JP2013185016A - Friction material composition, and friction material and friction member using the friction material composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a friction material composition, capable of providing a friction material which is excellent in noise characteristics after being left in cold (about 5°C or lower) and can improve each performance of effectiveness, noise and abrasion in a well-balanced manner, and a friction material and a friction member using the friction material composition.SOLUTION: A friction material composition includes: a fibrous base material, a bonding material, an organic filler and an inorganic filler. The friction material composition includes, as the fibrous base material, 1-10 mass% of cellulose fibers having an average fiber length of 0.1-50 μm and an aspect ratio of 1.5 or more. A friction material and a friction member using the friction material composition are also provided.

Description

  The present invention relates to a friction material composition suitable for friction materials such as disc brake pads and brake linings used for braking of automobiles, etc., and a friction material and a friction member using the friction material composition.

  In automobiles and the like, friction materials such as disc brake pads and brake linings are used for braking. Friction materials such as a disc brake pad and a brake lining play a role of braking by friction with a disc rotor, a brake drum, or the like as a counterpart material. For this reason, the friction material is required not only to have an appropriate friction coefficient and stability of the friction coefficient (effect characteristics) depending on the use conditions, but also to make it difficult for squeal (squeal characteristics) and to have a long life of the friction material. (Abrasion resistance) is required.

  By the way, the fundamental performance required for automobiles is “run, turn, stop”. Whether a driver can enjoy the pleasure of driving as well as safety depends on how well these three performances are provided in a well-balanced manner. In recent years, characteristics related to “running” and “turning” have been greatly improved due to improvements in automobile technology.

  On the other hand, squeal (hereinafter also referred to as brake squeal) is one of the characteristics related to “stop”. In particular, with the advent of hybrid vehicles and electric vehicles in recent years, the quietness of the drive train engine has been improved, and as a result, the squeaking of the friction material has become increasingly perceptible. For this reason, there is an increasing demand for suppressing noise.

  There are various conditions for the occurrence of brake squeal, particularly when braking is performed at a low speed and a reduced speed after being left under low temperature and high humidity conditions. For example, a brake squeal is likely to occur when the first braking is performed after starting a car that has been left overnight in the morning. Also, under such conditions (when braking is performed at a low speed and a reduced speed), the quietness of the driving system engine of the automobile is extremely high, and even a slight brake squeal is easily perceived.

As a technique for reducing such brake squeal, a method for suppressing the coefficient of friction after being left under low temperature and high humidity conditions has been reported. For example, a method using hydrophobic silica to suppress moisture absorption of the friction material (for example, see Patent Document 1), a method using an aromatic-modified phenol resin as a binder (for example, see Patent Document 2), a silicone-based material A method using a silicone-impregnated porous body made of an inorganic porous body impregnated with oil (for example, see Patent Document 3), a method for reducing pores in a friction material (for example, see Patent Document 4), an organic base A method using a composite friction modifier comprising a material and a layered clay mineral has been proposed (for example, see Patent Document 5).
However, in the friction materials described in these Patent Documents 1 to 5, it is difficult to sufficiently suppress brake squeal at a very low temperature of 5 ° C. or less.

  Further, the friction material is required to have a balance between effectiveness, squealing and wear, and it is not sufficient to improve only the squealing characteristics. However, these characteristics tend to be in a trade-off relationship with each other. For example, if the friction coefficient is lowered by reducing the additive amount of the abrasive in order to improve the squealing characteristics, the effectiveness characteristics are degraded. Further, even if a large amount of lubricant is added to improve wear resistance, the friction coefficient is lowered. For this reason, it has been difficult to improve the performance, squealing, and wear performance in a well-balanced manner.

JP 2003-003155 A Japanese Patent Laid-Open No. 11-286676 JP-A-10-245544 JP-A-11-325141 JP 2009-173754 A

  Therefore, the present invention provides a friction material composition that provides a friction material that has excellent squeal characteristics after being left cold (about 5 ° C. or less) and that can improve the performance, squealing, and wear performance in a balanced manner. The purpose is to provide. Another object of the present invention is to provide a friction material and a friction member using the friction material composition.

As a result of intensive studies, the present inventors have found that the above-mentioned problems can be solved by including specific cellulose fibers as a fiber base material in the friction material composition, and have completed the present invention.
That is, the present invention relates to the following.

