JP3490223B2 - Pneumatic tire - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire, and more particularly, to a high elasticity and fracture resistance characteristic of a bead filler (stiffener) disposed in a tire bead portion. The present invention relates to a pneumatic tire in which the bead filler has an improved folding resistance and a reduced rolling resistance by achieving a high degree of compatibility. [0002] The bead portion of a pneumatic radial tire is
As shown in FIG. 1, a carcass ply 1a disposed substantially in the radial direction is provided.
b, a high hardness bead filler 5 is provided. In the illustrated example, a metal reinforcing layer 3 and an organic fiber reinforcing layer 4 that are oblique to the radial direction are disposed outside the folded portion 1b of the carcass ply 1a. Conventionally, in a pneumatic tire, a bead portion is wound around a cord end of a fiber or a steel wire forming a carcass ply, and at the same time, it is necessary to define a size of an inner circumference of the tire and secure a fitting with a rim. The bead filler generally has JIS hardness A (JIS K
Spring type hardness A type determined in accordance with 6301) is 7
Very hard rubber, 0-98, is used. In order to increase the elasticity of such a bead filler rubber, conventionally, techniques such as increasing the amount of carbon black and increasing the amount of a vulcanizing agent such as sulfur and a vulcanization accelerator have been employed. Also known is a method of increasing the elasticity of rubber by blending resorcinol or a phenolic resin. [0005] However, increasing the elasticity of the conventional bead filler rubber has not always been sufficiently satisfactory. In other words, techniques such as increasing the amount of carbon black or vulcanizing agent deteriorate the fracture resistance such as elongation at break, and in particular, increasing the amount of carbon black causes deterioration of the heat generation characteristics, and increasing the amount of sulfur tends to cause thermal deterioration. In any case, there is a problem that the life of the tire is shortened. [0006] The blending of a resorsi-based resin has a small effect on increasing the elasticity, and the blending of a phenolic resin results in a highly elastic rubber, but the elongation at break is reduced, and both the enhanced elasticity and the fracture resistance are compatible. That was not enough. Accordingly, an object of the present invention is to provide a pneumatic pneumatic tire in which the bead filler rubber is highly compatible with high elasticity and fracture resistance, thereby improving the bend resistance of the bead filler and reducing the rolling resistance. To provide tires. Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a novolak obtained by a specific reaction system is added to a rubber composition for a bead filler having a conventional compounding content. The present inventors have found that the above object can be achieved by mixing a predetermined amount of a resin and a compound capable of providing a methylene group upon heating, thereby completing the present invention. That is, a pneumatic tire according to the present invention is a pneumatic tire having a bead portion provided with a bead filler, wherein the bead filler rubber has a rubber component 100 composed of natural rubber, synthetic rubber, or a mixed rubber thereof. Xylenol (A) and phenols (B) composed of phenol, cresol or a mixture thereof with respect to parts by weight of aldehyde compound in a molar ratio (A / B) of 25/75 to 75/25. Novolak resin having a softening point of 90 to 150 ° C. obtained by co-condensation using
25 parts by weight, and 0.5 to 25 parts by weight of a compound capable of donating a methylene group upon heating. Hereinafter, a pneumatic tire according to the present invention will be described in detail. In the pneumatic tire of the present invention, as a rubber component used in the bead filler, a single rubber or a blend rubber arbitrarily selected from natural rubber and various synthetic rubbers can be used. Polyisoprene rubber, styrene-butadiene copolymer rubber, polybutadiene rubber, butyl rubber,
Examples include halogenated butyl rubber, but are not limited thereto. The co-condensed novolak resin used in the present invention includes xylenol, preferably 3,5-xylenol as the component (A) and phenols such as phenol or cresol, preferably phenol, as the component (B). The molar ratio (A / B) is 25/75 to 75/2
5, preferably obtained by co-condensing with an aldehyde compound at a ratio of 40/60 to 60/40. The aldehyde compound used in such a co-condensation reaction is formaldehyde, acetaldehyde, benzaldehyde, salicylaldehyde, acrolein and the like, and formaldehyde is industrially preferred from the viewpoints of economy, safety and the like. The co-condensation resin herein refers to xylenol or a xylenol-aldehyde compound resin,
