JP2001233998A - Rubber composition for coating steel cord, and pneumatic tire using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition which is excellent in both the initial adhesiveness and the resistance of adhesiveness to thermal degradation deterioration with maintaining the heat resistance of the rubber at a definite level of higher, and to provide a pneumatic tire by applying it. SOLUTION: The rubber composition for coating steel cords is characterized in that 100 pts.wt. of (A) a rubber component is so blended with (B) a cobalt salt of an organic acid and (C) a cobalt hydroxide as the whole content of the cobalt element in the sum total of components (B) and (C) is 0.02-0.4 pt.wt., and in that a blend amount of component (B) satisfies 20-230 as a of value multiplying an organic acid residue amount (parts by weigh) exclusive of the cobalt element in component (B) by an acid value of the organic acid, the constituent of component (B). This rubber composition is applied to the pneumatic tire.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition for steel cord coating and a pneumatic tire using the same, and more particularly, to a steel cord coating having improved initial adhesion and heat-resistant adhesion to steel cord. And a steel cord-rubber composite comprising the rubber composition and a steel cord.

[0002]

2. Description of the Related Art In general, a steel cord is used as a reinforcing material for a carcass material or a belt material in an automobile tire. Particularly, in a heavy-duty tire, the load on the tire is large, and since the gauge is thick, the internal heat generation is large, and the adhesive layer between the steel cord and the rubber is likely to be broken by heat. Conventionally, this steel cord is usually plated with brass in order to increase the adhesive force with rubber and enhance its reinforcing effect. On the other hand, the coating rubber composition in contact with the steel cord usually contains a cobalt salt of an organic acid as an adhesion promoter in order to enhance the adhesion to the rubber. However, when a large amount of this organic acid cobalt salt is used, although the adhesiveness immediately after vulcanization, that is, the initial adhesiveness, is excellent, heat generation during use accelerates thermal deterioration of the rubber,
There is an inconvenience that the adhesiveness against heat deterioration is poor. On the other hand, when the amount of the organic acid cobalt salt is small, the deterioration of adhesion is small, but sufficient initial adhesion cannot be obtained. Further, a method has been proposed in which a metal salt of another organic acid is blended in place of the cobalt salt of the organic acid (for example, International Publication WO97 / 49).
No. 776), even in such a method, the adhesive force immediately after vulcanization is not always satisfactory, and the metal salt of an organic acid instead of cobalt has not yet been put to practical use.

[0003]

SUMMARY OF THE INVENTION The present invention provides a rubber composition for a steel cord coating having improved initial adhesion to a steel cord and heat-resistant adhesiveness under such a circumstance. It is intended to provide a steel cord-rubber composite, particularly a pneumatic tire.

[0004]

DISCLOSURE OF THE INVENTION The present inventors have developed a rubber composition for a steel cord coating, wherein a rubber composition containing a cobalt salt of an organic acid has a high level of both initial adhesiveness and heat-resistant adhesiveness. As a result of intensive research to develop a product, it has been found that it is effective to mix cobalt hydroxide with a cobalt salt of an organic acid.
That is, since cobalt hydroxide has a very low affinity for rubber, simply adding it does not effectively function in the adhesion reaction, but when a cobalt salt of an organic acid and cobalt hydroxide are used in combination, The organic acid separated from the cobalt salt of the organic acid by the adhesive reaction reacts with the cobalt hydroxide to form again the cobalt salt of the organic acid having an affinity for rubber, which is transferred to the interface between the steel cord and the rubber. It was found that this greatly contributes to the adhesion reaction between steel cord and rubber. Furthermore, although the thermal history of the adhesive layer for vulcanization varies greatly depending on the tire size, vulcanization at a relatively low temperature for a long time, such as for large heavy duty pneumatic tires such as buses, trucks and construction vehicles. In this case, it was also found that the properties of the organic acid itself that forms the cobalt salt of the organic acid play a very important role in the adhesive reaction. The present invention has been completed based on such findings.

