Evaluation method of rubber composition

Abstract

To provide a rubber composition assessment method for three-dimensionally detecting metal components that affect adhesion to metal members.SOLUTION: A rubber composition assessment method provided herein uses a rubber composition to be in contact with a metal containing copper and / or zinc as a sample to three-dimensionally quantify zerovalent, monovalent, and divalent copper components and / or zinc compounds present in the sample by the X-ray absorption fine structure analysis.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating a rubber composition to detect whether its adhesion to a metal member is good or bad. [Background technology]

[0002] A rubber composition that comes into contact with metal components that make up a tire must firmly bond the metal components and adjacent rubber materials. For example, a rubber composition for metal bonding is required to firmly bond the brass-plated steel wire and belt-coating rubber inside the tire and to improve adhesion durability (see, for example, Patent Document 1). To ensure initial adhesive strength and prevent a decrease in adhesive strength due to deterioration, it is necessary to evaluate the state of adhesion between the rubber and the brass-plated steel wire and the degree of deterioration. Conventionally, tensile tests, peel tests, etc. have been performed to evaluate the state of adhesion and the degree of deterioration. However, these evaluation methods, which require strong adhesion between the rubber and the brass-plated steel wire, have not been able to microscopically determine the appropriate rubber composition and vulcanization conditions of the rubber composition for metal bonding or to grasp the state of deterioration in more detail.

[0003] Adhesion between rubber and metal materials is severely damaged by moist heat aging, and it is thought that the brass components of brass-plated steel wire and the copper components (Cu) and zinc compounds (Zn) in the metal sulfide layer ionize and diffuse into the rubber, accelerating deterioration associated with moist heat aging and reducing adhesion. Therefore, there was a need for a method to three-dimensionally quantify and evaluate how metal components diffuse into the rubber and increase or decrease in rubber materials that come into contact with metal materials. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-250310 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a method for evaluating a rubber composition that three-dimensionally detects metal components that affect adhesion to metal members. [Means for solving the problem]

[0006] The method for evaluating a rubber composition of the present invention, which achieves the above-mentioned object, is characterized by using a rubber composition that comes into contact with a metal containing copper and / or zinc as a sample and three-dimensionally quantifying the zero-valent, monovalent, and divalent copper components and / or zinc compounds present in the sample by computer tomography-X-ray absorption fine structure analysis. [Effects of the Invention]

[0007] The rubber composition evaluation method of the present invention three-dimensionally quantifies the zero-, monovalent, and divalent copper components and / or zinc compounds present in the rubber composition using computer tomography-X-ray absorption fine structure analysis, making it possible to three-dimensionally detect the diffusion and increase / decrease of metal components that affect adhesion to metal components. By microscopically understanding the increase / decrease of metal components in rubber, particularly under humid and hot environments, rubber composition design and vulcanization conditions can be improved more efficiently.

[0008] The evaluation method of the present invention includes an initial evaluation step of measuring the zero-valent, monovalent, and divalent copper components and / or zinc compounds in the sample, and a post-treatment evaluation step of measuring the zero-valent, monovalent, and divalent copper components and / or zinc compounds in the sample after subjecting the sample to moist heat aging treatment, and can calculate at least one selected from (1) the amount of decrease in zero-valent copper components before and after moist heat aging treatment, (2) the ratio of monovalent copper components after treatment to initial monovalent copper components, and (3) the increase in the proportion of ZnS present in all zinc compounds before and after moist heat aging treatment.

[0009] Furthermore, the sample may be rotated while capturing projection images at each rotation angle to perform the computer tomography-X-ray absorption fine structure analysis.

[0010] Furthermore, the sample is preferably a cured product of a rubber composition containing 0.1 to 10 mass% of brass powder having a particle size of 1 to 100 μm, and the brass powder preferably contains 50 to 90 mass% of copper and 50 to 10 mass% of zinc. By compounding the brass powder in this way into the rubber composition for metal bonding to be evaluated, it is possible to detect the increase or decrease in the metal components of the brass powder diffusing three-dimensionally into the rubber before and after moist heat aging, and to understand the relationship with moist heat adhesion.

[0011] The moist heat aging treatment is carried out under conditions of 70°C, 96% RH, and 2 weeks, and at least one of the following can be evaluated: (4) whether the abundance ratio of zero-valent copper components after the moist heat aging treatment is 10 to 80% relative to the initial monovalent copper components, (5) whether the increase in divalent copper components before and after the moist heat aging treatment is 110 to 300% relative to the initial monovalent copper components, and (6) whether the increase in the abundance ratio (%) of ZnS in all zinc compounds before and after the moist heat aging treatment is 40% or less. If the above evaluation results show that the abundance ratio of (4) is 10 to 80% or the increase in (5) is 110 to 300%, the moist heat adhesion of the rubber composition for metal bonding is improved.

