JP2003003155A - Friction material - Google Patents

Abstract

(57) [Summary] An object of the present invention is to reduce a squeal phenomenon that occurs at the first braking after a vehicle has been parked outdoors for a long time. A friction material comprising a base fiber, a binder and a friction modifier, wherein hydrophobic silica is 0.1 to 3% by weight based on 100% by weight of the entire friction material. It is characterized by including. The hydrophobic silica has a particle size of 1
Desirably, it is 0 to 40 nm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a friction material for a brake used in an automobile or the like, and more particularly to a friction material for reducing a squeal phenomenon occurring during braking.

[0002]

2. Description of the Related Art Friction materials for disc brakes used in vehicles such as automobiles are parts that require a stable predetermined friction coefficient (μ) under a wide range of brake use conditions. A wide range of brake use conditions include weather factors such as temperature, humidity and rainfall, road conditions such as submergence and snow melting salt, and infrastructure factors such as the degree of pavement. It is required to generate power and have proper durability.

Further, for vehicles left in a blue sky parking lot or in an environment of high humidity, reduction of squeal that occurs during first braking after long-time parking has been demanded.

The squealing phenomenon at the time of the first braking after parking for a long time is because the frictional interface of the disc brake pad absorbs moisture in the atmosphere to change the properties of the frictional interface, so that the frictional coefficient temporarily increases. Has been found to occur.

Various methods have been tried to reduce the influence of water. For example, it is a method of reducing the total porosity in the friction material or reducing the distribution of pore diameters in the friction material. However, these methods have an adverse effect not only on the coefficient of friction during normal use but also on the braking effectiveness especially during a fade, and therefore pores cannot be extremely reduced. Further, even with a method of reducing the distribution of pore diameters in the friction material, the absorption of water is recognized, and the generation of squeal during the first braking after parking for a long time cannot be reduced.

[0006] Further, a method of applying moisture-proof material such as coating of aramid fiber or imparting water repellency of resin may be adopted. That is, it is a method of treating the surface with a silane coupling agent or silicone oil. Silicon has a low wettability to aramid fiber, and in the case of an oil type, there is a problem that bleeding occurs due to aging under high temperature and the braking efficiency is reduced.

At present, the method for solving the squealing phenomenon has not been established yet.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to reduce the occurrence of squeal during the first braking after parking for a long time.

[0009]

[Means for Solving the Problems] As described above, many attempts have been made to reduce the squealing phenomenon, but all of these have been effective in improving the hygroscopicity of the pad only. It is thought that there was no. Normally, a part of the pad is transferred to the surface of the rotor friction surface to form a transfer film attached to the rotor friction surface. Therefore, it is considered that the effect cannot be exhibited unless both the pad and the rotor are made moisture-proof.

The friction material of the present invention is a friction material formed by mixing and forming a base fiber, a binder, and a friction modifier. When the total weight of the friction material is 100% by weight, hydrophobic silica is 0%. ．
It is characterized by containing 1 to 3% by weight. Further, the hydrophobic silica preferably has a particle size of 10 to 40 nm.

That is, by internally adding hydrophobic silica at the time of making the pad, not only the hygroscopicity of the pad is suppressed but also the hygroscopicity of the transfer film formed on the friction surface of the rotor is prevented, and other frictional characteristics are obtained. It is possible to reduce the squealing phenomenon during the first braking after parking for a long time while maintaining the above.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The friction material of the present invention is a friction material formed by mixing and forming a base fiber, a binder, and a friction modifier, and when the whole friction material is 100% by weight, it is hydrophobic. Of 0.1 to 3% by weight of silica. If the hydrophobic silica content is 0.1% by weight or less, a sufficient effect cannot be obtained,
Further, if it exceeds 3% by weight, it becomes difficult to uniformly mix. The particle size of the hydrophobic silica is preferably 10 to 40 nm. This is because if the particle size is 10 nm or less, secondary agglomeration tends to occur, while if it is larger than 40 nm, the film forming property on the rotor is deteriorated.

Generally, as the hydrophobic compound, silicone-based and fluorine-based oils, rubbers, resins, surfactants and the like can be considered. However, since these have poor heat resistance, hydrophobic silica is desirable as an additive for the friction material.

The friction material used in the present invention is obtained by compounding and molding a base fiber, a binder, a friction modifier and a filler. As the base fiber, those used in conventional friction materials can be used. For example, rock wool, glass fiber, silicate fiber, alumina fiber, carbon fiber, potassium titanate fiber, silicate fiber, metal fiber such as steel fiber, copper fiber, brass fiber, bronze fiber, hemp, cotton, aramid fiber, phenol fiber. Organic fibers such as can be used. As the base fiber, it is particularly preferable to use aramid fiber. Moreover, you may mix | blend another base material fiber with an aramid fiber.

