Friction material composition, friction material and friction member

Abstract

A friction material composition comprising a novolac-type phenolic resin and carboxymethyl cellulose or a salt thereof.

Description

Friction material composition, friction material, and friction member

[0001] This disclosure relates to friction material compositions, friction materials, and friction members.

[0002] Automobiles, railway vehicles, and various industrial machinery use friction materials such as disc brake pads and brake linings for braking. These friction materials perform their braking function by rubbing against opposing materials such as disc rotors and brake drums.

[0003] To provide a friction material composition that does not contain copper or has a low copper content and can exhibit excellent wear resistance during repeated high-speed braking, a friction member comprising a friction material and a backing metal is disclosed, wherein the friction material contains magnesium oxide and titanate, and does not contain copper, or if it does, the copper content is less than 0.5% by mass as copper element, and the maximum primary particle diameter of the magnesium oxide is 50 μm or more (see, for example, Patent Document 1). Furthermore, to provide a friction material composition that can obtain a friction material with excellent wear resistance and initial effectiveness without worsening aggressiveness to the mating material while having high strength in a so-called copper-free friction material, a friction material composition containing a friction modifier and a binder is disclosed, wherein the copper content in the friction material composition is 0.5% by mass or less in terms of copper element, and the fibrous base material contains regenerated cellulose fibers (see, for example, Patent Document 2).

[0004] Patent Document 1: Japanese Unexamined Patent Publication No. 2020-158568 Patent Document 2: Japanese Unexamined Patent Publication No. 2018-070833

[0005] On the other hand, regarding the use of fossil fuels, there are concerns about resource depletion and the carbon dioxide (CO2) released during incineration. ２ There are concerns about global warming due to the increase in CO2 emissions. Therefore, it is important to reduce the use of fossil fuels and reduce CO2 emissions from fossil fuels. ２From the perspective of reducing emissions, there is a growing movement to replace fossil resources with carbon-neutral biomass-derived materials (bioplastics) as alternative materials. This disclosure has been made in view of the above-mentioned conventional circumstances, and aims to provide a friction material composition that includes biomass-derived materials and can suppress the occurrence of fade phenomena, as well as a friction material and friction member using this friction material composition.

[0006] The specific means for achieving the above objectives are as follows: <1> A friction material composition comprising a novolac-type phenolic resin and carboxymethylcellulose or a salt thereof. <2> The friction material composition according to <1>, wherein the content of carboxymethylcellulose or a salt thereof in relation to the total amount of the friction material composition is 0.1% by mass to 8% by mass. <3> The friction material composition according to <1> or <2>, wherein the mass loss rate of carboxymethylcellulose or a salt thereof when heated at a heating rate of 10°C / min to 500°C is 30% by mass to 70% by mass. <4> The friction material composition according to any one of <1> to <3>, further comprising cellulose fibers, wherein the content of the cellulose fibers in relation to the total amount of the friction material composition is 1% by mass to 20% by mass. <5> The friction material composition according to any one of <1> to <4>, further comprising aramid fibers, wherein the content of the aramid fibers in relation to the total amount of the friction material composition is 0.5% by mass to 5% by mass. <6> A friction material formed using the friction material composition described in any one of <1> to <5>. <7> A friction member containing the friction material described in <6>.

[0007] According to this disclosure, it is possible to provide a friction material composition that includes biomass-derived materials and can suppress the occurrence of fade phenomena, as well as a friction material and friction member using this friction material composition.

[0008] The embodiments of this disclosure are described in detail below. However, this disclosure is not limited to the embodiments described below. In the embodiments described below, the components (including elemental steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit this disclosure.

[0009] In this disclosure, numerical ranges indicated using "~" include the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages in this disclosure, the upper or lower limit of one numerical range may be replaced by the upper or lower limit of another numerical range described in stages. Also, in numerical ranges described in this disclosure, the upper or lower limit of that numerical range may be replaced by the values ​​shown in the examples. In this disclosure, each component may contain multiple types of the corresponding substance. If multiple types of the substance corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple types of substances present in the composition, unless otherwise specified. In this disclosure, each particle corresponding to each component may contain multiple types of particles. If multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for the mixture of the multiple types of particles present in the composition, unless otherwise specified. In this disclosure, the term "layer" includes cases where, when observing the region in which the layer exists, it is formed not only over the entire region but also over only a portion of the region.

