JP2019177799A - Pneumatic tire - Google Patents

Abstract

To provide a pneumatic tire that has low heat build-up properties, and includes a reinforcement layer in which a PET fiber is coated with a rubber composition having excellent flexural fatigue resistance and adhesiveness.SOLUTION: A pneumatic tire has a reinforcement layer including aligned organic fiber cords. The organic fiber cord is composed of polyethylene terephthalate fiber. The reinforcement layer has an organic fiber cord coated with a rubber composition. The rubber composition contains a rubber component and a liquid butadiene polymer. The liquid butadiene polymer has a number average molecular weight of 5000 or more and 100000 or less. The vinyl content is 30 mol% or more.SELECTED DRAWING: Figure 1

Description

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

  A pneumatic tire has a reinforcing layer represented by a carcass layer, a breaker layer, a band layer, etc., and such a reinforcing layer covers a steel cord or an organic fiber cord with a rubber composition and press vulcanizes it. Is obtained.

  As a cord used for the reinforcing layer, it is known to use a cord of cellulose fiber which is an organic fiber (Patent Document 1). However, although the cellulose fiber cord is effective from the viewpoint of utilization of recycled resources, it is not necessarily good from the viewpoint of environmental load because carbon disulfide is used when the raw material is produced.

  On the other hand, polyethylene terephthalate fiber (PET fiber) is characterized in that it is favorable from the viewpoint of environmental load because it does not use carbon disulfide at the time of manufacture, and also has high strength.

JP 2014-189212 A

  However, PET fibers are temperature dependent and have the property of easily generating heat. Therefore, when PET fiber is used as the cord used for the reinforcing layer of the tire, it is desirable that the rubber composition covering the cord has low heat build-up. Further, such a cord coating rubber composition is desired to have excellent bending fatigue resistance and adhesiveness as original characteristics.

  Under the above-mentioned problems, the present invention provides a pneumatic tire comprising a reinforcing layer coated with PET fibers with a rubber composition that has low heat build-up and is excellent in bending fatigue resistance and adhesion. For the purpose.

  As a result of intensive studies, the present inventors have, as a result of intensive studies, in a pneumatic tire having a reinforcing layer, a rubber composition containing an organic fiber cord composed of PET fibers of the reinforcing layer and a rubber component and a predetermined liquid butadiene-based polymer It was found that the above-mentioned problems can be solved by coating with, and further studies were made to complete the present invention.

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 includes a rubber component and a liquid butadiene-based polymer,
A pneumatic tire having a liquid butadiene-based polymer having a number average molecular weight of 5,000 to 100,000 and a vinyl content of 30 mol% or more;
[2] The pneumatic tire according to [1], wherein the liquid butadiene-based polymer is at least one selected from the group consisting of a liquid butadiene polymer, a liquid styrene butadiene copolymer, and a liquid isoprene butadiene copolymer. ,
[3] The pneumatic tire according to [1] or [2], wherein the content of the liquid butadiene-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], wherein the rubber component includes 20 to 100% by mass of isoprene-based rubber and 0 to 80% by mass of styrene butadiene rubber.
[5] The pneumatic tire according to any one of [1] to [4], wherein the reinforcing layer is at least one selected from the group consisting of a carcass layer, a breaker layer, and a band layer.
About.

  ADVANTAGE OF THE INVENTION According to this invention, the pneumatic tire which comprises the reinforcement layer which coat | covered PET fiber with the rubber composition which is low exothermic property, and is excellent also in bending fatigue resistance, and adhesiveness can be provided. .

It is an example of the fragmentary sectional view of a pneumatic tire.

  One embodiment is a pneumatic tire including a reinforcing layer configured by arranging organic fiber cords, wherein the organic fiber cord is formed of polyethylene terephthalate fiber, and the reinforcing layer is organic A fiber cord is coated with a rubber composition, the rubber composition contains a rubber component and a liquid butadiene polymer, and the number average molecular weight of the liquid butadiene polymer is from 5,000 to 100,000. A pneumatic tire having a vinyl content of 30 mol% or more.

