JP5870507B2 - Expandable rubber composition - Google Patents

Description

  The present invention relates to an expandable rubber composition, and more particularly to an expandable rubber composition that suppresses a decrease in tensile breaking strength while increasing an expansion ratio.

  In recent years, it has been proposed to use a foamable rubber composition as a constituent member of a pneumatic tire. For example, Patent Document 1 proposes that a tread portion of a studless tire is constituted by a rubber composition containing a chemical foaming agent.

  Such a foamable rubber composition is characterized in that by increasing the foaming ratio, the weight can be reduced, the material properties can be made flexible, and the functionality of a large number of bubbles can be added. However, when the expansion ratio is increased, there is a problem that the rubber strength such as the tensile strength at break of the foamable rubber composition is lowered. For this reason, development of a foamable rubber composition that suppresses a decrease in tensile breaking strength while increasing the expansion ratio is demanded.

JP 2006-274045 A

  An object of the present invention is to provide a foamable rubber composition that suppresses a decrease in tensile breaking strength while increasing the expansion ratio.

The foamable rubber composition of the present invention that achieves the above object comprises 0.1 to 20 parts by weight of a chemical foaming agent, 1 to 10 parts by weight of resorcin or resorcin resin, 100 parts by weight of diene rubber, It is characterized in that 1 to 15 parts by weight of a resorcin resin curing agent is blended and short fibers are not blended .

  According to the foamable rubber composition of the present invention, 0.1 to 20 parts by weight of chemical foaming agent, 1 to 10 parts by weight of resorcin or resorcin resin, and curing of resorcin and resorcin resin with respect to 100 parts by weight of diene rubber. Since 1 to 15 parts by weight of the agent is blended, before the chemical foaming and vulcanization proceed during heating, the curing reaction of resorcin and resorcin resin proceeds and a fine network structure is formed. For this reason, it can suppress that the gas produced | generated by the subsequent chemical foaming leaks to the exterior of the rubber molding during a heating process, and acts on foaming of a rubber molding efficiently. For this reason, even if it reduces the compounding quantity of a chemical foaming agent, the expansion ratio of a molded object can be made high. Also, by reducing the amount of chemical foaming agent, vulcanization that is competitive with chemical foaming is not hindered, and the crosslinking density of the vulcanized rubber is increased, and the resorcin and resorcin resin cured product When the rubber matrix becomes hard, the tensile breaking strength of the vulcanized foamed rubber molded product can be increased. Further, by increasing the crosslinking density, the loss tangent (tan δ) of the foamed rubber molded product can be reduced, and the heat generation can be reduced.

It is preferable to blend 20 to 100 parts by weight of at least one filler selected from carbon black, silica, calcium carbonate, clay, mica, diatomaceous earth, and talc with respect to 100 parts by weight of the diene rubber. The tensile strength at break can be further increased.

  The curing agent for the resorcin and resorcin resin is preferably polyvalent methoxymethylol melamine and / or hexamethylenetetramine.

  As said chemical foaming agent, a nitroso type foaming agent and / or an azo type foaming agent are preferable, and the foaming ratio of a foamable rubber composition can be made higher.

  It is preferable to add 0.1 to 20 parts by weight of urea with respect to 100 parts by weight of the diene rubber, and urea can act as a foaming auxiliary agent to increase the expansion ratio of the foamable rubber composition.

  The diene rubber preferably contains 20% by weight or more of natural rubber in 100% by weight of the diene rubber, so that the tensile breaking strength of the foamable rubber composition can be further increased.

  The foamed rubber laminate formed by laminating the foamed rubber layer molded from the foamable rubber composition described above and the reinforcing rubber layer coated with the fiber cord has the surface appearance of the foamed molded product while increasing the foaming ratio as the rubber laminate. It can be excellent.

A foamed rubber laminate comprising reinforcing rubber layer formed by molding a foamed rubber composition described above foamed rubber layer and composed of adjacent foam rubber layer, in a state in which the reinforcing rubber layer is coated with a fiber cord A certain foamed rubber laminate can improve the surface appearance of the foamed molded product while increasing the expansion ratio of the rubber laminate.

