JP2005098754A - Aging test method of automobile tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a durability test method capable of acquiring in a short time, deterioration with age equivalent to actual running in a high-temperature and high-humidity using environment represented by a tropical rain forest climate, in order to evaluate mainly the BEL-resistance of an automobile tire. <P>SOLUTION: In an aging acceleration test of the automobile tire, this test method is characterized by being exposed alternately to a wet heat cycle and a dry heat cycle. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention mainly evaluates the BEL resistance of automobile tires so that the deterioration over time is the same as that of automobile tires driven in a hot and humid environment such as a rainforest climate. The present invention relates to an aging test method that can be obtained quickly and with a high correlation with the actual use environment by promoting aging.

  Conventionally, in the hot and humid use environment represented by the tropical rainforest climate and tropical monsoon climate that belong to the climate class called tropical with a temperature of 18 ° C or more throughout the year according to the Köppen climate classification, BEL (Breaker Edge Looseness or Band Edge Looseness) is known to occur easily. In other words, the edge band is provided on the outside of the breaker or belt laminated on the tire crown for the high speed stability of high performance tires for automobiles. This is a problem in terms of ensuring the durability of tires in the environment.

Therefore, development of a tire excellent in BEL resistance is required, but there is no fixed method for evaluating the BEL resistance, and there are many problems in the conventional methods. As a method for evaluating the BEL resistance, roughly two methods are known. One is a method for evaluating an automobile tire actually run in a use environment in a rainforest climate and a tropical monsoon climate, and the other is a method for evaluating an automobile tire by promoting aging in an artificial environment.
First, the method of evaluating an automobile tire actually run in a use environment in a rainforest climate and a tropical monsoon climate has a drawback that it takes a lot of time to obtain a result. This is because such a method needs to be evaluated later after the actual running. In addition, the prolonged warranty life of automotive tires in recent years has made it more difficult to obtain results in a short time. Therefore, it is difficult to say that the evaluation after actual use is a test method suitable for developing an automobile tire excellent in BEL resistance.

In addition, several test methods have been known so far for the evaluation of automobile tires by promoting aging in an artificial environment, and all of them are optimal for developing automobile tires having excellent BEL resistance. There is a problem that cannot be said to be an evaluation method.
For example, JIS K6301-1975 known as such an aging test method is defined as an aging acceleration test of vulcanized rubber in air or oxygen, and is also used for evaluation of BEL resistance. Although environmental factors can evaluate the effects of oxygen concentration, temperature, and time on the aging of automobile tires, humidity is not added to environmental factors, so the durability of automobile tires in high-temperature and high-humidity environments There is a problem as a method for evaluating BEL resistance.

  Further, the humidity resistance performance test described as a reference in JIS D4230-1978 is also known as an aging test method. This is a test method in which a tire for automobile after being held in an environment of 35 to 41 ° C. and 90 to 100% humidity for 20 days is subjected to a high-speed durability performance test, and rubber deterioration is evaluated by visual inspection. Unlike JIS K6301, the influence of humidity on aging can be evaluated. However, since only visual inspection is performed, BEL generated inside the tire cannot be evaluated with high accuracy. In addition, 20 days are required for the aging treatment itself, and more days are required for evaluation, so it cannot be said that it is a method for evaluating BEL resistance in a short period of time.

Furthermore, as a method for evaluating the BEL resistance itself, an aging promotion test using high concentration oxygen disclosed in Japanese Patent No. 3373737 is known. It is a test method that can improve the aging effect compared to the aging promotion test using air and can also evaluate the influence of humidity on aging, but it promotes aging in a high oxygen-rich environment that does not exist in nature. Therefore, it does not match the environment where BEL actually occurs, and there is a question about the correlation with the actual use environment.
From the above, in developing an automobile tire excellent in BEL resistance, a test method that has excellent correlation with an actual use environment of high temperature and high humidity and can obtain a result in a short time has been desired.
Japanese Patent No. 3373737 (page 1-2) JP 2001-287506 A (page 2) Japanese Industrial Standards, JIS Handbook 19, published on April 12, 1986, p. 408 Japanese Industrial Standards, JIS Handbook 28, published on January 31, 2002, P.I. 470

  Since the present invention mainly evaluates the BEL resistance of an automobile tire, a durability test capable of obtaining deterioration over time corresponding to actual use in a hot and humid environment typified by a rainforest climate in a short time. It is about the method.

