JPH0562916B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Industrial Application] The present invention relates to a polyimide friction material that has excellent heat resistance, wear resistance, and mechanical properties, and has a moderately high coefficient of friction that is stable against temperature changes. The polyimide friction material of the present invention is widely used as a forming material for parts in all fields, such as automobiles, office equipment, electrical and electronic equipment, aerospace equipment, automatic labor-saving equipment, and general industrial equipment. It is particularly suitable for use as a sliding material for clutches or brakes in automobiles, machine tools, etc. [Prior art and its problems] Conventionally, compositions made of synthetic resins such as phenolic resins and melamine resins as a binder and mineral fibers such as asbestos fibers as fillers have been used as friction materials for brakes, clutches, etc. However, friction materials made of such compositions are susceptible to the effects of thermal deterioration components of the resin transferred to the other surface during braking at high speeds and high loads, especially during braking at high temperatures. This has the disadvantage of lowering the friction coefficient and reducing braking performance. For example, a friction material made of the above-mentioned composition containing a phenolic resin exhibits a significant decrease in the coefficient of friction at high temperatures of 150 to 200°C. In addition, asbestos fibers blended as a filler are undesirable because they may scatter around the friction material as it wears out and have an adverse effect on ligaments. In order to eliminate the drawbacks of friction materials made of the above compositions, aromatic polyimide resin is used as a binder to increase heat resistance, and various inorganic fillers (potassium titanate whiskers, mineral fibers, asbestos, iron Friction materials containing one to three components selected from powder, talc, calcium carbonate, and silica sand are known (Japanese Patent Application Laid-open No. 144363/1983). Also,
In consideration of the effects of asbestos fibers on the human body, a friction material is known in which polyimide resin is blended with potassium titanate fibers and/or processed mineral fibers and iron powder (Japanese Patent Laid-Open No. 59-207980). Brake slide materials made from these friction materials have excellent wear resistance under high speeds and high loads, but the stability of braking against changes in temperature of the friction slide surface due to sliding time or temperature changes in the atmosphere may be affected. That is, the stability of the friction coefficient was not necessarily satisfactory. In addition, in order to increase mechanical strength such as bending strength and impact strength, abrasion resistance, and limit PV value (P = friction surface pressure, V = friction velocity), glass fiber, asbestos fiber, potassium titanate fiber Friction materials containing inorganic fibers such as processed mineral fibers and heat-resistant organic fibers such as aromatic amide fibers and aromatic polyester fibers are known as binders, but those containing glass fibers are known. , the damage to the mating material is significant, and those containing asbestos fibers, potassium titanate fibers, processed mineral fibers, etc. cause relatively less damage to the mating material compared to glass fiber, but as the blending ratio increases, it cannot be ignored. In addition, those containing heat-resistant organic fibers do not damage the mating material and are excellent in this respect, but have poor mechanical workability and the processed surface is rough, resulting in poor surface smoothness.
