Flame-retardant vibration-proof rubber molding and its manufacturing method

Abstract

To provide a flame-retardant vibration-proof rubber molding superior in flame retardancy, cold resistance and durability, and its manufacturing method.SOLUTION: A flame-retardant vibration-proof rubber molding 10 includes: an elastic portion 7; and a coating layer 8 for covering the elastic portion 7. The elastic portion 7 includes natural rubber as its main component. The coating layer 8 is composed of a rubber composition including isoprene rubber having flame retardancy higher than that of the elastic portion 7, as a main component. The rubber composition includes: a rubber component including 50 mass% or more of isoprene rubber having cis-1, 4 connection amount of 95% or more; and magnesium hydroxide and / or aluminum hydroxide of 120 pts.mass or more with respect to 100 pts.mass of the rubber component.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a flame-retardant vibration-proof molded rubber body and a method for producing the same. [Background technology]

[0002] For example, in a railway vehicle, anti-vibration rubber is interposed between a bogie frame that runs on rails and an axle side member. Also, to assist the displacement of an air spring provided between the bogie frame and a car body, anti-vibration rubber is interposed as a stopper between the air spring and the bogie frame. The anti-vibration rubber is configured to include an elastic portion. This anti-vibration rubber absorbs and reduces shocks caused by the snake motion and vertical movement of the railway vehicle.

[0003] In recent years, there has been a demand to improve the flame retardancy of anti-vibration rubber in consideration of the risk of fire. One method of improving flame retardancy is to compound the rubber material in the elastic part with a flame retardant compound. For example, natural rubber (NR) can be compounded with an organic flame retardant such as a bromine-based flame retardant or a flame retardant such as a metal oxide. However, organic flame retardants are difficult to adopt due to the environmental burden, and flame retardants such as metal oxides have the problem of reducing mechanical properties such as tensile strength and durability.

[0004] The vibration-proof rubber in Patent Document 1 is made flame-retardant by providing a fireproof layer mainly made of chloroprene rubber (CR) on the surface of the elastic part made of a conventional rubber material mainly made of NR. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US Patent Application Publication No. 2017 / 0267260 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the vibration-proof rubber of Patent Document 1 is imparted with flame retardancy by the fireproof layer, but its cold resistance and durability are impaired. That is, in Patent Document 1, a CR-based rubber having a glass transition temperature (Tg) of -20°C to -30°C is used as the main component of the fireproof layer, and an NR-based rubber having a Tg of -45°C to -50°C is used as the main component of the elastic part, so that when used in a low-temperature environment, there is a problem that the fireproof layer and the elastic part have different hardness, and the fireproof layer and the elastic part are easily peeled off. In addition, in Patent Document 1, in order to bond the elastic part mainly made of NR and the fireproof layer mainly made of CR, it is necessary to add triallyl isocyanurate (TAIC) or dicumyl peroxide (DCP) to the CR-based rubber, which is the main component of the fireproof layer, and there are restrictions on the compounding.

[0007] SUMMARY OF THE PRESENT EMBODIMENTS Accordingly, an object of the present invention is to provide a flame-retardant vibration-proof molded rubber product that is excellent in flame retardancy, cold resistance and durability, and a method for producing the same. [Means for solving the problem]

[0008] The flame-retardant vibration-proof rubber molded body of the present invention comprises an elastic part and a coating layer covering at least a portion of the elastic part, the elastic part containing natural rubber as a main component, and the coating layer being composed of a rubber composition containing isoprene rubber as a main component, the isoprene rubber having higher flame retardancy than the elastic part.

[0009] In the method for producing a flame-retardant vibration-proof rubber molded body according to the present invention, the coating layer is formed on the outer peripheral surface of the elastic portion by molding with a mold using the elastic portion as a core. Effect of the Invention

[0010] In the present invention, an elastic part mainly made of natural rubber (NR) is covered with a coating layer mainly made of isoprene rubber (IR) which has higher flame retardancy than NR. Since the main component of the elastic part and the main component of the coating layer are made of the same type of rubber component, the elastic part and the coating layer are closely bonded, and the difference in hardness between the elastic part and the coating layer is unlikely to occur in a low temperature environment. Therefore, according to the present invention, it is possible to provide a flame-retardant vibration-proof rubber molding having excellent flame retardancy, cold resistance, and durability, and a manufacturing method thereof. [Brief description of the drawings]

[0011] [Figure 1] 1 is a vertical cross-sectional view showing a flame-retardant vibration-proof molded rubber body according to a first embodiment. [Diagram 2] 1 is a graph showing the relationship between temperature and hardness of natural rubber and chloroprene rubber. [Diagram 3] FIG. 6 is a vertical cross-sectional view showing a flame-retardant vibration-proof molded rubber body according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the embodiment will be described in detail with reference to the drawings. In the following description, the direction in which the axis P extends (the vertical direction on the paper in FIG. 1) is defined as the up-down direction (vertical direction).

