JP3109790B2 - Friction material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a friction material used as a brake pad, a lining, or a clutch facing of a vehicle, an industrial machine or the like.

[0002]

2. Description of the Related Art A friction material used for a disc brake pad, a drum brake shoe, and the like of an automobile frictionally engages with a disc rotor and a brake drum, which are mating members, and plays an important role of converting kinetic energy into heat energy. I am carrying it. For this reason, the friction material always generates heat and becomes high temperature. Therefore, such a friction material is required to have stable friction characteristics with a small change in friction coefficient even with a temperature change, in addition to heat resistance, wear resistance and the like.

Therefore, conventionally, in order to satisfy these various characteristics, the friction material is constituted as a composite material.
That is, the friction material is a fiber substrate forming a skeleton such as aramid fiber and potassium titanate fiber, a resin binder such as a phenol resin binding and holding the fiber substrate, and a matrix of these fibers and the binder. It is generally composed of various fillers that are dispersed and filled. Examples of the filler include fillers such as barium sulfate and calcium carbonate, solid lubricants such as graphite and molybdenum disulfide, cashew dust, metal powder, abrasives such as silica, and other friction adjusting agents. Additives and the like are used.

Here, cashew dust is obtained by condensing cashew nut shell liquid (cashew nut shell liquid) or a polymer thereof with aldehydes such as furfural and the like, hardening this, cooling it, and pulverizing it. It is widely used as a friction modifier to improve abrasion and stabilize the friction coefficient. And the friction material, after uniformly mixing the above-mentioned friction material raw materials including this cashew dust, pressurize the powdery mixture and pre-mold,
It is generally manufactured by thermoforming under pressure.

However, this cashew dust generally has a center particle diameter of 50 to 500 μm and has a large particle size as compared with other compounding agents. Therefore, when a material having a particle size of 100 μm or more is used, the friction material Sedimentation during mixing or filling in a preforming mold and segregation is likely to occur. When the cashew dust segregates in the friction material, the wear characteristics and friction characteristics of the friction material become non-uniform. Moreover, cashew dust has no binding force to phenolic resin, which is generally used as a resin binder, and has a large thermal expansion itself. The segregated portion also serves as a starting point for cracking.

In order to prevent such segregation of cashew dust, various means have conventionally been known. The most commonly known means is a method using an organic solvent, and a method in which the friction material is mixed with the organic solvent in a wet manner. Further, a method using a liquid epoxy resin or a liquid phenol resin as a mixing aid, and a method using a liquid phenol resin modified with an oxygen-containing oligomer as a mixing aid (JP-A-2-133431, JP-A-2-2431)
-133432) is also known.

[0007] Unlike these methods, Japanese Patent Laid-Open No.
JP-A-156235 proposes that cashew dust to be used be coated with a highly viscous material. The high-viscosity material includes cashew nut shell, ethylene glycol and propylene glycol, and has a viscosity of 2 to 20 PS /
It is stated that 25 ° C. is preferred.

As means for preventing segregation of cashew dust, there is another means disclosed in Japanese Patent Application Laid-Open No. 6-25651 proposed by the present applicant. Milled glass fiber,
A fiber holding phenol fiber, aramid fiber and the like is used.

[0009]

As described above, various means for preventing segregation of cashew dust are known, and according to these means, segregation of cashew dust is effectively prevented. be able to.

[0010] However, the method using an organic solvent is as follows.
A drying step for removing the organic solvent later is necessary, which increases man-hours and costs.
In addition, the method of using a mixing aid such as a liquid epoxy resin or a liquid phenol resin requires the use of a relatively large amount of the mixing aid in order to effectively prevent segregation of cashew dust. It reduces the fade resistance of the friction material or, in some cases, reduces the friction characteristics.

