Method for evaluating adhesion between rubber and metal

Abstract

To provide a method for evaluating adhesion between rubber and metal, that enables the adhesion between vulcanized rubber and metal to be grasped with high accuracy.SOLUTION: In a data acquisition step S110, an elongated sample Sb is used, and at least one component of the metal components derived from metals is treated as the analysis target component, and metal compounds with different analysis target components and metal compounds of the same type of analysis target component but with different valences are treated as elements of different types, and X-ray transmission image data D1b and analysis image data D2b of the elongated sample Sb in a state of being elongated by an elongation device 2 are acquired. In an evaluation step S120, a calculation device 4 performs data processing to identify voids present in the elongated sample Sb based on the X-ray transmission image data D1b, and determines the type of each element of the analysis target component that exists around the position in the analysis image data D2b that corresponds to the position where the void is identified in the X-ray transmission image data D1b.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating adhesion between rubber and metal, and more particularly to a method for evaluating adhesion between rubber and metal that can grasp the adhesion between vulcanized rubber and metal with high accuracy. [Background technology]

[0002] Rubber products such as tires use metal materials such as steel cord. Generally, the adhesion between metal materials and vulcanized rubber is evaluated using the results of a wire pull-out test in accordance with JIS G 3510-1992. This wire pull-out test requires a large number of steps in the manufacturing and testing of test samples, which can easily lead to variations in test results.

[0003] To evaluate the performance of elastic materials such as rubber and elastomers, a method has been proposed in which voids formed in a stretched test specimen are captured as X-ray projection images, and the performance of the test specimen is evaluated based on the change in void volume over time (see Patent Document 1). This evaluation method evaluates the wear performance, tear resistance, crack resistance, and other properties of the elastic material by analyzing the X-ray projection images of the test specimen, but does not evaluate the adhesion between vulcanized rubber and metal. Therefore, further ingenuity is needed to accurately grasp the adhesion between vulcanized rubber and metal compared to conventional techniques. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-190433 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 adhesion between rubber and metal, which can grasp the adhesion between vulcanized rubber and metal with high accuracy. [Means for solving the problem]

[0006] The method for evaluating the adhesion between rubber and metal of the present invention, which achieves the above-mentioned object, uses vulcanized rubber obtained by vulcanizing unvulcanized rubber containing a metal with sulfur as an evaluation sample, and utilizes data obtained by irradiating the sample with X-rays. The method includes a data acquisition step in which the vulcanized rubber in an elongated state is used as the sample, and X-ray transmission image data and analytical image data are obtained as the data, and an evaluation step, in which at least one component of the metal components derived from the metal is used as an analysis target component, and metal compounds of different analysis target components and metal compounds of the same type of analysis target component but with different valences are used as analysis target components of different types, respectively. The method is characterized in that the X-ray transmission image data is obtained by treating the sample as an element, and the irradiation energy of X-rays irradiated to the sample is set to a predetermined fixed value near the absorption edge of the component to be analyzed, and the analysis image data is generated by X-ray absorption fine structure analysis using a plurality of data obtained by changing the irradiation energy of the X-rays within a predetermined energy region including the absorption edge of the component to be analyzed, and the evaluation step involves using a computing device to perform data processing to identify voids present in the sample based on the X-ray transmission image data, and determining the type of each of the elements of the component to be analyzed that are present around a position in the analysis image data that corresponds to the position where the void was identified in the X-ray transmission image data. [Effects of the Invention]

[0007] According to the present invention, in the evaluation step, by using multiple different types of data, the X-ray transmission image data and the analytical image data, the type of each of the elements of the analysis target components present around the voids in the sample can be determined with high accuracy. Since voids occur in the stretched sample as moist heat aging progresses, the progress of moist heat aging in the sample can be determined by determining the type of each of the elements of the analysis target components present around the voids. The progress of moist heat aging is closely related to the degree of deterioration in adhesion between the vulcanized rubber and the metal. Therefore, by using the present invention, the adhesion between the vulcanized rubber and the metal can be determined with high accuracy. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is an explanatory diagram illustrating an evaluation system. [Figure 2] FIG. 1 is a flow chart showing an example of the procedure of an embodiment of a method for evaluating adhesion between rubber and metal. [Figure 3] 2 is an explanatory diagram illustrating a sample and a detection unit in a state stretched by the stretching device of FIG. 1. FIG. [Figure 4] FIG. 1 is an explanatory diagram illustrating a copper particle, voids present around the particle, and each element of the copper component. [Figure 5] FIG. 1 is an explanatory diagram illustrating the distribution of copper components in X-ray transmission image data of a sample before elongation. [Figure 6] FIG. 1 is an explanatory diagram illustrating the distribution of copper components in X-ray transmission image data of an elongated sample with an elongation rate of 11%. [Figure 7] FIG. 1 is an explanatory diagram illustrating the distribution of copper components in X-ray transmission image data of an elongated sample with an elongation rate of 22%. [Figure 8] FIG. 10 is an explanatory diagram illustrating the distribution of voids in X-ray transmission image data of a sample before elongation. [Figure 9] FIG. 1 is an explanatory diagram illustrating the distribution of voids in X-ray transmission image data of an elongated sample with an elongation rate of 11%. [Figure 10] FIG. 1 is an explanatory diagram illustrating the distribution of voids in X-ray transmission image data of an elongated sample with an elongation rate of 22%. [Figure 11] FIG. 1 is an explanatory diagram illustrating analytical image data of an elongated sample with an elongation rate of 22%. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, the method of the present invention for evaluating adhesion between vulcanized rubber and metal will be described based on the embodiment shown in the drawings.