  While not intending to be bound by theory, by using a predetermined liquid butadiene-based polymer, it is possible to obtain a rubber composition for cord coating that has low heat buildup and is excellent in bending fatigue resistance and adhesion. Possible mechanisms are as follows. That is, in the present embodiment, the liquid butadiene-based polymer has a structure similar to that of the rubber constituting the rubber component as compared with the oil used for the same purpose, so that it can be easily mixed therewith. Moreover, since it is a relatively low molecule, it can easily enter between the molecules of the rubber component. For this reason, it has the characteristic that it is easy to disperse | distribute to a rubber component, without forming a sea island state between rubber components. Since the liquid butadiene polymer is cured by vulcanization, the liquid butadiene polymer dispersed in the rubber component is cured as described above, so that the network in the rubber is strengthened and the bending fatigue resistance and the adhesiveness are improved. It is presumed that the heat generation is reduced by improving the molecular chain movement in the rubber. Further, since the liquid butadiene-based polymer has a glass transition temperature lower than that of oil, it is considered that this point also contributes to a decrease in heat generation, bending fatigue resistance, and adhesion.

  The liquid butadiene-based polymer has a vinyl content of 30 mol% or more. Since such vinyl groups are cross-linked by vulcanization, the network in the rubber is strengthened by the cross-linking of the vinyl groups, and the bending resistance is increased. It is presumed that the heat build-up and the adhesiveness are improved, and the exothermic property is lowered by suppressing the movement of the molecular chain in the rubber.

<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 typical reinforcing layers of a pneumatic tire.

  The reinforcing layer according to this embodiment is formed by arranging a plurality of organic fiber cords and coating them with a coating rubber composition. As described above, the reinforcing layer according to the present embodiment may be any reinforcing layer in the pneumatic tire, but forms a basic skeleton of the pneumatic tire and has a large ratio in the tire. A carcass layer is preferred.

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

  The organic fiber cord preferably has a breaking strength of 2.0 cN / dtex or more from the viewpoint of sufficient durability. The organic fiber cord preferably has an intermediate elongation of 3.0% to 4.6% from the viewpoint of facilitating the production and improving the rigidity and the handling stability. In addition, the organic fiber cord has a dimensional stability index of 5.0% to 9.0% from the viewpoint of facilitating the manufacture and stabilizing the tire width dimension during post-cure inflation. preferable. In addition, the organic fiber cord has a twist coefficient of 2000 to 35000, preferably 20000 to 35000, from the viewpoint of sufficient fatigue resistance and rigidity. In this specification, both the breaking strength and the intermediate elongation are values measured according to JIS L 1017. The intermediate elongation is a value at a load of 2.0 cN / dtex. The dimensional stability index is the sum of the dry heat shrinkage rate and the intermediate elongation described above, and the dry heat shrinkage rate is a value measured according to JIS L 1017 under a temperature condition of 180 ° C. The twist coefficient is K according to the formula: K = T × D1 / 2 (where T is the number of upper twists of the organic fiber cord (times / 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. The total fineness of the organic fiber cord is not particularly limited, but for example, it is preferably set in the range of 1100 dtex to 3500 dtex, preferably 1100 to 3300 dtex. By setting the total fineness within such a range, a high strength level can be obtained. About the said organic fiber cord, it is preferable to make it the difference of the elongation rate at the time of applying the load of 70% of the tensile load at the time of a cutting | disconnection in the tensile test to 11%-16%. Thus, by setting the difference between the elongation rate at the time of cutting and the elongation rate under specific conditions, high toughness can be ensured and the trauma resistance can be improved.

