FRICTIONAL MATERIALAND METHOD FOR PRODUCING SAME

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to frictional materials and methods for producing frictional materials. More particularly, the invention relates to frictional materials having a granulated material containing resin binder and fiber base material and to methods for producing such frictional materials. For example, frictional materials according to the invention and frictional materials obtained in production methods according to the invention can be effectively applied to brake pads for vehicles, brake linings for vehicles, and clutch facings for vehicles.

2. Description of the Related Art

[0002] In general, frictional material for vehicle brake pads, and the like, contains resin binder (e.g., phenol resin), fiber based material selected from non-organic fiber, organic fiber, and metal fiber, and filler (e.g., friction adjuster). Such friction material is produced by mixing fiber base material, and resin binder, filler, and the like which are powders, in a dried condition and then heating and pressure-forming the mixture.

[0003] As one of such frictional materials, Japanese Patent Application Publication No. 04-139290 (JP-A-4- 139290) describes a frictional material that is obtained by mixing a granulated material that is composed of fillers and resin binder (phenol resin), reinforced fiber, resin binder (phenol resin), and then heating and pressure-forming the obtained mixture. The granulated material is, for example, obtained by mixing metal dust, solid lubricant (graphite), metal oxide, fillers (e.g., cashew dust, non-organic filler), and phenol resin while heating them to 80 ⁰ C, and then cooling them.

[0004] In the case of a frictional material containing granulated materials as the above-described fillers, because resin binders are contained in the granulated materials,

the resin binders are sufficiently provided in the gaps in each filler. Therefore, the adhesiveness between the fillers and the resin binders increases, and thus the function of each filer (e.g., improvement of anti-wear performance) further improves. Further, due to the resin binders provided between the reinforced fibers and the granulated materials, the anti-noise performance is high.

[0005] However, even if a frictional material containing granulated material is used, the friction coefficient of the frictional material decreases in a severe condition, such as when the temperature and pressure at the frictional surface of the frictional material are high, and therefore it is difficult to obtain a high heat resistance (e.g., anti-fade performance). For example, in general, the temperature at the frictional surface of a vehicle brake pad increases up to approx. 800 ⁰ C at maximum. If the temperature at the frictional surface of the frictional material increases up to such a high temperature, the resin binders contained in the frictional material are carbonized, whereby gaps are created in the frictional material. In this case, for example, hard particles that are preferred to be present at the frictional surface of the frictional material are buried in the frictional material. In this case, the load on the hard particles decreases, and therefore the cutting effects of the hard particles deteriorate, resulting in a decrease in the frictional coefficient of the frictional material.

[0006] On the other hand, Japanese Patent Application Publication No. 2006-306970 (JP-A-2006-306970) describes a frictional material that is obtained by carbonizing, through calcination, a mixture of organic material (pitch, phenol resin), non-organic filler (e.g., alumina, magnesium oxide), solid lubricant (e.g., synthetic graphite), metal dusts (e.g., copper dusts, aluminum dusts). According to this publication, organic material is heated, under certain load, at 550 to 1300 ⁰ C in an inactive gas atmosphere, whereby the organic material is carbonized through calcination and thus binder is obtained.

[0007] However, if carbonized organic material is used as binder in a frictional material, the anti-noise performance of the frictional material is relatively low although its heat resistance, such as anti-fade performance, is high.

SUMMARY OF THE INVENTION

[0008] The invention provides frictional materials that provide both improved heat resistance (e.g., anti-fade performance) and improved anti-noise performance.

[0009] The first aspect of the invention relates to a frictional material. This frictional material has a resin binder and a carbonized granulated material dispersedly provided in the resin binder. The carbonized granulated material is obtained by carbonizing a granulated material containing a fiber base material, a resin binder, and at least one kind of filler.

[0010] According to the frictional material of the first aspect of the invention, the carbonized granulated material contains no or almost no organics (e.g., resin binder). Therefore, the amount of organics (e.g., resin binder) contained in the friction material is very small as compared to a frictional material containing non-carbonized granulated materials, and this significantly improves the heat resistance, such as the anti-fade performance.