This adversely affects not only the dimensional accuracy of the device component but also the change in friction coefficient over time. [Means for Solving the Problems] As a result of various studies aimed at solving the problems, the present inventors have added fluororesin powder and specific transition metals to aromatic polyimide resin powder. By heating and compression molding a polyimide composition made by adding specific amounts of powder and/or oxide powder of the transition metal, it has excellent heat resistance and abrasion resistance, and is resistant to temperature changes on the sliding surface. It has been found that a friction material can be obtained which has a stable friction coefficient and hardly damages the mating material. The present invention was made based on the above findings, and
To 100 parts by weight of aromatic polyimide resin powder, add 5 to 30 parts by weight of fluororesin powder and 1 to 30 parts by weight of transition metal powder having an unpaired electron in the d orbital and/or oxide powder of the transition metal. The present invention provides a polyimide-based friction material obtained by heating and compression molding a polyimide-based composition. The polyimide friction material of the present invention will be described in detail below. The aromatic polyimide resin powder constituting the polyimide composition used in the present invention undergoes polymerization and imidization from a tetracarboxylic acid component such as an aromatic tetracarboxylic acid or its dianhydride, and an aromatic diamine component. It may be any powder made of the heat-resistant aromatic polyimide polymer obtained in this way, or it may be a mixed powder of two or more thereof. As the aromatic tetracarboxylic acid component,
Pyromellitic acid, 3,3',4,4'-biphenyltetracarboxylic acid, 2,3,3',4'-biphenyltetracarboxylic acid, 3,3',4,4'-benzophenonetetracarboxylic acid acid, bis(3,4-dicarboxyphenyl) ether, bis(3,4-dicarboxyphenyl) thioether, bis(3,4-dicarboxyphenyl)methane, 2,2-bis(3,4 -dicarboxyphenyl)propane, dianhydrides of these acids, or mixtures of the above-mentioned compounds. In particular, in the present invention, biphenyltetracarboxylic acids are mainly used. Ingredients (containing approximately 50 mol% or more, especially
It is preferable to use a tetracarboxylic acid component having a content of 70 mol % or more in terms of the moldability of the resulting aromatic polyimide resin powder and the physical properties of the molded product. As the aromatic diamine component, 4,4'-
Diaminodiphenyl ether, 4,4'-diaminodiphenyl thioether, 4,4'-diaminodiphenylmethane, 4,4'-diaminobenzophenone, o-, m- or p-phenylenediamine, etc.
Alternatively, in the present invention, 4,4'-diaminodiphenyl ether is used as the main component (for example, containing about 40 mol% or more, particularly 50 mol% or more, more preferably containing 4,4'-diaminodiphenyl ether).
It is preferable to use an aromatic diamine component (containing 70 mol% or more). The above-mentioned aromatic polyimide resin powder is not particularly limited in its manufacturing method, and for example, the above-mentioned tetracarboxylic acid component and aromatic diamine component are used in approximately equal moles to form a highly concentrated polyimide resin powder in an organic polar solvent. Either polymerize and imidize at a polymerization temperature and precipitate as a high molecular weight aromatic polyimide resin powder, or
Alternatively, both of the above components are polymerized in an organic polar solvent at a relatively low temperature to produce a high molecular weight aromatic polyamic acid, and a polyamic acid-insoluble solvent is added to the polymerization solution to precipitate aromatic polyamic acid powder. Then, the powder is heated and imidized (imide cyclization by dehydration reaction of the acid-amide bond of polyamic acid) to produce an aromatic polyimide resin powder. The aromatic polyimide resin powder is not one in which low molecular weight substances react to form a three-dimensional network structure like phenolic resin or thermosetting polyimide resin, but it is a linear high molecular weight substance, so it is difficult to machine the molded body. The target strength is high. However, most aromatic polyimide resin powders are non-melt moldable.
During molding, the mechanical strength is determined by the adhesion strength between powder particles. Therefore, if the average particle size of the aromatic polyimide resin powder is too large, when molded, the adhesion (partial welding) between the particles of the powder will be insufficient, resulting in poor wear resistance and bending of the molded product. This is not appropriate as mechanical strength such as strength will be reduced. Therefore, the aromatic polyimide resin powder has an average particle size of about 40 μm or less, preferably 30 μm or less, more preferably 20 μm or less, and about 0.1 to 20 μm.
