JP2008208314A - Friction material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a friction material excellent in high temperature characteristics. <P>SOLUTION: The friction material 2 comprises a reinforcing fiber, a filler, a rubber composition and a binder resin. The rubber composition contains a carbon nanofiber having 0.5-500 nm average diameter uniformly dispersed in a nitrile rubber which is a matrix and has 100-3,000 μsec first spin-spin relaxation time (T2n) in a non-crosslinked material measured by the Hahn echo method using pulsed NMR at 150°C, and <0.2 component fraction (fnn) of a component having the second spin-spin relaxation time (T2nn). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a friction material excellent in high temperature characteristics.

  For friction materials used for disc brake pads, drum brake shoes, clutch facings for clutches, etc. of automobiles and other vehicles, thermosetting phenol resin is used as a matrix (base material), and inorganic and organic fibers. A friction material containing a reinforcing fiber such as a filler and a filler containing vulcanized rubber powder is known (see, for example, Patent Document 1). Examples of the vulcanized rubber powder used as the filler include silicone rubber (Q), fluorine rubber (FKM), ethylene / propylene rubber (EPDM), and nitrile rubber (NBR). Nitrile rubber is generally used. It was. Nitrile rubber in the friction material increases the coefficient of friction by making the contact between the friction material and the disc rotor uniform, for example, due to its flexibility, and for example, the noise of the disc brake due to its damping characteristic (loss tangent (tan δ)). Was reduced. However, although nitrile rubber is excellent in damping characteristics and dynamic elastic modulus near room temperature, the damping characteristics (loss tangent (tan δ)) at a high temperature, for example, 120 ° C. or higher are low, and the deterioration start temperature is relatively low. Therefore, for example, when the friction material becomes high temperature due to continuous braking of the disc brake, the dynamic elastic modulus and damping characteristics of the nitrile rubber contained in the friction material decrease, the friction coefficient of the friction material decreases, Uneven wear sometimes occurred.

  Further, a friction material containing a thermosetting resin as a matrix and carbon nanofibers as a filler has been proposed (see, for example, Patent Document 2). However, carbon nanofibers are expensive, and their use as fillers for improving the mechanical strength of friction materials has not yet progressed. In particular, the carbon nanofibers easily aggregate and are difficult to uniformly disperse in the resin matrix. As a result, a sufficient effect cannot be obtained as a whole unless the blending ratio of the carbon nanofibers is increased.

According to the carbon fiber composite material manufacturing method previously proposed by the present inventors, it is possible to improve the dispersibility of carbon nanofibers, which has been considered difficult so far, and to uniformly disperse the carbon nanofibers in the elastomer. (For example, see Patent Document 3). According to such a method for producing a carbon fiber composite material, an elastomer and carbon nanofibers are kneaded, and dispersibility of carbon nanofibers having high cohesiveness is improved by shearing force. More specifically, when the elastomer and the carbon nanofiber are mixed, the viscous elastomer penetrates into the carbon nanofiber, and a specific part of the elastomer has a high activity of the carbon nanofiber due to chemical interaction. In this state, when a strong shearing force is applied to a mixture of an elastomer having high molecular mobility (elasticity) and carbon nanofibers, the carbon nanofibers are deformed as the elastomer is deformed. The fibers also moved, and the aggregated carbon nanofibers were separated and dispersed in the elastomer by the restoring force of the elastomer due to elasticity after shearing. Thus, by improving the dispersibility of the carbon nanofibers in the matrix, expensive carbon nanofibers can be efficiently used as fillers for composite materials.
JP 2005-336340 A JP 2004-217828 A JP 2005-97525 A

  An object of the present invention is to provide a friction material having excellent high temperature characteristics.

The friction material according to the present invention is
A friction material comprising a reinforcing fiber, a filler, a rubber composition, and a binder resin,
The rubber composition is a non-crosslinked product in which carbon nanofibers having an average diameter of 0.5 to 500 nm are uniformly dispersed in a nitrile rubber as a matrix and measured at 150 ° C. by a Hahn echo method using pulse NMR. The first spin-spin relaxation time (T2n) is 100 to 3000 μs, and the component fraction (fnn) of the component having the second spin-spin relaxation time (T2nn) is less than 0.2.

  According to the friction material of the present invention, since T2n and fnn of the rubber composition are in such a range, the carbon nanofibers are uniformly dispersed in the nitrile rubber, and thereby the deterioration start temperature of the rubber composition. Thus, the rubber composition can maintain excellent damping characteristics and high dynamic modulus even at high temperatures. As a result, the friction material according to the present invention has a high coefficient of friction at high temperatures, and can reduce squeal at high temperatures due to contact with the friction target member. Moreover, according to the friction material concerning this invention, the amount of wear can be reduced by the uniform contact with a to-be-rubbed member.

  In the friction material according to the present invention, the rubber composition may be a non-crosslinked body.

  In the friction material according to the present invention, the rubber composition may be a crosslinked body.

  In the friction material according to the present invention, the rubber composition may include 5 to 100 parts by weight of the carbon nanofibers with respect to 100 parts by weight of the nitrile rubber.

  In the friction material according to the present invention, the rubber composition may include 40 to 80 parts by weight of carbon black and 5 to 20 parts by weight of the carbon nanofibers with respect to 100 parts by weight of the nitrile rubber.

  In the friction material according to the present invention, the rubber composition may have a loss tangent (tan δ) at 200 ° C. of 0.05 to 1.00.

  In the friction material according to the present invention, the rubber composition may have a dynamic elastic modulus (E ′) at 200 ° C. of 10 MPa to 1000 MPa.

  In the friction material according to the present invention, the rubber composition may have a deterioration start temperature of 160 ° C. to 300 ° C. in thermomechanical analysis.

  In the friction material according to the present invention, the binder resin may be a phenol resin.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a front view showing a pad 1 using a friction material 2 according to the present embodiment. FIG. 2 is a partially cutaway plan view showing the pad 1 using the friction material 2 according to the present embodiment. FIG. 3 is a rear view of the pad 1 using the friction material 2 according to the present embodiment. FIG. 4 is a longitudinal sectional view showing an example of a disc brake 10 used for a vehicle brake.