In the present invention, in order to achieve the above object, the following measures are taken. That is, in the aging promotion test of an automobile tire, the test method is characterized in that the tire is alternately exposed to a wet heat cycle and a dry heat cycle.
In the present invention, the inventors have focused on daily fluctuations in temperature and humidity in a high temperature and high humidity environment. FIG. 1 shows changes in daily temperature and humidity in a use region having a rainforest climate. It can be seen from the figure that the temperature is relatively stable throughout the day and night, but the humidity varies greatly from 60 to 98%. In other words, even in such hot and humid areas, the humidity fluctuates violently throughout the day. Therefore, the inventor considered that such temperature and humidity fluctuation cycles become a strong aging factor for automobile tires, and BEL tends to occur.

In other words, instead of testing in an environment maintained at a constant aging condition, it was considered that alternating exposure to a plurality of aging cycles had a higher correlation with aging in the actual use environment. For this reason, the aging cycle at night in a hot and humid environment is referred to as a moist heat cycle, and the day aging cycle in the same environment is referred to as a dry heat cycle. That is, in the aging promotion test of an automobile tire, the test method is characterized by alternately exposing to a wet heat cycle and a dry heat cycle.
The wet heat cycle constituting the aging test method is performed at a temperature of 60 to 95 ° C., preferably 70 to 90 ° C., in a constant temperature and humidity atmosphere maintained at a relative humidity of 70 to 100%, preferably 80 to 100%. This is a cycle that promotes aging by introducing. Below this temperature, a sufficient aging promoting effect cannot be obtained, and above this temperature, there is a risk of adversely affecting the rubber composition. As for humidity, when the humidity is 70% or less, the effect of promoting aging cannot be sufficiently obtained.

Further, the dry heat cycle is a cycle in which aging is promoted by putting a sample into a constant temperature atmosphere maintained at a temperature of 60 to 95 ° C, preferably 70 to 90 ° C. The effect above or below this temperature is the same as the wet heat cycle described above, and the effect of implementation cannot be sufficiently obtained. Since humidity is not controlled, it varies depending on the measurement environment. However, when the cycle is obtained from room temperature in a thermostatic chamber or the like, it does not exceed 20%, and is completely different from the wet heat cycle.
Since the aging cycle of the present invention was obtained with reference to the daily fluctuations in temperature and humidity in the region where the rainforest climate is used, the wet heat cycle corresponding to the night of the day and the dryness corresponding to the day of the day are used. A thermal cycle is required once a day. That is, the test method is characterized in that the wet heat cycle and the dry heat cycle are performed at least once a day. However, in the actual environment, the change in temperature and humidity may be variously changed due to the influence of squall or the like peculiar to the tropical climate. Therefore, it is possible to repeat both cycles twice or more.

In addition, the repetition of the wet heat cycle and the dry heat cycle can be repeated according to the measured values of the temperature and humidity of the environment assuming the use environment in advance. In other words, the test method is characterized in that the repeating pattern of the wet heat cycle and the dry heat cycle matches the environment of the region where it is used. Even in the rainforest climate, the change in temperature and humidity is not completely the same depending on the region, so it is possible to determine the number of repetitions of both cycles and the time to hold them in both cycles assuming the use environment.
Therefore, it is necessary to measure changes in the temperature and humidity of the environment in the area of use. That is, in order to obtain a repeating pattern of a wet heat cycle and a dry heat cycle, the test method is characterized by measuring the temperature and humidity of a rainforest climate or a tropical monsoon climate. For example, when the environment in a certain use area is 16 hours at night and 8 hours in the daytime, means for alternately repeating the wet heat cycle 16 hours and then the dry heat cycle 8 hours in order to promote aging in the environment of the use area. Can take. The boundary between nighttime and daytime is not uniquely determined, but in the measured values of temperature and humidity, the boundary value is determined to determine day and night. By setting such test conditions, an aging test can be performed in accordance with an environment in which an automobile tire is actually used.

