JPH0971768A - Friction material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a friction material which can retain the effect of reducing low-frequency noises even after an intensive thermal history. SOLUTION: This friction material comprises a fibrous base, a binder resin, and a filler containing as a component thereof a mica for reducing low-frequency noises. The mica is a synthetic fluoromica such as fluorophlogopite or fluorotetrasilicomica. Because of the cleavability of the synthetic fluoromica, cohesion to a mating material and the resulting stick slipping are inhibited, and hence low-frequency noises (muffled sound) can be diminished. Because of the high thermal stability of the synthetic fluoromica, even after the friction material has undergone an intensive thermal history by severe braking, etc., its crystal structure is not destroyed and the fluoromica retains its cleavability. Thus, the effect of reducing low-frequency noises can be maintained.

Description

Detailed Description of the Invention

[0001]

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

[0002]

Friction materials such as disc brake pads and drum brake linings used in automobiles and the like play an important role in converting kinetic energy into heat energy by frictionally engaging the mating disc rotor and brake drum. Is responsible for Therefore, not only is the friction material required to have excellent wear resistance, but it is also necessary to have a sufficiently high coefficient of friction, and moreover, heat is constantly generated during braking, and the temperature is high. Stable friction characteristics with little change in friction coefficient are required. Furthermore, it is also necessary that there is no aggressiveness to the mating material, that noise (abnormal noise, squeaking) does not occur during braking, and the like, and the characteristics required for the friction material cover many items.

Therefore, conventionally, in order to satisfy these various characteristics, the friction material is constructed as a composite material. That is, the friction material is a fiber base material such as aramid fiber or potassium titanate fiber that forms the skeleton, a resin binder such as a phenol resin that holds the fiber base material, and the fiber base material and the binder. And various fillers which are dispersed and filled in the matrix.

Examples of the filler include body fillers such as barium sulfate and calcium carbonate, solid lubricants such as graphite and molybdenum disulfide, cashew dust, abrasive agents such as silica and zirconium silicate, and other friction agents. Additives and the like have been used to improve and adjust performance or related properties. Here, the extender filler is mainly blended in order to make the friction material have sufficient physical strength, heat resistance, wear resistance and the like. Further, the solid lubricant is used to ensure the wear resistance of the friction material by virtue of its lubricating coating. Cashew dust is a pulverized product of a resin cured product obtained by polycondensing cashew nut shell liquid with a curing agent such as formaldehyde or furfural, and is mainly used for improving and stabilizing the friction coefficient. The cashew dust, together with the solid lubricant, also has a function of reducing high-frequency noise, which is usually called brake squeal. Further, the abrasive agent is used for improving the coefficient of friction by its grinding action and for keeping the friction engagement surface of the mating material clean.

In addition to these, various kinds of filler components to be mixed with the friction material are known and used. One such filler is, for example, mica,
A plane network crystal structure of talc or the like, that is, a silicate-bonded silicate group develops into a secondary plane network, and a layered crystal structure in which the layers are bonded by a weak Van der Waals force, that is,
It is an inorganic substance having a cleavable crystal structure. The purpose of incorporating such mica as a filler in the friction material is to reduce low-frequency noise (goo noise).

Regarding the use of mica or the like having such a plane network crystal structure (cleavable crystal structure), for example, JP-A-3-181628 and JP-A-3-239.
784, JP-A-4-60225, JP-A-6
In Japanese Patent Laid-Open No. 9944 and Japanese Patent Laid-Open No. 6-9945, various concrete modes are disclosed. And
As the mica, phlogopite or muscovite is generally used because it has almost perfect cleavage and can be obtained in a relatively large amount as a high-quality natural product.

[0007]

By the way, in recent years,
Along with the dynamic performance of automobiles, comfort and quietness have been significantly improved. Among them, noise generated during braking is also important, and not only high-frequency noise (squeal) called brake squeal generated during sudden braking, but also low-frequency noise with a frequency of about 100 to 1000 Hz. It is also required to reduce the generation of noise (goo sound) as much as possible.

