JP4767234B2 - Sliding coating structure - Google Patents

Description

  The present invention relates to a sliding coating structure comprising a metal substrate and a coating covering the surface of the metal substrate, and more particularly to a sliding part such as a skirt, ring groove, pin hole, etc. of an internal combustion engine piston such as a gasoline engine. The present invention relates to a suitable sliding covering structure.

  2. Description of the Related Art In recent years, in internal combustion engines such as gasoline engines, in order to realize high rotation, high compression ratio, light weight, and improved fuel efficiency, the use of light alloys as part materials has been promoted together with the reduction in part size. Since aluminum materials representing light alloys have lower wear resistance, seizure resistance, and the like than iron-based materials, it has been proposed to form a lubricating film on the surface of the sliding portion.

  Patent Document 1 discloses that at least one of polyamide-imide resin and polyimide resin as a binder is 50 to 73 wt%, polytetrafluoroethylene 3 to 15 wt%, molybdenum disulfide 20 to 30 wt% and graphite as a solid lubricant. There is disclosed a sliding resin composition comprising 2 to 8 wt%, wherein the total amount of the solid lubricant is 27 to 50 wt%.

  Patent Document 2 discloses a sliding member having a base material and a coating layer made of a dry film lubricant formed on at least a part of a surface serving as a sliding surface of the base material. The dry film lubricant has a polyamideimide resin, at least one film modifier selected from epoxy silane and epoxy resin, and at least one hard particle selected from silicon nitride and alumina, and A sliding member characterized by containing at least one solid lubricant selected from polytetrafluoroethylene, molybdenum disulfide, and graphite is disclosed.

  However, even when the sliding resin compositions described in Patent Documents 1 and 2 are applied, the lubrication effect is still insufficient, and further improvement has been desired.

Patent No. 3017626 JP 2004-149622 A

  An object of the present invention is to provide a sliding coating structure that further enhances the lubrication effect and has excellent sliding characteristics as compared with the prior art.

To achieve the above object, the present invention is a sliding coating structure comprising a metal substrate and a lubricating coating covering the surface of the metal substrate,
The lubricating coating is composed of a heat-resistant resin having a polyamide-imide resin and molybdenum disulfide particles, the weight percentage of the heat-resistant resin in the lubricating coating is 52 to 84 wt%, and the weight percentage of molybdenum disulfide particles is 48. And the average particle diameter of the molybdenum disulfide particles measured by a laser diffraction / scattering particle size distribution measurement method is in the range of 0.7 to 2.7 μm, and the metal substrate has a center line Provided is a sliding covering structure characterized in that the average roughness (Ra) is in the range of 0.2 to 0.6 μm.

According to the present invention, the composition of the lubricating coating is composed only of a heat-resistant resin having a specified amount of polyamideimide resin and molybdenum disulfide (MoS ₂ ) particles, and the molybdenum disulfide average particle diameter, By defining the surface roughness and reducing the surface roughness, it is possible to achieve a low friction coefficient (μ) and a low wear amount that cannot be obtained by the prior art.

The reason why each configuration of the sliding covering structure of the present invention is limited will be described.
Hereinafter, “particle diameter” simply represents the volume cumulative average particle diameter (D ₅₀ ) measured by a laser diffraction / scattering particle size distribution measurement method,
“Surface roughness Ra” or “base roughness Ra” represents the centerline average roughness (Ra) measured according to JIS B0601-1994.

[Responsive Component of Lubricating Film and Content of Each Component] The first feature of the present invention is that the lubricating film of the present invention comprises only a heat-resistant resin having a specified amount of polyamideimide resin and molybdenum disulfide particles. It is a point. This is a fundamental difference from the prior art.

