JPH07102080A - Production of friction material - Google Patents

Abstract

PURPOSE:To produce a friction material with a small variation in strengths and a high coefficient of friction by mixing a raw material mixture comprising a carbon fiber, a binder, and a friction modifier with a granulation binder. granulating the resulting mixture, and thermally press molding the granules. CONSTITUTION:Any kind of carbon fiber may be used. A carbon fiber with a length of 100mm or lower is used in an ant. of 0.5-15wt.% of the raw material mixture for a friction material. The frequency distributin of weighted mean of length of the fiber pref. has two peaks: one is at lower than 0.5mm and the other, at 0.5mm or higher. A phenol resin is suitable as the binder and is used in an amt. of 5-50wt.% of the raw material mixture. Graphite, etc., are used as the friction modifier in an amt. of 1-30wt.% (in the case of graphite). Water, etc., are used as the granulation binder in an amt. of 10-50wt.% based on the total solid. Granulation is done by feeding the fiber component into a production apparatus, disaggregating the fiber component, feeding the powder components into the apparatus in the order of weight from a lightweight one to a heavy one, and feeding the granulation binder. The granule size is 0.1-10mm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a friction material for braking a rotating part of an automobile, an aircraft, a construction machine, a two-wheeled vehicle or the like.

[0002]

2. Description of the Related Art Conventionally, a large amount of asbestos has been used as a heat resistant reinforcing fiber in a friction material. However, the impact of asbestos on the human body becomes a major social issue, and asbestos-containing friction materials that generate wear powder when used are
It is being replaced by other fiber materials. As an alternative fiber material, aramid fiber (Dupont Toray Kevlar Co., Ltd. technical data DTK-T01 91.2), acrylic fiber (JP-A-62-106133, JP-A-63-18).
3950), carbon fiber (Japanese Patent Laid-Open No. 55-157).
671, Japanese Patent Publication No. 59-4455, Japanese Patent Laid-Open No. 5
No. 5-104378, etc.) has been proposed and used. Among these alternative fiber materials, carbon fiber is particularly excellent in terms of heat resistance, wear resistance, and reinforcing property (carbon fiber: March 1, 1986, published by Modern Editing Co., pp55.
7-567).

The friction material is usually manufactured by mixing a fibrous material, a friction adjusting material and a resinous binder, and heating and pressing. When using the above-mentioned alternative fiber, it is necessary to uniformly mix the alternative fiber with other components (mainly powder) to obtain a molded product having a high relative density. At this time, it is important to effectively utilize various excellent properties of the substitute fiber (for example, strength, elastic modulus, friction and wear resistance, heat resistance, etc.). A technique for uniformly mixing the fiber material and other powder materials (friction modifier and resin-based binder) is to encapsulate the resin-based binder and mix all materials in the presence of water to generate dust. A method of suppressing uneven distribution of material components while preventing generation (Japanese Patent Laid-Open No. 177482/1993), a method of shaping the friction material after mixing, and heat-forming (Japanese Patent Laid-Open No. 54-54).
-107487), after granulating the powder material in advance,
A method of mixing with a fiber material (JP-A-4-139290) has been proposed. Further, a method of beating organic fibers such as aramid fibers, acrylic fibers, and rayon fibers to fibrillize the fiber tips to facilitate inclusion of powder material is also widely used. (Technical data DTK-T01 91.2, DuPont Toray Kevlar Co., Ltd., JP-A-5-17250, JP-A-2-76935).

However, in the above method, in order to uniformly disperse and mix the carbon fibers, it is necessary to make the fiber length very short to reduce the reinforcing effect (Japanese Patent Publication No. 59-4).
455), carbon fibers cannot be fibrillated like organic fibers. In particular, when carbon fibers having a weighted average fiber length of 0.5 mm or more are used, the mixing of the entire material becomes non-uniform, and variations in strength and friction characteristics of the product become large, making it difficult to put into practical use. Further, in order to improve the mixing and dispersibility, when a large amount of fibrillated organic fibers are mixed with the carbon fibers to be used, the original function of the carbon fibers is to improve the heat resistance of the friction material. Not fully demonstrated by being.