  The friction material 2 according to the present embodiment is a friction material including a reinforcing fiber, a filler, a rubber composition, and a binder resin, and the rubber composition has an average diameter on a nitrile rubber that is a matrix. The first spin-spin relaxation time (T2n) in the non-crosslinked body, measured at 150 ° C. by the Hahn echo method using pulsed NMR, is uniformly dispersed. The component fraction (fnn) of the component having the second spin-spin relaxation time (T2nn) is less than 0.2.

(pad)
As shown in FIG. 4, the structure of the disc brake 10 used in an automobile or the like is transmitted to the hydraulic chamber 14 of the caliper body 11 by, for example, hydraulic pressure by a hydraulic device, presses the piston 12, and the pressing force presses the pad. The first and first friction members 2 and 2 are pressed so as to sandwich the disk-shaped disk rotor 13, and the rotation of the disk rotor 13 is braked by the friction action. As shown in FIGS. 1 to 3, the pad 1 of the disc brake 10 includes a metal back plate 3 (hereinafter referred to as “plate 3”) pressed against the caliper body 11 and the piston 12 via the shim plate 5. The friction material 2 is configured to generate a frictional force in contact with the disk rotor 13. The friction material 2 has a flat surface 21 that comes into contact with the disk rotor 13, and a part of the friction material 2 enters the two binding holes 4, 4 formed in the plate 3, so that the friction material 2 is firmly bonded to the plate 3. It is worn. The type of the disc brake 10 is not limited to the pin slide type as in the present embodiment, but may be an opposed type disc brake in which pistons are arranged on both sides of the disc rotor, and the number of pistons and the shape of the shim plate are also the same. The present invention is not limited to the embodiment. In the present embodiment, the friction material 2 used for the pad 1 of the disc brake 10 has been described. However, the friction material 2 can be applied to, for example, a friction material for a shoe of a drum brake (not shown) or a clutch facing for a clutch. is there.

(Reinforcing fiber, filler, binder resin)
Conventionally used materials can be appropriately selected and used as the reinforcing fibers and fillers to be mixed with the binder resin. Examples of such reinforcing fibers include inorganic fibers such as alumina fibers, glass fibers, rock wool, potassium titanate fibers, ceramic fibers, silica fibers, kaolin fibers, bauxite fibers, cananoid fibers, boron fibers, magnesia fibers, and metal fibers. Organic fibers such as fiber, polyester fiber, polyamide fiber, polyimide fiber, polyvinyl alcohol modified fiber, polyvinyl chloride fiber, polypropylene fiber, polybenzimidazole fiber, acrylic fiber, carbon fiber, phenol fiber, nylon fiber, and cellulose fiber One or two or more selected from the above can be used in combination. Examples of the filler include organic fillers such as cashew dust and melamine dust, carbon black, barium sulfate, calcium carbonate, magnesium carbonate, silicon carbide, boron carbide, titanium carbide, silicon nitride, boron nitride, alumina, and silica. Inorganic fillers such as zirconia, graphite, talc and metal powder, lubricants, and pH adjusters can be used alone or in combination.

  The binder resin that is the binder of the reinforcing fiber and filler of the friction material 2 according to the present embodiment is preferably a thermosetting phenol resin, but other curable resins such as unsaturated polyester resins, epoxy resins, Resins such as vinyl ester resins, alkyd resins, acrylic resins, melamine resins, xylene resins, guanamine resins, diallyl phthalate resins, allyl ester resins, furan resins, imide resins, urethane resins, and urea resins can be used. Specific examples of the phenol resin include a resol type phenol resin and a novolac type phenol resin, and a novolac type phenol resin is preferable. Such a phenol resin may be modified or unmodified. Binder resin can be used individually by 1 type or in mixture of 2 or more types. In particular, in a field where airtightness is required, it is preferable to select a resin that does not generate gas in the curing reaction, such as a combination of an epoxy resin and a phenol resin. By using these resins, it is possible to obtain a molded product having high airtightness without voids in the cured product.

(Rubber composition)
The rubber composition is a non-crosslinked product in which carbon nanofibers having an average diameter of 0.5 to 500 nm are uniformly dispersed in a nitrile rubber as a matrix and measured at 150 ° C. by a Hahn echo method using pulse NMR. The first spin-spin relaxation time (T2n) is 100 to 3000 μs, and the component fraction (fnn) of the component having the second spin-spin relaxation time (T2nn) is less than 0.2. The rubber composition can be blended with the friction material in the form of a non-crosslinked body. The rubber composition can be crosslinked and blended with the friction material. The rubber composition had a first spin-spin relaxation time (T2n) of 100 to 2000 μs measured in a crosslinked product at 150 ° C. by the Hahn echo method using pulsed NMR, and a second spin-spin. The component fraction (fnn) of the component having the relaxation time (T2nn) is preferably less than 0.2.

  T2n and fnn of the rubber composition can represent that the carbon nanofibers are uniformly dispersed in the matrix nitrile rubber. That is, the fact that the carbon nanofibers are uniformly dispersed in the nitrile rubber can be said to be a state where the nitrile rubber is restrained by the carbon nanofibers. In this state, the mobility of the nitrile rubber molecules constrained by the carbon nanofibers is smaller than that when not constrained by the carbon nanofibers. Therefore, the first spin-spin relaxation time (T2n), the second spin-spin relaxation time (T2nn), and the spin-lattice relaxation time (T1) of the rubber composition according to the present embodiment are the same as those of the carbon nanofiber. It becomes shorter than the case of the nitrile rubber which does not contain, and becomes shorter especially when the carbon nanofibers are uniformly dispersed. In addition, the spin-lattice relaxation time (T1) in the crosslinked body changes in proportion to the mixing amount of the carbon nanofibers.

