JP5221623B2 - Rubber composition for bladder and bladder - Google Patents

Description

The present invention relates to a rubber composition for bladder and a bladder using the same.

In the tire manufacturing process, a vulcanized rubber structure having rubber elasticity is manufactured by subjecting a green tire produced by molding each member to a vulcanizing process. In the vulcanization process, generally, a mold is attached to a jacket-type hot platen and heated from the outer surface of the tire, and a bladder in the form of a bag is inserted into the tire and steam or the like is injected to heat from the inner surface. Is done.

In heating from the inner surface of the tire, the bladder is subject to oxidative degradation and polymer degradation due to oxygen in water vapor and harmful acidic substances such as hydrogen sulfide and nitric acid generated during tire vulcanization. Moreover, since the bladder is exposed to the air in a high temperature state every time the tire is separated from the tire, the deterioration of the outside of the bladder also proceeds by this.

On the other hand, zinc oxide, which functions as an adsorbent for such harmful acidic substances and plays the role of improving the life of the bladder, is usually blended. In order to improve the service life, it is important to improve the dispersibility of zinc oxide. However, in a normal kneading method using Banbury or the like, sufficient dispersibility cannot be obtained, and the function as an adsorbent is sufficient. It could not be said that it was demonstrated. In addition, the agglomerated zinc oxide became fracture nuclei and caused cracks.

Patent Document 1 discloses a rubber composition for a bladder that prevents aggregation of zinc oxide and extends the life of the bladder by blending a large amount of sulfur. However, there is still room for improvement in extending the life of bladders. Patent Document 2 discloses a tread rubber composition containing fine particle zinc oxide, but the fine particle zinc oxide is not sufficiently dispersed, and there is still room for improvement in terms of extending the life of the bladder. is there. Moreover, application to a rubber composition for bladders has not been studied.

JP-A-2005-75891 JP 2008-101127 A

An object of the present invention is to solve the above-mentioned problems, and to provide a rubber composition for a bladder that can sufficiently achieve a long life of the bladder, and a bladder manufactured using the rubber composition.

As a result of various attempts to extend the life of the bladder, the present inventors have obtained a master batch obtained by mixing zinc oxide and ethylene propylene diene copolymer and / or butyl rubber (A). It has been found that the use can reduce the cohesive strength of zinc oxide, improve the dispersibility of zinc oxide, and sufficiently achieve a long life of the bladder.
That is, the present invention relates to a rubber component and a rubber composition for a bladder including a master batch obtained by mixing zinc oxide with an ethylene propylene diene copolymer and / or a butyl rubber (A).

In the master batch, the total content of the ethylene propylene diene copolymer and the butyl rubber (A) is preferably 10 to 180 parts by mass with respect to 100 parts by mass of the zinc oxide.

The master batch is preferably obtained by further mixing an ethylene vinyl acetate copolymer.

It is preferable that the content of the zinc oxide derived from the master batch is 0.5 to 10 parts by mass with respect to 100 parts by mass of the rubber component.

In 100% by mass of the rubber component, the content of butyl rubber (B) is preferably 90 to 100% by mass, and the content of chloroprene rubber is preferably 0 to 10% by mass.

The master batch is preferably obtained by further mixing a crosslinked resin.

The present invention also relates to a bladder produced using the rubber composition.

According to this invention, since it is a rubber composition for bladders containing a specific masterbatch, the lifetime improvement of a bladder can fully be achieved. As a result, it is possible to reduce the number of times the bladder is replaced during tire manufacturing, and it is possible to increase tire manufacturing productivity.

The rubber composition for bladders of the present invention contains a rubber component and a master batch (MB) obtained by mixing zinc oxide with an ethylene propylene diene copolymer and / or a butyl rubber (A).

〔Master Badge〕
First, the master batch will be described below.
The master batch is obtained by mixing zinc oxide with an ethylene propylene diene copolymer and / or a butyl rubber (A).

Examples of zinc oxide include zinc oxide conventionally used in the rubber industry (such as zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd.), and fine zinc oxide having an average primary particle size of 200 nm or less (zinccock manufactured by Hux Itec Corp.). Super F-1 etc.). Among these, fine particle zinc oxide is preferable because the life of the bladder can be sufficiently improved.

