WO2012111763A1

WO2012111763A1 - Friction material and friction material production method

Info

Publication number: WO2012111763A1
Application number: PCT/JP2012/053689
Authority: WO
Inventors: 祐樹高橋; 生栗原; 洋介川上
Original assignee: 曙ブレーキ工業株式会社
Priority date: 2011-02-18
Filing date: 2012-02-16
Publication date: 2012-08-23

Abstract

Provided are a highly heat-resistant friction material that is suitable for high heat / high loads and can be produced by simply adding a baking process to processes that are similar to those for organic friction materials, and a production method therefor. The friction material, obtained from a fiber matrix, a friction-adjusting material, a binder and an inorganic material, is produced by thermoforming a raw material that comprises a silicon-containing polymer and a nanoparticle material or swelling clay minerals, then heat-treating at a temperature of 160 - 350°C for one to ten hours in an oxidizing atmosphere to cross-link the silicon-containing polymer with oxygen, and then baking. Selecting one or more compounds from the group consisting of polycarbosilane, polyorganoborosilazane, polyborosiloxane, polycarbosilazane, and perhydropolysilazane for the silicon-containing polymer is desirable.

Description

Friction material and friction material manufacturing method

The present invention relates to a friction material for brakes used in automobiles, railways, aircraft, industrial machines, and the like, and in particular, a friction material excellent in heat resistance capable of withstanding high temperature and high load, which can be reduced in size and weight, and It relates to the manufacturing method.

Friction materials mainly used in automobiles are molded with thermosetting resins such as phenol resin as binders (binders), but because the binders are organic materials, the friction coefficient at high speed There is a problem that the friction material sticks due to a decrease in temperature and thermal deformation or deterioration of the organic material due to braking heat. In recent years, the performance required of friction materials has been reduced in size and weight for the purpose of energy saving, and the load on the friction materials has become increasingly severe. In order to solve these problems, Patent Documents 1 to 3 propose friction materials made of copper-based sintered alloys, C / C composites, CMC (ceramic matrix composites), friction materials obtained by firing and carbonizing organic materials, and the like. .
However, these friction materials still have problems such as difficulty in the production method, high energy in production, and higher cost than conventional products.

Further, Patent Document 1 and Patent Document 2 propose a friction material that is a binder obtained by sintering and carbonizing an organic material containing pitch. In general, when manufacturing a friction material by carbonizing an organic material into a binder, the raw materials such as an organic material, an inorganic filler, a solid lubricant, and a metal material are mixed, and this mixture is vacuumed and reduced gas. Then, the temperature is raised to about 550 to 1000 ° C. while applying a necessary load in any atmosphere of an inert gas. As a result, the organic material is carbonized to function as a binder, and a friction material is manufactured. However, when pitch is blended as a binder of the fired friction material, it contains a trace amount of benzopyrene, which is a harmful component, and there is a possibility that its use is restricted due to recent environmental regulations. When the use is prohibited in the future, an alternative raw material will be required as a binder for the fired friction material.

On the other hand, a general disc brake friction material is molded using a thermosetting resin typified by phenol resin as a binder, but gas is generated by a thermosetting reaction of the organic binder in the thermoforming process. If the generated gas is confined in the thermoformed friction material and the gas pressure is too high, it is released at a time when the press pressure is released, causing cracks and blisters.

Patent Document 4 describes a technique for providing a friction material that contains an organometallic compound together with a thermosetting resin, has a low volatile content during high temperature operation, and has excellent fade resistance and wear resistance. However, even a friction material using such an inorganic binder causes the same phenomenon.

As a solution for cracks and blisters in friction materials using phenolic resin as a binder, Patent Document 5 changes the punch material of the thermoforming die to one with increased thermal conductivity, and provides a temperature gradient to reduce the generated gas. There are ways to encourage emissions. Patent Document 6 also describes a solution that suppresses rapid gas expansion by repeating pressurization and depressurization during molding and controlling the release of pressure during depressurization.
In Patent Document 7, when a friction material raw preform is thermoformed using a friction material thermoforming mold including a presser mold, a middle mold, and a press mold, a temperature difference is provided between the presser mold and the press mold. At the time of molding, the part where the preform is finally cured is brought to either the pressing mold or the pressing mold, and the pressing mold or pressing mold corresponding to this final curing part is entered into the final curing part, and the mold Describes a degassing method in the thermoforming process of the friction material, in which a protrusion having a degassing path leading to the outside is provided so that degassing can be performed from the final hardened portion.
However, even if these methods are used, it is still not sufficient, and it has been confirmed that the product gradually expands after completion of thermoforming, causing cracks and blisters, and even if these measures are taken, it has not been solved. .

Japanese Unexamined Patent Publication No. 2006-306970 Japanese Patent Laid-Open No. 11-132270 Japanese Laid-Open Patent Publication No. 3-51531 Japanese Unexamined Patent Publication No. 7-292349 Japanese Unexamined Patent Publication No. 2003-232392 Japanese Unexamined Patent Publication No. 2003-145565 Japanese Unexamined Patent Publication No. 2003-127155

As described above, when manufacturing a disc brake pad that can withstand high temperatures and high loads, the binding material may be fired and carbonized to produce a friction material. However, the manufacturing process is difficult and the energy required for manufacturing is high. There are problems in practicality such as higher consumption and cost than conventional products. If we can provide a high heat-resistant pad that can be manufactured simply by adding a baking process to the same manufacturing process as that of organic friction materials (NAO material, Non-Asbestos-Organic), then the problem of high energy production described above Can be solved.
Accordingly, one of the objects of the present invention is to provide a high heat-resistant friction material that is suitable for high temperature and high load and that can be manufactured simply by adding a baking process to the same process as the organic friction material.