On the other hand, Japanese Unexamined Patent Publication No.
According to the means proposed in Japanese Patent Publication No. 235, the surface of cashew dust is simply coated with a high-viscosity material, so that it is simple and the amount of coated high-viscosity material is small relative to the entire friction material. Therefore, the fade resistance and friction characteristics of the friction material are not reduced. However, cashew nut shell (liquid), ethylene glycol, and propylene glycol used as the highly viscous material are liquids having only relatively high viscosities, and are hard to cure even when thermoforming a friction material, or harden. do not do. For this reason, these viscous materials cannot not only sufficiently retain cashew dust in the friction material, but also may reduce the retention.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a friction material which prevents segregation of cashew dust and improves the retention of cashew dust in the friction material.

[0013]

The friction material according to the present invention is a friction material obtained by thermoforming a powdery mixture containing a fiber base material, a resin binder, cashew dust and other fillers. The average degree of polymerization is 2.
And a polymer of cashew nut shell liquid monomer is from 5 to 4.0, the process dust composition is its curing agent 0.5
It is coated with a viscous liquid mixture with hexamethylenetetramine of .about.0.8 (%) .

[0014] Here, the cashew nut shell liquid, but also used as a raw material for producing cashew dust, a liquid (oil) extracted from cashew nut shells composed mainly of cardanol. In the present invention, the cashew nut shell liquid containing cardanol as a main component is used as a dimer or a polymer obtained by heating the monomer under, for example, an acid catalyst. The degree of polymerization is 2.0 to
4.0. If the average degree of polymerization is low, the ratio of the monomer of the cashew nut shell liquid increases, and rash is likely to occur when the skin touches the skin. Even if hexamethylenetetramine is added, the friction material is hardly cured during thermoforming. Conversely, if the average degree of polymerization is high, the viscosity becomes too high, making the coating process difficult, and the coated cashew dusts tend to aggregate with each other to form lumps. For this reason,
As the cashew nut shell liquid polymer, those having an average degree of polymerization in the range of 2.0 to 4.0 are used, and those having an average degree of polymerization in the range of 2.5 to 4.0 are preferably used. This polymer has a viscosity of 20 to 300 P
It is preferably about S.

The viscous cashew nut shell liquid polymer is used as a mixture with hexamethylenetetramine as a curing agent thereof. The amount of hexamethylenetetramine added is not particularly limited as long as it acts as a curing agent.
Cashew nut shell liquid polymer 6 ~
About 12% by weight is preferred.

The coating of the viscous liquid mixture of the cashew nut shell liquid monomer polymer and hexamethylenetetramine can be easily performed, for example, by mixing cashew dust and the viscous liquid mixture and stirring the mixture. Can be done. In this case, if the coating amount of the viscous liquid mixture is too small, it is not possible to obtain a sufficient effect on segregation prevention of cashew dust and retention in the friction material. Easier to do. Therefore, the coating amount of the cashew nut shell liquid polymer depends on the cashew dust particle size and the like, but is generally preferably about 4 to 15% by weight based on the coated cashew dust. Preferably 6 to 12% by weight
It is.

In the friction material of the present invention, components other than cashew dust are the same as in the conventional case.

As the fiber base material, glass fiber, rock wool, silicate fiber, alumina fiber, carbon fiber,
Potassium titanate fiber, inorganic fiber such as slag wool, steel fiber, stainless steel fiber, metal fiber such as copper fiber, aramid fiber, novoloid fiber, nylon fiber,
Organic fibers such as rayon fibers can be used. And these fibers are used alone or in appropriate combination,
It can be used according to the specific type or application of the friction material.

As the resin binder, a phenol resin, a melamine resin, an epoxy resin, or a polyimide resin,
Polyester resin, rubber such as SBR, etc. can be used. However, among these, phenolic resins or modified products thereof are also the ones most commonly used,
It is suitable.

Examples of the filler include fillers such as barium sulfate and calcium carbonate, and solid lubricants such as graphite, molybdenum disulfide and trimonized antimony. If necessary, rubber powder may be used. , Copper powder, zinc powder,
Metal powders such as brass powders, abrasives such as silica, or other additives for adjusting friction can be used.

The friction material of the present invention is obtained by sufficiently uniformly mixing the above cashew dust with a fiber base material, a resin binder, and other fillers, preforming the powder mixture, and then heating the mixture. It can be manufactured by an ordinary thermoforming method of pressing.

