JPH02214729A - Frictional material - Google Patents

Abstract

PURPOSE:To provide the title material having tightly integrated link, improved in frictional coefficient and wear resistance, comprising an acrylic fibrous material having special texture, resin and filler. CONSTITUTION:The objective material comprising (A) an acrylic fibrous material, (B) a resin and (C) a filler. The component A has the following characteristics: many openings of unspecified shape are present on the transverse section, each of the openings forming, within the fiber, nearly parallel stringy (straw-like) voids >=60mu in length along the fiber direction, thus defining the backbone; numerous fine beard-like filaments branched from the backbone are present on the surface of this backbone; and the backbone itself is partially split in its long direction into a plurality of fibers.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a friction material containing acrylic fibers having a specific fiber morphology as a base material.

(Prior Art) Friction materials for clutches or brakes of various types of power machines, including automobiles, have often used asbestos as a base material. However, it has been pointed out that asbestos dust is a contributing factor to the development of lung cancer, and a fiber base material that can replace asbestos is required. In response to such demands, attempts have been made to use various organic fibers, but recently friction materials based on acrylic fibers have been attracting attention.

For example, in JP-A-62-106133, a friction material obtained by impregnating a thermosetting resin into a paper-made base material made by mixing fibers including fibrillated acrylic fibers and a filler, and curing the resin. materials are disclosed. Also, JP-A-63-1
No. 83950 discloses a friction material containing a thermosetting resin, a fibrous reinforcing material, and fibrillated acrylic fibers.

The fibrillated acrylic fibers used in the friction materials described in these patent publications are produced using commonly known acrylic fibers using a fiber beating method commonly used in the paper industry. Bulb-shaped scum made by beating and fibrillating.

It is a rill fiber.

These fibrillated acrylic fibers improve the fracture strength of friction materials due to their compatibility with resin, and because they are fibrillated fibers, they generate many fine pores in friction materials. This has the effect of improving the oil retention ability of the friction material. Furthermore, it also has the effect of improving the shape retention during preforming of the friction material.

As described above, fibrillated acrylic fibers are one of the base materials with excellent performance, but there is a demand for friction materials with even higher performance, and it is desirable to improve the fibers that serve as the base material. It is rare.

(Issue R to be solved by the invention) In other words, there is an even higher demand for an increase in the friction coefficient of friction materials and their wear resistance, and the present invention provides a friction material that is superior to conventional ones by improving the fiber base material. It is.

(Means for Solving the Problems) The present invention is characterized in that acrylic fibers with a special fiber morphology have a high coefficient of friction, and also meet important factors in obtaining a friction material with excellent wear resistance. This discovery led to the completion of the present invention.

That is, the present invention has a large number of openings having an unspecified shape in the cross section of the fiber, and each of the openings has a length of 60 μ or more approximately parallel to the length direction of the fiber inside the fiber. The trunk is made of acrylic fibers forming striated (straw-like) voids, and the surface of the trunk has many fine whisker-like filaments that are separated from the trunk, and the trunk is partially This is a friction material that contains an acrylic fibrous material, a resin, and a filler that is split into a plurality of fibers along the length of the trunk.

Hereinafter, the friction material of the present invention will be explained in more detail.

The friction material of the present invention is characterized in that acrylic fibers having a special fiber morphology are used as the base fibers. That is, the fiber serving as the base material used in the present invention has a large number of openings having an unspecified shape in the cross section of the fiber, and each of the openings extends approximately along the length direction of the fiber inside the fiber. Acrylic fibers (hereinafter referred to as
(referred to as the acrylic fiber of the present invention) as a trunk, and the surface of the trunk has many fine whisker-like filaments that are divided from the trunk,
The present invention is an acrylic fibrous material (hereinafter referred to as the acrylic fibrous material of the present invention) in which the trunk is partially split in the length direction of the trunk and separated into a plurality of fibers.

By using fibers having such a special fiber morphology as a base material of a friction material, it is possible to increase the friction coefficient and improve the wear resistance of the friction material.

The reason for this is not necessarily clear, but since the acrylic fibrous material of the present invention has many linear voids in its trunk, the resin and filler enter the voids. Furthermore, since the stem has a large number of fine whisker-like filaments on its surface, the resin and filler can sufficiently penetrate into the space formed by the stem and the whisker-like filaments, resulting in a fibrous material as a whole. It is thought that this is because the resin and filler are extremely closely integrated.

FIG. 1 and FIG. 2 are electron micrographs (4,000x magnification) of the cross section and longitudinal section of the acrylic fiber of the present invention.
FIG. 3 is an electron micrograph (100x magnification) of the acrylic fibrous material of the present invention obtained from the acrylic fiber.

