Test method for wear resistance performance, method of manufacturing tread rubber, method of manufacturing tire, and tire

Abstract

A test method of accurately evaluating wear resistance performance of a rubber material when used as a tread rubber of a tire, comprises the steps of: preparing a test piece of the rubber material having a ground contact surface extending in a circumferential direction; abrading the ground contact surface by rolling the test piece on a running surface of a wear testing machine at a slip ratio of not more than 3.5%; and evaluating the wear resistance performance of the test piece by comparing the amount of wear of the test piece with a predetermined threshold value.

Claims

1. A test method of evaluating wear resistance performance of a rubber material when used as a tread rubber of a tire, comprising a step of preparing a test piece of the rubber material having a ground contact surface extending in a circumferential direction, a step of abrading the ground contact surface by rolling the test piece on a running surface of a wear testing machine at a slip ratio of not more than 3.5%, and a step of evaluating the wear resistance performance of the test piece by comparing the amount of wear of the test piece with a predetermined threshold value.

2. The test method according to claim 1, wherein the wear testing machine is a Laboratory Abrasion Tester LAT100.

3. The test method according to claim 2, wherein in the step of evaluating the wear resistance performance, when the wear amount per unit area (cc/sq.Math.m) of the test piece is less than or equal to a first threshold value which is 3.0×10.sup.−5×the slip ratio (%).sup.1.4, the wear resistance performance of the test piece is evaluated as being good.

4. The test method according to claim 2, wherein in the step of evaluating the wear resistance performance, when the wear amount per unit area (cc/sq.Math.m) of the test piece is less than or equal to a first threshold value which is 2.5×10.sup.−5×the slip ratio (%).sup.1.4, the wear resistance performance of the test piece is evaluated as being good.

5. The method according to claim 1, wherein in the step of abrading the ground contact surface, the contact pressure of the ground contact surface is 0.1 to 1 MPa, the rolling speed is 1 to 50 km/h, and the rolling distance is 10 to 30 km.

6. The test method according to claim 5, wherein in the step of evaluating the wear resistance performance, when the wear amount per unit area (cc/sq.Math.m) of the test piece is less than or equal to a first threshold value which is 3.0×10.sup.−5×the slip ratio (%).sup.1.4, the wear resistance performance of the test piece is evaluated as being good.

7. The test method according to claim 5, wherein in the step of evaluating the wear resistance performance, when the wear amount per unit area (cc/sq.Math.m) of the test piece is less than or equal to a first threshold value which is 2.5×10.sup.−5×the slip ratio (%).sup.1.4, the wear resistance performance of the test piece is evaluated as being good.

8. The test method according to claim 1, wherein in the step of evaluating the wear resistance performance, when the wear amount per unit area (cc/sq.Math.m) of the test piece is less than or equal to a first threshold value which is 3.0×10.sup.−5×the slip ratio (%).sup.1.4, the wear resistance performance of the test piece is evaluated as being good.

9. The test method according to claim 8, wherein the step of evaluating the wear resistance performance includes: comparing the wear amount per unit area (cc/sq.Math.m) of the test piece with a second threshold value which is 1.0×10.sup.−6×the slip ratio (%).sup.1.4.

10. The test method according to claim 8, wherein the step of evaluating the wear resistance performance includes: comparing the wear amount per unit area (cc/sq.Math.m) of the test piece with a second threshold value which is 3.0×10.sup.−6×the slip ratio (%).sup.1.4.

11. A method of manufacturing a tread rubber based on the composition of the rubber material of the test piece whose wear resistance performance is evaluated as being good through the test method according to claim 8.

12. A method of manufacturing a tire comprises a step of manufacturing a tread rubber based on the composition of the rubber material of the test piece whose wear resistance performance is evaluated as being good through the test method according to claim 8.

13. The test method according to claim 1, wherein in the step of evaluating the wear resistance performance, when the wear amount per unit area (cc/sq.Math.m) of the test piece is less than or equal to a first threshold value which is 2.5×10.sup.−5×the slip ratio (%).sup.1.4, the wear resistance performance of the test piece is evaluated as being good.

