JP5407083B2 - Wet friction material - Google Patents

Description

  The present invention relates to a wet friction material, and more particularly to a wet friction material such as a brake and a clutch used in oil in industrial machines, railway vehicles, luggage vehicles, passenger cars and the like.

As the wet friction material, the paper friction material based on organic fibers is the mainstream, blending aramid fiber with pulp for the purpose of increasing the strength of the base material, and papermaking what blended various materials as a friction modifier, It is produced by impregnating and curing a phenol resin.
Reference Document 1 includes a friction material base material having a three-layer structure in which a woven fabric is interposed between dry nonwoven fabrics, the surface is filled with a friction modifier, and the entire three layers are impregnated with a thermosetting resin. Disclosure of compression-molded wet friction material, and description of improving the dynamic friction coefficient and static-dynamic ratio by managing the basis weight of the friction material base material in the wet friction material, the porosity and pore diameter of the final finished friction material Has been.
Cited Document 2 discloses a paper-based wet friction material containing 5 to 10% by volume of a fiber ball in a small spherical shape in which fibers are randomly entangled to prevent seizure and delamination of paper fibers. The material has been described to prevent the above and improve the durability.
However, it is difficult for wet friction materials to control the change in friction coefficient in continuous use, and it is necessary to develop a technique for improving the friction coefficient stability (durability) in continuous use.
JP-A-7-280008 JP-A-7-180736

  An object of the present invention is to provide a wet friction material having excellent durability.

  The present invention is a wet friction material comprising a binder, pulp, aramid fiber, and a flame resistant fiber having a PAN-based fiber as a precursor and flameproofed at 200 to 300 ° C. in an oxidizing atmosphere, the aramid fiber, It is a wet friction material containing 5.6 / 1 to 1/3 in the former / the latter (mass ratio) with the flame resistant fiber.

  The present invention can provide a wet friction material having excellent friction coefficient stability in continuous use. Moreover, this invention can provide the wet friction material with few thickness changes in continuous use.

The wet friction material of the present invention is a wet friction material comprising a binder, pulp, aramid fibers, and flame resistant fibers that are flame resistant at 200 to 300 ° C. in an oxidizing atmosphere using a PAN-based fiber as a precursor, The aramid fiber and the flame resistant fiber are contained in the former / the latter (mass ratio) of 5.6 / 1 to 1/3.
According to the present invention, it is considered that the existence probability of pores having a large diameter can be increased by the above-described configuration, the oil absorption / extraction property is improved, the cooling effect of the wet friction material is improved, and the durability is improved.
The flame resistant fiber used in the present invention will be described.
This flame-resistant fiber is obtained by making flame resistant at 200 to 300 ° C. in an oxidizing atmosphere, for example, air, using a PAN-based fiber as a precursor.
Here, the PAN-based fiber means a fiber made of a homopolymer or copolymer of acrylonitrile or a mixed polymer of these polymers. Monomers that can be copolymerized include (meth) acrylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, and chloride. Vinyl halides such as vinyl, vinyl bromide, vinylidene chloride, acids such as (meth) acrylic acid, itaconic acid, crotonic acid and their salts, maleic imide, phenylmaleimide, (meth) acrylamide, styrene, α -Polymerizable unsaturated monomer containing a sulfo group such as methylstyrene, vinyl acetate, sodium styrene sulfonate, sodium allyl sulfonate, sodium β-styrene sulfonate, sodium methallyl sulfonate, 2-vinyl pyridine, 2- Polymerizable unsaturated compounds containing pyridine groups such as methyl-5-vinylpyridine Although 1 or more types, such as a summon monomer, are mentioned, it is not limited to these. (Meth) acrylic acid means one or two selected from acrylic acid and methacrylic acid. (Meth) acrylate is the same as above.
In addition, the flame resistant fiber used in the present invention preferably has a LOI (limit oxygen index) of JIS K7201 of 50 to 60 in order to ensure heat resistance.

