JP2990565B2 - Friction material - Google Patents

Abstract

PURPOSE:To improve the friction and abrasion characteristics of a friction material to be used as a sliding part of a braking apparatus of automobile, etc. CONSTITUTION:A friction material is produced by bonding and forming base fibers with a resin binder. In this process, 3-50wt.% of polycrystalline fiber having composite phase consisting of potassium hexatitanate crystal and titania crystal is compounded as the base fiber. The friction face is imparted with high friction coefficient and abrasion resistance over a wide temperature range from low temperature to high temperature owing to the high heat-resistance, shearing strength and abrasion resistance of the base fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a friction material useful as a sliding member such as a brake lining and a disk pad constituting a braking device in an automobile, a railway wheel, an aircraft, an industrial machine and the like.

[0002]

2. Description of the Related Art As a typical sliding member in the above-described braking device, a friction material formed by binding asbestos fiber as a base fiber and dispersing the same in a resin binder has been used. In response to requests from the automotive industry, etc. regarding the improvement of properties, and environmental health issues such as carcinogenicity that has been pointed out with asbestos fibers, the development of alternatives has been requested. Attempts have been made to commercialize friction materials using potassium fibers as base fibers (Japanese Patent Application Laid-Open Nos. 61-191599 and 1-2).
No. 94553). Potassium titanate fiber is a synthetic inorganic compound represented by the general formula K ₂ O.nTiO ₂ , and potassium hexatitanate fiber (K ₂ Ti ₆ O ₁₃ ) is a typical example. This material has excellent heat resistance and is effective in preventing the fade phenomenon. Its hardness is around Mohs' hardness of 4, and its aggressiveness is small, it does not absorb moisture and does not react with water. It has desirable properties such as being effective in preventing abnormal effects of the above.

[0003]

As disclosed in the above publication, by applying potassium hexatitanate fiber instead of asbestos fiber, the abrasion resistance of the friction material is remarkably improved and the friction material is heated to 300 ° C. The friction coefficient does not decrease unlike the friction material using asbestos fibers even in a temperature range on the high temperature side exceeding the above. However, on the other hand, the friction coefficient on the low temperature side (about 250 ° C. or less) is at a lower level than the friction material using asbestos fibers, on the other hand, on the other hand. In recent years, as the speed of the vehicle increases, the friction material of the braking unit has been required to have a higher friction coefficient. Therefore, the present invention relates to a friction material having potassium titanate fiber as a base fiber, which stably maintains a high friction coefficient over a wide temperature range from a low temperature to a high temperature and has a high degree of wear resistance. It is intended to provide.

[0004]

According to the present invention, there is provided a friction material comprising a base fiber bound with a resin binder, wherein a composite polycrystalline fiber comprising potassium hexatitanate crystal and titania crystal is used as the base fiber. It is characterized by containing 3 to 50% by weight.

[0005]

[Function] Polycrystalline fiber having a composite phase composed of potassium hexatitanate crystal and titania crystal (hereinafter, also referred to as “potassium hexatitanate composite fiber” or simply “composite fiber”)
Has the same or better thermal stability than single-phase fiber consisting only of potassium hexatitanate crystals,
Compared with single-phase fiber, it has high shear strength and high hardness and high wear resistance. Further, the composite fiber has minute surface irregularities due to the mixture of two phases, and the surface irregularities enhance the bonding between the resin binder and the interface between the fibers. The friction material of the present invention using the potassium hexatitanate composite fiber having the above characteristics as the base fiber has a higher friction coefficient than the friction material using the potassium hexatitanate single-phase fiber. The temperature dependence of the friction coefficient is small, and the high friction coefficient is stably maintained over a wide temperature range from a low temperature to a high temperature. With respect to abrasion resistance, the friction material of the present invention has higher abrasion resistance than a friction material using asbestos fibers from a low temperature range to a high temperature range.

Hereinafter, the present invention will be described in detail. The required minimum amount of titania crystals in the potassium hexatitanate composite fiber used as the base fiber depends on the friction and wear characteristics required for the intended friction material. However, in order to clearly exhibit the composite effect, the volume is at least 1% by volume. It is preferred that

The titania crystal in the composite fiber has an anatase phase and a rutile phase having different crystal structures, and both have different hardnesses. The hardness (Mohs hardness) of the anatase phase is about 5.5 to 6.0. That of the rutile phase is about 7.0-7.5
It is. The titania crystal in the composite fiber used in the present invention may be any of them, or may be a mixed phase of both. If more importance is placed on wear resistance, the rutile phase is advantageous.