14. The test method according to claim 13, wherein the step of evaluating the wear resistance performance includes: comparing the wear amount per unit area (cc/sq.Math.m) of the test piece with a second threshold value which is 1.0×10.sup.−6×the slip ratio (%).sup.1.4.

15. The test method according to claim 13, wherein the step of evaluating the wear resistance performance includes: comparing the wear amount per unit area (cc/sq.Math.m) of the test piece with a second threshold value which is 3.0×10.sup.−6×the slip ratio (%).sup.1.4.

16. A tire comprising a tread rubber of which wear amount per unit area (cc/sq.Math.m) is less than or equal to a first threshold value which is 3.0×10.sup.−5×a slip ratio (%).sup.1.4, when a test piece is cut out from the tread rubber and the wear amount per unit area (cc/sq.Math.m) is measured by abrading the test piece on a moving abrasive surface of a wear testing machine at the slip ratio of not more than 3.5%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flow chart showing a test method of evaluating the wear resistance performance according to the present invention.

(2) FIG. 2 is a perspective view showing an example of a test piece of a rubber material.

(3) FIG. 3 is a perspective view showing a wear testing machine.

(4) FIG. 4 is a plan view showing a step of abrading the test piece.

(5) FIG. 5 is a diagram for explaining the slip ratio.

(6) FIG. 6 is a graph showing a first threshold value as a function of the slip ratio.

DETAILED DESCRIPTION OF THE INVENTION

(7) Embodiments of the present invention will now be described in detail in conjunction with accompanying drawings.

(8) A test method for wear resistance performance as an embodiment of the present invention (hereinafter sometimes referred to simply as the “test method”) is a method of evaluating the wear resistance performance of a rubber material when used as a tread rubber of a tire.

(9) FIG. 1 is a flowchart showing the procedure of the test method which includes a step S1 of preparing a test piece of the rubber material (preparing step S1), a step S2 of abrading the test piece (abrading step S2), and a step S3 of evaluating the abrasion of the test piece (evaluating step S3).

(10) In the preparing step S1, the test piece 1 having a ground contact surface 1s extending in a circumferential direction as shown in FIG. 2 is prepared.

(11) In this embodiment, the test piece 1 is formed by attaching a strip of the rubber material 3 to the outer circumferential surface of a cylindrical support 2.

(12) The cylindrical support 2 is provided at the center thereof with a central hole 2H for mounting this cylindrical support 2 to a support shaft 4 as shown in FIG. 3.

(13) The outer circumferential surface of the rubber material 3 constitutes the ground contact surface 1s.

(14) The thickness T of the strip of the rubber material 3 is preferably set in a range from 0.5 to 4.0 mm. The width W2 of the outer circumferential surface of the cylindrical support 2 is preferably set in a range from 15 to 22 mm. The outer diameter D2 of the cylindrical support 2 is preferably set in a range from 50 to 120 mm.

(15) In the abrading step S2, as shown in FIG. 3, in order to abrade the ground contact surface 1s, the test piece 1 is rolled on the running surface 5s of the wear testing machine 5 at a slip ratio α of 3.5% or less.

(16) Since the abrading step S2 is performed under the slip ratio α of 3.5% or less, namely, a low severity condition as described above, it is possible to accurately predict the actual wear resistance performance of a tire in actual vehicle running conditions.

(17) Here, the slip ratio α is larger than 0%, and may have a value near zero. But, in order to shorten the process time of the abrasion process S2, it is preferred that the slip ratio α is 1% or more, more preferably 2% or more.

(18) In the present embodiment, the wear testing machine 5 is a Laboratory Abrasion Tester LAT100. The wear testing machine 5 comprises a rotatable abrasive disc 7, a test piece support 8 for supporting the test piece 1, and a base 9 for supporting the abrasive disc 7 and the test piece support 8.

(19) The abrasive disc 7, the test piece support 8 and the base 9 are housed in a housing (not shown) provided with, for example, a switch for operating and stopping the wear testing machine 5.

(20) In the present embodiment, a disc-like grind wheel placed on a turntable 11 is used as the abrasive disc 7. The turntable 11 is integrally rotatably supported by a support shaft 12 protruding from the base 9.

(21) In the present embodiment, the support shaft 12 is coupled to a motor (not shown) or the like built in the base 9.

