JP2005207437A - Friction material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a friction material that prevents occurrence of low frequency abnormal noise simultaneously while securing abrasion resistance required for the friction material and stable performance such as friction coefficient, and has low grinding property of the rotor surface of a partner material. <P>SOLUTION: The friction material that is formed by heating, pressurizing and molding, and hardening a friction material composite mainly composed of a fiber base material, a bonding material, and a filler contains unbaked vermiculite of 250-710 μm of mean particle diameters as the filler. Thus, the unbaked vermiculite with a certain diameter has a suitable inter-layer strength but does not excessively grind a rotor, so that only transfer coating with an excessive thickness formed in the rotor surface of the partner material can be moderately removed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a friction material used for a disk pad, such as a disk pad, a brake lining, and a clutch facing for automobiles and various industrial machines.

The friction material is obtained by heating, pressing, and curing a friction material composition mainly composed of a fiber base material, a binder, and a filler. These friction material composition materials are required for friction materials that have good wear resistance, a stable friction coefficient against changes in pressure, temperature, etc., good grindability of the mating rotor surface, and no squealing. Various raw materials are used to ensure the performance.
In the patent document 1, the present applicant discloses an invention for obtaining a friction material that exhibits stable friction performance and excellent squeal performance by adding resin-coated vermiculite to the friction material composition.

By the way, with the sophistication of customer requirements accompanying technological advancement, abnormal noise called low-frequency creep glones has become a problem in brake devices using friction materials. This low-frequency noise is caused by stick-slip generated between the transfer film that has grown to an excessive thickness and the friction material wear powder and decomposition products transferred to the rotor surface of the mating material, and the friction material. It is said that.
On the other hand, the calcined vermiculite used in the example of Patent Document 1 is an accordion-like foamed layer between flat network crystals that are heated by rapid heating at a high temperature, and the layers are expanded. In some cases, stick slip cannot be effectively prevented because of its low ability to remove the transfer film that has grown to an excessive thickness on the rotor surface. In addition, if raw unburned vermiculite is used in a state where it is simply coated with a resin, the interlayer strength is too strong, and there is a risk of grinding to the rotor surface of the counterpart material.

Stick-slip is also considered to occur easily when the coefficient of static friction is large and the coefficient of dynamic friction is small.
Patent Document 2 describes an invention in which a soft inorganic raw material having two or more types of planar network crystal structures is added. It is intended to reduce the coefficient of static friction by combining various raw materials. However, such a raw material generally does not have a sufficient effect unless it has a large particle diameter, but it is easy to segregate in the friction material composition because it combines two or more large particle diameter raw materials, and the strength of the raw material However, there is a disadvantage that the wear resistance of the friction material is lowered due to weakness.

Patent No. 2827140 Japanese Patent No. 2874296

  The present invention has been made in view of the above circumstances, and while ensuring the performance required for a friction material such as wear resistance and a stable friction coefficient, the occurrence of low-frequency abnormal noise is prevented at the same time, and the rotor surface of the counterpart material It is an object to provide a friction material having low grindability.

As a result of diligent studies to achieve the above-mentioned object, the present inventor replaced the calcined vermiculite generally used in the past with a non-fired vermiculite (raw stone) having a constant particle size and particle size distribution. It has been found that the occurrence of slip can be suppressed.
Since unsintered vermiculite has a planar network crystal structure, it has the effect of reducing the coefficient of static friction. In addition, the use of non-fired vermiculite with a relatively small constant particle size and particle size distribution makes it difficult to segregate in the friction material composition, maintains the wear resistance of the friction material, and controls the hardness, so it is formed on the rotor surface of the counterpart material Only the transferred film having an excessive thickness can be removed moderately.

