Method for evaluating friction performance of rubber composition and method for manufacturing tire

Abstract

To provide a method for evaluating a rubber composition with which the frictional performance of a rubber composition can be accurately evaluated.SOLUTION: A method for evaluating a rubber composition includes the steps of: (A) when a model whose material is assumed to be a rubber composition slides on a surface with a projection, calculating, through simulation, tensile stress and compressive stress generated in the model near the projection; (B) determining reference stress based on one or both of the tensile stress and the compressive stress; (C) obtaining tensile strain and compressive strain of the rubber composition when the reference stress is applied thereto; and (D) comparing the tensile strain and the compressive strain with each other.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for evaluating a rubber composition, and more particularly, to a method for evaluating the friction performance of a rubber composition. [Background technology]

[0002] A pneumatic tire has a tread. The main material of the tread is a crosslinked rubber composition. The tread is in direct contact with the road surface. The tread rubs against the road surface. For a tire, the friction performance of the rubber composition of the tread is an important characteristic.

[0003] JP 2017-67453 A discloses a method for evaluating the friction performance of a rubber composition by utilizing the viscoelasticity of the rubber composition. In this method, the friction coefficient is predicted based on the loss tangent. In this method, the friction performance can be evaluated without performing a friction test. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP2017-67453A Summary of the Invention [Problem to be solved by the invention]

[0005] The evaluation method disclosed in JP 2017-67453 A has insufficient evaluation accuracy. An object of the present invention is to provide a method for evaluating a rubber composition that can be efficiently performed and can evaluate friction performance with high accuracy. [Means for solving the problem]

[0006] The method for evaluating the friction performance of a rubber composition according to the present invention includes: (A) calculating, by simulation, tensile or compressive stresses generated in a model in the vicinity of a protrusion when the model, the assumed material of which is a rubber composition, slides on a surface having a protrusion; (B) determining a reference stress based on the tensile or compressive stress; (C) determining the tensile strain and compressive strain of the rubber composition when the reference stress is applied; and (D) Step of comparing the tensile strain with the compressive strain Includes.

[0007] Preferably, in step (A), the tensile stress or compressive stress is calculated by a finite element method.

[0008] Preferably, step (C) comprises: (C-1) A step of subjecting a first test piece made of the rubber composition to a tensile test to measure the tensile strain. and (C-2) A step of subjecting a second test piece made of the rubber composition to a compression test to measure the compression strain. Preferably, the shape of the second test piece subjected to the compression test in step (C-2) is the same as the shape of the first test piece subjected to the tensile test in step (C-1).

[0009] Preferably, in step (D) the difference or ratio of the two strains is calculated.

[0010] Preferably, this method evaluates the coefficient of friction of a rubber composition on a wet road surface in comparison with the coefficient of friction of the rubber composition on a dry road surface.

[0011] According to another aspect, a method for manufacturing a tire according to the present invention includes the steps of: (A) calculating, by simulation, tensile or compressive stresses generated in a model in the vicinity of a protrusion when the model, the assumed material of which is a rubber composition, slides on a surface having a protrusion; (B) determining a reference stress based on the tensile or compressive stress; (C) determining the tensile strain and compressive strain of the rubber composition when the reference stress is applied; (D) Step of comparing the tensile strain with the compressive strain (E) determining whether the rubber composition is acceptable or not based on the comparison; (F) determining tire tread specifications based on the composition of the accepted rubber composition; and (G) Producing a tread having this specification. Includes.

[0012] According to another aspect, the method for evaluating the friction performance of a rubber composition according to the present invention comprises: (1) calculating, by simulation, tensile and compressive stresses generated in a model, the assumed material of which is a rubber composition, near a surface having protrusions when the model slides on the surface having protrusions; (2) determining a first reference stress based on the tensile stress and a second reference stress based on the compressive stress; (3) determining a tensile strain of the rubber composition when the first standard stress is applied and a compressive strain of the rubber composition when the second standard stress is applied; and (4) comparing the tensile strain with the compressive strain Includes.

