JP7682160B2 - Rubber Additives - Google Patents

Description

The present invention relates to a rubber additive, a rubber composition, a method for producing a rubber composition, and a rubber molded body and a tire component.

Rubber is an amorphous and soft polymeric substance, mainly composed of organic polymers such as natural rubber and synthetic rubber, and is a material (elastic rubber) with a high elastic limit and low elastic modulus. Taking advantage of such properties of rubber, rubber compositions containing rubber are used in various fields such as tires, sealing materials, and vibration-isolating and vibration-proof materials.
Rubber compositions for tires and the like are blended with inorganic fillers to improve the elastic modulus. In addition, a technique for blending polyesters has been proposed to take advantage of the properties of rubber and to satisfy various required physical properties.

For example, Japanese Patent Laid-Open No. 3-115337 (Patent Document 1) discloses an elastomer composition that contains a vulcanizable rubber component and an aliphatic polyester having an aliphatic diol and a specific aromatic diol as constituent components, as an elastomer composition that is excellent in heat resistance, mechanical properties, and processability in addition to flexibility and elasticity.
Japanese Patent Laid-Open No. 2012-136586 (Patent Document 2) discloses a rubber composition that contains a specific low-polarity diene-based rubber, a specific thermoplastic polyester resin, and a specific high-polarity diene-based rubber in specific proportions as a rubber composition that can achieve high elasticity while suppressing a significant decrease in tensile elongation and ensuring processability.
Japanese Patent Laid-Open No. 2020-2322 (Patent Document 3) discloses a rubber composition having excellent air permeation prevention performance and processability, which contains 5 to 32 parts by mass of polyester per 100 parts by mass of a rubber component consisting of an isobutylene-based rubber and a diene-based rubber.
U.S. Pat. No. 4,327,199 (Patent Document 4) discloses a thermoplastic composition comprising a mixture of about 25 to 98 parts by weight of an acrylic rubber and about 75 to 2 parts by weight of a thermoplastic crystalline polyester per 100 parts by weight of the combined amount of the rubber and the thermoplastic crystalline polyester.

The present invention relates to a rubber additive comprising a polyester which is a polycondensation product of an alcohol component and a carboxylic acid component, in which the content of an aliphatic diol having 2 to 16 carbon atoms in the alcohol component is 85% by mass or more, and the content of an aliphatic dicarboxylic acid compound having 2 to 16 carbon atoms in the carboxylic acid component is 50% by mass or more.

Increasing the amount of inorganic filler in a rubber composition tends to increase heat generation. For example, the techniques of Patent Documents 1 to 4 mentioned above improve the elastic modulus to a certain extent, but are insufficient in terms of heat generation suppression.
The present invention relates to a rubber additive capable of producing a rubber molded article that is resistant to deformation (has a high storage modulus) and has low heat build-up even when deformed (has a small loss tangent), a rubber composition containing the additive, a method for producing the rubber composition, and a rubber molded article and a tire component.

The present inventors have discovered that a rubber additive comprising a polyester, which is a polycondensate of an alcohol component containing a specific aliphatic diol and a carboxylic acid component containing a specific aliphatic dicarboxylic acid compound, can solve the above problems.
That is, the present invention relates to the following [1] to [5].
[1] A rubber additive comprising a polyester which is a polycondensation product of an alcohol component and a carboxylic acid component, wherein the content of an aliphatic diol having 2 to 16 carbon atoms in the alcohol component is 85% by mass or more, and the content of an aliphatic dicarboxylic acid compound having 2 to 16 carbon atoms in the carboxylic acid component is 50% by mass or more.
[2] A rubber composition comprising the rubber additive according to [1] above, a rubber component, and an inorganic filler.
[3] A method for producing a rubber composition, comprising kneading the rubber additive according to [1] above, a rubber component, and an inorganic filler at a temperature of 110°C or higher to obtain a rubber kneaded product, and then adding sulfur to the obtained rubber kneaded product and mixing at a temperature of less than 140°C.
[4] A rubber molded article obtained by vulcanizing the rubber composition described in [2] above.
[5] A tire component using the rubber additive, rubber composition, or rubber molded article.

According to the present invention, it is possible to provide a rubber additive that can produce a rubber molded article that is resistant to deformation (has a high storage modulus) and has low heat generation even when deformed (has a small loss tangent), as well as a rubber composition and a rubber molded article that contain the same.

