JP6958352B2 - Filler for friction material - Google Patents

Description

The present invention relates to a filler for a friction material.

Friction materials used for brake pads of braking devices such as automobiles are mainly composed of various fibrous substrates, fillers such as friction modifiers, and various thermosetting polymers for binding them. It consists of a binder and the like. The friction material is produced by filling a mold with a mixture of these components and then pressurizing and heating to cure the binder.

Organic fibers such as polyamide fibers and aramid fibers, ceramic fibers, glass fibers, rock wool, and synthetic inorganic compound fibers such as potassium titanate are used as the fibrous base material, and barium sulfate is used as the filler. Various inorganic compound powders such as calcium carbonate and metal powders are used. Further, for the purpose of adjusting friction, solid lubricants such as graphite and molybdenum disulfide and cashew dust are added.

The characteristics required for the friction material are that it has a large braking force, that it has abrasion resistance, that the change in braking force due to changes in temperature, pressure, etc. is small and stable, and that it has high mechanical strength. and so on.

Conventionally, magnetite has been used as a filler for a friction material (see, for example, Patent Documents 1 and 2).

JP-A-2009-298847 Japanese Unexamined Patent Publication No. 2011-236332

Patent Document 1 describes that iron oxide having an average particle size of 3.5 μm or more is used as the friction adjusting material, but the average particle size of iron oxide disclosed in Examples is 3.5 μm. Iron oxide with a larger particle size is not specifically disclosed. Patent Document 2 describes that iron oxide and a resin are compounded, but it is not preferable because it cannot sufficiently exhibit magnetite characteristics, polishability, etc. due to the large amount of resin components.

The present invention provides a filler for a friction material, which is excellent in polishability and can be expected to improve dispersibility in a resin.

The object can be achieved by the present invention as follows.

That is, the present invention is a filler for a friction material, which contains magnetite as a main component and has an average particle size of 10 to 100 μm (Invention 1).

Further, the present invention is the filler for a friction material according to the present invention 1 having a true specific gravity of 4.8 g / cm ^{3 or more (the present invention 2).}

Further, the present invention is the filler for a friction material according to the present invention 1 or 2 having a carbon content of 0.4 wt% or less (the present invention 3).

Further, the present invention is the filler for a friction material according to any one of the present inventions 1 to 3 having a BET specific surface area of 4 m ^{2 / g or less (the present invention 4).}

Further, the present invention is the filler for a friction material according to any one of the present inventions 1 to 4, which has a crushing strength of 0.2 to 100 MPa (the present invention 5).

The filler for friction material according to the present invention has a large particle size and is excellent in abrasiveness, and is therefore suitable as a filler for friction material. Moreover, since the particle size is large, it can be expected to improve the dispersibility in the resin. Furthermore, by controlling the crushing strength of the granulated product, it is possible to contribute to the optimization of various properties of the friction material.

The configuration of the present invention will be described in more detail as follows.

First, the filler for friction material according to the present invention will be described.

The filler for a friction material according to the present invention contains magnetite as a main component as a crystal phase, and preferably contains at least 50 wt%. By controlling the magnetite content within the above range, the polishability can be made excellent. The upper limit of the magnetite content is 100%, more preferably 99.8%. As another constituent phase, FeO is preferably contained in an amount of 50 wt% or less, more preferably 40 wt% or less. Further, hematite may be contained in an amount of 10 wt% or less.

The filler for friction material according to the present invention has an average particle size (D50) of 10 to 100 μm. By controlling the average particle size within the above range, it is expected that the abrasiveness will be excellent and the dispersibility in the resin will be improved. The preferred average particle size (D50) is 15 to 98 μm, more preferably 20 to 95 μm.

The filler for friction material according to the present invention preferably has a true specific gravity of 4.8 g / cm ³ or more. By controlling the true specific gravity within the above range, the particles become dense particles for friction materials and have excellent polishability. More preferred true specific gravity is ^{4.9g / cm 3 ~5.6g / cm 3} , even more preferably ^{5.0g / cm 3 ~5.5g / cm 3} .