The average primary particle diameter of the fine particle zinc oxide is preferably 200 nm or less, more preferably 130 nm or less. The average primary particle diameter of zinc oxide is preferably 20 nm or more, more preferably 30 nm or more. Within the above range, the life of the bladder can be sufficiently improved.
In addition, in this invention, an average primary particle diameter represents the average particle diameter (average primary particle diameter) converted from the specific surface area measured by BET method by nitrogen adsorption.

An ethylene propylene diene copolymer (EPDM) is a copolymer in which a relatively small amount of a third component is introduced into an ethylene-propylene rubber, which is a copolymer of ethylene and propylene, and a double bond is provided in the polymer molecule. is there. EPDM is inferior to butyl rubber from the viewpoint of gas permeability and resistance to steam, but it has very few double bonds like butyl rubber, and is excellent in aging, ozone, and chemical durability.

Examples of the third component include ethylidene norbornene (ENB), 1,4-hexadiene, dicyclopentadiene and the like.

As commercially available products of EPDM, for example, Esprene EPDM series manufactured by Sumitomo Chemical Co., Ltd., EP96 manufactured by JSR Co., Ltd. and the like can be suitably used.

Examples of the butyl rubber (A) include halogenated butyl rubber (X-IIR) such as brominated butyl rubber (Br-IIR) and chlorinated butyl rubber (Cl-IIR), butyl rubber (IIR) (hereinafter referred to as halogenated butyl rubber and For example, non-halogenated butyl rubber). These butyl rubbers (A) may be used alone or in combination of two or more. Of these, non-halogenated butyl rubber is preferable from the viewpoint of high heat resistance.

The content of isoprene in the non-halogenated butyl rubber is preferably 3 mol% or less, and more preferably 2 mol% or less. When it exceeds 3 mol%, the heat resistance of the bladder is lowered, and it may be difficult to obtain the effect of improving the bladder life. The content of isoprene in the non-halogenated butyl rubber is preferably 0.5 mol% or more, more preferably 0.7 mol% or more, and still more preferably 1 mol% or more. If it is less than 0.5 mol%, the rubber strength cannot be improved by crosslinking, and the bladder life may be reduced.

The butyl rubber (A) usually has only a double bond site of 0.5% or less, and the number of crosslinks is extremely small even when crosslinks are performed. The butyl rubber (A) can usually be produced by mixing and reacting isobutylene and isoprene monomers.

The master batch is preferably obtained by further mixing ethylene vinyl acetate copolymer (EVA). By using the EVA, the dispersibility of zinc oxide can be improved, and a sufficient bladder life can be obtained. In addition, granulation (solidification) of the master batch and automatic weighing are possible, and sufficient handling properties can be obtained. By using EVA in combination with EPDM in the master batch, a particularly excellent life improvement effect can be obtained.

The master batch is preferably obtained by further mixing a crosslinked resin. Thereby, the dispersibility of zinc oxide can be improved, the appropriate kneading torque is generated by the zinc oxide in the masterbatch, and the dispersibility of the crosslinked resin itself can be improved. Therefore, a sufficient bladder life can be obtained.

Examples of the crosslinked resin include alkylphenol formaldehyde resins. Although there is no restriction | limiting in particular about the kind of alkylphenol formaldehyde resin, From the point which is excellent in heat resistance, the non-halogenated thing which is not halogenated is preferable. The content of methylol groups in the alkylphenol formaldehyde resin is usually 7 to 10% by mass.

The method for preparing the masterbatch is not particularly limited as long as the above components can be mixed (kneaded), for example, EPDM and butyl rubber (A), if necessary, a step of masticating EVA, and A method of preparing a master batch by performing the obtained kneaded product and zinc oxide, and if necessary, a step of kneading a crosslinked resin is mentioned.

As the kneading method and the kneading method, conventionally known methods can be used without any particular limitation. For example, a closed kneader such as a Banbury mixer, a kneader, an open roll, or the like can be preferably used.

In the preparation of the master batch, the mastication conditions are usually 80 to 200 ° C. and 3 to 10 minutes. The kneading conditions are usually 120 to 200 ° C. and 3 to 10 minutes. Thereby, the effect of this invention is acquired favorably.

