JP6786915B2 - Evaluation method of rubber composition for tires - Google Patents

Description

The present invention relates to a method for evaluating a rubber composition used for a tire, and more specifically, for a tire, which makes it possible to accurately determine a rubber composition for a tire suitable as a cap compound for a heavy-duty tire at low cost. The present invention relates to an evaluation method of a rubber composition.

Large heavy-duty tires, such as construction vehicle tires, are generally used under high load conditions with a thick cap tread. In such a pneumatic tire, since the amount of heat generated by the cap tread is large, the deterioration characteristic due to the heat generation is important as the durability performance.

As one method for reducing the calorific value of the cap tread of a pneumatic tire, it has been proposed to form a shallow groove in the block divided into the tread portion and subdivide the block into a plurality of small blocks. (See, for example, Patent Document 1). In addition to devising the structure of the tread portion, it goes without saying that a rubber composition having low heat generation is being sought as a cap compound.

Conventionally, as a method of evaluating the heat generation characteristics of a cap tread, a pneumatic tire is actually vulcanized, a running test is performed using the actual tire, and after running under predetermined conditions, the tread portion is perforated and the deep portion is reached. The temperature is actually measured. The ultimate temperature is the temperature at which the calorific value of the tread and the heat dissipation are in equilibrium, and it is important to optimize such the ultimate temperature in order to improve the durability performance.

However, as described above, when actually vulcanizing a pneumatic tire and actually measuring the temperature reached in the deep part of the tread after running, it is necessary to prepare a large number of test tires, and there is a problem that the test cost is high. is there. In particular, since the material cost of large heavy-duty tires is high, it is desired to reduce the number of evaluation tires.

JP-A-2015-134571

An object of the present invention is to provide a method for evaluating a rubber composition for a tire, which makes it possible to accurately determine a rubber composition for a tire suitable as a cap compound for a heavy-duty tire at low cost.

In the method for evaluating a rubber composition for a tire of the present invention for achieving the above object, a vulcanized test piece made of the rubber composition for a tire is prepared, and the test piece is subjected to measurement while measuring the temperature of the test piece. On the other hand, a compressive load of the pulse waveform is applied, and the adiabatic temperature rise amount 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. A method for evaluating a rubber composition for a tire , which evaluates the rubber composition for a tire based on the amount of increase in the adiabatic temperature .
When the maximum value of the compressive load is 1000 kPa, the minimum value of the compressive load is 100 kPa, and one cycle of the pulse waveform is 2.5 seconds, the heat insulation is performed when the temperature of the test piece is 60 ° C. When the amount of temperature rise is 0.05 ° C./cycle or less, it is judged that the heat generation as a cap tread is low.
Alternatively, when the maximum value of the compressive load is 1000 kPa, the minimum value of the compressive load is 100 kPa, and one cycle of the pulse waveform is 2.5 seconds, the temperature of the test piece is 70 ° C. When the amount of increase in the adiabatic temperature is 0.04 ° C./cycle or less, it is determined that the heat generating property of the cap tread is low .

As a result of diligent research on the evaluation method of the rubber composition for tires, the present inventor applies a compressive load of a pulse waveform to the test piece, and the energy injected into the test piece and the energy returned from the test piece It was found that the amount of heat insulation temperature increase per cycle of the pulse waveform calculated based on the balance is particularly useful for evaluating the heat generation characteristics of the rubber composition used for the cap compound of heavy-duty tires. The present invention was reached based on this finding.

That is, in the present invention, a vulcanized test piece made of a rubber composition for a tire is prepared, a compression load of a pulse waveform is applied to the test piece while measuring the temperature of the test piece, and the test piece is subjected to a compression load. The amount of heat insulation temperature rise per cycle of the pulse waveform is calculated based on the balance between the energy injected into the tire and the energy returned from the test piece, and the rubber composition for tires is evaluated based on the heat insulation temperature rise. By doing so, it is possible to accurately determine the heat generation characteristics of the rubber composition used for the cap compound of a heavy-duty tire at low cost.