1. A friction material composition comprising a fiber base material, a binder, an organic filler, and an inorganic filler. As the fiber base material, 1 cellulose fiber having an average fiber length of 0.1 to 50 μm and an aspect ratio of 1.5 or more is used. A friction material composition containing 10 mass%.
2. 2. The friction material composition as described in 1 above, wherein the cellulose fiber has an aspect ratio of 1.5 to 40.
3. A friction material obtained by heating and pressing the friction material composition according to 1 or 2 above.
4). 4. A friction member formed using the friction material according to 3 and a back metal.

According to the present invention, when used for a friction material such as an automobile disc brake pad or brake lining, it has excellent squeal characteristics after being left cold (about 5 ° C. or less), and the performance, squealing and wear performances. It is possible to provide a friction material composition capable of improving the balance in a balanced manner. Further, according to the present invention, there is provided a friction material composition that is excellent in squeal characteristics in a normal use temperature range (about 50 to 250 ° C.), excellent in wear resistance, and further provides a friction material having sufficient effect characteristics. Can be provided. In other words, according to the present invention, the friction material composition that can maintain or improve the performance of squealing and wear, which tends to be in a trade-off relationship, while improving the squealing characteristics after being left cold. Things can be provided.
Moreover, according to this invention, the friction material and friction member which have the said characteristic can be provided by using the said friction material composition.

It is the schematic which shows the calculation method of friction coefficient (micro | micron | mu) -vehicle speed V (km / h) negative gradient.

Hereinafter, the friction material composition of the present invention will be described in detail.
The friction material composition, friction material and friction member of the present invention do not contain asbestos, that is, non-asbestos friction material composition, non-asbestos friction material and non-asbestos friction member.

<Friction material composition>
The friction material composition of the present invention is a friction material composition including a fiber base material, a binder, an organic filler, and an inorganic filler. The fiber base material has an average fiber length of 0.1 to 50 μm and an aspect ratio. Contains 1.5 or more cellulose fibers.

[Fiber base]
The friction material composition of the present invention contains a fiber base material. The fiber base material exhibits a reinforcing action in the friction material. Examples of the fiber base material include organic fibers, metal fibers, and inorganic fibers.

The friction material composition of the present invention contains, as organic fibers, cellulose fibers having an average fiber length of 0.1 to 50 μm and an aspect ratio of 1.5 or more. Cellulose fibers are natural wood fibers made from wood, vegetative plants, old newspapers, cardboard and the like.
Cellulose fibers were generally considered to thermally decompose at around 300 ° C. and reduce the friction coefficient of the friction material. However, the present inventors have found that when a specific amount of cellulose fiber having a specific average fiber length and aspect ratio is used, the squealing characteristics and the wear resistance can be improved without deteriorating the effectiveness characteristics. .
When cellulose fibers having the above-mentioned specific average fiber length and aspect ratio are used, the elastic modulus of the friction material is lowered and vibration damping is improved, and the degradation products generated by thermal decomposition of the cellulose fibers and the dense pores cause sliding. It is considered that the moving surface (for example, the surface where the friction material contacts the brake rotor) is stabilized, and as a result, the wear resistance can be improved and the squealing property can be further improved without impairing the effectiveness characteristics. More specifically, since the cellulose fiber used in the present invention starts thermal decomposition at around 200 ° C., its thermal decomposition temperature is higher than that of the cellulose fiber, for example, compared with other organic fibers such as aramid fiber. Many decomposition products remain in the friction material. These pyrolysates have a Mohs hardness lower than that of the material used for the counterpart material (for example, brake rotor), and stabilize the sliding surface by being interposed in the sliding surface. Therefore, it is considered that the wear resistance is improved.

The average fiber length of the cellulose fiber used by this invention is 0.1-50 micrometers. When the average fiber length of the cellulose fiber exceeds 50 μm, the pore diameter formed after pyrolysis of the cellulose fiber cannot be suppressed below a certain level, the pore size is large and the dispersibility of the pores becomes uneven, and friction Since the contact area between the material and the counterpart material is not stable, the friction coefficient becomes unstable. On the other hand, if the average fiber length of the cellulose fibers is less than 0.1 μm, the elastic modulus of the friction material is increased and the squealing characteristics are deteriorated.
The average fiber length of the cellulose fibers is preferably 0.5 to 50 μm from the viewpoints of denseness and dispersibility of pores formed after pyrolysis. Moreover, it is more preferable that it is 0.5-30 micrometers, and it is further more preferable that it is 1-10 micrometers.
Here, the average fiber length refers to a number average fiber length indicating an average value of the lengths of all corresponding fibers. For example, 50 cellulose fibers used as a friction material composition raw material are selected at random, the fiber length is measured with a scanning electron microscope (SEM), and an average value is shown.

