JP2007063399A - Wet friction material and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wet friction material usable for a clutch facing or the like of a transmission system in a speed changer for an automobile. <P>SOLUTION: The wet friction material is obtained by forming a slurry comprising an organic fiber pulp such as an aromatic polyamide fibrillated so as to have 3-20 m<SP>2</SP>specific surface area, an inorganic filler and a bacteria cellulose in a composition ratio of (20-80):(80-20):(0.5-10) respectively, using a paper-like material obtained by subjecting the slurry to papermaking as a base material, combining 20-70 pts.wt. binder resin with 100 pts.wt. base material, and pressurizing and hardening the product by hot pressing. The wet friction material has excellent shear strength, durability, etc. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a wet friction material used for clutch facing of a power transmission system in an automatic transmission such as an automobile, and a manufacturing method thereof.
More specifically, it is a wet friction material obtained by impregnating a binder resin with a paper-like base material in which bacterial cellulose produced from microorganisms is uniformly dispersed, and has excellent adhesion between the base material and the binder resin. The present invention relates to a wet friction material having improved characteristics and a method for producing the same.

  In general, wet friction materials used for clutch facings of power transmission systems such as automobiles are disclosed in, for example, Japanese Patent Publication No. 58-47345 (Patent Document 1) and Japanese Patent Application Laid-Open No. 11-201206 (Patent Document 2). As described above, a fibrous material and various inorganic fillers such as a friction modifier and a solid lubricant are made to obtain a paper-like base material, which is impregnated with a binder resin such as a phenol resin and heat-cured. Manufactured.

  In particular, in the prior art, cellulose fibers such as wood pulp and linter pulp were often used as the fibrous material because of their low cost. However, recent increases in the output of automobile engines, downsizing of transmissions, etc. Therefore, the requirements regarding the heat resistance of the wet friction material are becoming strict. For this reason, it is disadvantageous to use only cellulose fibers that are inferior in heat resistance as the fibrous material of the wet friction material base. Rather, pulp obtained by highly fibrillating para-type aramid fibers with excellent heat resistance is used. As a main material, in some cases, it has become mainstream to use a combination of such heat-resistant organic fibers and cellulose fibers.

  However, organic fiber pulp typified by para-type aramid fiber has a problem that its surface is chemically inactive, and therefore has a lower adhesive force with a binder resin typified by phenol resin than cellulose fiber. That is, when organic fiber pulp is used as a wet friction material, the present situation is that it cannot sufficiently meet the demands for mechanical properties such as shear characteristics and durability.

In view of such a current situation, in order to improve the adhesion between the paper base material and the binder resin, a means of blending a large amount of cellulose fibers in the composite material is mentioned as an improvement method. Since it falls, it was difficult to make resin adhesiveness and heat resistance compatible.
As a method for overcoming this problem, Japanese Patent Laid-Open No. 9-302105 (Patent Document 3) reports a method of adding bacterial cellulose as a part of a fiber reinforcing material to a friction material. In this method, bacterial cellulose has a smaller fiber diameter and a larger specific surface area than wood pulp and linter pulp, so the contact area with the binder resin is increased by adding a small amount of bacterial cellulose. The improvement of adhesiveness can be expected. However, this report is not intended to improve the adhesive strength with the binder resin and the mechanical properties. Furthermore, although bacterial cellulose is a material that tends to be entangled in a complicated manner because of its thin fiber diameter, a method for uniformly dispersing it has not been sufficiently studied.

  As described above, there is no prior art regarding means for improving the mechanical properties of wet friction materials represented by shearing characteristics by improving the adhesion between the paper base material and the binder resin without impairing the heat resistance. It can be said that there was not enough knowledge.

Japanese Examined Patent Publication No. 58-47345 Japanese Patent Laid-Open No. 11-201206 JP-A-9-302105

  The present invention is a wet friction material obtained by impregnating a binder resin with a paper-like base material in which bacterial cellulose is uniformly dispersed, and has excellent adhesion to the binder resin without impairing heat resistance. The present invention provides a wet friction material excellent in mechanical properties such as shear characteristics and a method for producing the same.

  The inventors of the present invention have made extensive studies on a method for improving the mechanical properties of the wet friction material by improving the adhesion between the paper-like base material and the binder resin without impairing the heat resistance. As a result, it has been found that mechanical properties such as shear properties are greatly improved by adding a small amount of bacterial cellulose.

