JP6376187B2 - Evaluation method of rubber composition for tire - Google Patents

Description

The present invention relates to a method for evaluating a rubber composition used in a tire, and more particularly to a method for evaluating a rubber composition for a tire suitable as an index of rolling resistance.

  When the pneumatic tire rolls, the generation and disappearance of the ground contact state are repeated repeatedly. At this time, (1) work energy injected into the tire from the road surface is converted into heat, and (2) converted heat. Heats in and out through the process of warming the rubber of the tire and (3) the heat of the tire being taken away by the surroundings. That is, the pneumatic tire functions as a heat engine when traveling.

  Conventionally, when developing a rubber composition for a tire, a rubber composition having a low rolling resistance has been selected by paying attention mainly to the process (1) and using the heat generation characteristics of the rubber composition as an index. For example, when a rubber composition having a low loss tangent tan δ at 60 ° C. is applied to a cap tread rubber layer of a pneumatic tire, it is a general understanding that rolling resistance is reduced (see, for example, Patent Document 1).

  However, since the pneumatic tire functions as a heat engine including the processes (1) to (3) described above during running, the rolling resistance is not always accurately evaluated using only the loss tangent tan δ at 60 ° C. as an index. The current situation is not possible.

JP 2010-196004 A

The objective of this invention is providing the evaluation method of the rubber composition for tires suitable as a parameter | index of rolling resistance.

In order to achieve the above object, a method for evaluating a tire rubber composition according to the present invention comprises preparing a vulcanized test piece made of a tire rubber composition and measuring the temperature of the test piece on the test piece. On the other hand, a compression load of a pulse waveform is applied, and the amount of adiabatic temperature increase ΔTad (° C./°C) per cycle of the pulse waveform is based on the balance between the energy injected into the test piece and the energy returned from the test piece. Cycle), while measuring the thermal diffusivity α (mm ² / sec) of the tire rubber composition, and based on the calculated value of the adiabatic temperature rise ΔTad and the thermal diffusivity α at an arbitrary temperature. The rubber composition for tires is evaluated.

Moreover, the pneumatic tire for passenger cars of the present invention, which is determined to have low rolling resistance in the evaluation method, includes a tire constituent member made of a rubber composition containing carbon black and / or silica as a reinforcing material in a diene elastomer. In the pneumatic tire for passenger cars, the product of the amount of heat insulation temperature increase ΔTad (° C./cycle) at 60 ° C. and the square root of the thermal diffusivity α (mm ² / sec) of the tire constituent member made of the tire rubber composition is It is 0.0007 or less.

  As a result of earnest research on the evaluation method of the rubber composition for a tire, the insulative temperature increase amount ΔTad is an index indicating the ease of increasing the tire temperature, and the thermal diffusivity α is an index of the ease of cooling the tire, The calculation values of the adiabatic temperature rise ΔTad and the thermal diffusivity α were found to be useful in evaluating the rolling resistance, and the present invention was reached based on the knowledge.

That is, in the present invention, a vulcanized test piece made of a rubber composition for a tire is prepared, and a compression load having a pulse waveform is applied to the test piece while measuring the temperature of the test piece. The adiabatic temperature rise ΔTad (° C./cycle) per cycle of the pulse waveform is calculated based on the balance between the energy injected into the test piece and the energy returned from the test piece, while the heat of the tire rubber composition is calculated. By measuring the diffusivity α (mm ² / sec) and evaluating the tire rubber composition based on the calculated value of the adiabatic temperature rise ΔTad and the thermal diffusivity α at an arbitrary temperature, the tire rubber composition It is possible to accurately evaluate the rolling resistance of a pneumatic tire using an object.

  In the method for evaluating a tire rubber composition according to the present invention, it is preferable to evaluate the tire rubber composition based on the product of the adiabatic temperature rise ΔTad and the square root of the thermal diffusivity α at an arbitrary temperature. In particular, it is appropriate to determine that the rolling resistance is low when the product of the adiabatic temperature rise ΔTad at 60 ° C. and the square root of the thermal diffusivity α is 0.0007 or less.

