JP2014185231A - Rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition in which a cashew-modified resol type phenol resin is compounded as a curing agent for a novolac type phenol resin, the cashew-modified resol type phenol resin, when compounded into rubber, exhibiting high curability and being able to impart a high elastic modulus to the rubber composition without deteriorating toughness and elongation.SOLUTION: The rubber composition comprises rubber, silica and a novolac type phenol resin, in which a content of the silica is 30 parts by mass or more and 90 pts.mass or less with respect to 100 pts.mass of the rubber, and a content of the novolac type phenol resin is 0.1 pt.mass or more and 30 pts.mass or less with respect to 100 pts.mass of the rubber. The composition includes a cashew-modified resol type phenol resin as a curing agent of the novolac type phenol resin; and a content of the cashew-modified resol type phenol resin is 20 pts.mass or more and 500 pts.mass or less with respect to 100 pts.mass of the novolac type phenol resin.

Description

  The present invention relates to a rubber composition, and more particularly to a rubber composition in which a cashew-modified resol type phenol resin is blended as a curing agent for a novolak type resin.

  Phenolic resins are used in various types of applications such as civil engineering / building materials, various industrial product materials, and general-purpose daily necessities. Among these, the rubber material is a composite material made by adding various additives such as phenolic resin to raw rubber, and attempts to improve various properties such as required wear resistance, crack resistance, and trauma resistance. It has been.

  For example, rubbers that are the main raw materials include various synthetic rubbers such as BR (butadiene rubber) and SBR (styrene-butadiene rubber) and natural rubbers. These rubber materials have wear resistance and mechanical strength. In order to give it, a method of blending a thermosetting resin having a high elastic modulus such as a phenol resin, or blending a large amount of a compounding agent such as sulfur, a vulcanization accelerator, or carbon black has been implemented. .

  When a phenol resin is blended with various materials such as a rubber material, a novolac type phenol resin is usually used together with hexamethylenetetramine or hexamethoxymethylmelamine as a curing agent (see, for example, Patent Document 1). However, the rubber composition has a problem that the properties are difficult to improve. As a cause of this, there is a possibility that the curing of the phenol resin is delayed in the silica-containing system.

  In order to sufficiently cure the phenol resin within the rubber vulcanization time, attempts have been made to improve curability by adding a phenol resin curing accelerator or the like. However, it is hard to say that a sufficient effect has been observed.

JP 2011-195647 A

  The present invention cures a novolac phenolic resin with a cashew-modified resol type phenolic resin that is excellent in curability and can impart a high elastic modulus to the rubber composition without causing a decrease in toughness or elongation when blended with rubber. A rubber composition formulated as an agent is provided.

  Such an object is achieved by the following present invention.

  The rubber composition of the present invention is a rubber composition containing rubber, silica and a novolac-type phenol resin, and the silica content is in a range of 30 parts by mass or more and 90 parts by mass or less with respect to 100 parts by mass of the rubber. And the content of the novolac type phenol resin is in the range of 0.1 parts by weight to 30 parts by weight with respect to 100 parts by weight of the rubber, and a cashew-modified resol type phenol as a curing agent for the novolac type phenol resin. The cashew-modified resol type phenol resin is contained in a range of 20 parts by mass or more and 500 parts by mass or less with respect to 100 parts by mass of the novolac type phenol resin.

  The rubber composition of the present invention may have a cashew modification rate of 5% by mass or more and 80% by mass or less of the cashew modified resol type phenol resin.

  In the rubber composition of the present invention, the water content of the cashew-modified resol type phenol resin may be 5% by mass or less.

  The rubber composition of the present invention may include the cashew-modified resol type phenol resin supported on the silica.

  In the rubber composition of the present invention, the rubber composition may be used for tire treads.

  According to the present invention, it is possible to obtain a rubber composition having excellent curability and having a high elastic modulus without causing a decrease in toughness or elongation.

