JP5602403B2 - Rubber composition for coating steel cord - Google Patents

Description

  The present invention relates to a rubber composition for coating a steel cord, which is optimal as a coating rubber for a steel cord and can exhibit an effect excellent in initial adhesion to the steel cord and heat-resistant adhesion.

  For rubber articles that require particularly high strength, such as automobile tires, conveyor belts, hoses, etc., steel with a metal reinforcement such as steel cord coated with coated rubber for the purpose of reinforcing the rubber and improving its strength and durability A cord-rubber composite is used. Here, in order for such a steel cord-rubber composite to exhibit a high reinforcing effect and to obtain reliability, stable and strong adhesion is required between the covering rubber and the metal reinforcing material.

  In order to obtain a steel cord-rubber composite exhibiting such high adhesion between the coated rubber and the metal reinforcing material, a coated rubber in which a metal reinforcing material such as a steel cord plated with zinc or brass is mixed with sulfur. So-called direct vulcanization bonding is widely used, which is embedded in the rubber and bonded together at the same time as rubber vulcanization during heat vulcanization. Up to now, various studies on the direct vulcanization adhesion have been made in order to further improve the adhesion between the coated rubber and the metal reinforcing material by the direct vulcanization adhesion.

  For example, Patent Document 1 discloses a method for manufacturing a steel cord-rubber composite reinforcing steel cord obtained by twisting a plurality of filaments manufactured by wet drawing a brass-plated steel wire. A method of attaching resorcin to a filament surface by adding resorcin as an adhesion improver between a steel cord and a coated rubber in a wet lubricant sometimes used is disclosed. In Patent Document 2, the surface of the steel wire and the steel cord to be used is washed with an acidic or alkaline solution to remove the phosphorus compound (derived from the lubricant used when producing the steel cord) as an adhesion reaction inhibitor. Discloses a technique for improving the adhesion to the coated rubber.

  On the other hand, in order to improve the initial adhesion between coated rubber and metal reinforcement in direct vulcanization bonding generally used for tires, etc., rubber composition containing cobalt salt as adhesion promoter as steel cord coating rubber Many things are used.

JP 2004-66298 A JP 2001-234371 A

  However, for example, in the case of the method described in Patent Document 1, if resorcin is altered due to heat generation during wire drawing of a steel filament, a sufficient effect as an adhesion improver between the steel cord and the coated rubber may not be expected. Therefore, some alternative is required. Further, Patent Document 2 has only been intensively studied on subjecting a steel cord to a cleaning treatment, and a detailed study on coated rubber is still desired.

  In addition, even if the steel cord covering rubber that has been adopted conventionally is used, the amount of cobalt salt is reduced as much as possible from the viewpoint of improving durability against deterioration of the covering rubber and crack growth. Is desirable.

  Therefore, the present invention provides a steel cord that can realize a steel cord-rubber composite that provides excellent durability to the resulting rubber article while further improving the initial adhesion and heat-resistant adhesion between the coated rubber and the steel cord. An object is to provide a rubber composition for coating.

In order to solve the above-mentioned problems, the present inventors have found a rubber composition for coating a steel cord containing a specific component including a boron-containing compound in a specific amount, and have completed the present invention.
That is, the steel cord-rubber composite of the present invention is a steel cord-rubber composite comprising a steel cord with brass plating and a rubber composition for coating a steel cord,
The steel cord with brass plating is manufactured by immersing a brass-plated steel wire in an aqueous solution containing a cobalt salt and then twisting a plurality of them, or after twisting a plurality of brass-plated steel wires. are those prepared by immersing in an aqueous solution containing cobalt salt, and, when measured by XPS (X-ray photoelectron spectroscopy), zinc on the outermost surface is an amount of 4.93 to 15 atomic%, further The outermost surface contains cobalt in an amount of 2.0 atomic% or less,
The steel cord covering rubber composition contains 0.005 to 0.08 parts by mass of a boron-containing compound in terms of boron and 1 to 10 parts by mass of sulfur with respect to 100 parts by mass of the rubber component. Furthermore, it is desirable that the rubber composition for covering a steel cord contains cobalt in an amount of less than 0.04 parts by mass with respect to 100 parts by mass of the rubber component.
The boron-containing compound is preferably boric acid.

According to the rubber composition for coating a steel cord of the present invention, excellent initial adhesiveness and heat-resistant adhesiveness with the steel cord can be exhibited, and durability against deterioration of the coated rubber, crack growth, and the like is improved. Can also be achieved.
Therefore, by using such a rubber composition, it is possible to realize a steel cord-rubber composite useful as a high-performance tire reinforcing material.