[0010] An embodiment of a method for evaluating the adhesion between rubber and metal, illustrated in FIG. 2, is carried out using an evaluation system 1 illustrated in FIG. 1. In this evaluation method, a vulcanized rubber obtained by vulcanizing unvulcanized rubber containing a metal with sulfur is used as an evaluation sample, and an X-ray absorption fine structure imaging analyzer 3 (hereinafter referred to as XAFS imaging analyzer 3) equipped with a stretching device 2 is used. This evaluation method includes a data acquisition step S110 and an evaluation step S120. Specifically, a sample in an unstretched state is referred to as a pre-stretching sample Sa, and a sample stretched by the stretching device 2 is referred to as an stretched sample Sb. In the data acquisition step S110, X-ray transmission image data D1a and D1b of the pre-stretching sample Sa and the stretched sample Sb, respectively, and analysis image data D2b of the stretched sample Sb are acquired. In the evaluation step S120, the calculation device 4 identifies voids based on the acquired X-ray transmission image data D1a and D1b, and evaluates the adhesion between the vulcanized rubber and the metal by determining the type of metal compound (Cu, Cu2S, CuS, Zn, ZnS, etc.) present around the position in the analysis image data D2b corresponding to the position where the void was identified in the X-ray transmission image data D1b.

[0011] The evaluation system 1 illustrated in Fig. 1 includes a calculation device 4 to which X-ray transmission image data D1a and D1b and analysis image data D2b acquired by an XAFS imaging analysis device 3 attached to a stretching device 2 are input. In Fig. 1, a part of the XAFS imaging analysis device 3 is cut away to show the stretching device 2 and a detection unit 10.

[0012] The stretching device 2 can be configured to uniaxially stretch the sample when acquiring two-dimensional image data such as X-ray transmission image data D1a, D1b, or analysis image data D2b. When acquiring three-dimensional image data such as X-ray transmission image data D1a, D1b, or analysis image data D2b, the stretching device 2 can be configured to rotate the sample uniaxially stretched around a rotation axis whose axial direction is the stretching direction of the sample. Three-dimensional image data can be obtained by image processing multiple two-dimensional image data acquired by rotating the sample. The stretching device 2 can be configured as a known stretching device. The XAFS imaging analyzer 3 can be configured as a known XAFS imaging analyzer that measures and analyzes the X-ray absorption spectrum of the stretched sample S using computer tomography-X-ray absorption fine structure analysis (hereinafter, CT-XAFS). The calculation device 4 receives and stores various data and processes the data. The calculation device 4 can be configured as a known computer. The arithmetic device 4 includes a processing unit (CPU) 5, a main storage unit (memory) 6, and an auxiliary storage unit (for example, HDD) 7.

[0013] In the evaluation system 1, when the X-ray transmission image data D1a, D1b and the analysis image data D2b acquired by the XAFS imaging analysis device 3 are input to the calculation device 4, and a predetermined program is started and executed by the input unit 8, the calculation device 4 executes each data processing instructed by the program. Then, the calculation device 4 executes each data processing and outputs the evaluation results obtained by executing each data processing to the output unit 9.

[0014] The specimen used for evaluation is a metal-rubber composite material manufactured by vulcanizing unvulcanized rubber containing metal with sulfur. The metal-rubber composite material contains a metal material such as metallic wire or metal powder and vulcanized rubber in contact with the metal material. The metal-rubber composite material simulates rubber products such as tires, and the specimen used is vulcanized rubber in contact with a metallic material, brass-plated steel cord.

[0015] The sample of this embodiment uses vulcanized rubber containing 0.1% to 10% by mass of metal powder with a particle diameter (major axis) of 1 μm to 100 μm. The metal powder preferably contains at least one of copper and zinc, and may contain both copper and zinc. The metal powder may be, for example, brass powder containing 50% to 90% by mass of copper and 50% to 10% by mass of zinc. A metal-rubber composite material such as this sample roughly reproduces the state of vulcanized rubber in contact with a brass-plated steel cord in a rubber product such as a tire. Therefore, by using this sample, the adhesion between the brass-plated steel cord and vulcanized rubber in a rubber product such as a tire can be evaluated in accordance with the actual rubber product.

[0016] The unvulcanized rubber may be any rubber component (polymer) that can be crosslinked with a sulfur-containing crosslinking agent, such as natural rubber (NR) or synthetic rubbers such as styrene-butadiene rubber (SBR), butadiene rubber (BR), and isoprene rubber (IR). The crosslinking agent may contain at least sulfur, and sulfur may be used in combination with an organic peroxide such as a peroxide. The unvulcanized rubber may contain additives other than the crosslinking agent, such as vulcanization accelerators such as zinc oxide, fillers such as silica or carbon black, adhesion promoters such as cobalt stearate, antioxidants, silane coupling agents, processing aids, flame retardants, reinforcing materials, and colorants.

