JP7127467B2 - Test method for pneumatic tires - Google Patents

Description

The present invention relates to a method for testing pneumatic tires.

In pneumatic tires such as passenger car tires, TGC (tread groove cracks) may be found in the tread as a form of damage in the market, for example, after long-term use. TGC refers to a phenomenon in which cracks occur in the bottom of grooves in a tire tread due to fatigue due to repeated strain. This TGC is likely to occur when the surface of the tread deteriorates mainly due to ultraviolet rays and ozone in the atmosphere. The generation of this TGC has a great influence on the appearance of the pneumatic tire.

BACKGROUND ART Conventionally, as a durability test of a tire, a running test of the tire is carried out using a bench test apparatus having a drive drum. Prior to running tests, test tires are sometimes subjected to deterioration treatment by heating, deterioration treatment by ozone or oxygen, and the like. These treatments are intended to replicate damage to tires in the market by accelerating the deterioration of the tires tested. Such tests are used to evaluate the durability of tires.

Patent Literature 1 discloses a test method for reproducing surface cracks such as TGC and rapidly evaluating tire durability.
Specifically, Patent Document 1 describes a thermal deterioration treatment process in which a test tire filled with internal pressure is held in a high-temperature atmosphere, and the test tire subjected to this thermal deterioration treatment and filled with internal pressure, An ozone deterioration treatment process held in an ozone atmosphere, and a running test in which the above-mentioned test tire subjected to this ozone deterioration treatment is rotated with a test internal pressure and a test load applied by a bench test device. and wherein the ozone deterioration treatment step and the running test step are repeated in that order one or more times.
The test method disclosed in Patent Literature 1 is effective as a test method for evaluating the occurrence of TGC and the like, which is considered to be caused by the decrease in antioxidant contained in tires.

JP 2014-100977 A

The following mechanism is also considered as a mechanism of generation of TGC in tires in the market. Namely
(1) Wax deposits on the groove bottom surface of the tire tread, forming a wax layer with uneven thickness on the groove bottom surface of the tire tread,
(2) Cracking occurs at thin portions of the wax layer due to repeated strain occurring in the groove bottom of the tire tread,
(3) It is believed that the cracked portion is attacked by ozone, and a crack (TGC) is generated at the groove bottom of the tire tread.
On the other hand, in the test method disclosed in Patent Document 1, it is difficult to reproduce the uneven wax layer in thickness formed on the groove bottom surface of the tire tread. It was difficult to evaluate tire durability.

The present invention has been made in view of the current situation, and is intended to prevent tread groove cracks (TGC) caused by the formation of a wax layer having an uneven thickness on the groove bottom surface of the tire tread in tires on the market. It is an object of the present invention to provide a pneumatic tire testing method that can reproduce and rapidly evaluate the durability of a tire against TGC.

A method for testing a pneumatic tire according to the present invention includes:
(a) a pretreatment step of holding the test tire filled with internal pressure at a temperature of −45° C. to −15° C., which is the melting point of the wax contained in the test tire;
(b) a running test step in which the test tire that has undergone the pretreatment step is rotated by a bench test device;
(c) an ozone treatment step of leaving the test tire that has undergone the running test step under an ozone atmosphere;
and after performing step (a), step (b) and step (c) are alternately performed in that order.

In the step (a), the temperature at which the test tire is held is preferably -30°C to -20°C, which is the melting point of the wax.
In the above step (a), it is preferable that the test tire is held for 7 to 21 days.

In the pneumatic tire test method, the following step (d) is performed between the step (a) and the step (b) and/or between the step (b) and the step (c). preferably.
(d) A cleaning step for cleaning the surface of the test tire.

The step (b) is preferably carried out so that the groove bottom surface temperature of the test tire is -45°C to -15°C, which is the melting point of the wax contained in the test tire.
In the above step (c), the test tire was held at a temperature of 20 to 50°C, an ozone concentration of 10 to 50 pphm, a holding time of the test tire for 1 to 14 days, and the test internal pressure was normal internal pressure - It is preferable that the internal pressure is 70 kPa to the normal internal pressure, and the test load is from the normal load to 150% of the normal load.

In the pneumatic tire test method, it is preferable that after performing the step (a), the steps (b) and (c) are repeated in this order two or more times.

According to the method for testing a pneumatic tire according to the present invention, it is possible to accurately reproduce tread groove cracks (TGC) of tires that occur in the market, thereby reliably evaluating the crack resistance performance of tires. can.

