Rubber composition for covering steel wire

Abstract

To provide a rubber composition for covering a steel wire that maintains hardness and exhibits favorable adhesion to the steel wire along with long-term maintenance of durability in consideration of the extended service period of tires.SOLUTION: The problem is solved by a rubber composition for covering a steel wire, the rubber composition comprising, with respect to 100 pts.mass of a diene rubber comprising natural rubber and / or synthetic isoprene rubber: 40 to 80 pts.mass of a filler composed of carbon black and / or silica; 1 to 20 pts.mass of zinc oxide; and 0.2 to 12 pts.mass of a metal compound having a pH of less than 7.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition for steel wire coating, and more particularly to a rubber composition for steel wire coating that has good adhesion to steel wire while maintaining hardness and is capable of maintaining durability over a long period of time. [Background technology]

[0002] A pneumatic tire is primarily composed of a pair of bead sections and sidewall sections, and a tread section that connects to both sidewall sections. A carcass layer is provided on the inside of the tire, and both ends of the carcass layer are folded back to enclose the bead cores from the inside to the outside of the tire. The tread portion is composed of a cap tread and an undertread, and a belt layer is disposed between the undertread and the carcass layer. Since this belt layer is subjected to strong impacts and large loads, steel wires coated with metal plating compounds are used as reinforcing materials. The rubber covering these steel wires must have good adhesion to the steel wires, and for this purpose, there is a method of blending organic metal salts into the rubber (see, for example, Patent Documents 1 to 3 below).

[0003] On the other hand, as the period of use of tires becomes longer, rubber compositions for coating steel wires are required to maintain durability over a long period of time in addition to good adhesion to steel wires. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6977243 [Patent Document 2] Patent No. 7328508 [Patent Document 3] Patent No. 7339506 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a rubber composition for coating steel wires, which has good adhesion to steel wires while maintaining hardness, and is capable of maintaining durability over a long period of time. [Means for solving the problem]

[0006] As a result of extensive research, the inventors discovered that the above-mentioned problems can be solved by a rubber composition in which a diene-based rubber is blended with specific amounts of filler and zinc oxide, and a specific amount of a metal compound having a specific pH, and thus were able to complete the present invention.

[0007] That is, the present invention provides a rubber composition for covering a steel wire coated with a metal plating compound, The rubber composition for steel wire coating is characterized by containing 40 to 80 parts by mass of a filler consisting of carbon black and / or silica, 1 to 20 parts by mass of zinc oxide, and 0.2 to 12 parts by mass of a metal compound having a pH of less than 7, relative to 100 parts by mass of a diene rubber including natural rubber and / or synthetic isoprene rubber. [Effects of the Invention]

[0008] According to the present invention, a rubber composition for coating a steel wire can be provided which maintains hardness, has good adhesion to the steel wire, and is capable of maintaining durability over a long period of time, by blending specific amounts of filler and zinc oxide with a diene rubber and also blending specific amounts of a metal compound having a specific pH.

[0009] As described above, the rubber composition for coating a steel wire of the present invention contains a metal compound having a pH of less than 7 (hereinafter, sometimes referred to as a specific metal compound). The metal contained in the metal plating compound coating the steel wire combines with sulfur in the rubber during vulcanization, providing adhesion between the rubber and the steel wire. However, the metal easily diffuses into the rubber, forming a depleted layer with reduced metal density. The presence of a large number of depleted layers can lead to problems, such as breakdown (peel-off between the rubber and the steel wire) initiated by the depleted layer during, for example, moist heat degradation. For example, if the metal plating compound is brass plating, copper ions and zinc ions combine with sulfur ions in the rubber during vulcanization to form copper-sulfur compounds and zinc-sulfur compounds combined with zinc oxide. These compounds enhance adhesion between the rubber and the steel wire. However, copper and zinc easily diffuse into the rubber, forming a depleted layer with reduced copper and zinc metal density on the steel wire side. This depleted layer can then initiate breakdown. In the present invention, the incorporation of the specific metal compound facilitates the movement of the specific metal compound in the rubber, particularly during moist heat degradation, i.e., in the presence of water. This prevents excessive diffusion of the metal contained in the metal plating compound coating the steel wire into the rubber, and minimizes the occurrence of the depleted layer. This allows for the maintenance of good adhesion and durability with the steel wire over a long period of time. It also prevents a decrease in hardness. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will now be described in further detail. (Diene rubber) The diene rubber used in the rubber composition of the present invention essentially comprises natural rubber (NR) and / or synthetic isoprene rubber (IR). The blending amount of NR and / or IR is preferably 80 parts by mass or more per 100 parts by mass of the total diene rubber. In addition to NR and IR, other diene rubbers can also be used, such as butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), and acrylonitrile-butadiene copolymer rubber (NBR). These may be used alone or in combination of two or more. There are no particular limitations on the molecular weight or microstructure, and the diene rubber may be terminally modified with amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl, or the like, or may be epoxidized. The weight average molecular weight (Mw) of the diene rubber is not particularly limited, but for reasons such as better effects of the present invention, it is preferably 100,000 to 5,000,000, more preferably 200,000 to 3,000,000, and even more preferably 300,000 to 2,000,000. In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are values calculated as standard polystyrene obtained by gel permeation chromatography (GPC) measurement.

