JP2017172677A - Piston seal member, and disc brake using piston seal member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piston seal member capable of reducing environmental load and having excellent high-temperature characteristic and durability, and a disc brake using the piston seal member.SOLUTION: A piston seal member 8 liquid-tightly and slidably holds a cylinder hole 6a and a piston 5 sliding in the cylinder hole 6a. The piston seal member 8 is composed of a rubber composition including 0.1 pts.mass-60 pts.mass of at least one of oxidized cellulose fiber and cellulose nanofiber to 100 pts.mass of rubber. The rubber includes at least one of ethylene-propylene rubber and styrene-butadiene rubber. An average value of a fiber diameter of the oxidized cellulose fibber is 10 μm-30 μm. An average value of a fiber diameter of the cellulose nanofiber is 1 nm-200 nm.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a piston seal member and a disc brake using the piston seal member.

  The piston seal member is generally formed of a 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 (see, for example, Patent Document 1). 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, and the driver may feel uncomfortable with the brake operation.

  In view of this, a piston seal member formed of a rubber composition in which at least 100 parts by mass of carbon black is added to 100 parts by mass of ethylene / propylene rubber (EPDM) has been proposed (for example, see Patent Document 2).

  Further, a piston seal member made of a rubber composition containing two types of carbon black and carbon nanofibers has been proposed (see, for example, Patent Document 3).

  In recent years, cellulose nanofibers obtained by defusing natural cellulose fibers into nanosizes have attracted attention. Natural cellulose fiber is biomass that uses pulp such as wood as a raw material, and it is expected to reduce the environmental load by effectively using this.

  Then, the manufacturing method of the rubber composition using at least one of an oxidized cellulose fiber and a cellulose nanofiber is proposed (refer patent document 4).

Japanese Examined Patent Publication No. 3-59291 JP 2004-316773 A JP 2008-223780 A Japanese Patent Laying-Open No. 2015-98576

  An object of the present invention is to provide a piston seal member that reduces environmental load and is excellent in high-temperature characteristics and durability, and a disc brake using the piston seal member.

[Application Example 1]
The piston seal member according to this application example 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,
The piston seal member is composed of a rubber composition containing 0.1 to 60 parts by mass of at least one of oxidized cellulose fiber and cellulose nanofiber with respect to 100 parts by mass of rubber.
The rubber includes at least one of ethylene / propylene rubber and styrene / butadiene rubber,
The oxidized cellulose fiber has an average fiber diameter of 10 μm to 30 μm,
Cellulose nanofibers have an average fiber diameter of 1 nm to 200 nm.

  According to the piston seal member according to this application example, it is possible to reduce the environmental load by including at least one of the oxidized cellulose fiber and the cellulose nanofiber, and it is excellent in high temperature characteristics and durability.

[Application Example 2]
In the piston seal member according to this application example,
The rubber composition may have an average value of linear expansion coefficient at 20 ° C. to 150 ° C. of 50 ppm (1 / K) to 180 ppm (1 / K).

[Application Example 3]
In the piston seal member according to this application example,
The rubber composition may have a storage modulus of 15 MPa or more at 30 ° C. and 150 ° C. in a dynamic viscoelasticity test at a frequency of 1 Hz in accordance with JIS K6394.

[Application Example 4]
In the piston seal member according to this application example,
The piston seal member may be used for a caliper body of a disc brake.

[Application Example 5]
The disc brake according to this application example is
The piston seal member;
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, and the piston inserted into the cylinder hole is brought into close contact with the liquid-tight movable state and is advanced by hydraulic pressure. The piston is rolled back.

  According to the disc brake according to this application example, the piston seal member includes at least one of the oxidized cellulose fiber and the cellulose nanofiber, so that the environmental load can be reduced. Further, according to the disc brake according to this application example, the piston seal member is excellent in high temperature characteristics and durability, so that stable piston operability is maintained even at high temperatures, and the liquid tightness between the piston and the cylinder is maintained for a long time. Can be maintained.

It is sectional drawing which shows typically the piston seal member which concerns on one Embodiment. It is sectional drawing which shows typically the disc brake containing the piston seal member shown in FIG. It is a figure which shows typically the dispersion | distribution process in the manufacturing method of the rubber composition which concerns on one Embodiment. It is a figure which shows typically the dispersion | distribution process in the manufacturing method of the rubber composition which concerns on one Embodiment. It is a figure which shows typically the dispersion | distribution process in the manufacturing method of the rubber composition which concerns on one Embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below do not unduly limit the contents of the present invention described in the claims. In addition, not all of the configurations described below are essential constituent requirements of the present invention.

  The piston seal member according to the present embodiment 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 consists of a rubber composition containing 0.1 to 60 parts by mass of at least one of oxidized cellulose fiber and cellulose nanofiber with respect to 100 parts by mass, and the rubber is at least one of ethylene / propylene rubber and styrene / butadiene rubber. The oxidized cellulose fibers have an average fiber diameter of 10 μm to 30 μm, and the cellulose nanofibers have an average fiber diameter of 1 nm to 200 nm.

  The disc brake according to the present embodiment includes the piston seal member, a cylinder having a cylinder hole, and a piston inserted into the cylinder hole, and the piston seal member is formed on an inner peripheral wall of the cylinder hole. The piston inserted into the formed annular groove and brought into close contact with the piston inserted in the cylinder hole in a liquid-tight movable state is rolled back.

