JP2005170970A - Adhesive rubber composition for steel cord and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adhesive rubber composition for steel cords remarkably improving adhesion (heat-resistant adhesion) after heat aging while maintaining the adhesion (initial adhesion) to the steel cords just after vulcanization. <P>SOLUTION: The adhesive rubber composition for the steel cords is characterized in that sulfur and zinc white are compounded with a rubber component containing ≥50 mass% of natural rubber and/or synthetic polyisoprene rubber, the amount of the sulfur compounded is 5-8 pts. mass based on 100 pts. mass of the rubber component, and the mass ratio (zinc white/sulfur) of the zinc white to the sulfur is ≥2.2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an adhesive rubber composition for steel cords and a pneumatic tire using the adhesive rubber composition, and more particularly to adhesion (initial adhesion) immediately after vulcanization with a steel cord plated with brass. The present invention relates to an adhesive rubber composition for coating a steel cord, which is significantly improved in adhesiveness (heat-resistant adhesiveness) after heat aging while maintaining.

  Conventionally, steel cords have been used as reinforcing materials in order to improve the performance of rubber articles such as automobile tires and conveyor belts. In general, the steel cord is subjected to brass plating or the like in order to enhance its reinforcing effect, that is, the adhesive force with rubber. Moreover, in order to improve the adhesive force of rubber | gum and a steel cord, various devices are given to the rubber composition which coat | covers a steel cord. For example, an appropriate amount of an adhesion promoter such as an organic acid cobalt salt is added to the rubber composition covering the steel cord so that the initial adhesion is completed at the required vulcanization temperature and time.

  However, due to the recent expansion of the use area of steel radial tires reinforced with steel cords and the extension of the period of use of the tires, the influence of heat and humidity on the steel cord covering rubber has increased. It is known that the adhesiveness of the tire is lowered, causing a tire failure. Therefore, it is required to further improve the durability of the tire reinforced with the steel cord.

  Conventionally, in an adhesive rubber composition for coating a steel cord, in order to promote the adhesion between the brass-plated cord and the rubber in order to ensure the adhesion immediately after vulcanization of the tire, that is, the initial adhesion, the above-mentioned In general, an organic acid cobalt salt is blended as an adhesion promoter as described above, but it is known that an adhesive system using the organic acid cobalt salt lowers the adhesive force due to heat. Therefore, in order to obtain sufficient adhesion durability while responding to the longer life and size of the tire, it is desired to suppress the decrease in the adhesion between the steel cord and the rubber due to heat. Under such a request, a number of techniques for improving the adhesion between the steel cord and rubber have been disclosed. Even if the amount of the organic acid cobalt salt is reduced, the initial adhesion is excellent and the heat resistance is stable. An adhesive rubber composition for steel cord having adhesiveness and a steel cord-rubber composite using the same have been proposed.

For example, a technique using a rubber composition containing nickel (II) acetylacetonate for a steel cord coating rubber (see Patent Document 1), a cobalt salt of rosin as an organic acid cobalt salt, a specific iodine adsorption amount and DBP A technique for using a rubber composition containing carbon black having an oil absorption amount as a coating rubber for steel cord (see Patent Document 2), a technique for providing a cobalt plating layer on the surface of a steel cord (see Patent Document 3), and acetylacetone as a rubber component Technology using a rubber composition containing cobalt and sulfur and a steel cord provided with a brass plating layer having a copper / zinc ratio of 60/40 to 65/35 (see Patent Document 4), moisture before vulcanization Technology using a rubber composition having a specific content in a specific range and a steel cord coated with cobalt (see Patent Document 5) ), A technique in which a diene rubber component and an organic solvent containing a cobalt compound are attached to a galvanized steel cord, and then coated with a rubber composition containing no cobalt compound and vulcanized (see Patent Document 6), Technology using rubber composition containing organic carboxylic acid cobalt-boron metal soap as adhesion promoter for steel cord coating rubber (see Patent Document 7), rosin or derivatives thereof, sulfur, organic acid cobalt salt and rubber component A technique using a rubber composition containing an organic chlorine compound and a galvanized steel cord (see Patent Document 8), a silica powder having a nitrogen adsorption specific surface area (BET) of 150 m ² / g or less relative to the rubber component A technology that uses a rubber composition containing a steel cord as a coating rubber for steel cord (see Patent Document 9), and a porous inorganic filler for the rubber component In a steel cord-rubber composite composed of an inner coating layer that directly coats a steel cord and an outer coating layer that wraps the outer coating layer using a compounded rubber composition as a steel cord coating rubber (see Patent Document 10) In addition, a technique (see Patent Document 11) that separates the functions of the inner coating layer and the outer coating layer by changing the content ratios of sulfur and cobalt compounds is disclosed.