[0017] In a metal-rubber composite material, metal components originating from the metal are present at the adhesive interface between the vulcanized rubber and the metal material. In this embodiment, at least one of the metal components originating from the metal is treated as the component to be analyzed. For example, when a brass-plated steel cord is used as the metal material, the metal components are copper and zinc, and either one of the copper and zinc components or both of the copper and zinc components are used as the components to be analyzed.

[0018] In this embodiment, metal compounds with different analysis target components and metal compounds with the same analysis target component but different valences are treated as separate elements of different types. For example, when the analysis target component is a copper component, the zero-valent copper component (Cu) is treated as a metallic crystalline copper (Cu), the monovalent copper component (Cu + ) as cuprous sulfide (CuS), divalent copper component (Cu 2+ ) and copper (II) sulfide (CuS) are treated as separate elements of different types. Similarly, if the component being analyzed is zinc, the zero-valent zinc component (Zn) is treated as metallic crystalline zinc (Zn), the divalent zinc component (Zn 2+ ) and zinc sulfide (ZnS) are treated as separate elements of different types. In this way, even if the target component is the same, treating metal compounds with different valences as separate elements of different types is advantageous for accurately understanding the change in valence (ionization and sulfidation reaction) of metal components due to moist heat aging in metal-rubber composite materials. Depending on the compounding of the vulcanized rubber and the state of moist heat aging of the vulcanized rubber, divalent copper components (Cu 2+ ) and copper sulfate (CuSO4) can be treated as individual elements, and the divalent zinc component (Zn 2+ ) and zinc oxide (ZnO) can be treated as an individual element. In addition to particles of metal compounds consisting of a single element, the sample also contains particles of metal compounds consisting of multiple elements.

[0019] Next, each step (S110, S120) of the procedure of the method for evaluating the adhesion between rubber and metal shown in FIG. 2 will be described in detail.

[0020] In the data acquisition step S110, X-ray transmission image data D1a and D1b of the pre-extension sample Sa and the extended sample Sb, respectively, and analytical image data D2b of the extended sample Sb are acquired using the XAFS imaging analysis device 3. The X-ray transmission image data D1a and D1b and analytical image data D2b acquired in this data acquisition step S110 are input to the calculation device 4.

[0021] In step S111, a sample is prepared. The sample is taken from a desired metal-rubber composite material and includes an adhesive interface between vulcanized rubber and a metal material. For example, the sample includes an adhesive interface between vulcanized rubber and a steel cord. The sample of this embodiment is taken from vulcanized rubber containing metal powder, and the sample contains an adhesive interface between the metal derived from the metal powder and the vulcanized rubber, reproducing a state roughly similar to the state of the adhesive interface between vulcanized rubber and a steel cord. Details such as the shape and size of the sample will be described later.

[0022] The sample used in step S111 is subjected to a predetermined moist heat aging treatment. The conditions for the moist heat aging treatment are, for example, a heating temperature of 70°C, a humidity of 96% RH, and a treatment period of approximately three days. The conditions for the moist heat aging treatment can be appropriately changed depending on the type of metal component contained in the sample, the rubber composition and vulcanization conditions, the usage environment of the metal-rubber composite material, and other factors. For example, the heating temperature is set to 50°C to 100°C, the humidity to 50% RH to 100% RH, and the treatment period to one week to one month. Samples that have undergone such moist heat aging treatment generally reproduce the condition of rubber products that have undergone moist heat aging, and are therefore advantageous for understanding the degree of deterioration in adhesion between vulcanized rubber and metal that accompanies the progression of moist heat aging.

[0023] In steps S112 and S113, X-ray transmission image data D1a of the pre-extension sample Sa and X-ray transmission image data D1b of the extended sample Sb are obtained using CT measurement by the XAFS imaging analysis device 3 attached to the stretching device 2. In step S114, analysis image data D2b of the extended sample Sb is obtained using CT-XAFS measurement by the XAFS imaging analysis device 3. The pre-extension sample Sa and the extended sample Sb are the same sample, differing only in their extension states. The pre-extension sample Sa is attached to the stretching device 2 and is not extended, i.e., in an unextended state (0% extension rate). The extended sample Sb is in a state where it has been uniaxially extended at a desired extension rate by the stretching device 2.

[0024] The stretching rate of the stretched sample Sb by the stretching device 2 may be such that voids are formed in the stretched sample Sb. This stretching rate is calculated by {(length of stretched sample Sb - length of sample Sa before stretching) / length of sample Sa before stretching} x 100 (%), and can be set to any value within the range of 5% to 50%, for example. If the stretching rate is less than 5%, voids are unlikely to form.

[0025] 3 shows how X-rays are irradiated onto the elongated sample Sb and how two-dimensional image data D3 is acquired by the detector 10. To make this process easier to understand, the stretching device 2 is omitted from FIG. 3. The white arrows in FIG. 3 indicate the elongation direction and circumferential direction of rotation of the elongated sample Sb, and the area surrounded by the dashed line indicates the area irradiated with X-rays.