  First, among the prior arts, Patent Document 1 uses polyamideimide and three types of solid lubricants of molybdenum disulfide particles, polytetrafluoroethylene (PTFE), and graphite (C). As will be described in detail in the following examples, the present inventor has only molybdenum disulfide particles that are solid lubricants that minimize the value of the friction coefficient μ of the lubricating coating among the above three types of solid lubricants. It has been found that by using selectively, a low friction coefficient μ and a low wear amount that cannot be obtained by Patent Document 1 using three kinds of solid lubricants in combination are obtained.

  In Patent Document 2, silicon nitride and / or alumina is used as the hard particles in addition to any one of the above three types of solid lubricants. However, in the sliding coating structure of the present invention, by limiting the constituent components of the lubricating coating to only the heat-resistant resin having polyamide-imide resin and molybdenum disulfide particles, the characteristics of the sliding member described in Patent Document 2 are achieved. In comparison, a low friction coefficient μ and excellent seizure resistance are realized.

  Next, another feature of the configuration of the present invention is that the weight percentage of the heat-resistant resin having the polyamideimide resin and the molybdenum disulfide particles constituting the lubricating coating is limited to a specific range. That is, the weight percentage of the heat-resistant resin having the polyamideimide resin in the lubricating coating is limited to the range of 52 to 84 wt%, and the weight percentage of the molybdenum disulfide particles is limited to the range of 48 to 16 wt%. Good adhesion can be ensured, and the friction coefficient μ and the wear amount of the lubricating coating can be stably reduced as compared with the conventional case.

[Reason for limiting the average particle diameter of the molybdenum disulfide measured by the laser diffraction / scattering particle size distribution measurement method is in the range of 0.7 to 2.7 μm] The structure of the present invention is a solid lubricant having a small particle diameter. It is characterized by using molybdenum disulfide (MoS ₂ ) particles. That is, the volume cumulative average particle diameter D ₅₀ (= particle diameter) of the molybdenum disulfide (MoS ₂ ) particles measured by a laser diffraction / scattering particle size distribution measurement method needs to be in the range of 0.7 to 2.7 μm. It is. By using only molybdenum disulfide (MoS ₂ ) having such a fine particle diameter, the adhesion of the resulting lubricating coating to the substrate is excellent, and the surface roughness Ra and the coefficient of friction μ of the coating are reduced. be able to.
The particle diameter of the molybdenum disulfide is in the range of 0.7 to 2.7 μm. From the standpoint of blendability in the resin composition and availability of molybdenum disulfide (MoS ₂ ) particles, the particle diameter is A range of 1.3 to 2.1 μm is particularly preferable. Incidentally, molybdenum disulfide such small particle size (MoS ₂₎ particles by grinding using a mechanical force commercial molybdenum disulfide (MoS ₂₎ particles, etc., can be easily prepared.

[The above metal base material has a centerline average roughness (Ra) in the range of 0.2 to 0.6 μm] Reason for limitation The centerline average roughness of the metal base material surface (underlayer) on which the lubricating film is formed (Ra) is limited to a range of 0.2 to 0.6 μm to increase the smoothness of the surface of the base material, and the lubricating film formed thereon is reflected in this to ensure high smoothness, The center line average roughness (Ra) of the lubricating coating can be reduced, and the friction coefficient μ and the wear amount can be reduced.

  The sliding coating structure of the present invention comprises a heat-resistant resin having a polyamideimide resin and molybdenum disulfide particles on the surface of the metal substrate having the specific centerline average roughness (Ra) (base), The weight percentage of the heat-resistant resin in the lubricating coating is 52 to 84 wt%, the weight percentage of the molybdenum disulfide particles is 48 to 16 wt%, and the average of the molybdenum disulfide measured by the laser diffraction scattering particle size distribution measurement method It can be obtained by forming a lubricating coating having a particle size in the range of 0.7 to 2.7 μm.

  As long as the center line average roughness (Ra) of the surface (base) of the metal base material is in the range of 0.2 to 0.6 μm, the type and shape of the metal base material are not limited. The sliding covering structure can be selected as appropriate according to the type of sliding member. In particular, it is preferably a metal substrate containing one or more kinds of metals selected from aluminum, iron, copper, nickel, chromium, titanium and the like, and may be a metal substrate made of an alloy containing these metals. Furthermore, if desired, it may be a metal substrate subjected to a surface treatment such as alkali degreasing.