Moreover, the pneumatic tire for passenger cars according to the present invention is a square root of a heat insulation temperature increase ΔTad (° C./cycle) and a thermal diffusivity α (mm ² / second) at 60 ° C. of a tire constituent member made of a rubber composition for a tire. And the product is 0.0007 or less, the rolling resistance is low.

  When the tire constituent member is a cap tread rubber layer, it is preferable that the product of the adiabatic temperature rise ΔTad at 60 ° C. and the square root of the thermal diffusivity α is 0.0007 or less. When the tire constituent member is an under tread rubber layer, it is preferable that the product of the adiabatic temperature rise ΔTad at 60 ° C. and the square root of the thermal diffusivity α is 0.0005 or less. Furthermore, when the tire constituent member is a sidewall rubber layer, it is preferable that the product of the heat insulation temperature increase ΔTad at 60 ° C. and the square root of the thermal diffusivity α is 0.0006 or less. Thus, there is an appropriate threshold value depending on the type of tire constituent member.

It is a perspective view which shows the test piece used with the evaluation method of the rubber composition for tires which concerns on this invention. It is a side view which shows the principal part of the apparatus which applies a compressive load with respect to a test piece. It is a graph which shows the pulse waveform (1 cycle) of the compressive load loaded with respect to a specimen over time. It is a graph which shows the compressive load applied to a test piece, and the compression displacement of a test piece with time. It is a graph which shows the built-in work amount of a test piece with time. It is a graph which shows the relationship between the temperature of a test piece, and the heat insulation temperature rise amount (DELTA) Tad. It is a graph which shows the relationship between the square root of thermal diffusivity (alpha), and the heat insulation temperature rise amount (DELTA) Tad. 1 is a meridian cross-sectional view showing a passenger car pneumatic tire according to an embodiment of the present invention.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a test piece used in the tire rubber composition evaluation method according to the present invention. As shown in FIG. 1, a test piece 1 is a vulcanized cylinder made of a tire rubber composition to be tested. The shape and dimensions of the test piece 1 can be arbitrarily selected as long as the ratio of the height h to the diameter d is 0.5 ± 0.05 and is within the test capability of the test apparatus. A cylindrical body having a height h of 5 mm to 10 mm and a diameter d of 10 mm to 20 mm can be used. More specifically, a cylindrical body having a height h of 8.5 mm and a diameter of 17 mm is used.

  FIG. 2 shows a main part of a device for applying a compressive load to the test piece. As shown in FIG. 2, the test piece 1 is disposed between the lower support member 11 and the upper pressing member 12. While the position of the support member 11 is fixed, the pressing member 12 is configured to be able to reciprocate along the vertical direction, with respect to the test piece 1 sandwiched between the support member 11 and the pressing member 12. Thus, a compressive load F is applied. Further, the temperature of the test piece 1 is detected by a temperature sensor (not shown). As the temperature sensor, a contact-type or non-contact-type temperature sensor can be used. Fixing the test piece to the compression surface is important. Use a file that has been cut to prevent slipping during the test, or use a test piece and a pressing member to prevent slippage. Fix with adhesive. When slipping occurs, the test stroke becomes large and the measured adiabatic temperature rise is greatly calculated, so that it is necessary to remeasure under the condition that no slipping occurs in order to obtain a correct value.