Another problem of the present invention is that when an organic resin containing pitch is used as a binder, harmful component benzopyrene may be discharged in the manufacturing process. It is intended to be applied as a material.
In addition, in a friction material using an inorganic binder, it has been confirmed that the conventional molding method gradually expands after completion of thermoforming, causing cracks and blisters, and even when various measures are taken, it cannot be solved. Accordingly, another object of the present invention is to develop a molding method for obtaining a friction material having excellent quality capable of eliminating molding defects such as cracks and blisters of a product after completion of thermoforming.

The present inventor has studied various molding conditions and various binders of friction materials in order to produce a high heat-resistant friction material or a fired friction material in an existing production process. As a result, the present invention is described in the following (1) to (12). Solved the problem.
(1) In a friction material composed of a fiber base material, a friction modifier, a binder, and an inorganic material, a raw material containing a silicon-containing polymer and a nanoparticle material or a swellable clay mineral as the binder is heat-treated in an oxidizing atmosphere. A friction material characterized in that a silicon-containing polymer is cross-linked with oxygen and cross-linked with oxygen, followed by firing to form a Si—C network.
(2) The friction material according to (1), wherein the heat treatment is performed at a temperature of 160 to 350 ° C. for 1 to 10 hours.

(3) The above (1) or (), wherein the silicon-containing polymer is one or more compounds selected from the group consisting of polycarbosilane, polyorganoborosilazane, polyborosiloxane, polycarbosilazane, and perhydropolysilazane. The friction material according to 2).
(4) The friction material as described in any one of (1) to (3) above, wherein the silicon-containing polymer is blended in an amount of 5 to 10% by mass of the entire friction material composition.
(5) The friction material according to any one of (1) to (4) above, wherein the nanoparticle material is contained in an amount of 15 to 50 parts by mass with respect to 100 parts by mass of the silicon-containing polymer.
(6) The friction material according to any one of (1) to (5), wherein the nanoparticle material is silica.
(7) The friction material according to (6), wherein the silica is an organosilica sol.

(8) The friction material according to any one of (1) to (4), wherein the swellable clay mineral is a swellable clay mineral that has been subjected to an organic treatment.
(9) The friction material according to any one of (1) to (4) and (8), wherein the swellable clay mineral is montmorillonite.

(10) In a method for producing a friction material comprising a fiber base material, a friction modifier, a binder, and an inorganic material, including at least preforming, thermoforming, and heat treatment steps, a silicon-containing polymer and a nanoparticle material or The raw material containing the swellable clay mineral is thermoformed and then infusibilized by heat treatment in an oxidizing atmosphere at a temperature of 160 to 350 ° C. for 1 to 10 hours to crosslink the silicon-containing polymer with oxygen. Then, a method for producing a friction material, which is fired.
(11) The method for producing a friction material as described in (10) above, wherein the heating rate of the heat treatment in the infusibilization treatment is 14 to 140 ° C. per hour.
(12) The method for producing a friction material according to (10) or (11), wherein the heat treatment in the infusibilization treatment is performed using millimeter wave heating.

(13) The method for producing a friction material as described in any one of (10) to (12) above, wherein after the heat treatment, firing is further performed at a temperature of 800 to 1000 ° C. for 1 to 2 hours.
(14) The method for producing a friction material as described in any one of (10) to (13) above, wherein the preforming is preformed at a pressure of 25 to 300 MPa.

Since the base material strengthening mechanism is formed by cross-linking with oxygen by changing the binder from an organic material such as a straight phenol resin to a silicon-containing polymer, the heat resistance can be improved as compared with a conventional friction material. Further, it was found that if the silicon-containing polymer is heated in an oxidizing atmosphere, it does not flow out during the heat treatment, so that it can be used as a binder for a friction material. A more detailed study revealed that the silicon-containing polymer had a problem that if the precuring temperature was less than 300 ° C., the resin was too soft and oozed out before pressure was applied (for example, Japanese Patent Application Laid-Open No. 2002-255650). In the present invention, in order to more effectively suppress the exudation of the silicon-containing polymer during infusibilization, the nanoparticle material (hereinafter simply referred to as “nanoparticles”) is used together with the silicon-containing polymer. It has also been found that outflow during heating of the silicon-containing polymer can be suppressed by containing a swellable clay mineral. In addition, silicon-containing polymers are sensitive to temperature changes and may suddenly drop in viscosity during infusibilization, but by incorporating nanoparticles or swellable clay minerals, the melt viscosity is increased and the viscosity changes. Therefore, the infusibilization process can be completed in a short time, and the friction material can be manufactured at a low cost and in a short time. Nanoparticles or organically treated swellable clay minerals can be finely dispersed, so the amount of nanoparticles or swellable clay minerals can be added in a small amount, with little effect on friction performance, and effective formation of ceramic networks Can help and strengthen.