According to the present invention, it is possible to obtain an additive for rubber that can give a rubber molded article that is less likely to deform and has low heat generation even when deformed. The reason for this is not necessarily clear, but is thought to be as follows.
The polyester constituting the rubber additive of the present invention is obtained by polycondensation of an alcohol component containing an aliphatic diol having from 2 to 16 carbon atoms and a carboxylic acid component containing an aliphatic dicarboxylic acid compound having from 2 to 16 carbon atoms. Here, since the alcohol component and the carboxylic acid component of the polyester are both aliphatic compounds having from 2 to 16 carbon atoms, it is considered that this polyester is incompatible with the rubber component in the rubber composition and rubber molded product contained therein, forms fine crystals, and forms a polyester network in the rubber component.
It is believed that the formation of this polyester network allows the resulting rubber molding to exhibit a high storage modulus, and that the presence of the polyester network, which is not compatible with the rubber component, prevents the loss tangent (tan δ) from becoming large even during deformation, thereby enabling the rubber molding to exhibit low heat buildup.

[Rubber additives]
The rubber additive of the present invention is a rubber additive comprising a polyester which is a polycondensation product of an alcohol component and a carboxylic acid component, in which the content of an aliphatic diol having 2 to 16 carbon atoms in the alcohol component is 85 mass% or more, and the content of an aliphatic dicarboxylic acid compound having 2 to 16 carbon atoms in the carboxylic acid component is 50 mass% or more.
The rubber additive of the present invention can be used in the production of a rubber composition as an additive composition mixed with various additives, such as a silane coupling agent, an antiaging agent, a scorch inhibitor, a softener, stearic acid, process oil, etc., as necessary.

(Aliphatic diol)
From the viewpoint of improving the storage modulus and reducing tan δ of the resulting rubber molded article, the alcohol component of the polyester according to the present invention contains 85% by mass or more of an aliphatic diol having 2 to 16 carbon atoms in the alcohol component. If the content of the aliphatic diol having 2 to 16 carbon atoms in the alcohol component is less than 85% by mass, the storage modulus of the resulting rubber molded article is not sufficiently improved and tan δ cannot be reduced, which is not preferable.
The content of the aliphatic diol having 2 to 16 carbon atoms in the alcohol component is preferably 90% by mass or more, more preferably 92% by mass or more, even more preferably 95% by mass or more, and still more preferably substantially 100% by mass.

The chain hydrocarbon group in the aliphatic diol may be linear or branched, but from the viewpoint of improving the storage modulus and decreasing tan δ of the resulting rubber molded article, it is preferable that it is a linear hydrocarbon group, and the hydroxy group is preferably located at the end of the hydrocarbon chain.
That is, the aliphatic diol is preferably a linear alkanediol having 2 to 16 carbon atoms, and more preferably an α,ω-linear alkanediol having 2 to 16 carbon atoms.
From the same viewpoints as above, the carbon number of the aliphatic diol is 2 or more, preferably 4 or more, more preferably 6 or more, and even more preferably 8 or more, and from the viewpoint of improving the crystallinity of the polyester in the rubber composition and the rubber molded product, the carbon number is 16 or less, preferably 14 or less, and more preferably 12 or less.

Aliphatic diols having 2 to 16 carbon atoms, particularly α,ω-straight-chain alkanediols having 2 to 16 carbon atoms, include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, etc. Among these, one or more selected from ethylene glycol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, and 1,12-dodecanediol are preferred, one or more selected from ethylene glycol and 1,12-dodecanediol are more preferred, and 1,12-dodecanediol is even more preferred.

The alcohol component may contain an alcohol other than the aliphatic diol having 2 to 16 carbon atoms, provided that the object of the present invention is not impaired. Examples of the alcohol component other than the aliphatic diol having 2 to 16 carbon atoms include aromatic diols such as alkylene oxide adducts of bisphenol A, trihydric or higher polyhydric alcohols such as glycerin, pentaerythritol, and trimethylolpropane, and monohydric alcohols.
The above alcohol components may be used alone or in combination of two or more kinds.

(Aliphatic dicarboxylic acid compound)
The carboxylic acid component of the polyester according to the present invention contains 50 mass % or more of an aliphatic dicarboxylic acid compound having 2 to 16 carbon atoms in the carboxylic acid component, from the viewpoint of improving the storage modulus and reducing tan δ of the obtained rubber molded body.
The content of the aliphatic dicarboxylic acid compound having 2 to 16 carbon atoms in the carboxylic acid component is preferably 60 mass% or more, more preferably 70 mass% or more, even more preferably 80 mass% or more, still more preferably 90 mass% or more, and even more preferably substantially 100 mass%.

The chain hydrocarbon group in the aliphatic dicarboxylic acid compound may be linear or branched, but from the viewpoint of improving the storage modulus and reducing tan δ of the resulting rubber molded article, it is preferable that it is a linear hydrocarbon group, and the carboxy group is preferably located at the end of the hydrocarbon chain.
That is, the aliphatic dicarboxylic acid compound is preferably a straight-chain aliphatic dicarboxylic acid having 2 to 16 carbon atoms, and more preferably an α,ω-straight-chain aliphatic dicarboxylic acid having 2 to 16 carbon atoms.
From the same viewpoints as above, the number of carbon atoms in the aliphatic dicarboxylic acid compound is 2 or more, preferably 4 or more, more preferably 6 or more, and even more preferably 10 or more, and is 16 or less, preferably 14 or less, and more preferably 12 or less.

