JP2008120940A - Pneumatic tire - Google Patents

Abstract

Provided is a pneumatic tire provided with a two-layer structure tread capable of improving the weather resistance of a cap rubber by suppressing the transition to the anti-aging agent or the wax in the cap rubber or the transition speed of the cap rubber. To do.
A tread 2 has a two-layer structure of a cap rubber 21 on a tire tread surface side and a base rubber 22 disposed inside the cap rubber 21. The cap rubber 21 and the base rubber 22 are made of a diene system. In the pneumatic tire 1 comprising a rubber composition containing rubber as a rubber component, the volume ratio of the softening agent contained in the base rubber 22 to the softening agent contained in the cap rubber 21 is 0.5 or less, The cap rubber 21 contains 10 to 60 parts by weight of a liquid polymer having a number average molecular weight of 3,000 to 90,000 as the softening agent with respect to 100 parts by weight of the diene rubber component.
[Selection] Figure 1

Description

  The present invention relates to a pneumatic tire, and more particularly, to a pneumatic tire including a two-layer structure tread in which the weather resistance of a tread is improved while maintaining the processability and rolling resistance characteristics of a rubber composition.

  As automobile fuel efficiency needs increase, it is strongly required to further reduce the rolling resistance of pneumatic tires, and at the same time, it is required to improve handling stability (wet grip performance) and wear resistance on wet road surfaces. ing.

  Conventionally, a tire having a two-layer structure (cap / base structure) tread in which a tread is divided into a cap rubber on the tire tread side and a base rubber disposed on the inside of the cap rubber has been generally used (for example, Patent Document 1). In a tire having such a cap / base structure tread, in order to improve the rolling resistance, a rubber composition having a high friction coefficient is used for the cap rubber, and a rubber composition having a low energy loss is used for the base rubber. Things have been done.

  In order to improve the friction coefficient, such a rubber composition of cap rubber can increase energy loss by adding a large amount of a reinforcing filler such as carbon black and a softening agent such as process oil. In order to reduce energy loss, a rubber composition in which a reinforcing filler or softening agent is used in a smaller amount than cap rubber is used.

However, when the cap rubber and the base rubber are bonded to the cap / base structure, a softening agent that easily shifts to process oil in the cap rubber during use of the tire due to a difference in the concentration of the softening agent contained in the cap rubber and the base rubber. Shifts to the base rubber side with time, and at that time, the anti-aging agent and wax in the cap rubber together with the softening agent are transferred to the base rubber together. As a result, the anti-aging agent and the wax in the cap rubber are reduced, the weather resistance thereof is lowered, and there is a problem that cracks occur in the tread groove bottom and the shoulder due to the influence of ozone, ultraviolet rays and the like.
JP 2006-76355 A

  In view of the above problems, the object of the present invention is to suppress the transition of the anti-aging agent and the wax in the cap rubber to the base rubber or the transition speed while maintaining the processability and rolling resistance of the rubber composition. An object of the present invention is to provide a pneumatic tire provided with a two-layer structure tread capable of improving the weather resistance of a cap tread.

  In order to solve the above-mentioned problems, the present inventor has intensively studied and used a liquid polymer excellent in compatibility with a diene rubber as a cap rubber instead of a conventional process oil as a softener. As a result, it was found that the migration of the antioxidant and the wax to the base rubber was suppressed, and the present invention was achieved.

  That is, in the present invention, the tread has a two-layer structure of a cap rubber on the tire tread side and a base rubber disposed inside the cap rubber. The cap rubber and the base rubber include a diene rubber as a rubber component. In the pneumatic tire comprising the rubber composition, the volume ratio of the softening agent contained in the base rubber to the softening agent contained in the cap rubber is 0.5 or less, and the cap rubber serves as the softening agent. A pneumatic tire comprising 10 to 60 parts by weight of a liquid polymer having a number average molecular weight of 3,000 to 90,000 with respect to 100 parts by weight of the diene rubber component.

