Friction material

Abstract

This friction material contains a fiber base material, a friction modifier and a binder. The content of copper in the friction material is not more than 0.5 mass % in terms of elemental copper, and the content of the binder is at least 10 mass %. Furthermore, the friction material contains calcium hydroxide and zinc, and has a pH of at least 11.7.

Claims

1. A friction material comprising: a fiber base material; a friction modifier; and a binder, wherein a content of copper is 0.5% by mass or less in terms of copper element, wherein a content of the binder is 10% by mass or more, wherein the friction material contains calcium hydroxide and zinc, wherein the friction material has pH of 113 or more, wherein a content of the zinc is from 1% by mass to 5% by mass, wherein the zinc comprises a powder having an average particle diameter in a range of 1 m to 10 m, wherein the calcium hydroxide comprises powder having an average particle diameter in a range of 5 m to 50 m, wherein the fiber base material comprises a bio-soluble inorganic fiber, and wherein the binder consists of at least one selected from the group consisting of an acrylic rubber-modified phenol resin, a silicone rubber-modified phenol resin, an NBR rubber-modified phenol resin, a cashew-modified phenol resin, an epoxy-modified phenol resin and an alkylbenzene-modified phenol resin.

2. The friction material according to claim 1, wherein a content of the calcium hydroxide is from 2% by mass to 6% by mass.

3. The friction material according to claim 1, wherein the bio-soluble inorganic fiber is at least one selected from the group consisting of SiO.sub.2CaOMgO-based fiber, SiO.sub.2CaOMgOAl.sub.2O.sub.3-based fiber and SiO.sub.2MgOSrO-based fiber.

4. A friction material comprising: a fiber base material; a friction modifier; and a binder, wherein a content of copper is 0.5% by mass or less in terms of copper element, wherein a content of the binder is 10% by mass or more, wherein the friction material contains calcium hydroxide and zinc, wherein the friction material has pH of 11.7 or more, wherein a content of the zinc is from 1% by mass to 5% by mass, wherein the zinc comprises a powder having an average particle diameter in a range of 1 m to 10 m, wherein the calcium hydroxide comprises powder having an average particle diameter in a range of 5 m to 50 m, wherein the fiber base material comprises a bio-soluble inorganic fiber, wherein the binder consists of at least one selected from the group consisting of a straight phenol resin, an acrylic rubber-modified phenol resin, a silicone rubber-modified phenol resin, an NBR rubber-modified phenol resin, a cashew-modified phenol resin, an epoxy-modified phenol resin and an alkylbenzene-modified phenol resin, and wherein a content of the fiber base material is 10% by mass or more and 50% by mass or less.

5. The friction material according to claim 4, wherein a content of the calcium hydroxide is from 2% by mass to 6% by mass.

6. The friction material according to claim 4, wherein the bio-soluble inorganic fiber is at least one selected from the group consisting of SiO.sub.2CaOMgO-based fiber, SiO.sub.2CaOMgOAl.sub.2O.sub.3-based fiber and SiO.sub.2MgOSrO-based Fiber.

7. A friction material comprising: a fiber base material; a friction modifier; and a binder, wherein a content of copper is 0.5% by mass or less in terms of copper element, wherein a content of the binder is 10% by mass or more, wherein the friction material contains calcium hydroxide, zinc, and zirconium silicate, wherein the friction material has pH of 11.7 or more, wherein a content of the zinc is from 1% by mass to 5% by mass, wherein the zinc comprises a powder having an average particle diameter in a range of 1 m to 10 m, wherein the calcium hydroxide comprises powder having an average particle diameter in a range of 5 m to 50 m, wherein the fiber base material comprises a bio-soluble inorganic fiber, and wherein the binder consists of at least one selected from the group consisting of a straight phenol resin, an acrylic rubber-modified phenol resin, a silicone rubber-modified phenol resin, an NBR rubber-modified phenol resin, a cashew-modified phenol resin, an epoxy-modified phenol resin and an alkylbenzene-modified phenol resin.

8. The friction material according to claim 7, wherein a content of the calcium hydroxide is from 2% by mass to 6% by mass.

