Coating composition and dry lubricating film

Abstract

To provide a coating composition that imparts a dry lubricating film maintaining lubricity through an approach different from conventional methods, and to provide the dry lubricating film.SOLUTION: The present invention relates to a coating composition for forming a dry lubricating film, the coating composition comprising, as a binder, a resin having a tensile elongation at break of 30% or less as measured in accordance with JIS K7113:1995, wherein a solid lubricant is dispersed in the binder, and a content ratio (P / B) of the solid lubricant (P) relative to the binder (B) is 1.5 or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a coating composition for forming a dry lubricating coating, and to a dry lubricating coating. [Background technology]

[0002] Conventionally, dry lubricating coatings in which solid lubricants are dispersed in resin have been used to improve initial break-in and seizure resistance in office automation equipment, home appliances, automobiles, industrial machinery, etc. These dry lubricating coatings are formed by applying a composition containing a solid lubricant and a binder resin to the surface of a metal part, or the surface of a rubber or resin part, in an appropriate thickness, and then drying or heat-curing the composition to form a film (see, for example, Patent Documents 1 and 2).

[0003] As an example of its use, a dry lubricating coating is formed on the surface of automobile parts, specifically pistons, in order to improve sliding properties and wear resistance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6297795 [Patent Document 2] Patent No. 5483349 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional dry lubricating coatings have maintained their lubricity by, for example, using high-strength resins to impart wear resistance to the coating itself, but other methods for maintaining lubricity have not been fully explored.

[0006] The present invention has been proposed in view of the above-mentioned conventional circumstances, and has as its object to provide a coating composition that provides a dry lubricating coating that maintains lubricity by a method different from conventional methods, and to provide such a dry lubricating coating. [Means for solving the problem]

[0007] The present inventors conducted extensive research to solve the above-mentioned problems. As a result, they discovered that the above problems could be solved by using a resin with a predetermined tensile elongation at break as the binder component of a dry lubricating coating, which led to the completion of the present invention. Specifically, the present invention is as follows:

[0008] (1) The first aspect of the present invention is a coating composition for forming a dry lubricating coating, which contains a resin as a binder having a tensile elongation at break of 30% or less as measured in accordance with JIS K7113:1995, a solid lubricant dispersed in the binder, and a content ratio (P / B) of the solid lubricant (P) to the binder (B) of 1.5 or more.

[0009] (2) A second aspect of the present invention is the coating composition of the first aspect, wherein the resin is an alkyl acetalized polyvinyl alcohol resin.

[0010] (3) A third aspect of the present invention is the coating composition according to the first or second aspect, wherein the content of the resin is 10% by mass to 40% by mass based on the total solid content.

[0011] (4) A fourth aspect of the present invention is a coating composition according to any one of the first to third aspects, wherein the content of the solid lubricant is 60% by mass to 90% by mass based on the total solid content.

[0012] (5) A fifth aspect of the present invention is a coating composition according to any one of the first to fourth aspects, wherein the solid lubricant is one or more selected from the group consisting of molybdenum disulfide, polytetrafluoroethylene, graphite, and tungsten disulfide.

[0013] (6) A sixth aspect of the present invention is a dry lubricating coating formed on the surface of a member to form a sliding layer, the dry lubricating coating containing a resin as a binder having a tensile elongation at break of 30% or less as measured in accordance with JIS K7113, a solid lubricant contained in the binder, and a content ratio (P / B) of the solid lubricant (P) to the binder (B) of 1.5 or more. [Effects of the Invention]

[0014] According to the present invention, a dry lubricating coating that maintains lubricity can be formed by a method different from conventional methods. DETAILED DESCRIPTION OF THE INVENTION

[0015] Specific embodiments of the present invention (hereinafter referred to as "present embodiments") will be described in detail below. Note that the present invention is not limited to the following embodiments, and various modifications can be made without departing from the scope of the present invention.