[0026] The shape and size of the sample can be selected arbitrarily, but it is preferable that the entire elongated sample Sb in the elongated state is projected as the 2D image data D3. A shape that satisfies this condition is, for example, a cylindrical body such as a square pillar or a cylinder. The width dimension rs of this cylinder in the direction perpendicular to the elongation direction is preferably smaller than the X-ray beam diameter rb of the XAFS imaging analysis device 3. Specifically, if the cylinder is a cylinder, the diameter of the circles on both bases should be smaller than the beam diameter rb, and if the cylinder is a regular square pillar, the length of the diagonal of the square on both bases should be smaller than the beam diameter rb. Furthermore, the length hr of the cylinder in the elongated state (the length of the elongated sample Sb) is preferably smaller than the beam diameter rb. Therefore, the length hr of the cylinder in the unelongated state is set based on the beam diameter rb and the elongation rate of the elongated sample Sb by the elongation device 2. For example, when the X-ray beam diameter rb is about 1 mm and the elongation rate by the elongation device 2 is about 20%, the sample is formed of a cylinder having a circular bottom surface with a width dimension (diameter) rs of less than 1.0 mm and a length hr of about 0.84 mm when not elongated.

[0027] In steps S112 and S113, CT measurement is performed with the X-ray irradiation energy (photon energy) of the sample set to a fixed value near the absorption edge of the component being analyzed. When the component being analyzed is copper, the fixed value may be a value in the range of 8.7 keV to 10.8 keV, e.g., 9 keV. In steps S112 and S113, the X-ray irradiation energy is set to a fixed value, and a sample with a desired elongation is rotated. A large number of two-dimensional image data D3 indicating the amount of X-ray absorption in the sample is acquired using the XAFS imaging analyzer 3. Next, each two-dimensional image data D3 is subjected to image processing to obtain three-dimensional image data as X-ray transmission image data D1a and D1b. In each of the X-ray transmission image data D1a and D1b, the smaller the amount of absorption of the irradiated X-rays (the greater the degree of X-ray penetration), the more closely it resembles black. The larger the amount of X-ray absorption (the smaller the degree of X-ray penetration), the more closely it resembles white. Since voids present in the sample hardly absorb X-rays, in each of the X-ray transmission image data D1a and D2Ba, areas that are closer to black indicate voids.

[0028] In step S114, CT-XAFS measurement is performed by varying the irradiation energy of X-rays irradiated onto the sample within a predetermined energy range. The predetermined energy range includes at least a region of approximately 50 eV around the absorption edge of the selected target component, and preferably also includes a region from the K-shell absorption edge to approximately 1500 eV. X-ray absorption near edge structure (XANES) appears in the region of approximately 50 eV around the absorption edge, and extended X-ray absorption fine structure (EXAFS) appears in the region from the absorption edge to approximately 1500 eV. When the target component is copper, the predetermined energy range is, for example, 8.7 keV to 10.8 keV. In step S114, the X-ray irradiation energy is varied within the predetermined energy range while the sample is rotated at the desired elongation rate, and multiple sets of two-dimensional image data D3 indicating the amount of X-ray absorption in the sample for each irradiation energy are acquired using the XAFS imaging analyzer 3. Next, by analyzing the amount of X-ray absorption and the detected intensity and shape of the absorption peak in the X-ray absorption near edge structure (XANES) in the acquired two-dimensional image data D3, three-dimensional analytical image data D2b is acquired, which shows the valence of the metal component and the local structure at the atomic level (interatomic distance, coordination number). In other words, the analytical image data D2b shows the distribution of each element (metal compound) of the component to be analyzed.

[0029] In step S113, the elongation rate of the elongated sample Sb can be increased stepwise by the elongation device 2 to obtain a plurality of X-ray transmission image data D1b with different elongation rates. In this way, a plurality of X-ray transmission image data D1b with different elongation rates can be obtained. When obtaining a plurality of X-ray transmission image data D1b, the elongation rate of the elongated sample Sb can be increased stepwise, for example, from 0% by about 10% to 20%. When a plurality of X-ray transmission image data D1b is obtained in step S113, CT-XAFS measurement can be performed in step S114 only on the elongated sample Sb with the largest elongation rate.

[0030] In the evaluation step S120, the calculation device 4 identifies voids based on the acquired X-ray transmission image data D1a and D1b (S121). Next, the type of metal compound (Cu, Cu2S, CuS, Zn, ZnS, etc.) present around the position in the analysis image data D2b corresponding to the position where the void was identified in the X-ray transmission image data D1b is identified (S122). That is, in this evaluation step S120, each element of the analysis target component present around the void present in the elongated sample Sb is identified using two types of data, the X-ray transmission image data D1a and D1b and the analysis target data D2b.

[0031] In step S121, the calculation device 4 performs data processing to identify voids present in the elongated sample Sb based on the X-ray transmission image data D1a and D1b. In this data processing, voids are identified using the X-ray transmittance and absorption amount, which differ for each component in the X-ray transmission image data D1a and D1b. The X-ray transmittance of voids is greater than the X-ray transmittance of vulcanized rubber or metal component particles, and the X-ray absorption amount of voids is less than the X-ray absorption amount of vulcanized rubber or metal component particles. Therefore, locations where the X-ray transmittance in the X-ray transmission image data D1a and D1b is greater than the X-ray transmittance of vulcanized rubber or metal component particles, or locations where the X-ray absorption amount in the X-ray transmission image data D1a and D1b is less than the X-ray absorption amount of vulcanized rubber or metal component particles, are identified as voids. In this embodiment, voids are identified using the ratio of the amount of X-ray absorption of each component, with the maximum value of the amount of X-ray absorption by the component to be analyzed in the X-ray transmission image data D1a and D1b being set to 100%.