That is, the present invention relates to (A) a rubber component,
The cobalt salt of the organic acid (B) and the cobalt hydroxide (C) per 100 parts by weight thereof were defined as the total cobalt element content in the total of the components (B) and (C) in the range of 0.02 to 0.4.
(B) The amount of the organic acid residue (parts by weight) excluding the cobalt element content in the (B) component and the amount of the organic acid forming the (B) component It is intended to provide a rubber composition for steel cord coating, which satisfies 20 to 230 as a value multiplied by the acid value of an acid. Further, according to the present invention, in a tire having a steel cord carcass ply and at least one steel belt disposed radially outward of the tire, the coating rubber of the carcass ply and / or the belt is the rubber composition described above. It is intended to provide a rubber composition for a pneumatic tire. Further, the present invention also provides a steel cord-rubber composite comprising the above rubber composition and a steel cord.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION As the rubber component (A) in the rubber composition of the present invention, natural rubber or synthetic rubber is used. As synthetic rubber, for example, ethylene
Propylene / diene rubber (EPDM), styrene / butadiene copolymer rubber (SBR), butadiene rubber, isoprene rubber, butyl rubber, halogenated butyl rubber, copolymer of isobutylene and p-halogenated methylstyrene,
Acrylonitrile-butadiene copolymer rubber (NBR) and the like. The rubber component in the present invention is appropriately selected from one or more of natural rubber and the above synthetic rubber depending on the use of the rubber product using a steel cord as a reinforcing material. As the rubber component, a rubber component containing a natural rubber and / or a synthetic isoprene rubber in a proportion of 50% by weight or more is particularly preferable from the viewpoints of adhesive properties and rubber breaking properties.

In the rubber composition of the present invention, a cobalt salt of an organic acid is used as the component (B). Here, the organic acid may be saturated, unsaturated, linear or branched, and may be, for example, naphthenic acid such as cyclohexanoic acid (cyclohexanecarboxylic acid) or alkylcyclopentane having a fatty acid side chain; hexane Acids, octanoic acid, decanoic acid (including branched carboxylic acids such as neodecanoic acid), dodecanoic acid, tetradecanoic acid, hexadecanoic acid,
Saturated fatty acids such as octadecanoic acid; unsaturated fatty acids such as methacrylic acid, oleic acid, linoleic acid and linolenic acid;
Resin acids such as rosin, tall oil acid and abietic acid are exemplified. In addition, such an organic acid can replace a part of the cobalt metal with a compound containing boron, boric acid, aluminum or the like.

Further, the present inventors have also found that the acid value of the organic acid forming the component (B) is closely related to the adhesive action. Here, the acid value of the organic acid is mg of potassium hydroxide required to neutralize 1 g of the target organic acid.
This is a value obtained as a number. In a tire using a cobalt salt of an organic acid having a high acid value, when used for a long time, the adhesive performance tends to be further reduced due to heat generation. Therefore, from the viewpoint of adhesion deterioration, it is desirable to use a smaller amount of a cobalt salt composed of an organic acid having a low acid value, but in this case, the initial reaction of adhesion is not sufficiently performed, and the performance of the tire is not sufficiently exhibited. . From this perspective,
The compounding amount of the organic acid cobalt salt as the component (B) used in the present invention is such that the organic acid residue amount (parts by weight) a excluding the cobalt element content in the component (B) and the component (B) are used. 20 to 2 as an a × b value multiplied by the acid value b of the organic acid to be formed
30 must be satisfied. If this value is less than 20, the amount of the organic acid deviating from the cobalt salt of the organic acid at the time of the adhesion reaction is too small, or the addition amount of the cobalt salt of the organic acid is too small to coexist with the reaction with the organic acid. Cobalt hydroxide is not used effectively. On the other hand, the value is 230
When it exceeds, adhesion deterioration due to the organic acid is promoted.
In consideration of the adhesive performance in both the initial adhesive property and the deterioration-resistant adhesive property, the a × b value is preferably from 30 to 200, and more preferably from 50 to 150.

Further, in the rubber composition of the present invention, as the component (C), cobalt hydroxide [Co (O
H) ₂ ] is required to be used in combination with a cobalt salt of an organic acid. The compounding amount of the component (C) is 0.02 to 0.4 parts by weight as the total content of the cobalt element in the total of the components (B) and (C) with respect to 100 parts by weight of the rubber component. If it is less than 0.02 parts by weight, the initial adhesiveness is not sufficient. On the other hand, if it exceeds 0.4 part by weight, the aging characteristics of rubber become too poor. Considering the effect of improving the initial adhesion and heat-deterioration adhesion and other physical properties, the total content of cobalt element in the total of the component (B) and the component (C) is 0.02 to 0.02.
Preferably it is 0.3 parts by weight. Further, the rubber composition of the present invention usually contains sulfur. The sulfur content is preferably in the range of 3 to 8 parts by weight per 100 parts by weight of the rubber component. If this content is less than 3 parts by weight, it is possible to supply sufficient sulfur for producing Cu _x S (generated by the reaction between copper and sulfur during brass plating of a steel cord), which is a source of adhesive strength. And the adhesive strength may be insufficient. On the other hand, if the content exceeds 8 parts by weight, Cu _x S is excessively generated, so that cohesive failure of the enlarged Cu _x S occurs, the adhesive strength decreases, and the heat aging resistance as rubber properties tends to decrease. Can be

