JP2001026767A - Wet friction material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To express a large friction coefficient and ensure a high shear strength by using an organic paper-like base material. SOLUTION: This wet friction material is obtained by impregnating a paper- like base material with an organic-inorganic composite binder in a state compressed in the thickness direction and then thermally treating the impregnation product. The impregnation of the organic-inorganic composite binder permits the expression of a large friction coefficient, and the impregnation of the organic-inorganic composite binder in the state that the paper-like base material is compressed to enhance the density of the fibers further improves the shear strength of the wet friction material.

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 shear strength was not sufficient, resulting in low durability.

The present invention has been made in view of such circumstances, and it is an object of the present invention to develop a large coefficient of friction using an organic paper-like base material and to secure high shear strength.

[0009]

[MEANS FOR SOLVING THE PROBLEMS]
Ming's wet friction material is characterized by a paper-like base made of fibrous material.
Material and metal atoms and organic chains in the molecule
Wet friction material consisting of an organic-inorganic composite binder
The fiber density of the paper-like substrate is 0.25 to 0.35 g / cm ^ThreeIs
It is in.

The method for producing a wet friction material of the present invention capable of producing the above-mentioned wet friction material is characterized by a paper-like substrate made of a fibrous material and a substrate having a metal atom and an organic chain in a molecule. A method for producing a wet friction material comprising an organic-inorganic composite binder impregnated with an organic-inorganic composite binder in a state where a paper-like base material is compressed in the thickness direction, and then performing a heat treatment.

[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 binds a fibrous material by impregnating a sol solution prepared by hydrolyzing an organic group-substituted metal alkoxide into a paper-like substrate made of a fibrous material, followed by drying and firing. It is.

However, in the wet friction material using only the organic-inorganic composite binder, although the Si skeleton of the organic-inorganic composite binder is concentrated on the surface layer, a high friction coefficient is exhibited. There was a problem that strength was not obtained and durability was insufficient.

Therefore, in the method for producing a wet friction material of the present invention, an organic-inorganic composite binder is impregnated in a state where a paper-like substrate is compressed in the thickness direction, and then heat treatment is performed. By compressing the paper-like substrate in this way, the fiber density increases,
By impregnating the organic-inorganic composite binder in that state, the shear strength is improved.

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

In order to form a paper-like substrate, a fibrous material selected from the above can be dispersed in water and formed by a known papermaking method.

The paper-like substrate can be compressed in the thickness direction by a roller press, a plate press or the like. You may dry the paper made and compress it,
Since the compression shape may change due to the elasticity of the fiber, it is preferable to compress the paper containing water immediately after papermaking and then dry it. This has the effect of preventing deformation of the fibers after compression, and also has the effect of shortening the drying time since water is removed during compression. Alternatively, the paper-like substrate may be dried and impregnated with the organic-inorganic composite binder, and then compressed.

The degree of compression of the paper-like substrate is such that the fiber density is 0.25.
It is desirable to compress to 0.35 g / cm ³ .
If the fiber density of the compressed base material is lower than 0.25 g / cm ³ , sufficient shear strength cannot be obtained, and if the fiber density is higher than 0.35 g / cm ^{3, the} base material becomes too hard and the followability to the mating material is reduced. Since the contact area is reduced, the coefficient of friction is reduced.

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 metal alkoxide substituted with an organic group 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.

It is desirable that the sol solution 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.

The trivalent metal element is preferably contained in the range of 0.1 to 5% with respect to 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.

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 divalent 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 paper-like substrate with the organic-inorganic composite binder, a first step of preparing a sol solution by hydrolyzing at least the organic group-substituted metal alkoxide, and impregnating the sol solution into the paper-like substrate And the second step of preparing the impregnated base material in this order.

The first step can be carried out by adding water to at least an alcohol solution of an 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 on a paper-like base material to prepare an impregnated base material in which the sol is impregnated between fibers.

It is desirable that the paper-like substrate used in the second step has been 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 heat treatment 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 the acid solution or spraying the acid solution on the paper-like substrate to impregnate the paper-like substrate.

Other methods for introducing a hydroxyl group include a method of treating in an aqueous alkali solution such as an aqueous solution of sodium hydroxide, 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.

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

This second step may be carried out under normal pressure, but is preferably carried out under increased or reduced pressure. This makes it easier to replace the air in the paper-like substrate with the organic-inorganic composite binder, and the impregnation can be performed quickly. This is particularly effective when performing the second step after compressing the paper-like substrate. It is. When the second step is performed before the compression, the compression processing is performed after the second step. Also in this case, it can be performed in the same manner as described above using a roller press, a plate press or the like.