On the other hand, carbon fibers tend to have an unfavorable tendency to lower the friction coefficient of the friction material depending on the method of use (carbon fibers: March 1, 1986, published by Kyodo Shosha, pp 557-567). Therefore, in a friction material that uses a woven or non-woven fabric of carbon fibers, the fibers are formed by a method such as making a notch (JP-A-4-234476) or performing needling (JP-B-4-61827). A method of three-dimensionally orienting has been proposed. However, it is very expensive to use a woven or non-woven fabric of carbon fibers in a normal friction material. On the other hand, in the case of using short cost carbon short fibers, no method has been found for randomizing the orientation.

A method for shaping the carbon fiber itself into a spherical shape, a granular shape or a cylindrical shape (Japanese Patent Application Laid-Open No. 4-300353, Japanese Patent Application Laid-Open No. 64-26652, etc.) has been proposed. There is a method to shape a material with a very large difference in specific gravity, from about 1.6 of carbon fiber to about 9 of metal component at the maximum, by only containing a small amount of carbon fiber, and randomizing the orientation of carbon fiber. do not do.

[0007]

DISCLOSURE OF THE INVENTION The present invention suppresses the disadvantage of carbon fibers that effectively utilizes the reinforcing effect of carbon fibers to reduce variations in the strength of the friction material and lowers the friction coefficient depending on the method of use. At the same time, the main object is to provide a method for manufacturing a friction material at low cost.

[0008]

The present inventor has conducted extensive studies while paying attention to the problems of the prior art, and as a result, carbon fiber,
By granulating a raw material mixture consisting of a binder and a friction modifier in advance, we succeeded in producing a friction material having a very small variation in strength and a random carbon fiber orientation and a high friction coefficient.

That is, the present invention provides the following method for producing a friction material; A method for producing a friction material, which comprises mixing a granulating binder into a friction material raw material composed of carbon fiber, a binder and a friction modifier, granulating the granulated material, and then heat-pressing the granulated body.

2. The method for producing a friction material according to the above item 1, wherein a carbon fiber having a weighted average fiber length of 0.5 mm or more is used.

3. In the weighted average fiber length frequency distribution,
3. The method for producing a friction material according to the above item 1 or 2, wherein carbon fibers having two maximum values in fiber lengths of less than 0.5 mm and 0.5 mm or more are used.

4. 4. The method for producing a friction material according to the above item 1, 2 or 3, which uses a carbon fiber made of an anisotropic pitch as a raw material.

5. It is possible to mix a granulation binder with a friction material raw material composed of carbon fibers, organic fibers having tentacle-like branched fibers, a binder, and a friction modifier, granulate the granules, and then heat and press mold the granules. A method for manufacturing a characteristic friction material.

6. The method for producing a friction material according to the above item 5, wherein a carbon fiber having a weighted average fiber length of 0.5 mm or more is used.

7. In the weighted average fiber length frequency distribution,
7. The method for producing a friction material according to the above item 5 or 6, wherein a carbon fiber having two maximum values in fiber lengths of less than 0.5 mm and 0.5 mm or more is used.

8. Item 8. The method for producing a friction material according to Item 5, 6 or 7 above, which uses carbon fibers made of anisotropic pitch as a raw material.

The weighted average fiber length in the present specification means the fiber length represented by the following formula.

[0018]

[Equation 1]

The weighted fiber length distribution means a distribution in which the weight ratio of each frequency is represented as frequency in the fiber length frequency distribution.

In the present invention, as the carbon fiber, any type such as pitch type, PAN type, phenol resin type and rayon type may be used. The length of the carbon fiber is 100 mm or less in order to form a granulated body,
More preferably, it is 10 mm or less. The length of the carbon fiber is 0.5m in order to further enhance the reinforcing effect.
It is preferable that m is the lower limit. The amount of carbon fiber is preferably 0.5 to 15% by weight, and more preferably 1 to 10% by weight in the raw material mixture for producing a friction material. If the amount of carbon fiber is less than 0.5% by weight,
While a sufficient reinforcing effect cannot be obtained, if it exceeds 15% by weight, the material cost becomes too high. In order to increase the coefficient of friction of the friction material by including carbon fibers that contribute more to the longitudinal orientation in the granulated material, in the weighted average fiber length frequency distribution with the fiber length intervals as defined below, 0.5
It is preferable to use carbon fibers having two maximum values in the fiber length of less than 0.5 mm and 0.5 mm or more.