Examples of aliphatic dicarboxylic acid compounds having from 2 to 16 carbon atoms, particularly α,ω-linear aliphatic dicarboxylic acids having from 2 to 16 carbon atoms, include succinic acid (carbon number: 4), fumaric acid (carbon number: 4), sebacic acid (carbon number: 10), dodecanedioic acid (carbon number: 12), tetradecanedioic acid (carbon number: 14), hexadecanedioic acid (carbon number: 16), and succinic acid having an alkyl group or alkenyl group on the side chain, and examples of aliphatic dicarboxylic acid compounds include their acid anhydrides and their alkyl esters having from 1 to 3 carbon atoms. Among these, one or more selected from sebacic acid, dodecanedioic acid, tetradecanedioic acid, and hexadecanedioic acid are preferred, one or more selected from dodecanedioic acid and tetradecanedioic acid are more preferred, and dodecanedioic acid is even more preferred.
In the present invention, the carboxylic acid component includes not only free acids but also anhydrides that decompose during the reaction to generate acids, and alkyl esters having from 1 to 3 carbon atoms, provided that the number of carbon atoms in the alkyl ester moiety is not included in the number of carbon atoms in the aliphatic dicarboxylic acid compound.

The carboxylic acid component may contain other carboxylic acid compounds other than aliphatic dicarboxylic acid compounds having 2 to 16 carbon atoms, as long as the object of the present invention is not impaired. Examples of other carboxylic acid compounds include aromatic dicarboxylic acid compounds such as terephthalic acid and isophthalic acid, trivalent or higher polyvalent carboxylic acid compounds such as trimellitic acid and pyromellitic acid, and monovalent carboxylic acid compounds.

The total content of the aliphatic diol having 2 to 16 carbon atoms and the aliphatic dicarboxylic acid compound having 2 to 16 carbon atoms is preferably 85% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably substantially 100% by mass, in the raw material monomers for the polyester.

In addition, the content of the aliphatic dicarboxylic acid compound having 2 to 16 carbon atoms per 100 moles of aliphatic diol is preferably 75 moles or more, more preferably 85 moles or more, even more preferably 95 moles or more, and is preferably 115 moles or less, more preferably 110 moles or less, even more preferably 105 moles or less.

(Production of polyester)
The polyester according to the present invention can be produced by a known method. For example, the polycondensation reaction between the alcohol component and the carboxylic acid component can be carried out in an inert gas atmosphere, in the presence of an esterification catalyst, an esterification promoter, a polymerization inhibitor, etc., if necessary, at a temperature of preferably 160° C. to 240° C., more preferably 190° C. to 230° C.
Examples of the esterification catalyst include tin catalysts, titanium catalysts, and metal compounds such as antimony trioxide, zinc acetate, and germanium dioxide. From the viewpoint of the reaction efficiency of the esterification, preferred are tin compounds such as dibutyltin oxide and tin(II) 2-ethylhexanoate, and titanium compounds such as titanium diisopropylate bistriethanolaminate.
The amount of the esterification catalyst used is preferably 0.01 parts by mass or more and 1.5 parts by mass or less, and more preferably 0.1 parts by mass or more and 1.0 parts by mass or less, based on 100 parts by mass of the total amount of the alcohol component and the carboxylic acid component.

The esterification promoter is preferably a pyrogallol compound, and specific examples thereof include pyrogallol, gallic acid, gallic acid esters, benzophenone derivatives, and catechin derivatives, with gallic acid being preferred from the viewpoint of reactivity.
The amount of the esterification promoter used is preferably 0.001 part by mass or more and 0.5 part by mass or less, and more preferably 0.01 part by mass or more and 0.1 part by mass or less, based on 100 parts by mass of the total amount of the alcohol component and the carboxylic acid component.
The polymerization inhibitor may, for example, be tert-butylcatechol.
The amount of the polymerization inhibitor used is preferably 0.001 parts by mass or more and 0.5 parts by mass or less, and more preferably 0.01 parts by mass or more and 0.1 parts by mass or less, based on 100 parts by mass of the total amount of the alcohol component and the carboxylic acid component.

From the viewpoint of improving the storage modulus and reducing tan δ of the obtained rubber molded article, the weight average molecular weight of the polyester according to the present invention is preferably 3,000 or more, more preferably 5,000 or more, even more preferably 6,000 or more, still more preferably 7,000 or more, and is preferably 100,000 or less, more preferably 50,000 or less, even more preferably 40,000 or less, still more preferably 30,000 or less, and still more preferably 20,000 or less.
From the viewpoint of improving the storage modulus and reducing tan δ of the resulting rubber molded article, the melting point of the polyester according to the present invention is preferably 60° C. or higher, more preferably 70° C. or higher, and even more preferably 75° C. or higher, and is preferably 150° C. or lower, more preferably 120° C. or lower, and even more preferably 110° C. or lower.
The weight average molecular weight and melting point of the polyester can be measured by the method described in the examples.

