Friction material

Abstract

To provide a friction material having good abrasion resistance while maintaining high effective characteristics.SOLUTION: A friction material comprising: a friction modifier; a binder; and a fiber base material, wherein tin sulfide is contained as the friction modifier, and a phenol resin composition containing a novolac-type phenol resin, an epoxy resin, and a solid resol-type phenol resin, and a thermosetting resin are contained as the binder.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a friction material, and more particularly to a friction material used for brake pads, brake linings, clutch facings, etc. for industrial machinery, railway vehicles, freight cars, passenger cars, etc. [Background technology]

[0002] Friction materials are used in brakes such as disc brakes and drum brakes, or clutches, and perform braking by friction with mating materials such as disc rotors.

[0003] Friction materials are made up of raw materials such as a fibrous base material that acts as a reinforcement, a friction modifier that imparts friction and adjusts the friction performance, and a binder that binds these components together.

[0004] Various resin materials can be used as the binder. For example, Patent Document 1 describes a friction material containing 5 to 25 volume % of phenolic resin powder with an average particle size of 10 μm or less as the binder. Patent Document 2 describes a brake friction material containing 6.0 to 6.6 mass % of unmodified phenolic resin and 1 to 2 mass % of unvulcanized nitrile rubber powder as the binder.

[0005] On the other hand, from the viewpoint of manufacturing efficiency, shortening the thermoforming time is desired. For example, Patent Document 3 describes a method for manufacturing a friction material, which includes the steps of (a) mixing raw materials including a fibrous substance, a friction modifier, and a binder to obtain a raw material mixture, (b) adding a solid rubber at room temperature to a part of the raw material mixture to coat the raw material mixture, (c) further adding and mixing the remainder of the raw material mixture to obtain a friction material composition, and (d) pressure-molding the friction material composition at 0 to 100°C, in which the pressure-molding is performed in several seconds to several tens of seconds. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-097286 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-057693 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-075107 Summary of the Invention [Problem to be solved by the invention]

[0007] Friction materials are generally produced by mixing raw materials such as a fiber base material, a friction modifier, and a binder, thermoforming the mixture into a predetermined shape, and then heat treating and processing the mixture. The phenolic resins described in Patent Documents 1 and 2 require the resin to gel before hardening during thermoforming, which means that thermoforming takes time, leaving room for improvement.

[0008] Furthermore, in the manufacturing method described in Patent Document 3, pressure molding is carried out in a few seconds to a few tens of seconds, but since it is necessary to add rubber that is solid at room temperature to part of the raw material mixture, there is a concern that heat resistance may decrease.

[0009] An object of the present invention is to provide a friction material that has good wear resistance while maintaining high effectiveness characteristics. [Means for solving the problem]

[0010] As a result of extensive research, the inventors have found that the above-mentioned problems can be solved by using tin sulfide as a friction modifier and a specific phenolic resin composition described below in combination with a thermosetting resin as a binder.

[0011] That is, the present invention relates to the following friction material. A friction material comprising a friction modifier, a binder, and a fibrous base material, The friction modifier contains tin sulfide, The friction material contains, as the binder, a phenolic resin composition containing a novolac-type phenolic resin, an epoxy resin, and a solid resol-type phenolic resin, and a thermosetting resin. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a friction material that has good wear resistance while maintaining high effectiveness characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, the friction material according to the embodiment of the present invention will be described in detail.

[0014] A friction material according to an embodiment of the present invention is a friction material comprising a friction modifier, a binder, and a fibrous base material, wherein the friction modifier contains tin sulfide, and the binder contains a phenolic resin composition containing a novolac phenolic resin, an epoxy resin, and a solid resol phenolic resin, and a thermosetting resin.

[0015] <Friction adjustment material> Friction modifiers are used to impart desired friction characteristics, such as wear resistance, heat resistance, and fade resistance, to the friction material. Examples of friction modifiers include inorganic fillers, organic fillers, abrasives, solid lubricants, and metal powders.