[0032] In step S121, by comparing the void occurrence conditions in the X-ray transmission image data D1a and D1b of the pre-stretched sample Sa and the stretched sample Sb, it is possible to distinguish between voids caused by separation between the vulcanized rubber and the metal due to stretching of the sample and voids that were pre-existing inside the sample and developed during the manufacturing process, etc. Also, in step S121, by comparing the void growth conditions in the X-ray transmission image data D1 of the pre-stretched sample Sa and the stretched sample Sb, it is possible to distinguish between voids that have grown more (increased in volume) relative to the elongation rate and voids that have grown at the same rate as the elongation rate. Around voids that have grown more relative to the elongation rate, the separation between the vulcanized rubber and the metal is more advanced, while around voids that have grown at the same rate as the elongation rate, the separation between the vulcanized rubber and the metal is not advanced. In other words, voids that have grown at the same rate as the elongation rate are not related to the separation between the vulcanized rubber and the metal. In this way, by selecting voids to be identified based on the state of void generation and growth, it is possible to exclude voids that were already present inside the sample and voids that are not related to the dissociation between the vulcanized rubber and the metal, and to identify only voids that result from the dissociation between the vulcanized rubber and the metal as the sample is stretched. In this step S121, the number of identified voids is not limited to one, and multiple voids may be identified.

[0033] Furthermore, in step S121, voids occurring at the adhesive interface between the vulcanized rubber and the metal may be identified as the specific target. This adhesive interface is formed around metal crystal particles of the component to be analyzed. Therefore, in step S121, metal crystal particles of the component to be analyzed are identified, and voids existing at the adhesive interface around the identified particles are identified as the specific target. The particles of the component to be analyzed, like the voids, are identified using the proportion of X-ray absorption by each component, with the maximum X-ray absorption by the component to be analyzed in the X-ray transmission image data D1 being set to 100%. Specifically, the distribution of metal component particles and the distribution of voids in the X-ray transmission image data D1a and D1b of the pre-elongation sample Sa and the elongated sample Sb, respectively, are compared to identify the voids occurring at the adhesive interface between the vulcanized rubber and the metal.

[0034] In step S122, the type of each element of the analysis target component present around the position in the analysis image data D2b corresponding to the position where the void was identified in the X-ray transmission image data D1b is identified. For example, the calculation device 4 outputs the X-ray transmission image data D1b and the analysis image data D2b as the analysis result to the output unit 9. Alternatively, data in which the X-ray transmission image data D1b and the analysis image data D2b are superimposed is output to the output unit 9 as the analysis result. Based on the data output to the output unit 9, the type of each element of the analysis target component present around the position in the analysis image data D2b corresponding to the position where the void was identified in the X-ray transmission image data D1b is identified.

[0035] Figure 4 shows a schematic representation of a copper (Cu) particle of metallic crystals in the elongated sample Sb with an elongation of 22% and the voids that have formed around the particle. The gray solid in the center of Figure 4 represents a copper (Cu) particle of metallic crystals, and the multiple gray solids surrounding the copper particle represent voids. The solid triangular prism in Figure 4 represents a cuprous sulfide (CuS) particle, and the hexagonal prism represents a cupric sulfide (CuS) particle. The dashed-dotted line in Figure 4 indicates the outer edge of the adhesive interface around the void, and the dashed line indicates the outer edge of the copper particle.

[0036] The periphery of the void refers to a predetermined region on the outer periphery of the void. The predetermined region can be set arbitrarily, but it need only encompass the entire periphery of the void and include elements that influenced the formation and growth of the void. These elements are present at the adhesive interface formed around the metal crystal particle of the component to be analyzed. Therefore, it is not necessary to identify the type of each element of the component to be analyzed throughout the entire periphery of the void; it is sufficient to identify the type of each element of the component to be analyzed that exists in the region between the void and the metal crystal particle of the component to be analyzed, i.e., the adhesive interface formed around the particle. The adhesive interface is a region that extends from the periphery of the particle outward, for example, by approximately 10 μm to 30 μm, and surrounds the entire periphery of the particle.

[0037] Copper (Cu) particles are surrounded by cupric sulfide (CuS) and cuprous sulfide (CuS), with a high concentration of cupric sulfide in the areas between the voids and the copper particles. It is known that metallic crystalline copper and cuprous sulfide transform into the more brittle cupric sulfide as moist heat aging progresses. Therefore, the presence of cupric sulfide at the adhesive interface around the copper particles indicates the progression of moist heat aging. Thus, the occurrence and growth of voids in stretched samples is related to the increase in cupric sulfide as moist heat aging progresses, and an increase in cupric sulfide tends to increase the rate of void occurrence and growth.

