JP7045902B2 - Brake friction material - Google Patents

Description

The present invention relates to a brake friction material.

Conventionally, in brake friction materials for automobiles and the like, metal fibers such as copper fibers, organic fibers such as aramid fibers, wollastonite, sepiolite, potassium titanate fiber, sodium sodium titanate polycrystalline fiber, carbon fiber, rock wool. Inorganic fibers such as, binders such as phenolic resin, lubricants such as graphite and molybdenum disulfide, friction modifiers such as alumina powder, zircon sand, cashew dust, ceramic powder and metal powder, and barium sulfate. By mixing the filler and the pH adjusting material such as calcium hydroxide, it is adjusted to satisfy the braking characteristics such as strength, adhesiveness, friction characteristics, wear characteristics, and squealing characteristics (see Patent Document 1). ..

Of the above materials, carbon fiber has the demerit of lowering the coefficient of friction, but has excellent properties such as light weight, high strength, and high heat resistance, so it is possible to reinforce the lining material and improve heat resistance. It is used for the purpose (see Patent Document 2).
Further, in order to provide a brake friction material having strength and durability and capable of suppressing fade phenomenon, a friction material in which fiber blocks containing 3 to 30% by mass of carbon fibers are dispersed is disclosed (Patent Document 3). reference).
Further, a friction material containing carbon fibers having a functional group introduced on the surface is also known in order to strengthen the bond with the binder and exert a better reinforcing effect (see Patent Document 4).

Japanese Unexamined Patent Publication No. 2012-23364 Japanese Unexamined Patent Publication No. 55-157672 Japanese Unexamined Patent Publication No. 2-212634 Japanese Unexamined Patent Publication No. 2010-285578

As described above, when carbon fiber is used as a material for brake friction materials, attention has been paid to its excellent mechanical properties, while attention has been paid to conductivity, which is one of the excellent properties of carbon fiber. I wasn't.
Since the brake friction material is always used in an environment exposed to wind and rain, the surface is painted to prevent rust at the boundary between the lining material made of the brake friction material and the back plate to ensure reliability. It has been subjected.

From the viewpoint of reducing the environmental load and cost, powder coating is used for coating, which does not use a solvent and allows the paint to be used without waste. Since this is a method in which a charged powder coating material is attached to an object to be coated and then fired as it is to form a coating film, it is necessary to ground the object to be coated in order to release the electric charge due to static electricity.

By the way, in order to reduce the environmental load in some countries, laws and regulations are being promoted to regulate copper metal fibers contained in general brake friction materials. Therefore, the present inventor is conducting research and development on a brake friction material excluding copper metal fibers. However, since the brake friction material containing copper metal fibers is excellent in conductivity, it is advantageous for the above-mentioned powder coating, but the brake friction material containing no copper metal fibers lacks conductivity and is powder. It was found that when coating was performed, a coating film having a sufficient thickness could not be formed. If the thickness of the coating film is insufficient, rust is generated from the boundary between the lining material made of the brake friction material and the back plate, and when this rust develops, the lining material may peel off from the back plate.
That is, copper fiber has been used for the conventional lining material, but by eliminating this, the conductivity is lost, grounding becomes difficult, a sufficient coating film is not formed, and the adhesive strength is increased due to the generation of rust. There was a problem that it was lowered and as a result, long-term reliability was impaired.

Therefore, in the present invention, powder coating is possible without using copper fibers, long-term reliability of the product can be maintained, sufficient friction characteristics can be ensured, and a material containing copper is not contained. It is intended to provide a brake friction material.

The brake friction material of the present invention is a brake friction material containing at least a reinforcing fiber material, a binder, a friction adjusting material, a filler, and a pH adjusting material, and the total amount of the brake friction material is 100% by mass. It is characterized in that it does not contain a material containing copper, contains carbon fibers of 0.05% by mass or more and 0.1% by mass or less, and the fiber length of the carbon fibers is 1 mm or more.

According to the present invention, it is possible to reduce the environmental load by not using a material containing copper. In addition, by containing carbon fiber with an optimized blending amount and fiber length instead of copper fiber, it is possible to effectively impart conductivity to the brake friction material and improve powder coatability. It is possible to prevent the occurrence of rust during long-term use.
Therefore, according to the present invention, a brake friction material that does not contain a material containing copper substantially, is easy to powder coat, secures excellent friction characteristics, and can prevent the occurrence of rust during long-term use. Can be provided.