The present invention is described in detail below.
First, the rubber composition of the present invention will be described.
The rubber composition of the present invention is a rubber composition containing rubber, silica and a novolac-type phenolic resin, and the silica content is in the range of 30 parts by mass or more and 90 parts by mass or less, preferably 100 parts by mass of rubber. Is in the range of 40 parts by mass or more and 85 parts by mass or less, and the content of the novolac type phenol resin is in the range of 0.1 parts by mass or more and 30 parts by mass or less, preferably 5 parts by mass or more with respect to 100 parts by mass of the rubber. 25 parts by mass or less, including a cashew modified resol type phenol resin as a curing agent for the novolak type phenol resin, and the content of the cashew modified resol type phenol resin is 20 parts by mass with respect to 100 parts by mass of the novolac type phenol resin. Part or more and 500 parts by mass or less, preferably 30 parts by mass or more and 180 parts by mass or less. Thereby, it is excellent in sclerosis | hardenability and can obtain the rubber composition which has a high elasticity modulus, without causing the fall of toughness and elongation. If the content of silica is more than the above range, workability may be deteriorated, and if it is less than the above range, the strength of the rubber composition may be lowered. Further, if the content of the novolac type phenol resin and the cashew modified resol type phenol resin is larger than the above range, the viscosity of the unvulcanized rubber may be increased, and the workability may be deteriorated. There is a risk that it will not be obtained.

  The rubber used in the rubber composition of the present invention is not particularly limited. For example, styrene butadiene rubber (SBR), butadiene rubber (BR), natural rubber (NR), isoprene rubber (IR), ethylene propylene diene rubber (EPDM), Isoprene butadiene rubber (IBR), butyl rubber (IIR), acrylonitrile-butadiene rubber (NBR) and the like can be mentioned, and these can be used alone or in any combination. Of these, NR, SBR, IR, and BR are preferably used from the viewpoint of rubber strength.

The silica used in the rubber composition of the present invention is not particularly limited, but preferably has a nitrogen adsorption specific surface area of 50 m ² / g or more and 300 m ² / g or less. If it is less than the lower limit, the reinforcing effect tends to be small. Moreover, when the said upper limit is exceeded, there exists a tendency for the dispersibility of a silica to worsen. Examples of commercially available silica include nip seal AQ (manufactured by Tosoh Silica Co., Ltd.), Tokusil U (manufactured by Tokuyama Co., Ltd.), and the like.

Although the novolak type phenol resin used for the rubber composition of the present invention is not particularly limited, it can be obtained by reacting phenols and aldehydes under an acidic catalyst. Examples of the phenols used in the novolak type phenol resin used in the rubber composition of the present invention include cresols such as phenol, o-crezo ddole, m-cresol, p-cresol, 2,3-xylenol, 2 , 4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, xylenols such as 3,5-xylenol, ethyl such as o-ethylphenol, m-ethylphenol, p-ethylphenol Phenols, isopropylphenol, butylphenol, butylphenols such as p-tert-butylphenol, p-tert-amylphenol, p-octylphenol, p-nonylphenol, alkylphenols such as p-cumylphenol, fluorophenol, chlorophenol Halogenated phenols such as bromophenol and iodophenol, phenol-substituted products such as p-phenylphenol, aminophenol, nitrophenol, dinitrophenol and trinitrophenol, and monofunctional groups such as 1-naphthol and 2-naphthol. Examples include phenols, resorcin dx, alkylresorcinol, pyrogallol, catechol, alkylcatechol, hydroquinone, alkylhydroquinone, phloroglucin, bisphenol A, bisphenol F, bisphenol S, and dihydroxynaphthalene. These can be used individually or in mixture of 2 or more types.

  Among these phenols, those selected from phenol and cresols are preferable. What uses these is excellent in sclerosis | hardenability, and can raise the mechanical strength in the rubber composition using the phenol resin of this invention.

  Examples of aldehydes used in the novolak type phenolic resin used in the rubber composition of the present invention include substances that generate aldehydes such as aqueous formaldehyde solution and paraformaldehyde.

  Examples of the acidic catalyst used for the novolak-type phenol resin used in the rubber composition of the present invention include, for example, acids such as oxalic acid, hydrochloric acid, sulfuric acid, diethylsulfuric acid, paratoluenesulfonic acid, and metal salts such as zinc acetate. More than one type can be used together. Although the usage-amount of the said acidic catalyst is not specifically limited, Usually, it is 0.001 mol or more and 0.1 mol or less with respect to 1 mol of phenols.