    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 this embodiment, a floating type disc brake for a vehicle will be described as an example.

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

  The disc brake 20 includes a bracket 3 fixed to a vehicle body (not shown), and a caliper body 1 supported by the bracket 3 in a slidable state. The caliper body 1 includes an action part 1b and a reaction part 1c, and the piston 5 and the cylinder 6 are in the action part 1b. 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 friction pad 4 b is moved by being pushed by the piston 5 inserted into the cylinder hole 6 a and is in 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. An annular piston seal member 8 is fitted in the piston seal groove 7. The material of the piston seal member 8 and the manufacturing method thereof 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. The type of the disc brake 20 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 piston seal member are the same. It is not limited to the embodiment.

2. Piston seal member The piston seal member 8 concerning this embodiment is the piston seal member 8 which hold | maintains the cylinder hole 6a and the piston 5 which slides in this cylinder hole 6a liquid-tightly and so that sliding is possible. The piston seal member 8 can be used for a caliper body 1 of a disc brake 20 as shown in FIG.

  The piston seal member 8 is made of a rubber composition containing 0.1 to 60 parts by mass of at least one of oxidized cellulose fiber and cellulose nanofiber with respect to 100 parts by mass of rubber. Here, “parts by mass” indicates “phr” unless otherwise specified, and “phr” is an abbreviation for “parts per undred of resin or rubber”, and represents the percentage of external additives such as additives to rubber and the like. It is.

  The rubber composition is a rubber composition in which at least one of defibrated oxidized cellulose fiber and cellulose nanofiber is dispersed. The rubber composition may further contain carbon black.

  For example, when the rubber composition is used in a piston seal member of a disc brake, the amount of change in the brake lever stroke with the temperature change is small, that is, the thermal stability is good, and the disc brake does not cause poor drag. It is desirable. In order to obtain such a piston seal member, it is desirable to keep the average value of the linear expansion coefficient low in order to improve the thermal stability. The rubber composition may have an average coefficient of linear expansion of 50 ppm (1 / K) to 180 ppm (1 / K) at 20 ° C. to 150 ° C. Since the average value of the linear expansion coefficient at 20 ° C. to 150 ° C. of the piston seal member is less than 50 ppm (/ K), it is about the same as that of metal. Is desirable. Further, in order to suppress a decrease in sealing performance due to thermal expansion accompanying a temperature rise, it is desirable that the average value of the linear expansion coefficient of the piston seal member at 20 ° C. to 150 ° C. is 180 ppm (/ K) or less. In the rubber composition, the average value of the linear expansion coefficient in the test can be 50 ppm (1 / K) to 170 ppm (1 / K), and is further 50 ppm (1 / K) to 160 ppm (1 / K). be able to.

  The rubber composition may have a storage elastic modulus of 15 MPa or more at 30 ° C. and 150 ° C. in a dynamic viscoelasticity test at a frequency of 1 Hz in accordance with JIS K6394. By using such a rubber composition, a piston seal member having excellent heat resistance can be obtained. And since such a piston seal member can maintain a high storage elastic modulus at the time of normal temperature and high temperature, it can prevent the fall of sealing performance and followable | trackability.

  The rubber composition has a large number of times until the test piece breaks in a fatigue test (described later in Examples). That is, the rubber composition is excellent in fatigue life, and a piston seal member excellent in fatigue durability can be obtained.

  In addition, the rubber composition has at least one of oxidized cellulose fibers and cellulose nanofibers defibrated to rubber and has a diameter of at least one of oxidized cellulose fibers and cellulose nanofibers having a diameter of 0.1 mm or more. It is preferable not to have an aggregate of 1 mm or more. The aggregate containing at least one of the oxidized cellulose fiber and the cellulose nanofiber is a mass in which these fibers are gathered together. The aggregate of the oxidized cellulose fiber, the aggregate of the cellulose nanofiber, and the oxidized cellulose fiber and the cellulose It contains aggregates composed of nanofibers.

  According to the rubber composition in the present embodiment, it does not have an aggregate and is reinforced by dispersing in a state where at least one of oxidized cellulose fiber and cellulose nanofiber is defibrated, and has rigidity, strength, and low linear expansion. Excellent coefficient and fatigue resistance. However, it is difficult to prove that aggregates of cellulose nanofibers are not present in the rubber composition. When only the cellulose nanofiber is contained in the rubber composition, the aggregate can be confirmed by observation with an optical microscope (see Patent Document 4). Since the same dispersion process is used in this embodiment, the rubber composition does not have an aggregate of 0.1 mm or more of cellulose nanofibers.

3. Rubber The rubber constituting the rubber composition contains at least one of ethylene / propylene rubber and styrene / butadiene rubber.

As will be described later, in the process of mixing oxidized cellulose fibers and / or cellulose nanofibers with rubber, a rubber latex solution is used. However, since ethylene / propylene rubber is not currently marketed as a latex, styrene / butadiene rubber is used. A mixture obtained by mixing oxidized cellulose fibers and / or cellulose nanofibers with ethylene / propylene rubber is mixed.