[0010] <Friction Material Composition> The friction material composition of this disclosure comprises a novolac-type phenolic resin and carboxymethylcellulose or a salt thereof (hereinafter sometimes referred to as a CMC compound). The friction material composition of this disclosure may also contain other components besides the above components.

[0011] CMC compounds are water-soluble polymers obtained from natural cellulose and are classified as biomass-derived materials. Therefore, CMC compounds are suitable as alternative materials to fossil resources. As a result of diligent research, the inventors discovered that using CMC compounds as a component of a friction material composition can suppress the occurrence of fade phenomena, thus completing the present invention.

[0012] (Bonding Agent) The friction material composition of this disclosure contains a novolac-type phenolic resin. The novolac-type phenolic resin can function as a binder that binds and integrates the components contained in the friction material composition, giving it a predetermined shape and strength. By using a novolac-type phenolic resin as a binder, it is possible to form a friction material that exhibits good heat resistance, moldability, and coefficient of friction. The friction material composition of this disclosure may also contain other binders besides the novolac-type phenolic resin. Examples of other binders include resol-type phenolic resins, epoxy resins, and polyimide resins. When binders other than the novolac-type phenolic resin are used in combination, the proportion of the novolac-type phenolic resin in the binder contained in the friction material composition is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more. The proportion of the novolac-type phenolic resin in the binder contained in the friction material composition may also be 100% by mass. The proportion of the novolac-type phenolic resin in the binder contained in the friction material composition is preferably 50% by mass to 100% by mass.

[0013] The binder content is preferably 4% to 20% by mass, more preferably 5% to 15% by mass, and even more preferably 6% to 10% by mass, based on the total amount of the friction material composition. By setting the binder content in the range of 4% to 20% by mass relative to the total amount of the friction material composition, the decrease in the strength of the friction material can be further suppressed.

[0014] (CMC Compounds) The friction material composition of this disclosure contains CMC compounds. The inclusion of CMC compounds in the friction material composition makes it possible to suppress the occurrence of fade phenomena. Examples of CMC compounds include carboxymethylcellulose, sodium carboxymethylcellulose, calcium carboxymethylcellulose, and ammonium carboxymethylcellulose. CMC compounds may be used individually or in combination of two or more.

[0015] The degree of etherification of the CMC compound is not particularly limited, but for example, 0.3 to 2.0 is preferred, 0.4 to 1.5 is more preferred, and 0.5 to 1.0 is even more preferred.

[0016] For the CMC compound, the mass loss rate when heated at a heating rate of 10°C / min to 500°C (hereinafter sometimes referred to as the 500°C thermal loss) is preferably 30% to 70% by mass, more preferably 32% to 60% by mass, and even more preferably 34% to 50% by mass. If the 500°C thermal loss of the CMC compound is 30% by mass or more, when forming a friction material using the friction material composition of this disclosure, an appropriate amount of voids are more easily generated in the friction material by the scorching treatment described later, and as a result, the occurrence of the fade phenomenon tends to be more easily suppressed. On the other hand, if the 500°C thermal loss of the CMC compound is 70% by mass or less, when forming a friction material using the friction material composition of this disclosure, the generation of excessive voids in the friction material by the scorching treatment described later tends to be suppressed, and the reduction in the strength of the friction material tends to be suppressed.

[0017] The 500°C thermal loss for CMC compounds is determined using a thermogravimetric analyzer, where 10 mg of the CMC compound is heated from 25°C at a heating rate of 10°C / min and the mass loss rate is calculated as the mass loss rate when it reaches 500°C. In cases where the friction material composition of this disclosure uses two or more CMC compounds in combination, the 500°C thermal loss for the CMC compounds refers to the value for the mixture of the two or more CMC compounds.