Considering the running environment of heavy-duty tires, as specific test conditions, the maximum value of the compressive load is set to 800 kPa to 1200 kPa, the minimum value of the compressive load is set to 20% or less of the maximum value, and one cycle of the pulse waveform is set. It is preferably 2.0 seconds to 3.0 seconds. By setting such conditions, the heat generation characteristics of the rubber composition used for the cap compound of heavy-duty tires can be accurately determined at low cost.

In particular, when the maximum value of the compressive load is 1000 kPa, the minimum value of the compressive load is 100 kPa, and one cycle of the pulse waveform is 2.5 seconds, the adiabatic temperature rise amount when the temperature of the test piece is 60 ° C. When the temperature is 0.05 ° C./cycle or less, it can be determined that the heat generating property of the cap tread is low. That is, under the above test conditions, it is the amount of heat insulation temperature rise per cycle of the pulse waveform calculated based on the balance between the energy injected into the test piece and the energy returned from the test piece, and is the test piece. A tire rubber composition having an adiabatic temperature increase of 0.05 ° C./cycle or less corresponding to a time when the temperature is 60 ° C. is effective as a cap compound for heavy-duty tires.

When the maximum value of the compressive load is 1000 kPa, the minimum value of the compressive load is 100 kPa, and one cycle of the pulse waveform is 2.5 seconds, the adiabatic temperature rise amount when the temperature of the test piece is 70 ° C. When is 0.04 ° C./cycle or less, it can be determined that the heat generating property of the cap tread is low. That is, under the above test conditions, it is the amount of heat insulation temperature rise per cycle of the pulse waveform calculated based on the balance between the energy injected into the test piece and the energy returned from the test piece, and is the test piece. A tire rubber composition having an adiabatic temperature increase of 0.04 ° C./cycle or less corresponding to a time when the temperature is 70 ° C. is effective as a cap compound for heavy-duty tires.

It is a perspective view which shows the test piece used in the evaluation method of the rubber composition for a tire which concerns on this invention. It is a side view which shows the main part of the apparatus which applies a compressive load to a test piece. It is a graph which shows the pulse waveform (1 cycle) of the compression load applied to the test piece with time. It is a graph which shows the compressive load applied to the test piece and the compressive 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, the amount of heat insulation temperature rise, and the amount of heat dissipation.

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 evaluation method for a rubber composition for a tire according to the present invention. As shown in FIG. 1, the test piece 1 is a vulcanized columnar body made of a rubber composition for a tire 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 capacity of the test device. 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 cylinder having a height h of 8.5 mm and a diameter of 17 mm is used.

FIG. 2 shows a main part of an apparatus for applying a compressive load to a test piece. As shown in FIG. 2, the test piece 1 is arranged 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 reciprocally movable along the vertical direction with respect to the test piece 1 sandwiched between the supporting member 11 and the pressing member 12. The compression 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 and a non-contact type temperature sensor can be used. It is important to fix the test piece to the compressed surface, and use a file that has been filed to prevent slippage during the test, or use a file and the pressing member to prevent slippage. Fix it with adhesive. When slip occurs, the test stroke becomes large and the measured heat insulation temperature rise is calculated to be large, so it is necessary to remeasure under the condition that slip does not occur in order to obtain the 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. 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 the range of 800 kPa to 1200 kPa as the maximum compressive stress applied to the test piece, and the minimum value Fmin of the compressive load F is similarly 20 of the maximum value Fmax as the maximum compressive stress applied to the test piece. It is set to% or less, and one cycle of the pulse waveform is set in the range of 2.0 seconds to 3.0 seconds. More specifically, the maximum value Fmax of the compressive load F is set to 1000 kPa as the maximum compressive stress applied to the test piece, and the minimum value Fmin of the compressive load F is set to 100 kPa as the maximum compressive stress applied to the test piece. The cycle is 2.5 seconds (0.4 Hz). In this case, the fluctuation range of the pulse waveform is 900 kPa. At the time of the load load test, the compression load F having a pulse waveform as shown in FIG. 3 is repeatedly applied to the test piece 1. As a device for applying such a compressive load, for example, an electric actuator type compression load device (500N) manufactured by GABO or an electro-hydraulic servo type test device manufactured by INSTRON can be used.

