JP2012149357A - Steel cord-rubber composite - Google Patents

Abstract

The present invention relates to a steel cord / rubber composite that has excellent adhesion to a steel cord and can suppress a decrease in modulus even when the rubber composition constituting the coated rubber does not contain a cobalt salt. Provide the body.
The steel cord is obtained by washing a steel wire with an aqueous solution containing a cobalt salt and then twisting a plurality of the steel wires, and the rubber composition contains an organic acid metal salt.
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Description

  The present invention is excellent in adhesiveness with a steel cord and suppresses a decrease in modulus even when the cobalt composition is not contained in the steel cord / rubber composite, particularly the rubber composition constituting the coated rubber. It relates to a steel cord / rubber composite.

  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, a stable and strong adhesion is required between the covering rubber and the metal reinforcing material.

  In order to obtain a steel cord / rubber composite with stable and strong adhesion between the coated rubber and the metal reinforcing material, a metal reinforcing material such as steel cord plated with zinc or brass is coated with sulfur. So-called direct vulcanization bonding, which is embedded in rubber and bonded together at the same time as vulcanization of rubber during heat vulcanization, is widely used. Until now, various examinations regarding the direct vulcanization adhesion have been made in order to improve the adhesion between the coated rubber and the metal reinforcing material by the direct vulcanization adhesion.

For example, as disclosed in Patent Document 1, the surfaces of steel wires and steel cords to be used are washed with an acidic or alkaline solution, and a phosphorus compound that is an adhesion reaction inhibitor (derived from a lubricant used in the production of steel cords). There is a technique for improving the adhesiveness with the coated rubber by removing ().
However, the above solution is an acidic or alkaline solution, and it is preferable to use another material from the viewpoint of the environment. Furthermore, in view of the manufacturing process, a method of treating with a solution in a neutral region is preferable for safety.

In addition, as disclosed in Patent Document 2, in a method of manufacturing a steel cord for reinforcing a steel cord / rubber composite formed by twisting a plurality of filaments manufactured by wet-drawing a brass-plated steel wire There is a method in which resorcin is attached to the filament surface by adding resorcin, which is considered as an adhesion improver between the steel cord and the coated rubber, to the wet lubricant used at the time of steel wire drawing.
However, since resorcinol changes in quality due to the heat generated when the steel filament is drawn, further improvement is desired for improving the adhesion durability between the steel cord and the covering rubber.

  On the other hand, in order to improve the initial adhesion between the coated rubber and the metal reinforcing material in the direct vulcanization adhesion generally used for tires, etc., a rubber composition in which a cobalt salt as an adhesion promoter is blended with the coated rubber is used. Is known. However, in the case of a coated rubber made of a rubber composition blended with a cobalt salt, compared to a coated rubber made of a rubber composition not blended with a cobalt salt, there is a great demerit in durability against degradation of the coated rubber and crack growth. There is.

  Therefore, for example, as disclosed in Patent Document 3, a rubber cord obtained by blending a steel cord formed by twisting a plurality of steel wires having brass plating on the peripheral surface and a predetermined amount of a boron-containing compound is used. There is a technique in which good adhesion to steel rubber can be ensured by covering with the used covering rubber even when the covering rubber does not contain cobalt.

JP 2001-234371 A JP 2004-66298 A JP 2009-215673 A

Examination of the technique disclosed in Patent Document 3 shows that, although it is possible to ensure the adhesion between a certain steel cord and the covering rubber, in recent years, further improvement in the adhesion is desired.
In addition, since the rubber composition constituting the coated rubber does not contain cobalt, further improvement is desired for the suppression of the decrease in modulus.

  Therefore, the present invention provides a steel cord / rubber composite that has excellent adhesion to a steel cord and can suppress a decrease in modulus even when the rubber composition constituting the coated rubber does not contain a cobalt salt. The purpose is to provide.

  As a result of intensive studies to achieve the above object, the present inventor can improve the initial adhesion between the steel cord and rubber by washing the steel wire constituting the steel cord with an aqueous solution containing a cobalt salt, Furthermore, the present inventors have found that a certain modulus can be ensured by blending an organic acid metal salt in the rubber composition covering the steel cord, and the present invention has been completed.

  That is, in the steel cord / rubber composite of the present invention, the steel cord is obtained by washing a steel wire with an aqueous solution containing a cobalt salt and then twisting a plurality of the wires, and the rubber composition comprises an organic acid metal salt. It is characterized by including.

  In the steel cord / rubber composite of the present invention, it is preferable that the metal of the organic acid metal is zinc and the organic acid is stearic acid.

  In a preferred example of the steel cord / rubber composite of the present invention, it is more preferable that the rubber composition contains 0.5 to 5 parts by mass of the organic acid metal salt to 100 parts by mass of the rubber component.