[0012] The rubber composition for metal bonding of the present invention preferably has the following evaluation results using the above-mentioned rubber composition evaluation method: (4) the abundance ratio of zero-valent copper components after the moist heat aging treatment is 10 to 80% when the initial monovalent copper component is taken as 100%, and (5) the increase in the amount of divalent copper components before and after the moist heat aging treatment is 110% to 300% when the initial monovalent copper component is taken as 100%.

[0013] Furthermore, the rubber composition for metal bonding preferably contains 100 parts by mass of diene rubber containing 50% by mass or more of natural rubber, 5 to 12 parts by mass of zinc oxide, 4 to 10 parts by mass of sulfur, and 0.5 to 10 parts by mass of lignin fermentation residue and / or lignin extract. By blending a highly water-absorbent component such as a lignin fermentation residue and / or lignin extract into the rubber for metal bonding, it is possible to improve the adhesion after moist heat aging even if the initial adhesion remains the same.

[0014] In the method for producing a rubber composition for metal bonding comprising the above-mentioned rubber composition, the rubber composition containing zinc oxide is preferably mixed for at least 10 minutes, and the rubber composition containing sulfur is preferably mixed for at least 5 minutes. By setting the mixing times after compounding zinc oxide and sulfur within the above-mentioned ranges, the abundance ratio of (4) and the increase in (5) can be set within the specified ranges, and excellent adhesion after moist heat aging can be achieved. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a graph illustrating the change in the abundance ratio of zero-valent, monovalent, and divalent copper components in a sample. DETAILED DESCRIPTION OF THE INVENTION

[0016] The rubber composition evaluation method of the present invention uses a rubber composition that comes into contact with a metal containing copper and / or zinc, i.e., a rubber composition for metal bonding, as a sample. The evaluation method of the present invention makes it possible to evaluate the adhesion after moist heat aging when a metal material and a rubber material are bonded via the rubber composition for metal bonding.

[0017] The rubber composition evaluation method of the present invention is characterized by three-dimensionally quantifying zero-valent, monovalent, and divalent copper components and / or zinc compounds present in a sample rubber composition for metal bonding by computer tomography-X-ray absorption fine structure analysis. That is, zero-valent copper Cu, monovalent copper Cu, and zinc compounds diffused in the rubber composition for metal bonding from the vicinity of the metal surface to distant regions are analyzed. + , and divalent copper Cu 2+ and / or zinc compounds are three-dimensionally quantified. By three-dimensionally quantifying the amount of zinc compounds in the rubber composition, it is possible to obtain more three-dimensional local information distribution and shape information that cannot be obtained by measuring the X-ray absorption fine structure of the rubber composition using a transmission method.

[0018] Three-dimensional quantitative determination of copper (Cu) and zinc (Zn) by X-ray absorption fine structure analysis can be achieved, for example, by rotating the sample while performing X-ray absorption fine structure analysis. For example, a cylindrical rubber sample with a diameter of 100 μm to 2 mm can be prepared and irradiated with X-rays while rotating it at small increments of ±90 degrees relative to the X-ray optical axis. The X-ray irradiation energy should be 8857 eV to 9357 eV (copper K-shell absorption edge), where copper K-edge absorption occurs. Furthermore, the energy should be 9640 eV to 9700 eV (zinc K-shell absorption edge), where zinc K-edge absorption occurs.

[0019] The measurement conditions for computed tomography-X-ray absorption fine structure analysis are not particularly limited. For example, the method can be performed using a device capable of supplying X-rays, as follows: X-rays are irradiated onto a sample, and as the X-ray energy is increased, X-ray absorption is detected at the copper K-absorption edge and zinc K-absorption edge. The X-rays transmitted through the sample are projected two-dimensionally and imaged to obtain a two-dimensional image of the sample's absorption. Furthermore, two-dimensional absorption images can be captured while rotating the sample by a small angle. By analyzing the X-ray absorption amount and the intensity and shape of the absorption peaks in each image, copper quantification, evaluation of valence, and quantification of zinc compounds can be performed. By reconstructing the quantitative copper images, valence images, and zinc compound images, three-dimensional images of copper distribution, copper valence, and zinc compound distribution can be obtained.