  The blending ratio of the ethylene / propylene rubber and the styrene / butadiene rubber in the rubber composition is not particularly limited, but EPDM is preferably 40% by mass or more from the viewpoint of heat resistance.

3-1. Ethylene / propylene rubber EPDM (ethylene / propylene / diene copolymer) is preferably used as the ethylene / propylene rubber. The ethylene / propylene rubber may have a propylene content of 35 to 60% by mass and a propylene content of 37 to 55% by mass. When the propylene content is 35% by mass or more, the rubber composition does not become too rigid and has flexibility. Moreover, if propylene content is 60 mass% or less, it has a moderate softness | flexibility as a piston seal member.

3-2. Styrene / butadiene rubber As the styrene / butadiene rubber, emulsion polymerization SBR (E-SBR), solution polymerization SBR (S-SBR), and the like can be used. The styrene content of the styrene-butadiene rubber is not particularly limited, but may be 10 to 50% by mass, preferably 20 to 25% by mass.

  The oxidized cellulose fiber and cellulose nanofiber will be described later.

4). Manufacturing method of rubber composition The manufacturing method of the rubber composition used for the piston seal member is a mixing step in which an aqueous solution containing at least one of oxidized cellulose fibers and cellulose nanofibers and rubber latex are mixed to obtain a first mixture. And a drying step of drying the first mixture to obtain a second mixture, and a dispersion step of obtaining a rubber composition by passing the second mixture through an open roll. .

4-1. Raw material First, the raw material used for a mixing process is demonstrated.

4-1-1. Aqueous solution The aqueous solution includes an aqueous solution containing oxidized cellulose fibers, an aqueous solution containing cellulose nanofibers, and an aqueous solution containing oxidized cellulose fibers and cellulose nanofibers.

  The aqueous solution containing oxidized cellulose fibers can be produced, for example, by an oxidation process in which natural cellulose fibers are oxidized to obtain oxidized cellulose fibers.

  The aqueous solution containing cellulose nanofibers can be obtained, for example, by a production method including an oxidation step of oxidizing natural cellulose fibers to obtain oxidized cellulose fibers, and a refining step of refining oxidized cellulose fibers.

  The aqueous solution containing oxidized cellulose fibers and cellulose nanofibers can be obtained by mixing an aqueous solution containing oxidized cellulose fibers and an aqueous solution containing cellulose nanofibers.

  Here, natural cellulose fibers include, for example, wood pulp, cotton-based pulp, bacterial cellulose and the like. More specifically, examples of the wood pulp include coniferous pulp, hardwood pulp, and the like. Examples of the cotton pulp include cotton linter and cotton lint. Non-wood pulp includes Mention may be made of straw pulp, bagasse pulp and the like. At least one of these natural cellulose fibers can be used.

  Natural cellulose fibers have a structure composed of cellulose microfibril bundles and lignin and hemicellulose filling them. That is, it is presumed that the cellulose microfibril and / or the cellulose microfibril bundle has a structure in which hemicellulose covers and further this is covered with lignin. Cellulose microfibrils and / or cellulose microfibril bundles are firmly bonded by lignin to form plant fibers. Therefore, it is preferable that lignin in the plant fiber is removed in advance from the viewpoint that aggregation of the cellulose fiber in the plant fiber can be prevented. Specifically, the lignin content in the plant fiber-containing material is usually about 40% by mass or less, preferably about 10% by mass or less. Further, the lower limit of the lignin removal rate is not particularly limited, and it is preferably as close to 0% by mass. The lignin content can be measured by the Klason method.

  As the cellulose microfibril, a cellulose microfibril having a width of about 4 nm exists as a minimum unit, and this can be called a single cellulose nanofiber. In the present invention, the “cellulose nanofiber” is a material obtained by unraveling natural cellulose fibers and / or oxidized cellulose fibers to the nanosize level. In particular, the average value of the fiber diameters can be 1 nm to 200 nm, and further 1 nm. Can be ˜150 nm, in particular cellulose microfibrils and / or cellulose microfibril bundles of 1 nm to 100 nm. That is, the cellulose nanofiber can include a single cellulose nanofiber alone or a bundle of a plurality of single cellulose nanofibers.

  The aspect ratio (fiber length / fiber diameter) of the cellulose nanofiber can be an average value of 10 to 1000, more preferably 10 to 500, and particularly preferably 100 to 350.

  In addition, the average value of the fiber diameter and fiber length of a cellulose nanofiber is an arithmetic average value measured about at least 50 or more of the cellulose nanofiber within the visual field of an electron microscope.

  First, an oxidation process adds water with respect to the natural cellulose fiber used as a raw material, processes with a mixer etc., and prepares the slurry which disperse | distributed the natural cellulose fiber in water.

  Next, natural cellulose fibers are oxidized in water using an N-oxyl compound as an oxidation catalyst to obtain oxidized cellulose fibers. Examples of N-oxyl compounds that can be used as an oxidation catalyst for cellulose include 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (hereinafter also referred to as TEMPO), 4-acetamide-TEMPO, 4-carboxy-TEMPO, 4-phosphonooxy-TEMPO, etc. can be used.

