JP2017227544A - Tire vulcanization bladder rubber composition and evaluation method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tire vulcanization bladder rubber composition capable of estimating the occurrence state of bladder buckles at a testing stage, and thereby suppressing the occurrence of bladder buckles to suppress generation of bladder chips or tire chips, and an evaluation method thereof.SOLUTION: A test piece comprising a tire vulcanization bladder rubber composition is formed, the initial modulus of the test piece is measured, distortion within a bladder stretch range is repeatedly applied to the test piece under an atmosphere within a tire vulcanization temperature range, the residual modulus of the test piece is measured by an optional number of elongation times, and the tire vulcanization bladder rubber composition is evaluated on the basis of the ratio of the residual modulus to the initial modulus of the test piece. Then, the tire vulcanization bladder rubber composition in which the ratio of the residual modulus to the initial modulus of the test piece is 80% or more is adopted.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a rubber composition used for a tire vulcanization bladder and a method for evaluating the same, and more specifically, it is possible to estimate the occurrence of a bladder buckle at a test stage, thereby suppressing the occurrence of a bladder buckle. The present invention relates to a rubber composition for a tire vulcanization bladder that can suppress generation of bladder waste and tire waste and an evaluation method thereof.

  When vulcanizing a pneumatic tire, insert a bladder inside the green tire set in the mold and heat the green tire from the outside through the mold, while introducing a heating and pressurizing medium into the bladder Thus, the green tire is heated from the inside. Such a tire vulcanization bladder generally reaches the end of its life when it is used about 500 times while repeatedly expanding and contracting at a high temperature.

  A rubber composition (compound) having a high elongation at break is effective for improving the bladder life, and such a rubber composition is being developed every day. Then, a test piece made of the rubber composition that has been prototyped is subjected to a tensile test under normal temperature conditions or high temperature conditions, or a tensile test is performed after aging, and the tire is based on the tensile characteristics obtained by such a tensile test. Evaluation of rubber compositions used in vulcanization bladders has been carried out.

  However, in the tensile characteristics obtained by the tensile test as described above, the expansion and contraction conditions when the bladder is actually used are not reproduced. Therefore, even if such tensile characteristics are good, the tire is actually tired. When a vulcanization bladder is manufactured and a pneumatic tire is vulcanized, a bladder buckle may occur when vulcanization is performed several times to several tens of times. The bladder buckle is a phenomenon in which the bladder is in contact with the inner surface of the tire in a state of being bent when inflated due to the fact that the bladder slightly extends and becomes larger than the tire inner surface dimension. When such a bladder buckle is generated, in addition to the bladder itself becoming waste, the vulcanized tire also becomes waste, resulting in unnecessary costs.

  In addition, as a method for evaluating the service life of the tire vulcanization bladder while taking into account the usage environment of the tire vulcanization bladder, a test sheet made of vulcanized rubber is sandwiched between a pair of heated pressure resistant molds having a concave space, and the pressure resistant mold A first operation for supplying a heated gas from one of the two for a predetermined time to expand the test sheet and press-fitting the inner surface of the other pressure-resistant mold, and a second operation for discharging the heated gas and releasing the expansion of the test sheet for a predetermined time It has been proposed to repeat the above until the deterioration of the test sheet reaches a predetermined standard (see, for example, Patent Document 1).

  However, with such a life evaluation method, although it is possible to evaluate the final life of the bladder, it is impossible to grasp any bladder buckle that tends to occur immediately after the start of use of the bladder.

JP 2006-145476 A

  The object of the present invention is to enable estimation of the occurrence of bladder buckles at the test stage, thereby suppressing the occurrence of bladder buckles and suppressing the generation of bladder waste and tire waste. An object of the present invention is to provide a rubber composition for bladder and an evaluation method thereof.

  In order to achieve the above object, a method for evaluating a rubber composition for a tire vulcanization bladder according to the present invention comprises preparing a test piece comprising a rubber composition for a tire vulcanization bladder, measuring an initial modulus of the test piece, The test piece is repeatedly subjected to strain within the bladder stretch range in an atmosphere within the tire vulcanization temperature range, the residual modulus of the test piece is measured at any number of expansions and contractions, and the residual modulus relative to the initial modulus of the test piece is measured. The rubber composition for a tire vulcanization bladder is evaluated based on a modulus ratio.

  Further, the rubber composition for a tire vulcanization bladder of the present invention for achieving the above object is a test piece made of a rubber composition for a tire vulcanization bladder, the initial modulus of the test piece is measured, and the test A strain within a bladder stretch range of 10% to 150% is repeatedly given to the piece in an atmosphere within a tire vulcanization temperature range of 150 ° C. to 200 ° C., and the stretch is repeated 2 to 30 times. In the test condition of measuring the residual modulus of the test piece, the ratio of the residual modulus to the initial modulus of the test piece is 80% or more.