[0011] (filler) The rubber composition of the present invention contains a filler made of carbon black and / or silica. From the viewpoint of improving the effect of the present invention, the nitrogen adsorption specific surface area (N2SA) of the carbon black is 30 to 100 m 2 In this specification, the nitrogen adsorption specific surface area (N2SA) of carbon black is measured in accordance with JIS K6217-7. In order to improve the effect of the present invention, the CTAB adsorption specific surface area of silica is 100 to 200 m 2In this specification, the CTAB adsorption specific surface area of silica is a value obtained by measuring the amount of n-hexadecyltrimethylammonium bromide adsorbed onto the silica surface in accordance with JIS K6217-3:2001 "Part 3: Determination of specific surface area - CTAB adsorption method."

[0012] (Specific metal compounds) The specific metal compound used in the rubber composition of the present invention is a metal compound having a pH of less than 7. However, the specific metal compound does not include zinc oxide and does not include organic metal salts. Note that organic acid metal salts such as organic acid cobalt can be compounded in the rubber composition as needed, but in this case, the organic acid metal salts are not included in the scope of the specific metal compound. In the present invention, a "metal compound having a pH of less than 7" refers to a metal compound that is dissolved or dispersed in water at a ratio of 0.1 mol / L at 20°C, and the pH is measured by a standard method using a pH meter. For example, the measurement can be performed in accordance with JIS Z8802:2011. Note that if the metal compound is poorly water-soluble, it is not necessary to completely dissolve the metal compound in water, and the pH is measured in the presence of a precipitate. From the viewpoint of achieving the effects of the present invention satisfactorily, the specific metal compound suitable for the present invention preferably has a pH of 3 to 6, and specific types include metal chlorides, nitrates, and / or iodides, more specific examples of which include chlorides, nitrates, and / or iodides of alkali metals and chlorides, nitrates, and / or iodides of alkaline earth metals. Examples include potassium chloride, potassium nitrate, potassium iodide, sodium sulfate, lithium chloride, magnesium sulfate, etc. Furthermore, from the viewpoint of improving the effects of the present invention, when the metal plating compound is brass plating, the specific metal compound is preferably potassium chloride, potassium nitrate, or potassium iodide.

[0013] (Rubber composition blending ratio) The rubber composition of the present invention is characterized by comprising 40 to 80 parts by mass of a filler consisting of carbon black and / or silica, 1 to 20 parts by mass of zinc oxide, and 0.2 to 12 parts by mass of a specific metal compound, blended with 100 parts by mass of diene rubber. If the amount of filler mixed is less than 40 parts by mass per 100 parts by mass of diene rubber, the hardness decreases, whereas if it exceeds 80 parts by mass, the adhesion to the wire decreases. If the amount of the specific metal compound is less than 0.2 parts by mass per 100 parts by mass of diene rubber, the amount is too small to achieve the effects of the present invention, and conversely, if it exceeds 12 parts by mass, the adhesion to the wire decreases.

[0014] From the viewpoint of improving the effects of the present invention, the amount of filler is preferably 55 to 65 parts by mass, the amount of zinc oxide is preferably 5 to 15 parts by mass, and the amount of specific metal compound is preferably 2 to 5 parts by mass, relative to 100 parts by mass of diene rubber.

