Rubber composition for coating steel wire

Abstract

As the period of use of tires is prolonged, a rubber composition for coating a steel wire is required to have good adhesion to a steel wire and excellent durability even after hot water degradation while maintaining physical properties at break and low heat build-up.SOLUTION: The problem is solved by a rubber composition for coating a steel wire in which 40 to 80 parts by mass of a filler composed of carbon black and / or silica and 0.1 to 15 parts by mass of clay are blended with respect to 100 parts by mass of a diene-based rubber containing a natural rubber and / or a synthetic isoprene rubber, a value obtained by subtracting a CTAB adsorption specific surface area (m2 / g) from a nitrogen-adsorption specific surface area (m2 / g) of the clay is less than 1, the clay has a composition of xAl2O3, ySiO2, and zH2O, and y / x is less than 5.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 maintains good fracture properties and low heat buildup, while also exhibiting good adhesion to steel wires and excellent durability even after hot water degradation. [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 subject to strong impacts and heavy 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 one method for achieving this is to blend organic metal salts into the rubber.

[0003] On the other hand, as tire usage periods become longer, rubber compositions for steel wire coatings are required to have durability in addition to good adhesion to the steel wire. For example, Patent Document 1 below proposes a rubber composition for steel cord coatings containing a rubber component and a porous inorganic filler. Patent Document 2 below also proposes a rubber composition containing an inorganic compound, in which the inorganic compound is aluminum silicate represented by the general formula (1): xAl2O3·ySiO2·zH2O (in general formula (1), x and y are each independently an integer, y / x≧5, and z is a positive number), and the inorganic compound is present in an amount of less than 15 parts by weight per 100 parts by weight of the rubber component in the rubber composition. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-7838 [Patent Document 2] Japanese Patent Publication No. 2020-59839 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 maintains good breaking properties and low heat buildup, and which has good adhesion to steel wires and excellent durability even after deterioration in hot water. [Means for solving the problem]

[0006] As a result of extensive research, the inventors have discovered that the above-mentioned problems can be solved by a rubber composition in which a diene rubber is blended with a filler and a specific amount of non-porous clay having a specific composition, and have thus completed the present invention.

[0007] That is, the present invention provides a rubber composition for coating a steel wire, comprising: The rubber composition is prepared by compounding 40 to 80 parts by mass of a filler made of carbon black and / or silica and 0.1 to 15 parts by mass of clay with 100 parts by mass of a diene rubber containing natural rubber and / or synthetic isoprene rubber, The nitrogen adsorption specific surface area (m 2 / g to the CTAB adsorption specific surface area (m 2 / g) is less than 1, The clay has a composition of xAl2O3·ySiO2·zH2O (wherein x is an integer of 1 to 3, y is an integer of 1 to 5, and z is an integer of 0 to 5), and The y / x ratio is less than 5. The present invention provides a rubber composition for coating steel wires, characterized in that [Effects of the Invention]

[0008] According to the present invention, a rubber composition for coating steel wire can be provided which maintains fracture properties and low heat buildup, has good adhesion to steel wire even after hot water degradation, and has excellent durability, by blending a diene rubber with a filler and a non-porous clay having a specific composition in specific amounts.