Japanese Patent Publication No. 1-57695 JP 58-89631 A JP-A-64-31837 Japanese Patent Laid-Open No. 5-65370 JP-A-5-247271 Japanese Patent Laid-Open No. 10-324753 Japanese Patent No. 2823857 Japanese Patent Laid-Open No. 11-21389 JP 2000-7839 A JP 2000-7838 A JP 2002-338749 A

  However, the compatibility between the initial adhesion and the heat-resistant adhesion between the steel cord and the coating rubber remains an important issue. In particular, pneumatic tires for large trucks and buses and construction vehicles have large member dimensions, so that dynamic input increases and heat history due to running is large. For this reason, it is not difficult to imagine that there is an aspect that cannot be measured by conventional knowledge in the adhesion after heat deterioration due to running at a site that receives a large dynamic input and generates a large amount of heat.

  Accordingly, an object of the present invention is to maintain an adhesive property (initial adhesive property) immediately after vulcanization to a steel cord, while greatly improving the adhesive property (heat resistant adhesive property) after heat aging. It is to provide a composition. Another object of the present invention is to provide a highly durable pneumatic tire using such an adhesive rubber composition for steel cords for a belt and / or carcass.

  As a result of intensive investigations to achieve the above object, the present inventors have determined that the ratio of zinc white to sulfur in a specific range in the adhesive rubber composition for steel cord can reduce the heat resistant adhesiveness. The present inventors have found that it can be significantly suppressed and have completed the present invention. In particular, in an adhesive rubber composition for steel cords of large tires, although sulfur promotes rubber deterioration and adhesion deterioration, the amount of sulfur cannot be significantly reduced to satisfy various required characteristics. On the other hand, it has been found that by defining the ratio of zinc white and sulfur within a specific range, it is possible to suppress deterioration of rubber and adhesion deterioration while satisfying various required characteristics.

  That is, the adhesive rubber composition for steel cords of the present invention comprises sulfur and zinc white blended with a rubber component containing 50% by mass or more of natural rubber and / or synthetic polyisoprene rubber. The blending amount is 5 to 8 parts by mass with respect to 100 parts by mass of the rubber component, and the mass ratio of zinc white to sulfur (zinc white / sulfur) is 2.2 or more.

  In a preferred example of the adhesive rubber composition for steel cords of the present invention, the mass ratio (zinc white / sulfur) between the zinc white and the sulfur is 2.5 or more.

  The pneumatic tire of the present invention is a pneumatic tire in which a steel cord-rubber composite comprising a steel cord and a covering rubber covering the steel cord is used for at least one of a belt and a carcass. An adhesive rubber composition for cords is used.

  Another pneumatic tire of the present invention is a steel cord-rubber composite comprising a steel cord, an inner covering rubber layer covering the steel cord, and an outer covering rubber disposed outside the inner covering rubber layer. In the pneumatic tire using at least one of the belt and the carcass, the above-mentioned adhesive rubber composition for steel cord is used for the inner covering rubber layer, and a rubber composition of another blend is used for the outer covering rubber. Features. Here, the thickness of the inner coating rubber layer is preferably in the range of 0.5 to 2.5 mm, and the rubber composition of other blends has a sulfur blending amount as compared with the adhesive rubber composition for steel cords. A rubber composition having excellent properties other than adhesion is preferred.

