JP7283189B2 - Friction performance evaluation method - Google Patents

Description

The present invention relates to a friction performance evaluation method. Specifically, the present invention relates to a friction performance evaluation method for a rubber member.

When a tire-mounted vehicle travels on a road surface, the outer surface of the tire comes into contact with the road surface. The friction performance of the rubber member forming the outer surface of the tire affects the grip performance and the like of the tire.

Regarding the frictional performance of rubber members, the contributions of hysteresis friction and adhesive friction are known. Hysteresis friction is defined as the energy loss that accompanies cyclical deformation and recovery of a rubber member. Adhesive friction means friction caused by adhesion and shear between the rubber member and the road surface.

Until now, it has been believed that hysteresis friction particularly contributes greatly to the friction performance of rubber members on road surfaces on which vehicles travel (hereinafter referred to as actual road surfaces). However, evaluation results of friction performance based solely on hysteresis friction do not necessarily correlate with tire grip performance on actual road surfaces.

It is also known that an increase in hysteresis friction improves tire grip performance, but reduces rolling resistance (fuel efficiency). When aiming to improve overall tire performance, it is considered that there is a limit to designing rubber compounds based solely on the evaluation of hysteresis friction.

Conventionally, various methods for evaluating the friction performance of rubber members have been studied. Japanese Patent Application Laid-Open No. 2018-154748 (Patent Document 1) discloses an evaluation method in which the same sample is continuously (repeatedly) friction-tested using a linear friction tester. Japanese Patent Application Laid-Open No. 2016-200563 (Patent Document 2) proposes a method of evaluating adhesive friction (adhesive friction) by performing a friction test on a road surface sprinkled with surfactant-containing water.

JP 2018-154748 A JP 2016-200563 A

According to the method disclosed in Patent Literature 1, it is possible to evaluate friction performance to which hysteresis friction contributes, but it is not possible to evaluate friction performance including adhesive friction. In Patent Document 2, the coefficient of friction on wet road surfaces is measured at test speeds of 3 to 20 km/h. The contribution of adhesive friction on wet road surfaces is small. At high test speeds, the contribution of adhesive friction becomes even smaller. There is room for improvement in the measurement accuracy of adhesive friction obtained by the method of Patent Document 2. A method for easily and accurately evaluating friction performance including adhesive friction has not yet been proposed.

SUMMARY OF THE INVENTION An object of the present invention is to provide an evaluation method capable of accurately evaluating the friction performance of a rubber member.

The friction performance evaluation method according to the present invention includes:
(1) A preparation step of preparing a friction test device with a simulated road surface and a rubber member, and (2) Using this friction test device, measure the friction coefficient of this rubber member at a sliding speed of 2 mm/sec or more. It has a measurement process. In this evaluation method, the friction coefficient obtained when the simulated road surface is dry is assumed to be μ _d , and the friction coefficient obtained when the simulated road surface is wet is assumed to be _{μ w .} Using _w as an index, the friction performance of the rubber member is evaluated.

Preferably, in this evaluation method, friction performance based on adhesive friction of the rubber member is evaluated.

Preferably, this evaluation method further includes a pretreatment step of friction-treating at least one surface of the rubber member before the measurement step.

Preferably, this simulated road surface is an asphalt road surface.

Preferably, the sliding speed in this measuring step is 2 mm/sec or more and 100 mm/sec or less.

According to the evaluation method of the present invention, the friction performance of a rubber member can be evaluated easily and accurately. The evaluation results obtained by this evaluation method correlate with high accuracy with the results of actual vehicle running tests in which tires made of this rubber member are mounted. This evaluation method is useful for tire development.

FIG. 1 is a flow chart of an evaluation method according to one embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the details of the present invention will be described based on preferred embodiments with reference to the drawings as appropriate, but the present invention should not be construed in a limited manner based on this description.

FIG. 1 is a flow chart showing an evaluation method according to one embodiment of the present invention. This evaluation method has a preparation process, a pretreatment process, a measurement process and an evaluation process.

The preparation step is a step of preparing a rubber member to be subjected to this evaluation method and a friction test device provided with a simulated road surface. The pretreatment step is a step of rubbing at least one surface of the prepared rubber member. The measurement step is a step of measuring the coefficient of friction of the rubber member using the prepared friction test device. The evaluation step is a step of evaluating the friction performance of the rubber member using the coefficient of friction obtained in the measurement step as an index.

