JP2014119399A - Wear resistance evaluation method of rubber product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of easily evaluating the wear resistance of a rubber product in a short time.SOLUTION: The wear resistance evaluation method of a rubber product includes the steps of: (1) obtaining a rubber composition; (2) measuring the value of storage elastic modulus Eof the rubber composition and the value of fracture energy F of the rubber composition; and (3) substituting the value of storage elastic modulus Eand the value of fracture energy F into a function that is correlated with the storage elastic modulus Eand correlated with the inverse number of the fracture energy F, and calculating the wear resistance coefficient of the rubber composition.

Description

  The present invention relates to a method for evaluating the wear resistance of a rubber product.

  Tread wear resistance is one of the important performances for a tire. In the evaluation of wear resistance, a tire is mounted on a vehicle. As the vehicle travels, the tread gradually wears. By measuring the degree of wear, the wear resistance can be evaluated. A method for evaluating the wear resistance of a tire mounted on a vehicle is described in Japanese Unexamined Patent Application Publication No. 2009-292434.

  The wear resistance of the tread can also be evaluated by a drum type testing machine. In this evaluation method, a tire mounted on a shaft rotates on a drum. Due to the rotation, the tread is gradually worn. By measuring the degree of wear, the wear resistance can be evaluated. A tire evaluation method using a drum type testing machine is described in Japanese Patent Application Laid-Open No. 2003-50190.

JP 2009-292434 A JP 2003-50190 A

  In the evaluation method in which a tire is mounted on a vehicle, the tire needs to be manufactured. Even in an evaluation method using a drum, a tire needs to be manufactured. Tire production takes time and effort.

  This rubber product also needs to be manufactured in the evaluation of wear resistance of rubber products other than tires. Manufacture of this rubber product takes time and effort.

  An object of the present invention is to provide a method by which the wear resistance of a rubber product can be evaluated easily and in a short time.

The method for evaluating the abrasion resistance of a rubber product according to the present invention,
(1) obtaining a rubber composition;
(2) measuring the storage elastic modulus E ^* value of the rubber composition and the fracture energy F value of the rubber composition; and (3) determining the storage elastic modulus E ^* value and the fracture energy F value. And substituting into a function correlating with the storage elastic modulus E ^* and correlating with the reciprocal of the fracture energy F, and calculating a wear resistance coefficient of the rubber composition.

  In this evaluation method, a rubber composition for a tire tread can be used.

Preferably, the temperature for measuring the value of the storage elastic modulus E ^* and the temperature for measuring the value of the fracture energy F in step (2) are determined based on a time-temperature conversion rule.

Preferably, the function used in step (3) is represented by the following mathematical formula.
W = c (F ^a / E ^{* b} ) (4)
In this mathematical formula, a, b and c are constants.

  In the evaluation method according to the present invention, it is not necessary to manufacture the rubber product when evaluating the wear resistance of the rubber product. In this method, the wear resistance can be easily evaluated in a short time.

FIG. 1 is a graph showing the temperature dependence of the storage elastic modulus E ^* of the rubber composition. FIG. 2 is a graph showing the temperature dependence of the fracture energy F of the rubber composition. FIG. 3 is a graph showing the relationship between predicted values obtained by multiple correlation analysis and tire test results.

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

  In the present embodiment, the wear resistance of a tire that is an example of a rubber product is evaluated. Specifically, the abrasion resistance of the tire tread is evaluated.

  In this embodiment, the wear resistance of the tread is evaluated by the wear resistance coefficient. The wear resistance coefficient is a travel distance (km) required for the tread to wear by 1 mm.

The wear phenomenon is a phenomenon in which the tread slides on the road surface having unevenness while sliding with respect to the road surface. At this time, the tread is deformed from the road surface. The frequency of this deformation is 1 × 10 ⁴ Hz-1 × 10 ⁶ Hz. This frequency is high. On the other hand, the time-temperature conversion rule holds for rubber physical properties. For example, rubber physical properties measured under high temperature and high frequency conditions correlate with rubber physical properties measured under low temperature and low frequency conditions.

In this embodiment, the storage elastic modulus E ^* and the fracture energy F are measured as the rubber physical properties. In this embodiment, first, the temperature at which wear resistance is to be evaluated is determined. Based on this temperature, the temperature at which the storage modulus E ^* and the fracture energy F are measured is determined. As described above, the frequency of deformation that the tread receives from the road surface is high. Therefore, based on the time-temperature conversion rule, a temperature lower than the temperature at which the wear resistance is to be evaluated is selected, and the storage elastic modulus E ^* and the fracture energy F are measured.

Examples of measured temperatures determined based on the time-temperature conversion rule are shown below.
Summer conditions Road surface temperature: 27 ° C Measurement temperature: 0 ° C
Winter conditions Road surface temperature: 7 ° C Measurement temperature: -40 ° C

  The greater the contact area M between the road surface and the tread, the smaller the shear force applied per unit area. As the shearing force is smaller, wear is suppressed. Therefore, the following mathematical formula (1) is established between the contact area M and the wear resistance coefficient W.