[0016] 1. Coating composition for forming a dry lubricating coating The coating composition according to this embodiment is a coating composition for forming a dry lubricating coating. In particular, this coating composition is a coating composition for forming a dry lubricating coating that maintains lubricity by a method different from conventional methods.

[0017] Specifically, the coating composition according to this embodiment is characterized in that it contains a resin as a binder having a tensile elongation at break of 30% or less as measured in accordance with JIS K7113:1995, a solid lubricant is dispersed in the binder, and the content ratio (P / B) of the solid lubricant (P) to the binder (B) is 1.5 or more. The coating composition is composed of solid components (active ingredients) such as the binder resin and the solid lubricant dissolved in a solvent, which is a volatile component.

[0018] The reason why the dry lubricating coating formed by the coating composition according to this embodiment is able to maintain lubricity is believed to be as follows: Resins with a tensile elongation at break of 30% or less are prone to fracture rather than elastic deformation under shear, and when a dry lubricating coating containing such a resin is formed, wear debris is actively produced. The wear debris exerts its lubricity by repeatedly adsorbing and desorbing on the surface of the sliding member, so even if the coating wears, the effect of the wear debris allows the lubrication to be maintained.

[0019] <1-1. About the components> [Binder resin] The coating composition according to this embodiment contains, as a binder, a resin (hereinafter also referred to as "resin (A1)") having a tensile elongation at break of 30% or less as measured in accordance with JIS K7113:1995.

[0020] The tensile elongation at break of resin (A1) is preferably 25% or less, more preferably 20% or less. The lower limit of the tensile elongation at break of resin (A1) is not particularly limited, but is, for example, 1% or more, 3% or more, or 5% or more. In this specification, the tensile elongation at break of resin (A1) is a value measured in accordance with JIS K7113:1995 using a No. 1 test piece at a temperature of 23°C and a pulling rate of 1 mm / min.

[0021] Examples of resin (A1) include alkyl acetalized polyvinyl alcohol (polyvinyl acetal) resin, acrylic resin, nitrocellulose, etc. Among these, alkyl acetalized polyvinyl alcohol resin is preferred because it has good solubility in alcohols and water, can form a dry lubricating coating even on sliding members with low solvent resistance, and has a wide range of organic solvents available for dissolution.

[0022] Alkyl acetalized polyvinyl alcohol resins are synthesized by acetalization reaction of polyvinyl alcohol with an aldehyde. Examples of aldehydes include acetaldehyde (including paraacetaldehyde), propionaldehyde, glyoxal, butyraldehyde, n-octylaldehyde, amylaldehyde, hexylaldehyde, heptylaldehyde, 2-ethylhexylaldehyde, cyclohexylaldehyde, furfural, glutaraldehyde, benzaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, and β-phenylpropionaldehyde. Among these, butyraldehyde is preferred from the viewpoint of ease of production. That is, the alkylacetalized polyvinyl alcohol resin is preferably a polyvinyl butyral resin.

[0023] The glass transition temperature of the alkylacetalized polyvinyl alcohol is preferably 70° C. or lower.

[0024] Examples of commercially available alkyl acetalized polyvinyl alcohol resins include S-LEC (manufactured by Sekisui Chemical Co., Ltd.) such as S-LEC BH-3, S-LEC BX-6, S-LEC KS-1, S-LEC KS-10, and S-LEC KS-3.

[0025] The content of resin (A1) is not particularly limited and may be appropriately set from the viewpoint of the content ratio of the solid lubricant described below, but is preferably 10% by mass to 40% by mass, more preferably 15% by mass to 35% by mass, and even more preferably 20% by mass to 30% by mass, based on the total solid content (active ingredients) contained in the coating composition. Within the above range, lubricity is easily maintained.

