JP2007297005A - Rubber composition for tire bead cover, and heavy duty pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the durability of a bead part by realizing the good adhesiveness to a carcass cord, and the high rigidity at a high temperature. <P>SOLUTION: A rubber composition forms a bead cover 4 provided between a bead core 3 embedded in a bead part 2 and a carcass layer 1 consisting of steel cords wound therearound. The rubber composition contains 55-85 pts.wt. carbon black to 100 pts.wt. diene-based rubber, organic acid cobalt salt of the amount corresponding to 0.05-0.4 pts.wt. in terms of cobalt, 0.3-3 pts.wt. resorcinol or resorcinol derivative, and methylene donor of the weight corresponding to 0.5-2 times the blend. The Mooney viscosity ML(1+4)(100°C) of unvulcanized stuff is 60-100. The storage elastic modulus E' of a vulcanized stuff at 80°C is ≥16 MPa, and the dynamic creeping property thereof is ≤10%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rubber composition for a bead cover and a heavy duty pneumatic tire using the same.

  As shown in FIG. 1, a heavy-duty pneumatic tire used in heavy-duty vehicles such as trucks and buses generally has at least one carcass layer (1) formed by arranging a plurality of steel cords in the tire radial direction. ) And both ends of the carcass layer (1) are wound around the bead core (3) from the inside to the outside at the bead portions (2) on both sides and locked.

  In such a heavy-duty tire, if the rubber gauge between the bead core (3) and the steel cord of the carcass layer (1) (hereinafter sometimes referred to as a carcass cord) is not sufficient, the bead core (3) and the carcass cord are rolled during tire rolling. May be in direct contact with each other, leading to failure such as breakage of the carcass cord and possibly deteriorating the durability of the bead portion (2). In particular, the contact between the bead core (3) and the carcass cord is likely to occur at the apex portion of the bead core (3) having a polygonal cross section as shown in the figure. In order to prevent this, the bead core (3) and the carcass layer (1) A bead cover (4) as a rubber member is disposed between the two and a method for thickening the rubber gauge in this portion is employed.

  However, there is a possibility that the bead cover rubber may come into contact with the carcass cord due to the tire molding process and the flow of rubber during rolling of the tire. In that case, the adhesion of the carcass cord is poor in the bead cover made of a normal rubber composition. Produce.

Therefore, as a countermeasure, a method of adding an adhesion promoter such as organic acid cobalt to the rubber composition for bead covers is used (see Patent Documents 1 to 3 below), but the adhesion to the carcass cord is not always sufficient. In other words, the durability of the bead portion may be reduced. Therefore, there is a need for a bead cover rubber that is superior in adhesion to a carcass cord and has a higher rigidity than conventional ones.
JP 2004-50986 A JP 2004-322815 A JP 2004-189146 A

  The present invention has been made in view of the above points, and is a rubber for a bead cover that can improve the durability of the bead portion by being excellent in adhesiveness with a carcass cord and being excellent in rigidity at high temperature. An object is to provide a composition and a heavy duty pneumatic tire using the composition.

  As a result of intensive studies in view of the above points, the present inventor has added an organic acid cobalt salt to a diene rubber together with a predetermined amount of carbon black, and further blended with a specific adhesive resin, thereby improving adhesiveness. In addition, it has been found that the durability at the bead portion of the tire can be improved by using this for a bead cover by obtaining a material having excellent elastic modulus at high temperature and dynamic creep resistance. It came to be completed.

  That is, the rubber composition for a tire bead cover according to the present invention is an amount corresponding to 55 to 85 parts by weight of carbon black and 0.05 to 0.4 parts by weight in terms of cobalt with respect to 100 parts by weight of the diene rubber. An organic acid cobalt salt, 0.3 to 3 parts by weight of resorcin or resorcin derivative, and a methylene donor having a weight corresponding to 0.5 to 2 times the blending amount of the resorcin or resorcin derivative. The Mooney viscosity ML (1 + 4) 100 ° C. of the vulcanized product is 60 to 100, the storage elastic modulus E ′ (80 ° C.) at 80 ° C. of the vulcanized product is 16 MPa or more, and the dynamic creep property (80 ° C.). 10% or less.

  The heavy duty pneumatic tire according to the present invention comprises a bead core embedded in a pair of bead portions and a plurality of steel cords arranged in the tire radial direction, and spans between the pair of bead portions. A heavy-duty pneumatic tire comprising: a carcass layer extending at both ends and wound around the bead core; and a bead cover provided between the bead core and the carcass layer. It is formed from a composition.