The polyester according to the present invention may be a modified polyester which has been modified to such an extent that its properties are not substantially impaired. Examples of the modified polyester include urethane-modified polyester in which polyester is modified with a urethane bond, epoxy-modified polyester in which polyester is modified with an epoxy bond, and composite resin having two or more resin components including a polyester component and an addition polymerization resin component.
The polyester according to the present invention preferably contains 98% by mass or more of polyester moieties, more preferably consists essentially of polyester moieties, and further preferably consists of polyester moieties only.

[Rubber composition]
The rubber composition of the present invention contains a rubber additive comprising the polyester of the present invention, and a rubber component, and preferably further contains an inorganic filler.
<Rubber additives>
The rubber additive of the present invention is as described above.

<Rubber component>
The rubber component used in the present invention is not particularly limited, and natural rubber and synthetic rubber can be used. Among these, one or more types selected from natural rubber and diene-based synthetic rubber are preferred from the viewpoints of abrasion resistance, availability, etc.
Examples of natural rubber include SMR, SIR, STR, and RSS, with SMR20, STR20, RSS#3, RSS#4, and the like being preferred.
Natural rubber can be used after being modified. Examples of modified natural rubber include epoxidized natural rubber and hydrogenated natural rubber.
Examples of diene-based synthetic rubbers include polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), chloroprene rubber, and butyl rubber.

Among these, from the viewpoints of abrasion resistance, availability, etc., one or more selected from natural rubber, modified natural rubber, IR, BR, SBR, and NBR are preferred, and one or more selected from BR, SBR, and natural rubber are more preferred. BR or SBR can also be used in combination with natural rubber.
The copolymer rubber may be a block copolymer or a random copolymer, but from the viewpoint of improving the storage modulus and decreasing tan δ of the resulting rubber molded article, a random copolymer is preferred.
The rubber components may be used alone or in combination of two or more kinds.

<Inorganic filler>
The inorganic filler used in the present invention is not particularly limited, and examples thereof include silica, carbon black, etc. Furthermore, alumina, calcium carbonate, clay, talc, zeolite, diatomaceous earth, etc. may also be used as necessary.

(silica)
The silica to be used is not particularly limited, and examples thereof include wet silica, dry silica, colloidal silica, etc. Among these, wet silica mainly composed of hydrated silicic acid is preferred. The wet silica includes precipitated silica, gel silica, and sol-gel silica, and precipitated silica is more preferred.
The BET specific surface area of the silica (measured in accordance with ISO 5794/1) is, from the viewpoints of dispersibility in the rubber composition and rubber molded article and rubber reinforcement, preferably 50 m ² /g or more, more preferably 100 m ² /g or more, even more preferably 150 m ² /g or more, and preferably 350 m ² /g or less, more preferably 300 m ² /g or less, even more preferably 250 m ² /g or less.
From the viewpoints of dispersibility in the rubber composition and the rubber molded product and rubber reinforcement, the average secondary particle size of the silica is preferably 10 μm or more, more preferably 15 μm or more, even more preferably 18 μm or more, and is preferably 100 μm or less, more preferably 80 μm or less, even more preferably 50 μm or less.

Examples of commercially available silica products include products manufactured by Tosoh Silica Corporation under the trade names of Nipsil AQ (BET specific surface area: 205 ^m2 /g) and Nipsil KQ (BET specific surface area: 240 ^m2 /g), and products manufactured by Evonik under the trade name of Ultrasil VN3 (BET specific surface area: 175 ^m2 /g).

(Carbon Black)
The carbon black to be used is not particularly limited, and examples thereof include carbon black of grades such as SAF, ISAF, IISAF, N339, HAF, FEF, GPF, SRF, etc., with high, medium, or low structure, as well as carbon and silica dual phase fillers in which silica is supported on the surface of carbon black, etc. Among these, carbon black of grades SAF, ISAF, IISAF, N339, HAF, and FEF are preferred.
The DBP absorption of carbon black (measured in accordance with ASTM D2414-65T) is preferably 70 cm ³ /100 g or more, more preferably 80 cm ³ /100 g or more, and even more preferably 90 cm ³ /100 g or more.
The nitrogen adsorption specific surface area (N ₂ AS, measured in accordance with JIS K 6217-2:2017) of the carbon black is preferably 50 m ² /g or more, more preferably 60 m ² /g or more, and even more preferably 70 m ² /g or more.