As the binder, those used in conventional friction materials can be used. For example, resins such as phenol resin, epoxy resin and polyimide resin can be mentioned.

As the friction modifier, besides hydrophobic silica,
Hard inorganic substances, lubricants, organic dusts, metal powders and the like are used, and examples of the hard inorganic substances include iron oxides of metal oxides, alumina, zirconium oxide of ceramics, zirconium silicate, magnesium oxide, silica and the like. Examples of the lubricant include graphite, molybdenum disulfide of metal sulfide, antimony trisulfide, and the like, and examples of the filler include barium sulfate, calcium carbonate, slaked lime, mica, kaolin, talc, and the like.

The blending ratio of the base fiber is 10 to 30% by volume.
Is preferable, more preferably 15 to 25% by volume,
The binder is preferably 10 to 30% by volume, more preferably 15 to 20% by volume, and the hard inorganic substance is 1 to 10% by volume.
Is preferable, more preferably 3 to 8% by volume, the lubricant is preferably 5 to 15% by volume, more preferably 8 to 13% by volume, and the metal powder is preferably 1 to 10% by volume, more preferably 2%. ˜6% by volume and the filler is in the range of 0-40% by volume.

The friction material of this embodiment is manufactured by a usual method for manufacturing a friction material. For example, a composition for friction material in which raw materials such as base fiber, binder, and friction modifier are sufficiently mixed at a predetermined ratio is molded into a predetermined shape by pressure thermoforming, and then heat treatment is further performed. Can be made.

A detailed description will be given below with reference to test examples. (Preparation of Friction Material) (Sample 1) 12% by volume of aramid fiber as base fiber, 13% by volume of potassium titanate as inorganic fiber, 20% by volume of phenol resin as binder, silicic acid which is a hard inorganic substance as friction modifier 3% by volume of zirconium, 10% by volume of graphite as a lubricant, 18% by volume of cashew dust as an organic dust, 6% by volume of copper powder, and 18% by volume of barium sulfate as a filler are 100% by weight of a hydrophobic silica. As a Taranox TM
0.5% by weight of # 500 was added and mixed with a mixer for 2 to 5 minutes to obtain a friction material composition.

This composition was applied at a surface pressure of 30 Mpa and a temperature of 160.
Pressure molding was performed at 5 ° C. for 5 minutes. After molding, heat treatment was performed at 220 ° C. for 8 hours to produce a friction material. (Sample 2) A friction material was prepared under the same composition and conditions as in Sample 1, except that the amount of hydrophobic silica added was 1.0% by weight. (Sample 3) In the compounding composition of Sample 1, hydrophobic silica was added from Taranox TM # 500 to AEROSIL R97.
A friction material was prepared under the same composition and conditions as in Sample 1, except that the addition amount was changed to 2 and the addition amount was changed to 0.1% by weight. (Sample 4) A friction material was produced under the same composition and conditions as in Sample 3, except that the amount of hydrophobic silica added was changed to 0.5% by weight. (Sample 5) A friction material was prepared under the same composition and conditions as in Sample 1, except that hydrophobic silica was not added in the composition of Sample 1. (Sample 6) A friction material was prepared under the same composition and conditions as in Sample 3, except that the amount of hydrophobic silica added was changed to 1.5% by weight. (Sample 7) A friction material was produced under the same composition and conditions as in Sample 3, except that the amount of hydrophobic silica added was changed to 0.05% by weight. (Evaluation of Friction Material) With respect to each friction material obtained as described above, the hygroscopicity, the friction coefficient increase value and the water repellency of the rotor friction surface were measured and evaluated.

Hygroscopicity α is W ₀ ; dry weight of friction material (k
g), W ₁ ; When the friction material is weight (kg) after being left for 24 hours in an atmosphere of a temperature of 30 ° C. and a humidity of 80%, the evaluation is α = (W ₁ −W ₀ ) / W ₀ × 100%. did.

An inertial friction wear tester was used to evaluate the coefficient of friction, and the rotating disk was FC200 with a surface roughness of 2.
The one finished to 0Z or less was used. The brake is equipped with a very general pin slide type floating disc brake with a hydraulic cylinder diameter of 51 mm and an inertia moment of 5.0 kg.
By loading m · s ² , a passenger car having a tire radius of 0.3 m was simulated and the fitting was performed according to JASO-C406-82.

