JPH09278906A - Friction material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve frictional abrasion characteristics of a friction material to be used in a damping device in an automobile brake, etc. SOLUTION: This friction material is obtained by bonding and molding a mixture composed of a resin and a base material. In the friction material, highly dense composite polycrystal fibers composed of potassium hexatitanate crystal and titania crystal are compounded as the base material. A phase mixing ratio (mole ratio) of titania crystal/potassium hexatitanate crystal in the composite polycrystal fibers is preferably 1/20 to 20/1. The fibers preferably have the following sizes: fiber diameter is 20-50μm; fiber length is 100-400μm. The compounding ratio of the fibers in the resin is e.g. 3-50wt.%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a friction material constituting a sliding surface such as a brake lining, a disc pad, a clutch facing, etc. in a braking device for automobiles, railway vehicles, aircrafts, industrial machines and the like.

[0002]

2. Description of the Related Art As a friction material for a braking device, a resin (phenol resin, epoxy resin, etc.) is used as a binder, a base material is dispersed therein, and a friction / wear modifier (barium sulfate, etc.) is added as necessary. It is produced by binding and molding the mixture under heat and pressure. Asbestos fibers have been conventionally used as the base material, but asbestos fibers have recently been pointed out to have a carcinogenic problem. Further, although the friction material based on asbestos fiber shows a stable friction coefficient in a relatively low temperature range, wear damage remarkably increases as the friction surface becomes hot, and the friction coefficient sharply decreases and fades. Is likely to occur. To meet the demands for downsizing and weight reduction of automobile brake devices, a friction material having a high coefficient of friction and capable of stably maintaining a high coefficient of friction in a wide temperature range is required. As the friction material, a friction material having potassium titanate fiber as a base material instead of asbestos fiber has been proposed. Potassium titanate fibers have the general formula: K ₂ Ti _n O _2n
+1 [in the formula, n = 2 to 8] is a synthetic inorganic compound fiber, and above all, potassium hexatitanate fiber [K ₂ Ti ₆ O ₁₃ ] having a tunnel type crystal structure is required as a base material. It has excellent wear resistance, heat resistance, and reinforcement. Known methods for industrial production of potassium titanate fiber include firing method, flux method, and melting method. However, potassium hexatitanate fiber having a polymorphic form produced by the melting method is used for producing whisker. Compared with fine single crystal fibers, it has an excellent effect of improving the friction and wear characteristics of friction materials.

[0003]

By using potassium hexatitanate polycrystal fiber as the base fiber, it is possible to obtain improved friction and wear characteristics which cannot be obtained with asbestos fiber over a wide temperature range. Become. The present inventors have found that, regarding the base fiber, the conventional potassium hexatitanate polycrystalline fiber produced by the melting method includes a large number of cracks in the crystal grain boundaries, and instead of this, it has a high density of few grain boundary cracks. By using a polycrystalline fiber, it is possible to strengthen the reinforcing action as a base material, and further, instead of the polycrystal structure of potassium hexatitanate single phase, a mixed phase polycrystal structure of potassium hexatitanate crystal and titania crystal It has been found that, by setting the above, it is possible to further improve the fade resistance property, the friction coefficient and the like of the friction material.
The present invention has been made based on this finding.

[0004]

The friction material of the present invention is a friction material obtained by binding and molding a mixture of a resin and a base material. The base material is composed of potassium hexatitanate crystals and titania crystals. It is characterized in that it is blended with highly dense composite polycrystalline fibers.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The highly dense composite polycrystalline fiber which is the base fiber is produced by the improved melting method described below. This has a highly dense fiber morphology in which the generation of cracks at grain boundaries is suppressed and prevented, unlike the polycrystalline fibers produced by the conventional melting method, and has high shear strength and excellent reinforcing properties. Also, potassium hexatitanate crystal (Mohs hardness: about 5.5)
In addition, since it has a composite polycrystalline structure in which titania crystals (Mohs hardness: rutile phase about 7 to 7.5, anatase phase about 5.5 to 6) are mixed, it is harder than potassium hexatitanate single phase polycrystalline fiber. As an effect of this high-density and mixed-phase crystal structure, the high friction coefficient and wear resistance of the friction material can be stably maintained from the low speed region to the high speed region, and its face-to-face damage property is also good. .

