JP2013203905A - Sliding member and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sliding member which can stably obtain a low friction characteristic and wearing resistance, by reducing friction loss on a sliding surface (small friction coefficient (μ) is attained) by using a particulate graphite.SOLUTION: A graphite layer 15 that contains oriented specific graphite particles 17 in an oriented state, whose half width at half maximum in a rocking curve in a graphite-2H 002 diffraction position by X-ray diffraction measurement is 5 degrees or less is provided along a sliding direction, on all faces of a skirt part 13 that is the sliding surface of a piston for an engine.

Description

  The present invention relates to a sliding member and a manufacturing method thereof.

  For materials having a low coefficient of friction (μ) (low μ characteristics), solid lubricants such as graphite and molybdenum disulfide powder having a layered crystal structure with low shear resistance and molded articles thereof are known. . Specifically, a graphite molded body (such as a carbon product for machinery) obtained by molding and sintering powders such as artificial graphite and natural graphite, and a resin or metal is added to these molded bodies in order to increase strength and wear resistance. What is impregnated is known. Also, scaly graphite or scaly graphite is blended as a solid lubricant component, and a solid lubricant composed of a predetermined amount of molybdenum disulfide, scaly graphite or scaly graphite, and polytetrafluoroethylene is bound by a binder such as polyamideimide. There is known a resin composite material in which a coating film is applied to a substrate (see, for example, Non-Patent Document 1 and Patent Documents 1 and 2).

  In recent years, in order to improve fuel consumption, automotive units such as drive system units such as engines, transmissions, and reduction gears have been required to reduce friction loss. Further, as a sliding member used for these, a material having a lower friction (low μ material) is required.

  As a technique related to the above, a solid lubricant plate crystal particle having a layered crystal structure in which (001) planes having a small shear force are stacked in parallel is used, and (001) of the solid lubricant plate crystal particle on the sliding surface is used. ) A sliding member having a plane orientation index of 90% or more has been proposed (for example, see Patent Document 3). This sliding member is said to have a low coefficient of friction and excellent wear resistance.

  Further, the sliding member is provided with a sliding surface provided with an A-side containing highly oriented graphite having a half-width of 7 ° or less in the rocking curve and a B-side containing a material having higher wear resistance than the highly oriented graphite. Is disclosed (for example, see Patent Document 4).

JP 2000-136397 A JP 2005-89514 A JP 2007-270894 A JP 2010-223288 A

Catalog "Carbon Carbon Products", Toyo Tanso Co., Ltd.

  Among the above-mentioned conventional techniques, when solid lubricant components such as graphite described in Patent Documents 2 and 3 are analyzed in detail, since they are actually secondary particle bodies, they are not flat particles and have an aspect ratio. The ratio is small, and the individual particles forming the secondary particle body are present in a random direction. In such particles, since the primary particles can only exist in an agglomerated state, particles having a structure in which (001) crystal planes are uniformly stacked in parallel are not recognized, and exhibit excellent low friction characteristics. Orientation is not obtained. That is, there are crystal planes other than the c plane (such as the (001) plane) (such as the (101) plane and the (100) plane) that are effective for reducing friction on the sliding surface. I can't expect it.

  Further, as conventional sliding members using highly oriented graphite, as highly oriented graphite, block-like highly oriented pyrolytic graphite (HOPG), graphite obtained by carbonizing a laminated polymer film, Crystalline graphite or quiche graphite can be mentioned. Among these, HOPG and single crystal graphite are in a block shape, and graphite obtained by carbonizing the laminated polymer film is in a block shape or a sheet shape. Since these graphite materials are single crystal lumps or graphite sheets that are much larger than the particles, it has been difficult to refine them while maintaining the crystal structure. For this reason, it is difficult to maintain a high orientation of graphite uniformly on the minute contact surface, and sufficient wear resistance cannot be secured when the sliding area is small. In addition, it has been difficult to form a sliding surface by a coating method excellent in mass productivity. Further, quiche graphite, which is a fine powder of crystalline graphite, is difficult to obtain in large quantities and is also expensive. Furthermore, the method using such highly oriented graphite was inferior in productivity.

  Under the circumstances as described above, a sliding material capable of achieving all of mass productivity, low friction characteristics, and wear resistance has been required.

  The present invention has been made in view of the above, and when using particulate graphite, the friction loss on the sliding surface is higher than that of a conventional composition containing a solid lubricant such as standard graphite. An object of the present invention is to provide a sliding member that is reduced (expresses a small coefficient of friction (μ)) and stably obtains low friction characteristics and wear resistance, and a method for manufacturing the same. And

  The present invention aligns flat graphite particles that are fine particles but have a large aspect ratio of 20 or more so that the graphene surface forms a sliding surface in the matrix resin (parallel or substantially parallel to the sliding surface). The knowledge that it is easy to obtain the ultra-low friction characteristic that is expressed specifically only on the c-plane (crystal plane with the c-axis as the normal direction) such as the (100) plane corresponding to the graphene plane of the graphite crystal And have been achieved based on such findings.

  In order to achieve the above object, the sliding member according to the first invention is provided on at least a part of the sliding surface between the base material and the mating member in the base material, and the matrix resin and the average particle size 40 m or less, including oriented graphite particles having an aspect ratio of 20 or more, which is the ratio of the average particle diameter to the average thickness, and the content ratio of the oriented graphite particles to the total amount of the matrix resin and the oriented graphite particles is based on mass And a graphite layer that is 30% or more and 90% or less, and a half width at a rocking curve at a graphite-2H 002 diffraction position by X-ray diffraction measurement of the graphite layer is 5 ° or less. .

In the sliding member according to the first invention, the sliding surface has a graphene surface (hereinafter also referred to as “c-plane”) such as a (100) plane parallel or substantially parallel to the surface to be the sliding surface. It is composed of a graphite layer containing oriented graphite particles oriented so as to have a predetermined ratio.
That is, the sliding surface of the sliding member includes oriented graphite particles having a plate shape having an aspect ratio of 20 or more while being fine particles having an average particle diameter of 40 m or less, and is oriented in the matrix resin. Thus, a graphite layer having a sharp diffraction peak having a half width (Half Width at Half Maximum) of 5 ° or less in the rocking curve at the graphite-2H002 diffraction position by X-ray diffraction measurement is formed.
With such a configuration, a resin composite material in which fine graphite particles (fine graphite particles) having a structure in which a plurality of graphenes are stacked in a parallel orientation state and having a flat flake shape is highly oriented and dispersed in a matrix resin slides. Since the surface is constituted, an ultra-low friction characteristic that is specifically expressed on the c-plane of the graphite crystal is developed on the sliding surface. This ultra-low friction characteristic is manifested when the content ratio of the oriented graphite particles to the total amount of the matrix resin and the oriented graphite particles is within a predetermined range of 30% or more and 90% or less on the mass basis.
On the other hand, in the conventional sliding member, the sliding surface when the particulate material is used is not limited to the c-plane such as the (001) plane which is effective for reducing friction, but the a-plane [(( 101) plane, (100) plane, etc.] exist, and an ideal low shear orientation plane cannot be obtained.
Further, instead of using a single crystal mass (for example, HOPG and single crystal graphite) much larger than the particles or a graphite sheet obtained by carbonizing the laminated polymer film, the graphite particles are dispersed in a matrix resin to be predetermined. By using it in the state of the resin composite structure oriented in the direction, it is possible to perform coating formation with excellent productivity. In addition, superior wear resistance can be obtained as compared with conventionally used resin-based sliding materials.

  The half width at half maximum is a diffraction peak in which one axis (for example, the horizontal axis) is the sample rotation angle ω (°; degree) and the other axis (for example, the vertical axis) is the diffraction intensity, and the vertical axis is the maximum peak value. This is the width of the horizontal axis ω of the diffraction peak at a position having half the diffraction intensity.

  For the graphite layer of the sliding member according to the first invention, a thermosetting resin is suitably used as the matrix substrate. Since the sliding member may reach a high temperature by sliding, the shape of the graphite layer is stably maintained by using a thermosetting resin, and the desired wear resistance can be easily obtained in the long term.

  Moreover, as a matrix resin, it is preferable to use a thermosetting polyamide imide among thermosetting resins.

  The aspect ratio of the oriented graphite particles is preferably 20 or more and 1500 or less.

The thickness of the graphite layer is preferably 3 μm or more and 40 μm or less.
Moreover, the graphite layer tends to further improve the wear resistance of the sliding surface by containing smaller-sized oriented graphite particles as a main component. Therefore, the graphite layer preferably contains graphite particles having an average particle diameter of 1 to 20 μm in a range of 30% to 90% by mass ratio with respect to the total amount of the matrix resin and the oriented graphite particles. Thus, further excellent wear resistance can be obtained.

The sliding member according to the first invention is preferably configured as a piston in an internal combustion engine such as an engine, a piston ring provided on the piston, a piston pin, or a shaft and / or bush in a slide bearing structure. Specifically, a graphite layer is provided on at least a part of a skirt of an engine piston, at least a part of a piston ring, at least a part of a piston pin, or at least a part of a shaft and / or bush of a plain bearing structure. As a result, the coefficient of static friction of the sliding surface can be kept small, the friction loss during sliding can be reduced more effectively, and at the same time, wear resistance can be ensured.