The front view which shows the brake pad as an application example of the brake friction material of this embodiment. The graph which shows the correlation between the friction coefficient and the carbon fiber compounding amount in a plurality of brake friction materials produced in an Example and a comparative example. The graph which shows the correlation of the electric resistance value and the carbon fiber compounding amount in a plurality of brake friction materials produced in an Example and a comparative example.

Hereinafter, a mode for implementing the brake friction material will be described.
It should be noted that this embodiment is specifically described in order to better understand the gist of the invention, and is not limited to the present invention unless otherwise specified.

The brake friction material of the present embodiment is a brake friction material used for a brake pad for a disc brake used for braking a vehicle such as an automobile, a brake shoe for a drum brake, and the like. These brake pads and brake shoes abut against braked members such as disc rotors and brake drums to generate frictional force, thereby braking the vehicle.

FIG. 1 shows a brake pad 1 for a disc brake as an example. The brake pad 1 is composed of a back plate 2 and a brake friction material 3 adhered to the surface of the back plate 2. The brake pad 1 is supported by the non-rotating portion of the vehicle on the back plate 2, and the side opposite to the brake friction material 3 on the back plate 2 is pressed by the disc brake caliper, so that the brake friction material 3 is a wheel. It comes into contact with the disc that rotates with it and brakes the rotation of the disc.

The brake friction material 3 of the present embodiment has a total amount of the brake friction material of 100% by mass in the brake friction material containing at least a reinforcing fiber material, a binder, a friction adjusting material, a filler, and a pH adjusting material. When this is done, it is characterized in that it does not contain a material containing a copper element, contains carbon fibers of 0.05% by mass or more and 0.1% by mass or less, and has a fiber length of 1 mm or more. ..
In the brake friction material 3 of the present embodiment, an aramid fiber or the like can be applied as the reinforcing fiber, and a phenol resin or the like can be applied as the binder. Further, cashew dust, rubber powder, etc. can be applied as an organic friction adjusting material, powder such as zinc powder or powder such as zirconium oxide can be applied as an inorganic friction adjusting material, and barium sulfate can be applied as a filler. Etc. can be applied, and calcium hydroxide or the like can be applied as a pH adjusting material.
Further, in the brake friction material 3 of the present embodiment, in addition to the various materials, graphite, mica, coke, antimony trisulfide, molybdenum disulfide and the like may be contained as a lubricating material, and potassium titanate fiber may be contained as an inorganic fiber. , Wollastonite, rock wool, etc. may be included.

In the brake friction material 3 of the present embodiment, it is desirable that the content of carbon fibers is 0.05% by mass or more and 0.1% by mass or less, and by containing carbon fibers in this range, conductivity is improved. It can be secured and the friction coefficient can be set to a suitable value.
When the content of the carbon fiber is less than 0.05% by mass, the conductivity of the brake friction material 3 cannot be sufficiently ensured, and the powder coatability is deteriorated. If the carbon fiber content exceeds 0.1% by mass, the friction coefficient of the brake friction material 3 may drop sharply.

In the brake friction material 3 of the present embodiment, it is necessary to set the fiber length of the carbon fiber to 1 mm or more, and by setting the fiber length of the carbon fiber to 1 mm or more, it becomes easy to obtain conductivity, and the above-mentioned blending amount It becomes possible to obtain good paintability.
If the fiber length of the carbon fiber is less than 1 mm, it is necessary to increase the blending amount of the carbon fiber in order to obtain conductivity, and as a result, the coefficient of friction does not satisfy the target range.
When the fiber length of the carbon fiber is in the range of 1 mm or more and less than 10 mm, there is no effect on the coatability and friction characteristics. However, since carbon fibers having a fiber length in this range tend to aggregate, care must be taken when blending them. If a large amount of aggregated carbon fibers are contained, the aggregates are mixed in the brake friction material 3 and the brake is braked. Aggregates may be exposed on the surface of the friction material 3 and the appearance may be poor. Therefore, the fiber length of the carbon fiber is preferably 10 mm or more in consideration of the problem of poor appearance as well as excellent coatability and friction characteristics.

The brake friction material 3 described above is obtained by weighing each of the above-mentioned components in a required amount, mixing them, and compression-molding the mixed material into a desired shape using a mold. Further, the brake pad 1 shown in FIG. 1 can be obtained by adhering this compression molded product to the back plate 2 with an adhesive and performing necessary polishing and grooving.