9. The friction material according to claim 7, wherein the bio-soluble inorganic fiber is at least one selected from the group consisting of SiO.sub.2CaOMgO-based fiber, SiO.sub.2CaOMgOAl.sub.2O.sub.3-based fiber and SiO.sub.2MgOSrO-based fiber.

Description

MODE FOR CARRYING OUT THE INVENTION

(1) Modes for carrying out the present invention will be described in detail below. However, the following embodiments are only examples, and the present invention should not be construed as being limited thereto.

(2) In this description, % by mass and % by weight have the same meanings.

(3) In a friction material in the present invention, a copper component is not substantially contained in the friction material. Here, a copper component is not substantially contained means that a copper component is not contained as an active substance for exhibiting functions such as abrasion resistance, and does not mean that, for example, a copper component as an impurity or the like inevitably slightly contained in the friction material is not contained. Specifically, it means that the content thereof is 0.5% by mass or less based on the whole amount of the friction material. Examples of the copper components also include copper itself, copper alloys of copper and other metals such as zinc, nickel, manganese, aluminum or tin, and copper compounds such as copper oxides and copper sulfides.

(4) In the blending for the friction material, materials usually employed are used, as long as they are in accordance with the spirit of the present invention. As fiber base materials for reinforcement, examples thereof include organic fibers, inorganic fibers, metal fibers and the like. However, copper component-containing copper fiber, bronze fiber and brass fiber are not used.

(5) As the organic fibers, examples thereof include aromatic polyamide (aramid) fiber, flame-resistant acrylic fiber, cellulose fiber and the like, and these may be used individually or in combination of two or more kinds thereof.

(6) Examples of the inorganic fibers include ceramic fibers such as potassium titanate fiber and alumina fiber, glass fiber, carbon fiber, rock wool and the like, and examples of the metal fibers include steel fiber and the like. These may be used individually or in combination of two or more kinds thereof.

(7) As the inorganic fiber to be used in the present invention, bio-soluble inorganic fiber is preferred from the point of a small influence on human body. The bio-soluble inorganic fiber mentioned herein means an inorganic fiber having a feature that even when incorporated into human body, it is decomposed in a short period of time and eliminated from the body. Specifically, it indicates an inorganic fiber satisfying that the total amount of alkali metal oxides and alkaline earth metal oxides (the total amount of oxides of sodium, potassium, calcium, magnesium and barium) is 18% by mass or more in a chemical composition thereof, that the mass half-life of the fiber of 20 m or more is within 40 days in a respiratory short-term biodurability test, and that there is no evidence of excessive carcinogenicity in an intraperitoneal test, or that there is no relating pathogenicity or tumor occurrence in a long-term respiration test (Note Q (exclusion from application of carcinogenicity) of EU directive 97/69/EC).

(8) Examples of such bio-soluble inorganic fiber include bio-soluble ceramic fiber and bio-soluble rock wool, such as SiO.sub.2CaOMgO-based fiber, SiO.sub.2CaOMgOAl.sub.2O.sub.3-based fiber and SiO.sub.2MgOSrO-based fiber, and the like.

(9) The content of the fiber base material is preferably from 5% by mass to 50% by mass, and more preferably from 5% by mass to 30% by mass, based on the whole amount of the friction material, in order to secure sufficient mechanical strength.

(10) The binder to be used in the present invention unifies a friction modifier, the fiber base material and the like which are contained in the friction material to give strength. There is no particular limitation on the binder contained in the friction material in the present invention, and a thermosetting resin usually used as a binder in a friction material can be used.

(11) Examples of the above-mentioned thermosetting resins include straight phenol resins, various phenol resins modified with elastomers or the like, such as acrylic rubber-modified phenol resins, silicone rubber-modified phenol resins and NBR rubber-modified phenol resins, various modified phenol resins such as cashew-modified phenol resins, epoxy-modified phenol resins and alkylbenzene-modified phenol resins, melamine resins, epoxy resins, polyimide resins and the like, and these may be used individually or in combination of two or more kinds thereof.