[0022]

In the present invention, the surface of cashew dust is coated with a viscous liquid mixture of a cashew nut shell liquid monomer polymer having an average degree of polymerization of 2.0 to 4.0 and hexamethylenetetramine. The cashew dust coated with the viscous liquid mixture adheres to these materials when mixed with the fibrous base material, the resin binder, and other fillers, and is uniformly dispersed without settling. For this reason, segregation of cashew dust is prevented. In addition, since the cashew nut shell liquid monomer polymer is cured by hexamethylenetetramine during thermoforming of the friction material, the cashew dust binds to the resin binder and other friction material components via the cured material on the surface. Is done. For this reason, cashew dust is firmly held in the friction material.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to an embodiment in which the present invention is applied to a disc brake pad.

<Surface Treatment of Cashew Dust> A cashew nut shell liquid monomer polymer (hereinafter simply referred to as “cashew polymer”) and hexamethylenetetramine (hexamine) are applied to the surface of cashew dust having an average particle size of about 200 μm. The viscous liquid mixture was coated to prepare various surface-treated cashew dusts (treated dusts) used in the examples of the present invention.

FIG. 1 shows the average degree of polymerization and the viscosity (PS / 25 ° C.) of the cashew polymer used herein, the composition of the prepared treated dust, ie, the amount of the cashew polymer and hexamine adhering to the cashew dust, It shows.

As shown in FIG. 1, the cashew polymer was used by changing its average polymerization degree. The average polymerization degree was 2.0 (viscosity 3 PS) in Example 1, and the average polymerization degree was 2.times. 5 (viscosity 15 PS). In Example 3, the average degree of polymerization was 3.
0 (viscosity 25 PS), and in Example 4, the average degree of polymerization was 3.5.
(Viscosity 100 PS), and in Examples 5 to 9, those having an average degree of polymerization of 4.0 (viscosity 290 PS) were used. The cashew polymer and hexamine are mixed at a ratio of approximately 12 parts by weight to 1 part by weight, and the viscous liquid mixture is used in Examples 1 to 5 in a proportion of 9.0 with respect to the total amount of the treated dust. % By weight (91.0% by weight of cashew dust, 8.3% by weight of cashew polymer, 0.7% by weight of hexamine). Similarly, in Example 6, 5.0% by weight, and in Example 7, 7.0% by weight. % By weight, 11.0 in Example 8.
Cashew dust was coated at a ratio of 13.0% by weight in Example 9 and 13.0% by weight in Example 9.

For comparison, untreated cashew dust was prepared as Comparative Example 1. In Comparative Example 2,
The cashew nut shell liquid was not polymerized and used as a monomer (polymerization degree: 1.0, viscosity: 0.5 PS), and the cashew dust was surface-treated under the same conditions as in Example 1 except for the above. In Comparative Example 3, under the same conditions as in Example 5, but without using hexamine, only cashew polymer was coated on cashew dust. Further, in Comparative Example 4, a cashew polymer having an average degree of polymerization of 4.5 (viscosity was 300 PS or more, which was not measured here) was used, and the cashew dust was coated under the same conditions as in Example 1 except for the above. .

<Manufacture of Pads> The disc brake pads (PD5) of Examples 1 to 9 and Comparative Examples 1 to 4 were prepared using the cashew dust surface-treated as described above.
1 type caliper).

Here, the friction material had the composition shown in Table 1 below.

[0030]

[Table 1]

In this case, untreated cashew dust is used in the case of Comparative Example 1. And
The friction material raw material of this composition including the surface-treated cashew dust is dry-mixed sufficiently uniformly with a V-type blender, and then this powdery mixture is charged into a preforming mold, and 200 kg at normal temperature.
/ Cm ² for 1 minute to preform.

The preform of the friction material was set in a thermoforming mold together with a back metal having a surface coated with a phenol resin adhesive in advance, and a pressure of 400 kg / cm ^{2 and} a temperature of 160 ° C.
For 10 minutes. And this is 250 ° C
For 120 minutes. Thus, a disc brake pad was obtained.