(22) Therefore, the abrasive disc 7 can rotate around the axis (j) of the support shaft 12 by the drive of the motor or the like.

(23) The running surface 5s is formed by the abrasive surface of the abrasive disc 7. The running surface 5s of this example is a grinding surface, and preferably the particle size thereof is set in a range from 60 to 240 mesh, for example.

(24) The abrasive disc 7 is not limited to the disc-like grind wheel, and may be a disk-like simulated road surface, for example, made from asphalt, concrete or the like.

(25) The diameter of the running surface 5s (a circular running course) is preferably set in a range from 150 to 1,500 mm.

(26) The test piece support 8 comprises a support shaft portion 13 rotatably supporting the test piece 1 about an axis (n) orthogonal to the axis (j), and a cylinder mechanism 14 moving the test piece 1.

(27) The support shaft portion 13 comprises the support shaft 4 whose one end portion is inserted into the central hole 2H (shown in FIG. 2) of the test piece 1, and a fixing part 16 which supports the other end portion of the support shaft 4.

(28) The cylinder mechanism 14 comprises a rod 18 which can be expanded and contracted in the longitudinal direction, a cylinder 19 which supports the rod 18 to be movable into and out of the cylinder, and a motor (not shown) for expanding and contracting the rod 18. One end portion of a connecting member 20 is fixed to the tip of the rod 18. The fixing part 16 is fixed to the other end portion of the connecting member 20. Thus, by expanding the rod 18, the cylinder mechanism 14 can separate the test piece 1 from the running surface 5s.

(29) In the present embodiment, the cylinder 19 is supported on the base 9 so as to be rotatable around an axis (m), therefore, the test piece support 8 can set the slip angle θ (shown in FIG. 4) of the test piece 1 with respect to the running surface 5s.

(30) Incidentally, the slip angle θ is, as shown in FIG. 4, an angle between the direction orthogonal to the rotational axis of the test piece 1, and the traveling direction A1 of the test piece 1 which is orthogonal to a straight line X drawn between the axis (j) of the running surface 5s and the center Fj of the ground contact area F where the running surface 5s and the test piece 1 are in contact with each other.

(31) In the abrading step S2, in order to limit the slip ratio α to 3.5% or less, the slip angle θ is preferably set to be not more than 2 degrees, more preferably not more than 1 degree, most preferably 0 degree.

(32) when the slip angle θ is 0 degree, as shown in FIG. 5, the slip ratio α can be obtained by the following expression (1)
α=(W/2R)×100(%)  (1)
wherein

(33) “W” is the width of the rubber material 3 and corresponds to the width of the ground contact area F, and

(34) “R” is a distance from the axis (j) of the running surface 5s to the center Fj of the ground contact area F and corresponds to the turning radius of the test piece 1.

(35) Here, the circumferential length of the circle centered on the axis (j) and passing through the ground contact area center Fj is 2πR. The circumferential length of the circle centered on the axis (j) and passing through the outermost point of the ground contact area F is 2π(R+W/2).

(36) When the test piece 1 rolls without slipping at the position of the ground contact area center Fj, a slip corresponding to the difference in circumferential length (namely, 2π(R+W/2)−2πR=πW) occurs in the test piece 1. Thus, a slip ratio corresponding to πW/2πR=W/2R is generated.

(37) Therefore, in order to limit the slip ratio α to 3.5% or less, it is necessary to set the width W of the rubber material 3 to be small and/or set the turning radius R to be large. For that purpose, the turning radius R is preferably set to be not less than 100 mm.

(38) For example, when the turning radius R is 150 mm, the width W of the rubber material 3 needs to be set to 10.5 mm or less.

(39) When the slip angle θ is 2 degrees or less, the influence of the slip angle θ on the slip is low and almost ignorable, therefore, the expression (1) can be used for practical purposes.

(40) In the abrading step S2, in order to abrade the rubber material 3 under a lower severity condition, the rolling speed V (circumferential velocity) of the test piece 1 is preferably set in a range from 1 to 50 km/h.

(41) Preferably, the load applied to the test piece is set so that the average pressure of the ground contact area F becomes in a range from 0.1 to 1 MPa, more preferably 0.2 to 0.8 MPa.