The filler for friction material according to the present invention preferably has a carbon content of 0.4 wt% or less. By controlling the amount of carbon within the above range, a large amount of iron compound such as magnetite is contained, and the polishability is excellent. A more preferable carbon content is 0 to 0.35 wt%, and even more preferably 0 to 0.3 wt%.

The filler for friction material according to the present invention preferably has a BET specific surface area of 4.0 m ² / g or less. By controlling the BET specific surface area value within the above range, the polishability becomes excellent. A more preferable specific surface area value is 0.01 to 3.9 m ² / g, and even more preferably 0.02 to 3.8 m ² / g.

The shape of the filler for the friction material according to the present invention is preferably spherical. This is because the more spherical the shape, the easier it is to blend with the resin, and the more fluid it is, the easier it is to mold.

The filler for friction material according to the present invention is preferably black and achromatic, with a ^* preferably within ± 3 and b ^* preferably within ± 3 of the hues.

The filler for friction material according to the present invention preferably has a crushing strength of 0.1 MPa or more. The filler for friction material according to the present invention is suitable for friction material because it can maintain high strength even if the amount of carbon is small. If the crushing strength of the filler for the friction material is less than 0.1 MPa, it is difficult to maintain the spherical shape. A more preferable crushing strength is 0.2 to 100 MPa, and even more preferably 0.3 to 99 MPa. In the present invention, since the particle size and crushing strength affect the polishing / friction performance, the particle size and crushing strength can be controlled and adjusted to the polishing / friction performance.

Further, impurities derived from various raw materials may be unavoidably mixed in the filler for friction material according to the present invention.

Next, a method for producing a filler for a friction material according to the present invention will be described.

The filler for friction material according to the present invention can be produced, for example, as follows.

A granulated product having a predetermined size was prepared by using one or more selected from magnetite particle powder, hematite particle powder, and gateite particle powder having an average particle size of primary particles of 0.05 to 5.0 μm, and obtained granulated product. Is fired in a temperature range of 500 to 1200 ° C. to produce a filler for a friction material.

If necessary, one or more oxides, hydroxides, oxalates, carbonates and the like selected from Ca, Al, Ti, Si, Mg, Zn, Ni, Mn, Cu and Co may be used in combination.

Further, the particle morphology of the various raw material powders may be any morphology such as a cube, a polyhedron, a needle, and a plate. The average particle size of the primary particles of this raw material powder is preferably 0.05 to 5.0 μm, more preferably 0.1 to 3.0 μm. That is, if the average particle size of the primary particles is less than 0.05 μm, the slurry viscosity tends to be high and problems tend to occur during spray drying, and if it exceeds 5.0 μm, the surface roughness of the sintered body becomes large. This is because the specific surface area tends to be too large and the filling rate tends not to increase.

The granulated product may be produced according to a conventional method, but spray drying of a slurry containing a raw material is preferable from the viewpoint of controlling the particle size of the granulated product. The particle size of the granulated product can be adjusted by adjusting the solid content concentration of the slurry.

A resin component may be used when making a slurry in the process of manufacturing the filler for friction material according to the present invention. As the resin component, cellulose, polyvinyl alcohol (PVA), acrylic acid, polyacrylic acid amide, urethane, starches and the like can be used, and those that are burnt down in the subsequent heat treatment are preferable. The amount of the resin component added is preferably 0.3 to 5 parts by weight, with the starting material as 100 parts by weight.