FIG. 1 is a partial cross-sectional view schematically showing an example of a tire subjected to execution of a test method according to one embodiment of the present invention. FIG. 2 is a diagram for explaining the order of steps executed in the test method according to one embodiment of the present invention. FIG. 3 is a perspective view schematically showing an example of a bench test apparatus used for executing the test method according to one embodiment of the present invention. 4A and 4B are SEM images of the wax layer formed on the surface of the groove bottom in the pretreatment step performed in Example 1. FIG. 4A is the SEM image of the surface of the wax layer, and FIG. 4B is the cross section of the wax layer. is an SEM image of.

Hereinafter, a preferred embodiment of the method for testing a pneumatic tire according to the present invention will be described with reference to the drawings as appropriate.

In the present invention, a state in which the tire is mounted on a normal rim, the internal pressure of the tire is adjusted to the normal internal pressure, and no load is applied to the tire is referred to as a normal state. In the present invention, the dimensions and angles of the tire and each portion of the tire are measured under normal conditions unless otherwise specified.

As used herein, the term "regular rim" means a rim defined in the standards on which tires rely. A "standard rim" in the JATMA standard, a "design rim" in the TRA standard, and a "measuring rim" in the ETRTO standard are regular rims.

As used herein, the normal internal pressure means the internal pressure defined in the standards on which the tire relies. The "maximum air pressure" in JATMA standards, the "maximum value" in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in TRA standards, and the "INFLATION PRESSURE" in ETRTO standards are regular internal pressures.

As used herein, the normal load means the load defined in the standard on which the tire relies. "Maximum load capacity" in the JATMA standard, "maximum value" in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and "LOAD CAPACITY" in the ETRTO standard are normal loads.

[Test tires]
First, pneumatic tires to be evaluated in the above test method will be described.
FIG. 1 is a partial cross-sectional view schematically showing an example of a tire subjected to execution of the test method according to this embodiment.
The pneumatic tire 2 shown in FIG. 1 is a tire that can be evaluated by the above test method. In FIG. 1, the vertical direction is the radial direction of the tire, the horizontal direction is the axial direction of the tire, and the direction perpendicular to the paper surface is the circumferential direction of the tire.
The pneumatic tire 2 shown in FIG. 1 has a substantially symmetrical shape centered on the dashed-dotted line CL. This dashed-dotted line CL represents the equatorial plane of the tire 2 . Only the main parts of the tire are shown in FIG. This tire 2 comprises a tread 4 , sidewalls 6 , beads 8 , carcass 10 and belt 12 . This tire 2 is of the tubeless type. This tire 2 can be mounted on a passenger car.

The tread 4 is made of a crosslinked rubber composition (hereinafter also simply referred to as rubber), and contains wax and the like in addition to the rubber component. The tread 4 has a shape that is convex radially outward. The outer peripheral surface of the tread 4 constitutes a tread surface 18 that contacts the road surface. Grooves 20 are cut in the tread surface 18 . The grooves 20 form a tread pattern. In the market, cracks (TGC) may occur at the bottom of the grooves 20 due to deterioration due to long-term use of the tire 2 .

The bead 8 has a core 14 and an apex 16 extending radially outward from the core 14 .

The carcass 10 consists of carcass plies 22 . The carcass ply 22 is composed of a large number of cords (not shown) arranged in parallel and a topping rubber. A carcass ply 22 spans between the beads 8 on both sides and runs along the tread 4 and the sidewalls 6 . The carcass ply 22 is folded back around the core 14 from the inner side to the outer side in the axial direction.

The belt 12 is laminated radially outward of the carcass 10 . Belt 12 reinforces carcass 10 . In this tire 2, the belt 12 has a two-layer structure. The belt 12 is not limited to a two-layer structure, and may have a single layer or three or more layers.

[Test procedure]
The procedure of the test method for the pneumatic tire will be explained.
FIG. 2 is a diagram for explaining the order of steps executed in the test method according to the present embodiment.
In the above test method, as shown in FIG. 2, (i) pretreatment step S1 is first performed.
Thereafter, (ii) first cleaning step S2, (iii) running test step S3, (iv) second cleaning step S4 and (v) ozone treatment step S5 are performed in this order.
Here, (i) the pretreatment step S1, (iii) the running test step S3 and (v) the ozone treatment step S5 are essential steps. On the other hand, (ii) the first cleaning step S2 and (iv) the second cleaning step S4 are optional steps, and may be performed as necessary.