[0013] According to yet another aspect, a method for manufacturing an ear according to the present invention comprises: (1) calculating, by simulation, tensile and compressive stresses generated in a model, the assumed material of which is a rubber composition, near a surface having protrusions when the model slides on the surface having protrusions; (2) determining a first reference stress based on the tensile stress and a second reference stress based on the compressive stress; (3) determining a tensile strain of the rubber composition when the first standard stress is applied and a compressive strain of the rubber composition when the second standard stress is applied; (4) comparing the tensile strain with the compressive strain (5) determining whether the rubber composition is acceptable or not based on the comparison; (6) determining tire tread specifications based on the composition of the accepted rubber composition; and (7) Producing a tread having this specification Includes. Effect of the Invention

[0014] The evaluation method according to the present invention makes it possible to evaluate the friction performance of a rubber composition with high accuracy. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a flow chart showing an evaluation method according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing a part of a model used in the evaluation method of FIG. [Diagram 3] FIG. 3 is a schematic diagram showing the model of FIG. 2 together with a model of a protrusion. [Figure 4] FIG. 4 is a graph showing the stress-strain curve used in the evaluation method of FIG. [Diagram 5] FIG. 5 is a graph showing a curve of strain difference vs. reduction in friction coefficient used in the evaluation method of FIG. [Figure 6] FIG. 6 is a graph showing the curve of strain difference-friction coefficient used in the evaluation method of FIG. [Figure 7] FIG. 7 is a graph showing a stress-strain curve used in an evaluation method according to another embodiment of the present invention. [Figure 8] FIG. 8 is a flow chart showing a method for manufacturing a tire according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the drawings as appropriate.

[0017] FIG. 1 is a flow chart showing an evaluation method according to an embodiment of the present invention. In this evaluation method, a model is created (STEP 1). This model 2 is shown in FIG. 2. This model 2 has a large number of meshes 4. This model 2 does not actually exist. This model 2 is hypothetical. The assumed material of this model 2 is a rubber composition. Therefore, this model 2 has elasticity. A rubber composition with a detailed composition specified, such as the type of base rubber, the type of additive, and the amount of additive, is assumed as the material. A rubber composition with detailed properties specified, such as hardness, is assumed as the material.

[0018] This model 2 is subjected to a simulation (STEP 2). A typical method of the simulation is the finite element method (FEM). FIG. 3 shows an analysis using the finite element method. FIG. 3 also shows a model of a surface 8 having protrusions 6 together with the model 2 shown in FIG. 2. Although not shown, the surface 8 is also divided into a large number of meshes. In this embodiment, the protrusions 6 are rigid bodies. The size of the rubber composition model 2 is sufficiently larger than the size of the protrusions 6.

[0019] In this simulation, the model 2 moves in the direction of arrow A in FIG. 3. The model 2 moves while sliding on the surface 8. This movement causes tensile stress to occur in the model 2 on the front side of the protrusion 6 (the right side in FIG. 3). The tensile stress for each mesh 4 is calculated by the simulation. These tensile stresses have a distribution. The tensile stress of the mesh 4 close to the protrusion 6 is large. From these tensile stresses, a representative value Vt is determined. The average value of the multiple tensile stresses may be set to the representative value Vt. The maximum value of the multiple tensile stresses may be set to the representative value Vt. The representative value Vt may also be determined by other means.

[0020] Due to the movement of the model 2, compressive stress is generated in the model 2 behind the protrusion 6 (left side in FIG. 3). The compressive stress for each mesh 4 is calculated by simulation. These compressive stresses have a distribution. The compressive stress in the mesh 4 close to the protrusion 6 is large. From these compressive stresses, a representative value Vc is determined. The average value of the multiple compressive stresses may be set to the representative value Vc. The maximum value of the multiple compressive stresses may be set to the representative value Vc. The representative value Vc may also be determined by other means.

[0021] Examples of software suitable for the simulation include "LS-DYNA" (trade name) from Livermore Software Technology, Inc., and "Abaqus" (trade name) from Dassault Systemes.

[0022] Based on the representative value Vt of the tensile stress and the representative value Vc of the compressive stress obtained by the simulation, a reference stress Rs is determined (STEP 3). The average of the representative values ​​Vt and Vc may be the reference stress Rs. The larger of the representative values ​​Vt and Vc may be the reference stress Rs. The smaller of the representative values ​​Vt and Vc may be the reference stress Rs. The reference stress Rs may be determined by other means.

[0023] The reference stress Rs may be determined based on the representative value Vt without taking the representative value Vc into consideration. In this case, it is not necessary to calculate the compressive stress in the simulation (STEP 2).

[0024] The reference stress Rs may be determined based on the representative value Vc without taking into account the representative value Vt. In this case, it is not necessary to calculate the tensile stress in the simulation (STEP 2).