  In the steel cord / rubber composite of the present invention, the steel wire to be cleaned has a transition metal concentration other than Zn and Cu of 0.01% by mass or more, a phosphorus concentration of 2.5% by mass or less, and a zinc concentration of 15% by mass. It is preferable that the peripheral surface is subjected to the following brass plating.

  Further, the steel wire is preferably one obtained by drawing the steel wire subjected to the brass plating, and the cobalt salt is cobalt chloride, cobalt nitrate, cobalt sulfate, cobalt acetate, cobalt citrate, gluconic acid. Most preferred is cobalt or acetylacetonatocobalt.

  Further, the pH of the aqueous solution containing the cobalt salt is preferably in the range of 5-8.

  According to the present invention, a steel cord / rubber composite that has excellent adhesion to a steel cord and can suppress a decrease in modulus even when the cobalt composition is not contained in the rubber composition that constitutes the coated rubber. Can be provided.

  The steel cord / rubber composite according to the present invention is obtained by coating a steel cord with a rubber composition, and the steel cord is formed by twisting a plurality of steel wires after washing the steel wire with an aqueous solution containing a cobalt salt. The rubber composition includes an organic acid metal salt.

In addition to being able to enhance the adhesive strength of the rubber composition by activating the metal of the organic acid metal salt and the organic acid by blending the organic acid metal salt in the rubber composition, the rubber physical properties of the rubber composition are improved. Even if it is a case where it does not mix | blend cobalt, the modulus fall of a rubber composition can be suppressed effectively. Furthermore, by cleaning the steel wire constituting the steel cord with an aqueous solution containing a cobalt salt, the surface of the steel wire is oxidized over time, and the ZnO layer that inhibits adhesion to the coated rubber is dissolved. As a result, the Cu / Zn layer is exposed, so that Cu is extracted from the Cu / Zn layer during vulcanization of the steel cord / rubber composite, and copper sulfide (Cu _x S, x is 1 or 2) formed in the coated rubber. ), It is possible to improve the initial adhesion between the steel cord and the covering rubber. As a result, even in the case where the transition rubber salt such as cobalt, which causes a decrease in the durability of the coated rubber as described above, is not added to the coated rubber, the rubber composition is coated with the steel cord. The initial adhesion between the steel cord and the steel cord can be improved.

In addition, when a cobalt salt is not contained in the aqueous solution used for the cleaning, the ZnO layer cannot be sufficiently dissolved, so that desired initial adhesiveness cannot be obtained.
Moreover, when the organic acid metal salt is not contained in the rubber composition, the physical properties of the rubber cannot be improved, and the decrease in the modulus cannot be suppressed.

In addition, the organic acid metal salt is activated by the organic acid, can strengthen the adhesive strength of the rubber composition, and is contained in the rubber composition, thereby suppressing a decrease in the modulus of the rubber composition. The metal is preferably zinc from the viewpoint that the effect can be effectively exhibited.
Similarly, the organic acid is preferably stearic acid from the viewpoint that the above effects can be effectively exhibited.

  In the steel cord / rubber composite of the present invention, the rubber component is preferably blended in an amount of 0.5 to 5 parts by mass of the organic acid metal salt with respect to 100 parts by mass of the rubber component. When the compounding amount of the organic acid metal salt is less than 0.5 parts by mass with respect to the rubber component, the compounding amount is too small, so that the effect of the present invention is sufficient (adhesiveness to the steel cord is excellent and the decrease in the modulus is suppressed. On the other hand, if the blending amount exceeds 5 parts by mass with respect to the rubber component, the blending amount is too large, so that the amount of free acid in the rubber increases and the effect of the present invention is achieved. In addition to not being able to be obtained, zinc stearate that could not be dissolved in the rubber may become a starting point of cracking.

  Furthermore, in the steel cord / rubber composite of the present invention, the rubber composition preferably further contains 1 to 10 parts by mass, more preferably 2 to 8 parts by mass of sulfur with respect to 100 parts by mass of the rubber component. 4 to 6 parts by mass are more preferable. Here, if the sulfur content of the coated rubber is less than 1 part by mass with respect to 100 parts by mass of the rubber component, a sufficient effect on the initial adhesiveness may not be expected, and if it exceeds 10 parts by mass, the physical properties of the rubber May decrease.

Furthermore, it is preferable that the rubber composition further contains N-cyclohexyl-2-benzothiazolesulfenamide as an accelerator for improving the vulcanization rate.
About the compounding quantity, it is preferable to set it as the range of 0.01-2 mass parts with respect to 100 mass parts of rubber components.

  The rubber composition preferably does not contain cobalt. Coated rubber using a rubber composition that does not contain cobalt is less resistant to deterioration due to heat, humidity, and oxygen and crack growth than coated rubber using a rubber composition containing cobalt. It is because it can plan.