[0018] The CMC compound content is preferably 0.1% to 8% by mass, more preferably 1% to 7% by mass, and even more preferably 2% to 6% by mass, based on the total amount of the friction material composition. By setting the CMC compound content in the range of 0.1% to 8% by mass relative to the total amount of the friction material composition, the occurrence of fade phenomena can be further suppressed.

[0019] (Fiber base material) The friction material composition of this disclosure may contain a fiber base material. The fiber base material is included to provide a reinforcing effect in the friction material. Examples of fiber base materials include organic fibers such as cellulose fibers, aramid fibers, acrylic fibers, and phenolic resin fibers which may have a crosslinked structure, as well as inorganic fibers, metal fibers, and carbon fibers. The fiber base material may be used alone or in combination of two or more types. Among these, cellulose fibers, aramid fibers, and inorganic fibers are preferred, and cellulose fibers and aramid fibers are more preferred.

[0020] The friction material composition of this disclosure may contain one or more types of cellulose fibers. Examples of cellulose fibers include natural cellulose fibers, regenerated cellulose fibers, and pulp crushed products. Regenerated cellulose fibers are obtained by chemically dissolving natural cellulose contained in wood pulp, cotton, etc., using a solvent, extracting the cellulose, spinning it, and then re-forming it into fibers; known types can be used.

[0021] Examples of regenerated cellulose fibers include rayon fibers, lyocell fibers, cupro fibers, and polynosic fibers.

[0022] Pulp crushed products refer to kraft pulp that has been crushed and not chemically spun, and any known type can be used. Crushed recycled paper pulp can also be used.

[0023] The fiber length of the cellulose fiber is not particularly limited and may be 5000 μm or less, or from the viewpoint of dispersion, it may be 2000 μm or less, or 1000 μm or less. The lower limit of the fiber length of the cellulose fiber is not particularly limited and may be 500 μm or more. The fiber length of the cellulose fiber is preferably 500 μm to 5000 μm.

[0024] The fiber diameter of the cellulose fiber is not particularly limited and may be 5 μm to 100 μm, 10 μm to 50 μm, or 15 μm to 30 μm.

[0025] The fiber length of a cellulose fiber refers to the number-mean fiber length, which is the average length of the cellulose fibers. The fiber length of a cellulose fiber is the arithmetic mean obtained when 50 cellulose fibers are randomly selected and their lengths are measured using an electron microscope. The fiber diameter of a cellulose fiber refers to the number-mean fiber diameter, which is the average diameter of the cellulose fibers. The fiber diameter of a cellulose fiber is the arithmetic mean obtained when 50 cellulose fibers are randomly selected and their diameters are measured using an electron microscope.

[0026] When cellulose fibers are regenerated cellulose fibers, the fiber length or fiber diameter of the cellulose fibers can be adjusted by adjusting the concentration of the spinning solution and the spinning conditions during the production of regenerated cellulose.

[0027] From the viewpoint of suppressing fade, the cellulose fiber content is preferably 1% by mass or more relative to the total amount of the friction material composition. From the viewpoint of the moldability of the friction material composition (e.g., tablet moldability), it is preferably 4% by mass or more. The cellulose fiber content may be 20% by mass or less, 10% by mass or less, or 5% by mass or less relative to the total amount of the friction material composition. The cellulose fiber content is preferably 1% by mass to 20% by mass relative to the total amount of the friction material composition.

[0028] The friction material composition of this disclosure may contain one or more types of aramid fibers. The fiber length of the aramid fibers is not particularly limited and may be 5000 μm or less, or from the viewpoint of dispersion, 2000 μm or less, or 1500 μm or less. The lower limit of the fiber length of the aramid fibers is not particularly limited and may be 500 μm or more, or 800 μm or more. The fiber length of the aramid fibers is preferably between 500 μm and 5000 μm.

[0029] The fiber diameter of the aramid fiber is not particularly limited and may be 5 μm to 100 μm, 10 μm to 50 μm, or 15 μm to 30 μm.