<Rubber component>
As the rubber component of the rubber composition for covering a cord, any of those usually used in this field can be suitably used, but is preferably one containing isoprene-based rubber. Examples of the isoprene-based rubber include natural rubber (NR), modified natural rubber, and isoprene rubber (IR). Of these, NR is preferred. NR includes deproteinized natural rubber (DPNR) and high-purity natural rubber (HPNR). Modified natural rubber includes epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Etc. Moreover, as NR, what is common in tire industry, such as SIR20, RSS # 3, TSR20, can be used, for example. 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 in 100% by mass of the rubber component from the viewpoint of heat generation suppression effect and the like. The content of the isoprene-based rubber is more preferably 25% by mass or more, further preferably 30% by mass or more, further preferably 35% by mass or more, further preferably 40% by mass or more, further preferably 50% by mass or more, and further preferably. Is 60% by mass or more. Further, the content of the isoprene-based rubber may be 100% by mass.

  Examples of rubber components other than isoprene rubber include diene rubbers such as butadiene rubber (BR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), and chloroprene rubber (CR), and butyl rubber (IIR). Among these, SBR and BR are preferable, and SBR is more preferable 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. For example, BR1220 manufactured by Nippon Zeon Co., Ltd., BR150B manufactured by Ube Industries, Ltd., high cis content BR, 1, VCR412, VCR617 manufactured by Ube Industries, etc. Commonly used in the tire industry, such as BR containing 2-syndiotactic polybutadiene crystal (SPB), BR synthesized using Nd-based catalysts such as BUNA CB 25 and BUNA CB 24 manufactured by LANXESS, can be used. In addition, tin-modified butadiene rubber (tin-modified BR) modified with a tin compound can also be used.

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

The styrene content of SBR is preferably 5% by mass or more, more preferably 10% by mass or more, further preferably 15% by mass or more, and further preferably 20% by mass or more from the viewpoint of workability. The styrene content is preferably 50% by mass or less, more preferably 45% by mass or less, further preferably 40% by mass or less, further preferably 35% by mass or less, and further preferably 30% by mass or less from the viewpoint of low fuel consumption. Particularly preferred. Incidentally, styrene content of SBR is calculated by H ¹ -NMR measurement.

  In the case where 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 an effect of suppressing heat generation. The content of the rubber component is more preferably 75% by mass or less, further preferably 70% by mass or less, further preferably 65% by mass or less, and further preferably 60% by mass or less. The content of the rubber component may be 0% by mass, or is preferably 5% by mass or more, preferably 10% by mass or more, preferably 20% by mass or more, and 30% by mass or more. It is preferable that it is 40 mass% or more.

  A preferable combination of rubbers constituting the rubber component includes a rubber component including isoprene-based rubber and styrene-butadiene rubber, and a rubber component composed only of isoprene-based rubber and styrene-butadiene rubber is particularly preferable.

<Liquid butadiene polymer>
The liquid butadiene-based polymer of the cord coating rubber composition has a number average molecular weight (Mn) of 5000 (5,000) or more and 100,000 (100,000) or less. When Mn is less than 5000, the bending fatigue resistance and the like cannot be sufficiently exhibited. On the other hand, when the molecular weight exceeds 100,000, the polymer becomes relatively high, so that the liquid butadiene-based polymer is difficult to enter between the molecules of the rubber component, so that a sufficient effect cannot be expected. Mn is preferably 5500 or more. Further, Mn is preferably 90,000 or less, and more preferably 80,000 or less. Here, Mn is a value measured using a gel permeation chromatograph (GPC) and converted from standard polystyrene. In addition, the liquid butadiene type polymer in this specification is a diene polymer in a liquid state at normal temperature (25 ° C.).