  In the present invention, the liquid polymer is preferably a diene liquid polymer.

The pneumatic tire according to claim 1.

  The liquid polymer is a functional group-containing liquid polymer having at least one functional group selected from the group consisting of a hydroxyl group, a carboxyl group, an amino group, an epoxy group, an acid anhydride group, a mercapto group, and a cyano group at the molecular end. It is preferable that

  In the pneumatic tire of the present invention, by using a liquid polymer as a softening agent for the cap rubber of the cap / base structure tread, the liquid polymer excellent in compatibility with the diene rubber has little movement in the rubber. Therefore, the weather resistance of the cap rubber can be maintained, and the tire durability and appearance can be improved by suppressing the transition of the anti-aging agent and the wax in the cap rubber to the base rubber or the speed of the transition.

  FIG. 1 is a half sectional view showing a pneumatic tire 1 for a passenger car according to one embodiment of the present invention.

  A pneumatic tire 1 (hereinafter, the pneumatic tire may be simply referred to as a “tire”) includes a pair of bead portions 4 that are assembled into a rim, and sidewall portions 3 that extend outward in the tire radial direction from the bead portions 4. The tread portion 2 is configured to contact the road surface provided between the sidewall portions 3 and 3, and the tread portion 2 includes a cap rubber 21 on the tire tread side and a base rubber 22 disposed on the inner side of the cap rubber 21. It is a tire having a tread with a so-called cap / base structure having a two-layer structure divided into two.

  The tire 1 includes a carcass 6 in which a carcass ply made of an organic fiber cord such as polyester and the like disposed radially around a bead core 5 embedded in a pair of bead portions 4 is folded back from the inside of the tire to the outside and locked. The belt 7 made of two cross belt plies using steel cords arranged inside the tread portion 2 and the outer periphery of the belt 7 are spirally wound at an angle of approximately 0 ° with respect to the tire circumferential direction. A radial tire for a passenger car having a single cap ply 8 made of an organic fiber cord such as nylon that is turned is shown.

  The rubber composition used for the cap rubber 21 and the base rubber 22 of the tire 1 according to the present invention comprises a diene rubber as a rubber component, a reinforcing filler such as carbon black or silica, a softening agent such as process oil, and weather resistance. It consists of a rubber composition containing an anti-aging agent for ensuring the properties and a compounding agent for tread rubber including wax.

  The cap rubber 21 is in contact with the road surface to improve the friction coefficient, and in order to ensure low rolling resistance, grip performance, and wear resistance, a reinforcing filler such as carbon black is 40 to 100 parts per 100 parts by weight of the rubber component. A rubber composition containing 10 parts by weight and 10 parts by weight of a softening agent and having increased energy loss is used. On the other hand, the base rubber 22 has a reinforcing property such as carbon black to reduce energy loss and suppress heat generation. A rubber composition is used in which the filler is blended in an amount of 20 to 50 parts by weight with respect to 100 parts by weight of the rubber component and the softener is blended in an amount of about 2 to 20 parts by weight from the cap rubber.

  In the present invention, the rubber composition of the cap rubber and the base rubber uses various diene rubbers as the rubber component. Examples of the diene rubber include natural rubber (NR), polyisoprene rubber (IR), styrene-butadiene copolymer rubber (SBR), polybutadiene rubber (BR), and syndiotactic-1,2-polybutadiene. Examples include butadiene rubber (SPB), terminal-modified low-cis BR, butyl rubber (IIR), halogenated butyl rubber, ethylene-propylene-diene terpolymer rubber (EPDM), and these are used alone or in combination of two or more. Can be used.

  In the case of using the above-mentioned blend, blending can be carried out at an arbitrary ratio, but preferable ratios are 80 to 40% by weight of SBR and NR, and 20 to 60% by weight of BR, preferably the BR content is 40% by weight or less. is there.