That is, the present invention provides the following friction material.
(1) In a friction material obtained by heating, pressing, and curing a friction material composition mainly composed of a fiber base material, a binder, and a filler, unfired vermiculite having an average particle size of 250 to 710 μm as the filler Containing friction material.
(2) The friction material according to (1), which contains unburned vermiculite having an average particle size of 460 to 580 μm and a particle size distribution as follows as the filler.
Particle size ratio Less than 300 μm 0-35% by mass
More than 300 μm and less than 600 μm 60-100% by mass
600 μm or more 0-5% by mass
(3) The friction material according to (1) or (2), wherein unfired vermiculite is coated with a silicone rubber composition.
(4) The friction material according to (3), wherein the silicone rubber composition comprises 100 parts by mass of thermally crosslinkable millable rubber, 0.1 to 3 parts by mass of an organic peroxide, and 35 to 60 parts by mass of a reinforcing filler.
(5) The friction material according to (4), wherein the thermally crosslinkable millable rubber is methyl vinyl silicone rubber, the organic peroxide is dicumyl peroxide (DCP), and the reinforcing filler is dry silica.

The friction material of (1) can reduce the occurrence of low-frequency noise while maintaining a stable friction coefficient by using unfired vermiculite with a limited average particle size.
In addition to (1), the friction material of (2) can obtain wear resistance and good mating material rotor surface grindability.
The friction materials (3) to (5) are coated with a silicone rubber composition having high tackiness and water repellency on the surface of the unburned vermiculite, so that a large amount of unburned vermiculite is segregated in the raw material mixture. In addition, it is difficult to drop off from the surface of the friction material when the product is used, and it has the effect of further reducing the occurrence of low-frequency noise without causing rust on the surface of the rotor of the mating material due to its high water repellency.

The present invention uses unfired vermiculite with a small average particle size (250-710 μm).
By further adjusting this, the average particle size can be preferably 460 to 580 μm, more preferably 500 to 550 μm, and the particle size distribution can be preferably as follows.
Particle size ratio Less than 300 μm 0-35% by mass
More preferably 0 to 17% by mass
More than 300 μm and less than 600 μm 60-100% by mass
More preferably 80-100% by mass
600 μm or more 0-5% by mass
More preferably 0 to 3% by mass
If the average particle size and particle size distribution are within these ranges, the dispersibility of the unfired vermiculite is good, the wear resistance of the friction material can be maintained, and the rotor surface of the counterpart material is not excessively ground.
Although there is no restriction | limiting in particular about the addition amount of a non-baking vermiculite, It is preferable to set it as 5-25 volume% with respect to friction material composition whole quantity, and it is more preferable to set it as 10-20 volume%. Within this range, the effect of the present invention can be obtained more preferably while maintaining the mechanical strength of the friction material.

Silicone rubbers to be coated on the unfired vermiculite can be classified into thermal crosslinking type, low temperature curing type, room temperature curing type from the viewpoint of crosslinking temperature, and millable rubber (rubber that can be kneaded) and liquid from the viewpoint of properties. Thermally crosslinkable millable rubber is preferred from the viewpoint of adhesive strength.
Examples of rubber base materials include dimethyl silicone rubber, methyl vinyl silicone rubber, methyl phenyl silicone rubber, and fluoro silicone rubber. From the viewpoint of adhesive strength, crosslinking characteristics, and compression set characteristics, the degree of polymerization of the polymer is 5,000 to 10,000. 000 methyl vinyl silicone rubber is preferred.
The crosslinking agent is preferably dicumyl peroxide (DCP), which is an organic peroxide that decomposes when heated and the generated radicals act as a crosslinking agent for silicone rubber.
As the reinforcing filler, there are dry method silica and wet method silica, but dry method silica is preferable in terms of water repellency and adhesive strength. The dry silica has a primary particle diameter of 50 nm or less, and a BET specific surface area of preferably 100 m 2 / g or more, and more preferably 150 m 2 / g or more. In addition, a plasticizer may be added for the purpose of promoting dispersion of the reinforcing filler and prevention of plasticization return, and an additional filler may be added as necessary.

The composition of the silicone rubber composition is preferably 0.1 to 3 parts by weight of organic peroxide and 25 to 55 parts by weight of reinforcing filler with respect to 100 parts by weight of silicone raw rubber.
The amount of the silicone rubber composition coated on the unburned vermiculite is preferably 5 to 20 parts by mass with respect to 100 parts by mass of the unburned vermiculite. As the coating method, a pressure kneader is preferably used.
If each component is within these ranges, the unburned vermiculite is prevented from segregating in the raw material mixture, and it is difficult for the vermiculite to fall off from the friction material surface when the product is used. The generation of rust can be suppressed.