  As another example, the sliding member according to the first invention has at least a shaft and a bush, and the graphite layer (graphite surface) is provided on at least one of the outer peripheral surface of the shaft and the inner peripheral surface of the bush. It can be configured as a plain bearing structure. Further, as another example, the sliding member according to the first invention includes an outer peripheral surface of the inner roller, and an inner periphery of an outer roller provided coaxially with the inner roller and rotatably around the inner roller. A sliding roller structure in which highly oriented graphite is provided on at least one of the surfaces can be used.

  Shear resistance to the sliding surface of the shaft and bush in the sliding bearing structure (that is, the outer peripheral surface of the shaft and the inner peripheral surface of the bush), or the sliding surface (sliding surface) of the inner roller and outer roller in the sliding roller structure. By providing a graphite surface using oriented graphite particles having a small size, the friction coefficient (μ value) of the sliding surface can be kept low (preferably 0.05 or less), and the wear resistance of the sliding surface can be secured. .

  In the manufacturing method of the sliding member according to the second invention, oriented graphite particles having an average particle diameter of 40 m or less and an aspect ratio which is a ratio of the average particle diameter to the average thickness of 20 or more are dispersed in a solvent. A dispersion and a matrix resin are mixed to prepare a coating solution for forming a graphite layer in which the ratio of the oriented graphite particles to the total amount of the matrix resin and the oriented graphite particles is 30% to 90% on a mass basis. By applying the graphite layer-forming coating solution to a sliding surface that slides on the base material with the preparation step, the graphite particles have a c-plane (graphene surface) as a sliding surface. A graphite layer having a half-width of 5 ° or less in a rocking curve at a graphite-2H 002 diffraction position by X-ray diffraction measurement And a coating process to be formed.

  In the manufacturing method of the sliding member according to the second invention, by applying a coating solution for forming a graphite layer containing the orientation graphite particles having a plate shape mixed with the matrix resin as described above, The oriented graphite particles can be oriented so that the (100) plane of the plate-like oriented graphite particles is parallel or substantially parallel to the sliding surface, and the oriented graphite particles are oriented and contained. As a result, a graphite layer having a half width at half maximum of 5 ° or less is obtained. As a result, a sliding surface having a low friction coefficient (μ value) (preferably 0.05 or less) is easily formed. In the second invention, the productivity is particularly excellent as compared with a production method using a single crystal lump or a graphite sheet much larger than the particles.

  In general, the c-plane, which is parallel to the direction perpendicular to the laminating direction of graphite having a layered structure, has a low interaction force between layers and a low shear resistance. Although it can be reduced, the intermolecular bonds between the 6-membered ring molecular layers of the graphite structure are weak, and delamination tends to occur, and the wear resistance tends to be low. In the first or second invention, the graphite particles are dispersed. By orienting in a specific direction, excessive wear of graphite can be prevented, and friction loss caused by sliding over a long period can be reduced.

  The sliding member according to the first invention and the manufacturing method of the sliding member according to the second invention are, for example, for reducing friction loss in a drive system unit such as an engine, an automatic transmission, a manual transmission, and a reduction gear. For example, it is effective for constructing an engine and a drive system unit with improved fuel efficiency.

  According to the present invention, when particulate graphite is used, the friction loss on the sliding surface is further reduced (small friction coefficient (μ) compared to a composition containing a conventional solid lubricant such as standard graphite. ) Is developed, and a sliding member and a method for manufacturing the same that can stably obtain low friction characteristics and wear resistance are provided.

It is a perspective view which shows the piston which concerns on 1st Embodiment of this invention. It is a schematic sectional drawing which expands and shows the graphite layer of FIG. It is a conceptual diagram for demonstrating the shape of a specific graphite particle. (A) is an SEM photograph of fine graphite particles having an aspect ratio of 20 or more, and (B) is an SEM photograph of multilayer graphene particles prepared by peeling HOPG. (A) is the SEM photograph which expands and shows the particle state of the conventional exfoliated graphite particle, (B) is the SEM photograph which expands and shows the particle state of the other conventional exfoliated graphite particle. (A) is a perspective view which shows the connecting rod bearing which concerns on 1st Embodiment of this invention, (B) is a schematic sectional drawing which shows the cross-section of (A). (A) is an appearance photograph showing the surface of the oriented graphite particle-containing resin composite material (graphite ratio: 60% by mass) of Example, and (B) is an appearance photograph showing the surface of the graphene nanoparticle-containing resin composite material. And (C) is an appearance photograph showing the surface of the exfoliated graphite particle-containing resin composite. It is a cross-sectional SEM photograph which shows the cross-sectional structure of a fine graphite particle containing resin composite material coating sample piece (graphite ratio: 40 mass%). MoS is a sectional SEM photograph showing a ₂ cross-sectional structure of the coating sample pieces were coated with particle-containing resin composite. It is a graph which shows the rocking curve of the resin composite material containing a fine graphite particle. It is a schematic explanatory drawing for demonstrating a friction abrasion test. It is a graph which compares and shows the friction coefficient (micro) of each test material in the conditions in oil. It is a graph which compares and shows the abrasion loss of each test material in the conditions in oil. It is a graph which compares and shows the friction coefficient (micro) of each test material in the conditions in oil. It is a graph which compares and shows the abrasion loss of each test material in the conditions in oil.

  Hereinafter, with respect to the sliding member of the present invention, with reference to the drawings, oriented graphite particles (hereinafter sometimes referred to as “specific graphite particles” in the embodiments) are oriented, and X-rays are partially formed on the sliding surface. An embodiment provided with a graphite surface having a half-width of 5 ° or less in a rocking curve at a graphite-2H 002 diffraction position by diffraction measurement will be described as an example, and through the description, a method for manufacturing a sliding member of the present invention will also be described. It will be described in detail.

(First embodiment)
1st Embodiment of the sliding member of this invention is described with reference to FIGS. When the piston reciprocates by forming a graphite layer in which specific graphite particles are oriented on the skirt, which is the sliding surface of the piston that reciprocates in the engine, the sliding member of this embodiment The friction loss and the sliding wear are reduced.

  As shown in FIG. 1, the piston of the present embodiment, which is a sliding member, has graphite on the surface of a skirt portion 13 positioned below from the top surface 11 of a piston main body portion 10 made of aluminum alloy via a ring groove portion 12. The layer 15 is provided in a film shape with a predetermined thickness. By providing the graphite layer 15, the skirt portion stably exhibits low friction characteristics and wear resistance when the skirt portion slides with the mating member using the graphite surface as a sliding surface.

  The skirt portion has graphite particles oriented on its surface, so that the half width at the rocking curve at the graphite-2H002 diffraction position by X-ray diffraction measurement is 5 ° or less. Since the skirt part plays a role of maintaining the posture while sliding with the counterpart cylinder bore when the piston reciprocates, the surface layer has a half-value half width of 5 ° or less, thereby reducing the friction during the reciprocating movement, Friction loss can be suppressed.

  As shown in FIG. 2, the graphite layer 15 is a layer in which specific graphite particles 17 are dispersed in a matrix resin 19. The specific graphite particles 17 dispersed in the matrix resin 19 are oriented such that the c-plane corresponding to the graphene surface is parallel or substantially parallel to the surface of the graphite layer 15. A sliding surface is constituted by the matrix resin 19.

  The matrix resin functions as a binder component to disperse specific graphite particles and maintain the dispersed state, and has less sliding wear when sliding than graphite particles. Wear is further reduced by distributing the load to the portions. Since the sliding surface is composed of graphite particles having a low coefficient of friction (μ) and a resin component, the effect of reducing friction loss and the effect of improving wear resistance generated during sliding are large.

  The matrix resin is not particularly limited as long as it is a resin having higher wear resistance than the specific graphite particles (orientated graphite particles). Examples of the matrix resin include (1) thermoplastic general-purpose plastics such as polystyrene resin, polypropylene resin, and acrylic resin, (2) polyphenylene ether resin, polyamide resin, polyacetal resin, polyethylene terephthalate resin, polybutylene terephthalate resin, and Thermoplastic engineering plastics such as ultra-high molecular weight polyethylene resin, (3) Polyamideimide resin, polyphenylene sulfide resin, polyetheretherketone resin, liquid crystal polymer resin, polytetrafluoroethylene resin, polyetherimide resin, polyarylate resin, polysulfone Thermoplastic super engineering plastics such as resin, polyimide resin, and polyetherimide resin, (4) thermosetting polyamideimide, epoxy Examples thereof include thermosetting resins such as xy resin, phenol resin, bismaleimide resin, melamine resin, polyurethane resin, unsaturated polyester resin, and thermosetting polyimide resin. These resins may be used alone or in combination of two or more.

Among the matrix resins, from the viewpoint of excellent wear resistance, heat resistance, and mass productivity, thermoplastic engineering plastics (e.g., polyphenylene ether resin, polyamide resin, polyacetal resin, polyethylene terephthalate resin, polybutylene terephthalate resin, And super high molecular weight polyethylene resins), thermoplastic super engineering plastics (eg, polyamideimide resin, polyphenylene sulfide resin, polyetheretherketone resin, liquid crystal polymer resin, polytetrafluoroethylene resin, polyetherimide resin, polyarylate resin) , Polysulfone resin, polyimide resin, and polyetherimide resin) are preferable.
Furthermore, from the viewpoint of maintaining stable wear resistance and strength even when the temperature of the sliding part rises, thermosetting polyamideimide, epoxy resin, phenol resin, bismaleimide resin, melamine resin, polyurethane resin, unsaturated resin Thermosetting resins such as polyester resins and thermosetting polyimides are preferred.
In place of all or a part of the matrix resin, matrix resin precursor monomers and oligomers, precursors of matrix resins such as metal salts, metals having a melting point of 600 ° C. or less, and the like may be used.