After the oxidation step, for example, a purification step of repeating washing with water and filtration can be carried out to remove impurities other than oxidized cellulose fibers contained in the slurry, such as unreacted oxidant and various by-products. The solvent containing the oxidized cellulose fiber is, for example, in a state of being impregnated with water. At this stage, the oxidized cellulose fiber is not defibrated up to the unit of cellulose nanofiber. As the solvent, water can be used. For example, in addition to water, organic solvents (alcohols, ethers, ketones, etc.) soluble in water can be used depending on the purpose.

  Oxidized cellulose fiber has a carboxyl group by modifying a part of the hydroxyl group of cellulose nanofiber with a substituent having a carboxyl group.

  The average value of the fiber diameter of the oxidized cellulose fiber can be 10 μm to 30 μm. In addition, the average value of the fiber diameter of an oxidized cellulose fiber is an arithmetic average value measured about at least 50 or more of the oxidized cellulose fiber in the visual field of an electron microscope.

  The oxidized cellulose fiber can be a bundle of cellulose microfibrils. Oxidized cellulose fibers do not need to be fibrillated to the unit of cellulose nanofibers in the mixing step and the drying step described later. Oxidized cellulose fibers can be fibrillated into cellulose nanofibers in the refinement process.

  In the micronization step, the oxidized cellulose fiber can be stirred in a solvent such as water, and cellulose nanofibers can be obtained.

  In the miniaturization step, the solvent as the dispersion medium can be water. Moreover, as a solvent other than water, water-soluble organic solvents such as alcohols, ethers, and ketones can be used alone or in combination.

  The agitation treatment in the miniaturization process includes, for example, a disaggregator, a beater, a low pressure homogenizer, a high pressure homogenizer, a grinder, a cutter mill, a ball mill, a jet mill, a short axis extruder, a twin screw extruder, an ultrasonic agitator, and a home juicer mixer. Etc. can be used.

  Moreover, solid content concentration of the solvent containing the oxidized cellulose fiber in the refining treatment can be, for example, 50% by mass or less. When this solid content concentration exceeds 50% by mass, high energy is required for dispersion.

  An aqueous solution containing cellulose nanofibers can be obtained by the refinement process. The aqueous solution containing cellulose nanofibers can be a colorless, transparent or translucent suspension. In the suspension, cellulose nanofibers, which are fibers oxidized and defibrated and refined, are dispersed in water. That is, in this aqueous solution, the cellulose nanofibers can be obtained by weakening the strong cohesive force between the microfibrils (hydrogen bonding between the surfaces) by introducing carboxyl groups in the oxidation process and further through the refinement process. And by adjusting the conditions of the oxidation step, the carboxyl group content, polarity, average fiber diameter, average fiber length, average aspect ratio, etc. can be controlled.

  The aqueous solution thus obtained can contain 0.1% by mass to 10% by mass of cellulose nanofibers. Moreover, for example, it can be an aqueous solution diluted to a solid content of 1% by mass of cellulose nanofibers. Furthermore, the aqueous solution can have a light transmittance of 40% or more, a light transmittance of 60% or more, and particularly 80% or more. The transmittance of the aqueous solution can be measured as the transmittance at a wavelength of 660 nm using an ultraviolet-visible spectrophotometer.

4-1-2. Rubber Latex As the rubber latex, styrene / butadiene rubber produced by emulsion polymerization can be used.

  The rubber latex has a large number of fine rubber particles dispersed in a dispersion solvent.

4-1-3. Carbon black Carbon black of various grades using various raw materials can be used. The carbon black can be 10 nm to 500 nm, and the average particle size can be 100 nm or more and 300 nm or less. The average particle diameter of carbon black can be obtained by observing by imaging with a scanning electron microscope and measuring 2000 or more particle diameters of basic constituent particles and arithmetically averaging them.

  As such carbon black, for example, reinforcing carbon black such as SAF, ISAF, HAF, SRF, T, GPF, FT, and MT can be used. By using carbon black having a relatively large particle size, the rubber composition is reinforced with oxidized cellulose fibers and cellulose nanofibers in which rubber components in the gaps formed between the carbon blacks are dispersed while maintaining the flexibility of the rubber composition. be able to. As the carbon black, MT grade carbon black can be used.

4-1-4. Rubber As the rubber, solid rubber other than the rubber latex described above, styrene / butadiene rubber (SBR), ethylene / propylene rubber (EPR, EPDM), and a mixture 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 low polarity rubber such as ethylene / propylene rubber (EPDM) generates free radicals by setting the kneading temperature to a relatively high temperature (for example, 50 to 150 ° C. in the case of EPDM). Cellulose nanofibers 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 reason why the solid rubber is blended in addition to the rubber latex is that the entire rubber component of the piston seal member is manufactured from the rubber latex because it has too much moisture and is not practical in terms of processing. The solid rubber component may be the same type as the rubber used in the rubber latex, or may be a rubber that is compatible with the rubber component of the rubber latex.

4-2. Each manufacturing process FIGS. 3-5 is a figure which shows typically the manufacturing method of the rubber composition which concerns on one Embodiment.

4-2-1. Mixing step In the mixing step, an aqueous solution containing at least one of oxidized cellulose fibers and cellulose nanofibers and rubber latex are mixed to obtain a first mixture. As the mixing step, for example, a roll kneading method using a roll kneading device, a stirring operation using a propeller type stirring device, a homogenizer, a rotary stirring device, and an electromagnetic stirring device, or a manual stirring operation can be used. In particular, a roll kneading method can be used for the mixing step.

