JP5993134B2 - 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. The groove 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 of evaluating the groove bottom crack resistance performance of such a tread groove, for example, as shown in FIG. 5, a notch k is provided in the groove bottom c of the tire t and the opening amount of the notch k is measured. 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 present invention is a method for evaluating groove bottom crack resistance performance of a tread groove provided in a tread rubber of a tire, the test piece creating step for creating a test piece in which the tread groove is formed, and the test piece A test step of performing a groove bottom crack resistance performance test using the test piece, and the test piece preparation step includes a plate-like rubber base material made of the same rubber composition as the tread rubber, and one of the rubber base materials. Adhering to a backing material made of a metal material attached to the surface, the test step is the difference in thermal shrinkage by cooling the test piece to at least room temperature after vulcanization in the test piece preparation step It is characterized in that it is performed in a state where a tensile stress based on the above is applied to the rubber base material .

The present invention is a method for evaluating groove bottom crack resistance performance of a tread groove provided in a tread rubber of a tire, the test piece creating step for creating a test piece in which the tread groove is formed, and the test piece A test step of performing a groove bottom crack resistance performance test using the test piece, and the test piece preparation step includes a plate-like rubber base material made of the same rubber composition as the tread rubber, and one of the rubber base materials. An evaluation step of evaluating a groove bottom cracking performance after the test step, the test piece is attached to a groove bottom of the tread groove, and is attached to a backing material made of a metal material attached to a surface. A depth cut is provided, and the evaluation step evaluates pass / fail based on a strain amount e calculated by the following equation using the groove bottom width h and the cut opening amount b before providing the cut. Including a process.
e = b / (h−b)

In the method for evaluating groove-resistant bottom crack performance of a tread groove according to the present invention, it is desirable that the test piece preparation step bonds the rubber base material and the backing material by vulcanization.

In the method for evaluating groove-resistant bottom crack performance of a tread groove according to the present invention, it is desirable that the test piece preparation step includes a step of forming the tread groove by vulcanization on the other surface of the rubber base material. .

In the method for evaluating groove bottom crack resistance of the tread groove according to the present invention, it is desirable that the thickness of the backing material is 1.0 to 6.0 mm.

Evaluation method of耐溝bottom cracking performance of the tread grooves of the present invention, the test piece, the groove bottom of the tread grooves, the Ru provided cuts of small depth is preferable.

In the evaluation method of the groove-resistant bottom crack performance of the tread groove according to the present invention, it is desirable that the opening amount of the notch is measured in the test step.

  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.

  In the test piece preparation step, a plate-like rubber base material made of the same rubber composition as the tread rubber is bonded to a backing material made of a metal material attached to one surface of the rubber base material. To do. Such a test piece can reproduce distortions and cracks that approximate the basic structure of an actual tire (including belt ply and tread rubber). 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. Furthermore, the test piece made of such a simple material has extremely small individual difference (difference in structure) in each test piece, so that the test reproducibility is high and the reliability is improved. Therefore, the evaluation method of the present invention can 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) thru | or (c) is the schematic explaining the test preparation process. (A) thru | or (c) is sectional drawing explaining the evaluation process of other embodiment of this invention. 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. 5, the method for evaluating the groove-resistant bottom crack performance of the tread groove of the present invention (hereinafter sometimes simply referred to as “evaluation method”) is a tread groove provided in a tread portion ta of a tire t. 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, a groove bottom at the center in the longitudinal direction of the other surface 5b (upper surface in FIG. 1) opposite to the one surface 5a of the rubber base material 5. A tread groove 4 having a flat horizontal bottom 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. Normally, the groove width W1 of these tread grooves 4 is 3 to 10 mm and the groove depth D1 is 2 to 10 mm in the case of a passenger car tire.

  The backing material 6 is made of a metal material. Since the metal material has a smaller thermal shrinkage rate than rubber, when the rubber base material 5 and the backing material 6 are vulcanized and bonded, stress in the tensile direction is applied to the rubber base material. In the rubber base material 5 fixed to the backing material 6 as described above, for example, a strain approximate to a strain generated in an actual tire provided with a metal cord is generated. In addition, as a metal material, copper, titanium, steel etc. are desirable, for example, and aluminum is suitably employ | adopted especially from a viewpoint of economical efficiency or workability.

  The backing material 6 of the present embodiment is not particularly limited in size, and is formed with a size approximate to that of the rubber base material 5 from the viewpoint of stably fixing the rubber base material 5. desirable. As a specific example, the width Wb of the backing material 6 is preferably 90 to 120% of the width Wa of the rubber base material 5, and the length Lb is preferably 90 to 120% of the length La of the rubber base material 5. The backing material 6 of this embodiment is formed with the same width and length as the rubber base material 5.

  In addition, the thickness Tb of the backing material 6 is preferably 1 to 6 mm in order to increase the correlation between the strain generated in the actual tire and the strain generated in the rubber base material 5 of the present embodiment.

