JP2009132817A - Friction material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a friction material that can effectively suppress the occurrence of metal catch and a low-frequency noise and a squeal due to the metal catch by allowing cast iron raw materials to be uniformly dispersed in the friction material. <P>SOLUTION: The friction material is a non-asbestos friction material containing a cast iron fiber as a fibrous base material, which is characterized in that it additionally contains an organic fiber as a fibrous base material wherein the blending amount of the cast iron fiber is 2.5-120% by volume based on the blending amount of the organic fiber. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a friction material such as a brake pad, a brake lining, and a clutch facing used in contact with a disk rotor or a drum of a vehicle, and more specifically, a metal catch by welding between a friction material and a counterpart material at high temperature sliding. It is related with the friction material which suppresses a low frequency squeal by suppressing.

  When the friction material slides into contact with a mating material such as a disk rotor during braking of the vehicle, the frictional heat increases the temperature of the friction material. Therefore, in order to improve heat dissipation and wear resistance, the friction material is mixed with a metal raw material such as steel fiber. However, when the friction material reaches a high temperature range due to sliding with the mating material, the metal material in the friction material melts and adheres to the mating material, resulting in a squeal and noise with a frequency of 2 kHz or less. To do. Therefore, conventionally, graphite is generally blended with the friction material as a lubricant for preventing metal catch. However, since graphite is only dispersed and held in the friction material, there is a risk that the graphite will fall off the sliding surface when the friction material slides against the counterpart material. Therefore, while using graphite, a friction material has been developed in which a cast iron raw material containing graphite is blended on the structure in place of steel fibers.

  For example, in Patent Document 1, in a sintered friction material mainly composed of metal powder, cast iron fiber containing at least 3.3% by weight of carbon is blended in an amount of 5 to 50% by weight based on the total amount of the friction material. This prevents graphite as a lubricant from falling off the sliding surface when the friction material slides. Further, there are Patent Document 2 and Patent Document 3 as friction materials in which spheroidal graphite cast iron fibers are blended instead of steel fibers. In the friction material of Patent Document 2, a spheroidal graphite cast iron fiber having a ferrite content of 15 to 20% is used as a fiber base for the purpose of reducing the aggressiveness of the steel fiber against the mating material. In the friction material of Patent Document 3, spheroidal graphite cast iron containing 2.4 to 4.2% by weight of carbon instead of steel fiber for the purpose of improving wear resistance and having a low coefficient of friction and heat conduction. Using fiber. Here, the spheroidal graphite cast iron fiber is blended in an amount of less than 5 to 40% by volume with respect to the entire friction material, and has a fiber diameter of 10 to 100 μm and a length of 1 to 10 mm.

JP 61-23744 A JP 58-77936 A JP-A-1-203728

  In Patent Document 1, since a powdered cast iron raw material is blended, there is a problem of uniform dispersibility when various raw materials are mixed at the time of manufacturing the friction material, and the cast iron powder segregates in the friction material and has good lubricity. There is a risk that it cannot be secured. On the other hand, in patent document 2 and patent document 3, since the cast iron fiber is mix | blended, possibility of segregation is low compared with patent document 1, but since only cast iron fiber is used as a fiber base material, uniform dispersibility There is a limit to this, and it does not lead to a fundamental solution to the squeal generated by the metal catch.

  Accordingly, an object of the present invention is to provide a friction material that can significantly suppress a metal catch and low-frequency noise and noise due to the cast iron material being uniformly dispersed in the friction material.

  The present invention is a non-asbestos friction material containing cast iron fibers as a fiber base material, and further contains organic fibers as the fiber base material. The compounding amount of the cast iron fiber is 2.5 to 120% on a volume basis with respect to the compounding amount of the organic fiber. The cast iron fiber here is preferably spheroidal graphite cast iron having a fiber diameter of 10 to 100 μm, a length of 1 to 5 mm, and a carbon content of 2.5 to 4.0% by weight.

  According to the present invention, since organic fibers are blended as a fiber base material in addition to cast iron fibers, the uniform dispersibility of various raw materials is improved, and the metal catch associated with the sliding between the friction material and the counterpart material is efficiently suppressed. Therefore, the occurrence of squealing and low-frequency squealing is significantly suppressed.

  The friction material of the present invention is a non-asbestos friction material (NAO material) containing a fiber base material that is not asbestos, a filler, and a binder (binder resin) that binds the fiber base material and the filler. . The friction material of the present invention can be applied as a friction material for brake pads and brake linings used in contact with disk rotors and drums of vehicles such as automobiles and trains and airplanes, and clutch facing.