  Further, in the state where the nitrile rubber molecules are constrained by the carbon nanofibers, it is considered that the non-network component (non-network chain component) decreases for the following reason. In other words, when the molecular mobility of nitrile rubber is generally reduced by carbon nanofibers, the non-network component becomes more difficult to move, making it easier to behave the same as the network component. Since the (end chain) is easy to move, the non-network component is considered to decrease because it is easily adsorbed to the active site of the carbon nanofiber. Therefore, the component fraction (fnn) of the component having the second spin-spin relaxation time (T2nn) is smaller than that of a nitrile rubber alone not containing carbon nanofibers. Since the component fraction (fn) of the component having the first spin-spin relaxation time (T2n) is fn + fnn = 1, the component fraction (fn) is larger than that of a nitrile rubber alone not including carbon nanofibers.

  From the above, in the rubber composition according to the present embodiment, the carbon nanofibers are uniformly dispersed when the measurement value obtained by the Hahn echo method using the pulse method NMR is in the above range. Recognize.

  The spin-lattice relaxation time (T1) measured by the inversion recovery method using pulsed NMR is a measure representing the molecular mobility of a substance together with the spin-spin relaxation time (T2). Specifically, the shorter the spin-lattice relaxation time of the nitrile rubber, the lower the molecular mobility, the harder the nitrile rubber, and the longer the spin-lattice relaxation time, the higher the molecular mobility, and the softer the nitrile rubber. .

The rubber composition preferably has a loss tangent (tan δ) at 200 ° C. of 0.05 to 1.00, more preferably 0.05 to 0.5. Loss tangent (tan δ) is determined by performing a dynamic viscoelasticity test, dynamic shear modulus (E ′, unit is dyn / cm ² ) and dynamic loss modulus (E ″, unit is dyn / cm ² ) And calculating the loss tangent (tan δ = E ″ / E ′). When the loss tangent (tan δ) at 200 ° C. is 0.05 or more, a rubber composition having high damping characteristics in a high temperature region (200 ° C.) can be obtained.

  The rubber composition preferably has a dynamic elastic modulus (E ′) at 200 ° C. of 10 MPa to 1000 MPa, more preferably 10 MPa to 300 MPa.

  The rubber composition preferably has a deterioration start temperature of 160 ° C. to 300 ° C., more preferably 200 ° C. to 300 ° C. in thermomechanical analysis. The deterioration start temperature in the thermomechanical analysis is a temperature at which a deterioration phenomenon including softening deterioration (expansion) and hardening deterioration (shrinkage) starts. From the characteristic graph of the temperature-linear expansion coefficient differential value obtained by the thermomechanical analysis. It is obtained by measuring the temperature at which the deterioration phenomenon has started. It is desirable that the deterioration start temperature of the rubber composition is high, since the deterioration of the rubber composition does not start even at a high temperature, so that the maximum temperature at which the friction material 2 can be used increases. The rubber composition can be said to be in a state where the nitrile rubber is restrained by the carbon nanofibers because the carbon nanofibers are well dispersed in the nitrile rubber. Therefore, the nitrile rubber has a smaller molecular motion than the case where the carbon nanofiber is not included, and as a result, the deterioration start temperature moves to the high temperature side.

(Method for producing rubber composition)
A method for producing the rubber composition will be described. FIG. 5 is a diagram schematically showing a method for producing a rubber composition by the open roll method.

  As shown in FIG. 5, the first roll 100 and the second roll 200 are arranged at a predetermined interval d, for example, 0.5 mm to 1.0 mm, and the rotational speed in the direction indicated by the arrow in FIG. It rotates by V1 and V2 by forward rotation or reverse rotation. The nitrile rubber thrown into the open roll is an uncrosslinked body, and preferably has a spin-spin relaxation time (T2n / 30 ° C.) of the network component measured at 30 ° C. by the Hahn echo method using pulse NMR. Is from 100 to 3000 μsec, more preferably from 200 to 1000 μsec. First, the nitrile rubber 30 wound around the second roll 200 is masticated, and nitrile rubber molecular chains are appropriately cut to generate free radicals. Carbon nanofibers usually have a six-membered ring of carbon atoms and a closed end with a five-membered ring introduced at the tip. Since it is easy to generate and it is easy to produce | generate a radical and a functional group in the part, it will be in the state in which the free radical of a nitrile rubber will be easy to be combined with carbon nanofiber by mastication.

  Next, carbon nanofibers 40 having an average diameter of 0.5 to 500 nm are put into a bank 32 of nitrile rubber 30 wound around the second roll 200 and kneaded. The step of mixing the nitrile rubber 30 and the carbon nanofiber 40 is not limited to the open roll method, and a closed kneading method or a multiaxial extrusion kneading method can also be used.

  Further, the roll interval d between the first roll 100 and the second roll 200 is preferably set to 0.5 mm or less, more preferably 0 to 0.5 mm, and the mixture is put into an open roll and thinned. Repeat several times. The number of thinning is preferably about 5 to 10 times, for example. When the surface speed of the first roll 100 is V1 and the surface speed of the second roll 200 is V2, the ratio of the surface speeds (V1 / V2) in thinness is 1.05 to 3.00. It is preferably 1.05 to 1.2. By using such a surface velocity ratio, a desired shear force can be obtained. The thin rubber composition is rolled with a roll and dispensed into a sheet. In this thinning process, in order to obtain as high a shearing force as possible, the roll temperature is preferably set to a relatively low temperature of 0 to 50 ° C, more preferably 5 to 30 ° C. The temperature is also preferably adjusted to 0 to 50 ° C. Due to the shearing force thus obtained, a high shearing force acts on the nitrile rubber 30 and the aggregated carbon nanofibers 40 are separated from each other so that they are pulled out one by one into the nitrile rubber molecule. Distributed in. In particular, since the nitrile rubber 30 has elasticity, viscosity, and chemical interaction with the carbon nanofibers 40, the carbon nanofibers 40 can be easily dispersed. And the rubber composition excellent in the dispersibility and dispersion stability of carbon nanofiber 40 (it is hard to re-aggregate carbon nanofiber) can be obtained.