In the rubber composition of the present invention, in addition to the above-mentioned components, a compounding agent usually used in the rubber industry can be appropriately compounded in a usual compounding amount. Specifically, softeners such as aroma oil, guanidines such as diphenylguanidine,
Thiazoles such as mercaptobenzothiazole, N,
Vulcanization accelerators such as sulfenamides such as N'-dicyclohexyl-2-benzothiazolylsulfenamide, thiurams such as tetramethylthiuram disulfide, vulcanization accelerators such as zinc oxide, poly (2,2 , 4-trimethyl-1,2-dihydroquinoline) and aging inhibitors such as amines such as phenyl-α-naphthylamine.

Among these, fillers such as carbon black are used to determine the tensile strength, breaking strength, tensile stress,
Known as a reinforcing agent for increasing hardness, etc. and improving abrasion resistance and tensile resistance, zinc oxide is known as a vulcanization aid that forms a complex compound with fatty acids to enhance the vulcanization accelerating effect. ing. Further, the steel cord to which the rubber composition of the present invention is applied is preferably plated with brass, zinc, or an alloy containing nickel or cobalt to improve the adhesion to rubber. ,
In particular, those subjected to a brass plating treatment are preferable.
When the content of Cu in the brass plating of the steel cord is 80% by weight or less, preferably 55 to 75% by weight, good and stable adhesion can be obtained. The twist structure of the steel cord is not particularly limited. The present invention also provides a steel cord-rubber composite comprising the rubber composition for steel cord coating and a steel cord, and the composite is used, for example, as a carcass or belt material for a heavy-duty pneumatic tire. It is preferably used.

[0012]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In addition, various characteristics of the obtained rubber composition were evaluated according to the following methods. (1) Initial adhesiveness Steel cords (1 × 5 structure, wire diameter 0.25 mm) plated with brass (Cu: 63% by weight, Zn: 37% by weight) are arranged in parallel at 12.7 mm intervals, and the embedded length is set. 12.7mm
This steel cord was coated on both sides with a sheet made of each rubber composition, and this was coated at 145 ° C. × 1
The sample was vulcanized under the condition of 80 minutes to produce a sample having a thickness of 12 mm. Using this sample, a steel cord was drawn at −90 ° C. At that time, a portion (area) covered with rubber on the surface of the drawn steel cord was determined as a ratio to the entire surface of the cord. (%). The higher the value, the better.

(2) Resistance to heat-induced deterioration and adhesion In the same manner as in (1) above, vulcanization was performed at 145 ° C. for 180 minutes to prepare a sample, which was then placed under a nitrogen atmosphere.
After deterioration at 0 ° C. for 10 days, the steel cord was pulled out in the same manner as in (1) above, and the rubber coverage (%) at that time was determined. The higher the value, the better. (3) Heat resistance of rubber: 145 ° C. for each rubber composition
The sheet was vulcanized under conditions of × 40 minutes to produce a sheet having a thickness of 2.0 mm. A part of the vulcanized sheet was aged in an oven at 100 ° C. for 24 hours. Samples of JIS No. 3 dumbbells were prepared from the sheets before and after deterioration, and JIS
A tensile test was performed according to K6301-1995. The ratio of the breaking strength before and after the deterioration was used as an index of the heat-resistant deterioration performance. The larger the value of the strength at break after deterioration / the strength at break before deterioration, the better the heat deterioration performance.