[0025] Next, a first test piece is molded (STEP 4). The material of this first test piece is the rubber composition assumed in model 2 used in the simulation. This first test piece is subjected to a tensile test (STEP 5). The tensile test is performed by a known method. An example of the tensile test method is specified in "JIS K 6251". An example of a device suitable for the tensile test is "Auto Graph" manufactured by Shimadzu Corporation. A stress-strain curve is obtained by the tensile test. An example of the stress-strain curve is shown in FIG. 4. In FIG. 4, the symbol St is the tensile strain when the reference stress Rs is applied to the first test piece.

[0026] In this method, a first test piece is molded and the tensile strain St is measured. The tensile strain St may be calculated by simulation.

[0027] Next, a second test piece is molded (STEP 6). The material of this second test piece is the same as the material of the first test piece. In other words, the material of the second test piece is the rubber composition assumed in the model 2 used in the simulation. Preferably, the shape of the second test piece is the same as the shape of the first test piece. This second test piece is subjected to a compression test (STEP 7). The compression test is performed by a known method. An example of the compression test method is specified in "JIS K 6254". An example of a device suitable for the compression test is the aforementioned product name "auto graph". A stress-strain curve is obtained by the compression test. An example of the stress-strain curve is shown in FIG. 4. In FIG. 4, the symbol Sc is the compression strain when the second test piece is loaded with the reference stress Rs.

[0028] In this method, a second test piece is molded and the compressive strain Sc is measured. The compressive strain Sc may be calculated by simulation.

[0029] The compression test (STEP 7) may be performed prior to the tensile test (STEP 5). The tensile test (STEP 5) and the compression test (STEP 7) may be performed in parallel.

[0030] The tensile strain St and the compressive strain Sc are compared (STEP 8). In this embodiment, the difference (St-Sc) is calculated as the comparison. The friction performance is evaluated based on the difference (St-Sc) (STEP 9). The difference (St-Sc) is a type of strain parameter.

[0031] A graph used for this evaluation is shown in FIG. 5. This graph is prepared prior to carrying out the evaluation method according to the present invention. This graph is obtained by measuring the friction coefficients of many rubber compositions. In this graph, the horizontal axis is the difference (St-Sc). In this graph, the vertical axis is an index Id that represents the amount of decrease in the friction coefficient μw on a wet road surface from the friction coefficient μd on a dry road surface. This index Id is calculated by the following formula. Id = -(1 - μw / μd) This Id is a type of friction coefficient parameter. This index Id can be used to evaluate the friction coefficient μw on a wet road surface in comparison with the friction coefficient μd on a dry road surface.

[0032] In a typical rubber composition, the friction coefficient μw on a wet road surface is smaller than the friction coefficient μd on a dry road surface. is large In the rubber composition, the difference between the friction coefficient μw and the friction coefficient μd is small, in other words, the friction performance of this rubber composition is less dependent on the condition of the road surface.

[0033] As shown in FIG. 5, the index Id is large for a rubber composition with a difference (St-Sc) of about 0.21. In other words, for a rubber composition with a difference (St-Sc) of 0.21 or close to this, the friction performance is less dependent on the road surface condition. In this embodiment, a rubber composition with a difference (St-Sc) of 0.21 or close to this is evaluated as having "excellent friction performance". A rubber composition with a difference (St-Sc) significantly smaller than 0.21 is evaluated as having "poor friction performance". A rubber composition with a difference (St-Sc) significantly larger than 0.21 is evaluated as having "poor friction performance". In an evaluation method in which a graph other than that of FIG. 5 is used, the preferred difference (St-Sc) may be other than 0.21.

[0034] In actual sliding, the rubber composition repeats tensile deformation and restoration. The rubber composition further repeats compressive deformation and restoration. The behavior of sliding is complicated. The present inventors have found that the friction performance of a rubber composition can be accurately determined by comparing the tensile strain and the compressive strain. In this evaluation method, it is not necessary to actually measure the friction coefficient of the rubber composition. This evaluation method is simple.

[0035] Other values ​​may be set as the horizontal axis of the graph in Fig. 5. In other words, the friction performance may be evaluated based on other strain parameters. Examples of the other strain parameters include the difference (Sc-St), the ratio (St / Sc), and the ratio (Sc / St). The value obtained by substituting the tensile strain St and the compressive strain Sc into a predetermined relational expression may be used as the strain parameter.