If the brake friction material 3 has the above-mentioned composition, the environmental load can be reduced by not using the copper element-containing material used for the conventional brake pad. In addition, by containing carbon fiber with an optimized blending amount and fiber length in the desired range instead of copper fiber, it is possible to effectively impart conductivity to the brake friction material and improve powder coatability. By doing so, it is possible to form the brake friction material 3 having a sufficient thickness, and it is possible to provide the brake friction material 3 which can prevent the occurrence of rust during long-term use. That is, since a coating film having a sufficient thickness can be formed by improving the powder coatability, the brake friction material 3 having a sufficient thickness can be obtained by firing the coating film, and there is a risk of rusting. Brake friction material 3 without rust can be formed.
Therefore, according to the present embodiment, it does not substantially contain a copper element, can reduce the environmental load, has good powder coatability, and is used for a long period of time while ensuring excellent friction characteristics. It is possible to provide a brake friction material 3 that can prevent the occurrence of rust at the time.

After thoroughly cleaning the back plate for attaching the brake friction material, an adhesive was applied to the surface in contact with the brake friction material and dried.
Next, as shown in Tables 1 and 2 below, it contains 0.05 to 0.1% by mass of carbon fiber, and the other components are phenol resin as a binder, aramid fiber as a reinforcing fiber, and titanium as an inorganic fiber. Potassium acid fiber, wollastonite, sepiolite, rock wool, ceramic fiber, graphite as lubricant, mica, coke, antimon trisulfide, molybdenum disulfide, PTFE, cashew dust, rubber powder, NBR, acrylic as organic friction adjuster. Rubber, zirconium oxide, zirconium silicate, zinc powder, vermiculite, talc as an inorganic friction adjuster, calcium hydroxide as a pH adjuster, and barium sulfate as a filler were blended so as to have the contents as shown in each table. In Tables 1 and 2, the unit of the blending amount of each component is all mass%.

The mixture of each compounding ratio shown in Tables 1 and 2 was put into a predetermined mold at room temperature and cold-molded at a pressure of 50 MPa.
The cold-molded product having each of these compositions and the back metal coated with the adhesive were put into a mold set at 150 ° C. and heat-compressed at a predetermined pressure and time to obtain a molded product. Further, the molded product was taken out from the mold and heat-treated at 220 ° C. for 6 hours to perform polishing, grooving, and powder coating to prepare the brake pads of Examples 1 to 6.
Further, when the brake pads are manufactured under the same manufacturing conditions as those of the above-mentioned Examples, the brakes of Comparative Examples 1 to 8 manufactured by removing the fiber length of the carbon fibers and the blending amount of the carbon fibers from the desirable ranges described above. A pad was made.
Table 1 below shows the fiber lengths of the carbon fibers used for the brake pads of Examples 1 to 6, and Table 1 shows the blending amount (% by mass) of the materials used. In addition, Table 2 shows the fiber lengths of the carbon fibers used for the brake pads of Comparative Examples 1 to 8, and Table 2 shows the blending amount (mass%) of the materials used.
The appearance of the brake pads of Examples 1 to 6 and Comparative Examples 1 to 8 is the same as that of the brake pads shown in FIG.

The brake pads of Examples and Comparative Examples manufactured as described above were evaluated for powder coatability and friction characteristics (Japanese Automotive Standards Organization JASO C407 "Truck / Bus-Brake Device-Dynamometer Test Method").
The coating film thickness on the side surface of the brake pad is used to evaluate the powder coating property, and the deceleration of 3.0 m / s ² in the second efficacy test of JASO C407 as a representative value of the friction coefficient is used to evaluate the friction characteristic. It was decided to use the measured value of.
In the evaluation of friction characteristics, when the measured value of deceleration of 3.0 m / s ² in the second efficacy test was 0.37 or more, it was judged that the friction characteristics were excellent, and OK was displayed in the friction characteristics column. ..
In the evaluation of friction characteristics, if the measured value of deceleration of 3.0 m / s ² in the second efficacy test is less than 0.37, it is judged that the friction characteristics are inferior, and NG is displayed in the friction characteristics column. ..
The results of these evaluations are shown in Tables 3 and 4 below.