Moreover, the aspect ratio of the cellulose fiber used by this invention is 1.5 or more. The upper limit of the aspect ratio is not particularly limited, but is preferably 40 or less.
Here, the aspect ratio is represented by A / B, where the length in the major axis direction of the cellulose fiber is the fiber length (A) and the length in the minor axis direction is the fiber diameter (B), and is usually extracted arbitrarily. It is a value obtained by averaging the A / B values of about 50 fibers. Here, when determining the fiber length (A) and the fiber diameter (B), the fibers are enlarged with a scanning electron microscope (SEM) and observed from various directions to take into account the three-dimensional characteristics of the fibers. There is a need. For example, when the fiber is branched, the length of the longest portion of the fiber projected in the two-dimensional field of view in the SEM image is the fiber length (A) and is orthogonal to the fiber length (A). Let the length of the longest part be a fiber diameter (B).

  In the present invention, when cellulose fibers having an aspect ratio of less than 1.5 are used, the elastic modulus of the friction material is increased because the cellulose fibers in the friction material and the dispersibility of pores generated by the thermal decomposition of the cellulose fibers are poor. Efficacy is reduced. The aspect ratio of the cellulose fiber is preferably 1.5 to 40 from the viewpoint of the elastic modulus imparted to the friction material. Moreover, it is more preferable that it is 2-20, and it is further more preferable that it is 2-10.

  Content of the cellulose fiber of this invention is 1-10 mass% in a friction material composition. When the content of the cellulose fiber exceeds 10% by mass, the coefficient of friction decreases, and when the content is less than 1% by mass, the wear resistance and squeal characteristics are deteriorated. The cellulose fiber content is preferably 1 to 6% by mass, more preferably 1 to 5% by mass, and even more preferably 2 to 4% by mass.

  As an organic fiber, an aramid fiber, an acrylic fiber, a phenol resin fiber, etc. other than the said cellulose fiber can be used, and can be used 1 type or in combination of 2 or more types. Among these, it is preferable to use an aramid fiber from a viewpoint of heat resistance and a reinforcing effect.

  As the metal fiber, copper fiber, brass fiber, bronze fiber, iron fiber, titanium fiber, zinc fiber, aluminum fiber, or the like can be used, and one or a combination of two or more can be used. Among these, from the viewpoint of thermal conductivity, melting point, ductility, tensile strength, etc., it is preferable to use copper fiber, but from the viewpoint of environmental friendliness, copper fiber is not substantially contained (for example, friction In the material composition, 5% by mass or less) is preferable. The friction material composition of the present invention can provide a friction material having sufficient effect, squealing, and wear characteristics even when it contains substantially no copper fiber.

  As the inorganic fiber, ceramic fiber, biodegradable ceramic fiber, mineral fiber, carbon fiber, glass fiber, potassium titanate fiber, aluminosilicate fiber and the like can be used, and one kind or a combination of two or more kinds can be used. However, from the viewpoint of environmental friendliness, it is preferable not to contain attractive potassium titanate fibers.

The mineral fiber referred to here is a man-made inorganic fiber melt-spun mainly composed of blast furnace slag such as slag wool, basalt such as basalt fiber, and other natural rocks, and is a natural mineral containing Al element. Is more preferable. Specifically, those containing SiO ₂ , Al ₂ O ₃ , CaO, MgO, FeO, Na ₂ O, etc., or those containing one or more of these compounds can be used, more preferably. Of these, those containing Al element can be used as mineral fibers. Since the adhesive strength with each component in the friction material composition tends to decrease as the average fiber length of the entire mineral fiber contained in the friction material composition increases, the average fiber length of the entire mineral fiber is preferably 500 μm or less. More preferably, it is 100-400 micrometers. Here, the average fiber length means the number average fiber length as described above.

