JP7172098B2 - pneumatic tire - Google Patents

Description

The present invention relates to a pneumatic tire having a reinforcing layer.

Pneumatic tires have reinforcing layers typified by carcass layers, breaker layers, band layers, etc. Such reinforcing layers are formed by coating steel cords or organic fiber cords with a rubber composition and press-vulcanizing them. obtained by

It is known to use cellulose fiber cords, which are organic fibers, as the cords used in the reinforcing layer (Patent Document 1). However, although cellulose fiber cords are effective from the viewpoint of utilization of recycled resources, they are not necessarily good from the viewpoint of environmental load because carbon disulfide is used in the production of raw materials.

On the other hand, polyethylene terephthalate fibers (PET fibers) do not use carbon disulfide during production, so they are good from the standpoint of environmental load and have high strength.

JP 2014-189212 A

However, PET fibers are temperature dependent and tend to generate heat. Therefore, when PET fibers are used as cords for reinforcing layers of tires, the rubber composition covering them is desired to have low heat build-up. In addition, it is desired that such a cord coating rubber composition should also have excellent bending fatigue resistance and adhesiveness as inherent properties.

In view of the above problems, the present invention provides a pneumatic tire comprising a reinforcing layer in which PET fibers are coated with a rubber composition having low heat build-up, excellent bending fatigue resistance, and adhesiveness. for the purpose.

As a result of intensive studies, the present inventors have found that, in a pneumatic tire having a reinforcing layer, the organic fiber cord composed of PET fibers of the reinforcing layer is a rubber composition containing a rubber component and a predetermined liquid diene-based polymer. The inventors have found that the above problems can be solved by coating with, and have completed the present invention after further studies.

That is, the present invention
[1] A pneumatic tire comprising a reinforcing layer formed by arranging organic fiber cords,
The organic fiber cord is composed of polyethylene terephthalate fiber,
The reinforcing layer is formed by coating an organic fiber cord with a rubber composition,
The rubber composition comprises a rubber component and a liquid diene polymer,
A pneumatic tire in which the liquid diene-based polymer has a number average molecular weight of 25,000 or more and 100,000 or less,
[2] The liquid diene-based polymer is at least one selected from the group consisting of a liquid butadiene polymer, a liquid isoprene polymer, a liquid styrene-butadiene copolymer, a liquid styrene-isoprene copolymer and a liquid isoprene-butadiene copolymer. The pneumatic tire according to [1] above,
[3] The pneumatic tire according to [1] or [2] above, wherein the content of the liquid diene-based polymer is 0.1 to 20 parts by mass with respect to 100 parts by mass of the rubber component;
[4] The pneumatic tire according to any one of [1] to [3] above, wherein the rubber component contains 20 to 100% by mass of isoprene rubber and 0 to 80% by mass of styrene-butadiene rubber;
[5] The pneumatic tire according to any one of [1] to [4] above, wherein the reinforcing layer is at least one selected from the group consisting of a carcass layer, a breaker layer and a band layer;
Regarding.

According to the present invention, it is possible to provide a pneumatic tire comprising a reinforcing layer in which PET fibers are coated with a rubber composition having low heat build-up and excellent bending fatigue resistance and adhesiveness. .

It is an example of a partial cross-sectional view of a pneumatic tire.

One embodiment is a pneumatic tire comprising a reinforcing layer formed by arranging organic fiber cords, wherein the organic fiber cords are made of polyethylene terephthalate fibers, and the reinforcing layer is an organic A fiber cord is coated with a rubber composition (rubber composition for cord coating), the rubber composition contains a rubber component and a liquid diene-based polymer, and the number average of the liquid diene-based polymer is The pneumatic tire has a molecular weight of 25,000 or more and 100,000 or less.