  The liquid butadiene-based polymer has a vinyl content (1,2-bonded butadiene unit amount) of 30 mol% or more. When the vinyl content is 30 mol% or more, improvement in bending fatigue resistance, durability, adhesion, and low heat buildup can be expected. The vinyl content is preferably 35 mol% or more, more preferably 40 mol% or more, further preferably 45 mol% or more, and further preferably 50 mol% or more. Although there is no restriction | limiting in particular about the upper limit of a vinyl content, Usually, even when a liquid butadiene type polymer is a butadiene homopolymer, it is about 70 mol%. The vinyl content of the liquid butadiene-based polymer can be measured by infrared absorption spectrum analysis.

  Examples of the liquid butadiene-based polymer include a liquid butadiene polymer (liquid BR), a liquid styrene butadiene copolymer (liquid SBR), and a liquid isoprene butadiene copolymer (liquid IRBR). Of these, liquid BR is preferred. A liquid butadiene-type polymer may be used independently and may use 2 or more types together.

  The liquid butadiene-based polymer may be hydrogenated or may be functionalized with a functional group such as a carboxy group. When the liquid butadiene-based polymer is a copolymer, it may be a random copolymer of each monomer or a block copolymer. The liquid butadiene-based polymer includes any of these unless otherwise specified.

As the liquid butadiene-based polymer, for example, any product sold under the trade name of Claprene (registered trademark) by Kuraray Co., Ltd. can be suitably used. More specifically, as the liquid BR, for example, LBR-302 (Mn: 5500), LBR-307 (Mn: 8000), LBR-305 (Mn: 26000), LBR-300 ^* (Mn: 45000), LBR- 361 (Mn: 5500), LBR-352 (Mn: 9000, vinyl content: 50 mol% or more), and the like. Examples of the liquid SBR include L-SBR-820 (Mn: 8500), L-SBR-841 (Mn: 10,000), and the like. L-SBR-820 and L-SBR-841 are both random copolymers. Examples of liquid IRBR include LIR-390 (Mn: 48000). LIR-390 is a block copolymer.

  Content with respect to 100 mass parts of rubber components in the case of containing a liquid butadiene-type polymer is the range of 0.1-20 mass parts from a viewpoint that the effect of this suitable embodiment is acquired. 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 still more preferably 12 parts by mass or less.

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

(Carbon black)
By containing carbon black, the coating rubber composition can obtain better reinforcement, 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 reinforcement. More preferably. Further, N ₂ SA of carbon black is preferably 125 m ² / g or less, more preferably 115 m ² / g or less, from the viewpoint of low fuel consumption, workability (sheet rolling property), and the like, and 105 m More preferably, it is ² / g or less. The nitrogen adsorption specific surface area of carbon black is a value measured by JIS K 6217, method A on page 7.

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

  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 from the viewpoint of sufficient reinforcement. More preferably it is. Further, the content of carbon black is preferably 55 parts by mass or less, and preferably 50 parts by mass or less from the viewpoints of low heat build-up, elongation at break, workability (sheet rollability), durability, and the like. More preferred.

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

  The silica is not particularly limited, and examples thereof include dry process silica (anhydrous silicic acid), wet process silica (hydrous silicic acid), and the like, but wet process silica is preferable because of its large number of silanol groups.

From the viewpoint of durability and the like, 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, from the viewpoint of durability and the like, 110 m ^2. / G or more is more preferable. The N ₂ SA of the silica, low fuel consumption, from the viewpoint of workability (sheet rolling property), preferably at 250 meters ² / g or less, more preferably at most 235m ² / g, 220m ² / 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.

  In the case of containing the silica, the content is preferably 5 parts by mass or more and 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, and the like. preferable. Further, 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 from the viewpoint of dispersibility and complex elastic modulus E *. preferable.

