JP5756287B2 - Evaluation method of groove crack resistance of tread groove - Google Patents

Description

  The present invention relates to an evaluation method capable of evaluating the groove bottom crack resistance performance of a tread groove using a test piece having a simple structure without actually manufacturing a tire.

  A tread groove for drainage is provided in the tread portion of the tire. However, the bottom of the tread groove is susceptible to cracking due to various effects such as ultraviolet rays as well as air pressure and stress at the time of ground contact. Conventionally, as a method for evaluating the groove bottom crack resistance performance of such a tread groove, for example, as shown in FIG. Thus, a method for evaluating the groove bottom crack resistance is known. In this method, the groove bottom crack resistance test is performed using the property that the opening amount of the notch k changes depending on the magnitude of strain generated in the tread groove g provided in the tread portion ta.

  However, in this method, since it is necessary to actually manufacture the tire t, there is a problem that much cost and time are required for evaluation. Further, since the strain generated in the tread groove g depends not only on the rubber composition of the tread rubber but also on the structure and size of the tire, there is a problem that the groove bottom crack resistance performance cannot be correctly evaluated. Related technologies include the following.

Japanese Patent Laid-Open No. 10-260123 Japanese Utility Model Publication No. 2001-21470 JP 2004-317316 A Japanese Patent Application Laid-Open No. 07-232511

  The present invention has been devised in view of the above-described problems. A test piece having a simple structure is used to reproduce the distortion easily generated in the tire without actually manufacturing the tire, and the tread groove The main purpose is to provide an evaluation method that can accurately evaluate the groove bottom crack resistance of the steel.

The invention according to claim 1 of the present invention is a method for evaluating a groove bottom crack resistance performance of a tread groove provided in a tread rubber of a tire, and a test for producing a test piece in which the tread groove is formed. And a test step of performing a groove bottom crack performance test using the test piece, and the test piece preparation step includes a plate-like rubber substrate made of the same rubber composition as the tread rubber, And adhering to a backing material made of a material attached to one surface of the rubber base material and having a thermal contraction rate smaller than that of the rubber base material by vulcanization, and to the other surface of the rubber base material, Including the step of forming the tread groove by vulcanization or prior to vulcanization, and the test step is based on the difference in the heat shrinkage rate by cooling the test piece to at least room temperature after the vulcanization. The tensile stress is Characterized in that it is performed in a state of being loaded in serial rubber substrate.

The invention according to claim 2 is a method for evaluating a groove bottom crack resistance performance of a tread groove provided in a tread rubber of a tire, and a test piece creating step of creating a test piece having the tread groove formed therein. And a test step of performing a groove bottom crack resistance test using the test piece, wherein the test piece preparation step includes a plate-like rubber base material made of the same rubber composition as the tread rubber, and the rubber. A backing material made of a material attached to one surface of the base material and having a thermal contraction rate smaller than that of the rubber base material is bonded by vulcanization, and the other surface of the rubber base material is bonded by the vulcanization. Or the process of forming the said tread groove | channel before vulcanization | cure, The said backing material consists of a metal plate with a thickness of 0.1-1.0 mm, It is characterized by the above-mentioned .

The invention according to claim 3, wherein the backing material, the tread grooves of claim 1 Symbol placement and a plurality of metal cords of which are arranged in a direction intersecting the longitudinal direction a metal cord ply rubberized of the tread grooves This is a method for evaluating the groove bottom crack resistance of the steel.

According to a fourth aspect of the present invention, the test piece is provided with a small depth of cut in the groove bottom of the tread groove, and the amount of opening of the cut is measured in the test step. The groove bottom crack resistance evaluation method for a tread groove according to any one of the above.

The invention according to claim 5 is the evaluation method of the groove bottom crack resistance performance of the tread groove according to claim 4 , wherein the cut is formed as a closed cut with both ends closed .

  The method for evaluating the groove-resistant bottom crack performance of the tread groove according to the present invention includes a test piece creating step for producing a test piece having a tread groove provided on a tread rubber of a tire, and a groove-resistant bottom crack using the test piece. And a test process for performing a performance test. Such an evaluation method of the groove bottom crack resistance performance of the tread groove does not need to actually manufacture a tire because a groove bottom crack performance test is performed using a test piece. Therefore, in the evaluation method of the present invention, it is possible to perform a groove bottom crack resistance test with reduced cost and test time.