Although it is not intended to be bound by theory, by using a predetermined liquid diene-based polymer, it is possible to obtain a rubber composition for covering cords that has low heat build-up, excellent bending fatigue resistance, and excellent adhesiveness. Possible mechanisms are as follows. That is, in the present embodiment, the liquid diene-based polymer is similar in structure to the rubber that constitutes the rubber component compared to the oil used for the same purpose, so it is easier to mix with the rubber. In addition, since it has a relatively low molecular weight, it easily enters between the molecules of the rubber component. Therefore, it has the characteristic of being easily dispersed in the rubber component without forming a sea-island state with the rubber component. Since the liquid diene-based polymer is cured by vulcanization, the hardening of the liquid diene-based polymer dispersed in the rubber component strengthens the network in the rubber and improves bending fatigue resistance and adhesiveness. It is presumed that heat buildup is reduced by suppressing the movement of molecular chains in the rubber. Furthermore, since the liquid diene-based polymer has a lower glass transition temperature than the oil, it is considered that this point also contributes to the decrease in heat build-up, resistance to bending fatigue, and improvement in adhesiveness.

The liquid diene-based polymer has a number average molecular weight of 25,000 or higher. It is believed that the improvement in bending fatigue resistance and the reduction in adhesion and heat build-up are further enhanced.

<Reinforcing layer>
In the present embodiment, the reinforcing layer is not particularly limited, and may be any reinforcing layer in a pneumatic tire. FIG. 1 shows an example of a partial cross section of a pneumatic tire. Here, the carcass layer 4, the breaker layer 5 and the band layer 6 are representative reinforcing layers of a pneumatic tire.

The reinforcing layer according to the present embodiment is formed by arranging a plurality of organic fiber cords and covering them with a covering rubber composition. As described above, the reinforcing layer according to the present embodiment may be any reinforcing layer in the pneumatic tire. , preferably a carcass layer.

<Organic fiber cord>
The organic fiber cord of this embodiment is made of polyethylene terephthalate fiber (PET fiber) from the viewpoint of steering stability during high-speed running.

From the viewpoint of sufficient durability, the organic fiber cord preferably has a breaking strength of 2.0 cN/dtex or more. Further, the organic fiber cord preferably has an intermediate elongation of 3.0% to 4.6% from the viewpoint of facilitating its production and improving rigidity and steering stability. Further, the organic fiber cord should have a dimensional stability index of 5.0% to 9.0% from the viewpoint of facilitating its production and stabilizing the tire width dimension during post-cure inflation. preferable. Further, the organic fiber cord preferably has a twist coefficient of 2000 to 35000, preferably 20000 to 35000, from the viewpoint of sufficient fatigue resistance and rigidity. As used herein, both breaking strength and intermediate elongation are values measured according to JIS L 1017. Intermediate elongation is the value at the time of 2.0 cN/dtex load. The dimensional stability index is the sum of the dry heat shrinkage rate and the above-mentioned intermediate elongation, and the dry heat shrinkage rate is a value measured in accordance with JIS L 1017 under temperature conditions of 180°C. The twist coefficient is K by the formula: K=T×D1/2 (where T is the number of ply twists of the organic fiber cord (twists/10 cm) and D is the total fineness (dtex) of the organic fiber cord). is a coefficient represented by The twist coefficient can be set by adjusting the spinning speed when manufacturing the organic fiber cord. Although the total fineness of the organic fiber cord is not particularly limited, it is preferably set in the range of, for example, 1100 to 3500 dtex, preferably 1100 to 3300 dtex. A high tenacity level can be obtained by setting the total fineness to such a range. For the organic fiber cord, it is preferable that the difference between the elongation at break in the tensile test and the elongation at 70% of the tensile load at break is 11% to 16%. By setting the difference between the elongation rate at the time of cutting and the elongation rate under specific conditions in this way, it is possible to ensure high toughness and improve resistance to trauma.

<Rubber component>
As the rubber component of the rubber composition for coating a cord, any one that is commonly used in this field can be suitably used, but one containing an isoprene-based rubber is preferred. Examples of isoprene-based rubber include natural rubber (NR), modified natural rubber, isoprene rubber (IR), and the like. Among these, NR is preferred. NR also includes deproteinized natural rubber (DPNR), high-purity natural rubber (HPNR), modified natural rubbers include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber etc. As NR, for example, SIR20, RSS#3, TSR20, etc., which are commonly used in the tire industry can be used. The isoprene-based rubbers may be used alone or in combination of two or more.

