HK1070046B - Repidocrocite type lithium potassium titanate, method for preparation thereof, and friction material - Google Patents

Description

Lepidocrocite type lithium potassium titanate, method for producing same, and friction material

Technical Field

The invention relates to lepidocrocite type lithium potassium titanate and a preparation method thereof, and also relates to a friction material.

Technical Field

Previously used friction materials for forming brake components have been asbestos in the form of asbestos dispersed in and bonded by organic or inorganic binders. However, this material does not have sufficient heat resistance and friction properties such as coefficient of friction and abrasion resistance, which are reduced in a high temperature region, and deterioration thereof is often caused when braking is performed. When braking is performed, the contact of the friction material with the high speed brake pads causes frequent occurrence of "brake noise". Asbestos is a known carcinogen and is prone to dust formation. The operators inhale asbestos during their operation, and the use of asbestos has been increasingly restricted in view of such environmental hygiene problems. Under these circumstances, there is an urgent need to develop a substitute for asbestos.

In response to such a demand, the use of non-carcinogenic potassium titanate fiber friction materials as friction control agents has been proposed and has been widely used mainly for brake pads of automobiles. The friction material containing potassium titanate fiber has excellent sliding performance and excellent braking effect. However, they have little detrimental effect on the brake pad, which is a very advantageous advantage. However, this material has insufficient wear resistance, and particularly in a high temperature region, it wears at a high rate. They also do not provide an effective solution to the "brake noise" emitted by the brake. Further, since they are in the form of fibers, potassium titanate fibers are bulky and have poor flowability, and tend to deposit on the wall of the feed passage and clog the passage in the production of a friction material, which is problematic.

Japanese patent No.3027577 describes a friction material using lepidocrocite-type lithium potassium titanate as a friction control agent. Such friction materials have stable wear resistance at low to high temperature regions.

Disclosure of Invention

The object of the present invention is to provide a novel lepidocrocite type lithium potassium titanate material useful as a friction control agent, a method for producing the same, and a friction material containing the same.

Lepidocrocite-type potassium lithium titanate (hereinafter abbreviated as KTLO unless otherwise specified) of the present invention can be represented by the formula K_0.5-0.7Li_0.27Ti_1.73O_3.85-3.95And (4) showing.

The arithmetic mean value of the long diameter and the short diameter of the KTLO is 0.1-100 microns, the ratio of the long diameter to the short diameter is 1-less than 10, the thickness is 50-5000nm, and the KTLO is in a sheet shape.

The KTLO has a layered structure and has heat resistance and wear resistance which are not influenced by temperature. Since KTLO is not present in the form of fibers, unlike potassium titanate fibers, it does not significantly block the feed channel during production and does not degrade the operating environment due to the presence of respirable fibers.

The manufacturing method of the present invention canThe KTLO of the present invention is characterized by the following steps in having formula K_0.8Li_0.27Ti_1.73O₄An aqueous slurry of lepidocrocite-type lithium potassium titanate of the composition shown is added with an acid while adjusting the slurry pH to 6-8, solids are separated from the slurry, and the solids are calcined.

The friction material is characterized by containing KTLO as a friction control agent. The friction material of the present invention contains the KTLO of the present invention as a friction control agent, and therefore, can exhibit extremely stable wear properties (such as wear resistance and friction coefficient) in a low-temperature to high-temperature region even in long-term use over several tens of hours.

Therefore, the friction material of the present invention is used for brake parts such as clutch pads, brake linings and disc pads installed in brake devices of automobiles, airplanes, trains and factory equipment, not only to improve and stabilize the braking function but also to extend the service life thereof.

The reason why the friction material containing the KTLO of the present invention provides such excellent performance is not clear, but it is presumed that the KTLO of the present invention is due to the formula K of the prior art_0.8Li_0.27Ti_1.73O₄Structural differences between the indicated lepidocrocite-type lithium potassium titanate (hereinafter referred to as KTLO-a unless otherwise specified).

Lepidocrocite-type lithium potassium titanate (KTLO) of the present invention generally has a composition represented by the following formula:

K_0.5-0.7Li_0.27Ti_1.73O_3.85-3.95(1) the potassium content is in the range of 0.5-0.7 mole.

The KTLO of the present invention has an orthorhombic layered structure, and generally has a lamellar shape similar to mica, shell fragments, and the like.