In the above test method, after each step (i) to (v) is performed once, the steps (ii) to (v) may be repeated once or more times. Even when the above steps (ii) to (v) are repeated, steps (ii) and (iv) are optional steps.
In the above test method, it is preferable to repeat each step (i) to (v) once, and then repeat the steps (ii) to (v) once, twice, or three times.

Each of the above steps (i) to (v) will be described below.
The test method is intended to reproduce the tire TGC that occurs in the market. Therefore, the test tire 2 to be tested is a tire that is mounted on a test rim corresponding to a normal rim and filled with air.

[(i) Pretreatment step]
In this pretreatment step S1, wax is deposited on the surface of the bottom of the groove 20 of the test tire 2 (herein also referred to as the groove bottom surface) to form a wax layer having a non-uniform thickness. This is the process for the purpose. When a wax layer having an uneven thickness is formed on the groove bottom surface, the surface is observed as an uneven surface.
In order to form a wax layer having a non-uniform thickness on the groove bottom surface, in this step, the test tire 2 is held in a constant temperature bath.

The internal temperature of the constant temperature bath is set to a temperature of −45° C. to −15° C. which is the melting point of the wax contained in the test tire 2 (tread 4). By maintaining the sample tire 2 at the above temperature, the deposition of the wax can be promoted and the thickness of the formed wax layer can be made uneven.
On the other hand, if the internal temperature of the constant temperature bath is lower than -45°C, which is the melting point of the wax, the wax may not precipitate sufficiently. Further, when the temperature inside the constant temperature bath is higher than the melting point of wax of −15° C., the wax precipitates, but the wax layer formed has a substantially uniform thickness and a smooth surface. Furthermore, the wax may back up into the rubber over time.
The internal temperature of the constant temperature bath is preferably -30°C to -20°C, which is the melting point of the wax.
In the present invention, the melting point of wax is the peak top temperature measured using a differential scanning calorimeter (DSC). For example, using a differential scanning calorimeter (Thermo plus DSC8230, manufactured by Rigaku), the temperature is raised at a rate of 5° C./min, and the resulting melting peak top can be taken as the melting point.
Further, in the present invention, when the temperature is expressed as "the temperature of −X° C. of the melting point of the wax", it means the temperature obtained by subtracting X° C. from the melting point of the wax. Thus, for example, "the melting point of wax at −45° C." is the temperature obtained by subtracting 45° C. from the melting point of wax.

In this step, the time (holding time) for holding the test tire 2 in the constant temperature bath is preferably 7 to 21 days. In this case, the deposition of the wax is promoted and the thickness of the formed wax layer is not uniform.
If the holding time is less than 7 days, the wax may not be sufficiently deposited on the groove bottom surface of the test tire 2 . On the other hand, if the holding time exceeds 21 days, even if the wax layer is formed, the thickness may be poorly uniform and the surface of the wax layer may become nearly smooth.
More preferably, the holding time is 10 to 17 days.

[(ii) First washing step]
This first washing step S2 is a step for washing away stains adhering to the tire surface including the groove bottom surface of the test tire 2 and chemicals such as anti-aging agents deposited on the surface of the test tire 2.
In this step, the surface of the test tire 2 may be sprayed with water or water containing a detergent.
Further, when performing this step, it is necessary to avoid removing the wax deposited on the groove bottom surface of the test tire 2 in the pretreatment step S1. Therefore, in this step, for example, the surface of the test tire 2 is not rubbed.
As described above, this first cleaning step S2 is an optional step that is performed as necessary.

[(iii) Running test step S3]
In the running test step S3, a tire running test is performed for the purpose of reproducing cracks in the wax layer having a non-uniform thickness formed on the groove bottom surface of the groove 20 of the test tire 2 in the pretreatment step S1. It is a process to do.
In this step, in order to reproduce the cracking of the wax layer, the test tire 2 is rotated by a bench test device (see FIG. 3) in a state where the test internal pressure is filled and the test load is applied. do the test.

<Bench test equipment (driving test equipment)>
FIG. 3 is a perspective view schematically showing an example of a bench test apparatus used for executing the test method according to this embodiment.
A bench test device 32 shown in FIG. 3 is a device for conducting a running test of the tire 2 .
The bench test apparatus 32 includes a test rim 34 on which the test tire 2 is mounted, a support device 36 that supports the rim 34, and a drive drum 38 that drives the test tire 2 to rotate.