The content of the isoprene-based rubber is preferably 20 to 100% by mass based on 100% by mass of the rubber component from the viewpoint of the heat generation suppressing effect. The content of isoprene-based rubber is more preferably 25% by mass or more, more preferably 30% by mass or more, still more preferably 35% by mass or more, still more preferably 40% by mass or more, still more preferably 50% by mass or more, still more preferably is 60% by mass or more. Also, the content of the isoprene-based rubber may be 100% by mass.

Rubber components other than isoprene rubber include butadiene rubber (BR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), diene rubber such as chloroprene rubber (CR), butyl rubber (IIR), and the like. Of these, SBR and BR are preferred, and SBR is more preferred, from the viewpoint of reversion resistance, heat resistance, bending fatigue resistance, and the like. Rubber components other than isoprene-based rubber may be used alone or in combination of two or more.

The BR is not particularly limited. BR containing 2-syndiotactic polybutadiene crystals (SPB), BR synthesized using an Nd-based catalyst such as BUNA CB 25 and BUNA CB 24 manufactured by LANXESS, and the like commonly used in the tire industry can be used. Tin-modified butadiene rubber modified with a tin compound (tin-modified BR) can also be used.

Examples of SBR include, but are not limited to, emulsion-polymerized styrene-butadiene rubber (E-SBR), solution-polymerized styrene-butadiene rubber (S-SBR), modified SBR modified with 3-aminopropyldimethylmethoxysilane, and the like. Among them, E-SBR is preferable because it has a high molecular weight polymer component and is excellent in elongation at break. As SBR, for example, one manufactured by Sumitomo Chemical Co., Ltd. can be used.

From the viewpoint of processability, the styrene content of SBR is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and even more preferably 20% by mass or more. Further, from the viewpoint of fuel efficiency, the styrene content is preferably 50% by mass or less, more preferably 45% by mass or less, even more preferably 40% by mass or less, further preferably 35% by mass or less, and 30% by mass or less. Especially preferred. The styrene content of SBR is calculated by H ¹ -NMR measurement.

When a rubber component other than isoprene-based rubber is used, the content in 100% by mass of the rubber component is preferably 0 to 80% by mass in 100% by mass of the rubber component from the viewpoint of heat generation suppression effect. The content of the rubber component is more preferably 75% by mass or less, still more preferably 70% by mass or less, still more preferably 65% by mass or less, still more preferably 60% by mass or less. The content of the rubber component may be 0% by mass, or preferably 5% by mass or more, preferably 10% by mass or more, preferably 20% by mass or more, or 30% by mass or more. is preferably 40% by mass or more.

A preferred combination of rubbers constituting the rubber component includes a rubber component containing isoprene rubber and styrene-butadiene rubber, and a rubber component consisting of isoprene-based rubber and styrene-butadiene rubber alone is particularly preferred.

<Liquid diene polymer>
The number average molecular weight (Mn) of the liquid diene-based polymer of the rubber composition for coating a cord is 25,000 (25,000) or more and 100,000 (100,000) or less. When Mn is 25000 or more, bending fatigue resistance and the like are sufficiently exhibited. On the other hand, if the molecular weight exceeds 100,000, the rubber component becomes relatively high in molecular weight, making it difficult for the liquid diene-based polymer to enter between the molecules of the rubber component. Mn is preferably 30,000 or more, more preferably 35,000 or more, even more preferably 40,000 or more, still more preferably 44,000 or more, and even more preferably 50,000 or more. Moreover, Mn is more preferably 90,000 or less, and still more preferably 80,000 or less. Here, Mn is a value measured using a gel permeation chromatograph (GPC) and converted from standard polystyrene. The liquid diene-based polymer in this specification is a diene-based polymer that is liquid at room temperature (25° C.).

Liquid diene polymers include liquid butadiene polymer (liquid BR), liquid isoprene polymer (liquid IR), liquid styrene-butadiene copolymer (liquid SBR), liquid styrene-isoprene copolymer (liquid SIR) and liquid isoprene-butadiene. A copolymer (liquid IRBR) and the like are included. Among these, liquid BR, liquid IR, and liquid SBR are preferred. The liquid diene-based polymer may be used alone or in combination of two or more.