(42) Further, as the abrading step S2 is performed under the condition that the slip ratio α is low, in order to ensure that the wear amount G of the test piece 1 becomes sufficient, the rolling distance L (running distance) of the test piece 1 is set in a range from 10 to 30 km, preferably 20 to 30 km. Such distance is considerably longer than conventional.

(43) In the abrading step S2, it is preferable to abrade the rubber material 3 in the presence of sand-like particles between the test piece 1 and the running surface 5s. Thereby, it is possible to suppress the abrasion powder from reattaching to the test piece 1, which helps to improve the measurement accuracy of the wear amount of the test piece 1.

(44) In the next evaluating step S3, the wear resistance performance of the test piece 1 is evaluated by comparing the amount of wear of the test piece 1 caused in the abrading step S2 with a predetermined threshold value K.

(45) Specifically, when the wear amount G0 per unit area (cc/sq.Math.m) of the test piece 1 is equal to or less than a first threshold value K1 determined by the following expression (2)
K1=3.0×10.sup.−5×the slip ratio (%).sup.1.4  (2),
the wear resistance performance of the test piece 1 is evaluated as being good, wherein

(46) the wear amount G0 per unit area is a value obtained by dividing the wear amount G in cc caused in the abrading step S2 by the total area W×L in sq.Math.m which is the product of the width W of the ground contact surface 1s and the rolling distance L, namely, G0=G/(W×L).

(47) For example, the wear amount G (unit cc) can be obtained from the difference in the weight of the test piece 1 measured before and after the abrading step S2.

(48) The expression (2) is derived from the results of experiments conducted by the inventor.

(49) Specifically, a cylindrical reference test piece 1A is prepared from a standard rubber material having the composition evaluated to be excellent in the wear resistance performance in actual vehicle running conditions.

(50) Then, according to the abrading step S2, the reference test piece 1A was subjected to the abrasion test. At this time, a plurality of abrasion tests were conducted changing the slip rate α (%), and data of the wear amount G for each slip rate α (%) was obtained, wherein the slip ratio α (%) was changed by changing the width W of the rubber material 3.

(51) Then, through regression analysis of the data, a regression expression (power regression expression) shown in FIG. 6 was obtained.

(52) Therefore, when the abrasion test based on the abrading step S2 is performed on the test piece 1 to be evaluated, if the obtained wear amount G0 per unit area is equal to or less than the first threshold value K1 obtained by the expression (2), then the wear resistance performance of the test piece 1 can be evaluated as being good, that is, the wear resistance performance of the test piece 1 is equal to or better than that of the reference test piece 1A.

(53) It is preferable to use the first threshold value K1 obtained by the following expression (3), instead of the expression (2),
K1=2.5×10.sup.−5×the slip ratio (%).sup.1.4  (3).
Thereby, it becomes possible to more reliably evaluate the wear resistance performance as being good.

(54) If the wear amount G0 per unit area obtained in the abrading step S2 is too small, there is a possibility of adversely affecting other performance required for a tread rubber such as road grip performance. Therefore, it is preferable that the evaluating step S3 further includes: comparing the wear amount G0 per unit area with a second threshold value K2 obtained by the following expression (4):
K2=1.0×10.sup.−6×the slip ratio (%).sup.1.4  (4).

(55) If the wear amount G0 per unit area is smaller than the second threshold value K2 in this comparison, there is a possibility that other performance required for the tread rubber becomes inferior, therefore, it is possible to direct attention to other performance than the wear resistance performance.

(56) It is more preferable to use the second threshold value K2 obtained by the following expression (5), instead of the expression (4),
K2=3.0×10.sup.−6×the slip ratio (%).sup.1.4  (5).

(57) In the test method of the present invention, the rubber material 3 used to make the test piece 1 can be formed by vulcanizing the composition to be evaluated into a strip shape. Further, it is also possible to cut out from the tread portion of the vulcanized tire to form the strip of the rubber material 3. Furthermore, the entire test piece 1 can be formed from the rubber material 3, including a portion like the cylindrical support 2.