[0011] According to the frictional material of the first aspect of the invention, because the resin binder is provided between the carbonized granulated materials, the spring constant of the frictional material is smaller than that of a frictional material using carbonized organic material as binder, and therefore the anti-noise performance is high.

[0012] As such, the frictional material of the first aspect of the invention provide both improved heat resistance (e.g., anti-fade performance) and improved anti-noise performance.

[0013] With regard to the above-described frictional material, if the entire mass of the frictional material is 100 pts. mass, the ratio of the resin binder contained in the frictional material is preferably 5 to 25 pts. mass, more preferably 5 to 20 pts. mass, more preferably 10 to 15 pts. mass, and more preferably 12 pts. mass.

[0014] The second aspect of the invention relates to a method for producing a frictional material. This method includes: a granulated material preparation process that prepares a granulated material containing a fiber base material, a resin binder, and at least

one kind of filler; a carbonization process that obtains a carbonized granulated material by carbonizing the granulated material; and a forming process that forms a frictional material by heating and pressure-forming a first mixture containing a resin binder and the carbonized granulated material.

[0015] According to the method of the second aspect of the invention, it is possible to obtain a frictional material in which the carbonized granulated material that is obtained by carbonizing granulated material containing fiber base material, resin binder, and at least one kind of filler is dispersedly provided in the resin binder.

[0016] According to the method of the second aspect of the invention, it is possible to improve both the heat resistance, such as the anti-fade performance that deteriorates if the amount of resin binder contained in the frictional material is too large, and the anti-noise performance that deteriorates if the amount of resin binder contained in the frictional material is too small.

[0017] The method of the second aspect of the invention may be such that, in the granulated material preparation process, a second mixture is obtained by mixing the fiber base material, the resin binder, and the filler, and then the second mixture is heated and then cooled, whereby a granulated material is prepared. In this case, the second mixture may be heated at 70 to 90 ⁰ C. The method of the second aspect of the invention may be such that, in the carbonization process, the granulated material is carbonized by being heated in an inactive gas atmosphere. In this case, the granulated material may be heated at 550 to 1300 ⁰ C in the inactive gas atmosphere. Further, the method of the second aspect of the invention may be such that, in the forming process, the first mixture is pressure-formed while being heated, and the first mixture is then hardened by being heated, whereby a frictional material is prepared. In the forming process, the first mixture may be heated at 150 to 180 °C. In the forming process, the first mixture may be pressure-formed at 10 to 30 MPa. In the forming process, the first mixture may be heated at 200 to 250 ⁰ C for hardening.

[0018] The frictional materials according to the first and second aspects of the invention can be effectively used especially as dry-type frictional materials (e.g., disk

brakes, drum brake linings, clutch facings) the surfaces of which tend to become high in temperature, whereby the heat resistance (e.g., anti-fade performance) and the anti-noise performance can be both achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The features, advantages, and technical and industrial significance of this invention will be described in the following detailed description of example embodiments of the invention with reference to the accompanying drawings, in which like numerals denote like elements, and wherein^

FIG. 1 is a cross-sectional view schematically showing the structure of a frictional material according to an example embodiment of the invention;

FIG. 2 is a graph illustrating the result of examination on the anti-fade performances of a brake pad of the example embodiment of the invention and a brake pad according to a first comparative example;

FIG 3 is a graph illustrating the result of examination on the friction coefficients of a brake pad of the example embodiment of the invention and a brake pad according to the first comparative example;

FIG 4 is a graph illustrating the result of examination on the anti-noise performances of a brake pad of the example embodiment of the invention and a brake pad according to a second comparative example; and

FIG 5 is a graph showing the friction coefficients of the brake pads of the example embodiment each containing a specific amount of resin binder.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] Hereinafter example embodiments of the invention will be described in detail. It is to be understood that the following example embodiments are only exemplary and therefore the frictional materials and the frictional material production methods of the invention are not limited by any of the example embodiments presented in this

specification. That is, the frictional materials and the frictional material production methods of the invention may be modified and improved as needed by those skilled in the art within the scope of the invention.

