JPH11240981A - Rubber composition for tire bead filler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition that is useful as a rubber material arranged to the bead of the tire, particularly a rubber composition that is useful as a bead filler with increased elasticity without damage to its fatigue resistance. SOLUTION: This rubber composition for bead fillers of tires comprises (A) 100 pts.wt. of the rubber components including 10-40 wt.% of a syndiotactic 1,2-polybutadiene-modified cis-1,4-polybutadiene and 90-60 wt.% of diene rubbers other than syndiotactic 1,2-polybutadiene-modified cis-1,4-polybutadiene rubber, (B) 3-20 pts.wt. of silica, (C) 0.5-3 pts.wt. of resorcin or a resorcinol derivative, in addition, 0.8-2.0-fold weight of hexamethylenetetramine or a melamine derivative based on the formulated resorcin or resorcin derivative and has a storage elastic modulus (E') of 8-15 MPa, when the vulcanized product is at 30 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high elastic modulus rubber member disposed in a bead portion, and more particularly to a rubber composition used for a bead filler.

[0002]

2. Description of the Related Art Generally, in order to effectively apply a force generated on a rim, which changes a traveling direction of a tire when a steering wheel of a car is turned, to a tire, the tire has a high rigidity of a bead portion and a large lateral force is applied to a carcass. Designed to occur. Therefore, the bead filler that fills the space surrounded by the wound-up portion, the carcass ply body, and the bead core formed when the end of the carcass ply is folded back from the inside to the outside along the bead core and locked is also high. It is formed of a rubber composition having an elastic modulus. In the bead filler, a rubber composition in which the amount of carbon black is larger than the rubber composition used for other rubber members of the tire to increase the elastic modulus, a novolak type phenol resin is compounded to increase the elastic modulus. Rubber composition (JP-B-57-30856), a rubber composition having a high elastic modulus by blending a novolak-type oil-modified phenolic resin and short fibers (JP-A-6-19247).
9), a rubber composition (JP-A-7-315014) in which short fibers and an olefin-based resin are blended to increase the elastic modulus has been used.

[0003]

In the method of increasing the amount of carbon black, the amount of heat generated when the carbon black is repeatedly deformed increases as the amount of carbon black increases. Was not obtained. In the method of mixing novolak type phenolic resin, the phenolic resin is not compatible with the rubber normally used for tires, and when mixed in large amounts, unreacted substances remain and act as foreign substances. As a result, the compounding amount was limited and satisfactory elastic modulus could not be obtained. The short fiber blended in the rubber composition acts as a foreign substance and reduces the fatigue resistance, so that the blending amount is limited. As described above, since a sufficiently satisfactory elastic modulus was not obtained even by combining the conventional methods, a rubber composition for a bead filler having a higher elastic modulus without impairing physical properties such as fatigue resistance has been demanded. .

In view of the above, it is an object of the present invention to provide a rubber composition having a high modulus of elasticity without impairing the fatigue resistance used for a rubber member disposed in a bead portion of a tire, in particular, a bead filler. .

[0005]

In order to achieve the above object, the following findings were obtained through repeated trial and error. That is, the composition of cis-1,4-bonded polybutadiene rubber modified with syndiotactic-1,2-bonded polybutadiene has an elastic modulus higher than that of a rubber composition in which the same amount of carbon black is blended using another diene rubber. Although it has the feature of being higher, there is a problem that the fatigue resistance is slightly inferior. However, if the amount of carbon black is reduced by blending with another diene rubber, the elastic modulus can be increased without impairing the fatigue resistance, and the problem is solved. On the other hand, resorcinol or a resorcinol resorcinol derivative obtained by reacting resorcinol with formalin has a greater elasticity increasing effect when compounded with rubber than a novolac phenolic resin, so that a high amount of elasticity can be obtained with a small amount of compounding. In addition, it does not have the above-mentioned problem of poor compatibility with rubber, which is observed when a large amount of novolac-type phenol resin is blended to increase the elastic modulus. A rubber composition in which cis-1,4-bonded polybutadiene rubber modified with syndiotactic-1,2-bonded polybutadiene is blended with another diene-based rubber and carbon black is further blended with resorcinol or a resorcinol derivative, Tires in which a bead filler is formed with a rubber composition having a high ratio, cracks tend to occur in the bead filler and bead durability is reduced,
Cracking can be suppressed by adding a small amount of silica, and as a result, the bead durability can be maintained or improved even if the elastic modulus is made higher than before.