Examples 1 to 6 include carbon fiber, phenol resin (binding material), aramid fiber (reinforced fiber), inorganic fiber, lubricant, organic friction adjusting material, inorganic friction adjusting material, pH adjusting material, and filler. , The sample has a carbon fiber length of 1 to 25 mm and a carbon fiber content of 0.05 to 0.1% by mass. In Examples 1 to 6, the boundary coating film had a sufficient thickness and was excellent in friction characteristics. When the boundary coating film has a sufficient thickness, it is possible to form a brake friction material that does not cause rust even after long-term use.
Examples 1 to 6 are examples in which the copper content is 0% and the environmental load can be reduced. However, since carbon fibers having a suitable blending amount and a suitable fiber length are contained, the powder coatability is improved. It is excellent, does not cause rust even after long-term use, and has excellent friction characteristics.

Comparative Examples 1 and 2 are examples in which carbon fibers having a short fiber length are blended, but the conductivity required for powder coating cannot be obtained with the blended amount within the specified amount, and the thickness of the coating film at the boundary portion is insufficient. Since a coating film having a sufficient thickness could not be obtained, there was a problem in coatability.
In Comparative Examples 3 to 5, since the amount of carbon fiber blended is small, the conductivity required for powder coating cannot be obtained even if the fiber length of the carbon fiber is lengthened, and the thickness of the coating film at the boundary is insufficient, which is sufficient. Since a coating film having a sufficient thickness could not be obtained, there was a problem in coatability.
Comparative Examples 6 to 8 are examples in which the amount of carbon fiber blended was increased, and although there was no problem in conductivity, the measured value of deceleration of 3.0 m / s ² in the second efficacy test was low (0.37). The result was that the friction characteristics were inferior.
From the correlation between the carbon fiber content and the friction coefficient, which will be described later, a sample having a carbon fiber content of 0.1% by mass or less, a sample having a carbon fiber content of 0.15% by mass, or more. It is known that the level deviation of the coefficient of friction is large with respect to the sample having the content of. The level of the coefficient of friction indicated by the sample with a carbon fiber content of 0.1% by mass or less, and the level of the coefficient of friction indicated by the sample with a carbon fiber content of 0.15% by mass or higher. Since the boundary between the two is 0.37, the boundary that can be grasped as 0.37 or more and less than 0.37 is grasped as a boundary standard from the viewpoint of distinguishing the magnitude level of the coefficient of friction obtained for the carbon fiber blending amount. can.

Next, in order to know the influence of the blending amount of carbon fiber on the friction characteristics of the brake friction material, Comparative Examples 9 to 14 of the blending amounts shown in Table 5 were prepared, and the friction characteristics of each example were evaluated.
For the evaluation of the friction characteristics, the measured value of deceleration of 3.0 m / s ² in the second efficacy test of JASO C407 was used as a representative value of the friction coefficient.
The results are shown in Table 5, and the correlation between the coefficient of friction and the amount of carbon fiber compounded is shown in FIG.
In Table 5, the carbon fiber blending amount is shown by comparing the numerical values of Example 6 with the numerical values of Comparative Examples 9 to 14 for comparison with Examples.

In Example 6, as shown in Table 1 above, the carbon fiber compounding amount was 0.1% by mass, the carbon fiber length was 25 mm, the phenol resin was 7.0% by mass, the aramid fiber was 3.0% by mass, and the inorganic fiber was 30.0. A sample having a composition of mass%, lubricating material 11.5% by mass, organic friction adjusting material 6.0% by mass, inorganic friction adjusting material 10.0% by mass, pH adjusting material 3.0% by mass, and balance filler. Is. In order to compare with the sample of Example 6, the carbon fiber compounding amount was varied in a form in which a part of the filler was replaced with carbon fiber, and the samples of Comparative Examples 9 to 14 were prepared with the other components having the same compounding amount.

As shown in the results shown in Table 5 and FIG. 3, the sample in which the amount of carbon fiber blended was in the range of 0.1% by mass or less had an excellent value of the coefficient of friction (second efficacy), but 0.1 mass. It was found that the value of the coefficient of friction (second efficacy) decreased sharply in the sample containing carbon fibers exceeding%.
From this, it was found that the blending amount of carbon fiber in the brake friction material is preferably 0.1% by mass or less.