  As the roll kneading apparatus used for the roll kneading method, for example, an open roll can be used. Moreover, the roll kneading apparatus used for the roll kneading method can use, for example, two rolls or three rolls.

The mixture of the aqueous solution and the rubber latex is gradually introduced into a roll kneading apparatus in which the distance between the rolls is set to a predetermined interval. The distance between the rolls can be set to such a distance that the mixture of the aqueous solution and the rubber latex is wound around the rolls, and the mixture does not fall between the rolls. The mixture charged in the roll kneader is gradually increased in viscosity by being kneaded. When the viscosity of the mixture becomes high, the mixture can be taken out from the roll kneading apparatus, and the distance between the rolls can be set to be further narrowed, and can be charged again into the roll kneading apparatus. This step can be performed multiple times.

  By performing the mixing step, it can be expected that at least one of the oxidized cellulose fiber and the cellulose nanofiber enters the rubber fine particles while passing between the rolls. In particular, by using the roll kneading method, the reinforcing effect by the fibers can be further improved as compared with other stirring operations.

  The 1st mixture obtained at a mixing process is 0.1 mass part-60 mass parts at least one of an oxidized cellulose fiber and a cellulose nanofiber with respect to 100 mass parts of rubber solid components by the mass ratio after a drying process. Can be included. When at least one of the oxidized cellulose fiber and the cellulose nanofiber is 0.1 part by mass or more, a reinforcing effect is obtained, and if it is 60 parts by mass or less, processing after the drying step is possible.

4-2-2. Drying step The drying step is a step of obtaining the second mixture by drying the first mixture obtained in the mixing step. For example, since the first mixture contains moisture, a general method for removing water can be adopted. For example, a known drying method such as natural drying, oven drying, freeze drying, spray drying, or pulse combustion can be employed for the drying process.

  The drying step can be performed at a temperature at which the rubber, oxidized cellulose fiber, and cellulose nanofiber are not thermally decomposed. For example, the drying step can be performed by heating at 100 ° C.

  The second mixture includes a rubber component and at least one of oxidized cellulose fiber and cellulose nanofiber. A 2nd mixture can contain 0.1-60 mass parts of at least one of an oxidized cellulose fiber and a cellulose nanofiber with respect to 100 mass parts of rubber | gum, for example. Furthermore, the second mixture can contain 1 part by mass to 50 parts by mass of at least one of the oxidized cellulose fiber and the cellulose nanofiber, and particularly can contain 5 parts by mass to 40 parts by mass. When at least one of oxidized cellulose fibers and cellulose nanofibers is contained in an amount of 0.1 parts by mass or more in the second mixture, a reinforcing effect of the rubber composition can be obtained, and at least one of oxidized cellulose fibers and cellulose nanofibers in the solvent. If it contains 60 mass parts or less, it can process easily.

4-2-3. Dispersing Step In the dispersing step, a rubber composition can be obtained by thinly passing the second mixture containing at least one of oxidized cellulose fibers and cellulose nanofibers with an open roll.

  First, before thinning, as shown in FIG. 3, the second mixture 130 wound around the first roll 110 can be masticated, and the molecular chains of the rubber in the second mixture are moderated. To produce free radicals. The free radicals of the rubber generated by mastication are likely to be combined with at least one of oxidized cellulose fibers and cellulose nanofibers.

Next, as shown in FIG. 4, a kneading step is performed in which the compounding agent 180 is appropriately charged into the bank 134 of the second mixture 130 wound around the first roll 110 and kneaded to obtain an intermediate mixture. it can. Here, the compounding agent 180 includes a reinforcing agent containing carbon black, solid rubber other than rubber latex, and further includes, for example, a crosslinking agent, a vulcanizing agent, a vulcanization accelerator, a vulcanization retarder, a softening agent, a plasticizer, Curing agents, reinforcing agents, fillers, anti-aging agents, colorants, acid acceptors and the like can be included. These compounding agents can be added to the rubber at an appropriate time during the mixing process.

  The step of obtaining the intermediate mixture 136 (FIG. 5) by the steps of FIGS. 3 and 4 is not limited to the open roll method, and for example, a closed kneading method or a multi-screw extrusion kneading method can also be used.

  The intermediate mixture 136 (FIG. 5) is obtained by combining oxidized cellulose fibers and cellulose with respect to 100 parts by mass of rubber in which the rubber solid component in the rubber latex in the mixing step and the rubber component in the compounding agent 80 added in the dispersing step are combined. At least one of the nanofibers may include 0.1 to 60 parts by mass. By adding rubber in the dispersion step, the load of the drying step can be reduced by using a small amount of rubber latex in the mixing step. Therefore, the rubber component added in the dispersing step is preferably more than the rubber solid component in the rubber latex, and can be, for example, 50 mass% to 99 mass% in the rubber component in the intermediate mixture 136.