[Fiber base]
As the fiber base material, cast iron fiber and organic fiber are used in combination. Steel fiber is not blended. Cast iron fibers have a higher carbon content than steel fibers, which improves the lubricity of the fibers themselves. Therefore, the counterpart material attack is lower than that of the steel fiber, and the wear amount of the counterpart material due to sliding of the friction material is reduced. As cast iron fiber, spheroidal graphite cast iron (ductile cast iron) fiber is preferable. Spheroidal graphite cast iron is excellent in tensile strength, toughness, etc., and has several times the strength of gray cast iron (ordinary cast iron), thus ensuring good friction material strength. The carbon content in the cast iron fiber is preferably 2.5 to 4.0% by weight, more preferably 3.0 to 3.8% by weight. If the carbon content in the cast iron fiber is less than 2.5% by weight, the lubricity of the fiber itself is insufficient and the opponent attack is increased. If the carbon content in the cast iron fiber exceeds 4.0% by weight, the strength and friction coefficient of the friction material may be insufficient. Further, from the viewpoint of the friction material strength, the fiber diameter of the cast iron fiber is preferably 10 to 100 μm and the length 1 to 5 mm. More preferably, the fiber diameter is 30 to 80 μm and the length is 2 to 4 mm.

  The organic fiber used in combination with the cast iron fiber is not particularly limited, and examples thereof include synthetic resin fibers such as aramid fiber, polyester fiber, and kao wool fiber, and natural fibers such as pulp. These organic fibers may be used alone or in combination of two or more. The fiber diameter of the organic fiber is equal to or greater than that of the cast iron fiber, and the length thereof is longer than that of the cast iron fiber. Organic fibers are more flexible than cast iron fibers. By blending such organic fibers in the friction material, the organic fibers are intertwined in a complicated manner, and the cast iron fibers are captured by the intricately intertwined organic fibers. Thereby, when mixing various raw materials for friction material manufacture, the uniform dispersibility of cast iron fiber improves (it is not unevenly distributed).

  The blending amount of the cast iron fiber in the friction material is 2.5 to 120% on a volume basis with respect to the blending amount of the organic fiber, that is, the organic fiber: cast iron fiber on the volume basis is 40: 1 to 1: 1.2. To do. When the blending amount of the cast iron fiber is less than 2.5% with respect to the blending amount of the organic fiber, the uniform dispersibility of the cast iron fiber cannot be ensured. On the other hand, when the compounding amount of the cast iron fiber exceeds 120% with respect to the compounding amount of the organic fiber, the lubricity is lowered. Therefore, if the relative ratio between the cast iron fiber and the organic fiber is out of the above relationship, squeal and abnormal noise are likely to occur. Preferably it is 5 to 120% (20: 1 to 1: 1.12), more preferably 20 to 100% (5: 1 to 1: 1), still more preferably 40 to 60% (5: 2 to 5). : 3). In addition, if it is a metal fiber which is a soft metal rather than cast iron, such as copper fiber, it can mix suitably in the range which does not have a bad influence on a friction material.

  What is necessary is just to let the compounding quantity of the whole fiber base material be about 20-50 vol% (volume%) with respect to the whole friction material. When the fiber base material is less than 20 vol%, the mechanical strength of the friction material decreases. On the other hand, if the fiber substrate exceeds 50 vol%, the blending ratio of other fillers and the like is decreased, and various performances such as a friction coefficient are deteriorated. Preferably it is 25-50 vol%, More preferably, it is 30-45 vol%.

[Binder]
The binder binds the fiber base material to the filler, and various thermosetting synthetic resins and rubbers conventionally used as a binder for NAO materials can be used. Examples of the thermosetting resin include phenol resin, imide resin, rubber-modified phenol resin, melamine resin, and epoxy resin. Examples of rubber include NBR, nitrile rubber, and acrylic rubber. Among them, a phenol resin having good heat resistance is preferable. These binders can also be used individually by 1 type, and can also be used in combination of 2 or more type. What is necessary is just to let the compounding quantity of a binder be about 10-40 vol% with respect to the whole friction material. When the blending amount of the binder is less than 10 vol%, the strength of the friction material is lowered. On the other hand, if the blending amount of the binder exceeds 40 vol%, the friction coefficient and the like are lowered because the blending amount of the fiber base material and the filler is low. Preferably it is 20-35 vol%, More preferably, it is 25-30 vol%.