  The cashew-modified resol type phenol resin used in the rubber composition of the present invention is modified with cashew oil, and the modification rate is preferably 5% by mass or more and 80% by mass or less, more preferably. It is 10 mass% or more and 70 mass% or less. Thereby, sclerosis | hardenability can be improved. If the amount of modification by cashew oil is more than the above range, the resin cannot be maintained in a solid state, so the workability may be very poor. If the amount is less than the above range, the compatibility with rubber deteriorates. Strength may be reduced. By modifying with cashew oil, compatibility with rubber is improved and the rubber composition can be effectively reinforced.

Examples of the phenols used in the cashew-modified resol type phenol resin used in the rubber composition of the present invention include, for example, cresols such as phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2, Xylenols such as 4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, 3,5-xylenol, and ethylphenol such as o-ethylphenol, m-ethylphenol, p-ethylphenol , Butylphenols such as isopropylphenol, butylphenol, p-tert-butylphenol, alkylphenols such as p-tert-amylphenol, p-octylphenol, p-nonylphenol, p-cumylphenol, fluorophenol, chlorophenol Nord, bromophenol, halogenated phenols such as iodophenol, p- phenylphenol, aminophenol, nitrophenol,
Phenol substitutes such as dinitrophenol and trinitrophenol, and monofunctional phenols such as 1-naphthol and 2-naphthol, resorcin, alkylresorcinol, pyrogallol, catechol, alkylcatechol, hydroquinone, alkylhydroquinone, phloroglucin, bisphenol A And polyfunctional phenols such as bisphenol F, bisphenol S, and dihydroxynaphthalene. These can be used individually or in mixture of 2 or more types.

  Among these phenols, those selected from phenol and cresols are preferable. Those using these are excellent in curability and can increase the mechanical strength of the rubber composition using the cashew-modified resol type phenol resin of the present invention.

  Examples of formaldehydes used in the cashew-modified resol type phenolic resin used in the rubber composition of the present invention include substances that generate formaldehyde such as aqueous formaldehyde solution and paraformaldehyde.

  The cashew-modified resol type phenol resin used in the rubber composition of the present invention is obtained by, for example, reacting the above-described phenols and cashew oil in the presence of an acidic catalyst, and then reacting aldehydes in the presence of an alkaline catalyst. Can be obtained.

  Examples of the acidic catalyst include Friedel-Craft type catalysts such as p-toluenesulfonic acid, methanesulfonic acid, boron trifluoride, stannic chloride, ferric chloride, perfluoromethanesulfonic acid, and the like. More than one type can be used together. As the usage-amount of the said acidic catalyst, it can be 0.001-0.05 mol normally with respect to 1 mol of phenols.

  Examples of the alkali catalyst used in the cashew-modified resol type phenol resin used in the rubber composition of the present invention include, for example, alkali metal hydroxides such as sodium hydroxide, lithium hydroxide, and potassium hydroxide, ammonia water, triethylamine, and the like. Alkali earth metal oxides and hydroxides such as tertiary amine, calcium, magnesium, and barium, alkaline substances such as sodium carbonate, hexamethylenetetramine, and the like can be used alone or in combination. Although the usage-amount of the said alkaline catalyst is not specifically limited, Usually, it is 0.001 mol or more and 0.1 mol or less with respect to 1 mol of phenols.

  The cashew-modified resol-type phenol resin used in the rubber composition of the present invention preferably has a water content of 5% by mass or less. If moisture is contained in the rubber composition, it may cause vulcanization inhibition. Furthermore, when the rubber composition after vulcanization is used in contact with metal, it may corrode the metal. Therefore, it is preferable that the amount of water is as small as possible. The water content can be reduced by sufficient dehydration during the synthesis of the cashew-modified resol type phenolic resin. The amount of water in the cashew-modified resol type phenol resin used in the rubber composition of the present invention can be measured, for example, with a Karl Fischer moisture meter.

  In this invention, what was carry | supported on the silica mentioned above can be used as cashew modified | denatured resol type phenol resin. As a method for producing the resin-supported silica, a method in which silica treated with a silane coupling agent and a cashew-modified resol type phenol resin are mixed while heating, a cashew modified resol type phenol resin dissolved in an organic solvent and a silane coupling agent treatment A method of volatilizing the organic solvent after mixing with the prepared silica is mentioned, but it is not particularly limited. Examples of the mixer include a mixer, a kneader, and rolls.

In addition to rubber, silica, novolac-type and cashew-modified resol-type phenolic resins, the method for producing the rubber composition of the present invention includes other reinforcing agents (fillers), anti-aging agents, vulcanization accelerators, and resin curing agents. Etc. can be kneaded into a composition, which can be used for vulcanization or crosslinking.