  The specific graphite particles are small particles having an average particle diameter of 40 m or less, and are graphite particles (graphite particles) having a large plate shape with an aspect ratio of 20 or more, as shown in FIG. As shown in FIG. 2, the particles are two-dimensionally oriented such that the c-plane corresponding to the graphene plane is along the surface of the skirt portion 13. In the graphite layer 15 serving as the sliding surface, the specific graphite particles have an orientation state suitable for reducing friction when the counterpart material slides, that is, the c-plane such as the (100) plane has at least a part of the sliding surface. It is contained in a state of being oriented parallel or substantially parallel to the surface of the graphite layer so as to form. In other words, in the specific graphite particles, the carbon hexagonal mesh surface forming the c-plane is oriented substantially parallel to the surface of the skirt portion 13. Therefore, when the piston reciprocates, the reciprocating direction and the c-plane (crystal plane with the c-axis as the normal direction) of the specific graphite particles become substantially parallel.

The rocking curve at the graphite-2H 002 diffraction position is a diffraction line curve obtained by measuring the diffraction intensity while fixing the detector angle (diffraction angle 2θ) to the graphite-2H 002 diffraction position and rotating the rotation angle ω of the sample. And shows the distribution of the inclination of the graphite c-plane [(100) plane] relative to the sample surface. This rocking curve shows a sharper peak as the graphite c-plane is evenly distributed in parallel to the sample surface. Conversely, if the rocking curve is distributed with various inclination angles with respect to the sample surface, the rocking curve is broad. It becomes something. Such rocking curve spread is caused by the half-width of the rocking curve (diffraction peak at a position where the vertical axis has a diffraction intensity half that of the maximum peak value in the diffraction peak drawn with the sample rotation angle ω on the horizontal axis and the diffraction intensity on the vertical axis. (Width of the horizontal axis ω). In other words, Half Width at Half Maximum indicates that the smaller the value is, the c-plane exists in parallel to the graphite surface (that is, the surface that becomes the sliding surface). It can be said that the sample has
The measurement can be performed using an X-ray diffractometer (for example, RINT-2200, manufactured by Rigaku Corporation). For more precise measurement, normal two-axis measurement of ω and 2θ is insufficient, and a sample table that can create a pole figure etc. (for example, a multipurpose sample attached to RINT-2200 manufactured by Rigaku Corporation) The rocking curve is measured in advance in the driving direction that is 90 ° different from the driving direction of the ω-axis and 2θ-axis using a table, etc., and the rocking with respect to the ω-axis is crossed across the maximum point of the diffraction peak. It is necessary to set it so that a curve can be drawn.

  The half width at half maximum (Half Width at Half Maximum; hereinafter also simply referred to as “half width at half maximum”) in the rocking curve is preferably as small as possible in order to further reduce the friction loss on the sliding surface. Further, it is preferably 4 ° or less, particularly preferably 2 ° or less.

  The aspect ratio of specific graphite particles is the ratio of the average particle diameter of the particles to the average thickness of the particles contained in the graphite layer. The aspect ratio of the specific graphite particles in the present invention is 20 or more, preferably 40 or more. There is no particular limitation on the upper limit of the aspect ratio. If the aspect ratio calculated from the average value is less than 20, the friction coefficient (μ value) of the sliding surface cannot be kept low (preferably 0.05 or less).

  The average particle diameter (d) of the specific graphite particles is an average value of the length A of each particle shown in FIG. 3, and the average particle diameter (d) is 40 m or less. Among these, the average particle diameter d is more preferably 1 μm or more and 20 μm or less. When the average particle size of the specific graphite particles is 40 m or less, it is easy to handle the formation of the graphite layer, and it is advantageous in that it does not hinder the dispersion or coating operation when the graphite layer is formed by coating.

The average thickness (T) of the specific graphite particles is an average value of the thickness B of each particle shown in FIG. 3, and the average thickness (T) is preferably in a range satisfying the following formula.
T ≦ 1/10 × d [d: average particle diameter [μm]]
The average thickness (T) of the specific graphite particles being d / 10 or less means that the particles are flaky particles. An average thickness (T) of d / 10 or less is preferable in that the aspect ratio is large and a large area of the graphene surface can be secured.

  Although there is no restriction | limiting in particular about the range of individual thickness of a specific graphite particle, 0.3-1000 nm is preferable, 0.7-500 nm is more preferable, 0.7-100 nm is especially preferable.

  The average particle diameter (d) of the specific graphite particles is a value calculated from, for example, an SEM photograph by observing or photographing the particles with a scanning electron microscope (SEM). The average thickness (T) of the specific graphite particles is a value observed and measured in a tapping mode using a scanning probe microscope (“NanoScope V D3100” manufactured by Digital Instruments).

The specific graphite particles are plate-like particles that are thinly laminated so that graphene has a predetermined aspect ratio, and powdery or granular particles can be appropriately selected and used. As specific examples of graphite particles,
(1) Flaky graphite particles obtained by pulverizing known graphite having a graphite structure (artificial graphite, natural graphite (for example, flaky graphite, massive graphite, earthy graphite)) so that the graphite structure is not destroyed Can be mentioned. Such flaky graphite particles exhibit high orientation in a direction in which the (100) plane is parallel or substantially parallel to the sliding surface.
Specifically, raw material graphite particles, an aromatic vinyl copolymer containing a vinyl aromatic monomer unit represented by the following formula (1), a hydrogenated product, and a solvent are mixed, and the resulting mixture is mixed. Fine graphite particles produced by removing the solvent after the grinding treatment are preferred. Details of the method for producing the fine graphite particles will be described later.

That is, as a preferable example of the specific graphite particles, fine graphite particles including flaky graphite particles and an aromatic vinyl copolymer having a structural unit derived from a vinyl aromatic monomer represented by the following formula (1) can be given. It is done.
_{- (CH 2 -CHX) - ···} (1)
In the formula (1), X represents a phenyl group, a naphthyl group, an anthracenyl group, or a pyrenyl group. These groups may be unsubstituted or have a substituent.

  It is preferable that a functional group such as a hydroxyl group, a carboxyl group, or an epoxy group is bonded to the surface of the flaky graphite particles (preferably a covalent bond). The functional group has an affinity with an aromatic vinyl copolymer, which will be described later, and the amount of adsorption and the adsorption force of the aromatic vinyl copolymer to the graphite particles increase. Therefore, the flaky graphite particles tend to be highly dispersible in the matrix resin and the solvent.

  The functional group is 50% or less (more preferably 20% or less, particularly preferably 10% or less) of the total number of carbon atoms in the vicinity of the surface of the flaky graphite particles (preferably, a region from the surface to a depth of 10 nm). It is preferably bonded to a carbon atom. When the ratio of the carbon atom to which the functional group is bonded is 50% or less, the hydrophilicity of the flaky graphite particles increases, so that the affinity with the aromatic vinyl copolymer can be maintained. The lower limit of the proportion of carbon atoms to which the functional group is bonded is not particularly limited, but is preferably 0.01% or more. The functional group such as a hydroxyl group can be quantified by X-ray photoelectron spectroscopy (XPS), and is determined by measuring the amount of the functional group present in the region from the particle surface to a depth of 10 nm. When the thickness of the flaky graphite particles is 10 nm or less, the amount of functional groups present in the entire region of the flaky graphite particles is measured.

  The aromatic vinyl copolymer has a structural unit derived from the vinyl aromatic monomer represented by the formula (1), and preferably has the structural unit and a structural unit derived from another monomer. In the present invention, a copolymer obtained by further copolymerizing the aromatic vinyl copolymer with another vinyl monomer may be used as the aromatic vinyl copolymer.

  The structural unit derived from the vinyl aromatic monomer constituting the aromatic vinyl copolymer exhibits adsorptivity to graphite particles, and the structural unit derived from the other monomer exists in the vicinity of the matrix resin, the solvent, and the graphite particle surface. The affinity with the functional group is shown. Therefore, such an aromatic vinyl copolymer is adsorbed on the flaky graphite particles, reduces the cohesive force between the graphite particles, and gives the graphite particles affinity with a matrix resin or a solvent, thereby producing fine graphite. The particles can be highly dispersed in the matrix resin or the solvent.

In addition, since the structural unit derived from the vinyl aromatic monomer is easily adsorbed on the graphite particles, the higher the content of the structural unit derived from the vinyl aromatic monomer, the greater the amount of adsorption on the flaky graphite particles. In addition, the dispersibility of the fine graphite particles in the matrix resin or the solvent is increased.
As a content ratio in the copolymer of the structural unit derived from a vinyl aromatic monomer, 10-98 mass% is preferable with respect to the whole copolymer, 30-98 mass% is more preferable, 50-95 mass% is Particularly preferred. When the content ratio of the structural unit derived from the vinyl aromatic monomer is 10% by mass or more, the amount of adsorption to the graphite particles can be maintained, and the dispersibility of the graphite particles can be maintained well. When the content ratio of the structural unit derived from the vinyl aromatic monomer is 98% by mass or less, the affinity for the matrix resin and the solvent can be imparted to the graphite particles, and the dispersibility of the fine graphite particles can be maintained well. .

