12 included in the anti-slip member 10 is preferably 1 volume % or more and 5 volume % or less, more preferably 2 volume % or more and 4 volume % or less, without limitation thereto. More suitably, it is preferable that the above proportion of the water-soluble particles 12 be included in an internal region, which is a portion of the anti-slip member 10 from which the surface layer region is excluded. In other words, the anti-slip member 10 includes the surface layer region having the recesses as a result of the disappearance of the water-soluble particles 12 and the internal region provided inside the surface layer region, and the proportion of the water-soluble particles 12 included in the internal region is preferably 1 volume % or more and 5 volume % or less, more preferably 2 volume % or more and 4 volume % or less. The proportion of the water-soluble particles 12 included in the anti-slip member 10 falls within the above range to thereby more effectively increase the wet-grip performance of the anti-slip member 10.

The proportion of the water-soluble particles 12 included in the anti-slip member 10 is preferably 5 volume % or less, more preferably 4 volume % or less, in terms also of maintaining sufficient mechanical strengths, such as tensile strength or tear strength, of the anti-slip member 10. When the proportion of the water-soluble particles 12 included in the anti-slip member 10 is too large, the mechanical strengths of the anti-slip member 10 are easily reduced by the water-soluble particles 12 present in the anti-slip member 10, which could cause the anti-slip member for the wearable equipment or the sports equipment to fail to exhibit the required mechanical strengths. Further, when the content of the water-soluble particles 12 in the anti-slip member 10 is excessive, larger portions of the water-soluble particles 12 make contact with each other in the anti-slip member 10. When those water-soluble particles 12 exposed on the surface of the anti-slip member 10 are wet with water to dissolve, water-soluble particles 12 in contact with the wet particles 12 directly or via other water-soluble particles 12 within the anti-slip member 10 may also dissolve in association with the wetting if excessively large portions of the water-soluble particles 12 make contact with each other. If this is the case, pores like those in a sponge occur in the regions in which the water-soluble particles 12 were present within the anti-slip member 10 once wet, which could possibly result in a significant reduction of the mechanical strengths of the anti-slip member 10.

The proportion in volume % of the water-soluble particles 12 included in the anti-slip member 10 can be determined by, for example, the following method: all those water-soluble particles 12 seen on each of two or more randomly selected cross-sectional surfaces of the anti-slip member 10 are caused to disappear (by, for example, being eluted by water), and thereafter the area of all recesses, which are formed as a result of the disappearance of the water-soluble particles 12, visible on each of the cross-sectional surfaces are for example observed using a microscope to calculate the total area ratio of the recesses to the cross-sectional surface. This measurement and calculation are performed for at least two or more cross-sectional surfaces, and the value obtained by raising the average of the respective calculated total area ratios to the power of 3/2 can be regarded as the proportion in volume % of the water-soluble particles 12 included in the anti-slip member 10. The content of the water-soluble particles 12 within the internal region, which is the portion of the anti-slip member 10 from which the surface layer region is excluded, can be measured for the anti-slip member 10 after scraping off the surface of the anti-slip member 10 in a uniform thickness until the recesses as a result of the disappearance of the water-soluble particles 12 become no longer visible (e.g., to a depth of 100 μm from the surface) to remove the surface layer region.

It is preferable that the water-soluble particles 12 dispersed in the elastomer 11 of the anti-slip member 10 be substantially uniformly dispersed in the elastomer 11. Since the water-soluble particles 12 are uniformly dispersed in the elastomer 11, the water-soluble particles 12 or the recesses C are also substantially uniformly dispersed over the entire surface of the anti-slip member 10. This configuration allows air discharged from the recesses C to be widely present between the surface of the anti-slip member 10 and the object G in the entire surface of the anti-slip member 10. Therefore, the wet-grip performance can be more effectively increased in the entire surface of the anti-slip member 10. In the anti-slip member 10, the water-soluble particles 12 or the recesses C do not necessarily have to be dispersed over the entire surface of the anti-slip member 10. Even if the water-soluble particles 12 or the recesses C are unevenly dispersed in a certain region of the surface of the anti-slip member 10, the wet-grip performance of the wet-grip member 10 can still be increased.