That is, the fiber length interval is 0.1 mm when the fiber length is less than 1 mm, 0.25 mm when the fiber length is 1 mm or more and less than 2 mm, and 1 m when the fiber length is 2 mm or more.
Take m intervals.

0.5 mm in the weighted average fiber length distribution
It is preferable that the maximum value of the fiber length exceeding 10 becomes the maximum value. When the maximum value of the fiber length of 0.5 mm or less becomes the maximum value, the strength decreases. In weighted average fiber length,
The ratio of the frequency of the maximum value of 0.5 mm or less to the frequency of the maximum value of more than 0.5 mm depends on the fiber length of each maximum value, but is preferably 3% or more. If this ratio is less than 3%, the effect of increasing the friction coefficient is not sufficiently exerted.

In order to more easily obtain carbon fibers having such an average fiber length distribution, carbon fibers having a weighted average fiber length of 0.5 mm or more and short carbon fibers of less than 0.5 mm may be used in combination.

In order to increase the friction coefficient of the friction material, it is preferable to use carbon fibers made of anisotropic pitch as a raw material.

As the binder, novolac type and resol type phenol resins, epoxy resins, vinyl acetate resins, urethane resins, melamine resins, cross-linking type aromatic thermosetting resins and the like which are known as binders for friction materials are used. They can be used alone or in combination of two or more. In order to increase the heat resistance of the friction material, it is more preferable to use a phenol resin, a cross-linking type aromatic thermosetting resin, or the like.
The amount of the binder is preferably about 5 to 50% of the raw material mixture. When the amount of the binder is less than 5% by weight, the binding force is weakened, while when it is more than 50% by weight, the abrasion amount of the friction material is too large and the heat resistance is also lowered.

Friction modifiers include copper, brass, bronze,
Metal powders and particles such as iron and stainless steel, graphite, barium sulfate, alumina, magnesia, chromium oxide, wollastonite, calcium carbonate, diatomaceous earth, dolomite, magnesium carbonate and other inorganic compound powders and particles, cashew dust, rubber dust, etc. Organic compound powders and granules of can be used. These may be used alone or in combination of two or more, depending on the performance required for the wear material. The particle size of the friction modifier is not particularly limited and can be appropriately determined according to the characteristics required of the friction material. For example, when a metal is used, the particle size may be selected from about 10 μm to 5 mm, when an inorganic compound is used, about 1 μm to 1 mm, and when an organic compound is used, the particle size may be selected from about 10 μm to 1 mm.

When metal powder and / or particles are used as the friction modifier, the amount added is preferably about 5 to 80% by weight, and preferably 10 to 50% by weight, depending on the type of metal.
The degree is particularly preferable. When the addition amount is less than 5% by weight, the friction coefficient is difficult to stabilize, while when it exceeds 80% by weight, the amount of wear of the mating material becomes too large.

When graphite is used as the friction modifier, the amount of addition is preferably about 0.5 to 30% by weight.
It is particularly preferably about 20% by weight. If the amount added is less than 0.5% by weight, the amount of wear becomes too large, whereas if it exceeds 30% by weight, abnormal noise is generated.

When an organic compound such as cashew dust or rubber dust is used as the friction modifier, the addition amount is preferably about 1 to 30% by weight, particularly preferably about 3 to 10% by weight. When the addition amount is less than 1% by weight, the friction coefficient is difficult to stabilize, while when it exceeds 30% by weight, the wear amount becomes too large.

In order to increase the coefficient of friction, these friction modifiers may be used in combination with metal fibers such as copper, brass, iron and stainless steel, and inorganic fibers such as rock wool, ceramics fibers and glass fibers. it can.