(Composition of master batch)
The total content of EPDM and butyl rubber (A) is preferably 10 parts by mass or more, more preferably 20 parts by mass or more with respect to 100 parts by mass of zinc oxide in the masterbatch. If the content is less than 10 parts by mass, kneading torque is hardly generated, zinc oxide is not well dispersed, and the amount of binder (EPDM and butyl rubber (A)) used in a predetermined masterbatch is too small. May cause a drop. Moreover, this content becomes like this. Preferably it is 180 mass parts or less, More preferably, it is 100 mass parts or less, More preferably, it is 40 mass parts or less. If it exceeds 180 parts by mass, the dispersion of zinc oxide becomes insufficient, and the bladder life may be reduced.

In addition, when using EPDM and EVA together, these total content becomes like this. Preferably it is 10 mass parts or more with respect to 100 mass parts of zinc oxide in a masterbatch, More preferably, it is 20 mass parts or more. The content is preferably 180 parts by mass or less, more preferably 100 parts by mass or less, and still more preferably 50 parts by mass or less. When the total content is within the above range, the dispersibility of zinc oxide can be sufficiently improved, and the amount of the binder can be appropriately adjusted, and the effects of the present invention can be obtained satisfactorily.
When a large amount of binder is blended in the masterbatch, the performance is inferior to that of butyl rubber, and the carbon black normally blended in the rubber composition does not sufficiently enter the binder in the finish kneading, so there is a problem in terms of reinforcement. There is a risk of becoming.

When used in combination, the EVA content may be appropriately set in consideration of dispersibility and the like, but is preferably 3% by mass or more in the total amount of EPDM and EVA of 100% by mass. Moreover, EVA content becomes like this. Preferably it is 60 mass% or less, More preferably, it is 30 mass% or less. If the content is out of the above range, the effect of improving the dispersibility of zinc oxide by EVA may not be sufficiently obtained.

In the present specification, polymer components (EPDM, butyl rubber (A), EVA, crosslinked resin, etc.) in the master batch of the present invention are distinguished from rubber components (butyl rubber (B), chloroprene rubber, etc.). Concept.

In 100% by mass of zinc oxide contained in the rubber composition of the present invention, the proportion used in the master batch is preferably 80% by mass or more, more preferably 90% by mass or more, from the viewpoint of improving the dispersibility of zinc oxide. More preferably, it is 100 mass%.

Further, the content of zinc oxide in the rubber composition of the present invention is preferably 1 part by mass or more, more preferably 100 parts by mass of a rubber component (rubber component blended separately from the masterbatch) described later. 3 parts by mass or more. The content is preferably 20 parts by mass or less, more preferably 10 parts by mass or less. When the content is within the above range, the effect of the present invention can be obtained satisfactorily.

Non-diene rubbers such as butyl rubber, ethylene-propylene-diene rubber (EPDM), natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), Diene rubbers such as styrene butadiene rubber (SBR), epoxidized natural rubber (ENR), acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), and styrene-isoprene-butadiene copolymer rubber (SIBR) can be blended. Of these, the combined use of butyl rubber (B) and CR is preferable from the viewpoint of comprehensively ensuring the deterioration resistance (oxidative decomposition) resistance, crack resistance, chemical resistance and vulcanization speed of bladder rubber.

The butyl rubber (B) (butyl rubber blended separately from the masterbatch) is not particularly limited, and the same butyl rubber (A) as that described above can be suitably used.

The content of the butyl rubber (B) in 100% by mass of the rubber component is preferably 90% by mass or more, more preferably 92% by mass or more. If it is less than 90% by mass, the heat resistance, deterioration resistance, crack resistance and chemical resistance of the rubber composition are lowered, and the life of the bladder may not be improved. The content of butyl rubber may be 100% by mass, but is preferably 97% by mass or less, more preferably 95% by mass or less. If it exceeds 97 mass%, it may be difficult to maintain the hardness and tensile strength necessary for a bladder.

When blending CR, the content of CR in 100% by mass of the rubber component is preferably 1% by mass or more, more preferably 3% by mass or more. If it is less than 1% by mass, it may be difficult to maintain the rigidity required for the bladder. Moreover, this content becomes like this. Preferably it is 10 mass% or less, More preferably, it is 7 mass% or less. If it exceeds 10% by mass, the content of butyl rubber may be reduced, and sufficient heat resistance may not be obtained.
When the content is 3% by mass or less, the crosslinking with the crosslinking resin is loosened. Therefore, it is preferable to use a masterbatch containing the butyl rubber (A) and the crosslinking resin.

