JPH07110563B2 - Radial tire - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a radial tire for a vehicle, and more specifically, it has improved adhesion between a steel cord constituting a steel belt layer and a coat rubber (cover rubber). so,
The present invention relates to a radial tire that can withstand severe use conditions such as high temperature and high humidity.

[Prior art]

Generally, one of the factors that influences the durability of a radial tire having a steel belt layer used in passenger cars, trucks, buses, etc. is the adhesion between the steel cord and the coated rubber forming the steel belt layer. .

In order to improve the adhesion between the steel cord of the steel belt layer and the coated rubber, for example, as described on page 122 of "Points for selecting rubber material (published by Japan Standards Association)", the steel cord is plated with brass. And adding an organic acid cobalt salt or the like to the coated rubber.

However, since the tire is exposed to high heat and high temperature conditions during the vulcanization process, various chemical reactions can occur in the coated rubber. Particularly, in so-called HRH-based coated rubber, amine or ammonia is generated when the phenol-based resin-forming component is converted into a three-dimensional resin during vulcanization, resulting in adhesion deterioration. As measures against this, Japanese Patent Laid-Open Nos. 57-137332 and 5
As disclosed in Japanese Patent Publication No. 7-137333, there is a method of trapping amine or ammonia by using a compound selected from an epoxy compound and an isocyanate compound to prevent adhesion.

However, when these compounds are blended with the coated rubber used for the tire, the physical properties required for the coated rubber, particularly the tensile strength and the modulus are greatly lowered, and the high-speed durability is deteriorated.

Further, the tire is composed of many parts such as a tread and a carcass layer in addition to the steel belt layer, and since the respective rubber compositions are different, compounding agents that can migrate in the rubber interfere with each other, and the coated rubber of the steel belt layer. Even if the composition is optimized in advance, the composition may change when a product is obtained through molding and vulcanization, and the desired adhesiveness may not be obtained.

Especially for tires with two or more steel belt layers,
Among the surfaces of the steel cord of the steel belt layer closest to the tread (hereinafter referred to as the last belt layer), the surface facing the tread side is likely to cause a decrease in adhesion. The main reason for this is that it is the closest to the water that enters from the outside of the tire, and that it is the closest to the tread, so that the transfer of oil, sulfur, accelerator, etc. between the coat rubber and the tread rubber is large.

As a measure against this, conventionally, a method of protecting the last belt layer by newly providing an undertread between the last belt layer and the tread has been performed.
For example, there are JP-A-54-132904, JP-A-55-127207, JP-A-57-4407, JP-A-58-76308 and JP-A-58-116204. In particular, JP-A-57-4407 describes that the cause of the reduction in adhesion is that the blended sulfur in the coated rubber migrates to the tread to cause a reduction in adhesion, and the undertread with a large amount of sulfur is effective. .

However, even if these methods of providing the undertread are used, it is possible to improve the adhesion between the steel cord and the rubber only up to the tire when it is a new one, and it is possible to reduce the adhesion when the operating conditions are high temperature and high humidity. I couldn't prevent it enough.

The first reason is that, for example, when a tread containing a large amount of a sulfenamide accelerator is used, it is less likely that the compounded sulfur in the coat rubber will migrate to the tread rubber layer when running under high temperature and high humidity. Even if it is prevented by the tread layer, the adhesion-inhibiting substance migrates from the tread rubber layer to the coat rubber, and the adhesion is deteriorated together with the tread shape and the coat rubber composition.

Further, as a second reason, in a tire having a nylon belt layer between a steel belt layer and a tread layer, the last belt layer is not directly protected by the undertread layer for improving high-speed durability and steering performance. Instead, it will contact the nylon belt layer. As a result, the compounded sulfur in the coated rubber migrates to the nylon belt layer, and as a matter of course, the effect of improving the adhesiveness cannot be expected.

As a result of a detailed study on the decrease in adhesion between the steel cord and the coat rubber under high temperature and high humidity, the present inventors have found that a mechanism in which some substance diffuses from the tread portion toward the steel belt layer and destroys the adhesive layer. The conclusion was reached.