The coating state is not necessarily required to completely cover the unfired vermiculite with the silicone rubber composition, and is effective even when it is partially covered.
Unburned vermiculite contains about 4 to 7% of moisture in the crystal layer, and generates water vapor when the friction material is heated and pressure-molded. It is more preferable to use after drying for about an hour.

As other fillers, organic fillers and inorganic fillers usually used for friction materials can be arbitrarily used. Examples of the organic filler include cashew dust, tire liquor, and acrylic rubber (vulcanized product). These can be used alone or in combination of two or more. The addition amount of the organic filler is 3 to 30% by volume, preferably 5 to 25% by volume, based on the entire friction material composition.
On the other hand, as inorganic fillers, barium sulfate, calcium carbonate, slaked lime, calcined vermiculite, mica, plate-like potassium titanate, scale-like potassium magnesium titanate, zirconium silicate, zirconium oxide, magnesium oxide, alumina, silicon carbide, etc. Hard inorganic abrasives, metals such as iron, copper, brass, bronze, aluminum, black iron oxide and zinc oxide, metal oxide particles, and solid lubricants such as graphite and tin sulfide. These can be used alone or in combination of two or more. The inorganic filler is 30 to 80% by volume, preferably 40 to 70% by volume of the entire friction material composition, including the unfired vermiculite of the present invention.

  As the fiber base material, those usually used for friction materials can be used. Metal fibers such as steel fibers, stainless fibers, copper fibers, brass fibers, bronze fibers, and aluminum fibers; inorganic fibers such as ceramic fibers, potassium titanate fibers, glass fibers, rock wool, artificial mineral fibers, wollastonite, and sepiolite; Aramid fiber, carbon fiber, polyimide fiber, cellulose fiber, organic fiber such as acrylic fiber; and the like. These can be used alone or in combination of two or more. The addition amount of the fiber base is 5 to 40% by volume, preferably 7 to 30% by volume, based on the entire friction material.

  As the binder, those usually used for friction materials can be used. Examples thereof include phenol resin, acrylic rubber-modified phenol resin, nitrile butadiene rubber-modified phenol resin, melamine resin, epoxy resin, nitrile butadiene rubber, and silicone rubber. These can be used alone or in combination of two or more. The addition amount of the binder is 5 to 30% by volume, preferably 7 to 25% by volume, and more preferably 10 to 20% by volume with respect to the entire friction material.

In the method for producing a friction material of the present invention, the above components are uniformly mixed using a mixer such as a Redige mixer or an Eirich mixer and preformed in a molding die, and the preform is molded at a molding temperature of 413 to 413. It is heated and pressure-molded at 455K and a molding pressure of 10-25 MPa for 5-15 minutes. Next, the obtained molded product is heat-treated (post-cured) for 2 to 12 hours at a temperature of 413 to 523 K, and then painted, baked, and polished as necessary to obtain a finished product.
When manufacturing a disk pad for an automobile or the like, a preformed product is placed on an iron or aluminum plate that has been previously washed, surface-treated, and coated with an adhesive, and heated in a molding die in this state. It can be produced by pressure molding, heat treatment, painting, baking and polishing.

  The friction material of the present invention can be widely used in various applications such as disk pads, brake linings, clutch facings, etc. for automobiles, large trucks, various industrial machines and the like.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example.

