Degradation test method for rubber composition

Abstract

To provide a highly accurate degradation test method for rubber compositions.SOLUTION: The degradation test method for rubber compositions includes: a preparation step of preparing a cylindrical vulcanized rubber test piece having at least an outer layer rubber and an inner layer rubber; a heating step of heating the vulcanized rubber test piece; and an abrasion step of abrading a surface of the vulcanized test piece by pressing it against a pressing portion while rotating the vulcanized test piece circumferentially. The vulcanized rubber test piece is obtained by vulcanization-bonding at least an outer layer rubber composition containing a plasticizer and an inner layer rubber composition having a different formulation from the outer layer rubber composition. The heating step and the abrasion step are performed simultaneously.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for testing the deterioration of a rubber composition. [Background technology]

[0002] In general, hardening of pneumatic tires due to changes over time is a factor that causes a decline in tire performance. While the physical properties and performance of new tires are important, performance decline due to changes in rubber over time is often not given much importance due to the lack of a method for accurately evaluating it. There is also a need for a simple and accurate method for evaluating the wear performance of vulcanized rubber that reflects market evaluations of changes in rubber hardness. Patent Document 1 proposes a method for evaluating physical and chemical wear based on the amount of wear in air and in a nitrogen atmosphere, as well as a rubber composition that suppresses wear. However, further improvements are needed in methods for evaluating changes in rubber over time. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-46069 Summary of the Invention [Problem to be solved by the invention]

[0004] The hardening phenomenon due to changes over time is thought to be caused by the plasticizer components contained in the cap rubber in the tread portion that comes into contact with the road leaking out onto the road, or by the plasticizer in the cap rubber diffusing internally into the internal rubbers, such as the base rubber and breaker rubber, that are placed inside the cap rubber. The behavior of the softener in the cap rubber diffusing into the internal rubber is thought to be reproducible by placing a tire rubber piece containing the cap rubber, base rubber, and breaker rubber in a heating oven, but because the external leak and internal diffusion described above are thought to be the cause of the hardening in an actual tire, this type of processing method is thought to lack reproducibility as a method for simulating changes in a tire.

[0005] As a result of extensive research, the present inventors have noticed that the outflow and internal diffusion of plasticizer in the outer layer rubber have a significant effect on the hardening of the outer layer rubber, and have discovered a method that did not previously exist to evaluate both the outflow and internal diffusion of plasticizer in the outer layer rubber, thereby completing the present invention.

[0006] An object of the present invention is to solve the above problems and to provide a highly accurate method for testing the deterioration of a rubber composition. [Means for solving the problem]

[0007] The present invention includes the steps of: preparing a cylindrical vulcanized rubber test piece having at least an outer rubber layer and an inner rubber layer; a heating step of heating the vulcanized rubber test piece; and a wearing step of the vulcanized test piece by rotating the vulcanized test piece in a circumferential direction and pressing the vulcanized test piece against a pressing part to wear down the surface of the vulcanized test piece, The vulcanized rubber test piece is obtained by vulcanizing and bonding at least an outer layer rubber composition containing a plasticizer and an inner layer rubber composition having a different formulation from the outer layer rubber composition, The heating step and the abrasion step are performed simultaneously. The present invention relates to a method for testing the deterioration of a rubber composition. [Effects of the Invention]

[0008] The present invention provides a rubber composition degradation testing method that includes a preparation step of preparing a cylindrical vulcanized rubber test piece having at least an outer layer rubber and an inner layer rubber, a heating step of heating the vulcanized rubber test piece, and an abrasion step of rotating the vulcanized rubber test piece in a circumferential direction while pressing it against a pressing unit to abrade the surface of the vulcanized rubber test piece, wherein the vulcanized rubber test piece is formed by vulcanizing and bonding at least an outer layer rubber composition containing a plasticizer and an inner layer rubber composition having a different formulation from the outer layer rubber composition, and the heating step and the abrasion step are performed simultaneously, thereby providing a highly accurate rubber composition degradation testing method. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing one embodiment of a pneumatic tire to which the above-described rubber composition degradation test method can be applied. [Figure 2] FIG. 2 is a flowchart showing one embodiment of the method for testing the deterioration of the rubber composition. [Figure 3] FIG. 3 is a front view of the test piece prepared in the preparation step of FIG. [Figure 4] FIG. 4 is a cross-sectional view of the test piece of FIG. 3 taken along line IV-IV. [Figure 5] FIG. 5 is a plan view showing a part of the polishing plate used in each measurement step of FIG. [Figure 6] FIG. 6 is a partial cross-sectional view of the polishing plate of FIG. 5 taken along line VI-VI. [Figure 7] FIG. 7 is a schematic diagram for explaining the wear test in each measurement step of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] The degradation test method includes the steps of: preparing a cylindrical vulcanized rubber test piece having at least an outer layer rubber and an inner layer rubber; heating the vulcanized rubber test piece; and abrading the surface of the vulcanized rubber test piece by rotating the vulcanized rubber test piece circumferentially and pressing it against a pressing unit. The cylindrical vulcanized rubber test piece has at least an outer layer rubber and an inner layer rubber, which are formed by at least vulcanizing and bonding an outer layer rubber composition containing a plasticizer to an inner layer rubber composition having a different formulation from the outer layer rubber composition. In the degradation test method, the heating step and the abrasion step are performed simultaneously. This allows for easy measurement of the degradation over time of a rubber composition constituting a tire or the like having an outer layer rubber and an inner layer rubber, thereby making it possible to easily evaluate the degradation over time.