The rim 34 is rotatably supported on the rotating shaft 40 of the supporting device 36 . The support device 36 includes a rotation drive device and a brake mechanism (not shown). The support device 36 can make the rotating shaft 40 rotatable, drive it to rotate without depending on the drive drum 38, and restrain it (brake it). These actions of the support device 36 allow the test tire 2 to be accelerated, decelerated and stopped rotating.
A support device 36 and a drive drum 38 are mounted on the test rack 33 . The drive drum 38 is rotated by an electric motor (not shown). The support device 36 can vertically move the test tire 2 by a lifting device such as a fluid pressure cylinder (not shown). As a result, the test tire 2 can move away from and approach the driving drum 38 . The test tire 2 mounted on the rim 34 is pressed against the driving drum 38 by the lifting device, and a predetermined load is applied. The test tire 2 can be rotationally driven by the driving drum 38 in this state. Furthermore, the support device 36 is configured to be able to adjust the slip angle when the test tire 2 is pressed against the driving drum 38 .

<Running test>
A bench test device 32 is used for the running test. This running test is also called a bench test. This running test is performed on the test tire 2 that has undergone the pretreatment step S1.
In this test, the test rim 34 with the test tire 2 mounted thereon is attached to the rotating shaft 40 of the supporting device 36 . After the test tire 2 is filled with a predetermined test internal pressure, the running test is started. The test tire 2 is pressed against the outer peripheral surface of the drive drum 38 with a predetermined test load by the supporting device 36 . The test tire 2 is run in this state.

In the running test step S3, the running condition is such that the groove bottom surface temperature of the tire 2 is -45°C to -15°C, which is the melting point of the wax contained in the tire 2 (tread 4), preferably at the melting point of the wax. The test tire 2 is run under running conditions such that the temperature is -30°C to -20°C.
The groove bottom surface temperature of the test tire 2 may be measured by a known method such as measurement using an infrared radiation thermometer.

In this running test step S3, the running conditions for keeping the groove bottom surface temperature of the test tire 2 within the above range are not particularly limited, and the running test speed, test internal pressure, test load, slip angle, running period, etc. are appropriately selected. It should be adjusted by doing
The running test speed may be set, for example, in the range of 20 to 60 km/hour.
The test internal pressure may be set, for example, within a range of "regular internal pressure -70 kPa" or more and below the normal internal pressure.
The test load may be set, for example, within a range of "normal load" or more and "150% of normal load" or less.
The slip angle may be set, for example, within a range of -3° to 3°.
The running period may be set to, for example, 10 to 100 hours.
By appropriately setting these running conditions and controlling the groove bottom surface temperature during running of the test tire 2 within the above range, in this running test step S3, the groove bottom surface of the test tire 2 was formed with Cracking of the wax layer can be reproduced.

[(iv) Second washing step]
In the second washing step S4, the dirt adhering to the surface of the test tire 2 and chemicals such as anti-aging agents deposited on the surface of the test tire 2 are washed away from the test tire 2 after the running test step S3. It is a process for
A specific cleaning method is the same as in the first cleaning step S2.
As described above, this second cleaning step S4 is an optional step that is performed as necessary.

[(v) Ozone treatment step]
This ozone treatment step S5 is a step performed for the purpose of generating cracks in the groove bottom surface (rubber surface of the groove bottom) of the test tire 2 .
The test tire 2 that has undergone the running test step S3 has cracks in the wax layer formed on the rubber surface of the groove bottom of the test tire 2 . When cracks occur in the wax layer, in this step, ozone that has penetrated through the cracked portions of the wax layer reaches the rubber surface of the groove bottom of the test tire 2 and attacks the rubber. As a result, a crack starting point is generated on the rubber surface of the groove bottom of the test tire 2, and the crack grows further.
Therefore, by going through this ozone treatment step S5, it is possible to reproduce the crack generation (TGC generation) on the groove bottom surface of the test tire 2 .

In this ozone treatment step S5, in order to reproduce cracks that occur on the rubber surface of the groove bottom of the test tire 2 when the groove bottom rubber surface is attacked by ozone, a predetermined It is preferable to hold the test tire 2 with the test load applied.