Hereinafter, the present invention will be specifically described.
The rubber composition for coating a steel cord of the present invention contains a boron-containing compound in an amount of 0.01 to 0.1 parts by mass in terms of boron and 1 to 10 parts by mass of sulfur with respect to 100 parts by mass of the rubber component. It is characterized by that.

  The rubber composition for coating a steel cord includes a boron-containing compound. Such a boron-containing compound has an effect of further improving the adhesion durability between the steel cord and the covering rubber and bringing about an antirust effect. Content of a boron containing compound is 0.005-0.08 mass part in conversion of boron with respect to 100 mass parts of rubber components, Preferably it is 0.01-0.06 mass part, More preferably, it is 0.02-0. The amount is 055 parts by mass. If the boron-converted amount of the boron-containing compound is less than 0.005 parts by mass, the adhesion durability between the steel cord and the coated rubber may not be sufficiently improved, and if it exceeds 0.08 parts by mass In addition, the initial vulcanization rate of the rubber may be decreased, and the destruction physical properties of the rubber may be decreased. In any case, it may be a factor that adversely affects the adhesion between the steel cord and the covering rubber.

  Here, the boron-containing compound is not particularly limited as long as it contains boron, and specific examples include boric acid, ammonium borate, zinc borate, and tetrafluoroboric acid. Of these, boric acid is preferred from the viewpoints of availability and low cost. These may be used individually by 1 type, and may be used in combination of 2 or more types.

  The rubber composition for coating a steel cord of the present invention further contains sulfur that acts as a rubber vulcanizing agent. The content of sulfur is 1 to 10 parts by mass, preferably 2 to 9 parts by mass, more preferably 3 to 8 parts by mass with respect to 100 parts by mass of the rubber component. If the sulfur content is less than 1 part by mass, the vulcanization will be insufficient and the adhesion may be reduced. If it exceeds 10 parts by mass, the deterioration resistance of the rubber may be reduced.

  The steel cord coating rubber composition of the present invention preferably further contains cobalt in an amount of less than 0.04 parts by mass with respect to 100 parts by mass of the rubber component. Therefore, it is not always necessary to contain cobalt, and it is possible not to add cobalt at all. Thus, by reducing the compounding quantity of cobalt, it also becomes possible to reduce cost, suppressing the fall of the physical property in covering rubber | gum effectively.

  The rubber component of the rubber composition is not particularly limited as long as it is employed in rubber articles such as automobile tires, conveyor belts, hoses, and the like. For example, natural rubber, polybutadiene rubber, polyisoprene rubber, ethylene-propylene A copolymer, an isobutylene-isoprene copolymer, a polychloroprene rubber, etc. are mentioned. These may be used individually by 1 type, and may be used in combination of 2 or more types. Among these, natural rubber is preferred from the viewpoint of suppressing the deterioration of rubber physical properties while further improving the adhesiveness.

  Furthermore, in addition to the rubber component, boron compound, sulfur and cobalt, the rubber composition may be appropriately mixed with additives usually employed in the rubber industry as long as the object of the present invention is not impaired. Specific examples include fillers such as resins and carbon black, oils such as process oil, vulcanizing agents other than sulfur, vulcanization accelerators, anti-aging agents, softeners, zinc oxide and stearic acid. . Then, these rubber components, boron compounds, and sulfur, if necessary, cobalt or the above additives are added, kneaded with a Banbury mixer, a kneader, etc. by a conventional method, and then heated and extruded, whereby the steel cord covering rubber A composition can be obtained.

  A steel cord-rubber composite can be obtained by using the rubber composition for coating a steel cord, coating the steel cord by a conventional method, and vulcanizing. Such a steel cord-rubber composite exhibits excellent durability, and is optimal as a reinforcing material for tire carcass plies, belt plies and the like.

  The steel cord used at this time is preferably a steel cord with brass plating. Such a steel cord is brass-plated. For example, a steel wire can be manufactured by twisting a plurality of these steel wires by performing brass plating on the peripheral surface of the steel wire and then performing wire drawing. As for this plating composition, copper is 70 mass% or less normally, Preferably it is 60-65 mass%, and zinc is 30 mass% or more, Preferably it is 35-40 mass%.

  Further, when the steel cord with brass plating is used, when the outermost surface of the steel cord is measured by XPS (X-ray photoelectron spectroscopy) method, phosphorus is 0.2 to 4.0 atomic% on the outermost surface, preferably It is desirable to be contained in an amount of 0.3 to 3.0 atomic%, more preferably 0.4 to 2.0 atomic%. If the phosphorus content is less than 0.2 atomic%, the steel cord may have poor storage stability. For example, if it exceeds 4.0 atomic%, the initial steel cord with brass plating and the coated rubber There is a possibility that the bonding speed may decrease.