The lubricating film according to the sliding coating structure of the present invention is substantially composed of a heat-resistant resin having a polyamideimide resin having a weight percentage of 52 to 84 wt%, and 48 to 16 wt% molybdenum disulfide particles. The lubricating coating composition having an average particle diameter of the molybdenum disulfide measured by a laser diffraction / scattering particle size distribution measuring method in a range of 0.7 to 2.7 μm is cured. Is.
Here, the “component for forming a lubricating coating” is a non-volatile component such as a heat-resistant resin having the polyamide-imide resin and molybdenum disulfide particles, and a solvent for dispersing these components before curing. Not included.

  A heat-resistant resin having a polyamide-imide resin is a binder that forms a lubricating film, and forms a lubricating film having excellent heat resistance. The heat-resistant resin is preferably substantially composed only of a polyamideimide resin, but may be a mixture containing one or two or more other heat-resistant resins as desired. As the other heat-resistant resin, one or more kinds of heat-resistant resins selected from the group consisting of polyimide resin, polyetherimide resin, polyethersulfone resin, polyetherketone resin, phenol resin, and epoxy resin are preferably used. be able to. The mixing ratio of the polyamide-imide resin and the other heat-resistant resin is preferably in the range of 100: 0 to 80:20 by weight, and the mixing ratio is 100: 0, that is, the heat-resistant resin is substantially a polyamide-imide resin. Most preferably, it consists of only. Moreover, it is preferable to mix | blend this heat resistant resin with the said lubricating coating composition in the form melt | dissolved in the organic solvent. The type of the organic solvent and the concentration of the heat-resistant resin are arbitrary, but the organic solvent is preferably a volatile aprotic polar solvent or the like. The heat-resistant resin having a polyamideimide resin is preferably applied on the member in a state of being dispersed in an organic solvent at a concentration of 10 to 50 wt% to form a lubricating film, and N-methyl-2- It is particularly preferable to select pyrrolidone (NMP) from the viewpoint of the uniformity of the resulting lubricating coating.

  A lubricating coating composition used for forming the sliding coating structure of the present invention is prepared by preparing a predetermined amount of the above-mentioned polyamideimide resin and molybdenum disulfide having a particle diameter in the range of 0.7 to 2.7 μm. These organic solvents can be used as a solvent, and can be prepared by stirring and mixing uniformly using mechanical force. In addition, it is preferable to mix | blend a polyamideimide resin with the lubricating coating composition in the form previously melt | dissolved in the organic solvent at the time of manufacture of this composition.

  As the organic solvent used for the preparation of the lubricating coating composition, volatile aprotic polar solvents and the like are preferably used. Specifically, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, esters such as methyl acetate and ethyl acetate, aromatic hydrocarbons such as toluene and xylene, methyl chloroform, trichloroethylene, trichlorotrifluoroethane, etc. Examples of the organic halogen compounds are N-methyl-2-pyrrolidone (NMP), methylisopyrrolidone (MIP), dimethylformamide (DMF), and dimethylacetamide (DMAC), and N-methyl-2-pyrrolidone (NMP) is It can be particularly preferably used. These organic solvents can be used alone or in combination.

  The apparatus for obtaining the mechanical force for preparing the lubricating coating composition, and the processing time required for uniform stirring and mixing can be appropriately selected according to the production amount and process of the lubricating coating composition. Can be used for dissolution and dispersion as kneaders, dissolvers, mixers, high-speed dispersers, sand mills, roll mills, ball mills, attritors, dyno mills, GP mills, homogenizers, ultrasonic dispersers, bead mills, Banbury mixers, millstone mills Can be illustrated. These devices can be used alone or in combination. It is particularly preferable to perform the stirring and mixing treatment for 0.5 to 3 hours using an apparatus such as a kneader.

