JP2007064377A - Piston seal member and disk brake using the piston seal member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piston seal member of a recyclable rubber composition and a disk brake using the piston seal member. <P>SOLUTION: The piston seal member 8 holds a cylinder hole 6a and a piston 5 sliding in the cylinder hole 6a in a liquid-tight and slidable manner. The piston seal member 8 is formed of an uncrosslinked rubber composition containing rubber having unsaturated bond or group with an affinity to carbon nano fiber and the carbon nano fiber dispersed in the rubber. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a piston seal member formed of an uncrosslinked rubber composition and a disc brake using the piston seal member.

  The piston seal member is generally formed from a crosslinked rubber composition containing rubber as a main component. For example, a caliper body incorporating a piston and a cylinder is attached to a disc brake for a vehicle, and a piston seal member is attached to an annular groove formed on the inner peripheral surface of the cylinder. In the disc brake, the brake pad is pressed against the disc rotor fixed to each wheel by the brake fluid pressure, and the wheel is stopped by the frictional force of the brake pad as a friction material. The piston seal member has a role of sealing the brake fluid and a role of returning (rolling back) the piston advanced by the brake fluid pressure. Here, the brake pad is pressed against the disc by the forward movement of the piston in the cylinder hole by the brake fluid pressure.

  That is, by mounting this piston seal member, the cylinder and the piston inserted into the hole of the cylinder can be brought into close contact with each other in a state where the piston can be moved in a liquid-tight manner. Further, the piston advanced by the hydraulic pressure is rolled back by the piston seal member. Therefore, this piston seal member is required to have both toughness for reliably sealing the brake fluid and elasticity for returning the piston advanced by the hydraulic pressure to its original position (rollback).

  Further, the caliper body of the disc brake becomes hot during operation due to frictional heat generated between the disc rotor and the brake pad. In connection with this, a piston seal member is also exposed to high temperature. A piston seal member made of a rubber composition is thermally expanded at a high temperature, and the elastic modulus of the piston seal member is lowered. In this case, the amount of rollback of the piston changes due to the thermal expansion of the piston seal member and the decrease in the elastic modulus of the piston seal member, and the braking allowance changes. For example, in a disc brake of a motorcycle, the stroke amount of the brake lever changes, which may cause a driver to feel uncomfortable.

  Therefore, a piston seal member is proposed that is molded from a rubber composition in which at least 100 parts by weight of carbon black is added to 100 parts by weight of ethylene / propylene rubber (see, for example, Patent Document 1).

  Further, a piston seal member made of rubber containing at least one of carbon fiber (including carbon nanofiber) and fullerene has been proposed (see, for example, Patent Document 2).

However, the piston seal member formed with the conventional crosslinked rubber composition cannot be recycled. Recycling of rubber compositions has been eagerly desired to improve the recycling rate in industries that promote environmental protection, particularly in the automobile industry.
JP 2004-316773 A Japanese Patent Laid-Open No. 2004-232786

  Accordingly, an object of the present invention is to provide a piston seal member made of a recyclable rubber composition and a disc brake using the piston seal member.

A piston seal member according to the present invention is a piston seal member that holds a cylinder hole and a piston that slides in the cylinder hole in a liquid-tight and slidable manner,
It is characterized by being formed of a non-crosslinked rubber composition comprising a rubber having an unsaturated bond or group having affinity for carbon nanofibers, and carbon nanofibers dispersed in the rubber.

  Since the piston seal member according to the present invention is formed of a non-crosslinked rubber composition, it can be kneaded and reused (recycled) by applying a shearing force again after use. Moreover, even if the rubber composition is non-crosslinked, it is reinforced with carbon nanofibers to provide flexibility and strength, and can be used as a piston seal member without being crosslinked. In particular, a non-crosslinked rubber composition in which carbon nanofibers are dispersed has a flow temperature of 150 ° C. or higher and does not flow even at a high temperature. Therefore, the piston seal is the same as a crosslinked rubber composition in a non-crosslinked state. Can be used as a member. Further, according to the piston seal member of the present invention, since the compression set and the tensile set are small, the liquid tightness between the piston and the cylinder can be reliably maintained.

In the piston seal member according to the present invention, the non-crosslinked rubber composition contains 5 to 100 parts by weight of the carbon nanofibers with respect to 100 parts by weight of the rubber.
The carbon nanofiber may have an average diameter of 0.7 to 15 nm and an average length of 0.5 to 100 μm.