[0013] (First embodiment) FIG. 1 is a vertical cross-sectional view showing a flame-retardant vibration-proof molded rubber 10 according to the first embodiment. 1, the flame-retardant vibration-proof rubber molded body 10 according to the first embodiment is interposed, for example, between a bogie frame and an axle side member of a railway vehicle (not shown), or between the bogie frame and an air spring 100. The air spring 100 includes, for example, an upper plate 1 attached to the car body, a lower plate 2 disposed below the upper plate 1, and a cylindrical flexible member 3 (diaphragm) interposed between the upper plate 1 and the lower plate 2. The flame-retardant vibration-proof rubber molded body 10 is interposed, for example, between the lower plate 2 of the air spring 100 and a support frame 4 of a wheel.

[0014] The flame-retardant anti-vibration rubber molded body 10 (also called a half-hourglass stopper) is shaped like an upside-down thick bowl (like the upper half of a sphere, a half-hourglass shape) as shown in Fig. 1. The flame-retardant anti-vibration rubber molded body 10 has a curved side surface that bulges out laterally. The flame-retardant anti-vibration rubber molded body 10 is generally disposed so that its center is located on the axis P that passes through the center of the air spring 100 on the cross section shown in Fig. 1.

[0015] The flame-retardant vibration-proof rubber molded body 10 has a top plate 5 and a bottom plate 6 attached to the top and bottom, respectively.

[0016] Here, the flame-retardant vibration-proof rubber molded body 10 includes an elastic portion 7 and a covering layer 8 that covers the elastic portion 7. The elastic portion 7 and the covering layer 8 are integrated together by vulcanization adhesion.

[0017] The elastic portion 7 contains natural rubber as a main component. The elastic portion 7 is formed of, for example, a rubber compound used in known anti-vibration rubber. The elastic portion 7 is made of a homogeneous material and is in a block shape.

[0018] The covering layer 8 is vulcanization bonded to the side surface of the elastic portion 7 and integrated therewith. The covering layer 8 covers at least a portion of the elastic portion 7. The covering layer 8 covers the side surface of the elastic portion 7. This allows the flame-retardant vibration-proof rubber molded body 10 to have flame retardancy. The covering layer 8 preferably covers at least the portion of the side surface of the elastic portion 7 that is farthest from the axis P. This allows the flame-retardant vibration-proof rubber molded body 10 to have flame retardancy effectively. The covering layer 8 preferably covers the entire surface of the side surface of the elastic portion 7. This allows the flame-retardant vibration-proof rubber molded body 10 to have flame retardancy more effectively.

[0019] The coating layer 8 preferably has a thickness of, for example, 2.0 mm or more, which satisfies the requirement for high flame retardancy, such as when the flame-retardant vibration-proof rubber molded body 10 is used in a railway vehicle.

[0020] The coating layer 8 is mainly composed of isoprene rubber (IR) and has higher flame retardancy than the elastic part 7. The coating layer 8 meets the European standard EN45545-2, which specifies the requirements for the combustion behavior of materials and parts used in railway vehicles, and specifically, shows excellent flame retardancy in a heat generation test conforming to ISO5660-1. That is, the coating layer 8 shows excellent flame retardancy in a heat generation test conforming to ISO5660-1, compared to the elastic part 7. The coating layer 8 is preferably composed of a rubber composition containing a rubber component containing 50 mass% or more of isoprene rubber having a cis-1,4 bond amount of 95% or more and 120 mass parts or more of magnesium hydroxide and / or aluminum hydroxide per 100 mass parts of the rubber component. The compounding of the rubber composition constituting the coating layer 8 can be the compounding described in JP2020-070306A.

[0021] (Manufacturing method) An example of a method for producing the flame-retardant vibration-proof molded rubber body 10 will be described below. First, unvulcanized NR rubber is supplied into an elastic part mold used for molding the elastic part 7, and is heated and vulcanized to mold the elastic part 7.