(12) The content of the binder is preferably 10% by mass or more based on the whole amount of the friction material, in order to secure sufficient mechanical strength and abrasion resistance. Further, as the upper limit thereof, it is more preferably 15% by mass or less.

(13) In the friction material in the present invention, zinc which can be expected to have a rust preventing function is blended as the friction modifier.

(14) Zinc may be either powdery or fibrous. When it is powdery, the average particle diameter thereof is preferably from 1 m to 10 m, and more preferably from 1 m to 7 m, from the viewpoint of abrasion resistance.

(15) The content of zinc is preferably from 1% by mass to 5% by mass, and more preferably from 2% by mass to 4% by mass. When the blending amount of zinc is 1% by mass or more, it is preferred in terms of the rust preventing function, and in the case of 5% by mass or less, it is preferred in terms of securing the effectiveness.

(16) The pH of the friction material in the present invention is 11.7 or more, preferably 11.8 or more, and particularly preferably 12 or more. When the pH of the friction material is within such a range, the rust preventing performance can be further improved, and the friction material suppressed in the occurrence of noise can be obtained.

(17) The pH of the friction material can be identified by mixing the friction material pulverized and water, allowing the resulting mixture to stand for a predetermined period of time, followed by filtration, and measuring the pH of a filtrate.

(18) In the present invention, in order to control the pH of the whole friction material to 11.7 or more as described above, it is desirable to add calcium hydroxide as a pH control material.

(19) Further, the blending amount thereof can be determined at the discretion of those skilled in the art, based on the set pH. For example, when calcium hydroxide is used, it is preferably from 1% by mass to 10% by mass, and more preferably from 2% by mass to 6% by mass, based on the whole amount of the friction material.

(20) When calcium hydroxide is used, a powder having an average particle diameter of preferably from 5 m to 100 m, more preferably from 5 m to 50 m is used, thereby being able to continuously maintain the pH of the friction material. Within this range, the pH of the whole friction material can be controlled, and the partial generation of rust on a counterpart material (rotor) can be prevented. The average particle diameter is a value (median value) measured with a laser diffraction particle size analyzer.

(21) In addition to the above, the following inorganic filler, organic filler, abrasive, solid lubricant or the like can be appropriately mixed as the friction modifier contained in the friction material in the present invention.

(22) Examples of the abrasives include alumina, silica, magnesia, zirconia, zirconium silicate, chromium oxide, triiron tetraoxide (Fe.sub.3O.sub.4), chromite and the like. Examples of the solid lubricants include graphite, coke, antimony trisulfide, molybdenum disulfide, tin sulfide, polytetrafluoroethylene (PTFE) and the like. Examples of the inorganic fillers include inorganic compounds such as magnesium carbonate, barium sulfate and calcium carbonate, non-whisker-shaped titanic acid compounds such as potassium titanate, lithium titanate, lithium potassium titanate, sodium titanate, calcium titanate, magnesium titanate and magnesium potassium titanate, scale-shaped inorganic substances such as mica and vermiculite, powders of metals such as aluminum, tin and zinc, and the like. These may be used individually or in combination of two or more kinds thereof.

(23) The content of the abrasive is preferably from 1% by mass to 20% by mass based on the whole amount of the friction material, depending on friction properties required, the content of the solid lubricant is preferably from 1% by mass to 15% by mass based on the whole amount of the friction material, and the content of the inorganic filler is preferably from 40% by mass to 60% by mass based on the whole amount of the friction material.

(24) As the organic filler, cashew dust, a rubber component or the like can be used. Examples of the above-mentioned rubber components include tire rubber, natural rubber, acrylic rubber, isoprene rubber, polybutadiene rubber, nitrile-butadiene rubber, styrene-butadiene rubber and the like, and these may be used individually or in combination of two or more kinds thereof. Further, the cashew dust and the rubber component may be used together.

(25) The organic filler is used in an amount of preferably 1% by mass to 15% by mass, more preferably 1% by mass to 10% by mass, based on the whole friction material.

(26) As a specific embodiment of a method for producing the friction material in the present invention, conventional production steps can be used. For example, the friction material can be produced by blending the above-mentioned respective components, and subjecting the resulting blend to steps such as preforming, thermoforming, heating and grinding, according to an ordinary production method.