  According to the piston seal member of the present invention, by reinforcing a large amount of very thin carbon nanofibers, a decrease in physical properties at a high temperature is small, and stable liquid tightness between the piston and the cylinder with respect to temperature change is achieved. Can be maintained.

  In addition, when the unsaturated bond or group of rubber is bonded to the active part of carbon nanofiber, particularly the radical at the end of carbon nanofiber, the cohesive force of carbon nanofiber can be weakened and its dispersibility can be increased. . As a result, in the piston seal member, carbon nanofibers are uniformly dispersed in rubber as a base material.

The disc brake according to the present invention includes the piston seal member of the present invention,
A cylinder having a cylinder hole;
A piston inserted into the cylinder hole,
The piston seal member is fitted into an annular groove formed in the inner peripheral wall of the cylinder hole,
The piston inserted into the cylinder hole is brought into close contact with the fluidly movable state, and the piston advanced by hydraulic pressure is rolled back.

  According to the disc brake of the present invention, the piston seal member of the present invention is fitted into the annular groove, so that stable operability of the piston and liquid tightness between the piston and the cylinder can be maintained in a wide temperature range. . Moreover, since the piston seal member according to the present invention is formed of an uncrosslinked rubber composition, the recycling rate in the vehicle can be improved.

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

  FIG. 1 is a cross-sectional view schematically showing a piston seal member 8 according to an embodiment of the present invention. FIG. 2 is a sectional view schematically showing the disc brake 20 including the piston seal member 8 shown in FIG. In the present embodiment, as an example, a floating type disc brake for a vehicle (see FIG. 2) will be described.

(Disc brake)
The disc brake 20 according to the present embodiment includes an annular piston seal member 8, a cylinder 6 having a cylinder hole 6a, and a piston 5 inserted into the cylinder hole 6a. The piston seal member 8 has a cylinder hole. The piston 5 fitted in the annular piston seal groove 7 formed in the inner peripheral wall of 6a is brought into close contact with the piston 5 inserted in the cylinder hole 6a in a liquid-tight movable state, and the piston 5 advanced by the hydraulic pressure is moved. Roll back.

  The disc brake 20 is provided with a caliper body 1 including a piston 5 and a cylinder 6. The caliper body 1 includes an action part 1b and a reaction part 1c. The action part 1b and the reaction part 1c are integrally formed via the bridge part 1a.

  A pair of friction pads 4b and 4c are arranged facing the friction surfaces on both sides of the disk rotor 2 that rotates integrally with the wheels (not shown). A caliper body 1 that presses the friction pads 4b and 4c against the disc rotor 2 is connected to the bracket 3 via a slide pin (not shown) so as to be able to advance and retract. The caliper body 1 includes an action portion 1b disposed on the back surface of one friction pad 4b, a reaction portion 1c disposed on the back surface of the other friction pad 4c, and the action portion 1b and the reaction portion straddling the outer periphery of the disk rotor 2. It is comprised with the bridge part 1a which connects 1c.

  The disc brake 20 is supported in a slidable state on a bracket 3 fixed to a vehicle body (not shown). Moreover, as shown in FIG. 2, the piston 5 and the cylinder 6 are formed in the action part 1b.

  The friction pad 4 b is pushed and moved by the piston 5 inserted into the hole 6 a of the cylinder 6, and comes into contact with one side surface of the disk rotor 2. The friction pad 4 c is moved by being pushed by the reaction portion 1 c and is in contact with the other side surface of the disk rotor 2. Braking is performed by the above operation.

  An annular piston seal groove 7 is provided on the inner peripheral wall of the cylinder hole 6a. A piston seal member 8 is fitted in the piston seal groove 7. The material of the piston seal member 8 will be described later.

  The hydraulic chamber 9 is provided between the bottom of the piston 5 and the cylinder 6. Brake fluid is supplied to the hydraulic chamber 9 from the supply port 10. The piston seal member 8 has a function of sealing the brake fluid and a function of rolling back the piston 5 that has moved forward when the hydraulic pressure in the hydraulic pressure chamber 9 decreases. The supply port 10 is connected to an output port (not shown) of a master cylinder (not shown), which is a hydraulic pressure source, via a hydraulic pressure path 28.

  As shown in FIG. 1, the piston seal groove 7 has a chamfered corner 7a and a chamfered corner 7b. The piston seal member 8 follows the sliding surface of the piston 5 as the piston 5 slides forward in the direction of the black arrow shown in FIG. 1 (the disk rotor 2 side in FIG. 2). A part enters the chamfer corner 7a. When the hydraulic pressure in the hydraulic chamber 9 decreases, the piston 5 is rolled back in the direction opposite to the arrow by being restored by the elasticity of the piston seal member 8.