Further, in order to further improve the uniform dispersibility of the raw material mixture, it is preferable to add organic fibers having fibers branched in a tentacle shape. These organic fibers can be obtained by treating ordinary pulp, filament, roving or short fibers with a beating machine or the like. As such an organic fiber, aramid fiber, acrylic fiber or the like can be used. The amount of the organic fiber added varies depending on the physical properties required for the friction material, but is preferably 10% or less of the weight of the raw material mixture in order to prevent the heat resistance of the friction material improved by the use of carbon fiber from being reduced. It is more preferable to be 5% or less.

As the granulating binder, liquid binders used in the production of various powders or granules can be used. Examples of such a binder include water, methyl ethyl ketone, various alcohols, toluene, benzene, chloroform, carbon tetrachloride, and other liquids; polyvinyl alcohol, polyvinyl butyral, carboxymethyl cellulose, various rubbers, acrylic resins, phenol resins, epoxy resins, furan resins. Aqueous solutions of organic compounds and solutions or dispersions of methyl ethyl ketone, various alcohols, chloroform, carbon tetrachloride, etc .; Alumina sol, silica sol, water glass, aqueous solutions of inorganic compounds such as condensed polyphosphate and methyl ethyl ketone, various alcohols, chloroform, tetrachloride A solution or dispersion of carbon or the like can be used. As the solvent or dispersion medium,
It is most preferable to use water that does not require a safety device such as explosion-proof, a ventilation device such as exhaust, a protective device such as a gas mask.

In order to carry out the granulation according to the present invention, a rolling or fluid type granulating apparatus such as an ordinary omni mixer, a pan pelletizer and a Henschel mixer is used. Granulation is usually performed by the following procedure. First, a fiber component (carbon fiber or carbon fiber and organic fiber) is put into the apparatus to defibrate the fiber. When using two or more kinds of fibers, add them in order from the lightest one. The defibration time varies depending on the type of fiber, the fiber length, etc., but is preferably within 1 minute in order to prevent reaggregation of fibers (generation of pills). After defibration, powder components are added in order from the lightest one. Next, after adding all the components and thoroughly mixing, a liquid granulating binder is added. The amount of the granulating binder depends on the solid content concentration in the granulating binder, but it is preferable to add about 10 to 50% of the weight of the solid content after mixing. If the amount added to the weight of the solid content is less than 10%, it becomes difficult to form granules, while 50
When it exceeds%, the liquid exudes from the granules.
When the binder for liquid granulation contains solid content (non-volatile content), the content of resin or solid content in the binder is selected according to the type of friction material, blending ratio, final friction material characteristics, etc. Therefore, it is not particularly limited, but the solid content concentration is preferably 50% by weight or less. When the solid content concentration exceeds 50% by weight,
The liquid binder becomes viscous and it becomes difficult to mix the raw materials. The particle size of the granulated product can be adjusted by various means depending on the amount of the liquid binder used. That is, the larger the amount of binder liquid, the larger the granules can be made, and the smaller the amount, the smaller. Further, when the granulation time is constant, the particle size of the granulated product can be increased as the rotation speed of the rolling blade during granulation increases, and the particle size can be decreased as the rotation speed decreases. Furthermore, in the device with the chopper blade for crushing the huge particle mass of the granulated body,
The larger the number of revolutions of the chopper blade, the smaller the grain size, and the smaller the number of revolutions, the larger the grain size. Moisture and volatile components in the granulated product can be removed by evaporation during heat molding, but it is preferable to dry before granulation. In order to further increase the strength of the friction material after molding, it is preferable to add a part of the binder after the granulation operation and continue mixing. The addition and mixing of the binder after the completion of the granulation may be performed for a short time without applying a shearing force, using a mixer such as a tumbler, a V-type mixer, and a Henschel mixer. The amount of binder added and mixed after granulation is
From the point of uniformity in the granulated material, the total friction material solid content is 5
It is preferable that the content be less than or equal to wt%. The addition and mixing after granulation is preferably within 30 seconds in order to maintain the shape of the granulated body.

The particle size of the granulated product is not particularly limited, but is usually about 0.1 to 10 mm, more preferably about 0.1 to 5 mm.