[0022] Separately, an IR-based rubber composition is prepared according to the compounding recipe described in JP 2020-070306 A. Then, the molded elastic part 7 is used as a core and placed in a coating layer mold that is an outer mold used to mold the coating layer 8. After the coating layer mold reaches a predetermined temperature, the unvulcanized rubber, which is the prepared IR-based rubber composition that will become the coating layer 8, is poured between the elastic part 7 and the coating layer mold to fill it, and heated and vulcanized. Here, at the interface between the filled unvulcanized rubber and the already molded elastic part 7, the vulcanization reaction between the same type of rubber components is promoted. Since the vulcanizing agent is consumed when molding the elastic part 7, the concentration of the vulcanizing agent in the elastic part 7 is lower than the concentration of the vulcanizing agent in the unvulcanized rubber. Since there is a large gradient in the concentration of the vulcanizing agent between the unvulcanized rubber and the elastic part 7, by performing vulcanization molding, the vulcanizing agent flows from the unvulcanized rubber with a high concentration to the elastic part 7 with a low concentration, and fuses and adheres firmly. As described above, the manufacturing method for the flame-retardant vibration-proof rubber molded body is to form the coating layer 8 on the outer peripheral surface of the elastic part 7 by die molding using the elastic part 7 as a core. This makes it possible to manufacture a highly durable flame-retardant vibration-proof rubber molded body 10 in which the elastic part 7 and the coating layer 8 are tightly bonded together.

[0023] (Action and Effects) The flame-retardant vibration-proof rubber molded body 10 has excellent flame retardancy because the elastic part 7, which is mainly made of NR, is covered with the coating layer 8, which is mainly made of IR, which has higher flame retardancy than NR. In addition, because the main component of the elastic part 7 and the main component of the coating layer 8 are made of the same type of rubber component, the interface between the elastic part 7 and the coating layer 8 is more easily compatible in the vulcanization process, and the elastic part 7 and the coating layer 8 are closely bonded, resulting in excellent durability. Furthermore, the glass transition temperature (Tg) of NR, which is the main component of the elastic part 7, and IR, which is the main component of the coating layer 8, is -45°C to -50°C, and there is little difference in hardness between the elastic part 7 and the coating layer 8, resulting in excellent cold resistance.

[0024] FIG. 2 is a graph showing the relationship between temperature and hardness of natural rubber (NR) and chloroprene rubber (CR). Although not shown in FIG. 2, isoprene rubber (IR) has a similar graph to that of NR. Hardness is measured with a type A durometer conforming to Japanese Industrial Standard JIS K6253. As shown in FIG. 2, compared with CR, which has a Tg of -20°C to -30°C lower than that of NR (IR), NR (IR) shows a smaller increase in hardness and maintains flexibility up to a lower temperature. For example, when a coating layer is formed using CR as a main component as described in Patent Document 1, the flexibility of the coating layer is impaired as the temperature decreases, and a difference in hardness occurs between the elastic portion and the coating layer. When a difference in hardness occurs between the elastic portion and the coating layer, the load applied to the interface between the elastic portion and the coating layer increases, and the coating layer becomes more likely to peel off from the elastic portion. In contrast, in the flame-retardant vibration-proof rubber molded body 10, the main component of the elastic portion 7 and the main component of the coating layer 8 are composed of the same type of rubber component, and even when the temperature at which it is used drops, the elastic portion 7 and the coating layer 8 have the same flexibility, so that the load on the interface between the elastic portion 7 and the coating layer 8 can be reduced.

[0025] Because the flame-retardant anti-vibration rubber molded body 10 is provided with flame retardancy by the coating layer 8, it is not necessary to add a flame retardant to the elastic part 7, and it is possible to suppress deterioration of the mechanical properties of the elastic part 7. However, if a flame-retardant anti-vibration rubber molded body is manufactured by adding a large amount of flame retardant to the elastic part 7 to the extent that sufficient flame retardancy is achieved, the mechanical properties of tensile strength and durability will decrease.