The above ozone concentration is preferably 10 to 50 pphm. It is preferable that the test load is not less than the normal load and not more than "150% of the normal load". When these conditions are satisfied, it is suitable for reproducing the generation of cracks on the rubber surface of the groove bottom of the test tire 2 .
On the other hand, when the ozone concentration is less than 10 pphm or the test load is less than the normal load, cracks and their starting points may be less likely to occur on the rubber surface of the groove bottom of the test tire 2 . In addition, when the ozone concentration exceeds 50 pphm or the test load exceeds 150% of the normal load, a crack larger (longer in length) than a crack occurring in a tire on the market is formed in the test tire 2. There is a risk that it will occur and that the order of superiority and inferiority in the market cannot be reproduced.

In the ozone treatment step S5, the holding temperature of the test tire 2 is 20 to 50° C., the holding time of the test tire 2 is 1 to 14 days, and the test internal pressure of the test tire 2 is "regular internal pressure -70 kPa" or more. It is preferable that the internal pressure is equal to or less than the normal internal pressure. By satisfying these conditions, it becomes easier to reproduce the generation of cracks on the rubber surface of the groove bottom of the test tire 2 .

In order to perform the ozone treatment step S5 under such conditions, for example, the test tire 2 is attached to the bench test device 32 used in the running test step S3, and the test tire 2 is heated without rotating the driving drum 38. is pressed against the driving drum 38 with a predetermined load, and while maintaining this state, the test tire 2 is covered with a hood or the like, and the test tire 2 is exposed to the ozone atmosphere.
When the running test step S3 and the ozone treatment step S5 are repeatedly performed, by adopting the above method, it is possible to reduce the trouble of attaching and detaching the test tire 2 to and from the bench test device 32 .
Of course, after the running test step S3 or the second washing step S4 is completed, the test tire 2 is removed from the bench test device 32, and the test tire 2 is separately tested by another device that applies a load to the test tire 2. The test tire 2 may be held and exposed to the ozone atmosphere in that state.

By sequentially performing such (i) pretreatment step to (v) ozone treatment step, a wax layer with uneven thickness is formed on the groove bottom surface of the tire, cracks occur in this wax layer, and the wax layer It is possible to reproduce the phenomenon that cracks occur in the rubber under the cracked part.
It should be noted that the observation point for the presence or absence of cracks after the ozone treatment step S5 is preferably a point where a predetermined load is applied and the surface strain is increased in the ozone treatment step S5. This is because this portion can reproduce the occurrence of TGC with good reproducibility.

In the pneumatic tire test method according to the embodiment of the present invention, after each step of (i) the pretreatment step to (v) the ozone treatment step is performed once, (ii) the first cleaning step to ( v) Each step of the ozonation process is preferably repeated.
In the first ozone treatment step S5, cracks can be expected to occur on the rubber surface of the groove bottom of the tire. In many cases, the starting point of a crack that has not grown to a crack remains.
Therefore, by performing the running test step S3 again after completing the first ozone treatment step S5, cracks can grow from the starting point of the cracks generated in the first ozone treatment step S5. This brings the test method of the present embodiment closer to reproducing the TGC that occurs in tires on the market.
Further, when the ozone treatment step S5 is performed a plurality of times, it is preferable that the locations where the load is applied to the test tire 2 are the same as much as possible, from the viewpoint of approximating the reproduction of the TGC that occurs in tires on the market.

In the pneumatic tire test method according to the embodiment of the present invention, each step of (i) pretreatment step to (v) ozone treatment step is performed once from the viewpoint of more accurately reproducing TGC that occurs in tires on the market. After that, it is preferable to repeat the steps from (ii) the first washing step to (v) the ozone treatment step twice.

In the present embodiment, the test tire 2 after the ozone treatment step S5 is checked for the presence or absence of cracks and the dimensions of the cracks by visual inspection or microscopic observation, and the results are recorded. be. From these records, the durability performance of tires against TGC can be compared and evaluated.

In the above test method for pneumatic tires, after each step of (i) pretreatment step to (v) ozone treatment step is performed once, (ii) first cleaning step to (v) ozone treatment step , it is not always necessary to end the test when the (v) ozone treatment process is completed, and in some cases, the test may be completed when the (iii) running test process is completed.
Therefore, in the pneumatic tire testing method according to the embodiment of the present invention, the final step is usually (v) the ozone treatment step, but may include (iii) the running test step. Furthermore, when the (iv) second washing step is performed, the (iv) second washing step may be the final step.