Furthermore, since the production can be handled only with the existing equipment, the production costs are equivalent and there is no need for capital investment.
In addition, when pitch is used as a binder for fired friction materials, benzopyrene, which is a harmful substance, may be discharged in a small amount in the production process. However, if it is replaced with a silicon-containing polymer, the fired friction material is excellent in heat resistance without environmental pollution. Can be used.

Furthermore, when a silicon-containing polymer is used as a binder for the friction material, the generation of cracks and bulges cannot be completely suppressed. However, if a silicon-containing polymer is used for pre-molding at high pressure, Little change in thickness. Therefore, it is possible to prevent generation of cracks and blisters without blocking the gas discharge port, and to manufacture a friction material with excellent quality. In addition, the near net shape can be formed, and since there is no fluctuation compared with a normal preform, handling is good. The pre-forming pressure of a normal organic friction material is 25 to 35 MPa. In the present invention, pre-forming at a pressure exceeding this is referred to as pre-forming at high pressure, specifically at 25 to 300 MPa. Preferably there is.

FIG. 1 is a diagram showing the results of DTA (differential thermal analysis) in air for only polycarbosilane (binder D) and an inorganic binder (binder B) in which polycarbosilane and nanosilica particles are mixed. 2A shows a friction material containing only polycarbosilane as a binder (Reference Example 1), and FIG. 2B shows a friction material containing polycarbosilane and nanosilica particles (Example 3). ) Are electron micrographs each showing a mapping of silicon elements of a friction material (Example 7) containing polycarbosilane and chain-like nanosilica particles.

Hereinafter, embodiments of the present invention will be described in detail.
The silicon-containing polymer used in the present invention is used in, for example, a method of directly shaping and firing a ceramic product made of SiC, a method of impregnating a preform, and then converting to ceramic by thermal decomposition. A silicon-containing polymer known as a ceramic precursor can be used.

A porous carbon fiber is infiltrated with a silicon-containing polymer, and a porous CC initial body is produced by thermal decomposition. Liquid porous silicon (silicon-containing polymer) is infiltrated into the porous CC initial body, and heating is performed at that time. Examples of manufacturing friction material by making ceramics into SiC (see Patent Document 2), and examples of using a silicon-containing polymer as a binder together with a thermosetting resin, and crosslinking the thermosetting resin and the silicon-containing polymer (patent) Although the polymer is used as a binder (binder), it is thermoformed, infusibilized by heat treatment in an oxidizing atmosphere, crosslinked with oxygen, and fired. There has been no report of a friction material in which a Si—C network is formed.
The feature of the present invention is to produce a friction material using a silicon-containing polymer as a binder only by adding a baking step to the same production method as in the case of an organic friction material using a phenol resin as a binder.

Specific examples of the silicon-containing polymer include thermally decomposable polymers composed of groups such as polycarbosilane, polyorganoborosilazane, polyborosiloxane, polycarbosilazane, and perhydropolysilazane.
In the present invention, it is not necessary that the binder is a silicon-containing polymer, and other resins can be used in combination with the silicon-containing polymer. This will be described later.

Considering price and availability, polycarbosilane is preferable among the silicon-containing polymers as the binder (binding material) used in the present invention. The type of polycarbosilane used in the present invention is not particularly limited. For example, it is an organosilicon polymer containing at least 30% by mass or more of a repeating unit represented by the following general formula I, general formula II or general formula III. .

(Wherein R ¹ represents a hydrogen atom, an alkyl group or a hydroxyl group, R ² represents an alkyl group, a phenyl group or a halogen atom, and n represents an integer.)
The polycarbosilane may be a homopolymer, a copolymer, a block, a graft or a blend. The number average molecular weight of the polycarbosilane in the present invention is usually 500 to 10,000.

Various types of nanoparticle materials can be used as the nanoparticles of the present invention, for example, silica particles such as diatomaceous earth, Celite®, Celatom®, and / or silicon dioxide. And nanoparticles of resin powders such as phenol resins, silicone resins, epoxy resins, and mixtures thereof, and carbon powders and / or particles of partially and / or completely carbonized nanoparticles. Furthermore, a mixture of these nanoparticle materials may be used. Moreover, the particle | grain form of a nanoparticle is not specifically limited, The substantially spherical shape, a rectangular parallelepiped shape, plate shape, linear shape like a fiber, and the branched branched shape can be used. By using nanoparticles with silicon-containing polymers, the nanoparticles are finely dispersed in the silicon-containing polymer at the nano level, the melt viscosity is increased by the volume effect, and the silicon-containing polymer flows out of the friction material in the infusibilization process. In order to prevent this, a dense network having a high ceramic content in the friction material can be formed even if the infusibilization treatment is performed at a high temperature for a short time.

These nanoparticles are nanoparticles having a primary particle size ranging from about 10 to about 150 nm in diameter, preferably from about 10 to about 50 nm. Further, nanoparticles having an average nanoparticle diameter of about 15 nm to about 30 nm as the primary nanoparticle size are preferred.