The conjugate fiber is a polycrystalline fiber having a plate shape, and its size is not particularly limited. However, from the viewpoint of stability as a base fiber, the plate fiber has a fiber diameter of about 20 to
Those having a size of 50 μm and a length of about 100 to 400 μm are suitable.

In the friction material of the present invention, the compounding ratio of the composite fiber is set to 3% by weight or more.
This is because the compounding effect cannot be sufficiently exerted. The reason why the upper limit is 50% by weight is that if it exceeds that, the effect of improving the friction and wear characteristics is almost saturated, and there is no advantage of increasing the amount further.

[0010] The friction material of the present invention may contain, in addition to the potassium hexatitanate composite fiber as a base fiber, various fibrous fillers known as base fibers of the friction material, such as resin fibers (aramid fibers), if desired. Etc.), metal fiber (steel fiber,
One or more of carbon fiber, glass fiber, ceramics fiber, rock wool, wood pulp, etc., and potassium hexatitanate composite fiber for reinforcement of friction material, etc. In addition, an appropriate amount (for example, 1 to 60% by weight) is blended. These fibrous fillers may be used, if necessary, for the purpose of improving dispersibility and adhesiveness with a binder, for example, silane coupling agents (vinyl silane, amino silane, epoxy silane, methacryloxy silane, mercapto xylan, etc.), or It is used after being subjected to a surface treatment with a titanate-based coupling agent (isopropyl triisostearoyl titanate, di (dioctylpyrophosphate) ethylene titanate, etc.).

Further, the friction material of the present invention includes various additives commonly used as friction modifiers, such as vulcanized or unvulcanized natural / synthetic rubber powder, cashew resin particles, resin dust, rubber dust and the like. Organic powder, or inorganic powder such as natural / artificial graphite, molybdenum disulfide, antimony trisulfide, barium sulfate, calcium carbonate, zonotlite, flaky inorganic filler such as mica or vermiculite, copper,
Metal powders such as aluminum, zinc, iron, and stainless steel, and oxide powders such as alumina, silica, chromium oxide, titanium oxide, iron oxide, antimony trioxide, and copper oxide are required for the friction characteristics required for products, for example, friction coefficient A suitable amount (for example, 20 to 80% by weight) alone or in combination of two or more kinds according to the wear resistance, vibration characteristics, pear, etc. It is not different from that of the conventional friction agent in that the following is prepared into a composition formulated as needed.

[0012] The resin serving as a binder is, for example, a thermosetting resin such as an epoxy resin, a phenol resin, a formaldehyde resin, a polyester resin, a polyamide resin, an alkyd resin, a silicone resin, a polyimide resin, or a modified resin thereof, or a natural rubber. Various binders used for this type of friction material, such as styrene butadiene rubber and nitrile rubber, may be appropriately used.

The composition of the friction material of the present invention is the same as that of the conventional friction material except that a predetermined amount of potassium hexatitanate composite fiber is contained as a base fiber. No conditions or restrictions are added, and the raw material composition is prepared by first dispersing the base fiber in a resin as a binder and adding a friction modifier and other additives to be mixed as desired according to a conventional method. Then, binding molding is performed under heat and pressure by mold molding or the like.Alternatively, the raw material composition is dispersed and suspended in water, etc. After being formed into a body or a sheet, it is subjected to binding and molding under heat and pressure, and thereafter, the binding molded product is appropriately subjected to machining and polishing to obtain a desired friction agent.

The potassium hexatitanate composite fiber as the base fiber can be produced by modifying a part of the processing conditions in the production process of the potassium hexatitanate single-phase fiber by the melting method. That is, a mixture of a titanium compound (purified anatase or the like) and a potassium compound (potassium carbonate or the like) (molar ratio of TiO ₂ / K ₂ O: about 2) is heated and melted, and the melt is cooled and solidified to form an initial phase. A fiber mass, which is a bundle of potassium dititanate fibers (K ₂ Ti ₂ O ₅ ), is obtained, treated with a washing liquid, and K ⁺ ions are eluted and defibrated (separating the bonds between fibers). , And then, in the step of producing potassium titanate fiber comprising a step of baking, an aqueous solution of an acid (for example, a 0.01 to 1% aqueous sulfuric acid solution) is used as a washing liquid for treating the fiber mass, and the potassium in the fiber is removed. The K ⁺ ions were eluted until the amount reached 1 to 13.5% by weight, and the recovered fiber was baked for 9 hours.
By performing in a temperature range of 00 to 1300 ° C., a composite fiber composed of titania crystals and potassium hexatitanate is obtained.
The form of the fiber is about 20 to 50 μm in fiber diameter and about 1 in length.
It is a plate-like polycrystalline fiber having a thickness of 00 to 400 µm. If the calcination treatment is performed on the low temperature side (about 970 ° C. or less), the titania crystals precipitate as an anatase phase, and on the high temperature side (about 1050 ° C. or more) as a rutile phase, an intermediate temperature range (about 1000 ° C.).
(Before and after), both precipitate as mixed phases.

