JPH0712158A - Friction material - Google Patents

Abstract

PURPOSE:To make mechanical strength and a friction characteristic well- balanced and minimize the dispersion of various characteristics. CONSTITUTION:Friction material is formed of twist yarn formed by twisting glass fiber continuous yarn, containing admixture mainly composed of a friction conditioner and a binder, and glass fiber contiinuous yarn, mainly containing a binder, by the specified number. In this friction material, the continuous yarn mainly containing the binder has numerous micro cavities.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a friction material used for power transmission and braking of automobiles and industrial machines.

[0002]

Brake linings, disc pads and clutch facings are generally used as friction materials for automobiles and industrial applications. Conventionally, asbestos (asbestos) has been used as a fiber base material, but development of non-asbestos friction materials has been desired due to the problem of asbestos pollution. Further, in recent years, the use of organic solvents has been reconsidered from the viewpoints of the global environment, work environment, safety during production, and the like. At present, a friction material using a fiber base material such as glass fiber, carbon fiber, aromatic polyamide fiber, rock wool, ceramic fiber and various steel fibers has been developed and put into practical use as a substitute for asbestos. However, these materials are highly elastic and hard as compared with asbestos and have low heat resistance, so various friction modifiers are added to improve the properties, and in order to uniformly adhere the friction modifier to the base material, Generally, a mixture in which a friction modifier is dispersed in a solution in which a composition of rubber and a resin is dissolved in an organic solvent is used. In recent years, halogen-based organic solvents have been widely used in order to prevent combustion and explosion during manufacturing work.

On the other hand, the balance between the strength and the friction characteristics of the friction material has been examined in terms of the type and amount of the fiber base material or the type and amount of the friction modifier and the binder. However, even if the types and blending amounts of these various materials are examined, it is difficult to maintain the balance between the strength and friction characteristics of the friction material in an optimum manner. For example, a papermaking method or a molding method using a fibrous material as a fiber base material is known (Japanese Patent Laid-Open No. 61-63797 and Japanese Laid-Open Patent Application No. 3-210338).
No. Since this method is a method (a kind of molding method) of mixing a fiber base material cut into short pieces and an admixture, a mechanical strength is likely to be lowered. In addition, as a method of manufacturing a friction material using a water solvent, a friction modifier is surface-treated so as to easily adhere to a fiber base material (Japanese Patent Laid-Open No. 3-6).
However, the problem of keeping the balance between the strength and friction characteristics of the friction material in an optimum manner has not been solved yet.

That is, in order to increase the breaking strength at high speed rotation or the breaking strength at high load, it is sufficient to increase the amount of the binder, but if this amount is increased, there is a drawback that the friction coefficient decreases at high temperature. To prevent this, there are methods such as decreasing the amount of binder, increasing the porosity, and increasing the amount of friction modifier. In either case, breaking strength tends to decrease, and various properties should be balanced. Also, it is difficult to reduce the variation.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned drawbacks of the prior art, and to provide a friction material in which mechanical strength and friction characteristics are well balanced and variations in various characteristics are small. is there.

[0006]

According to the present invention, a continuous yarn containing a mixture containing a friction modifier and a binder as main components and a continuous yarn containing mainly a binder are twisted together in a predetermined number. The present invention relates to a friction material characterized in that a continuous yarn mainly composed of a twisted yarn having a number of fine voids is contained.

In the present invention, the continuous yarn is composed of inorganic fibers such as glass fibers, carbon fibers and ceramic fibers and organic fibers such as aromatic polyamide resin fibers, phenol resin fibers and polyacrylonitrile fibers, which may be used alone or Used together or in combination with metal fibers and the like. In particular, although the material thereof is not limited, it is preferable to mainly use glass fiber because it is easy to process, inexpensive, and versatile. Here, the continuous yarn refers to a bundle of dozens of strands obtained by bundling filaments having a diameter of several μm to several tens μm with a sizing agent.

The amount of the fibers constituting the continuous yarn in the friction material varies depending on the type of the fibers used. When glass fibers are used as the continuous yarn, the amount of the glass fibers depends on the balance and control of friction characteristics. From the standpoint of ease of use, it is preferable to add 30 to 60% by weight to the friction material.