  However, bacterial cellulose itself is very entangled, and bacterial cellulose aggregates and localizes on a part of the paper substrate simply by adding it to the paper material. In addition to unevenness in the adhesive strength of the material with the binder resin, there was a problem that unevenness occurred in the physical properties (shear strength) of the wet friction material.

  Therefore, as a result of further studies, the culture solution containing bacterial cellulose that has been purified without washing the bacterial cellulose that has been cultured in the culture solution, without being purified, or purified by washing with alkali without purification. Was added to a slurry containing organic fiber pulp to make paper, and it was found that entanglement between bacterial celluloses can be suppressed and a paper-like substrate in which bacterial cellulose is uniformly dispersed can be obtained. As a result, not only the effect of improving the adhesive force between bacterial cellulose and the binder resin is sufficiently exhibited even with a small amount of blending, but also a wet friction material with uniform mechanical properties can be obtained, and the present invention has been achieved. .

  Thus, according to the present invention, there is provided a wet friction material obtained by impregnating a binder resin with a paper-like substrate in which bacterial cellulose is uniformly dispersed, and the adhesiveness with the binder resin is reduced without impairing heat resistance. A wet friction material excellent in mechanical properties such as excellent shear properties and a method for producing the same are provided.

  That is, the invention according to claim 1 of the present invention is a wet friction material, and is a paper-like material obtained by making a slurry containing organic fiber pulp, bacterial cellulose and inorganic filler obtained by fibrillating organic fibers. A wet friction material characterized in that the bacterial cellulose is dispersed as uniformly as possible in the paper-like material as a base material. The wet friction material of the present invention has the advantages of excellent adhesion to the binder resin and excellent mechanical properties such as shear properties without impairing heat resistance.

  The invention according to claim 2 is the invention according to claim 1, wherein the fibrillated organic fiber to be the organic fiber pulp is at least one selected from the group consisting of aromatic polyamide fiber, aromatic polyester fiber and polybenzazole fiber. It is a wet friction material specified to contain seeds. This fiber pulp is suitable for a wet friction material because of its inherently high mechanical strength and excellent heat resistance.

  The invention according to claim 3 is the invention according to claim 1, wherein the content of bacterial cellulose in the paper-like material is specified in the range of 0.5 to 10% by weight.

  The invention according to claim 4 is a method for producing a wet friction material, wherein bacterial cellulose cultured in a culture solution is purified as it is without being dried in a culture solution containing bacterial cellulose, or washed with an alkali. A culture solution containing bacterial cellulose is prepared, and then the culture solution is mixed with a component containing organic fiber pulp and an inorganic filler to prepare a slurry. The present invention relates to a production technique in which a binder resin is impregnated and then pressed and cured by hot pressing.

  According to the present invention, a paper-like material in which bacterial cellulose is uniformly dispersed is obtained from a slurry obtained by mixing a dispersion of bacterial cellulose and a component containing organic fiber pulp and various inorganic fillers. By using it as a base material, a wet friction material having excellent mechanical properties such as tensile shear strength can be obtained, which is particularly useful as a clutch facing of a power transmission system in a transmission such as an automobile.

Hereinafter, embodiments of the present invention will be described in detail.
The wet friction material of the present invention is based on a paper-like material obtained by making a slurry containing organic fiber pulp, bacterial cellulose and inorganic filler obtained by highly fibrillating organic fibers.

Here, the organic fiber pulp referred to in the present invention refers to an organic fiber having a rigid molecular structure fibrillated by means such as a refiner, beater, mill, high-pressure homogenizer, and grinding device. The degree of fibrillation, which has been relatively highly fibrillated, preferably ^{3m 2} / ^g~20m 2 / g in specific surface ^area, 5m ² / ^g~15m 2 / g is more preferable. Thus, organic fiber pulp relatively highly fibrillated can be preferably used.

  As the organic fibers in the present invention, liquid crystalline polymer fibers having a high degree of molecular orientation are preferable, and aromatic polyamide fibers, aromatic polyester fibers, and polybenzazole fibers can be particularly preferably used. These liquid crystalline polymer fibers are suitable in terms of mechanical strength, heat resistance, and ease of fibrillation.