[0011] The rubber composition degradation test method can be suitably applied to, for example, an outer layer rubber constituting an outer layer component of a tire and an inner layer rubber constituting an inner layer component disposed inward of the outer layer component. Specifically, the degradation test method can be applied to a cylindrical vulcanized rubber test piece having an outer layer rubber, such as a cap rubber in the road-contacting portion of the tread, and an inner layer rubber, such as a base rubber or breaker rubber, disposed inside the cap rubber. In this case, a cylindrical vulcanized rubber test piece is prepared by vulcanizing and bonding at least a rubber composition for a cap rubber (corresponding to an outer layer rubber composition) containing a plasticizer and a rubber composition for a base rubber or a breaker rubber (corresponding to an inner layer rubber composition) with a different formulation from the cap rubber composition. Next, a heating step is performed to heat the vulcanized rubber test piece, and a wear step is simultaneously performed to wear the surface of the vulcanized rubber test piece by pressing the vulcanized test piece against a pressing unit while rotating it circumferentially. Because this method involves heating and abrasion simultaneously, it is easier to accurately reproduce the state of tire tread degradation due to driving in a short period of time compared to, for example, a method that only involves abrasion.

[0012] Hereinafter, details will be described based on preferred embodiments with reference to the drawings as appropriate, but the above-mentioned rubber composition degradation test method is not limited to the following embodiments and various modifications are possible within the scope of the claims. In addition, unless otherwise specified in this specification, "X to Y" means "X or more and Y or less", and "%" means "mass %".

[0013] Hereinafter, an evaluation method according to one embodiment of the rubber composition deterioration test method will be specifically described with reference to FIGS.

[0014] FIG. 1 is a cross-sectional view showing a tire 2 according to one embodiment. In this drawing, the vertical direction is the radial direction of the tire 2, the horizontal direction is the axial direction of the tire 2, and the direction perpendicular to the paper surface is the circumferential direction of the tire 2. In FIG. 1, the dashed-dotted line CL represents the equatorial plane of the tire 2. Note that in FIG. 1, only the cross-sectional outline of each component is shown.

[0015] The tire 2 includes a tread 4, a pair of sidewalls 6, a pair of beads 8, a carcass 10, a belt 12, a band 14, and an inner liner 16. The tire 2 is a pneumatic tire mounted on a passenger vehicle.

[0016] The tread 4 has a shape that is convex outward in the radial direction. The tread 4 has a tread surface 20. The tread surface 20 has grooves 22 formed therein.

[0017] Each sidewall 6 extends substantially radially inward from an end of the tread 4. Each bead 8 is located radially inward of the sidewall 6. Each bead 8 includes a core 24 and an apex 26 extending radially outward from the core 24. The carcass 10 is made up of a carcass ply 28. The carcass ply 28 is laid between both beads 8 and extends along the tread 4 and sidewall 6. The carcass ply 28 is folded around the core 24 from the axially inner side to the axially outer side.

[0018] The belt 12 is located radially inside the tread 4 and is laminated with the carcass 10. The belt 12 is composed of an inner layer 12a and an outer layer 12b. The band 14 is laminated radially outside the belt 12. Although not shown, the band 14 is composed of a cord and a topping rubber. The cord extends substantially in the circumferential direction and is wound spirally. The band 14 has a so-called jointless structure. The inner liner 16 is located radially inside the carcass 10 and is joined to the inner surface of the carcass 10.

[0019] 2 shows a flowchart of one embodiment of the rubber composition degradation test method. As shown in the figure, this method includes a preparation step, a heating step, and an abrasion step, and further includes the heating step of abrading the rubber composition while heating it, and an evaluation step of evaluating the degradation of the rubber composition over time based on the results of the abrasion step. The degradation test method may further include other steps.

[0020] In the preparation step, an outer layer rubber composition containing a plasticizer and an inner layer rubber composition having a different formulation from the outer layer rubber composition are used. For example, an unvulcanized rubber sheet made of the outer layer rubber composition, an unvulcanized rubber sheet made of the inner layer rubber composition, and, if necessary, other unvulcanized rubber sheets are vulcanized and bonded together to prepare a cylindrical vulcanized rubber test piece having at least an outer layer rubber formed from the outer layer rubber composition and an inner layer rubber formed from the inner layer rubber composition. If the formulations are the same, there is a concern that the internal diffusion of the plasticizer cannot be evaluated.

[0021] The cylindrical vulcanized rubber test piece is preferably prepared by first vulcanizing a sheet of unvulcanized inner layer rubber composition (first vulcanization), then attaching a sheet of outer layer rubber composition to the surface of the vulcanized inner layer rubber sheet, and vulcanizing both sheets (second vulcanization) to achieve a vulcanization bond. If two or more unvulcanized rubbers with different formulations are vulcanized once to form a vulcanization bond, the two rubbers may mix during vulcanization, resulting in an uneven thickness of the outer layer rubber around the circumference of the test piece, potentially making it difficult to accurately evaluate changes in the plasticizer in the outer layer rubber. For example, the inner layer rubber may be vulcanized, and then the unvulcanized outer layer rubber may be wrapped around the vulcanized inner layer rubber and vulcanized to achieve a uniform thickness of the outer layer rubber around the circumference of the test piece, allowing for accurate evaluation of changes in the plasticizer in the outer layer rubber.

[0022] In the tire 2 of FIG. 1 , for example, a cylindrical vulcanized rubber test piece having an outer rubber layer and an inner rubber layer can be used that includes at least the tread rubber (vulcanized rubber obtained by vulcanizing a tread rubber composition) that constitutes the tread 4, the belt rubber (vulcanized rubber obtained by vulcanizing a belt rubber composition) that constitutes the belt 12, and / or the band rubber (vulcanized rubber obtained by vulcanizing a band rubber composition) that constitutes the band 14. Specifically, first, a sheet of unvulcanized tread rubber composition is vulcanized, and then a sheet of unvulcanized belt rubber composition and / or a sheet of band rubber composition are attached to the surface of the prepared vulcanized tread rubber sheet, and both are vulcanized to form a vulcanization bond. Then, by appropriately cutting or the like, a cylindrical vulcanized rubber test piece having the tread rubber and the belt rubber and / or the band rubber can be prepared. To evaluate the ease of plasticizer diffusion between tire components, it is desirable that at least two or more types of rubber are vulcanized and bonded together. If the material is not vulcanized and bonded, for example, if it is bonded with an adhesive, the adhesive phase will inhibit the diffusion of the plasticizer, so there is a concern that it may not be suitable for evaluating the diffusion of the plasticizer.

