JPH07110562B2 - 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, in addition to the steel belt layer, tires are composed of many parts such as treads and carcasses, and since the rubber compositions are different, the compounding agents that can migrate in rubber such as sulfur and oil interfere with each other and the steel belt Even if the composition of the coat rubber of the layer is optimized in advance, the composition may change when the product is obtained through molding and vulcanization, and the desired adhesiveness may not be obtained.

In particular, in a tire having two or more steel belt layers, the surface of the steel cord of the steel belt layer closest to the tread (hereinafter referred to as the last belt layer), which faces the tread side, is likely to cause a decrease in adhesion. The main reason for this is that it is the closest to the moisture that enters from the outside of the tire, and that it is 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 sulfenamide-based accelerator is used, the adhesion-inhibiting substance is transferred from the tread rubber to the coat rubber when traveling under high temperature and high humidity, and the tread shape and Adhesion deteriorates in combination with the coat rubber composition.

Further, as a second reason, for a tire having a nylon belt layer between the steel belt layer and the tread for improving high-speed durability and steering performance, the last belt layer is not directly protected by the undertread layer, and instead, Since it comes into contact with the nylon belt layer, the effect of improving the adhesiveness cannot be expected as a matter of course.

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 kind of substance will destroy the adhesive layer, but vulcanize a tire with no grooves on the tread (slick pattern tire), put it in a high temperature, high humidity oven as it is, aged, and tread and steel belt interlayer In the peel test, the adhesive deterioration was found to be almost uniform, whereas the same grooveless tire was vulcanized and a groove was formed by regroove, and the aging and peel test were conducted under the same conditions. Adhesive deterioration of the steel belt layer in the part to be applied is unlikely to occur. 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, so when a large amount is migrated, deterioration is remarkable, 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
The following conditions were satisfied, and 0.5 to 0.5% of alkyl etherified methylol melamine was added to the rubber sheet layer.
It is composed of 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 ).

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 , the total sulfur S _R of the rubber sheet layer, 0.8 × S _C ≤ S _R ≤ 1.2 × S _C , 0.
8 x W _S ≤ W _R , 0.3 mm <a ₂ <1.2 mm, 0.6 mm <(a ₁ + a ₂ ) <2.
The rubber sheet layer 7 that satisfies the condition of 0 mm is the last belt layer 2a.
Is arranged on the tread rubber layer 1 side. 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 contains 0.5 to 4.0% by weight, preferably 0.5 to 3.0% by weight of alkyl etherified methylol melamine.

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 alkyl etherified methylol melamine compounded is less than 0.5% by weight, no effect is obtained, and if it exceeds 4.0% by weight, the breaking strength is remarkably reduced, and the heat generated during running is high, which is not preferable because the durability is poor.

The alkyl etherified methylol melamine is a compound represented by the following structural formula.

Where X is hydrogen or -CH ₃ or C ₂ H ₅ or -C ₃ H ₇ , R
₁ , R ₂ , R ₃ , R ₄ and R ₅ are each hydrogen or a —CH ₂ OX group (provided that X is
Is as described above). Further, when three or more groups of R _{1 to} R ₅ are CH ₂ OX (where X is as described above), the effect is great.

Specific products include Cymel 303 (Mitsui Cyanamid, methyl etherified hexamethylol melamine), Cymel 235 (Mitsui Cyanamid, methyl etherified and butoxy etherified hexamethylol melamine mixture), Sumikanol. 508 (Sumitomo Chemical Co., Ltd., modified form of alkyl etherified methylol melamine)
Etc.

The rubber composition of the rubber sheet layer 7 is required to satisfy the total amount of sulfur and the amount of alkyl etherified methylol melamine. Therefore, the coated rubber of the steel belt layer may be a rubber composition containing alkyl etherified methylol melamine. For example, the same rubber as that may be used, 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 the adhesion. The rubber sheet layer 7 is not limited to these because it does not have these restrictions.