The KTLO of the present invention may have an arithmetic average of a long diameter and a short diameter ((long diameter + lower diameter)/2), a ratio of the long diameter to the short diameter (long diameter/short diameter), and an average thickness in a wide range, and may be appropriately selected depending on the desired end use. In order to provide sufficient heat resistance and sliding properties to a friction material containing KTLO as a friction-controlling agent, KTLO is used whose arithmetic mean of long and short diameters is generally in the range of about 0.1 to 100 micrometers, preferably 1 to 30 micrometers, the ratio of long to short diameters is 1 to less than 5, preferably 1 to less than 3, and the thickness is generally in the range of 50 to 5,000nm, preferably 200 to 2,000 nm. These values can be determined by scanning electron microscopy. KTLO preferably has an arithmetic mean of long and short diameters in the range of about 0.1-100 microns, a ratio of long to short diameters of 1 to less than 10, a thickness generally in the range of 50-5000nm, and a flake shape.

The KTLO of the present invention can be produced, for example, by adding an acid to an aqueous slurry of KTLO-a, mixing, separating the solids from the slurry, and then calcining.

For the production of KTLO-a, for example, by mixing raw materials of titanium, potassium and lithium, adding a flux, followed by thorough mixing, and calcining the mixture at 1,100 ℃ of 1,000 ℃ for 1 to 8 hours.

Or the titanium source material may be selected from titanium-containing compounds, and specific examples thereof include titanium dioxide, rutile, wet cake of titanium hydroxide, hydrous titanium dioxide, and the like. These titanium raw materials may be used alone or in combination. The potassium source material may be selected from compounds that form potassium oxide when heated, and specific examples of such compounds include potassium oxide, potassium carbonate, potassium hydroxide, potassium nitrate, and the like. These potassium materials may be used alone or in combination. The potassium feed may also be mixed with small amounts of one or more oxides, carbonates, hydroxides and nitrates of any other alkali metal. Examples of the lithium raw material include lithium hydroxide, lithium carbonate, lithium fluoride, and the like. These lithium raw materials may be used alone or in combination.

The titanium, potassium and lithium raw materials were mixed in a standard ratio of Ti: K: Li of 1.73: 0.8: 0.27 (molar ratio), allowing each deviation to be within about 5%. However, large deviations from the stated ratios sometimes lead to Li as a by-product₂TiO₃And/or K₂Ti₆O₁₃These by-products are not plate-like.

Examples of the flux include potassium chloride, potassium fluoride, potassium molybdate, potassium tungstate, and the like. Among these fluxes, potassium chloride is particularly preferable. The flux is added to the raw materials in a molar ratio (raw material: flux) of 3: 1 to 3: 15, preferably 3: 3.5 to 3: 10. The low addition of flux can improve the economic advantage. However, if the amount of the flux added is too large, the flaky crystals are disadvantageously broken.

The calcination may be carried out by any equipment such as an electric furnace, a muffle furnace, etc. In mass production, it is preferred to calcine the raw material, which is pre-pressed into a brick shape or a cylinder shape, using a tunnel kiln. Preferably, the calcination is carried out at 1,100 ℃ in the range of 1,000-plus-1,100 ℃ for a holding time of 1 to 24 hours. The temperature can be increased or decreased at any rate, preferably at a rate of 3 to 7 deg.C/minute. Too high a calcination temperature will result in a sheet-like product of large size. However, if the calcination temperature exceeds 1,100 ℃, the product shape may be deteriorated due to melting. Too long a holding time increases the size of the particles produced. After calcination, the product may be subjected to wet pulverization. Specifically, the slurry is pulverized and ground by a jaw crusher, a box grinder or the like, dispersed in water, and stirred to 5 to 10% by weight. If necessary, the slurry can be further classified, filtered and dried to obtain the flaky lithium potassium titanate.

The concentration of the aqueous slurry of KTLO-a is not particularly limited and may be appropriately selected from a wide range. From a processing standpoint, the concentration of the aqueous slurry is maintained at about 1 to 30 weight percent, preferably about 2 to 15 weight percent.

The acid to be used is not particularly limited and may be selected from known acids including inorganic acids such as sulfuric acid, hydrochloric acid and nitric acid: organic acids such as acetic acid and the like. These acids may be used in combination, if necessary. The acid is added to the aqueous slurry in an amount effective to maintain the slurry pH in the range of 6 to 8, preferably 6.5 to 7.5. The pH of the aqueous slurry was measured after the addition of the acid, and then, stirred for about 1 to 5 hours. The acid is generally used in the form of an aqueous solution thereof, and the concentration thereof is not particularly limited and can be selected from a wide range. Generally in the range of about 1-80% by weight.