Among these, the use of nanosilica particles whose nanoparticle material is silica is preferable because it can assist and strengthen the formation of a ceramic network. This is presumably because the base material strength is improved by the reaction and sintering between the silicon component in the silicon-containing polymer and the nanosilica particles. As silica, colloidal silica is preferable from the viewpoint of dispersibility in the matrix, and organic solvent dispersible colloidal silica (organosilica sol) is more preferable.
The silica is not particularly limited. Specifically, as a spherical organosilica sol dispersed in an organic solvent, methanol silica sol, MA-ST-M, IPA-ST manufactured by Nissan Chemical Industries, Ltd. IPA-ST-L, IPA-ST-ZL, EG-ST, EG-ST-ZL, DMAC-ST, DMAC-ST-ZL, NPC-ST-30, PGM-ST, MEK-ST, MEK-ST -ZL, MIBK-ST, MIBK-ST, PMA-ST, EAC-ST, NBAC-ST, XBA-ST, TOL-ST, etc., Nanotech slurry of CI Kasei Co., Ltd., etc. Examples of the chain organosilica sol include IPA-ST-UP and MEK-ST-UP manufactured by Nissan Chemical Industries, Ltd.

Among these, the use of a chain-like organosilica sol is preferable because a high-density friction material can be produced and a friction material with excellent performance can be obtained. Here, the chain-like organosilica sol means a specific number of spherical colloidal silica particles as primary particles, colloidal silica having a shape connected in series or partially branched. It is presumed that the chain particles in the silicon-containing polymer have orientation during molding, and a high-density friction material is produced. Further, by dispersing the chain particles in the silicon-containing polymer, the melt viscosity can be further increased, and the binder outflow can be further suppressed. Furthermore, since the chain particles can be finely dispersed, the addition amount is small, and the influence on the friction performance is small, which is preferable.

Examples of the swellable clay mineral that can be used in the present invention include smectite clay minerals such as montmorillonite, saponite, beidellite, nontronite, hectorite, and stevensite, vermiculite, halloysite, and synthetic fluorine mica. These may be natural products or synthetic products. Among these, montmorillonite, saponite, and synthetic fluorine mica are particularly preferable from the viewpoints of being easily organically treated and improving the reinforcing property as a filler.

These swellable clay minerals have a layered structure, and are preferably subjected to an organic treatment in that an interlayer compound is formed by the organic treatment, and the interlayer is enlarged and delamination is likely to occur. Examples of the organic compound used for the organic treatment include amines and quaternary ammonium salts. For these organic compounds, it is preferable to select and use optimal ones in consideration of the types of clay minerals and dispersion solvents used (mainly polar) and the types of silicon-containing polymers used.

Examples of amines that can be used include aliphatic amines having 1 to 18 carbon atoms and aromatic amines. Specific examples of the aliphatic amine include diethylamine, amylamine, dodecylamine, hexadecylamine, stearylamine, didodecylmethylamine hydrochloride and odorous acid salt, and specific examples of the aromatic amine include aniline and toluidine. , Xylidine, phenylenediamine and the like. Of these amines, aniline is particularly preferred. On the other hand, preferred examples of the quaternary ammonium salt include dodecyltrimethylammonium chloride, dimethylstearylbenzylammonium chloride, trimethylstearylammonium chloride, dimethyldioctadecylammonium chloride (Esben NX), and oleylbis (2-hydroxyethyl) methylammonium chloride. be able to. Among these, dimethyl dioctadecyl ammonium chloride is particularly suitable.

The organic treatment of the swellable clay mineral can be appropriately performed by a conventionally known method. For example, after the swollen clay mineral is put into water and stirred to form a uniform liquid separation of the clay mineral, the organic compound or a salt thereof is added. By adding the liquid dissolved in water to the clay mineral dispersion and stirring, the organic compound is inserted between the layers of the clay mineral and the supported clay mineral is precipitated, so the precipitate is separated, recovered and dried. Thus, an organically treated swellable clay mineral powder can be obtained.

In the present invention, by using these swellable clay minerals together with a silicon-containing polymer, the formation of a ceramic network can be assisted and strengthened, and the infusibilization process can be completed in a short time. This is because the swellable clay mineral is finely dispersed at the nano level in the silicon-containing polymer, the melt viscosity is increased due to the volume effect, and the silicon-containing polymer is prevented from flowing out of the friction material in the infusibilization process, and cracks, It is presumed that a dense network having a high ceramic content in the friction material can be formed even if the infusibilization treatment is performed at a high temperature for a short time.

In the present invention, for example, a silicon-containing polymer is introduced into an organic solvent such as xylene, toluene, hexane, butanone, and the resin solution obtained by stirring is charged with a nanoparticle solution or a swellable clay mineral into the resin solution. Further, after stirring and dispersing the nanoparticles or the swellable clay mineral, the above solution is desolvated, and the bulk resin is recovered and pulverized to obtain a raw material powder for a friction material.

The amount of nanoparticles or swellable clay mineral added to the silicon-containing polymer is not particularly limited as long as the nanoparticles or swellable clay mineral functions effectively, but the addition of nanoparticles or swellable clay mineral is not limited. If the amount is too large, the flowability of the binder is lost, the wettability / adhesion with the adherend is reduced, and nanoparticles or swellable clay minerals are present at the binder / adhesive interface, Since the contact area of the adherend becomes small, the function as a binder is lost for reasons such as inhibiting adhesion, which is not preferable. Usually, it is preferable to contain nanoparticles in the range of 15 to 50 parts by mass or swellable clay mineral in the range of 1 to 10 parts by mass with respect to 100 parts by mass of the silicon-containing polymer.