[0023] Fig. 3 is a front view of a vulcanized rubber test piece 32 prepared in this embodiment. In Fig. 3, the up-down direction is the circumferential direction, and the left-right direction is the axial direction. Fig. 4 is a cross-sectional view taken along line IV-IV in Fig. 3. In Fig. 4, the direction perpendicular to the paper surface is the axial direction.

[0024] As shown in Figures 3 and 4, the vulcanized rubber specimen 32 is cylindrical. The vulcanized rubber test piece 32 may have an outer diameter of 78 mm, an inner diameter of 34 mm, and an axial width of 18 mm, for example.

[0025] The double-headed arrow W shown in Fig. 3 indicates the axial width of the vulcanized rubber test piece 32. The axial width W of the vulcanized rubber test piece 32 is not particularly limited, but from the viewpoint of easily installing the outer layer rubber necessary for evaluating plasticizer outflow, it is preferably 10 mm or more, more preferably 15 mm or more, and from the viewpoint of making the vulcanization mold compact, it is preferably 30 mm or less, more preferably 25 mm or less.

[0026] The double-headed arrows di and do shown in FIG. 4 represent the inner diameter and outer diameter of the vulcanized rubber test piece 32, respectively. The inner diameter di of the vulcanized rubber test piece 32 is not particularly limited, but from the viewpoint of easily installing the outer layer rubber necessary for evaluating the outflow of plasticizer, it is preferably 10 mm or more, more preferably 30 mm or more, and from the viewpoint of making the vulcanization mold compact, it is preferably 90 mm or less, more preferably 40 mm or less. The outer diameter do of the vulcanized rubber test piece 32 is not particularly limited, but is preferably 50 mm or more, more preferably 75 mm or more, from the viewpoint of easily installing the outer layer rubber necessary for evaluating plasticizer outflow, and is preferably 150 mm or less, more preferably 85 mm or less, from the viewpoint of making the vulcanization mold more compact.

[0027] The vulcanized rubber test piece 32 in FIGS. 3 and 4 has an outer rubber layer 32o and an inner rubber layer 32i. The thickness To of the outer rubber layer 32o is preferably 1 mm or more, more preferably 2 mm or more, and is preferably 15 mm or less, more preferably 7 mm or less. The thickness Ti of the inner rubber layer is preferably 10 mm or more, more preferably 15 mm or more, and is preferably 25 mm or less, more preferably 20 mm or less.

[0028] There are no particular limitations on the method for obtaining tire components made of vulcanized rubber. Furthermore, there are no particular limitations on the apparatus and equipment for manufacturing the tire 2 equipped with the tire components made of vulcanized rubber, and known apparatus and equipment can be used. For example, the tire 2 equipped with the tread 4 containing vulcanized rubber and the belt 12 and / or band 14 containing vulcanized rubber is manufactured by the following procedure.

[0029] First, an unvulcanized rubber composition for each component is prepared, containing a base rubber and various additives typically used in the tire field. Next, this rubber composition is extruded into shapes such as a tread 4, belt 12, or band 14, and then laminated with other tire components on a known tire building machine to obtain a raw cover (unvulcanized tire). This raw cover is placed in a mold. The outer surface of the raw cover abuts against the cavity surface of the mold. The inner surface of the raw cover abuts against a bladder or core. The raw cover is pressurized and heated within the mold. The pressure and heat cause the rubber composition of the raw cover to flow. The heat causes a crosslinking reaction in the rubber, resulting in the tire 2. A mold having an uneven pattern on its cavity surface is used, thereby forming the uneven pattern in the tire 2.

[0030] In the cylindrical vulcanized rubber test piece 32 having an outer layer rubber and an inner layer rubber, the types of base rubber, plasticizer, and various additives blended into the outer layer rubber composition containing a plasticizer and the inner layer rubber composition are not particularly limited.

[0031] Preferred examples of the base rubber include natural rubber, styrene butadiene rubber, butadiene rubber, epoxidized natural rubber, isoprene rubber, ethylene propylene diene rubber, chloroprene rubber, acrylonitrile butadiene rubber, acrylonitrile butadiene styrene rubber, etc. Two or more types of base rubbers may be used in combination.

[0032] In this specification, the plasticizer is a material that imparts plasticity to the rubber component, and is a concept that includes both plasticizers that are liquid (liquid state) at 25°C and plasticizers that are solid at 25°C. Examples of the plasticizer include resin components, oils, liquid polymers, and ester-based plasticizers. These plasticizers may be derived from petroleum, biomass, or naphtha recycled from rubber or non-rubber products. Low-molecular-weight hydrocarbon components obtained by pyrolysis and extraction of used tires or products containing various components may also be used as plasticizers. These plasticizers may be used alone or in combination.

[0033] Other additives include known compounding materials in the rubber field, such as fillers (silica, carbon black, etc.), silane coupling agents, antioxidants, stearic acid, zinc oxide, wax, sulfur, and vulcanization accelerators.

[0034] The outer layer rubber composition containing a plasticizer has a plasticizer content Po (parts by mass) per 100 parts by mass of the rubber component of preferably 1 part by mass or more, more preferably 5 parts by mass or more, even more preferably 7 parts by mass or more, and is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, even more preferably 60 parts by mass or less.

[0035] The rubber composition for the inner layer has a plasticizer content Pi (parts by mass) per 100 parts by mass of the rubber component of preferably 0 parts by mass or more, more preferably 1 part by mass or more, even more preferably 5 parts by mass or more, and preferably 90 parts by mass or less, more preferably 70 parts by mass or less, even more preferably 50 parts by mass or less.