[0038] As described above, according to this embodiment, voids are identified using the X-ray transmission image data D1a and D1b, and the type of each element of the analysis target component surrounding the position in the analysis image data D2b corresponding to the position where the void was identified in the X-ray transmission image data D1b is identified. In this way, by using multiple different types of data, the type of each element of the analysis target component present around the void can be identified with high accuracy. Since the degree of void generation and growth varies depending on the progress of moist heat aging in the elongated sample Sb, identifying the type of each element of the analysis target component present around the void can be used to determine the progress of moist heat aging in the elongated sample Sb. The progress of moist heat aging is closely related to the degree of deterioration in adhesion between vulcanized rubber and metal. Therefore, identifying the type of each element of the analysis target component present around the void can be used to determine the adhesion between vulcanized rubber and metal with high accuracy. This significantly contributes to preventing adhesive failure and adhesion deterioration in metal-rubber composite materials.

[0039] To evaluate the adhesion between vulcanized rubber and metal, the analysis results output to the output unit 9 can be used as is, but it is also preferable to calculate the feature amount of the analysis target component present around the identified voids using the calculation device 4 based on the analysis results, and use the calculated feature amount as the evaluation index. This feature can be selected arbitrarily. In addition, the feature amount of the analysis target component present at the adhesive interface around the metal crystal particles of the analysis target component near the identified voids can also be used as the evaluation index.

[0040] For example, the sulfidity of the analyzed component present around the voids is used as an evaluation index. The sulfidity indicates the proportion of the analyzed component that has been sulfided. For example, the sulfidity of the copper component is calculated as the ratio of the amount of cupric sulfide (CuS) present to the amount of all copper components (Cu, CuS, CuS) present around the voids. Similarly, the sulfidity of the zinc component is calculated as the ratio of the amount of zinc sulfide (ZnS) present to the amount of all zinc components (Zn, ZnS) present around the voids. The sulfidity of the analyzed component is highly correlated with the degree of progress of moist heat aging; the higher the sulfidity, the greater the degree of progress of moist heat aging. Therefore, by using the sulfidity of the analyzed component as an evaluation index, the adhesion between vulcanized rubber and metal can be more accurately determined.

[0041] Additionally, the abundance ratio of each element in the same type of analyzed component present around the voids is used as an evaluation index. The abundance ratio is the ratio of the abundance of each element of a different type to the abundance of all elements in the analyzed component. In samples not subjected to moist heat aging, the abundance ratio of copper (Cu) and cuprous sulfide (CuS) is higher than the abundance ratio of cupric sulfide (CuS). On the other hand, in samples subjected to moist heat aging, the abundance ratio of cupric sulfide (CuS) is higher than the abundance ratio of copper (Cu) and cuprous sulfide (CuS). Similarly, in samples not subjected to moist heat aging, the abundance ratio of zinc (Zn) is higher than the abundance ratio of zinc sulfide (ZnS), and in samples subjected to moist heat aging, the abundance ratio of zinc sulfide (ZnS) is higher than the abundance ratio of zinc (Zn). Thus, the abundance ratio of each element in the same type of analyzed component is highly correlated with the degree of moist heat aging. The greater the abundance ratio of metal sulfides with higher valences, the greater the degree of moist heat aging. Therefore, by using the abundance ratio of each element in the same type of analyzed component present around the void as an evaluation index, it is possible to more accurately grasp the adhesion between vulcanized rubber and metal.

[0042] In the above-described embodiment, the adhesion between vulcanized rubber and metal was evaluated using the unstretched sample Sa and the stretched sample Sb. However, the adhesion between vulcanized rubber and metal can also be evaluated using only the stretched sample Sb. For example, the adhesion of multiple stretched samples Sb obtained by subjecting multiple new samples with different specifications to the same moist heat aging treatment can be evaluated. This allows the relative superiority and inferiority of adhesion after moist heat aging treatment to be determined (the relative superiority and inferiority of each specification can be determined). In other words, it is not necessary to evaluate the adhesion in an unstretched state (a state with an elongation rate of 0%). Note that, when evaluating adhesion using only stretched samples Sb, the porosity (number of voids and void size) of each stretched sample Sb does not affect the superiority or inferiority of adhesion. For example, the stretched sample Sb with a larger porosity may have superior adhesion. Furthermore, when evaluating using only stretched samples Sb, it is preferable to obtain multiple X-ray transmission image data D1b for stretched samples Sb with different elongations. [Example]

[0043] Using the vulcanized rubber samples shown in Table 1 below, the adhesion between the vulcanized rubber and metal was evaluated using the same procedure as the evaluation method shown in FIG. 2 above.

[0044] [Table 1]

[0045] In the sample formulations shown in Table 1, the amount of each compounding ingredient is shown as parts by mass relative to 100 parts by mass of the rubber component (natural rubber). One part by mass of brass powder was mixed with unvulcanized rubber obtained by blending each of the compounding ingredients shown in Table 1 to produce samples. The brass powder had a mixture ratio of 75% copper and 25% zinc, with a particle size ranging from 0.2 μm to 3 μm. The produced samples were subjected to a moist heat aging treatment under the conditions of a heating temperature of 70°C, humidity of 96% RH, and a treatment period of 3 days.