[0020] The rubber composition evaluation method can evaluate the change in valence, diffusion state, and increase / decrease of copper and / or zinc compounds before and after moist heat aging treatment in a sample that is in contact with or contains metal components containing copper and / or zinc, such as wire, plate, or powder. That is, as shown in Figure 1, the zero-valent copper component (Cu) and monovalent copper component (Cu + )i, and divalent copper component (Cu 2+ )i in the initial evaluation process, and after the sample is subjected to a moist heat aging treatment (after 14 days in the example in Figure 1), the zero-valent copper component (Cu)t and the monovalent copper component (Cu +)t, and divalent copper component (Cu 2+ )t in the initial sample. + )i, and divalent copper component (Cu 2+ )i is the abundance ratio of each copper component, and the sum of the three is 1.0. That is, (Cu)i + (Cu + )i+(Cu 2+ )i = 1.0. Similarly, the zero-valent copper component (Cu)t and the monovalent copper component (Cu + )t, and divalent copper component (Cu 2+ )t is the abundance ratio of each copper component, and the sum of the three is 1.0. That is, (Cu)t + (Cu + )t+(Cu 2+ )t = 1.0. Note that Figure 1 illustrates the change in the abundance ratio of zero-valent, monovalent, and divalent copper components in the sample, but the change in the abundance ratio of zinc compounds can be similarly explained. In the following explanation, the zero-valent zinc compound in the initial sample will be referred to as (Zn)i, the divalent zinc sulfide as (ZnS)i, the zero-valent zinc compound in the sample after moist heat aging as (Zn)t, and the divalent zinc sulfide as (ZnS)t.

[0021] Humid heat aging treatment is performed as an accelerated test for rubber-to-metal adhesion durability. Although pseudo-adhesion may satisfy the adhesion conditions before humid heat aging, the accuracy of adhesion evaluation improves based on the quality of adhesion after humid heat aging. Conditions for humid heat aging treatment include, for example, 70°C, 96% RH, and two weeks. The conditions for humid heat aging treatment may be changed as appropriate depending on the rubber composition of the rubber composition for metal bonding, the vulcanization conditions, and the usage environment.

[0022] The rubber composition evaluation method includes an initial evaluation step of measuring zero-valent, monovalent, and divalent copper components and / or zinc compounds in a sample, and a post-treatment evaluation step of measuring zero-valent, monovalent, and divalent copper components and / or zinc compounds in the sample after subjecting the sample to a moist heat aging treatment, and can calculate at least one of the following (1), (2), and (3): (1) The decrease in the amount of zero-valent copper component before and after moist heat aging treatment [(Cu)i-(Cu)t] (2) The initial monovalent copper content (Cu + )i after treatment with monovalent copper (Cu + )t ratio ((Cu + )t / (Cu + )i) (3) Increase in the proportion of ZnS in all zinc compounds before and after moist heat aging

[0023] Furthermore, the rubber composition can be evaluated by calculating at least one selected from the following (4), (5), and (6). (4) The zero-valent copper component (Cu)t after the moist heat aging treatment is reduced to the initial monovalent copper component (Cu + )i is 100%; (Cu)t / (Cu + )i×100 (5) The increase in divalent copper content [(Cu 2+ )t-(Cu 2+ )i] is the initial monovalent copper component (Cu + )Percentage where i is 100%; [(Cu 2+ )t-(Cu 2+ )i] / (Cu + )i×100 (6) The increase in the percentage of zinc sulfide (ZnS) in all zinc compounds before and after moist heat aging [(ZnS)t-(ZnS)i]

[0024] The percentage of the zero-valent copper component (Cu)t / (Cu + )i×100 is preferably 10 to 80%, more preferably 30 to 70%. In addition, the percentage of the increase in the divalent copper component [(Cu 2+ )t-(Cu 2+ )i] / (Cu +)i × 100 is preferably 110 to 300%, more preferably 120 to 200%. Furthermore, the increase in the proportion (%) of ZnS in all zinc compounds before and after the moist heat aging treatment in (6) above, [(ZnS)t - (ZnS)i], is preferably 40% or less, more preferably 20% to 35%. By satisfying the relationships in (4), (5) and / or (6) above, the durable adhesiveness after the moist heat aging treatment can be made even better.

[0025] The rubber composition is evaluated by blending 0.1 to 10 mass% of brass powder having a particle size of 1 to 100 μm with a rubber composition for metal bonding, the rubber composition being evaluated for durable adhesion after moist heat aging. The brass powder is preferably comprised of 50 to 90 mass% copper and 50 to 10 mass% zinc. By evaluating a sample in which such brass powder has been blended with the rubber composition for metal bonding to be evaluated, the adhesive performance of the rubber composition for metal bonding when it comes into contact with a brass-plated steel wire can be evaluated in more detail.