By subjecting the impregnated substrate to a heat treatment,
The hydroxide sol becomes a gel and firmly binds the fibers of the substrate. 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 is more strongly bonded to the organic fiber by heat treatment, so that the strength is reduced. Further improve. The organic group also has the effect of improving flexibility and increasing the coefficient of friction.

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 fibers are oriented so as to be close to each other in the second step, and the gel and the fibers are strongly solidified by the heat treatment. The strength is further improved due to the bonding.

The heat treatment is desirably performed at 150 to 300 ° C. for 0.5 to 1.0 hour. If the heat treatment temperature is lower than this or the heat treatment time is shorter than this, sufficient strength cannot be obtained. If the heat treatment temperature is higher than this or the heat treatment time is longer than this, organic substances are decomposed and the frictional characteristics are reduced.

The heat treatment 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 a small amount of ammonia is contained, but the maximum effect is obtained if about 10% by volume is contained in the atmosphere air during the heat treatment.

The heat treatment is preferably 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.

The wet friction material obtained according to the present invention can contain various fillers as in the prior art. 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 One or more kinds of butadiene rubber, styrene butadiene rubber, silicon rubber, fluorine rubber 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.

When various fillers 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 substrate. May be contained. It is also preferable to supply the filler during the compression of the paper-like substrate and to include the filler in the substrate simultaneously with the compression. In addition, a filler can be sprinkled on the surface of a paper-like base material impregnated with an organic-inorganic composite binder and adhered.

[0043]

(Embodiment 1) FIGS. 1 and 2 schematically show the manufacturing method of this embodiment.

First, an aramid fiber as a fibrous material is introduced into water, stirred and dispersed (1), and paper is formed using a paper machine to form a paper body (2). Next, the paper body was pressed in the thickness direction with a roller press device (3), and dried to obtain a compressed paper-like substrate (4). The fiber density of this substrate is 0.29 g / cm ³ .

On the other hand, 27.6 parts by weight of ethanol and 20.8 parts by weight of methyltriethoxysilane (CH ₃ Si (OC ₂ H ₅ ) ₃ ) were weighed in a glass container 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, the compressed paper-like base material is punched into a friction material in the form of a press (5), immersed in the sol solution and impregnated with a predetermined amount of the sol solution to obtain an impregnated base material. (6). The impregnation amount of the sol solution is 30% by weight as a sol.

Then, the obtained impregnated substrate was air-dried at 30 ° C. for 24 hours (7), and then heat-treated at 100 ° C. in the air for 1 hour (8). The obtained dried base material was press-formed at 180 ° C. for 10 minutes (9) to obtain a wet friction material having a predetermined shape (10).

Table 1 summarizes the structure of the wet friction material. The shear strength of the wet friction material was measured using a tensile tester. The results are shown in FIG.

Example 2 The wet friction material of this example was manufactured in the same manner as in Example 1 except that a mixed fiber of aramid fiber 90% by weight and cellulose fiber 10% by weight was used as the fibrous material. . The fiber density of the compressed paper-like substrate is 0.29 g / cm ³ . Then, the shear strength was measured in the same manner as in Example 1, and the results are shown in FIG.

Example 3 The wet friction material of this example was manufactured in the same manner as in Example 1 except that a mixed fiber of 70% by weight of aramid fiber and 30% by weight of cellulose fiber was used as the fibrous material. . The fiber density of the compressed paper-like substrate is 0.33 g / cm ³ . Then, the shear strength was measured in the same manner as in Example 1, and the results are shown in FIG.

Example 4 A wet friction material of this example was manufactured in the same manner as in Example 1 except that a mixed fiber of 50% by weight of aramid fiber and 50% by weight of cellulose fiber was used as the fibrous material. . The fiber density of the compressed paper-like substrate is 0.32 g / cm ³ . Then, the shear strength was measured in the same manner as in Example 1, and the results are shown in FIG.

(Comparative Example 1) A mixed fiber of 70% by weight of aramid fiber and 30% by weight of cellulose fiber was used as the fibrous material, compression was not performed by a roller press device, and the impregnation amount of the sol solution was 35% by weight. A wet friction material of this example was manufactured in the same manner as in Example 1 except that the above conditions were satisfied. The fiber density of the paper-like base material that is not compressed is 0.17 g /
cm ^3. Then, the shear strength was measured in the same manner as in Example 1, and the results are shown in FIG.

