting mixture is diluted with a diluting agent. Anything may be used as the diluting agent, but for example, N-methylpyrrolidone (NMP) is used. The mixing ratio of the diluting agent is, for example, 30 to 70 vol % with respect to the solid content.
In step S4, the surfaces of the base material are coated with the coating material. The coating material is applied through pad printing, roll coating, or spray coating, for example. If the thickness of the coating material that can be applied in one instance is limited, two or more instances of coating may be performed. In step S5, the coating layers are dried and fired. The surface roughnesses of the coating layers are preferably 5 μmRz or less, for example.
Test pieces of the sliding member were produced under various conditions and their characteristics were evaluated. More specifically, multiple test pieces were produced in four segments in each of Test Examples 1 to 4. In Test Examples 1 to 4, the materials and compositions of coating layer 32 are the same. PAI was used as the binder resin and MoS2 and graphite were used as the solid lubricant. Cast iron (FDC700) was used as the base material in Test Examples 1 to 4.
In Test Examples 1 to 4, the methods for applying the coating material for forming the coating layers and the film thicknesses of the coating layers are different. More specifically, the coating layers were formed through pad printing in Test Examples 1, 2, and 4, whereas the coating layers were formed through roll coating in Test Example 3. Regarding the film thicknesses, the film thicknesses were changed in a range of 3 to 19 μm for the test pieces to which the coating material was applied through pad printing. Seizure resistance tests were performed for Test Examples 1 to 4. Seizure resistance was tested by causing the swash plate and shoes to slide under the following conditions. The experimental conditions were obtained by envisioning the lubricating state in the compressor. Also, the unaided eye was used to check whether or not wearout of the coating layers occurred in the following experiments.
Environment: coolant+refrigerating machine oil
Rotation rate: 7200 rpm (swash plate rotation)
Load: gradually increasing (maximum 14 MPa)
Table 1 shows the characteristics of Test Examples 1 to 4 and the results of the seizure test and wearout test. Note that the manufacturing costs are also included in Table 1.
Upon comparing the samples with coating layers applied through pad printing (Test Examples 1, 2, and 4) and the samples with coating layers applied through roll coating (Test Example 3), a trend was observed in which the samples coated through pad printing had higher orientation ratios. With pad coating, the desired film thickness is obtained by layering thin films. The film thickness per layer becomes approximately equal to the size of the additive, and an effect of pressing down the additive is obtained, whereby a high orientation ratio is obtained. On the other hand, a film with a desired thickness is applied in one instance with roll coating. For this reason, if the size of the additive is used as a reference, the film thickness is thicker (thicker than with pad coating), the effect of pressing down the additive weakens, and a relatively low orientation ratio is obtained.
Upon comparing Test Examples 1 to 3 and Test Example 4, an effect was obtained in which test pieces with thin film thicknesses (Test Example 4) had lower seizure resistances compared to test pieces with thick film thicknesses (Test Examples 1 to 3). Note that although differences between seizure resistances could not be evaluated for Test Example 1 and Test Example 3 due to limitations of the testing apparatus, it is thought that the seizure surface pressure increases accompanying an increase in the orientation ratio (relative c-axis intensity), as disclosed in the specification of JP 4827680B.
Upon comparing Test Example 1 and Test Example 3, Test Example 3 had a lower manufacturing cost. This is due to the following reason. With roll coating, the accuracy is relatively low from the viewpoint of surface flatness and parallelism. With Test Example 3, cutting was performed after firing in order to increase surface flatness and parallelism. For this reason, the coating material was applied more thickly as a machining allowance, which caused a decrease in yield. With pad printing, cutting is not needed since sufficient accuracy can be obtained. Accordingly, the yield of the coating material is good, and the machining cost is low since cutting can be omitted.
Note that the sliding member according to the present invention is not limited to being used as swash plate 3 of compressor 1. The sliding member according to the present invention may be used as a sliding member that is not used in a swash plate compressor, such as a half bearing or a bushing. The materials, compositions, film thicknesses, and the like of the coating layers in the test examples are merely examples. The present example is not limited thereto.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-149264 | Jul 2015 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/068368 | 6/21/2016 | WO | 00 |
