JP2001026657A - Wet-type friction material and preparation thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a large coefficient of friction by using a substrate made of an org. material in the shape of paper, and to realize a high torque capacity by increasing an area in contact with the counterpart member. SOLUTION: The concn. of an org./inorg. composite binder substrate having a metal atom and an org. chain in a molecule is made to be higher in the surface layer part on the friction surface side than in the part excepting the surface layer part, the surface layer part being not deeper than 10% of the total thickness from the surface. A high coefficient of friction is realized through increase of rigidity by increasing the amt. of the org./inorg. composite binder in the part on the friction surface side. A flexibility is insured by decreasing the amt. of the org./inorg. composite binder in the part on the surface side which is opposite to the friction surface side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wet friction material used for clutch facing of a power transmission system of an automobile, an industrial machine, a railway vehicle, and the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Facing of a wet clutch, for example, is disclosed in, for example, Japanese Patent Publication No. 58-47345, based on an organic fiber as a base material, and blending various friction modifiers with the phenol resin. A paper-type friction material obtained by impregnating and solidifying a binder made of a thermosetting resin is often used.

However, the above-mentioned wet friction material has a problem that heat resistance is low and a friction coefficient is small since both the paper-like base material and the binder are organic.
Various measures have been taken to solve this problem.

As a countermeasure, for example, in clutch facing, the number of friction plates is increased or the area is increased. However, if you take such measures,
The wet clutch structure is complicated and large-scale, resulting in large energy loss and high cost.

[0005] On the other hand, attempts have been made to apply, for example, a copper-based sintered friction material to a wet clutch. If such a sintered friction material can be used, even if the number of friction plates is small and the area is small, the heat resistance and the pressure resistance can be satisfied, and the above problem can be solved.

Japanese Patent Application Laid-Open No. H7-197016 discloses a wet friction material using a silicone resin having a siloxane bond and an organic group as a binder. Such a silicone resin is flexible and flexible due to a siloxane bond. Therefore, the friction material using the silicone resin as a binder has an increased contact area with a mating material and can secure a high torque capacity. Further, since the distortion characteristics of the friction material become appropriate, the friction coefficient is stabilized.

[0007]

However, many sintered metal-based friction materials often have a friction coefficient smaller than that of organic friction materials, and have a low friction characteristic for a recent high performance automobile wet clutch. It was not enough. Also, JP-A-7-1970
The friction material disclosed in Japanese Patent Publication No. 16 has a coefficient of friction of 0.2
And the abrasion resistance is not sufficient.

The present invention has been made in view of such circumstances, and uses an organic paper-like base material to develop a large coefficient of friction and increase the contact area with a mating material to achieve a high torque capacity. The purpose is to express.

[0009]

The wet friction material of the present invention which solves the above-mentioned problems is characterized by a paper-like base made of a fibrous material and a base having a metal atom and an organic chain in a molecule. A wet friction material comprising an impregnated organic-inorganic composite binder, wherein the concentration of the organic-inorganic composite binder is such that the surface portion within 10% of the total thickness from the surface on the friction surface side of the base material is more than the portion excluding the surface layer portion Being high.

A feature of the method for producing a wet friction material of the present invention, which is most suitable for producing the above-mentioned wet friction material, is that a paper-like base made of a fibrous material has metal atoms and organic chains in the molecule. In a method for producing a wet friction material in which a fibrous material is bound by an organic-inorganic composite binder by impregnating a solution of an organic-inorganic composite binder and then drying the solvent, the friction surface side is gravitationally impregnated with the organic-inorganic composite binder solution And drying it so that the concentration of the organic-inorganic composite binder in the substrate becomes higher on the friction surface side.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventor has focused on a binder as an element of a friction material in order to express a high friction coefficient, and as a result of diligent research, has found that an organic-inorganic material having a metal atom and an organic chain in a molecule. A composite binder has been developed. This organic-inorganic composite binder impregnates a sol solution prepared by hydrolyzing at least one of a metal alkoxide and an organic group-substituted metal alkoxide into a paper-like substrate made of a fibrous material, and
Firing combines the fibrous materials.