The rubber composition of the present invention usually further contains a crosslinked resin separately from the master batch. As a result, the effects of the present invention can be obtained well. The cross-linked resin is not particularly limited, and those similar to the cross-linked resin in the master batch can be suitably used.

The total content of the crosslinked resin and the other crosslinked resin contained in the master batch is preferably 2 parts by mass or more, more preferably 5 parts by mass or more with respect to 100 parts by mass of the rubber component. The content is preferably 20 parts by mass or less, more preferably 15 parts by mass or less. When the content is within the above range, the effect of the present invention can be obtained satisfactorily.

In addition, content of the crosslinked resin contained in the master batch in the total 100 mass% of the crosslinked resin and the other crosslinked resin contained in the master batch is preferably 10 to 100 mass%. When the content is within the above range, the effect of the present invention can be obtained well.

The rubber composition of the present invention usually contains carbon black. Examples of carbon black that can be used include GPF, FEF, HAF, ISAF, and SAF, but are not particularly limited. By blending carbon black, it is possible to enhance the reinforcement.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 40 m ² / g or more, more preferably 60 m ² / g or more. If it is less than 40 m ² / g, the reinforcing force is insufficient, and the bladder life may be easily lowered. Further, the N ₂ SA of the carbon black is preferably 120 m ² / g or less, more preferably 100 m ² / g or less. When it exceeds 120 m ² / g, it is difficult to disperse the filler, crack resistance (durability) may be lowered or locally hardened, and the bladder life may be lowered.
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by A method of JISK6217.

When carbon black is blended, the carbon black content is preferably 40 parts by mass or more, and more preferably 50 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 40 parts by mass, it may be difficult to obtain sufficient reinforcement. Further, the carbon black content is preferably 80 parts by mass or less, more preferably 70 parts by mass or less. When the amount exceeds 80 parts by mass, it is difficult to disperse the filler, the crack resistance (durability) may be lowered, or it may become locally hard, and the bladder life may be reduced.

In addition to the above components, the rubber composition for bladders of the present invention includes oil, anti-aging agent, mold release agent, stearic acid, inorganic filler (white carbon, silica, activated calcium carbonate, talc, alumina, etc.), organic Reinforcing agents (high impact styrene resin, coumarone indene resin, phenol resin, lignin, modified melamine resin, petroleum resin, etc.), heat resistance improver, flame retardant, thermal conductivity imparting agent and the like can be added.

The rubber composition of the present invention preferably contains oil. By blending oil, processability can be improved and the strength of the rubber can be increased. As the oil, for example, process oil, vegetable oil, or a mixture thereof can be used. Of these, vegetable oils and castor oil are preferably used because they are less likely to volatilize, bleed on the bladder surface and prevent adhesion to the tire cover.

When the rubber composition of the present invention contains oil, the content of oil is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 0.5 parts by mass, there is a risk that adhesion between the bladder and the tire cover is likely to occur after vulcanization. The oil content is preferably 10 parts by mass or less, more preferably 7 parts by mass or less. When it exceeds 10 mass parts, the ratio of butyl rubber will fall and a bladder life will fall.

As the anti-aging agent, for example, a phenol-based anti-aging agent (monophenol-based anti-aging agent, bisphenol-based anti-aging agent, polyphenol-based anti-aging agent) that increases heat resistance is preferably used.

It is preferable to mix a release agent with the rubber composition of the present invention. Thereby, when a crosslinked resin is used, it can suppress that the crosslinked resin adheres in a Banbury. As a mold release agent, a mixture of a fatty acid metal salt and a fatty acid amide can be suitably used. Here, the content of the release agent is preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the rubber component.

The rubber composition for bladders of the present invention can be prepared by mixing the rubber component, masterbatch, and other components (carbon black and the like), and can be produced, for example, by the following method.

First, the kneading process will be described. The kneading process of the present embodiment includes a base kneading process and a finishing kneading process. In the kneading step, for example, the components are kneaded using a kneader. A conventionally known kneader can be used, and examples thereof include a Banbury mixer, a kneader, and an open roll.