  Furthermore, thinning can be performed as shown in FIG. The thinning step can be a step of obtaining an uncrosslinked rubber composition 150 by thinning at 0 ° C. to 50 ° C. using an open roll 100 having a roll interval of 0.5 mm or less. In this step, the roll interval d between the first roll 110 and the second roll 120 is set to, for example, 0.5 mm or less, more preferably 0 mm to 0.5 mm, and the intermediate mixture obtained in FIG. 136 can be put into the open roll 100 and thinning can be performed once to several times. For example, the thinning can be performed about 1 to 10 times. When the surface speed of the first roll 110 is V1, and the surface speed of the second roll 120 is V2, the ratio of the surface speeds (V1 / V2) in thinness is 1.05 to 3.00. And can be 1.05-1.2. By using such a surface velocity ratio, a desired shear force can be obtained.

  The rubber composition 150 extruded from between the narrow rolls as described above is greatly deformed as shown in FIG. 5 by the restoring force due to the elasticity of the rubber, and at that time, at least one of the oxidized cellulose fiber and the cellulose nanofiber moves greatly together with the rubber. To do. The rubber composition 150 obtained through thinning is rolled with a roll and dispensed into a sheet having a predetermined thickness, for example, 100 μm to 500 μm.

  In this thinning process, in order to obtain as high a shearing force as possible, the roll temperature can be set to, for example, 0 ° C. to 50 ° C., and further set to a relatively low temperature of 5 ° C. to 30 ° C. be able to. The measured temperature of the rubber composition can also be adjusted to 0 ° C. to 50 ° C., and further adjusted to 5 ° C. to 30 ° C.

  By adjusting to such a temperature range, it is possible to defibrate at least one of oxidized cellulose fiber and cellulose nanofiber using the elasticity of rubber, and disperse the defibrated cellulose nanofiber in the rubber composition. it can.

  Due to the high shearing force in this thinning process, a high shearing force acts on the rubber, and at least one of the aggregated oxidized cellulose fibers and cellulose nanofibers is separated from each other so as to be pulled out one by one into the rubber molecules. , Dispersed in rubber. In particular, since rubber has elasticity and viscosity, at least one of oxidized cellulose fiber and cellulose nanofiber can be defibrated and dispersed. And the rubber composition 150 excellent in the dispersibility and dispersion stability (at least one of an oxidized cellulose fiber and a cellulose nanofiber is hard to re-aggregate) of at least one of an oxidized cellulose fiber and a cellulose nanofiber can be obtained.

  More specifically, when rubber and at least one of oxidized cellulose fiber and cellulose nanofiber are mixed with an open roll, rubber having viscosity penetrates into at least one of oxidized cellulose fiber and cellulose nanofiber. When the surface of at least one of the oxidized cellulose fiber and the cellulose nanofiber is moderately high by, for example, oxidation treatment, it can be easily bonded to a rubber molecule. Next, when a strong shearing force was applied to the rubber, at least one of the oxidized cellulose fiber and the cellulose nanofiber moved with the movement of the rubber molecules, and further aggregated by the restoring force of the rubber due to elasticity after shearing. At least one of the oxidized cellulose fiber and the cellulose nanofiber is separated and dispersed in the 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.

4-2-4. Coagulation step A coagulation step of coagulating the rubber latex in the first mixture can be further included between the mixing step and the drying step.

  Since the first mixture obtained in the mixing step in 4-2-1 contains a large amount of moisture as it is, it takes a long time to remove moisture in the drying step in 4-2-2. . Therefore, in the coagulation step, a predetermined amount of a known coagulant that coagulates rubber latex is added to the first mixture that is an aqueous solution, and the mixture is stirred and mixed. The rubber component in the first mixture is solidified by the coagulant. The coagulation step can include dehydration and washing for the coagulum. Dehydration and washing can be repeated multiple times.

  The dehydration in this step only needs to remove water to the extent that the drying time in the drying step can be shortened, and separates the solidified rubber component and moisture to some extent. Dehydration can be performed using, for example, a general rotary dehydrator (centrifugation), a rubber film roll, a press machine, or the like. Moreover, the washing | cleaning in this process can be performed with water, for example.

  As the coagulant, a known latex coagulant can be appropriately employed depending on the type of rubber latex in the first mixture. As the coagulant, for example, a known acid or salt can be used, and the polymer flocculant may be used in place of or together with the salt. Examples of the acid used for the coagulant include formic acid, acetic acid, propionic acid, citric acid, oxalic acid, sulfuric acid, hydrochloric acid, and carbonic acid. As a salt used for the coagulant, for example, sodium chloride, aluminum sulfate, calcium nitrate and the like can be used. As the polymer flocculant, any of anionic, cationic and nonionic polymer flocculants can be used.

  Since a large amount of water can be removed from the first mixture in the coagulation process, the heating time of the drying process performed after the coagulation process can be shortened, and the working efficiency is improved.

4-2-5. Molding process of piston seal member The kneaded rubber composition is molded by a rubber molding process generally employed using a mold having a desired piston seal member shape. Examples of the molding process include press molding, extrusion molding, and injection molding. In the molding step, the rubber component of the rubber composition containing a crosslinking agent is crosslinked. As the cross-linking agent, for example, a known cross-linking agent applied to rubber appropriately selected according to the use can be used.

  When the piston seal member thus obtained is used for a disc brake, the environmental impact can be reduced by including at least one of oxidized cellulose fiber and cellulose nanofiber. Further, according to such a disc brake, the piston seal member is excellent in high temperature characteristics and durability, so that stable piston operability is maintained even at high temperatures, and liquid tightness between the piston and the cylinder is maintained for a long time. be able to.