An elastomer generally used as an anti-slip material, which can exhibit sufficient grip performance to the object with which the elastomer makes contact, is used as the elastomer 11. Examples of the elastomer include a vulcanized rubber such as a natural rubber (NR), an isoprene rubber (IR), a butadiene rubber (BR), a styrene butadiene rubber (SBR), a chloroprene rubber (CR), an acrylonitrile butadiene rubber (NBR), a butyl rubber (IIR), and a silicone rubber (Si); and a thermoplastic elastomer such as a styrene-based elastomer (TPS), an olefin-based elastomer (TPO), a urethane-based elastomer (TPU), a polyester-based elastomer (TPEE), polyamide-based elastomer (TPA), polyvinyl chloride (PVC), and an ethylene-vinyl acetate copolymer (EVA). These can be solely used, or two or more kinds of them can be used in combination with each other.

It is preferable that an appropriate elastomer be selected as the elastomer 11 according to the characteristics required for the wearable equipment or sports equipment for which the anti-slip member is used. For example, when the anti-slip member is used for a shoe sole of a shoe, BR, SBR, NR, or IR, which is excellent in tensile strength, tear strength, and abrasion resistance, is appropriately selected as the elastomer 11.

The hardness of the elastomer 11 of this embodiment can be appropriately set according to the intended use of the anti-slip member. For example, when the anti-slip member is used for a shoe sole of a shoe, the hardness of the elastomer 11 is preferably in a range of 55 to 75 in the type A durometer hardness according to JIS K 6253-3:2012. For the anti-slip member used for the grip of a bat or racket, or used for a glove or wear, the hardness of the elastomer 11 is preferably in a range of 40 to 60 in the type A durometer hardness. The wet-grip performance of the anti-slip member 10 achieved by the water-soluble particles 12 included therein tends to be more remarkably improved as the elastomer 11 has a lower hardness. In this regard, it is more preferable that the hardness of the elastomer 11 be a type A durometer hardness of 65 or less.

The wet-grip performance of the anti-slip member 10 achieved by the water-soluble particles 12 included therein tends to be more remarkably improved as the elastomer 11 has a lower initial elastic modulus (tensile elastic modulus). In this regard, the initial elastic modulus of the elastomer 11 is preferably 20 MPa or less, more preferably 10 MPa or less. The initial elastic modulus of the elastomer 11 is preferably 1 MPa or more. The initial elastic modulus of the elastomer 11 can be determined from the gradient of the stress-strain curve in a low-strain area in the tensile test according to JIS K6251:2017 “Rubber, vulcanized or thermoplastic—Determination of tensile stress-strain properties” (for example, gradient of the stress-strain curve corresponding to a portion between two strain points of ε1=0% and ε2=5%).

The elastomer 11 can be a non-foamed product or a foamed product as long as the recesses C, which are formed as a result of the disappearance of the water-soluble particles 12 and have substantially the same size as the water-soluble particles 12, can be formed on the surface thereof. Nevertheless, the elastomer 11 included in the anti-slip member 10 is preferably a non-foamed product since the surface of the anti-slip member 10 desirably has a flat surface capable of making contact with the object G to increase its contact area with the object G near each of the disappearing portions of the water-soluble particles 12. In this embodiment, the elastomer 11 is depicted as a non-foamed product.

The anti-slip member 10 can further include an inorganic filler such as silica, alumina, calcium carbonate, magnesium carbonate, carbon black, graphite, talc, or clay. When a portion of the anti-slip member 10 other than the water-soluble particles 12 is considered as a matrix, the matrix itself preferably has hydrophilicity. Thus, an inorganic filler excellent in hydrophilicity is suitably included in the anti-slip member 10. As the inorganic filler included in the anti-slip member 10, suitably selected is silica in a particulate form having a surface on which a number of silanol groups (—Si—OH) each as a hydrophilic functional group are present.

The silica can be a wet silica or a dry silica. The wet silica can be a precipitated silica, a gelled silica, or a colloidal silica. The dry silica can be a fumed silica or an arc silica. The silica is preferably the wet silica. It is preferable that the wet silica include aggregated particles each formed to have a plurality of primary particles of about 20 nm aggregated with each other. The wet silica is preferably the precipitated silica, which includes a large number of aggregated particles easily decomposed into the primary particles, in terms of being easily handled and excellent in dispersibility of the primary particles into rubber.