  The test piece preparation step includes a plate-like rubber base material made of the same rubber composition as the tread rubber, and is attached to one surface of the rubber base material and has a thermal shrinkage rate than the rubber base material. A step of bonding a backing material made of a small material by vulcanization and forming the tread groove on the other surface of the rubber base material by the vulcanization or prior to vulcanization. Since such a test piece can apply stress to the rubber base material due to the difference in the heat shrinkage rate between the rubber base material and the backing material, the actual tire basic structure (belt ply and tread rubber and Can be reproduced. In addition, variations in distortion depending on the tire size and internal structure (for example, the number and arrangement angle of belt cords) can be eliminated, and all rubber compositions can be evaluated under the same conditions. Therefore, in the evaluation method of the present invention, it is possible to accurately evaluate the groove bottom crack resistance performance of the tread groove.

It is a perspective view of the test piece of one Embodiment of this invention. (A) is a top view of FIG. 1, (b) is a side view of FIG. (A) is sectional drawing of the tread groove | channel and cutting of one Embodiment of this invention, (b) is sectional drawing of the tread groove | channel and cutting of other embodiment. It is a perspective sectional view of a tire which shows the conventional test method of groove bottom crack-proof performance.

Hereinafter, an embodiment of a method for evaluating groove bottom crack resistance of a tread groove according to the present invention will be described with reference to the drawings.
As shown in FIG. 4, a tread groove provided in a tread portion ta of a tire t is used as an evaluation method for groove-resistant bottom crack performance of a tread groove of the present invention (hereinafter, simply referred to as “evaluation method”). The groove bottom crack performance of g is evaluated. The present invention is characterized in that the groove bottom crack resistance of the tread groove can be easily and accurately evaluated without actually manufacturing a tire.

  The tire t evaluated by the evaluation method of the present embodiment is, for example, a pneumatic tire of various categories such as a heavy load tire, a passenger tire, or a motorcycle tire (hereinafter may be simply referred to as “tire”). It does not matter whether it exists and exists.

  In the evaluation method of the present embodiment, as shown in FIG. 1, a test piece creating step for creating a test piece 3 in which a tread groove 4 provided in a tread rubber of a tire (not shown) to be tested is formed. And a test step of performing a groove bottom crack performance test using the test piece 3.

  The test piece 3 was attached to a plate-like rubber base material 5 made of the same rubber composition as a tread rubber of a tire (not shown) to be tested, and one surface 5a of the rubber base material 5. For example, it is composed of a plate-like backing material 6, and the rubber base material 5 and the backing material 6 are bonded together. Such a rubber base material 5 is not particularly limited in size, but in order to perform a groove bottom crack resistance test smoothly and accurately, for example, as shown in FIG. The width Wa of the material 5 is preferably 15 to 40 mm, the length La is 60 to 200 mm, and the thickness Ta is 4 to 12 mm.

  Further, the rubber base material 5 of the present embodiment has, for example, the rubber base 5 at the center in the longitudinal direction of the other surface 5b (upper surface in FIG. 1) opposite to the one surface 5a. A tread groove 4 having a semicircular cross section extending in the width direction of the substrate 5 is formed. Such a tread groove 4 is preferably reproduced as a shape of a groove (not shown) provided in a tire to be tested. Usually, the groove width W1 of these tread grooves 4 is preferably 3 to 10 mm and the groove depth D1 is 2 to 10 mm in the case of a tire for a passenger car.

  In addition, the tread groove | channel 4 is not limited to such a shape, For example, as FIG.3 (b) shows, a groove bottom may be formed as a flat horizontal bottom.

  The backing material 6 is made of a material having a thermal contraction rate smaller than that of the rubber base material 5. The backing material 6 of this embodiment is composed of a sheet-like metal cord ply 7 in which a plurality of (seven in this embodiment) metal cords 7 a arranged in a direction crossing the longitudinal direction of the tread groove 4 are covered with rubber. . Thus, the metal cord ply 7 made of rubber and metal cord has a thermal contraction rate lower than that of the rubber base material 5 because the metal cord 7a has a smaller thermal contraction rate than rubber. .

  The backing material 6 of the present embodiment is not particularly limited in size, but from the viewpoint of stably fixing the rubber base material 5, both the width Wb and the length Lb than the rubber base material 5 are used. It is desirable to form large. As an example, the width Wb of the backing material 6 is preferably 105 to 120% of the width Wa of the rubber base material 5, and the length Lb is preferably 110 to 130% of the length La of the rubber base material 5.