In the evaluation method according to the present invention, in the measurement step, the friction coefficient μ _d on a dry road surface and the friction coefficient μ _w on a wet road surface are measured at a sliding speed of 2 mm / sec or more, and the friction coefficient μ _d and the friction coefficient μ _{w are} measured. Using the difference μ _d −μ _w as an index, the friction performance of the rubber member on the simulated road surface is evaluated.

Adhesive friction and hysteresis friction are reflected in the friction coefficient _μd obtained on a dry road surface. At this test condition, the contribution due to adhesive friction is large. On the other hand, the contribution of adhesive friction to the friction coefficient _μw obtained on wet road surfaces is negligibly small. In this evaluation method, by using the difference μ _d −μ _w as an index, it is possible to obtain an evaluation result that fully reflects the adhesive friction of the rubber member with respect to the simulated road surface. The evaluation results obtained by this evaluation method correlate with high accuracy with the results of actual vehicle running tests in which tires made of this rubber member are mounted.

In the evaluation method according to this embodiment, at least two rubber members having the same composition, shape and size are prepared in the preparation step. In the measurement step to be described later, one rubber member is used to measure the coefficient of friction _μd on a dry road surface, and the other rubber member is used to measure the coefficient of friction _μw on a wet road surface.

In the evaluation method according to the present invention, the method of preparing the rubber member in the preparation step is not particularly limited. For example, according to a predetermined composition, the base rubber and various additives are put into an open roll, Banbury mixer, or the like and kneaded to form an unvulcanized rubber. Next, the unvulcanized rubber may be heated and pressurized in a mold of a predetermined shape to produce a sheet of vulcanized rubber, and the sheet may be subjected to cutting or the like to prepare a rubber member. In addition, after extruding unvulcanized rubber according to the shape of the tread etc., it is combined with other tire members and heated and pressurized in a vulcanizer to manufacture a tire, and the vulcanized rubber forming the tire surface A rubber member may be prepared by cutting out into a predetermined shape. Furthermore, vulcanized rubber collected from the tread of a commercially available tire may be prepared as the rubber member.

The composition of the vulcanized rubber forming the rubber member is not particularly limited as long as the object of the present invention is achieved. For example, base rubbers include natural rubber, polybutadiene, styrene-butadiene copolymer, polyisoprene, ethylene-propylene-diene terpolymer, polychloroprene, acrylonitrile-butadiene copolymer and isobutylene-isoprene copolymer. mentioned. Examples of additives include fillers, resins, oils, waxes, carboxylic acids and/or salts thereof, zinc oxide, plasticizers, sulfur, vulcanization accelerators, anti-aging agents, and the like. Preferably, the composition of the vulcanized rubber that constitutes the tire surface is used. Typically, compositions for tread rubber are applied.

In this evaluation method, there are no particular restrictions on the shape and size of the rubber member. A shape and size that can be measured by a friction tester, which will be described later, are appropriately selected. A plate-like or sheet-like rubber member having a predetermined thickness is preferably used. From the standpoint of handleability and measurement accuracy, the thickness of the rubber member is preferably 2 mm or more, more preferably 3 mm or more. A preferable thickness of the rubber member is 20 mm or less.

Preferably, the rubber member has at least one measuring surface on which the coefficient of friction can be measured. When the rubber member is plate-like or sheet-like, either the upper surface or the lower surface may be used as the measurement surface. From the viewpoint of measurement accuracy, the area of the measurement surface is preferably 100 mm ² or more. A preferable area from the viewpoint of handleability is 6400 mm ² or less.

As long as the effect of the present invention can be obtained, the planar shape and size of the measurement surface are not particularly limited. For example, a rubber member having a square or rectangular measurement surface in plan view can be preferably used. When the measurement surface is square or rectangular in plan view, the length of one side is preferably 10 mm or more, more preferably 12 mm or more, from the viewpoint of measurement accuracy. From the viewpoint of ease of handling, the length of one side of the measurement surface is preferably 80 mm or less.

In the preparation step, a friction test device having a simulated road surface is prepared together with the rubber member. The type of the friction test device is not particularly limited as long as it can measure the coefficient of friction on a dry road surface and a wet road surface at the sliding speed described above. Preferably, the friction test apparatus further comprises means for adjusting the temperature of the simulated road surface. A specific example of such a friction tester is a friction tester manufactured by BULKER (trade name “UMT TriboLab”).