<Other ingredients>
In addition to the above-mentioned components, the rubber composition of the present invention may contain, if desired, various additives usually used in the rubber industry, such as a silane coupling agent, an antioxidant, a scorch inhibitor, a softener, stearic acid, process oil, zinc oxide, a vulcanizing agent, and a vulcanization accelerator, within the scope of the object of the present invention.
The silane coupling agent can be used from the viewpoint of reducing heat generation of the obtained rubber molded article. Preferred examples of the silane coupling agent include polysulfide-based silane coupling agents.
The silane coupling agents can be used alone or in combination of two or more kinds.
Examples of commercially available silane coupling agents include Si75 and Si69 manufactured by Evonik Co., Ltd., KBE-846 manufactured by Shin-Etsu Chemical Co., Ltd., and Kabras 2A, Kabras 2B, and Kabras 4 manufactured by Daiso Co., Ltd.

[Method of manufacturing rubber composition]
The rubber composition of the present invention can be produced by blending the rubber additive comprising the polyester of the present invention, a rubber component, and, if necessary, an inorganic filler, and further blending the various additives described above, if necessary. More specifically, for example, a method can be mentioned in which the components described above are kneaded preferably at 110° C. or higher to obtain a rubber kneaded product, and then sulfur is added and mixed into the obtained rubber kneaded product.
That is, the method for producing a rubber composition of the present invention is a method of kneading a rubber additive comprising a polyester which is a polycondensate of an alcohol component and a carboxylic acid component, wherein the alcohol component has an aliphatic diol content of 2 to 16 carbon atoms of 85 mass% or more and the carboxylic acid component has an aliphatic dicarboxylic acid compound content of 2 to 16 carbon atoms of 50 mass% or more, one or more rubber components selected from natural rubber, modified natural rubber, IR, BR, SBR, and NBR, and an inorganic filler at a temperature of 110°C or more to obtain an unvulcanized rubber kneaded product, and then adding sulfur to the obtained unvulcanized rubber kneaded product and mixing at a temperature of less than 140°C.
From the viewpoint of preventing a vulcanization reaction, the temperature at which sulfur is added and mixed is preferably less than 140° C., more preferably 130° C. or less, even more preferably 125° C. or less, and still more preferably 120° C. or less. In addition to sulfur, a vulcanization accelerator and the like can be added as necessary and mixed with the rubber kneaded product to obtain an unvulcanized rubber composition.
The resulting unvulcanized rubber composition can be molded by a known method and vulcanized by heating or heating and pressurizing, as described below, to form a rubber molded article.
The content of each component in the rubber composition will be described below, and the content means both the total amount and the blending amount.

<Content of each ingredient>
In the rubber composition of the present invention, the content of the rubber additive consisting of polyester is, from the viewpoint of improving the storage modulus and reducing tan δ of the obtained rubber molded body, preferably 1 part by mass or more, more preferably 1.8 parts by mass or more, even more preferably 2.5 parts by mass or more, and even more preferably 4 parts by mass or more, per 100 parts by mass of the rubber component, and from the viewpoint of maintaining the physical properties of the rubber component, preferably 30 parts by mass or less, more preferably 22 parts by mass or less, even more preferably 18 parts by mass or less, and even more preferably 12 parts by mass or less.

From the viewpoint of maintaining the physical properties of the rubber component, the content of the rubber component in the rubber composition consisting of the rubber additives, the rubber component and the inorganic filler is preferably 30% by mass or more, more preferably 35% by mass or more, even more preferably 40% by mass or more, still more preferably 45% by mass or more, and is preferably 80% by mass or less, more preferably 70% by mass or less, even more preferably 65% by mass or less, still more preferably 60% by mass or less.

The content of the inorganic filler is preferably 30 parts by mass or more, more preferably 35 parts by mass or more, even more preferably 40 parts by mass or more, and even more preferably 45 parts by mass or more, per 100 parts by mass of the rubber component, from the viewpoint of improving the abrasion resistance, etc., of the obtained rubber molded body, and is preferably 200 parts by mass or less, more preferably 180 parts by mass or less, even more preferably 150 parts by mass or less, even more preferably 100 parts by mass or less, and even more preferably 80 parts by mass or less, from the viewpoint of reducing the heat generation property of the rubber molded body.

When a silane coupling agent is contained in the rubber composition, the content of the silane coupling agent is, from the viewpoint of reducing the heat generation properties of the obtained rubber molded body, preferably 1 part by mass or more, more preferably 2 parts by mass or more, even more preferably 4 parts by mass or more, and preferably 15 parts by mass or less, more preferably 13 parts by mass or less, even more preferably 10 parts by mass or less, per 100 parts by mass of inorganic filler.

[Rubber Molded Body]
The rubber molded article of the present invention is obtained by vulcanizing the unvulcanized rubber composition of the present invention.
The unvulcanized rubber composition can be molded by a known method and heated or heated and pressurized at a temperature of preferably 140° C. or higher, more preferably 145° C. or higher, and preferably 200° C. or lower, more preferably 180° C. or lower, to form a vulcanized rubber molded article.
The contents and preferred ranges of the rubber additive comprising polyester, the rubber component and the inorganic filler in the rubber molded product are the same as those in the rubber composition.
The obtained rubber molded article has excellent low heat build-up properties, abrasion resistance, and the like, and can therefore be suitably used as rubber molded articles for tire components such as tires, tire inner liners, treads, tread bases, carcasses, sidewalls, and bead portions, as well as various rubber belts, various sealing materials, vibration isolating and anti-vibration materials, shoe soles, and the like.