[0036] The difference (|Po-Pi|) between the plasticizer content Po (parts by mass) per 100 parts by mass of the rubber component of the outer layer rubber composition and the plasticizer content Pi (parts by mass) per 100 parts by mass of the rubber component of the inner layer rubber composition is desirably 5 parts by mass or more, from the viewpoint of ensuring a concentration gradient of the plasticizer between the rubbers to promote diffusion and correctly evaluating changes in the plasticizer in the outer layer rubber. The above |Po-Pi| is preferably 7 parts by mass or more, more preferably 9 parts by mass or more, and is preferably 70 parts by mass or less, more preferably 40 parts by mass or less. It is desirable that Po>Pi.

[0037] In the rubber composition for the outer layer, the sulfur content is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and preferably 10.0 parts by mass or less, more preferably 5.0 parts by mass or less, per 100 parts by mass of the rubber component.

[0038] In the rubber composition for the inner layer, the sulfur content is preferably 2.0 parts by mass or more, more preferably 3.0 parts by mass or more, per 100 parts by mass of the rubber component, from the viewpoint of enabling two vulcanizations and achieving good vulcanization adhesion between the outer layer rubber and the inner layer rubber, and is also preferably 20.0 parts by mass or less, more preferably 10.0 parts by mass or less.

[0039] The method for preparing the vulcanized rubber test piece 32 is not particularly limited. For example, the base rubber and various additives described above may be introduced into an open roll, a Banbury mixer, or the like, and kneaded to prepare a rubber composition. The vulcanized rubber test piece 32 may then be prepared by heating and pressurizing the rubber composition in a mold of a predetermined shape. Alternatively, the prepared rubber composition may be press-vulcanized to produce a rubber sheet, which may then be appropriately cut and attached to the outer circumferential surface of a rotating body to prepare the vulcanized rubber test piece 32. Furthermore, the prepared rubber composition may be extruded to match the shape of the tread 4, belt 12, band 14, or the like, and then heated and pressurized together with other tire components in a vulcanizer to produce a tire 2. Sheet-shaped rubber pieces cut from the tread 4, belt 12, band 14, or the like of the tire 2 may then be attached to the outer circumferential surface of a rotating body to prepare the vulcanized rubber test piece 32. The material of the rotating body to which the rubber sheet or sheet-shaped rubber pieces are attached is not particularly limited. However, from the viewpoint of improving evaluation accuracy, vulcanized rubber having a hardness comparable to that of the rubber sheet or rubber pieces is preferred.

[0040] The vulcanization in producing the vulcanized rubber test piece 32 is not particularly limited and may be carried out by a known method and under known conditions, for example, by subjecting a rubber composition kneaded with a vulcanizing agent and a vulcanization accelerator to a vulcanization treatment such as press vulcanization. The vulcanization temperature is not particularly limited, but is preferably 120°C or higher, more preferably 140°C or higher, and is preferably 200°C or lower, more preferably 180°C or lower.

[0041] In the above degradation test method, the number of vulcanized rubber test pieces 32 prepared in the preparation step is not particularly limited, but from the viewpoint of evaluation accuracy, it is preferable that two or more vulcanized rubber test pieces 32 are provided in each step.

[0042] In the degradation test method, a heating step of heating the vulcanized rubber test piece 32 prepared in the preparation step and an abrasion step of abrading the surface of the vulcanized test piece 32 by rotating the vulcanized test piece 32 in the circumferential direction and pressing it against a pressing part, respectively. For example, in an accelerated degradation tester equipped with a test piece rotating means for rotating a cylindrical vulcanized rubber test piece having at least two types of outer and inner rubber layers with different formulations vulcanized and bonded together, and a mechanism for raising the rubber temperature to 80°C or higher, the test piece is rolled while abrading the outer rubber layer at a temperature of 80°C or higher and 160°C or lower at a pinhole depth of 1.0 mm into the test piece, thereby providing a test method for evaluating the outflow of plasticizer from the outer rubber layer under the influence of abrasion.

[0043] In this specification, the phrase "the heating step and the abrasion step are performed simultaneously" means that the heating step and the abrasion step are performed so as to overlap in time. In other words, the phrase is not particularly limited as long as it is an embodiment other than an embodiment in which the heating step is started and finished after the abrasion step is started and finished, or an embodiment in which the heating step is started and finished after the abrasion step is started and finished. For example, an embodiment in which the heating step and the abrasion step are started and finished simultaneously, an embodiment in which the abrasion step is started after the heating step is started and before the end of the heating step, and the heating step and the abrasion step are finished, or an embodiment in which the heating step is started after the abrasion step is started and before the end of the abrasion step, and the heating step and the abrasion step are finished, etc. are possible.

[0044] The heating temperature in the heating step is appropriately determined according to the usage environment of the vulcanized rubber to be evaluated.

[0045] The heating step of heating the vulcanized rubber test piece 32 can be carried out using known heating means. The diffusion of plasticizers in the outermost rubber of a tire into the inner rubber is accelerated by time and temperature. Because this diffusion can take several years, it is necessary to heat the rubber test specimen in order to quickly reproduce this phenomenon.

[0046] In the heating step, the temperature to which the vulcanized rubber test piece 32 is heated is preferably 80°C or higher, more preferably 90°C or higher. Therefore, in the degradation test method, it is desirable that the test machine used be equipped with a mechanism that can reach temperatures of 80°C or higher. One method for heating the test piece is to press a friction plate against the test piece with a certain load, thereby heating it to 80°C or higher through frictional heat. Another heating method may be to use a device that applies heat to the test piece, such as a chamber. There is no particular upper limit to the heating temperature, but it is preferably 160°C or lower, more preferably 140°C or lower.

[0047] In the above heating step, the temperature of the vulcanized test piece 32 at a needle penetration depth of 1.0 mm is controlled to preferably 40°C or higher, more preferably 60°C or higher, and even more preferably 80°C or higher, from the viewpoint of promoting the outflow of plasticizer from the outer layer rubber and ensuring accurate evaluation, and is also controlled to preferably 160°C or lower, more preferably 140°C or lower, from the viewpoint of preventing destruction of the rubber during the test and ensuring accurate evaluation.

