JPH07292128A - Frictional material - Google Patents

Abstract

PURPOSE:To improve the crack resistance of a frictional material without affecting other characteristics thereof. CONSTITUTION:This frictional material is obtained by forming thereof into a two-layer structure of a frictional material layer on the frictional surface side containing a fibrous substrate, a resin binder and a filler and a frictional material layer on the back board side containing a resin having a high heat- resistant strength as a binder and different from the frictional material layer on the frictional surface side only in the kind of the resin binder and the same with other compositions. The thickness of the frictional material layer on the back board side is 5-30% based on the whole frictional material to form a part in a region near the back board tending to cause cracks. Since the resin having the high heat-resistant strength is used as the binder in the frictional material layer on the back board side, crack resistance is improved. For example, xylylene-modified phenol resins, etc., can be used as the binder.

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 brake pads, linings, clutch facings, etc. for vehicles, industrial machines and the like.

[0002]

Friction materials used for automobile disc brake pads, drum brake shoes and the like play an important role in converting kinetic energy into heat energy by frictionally engaging with its counterpart members such as a disc rotor and a brake drum. I carry it. Therefore, the friction material always generates heat and becomes high temperature. Therefore, such a friction material is required not only to have heat resistance and wear resistance, but also to have stable friction characteristics with a small change in friction coefficient due to temperature changes. Further, it is necessary that the aggression with respect to the mating member is small and that noise (squeaking) and judder are not generated, and the characteristics required of the friction material cover many items.

Therefore, conventionally, the friction material is formed as a composite material in order to satisfy these various characteristics.
That is, the friction material is generally composed of a fiber base material forming a skeleton, a resin binder for binding and holding the fiber base material, and various fillers dispersed and filled in a matrix of these fibers and the binder. It is configured. As the fiber base material, inorganic fiber such as potassium titanate fiber, organic fiber such as aramid fiber, metal fiber such as steel fiber, etc. are used, and as the resin binder, thermosetting such as phenolic resin is used. Resins are commonly used. Further, as a filler, a body filler such as barium sulfate or calcium carbonate,
Solid lubricants such as graphite and molybdenum disulfide, organic polymer powders such as cashew dust which is a cured product of cashew oil, abrasives such as silica, and other additives for friction adjustment are used.

Such a friction material is used as a disc brake pad or the like by integrally joining with a steel back plate (back metal) which forms a support thereof. Conventionally, this bonding is generally performed by adhesion, and a thermosetting resin adhesive such as a phenol resin or an epoxy resin, or a crosslinkable rubber adhesive is used. Note that this adhesion is generally performed simultaneously with the molding of the friction material by press-molding the preformed friction material together with the back plate.

[0005]

Here, it is necessary that the friction material and the back plate are firmly joined to each other. However, when a strong heat load is repeated on the friction material, cracks are generated. I have something to do. The cracks after the thermal history mainly occur because the friction material differs from the back plate in terms of thermal expansion and contraction rates, and are likely to occur near the back plate where stress is concentrated during heat load. Then, when cracks occur, the cracks gradually progress due to further repeated heat loads, and finally the friction material may peel off, resulting in an unexpected danger. Therefore, the fact that cracks do not occur even when subjected to heat history (crack resistance) is one of the important performances of the friction material, in addition to the above-mentioned performances.

In particular, in recent years, speeding up of automobiles,
The heat resistance of the friction material is increasing due to the higher grade, and the crack resistance is becoming more important.

The occurrence of such cracks is partly due to the decrease in strength of the resin binder due to heat. Therefore, in order to improve the crack resistance, a resin having particularly high heat resistance, for example, a phenol resin modified with an aromatic hydrocarbon resin such as a xylene resin may be used as the resin binder of the friction material.

However, when such a resin having only high heat resistance is used as a binder for the friction material, crack resistance is improved, but, for example, squeaking occurs during braking, and the friction material It also affects and reduces other performance of the. Therefore, it is necessary to further change the composition of the fibrous base material or the filler in order to restore the deteriorated properties. However, doing so affects other properties. As described above, it is not easy to improve the crack resistance while maintaining the characteristics of the friction material.