  The total content when silica and carbon black are used in combination 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, dispersibility of the filler, and the like. More preferably, it is 35 parts by mass or more. The total content is preferably 60 parts by mass or less, and 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 rubber composition for cord coating can contain zinc oxide. As zinc oxide, any of those usually used in this field can be suitably used. The content of zinc oxide is preferably 2 parts by mass or more and more preferably 2.5 parts by mass or more with respect 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 rubber composition for cord coating may contain a methylene donor. Thereby, the adhesiveness between the cord and the rubber can be further strengthened. Examples of the methylene donor include a partial condensate of hexamethoxymethylol melamine (HMMM) and a partial condensate of hexamethylol melamine pentamethyl ether (HMMPME). Among these, a partial condensate of HMMM is preferable from the viewpoint of 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, and 0.20 parts by mass with respect to 100 parts by mass of the diene rubber component from the viewpoint of the rigidity improving effect. Part or more is more preferable. In addition, the content of the compound that donates a methylene group is preferably 0.5 parts by mass or less, and more preferably 0.4 parts by mass or less from the viewpoints of rigidity and low heat build-up.

<Other ingredients>
In addition to the above components, the cord coating rubber composition contains 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. Further, a vulcanization accelerator and the like can be appropriately blended.

(Vulcanizing agent)
Sulfur can be suitably 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 sulfur content 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 resistance and durability. Moreover, this content becomes like this. Preferably it is 10.0 mass parts or less, More preferably, it is 6.0 mass parts or less. In addition, content of sulfur means content of sulfur content.

(Vulcanization accelerator)
As the vulcanization accelerator, any of those usually used in the field of the tire industry can be suitably used. Examples of such a vulcanization accelerator include guanidine-based, aldehyde-amine-based, and aldehyde-ammonia-based. , Thiazole-based, sulfenamide-based, thiourea-based, thiuram-based, dithiocarbamate-based, and zanddate-based compounds. These vulcanization accelerators may be used alone or in combination of two or more. Among these, from the viewpoint of dispersibility in rubber and stability of vulcanization properties, sulfenamide vulcanization accelerators [N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl 2-benzothiazolylsulfenamide (CBS), N, N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS), N, N-diisopropyl-2-benzothiazolesulfenamide, etc.], N-tert -Butyl-2-benzothiazolylsulfenimide (TBSI), di-2-benzothiazolyl disulfide (DM) and the like are preferable, and TBBS, CBS, TBSI and DM are more preferable.

  The content of the vulcanization accelerator is preferably 0.3 parts by mass or more, and 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 crosslinking density, bending fatigue resistance, and the like. . Moreover, 2.0 mass parts or less are preferable and, as for content of a vulcanization accelerator, 1.5 mass parts or less are more preferable.

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

  The rubber composition for cord coating is used as a rubber composition for coating an organic fiber cord composed of PET fibers. The composite obtained by coating the organic fiber cord with the rubber composition is used as a reinforcing layer of a pneumatic tire, for example, as a carcass layer, a breaker layer, a band layer, or the like. Especially, since it forms the basic frame of a pneumatic tire and the ratio which occupies in a tire is large, it is preferable to use for a carcass layer.

<Pneumatic tire>
The pneumatic tire of this embodiment is manufactured by a normal method using an organic fiber cord composed of PET fibers and the rubber composition. That is, an organic fiber cord is coated with the rubber composition and formed into a tire member (for example, carcass) as a reinforcing layer, and then the tire member is bonded to another tire member to form an unvulcanized tire. A pneumatic tire can be manufactured by molding and then vulcanizing the unvulcanized tire.

  The pneumatic tire of the present embodiment is suitably used as a passenger car tire, truck / bus tire, motorcycle tire, competition tire, and the like, and particularly preferably used as a passenger car tire.

<Others>
In the present specification, when the numerical range is expressed as “1 to 100 parts by mass”, it means that the numerical values at both ends (“1” and “100” in the above) are included unless otherwise specified.

