JP2006199808A - Phenol resin composition for compounding into rubber and rubber composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition capable of exhibiting sufficient curing rate and improving hardness and elastic modulus of novolak phenol resin product without using hexamethylene tetramine as a curing agent for novolak phenol resin products. <P>SOLUTION: The phenol resin composition for compounding into a rubber contains a modified novolak type phenol resin using a modifier containing an aliphatic double bond and a polyacetal resin as essential components. In the novolak phenol resin, an acidic substance which is a reaction catalyst for the resin is remaining. The novolak phenol resin is preferably modified with cashew oil. The rubber composition contains the novolak phenol resin and a polyacetal resin together with rubber component as essential components. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a rubber compounding phenol resin composition containing a novolac type phenol resin and a polyacetal resin as essential components, and a rubber composition containing the compound.

Phenolic resins are used in various applications such as blending into tires for automobiles and aircraft, civil engineering and construction materials, various industrial product materials, and general daily necessities. Among these, rubber materials used for automobile tires, etc. are composite materials made by adding various additives to raw rubber, and required wear resistance, crack resistance, trauma resistance, low heat generation Various characteristics have been improved.
For example, rubber, which is the main raw material of tires, is made of synthetic rubber such as BR (butadiene rubber) and SBR (styrene-butadiene rubber) and natural rubber, and these rubber materials have wear resistance suitable for tire applications. In order to give performance and mechanical strength, a high-modulus thermosetting resin such as phenol resin is blended, or a large amount of blending agents such as sulfur, hexamethylenetetramine, vulcanization accelerator, and carbon black are blended. The method to do is carried out.

When a phenol resin is blended with various materials such as rubber materials, a novolac type phenol resin is usually used together with hexamethylenetetramine as a curing agent (see, for example, Patent Document 1). This hexamethylenetetramine is a mutagenic substance. There are reports to that effect, and there is a strong demand for reduction or abolition.

On the other hand, hexamethoxymethylol melamine, epoxy resin, resol-type phenol resin, etc. are used as an alternative to hexamethylenetetramine (see, for example, Patent Document 2), but hexamethoxymethylol melamine is slow in curable and liquid and difficult to handle. In addition, since the molecular weight per equivalent is larger than that of hexamethylenetetramine, the blending amount is large and the price is expensive, which is a practical problem.
Epoxy resins and resol type phenol resins are also used as curing agents. However, if the amount is not the same as or greater than the amount of novolac type phenol resin, sufficient curability cannot be obtained. In addition, it was necessary to consider the preservability of the resin itself.

In addition, there is a technique that uses a novolac-type phenol resin and a polyacetal resin together with an acidic compound (see, for example, Patent Document 3). In this method, the polyacetal resin is decomposed by the action of an acidic compound to generate formaldehyde, which is reacted with a novolac type phenol resin to be cured.
However, in this method, since the decomposition of the polyacetal resin proceeds rapidly by the addition of an acidic compound, it is difficult to control the curing rate. In addition, since acidic compounds have corrosiveness and irritation, there is a problem that depending on the method of using the resin composition, the corrosion of the apparatus and the environmental hygiene are adversely affected.

JP 2004-137376 A Japanese Patent Laid-Open No. 11-080432 JP 2004-269856 A

The present invention is a rubber composition capable of improving a sufficient curing speed, hardness, and elastic modulus without using hexamethylenetetramine as a curing agent when a novolak type phenol resin is blended with a rubber component in the product. It provides things. Product

Such an object is achieved by the following present inventions (1) to (5).
(1) A phenolic resin composition for rubber compounding, comprising a modifier novolak type phenolic resin (a) containing an aliphatic double bond and a polyacetal resin (b) as essential components.
(2) The phenolic resin composition for rubber blending according to (1), wherein the novolac type phenol resin (a) is one in which an acidic substance that is a reaction catalyst of the resin remains.
(3) The phenol resin composition for rubber blending according to (1) or (2), wherein the novolac type phenol resin (a) is modified with cashew oils.
(4) The novolac type phenol resin (a) is a phenol resin composition for rubber compounding according to (2) or (3), wherein the reaction catalyst is sulfuric acid (5) together with the rubber component (1) to ( 4) A rubber composition characterized by containing a novolac-type phenol resin (a) and a polyacetal resin (b) according to any one of 4) as essential components.