It is preferable that about 80% by weight or more of the particles have a particle size of 50 μm. In addition, the fluororesin powder constituting the polyimide composition used in the present invention includes a tetrafluoroethylene homopolymer, a copolymer of tetrafluoroethylene and hexafluoropropylene, and a copolymer of tetrafluoroethylene and hexafluoropropylene. Examples include copolymers with other monomers, and among them, tetrafluoroethylene copolymers containing at least 75% by weight or more, preferably 90% by weight or more of tetrafluoroethylene, especially tetrafluoroethylene Ethylene homopolymers are preferred. In the above-mentioned tetrafluoroethylene copolymer, the monomer other than tetrafluoroethylene is selected from the group consisting of ethylene, propylene, hexafluoropropylene, polyfluoroalkyl vinyl ether, and chlorotrifluoroethylene. Preferably, one or more types of monomers are used. The average particle size of the fluororesin powder is 40 μm.
or less, preferably 30 μm or less, more preferably
It is preferable that about 80% by weight or more of particles having a particle size of 20 μm or less and 1 to 50 μm are contained. If the average particle diameter of the fluororesin powder is too large, wear resistance will deteriorate. Further, the transition metal powder and transition metal oxide powder constituting the polyimide composition used in the present invention are transition metals having an unpaired electron in the d orbital, and are preferably metals that easily chemically adsorb oxygen. and powders of oxides of transition metals, which have a high coefficient of friction when sliding against themselves or a friction material's mating material (metal, ceramic, etc.), and can cause damage to each other or the mating material due to frictional heat, etc. A material that does not easily form large transferred particles with the material is suitable for obtaining a high and stable coefficient of friction. Specifically, the transition metal powders include powders of metals such as titanium, chromium, manganese, iron, cobalt, nickel, molybdenum, and tungsten, and the transition metal oxide powders include powders of metals such as titanium, chromium, manganese, iron, cobalt, nickel, molybdenum, and tungsten. Metal oxides, especially TiO ₂ , Cr _2
O3 , _{MnO2 , Fe2O3} , CoO, NiO, _MoO2 , _WO2
Suitable examples include stable oxide powders such as . The transition metal powder and transition metal oxide powder have an average particle size of 40 μm or less, preferably
20 μm or less, more preferably about 10 μm or less,
In addition, it is preferable that about 80% by weight or more of particles having a particle size of 0.1 to 40 μm are contained. If the average particle size of these powders is too large, the proportion of the powders present on the friction surface of the friction material decreases, resulting in a decrease in the coefficient of friction.
Further, the particle shape of these powders is not particularly limited, and may be any shape such as a lump, a rod, or a spherical shape. The polyimide friction material of the present invention comprises 100 parts by weight of the aromatic polyimide resin powder, 5 to 30 parts by weight, preferably 5 to 25 parts by weight, of the fluororesin powder, and the transition metal powder and/or the transition metal oxide. 1 to 30 parts by weight, preferably 2 to 25 parts by weight of powder,
Conventionally known methods such as Henschel mixer,
Dry mixing using a mixer such as a ball mixer or tumbler mixer, or wet mixing in the presence of water or an organic solvent using the above mixer, followed by deaeration under reduced pressure and/or deaeration by heating to remove the solvent. A polyimide composition obtained by mixing by a method such as a method of removing the polyimide is molded into a linear, rod-like, plate-like, sheet-like, or other arbitrary shape using a compression molding machine or the like under heating and pressure. It is molded into. If the amount of the fluororesin powder added is less than 5 parts by weight, it will not be effective in suppressing an increase in the coefficient of friction when the temperature of the friction surface is relatively low, and if it exceeds 30 parts by weight, the friction for braking will be The friction coefficient of the material becomes too low and the mechanical strength deteriorates. Further, if the amount of the transition metal powder and/or the transition metal oxide powder added is less than 1 part by weight, there is no effect of suppressing the decrease in the coefficient of friction when the ambient temperature or the temperature of the friction surface is high, and the resistance is low. Abrasion resistance worsens,
Moreover, if it exceeds 30 parts by weight, mechanical strength and abrasion resistance will deteriorate. The heating and compression molding of the polyimide composition is
For example, when a ram extrusion molding machine is used as a compression molding machine, the temperature is 250°C or higher, preferably 300°C or higher.