  Examples of the substituent that the group represented by X in the formula (1) may have include an alkoxy group (for example, a methoxy group), a carbonyl group, an amide group, an imide group, a carboxyl group, and a carboxylate group. In particular, from the viewpoint of improving the dispersibility of the fine graphite particles, an alkoxy group such as a methoxy group is preferable, and a methoxy group is more preferable.

  Examples of the structural unit derived from the vinyl aromatic monomer include structural units derived from monomers such as styrene, vinyl naphthalene, vinyl anthracene, vinyl pyrene, vinyl anisole, vinyl benzoate, and acetyl styrene. Among these, from the viewpoint of enhancing the dispersibility of the fine graphite particles, a structural unit derived from styrene, vinyl naphthalene, or vinyl anisole is preferable.

  The structural unit derived from the other monomer is not particularly limited. For example, (meth) acrylic acid, (meth) acrylate compound, (meth) acrylamide compound, vinylimidazole compound, vinylpyridine compound More preferred are monomer units derived from at least one monomer selected from the group consisting of maleic anhydride and maleimide compounds. By using an aromatic vinyl copolymer containing such a monomer unit, the affinity of the graphite particles for the matrix resin and the solvent can be improved, and the graphite particles can be favorably dispersed in the matrix resin and the solvent. it can.

  Examples of the (meth) acrylate compound include alkyl (meth) acrylate, substituted alkyl (meth) acrylate (for example, hydroxyalkyl (meth) acrylate, aminoalkyl (meth) acrylate), and the like. Examples of the (meth) acrylamide compound include (meth) acrylamide, N-alkyl (meth) acrylamide, N, N-dialkyl (meth) acrylamide and the like. Examples of the vinylimidazole compound include 1-vinylimidazole. Examples of the vinylpyridine compound include 2-vinylpyridine and 4-vinylpyridine. Examples of the maleimide compound include maleimide, alkylmaleimide, and arylmaleimide.

  Among the other monomers, from the viewpoint of enhancing the dispersibility of the fine graphite particles, alkyl (meth) acrylate, hydroxyalkyl (meth) acrylate, aminoalkyl (meth) acrylate, N, N-dialkyl (meth) acrylamide, 2- Vinyl pyridine, 4-vinyl pyridine and arylmaleimide are preferred, hydroxyalkyl (meth) acrylate, N, N-dialkyl (meth) acrylamide, 2-vinylpyridine and arylmaleimide are more preferred, and phenylmaleimide is particularly preferred.

The aromatic vinyl copolymer is not limited in number average molecular weight (Mn), but preferably 1,000 to 1,000,000, more preferably 5,000 to 100,000. If the number average molecular weight of the aromatic vinyl copolymer is 1000 or more, the adsorption ability to the graphite particles can be maintained, and if it is 1 million or less, the solubility in a solvent can be maintained, the viscosity is good, and the handling property is excellent. .
The number average molecular weight of the aromatic vinyl copolymer was measured by gel permeation chromatography (column: Shodex GPC K-805L and Shodex GPC K-800RL (both manufactured by Showa Denko KK), eluent: chloroform). It is a value converted with standard polystyrene.

  In the fine graphite particles (orientated graphite particles), either a random copolymer or a block copolymer may be used as the aromatic vinyl copolymer. Among these, a block copolymer is preferable from the viewpoint of improving the dispersibility of the specific graphite particles, and a random copolymer is preferable from the viewpoint of being inexpensive.

The content of the aromatic vinyl copolymer is preferably 10 ⁻⁷ to 10 ⁻¹ part by mass with respect to 100 parts by mass of the flaky graphite particles constituting the fine graphite particles, and 10 ⁻⁵ to 10 ^{−1 part by} mass. Part is more preferred. When the content of the aromatic vinyl copolymer is not less than the lower limit value, the adsorption to the graphite particles is good, and the dispersibility when dispersed is excellent. Further, when the content is not more than the upper limit value, the presence of a free aromatic vinyl copolymer that is not directly adsorbed on the graphite particles can be suppressed.

  As described above, the fine graphite particles have a high affinity with the matrix resin and the solvent, and can be highly dispersed in the matrix resin. Further, the fine graphite particles are excellent in dispersibility in a solvent. For example, when a graphite layer is formed by mixing a matrix resin and fine graphite particles in a solvent, the fine graphite particles can be easily and Highly dispersible.

  Examples of the graphite particles (raw material graphite particles) used as raw materials in the production of the fine graphite particles include known graphites having a graphite structure (artificial graphite, natural graphite (for example, flaky graphite, massive graphite, earthy graphite)). It is done. Among the raw material graphite particles, those that become flaky graphite particles having a thickness in the above range by pulverization are preferable. Examples of such raw material graphite particles include those obtained by agglomerating the flaky graphite particles (primary particles) (secondary particles). Although there is no restriction | limiting in particular as a particle diameter of such a raw material graphite particle, 0.01-5 mm is preferable and 0.05-1 mm is more preferable.

  Moreover, it is preferable that functional groups such as a hydroxyl group, a carboxyl group, and an epoxy group are bonded (preferably covalently bonded) to the surface of the flaky graphite particles constituting the raw graphite particles. The functional group has an affinity for an aromatic vinyl copolymer. The adsorption amount and adsorption force of the aromatic vinyl copolymer to the graphite particles are increased, and the dispersibility of the obtained graphite particles in the matrix resin and the solvent is enhanced.

  Such a functional group is 50% or less (more preferably 20% or less, particularly preferably 10% or less) of the total carbon atoms in the vicinity of the surface of the flaky graphite particles (preferably, a region from the surface to a depth of 10 nm). ) Is preferably bonded to a carbon atom. When the ratio of the carbon atom to which the functional group is bonded is 50% or less, the affinity with the aromatic vinyl copolymer can be kept good. The lower limit of the proportion of carbon atoms to which the functional group is bonded is not particularly limited, but the lower limit is preferably 0.01%.

  As the hydrogen peroxide, a compound having a carbonyl group (for example, urea, carboxylic acid (benzoic acid, salicylic acid, etc.), ketone (acetone, methyl ethyl ketone, etc.), carboxylic acid ester (methyl benzoate, ethyl salicylate, etc.)) Complexes with hydrogen peroxide; those in which hydrogen peroxide is coordinated to compounds such as quaternary ammonium salts, potassium fluoride, rubidium carbonate, phosphoric acid and uric acid. Such hydrogen peroxide acts as an oxidant when producing fine flaky graphite particles according to the present invention, and facilitates delamination between carbon layers without destroying the graphite structure of the raw graphite particles. Is. That is, hydrogen peroxide enters between the carbon layers to oxidize the surface of the layer, and proceeds with cleavage. At the same time, the aromatic vinyl copolymer penetrates into the cleaved carbon layer and stabilizes the cleavage surface. Promoted. As a result, the aromatic vinyl copolymer is adsorbed on the surface of the plate-like graphite particles, and the fine flaky graphite particles can be highly dispersed in the matrix substrate or the solvent according to the present invention. .

  The solvent used for the production of the fine graphite particles is not particularly limited, but dimethylformamide (DMF), chloroform, dichloromethane, chlorobenzene, dichlorobenzene, N-methylpyrrolidone (NMP), toluene, dioxane, propanol, γ- Picoline, acetonitrile, dimethyl sulfoxide (DMSO), and dimethylacetamide (DMAC) are preferable, and dimethylformamide (DMF), chloroform, dichloromethane, chlorobenzene, dichlorobenzene, N-methylpyrrolidone (NMP), and toluene are more preferable.

  When producing fine graphite particles (orientated graphite particles), first, the raw graphite particles, the aromatic vinyl copolymer, the hydrogen peroxide, and the solvent are mixed. The mixing amount of the raw material graphite particles is preferably 0.1 to 500 g / L, more preferably 10 to 200 g / L, per liter of the solvent. The mixing amount of the raw material graphite particles is economically advantageous in that solvent consumption is suppressed to 0.1 g / L or more, and it is 500 g / L or less to maintain the viscosity of the liquid and improve the handleability. Can be maintained.

  The mixing amount of the aromatic vinyl copolymer is preferably 0.1 to 1000 parts by mass, more preferably 0.1 to 200 parts by mass with respect to 100 parts by mass of the raw graphite particles. When the mixing amount of the aromatic vinyl copolymer is 0.1 parts by mass or more, the dispersibility of the obtained fine graphite particles can be kept good. Further, when the mixing amount of the aromatic vinyl copolymer is 1000 g / L or less, the solubility in the solvent is maintained, and the viscosity of the liquid is maintained and the handling property is excellent.

  In addition, the mixing amount of the hydrogen peroxide is preferably 0.1 to 500 parts by mass, and more preferably 1 to 100 parts by mass with respect to 100 parts by mass of the raw graphite particles. When the mixing amount of the hydrogen peroxide is 0.1 parts by mass or more, the dispersibility of the obtained fine graphite particles can be kept good. Moreover, when the mixing amount of the hydrogen peroxide is 500 parts by mass or less, the raw graphite particles are not excessively oxidized, and the conductivity of the obtained fine graphite particles can be favorably maintained.