(58) Aside from the above-described Laboratory Abrasion Tester LAT100 which is commercially available, another machine can be used as the wear testing machine 5 as far as it has the same function as that of the Laboratory Abrasion Tester LAT100, namely, a function to abrade the outer circumferential surface (ground contact surface 1s) of the test piece 1 by making the outer circumferential surface contact with the surface of the rotatably supported abrasive disc 7, and making the test piece 1 roll over the surface of the rotatably supported abrasive disc 7.

(59) The method of manufacturing a tread rubber according to the present invention is characterized in that the tread rubber is manufactured based on the composition of the rubber material of the test piece 1 of which wear resistance performance has been evaluated as being good in the test method.

(60) In the manufacturing of the tread rubber, various known methods can be employed except for the use of the composition of the rubber material of the test piece 1 of which wear resistance has been evaluated as being good by the above-described test method.

(61) The method of manufacturing a tire according to the present invention is characterized by comprising a step of manufacturing a tread rubber based on the composition of the rubber material of the test piece 1 of which wear resistance performance has been evaluated as being good in the test method. In the manufacturing of the tire, various known methods can be employed except for the manufacturing of the tread rubber based on the composition of the rubber material of the test piece 1 of which wear resistance performance has been evaluated as being good by the above-described test method.

(62) The tire according to the present invention is characterized by a tread portion of which ground contact surface is formed by a tread rubber manufactured based on the composition of the rubber material of the test piece 1 of which wear resistance performance has been evaluated as being good by the above-described test method.

(63) In other words, the tire has the tread rubber of which wear amount per unit area (cc/sq.Math.m) is less than or equal to a first threshold value which is 3.0×10.sup.−5×a slip ratio (%).sup.1.4, when a test piece is cut out from the tread rubber and the wear amount per unit area (cc/sq.Math.m) is measured by abrading the test piece on a moving abrasive surface of a wear testing machine at the slip ratio of not more than 3.5%.

(64) In the tire, various known tire structures can be employed except for the tread rubber.

(65) While detailed description has been made of preferable embodiments of the present invention, the present invention can be embodied in various forms without being limited to the illustrated embodiments.

EXAMPLE

(66) Test pieces were prepared from three rubber materials A, B and C having different chemical compositions shown in Table 1. And the wear resistance performances thereof were evaluated according to the procedure shown in FIG. 1. The preparing step S1, the abrading step S2 and the evaluating step S3 are as follows.

(67) <Preparing Step S1>

(68) rubber materials A-C

(69) thickness T: 2.0 mm

(70) width W: 9.0 mm cylindrical support 2

(71) width W2: 18.0 mm

(72) outer diameter D2: 80 mm

(73) <Abrading step S2>

(74) wear testing machine 5: Laboratory Abrasion Tester LAT100 manufactured by Heisen Yoko Co., Ltd. load: 20 N rolling speed v: 20 km/h rolling distance L: 80 km slip angle θ: 0 degree turning radius R: 150 mm slip ratio α: 3%
<Evaluating Step S3> wear amount GOA per unit area of rubber material A: 8.2×10.sup.−5 (cc/sq.Math.m) wear amount GOB per unit area of rubber material B: 7.8×10.sup.−5 (cc/sq.Math.m) wear amount GOC per unit area of rubber material C: 7.1×10.sup.−5 (cc/sq.Math.m) first threshold value K1 obtained from expression (2): 13.3×10.sup.−5

(75) Thus, the wear amounts G0A, G0B and G0C of the rubber materials A, B and C were all smaller than the first threshold value K1, and the rubber materials A, B and C can be supposed to have good wear resistance performance.

(76) As the wear resistance performances of the rubber materials A to C, the wear amounts G0A, G0B and G0C are indicated in Table 2 by an index based on the wear amount G0A being 100, wherein the larger the value, the better the wear resistance.

Comparative Example

(77) For comparison, under a condition of the slip ratio α of 5.7% as a high severity condition, the abrading step S2 was performed in the same way as above. The rubber materials A, B and C were the same as above. The difference was only the slip ratio α. And the wear amount G1A per unit area of the rubber material A, the wear amount G1B per unit area of the rubber material B, and the wear amount G1C per unit area of the rubber material c were measured.