  3A to 3C show a test piece creation process for manufacturing such a test piece 3. In the present embodiment, a vulcanization mold 9 is used in which an unvulcanized rubber base material 5 and a backing material 6 are bonded together by vulcanization.

  As shown in FIG. 3B, the vulcanization mold 9 includes a frame body 9a having a cavity C on which an unvulcanized rubber base material 5 and a backing material 6 are placed, and the frame body. A lid 9b that is detachably fixed to 9a and closes the cavity C is included. The cavity C is a bottomed space with the upward surface 9a side open, and is formed in a substantially rectangular parallelepiped shape.

  The lid body 9b has a downward surface 9b1 which is in contact with the upward surface 9a1 of the frame body 9a and closes the cavity C and has a groove-forming convex portion 11 protruding into the cavity C of the frame body 9a. The convex portion 11 has an inverted shape of the tread groove 4 formed in the rubber base material 5.

  As a manufacturing method of the test piece 3 of this embodiment, first, the backing material 6 and the rubber substrate 5 are arranged in the cavity C in this order. Next, the lid body 9b is placed on the upward surface 9a1, and the frame body 9a and the lid body 9b are fixed and vulcanized with a fastening member such as a bolt (not shown), for example. In addition, it is desirable to apply | coat the primer (For example, the product name: Chemlock by the road far yeast company) which accelerates | stimulates the vulcanization | cure adhesion | attachment of rubber | gum and a metal to the one surface 5a of the rubber base material 5. FIG.

  Moreover, the other surface 5b of the rubber base material 5 is pressed by the convex part 11 by this vulcanization, and the tread groove | channel 4 is formed.

  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. A distortion approximate to the distortion generated in the portion 2 occurs. Further, since the test piece 3 is vulcanized and bonded to the rubber base material 5 and the backing material 6 made of a metal material, the distortion generated in the tread groove 4 of the test piece 3 is, for example, a belt ply made of a metal material It approximates the distortion of the tire groove where the rubber of the tread part is bonded by vulcanization. Moreover, the test piece 3 made of such a simple constituent material has a small individual difference in the heat shrinkage rate for each test piece 3, so that the test reproducibility is high and the reliability is improved. Moreover, 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 b of 8 is measured.

  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, thereby pulling based on the difference in thermal shrinkage between the rubber base material 5 and the backing material 6. It is desirable that the stress (strain) is performed in a state where the rubber base material 5 is loaded. That is, at the interface between the rubber base material 5 and the rubber base material 5, the backing material 6, which has a lower thermal shrinkage rate than the rubber base material 5 and has a high rigidity, suppresses warping of the rubber base material 5. Stress (strain) P (shown in FIGS. 2B and 4A) acts. Therefore, since the test piece 3 cooled to room temperature generates a strain in the tread groove 4 that approximates the actual basic structure of the tire, the test process using such a test piece 3 is more accurate. It is possible to evaluate the groove bottom crack resistance performance.

  The cut 8 of this embodiment is preferably formed as a closed cut with both ends closed in order to accurately measure the opening amount b of the cut 8 and accurately evaluate the groove bottom crack resistance performance. Further, it is desirable that the tread groove 4 is disposed in the center portion in the longitudinal direction and the width direction so that the strain acts evenly. The opening amount b is the maximum width in the direction perpendicular to the length of the notch 8.

  The size of the notch 8 is not particularly limited, but the depth D2 is preferably 0.5 to 3.0 mm in consideration of the size of the rubber base 5 and the measurement accuracy. Further, the cut 8 is formed by a cutting tool such as a knife having a blade thickness of 1.0 to 2.0 mm, for example.

  The length Lc of the cut 8 is desirably 50% or more of the groove bottom width h (shown in FIG. 4A) before the cut 8 of the tread groove 4 is provided. As a result, when a predetermined time elapses after the cut is provided, the opening b of the cut 8 is saturated, and in the vicinity of the cut 8, the tensile stress (strain) P of the rubber base material 5 is substantially 0 (zero). become. Therefore, since the opening amount b measured by the length Lc of the notch 8 takes into account the strain acting on the tread groove 4, the groove bottom crack resistance can be evaluated with higher accuracy. The groove bottom width h is a width in a state where the above-described tensile stress P is applied.

Then, after this test process, an evaluation process for evaluating the groove bottom crack resistance is performed. In the evaluation process of the present embodiment, for example, a table showing a correlation between the previously measured opening amount b of the notch 8 and the groove bottom crack resistance (for example, an ozone test) is newly measured this time. The groove bottom crack resistance is evaluated in comparison with the amount of opening b.