The liquid diene-based polymer may be hydrogenated or functionalized with a functional group such as a carboxyl group. Moreover, when the liquid diene-based polymer is a copolymer, it may be a random copolymer or a block copolymer of each monomer. Unless otherwise specified, the liquid diene-based polymer includes any and all of these.

As the liquid diene-based polymer, for example, any product sold by Kuraray Co., Ltd. under the trade name of Kuraprene (registered trademark) can be suitably used. More specifically, examples of liquid BR include LBR-300 ^* (Mn: 45000). Examples of liquid IR include LIR-50 (Mn: 54000). Examples of liquid SIR include LIR-310 (Mn: 32000). LIR-310 is a block copolymer. Examples of liquid IRBR include LIR-390 (Mn: 48000). LIR-390 is a block copolymer. Examples of the hydrogenated liquid diene-based polymer include LIR-290 (Mn: 31000), which is a hydrogenated liquid IR. Carboxylated liquid diene-based polymers include LIR-410 (Mn: 30,000) and LIR-403 (Mn: 34,000), which are carboxylated liquid IRs.

When the liquid diene-based polymer is contained, the content relative to 100 parts by mass of the rubber component is in the range of 0.1 to 20 parts by mass from the viewpoint of obtaining the advantageous effect of the present embodiment. The content is preferably 1.5 parts by mass or more, more preferably 3.0 parts by mass or more, and still more preferably 4.0 parts by mass or more. On the other hand, the content is preferably 18 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 12 parts by mass or less.

<Filler>
The cord coating rubber composition may contain a filler. Any common filler can be used, and examples of such fillers include carbon black and silica.

(Carbon black)
By containing carbon black, the rubber composition for coating can obtain better reinforcing properties, and can improve the complex elastic modulus, low heat build-up, elongation at break, and durability in a well-balanced manner.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 40 m ² /g or more, more preferably 60 m ² /g or more, and 70 m ² /g or more, from the viewpoint of sufficient reinforcing properties. is more preferable. In addition, the N ₂ SA of carbon black is preferably 125 m ² /g or less, more preferably 115 m ² /g or less, more preferably 105 m 2 /g or less, from the viewpoint of fuel efficiency, processability (sheet rollability), etc. ² /g or less is more preferable. The nitrogen adsorption specific surface area of carbon black is a value measured by A method on page 7 of JIS K 6217.

From the viewpoint of abrasion resistance, the DBP oil absorption of carbon black is preferably 50 ml/100 g or more, more preferably 55 ml/100 g or more, and even more preferably 60 ml/100 g or more. From the viewpoint of grip performance, the DBP oil absorption is preferably 250 ml/100 g or less, more preferably 200 ml/100 g or less, still more preferably 135 ml/100 g or less, and even more preferably 100 ml/100 g or less. The DBP oil absorption of carbon black is a value measured according to JIS K 6217-4:2008.

From the viewpoint of sufficient reinforcing properties, the content of carbon black is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and 25 parts by mass or more with respect to 100 parts by mass of the rubber component. It is even more preferable to have In addition, the content of carbon black is preferably 55 parts by mass or less, and preferably 50 parts by mass or less, from the viewpoint of low heat build-up, elongation at break, workability (sheet rollability), durability, etc. more preferred.

(silica)
Inclusion of silica can contribute to improvement in elongation at break and cord adhesion.

Silica is not particularly limited and includes, for example, dry silica (anhydrous silicic acid), wet silica (hydrous silicic acid) and the like, but wet silica is preferred because it contains many silanol groups.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 80 m ² /g or more, more preferably 100 m ² /g or more, more preferably 110 m ² from the viewpoint of durability at break. /g or more is more preferable. In addition, the N ₂ SA of silica is preferably 250 m ² /g or less, more preferably 235 m ² /g or less, more preferably 220 m ² from the viewpoint of fuel efficiency, workability (sheet rollability), etc. /g or less is more preferable. The nitrogen adsorption specific surface area of silica is a value measured by the BET method according to ASTM D3037-81.