[0030] The fiber length of aramid fibers refers to the number-mean fiber length, which is the average length of aramid fibers. This is the arithmetic mean obtained when 50 aramid fibers are randomly selected and their lengths are measured using an electron microscope. The fiber diameter of aramid fibers refers to the number-mean fiber diameter, which is the average diameter of aramid fibers. This is the arithmetic mean obtained when 50 aramid fibers are randomly selected and their diameters are measured using an electron microscope.

[0031] From the viewpoint of suppressing the fade phenomenon, the aramid fiber content may be 0.5% to 5% by mass, 1% to 4% by mass, 1.2% to 3% by mass, 1.5% to 2.5% by mass, or 1.7% to 2.3% by mass, based on the total amount of the friction material composition.

[0032] Examples of inorganic fibers include ceramic fibers, biodegradable ceramic fibers, mineral fibers, glass fibers, potassium titanate fibers, silicate fibers, wollastonite, etc.

[0033] Mineral fibers refer to man-made inorganic fibers obtained by melt spinning with blast furnace slag such as slag wool, basalt such as basalt fiber, and other natural rocks as the main components. As mineral fibers, it is preferable that they are fibers derived from natural minerals containing Al element. Specifically, SiO ２ , Al ２ O ３ , CaO, MgO, FeO, Na ２ O, etc. can be used alone or in combination of two or more, and more preferably, those containing Al element among these can be preferably used as mineral fibers.

[0034] Mineral fibers are preferably bio-soluble. The bio-soluble mineral fibers referred to here are mineral fibers that have the characteristic of being partially decomposed and discharged outside the body within a predetermined time even when taken into the human body. Specifically, the total content rate of alkali metal oxides and alkaline earth metal oxides (total content rate of oxides of sodium, potassium, calcium, magnesium and barium) in the chemical composition is 18% by mass or more, and in the short-term biopersistence test by respiration, the mass half-life of fibers of 20 μm or more is within 40 days, or there is no evidence of excessive carcinogenicity in the intraperitoneal test, or there is no related pathogenicity and tumorigenesis in the long-term respiration test (EU Directive 97 / 69 / EC, Nota Q (excluding carcinogenic application)). Examples of such bio-soluble mineral fibers include SiO ２ -Al ２ O ３ -CaO-MgO-FeO-Na ２ O-based fibers, etc., and fibers containing SiO ２ , Al ２ O ３ , CaO, MgO, FeO, Na ２ O, etc. in any combination. Commercially available products include Roxul series manufactured by LAPINUS FIBERS B.V. etc. In "Roxul", SiO ２ , Al ２ O ３, CaO, MgO, FeO, Na ２ O, etc. are included.

[0035] As the metal fiber, in order to improve crack resistance and wear resistance, fibers of copper or copper alloy can be used. As the fibers of copper or copper alloy, copper fibers, brass fibers, bronze fibers, etc. can be used.

[0036] Also, as the metal fiber, other metal fibers other than copper and copper alloy may be used. Other metal fibers other than copper and copper alloy may be included from the viewpoints of improving the friction coefficient and crack resistance.

[0037] As the other metal fibers other than copper and copper alloy, fibers of simple metals such as aluminum, iron, zinc, tin, titanium, nickel, magnesium, silicon, etc. or alloys, fibers mainly composed of metals such as cast iron fibers, etc. can be mentioned.

[0038] From the viewpoint of reducing the environmental load, the total content rate of the metal fiber is preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less with respect to the total amount of the friction material composition. The friction material composition may not contain metal fibers.

[0039] As the carbon fiber, flame-resistant fibers, pitch-based carbon fibers, PAN (polyacrylonitrile)-based carbon fibers, activated carbon fibers, etc. can be used.

[0040] The total content rate of the fiber base material is preferably 5% by mass to 40% by mass, more preferably 5% by mass to 30% by mass, and even more preferably 6% by mass to 20% by mass with respect to the total amount of the friction material composition.

[0041] (Inorganic filler) The friction material composition of the present disclosure may contain an inorganic filler. The inorganic filler may be used alone or in combination of two or more.