The acrylic fiber of the present invention, as shown in FIG.
It has many openings with unspecified shapes in its cross section. That is, the shape of the opening is approximately circular;
Its shape and size are irregular, such as those that are flat, those that have repeated sharp bends in green, and those that have a large or small cross-sectional opening.

■ Due to the presence of many such unspecified voids,
The resin and filler can enter into this portion, contributing to their denser integration.

(2) Furthermore, the presence of a large number of such voids allows fine whisker-like filaments to more easily appear on the outer surface of the fiber.

■Also, the number of voids is approximately 10 in the cross section of the fiber.
If zero or more are present, the more fine whisker-like filaments are likely to occur.

FIG. 2 shows a longitudinal cross section of the acrylic fiber of the present invention, and the black striped portions are voids.

From this drawing, it can be seen that the openings form substantially parallel linear (straw-shaped) voids inside the fibers in the longitudinal direction of the fibers. It is preferable that the length is 60μ or more; if it is shorter than 60μ, fine whisker-like filaments will be difficult to generate and the effect of improving the performance of the friction material cannot be expected; if the length is 60μ or more, The longer the fiber is, the more whisker-like filaments are likely to occur, and it is preferable that the fiber is continuous over the entire length of the fiber.

FIG. 3 shows the acrylic fibrous material of the present invention, where the thick part is the acrylic fiber (trunk) described above, and the outer surface of this fiber has fine whisker-like branches branching from the fiber. It can be seen that many filaments occur. In addition, the acrylic fiber (trunk) is split into thin fibers at unspecified points along its length.
These thin fibers are observed to be bundled or randomly intertwined.

The formation of such fine whisker-like filaments and the fragmentation of the stem due to partial cracking of the stem are due to the resin and filler penetrating into the spaces created by them. It is extremely beneficial for tight integration, which serves to increase the coefficient of friction and improve the wear resistance of the friction material.

The cross-section and longitudinal cross-section of the fine fibers in the part where the main acrylic fiber is split differs depending on the degree of splitting, but if there are few splits, for example, 2 to 1 split.
In the case of 0 division, the number of openings in the cross section is equal to the original fiber (
However, other than this point, it is basically the same as the original fiber (trunk), and if there are many divisions, openings will be created in the cross section of the divided thin fibers. may not be accepted.

In addition, the fine whisker-like filaments that separate from the trunk are
Depending on the degree of division from the trunk, an opening may or may not be recognized in the cross section. That is, when the fine whisker-like fibers are thick, openings are observed, and when they are extremely fine, no openings are observed, and such whisker-like filaments are usually mixed.

The above-mentioned acrylic fibrous material of the present invention contains 1
It is 0 to 80% (% represents weight, the same applies hereinafter), preferably 20 to 60%. When the amount of fiber is less than 10%, there is almost no improvement in the coefficient of friction and wear resistance when the fiber is used as a base material, and when it exceeds 80%, the amount of fiber is too large. It becomes unsuitable as a friction material. Also, resin is 20-70% and filler is 10-50%.
is preferred.

The resin used in the present invention is a resin commonly used for friction materials, and includes phenolic resin, epoxy resin, polyimide resin, melamine resin, natural or synthetic rubber, and the like.

Further, fillers used in the present invention to improve the characteristics of friction materials include metal powder, silica, clay, wollastonite, mica, talc, diatomaceous earth, calcium carbonate, magnesium carbonate, cashew dust, graphite, etc.
At least one of these is used.

Furthermore, to improve the properties of friction materials, glass fibers,
It may contain metal fibers, carbon fibers, flame-resistant fibers, or other fiber materials such as polyvinyl alcohol fibers, polyamide fibers, polyester fibers, acrylic fibers, and cotton.

In the acrylic fibrous material of the present invention, since the acrylic fiber serving as the backbone has many linear (straw-like) voids, the resin and filler can easily penetrate into the voids. In addition, the above resin and filler invade the spaces created by partial cracks in the trunk and minute whisker-like filaments generated from the trunk, and these kings are bonded extremely tightly, resulting in integrated friction. Becomes a material. As a result, the friction material of the present invention has a high coefficient of friction and excellent wear resistance.

Next, a method for manufacturing the friction material of the present invention will be explained.

As described above, the friction material of the present invention is characterized by the fiber used as its base material, and this fiber is a novel fiber different from conventionally known acrylic fibers.

This acrylic fiber contains at least 6 acrylonitrile.
0% by weight (% below indicates weight unless otherwise specified) and 40%
% of acrylonitrile and a copolymerizable ethylene monomer, or a mixture of at least two acrylic polymers. In the case of the mixed polymer, it is necessary that the content of acrylonitrile is 60% or more based on the weight of the mixed polymer. If the content of acrylonitrile is less than 60%, the compatibility with the resin will be poor (and the effect of improving the friction coefficient and wear resistance of the friction material will be small).