When the silica is contained, the content is preferably 5 parts by mass or more, more preferably 7 parts by mass or more, with respect to 100 parts by mass of the rubber component, from the viewpoint of elongation at break, durability, etc. preferable. In addition, from the viewpoint of dispersibility and complex elastic modulus E*, the content of silica is preferably 17 parts by mass or less, more preferably 15 parts by mass or less, and further preferably 13 parts by mass or less. preferable.

When silica and carbon black are used together, the total content is preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component, from the viewpoint of elongation at break, complex elastic modulus, filler dispersibility, etc. It is more preferably 35 parts by mass or more. The total content is preferably 60 parts by mass or less, more preferably 55 parts by mass or less, from the viewpoint of low heat build-up, elongation at break, and the like.

<Zinc oxide>
The cord coating rubber composition may contain zinc oxide. Any zinc oxide commonly used in this field can be suitably used. The content of zinc oxide is preferably 2 parts by mass or more, more preferably 2.5 parts by mass or more, relative to 100 parts by mass of the rubber component. On the other hand, the content of zinc oxide is preferably 10 parts by mass or less, more preferably 8 parts by mass or less.

<Methylene donor>
The cord coating rubber composition may contain a methylene donor. Thereby, the adhesion between the cord and the rubber can be further strengthened. Examples of methylene donors include partial condensates of hexamethoxymethylolmelamine (HMMM) and partial condensates of hexamethylolmelamine pentamethyl ether (HMMPME). Among them, a partial condensate of HMMM is preferable because of its excellent reactivity.

The content of the methylene donor is preferably 0.05 parts by mass or more, more preferably 0.10 parts by mass or more, more preferably 0.20 parts by mass with respect to 100 parts by mass of the diene rubber component, from the viewpoint of improving rigidity. Part or more is more preferable. In addition, the content of the methylene group donating compound is preferably 0.5 parts by mass or less, more preferably 0.4 parts by mass or less, from the viewpoint of rigidity and low heat build-up.

<Other ingredients>
In addition to the above components, the rubber composition for cord coating may contain compounding agents generally used in the production of rubber compositions, such as silane coupling agents, stearic acid, various anti-aging agents, oils, waxes, and vulcanizing agents. , a vulcanization accelerator, and the like can be appropriately blended.

(vulcanizing agent)
Sulfur can be preferably used as the vulcanizing agent. As sulfur, powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and the like can be used. The content of sulfur is preferably 3.0 parts by mass or more, more preferably 3.5 parts by mass or more with respect to 100 parts by mass of the rubber component, from the viewpoint of sufficient wet heat peel resistance, durability, and the like. Also, the content is preferably 10.0 parts by mass or less, more preferably 6.0 parts by mass or less. In addition, the content of sulfur means the content of sulfur.

(Vulcanization accelerator)
As the vulcanization accelerator, any of those commonly used in the field of the tire industry can be suitably used. , thiazole-based, sulfenamide-based, thiourea-based, thiuram-based, dithiocarbamate-based, and xandate-based compounds. These vulcanization accelerators may be used alone or in combination of two or more. Among them, from the viewpoint of dispersibility in rubber and stability of vulcanized physical properties, sulfenamide-based vulcanization accelerators [N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl -2-benzothiazolylsulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS), N,N-diisopropyl-2-benzothiazolylsulfenamide, etc.], N-tert -Butyl-2-benzothiazolylsulfenimide (TBSI), di-2-benzothiazolyl disulfide (DM) and the like are preferred, and TBBS, CBS, TBSI and DM are more preferred.

The content of the vulcanization accelerator is preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, with respect to 100 parts by mass of the rubber component, from the viewpoint of suitable cross-linking density, bending fatigue resistance, etc. . Moreover, the content of the vulcanization accelerator is preferably 2.0 parts by mass or less, more preferably 1.5 parts by mass or less.

<Rubber composition for cord coating>
A cord coating rubber composition is produced by a general method. That is, it can be produced by kneading each of the above components with a Banbury mixer, a kneader, an open roll, or the like, and then vulcanizing. For kneading, it is preferable to first knead the components other than the vulcanizing agent and the vulcanization accelerator, and then add the vulcanizing agent and the vulcanization accelerator to the kneaded product and knead.