[0048] In this specification, the "temperature at a pinpoint depth of 1.0 mm" means the temperature of rubber when the needle of a needle thermometer is inserted 1.0 mm into the rubber. The "temperature at a 1.0 mm pinpoint depth" is measured by inserting a pinpoint thermometer 1.0 mm into the surface of the sample immediately after testing and reading the temperature at that time.

[0049] The abrasion step of abrading the vulcanized rubber test piece 32 can be performed using a known abrasion tester capable of abrading test pieces. The type of abrasion tester is not particularly limited, and known abrasion testers such as a DIN abrasion tester, a Lambourn abrasion tester, or an LAT100 abrasion tester may be used, or a test apparatus 100 shown in FIG. 7 may be used.

[0050] The abrasion tester is usually equipped with a simulated road surface for abrading the test specimen. The type of simulated road surface provided in the abrasion tester is not particularly limited. For example, the simulated road surface may be a grindstone, sandpaper, safety walk, or the like, or may be an asphalt road surface, a concrete road surface, or the like. When a grindstone is used as the simulated road surface, the grain size thereof is preferably #60 to #240.

[0051] In the abrasion test, the simulated road surface is pressed against a test piece made of vulcanized rubber, and the test piece and the simulated road surface are moved relative to each other for a predetermined period of time while a load is applied at a predetermined pressure. The method for moving the test piece and the simulated road surface relative to each other is not particularly limited. The test piece may be fixed and the simulated road surface may be moved, or the simulated road surface may be fixed and the test piece may be moved, or the two may be moved relative to each other.

[0052] For example, when performing the abrasion step on a cylindrical vulcanized rubber test piece 32 using the test apparatus 100 shown in Figure 7, the simulated road surface provided in the test apparatus 100 is pressed against the vulcanized rubber test piece 32 to apply a load, and the vulcanized rubber test piece 32 is rotated in its circumferential direction, thereby moving the vulcanized rubber test piece 32 and the simulated road surface relative to each other.

[0053] The load applied to the vulcanized rubber test piece 32 is not particularly limited. In order to reproduce the driving conditions of an actual road surface, the pressing force from the pressing part to the cylindrical vulcanized test piece 32 in the abrasion step is preferably 5000 N / m 2 More than 10,000N / m 2 In addition, from the viewpoint of preventing deformation and damage of the vulcanized rubber test piece 32, it is preferable to set the load to 300,000 N / m 2 Less than or equal to 200,000 N / m2 The following is the result.

[0054] In the abrasion step, the vulcanized rubber test piece 32 is rotated in the circumferential direction and pressed against the pressing unit to abrade the surface of the vulcanized rubber test piece 32. The rotation speed of the cylindrical vulcanized test piece 32 in the circumferential direction is preferably 10 rpm or higher, more preferably 100 rpm or higher, from the viewpoint of reproducing the plasticizer leakage and abrasion of the outer rubber layer of the test piece and accurately evaluating the plasticizer leakage of the outer rubber layer. Furthermore, from the viewpoint of preventing damage to the test piece and accurately evaluating the plasticizer leakage of the outer rubber layer, it is desirable to adjust the rotation speed to preferably 40,000 rpm or lower, more preferably 20,000 rpm or lower, and even more preferably 10,000 rpm or lower. Because the tire is rolling, the rubber sample must be rolling to reproduce the behavior of tire rubber during running. This is because the plasticizer in the outermost rubber of the tire may leak onto the road surface during running and may diffuse into the inner rubber, which contains less plasticizer.

[0055] The rotation time of the vulcanized rubber test piece 32 is appropriately selected within the range of the amount of wear that can be evaluated, but from the viewpoint of measurement accuracy, the rotation time is preferably 5 minutes or more. From the viewpoint of suppressing heat generation and deformation of the vulcanized rubber test piece 32, the rotation time is preferably 120 minutes or less.

[0056] In the abrasion step, the abrasion test may be performed with a slip angle applied to the vulcanized rubber test piece 32. Here, the slip angle is the angle between the rotation plane (equatorial plane) of the cylindrical vulcanized rubber test piece 32 and the direction of movement relative to the simulated road surface. The slip angle is not particularly limited. From the viewpoints of evaluation accuracy and abrasion efficiency, the slip angle is preferably between 0° and 15°.

[0057] A polishing plate having one or many linear protrusions is preferred as a simulated road surface for the abrasion test. The number and arrangement of the linear protrusions on the polishing plate are not particularly limited and are selected appropriately depending on the shape of the vulcanized rubber test piece 32. The material of the polishing plate and the material of each linear protrusion may be the same or different. From the viewpoints of test efficiency and durability, aluminum, stainless steel, iron, etc. are preferably used as the material.

[0058] The length of the linear projections is not particularly limited and may be appropriately selected depending on the shape and size of the vulcanized rubber test piece 32 .

[0059] The cross-sectional shape of the linear protrusions 36 is not particularly limited and may be appropriately selected from a mountain shape, a rectangle, a polygon, etc. The polishing plate 34 may have a plurality of linear protrusions 36 with different cross-sectional shapes.

[0060] Figure 5 is a plan view showing an example of a polishing plate 34 having linear protrusions. In Figure 5, the left-right direction is the length direction, the up-down direction is the width direction, and the direction perpendicular to the paper surface is the height direction. Figure 6 is a cross-sectional view taken along line VI-VI in Figure 5. In Figure 6, the left-right direction is the width direction, and the up-down direction is the height direction.

[0061] 5 and 6 is used for a cylindrical vulcanized rubber test piece 32 as shown in Figures 3 and 4, the length L of the linear projections 36 is preferably greater than the axial width W of the vulcanized rubber test piece 32 in order to ensure contact with the vulcanized rubber test piece 32. Specifically, the length L of the linear projections 36 is preferably 20 mm or more, and more preferably 30 mm or more. There is no particular upper limit to the length L, but from the viewpoint of making the device more compact, it is preferably 200 mm or less.