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

(1) Preparation of sample (1-1) Examples 1-4
Obtaining an aqueous solution:
Cellulose nanofibers were obtained in the same manner as in the method disclosed in Production Example 1 of JP2013-18918A.

  Specifically, after sufficiently stirring bleached kraft pulp of softwood with ion-exchanged water, TEMPO 1.25% by mass, sodium bromide 12.5% by mass, sodium hypochlorite 28.4% with respect to 100 g of pulp mass. Mass% was added in this order at 20 ° C. Sodium hydroxide was added dropwise to maintain the pH at 10.5, and an oxidation reaction was performed. After the oxidation reaction was performed for 120 minutes, dropping was stopped to obtain an aqueous solution containing 10% by mass of TEMPO-oxidized oxidized cellulose fiber. The oxidized cellulose fiber had a fiber diameter of 10 μm to 30 μm and a fiber length of 1 mm to 5 mm, which were the same as those of the original pulp.

Furthermore, the oxidized cellulose fiber was sufficiently washed with ion-exchanged water and then dehydrated. Thereafter, the oxidized cellulose fiber was adjusted to a solid content of 1% by mass with ion-exchanged water and refined using a high-pressure homogenizer to obtain an aqueous dispersion containing 1% by mass of cellulose nanofibers. The average fiber diameter of the cellulose nanofiber was 3.3 nm, and the average aspect ratio was 225.

Mixing process:
Styrene-butadiene rubber (hereinafter referred to as “SBR”) latex (JSR Co., Ltd. 0561: aqueous dispersion with a solid content of 69% by mass, 10.3 pH, viscosity 440 (mPa · s), surface tension 32 (mN / m), average particle size 700 (nm), Tg-63 ° C.) and mixed at a rotational speed of 10,000 rpm using a juicer mixer.

  After mixing by the mixer, the mixture was passed through a three roll (M-50) manufactured by EXAKT having a nip of 10 μm at a rotation speed of 200 rpm to perform additional mixing to obtain a first mixture.

Drying process:
The first mixture was heat-dried in an oven set at 50 ° C. for 4 days to obtain a second mixture. The blending ratio in the second mixture after drying was SBR solid content of 100 phr and cellulose nanofibers of 60 phr.

Dispersion process:
The second mixture was masticated at a roll interval of 1.5 mm, and SBR, EPDM and carbon black, which are solid rubbers, were added and kneaded to obtain a mixture having the composition shown in Table 1. Further, this mixture was put into an open roll having a roll gap of 0.3 mm, and thinned at 10 to 30 ° C. to obtain a rubber composition sample. At this time, the surface speed ratio of the two rolls was set to 1.1. Thinning was repeated 5 times. In addition, the compounding quantity in Table 1 and Table 2 is a mass part (phr).

Vulcanization process:
A sheet obtained by adding 8 parts by mass of peroxide as a cross-linking agent to a rubber composition sample obtained through thinning and compression-molding the sheet at 170 ° C. for 10 minutes, and forming a sheet-like cross-linked rubber composition sample having a thickness of 1 mm Got.

(1-2) Comparative Examples 1-3
In Comparative Examples 1 to 3, each raw material was put into an open roll having a roll gap of 1.5 mm and kneaded so as to have the composition shown in Table 2, and further 8 parts by mass of peroxide was added as a crosslinking agent. The sheet was compression molded at 170 ° C. for 10 minutes to obtain a sheet-like crosslinked rubber composition sample having a thickness of 1 mm.

In Tables 1 and 2,
“SBR” is a blending amount obtained by adding 1503 manufactured by JSR, 23.5% bound styrene, specific gravity 0.93, Mooney viscosity 52 (ML _{1 + 4} (100 ° C.)) in addition to the solid content of the SBR latex described above.
“EPDM” is EP24 manufactured by JSR, specific gravity 0.87, Mooney viscosity 42 (ML _{1 + 4} (100 ° C.)),
"MT carbon" is carbon black of MT grade (average particle diameter and DBP oil absorption are manufacturer's published values) with an average particle diameter of 200 nm and DBP oil absorption of 25 ml / 100 g.
“Cellulose” was an oxidized cellulose nanofiber having an average fiber diameter of 3.3 nm and an average aspect ratio of 225 obtained in the above step.

(2) Basic characteristic test The rubber hardness (Hs (JIS A)) of the rubber composition sample was measured based on the JIS K6253 test.

  About the rubber composition sample, a stress (σ50 (MPa)) at 50% deformation was punched into a JIS No. 6 dumbbell shape, and 23 ± 2 ° C. using a tensile tester manufactured by Shimadzu Corporation. A tensile test was performed based on JIS K6251 at a tensile speed of 500 mm / min.

(3) Dynamic viscoelasticity test About a rubber composition sample, it is a test piece of 40 mm x 1 mm x 2 mm (width) with a strip piece, and a distance between chucks of 20 mm is measured using a dynamic viscoelasticity tester DMS6100 manufactured by SII. A dynamic viscoelasticity test was performed based on JIS K6394 at a temperature of −100 to 300 ° C. (temperature increase pace 3 ° C./min), dynamic strain ± 0.05%, and frequency 1 Hz, and a temperature range of −50 ° C. to 150 ° C. The storage elastic modulus (E ′ (MPa)) was measured. Tables 3 and 4 show the storage elastic modulus at 30 ° C and 150 ° C.

