JP2012051148A - Method for producing pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve wet performance without spoiling abrasion resistance.SOLUTION: A pneumatic tire having a tread rubber part made of a rubber composition containing at least 50 pts.mass of diene rubber (styrene butadiene rubber) having a glass transition temperature of at least -45°C in 100 pts.mass of a rubber component is vulcanization-molded, and the surface of the tread rubber part after being vulcanization-molded is irradiated with electron beams. By giving a compound having a carbon-carbon double bond (a vinyl group, an isopropenyl group, an allyl group, etc.) and a hydrophilic group (a carboxyl group, a hydroxyl group, etc.) in a molecule to the surface of the tread rubber part irradiated with electron beams, the compound is reacted with the diene rubber of the surface of the tread rubber part.

Description

  The present invention relates to a pneumatic tire.

  Conventionally, in order to improve the running performance on a wet road surface (hereinafter referred to as wet performance) in a pneumatic tire, a diene rubber having a high glass transition point is used for the rubber composition constituting the tread rubber portion, a filler, There is a method of increasing the amount of oil blended. However, these methods are accompanied by a decrease in wear resistance.

Japanese Patent Laid-Open No. 04-045114 Japanese Patent Application Laid-Open No. 10-025358 Japanese Patent Laid-Open No. 2001-2333020 JP 2009-166712 A JP 2009-173048 A

  The present inventor has intensively studied to improve the wet performance without impairing the wear resistance, and irradiates the tread rubber part of a vulcanized pneumatic tire with a compound having a specific functional group by electron beam irradiation. It was considered to be combined using.

  As a technique for imparting a compound to a rubber polymer using electron beam irradiation, the above-mentioned Patent Document 1 discloses that a crosslinked silicone rubber is impregnated with a radical polymerizable monomer and then the monomer is polymerized by electron beam irradiation. Is disclosed. Further, Patent Document 2 discloses that a monomer is applied to a natural rubber latex film and a polymer film is formed by electron beam irradiation. However, Patent Document 1 aims to increase the hardness of silicone rubber, and Patent Document 2 aims to improve the adhesiveness of rubber products, both of which are technologies unrelated to pneumatic tires. It is.

  On the other hand, as related to the pneumatic tire, the above-mentioned Patent Document 3 discloses that the end of the block while maintaining the grip on the snowy and snowy road surface by irradiating the tread surface of the vulcanized tire with an electron beam. Increasing the rigidity in the vicinity is disclosed. Similarly, Patent Documents 4 and 5 also disclose that the tire surface is irradiated with an electron beam in order to increase the block rigidity and improve the handling stability and wear resistance while maintaining the grip. ing. However, none of these documents disclose or suggest that a specific compound is applied and irradiated with an electron beam.

  An object of this invention is to provide the pneumatic tire which can improve wet performance, without impairing abrasion resistance, and its manufacturing method.

  The method for producing a pneumatic tire according to the present invention includes an air having a tread rubber portion made of a rubber composition containing 50 parts by mass or more of a diene rubber having a glass transition point of −45 ° C. or more in 100 parts by mass of a rubber component. After vulcanizing and molding a compound having a carbon-carbon double bond and a hydrophilic group in the molecule, a step of vulcanizing and molding the tire, a step of irradiating the surface of the tread rubber part after vulcanization with an electron beam And a step of applying to the surface of the tread rubber part.

  The pneumatic tire according to the present invention is a pneumatic tire provided with a tread rubber portion made of a rubber composition containing a diene rubber having a glass transition point of −45 ° C. or more in 50 parts by mass or more in 100 parts by mass of a rubber component. In addition, a compound having a carbon-carbon double bond and a hydrophilic group in the molecule is reacted with the diene rubber on the surface of the tread rubber portion by electron beam irradiation on the surface of the tread rubber portion. .

  According to the present invention, since a hydrophilic group can be introduced to a pneumatic tire after vulcanization limited to the surface of the tread rubber portion, a water film on a wet road surface without impairing wear resistance. The wet performance can be improved by increasing the affinity between rubber and rubber.

1 is a half sectional view of a pneumatic tire according to an embodiment.

  Embodiments of the present invention will be described below.