Comparative Example 1 100 parts by weight of natural rubber, 60 parts by weight of carbon black (N330, manufactured by Tokai Carbon Co., Ltd.), zinc oxide 8
Parts by weight, vulcanization accelerator N, N'-dicyclohexyl-2-
Benzothiazolylsulfenamide [manufactured by Ouchi Shinko Chemical Co., Ltd., trade name: Noxeller DZ] 1 part by weight, antioxidant N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine [Ouchi Shinko Chemical Industry Co., Ltd.
Nocrack 6C] 2 parts by weight and 5 parts by weight of sulfur are mixed and vulcanized at 145 ° C. for 180 minutes to prepare a rubber composition, and the initial adhesiveness, heat-resistant adhesiveness, and rubber heat resistance are prepared. Was evaluated. Table 2 shows the results. Comparative Examples 2 to 9 According to Table 1, cobalt naphthenate (acid value: 200 mg · KOH / g) or cobalt neodecanoate (acid value: 340 mg · KOH / g) was further added to the composition of Comparative Example 1. A rubber composition was prepared in the same manner as in Example 1, and the initial adhesion, the heat-resistant aging adhesion, and the heat resistance of the rubber were evaluated.
Table 2 shows the results.

Examples 1 to 6 and Comparative Examples 10 to 12 According to the composition of Comparative Example 1, according to Table 1, cobalt naphthenate (acid value 200 mg · KOH / g) or cobalt neodecanoate (acid value 340 mg · KOH) / G) together with cobalt hydroxide, and a rubber composition was prepared in the same manner as in Comparative Example 1, and the initial adhesion, the heat-resistant aging adhesion, and the heat resistance of the rubber were evaluated. Table 2 shows the results.

[0016]

[Table 1]

(Note) * 1, * 2: Each compounding amount is shown in parts by weight per 100 parts by weight of the rubber component. * 3: The total cobalt content is the cobalt element content (parts by weight) in the total of the cobalt salt of the organic acid and the cobalt hydroxide.

[0018]

[Table 2]

In Tables 1 and 2, Comparative Examples 2 to 7
Is a conventional rubber composition blended with cobalt naphthenate, but even in Comparative Example 5 having the highest initial adhesiveness, the adhesiveness against heat degradation is insufficient. On the other hand, Examples 1 to 5 of the present invention in which cobalt hydroxide was blended together with cobalt naphthenate
It can be seen that the rubber composition of (1) has good initial adhesiveness and heat-resistant adhesiveness. Further, in Example 6, in which cobalt neodecanoate was used in place of cobalt naphthenate in Example 3, good effects similar to those described above were obtained. In addition, even when the cobalt naphthenate and the cobalt hydroxide were used in combination, Comparative Examples 10 and 12 showed that the value of the amount of the organic acid residue x the acid value was not within the range of the present invention, so that the initial adhesiveness and the heat-resistant adhesiveness Compatibility with the rubber composition was not obtained, and in Comparative Example 11, the heat resistance of the rubber was very poor because the total cobalt content exceeded 0.4 parts by weight.

[0020]

The rubber composition for coating a steel cord according to the present invention is excellent in the initial adhesiveness to a steel cord and the heat-resistant adhesiveness. When this rubber composition is used as a carcass or belt coating rubber composition for pneumatic tires, particularly pneumatic tires for heavy loads, the initial adhesive property is maintained while keeping the heat resistance of the rubber at or above a certain level. In addition, a pneumatic tire with further improved running durability can be manufactured because of excellent heat resistance and heat-resistant adhesiveness.

Claims (5)

[Claims] 1. A rubber component containing (B) a cobalt salt of an organic acid and (C) cobalt hydroxide per 100 parts by weight of the rubber component, and a total of cobalt elements in the total of the components (B) and (C). The content of the component (B) is adjusted to be 0.02 to 0.4 parts by weight, and the amount of the organic acid residue (parts by weight) excluding the cobalt element content in the component (B). ) And a value obtained by multiplying the acid value of the organic acid forming the component (B) by 20 to 230. 2. The compounding amount of the cobalt salt of the organic acid as the component (B) is such that the amount of the organic acid residue (parts by weight) excluding the content of the cobalt element in the component (B) and the component (B) are The rubber composition for steel cord coating according to claim 1, which satisfies 50 to 150 as a value multiplied by the acid value of the organic acid to be formed. 3. A tire having a steel cord carcass ply and at least one steel belt disposed radially outside the tire, wherein the coating rubber of the carcass ply and / or the belt is coated with a rubber. A pneumatic tire which is the rubber composition according to any one of the above. 4. A heavy-duty pneumatic tire.
The pneumatic tire as described. 5. A steel cord-rubber composite comprising the rubber composition according to claim 1 and a steel cord.