Further, in another evaluation process of the present embodiment, as shown in FIGS. 4A to 4C, the following formula is used by using the groove bottom width h before the cut 8 is provided and the opening amount b of the cut 8. The quality is evaluated on the basis of the strain amount e calculated in (1).
e = b / (h−b)

  That is, since the denominator (hb) of the above formula indicates the groove bottom width from which the tensile stress is removed, if the opening amount b of the notch 8 is made dimensionless using this denominator, an accurate strain amount is shown. Therefore, in this evaluation step, the groove bottom crack resistance can be evaluated with high accuracy even for the test pieces 3 having different groove bottom widths. As shown in FIG. 4, the groove bottom width h is a groove width at a position t1 that is moved 1 mm outward from the deepest portion of the tread groove 4 in the tire radial direction.

  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.

  In order to confirm the effects of the present invention, a groove bottom crack resistance test based on the opening amount of the notch (hereinafter sometimes simply referred to as “the present application test”) and a crack resistance performance test based on ozone irradiation (hereinafter simply referred to as “ozone”). Sometimes called "test". In these tests, common test pieces of the present invention were 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: 40 x 15.0 x 60 (mm)
Groove bottom width before incision: 30 mm
<Tread groove (arc-shaped groove)>
Groove width x depth: 8.0 x 8.0 (mm)
<Backing material (aluminum alloy)>
Width x length: 40 x 60 (mm)
<Vulcanization conditions>
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 natural rubber (NR) and butadiene rubber (BR), each of which is 50% by mass of rubber polymer, and the rubber compositions E to H are rubber polymers of styrene butadiene rubber (SBR), 100%. It is.
The test method is as follows.

<Application test>
A notch having a depth of 2 mm and a length of 20 mm was provided at the center of the groove bottom of the test piece, and the opening amount of the notch was measured 60 minutes after the notch was provided. In addition, the amount of opening is measured by applying the titanium oxide fine powder to the vicinity of the notch and attaching it, and transferring the attached titanium oxide fine powder with a semi-transparent material having a small stretch, for example, Mendin tape (registered trademark). Measured using a projector. The backing materials were 0.5, 1.0, 3.0, 6.0, and 7.0 mm thick and tested for each.

<Ozone test>
According to JISK6259, the test piece was exposed for 96 hours continuously under the conditions of ozone concentration of 50 ± 5 pphm and tensile amount of 40 ± 2%, and the number of cracks was observed and recorded based on the following criteria. The number of cracks that cannot be counted with the naked eye is 1, 1, less than 3, 2 cracks, 3 to 5 cracks, 3, 6 to 8 cracks, and 9 cracks Was rated 5. The test results are shown in Table 1.

  As a result of the test, when the thickness of the backing material is 1.0 to 6.0 mm, it can be understood that there is a correlation between the amount of opening of the cut by the present application test and the number of cracks in the ozone test. That is, as the opening amount of the cut increases, the number of cracks also increases. On the other hand, when the backing material is 0.5 and 7.0 mm, it is difficult to say that there is a correlation between them. It has been found that the test result of the ozone test approximates a crack that occurs in a tire that has actually been run for a long period of time. Accordingly, it can be understood that the evaluation method of the present invention can accurately evaluate the groove bottom crack resistance. Further, it can be easily understood that the groove bottom crack resistance can be evaluated in the evaluation process of the other embodiment without unifying the groove bottom width before providing the cut.

DESCRIPTION OF SYMBOLS 1 Tire 2 Tread rubber 3 Test piece 4 Tread groove 5 Rubber base material 6 Backing material

Claims (6)

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,
In the test piece preparation step, a plate-like rubber base material made of the same rubber composition as the tread rubber is bonded to a backing material made of a metal material attached to one surface of the rubber base material.
The test step is performed in a state where tensile stress based on the difference in thermal shrinkage is loaded on the rubber base material by cooling the test piece to at least room temperature after vulcanization in the test piece preparation step. A method for evaluating groove bottom crack resistance of a tread groove. A method for evaluating groove bottom crack resistance performance 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,
In the test piece preparation step, a plate-like rubber base material made of the same rubber composition as the tread rubber is bonded to a backing material made of a metal material attached to one surface of the rubber base material.
After the test step, including an evaluation step for evaluating the groove bottom crack resistance performance,
The test piece is provided with a small depth of cut at the bottom of the tread groove,
The evaluation step includes a step of evaluating pass / fail based on a strain amount e calculated by the following equation using a groove bottom width h before the cut is provided and an opening amount b of the cut. Evaluation method of groove crack resistance of tread groove.
e = b / (h−b)   The said test piece preparation process is an evaluation method of the groove bottom crack-proof performance of a tread groove of Claim 1 or 2 which adhere | attaches the said rubber base material and the said backing material by vulcanization | cure. The said test piece preparation process includes the process of pressing the convex part of a vulcanization metal mold | die and forming the said tread groove | channel on the other surface of the said rubber base material at the time of the said vulcanization | cure . The evaluation method of the groove-resistant crack performance of a tread groove as described in 2.   The method for evaluating groove bottom crack resistance of a tread groove according to any one of claims 1 to 4, wherein the backing material has a thickness of 1.0 to 6.0 mm. 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 5, wherein an opening amount of the notch is measured in the test step.

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