[0026] The amount of brass powder blended is preferably 0.1 to 10 mass%, more preferably 0.5 to 5 mass%, based on 100 mass% of the rubber composition for bonding metal to the sample. The particle size of the brass powder is preferably 1 to 100 μm, more preferably 1 to 20 μm. Furthermore, the composition of the brass powder is preferably 50 to 90 mass% copper, 50 to 10 mass% zinc, more preferably 60 to 80 mass% copper, and 40 to 20 mass% zinc.

[0027] The rubber composition for metal bonding of the present invention is, before and after a moist heat aging treatment under conditions of 70°C, 96% RH, and 2 weeks, the percentage of the abundance ratio of the zero-valent copper component (Cu)t / (Cu + )i×100 is preferably 10 to 80%, more preferably 30 to 70%. In addition, the increase in the divalent copper component (5) [(Cu 2+ )t-(Cu 2+ )i] is the initial monovalent copper component (Cu + ) i is 100%; [(Cu 2+ )t-(Cu2+ )i] / (Cu + )i×100 is preferably 110 to 300%, more preferably 120 to 200%. When the rubber composition for metal bonding satisfies the above relationship (4) and / or (5), the durable adhesion after moist heat aging treatment can be made more excellent. Preferably, the rubber composition satisfies both the above relationships (4) and (5).

[0028] The rubber composition for metal bonding may be prepared by compounding 100 parts by mass of diene rubber containing 50% or more by mass of natural rubber with 5 to 12 parts by mass of zinc oxide, 4 to 10 parts by mass of sulfur, and 1 to 10 parts by mass of lignin fermentation residue and / or lignin extract.

[0029] In the rubber composition for metal bonding, the diene rubber may contain natural rubber and / or synthetic isoprene rubber, preferably natural rubber. The content of natural rubber is preferably 50% by mass or more, more preferably 80% by mass or more, and even more preferably 90 to 100% by mass, based on 100% by mass of the diene rubber. By making the content of natural rubber 50% by mass or more, adhesion to metal members (e.g., pull-out strength and cross-ply peel strength) can be ensured.

[0030] The rubber composition for metal bonding of the present invention can contain diene rubbers other than natural rubber and synthetic isoprene rubber. Examples of other diene rubbers include butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, butyl rubber, and halogenated butyl rubber. Among these, butadiene rubber, styrene-butadiene rubber, and halogenated butyl rubber are preferred. These diene rubbers can be used alone or in any blend. The content of the other diene rubber is preferably 50% by mass or less, more preferably 20% by mass or less, and even more preferably 0 to 10% by mass, based on 100% by mass of the diene rubber.

[0031] The rubber composition for metal bonding preferably contains 5 to 12 parts by mass, more preferably 8 to 10 parts by mass, of zinc oxide per 100 parts by mass of diene rubber. When the amount of zinc oxide is 5 parts by mass or more, durable adhesion can be ensured under heat and wet heat conditions, which is preferable. Furthermore, heat buildup can be suppressed, and rubber hardness can be maintained and improved. Furthermore, by limiting the amount of zinc oxide to 12 parts by mass or less, deterioration of durable adhesion under heat can be suppressed.

[0032] The rubber composition for metal bonding preferably contains 4 to 10 parts by mass of sulfur per 100 parts by mass of diene rubber, more preferably 4 to 9 parts by mass, even more preferably 5 to 8 parts by mass, and even more preferably 6 to 8 parts by mass. When the amount of sulfur is 4 parts by mass or more, it is possible to suppress a decrease in durable adhesion and rubber hardness under wet heat conditions. Furthermore, when the amount of sulfur is 10 parts by mass or less, it is possible to suppress a decrease in the aging resistance of the rubber and durable adhesion under wet heat conditions.

[0033] The rubber composition for metal bonding preferably contains 0.5 to 10 parts by mass, more preferably 1 to 5 parts by mass, and even more preferably 2 to 5 parts by mass of lignin fermentation residue and / or lignin extract per 100 parts by mass of diene rubber. When the amount of lignin fermentation residue and / or lignin extract is 0.5 parts by mass or more, adhesion durability can be improved while maintaining a balance of physical properties. Furthermore, when the amount of lignin fermentation residue and / or lignin extract is 10 parts by mass or less, adhesion durability can be improved without reducing breaking strength.