  Furthermore, the rubber composition is not particularly limited as a rubber component, but for example, natural rubber, polybutadiene rubber, polyisoprene rubber, ethylene-propylene copolymer, isobutylene-isoprene copolymer, polychloroprene, and other diene series. You may mix | blend rubber | gum. These may be blended singly or in combination of two or more.

  Furthermore, the rubber composition may contain, as necessary, oil such as resin, carbon black, process oil, vulcanizing agent, vulcanization accelerator, anti-aging agent, softening agent, zinc oxide, and stearic acid. Additives usually used in the rubber industry can be appropriately selected and blended within a range not impairing the object of the present invention.

  The rubber composition used in the steel cord / rubber composite of the present invention is prepared by compounding an organic acid metal salt with a rubber component, adding the above components as necessary, kneading by a conventional method, heating and extruding. Can be manufactured.

  In addition, the steel wire to be cleaned is coated with brass plating whose transition metal concentration excluding Zn and Cu is 0.01 mass% or more, phosphorus concentration is 2.5 mass% or less, and zinc concentration is 15 mass% or less. It is preferable that a plurality of steel wires applied to is twisted. This is because the corrosion resistance of the steel cord is improved by the sacrificial anticorrosive effect of the brass plating.

  The steel wire is washed with an aqueous solution containing the cobalt salt after the brass plating and the wire drawing.

  The thickness of the brass plating is preferably about 0.1 to 10 nm. If the thickness is less than 0.1 nm, the plating is not sufficiently formed, so that the sacrificial anticorrosive effect cannot be fully exhibited and the corrosion resistance of the steel cord may be lowered. There is a risk that it cannot be secured sufficiently. On the other hand, when the thickness of the plating exceeds 10 nm, in addition to the fact that the plating becomes too thick, the anticorrosion effect by the plating is saturated, which is not economical.

  Further, in the cleaning of the steel wire, cobalt that serves as an adhesion promoter between the rubber composition and the plated steel cord is used. Specific cobalt salts include cobalt chloride, cobalt nitrate, cobalt sulfate, cobalt acetate, Cobalt citrate, cobalt gluconate or cobalt acetylacetonate is preferred.

  Furthermore, the pH of the aqueous solution used for the washing is preferably in the range of 5-8. The pH of the aqueous solution has an adverse effect on the plating both above and below, so that the adhesion between the steel cord and the rubber composition is lowered. Furthermore, from the viewpoint of environmental load, the pH of the aqueous solution used for the washing is preferably in the neutral range of 5-8. For example, in the case of an aqueous solution containing cobalt acetate, the washing conditions are preferably 10 g / L and the washing time is preferably 30 to 60 seconds, and the washing time can be appropriately determined according to the concentration of the aqueous solution.

  The steel cord / rubber composite of the present invention is not particularly limited, but can be widely used in the manufacture of various rubber products and parts such as tires, motion transmission belts, conveyor belts and hoses.

  Further, a tire characterized by applying the steel cord / rubber composite of the present invention as a reinforcing material can also be produced. The tire of the present invention is not particularly limited except that the steel cord / rubber composite of the present invention is used, and a known tire configuration can be employed as it is.

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

(Examples 1-3, Comparative Examples 3-5)
Steel wires plated with brass (Cu: 63 mass%, Zn: 37 mass%) are twisted to produce three 1x5 steel cords (outer diameter 0.5mm, length 300mm), and then this steel The cord was washed with a 10 g / L cobalt acetate aqueous solution (pH 6.0) for 30 seconds and dried at 50 ° C. for 1 minute. After that, three steel cords are arranged in parallel at 10mm intervals, coated from the top and bottom directions with each rubber composition blended as shown in Table 1, vulcanized at 100 ° C for 20 minutes, and steel cord / rubber composite A body sample was made.

(Comparative Examples 1, 2, and 6)
Twist steel wires plated with brass (Cu: 63% by mass, Zn: 37% by mass) to produce three 1 × 5 steel cords (outer diameter: 0.5mm, length: 300mm). A steel cord / rubber composite sample was prepared by arranging in parallel at intervals, covering with a rubber composition blended as shown in Table 1 from both the top and bottom directions, and vulcanizing at 100 ° C. for 20 minutes.

<Evaluation>
The following items were evaluated for each sample obtained in Examples 1 to 3 and Comparative Examples 1 to 6.

(Tensile stress)
For the unvulcanized rubber composition of each sample, the tensile stress at 300% elongation was measured as a representative indicator of physical properties. Specifically, using a JIS No. 3 dumbbell-type test piece, the tensile stress at 100% elongation was measured according to JIS K 6251-2004, and displayed as an index when the tensile stress of Comparative Example 1 was taken as 100. In addition, about the index value of each sample, the larger the numerical value, the greater the tensile stress at 100% elongation, and the better.