[0009] As described above, the rubber composition for coating a steel wire of the present invention contains non-porous clay. One known technique for improving the adhesion between steel wire and rubber is to coat the steel wire with a metal plating compound. The metal contained in this metal plating compound bonds with sulfur in the rubber during vulcanization, improving adhesion between the rubber and the steel wire. However, the metal easily diffuses into the rubber, forming a depleted layer with reduced metal density. If a large number of such depleted layers are present, for example, hot water degradation may occur, which may cause peeling between the rubber and the steel wire. For example, if the metal plating compound is brass plating, copper ions and zinc ions bond with sulfur ions in the rubber during vulcanization to form copper-sulfur compounds or zinc-sulfur compounds complexed with zinc oxide. These compounds improve the 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 then becomes the starting point for the above-mentioned problems. In the present invention, non-porous clay is blended. The aluminum contained in the clay facilitates mobility in the rubber, particularly during hot water 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 provides excellent adhesion to the steel wire and durability. Furthermore, the rubber exhibits improved handling stability by suppressing deterioration in breaking properties, and its low heat buildup makes it environmentally friendly. 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. Specific examples of carbon black include furnace carbon blacks such as SAF, ISAF, HAF, FEF, GPE, and SRF. These may be used alone or in combination of two or more. From the viewpoint of improving the effects 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) is measured in accordance with JIS K6217-7. The silica is not particularly limited, but examples thereof include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, and aluminum silicate. Silica made from biomass materials such as rice husks may also be used. These may be used alone or in combination of two or more. From the viewpoint of improving the effects of the present invention, the silica should have a CTAB adsorption specific surface area of ​​100 to 200 m. 2 In this specification, the CTAB adsorption specific surface area 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] (clay) The clay used in the present invention has a composition of xAl2O3·ySiO2·zH2O (wherein x is an integer of 1 to 3, y is an integer of 1 to 5, and z is an integer of 0 to 5), and The y / x ratio is less than 5, preferably 1 to 3, and more preferably 2 on average. The clay used in the present invention is non-porous, and the term "non-porous" used here refers to the clay's nitrogen adsorption specific surface area (m 2 / g to the CTAB adsorption specific surface area (m 2 / g) is less than 1. The nitrogen adsorption specific surface area (N2SA) is a measurement method for measuring the total specific surface area including the pores of the particles, while the CTAB adsorption specific surface area is a measurement method for measuring the external surface area excluding the micropores of the particles. Therefore, the nitrogen adsorption specific surface area (m 2 / g to the CTAB adsorption specific surface area (m 2 When the value obtained by subtracting the porosity (%) (p / g) is less than 1, it means that the clay has almost no pores. When the clay is non-porous, moisture adsorption is prevented and the decrease in adhesiveness after hot water degradation can be suppressed, thereby enhancing the above-mentioned effects of the present invention. Furthermore, from the viewpoint of improving the effects of the present invention, particularly from the viewpoint of increasing the adhesiveness to the steel wire after hot water degradation, the Al ratio of the clay is preferably 20 atomic % or more, and more preferably 20 to 80 atomic %. The Al ratio of the clay can be measured using X-ray fluorescence analysis (XRF). In addition, from the viewpoint of improving the effects of the present invention, particularly from the viewpoint of suppressing the deterioration of fracture properties, the nitrogen adsorption specific surface area (N2SA) of the clay is 5.0 m 2 / g or more, and 5 to 200m 2 / g Further, the clay used in the present invention may be surface-modified.

[0013] (Rubber composition blending ratio) The rubber composition of the present invention is characterized by compounding 40 to 80 parts by mass of a filler made of carbon black and / or silica and 0.1 to 15 parts by mass of clay with respect to 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 clay is less than 0.1 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 15 parts by mass, the break properties will decrease and low heat buildup will not be maintained.

[0014] From the viewpoint of improving the effects of the present invention, the compounding amount of the filler is preferably 55 to 75 parts by mass and the compounding amount of the clay is preferably 1 to 10 parts by mass per 100 parts by mass of the diene rubber.

[0015] In the amount of filler blended, the amount of carbon black blended is preferably 20 to 60 parts by mass per 100 parts by mass of diene rubber. Although the filler may be carbon black alone, when silica is used in combination, the amount of silica blended is preferably 5 parts by mass or more, more preferably 10 to 50 parts by mass.

[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 fillers other than those mentioned above, organic acid metal salts such as organic acid cobalt salts, various oils, antioxidants, and plasticizers, and these additives can be kneaded by a general 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 to be coated with the rubber composition of the present invention is preferably 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 1, Examples 1 to 4, Comparative Examples 1 to 3 In the formulation (parts by mass) shown in Table 1, the components excluding the vulcanization system (vulcanization accelerator, sulfur) were kneaded for 5 minutes in a 1.7-liter internal Banbury mixer, then discharged from the mixer and cooled to room temperature to obtain an unvulcanized rubber composition. Subsequently, the unvulcanized rubber composition was vulcanized at 170°C for 10 minutes to prepare test specimens.