  In the present invention, the softener contained in each rubber composition of the cap rubber 21 and the base rubber 22 has a volume ratio of the softener in the base rubber to 0.5 or less of the softener in the cap rubber. It is blended as follows. The blending amount of this softener is indicated by a volume ratio calculated from the volume of the softener before kneading into rubber. If the volume ratio exceeds 0.5, the amount of softener in the base bomb becomes excessive and rolling resistance is increased. Properties and coefficient of friction become inferior.

  In the present invention, the cap rubber is replaced with a liquid polymer having a number average molecular weight of 3,000 to 90,000 per 100 parts by weight of the rubber component in place of a conventional mineral oil softener such as process oil as a softener. ~ 60 parts by weight is used.

  Since the liquid polymer has excellent compatibility with the diene rubber, the migration in the rubber composition can be suppressed to a very low level, thereby allowing the anti-aging agent or the wax in the cap rubber to migrate to or transfer to the base rubber. It is possible to suppress the deterioration of the anti-aging agent and the wax in the cap rubber and maintain the weather resistance of the cap rubber.

  This liquid polymer is a liquid polymer at room temperature. If the number average molecular weight is less than 3,000, the migration of the liquid polymer is not much different from that of process oil, and the effect of improving the weather resistance and appearance is not obtained, and if it exceeds 90,000, the softening effect is insufficient. Processability cannot be obtained. A more preferable range of the number average molecular weight is 3,000 to 60,000.

  Moreover, it is preferable that the said liquid polymer consists of a diene liquid polymer from a viewpoint of improving compatibility with the diene rubber component which comprises a rubber composition.

  Examples of the diene liquid polymer include butadiene polymer, isoprene polymer, and styrene butadiene polymer.

  Moreover, it is preferable to use the liquid polymer having a molecular end modified with a functional group having a hetero atom. By modifying with functional groups, interaction with fillers such as carbon black and silica improves compatibility with fillers, thereby improving dispersibility and improving the strength and fatigue resistance of rubber compositions. In addition, the effect of improving weather resistance by improving dispersibility can also be expected.

Examples of such a functional group include a hydroxyl group, a carboxyl group, an amino group, an epoxy group, an acid anhydride group, a mercapto group, and a cyano group, and these may be used alone or in combination of two or more. Here, the hydroxyl group (—OH) includes a phenol group as well as a methylol group (—CH ₂ OH) and an ethylol group. Examples of the carboxyl group include maleic acid, phthalic acid, acrylic acid, and methacrylic acid. Further, the amino group may be any of a primary amino group, a secondary amino group, and a tertiary amino group, and may be an aliphatic amino group or an aromatic amino group. The acid anhydride group consists of an anhydride of a dicarboxylic acid such as maleic acid or phthalic acid.

  The liquid polymer is blended in an amount of 10 to 60 parts by weight with respect to 100 parts by weight of the rubber component. When the blending amount of the liquid polymer is less than 10 parts by weight, the effect of the present invention cannot be obtained. When the blending amount exceeds 60 parts by weight, the dispersibility of the reinforcing filler such as carbon black is deteriorated, and the strength and fatigue resistance are lowered. Accompanied by.

  In the present invention, the cap rubber is not formulated with a softening agent such as process oil as a softening agent, but when contained in the rubber composition as an unavoidable component, preferably less than 1 part by weight, preferably It is preferably 0.5 parts by weight or less, more preferably 0.2 parts by weight, and it is desirably close to 0 parts by weight.

  The base rubber contains various softeners such as conventional vegetable oil-based softeners and mineral oil-based softeners as softeners, but process oils such as aromatic oils, paraffin oils, and naphthenic oils are mainly used. Can be used for

  Further, as the reinforcing filler, organic reinforcing agents such as carbon black, silica, clays, calcium carbonate, magnesium silicate (talc), high styrene resin and coumarone indene resin can be used. Among these, carbon black and silica are preferable in terms of the reinforcing effect and rolling resistance characteristics.