The low frequency noise, which is also called goo sound, is
At the time of frictional engagement between the friction material and the mating material, the friction material component or its decomposed material adheres to the mating material (rotor), and sticking of the adhered film and the friction material, that is, the friction coefficient This is caused by the occurrence of momentary fluctuations. Although the low-frequency noise is less noticeable than the high-frequency noise, it is uncomfortable for the user and impairs the high-class feeling of the automobile.

In order to reduce the occurrence of such low frequency noise, as described above, the combination of mica such as phlogopite or muscovite, which is an inorganic substance having a plane reticulated crystal structure (cleavable crystal structure), is used. Is known to be effective. Regarding the low frequency noise reduction effect of this mica,
It is generally believed to be in its cleavability. That is, the adhesion between the friction material and the mating material that cause stick-slip is suppressed by the fact that the mica filled in the friction material is cleaved in the form of scales and peels off to form a slippery surface, That is to be avoided. In addition, since the low frequency noise can be reduced to a practically sufficient level by mixing mica, in recent years, mica is often used as a part of the filler of the friction material.

However, even a friction material in which mica is blended as a part of the filler in this way to reduce low-frequency noise is used, for example, while being mounted on a disc brake of an automobile and used. Occurrences of low frequency noise increased again and were frequently found. That is, the low frequency noise performance, which was good in the initial stage of use, deteriorates thereafter.

A detailed investigation into such a case shows that the deterioration of the low frequency noise performance is such that the braking conditions are becoming more and more severe with the increase in speed and output of automobiles. It has been found that this occurs particularly when the friction material undergoes a strong thermal history, such as when repeated braking from a high speed close to 100 km per hour is repeated. However, such a decrease in low-frequency noise performance occurs only when the friction material is particularly severely used, and does not occur under normal general use conditions, but is not preferable in any case. . In addition, the chance of adding a strong thermal history to the friction material due to severe braking tends to increase more and more in the future.

[0012] Therefore, an object of the present invention is to provide a friction material capable of reducing the generation of low frequency noise even after a strong thermal history.

[0013]

The present inventor has paid attention to the fact that an increase in low frequency noise occurs after a strong thermal history, and as a result of further tests and examinations, as a result, such a planar reticulated crystal structure (cleavability) was obtained. It has been found and confirmed that the above problems can be effectively solved by using a synthetic fluorine mica as a mica having a crystal structure).

That is, the friction material according to the present invention is a friction material containing a fiber base material, a resin binder, and mica and other fillers, wherein the mica is made of synthetic fluorine mica. Is.

According to the friction material of the present invention, since synthetic fluorine mica is used as mica for reducing the generation of low frequency noise, as will be understood from the examples below, the low frequency after thermal history is used. It is possible to prevent an increase in noise generation. This is considered as follows, together with the reason why the generation of low-frequency noise after thermal history increases when normal natural mica is used.

That is, natural mica such as phlogopite has crystal water (structure water) in the form of hydroxyl groups in its crystal structure.
The water of crystallization is released from a temperature of about ℃ and decomposes. Therefore, in a friction material in which a normal natural mica is used, when a strong thermal history is applied as in the case where braking from a high speed is repeated, the cleaved crystal structure of the mica collapses, and as a result, The effect of reducing low frequency noise due to the cleaving property is lost. This is the reason why the generation of low-frequency noise increases after the thermal history.

On the other hand, synthetic fluoromica has a chemical structure in which a hydroxyl group in natural mica is replaced by fluorine and does not contain a hydroxyl group, and therefore has high thermal stability and is similar to natural mica. Does not disassemble easily. That is, even if it undergoes a strong thermal history, its cleavable crystal structure is unlikely to collapse. It is considered that this is the reason why the friction material of the present invention can effectively reduce the generation of low-frequency noise even after thermal history, as in the initial stage of use.