  According to the present invention, by using the rubber composition as a rubber for a bead cover, a high elastic modulus and sufficient adhesion with a steel cord can be obtained, and the durability of the tire bead portion can be improved.

  Hereinafter, matters related to the implementation of the present invention will be described in detail.

  In the rubber composition according to the present invention, examples of the diene rubber used as a rubber component include natural rubber, isoprene rubber, styrene butadiene rubber, butadiene rubber, and the like. You may use together. Preferably, a blend rubber of 100% by weight of natural rubber and / or isoprene rubber or 60% by weight or more of natural rubber and / or isoprene rubber and 40% by weight of other diene rubbers such as styrene butadiene rubber and butadiene rubber is used. Is to use.

  In the rubber composition according to the present invention, 55 to 85 parts by weight of carbon black is blended with 100 parts by weight of the diene rubber. When the blending amount of carbon black is less than the above range, high rigidity at high temperature cannot be obtained, and excellent durability of the bead portion cannot be obtained. On the contrary, if the blending amount exceeds the above range, the tire moldability deteriorates. The type of carbon black is not particularly limited, and various types of carbon black can be used as long as the rigidity value described later can be obtained.

  The rubber composition according to the present invention contains an organic acid cobalt salt. The organic acid cobalt salt improves adhesion to the steel cord and contributes to an increase in the elastic modulus of the bead cover rubber. Examples of the organic acid cobalt salt include fatty acid cobalt salts such as cobalt stearate, cobalt naphthenate, and cobalt neodecanoate.

  The organic acid cobalt salt is blended so that the addition amount as cobalt is 0.05 to 0.4 parts by weight with respect to 100 parts by weight of the diene rubber. Adhesiveness is inferior in it being less than 0.05 weight part. On the contrary, even if it exceeds 0.4 part by weight, the effect of increasing the amount is not recognized. A more preferable blending amount is 0.2 parts by weight in terms of cobalt.

  In the rubber composition according to the present invention, 0.3 to 3 parts by weight of resorcin or a derivative thereof is blended with 100 parts by weight of a diene rubber, and a methylene group is donated to the resorcin or the derivative and cured. The methylene donor to be added is blended at a weight corresponding to 0.5 to 2 times the blending amount of resorcin or a derivative thereof. When resorcin or a derivative thereof and a methylene donor are used in combination, a decrease in elastic modulus and an increase in sag at a high temperature can be suppressed as compared with the case where a normal novolac type phenol resin is blended. A more preferable amount of resorcin or a derivative thereof is 1 to 3 parts by weight.

  Examples of the methylene donor include hexamethylenetetramine, melamine derivatives, paraformaldehyde and the like, and hexamethylenetetramine or melamine derivatives are particularly preferable. Examples of the melamine derivative include methylol melamine such as hexamethoxymethyl melamine and hexamethylol melamine.

  Examples of the resorcin derivative include resorcin-aldehyde condensate, resorcin-alkylphenol-aldehyde cocondensate, resorcin-arylphenol-aldehyde cocondensate, and resorcin-aralkylphenol-aldehyde cocondensate.

  In addition to the components described above, the rubber composition according to the present invention is generally used in rubber compositions for tire bead covers, such as anti-aging agents, zinc white, stearic acid, vulcanizing agents, and vulcanization accelerators. Various additives can be blended. Moreover, as said vulcanizing | curing agent, sulfur is preferable and it is preferable that 5-10 weight part of sulfur is mix | blended with respect to 100 weight part of diene rubbers.

  The rubber composition for bead covers according to the present invention has a Mooney viscosity ML (1 + 4) at 100 ° C. of 60 to 100 of the unvulcanized product. If the Mooney viscosity is smaller than the above range, the bead cover thickness at the time of tire molding is reduced, and the durability of the bead portion is impaired. Conversely, if the Mooney viscosity is greater than the above range, the moldability of the tire is impaired. Here, Mooney viscosity is a value measured according to JIS K6300-1: 2001.