  The foam rubber laminate is preferably used for a pneumatic tire. A pneumatic tire using a foamed rubber laminate is excellent in tire durability, reduces the tire weight, and reduces heat generation, so that fuel efficiency can be improved.

  In the foamable rubber composition of the present invention, examples of the diene rubber include natural rubber (NR), isoprene rubber (IR), styrene butadiene rubber (SBR), butadiene rubber (BR), acrylonitrile butadiene rubber (NBR), and butyl rubber. (IIR), chlorinated butyl rubber (Cl-IIR), brominated butyl rubber (Br-IIR), chloroprene rubber (CR), ethylene propylene diene rubber (EPDM), styrene isoprene rubber, styrene isoprene butadiene rubber, isoprene butadiene rubber, etc. It can be exemplified and can be used alone or as any blend. Of these, natural rubber, styrene butadiene rubber, butadiene rubber, and butyl rubber are preferable. In particular, it is preferable to contain natural rubber, and the natural rubber is preferably contained in an amount of 20% by weight or more, more preferably 30 to 100% by weight in 100% by weight of the diene rubber. By setting the content of natural rubber in such a range, the tensile breaking strength of the foamable rubber composition can be further increased.

  The foamable rubber composition of the present invention contains resorcin or resorcin resin and these curing agents. By containing resorcin or resorcin resin and these curing agents, when the foamable rubber composition is heated, curing of resorcin or resorcin resin proceeds prior to chemical foaming and vulcanization, and a fine network composed of resorcin and resorcin resin. A structure is formed. Since the unvulcanized rubber comes to be supported by this fine network structure, when the temperature becomes higher and chemical foaming occurs thereafter, the generated foaming gas is composed of the rubber composition during the heating process. Leakage from the molded body to the outside can be suppressed. As a result, the foaming gas efficiently acts to foam the rubber molded body inside the rubber molded body, and the expansion ratio can be further increased. That is, even if the compounding amount of the chemical foaming agent is reduced, the expansion ratio can be increased.

  The foamable rubber composition of the present invention can preferably have a foaming ratio of 2 times or more, more preferably 2 to 4 times. Thus, a high expansion ratio of 2 times or more could not be realized unless a two-step heating process is performed. In the present invention, a rubber foam having a high expansion ratio and excellent tensile strength can be formed by heating an unvulcanized rubber molded body made of a foamable rubber composition in one step.

  In foaming and vulcanization molding of molded products made of foamable rubber compositions, chemical foaming and vulcanization are competitive reactions, and if one of the reactions is prioritized, the progress of the other reaction is inhibited. Is done. As described above, in the present invention, by containing resorcin or resorcin resin and these curing agents, it is possible to increase the expansion ratio while reducing the blending amount of the chemical foaming agent, so that the progress of vulcanization can be easily adjusted. And the crosslinking density of the vulcanized foamed rubber molding can be increased. The tensile strength at break can be increased by increasing the cross-linking density and by hardening the rubber matrix by the network structure made of resorcin or resorcin resin described above. Furthermore, since the crosslink density of the foamed rubber molded body is increased, the loss tangent (tan δ) can be reduced and the heat generation can be reduced.

  As resorcin and resorcin resin, what is usually used for an industrial rubber composition can be used. Resorcin resin is a compound obtained by reacting resorcin and formaldehyde. For example, Penacolite Resin B-18-S, B-19-S, B-20-S, B-20-S, B-21-S manufactured by INDSPEC Chemical Corporation. And SUMIKANOL 620 manufactured by Sumitomo Chemical Co., Ltd. can be exemplified.

  The amount of resorcin and resorcin resin is 1 to 10 parts by weight, preferably 2 to 8 parts by weight, based on 100 parts by weight of the diene rubber. When the blending amount of resorcin and resorcin resin is less than 1 part by weight, a fine network structure of resorcin and resorcin resin cannot be sufficiently formed at the initial stage of heating. When the compounding amount of resorcin and resorcin resin exceeds 10 parts by weight, the crosslinking density becomes too high and foaming is inhibited.