It is not clear what substance will break the adhesive layer,
When a tire with no grooves on the tread (slick pattern tire) is vulcanized, placed in a high temperature, high humidity oven as it is, and aged, and a peel test between the tread and the steel belt layer is performed, almost uniform adhesion deterioration is observed. On the other hand, similarly, if a tire having no groove is vulcanized and a groove is provided by a regroove, and an aging and peeling test is performed under the same conditions, adhesion deterioration of the steel belt layer corresponding to the portion below the groove hardly occurs. This phenomenon is that some substance migrates from the tread rubber to the steel belt layer under high temperature and high humidity and the tread is thick, and therefore when a large amount migrates, deterioration is remarkable, and the tread is thin like the groove bottom, and therefore a small amount. It can be explained that deterioration is unlikely to occur if only this shift occurs. Further, the more vulcanization accelerator is contained in the tread rubber composition, the more easily the adhesive deterioration occurs, so it is presumed that the substance that destroys the adhesive layer is the vulcanization accelerator itself or amines of the accelerator decomposition product. ing. That is, the adhesion deterioration can be prevented by more positively capturing the adhesion inhibiting substance without physically transferring it to the belt coat rubber. As a result of intensive studies on the above, the present invention has been accomplished.

[Object of the Invention]

Therefore, the present invention effectively prevents the adhesiveness between the steel cords constituting the steel belt layer and the coat rubber from being deteriorated by moisture, and is capable of sufficiently running even under a bad environment of high temperature and high humidity. The purpose is to provide a radial tire that has

[Structure of Invention]

Therefore, the radial tire of the present invention has a tread rubber layer containing 0.5 parts by weight or more of a sulfenamide-based vulcanization accelerator with respect to 100 parts by weight of a raw rubber, and at least two or more steel belt layers. Interposing a rubber sheet layer,
The distance between the steel cord of the steel belt layer located closest to the tread rubber layer and the boundary surface between this steel belt layer and the rubber sheet layer is a ₁ , and the width of the steel belt layer located closest to the tread rubber layer is W. _S , the width of the rubber sheet layer
W _R , the thickness of the rubber sheet layer was a ₂ , the total sulfur content of the tread rubber layer was S _T , the total sulfur content of the coated rubber of the steel belt layer was S _C , and the total sulfur content of the rubber sheet layer was S _R If
It is constituted so that the following conditions are satisfied, and 0.5 to 4.0% by weight of an epoxy compound is mixed in the rubber sheet layer.

0.2 mm ≤ a ₁ ≤ 0.8 mm, (0.8 x W _S ) ≤ W _R , 0.3 mm <a ₂ <1.2 mm, 0.6 mm <(a ₁ + a ₂ ) <2.0 mm, 1.0 wt% <S _T , 2.8 wt % <S _C <3.6% by weight, (1.8 ×
S _T ) <S _C , (0.8 × S _C ) ≦ S _R ≦ (1.2 × S _C ).

Hereinafter, the configuration of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a partial cross-sectional explanatory view of an example of the radial tire of the present invention. In FIG. 1, 1 is a tread rubber layer, 2
Reference numerals a and 2b denote steel belt layers provided inside the tread rubber layer 1, and the steel belt layers 2a and 2b are composed of a plurality of steel cords 3a and 3b and a coat rubber 4. Also, inside the steel belt layers 2a, 2b,
The carcass layer 5 and the liner layer 6 are sequentially laminated and provided. The steel belt layers 2a and 2b have the same thickness, and a rubber sheet layer 7 of the same type as the coat rubber is interposed between the steel belt layer 2a and the tread rubber layer 1.

(1) In the present invention, 0.5 part by weight or more of a sulfenamide-based vulcanization accelerator is blended in the tread rubber layer 1 with respect to 100 parts by weight of the raw rubber.

Here, the sulfenamide vulcanization accelerator is, for example, N,
N-dicyclohexyl-2-benzothiazole sulfenamide, N-cyclohexyl-2-benzothiazole sulfenamide, N-oxydiethylene-2-benzothiazole sulfenamide, N, N-diisopropyl-
2-benzothiazole sulfenamide, N-tert-butyl-2-benzothiazole sulfenamide and the like.