[0016] (tin sulfide) The friction material according to the embodiment of the present invention contains tin sulfide as a friction modifier. By containing tin sulfide as a friction modifier, it is possible to achieve both high effectiveness and wear resistance of the friction material.

[0017] The content of tin sulfide is preferably 0.1 to 5 mass%, more preferably 0.5 to 4 mass%, and even more preferably 1 to 3 mass% of the entire friction material. If the content of tin sulfide is equal to or greater than the lower limit, the friction material will have sufficient wear resistance, which is preferable, while if the content is equal to or less than the upper limit, the friction material will have sufficient effectiveness, which is preferable.

[0018] (Friction modifiers other than tin sulfide) The friction material according to the embodiment of the present invention may further contain a friction modifier other than tin sulfide. Examples of the friction modifier that can be further contained are shown below.

[0019] Examples of inorganic fillers include titanates such as potassium titanate, lithium titanate, lithium potassium titanate, sodium titanate, calcium titanate, magnesium titanate, and magnesium potassium titanate, as well as inorganic materials such as barium sulfate, calcium carbonate, calcium hydroxide, vermiculite, and mica. These may be used alone or in combination of two or more.

[0020] The inorganic filler can be used in an amount of preferably 30 to 80 mass %, more preferably 40 to 70 mass %, based on the total mass of the friction material.

[0021] Examples of organic fillers include various rubber powders (raw rubber powder, tire powder, etc.), rubber dust, resin dust, cashew dust, tire tread, melamine dust, etc. These can be used alone or in combination of two or more.

[0022] The organic filler can be used in an amount of preferably 0.1 to 15 mass %, more preferably 0.3 to 10 mass %, based on the total amount of the friction material.

[0023] Examples of abrasives include zirconium oxide, alumina, silica, magnesium oxide, zirconia, zirconium silicate, chromium oxide, iron oxide (e.g., iron oxide (FeO)), chromite, etc. These can be used alone or in combination of two or more.

[0024] The abrasive material can be used in an amount of preferably 1 to 20 mass %, more preferably 3 to 18 mass %, based on the total mass of the friction material.

[0025] Examples of solid lubricants include graphite, coke, antimony trisulfide, molybdenum disulfide, polytetrafluoroethylene (PTFE), etc. These can be used either alone or in combination of two or more.

[0026] The solid lubricant can be used in an amount of preferably 1 to 25 mass %, more preferably 3 to 20 mass %, based on the total mass of the friction material.

[0027] Examples of metal powders include powders of aluminum, tin, zinc, etc. These can be used alone or in combination of two or more.

[0028] The metal powder can be used in an amount of preferably 1 to 10 mass %, more preferably 1 to 5 mass %, based on the total mass of the friction material.

[0029] The total content of the friction modifiers containing tin sulfide may be adjusted appropriately depending on the desired friction characteristics, and is preferably 60 to 90 mass % and more preferably 65 to 88 mass % of the total friction material.

[0030] <Fiber base material> The fibrous base material is used to reinforce the friction material. Examples of the fibrous substrate include organic fibers, inorganic fibers, metal fibers, etc. Each of the fibrous substrates may be used alone or in combination of two or more.

[0031] Examples of organic fibers include aromatic polyamide (aramid) fibers and flame-resistant acrylic fibers.

[0032] Examples of inorganic fibers include biosoluble inorganic fibers, ceramic fibers, glass fibers, carbon fibers, rock wool, etc. Examples of biosoluble inorganic fibers include biosoluble ceramic fibers such as SiO-CaO-MgO fibers, SiO-CaO-MgO-AlO fibers, and SiO-MgO-SrO fibers, and biosoluble rock wool.

[0033] The metal fibers include, for example, steel fibers, but it is preferable not to use copper fibers or bronze fibers containing copper.

[0034] From the viewpoint of ensuring the strength of the friction material, the content of the fibrous base material is preferably 3 to 30 mass %, more preferably 4 to 20 mass %, based on the entire friction material.