  FIG. 1 shows an example of a pneumatic radial tire according to the embodiment. The tire includes a tread portion (1), a pair of left and right bead portions (2), and a pair of left and right sidewall portions (3) interposed between the tread portion (1) and the bead portion (2). The carcass layer (4) disposed on the radially inner side of the tread portion (1) is wound from the inside of the bead core (5) to the outside by the bead portion (2) through the side wall portions (3) on both sides. It is locked by.

  A belt layer (6) is disposed on the outer peripheral side of the carcass layer (4) in the tread portion (1), and a tread rubber portion (7) constituting a ground contact surface is provided on the outer peripheral side of the belt layer (6). It has been. The surface of the tread rubber portion (7) is provided with a plurality of grooves (8) such as a longitudinal groove extending in the circumferential direction and a lateral groove extending in a direction crossing the circumferential groove. A pneumatic tire having such a structure can be produced by producing a green tire (unvulcanized tire) and then vulcanizing it in accordance with a conventional method.

  In the present embodiment, as a rubber composition for forming the tread rubber part (7), a rubber containing 50 parts by mass or more of a diene rubber having a glass transition point (Tg) of −45 ° C. or more in 100 parts by mass of a rubber component. Use the composition.

  Examples of the diene rubber having a glass transition point of −45 ° C. or higher include styrene butadiene rubber, styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, and styrene-isoprene-butadiene copolymer rubber. Of these, styrene butadiene rubber (SBR) is particularly preferred. When the glass transition point of the diene rubber is less than −45 ° C., the movement of the diene rubber polymer is large in the normal temperature range, and the radicals generated on the polymer due to electron beam irradiation are quickly lost. Therefore, the reaction rate between the compound having a carbon-carbon double bond and a hydrophilic group in the molecule is lowered, and the effect of improving the wet performance becomes insufficient. Although the minimum of a glass transition point is not specifically limited, Considering the use as a tread rubber part of a tire, 0 degrees C or less is preferable, More preferably, it is -10 degrees C or less. The glass transition point is a value measured by a differential scanning calorimetry (DSC) method at a rate of temperature increase of 20 ° C./minute (measurement temperature range: −150 ° C. to 50 ° C.) in accordance with JIS K7121.

  The rubber component contains 50% by mass or more of a diene rubber having a glass transition point of −45 ° C. or higher. More preferably, it is 60 mass% or more. If it is less than 50 mass%, the improvement effect of wet performance will become inadequate. The rubber component may be a diene rubber having a glass transition point of −45 ° C. or more, or may be a blend with another diene rubber. As other diene rubbers to be blended, various diene rubbers having a glass transition point of less than −45 ° C. can be used. For example, polybutadiene rubber (BR), natural rubber (NR), polyisoprene rubber (IR) and the like, and styrene butadiene rubber, styrene-isoprene copolymer rubber, butadiene having a glass transition point of less than −45 ° C. -Isoprene copolymer rubber and styrene-isoprene-butadiene copolymer rubber may be used.

  Carbon rubber and / or silica can be blended with the rubber composition as a filler. Although the compounding quantity of this filler is not specifically limited, It is preferable that it is 40-200 mass parts with respect to 100 mass parts of said rubber components, More preferably, it is 60-120 mass parts. The carbon black is not particularly limited, but those of SAF class (N100 series), ISAF class (N200 series), HAF class (N300 series) (both ASTM grade) are preferably used. Examples of the silica include wet silica, dry silica, colloidal silica, and precipitated silica. It is particularly preferable to use wet silica containing hydrous silicic acid as a main component. In addition, when mix | blending a silica as a filler, it is preferable to use together silane coupling agents, such as sulfide silane and mercaptosilane, and a silane coupling agent is 2-25 mass parts normally with respect to 100 mass parts of silica. Can be used.

  In addition to the above rubber composition, various additives generally used in the rubber composition such as oil, zinc white, stearic acid, anti-aging agent, wax, vulcanizing agent, vulcanization accelerator, and the like are appropriately blended. Can do. Examples of the vulcanizing agent include sulfur and sulfur-containing compounds, and are not particularly limited. However, the blending amount is preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the rubber component. More preferably, it is 0.5-5 mass parts. Moreover, as a compounding quantity of a vulcanization accelerator, it is preferable that it is 0.1-7 mass parts with respect to 100 mass parts of said rubber components, More preferably, it is 0.5-5 mass parts.