  FIG. 3 shows the pulse waveform (1 cycle) of the compressive load applied to the test piece over time. As shown in FIG. 3, for example, a harbor sine wave can be applied as the pulse waveform. In addition, a sine wave may be applied. A compressive load F is applied to the test piece 1 based on such a pulse waveform. The maximum value Fmax of the compressive load F is set in a range of 300 kPa to 1000 kPa as the maximum compressive stress applied to the test piece, and the minimum value Fmin of the compressive load F is similarly 20 as the maximum compressive stress applied to the test piece. %, And one cycle of the pulse waveform is set in the range of 0.2 seconds to 0.3 seconds. More specifically, the maximum value Fmax of the compressive load F is set to 500 kPa as the maximum compressive stress applied to the test piece, the minimum value Fmin of the compressive load F is set to 50 kPa as the maximum compressive stress applied to the test piece, The cycle is 0.25 seconds (4 Hz). In this case, the fluctuation range of the pulse waveform is 450 kPa. This condition is a condition corresponding to low speed traveling of about 30 km / h. At the time of a load test, a compression load F having a pulse waveform as shown in FIG. As an apparatus for applying such a compressive load, for example, an electric actuator type compressive load apparatus (500N) manufactured by GABO or an electrohydraulic servo type test apparatus manufactured by INSTRON can be used.

  4 shows the compressive load applied to the test piece and the compression displacement of the test piece over time, FIG. 5 shows the built-in work of the test piece over time, and FIG. 6 shows the temperature of the test piece and the amount of adiabatic temperature rise. And the relationship with the amount of heat release. 4 to 6 calculate the balance (built-in work amount) between the energy injected into the test piece and the energy returned from the test piece from the time history data of the displacement and the load, and 1 of the pulse waveform is calculated based on the calculation. This is an example for explaining a method of calculating the amount of increase in adiabatic temperature per cycle, and does not necessarily coincide with the compression load of the pulse waveform used in the present invention.

As shown in FIG. 4, when a compression load F (N) having a pulse waveform is applied to the test piece 1, a compression displacement H (mm) is generated in the test piece 1 in accordance with the compression load F. Here, when the compression displacement ΔH in the minute time in one cycle and the average compression load F in the minute time are obtained, the work applied to the specimen from the outside of the specimen in the minute time from ΔW = F × ΔH. ΔW is calculated. At this time, the built-in work amount ΣΔW obtained by integrating the work amount ΔW applied to the specimen from the outside of the specimen is as shown in FIG. As shown in FIG. 5, since the energy injected into the test piece 1 made of the rubber composition is larger than the energy returned from the test piece 1, the built-in work amount ΣΔW as the balance is 1 of the pulse waveform. It increases after the cycle, and the increase is the loss energy ΔE per cycle. Assuming that all of the loss energy ΔE is converted into thermal energy and results in the temperature rise of the test piece 1, the adiabatic temperature rise amount ΔTad per cycle of the pulse waveform can be obtained from the following equation (1). Where C is the specific heat of the test piece, ρ is the density of the test piece, and V is the volume of the test piece.
ΔTad = ΔE / (C · ρ · V) (1)

  In FIG. 6, the horizontal axis indicates the temperature T (° C.) of the test piece 1, and the vertical axis indicates the adiabatic temperature increase ΔTad (° C./cycle). In FIG. 6, the temperature T of the test piece 1 starts from the environmental temperature T0. FIG. 6 shows a plot of the adiabatic temperature rise ΔTad per cycle of the pulse waveform calculated as described above in relation to the temperature T of the test piece 1. As shown in FIG. 6, in the temperature range of the tread rubber when a normal tire is used, the heat insulation temperature increase ΔTad tends to decrease as the temperature T of the test piece 1 increases. This adiabatic temperature rise amount ΔTad serves as an index indicating how easily the tire temperature rises.

On the other hand, the thermal diffusivity α (mm ² / sec) of the test piece 1 made of the rubber composition for tires is measured. The thermal diffusivity α can be measured in accordance with, for example, JIS R1689: 2011. This thermal diffusivity α is an index of the ease of cooling of the tire.