The phenolic resin composition for rubber compounding of the present invention cures a novolac type phenolic resin without using hexamethylenetetramine by causing a novolak type phenolic resin and a polyacetal resin as its curing agent to exist. By blending into the rubber composition, various properties such as the elastic modulus, abrasion resistance, and crack resistance of the rubber composition can be improved. In particular, when the novolac-type phenol resin is cashew oil-modified, the above-described property improving effect is excellent.
In the composition of the present invention, the mechanism by which the novolak type phenol resin is cured by the polyacetal resin is not clear, but in the novolak type phenol resin obtained in the presence of an acidic substance as a reaction catalyst, particularly sulfuric acid, the resin It contains an acidic substance such as sulfuric acid, and when heated, the acidic substance decomposes the polyacetal resin to generate formaldehyde, which is considered to cure the novolac phenolic resin.

The present invention relates to a phenol resin composition for rubber compounding containing a modifier novolak-type phenol resin (a) and polyacetal resin (b) containing an aliphatic double bond as essential components, and in particular, the novolak-type phenol. Resin (a) relates to a rubber compounding phenol resin composition in which an acidic substance that is a reaction catalyst of the resin remains.
Furthermore, the present invention relates to a phenol resin composition for rubber compounding, wherein the novolac type phenol resin (a) is modified with cashew oil.

First, the novolak-type phenol resin (a) (hereinafter sometimes simply referred to as “novolak resin”) used in the composition of the present invention will be described.
The novolak resin of the present invention is obtained by reacting phenols and aldehydes in the presence of an acidic catalyst.

  Although it does not specifically limit as phenols used in order to obtain the said novolak resin, For example, cresol, such as phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2 , 5-xylenol, 2,6-xylenol, 3,4-xylenol, xylenol such as 3,5-xylenol, ethylphenol such as o-ethylphenol, m-ethylphenol, p-ethylphenol, isopropylphenol, p- Isobutylphenol, butylphenol such as p-tert-butylphenol, p-tert-amylphenol, p-octylphenol, p-nonylphenol, alkylphenols such as p-cumylphenol, fluorophenol, chlorophenol, bromophenol Halogenated phenols such as diol and iodophenol, monohydric phenol substitutes such as p-phenylphenol, aminophenol, nitrophenol, dinitrophenol and trinitrophenol, and monovalent phenols such as 1-naphthol and 2-naphthol And polyphenols such as resorcin, alkylresorcin, pyrogallol, catechol, alkylcatechol, hydroquinone, alkylhydroquinone, phloroglucin, bisphenol A, bisphenol F, bisphenol S, and dihydroxynaphthalene. These can be used alone or in combination of two or more.

  The aldehydes are not particularly limited, but examples include formaldehyde, paraformaldehyde, trioxane, acetaldehyde, propionaldehyde, polyoxymethylene, chloral, hexamethylenetetramine, furfural, glyoxal, n-butyraldehyde, caproaldehyde, allylaldehyde. Benzaldehyde, crotonaldehyde, acrolein, tetraoxymethylene, phenylacetaldehyde, o-tolualdehyde, salicylaldehyde and the like. These can be used alone or in combination of two or more. Among these, it is preferable to use one or more aldehydes selected from formaldehyde and paraformaldehyde. Thereby, a novolac-type phenol resin can be obtained with a good yield.

  In the present invention, the novolak resin (a) is preferably a novolak resin modified with cashew oils (hereinafter referred to as cashew-modified novolak resin). Although not particularly limited, cashew oil is preferred. Since cashew oils contain cardanol and cardol, which are phenolic compounds having a long-chain alkenyl group, it is possible to obtain a phenol resin having a long-chain alkyl group or alkenyl group when used as a phenol resin modifier. it can. Therefore, when blended with rubber, it is excellent in compatibility with rubber, and when an alkenyl group is present, it has an effect of reacting with a double bond of rubber to improve the elastic modulus.

Moreover, since the cashew modified novolak resin is excellent in compatibility with the polyacetal resin, the curing rate of the composition can be increased and the curability can be improved. Furthermore, cashew oils are relatively inexpensive and easily available.
Moreover, cardanol, cardol obtained by distilling cashew oil, or these components can also be used individually or in combination as cashew oil, and this case is also contained in this invention.