(Comparative Example 2) A mixed fiber of 70% by weight of aramid fiber and 30% by weight of cellulose fiber was used as a fibrous material, compression was not performed by a roller press device, and the impregnation amount of the sol solution was 45% by weight. A wet friction material of this example was manufactured in the same manner as in Example 1 except that the above conditions were satisfied. The fiber density of the paper-like base material that is not compressed is 0.17 g /
cm ^3. Then, the shear strength was measured in the same manner as in Example 1, and the results are shown in FIG.

(Comparative Example 3) A mixed fiber of 90% by weight of aramid fiber and 10% by weight of cellulose fiber was used as the fibrous material, compression was not performed by a roller press device, and the impregnation amount of the sol solution was 45% by weight. A wet friction material of this example was manufactured in the same manner as in Example 1 except that the above conditions were satisfied. The fiber density of the paper-like base material that is not compressed is 0.70 g /
cm ^3. Then, the shear strength was measured in the same manner as in Example 1, and the results are shown in FIG.

(Comparative Example 4) A mixed fiber of 70% by weight of aramid fiber and 30% by weight of cellulose fiber was used as the fibrous material, compression was not performed by a roller press device, and the impregnation amount of the sol solution was 50% by weight. A wet friction material of this example was manufactured in the same manner as in Example 1 except that the above conditions were satisfied. The fiber density of the uncompressed paper-like substrate is 0.12 g /
cm ^3. Then, the shear strength was measured in the same manner as in Example 1, and the results are shown in FIG.

(Comparative Example 5) A mixed fiber of 70% by weight of aramid fiber and 30% by weight of cellulose fiber was used as a fibrous material, compression was not performed by a roller press device, and the impregnation amount of the sol solution was 40% by weight. A wet friction material of this example was manufactured in the same manner as in Example 1 except that the above conditions were satisfied. The fiber density of the paper-like substrate that is not compressed is 0.15 g /
cm ^3. Then, the shear strength was measured in the same manner as in Example 1, and the results are shown in FIG.

(Comparative Example 6) A mixed fiber of 70% by weight of aramid fiber and 30% by weight of cellulose fiber was used as a fibrous material, and 0.5 part by weight of cashew dust was further added. The wet friction material of this example was manufactured in the same manner as in Example 1 except that the impregnation amount of the sol solution was 40% by weight. The fiber density of the uncompressed paper substrate is 0.14 g / cm ³ . Then, the shear strength was measured in the same manner as in Example 1, and the results are shown in FIG.

[0058]

[Table 1]

<Evaluation> The wet friction material must have a shear strength of at least 0.2 MPa, more preferably at least 0.4 MPa. From FIG. 3, the friction material of each embodiment is
A higher shear strength of 0.4 MPa or more than that of each comparative example is shown, and it is clear that this is an effect of impregnating an organic-inorganic composite binder in a state where a paper-like substrate is compressed. It is also apparent that when the fiber density of the paper-like substrate is less than 0.25 g / cm ³ , the shear strength decreases.

As for the friction coefficient, each of the friction materials of Examples and Comparative Examples showed a large dynamic friction coefficient of 0.14 or more.

[0061]

According to the wet friction material of the present invention,
A large friction coefficient and high shear strength are exhibited, and the durability is excellent. Further, according to the method for producing a wet friction material of the present invention, the wet friction material of the present invention can be easily and stably produced.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a manufacturing process of a compressed paper-like base material in a manufacturing method of a wet friction material according to an embodiment.

FIG. 2 is an explanatory view showing a step of producing a wet friction material from a paper-like base material in the method of producing a wet friction material of Examples and Comparative Examples.

FIG. 3 is a graph showing the shear strength of the wet friction materials of Examples and Comparative Examples.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Fumio Ueda 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Shoji Nakanishi 1 Toyota Motor Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation F term (reference) 3J058 BA46 BA76 CD20 EA36 EA37 FA01 FA11 FA21 FA31 GA02 GA03 GA04 GA05 GA06 GA19 GA22 GA23 GA24 GA26 GA27 GA33 GA34 GA43 GA44 GA49 GA62 GA64 GA65 GA67 GA68 GA73 GA89 GA93 GA94

Claims (3)

[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. wet friction material fiber density shaped for the substrate characterized in that it is a 0.25~0.35g / cm ^3. 2. A method for producing 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 method for producing a wet friction material, comprising impregnating the organic-inorganic composite binder in a state where the paper-like base material is compressed in the thickness direction, and thereafter performing heat treatment. 3. The fiber density of the compressed paper-like substrate is
Method for manufacturing a wet friction material according to claim 2, characterized in that the 0.25~0.35g / cm ^3.