The cord covering rubber composition is used as a rubber composition for covering an organic fiber cord composed of PET fibers. A composite obtained by coating the organic fiber cord with the rubber composition is used as a reinforcing layer of a pneumatic tire, such as a carcass layer, a breaker layer, a band layer, and the like. Among them, it is preferably used for the carcass layer because it forms the basic skeleton of the pneumatic tire and accounts for a large proportion of the tire.

<Pneumatic tire>
The pneumatic tire of the present embodiment is manufactured by a normal method using organic fiber cords composed of PET fibers and the above rubber composition. That is, after coating the organic fiber cord with the rubber composition and molding it into the shape of a tire member (for example, carcass) which is a reinforcing layer, the tire member is laminated to another tire member to obtain an unvulcanized tire. A pneumatic tire can be produced by molding and then vulcanizing the unvulcanized tire.

The pneumatic tire of the present embodiment is suitably used as a tire for passenger cars, a tire for trucks and buses, a tire for motorcycles, a tire for racing, and the like, and is particularly suitably used as a tire for passenger cars.

<Others>
In this specification, when a numerical range is expressed as "1 to 100 parts by mass", it means including both numerical values ("1" and "100" in the above) unless otherwise specified.

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

Various chemicals used in Examples and Comparative Examples are listed below.
NR: TSR20
SBR: SBR1502 manufactured by Sumitomo Chemical Co., Ltd. (styrene content: 23.5% by mass)
Carbon black: Show Black N326 (N ₂ SA: 81 m ² /g, DBP oil absorption: 75 ml/100 g) manufactured by Cabot Japan Co., Ltd.
Zinc oxide: Zinc oxide No. 3 manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Stearic acid "Tsubaki" manufactured by NOF Corporation
Oil: Diana Process NH-70S manufactured by Idemitsu Kosan Co., Ltd.
Liquid diene-based polymer 1 (liquid BR): LBR-300 ^* (Mn: 45000) manufactured by Kuraray Co., Ltd.
Liquid diene polymer 2 (liquid BR): LBR-305 (Mn: 26000) manufactured by Kuraray Co., Ltd.
Liquid diene polymer 3 (liquid IR): LIR-30 (Mn: 28000) manufactured by Kuraray Co., Ltd.
Liquid diene polymer 4 (carboxylated liquid IR): LIR-403 (Mn: 34000) manufactured by Kuraray Co., Ltd.
Sulfur: insoluble sulfur manufactured by Shikoku Kasei Co., Ltd., Myucron OT-20 (20% oil treatment)
Vulcanization accelerator: Noxceler NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
Polyethylene terephthalate fiber (PET fiber): Polyethylene terephthalate fiber (cord structure (dtex): 1670T/2, total fineness: 3340dtex, breaking strength: 5.0cN/dtex, intermediate elongation: 3.5%, dry heat shrinkage: 2.8%, dimensional stability index: 6.3%, twist coefficient: 2000, difference in elongation rate (elongation rate at break in tensile test and elongation when 70% of tensile load at break is applied rate): 13.0%)

<Manufacture of rubber composition>
According to the compounding recipe shown in Table 1, using a 1.7 L Banbury mixer, among the compounding materials, materials other than sulfur and vulcanization accelerator are kneaded at 150° C. for 5 minutes to obtain a kneaded product. Next, sulfur and a vulcanization accelerator are added to the above-mentioned kneaded material, and kneaded for 5 minutes at 80° C. using a twin-screw open roll to obtain an unvulcanized rubber composition. Subsequently, the unvulcanized rubber composition is press-vulcanized at 170° C. for 12 minutes to obtain a vulcanized rubber composition.

<Manufacture of pneumatic tires>
The above unvulcanized rubber composition is used to cover aligned PET fibers to obtain an unvulcanized reinforcing layer. The unvulcanized reinforcing layer is used as a carcass layer, laminated with other tire members to form an unvulcanized tire, and press-vulcanized at 150° C. for 35 minutes to produce a pneumatic tire.