(Piston seal member)
The piston seal member 8 according to the present embodiment is capable of liquid-tight sliding between, for example, a cylinder hole 6a provided in the caliper body 1 of the disc brake 20 and a piston 5 that slides in the cylinder hole 6a. And a non-crosslinked rubber composition comprising a rubber having an unsaturated bond or group having an affinity for carbon nanofibers and carbon nanofibers dispersed in the rubber.

(Rubber)
First, the rubber according to this embodiment preferably has a molecular weight of 5,000 to 5,000,000, more preferably 20,000 to 3,000,000. When the molecular weight of the rubber is within this range, the rubber molecules are entangled with each other and are connected to each other. Therefore, the rubber easily penetrates into the aggregated carbon nanofibers, and thus has a great effect of separating the carbon nanofibers. If the molecular weight of the rubber is smaller than 5000, the rubber molecules cannot be sufficiently entangled with each other, and the effect of dispersing the carbon nanofibers is reduced even when a shearing force is applied in a later step. On the other hand, if the molecular weight of the rubber is greater than 5 million, the rubber becomes too hard and processing becomes difficult.

  The rubber preferably has a spin-spin relaxation time (T2n / 30 ° C.) of the network component in the uncrosslinked body of 100 to 3000 μsec, more preferably 200, measured at 30 ° C. by the Hahn echo method using pulsed NMR. Or 1000 μs. By having a spin-spin relaxation time (T2n / 30 ° C.) in the above range, the rubber can be flexible and have sufficiently high molecular mobility. Thus, when rubber and carbon nanofibers are mixed, the rubber can easily enter the gaps between the carbon nanofibers due to high molecular motion. If the spin-spin relaxation time (T2n / 30 ° C.) is shorter than 100 μsec, the rubber cannot have sufficient molecular mobility. Also, if the spin-spin relaxation time (T2n / 30 ° C.) is longer than 3000 μsec, the rubber tends to flow like a liquid and it becomes difficult to disperse the carbon nanofibers.

  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 rubber is measured by the Hahn-echo method using pulsed NMR, the first component having the first spin-spin relaxation time (T2n) having a short relaxation time and the relaxation A second component having a longer spin-spin relaxation time (T2nn) 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 rubber. Moreover, it can be said that the longer the first spin-spin relaxation time, the higher the molecular mobility and the softer the 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 rubber according to the present invention has a medium 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.

  The rubber has an unsaturated bond or group having affinity for the radical at the end of the carbon nanofiber in at least one of the main chain, the side chain, and the end chain, or generates such a radical or group. Easy to use. Such unsaturated bonds or groups include double bonds, triple bonds, α hydrogen, carbonyl groups, carboxyl groups, hydroxyl groups, amino groups, nitrile groups, ketone groups, amide groups, epoxy groups, ester groups, vinyl groups, halogen groups. , Urethane groups, burette groups, allophanate groups, and urea groups.

  Carbon nanofibers usually have a six-membered ring of carbon atoms and a closed end with a five-membered ring introduced at the tip. It tends to occur, and it is easy to generate radicals and functional groups in the part. In this embodiment, at least one of the main chain, side chain, and end chain of rubber has an unsaturated bond or group having high affinity (reactivity or polarity) with the radical of carbon nanofiber, so that rubber and carbon Nanofibers can be combined. This makes it possible to easily disperse the carbon nanofibers by overcoming the cohesive force. And when kneading rubber with carbon nanofibers, free radicals generated by breaking the molecular chains of rubber attack the defects of carbon nanofibers and guess that they generate radicals on the surface of carbon nanofibers it can.

  As rubber, natural rubber (NR), epoxidized natural rubber (ENR), styrene-butadiene rubber (SBR), nitrile rubber (NBR), chloroprene rubber (CR), ethylene propylene rubber (EPR, EPDM), butyl rubber (IIR) ), Chlorobutyl rubber (CIIR), acrylic rubber (ACM), silicone rubber (Q), fluorine rubber (FKM), butadiene rubber (BR), epoxidized butadiene rubber (EBR), epichlorohydrin rubber (CO, CEO), urethane rubber (U), rubbers such as polysulfide rubber (T), and mixtures thereof can be used. In particular, for the piston seal member that comes into contact with the brake fluid, ethylene / propylene rubber or styrene-butadiene rubber is preferable as the rubber. For example, a rubber having a low polarity such as ethylene propylene rubber (EPDM) generates free radicals by setting the kneading temperature to a relatively high temperature (for example, 50 ° C. to 150 ° C. in the case of EPDM). Can be dispersed. EPDM (ethylene / propylene / diene / copolymer), EPM (ethylene / propylene copolymer) and the like can be used as the ethylene / pyropyrene rubber, and EPDM is preferred. The rubber is usually used after being crosslinked and does not contain a thermoplastic elastomer.