[0036] The friction performance may be evaluated by a friction coefficient parameter other than the index Id. An example of this parameter is the friction coefficient μw on a wet road surface. In the graph shown in FIG. 6, the horizontal axis is the difference (St-Sc), and the vertical axis is the friction coefficient μw on a wet road surface. As shown in FIG. 6, a rubber composition with a difference (St-Sc) of about 0.23 has a large friction coefficient μw. In this embodiment, a rubber composition with a difference (St-Sc) of 0.23 or close to this is evaluated as having "excellent friction performance on a wet road surface." A rubber composition with a difference (St-Sc) significantly smaller than 0.23 is evaluated as having "poor friction performance on a wet road surface." A rubber composition with a difference (St-Sc) significantly larger than 0.23 is evaluated as having "poor friction performance on a wet road surface."

[0037] The friction coefficient parameter may be a friction coefficient μd on a dry road surface. The friction coefficient parameter may be a friction coefficient on a snowy or icy road surface. The friction coefficient parameter may be an equation representing the relationship between the friction coefficient on a snowy or icy road surface and the friction coefficient μd on a dry road surface.

[0038] The friction performance may be evaluated without using a graph. In this case, the quality of the friction performance is directly judged by comparing the tensile strain St and the compressive strain Sc. For example, a rubber composition having a difference (St-Sc) of 0.21 or close thereto is evaluated as having "excellent friction performance."

[0039] FIG. 7 is a graph showing a stress-strain curve used in an evaluation method according to another embodiment of the present invention. In the evaluation method shown in FIG. 1, both tensile stress and compressive stress are taken into consideration in determining the reference stress Rs (STEP 3). On the other hand, in the evaluation method shown in FIG. 7, a first reference stress Rs1 is determined based on the tensile stress, and a second reference stress Rs2 is determined based on the compressive stress. Based on the stress-strain curve shown in FIG. 7, a tensile strain St corresponding to the first reference stress Rs1 is measured, and a compressive strain Sc corresponding to the second reference stress Rs2 is measured. The tensile strain St and the compressive strain Sc are compared to evaluate the friction performance. The specific evaluation method is the same as the method in the embodiment shown in FIG. 1-6. The tensile strain may be calculated by a simulation using the first reference stress Rs1. The compressive strain Sc may be calculated by a simulation using the second reference stress Rs2.

[0040] Fig. 8 is a flow chart showing a method for manufacturing a tire according to one embodiment of the present invention. In this manufacturing method, similar to the evaluation method shown in Fig. 1, production of a model 2 (STEP 1), simulation (STEP 2), determination of a reference stress (STEP 3), molding of a first test piece (STEP 4), tensile test (STEP 5), molding of a second test piece (STEP 6), compression test (STEP 7), strain comparison (STEP 8), and evaluation of friction performance (STEP 9) are performed. The evaluation of friction performance (STEP 9) may be omitted.

[0041] Furthermore, in this manufacturing method, a pass / fail judgment of the rubber composition is made (STEP 10). In this step, it is judged whether or not the difference (St-Sc) is within a predetermined range. If the rubber composition does not pass this judgment, a model 2 of another rubber composition having a different composition is created (STEP 2). The steps from the simulation of this rubber composition (STEP 2) to the pass / fail judgment (STEP 10) are performed. By repeating these steps, a rubber composition with excellent friction performance is found.

[0042] If the rubber composition passes the judgment (STEP 10), the specifications of the tread are determined (STEP 11). Specifically, the composition of the rubber composition for the tread is determined. The composition of this rubber composition for the tread may be the same as the composition of the rubber composition that passed the judgment (STEP 10). The composition of this rubber composition for the tread may be different from the composition of the rubber composition that passed the judgment (STEP 10). In other words, the composition of the rubber composition for the tread may be determined with reference to the composition of the rubber composition that passed the judgment (STEP 10). The composition of the rubber composition for the tread may be determined so that the rubber composition for the tread has friction performance that is even better than that of the rubber composition that passed the judgment (STEP 10).

[0043] According to the determined specifications, the tread rubber is produced (STEP 12). This tread rubber is assembled with other rubber components (STEP 13). This assembly results in a raw cover (green tire). This raw cover is placed in a mold, where it is pressurized and heated (STEP 14). The pressure and heat cause the rubber composition to flow within the mold cavity. The heat causes the rubber molecules of the rubber composition to undergo a cross-linking reaction. In this manner, a tire is obtained. This tire has excellent friction performance. This manufacturing method makes it easy to obtain tires with excellent friction performance.

[0044] In this manufacturing method, a first test piece is formed, and the tensile strain St is measured (STEP 4, STEP 5). The tensile strain St may be calculated by simulation. In this manufacturing method, a second test piece is formed, and the compressive strain Sc is measured (STEP 6, STEP 7). The compressive strain Sc may be calculated by simulation.