Ethylene monomers that can be copolymerized with acrylonitrile include conventionally known monomers, such as acrylic acid, methacrylic acid, and their esters (methyl acrylate, ethyl acrylate, methyl methacrylate, methacrylate). ethyl acid, etc.), vinyl acetate, vinyl chloride, vinylidene chloride, acrylamide, methacrylamide, methacrylatelyl, allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acid, vinylpyridine, 2-methyl-
5-vinylpyridine, N,N-dimethylaminoethyl methacrylate, and the like.

The above polymers can be used in conventionally known solvents for acrylic polymers, such as organic solvents such as dimethylformamide, dimethylacetamide, and dimethyl sulfoxide, concentrated aqueous solutions of inorganic salts such as rhodan salt, zinc chloride, and nitric acid, and inorganic A spinning stock solution is prepared by dissolving it in a concentrated acidic aqueous solution. In this case, the optimum concentration of the polymer varies depending on the type of solvent, but is preferably approximately 10 to 30%.

Next, polyalkylene glycol is added to the spinning dope.

The polyalkylene glycol used in the present invention contains ethylene oxide and propylene oxide in a weight ratio of 80%.
: 20 to 20 : 80 random type copolymer or block type copolymer, and its number average molecular weight is s
, ooo to 50.000, preferably 10.000
~20,000. If the number average molecular weight is less than 5,000, continuous voids cannot be obtained in the length direction of the fiber, resulting in a microporous fiber having extremely fine, approximately spherical cavities. On the other hand, if the number average molecular weight exceeds 50,000, the fiber will have huge streak-like cavities, and moreover, the fiber will have many (but at most several tens of cavities) in the cross section of the fiber. Such fibers will not be split into fine fibers by external forces such as a columnar flow of liquid.

In particular, when the number average molecular weight is 10.000 to 20.000, fibers can be obtained which are fine along the length of the fiber and have elongated voids with an unspecified cross-sectional shape in the cross section of the fiber. .

Furthermore, the spinning dope prepared by dissolving the polyalkylene glycol as described above is then aged for a short time (4 hours in total).

Here, aging refers to, for example, leaving the spinning stock solution prepared by dissolving the acrylic polymer and polyalkylene glycol as it is without vigorous stirring or vibration, or gently moving the spinning stock solution. This refers to, for example, slowly transporting liquid through piping.

The amount of polyalkylene glycol added in the present invention is 5 to 20%, preferably 10 to 15%, based on the acrylic polymer.
%. If it is less than 5%, the number of voids in the cross section of the fiber is small (and the number is large, for example 10
If fibers with 0 or more openings cannot be obtained, and if the amount added exceeds 20%, the number of openings will increase, but if there are too many openings, the fibers may split during the fiber manufacturing process or the spinning may become unstable. Problems such as the inability to form a polyalkylene glycol occur.When the amount of polyalkylene glycol added is 10 to 15%, the number of openings, spinning stability, etc. are most balanced.

This spinning dope is extruded through a spinneret into a coagulating medium of the spinning dope, and after passing through steps such as water washing, stretching, and drying, it is further heat-set as required.

In such a manufacturing process, the polyalkylene glycol added to the spinning stock solution undergoes coagulation, water washing, stretching, etc.
Elutes from coagulated filaments. For the steps after spinning, conventionally known methods for producing acrylic synthetic fibers can be adopted as they are.

That is, the method for spinning the spinning dope is a wet spinning method in which the spinning solution is extruded into a dilute aqueous solution of a solvent, a dry spinning method in which the spinning solution is extruded into an inert gas such as air or nitrogen gas, or a spinning method in which the spinning solution is extruded into an inert gas such as air or nitrogen gas. A dry-wet spinning method, in which the material is once extruded and then introduced into a dilute aqueous solution of a solvent, can be employed. After spinning, the coagulated filament is washed with water and then stretched, simultaneously stretched with water, or washed with water after stretching to remove the solvent.

Next, the method for producing the acrylic fibrous material of the present invention will be described.

The acrylic fibrous material of the present invention can be obtained by beating the acrylic fiber produced by the above method using a beater used in the paper industry, such as a disc refiner. Depending on the beating conditions using this beater, such as fiber length, fiber concentration, rotor gap, rotor rotation speed, or number of beats, the degree of generation of fine whisker-like fibers and the degree of division of the stem portion can be changed. .

The degree of generation of these fine whisker-like filaments and the degree of division of the stem portion vary depending on the characteristics required of the friction material.
For boat fishing, it is preferable that the freeness is in the range of about 600 to 200 cc, which is used in the paper industry to express the degree of pulp beating, but the freeness is not limited to this range. , even if it is larger than 600cc, it is also 20
Even if it is smaller than 0 cc, it can be used depending on the characteristics of the friction material. In addition, the measurement of freeness is based on JIS P8121-1.
It was measured according to the method specified by 976.