[0006] The present invention has been made based on the above findings. That is, syndiotactic-1,2
10 to 40% by weight of a cis-1,4-bonded polybutadiene rubber modified with a linked polybutadiene and 90 to 60% by weight of a diene rubber other than the cis-1,4-bonded polybutadiene rubber modified with a syndiotactic-1,2-bonded polybutadiene And 100 parts by weight of the rubber component
20 parts by weight, resorcinol or resorcinol derivative 0.5
-3 parts by weight, further containing hexamethylenetetramine or a melamine derivative in an amount of 0.8 to 2.0 times the amount of the resorcinol or resorcinol derivative, and the storage modulus (E ') of the vulcanizate at a temperature of 30C. Is 8 to 15 MPa.

[0007]

DETAILED DESCRIPTION OF THE INVENTION Cis-1,4 modified with the syndiotactic-1,2-bonded polybutadiene used in the present invention.
Bonded polybutadiene rubber (hereinafter, cis-1,4-bonded polybutadiene rubber modified with syndiotactic-1,2-bonded polybutadiene is referred to as VCR)
Is a method described in JP-A-55-31802, that is, 1,3 in an organic solvent in the presence of a 1,2-polymerization catalyst.
-After polymerizing butadiene, the organic solvent solution of cis 1,4-polybutadiene rubber is added to the syndiotactic-1,2-bonded polybutadiene polymerization solution obtained by deactivating the catalyst, and the mixture is stirred and mixed. Syndiotactic-
A method obtained by separating a mixture of 1,2-bonded polybutadiene and cis-1,4-bonded polybutadiene rubber,
Alternatively, a method described in JP-A-5-194658, that is, 1,3-butadiene is first polymerized without complete conversion in the presence of a 1,4-polymerization catalyst to give cis 1,4
Polybutadiene, and then a 1,2-polymerization catalyst is charged into the polymerization system to allow 1,2-butadiene to undergo 1,2-polymerization. Alternatively, it can be obtained from Ube Industries under the brand name UBEPOL VCR.

The diene rubber other than the VCR is not particularly limited as long as it is a rubber component usually used as a rubber component of a rubber composition for a tire. Natural rubber, isoprene rubber (I)
R), low cis 1,4 butadiene rubber, high cis 1,4
Butadiene rubber, styrene-butadiene rubber (SBR)
Can be exemplified. Among these, natural rubber is preferable because it generates less heat, has a high elastic modulus, and has a large tear strength.

If the VCR blend ratio of the rubber component is lower than 10% by weight, the effect of increasing the elastic modulus by blending the VCR does not appear, and if it exceeds 40% by weight, the fatigue resistance is reduced and cracks are liable to occur. When used as a bead filler for a tire, bead durability is reduced.

The resorcinol derivative used in the present invention is obtained by condensation polymerization of resorcinol and formalin to such an extent that the reaction can proceed further if a methylene donor is added, and is commercially available from Sumitomo Chemical Co., Ltd. under the trade names Sumikanol 600 and 620. Have been. The melamine derivative is mono- or polymethoxymelamine obtained by reacting melamine with formalin or a mixture of both, and may contain an ether bond. These are commercially available from Sumitomo Chemical Co., Ltd. under the trade names Sumikanol 507 and 508. When the amount of the resorcinol or resorcinol derivative is less than 0.5 part with respect to 100 parts by weight of the rubber component (hereinafter, part by weight is simply referred to as part), the effect of increasing the elastic modulus exerted by these appears. On the other hand, if the amount exceeds 3 parts, the fatigue resistance of the vulcanized product decreases. The compounding amount of hexamethylenetetramine or melamine derivative added as the methylene donor of resorcinol or resorcinol derivative is made the usual amount, and is 0.8 to 2.0 times the weight of resorcinol or resorcinol derivative.

If the amount of silica is less than 3 parts by weight per 100 parts by weight of the rubber component, the effect of silica is not exhibited, and
If it exceeds 0 parts, the fatigue resistance decreases. It is preferable not to use a silane coupling agent usually added when silica is blended.

The amount of VCR, silica, resorcinol or resorcinol is adjusted within the above range so that the storage modulus of the vulcanizate at a temperature of 30 ° C. becomes 8 to 15 MPa, or the amount of carbon black is adjusted. To adjust. If the storage modulus is less than 8 MPa, the rubber elastic modulus cannot be improved, and if it is greater than 15 MPa, the fatigue resistance is reduced and the bead durability is reduced when used as a bead filler for a tire.