[0034] An example of a lignin fermentation residue is one obtained by crushing wood raw materials from trees while treating them with steam or the like, fermenting them with enzymes for 12 to 48 hours, and then drying the solid residue that remains.

[0035] For example, a lignin extract can be produced by crushing woody raw materials from trees, raising the temperature while passing hot water through them, treating them with pressurized hot water at 150°C to 220°C, and then cooling them while treating them, and then cooling them again to separate the water and solvent from the residue, and drying the residue.

[0036] The rubber composition for metal bonding preferably contains 30 to 80 parts by mass, more preferably 50 to 70 parts by mass, of carbon black blended with 100 parts by mass of diene rubber. A blending amount of carbon black of 30 parts by mass or more is preferred because it ensures rubber hardness and maintains and improves durable adhesiveness under heat and wet heat conditions. Furthermore, a blending amount of carbon black of 80 parts by mass or less can prevent the rubber viscosity and heat buildup from increasing. The carbon black preferably has a nitrogen adsorption specific surface area (N2SA) of 20 to 150 m 2 / g, more preferably 40 to 140m 2 / g. N2SA is 20m 2 / g or more is preferable because reinforcement can be ensured. 2 When the N2SA of carbon black is 1 / g or less, the heat buildup can be prevented from increasing. In this specification, the N2SA of carbon black is measured in accordance with JIS K6217-7.

[0037] The rubber composition for metal bonding may optionally contain a cobalt-containing compound. By including the cobalt-containing compound, the rubber composition for metal bonding can have better adhesion and durable adhesion. The amount of the cobalt-containing compound is preferably 0 to 5 parts by mass, more preferably 0.5 to 2.5 parts by mass, per 100 parts by mass of the diene rubber.

[0038] Examples of cobalt-containing compounds include organic cobalt salts and organic cobalt complexes, such as cobalt naphthenate, cobalt neodecanoate, cobalt stearate, cobalt rosinate, cobalt versatate, cobalt tallate, cobalt neodecanoate borate, and cobalt acetylacetonate. Among these organic cobalt salts, boron-containing organic cobalt salts are preferred, and for example, composite salts in which part of the organic acid is replaced with boric acid or the like are preferred.

[0039] The rubber composition for metal bonding can be blended with various additives that are generally used in rubber compositions for tires, such as vulcanization accelerators, various oils, antioxidants, plasticizers, etc., and can be used for vulcanization or crosslinking. The blending amounts of these additives can be conventional amounts as long as they do not contradict the object of the present invention.

[0040] The rubber composition for metal bonding of the present invention can be produced by mixing the above-mentioned components using a conventional rubber mixing machine, such as a Banbury mixer, kneader, or roll. When producing the rubber composition for metal bonding, it is recommended that the rubber composition containing zinc oxide be mixed for at least 10 minutes, more preferably 10 to 15 minutes, and that the rubber composition containing sulfur be mixed for at least 5 minutes, more preferably 5 to 8 minutes. By keeping the mixing times of the rubber compositions after compounding zinc oxide and sulfur within the above-mentioned ranges, the decrease in (4) and the increase in (5) can be kept within the specified ranges, thereby achieving excellent adhesion after moist heat aging.

[0041] The rubber composition for metal bonding is suitable as a rubber material that comes into contact with or coats metal components, and is particularly suitable for constituting a coating rubber for steel cords of pneumatic tires, and can be used as a rubber material that coats or comes into contact with steel cords and brass-plated steel in belt layers and / or carcass layers and / or bead portions.

[0042] The present invention will be further explained below with reference to examples, but the scope of the present invention is not limited to these examples. [Example]

[0043] To prepare 11 types of rubber compositions (Experimental Examples 1 to 13) with the formulations shown in Table 1, all components except sulfur and vulcanization accelerator were weighed and mixed in a 1.7-liter internal Banbury mixer for 5 minutes (2 minutes of mixing after zinc oxide was added), and the master batch was then discharged from the mixer and cooled to room temperature. This master batch was then fed into the same Banbury mixer and mixed again for 0 to 3 minutes. This master batch was then fed into the same Banbury mixer again, and sulfur and vulcanization accelerator were added and mixed for 3 to 10 minutes. After mixing, a rubber composition for metal bonding was obtained. 3% by mass of brass powder (bronze powder 3L7 manufactured by Dia Kogyo Co., Ltd.) having an average particle diameter of 3 μm and consisting of 75% by mass of copper and 25% by mass of zinc was added to 100% by mass of the rubber composition for metal bonding obtained above, and the mixture was mixed for 5 minutes using an open roll.