The above acrylic fibrous material is mixed with the above resin and formed into a friction material.

The friction material can be produced by a method in which a base material, such as a paper-like material or a nonwoven fabric, containing the fibrous material and filler of the present invention is previously produced, impregnated with a resin, molded, and cured; This can be done by a conventionally known method, such as a method in which a fibrous material, a resin, and a filler are triblended, molded, and cured.

(Examples) Hereinafter, the present invention will be specifically explained using Examples, but these are not intended to limit the scope of the present invention.

Example 1 Acrylonitrile 95.0%, methyl acrylate 4.5%
% and 0.5% sodium methallyl sulfonate, block type polyether of polyethylene oxide-polybropylene oxide-polyethylene oxide (number average molecular weight 10,000, ratio of polyethylene oxide and polypropylene oxide is 70:30) ) in dimethylformamide to obtain acrylic polymer 23.
%, and a spinning stock solution containing 2.3% block type polyether was prepared.

After allowing this spinning dope to stand still for 6 hours, it was passed through a spinneret.
It was extruded into a coagulation bath with a temperature of 35°C and a dimethylformamide concentration of 75%, and after washing with water, it was stretched 12 times in boiling water and 80°C.
The fiber was dried in hot air to produce a 1.5 d fiber.

An electron micrograph (4000x magnification) of a longitudinal section (hereinafter referred to as longitudinal section) of this fiber cut in the length direction is shown in FIG. 1, and a similar photograph of a cross section of the fiber is shown in FIG.

In FIG. 1, the black parts are voids, and it can be seen that the voids are continuous in a straight line (straw shape) approximately parallel to the length of the fiber.

Also, in Fig. 2, the black parts are openings,
There are many irregular openings with unspecified shapes, such as those with approximately circular cross-sections, those with flat shapes, those with repeated sharp bends at the edges, and those with large or small cross-sections. It can be seen that there is a mixture of

Next, this fiber was cut into a length of 15 flIol and dispersed in water to prepare a fiber dispersion having a fiber concentration of 10%. This fiber dispersion was treated with a papermaking disc refiner with a disc gap of 0.1 m, and the freeness was 450 cc.
It was beaten up to.

Figure 3 is an electron micrograph of the beaten fibers (100
It can be seen that many fine whisker-like filaments, which are separated from the fibers, are generated on the surface of the thick fiber portion (original acrylic fiber trunk).

It can also be seen that the main fibers are partially split in the length direction and separated into thin fibers.

Next, 50% of this fiber, 25% of phenolic resin, and 25% of calcium carbonate as a filler were mixed in a Henschel mixer, and a sufficient amount was compression-molded in a mold at 155 kg/cj and a temperature of 150°C. Manufactured pad material for automobile disc brakes.

This pad material was subjected to a constant speed friction test in accordance with JIS D-4411.

As a result, the coefficient of friction at 250°C was 0.45, and the amount of wear was 1.48xlO-'ai/kg·m.

Example 2 A brake pad material was produced by repeating the same operations as in Example 1 except that the fiber length was 5III1 and the fiber concentration in the dispersion was 1%.

When the obtained brake pad material was tested in the same manner as in Example 1, the friction coefficient was 0.45, and the amount of wear was 1.
47×10-'cj/kg-m, and a friction material having the same performance was obtained with good reproducibility.

Example 3 A brake pad material was manufactured by mixing 40% of the acrylic fibrous material manufactured in Example 1, 15% of glass fiber, 22% of diatomaceous earth, and 23% of phenolic resin, and repeating the operations of Example 1. .

The friction coefficient and wear amount of this brake pad material were examined in the same manner as in Example 1.

The coefficient of friction is 0.45 and the amount of wear is 1.46X I
O-'d7 kg-m.

(Effects of the Invention) Since the friction material of the present invention uses a fibrous material made of fibers with a special shape, the fibrous material, resin, and filler can be uniformly mixed and they can be more closely bonded together. is planned,
A friction material with improved friction coefficient and wear resistance.

[Brief explanation of the drawing]

Figures 1 and 2 are electron micrographs (4,000x magnification) showing the cross section and longitudinal section of the acrylic fiber used in the present invention.
It is. FIG. 3 is an electron micrograph (100x magnification) showing the fiber morphology of the fibrous material used in the present invention after beating treatment. (1 idiot)

Claims (1)

[Claims] The cross section of the fiber has a large number of openings having an unspecified shape, and each of the openings is in the shape of a stripe (straw) having a length of 60μ or more and approximately parallel to the length direction of the fiber inside the fiber. The trunk is made of acrylic fibers forming voids in the trunk, and the surface of the trunk has many fine whisker-like fibers branching from the trunk, and the trunk partially extends in the length direction of the trunk. A friction material comprising an acrylic fibrous material that is split and separated into a plurality of fibers, a resin, and a filler.