The content of silica in the anti-slip member 10 is preferably 10 mass parts or more based on 100 mass parts of the elastomer 11. The content of the silica is more preferably 20 mass parts or more, still more preferably 30 mass parts or more. The content of the silica in the anti-slip member 10 is preferably 100 mass parts or less based on 100 mass parts of the elastomer 11. The content of the silica is more preferably 90 mass parts or less, still more preferably 80 mass parts or more.

It is preferable that the anti-slip member 10 include a silane coupling agent together with the silica. The configuration can be such that the silane coupling agent in this embodiment has a hydrolyzable functional group at an end of the molecular chain, and further has an organic functional group other than the hydrolyzable functional group. The hydrolyzable functional group can be an alkoxy group, a phenoxy group, a carboxyl group, an alkenyloxy group, or the like. The organic functional group can be an epoxy group, a vinyl group, an acryloyl group, a methacryloyl group, an amino group, a sulfide group, a mercapto group, or the like. The silane coupling agent in this embodiment preferably has a sulfide group. That is, the silane coupling agent in this embodiment is preferably a sulfide-based silane coupling agent. The sulfide-based silane coupling agent can be a monosulfide-based silane coupling agent or a polysulfide-based silane coupling agent.

Examples of the sulfide-based silane coupling agent include bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, mercaptopropyltrimethoxysilane, mercaptopropyltriethoxysilane, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl-tetrasulfide, trimethoxysilylpropyl-mercaptobenzothiazoltetrasulfide, triethoxysilylpropyl-methacrylate-monosulfide, dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl-tetrasulfide, and 3-octanoylthio-1-propyltriethoxysilane. In this embodiment, a polysulfide-based silane coupling agent is preferable. The polysulfide-based silane coupling agent also functions effectively in crosslinking rubber. Among these, bis(3-triethoxysilylpropyl)tetrasulfide is preferable.

The silane coupling agent can be included in the anti-slip member 10 at a proportion of 1 mass part or more when the content of the silica in the anti-slip member 10 is set to 100 mass parts. The content of the silane coupling agent is preferably 6 mass parts or more, more preferably 7 mass parts or more, based on 100 mass parts of the silica. The content of the silane coupling agent is preferably 20 mass parts or less, more preferably 15 mass parts or less, based on 100 mass parts of the silica.

The anti-slip member 10 can further include a compound having excellent hydrophilicity such as polyethylene glycol. The polyethylene glycol preferably has a mass average molecular weight of 2,000 or more and 5,000 or less. The mass average molecular weight is determined as a polystyrene equivalent by the GPC method. The content of the polyethylene glycol in the anti-slip member 10 is preferably 0.1 mass part or more based on 100 mass parts of the elastomer 11. The content of the polyethylene glycol is more preferably 0.2 mass part or more, still more preferably 0.3 mass part or more. The content of the polyethylene glycol is more preferably 10 mass parts or less, still more preferably 2 mass parts or less.

The anti-slip member 10 can include a plasticizer such as paraffin oil (liquid paraffin). The content of a plasticizer having high hydrophobicity such as paraffin oil is preferably 30 mass parts or less based on 100 mass parts of the elastomer 11.

In addition to the above components, the anti-slip member 10 of this embodiment can further include other optional components such as a vulcanizing agent, a vulcanization accelerator, a crosslinking accelerator, a filler, an antioxidant, or an ultraviolet absorber.

The anti-slip member 10 preferably has a tensile strength of 12 MPa or more, which is measured according to JIS K6251:2017 “Rubber, vulcanized or thermoplastic—Determination of tensile stress-strain properties”, in terms of exhibiting the characteristics required for the shoe sole. The anti-slip member 10 preferably has a tensile elongation at break of 350% or more, which is measured according to the above JIS. The anti-slip member 10 preferably has a tear strength of 40 N/mm or more, which is obtained according to JIS K6252-1:2015 “Rubber, vulcanized or thermoplastic-Determination of tear strength—Part 1: Trouser, angle and crescent test pieces”. The tear strength can be measured using an angle-shaped test piece (with no cut).

The tensile strength of the anti-slip member 10 is more preferably 15 MPa or more, still more preferably 17 MPa or more. The tensile strength is generally 50 MPa or less. The tensile elongation at break of the anti-slip member 10 is more preferably 400% or more, still more preferably 500% or more. The tensile elongation at break is generally 1000% or less. The tear strength of the anti-slip member 10 is more preferably 50 N/mm or more, still more preferably 60 N/mm or more. The tear strength is generally 120 N/mm or less.