The mineral fiber used in the present invention is preferably biosoluble from the viewpoint of human harm. The term “biosoluble mineral fiber” as used herein refers to a mineral fiber having a characteristic that even if it is taken into the human body, it is partially decomposed and discharged outside the body in a short time. Specifically, the chemical composition is alkali oxide, alkaline earth oxide total amount (total amount of oxides of sodium, potassium, calcium, magnesium, barium) is 18% by mass or more, and in a short-term biopermanent test by respiration, A fiber that has a mass half-life of 20 μm or more within 40 days or no evidence of excessive carcinogenicity in an intraperitoneal test or that has no associated pathogenicity or tumor development in a long-term respiratory test (EU Directive 97 / 69 / EC Nota Q (carcinogenic exclusion)). Examples of such biodegradable mineral fibers include SiO ₂ —Al ₂ O ₃ —CaO—MgO—FeO—Na ₂ O fibers and the like, and include SiO ₂ , Al ₂ O ₃ , CaO, MgO, FeO, Na. Examples thereof include fibers containing ₂ O or the like in any combination. As a commercial item, LAPINUS FIBERS B.M. Examples include V Roxul series. “Roxul” includes SiO ₂ , Al ₂ O ₃ , CaO, MgO, FeO, Na ₂ O and the like.

The content of the fiber base material is preferably 5 to 40% by mass, more preferably 10 to 20% by mass, and further preferably 5 to 18% by mass in the friction material composition. When the content of the fiber base material is 5 to 40% by mass, an appropriate reinforcing effect can be imparted to the friction material while suppressing a decrease in effectiveness characteristics.
The fiber base material here contains the cellulose fiber.

[Binder]
The friction material composition of the present invention contains a binder. The binding material integrates an organic filler and a fiber base material included in the friction material composition to give strength. As the binder contained in the friction material composition of the present invention, a thermosetting resin usually used for a friction material can be used. Examples of the thermosetting resin include various modified phenolic resins such as phenolic resin, acrylic modified phenolic resin, silicone modified phenolic resin, cashew modified phenolic resin, epoxy modified phenolic resin, alkylbenzene modified phenolic resin, etc. Phenol resins, acrylic-modified phenol resins, and silicone-modified phenol resins are preferred, and these can be used alone or in combination of two or more. Moreover, it is preferable to use a phenol resin, an acrylic modified phenol resin, a silicone modified phenol resin, or an alkylbenzene modified phenol resin from the viewpoint of providing good heat resistance, moldability, and friction coefficient.

  The content of the binder is preferably 5 to 20% by mass, more preferably 5 to 15% by mass, and still more preferably 5 to 10% by mass in the friction material composition. By setting the content of the binder in the range of 5 to 20% by mass, it is possible to further suppress the strength reduction of the friction material, reduce the porosity of the friction material, and increase the elastic modulus. Vibration performance deterioration can be suppressed.

[Organic filler]
The friction material composition of the present invention contains an organic filler. The organic filler is included as a friction modifier for improving the sound vibration performance and wear resistance of the friction material. As an organic filler contained in the composition for a friction material of the present invention, cashew dust, a rubber component, or the like can be used.
The cashew dust is not particularly limited as long as it is obtained by pulverizing a hardened cashew nut shell oil and is usually used for a friction material.
Examples of the rubber component include tire rubber, acrylic rubber, isoprene rubber, NBR (nitrile butadiene rubber), SBR (styrene butadiene rubber) and the like, and these are used alone or in combination of two or more.
In addition, cashew dust and a rubber component may be used in combination, or cashew dust coated with a rubber component may be used, but from the viewpoint of sound vibration performance, it is preferable to use cashew dust and a rubber component in combination. .

  The content of the organic filler is preferably 1 to 20% by mass, more preferably 1 to 10% by mass, and further preferably 3 to 8% by mass in the friction material composition. By setting the content of the organic filler in the range of 1 to 20% by mass, it is possible to avoid deterioration of sound vibration performance such as squeal due to an increase in the elastic modulus of the friction material, deterioration of heat resistance, heat It is possible to avoid a decrease in strength due to history. Moreover, when using cashew dust and a rubber component together, it is preferable that cashew dust and a rubber component are the ratio of 2: 1-10: 1 by mass ratio, and it is 3: 1-9: 1. More preferably, it is 3: 1 to 8: 1.