  As aromatic polyamide fibers, poly-p-phenylene terephthalamide, poly-p-benzamide, poly-p-amide hydrazide, poly-p-phenylene terephthalamide-3,4-diphenyl ether terephthalamide, etc. are spun into fibers. Although what can be illustrated can be illustrated, it is not limited to these.

  The aromatic polyester is synthesized by combining monomers such as aromatic diol, aromatic dicarboxylic acid, and aromatic hydroxycarboxylic acid, and changing the composition ratio. For example, a copolymer of p-hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid can be mentioned, but it is not limited to this. The aromatic polyester fiber is a fiber obtained by spinning such a polymer.

  In addition, polybenzazole fibers can be obtained by spinning a random, sequential or block copolymer with polybenzazoles containing poly-p-phenylenebenzobisoxazole (PBO) homopolymer and substantially more than 85% PBO component. It is made into fiber.

  In this invention, it is also possible to mix | blend and use another pulp component in the said organic fiber pulp. Cellulose fibers such as linter pulp and wood pulp, organic fibers such as meta-aramid fibers, acrylic fibers, polyimide fibers, polyamide fibers, glass fibers, rock wool, potassium titanate fibers, silica fibers, alumina fibers, metal fibers, etc. Inorganic fibers can be used in combination as a fibrous material. As a paper-like material base, it is used in an appropriate amount within a range that does not impair mechanical strength and heat resistance.

  The inorganic filler in the present invention is added for the purpose of friction adjustment, solid lubrication, etc., for example, barium sulfate, calcium carbonate, magnesium carbonate, silicon carbide, titanium carbide, alumina, silica, cashew dust, diatomaceous earth, graphite, talc, kaolin, An appropriate amount of one or more kinds of magnesium oxide can be used at the same time.

  Bacterial cellulose in the present invention refers to bacterial cellulose produced by microorganisms. This bacterial cellulose contains cellulose and a heteropolysaccharide having cellulose as the main chain, and also contains glucan such as β-1,3 or β-1,2. In the case of heteropolysaccharides, constituents other than cellulose are hexoses such as mannose, fructose, galactose, xylose, arabinose, rhamnose, glucuronic acid, pentoses, organic acids, and the like. These polysaccharides may be composed of a single substance, but may be composed of two or more kinds of polysaccharides bonded together by hydrogen bonds or the like, and any of them can be used.

  Examples of microorganisms that produce bacterial cellulose in the present invention include Acetobacter aceti subsp. (Sarcina ventriculi), Bacterium xyloides, Judemonas bacteria, Agrobacterium bacteria and the like that produce bacterial cellulose can be used, but are not limited thereto.

  As a method for culturing bacterial cellulose, first, a culture solution in which a cellulose-producing bacterium is added to a medium containing monosaccharides such as fructose, minerals, and the like is produced under conditions optimal for the growth of bacterial cellulose. Cellulose-producing bacteria are usually aerobic, so during cultivation, the incubator can be mechanically agitated and shaken, or air or oxygen can be bubbled with a pump or other means to produce bacterial cellulose. Therefore, it is necessary to keep the culture solution and oxygen in contact with each other.

  At this time, if the organic fiber pulp is added to the culture solution and bacterial cellulose is produced in the presence of the organic fiber pulp, the viscosity of the dispersion is significantly increased by adding the organic fiber pulp. Due to bubbling or the like, oxygen cannot be sufficiently supplied to the culture solution, which may inhibit the production of bacterial cellulose. Insufficient supply of oxygen will stop bacterial cellulose production in some cases. Further, since the viscosity of the dispersion is increased, the produced bacterial cellulose is easily aggregated and easily entangled, and it is difficult to obtain a culture solution with less entanglement between bacterial celluloses intended in the present invention. The mixing with the organic fiber pulp is preferably carried out after the cultivation is completed.

In addition, even when culturing in a culture solution that does not contain organic fiber pulp, there is a concern that bacterial cellulose is intertwined in a complicated manner and dispersed bacterial cellulose cannot be obtained. For example, water-soluble polymers represented by agar and polyvinyl alcohol Is added as a dispersion stabilizer in an amount that does not hinder the physical properties of bacterial cellulose and its subsequent use, whereby a bacterial cellulose culture solution with less entanglement can be obtained.
The obtained culture broth containing bacterial cellulose can be used as it is, but since the culture broth contains cellulose-producing bacteria, waste products thereof, etc., it is desirable to purify by washing with alkali.