[0015] In terms of the amount of filler to be compounded, the amount of carbon black to be compounded is preferably 20 to 40 parts by mass, and the amount of silica to be compounded is preferably 30 to 50 parts by mass, per 100 parts by mass of diene rubber.

[0016] (Other ingredients) In addition to the above-mentioned components, the rubber composition of the present invention may contain various additives that are generally compounded in rubber compositions, such as vulcanization or crosslinking agents, vulcanization or crosslinking accelerators, silane coupling agents, various other fillers such as clay and talc, organic acid metal salts such as organic acid cobalt, various oils, antioxidants, and plasticizers, and these additives can be kneaded by a conventional method to form a composition that can be used for vulcanization or crosslinking. The amounts of these additives that can be compounded may be conventional amounts as long as they do not deviate from the object of the present invention.

[0017] The steel wire coated with the rubber composition of the present invention is coated with a metal plating compound. The metal plating compound is not particularly limited, but preferred examples include metal plating compounds selected from brass plating, copper-tin plating, copper plating, zinc plating, nickel plating, chromium plating, and copper-zinc-cobalt ternary plating.

[0018] Examples of applications of the rubber composition of the present invention include tires, belt conveyors, electric wires, hoses, vibration-isolating rubber, etc. In the case of tire applications, steel wires coated with the rubber composition of the present invention can be applied to belts embedded in undertreads, carcasses, beads (including bead cores and steel wires housed therein), etc.

[0019] The rubber composition of the present invention can be prepared, for example, by mixing the various components described above using a general-purpose mixer such as a Banbury mixer or a roll mixer, and can be used for the various applications described above by embedding steel wires in the rubber composition and vulcanizing the rubber composition in accordance with a conventional method.

[0020] In the case of tire applications, the manufacturing method is not particularly limited, and tires can be manufactured according to known techniques. The tires are preferably pneumatic tires, which can be filled with air, inert gases such as nitrogen, and other gases. [Example]

[0021] The present invention will be further explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0022] Standard Example, Examples 1 to 8, Comparative Examples 1 to 4 The components excluding the vulcanization system (vulcanization accelerator, sulfur) were mixed in a 1.7-liter internal Banbury mixer with the formulation (parts by mass) shown in Table 1 for 5 minutes, then discharged from the mixer and cooled to room temperature to obtain an unvulcanized rubber composition. The unvulcanized rubber composition was then vulcanized at 170°C for 10 minutes to prepare test specimens, and their hardness was measured. For the wire pull-out test, a wire was coated with the unvulcanized rubber composition, and the test specimens vulcanized under the vulcanization conditions were immersed in 70°C hot water for 2 weeks to undergo a hot water degradation treatment.

[0023] Hardness: Measured at 20°C in accordance with JIS K 6253. The results are expressed as an index, with the value of the standard example being 100. A larger index indicates higher hardness.

[0024] Pull-out force: In accordance with ASTM D-2, the steel wire was pulled out of the test piece after hot water aging, and the pull-out force at the time of pulling was measured. The results were expressed as an index, with the value of the standard example being 100. The larger this value, the better the adhesion to rubber after hot water aging and the better the long-term durability. Rubber adhesion amount: According to ASTM D-2229, the steel wire was pulled out from the test piece after hot water aging, and the rubber adhesion amount was measured. The results were expressed as an index, with the value of the standard example being 100. The larger this value, the better the adhesion to the rubber after hot water aging and the better the long-term durability. The results are shown in Table 1.

[0025] [Table 1]