[0026] The coating layer 8 may not contain a co-crosslinking agent or an organic peroxide crosslinking agent. Examples of the co-crosslinking agent include triallyl isocyanurate (TAIC), ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethallyl isocyanurate. Examples of the organic peroxide crosslinking agent include dicumyl peroxide (DCP), α,α'-(t-butylperoxy)diisopropylbenzene (Peroximon F-40 manufactured by Nippon Oil & Fats Co., Ltd.), and the like. For example, when the coating layer is composed mainly of CR-based rubber, the interface between the NR-based elastic portion and the CR-based coating layer is not compatible, and the CR-based coating layer is easily peeled off from the NR-based elastic portion. For this reason, it is necessary to use the above-mentioned co-crosslinking agent or organic peroxide crosslinking agent to improve the adhesion between the coating layer and the elastic portion (see Patent Document 1). In contrast, in the flame-retardant anti-vibration rubber molded body 10, the elastic portion 7 and the coating layer 8 are closely bonded, so that the coating layer 8 can be formulated without containing a co-crosslinking agent or an organic peroxide crosslinking agent. Furthermore, since the elastic portion 7 does not contain any organic flame retardant such as a bromine-based flame retardant, the burden on the environment can be reduced.

[0027] The flame-retardant anti-vibration rubber molded body 10 is an example of a rubber member having an elastic part containing natural rubber as a main component, and a coating layer provided on the outer surface of the elastic part and made of a rubber composition containing isoprene rubber as a main component, which has higher flame retardancy than the elastic part. The elastic part and coating layer of this rubber member have the same characteristics as the elastic part 7 and coating layer 8 of the flame-retardant anti-vibration rubber molded body 10. Therefore, the rubber member has the same action and effect as the flame-retardant anti-vibration rubber molded body 10, that is, excellent flame retardancy, cold resistance, and durability. The rubber composition constituting the coating layer of the rubber member preferably contains a rubber component containing 50 mass % or more of isoprene rubber having a cis-1,4 bond content of 95% or more, and 120 mass parts or more of magnesium hydroxide and / or aluminum hydroxide per 100 mass parts of the rubber component. The rubber member is suitable for vehicles (particularly railway vehicles).

[0028] The ratio of the elongation of the elastic part 7 to the elongation of the covering layer 8 (hereinafter, sometimes referred to as the elongation ratio) is preferably 0.8 or more and 1.2 or less. That is, when the elongation of the elastic part 7 is X and the elongation of the covering layer 8 is Y, 0.8≦X / Y≦1.2 is satisfied. The ratio of the elongation X of the elastic part 7 to the elongation Y of the covering layer 8 is X / Y. Here, the elongation may be the yield point elongation or the elongation at break defined in JIS K 6251:2017. That is, the ratio of the elongation at the yield point of the elastic part 7 to the elongation at the yield point of the covering layer 8 is preferably 0.8 or more and 1.2 or less. The ratio of the elongation at break of the elastic part 7 to the elongation at break of the covering layer 8 is preferably 0.8 or more and 1.2 or less. The ratio of the yield point elongation of the elastic part 7 to the yield point elongation of the coating layer 8 is 0.8 or more and 1.2 or less, and it is more preferable that the ratio of the elongation at break of the elastic part 7 to the elongation at break of the coating layer 8 is 0.8 or more and 1.2 or less. In this way, the elastic part 7 and the coating layer 8 are integrally molded so that the ratio of the elongation of the elastic part 7 to the elongation of the coating layer 8 is approximately 1.0, that is, the elongation of the elastic part 7 and the elongation of the coating layer 8 are almost the same. This makes it possible to reduce the difference in elongation (difference in strain) that occurs at the boundary between the elastic part 7 and the coating layer 8 when the flame-retardant vibration-proof molded rubber 10 is deformed. This makes it possible to make the coating layer 8 less likely to peel off from the elastic part 7.

[0029] It is more preferable that the ratio of the elongation of the elastic portion 7 to the elongation of the covering layer 8 (elongation at yield point or elongation at break) is 0.9 or more and 1.1 or less. This makes it possible to further reduce the difference in elongation (difference in strain) that occurs at the boundary between the elastic portion 7 and the covering layer 8 when the flame-retardant vibration-proof molded rubber 10 is deformed. This makes it possible to make the covering layer 8 less likely to peel off from the elastic portion 7.

[0030] The elongation of the elastic portion 7 (yield point elongation or break elongation) is preferably 390% to 590%, more preferably 470% to 540%. The elongation of the covering layer 8 is preferably 390% to 590%, more preferably 470% to 540%.