After the aqueous slurry is adjusted to a pH within the above-exemplified range, the solids present therein are separated by conventional separation methods such as filtration, centrifugation, and the like. The separated solid is washed with water if necessary.

The solid is then calcined. Typically, the calcination is carried out at about 400-700 ℃ and is complete after about 1-12 hours. After calcination, the resulting powder is further pulverized, either before or after being separated by a sieve.

The above process can obtain KTLO of the present invention. The invention also provides a friction material containing KTLO as a friction control agent. The friction material of the present invention contains a binder and a friction-controlling agent as main components.

Any binder commonly used in the friction material art may be used. Examples of the binder include organic binders and inorganic binders. Organic binders include thermosetting resins such as phenol resins, formaldehyde resins, melamine resins, epoxy resins, acrylic resins, aromatic polyester resins, and urea resins; elastomeric materials such as natural rubber, nitrile-based resins, butadiene rubber, styrene-butadiene rubber, neoprene rubber, polyisoprene rubber, acrylic rubber, high styrene rubber, and styrene propylene diene copolymer; thermoplastic resins such as polyamide resin, polyphenylene sulfide resin, polyether resin, polyimide resin, polyether ether ketone resin, thermoplastic liquid crystal polyester resin and the like. Examples of the inorganic binder include alumina sol, silica sol, silicone resin, and the like. The above-mentioned binders may be used alone, and if compatible, may be used in any mixture.

Used as the friction-controlling agent is KTLO of the present invention represented by the following formula (1).

The friction material of the present invention may also contain a fibrous substance. Any fibrous material conventionally used in the art may be used. Examples of the fibrous substance include resin fibers such as aramid fibers, metal fibers such as steel fibers and bronze fibers, carbon fibers, glass fibers, ceramic fibers, stone wool, pulp, and the like. These cellulosic materials may be used alone or in admixture. These cellulosic materials may be modified with silane coupling agents such as aminosilane, epoxysilane or vinylsilane coupling agents; titanate coupling agent, phosphate coupling agent and the like are subjected to surface treatment, so that the dispersing performance and the adhesive performance of the adhesive are improved.

The friction material of the present invention may further contain a friction-controlling agent conventionally used in the art, and examples thereof include organic powders such as natural or synthetic rubber powder (either vulcanized or unvulcanized), urushiol resin powder, resin dust and rubber dust, within a range not to impair the advantageous properties of the friction material; inorganic powders such as carbon black, graphite powder, molybdenum disulfide, barium sulfate, calcium carbonate, clay, mica, talc, diatomaceous earth, antigorite, sepiolite, montmorillonite, zeolite, sodium trititanate, sodium hexatitanate, potassium hexatitanate, and potassium octatitanate; metal powders such as copper, aluminum, zinc and iron powder; oxide powders such as alumina, silica, chromium oxide, titanium oxide, and iron oxide powders, and the like. These conventional friction control agents may be used alone or in any combination thereof.

The friction material of the present invention may further contain one or more of rust inhibitors, lubricants, and abrasives.

The components of the friction material of the present invention are mixed in a wide range in appropriately selected proportions according to various conditions including the type of binder used, the fibrous substance that may be added, the conventional friction-controlling agent and other additives, the sliding and mechanical properties required of the friction material to be produced, the intended end use, and the like. The friction material may generally contain 5 to 60 wt.%, preferably 10 to 40 wt.%, of the binder, 1 to 80 wt.%, preferably 3 to 50 wt.%, of the friction control agent (including conventional friction control agents), up to 60 wt.%, preferably 1 to 40 wt.%, of the fibrous material, and up to 60 wt.%, preferably 5 to 50 wt.%, of other additives, based on the total weight of the friction material.

In one embodiment, the friction control agent is lepidocrocite-type lithium potassium titanate having the formula K_0.5-0.7Li_0.27Ti_1.73O_3.85-3.95Composition of the representation. In a preferred embodiment, the lepidocrocite-type lithium potassium titanate has an arithmetic mean of a long diameter and a short diameter of 0.1 to 100 μm, a ratio of the long diameter to the short diameter of 1 to less than 10, and an average thickness of 50 to 5000nm, and is in a sheet form.

Preferred friction materials contain a cellulosic material, a binder and a friction control agent as the major components.