FIG. 4 shows the compressive load applied to the test piece and the compressive displacement of the test piece over time, FIG. 5 shows the amount of work built into the test piece over time, and FIG. 6 shows the temperature of the test piece and the amount of increase in heat insulation temperature. And the relationship with the amount of heat radiation. In FIGS. 4 to 6, the balance (built-in work amount) between the energy injected into the test piece and the energy returned from the test piece is calculated from the time history data of displacement and load, and the pulse waveform 1 is based on the calculation. This is an example for explaining a method of calculating the adiabatic temperature rise amount per cycle, and does not necessarily match the compressive 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 according to the compression load F. Here, when the compressive displacement ΔH in a minute time in one cycle and the average compressive load F in the minute time are obtained, the amount of work given to the specimen from the outside of the specimen in a 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 given 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, which is the balance, is 1 of the pulse waveform. It increases after the cycle, and the increase becomes the loss energy ΔE per cycle. Assuming that all the loss energy ΔE is converted into heat energy and results in the temperature rise of the test piece 1, the adiabatic temperature increase amount ΔTad per cycle of the pulse waveform can be obtained from the following equation (1). However, 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 represents the temperature T (° C.) of the test piece 1, and the vertical axis represents the adiabatic temperature increase amount ΔTad (° C./cycle). Further, 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 increase amount 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 adiabatic temperature increase amount ΔTad tends to decrease as the temperature T of the test piece 1 increases. By evaluating the rubber composition for tires based on such an adiabatic temperature increase amount ΔTad, it is possible to accurately determine the heat generation characteristics of the rubber composition used for the cap compound of a heavy-duty tire at low cost. ..

For example, for a heavy-duty tire using the rubber composition for a tire having the heat generation characteristics shown in FIG. 6 as a cap compound, the ultimate temperature Tend (termination temperature) of the deep part of the tread portion is actually measured based on a running test, and this is shown in FIG. When displayed in 6, it is possible to estimate the heat dissipation characteristics when this rubber composition for tires is actually used. That is, the temperature decrease amount ΔTre during one rotation (one cycle) of the tire based on heat dissipation tends to increase as the rubber temperature is higher, and the temperature decrease amount ΔTre based on heat dissipation and the heat insulation temperature increase at the reached temperature Tend in the steady state. Since the amount ΔTad is equivalent, the change curve of the temperature decrease amount ΔTre based on heat dissipation can be estimated. This heat dissipation characteristic is mainly determined by the running condition and the tire size, but is influenced by the tire surface shape and the cross-sectional structure. Here, when developing and designing a rubber composition for a tire and aiming to lower the ultimate temperature Tend, the required value of the adiabatic temperature increase amount ΔTad at the target ultimate temperature Tend is determined. That is, in the target reached temperature Tend, it is necessary to make the adiabatic temperature increase amount ΔTad equal to or less than the temperature decrease amount ΔTre based on heat dissipation. Therefore, a rubber composition satisfying such an adiabatic temperature increase amount ΔTad may be prepared and used as a cap compound. As a result, a rubber composition suitable as a cap compound for heavy-duty tires can be accurately selected at low cost based on a laboratory test using the test piece 1. Further, it is preferable to confirm the heat generation characteristics of the rubber composition selected by the laboratory test in an actual running test, but at least an excessive running experiment can be excluded.

In the above-mentioned evaluation method of the rubber composition for tires, in consideration of the running environment of heavy-duty tires (particularly tires for construction vehicles), as a specific test condition, the maximum value Fmax of the compressive load F is 800 kPa as the compressive stress. It is preferable that the minimum value Fmin of the compressive load F is set to about 1200 kPa, the compressive stress is set to 20% or less of the maximum value Fmax, and one cycle of the pulse waveform is set to 2.0 seconds to 3.0 seconds. By setting such conditions, the heat generation characteristics of the rubber composition used for the cap compound of heavy-duty tires can be accurately determined at low cost. If the test conditions deviate from the above range, the running environment of heavy-duty tires in which heat generation characteristics are important will not always be sufficiently reflected.