[0018]

The present invention will be described in more detail below.

As described above, in the friction material of the present invention, the synthetic fluorine mica is used as the mica compounded to reduce the low frequency noise. Such synthetic fluoromica itself is already well known and is generally used as a ceramic raw material such as a mica-glass binder (micarex) and a mica-phosphoric acid binder. And as a typical example thereof, fluorophlogopite [KMg ₃ (AlSi
₃ O ₁₀ ) F ₂ ], tetrafluorosilicon mica [KMg _2.5 (S
i ₄ O ₁₀ ) F ₂ ] and the like.

These synthetic fluoromica can be synthesized by melting an appropriate raw material under atmospheric pressure, or can be synthesized by a solid-phase reaction, and by ion substitution, various kinds of fluoromica can be produced. Can be synthesized. Specifically, for example, fluorophlogopite is mixed with potassium hexafluorosilicate, feldspar, magnesia, alumina, and quartz sand, and fired at a temperature equal to or higher than the melting point (1387 ° C.),
It can be synthesized by gradually cooling and crystallizing.

Such a synthetic fluoromica corresponds to the one in which the hydroxyl group contained in the water of crystallization (structure water) of natural mica is replaced by fluorine, and therefore has the same plane network crystal structure (cleavage) as natural mica. Crystalline structure).
That is, the crystal develops into a plane and is layered, and these layers are coupled by a weak Van der Waals force.
Therefore, the synthetic fluoromica has almost perfect bottom surface cleavage property like the natural mica, and as described above, by blending it with the friction material as the filler, the low frequency noise can be effectively reduced. . On the other hand, since synthetic fluoromica does not contain water of crystallization, it has high thermal stability and does not decompose even under high heat unlike natural mica. Therefore, even when the friction material is subjected to a strong thermal history due to severe braking or the like, its cleaved crystal structure is not destroyed, so that the effect of reducing low frequency noise is not lost and is effectively maintained.

This synthetic fluoromica has an average particle size of 50 to 50 as in the case of using conventional natural mica.
As a powder having a size of about 500 μm, it can be generally used in a mixing ratio of 3 to 25% by weight with respect to the entire friction material. If this ratio is too small, generally less than 3% by weight, the effect of reducing low frequency noise cannot be sufficiently obtained in practice. Moreover, the effect of reducing low-frequency noise improves as the blending ratio of synthetic fluoromica increases, but even if the blending amount is too large, the effect will not reach a peak, and a large blending amount will be the use of other fillers. Make it difficult. Therefore, it is preferable to mix it in a proportion of 25% by weight or less. A more preferable blending ratio of synthetic fluoromica is 5
１５15% by weight.

As a filler component for reducing low frequency noise, in addition to the above synthetic fluoromica, an inorganic substance having another cleavable crystal structure (planar reticulated crystal structure) may be used in combination. it can. And as such an inorganic substance, talc, vermiculite, kaolin, montmorillonite, chlorite, aluminum hydroxide, etc. can be mentioned, for example. However, since these inorganic substances have water of crystallization (structured water) and have relatively low thermal stability, the blending amount may be smaller than that of synthetic fluoromica even when they are used in combination. preferable. Similarly, general natural mica can be used in combination with synthetic fluoromica, but in order to effectively reduce low frequency noise even after thermal history, it is possible to use only synthetic fluoromica alone. preferable.

The other components forming the friction material, that is, the fibrous base material, the resin binder, and the other fillers are the same as conventional ones.

The fibrous base material, that is, the fibrous base material which is a fibrous component forming the skeleton of the friction material, includes aramid fiber,
Nylon fiber, rayon fiber, organic fiber such as phenol fiber, silica fiber, alumina fiber, alumina-silica fiber, potassium titanate fiber or whiskers, rock wool, slag wool, carbon fiber, or inorganic fiber such as glass fiber, copper Examples thereof include fibers, steel fibers, stainless steel fibers, metal fibers such as brass fibers, and the like. These fibers can be used alone or in appropriate combination depending on the specific type or application of the friction material. For example, in the case of a disc brake pad, these organic fibers, inorganic fibers, and metal fibers are generally used in an appropriate combination.