  According to the present invention, the amount of sulfur blended and the mass ratio of zinc white and sulfur are in a specific range, and the adhesion after heat aging is maintained while maintaining the adhesion (initial adhesion) immediately after vulcanization to the steel cord. It is possible to provide an adhesive rubber composition for steel cords with significantly improved (heat resistant adhesiveness). In addition, a carcass and / or belt using the steel cord adhesive rubber composition and the steel cord is provided, and the deterioration of the adhesion between the steel cord and the rubber due to heat during production and use is suppressed, which is excellent. A pneumatic tire having durability can be provided.

  The present invention is described in detail below. The adhesive rubber composition for steel cord of the present invention comprises sulfur and zinc white blended with a rubber component containing 50% by mass or more of natural rubber and / or synthetic polyisoprene rubber. Is 5 to 8 parts by mass with respect to 100 parts by mass of the rubber component, and the mass ratio of zinc white to sulfur (zinc white / sulfur) is 2.2 or more. In the rubber composition, the heat-resistant adhesiveness is greatly improved while maintaining the initial adhesiveness with the steel cord by regulating the sulfur blending amount and the zinc white / sulfur mass ratio within a specific range.

Conventionally, an organic acid cobalt salt generally used in an adhesive rubber composition for steel cords has an anchor effect by forming Cu _x S in an adhesive interface layer in a brass-plated steel cord-rubber adhesive system, It is considered to have an action of promoting the formation of chemical bonds in synchronization with the vulcanization reaction. Therefore, the initial adhesiveness of the adhesive rubber composition can be improved by blending the organic acid cobalt salt. On the other hand, when heat is applied after the vulcanization is completed, Cu _x S is further generated in the adhesive interface layer between the steel cord and the rubber, and the adhesive interface layer is enlarged to cause cohesive failure / brittleness of the Cu _x S layer. Bring about Further, when the crosslinking of the rubber component is completed, the newly formed Cu _x S cannot be directly bonded to the rubber component, so that the heat resistant adhesiveness of the rubber composition is considered to decrease. This tendency is particularly remarkable in a rubber composition having a large amount of sulfur. Therefore, it is considered important to prevent excessive Cu _x S from being generated by heating after the crosslinking of the rubber composition is completed in order to suppress the decrease in heat resistant adhesiveness.

On the other hand, by setting the zinc white / sulfur mass ratio in the rubber composition to 2.2 or more, preferably 2.5 or more, the ratio of sulfur that contributes to the crosslinking of the rubber in the vulcanization process during production can be improved. , Cu _x S which can not be chemically bonded to the rubber component in the adhesive interface layer by added after completion of the vulcanization heat can be suppressed from being produced in large quantities, as a result, improves the heat adhesion between the steel cord and the rubber composition be able to. In the steel cord adhesive rubber composition, when the zinc white / sulfur mass ratio is less than 2.2, a large amount of sulfur that does not contribute to crosslinking remains at the end of vulcanization, and due to the heat history during subsequent running, A large amount of Cu _x S that cannot be chemically bonded is produced. As a result, the adhesive interface layer between the steel cord and the rubber is fragile and easily breaks down, and the heat resistant adhesiveness is lowered.

  In the adhesive rubber composition for steel cords of the present invention, the rubber component contains 50% by mass or more of natural rubber (NR) and / or synthetic polyisoprene rubber (IR) in total. When the total content of the natural rubber and the synthetic polyisoprene rubber in the rubber component is less than 50% by mass, the initial adhesiveness between the steel cord and the adhesive rubber composition is lowered. In addition to natural rubber and synthetic polyisoprene rubber, other diene rubbers such as styrene-butadiene copolymer rubber (SBR) and polybutadiene rubber (BR) can be mixed with the rubber component.