  As the curing agent for resorcin and resorcin resin, those usually used in industrial rubber compositions can be used. For example, polymethoxymethylol melamine such as hexamethoxymethylol melamine and pentamethoxymethylol melamine, hexamethylenetetramine, hexa Examples thereof include methoxymethyl melamine and hexaethoxymethyl melamine. As the curing agent, polyvalent methoxymethylol melamine and / or hexamethylenetetramine is preferably used. These curing agents can be used alone or in combination. Such resin curing agents are known, and for example, commercially available products such as Sumikanol 507A (manufactured by Sumitomo Chemical Co., Ltd.), Cyrez 964RPC (manufactured by Cytec Industries Inc.), Sunseller HT (manufactured by Sanshin Chemical Industry Co., Ltd.), and the like can be used. it can.

  The amount of the resorcin and the resorcin resin curing agent is 1 to 15 parts by weight, preferably 3 to 12 parts by weight, per 100 parts by weight of the diene rubber. When the blending amount of the curing agent is less than 1 part by weight, a fine network structure composed of resorcin, a resorcin resin and a curing agent cannot be sufficiently formed at the initial stage of heating. Moreover, it is preferable that the compounding quantity of a hardening | curing agent is 1-2 times with respect to the compounding quantity (weight part) of the resorcinol and resorcin resin mentioned above. If it is less than 1 time (equal amount), the cross-linking reaction with resorcin resin or rubber is not performed sufficiently, and the effect is small, and even if blended in excess of 2 times, the effect reaches its peak and the mechanical strength of rubber is reduced. End up.

  In this invention, the rubber composition which comprises a foamable rubber composition shall contain a chemical foaming agent. By including a chemical foaming agent, the rubber molded body can be foamed. The compounding amount of the chemical foaming agent is preferably 0.1 to 20 parts by weight, more preferably 1.0 to 15 parts by weight with respect to 100 parts by weight of the diene rubber. When the compounding amount of the chemical foaming agent is less than 0.1 parts by weight, foaming during vulcanization becomes insufficient, and the foaming ratio cannot be increased. Moreover, when the compounding quantity of a chemical foaming agent exceeds 20 weight part, although the cost will increase, the effect of the raise of a foaming rate will reach a peak, and the smoothness of a foam surface will be impaired.

  Examples of the chemical foaming agent include nitroso-based foaming agents, azo-based foaming agents, carboxylic diamide-based foaming agents, sulfonyl hydrazide-based foaming agents, and azide-based foaming agents. Of these, nitroso foaming agents and / or azo foaming agents are preferred. These chemical foaming agents can be used alone or in admixture of two or more.

  Examples of the nitroso-based blowing agent include N, N′-dinitrosopentamethylenetetramine (DPT), N, N′-dimethyl-N, N′-dinitrosotephthalamide and the like. Examples of the azo foaming agent include azobisisobutyronitrile (AZBN), azobiscyclohexylnitrile, azodiaminobenzene, barium azodicarboxylate and the like. Azodicarbonamide (ADCA) or the like as a carbondiamide-based blowing agent, and sulfonyl hydrazide-based blowing agents as sulfonyl hydrazide (BSH), p, p'-oxybis (benzenesulfonyl hydrazide) (OBSH), toluenesulfonyl hydrazide (TSH) ), Diphenylsulfone-3,3′-disulfonylhydrazide and the like, and examples of the azide-based blowing agent include calcium azide, 4,4′-diphenyldisulfonyl azide, p-toluenesulfonyl azide and the like.

  The decomposition temperature of the chemical foaming agent is preferably 130 ° C to 190 ° C, more preferably 150 ° C to 170 ° C. By controlling the decomposition temperature of the chemical foaming agent within such a range, control of chemical foaming and vulcanization becomes easy. In this specification, the decomposition temperature of the chemical blowing agent is a temperature determined by measuring the heat of decomposition and weight loss using thermal analysis selected from differential scanning calorimetry (DSC) and thermogravimetry (TGA). is there.