[Filler]
Other fillers include, for example, organic dust such as cashew dust, resin dust, rubber dust, CaO compounds such as calcium silicate, dolomite, calcium sulfate, calcium carbonate, calcium hydroxide, alkali metal titanate, alkali metal titanate・ Metal powder such as Group 2 element salts such as titanium oxide, iron oxide, bronze, brass, copper, mica, mica, kaolin, talc, zonotlite, vermiculite, alumina, zirconium oxide, zirconium silicate, magnesium oxide, etc. Can be mentioned. Alumina, zirconium oxide, zirconium silicate, magnesium oxide and the like function as an abrasive. These fillers may be used alone or in combination of two or more. Generally, two or more kinds are mixed and blended. The filler is mainly blended to adjust so that various performances of the friction material can be effectively exhibited, and in a range of 100 vol% in total depending on the blending amount of the fiber base material and the binder. Appropriate amount is blended.

[Lubricant]
In the present invention, cast iron fibers having graphite are blended on the structure. However, since the lubricity of the entire friction material may not be sufficient only by this, it is preferable to blend a lubricant appropriately. Typical examples of the lubricant include graphite, and other metal sulfides such as molybdenum disulfide, antimony trisulfide, tin sulfide, zinc disulfide, iron sulfide, lead sulfide, cryolite, and boron nitride. Can be mentioned. These lubricants may be used alone or in combination of two or more. If a lubricant is also blended, the lubricant acts directly with the counterpart material, so that it is easy to ensure good lubricity. When the lubricant is also blended, the upper limit of the blending amount of the lubricant may be about 5 vol% with respect to the entire friction material. When the blending amount of the lubricant exceeds 5 vol%, not only a good friction coefficient can be obtained but also the friction material strength may be lowered. Preferably it is 4 vol% or less, More preferably, it is 3 vol% or less.

[Production method]
The friction material can be manufactured by, for example, a known molding method. Specifically, a fiber base material, a binder, and, if necessary, a filler containing a lubricant are sufficiently mixed with a mixer or the like, placed in a pressure mold, and preformed at room temperature. Next, the preform is obtained by hot pressing, followed by heat treatment. The pressure at the time of preforming or hot pressing may be about 10 to 100 MPa. Hot press temperature is about 130-200 degreeC. The heat treatment is performed at about 150 to 400 ° C. for about 2 to 48 hours. As the mixer, an Eirich mixer, a universal mixer, a Ladige mixer, or the like can be used. Note that a mixture of various raw materials may be directly hot pressed without preparing a preform.

(Example)
Example 1 and Comparative Example having the compositions shown in Tables 1 and 2 were prepared, and the average friction coefficient (μ), the amount of wear at each temperature, the occurrence of metal catch, and the presence or absence of abnormal noise or squeal were compared. evaluated. In addition, the numerical value of Table 1 and Table 2 is vol%.

  Each friction material was manufactured as follows. Various blends were mixed in a dry process for 5 minutes by an Eirich mixer to obtain a raw material mixture. This raw material mixture was heated and pressed under the conditions of a molding temperature of 160 ° C., a molding pressure of 20 MPa, and a molding time of 10 minutes. Finally, the molded product was cured at 230 ° C. for 3 hours. The cast iron fiber used in each example and comparative example was spheroidal graphite cast iron having a fiber diameter of 60 μm, a length of 2 mm, and a carbon content of 3.5% by weight.

The conditions of each test are as follows, and the results of each test are shown in Tables 3 and 4.
<Average friction coefficient>
The second potency test specified in JASO C406 (general performance) was tested five times with braking at an initial speed of 50 km / h and a hydraulic pressure of 4 MPa, and the average value at that time was determined.
<Abrasion amount of friction material>
Based on the provisions of JASO C427 (wear by temperature), the amount of wear of the friction material when braking from an initial speed of 50 km / h with a deceleration of 0.3 G was measured.
<Occurrence of metal catch>
After completion of each temperature in the friction material wear amount test, the surface of the friction material was visually confirmed. The judgment criteria at that time are as follows.
◎: None at all ○: None △: Slightly generated ×: Generated <Abnormal noise / squeal>
A total of 16 brakes are applied under the deceleration conditions of 0.1G, 0.2G, 0.3G, and 0.4G from the pre-braking speed of 60 km / h at pre-braking temperatures of 100 ° C., 200 ° C., 300 ° C. and 400 ° C., respectively. An actual car test on the street was conducted, and sensory evaluation was performed based on the auditory sense. The judgment criteria at that time are as follows.
◎: Cannot be heard at all conditions ○: Cannot be heard at all conditions △: May be heard to the extent that there is no discomfort ×: Often heard clearly