Next, a method for producing a novolak resin or cashew-modified novolak resin used in the composition of the present invention will be described.
The novolak resin can be obtained by reacting phenols and aldehydes in the presence of an acidic catalyst, for example, under reflux conditions.
Although it does not specifically limit as reaction molar ratio (F / P) of phenols (P) and aldehydes (F) at the time of synthesize | combining a novolak resin, 0.5-1.0 are preferable, Especially 0.6- 0.9 is preferred. If the reaction molar ratio is less than the lower limit, a solid novolak resin may not be obtained. If the reaction molar ratio exceeds the upper limit, gelation may occur depending on the reaction conditions.

The method for synthesizing the cashew-modified novolak resin is not particularly limited.For example, a method in which phenols, cashew oils, and an acidic catalyst are charged in a reaction apparatus and the aldehydes are sequentially added under reflux conditions and reacted. Alternatively, there may be mentioned a method in which an unmodified novolak resin and an acidic catalyst are charged in a reaction apparatus and reacted while adding cashew oils under reflux conditions.
The reaction molar ratio (F / P) between the phenols (P) and the aldehydes (F) when synthesizing the cashew-modified novolak resin is not particularly limited, but is preferably 0.5 to 1.0, particularly preferably 0.8. 6-0.9 is preferable. When the reaction molar ratio is less than the above lower limit value, a solid resin may not be obtained, and when the reaction upper limit value is exceeded, gelation may occur depending on the reaction conditions.

In the cashew-modified novolak resin, the rate of modification with the cashew oils is not particularly limited, but it is preferably 20 to 50% by weight of the cashew oil-modified novolak resin, more preferably 30 to 45 parts by weight.
If the modification rate is less than the lower limit, the effect of modification by cashew oils may not be sufficiently exhibited. On the other hand, when the above upper limit is exceeded, the cashew-modified novolak resin is difficult to solidify, and handling becomes difficult, and the reaction is difficult to control and a gelled product may be generated.

The acidic catalyst used when synthesizing the above novolak resin or cashew modified novolak resin is not particularly limited. For example, inorganic acids such as hydrochloric acid, sulfuric acid, phosphoric acid, phosphorous acid, oxalic acid, diethyl sulfuric acid, paratoluenesulfonic acid And organic acids such as organic phosphonic acid and metal salts such as zinc acetate. These can be used alone or in combination of two or more.
Among these, sulfuric acid such as sulfuric acid, diethyl sulfuric acid, and paratoluenesulfonic acid or sulfonic acid-based materials, and phosphoric acid-based materials such as phosphoric acid and phosphorous acid are preferable. Among these, sulfuric acid or sulfonic acid-based materials, particularly sulfuric acid is preferable. preferable.

The addition amount of the acidic catalyst is not particularly limited, but is preferably in the range of 0.05 to 5 parts by weight, particularly preferably 0.1 to 2 parts by weight with respect to 100 parts by weight of phenols.
If the addition amount of the acidic catalyst is less than the lower limit, the reaction may not proceed sufficiently. On the other hand, when the above upper limit is exceeded, a gelled product may be produced depending on the reaction conditions, as in the case where the reaction molar ratio is high.

  When synthesizing the novolak resin or the cashew-modified novolak resin, a reaction solvent can be used. The reaction solvent is not particularly limited, and water, an organic solvent, or the like can be used, but water is usually used. Moreover, you may carry out without using a reaction solvent, using paraformaldehyde as aldehydes. Examples of the organic solvent include alcohols such as methanol, ethanol, propanol, butanol, and amyl alcohol; ketones such as acetone and methyl ethyl ketone; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, and glycerin; ethylene glycol monomethyl ether, ethylene Examples include glycol ethers such as glycol monoethyl ether, diethylene glycol monomethyl ether and triethylene glycol monomethyl ether, ethers such as 1,4-dioxane, and aromatics such as toluene and xylene. These can be used alone or in combination of two or more.

  The molecular weight of the novolak resin or cashew-modified novolak resin is not particularly limited, but is preferably 400 to 1100 in terms of number average molecular weight, and more preferably 500 to 1000. When the number average molecular weight is within the above range, the handleability of the resin is good. If the number average molecular weight is below the lower limit, it may become a highly viscous material, or it may become a solidified substance during summer storage even if it is solidified, which may reduce the handleability. Moreover, when it exceeds the said upper limit, it may become difficult to melt | dissolve in solvents, or compatibility with a formulation may fall.