However, in a wet friction material using only the organic-inorganic composite binder, a high friction coefficient can be ensured, but flexibility is insufficient, and a contact area with a mating material cannot be increased.

Therefore, in the wet friction material of the present invention, the concentration of the organic-inorganic composite binder is configured such that the surface portion within 10% of the total thickness from the surface on the friction surface side of the base material is higher than the portion excluding the surface portion. By increasing the amount of the organic-inorganic composite binder on the friction surface side, the rigidity is improved, and a high friction coefficient is exhibited, so that the friction effect is promoted. Further, by reducing the amount of the organic-inorganic composite binder on the side opposite to the friction surface, flexibility can be ensured, and the contact area with the mating material can be increased, so that a high torque capacity can be exhibited.

The organic-inorganic composite binder is desirably contained in the surface layer portion within 10% of the total thickness from the surface on the friction surface side in an amount of 25 to 40% by weight. When the content of the organic-inorganic composite binder in the surface layer portion is less than 25% by weight, the friction coefficient decreases, and when it is more than 40% by weight, the flexibility decreases and the contact area with the mating material decreases. Further, even if the organic-inorganic composite binder is contained in an amount of 25 to 40% by weight exceeding 10% of the total thickness, the flexibility is reduced and the contact area with the counterpart material is reduced.

The organic-inorganic composite binder preferably contains 10 to 23% by weight in a portion other than the surface layer portion. If the content is less than 10% by weight, the rigidity is reduced and the shear strength becomes insufficient. If the content is more than 23% by weight, the flexibility is reduced and the contact area with the mating material is reduced.

In the wet friction material of the present invention, the fibrous materials constituting the paper-like substrate include glass fiber, rock wool, potassium titanate fiber, ceramic fiber, silica fiber, silica-alumina fiber, kaolin fiber, Inorganic fibers such as bauxite fiber, canonoid fiber, boron fiber, magnesia fiber, metal fiber, linter pulp, wood pulp, synthetic pulp, polyester fiber, polyamide fiber, polyimide fiber, polyvinyl alcohol modified fiber, polyvinyl chloride fiber, One or more kinds of organic fibers such as polypropylene fiber, polybenzimidazole fiber, acrylic fiber, carbon fiber, phenol fiber, nylon fiber, and cellulose fiber can be used.

The organic-inorganic composite binder has a metal atom and an organic chain in the molecule, and may be formed from a sol solution prepared by hydrolyzing an organic group-substituted metal alkoxide. As the organic group-substituted metal alkoxide, a metal alkoxide containing silicon (Si), aluminum (Al), zirconium (Zr), titanium (Ti) or the like in which a part of the alkoxyl group is substituted with an alkyl group is used. Can be used.

It is also preferable to use a metal alkoxide in which all of the alkoxyl groups are not substituted with an organic group. The weight ratio of the metal alkoxide to the organic group-substituted metal alkoxide is preferably in the range of metal alkoxide: organic group-substituted metal alkoxide = 3: 7 to 0:10.
If the amount of the metal alkoxide exceeds this range, the flexibility of the wet friction material decreases, and the friction coefficient decreases due to the decrease in the contact area.

The alkoxyl group of the metal alkoxide or the organic group-substituted metal alkoxide is preferably an alkoxyl group having 1 to 5 carbon atoms. The organic group of the organic group-substituted metal alkoxide preferably has 1 to 10 carbon atoms. By using an organic group-substituted metal alkoxide having an organic group having a carbon number in this range, the shear strength and the like of the obtained friction material are improved.

The sol solution preferably further contains a silicone resin containing an organic group in a siloxane skeleton. In this case, since a part of the binder of the obtained wet friction material is made of a soft silicone resin, the flexibility is improved and the friction coefficient can be further increased. The mixing amount of the silicone resin is preferably in the range of 5 to 70 parts by weight when the total of the organic-inorganic composite binder and the silicone resin is 100 parts by weight. When the amount of the silicone resin is larger than this, the coefficient of friction becomes smaller, and when the amount is smaller than this, the effect of the addition is hardly exhibited.