  In the tire rubber composition evaluation method according to the present invention, the tire rubber composition is evaluated based on the calculated value of the adiabatic temperature rise ΔTad and the thermal diffusivity α at an arbitrary temperature. More preferably, the tire rubber composition is evaluated based on the product of the adiabatic temperature increase ΔTad at an arbitrary temperature and the square root √α of the thermal diffusivity α. That is, it means that the smaller the heat insulation temperature increase ΔTad, the smaller the amount of heat generated by the rubber and the lower the rolling resistance. Further, since the heat temperature increase ΔTad decreases as the rubber temperature rises, it is desirable to keep the rubber temperature at a relatively high temperature from the viewpoint of reducing rolling resistance. Therefore, the smaller the thermal diffusivity α and the smaller the heat release from the rubber, the higher the rubber temperature, which means that the rolling resistance is lowered. In particular, √α indicates the heat conduction distance in a certain time, and the smaller the value, the less heat diffusion means that the rolling resistance becomes lower. By evaluating the tire rubber composition based on the calculated value of the adiabatic temperature rise ΔTad and the thermal diffusivity α having such characteristics, the rolling resistance of the pneumatic tire using the tire rubber composition is reduced. It can be evaluated with high accuracy.

  In evaluating the tire rubber composition based on the calculated value of the adiabatic temperature rise amount ΔTad and the thermal diffusivity α, the temperature is not particularly limited, but in consideration of the tire temperature during running, 60 It is preferable to refer to the adiabatic temperature rise ΔTad and the thermal diffusivity α at ° C. According to the experiment result of the present inventor, it is appropriate to determine that the rolling resistance is low when the product of the adiabatic temperature rise ΔTad at 60 ° C. and the square root of the thermal diffusivity α is 0.0007 or less. . The lower limit value of the product of the adiabatic temperature rise ΔTad at 60 ° C. and the square root √α of the thermal diffusivity α is not particularly limited, but the practical lower limit value is about 0.0001.

FIG. 7 shows the relationship between the square root of the thermal diffusivity α and the adiabatic temperature rise ΔTad. In FIG. 7, the horizontal axis represents the square root √α (mm · sec− ^{1 / 2} ) of the thermal diffusivity α at 60 ° C., and the vertical axis represents the adiabatic temperature increase ΔTad (° C./cycle) at 60 ° C. In FIG. 7, A is a plot of a rubber composition having a ΔTad × √α value of 0.00068, and B is a plot of a rubber composition having a ΔTad × √α value of 0.00073. X is a plot of pure rubber.

  When rubber compositions A and B are compared, according to the conventional index of rolling resistance, the amount of adiabatic temperature rise ΔTad at 60 ° C. is relatively small, that is, the loss tangent tan δ at 60 ° C. is relatively low. The object B is selected as a material having a low rolling resistance. However, when actually manufacturing tires using the rubber compositions A and B, in the tire using the rubber composition A, the tire temperature during running is maintained at about 62 ° C., whereas the rubber is In the tire using the composition B, since the square root √α of the thermal diffusivity α is larger than that of the rubber composition A, the tire temperature during running is maintained at about 55 ° C. As a result, the rubber composition B The rolling resistance of the tire is greater than that of the rubber composition A tire. That is, it can be determined that the rubber composition A having a value of ΔTad × √α of less than 0.0007 has a better rolling resistance than the rubber composition B having a value of ΔTad × √α of more than 0.0007.

  FIG. 8 shows a pneumatic tire for passenger cars according to an embodiment of the present invention. As shown in FIG. 8, the pneumatic tire of the present embodiment includes a tread portion 21 that extends in the tire circumferential direction and has an annular shape, and a pair of sidewall portions 22, 22 disposed on both sides of the tread portion 21. And a pair of bead portions 23, 23 disposed inside the sidewall portion 22 in the tire radial direction.

  A carcass layer 4 is mounted between the pair of bead portions 23 and 23. The carcass layer 24 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded back from the tire inner side to the outer side around the bead core 25 disposed in each bead portion 23. A bead filler 26 made of a rubber composition having a triangular cross section is disposed on the outer periphery of the bead core 25.