In the adhesive rubber composition for steel cords of the present invention, the amount of sulfur is 5 to 8 parts by mass with respect to 100 parts by mass of the rubber component. If the compounding amount of sulfur in the adhesive rubber composition is less than 5 parts by mass with respect to 100 parts by mass of the rubber component, Cu _x S cannot be sufficiently generated in the adhesive interface layer in the vulcanization process, and the initial adhesiveness When the amount exceeds 8 parts by mass, Cu _x S is excessively generated in the adhesive interface layer in the vulcanization step, and the initial adhesiveness is lowered. Further, if the amount of sulfur exceeds 8 parts by mass, it is necessary to add about 18 parts by mass or more of zinc white, which increases the compounding cost and deteriorates the dispersibility of zinc white in the rubber composition. In addition, the heat generation during running promotes the deterioration reaction of the rubber, and the physical properties after running are significantly reduced.

  Examples of the organic acid cobalt salt include cobalt naphthenate, cobalt stearate, cobalt neodecanoate, cobalt rosinate, cobalt versatate and cobalt tall oil. Further, the organic acid cobalt salt may be a complex salt in which a part of the organic acid is replaced with boric acid or the like, and specific examples include Manobond [trademark: manufactured by OMG].

  The adhesive rubber composition for steel cord of the present invention is filled with a compounding agent usually used in the rubber industry, such as carbon black and silica, in addition to the rubber component, sulfur, zinc white, and organic acid cobalt salt. Agents, softeners such as aroma oils, vulcanization accelerators, vulcanization acceleration aids, anti-aging agents, and the like can be appropriately selected and blended within a range that does not impair the object of the present invention. As these compounding agents, commercially available products can be suitably used. The adhesive rubber composition can be produced by blending the rubber component with various compounding agents appropriately selected as necessary together with sulfur and zinc white, and kneading, heating, extruding, and the like. .

  Next, the pneumatic tire of the present invention will be described in detail. The pneumatic tire of the present invention is characterized in that a steel cord-rubber composite using a steel cord and the above-described adhesive rubber composition for steel cord is used for at least one of a belt and a carcass. For example, as shown in FIG. 1, the steel cord-rubber composite has a structure in which a steel cord 1 is covered with a single covering rubber 2, as shown in FIG. 2. A structure comprising an inner covering rubber layer 3 to be coated and an outer covering rubber 4 disposed outside the inner covering rubber layer 3 may be employed. Moreover, as shown in FIG. 3, the steel cord 1 may have two or more layers.

  Here, in the steel cord-rubber composite of FIG. 1, the above-mentioned adhesive rubber composition for steel cord is used for the single coated rubber 2, and in the steel cord-rubber composite of FIG. 2 and FIG. By using the above-mentioned adhesive rubber composition for steel cords for the inner covering rubber layer 3, the heat resistant adhesiveness can be improved while maintaining the initial adhesiveness between the steel cord and the rubber. Further, in the steel cord-rubber composite of FIGS. 2 and 3, a rubber composition having a different composition can be used for the outer covering rubber 4, for example, more heat than the above-described adhesive rubber composition for steel cord. By using a rubber composition having excellent aging characteristics, the heat aging characteristics of the steel cord-rubber composite can be improved.

  When the steel cord is coated with two kinds of rubber compositions as in the steel cord-rubber composite shown in FIGS. 2 and 3, the thickness of the inner coating rubber layer 3 is preferably in the range of 0.5 to 2.5 mm. . If the thickness of the inner covering rubber layer 3 is less than 0.5 mm, the inner covering rubber layer 3 is likely to be affected by the outer covering rubber 4, and the desired adhesiveness may not be ensured. The function of the outer covering rubber 4 is impaired. The steel cord-rubber composite shown in FIGS. 2 and 3 is not particularly limited. For example, after the steel cord is coated with the adhesive rubber composition of the present invention, the rubber-coated cord is substantially planar. Can be produced by arranging a plurality of them together and sandwiching them with a rubber sheet made of a rubber composition of a different composition.

  The steel cord constituting the steel cord-rubber composite is preferably plated with brass, zinc or a metal containing nickel or cobalt in order to improve the adhesion with rubber, and is plated with brass. It is particularly preferred that Further, the size, twisted structure, twisting conditions, etc. of the steel cord are appropriately selected according to the required performance of the tire.