[0023] Breaking stress (TB): Measured at room temperature in a tensile test in accordance with JIS K6251. The results are expressed as an index, with Standard Example 1 being 100. A larger index means a higher breaking stress (TB). Elongation at break (EB): Measured at room temperature in a tensile test in accordance with JIS K6251. The results are expressed as an index, with Standard Example 1 being 100. A larger index means a higher elongation at break (EB). Tan δ (60° C.): Tested at 60° C. in accordance with JIS K6394. The results are expressed as an index, with Standard Example 1 being set at 100. A smaller index means lower heat buildup.

[0024] In the following wire pull-out test, a wire was coated with the unvulcanized rubber composition, and the test piece was vulcanized under the vulcanization conditions described above. The test piece was then immersed in hot water at 70°C for two weeks to carry out a hot water deterioration treatment, and then the test was carried out. Pull-out force: In accordance with ASTM D-2, the steel wire was pulled out from 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 for Standard Example 1 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 for Standard Example 1 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: CB HAF (Carbon black manufactured by Tokai Carbon Co., Ltd., Seast 300) *3: Zinc oxide (Zinc oxide type 3 manufactured by Seido Chemical Industry Co., Ltd.) *4: Clay 1 (see Table 2 below for details) *5: Clay 2 (see Table 2 below for details) *6: Clay 3 (see Table 2 below for details) *7: Synthetic aluminum silicate (see Table 2 below for details) *8: Antioxidant 6C (Flexis Santoflex 6PPD) *9: Organic acid Co NBC2 (DIC Corporation, neodecanoic acid cobalt borate, DICNATE NBC-II) *10: Sulfur (Akzo Nobel Krystex HT OT 20) *11: Vulcanization accelerator DZ (Noccela DZ manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)

[0027] Details of the clays 1 to 3 are shown in Table 2.

[0028] [Table 2]

[0029] From the results in Table 1, the rubber composition of each example is a compound in which 40 to 80 parts by mass of a filler made of carbon black and / or silica and 0.1 to 15 parts by mass of clay are blended with 100 parts by mass of diene rubber containing natural rubber and / or synthetic isoprene rubber, and the nitrogen adsorption specific surface area (m 2 / g to the CTAB adsorption specific surface area (m 2 / g) is less than 1, the clay has a composition of xAl2O3·ySiO2·zH2O, and the y / x ratio is less than 5. Therefore, it is clear that the sintered body has good adhesion to the steel wire even after degradation in hot water, and has excellent durability, while maintaining fracture properties and low heat buildup. On the other hand, in Comparative Example 1, the nitrogen adsorption specific surface area (m 2 / g to the CTAB adsorption specific surface area (m 2 / g) exceeds 1, the pull-out force and the amount of rubber adhesion decreased. In Comparative Example 2, the blending amount of clay exceeded the upper limit specified in the present invention, and therefore TB and EB decreased. In Comparative Example 3, the y / x ratio of the clay exceeded the upper limit specified in the present invention, and therefore the pull-out force and the amount of rubber adhesion decreased.

[0030] Standard Example 2, Examples 5 to 8, Comparative Examples 4 to 6 The above "Standard Example 1, Examples 1 to 4, Comparative Examples 1 to 3" were repeated, except that the blending of various raw materials in the above "Standard Example 1, Examples 1 to 4, Comparative Examples 1 to 3" was changed as shown in Table 3 below. Examples 5 to 8 and Comparative Examples 4 to 6 are compared with Standard Example 2. The results are shown in Table 1.