[0045] In this manufacturing method, the pass / fail judgment (STEP 10) may be made by a strain parameter other than the difference (St-Sc). For example, the pass / fail judgment may be made by the difference (Sc-St), the ratio (St / Sc), or the ratio (Sc / St). The pass / fail judgment may be made by a value obtained by substituting the tensile strain St and the compressive strain Sc into a predetermined relational expression. The pass / fail judgment (STEP 10) may be made by a friction coefficient parameter.

[0046] In this manufacturing method, the first standard stress Rs1 may be determined based on the tensile stress, and the second standard stress Rs2 may be determined based on the compressive stress. In this case, the tensile strain St corresponding to the first standard stress Rs1 is measured based on the stress-strain curve. The compressive strain Sc corresponding to the second standard stress Rs2 is measured based on the stress-strain curve. The tensile strain St and the compressive strain Sc are compared to make a pass / fail judgment (STEP 10). [Industrial Applicability]

[0047] The evaluation method described above is suitable for evaluating the friction performance of various rubber products such as shoe soles, floors, conveyors, etc. [Explanation of symbols]

[0048] 2. Model 4. Mesh 6...protrusion 8... sides

Claims

1. (A) calculating, by simulation, tensile or compressive stresses generated in a model in the vicinity of a protrusion when the model, the assumed material of which is a rubber composition, slides on a surface having a protrusion; (B) determining a reference stress based on the tensile stress or the compressive stress; (C) determining the tensile strain and compressive strain of the rubber composition when the reference stress is applied; and (D) comparing the tensile strain with the compressive strain. The friction performance evaluation method of the rubber composition comprising the steps of:

2. 2. The evaluation method according to claim 1, wherein in the step (A), the tensile stress or the compressive stress is calculated by a finite element method.

3. The above step (C) (C-1) A step of subjecting a first test piece made of the rubber composition to a tensile test to measure the tensile strain. and (C-2) A step of subjecting a second test piece made of the rubber composition to a compression test to measure the compression strain. The evaluation method according to claim 1 or 2, comprising:

4. The evaluation method according to claim 3, wherein the shape of the second test piece subjected to the compression test in the step (C-2) is the same as the shape of the first test piece subjected to the tensile test in the step (C-1).

5. 5. The evaluation method according to claim 1, wherein in the step (D), a difference or a ratio between the two strains is calculated.

6. 6. The evaluation method according to claim 1, wherein the friction coefficient of the rubber composition on a wet road surface is evaluated by comparing it with the friction coefficient of the rubber composition on a dry road surface.

7. (A) calculating, by simulation, tensile or compressive stresses generated in a model in the vicinity of a protrusion when the model, the assumed material of which is a rubber composition, slides on a surface having a protrusion; (B) determining a reference stress based on the tensile stress or the compressive stress; (C) determining the tensile strain and compressive strain of the rubber composition when the reference stress is applied; (D) comparing the tensile strain with the compressive strain. (E) determining whether the rubber composition is acceptable or not based on the comparison; (F) determining tire tread specifications based on the composition of the approved rubber composition; and (G) manufacturing said tread having said specifications. A tire manufacturing method comprising the steps of:

8. (1) calculating, by simulation, tensile and compressive stresses that occur in a model, the assumed material of which is a rubber composition, near a surface having protrusions when the model slides on the surface having protrusions; (2) determining a first reference stress based on the tensile stress and a second reference stress based on the compressive stress; (3) determining a tensile strain of the rubber composition when the first standard stress is applied and a compressive strain of the rubber composition when the second standard stress is applied; and (4) Comparing the tensile strain with the compressive strain. The friction performance evaluation method of the rubber composition comprising the steps of:

9. (1) calculating, by simulation, tensile and compressive stresses that occur in a model, the assumed material of which is a rubber composition, near a surface having protrusions when the model slides on the surface having protrusions; (2) determining a first reference stress based on the tensile stress and a second reference stress based on the compressive stress; (3) determining a tensile strain of the rubber composition when the first standard stress is applied and a compressive strain of the rubber composition when the second standard stress is applied; (4) Comparing the tensile strain with the compressive strain. (5) determining whether the rubber composition is acceptable or not based on the comparison; (6) determining tire tread specifications based on the composition of the approved rubber composition; and (7) manufacturing the tread having the above specifications; A tire manufacturing method comprising the steps of:

Images