It refers to a resin synthesized under conditions that allow a phenol or a phenol-aldehyde compound-based resin to react via an aldehyde. Molar ratio of this resin (A / B)
When 4 is smaller than 25/75, that is, when the ratio of xylenol is small, not only the elastic modulus of the obtained rubber composition is low, but also the fracture resistance is reduced. On the other hand, when the molar ratio (A / B) is larger than 75/25, that is, when the ratio of xylenol is large, the curing reaction of the resin becomes slow,
Further high elasticity of the rubber composition cannot be obtained, and uncured resin remains in the rubber composition after vulcanization, which undesirably deteriorates the heat generation characteristics of the rubber. In the present invention, the softening point of the resin is in the range of 90 to 150 ° C. This is because when the softening point is lower than 90 ° C, not only the elastic modulus of the obtained rubber composition is low, but also when a resin is stored, a blocking phenomenon occurs, which is not preferable. , The elastic modulus of the rubber composition is lowered and the heat generation characteristics are also deteriorated, which is not preferable. Further, in order to improve the exothermic characteristics of the obtained rubber composition, the resin has the following molecular weight distribution:
It is preferable that a high molecular weight component having a molecular weight of 5200 or more in terms of polystyrene is contained in an amount of 4 to 30% by a peak area ratio on a GPC chart. Here, if this area ratio is less than 4%, the effect of improving the heat generation characteristics is not sufficient, while if it exceeds 30%, the softening point of the resin becomes too high, and the dispersion in the rubber composition deteriorates. The heat generation characteristics are reduced. [0016] Further, in order to dramatically improve the elastic modulus, fracture resistance, and heat generation characteristics of the obtained rubber composition, the resin has an ortho bond (o) and a para bond (p). Is preferably a high ortho-co-condensed novolak resin having a ratio (o / p) of 2 or more. The catalyst used here is, for example, an organic acid salt, an inorganic acid salt or an oxide of a divalent metal ion such as an alkaline earth metal, zinc, manganese, and cadmium, and preferably zinc acetate. Further, the compounding amount of the co-condensed novolak resin is 0.5 to 25 parts by weight, preferably 0.5 to 10 parts by weight based on 100 parts by weight of rubber. When the amount is less than 0.5 part by weight, the effect of improving the elastic modulus by the addition is not sufficient. On the other hand, when the amount exceeds 25 parts by weight, not only the effect of increasing the amount is not obtained, but also the fracture resistance and the exothermic characteristics are deteriorated. Is not preferred. In the present invention, a compound capable of providing a methylene group at the time of heating is blended in order to increase the elasticity of the co-condensed novolak resin by making the above-mentioned co-condensed novolak resin effective by a three-dimensional network. Compounds capable of donating a methylene group upon heating include hexamethylenetetramine, polyvalent methylolated melamine derivatives, oxazoline derivatives, polyvalent methylolated acetylene ureas, and preferably hexamethylenetetramine and polyvalent methylolated melamine derivatives. ,
Particularly preferred is a polyvalent methylolated melamine derivative which does not adversely affect other members or the working environment during heating. The compounding amount of such a compound is 0.5 to 25 parts by weight, preferably 0.5 to 25 parts by weight, based on 100 parts by weight of rubber.
10 parts by weight. When the amount is less than 0.5 part by weight, the effect of addition is not sufficient, and when the amount exceeds 10 parts by weight, the effect of increasing the amount is no longer provided, which is not preferable. The rubber composition constituting the bead filler of the pneumatic tire of the present invention includes, in addition to the above-mentioned novolak resin and a compound capable of providing a methylene group upon heating, a usual reinforcing agent such as carbon black or silica, Compounding agents usually used in the rubber industry, such as an inhibitor, a softening agent, a vulcanization accelerator, a vulcanization accelerator, sulfur, and an adhesion promoter, can be appropriately compounded. EXAMPLE A rubber composition for a bead filler of a pneumatic tire was prepared according to the formulation shown in Tables 1 and 2 below. The 3,5 xylenol-phenol cocondensates (60/40), (10/90) and (90/10) shown in the table were prepared as follows. (A) Preparation Example of Cocondensate (60/40) 200 parts of phenol, 180 parts of 41.5% formalin (hereinafter referred to as primary formalin) and 3 parts of oxalic acid were mixed.