In the rubber composition of the present invention, in addition to the silica, resorcinol or resorcinol derivative, hexamethylenetetramine or melamine derivative described above, various compounding agents generally compounded in rubber compositions for tires can be arbitrarily compounded. , May be used in general amounts. Examples of optional additives include carbon black, sulfur, a vulcanization accelerator, and zinc white.

[0014]

EXAMPLES The rubber components shown in Table 1 or Table 2 were blended with carbon black and silica in parts by weight shown in Table 1 or Table 2, and 3 parts zinc white, 1 part stearic acid and 2 parts oil. , 1 part of an antioxidant (trade name: Nocrack 6C, manufactured by Ouchi Shinko Chemical Co., Ltd.), mixed according to a general method using a Banbury mixer, once discharged and cooled, and then mixed in an amount shown in Table 1 or Table 2. Was additionally mixed, discharged, cooled and further mixed with hexamethylenetetramine, 2 parts of sulfur and 1 part of a vulcanization accelerator CBS in the amounts shown in Table 1 or Table 2 to obtain a mixed rubber.

A sample was taken from the above mixed rubber, and the storage modulus was measured by the method described below. The results are shown in Table 1 or Table 2.

Further, a tire having a size of 11R22.5 using each of the above mixed rubbers as a bead filler was experimentally manufactured.
A durability test was performed on each prototype tire by the method described below. The results are shown in Table 1 or Table 2.

[0017]

[Table 1]

[0018]

[Table 2]

Storage elastic modulus: The mixed rubber was put into a mold and vulcanized at a temperature of 150 ° C. for 30 minutes to produce a test piece, and a viscoelastic spectrometer manufactured by Iwamoto Seisakusho was used.
The measurement was performed under the conditions of an extension rate of 15%, an amplitude of 1%, and a frequency of 50 Hz. Endurance: The prototype tire is assembled on a rim, filled with 0.9MPa internal pressure air, set on a drum tester, and run on a drum at a load of 5400 kg at a speed of 40 km / hr until a failure occurs. did. The durability is 10 compared to Comparative Example C1.
%, An improvement of less than ± 10% is indicated by Δ, and a decrease of 10% or more is indicated by X. Since the above load was set to about twice the design load, the failure occurred at the bead portion.

Each prototype tire other than 6 and 8 of the embodiment is
Although the bead filler was formed with the rubber composition having a higher elastic modulus than Comparative Example C1, the durability was 10 times higher than that of Comparative Example C1.
% Or more. On the other hand, by comparing each of Examples 1, 2, 3, 4 and Comparative Example C2 in which the compounding amount of the compounding agent is the same, the elastic modulus increases as the VCR blending ratio increases, and the VCR blending ratio increases. It can be seen that if the content is higher than 40% by weight, the durability decreases. Example 5
The comparison between Comparative Example C3 and Comparative Example C3 shows that silica has an effect of improving durability, but Examples 1, 5, and 6, Comparative Examples C3 and C4
Indicates that if the amount of silica is more than 20 parts, the effect of improving durability is not exhibited. In Comparative Examples C5, C6, C7 and C8 in which the amount of one or both of resorcin and hexamethylenetetramine is out of the specified range, no improvement in durability is observed.

[0021]

The rubber composition used for the bead filler is prepared by adding 10 to 40% by weight of VCR to the rubber component, and adding 3 to 20 parts of silica, resorcincin or resorcinol derivative to 0.5 to 3 parts per 100 parts of the rubber component. Parts of hexamethylenetetramine or melamine derivative in the amount of resorcinol or resorcinol derivative of 0.8 to 2.0.
By using a composition containing twice the weight, the modulus of elasticity increases, and when used as a bead filler, the bead durability of the tire is improved.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08L 61/34 C08L 61/34

Claims (1)

[Claims] 1. A cis-1,4-bonded polybutadiene rubber modified with syndiotactic-1,2-bonded polybutadiene 10 to 40% by weight and a cis-1,4-bonded polybutadiene modified with syndiotactic-1,2-bonded polybutadiene. 3 to 20 parts by weight of silica, 0.5 to 3 parts by weight of resorcinol or a resorcinol derivative are blended with 100 parts by weight of a rubber component comprising 90 to 60% by weight of a diene rubber other than rubber, and a hexamethylenetetramine or melamine derivative is further added. Characterized in that the vulcanizate has a storage elastic modulus (E ') of 8 to 15 MPa at a temperature of 30 ° C., which is 0.8 to 2.0 times the weight of resorcinol or a resorcinol compounding amount. Rubber composition.