Abrasion-resistant composite material

Abstract

A friction-resistant composite material having (A) a polyimide substrate and (B) a coating layer comprising a binder resin and a solid lubricant.

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims the benefit of U.S. Provisional Patent Application No. 63 / 213,833, filed on June 23, 2021, the disclosure of which is hereby expressly incorporated by reference in its entirety.

[0002] The present invention relates to an antifriction composite material comprising a polyimide substrate and a coating layer having a binder resin and a solid lubricant.

Background Art

[0003] Low friction and low wear characteristics may be required for components used in the automotive or aerospace industries. For example, metal or ceramic materials can be coated with a polymer antifriction coating. Typically, an antifriction coating (AFC) contains a solid lubricant and a matrix resin and can form a coating layer on an article. The solid lubricant helps to provide a lower friction surface. Graphite, molybdenum disulfide, and fluoropolymer particles such as PTFE are known as solid lubricants. To explain the technical field related to the present invention in more detail, several patents and publications are cited herein. U.S. Patent Application Publication No. 20120106882A discloses a bushing having a friction - reducing layer cast onto the surface of the bushing. International Publication No. 2014 / 021477A pamphlet discloses a coating composition comprising a polyamide - imide binder resin, a solid lubricant, and a specific solvent.

[0004] To form a composite material by combining materials having antifriction properties, it is necessary to recognize the adhesion properties when creating these materials. By understanding the properties and adhesion problems of individual components and forming a new composite material, synergistic antifriction qualities can be provided.

[0005] It is not common to apply a polymer coating with lower thermal and mechanical properties to a polyimide member (with better thermal / mechanical properties) to produce a novel material with excellent anti-friction performance, but it is required in multiple industries.

SUMMARY OF THE INVENTION

MEANS FOR SOLVING THE PROBLEM

[0006] Materials and processes for composite materials of polyimide coated with a polymer coating having excellent anti-friction quality and durability are provided herein.

[0007] In one embodiment, the present invention relates to a composite material comprising (A) a polyimide substrate and (B) a coating layer containing a binder resin and a solid lubricant, wherein at least a part of the surface of the polyimide substrate is covered by the coating layer.

[0008] In another embodiment, the present invention relates to a process for preparing a composite material, comprising the steps of: (i) preparing a polyimide substrate; (ii) applying a coating composition containing a binder resin, a solid lubricant and a solvent to the polyimide substrate; and (iii) curing the coating composition.

[0009] In a further embodiment, the present invention relates to an article formed of the above composition.

[0010] In a further embodiment, the present invention relates to a sliding structure comprising a first member made of polyimide and a second member made of metal, wherein the first member and the second member are in contact with each other, and at least one of the surfaces of the two members is covered by a coating layer, and the coating layer comprises (A) a polyimide substrate and (B) a coating layer containing a binder resin and a solid lubricant.

MODE FOR CARRYING OUT THE INVENTION

[0011] (A) A polyimide substrate and (B) a coating layer containing a binder resin and a solid lubricant are disclosed herein.

[0012] (A) Polyimide substrate Polyimides are high-temperature engineering polymers that exhibit an excellent combination of thermal stability, mechanical toughness, and chemical resistance. They have excellent dielectric properties and inherently low coefficients of thermal expansion. They are formed from diamines or diisocyanates and dianhydrides. DuPont Vespel® products are very high durability polyimides with excellent heat resistance, low wear and / or low friction properties, strength, and impact resistance for use in demanding applications where custom parts or stock shapes are desired. These polyimides are used as the polyimide substrates of the present invention. The polyimide substrate can include additives such as solid lubricants, reinforcing fillers, or any other functional fillers to improve thermal, mechanical, electrical, and / or tribological properties. The polyimide substrate can be processed by a wide range of modalities such as injection molding or compression molding.

[0013] (B) Coating layer The coating layer contains (B-1) a binder resin and (B-2) a solid lubricant.

[0014] (B-1) Binder resin The binder resin acts as a binder to disperse the solid lubricant and optionally any other additional components in the coating layer. Any resin can be used. Examples of the binder resin include, but are not limited to, polyamideimide, epoxy, phenolic resin, polyurethane, polybutyl titanate, or blends of the above resins. Preferably, the binder resin is polyamideimide. Polyamideimide is an amorphous polymer, either thermosetting or thermoplastic, having excellent mechanical properties, heat resistance, and chemical resistance. Polyamideimide is widely used as a coating and is prepared from an N-methyl-2-pyrrolidone (NMP) solution of isocyanate and trimellitic anhydride (TMA). Polyamideimide exhibits a combination of properties from both polyamides and polyimides, such as high strength, good lubricity, melt processability, excellent high heat resistance, and broad chemical resistance.