The foamable rubber composition may contain urea together with a chemical foaming agent. Urea acts as a foaming aid. By blending the urea-based foaming aid, the temperature at which the chemical foaming agent is thermally decomposed can be adjusted to be low. The blending amount of the urea foaming aid is preferably 0.1 to 20 parts by weight, more preferably 0.5 to 10 parts by weight, with respect to 100 parts by weight of the diene rubber. When the blending amount of the urea foaming auxiliary is less than 0.1 parts by weight, the thermal decomposition temperature of the chemical foaming agent cannot be adjusted sufficiently. Moreover, it is preferable that the compounding quantity of a urea type foaming adjuvant is 0.5 to 1.5 times with respect to the amount of chemical foaming agents mentioned above. When the amount is less than 0.5 times, the effect as an auxiliary agent cannot be obtained. When the amount is more than 1.5 times, the reaction does not react and becomes a foreign substance in the composition, resulting in a decrease in mechanical strength.

  In the present invention, by adding a filler, the tensile strength at break of the foamable rubber composition is further increased. The blending amount of the filler is preferably 20 to 100 parts by weight, more preferably 40 to 80 parts by weight with respect to 100 parts by weight of the diene rubber. If the blending amount of the filler is less than 20 parts by weight, the tensile breaking strength of the foamable rubber composition cannot be sufficiently increased. Moreover, when the compounding quantity of a filler exceeds 100 weight part, the workability of a foaming rubber composition will fall.

  Examples of the filler include carbon black, silica, calcium carbonate, clay, mica, diatomaceous earth, talc and the like. Of these, carbon black, silica, and calcium carbonate are preferable. Such fillers can be used alone or as any blend.

  The foamable rubber composition comprises a vulcanizing agent, a vulcanization accelerator, a vulcanization aid, a rubber reinforcing agent, a softening agent (plasticizer), an anti-aging agent, a processing aid, a foaming aid, a defoaming agent, and an activator. , Mold release agents, heat stabilizers, weathering stabilizers, antistatic agents, colorants, lubricants, thickeners, and other industrial rubber compositions and compounding agents commonly used in rubber foams can be added. . These compounding agents can be used in the usual compounding amounts as long as they do not contradict the object of the present invention, and can be added, kneaded or mixed by a usual preparation method.

  The foamable rubber composition of the present invention can be molded into a foamed rubber molded body by molding an unvulcanized rubber molded body and heating and foaming / vulcanizing it. The shape, size, and thickness of the unvulcanized molded product can be appropriately adjusted according to the shape, size, and thickness of the foamed rubber molded product after vulcanization molding. Moreover, the molding method generally used can be applied to the molding method of the unvulcanized molded body.

  In the present invention, a foamed rubber laminate can be formed by laminating a foamed rubber layer made of a foamed rubber molded product molded from a foamable rubber composition on a reinforcing rubber layer coated with a fiber cord. This foamed rubber laminate can further increase the tensile strength at break while being lightweight.

  In general, when a foamed unvulcanized rubber layer is laminated on a reinforcing rubber layer coated with fiber cords, and foaming and vulcanization molding is performed, the foaming gas moves to the reinforcing rubber layer in a pressurized mold and reinforces it. It becomes easy to collect around the fiber cord which comprises a rubber layer. For this reason, when the pressure is released to remove the foamed rubber molded body from the mold, the foamed gas that has locally accumulated around the fiber cord does not contribute to foaming of the rubber matrix and expands to form a part of the foamed rubber layer. There may be a molding defect in which the portion forms a small hemi-balloon-like (hemispherical shape with a diameter of 5 mm or more) air pocket.

  On the other hand, when the foamed rubber layer is formed of the foamable rubber composition of the present invention, it contains resorcin or resorcin resin and these curing agents, so that the foamed gas is difficult to move from the foamed rubber layer, and the adjacent reinforcing rubber It can suppress that the foaming gas compressed around the fiber cord of the layer accumulates. Thereby, after taking out from a metal mold | die, the shaping | molding defect by which a part of foaming rubber layer becomes a small semi-balloon shape can be prevented.