  General bacterial cellulose produced by cellulose-producing bacteria usually has a fiber diameter of 10 to 100 nm and a fiber length of 0.1 to 100 μm. However, other than these fiber diameters and fiber lengths, the wet friction material can be used.

Next, the manufacturing method of this invention is demonstrated.
In the method for producing a wet friction material in the present invention, first, a fibrous material containing at least organic fiber pulp, one or more inorganic fillers, and a slurry made of bacterial cellulose are prepared. By sufficiently disaggregating using a known stirrer such as a disaggregator, a slurry in which each component is uniformly dispersed can be obtained.

  In order to disperse the bacterial cellulose uniformly in the slurry, the bacterial cellulose cultured in the culture solution is not dried, but the bacterial culture solution containing the bacterial cellulose is purified as it is or washed with an alkali and purified. It is necessary to add culture medium.

  In general, bacterial cellulose has a high affinity with water, and thus has good dispersibility in water. However, since bacterial cellulose is very thin and fine, it easily aggregates and is intertwined in a complex manner. In particular, it is very difficult to uniformly disperse bacterial cellulose produced in a film or dried bacterial cellulose into water or the like again even if a strong stirring or shearing action is applied from the outside. As a result, it is very difficult to obtain a paper-like material in which the bacterial cellulose targeted in the present invention is uniformly dispersed. Therefore, it is important to prepare a slurry based on the above means.

Next, a process of making this slurry by using a known paper making apparatus to obtain a paper-like material will be described.
When manufacturing this paper-like material, the composition ratio of the fibrous material and the inorganic filler in the paper-like material is 20 to 80% by weight for the fibrous material and 20 to 80% by weight for the inorganic filler as described above. Is desirable. The bacterial cellulose content in the paper is preferably 0.5 to 10% by weight. The reason is that bacterial cellulose is very fine, so if it is added in a large amount, clogging is likely to occur when it is made with a known paper making apparatus, resulting in a longer drainage time and the workability of paper making. This is because remarkably decreases. Furthermore, when a wet friction material is produced using a paper-like material obtained by adding a large amount of bacterial cellulose, the heat resistance of the wet friction material itself is impaired because the bacterial cellulose component having low heat resistance increases. .

The obtained paper substrate can be impregnated with a binder resin such as a phenol resin, and pressurized and cured by hot pressing to obtain a wet friction material.
As described above, according to the method of the present invention, bacterial cellulose can be uniformly dispersed in a fibrous material containing organic fiber pulp, one or more inorganic fillers, and a paper-like material made of bacterial cellulose. Furthermore, a wet friction material having excellent mechanical properties and heat resistance can be obtained by impregnating the paper base material with a binder resin.

  Therefore, the composition ratio of the fibrous material and the inorganic filler in the paper-like material is 20 to 80% by weight for the fibrous material, 20 to 80% by weight for the inorganic filler, and 0.5 to 10% by weight for bacterial cellulose. It is in a uniformly dispersed state. Thus, in the present invention, the paper-like product has a composition of organic fiber pulp / inorganic filler / bacterial cellulose (weight ratio) = 20-80 / 80-20 / 0.5-10. . Furthermore, the blending ratio of the binder resin is in the range of 20 to 70% by weight with respect to the paper. However, if there is no problem in the performance and physical properties of the wet friction material, the composition range may deviate somewhat.

A supplementary explanation will be given on the most preferred embodiment of the present invention.
Organic fiber represented by aromatic polyamide, organic fiber pulp obtained by fibrillating to a specific surface area of about 3 m ² / g to ²⁰ m ² / g, an inorganic filler, and bacterial cellulose, 20 to 80:80 to A slurry containing 20: 0.5 to 10 (weight ratio) is used, and a paper-like material obtained by making this slurry is used as a base material, and 20 to 70% by weight of a binder resin is blended with respect to this paper-like material. And it is the wet friction material formed by pressurizing and hardening by a hot press.

And, this bacterial cellulose is uniformly dispersed in the paper-like material, so that the adhesiveness is improved and the heat resistance and durability are improved.
The present invention will be specifically described below based on examples. However, the present invention is not limited to these examples.