[0015] (B-2) Solid lubricant The solid lubricant has a function of improving the friction of the coating layer. Examples of the solid lubricant include, but are not limited to, molybdenum disulfide, graphite, and fluororesins such as polytetrafluoroethylene (PTFE), tetrafluoroethylene perfluoroalkyl vinyl ether copolymer, and tetrafluoroethylene hexafluoripropymene copolymer, and combinations thereof. The average primary particle size of the solid lubricant is preferably 0.1 to 20 micrometers, particularly preferably 0.1 to 10 micrometers. The average primary particle size of the solid lubricant can be measured by observation using an electron microscope or by laser diffraction and scattering methods. The content of the solid lubricant in the coating layer is preferably 5 to 90% by weight, more preferably 15 to 50% by weight, based on the weight of the coating layer.

[0016] (B-3) Other additives The coating layer can further contain other additional components such as hard particles, ultraviolet absorbers, antioxidants, thermal polymerization inhibitors, and leveling agents. Examples of hard particles include, but are not limited to, tungsten disulfide, aluminum oxide, zinc oxide, and polymer particles such as polyethylene particles and polyamide particles. The average primary particle diameter of the solid particles is preferably 0.1 to 20 micrometers, and more preferably 0.1 to 10 micrometers. The average primary particle diameter of the solid particles can be measured by the same method as described above for the solid lubricant. When the coating layer contains a solid lubricant, the total content of the solid lubricant and the solid particles is in the range of 5 to 90% by weight based on the weight of the coating layer.

[0017] (C) Process for preparing the composite material The coating layer can be processed by applying a coating composition containing a binder resin, a solid lubricant, and a solvent onto the surface of the polyimide substrate. Since the binder resin and the solid lubricant have already been disclosed, their descriptions can be incorporated herein. The solvent is also used to disperse the solid lubricant and other additional components in the composition as well as to dissolve the binder resin. Examples of the solvent include, but are not limited to, N-methyl-2-pyrrolidone (NMP), N-ethylpyrrolidone (NEP), N,N-dimethylacetamide, N,N-dimethylformamide, and 1,3-dimethyl-2-imidazolidinone (DMI). A well-known supplier of polyamide-imide is DuPont, which uses the trade name Molykote®. Polyamide-imide antifriction coatings (PAI AFCs) are available under the trade name Molykote® from DuPont USA Inc.

[0018] The coating composition can be applied in a wide variety of forms to at least a part of the surface of the polyimide substrate. Examples of methods for applying the coating composition include, but are not limited to, dipping method, spin coating method, flow coating method, spraying method, bar coating method, gravure coating method, roll coating method, blade coating method, air knife coating method, etc. The thickness of the applied coating composition is not particularly limited, but preferably, the thickness is 5 to 25 micrometers. After applying the coating composition, the applied composition is dried to remove the solvent and, if necessary, further cured to form a stable coating layer.

[0019] In an exemplary process of applying the AFC layer to a polyimide substrate: The coating composition is applied to the substrate by an HVLP (high volume / low pressure) spray device using an orifice diameter of 0.8 to 1.5 mm and a pressure of 10 to 75 psi. Usually, the member is preheated before coating application and after solvent cleaning to remove all solvents and residual oil on the surface. The coating is generally applied to the substrate in a thin and uniform coating film to achieve the desired dry film thickness (usually 10 to 30 micrometers) required for a given application.

[0020] Drying / curing is a two-step process that removes most of the solvent by a low-temperature flash at a temperature of 80 °C or lower for 5 to 10 minutes. After this flash process, additional coating films can be applied to the member to achieve the target film thickness. Final heat curing is required and varies slightly based on the resin chemistry of each coating, but generally speaking, the typical curing profile for these coatings applied to a polyimide substrate is 230 °C for 60 minutes.

[0021] (D) Article The article of the present invention contains polyimide, and at least a part of the surface of the article is covered with an anti-friction coating containing the binder resin and solid lubricant already disclosed. Examples of such articles include bearings, bushings, thrust washers, bumpers, wear pads, wear strips, tube clamps, bearings, insulators, valve seats, seals, and shrouds. The articles of the present invention can be used in the aerospace industry and transportation industries such as automobiles.

[0022] (E) Sliding structure In another embodiment of the present invention, the coating composition can generally be applied to a "counter" surface, typically made of metal, in a system including the present invention in the automotive and aerospace industries. Therefore, another embodiment of the present invention is a sliding structure including a first member made of polyimide and a second member made of metal, wherein the first member and the second member are in contact with each other, and at least one surface of the two members is covered with a coating layer, and the coating layer is a sliding structure including (A) a polyimide substrate and (B) a coating layer containing a binder resin and a solid lubricant.