The mixture was refluxed at a temperature higher than the boiling point of the reaction system for 15 minutes. This was quenched and kept at 60-70 ° C. for 1 hour. Next, 330 parts of 3,5-xylenol was added, and the temperature was raised. 150 parts of 41.5% formalin (hereinafter referred to as secondary formalin) was gradually added, and the mixture was refluxed for 2 hours. After completion of the reaction, the temperature was raised to 180 ° C. while removing water under normal pressure, and further, unreacted phenol and xylenol were removed under reduced pressure to obtain a co-condensation having a conversion of 60:40 and a softening point of 118 ° C. A resin was obtained. (B) Preparation of cocondensate (10/90) Using 780 parts of phenol, 450 parts of primary formalin, 4.5 parts of oxalic acid, 120 parts of 3,5-xylenol, and 70 parts of secondary formalin The reaction was carried out in the same manner as above to obtain a co-condensation resin having a conversion of 10:90 and a softening point of 116 ° C. (C) Preparation example of cocondensate (90/10) Using 80 parts of phenol, 95 parts of primary formalin, 1.5 parts of oxalic acid, 850 parts of 3,5-xylenol, and 350 parts of secondary formalin The reaction was carried out in the same manner as above to obtain a co-condensation resin having a conversion of 90:10 and a softening point of 116 ° C. The obtained rubber composition was applied to a bead filler to produce a pneumatic tire having a size of 185 / 70R14. Dynamic elastic modulus (E ') of the rubber composition
And elongation at break (EB) were measured, and the rolling resistance and bead filler breaking resistance of the prototype pneumatic tire were evaluated. The measuring method and the evaluation method are as follows. (A) Dynamic Elastic Modulus (E ') After vulcanizing a sheet having a thickness of 2 mm at 145 ° C. for 40 minutes, an initial load of 160 was measured by a viscoelasticity measuring device manufactured by Iwamoto Seisakusho Co., Ltd.
g, dynamic strain (1%) and dynamic elastic modulus (E ') at room temperature under the conditions of a frequency of 50 Hz. (B) Elongation at break (EB) After vulcanizing a sheet having a thickness of 2 mm at 145 ° C. for 40 minutes,
It was measured according to SK6301. (C) In the rolling resistance drum running test, after the drum having a diameter of 1707 mm is once driven to rotate, the clutch is disengaged, and the degree of deceleration during coasting rotation is indicated by an index with the tire measurement result of Comparative Example 1 taken as 100. did. The higher the value, the better the result. (C) Folding resistance to bead filler Based on the rim width according to the JATMA standard, the internal pressure is 3 kgf / cm.
² and a drum with a diameter of 1707 mm at a constant load of twice the maximum load of the JATMA standard, 80 km / h per hour.
, And the bead crack length during the 10,000 km running was measured, and the measurement result of the tire of Comparative Example 1 was taken as 100 to indicate an index. The higher the value, the better the result. The results obtained are shown in Tables 1 and 2 below. [Table 1] [Table 2] As described above, in the pneumatic tire of the present invention, the rubber composition for bead filler of the conventional compounding content is mixed with the novolak resin obtained by a specific reaction system, Sometimes by compounding a predetermined amount of a compound capable of providing a methylene group, the bead filler rubber can be highly compatible with high elasticity and fracture resistance, thereby improving the breaking resistance of the bead filler. At the same time, the rolling resistance of the tire is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial sectional view showing a structure of a bead portion of a pneumatic tire. [Description of Signs] 1a, 1b Carcass ply 2 Bead core 3 Metal reinforcing layer 4 Organic fiber reinforcing layer 5 Bead filler

Claims (1)

(57) [Claim 1] In a pneumatic tire having a bead filler disposed in a bead portion, the bead filler rubber is
Xylenol (A) and phenols (B) composed of phenol, cresol or a mixture thereof in a molar ratio (A / B) based on 100 parts by weight of a rubber component composed of natural rubber, synthetic rubber or a mixture of these rubbers. ) In the range of 25/75 to 75/25, 0.5 to 25 parts by weight of a novolak resin having a softening point of 90 to 150 ° C. obtained by co-condensation using an aldehyde compound, and a methylene group upon heating. And 0.5 to 25 parts by weight of a donable compound.