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

Various chemicals used in Examples and Comparative Examples are collectively shown below.
NR: TSR20
SBR: SBR1502 (styrene content: 23.5% by mass) manufactured by Sumitomo Chemical Co., Ltd.
Carbon Black: Show Black N326 manufactured by Cabot Japan Co., Ltd. (N ₂ SA: 81 m ² / g, DBP oil absorption: 75 ml / 100 g)
Zinc oxide: Zinc oxide No. 3 manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Stearic acid "Kashiwa" manufactured by NOF Corporation
Oil: Diana Process NH-70S manufactured by Idemitsu Kosan Co., Ltd.
Liquid butadiene polymer 1 (liquid BR): LBR-307 manufactured by Kuraray Co., Ltd. (Mn: 8000, vinyl content: 10 to 20 mol%)
Liquid butadiene polymer 2 (liquid BR): LBR-352 manufactured by Kuraray Co., Ltd. (Mn: 9000, vinyl content: 50 mol% or more)
Sulfur: Insoluble sulfur manufactured by Shikoku Kasei Kogyo Co., Ltd., Mucron OT-20 (20% oil treatment)
Vulcanization accelerator: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Polyethylene terephthalate fiber (PET fiber): Polyethylene terephthalate fiber (cord structure (dtex): 1670 T / 2, total fineness: 3340 dtex, breaking strength: 5.0 cN / dtex, intermediate elongation: 3.5%, dry heat shrinkage: 2.8%, dimensional stability index: 6.3%, twist coefficient: 2000, difference in elongation (elongation when a load of 70% of the tensile rate at the time of cutting and the tensile load at the time of cutting is applied) Difference from rate): 13.0%)

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

<Manufacture of pneumatic tires>
Using the unvulcanized rubber composition, the aligned PET fibers are covered to obtain an unvulcanized reinforcing layer. The unvulcanized reinforcing layer is used as a carcass layer and bonded to another tire member to form an unvulcanized tire, and press vulcanized at 150 ° C. for 35 minutes to produce a pneumatic tire.

<Evaluation>
Each index shown in Table 1 or a value close to it is obtained by performing the following tests using the vulcanized rubber composition obtained above.

(Bending fatigue resistance index)
Using a constant stress / constant strain fatigue tester (FT-3100) manufactured by Ueshima Seisakusho Co., Ltd., in accordance with the method of ISO6943. The test piece of dumbbell No. 3 made of the above vulcanized rubber composition was repeatedly subjected to 1 Hz, 30% strain, and the number of times until the test piece was broken was measured. To do. The larger the index, the higher the bending fatigue resistance and the better the durability.
(Bending fatigue resistance index) = {(number of times of each compounding) / (number of times of reference comparative example)} × 100

(Low exothermic 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 result is displayed as an index according to the following formula. The larger the index, the less heat is generated.
(Low exothermic 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 equal intervals are embedded in unvulcanized rubber is vulcanized at 160 ° C. for 20 minutes to produce a test sample. The PET fiber cord is pulled out based on ASTM D-2229-93a, the pulling force at that time is measured, and the measurement result is displayed as an index by the following calculation formula. It shows that it is excellent in drawing-out adhesiveness, so that an index | exponent is large. The target value is 96 or more, preferably 98 or more.
(Adhesiveness index) = {(Pulling force of each formulation) / (Pulling force of reference comparative example)} × 100

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 5 Breaker layer 6 Band layer

Claims (5)

A pneumatic tire comprising a reinforcing layer composed of 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 includes a rubber component and a liquid butadiene-based polymer,
A pneumatic tire in which the liquid butadiene-based polymer has a number average molecular weight of 5,000 to 100,000 and a vinyl content of 30 mol% or more. The pneumatic tire according to claim 1, wherein the liquid butadiene-based polymer is at least one selected from the group consisting of a liquid butadiene polymer, a liquid styrene butadiene copolymer, and a liquid isoprene butadiene copolymer. The pneumatic tire according to claim 1 or 2, wherein the content of the liquid butadiene-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 3, wherein the rubber component contains 20 to 100% by mass of isoprene-based rubber and 0 to 80% by mass of styrene butadiene rubber. The pneumatic tire according to any one of claims 1 to 4, 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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