  The pneumatic tire of the present invention has good initial adhesion and heat-resistant adhesion between steel cord and rubber in a carcass and / or belt, and is excellent in durability. Suitable for large tires such as vehicle tires. The pneumatic radial tire of the present invention is not particularly limited except that the steel cord-rubber composite is used for at least one of the carcass and the belt, and can be manufactured in the same manner as before. In addition, as gas with which the tire of the present invention is filled, normal or air with a changed oxygen partial pressure, or an inert gas such as nitrogen is exemplified.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

  A rubber composition having the formulation shown in Table 1 was prepared, and a steel cord [(3 + 9 + 15) × 0.22 + 1 structure] whose surface was plated with brass was coated with the rubber composition, and the steel having the structure shown in FIG. A cord-rubber composite was produced. The initial adhesion and heat resistant adhesion of the steel cord-rubber composite were measured by the following methods. For measurement of heat-resistant adhesion, a steel cord-rubber composite embedded in a rubber composition was used so that the end of the steel cord did not touch the outside air. The results are shown in Table 1.

(1) Initial adhesiveness Samples obtained by vulcanizing the test steel cord-rubber composites at 145 ° C. for 60 minutes, 150 minutes, 300 minutes, and 600 minutes were respectively prototyped. The vulcanized cord-rubber composite was subjected to a peel test in accordance with JIS K-6256 to peel the steel cord and rubber, and the rubber coverage on the steel cord was measured. The larger the value, the higher the coverage and the better the adhesiveness.

(2) Heat-resistant adhesion In the same way as the initial adhesion test, the test steel cord-rubber composite was vulcanized, and the vulcanized cord-rubber composite was left in a gear oven at 100 ° C for 20 days before initial adhesion. The adhesiveness was evaluated in the same manner as the evaluation of property.

* 1 Toast Carbon Co., Ltd., Seast 300.
* 2 N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine, manufactured by Ouchi Shinsei Chemical Co., Ltd., NOCRACK 6C.
* 3 Dainippon Ink Co., Ltd., cobalt naphthenate, Co content = 10.0 mass%.
* 4 N, N'-dicyclohexyl-2-benzothiazylsulfenamide, manufactured by Ouchi Shinsei Chemical Co., Ltd., Noxeller DZ.

The rubber compositions used in Comparative Examples 1 and 2 had inadequate initial adhesion particularly when the vulcanization time was short, and also had low heat resistant adhesion. This is because Cu _x S is not sufficiently generated because the amount of sulfur added to the rubber component 100 is less than 5 parts by mass.

  Comparative Examples 3 and 4 and Examples 1, 2 and 3 show the relationship between the zinc white / sulfur mass ratio and the adhesiveness when the amount of sulfur added to the rubber component 100 is 5 parts by mass. In any case, the initial adhesiveness was sufficiently high, but the rubber compositions used in Comparative Examples 3 and 4 had low heat resistant adhesiveness because the zinc white / sulfur mass ratio was less than 2.2. On the other hand, the rubber compositions used in Examples 1 to 3 have high heat-resistant adhesiveness because the zinc white / sulfur mass ratio is 2.2 or more, and in particular, Example 2 and the zinc white / sulfur mass ratio of 2.5 or more. The rubber composition No. 3 did not show a decrease in adhesion even after heat aging.

  In Comparative Examples 5, 6 and 7, and Examples 4, 5 and 6, the zinc white / sulfur mass ratio and adhesion when the compounding amount of sulfur with respect to the rubber component 100 is 6, 7, and 8 parts by mass. It shows the relationship. As is apparent from the comparison between Comparative Example 5 and Example 4, Comparative Example 6 and Example 5, and Comparative Example 7 and Example 6, the adhesiveness after heat aging is low when the zinc white / sulfur mass ratio is less than 2.2. On the other hand, when the zinc white / sulfur mass ratio is 2.2 or more, it can be seen that the decrease in adhesiveness after heat aging is suppressed.

Comparative Example 8 was a test of adhesion of a rubber composition having a zinc white / sulfur mass ratio of 2.2 or more and a sulfur compounding amount of 9 parts by mass with respect to the rubber component 100 to the steel cord. When 145 ° C. is 300 minutes or more, the initial adhesiveness is lowered, and the adhesiveness after heat aging is also lowered as vulcanized for a long time. This is because the amount of sulfur is too large, occur bloated Cu _x S layer upon vulcanization, further Cu _x S layer with heat after vulcanization is because bloated.