[0015]

EXAMPLES Example 1 (1) Production of Test Friction Material (Disk Pad) Base Material Blended Material Composition 30% by weight Binder (Phenol resin) [Hitachi Kasei Co., Ltd. "HP309NS"] 20 % By weight Friction modifier (barium sulfate) [“BA” manufactured by Sakai Chemical Industry Co., Ltd.] 50% by weight Pre-molding the above composition (pressure: 300 kgf / cm)
² , temperature: normal temperature, time: 1 minute), and then bond forming with a mold (pressing force: 150 kgf / cm ² , temperature: 170)
C., time: 5 minutes), and heat treatment (180 ° C.) after molding.
For 3 hours). After being removed from the mold, it is polished and subjected to the following friction material (disk pad) A1
To C1 were obtained.

Friction material A1 (Invention example) Potassium hexatitanate composite fiber (plate-like polycrystalline fiber) was used as a base fiber, fiber diameter (average) 30 μm, length (average) 200 μm [see Reference Example 1 below] ]. Friction material B1 (Comparative example) A potassium hexatitanate single-phase fiber (plate-like polycrystalline fiber) was used as the base fiber, and the fiber diameter (average) was 30 µm and the length (average) was 150 µm (see Reference Example 2 described later). Friction material C1 (comparative example) Asbestos fibers (6 classes) were used as base fibers.

(2) Friction and wear test For each of the test friction materials A1 to C1, JIS D4411 was used.
A constant speed friction and wear test according to the provisions of "brake for a motor vehicle Rye two Ig" (disc friction surface: FC25 gray cast iron, surface pressure: 10 kgf / cm ^2, friction speed: 7m / sec)
And the abrasion rate (cm ³ / kgm) and the friction coefficient (μ) were measured. 1 and 2 show the measurement results (FIG. 1: friction coefficient, FIG. 2: wear rate).

Example 2 (1) Production of Test Friction Material Using the following composition as a raw material, pre-forming and binding molding, heat treatment, and polishing were performed under the same conditions as in Example 1 above, and the test friction material ( Disc pads) A2 to C2 are obtained. Potassium titanate fiber (or asbestos fiber) ... 16% by weight Aramid fiber ("Kevlar pulp" (length 3mm) manufactured by Toray Industries, Inc.) ... 3% by weight Binder (phenol resin) ... 9% by weight Organic additive (Casyu dust) 9% by weight Others (lubricant such as graphite, inorganic powder such as barium sulfate, metal powder, oxide powder) 63% by weight

Friction material A2 (Invention example) Potassium hexatitanate composite fiber (plate-like polycrystalline fiber) was used as the potassium titanate fiber, and the fiber diameter (average) was 30 μm.
m, length (average) 200 μm [see Reference Example 1 below]. Friction material B2 (Comparative example) Potassium hexatitanate single-phase fiber (plate-like polycrystalline fiber) was used as potassium titanate fiber, fiber diameter (average) 30μ
m, length (average) 150 μm [see Reference Example 2 below]. Friction material C2 (comparative example) Asbestos fibers (6 classes) were used instead of potassium titanate fibers.

(2) Friction and wear test A constant speed friction and wear test similar to that of Example 1 was performed on each of the test materials A2, B2 and C2, and the results of FIG. 3 (friction coefficient) and FIG. Obtained.