  The tire of the present invention is produced by an ordinary method using the rubber composition of the present invention for a tire tread. That is, the rubber composition is extruded into a shape of a tread portion of a tire at an unvulcanized stage, and bonded on a tire molding machine by a usual method to form an unvulcanized tire. The unvulcanized tire can be heated and pressurized in a vulcanizer to obtain a tire.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. “Parts” described herein indicates “parts by mass”, and “%” indicates “% by mass”.

<Synthesis of cashew-modified resol type phenolic resin>
(Synthesis Example 1)
To a reaction apparatus equipped with a stirrer, a reflux condenser and a thermometer, 1000 parts of phenol, 1000 parts of cashew nut oil, and 1 part of paratoluenesulfonic acid were added, and the temperature was raised to 120 ° C. and reacted for 2 hours. After the reaction, 1379 parts of a 37% formaldehyde aqueous solution and 10 parts of sodium hydroxide were added and reacted at 60 ° C. for 2 hours. After cooling, the reaction system was depressurized to a vacuum of 5000 Pa, heated to 60 ° C., and distilled under reduced pressure to obtain 2520 parts of cashew-modified resol type phenol resin A. The resulting resin had a cashew modification rate of 45% and a moisture content of 2%.

(Synthesis Example 2)
To a reaction apparatus equipped with a stirrer, a reflux condenser and a thermometer, 1000 parts of phenol, 225 parts of cashew nut oil and 1 part of paratoluenesulfonic acid were added, and the temperature was raised to 120 ° C., followed by reaction for 2 hours. After the reaction, 1107 parts of a 37% aqueous formaldehyde solution and 10 parts of sodium hydroxide were added, and then reacted at 60 ° C. for 2 hours. After cooling, the reaction system was depressurized to a vacuum of 5000 Pa, heated to 60 ° C., and distilled under reduced pressure to obtain 1645 parts of cashew-modified resol type phenol resin B. The resulting resin had a cashew modification rate of 10% and a moisture content of 2%.

(Synthesis Example 3)
To a reaction apparatus equipped with a stirrer, a reflux condenser and a thermometer, 1000 parts of phenol, 1445 parts of cashew nut oil and 1 part of paratoluenesulfonic acid were added, and the temperature was raised to 120 ° C., followed by reaction for 2 hours. After the reaction, 1490 parts of a 37% aqueous formaldehyde solution and 10 parts of sodium hydroxide were added, followed by reaction at 60 ° C. for 2 hours. After cooling, the reaction system was depressurized to a vacuum of 5000 Pa, heated to 60 ° C., and distilled under reduced pressure to obtain C3006 parts of cashew-modified resol type phenol resin. The resulting resin had a cashew modification rate of 65% and a moisture content of 1%.

(Synthesis Example 4)
To a reactor equipped with a stirrer, a reflux condenser and a thermometer, 1000 parts of phenol, 1778 parts of cashew nut oil and 1 part of paratoluenesulfonic acid were added, and the temperature was raised to 120 ° C., followed by reaction for 2 hours. After the reaction, 1608 parts of a 37% formaldehyde aqueous solution and 10 parts of sodium hydroxide were added and reacted at 60 ° C. for 2 hours. After cooling, the reaction system was decompressed to a vacuum of 5000 Pa, heated to 60 ° C., and distilled under reduced pressure to obtain D3383 parts of cashew-modified resol type phenol resin. The resulting resin had a cashew modification rate of 85% and a moisture content of 1%.

(Synthesis Example 5)
To a reaction apparatus equipped with a stirrer, a reflux condenser and a thermometer, 1000 parts of phenol, 1000 parts of cashew nut oil, and 1 part of paratoluenesulfonic acid were added, and the temperature was raised to 120 ° C. and reacted for 2 hours. After the reaction, 1379 parts of a 37% formaldehyde aqueous solution and 10 parts of sodium hydroxide were added and reacted at 60 ° C. for 2 hours. After cooling, the reaction system was depressurized to a vacuum of 5000 Pa, heated to 60 ° C. and distilled under reduced pressure, and then 40 parts of water was added to obtain 2600 parts of cashew-modified resol type phenol resin E. The resulting resin had a cashew modification rate of 45% and a moisture content of 10%.