The material of the simulated road surface is not particularly limited, and is appropriately selected from various types of asphalt, concrete, grindstone, and the like. An asphalt road surface can be preferably used.

In the pretreatment step, at least one surface of the rubber member prepared in the preparation step is rubbed. By using this friction-treated surface as a measurement surface and subjecting it to a friction test in the measurement step to be described later, the measurement accuracy of the resulting friction coefficient is improved. As long as the effects of the present invention can be obtained, the measurement process may proceed without performing the pretreatment process.

In the pretreatment step, the method of rubbing the rubber member is not particularly limited. For example, a method of rubbing the measuring surface of the rubber member using a known friction test device can be preferably used. The type of the friction test device is not particularly limited as long as it has a friction surface (pseudo road surface) for rubbing the rubber member. As such a friction test device, a linear friction tester manufactured by HENTSCHEL (trade name “Portable friction tester”) is exemplified. The type of friction test device used in the pretreatment step and the type of friction test device prepared in the preparation step may be the same or different.

Specifically, the measuring surface of the rubber member is rubbed by pressing the measuring surface of the rubber member against the simulated road surface of the friction test apparatus and moving the measuring surface. The material of the simulated road surface is appropriately selected from various types of asphalt, concrete, grindstone, and the like. The rubber member may be friction-processed by repeatedly moving the rubber member two or more times on the simulated road surface. The number of times of movement of the rubber member is not particularly limited as long as the effects of the present invention are not hindered.

Friction treatment conditions by the friction test apparatus are appropriately selected according to the shape and size of the rubber member, the composition of the vulcanized rubber forming the rubber member, the material of the simulated road surface, and the like. For example, when performing friction treatment on an asphalt road surface, the sliding speed is preferably 1000 mm/sec or more, more preferably 1200 mm/sec or more, from the viewpoint of processing efficiency. From the viewpoint of improving the evaluation accuracy, the sliding speed is preferably 5000 mm/sec or less.

From the viewpoint of processing efficiency, the ground pressure to the rubber member is preferably 0.01 MPa or more, more preferably 0.02 MPa or more. From the viewpoint of deformation suppression, the preferable ground pressure is 0.5 MPa or less. This contact pressure is adjusted by the area of the measurement surface and the load applied to the rubber member.

In the measurement process, the rubber member is subjected to a friction test using the friction test apparatus prepared in the preparation process. Specifically, the measurement process includes a first step of performing a friction test on a dry road surface and a second step of performing a friction test on a wet road surface. The friction test in the first step gives the coefficient of friction _μd on a dry road surface. The friction test in the second step gives the coefficient of friction _μw on wet road surfaces.

In the evaluation method according to the present invention, the sliding speed in the friction tests of the first step and the second step is 2 mm/sec or more, preferably 2 mm/sec or more and 100 mm/sec or less. This sliding speed is low compared to the sliding speed commonly employed in rubber friction testing. At low sliding speeds, large adhesive friction acts between the simulated road surface and the rubber member. By setting the sliding speed within the above range, the evaluation accuracy of friction performance including adhesive friction is improved. From this point of view, the sliding speed is more preferably 90 mm/sec or less, and even more preferably 80 mm/sec or less.

In the friction test in the first step and the second step, while pressing the measuring surface of the rubber member against the simulated road surface, by moving a predetermined distance (sliding distance) at the sliding speed described above, the dynamic friction coefficient for this simulated road surface to measure Specifically, during the friction test, the position (displacement) of the rubber member moving on the simulated road surface and the dynamic friction coefficient at each position are measured, and the dynamic friction coefficient measured in a predetermined displacement section is expressed as the friction coefficient μ _d or It is obtained as the coefficient of friction μ _w .