  Such a test piece 3 is formed through a process in which the unvulcanized rubber base material 5 and the backing material 6 are fixed together by vulcanization.

  At the time of this vulcanization, the tread groove 4 is formed, for example, through a process of pressing a tread groove forming mold having a convex portion (not shown) against the other surface 5b of the rubber base material 5. However, the tread groove 4 may be formed in the rubber base material 5 prior to vulcanization.

  The test piece 3 formed by the test piece preparation process as described above has the rubber base material 5 formed of the same rubber composition as the tread rubber of the tire to be tested. Distortion approximate to the generated distortion occurs. In addition, since the structure of the test piece 3 approximates the basic structure of the tread portion of the tire, the strain generated in the tread groove 4 of the test piece 3 of the present embodiment approximates the basic structure of the tread portion of the tire. Distortion. Furthermore, by unifying the structure of the backing material 6 and the size of the test piece 3 in each test piece 3, the strain depending on these can be made constant.

  In the present embodiment, in the present embodiment, a notch 8 having a small depth is provided along the longitudinal direction of the tread groove 4 at the groove bottom of the tread groove 4 of the test piece 3. An opening amount of 8 is measured. Then, for example, the groove bottom crack resistance is evaluated from a table showing the correlation between the opening amount and the groove bottom crack resistance.

In such a test process, after the vulcanization in the test piece preparation process, the test piece 3 is cooled to at least room temperature, whereby the tensile strength based on the difference in thermal shrinkage between the rubber base material 5 and the backing material 6 is determined. stress Ru performed in a state of being loaded onto a rubber substrate 5. That is, the backing material 6 has a smaller thermal shrinkage rate at the time of cooling than the rubber base material 5, and a difference in shrinkage occurs at the interface between the two, so that the rubber base material 5 is pulled by the backing material 6. Thus, stress (strain) is generated on the surface of the rubber base material 5. Therefore, the test piece 3 cooled to at least room temperature can generate strain in the tread groove 4 that approximates the actual basic structure of the tire. For this reason, the test process using the test piece 3 cooled to room temperature can evaluate the groove-resistant crack resistance of the tread groove with higher accuracy.

  The notch 8 of this embodiment is preferably formed as a closed notch with both ends closed so that the opening amount of the notch 8 can be accurately measured from the viewpoint of accurately evaluating the groove bottom crack resistance performance. Moreover, it is desirable to arrange | position in the center part of the longitudinal direction of the tread groove | channel 4 in which distortion acts equally.

  Further, the size of the notch 8 is not particularly limited, but the depth D2 is 1.5 to 3 mm and the length Lc in consideration of the size of the rubber base 5 and the measurement accuracy. Is preferably about 25 to 35% of the width Wa of the rubber substrate 5. Such an incision 8 is formed by a cutting tool such as a knife having a blade thickness of 0.5 mm, for example.

  Further, the location of the cut 8 is preferably a location where a large strain due to tensile stress acts. From this point of view, for example, as shown in FIG. 3A, when the groove bottom of the tread groove 4 is formed in a semicircular arc shape, it is desirable that it be formed at the center of the groove bottom. For example, as shown in FIG. 3B, when the groove bottom of the tread groove 4 is horizontal and the groove bottom and the groove wall are connected in an arc shape, It is desirable to form in an arcuate part. The cut 8 extends in the normal direction with respect to the arc.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and can be implemented with various modifications. For example, in the above embodiment, the backing material 6 is the metal cord ply 7. However, in order to easily create the test piece 3, the backing material 6 is 0.1 to 1.0 mm. a metal plate having a thickness of (not shown).

  In order to confirm the effect of the present invention, the groove bottom crack resistance test by the evaluation method of the present invention (hereinafter sometimes simply referred to as “this application test”) and the crack resistance performance test by ozone irradiation (hereinafter simply referred to as “ozone”). Sometimes called "test". In both tests, a common test piece of the present invention was used except for the parameters shown in Table 1. The common specifications of main test pieces and the rubber composition are as follows.