The initial elastic modulus of the anti-slip member 10 is preferably 20 MPa or less, more preferably 12 MPa or less. The initial elastic modulus of the anti-slip member 10 is preferably 1 MPa or more. Similar to the case of the elastomer 11, the initial elastic modulus of the anti-slip member 10 can also be determined from the gradient of the stress-strain curve in a low-strain area in the tensile test according to JIS K6251:2017 (for example, gradient of the stress-strain curve corresponding to a portion between two strain points of ε1=0% and ε2=5%).

The anti-slip member 10 of this embodiment can be produced by kneading the above components, that is, the elastomer 11, the water-soluble particles 12, and optionally the silica, the silane coupling agent, the polyethylene glycol, and the like, using any method commonly practiced by those skilled in the art. For example, as the kneading method, a method of kneading the above components, for example, by a A kneading or B kneading step using an open roll, a kneader, or the like can be used.

(Wearable Equipment or Sports Equipment)

The wearable equipment or sports equipment of the present invention includes the anti-slip member 10. The wearable equipment or sports equipment of the present invention is not particularly limited as long as it is equipment to be worn by the user (wearer) or to be attached to the user (wearer) at the time of use, or equipment to be used when the user performs exercise, and can be, for example, shoes, wears, gloves, spectacles, bats, rackets, golf clubs, or the like.

FIG. 4 is a schematic view showing a shoe 20 as the wearable equipment of one embodiment, which has an anti-slip member 10 provided at a ground contact place of a shoe sole 23. The shoe 20 includes an upper member 21 covering the upper surface of the foot, and a midsole 22 and an outer sole 23 as a shoe sole arranged on the lower side of the upper member 21. Specifically, the shoe 20 is disposed at a ground contact place, and includes the outer sole 23 provided with the anti-slip member 10, and the midsole 22 disposed between the upper member 21 and the outer sole 23. In this embodiment, the shoe 20 includes both the midsole 22 and the outer sole 23, but the shoe 20 does not necessarily include both of them. That is, the shoe 20 can include only the outer sole 23 provided with the anti-slip member 10 as the shoe sole, and can include no midsole 22. In this case, the outer sole 23 can be formed of a foam in order to ensure the cushioning properties required for the midsole.

FIG. 5 is a bottom view of the shoe sole (outer sole) 23 of the shoe 20 provided with the anti-slip member 10. In the shoe sole 23, as shown in FIG. 5, the anti-slip member 10 can be provided in a region positioned within a range of 0% to 60% of the shoe sole 23 with respect to the longitudinal direction (hereinafter, also referred to as a front region of the shoe sole 23) and in a region within a range of 70% to 100% of the shoe sole 23 with respect to the longitudinal direction (hereinafter, also referred to as a rear region of the shoe sole 23) when the toe-side end is 0% and the heel-side end is 100% of the shoe sole 23 with respect to the longitudinal direction. Preferably, the anti-slip member 10 is provided in a region occupying 5 to 100% of the entire front region of the shoe sole 23, in a region occupying 5 to 100% of the entire rear region of the shoe sole 23, or in the both regions. Herein, the region positioned within the range of 0% to 60% of the shoe sole 23 with respect to the longitudinal direction means a region of the shoe sole 23 located closer to the toe side than a straight line defined by crossing, in a width direction at right angles, a longitudinal straight line passing through the toe-side end and the heel-side end at a point which is a 60% position of the longitudinal straight line. Similarly, the region positioned within the range of 70% to 100% of the shoe sole 23 with respect to the longitudinal direction means a region of the shoe sole 23 located closer to the heel side than a straight line which crosses in the width direction the longitudinal straight line at a 70% position defined in the same manner as above. These regions are designated by their respective areas of the bottom surface of the shoe sole 23 as viewed from its front as in FIG. 5.

Particularly preferably, in the shoe sole 23, the anti-slip member 10 is provided at each of the positions corresponding to the heel, the metatarsophalangeal joints, and the toe of the wearer. In the shoe sole 23, the positions corresponding to the heel, the metatarsophalangeal joints, and toe are likely to exhibit grip performance because they frequently make contact with the ground, and the contact area of each of them is relatively large. Therefore, the wet-grip performance of the shoe 20 can be more effectively increased by arranging the anti-slip member 10 at each of these positions of the shoe sole 23.