Preferably, the rubber member is repeatedly moved, and the displacement of the rubber member and the dynamic friction coefficient at each displacement are measured for each repetition, and the average value of the dynamic friction coefficients measured in a predetermined displacement section is defined as the friction coefficient μ _d or It is obtained as the coefficient of friction μ _w . The dynamic friction coefficient varies with movement (displacement) of the rubber member. By repeating the movement of the rubber member, fluctuations in the dynamic friction coefficient are reduced. By obtaining the dynamic friction coefficient in a predetermined section after the fluctuation of the dynamic friction coefficient is reduced, the measurement accuracy is improved. From this point of view, the preferred number of repetitions in the friction test is at least two. After the fluctuation of the dynamic friction coefficient is reduced, it is more preferable to repeat the movement of the rubber member, measure the dynamic friction coefficient in a predetermined section for each repetition, and obtain the average value as the friction coefficient μ _d or the friction coefficient μ _w . .

In the friction test of the first step and the second step, the contact pressure on the rubber member is adjusted according to the shape of the rubber member, the size of the measurement surface, etc. so that it becomes the contact pressure during running of the actual vehicle. . From the viewpoint of measurement accuracy, the ground pressure to the rubber member is preferably 0.01 MPa or more, more preferably 0.02 MPa or more. From the viewpoint of deformation suppression, the preferable ground pressure is 0.5 MPa or less. This contact pressure is adjusted by the area of the measurement surface and the load applied to the rubber member.

In the friction tests of the first step and the second step, the temperature of the simulated road surface (hereinafter referred to as road surface temperature) is not particularly limited, and is appropriately selected so that the friction performance can be evaluated at a desired temperature. A preferable road surface temperature is 0° C. or higher, more preferably 10° C. or higher. From the viewpoint of suppressing deformation of the rubber member, the preferable road surface temperature is 100° C. or less.

Other measurement conditions for the friction test in the first step and the second step are appropriately selected according to the shape and size of the rubber member, the composition of the vulcanized rubber forming the rubber member, the material of the simulated road surface, and the like. It is preferable that the measurement conditions in the first step and the measurement conditions in the second step are the same.

In the evaluation process, the difference μ d _{−μ w} between the friction coefficient μ _d on the dry road surface obtained in the first step and the friction coefficient μ _w on the wet road surface obtained in the second step was used as an index to determine the friction of the rubber member. Evaluate performance.

This difference μ _d −μ _w mainly reflects the contribution of adhesive friction. The degree of adhesive friction varies, for example, with changes in the composition of the vulcanized rubber forming the rubber member. Variations in the difference μ _d −μ _w with changes in the composition of the vulcanized rubber are large compared to other previously proposed indices. In other words, the evaluation results obtained using this difference μ _d −μ _w as an index clearly reflect the influence of the composition of the vulcanized rubber.

By using this evaluation method, it is possible to select the composition of the rubber member that greatly contributes to the adhesive friction. By using a rubber member having this composition as a tire member, it is possible to obtain a tire having excellent grip performance even when hysteresis friction cannot be increased in order to maintain rolling resistance (fuel efficiency), for example. . This evaluation method is useful for tire development.

The effects of the present invention will be clarified by showing more specific examples below, but the present invention should not be construed in a limited manner based on the description of these examples.

[Example]
(Production of rubber member)
According to the composition shown as A in Table 1 below, materials other than sulfur and a vulcanization accelerator were added to a 1.7 L Banbury mixer (manufactured by Kobe Steel, Ltd.) and kneaded at 150° C. for 3 minutes. The obtained kneaded product was taken out from the Banbury mixer, the amounts of sulfur and vulcanization accelerator shown in Table 1 were added, respectively, and then kneaded at 80 ° C. for 3 minutes using an open roll to obtain an unvulcanized product. Sulfur rubber was obtained. The obtained unvulcanized rubber was put into a mold and press vulcanized at 170° C. for 12 minutes to obtain a rubber sheet (thickness: 10 mm) made of vulcanized rubber. By cutting the obtained rubber sheet, rubber members A1 and A2 having the same shape and having a measurement surface (width 25 mm×length 60 mm) were produced.

Rubber members B1 and B2 and rubber members C1 and C2 having the same shape as the rubber members A1 and A2 were produced in the same manner except that the rubber compositions were changed to those shown as B and C in Table 1 below.