Further, a dispersant may be used when making a slurry in the process of manufacturing the filler for friction material according to the present invention. As this dispersant, a general surfactant can be used, and those having a functional group capable of binding to a hydroxyl group having on the particle surface of various raw materials such as iron oxide are preferable, and specifically, a polycarboxylic acid. Sodium salt, anionic polycarboxylic acid ammonium salt, lignin sulfonate, melamine sulfonate, sodium naphthalene sulfonate, sodium phosphate, sodium citrate, amines, metal salt or ammonium salt of polyacrylic acid, etc. Be done. Then, considering the residue of ionic impurities after firing, it is preferable to use an ammonium polycarboxylic acid salt. The amount of the dispersant added is preferably 0.1 to 5 parts by weight, with 100 parts by weight of the starting material.

In the production of the filler for friction material according to the present invention, the spray drying is preferably performed at a slurry concentration of 40 to 80% by weight, more preferably 50 to 70% by weight. That is, if it is less than 40% by weight, the slurry viscosity tends to be low and it tends to be difficult to adjust the particle size distribution, and if it exceeds 80% by weight, the slurry viscosity becomes high and it becomes difficult to secure a spherical shape. This is because there is a tendency.

The conditions for spray drying are not particularly limited, and may be appropriately selected depending on the slurry concentration, viscosity, and the like.

Further, in the present invention, firing is carried out at a temperature of about 500 to 1200 ° C. for 1 to 8 hours, although it depends on the iron oxide raw material. That is, if the temperature is lower than 500 ° C., the particles do not grow, so that they have no strength and cannot maintain a spherical shape. This is because when the temperature exceeds 1200 ° C., the sintered particles are fused to each other, and the number of snowball-shaped particles tends to increase. It is preferably 600 to 1180 ° C.

The firing atmosphere is preferably an inert gas atmosphere, preferably a nitrogen atmosphere, and a part of hydrogen may be mixed.

The obtained filler for friction material may be washed with water by a conventional method.

The filler for friction material according to the present invention can be used as a friction material by using a binder such as phenol resin, an adjusting agent such as titanium acid, an abrasive, and a filler.

Typical examples of the present invention are as follows.

The average particle size (D50) of the filler for the friction material was shown as a value measured by a "laser diffraction type particle size distribution meter HELOS" (manufactured by SYMPATEC).

The average particle size of the primary particles was calculated by image analysis of a "scanning secondary electron microscope" (manufactured by Hitachi High-Technologies Corporation).

The specific surface area of the filler for the friction material was shown as a value measured by the BET method using "Monosorb MS-11" (manufactured by Kantachrome Co., Ltd.).

The true specific gravity of the filler for the friction material is shown as a value measured by a "dry automatic density meter Accupic II-1340" (manufactured by Micromeritics).

The carbon content of the filler for the friction material is shown as a value measured by "carbon / sulfur analyzer EMIA-920V2" (manufactured by HORIBA).

The content of each crystal phase constituting the filler for the friction material was measured using TOPAS software of "Bruker AXS KK" (manufactured by Bruker AXS Co., Ltd.).

For the hue (a ^* value, b ^* value) of the filler for the friction material, 0.5 g of the sample and 0.5 ml of castor oil are kneaded with a Hoover type marler to form a paste, and 4.5 g of clear lacquer is added to this paste. , Kneaded and made into a paint, and applied on cast-coated paper using a 150 μm (6 mil) applicator to prepare a coating piece (coating thickness: about 30 μm). The coating piece was measured using a "color difference meter CR-400" (manufactured by Konica Minolta Sensing Co., Ltd.) and indicated by ^{a color index (a *} value, b ^{* value) according to JIS Z 8729.} ..

The crushing strength of the filler filler was determined by a single particle compression test (JIS R 1639-5). Using a micro-compression tester (MCT-W, Shimadzu Corporation), a compression test was performed on a single particle of 20 arbitrary particles, and the compression strength was obtained from the fracture test force and particle size, and arithmetically averaged.