(78) As the wear resistance performances of the rubber materials A to C, the wear amounts G1A, G1B and G1C are indicated in Table 2 by an index based on the wear amount G1A being 100, wherein the larger the value, the better the wear resistance.

(79) <Actual Vehicle Running Test>

(80) Pneumatic tires of size 215/60R16 (rim size 16×6.5J) having different tread rubbers having the compositions of the rubber materials A, B and C were manufactured.

(81) Each tire was mounted on all wheels of a Japanese 2000cc FR passenger car and run for 30,000 km in a tire test course. (tire pressure 230 kPa)

(82) After running, the wear amount of the tread rubber was measured in a tread crown portion, and based on the wear amount, the wear resistance performance of each tire is indicated in Table 2 by an index based on the wear amount of the rubber material A being 100, wherein the larger the value, the better the wear resistance.

(83) TABLE-US-00001 TABLE 1 (phr) rubber material A B C SBR 100 70 50 BR — 30 50 carbon black 1 65 65 65 carbon black 2 10 10 20 resin 25 20 22.5 wax 2 2 2 anti-aging agent 1 2.5 2.5 2.5 anti-aging agent 2 1 1 1 stearic acid 1.5 1.5 2 zinc oxide 2.5 2.5 2.5 sulfur 1.5 1.5 0.5 cross linker — — 1 vulcanization accelerator 1 1.5 1.5 1.5 vulcanization accelerator 2 2.5 2.5 2.5

(84) TABLE-US-00002 TABLE 2 Evaluation by Estimation by Estimation actual vehicle comparative according to running test example present invention rubber material A 100 100 100 rubber material B 105 140 105 rubber material C 115 130 115

(85) As shown by Table 2, it was confirmed that, by employing the test method according to the present invention, the wear resistance performance of a tire in actual vehicle running conditions can be predicted with high accuracy.

(86) The chemicals used for the compositions of Table 1 are as follows. SBR: Buna 5L4525-0 manufactured by LANXESS CO., Ltd. (styrene content 25% by mass, non-oil-extended, non-modified S-SBR) BR: Buna CB21 manufactured by LANXESS Co., Ltd. (high cis BR, BR synthesized using Nd catalyst, cis content: 98% by mass, ML (1+4) 100 degrees C.: 73, Mw/Mn: 2.4) Carbon black 1: Seast 9H manufactured by Tokai Carbon Co., Ltd. (DBP oil absorption 115 ml/g, BET specific surface area 110 sq.Math.m/g) Carbon black 2: PRINTEX XE 2B manufactured by Degussa, Inc. (N2SA: 1000 sq.Math.m/g, DBP: 420 ml/100 g) Resin: NOVARES C10 resin manufactured by Rutogar (liquid coumarone indene resin, softening point 10 degrees C.) Wax: Sunnoc N manufactured by Ouchi Shinko chemical industrial Co. Ltd. Anti-aging agent 1: NOCRAC 6C manufactured by Ouchi Shinko chemical industrial Co. Ltd. (N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine) Anti-aging agent 2: NOCRAC 224 manufactured by Ouchi Shinko chemical industrial Co. Ltd. (2,2,4-trimethyl-1,2-Dihydroquinoline polymer) Stearic acid: Stearic acid “TUBAKI” made by NOF Corporation Zinc oxide: Zinc flower type 2 made by Mitsui Metal Mining Co., Ltd. Sulfur: Powdered sulfur made by Tsurumi Chemical Industry Co., Ltd. Cross linker: vulcuren VP KA9188 manufactured by LANXESS CO., Ltd. (1,6-bis(N,N′-dibenzylthiocarbamoyldithio) hexane, sulfur content: 20.6% by mass) vulcanization accelerator 1: Noccella NS manufactured by ouchi Shinko chemical industrial co. Ltd. (N-tert-butyl-2-benzothiazolylsulfenamide) vulcanization accelerator 2: socoxynol D manufactured by Sumitomo Chemical co., Ltd. (diphenyl guanidine)

DESCRIPTION OF THE REFERENCE SIGNS

(87) 1 test piece 1s ground contact surface 3 rubber material 5 wear testing machine 5s running surface G, G0 wear amount K threshold value K1 first threshold value K2 second threshold value S1 preparing step S2 abrading step S3 evaluating step