  The ethylene / propylene rubber according to this embodiment preferably has a propylene content of 35 to 60% by weight, more preferably 37 to 55%. If the propylene content is less than 35% by weight, the ethylene component is too much and the rubber composition becomes rigid and the flexibility becomes low. On the other hand, if the propylene content exceeds 60% by weight, it is too soft and not preferable as a sealing member.

(Carbon nanofiber)
The carbon nanofiber according to the present embodiment has an average diameter of 0.7 to 15 nm and an average length of 0.5 to 100 μm. In the rubber composition of the piston seal member, the compounding amount of the carbon nanofiber is preferably 5 to 100 parts by weight with respect to 100 parts by weight of the rubber. When the blending amount of the carbon nanofibers in the rubber composition is less than 5 parts by weight, the reinforcing effect of the carbon nanofibers is small, and when it exceeds 100 parts by weight, the hardness and elastic modulus are unfavorable. Thus, by reinforce | strengthening with a very thin carbon nanofiber, the physical-property fall at high temperature can be made small. Carbon nanofibers thinner than 0.7 nm are difficult to obtain, and those exceeding 15 nm are not preferable because material properties (reinforcing effect) cannot be obtained.

  Examples of carbon nanofibers include so-called carbon nanotubes. Carbon nanotubes have a single-layer structure in which graphene sheets with carbon hexagonal mesh surfaces are closed in a cylindrical shape, or a multilayer structure in which these cylindrical structures are arranged in a nested manner. That is, the carbon nanotube may be composed of only a single-layer structure or a multilayer structure, and the single-layer structure and the multilayer structure may be mixed. 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”.

  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.

  The carbon nanofibers can be improved in adhesion and wettability with the rubber by performing a surface treatment in advance, for example, ion implantation treatment, sputter etching treatment, plasma treatment, etc. before being kneaded with the rubber.

  In the rubber composition according to the present embodiment, when the compounding amount of the carbon nanofiber is relatively small, for example, less than 20 parts by weight with respect to 100 parts by weight of the rubber, carbon black or fiber is used as a compounding agent other than the carbon nanofiber. Is preferably added. In that case, carbon black of various grades using various raw materials can be used as the carbon black. The carbon black preferably has a relatively high structure in which aggregates (so-called secondary aggregates) in which the basic constituent particles (so-called primary particles) are fused and connected are developed.

  The carbon black according to the present embodiment has an average particle size of 10 to 100 nm of basic constituent particles and an absorption amount of DBP of 80 ml / 100 g or more, more preferably an average particle size of 10 to 40 nm. The DBP absorption is 100 to 500 ml / 100 g. If the average particle size of the carbon black is less than 10 nm, processing (kneading) is difficult, and if the average particle size is larger than 100 nm, the reinforcing effect is inferior. Since the reinforcing effect of carbon black is affected by the height of the structure in which the aggregate is developed, the reinforcing effect is large when the DBP absorption amount is 80 ml / 100 g or more.

  As such carbon black, for example, carbon black such as ketjen black, SAF, SAF-HS, ISAF, ISAF-HS, HAF, HAF-HS, FEF, FEF-HS, SRF-HS can be used.

  In the rubber composition according to this embodiment, when a fiber is added as a compounding agent other than carbon nanofiber, the fiber is supple and excellent in flexibility, an average diameter of 1 to 100 μm, and an aspect ratio of 50 to 500 is preferable. . If the average diameter of the fibers is less than 1 μm, processing (kneading) is difficult, and if the average diameter is larger than 100 μm, the reinforcing effect is inferior.

  As the fiber, a flexible fiber excellent in flexibility is preferable, and natural fiber, metal fiber, synthetic fiber, or a mixture of these fibers can be used. As natural fibers, plant fibers such as cotton and hemp, and animal fibers such as wool and silk can be appropriately selected and used. As the metal fiber, stainless steel fiber, copper fiber or the like can be appropriately selected and used. As the synthetic fiber, an aliphatic polyamide fiber can be used. Polyester fibers, aromatic polyamide fibers, ceramic fibers and the like are not suitable because they are rigid and have no flexibility. Fibers may also be added along with carbon black.