The present inventor has noticed that cracks are generated near the back plate. The friction material has a two-layer structure, and the resin binder of the friction material on the back plate side is made of a resin having high heat resistance as described above to share the crack resistance property. It has been found that by improving the crack resistance without affecting the other properties of the friction material by making the material have a proper composition and preventing the occurrence of cracks between the two layers, it can be advantageously realized.

Therefore, an object of the present invention is to provide a friction material which can improve crack resistance without affecting other characteristics of the friction material.

[0011]

According to a first aspect of the present invention, there is provided a friction material comprising a fibrous base material, a resin binder, and a friction surface side friction material layer containing a filler and a resin having high heat resistance as a binder. ,
The friction surface side friction material layer is different from the friction surface side friction material layer only in the kind of the resin binder, and is provided with the back plate side friction material layer having the same composition.

Here, as the resin binder used for the back plate side friction material layer, polyimide resin or the like having high heat resistance can be used, but a resin of the same system as the friction surface side friction material layer is used. It is preferable to use since it does not reduce the adhesive strength at the interface between the two layers.

That is, the friction material of the invention according to claim 2 is
In the first aspect, the resin binder of the friction surface side friction material layer and the resin binder of the back plate side friction material layer are made of a phenolic resin in which the type or presence or absence of the modifying compound is different from each other.

In this case, it is preferable that the phenolic resin used as the resin binder in the back plate side friction material layer has a high heat resistance strength by modification. Examples of such modified compounds include resinous compounds of aromatic hydrocarbons obtained by reacting aromatic hydrocarbons such as benzene, toluene and xylene with aldehydes such as formaldehyde under strong acidity. You can

Further, in this friction material, the back plate side friction material layer is formed to have a sufficient thickness including a partial area where cracks are likely to occur after thermal history. However, if it is made too thick, the effective amount of the friction surface side friction material layer is reduced. Therefore, it is generally preferable in practice that the thickness of the back plate side friction material layer is about 5 to 30% of the total friction material.
However, this is not a limitation, and a thickness outside this range is also possible.

The fibrous base material and the filler forming the friction material are the same as in the conventional case. That is, as the fiber substrate, glass fibers, rock wool, silicate fibers, alumina fibers, carbon fibers, potassium titanate fibers, inorganic fibers such as slag wool, steel fibers, metal fibers such as stainless steel fibers, copper fibers, aramid Examples of the fiber include organic fibers such as fibers, novoloid fibers, nylon fibers and rayon fibers. These can be used alone or in combination as appropriate depending on the specific type or application of the friction material.

As the filler, use is made of a solid filler such as barium sulfate or calcium carbonate, a solid lubricant such as graphite or molybdenum disulfide, or an organic polymer powder such as cashew dust which is a hardened cashew oil. Yes, again
If necessary, an abrasive agent such as silica, or other additives for adjusting friction can be used. As the resin binder of the friction surface side friction material layer, an appropriate one can be used other than the phenol resin.

The friction material of the present invention can be produced from such a material by a method similar to the conventional method, for example, preforming and then hot pressing. In this case, the friction surface side friction material layer and the back plate side friction material layer may be separately preformed and then integrally formed at the time of heat and pressure molding, but they should be integrally formed at the preforming stage. Is preferred. As a result, the friction surface side friction material layer and the back plate side friction material layer are more favorably joined and integrated.

[0019]

In the invention according to claim 1, since a resin having a high heat resistance is used as the resin binder of the back plate side friction material layer, the back plate side friction material layer has high heat resistant adhesive strength and crack resistance. Has been increased. Therefore, cracks mainly occur in the portion close to the back plate, so that the crack resistance of the friction material can be improved. And since the back plate side friction material layer can improve the crack resistance, the friction surface side friction material layer can have any composition, thereby maintaining properties other than the crack resistance. it can.