[Inorganic filler]
The friction material composition of the present invention contains an inorganic filler. The inorganic filler is included as a friction modifier in order to avoid deterioration of the heat resistance of the friction material.
Examples of the inorganic filler used in the present invention include antimony trisulfide, tin sulfide, molybdenum disulfide, iron sulfide, bismuth sulfide, zinc sulfide, calcium hydroxide, calcium oxide, sodium carbonate, calcium carbonate, magnesium carbonate, and sulfuric acid. Barium, dolomite, coke, graphite, mica, iron oxide, vermiculite, granular potassium titanate, calcium sulfate, plate-like potassium titanate, talc, clay, zeolite, zirconium silicate, zirconium oxide, mullite, chromite, titanium oxide, magnesium oxide Further, activated alumina such as silica and γ-alumina can be used, and these can be used alone or in combination of two or more. In the present invention, the inorganic filler preferably contains graphite and barium sulfate from the viewpoint of reducing the aggressiveness to the facing material, and preferably contains zirconium oxide from the viewpoint of improving the friction coefficient.

  The content of the inorganic filler is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, and further preferably 40 to 70% by mass in the friction material composition. When content of an inorganic filler shall be 20-80 mass%, deterioration of heat resistance can be suppressed.

[Other ingredients]
Moreover, the friction material composition of this invention can mix | blend other materials as needed other than the said material. For example, metal powder such as copper powder, brass powder and zinc powder can be blended as the friction modifier, and the content of the metal powder is 1 to 6% by mass in the friction material composition. preferable.

<Friction material and friction member>
The friction material composition of the present invention can be used as a friction material for disc brake pads, brake linings, etc. of automobiles, or by subjecting the friction material composition of the present invention to a target shape by subjecting it to steps such as molding, processing, and pasting. It can also be used as a friction material for electromagnetic brakes and holding brakes.

The friction material composition of the present invention can be used as a friction member itself that becomes a friction surface to obtain a friction material. Examples of the friction material using the same include the following configurations.
(1) Configuration of only friction member (2) Configuration having a back metal and a friction member formed on the back metal and made of the friction material composition of the present invention to be a friction surface (3) Configuration of (2) above In the structure, a primer layer for the purpose of surface modification for enhancing the adhesion effect of the back metal between the back metal and the friction member, a configuration in which an adhesive layer for the purpose of bonding the back metal and the friction member is further interposed, etc. Can be mentioned.
The backing metal is usually used as a friction member in order to improve the mechanical strength of the friction member. As the material, metal or fiber reinforced plastic can be used. For example, iron, stainless steel, inorganic fiber Examples thereof include reinforced plastic and carbon fiber reinforced plastic. The primer layer and the adhesive layer may be those used for friction members such as brake shoes.

  The friction material composition of the present invention can be produced by using a generally used method, and can be produced by heating and pressing the friction material composition of the present invention. Specifically, for example, the friction material composition of the present invention is uniformly mixed using a mixer such as a Readyge mixer, a pressure kneader, or an Eirich mixer, and this mixture is preformed in a molding die to obtain a mixture. The obtained preform is molded for 2 to 10 minutes under the conditions of a molding temperature of 130 to 160 ° C. and a molding pressure of 20 to 50 MPa, and the obtained molded product is heat-treated at 150 to 250 ° C. for 2 to 10 hours. A friction material can be obtained. In addition, you may perform a coating, a scorch process, a grinding | polishing process etc. as needed.

Since the friction material composition of the present invention has an excellent balance of performance, squealing, and wear performance, it is useful as a “upper material” for friction members such as disc brake pads and brake linings. It can also be used as a “material”.
The “upper material” is a friction material that becomes the friction surface of the friction member, and the “underlay material” is a friction material that is interposed between the friction material that becomes the friction surface of the friction member and the back metal. It is a layer for the purpose of improving the shear strength and crack resistance in the vicinity of the adhesion part with the back metal.

According to the present invention, when used for a friction material such as an automobile disc brake pad or brake lining, the squeal characteristics after being left cold (about 5 ° C. or less or about −5 ° C. or less) are excellent and effective. Thus, it is possible to provide a friction material composition capable of improving each performance of squealing and wear in a balanced manner.
Furthermore, it is possible to provide a friction material composition that is excellent in squealing characteristics and wear resistance in a normal use temperature range (about 50 to 250 ° C.) and gives a friction material having sufficient effect characteristics.
That is, according to the present invention, while improving the squeal characteristics after being left cold, it can be maintained or improved without reducing the performance, squealing, and wear performances that tend to be in a trade-off relationship. A friction material composition, and a friction material and a friction member having the above characteristics can be provided.