The friction material of the present invention can be manufactured by various methods known in the art for manufacturing friction materials. A method is described in which the fibrous material, if desired, is dispersed in a binder, the friction-controlling agent and other optional ingredients are subsequently added to the binder either as a mixture or separately, the resulting mixture is poured into a mold, and heat and pressure are applied to bond the materials together.

Alternatively, another method may be employed in which the binder is melt kneaded in a twin screw extruder and the friction control agent, optional fibrous material and other components are added as a mixture through a hopper or separately into the extruder. The extrudate is then machined to the desired shape.

Alternatively, the fibrous material (if desired) may be dispersed in a binder to which the friction-controlling agent and other optional ingredients are subsequently added to form a mixture, the mixture may be dispersed in, for example, water, wet-laid on a wire, then dewatered to a sheet, the sheet may be bonded together by applying pressure and heat to the sheet in a press, and the resulting product may finally be suitably cut and polished to the desired shape.

Brief Description of Drawings

Fig. 1 is a graph of wear rate versus pad temperature for a-E pads.

Fig. 2 is a graph of the relationship between the coefficient of friction of the a-D disc pad and the disc pad temperature.

Best Mode for Carrying Out The Invention

The following examples, comparative examples and test examples specifically illustrate the present invention. In these examples, "part" and "%" mean "part by weight" and "% by weight", respectively.

Example 1

(1) Synthesis of KTLO-a

67.01 kg of titanium dioxide, 26.78 kg of potassium carbonate, 12.04 kg of potassium chloride, 5.08 kg of lithium hydroxide and also 10 l of water are mixed together as a binder. The mixture was pressed into a brick shape under a pressure of 14.7Mpa using a hydraulic press (Ymamoto Tekkosho, co., ltd.). The brick was calcined in an electric furnace (manufactured by Advantech Toyo co., ltd.) at 1050 ℃ for 1 hour, and then gradually cooled. The calcined product was pulverized to obtain a white powder having an arithmetic average of a long diameter and a short diameter of 22 μm, an average thickness of 2 μm, and a ratio of the long diameter to the short diameter of 3. The X-ray diffraction pattern of the white powder corresponds to ICDD card No.25-1353 (K)_xLi_xTi_2-0.5xO₈). ICP-AES analysis also showed that the powder composition was K_0.8Li_0.27Ti_1.73O₄。

(2) The invention KTLO (K)_0.6Li_0.27Ti_1.73O_3.9) Synthesis of (2)

79.2 l of 10.9% aqueous slurry was prepared using the above-mentioned KTLO-a, to which was subsequently added 4.7 kg of 10% aqueous sulfuric acid solution. The slurry was stirred for 2 hours and then its pH was adjusted to 7.0. The aqueous slurry is treated with a centrifuge. The resulting centrifuge cake (solid) was dispersed, dried at 110 ℃ for 5 hours, and then calcined in an electric furnace at 600 ℃ for 12 hours. The calcined product was gradually cooled and then passed through a 20-mesh sieve to obtain a white powder having an arithmetic mean of a long diameter and a short diameter of 22 μm, a mean thickness of 2 μm, and a ratio of the long diameter to the short diameter of 3. The white powder was determined to have a composition K by IPC-AES analysis_0.6Li_0.27Ti_1.73O_3.9. Therefore, it could be confirmed that KTLO of the present invention is a compound significantly different from KTLO-a.

(3) The invention KTLO (K)_0.5Li_0.27Ti_1.73O_3.85) Synthesis of (2)

79.2 l of 10.9% aqueous slurry was prepared using the above KTLO-a, to which was subsequently added 6.3 kg of 10% aqueous sulfuric acid. The slurry was stirred for 2 hours and then its pH was adjusted to 6.0. The aqueous slurry is treated with a centrifuge. The resulting centrifuge cake (solid) was dispersed, dried at 110 ℃ for 5 hours, and then calcined in an electric furnace at 600 ℃ for 12 hours. The calcined product was gradually cooled and then passed through a 20-mesh sieve to obtain a white powder having an arithmetic mean of a long diameter and a short diameter of 22 μm, a mean thickness of 2 μm, and a ratio of the long diameter to the short diameter of 3. The white powder was determined to have a composition K by IPC-AES analysis_0.5Li_0.27Ti_1.73O_3.85. Therefore, it could be confirmed that KTLO of the present invention is a compound significantly different from KTLO-a.