  Next, a steel cord-rubber composite having the structure shown in FIG. 4 was prototyped using the rubber composition shown in Table 2 and a steel cord [(3 + 9 + 15) × 0.22 + 1 structure] plated with brass. Then, the initial adhesiveness and heat resistant adhesiveness of the steel cord-rubber composite were measured in the same manner as described above, and the fracture strength after heat aging was further measured by the following method. The rubber composition of Formulation A is the adhesive rubber composition of the present invention, and the rubber composition of Formulation B is a highly heat aging rubber composition that has a low sulfur content and does not contain cobalt. For initial adhesion and heat-resistant adhesion, a cord-rubber composite vulcanized at 145 ° C. for 60 minutes was used as a sample. The results are shown in Table 3.

(3) Fracture strength after heat aging The portion 5 between the inner coated rubber layers of the steel cord-rubber composite shown in FIG. 4 was cut out, the fracture strength was measured according to JIS K6251, and the fracture strength of Example 10 was 100. As an index. The larger the index value, the higher the fracture strength and the better.

  The cord-rubber composites of Examples 7, 8 and 9 in which the inner coating rubber layer had a thickness of 0.5 to 2.5 mm had sufficiently high initial adhesion and heat-resistant adhesion. In addition, the cord-rubber composites of Examples 7, 8 and 9 had higher breaking strength of the outer covering rubber than the cord-rubber composite of Example 10, and the heat aging resistance of the rubber part was improved.

  Based on the above results, the adhesive rubber composition of the present invention was used for the inner coating rubber layer, while the performance of the coating rubber was limited due to the need to ensure heat-resistant adhesion between the steel cord and the coating rubber. In addition, it is understood that the performance of the covering rubber can be arbitrarily changed while ensuring the heat-resistant adhesion between the steel cord and the covering rubber by adopting the rubber composition having desired physical properties for the outer covering rubber.

It is a fragmentary sectional view of an example of the steel cord-rubber composite using the adhesive rubber composition of the present invention. It is a fragmentary sectional view of the other example of the steel cord-rubber composite using the adhesive rubber composition of this invention. It is a fragmentary sectional view of the other example of the steel cord-rubber composite using the adhesive rubber composition of this invention. It is a fragmentary sectional view of the steel cord-rubber composite used in comparative example 9 and examples 7-10.

Explanation of symbols

1 Steel cord 2 Coated rubber 3 Inner coated rubber layer 4 Outer coated rubber 5 Sample part for breaking strength measurement

Claims (5)

  Sulfur and zinc white are blended with a rubber component containing 50% by mass or more of natural rubber and / or synthetic polyisoprene rubber, and the blending amount of sulfur is 5 to 8 with respect to 100 parts by mass of the rubber component. An adhesive rubber composition for a steel cord, wherein the mass ratio of zinc white to sulfur (zinc white / sulfur) is 2.2 or more in terms of parts by mass.   2. The adhesive rubber composition for steel cord according to claim 1, wherein a mass ratio (zinc white / sulfur) between the zinc white and the sulfur is 2.5 or more. In a pneumatic tire using a steel cord-rubber composite made of a steel cord and a coated rubber covering the steel cord for at least one of a belt and a carcass,
A pneumatic tire using the steel rubber adhesive rubber composition according to claim 1 or 2 as the covering rubber. Pneumatic in which a steel cord-rubber composite comprising a steel cord, an inner covering rubber layer covering the steel cord, and an outer covering rubber disposed outside the inner covering rubber layer is used for at least one of a belt and a carcass In the tire,
A pneumatic tire using the adhesive rubber composition for steel cords according to claim 1 or 2 for the inner covering rubber layer, and a rubber composition of another composition for the outer covering rubber.   The pneumatic tire according to claim 4, wherein the inner covering rubber layer has a thickness of 0.5 to 2.5 mm.

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