Further, according to the friction material composition of the present invention, it is possible to suppress an increase in the friction coefficient and the negative gradient (μ−V negative gradient) of the friction coefficient with respect to the vehicle speed during one braking.
Here, the μ-V negative gradient indicates a negative gradient of μ (friction coefficient) with respect to V (vehicle speed) during one braking. In braking after leaving at low temperature and high humidity, μ increases as the vehicle speed decreases, and therefore, μ tends to show a negative negative gradient with respect to V. It has become clear from recent research reports (for example, Japanese Patent Application Laid-Open No. 2010-24429) that when this negative gradient is large, brake squealing with self-excited vibration as an excitation force is likely to occur.
Since the friction material using the friction material composition of the present invention can reduce the μ-V negative gradient after being left at a low temperature, it can suppress squealing.

  Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to these.

<Examples 1-5 and Comparative Examples 1-7>
[Production of disc brake pads]
The materials were blended according to the blending amounts (% by mass) shown in Tables 1 and 2, and the friction material compositions of Examples 1 to 5 and Comparative Examples 1 to 7 were obtained. In addition, the unit of the compounding quantity of each component of Table 1 and 2 is the mass% in a friction material composition.

This friction material composition is mixed with a ladyge mixer (manufactured by Matsubo Co., Ltd., trade name: ladyge mixer M20), and this mixture is preformed with a molding press (manufactured by Oji Machinery Co., Ltd.). The pre-molded product was heated and pressure-molded with a backing metal manufactured by Hitachi Automotive Systems, Ltd. using a molding press (manufactured by Sanki Seiko Co., Ltd.) for 5 minutes at a molding temperature of 145 ° C. and a molding pressure of 35 MPa. The molded product was heat treated at 200 ° C. for 4.5 hours, polished using a rotary polishing machine, subjected to scorch treatment at 500 ° C., and a disc brake pad (friction material thickness 9.5 mm, friction material projection area 52 cm). ² ) got.

The various materials used in the examples and comparative examples are as follows.
(Binder)
・ Phenolic resin: manufactured by Hitachi Chemical Co., Ltd. (trade name: HP491UP)
(Organic filler)
・ Cashew dust: Tohoku Kako Co., Ltd. (trade name: FF-1056)
・ SBR powder: manufactured by Misawa Toyo Co., Ltd. (trade name: powder TPA)
(Inorganic filler)
・ Graphite: manufactured by TIMCAL (trade name: KS75)
・ Potassium titanate: Otsuka Chemical Co., Ltd. (trade name: Terrases TF-S)
Ingredient: Potassium titanate, Shape: Flaky median diameter: 7 μm, Specific surface area: 3.5 m ² / g
-Barium sulfate: manufactured by Sakai Chemical Co., Ltd. (trade name: BA)
・ Alumina: Showa Denko Co., Ltd. (trade name: A-43-M)
・ Zirconium silicate: 1st rare element chemical industry (trade name: MZ1000B)
Antimony trisulfide: Chemtall Ges. m. b. Made by H (trade name: FRICSTAR)
・ Calcium hydroxide: manufactured by Chichibu Coal Industry Co., Ltd. (trade name: SA149)
・ Zeolite: Made by Mizusawa Chemical Co., Ltd. (trade name: Shilton B)
・ Zirconium oxide: manufactured by Daiichi Rare Element Chemical Co., Ltd. (trade name: BR3QZ)
(Fiber base)
・ Aramid fiber (organic fiber): manufactured by Toray DuPont Co., Ltd. (trade name: 1F538)
Copper fiber (metal fiber): manufactured by Sunny Metal (trade name: SCA-1070)
Mineral fiber (inorganic fiber): LAPINUS FIBERS B. Product made in V (trade name: RB240 Roxul 1000, average fiber length 300 μm)
Cellulose fiber A: manufactured by Rettenmeier Japan Co., Ltd. (trade name: NFC P 1011, average fiber length = 2 μm, aspect ratio = 4)
Cellulose fiber B: manufactured by Rettenmeier Japan Co., Ltd. (trade name: UFC100, average fiber length = 8 μm, aspect ratio = 2.7)
Cellulose fiber C: manufactured by Rettenmeier Japan Co., Ltd. (trade name: BE600-10TG, average fiber length = 18 μm, aspect ratio = 1.2)
Cellulose fiber D: manufactured by Rettenmeier Japan Co., Ltd. (trade name: BC200, average fiber length = 300 μm, aspect ratio = 15)
Cellulose fiber E: manufactured by Rettenmeier Japan Co., Ltd. (trade name: PZ8, average fiber length = 1400 μm, aspect ratio = 30)
In addition, the average fiber length and aspect ratio of the cellulose fiber were measured using the scanning electron microscope (SEM, apparatus name: VE-7800, product made by KEYENCE). The average fiber length was determined using the length in the major axis direction of the cellulose fiber as the fiber length. The aspect ratio is expressed by A / B, where the length in the major axis direction of the cellulose fiber is the fiber length (A) and the length in the minor axis direction is the fiber diameter (B), and about 50 arbitrarily extracted. The average of the A / B values of each fiber was taken.
(Other ingredients)
・ Zinc powder: Fukuda Metal Foil Powder Industry Co., Ltd. (trade name: Zn-At-200)