Details of the compounds listed in Table 1 are as follows.
SBR: Styrene-butadiene rubber manufactured by Asahi Kasei Corporation, trade name "Tafden 4850"
BR: Butadiene rubber manufactured by Asahi Kasei Chemicals, trade name "N103"
Carbon black: trade name "Niteron #55S" manufactured by Shin Nikka Carbon Co., Ltd.
Silica: Trade name "Ultrasil VN3" manufactured by Degussa
Coupling agent: silane coupling agent manufactured by Degussa, trade name “Si69”
Oil: Aroma oil manufactured by Japan Energy, trade name “Process X-260”
Resin: trade name "Sylvatraxx 4401" manufactured by Arizona Chemical Co.
Magnesium acetate: manufactured by Kishida Chemical Co., Ltd. Zinc oxide: manufactured by Mitsui Kinzoku Co., Ltd. under the trade name “zinchua 2”
Antiaging agent: N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd., trade name "Nocrac 6C"
Wax: Product name "Sannok N" manufactured by Ouchi Shinko Kagaku Co., Ltd.
Sulfur: powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator 1: Nt-butyl-2-benzothiazylsulfenamide manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "Noccellar NS"
Vulcanization accelerator 2: N,N'-diphenylguanidine manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd., trade name "Noccellar D"

(Preprocessing)
The measurement surface of each rubber member thus produced was subjected to friction treatment under the following conditions using a linear friction tester manufactured by HENTSCHEL (trade name: "Portable friction tester").
Road surface: Asphalt Road surface condition: Dry, 35°C
Sliding speed: 2000 mm/sec Load (ground pressure): 200 N (0.13 MPa)
Sliding distance: 620mm
Number of repetitions: 10 times

(Friction test 1: first step)
Next, using a friction tester manufactured by BULKER (trade name: "UMT TriboLab"), the rubber members A1, B1 and C1 were subjected to friction tests under the following conditions.
Road surface: Asphalt Road surface condition: Dry, 20°C
Sliding speed: 10mm/sec Load (ground pressure): 100N (0.07MPa)
Sliding distance: 20mm
Number of repetitions: 10 times

Of the data obtained by measuring 10 times continuously, the average value of the 6th to 10th measurements in the section of 5 mm to 15 mm was obtained and used as the coefficient of friction μ _d on the dry road surface.

(Friction test 2: second step)
Subsequently, the rubber members A2, B2 and C2 were subjected to a friction test in the same manner as the friction test 1, except that the measurement conditions were changed as follows.
Road surface: Asphalt Road surface condition: Wet, 20°C
Sliding speed: 10mm/sec Load (ground pressure): 100N (0.07MPa)
Sliding distance: 20mm
Number of repetitions: 10 times

Of the 10 consecutive measurements, the average value of the 6th to 10th measurements in the section of 5 mm to 15 mm was obtained and used as the coefficient of friction μ _w on the wet road surface.

(friction performance evaluation)
The difference (μ d _{−μ w} ) between the friction coefficient μ _d on dry road surface obtained with rubber members A1, B1 and C1 and the friction coefficient μ _w on wet road surface obtained with rubber members A2, B2 and C2 is calculated respectively. The index when the difference (μ _d −μ _w ) calculated from the rubber members A1 and A2 is 100 is shown in Table 2 below as I(μ _d −μ _w ). A larger value indicates a larger contribution of adhesive friction.

[Comparative example]
In the comparative example, a method of predicting the friction performance of the rubber member from the viscoelastic property value obtained from the rubber member after the friction treatment was carried out.

First, in the same manner as in Examples, rubber sheets (thickness: 8 mm) having compositions indicated as AC in Table 1 were obtained. The obtained rubber sheet was cut to produce rubber members A3, B3 and C3 having a measurement surface (60 mm×60 mm). Next, using a HENTSCHEL linear friction tester (trade name: "Portable friction tester"), the measurement surface of each rubber member was subjected to friction treatment under the following conditions.
Road surface: Asphalt Road surface condition: Dry, 35°C
Sliding speed: 2000 mm/sec Number of repetitions: 8 times

After collecting a test piece with a thickness of 2 mm from the measurement surface of each rubber member after friction treatment, using a viscoelastic spectrometer (trade name "DMA+450" manufactured by Metravib), the storage elastic modulus G was measured under the following measurement conditions. ' and loss modulus G'' were measured. The obtained measured values were converted by the temperature-frequency conversion rule to create a master curve showing the frequency dependence of storage modulus G' and loss modulus G''. .
Constant stress: 0.2 MPa
Frequency: 1-100Hz
Deformation mode: Shear Measurement temperature: -40°C to 80°C (every 10°C)

The friction performance of each rubber member was predicted by applying Persson's theoretical friction formula using the created master curve. The index when the friction performance of the rubber member A3 is 100 is shown in Table 2 below as I (calculation-μ). It shows that it is excellent in grip performance, so that a numerical value is large.