In the present invention, the friction modifier is not particularly limited and various ones can be used, for example, calcium carbonate, magnesium carbonate, zinc oxide, barium sulfate, clay, talc, carbon black, graphite. Powders of inorganic materials such as alumina, mica, fluorite, zirconia, hematite, silica, antimony sulfide, iron sulfide, molybdenum sulfide and sulfur, powders of metals such as iron, lead and copper, cashew dust, rubber dust, cured products of various resins Powders of organic substances such as powders of calcium carbonate and short fibers of calcium silicate are used.

The binder used in the present invention is not particularly limited, and various thermosetting resin compositions and / or rubber latex can be used. The thermosetting resin composition, phenol resin, methylated melamine resin, melamine resin, urea resin, polyamideimide resin,
Examples thereof include resin compositions such as polyimide resins and epoxy resins, and among these, phenol resin compositions and methylated melamine resin compositions are preferable. The amount of the thermosetting resin composition is generally in terms of the binding force to the fiber base material and the friction modifier, and the friction coefficient and the coefficient of friction of the friction material to adjust the friction material as a solid content relative to the friction material. 10-50% by weight
The amount contained is preferable. Further, as the rubber latex, a crosslinkable rubber latex is used, for example,
Examples thereof include nitrile butadiene rubber, acrylic rubber, natural rubber and chloroprene rubber. Generally, the amount of the rubber latex is preferably such that 5 to 20% by weight as a solid content is contained in the obtained friction material.

In addition to the above components, the friction material of the present invention may contain various additives, such as a dispersant, a flexibilizer, and a surfactant, if necessary. In particular, when an admixture is prepared with an aqueous solvent without using an organic solvent and a continuous yarn is impregnated with the mixture to prepare a coated cord, it is preferable to appropriately utilize the above-mentioned additives. . in this case,
A water-soluble polymer resin is mainly used as the dispersant.
As such a resin, methyl cellulose, carboxymethyl cellulose, polyvinyl pyrrolidone, polyvinyl alcohol, polyvinyl methyl ether, polyvinyl ethyl ether, etc., which generally have a thickening effect, are used. The amount of the dispersant added is preferably 10% by weight or less with respect to the friction material in terms of friction coefficient and mechanical strength, and is preferably 20% by weight or less in the total amount of the admixture.

As the flexibilizer, a substance which is compatible with the water-soluble polymer resin and does not affect the frictional properties is preferable, and glycols are preferable. The flexibilizer is for improving the molding processability of the prepreg coated with the admixture, and is scattered during molding and post-curing so that it does not exist in the friction material of the actual machine as much as possible. preferable. Suitable flexibilizers include, for example, lower glycols such as ethylene glycol, propylene glycol and diethylene glycol. The addition amount depends on the kind of the dispersant, but is 80 to 20% by weight based on the dispersant.
Is preferred.

The surfactant is used for enhancing the dispersion effect of the friction modifier and the stability of the dispersant and is not particularly limited, but anionic surfactant or nonionic surfactant is preferable as the effective surfactant. Used. It is preferable to use nonionic polyethylene glycol. Usually, the amount of the surfactant added is preferably 1 to 2% by weight based on the solid content of the mixture.

The present invention is to produce a friction material by appropriately combining the above-mentioned various materials to produce two kinds of coated cords and processing a twisted yarn in which a predetermined number of them are twisted together. One is a coated cord impregnated with a mixture of the above-mentioned various materials, and the other is a coated cord mainly impregnated with a binder.

As a method for impregnating and coating a mixture containing various materials on a continuous yarn, there are a doctor blade method, a roll coater method, a spraying method, an extrusion coating method using a metering pump, a dip impregnation method, and the like. The dip impregnation method is suitable for substantially uniformly impregnating. As a concrete measure for substantially uniformly impregnating the continuous yarn with the mixture, a method of sufficiently opening the continuous yarn, immersing the continuous yarn in the slurry of the mixture, impregnating it, and then pulling it up or shaking in the slurry Although there is a method of impregnating the continuous yarn substantially uniformly, the method of opening the fiber and the method of impregnation are not particularly limited.

In order to produce a continuous yarn containing mainly a binder, for example, a binder solution may be applied in a predetermined amount by a method such as a roll coater method, a spraying method or a dipping impregnation method. Is not meant to be limited.