(2) In the present invention, the average distance between the steel cord 3a of the last belt layer 2a and the steel cord 3b of the steel belt layer 2b adjacent to the last belt layer 2a is d, and the tread rubber layer 1 side of the last belt layer 2a is From the boundary surface X ₁ of the steel cord 3a to the surface of the steel cord 3a closest to the rubber sheet layer 7
a ₁ , the total sulfur content of the tread rubber layer 1 is S _T , and the total sulfur content of the coated rubber 4 of the steel belt layers 2a and 2b is S _C , 0.6 mm
≤d≤1.0 mm, a ₁ ≤0.8 mm, S _T > 1.0 wt%, 2.8 wt% <
Adhesion loss is likely to occur in tires with S _C <3.6 wt% and 1.8 × S _T <S _{C. To} prevent this, the width of the last belt layer is W _S , the width of the rubber sheet layer is W _R , and the thickness of the rubber sheet layer is Is a ₂ , and the total sulfur S _R of the rubber sheet layer is (0.8 × S _C ) ≤ S _R ≤ (1.2 ×
S _C ), (0.8 × W _S ) ≦ W _R , 0.3 mm <a ₂ <1.2 mm, 0.6 mm <
The rubber sheet layer 7 satisfying the condition of (a ₁ + a ₂ ) <2.0 mm is arranged on the tread rubber layer 1 side of the last belt layer 2a.
As a result, deterioration of adhesion is suppressed to some extent.

When d is 0.6 mm or less, the peeling force between the steel belt layers decreases, and when d is 1.0 mm or more, the tread separation resistance at high speed decreases. Sulfur migration occurs due to the difference in sulfur concentration between the two rubber compositions in contact with the boundary surface X ₁ , so if S _C is 2.8 wt% or less and S _C / S _T is 1.8 or less, adhesion deterioration due to migration is unlikely to occur. Become. Also,
When S _T is 1.0% by weight or less or S _C is 3.6% by weight or more, the adhesiveness between the boundary surfaces X ₁ and X ₂ between the tread rubber layer 1 and the steel belt layer 2a decreases. Transition from steel belt layer 2a to the tread rubber layer 1 so takes place from the interface in a ₁ is 0.8mm or more does not occur decreases virtually sulfur concentration in the vicinity of the steel wire surface, it does not occur even adhesion decreases.

The rubber sheet layer 7 for suppressing the transfer of sulfur preferably covers the entire width W _S of the last belt layer 2a, and it is necessary to cover at least 80% or more of the area thereof.

If the thickness a ₂ of the rubber sheet layer 7 is 0.3 mm or less, the rolling and laminating process becomes difficult, and if it is 1.2 mm or more, the tread separation resistance is deteriorated.
a ₂ ≤ 0.8 mm, the combined thickness of a ₁ and a ₂ (a ₁ + a ₂ )
Is less than 0.6 mm, the effect of suppressing migration is small, and if 2.0 mm or more, the tread separation resistance is deteriorated. Since the migration of sulfur is caused by the difference in sulfur concentration, the total sulfur content S _R of the rubber sheet layer 7 must be 100 ± 20% of the total sulfur content of the steel belt layers 2a and 2b.

As a method for disposing the rubber sheet layer 7, a usual method performed with an extruder, a calendar or the like is adopted. When the tread rubber layer 1 and the steel belt layers 2a and 2b are combined in the green tire molding process, the rubber sheet layer 7 needs to be arranged on the surface of the last belt layer 2a on the tread rubber layer 1 side. Therefore, the step of attaching the rubber sheet layer 7 may be previously attached to the last belt layer 2a in addition to the method of attaching it on the forming drum in the green tire forming step.

Further, in a tire having a nylon belt layer between the last belt layer 2a and the tread rubber layer 1, by arranging the rubber sheet layer 7 satisfying the above conditions between the last belt layer 2a and the nylon belt layer, Similar effects are obtained. That is, one or more nylon belt layers may be arranged on the rubber sheet layer 7.

(3) Further, in the present invention, the rubber sheet layer 7 is compounded with an epoxy compound in an amount of 0.5 to 4.0% by weight, preferably 0.5 to 3.0% by weight.

As a result, the adhesion-inhibiting substance is captured, and the adhesion deterioration at high temperature and high humidity is minimized. If the amount of the epoxy compound compounded is less than 0.5% by weight, there is no effect, and if it exceeds 4.0% by weight, the breaking strength is remarkably reduced, heat is generated during running, and high-speed durability is poor, which is not preferable.

The epoxy compound is, for example, a bisphenol type epoxy compound, a hydrogenated product thereof, a cycloaliphatic epoxy compound,
Phenol novolac type epoxy compounds, cresol novolac type epoxy compounds, glycidyl phthalate epoxide compounds, dimer acid type epoxy compounds, polyglycol type epoxy compounds, urethane modified epoxy compounds and the like. These may be used alone or in combination of two or more. Further, a solid epoxy compound at room temperature is superior in workability.