(Method for producing rubber composition)
As a method for producing a rubber composition according to the present embodiment, rubber and carbon nanofibers are supplied to a known mixer such as an open roll, a single or twin screw extruder, a Banbury mixer, a kneader, and kneaded. A method is mentioned. Fillers other than carbon nanofibers such as carbon black and fibers are preferably supplied to the mixer before supplying the carbon nanofibers. Usually, the same amount of process oil as that of carbon black is used in this kneading, but it is desirable not to use it in the production process of the rubber composition of the present invention. This is because in a hydraulic master cylinder using a piston seal member manufactured using process oil, the process oil dissolves into the working fluid, causing a change in performance of the working fluid over time and a change in heat resistance.

  For example, when an open roll method with a roll interval of 0.5 mm or less is used as a method for producing the rubber composition, the rubber is put into two rotating rolls arranged at an interval of 1.5 mm, for example. Next, a filler such as carbon black or fiber is added to the rubber, carbon nanofibers are further added, and the roll is rotated to obtain a mixture of rubber and carbon nanofibers. This mixture is put into an open roll set at an interval of 0.1 to 0.5 mm, and thinned, for example, about 10 times to obtain a rubber composition. Due to such thinness, a high shearing force acts on the rubber, and the aggregated carbon nanofibers are separated from each other so as to be pulled out one by one by rubber molecules and dispersed in the rubber. In particular, when a particulate filler such as carbon black is mixed prior to the carbon nanofiber, a turbulent flow is generated around the carbon black, and the carbon nanofiber can be easily dispersed.

  In this kneading step, in order to obtain as high a shearing force as possible, the rubber and carbon nanofiber are mixed at a relatively low temperature of preferably 0 to 50 ° C., more preferably 5 to 30 ° C. When EPDM is used as the rubber, it is desirable to perform a two-stage kneading process. In the first kneading process, in order to obtain as high a shearing force as possible, mixing of EPDM and carbon nanofibers is performed in the first step. The first temperature is 50 to 100 ° C. lower than the kneading step 2. The first temperature is preferably 0 to 50 ° C, more preferably 5 to 30 ° C. The dispersibility of the carbon nanofibers can be improved by setting the second temperature of the roll to a relatively high temperature of 50 to 150 ° C.

  In this kneading step, free radicals are generated in the rubber sheared by the shearing force, and the free radicals attack the surface of the carbon nanofibers, thereby activating the surface of the carbon nanofibers. At this time, rubber with a moderately long molecular weight and high molecular mobility penetrates into the carbon nanofibers, and a specific part of the rubber binds to a highly active part of the carbon nanofiber by chemical interaction. . In this state, when a strong shearing force acts on the mixture, the carbon nanofibers move with the movement of the rubber, and the aggregated carbon nanofibers are separated and dispersed in the rubber. The carbon nanofibers once dispersed are prevented from reaggregating due to chemical interaction with the rubber, and can have good dispersion stability. In short, in this kneading step, it is sufficient that the aggregated carbon nanofibers can be separated and a shearing force for cutting the rubber molecules to generate radicals can be given to the rubber.

(Characteristics of non-crosslinked rubber composition)
The non-crosslinked rubber composition according to the present embodiment has a dynamic modulus of elasticity of 8 MPa or more at 10 Hz, 30 ° C., and 150 ° C. In addition, this non-crosslinked rubber composition has a dynamic elastic modulus retention of 50% or more as the temperature rises from 30 ° C. to 150 ° C. As the piston seal member, it is preferable to stably maintain a high dynamic elastic modulus even at a high temperature. Particularly, when used as a piston seal in the caliper body of the disc brake according to the present embodiment, a desirable rollback amount is obtained. In order to have it, it is preferable that a dynamic elastic modulus is 8 Mpa or more. Further, when used as a piston seal in the caliper body of the disc brake according to the present embodiment, when the dynamic elastic modulus retention rate accompanying the temperature rise from 30 ° C. to 150 ° C. is 50% or more, even at high temperatures It has a desired rollback amount.

  Although the rubber composition is non-crosslinked, it has a small decrease in physical properties at a high temperature. For example, the compression set at a high temperature is small.

  In the non-crosslinked rubber composition, carbon nanofibers are uniformly dispersed in rubber as a base material. This can be said to be a state in which the rubber is restrained by the carbon nanofibers. In this state, the mobility of the 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 piston seal member according to this embodiment are the same as those of the carbon nanofiber. It becomes shorter than the case of rubber alone that does not contain.