In particular, when the maximum value Fmax of the compressive load F is 1000 kPa as the compressive stress, the minimum value Fmin of the compressive load F is 100 kPa as the compressive stress, and one cycle of the pulse waveform is 2.5 seconds, the temperature T of the test piece 1 When the adiabatic temperature increase amount ΔTad is 0.05 ° C./cycle or less, preferably as close to zero as possible, it can be determined that the heat generating property of the cap tread is low. That is, under the above test conditions, the adiabatic temperature rise amount ΔTad per cycle of the pulse waveform calculated based on the balance between the energy injected into the test piece 1 and the energy returned from the test piece 1 is used for the test. A tire rubber composition having an adiabatic temperature increase ΔTad of 0.05 ° C./cycle or less corresponding to a time when the temperature T of the piece 1 is 60 ° C. is effective as a cap compound for a heavy-duty tire. When the adiabatic temperature rise amount ΔTad at 60 ° C. is used as an index and the value is set as described above, the temperature reached by the tread portion of the heavy-duty tire can be reduced as compared with the conventional case.

Further, when the maximum value Fmax of the compressive load F is 1000 kPa as the compressive stress, the minimum value Fmin of the compressive load F is 100 kPa as the compressive stress, and one cycle of the pulse waveform is 2.5 seconds, the temperature T of the test piece 1 is set. When the adiabatic temperature increase ΔTad is 0.04 ° C./cycle or less, preferably as close to zero as possible (actually, it does not become zero due to the viscoelastic property of rubber). In addition, it can be determined that the heat generating property of the cap tread is low. That is, under the above test conditions, the adiabatic temperature rise amount ΔTad per cycle of the pulse waveform calculated based on the balance between the energy injected into the test piece 1 and the energy returned from the test piece 1 is used for the test. A tire rubber composition having an adiabatic temperature increase ΔTad of 0.04 ° C./cycle or less corresponding to a time when the temperature T of the piece 1 is 70 ° C. is effective as a cap compound for a heavy-duty tire. When the adiabatic temperature rise amount ΔTad at 70 ° C. is used as an index and the value is set as described above, the temperature reached by the tread portion of the heavy-duty tire can be reduced as compared with the conventional case. The reason why the adiabatic temperature increase amount ΔTad at 70 ° C. is specified separately from the adiabatic temperature increase amount ΔTad at 60 ° C. is that, for example, in the case of a tire having a large size exceeding 40 inches, the reached temperature tends to be higher.

For the three types of rubber compositions A1 to A3, vulcanized test pieces were prepared, a compression load of pulse waveform was applied to the test pieces while measuring the temperature of the test pieces, and the energy injected into the test pieces. Based on the balance between the amount of energy returned from the test piece and the energy returned from the test piece, the adiabatic temperature rise amount ΔTad per cycle of the pulse waveform was calculated and plotted against the temperature of the test piece. At that time, the maximum value of the compressive load was set to 1000 kPa as the compressive stress, the minimum value of the compressive load was set to 100 kPa as the compressive stress, and one cycle of the pulse waveform was set to 2.5 seconds. Based on the result, the adiabatic temperature increase amount ΔTad at the time when the temperature of the test piece was 60 ° C. was determined.

Further, the rubber compositions A1 to A3 were used as a cap compound to prepare tires for construction vehicles of Test Examples 1 to 3 having a tire size of 2700R49. After mounting the tires for construction vehicles of Test Examples 1 to 3 on the drum tester and running for 1 hour under the conditions of an air pressure of 500 kPa, a load of 200 kN, and a running speed of 10 km / h, the tread portion is positioned near the belt edge. The temperature reached at the center of the tread in the thickness direction was measured. The results are shown in Table 1.