  The lubricating coating constituting the sliding coating structure of the present invention is composed of a heat-resistant resin having a polyamideimide resin and molybdenum disulfide particles. On the other hand, the lubricating coating composition used for forming the lubricating coating is an additive (dispersant, anti-precipitation agent, thickening agent) for improving storage stability, coating suitability, etc. within the range not impairing the object of the present invention. An appropriate amount of an agent, an antifoaming agent, a leveling agent, and the like). Moreover, it does not prevent that these additives remain within the range of 0 to 5 wt% with respect to the total mass of the obtained lubricating coating. However, when a particle component such as a solid lubricant having a particle size exceeding 3.0 μm (particularly a solid lubricant made of graphite having a particle size exceeding 3.0 μm) is added, it is formed from the sliding member coating composition. The surface roughness of the resin coating layer increases, causing problems such as an increase in the coefficient of friction and an increase in the amount of wear. For this reason, the addition of such a component having a large particle size may impair the technical effect of the present invention and cannot be blended in the lubricating coating composition of the present invention.

  The lubricating coating composition used to form the sliding coating structure of the present invention can form a lubricating coating on the surface of the base material by coating and curing on the surface of the metal base material. The coating on the surface of the metal substrate can be performed by a known method such as brush coating, spray coating, roll coating, screen printing, knife coating, pad method coating or dip coating. It is preferable to apply by spraying.

  The lubricating coating composition used to form the sliding coating structure of the present invention is applied to the surface of the metal substrate, and then subjected to a heat treatment to remove the organic solvent in the composition, thereby removing the surface of the metal substrate. A lubricating coating can be formed. The conditions for forming the lubricating coating according to the present embodiment are preferably heat treatment at 100 to 280 ° C. for 60 to 240 minutes, and preferably heat treatment at 150 to 200 ° C. Furthermore, when forming the lubricating film according to the present embodiment, the organic solvent is removed at 60 to 100 ° C. for 5 to 120 minutes, and then further heated at 100 to 280 ° C. for 60 to 240 minutes for lubrication. A film can be formed.

  The thickness of the lubricating coating according to the present embodiment is arbitrary, but is preferably 4 to 15 μm, and particularly preferably 4 to 12 μm. When the film thickness of the lubricating coating is in the range of 4 to 15 μm, a sliding coating structure having high adhesion between the lubricating coating and the substrate can be obtained.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is further explained in full detail, this invention is not limited to these Examples. In addition, constituent elements in the following embodiments and examples include those that can be easily assumed by those skilled in the art or those that are substantially the same.

In this example and the like, the average particle size of the solid lubricant such as molybdenum disulfide particles is measured by the laser diffraction scattering type particle size distribution measuring method (D ₅₀ ) according to the following equipment and measurement conditions. Was measured.
Laser diffraction / scattering particle size distribution analyzer: Model LS-230 (manufactured by Beckman Coulter)
Measured value: Volume cumulative average particle size (D ₅₀ )
Measurement method: PIDS (polarized light scattering intensity difference measurement)
Dispersion medium: Xylene Sample concentration: 0.5 wt%
[Measurement conditions for average particle size of solid lubricant]
As a measurement sample, a xylene dispersion (0.5 wt% concentration) of each solid lubricant was prepared.
The sample for measurement was circulated in a flow cell of a laser diffraction / scattering particle size distribution analyzer: Model LS-230 at room temperature, and the volume cumulative average particle size (D ₅₀ ) of the solid lubricant sample was measured.

[Test Example 1]
By the method shown below, a test plate provided with a lubricating coating composed of polyamideimide resin (PAI) and molybdenum disulfide (MoS ₂ ) on the surface of an aluminum substrate was prepared. Moreover, each surface roughness Ra was measured according to the measuring method of the centerline average roughness (Ra) of JIS B0601-1994.
[Preparation of test plate with lubricating coating]
Each lubricating coating composition for forming the lubricating coating shown in Table 1 is knife coated on the surface of AC8B aluminum slope (surface roughness Ra 0.2 μm) degreased with alkali, dried at 80 ° C. × 30 minutes, and then 180 ° C. A test plate was prepared by forming a lubricating film on the aluminum substrate under the condition of × 90 minutes. The thickness of the lubricating coating was 13 μm.