  Further, in the state where the 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 rubber decreases overall due to carbon nanofibers, the non-network component becomes more difficult to move, making it easier to behave the same as the network component, and the non-network component ( It is considered that the non-network component is reduced due to the fact that the terminal chain is easy to move and 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 is smaller than that in the case of a rubber alone not including carbon nanofibers.

  From the above, it is desirable that the non-crosslinked rubber composition has a measured value obtained by the Hahn echo method using pulsed NMR in the following range.

  That is, in the non-crosslinked rubber composition, the first spin-spin relaxation time (T2n) measured at 150 ° C. is 100 to 3000 μsec, and the second spin-spin relaxation time (T2nn) is 1000 to 10,000 μm. Preferably, the component fraction (fnn) of the component having the second spin-spin relaxation time is less than 0.2.

  The spin-lattice relaxation time (T1) measured by the Hahn-echo 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 rubber, the lower the molecular mobility and the harder the rubber, and the longer the spin-lattice relaxation time, the higher the molecular mobility and the softer the rubber. Therefore, the piston seal member in which the carbon nanofibers are uniformly dispersed has low molecular mobility, and falls within the above-described ranges of T2n, T2nn, and fnn.

  In the non-crosslinked rubber composition, the flow temperature in the temperature dependence measurement of dynamic viscoelasticity is preferably 20 ° C. or more higher than the flow temperature of the raw rubber alone, and the flow temperature of the non-crosslinked rubber composition is 150. C. or higher is preferable, and 200.degree. C. or higher is more preferable. In the non-crosslinked rubber composition, carbon nanofibers are well dispersed in rubber. This can be said to be a state where rubber is restrained by carbon nanofibers as described above. In this state, the rubber has a smaller molecular motion than the case where no carbon nanofibers are contained, and as a result, the fluidity is lowered. By having such a flow temperature characteristic, the non-crosslinked rubber composition has a low temperature dependence of dynamic viscoelasticity, and as a result, has excellent heat resistance and remains a non-crosslinked piston seal member. Can be used.

  In addition, the non-crosslinked rubber composition contains carbon nanofibers, so that the surface tackiness is lowered and can be molded while not being crosslinked.

(Characteristics of piston seal member)
The kneaded rubber composition is extrusion molded or injection molded using a mold having the shape of a piston seal member. Generally, a rubber seal composition is formed by cross-linking to obtain a piston seal member. However, the piston seal member of this embodiment is formed without cross-linking and can be reused (recycled).

  Therefore, the piston seal member according to the present embodiment has the characteristics of the above-described non-crosslinked rubber composition as it is, and there is little change in physical properties in a wide temperature range from low temperature to high temperature, and particularly, thermal expansion is stable. Therefore, it can be used in a wide temperature range. Such a piston seal member is non-bridging, but its sliding resistance is stable against temperature changes over a wide temperature range, and the phenomenon of sticking to the piston is improved. Further, since the piston seal member has a small permanent set, there is little sealing failure. Further, when such a piston seal member is used for a caliper body of a disc brake, the operability of rolling back the piston can be stabilized in a wide temperature range.

  In addition, this invention is not limited to the said embodiment, In the range of the summary of this invention, it can deform | transform into various forms.

  For example, in the present embodiment, the piston seal member is built in the disc brake for a vehicle, but other piston seal members may be used. Particularly, it is useful in a piston seal member used in a low temperature region such as room temperature (30 ° C.) or a high temperature region of 150 ° C.

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

(Examples 1-6, Comparative Examples 1-3)
(A) Preparation of non-crosslinked rubber composition 1) A 6-inch open roll (roll temperature: 10 to 20 ° C) was charged with rubber and wound around a roll.
2) Carbon nanofibers (denoted as “CNT13” in Table 1) in the amount (parts by weight (phr)) shown in Table 1 with respect to 100 parts by weight (phr) of rubber were put into the rubber. In Examples 4 and 5, carbon black (described as “HAF-HS” in Table 1) was added to rubber, and in Examples 3 and 5, fibers (silk) were added to rubber. At this time, the roll gap was set to 1.5 mm.
3) When the carbon nanofibers were added, the mixture of rubber and carbon nanofibers was taken out from the roll.
4) The roll gap was narrowed from 1.5 mm to 0.3 mm, and the mixture was introduced to make it thin. At this time, the surface speed ratio of the two rolls was set to 1.1. Thinning was repeated 10 times.
5) The roll was set to a predetermined gap (1.1 mm), and the thinned mixture was charged and dispensed.