Furthermore, since the contact area M is inversely proportional to the storage elastic modulus E ^* of the tread, the above formula (1) is converted into the following formula (2).

  The wear of the tread correlates with the breaking energy F in the tensile test. If the fracture energy F is high, the tread is not easily worn. Therefore, the following formula (3) is established between the fracture energy F and the wear resistance coefficient W.

  From the above formulas (2) and (3), the following formula (4) is derived.

In the above formula, a, b and c are constants. These constants are determined in advance for each measurement temperature. The above mathematical formula (4) represents a function that correlates with the storage elastic modulus E ^* and correlates with the reciprocal of the fracture energy F. Instead of the above mathematical formula (4), a mathematical formula representing another function that correlates with the storage elastic modulus E ^* and correlates with the reciprocal of the fracture energy F may be used.

The value of the storage elastic modulus E ^{* and} the value of the fracture energy F are substituted into the mathematical formula (4). By this substitution, the wear resistance coefficient W of the rubber composition of the tread is calculated. The wear resistance of the rubber composition is evaluated by the wear coefficient W. A tire having a large wear coefficient W is excellent in wear resistance. A tire having a small wear coefficient W is inferior in wear resistance. In this evaluation method, wear resistance is quantified.

  This evaluation method does not require a tire to be manufactured. By this method, the wear resistance of the tread can be easily evaluated. By this method, the wear resistance of the tread can be evaluated in a short time.

  Hereinafter, the calculation method of the constants a, b, and c and the validity of the evaluation based on the above formula (4) will be described.

  Table 1 below shows the compositions of the rubber compositions AD. Each rubber composition contains natural rubber (NR) as a base rubber. The rubber composition further contains styrene butadiene rubber (SBR) or polybutadiene rubber (BR) as the base rubber.

  In the production of the rubber composition, base rubber, carbon black, silica and process oil were charged into a closed kneader (“MIXTRON BB” manufactured by KOBELCO) to obtain a base rubber. The rotation speed of the mixer is 115 rpm. The kneading was continued until the detected torque became constant. The discharge temperature was 160 ° C. and the kneading time was 5 minutes. This base rubber was put into an 8-inch open roll (Kansai Roll Co., Ltd.), and further, appropriate amounts of sulfur and a vulcanization accelerator were put in and kneaded. The kneading temperature was 110 ° C. or less, and the kneading time was 4 minutes. A rubber composition was obtained by kneading.

  The rubber composition was extruded to obtain a tread having a thickness of 10 mm. The tread and other tire members were assembled to obtain a raw cover. The raw cover was put into a mold and heated to obtain a tire. The heating temperature was 170 ° C. and the heating time was 12 minutes. The tire size was 195 / 65R15.

  A tire was attached to the vehicle, and the vehicle was driven on the road. This road included a highway, a general road and a mountain road. The travel distance was 8000 km. The wear resistance coefficient W was calculated by measuring the groove depth before and after running. This test was conducted in summer (July, average temperature: 21 ° C., average road surface temperature: 27 ° C.) and winter (November, average temperature: 7 ° C., average road surface temperature: 7 ° C.). The results are shown in Table 2 below.

  The difference between the wear resistance coefficient at low temperature and the wear resistance coefficient at high temperature of the rubber composition B is large. On the other hand, the temperature dependence of the wear resistance coefficient of the rubber composition C is smaller than that of the rubber composition B. The rubber composition C has a high wear resistance coefficient at a low temperature and a high wear resistance coefficient at a high temperature. The rubber composition D has characteristics intermediate between the characteristics of the rubber composition A and the characteristics of the rubber composition C. Thus, the tendency of the temperature dependence of the wear resistance coefficient differs depending on the composition.

The rubber composition was heated with a hot press to obtain a test sheet having a thickness of 2 mm. The heating temperature was 170 ° C. and the heating time was 12 minutes. From this sheet, a test piece having a width of 4 mm, a thickness of 2 mm, and a length of 40 mm was obtained. Using this test piece, the storage elastic modulus E ^* and the loss tangent tan δ were measured with a viscoelastic spectrometer (TYPE VES-F-III) manufactured by Iwamoto Seisakusho. The peak temperature of tan δ was defined as Tg. Details of the test conditions are as follows.
Distance between chucks: 30mm
Static initial stretch: 10%
Dynamic strain: 0.5%
Frequency: 10Hz
Temperature increase rate: 3 ° C / min Temperature range: -70 ° C to 50 ° C

The temperature dependency of the storage elastic modulus E ^* of the rubber composition AD is shown in the graph of FIG. In this graph, the horizontal axis represents temperature, and the vertical axis represents storage elastic modulus E ^* . As is apparent from this graph, the Tg of rubber compositions A and B is larger than the Tg of rubber compositions C and D. The -10 ° C. or less of the temperature, the storage modulus of the rubber composition A and B E ^* is greater than the storage modulus of the rubber composition C and D E ^*. This measurement result seems to reflect the Tg of SBR as the main component.