[0026] The binder resin may contain other resins as long as the effects of the binder resin are not impaired. Examples of other resins include polyurethane resins, polyester resins, urea resins, acrylic resins, and phenolic resins. The content of resin (A1) in 100% by mass of the binder resin is preferably 70% by mass or more, more preferably 80% by mass or more, particularly preferably 90% by mass or more, and most preferably 95% by mass or more, and may be 100% by mass, in order to facilitate maintenance of lubricity.

[0027] [Solid lubricant] The coating composition according to this embodiment is composed of the above-mentioned binder resin and a solid lubricant dispersed therein. The binder resin and the solid lubricant constitute the main solid components (active ingredients) of the coating composition and the dry lubricating coating formed by applying the coating composition to a substrate (member).

[0028] The solid lubricant is not particularly limited, and examples thereof include molybdenum disulfide (MoS2), polytetrafluoroethylene (PTFE), graphite, tungsten disulfide (WS2), boron nitride (BN), graphene, etc. Among them, the use of a solid lubricant selected from molybdenum disulfide, polytetrafluoroethylene, graphite, and tungsten disulfide is particularly preferred because it exhibits superior low friction properties and excellent chemical stability. These solid lubricants may be used alone or in combination.

[0029] The content of the solid lubricant is not particularly limited, but is preferably 60% by mass to 90% by mass, more preferably 65% ​​by mass to 85% by mass, and even more preferably 70% by mass to 80% by mass, based on the total solid content of the coating composition. Within the above range, lubricity is easily maintained.

[0030] The content ratio (P / B) of the solid lubricant (P) to the binder resin (B) is preferably in the range of 1.5 to 8.0, more preferably in the range of 1.5 to 6.0, and even more preferably in the range of 2.0 to 5.0. The content ratio refers to the mass ratio between the binder resin (B) and the solid lubricant (P).

[0031] [solvent] As described above, the coating composition is formed by dissolving solid components, including the binder resin and solid lubricant, in a solvent. When the coating composition is applied to the surface of a substrate (member) and then subjected to a treatment such as baking, the solvent volatilizes, forming a dry lubricating coating made of the solid components.

[0032] The solvent is not particularly limited, and is preferably selected taking into consideration its dissolving power for the binder resin used, drying properties, etc. Specific examples include water; alcohols such as ethanol, 1-propanol, and isopropanol; acetone, N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, cyclopentanone, and propylene glycol monomethyl ether (PGM). Among these, solvents selected from water and alcohols are preferred, and alcohols are more preferred, because they enable the formation of a dry lubricating coating even on sliding members with low solvent resistance. One type of solvent may be used alone, or multiple types may be used in combination.

[0033] [Other additives] The coating composition may contain various additive components as needed. Specific examples of additives that can be used include fillers, anti-settling agents, wetting and dispersing agents, antifoaming agents, and surface conditioners. These components, together with binder resins and solid lubricants, are used as solid-liquid components (active ingredients).

[0034] <1-2. Method of manufacturing coating composition> The method for producing the coating composition for forming a dry lubricating coating according to this embodiment is not particularly limited, and it can be produced by a conventionally known method.

[0035] Specifically, the binder resin (containing resin (A1)), which is a solid component, a solid lubricant, and a solvent, which is a volatile component, are blended and kneaded in predetermined content ratios, and the resulting mixture can be produced.

[0036] At this time, it is important to make the solid lubricant uniformly dispersed in the binder resin that has been uniformly dissolved in the solvent. Therefore, for example, the solvent is charged into a stirring vessel, and then the binder resin and the solid lubricant, weighed to obtain a predetermined blend ratio, are charged and stirred with a stirrer such as a dissolver stirrer or a ball mill until these materials are uniformly dissolved. After that, it is preferable to carry out a dispersion treatment to uniformly disperse the solid lubricant in the binder resin using a disperser such as a sand mill or a three-roll type, depending on the concentration of the active ingredient, etc.