[0035] <Binding material> The binder is used to integrate the fibrous base material and the friction modifier contained in the friction material. The friction material according to an embodiment of the present invention contains a phenolic resin composition (hereinafter also referred to as a "specific phenolic resin composition") containing a novolac-type phenolic resin, an epoxy resin, and a solid resol-type phenolic resin, and a thermosetting resin as a binder. The specific phenolic resin composition has the advantage of a fast curing rate, which allows for a reduction in thermoforming time, but the heat resistance of the resulting friction material is insufficient. By using the specific phenolic resin composition in combination with a thermosetting resin, it is possible to reduce the thermoforming time and obtain a friction material with good wear characteristics. This is thought to be because the use of a thermosetting resin with excellent heat resistance in combination allows the friction material to be produced without impairing moldability.

[0036] The novolac phenolic resin used in the specific phenolic resin composition is usually obtained by reacting phenols and aldehydes in the presence of an acid catalyst such as hydrochloric acid or sulfuric acid at a reaction molar ratio (F / P) of phenols (P) to aldehydes (F) of 0.5 to 0.9.

[0037] The phenols are not particularly limited, but examples thereof include phenol, orthocresol, meta-cresol, para-cresol, xylenol, para-tertiary butylphenol, para-octylphenol, paraphenylphenol, bisphenol A, bisphenol F, and resorcinol. Phenol and cresol are typically used. Similarly, the aldehydes are not particularly limited, but examples thereof include aldehydes such as formaldehyde, acetaldehyde, butylaldehyde, and acrolein, or mixtures thereof. While sources of these aldehydes or solutions of these aldehydes can also be used, formaldehyde is typically used. The form of the novolac phenolic resin thus obtained is not particularly limited, and any form, such as liquid, solid, or powder, can be used.

[0038] The content of the novolac phenolic resin in the specific phenolic resin composition is not particularly limited, but is preferably 50 to 95 mass % of the total composition, and more preferably 60 to 90 mass %. If the content of the novolac phenolic resin is equal to or less than the upper limit, the composition will cure sufficiently, and if it is equal to or greater than the lower limit, the resin will not cure too quickly and the fluidity during thermoforming will not decrease, resulting in good mechanical strength of the friction material.

[0039] The epoxy resin used in the specific phenolic resin composition is not particularly limited, but may be any resin having at least two epoxy groups per molecule and being solid or liquid at room temperature, such as bisphenol A type, bisphenol S type, phenol novolac type, cresol novolac type, biphenyl type, naphthalene type, aromatic amine type, etc. These may be used alone or in combination.

[0040] The content of the epoxy resin in the specific phenolic resin composition is not particularly limited, but is preferably 1 to 50 mass % of the total composition, and more preferably 5 to 40 mass %. If the content of the epoxy resin is within this range, the resin component is sufficiently cured, and sufficient mechanical strength as a friction material is obtained.

[0041] The solid resol-type phenolic resin used in the specific phenolic resin composition is usually prepared by reacting phenols and aldehydes in the presence of an alkaline catalyst such as an alkali metal hydroxide, a tertiary amine, an alkaline earth metal oxide or hydroxide, or an alkaline substance, with the reaction molar ratio (F / P) of phenols (P) to aldehydes (F) being preferably 0.7 to 3.0, more preferably 0.9 to 1.8.

[0042] The phenols used herein are not particularly limited, but examples thereof include phenol, orthocresol, meta-cresol, para-cresol, xylenol, para-tertiary butylphenol, para-octylphenol, paraphenylphenol, bisphenol A, bisphenol F, and resorcinol, with phenol and cresol being commonly used. Similarly, the aldehydes are also not particularly limited, but examples thereof include aldehydes such as formaldehyde, acetaldehyde, butylaldehyde, and acrolein, or mixtures thereof. While substances that generate these aldehydes or solutions of these aldehydes can also be used, formaldehyde is commonly used. The resol-type phenolic resin obtained in this manner is used in a solid form.