Next, the braking hydraulic pressure 1 from the vehicle speed of 20 km / h.
Inputting 0 kg / cm ² , the friction coefficient before leaving until stopping was recorded 3 times. The sample was left in an inertial friction and wear tester for 4 hours in an atmosphere of a temperature of 30 ° C. and a humidity of 80%, and then the friction coefficient after leaving the friction coefficient μb of 3 with the same test code as the friction coefficient before the leaving μa. I measured the number of times. The friction coefficient increase value Δμ was a value obtained by subtracting the average value of μa1 to 3 from the average value of μb1 to 3. In addition, the squeal was measured by a frequency analyzer when the squeaking exceeded a certain frequency and sound pressure.

After the dynamo test, the water absorption / desorption behavior on the friction surface of the rotor was measured by the following method. First, a sample of 20 mm length × 20 mm width × 20 mm thickness (here, the thickness is the thickness of the disk rotor) is cut out from the rotor. Next, the temperature of the sample was controlled by a plate electronic cooler (Peltier element type) and a temperature controller, and the absorption / desorption of water on the friction surface was measured by FT-IR. The back surface of the sample was previously polished with # 200 sandpaper to make the contact property with the plate electronic cooler constant. The sample was cooled from 20 ° C. to 11 ° C. where moisture in the atmosphere (22 ° C./54%) was condensed, and then heated back to 20 ° C. This operation is repeated twice with one cycle (20 ° C. → 11 ° C. → 20 ° C.) at certain temperature intervals (20 ° C. to 16 ° C.).
The IR spectrum of the sample surface is measured by the reflection method (incidence angle 70 °, high-sensitivity reflection condition) at 1 ° C: 1 ° C interval, 16 ° C to 11 ° C: 0.5 ° C interval), which leads to adsorption / condensation / desorption of water. The process was observed. 694 cm for water absorption and desorption
Focused on the absorbance at ^-1 . (Results) Table 1 shows the above performance evaluation results.

In Table 1, Samples 1 to 4 have hydrophobic silica added, although the addition amount and manufacturer are different. Therefore,
Compared to sample 5 in which no hydrophobic silica was added, the pad hygroscopicity was 1.0% or less, and Δμ was 0.1 or less, and no squeaking after standing was generated.

Samples 1 and 2 and Samples 3 and 4 show differences between manufacturers of hydrophobic silica. (Here, the average particle size of Taranox ™ # 500 is 7 nm,
The average particle size of OSIL R972 was 10 nm. )
Although the effect of the addition is recognized in both groups, when the pad hygroscopicity and the friction coefficient increase value Δμ are examined in detail, A
EROSIL R972 is Taranox TM # 50
It is judged that the effect is greater than 0.

Sample 6 is a hydrophobic silica AEROSIL R
972 was added by 1.5% by weight, pad hygroscopicity was 0.4%, and Δμ was 0.02, which is the lowest result in all the samples. However, the dispersion of the hydrophobic silica added in the production of the friction material was poor, and a uniform composition could not be obtained.

Sample 7 is prepared by adding 0.05% by weight of hydrophobic silica. Pad hygroscopicity is 1.2% and Δμ
Was 0.19, the second highest value after Sample 5, and the squeal after standing was not improved.

From the above results, by adding hydrophobic silicon to the pad composition, the hygroscopicity of the friction material can be suppressed and the change of the friction coefficient can be reduced, and the transition film of the pad formed on the friction surface of the rotor can also absorb moisture. It has been found that the sex can be suppressed and the squeaking phenomenon can be reduced.

[0030]

INDUSTRIAL APPLICABILITY The friction material of the present invention contains hydrophobic silica of 0.
By adding 1 to 3% by weight, it is possible to suppress moisture absorption to the pad and reduce the squeal phenomenon that occurs during the first braking after leaving the vehicle for a long time.

[0031]

[Table 1]

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Naoki Kotani             Aichi, 2-chome, Asahi-cho, Kariya city, Aichi prefecture             Within Seiki Co., Ltd. (72) Inventor Yoshihide Yamada             Okawagahara, Iino, Fujioka-cho, Nishikamo-gun, Aichi             1141 Address 1 Aisin Kako Co., Ltd. (72) Inventor Tsunehisa Kawade             Okawagahara, Iino, Fujioka-cho, Nishikamo-gun, Aichi             1141 Address 1 Aisin Kako Co., Ltd. F term (reference) 3J058 AA62 BA21 CA42 FA01 GA04                       GA07 GA19 GA23 GA24 GA29                       GA32 GA33 GA34 GA35 GA37                       GA39 GA43 GA45 GA55 GA57                       GA73 GA92

Claims (3)

[Claims] 1. A friction material comprising a base fiber, a binder, and a friction modifier, wherein the friction material contains hydrophobic silica as the friction modifier. 2. The friction material according to claim 1, wherein the hydrophobic silica is contained in an amount of 0.1 to 3% by weight based on 100% by weight of the friction material. 3. The hydrophobic silica has a particle size of 10 to 40 n.
The friction material according to claim 1 or 2, wherein m is m.