  Although it does not specifically limit as a fiber cord which comprises a reinforced rubber layer, For example, it is good to contain at least 1 sort (s) chosen from a polyester fiber, rayon fiber, and a polyamide fiber. By using such a fiber cord, the elongation of the reinforcing rubber layer can be limited to directions other than the fiber direction.

  A foamed rubber molded article made of the foamable rubber composition of the present invention and a foamed rubber laminate obtained by laminating this with a reinforcing rubber layer are useful as pneumatic tires or industrial buffer materials. The part used for the pneumatic tire is not particularly limited. For example, it is arranged as a sound absorbing material on the radially inner surface of the tire lumen, or a cap tread or a sidewall part constituting the tread part is constituted. It can be arranged as a side rubber. The pneumatic tire using the foamable rubber composition of the present invention can achieve light weight and low heat generation while ensuring mechanical strength and maintaining durability, so that fuel efficiency can be improved. it can. Moreover, the studless tire which formed the cap tread with the foaming rubber composition can obtain the outstanding snow and snow performance and drainage performance.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, the scope of the present invention is not limited to these Examples.

Preparation of foamable rubber composition and creation of unvulcanized molded body For seven types of rubber compositions (Examples 1 to 3 and Comparative Examples 1 to 4) having the composition shown in Table 1, sulfur and vulcanization accelerators, respectively. The blending components except the curing agent, the chemical foaming agent and the urea foaming auxiliary were weighed and kneaded for 5 minutes with a 1.7 L closed Banbury mixer, and the master batch was discharged at a temperature of 150 ° C. and cooled to room temperature. Thereafter, this master batch is subjected to a heating roll, and sulfur, a vulcanization accelerator, a curing agent, a chemical foaming agent and a urea foaming aid are added and mixed to prepare seven types of rubber compositions, and these rubber compositions. An unvulcanized rubber molded body made of

Vulcanization molding and evaluation of foamed rubber moldings Unvulcanized rubber moldings composed of the seven types of rubber compositions obtained (Examples 1 to 3 and Comparative Examples 1 to 4) were subjected to predetermined shapes (length 100 mm, width 100 mm). ). These were heated at a temperature of 180 for 15 minutes to be vulcanized. As a result, vulcanization and foaming of the unvulcanized rubber molding excluding Comparative Example 1 proceeded simultaneously, and a foamed rubber molding having a thickness of about 15 mm was molded. Moreover, the unvulcanized rubber molded article of Comparative Example 1 became a vulcanized rubber sheet that was vulcanized and not foamed.

  The specific gravity, average foaming ratio, tensile breaking strength, and exothermic property (tan δ) of the obtained foamed rubber molded body (Comparative Example 1 is an unfoamed vulcanized rubber sheet) were measured by the following methods, respectively. Are shown in Table 1.

Specific gravity and average foaming ratio The specific gravity of the unvulcanized rubber molding and the specific gravity of the foamed and vulcanized foamed rubber molding were measured at 23 ° C. in accordance with JIS K-6268, respectively. The ratio between the specific gravity of the unvulcanized rubber molded product and the specific gravity of the foamed rubber molded product was calculated and used as the average foaming ratio. The obtained results are shown in Table 1.

Tensile rupture strength The tensile rupture strength of the foamed rubber molded product was measured in accordance with JIS K-6251 by cutting out a JIS No. 3 dumbbell-shaped test piece at 23 ° C. and a tensile speed of 500 mm / min.

Exothermic (tan δ)
The tan δ of the foamed rubber molded product was measured at a strain of 10% ± 2%, a frequency of 20 Hz, and an ambient temperature of 30 ° C. using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho. The obtained results are shown in the “Exothermic” column of Table 1 as an index with the value of Comparative Example 1 being 100. The smaller the index, the lower the exothermic property and the better.