The following vermiculite was used. The average particle diameter is a value of 50% particle diameter measured by the laser diffraction particle size distribution method.
(A) Unfired, average particle size of 470 μm
Particle size ratio Less than 300μm 17% by mass
More than 300μm and less than 600μm 82% by mass
600% or more 1% by mass
(B) Unfired, average particle size of 520 μm
Particle size ratio Less than 300μm 14% by mass
More than 300μm and less than 600μm 84% by mass
600μm or more 2% by mass
(C) Unfired, average particle size of 570 μm
Particle size ratio Less than 300 μm 10% by mass
More than 300μm and less than 600μm 86% by mass
4% by mass over 600μm
(D) Unfired, average particle size of 250 to 710 μm (commercial product)
(E) Unsintered, (B) covered with silicone rubber composition To 100 parts by weight of (B) unsintered vermiculite, 10 parts by weight of silicone rubber composition was added and kneaded using a pressure kneader. It was prepared by separating the particles through a mesh sieve (JIS sieve opening standard size 1180 μm).
The silicone rubber composition is composed of 1 part by mass of dicumyl peroxide (DCP), a BET specific surface area of 200 m 2 / g, based on 100 parts by mass of a heat-crosslinked methyl vinyl silicone raw rubber having a degree of polymerization of 7,500. A dry process silica having a particle size of 20 nm and 40 parts by mass of silica and 5 parts by mass of polyorganosiloxane as a plasticizer were added and kneaded using a pressure kneader.
(F) Firing, average particle size 520 μm
Particle size ratio Less than 300μm 14% by mass
More than 300μm and less than 600μm 84% by mass
600μm or more 2% by mass
(G) Firing, average particle size of 250 to 710 μm (commercially available product)

The friction material composition having the composition shown in Table 1 was mixed for 5 minutes by a Redige mixer, and preliminarily molded by pressing at 10 MPa for 20 seconds in a pressure mold. This preform is molded for 6 minutes under conditions of a molding temperature of 423K and a molding pressure of 40MPa, then heat-treated (post-curing) at 473K for 5 hours, painted, baked, and polished, for passenger cars of Examples and Comparative Examples A brake pad was created.
The obtained brake pads were evaluated for low frequency noise, friction coefficient, disk pad wear, and rotor surface grindability by the following methods. The results are shown in Table 1.

Table 1

(1) Low-frequency abnormal noise Based on the JASO C402 test, the frequency of occurrence of low-frequency abnormal noise during braking was evaluated according to the following criteria by an actual vehicle test. Table 2 shows the test conditions.
A: 0%
○: More than 0% and 15% or less △: More than 15% and 30% or less ×: More than 30% (2) Friction coefficient Based on the JASO C406 test, the average μ of the second efficacy was evaluated based on the following criteria. .
◎: Greater than 0.41 ○: Greater than 0.38 and 0.41 or less Δ: Greater than 0.35 and 0.38 or less X: 0.35 or less (3) Disc pad wear, rotor surface grindability JASO C427 General wear In accordance with the test, the disc pad wear and the grindability of the rotor surface can be achieved under the test conditions of initial braking speed 30 to 80 km / h, braking deceleration 2 m / s2, braking temperature 50 to 200 ° C before braking, and total braking number 1600 times. Evaluation was made based on the following criteria. Table 3 shows the test conditions. The grindability of the rotor surface was evaluated by the 10-point average roughness Rz measured on the rotor surface after completion of the test according to JIS B0601.
(Disc pad wear)
◎: Less than 0.4 mm ○: 0.4 mm or more and less than 0.5 mm Δ: 0.5 mm or more and less than 0.6 mm x: 0.6 mm or more (rotor surface grindability)
A: Less than 30 μm ○: 30 μm or more and less than 40 μm Δ: 40 μm or more and less than 50 μm x: 50 μm or more

Table 2

Table 3

Claims (5)

A friction material obtained by heating, press-molding, and curing a friction material composition mainly composed of a fiber base material, a binder, and a filler, and contains unburned vermiculite having an average particle size of 250 to 710 μm as the filler. Friction material.
2. The friction material according to claim 1, wherein the filler contains unburned vermiculite having an average particle size of 460 to 580 μm and a particle size distribution as follows.
Particle size ratio Less than 300 μm 0-35% by mass
More than 300 μm and less than 600 μm 60-100% by mass
600 μm or more 0-5% by mass
The friction material according to claim 1 or 2, wherein the unfired vermiculite is coated with a silicone rubber composition.
The friction material according to claim 3, wherein the silicone rubber composition comprises at least 100 parts by mass of thermally crosslinkable millable rubber, 0.1 to 3 parts by mass of an organic peroxide, and 35 to 60 parts by mass of a reinforcing filler.
The friction material according to claim 4, wherein the thermally crosslinkable millable rubber is methyl vinyl silicone rubber, the organic peroxide is dicumyl peroxide (DCP), and the reinforcing filler is dry silica.