As the resin binder for binding and holding the fiber base material and the filler, phenol resin, melamine resin, epoxy resin, polyimide resin, polyester resin,
Alternatively, rubber such as SBR can be used. However, among these, the phenol resin and various modified products thereof are most preferable in terms of excellent heat resistance and high bond strength.

As the filler, in addition to the above synthetic fluoromica, a solid filler such as barium sulfate and calcium carbonate, a solid lubricant such as molybdenum dichloride, antimony trichloride and graphite, cashew dust or other fillers. Organic polymer powder, mainly metal powder such as copper powder, zinc powder and brass powder for improving thermal conductivity, abrasive agent such as silica and zirconium silicate, or other additives for friction adjustment etc. Can be used.

The friction material according to the present invention includes, for example, the above synthetic fluoromica, a fiber base material, a resin binder,
And other fillers are mixed, the mixture is preformed, and then the preformed body can be manufactured by a usual thermoforming method in which the preformed body is heated and pressed.

[0029]

The present invention will be described below in more detail with reference to examples and comparative examples.

[Preparation of Friction Material (Pad)] Friction materials of Examples 1 to 3 of the present invention were prepared with the compounding composition (% by weight) shown in FIG. For comparison with these, the friction materials of Comparative Examples 1 to 3 were also produced. The friction materials of these examples and comparative examples are specifically embodied as disc brake pads for automobiles.

As shown in FIG. 1, each of the friction materials (disc brake pads) of these Examples and Comparative Examples has a fibrous base material which is a fibrous component forming the skeleton of the friction material,
It is composed of a resin binder for binding and holding the fiber base material and various fillers dispersed and filled in the matrix of the fiber base material and the resin binder. However, in each of the examples and comparative examples, the type and composition of mica, which is a part of the filler, are variously changed.

More specifically, the fiber base material is 8% by weight of aramid fiber as a main material, 10% by weight of potassium titanate fiber for ensuring heat resistance and abrasion resistance, and heat resistance and friction coefficient are improved. Ceramic (alumina-
It is composed of a mixture of 8% by weight of (silica-based) fiber and 10% by weight of copper fiber mainly for ensuring thermal conductivity. Therefore, here, the friction material is formed as a non-steel friction material containing no steel fiber. The types and blending ratios of these fiber base materials are the same in each of the examples and comparative examples.

As the resin binder, a phenol resin (novolak resin) was used here, and was blended in each Example and Comparative Example at a ratio of 12% by weight.

Further, as a filler, 8% by weight of graphite (graphite), which is a solid lubricant for mainly improving the wear resistance in the low temperature region and the medium temperature region, and particularly the wear resistance in the high temperature region is improved. 3 wt% antimony trisulfide as a solid lubricant, 8 wt% cashew dust for adjusting and stabilizing the friction coefficient, 3 wt% zirconium silicate as an abrasive, and a friction material. 3% by weight of slaked lime to keep alkaline and improve rust prevention of back metal,
17% by weight of barium sulfate as a body filler and 10% by weight of mica for reducing low frequency noise were blended in each example and comparative example. However, in Comparative Example 3, mica was not added, and the amount of barium sulfate was increased to 27% by weight.

Here, the following four types of synthetic fluoromica and natural mica were prepared as the above mica.