The number average molecular weight is measured by the GPC method (gel permeation chromatography). In the GPC method, tetrahydrofuran was used as an elution solvent, a differential refractometer was measured as a detector under the conditions of a flow rate of 1.0 ml / min and a column temperature of 40 ° C., and the molecular weight was converted by standard polystyrene. The equipment used is as follows.
-Body: manufactured by TOSOH-"HLC-8120"
・ Analytical column: manufactured by TOSOH ・ One "G1000HXL", two "G2000HXL", one "G3000HXL"

  The form of the novolak resin or cashew-modified novolak resin used in the composition of the present invention is not particularly limited, but it is preferable to use a fine powder form. Thereby, mixing dispersibility with a polyacetal resin can be made favorable, and the sclerosis | hardenability of a composition can be improved. Furthermore, compatibility with rubber can be further increased.

Next, the polyacetal resin (b) used as a novolak resin curing agent in the composition of the present invention will be described.
The polyacetal resin used in the present invention is a kind of thermoplastic resin and is a polymer compound having an oxymethylene group as a main structural unit. Examples of the polyacetal resin include a homopolymer type polyacetal resin whose main chain is composed only of oxymethylene groups, and a copolymer type polyacetal resin containing a structural unit other than oxymethylene groups such as oxyethylene groups, for example, less than 50% by weight. is there. Moreover, what contains a mold release agent, antioxidant, etc. can also be used.

  As the polyacetal resin used in the present invention, a commercially available product thus prepared can be used. Examples of the homopolymer type polyacetal resin include “Derlin 500NC010” manufactured by DuPont and “Tenac 4010” manufactured by Asahi Kasei Corporation. Examples of the copolymer type polyacetal resin include “Duracon M90S” manufactured by Polyplastics Co., Ltd., “F30-01” manufactured by Mitsubishi Engineering Plastics Co., Ltd., and “Tenac C7520” manufactured by Asahi Kasei Co., Ltd. .

  Although it does not specifically limit as a form of the polyacetal resin used with the composition of this invention, It is preferable to use what is a fine powder form. Thereby, the mixing and dispersibility with the said novolak resin or cashew modified | denatured novolak resin can be made favorable, and the sclerosis | hardenability of a composition can be improved. Furthermore, compatibility with rubber can be further increased.

  In the composition of the present invention, the blending amount of the polyacetal resin (b) is not particularly limited, but is preferably 10 to 30 parts by weight with respect to 100 parts by weight of the novolak resin. Thereby, the sclerosis | hardenability of a composition and the external appearance of hardened | cured material can be made favorable. When the blending amount of the polyacetal resin is less than the lower limit, the curing rate of the composition may not be sufficient. On the other hand, when the above upper limit is exceeded, the amount of gas generated during curing increases and the appearance of the cured product may deteriorate.

In the composition of the present invention, the mechanism of the curing of the novolak resin or cashew-modified novolak resin by the polyacetal resin is not clear, but is presumed as follows.
The acidic catalyst used in the production of the novolak resin or cashew-modified novolak resin includes sulfate ion, phosphate ion, etc. contained in the resin, particularly when a sulfate-based material or a phosphate-based material is used as the catalyst. Yes. These ionic substances are considered to promote the decomposition of the polyacetal resin and the formation of formaldehyde at a stage where the temperature becomes higher than 120 ° C to 150 ° C.

Thus, in the composition of this invention, it is thought that the said acidic substance which exists in resin decomposes | disassembles a polyacetal resin in a predetermined temperature range, and accelerates | stimulates the production | generation of formaldehyde which is a hardening agent of resin.
For this reason, since the composition of the present invention does not proceed at a relatively low temperature range such as during storage and handling, it is excellent in handling workability, and formaldehyde is rapidly decomposed by decomposition of the polyacetal resin at a predetermined high temperature range. Therefore, the curing speed is high and the curability is good.
In the composition of the present invention, it is not necessary to add, for example, an acidic compound in order to accelerate the decomposition of the polyacetal resin, and therefore, workability and environmental problems can be easily avoided.

  The form of the composition of the present invention is not particularly limited. For example, a novolak resin or a cashew-modified novolak resin and a polyacetal resin are uniformly mixed with a kneading apparatus such as a kneading roll and then finely pulverized together. In addition to those obtained by dry mixing, for example, when mixing with other materials, the novolak resin or cashew-modified novolak resin and polyacetal resin can be used separately without mixing.