[0043] The content of the solid resol-type phenolic resin in the specific phenolic resin composition is not particularly limited, but is preferably 1 to 50 mass % of the total composition, and more preferably 5 to 40 mass %. When the content of the solid resol-type phenolic resin is equal to or greater than the above lower limit, the composition is cured sufficiently, and when the content is equal to or less than the above upper limit, the resin does not cure too quickly, and the fluidity during thermoforming is unlikely to decrease, so the mechanical strength of the cured product is unlikely to decrease.

[0044] The total content of the novolac phenolic resin and the solid resole phenolic resin in the specific phenolic resin composition is not particularly limited, but is preferably 55 to 95 mass %, more preferably 57 to 80 mass %, and even more preferably 59 to 70 mass % of the total composition. When the total content of the novolac phenolic resin and the solid resole phenolic resin is equal to or greater than the lower limit, the composition is sufficiently cured. When the total content is equal to or less than the upper limit, the resin does not cure too quickly and the fluidity during thermoforming is not reduced, resulting in good mechanical strength of the friction material.

[0045] In an embodiment of the present invention, a specific phenolic resin composition can be produced by melt-kneading raw materials including a novolac phenolic resin, an epoxy resin, a curing catalyst, and a solid resol phenolic resin. Here, it is preferable to melt-knead at least the novolac phenolic resin and the epoxy resin and / or curing agent using a pressure kneader. Furthermore, it is more preferable to uniformly mix the novolac phenolic resin, the epoxy resin, the curing catalyst, and the solid resol phenolic resin in a melted and flowing state without substantially curing the phenolic resin and the epoxy resin. The appropriate mixing temperature is a temperature at which the phenolic resin and the epoxy resin melt but do not initiate curing. Furthermore, using a pressure kneader allows the phenolic resin, the epoxy resin, and the curing catalyst to be uniformly dispersed.

[0046] As the specific phenolic resin composition, for example, the phenolic resin composition described in JP-A-2008-222851 can be used.

[0047] The friction material according to the embodiment of the present invention contains a thermosetting resin as a binder. A thermosetting resin is a resin that has the property of going from a liquid state to a solid state when heat is applied. By including the specific phenolic resin composition and a thermosetting resin as a binder, the curing rate of the specific phenolic resin composition is increased, thereby shortening the time required for thermoforming the friction material, and the heat resistance of the thermosetting resin improves the wear resistance of the friction material. Examples of thermosetting resins include straight phenolic resins, various modified phenolic resins with elastomers, melamine resins, epoxy resins, polyimide resins, etc. Examples of elastomer-modified phenolic resins include various modified phenolic resins such as acrylic rubber-modified phenolic resins, silicone rubber-modified phenolic resins, and NBR rubber-modified phenolic resins. These thermosetting resins can be used alone or in combination of two or more.

[0048] The mass ratio of the specific phenolic resin composition to the thermosetting resin is preferably 3:1 to 1:1, and more preferably 2:1 to 1:1. When the mass ratio is equal to or greater than the lower limit, the resin cures at a sufficient rate, and when the mass ratio is equal to or less than the upper limit, the resin cures sufficiently, resulting in a friction material with excellent wear resistance even when produced in a short thermoforming time.

[0049] The content of the specific phenolic resin composition is preferably 1 to 10 mass %, more preferably 3 to 8 mass %, of the entire friction material. When the content of the specific phenolic resin composition is equal to or greater than the lower limit, the resin curing speed is sufficient, and when the content is equal to or less than the upper limit, moldability is good, resulting in a friction material with excellent wear resistance even when thermoformed in a short time.

[0050] The content of the thermosetting resin is preferably 1 to 7 mass %, more preferably 2 to 6 mass %, of the entire friction material. When the content of the thermosetting resin is equal to or greater than the lower limit, sufficient heat resistance is achieved, and when the content is equal to or less than the upper limit, stable friction characteristics can be achieved. As a result, a friction material with excellent wear resistance can be obtained even when produced in a short thermoforming time.