  On the other hand, a plurality of belt layers 27 are embedded on the outer peripheral side of the carcass layer 24 in the tread portion 21. These belt layers 27 include a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and are arranged so that the reinforcing cords cross each other between the layers. In the belt layer 27, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set in a range of, for example, 10 ° to 40 °. As the reinforcing cord for the belt layer 27, a steel cord is preferably used. On the outer peripheral side of the belt layer 27, for the purpose of improving high-speed durability, at least one belt cover layer 28 in which reinforcing cords are arranged at an angle of, for example, 5 ° or less with respect to the tire circumferential direction is disposed. Yes. As the reinforcing cord of the belt cover layer 28, an organic fiber cord such as nylon or aramid is preferably used.

  In the pneumatic tire, a cap tread rubber layer 21 </ b> A and an under tread rubber layer 21 </ b> B are disposed on the outer peripheral side of the belt layer 27 in the tread portion 1. Further, a sidewall rubber layer 22A exposed on the outer surface of the tire is disposed on the sidewall portion 22. Further, a rim cushion rubber layer 23 </ b> A exposed on the outer surface of the tire is disposed on the bead portion 23. The tire constituent member including the cap tread rubber layer 21A, the under tread rubber layer 21B, the sidewall rubber layer 22A, and the rim cushion rubber layer 23A is a rubber composition containing carbon black and / or silica as a reinforcing material in a diene elastomer. It is composed of Examples of the diene elastomer include natural rubber (NR), isoprene rubber (IR), epoxidized natural rubber, styrene butadiene rubber (SBR), and butadiene rubber (BR, high cis BR and low cis BR). The compounding amount of carbon black and / or silica may be 30 parts by weight to 200 parts by weight with respect to 100 parts by weight of rubber.

In the pneumatic tire for a passenger car configured as described above, the tire component has a product of the adiabatic temperature rise ΔTad (° C./cycle) at 60 ° C. and the square root √α of the thermal diffusivity α (mm ² / sec). The rubber composition which is 0.0007 or less is used. When such a rubber composition is used, the rolling resistance is low.

  In particular, for the cap tread rubber layer 21A, it is preferable to use a rubber composition in which the product of the adiabatic temperature rise ΔTad at 60 ° C. and the square root √α of the thermal diffusivity α is 0.0007 or less. In addition, a rubber composition in which the product of the adiabatic temperature rise ΔTad at 60 ° C. and the square root √α of the thermal diffusivity α is 0.0005 or less is used for the undertread rubber layer 21B. Furthermore, it is preferable to use a rubber composition having a product of an adiabatic temperature increase ΔTad at 60 ° C. and a square root √α of the thermal diffusivity α of 0.0006 or less for the sidewall rubber layer 22A. Thereby, optimal heat generation characteristics can be imparted to various tire constituent members, and rolling resistance can be effectively reduced.

  Five types of pneumatic tires (Examples 1 to 3 and Comparative Examples 1 and 2) having the same configuration except for compounds A to E having different physical properties were used for the cap tread rubber layer. In addition, five types of pneumatic tires (Examples 4 to 6 and Comparative Examples 3 to 4) were prepared using compounds F to J having different physical properties for the undertread rubber layer and having the same configuration. Furthermore, five types of pneumatic tires (Examples 7 to 9 and Comparative Examples 5 to 6) were prepared using compounds K to O having different physical properties for the sidewall rubber layer and having the same configuration. The tire size is 195 / 65R15.

For the above-mentioned compounds A to O, a vulcanized test piece is prepared, a pulse waveform compression load is applied to the test piece while measuring the temperature of the test piece, and the energy injected into the test piece and the test piece While calculating the adiabatic temperature rise ΔTad (° C / cycle) per cycle of the pulse waveform based on the balance with the energy returned from the heat, the thermal diffusivity α (mm ² / sec) of the compounds A to O is calculated. The product of the adiabatic temperature rise ΔTad at 60 ° C. and the square root √α of the thermal diffusivity α was determined. For compounds A to O, tan δ at 60 ° C. was measured. The physical properties are as shown in Tables 1 to 3.