(Synthesis Example 6)
A reactor equipped with a stirrer, a reflux condenser and a thermometer was charged with 1000 parts of phenol, 1031 parts of a 37% aqueous formaldehyde solution and 10 parts of sodium hydroxide, and then the temperature was gradually raised and reacted at 60 ° C. for 1 hour. Furthermore, it was made to react at 100 degreeC for 1 hour. After cooling, the pressure of the reaction system was reduced to 5000 Pa, the temperature was raised to 60 ° C., and distillation under reduced pressure was performed to obtain a resol type phenol resin F1392 parts. The water content of the obtained resol type phenol resin F was 2%.

  Table 1 shows the cashew modification rate and water content in the resol type phenol resins synthesized in Synthesis Examples 1-6.

<Production of resin-supported silica>
250 parts of acetone, 2 parts of silane coupling agent (Z-6011 (3-aminopropyltriethoxysilane) manufactured by Toray Dow Corning Co., Ltd.), 100 parts of silica (Tosoh Silica Co., Ltd. Nipseal AQ) in a Henschel mixer After being charged and sufficiently stirred until uniformly mixed, the Henschel mixer system was distilled under reduced pressure at a vacuum of 5000 Pa to remove acetone and obtain a silica treated with a coupling agent. Subsequently, 10 parts of the resol type phenol resin synthesized in the synthesis example was added, and the mixture was sufficiently stirred at 80 ° C. until it was uniformly mixed to obtain resin-supported silica.

(Experimental Examples 1-18)
<Manufacture of rubber composition>
Using the various raw materials shown below and the resol-type phenol resins A to F obtained in Synthesis Examples 1 to 6 and the above-mentioned resin-supported silica, the blending ratio (parts by mass) shown in Table 2 Using a Labo Plast Mill 10C100 manufactured by Seiki Seisakusho, the mixture was heated and kneaded at 100 ° C. to obtain a rubber composition.
Natural rubber: Tochi, RSS3
Silica: Tosoh Silica Co., Ltd. Nip Seal AQ (Nitrogen adsorption specific surface area 205 m ² / g)
Novolac resin: Sumitomo Bakelite PR-50731
Zinc oxide: Sakai Chemical Industry Co., Ltd.
Stearic acid: NOF Co., Ltd. Beads stearic acid YR
Sulfur: Hosoi Chemical Industry Co., Ltd. Fine Sulfur Vulcanization accelerator: Ouchi Shinsei Chemical Industry Co., Ltd. MSA-G

<Preparation of vulcanized rubber sheet>
The obtained rubber composition was vulcanized with a hydraulic press at 160 ° C. for 20 minutes to prepare a vulcanized rubber sheet having a thickness of 2 mm.

<Evaluation items>
Table 2 shows the results of the following evaluation on the prepared vulcanized rubber sheet. In addition, each characteristic was shown by the relative value when the value of Experimental example 18 which did not mix | blend a phenol resin is set to 100. FIG.
<Evaluation of vulcanized rubber sheet>
Hardness (Type D)
Based on JIS K 6253, hardness (type D) was measured using a durometer manufactured by Toyo Seiki Co., Ltd. The relative hardness value when the value of Experimental Example 18 in which no phenol resin is blended is 100 is preferably 111 to 130, and particularly preferably 115 to 120.
Elongation at the time of cutting In accordance with JIS K6251, it was measured at a tensile speed of 50 mm / min using a strograph manufactured by Toyo Seiki Co., Ltd. 80-140 are preferable and the value of the elongation at the time of relative cutting when the value of Experimental example 18 which did not mix | blend a phenol resin is set to 100 is especially preferable 85-120.
Storage elastic modulus The storage elastic modulus at 50 ° C. was measured under the condition of dynamic strain of 2% using a dynamic viscoelasticity measuring apparatus manufactured by TA Instruments Japan. The relative storage elastic modulus is preferably 650 to 1200, particularly preferably 670 to 1100 when the value of Experimental Example 18 in which no phenol resin was blended is 100.