Since it is a necessary condition for the rubber composition of the rubber sheet layer 7 to satisfy the total amount of sulfur and the amount of epoxy compound, even if the coating rubber of the steel belt layer is a rubber composition containing an epoxy compound, the same rubber may be used. It is good, but the coated rubber of the steel belt layer has a limitation on the rubber composition because it directly contacts the steel cord, and it is necessary to add an organic acid cobalt salt or the like to improve adhesion. There are no restrictions such as the above, so you are not necessarily limited to this.

When the content of the sulfenamide-based vulcanization accelerator in the tread rubber layer 1 is less than 0.5 part by weight, the adhesion deterioration estimated to be due to the vulcanization accelerator or the decomposed product of the vulcanization accelerator hardly occurs. Therefore, it is not necessary to mix the epoxy compound with the rubber sheet layer 7.

Examples and comparative examples are shown below.

Examples, Comparative Examples Tires for passenger cars with two steel belt layers 155 SR 13
The size is used, the steel cord is brass plated with a copper content of about 63%, the tread rubber and the coat rubber of the steel belt layer are those shown in Table 1 below, and the tread rubber is N-cyclohexyl-2benzothiazole. It contains 1.4 parts by weight (0.78% by weight) of sulfenamide.
The total sulfur content is measured by the method of JIS K6350, and d = 0.8
mm, a ₁ = 0.4 mm, W _R = W _S. The rubber sheet layer was previously attached to the last belt and then molded into a green tire.

The compounding contents (A to J) of the rubber sheet layer are shown in Table 2.
A does not contain an epoxy compound, and B to G are those in which 0.3, 0.5, 1.0, 2.0, 3.0 and 4.0% by weight of the epoxy compound (ii) were sequentially added to A. H is A to which 3.0% by weight of the epoxy compound (iii) is added, and I is A to the epoxy compound (i).
3.0% by weight is added. J has the same contents as I except that the blending amount of sulfur is reduced.

Epoxy compound (i) ... Product name ELA128 (Sumitomo Chemical).

Epoxy compound (ii): Trade name Epikote 1001 (Shell Petroleum).

Epoxy compound (iii): Trade name Epikote 1007 (Shell Petroleum).

In Table 3, Standard Example 1 is a tire with normal specifications,
Comparative Example 1 is a tire having a ₁ + a ₂ = 0.95 mm and a rubber sheet layer containing no epoxy compound. Comparative Example 2 is a tire in which the rubber sheet layer obtained by adding 0.3% by weight of the epoxy compound (ii) to the rubber sheet layer of Comparative Example 1 is arranged. Comparative Example 10 is a tire having a rubber sheet layer with a gauge further thinned so that a ₁ + a ₂ = 0.75 mm. No epoxy compound was blended in this rubber sheet layer. Comparative example
For _{No. 12} , 3.0% by weight of epoxy compound (i) was added to the rubber sheet layer with a low sulfur content, and a ₁ + a ₂ = 0.75 mm
It is a tire. In Examples 3 to 7, a ₁ + a ₂ = 0.95 mm
Then, sequentially add epoxy or compound (ii) to the rubber sheet layer.
A tire in which 5,1.0,2.0,3.0,4.0% by weight is added and the rubber sheet layer is arranged. In Examples 8 and 9, the epoxy compound (ii) of Example 6 was replaced with the epoxy compound (iii), respectively.
And an epoxy compound (i) are substituted in the same amount. Example 11 has the same content of composition as Example 9, but a ₁ +
It is a tire with the thickness indicated by a ₂ reduced from 0.95 mm to 0.75 mm.

Each tire was vulcanized immediately after molding in the same manner as in a normal tire manufacturing process.

The prototype tire was designed with 70%
There are two conditions: one that is left in a steam oven with a temperature of 98 ° C and a humidity of 98% for 30 days, and another that is left in an air oven with a temperature of 100 ° C for 72 hours and then in a steam oven that has a temperature of 70 ° C and a humidity of 98% for 30 days. Deteriorated. The adhesion between the steel cord of the last belt layer and the coat rubber was evaluated by the rubber coverage of the steel cord after the peeling test between the tread rubber and the last belt layer. That is, if the entire surface of the steel cord on the tread side was covered with the coated rubber, the rubber coverage was 100%, and if the coated rubber was not attached at all and the steel cord was exposed, the rubber coverage was 0%.