As shown in Table 1, the composition of the lubricating coating and the particle size of the molybdenum disulfide particles constituting the lubricating coating were variously changed. The surface of the substrate was ground to a surface roughness Ra of 0.4 μm. However, sample no. No. 3 was lapped after grinding to have a surface roughness Ra of 0.2 μm.
In Table 1, PAI represents a polyamideimide resin.

Each test plate sample thus produced was subjected to the following load reciprocation test. The test results are shown in Table 1.
[Load reciprocation test]
1.0 mg of engine oil 5W-20 was applied to the surface of the prepared test plate, a roller was set, and the load was reciprocated under the following conditions to measure the friction coefficient (μ) of the test plate.
<Test conditions for light load reciprocating gauge test>
Load: 9.8N, 29.4N
Round trip speed: 120 cpm
Stroke: 100mm
Completion: 7200 cycles Test temperature: 25 ° C (room temperature)
Oil: Immersion or application test roller: φ7mm roller

As shown in Table 1, it is within the range of the coating composition of the present invention (PAI: MoS ₂ = 52: 48 to 84:16), and the particle diameter of molybdenum disulfide (MoS ₂ ) is 0.7 to ₂ . Sample No. in the range of 7 μm. 1, 2, 3, and 5 have a friction coefficient (μ) value in the range of 0.025 to 0.033, and a low friction coefficient (μ) value of 0.040 or less compared to other samples. Was realized.

On the other hand, Sample No. in which at least one of the coating composition and the particle diameter of molybdenum disulfide (MoS ₂ ) is outside the scope of the present invention. 4, 6, 7, 8, and 9 had a friction coefficient (μ) in the range of 0.046 to 0.075, and a low friction coefficient (μ) value of 0.040 or less could not be realized.

The surface roughness Ra of the lubricating coating of each sample shown in Table 1 is a composite of the particle diameter of molybdenum disulfide (MoS ₂ ) constituting the coating and the surface roughness Ra of the metal substrate (base). The result is considered. Sample No. within the scope of the present invention. 1, 2, 3, and 5 have a surface roughness Ra of the lubricant coating as small as 0.14 to 0.21 (μm), whereas the coating composition or the particle diameter of molybdenum disulfide (MoS ₂ ). Sample No. at least one of which is outside the scope of the present invention. 4, 6, 7, 8, and 9 have a coating surface roughness Ra of 0.53 to 1.85 (μm), which is a very large value, between the coating surface roughness Ra and the friction coefficient (μ). A strong correlation was observed.

[Test Example 2]
Sample No. 1 of Test Example 1 2 having a lubricating coating having the same coating composition and molybdenum disulfide (MoS ₂ ) particle diameter, and the surface roughness Ra of the substrate is in the range of 0.2 to 1.6 (μm) as shown in Table 2. Test plates varied in various ways were prepared in the same manner as in Test Example 1. For these samples, the friction coefficient (μ) of the test plate was measured in the same manner as in Test Example 1. The results are shown in Table 2.

  As shown in Table 2, the coefficient of friction (μ) increases as the surface roughness Ra of the substrate increases over the entire tested range, with Ra increasing from 0.4 μm to 0.8 μm. The coefficient of friction (μ) is increased from 0.035 to 0.045. If the increase in Ra and the increase in the friction coefficient (μ) are approximated by a linear relationship in this section (Ra = 0.4 to 0.8 μm), the surface roughness Ra of the base material should be 0.6 (μm) or less. For example, the friction coefficient (μ) is considered to be a low value of 0.040 or less.