[0021] Frictional material 10 according to an example embodiment of the invention is shown in FIG 1. The friction material 10 has resin binder 1 and carbonized granulated material 2 that is dispersedly provided in the resin binder 1.

[0022] The kind of the resin binder 1 is not limited to any specific kind. For example, typical resin binder may be used as the resin binder 1. For example, generally used phenol resin, polyimid resin, polyamide-imide resin, polyamide resin, aromatic polyester resin, polyphenylsulfone resin, polyetheretherketone resin, polyfluoroethylene resin, and their modified resins may be used.

[0023] The carbonized granulated material 2 is a carbonized material that is obtained by carbonizing granulated material containing fiber base material, resin binder, and at least one type of filler.

[0024] The kind of the fiber base material is not limited to any specific kind. That is, appropriate fiber base material may be selected according to the characteristics required of the friction material 10. For example, the friction material 10 may be metal fiber, such as copper fiber and aluminum fiber, or may be organic fiber or non-organic fiber.

[0025] The kind of the resin binding material that is used to obtain a granulated material for the carbonization of the carbonized granulated material 2 is not limited to any specific kind. Like the resin binder 1, for example, generally used phenol resin, polyimid resin, polyamide-imide resin, polyamide resin, aromatic polyester resin, polyphenylsulfone resin, polyetheretherketone resin, polyfluoroethylene resin, and their modified resins may be used.

[0026] The kind of the at least one filler contained in the carbonized granulated material 2 is not limited to any specific kind. For example, it may be at least one selected from various friction adjusters and fillers including graphite, sulfide (e.g., molybdenum disulfide, zinc sulfide), cashew dust, non-organic oxide (e.g., calcium

hydroxide, alumina, silica, zirconium silicate, zirconia), barium sulfate, ferric oxide, calcium carbonate, mica, kaolin, talc, and so on.

[0027] The size and shape of the carbonized granulated material 2 are not specifically limited, and its production method is not specifically limited either. For example, the grain size of the carbonized granulated material 2 may be approx. 1 to 10 mm.

[0028] Further, with regard to the carbonized granulated material 2, preferably, at least 90 wt% of the organics (e.g., the resin binder) contained in the granulated material before the above-described carbonization are carbonized, and more preferably said organics are entirely carbonized.

[0029] If the entire mass of the friction material 10 is 100 pts. mass, the ratio of the resin binder 1 is preferably 5-25 pts. mass, more preferably 5-20 pts. mass, and far more preferably 10-15 pts. mass, far more preferably, 12 pts. mass. If the ratio of the resin binder 1 contained in the friction material 10 is too low, the friction material 10 is difficult to be formed properly. On the other hand, if the ratio of the resin binder 1 contained in the friction material 10 is too high, the heat resistance (e.g., anti-fade performance ) of the frictional material 10 deteriorates significantly.

[0030] The friction material 10 of this example embodiment can be effectively used as, for example, dry-type friction materials for vehicles, such as brake pads (disk brake pads), brake linings, clutch facings, and so on.

[0031] The friction material 10 can be produced in the following production method. Note that this production method is only exemplary.

[0032] (Granulated Material Preparation Process)

Fiber base material, powdery resin binder, and at least one kind of filler are uniformly mixed in a dried condition by using a mixer, or the like, and then the obtained mixture is heated then cooled. Then, it is cut into pieces in predetermined sizes, whereby granulated material is obtained. The heating conditions are: heating temperature: approx. 70 to 90 ⁰ C, and heating time: approx. 5 to 120 min.

[0033] (Carbonization Process)

The granulated material obtained in the foregoing preparation process is then carbonized, whereby the carbonized granulated material 2 is obtained. The carbonization condition are: atmosphere: inactive gas atmosphere (e.g., argon gas), heating temperature: 550 to 1300 ⁰ C, and heating time: 1 to 4 hours.