[Reference Example 1] (actual vehicle test)
An unvulcanized rubber having the composition shown as A in Table 1 was obtained in the same manner as in Examples. The obtained unvulcanized rubber was extruded into a tread shape and combined with other tire members to obtain a green tire (size 205/55R16). A prototype tire A was manufactured by placing this green tire in a mold and vulcanizing it at 170° C. for 12 minutes.

After installing the prototype tire A on a regular rim, it was inflated with air at an internal pressure of 180 kPa and mounted on a test vehicle. This test vehicle was run on a dry asphalt road surface at a speed of 40 km/h, and the maximum friction coefficient μ _max from braking to stopping was measured. Similarly, prototype tires B and C having treads made of vulcanized rubbers of the formulations B and C shown in Table 1 were produced, and the maximum friction coefficient μmax was measured. The index when the measured value of the prototype tire A is 100 is shown in Table 2 below as I (μ _max ). It shows that it is excellent in grip performance, so that a numerical value is large.

[Reference example 2]
Rubber sheets having the compositions shown as AC in Table 1 were obtained in the same manner as in Examples. A test piece was taken from each of the obtained rubber sheets and subjected to a viscoelasticity test according to the method described in JIS K6394. A viscoelastic spectrometer (manufactured by Ueshima Seisakusho) was used as a measuring device, and the loss tangent (tan δ) was measured under the following conditions.
Temperature: 30°C
Initial strain: 10%
Dynamic strain: 2%
Frequency: 10Hz
The index when the loss tangent (tan δ) obtained for the test piece of composition A is 100 is shown in Table 2 below as I (tan δ). A smaller value indicates lower rolling resistance and better fuel efficiency.

(summary)
(1) As shown in Table 2, the evaluation result I(μ _d −μ _w ) of the example correlates with the evaluation result I(μ _max ) of Reference Example 1 (actual vehicle test). Furthermore, in the example, the change in the index due to the difference in composition is large compared to reference example 1. From this, it can be seen that the evaluation method according to the present invention can more clearly evaluate the grip performance on the actual road surface without actually manufacturing the tire. On the other hand, in the method of Comparative Example, evaluation results correlated with those of Reference Example 1 were not obtained.
(2) In composition B, both I(μ _d −μ _w ) and I(tan δ) increased compared to composition A. From the increase in I(μ _d −μ _w ), the contribution of adhesive friction is expected to improve the grip performance of the resulting tire. From the increase in I(tan δ), it is predicted that the hysteresis friction is improved and the grip performance is further improved, but the fuel efficiency is hindered.
(3) In composition C, I(μ _d −μ _w ) further increased, but I(tan δ) decreased. An increase in I(μ _d −μ _w ) is expected to improve grip performance due to the contribution of adhesive friction. From the decrease in I(tan δ), it is expected that the contribution of hysteresis friction is small and the low fuel consumption of the resulting tire is not hindered.

As described above, according to the evaluation method of the present invention, the contribution of adhesive friction can be separated from the friction performance and evaluated. By using this evaluation method, it becomes possible to design a more precise rubber composition for obtaining a tire member that achieves both grip performance and fuel efficiency. From the above evaluation results, the superiority of the present invention is clear.

The methods described above can also be applied to evaluate the friction performance of various tire components.

Claims (4)

A preparation step of preparing a friction test device with a simulated road surface and a rubber member;
a measuring step of measuring the friction coefficient of the rubber member at a sliding speed of 2 mm/sec or more and 100 mm/sec or less using the friction test device;
When the friction coefficient obtained when the simulated road surface is a dry road surface is μ _d and the friction coefficient obtained when the simulated road surface is a wet road surface is μ _w , the difference μ _d −μ _w is an index. As a friction performance evaluation method for evaluating the friction performance of the rubber member. 2. The evaluation method according to claim 1, wherein friction performance due to adhesive friction of said rubber member is evaluated. 3. The evaluation method according to claim 1, further comprising a pretreatment step of rubbing at least one surface of said rubber member before said measurement step. 4. The evaluation method according to any one of claims 1 to 3, wherein the simulated road surface is an asphalt road surface.

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