  Further, the aging test is mainly intended to evaluate the BEL resistance, but it does not mean that other evaluation methods cannot be carried out. For example, it can be used for the purpose of obtaining an aging state other than BEL of a tire in a rainforest climate or a tropical monsoon climate. Therefore, it can be used for tests other than the peel strength of JIS K6301 and JIS D4230, which are not directly related to BEL resistance. That is, it is a test method characterized by investigating the influence of aging on tire characteristics by measuring the characteristics of the tires for automobiles obtained by the aging promotion test. By such means, traveling stability indirectly related to BEL can be evaluated, and BEL resistance can be evaluated from various aspects.

  Nevertheless, the most direct method for evaluating the BEL resistance is a means for measuring the peel strength of a breaker or belt in which peeling occurs or an edge band. That is, the test method is characterized in that the measurement of tire characteristics is a measurement of peel strength between a plurality of laminated breakers, between a plurality of laminated belts, between a breaker and an edge band, or between a belt and an edge band. It is. By such means, the BEL resistance can be directly evaluated according to the index of peel strength.

  By carrying out the test method of the present invention, it is possible to promote aging that is very close to actual running in the use environment of a region in a rainforest climate or a tropical monsoon climate, compared to the aging test conditions that have been used conventionally. In addition, by arbitrarily changing the time distribution of the dry heat cycle and the wet heat cycle that constitute the aging test method, it is possible to artificially reproduce the aging due to actual running in the rainforest climate or tropical monsoon climate. It becomes possible. In addition, the BEL resistance can be evaluated in a shorter time than before by measuring the peel strength of a breaker or belt in which peeling mainly occurs in an automobile tire that has been accelerated in aging, or an edge band.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each figure, the same components are denoted by the same reference numerals, and redundant description is omitted.
Figure 1 shows the daily changes in temperature and humidity in Thailand that belong to the rainforest climate. From FIG. 1, it can be seen that the temperature does not change greatly throughout the day and night, but the humidity changes greatly in the range of 60 to 98%. In particular, the humidity is 80% or less from about 9 am to about 18:00 in the afternoon when the sunlight is high, and the humidity is lower than at night. Therefore, in this case, the dry heat cycle is performed in the time zone b shown in FIG. 1 from 9:00 am to 18:00 pm, and the wet heat cycle is performed in the time zone a before 9 am and the time zone c after 18:00 pm. The aging test method can be implemented by applying. In other words, in the aging promotion test for automobile tires, the test method is characterized by alternately exposing to a wet heat cycle and a dry heat cycle.

  As can be seen from FIG. 1, low humidity and high humidity always occur once a day. However, if you want to accelerate aging rapidly, or a phenomenon such as squall that reverses the relationship between humidity and temperature occurs. In easy-to-use areas, it may be better to repeat the cycle more than once. In any case, as an embodiment of the test method of the present invention, the wet heat cycle and the dry heat cycle are performed at least once a day. If the number of repetitions is too large, the holding time of each cycle is lowered, and the aging promoting effect itself may be impaired. In order to prevent these, it is preferable to take a holding time of at least 3 hours for each cycle of the wet heat cycle and the dry heat cycle.

  In addition, as described above, the environment of the region where the automobile tire is used is measured in advance as shown in FIG. 1, so that the repeated pattern of the wet heat cycle and the dry heat cycle matches the environment of the use region. A test method can be obtained. Furthermore, the aging test method should be carried out by actually measuring the temperature and humidity even in regions characterized by high temperatures and humidity, although the seasons are similar to those of tropical monsoon climates as areas where automobile tires are used. Can do. For example, a high temperature and high humidity environment in the rainy season and a high temperature and low humidity environment in the dry season are measured, and the aging cycle by the test method is combined with the conventional dry heat cycle, or the aging cycle by the test method is intermittently performed. be able to.