[0062] As shown in the figure, the polishing plate 34 has a reference surface 38 and one linear protrusion 36 protruding from the reference surface 38. The cross-sectional shape of the linear protrusion 36 is a mountain shape. In the example shown in the figure, the cross-sectional shape of the linear protrusion 36 is an equilateral triangle. The length of one side of this equilateral triangle is preferably 1 mm or more and 10 mm or less.

[0063] The double-headed arrow L shown in FIG. 5 indicates the length of the linear protrusion 36. The length L of the linear projection 36 is preferably 30 mm or more, and is preferably 70 mm or less.

[0064] In FIG. 6, the tip (apex) of the linear protrusion 36 is indicated by the symbol R. In the case of the linear protrusions 36 having a mountain-shaped cross section as exemplified in Figures 5 and 6, from the viewpoint of wear efficiency, the radius of curvature at the tip portion R of the linear protrusions 36 is preferably 1.00 mm or less, more preferably 0.80 mm or less, and even more preferably 0.60 mm or less. From the viewpoint of durability, the lower limit of the radius of curvature is 0.01 mm. The radius of curvature of the linear protrusions 36 is measured on the cross section shown in Figure 6.

[0065] From the viewpoint of easily reproducing the running conditions on an actual road surface in an abrasion test, the height of the linear protrusions 36 is preferably 1.0 mm or more, and more preferably 1.5 mm or more. From the viewpoint of preventing damage to the test piece 32, the height is preferably 10 mm or less. When the polishing plate 34 has a plurality of linear protrusions 36, the pitch of each linear protrusion 36 is preferably 0.5 mm or more and 6.0 mm or less.

[0066] 7 is a schematic diagram showing an example of an abrasion tester capable of performing the abrasion step, in which the up-down direction is the vertical direction and the left-right direction is the horizontal direction. In this abrasion step, a test device 100 is used.

[0067] 7 includes a fixed base 42 installed substantially horizontally, a movable plate 44 movably placed on the fixed base 42, and a pressure plate 46 erected on the movable plate 44. A pulley 48 is attached to the fixed base 42. A connecting member 52 is attached to the movable plate 44, and the connecting member 52 is connected to a load member 50 via the pulley 48. The pressure plate 46 has an attachment portion 56.

[0068] Although not shown, the testing device 100 has a holding means for rotatably holding the vulcanized rubber test piece 32 at a position relative to the mounting portion 56, and a rotating means for rotating the vulcanized rubber test piece 32. Fig. 7 shows the state in which the vulcanized rubber test piece 32 is held in the testing device 100 by the holding means.

[0069] In the abrasion step, the polishing plate 34 is attached to the attachment part 56 so that the surface having the linear protrusions 36 faces the vulcanized rubber test piece 32 and the longitudinal direction of the linear protrusions 36 is approximately parallel to the axial direction of the vulcanized rubber test piece 32. A predetermined load is then applied to the loading member 50. The loading member 50 pulls the movable plate 44, which is connected to the connecting member 52 via the pulley 48, in the direction of arrow G. This pulling force presses the linear protrusions 36 on the polishing plate 34, which is attached to the pressing plate 46 on the movable plate 44, against the vulcanized rubber test piece 32. At this time, a constant pressure load is applied in the direction of arrow F to the contact area between the vulcanized rubber test piece 32 and the linear protrusions 36.

[0070] Next, with a load applied to the vulcanized test piece 32, the testing apparatus 100 is operated, and the vulcanized test piece 32 is rotated by the rotation means in the direction indicated by the arrow S for a predetermined time, thereby moving the vulcanized test piece 32 and the polishing plate 34 relative to each other. Specifically, the vulcanized test piece 32 is rotated at a predetermined rotation speed and a slip angle of 0°. This rotation causes wear on the outer surface of the vulcanized test piece 32. Due to the wear, part of the vulcanized rubber that forms the outer surface of the vulcanized test piece 32 peels off from the vulcanized test piece 32.

[0071] In the abrasion step, the test device 100 is operated, and after a predetermined time has elapsed, the vulcanized test piece 32 is removed and the mass change W before and after the abrasion step can be measured. Next, the mass change is divided by the specific gravity d of the outer layer rubber 32o that constitutes the vulcanized test piece 32 to obtain the abrasion volume (unit: cm 3 ) can be obtained. Then, the wear volume is divided by the relative movement time between the vulcanized test piece 32 and the polishing plate 34, i.e., the rotation time (min) of the vulcanized test piece 32, to obtain the wear amount per unit time (unit: cm 3The method for measuring the specific gravity of vulcanized rubber will be described later in the Examples.

[0072] As mentioned above, the evaluation results of the above rubber composition degradation test method correlate with the results of market evaluations of the wear resistance, etc. of the tire 2 having outer and inner layer rubber components made of this vulcanized rubber.

[0073] In this specification, dimensions such as thickness are measured under normal conditions. "Normal conditions" refers to a tire mounted on a normal rim, inflated to the normal internal pressure, and unloaded. Here, "normal rim" refers to a rim specified for each tire by the standard system, including the standard on which the tire is based. For example, in the case of JATMA (Japan Automobile Tire Manufacturers Association), this refers to the standard rim for the applicable size listed in the "JATMA Year Book." In the case of ETRTO (The European Tire and Rim Technical Organization), this refers to the "Measuring Rim" listed in the "Standards Manual." In the case of TRA (The Tire and Rim Association, Inc.), this refers to the "Design Rim" listed in the "Year Book." JATMA, ETRTO, and TRA are referenced in this order, and if an applicable size is available at the time of reference, these standards are followed. For tires not specified by a standard, this refers to a rim that can be mounted on a rim and can maintain internal pressure, i.e., the rim with the smallest rim diameter and the next narrowest rim width, among rims that can prevent air leakage between the rim and tire. Additionally, "normal internal pressure" refers to the air pressure specified for each tire by each standard in the standard system, including the standard on which the tire is based. For JATMA, it refers to "maximum air pressure," for ETRTO, it refers to "INFLATION PRESSURE," and for TRA, it refers to the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES." Refer to JATMA, ETRTO, and TRA in that order, and follow the standard if there is an applicable size at the time of reference. In the case of a tire not specified in the standard, it refers to the normal internal pressure (250 KPa or more) of another tire size (specified in the standard) that is specified using the normal rim as the standard rim. Note that if multiple normal internal pressures of 250 KPa or more are listed, it refers to the smallest value among them. [Example]

[0074] Below, examples (embodiments) that are considered preferable for implementation will be shown, but the scope of the present invention is not limited to the examples.