However, in the shoe sole 23 of the shoe 20 of the present invention, the position at which the anti-slip member 10 is provided is not particularly limited. For example, the anti-slip member 10 can be provided at at least one of positions of the shoe sole 23 respectively corresponding to the heel, the metatarsophalangeal joints, and the toe, of the wearer, and can be provided at another position different from these positions. The anti-slip member 10 can be provided only in the front region of the shoe sole 23, or can be provided only in the rear region. Further, the anti-slip member 10 can be provided on the entire surface of the shoe sole 23, and the entire shoe sole 23 can be formed of the anti-slip member 10.

In order for the shoe 20 to exhibit high wet-grip performance, it is preferable that the anti-slip member 10 provided in the shoe sole 23 be configured to make contact with the ground through a widest possible area of the anti-slip member 10 when making contact with the ground. Therefore, unlike the conventionally known anti-slip member for the shoe sole, the anti-slip member 10 provided in the shoe sole 23 is preferably free from a large unevenness on its surface, and more preferably has a flat surface.

The shoe 20 of this embodiment is improved in wet-grip performance also to various grounds including grounds with non-paved surfaces by the anti-slip member 10 provided in the shoe sole 23, and among others, wet-grip performance to a road surface paved with concrete, asphalt or the like is particularly increased. In contrast, it should be noted that the shoe 20 of this embodiment, due to its wet-grip-performance enhancing mechanism, is almost unlikely to improve wet-grip performance on a frozen ground or ice.

The anti-slip member 10 of this embodiment is made of an elastomer composition having the water-soluble particles 12 dispersed in the elastomer 11, but the anti-slip member 10 can be formed by combining such an elastomer composition and a known elastic body having no water-soluble particles 12 dispersed in the elastomer 11 but having a general uneven surface for an anti-slip purpose. Further, the anti-slip member 10 can be formed integrally as an elastomer composition including both an internal region with the water-soluble particles 12 dispersed therein and an internal region with no water-soluble particles 12 dispersed therein.

FIG. 6 shows a rugby wear 30 as one embodiment of the wearable equipment of the present invention. In the rugby wear 30, as shown in FIG. 6, the anti-slip member 10 can be provided around each of the breast portions of the front body, the shoulder portions, and the armpit portions. The breast portions of the front body and their peripheries, and the armpit portions and their peripheries make contact with a ball as the object when the ball is held by a rugby player during a rugby game. Therefore, the rugby player wearing the rugby wear 30 in which the anti-slip member 10 is provided at each of these portions can enjoy an effect of making it difficult to slip the ball wet with perspiration out of these portions. In addition, the shoulder portions come into contact with the shoulders of a competing player when they form a scrum in the rugby game. Therefore, the rugby player wearing the rugby wear 30 in which the anti-slip member 10 is provided at each of these portions can enjoy an effect of making it difficult to slip on the shoulder portions when forming the scrum.

FIG. 7 shows a sports glove 40 as one embodiment of the wearable equipment of the present invention. In the sports glove 40, as shown in FIG. 7, the anti-slip member 10 can be provided between portions around the joints of each of the finger bones of the wearer, as well as around the tips of the metacarpal bones. A player wearing the sports glove 40 in which the anti-slip member 10 is provided at each of these portions can enjoy an effect of making it difficult to slip the holding object wet with water or perspiration out of the glove 40.

In one embodiment of the sports equipment of the present invention, the anti-slip member 10 can be provided on a grip of sports equipment such as a bat, a racket or a golf club. Such sports equipment with the anti-slip member 10 provided on the grip has an effect of making it hard for the grip wet with water or perspiration to be slippery, and therefore enabling the user to easily hold the sports equipment stably.

As described above, the anti-slip member for the wearable equipment or sports equipment of this embodiment is composed of the elastomer composition including the elastomer and the water-soluble particles dispersed in the elastomer. Thus, high grip performance can be exhibited even for an object wet with water, and therefore, the wet-grip performance is improved.

The average particle size of the water-soluble particles is preferably 10 μm or more and 100 μm or less. This configuration can more effectively increase the wet-grip performance of the anti-slip member.