  Further, the tires of Examples 1 to 9 and Comparative Examples 1 to 6 were assembled on a wheel having a rim size of 15 × 6 JJ, and rolling resistance was measured under conditions of an air pressure of 200 kPa, a load of 4.35 kN, and a speed of 80 km / h. The results are shown in Tables 1 to 3. In addition, the rolling resistance of Examples 1-3 and Comparative Examples 1-2 is shown by the index which makes the measured value of Example 1 100, and the rolling resistance of Examples 4-6 and Comparative Examples 3-4 is Example 4. The rolling resistance of Examples 7 to 9 and Comparative Examples 5 to 6 is indicated by an index with the measured value of Example 7 as 100.

  As shown in Table 1, with respect to the cap tread rubber layer, when tan δ is a small value, the rolling resistance may be greatly changed even by a difference of about 0.01, and the correlation between tan δ and the rolling resistance becomes low. For example, as in Example 2 and Comparative Example 2, even if the same tan δ, the rolling resistance may vary greatly due to the difference in thermal diffusivity α. However, Examples 1-3 using the rubber compositions A to C having a value of ΔTad × √α below 0.0007 used rubber compositions D to E having a value of ΔTad × √α exceeding 0.0007. The rolling resistance was clearly lower than those of Comparative Examples 1 and 2.

  As shown in Table 2, with respect to the undertread rubber layer, when tan δ is a small value, the rolling resistance may be greatly changed even by a difference of about 0.01, and the correlation between tan δ and the rolling resistance becomes low. For example, as in Example 4 and Comparative Example 4, even if the same tan δ, the rolling resistance may vary greatly due to the difference in thermal diffusivity α. However, Examples 4 to 6 using rubber compositions F to H having a value of ΔTad × √α lower than 0.0005 used rubber compositions I to J having a value of ΔTad × √α exceeding 0.0005. The rolling resistance was clearly lower than those of Comparative Examples 3-4.

  As shown in Table 3, with respect to the sidewall rubber layer, when tan δ is a small value, the rolling resistance may change greatly even by a difference of about 0.01, and the correlation between tan δ and the rolling resistance becomes low. For example, as in Example 7 and Comparative Example 6, even if the same tan δ, the rolling resistance may vary greatly due to the difference in thermal diffusivity α. However, Examples 7 to 9 using rubber compositions K to M having a value of ΔTad × √α less than 0.0006 used rubber compositions N to O having a value of ΔTad × √α exceeding 0.0006. The rolling resistance was clearly lower than those of Comparative Examples 5-6.

DESCRIPTION OF SYMBOLS 1 Test piece 11 Support member 12 Press member 21 Tread part 21A Cap tread rubber layer 21B Under tread rubber layer 22 Side wall part 22A Side wall rubber layer 23 Bead part 23A Rim cushion rubber layer

Claims (3)

A vulcanized test piece made of a rubber composition for a tire is prepared, and a compression load having a pulse waveform is applied to the test piece while measuring the temperature of the test piece, and energy injected into the test piece While calculating the adiabatic temperature rise amount ΔTad (° C./cycle) per cycle of the pulse waveform based on the balance with the energy returned from the test piece, the thermal diffusivity α ( mm ² / sec), and the tire rubber composition is evaluated based on a calculated value of the adiabatic temperature rise ΔTad and the thermal diffusivity α at an arbitrary temperature. Evaluation method.   2. The method for evaluating a tire rubber composition according to claim 1, wherein the tire rubber composition is evaluated based on a product of an adiabatic temperature rise amount ΔTad at an arbitrary temperature and a square root of a thermal diffusivity α. .   The tire rubber composition according to claim 2, wherein the rolling resistance is determined to be low when the product of the adiabatic temperature rise ΔTad at 60 ° C and the square root of the thermal diffusivity α is 0.0007 or less. Evaluation method of things.

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