[0075] [Test 1] In Test 1, a plurality of test pieces were prepared using rubber compositions with different compositions, and the wear test shown in Figure 7 was carried out. The amount of wear per unit time in an air atmosphere was calculated.

[0076] (Preparation of cylindrical vulcanized rubber test pieces) According to the composition shown as A in Table 1 (inner layer rubber) below, all materials except sulfur and vulcanization accelerators (DPG, CZ) were placed in a 1.7 L Banbury mixer (manufactured by Kobe Steel, Ltd.) and kneaded at 150°C for 3 minutes. The resulting kneaded mixture was removed from the Banbury mixer, and the sulfur and vulcanization accelerators in the amounts shown in Table 1 were added. The mixture was then kneaded using an open roll at 80°C for 3 minutes to obtain an unvulcanized inner layer rubber composition. The resulting unvulcanized inner layer rubber composition was placed in a mold and press-vulcanized at 170°C for 12 minutes to obtain inner layer rubber A. According to the composition shown as a in Table 2 (outer layer rubber) below, all materials except for sulfur and vulcanization accelerators (DPG, CZ) were placed in a 1.7 L Banbury mixer (manufactured by Kobe Steel, Ltd.) and kneaded for 3 minutes at 150°C. The resulting kneaded mixture was removed from the Banbury mixer, and the amounts of sulfur and vulcanization accelerator shown in Table 2 were added. The mixture was then kneaded for 3 minutes at 80°C using an open roll to obtain an unvulcanized outer layer rubber composition. The outer layer rubber composition was attached to the surface of the inner layer rubber A, and the two were vulcanized to prepare cylindrical test pieces (outer diameter 78 mm, inner diameter 34 mm, axial width 18 mm, inner layer rubber thickness 17 mm, outer layer rubber thickness 5 mm) shown in Figures 3 and 4.

[0077] Each test specimen was prepared in the same manner as the above test specimen, except that the composition of the rubber composition was changed to that shown as BC in Table 1 and bc in Table 2 according to the specifications in Table 3 below.

[0078] [Table 1]

[0079] [Table 2]

[0080] Details of the compounds listed in Tables 1 and 2 are as follows: NR:TSR20 SBR: NS612 manufactured by Zeon Corporation (S-SBR, non-oil extended, styrene content: 15% by mass, vinyl content: 30% by mass, Tg: -65°C, Mw: 780,000) BR: Ubepol BR150B (manufactured by Ube Industries, Ltd., cis content 97% by mass or more) Carbon black: Show Black N330 (manufactured by Cabot Japan Co., Ltd., N2SA75m 2 / g, DBP oil absorption 102ml / 100g) Oil: VIVATEC 500 (H&R TDAE oil) Zinc oxide: Two types of zinc oxide manufactured by Mitsui Mining & Metals Co., Ltd. Stearic acid: Stearic acid "Tsubaki" (NOF Corporation) Anti-aging agent: Antigen 6C (Sumitomo Chemical Co., Ltd., N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) Wax: Sunnock N (Ouchi Shinko Chemical Industry Co., Ltd.) Sulfur: Powdered sulfur manufactured by Karuizawa Sulfur Co., Ltd. Vulcanization accelerator 1: Sancerer CM-G (manufactured by Sanshin Chemical Industry Co., Ltd., N-cyclohexyl-2-benzothiazole sulfenamide) Vulcanization accelerator 2: Noccelaer D (N,N'-diphenylguanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0081] (wear test) First, a cylindrical test piece consisting of inner layer rubber compound A and outer layer rubber compound a was placed in a test apparatus with the basic configuration shown in Figure 7. A polishing plate with the configuration shown in Figures 5 and 6 was attached to the pressure plate of the test apparatus. This polishing plate had a single linear protrusion (50 mm long) with a mountain-shaped cross section (an equilateral triangle with sides of 5 mm and a tip radius of curvature of 0.01 mm). Next, the test apparatus was operated in an air atmosphere (room temperature, oxygen concentration 21% by volume, relative humidity 50%), and an abrasion test was performed under the following conditions until the thickness of the outer layer rubber was reduced to 1 to 2 mm. Load (pressure from the pressing part to the cylindrical vulcanized test piece): 16000N / m 2 Rotation speed: 1000 rpm Slip angle: 0° Pinhole depth 1.0mm Temperature: 105℃

[0082] (Calculation of difference in plasticizer amount in outer rubber before and after test) The difference in the amount of plasticizer in the outer rubber layer before and after the test was calculated by converting the amount of acetone extracted from the rubber after the test into parts by mass and calculating the mass of the plasticizer before the test. If this value is greater than 0, it indicates that plasticizer has migrated from the outer rubber layer to the inner rubber layer.

[0083] [Table 3]

[0084] In Table 3, inner layer rubber / outer layer rubber ratios 1 to 9 are vulcanized and bonded, and plasticizer migration was evaluated based on the difference in the amount of plasticizer in the outer layer rubber detected before and after the test. This demonstrates that the above-mentioned rubber composition degradation test method evaluates both the outflow and internal diffusion of plasticizer in the outer layer rubber, and provides a highly accurate degradation test method.