It is preferable that the anti-slip member include: the surface layer region having at least one of the water-soluble particles exposed on the surface and the recesses as a result of the disappearance of the water-soluble particles; and the internal region disposed inside the surface layer region, and that the proportion of the water-soluble particles included in the internal region be 1 volume % or more and 5 volume % or less. This configuration can more effectively increase the wet-grip performance of the anti-slip member. It is more preferable that the proportion of the water-soluble particles included in the internal region be 2 volume % or more and 4 volume % or less.

Preferably, the water-soluble particles include the inorganic salt. This configuration allows the water-soluble particles to have an advantage of being hardly subjected to chemical modification by heat at the time of producing the anti-slip member. More preferably, the inorganic salt is sodium chloride.

Preferably, the tensile elastic modulus of the elastomer is 10 MPa or less. This configuration can more efficiently increase the wet-grip performance of the anti-slip member.

Further, since the wearable equipment or sports equipment of this embodiment including the anti-slip member makes it possible to provide the wearable equipment or sports equipment with improved wet-grip performance.

When the wearable equipment is a shoe, the anti-slip member is generally disposed at the ground contact place of the shoe sole. In this case, it is preferable that the anti-slip member be disposed at at least one of positions configured to respectively correspond to a heel, metatarsophalangeal joints, and a toe, of the wearer.

The anti-slip member for the wearable equipment or sports equipment, the wearable equipment, and the sports equipment according to the present invention are not limited to the configuration of the aforementioned embodiment. Further, the anti-slip member for the wearable equipment or sports equipment, the wearable equipment, and the sports equipment according to the present invention are not limited to those having the aforementioned operational effects. Various modifications can be made to the anti-slip member for the wearable equipment or sports equipment, the wearable equipment, and the sports equipment according to the present invention without departing from the gist of the present invention.

Although detailed description beyond the above will not be repeated here, conventionally known technical matters on an anti-slip member for wearable equipment or sports equipment, wearable equipment, and sports equipment may be optionally employed in the present invention even if the matters are not directly described in the above.

EXAMPLES

Hereinafter, the present invention will be elucidated by way of specific examples and comparative examples of the present invention. However, the present invention is not limited to the following examples.

(Preliminary Study)

First, to examine how a recess formed on the surface of the anti-slip member affects wet-grip performance, a rubber with a recess formed on its surface and a rubber with no recess formed thereon were subjected to a friction test with a flat glass plate not wet with water and a flat glass plate wet with water.

Rubber

The rubbers used for the friction test were both silicone rubbers each having a hemispherical shape with a radius of curvature of 7.6 mm. One of the rubbers was a rubber SP1 of which the peak has a smooth flat surface with no recess or the like while the other one was a rubber SP2 of which the peak, which is to be in contact with the glass plate, has a recess of about 100 μm³. These rubbers had fluorescent particles kneaded therein to facilitate observation of their contact with the plate during the friction test.

Friction Test

As shown on the left side of FIG. 8, each of the rubbers SP1 and SP2 was placed on a flat glass plate GL that was dry (under a non-lubrication condition) or that was wet with water (under a water lubrication condition), so as to bring their peaks into contact with the surface of the flat glass plate GL. Thereafter, as shown on the right side of FIG. 8, the flat glass plate GL was caused to slide by 5.0 mm in a direction parallel to its surface on the rubber SP1, SP2 with its peak subjected to a vertical load F=0.0981 N and at a sliding velocity of 0.10 mm/s.

During this step, a continuous observation was performed for a true contact part between the rubber SP1, SP2 and the flat glass plate GL under each of the non-lubrication condition and the water lubrication condition using an apparatus shown in FIG. 8, and an image of the true contact part was captured after the flat glass plate was caused to slide by 5.0 mm. This apparatus includes a light source LS for illuminating the true contact part, and a CCD device CD for capturing an image of the true contact part. The true contact part was observed and its image was captured by a combination of the total reflection method and the light interference method.