The characteristics of the above-mentioned composite polycrystalline fiber as a base material can be arbitrarily adjusted by the amount ratio of potassium hexatitanate crystals and titania crystals, which are its constituent phases, but when the mixing ratio of titania crystals is small. However, when the effect of improving the friction and wear characteristics as a multi-phase effect is insufficient, and when the amount ratio is large, the opponent attack of the sliding surface becomes remarkable. From these points, the ratio of titania crystals / potassium hexatitanate crystals is appropriately in the range of 1/10 to 20/1 (molar ratio). The fiber size of the composite polycrystalline fiber is about 20 to 50 μm and the fiber length is about 100 to 4 from the viewpoints of uniform dispersibility in resin, reinforcing property, stability as a base fiber, and the like.
The range of 00 μm is preferable. The compounding ratio of the composite polycrystalline fiber in the resin is arbitrary, but it is usually suitable to set it in the range of about 3 to 50% by weight. If it is less than about 3% by weight, its compounding effect is small. On the other hand, if it exceeds 50% by weight, the effect of improving the friction and wear characteristics is almost saturated, and there is no benefit of further increasing the content.

In the friction material of the present invention, a known other material may be mixed and used as the base material together with the above-mentioned composite polycrystalline fiber. Examples thereof include polyamide (nylon) fiber, aramid fiber, steel fiber, stainless fiber, copper fiber, brass fiber, carbon fiber, glass fiber, alumina / silica fiber, rock wool and wood pulp. One or two or more of these are arbitrarily selected. The blending amount is not particularly limited, but may be blended in a range of about 10 to 65% by weight in total with the composite polycrystalline fiber. The base component is a silane coupling agent (aminosilane, vinylsilane, epoxysilane, methacryloxylan, mercaptoxylan, etc.) for the purpose of improving dispersibility, binding property with the binder resin, etc., if necessary. Alternatively, a surface treatment (coupling treatment) with a titanate-based coupling agent (isopropyl triisostearoyl titanate, di (dioctyl pyrophosphate) ethylene titanate, etc.) is performed according to a conventional method, and then used.

If desired, the friction material of the present invention is a known friction and wear modifier, for example, vulcanized or unvulcanized natural / synthetic rubber powder, cashew resin powder, organic powder such as resin dust and rubber dust, Natural / artificial graphite, molybdenum disulfide, antimony trisulfide, inorganic powder such as barium sulfate, calcium carbonate, metal powder such as copper, aluminum, zinc, iron, alumina, silica, chromium oxide, copper oxide, antimony trioxide, oxidation One or more components selected from oxide powders such as titanium and iron oxide are used in an appropriate amount (for example, 20 to 20) for the purpose of improving friction and wear characteristics (friction coefficient, wear resistance, vibration characteristics, pear, etc.). 70% by weight). Also, it is not different from ordinary friction materials in that various additives, for example, rust preventives, lubricants, abrasives, and the like are blended in an appropriate amount (for example, 50% by weight or less) in accordance with the use and usage mode.

The resin component which is a binder is a commonly used material such as phenol resin, formaldehyde resin,
Examples thereof include thermosetting resins such as epoxy resins and silicone resins, and thermosetting resins thereof (modified with cashew oil and dryness), and rubber resins such as natural rubber, styrene butadiene rubber, and nitrile rubber.

The preparation of the raw material mixture of the friction material of the present invention was carried out except that the above-mentioned composite polycrystalline fiber was used as the base material.
It is no different from conventional friction materials, and no special conditions or restrictions are imposed on the manufacturing process thereof. That is, a base material is dispersed in a binder resin, and a friction wear modifier, which is blended as necessary, and a rust preventive agent, a lubricant, an abrasive, etc. are added,
A raw material composition is prepared by uniformly mixing, and pre-molding is then performed by heating or pressurizing (pressurizing pressure of about 10-40
Binder forming at MPa, temperature about 150-200 ° C)
After taking out from the mold, if necessary, heat treatment (temperature about 150 to 200 ° C., holding time about 1 to 12 Hr) is performed, and then the molded body is subjected to machining and polishing to have a predetermined shape. Finish into friction material.

The above-mentioned composite polycrystalline fiber as the base material is
An improved melting process, namely TiO ₂ (or a titanium compound that produces TiO ₂ upon heating) and K ₂ O (or a potassium compound that produces M ₂ O upon heating),
TiO ₂ / K ₂ O (molar ratio) was heated and melted in a powder mixture mixed in a ratio of 1.5 to 2.5, and then the melt was cooled to form potassium dititanate fiber (primary phase fiber).
A step of obtaining a fiber mass consisting of, primary dipotassium treatment to obtain a hydrated potassium titanate fiber having a potassium content of 15 to 20% by weight, by immersing the fiber mass in a liquid to elute potassium in the fiber and defibrating the same. Step, pre-drying treatment step of heating and drying the obtained hydrated potassium titanate fiber at 100 to 400 ° C., preliminarily dried hydrated potassium titanate fiber is immersed in a liquid to elute potassium, and potassium content 13.
A secondary potassium removal treatment step of obtaining a hydrated potassium titanate fiber of less than 6% by weight and a calcination step of heating the hydrated potassium titanate fiber to 900 to 1300 ° C. to convert the crystal structure. It is manufactured by