  More specifically, when nitrile rubber and carbon nanofibers are mixed with an open roll, viscous nitrile rubber penetrates into the carbon nanofibers, and a specific part of the nitrile rubber is carbonized by chemical interaction. It binds to the highly active part of the nanofiber. Next, when a strong shearing force acts on the nitrile rubber, the carbon nanofibers move as the nitrile rubber molecules move, and the aggregated carbon nanofibers are separated by the restoring force of the nitrile rubber due to the elasticity after shearing. And dispersed in the nitrile rubber. According to this embodiment, when the rubber composition is extruded from between narrow rolls, the rubber composition is deformed thicker than the roll interval by the restoring force due to the elasticity of the nitrile rubber. The deformation can be presumed to cause the rubber composition on which a strong shear force has been applied to flow more complicatedly and to disperse the carbon nanofibers in the nitrile rubber. The carbon nanofibers once dispersed are prevented from reaggregating due to chemical interaction with the nitrile rubber, and can have good dispersion stability.

  The step of dispersing the carbon nanofibers in the nitrile rubber by a shearing force is not limited to the open roll method, and a closed kneading method or a multiaxial extrusion kneading method can also be used. In short, in this step, it is sufficient that a shear force capable of separating the aggregated carbon nanofibers can be applied to the nitrile rubber. In particular, the open roll method is preferable because it can measure and manage not only the roll temperature but also the actual temperature of the mixture.

  The method for producing a rubber composition may be used by mixing a cross-linking agent into a rubber composition dispensed after passing through and crosslinking to use as a rubber composition of a cross-linked body, or without cross-linking. You may shape | mold into a friction material as it is. Since the rubber composition is in the form of a sheet obtained by the open roll method, it is preferable that the rubber composition be pulverized into particles so that it can be easily mixed with the particulate filler. As a method for making the rubber composition into particles, a known method can be adopted, for example, roll pulverization by a shearing force of a roll or cut pulverization by a cutting blade, and the rubber composition is cooled or frozen in advance. You may grind | pulverize.

  In the method for producing a rubber composition according to the present embodiment, a compounding agent usually used for processing nitrile rubber can be added. A well-known thing can be used as a compounding agent. Examples of the compounding agent include a crosslinking agent, a vulcanizing agent, a vulcanization accelerator, a vulcanization retarder, a softening agent, a plasticizer, a curing agent, a reinforcing agent, a filler, an antiaging agent, and a coloring agent. it can. These compounding agents can be added to the nitrile rubber before the carbon nanofibers in the open roll, for example.

  In the method for producing a rubber composition according to the present embodiment, carbon nanofibers are directly mixed with nitrile rubber having rubber elasticity. However, the present invention is not limited to this, and the following method can also be adopted. . First, before mixing the carbon nanofibers, the nitrile rubber is masticated to reduce the molecular weight of the nitrile rubber. Since the viscosity of nitrile rubber decreases when the molecular weight decreases due to mastication, the nitrile rubber easily penetrates into the voids of the aggregated carbon nanofibers. The raw material nitrile rubber is a rubber-like material in which the first spin-spin relaxation time (T2n) of the network component in the uncrosslinked product is 100 to 3000 μsec, measured at 30 ° C. by the Hahn echo method using pulsed NMR. It is an elastic body. This raw material nitrile rubber is masticated to reduce the molecular weight of the nitrile rubber, and a liquid nitrile rubber having a first spin-spin relaxation time (T2n) exceeding 3000 μsec is obtained. The first spin-spin relaxation time (T2n) of the liquid nitrile rubber after mastication is 5 to 30 of the first spin-spin relaxation time (T2n) of the raw material nitrile rubber before mastication. It is preferable that it is double. This kneading is different from the general kneading performed in a state where the nitrile rubber is in a solid state. By applying a strong shearing force, for example, by an open roll method, the molecules of the nitrile rubber are cut and the molecular weight is significantly reduced. It is performed until it becomes a liquid state until it shows an unsuitable flow. For example, when the open roll method is used, this mastication is performed at a roll temperature of 20 ° C. (minimum mastication time 60 minutes) to 150 ° C. (minimum mastication time 10 minutes), and the roll interval d is, for example, 0.1 mm to 1 mm. At 0.0 mm, carbon nanofibers are put into a nitrile rubber that is masticated and liquid. However, since nitrile rubber is liquid and has a remarkably reduced elasticity, the aggregated carbon nanofibers are not very dispersed even when kneaded in a state where the free radicals of nitrile rubber and carbon nanofibers are combined.

  Therefore, after increasing the molecular weight of the nitrile rubber in the mixture obtained by kneading the liquid nitrile rubber and the carbon nanofibers to restore the elasticity of the nitrile rubber to obtain a mixture of the rubber-like elastic body, The carbon nanofibers are uniformly dispersed in the nitrile rubber by performing the open roll method thinning described in the above. A mixture of rubber-like elastic bodies having an increased molecular weight of nitrile rubber has a first spin-spin relaxation time (T2n) of 3000 μsec or less as measured by a Hahn echo method at 30 ° C. using pulse NMR. is there. Also, the first spin-spin relaxation time (T2n) of the rubber-like elastic mixture having an increased molecular weight of the nitrile rubber is equal to the first spin-spin relaxation time (T2n) of the raw material nitrile rubber before mastication. It is preferably 0.5 to 10 times. The elasticity of the mixture of rubber-like elastic bodies can be expressed by the molecular form of nitrile rubber (observable by molecular weight) and molecular mobility (observable by T2n). The step of increasing the molecular weight of the nitrile rubber is preferably performed for 10 hours to 100 hours by placing the mixture in a heating furnace set to a heat treatment, for example, 40 ° C. to 100 ° C. By such heat treatment, the molecular chain is extended by the bonding of free radicals of the nitrile rubber present in the mixture, and the molecular weight is increased. In addition, when the molecular weight of the nitrile rubber is increased in a short time, a small amount of a crosslinking agent, for example, ½ or less of an appropriate amount of the crosslinking agent is mixed, and the mixture is heated (for example, annealed) to be crosslinked. The molecular weight can be increased in a short time by the reaction. When the molecular weight of the nitrile rubber is increased by a crosslinking reaction, it is preferable to set the blending amount of the crosslinking agent, the heating time, and the heating temperature to such an extent that kneading is not difficult in the subsequent steps.