FIG. 9 and FIG. 10 show photographs of the true contact parts captured under the non-lubrication condition and the water lubrication condition, respectively. In each of FIG. 9 and FIG. 10, a region in black represents the true contact part, and a white region represents a portion of the flat glass plate GL not in contact with the rubber SP1, SP2. In FIG. 10, a gray region represents a portion of the flat glass plate GL in contact with water (i.e., wet), and a white region represents a portion of the flat glass plate GL in contact with neither the rubber SP1, SP2 nor water (i.e., in which air was present). Although not shown, the phenomenon was observed under the water lubrication condition that, in the true contact part between the rubber SP2 and the flat glass plate GL, air was present only in a portion with the recess before the flat glass plate GL was caused to slide, and bubbles spread across a wide range of the true contact part when the flat glass plate GL was caused to slide. The areas (true contact areas) of the black regions (true contact parts) derived from the photographs of FIG. 9 and FIG. 10 are obtained and shown as a graph in FIG. 11.

Further, the static friction coefficient between the rubber SP1, SP2 and the flat glass plate GL was measured after the flat glass plate GL was caused to slide by 5.0 mm. FIG. 12 shows the measured static friction coefficients.

As understood from FIGS. 9 to 12, under the non-lubrication condition, the true contact area between the rubber SP2 and the flat glass plate GL after the flat glass plate GL was caused to slide by 5.0 mm was slightly smaller than the true contact area with the rubber SP1 due to the recess formed on the surface of the rubber SP2, but the friction coefficient therebetween was substantially the same as that of the rubber SP1. Thus, it can be understood that the grip performance under the non-lubrication condition is hardly affected by the recess formed on the surface. Under the water lubrication condition, in contrast, it can be understood that the true contact area between the rubber SP2 and the flat glass plate GL after the flat glass plate GL was caused to slide by 5.0 mm was larger by about 38% than the true contact area with the rubber SP1, and the friction coefficient therebetween was also larger by about 27%. In addition, it can be understood that the rubber SP2 with the recess formed on the surface had a larger friction coefficient under the water lubrication condition than that under the non-lubrication condition. It is understood from the results that the wet-grip performance of a rubber with a recess formed on its surface increases so significantly under the water lubrication condition that it exceeds the wet-grip performance thereof under the non-lubrication condition.

(Study of Elastomer Composition)

Next, to examine the wet-grip performance, durability, or the like of various elastomer compositions forming the anti-slip member according to the present invention, various tests shown below were performed for various elastomer compositions according to examples and comparative examples below.

The following materials were prepared as materials of rubbers to be mixed into the elastomer compositions:

- IR: Isoprene rubber (high-cis type, Mooney viscosity: approx. 82)
- SiO₂: Precipitated silica
- CA: Silane coupling agent (bis(3-triethoxysilylpropyl)tetrasulfide)
- PEG: Polyethylene glycol (mass-average molecular weight: approx. 3000, melting point: approx. 60° C.)
- PO: Liquid paraffin (kinematic viscosity: approx. 40 mm²/s, molecular weight: 430)
- St: Stearic acid
- ZnO: Activated zinc oxide
- AO: 2,6-di-tert-butyl-4-methylphenol
- OZONOC: Colorless, non-contaminating ozone cracking inhibitor
- OA: Organic amine vulcanization accelerator

These materials were mixed and kneaded three separate times sequentially at the respective mixing ratios (mass ratios) shown in Table 1 below to prepare rubbers (a) to (e). Specifically, each of various IRs, which are primary kneading materials of the rubber raw material shown in Table 1 below, was kneaded under the condition of 80 to 130° C. for a minute using a kneader (apparatus name: DS3-10MWB, manufactured by Nihon Spindle Manufacturing Co., Ltd.) to obtain a primary kneaded material. The primary kneaded material thus obtained was mixed with SiO₂, PO, CA, St, and ZnO, which are secondary kneading materials, at the respective mixing ratios (mass ratios) shown in Table 1 below, and the mixture was kneaded under the condition of 80 to 130° C. for 5 minutes using a kneader (apparatus name: DS3-10MWB, manufactured by Nihon Spindle Manufacturing Co., Ltd.) to obtain a secondary kneaded material. The secondary kneaded material thus obtained was mixed with OA, PEG, and AO, which are tertiary kneading materials, at the respective mixing ratios (mass ratios) shown in Table 1 below, and the mixture was kneaded under the condition of 25 to 60° C. for 10 minutes using an open roll (apparatus name: KD-M2-8, manufactured by KNEADER MACHINERY CO., LTD.) to obtain each of the rubbers (a) to (e).