[0044] The rubber compositions obtained above were each vulcanized in a mold of a predetermined shape at 160°C for 20 minutes to prepare evaluation samples. Using the obtained evaluation samples, an accelerated moist heat aging test was conducted at a temperature of 70°C and a relative humidity of 96% RH for 2 weeks (336 hours), and evaluation samples after moist heat were prepared. Using the obtained evaluation samples and the evaluation samples after moist heat, the copper component and / or zinc compound in each sample were three-dimensionally quantified by computer tomography-X-ray absorption fine structure analysis using the following method.

[0045] Computed tomography-X-ray absorption fine structure analysis (quantitative analysis by CT-XAFS) In the CT-XAFS analysis, two-dimensional transmission XAFS images measured at different rotation angles relative to the X-ray optical axis were subjected to fitting analysis to obtain two-dimensional projection images of the amount of Cu and the amount of zinc compounds. Further linear combination analysis was performed to obtain two-dimensional projection images of the ratios of zero-valent Cu (brass), monovalent Cu (Cu2S), and divalent Cu, and / or two-dimensional projection images of zero-valent Zn (brass), divalent Zn (ZnO), and divalent Zn (ZnS). Three-dimensional images were obtained by reconstructing these images.

[0046] Based on the values ​​obtained by the above-mentioned computer tomography-X-ray absorption fine structure analysis, the following values ​​were calculated for the zero-valent, monovalent, and divalent copper components. (1) The amount of zero-valent copper component reduction [(Cu)i-(Cu)t] before and after moist heat aging treatment was calculated and recorded in the column "Amount of Cu reduction after moist heat treatment [(Cu)i-(Cu)t]" in Table 1. (2) The ratio of the monovalent copper content after treatment to the initial monovalent copper content [(Cu + )t / (Cu + )i] and calculate the "Before and after humidity and heat Cu + Ratio of (Cu + )t / (Cu + )i" column. (4) The percentage of zero-valent copper after moist heat aging treatment, when the initial monovalent copper is taken as 100%, [(Cu)t / (Cu + )i × 100] and the Cu abundance ratio after moist heating (Cu)t / (Cu + )i*100" column. (5) The percentage of increase in divalent copper content after moist heat aging, with the initial monovalent copper content taken as 100% [(Cu 2+ )t-(Cu 2+ )i] / (Cu + )i × 100 and calculate the value of "Cu after heat and humidity" in Table 1. 2+ Increase rate [(Cu 2+ )t-(Cu 2+ )i] / (Cu + )i×100" column.

[0047] Similarly, based on the values ​​obtained by computer tomography-X-ray absorption fine structure analysis, the following values ​​were calculated for zero-valent and divalent zinc compounds. (3) The increase in the proportion (%) of zinc sulfide (ZnS) in all zinc compounds before and after moist heat aging treatment was calculated and recorded in the column “Increase in the proportion of ZnS before and after moist heat aging treatment [(ZnS)t-(ZnS)i].”

[0048] Rubber attached after humidity and heat deterioration The resulting rubber composition was used to coat brass-plated steel cords arranged in parallel at 12.7 mm intervals, embedding them at an embedding length of 12.7 mm, and vulcanizing and bonding them at 160°C for 20 minutes to prepare rubber-bonded evaluation samples. The resulting rubber-bonded evaluation samples were subjected to accelerated humidity and heat aging tests at 70°C and 96% relative humidity for two weeks (336 hours). According to ASTM D-2229, steel cords were removed from the resulting humidity- and heat-aged rubber-bonded evaluation samples, and the amount of rubber coating (%) on their surfaces was evaluated. The results are reported in the "Rubber Bonding After Humid Heat Aging" column as an index, with the value of Experimental Example 1 being 100. A higher index indicates better durable adhesion to the steel cord after humidity and heat aging.

[0049] [Table 1]

[0050] The types of raw materials used in Table 1 are shown below. NR: Natural rubber, RSS#3 Carbon black: Tokai Carbon Co., Ltd. Seast 300 Cobalt stearate: manufactured by DIC Lignin residue: Solvent extraction residue, manufactured by Nippon Steel Engineering Co., Ltd. Lignin residue fermentation product: Fermentation residue, manufactured by Nippon Steel Engineering Co., Ltd. Zinc oxide: Three types of zinc oxide manufactured by Seido Chemical Industry Co., Ltd. Sulfur: Akzo Nobel Crystex HSOT20 Vulcanization accelerator: Noccela DZ manufactured by Ouchi Shinko Chemical Co., Ltd.