  As a result of intensive studies on a method for evaluating a rubber composition for a tire vulcanization bladder, the present inventor found that when a test piece was stretched under specific temperature conditions and strain conditions, the ratio of the residual modulus to the initial modulus of the test piece and the bladder The present inventors have found that there is a correlation with the buckle occurrence rate, and have arrived at the present invention based on the knowledge.

  That is, in the present invention, a test piece made of a rubber composition for a tire vulcanization bladder is prepared, an initial modulus of the test piece is measured, and a bladder stretch is performed on the test piece in an atmosphere within a tire vulcanization temperature range. Since the strain within the range is repeatedly applied, the residual modulus of the test piece is measured at any number of expansions and contractions, and the rubber composition for the tire vulcanization bladder is evaluated based on the ratio of the residual modulus to the initial modulus of the test piece. In the test stage, the occurrence of bladder buckles can be estimated. As a result, generation of bladder buckles can be suppressed, and generation of bladder waste and tire waste can be suppressed.

  In the present invention, the tire vulcanization temperature range is preferably 150 ° C. to 200 ° C., the bladder stretch range is 10% to 150%, and the number of expansions / contractions is preferably 2 to 30 times. By setting such conditions, it is possible to more accurately estimate the occurrence of bladder buckles at the test stage.

  In the present invention, when the ratio of the residual modulus to the initial modulus of the test piece is 80% or more, it is determined that the incidence of buckle of the tire vulcanization bladder formed from the rubber composition for the tire vulcanization bladder is low. Is preferred. According to the knowledge of the present inventors, when the ratio is 80% or more, the incidence rate of bladder buckles tends to be low.

  According to the present invention, a test piece made of a rubber composition for a tire vulcanization bladder is prepared, an initial modulus of the test piece is measured, and a tire vulcanization temperature range of 150 ° C. to 200 ° C. with respect to the test piece. In the test condition of repeatedly applying a strain within the bladder stretch range of 10% to 150% under the atmosphere of the test piece and measuring the residual modulus of the test piece with the number of expansions and contractions of 2 to 30 times, When a bladder is molded using a rubber composition for a vulcanized bladder in which the ratio of the residual modulus to the modulus is 80% or more, generation of bladder buckles can be suppressed, and generation of bladder waste and tire waste can be suppressed.

It is a meridian half section view showing an example of a tire vulcanization bladder concerning the present invention. It is a graph which shows the relationship between a modulus residual rate and the frequency | count of expansion / contraction. It is a graph which shows the relationship between a bladder buckle incidence rate and a modulus residual rate. It is a graph which shows the relationship between a bladder buckle incidence and 300% modulus.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows an example of a tire vulcanization bladder according to the present invention. As shown in FIG. 1, the bladder 10 includes a barrel portion 11 formed in a cylindrical shape, and flange-shaped grip portions 12 molded at both axial end portions of the barrel portion 11. Such a bladder 10 is disposed in a tire vulcanizer and is inserted inside the green tire during vulcanization. Then, by introducing a heating / pressurizing medium into the bladder 10, the green tire functions to be pressurized at the same time as being pressurized from the inside. The shape of the bladder 10 is not particularly limited, and any shape can be adopted depending on the structure of the tire vulcanizer.

  The above-described bladder 10 is integrally molded from a rubber composition. However, in view of the use environment that repeatedly receives strain in the vulcanization process, it is possible to select a rubber composition having an appropriate stretch characteristic. Required. Therefore, when applying an arbitrary rubber composition to the bladder 10, it is necessary to evaluate its characteristics in advance. Here, for example, by measuring the 300% modulus of the rubber composition for a tire vulcanization bladder, the stretch characteristics can be grasped to some extent. However, even when the rubber composition for a tire vulcanization bladder is evaluated based on the 300% modulus, when the bladder 10 is actually manufactured and the pneumatic tire is vulcanized, the vulcanization is performed several times to several tens of times. A bladder buckle may occur at the time of going. When the bladder buckle is generated, unnecessary bladder waste and tire waste are generated.

  In view of such a situation, the following method for evaluating a rubber composition for a tire vulcanization bladder is implemented. First, a vulcanized test piece made of a rubber composition for a tire vulcanization bladder is prepared, and an initial modulus of the test piece is measured. Next, a strain within the bladder stretch range is repeatedly applied to the test piece in an atmosphere within the tire vulcanization temperature range, and the residual modulus of the test piece is measured at an arbitrary number of expansions and contractions. As the initial modulus and the remaining modulus, for example, a 300% modulus can be measured, but the elongation percentage can be appropriately selected. Such a modulus can be obtained in accordance with a method of measuring a predetermined elongation tensile stress described in JIS-K6251 “Vulcanized rubber and thermoplastic rubber—How to obtain tensile properties”. Then, the rubber composition for the tire vulcanization bladder is evaluated based on the ratio of the residual modulus to the initial modulus of the test piece (hereinafter referred to as “modulus residual ratio”).