(Synthetic Fluorine Mica) Fluoro phlogopite [KMg ₃ (AlSi ₃ O ₁₀ ) F ₂ ] Fluorotetrasilicon mica [KMg _2.5 (Si ₄ O ₁₀ ) F ₂ ] (natural mica) Phlogopite [KMg ₃ (AlSi ₃ O ₁₀ ) (OH) ₂ ] muscovite [KAl ₂ (AlSi ₃ O ₁₀ ) (OH) ₂ ] Then, in Example 1, a fluorophlogopite mica which is a synthetic fluoromica, and in Example _{2 is also a} tetrafluorosilicic mica. Were used alone. Further, in Example 3, those synthetic fluoromica were used as an equal mixture of 5% by weight. On the other hand, in Comparative Example 1, phlogopite which is a natural mica was used, in Comparative Example 2, muscovite was used, and in Comparative Example 3, no mica was used.

In this way, friction materials of Examples and Comparative Examples were prepared with the same composition of components except that the type (quality) and composition of mica were changed. In addition, these friction materials (disc brake pads) were specifically manufactured as follows by a method of ordinary heat formation. That is, the friction material raw material having the above-described composition with or without mica was sufficiently mixed with a blender, and then this powdery mixture was put into a preforming die, and at room temperature, a pressure of 200 kg / cm ² was applied. Pressurized for ~ 2 minutes to form a pad-like preform of friction material. Next, the preform of this friction material is set in a thermoforming mold together with a backing metal having a surface coated with a phenolic resin adhesive, and thermoformed at a pressure of 400 kg / cm ² and a temperature of 160 ° C. for 10 minutes. did. Then, add this to 250 ℃
And heat treated for 120 minutes to obtain a friction material as a disc brake pad.

[Low Frequency Noise Evaluation Test] Next, regarding each friction material (disc brake pad) of the example and the comparative example produced by changing the type and composition of the mica in this way, the low frequency after the initial and thermal history An evaluation test on the occurrence of noise (goo sound) was conducted as follows.

(1) Lamination First, with respect to each friction material of the produced Examples and Comparative Examples,
Braking was carried out 200 times under the conditions of an initial braking speed of 65 km / h, a deceleration of 0.35 G, and a temperature before starting braking of 120 ° C., and the rubbing was performed. Then, the following initial low frequency noise evaluation test was performed on each friction material at the time of the second effect (stable period) after this rubbing.

(2) Initial low frequency noise evaluation test Regarding the low frequency noise evaluation test, the actual vehicle (1500c
A braking test using a PD51-18V type caliper brake (c class, PD51-18V) was performed, and the number of times low-frequency noise (goo noise) was generated during the braking was measured. Specifically, the initial braking speed is set to 40 km / h, and the conditions related to deceleration and pre-braking temperature are 0.2 to 0.8 G and 40 to 20 G, respectively.
A total of 100 braking tests were performed with various combinations within the range of 0 ° C. Then, the number of times when low-frequency noise (goo sound) that was more than audible to the ear was generated was counted.

(3) Thermal history test For each friction material subjected to this initial low frequency noise evaluation test, the initial braking speed was 100 km / h and the deceleration was 0.4.
Braking was repeated 10 times under the severe conditions of 5 G and a braking interval of 35 seconds, and a strong heat history was added to the friction material. The temperature before starting the first braking was set to 65 ° C., but it is considered that the sliding contact surface temperature of the friction material became nearly 800 ° C. at least instantaneously due to the repeated braking thereafter.

(4) Low frequency noise evaluation test after thermal history Next, for each friction material to which a strong thermal history was given by such severe braking, the low frequency noise evaluation test after the thermal history was conducted as described in (2) above. The same conditions were used. Then, a braking test was performed 100 times in the same manner, and the number of times when low-frequency noise (goo sound) that was slightly audible to the ear was generated was counted.

The numbers of occurrences of low frequency noises in the "initial" and "after thermal history" measured for each friction material of the example and the comparative example are shown together with FIG.