As is apparent from the results in Table 2, the rubber composition contains rubber, silica and a novolac type phenol resin, and the silica content is in the range of 30 parts by mass or more and 90 parts by mass or less with respect to 100 parts by mass of the rubber. The content of the novolak type phenol resin is in the range of 0.1 parts by mass or less and 30 parts by mass or less with respect to 100 parts by mass of the rubber, and includes a cashew modified resol type phenol resin as a curing agent for the novolac type phenol resin. In the vulcanized rubber sheets of Experimental Examples 1 to 10 in which the content of the cashew modified resol type phenol resin is in the range of 20 parts by mass or more and 500 parts by mass or less with respect to 100 parts by mass of the novolak type phenol resin, the phenol resin is blended. In comparison with the vulcanized rubber sheet of Experimental Example 18 that did not, the hardness was sufficiently improved by excellent curability, at the time of cutting Without causing a significant reduction in beauty, it resulted storage elastic modulus is remarkably improved.
In particular, the cashew-modified resol type phenol resins A to C synthesized in Synthesis Examples 1 to 3 having a cashew oil modification rate of 5% by mass or more and 80% by mass or less and a water content of 5% by mass or less. In the vulcanized rubber sheets of Experimental Examples 1 to 8, the balance in improving the hardness, maintaining the elongation at cutting and improving the storage elastic modulus was particularly excellent. The tendency was further remarkable in the vulcanized rubber sheet of Experimental Example 2 in which the cashew-modified resol type phenol resin A of Synthesis Example 1 was supported on silica. In the vulcanized rubber sheet of Experimental Example 9 in which the cashew modified resol type phenolic resin D of Synthesis Example 4 having a high modification rate was blended, the hardness and storage elastic modulus were not improved as much as Experimental Examples 1-8. This is presumably because the rubber was softened due to an increase in cashew components, and the rubber composition was not sufficiently reinforced. Further, even in the vulcanized rubber sheet of Experimental Example 10 in which the cashew-modified resol type phenol resin E synthesized in Synthetic Example 5 having a large amount of water was blended, the hardness and storage were as high as the vulcanized rubber sheets of Experimental Examples 1-8. The elastic modulus did not improve. This is presumably because moisture hinders curing, and curing within the vulcanization time was not necessarily sufficient. In addition, even in the vulcanized rubber sheets of Experimental Examples 11 and 12 in which the unmodified resol type phenol resin F synthesized in Synthesis Example 6 was blended, the hardness and storage modulus were not improved. This is presumably because the compatibility between the resin and the rubber deteriorated and the reinforcing effect of the rubber composition was not sufficient.

  On the other hand, in the vulcanized rubber sheet of Experimental Example 13 with a small amount of silica, the hardness decreased and the effect of improving the storage elastic modulus was inferior. In the vulcanized rubber sheet of Experimental Example 14 having a large amount of silica, the elongation at the time of cutting was significantly reduced. In addition, even when the vulcanized rubber sheet of Experimental Example 15 with a large amount of novolac resin was added, the elongation at break was significantly reduced. Furthermore, in the vulcanized rubber sheet of Experimental Example 16 in which the amount of the resol type phenolic resin is small, the hardness is remarkably lowered and the storage elastic modulus is not improved. On the contrary, in the vulcanized rubber sheet of Experimental Example 17 in which the amount of the resol type phenol resin was large, the elongation at break was significantly inferior.

According to the present invention, since it is possible to obtain a rubber composition having excellent curability and a high elastic modulus without causing a decrease in toughness or elongation, it is possible to achieve both toughness, elongation and high elasticity, such as treads for automobile tires. Can be suitably used for various applications for which is required.

Claims (5)

A rubber composition comprising rubber, silica and a novolac type phenolic resin,
The silica content is in the range of 30 parts by mass or more and 90 parts by mass or less with respect to 100 parts by mass of the rubber.
The content of the novolac type phenol resin is in a range of 0.1 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the rubber.
As a curing agent of the novolac type phenol resin, including cashew-modified resol type phenol resin,
The rubber composition, wherein a content of the cashew-modified resol type phenol resin is in a range of 20 parts by mass or more and 500 parts by mass or less with respect to 100 parts by mass of the novolac type phenol resin.   The rubber composition according to claim 1, wherein the cashew modified resol type phenol resin has a cashew modified ratio of 5% by mass or more and 80% by mass or less.   The rubber composition according to claim 1 or 2, wherein the cashew-modified resol type phenolic resin has a water content of 5% by mass or less.   The rubber composition according to any one of claims 1 to 3, wherein the cashew-modified resol-type phenolic resin is supported on the silica. The rubber composition according to any one of claims 1 to 4, wherein the rubber composition is used for a tire tread.