The carbon black is not particularly limited, and examples thereof include carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 25 to 120 m ² / g. Specifically, carbon black of ISAF, HAF, FEF, GPF class Can be used. Above all, the cap _{rubber, N} 2 SA of carbon black 80 to 120 ² / g are preferable from the viewpoint of abrasion resistance and rolling resistance, the base rubber _N 2 SA is 25~80m ² / g Carbon Black is preferable from the viewpoint of low heat generation.

The type of silica is not particularly limited, and examples thereof 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. As an example of silica, wet silica having a nitrogen adsorption specific surface area (BET) of 100 to 250 m ² / g and a DBP oil absorption of 100 ml / 100 g or more is preferable from the viewpoint of reinforcing effect and workability, manufactured by Tosoh Silica Industry Co., Ltd. Commercial products such as Nipsil AQ, VN3, Ultrazil VN3 manufactured by Degussa Co., Ltd. can be used. Further, a silane coupling agent such as bis (triethoxysilylpropyl) -tetrasulfide is preferably used in combination, and is used in an amount of 2 to 20% by weight of the amount of silica.

  Examples of the anti-aging agent include various anti-aging agents such as amine-ketone type, aromatic secondary amine type, phenol type, and benzimidazole type. Among these, aromatic secondary amine type and phenol type anti-aging agents which are effective against deterioration due to ozone and ultraviolet rays are preferable. Specific examples include N, N′-diphenyl-p-phenylenediamine, N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine, and the like.

  Furthermore, the above wax is a component mainly composed of chain saturated hydrocarbons such as paraffin wax and microcrystalline wax, and is a component that easily moves in rubber and blooms on the surface. A wax thin film is formed on the tread surface to form ozone. It works to block the generation of cracks such as ozone cracks by blocking UV light and ultraviolet rays.

  In the rubber composition according to the present invention, a rubber compounding agent generally used in a tread rubber composition can be appropriately blended as necessary in addition to the rubber and the blending components. For example, there are vulcanizing agents such as stearic acid, zinc oxide, resins, sulfur and the like, vulcanization accelerators, vulcanization acceleration assistants, etc., and the blending ratio thereof is not particularly limited.

  The rubber composition may be prepared by introducing the rubber component and the compounding component into a kneader such as a Banbury mixer according to a conventional method so that the components are uniformly kneaded. The rubber composition obtained is formed into a tread rubber with a predetermined cross-section using an extruder or the like, and various pneumatic tires such as for passenger cars and two-wheeled vehicles having a cap / base structure are manufactured by an ordinary method. can do.

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

  Table 1 shows the basic composition (parts by weight) of the rubber composition of cap rubber and base rubber. A rubber composition for cap rubber and base rubber is prepared by kneading a rubber composition containing a variable amount of the liquid polymer and aroma oil shown in Table 2 with a basic method using a Banbury mixer with a capacity of 200 liters. Was prepared. The rubber component, liquid polymer, and compounding agent used are as follows.

[Rubber component]
Styrene butadiene rubber (SBR): JSR Corporation, terminal-modified solution polymerization SBR “SL563”
・ Butadiene rubber (BR): Ube Industries, Ltd. “BR150B”
・ Natural rubber (NR): Made in Thailand RSS # 3

[Liquid polymer]
Liquid polymer A: Kuraray Co., Ltd. liquid polyisoprene “LIR50” (no terminal functional group. Number average molecular weight = 50,000)
Liquid polymer B: Ube Industries, Ltd. liquid polybutadiene “CTB2000” (functional group: —COOH. Number average molecular weight = 5,000)
Liquid polymer C: Idemitsu Petrochemical Co., Ltd. Liquid polybutadiene “RH-45” (functional group: —OH. Number average molecular weight = 2,800)