[Tire components]
The tire member of the present invention is formed using the rubber additive of the present invention, the rubber composition of the present invention, or the rubber molded article of the present invention.
The rubber additive, rubber composition, and rubber molded product of the present invention are as described above.

With respect to the above-described embodiment, the present invention further discloses the following <1> to <23>.
<1> A rubber additive comprising a polyester which is a polycondensate of an alcohol component and a carboxylic acid component, wherein the alcohol component contains an aliphatic diol having from 2 to 16 carbon atoms in an amount of 85% by mass or more, and the carboxylic acid component contains an aliphatic dicarboxylic acid compound having from 2 to 16 carbon atoms in an amount of 50% by mass or more.

<2> The rubber additive according to <1>, wherein the aliphatic diol is a linear alkane diol having 2 to 16 carbon atoms, and the aliphatic dicarboxylic acid compound is a linear aliphatic dicarboxylic acid having 2 to 16 carbon atoms.
<3> The rubber additive according to <1>, wherein the aliphatic diol is a linear alkane diol having 4 to 14 carbon atoms, and the aliphatic dicarboxylic acid compound is a linear aliphatic dicarboxylic acid having 2 to 16 carbon atoms.
<4> The rubber additive according to <1>, wherein the aliphatic diol is a linear alkane diol having 6 to 12 carbon atoms, and the aliphatic dicarboxylic acid compound is a linear aliphatic dicarboxylic acid having 2 to 16 carbon atoms.
<5> The rubber additive according to <1>, wherein the aliphatic diol is a linear alkane diol having 2 to 16 carbon atoms, and the aliphatic dicarboxylic acid compound is a linear aliphatic dicarboxylic acid having 4 to 14 carbon atoms.
<6> The rubber additive according to <1>, wherein the aliphatic diol is a linear alkane diol having 2 to 16 carbon atoms, and the aliphatic dicarboxylic acid compound is a linear aliphatic dicarboxylic acid having 6 to 12 carbon atoms.
<7> The rubber additive according to <1>, wherein the aliphatic diol is a linear alkane diol having 6 to 12 carbon atoms, and the aliphatic dicarboxylic acid compound is a linear aliphatic dicarboxylic acid having 6 to 12 carbon atoms.

<8> The rubber additive according to any one of <2> to <7>, wherein the linear alkanediol is an α,ω-linear alkanediol.
<9> The rubber additive according to any one of <2> to <8>, wherein the linear aliphatic dicarboxylic acid is an α,ω-linear aliphatic dicarboxylic acid.
<10> The rubber additive according to <1>, wherein the aliphatic diol is a linear alkane diol having 2 to 16 carbon atoms, the aliphatic dicarboxylic acid compound is a linear aliphatic dicarboxylic acid having 2 to 16 carbon atoms, and the weight average molecular weight of the polyester is 5,000 to 50,000.
<11> The rubber additive according to <1>, wherein the aliphatic diol is a linear alkane diol having 2 to 16 carbon atoms, the aliphatic dicarboxylic acid compound is a linear aliphatic dicarboxylic acid having 2 to 16 carbon atoms, and the weight average molecular weight of the polyester is 5,000 to 30,000.
<12> The rubber additive according to <1>, wherein the aliphatic diol is a linear alkane diol having 6 to 12 carbon atoms, the aliphatic dicarboxylic acid compound is a linear aliphatic dicarboxylic acid having 6 to 12 carbon atoms, and the weight average molecular weight of the polyester is 5,000 to 30,000.
<13> The rubber additive according to <1>, wherein the aliphatic diol is an α,ω-linear alkanediol having 6 to 12 carbon atoms, the aliphatic dicarboxylic acid compound is an α,ω-linear aliphatic dicarboxylic acid having 6 to 12 carbon atoms, and the weight average molecular weight of the polyester is 5,000 to 30,000.
<14> Use of a polyester which is a polycondensate of an alcohol component and a carboxylic acid component, in which the content of an aliphatic diol having from 2 to 16 carbon atoms in the alcohol component is 85% by mass or more, and the content of an aliphatic dicarboxylic acid compound having from 2 to 16 carbon atoms in the carboxylic acid component is 50% by mass or more, as a rubber additive.