[0023] Adhesiveness The adhesion mechanism between these two materials is mainly mechanical. The larger the exposed surface area, the more adhesion sites where the PAI resin binds to the polyimide. This is mainly due to the manufacturing method of compression molding and the micropores inherent in polyimide that can enable a higher surface area contact rate. It is important to evaporate all the solvents trapped in the micropores before coating, otherwise it may cause swelling on the coating surface. This is achieved by preheating the polyimide member until it exceeds the flash point of the solvent used for degreasing or up to the higher of exceeding 100°C to remove any residual moisture. After curing, the member can be cooled to ambient temperature before handling. The curing temperature of the PAI coating is based on the adhesion test results by the cross-cut tape peel test, pencil hardness test, and water jet pressure test.

Examples

[0024] Material Polyimide substrate (SP21): Vespel® SP21 supplied by DuPont was used. DuPont™ Vespel® SP-21 is graphite-reinforced, low-friction, and is used in a variety of applications with or without lubrication. Vespel® SP-21 has the highest physical strength, elongation, and toughness. Available as custom parts or stock shapes.

[0025] The formulation of the coating composition used in the examples is shown in Table 1.

[0026] [Table 1]

[0027] Coating method The coating compositions A to D in Table 1 were spray-coated on a PI substrate or a metal counter article to a thickness of 20 + / - 2 micrometers. Next, the substrate / metal counter article was placed in an oven and the PI substrate / metal counter article was heated at 80°C for 10 minutes. Thereafter, the composition was cured at 220°C for 60 minutes. Next, the volume loss and coefficient of friction (COF) were evaluated.

[0028] Examples 1 to 3 Friction and wear tests were conducted using a thrust washer setup in accordance with ASTM D3702. The samples were tested against 6061 aluminum at a pressure of 1.75 MPa and a speed of 0.7 m / s for 24 hours. The wear of the coated PI substrate was measured by the change in the height of the sample, and the volume lost during the test was calculated. The smaller the volume loss, the lower the wear.

[0029] When coated with coating composition A, the volume loss of the coated SP21 improved from 46.1 mm 3 to 30.1 mm 3 When coated with coating composition B, the SP21 had a volume loss of 29.5 mm 3had volume loss.

[0030]

Table 2

[0031] Examples 4 - 6 Friction and wear tests were conducted using a thrust washer setup according to ASTM D3702. The samples were tested for 24 hours at a pressure of 1.75 MPa and a speed of 0.7 m / s against 7075 aluminum. The wear of the coated polymer washers was measured by the change in the height of the samples, and the volume lost during the test was calculated. The smaller the volume loss, the lower the wear. Uncoated SP21 could not complete the 24 - hour test due to severe wear: both Coating Compositions A and B were able to run the test until completion.

[0032] When the aluminum surface was coated with Coating Composition A, the volume loss of SP21 improved from 145.8 mm 3 at 8 hours to 5.14 mm 3 at 24 hours. SP21 coated with Coating Composition B had a volume loss of 0.27 mm 3 at 24 hours.

[0033]

Table 3

[0034] Examples 7 - 11 Friction and wear tests were conducted using a block - on - ring tester according to ASTM G137. The samples were tested for 24 hours at a pressure of 1.29 MPa and a speed of 0.68 m / s against a 7075 aluminum ring. The wear of the polymer blocks was measured by the change in the height of the samples, and the volume lost during the test was calculated. The smaller the volume loss, the lower the wear.

[0035] When the aluminum ring was coated with coating compositions A to D, the volume loss of SP21 and the wear of the aluminum ring were significantly improved as shown in Table 4.

[0036]

Table 4

Claims

1. (A) a polyimide substrate, and (B) a coating layer comprising 55 to 77% by weight of a binder resin containing polyamideimide and 23 to 45% by weight of a solid lubricant containing molybdenum disulfide, graphite or a mixture thereof, based on the weight of the coating layer A method for preparing a composite material, comprising: at least a part of the surface of the polyimide substrate is covered with the coating layer, the method comprising: (i) a step of preparing a polyimide substrate (ii) a step of applying a coating composition containing a binder resin, a solid lubricant and a solvent to the polyimide substrate, and (iii) a step of curing the coating composition A method comprising the steps of.

2. The method according to claim 1, wherein the coating layer further comprises hard particles.

3. The method according to claim 1, wherein the thickness of the coating layer is 5 to 100 micrometers.

4. The method according to claim 1, wherein the solvent is selected from N-methyl-2-pyrrolidone, N-ethylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, and 1,3-dimethyl-2-imidazolidinone.

5. The method according to claim 1, wherein the coating composition is applied to the polyimide substrate by spray coating.

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