[Test Example 3]
Sample No. 1 of Test Example 1 Table 3 shows the results of testing the friction coefficient (μ) and the wear amount (μm) in comparison with the sample manufactured in accordance with the prior art disclosed in Patent Document 1.
[Abrasion amount]
For a test plate of aluminum alloy AC8B having a coating resin layer formed from each sliding member coating composition (sample), the surface roughness of the coating resin layer was measured before and after the friction coefficient measurement (load reciprocation test). Ra was measured by the above method. Further, the wear amount (μm) of the coating resin layer was measured from the difference in surface roughness Ra before and after the test.

From the results in Table 3, the test plate (sample No. 2) having a lubricating coating containing molybdenum disulfide (MoS ₂ ) having a particle diameter of 1.7 μm as a solid lubricant has a particle diameter of 9. Compared with a test plate (sample No. 31) having a lubricating coating containing 4 types of molybdenum disulfide (MoS ₂ ), graphite and polytetrafluoroethylene (PTFE), the friction coefficient (μ) and the amount of wear (Μm) was significantly reduced.

Sample No. of Comparative Example Reference numerals 32 and 33 are characteristic values of a test plate having a lubricating coating made of only graphite and only polytetrafluoroethylene (PTFE) as a solid lubricant. Compared with a test plate (sample No. 2) having a lubricating coating containing molybdenum disulfide (MoS ₂ ) having a particle diameter of 1.7 μm, sample No. 2 containing only graphite. For No. 32, both the coefficient of friction (μ) and the amount of wear (μm) were significantly inferior. Sample No. using only PTFE. 33 shows the friction coefficient (μ) value of sample No. However, the amount of wear (μm) was significantly inferior.

[Test Example 4]
Sample No. 1 of Test Example 1 2 (coating structure of the present invention) and Sample No. The same substrate surface roughness and the same lubricating coating as 31 (conventional coating structure) were applied to a piston skirt of a gasoline engine, an actual machine test was conducted, and the results of measuring the fuel consumption rate, motoring friction, and firing friction were They are shown in FIGS. 1, 2, and 3, respectively. The test conditions were as follows.

<Real machine test conditions>
A single cylinder engine is used, the displacement is about 660cc / cylinder, the bore diameter is 94mm, the stroke is 95mm, the engine oil is 0W-20, and the oil temperature is set to 80 ℃ ± 1 ℃. The test was performed by changing the load at an engine speed of 2000 rpm when measuring fuel consumption and firing friction.
As shown in the figure, it is confirmed that the fuel consumption rate, motoring friction, and firing friction are significantly improved in the present invention over the entire range of the torque value or the engine speed tested as compared with the prior art. It was.

  According to the present invention, there is provided a sliding coating structure that further enhances the lubricating effect as compared with the prior art and has excellent sliding characteristics.

The graph which shows the relationship between the fuel consumption rate at the time of applying the coating structure of this invention, and the conventional coating structure to the piston skirt of a gasoline engine, respectively, and a torque. The graph which shows the relationship between the motoring friction at the time of applying the coating structure of this invention, and the conventional coating structure to the piston skirt of a gasoline engine, respectively, and an engine speed. The graph which shows the relationship between the fire friction and torque at the time of applying the coating structure of this invention, and the conventional coating structure to the piston skirt of a gasoline engine, respectively.

Claims (1)

A sliding coating structure comprising a metal substrate and a lubricating coating covering the surface of the metal substrate,
The lubricating coating is composed of a heat-resistant resin having a polyamide-imide resin and molybdenum disulfide particles, the weight percentage of the heat-resistant resin in the lubricating coating is 52 to 84 wt%, and the weight percentage of molybdenum disulfide particles is 48. And the average particle diameter of the molybdenum disulfide particles measured by a laser diffraction / scattering particle size distribution measurement method is in the range of 0.7 to 2.7 μm, and the metal substrate has its center A sliding covering structure characterized in that the line average roughness Ra is in the range of 0.2 to 0.6 μm.

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