As a result of experimenting under the above conditions, the rubber coverage of new tires that are not affected by heat and moisture is good, but the rubber coverage of 70 ° C, 90% humidity, and 30 days storage is checked. And the standard example 1 falls considerably. That is, it can be seen that the adhesion deterioration is large without the rubber sheet layer 7. Further, from Comparative Example 12, the amount of sulfur in the rubber sheet layer is considerably smaller than the amount of sulfur in the belt layer coated rubber, and the thickness of the rubber sheet layer is thin, the epoxy compound of the adhesion inhibitor scavenger is compounded in the rubber sheet layer. However, the adhesion deterioration is large.

Further, when the rubber coverage after 100 hours at 72 ° C. for 72 hours in air at 70 ° C. and 98% humidity is observed, the adhesive deterioration of Comparative Examples 1, 2 and 10 becomes large. From the results of Comparative Example 1, even if the rubber sheet layer 7 in which the coat gauge and the sulfur compounding amount are optimized is arranged,
It can be seen that the adhesion deterioration cannot be prevented without disposing the epoxy compound. Further, from Comparative Example 2, it can be seen that the effect is small even if 0.3% by weight of the epoxy compound is blended in the rubber sheet layer 7 in which the cord gauge and the blending amount of sulfur are optimized. According to Comparative Example 10, even if the rubber sheet layer 7 having the optimized amount of sulfur is arranged, the thickness thereof is thin, and the rubber sheet layer containing no epoxy compound can hardly prevent the adhesion deterioration.

Examples 3 to 9 have less adhesion deterioration than the corresponding standard examples and comparative examples, and if the thickness of the rubber sheet layer 7 and the sulfur compounding amount are optimized, the epoxy compound is added to the rubber sheet layer 7 in an amount of 0.5 to 0.5%. It can be seen that addition of 4.0% by weight can prevent adhesion deterioration. Further, according to Example 11, even if the thickness of the rubber sheet layer is thin, if the sulfur compounding amount is optimized, by admixing 3.0% by weight of the epoxy compound in the rubber sheet layer 7, the adhesion deterioration to a satisfactory level. You can see that it can be prevented.

〔The invention's effect〕

As described above, the radial tire of the present invention has a high temperature,
Since there is little adhesion deterioration between the steel cord of the steel belt layer and the coated rubber under high humidity, there is an advantage of reducing the failure of the radial tire used under severe usage conditions such as high temperature and high humidity. Therefore, the tire of the present invention is suitable as a radial tire for passenger cars and a radial tire for truck buses that travel in a harsh environment.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional explanatory view of an example of the radial tire of the present invention. 1 ... Tread rubber layer, 2a, 2b ... Steel belt layer, 3
a, 3b ... Steel cord, 4 ... Coat rubber, 5 ... Carcass layer, 6 ... Liner layer, 7 ... Rubber sheet layer.

Claims (2)

[Claims] 1. A rubber sheet layer is interposed between a tread rubber layer containing 0.5 parts by weight or more of a sulfenamide vulcanization accelerator based on 100 parts by weight of a raw rubber and at least two steel belt layers. In the tire made to be, the distance from the steel cord of the steel belt layer located closest to the tread rubber layer to the boundary surface between the steel belt layer and the rubber sheet layer is a ₁ , and the tire cord is located closest to the tread rubber layer. The width of the steel belt layer is W _S , the width of the rubber sheet layer is W _R , the thickness of the rubber sheet layer is a ₂ , and the total sulfur content of the tread rubber layer is
S _T , the total sulfur content of the coated rubber of the steel belt layer is S _C ,
Radial tire characterized in that when the total sulfur content of the rubber sheet layer is S _R , the following conditions are satisfied and that the rubber sheet layer contains an epoxy compound in an amount of 0.5 to 4.0% by weight. 0.2 mm ≤ a ₁ ≤ 0.8 mm, (0.8 x W _S ) ≤ W _R , 0.3 mm <a ₂ <1.2 mm, 0.6 mm <(a ₁ + a ₂ ) <2.0 mm, 1.0 wt% <S _T , 2.8 wt % <S _C <3.6% by weight, (1.8 ×
S _T ) <S _C , (0.8 × S _C ) ≦ S _R ≦ (1.2 × S _C ). 2. The radial tire according to claim 1, wherein at least one nylon belt layer is arranged between the tread rubber layer and the rubber sheet layer.