<Evaluation>
By performing each of the following tests using the vulcanized rubber composition obtained above, each index described in Table 1 or a value close to it can be obtained.

(Bending fatigue resistance index)
A constant stress/constant strain fatigue tester (FT-3100) manufactured by Ueshima Seisakusho Co., Ltd. is used, and the test is performed according to the method of ISO6943. A dumbbell No. 3 test piece made of the above vulcanized rubber composition is repeatedly subjected to a strain of 1 Hz and 30%, and the number of times until the test piece breaks is measured. The measurement results are expressed as an index using the following formula. do. A larger index indicates higher bending fatigue resistance and superior durability.
(Bending fatigue resistance index) = {(number of times of each formulation) / (number of times of reference comparative example)} x 100

(low pyrogenicity index)
Using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd., the loss tangent tan δ of each vulcanized rubber composition at 70 ° C. was measured under the conditions of a frequency of 10 Hz, an initial strain of 10% and a dynamic strain of 2%. The results are indexed according to the following formula. A higher index indicates less heat generation.
(Low heat build-up index) = {(tan δ of reference comparative example) / (tan δ of each formulation)} × 100

(adhesion index)
A PET fiber cord-rubber composite in which PET fiber cords arranged at regular intervals are embedded in unvulcanized rubber is vulcanized at 160° C. for 20 minutes to prepare a test sample. The PET fiber cord is pulled out according to ASTM D-2229-93a, the pull-out force at that time is measured, and the measurement result is expressed as an index according to the following formula. A larger index indicates better drawing adhesion.
(Adhesion index) = {(pulling force of each formulation) / (pulling force of reference comparative example)} × 100

REFERENCE SIGNS LIST 1 tread portion 2 sidewall portion 3 bead portion 4 carcass layer 5 breaker layer 6 band layer

Claims (6)

A pneumatic tire comprising a reinforcing layer formed by arranging organic fiber cords,
The organic fiber cord is composed of polyethylene terephthalate fiber,
The reinforcing layer is formed by coating an organic fiber cord with a rubber composition,
The rubber composition comprises a rubber component and a liquid diene polymer,
The pneumatic tire, wherein the liquid diene-based polymer has a number average molecular weight of 25,000 or more and 100,000 or less.
[However, this excludes the case where the rubber composition contains a liquid isoprene rubber having a weight average molecular weight of 20,000 to 60,000 in an amount of 5 to 15% by weight based on the total amount of the rubber component and the liquid isoprene rubber. ] A pneumatic tire comprising a reinforcing layer formed by arranging organic fiber cords,
The organic fiber cord is composed of polyethylene terephthalate fiber,
The reinforcing layer is formed by coating an organic fiber cord with a rubber composition,
The rubber composition comprises a rubber component and a liquid diene polymer,
The liquid diene-based polymer comprises a liquid butadiene polymer (liquid BR), a liquid styrene-butadiene copolymer (liquid SBR), a liquid styrene-isoprene copolymer (liquid SIR), and a liquid isoprene-butadiene copolymer (liquid IRBR). is at least one selected from the group,
The pneumatic tire, wherein the liquid diene-based polymer has a number average molecular weight of 25,000 or more and 100,000 or less. The liquid diene-based polymer is at least one selected from the group consisting of a liquid butadiene polymer, a liquid isoprene polymer, a liquid styrene-butadiene copolymer, a liquid styrene-isoprene copolymer and a liquid isoprene-butadiene copolymer. 3. The pneumatic tire according to Item 1 or 2. The pneumatic tire according to any one of claims 1 to 3, wherein the content of the liquid diene-based polymer is 0.1 to 20 parts by mass with respect to 100 parts by mass of the rubber component. The pneumatic tire according to any one of claims 1 to 4, wherein the rubber component contains 20 to 100% by mass of isoprene rubber and 0 to 80% by mass of styrene-butadiene rubber. The pneumatic tire according to any one of claims 1 to 5, wherein the reinforcing layer is at least one selected from the group consisting of a carcass layer, a breaker layer and a band layer.

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