[0031] (Example) The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0032] (Preparation of Rubber Composition) Table 1 shows the compounding recipes of rubber compositions A, B, C, D, and E, as well as their mechanical properties including elongation at break and tensile strength. Each component was compounded with 100 parts by mass of the rubber component according to the compounding recipes in Table 1, and kneaded using a normal Banbury mixer to prepare five types of rubber compositions A, B, C, D, and E. Each component listed in Table 1 is shown below. The unit of compounding amount of each component listed in Table 1 is the relative "parts by mass," and "-" in the table indicates that the component was not compounded.

[0033] Rubber component (natural rubber): Rubber component mainly composed of RSS#3 Rubber component (isoprene rubber): Rubber component containing 50% or more by mass of product name "JSR IR2200" (98% or more isoprene rubber with 95% or more cis-1,4 bond content) (manufactured by JSR Corporation) Carbon black A: Product name "Seast V", manufactured by Tokai Carbon Co., Ltd. Carbon black B: Product name "Seast 3", manufactured by Tokai Carbon Co., Ltd. Zinc oxide: Product name "Zinc Oxide No. 3", Mitsui Mining & Smelting Co., Ltd. Anti-aging agent: Product name "Antigen 6C", manufactured by Sumitomo Chemical Co., Ltd. Magnesium hydroxide: Product name "Kisuma 5A", manufactured by Kyowa Chemical Industry Co., Ltd. Aluminum hydroxide: Product name "Hijilite H-32", manufactured by Showa Denko K.K. Sulfur: Oil-treated 150 mesh powdered sulfur, manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator: Trade name "Suncerer 22-C", manufactured by Sanshin Chemical Industry Co., Ltd.

[0034] [Table 1]

[0035] (Rubber manufacturing) Using five kinds of rubber compositions A, B, C, D and E, vulcanized rubber (test pieces) of Examples 1 to 4 and Comparative Examples 1 to 3 were prepared. In Example 1, first, rubber composition B was poured into a mold, heated and vulcanized at 150°C for 20 minutes, and an elastic part was molded. After the elastic part was molded, rubber composition A was poured into the mold with the elastic part in it, heated and vulcanized at 150°C for 20 minutes, and a vulcanized rubber was prepared. Example 1 is a vulcanized rubber in which a coating layer made of rubber composition A having flame retardancy is provided on the surface of an elastic part made of rubber composition B having low hardness. The amount of rubber composition A poured into the mold was adjusted so that the thickness of the coating layer was 2 mm. The amount of rubber composition B poured into the mold was adjusted so that the thickness of the soft layer was 23 mm. Therefore, the thickness of the vulcanized rubber of Example 1 is 25 mm. In Example 2, a vulcanized rubber was prepared in the same manner as in Example 1, except that a rubber composition C having a higher hardness than the rubber composition B was used instead of the rubber composition B. That is, Example 2 is a vulcanized rubber in which a coating layer made of a rubber composition A having flame retardancy is provided on the surface of an elastic part made of a rubber composition C having a high hardness. The amount of the rubber composition C poured into the mold was adjusted so that the thickness of the soft layer was 23 mm. Therefore, the thickness of the vulcanized rubber in Example 2 is 25 mm.

[0036] In Example 3, a vulcanized rubber was prepared in the same manner as in Example 1, except that a rubber composition D having a higher hardness than the rubber composition B was used instead of the rubber composition B. That is, in Example 3, a vulcanized rubber was prepared in which a coating layer made of a rubber composition A having flame retardancy was provided on the surface of an elastic part made of a rubber composition D having a higher hardness than the rubber composition B. The amount of the rubber composition D poured into the mold was adjusted so that the thickness of the soft layer was 23 mm. Therefore, the thickness of the vulcanized rubber in Example 3 was 25 mm. In Example 4, a vulcanized rubber was prepared in the same manner as in Example 1, except that a rubber composition E containing carbon black B instead of carbon black A blended in rubber composition B was used instead of rubber composition B. That is, in Example 4, a vulcanized rubber was prepared in which a coating layer made of a rubber composition A having flame retardancy was provided on the surface of an elastic part made of a rubber composition E containing carbon black B. The amount of the rubber composition E poured into the mold was adjusted so that the thickness of the soft layer was 23 mm. Therefore, the thickness of the vulcanized rubber in Example 4 was 25 mm.