[0026] *1:NR(RSS#3) *2: Carbon black (Seast 300 manufactured by Tokai Carbon Co., Ltd.) *3: Silica (Precipitated silica K160 manufactured by FengHai Rice Biotechnology Co., Ltd.) *4: Silane coupling agent (Si69, bis(3-triethoxysilylpropyl)tetrasulfide, manufactured by Evonik Degussa) *5: Zinc oxide (Zinc oxide type 3 manufactured by Seido Chemical Industry Co., Ltd.) *6: Potassium chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., pH=5) *7: Potassium nitrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., pH=6) *8: Potassium iodide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., pH=6) *9: Sodium sulfate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., pH = 5) *10: Lithium chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., pH=6) *11: Magnesium sulfate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., pH = 5) *12: Potassium sulfate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., pH = 7) *13: Potassium carbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., pH = 11) *14: Potassium chloride aqueous solution (aqueous solution in which the potassium chloride is dissolved in water. In Comparative Example 4, in which this aqueous solution was used, a brass-plated steel wire was coated with the potassium chloride aqueous solution, and the rubber composition did not contain potassium chloride.) *15: Anti-aging agent (Flexis Santoflex 6PPD) *16: Neodecanoic acid cobalt borate (DICNATE NBC-II manufactured by DIC Corporation) *17: Sulfur (Akzo Nobel Krystex HT OT 20) *18: Vulcanization accelerator (Noccela DZ manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)

[0027] As can be seen from the results in Table 1, the rubber composition of each example contains 40 to 80 parts by mass of a filler consisting of carbon black and / or silica, 1 to 20 parts by mass of zinc oxide, and 0.2 to 12 parts by mass of a specific metal compound per 100 parts by mass of diene rubber including natural rubber and / or synthetic isoprene rubber, and therefore has good adhesion to steel wire while maintaining hardness and is capable of maintaining durability over a long period of time. On the other hand, in Comparative Example 1, the specific metal compound was not used, but a metal compound with a pH of 7 was used, and therefore the pull-out force and the amount of rubber adhesion decreased. In Comparative Example 2, the specific metal compound was not used, but a metal compound with a pH of 11 was used, resulting in decreased hardness and pull-out force. In Comparative Example 3, the amount of the specific metal compound exceeded the upper limit specified in the present invention, and therefore the amount of rubber adhesion decreased. In Comparative Example 4, the specific metal compound was not compounded in the rubber composition, but was instead coated on a steel wire, and therefore the hardness and pull-out force were reduced.

[0028] The present disclosure includes the following inventions. Invention [1]: A rubber composition for covering a steel wire coated with a metal plating compound, The rubber composition for steel wire coating is characterized by containing 40 to 80 parts by mass of a filler consisting of carbon black and / or silica, 1 to 20 parts by mass of zinc oxide, and 0.2 to 12 parts by mass of a metal compound having a pH of less than 7, relative to 100 parts by mass of a diene rubber including natural rubber and / or synthetic isoprene rubber. Invention [2]: The rubber composition for coating a steel wire according to Invention [1], characterized in that the metal compound has a pH of 3 to 6. Invention [3]: A rubber composition for coating a steel wire according to Invention 1 or 2, characterized in that the metal compound is a chloride, a nitrate and / or an iodide. Invention [4]: A rubber composition for coating steel wire according to any one of Inventions 1 to 3, characterized in that the metal plating compound is a metal plating compound selected from brass plating, copper-tin plating, copper plating, zinc plating, nickel plating, chromium plating, and copper-zinc-cobalt ternary plating. Invention [5]: A tire, a belt conveyor, an electric wire, a hose, or a vibration-isolating rubber, which uses the rubber composition for coating a steel wire according to any one of Inventions 1 to 4.

Claims

1. A rubber composition for coating a steel wire coated with a metal plating compound, comprising: The rubber composition for steel wire coating is characterized by containing, per 100 parts by mass of diene rubber including natural rubber and / or synthetic isoprene rubber, 40 to 80 parts by mass of a filler made of carbon black and / or silica, 1 to 20 parts by mass of zinc oxide, and 0.2 to 12 parts by mass of a metal compound having a pH of less than 7.

2. 2. The rubber composition for coating a steel wire according to claim 1, wherein the metal compound has a pH of 3 to 6.

3. 2. The rubber composition for coating a steel wire according to claim 1, wherein the metal compound is a chloride, a nitrate and / or an iodide.

4. 2. The rubber composition for coating steel wire according to claim 1, wherein the metal plating compound is selected from brass plating, copper-tin plating, copper plating, zinc plating, nickel plating, chromium plating, and copper-zinc-cobalt ternary plating.

5. A tire, a belt conveyor, an electric wire, a hose or a vibration-isolating rubber, which uses the rubber composition for coating a steel wire according to claim 1.

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