The organic-inorganic composite binder has at least 4
It is preferable that two or more kinds of metal elements including a valent metal element are contained. This ensures a higher coefficient of friction and higher wear resistance. Although the reason for this is not clear, other metal elements are introduced into the space mainly composed of one metal element, so that an appropriate twist is generated in the molecule and internal stress occurs. It is thought that the skeletal strength of the organic-inorganic composite binder is increased by performing the method.

It is more desirable that the metal elements containing at least a tetravalent metal element have different valences. That is, for example, it is desirable to include a tetravalent metal element and a trivalent metal element, or to include a tetravalent metal element and a divalent metal element. Thereby, the coefficient of friction is further increased, and the wear resistance is further improved.

As the tetravalent metal element, silicon (Si),
Titanium (Ti) and zirconium (Zr) are exemplified. Examples of the trivalent metal element include aluminum (Al), gallium (Ga), and iron (Fe). Examples of the divalent metal include magnesium (Mg), calcium (Ca), and barium (B
a) and the like. In some cases, a monovalent metal element such as potassium (K) and sodium (Na) may be used.

It is preferable that the trivalent metal element is contained in the range of 0.1 to 5% based on the total number of atoms of the metal element in the organic-inorganic composite binder. Even if the amount of the trivalent metal element is smaller or larger than this range, the wear resistance is reduced. When the content is within this range, the wear resistance is significantly improved.

It is preferable that the divalent metal element is contained in the range of 0.2 to 10% based on the total number of metal elements in the organic-inorganic composite binder. Even if the amount of the trivalent metal element is smaller or larger than this range, the wear resistance is reduced. When the content is within this range, the wear resistance is significantly improved.

In order to impregnate the substrate with the organic-inorganic composite binder, a first step of preparing a sol solution by hydrolyzing at least an organic group-substituted metal alkoxide, and a paper-like substrate made of a fibrous material And a third step of drying and calcining the impregnated base material in order.

The first step can be carried out by adding water to at least an alcohol solution of the organic group-substituted metal alkoxide, thereby producing a sol solution of a hydroxide. In the first step, it is desirable to increase the reactivity by adding an acid or an alkali or by heating.

In the second step, the sol solution prepared in the first step is impregnated into a paper-like substrate made of a fibrous material to prepare an impregnated substrate in which the sol is impregnated between the fibers. When fillers such as various friction modifiers are used, they may be mixed in the sol solution prepared in the first step, or mixed with a fibrous material to form a paper-like base material. It may be contained in the material. In some cases, after the sol solution is impregnated into the base material, the sol solution may be sprinkled onto the base material surface and adhered.

The paper-like substrate used in the second step is desirably subjected to a hydroxyl group introduction treatment in advance. Due to the introduced hydroxyl group, the bonding strength between the paper-like substrate and the organic-inorganic composite binder is greatly improved, and the friction characteristics are further improved.

As the hydroxyl group introduction treatment, for example, there is a method of treating with an acid. As the acid, any of an inorganic acid and an organic acid can be used, but it is preferable to use an organic acid such as acetic acid and oxalic acid. When an organic acid is used, the acid component remaining during the firing in the third step described below is decomposed and disappears, so that the effect on the friction characteristics can be ignored.

The acid treatment can be easily carried out by immersing the paper-like substrate in an acid solution or spraying an acid solution to impregnate the paper-like substrate.

Other methods for introducing a hydroxyl group include a method of treating in an alkaline aqueous solution such as an aqueous sodium hydroxide solution, a method of treating in boiling water, and a supercritical steam treatment. Since a hydroxyl group can be introduced into the binder, the bonding strength with the organic-inorganic composite binder is greatly improved, and the friction characteristics are further improved.