<15> A rubber composition comprising the rubber additive according to any one of <1> to <13> above, and a rubber component.
<16> The rubber composition according to <15>, further comprising an inorganic filler.
<17> The rubber composition according to <15> or <16>, wherein the rubber component is at least one selected from the group consisting of natural rubber and diene-based synthetic rubber.
<18> The rubber composition according to any one of <15> to <17>, wherein the content of the rubber additive is 1 part by mass or more and 30 parts by mass or less per 100 parts by mass of the rubber component.
<19> A method for producing a rubber composition, comprising kneading the rubber additive according to any one of <1> to <13>, a rubber component, and an inorganic filler at a temperature of 110°C or higher to obtain a rubber kneaded product, and then adding sulfur to the obtained rubber kneaded product and mixing them at a temperature of less than 140°C.
<20> A rubber molded article obtained by vulcanizing the rubber composition according to any one of <15> to <18>.
<21> A tire member using the rubber additive according to any one of <1> to <13>.
<22> A tire member using the rubber composition according to any one of <15> to <18>.
<23> A tire member using the rubber molded article according to <20>.

<Measurement of Weight Average Molecular Weight of Polyester>
The molecular weight distribution was measured by the following gel permeation chromatography (GPC) method to determine the weight average molecular weight (Mw) of the polyester.
(1) Preparation of a sample solution The polymer was dissolved in chloroform so that the concentration was 0.5 g/100 mL. Next, this solution was filtered using a fluororesin filter (manufactured by Sumitomo Electric Industries, Ltd., product name: FP-200) with a pore size of 2 μm to remove insoluble components, and a sample solution was obtained.
(2) Using a molecular weight measuring device (manufactured by Tosoh Corporation, product name: CO-8010, analytical column: GMHXL + G3000HXL), chloroform was passed as an eluent at a flow rate of 1 ml per minute, and the column was stabilized in a thermostatic bath at 40 ° C. 100 μl of sample solution was injected therein for measurement. The molecular weight of the sample was calculated based on a calibration curve prepared in advance. For the calibration curve at this time, several types of monodisperse polystyrene (monodisperse polystyrene manufactured by Tosoh Corporation; 2.63 × 10 ³ , 2.06 × 10 ⁴ , 1.02 × 10 ⁵ , monodisperse polystyrene manufactured by GL Sciences Inc.; 2.10 × 10 ³ , 7.00 × 10 ³ , 5.04 × 10 ⁴ (number average molecular weight)) were used as standard samples.

<Measurement of Melting Point of Polyester>
Using a differential scanning calorimeter (manufactured by TA Instruments, product name: Q-100), the sample was cooled from room temperature (20° C.) to 0° C. at a temperature drop rate of 10° C./min, allowed to stand for 1 minute, and then heated to 180° C. at a temperature increase rate of 10° C./min, while measuring the melting point. The temperature of the highest endothermic peak observed was taken as the melting point of the polyester.

Production Examples 1 to 7 and Production Example 8 (Comparative Production Example) (Production of Polyesters A to G and H)
The raw material monomers shown in Table 1, 20 g of tin (II) 2-ethylhexanoate, and 5 g of tert-butylcatechol were placed in a 10 L four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer, and a thermocouple, and the mixture was maintained at 140° C. for 6 hours, heated to 200° C. over a period of 6 hours, and reacted at 200° C. for 1 hour and then at 8.3 kPa for 1 hour to obtain polyesters A to G and H. The results are shown in Table 1.

Details of each component shown in Table 1 are as follows.
[Alcohol content]
EG: Ethylene glycol 1,2-PD: 1,2-propanediol 1,12-DD: 1,12-dodecanediol GLY: Glycerin [carboxylic acid component]
DDA: Dodecanedioic acid TDDA: Tetradecanedioic acid TPA: Terephthalic acid TMA: Trimellitic acid

Examples 1 to 10, 12, Reference Examples 11, 1, and Comparative Examples 1 to 2
The raw material components shown in Table 2 were prepared, and the components except for zinc oxide, sulfur, and vulcanization accelerator were kneaded for 4 minutes at a maximum temperature of 150°C using a Banbury mixer according to the compounding recipe shown in Table 2. Next, zinc oxide, sulfur, and vulcanization accelerator were added, and kneaded for 2 minutes at a maximum temperature of 110°C to obtain an unvulcanized rubber composition.
The resulting unvulcanized rubber composition was heated at 160° C. for 30 minutes to obtain a sheet-like vulcanized rubber molding.