(4) Fatigue life test About the rubber composition sample, as a fatigue life (indicated as "fatigue (2 N / mm)" in Tables 3 and 4), the test sample was 10 mm x 4 mm wide x 1 mm thick (the long side was Punched into a strip-shaped test piece in a row direction), a 1 mm depth incision was made with a razor blade in the width direction from the center of the long side of the test piece, and the test piece was tested using a TMA / SS6100 testing machine manufactured by SII. The short side of both ends is held by a chuck, and a fatigue test is performed by repeatedly applying a tensile load (1 N / mm to 2 N / mm) under the condition of a frequency of 1 Hz in an air atmosphere at 120 ° C., and the test piece breaks. The number of times was measured until.

(5) Measurement of linear expansion coefficient About the rubber composition sample, the average value (ppm (1 / K)) of the linear expansion coefficient (CTE) in a measurement temperature range was measured. These results are shown in Tables 2-4. The measuring device was TMASS manufactured by SII, the shape of the measurement sample was 1.5 mm × 1.0 mm × 10 mm, the side long load was 25 KPa, the measurement temperature was 20 ° C. to 150 ° C., and the temperature increase rate was 3 ° C./min.

(6) Measurement of rollback amount and lever stroke increase amount A piston seal member is made of a rubber composition sample, and this piston seal member is fitted into an annular piston seal groove of a disc brake to operate the rollback amount and the master cylinder. The increase in lever stroke of the control lever was measured and its characteristics were evaluated.

  The rollback amount is measured by applying a hydraulic pressure of 0.5 MPa to the disc brake 20 10 times at a piston seal member 140 ° C., and then holding it at a hydraulic pressure of 6.9 MPa for 5 seconds. The amount of piston movement when the hydraulic pressure was released was measured.

  In addition, the amount of increase in lever stroke was measured by measuring the stroke of a brake lever for a motorcycle until the brakes began to work when the piston seal member was at 30 ° C and 140 ° C. The results of each evaluation test are shown in Tables 3 and 4.

(7) High temperature and high pressure operation durability test The piston seal member produced in the above (6) is attached to an endurance test disc brake, repeatedly operated at a fluid pressure of 13 MPa and a fluid temperature of 200 ° C., and the number of times the piston seal member broke. Asked. These results are shown in Tables 3 and 4. In addition, when it was able to endure 100,000 times of repeated operation and there was no liquid leakage or other abnormality, “◯” was entered in Tables 3 and 4.

  From the results of Tables 3 and 4, the rubber compositions of Examples 1 to 4 were reinforced with cellulose nanofibers, and the stress at 50% deformation, the storage elastic modulus, and the fatigue life were compared with the samples of Comparative Examples 1 to 3. Showed a high value. In particular, the rubber compositions of Examples 1 to 4 had a lower average value of linear expansion coefficient than the samples of Comparative Examples 1 to 3. Since the volume expansion of the piston seal member at high temperature was small, the rollback amount was 0.04 mm or more, and the lever stroke increase amount was as low as 7 mm or less.

  Moreover, from the results of Tables 3 and 4, it was found that the piston seal members of Examples 1 to 4 were excellent in high temperature and high pressure operation durability as compared with the piston seal members of Comparative Examples 1 to 3.

  The present invention is not limited to the above-described embodiments, and various modifications can be made. For example, the present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same objects and effects). In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that exhibits the same operational effects as the configuration described in the embodiment or a configuration that can achieve the same object. In addition, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

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 chamber, 10 ... Supply port, 20 ... Disc brake, 28 ... Hydraulic path, 100 ... Open roll, 110 ... First , 120 ... second roll, 130 ... second mixture, 134 ... bank, 136 ... intermediate mixture, 150 ... rubber composition, 180 ... compounding agent, V1, V2 ... rotational speed, d ... roll interval

Claims (5)

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,
The piston seal member is composed of a rubber composition containing 0.1 to 60 parts by mass of at least one of oxidized cellulose fiber and cellulose nanofiber with respect to 100 parts by mass of rubber.
The rubber includes at least one of ethylene / propylene rubber and styrene / butadiene rubber,
The oxidized cellulose fiber has an average fiber diameter of 10 μm to 30 μm,
The cellulose nanofiber is a piston seal member having an average fiber diameter of 1 nm to 200 nm. In claim 1,
The rubber composition is a piston seal member in which an average value of a linear expansion coefficient at 20 ° C. to 150 ° C. is 50 ppm (1 / K) to 180 ppm (1 / K). In claim 1 or 2,
The rubber composition is a piston seal member whose storage elastic modulus at 30 ° C. and 150 ° C. in a dynamic viscoelasticity test at a frequency of 1 Hz in accordance with JIS K6394 is 15 MPa or more. In any one of Claims 1-3,
The piston seal member is a piston seal member used for a caliper body of a disc brake. The piston seal member according to any one of claims 1 to 4,
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, and the piston inserted into the cylinder hole is brought into close contact with the liquid-tight movable state and is advanced by hydraulic pressure. A disc brake that rolls back the piston.

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