  According to the method for producing a rubber composition described here, the carbon nanofibers can be more uniformly dispersed in the nitrile rubber by reducing the viscosity of the nitrile rubber before the carbon nanofibers are added. . More specifically, the carbon nanofibers are agglomerated by using liquid nitrile rubber having a reduced molecular weight rather than mixing carbon nanofibers with nitrile rubber having a large molecular weight as in the production method described above. Nitrile rubber molecules can easily penetrate into the carbon nanofibers, and the carbon nanofibers can be more uniformly dispersed in a thin process. Moreover, since free radicals of nitrile rubber produced in large quantities by molecular cutting of nitrile rubber can be more firmly bonded to the surface of carbon nanofibers, carbon nanofibers can be evenly dispersed. . Therefore, according to the manufacturing method described here, the same performance can be obtained even with a smaller amount of carbon nanofibers than in the previous manufacturing method, and economical efficiency is improved by saving expensive carbon nanofibers.

(Nitrile rubber)
A nitrile rubber which is a matrix raw material for a rubber composition can be abbreviated as NBR, and is a synthetic rubber of an acrylonitrile-butadiene copolymer system, which has a rubbery elasticity at room temperature. Can be used. Nitrile rubber can change its physical properties by including acrylonitrile content in about 15-50%, for example, low nitrile less than 24%, medium nitrile 24-30%, medium high nitrile 30-36%, high nitrile 36 It can be classified by the amount of nitrile such that it exceeds ˜42% and exceeds nitrile 42%. The average molecular weight of the nitrile rubber is usually desirably 50,000 or more, more preferably 70,000 or more, and particularly preferably about 100,000 to 500,000.

  The nitrile rubber preferably has a spin-spin relaxation time (T2n / 30 ° C.) of the network component in the uncrosslinked body, measured at 30 ° C. by the Hahn echo method using pulsed NMR, preferably 100 to 3000 μsec, more preferably 200 to 1000 microseconds. By having a spin-spin relaxation time (T2n / 30 ° C.) in the above range, the nitrile rubber can be flexible and have sufficiently high molecular mobility, that is, moderate elasticity to disperse the carbon nanofibers. Will have. In addition, since elastomer has viscosity, when nitrile rubber and carbon nanofiber are mixed, nitrile rubber can easily enter the gaps between carbon nanofibers due to high molecular motion. If the spin-spin relaxation time (T2n / 30 ° C.) is shorter than 100 μsec, the nitrile rubber cannot have sufficient molecular mobility. Further, if the spin-spin relaxation time (T2n / 30 ° C.) is longer than 3000 μsec, the nitrile rubber tends to flow like a liquid and has low elasticity, so that it becomes difficult to disperse the carbon nanofibers as they are.

  The spin-spin relaxation time obtained by the Hahn-echo method using pulsed NMR is a measure representing the molecular mobility of a substance. Specifically, when the spin-spin relaxation time of the nitrile rubber is measured by the Hahn-echo method using pulsed NMR, a first component having a first spin-spin relaxation time (T2n) having a short relaxation time; A second component having a second spin-spin relaxation time (T2nn) having a longer relaxation time is detected. The first component corresponds to a polymer network component (skeleton molecule), and the second component corresponds to a polymer non-network component (branch and leaf component such as a terminal chain). The shorter the first spin-spin relaxation time, the lower the molecular mobility and the harder the nitrile rubber. Moreover, it can be said that the longer the first spin-spin relaxation time, the higher the molecular mobility and the softer the nitrile rubber.

  As a measurement method in the pulsed NMR method, the solid echo method, the CPMG method (Car Purcell, Mayboom, Gill method) or the 90 ° pulse method can be applied instead of the Hahn echo method. However, since the nitrile rubber according to the present invention has a moderate spin-spin relaxation time (T2), the Hahn echo method is most suitable. In general, the solid echo method and the 90 ° pulse method are suitable for short T2 measurement, the Hahn echo method is suitable for medium T2 measurement, and the CPMG method is suitable for long T2 measurement.

(Carbon nanofiber)
The carbon nanofibers preferably have an average diameter of 0.5 to 500 nm and an average diameter of 0.5 to 100 nm. The carbon nanofibers preferably have an average length of 0.01 to 1000 μm. The compounding amount of the carbon nanofiber can be appropriately set depending on the amount of the rubber composition blended with the friction material and the high temperature characteristics required for the friction material, but the carbon nanofiber is 5 to 100 weights with respect to 100 parts by weight of the nitrile rubber. In order to obtain the excellent high temperature characteristic of a friction material, it is preferable to contain a part. In particular, by adding carbon black as a reinforcing agent to the rubber composition, excellent high temperature characteristics of the friction material can be obtained even if the amount of carbon nanofibers is reduced, and carbon is added to 100 parts by weight of nitrile rubber. When 40 to 80 parts by weight of black is blended, it is preferable to include 5 to 20 parts by weight of carbon nanofibers.

  Examples of carbon nanofibers include so-called carbon nanotubes. Carbon nanotubes are single-walled carbon nanotubes (single-walled carbon nanotubes: SWNT) in which one sheet of graphite having a carbon hexagonal mesh surface is wound in one layer, and double-walled carbon nanotubes (double-walled carbon nanotubes: DWNT) in two layers. Multi-walled carbon nanotubes (MWNT: multiwall carbon nanotubes) wound in three or more layers are used as appropriate. A carbon material partially having a carbon nanotube structure can also be used. In addition to the name “carbon nanotube”, it may be called “graphite fibril nanotube”. Carbon nanofibers that have been graphitized at about 2300 ° C. to 3200 ° C. with a graphitization catalyst such as boron, boron carbide, beryllium, aluminum, and silicon may be used.