A dumbbell-shaped No. 3 test piece was obtained from the sheet. Using this test piece, a tensile test was performed with a tensile tester (Autograph AGS-J, manufactured by Shimadzu Corporation). The test was performed in accordance with the provisions of “JIS K 6251”. The tensile speed was 500 mm / min. The test was performed under conditions of -40 ° C, -10 ° C, 0 ° C and 23 ° C. The area surrounded by the stress-strain curve and the strain axis was determined. This area is the fracture energy F (MJ / m ³ ).

  The temperature dependence of the fracture energy F of the rubber composition A-D is shown in the graph of FIG. In this graph, the horizontal axis is the temperature, and the vertical axis is the fracture energy F. As is clear from this graph, the fracture energy F of the rubber composition C is large under all temperature conditions. At −40 ° C., the fracture energies F of the rubber compositions A and B are significantly smaller than the fracture energies F of the rubber compositions C and D. This measurement result seems to reflect that the elongation at break of the rubber composition is small at a temperature of Tg or less.

  The following formula (5) is obtained by transforming the above formula (4) into a logarithmic display.

As shown in FIGS. 1 and 2, the storage elastic modulus E ^* and the fracture energy F have temperature dependence. In calculating the wear resistance coefficient W, investigation was made as to which storage temperature modulus E ^* and fracture energy F should be used. First, a correlation analysis of the storage elastic modulus E ^* and the fracture energy F with respect to the wear resistance coefficient W was performed.
(X, y) = {(x _i , y _i )} (i = 1, 2,..., N)
Is given, the correlation coefficient R of x with respect to y is calculated by the following equation (6).

  The obtained correlation coefficients are shown in Table 3 below.

As is clear from Table 3, the wear resistance coefficient W under summer conditions has a high correlation with the fracture energy F of 0 °. On the other hand, the abrasion resistance coefficient W under winter conditions has a high correlation with the storage elastic modulus E ^* and the fracture energy F at −40 ° C. In other words, the test results on the tire have a high correlation with the rubber physical properties at a temperature lower than the road surface temperature. The reason seems to be that the tire slips on the road surface unevenness in the wear phenomenon at a high speed, and the above-mentioned time-temperature conversion law is involved.

In order to examine the relationship between the wear resistance coefficient W, the storage elastic modulus E ^*, and the fracture energy F, the above equation (5) is a multiple regression equation, the summer wear resistance coefficient logW is the target variable, and logE at 0 ° C. Multiple regression analysis was performed to optimize the constants a, b and c using ^* and logF as explanatory variables. The specific procedure is as follows.

  First, the above mathematical formula (5) was simplified to obtain the following mathematical formula (7).

Since the actual measurement value y _ove is the sum of the residuals e with the theoretical value y _est , the following mathematical formula (8) is obtained.

  Next, the coefficient is obtained by using the following formula (9) so that the sum of the squares of the residual e (residual sum of squares RSS) is minimized.

When this RSS is differentiated to zero by A, B ₁ and B ₂ , the following formula (10) is obtained.

  From the above Equation 10, when T is the number of data samples, the following normal equation is obtained.

By solving this normal equation, A, B ₁ and B ₂ are obtained as shown in the following equation.

By the same procedure, the constants a, b, and c are optimized using the above equation (5) as a multiple regression equation, the winter wear resistance logW as an objective variable, and logE ^* and logF at −40 ° C. as explanatory variables. Multiple regression analysis was performed.

  The relationship between the tire test result and the predicted value obtained by the multiple correlation analysis is shown in the graph of FIG. In this graph, the horizontal axis represents tire test results, and the vertical axis represents predicted values. Further, the obtained multiple correlation coefficient is shown in Table 4 below.

  It is clear from FIG. 3 and Table 4 that there is a high correlation between the wear resistance coefficient W measured on the tire and the wear resistance coefficient W predicted from the above formula (5). From this, it was proved that the evaluation method according to the present invention is appropriate.

  With the evaluation method according to the present invention, the wear resistance of various tires can be evaluated.

Claims (4)

(1) obtaining a rubber composition;
(2) measuring the storage elastic modulus E ^* value of the rubber composition and the fracture energy F value of the rubber composition; and (3) determining the storage elastic modulus E ^* value and the fracture energy F value. A method for evaluating the wear resistance of a rubber product, comprising the step of calculating a wear coefficient of the rubber composition by substituting it into a function that correlates with the storage elastic modulus E ^* and correlates with the inverse of the fracture energy F   The evaluation method according to claim 1, wherein the rubber composition is a rubber composition for a tire tread. The evaluation method according to claim 1 or 2, wherein the measurement temperature of the storage elastic modulus E ^* and the measurement temperature of the fracture energy F in the step (2) are determined based on a time-temperature conversion rule. . The evaluation method according to claim 1 or 2, wherein the function used in step (3) is expressed by the following mathematical formula.
W = c (F ^a / E ^{* b} ) (4)
(In this formula, a, b and c are constants.)

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