  Next, the obtained mixture is pulverized, and the raw graphite particles are pulverized into plate-like graphite particles by delamination. By adsorbing the aromatic vinyl copolymer onto the surface of the flaky graphite particles thus produced, fine graphite particles having excellent dispersion stability in a matrix resin or a solvent can be obtained.

  Examples of the pulverization treatment include ultrasonic treatment (oscillation frequency is preferably 15 to 400 kHz, output is preferably 500 W or less), treatment with a ball mill, wet pulverization, explosion, and mechanical pulverization. As a result, it is possible to obtain flaky graphite particles by pulverizing the raw graphite particles without destroying the graphite structure of the raw graphite particles. There is no restriction | limiting in particular about the temperature at the time of a grinding | pulverization process, For example, it can be set to -20-100 degreeC. Moreover, there is no restriction | limiting in particular also about pulverization processing time, For example, it can be set as 0.01 to 50 hours.

  Further, if necessary, the fine graphite particles obtained in the pulverization step and at least one of alkyl compounds, oligoolefins and polyolefins having the reactive site are mixed, and the aromatic in the fine graphite particles A step of introducing one or more hydrocarbon chains selected from an alkyl chain, an oligoolefin chain, and a polyolefin chain (hydrocarbon chain introduction step) can be provided in the vinyl copolymer. In this case, the aromatic vinyl copolymer needs to have a functional group, and the functional group and the reactive site are bonded to the aromatic vinyl copolymer to form an alkyl chain, an oligoolefin chain. And a hydrocarbon chain selected from polyolefin chains.

  In this hydrocarbon chain introduction step, it is necessary to mix the fine graphite particles obtained in the pulverization step, at least one of the alkyl compound, oligoolefin and polyolefin having the reactive site, and a solvent. The aromatic vinyl copolymer having a functional group is reacted with at least one of an alkyl compound, an oligoolefin, and a polyolefin having a reactive site by heating the mixture obtained according to the above. There is no restriction | limiting in particular as a solvent, What was illustrated as a solvent used for the graphite particle dispersion liquid of this invention can be used. The reaction temperature is preferably −10 to 150 ° C., and the reaction time is preferably 0.1 to 10 hours.

  The mixing amount of the fine graphite particles is preferably 1 to 200 g / L, more preferably 1 to 50 g / L per liter of the solvent. When the mixing amount of the fine graphite particles is 1 g / L or more, solvent consumption is suppressed, which is economically advantageous. Moreover, when the mixing amount of the fine graphite particles is 200 g / L or less, an increase in the viscosity of the liquid can be suppressed, and the handleability can be kept good.

  In addition, the mixing amount of the alkyl compound, oligoolefin, and polyolefin having the reactive site is preferably 0.001 to 500 parts by mass, and 10 to 500 parts by mass with respect to 100 parts by mass of the fine graphite particles. More preferred. When the mixing amount of the alkyl compound, the oligoolefin, and the polyolefin is 0.001 part by mass or more, the introduction amount of the alkyl chain, the oligoolefin chain, and the polyolefin chain does not decrease too much, and the fine graphite particles with respect to the hydrophobic solvent Dispersibility is improved. Moreover, when the mixing amount is 500 parts by mass or less, an increase in the viscosity of the liquid can be suppressed, and the handleability can be kept good.

  The fine graphite particles obtained as described above are in a state of being dispersed in a solvent, and can be recovered and used as flaky fine graphite particles by removing the solvent by filtration or centrifugation.

Examples of the specific graphite particles include the following (2) to (3) in addition to the fine graphite particles described above.
(2) Single-layer or multilayer graphite powder particles produced by peeling high-oriented pyrolytic graphite (HOPG) between graphite layers by the Scotch tape method or the like (3) Commercially available graphene on the market Powder particles (for example, Graphene Nanopowder manufactured by ATR)

An example of specific graphite particles is shown in FIG. FIG. 4 is an SEM photograph of specific graphite particles. The oriented graphite particles in the present invention are preferably flake particles as shown in FIGS. For example, the multilayer graphene powder shown in FIG. 4B has a flat flake shape, and has a structure in which a plurality of layers of graphene are stacked in parallel orientation.
Here, exfoliated graphite particles are provided as commercially available products on the market. Generally, exfoliated graphite particles conventionally provided are several μm as shown in FIGS. 5 (A) and 5 (B). It is a particle formed by agglomerating flaky graphite of about 10 μm to form an irregularly shaped secondary particle body. Therefore, in the conventional exfoliated graphite particles, the c-planes of the individual exfoliated graphite forming one secondary particle body are in a state in which they are oriented in random directions. Therefore, when a graphite layer is formed using conventional exfoliated graphite particles, a layer in which the graphite particles are oriented so that the graphite c plane is parallel to the sliding surface cannot be obtained. In such a layer, there is a crystal plane of a-plane [(101) plane, (100) plane, etc.) other than the c-plane on the sliding surface, and the effect of reducing friction loss cannot be expected so much.

In the graphite layer, the content ratio of the oriented graphite particles to the total amount of the matrix resin and the oriented graphite particles is 30% or more and 90% or less on the mass basis. If the content ratio of the oriented graphite particles is less than 30% and is too small, the friction coefficient (μ value) of the sliding surface does not decrease because of the relatively large amount of resin, and the sliding surface has wear resistance. Cannot be obtained. On the other hand, when the content ratio of the oriented graphite particles exceeds 90% and becomes too large, the amount of resin is relatively reduced, so that it becomes difficult to form the graphite layer itself, and it is difficult to form the graphite layer by the coating method.
The content ratio of the oriented graphite particles with respect to the total amount is preferably 40% or more and 90% or less on a mass basis, and the more preferable content ratio is 50 to 90% (more preferably 60 to 90%).

  Although the thickness of a graphite layer can be suitably selected according to the objective, a use, etc., generally 100 micrometers or less are preferable, 25-100 micrometers is more preferable, More preferably, it is 3-40 micrometers.

  The graphite layer 15 of the present embodiment is a coating layer formed by preparing a coating liquid containing specific graphite particles 17 and a matrix resin 19 and coating the coating liquid on the surface of the skirt portion 13. As a graphite material, it is not a graphite sheet obtained by carbonizing a conventionally used single crystal mass (for example, HOPG and single crystal graphite) or a laminated polymer film, but a relatively c-plane area by having an aspect ratio of a predetermined value or more. By using large graphite particles, it is possible to form a layer by a coating method, and it is excellent in productivity while having good low friction characteristics and wear resistance. Moreover, when forming a sliding surface using a graphite particle, a graphite particle can be easily orientated so that c surface may form a sliding surface by the application | coating method and the flow.

  In the above-described embodiment, the description has been made mainly on the piston for an engine configured by applying the graphite layer to the aluminum alloy (specifically, the piston skirt) as the sliding member as the sliding member. In addition to aluminum alloys, metal carriers such as iron, chromium, nickel, cobalt, rhodium, copper, brass, nickel-chromium, nickel-phosphorus, nickel-tungsten, nickel-cobalt, cobalt-tungsten, iron-nickel, Examples of the alloy include iron-phosphorus, iron-tungsten, and copper-nickel.

Further, specific examples of the base material constituting the sliding member are not limited to engine pistons, but include piston rings, piston pins, slide bearing structures, and the like.
In the case where such a base material is provided with a graphite layer as a sliding member, for example, in addition to an engine piston in which a graphite layer is provided on at least a part of the skirt portion (the entire surface in this embodiment), it is disposed on the piston. A piston ring provided with a graphite layer on at least a part of the outer peripheral surface, a piston pin provided with a graphite layer on at least a part of the outer peripheral surface, or at least one of a shaft and a bush. A slide bearing structure in which a graphite layer is provided at least in part can be provided.

The graphite layer can be formed by any method as long as it can form a layer containing oriented graphite particles oriented in the matrix resin so that the half width at half maximum in a predetermined rocking curve is 5 ° or less. May be. Especially, a graphite layer can be most suitably formed with the manufacturing method of the sliding member of this invention mentioned later.
The sliding member manufacturing method of the present invention comprises a dispersion liquid in which oriented graphite particles having an average particle diameter of 40 m or less and an aspect ratio which is a ratio of an average particle diameter to an average thickness of 20 or more are dispersed in a solvent. A preparation step of mixing a matrix resin and preparing a coating solution for forming a graphite layer in which the content ratio of the oriented graphite particles to the total amount of the matrix resin and the oriented graphite particles is 30% or more and 90% or less on a mass basis; By applying the graphite layer forming coating solution on the sliding surface of the base material with the counterpart material, the orientation resin particles are oriented in the matrix resin, and graphite-2H 002 by X-ray diffraction measurement is used. And a coating process for forming a graphite layer having a half-value half-width of 5 ° or less in the rocking curve at the diffraction position. There.

In the preparation step, a matrix resin is mixed with a dispersion in which oriented graphite particles having an average particle diameter of 40 m or less and an aspect ratio which is a ratio of the average particle diameter to the average thickness of 20 or more are dispersed in a solvent. To prepare a graphite layer forming coating solution. At this time, the content ratio of the oriented graphite particles to the total amount of the matrix resin and the oriented graphite particles is 30% by mass or more and 90% by mass or less.
The details and preferred embodiments regarding the content ratio of the oriented graphite particles and the matrix resin and the oriented graphite particles are as described above.