<Base kneading process>
In the base kneading step, for example, using a kneader, components other than the master batch, the cross-linked resin and the release agent (butyl rubber, carbon black, oil, chloroprene rubber, anti-aging agent, etc.) are kneaded. It is
The base kneading step has the following two steps (first base) because it ensures dispersibility of the carbon black used and suppresses thermal decomposition of other rubbers (eg, chloroprene rubber) that are inferior in heat resistance to butyl rubber. The kneading step and the second base kneading step are preferably performed separately.

<First base kneading step>
In the first base kneading step, for example, components such as butyl rubber, carbon black, and oil are kneaded using a kneader.
In the first base kneading step, it is preferable to knead a compounded rubber having a temperature at the start of kneading of 10 to 40 ° C. until it reaches 150 to 180 ° C. If it is lower than 150 ° C, it may be difficult to ensure the dispersibility of the carbon black. On the other hand, when the temperature exceeds 180 ° C., a gelation phenomenon due to carbon black occurs, and there is a possibility that the unit of the kneaded rubber sheet is lowered.

<Second base kneading process>
In the second base kneading step, for example, using a kneader, components such as chloroprene rubber and an antioxidant are further added and kneaded to the compounded rubber obtained by kneading in the first base kneading step. In the second base kneading step, it is preferable to knead a compounded rubber having a temperature at the start of kneading of 10 to 40 ° C. until it reaches 120 to 140 ° C. When the temperature is lower than 120 ° C., it is difficult to ensure dispersibility of the chloroprene rubber, and the homogeneity of the bladder rubber may be reduced, resulting in a decrease in bladder life. On the other hand, when it exceeds 140 ° C., the thermal decomposition of the chloroprene rubber proceeds, and the bladder life tends to decrease.

<Finish kneading process>
In the final kneading step, for example, the above master batch, and if necessary, components such as a cross-linking resin and a release agent are further added to the compounded rubber obtained by kneading in the second base kneading step using a kneader. And kneaded. In the present invention, since the master batch is used, even when fine zinc oxide, which is difficult to finely disperse, is used, the fine zinc oxide can be sufficiently dispersed without performing the finishing kneading step a plurality of times. For this reason, it is possible to produce an efficient rubber composition for a long-life bladder.

In the finishing kneading step, it is preferable to knead the compounded rubber having a normal temperature at the start of kneading until 90 to 105 ° C. If the temperature is lower than 90 ° C, the uniform diffusibility of zinc oxide may be insufficient. On the other hand, if the temperature exceeds 105 ° C, the crosslinking reaction may start.
Moreover, in the said finish kneading process, it is preferable that the rotation speed of a kneading machine shall be 20-45 rpm from the point of the dispersibility of zinc oxide and prevention of a crosslinking reaction.

<Crosslinking reaction process>
After performing the above kneading process, the rubber composition for bladders of the present invention is obtained by performing a crosslinking reaction process. The crosslinking reaction step can be performed, for example, by performing a crosslinking reaction at 170 to 210 ° C. for 30 to 240 minutes with the rubber composition (uncrosslinked rubber composition) obtained by the finishing kneading step.

The rubber composition of the present invention can be suitably used as a bladder for tire production.
The bladder can be manufactured by performing a crosslinking reaction after extruding with an extruder using the uncrosslinked rubber composition and forming the bladder into a bladder shape.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Various chemicals used below will be described together.
Butyl rubber 268: BUTYL268 manufactured by ExxonMobil Chemical Co., Ltd. (content of isoprene 1.7 mol%) (non-halogenated butyl rubber)
Butyl rubber 065: BUTYL065 manufactured by ExxonMobil Chemical Co., Ltd. (content of isoprene 1.05 mol%) (non-halogenated butyl rubber)
Chloroprene rubber: Neoprene W manufactured by Showa Denko K.K.
Carbon Black: Show Black N330 (N ₂ SA: 75 m ² / g) manufactured by Cabot Japan
Castor oil: Industrial No. 1 castor oil aging inhibitor manufactured by Toyokuni Oil Co., Ltd .: Nocrack NS-5 (2,2′-methylenebis (4-ethyl-6-tert-butylphenol) manufactured by Ouchi Shinsei Chemical Co., Ltd. ))
Mold release agent: WB16 (mixture of fatty acid metal salt (fatty acid calcium) and fatty acid amide) manufactured by Stractol Co., Ltd.
Cross-linked resin: Tacroll 201 (alkylphenol formaldehyde resin) manufactured by Taoka Chemical Co., Ltd.
Zinc oxide (1): Two types of zinc oxide (average primary particle size: 270 nm) manufactured by Mitsui Mining & Smelting Co., Ltd.
Zinc oxide (2): Ultrafine zinc oxide F-1 (average primary particle size: 100 nm) manufactured by Hakusui Tech Co., Ltd.
EPDM: Esprene EPDM301A manufactured by Sumitomo Chemical Co., Ltd.
EVA: Evaate EVA manufactured by Sumitomo Chemical Co., Ltd.
In addition, EPDM / EVA (compounding ratio) in MB1-2 was 1/1 (mass ratio).