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 alkyl etherified methylolmelamine into the rubber sheet layer 7.

Examples and comparative examples are shown below.

Examples, Comparative Examples Tires for passenger cars with two steel belt layers 155SR13
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 alkyl etherified methylol melamine,
B to G are those obtained by sequentially adding 0.3, 0.5, 1.0, 2.0, 3.0 and 4.0% by weight of alkyl etherified methylolmelamine (i) to A. H is methyl etherified and butoxy etherified hexamethylol melamine, that is, 3.0 wt% of alkyl etherified methylol melamine (ii) is added to A, and I is hexamethoxymethyl melamine (alkyl etherified methylol melamine). (Iii))
3.0% by weight is added. J has the same contents as I except that the blending amount of sulfur is reduced.

Alkyl etherified methylol melamine (i) ... Modified product of alkyl etherified methylol melamine, trade name Sumikanol 508 (Sumitomo Chemical).

Alkyl etherified methylol melamine (ii): Hexamethylol melamine, methyl etherified and butoxy etherified (trade name Cymel 235 (Mitsui Cyanamid)).

Alkyl etherified methylol melamine (iii) ... Hexamethoxymethyl melamine, trade name Cymel 303 (Mitsui Cyanamid).

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 alkyl etherified methylol melamine. Comparative Example 2 is a tire obtained by adding 0.3% by weight of alkyl etherified methylol melamine (i) to the rubber sheet layer of Comparative Example 1. 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. Alkyl etherified methylol melamine is not mixed in this rubber sheet layer. Comparative Example 12 is
A tire in which 3.0% by weight of alkyl etherified methylol melamine (iii) was added to a rubber sheet layer containing a small amount of sulfur to obtain a ₁ + a ₂ = 0.75 mm. Examples 3 to 7
Is a ₁ + a ₂ = 0.95 mm, and the alkyl etherified methylol melamine (i) is sequentially applied to the rubber sheet layer at 0.5, 1.0, 2.0, 3.
A tire in which 0,4.0% by weight is added and the rubber sheet layer is arranged. In Examples 8 and 9, the alkyl etherified methylol melamine (i) of Example 6 was replaced with the alkyl etherified methylol melamine (ii) and the alkyl etherified methylol melamine (iii) in equal amounts. Example 11 has the same composition as that of Example 9, except that a ₁
It is a tire with the thickness indicated by + a ₂ changed 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 an experiment 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, 98% humidity, and 30 days is observed. 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, when the amount of sulfur in the rubber sheet layer is considerably smaller than the amount of sulfur in the belt-coated rubber and the thickness of the rubber sheet layer is thin, the amine scavenger alkyl etherified methylol melamine 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 unless the alkyl etherified methylol melamine is arranged. Further, from Comparative Example 2, it can be seen that even if 0.3% by weight of alkyl etherified methylol melamine is blended in the rubber sheet layer 7 in which the cord gauge and the blending amount of sulfur are optimized, the effect is small. Comparative example
As shown in FIG. 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 alkyletherified methylolmelamine can hardly prevent the adhesion deterioration.

Examples 3 to 9 have less adhesion deterioration than the corresponding standard examples and comparative examples, the thickness of the rubber sheet layer 7 and the sulfur compounding amount are optimized, and the alkyl etherified methylol melamine is added to the rubber sheet layer 7 at 0.5%. It can be seen that the addition deterioration can be prevented by adding up to 4.0% by weight. Further examples
11 indicates that even if the thickness of the rubber sheet layer is thinned, if the amount of sulfur is optimized, compounding 3.0% by weight of alkyl etherified methylol melamine into the rubber sheet layer 7 causes deterioration of adhesion to a satisfactory level. I know that I can prevent it.

〔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.

[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 ,
When the total sulfur content of the rubber sheet layer is S _R , the following conditions are satisfied, and 0.5 to 4.0% by weight of alkyl etherified methylol melamine is added to the rubber sheet layer to provide a radial characteristic. tire. 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.