The composition of the present invention can be made into a rubber composition having excellent mechanical properties such as elastic modulus by, for example, blending with an elastomer such as rubber and curing for rubber blending.
Specifically, for example, various rubbers, carbon black, cashew-modified novolak resin, and the like are previously kneaded at about 150 ° C. with a Banbury mixer or the like, and then polyacetal resin, sulfur, curing accelerator, etc. at about 100 ° C. And a method of kneading at about 100 ° C. using a kneading apparatus such as a kneading roll, a pressure kneader, a kneader, or a twin screw extruder after mixing all the above-mentioned compounds. .

  Hereinafter, the present invention will be specifically described based on examples. However, the present invention is not limited to the examples. Further, “parts” and “%” described in the text all indicate “parts by weight” and “% by weight”.

<Production Example 1>
A 3 L three-necked flask was charged with 1000 parts of phenol, 500 parts of cashew oil, 690 parts of 37% formalin (reaction molar ratio 0.8) and 10 parts of sulfuric acid, and reacted at 100 ° C. under reflux for 1 hour. Then, it heated up at 230 degreeC, distilling under reduced pressure at 5000 Pa, and obtained 1140 parts of cashew modified | denatured novolak resins (A). The number average molecular weight of this resin was 1040, and the softening point was 98 ° C.

<Production Example 2>
A 3 L three-necked flask was charged with 1000 parts of a novolak resin “PR-53194” (softening point 90 ° C.) manufactured by Sumitomo Bakelite Co., Ltd. and 10 parts of sulfuric acid, and 400 parts of cashew oil was refluxed at 100 ° C. for 1 hour. I added it. After reacting at 100 ° C. for 1 hour, the mixture was heated to 200 ° C. under reduced pressure distillation at 5000 Pa and reacted for 2 hours to obtain 1250 parts of cashew-modified novolak resin (B). The number average molecular weight of this resin was 870, and the softening point was 92 ° C.

In order to examine the curability of the cashew-modified novolak resin and the polyacetal resin, both resins were mixed and the gelation time, which is an index of the curing rate, was measured.
The measuring method of gelation time is as follows. That is, 1 g of a sample was melted on a hot plate maintained at 165 ° C., and the time until the resin composition did not pull the yarn even when the spatula was lifted while stirring with a spatula was measured. The shorter this time, the faster the curing rate.

<Example 1>
10 parts of the cashew-modified novolak resin A obtained in Production Example 1 was pulverized using a mortar and dry blended with 1 part of a copolymer type polyacetal resin (Tenac C4520 manufactured by Asahi Kasei Co., Ltd., hereinafter referred to as (C)).

<Example 2>
10 parts of cashew-modified novolak resin A obtained in Production Example 1 was pulverized using a mortar, and dry blended with 1 part of a homopolymer type polyacetal resin (Delin 500NC010, hereinafter referred to as (D)) manufactured by DuPont.

<Example 3>
10 parts of the cashew-modified novolak resin obtained in Production Example 2 was pulverized using a mortar and dry blended with 1 part of the copolymer type polyacetal resin (C).

<Example 4>
10 parts of the cashew-modified novolak resin obtained in Production Example 2 was pulverized using a mortar and dry blended with 1 part of a homopolymer type polyacetal resin (D).

Table 1 shows the gel time measurement results.

  Next, using the compounding composition (parts by weight) shown in Table 2, a rubber composition was prepared, and rubber physical properties were measured. As the curing agent, polyacetal resin was used in Examples 5 to 8, and hexamethoxymethylol melamine was used in Comparative Examples 1 to 4.

<Example 5>
10 parts of the cashew-modified novolak resin (A) obtained in Production Example 1, 1 part of the copolymer type polyacetal resin (C), and other components were kneaded with a heating roll at 100 ° C.

<Example 6>
10 parts of the cashew-modified novolak resin (A) obtained in Production Example 1, 1 part of the homopolymer type polyacetal resin (D), and other components were kneaded with a heating roll at 100 ° C.

<Example 7>
10 parts of the cashew-modified novolak resin (B) obtained in Production Example 2, 1 part of the copolymer type polyacetal resin (C), and other components were kneaded with a heating roll at 100 ° C.