In this way, uncrosslinked rubber compositions of Examples 1 to 6 and Comparative Examples 1 to 3 were obtained. In Table 1, as for the raw rubber, “EPDM” is ethylene / propylene rubber, and “SBR” is styrene-butadiene rubber. In Table 1, “CNT13” is a multi-wall carbon nanotube having an average diameter of about 13 nm. “HAF-HS” is an HAF having an average particle size of 27 nm, a DBP absorption of 101 ml / 100 g, and a nitrogen specific surface area of 82 m ² / g. -HS grade carbon black, "silk thread" is a silk thread having an average diameter of about 3 m and an average length of about 6 mm, and PO is a peroxide (crosslinking agent).

(B) Production of Piston Seal Member The rubber composition obtained in (a) was injection molded to obtain uncrosslinked piston seal members of Examples 1 to 6 and Comparative Examples 2 and 3. Comparative Example 1 was cross-linked after being formed into a piston seal member.

(C) Observation with an electron microscope About the uncrosslinked rubber composition, the dispersion state of carbon nanofiber and carbon black was observed using an electron microscope (SEM). In all the samples, it was observed that carbon nanofibers and carbon black were uniformly dispersed in the rubber.

(D) Measurement of static physical properties For each uncrosslinked rubber composition, rubber hardness (JISA), tensile strength (TB) and cut elongation (EB) were measured. The rubber hardness (JISA) was measured according to JIS K 6253. TB and EB were measured according to JIS K 6521-1993. These results are shown in Table 1.

(E) Measurement of dynamic physical properties For each uncrosslinked rubber composition, E ′ (dynamic viscoelastic modulus) at 30 ° C. and 150 ° C. was measured according to JIS K 6521-1993. Further, the ratio of E ′ at 150 ° C. to E ′ at 30 ° C. (E ′ retention (%) = E ′ (30 ° C.) / E ′ (150 ° C.) · 100) is calculated as E ′ retention (%). did. These results are shown in Table 1.

(F) Measurement of flow temperature The flow temperature was measured by dynamic viscoelasticity measurement (JIS K 6394) for the raw material rubber alone and the non-crosslinked rubber composition. Specifically, the flow temperature was determined by applying a sine vibration (± 0.1% or less) to a sample having a width of 5 mm, a length of 40 mm, and a thickness of 1 mm, and measuring the stress and phase difference δ generated thereby. At this time, the temperature was changed from −70 ° C. to 200 ° C. at a rate of temperature increase of 2 ° C./min. The results are shown in Table 1. In Table 1, the case where no sample flow phenomenon was observed up to 200 ° C. was described as “200 ° C. or higher”.

(G) Measurement of flexibility using pulse method NMR Each uncrosslinked rubber composition was measured by the Hahn echo method and the iterative method using pulse 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. The uncrosslinked rubber composition was measured by inserting it into a sample tube up to an appropriate range of the magnetic field. The measurement temperature was 150 ° C. By this measurement, the component fraction (fnn) of the component having the second spin-spin relaxation time of the sample was obtained. The results are shown in Table 1.

(H) Evaluation of recyclability Whether or not a product (piston seal member) can be produced by repeating the process of kneading each piston seal member with an open roll and injection molding to create the piston seal member five times. Evaluated. The results are shown in Table 1. In Table 1, “◯” indicates that the product could be created, “×” indicates that the product could not be recycled, and “−” indicates that the recycling test was not performed.

(I) Rollback amount evaluation test and lever stroke increase amount evaluation test A piston seal member formed by adjusting a rubber composition is fitted into the annular piston seal groove of the disc brake, and the rollback amount evaluation test and illustration are shown. An evaluation test was performed on the amount of increase in the lever stroke of an operation lever (not shown) that operates the master cylinder, and its characteristics were evaluated. The results are shown in Table 1. The rollback amount was measured by applying a hydraulic pressure of 0.5 MPa to the disc brake 10 times at a piston seal member 140 ° C. and operating it for 5 seconds at a hydraulic pressure of 6.9 MPa. The amount of piston movement when the hydraulic pressure was released was measured. Further, the amount of increase in lever stroke ("change in lever stroke" in Table 1) was measured by measuring the stroke of a brake lever for a two-wheeled vehicle until the brake effect began when the piston seal member was at 30 ° C and 140 ° C. Furthermore, the presence or absence of dragging was confirmed as the durability evaluation of the piston seal member. In Table 1, “◯” indicates that no dragging was observed, and “x” indicates that dragging was observed.

(J) Evaluation of surface adhesion Formability was evaluated by the surface adhesion of the piston seal member. The results are shown in Table 1. “X” was entered when the surface was highly sticky and molding was difficult, and “◯” was entered when the surface was low and easy to mold.