  From the results of Tables 3 and 4, Examples 1 to 6, in which an appropriate amount of organic fiber is blended in addition to cast iron fiber, all average friction coefficient, wear resistance, occurrence of metal catch, and all surfaces of abnormal noise and squeal Good results have been obtained. When it sees in detail, it exists in the tendency for an average friction coefficient to become large in proportion to the compounding quantity of cast iron fiber from the result of Examples 1-5 with the same compounding quantity of organic fiber. In addition, from the results of Examples 1 to 3 in which the blending amount of graphite is substantially the same, the wear amount of the friction material tends to decrease as the blending amount of the cast iron fiber increases. Thereby, it can be seen that the cast iron fiber has a good coefficient of friction and at the same time can exhibit significant lubricity. On the other hand, in Examples 4 and 5 in which the blending amount of graphite was small compared to the other examples, the wear amount of the friction material was large. Therefore, it can be seen that the cast iron fiber has significant lubricity, but if it is desired to further improve the lubricity, it is preferable to also add graphite as a lubricant. In Example 1 in which the blending amount of the cast iron fiber relative to the organic fiber is small, there is a little difficulty in the generation of metal catch and abnormal noise. Further, in Example 5 in which the amount of cast iron fiber is larger than that of organic fiber, there is a little difficulty in the generation of squeal. Thereby, the blending ratio of organic fiber: cast iron fiber is preferably 40: 1 to 1: 1.2, that is, the blending amount of cast iron fiber is preferably 2.5 to 120% on a volume basis with respect to the blending amount of organic fiber. I understood it. Further, from the result of Example 6, even if the blending amount of the organic fiber and the cast iron fiber is changed, if the relative ratio of the organic fiber and the cast iron fiber is in an appropriate range, the wear amount is small and abnormal noise or The occurrence of squeal is significantly suppressed. This is considered due to the fact that the uniform dispersibility of the cast iron fiber is good by blending an appropriate amount of organic fiber into the friction material. In addition, Examples 3 and 6 in which the ratio of organic fiber: cast iron fiber was 2: 1 showed good results with a good overall balance as compared with the other examples. Thereby, it turned out that the range which is about 40 to 60% of the compounding quantity of cast iron fiber on the volume basis with respect to the compounding quantity of organic fiber is most preferable.

  On the other hand, the comparative example 1 which has not mix | blended cast iron fiber has generated the metal catch and the abnormal noise based on this. This is because the lubricity by cast iron fiber is not obtained. However, even in Comparative Example 2 in which no organic fiber was blended, metal catches and abnormal noises and noises based on the metal catches occurred. This is because the cast iron fibers are not uniformly dispersed because no organic fibers are blended. Moreover, even in Comparative Example 3 in which the amount of cast iron fiber is too large relative to the organic fiber, metal catches and abnormal noise and squeal based on this are generated. This is presumably because the cast iron fibers are partially unevenly distributed due to the amount of cast iron fibers exceeding the amount that can be captured by the organic fibers. From the results of Comparative Example 4, it can be seen that even when organic fibers are blended, good lubricity cannot be obtained only by using steel fibers. From the results of Comparative Examples 5 and 6 in which the amount of graphite, which is a lubricant, was increased, the amount of wear and metal catch characteristics were significantly improved by increasing the amount of lubricant, but on the other hand, the friction coefficient deteriorated and Sound generation has not been suppressed. Therefore, it can be seen that even if the amount of the lubricant is simply increased, a good friction material cannot be obtained unless cast iron fibers are used.

Claims (3)

A non-asbestos friction material containing cast iron fiber as a fiber base material,
Furthermore, the friction material characterized by containing an organic fiber as a fiber base material.   The friction material according to claim 1, wherein a blending amount of the cast iron fiber is 2.5 to 120% on a volume basis with respect to a blending amount of the organic fiber. The cast iron fiber has a fiber diameter of 10 to 100 μm and a length of 1 to 5 mm.
The friction material according to claim 1 or 2, wherein the friction material is spheroidal graphite cast iron having a carbon content of 2.5 to 4.0% by weight.