[0037] In Comparative Example 1, rubber composition B was poured into a mold, and heated and vulcanized at 150°C for 20 minutes to produce a vulcanized rubber. Comparative Example 1 is a vulcanized rubber made only of rubber composition B. The amount of rubber composition B poured into the mold was adjusted so that the thickness of the vulcanized rubber was 25 mm. Comparative Example 2 is a vulcanized rubber made only of rubber composition C. Comparative Example 3 is a vulcanized rubber made only of rubber composition A. The thickness of each vulcanized rubber in Comparative Examples 1 to 3 is 25 mm.

[0038] Performance evaluation was carried out on Examples 1 to 4 and Comparative Examples 1 to 3, which are vulcanized rubbers (test pieces) made by combining the rubber compositions shown in Table 1. Table 2 shows the combinations of the rubber compositions constituting the vulcanized rubbers (test pieces) of Examples 1 to 4 and Comparative Examples 1 to 3, the elongation ratios (X / Y), the durability evaluation of the coating layer in the products, and the MARHE values.

[0039] [Table 2]

[0040] <Durability> As shown in Table 2, the durability of the products (Examples 1 to 3) in which rubber composition A was used for the coating layer and rubber composition B, C, or D was used for the elastic portion was all good (indicated by the symbol "◯" in Table 2). The durability of the product (Example 4) in which rubber composition A was used for the coating layer and rubber composition E was used for the elastic portion was satisfactory (indicated by the symbol "△" in Table 2), but since the ratio (X / Y) of the elongation of the elastic portion to the elongation of the coating layer was small, it is considered to be at the limit where peeling and the like occurs.

[0041] <Combustion performance> EN45545-2 specifies that the evaluation of the flame retardancy of the main rubber components used in railway vehicles is to be performed by a heat release test using the cone calorimeter method in accordance with ISO 5660-1, and the MARHE value measured by this method is required to be a specified value or less. Specifically, for hazard levels (HL) 1 and 2, the MARHE value is required to be 90 or less, and for HL3, the MARHE value is required to be 60 or less. Therefore, for the vulcanized rubber obtained in the examples and comparative examples, samples of 100 mm x 100 mm x 25 mm were prepared in accordance with ISO 5660-1. The test time was 20 minutes, the measurement interval was 2 seconds, and the radiation amount was 25 kW / m 2 The heat release rate of the above sample was measured under the above measurement conditions, and the measurement results were substituted into the following formula (1) to calculate the ARHE (average rate of heat emission), and the maximum value was taken as the MARHE (maximum average rate of heat emission). The integrated value was calculated every 2 seconds, and the maximum value of the ARHE was taken as the MARHE. Combustion performance was evaluated based on the MARHE value. The results are shown in Table 2.

[0042]

number

[0043] As shown in Table 2, the MARHE values ​​of Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were 62, 52, 241, 188, and 30, respectively. The MARHE values ​​of Example 3 and Example 4 were all less than 90.

[0044] From Table 2, comparing Examples 1 and 2 with Comparative Examples 1 and 2, it was confirmed that Examples 1 and 2, in which a flame-retardant coating layer was provided on the surface of the elastic part, had a lower MARHE value than Comparative Examples 1 and 2, which consisted only of an elastic part without a coating layer. All of Examples 1, 2, 3, and 4 have MARHE values ​​of less than 90, and have excellent flame retardancy that meets the requirements of HL1 and 2. Comparing Example 1 and Example 2, it was confirmed that Example 2, in which the elastic part is rubber composition C, has a lower MARHE value than Example 1, in which the elastic part is rubber composition B, and meets the requirements of HL3. It can be seen that by using rubber composition C, which has a higher hardness than rubber composition B, as the material for the elastic part, better flame retardancy is expressed. It should be noted that Comparative Example 3, which is made of rubber composition A having flame retardancy, is excellent in terms of flame retardancy, but has a reduced tensile strength or durability, which are mechanical properties.

[0045] Second embodiment Next, a flame-retardant anti-vibration rubber molded body 20 according to a second embodiment will be described. In the following, description of matters common to the flame-retardant anti-vibration rubber molded body 20 and the flame-retardant anti-vibration rubber molded body 10 according to the first embodiment may be omitted. Fig. 3 is a cross-sectional view showing the flame-retardant anti-vibration rubber molded body 20 according to the second embodiment. As shown in Fig. 3, the flame-retardant anti-vibration rubber molded body 20 according to the second embodiment is interposed, for example, between a bogie frame and an axle side member of a railway vehicle (not shown), between the bogie frame and an air spring 100, etc., similar to the flame-retardant anti-vibration rubber molded body 10 according to the first embodiment.