  Single-walled carbon nanotubes or multi-walled carbon nanotubes are manufactured to a desired size by an arc discharge method, a laser ablation method, a vapor phase growth method, or the like. The arc discharge method is a method of obtaining multi-walled carbon nanotubes deposited on a cathode by performing an arc discharge between electrode materials made of carbon rods in an argon or hydrogen atmosphere at a pressure slightly lower than atmospheric pressure. In addition, the single-walled carbon nanotube is obtained by mixing the carbon rod with a catalyst such as nickel / cobalt to cause arc discharge and adhering to the inner surface of the processing vessel. The laser ablation method melts and evaporates the carbon surface by irradiating a strong YAG laser pulsed laser beam onto a carbon surface mixed with a target catalyst such as nickel / cobalt in a rare gas (eg argon). This is a method for obtaining single-walled carbon nanotubes. The vapor phase growth method is a method in which hydrocarbons such as benzene and toluene are thermally decomposed in the gas phase to synthesize carbon nanotubes. More specifically, a fluid catalyst method, a zeolite supported catalyst method, and the like can be exemplified. Carbon nanofibers are improved in adhesion and wettability with nitrile rubber by performing surface treatment, for example, ion implantation treatment, sputter etching treatment, plasma treatment, etc. in advance before being kneaded with nitrile rubber. be able to.

(Friction material manufacturing method)
The method for manufacturing the friction material 2 according to the present embodiment is not particularly limited, but is formed into a desired shape using a generally known molding method such as compression molding, transfer molding, injection molding, or injection compression molding. And can be cured by heating. A method for manufacturing the friction material 2 according to the present embodiment will be described in detail with reference to FIGS. FIG. 6 is a process diagram showing a manufacturing process of the friction material 2 according to the embodiment of the present invention. FIG. 7 is an explanatory diagram for explaining a temporary forming process for manufacturing the friction material 2 according to the embodiment of the present invention. FIG. 8 is an explanatory diagram for explaining a heating / pressurizing process for manufacturing the friction material 2 according to the embodiment of the present invention.

  The friction material 2 according to the present embodiment can be manufactured by the manufacturing process shown in FIG. In this manufacturing process, first, after forming the binding holes 4 and 4 in the metal plate 3, various surface treatments are performed, and then drying is performed. For such surface treatment, a degreasing process for degreasing the plate 3, a shot processing process for increasing the binding strength between the friction material 2 and the plate 3 by injecting granular materials toward the surface of the plate 3, For example, an adhesive application step of applying a thermosetting adhesive to the plate 3 to the surface of the plate 3 is included. On the other hand, the friction material 2 is molded in a separate process from the processing process of the plate 3. In forming the friction material 2, the raw materials of the friction material 2 are mixed, and then, a predetermined amount is measured and temporarily molded to form a plate-like temporary molded body. At this time, the raw material of the friction material 2 used as the raw material includes the above-described reinforcing fiber, filler, rubber composition, and binder resin.

  As shown in FIG. 7, the raw material of the friction material 2 (reinforcing fiber, filler particles, rubber composition particles, binder resin) sufficiently mixed in advance by a mixer is temporarily formed on a mounting table 54. The mold 52 is filled. And the raw material of the friction material 2 is pressed with the press die 50, and temporary molding is performed, and the temporary molded body 65 is obtained.

  As shown in FIG. 8, the temporary molded body 65 obtained by the temporary molding is heated and pressure-molded by a press machine and formed into the friction material 2 integrated with the plate 3. In the heating and pressure molding, first, a temporary molded body 65 is placed in a mold 62 on a mounting table 64 of a press machine, and the plate 3 is set at a predetermined position on the temporary molded body 65. The molded body 65 is heated while being pressed. By this heating and pressure molding, the binder resin blended in the raw material of the temporary molded body 65 is dissolved and fluidized, and then cured to firmly bond the raw materials of the temporary molded body 65 together with the surface of the plate 3. Both are firmly bound to form the friction material 2. The friction material 2 obtained by performing such heating and pressure molding is fired in an oven for several hours in order to make the binding between the friction material 2 and the plate 3 even more complete. . The friction material that has undergone the firing process becomes a product (pad 1) through a groove processing for forming a groove in the friction material 2, a polishing process for polishing the surface of the friction material 2, a post-processing process such as painting, and the like.

  The amount of the rubber composition blended in the friction material 2 can be adjusted as appropriate depending on the high temperature characteristics required of the friction material 2, but in order to improve the high temperature characteristics of the friction material 2, 2 to 10 wt% It is preferable to include.

  The friction material 2 has an excellent damping characteristic and a high dynamic elastic modulus even at high temperatures, so that the friction material 2 has a high friction coefficient at high temperatures and can reduce squeal at high temperatures due to contact with the friction target member. it can. Moreover, according to the friction material concerning this invention, the amount of wear can be reduced by the uniform contact with a to-be-rubbed member.

  Examples of the present invention will be described below, but the present invention is not limited thereto.

(1) Preparation of Samples of Examples 1 to 8 and Comparative Examples 1 and 2 A 6-inch open roll (roll temperature 10 to 20 ° C., roll interval 1.5 mm) was charged with a predetermined amount of nitrile rubber (100 weight) shown in Table 1. Part (phr)), wound around a roll and masticated for 5 minutes, and then the amount of carbon nanofibers and / or carbon black shown in Table 1 was added, and the mixture was taken out from the open roll. And the roll space | interval was narrowed from 1.5 mm to 0.3 mm, the mixture was again thrown into the open roll, and thinning was repeated 5 times. At this time, the surface speed ratio of the two rolls was set to 1.1. Further, the rubber composition obtained through thinning was set by setting the roll gap to 1.1 mm and dispensed.

  The dispensed rubber composition was press-molded at 90 ° C. for 5 minutes, and each was molded into a sheet-like uncrosslinked rubber composition sample having a thickness of 1 mm. Also, among the separated rubber compositions, peroxides as a crosslinking agent were blended in the rubber compositions of Examples 1 to 6 and 8 and Comparative Examples 1 and 2, and mixed with an open roll to make the roll gap 1 Dispensing at 1 mm. The separated rubber composition was press-crosslinked at 175 ° C. for 20 minutes, and the crosslinked rubber composition samples of Examples 1 to 6, 8 and Comparative Examples 1 and 2 were molded.