<Example 8>
10 parts of the cashew modified novolak resin (B) obtained in Production Example 2, 1 part of the homopolymer type polyacetal resin (D), and other components were kneaded with a heating roll at 100 ° C.

<Comparative Example 1>
10 parts of the cashew-modified novolak resin (A) obtained in Production Example 1, 1 part of hexamethoxymethylolmelamine, and other components were kneaded with a heating roll at 100 ° C.

<Comparative example 2>
10 parts of the cashew-modified novolak resin (A) obtained in Production Example 1, 3 parts of hexamethoxymethylolmelamine, and other components were kneaded with a heating roll at 100 ° C.

<Comparative Example 3>
10 parts of cashew-modified novolak resin (B) obtained in Production Example 2, 1 part of hexamethoxymethylolmelamine, and other components were kneaded with a heating roll at 100 ° C.

<Comparative example 4>
10 parts of cashew-modified novolak resin (B) obtained in Production Example 2, 3 parts of hexamethoxymethylolmelamine, and other components were kneaded with a heating roll at 100 ° C.

(Note to table)
(1) Natural rubber: Tochi Co., Ltd. (2) Carbon black: Mitsubishi Chemical Co., Ltd., HAF
(3) Zinc flower: manufactured by Sakai Chemical Co., Ltd., zinc oxide (4) Vulcanization accelerator: N-oxydiethylene-2-benzothiazole sulfenamide

[Measurement of rubber properties]
Various rubber compositions were vulcanized with a hydraulic press at 180 ° C. for 5 minutes to produce a vulcanized rubber sheet having a thickness of 2 mm. Using this rubber sheet, hardness (JIS, Shore A), 25% tensile modulus, and elastic modulus were measured. The hardness was measured with a durometer manufactured by Toyo Seiki Co., Ltd. The 25% tensile modulus was measured using a strograph manufactured by Toyo Seiki Co., Ltd. at a tensile speed of 50 mm / min. In addition, the elastic modulus was measured by using a DMS6100 manufactured by Seiko Instruments Inc. under the tensile conditions of 60 ° C. and 10 Hz.

Table 3 shows the measurement results.

  As is clear from Table 3, the rubber composition containing the cashew-modified novolak resin of Examples 5 to 8 and the polyacetal resin was compared with the rubber composition containing hexamethoxymethylol melamine of Comparative Examples 1 to 4 as a curing agent. Thus, the hardness, 25% tensile modulus, and elastic modulus were improved.

  Moreover, about the rubber composition obtained in Example 5 and the comparative example 2, the hardening behavior at the time of 180 degreeC vulcanization | cure was measured with Toyo Seiki Co., Ltd. Mooney viscometer AM-3. A graph of these results is shown in FIG. Comparing these graphs, the curing behavior of Example 5 using a polyacetal resin as a curing agent was faster than that of Comparative Example 2 in which hexamethoxymethylol melamine was added as a curing agent in an amount three times (weight ratio) of the polyacetal resin. It was observed to reach

  The phenol resin composition for rubber compounding of the present invention can realize a rubber composition that does not contain a curing agent such as hexamethylenetetramine by containing cashew-modified novolak resin and polyacetal resin as essential components. A rubber composition in which this phenol resin composition for compounding rubber is blended can ensure a sufficient vulcanization speed and is excellent in hardness, elastic modulus and the like, and can be used for tires, packings, gaskets and the like.

It is a graph which shows the result of having measured the hardening behavior of the rubber composition obtained in Example 5 and Comparative Example 2 with the Mooney viscometer.

Claims (5)

A phenolic resin composition for rubber compounding, comprising a modifier novolak-type phenolic resin (a) and a polyacetal resin (b) containing an aliphatic double bond as essential components. The phenol resin composition for rubber compounding according to claim 1, wherein the novolac type phenol resin (a) is one in which an acidic substance which is a reaction catalyst of the resin remains. The phenolic resin composition for rubber blending according to claim 1 or 2, wherein the novolac type phenolic resin (a) is modified with cashew oils. The phenolic resin composition for rubber blending according to claim 2 or 3, wherein the novolac type phenol resin (a) has a reaction catalyst of sulfuric acid. A rubber composition characterized by containing a novolak type phenol resin (a) and a polyacetal resin (b) according to any one of claims 1 to 4 as essential components together with a rubber component.