  The solvent constituting the dispersion is not particularly limited, but dimethylformamide (DMF), chloroform, dichloromethane, chlorobenzene, dichlorobenzene, N-methylpyrrolidone (NMP), hexane, toluene, dioxane, propanol, γ-picoline, Acetonitrile, dimethyl sulfoxide (DMSO), and dimethylacetamide (DMAC) are preferable, and dimethylformamide (DMF), chloroform, dichloromethane, chlorobenzene, dichlorobenzene, N-methylpyrrolidone (NMP), hexane, and toluene are more preferable.

  In the case where the solvent is a hydrophobic solvent, the oriented graphite particles are provided with at least one hydrocarbon chain of an alkyl chain, an oligoolefin chain, and a polyolefin chain from the viewpoint of further improving dispersion stability. It is preferable that As the hydrophobic solvent, N-methylpyrrolidone (NMP) is preferable.

  The concentration of the oriented graphite particles in the dispersion is preferably 0.1 to 200 g / L, more preferably 1 to 100 g / L, per liter of the solvent. When the concentration of the oriented graphite particles is 0.1 g / L or more, solvent consumption is suppressed, which is economically advantageous. Further, when the concentration of the oriented graphite particles is 200 g / L or less, an increase in viscosity due to contact between the graphite particles is suppressed, and the fluidity can be kept good.

  A dispersion liquid in which oriented graphite particles are dispersed in a solvent is first a raw material graphite particle, an aromatic vinyl copolymer having a structural unit derived from a vinyl aromatic monomer represented by the above formula (1), hydrogen peroxide Compound and solvent are mixed, and the resulting mixture is pulverized. If necessary, the aromatic vinyl copolymer in the resulting graphite particles is added to at least one of an alkyl chain, an oligoolefin chain, and a polyolefin chain. It can be prepared by a method of further introducing seed hydrocarbon chains. In this method, the oriented graphite particles can be obtained in a state where they are dispersed in a solvent, that is, as a dispersion containing the oriented graphite particles.

The mixing amount of the raw material graphite particles, the mixing amount of the aromatic vinyl copolymer, and the mixing amount of the hydrogenated product are as described above, and the preferred embodiment is the same as described above.
The dispersion treatment when preparing the dispersion can be performed using, for example, an ultrasonic disperser. The dispersion conditions may be appropriately selected in consideration of the compounding ratio of various components, the viscosity of the liquid, and the desired dispersion state.

  The obtained oriented graphite particles may be used in the state of a dispersion, or may be used after the obtained dispersion is filtered or centrifuged to remove the solvent. Furthermore, the obtained graphite particles may be redispersed in a solvent to prepare a new dispersion and use it.

  The coating process constituting the manufacturing method of the sliding member of the present invention is performed by applying the coating liquid for forming the graphite layer obtained in the preparation process on the sliding surface of the base material with the counterpart material, thereby forming a matrix. A graphite layer containing oriented graphite particles oriented in the resin and having a half-width of 5 ° or less in a rocking curve at the graphite-2H002 diffraction position by X-ray diffraction measurement is formed. Since the graphite particles contained in the coating liquid have a high aspect ratio, the graphite particles are easily oriented by the flow during coating, and the coating liquid is applied to a thin film, so that the graphite particles are more than those applied to a thick film. It can be a highly oriented graphite layer.

  The coating can be suitably performed by a method appropriately selected from known coating methods such as spray coating, bar coating, dipping, and electrostatic coating.

  After coating the coating solution for forming a graphite layer on the surface of the substrate, the graphite layer is formed by drying the coating film by a desired method. The drying conditions may be selected according to various conditions such as the composition of the coating solution and the coating thickness. The drying method is not particularly limited, and may be a method using a heater, a blower, or the like to apply heat and / or air to the coating surface or the back surface thereof for drying.

(Second Embodiment)
A second embodiment of the sliding member of the present invention will be described with reference to FIG. The sliding member of this embodiment forms a sliding surface by forming a graphite layer in which specific graphite particles are oriented in the vicinity of the layer surface in a sliding bearing portion of a connecting rod bearing.

  The connecting rod bearing 20 of the present embodiment, which is a sliding member, is a U-shaped metal member that is disposed between the connecting rod and the crankshaft.

  As shown in FIG. 6, the connecting rod bearing 20 that is a sliding member is one of the curved surfaces of the connecting rod bearing main body 23 made of aluminum or an alloy thereof, copper or an alloy thereof, that is, the side on which the counterpart material slides. A graphite layer 21 is formed on the surface in a film shape with a predetermined thickness. By providing the graphite layer 21, low friction characteristics and wear resistance when the curved surface provided with the graphite layer of the connecting rod bearing is slid with the mating member as a sliding surface are stably expressed.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof. Unless otherwise specified, “part” is based on mass.

In addition, a number average molecular weight (Mn) is the value converted into standard polystyrene, measured on condition of the following using gel permeation chromatography Shodex GPC101 (made by Showa Denko KK).
<Measurement conditions>
Column: Shodex GPC K-805L (manufactured by Showa Denko KK)
Shodex GPC K-800RL (manufactured by Showa Denko KK)
・ Eluent: Chloroform ・ Measurement temperature: 25 ° C.
Sample concentration: 0.1 mg / ml
・ Detection means: RI

Example 1
[Preparation of fine graphite particle-containing resin composite and sample piece]
-Production of fine graphite particles-
(1) 36 g of styrene (ST), 4 g of N, N-dimethylmethacrylamide (DMAA), 160 mg of azobisisobutyronitrile and 40 g of methyl ethyl ketone are mixed and polymerized at 85 ° C. for 6 hours in a nitrogen atmosphere. It was. After cooling, the mixture was purified by reprecipitation with a 1: 1 mixed solvent of chloroform and ether to obtain 25.3 g of ST / DMAA random copolymer (= 9: 1 [mass ratio]). The number average molecular weight (Mn) of the ST / DMMAA random copolymer was about 50,000.

(2) 125 g of exfoliated graphite powder (product name: EXP-P) manufactured by Nippon Graphite Co., 125 g of hydrogen peroxide-urea complex, 12.5 g of the ST / DMA random copolymer, and N, N-dimethyl Formamide (DMF; solvent) (5000 ml) was mixed and treated 10 times at a cylinder pressure of 400 MPa using a wet pulverizer (Starburst Lab manufactured by Sugino Machine). Through such a procedure, the flaky graphite primary particles were peeled off from the irregular shaped graphite secondary particles to obtain a solution in which fine graphite particles were uniformly dispersed in the DMF solvent. Subsequently, an aggregated powder of fine graphite particles was collected by filtering the obtained dispersion solution. The collected powder was dried under reduced pressure and pulverized by a mill pulverizer to obtain fine graphite particles.

-Preparation of fine graphite particle-dispersed resin solution-
The fine graphite particles were prepared as oriented graphite particles. By mixing 0.5 g of the fine graphite particles with 5 g of N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP; solvent) and stirring the resulting solution for 10 minutes with an ultrasonic cleaner, A fine graphite particle-dispersed NMP solution in which graphite particles were uniformly dispersed was obtained. The fine graphite particle-dispersed NMP solution and a solution of thermosetting polyamideimide (hereinafter abbreviated as PAI) (HPC-5011-29 manufactured by Hitachi Chemical Co., Ltd.) are mixed at various ratios shown in Table 1 below. 6 types of fine graphite particle-dispersed PAI resin solutions were prepared. Here, the fine graphite particle-dispersed PAI resin solution is diluted with an NMP solvent so that the PAI is 29 mass%. The shape of the fine graphite particles will be described later.

-Preparation of resin composite-coated sample pieces-
Next, the fine graphite particle-dispersed PAI resin solution was applied by spray application to the surface of a plate test piece made of SUS440C steel as a base material. After coating, after air drying for about 1 hour, the PAI is cured by heating and pressing the plate specimen at a temperature of 290 ° C. and a surface pressure of 10 MPa for 2 hours. A resin composite-coated sample piece (fine graphite particle-containing resin composite-coated sample piece) coated with a dispersed fine graphite particle-containing resin composite (graphite layer) having a thickness of 14 to 20 μm was prepared.

[Production of graphene nanoparticle-containing resin composite and sample piece]
-Preparation of graphene nanoparticle dispersed resin solution-
Similar to the preparation of the resin composite containing the fine graphite particles, graphene nanoparticles prepared as oriented graphite particles (ATR, Graphene Nanopowder, AO-3, average particle diameter: 4.5 μm, average particle size) Graphene nanoparticle-dispersed NMP solution in which 0.34 g of NMP 5.88 g is mixed with NMP 5.88 g and stirred for 10 minutes with an ultrasonic cleaner to uniformly distribute graphene nanoparticles. Got. 6.22 g of this graphene nanoparticle-dispersed NMP solution and 0.77 g of a thermosetting polyamideimide (hereinafter abbreviated as PAI) solution (HPC-5011-29, manufactured by Hitachi Chemical Co., Ltd.) are mixed to obtain graphene nano A particle-dispersed PAI resin coating solution was prepared. Here, the graphene nanoparticle-dispersed PAI resin solution is diluted with an NMP solvent so that the PAI is 29 mass%.