[Test Results] As shown in FIG. 1, in the friction material of Comparative Example 3 in which mica was not mixed as a filler, low frequency noise was generated at a considerably high frequency from the initial stage (43
), The high incidence has not changed even after the heat history. On the other hand, in the friction materials of Comparative Example 1 and Comparative Example 2 in which phlogopite and muscovite were mixed, respectively, the occurrence of low-frequency noise was significantly reduced in each case.
The number has decreased to 7 and 7. That is, by adding mica to the friction material, the occurrence of low frequency noise is effectively reduced and suppressed.

However, in the friction materials of Comparative Examples 1 and 2 using the natural mica as the mica, the number of occurrences of low frequency noise was increased after the strong thermal history was added by the above thermal history test. It increased again and became 24 times and 22 times respectively. The number of occurrences of low-frequency noise after the thermal history is sufficiently smaller than that in the case of Comparative Example 3 (45 times) in which mica is not mixed, but it corresponds to about three times the initial value. is there. That is, the low frequency noise performance, which was good at the beginning, is significantly deteriorated after the thermal history.

However, these Comparative Example 1 and Comparative Example 2
On the other hand, in the friction materials of Examples 1 to 3 in which the synthetic fluoromica and the fluorotetrasilicic mica were used as the mica, the low frequency noise was generated 8 times at the initial stage and 7 times at the initial stage. And 8 times, and even after the thermal history, it increased only about once, that is, 9 times, 8 times, and 9 times, respectively. That is, in the friction materials of these examples using the synthetic fluoromica, not only the occurrence of low-frequency noise was satisfactorily reduced as in Comparative Examples 1 and 2, but also the strong thermal history Even after the addition of, was maintained at a good level almost equal to the initial level. It should be noted that there is substantially no difference in the effect of reducing the low-frequency noise between the examples, and no particular tendency is observed in the action due to the difference in the specific type of synthetic fluoromica.

Such a result is considered to be due to the following reason as described above. That is, in the friction materials of Comparative Example 1 and Comparative Example 2, when the natural mica is heated strongly, the hydroxyl groups forming the crystal structure thereof become water and are dehydrated. It is thought that it collapsed and lost its cleaving property, and as a result, the effect of reducing low-frequency noise was lost, and the number of times it was generated increased. However, synthetic fluoromica, which is a mica having a molecular structure in which its hydroxyl group is replaced by fluorine, has high thermal stability and does not dehydrate as such when heated, so its low-frequency noise reducing action is even after thermal history. It will not be lost, but will be maintained.

This is a speculation only. However, the test results show that the use of synthetic fluorine mica as the mica can favorably reduce the occurrence of low-frequency noise even after thermal history.

Regarding the friction material of the present invention,
Although the disc brake pad has been described as an example, the present invention is not limited to the disc brake pad, and the lining of the drum brake,
Alternatively, it can be similarly applied to other friction materials such as clutch facings. Further, the types and blending ratios of the fiber base material, the resin binder, and the filler forming the friction material are not limited to those in this embodiment, but can be variously modified.

[0050]

As described above, the friction material according to the present invention is a friction material containing a fiber base material, a resin binder, mica and other fillers, and the mica is made of synthetic fluorine mica. It is characterized by.

Therefore, according to this friction material, since the mica compounded as a part of the filler for reducing the low frequency noise (goo noise) is made of synthetic fluorine mica having high thermal stability, it is severe. Even if it receives a strong thermal history due to repeated repeated braking, its cleavable crystal structure does not collapse, and the effect of reducing low frequency noise is maintained. That is, the friction material according to the present invention has an effect of reducing low-frequency noise as in the initial stage of use even after receiving a strong thermal history.

[Brief description of drawings]

FIG. 1 is a table showing the composition (% by weight) of friction materials (disc brake pads) of Examples and Comparative Examples of the present invention and the results of an evaluation test regarding the generation of low frequency noise.

Claims (1)

[Claims] 1. A friction material comprising a fibrous base material, a resin binder, and mica and other fillers, wherein the mica is made of synthetic fluorine mica.