  At this time, the outermost surface of the steel cord with brass plating means a region where the thickness in the depth direction from the surface of the steel cord is measured by XPS (X-ray photoelectron spectroscopy), more specifically. It means a thickness of about several nanometers corresponding to the emission depth of photoelectrons generated when the surface of a steel cord with brass plating is irradiated with X-rays.

  Further, it is desirable that zinc is contained in a specific amount on the outermost surface of the steel cord with brass plating, and is usually 4.93 to 15 atomic%, preferably 4.95 to 14 atomic%, more preferably 5. An amount of 0 to 13 atomic percent is preferred. If the zinc content is less than 4.93 atomic percent, the resulting steel cord-rubber composite may have insufficient adhesion durability. If the zinc content exceeds 15 atomic percent, the initial adhesion rate between the steel cord and the coated rubber may be insufficient. May decrease.

  Further, the outermost surface of the steel cord with brass plating desirably contains a metal having an ionization tendency smaller than zinc and larger than copper in an amount of 2.0 atomic% or less, more preferably 1.8 atomic% or less, The amount is most preferably 1.6 atomic% or less. When such a metal exceeds 2.0 atomic%, the amount of zinc present on the outermost surface of the steel cord with brass plating may be below the lower limit.

  Here, as a metal whose ionization tendency is smaller than zinc and larger than copper, for example, chromium (Cr), iron (Fe), cadmium (Cd), cobalt (Co), nickel (Ni), tin (Sn), lead (Pb) etc. are mentioned. Of these, cobalt is preferable. Cobalt is blended with conventional coated rubber as an adhesion promoter to further improve adhesion, but depending on the amount of cobalt contained in the coated rubber, the durability of the coated rubber itself against heat, moisture, and oxidation In the rubber composition for coating a steel cord of the present invention, the cobalt content is reduced. Therefore, if a steel cord with brass plating containing an appropriate amount of cobalt is adopted, the effect of cobalt itself can be fully utilized, and the steel cord that reduces costs while effectively suppressing the deterioration of rubber properties- It is also possible to obtain a rubber composite.

  Further, it is desirable that the outermost surface of the steel cord with brass plating contains zinc in an amount of 30 to 90 atomic%, preferably 35 to 80 atomic% with respect to 100 atomic% in total of zinc and copper. If the steel cord with brass plating contains zinc in an amount within the above range, a synergistic effect with a desired effect in the rubber composition for coating a steel cord of the present invention can be sufficiently exhibited.

  As described above, the outermost surface of the steel cord with brass plating contains phosphorus, zinc, and a metal having an ionization tendency smaller than zinc and larger than copper in the above-mentioned specific amount. It is better to immerse in an aqueous solution containing a larger metal as a metal salt. At this time, after dipping the steel wire, a plurality of the steel cords may be twisted to manufacture a steel cord, or after a plurality of steel wires are twisted, the steel cord may be manufactured by dipping.

  The metal salt is not particularly limited as long as it exhibits high solubility in water. For example, metal chloride, metal carbonate, metal nitrate, metal sulfate, metal acetate, metal citrate, gluconic acid A metal salt, an acetylacetone metal salt, etc. are mentioned. Especially, it is desirable that the aqueous solution containing this metal salt achieves a suitable pH value described later, and from this point of view, it is preferably an acetic acid metal salt.

  The aqueous solution containing the metal salt has a concentration of usually 0.001-1 mol / L, preferably 0.005-0.5 mol / L, more preferably 0.01-0.2 mol / L, and its pH is It is usually 6.1 to 8.0, preferably 6.3 to 7.5, and more preferably 6.5 to 7.2. When it is an aqueous solution containing a metal salt having a concentration and pH value within the above range, there is no risk of adversely affecting brass plating, and phosphorus, zinc and ionization tendency on the outermost surface of the steel cord are smaller than zinc and more than copper. It becomes easy for a large amount of metal to be present in a predetermined amount. Moreover, this pH value is suitable also from a viewpoint which considers the safety | security at the time of an environment or manufacture.

  In addition, what is necessary is just to set suitably the time which immerses a steel cord in the aqueous solution containing the said metal salt, However, It is 0.05-30 second normally, Preferably it is 0.1-20 second.

  Through such a dipping process, the surface of the steel wire or steel cord is cleaned, and the component (ZnO or ZnO) that is said to inhibit adhesion to the coated rubber formed with the rubber composition for coating a steel cord of the present invention. When the phosphorus compound or the like is moderately removed, the initial adhesion between the steel cord and the covering rubber can be further improved.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.