<Evaluation Test> Regarding the disc brake pads of Examples 1 to 9 and Comparative Examples 1 to 4 manufactured as described above, the state of segregation of cashew dust,
The presence or absence of cashew dust lumps in the friction material, the cashew dust retention in the friction material, the surface condition of the side surface of the friction material, and the strength of the friction material were tested and evaluated.

Regarding the state of segregation of cashew dust (segregation state of dust), the above-mentioned powdery mixture of the friction material is placed in a transparent bag, and shaken to observe how cashew dust falls to the lower part of the bag. By doing that. The criteria for the evaluation are as follows. ×: Cashew dust dropped much after shaking 5 times △: Cashew dust dropped much after shaking 10 to 20 ○: Cashew dust did not drop much even after shaking 20 times Existence of lump of cashew dust in friction material Regarding (presence / absence of lump of dust), friction surfaces of ten friction materials (pads) were observed to check presence / absence of lump of cashew dust. Then, according to the number of friction materials having the cashew dust lump, the following evaluation was made. ×: 6 or more △: 6 or less ○: 3 or less Regarding the retention of cashew dust in the friction material (dust retention), the cashew dust on the friction surface was pinched with a needle to make it easier to remove. It has been examined. The criteria for the evaluation are as follows. ×: Can be easily removed by gently pecking △: Can be easily removed by strong pecking ○: Difficult to remove even with strong pecking Friction material is made by hardening the fiber base material and filler with a small amount of resin binder For this reason, fine wrinkles (wrinkles) tend to be formed on the surface, and this state is examined by observing the side surface of the friction material. The criteria for the evaluation are as follows. ×: Many wrinkles △: Little wrinkles ○: Almost no wrinkles are observed. Regarding the strength of the friction material, JASO C437
The shear strength (kgf) of the pad (for PD51 type caliper) was measured according to the -84 method of testing the adhesive strength of a friction material.

<Evaluation Results> The results of the above evaluation tests are shown in FIG.
Shown along with.

As shown in the evaluation results of FIG. 1, the cashew dust surface has an average degree of polymerization of 2.0 to 4.0, cashew polymer (polymer of cashew nut shell liquid monomer) and hexamine (hexamethylenetetramine). In Examples 1 to 9 in which the mixture of the above was coated, good results were obtained with respect to the segregation state of cashew dust and the presence or absence of lumps. This indicates that the average degree of polymerization was 2.0 to 2.0, as can be seen from a comparison with Comparative Example 1 using untreated cashew dust.
The cashew polymer of 4.0 has a high viscosity, because the cashew dust coated on the surface adheres to and is retained by other materials in the powdery mixture of the raw material of the friction material and is well dispersed. However, in Comparative Example 4 using a cashew polymer having an average degree of polymerization of 4.5, segregation of cashew dust was prevented because the viscosity was too high.
There was a tendency for the cashew dust to agglomerate with each other to form lumps. In Comparative Example 2 using a non-polymerized cashew monomer, the same good results as those of the example were obtained. However, since this cashew monomer is liable to rash when touched on the skin, This is undesirable. Therefore, as can be seen from these results, the average degree of polymerization of the cashew polymer used is preferably from 2.0 to 4.0.

The effects of the first to ninth embodiments are particularly exhibited in the retention of cashew dust in the friction material.
That is, as can be seen from a comparison with Comparative Example 3 in which hexamine was not added to the cashew polymer, by adding hexamine, which is a curing agent, to the cashew polymer, the cashew polymer was cured during thermoforming of the friction material. And the cashew dust is firmly bound to the resin binder (phenolic resin) and other friction material components via the cured cashew polymer. Then, by holding the cashew dust in the friction material in this manner, the generation of crack nuclei is further reduced. In addition, the addition of hexamine enhances the retention of cashew dust, and the cashew polymer coated and cured on the surface of cashew dust assists and promotes the flow of the resin binder during thermoforming of the friction material. Therefore, as shown in the evaluation result of the side surface state of the friction material, wrinkles generated on the surface of the friction material are reduced. At the same time, as shown in the measurement results of the strength of the friction material, the strength and adhesion strength of the friction material are greatly enhanced.