[0051] As is clear from Table 1, the rubber compositions for metal bonding of Experimental Examples 2 to 9 and 11 had a high percentage of zero-valent copper component after the moist heat aging treatment relative to the initial monovalent copper component [(Cu)t / (Cu + )i×100] satisfies 10 to 80%, and the percentage increase in the amount of divalent copper component before and after moist heat aging treatment, when the initial monovalent copper component is taken as 100%, [((Cu 2+ )t-(Cu 2+)i) / (Cu + )i × 100] satisfies 110 to 300%, and the increase in the abundance ratio (%) of zinc sulfide (ZnS) in all zinc compounds before and after moist heat aging treatment [(ZnS)t - (ZnS)i] is 40% or less. Therefore, it was confirmed that the rubber adhesion after moist heat aging was improved to a level equal to or higher than that of Experimental Example 1. The rubber composition for metal bonding of Experimental Example 10 had a percentage increase in the amount of divalent copper component before and after moist heat aging treatment, [((Cu 2+ )t-(Cu 2+ )i) / (Cu + )i × 100] exceeded 300%, and the increase in the abundance ratio (%) of zinc sulfide (ZnS) in all zinc compounds before and after moist heat aging treatment [(ZnS)t - (ZnS)i] exceeded 40%, confirming that the rubber adhesion after moist heat aging was inferior to that of Experimental Example 1.

[0052] As is clear from Table 1, the rubber composition for metal bonding of Experimental Example 12 has a high percentage of zero-valent copper component after the moist heat aging treatment relative to the initial monovalent copper component [(Cu)t / (Cu + )i×100] exceeds 80%, and the percentage increase in the amount of divalent copper component before and after moist heat aging treatment, when the initial monovalent copper component is taken as 100%, [((Cu 2+ )t-(Cu 2+ )i) / (Cu + )i × 100] exceeds 300%, and the increase in the abundance ratio (%) of zinc sulfide (ZnS) in all zinc compounds before and after moist heat aging treatment [(ZnS)t - (ZnS)i] exceeds 40%, so it was confirmed that the rubber adhesion after moist heat aging was at or below the level of Experimental Example 1.

[0053] The rubber composition for metal bonding of Experimental Example 13 had a percentage increase in the amount of divalent copper component before and after moist heat aging treatment, [((Cu 2+ )t-(Cu 2+ )i) / (Cu +)i × 100] exceeds 300%, and the increase in the abundance ratio (%) of zinc sulfide (ZnS) in all zinc compounds before and after moist heat aging [(ZnS)t - (ZnS)i] exceeds 40%, confirming that the rubber adhesion after moist heat aging falls to the level of Experimental Example 1 or below.

[0054] The present invention includes the following inventions. Invention [1] A method for evaluating a rubber composition, characterized by using a rubber composition that comes into contact with a metal containing copper and / or zinc as a sample and three-dimensionally quantifying the zero-valent, monovalent, and divalent copper components and / or zinc compounds present in the sample by computer tomography-X-ray absorption fine structure analysis. Invention [2] A method for evaluating a rubber composition according to invention [1], comprising an initial evaluation step of measuring zero-valent, monovalent, and divalent copper components and / or zinc compounds in the sample, and a post-treatment evaluation step of measuring zero-valent, monovalent, and divalent copper components and / or zinc compounds in the sample after subjecting the sample to moist heat aging treatment, wherein at least one selected from (1) the amount of decrease in zero-valent copper components before and after moist heat aging treatment, (2) the ratio of monovalent copper components after treatment to initial monovalent copper components, and (3) the amount of increase in the proportion of ZnS present in all zinc compounds before and after moist heat aging treatment is calculated. Invention [3] A method for evaluating a rubber composition according to invention [1] or [2], characterized in that the sample is rotated and projection images are taken at each rotation angle to perform computer tomography-X-ray absorption fine structure analysis. Invention [4] The method for evaluating a rubber composition according to any one of inventions [1] to [3], characterized in that the sample is a cured product of a rubber composition containing 0.1 to 10 mass% of brass powder having a particle size of 1 to 100 μm, and the brass powder is composed of 50 to 90 mass% of copper and 50 to 10 mass% of zinc. Invention [5] A method for evaluating a rubber composition according to any one of Inventions [2] to [4], characterized in that the moist heat aging treatment is carried out under conditions of 70°C, 96% RH, and 2 weeks, and at least one selected from the following is evaluated: (4) whether the abundance ratio of zero-valent copper components after the moist heat aging treatment is 10 to 80% when the initial monovalent copper components are taken as 100%, (5) whether the increase in the amount of divalent copper components before and after the moist heat aging treatment is 110 to 300% when the initial monovalent copper components are taken as 100%, and (6) whether the increase in the abundance ratio (%) of ZnS in all zinc compounds before and after the moist heat aging treatment is 40% or less. Invention [6] A rubber composition for metal bonding, characterized in that the evaluation results of the rubber composition evaluation method described in Invention [5] are: (4) the abundance ratio of zero-valent copper components after the moist heat aging treatment is 10 to 80% when the initial monovalent copper components are taken as 100%, and (5) the increase in the amount of divalent copper components before and after the moist heat aging treatment is 110 to 300% when the initial monovalent copper components are taken as 100%. Invention [7] A rubber composition for metal bonding according to invention [6], characterized in that 100 parts by mass of diene rubber containing 50% by mass or more of natural rubber is blended with 5 to 12 parts by mass of zinc oxide, 4 to 10 parts by mass of sulfur, and 0.5 to 10 parts by mass of lignin fermentation residue and / or lignin extract. Invention [8] A method for producing a rubber composition for metal bonding according to invention [7], characterized in that the rubber composition containing zinc oxide is mixed for at least 10 minutes, and the rubber composition containing sulfur is mixed for at least 5 minutes.