[0042] Examples of inorganic fillers include graphite, zirconia (zirconium dioxide), metal sulfides, mica, titanates, coke, calcium hydroxide (slaked lime), calcium oxide, sodium carbonate, calcium carbonate, magnesium carbonate, barium sulfate, dolomite, iron oxide, vermiculite, calcium sulfate, talc, clay, zeolite, zircon (zirconium silicate), mullite, chromite, titanium dioxide, magnesium oxide, silica, garnet, alumina such as α-alumina and γ-alumina, and silicon carbide.

[0043] Examples of graphite include artificial graphite such as petroleum pitch and coal pitch, as well as natural graphite.

[0044] If the friction material composition of this disclosure contains graphite, the graphite content may be 1% to 12% by mass, 2% to 10% by mass, or 3% to 8% by mass, based on the total amount of the friction material composition.

[0045] Examples of metal sulfides include antimony trisulfide, tin sulfide, tin disulfide, molybdenum disulfide, iron sulfide, iron disulfide, bismuth sulfide, zinc sulfide, and tungsten disulfide.

[0046] Examples of titanates include potassium titanate, lithium potassium titanate, sodium titanate, and magnesium potassium titanate.

[0047] The inorganic filler may contain at least one selected from the group consisting of graphite, zirconia, metal sulfides, titanates, barium sulfate, calcium hydroxide, zircon, and alumina.

[0048] The inorganic filler may contain titanates (preferably potassium titanate, lithium potassium titanate, or magnesium potassium titanate). The content of titanates (preferably potassium titanate, lithium potassium titanate, or magnesium potassium titanate) is preferably 40% by mass or less, more preferably 10% to 35% by mass, and even more preferably 15% to 30% by mass, based on the total amount of the friction material composition.

[0049] The inorganic filler may contain barium sulfate. The barium sulfate content is preferably 50% by mass or less, more preferably 10% to 45% by mass, and even more preferably 15% to 35% by mass, based on the total amount of the friction material composition.

[0050] The inorganic filler content may be 30% to 85% by mass, 50% to 80% by mass, or 60% to 80% by mass, based on the total amount of the friction material composition.

[0051] (Organic Filler) The friction material composition of this disclosure may contain an organic filler. Examples of organic fillers include cashew particles. The organic filler may be used alone or in combination of two or more types.

[0052] The content of the organic filler may be 3% to 20% by mass, 4% to 15% by mass, or 5% to 10% by mass, based on the total amount of the friction material composition.

[0053] (Other Materials) The friction material composition of this disclosure may contain other materials other than the components described above, as needed. Examples of other materials include fluorine-based polymers such as PTFE (polytetrafluoroethylene), rubber powder, and metal powder. These other materials may be used individually or in combination of two or more.

[0054] Examples of rubber components that make up rubber powder include tire rubber, natural rubber, acrylonitrile-butadiene rubber (NBR), acrylic rubber, isoprene rubber, polybutadiene rubber (BR), styrene-butadiene rubber (SBR), and silicone rubber. The rubber powder may also be tire powder composed of tire rubber.

[0055] The shape of the friction material composition of this disclosure is not particularly limited and may be in the form of a powder, a tablet, or the like.

[0056] <Friction Material> The friction material of this disclosure is a component formed using the friction material composition of this disclosure. The friction material of this disclosure can be used as a friction material for disc brake pads, brake linings, etc., used in automobiles and the like.

[0057] The friction material of this disclosure can be manufactured by molding the friction material composition of this disclosure in a commonly used manner. Preferably, it is manufactured by heat-pressure molding. Specifically, the friction material composition of this disclosure is mixed using a mixer such as a Redigge mixer, a pressure kneader, or an Eich mixer, and this mixture is pre-molded in a molding die. The resulting pre-molded product is then heated and molded at a molding temperature of 140°C to 160°C and a molding pressure (molding surface pressure) of 20 MPa to 50 MPa for 4 to 10 minutes, and the resulting molded product is heat-treated at 180°C to 300°C for 0.5 to 10 hours. Painting, scorching, polishing, etc., may also be performed as needed.