The process for producing the friction material of the present invention usually comprises the steps of blending the friction material, stirring, preforming, thermoforming, heating, firing and polishing, and is the same as the conventional process for producing the friction material.
In the embodiment, it is applied to manufacture brake friction materials such as brake pads of disc brake devices and brake linings of drum brake devices mounted on vehicles, etc., and various granular components (raw materials) ) Are mixed in a predetermined ratio to form a friction material base material, and the step of mixing and stirring is performed. The friction material base material is put into a preforming mold and pressure-molded to obtain a preform with a predetermined shape. A preforming step, a thermoforming step of obtaining a thermoformed body molded into a predetermined friction material shape by being put into a thermoforming mold together with a preformed body and subjected to a thermoforming process at a predetermined molding pressure and temperature; By performing post-heat treatment, polishing treatment or the like on the molded body as appropriate, a post-treatment step for completing a friction material having a desired shape is sequentially performed.

In the present invention, heat treatment and baking treatment in an oxidizing atmosphere are performed as the subsequent heat treatment. The silicon-containing polymer is infusible and cross-linked with oxygen by heat treatment in an oxidizing atmosphere, and then a network-like silicon-carbon (Si-C network) structure is built in the binder by firing treatment.

In a normal thermoforming process, a thermoforming apparatus is used, and a pressure forming process for forming a preformed body and a depressurization (degassing) process for releasing the forming pressure are alternately repeated as many times as necessary. At the same time, in this depressurization process, the gas generated in the thermoforming mold is discharged by opening the thermoforming mold.

There are no particular restrictions on the conditions for preforming the friction material composition, heating and pressing, heat treatment in an oxidizing atmosphere, and firing conditions, but the temperature during thermoforming is 150 to 180 ° C., the pressure is 30 to 50 MPa, and the pressure is increased. It is desirable to mold under a pressure time of 300 to 500 seconds.
The heat treatment in an oxidizing atmosphere is desirably performed under conditions of 160 to 350 ° C. (preferably 160 to 300 ° C.), a pressure of 0.1 to 0.3 MPa, and a treatment time of 1 to 10 hours. Within these condition ranges, the outflow of the silicon-containing polymer is suppressed and the dimensional stability is also good.

Furthermore, the heat treatment in the oxidizing atmosphere can be further controlled by controlling the rate of temperature rise to a low speed or by using millimeter wave heating, thereby further suppressing the outflow of the silicon-containing polymer. It can be manufactured and is preferable. In addition, the residual inorganic component contained in the binder increases, and a denser ceramic network can be formed.

As a method of performing heat treatment in an oxidizing atmosphere by controlling the rate of temperature increase to a low rate, for example, the temperature reaches 300 ° C. at a rate of temperature increase of 14 to 140 ° C. per hour under a pressure of 0.1 to 0.3 MPa. By heating for 1 to 10 hours until the silicon-containing polymer flows out, it can be satisfactorily suppressed. Further, as described above, the heat treatment in an oxidizing atmosphere is desirably 160 ° C. to 300 ° C., but the rate of temperature increase up to 160 ° C. is not particularly limited and is arbitrary.

It is also preferable to perform heat treatment in an oxidizing atmosphere using millimeter wave heating. The millimeter wave in this case refers to an electromagnetic wave having a frequency of 20 GHz to 300 GHz (that is, a wavelength of 15 mm to 1 mm), and the millimeter wave heating refers to dielectric heating using the millimeter wave band electromagnetic wave. Millimeter wave heating can be performed by using a millimeter wave heating apparatus using a gyrotron oscillation tube.
For example, a treatment time of 1 to 5 hours under a pressure of 250 to 350 ° C. and 0.1 to 0.3 MPa is preferable. By performing millimeter wave heating, the outflow of the silicon-containing polymer is suppressed as described above, a dense ceramic network is formed, and the heat treatment time can be shortened.

The firing is preferably performed in a vacuum, a reducing gas, or an inert gas atmosphere under conditions of a temperature of 800 to 1000 ° C. and a pressure of 0.5 MPa, and a treatment time of 1 to 2 hours.
When the firing temperature is 800 ° C. or higher, a sufficient Si—C reinforced network is achieved, and when it is 1000 ° C. or lower, other blended raw materials are not lost or dissolved, and stable friction performance is obtained. ,preferable. Also, sufficient mechanical strength as a friction structure can be obtained.
The firing time (keep time) is preferably 1 hour or longer in order to complete the reaction for forming a network of Si components and considering the stability of physical properties. A firing time exceeding 2 hours is an excessively high energy production, which is not preferable from the viewpoint of cost. Since there is a concern about the expansion of the sample in the firing step, it is preferable to apply a load of about 0.5 MPa to improve the dimensional stability.

Various blended materials are used to ensure desired friction material characteristics, but metal fibers such as copper fibers and steel fibers are suitable as the fiber base material in terms of impact strength and temperature.
In consideration of heat resistance, inorganic materials can be mentioned. Examples thereof include ceramics that can withstand heat treatment temperatures such as zirconia, alumina, titania, magnesia, calcium fluoride, boron nitride, and SiC.

Also, the friction material of the present invention can contain various friction modifiers that are usually used. As such a friction modifier, materials such as graphite, iron, aluminum, copper, brass, bronze and the like are used. When these materials are actually used, it is conceivable to use a combination of a plurality of types of materials in consideration of various shapes and sizes such as granules and fibers in addition to powders.