[0046] The flame-retardant vibration-proof molded rubber body 20 includes an elastic portion 27 and a covering layer 28 that covers the elastic portion 27.

[0047] Unlike the elastic part 7 of the first embodiment, the elastic part 27 has soft layers 271 and hard layers 272 that are alternately stacked. The elastic part 27 may include a plurality (for example, four) of soft layers 271 and a plurality (for example, three) of hard layers 272. The elastic part 27 has a layered structure in which the soft layers 271 and the hard layers 272 are alternately stacked in a direction along the axis P, i.e., in the vertical direction.

[0048] The soft layer 271 contains natural rubber (NR) as a main component. For example, a rubber compound used as a known anti-vibration rubber can be used as the rubber material of the soft layer 271. The soft layer 271 is annular with a predetermined thickness. The multiple soft layers 271 may have the same shape.

[0049] The hard layer 272 has a higher hardness than the soft layer 271. The hard layer 272 may have a higher elastic modulus or rigidity than the soft layer 271. The hard layer 272 may be made of metal. The hard layer 272 may contain natural rubber (NR) as a main component. The hard layer 272 is annular in shape and has a predetermined thickness. The multiple hard layers 272 may have the same shape.

[0050] The soft layer 271 and the covering layer 28 of the elastic portion 27 are integrated by vulcanization bonding. The covering layer 28 is integrated by vulcanization bonding to the side surface of the soft layer 271 of the elastic portion 27. The covering layer 28 covers at least a part of the elastic portion 27. The covering layer 28 covers the side surface of the elastic portion 27. The covering layer 28 covers at least the side surface of the soft layer 271. It is preferable that the covering layer 28 covers the entire side surface of the elastic portion 27. It is preferable that the covering layer 28 covers at least the part of the side surface of the soft layer 271 of the elastic portion 27 that is farthest from the axis P. This makes it possible to effectively impart flame retardancy to the flame-retardant vibration-proof rubber molded body 20.

[0051] The flame-retardant anti-vibration rubber molded body 20 is an example of a rubber member having a soft layer 271 containing natural rubber as a main component and a covering layer 28 provided on the surface of the soft layer 271 and made of a rubber composition containing isoprene rubber as a main component, which has higher flame retardancy than the soft layer 271. The soft layer 271 and covering layer 28 of the rubber member have the same configuration as the soft layer 271 and covering layer 28 of the flame-retardant anti-vibration rubber molded body 20. Therefore, the rubber member has the same action and effect as the flame-retardant anti-vibration rubber molded body 20, that is, excellent flame retardancy, cold resistance, and durability. The rubber composition constituting the covering layer 28 of the rubber member preferably contains a rubber component containing 50 mass % or more of isoprene rubber having a cis-1,4 bond amount of 95% or more, and 120 mass parts or more of magnesium hydroxide and / or aluminum hydroxide per 100 mass parts of the rubber component. The rubber member is suitable for vehicles (particularly railway vehicles).

[0052] The manufacturing method for the flame-retardant vibration-proof rubber molded body 20 according to the second embodiment is similar to the manufacturing method for the flame-retardant vibration-proof rubber molded body 10 according to the first embodiment, in which the coating layer 28 is formed on the outer peripheral surface of the elastic part 27 by die molding using the elastic part 27 as a core. This makes it possible to manufacture a highly durable flame-retardant vibration-proof rubber molded body 20 in which the elastic part 27 and the coating layer 28 are closely bonded to each other.

[0053] Although the embodiment has been described above, the present invention is not limited to the above-described embodiment, and can be modified as appropriate within the scope of the spirit of the present invention.

[0054] The flame-retardant vibration-proof rubber molded body 10, 20 according to this embodiment includes an elastic portion 7, 27 and a covering layer 8, 28 that covers at least a part of the elastic portion 7, 27. The elastic portion 7, 27 contains natural rubber as a main component. The covering layer 8, 28 is made of a rubber composition containing isoprene rubber as a main component, which has higher flame retardancy than the elastic portion 7, 27. This makes it possible to provide a flame-retardant vibration-proof rubber molded body that is excellent in flame retardancy, cold resistance, and durability.

[0055] The manufacturing method of the flame-retardant anti-vibration rubber molded body 10, 20 according to the present invention forms the coating layer 8, 28 on the outer peripheral surface of the elastic part 7, 27 by die molding using the elastic part 7, 27 as a core. This makes it possible to provide a flame-retardant anti-vibration rubber molded body that is excellent in flame retardancy, cold resistance, and durability.