-Preparation of resin composite-coated sample pieces-
Next, the graphene nanoparticle-dispersed PAI resin solution was applied to the surface of a plate test piece made of SUS440C steel as a base material by spray coating. After the coating, after air drying for about 1 hour, the PAI is cured by heating and pressing the plate specimen at a temperature of 290 ° C. and a surface pressure of 10 MPa for 2 hours, so that the graphene nanoparticles are contained in the PAI. A resin composite-coated sample piece (graphene nanoparticle-containing resin composite-coated sample piece) coated with the dispersed graphene nanoparticle-containing resin composite (graphite layer) having a thickness of 36 μm was prepared.

[Production of exfoliated graphite particle-containing resin composite and sample piece (for comparison)]
-Preparation of exfoliated graphite particle dispersed resin solution-
Next, exfoliated graphite particles (EXP-P, manufactured by Nippon Graphite Co., Ltd., average particle size: 50 μm, average thickness of particles: 5 μm, aspect ratio, which is a general flaky graphite powder commercially available for comparison. 10), 0.3 g of the exfoliated graphite particles were mixed with 6 g of NMP, and stirred for 10 minutes with an ultrasonic cleaner to obtain an exfoliated graphite particle-dispersed NMP solution in which the exfoliated graphite particles were dispersed. Obtained. 6.3 g of this exfoliated graphite particle-dispersed NMP solution and 0.69 g of a thermosetting polyamide-imide (hereinafter abbreviated as PAI) solution (HPC-5011-29, manufactured by Hitachi Chemical Co., Ltd.) are mixed. A graphite particle-dispersed PAI resin coating solution was prepared.
In addition, an average particle diameter is the value which measured and averaged arbitrary 10 particle diameters from the image observed using the scanning electron microscope (SEM), and the average thickness of particle | grains is optical three-dimensional. This is a value obtained by measuring and averaging the thickness of any 10 particles using a shape measuring machine (Newview 5022 manufactured by zygo).

-Preparation of resin composite-coated sample pieces-
Here, although spray application using the exfoliated graphite particle-dispersed PAI resin coating liquid was attempted, since the average particle size includes relatively large exfoliated graphite particles of 50 μm, such exfoliated graphite particles are dispersedly contained. In the solution, the φ0.5 mm spray nozzle was clogged with particles, and spray coating could not be performed.
Therefore, in the present example, the exfoliated graphite particle-dispersed PAI resin coating liquid was applied to the surface of a plate test piece made of SUS440C steel by brush application. After coating, after air drying for about 1 hour, the PAI is cured by heating and pressing the plate specimen at a temperature of 290 ° C. and a surface pressure of 10 MPa for 2 hours, so that exfoliated graphite particles are contained in the PAI. A comparative resin composite-coated sample piece (exfoliated graphite particle-containing resin composite-coated sample piece) covered with a dispersed resin composite (graphite layer) having a thickness of 30 μm was prepared.

~ Hue ~
Of the resin composite-coated sample pieces prepared as described above, a fine graphite particle-containing resin composite-coated sample piece having a graphite ratio of 60% by mass, a graphene nanoparticle-containing resin composite-coated sample piece, and a comparative thin piece The appearance of the graphite composite particle-containing resin composite-coated sample piece was observed. An appearance photograph of each resin composite-coated sample piece is shown in FIG.
As shown in FIGS. 7A to 7B, the resin composite-coated sample piece in which fine graphite particles or graphene nanoparticles are highly oriented and dispersed exhibited a silvery appearance with a metallic luster. In the resin composite-coated sample piece in which exfoliated graphite particles (EXP-P) that are generally used in the past shown in FIG. 7 (C) are dispersed, black was derived from the hue of general graphite (graphite). . As described above, the oriented graphite particles in the present invention are different in appearance from the exfoliated graphite particles conventionally used, and can be judged visually.

~ Particle shape and orientation ~
Next, using a fine graphite particle-containing resin composite-coated sample piece having a graphite ratio of 40 mass% as a representative sample, a cross-sectional SEM photograph of the cross-section was observed. A cross-sectional SEM photograph is shown in FIG.
As shown in FIG. 8, the fine graphite particle-containing resin composite-coated sample piece has an average particle diameter of several μm to 10 μm (average of about 5 μm) and an average thickness of several tens to 200 nm (average of about 100 nm). The flake-shaped fine graphite particles having a ratio of the average particle diameter to the average thickness of the particles (aspect ratio) of about 50 are dispersed in the PAI resin in a state of being oriented in a direction parallel to the coated surface (that is, the graphite surface). The situation was confirmed.
For comparison with this, a cross-sectional SEM photograph of a resin composite material in which MoS ₂ (molybdenum disulfide) particles used for coating the piston skirt for the purpose of reducing engine friction is dispersed in PAI is shown in FIG. Shown in The MoS ₂ particles dispersed in the PAI are layered compounds like graphite, and the average particle size of the MoS ₂ particles is about several μm to 8 μm, which is about the same as the fine graphite particles shown in FIG. It can be seen that the thickness is about several hundred nm to 1 μm, which is thicker than the fine graphite particles. It is considered that this is because the MoS ₂ particles are not dispersed in a state in which the fine graphite particle-containing resin composite is oriented in the direction parallel to the surface.

-Rocking curve and half-width at half maximum-
In order to quantify the orientation of the resin composite material containing fine graphite particles coated on the resin composite material-coated sample piece, an X-ray diffractometer (RINT-2200, manufactured by Rigaku Corporation) was used to obtain graphite-2H. The rocking curves at the 002 diffraction position were measured, and their half-value half widths were obtained. Measurement conditions are X-ray acceleration voltage: 40 kV, current: 30 mA, divergence slit: 1 deg, scattering slit: 1 deg, light receiving slit: 0.3 mm, FT: 0.05 deg / step, scan speed: 2.0 deg / min It was.

The rocking curve of the fine graphite particle-containing resin composite is shown in FIG. FIG. 10 shows, for comparison, a block-shaped product of highly oriented graphite (Panasonic Graphite PCGX10, manufactured by Panasonic Corporation), a graphite sheet (PGS, manufactured by Panasonic Corporation), and generally used isotropic graphite powder. The rocking curve of the molded body (carbon IG-11 for graphite machine, manufactured by Toyo Tanso Co., Ltd.) is also shown.
As shown in FIG. 10, the rocking curve of the fine graphite particle-containing resin composite is an isotropic graphite powder molded body using particles in the same manner as these, both having a graphite ratio of 40 mass% and 53 mass%. In comparison, it shows a sharper peak, and it can be seen that high orientation close to that of a highly oriented graphite sheet is obtained even when particulate graphite is used instead of crystal lumps or sheets.

  Moreover, the half width at half maximum of the resin composite material containing fine graphite particles and the resin composite material containing graphene nanoparticles was measured. The measurement results are shown in Table 1. As shown in Table 1, although the half-width at half maximum of the fine graphite particles (orientated graphite particles) resin composite was slightly varied, good values in the range of 2.5 ° to 4.2 ° were obtained. .

  As described above, the fine graphite particle-containing resin composite and the graphene nanoparticle-containing resin composite have a structure in which the oriented graphite particles are well dispersed and the c-plane is oriented approximately parallel to the coated surface. It is thought that.

~ Friction and wear characteristics ~
In evaluating the friction and wear characteristics, in addition to the above sample pieces, the following comparative sample pieces were prepared in order to compare the friction and wear characteristics.
[I] Comparative sample piece a
Only the thermosetting polyamide-imide solution (HPC-5011-29 manufactured by Hitachi Chemical Co., Ltd.) was spray-coated on the surface of the plate test piece made of SUS440C steel, and the fine graphite particle-containing resin composite described above was applied. Similar to production, after air-drying for about 1 hour, a PAI resin-cured sample piece for comparison, in which the PAI resin was cured, was produced by heating and pressing at a temperature of 290 ° C. and a surface pressure of 10 MPa for 2 hours. did.
[Ii] Sample piece b for comparison
A polyamide-imide resin solution (PA-744, Toray Dow Corning Co., Ltd.) dispersed with MoS ₂ particles, which is used to coat the piston skirt for the purpose of reducing friction in automobile engines, is made of SUS440C steel. After spray coating on the surface of the plate test piece, and air drying for about 1 hour as in the preparation of the resin composite material containing fine graphite particles described above, 2 under conditions of a temperature of 290 ° C. and a surface pressure of 10 MPa. A comparative sample piece b was produced by heat-pressing for a period of time.
[Iii] Comparative sample piece c
A polyamide-imide resin solution (RA-530, Taiho Kogyo Co., Ltd.) in which MoS ₂ particles are dispersed, which is used to coat a sliding rod bearing for the purpose of reducing friction of an automobile engine, was made of SUS440C steel. As with the production of the fine graphite particle-containing resin composite as described above, spray coating is applied to the surface of the plate test piece, and after air drying for about 1 hour, heating is performed for 2 hours under conditions of a temperature of 290 ° C. and a surface pressure of 10 MPa. The sample piece c for comparison was produced by pressing.