  The rubber composition is prepared by kneading using a rubber kneader such as a normal Banbury mixer or kneader, and is vulcanized and molded at 140 to 180 ° C. according to a conventional method, for example, to form a tread for a pneumatic tire. A rubber part (7) can be formed. The tread rubber portion of the pneumatic tire includes a two-layer structure of a cap rubber and a base rubber, and a single-layer structure in which both are integrated, but is preferably used for the rubber constituting the ground contact surface. . That is, if it has a single layer structure, the tread rubber portion is preferably made of the rubber composition, and if it has a two-layer structure, the cap rubber is preferably made of the rubber composition.

  After vulcanization molding as described above, in the present embodiment, the surface of the tread rubber portion (7) is irradiated with an electron beam. By irradiating with an electron beam, radicals can be generated at the carbon-carbon double bond (C═C) portion or C—H bond portion of the diene rubber existing on the tread surface. The surface of the tread rubber portion (7) includes not only the tread surface portion but also the side surface portion and the bottom surface portion of the groove (8).

  Although it does not specifically limit as irradiation conditions of an electron beam, It is preferable that acceleration voltage is 150-1000 kV, More preferably, it is 200-500 kV, and irradiation dose is 10-400 kGy, More preferably, it is 50-250 kGy.

  A monomer is added to the surface of the tread rubber portion (7) irradiated with the electron beam in this manner when the generated radical is present (that is, before the radical disappears). Here, the monomer refers to a low molecular compound having a carbon-carbon double bond and a hydrophilic group in the molecule. The method for applying the monomer is not particularly limited. For example, when the monomer is liquid, it is diluted as it is or with a solvent such as water, or when the monomer is solid, it is dissolved in a solvent such as water. A liquid (a liquid containing a monomer) is prepared, and the monomer liquid may be applied to the surface of the tread rubber portion (7). The application method is not particularly limited, and various methods such as brushing, spraying, and dipping the tread rubber portion (7) in a tank containing the monomer liquid can be employed. When the monomer is a gas, the monomer can be imparted also by placing a pneumatic tire in an atmosphere filled with the monomer.

  After adding the monomer, it is allowed to stand for a predetermined time. In addition, when letting it stand, you may put in an oven etc. and heat (for example, 30-80 degreeC).

  In the monomer applied to the surface of the tread rubber portion (7), the carbon-carbon double bond portion in the molecule reacts with the diene rubber on the surface of the tread rubber portion (7) by radical polymerization reaction. That is, the monomer is bonded to the diene rubber polymer by the reaction of the carbon-carbon double bond of the monomer with the radical of the diene rubber generated by electron beam irradiation. In addition, a graft polymer having a diene rubber polymer as a trunk and a polymer portion formed by linking the monomers as side chains may be formed by sequentially linking monomers by a radical polymerization reaction.

  Thereby, the hydrophilic group which a monomer has is introduce | transduced on the surface of a tread rubber part (7) (In addition, the surface treatment part (hydrophilic film) by this monomer was shown with the code | symbol 9 in FIG. 1). Therefore, the affinity between the water film on the wet road surface and the tread rubber portion (7) can be enhanced, and the drainage effect by the blocks and grooves of the tread rubber portion (7) can be enhanced, so that the wet performance is improved. Since the monomer does not penetrate into the tread rubber part (7), the hydrophilic group is introduced only on the surface of the tread rubber part (7). Therefore, when the tread rubber portion (7) is worn out, the tread portion itself is exposed to the internal rubber so that the effect of increasing the affinity cannot be obtained. However, as shown in FIG. Since the surface treatment portion (9) is also present on the bottom surface portion, the effect of improving the wet performance can be maintained. Moreover, since it is modification | reformation of only the surface, the abrasion resistance as a whole tread rubber part (7) can be maintained.

The amount of the monomer applied to the surface of the tread rubber part (7) is not particularly limited and can be, for example, 100 to 10,000 g / m ² .