[0034] (Forming Process)

The carbonized granulated material 2 obtained in the foregoing carbonization process and the powdery resin binder 1 are then mixed. Then, the obtained mixture is heated and pressure-formed into a given shape using a metal mold. The molding conditions are: heating temperature: approx. 150 to 180 ⁰ C, pressure: approx. 10 to 30 MPa, time of pressure-forming with heating: approx. 5 to 20 min.

[0035] Next, the obtained product is then heated for hardening, whereby the friction material 10 is obtained. Thus, the friction material 10 is obtained by mixing the carbonized granulated material 2 and the resin binder 1 and then pressure-forming the obtained mixture while heating it. The heating hardening conditions are: heating temperature: approx. 200 to 250 ⁰ C, and heating time: approx. 1 to 6 hours.

[0036] According to the example embodiment, as such, the friction material 10 is obtained which dispersedly contains the carbonized granulated material 2 that is obtained by carbonizing the granulated material containing fiber base material, resin binder, and at least one kind of filler. In the friction material 10, the carbonized granulated material 2 containing no or almost no organics (e.g., resin binder) is dispersedly provided in the resin binder 1. Therefore, the amount of organics (e.g., resin binder) contained in the friction material 10 is very small, and this significantly improves the heat resistance, such as the anti-fade performance. Further, because the resin binder 1 is provided between the carbonized granulated materials 2, the spring constant of the friction material 10 is small, and thus the anti-noise performance is high.

[0037] The friction material 10 of the example embodiment has both improved heat resistance (e.g., anti-fade performance) and improved anti-noise performance.

[0038] Hereinafter, frictional material and a frictional material production method according to the invention will be described in more detail.

[0039] (EXAMPLE EMBODIMENT)

A disk brake pad for vehicle is produced using a frictional material according to an example embodiment of the invention.

[0040] Table 1 shown below indicates the prepared materials and their amounts.

[0041] (Table 1)

[0042] (Granulated material Preparation Process)

Fiber base material such as non-organic fiber (potassium titanate fiber), brass fiber, aramid fiber, resin binder such as phenol resin powder, and various powders such as graphite, sulfide (molybdenum disulfide), cashew dust, calcium hydroxide, and barium sulfate which function as fillers were mixed in a dried condition. The mixing was uniformly performed for 5 minutes using EIRICH mixer.

[0043] Then, the obtained mixture was cooled at 80 ⁰ C for 60 minutes, and then it was cut into pieces in predetermine sizes, whereby granulated material was obtained.

[0044] (Carbonization Process)

The granulated material was then heated in argon gas at 1000 ⁰ C for 4 hours for carbonization, whereby carbonized granulated material 2 having a diameter of approx. 3 to 5 mm was obtained.

[0045] In the carbonized granulated material 2 thus obtained, all the organics (e.g., resin binder) contained in the granulated material before the carbonization had been all carbonized.

[0046] (Forming Process) The carbonized granulated material 2 obtained in the foregoing carbonization process and

the resin binder 1 (phenol resin powder) were mixed. Then, the obtained mixture was put in a metal mold that had been heated up to 160 ⁰ C and then pressure-heated therein at a pressure of 19.6 MPa for 10 minutes, and then it was heated in the metal mold at 230 ⁰ C for three hours for hardening, whereby a disk brake pad having a desire shape was obtained.

[0047] If the entire mass_of the obtained disk brake pad is 100 pts. mass, the ratio of the phenol resin contained in the disk brake pad produced in the manner described above was 12 pts. mass.

[0048] (First comparative example)

In this example, a disk brake pad was produced in a procedure identical to that of the foregoing example embodiment except that the carbonization process was not performed.

[0049] That is, in this comparative example, the respective materials shown in Table 1 above were prepared, and granulated material is prepared through the granulated material preparation process of the foregoing example embodiment. Then, a disk brake pad having a desired shape was produced using the obtained granulated material through the preparation process of the foregoing example embodiment.

[0050] If the entire mass of the obtained disk brake pad is 100 pts. mass, the ratio of the phenol resin contained in the disk brake pad of the first comparative example was 26 pts. mass.