(4) The invention KTLO (K)_0.7Li_0.27Ti_1.73O_3.95) Synthesis of (2)

79.2 l of 10.9% aqueous slurry was prepared using the above-mentioned KTLO-a, to which was subsequently added 1.2 kg of 10% aqueous sulfuric acid solution. The slurry was stirred for 2 hours and then its pH was adjusted to 8.0. The aqueous slurry is treated with a centrifuge. The resulting centrifuge cake (solid) was dispersed, dried at 110 ℃ for 5 hours, and then calcined in an electric furnace at 600 ℃ for 12 hours. The calcined product was gradually cooled and then passed through a 20-mesh sieve to obtain a white powder having an arithmetic mean of a long diameter and a short diameter of 22 μm, a mean thickness of 2 μm, and a ratio of the long diameter to the short diameter of 3. The white powder was determined to have a composition K by IPC-AES analysis_0.7Li_0.27Ti_1.73O_3.95. Therefore, it could be confirmed that KTLO of the present invention is a compound significantly different from KTLO-a.

Example 2

20 parts of KTLO obtained in example 1,10 parts of aramid fiber (product name: Kevlar Pulp, average fiber length 3 mm), 20 parts of phenol resin (binder), and 50 parts of barium sulfate were mixed. The mixture was preformed at room temperature under 29.4MPa for 1 minute, combined in a mold under 14.7MPa for 5 minutes at 170 ℃ and heat treated at 180 ℃ for 3 hours. The molded product was taken out of the mold and polished to prepare disk pads A-C (JISD4411 test pieces).

Comparative example 1

The procedure of example 2 was repeated except that KTLO-a was used instead of KTLO to manufacture a disc pad D.

Comparative example 2

The procedure of example 2 was followed, except that 30 parts of potassium hexatitanate (cross-sectional diameter of 5 to 10 μm, ratio of long to short diameters of 5) was used instead of 30 parts of KTLO and aramid fibers, to manufacture a disc pad E.

Test example 1: frictional wear test

The prepared disc pads A to E were subjected to a constant-speed wear test (friction disc surface: consisting of FC 25 gray cast iron, surface pressure: 0.98MPa, friction rate: 7 m/s) in accordance with the standard described in JIS D4411 "automobile Friction Lining", and the wear rate (cm)³/kgm) and coefficient of friction (. mu.). The results are shown in FIGS. 1 and 2.

The friction control agents contained in the disc pads a to E are as follows:

a disc pad A: KTLO (K)_0.5Li_0.27Ti_1.73O_3.85)

A disc pad B: KTLO (K)_0.6Li_0.27Ti_1.73O_3.9)

A disc pad C: KTLO (K)_0.7Li_0.27Ti_1.73O_3.95)

A disc pad D: KTLO-a (K)_0.8Li_0.27Ti_1.73O₄)

A disc pad E: potassium hexatitanate(K₂Ti₆O₁₃)

As can be seen from fig. 1 and 2, the disc pads a-C using the KTLO of the present invention showed reduced wear, i.e., excellent wear resistance at 300 ℃ or higher. The coefficient of friction is also shown to be relatively stable to temperature changes.

Industrial applications

The present invention provides lepidocrocite-type lithium potassium titanate suitable for use as a friction control agent.

The friction material of the present invention contains the above lepidocrocite type lithium potassium titanate as a friction control agent, has stable frictional wear properties at low temperature to high temperature regions, and maintains stable wear resistance properties in long-term use.

Claims (4)

1. Lepidocrocite type lithium potassium titanate having the formula K_0.5-0.7Li_0.27Ti_1.73O_3.85-3.95Composition of the representation.

2. The lepidocrocite-type potassium lithium titanate according to claim 1, wherein the lepidocrocite-type potassium lithium titanate has an arithmetic average of a long diameter and a short diameter of 0.1 to 100 μm, a ratio of the long diameter to the short diameter of 1 to less than 10, and an average thickness of 50 to 5000nm, and is in a sheet form.

3. A method for producing lepidocrocite-type lithium potassium titanate according to claim 1 or 2, characterized in that the method comprises: in the formula K_0.8Li_0.27Ti_1.73O₄An acid is added to an aqueous slurry of lepidocrocite-type lithium potassium titanate of the composition shown, the pH of the slurry is adjusted to 6-8, the solids are separated from the slurry and then calcined at 400-700 ℃.

4. A friction material comprising 1 to 80% by weight of the lepidocrocite-type lithium potassium titanate according to claim 1 or 2 as a friction control agent.