If the paper-like base material is subjected to the hydroxyl group introduction treatment, the affinity between the hydroxide formed in the second step and the paper-like base material increases, and the hydroxyl group of the hydroxide and the paper-like base material are changed. It is considered that the hydroxyl groups of the base material are oriented so as to be close to each other.

Then, by drying and firing the impregnated base material in the third step, the hydroxide sol becomes a gel, and the fibers of the base material are firmly bonded. If a large amount of the organic group-substituted metal alkoxide is used in the first step, the organic group is oriented so as to be close to the organic fiber of the base material in the second step, and more strongly bonded to the organic fiber in the third step. Strength is further improved.
The organic group also has the effect of improving flexibility and increasing the coefficient of friction.

In addition, if the hydroxyl group introduction treatment has been performed on the paper-like base material in advance in the second step, the hydroxide and the fiber are oriented so as to be close to each other in the second step, and the gel and the fiber are oriented in the third step. Are firmly bonded, so that the strength is further improved.

The firing in the third step is desirably performed at 150 to 300 ° C. for 0.5 to 1.0 hour. If the firing temperature is lower than this or the firing time is shorter than this, it is difficult to generate a gel, and sufficient strength cannot be obtained. On the other hand, if the firing temperature is higher or the firing time is longer than this, organic substances are decomposed and the frictional characteristics are reduced.

The third step is preferably performed in an atmosphere containing ammonia. Thereby, it is considered that the metal element in the sol is partially nitrided, and the coefficient of friction further increases.
The effect can be obtained if the ammonia is contained at all, but the maximum effect can be obtained if the atmosphere air in the third step contains about 10% by volume.

The third step is desirably performed under supercritical conditions. The supercritical condition is a condition in which the organic matter contained in the base material and the sol is in a state immediately before vaporization, and is a state in which molecular motion is extremely active. The temperature at which the supercritical state is reached by pressurization increases, and molecular motion becomes more active.
High pressure conditions are assumed. In other words, by using high-temperature, high-pressure supercritical conditions, it is possible to improve the reactivity while preventing the decomposition of organic substances, and to stably produce a friction material having a large friction coefficient with less unreacted portions remaining. Becomes possible.

Various fillers can be contained in the wet friction material of the present invention as in the conventional case. As the filler, for example, barium sulfate, calcium carbonate, magnesium carbonate, silicon carbide, boron carbide, titanium carbide, silicon nitride, boron nitride, alumina, silica, zirconia, cashew dust, rubber dust, diatomaceous earth, graphite, talc, kaolin , Magnesium oxide, molybdenum disulfide, nitrile rubber, acrylonitrile-butadiene rubber, styrene-butadiene rubber, silicon rubber, fluororubber and the like can be used in an appropriate amount. If the particle size of the filler exceeds 50 μm, the unevenness of the friction material surface becomes large and the total contact area with the mating material becomes relatively small.

Now, a total thickness of 10% from the surface on the friction surface side of the base material.
In order to make the concentration of the organic-inorganic composite binder in the surface layer portion within% by mass higher than that in the portion other than the surface layer portion, various production methods can be considered.

The most easily conceivable method is a method in which an impregnated base material having a high organic-inorganic composite binder concentration and an impregnated base material having a low organic-inorganic composite binder concentration are respectively produced and laminated. However, in this method, two types of impregnated substrates are required to be manufactured and a laminating step is required, so that there is a problem that the number of steps is large and productivity is low.

Therefore, in the manufacturing method of the present invention, after the impregnation with the solution of the organic-inorganic composite binder, the friction surface side is arranged in the direction of gravity and dried. The solution of the organic-inorganic composite binder refers to the sol solution prepared in the first step described above. With this configuration, the concentration of the organic-inorganic composite binder in the solution is increased by drying the solvent on the friction surface side, and the solution is supplied to the friction surface side one after another by its own weight. It is considered that the organic-inorganic composite binder increases in the surface layer portion on the friction surface side in the direction of gravity and decreases in other portions. According to this method,
After the impregnation with the solution of the organic-inorganic composite binder, it is only necessary to dry with the friction surface side down, so that the productivity is high without increasing the number of steps.