As shown in FIGS. 1 and 3, the friction materials A1 and A2 of the invention (using potassium hexatitanate composite fiber)
Does not decrease the friction coefficient (μ) in a high temperature range like the friction materials C1 and C2 using asbestos fibers, and has a higher friction coefficient than the friction materials B1 and B2 (using potassium hexatitanate single phase fiber). The high friction coefficient is stably maintained over a wide temperature range from a low temperature to a high temperature. Further, as is clear from FIGS. 2 and 4, the friction materials A1 and A2 of the invention examples are the same as the friction materials C1 and C2 (using asbestos fiber) and the friction materials B1 and B2 (using potassium hexatitanate single-phase fiber). In comparison, it has significantly higher wear resistance from low to high temperatures.

[0022]

REFERENCE EXAMPLE Reference Example 1 (Production of potassium hexatitanate composite fiber) (1) Preparation of starting materials Purified anatase powder (purity 99.8%) and industrial potassium carbonate powder (purity 99.5%) TiO ₂ / K ₂ O
Was blended so that the molar ratio of 1.8 was obtained. (2) Heating and melting The starting material mixed powder is put in a platinum crucible and heated at 1050 ° C. for 4 hours.
It took 0 minutes to heat and melt. (3) Cooling and solidification The heated melt was poured into a dish-like container (made of copper) to obtain a fiber mass which was a bundle of primary phase potassium dititanate fibers. (4) Removal of potassium and fibrillation treatment Sulfuric acid is added to water 150 times the amount (by weight) of the fiber mass to obtain a 0.1% sulfuric acid aqueous solution, and the fiber mass is added thereto. Has a potassium content of about 9% (Ti
K ⁺ ions were eluted until the molar ratio of O ₂ / K ₂ O reached about 9.7), and defibration was performed. (5) Firing treatment The defibrated fibers are collected from the washing liquid, and dehydrated and dried (air-dried).
After that, it was put into an alumina crucible and fired at a temperature of 1150 ° C. for 2 hours. The obtained fiber is a plate-like polycrystalline fiber having a composite phase composed of potassium hexatitanate crystal-titania crystal (rutile phase). Fiber diameter (average) 30 μm, length (average) 200 μm. FIG. 5 shows a scanning electron microscope image (200 magnification) of the fiber.
0). 6TK is a potassium hexatitanate crystal phase, and T is a titania crystal phase. The titania crystal phase T is dispersed and precipitated in the potassium hexatitanate crystal phase 6TK. Its content (molar ratio of crystalline phase of titania / crystalline phase of potassium hexatitanate) is about 3.7.

Reference Example 2 (Production of potassium hexatitanate single-phase fiber) As the washing solution in the “depotassium / fibrillation treatment” in Reference Example 1, water (a fibrous mass of 150
Times the amount of K ⁺ until the potassium content of the fiber is about 13.6% by weight (TiO ₂ / K ₂ O molar ratio about 6).
A fiber was obtained through steps under the same processing conditions except that the ions were eluted. The obtained fiber is a single-phase plate-like polycrystalline fiber composed of potassium hexatitanate crystals. FIG. 6 is a scanning electron microscope image (2,000 magnification) of the fiber. Fiber diameter (average) 30 μm, length (average) 150 μm.

[0024]

The friction material of the present invention has a high friction coefficient and wear resistance over a wide temperature range from a low temperature to a high temperature. Therefore, it is suitable as a brake lining, a disk pad, and the like in a braking device of an automobile, a vehicle, an aircraft, and various industrial machines, and is particularly suitable as a friction material for a vehicle or the like that requires a high friction coefficient for high-speed driving, and has an improved braking function. -Stabilization, improvement of service life, etc. are obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing a measurement result of a friction coefficient by a constant-speed friction wear test.

FIG. 2 is a graph showing a measurement result of a wear rate by a constant-speed friction wear test.

FIG. 3 is a graph showing a measurement result of a friction coefficient by a constant-speed friction wear test.

FIG. 4 is a graph showing a wear rate measurement result by a constant speed friction wear test.

FIG. 5 is a micrograph (magnification: 2,000) of a drawing showing a potassium hexatitanate composite fiber as a base fiber.

FIG. 6 is a micrograph (magnification: 2000) of a drawing showing a potassium hexatitanate single phase fiber as a base fiber.

[Explanation of symbols]

6TK: potassium hexatitanate crystal phase, T: titania crystal phase.

Claims (1)

(57) [Claims] 1. A friction material comprising a base fiber bound with a resin binder, wherein the base fiber is a composite polycrystalline fiber composed of potassium hexatitanate crystal and titania crystal in an amount of 3 to 50.
A friction material characterized by containing by weight.