The monomer has at least one unsaturated group represented by H ₂ C═CR— (wherein R is a hydrogen atom or a methyl group) as a radical-polymerizable carbon-carbon double bond, and has a hydrophilic group. It is preferable to use one having at least one carboxyl group or hydroxyl group having a high affinity for water on the road surface. More specifically, a compound represented by the following general formula (1) is used as the monomer.

  In the formula, R represents a hydrogen atom or a methyl group, X represents a carboxyl group or a hydroxyl group, A represents a C 1-10 divalent organic group which may contain an oxygen atom, and n represents 0 or 1. A is more preferably a C 1-8 divalent organic group which may contain an ester bond or an ether bond.

More specifically, the monomer includes a vinyl group (H ₂ C═CH—), an isopropenyl group (H ₂ C═C (CH ₃ ) —), an allyl group (H ₂ C═CH—) necessary for radical polymerization. A compound having any one of CH ₂ —) and having at least one carboxyl group (—COOH) and hydroxyl group (—OH) having high affinity with water on the road surface. As what has, methacrylic acid, acrylic acid, 4-vinyl benzoic acid, 3-butenoic acid etc. are mentioned, As what has a hydroxyl group, allyl alcohol, 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, 6-hepten-1-ol, 7-octen-1-ol, 8-nonen-1-ol, 9-decene-1-ol, 10-undecen-1-ol, 3 − Examples include alkenol such as methyl-3-buten-1-ol, 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, and the like, and these can be used alone or in combination of two or more.

  In the said embodiment, although the monomer was provided after irradiating an electron beam, you may irradiate an electron beam after providing a monomer. That is, in the present invention, the surface of the tread rubber part after vulcanization molding may be irradiated with an electron beam, and then the above monomer may be added to the surface of the tread rubber part irradiated with the electron beam. After the above monomer is applied to the surface of the tread rubber part after molding, the surface of the tread rubber part may be irradiated with an electron beam, and further, the electron beam irradiation and the monomer application may be performed simultaneously. The monomer can be reacted with the surface of the tread rubber part.

  The pneumatic tire to which the present invention can be applied is not particularly limited, and can be applied to various pneumatic tires such as tires for passenger cars and tires for heavy loads such as trucks and buses.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

(First embodiment)
The rubber compositions of Examples 1-1 to 1-3 and Comparative Examples 1-1 to 4 were prepared according to a conventional method using a Banbury mixer. The rubber component of each rubber composition is as shown in Table 1 below. In addition, the mass part of the rubber component in Table 1 is a mass part as a polymer component excluding oil blended in the oil fraction. Details of each rubber component are as follows.

SBR 1739: styrene butadiene rubber “Nipol 1739” manufactured by Nippon Zeon Co., Ltd. (Tg = −35 ° C., 37.5 parts by mass oil-extended rubber)
・ BR: Ube Industries, Ltd. butadiene rubber "UBEPOL BR150"

  In each rubber composition, 75 parts by mass of silica ("Ultrasil VN3" manufactured by Evonik), 6 parts by mass of a silane coupling agent ("Si69" manufactured by Evonik), aroma, per 100 parts by mass of the rubber component 35 parts by mass of oil ("Extract 4 S" manufactured by Showa Shell Sekiyu KK) (however, the total amount including the oil component of the rubber component), anti-aging agent (N-phenyl-N '-(1, 3-dimethylbutyl) -p-phenylenediamine) 2 parts by mass, stearic acid (industrial stearic acid) 2 parts by mass, zinc oxide (No. 1 zinc white) 3 parts by mass, wax (manufactured by Nippon Seiwa Co., Ltd.) Wax ") 2 parts by mass, vulcanization accelerator (N-tert-butyl-2-benzothiazolesulfenamide) 1.5 parts by mass, and sulfur (5% oil-treated powder sulfur) 2 parts by mass were blended.

  Using the obtained rubber composition as a rubber composition for a tread, a 195 / 65R15 pneumatic radial tire was vulcanized and molded in accordance with a conventional method, followed by electron beam irradiation and monomer coating according to the conditions shown in Table 1. A pneumatic tire was manufactured.