[0085] The present invention (1) includes a preparation step of preparing a cylindrical vulcanized rubber test piece having at least an outer layer rubber and an inner layer rubber; a heating step of heating the vulcanized rubber test piece; and a wearing step of the vulcanized test piece by rotating the vulcanized test piece in a circumferential direction and pressing the vulcanized test piece against a pressing part to wear down the surface of the vulcanized test piece, The vulcanized rubber test piece is obtained by vulcanizing and bonding at least an outer layer rubber composition containing a plasticizer and an inner layer rubber composition having a different formulation from the outer layer rubber composition, The heating step and the abrasion step are performed simultaneously. The method for testing the deterioration of a rubber composition is characterized by the following.

[0086] The present invention (2) is a method for testing deterioration of a rubber composition according to the present invention (1), wherein the vulcanized rubber test piece is obtained by vulcanizing the rubber composition for the inner layer, attaching the rubber composition for the outer layer onto the obtained inner layer rubber, and vulcanizing both to achieve vulcanization adhesion.

[0087] The present invention (3) is a method for testing deterioration of a rubber composition according to the present invention (1) or (2), wherein the rubber composition for the inner layer has a sulfur content of 2.0 parts by mass or more per 100 parts by mass of the rubber component.

[0088] The present invention (4) is a degradation test method for a rubber composition in any combination with any of the present inventions (1) to (3), in which the difference (|Po-Pi|) between the content Po (parts by mass) of plasticizer per 100 parts by mass of the rubber component of the outer layer rubber composition and the content Pi (parts by mass) of plasticizer per 100 parts by mass of the rubber component of the inner layer rubber composition is 5 parts by mass or more.

[0089] The present invention (5) is a method for testing the deterioration of a rubber composition in any combination with any of the present inventions (1) to (4), wherein the cylindrical vulcanized rubber test piece has an outer diameter of 50 mm or more and 150 mm or less, an inner diameter of 10 mm or more and 90 mm or less, and an axial width of 10 mm or more and 30 mm or less.

[0090] The present invention (6) is a method for testing the deterioration of a rubber composition in any combination with any of the present inventions (1) to (5), wherein in the abrasion step, the rotation speed of the vulcanized test piece in the circumferential direction is 10 rpm or more and 10,000 rpm or less.

[0091] The present invention (7) is a method for testing the deterioration of a rubber composition in any combination with any of the present inventions (1) to (6), wherein the heating step controls the temperature of the vulcanized test piece at a needle puncture depth of 1.0 mm to be 80°C or higher and 160°C or lower.

[0092] In the present invention (8), in the abrasion step, the pressing force by the pressing part is 5000 N / m 2 More than 300000N / m 2 The following is a method for testing the deterioration of a rubber composition in any combination with any of the present inventions (1) to (7). [Explanation of symbols]

[0093] 2. Tires 4. Tread 6. Sidewall 8. Bead 10. Carcass 12. Belt 12a...inner layer 12b...outer layer 14...Band 16···Inner liner 20 Tread surface 22...Groove 24 cores 26 Apex 28···Carcass ply CL···Equatorial plane of tire 32... Test piece 32i···Inner layer rubber 32o···Outer rubber 34...polishing plate 36... Linear process 38...Reference plane 42...Fixed stand 44··· Movable plate 46 Pressing plate 48 Pulley 50 Load-bearing member 52 Connection member 56 Mounting part 100 Test equipment

Claims

1. a preparation step of preparing a cylindrical vulcanized rubber test piece having at least an outer rubber layer and an inner rubber layer; a heating step of heating the vulcanized rubber test piece; and a wearing step of the vulcanized test piece by rotating the vulcanized test piece in a circumferential direction and pressing the vulcanized test piece against a pressing part to wear down the surface of the vulcanized test piece, The vulcanized rubber test piece is obtained by vulcanizing and bonding at least an outer layer rubber composition containing a plasticizer and an inner layer rubber composition having a different formulation from the outer layer rubber composition, The heating step and the abrasion step are performed simultaneously. A method for testing deterioration of a rubber composition, comprising:

2. 2. The method for testing deterioration of a rubber composition according to claim 1, wherein the vulcanized rubber test piece is obtained by vulcanizing the inner layer rubber composition, attaching the outer layer rubber composition to the obtained inner layer rubber, and vulcanizing both to form a vulcanization bond.

3. 3. The method for testing deterioration of a rubber composition according to claim 1, wherein the rubber composition for the inner layer has a sulfur content of 2.0 parts by mass or more per 100 parts by mass of the rubber component.

4. 3. The method for testing deterioration of a rubber composition according to claim 1 or 2, wherein the difference (|Po-Pi|) between the content Po (parts by mass) of the plasticizer per 100 parts by mass of the rubber component of the outer layer rubber composition and the content Pi (parts by mass) of the plasticizer per 100 parts by mass of the rubber component of the inner layer rubber composition is 5 parts by mass or more.

5. 3. The method for testing deterioration of a rubber composition according to claim 1 or 2, wherein the cylindrical vulcanized rubber test piece has an outer diameter of 50 mm or more and 150 mm or less, an inner diameter of 10 mm or more and 90 mm or less, and an axial width of 10 mm or more and 30 mm or less.

6. 3. The method for testing deterioration of a rubber composition according to claim 1, wherein in the abrasion step, the rotation speed of the vulcanized test piece in the circumferential direction is 10 rpm or more and 10,000 rpm or less.

7. 3. The method for testing deterioration of a rubber composition according to claim 1, wherein the temperature of the vulcanized test piece at a needle puncture depth of 1.0 mm is controlled to be 80°C or higher and 160°C or lower in the heating step.

8. In the abrasion step, the pressing force by the pressing part is 5000 N / m ２ More than 300000N / m ２ 3. The method for testing deterioration of a rubber composition according to claim 1, wherein the following is true:

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