Claims

1. A method for evaluating a rubber composition, characterized in that a rubber composition that comes into contact with a metal containing copper and / or zinc is used as a sample, and zero-valent, monovalent, and divalent copper components and / or zinc compounds present in the sample are three-dimensionally quantified by computer tomography-X-ray absorption fine structure analysis.

2. 2. The method for evaluating a rubber composition according to claim 1, further comprising an initial evaluation step of measuring zero-valent, monovalent, and divalent copper components and / or zinc compounds in the sample, and a post-treatment evaluation step of measuring zero-valent, monovalent, and divalent copper components and / or zinc compounds in the sample after subjecting the sample to a moist heat aging treatment, wherein at least one selected from (1) the amount of decrease in zero-valent copper components before and after the moist heat aging treatment, (2) the ratio of monovalent copper components after the treatment to the initial monovalent copper components, and (3) the amount of increase in the proportion of ZnS present in all zinc compounds before and after the moist heat aging treatment is calculated.

3. The method for evaluating a rubber composition according to claim 1 or 2, wherein the sample is rotated and projection images are taken at each rotation angle to perform computer tomography-X-ray absorption fine structure analysis.

4. The sample is a cured product of a rubber composition containing 0.1 to 10 mass% of brass powder having a particle size of 1 to 100 μm, and the brass powder is composed of 50 to 90 mass% of copper and 50 to 10 mass% of zinc. The rubber composition evaluation method according to claim 1 or 2.

5. The method for evaluating a rubber composition according to claim 2, characterized in that the moist heat aging treatment is performed under conditions of 70°C, 96% RH, and 2 weeks, and at least one of the following is evaluated: (4) whether the abundance ratio of zero-valent copper components after the moist heat aging treatment is 10 to 80% when the initial monovalent copper components are taken as 100%, (5) whether the increase in the amount of divalent copper components before and after the moist heat aging treatment is 110 to 300% when the initial monovalent copper components are taken as 100%, and (6) whether the increase in the abundance ratio (%) of ZnS in all zinc compounds before and after the moist heat aging treatment is 40% or less.

6. The rubber composition for metal bonding, characterized in that the evaluation results of the rubber composition evaluation method described in claim 5 are: (4) the abundance ratio of zero-valent copper components after the moist heat aging treatment is 10 to 80% when the initial monovalent copper component is taken as 100%, and (5) the increase in the amount of divalent copper components before and after the moist heat aging treatment is 110 to 300% when the initial monovalent copper component is taken as 100%.

7. 7. The rubber composition for metal bonding according to claim 6, characterized in that 100 parts by mass of diene rubber containing 50% by mass or more of natural rubber is blended with 5 to 12 parts by mass of zinc oxide, 4 to 10 parts by mass of sulfur, and 0.5 to 10 parts by mass of a lignin fermentation residue and / or a lignin extract.

8. 8. The method for producing a rubber composition for metal bonding according to claim 7, wherein the rubber composition containing zinc oxide is mixed for at least 10 minutes, and the rubber composition containing sulfur is mixed for at least 5 minutes.

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