[Example 1]
(Bacterial cellulose culture)
To a 200 ml Erlenmeyer flask, 40 g / L of a culture solution containing fructose as a main component and containing salts such as magnesium sulfate and water-soluble vitamins such as inositol was added. Thus, a culture solution was obtained. Furthermore, 0.2% by weight of agar was added to the culture solution as a dispersion stabilizer for bacterial cellulose. While maintaining the pH of this culture solution at pH 4-6 with acid and alkali, shaking culture was performed at 30 ° C. for 120 hours. At this time, the shaking speed was 180 rpm.

Thereafter, in order to remove cellulose-producing bacteria, waste products, and the like, the obtained culture solution was washed and purified with an alkali to obtain a bacterial cellulose dispersion.
The concentration of bacterial cellulose in this dispersion was calculated by dry weight method and found to be 3.9% by weight.

(Production of wet friction material)
In 2 liters of water, 60 parts by weight of pulp (trade name “Twaron 1097”, manufactured by Teijin Techno Products Co., Ltd.) made of para-type aromatic polyamide fibers as organic fiber pulp, diatomaceous earth (trade name “Radiolite #”) 200 "(manufactured by Showa Chemical Co., Ltd.) and 100 parts by weight of the bacterial cellulose dispersion obtained in the above step (3.9 parts by weight of bacterial cellulose) were added, and this was added to a JIS standard disintegrator. Was disaggregated at 3000 rpm for 3 minutes to obtain a slurry. Further, this slurry was made with a TAPPI square paper machine, press dehydrated, and then dried with a dryer at 120 ° C. for 2 hours to obtain a paper-like material with a basis weight of 300 g / m ² .

  The dispersion state of bacterial cellulose in the obtained paper can be observed with a microscope. In order to facilitate microscopic observation, bacterial cellulose may be selectively stained with a dye. Bacterial cellulose was very uniformly dispersed in the paper-like material obtained by the above paper machine.

Furthermore, the bacterial cellulose content in the obtained paper can be accurately known by thermogravimetric analysis of the paper.
That is, the thermal decomposition temperature of bacterial cellulose is 300 to 350 ° C., whereas para-type aromatic polyamide fiber pulp and diatomaceous earth are not decomposed at a temperature of 450 ° C. or lower, and weight loss does not occur. Therefore, in the thermogravimetric analysis of the paper-like material, the weight loss in the temperature range of 300 to 400 ° C. can be regarded as almost bacterial cellulose. The bacterial cellulose content in the paper material thus measured was 3.1% by weight. Therefore, the composition of the paper-like material in this example was organic fiber pulp / inorganic filler / bacterial cellulose = 58.1 / 38.8 / 3.1 (weight ratio).

  Next, the obtained paper-like material was immersed in a phenol resin ethanol solution having a concentration of 9% by weight obtained by diluting a liquid phenol resin (product number PR-53123, manufactured by Sumitomo Bakelite Co., Ltd.) with ethanol. And then dried at room temperature for 24 hours to obtain a prepreg. At this time, the impregnation amount of the phenol resin was 35% with respect to the paper-like material. Therefore, the composition of the friction material in this example was organic fiber pulp / inorganic filler / bacterial cellulose / binder resin = 43.0 / 28.7 / 2.2.3 / 26.0 (weight ratio).

Further, this prepreg was pressed at 180 ° C. for 5 minutes with a pressing machine at a surface pressure of 60 kg / cm ² , and further cured in an oven at 180 ° C. for 2 hours, so that the thickness was 0.55 mm and the basis weight was 400 g / m. ^2. A wet friction material having a porosity of 50% by volume was obtained.

[Comparative Example 1]
The bacterial cellulose dispersion obtained by culturing in the same manner as in Example 1 was separated by filtration, and the bacterial cellulose was taken out. Furthermore, this was dried at 80 degreeC and solid content of bacterial cellulose was obtained.
Next, a paper-like material was obtained in the same manner as in Example 1 except that 3.9 parts by weight of the solid content of bacterial cellulose was added instead of the bacterial cellulose dispersion.
As a result of thermogravimetric analysis of the paper-like material, the bacterial cellulose content in the paper-like material was 3.4% by weight.
Subsequently, a wet friction material having a thickness of 0.55 mm, a basis weight of 400 g / m ² , and a porosity of 50% by volume was obtained in the same manner as in Example 1.