However, in Example 1, since the average degree of polymerization of the cashew polymer was as low as 2.0 and the curing with hexamine was insufficient, the retention of cashew dust tended to be slightly weak. Therefore, it can be seen that the average degree of polymerization of the cashew polymer is more preferably from 2.5 to 4.0 in order to obtain the best results with respect to the retention of cashew dust. Further, when the amount of the mixture of the cashew polymer and the hexamine to be coated on the surface of the cashew dust is small, as in Example 6, the effect of preventing segregation of the cashew dust and the retention of the cashew dust tend to decrease. If the amount is too large, there is a tendency that cashew dust clumps are likely to occur as in Example 9. Therefore, it is understood from this evaluation result that the coating amount of the mixture of the cashew polymer and hexamine is most preferably about 6 to 12% by weight of the entire cashew dust after the treatment.

By coating the surface of the cashew dust with a mixture of the cashew polymer and hexamine, segregation of the cashew dust can be prevented, and the cashew dust can be retained in the friction material. Can be enhanced. And, unlike the monomer, this cashew polymer is safe for workers because it is hard to rash even if it touches the skin. In addition, the cashew polymer helps the flow of the resin binder during thermoforming, so it can not only reduce the wrinkles generated on the friction material surface and improve the appearance, but also enhance the strength and durability of the friction material Can be. Furthermore, the cured product of the cashew polymer is similar to cashew dust and has a low content in the entire friction material, so that it does not affect the friction characteristics. In addition, since only cashew dust is coated, a friction material having the above effects can be manufactured at low cost.

In the above, the disc brake pad has been described as an example. However, the present invention is not limited to this.
Alternatively, it can be applied to various friction materials such as clutch facing.

[0041]

As described above, the friction material of the present invention is a friction material obtained by thermoforming a powdery mixture containing a fibrous base material, a resin binder, cashew dust and other fillers. , The average degree of polymerization is 2.5-4.
0 is a viscous liquid mixture of a cashew nut shell liquid monomer polymer and hexamethylenetetramine having a treated dust composition of 0.5 to 0.8 (%) .

Therefore, since a high-viscosity cashew nut shell liquid monomer polymer is used, the cashew dust coated with the cashew nut shell adheres to the fiber base material or other filler in the powdery mixture of the raw material of the friction material. Since the particles are uniformly dispersed, the segregation can be effectively prevented. In addition, since the cashew polymer has hexamethylenetetramine as a curing agent added thereto, the cashew polymer coated on the surface of the cashew dust is cured during thermoforming of the friction material. Bonded to the resin binder and other friction material components through the cured cashew polymer, the retention in the friction material is enhanced.

[Brief description of the drawings]

FIG. 1 shows the surface-treated cashew dust (coated with a viscous liquid mixture of cashew polymer and hexamine) used for the disc brake pads of Examples and Comparative Examples of the present invention, and the results of an evaluation test thereof. FIG.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toru Honma 1st Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Toshihiko Yuasa 2-1, Asahimachi, Kariya City, Aichi Prefecture Aisin Seiki Co., Ltd. JP-A-5-156235 (JP, A) JP-A-56-63123 (JP, A) JP-A-2-133431 (JP, A) JP-A-2-133432 (JP, A) JP-A-6-25651 (JP, A) JP-A-63-72927 (JP, A) JP-A-60-92332 (JP, A) JP-A-58-47079 (JP, A) (58) (Int.Cl. ⁷ , DB name) F16D 69/02 C08J 5/14 C09K 3/14 520

Claims (1)

(57) [Claims] 1. A friction material obtained by thermoforming a powdery mixture containing a fibrous base material, a resin binder, cashew dust and other fillers, wherein the surface of the cashew dust has an average degree of polymerization of 2.5 to
It is characterized by being coated with a viscous liquid mixture of a cashew nut shell liquid polymer of 4.0 and hexamethylenetetramine having a treated dust composition of 0.5 to 0.8 (%). And friction material.