In the present invention, a silicon-containing polymer is used as a binder, but other organic resins may be used in combination as long as the performance of the friction material is not impaired. As the binder, known thermosetting resins such as phenol resin (straight phenol resin), furan resin, xylene resin, urea resin, melamine resin, aniline resin, unsaturated polyester resin, polyimide resin, epoxy resin, etc. Although phenol can be selected from among them, a phenol resin is preferable in terms of availability and ease of handling. The mixing ratio of these resins is up to about 50% by mass of the binder.

Various blending compositions can be selected as the composition of the friction material. That is, these may be mixed singly or in combination of two or more according to the friction characteristics required for the product, for example, the friction coefficient, wear resistance, vibration characteristics, squeal characteristics, and the like.
As a general compounding composition, when the total compounding material of the friction material is 100% by mass, the fiber base material is 10 to 50% by mass, the inorganic material is 15 to 50% by mass, the binder is 5 to 10% by mass, and the metal powder 1 ~ 10% by mass.

Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to only these examples.

<Examples 1 to 6 and Reference Examples 1 and 2>
The trial production conditions and manufacturing flow of Examples 1 to 6 and Reference Examples 1 and 2 are as follows.

1. Preparation of inorganic binder (1) Preparation of inorganic binders A to C Xylene solution of silicon-containing polymer (Ube Industries, Ltd .: VZ-100, 50% solution) and nanosilica MEK solution (Ci Kasei): SIMEK, 15% solution) was mixed with the formulation shown in Table 1, and then heated and dried in a vacuum oven at 150 ° C. for 24 hours. After drying, the binder was pulverized to obtain powdered inorganic binders A to C.

(2) Preparation of Inorganic Binder D The xylene solution (VZ-100, 50% solution) of the above silicon-containing polymer was dried by heating in a vacuum oven at 150 ° C. for 24 hours. After drying, the binder was pulverized to obtain a powdery inorganic binder D.

2. Mixing of raw materials The raw materials shown in Table 2 were charged into an Eirich mixing stirrer in the blending amounts shown in Table 2 to obtain a chopper rotation speed of 1500 rpm and a bread rotation speed of 42 rpm, and the mixture was stirred at room temperature for 2 minutes.

3. Preliminary molding The above mixture was put into a mold of a preforming press and subjected to pressure molding at room temperature and 25 MPa for 5 seconds to prepare a preform. (Sample size: 100x50mm)
4). Thermoforming The preform was heat-pressed with a small heat press machine at a molding temperature of 160 ° C., a surface pressure of 50 MPa, and a molding time of 7 minutes to produce a thermoformed body.
5. Heat treatment (infusibilization)
The thermoformed body was set on a heating jig and heated at a predetermined speed shown in Table 3 up to 300 ° C. in an oven while maintaining the pressure at 0.2 MPa to perform infusibilization.
6). Firing The infusibilized product was put into a firing furnace and fired at 800 ° C. in an argon gas atmosphere while maintaining a pressure of 0.5 MPa to obtain a friction material.

[Results of physical property evaluation]
Various evaluations of the friction material were performed according to the following measurement methods.
(1) Flowability test of inorganic binder 0.3 g of inorganic binders A to D are weighed, and a cylindrical formed body having a diameter of 7 mm and a height of 7 mm is produced by compression molding at room temperature. After holding the glass plate inclined at an angle of 20 ° and adjusting the heating to a glass plate temperature of 275 ° C. in an oven, the cylindrical formed body is placed on the glass plate and held in the oven for 15 minutes. After the glass plate is taken out and sufficiently cooled, the distance through which the inorganic binder flows is measured.

(2) Evaluation of seepage of inorganic binder The outer periphery of the molded body after the infusibilization treatment is visually observed, and the degree of seepage is evaluated according to the following rating.
5 points: no bleeding, 4 points: slight bleeding, 3 points: bleeding, 2 points: large bleeding, 1 point: maximum bleeding

(3) Evaluation of physical properties and friction performance of friction material a. Measure the thickness of the friction material after firing (targeted at 15 mm) and the Rockwell hardness.
b. The state of the shape of the friction material after firing was evaluated in three stages: “◯; good”, “Δ; acceptable”, “x; poor”.

Table 3 shows various physical properties of the friction material. In Examples 1 to 6 and Reference Examples 1 and 2, samples having good physical properties could be obtained by performing heat treatment in an oxidizing atmosphere. In these friction materials, it is presumed that the Si component constituting the polycarbosilane was heated in an oxidizing atmosphere to promote the oxidation reaction, promote the strengthening of the matrix, and ensure good physical properties.

Further, FIG. 1 shows the results of DTA (differential thermal analysis) in the air of only polycarbosilane (binder D) and an inorganic binder (binder B) in which polycarbosilane and nano silica particles are mixed. In the inorganic binder in which polycarbosilane and nanosilica particles are mixed, an exothermic peak is observed at around 200 ° C to 400 ° C. Since the infusibilization reaction of polycarbosilane starts at about 200 ° C., it is presumed that in the binder B, crosslinking is caused by polycarbosilane and silanol groups (—Si—OH) on the surface of the nanosilica particles. From the above, it is presumed that a stronger bond is produced in the case of adding nanosilica particles than in the case of polycarbosilane alone.