  FIG. 2 is a graph showing the relationship between the modulus remaining rate and the number of expansions and contractions. As shown in FIG. 2, when the strain within the bladder stretch range is repeatedly applied to the test piece in an atmosphere within the tire vulcanization temperature range, the residual modulus of the test piece decreases with an increase in the number of expansions and contractions. . In particular, the residual modulus of the test piece is greatly reduced in the initial stage, and thereafter, the residual modulus tends to gradually decrease. Observing such a change in modulus is useful for estimating the occurrence of bladder buckles in actual tire vulcanization. That is, it can be estimated that the rubber composition for a tire vulcanization bladder that maintains a high modulus remaining rate even when the number of expansions / contractions increases is unlikely to generate a bladder buckle. As a result, since an appropriate rubber composition for a tire vulcanization bladder is selected, generation of bladder buckles in an actual vulcanization process can be suppressed, and generation of bladder waste and tire waste can be suppressed.

  In the method for evaluating a rubber composition for a tire vulcanization bladder described above, the tire vulcanization temperature range is preferably 150 ° C to 200 ° C. Since such a temperature range corresponds to the heating temperature in the actual vulcanization process, it is effective in estimating the occurrence of bladder buckles in the actual vulcanization process. If the ambient temperature that gives strain to the test piece is out of the above range, it will be difficult to estimate the occurrence of bladder buckles in the actual vulcanization process.

  The bladder stretch range is 10% to 150%, more preferably 30% to 100%. Since such a stretch range corresponds to the bladder stretch range in the actual vulcanization process, it is effective in estimating the occurrence situation of the bladder buckle in the actual vulcanization process. If the strain applied to the test piece is out of the above range, it will be difficult to estimate the occurrence of bladder buckles in the actual vulcanization process. When the test piece is stretched, strain within the above-mentioned bladder stretch range is given, but when the test piece is shrunk, the strain is returned to 0%, and such expansion and contraction is repeated. However, there is no particular problem even if a strain of about 10% is left when the specimen is contracted. Moreover, it is desirable that the holding time when applying the strain is 0 seconds to 10 seconds.

  The number of expansions / contractions can be, for example, about 2 to 200 times, preferably 2 to 30 times, more preferably 20 to 30 times. By giving strain to the test piece with such number of expansions and contractions, it is possible to estimate the occurrence of bladder buckles in the actual vulcanization process. Increasing the number of expansions / contractions makes it possible to accurately estimate the occurrence of bladder buckles. However, if the number of expansions / contractions is excessive, the test time becomes longer than necessary.

  In the method for evaluating a rubber composition for a tire vulcanization bladder described above, the threshold of the modulus remaining rate for determining that the incidence rate of the bladder buckle is low is not particularly limited, but the modulus remaining rate is 80% or more. In some cases, it can be determined that the tire vulcanization bladder molded from the rubber composition for a tire vulcanization bladder has a low buckle generation rate. When the modulus remaining rate is 80% or more, the incidence rate of bladder buckles tends to be low.

  In view of the above-mentioned knowledge, a test piece made of a rubber composition for a tire vulcanization bladder is prepared, an initial modulus of the test piece is measured, and a tire vulcanization temperature that is 150 ° C. to 200 ° C. with respect to the test piece. When repeatedly applying a strain within the bladder stretch range of 10% to 150% under an atmosphere within the range and measuring the residual modulus of the test piece between 2 and 30 times, the initial modulus of the test piece It is desirable to use a rubber composition for a vulcanized bladder having a residual modulus ratio of 80% or more. When the bladder 10 is molded using such a rubber composition for a vulcanized bladder, generation of bladder buckles in the actual vulcanization process can be suppressed, and generation of bladder waste and tire waste can be suppressed.

  A rubber composition for a tire vulcanization bladder containing butyl rubber as a rubber component is used. The amount of carbon black, the amount of oil, and the vulcanization time are varied as shown in Table 1, and the width is 10 mm and the thickness is 2 mm. Strip-shaped test pieces were prepared (Test Examples 1 to 6). Each test piece is attached to a tensile test apparatus having a chuck interval of 40 mm, and the initial modulus of each test piece is measured under the conditions of a temperature of 180 ° C. and a strain of 80%. The residual modulus of each test piece when the number of expansions / contractions was 20 was measured. And about each test piece, the ratio (modulus residual ratio) of the residual modulus with respect to an initial modulus was calculated | required. In addition, using the same rubber composition, the 300% modulus when the rubber composition was largely deformed was also measured.