  In detail, in Example 1-1, the conditions of temperature: room temperature, acceleration voltage: 200 kV, and irradiation dose: 200 kGy are applied to the surface of the tread rubber portion using an electron beam irradiation device for the vulcanized tire. Then, an electron beam was irradiated. Immediately after the irradiation, the tread rubber portion of the tire was immersed in a monomer solution to give a monomer to the surface of the tread rubber portion. As the monomer liquid, a 50% by mass aqueous solution of monomer A: methacrylic acid was used. Thereafter, the tread rubber part was taken out of the monomer liquid and allowed to stand at room temperature for 4 hours to obtain a pneumatic tire in which the monomer was bonded to the tread rubber part surface.

  In Example 1-2, a pneumatic tire was obtained in the same manner as in Example 1-1, except that a 50% by mass aqueous solution of monomer B: 2-hydroxyethyl methacrylate was used as the monomer liquid. In Example 1-3, a pneumatic tire was obtained in the same manner as in Example 1 except that a 50 mass% aqueous solution of monomer C: allyl alcohol was used as the monomer liquid.

  Comparative Example 1-1 is an example in which electron beam irradiation and monomer application were not performed as controls. Comparative Example 1-2 is an example in which a monomer liquid was applied without electron beam irradiation, and was the same as Example 1-1 except that electron beam irradiation was not performed. Comparative Example 1-3 was an example in which the electron beam was irradiated but the monomer liquid was not applied, and was the same as Example 1-1 except that the monomer liquid was not applied. Comparative Example 1-4 is an example in which a conventional wet performance improvement method is applied, and is an example in which the ratio of SBR1739 is increased with respect to Comparative Example 1-1.

  About each obtained pneumatic tire, wet performance and abrasion resistance were evaluated. Each evaluation method is as follows.

・ Wet performance: Four wheels are mounted on a 2000cc FR vehicle (rim size: 15x6, air pressure: 210kPa), and ABS is applied by applying braking force from a speed of 100km / h on a wet road surface (paved road surface with a depth of 1mm). It evaluated by measuring the braking distance until it stops when it act | operates, and it displayed with the index | exponent which set the value of the comparative example 1-1 to 100 about the reciprocal number of braking distance. The larger the value, the shorter the braking distance and the better the wet braking performance.

-Abrasion resistance: Four tires were mounted on a taxi, the remaining groove depth after running at 20000 km was measured while rotating about every 5000 km, and the value was expressed as an index with the value of Comparative Example 1-1 as 100. The larger the value, the deeper the remaining groove depth and the better the wear resistance.

  The results are as shown in Table 1, and in Examples 1-1 to 3 in which a monomer having a hydrophilic group was applied to the tread rubber surface, wet performance could be improved without impairing wear resistance. . On the other hand, in Comparative Example 1-2 in which the electron beam irradiation was not performed and Comparative Example 1-3 in which the electron beam irradiation was performed but no monomer was applied, no effect of improving the wet performance was observed. In Comparative Example 1-4 in which the amount of high-Tg SBR was increased, the wet performance was improved, but the wear resistance was impaired.

(Second embodiment)
A pneumatic tire was manufactured in the same manner as in the first example except that the composition of the rubber component was SBR1739 / BR = 55/45 as shown in Table 2. More specifically, Example 2-1 is Example 1-1, Comparative Example 2-1 is Comparative Example 1-1, Comparative Example 2-2 is Comparative Example 1-2, and Comparative Example 2-3 is Comparative Example 1. -3, and only the composition of the rubber component is different. About the obtained pneumatic tire, it carried out similarly to 1st Example, and evaluated wet performance and abrasion resistance. However, the evaluation criteria was Comparative Example 2-1. The results are as shown in Table 2. In Example 2-1, in which a monomer having a hydrophilic group was applied to the tread rubber surface, the wet performance could be improved without impairing the wear resistance.

(Third embodiment)
A pneumatic tire was manufactured in the same manner as in the first example except that the composition of the rubber component was SBR1739 / BR = 35/65 as shown in Table 3. More specifically, Comparative Example 3-1 is Comparative Example 1-1, Comparative Example 3-2 is Comparative Example 1-2, Comparative Example 3-3 is Example 1-1, and only the composition of the rubber component is used. Different. About the obtained pneumatic tire, it carried out similarly to 1st Example, and evaluated wet performance and abrasion resistance. However, the evaluation standard was Comparative Example 3-1. The results are as shown in Table 3, and in this case, since the blending ratio of high-Tg SBR is small, as shown in Comparative Example 3-3, both electron beam irradiation and monomer coating were performed. There was no improvement in wet performance.