The characteristic treatment step in the above-mentioned manufacturing step is that the potassium removal treatment of the primary phase fiber mass is carried out as a two-step treatment of a primary treatment and a secondary treatment, and a preliminary drying treatment is carried out in between. It is in. By passing through this treatment step, it is possible to obtain a composite polycrystalline fiber with few grain boundary cracks and high density. Further, when the potassium content of the hydrated potassium titanate fiber after the secondary potassium removal treatment is adjusted to 13.6% by weight, the final product fiber is potassium hexatitanate single phase crystal fiber, but less potassium By adjusting the content (less than 13.6%), a mixed phase polycrystalline fiber with titania crystals can be obtained. The amount ratio of titania crystals / potassium hexatitanate crystals of the composite polycrystalline fiber can be arbitrarily controlled to be high or low depending on the amount of potassium removed in the secondary potassium removal treatment. Further, the titania crystal precipitates as a rutile phase when the heat treatment after the secondary potassium removal treatment is performed in a relatively high temperature range (about 970 ° C. or higher), and as an anatase phase in a lower temperature range, and the intermediate temperature thereof. In the region, it can be precipitated as a mixed phase of both.

[0013]

【Example】

(1) Preparation of raw material composition See Table 1. The base materials A _{1 to} A ₃ , B, and C used are as shown in Table 2 (manufacturing of each base material is described in Reference Example 1 to be described later).
According to Reference Example 3). The fiber size is 30 μm in fiber diameter (average) and 150 μm in fiber length (average). In Table 2,
"○" in the "Grain boundary crack" column indicates that there are few cracks,
“X” indicates that many cracks were generated. FIG. 1 shows the fiber morphology of a base material A ₁ (composite polycrystalline fiber according to Reference Example 1), and FIG. 2 shows the fiber morphology of a base material B (composite polycrystalline fiber according to Reference Example 2 below). Also, magnification × 200
0). In the base material B (FIG. 2), a large number of coarse cracks d are generated at the crystal grain boundaries. Substrate C (potassium hexatitanate single-phase polycrystalline fiber according to Reference Example 3 described later) also has a fiber morphology in which a large number of similar fine cracks are present at crystal grain boundaries. On the other hand, the base material A ₁ (FIG. 1) has few cracks d at the grain boundaries,
And it is extremely fine. Substrate A ₂ and A ₃ (composite polycrystalline fibers according to the same Reference Example 1 and the substrate A ₁₎ is also provided with a fiber type substrates A ₁ Like little intergranular cracking high dense.

(2) Fabrication of friction material Preform the raw material composition (pressing force: 14.7 MPa = 150 kg / cm)
² 、 Temperature: normal temperature, time: 1 minute), and then binding molding with a mold (pressing force: 14.7 MPa = 150 kg / cm ² , temperature: 170)
℃, pressurizing and holding time: 5 minutes), after molding, mold release and heat treatment in a drying furnace (hold at 180 ℃ for 3 hours). After that, cut it to a specified size, add polishing process, and test friction material (
Get the disk pad).

(3) Friction test For each friction material to be tested, a second efficacy test in accordance with "JASO C 406 Passenger car brake device dynamometer test method" was performed, and the abrasion damage condition of the mating material surface after the friction test ( The surface damage is evaluated by the surface roughness measurement). (Test conditions) Initial braking speed: 50 km / h, 100 km / h. Deceleration: 0.1G, 0.3G, 0.6G Counterpart material type: FC 250 cast iron material Table 3 shows the test results. In the table, the symbols of "face-to-face damage column" are as follows. ⊙: No damage ○: Almost no damage ×… Damage occurred.

Comparative example No. 11 (using base fiber B) has a high friction coefficient, but is inferior in face-to-face damage property.
o.12 (using the base fiber C) has a good face-to-face damage property, but has a low friction coefficient. On the other hand, invention examples (No. 1 to 3
The friction material (1) has both a high friction coefficient and good face-to-face damage.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

[Table 3]

[0020]

[Reference example]

Reference Example 1 - the high dense composite polycrystalline fibers (base material A _1, A _2, A ₃₎ manufacturing ── (a) Preparation of the starting material purification anatase powder (purity 99.8%), potassium carbonate powder ( 99.5%) and TiO ₂ / K ₂ O (molar ratio) is 1.
Mix in a ratio of 8 and mix evenly. (B) Heating melting and cooling solidification The starting material was put into a platinum crucible and heated to 1050 ° C in a heating furnace.
Hold for 40 minutes. The melt is poured into a copper dish and cooled and solidified to obtain a fiber mass composed of potassium dititanate crystal fibers.