The molding temperature may be selected in an appropriate temperature range depending on the flow characteristics and hardening characteristics of the binder material used, but a density of 90% or more of the theoretical density calculated from the density of the friction material constituent material is obtained. Therefore, the temperature is preferably 120 ° C. or higher, and more preferably about 150 to 200 ° C. The molding pressure varies depending on the molding method used, but is preferably 5 MPa or more in order to obtain a density of 90% or more of the theoretical density calculated from the density of the friction material constituent material.

The fibers such as carbon fibers existing on the surface of the molded body thus obtained are directly affected by the pressing surface, so that the random orientation with respect to the friction surface obtained by granulation is parallel to the pressing surface. The orientation may change. In such a case, a friction material in which the fibers are randomly oriented with respect to the friction surface can be obtained by grinding or cutting the surface of the molded body.

[0037]

According to the method of the present invention, a friction material having a small variation in strength can be obtained while effectively utilizing the reinforcing effect of carbon fibers. Also, the fibers such as carbon fibers in the friction material,
It is oriented in a random direction, whereby a friction material having a high friction coefficient can be obtained.

Further, in the present invention, an expensive carbon fiber woven fabric or woven fabric, and further, an expensive and special device are not required, so that a high-performance friction material can be obtained at an inexpensive cost which is the same as a normal friction material. To be

[0039]

【Example】

Example 1 Carbon fiber (manufactured by Donac Co., Ltd. S-231; average fiber diameter 13 μm, weighted average fiber length 3 mm, tensile strength 800 M)
Pa, tensile elastic modulus 40 GPa) 200 g and aramid fiber (Dupont Toray Kevlar Kevlar Kevlar dry pulp 1F302; average fiber length 2 mm) 50 g were added to a high speed mixer (Fukae Kogyo KK), and 1
It was defibrated for 0 seconds. Next, 150 g of cashew dust (H-9109 manufactured by Cashew Co., Ltd.), 200 g of phenol resin (Belpearl S-899 manufactured by Kanebo Co., Ltd.),
250 g of graphite (SC-60 manufactured by Chuetsu Graphite Co., Ltd.), 25 g of alumina (average particle size 10 μm), 925 g of barium sulfate (manufactured by Sakai Chemical Industry Co., Ltd.) and copper powder (CE- manufactured by Fukuda Metal Foil & Powder Co., Ltd.) 15) 675 g were added sequentially and each addition was mixed for 10 seconds. Next, liquid phenol resin water dilution (PE manufactured by Dainippon Ink and Chemicals, Inc.)
-201-L; solid content concentration 14% by weight) 800 cc was added and granulated.

The obtained granules were dried at 80 ° C. for 4 hours, and then 50 g of a phenol resin (Bellpearl S-899 manufactured by Kanebo Co., Ltd.) was added to a dry weight of 2500 g and mixed in a polyethylene bag for 15 seconds. Then mix 1
Molded at 70 ° C. and 11 MPa, further heat-treated at 210 ° C. for 6 hours, and width 13 mm × length 125 mm × thickness 2-4
A friction material of mm was obtained.

The bending strength of the obtained friction material (5 samples) was measured at a crosshead speed of 2 mm / min and a span of 50 mm. The measurement results are shown in Table 1.

Further, the friction material molded body was cut in the width direction, polished, and then observed by a scanning electron microscope. It was confirmed that the cross section had no branching and the carbon fibers were randomly oriented.

After the friction material molded body was obtained in the same manner as above, a new surface was cut out to obtain a new surface of 30 mm × 30 mm.
The friction coefficient of the cut surface of the sample was measured using a constant speed friction tester at a surface pressure of 2 MPa and a sliding speed of 10 m / s. The measurement results are also shown in Table 1.

Example 2 The same carbon fiber as in Example 1 (S-23 manufactured by Donac Co., Ltd.)
1) 175 g and other carbon fibers (D-Nak Corporation S-
242; weighted average fiber length 0.37 mm, other physical properties are the same as S-231) A friction material (5 samples) was prepared in the same manner as in Example 1 except that a mixture with 25 g was used, and bending strength was measured. Was done. In this example, the weighted average fiber length distribution of the carbon fiber mixture is 0.3-0.4 mm and 1-
It had a maximum value of 2 mm.