(Production example)
(Preparation of MB)
In accordance with the formulation shown in Table 2, using a Banbury mixer, each material of EPDM, EVA and IIR was added and kneaded, heated to about 100 ° C., then zinc oxide, and optionally a crosslinked resin Was added in small portions and kneaded to a discharge temperature of about 130 ° C. to obtain a master batch.

(Comparative example)
According to the formulation shown in Table 1, using a 240 L Banbury mixer, first, non-halogenated butyl rubber (butyl rubber 065 and butyl rubber 268), carbon black, and castor oil were mixed at 160 ° C. until kneading (kneading). Kneading was performed at a starting temperature of 30 ° C. After cooling, chloroprene rubber and an anti-aging agent were added and kneaded from 30 ° C to 130 ° C. Further, after cooling, zinc oxide and a crosslinked resin were added and kneaded until the temperature reached 30 ° C. to 100 ° C. (first finish kneading step). Next, the kneaded product was once cooled to 30 ° C. (cooling step), then charged again into a Banbury mixer and kneaded to 100 ° C. (second finishing kneading step (remill)) to obtain an uncrosslinked rubber composition.

(Examples and reference examples )
According to the formulation shown in Table 2, instead of adding zinc oxide in the first finishing kneading step, the masterbatch obtained in the above production example, a release agent, and a crosslinked resin are added, and the cooling step and the second finishing kneading step ( An uncrosslinked rubber composition was obtained under the same conditions as in the comparative example except that no remilling was performed.

The obtained uncrosslinked rubber composition was molded into a bladder shape and subjected to a crosslinking reaction at 200 ° C. for 30 minutes, whereby a bladder (tire size: 195 / 65R15, bladder stretch (periphery: 1.08, Circum: 1. 25), bladder gauge: 5 mm).

The obtained bladder is used for tire molding (180 ° C., tire vulcanization conditions for 12 minutes), and the number of times of use is 600 to 1000 times. As a result of observing the presence / absence of occurrence, when the lamination grew in the state of the bladder rubber and the length was 5 mm or more, the number of times of use was defined as the number of times of bladder life.

The Example which used the said masterbatch was able to improve the lifetime of a bladder compared with the comparative example.

Claims (8)

A rubber composition for a bladder comprising a rubber component and a master batch obtained by mixing zinc oxide and an ethylene propylene diene copolymer. The master batch according to claim 1 Symbol placement bladder rubber composition obtained by further mixing the ethylene-vinyl acetate copolymer. The rubber composition for bladders according to claim 1 or 2 , wherein the content of zinc oxide derived from the master batch is 0.5 to 10 parts by mass with respect to 100 parts by mass of the rubber component. The rubber composition for a bladder according to any one of claims 1 to 3 , wherein the master batch is obtained by further mixing a crosslinked resin. The rubber composition for bladders according to any one of claims 1 to 4 , comprising 40 to 80 parts by mass of carbon black with respect to 100 parts by mass of the rubber component. The rubber composition for a bladder according to claim 5, wherein the carbon black has a nitrogen adsorption specific surface area of 40 to 120 m ² / g. The rubber composition for bladders according to any one of claims 1 to 6 , comprising 0.1 to 10 parts by mass of a release agent with respect to 100 parts by mass of the rubber component. Bladders produced using the rubber composition according to any one of claims 1-7.