[Manufacture of steel cords]
A brass-plated (Cu: 63 mass%, Zn: 37 mass%) steel wire is twisted to produce a steel cord having a 1 × 3 structure, and this steel cord is then added to a 0.1 mol / L cobalt acetate aqueous solution (acetic acid The pH was adjusted to 6.8) for 10 seconds, and the excess adhering liquid was removed by air blow, followed by drying at 50 ° C. for 1 minute. The composition of the outermost surface of the steel wire after immersion was measured by X-ray photoelectron spectroscopy (X-ray photoelectron spectroscopy: XPS, Quantum 2000, ULVAC-PHI Co., Ltd.). Phosphorus (P) was 0.9 atomic%. Zinc (Zn) was 7.0 atomic%, the ratio of zinc to the total of zinc and copper (Zn / Zn + Cu) was 38 atomic%, and cobalt (Co) was 1.6 atomic%.

[Example 1, Comparative Examples 1-2]
The steel cords were arranged in parallel, coated with a rubber composition having the composition shown in Table 1 from both the upper and lower directions, and vulcanized under the conditions shown in Table 1 to prepare a sample. About this sample, initial adhesiveness, a deterioration physical property, and crack growth property were evaluated with the following method. The obtained evaluation results are shown in Table 1.

<< Evaluation method of initial adhesiveness >>
Each sample was vulcanized at 160 ° C. for 4 minutes, 160 ° C. for 6 minutes, and 160 ° C. for 8 minutes, and allowed to stand at 100 ° C. for 15 days. Then, in accordance with ASTM-D-2229, a steel cord was attached from each sample. Withdrawal, the rubber coating state was visually observed, and the rubber coverage was displayed as 0 to 100%, which was used as an index of initial adhesiveness.

<< Evaluation method for heat-resistant adhesiveness >>
Each sample was vulcanized at 160 ° C. for 20 minutes and allowed to stand at 70 ° C. and 95% relative humidity for 7 days. Then, in accordance with ASTM-D-2229, the steel cord was pulled out from each sample, and the rubber coating state was visually observed. The rubber coverage was observed and displayed as 0 to 100%, which was used as an index of heat resistant adhesion.

<Evaluation method of deterioration physical properties of rubber>
After vulcanizing unvulcanized rubber for 20 minutes at 160 ° C for 2 days at 100 ° C (thermal deterioration conditions) or after aging at 70 ° C and 100% humidity for 4 days (humid heat deterioration conditions), conform to JIS K6251 Then, Eb (elongation at break (%)) and Tb (tensile strength (MPa)) are measured by performing a tensile test, TF after heat deterioration (Toughness: Eb × Tb), and TF (Toughness of wet heat deterioration) : Eb × Tb), and Comparative Example 1 was set to 100 and indicated as an index.

<Method for evaluating crack growth of rubber>
Each sample was subjected to a constant stress fatigue test using a Ueshima Fatigue Testing Machine, the number of times until fracture was measured, and Comparative Example 1 was set as 100, which was displayed as an index. The larger the value, the better the crack growth resistance.

* 1 Ouchi Shinsei Chemical Industry Co., Ltd., Nocrack 6C, N-phenyl-N '-(1,3-dimethylbutyl) -p-phenylenediamine * 2 Ouchi Shinsei Chemical Industry Co., Ltd., Noxeller DZ, N, N′-dicyclohexyl-2-benzothiazolylsulfenamide * 3 Manufactured by OMG, Manobond C22.5, Cobalt content 22.5% by mass
* 4 Tokyo Chemical Industry Co., Ltd.

  As is apparent from the results of Table 1, Example 1 employing a rubber composition containing a boron-containing compound and sulfur in a specific amount identifies Comparative Example 1 that does not contain a boron-containing compound, and a boron-containing compound. As compared with Comparative Example 2 containing more than the above amount, it is understood that not only the initial adhesiveness is excellent, but also good heat-resistant adhesiveness is exhibited and good rubber physical properties can be maintained.

Claims (3)

A steel cord-rubber composite comprising a steel cord with brass plating and a rubber composition for coating the steel cord,
The steel cord with brass plating is manufactured by immersing a brass-plated steel wire in an aqueous solution containing a cobalt salt and then twisting a plurality of them, or after twisting a plurality of brass-plated steel wires. are those prepared by immersing in an aqueous solution containing cobalt salt, and, when measured by XPS (X-ray photoelectron spectroscopy), zinc on the outermost surface is an amount of 4.93 to 15 atomic%, further The outermost surface contains cobalt in an amount of 2.0 atomic% or less,
The steel cord covering rubber composition contains 0.005 to 0.08 parts by mass of a boron-containing compound in terms of boron and 1 to 10 parts by mass of sulfur with respect to 100 parts by mass of the rubber component. Features steel cord-rubber composite.   The steel cord-rubber composite according to claim 1, wherein the rubber composition for covering a steel cord contains cobalt in an amount of less than 0.04 parts by mass with respect to 100 parts by mass of the rubber component. body.   The steel cord-rubber composite according to claim 1 or 2, wherein the boron-containing compound is boric acid.