(K) Measurement of compression set (sag resistance) and high temperature constant load fatigue Compression set (JIS K6262) was measured for each rubber composition. The compression set was performed under conditions of 150 ° C., 70 hours, and 25% compression. The compression set is an evaluation of the so-called sag resistance of the piston seal member. For high temperature constant load fatigue, a load of 150 ° C. and 2 MPa was repeatedly applied to determine the number of times of fracture. These results are shown in Table 1.

  From Table 1, according to Examples 1 to 6 of the present invention, the following was confirmed. That is, the non-crosslinked rubber compositions of Examples 1 to 6 exhibited the same static physical properties and dynamic physical properties as the cross-linked rubber compositions. In particular, the retention rate and flow temperature of the dynamic elastic modulus from room temperature to high temperature were high, and it was found that the physical property decrease at high temperature was small while being non-crosslinked. In addition, the rubber compositions of Examples 1 to 6 had a compression set of 30% or less, and the evaluation of set resistance was good. Since the piston seal members of Examples 1 to 6 had a rollback amount of 0.04 mm or more and a lever stroke increase amount of 20 mm or less, good evaluation was obtained. Furthermore, no drag was observed in the piston seal members of Examples 1 to 6. Moreover, the crosslinked rubber composition of Comparative Example 1 had a problem in recyclability. The rubber compositions of Comparative Examples 2 and 3 were not evaluated for recyclability because of their high surface tackiness and difficulty in molding. In the rubber compositions of Comparative Examples 2 and 3, the compression set greatly exceeded 30% and was 80% or more. Since the piston seal members of Comparative Examples 2 and 3 had a rollback amount of less than 0.04 mm and a lever stroke increase amount of more than 20 mm, it was evaluated that the driver felt uncomfortable when operating the brake. Further, drag was observed in the piston seal members of Comparative Examples 2 and 3.

  As shown in Table 1, the piston seal members of Examples 1 to 6 had an Fnn of less than 0.2 according to the Hahn echo method.

  As shown in Table 1, the flow temperature in the non-crosslinked rubber composition is 200 ° C. or higher, and has excellent heat resistance, so that it can be used as a piston seal member without being cross-linked. In particular, recyclability was good because it can be used as a piston seal member without cross-linking.

It is sectional drawing which shows typically the piston seal member which concerns on one embodiment of this invention. It is sectional drawing which shows typically the disc brake containing the piston seal member shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Caliper body 1a Bridge part 1b Action part 1c Reaction part 2 Disc rotor 3 Bracket 4b, 4c Friction pad 5 Piston 6 Cylinder 6a Cylinder hole 7 Piston seal groove 7a, 7b Chamfer corner 8 Piston seal member 9 Hydraulic pressure chamber 10 Supply port 11 Boot 20 Disc brake 28 Hydraulic path

Claims (7)

A piston seal member that holds a cylinder hole and a piston that slides in the cylinder hole in a liquid-tight and slidable manner,
A piston seal member formed of a non-crosslinked rubber composition comprising a rubber having an unsaturated bond or group having affinity for carbon nanofibers, and carbon nanofibers dispersed in the rubber. In claim 1,
The non-crosslinked rubber composition contains 5 to 100 parts by weight of the carbon nanofibers with respect to 100 parts by weight of the rubber.
The carbon nanofiber is a piston seal member having an average diameter of 0.7 to 15 nm and an average length of 0.5 to 100 μm. In claim 1 or 2,
The rubber is a piston seal member having a molecular weight of 5,000 to 5,000,000. In any of claims 1 to 3,
The rubber is a piston seal member in which the spin-spin relaxation time (T2n) of a network component in an uncrosslinked body is 100 to 3000 μsec, as measured at 30 ° C. by a Hahn echo method using pulse NMR. In any of claims 1 to 4,
The rubber is a piston seal member made of ethylene / propylene rubber or styrene-butadiene rubber. In any of claims 1 to 5,
The piston seal member, wherein a flow temperature of the non-crosslinked rubber composition is 150 ° C or higher. A piston seal member according to any one of claims 1 to 6,
A cylinder having a cylinder hole;
A piston inserted into the cylinder hole,
The piston seal member is fitted into an annular groove formed in the inner peripheral wall of the cylinder hole,
A disc brake for bringing the piston inserted into the cylinder hole into contact with the piston so as to be movable in a liquid-tight manner, and rolling back the piston that has been advanced by hydraulic pressure.

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