Various performances of the disc brake pads of Examples 1 to 5 and Comparative Examples 1 to 7 formed by the above-described method were evaluated using a brake dynamo tester (manufactured by Shin Nippon Toki Co., Ltd.).
In the experiment, a general pin-slide type collet caliper and a ventilated disc rotor (FC250) manufactured by Kiriu Corporation were used, and evaluation was performed with the moment of inertia of the Skyline V35 manufactured by Nissan Motor Co., Ltd.

(Evaluation of efficacy characteristics)
The friction coefficient was calculated in accordance with the Japan Society of Automotive Engineers standard JASO C406, and the average value of the friction coefficient in the second efficacy test was calculated. In Table 1, V50, V100, and V130 indicate vehicle speeds before braking, and indicate 50 km / h, 100 km / h, and 130 km / h, respectively.

(Evaluation of wear resistance (wear characteristics))
The test was based on JASO C427, and the amount of wear of the disk pad (friction material) at brake temperatures before braking of 100, 200, 300, and 400 ° C. was measured.

(Evaluation of squeal characteristics)
In order to generate the brake squeeze significantly, the squeal test was conducted without using a damping shim generally attached to the disc brake pad to prevent the squeal. This makes it possible to effectively compare and evaluate the squeal characteristics between conditions.

First, a method for evaluating the warm sound characteristics will be described. After slid in accordance with JASO C427 (initial speed 50km / h, deceleration 0.3G, brake temperature 100 ° C before braking, 200 times of braking), brake temperature in an environment of temperature 20 ° C and humidity 60% RH Is changed to 50, 100, 150, 200, 250, 200, 150, 100, 50 ° C., and the liquid pressure is 0.20, 0.49, 0.98, 1.47, 1.96 at each temperature condition. Braking was performed once at 2.45, 2.94, and 3.43 MPa. Each of the above brakings was repeated twice, for a total of 144 brakings. Among them, the occurrence rate of brake squeal measured at a sound pressure of 70 dB or more was evaluated for each of the disc brake pads of Examples 1 to 5 and Comparative Examples 1 to 7, and was defined as warm squeal performance.
The occurrence rate of brake squeal can be obtained by the following equation.
Incidence rate of warm squeal = ((number of times sound pressure of 70 dB or more occurred) ÷ 144) x 100 (%)

Next, the evaluation of cold air (5 ° C.) squeal characteristics will be described. After the warm-up squeal section (after evaluating the warm-up squeal characteristics), the re-matching (initial speed 50 km / h, deceleration 0.3 G, brake temperature before braking 100 ° C., number of brakings 50 times) was performed. After that, it was left for 4 hours in an environment of temperature 5 ° C. and humidity 40% RH, and braking at a vehicle speed of 10 km / h and a brake hydraulic pressure of 0.5 MPa was repeated 50 times at an interval of 120 seconds. Among them, the occurrence rate of brake squeal measured at a sound pressure of 70 dB or more was evaluated for each of the disc brake pads of Examples 1 to 5 and Comparative Examples 1 to 7, and was defined as cold air (5 ° C.) squeal performance.
Cold air (5 ° C) squeak occurrence rate = ((number of occurrences of sound pressure of 70 dB or more) ÷ 50) x 100 (%)