[0046] In the data acquisition step S110, CT and CT-XAFS measurements were performed using the SPring-8 BL36XU synchrotron radiation facility as the XAFS imaging analyzer 3. The specimen used was a cylinder with a diameter of 0.8 mm at both bases and a height (length in the elongation direction) of 0.4 mm, extracted from a sample that had been subjected to moist heat aging. Each base of the cylinder was attached to a stretching device 2, and the cylinder was stretched to elongations of 0%, 11%, and 22%. The copper component was used as the target component, and the X-ray irradiation energy in the CT measurement was 9 keV to acquire three-dimensional X-ray transmission image data D1a and D1b at different elongation states. The X-ray irradiation energy in the CT-XAFS measurement was varied within the range of 8.7 keV to 10.8 keV, which includes the K-shell absorption edge of the copper component. The sample was stretched at an elongation rate of 22% and the X-ray absorption fine structure was measured multiple times while being rotated, and three-dimensional analytical image data D2b shown in FIG. 11 was obtained.

[0047] In the evaluation step S120, the maximum X-ray absorption of the copper component in the acquired X-ray transmission image data D1a and D1b was used as the reference (100%). The percentage of X-ray absorption of the copper component was set to more than 8.9% and less than 100%, the percentage of X-ray absorption of the vulcanized rubber was set to more than 0.7% and less than 8.9%, and the percentage of X-ray absorption of the voids was set to 0% or more and less than 0.7%. Figures 5, 6, and 7 show the distribution of metal components in the X-ray transmission image data D1a and D1b at elongations of 0%, 11%, and 22%, respectively. Figures 8, 9, and 10 show the distribution of voids in the X-ray transmission image data D1a and D1b at elongations of 0%, 11%, and 22%, respectively. In Figures 5 to 7, the black areas indicate metal components, and the white areas indicate vulcanized rubber and voids. In Figures 8 to 10, the black areas indicate voids, and the white areas indicate metal components and vulcanized rubber.

[0048] Figure 11 shows a three-dimensional visualization of the copper component metal crystals, copper (Cu), cuprous sulfide (CuS), and cupric sulfide (CuS), in a sample stretched at an elongation rate of 22%. In Figure 11, the gray areas represent copper (Cu) and cuprous sulfide (CuS), and the white areas represent cupric sulfide (CuS).

[0049] Based on the X-ray transmission image data D1a and D1b shown in Figures 5 to 10, voids that existed around copper particles in a sample stretched at 22% elongation and that developed as the elongation increased were identified. Next, the elements of the copper component present around the position in the analysis image data D2b shown in Figure 11, which corresponds to the position where the void was identified in the X-ray transmission image data D1b shown in Figure 10, were identified. As a result, it was found that the presence of cupric sulfide affects the rate of void formation and growth. Furthermore, voids due to adhesion delamination between the vulcanized rubber and the metal were observed near the copper particles, and the presence of cupric sulfide particles was confirmed around the voids.

[0050] The present invention is not limited to a specific embodiment, and various modifications and variations are possible within the scope of the gist of the present invention.

[0051] The present disclosure includes the following inventions. Invention 1: A method for evaluating adhesion between rubber and metal, which uses vulcanized rubber obtained by vulcanizing unvulcanized rubber containing metal with sulfur as an evaluation sample, and utilizes data obtained by irradiating the sample with X-rays, The method includes a data acquisition step of acquiring X-ray transmission image data and analytical image data as the data by using the vulcanized rubber in a stretched state as the sample, and an evaluation step, In the data acquisition step, at least one type of component among the metal components derived from the metal is treated as an analysis target component, and metal compounds having different analysis target components and metal compounds of the same type of analysis target component but with different valences are treated as particles of different types, and the X-ray transmission image data is obtained by setting the irradiation energy of the X-rays irradiated to the sample to a predetermined fixed value near the absorption edge of the analysis target component, and the analysis image data is obtained by X-ray absorption fine structure analysis using a plurality of data obtained by changing the irradiation energy of the X-rays within a predetermined energy region including the absorption edge of the analysis target component, In the evaluation process, a calculation device performs data processing to identify voids present in the sample based on the X-ray transmission image data, and the type of each particle of the component to be analyzed present around a position in the analysis image data corresponding to the position where the void was identified in the X-ray transmission image data is determined. This is a method for evaluating adhesion between rubber and metal. Invention 2: In the evaluation step, the calculation device calculates the sulfidity of the component to be analyzed around a position in the analysis image data corresponding to the position where the void is identified in the X-ray transmission image data, and the sulfidity is used as an evaluation index to evaluate the adhesion between the vulcanized rubber and the metal. This is the method for evaluating adhesion between rubber and metal described in Invention 1. Invention 3: The method for evaluating adhesion between rubber and metal according to Invention 1 or 2, wherein in the evaluation step, the computing device calculates an abundance ratio of each of the metal compounds of the same type of metal component around a position in the analysis image data corresponding to the position where the void is identified in the X-ray transmission image data, and the abundance ratio is used as an evaluation index to evaluate the adhesion between the vulcanized rubber and the metal. Invention 4: The vulcanized rubber in an unstretched state was used as the sample, and this sample was referred to as a pre-stretched sample, and the sample in the stretched state was referred to as a stretched sample. A method for evaluating adhesion between rubber and metal according to any one of Inventions 1 to 3, wherein in the evaluation step, the voids present in each of the pre-stretch sample and the stretched sample are identified based on the X-ray transmission image data of the pre-stretch sample and the stretched sample, and the voids that have occurred due to stretching are identified from the voids present in the stretched sample based on a comparison between the voids in the pre-stretch sample and the voids in the stretched sample. Invention 5: In the data acquisition step, the elongation of the sample is increased stepwise to acquire a plurality of pieces of X-ray transmission image data with different elongations; A method for evaluating adhesion between rubber and metal according to any one of Inventions 1 to 4, in which the evaluation step identifies the voids present in each of the samples having different elongation rates based on the X-ray transmission image data, and identifies the voids that have occurred as the elongation rate increases from the voids present in the sample having the highest elongation rate based on a comparison of the voids in each of the samples. Invention 6: A method for evaluating adhesion between rubber and metal according to any one of Inventions 1 to 5, wherein in the evaluation step, the computing device executes data processing to identify particles of the component to be analyzed based on the X-ray transmission image data, and identifies the voids present around the particles of the component to be analyzed from among the voids present in the sample. Invention 7: The method for evaluating adhesion between rubber and metal according to any one of Inventions 1 to 6, wherein three-dimensional image data is acquired as the X-ray transmission image data. Invention 8: A method for evaluating adhesion between rubber and metal according to any one of Inventions 1 to 7, wherein the sample is a cylinder whose width dimension in a direction perpendicular to the extension direction of the sample is smaller than the beam diameter of the X-rays. [Explanation of symbols]