The measurement results of the friction coefficient of the obtained molded body were measured in the same manner as in Example 1. Table 1 shows the measurement results of the bending strength and the friction coefficient.

Example 3 Carbon fiber using anisotropic pitch as a raw material (average fiber diameter 11 μm
m, weighted average fiber length 3 mm, tensile strength 1.8 GPa,
Friction materials (5 samples) were prepared in the same manner as in Example 1 except that the tensile elastic modulus was 130 GPa), and bending strength and friction coefficient were measured in the same manner as in Example 1. The measurement results of the bending strength and the friction coefficient are also shown in Table 1.

Comparative Example 1 Carbon fibers (S-231 manufactured by Donac Co., Ltd .; average fiber diameter 1) were prepared by using the same materials as in Example 1 and having the same composition.
3 μm, weighted average fiber length 3 mm) and aramid fibers were added to a Phoenix blender (Oster) for 10
After defibrating for seconds, add liquid phenol resin water dilution,
Mix for an additional 10 seconds.

After drying the resulting mixture at 80 ° C. for 4 hours, the same amount of cashew dust, phenolic resin, graphite, barium sulfate and copper as in Example 1 were sequentially added to the same Phoenix blender, and each addition was repeated. Mixing was performed for 10 seconds. Using this mixture, 5 samples of friction materials were prepared and measured in the same manner as in Example 1. The measurement results of the bending strength are shown in Table 1.

Comparative Example 2 Using the same machine and using the same amount of the same materials as in Example 1, first, a granulate was prepared with a composition excluding carbon fiber and aramid fiber with a high speed mixer, and then with a V-type mixer. The granules were mixed with carbon fibers and aramid fibers. Next, the mixed product was heat-molded in the same manner as in Example 1 to prepare a friction material, and the bending strength and the friction coefficient were measured.

[0050]

[Table 1]

As is clear from the results shown in Table 1, the products of the present invention are excellent in both bending strength and friction coefficient. In particular, the product according to Example 2 has two maximum values in the weighted average fiber length frequency, so that the friction coefficient is improved as compared with the product according to Example 1. Furthermore, since the product according to Example 2 uses the carbon fiber made of anisotropic pitch as a raw material, it is remarkably excellent in both bending strength and friction coefficient.

On the other hand, the product according to Comparative Example 1 obtained by simply mixing and molding each material without granulating the materials in advance has a large variation in bending strength and a low friction coefficient. Further, the product according to Comparative Example 2, which is manufactured by granulating a material other than the fiber material, mixing the other material, and molding, is insufficient in both bending strength and friction coefficient.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Satoshi Tamiya 1-2-2 Hirabayashi Kita, Suminoe-ku, Osaka-shi, Osaka

Claims (8)

[Claims] 1. A friction material comprising: a raw material for a friction material, which comprises a carbon fiber, a binder and a friction modifier, and a binder for granulation. Production method. 2. The method for producing a friction material according to claim 1, wherein carbon fibers having a weighted average fiber length of 0.5 mm or more are used. 3. In the weighted average fiber length frequency distribution, 0.5
The method for producing a friction material according to claim 1 or 2, wherein carbon fibers having maximum values in two fiber lengths of less than 0.5 mm and 0.5 mm or more are used. 4. The method for producing a friction material according to claim 1, 2 or 3, wherein carbon fibers made of an anisotropic pitch as a raw material are used. 5. A granulating binder is mixed with a friction material raw material consisting of carbon fibers, organic fibers having tentacle-like branched fibers, a binder and a friction modifier, and the granulated body is heated. A method for producing a friction material, which comprises pressure forming. 6. The method for producing a friction material according to claim 5, wherein carbon fibers having a weighted average fiber length of 0.5 mm or more are used. 7. In the weighted average fiber length frequency distribution, 0.5
The method for producing a friction material according to claim 5 or 6, wherein carbon fibers having two maximum values for fiber lengths of less than 0.5 mm and 0.5 mm or more are used. 8. The method for producing a friction material according to claim 5, 6 or 7, which uses carbon fibers made of anisotropic pitch as a raw material.