[0056] More specifically, the manufacturing method for the flame-retardant vibration-proof rubber molded body 10 according to the first embodiment includes: (i) an elastic part preparation step of preparing an elastic part 7 containing natural rubber as a main component; (ii) a rubber composition preparation step of preparing an adjusted IR-based rubber composition; and (iii) a coating layer formation step of placing the elastic part 7 as a core in a coating layer mold which serves as an outer mold used to mold the coating layer 8, and after the coating layer mold has reached a predetermined temperature, pouring and filling the space between the elastic part 7 and the coating layer mold with unvulcanized rubber which is the prepared IR-based rubber composition which will become the coating layer 8, and then heating and vulcanizing the rubber to form the coating layer 8 on the outer peripheral surface of the elastic part 7.

[0057] In the above-mentioned elastic part preparation step, an elastic part 7 is prepared in which the concentration of the vulcanizing agent in the elastic part 7 is appropriately lower than the concentration of the vulcanizing agent in the unvulcanized rubber. In the above-mentioned coating layer formation step, the vulcanization reaction between the same kind of rubber components is promoted at the interface between the filled unvulcanized rubber and the already molded elastic part 7, and by performing vulcanization molding, the vulcanizing agent flows from the unvulcanized rubber with a high concentration to the elastic part 7 with a low concentration, and they are fused and firmly bonded, and the coating layer 8 is formed on the outer peripheral surface of the elastic part 7 by mold molding using the elastic part 7 as a core.

[0058] The elastic part preparation process includes a molding process in which NR-based unvulcanized rubber is supplied into an elastic part mold used for molding the elastic part 7, and heated and vulcanized to mold the elastic part 7. In this molding process, the vulcanizing agent is consumed when molding the elastic part 7, and the concentration of the vulcanizing agent in the elastic part 7 is made lower than the concentration of the vulcanizing agent in the unvulcanized rubber.

[0059] The manufacturing method of the flame-retardant vibration-proof rubber molded body 20 according to the second embodiment includes an elastic part preparation step of preparing an elastic part 27 having at least a soft layer 271 containing natural rubber (NR) as a main component and having a laminated structure in which the soft layer 271 and the hard layer 272 are alternately laminated in the vertical direction. The other steps are the same as those in the first embodiment, and include the above-mentioned rubber composition preparation step and coating layer formation step. As a result, the manufacturing methods of the first and second embodiments can provide flame-retardant vibration-proof rubber molded bodies 10, 20 that are excellent in flame retardancy, cold resistance, and durability. [Explanation of symbols]

[0060] 100 Air spring 10,20 Flame-retardant anti-vibration rubber molding 1 Top plate 2 Bottom plate 3 Flexible member 4 Support frame 5 Top plate 6 Bottom plate 7 Elastic part 8 Covering layer P axis center

Claims

1. The elastic portion includes an elastic layer and a coating layer that covers at least a portion of the elastic portion. The elastic portion contains natural rubber as a main component, The coating layer is a flame-retardant vibration-proof rubber molded body composed of a rubber composition containing, as a main component, isoprene rubber having higher flame retardancy than the elastic portion.

2. The elastic portion is a homogeneous mass.

2. The flame-retardant vibration-proof molded rubber article according to claim 1.

3. The elastic portion has a laminated structure in which soft layers and hard layers are alternately laminated in the vertical direction.

2. The flame-retardant vibration-proof molded rubber article according to claim 1.

4. The rubber composition includes a rubber component containing 50% by mass or more of isoprene rubber having a cis-1,4 bond content of 95% or more, and 120 parts by mass or more of magnesium hydroxide and / or aluminum hydroxide per 100 parts by mass of the rubber component. The flame-retardant vibration-proof molded rubber article according to any one of claims 1 to 3.

5. At least one of a ratio of the yield point elongation of the elastic portion to the yield point elongation of the coating layer and a ratio of the elongation at break of the elastic portion to the elongation at break of the coating layer is 0.8 or more and 1.2 or less. The flame-retardant vibration-proof molded rubber article according to any one of claims 1 to 3.

6. The coating layer is formed on the outer peripheral surface of the elastic portion by molding using the elastic portion as a core. A method for producing the flame-retardant vibration-proof rubber molding according to any one of claims 1 to 3.

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