Next, in order to know the influence of the amount of carbon fiber compounded on the electric resistance value of the brake friction material and the powder coatability, Comparative Examples 15 to 19 of the compounding amount shown in Table 6 were prepared, and the electric resistance value of each example was prepared. And the powder coatability was evaluated.
The measurement results are shown in Table 6, and the correlation between the electric resistance value (kΩ) and the amount of carbon fiber compounded is shown in FIG.
In Table 6, the values of Examples 3 and 6 are shown in comparison with the values of Comparative Examples 15 to 19 for comparison with the examples of the carbon fiber compounding amount.

In Example 3, as shown in Table 1 above, the carbon fiber compounding amount is 0.05% by mass, the carbon fiber length is 25 mm, the phenol resin is 7.0% by mass, the aramid fiber is 3.0% by mass, and the inorganic fiber is 30.0. A sample having a composition of mass%, lubricating material 11.5% by mass, organic friction adjusting material 6.0% by mass, inorganic friction adjusting material 10.0% by mass, pH adjusting material 3.0% by mass, and balance filler. Is. In order to compare with the samples of Examples 3 and 6, the carbon fiber compounding amount was varied in a form in which a part of the filler was replaced with carbon fiber, and the other components were prepared with the same compounding amount as the samples of Comparative Examples 15 to 19. did.

As shown in the results shown in Table 6 and FIG. 3, the sample not containing carbon fiber shows a large electric resistance that powder coating cannot be applied, but the sample containing 0.05% by mass of carbon fiber. Is the electric resistance value that can be coated with powder or the like, and the sample containing 0.1% by mass or more of carbon fiber has a lower electric resistance value, so that the coating could be performed without any problem.
Further, when considered together with the evaluation results of the friction coefficient shown in Table 5 and FIG. 2, it can be seen that the blending amount of carbon fiber in the brake friction material is preferably 0.1% by mass or less.

Next, in order to understand the influence of the carbon fiber length blended in the brake friction material, a sample having a carbon fiber length of 0.15 mm (carbon fiber blending amount 0.1% by mass) and a sample having a carbon fiber length: 0.4 mm. (Carbon fiber blending amount 0.1% by mass), Carbon fiber length: 1 mm sample (Carbon fiber blending amount 0.1% by mass), Carbon fiber length: 3 mm sample (Carbon fiber blending amount 0.1% by mass), A sample with a carbon fiber length of 10 mm (carbon fiber blending amount 0.1% by mass) and a sample with a carbon fiber length: 25 mm (carbon fiber blending amount 0.1% by mass) were prepared, and these brake friction materials were individually prepared. Brake pads having the shape shown in FIG. 1 were produced using the carbon fibers, and the appearance of each brake pad was observed.
Regarding the brake friction material used in this test, the other components were phenol resin 7.0% by mass, aramid fiber 3.0% by mass, inorganic fiber 30.0% by mass, lubricant 11.5% by mass, and organic. It has a composition of 6.0% by mass of the system friction adjusting material, 10.0% by mass of the inorganic friction adjusting material, 3.0% by mass of the pH adjusting material, and the balance filler.

When the appearance of each of the obtained brake pads was visually inspected, no particular problem was found on the surface of the brake pads in the samples having carbon fiber lengths of 0.15 mm, 0.4 mm, 10 mm and 25 mm, but the carbon fibers were found. In the sample with a length of 1 mm and 3 mm, the presence of carbon fiber aggregates could be confirmed at 2 to 3 points on the surface of the brake pad.
The presence of carbon fiber aggregates on the surface of the brake friction material can result in poor appearance. Since the formation of carbon fiber aggregates alone does not affect the paintability and friction characteristics, it does not pose a problem in terms of characteristics as a brake friction material, but the appearance when the brake pads are formed from the brake friction material is also taken into consideration. In this case, it is preferable to select and use carbon fibers having a fiber length of 10 mm or more.

1 ... Brake pad, 2 ... Back plate, 3 ... Brake friction material.

Claims (2)

In a brake friction material containing at least a reinforcing fiber material, a binder, a friction adjuster, a filler, and a pH adjuster.
When the total amount of the brake friction material is 100% by mass, it does not contain a material containing copper and contains carbon fibers of 0.05% by mass or more and 0.1% by mass or less. A brake friction material having a length of 1 mm or more. The brake friction material according to claim 1, wherein the carbon fiber has a fiber length of 10 mm or more.

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