  This rubber composition sample is mixed with the reinforcing fibers, particulate filler and binder resin shown in Table 1, and is heated and pressure-molded by a press machine to form a friction material. And the friction material obtained by shape | molding was further baked, and the friction material of Examples 1-8 and Comparative Examples 1 and 2 was obtained.

  In Table 1, the binder resin as the raw material of the friction material is particulate “phenol resin”, the reinforcing fibers are “aramid fiber” and “inorganic fiber”, and the filler is particulate “cashew dust”, “metal material”, “ They were “inorganic material”, “lubricant” and “pH adjuster”. In Table 1, “NBR” as a raw material of the rubber composition is a nitrile rubber of medium to high nitrile, “MWNT13” is a vapor growth multi-wall carbon nanotube having an average diameter of about 13 nm, and “MWNT100” has an average diameter of about It was a 100 nm vapor grown multi-wall carbon nanotube, and “HAF” was a HAF grade carbon black. In Table 1, “Friction material blending ratio” is expressed in weight%, and “Rubber composition blending ratio” is expressed in parts by weight (phr).

(2) Measurement using pulsed method NMR About the raw material rubbers of Examples 1 to 8 and Comparative Examples 1 and 2 and rubber composition samples of each non-crosslinked body, measurement was performed by the Hahn echo method using pulsed method NMR. . This measurement was performed using “JMN-MU25” manufactured by JEOL Ltd. The measurement was performed under the conditions of the observation nucleus of ¹ H, the resonance frequency of 25 MHz, and the 90 ° pulse width of 2 μsec. The Pi was changed in various ways using the pulse sequence of the Hahn-echo method (90 ° x-Pi-180 ° x). The decay curve was measured. Further, the sample was measured by inserting it into a sample tube up to an appropriate range of the magnetic field. As shown in parentheses in Table 1, the measurement temperatures were 30 ° C. and 150 ° C. By this measurement, the first spin-spin relaxation time (T2n / 30 ° C.) of the raw rubber, the first spin-spin relaxation time (T2n / 150 ° C.) and the second spin for each uncrosslinked rubber composition sample. -The component fraction (fnn / 150 ° C) of the component having the spin relaxation time (T2nn / 150 ° C) was determined. The measurement results are shown in Table 1.

(3) Thermomechanical analysis (TMA)
About the test piece which cut out the rubber composition sample of the crosslinked body of Examples 1-6, 8 and Comparative Examples 1 and 2, and the rubber composition sample of the non-crosslinked body of Example 7 into 1.5 mm x 1.0 mm x 10 mm Using a thermomechanical analyzer (TMA-SS6100) manufactured by SII, the linear expansion coefficient in the atmosphere was measured at a side long load of 25 KPa, a measurement temperature of −100 to 300 ° C., and a heating rate of 3 ° C./min. From the temperature change characteristic of the obtained linear expansion coefficient, the deterioration start temperature (° C.) at which softening deterioration or hardening deterioration starts was measured. More specifically, the deterioration start temperature is a crosslinking type in that the linear expansion coefficient is extremely increased in the temperature (° C.)-Differential linear expansion coefficient (ppm / K) graph of each rubber composition sample. It was judged that the chain-breaking type softening deterioration (expansion) had started at the point where the hardening deterioration (shrinkage) or the linear expansion coefficient was extremely reduced, and was set as the deterioration start temperature. These results are shown in Table 1.

(4) Dynamic Viscoelasticity Test The crosslinked rubber composition samples of Examples 1 to 6, 8 and Comparative Examples 1 and 2 and the uncrosslinked rubber composition sample of Example 7 were formed into strips (40 × 1 × 5 (width) mm), using a dynamic viscoelasticity tester DMS6100 manufactured by SII, the distance between chucks is 20 mm, the measurement temperature is −100 to 300 ° C., the dynamic strain is ± 0.05%, A dynamic viscoelasticity test was performed at a frequency of 10 Hz based on JIS K6394, and a dynamic elastic modulus (E ′, unit is MPa) and a loss tangent (tan δ) were measured. Table 1 shows the measurement results of the dynamic elastic modulus (E ′) at the measurement temperatures of 30 ° C. and 200 ° C. Table 1 shows the measurement results of loss tangent (tan δ) at measurement temperatures of −10 ° C., 30 ° C., and 200 ° C. Furthermore, Table 1 shows the peak temperature of the loss tangent (tan δ) in the region near the glass transition point (Tg) as the lowest usable temperature (° C.). The minimum use temperature is the limit temperature for use as a rubber composition because the rubber composition becomes too hard in the region lower than this temperature and loses cushioning properties.

(5) Fade test A load cell is subjected to a fade test in which the friction materials of Examples 1 to 8 and Comparative Examples 1 and 2 are pressed against a rotating FC250 (graphite cast iron, specific gravity 7.2) disk rotor for braking under the following test conditions. It carried out using.
(Test conditions)
Vehicle speed: (initial speed) 60 km / h-(final speed) 0 km / h
Deceleration: 0.4G
Braking interval: 20 sec
Table 1 shows the maximum temperature (° C.) of the disc rotor in the 24th fade test, the friction coefficient (μ) in the 24th fade test, and the total wear amount (mm) of the friction material in the fade test. The temperature of the disk rotor is a temperature measured while the disk rotor is stopped, and the friction coefficient is the highest value during braking. Further, FIG. 9 shows a graph of the number of braking times-the maximum disk rotor temperature in the fade tests of Examples 2 and 8 and Comparative Example 1, and FIG. 10 shows a graph of the number of braking times-the maximum value of the friction coefficient. In FIG. 9, the number of braking times-disc rotor temperature (° C.) characteristics of Example 2 is A, the number of braking times of Example 8—disk rotor temperature (° C.) characteristics is B, the number of braking times of Comparative Example 1—disk rotor temperature (° C.). ) Characteristics are indicated by C. In FIG. 10, the braking frequency-friction coefficient (μ) characteristic of Example 2 is D, the braking frequency-friction coefficient (μ) characteristic of Example 8 is E, and the braking frequency-friction coefficient (μ) characteristic of Comparative Example 1 is E. Indicated by F.