[0058] <Friction Members> The friction members of this disclosure include the friction material of this disclosure. In the friction members of this disclosure, it is preferable that the friction material of this disclosure constitutes the friction surface of the friction member. Examples of the friction members of this disclosure include the following configurations: (1) A configuration consisting only of friction material (2) A configuration comprising a backing plate and the friction material of this disclosure which forms a friction surface provided on the backing plate (3) In the configuration of (2) above, a primer layer for surface modification to enhance the adhesion effect of the backing plate to the friction material and an adhesive layer for bonding the backing plate and the friction material are further interposed between the backing plate and the friction material.

[0059] The present disclosure will be described in further detail below with reference to examples, but the present disclosure is not limited in any way by these examples.

[0060] [Preparation of Disc Brake Pads] Materials were blended according to the blending ratios shown in Table 1 to obtain the friction material compositions of the Examples and Comparative Examples. The units of the blending amounts of each component in Table 1 are in mass % of the friction material composition. In Table 1, "-" means that the corresponding component is not contained. Also, "phenol novolac resin" in Table 1 means "novolac-type phenolic resin".

[0061] The following components were used as cellulose fibers. The following components were used as CMC compounds. • Cellulose fiber: Fiber length: 900 μm, fiber diameter: 20 μm • CMC-1: Loss at 500°C: 38% by mass, degree of etherification: 0.8 • CMC-2: Loss at 500°C: 55% by mass, degree of etherification: 0.7

[0062] This friction material composition was mixed in a Redigge mixer (manufactured by Matsubo Co., Ltd., product name: Redigge Mixer M20), and the mixture was pre-formed at 30 MPa. The resulting pre-formed material was then heated and pressurized together with an iron backing plate (6 mm thick) for 5 minutes at a molding temperature of 150°C and a molding surface pressure of 20 MPa to 40 MPa. The resulting molded product was heat-treated for 2 hours and polished using a rotary polishing machine. Subsequently, a scorching treatment was performed to produce a product with a thickness of 10 mm and a projected area of ​​60 cm². ２ We manufactured a disc brake pad equipped with the following friction material.

[0063] General performance tests were conducted in accordance with JASO C406. Specifically, a 1 / 5 scale tester (inertia 3.0 kg·m) was used. ２ Using 18 mm x 44 mm test pieces cut from the disc brake pads manufactured in each example and comparative example, the average friction coefficient μ (Min. Avg. μ) and minimum value (Min. min. μ) of the 1st Fade test, an indicator of fade suppression, were determined. In Table 1, a higher value for fade suppression indicates that the fade phenomenon is suppressed.

[0064]

[0065] As is clear from the evaluation results in Table 1, the brake pads formed using the friction material composition of the examples were able to suppress the fade phenomenon more effectively than the brake pads formed using the friction material composition of the comparative examples.

[0066] The disclosure of Japanese Patent Application No. 2024-193897, filed on November 5, 2024, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

Claims

1. A friction material composition comprising a novolac-type phenolic resin and carboxymethylcellulose or a salt thereof.

2. The friction material composition according to claim 1, wherein the content of carboxymethylcellulose or a salt thereof relative to the total amount of the friction material composition is 0.1% by mass to 8% by mass.

3. The friction material composition according to claim 1, wherein the mass loss rate of the carboxymethylcellulose or a salt thereof when heated at a heating rate of 10°C / min to 500°C is 30% by mass to 70% by mass.

4. The friction material composition according to claim 1, further comprising cellulose fibers, wherein the content of the cellulose fibers relative to the total amount of the friction material composition is 1% by mass to 20% by mass.

5. The friction material composition according to claim 1, further comprising aramid fibers, wherein the content of the aramid fibers relative to the total amount of the friction material composition is 0.5% by mass to 5% by mass.

6. A friction material formed using the friction material composition described in any one of claims 1 to 5.

7. A friction member comprising the friction material described in claim 6.

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