  The wet heat cycle and the dry heat cycle can be performed under the test conditions shown in Table 1. The wet heat cycle is a cycle in which the temperature is 60 to 95 ° C., preferably 70 to 95 ° C., and is exposed to a constant temperature and humidity atmosphere maintained at a relative humidity of 70 to 100%, preferably 80 to 100%. Is a cycle of exposure in a constant temperature atmosphere maintained at a temperature of 60 to 95 ° C, preferably 70 to 95 ° C. In both cycles, a sufficient aging promoting effect cannot be obtained at a temperature of 70 ° C. or lower, and a risk of adversely affecting the rubber composition occurs at a temperature of 100 ° C. or higher. Regarding the humidity, when the humidity is 70% or less, the effect of promoting aging cannot be sufficiently obtained, and when the humidity is 100% or more, it cannot be carried out.

  A cross-sectional view of a tire used for the aging test method is shown in FIG. FIG. 2 shows an example of a radial tire, but any tire for automobiles can be used for the test method regardless of radial or bias. In the sectional view of the radial tire in FIG. 2, there is a breaker in the tread portion 2 outside the bead ply 1. Since FIG. 2 is a radial tire, it is referred to only as a breaker. However, the BEL which is the object of evaluation by the test method according to the present invention is the separation between the breaker 3 or 4 and the edge band 5, or between the breakers 3 and 4 to be laminated Indicates peeling. Therefore, the sample to be used for the test can be a sample cut from a tire including these or the tire itself. This is because the characteristic of the test method is to investigate the influence of aging on the tire characteristics by measuring the characteristics of the tire.

Although the evaluation of the degree of aging is performed on the automobile tire obtained by the aging promotion test, the evaluation method is not limited to only the peel strength considered to be directly related to the evaluation of the BEL resistance. For example, the evaluation method described in JIS K6301 and JIS D4230 can also be implemented, and the influence which aging has on a tire can also be investigated. Furthermore, BEL resistance, which is the main purpose, can be evaluated from multiple aspects by performing a high-speed durability performance test or the like as an evaluation method.
Furthermore, in order to directly evaluate the BEL resistance, it is necessary to measure the peel strength between a plurality of laminated breakers, between a plurality of laminated belts, between a breaker and an edge band, or between a belt and an edge band. it can. The peel strength can be measured in accordance with JIS K6301 as a sample piece having a width of 25.0 ± 0.5 mm and 100 mm or more.

  Hereinafter, although the test method of this invention is demonstrated and mentioned about the Example and comparative example which are shown in FIG. 4, this invention is not limited to these Examples. In all examples and comparative examples, aging was promoted under the test conditions shown in FIG. The test tire used for the evaluation is a 195 / 65R15 radial tire similar to that shown in FIG. The test time for aging test conditions is 1 week, 2 weeks, and 3 weeks, but the actual blank traveled for 3 years in a rainforest climate environment. In Examples and Comparative Examples, a breaker and an edge band were taken out from tires whose aging was promoted under each test condition, and BEL resistance was judged by measurement of peel strength and evaluation thereof. B / B in FIG. 4 is the peel strength of the two breakers to be laminated (corresponding to reference numerals 3 and 4 in FIG. 2), and B / E is the peel strength between the breaker and the edge band. The peel strength was measured according to a rubber and rubber peel strength measuring method specified in JIS K6301 as a sample piece having a width of 25.0 ± 0.5 mm and 100 mm or more. The evaluation of BEL resistance is an evaluation determined based on whether or not the examples and comparative examples have low peel strength compared to the measured values in actual use. Expressed as a three-level evaluation, ◎ is good, ○ is usable as a test method, and × indicates nonconformity as a test. Such evaluation can also be determined from the graph of the evaluation results shown in FIG. FIG. 3 shows the measurement results, with B / B on the horizontal axis and B / E on the vertical axis. The peel strength decreases and the BEL resistance decreases as the position near the origin decreases. Represents that The region of B / B peel strength of 90 N / 25 mm or less and the B / E peel strength of 130 N / 25 mm or less in FIG. 3 is indicated by ○ or ◎ if the measurement result of aging for 3 weeks is included in the region. In the case where the peel strength is greater than this, it was marked as x. In addition, the thing which obtained the strong aging acceleration | stimulation effect lower than the measured value of actual use was set as (double-circle).