Specifically, for example, the following method can be used to obtain the friction material. A thermosetting resin powder as a binder is dispersed and dissolved in water or an organic solvent. At this time, if necessary, a dispersant, a flexibilizer or a surfactant is added. Next, a friction modifier is added to prepare a uniform dispersion, and rubber latex and water for adjusting the solid content are further added and mixed with stirring to obtain a mixture. The obtained mixture is uniformly applied to a continuous yarn such as glass roving to obtain a coated product, and a volatile component of the coated product is removed by drying or the like to obtain a coated string A.
The method for applying the mixture is not particularly limited,
Dip impregnation is preferred. The method of removing water as a solvent is not particularly limited, but it is necessary to take care so that the resin component in the mixture does not harden.

Separately, an aqueous solution of a binder or a solution in an organic solvent is impregnated with the continuous yarn, or an aqueous dispersion of the binder is uniformly applied and impregnated on the continuous yarn to prepare a coated string B. Next, a predetermined number of these two types of coated cords are twisted together to form a coated twisted yarn, and the coated twisted yarn is further wound into a ring to obtain a preform. The obtained annular body is put in a mold or the like for thermocompression molding, and then the molded product is heat-treated under predetermined heating conditions to completely cure the resin, whereby a friction material having a desired shape can be obtained.

In the above method, the ratio of the fibrous base material to the admixture in the coated product is preferably 30/70 to 60/40 by weight of the fibrous base material / admixture (solid content). If the adhering amount of the admixture is too large, the mechanical strength of the friction material decreases, and if the adhering amount of the admixture is small, the friction characteristics become unstable, the wear increases, and the strength decreases due to the change with time of friction.

[0020]

The friction material according to the present invention comprises a continuous yarn (fiber base material), a friction modifier, a binder (thermosetting resin composition), a rubber latex, a dispersant, a flexibilizer and a surfactant. It is a composite material. The properties required of the friction material include not only friction performance but also mechanical strength, wear resistance and the like. It is important that these properties always show stable and constant values.To this end, one fiber base material is uniformly impregnated with a mixture such as a friction modifier, and The base material is firmly adhered with a binder, but it is an essential requirement that uniform voids are generated due to the volume reduction accompanying drying. A predetermined number of the above two kinds of fiber base materials are twisted together and molded, and then a base material mainly containing a binder and voids are formed around the base material, and the voids play a role of absorbing a liquid substance generated at a high temperature. This prevents the friction coefficient from decreasing at high temperatures. Since the continuous yarn in which the admixture is uniformly impregnated is a strong composite material, the breaking strength and the abrasion property are good. Further, the binder is mainly impregnated, and the continuous yarn that creates voids has the fibers bonded to each other with the binder having excellent adhesive strength, so that the breaking strength is not significantly reduced.

[0021]

EXAMPLES Next, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

The materials used in the following examples and comparative examples are as follows. The continuous yarn is glass roving (manufactured by Fuji Fiber Glass, 1.8 g / m). The friction modifier is zinc oxide (made by Wako Pure Chemical Industries, for chemicals) 2% by weight, barium sulfate (Sakai Chemical Co., BC) 40% by weight, carbon black (Mitsubishi Carbon, # 44) 6
% By weight, graphite (made by ABRAMWELL in the UK) 3% by weight, silica powder (made by Tatsumori, crystallite) 10% by weight, calcium silicate short fibers (made by NYCO in the United States, trade name Wollastonite)
20% by weight, 14% by weight of cashew-modified friction dust (manufactured by Cashew Co., Ltd., WD-1350) and 5% by weight of finely divided sulfur (manufactured by Hosoi Chemical Co., Ltd.) were uniformly mixed with a V-type blender.

The thermosetting resin composition as the binder is a novolac phenol resin (HD-49 manufactured by Hitachi Chemical Co., Ltd.).
1, containing 7% by weight of hexamine) and a methylated melamine resin (manufactured by Nippon Carbide, S-260). The rubber latex is NBR latex (manufactured by Zeon Corporation, LX51
3, solid content 45% by weight). The dispersant is polyvinyl alcohol (manufactured by Wako Pure Chemical Industries, polymerization degree: 1500) 10
A weight% aqueous solution was used. Ethylene glycol (manufactured by Wako Pure Chemical Industries, for chemicals) was used as the flexibilizer. As the surfactant, polyethylene glycol nonylphenol (Emulgen 910, manufactured by Kao Kagaku) was used. Ion-exchanged water was used as the solvent.