(Physical properties after rubber deterioration)
Regarding physical properties after rubber deterioration, each sample was vulcanized at 145 ° C. for 30 minutes, then aged at 100 ° C. for 2 days, and then subjected to a tensile test according to JIS K6251 to obtain Eb (elongation at break (%)). ) And Tb (tensile strength (MPa)) were measured, and evaluation was performed by calculating TF (toughness: Eb × Tb). In addition, about TF of each sample, it shows by the index value when TF of the comparative example 1 is set to 100, and TF is so large and favorable that a numerical value is large.

(Adhesiveness)
Regarding heat-resistant adhesiveness, each sample was heated at 145 ° C. for 30 minutes and then left in a gear oven at 100 ° C. for 15 days for deterioration. The rubber coating state of each of these samples was visually observed, and evaluation was performed by displaying it at 0 to 100%.

(Adhesive durability when wearing tires)
A belt layer was formed from each of the steel cord / rubber composites obtained in the above Examples and Comparative Examples, and a pneumatic rasil tire of size TBR11R22.5 equipped with the belt layer was prototyped by a conventional method.
Each prototype tire obtained was evaluated for indoor drums. Specifically, after normal running pressure, normal load, constant speed, step load running (120 hours), steel cord was pulled out from the steel cord cut sample of the crossing layer, and the rubber The coating state was observed visually. The observation results were evaluated based on an index (%) when Comparative Example 1 was used as a reference (index display: 100). The larger the value, the more rubber coating and the better the adhesion durability.

(Crack durability when wearing tires)
A belt layer was formed from each of the steel cord / rubber composites obtained in the above Examples and Comparative Examples, and a pneumatic rasil tire of size TBR11R22.5 equipped with the belt layer was prototyped by a conventional method.
Each of the obtained prototype tires was evaluated for indoor drums, specifically, normal internal pressure, normal load, constant speed, step load running (120 hours), and crack length developed from the belt end after the test. The measurement results were evaluated based on an index (%) when Comparative Example 1 was used as a reference (index display: 100). It shows that it is excellent in crack durability, so that a numerical value is large.

* 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-benzothiazylsulfenamide * 3 Manobond C22.5, Cobalt content: 22.5% by mass, manufactured by OMG
* 4 Tokyo Chemical Industry Co., Ltd.

  As can be seen from the results in Table 1, Comparative Example 1 in which no organic acid metal salt was blended in the rubber composition was used for the examples even when the cobalt salt conventionally used as an adhesion promoter was not included. Compared to ˜5, particularly high effects are exhibited with respect to 100% modulus and crack durability at the time of tire mounting, and it is also found that high effects are exhibited in any of the other evaluation items. Furthermore, Examples 1 to 3 in which the steel wire was cleaned using an aqueous solution containing a cobalt salt were compared with Comparative Example 6 in which the cleaning was not performed. It was found to have a high effect on crack durability.

  According to the present invention, a steel cord / rubber composite that has excellent adhesion to a steel cord and can suppress a decrease in modulus even when the cobalt composition is not contained in the rubber composition that constitutes the coated rubber. Can be provided.

Claims (8)

A steel cord / rubber composite comprising a rubber cord coated with a rubber composition,
The steel cord is formed by washing a steel wire with an aqueous solution containing a cobalt salt and then twisting a plurality of the steel wires, and the rubber composition contains an organic acid metal salt.   The steel cord / rubber composite according to claim 1, wherein the metal of the organic acid metal is zinc.   The steel cord / rubber composite according to claim 1, wherein the organic acid of the organic acid metal is stearic acid.   The steel cord / rubber composite according to claim 1, wherein the rubber composition contains 0.5 to 5 parts by mass of the organic acid metal salt with respect to 100 parts by mass of the rubber component.   The steel wire to be cleaned is subjected to brass plating with a transition metal concentration other than Zn and Cu being 0.01% by mass or more, a phosphorus concentration being 2.5% by mass or less, and a zinc concentration being 15% by mass or less on the peripheral surface. The steel cord / rubber composite according to claim 1, wherein the steel cord / rubber composite is provided.   6. The steel cord / rubber composite according to claim 5, wherein the steel wire to be washed is a wire obtained by drawing the steel wire subjected to the brass plating.   The steel cord / rubber composite according to claim 1, wherein the cobalt salt is cobalt chloride, cobalt nitrate, cobalt sulfate, cobalt acetate, cobalt citrate, cobalt gluconate, or acetylacetonato cobalt.   The steel cord / rubber composite according to claim 1, wherein the aqueous solution containing the cobalt salt has a pH of 5 to 8.