[0051] When the thermosetting resin is a straight phenolic resin, the total content of the phenolic resin contained in the specific phenolic resin composition is preferably 1 to 15 mass % based on the entire friction material.

[0052] The binder may contain other resins in addition to the specific phenolic resin composition and thermosetting resin described above.

[0053] In order to ensure sufficient mechanical strength and wear resistance, the content of the binder is preferably 1 to 20 mass % and more preferably 3 to 15 mass % based on the total friction material.

[0054] The friction material according to the embodiment of the present invention may contain other materials in addition to the fibrous base material, friction modifier, and binder, as required.

[0055] However, from the viewpoint of reducing the environmental impact, the friction material according to the embodiment of the present invention does not contain a copper component. "Containing no copper component" means that the friction material does not substantially contain a copper component, and does not exclude the unavoidable inclusion of a copper component. More specifically, this means that the copper content as an element is 0.5 mass% or less with respect to the entire friction material.

[0056] The friction material according to an embodiment of the present invention uses tin sulfide as a friction modifier and a specific phenolic resin composition and a thermosetting resin as a binder, thereby achieving both high effectiveness and good wear resistance.

[0057] The friction material of the present invention can be produced by known production processes, for example, by subjecting the friction material composition to preforming, thermoforming, heating, polishing, and other processes. A method for manufacturing a brake pad having a friction material generally includes the following steps. (a) A process in which a steel plate (pressure plate) is formed into a predetermined shape using a sheet metal press. (b) A process of degreasing, chemical conversion coating, and primer coating the pressure plate, and then applying an adhesive. (c) A process of blending a fiber base material, a friction modifier, a powder raw material such as a binder, and the like, and mixing the resulting homogenized friction material composition to form a preform at room temperature under a predetermined pressure. (d) A thermoforming process in which the preform and the pressure plate coated with adhesive are bonded together by applying a predetermined temperature and pressure (forming temperature: 130 to 180°C, forming pressure: 30 to 80 MPa, thermoforming time: 1 to 10 minutes). (e) After-curing (150-300°C, 1-5 hours) and final finishing process such as polishing, surface baking, painting, etc. Through these steps, the friction material according to the embodiment of the present invention can be manufactured. In particular, with regard to the heat-forming time in step (d), conventional friction materials preferably require 4 minutes or more, more preferably 5 minutes or more, whereas the friction material according to the embodiment of the present invention can be produced with heat-forming time of 3 minutes or less to obtain a friction material with excellent formability and wear resistance.

[0058] Based on the above, the present specification discloses the following friction material. [1] A friction material comprising a friction modifier, a binder, and a fibrous base material, The friction modifier contains tin sulfide, The friction material contains, as the binder, a phenolic resin composition containing a novolac-type phenolic resin, an epoxy resin, and a solid resol-type phenolic resin, and a thermosetting resin. [2] The friction material according to [1], wherein the content of the tin sulfide is 0.1 to 5 mass % based on the total mass of the friction material. [3] The friction material according to [1] or [2], wherein the content of the phenolic resin composition is 1 to 10 mass % based on the entire friction material. [4] The friction material according to any one of [1] to [3], wherein the content of the thermosetting resin is 1 to 7 mass % based on the entire friction material. [Example]

[0059] The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0060] <Production of friction materials> (Examples 1 to 3, Comparative Examples 1 and 2) The ingredients shown in Table 1 were placed in a mixer and mixed at room temperature for 4 minutes to obtain a friction material composition. The obtained friction material composition was then subjected to the following steps: (i) preforming, (ii) thermoforming, and (iii) heat treatment to produce brake pads equipped with the friction material. (i) Preforming The mixture was placed in a mold of a preforming press and molded at room temperature under 20 MPa for 10 seconds to prepare a preform. (ii) Thermoforming This preform was placed in a thermoforming mold, and a metal plate (pressure plate) to which an adhesive had been applied was placed on top of it, followed by heat and pressure molding at 150°C and 50 MPa for 2 minutes. (iii) Heat treatment This hot-pressed compact was heat-treated at 250° C. for 3 hours, and then the surface was polished. Next, the surface of this hot-pressed molded body was given a finish coating to obtain a friction material.