(27) Steps commonly used in the production of a brake pad including the friction material are shown below:

(28) (a) a step of forming a pressure plate into a predetermined shape by a sheet-metal press;

(29) (b) a step of subjecting the above-mentioned pressure plate to degreasing treatment, chemical conversion treatment and primer treatment;

(30) (c) a step of preparing a preformed body by blending raw materials such as the fiber base material, the friction modifier and the binder, sufficiently homogenizing them by stirring, and performing forming at room temperature and a predetermined pressure;

(31) (d) a thermoforming step of integrally fixing both members of the above-mentioned preformed body and the pressure plate coated with an adhesive, by applying a predetermined temperature and pressure (forming temperature: 130 C. to 180 C., forming pressure: 30 MPa to 80 MPa, forming time: 2 minutes to 10 minutes); and

(32) (e) a step of performing after-curing (150 C. to 300 C., 1 hour to 5 hours), and finally performing finishing treatments such as grinding, scorching and painting.

EXAMPLES

(33) The present invention is more specifically described below by examples. However, the present invention should not be limited to these examples alone.

Examples 1 to 4 and Comparative Examples 1 to 5

Preparation of Friction Materials

(34) Steps of preparing a friction material are as follows.

(35) 1. Mixing of Raw Materials

(36) Blending raw materials were collectively put in a mixer, followed by mixing and stirring at room temperature for 5 minutes. As the specific raw materials, the raw materials shown below were used. Each specific blending ratio is shown in the table.

(37) Phenol resin: manufactured by Sumitomo Bakelite Co., Ltd.

(38) Calcium hydroxide: manufactured by Chichibu Lime Industry Co., Ltd.

(39) Zinc: manufactured by Sakai Chemical Industry Co., Ltd.

(40) 2. Preparation Steps

(41) Each mixture composed of the above-mentioned blending materials was subjected to steps such as preforming, thermoforming, heating and grinding, thereby preparing the friction material.

(42) (1) Preforming

(43) The mixture of the above-mentioned raw materials was put in a mold for preforming press, followed by forming at room temperature under 15 MPa for 10 seconds, thereby preparing a preformed body.

(44) (2) Thermoforming

(45) This preformed body was put in a thermoforming mold, and a metal plate (pressure plate: P/P) previously coated with an adhesive was laminated thereon, followed by thermopressure forming at 150 C. under 45 MPa for 5 minutes.

(46) (3) Heat Treatment

(47) After this thermopressure formed body was heat-treated at 250 C. for 3 hours, grinding was performed so as to have a predetermined thickness of 15 mm, and painting was performed, thereby obtaining the friction material (pad area: 20 cm.sup.2).

(48) The following evaluations were performed by using the above-mentioned friction material.

(49) 1. pH Test

(50) (1) The friction material is pulverized with a drill to prepare a powdery sample.

(51) (2) 6 g of the sample and 200 ml of distilled water are added into a beaker, followed by stirring and allowing to stand for 16 hours.

(52) (3) Filtering is performed while well stirring the sample, and the pH of a filtrate is measured with a pH meter.

(53) 2. Seizure Due to Corrosion (Sticking Property)

(54) Evaluation was performed in a vehicle by operations shown below (evaluation was performed in Rr built-in). As a counterpart material (rotor), a cast iron material (FC250) was used.

(55) (1) Burnishing: speed: 40 km/h, deceleration: 1.96 m/s.sup.2, pad IBT: 50 C. or lower, the number of times that braking was applied: 30 times

(56) (2) Watering: 15 L/min for 3 minutes

(57) (3) Braking 3 times in creeping

(58) (4) Standing outdoors with a parking brake applied to 11 notch

(59) (5) Confirmation of sticking

(60) (6) The operations of Nos. (2) to (5) were repeated.

(61) In the test on the first day, the second day and third days, and after standing for three nights, the sound pressure of the vehicle was measured. Further, the rusting ratio (%) on a rotor surface after standing for three nights was calculated.
Rusting ratio (%)=(rotor rusting area of pad contact part)/(pad area)100

(62) Evaluation of the rusting ratio was carried out by A, B and C, and judgment was made by the rusting ratio according to criteria for judgment as described below.