<Rubber base material>
Width x thickness x length: 25 x 6.3 x 150 (mm)
<Tread groove (arc-shaped groove)>
Groove width x depth: 4.8 x 2.4 (mm)
<Backing material (metal cord ply)>
Width x thickness x length: 27 x 2 x 180 (mm)
Metal cord: 7 strands of 5 strands of 0.2mmφ steel wire <Vulcanization conditions>
After forming a tread groove on the rubber substrate, it was vulcanized.
Vulcanization temperature: 170 ° C
Vulcanization time: 20 minutes <Rubber composition>
Rubber composition A: carbon 60 phr
Rubber composition B: 60 phr of silica
Rubber composition C: carbon 40 phr
Rubber composition D: Silica 40 phr
Rubber composition E: Carbon 60 phr
Rubber composition F: Silica 60 phr
Rubber composition G: Carbon 40 phr
Rubber composition H: Silica 40 phr
The rubber compositions A to D are rubber polymers of 100% styrene butadiene rubber (SBR), and the rubber compositions E to H are rubber polymers of 50% by mass of natural rubber (NR) and butadiene rubber (BR). It is.
The test method is as follows.

<Application test>
A notch having a depth of 2 mm and a length of 8 mm was provided at the center of the groove bottom of the test piece, and the opening amount of the notch was measured 30 to 40 minutes after the notch was provided.

<Ozone test>
According to JISK6259, after exposing the test piece to the conditions of ozone concentration 50 ± 5 pphm and tensile amount 40 ± 2% for 96 hours continuously, Observed and recorded based on the criteria. Regarding the number of cracks, the number of cracks was evaluated as A, the number of cracks as B, and the number of cracks as C. As for the size and depth of the crack, 1 is one that cannot be seen with the naked eye but can be confirmed with a 10-fold magnifier, 2 that can be confirmed with the naked eye, 3 that is deep and relatively large (less than 1 mm), 3 A deep and large crack (1 mm or more and less than 3 mm) was evaluated as 5 when a crack or cutting of 4 or 3 mm or more was likely to occur. The test results are shown in Table 1.

  As a result of the test, it can be understood that there is a correlation between the amount of opening of the cut by the test of the present application and the state of the crack in the ozone test. In addition, it has been found that the test result of the ozone test is similar to a crack that occurs in a tire that is actually run for a long period of time. Therefore, it can be understood that the evaluation method of the present invention can accurately evaluate the groove bottom crack resistance.

DESCRIPTION OF SYMBOLS 1 Tire 2 Tread rubber 3 Test piece 4 Tread groove 5 Rubber base material 6 Backing material 7 Metal cord ply 7a Metal cord

Claims (5)

A method for evaluating groove bottom crack resistance of a tread groove provided in a tread rubber of a tire,
A test piece creating step of creating a test piece in which the tread groove is formed;
A test process for performing a groove bottom crack resistance test using the test piece,
The test piece preparation step includes a plate-like rubber base material made of the same rubber composition as the tread rubber, and a material attached to one surface of the rubber base material and having a smaller thermal shrinkage than the rubber base material. Adhering to the backing material consisting of
Forming the tread groove on the other surface of the rubber substrate by the vulcanization or prior to vulcanization ,
After the vulcanization , the test step is performed in a state where a tensile stress based on the difference in the thermal shrinkage rate is loaded on the rubber base material by cooling the test piece to at least room temperature. An evaluation method of the groove bottom crack resistance performance of the tread groove. A method for evaluating groove bottom crack resistance of a tread groove provided in a tread rubber of a tire,
A test piece creating step of creating a test piece in which the tread groove is formed;
A test process for performing a groove bottom crack resistance test using the test piece,
The test piece preparation step includes a plate-like rubber base material made of the same rubber composition as the tread rubber, and a material attached to one surface of the rubber base material and having a smaller thermal shrinkage than the rubber base material. Adhering to the backing material consisting of
Forming the tread groove on the other surface of the rubber substrate by the vulcanization or prior to vulcanization,
The said backing material consists of a metal plate with a thickness of 0.1-1.0 mm, The evaluation method of the groove-resistant bottom crack performance of a tread groove characterized by the above-mentioned.   The method for evaluating groove bottom crack resistance of a tread groove according to claim 1, wherein the backing material is a metal cord ply in which a plurality of metal cords arranged in a direction crossing the longitudinal direction of the tread groove are covered with rubber. The test piece is provided with a small depth of cut at the bottom of the tread groove,
The method for evaluating groove bottom crack resistance of a tread groove according to any one of claims 1 to 3, wherein an opening amount of the notch is measured in the test step. 5. The method for evaluating groove bottom crack resistance of a tread groove according to claim 4, wherein the cut is formed as a closed cut with both ends closed.

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