Filling the mold with the polyimide composition at a molding temperature of 500°C, and using a ram at 100 to 1500 kg/cm ² ,
Preferably 150 to 1000Kg/cm ² , particularly preferably 150
Extrusion (pushing/compression) of the polyimide composition into a mold under a pressure of ~700Kg/cm ² is performed alternately, and while the polyimide composition is heated and adhered in the mold, a long piece is formed. This can be done by gradually extruding the molded body. In addition, the polyimide composition used in the present invention may be used as long as it does not adversely affect the properties of the polyimide friction material of the present invention, such as heat resistance, wear resistance, moderately high friction coefficient, and stability. , various organic or inorganic fillers can be added as appropriate. Specific examples of such fillers include glass fibers, carbon fibers, graphite fibers, wollastonite, potassium titanate whiskers, silicone carbide whiskers, sapphire whiskers, and heat-resistant inorganic monomers such as copper wires, steel wires, and stainless steel wires. Single fiber: Heat-resistant inorganic composite fibers such as so-called boron fibers or silicon carbide fibers made by depositing boron or silicon carbide on tungsten cord or carbon fibers; Heat-resistant organic fibers such as aromatic amide fibers; Glass beads, silica balloons , diatomaceous earth, asbestos, calcium carbonate, and other inorganic powders for improving heat insulation; graphite, carbon, mica, talc, and other inorganic powders for lubricity adjustment; and carbon black and other inorganic powders for coloring. . [Function] The polyimide friction material of the present invention is produced by heating and heating a polyimide composition obtained by adding fluororesin powder, transition metal powder and/or transition metal oxide powder to aromatic polyimide resin powder. It is obtained by compression molding, and it is possible to obtain a stable coefficient of friction against temperature changes on the friction surface, which fluctuates depending on the atmospheric temperature during friction and the friction distance (time). In polyimide friction materials, the fluororesin component mainly suppresses the increase in the coefficient of friction that occurs when the friction distance is short to medium, that is, when the temperature of the friction surface is relatively low, and the fluororesin component also suppresses the increase in the coefficient of friction that occurs when the friction distance is short to medium, that is, when the temperature of the friction surface is relatively low. The metal oxide component suppresses a decrease in the coefficient of friction that occurs mainly when the ambient temperature is high or when the friction distance is long, that is, when the temperature of the friction surface is high, and improves wear resistance. [Example] Examples of the present invention are listed below along with comparative examples,
The present invention will be explained in more detail, but the present invention is not limited to these examples. Examples 1 to 10 After dry mixing each raw material in a small Henschel mixer according to the compounding ratio shown in Table 1 below, this was compression molded under conditions of 320 to 370°C and 800 to 1500 Kg/cm ² to form a molded product. (Polyimide friction material of the present invention) was obtained. The friction coefficient and wear coefficient of the obtained molded body were measured according to the measurement method described below. The results are shown in Table 1 below. [Measurement method] Friction coefficient: Using a thrust type friction/wear tester that can heat the mating material, load 2.0Kg/cm ² and sliding speed 150/min.