The types of raw materials used in Table 1 are shown below.
NR: natural rubber, PT. NURISA SIR20
BR: Butadiene rubber, Nippon Zeon BR1220
・ CB: Carbon black, Seast F made by Tokai Carbon
-Zinc oxide: 3 types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd.-Stearic acid: Bead stearic acid paulownia manufactured by Chiba Fatty Acid Company-Anti-aging agent: VULKANOX 4020 manufactured by Bayer
・ Oil: Idemitsu Kosan Diana Process NH-60
Resorcin resin: Penacolite Resin B-18-S manufactured by INDSPEC Chemical
・ Sulfur: 150mesh gold powder stamped by Tsurumi Chemical Co., Ltd.
・ Vulcanization accelerator: Noxeller CZ-G manufactured by Ouchi Shinsei Chemical Co., Ltd.
Curing agent: Partial condensate of pentamethoxymethylol melamine, Sumikanol 507A manufactured by BARA Chemical
・ Chemical foaming agent: Nitroso-based foaming agent, Cellular D manufactured by Eiwa Kasei Kogyo Co., Ltd., and the decomposition start temperature is adjusted to 130 ° C. in combination with the following urea-based foaming aids ・ Urea: Cell paste K4 manufactured by Eiwa Chemical Industries

  From the results in Table 1, the foamed rubber molded bodies of Examples 1 to 3 ensure a tensile breaking strength of 10 MPa or more while having a high foaming ratio of 2 times or more, and tensile rupture as compared with the unfoamed rubber molded bodies. It was confirmed that the strength was suppressed from decreasing. It was also confirmed that heat generation was reduced. On the other hand, the vulcanized rubber sheet of Comparative Example 1 has high tensile strength but high specific gravity because it is not foamed. Since the foamed rubber molded article of Comparative Example 2 did not contain resorcin and resorcin resin and its curing agent, the foaming gas does not contribute to leakage foaming from the rubber molded article during the heating process, so the foaming ratio can be increased. Can not. Further, it was confirmed that the exothermic property increased because the vulcanization of the foamed rubber was inhibited and the vulcanization density could not be sufficiently increased. The foamed rubber molded article of Comparative Example 3 was found to have a significantly reduced foaming ratio, although the amount of vulcanization accelerator was increased with respect to Comparative Example 2 to increase the vulcanization density and lower the exothermic property. In the foamed rubber molded body of Comparative Example 4, the vulcanization accelerator was reduced and the chemical foaming agent and urea were increased with respect to Comparative Example 2, so that the expansion ratio was higher, but the tensile breaking strength and exothermicity were both Inferiority was observed.

Molding and Evaluation of Foam Rubber Laminate A rubber composition having the composition shown in Table 2 was prepared as a base rubber composition constituting a reinforcing rubber layer coated with a fiber cord. First, the components except for sulfur and the vulcanization accelerator were weighed, kneaded for 5 minutes with a 1.7 L closed Banbury mixer, the master batch was discharged at a temperature of 150 ° C., and cooled at room temperature. Thereafter, this master batch was subjected to a heating roll, and sulfur and a vulcanization accelerator were added and mixed to prepare a base rubber composition.

The types of raw materials used in Table 2 are shown below.
NR: natural rubber, PT. NURISA SIR20
SBR: styrene-butadiene rubber, Nipol 1502 manufactured by Nippon Zeon
・ CB: Carbon black, Seast F made by Tokai Carbon
-Zinc oxide: 3 types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd.-Stearic acid: Bead stearic acid paulownia manufactured by Chiba Fatty Acid Company-Anti-aging agent: VULKANOX 4020 manufactured by Bayer
・ Oil: Idemitsu Kosan Diana Process NH-60
・ Sulfur: 150mesh gold powder stamped by Tsurumi Chemical Co., Ltd.
・ Vulcanization accelerator: Noxeller CZ-G manufactured by Ouchi Shinsei Chemical Co., Ltd.

  Using this base rubber composition, a fiber cord (a polyester fiber cord manufactured by Toyobo Co., Ltd., 1670/2 (total fineness of 1670 dtex, 2 twists)) is rubberized so as to have a driving density of 50/5 cm. A vulcanized rubber reinforcement layer was formed.