Examples and comparative examples will be described below in accordance with the above measurement method and evaluation results. In Example 1, the aging condition is a set temperature of 60 ° C. for both the dry heat cycle and the wet heat cycle. The set time for both cycles was 9 hours for the dry heat cycle and 15 hours for the wet heat cycle according to the time ratio of day and night in FIG.
In Example 1, the set temperature of both cycles is 10 ° C. higher than that of Comparative Example 3. While the result of the third week of Comparative Example 3 is the region indicated by “x” in FIG. 3, Example 1 is included in the region “◯”. However, the drop in peel strength is not as high as that of a blank blank. From these, it can be seen that 60 ° C. indicates the lower limit of the set temperature as the set temperature of the aging cycle.

  In Example 2, the set temperature of both cycles is 80 ° C., and the set humidity of the wet heat cycle is 70%. The set humidity is 10% higher than that of the comparative example 4, and the result of the third week of the comparative example 4 is in the region of x in FIG. 3, while the example 2 is included in the region of ◯. However, the drop in peel strength is not as high as that of a blank blank. From these, it can be seen that 70% indicates the lower limit of the set humidity as the set humidity of the wet heat cycle.

  In Example 3, the set temperature of both cycles is 80 ° C., and the set humidity of the wet heat cycle is 80%. Compared with Examples 1 and 2, it can be seen that the peel strength is drastically decreased and that strong aging is being accelerated. From these facts, in the test conditions where the set temperature of both cycles exceeds 80 ° C and the set humidity of the wet heat cycle exceeds 80%, the degree of aging when actually running in the rainforest climate area for 3 years is shown. It turns out that the aging promotion effect which surpasses is acquired in three weeks.

Comparative Example 1

  Comparative Example 1 is a conventional aging cycle composed of only a dry heat cycle. The result of the third week is in the region of x in FIG. 3, and the aging promoting effect is insufficient.

Comparative Example 2

  Comparative Example 2 is a conventional aging cycle constituted only by a wet heat cycle. The result of the third week is in the region of x in FIG. 3, and the aging promoting effect is insufficient.

Comparative Example 3

  In Comparative Example 3, the set temperature of the wet heat cycle and the dry heat cycle is as low as 50 ° C., and the result of the third week is also in the region of x in FIG. 3, and the aging promoting effect is insufficient.

Comparative Example 4

  In Comparative Example 4, the set humidity of the wet heat cycle is as low as 60%, and the result of the third week is also in the region of x in FIG. 3, and the aging promoting effect is insufficient.

  The test method can be used as a method for promoting aging in a hot and humid rainforest climate or a tropical monsoon climate of automobile tires. Such aging conditions can be applied to rubber or rubber for other automotive parts, industrial equipment, transportation vehicle parts, etc. It can also be used as an aging test for products containing. Further, by using a measurement method other than the peel strength measurement after the aging test, it can be used as a deterioration durability test for rubber and rubber products.

Fig. 1 shows the changes in daily temperature and humidity in an area belonging to the rainforest climate. FIG. 2 is a view showing a cross section of an automobile tire 195 / 65R15 radial tire. FIG. 3 is a diagram showing the peel strength measurement results of samples cut out from tires aged in accordance with Examples and Comparative Examples. FIG. 4 shows the aging conditions of Examples and Comparative Examples and the peel strength measurement results.

Claims (6)

  An aging test method for an automobile tire, wherein the aging acceleration test for an automobile tire is alternately exposed to a wet heat cycle and a dry heat cycle.   The aging test method for an automobile tire according to claim 1, wherein the wet heat cycle and the dry heat cycle are performed at least once a day.   The aging test method for an automobile tire according to claim 1 or 2, wherein a repeating pattern of the wet heat cycle and the dry heat cycle matches an environment of a use region.   The automobile tire according to any one of claims 1 to 3, wherein temperature and humidity of a rainforest climate or a tropical monsoon climate are measured in order to obtain a repeating pattern of the wet heat cycle and the dry heat cycle. Aging test method.   5. The effect of aging on tire characteristics is investigated by measuring the characteristics of the tires for automobiles obtained by the aging promotion test. 6. Aging test method for automobile tires. The measurement of the tire characteristics is a measurement of peel strength between a plurality of laminated breakers, between a plurality of laminated belts, between a breaker and an edge band, or between a belt and an edge band, and measuring the peel strength. The aging test method for an automobile tire according to any one of claims 1 to 5, wherein the BEL resistance is evaluated by:

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