(C) Primary potassium removal treatment The fiber mass was immersed in water (50 times the weight of the fiber mass), the potassium was eluted with stirring with a propeller and disentangled to obtain a potassium content of 17.5% by weight. Obtain hydrated potassium titanate. (D) Preliminary Drying Treatment The above hydrated potassium titanate fiber was dehydrated, charged into a heating furnace, and dried at 250 ° C. for 14 hours.

(D) Secondary potassium removal treatment Preliminarily dried hydrated potassium titanate fibers were added to water (100 times the fiber weight), sulfuric acid was added, and a predetermined potassium content was obtained under stirring with a propeller. Elute potassium until By this secondary potassium removal treatment, hydrated potassium titanate fibers A ₁ (potassium content 7.0% by weight), A ₂ (same as
9.0% by weight) and A ₃ (11.0% by weight).

(E) Baking treatment Each of the hydrated potassium titanate fibers A _1, A _{2 and} A ₃ was dehydrated and then subjected to a heat treatment (1150 ° C. × 2 Hr) for crystal structure conversion in a heating furnace. As a result, highly dense composite polycrystalline fibers A ₁ , A ₂ , and A ₃ were obtained (see Table 2 for the composition and crystal constitution of each fiber). The fiber size is 30 μm in fiber diameter (average) and 150 m in fiber length (average).

Reference Example 2 Production of Composite Polycrystalline Fiber (Base Material B) (a) Preparation of Starting Material Same as Reference Example 1. (B) Heat melting and cooling solidification Same as Reference Example 1. (C) Depotassium treatment The primary phase fiber mass is put into water (100 times the fiber weight), sulfuric acid is added, and then potassium is eluted with stirring with a propeller and defibrated to obtain hydrated potassium titanate (potassium). The content was 7.0% by weight). (D) Baking treatment The hydrated potassium titanate fiber was subjected to a treatment under the same conditions as the firing treatment of Reference Example 1 to obtain a composite polycrystalline fiber B (see Table 2 for fiber composition, crystal structure, etc.). . The fiber size is 30 μm in fiber diameter (average) and 200 μm in fiber length (average).

[Reference Example 3] -Production of potassium hexatitanate single-phase polycrystalline fiber (base material C)-(a) Preparation of starting material Same as Reference Example 1. (B) Heat melting and cooling solidification Same as Reference Example 1. (C) Depotassium treatment The primary phase fiber mass is put into water (100 times the fiber weight), sulfuric acid is added, and then potassium is eluted with stirring with a propeller and defibrated to obtain hydrated potassium titanate (potassium). Content 13.6% by weight). (D) Firing treatment The hydrated potassium titanate fiber was subjected to the treatment under the same conditions as the firing treatment of Reference Example 1 to obtain a composite polycrystalline fiber C (see Table 2 for the crystal constitution of each fiber). The fiber size is 30 μm in fiber diameter (average) and 200 μm in fiber length (average).

[0026]

The friction material of the present invention has improved friction characteristics as a compounding effect of the highly dense potassium hexatitanate-titania composite polycrystalline fiber, and has a wide range from low speed to high speed. It can maintain a high coefficient of friction in a stable manner and is useful as a brake lining, a disc pad, a clutch facing, etc. that constitutes a braking device for automobiles, vehicles, aircraft, and various industrial machines. It is possible to deal with such problems, and it is possible to obtain the effects of improving and stabilizing the braking function and improving durability.

[Brief description of drawings]

FIG. 1 is a drawing-substitute micrograph (× 2000) showing a highly dense potassium hexatitanate-titania composite polycrystalline fiber used as a base material of a friction material of the present invention.

FIG. 2 is a drawing-substitute micrograph (× 2000) showing a potassium hexatitanate-titania composite polycrystalline fiber used as a base material of a conventional friction material.

[Explanation of symbols]

 d: Grain boundary crack

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display area F16D 69/02 F16D 69/02 K // C30B 29/32 C30B 29/32 B D01F 9/08 D01F 9/08 Z

Claims (2)

[Claims] 1. A friction material obtained by binding and molding a mixture of a resin and a base material, wherein a highly dense composite polycrystalline fiber composed of potassium hexatitanate crystals and titania crystals is added as the base material. A friction material characterized by being. 2. The mixed phase ratio (molar ratio) of titania crystals / potassium hexatitanate crystals of the composite polycrystalline fiber is 1/10 to 2
It is 0/1, The friction material of Claim 1 characterized by the above-mentioned.