  In the rubber composition for bead covers according to the present invention, the vulcanized product has the following physical properties. That is, the storage elastic modulus E ′ (80 ° C.) of the vulcanizate is 16 MPa or more and the dynamic creep property (80 ° C.) satisfies 10% or less. Unless these physical properties are satisfied, excellent durability of the bead portion cannot be obtained. That is, it is not possible to sufficiently prevent the sag while securing the rigidity of the bead cover that becomes high temperature when the tire rolls. The upper limit of E ′ is not particularly limited, but is usually 30 MPa or less.

  Here, the storage elastic modulus E ′ is a value measured using a viscoelasticity measuring device under measurement conditions of initial strain: 5%, dynamic strain: ± 2%, frequency: 10 Hz, and temperature of 80 ° C. The dynamic creep property is a deformation rate of the sample after being vibrated for a certain period of time under the same measurement conditions using the measurement apparatus.

  The rubber composition comprising the above is used as a rubber composition for constituting a bead cover of a pneumatic radial tire, and the bead cover can be formed by vulcanization molding according to a conventional method. The rubber composition is preferably used for a tire having a carcass layer made of a steel cord, and is therefore suitable for a bead cover of a heavy duty tire used for a large vehicle such as a truck or a bus.

  As an example, FIG. 1 shows a configuration around a bead portion of a heavy duty pneumatic tire. An annular bead core (3) formed by winding a bead wire in the tire circumferential direction is embedded in the pair of left and right bead portions (2), and a rubber bead filler (5) is disposed on the outer periphery in the radial direction of the bead core (3). Is arranged.

  A carcass layer (1) extending between the pair of bead portions (2) is provided. The carcass layer (1) is composed of at least one layer in which a plurality of steel cords are arranged in the tire radial direction and covered with a coating rubber, and both end portions are bead cores (3) at the bead portions (2). It is locked by being rolled up from the tire inner side to the outer side.

  A bead cover (4) is provided between the bead core (3) and the carcass layer (1), and the bead cover (4) is made of the rubber composition described above. More specifically, in this embodiment, the bead cover (4) is provided around the bead core (3) so as to wrap the entire core.

  In this example, the cross-sectional shape of the bead core (3) is a hexagonal shape, but is not limited to this, and various shapes such as a square shape can be adopted. Further, the bead cover (4) around the bead core (3) is not limited to wrapping the entire bead core (3) as shown in the figure, and is disposed at least between the bead core (3) and the carcass layer (1). If so, various forms can be adopted.

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

  Using a Banbury mixer, a rubber composition for bead covers was prepared according to the formulation shown in Table 1 below. Details of each compound in Table 1 are as follows.

・ NR: Natural rubber “RSS # 3”,
・ SBR: “SBR1502” manufactured by JSR,
Carbon black (HAF): “Carbon black N326” manufactured by Showa Cabot,
・ Cobalt stearate: “Cobalt stearate” manufactured by Nikko Materials,
Resorcin derivative: “SUMIKANOL 620” (resorcin-alkylphenol-formalin co-condensation resin) manufactured by Sumitomo Chemical,
Melamine derivative: “CYREZ964RPC” (hexamethoxymethylmelamine) manufactured by Mitsui Cytec,
Novolac type phenolic resin: “Sumilite Resin PR-TY-24” (oil-modified alkylphenol resin) manufactured by Sumitomo Bakelite,
・ Zinc flower: “Zinc flower 3” manufactured by Mitsui Mining & Smelting Co., Ltd.
・ Stearic acid: “Lunac S-25” manufactured by Kao,
Anti-aging agent: “Sant Flex 6PPD” manufactured by Flexis,
・ Vulcanization accelerator: “Noxeller NS-P” manufactured by Ouchi Shinsei Chemical Industry,
Sulfur: “Miklon HS OT-20” manufactured by Flexis.

  About each rubber composition, while measuring the Mooney viscosity at the time of unvulcanized | cured, the storage elastic modulus E ', dynamic creep property, and adhesiveness of the vulcanized material were measured. The measuring method is as follows.

Mooney viscosity ML (1 + 4) 100 ° C .: Measured according to JIS K6300-1: 2001.

-Storage elastic modulus E '(80 degreeC): About the test piece (length x width x thickness = 20 mm x 5 mm x 1 mm) vulcanized at 150 degreeC x 30 minutes, it measured using the Toyo Seiki spectrometer. The measurement conditions were as follows: at a temperature of 80 ° C., vibrations with an initial strain of 5%, a dynamic strain of ± 2%, and a frequency of 10 Hz were applied in the length direction.