The effects of the present invention will be clarified by examples below, but the present invention should not be construed in a limited manner based on the description of these examples.

(Example 1)
The above-described (i) pretreatment step, (ii) first cleaning step, (iii) running test step, (iv) second cleaning step and (v) ozone treatment for the radial tire for passenger cars (test tire) Each step was performed once in this order, and then steps (ii) to (v) were repeated twice under the same conditions as the first time.
In the test tire, the rubber constituting the tread contains wax having a melting point of 65°C. The rubber also contains anti-aging agents. The size of the test tire is 175/65R15.
Specifically, each step was performed as follows.

(i) Pretreatment step: The test tire was placed in a constant temperature bath whose internal temperature was set to -25°C, the melting point of the wax contained in the test tire. Here, a plurality of test tires were placed in a constant temperature bath.
The test tires were held in a constant temperature bath for 14 days and then taken out.
After taking out the test tire from the constant temperature bath, this test tire was attached to the bench test apparatus 32 shown in FIG. In this state, the subsequent steps were carried out.

In addition, a sample for measuring the thickness of the wax layer formed on the groove bottom surface was prepared from one of the test tires taken out from the constant temperature bath, and FT-IR (Fourier transform The thickness of the wax layer was measured using an infrared spectrophotometer). The peak intensity obtained by this measurement was defined as the thickness index of the wax layer, and the peak intensity obtained in this example was defined as 100 for the thickness index.

Furthermore, a sample for observing the wax layer formed on the groove bottom surface with a SEM (scanning electron microscope) was prepared from the test tire, and this sample was used to observe the surface of the wax layer (observation magnification of 1000 times). And the cross section (observation magnification of 10000 times) was observed with SEM. In addition, cross-sectional observation was performed by attaching a protective film to the upper surface of the wax layer.
One of the results of SEM observation is shown in FIG. 4A and 4B are SEM images of the wax layer, FIG. 4A being an SEM image of the surface of the wax layer, and FIG. 4B being an SEM image of the cross section of the wax layer.
Furthermore, the amount of unevenness of the wax layer was measured using the SEM image of the cross section of the wax layer. Specifically, the thickness difference between the thickest portion and the thinnest portion of the wax layer was calculated. Here, five observation images were acquired, the difference in thickness was calculated for each image, and the average value was used as the unevenness amount of the wax layer in this example. This unevenness amount was used as a reference amount for comparison with other examples and comparative examples.

(ii) First washing step: Water was applied to the test tire using a hose to wash the surface of the test tire.
(iii) Running test step: The test tire was run for 1 day under the condition that the groove bottom surface temperature during running was 40°C.
At this time, the test internal pressure of the test tire was normal internal pressure -50 kPa, the test load was 150% of the normal load, the slip angle was 0°, the running speed was in the range of 20 to 60 km/h, and the groove bottom surface temperature was 40°C. was adjusted so that

(iv) Second washing step: Water was applied to the test tire using a hose to wash the surface of the test tire.
(v) Ozone treatment step: The test tire was held in an ozone atmosphere for 3 days while attached to the bench test device 32 .
At this time, the ozone concentration was set to 30 pphm, the test internal pressure of the test tire was normal internal pressure -50 kPa, and the test load was 150% of the normal load.

After each step was performed a predetermined number of times, the test tire was removed from the bench test device 32 and evaluated as follows.
First, a sample was prepared for observing the wax layer formed on the groove bottom surface of the test tire after completion of the test with an SEM (scanning electron microscope). times) were observed by SEM. At this time, the sample was cut from the portion where the load was applied in the ozone treatment step.

Next, the crack length was evaluated based on the obtained SEM image.
For the evaluation of the crack length, first, based on the above SEM image, it was observed whether or not cracks occurred in the wax layer and further cracks occurred in the rubber. Then, when cracks were found on the rubber surface of the groove bottom, the crack with the longest length was specified in the obtained image, and the length of the crack was measured. Here, five observation images were acquired, the length of the crack was measured for each image, and the average value was used as the crack length in this example.

(Example 2-4/Comparative Example 1-2)
(i) The internal temperature of the constant temperature bath and the holding period in the constant temperature bath in the pretreatment process, (ii) the presence or absence of the first washing process, and (iv) the presence or absence of the second washing process were changed as shown in Table 1. The test was performed in the same manner as in Example 1, except that
Furthermore, the test results were evaluated in the same manner as in Example 1, and the results are shown in Table 1 together with the results of Example 1.