Further, since the back plate side friction material layer has the same composition as the friction surface side friction material layer except for the type of resin binder, there is no difference in thermal expansion and contraction characteristics from the friction surface side friction material layer. . Therefore, no crack occurs between the back plate side friction material layer and the friction surface side friction material layer.

In the invention according to claim 2, the resin binder of the friction surface side friction material layer and the resin binder of the back plate side friction material layer in claim 1 differ from each other in the type or presence or absence of the modifying compound. Since it is made of the same type of resin, it is possible to obtain sufficient adhesive strength at the boundary surface between both layers by using the same type of resin.

[0022]

EXAMPLES Examples will be described below in which the present invention is applied to a brake pad.

<Composition of Friction Material> FIG. 1 shows the composition of the friction material in Examples and Comparative Examples.

Further, as shown in FIG. 1, there are four types of compositions of the friction material, Compositions A to D. As the binder in this composition, three kinds of resin a, resin b, and resin c are used as described below.

Here, aramid fiber, potassium titanate fiber, and rock wool were used as the fiber base material.

A phenolic resin was used as the binder, and the following were used as the resin a, the resin b and the resin c.

Resin a: Alkylbenzene cashew modified phenolic resin Resin b: Xylylene modified phenolic resin Resin c: Unmodified phenolic resin As the filler, graphite, cashew dust, mica, slaked lime, barium sulfate, copper powder and copper fiber are used. I was there.

<Preparation of Brake Pad> After combining any of the four compositions A to D of the above-mentioned friction agent with any of the resins a to c as a binder and preforming a mixture prepared accordingly , Heat treatment is performed, and the brake pads (PD51 of Examples 1 and 2 and Comparative Examples 1 to 9)
(For type caliper) was made according to the general method for making a brake pad.

The heat treatment was carried out by thermoforming at a temperature of 160 ° C. and a pressure of 400 kg / cm ² for 10 minutes, and then at a temperature of 2
The heat treatment is performed at 50 ° C. for 120 minutes.

The structures of the brake pads of these examples and comparative examples are shown in FIG.

As shown in FIG. 2, Example 1 and Example 2 are brake pads molded from two layers of a friction surface side friction material layer (S layer) and a back plate side friction material layer (T layer). . The composition of the S layer and the T layer of Examples 1 and 2 is composition A, and regarding the binder, the S layer of Example 1 is resin a and the T layer is resin b, and the binder of Example 2 is The S layer is the resin c and the T layer is the resin b.

Comparative Examples 1 to 6 are brake pads molded from one layer.

In Comparative Examples 1 to 4, the blending composition is Composition A in Comparative Example 1, Composition B in Comparative Example 2, Composition C in Comparative Example 3, and Composition D in Comparative Example 4, and all of the binders are used. Resin a.

In Comparative Example 5 and Comparative Example 6, the compounding composition is composition A, and the binder is resin b in Comparative Example 5 and resin c in Comparative Example 6.

Comparative Examples 7 to 9 are brake pads molded from two layers, S layer and T layer, as in Examples 1 and 2, and the composition of the S layer is composition A. ,
All of the binders are resin a.

The composition of the T layer is composition B in comparative example 7, composition C in comparative example 8 and composition D in comparative example 9, and the binder is resin a in all cases.

<Evaluation Test> Each of the above Examples and Comparative Examples was tested for their adhesive strength, crack resistance and squeal occurrence. The result is shown in FIG.

The adhesive strength is JASO C-437-84.
The adhesive strength of the PD51 type caliper pad was measured according to the above.

The crack resistance was evaluated by the presence or absence of cracks after the heat history. And using PD51-18V type caliper brake, inertia 5.5kg ・ fm ・ s
Under the conditions of ² , the state of the pad after the first fade and the second fade according to JASO-C406-82 was examined and evaluated according to the following criteria.

◯: No cracks Δ: Some cracks ×: Cracks Squealing occurs at a vehicle speed of 10 to 50 km / h and a hydraulic pressure of 2 to 40 k
The state of squeaking of the brake pad at g / cm ² and a temperature of 50 to 200 ° C. was examined and evaluated according to the following criteria.