As shown in Table 1, in Test Examples 1 and 2 using the rubber compositions A1 and A2 in which the adiabatic temperature increase amount ΔTad at the time when the temperature of the test piece was 60 ° C. was 0.05 ° C./cycle or less, The temperature reached by the tread after running was relatively low. On the other hand, in Test Example 3 using the rubber composition A3 in which the adiabatic temperature increase amount ΔTad at the time when the temperature of the test piece was 60 ° C. exceeded 0.05 ° C./cycle, the tread portion after running was used. The temperature reached was relatively high. As can be seen from this, the adiabatic temperature increase amount ΔTad at 60 ° C. is extremely effective as an index for determining the heat generation characteristics of the rubber composition used for the cap compound.

Next, vulcanized test pieces were prepared for the three types of rubber compositions A4 to A6, and a compression load of a pulse waveform was applied to the test pieces while measuring the temperature of the test pieces, and the test pieces were injected. The adiabatic temperature rise amount ΔTad per cycle of the pulse waveform was calculated based on the balance between the energy obtained and the energy returned from the test piece, and plotted against the temperature of the test piece. At that time, the maximum value of the compressive load was set to 1000 kPa as the compressive stress, the minimum value of the compressive load was set to 100 kPa as the compressive stress, and one cycle of the pulse waveform was set to 2.5 seconds. Based on the result, the adiabatic temperature increase amount ΔTad at the time when the temperature of the test piece was 70 ° C. was determined.

Further, the rubber compositions A4 to A6 were used as a cap compound to prepare tires for construction vehicles of Test Examples 4 to 6 having a tire size of 2700R49. After mounting the tires for construction vehicles of Test Examples 4 to 6 on the drum tester and running for 1 hour under the conditions of an air pressure of 500 kPa, a load of 200 kN, and a running speed of 10 km / h, the tread portion is positioned near the belt edge. The temperature reached at the center of the tread in the thickness direction was measured. The results are shown in Table 2.

As shown in Table 2, in Test Examples 4 and 5 using the rubber compositions A4 and A5 in which the adiabatic temperature increase amount ΔTad at the time when the temperature of the test piece was 70 ° C. was 0.04 ° C./cycle or less, The temperature reached by the tread after running was relatively low. On the other hand, in Test Example 6 using the rubber composition A6 in which the adiabatic temperature increase amount ΔTad at the time when the temperature of the test piece was 70 ° C. exceeded 0.04 ° C./cycle, the tread portion after running was used. The arrival temperature of was relatively high. As can be seen from this, the adiabatic temperature increase amount ΔTad at 70 ° C. is extremely effective as an index for determining the heat generation characteristics of the rubber composition used for the cap compound.

1 Test piece 11 Support member 12 Pressing member

Claims (2)

A vulcanized test piece made of a rubber composition for a tire is prepared, a compression load of a pulse waveform is applied to the test piece while measuring the temperature of the test piece, and the energy injected into the test piece is used. The amount of increase in adiabatic temperature per cycle of the pulse waveform is calculated based on the balance with the energy returned from the test piece, and the rubber for tire is evaluated based on the amount of increase in adiabatic temperature. A method for evaluating a composition
When the maximum value of the compressive load is 1000 kPa, the minimum value of the compressive load is 100 kPa, and one cycle of the pulse waveform is 2.5 seconds, the heat insulation is performed when the temperature of the test piece is 60 ° C. A method for evaluating a rubber composition for a tire, which comprises determining that the heat generating property of a cap tread is low when the amount of temperature rise is 0.05 ° C./cycle or less. A vulcanized test piece made of a rubber composition for a tire is prepared, a compression load of a pulse waveform is applied to the test piece while measuring the temperature of the test piece, and the energy injected into the test piece is used. The amount of increase in adiabatic temperature per cycle of the pulse waveform is calculated based on the balance with the energy returned from the test piece, and the rubber for tire is evaluated based on the amount of increase in adiabatic temperature. A method for evaluating a composition
When the maximum value of the compression load is 1000 kPa, the minimum value of the compression load is 100 kPa, and one cycle of the pulse waveform is 2.5 seconds, the heat insulation is performed when the temperature of the test piece is 70 ° C. A method for evaluating a rubber composition for a tire, which comprises determining that the heat generating property of a cap tread is low when the amount of temperature rise is 0.04 ° C./cycle or less.

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