Example The above materials were mixed in the following order according to the composition of the mixture shown in Table 1 to prepare a mixture. That is, a thermosetting resin composition, a flexibilizer and a surfactant were added to a polyvinyl alcohol aqueous solution as a dispersant, and the mixture was stirred and mixed with a high speed mixer to obtain a uniform solution. Then, a friction modifier was added and stirred to uniformly disperse. After that, the stirring was changed to propeller stirring, and while adding rubber latex and stirring, a solvent for solid content adjustment was added so that the solid content was 50% by weight and stirred to obtain a mixture having the composition shown in Table 1. Obtained.
Separately from this, the materials were mixed in the following order according to the binder composition of the recipe shown in Table 1 to obtain a binder composition. That is, a melamine resin was uniformly dispersed in ion-exchanged water and dissolved, and then a phenol resin was added and mixed to obtain a uniform binder dispersion.

After the continuous yarn was sufficiently opened to uniformly impregnate the mixture or the dispersion liquid of the binder, it was dried under the conditions shown in Table 2 to obtain a coated cord A and a coated cord B. It was The three coated strings A thus obtained and one coated string B were twisted together and then rolled up in a ring to obtain a preform. The obtained annular body was put into a mold and subjected to thermocompression molding, and then the molded product was heat-treated at 220 ° C. to post-cure the resin to obtain a friction material. The porosity of the coated string B coated with the binder was 37% when calculated from the density, volume and weight of the material.

[0026]

[Table 1]

[0027]

[Table 2]

Comparative Example After only four coated strings A produced in the above examples were twisted together, molding and heat treatment were carried out in the same manner as in the examples to produce friction materials.

The coated strings A and B produced in the examples and the friction materials produced in the examples and the comparative examples were evaluated as follows, and the results are shown in Table 3. (A) Drying property of coated string Each of the coated strings A and B is dried at 170 ° C. for 30 minutes,
The dryness is evaluated by obtaining the volatile content. Evaluation was performed using three samples each. (B) Appearance of coated string It was visually observed. (C) Mixture distribution in the coated cord About 1 m of the coated cord was torn vertically, and the distribution of the admixture on the surface and inside was visually observed and evaluated.

(D) Appearance of friction material The surface of the friction material is ground and the appearance is visually observed when the thickness is 3.5 mm. (E) Wear rate A part is cut out from the friction material to make a test piece, and JIS-D
It is installed in a constant-speed wear tester specified in 4411 for operation, and pressed at a pressure of 4.9 × 10 ⁵ Pa (5 kgf / cm ² ) for 3
The wear rate (cm ³ / kgf · m × 10 ⁻⁷ ) at 50 ° C. is measured. (F) Burst strength The friction material was attached to the rotary fracture strength tester and the ambient temperature was set to 2
Rotation was performed at 2500 rpm for 5 minutes at 00 ° C., and then the rotation speed was increased at a speed of 100 rotations per second, and the rotation speed at break was examined. (G) Friction coefficient Measured at 300 ° C.

[0031]

[Table 3]

As is clear from the results shown in Table 3, the distribution of the admixture in the coated cords produced in Examples and Comparative Examples is uniform, the appearance of the friction material is good, and the burst strength and the wear rate are high. There was no difference between the two, but 30
With respect to the friction coefficient at 0 ° C., the friction materials produced in the examples of the present invention showed uniformly high values of 0.27 to 0.30, but those produced in the comparative examples were 0.18 to The variation was as large as 0.25, and the value was also small.

[0033]

The friction material according to the present invention has a burst strength,
It is excellent in both wear rate and friction coefficient at high temperature, has a high level of balance between mechanical strength and friction characteristics, and has little variation in various performance values. Therefore, the friction material of the present invention can be effectively used for a power transmission device, a braking device and the like in an industrial machine of an automobile. Further, since the friction material according to the present invention does not require the use of an organic solvent in the production, it does not pollute the global environment or the work environment and is excellent in work safety.

Claims (1)

[Claims] 1. A twisted yarn obtained by twisting a predetermined number of continuous yarns containing a mixture containing a friction modifier and a binder as main components and continuous yarns containing the binder, mainly comprising the binder. A friction material characterized in that the continuous yarn contained therein has a large number of fine voids.