[0051] (Second comparative example)

In this example, the respective materials shown in Table 1 were mixed in a dried condition. The amount of each material was as shown in Table 1. Then, the obtained mixture was put in the metal mold that had been heated up to 160 °C and then heated therein at a pressure of 19.6 MPa for 10 minutes for pressure forming, and then it was heated in the metal mold at 230 ⁰ C for three hours for hardening.

[0052] Then, the obtained product was carbonized by being heated in an argon gas atmosphere at 1000 ⁰ C for four hours, whereby a carbonized disk brake pad in which the organics (e.g., phenol resin) had been carbonized was obtained.

[0053] If the entire mass of the obtained disk brake pad is 100 pts. mass, the ratio of

the phenol resin contained in the disk brake pad was 0 pts. mass.

[0054] (Examination of heat-resistance)

The friction coefficient of the brake pad of the example embodiment of the invention and the brake pad of the first comparative example were examined based on Japanese Automobile Standards Organization (JASO) C 406. FIG. 2 shows the examination result based on "First Fading Test", and FIG 3 shows the examination result based on "Second Effect Test".

[0055] As shown in FIG. 2, the anti-fade performance of the disk brake pad of the example embodiment of the invention that contains the carbonized granulated material was much higher than that of the disk brake pad of the first comparative example that contains granulated material including phenol resin.

[0056] Further, as shown in FIG. 3, in a high frictional-face hydraulic pressure range of 5 MPa or higher, the rate of decrease in the frictional coefficient of the brake pad of the first comparative example is higher than the rate of decrease in the frictional coefficient of the brake pad of the example embodiment of the invention.

[0057] As such, it was confirmed that a brake pad containing carbonized granulated material provides a higher anti-fade performance and provides a high frictional coefficient even under a severe condition where the pressure at the friction surface of the brake pad is high at a high temperature, thus exhibiting a high heat resistance.

[0058] (Anti-noise performance)

An anti-noise performance test was conducted to the brake pad of the example embodiment of the invention and the brake pad of the second comparative example by actually mounting them in vehicles. FIG. 4 shows the result of the test. Note that "NOISE RATE (%)" in FIG 4 represents the ratio of the number of times brake noises were created to the number of times braking was performed.

[0059] As shown in FIG 4, the anti-noise performance of the brake pad of the example embodiment of the invention that contains the carbonized granulated material was significantly higher than that of the carbonized brake pad of the second comparative example.

[0060] As such, it was confirmed that a brake pad containing carbonized granulated material provides a higher anti-noise performance.

[0061] (Examination of composition ratio of resin binder)

When preparing the granulated material in the foregoing example embodiment, various brake pads each containing resin binder at the composition ratio indicated in Table 2 below were produced by, for example, replacing part of phenol resin with barium sulfate or by replacing part of barium sulfate with phenol resin.

[0062] The friction coefficients of the obtained brake pads were examined under Japanese Automobile Standards Organization (C 406). Note that the examination was performed based on the result of "First Fade Test". FIG. 5 and Table 2 show the result of the examination.

[0063] Table 2

[0064] As shown in Table 2 and FIG. 5, assuming that the entire mass of the brake pad is 100 pts. mass, if the ratio of the resin binder contained in the brake pad is higher than 25 pts. mass, the anti-fade performance value Minμ is lower than the target value that is at least 0.15.

[0065] Further, if the amount of the resin binder contained in the brake pad was within 5 to 20 pts. mass, Minμ became 0.2 or more, exhibiting an improved anti-fade performance. Further, when the amount of the resin binder contained in the brake pad was within 10 to 15 pts. mass, Minμ became 0.25 or more, exhibiting a further improved anti-fade performance. Furthermore, when the amount of the resin binder contained in the brake pad was 12 pts. mass, Minμ became 0.28, exhibiting a furthermore improved anti-fade performance.

[0066] When the amount of the resin binder was smaller than 5 pts. mass, it was difficult to form the brake pad.

[0067] Thus, it was confirmed through the examination that the ratio of resin binder contained in the brake pad is preferably 5 to 25 pts. mass, more preferably 5 to 20 pts.

mass, more preferably 10 to 15 pts. mass, and far more preferably 12 pts. mass.