(1) Wax layer thickness index The thickness of the wax layer formed on the groove bottom surface was measured by FT-IR in the same manner as in Example 1, and the measurement result (peak intensity) of Example 1 was set to 100. The results are shown in Table 1 as relative values.
(2) Degree of Unevenness of Wax Layer In the same manner as in Example 1, the amount of unevenness of the wax layer formed on the groove bottom surface after the pretreatment process was completed was obtained. Thereafter, the amount of unevenness of the obtained wax layer was compared with the amount of unevenness of the wax layer of Example 1, and the degree of unevenness of the wax layer was evaluated according to the following criteria.
A: The amount of unevenness is 75% or more of the amount of unevenness in Example 1.
Good: The amount of unevenness is 50% or more and less than 75% of the amount of unevenness in Example 1.
Δ: The amount of unevenness is 25% or more and less than 50% of the amount of unevenness in Example 1.
x: The amount of unevenness is less than 25% of the amount of unevenness in Example 1.

(3) Degree of crack generation The length of the crack generated on the rubber surface of the groove bottom was measured in the same manner as in Example 1, and the result was expressed as a relative value when the length of the crack in Example 1 was set to 100. Table 1 shows.

From the results of the above examples/comparative examples, according to the present invention, a wax layer having a non-uniform thickness is formed on the groove bottom surface of the tire tread, and the repeated strain generated on the groove bottom of the tire tread reduces the thickness of the wax layer. It was clarified that the TGC caused by the cracks occurring in the steel and attacking the cracked portions with ozone can be reproduced.
Therefore, it has been clarified that the pneumatic tire test method of the present invention is suitable as a method for evaluating durability against TGC caused by the above mechanism.
In addition, in the evaluation results of Comparative Examples 1 and 2, the thickness index of the wax layer was low in both cases, and the degree of unevenness of the wax layer was evaluated as "x". Regarding this, in Comparative Example 1, the wax was not precipitated in the pretreatment step in the first place, and the above results were obtained. It is presumed that the wax returned to the rubber while it was in use, resulting in the above results.

The method for testing a pneumatic tire according to the present invention is suitable for evaluating the durability of tires against tread groove cracks (TGC).

2...Tire 4...Tread 6...Sidewall 8...Bead 10...Carcass 12...Belt 14...Core 16...Apex 18...Tread surface 20. Groove 22 Carcass ply 32 Bench test device 33 Test stand 34 Rim 36 Support device 38 Drive drum 40 Rotation (of the support device) Axis S1... Pretreatment process S2... First cleaning process S3... Running test process S4... Second cleaning process S5... Ozone treatment process

Claims (7)

(a) a pretreatment step of holding the test tire filled with internal pressure at a temperature of −45° C. to −15° C., which is the melting point of the wax contained in the test tire;
(b) a running test step in which the test tire that has undergone the pretreatment step is rotated by a bench test device;
(c) an ozone treatment step of leaving the test tire that has undergone the running test step in an ozone atmosphere;
including
A method for testing a pneumatic tire, wherein after performing step (a), step (b) and step (c) are alternately performed in this order. 2. The method for testing a pneumatic tire according to claim 1, wherein in said step (a), the temperature at which the test tire is held is -30° C. to -20° C. of the melting point of said wax. The method for testing a pneumatic tire according to claim 1 or 2, wherein the test tire is held for 7 to 21 days in the step (a). Any one of claims 1 to 3, wherein the following step (d) is performed between the step (a) and the step (b) and/or between the step (b) and the step (c) The test method for pneumatic tires described in .
(d) A cleaning step for cleaning the surface of the test tire. 5. Any one of claims 1 to 4, wherein the step (b) is carried out so that the groove bottom surface temperature of the test tire is -45°C to -15°C, which is the melting point of the wax contained in the test tire. The method for testing a pneumatic tire according to 1. In the step (c), the holding temperature of the test tire is 20 to 50° C., the ozone concentration is 10 to 50 pphm, the holding time of the test tire is 1 to 14 days, and the test internal pressure is normal internal pressure − The method for testing a pneumatic tire according to any one of claims 1 to 5, wherein the internal pressure is from 70 kPa to the normal internal pressure, and the test load is from the normal load to 150% of the normal load. The method for testing a pneumatic tire according to any one of claims 1 to 6, wherein after performing the step (a), the step (b) and the step (c) are repeated in this order two or more times.

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