Details of each component shown in Table 2 are as follows.
[Rubber component]
*1: Emulsion-polymerized SBR manufactured by Nippon Zeon Co., Ltd., product name: NIPOL 1502, styrene content 23.5% by mass
〔polyester〕
*2: Polyesters A to G and H obtained in Production Examples 1 to 7 and Production Example 8 (Comparative Production Example)
〔silica〕
*3: Manufactured by Tosoh Silica Corporation, product name: Nipsil AQ, BET specific surface area 205 m ² /g
[Carbon Black]
*4: HAF, manufactured by Tokai Carbon Co., Ltd., product name: Seast 3, DBP absorption: 101 cm ³ /100 g, N ₂ AS: 79 m ² /g
[Polysulfide-based silane coupling agents]
*5: Bis(3-triethoxysilylpropyl)tetrasulfide, manufactured by Evonik, trade name: Si69

〔others〕
*8: N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name: Nocrac 6C
*9: Kao Corporation, product name: Lunac S-70V
*10: Naphthenic process oil, manufactured by Nippon San Oil Co., Ltd., product name: SUNTHENE 410
*11: Zinc oxide (first grade), manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.
*12: Sulfur (powder, chemical grade), manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.
*13: Sulfenamide vulcanization accelerator, N-cyclohexyl-2-benzothiazolyl sulfenamide, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., product name: Noccela CZ-G
*14: Guanidine vulcanization accelerator, 1,3-diphenylguanidine, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., product name: Noccelaer D

<Measurement of storage modulus (G') and loss tangent (tan δ)>
The storage modulus (G') and loss tangent (tan δ) of the obtained sheet-like rubber molding were measured using a viscoelasticity measuring device (TA Instruments, ARES-G2) under conditions of a temperature of 50°C, a dynamic strain of 5%, and a frequency of 10 Hz. The results are shown in Table 2.
In Table 2, the storage modulus and loss tangent of the crosslinked rubber of Comparative Example 1 are shown as relative values, assuming that they are 100.
A larger relative value of the storage modulus (G') indicates a larger storage modulus, higher block rigidity when used in a tire, and more excellent vehicle handling stability.
If the relative value of the storage modulus (G') of the crosslinked rubber is 102 or more, it is usable in practice, preferably 108 or more, and more preferably 110 or more.
Also, the smaller the relative value of tan δ, the smaller the rolling resistance of the tire when used in a tire, the smaller the heat generation, and the more excellent the fuel economy.
If the relative value of the loss tangent (tan δ) of the crosslinked rubber is 108 or less, it is sufficient for practical use.

From Table 2, it can be seen that the rubber molded articles obtained in Examples 1 to 10 and 12 of the present invention do not show a large increase in loss tangent (tan δ) with respect to an increase in storage modulus (G') compared to the rubber molded articles obtained in Reference Example 1 and Comparative Examples 1 and 2, and the rubber molded articles are less likely to deform and have low heat buildup even when deformed.

According to the present invention, it is possible to provide a rubber additive capable of obtaining a rubber molded article that is resistant to deformation (has a high storage modulus) and has low heat generation even when deformed (has a low loss tangent), a rubber composition containing the additive, a method for producing the rubber composition, and a rubber molded article and a tire component. The obtained rubber molded article and the like can be particularly suitably used for various tires for passenger cars, small and medium trucks, and large vehicles (large trucks, buses, construction vehicles, etc.), tire components such as tire treads, as well as various rubber belts, various sealing materials, vibration-isolating and vibration-proof materials, shoe soles, etc.

Claims (15)

The rubber additive comprises a polyester which is a polycondensate of an alcohol component and a carboxylic acid component, wherein the content of an aliphatic diol having 2 to 16 carbon atoms in the alcohol component is 100 mass%, and the content of an aliphatic dicarboxylic acid compound having 6 to 16 carbon atoms in the carboxylic acid component is 50 mass% or more. The rubber additive according to claim 1, wherein the aliphatic diol is an α,ω-linear alkanediol having 2 to 16 carbon atoms. 3. The rubber additive according to claim 1, wherein the aliphatic dicarboxylic acid compound is an α,ω-straight-chain aliphatic dicarboxylic acid having 6 to 16 carbon atoms. The rubber additive according to any one of claims 1 to 3, wherein the weight average molecular weight of the polyester is 3,000 or more and 100,000 or less. The rubber additive according to any one of claims 1 to 4, wherein the melting point of the polyester is 60°C or higher and 150°C or lower. A rubber composition containing the rubber additive according to any one of claims 1 to 5 and a rubber component. The rubber composition according to claim 6, further comprising an inorganic filler. The rubber composition according to claim 6 or 7, wherein the rubber component is at least one selected from natural rubber and diene-based synthetic rubber. The rubber composition according to any one of claims 6 to 8, wherein the content of the rubber additive is 1 part by mass or more and 30 parts by mass or less per 100 parts by mass of the rubber component. A method for producing a rubber composition, comprising kneading the rubber additive according to any one of claims 1 to 5, a rubber component, and an inorganic filler at a temperature of 110°C or higher to obtain a rubber mixture, and then adding sulfur to the obtained rubber mixture and mixing at a temperature of less than 140°C. A rubber molded article obtained by vulcanizing the rubber composition according to any one of claims 6 to 9. A tire component using the rubber additive according to any one of claims 1 to 5. A tire component using the rubber composition according to any one of claims 6 to 9. A tire component using the rubber molded article according to claim 11. Use of the rubber composition according to any one of claims 6 to 9 as a tire component.