◯: No squeal was generated Δ: Squeal was slightly generated ×: Squeal was generated <Test results> As shown in FIG. 2, xylile modified phenol having a high heat resistance as a binder of the back plate side friction material layer (T layer). In Examples 1 and 2 using the resin, the crack resistance (the fact that cracks do not occur after thermal history) is good, and other performance, that is, squeaking is good.

On the other hand, in the case where the brake pad is composed of one layer as in Comparative Examples 1 to 6, when crack resistance is improved, other characteristics are deteriorated, and squeal is sought to be eliminated. Then, the crack resistance tended to decrease.

Further, as in Comparative Examples 7 to 9, the brake pads are composed of two layers, but when the compositions of the friction materials of the two layers are different, the crack resistance is improved as compared with the case of one layer. But it's not enough.

Comparative Example 1, Comparative Example 5 and Comparative Example 6 are one-layered brake pads. In Comparative Example 1, resin a was used as the binder, and in Comparative Example 6, resin c was used. No squeaking occurred.

Further, in Comparative Example 5, when the resin b having excellent heat resistance was used as the binder, no crack was generated, but
A squeal occurred.

The comparative example 1 is the friction surface side friction material layer (S layer), and the comparative example 5 is the back plate side friction material layer (T layer) is the example 1, and the comparative example 6 is also used. Example 2 is an example in which S is an S layer. From this result, the resin a having a high heat resistance as a resin binder of the back plate side friction material layer (T layer) is obtained.
And the composition of the back plate side friction material layer (T layer) is the same as the composition A of the friction surface side friction material layer (S layer) except for the type of resin binder, It can be seen that the crack resistance can be improved without affecting other properties such as.

The friction material of the present embodiment has been described mainly using the brake pad as an example. However, the present invention is not limited to this, and various types such as a lining of a drum brake or a clutch facing are provided. Can be applied to the friction material.

[0048]

As described above, the friction material of the invention according to claim 1 comprises a friction surface side friction material layer containing a fiber base material, a resin binder, and a filler, and a resin having high heat resistance as a binder. age,
The friction surface side friction material layer is different from the friction surface side friction material layer only in the kind of the resin binder, and is provided with the back plate side friction material layer having the same composition.

Therefore, since the friction material has a two-layer structure and the back plate side where cracks are likely to occur due to thermal history is a crack resistant friction material using a resin having high heat resistance as a binder, The surface side friction material layer can maintain the required friction material characteristics while improving crack resistance. Further, since the friction surface side friction material layer and the back plate side friction material layer have the same composition except that the type of resin binder is different,
There is no difference in thermal expansion and contraction characteristics between the two layers, so
There is no new crack between the two layers.

The friction material of the invention according to claim 2 is
In the first aspect, the resin binder of the friction surface side friction material layer and the resin binder of the back plate side friction material layer are made of a phenolic resin in which the type or presence or absence of the modifying compound is different from each other.

Therefore, the same type of resin binder is used for the friction surface side friction material layer and the back plate side friction material layer, and phenolic resins differing only in the type or presence or absence of the modifying compound. Therefore, since the bonding property between both layers is good and the curing temperature is about the same, the integral molding can be easily performed.

[Brief description of drawings]

FIG. 1 is a table showing a composition of a friction material used for manufacturing brake pads of Examples and Comparative Examples of the present invention.

FIG. 2 is a table showing the configurations and evaluation test results of brake pads of Examples and Comparative Examples of the present invention.

Claims (2)

[Claims] 1. A friction surface side friction material layer containing a fiber base material, a resin binder, and a filler, and a resin having high heat resistance as a binder, and the friction surface side friction material layer is a kind of resin binder. A friction material comprising a back plate side friction material layer having the same composition except for the above. 2. The resin binder of the friction surface side friction material layer and the resin binder of the back plate side friction material layer are made of phenolic resins having different types or different types of modifying compounds. The friction material according to claim 1.