  From Table 1, according to Examples 1 to 8 of the present invention, the following was confirmed. That is, the deterioration start temperature of the rubber composition samples of Examples 1 to 8 of the present invention was higher than the deterioration start temperature of the rubber composition samples of Comparative Examples 1 and 2, and was 160 ° C. or higher. Moreover, according to the rubber composition samples of Examples 1 to 8 of the present invention, it was found that the dynamic elastic modulus (E ′) at 200 ° C. is 10 MPa or more and maintains high rigidity even at high temperatures. . Since the rubber composition samples of Comparative Examples 1 and 2 had deterioration start temperatures of 115 ° C. and 152 ° C., they were softened at 200 ° C. and could not be measured. According to Examples 1 to 8 of the present invention, the dynamic elastic modulus (E ′) at room temperature (30 ° C.) is 25 MPa or higher, higher than those of Comparative Examples 1 and 2, and has high rigidity at room temperature (30 ° C.). Was. Therefore, since the friction material of Examples 1-8 contains the rubber composition which maintained the high dynamic elastic modulus from low temperature to high temperature, it can maintain a high friction coefficient. As shown in FIG. 9, when the number of times of braking increases, the temperature of the disk rotor also increases, and the temperature of the friction material that contacts the disk rotor also increases. However, as shown in FIG. 10, even when the temperature of the friction material increases, the friction material samples of Examples 2 and 8 maintain a high friction coefficient as compared with the low friction coefficient of the friction material sample of Comparative Example 1. There was little change.

  Furthermore, according to Examples 1 to 8 of the present invention, the loss tangent (tan δ) at 200 ° C. was 0.05 or more, and it was found that high damping characteristics were maintained particularly at high temperatures. The rubber compositions of Comparative Examples 1 and 2 had deterioration initiation temperatures of 115 ° C. and 152 ° C., and therefore were softened at 200 ° C. and could not be measured. According to Examples 1 to 8 of the present invention, the loss tangent (tan δ) at a low temperature (−10 ° C.) is 0.2 or more, and the loss tangent (tan δ) is 0.1 or more even at room temperature (30 ° C.). It had a relatively high attenuation characteristic. Therefore, since the friction material of Examples 1-8 contains the rubber composition which has the damping characteristic excellent from low temperature to high temperature, the squeal in a brake can be reduced in the wide range from low temperature to high temperature, for example.

  Moreover, according to the friction material of Examples 1-8 of this invention, compared with the friction material of the comparative examples 1 and 2, there was little abrasion amount. In Example 4 and Example 8 of the present invention, the composition of the rubber composition was the same, and the content ratio of the rubber composition in the friction material was different, but there was no significant difference in the friction coefficient and the wear amount.

It is a front view of the pad for disc brakes concerning one embodiment of the present invention. 1 is a partially cutaway plan view of a pad for a disc brake according to an embodiment of the present invention. It is a rear view of the pad for disc brakes concerning one embodiment of the present invention. It is a longitudinal section showing the structure of the disc brake concerning one embodiment of the present invention. It is a figure which shows typically the manufacturing method of the rubber composition by an open roll method. It is process drawing which shows the manufacturing process of the friction material concerning one embodiment of this invention. It is explanatory drawing for demonstrating the temporary forming process which manufactures the friction material concerning one embodiment of this invention. It is explanatory drawing for demonstrating the heating and pressurizing process which manufactures the friction material concerning one embodiment of this invention. It is a figure which shows the frequency | count of braking by the fade test of Example 2, 8 and the comparative example 1-disk rotor temperature (degreeC). It is a figure which shows the frequency | count of braking-friction coefficient (micro) by the fade test of Example 2, 8 and the comparative example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pad 2 Friction material 3 Plate 5 Shim board 10 Disc brake 11 Caliper body 12 Piston 13 Disc rotor 14 Hydraulic chamber 30 Nitrile rubber 40 Carbon nanofiber 100 1st roll 200 2nd roll d Roll interval V1 1st roll Surface speed V2 Surface speed A of the second roll Number of braking in Example 2-Disk rotor temperature (° C) characteristic B Number of braking in Example 8-Disk rotor temperature (° C) characteristic C Number of braking in Comparative Example 1-Disk Rotor temperature (° C.) characteristic D Number of times of braking in Example 2-friction coefficient characteristic E Number of times of braking in Example 8-friction coefficient characteristic F Number of times of braking in Comparative Example 1-Friction coefficient characteristic

Claims (9)

A friction material comprising a reinforcing fiber, a filler, a rubber composition, and a binder resin,
The rubber composition is a non-crosslinked product in which carbon nanofibers having an average diameter of 0.5 to 500 nm are uniformly dispersed in a nitrile rubber as a matrix and measured at 150 ° C. by a Hahn echo method using pulse NMR. The first spin-spin relaxation time (T2n) is 100 to 3000 μs, and the component fraction (fnn) of the component having the second spin-spin relaxation time (T2nn) is less than 0.2. Wood. In claim 1,
The rubber composition is a friction material which is a non-crosslinked body. In claim 1,
The rubber composition is a friction material which is a crosslinked body. In any one of Claims 1-3,
The rubber composition is a friction material including 5 to 100 parts by weight of the carbon nanofibers with respect to 100 parts by weight of the nitrile rubber. In claim 4,
The rubber composition includes 40 to 80 parts by weight of carbon black and 5 to 20 parts by weight of the carbon nanofibers with respect to 100 parts by weight of the nitrile rubber. In any one of Claims 1-5,
The rubber composition is a friction material having a loss tangent (tan δ) at 200 ° C. of 0.05 to 1.00. In any one of Claims 1-5,
The rubber composition is a friction material having a dynamic elastic modulus (E ′) at 200 ° C. of 10 MPa to 1000 MPa. In any one of Claims 1-5,
The rubber composition is a friction material having a deterioration start temperature in a thermomechanical analysis of 160 ° C to 300 ° C. In any one of Claims 1-8,
The binder resin is a friction material, which is a phenol resin.

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