In this method, the concentration of the organic-inorganic composite binder on the friction surface side can be adjusted by adjusting the dry state from the surface, and the wet friction material according to claim 2 can be easily manufactured. Can be. For example, warm air is supplied to the friction surface side, and cool air is supplied to the opposite side. In this way, the friction surface will dry faster than the opposite surface,
The amount of the solution supplied to the friction surface increases. Therefore, by appropriately setting the temperature or air volume of the hot or cold air, the surface layer within 10% of the total thickness contains 25-40% by weight of the organic-inorganic composite binder, and the parts other than the surface layer are organic. The friction material of the present invention containing 10 to 23% by weight of the inorganic composite binder can be stably manufactured.

After impregnation with the solution of the organic-inorganic composite binder,
It is also preferable to apply a solution of a binder different from the organic-inorganic composite binder to the surface on the side opposite to the friction surface side, and then arrange the friction surface side in the direction of gravity to dry. By doing so, although drying from the friction surface proceeds, drying from the opposite surface is delayed, so that the concentration difference in the thickness direction of the organic-inorganic composite binder can be further increased. As a binder different from the organic-inorganic composite binder, a phenol resin or the like can be used. The same operation and effect can be obtained by drying while applying only the solvent to the surface opposite to the friction surface side.

In addition, centrifugal force can also be used as a method of drying by arranging the friction surface side in the direction of gravity. That is, the substrate impregnated with the solution of the organic-inorganic composite binder may be placed in a centrifuge such that the friction surface side is in the centrifugal direction, and dried while rotating the centrifuge.

After impregnation with the solution of the organic-inorganic composite binder, forced drying may be performed from both sides of the substrate. By doing so, the organic-inorganic composite binder concentration in the central portion in the thickness direction is low, and the organic-inorganic composite binder concentration in the surface layer portions on both side surfaces is high. Thus, the friction material of the present invention can be manufactured.

[0047]

EXAMPLES (Example 1) Ethanol 27.6 parts by weight of a glass container and methyl triethoxysilane _{(CH 3 Si (OC 2 H} 5) 3) 2
0.8 parts by weight was weighed and stirred for 10 minutes. Thereafter, while stirring this solution, 20 parts by weight of a 0.05 N aqueous hydrochloric acid solution was added dropwise, and further stirred for 24 hours to prepare a sol solution.

Next, a paper base material comprising 20 parts by weight of cellulose fiber, 80 parts by weight of aramid fiber, and 10 parts by weight of cashew dust prepared by a fourdrinier machine is prepared and formed into a predetermined shape. After cutting, a predetermined amount of the sol solution was impregnated to obtain an impregnated base material.

Then, the obtained impregnated base material is placed on a wire mesh with the friction side facing downward, and is blown dry by blowing air from below the wire mesh at room temperature for 1 hour.
Calcination was carried out at ℃ for 1 hour.

The obtained dried substrate was compression molded at 180 ° C. for 10 minutes to obtain a wet friction material having a predetermined shape. Attach the wet friction material to both sides of the metal plate using an adhesive,
The samples were heated and adhered for 30 minutes and subjected to the test. In this test piece, the opposite side of the friction surface side is adhered to the metal plate, and the friction surface side is exposed.

First, the friction coefficient was measured using a SAE # 2 friction tester under the conditions shown in Table 1. The results are shown in FIG.
Further, the resin ratio of the wet friction material on the friction surface side and the metal plate side was measured, and the results are shown in FIG.

[0052]

[Table 1]

(Example 2) The obtained impregnated base material was placed on an iron plate with the friction surface facing downward, and then a solvent (ethanol) was sprayed on the surface facing upward opposite to the friction surface. Except that after drying,
The wet friction material of this example was manufactured. Then, the coefficient of friction and the resin ratio were measured in the same manner as in Example 1, and the results are shown in FIGS.