(63) A: The rusting ratio (%) was less than 50%.

(64) B: The rusting ratio (%) was 50% or more and less than 80%.

(65) C: The rusting ratio (%) was 80% or more.

(66) <Evaluation Results>

(67) The evaluation results of the friction materials are shown in Table 1.

(68) It has been found that, as compared to Comparative Example 1 of the conventional friction material in which copper was blended, in the friction materials of Examples 1 to 4, they show performance equivalent to or more than that thereof for the rusting ratios in the sticking evaluation, even when no copper was blended, and accordingly the sound pressure generated at the time of creep starting is decreased. Further, particularly, in the friction materials of Examples 2 to 4 having pH exceeding 12, the rusting ratios significantly decrease as low as 15% or less, and this shows remarkable synergistic effect by combinations of the blending materials in the present invention.

(69) Furthermore, from a comparison of Comparative Example 5 and Example 1, it has been found that an increase of 1% by mass in the content of the binder improves the strength of the friction material, thereby decreasing the rusting ratio of the rotor, so that the content of the binder also becomes an important requirement.

(70) TABLE-US-00001 TABLE 1 Comparative Example Example (% by mass) 1 2 3 4 5 1 2 3 4 Blending Binder Phenol Resin 9 9 9 9 9 10 10 10 11 Composition Friction Organic Filler Cashew Dust 5 5 5 5 5 5 5 5 5 Modifier Rubber Dust 5 5 5 5 5 5 5 5 5 Inorganic Filler Barium Sulfate 21 26 26 25 25 24 24 23 22 Potassium Titanate 21 27 26 26 25 25 24 24 22 Mica 4 4 4 4 4 4 4 4 4 Calcium Hydroxide 2 2 0 1 2 2 3 4 6 Abrasive Zirconium Silicate 3 3 3 3 3 3 3 3 3 Iron Oxide 4 4 4 4 4 4 4 4 4 Solid Lubricant Graphite 5 5 5 5 5 5 5 5 5 Metal Powder Zinc 0 0 3 3 3 3 3 3 3 Fiber Base Organic Fiber Aramid Fiber 5 5 5 5 5 5 5 5 5 Material Inorganic Fiber Bio-Soluble Inorganic 5 5 5 5 5 5 5 5 5 Fiber Metal Fiber Copper Fiber 11 0 0 0 0 0 0 0 0 Total 100 100 100 100 100 100 100 100 100 pH of Friction Material 11.6 11.8 10.7 11.5 11.8 11.8 12.3 12.5 12.5 Sticking Evaluation Sound Pressure (dB) First Day 46.2 54.2 56.5 51.3 42.0 46.3 44.8 46.8 46.4 (Vehicle) Second Day 54.5 62.5 66.4 60.2 48.5 50.5 43.3 43.7 50.5 Third Day 55.6 68.5 65.2 66 45.9 51.6 45.2 48.7 48.6 Standing for 60.5 *71.3 *73.5 *71.8 62.2 56.5 56.9 49.7 49.2 Three Nights Rusting Ratio (%) 45 90 95 100 50 45 15 5 5 Evaluation of Rusting Ratio A C C C B A A A A *Not creep startable

(71) While the present invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the present invention. This application is based on Japanese Patent Application No. 2013-234268 filed on Nov. 12, 2013, the contents of which are incorporated herein by reference.

INDUSTRIAL APPLICABILITY

(72) The friction material in the present invention can decrease the generation of rust caused by sticking which becomes liable to occur due to blending no copper fiber, by adjusting the content of the binder to 10% by mass or more, blending calcium hydroxide and zinc, and maintaining the pH of the friction material to 11.7 or more. Accordingly, the occurrence of noise can be suppressed, and friction properties equivalent to that of the case where copper fiber is blended can be secured, so that demand as the friction material containing substantially no copper component and suitable for a wide variety of types of vehicles such as passenger automobiles is expected.