・ Dynamic creep property (80 ° C.): For a test piece (length × width × thickness = 20 mm × 5 mm × 1 mm) vulcanized at 150 ° C. × 30 minutes, the temperature is set to 80 ° C. using a Toyo Seiki spectrometer. Then, the deformation rate (%) of the length of the test piece after applying vibration of initial strain: 5%, dynamic strain: ± 2%, frequency: 10 Hz in the length direction for 30 minutes was obtained by the following formula.

Rate of change (%) = [(B−A) / A] × 100
Here, A is the length before the test, and B is the length after the test.

Adhesiveness: An adhesion pull-out test between a steel cord and rubber was performed in accordance with ASTM D2229. The rubber adhesion rate (%) to the steel cord after drawing was determined. It shows that adhesiveness is so favorable that a numerical value is large.

  Each rubber composition was evaluated for tire moldability and tire durability. The evaluation method is as follows.

-Tire moldability: Each rubber composition was used as a bead cover rubber, and when making 11R22.5 14PR size trial tires for trucks and buses, the workability when wrapping the bead cover rubber around the bead core was evaluated. Comparative example 4 close to the conventional bead cover was used as a control, and those that were equal to or better than this were evaluated as “◯”, those that were slightly deteriorated were evaluated as “Δ”, and those that were deteriorated were evaluated as “×”.

Tire durability: The prototype tire produced as described above was run on a drum tester under conditions of an internal air pressure of 900 kPa (about twice the design load), a load of 5400 kg, and a speed of 40 km / h. The running time until the occurrence was evaluated, and with Comparative Example 1 as a control, the better one was evaluated as “◯”, and the inferior one as “×”.

  The results are as shown in Table 1, and in Examples 1 to 3, the Mooney viscosity at the time of unvulcanization is within a predetermined range, the tire formability is excellent, and the adhesion to the steel cord is excellent. The elastic modulus at high temperature and dynamic creep resistance were excellent, and the durability of the tire bead portion could be improved.

  On the other hand, in Comparative Example 1, the blending amount of carbon black was small, the Mooney viscosity was too low, the rigidity at high temperature was low, and the durability of the bead portion was inferior. In Comparative Example 2, the amount of carbon black was large, the Mooney viscosity was too high, and the tire moldability was poor (durability could not be evaluated due to molding failure). Further, in Comparative Example 3, since fatty acid cobalt was not added, the rigidity at high temperature was lower than that in Examples, and the adhesiveness was low, so that the durability was inferior. Further, in Comparative Example 4, since no adhesive resin was added, the adhesiveness was low and the durability was inferior. Moreover, in the comparative example 5, since fatty acid cobalt and adhesive resin were not added, adhesiveness was low and it was inferior to durability. Further, in Comparative Examples 6 and 7, since a large amount of the novolak type phenol resin was blended, although the rigidity at high temperature was high, the dynamic creep resistance at high temperature was inferior and the tire durability was inferior.

  The rubber composition for a bead cover of the present invention can be used for various pneumatic tires, and is particularly suitably used as a rubber for a bead cover of a large tire used for a truck or a bus, that is, a heavy duty tire. it can.

It is sectional drawing which shows an example of the bead part of the pneumatic radial tire for heavy loads.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Carcass layer, 2 ... Bead part, 3 ... Bead core, 4 ... Bead cover, 5 ... Bead filler

Claims (2)

Carbon black in an amount of 55 to 85 parts by weight, an organic acid cobalt salt equivalent to 0.05 to 0.4 parts by weight in terms of cobalt, and resorcin or resorcin derivative 0.3 to 3 with respect to 100 parts by weight of diene rubber Parts by weight, and a methylene donor having a weight corresponding to 0.5 to 2 times the blending amount of the resorcin or resorcin derivative,
Mooney viscosity ML (1 + 4) 100 ° C. of the unvulcanized product is 60-100,
A rubber composition for a bead cover of a tire, wherein the vulcanizate has a storage elastic modulus E ′ (80 ° C.) at 80 ° C. of 16 MPa or more and a dynamic creep property (80 ° C.) of 10% or less. A bead core embedded in a pair of bead portions and a plurality of steel cords arranged in the tire radial direction, extending between the pair of bead portions and having both ends wound up around the bead core. A heavy duty pneumatic tire comprising a carcass layer and a bead cover provided between the bead core and the carcass layer, wherein the bead cover is made of the rubber composition according to claim 1. Heavy duty pneumatic tire.

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