[0037] Although an example has been described in which the binder resin and the solid lubricant are put into the solvent and then kneaded and dispersed, the present invention is not limited to this, and the composition may be prepared by diluting the mixture by adding a solvent after the dispersion treatment.

[0038] 2. Formation of a dry lubricating film using a coating composition As described above, the coating composition according to this embodiment is for forming a dry lubricating coating, and the dry lubricating coating can be formed by applying this coating composition to the substrate (member) to be coated and then subjecting it to a curing treatment.

[0039] <2-1. Method for forming a dry lubricating film> (subject to be coated) Examples of the substrate include metal members, rubber members, resin members, etc., and a coating film can be formed by applying the coating composition to the surface of these members. Among these, members selected from rubber members and resin members are preferred, and resin members are more preferred.

[0040] (Application method) The method for applying the coating composition to the substrate is not particularly limited, and like general coatings, it can be carried out by techniques such as air spray coating, dipping coating, brush coating, tumbling by spraying, screen printing, etc. The selection of these coating methods can be appropriately determined depending on the shape of the substrate and the amount to be treated.

[0041] Prior to applying the coating composition to the substrate, the substrate may be subjected to a degreasing treatment, a surface treatment to improve the adhesion of the coating, or a cleaning treatment.

[0042] (thickness of dry lubricating film) There are no particular limitations on the thickness of the dry lubricating coating to be formed and it may be determined appropriately depending on the application of the object to be coated, but for example, a thickness of approximately 5 μm to 50 μm is preferred, and a thickness of approximately 10 μm to 15 μm is more preferred.

[0043] When applying the coating composition to the substrate, it is preferable to determine the amount of coating to be applied so that the dry coating obtained by curing the coating (dry lubricating coating composition) by heating or other means will have the desired film thickness (dry film thickness).

[0044] (hardening treatment) The curing treatment of the coating film formed by applying the coating composition to the substrate is not particularly limited, and can be carried out by a conventional coating drying method or baking method.

[0045] <2-2.Dry lubricant film> As described above, a dry lubricating coating can be formed by applying the coating composition to the surface of a substrate such as a resin member and curing it. Specifically, the dry lubricating coating formed by the coating composition according to this embodiment contains a resin as a binder having a tensile elongation at break of 30% or less as measured in accordance with JIS K7113:1995, and the binder contains a solid lubricant, with the content ratio (P / B) of the solid lubricant (P) to the binder (B) being 1.5 or more.

[0046] A dry lubricating coating formed on the surface of a member such as a resin member to be coated can constitute a sliding layer on that member. [Example]

[0047] EXAMPLES The present invention will be explained in more detail below by showing examples and comparative examples, but the present invention is not limited to these examples and comparative examples.

[0048] Examples and Comparative Examples A coating composition for forming a dry lubricating coating was prepared, and the resulting coating composition was applied to an object to be coated and cured to form a dry lubricating coating. The properties of the dry lubricating coating were evaluated by carrying out the following tests.

[0049] [Manufacture of coating composition for forming dry lubricating film] In Examples 1 to 4 and Comparative Examples 1 to 5, the ingredients were weighed and mixed to obtain the mass blending ratios shown in Table 1 below. A solvent (a mixed solvent of ethanol and 1-propanol) in which these active ingredients dissolve was added, and the mixture was kneaded using a Dispermat to prepare a coating composition. Furthermore, a dispersion treatment was carried out using a sand mill to uniformly disperse the solid lubricant in the coating composition. Each coating composition contained a dispersant as an additive.

[0050] [Formation of dry lubricating film (preparation of test pieces)] Next, a resin plate (polyacetal resin (POM), size 120 mm x 40 mm x 1 mm) was used as the substrate, and the resulting coating composition was applied uniformly to its surface by immersion. The resin plate with the coating film formed was then dried at 25°C for 60 minutes to form a dry lubricating coating. The thickness of the dry lubricating coating after drying was 15 μm.