Example 1
1 kg of magnetite particle powder, 10 g of polyvinyl alcohol, 10 g of ammonium polycarboxylic acid salt and 1 kg of water were mixed in a ball mill for 2 hours to obtain a slurry containing the magnetite particle powder. This slurry was granulated and dried by spray drying to prepare complex particles having an average particle size of 50.3 μm. Next, the particles were placed in a rotary heat treatment furnace and heated at 850 ° C. for 3 hours in a nitrogen atmosphere. After cooling to room temperature, it was taken out to obtain a filler for a friction material. The characteristics are shown in Table 2.

Example 2
1 kg of magnetite powder, 20 g of polyvinyl alcohol, 5 g of lignin sulfonate and 1 kg of water were mixed in a ball mill for 2 hours to obtain a slurry containing magnetite particle powder. This slurry was granulated and dried by spray drying to prepare complex particles having an average particle size of 53.1 μm. Next, the particles were placed in a rotary heat treatment furnace and heated at 750 ° C. for 3 hours in a nitrogen atmosphere. After cooling to room temperature, it was taken out to obtain a filler for a friction material. The characteristics are shown in Table 2.

Example 3
750 g of goethite powder, 250 g of goethite powder, 10 g of polyvinyl alcohol, 5 g of ammonium polyacrylate and 1 kg of water were mixed in a ball mill for 2 hours to obtain a slurry containing the goethite powder and the goethite powder. This slurry was granulated and dried by spray drying to prepare complex particles having an average particle size of 47.7 μm. Next, the particles were placed in a pusher-type firing furnace and heated at 950 ° C. for 3 hours in a nitrogen atmosphere. After cooling to room temperature, it was taken out to obtain a filler for a friction material. The characteristics are shown in Table 2.

Examples 4-9
A filler for a friction material was obtained in the same manner as in Example 1 except that the blending ratio of the iron oxide raw material, the addition amount of the resin and the dispersant, and the firing temperature were variously changed. Table 1 shows the manufacturing conditions at this time, and Table 2 shows various characteristics of the obtained filler for friction material.

Comparative Example 1
The slurry used in Example 1 in which 1 kg of magnetite powder, 10 g of polyvinyl alcohol, 10 g of ammonium polycarboxylic acid salt, and 1 kg of water were mixed in a ball mill for 2 hours was granulated and dried by spray drying to obtain an average particle size of 50.3 μm. It was made into a complex particle. Table 2 shows various characteristics of the obtained complex particles.

Comparative Examples 2, 3
A filler for a friction material was obtained in the same manner as in Comparative Example 1 except that the blending ratio of the iron oxide raw material and the addition amounts of the resin and the dispersant were changed. Table 1 shows the manufacturing conditions at this time, and Table 2 shows various characteristics of the obtained filler for friction material.

Comparative Example 4
A filler for a friction material was obtained in the same manner as in Example 1 except that the blending ratio of the iron oxide raw material, the amount of the resin and the dispersant added, the firing temperature, and the firing atmosphere were changed. Table 1 shows the manufacturing conditions at this time, and Table 2 shows various characteristics of the obtained filler for friction material.

The filler for friction material according to the present invention has a large particle size and is excellent in abrasiveness, and is therefore suitable as a filler for friction material. Moreover, since the particle size is large, it can be expected to improve the dispersibility in the resin.

Claims (4)

It contains at least 50 wt% magnetite, has an average particle size of 10-100 μm, and has a true specific density of 4.8 g / cm. ³ A method for producing a filler for a friction material, which is characterized by the above, and is one or more selected from magnetite particle powder, hematite particle powder, and gateite particle powder having an average particle size of primary particles of 0.05 to 5.0 μm. A method for producing a filler for a friction material, which comprises firing the obtained granulated product in a temperature range of 500 to 1200 ° C. in a nitrogen atmosphere. The method for producing a filler for a friction material according to claim 1, wherein the carbon content is 0.4 wt% or less . BET specific surface area is 4m ² The method for producing a filler for a friction material according to claim 1, wherein the content is / g or less. The method for producing a filler for a friction material according to claim 1 or 2, wherein the crushing strength is 0.2 to 100 MPa .