[0061] As the phenolic resin composition, a phenolic resin composition manufactured by Sumitomo Bakelite Co., Ltd. (a phenolic resin composition containing a total of 65 mass % of novolac type phenolic resin and solid resol type phenolic resin, and 35 mass % of epoxy resin) was used. As the thermosetting resin, a straight phenolic resin was used.

[0062] The obtained friction materials were evaluated for effectiveness and wear resistance according to the following methods and criteria.

[0063] <Initial efficacy characteristics> The initial effectiveness was evaluated as follows. The μ1 used for the evaluation of initial effectiveness was measured by cutting a test piece (20 mm × 30 mm) from the obtained friction material and testing it using a 1 / 7 scale tester in an AK-Master performance test in accordance with SAE J2522 at speeds of 40 km / h and 80 km / h and a deceleration of 2 m / s. 2 and 6 m / s 2 The coefficient of friction was calculated as the average (first effect) of the A (good): μ1 was 0.37 or more. B (poor): μ1 was less than 0.37.

[0064] <Fade characteristics> The evaluation of the fade characteristics was carried out as follows: The μ2 used for the evaluation of the fade characteristics was determined as the minimum value of the friction coefficient (instantaneous minimum friction coefficient) in the first fade test by cutting a test piece (20 mm × 30 mm) from the obtained friction material and using a 1 / 7 scale tester in the AK-Master performance test in accordance with SAE J2522. A (good): μ2 was 0.18 or more. B (poor): μ2 was less than 0.18.

[0065] <Wear resistance> The wear resistance was evaluated as follows: The pad wear amount used for the wear resistance evaluation was determined by cutting a test piece (20 mm × 30 mm) from the obtained friction material, measuring the pad thickness at four points using a 1 / 7 scale tester at the end of the AK-Master performance test in accordance with SAE J2522, and calculating the average wear amount. A (good): The average pad wear was less than 0.175 mm. B (bad): The average pad wear was 0.175 mm or more.

[0066] The results of each test are shown in Table 1.

[0067] [Table 1]

[0068] From the above results, it was found that the friction materials of Examples 1 to 3, which used tin sulfide as a friction modifier and a specific phenolic resin composition and a thermosetting resin as a binder, had good wear resistance while maintaining high effectiveness. On the other hand, it was found that the friction material of Comparative Example 1, which does not use tin sulfide as a friction modifier, and the friction material of Comparative Example 2, which does not use a specific phenolic resin composition and a thermosetting resin in combination as a binder, do not achieve at least one of maintaining high effectiveness characteristics and wear resistance. [Industrial Applicability]

[0069] The friction material of the present invention can be used for brake pads, brake linings, clutch facings, etc. for industrial machines, railway vehicles, freight cars, passenger cars, etc.

Claims

1. A friction material comprising a friction modifier, a binder, and a fibrous base material, The friction modifier contains tin sulfide, The friction material contains, as the binder, a phenolic resin composition containing a novolac-type phenolic resin, an epoxy resin, and a solid resol-type phenolic resin, and a thermosetting resin.

2. 2. The friction material according to claim 1, wherein the content of the tin sulfide is 0.1 to 5 mass % based on the total amount of the friction material.

3. 3. The friction material according to claim 1, wherein the content of the phenolic resin composition is 1 to 10% by mass based on the total mass of the friction material.

4. 3. The friction material according to claim 1, wherein the content of the thermosetting resin is 1 to 7 mass % based on the total mass of the friction material.

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