(Fourth embodiment)
In place of SBR1739, a styrene butadiene rubber “VSL5525-1” (Tg = −20 ° C.) manufactured by LANXESS was used, and a pneumatic tire was produced in the same manner as in the first example. More specifically, Example 4-1 is Example 1-1, Example 4-2 is Example 1-2, Example 4-3 is Example 1-3, and Comparative Example 4-1 is Comparative Example 1. -1, Comparative Example 4-2 differs from Comparative Example 1-2, and Comparative Example 4-3 differs from Comparative Example 1-3 only in the rubber component. About the obtained pneumatic tire, it carried out similarly to 1st Example, and evaluated wet performance and abrasion resistance. However, the evaluation standard was Comparative Example 4-1. The results are as shown in Table 4. In Examples 4-1 to 3 in which a monomer having a hydrophilic group was applied to the tread rubber surface, the wet performance could be improved without impairing the wear resistance. .

(5th Example)
Instead of SBR1739, SBR1723: Nippon Zeon Co., Ltd. styrene butadiene rubber “SBR1723” (Tg = −55 ° C., 37.5 parts by mass oil-extended rubber) was used. A tire was produced. More specifically, Comparative Example 5-1 is different from Comparative Example 1-1, Comparative Example 5-2 is Comparative Example 1-2, and Comparative Example 5-3 is different from Example 1-1 only in the rubber component. About the obtained pneumatic tire, it carried out similarly to 1st Example, and evaluated wet performance and abrasion resistance. However, the criterion for evaluation was Comparative Example 5-1. The results are as shown in Table 5. In this case, since the glass transition point of SBR was low, as shown in Comparative Example 5-3, the wet performance was performed even though both electron beam irradiation and monomer coating were performed. The improvement effect was not seen.

  As shown in the above examples, after vulcanizing and molding a tire having a tread comb portion using a specific amount of SBR having a high Tg, irradiation with an electron beam and treatment with a monomer having a hydrophilic group are performed. As a result, the wet performance could be improved without impairing the wear resistance.

DESCRIPTION OF SYMBOLS 1 ... Tread part, 2 ... Bead part, 3 ... Side wall part, 4 ... Carcass layer, 5 ... Bead core, 6 ... Belt layer, 7 ... Tread rubber part, 8 ... Groove, 9 ... Surface treatment part

Claims (4)

Vulcanizing and molding a pneumatic tire having a tread rubber portion made of a rubber composition containing a diene rubber having a glass transition point of −45 ° C. or higher in a rubber component containing 50 parts by mass or more in 100 parts by mass of a rubber component;
Irradiating the surface of the tread rubber part after vulcanization with an electron beam;
Adding a compound having a carbon-carbon double bond and a hydrophilic group in the molecule to the surface of the tread rubber portion after vulcanization molding;
The manufacturing method of the pneumatic tire containing this. The compound has at least one group represented by H ₂ C═CR— (wherein R is a hydrogen atom or a methyl group) as the carbon-carbon double bond, and the hydrophilic group includes a carboxyl group and a hydroxyl group. The method for producing a pneumatic tire according to claim 1, comprising at least one. The method for producing a pneumatic tire according to claim 1, wherein the compound is represented by the following general formula (1).

(In the formula, R represents a hydrogen atom or a methyl group, X represents a carboxyl group or a hydroxyl group, A represents a C 1-10 divalent organic group that may contain an oxygen atom, and n represents 0 or 1). A pneumatic tire having a tread rubber portion made of a rubber composition containing a diene rubber having a glass transition point of -45 ° C or higher in a rubber component of 50 parts by mass or more in 100 parts by mass of a rubber component,
An air characterized by reacting a compound having a carbon-carbon double bond and a hydrophilic group in the molecule with the diene rubber on the surface of the tread rubber portion by electron beam irradiation on the surface of the tread rubber portion. Enter tire.

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