  Next, a large number of tire vulcanization bladders each having a cylindrical shape were molded using the rubber compositions for tire vulcanization bladders of Test Examples 1 to 6. At that time, the vulcanization time of the tire vulcanization bladder was made the same as the vulcanization time of the corresponding test piece. The tire vulcanization bladder thus obtained was placed in a tire vulcanizer, and a pneumatic tire was actually vulcanized. And about the tire vulcanization bladder of Test Examples 1-6, the presence or absence of the occurrence of a bladder buckle was confirmed when 20 tires were vulcanized, and the bladder buckle occurrence rate was determined. The results are shown in Table 1. FIG. 3 is a graph showing the relationship between the bladder buckle occurrence rate and the modulus remaining rate, and FIG. 4 is a graph showing the relationship between the bladder buckle occurrence rate and the 300% modulus.

  As shown in Table 1, in Test Examples 1 to 6, when the modulus remaining rate was 80% or more, the bladder buckle generation rate tended to be low. In addition, as shown in FIG. 3, a correlation was observed between the bladder buckle occurrence rate and the modulus remaining rate, and the bladder buckle occurrence rate decreased as the modulus remaining rate increased. On the other hand, as shown in FIG. 4, no strong correlation was observed between the incidence of bladder buckles and the 300% modulus. As is clear from this, the ratio of the remaining modulus to the initial modulus of the test piece (modulus remaining rate) is useful as an index for estimating the occurrence of bladder buckles at the test stage.

  Moreover, the test piece similar to the above was produced about the rubber composition for tire vulcanization bladders shown in Table 2 (Test Examples 11-16). Each test piece is attached to a tensile test apparatus having a chuck interval of 40 mm, and the initial modulus of each test piece is measured under the conditions of a temperature of 150 ° C. and a strain of 150%. The residual modulus of each test piece when the number of expansions / contractions was 20 was measured. And about each test piece, the ratio (modulus residual ratio) of the residual modulus with respect to an initial modulus was calculated | required. In addition, using the same rubber composition, the 300% modulus when the rubber composition was largely deformed was also measured.

  Next, a large number of tire vulcanization bladders each having a cylindrical shape were molded using the rubber compositions for tire vulcanization bladders of Test Examples 11 to 16. At that time, the vulcanization time of the tire vulcanization bladder was made the same as the vulcanization time of the corresponding test piece. The tire vulcanization bladder thus obtained was placed in a tire vulcanizer, and a pneumatic tire was actually vulcanized. And about the tire vulcanization bladder of Test Examples 11-16, the presence or absence of generation | occurrence | production of the bladder buckle was confirmed when 20 tires were vulcanized, and the bladder buckle incidence rate was calculated | required. The results are shown in Table 2.

  As shown in Table 2, also in Test Examples 11 to 16, when the modulus remaining rate was 80% or more, the bladder buckle generation rate tended to be low.

10 Bladder 11 Body 12 Gripping part

Claims (4)

  A test piece made of a rubber composition for a tire vulcanization bladder is prepared, an initial modulus of the test piece is measured, and a strain within a bladder stretch range is repeatedly applied to the test piece in an atmosphere within a tire vulcanization temperature range. The residual modulus of the test piece is measured at an arbitrary number of expansions and contractions, and the rubber composition for the tire vulcanization bladder is evaluated based on the ratio of the residual modulus to the initial modulus of the test piece. Evaluation method of rubber composition for tire vulcanization bladder.   2. The tire according to claim 1, wherein the tire vulcanization temperature range is 150 ° C. to 200 ° C., the bladder stretch range is 10% to 150%, and the expansion / contraction frequency is 2 to 30 times. Evaluation method of rubber composition for tire vulcanization bladder.   When the ratio of the residual modulus to the initial modulus of the test piece is 80% or more, it is determined that the tire vulcanization bladder formed from the rubber composition for a tire vulcanization bladder has a low buckle generation rate. The evaluation method of the rubber composition for tire vulcanization bladders according to claim 1 or 2.   A test piece made of a rubber composition for a tire vulcanization bladder was prepared, an initial modulus of the test piece was measured, and the test piece was 10 in an atmosphere within a tire vulcanization temperature range of 150 ° C. to 200 ° C. The residual modulus relative to the initial modulus of the test piece is measured under the test condition in which the residual modulus of the test piece is measured repeatedly between 2 and 30 times by repeatedly applying a strain within a bladder stretch range of from% to 150%. The rubber composition for a tire vulcanization bladder, characterized in that the ratio of is 80% or more.

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