In the wet friction material of the present invention, in addition to pulp, an aramid fiber and the flame resistant fiber are 5.6 / 1 to 1/3 in the former / the latter (mass ratio), preferably 5/6 to 6/5. More preferably, it is 1/1.
By setting the above range, the flame resistant fiber is interposed between the aramid fiber and the pulp, so that the pores of the wet friction material can be secured and the mechanical strength of the wet friction material can be improved. It is effective to demonstrate.
The size and the amount of the flame resistant fiber used to make the above effect more effective are as follows. The flame resistant fiber preferably has a fiber diameter of 10 to 20 μm and a fiber length of 0.8 to 1.5 mm.
The flame resistant fiber is preferably blended in an amount of 5 to 35% by mass with respect to the entire wet friction material.

The aramid fiber used in the present invention means an aromatic polyamide fiber, and includes polyparaphenylene terephthalamide fiber, polymetaphenylene terephthalamide fiber, polyparaphenylene isophthalamide fiber, polymetaphenylene isophthalamide fiber, diaminodiphenyl ether and Examples thereof include fibers obtained from a condensate with terephthalic acid or isophthalic acid.
The aramid fiber preferably has a fiber diameter of 15 to 20 μm and a fiber length of 0.6 to 1.2 mm. By setting it as the said range, it becomes easy to interpose a flame-resistant fiber between aramid fibers as mentioned above, and is effective in exhibiting the effect of the present invention.
The pulp used in the present invention preferably has a fiber diameter of 20 to 30 μm and a fiber length of 0.8 to 1.2 mm. By setting it as the said range, it becomes easy to interpose a flame-resistant fiber between pulp as mentioned above, and is effective in exhibiting the effect of this invention.
The pulp is not particularly limited as long as it is mainly composed of cellulose fibers, and examples thereof include those obtained from cotton, wood, grass, straw, bamboo and the like, and examples thereof include linter pulp.

Examples of the binder used in the present invention include thermosetting resins such as phenol resins (including various modified phenol resins such as straight phenol resins and rubbers), melamine resins, epoxy resins, polyimide resins, and polyamide resins. .
The binder is preferably blended in an amount of 25 to 45 mass% with respect to the entire wet friction material.

The wet friction material of the present invention can be composed of only the above-mentioned binder and the above-mentioned specific various fibers, but preferably contains other combined components.
Examples of the friction modifier as a combination component include, for example, metal oxides such as alumina, silica, iron oxide, magnesia, zirconia, chromium oxide, and molybdenum dioxide, organic substances such as synthetic rubber and cashew resin, copper, aluminum, and zinc. Examples thereof include metals, minerals such as vermiculite and mica, salts such as calcium carbonate, graphite, hard porous carbon materials, coke and the like, and these can be used alone or in combination of two or more. These are used as a powder or the like, and various particle sizes are selected. The hard porous carbon material is obtained by firing a mixture of rice bran, rice bran, rice husk, soybean hulls and other potatoes and a thermosetting resin such as phenol resin (including those mentioned above), furan resin, melamine resin, etc. Can be formed. The friction modifier is usually used in an amount of 30 to 55 mass% with respect to the entire friction material.

  The wet friction material of the present invention can be produced by blending each of the above components except the binder, papermaking, impregnating the binder with the binder, drying and then heat-curing.

  Hereinafter, the present invention will be described specifically by way of examples. However, the present invention is not limited to only these examples.

Examples 1 to 5 and Comparative Example 1
Papers were prepared by blending materials excluding the binders of the raw material composition (mass%) shown in Table 1. In Comparative Example 1, the flame resistant fiber is removed. A paper product was impregnated with a binder so that the impregnation ratio of the binder was 25 to 31% by mass and dried, and placed on a plate. Shim thickness: 1.6 mm, 160 ° C., 2 minutes, 6 MPa, then And heated at 220 ° C. for 20 minutes to prepare a wet friction material having a thickness of 0.4 mm. The binders in Table 1 show the average impregnation rate (mass% with respect to the paper-made product).