Next, evaluation of cold air (−5 ° C.) squeal characteristics will be described. After the cold air (5 ° C.) squeal section (after evaluating the cold air (5 ° C.) squeal characteristics), re-grinding (initial speed 50 km / h, deceleration 0.3 G, brake temperature before braking 100 ° C., braking frequency 50 After being carried out for 4 hours in an environment at a temperature of −5 ° C., braking at a vehicle speed of 10 km / h and a brake hydraulic pressure of 0.5 MPa was repeated 50 times at an interval of 120 seconds. Among them, the occurrence rate of brake squeal measured at a sound pressure of 70 dB or more was evaluated for each of the disc brake pads of Examples 1 to 5 and Comparative Examples 1 to 7, and was regarded as cold air (−5 ° C.) squeal performance.
Cold air (−5 ° C.) squeal occurrence rate = ((number of occurrences of sound pressure of 70 dB or more) ÷ 50) × 100 (%)

(Evaluation of μ-V negative slope)
The vehicle speed (V) in cold air (5 ° C.) and cold air (−5 ° C.) is plotted on the horizontal axis and the friction coefficient (μ) is plotted on the vertical axis, and the relationship between the friction coefficient (μ) and the vehicle speed (V) is plotted. A linear approximation of the change of the friction coefficient (μ) with respect to the vehicle speed (V) between 8 km / h or less where the friction coefficient after braking starts is relatively stable and 1.0 km / h or more before braking ends, and the slope is μ -V negative slope. This μ-V gradient was calculated as an average value for a total of 100 brakings, 50 brakings after being left in each environment at 5 ° C. and −5 ° C.
The μ-V negative gradient is preferably closer to 0 from the viewpoint of sufficiently suppressing squealing.
FIG. 1 is a schematic diagram showing a method for calculating a μ-V negative gradient. The straight line A is a straight line obtained by linearly approximating the change of the friction coefficient (μ) with respect to the vehicle speed (V). The slope of this straight line A is a μ-V negative slope.

As in Examples 1 to 5, the friction material using the friction material composition containing cellulose fibers having a specific average fiber length and aspect ratio is improved in warm air and cold air (5 ° C. and −5 ° C.). I found out that It was also found that the material has excellent wear resistance and has sufficient effect properties as a friction material. In addition, as in Example 2, it was found that a friction material excellent in effectiveness, squealing and wear characteristics can be provided even when copper fiber is not used.
On the other hand, in Comparative Examples 1 and 7 in which no cellulose fiber was used, the occurrence rate of squeal could not be suppressed. Moreover, even in Comparative Example 2 in which the cellulose fiber content was less than 1% by mass and in Comparative Example 3 in which the cellulose fiber content was more than 10% by mass, the occurrence rate of squealing could not be suppressed. Furthermore, in Comparative Example 4 in which the aspect ratio of the cellulose fiber was less than 1.5 and Comparative Examples 5 and 6 in which the average fiber length of the cellulose fiber was greater than 50 μm, the occurrence rate of squealing could not be suppressed.
As shown in Tables 1 and 2, when the friction material composition for a brake pad for a passenger car of the present invention is a friction material, compared with the friction material composition of the comparative example, while maintaining the effectiveness characteristics, Abrasion resistance and squeal characteristics can be improved.

  When the friction material composition of the present invention is used as a friction material, for example, it has excellent squeal characteristics after being left cold (about 5 ° C. or less) and has a good balance of performance, squealing and wear performance. In particular, it is useful for friction materials and friction members such as automobile disc brake pads and brake linings.

Claims (4)

  A friction material composition comprising a fiber base material, a binder, an organic filler, and an inorganic filler. As the fiber base material, 1 cellulose fiber having an average fiber length of 0.1 to 50 μm and an aspect ratio of 1.5 or more is used. A friction material composition containing 10 mass%.   The friction material composition according to claim 1, wherein the cellulose fiber has an aspect ratio of 1.5 to 40.   A friction material obtained by heat-pressing the friction material composition according to claim 1.   A friction member formed using the friction material according to claim 3 and a back metal.

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