Also, the friction performance of the friction material containing only polycarbosilane (Reference Example 1) and the friction material containing polycarbosilane and nanosilica particles (Example 3) was evaluated. The results are shown in Table 4. Various evaluations of the friction material were performed according to the following measurement methods.

1) Performance test (according to JASO C406-82)
The produced sample was processed into a test piece (13 × 35 mm), and a performance test was performed using a small dynamo inertial friction tester. Table 4 shows the results of the second efficacy and the first fade.
(1st fade test method)
Initial speed: 100 km / h → 3 km / h
Deceleration: 0.45G
Number of brakings: 9 times Braking cycle: 35 seconds Note that the fade rate (%) = [(min μ (minimum μ)) / first μ] × 100.

2) Measurement of rotor / pad wear amount Further, after the performance test was completed, the rotor / pad wear amount (μm / mm) was measured to evaluate the rotor aggression (partner material aggression).

From the results in Table 4, since both Reference Example 1 and Example 3 show equivalent friction performance, it is considered that there is no influence on the friction performance by adding nano silica particles.

Furthermore, the silicon element mapping measurement result by EPMA of Reference Example 1 and Example 3 is shown in FIG. It can be seen from Reference Example 1 that the binder forms a Si network. In Example 3, since nano silica particles are added, the strength is detected to be higher than that in Reference Example 1. Segregation due to the addition of nanosilica particles is not observed, and the silica is uniformly dispersed in the Si network. Since Example 3 has high hardness, it is presumed that the network formation is enhanced.

<Examples 7 and 8>
The prototype conditions and manufacturing flow of Examples 7 and 8 are as follows.

1. Preparation of Inorganic Binder (1) Preparation of Inorganic Binders E and F As a nanosilica solution, in inorganic binder E, MEK solution of nanosilica (chain particles) (manufactured by Nissan Chemical Industries, Ltd .: MEK-ST-UP, solid content 20 %) Was used in the inorganic binder F, except that a xylene solution of nano silica (manufactured by Nissan Chemical Industries, Ltd .: XBA-ST, solid content 30%) was used and mixed in the composition shown in Table 5 respectively. In the same manner as in the preparation method, powdered inorganic binders E and F were obtained.

The raw materials shown in Table 6 were mixed in the same manner as in Example 1 except that the raw materials were mixed with the total amount of BR> Z shown in Table 6. Friction treatment) and firing were performed to produce a friction material. Table 7 shows the results of evaluating the obtained friction materials in the same manner as in Examples 1 to 6.

Examples 7 and 8 were able to obtain samples having good physical properties as in Examples 1 to 6 by performing heat treatment in an oxidizing atmosphere. In these friction materials, it is presumed that the Si component constituting the polycarbosilane was heated in an oxidizing atmosphere to promote the oxidation reaction, promote the strengthening of the matrix, and ensure good physical properties. Due to the flowability lowering effect at the time of melting, there is almost no oozing out during the infusibilization process, and a friction material with a stable quality can be obtained, and a higher density can be expected.

Also, the friction performance of the friction material (Example 7) containing polycarbosilane and chain-like nanosilica particles was evaluated. The results are shown in Table 8. From the results of Table 8, since Example 7 also exhibits the friction performance equivalent to that in Reference Example 1 above, it is considered that there is no influence on the friction performance due to the addition of the chain nanosilica particles.

Furthermore, the silicon element mapping measurement result by EPMA of Example 7 is shown in FIG. In Example 7, since chain-like nanosilica particles are added, the strength is detected to be higher than that in Reference Example 1. Segregation due to the addition of the chain-like nanosilica particles is not observed, and it is presumed that the network formation is strengthened because it is uniformly dispersed in the Si network.

From the above, from the results of Examples 1 to 8 and Reference Examples 1 and 2, the flow rate of the binder is suppressed by making the temperature increase rate at the time of the infusible treatment low, and it is difficult to see out the present invention. Thus, by including nanoparticles, the flowability at the time of melting of the silicon-containing polymer is reduced, and even if the heating rate during the infusibilization treatment is not slowed, there is almost no oozing out of the binder. It can be seen that an equivalent friction material can be obtained. Compared with Examples 5 and 6, Examples 1 to 4 have a more appropriate amount of nanosilica particles, good flowability of the binder, and a friction material with better quality can be obtained. I understand.

<Examples 9 to 14 and Reference Examples 3 and 4>
The trial production conditions and production flow of Examples 9 to 14 and Reference Examples 3 and 4 are as follows.

1. Preparation of inorganic binder (1) Preparation of inorganic binders G to I A xylene solution of a silicon-containing polymer (manufactured by Ube Industries, Ltd .: VZ-100, 50% solution) and an organically treated montmorillonite powder (manufactured by Hojun: Sven NK) ) Was mixed with the formulation shown in Table 9, and then heated and dried in a vacuum oven at 150 ° C. for 24 hours. After drying, the binder was pulverized to obtain powdered inorganic binders GI.

(2) Preparation of inorganic binder J The silicon-containing polymer xylene solution (VZ-100, 50% solution) was heat-dried in a vacuum oven at 150 ° C. for 24 hours. After drying, the binder was pulverized to obtain a powdery inorganic binder J.

2. Mixing of raw materials The raw materials shown in Table 10 were charged into an Eirich mixing stirrer in the blending amounts shown in Table 10, and the chopper rotation speed was 1500 rpm and the bread rotation speed was 42 rpm, and the mixture was stirred at room temperature for 2 minutes.