Details of the materials are as follows.
Flame resistant fiber: PAN (acrylonitrile homopolymer) made flame resistant, having a fiber diameter of 10 μm and a fiber length of 1 mm.
Aramid fiber: Fiber diameter is 12-15 μm, fiber length is 1.2 mm.
The hardness and pore distribution of the obtained wet friction material were measured by the following methods. Moreover, the durability test of this wet friction material was implemented.
(hardness)
An automatic hardness meter manufactured by Akashi Seisakusho Co., Ltd. (model: ARK-F3000) was used, and the scale was measured with a flat indenter of HRV and Φ5. The results are shown in Table 1.
(Pore distribution)
Log differential pore volume distribution [dV / dLogD] against pressure was measured using a mercury intrusion pore distribution measuring device manufactured by Shimadzu Corporation (model: Autopore IV9505). The obtained results are shown in FIG. In addition, Table 2 shows the pore distribution when the pressure is predetermined. In addition, the value of the pressure 30 is the integration of the porosity of the pressure 0-30, the value of the pressure 50 is the integration of the porosity of the pressure 30-50, the value of the pressure 100 is the integration of the porosity of the pressure 50-100, The value of pressure 1000 indicates the integration of the porosity of pressure 100-1000.

From the above table, it can be determined that the hardness of Example 1 is equivalent to that of Comparative Example 1. Regarding the pore distribution, referring to the above table and FIG. 1, when looking at Example 1, the amount of pores on the low pressure side [30 psia (0.2 MPa)] is about twice as large as that of Comparative Example 1. Further, in Examples 2 to 5 whose hardness is slightly lower than that of Comparative Example 1, with respect to the same pore distribution, the amount of pores is increased by about 2.4 to 4.5 times compared to Comparative Example 1. Thus, in the embodiment, it can be seen that the amount of pores tends to shift to the low pressure side in terms of pore distribution, and the total amount of pores also increases in the embodiments. Therefore, it can be seen that the distribution of large pore diameters increased when flame resistant fibers were blended in the examples.
(An endurance test)
The test conditions shown in Table 3 below were performed. The results are shown in FIGS. 2 and 3 and Table 4. Table 4 shows the change in thickness.
The test end judgment was made when the value of μd (1200) at 2000 braking was reduced by 10%. μd (1200) is a dynamic friction coefficient at 1200 revolutions per second (FIG. 2). Further, μ0 is a dynamic friction coefficient at the time of stop, and the test end determination was made at the time of the above determination (FIG. 3).

In FIG. 2, when Examples 1 and 3 and Comparative Example 1 are compared, it can be seen that the μd (1200) stability is about 1.7 to 3 times more stable than Comparative Example 1. Moreover, the increase of μ0 is also suppressed from FIG. The reason is considered to be that the pore distribution is configured with a large pore diameter, so that the oil absorption and discharge properties are improved, the cooling effect of the wet friction material is improved, and the life is extended. Further, the thickness change rate of the wet friction material is smaller in the embodiment where the number of times of braking is larger. From this, it can be seen that the flame resistant fiber contributes also in terms of compressive strength.
As described above, in the present invention, a wet friction material with good durability can be obtained by configuring and controlling the pore distribution with a large pore diameter.

It is a graph of the result of having measured Log differential pore volume distribution [dV / dLogD] with respect to pressure with a mercury intrusion formula. It is a graph which shows the change of (micro | micron | mu) d (1200) at the time of 2000 times braking in the durability test of a wet friction material. It is a graph which shows the change of (mu) 0 in the endurance test of a wet friction material.

Claims (3)

  A wet friction material comprising a binder, a pulp, an aramid fiber, and a flame resistant fiber having a PAN-based fiber as a precursor and flameproofed at 200 to 300 ° C. in an oxidizing atmosphere, the aramid fiber and the flame resistant fiber, A wet friction material containing 5.6 / 1 to 1/3 in terms of the former / the latter (mass ratio).   The wet friction material according to claim 1, wherein the flame resistant fiber has a fiber diameter of 10 to 20 µm and a fiber length of 0.8 to 1.2 mm.   The friction material according to claim 1 or 2, wherein the flame resistant fiber is blended in an amount of 5 to 35 mass% with respect to the entire wet friction material.

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