m, mating material S45C steel, no lubrication, under conditions of continuous operation, when the sliding time (test time) is 15 minutes, the friction coefficient when the mating material is not heated (room temperature), and the sliding time is 120
At the time of the minute, the friction coefficient was determined when the mating material was not heated (room temperature) and when it was heated (150°C). Wear coefficient Using the same testing machine as for measuring the friction coefficient, load
3.9Kg/cm ² , sliding speed 128m/min, mating material S45C
Determined from the results of a wear test on steel, no lubrication, test time of 100 hours (continuous operation), and when the mating material was not heated (room temperature). Furthermore, the radial crushing strength of the molded bodies obtained in Examples 1 and 2 was further measured according to the following measurement method, and the radial crushing strength of the molded body obtained in Example 1 was 9.5 kg/mm ² . The radial crushing strength of the molded article obtained in Example 2 was 7.2 Kg/mm ² . A test piece (inner diameter
A radial crushing strength (JIS Z 2507, unit: Kg/mm ² ) of the test piece was determined. Comparative Examples 1 to 10 As shown in Table 2 below, in Comparative Example 1, no tetrafluoroethylene resin powder and metal powder and/or metal oxide powder were blended, and in Comparative Example 2, metal powder and/or metal oxide powder was not blended. Does not contain oxide powder,
In Comparative Example 3, no tetrafluoroethylene resin powder was blended, in Comparative Example 4, 35 parts by weight of tetrafluoroethylene resin powder was blended, and in Comparative Example 5, 35 parts by weight of tungsten powder was blended as transition metal powder. However, in Comparative Examples 6 to 10, metals and metal oxides outside the scope of the present invention, such as tin powder (Comparative Example 6), lead powder (Comparative Example 7), cadmium oxide powder (Comparative Example 8), and magnesium oxide were used. Powder (Comparative Example 9)
Molded bodies were obtained in exactly the same manner as in Examples 1 to 10, except that 3 and antimony trioxide powder (Comparative Example 10) were blended, and their physical properties were measured. The results are shown in Table 2 below. Notes 1 to 4 in Tables 1 and 2 below are as follows. Note 1: Use aromatic polyimide resin powder obtained by polymerizing and imidizing 3,3',4,4'-biphenyltetracarboxylic dianhydride and 4,4'-diaminodiphenyl ether. Note 2: Uses KTL600 manufactured by Kitamurasha. Note 3: Uses Teflon 7J manufactured by Mitsui Dupont Fluorochemicals. Note 4: Metal oxide solid solution manufactured by Mitsubishi Metals [components]
CoO, Cr ₂ O ₃ , Fe ₂ O ₃ , MnO ₂ ] was used.

【table】

〔Effect of the invention〕

The polyimide friction material of the present invention has excellent heat resistance, abrasion resistance, and mechanical properties, and has a moderately high coefficient of friction that is stable against temperature changes.For example, it is used for automobiles and office equipment. ,electricity·
It can be widely used as a forming material for parts in all fields such as electronic equipment, aerospace equipment, automatic labor-saving equipment, and general industrial machinery, especially as a sliding material for clutches and brakes in automobiles, machine tools, etc. It is suitably used as, etc.

Claims (1)

[Scope of Claims] 1 100 parts by weight of aromatic polyimide resin powder, 5 to 30 parts by weight of fluororesin powder, and a transition metal powder having an unpaired electron in the d orbital and/or an oxide powder of the transition metal 1 A polyimide-based friction material obtained by heating and compression molding a polyimide-based composition prepared by adding ~30 parts by weight. 2. Claim 1, wherein the transition metal powder is a powder of one or more metals selected from the group consisting of titanium, chromium, manganese, iron, cobalt, nickel, molybdenum, and tungsten.
Polyimide friction material described in Section 1. 3. The transition metal oxide powder is titanium oxide, chromium oxide, manganese oxide, iron oxide, cobalt oxide, nickel oxide, molybdenum oxide,
The polyimide friction material according to claim 1, which is a powder of one or more metal oxides selected from the group consisting of tungsten oxide and tungsten oxide. 4 Aromatic polyimide resin powder has an average particle size of 30μ
The polyimide friction material according to claim 1, which is a powder having a particle size of m or less. 5. The polyimide friction material according to claim 1, wherein the fluororesin powder is a powder with an average particle size of 30 μm or less. 6. The polyimide friction material according to claim 1, wherein the transition metal powder has an average particle size of 20 μm or less. 7. The polyimide friction material according to claim 1, wherein the transition metal oxide powder has an average particle size of 20 μm or less. 8 Aromatic polyimide resin powder contains biphenyltetracarboxylic acid as a main component (contains about 50 mol% or more)
The polyimide system according to claim 1, which is produced from a tetracarboxylic acid component, and an aromatic diamine component whose main component is 4,4'-diaminodiphenyl ether (containing about 50 mol% or more). Friction material.