3. Preliminary molding The above mixture was put into a mold of a preforming press and subjected to pressure molding at room temperature and 25 MPa for 5 seconds to prepare a preform. (Sample size: 100x50mm)
4). Thermoforming The preform was heat-pressed with a small heat press machine at a molding temperature of 160 ° C., a surface pressure of 50 MPa, and a molding time of 7 minutes to produce a thermoformed body.
5. Heat treatment (infusibilization)
The thermoformed body was set on a heating jig and heated at a predetermined speed shown in Table 3 up to 300 ° C. in an oven while maintaining the pressure at 0.2 MPa to perform infusibilization.
6). Firing The infusibilized product was put into a firing furnace with a hot press, and fired at 1000 ° C. in an argon gas atmosphere while maintaining a pressure of 0.5 MPa to obtain a friction material.

Table 11 shows various physical properties of the friction material. In Examples 9 to 14 and Reference Examples 3 and 4, samples having good physical properties could be obtained by performing heat treatment in an oxidizing atmosphere. These friction materials did not lose weight due to crosslinking with oxygen in the atmosphere, and the Si component constituting polycarbosilane was heated in an oxidizing atmosphere to promote the oxidation reaction and strengthen the matrix. It is presumed that good physical properties were secured.

Moreover, the friction performance of the friction material (Reference Example 3) containing only polycarbosilane and the friction material (Example 14) containing polycarbosilane and montmorillonite was evaluated in the same manner as described above.
These results are shown in Table 12. Since both Reference Example 3 and Example 14 show equivalent friction performance, it is considered that there is no influence on the friction performance due to the addition of montmorillonite.

From the results of Examples 9 to 14 and Reference Examples 3 and 4, by lowering the temperature increase rate during the infusibilization treatment, the flow of the binder is suppressed and it is difficult to ooze out. By including minerals, the flowability at the time of melting of the silicon-containing polymer is reduced, and even if the heating rate during the infusibilization treatment is not slowed, there is almost no oozing out of the binder. It turns out that the friction material equivalent to Example 3 is obtained.

This application includes Japanese patent applications filed on February 18, 2011 (Japanese Patent Application No. 2011-33399), Japanese patent applications filed on March 1, 2011 (Japanese Patent Application No. 2011-44339), and applications filed on December 26, 2011. This is based on Japanese Patent Application (2011-284262), the contents of which are incorporated herein by reference.

The friction material obtained by infusibilizing and firing the silicon-containing polymer containing the nanoparticle material or swellable clay mineral of the present invention as a binder uses a highly heat-resistant brake pad with excellent braking performance using existing manufacturing equipment Can be provided. Therefore, the friction material of the present invention is useful as a high heat resistance friction material used as a brake pad, brake lining, clutch facing, etc. for automobiles, railways, industrial machines and the like.

Claims

Friction material composed of fiber base material, friction modifier, binder and inorganic material, infusible by heat-treating raw material containing silicon-containing polymer and nano-particle material or swellable clay mineral as the binder in an oxidizing atmosphere A friction material, wherein a silicon-containing polymer is cross-linked with oxygen and then fired to form a Si—C network.
The friction material according to claim 1, wherein the heat treatment is performed at a temperature of 160 to 350 ° C for 1 to 10 hours.
The said silicon-containing polymer is one or two or more compounds selected from the group of polycarbosilane, polyorganoborosilazane, polyborosiloxane, polycarbosilazane, and perhydropolysilazane. Friction material.
The friction material according to any one of claims 1 to 3, wherein the silicon-containing polymer is blended in an amount of 5 to 10% by mass of the entire friction material composition.
The friction material according to any one of claims 1 to 4, wherein the nanoparticle material is contained in an amount of 15 to 50 parts by mass with respect to 100 parts by mass of the silicon-containing polymer.
The friction material according to any one of claims 1 to 5, wherein the nanoparticle material is silica.
The friction material according to claim 6, wherein the silica is an organosilica sol.
The friction material according to any one of claims 1 to 4, wherein the swellable clay mineral is an organically treated swellable clay mineral.
The friction material according to any one of claims 1 to 4 and 8, wherein the swellable clay mineral is montmorillonite.
In a method for producing a friction material comprising a fiber base material, a friction modifier, a binder, and an inorganic material, including at least preforming, thermoforming and heat treatment steps, a silicon-containing polymer and a nanoparticle material or a swellable clay as the binder After thermoforming the raw material containing the mineral, it is infusible by heat treatment in an oxidizing atmosphere at a temperature of 160 to 350 ° C. for 1 to 10 hours to crosslink the silicon-containing polymer with oxygen, A method for producing a friction material, characterized by being fired.
The method for producing a friction material according to claim 10, wherein the heating rate of the heat treatment in the infusibilization treatment is performed at 14 to 140 ° C per hour.
The method for manufacturing a friction material according to claim 10 or 11, wherein the heat treatment in the infusibilization process is performed using millimeter wave heating.
The method for producing a friction material according to any one of claims 10 to 12, wherein after the heat treatment, firing is further performed at a temperature of 800 to 1000 ° C for 1 to 2 hours.
The method for manufacturing a friction material according to any one of claims 10 to 13, wherein the preforming is preformed at a pressure of 25 to 300 MPa.