[0031] [Table 3]

[0032] *12: Silica (Precipitated silica K160 manufactured by FengHai Rice Biotechnology Co., Ltd.) *13: Silane coupling agent (Si69, bis(3-triethoxysilylpropyl)tetrasulfide, manufactured by Evonik Degussa)

[0033] From the results in Table 3, the rubber composition of each example is a compound in which 40 to 80 parts by mass of a filler made of carbon black and / or silica and 0.1 to 15 parts by mass of clay are blended with 100 parts by mass of diene rubber containing natural rubber and / or synthetic isoprene rubber, and the nitrogen adsorption specific surface area (m 2 / g to the CTAB adsorption specific surface area (m 2 / g) is less than 1, the clay has a composition of xAl2O3·ySiO2·zH2O (where x is an integer of 1 to 3, y is an integer of 1 to 5, and z is an integer of 0 to 5), and the y / x ratio is less than 5. Therefore, it is clear that the sintered body maintains good fracture properties and low heat buildup, and has good adhesion to steel wire even after hot water degradation, and has excellent durability. On the other hand, in Comparative Example 4, the nitrogen adsorption specific surface area (m 2 / g to the CTAB adsorption specific surface area (m 2 / g) exceeds 1, the pull-out force and the amount of rubber adhesion decreased. In Comparative Example 5, the blending amount of clay exceeded the upper limit specified in the present invention, so that TB and EB decreased and tan δ (60° C.) deteriorated. In Comparative Example 6, the y / x ratio of the clay exceeded the upper limit specified in the present invention, and therefore tan δ (60° C.) deteriorated, and the pull-out force and the amount of rubber adhesion decreased.

[0034] The present disclosure encompasses the following embodiments. Embodiment 1: A rubber composition for coating a steel wire, comprising: The rubber composition is prepared by compounding 40 to 80 parts by mass of a filler made of carbon black and / or silica and 0.1 to 15 parts by mass of clay with 100 parts by mass of a diene rubber containing natural rubber and / or synthetic isoprene rubber, The nitrogen adsorption specific surface area (m 2 / g to the CTAB adsorption specific surface area (m 2 / g) is less than 1, The clay has a composition of xAl2O3·ySiO2·zH2O (where x is an integer of 1 to 3, y is an integer of 1 to 5, and z is an integer of 0 to 5), and The y / x ratio is less than 5. A rubber composition for coating steel wires, comprising: Embodiment 2: 2. The rubber composition for coating a steel wire according to embodiment 1, wherein the clay has an Al ratio of 20 atomic % or more. Embodiment 3: The nitrogen adsorption specific surface area of ​​the clay is 5.0 m 2 / g or more of the rubber composition for coating a steel wire according to embodiment 1 or 2. Embodiment 4: 4. The rubber composition for coating a steel wire according to any one of embodiments 1 to 3, wherein the filler contains silica, and the amount of silica mixed is 5 parts by mass or more per 100 parts by mass of the diene rubber. Embodiment 5: 5. The rubber composition for coating a steel wire according to any one of embodiments 1 to 4, wherein the steel wire is coated with a metal plating compound, and 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. Embodiment 6: A tire, a belt conveyor, an electric wire, a hose or a vibration-isolating rubber using the rubber composition for coating a steel wire according to any one of the first to fifth embodiments.

Claims

1. A rubber composition for coating a steel wire, comprising: the rubber composition is a blend of 40 to 80 parts by mass of a filler made of carbon black and / or silica and 0.1 to 15 parts by mass of clay with 100 parts by mass of a diene-based rubber including natural rubber and / or synthetic isoprene rubber, The nitrogen adsorption specific surface area (m ２ / g) to the CTAB adsorption specific surface area (m ２ / g) is less than 1, The clay is xAl ２ O ３ ySiO ２ ・zH ２ O (wherein x is an integer of 1 to 3, y is an integer of 1 to 5, and z is an integer of 0 to 5), and The y / x ratio is less than 5. A rubber composition for coating steel wires, comprising:

2. 2. The rubber composition for coating a steel wire according to claim 1, wherein the clay has an Al ratio of 20 atomic % or more.

3. The nitrogen adsorption specific surface area of ​​the clay is 5.0 m ２ 2. The rubber composition for coating a steel wire according to claim 1, wherein the modulus of elasticity is 1 / g or more.

4. 2. The rubber composition for coating a steel wire according to claim 1, wherein the filler contains silica, and the amount of silica mixed is 5 parts by mass or more per 100 parts by mass of the diene rubber.

5. 2. The rubber composition for coating a steel wire according to claim 1, wherein the steel wire is coated with a metal plating compound, and 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.

6. 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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