  This unvulcanized rubber reinforcing layer was cut into a predetermined shape (length 100 mm, width 100 mm), and the unvulcanized rubber sheet obtained in Comparative Example 1 and the foams obtained in Comparative Examples 2 and 4 and Example 2 were used. An unvulcanized rubber molded body made of a conductive rubber composition was laminated, and an unvulcanized rubber laminated body (Comparative Example 5) and a foamed rubber laminated body (Comparative Examples 6, 7 and Example 4) were molded. These were vulcanized at 180 ° C. for 10 minutes to form rubber laminates and foamed rubber laminate vulcanizates.

  The expansion ratio and appearance of the obtained rubber laminate and foamed rubber laminate were evaluated by the following methods.

Average foaming ratio of the laminate The specific gravity of the unvulcanized rubber laminate and the specific gravity of the foamed / vulcanized foamed rubber laminate were measured at 23 ° C. in accordance with JIS K-6268, respectively. The ratio of the specific gravity of the unvulcanized rubber laminate and the specific gravity of the foam rubber laminate was calculated to obtain the average foaming ratio of the laminate. The obtained results are shown in Table 3.

Appearance Evaluation The surface appearance of the obtained foamed rubber laminate on the foamed rubber layer side (Comparative Example 5 is an unfoamed vulcanized rubber layer) was visually observed and evaluated based on the following criteria. The obtained results are shown in Table 3.
“◎”: Surface smoothness equivalent to the surface of the unvulcanized vulcanized rubber.
“◯”: Although rough skin is slightly observed, it has surface smoothness with no practical problem.
“Δ”: A surface property in which rough skin is recognized and cannot be used practically.
“X”: A small semi-balloon-like (diameter 5 mm or more) air pocket is formed, and the surface irregularities are large.

  The foamed rubber laminate (Example 4) including the foamed rubber layer made of the foamable rubber composition of the present invention was confirmed to have an excellent surface appearance while having a foaming ratio of 2 times or more as the laminate. It was. On the other hand, in the foamed rubber laminates of Comparative Examples 6 and 7, it was confirmed that the foaming ratio of the laminate was as small as less than 2 and that rough skin and air retention occurred on the foamed rubber layer side.

Claims (9)

0.1 to 20 parts by weight of chemical foaming agent, 1 to 10 parts by weight of resorcin or resorcin resin, 1 to 15 parts by weight of the curing agent of resorcin and resorcin resin, and 100 parts by weight of diene rubber , and A foamable rubber composition characterized by not containing short fibers . 2. The composition according to claim 1, wherein 20 to 100 parts by weight of at least one filler selected from carbon black, silica, calcium carbonate, clay, mica, diatomaceous earth, and talc is blended with 100 parts by weight of the diene rubber. The expandable rubber composition as described.   The foamable rubber composition according to claim 1 or 2, wherein the curing agent for the resorcin and the resorcin resin is polyvalent methoxymethylol melamine and / or hexamethylenetetramine.   The foamable rubber composition according to claim 1, 2 or 3, wherein the chemical foaming agent is a nitroso foaming agent and / or an azo foaming agent.   The foamable rubber composition according to any one of claims 1 to 4, wherein 0.1 to 20 parts by weight of urea is blended with 100 parts by weight of the diene rubber.   The foamable rubber composition according to any one of claims 1 to 5, wherein the diene rubber contains 20% by weight or more of natural rubber. A foamed rubber laminate comprising a foamed rubber layer formed from the foamable rubber composition according to claim 1 and a reinforcing rubber layer adjacent to the foamed rubber layer, wherein the reinforcing rubber A foam rubber laminate, wherein the layer is in a state of covering a fiber cord.   The foamed rubber laminate according to claim 7, wherein the fiber cord contains at least one selected from polyester fiber, rayon fiber, and polyamide fiber.   A pneumatic tire using the foamed rubber laminate according to claim 7 or 8.