As test materials, six kinds of fine graphite particle-containing resin composite-coated sample pieces having a graphite ratio of 25 to 90% by mass, comparative exfoliated graphite particle-containing resin composite-coated sample pieces, and comparative sample pieces a to 11 for the ring-on-plate friction and wear test shown in FIG. 11 under lubricating conditions using gasoline engine oil (ILSAC GF-5 standard oil, viscosity grade: 0W-20, manufactured by Toyota Motor Corporation) as the lubricating oil. Carried out. As a counterpart material, a grooved cylindrical test piece made of SUJ-2 steel material which was quenched and tempered to Vickers hardness HV740 was used. Its surface roughness is 0.3 μm Rzjis, and the apparent contact area of the friction surface is 200 mm ² . As the test temperature, the temperature of the lubricating oil was adjusted to be constant at 80 ° C. Further, the sliding speed was kept constant at 100 mm / second, a load of 20 kgf was applied so that the surface pressure was about 1 MPa, and after holding for 120 minutes, the average value of the friction coefficient (μ) was read for 30 seconds immediately before the end of the test. .
The wear resistance was evaluated using the wear depth of the resin composite in the plate specimen after the test as an index. The wear depth was evaluated by the difference in height between the sliding portion and the non-sliding portion after the frictional wear test measured by a stylus type roughness meter.

FIG. 12 shows the evaluation results of the friction coefficient (μ) obtained in the friction wear test.
In the comparative sample piece a in which only PAI is applied without blending the graphite particles, the friction coefficient (μ) is about 0.095, and the conventional exfoliated graphite particles widely used are dispersed by 60% by mass. The friction coefficient (μ) of the exfoliated graphite particle-containing resin composite was about 0.105. That is, in this test condition where the engine oil is in a friction state, the effect of reducing μ by using conventional exfoliated graphite particles was not recognized.
On the other hand, in the 6 types of fine graphite particle-containing resin composites containing fine graphite particles dispersedly, the friction system number (μ) is small, and the friction reducing effect due to the highly oriented dispersion of fine graphite particles. Admitted. Among them, in the sample piece coated with a fine graphite particle-containing resin composite having a graphite ratio of 25% by mass, a piston skirt resin coating material or a bearing resin coating that has been conventionally used as a material exhibiting low friction characteristics is used. It is possible to obtain only μ less than or equal to that of the comparative sample pieces b and c. However, when the graphite ratio is more than 25% by mass, it is superior to the comparative sample pieces b and c assuming a conventional product. Low friction characteristics are appearing. Furthermore, when the graphite ratio was 53% by mass or more, particularly excellent low friction characteristics with μ of 0.02 or less were obtained.

Next, the amount of wear of each specimen after the friction test is shown in FIG.
The sample piece for comparison a, in which only PAI is applied without compounding graphite particles, is manufactured assuming conventional products (resin coating material for piston skirt and resin coating material for bearing) that are supposed to exhibit low friction characteristics. The wear depth is larger than the comparative sample pieces b and c. On the other hand, the fine graphite particle-containing resin composite-coated sample piece with a graphite ratio of 40% by mass or more has a wear depth less than or equal to that of the comparative sample pieces b and c, and can withstand application to actual engine parts. The excellent wear resistance obtained was obtained.

Furthermore, in order to compare the influence of the type of graphite particles, the graphite ratio is constant at 60% by mass, the sample composite-coated sample piece containing fine graphite particles, the sample resin-coated sample piece containing graphene nanoparticles, and exfoliated graphite particles The μ characteristics of the resin composite-coated sample pieces were evaluated by the same friction and wear test as described above. FIG. 14 shows the characteristics (μ characteristics) of the coefficient of friction (μ).
As shown in FIG. 14, in the fine graphite particle-containing resin composite-coated sample piece having a half-value half-width of 3.4 ° and the graphene nanoparticle-containing resin composite-coated sample piece having a half-value half width of 4.2 °, Compared with a sample piece coated with a exfoliated graphite particle-containing resin composite material in which general exfoliated graphite particles are dispersed, a better low μ characteristic was exhibited.

Further, the amount of wear after the friction test is shown in FIG.
The fine graphite particle-containing resin composite-coated sample piece and the graphene nanoparticle-containing resin composite-coated sample piece are both generalized exfoliated graphite particle-containing resin composite-coated sample pieces and PAI. As compared with the comparative sample piece a coated with, excellent wear resistance was exhibited. Here, the exfoliated graphite particle-containing resin composite material that has been generally used in the past has a larger amount of wear than the comparative sample piece a to which only the PAI resin is applied. This is probably because the particle size is as large as about 50 μm, and irregular particles fall off due to wear and intervene on the sliding surface, and the particles serve as an abrasive to promote wear. On the other hand, when specific graphite particles having an orientation such as fine graphite particles having an aspect ratio of about 50 or graphene nanoparticles having about 375 are used, the thickness is small in the sliding direction, and even if dropped, the abrasive action is achieved. It is possible that it has not occurred.

  As described above, regarding the graphite of the layered compound that has been widely used as a solid lubricant conventionally, the low-friction mechanism has been studied in detail, and the layer molecular plane of graphite (graphite plane), that is, c-plane (001 plane). By aligning the graphite particles so as to be parallel to or substantially parallel to the sliding direction, it has a particularly excellent low friction against conventional graphite materials called exfoliated graphite particles or flaky graphite. The knowledge that the characteristic was acquired was acquired. The present invention has been achieved based on such findings. In addition, when rubbing using graphite with layered molecules oriented parallel to the sliding direction, a part of the surface peels off and adheres to the surface of the other material, forming a graphite transfer layer. it can. As a result, even when the friction member rubs against an arbitrary mating friction member, the frictional state at the true contact portion is a sheared state between graphites. Only the small intermolecular force is dominant in the interaction force between the graphite c-planes, the shear resistance is extremely small, and a small friction coefficient can be expressed.

  When sliding in parallel to the graphite c surface where the interaction force between the layers is small, there is a concern that excessive wear is likely to occur due to delamination if a local high surface pressure shear force is applied under high load conditions. The In particular, by forming a layer using a coating solution in which graphite particles are dispersed in a matrix resin, both the graphite portion and the matrix resin exist on the surface of the formed graphite layer, and the sliding surface is graphite. It is conceivable that an excessive load applied to the graphite part is suppressed and excellent wear resistance is ensured by being composed of particles and matrix resin.

In the present invention, as described above, a resin layer is formed during coating by forming a graphite layer covering the substrate surface by applying a resin solution in which flaky graphite particles are dispersed to the substrate surface. Due to the flow of the solution, the c-plane of the graphite particles is easily oriented parallel or substantially parallel to the surface of the graphite layer, and the orientation of the graphite particles on the finally formed graphite surface can be enhanced.
In addition, the presence of both the graphite portion and the matrix resin on the graphite surface serving as the sliding surface enables the graphite to function as a transfer material to the counterpart material or a supply source of the solid lubricant. In the sliding surface, the graphite c surface on the surface of the graphite layer and the graphite c surface transferred to the surface of the counterpart material come into contact with each other, whereby the friction coefficient (μ) can be further reduced.

DESCRIPTION OF SYMBOLS 10 ... Piston 11 ... Top surface 13 of piston ... Skirt part 15, 21 ... Graphite layer (graphite surface)
17 ... Specific graphite particles (oriented graphite particles)
20 ... Connecting rod bearing

Claims (7)

A substrate;
Provided on at least a part of the sliding surface of the base material with the counterpart material, the matrix resin and the average particle diameter are 40 μm or less, and the aspect ratio, which is the ratio of the average particle diameter to the average thickness, is 20 or more. A graphite layer containing oriented graphite particles, wherein the content ratio of the oriented graphite particles to the total amount of the matrix resin and the oriented graphite particles is from 30% to 90% on a mass basis;
And a half-width at half maximum in a rocking curve at a graphite-2H002 diffraction position by X-ray diffraction measurement of the graphite layer is 5 ° or less.   The matrix resin contains a thermosetting resin, the average particle diameter of the oriented graphite particles is 1 to 20 μm, and the content ratio of the oriented graphite particles is 40% or more and 90% or less on a mass basis. Item 2. The sliding member according to Item 1.   The sliding member according to claim 1 or 2, wherein at least one of the matrix resins is a thermosetting polyamideimide.   The sliding member according to any one of claims 1 to 3, wherein the aspect ratio is 20 or more and 1500 or less.   The sliding member according to any one of claims 1 to 4, wherein a thickness of the graphite layer is 3 µm or more and 40 µm or less.   An engine piston having the graphite layer provided on at least a part of the skirt portion, a piston ring disposed on the piston and provided with the graphite layer on at least a part of the outer peripheral surface, and the graphite on at least a part of the outer peripheral surface A piston pin provided with a layer, or a sliding bearing structure having at least a shaft and a bush and at least a part of at least one of the shaft and the bush provided with the graphite layer. The sliding member according to any one of claims 1 to 5. A matrix resin is mixed with a dispersion in which oriented graphite particles having an average particle diameter of 40 m or less and an aspect ratio which is a ratio of an average particle diameter to an average thickness of 20 or more are dispersed in a solvent, and the matrix resin is mixed. And a preparation step of preparing a coating solution for forming a graphite layer in which the content ratio of the oriented graphite particles with respect to the total amount of the oriented graphite particles is 30% or more and 90% or less on a mass basis,
By applying the above-mentioned coating liquid for forming a graphite layer on the sliding surface of the substrate with the counterpart material, the oriented graphite particles are oriented in the matrix resin, and the graphite-2H 002 diffraction position by X-ray diffraction measurement A coating step of forming a graphite layer having a half width at half maximum in a rocking curve of 5 ° or less;
The manufacturing method of the sliding member which has these.