[0052] 1. Rating System 2 Stretching device 3 X-ray absorption fine structure imaging measurement device (XAFS imaging measurement device) 4 Arithmetic unit 5. Processing unit 6 Main memory 7 Auxiliary storage 8 Input section 9 Output section Sa Sample before extension Sb elongated sample D1a, D1b X-ray transmission image data D2b analysis image data

Claims

1. A method for evaluating adhesion between rubber and metal, which uses vulcanized rubber obtained by vulcanizing unvulcanized rubber containing metal with sulfur as an evaluation sample, and utilizes data obtained by irradiating the sample with X-rays, The method includes a data acquisition step of acquiring X-ray transmission image data and analytical image data as the data by using the vulcanized rubber in a stretched state as the sample, and an evaluation step, In the data acquisition step, at least one type of component among the metal components derived from the metal is treated as an analysis target component, and metal compounds having different analysis target components and metal compounds of the same type of analysis target component but with different valences are treated as elements of different types, and the X-ray transmission image data is obtained by setting the irradiation energy of the X-rays irradiated to the sample to a predetermined fixed value near the absorption edge of the analysis target component, and the analytical image data is obtained by X-ray absorption fine structure analysis using a plurality of data obtained by changing the irradiation energy of the X-rays within a predetermined energy region including the absorption edge of the analysis target component. In the evaluation process, a calculation device performs data processing to identify voids present in the sample based on the X-ray transmission image data, and the type of each of the elements of the components to be analyzed present around the position in the analysis image data corresponding to the position where the void was identified in the X-ray transmission image data is determined. This is a method for evaluating adhesion between rubber and metal.

2. 2. The method for evaluating adhesion between rubber and metal according to claim 1, wherein in the evaluation step, the arithmetic device calculates the degree of sulfidation of the component to be analyzed around a position in the analysis image data corresponding to the position where the void is identified in the X-ray transmission image data, and the degree of sulfidation is used as an evaluation index to evaluate the adhesion between the vulcanized rubber and the metal.

3. 2. A method for evaluating adhesion between rubber and metal as described in claim 1, wherein in the evaluation process, the calculation device calculates the abundance ratio of each metal compound of the same type of metal component around a position in the analysis image data corresponding to the position where the void is identified in the X-ray transmission image data, and the abundance ratio is used as an evaluation index to evaluate the adhesion between the vulcanized rubber and the metal.

4. The vulcanized rubber in an unstretched state was used as the sample, and this sample was referred to as a pre-stretched sample, and the sample in the stretched state was referred to as a stretched sample.

2. A method for evaluating adhesion between rubber and metal as described in claim 1, wherein in the evaluation process, the voids present in each of the pre-stretch sample and the stretched sample are identified based on the X-ray transmission image data of the pre-stretch sample and the stretched sample, and the voids that have occurred due to stretching are identified from the voids present in the stretched sample based on a comparison between the voids in the pre-stretch sample and the voids in the stretched sample.

5. In the data acquisition step, the elongation of the sample is increased stepwise to acquire a plurality of pieces of X-ray transmission image data with different elongations; A method for evaluating adhesion between rubber and metal as described in claim 1 or 4, wherein in the evaluation process, the voids present in each of the samples with different elongation rates are identified based on the X-ray transmission image data of each sample, and based on a comparison of the voids in each sample, the voids that occur as the elongation rate increases are identified from the voids present in the sample with the highest elongation rate.

6. A method for evaluating adhesion between rubber and metal as described in claim 1 or 4, wherein in the evaluation process, the calculation device performs data processing to identify particles of the component to be analyzed based on the X-ray transmission image data, and identifies the voids present around the particles of the component to be analyzed from among the voids present in the sample.

7. The method for evaluating adhesion between rubber and metal according to claim 1 or 4, wherein three-dimensional image data is acquired as the X-ray transmission image data.

8. 5. The method for evaluating adhesion between rubber and metal according to claim 1, wherein the sample is a columnar body whose width in a direction perpendicular to the extension direction of the sample is smaller than the beam diameter of the X-rays.

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