[Comparative Example 2]
When cultivating bacterial cellulose, Twaron 1097 as organic fiber pulp was added to the culture solution at 15 g / L, and bacterial cellulose was cultured in the same manner as in Example 1. The bacterial cellulose / organic fiber pulp dispersion thus obtained was prepared so that the organic fiber pulp was 60% by weight, and a paper-like material was obtained in the same manner as in Example 1. As a result of thermogravimetric analysis of the paper-like material, the bacterial cellulose content in the paper-like material was 1.6% by weight.
Further, a wet friction material having a thickness of 0.55 mm, a basis weight of 400 g / m ² , and a porosity of 50% by volume was obtained in the same manner as in Example 1.

[Comparative Example 3]
A paper-like material was obtained in the same manner as in Example 1 except that 3.9 parts by weight of commercially available linter pulp was added instead of the bacterial cellulose dispersion.
As a result of thermogravimetric analysis of the paper-like material, the linter pulp content in the paper-like material was 3.8% by weight.
Subsequently, a wet friction material having a thickness of 0.55 mm, a basis weight of 400 g / m ² , and a porosity of 50% by volume was obtained in the same manner as in Example 1.

[Comparative Example 4]
A paper-like material and a wet friction material were obtained in the same manner as in Example 1 except that the bacterial cellulose dispersion was not added during the production of the paper-like material.
The resulting wet friction material had a thickness of 0.55 mm, a basis weight of 400 g / m ² , and a porosity of 50% by volume.

(Physical property measurement)
Various physical property measurements were performed on the samples obtained in Example 1 and Comparative Examples 1 to 4 according to the measurement methods described below.
(1) Dispersibility of bacterial cellulose in paper-like material 20 arbitrary positions of the obtained paper-like material were observed with a scanning electron microscope at a magnification of 10,000 times, and the dispersibility of bacterial cellulose in the paper-like material was observed. evaluated.
In addition, since the fiber diameter of bacterial cellulose is 10-100 nm and the fiber diameter is clearly thinner than “Twaron 1097” used as the organic fiber pulp, the bacterial cellulose can be easily discriminated.

(2) Tensile shear strength of wet friction material The tensile shear strength of the wet friction material obtained by the following test method and conditions was measured. The test piece obtained as described below was subjected to shear fracture of the wet friction material by fixing one end and pulling the other end vertically, and the tensile shear strength was measured.
Testing machine: INSTRON 5565 type (manufactured by INSTRON)
Test piece: One side of a wet friction material cut to 20 mm × 20 mm was bonded to the end of a 20 mm × 100 mm sandblast plate using a commercially available two-component epoxy adhesive. Subsequently, the other surface was similarly bonded to a sandblast plate with an adhesive to obtain a test piece.
Temperature: Distance between room temperature gauges: 25mm
Tensile speed: 10 mm / min

Table 1 shows the measurement results of dispersibility and shear strength of the samples of Example 1 and Comparative Examples 1 to 4 described above.

The dispersibility of bacterial cellulose in the paper was determined according to the following criteria and is shown in Table 1.
A: Bacterial cellulose was observable at 11 or more of the observed 20 locations, and the bacterial cellulose was uniformly dispersed and no aggregates were observed.
Δ: Bacterial cellulose was observed in 11 or more of the observed 20 locations, but aggregates of bacterial cellulose were observed therein.
X: Out of 20 observed locations, bacterial cellulose was observed at 10 locations or less, and aggregates of bacterial cellulose were observed therein.
-: No bacterial cellulose added

In Example 1, it was observed that bacterial cellulose was almost uniformly dispersed in the obtained paper. This is considered to be due to the fact that the bacterial cellulose is easily dispersed uniformly in the slurry by adding it in the state of a dispersion.
Moreover, the tensile shear strength evaluated as a mechanical characteristic improved about 30% compared with the comparative example 4 which did not add bacterial cellulose. This is considered to be due to the fact that by adding bacterial cellulose, the resin adhesion was improved due to the increased affinity between the phenolic resin as the binder resin and the paper substrate.