(Comparative Example 1) The same procedure as in Example 1 was carried out except that the impregnated base material was erected during ventilation drying so that the drying conditions on the friction surface side and the opposite side were the same. A wet friction material was manufactured. Then, the coefficient of friction and the resin ratio were measured in the same manner as in Example 1, and the results are shown in FIGS.

(Comparative Example 2) The wet friction material of this comparative example was manufactured in the same manner as in Example 1 except that the surface opposite to the friction surface side was placed on a wire mesh at the time of ventilation drying. .
Then, the coefficient of friction and the resin ratio were measured in the same manner as in Example 1, and the results are shown in FIGS. <Evaluation> As shown in FIG. 1, the wet friction material of each embodiment has a higher friction coefficient than the comparative example. Also, when looking at FIG. 2, the resin ratio on the friction surface side is higher than that on the metal plate side in each of the examples, whereas in Comparative Example 1, the difference in the resin ratio between the friction surface side and the metal plate side is almost the same. However, in Comparative Example 2, it was reversed.

That is, it is apparent that the wet friction material of the example exhibits a high friction coefficient because the concentration of the organic-inorganic composite binder on the friction surface side is 30% by weight or more, which is higher than that on the metal plate side. is there.

When the results of Examples are compared, the wet friction material of Example 2 shows a higher friction coefficient than that of Example 1 and is particularly excellent in friction characteristics. From FIG. 2, it is considered that this difference is related to the concentration of the organic-inorganic composite binder on the metal plate side, and it is considered that the concentration of the organic-inorganic composite binder on the metal plate side is desirably 23% by weight or less.

[0058]

According to the wet friction material of the present invention,
Since a high coefficient of friction is exhibited and flexibility can be ensured, a contact area with a counterpart material is increased, and a high torque capacity is exhibited. Further, according to the method for producing a wet friction material of the present invention, the above-mentioned wet friction material of the present invention can be easily and stably produced without increasing the number of steps.

[Brief description of the drawings]

FIG. 1 is a bar graph showing friction coefficients of wet friction materials of an example and a comparative example.

FIG. 2 is a bar graph showing the resin ratio on the friction surface side and the metal plate side of the wet friction materials of Examples and Comparative Examples.

Continued on front page F-term (reference) 3J058 BA44 BA61 BA76 DD28 FA01 FA11 FA21 FA31 GA02 GA03 GA04 GA05 GA06 GA19 GA22 GA23 GA24 GA26 GA27 GA31 GA33 GA34 GA41 GA49 GA52 GA73 GA93 GA94 4F071 AA09 AA20 AA24 AA29 AA33 AA73 AB03 AB06 AB18 AB20 AB27 AB28 AB29 AB30 AC05 AD01 AE12 AE17 AF28 AG09 AG12 AG34 AH07 AH17 DA01 DA03 DA11

Claims (4)

[Claims] 1. A wet friction material comprising a paper-like substrate made of a fibrous material, and an organic-inorganic composite binder having a metal atom and an organic chain in a molecule and impregnated in the substrate, A wet friction material, wherein the concentration of the organic-inorganic composite binder is higher in a surface portion within 10% of a total thickness from a surface on a friction surface side of the base material than in a portion excluding the surface layer portion. 2. An organic-inorganic composite binder is contained in the surface layer portion in an amount of 25 to 40% by weight, and a portion other than the surface layer portion contains an organic-inorganic composite binder in an amount of 10 to 23% by weight. Item 4. The wet friction material according to Item 1. 3. An organic-inorganic composite binder comprising a paper-like substrate made of a fibrous material impregnated with a solution of an organic-inorganic composite binder having a metal atom and an organic chain in a molecule, and then drying the solvent. In the method for producing a wet friction material that binds the fibrous material according to the method, after the impregnation of the organic-inorganic composite binder solution, the friction surface side is disposed in the direction of gravity and dried, and the organic-inorganic composite binder in the base material is dried. A method for producing a wet friction material, wherein the concentration is higher on the friction surface side. 4. The method for producing a wet friction material according to claim 3, wherein the concentration of the organic-inorganic composite binder on the friction surface side is adjusted by adjusting a dry state from a surface.