[0051] <Evaluation test and evaluation results> [Lubricity (average friction coefficient)] The dynamic friction coefficient of the lubricating coating on the test piece was measured by the following friction and wear test. The measurement results are shown in Table 1 below. Equipment used: Friction player (manufactured by Rhesca Co., Ltd.) Measurement temperature: 25℃ Load: 2N Counterpart: 10mmφ SUJ-1 Ball

[0052] [Lubricity (durability time)] The friction and wear test for [lubricity (average friction coefficient)] was continued for 360 minutes, and the time until an abnormality occurred (when the dynamic friction coefficient value exceeded 0.3, it was considered that lubricity had been lost and an abnormality had occurred) was measured. The measurement results are shown in Table 1 below. "360 minutes" means that no abnormalities occurred during the friction and wear test.

[0053] [Amount of wear debris] After the friction and wear test (360 minutes) for [Lubricity (Durability Time)], the wear depth of the lubricating coating on the test piece was measured using the measuring equipment listed below, and the amount of wear debris was evaluated according to the following criteria. The results are shown in Table 1 below. The greater the wear depth of the lubricating coating, the greater the amount of wear debris generated. <Measuring equipment> Laser microscope (Keyence VK-X3000) <Standards> High: Wear depth of lubricating film is 10 μm or more Medium: Wear depth of lubricating film is over 5 μm and less than 10 μm Low: Wear depth of lubricating film is 5 μm or less

[0054] [Table 1]

[0055] Details of the binder resins and solid lubricants in Table 1 are as follows: Alkyl acetalized polyvinyl alcohol resin: S-LEC BL-1 manufactured by Sekisui Chemical Co., Ltd. (tensile elongation at break: 20%, Tg: 70°C) Polyolefin resin: Hardlen 13-LP (tensile elongation at break: 60%) manufactured by Toyobo MC Co., Ltd. Acrylic resin: DIC Corporation's Acrydic A-136-55 (tensile elongation at break: 50%) Nitrocellulose: RS1 / 2 manufactured by KCNC (tensile elongation at break: 40%) PTFE: KTL-2N manufactured by Kitamura Co., Ltd. Graphite: 2000M manufactured by Ito Graphite Industries Co., Ltd.

[0056] In Examples 1 to 4, which contained a resin with a tensile break elongation of 30% or less as a binder and had a P / B of 1.5 or more, the amount of wear debris was large and lubricity was maintained for a long time. On the other hand, in Comparative Examples 1 to 5, the amount of wear debris was small and lubricity was maintained for a short time. From these results, it is believed that the dry lubricating coating according to this embodiment maintains lubricity by actively generating wear debris.

Claims

1. A coating composition for forming a dry lubricating coating, comprising: The adhesive sheet contains, as a binder, a resin having a tensile elongation at break of 30% or less as measured in accordance with JIS K7113:1995, A solid lubricant is dispersed in the binder, a content ratio (P / B) of the solid lubricant (P) to the binder (B) is 1.5 or more; Paint composition.

2. 2. The coating composition of claim 1, wherein the resin is an alkyl acetalized polyvinyl alcohol resin.

3. The coating composition according to claim 1 or 2, wherein the content of the resin is 10% by mass to 40% by mass based on the total solid content.

4. 3. The coating composition according to claim 1, wherein the content of the solid lubricant is 60% by mass to 90% by mass based on the total solid content.

5. 3. The coating composition according to claim 1, wherein the solid lubricant is at least one selected from the group consisting of molybdenum disulfide, polytetrafluoroethylene, graphite, and tungsten disulfide.

6. A dry lubricating coating formed on the surface of a member to form a sliding layer, The adhesive sheet contains, as a binder, a resin having a tensile elongation at break of 30% or less as measured in accordance with JIS K7113, a solid lubricant is contained in the binder; a content ratio (P / B) of the solid lubricant (P) to the binder (B) is 1.5 or more; Dry lubricating film.

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