[Combination agent]
・ Carbon black (ISAF): Tokai Carbon Co., Ltd. “Seast 6”
・ Carbon black (FEF): Tokai Carbon Co., Ltd. “Seast SO”
・ Aroma oil: Japan Energy “X-140”
Anti-aging agent (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine): Ouchi Shinsei Chemical Co., Ltd. “NOCRACK 6C”
・ Wax (paraffin wax): Nippon Seiwa Co., Ltd. “Ozoace-0355”
・ Stearic acid: Kao Corporation “Lunac S-20”
・ Zinc oxide: Mitsui Kinzoku Mining Co., Ltd. “Zinc Hua 1”
・ Sulfur: Hosoi Chemical Co., Ltd. “5% oil-treated powder sulfur”
・ Vulcanization accelerator (N-tetrabutyl-2-benzothiazole sulfenamide): Ouchi Shinsei Chemical Co., Ltd. “Noxeller NS-P”

  The process of each cap rubber composition obtained and the weather resistance of the cap rubber were evaluated by the following method for the sample in which the cap rubber and the base rubber were combined so that the softener volume ratio shown in Table 2 was obtained. Next, a test tire for a passenger car of size 185 / 70R14 having a cap / base structure tread was manufactured according to a conventional method by combining the cap rubber and the base rubber. The rolling resistance of the manufactured tire was evaluated by the following method. The results are shown in Table 2.

[Machinability]
The Mooney viscosity (ML1 + 4 (100 ° C.)) was measured in accordance with JIS K6300 and indicated as an index with Comparative Example 1 taken as 100. The smaller the value, the better.

[Weatherability]
In accordance with JIS K6259, a vulcanized sample (160 ° C. × 30 minutes vulcanization) having a size of 5 × 5 cm in which a cap rubber having a sheet thickness of 2 mm and a base rubber was bonded together was prepared. The sample was allowed to stand in a gear oven adjusted to 100 ° C., and after aging for 10 days, the ozone dynamic test test of JIS K6259 was indicated by an index with the occurrence time of ozone cracks on the cap rubber side as Comparative Example 1 being 100. The higher the value, the better.

[Rolling resistance]
The rolling resistance of each tire was measured according to J1269 described in American Automobile Engineers Association Standard SAE. The comparative example 1 is indicated by an index of 100. The smaller the value, the better.

  From the results in Table 2, Examples 1 and 2 according to the present invention can maintain or improve workability and rolling resistance equivalent to those of Comparative Example 2 (conventional example) and can greatly improve weather resistance. On the other hand, in Comparative Example 1 in which the softener volume ratio exceeds 0.5, rolling resistance deteriorates, and when the liquid polymer A is used as the softener (Comparative Example 4), the softener volume ratio exceeds 0.5. Although weather resistance can be improved, rolling resistance deteriorates. In addition, it can be seen that the liquid polymer C (Comparative Example 3) having a small molecular weight does not have an improvement in weather resistance compared to the Examples.

  The present invention can be applied to pneumatic tires for various uses such as tires for two-wheeled vehicles including passenger cars.

It is a half sectional view of the pneumatic tire of an embodiment.

Explanation of symbols

1 …… Pneumatic tire 2 …… Tread part 3 …… Side wall part 4 …… Bead part 21 …… Cap rubber 22 …… Base rubber

Claims (3)

The tread has a two-layer structure of a cap rubber on the tire tread side and a base rubber disposed on the inside of the cap rubber, and the cap rubber and the base rubber are made of a rubber composition containing a diene rubber as a rubber component. In the pneumatic tire
The volume ratio of the softener contained in the base rubber to the softener contained in the cap rubber is 0.5 or less;
The cap rubber contains 10 to 60 parts by weight of a liquid polymer having a number average molecular weight of 3,000 to 90,000 as the softening agent with respect to 100 parts by weight of the diene rubber component. The pneumatic tire according to claim 1, wherein the liquid polymer is a diene liquid polymer. The liquid polymer is a functional group-containing liquid polymer having at least one functional group selected from the group consisting of a hydroxyl group, a carboxyl group, an amino group, an epoxy group, an acid anhydride group, a mercapto group, and a cyano group at the molecular end. The pneumatic tire according to claim 1 or 2, characterized in that.

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