  In Comparative Example 1, the tensile shear strength was improved by about 15% compared to Comparative Example 4. However, although the bacterial cellulose content was almost the same as in Example 1, the tensile shear strength was low. This is probably because the bacterial cellulose aggregated in the paper-like material without being uniformly dispersible, and as a result, the effect of bacterial cellulose was not sufficiently developed. Actually, as a result of observing the paper-like material with a scanning microscope, many bacterial celluloses were observed to aggregate and exist on a part of the paper. For this reason, once dried bacterial cellulose solids are intricately entangled with each other, it is difficult to disperse them uniformly in the slurry by a normal disaggregation method, and it is necessary to apply higher agitation and shearing. It is believed that there is.

  In Comparative Example 2, the tensile shear strength was about 10% higher than that in Comparative Example 4, but when the paper-like material was observed with a scanning microscope, bacterial cellulose did not uniformly disperse and formed aggregates. Was observed. This is presumably because the bacterial cellulose was cultured in the presence of organic fiber pulp, so that the viscosity of the system increased significantly and the bacterial cellulose was not uniformly dispersed. Furthermore, despite the culture conditions similar to those in Example 1, the bacterial cellulose content in the paper was small. This is considered to be because the viscosity of the system was greatly increased, and it was impossible to sufficiently supply oxygen to the culture solution due to shaking, thereby inhibiting the production of bacterial cellulose.

  In Comparative Example 3, the tensile shear strength was the same as in Comparative Example 4. This is because linter pulp itself is a cellulosic material and has a high affinity with the binder resin, but the specific surface area is clearly smaller than that of bacterial cellulose. It is thought that it did not appear.

  As described above, it was recognized that the addition of bacterial cellulose improved mechanical properties such as tensile shear strength. Among them, paper-like materials were obtained by using a culture solution in which bacterial cellulose was dispersed. It was clarified that the dispersibility of bacterial cellulose in the medium was improved and the effect of the addition was expressed more efficiently.

[Examples 2 to 5]
In Example 1, except that the amount of addition of the bacterial cellulose dispersion was changed to 50 parts by weight, 200 parts by weight, 300 parts by weight and 400 parts by weight, respectively, the same conditions as in Example 1 were carried out. The paper-like material of Example 2, Example 3, Example 4, and Example 5 was obtained.
The content of bacterial cellulose in the obtained paper was 1.5% by weight, 6.1% by weight, 9.2% by weight and 11.9% by weight, respectively. In the case of Example 5 having a high content of bacterial cellulose, clogging occurred in the difference in papermaking, and the time required to obtain a paper-like product was longer than in Examples 1 to 4.

なお紙状物中におけるバクテリアセルロースの分散性の表記記号は表１と同様である。

The notation symbols for the dispersibility of bacterial cellulose in the paper-like material are the same as in Table 1.

  According to the present invention, a paper-like material in which bacterial cellulose is uniformly dispersed is obtained from a slurry obtained by mixing a dispersion of bacterial cellulose and a component containing organic fiber pulp and various inorganic fillers. By using it as a base material, a wet friction material having excellent mechanical properties such as tensile shear strength can be obtained, which is particularly useful as a clutch facing of a power transmission system in a transmission such as an automobile.

Claims (4)

  A wet friction material, which is based on a paper-like material obtained by making a slurry containing organic fiber pulp obtained by fibrillating organic fibers, bacterial cellulose and an inorganic filler, and the bacterial cellulose is contained in the paper-like material. Wet friction material characterized by being dispersed in   The wet friction material according to claim 1, wherein the fibrillated organic fiber to be an organic fiber pulp contains at least one selected from the group consisting of an aromatic polyamide fiber, an aromatic polyester fiber and a polybenzazole fiber.   The wet friction material according to claim 1, wherein the content of bacterial cellulose in the paper is 0.5 to 10% by weight.   Bacterial cellulose cultivated in a culture solution is left as a culture solution containing bacterial cellulose without drying, or a culture solution containing bacterial cellulose that has been purified by washing with alkali, and then the culture solution is treated with organic fiber pulp and A slurry is prepared by mixing with a component containing an inorganic filler, and the slurry is made into a paper to obtain a paper-like material. The paper-like material is further impregnated with a binder resin, and then pressed and cured by hot pressing. A method for producing a wet friction material.