TABLE 1

Material
(a)
(b)
(c)
(d)
(e)

Primary
IR
100
100
100
100
100

Secondary
SiO₂
44
51
60
69
80

PO
20
20
20
20
20

CA
4.4
5.1
6.0
6.9
8.0

St
2
2
2
2
2

ZnO
5
5
5
5
5

Tertiary
OA
1
1
1
1
1

PEG
1
1
1
1
1

OZONOC
0.5
0.5
0.5
0.5
0.5

AO
1
1
1
1
1

Total
178.9
186.6
196.5
206.4
218.5

As the water-soluble particles to be mixed into each of the elastomer compositions, sodium chloride (NaCl) particles respectively having average particle sizes of 5 μm 10 μm 20 μm 45 μm and 300 μm were prepared.

In addition to the rubber and sodium chloride particles described above, the following materials were prepared as other materials to be mixed into each of the elastomer compositions:

- TiO2: Titanic oxide
- S: Sulfur
- DM: di-2-benzothiazolyl disulfide
- TS: Tetramethylthiuram monosulfide

Comparative Examples 1 to 5 and Examples 1 to 13

Each of the rubbers prepared as described above, the sodium chloride particles, and the above other materials were mixed together at the respective mixing ratios (mass ratios) shown in Table 2 below, and each of the mixtures was kneaded under the condition of 25 to 60° C. for 10 minutes using an open roll (apparatus name: KD-M2-8, manufactured by KNEADER MACHINERY CO., LTD.) to obtain each of the elastomer compositions.

TABLE 2

C. Ex. 1
C. Ex. 2
C. Ex. 3
C. Ex. 4
C. Ex. 5
Ex. 1

(a)
178.90

(b)

186.60

(c)

196.50

196.50

(d)

206.60

(e)

218.50

S
2.0
2.0
2.0
2.0
2.0
2.0

DM
1.0
1.0
1.0
1.0
1.0
1.0

TS
0.1
0.1
0.1
0.1
0.1
0.1

NaCl 5 μm

NaCl 10 μm

4.05

NaCl 20 μm

NaCl 45 μm

NaCl 300 μm

TiO₂
35.02
36.11
37.22
38.29
39.67
37.62

Total
182.00
189.70
199.60
209.50
221.60
203.66

Ex. 2
Ex. 3
Ex. 4
Ex. 5
Ex. 6
Ex. 7

(a)

(b)

(c)
196.50
196.50
196.50
196.50
196.50
196.50

(d)

(e)

S
2.0
2.0
2.0
2.0
2.0
2.0

DM
1.0
1.0
1.0
1.0
1.0
1.0

TS
0.1
0.1
0.1
0.1
0.1
0.1

NaCl 5 μm

12.45

NaCl 10 μm
8.21
12.45
16.79
21.22

NaCl 20 μm

12.45

NaCl 45 μm

NaCl 300 μm

TiO₂
38.02
38.43
38.86
39.29
38.43
38.43

Total
207.81
212.05
216.39
220.82
212.05
212.05

Ex. 8
Ex. 9
Ex. 10
Ex. 11
Ex. 12
Ex. 13

(a)

178.90

(b)

186.60

(c)
196.50
196.50

(d)

206.60

(e)

218.50

S
2.0
2.0
2.0
2.0
2.0
2.0

DM
1.0
1.0
1.0
1.0
1.0
1.0

TS
0.1
0.1
0.1
0.1
0.1
0.1

NaCl 5 μm

NaCl 10 μm

11.72
12.08
12.81
13.27

NaCl 20 μm

NaCl 45 μm
12.45

NaCl 300 μm

12.45

TiO₂
38.43
38.43
37.22
38.29
39.67
38.43

Total
212.05
212.05
193.72
201.78
222.31
234.87

Measurement of Hardness

The hardness of each of the elastomeric compositions of Comparative Examples 1 to 5 and Examples 1 to 13 was measured using “Asker Rubber Hardness Meter Type A” manufactured by Kobunshi Keiki Co., Ltd., as a type A durometer according to JIS K 6253-3:2012. The results are shown in Table 3 below. As can be seen from Table 3, the rubbers (a), (b), (c), (d), and (e) of Comparative Examples 1 to 5 correspond to rubbers having hardness values of 55, 60, 65, 70, and 75, respectively.

Measurement of Initial Elastic Modulus, Tensile Strength, and Elongation at Break

Each of the elastomer compositions of Comparative Examples 1 to 5 and Examples 1 to 13 was cut into a flat plate having a thickness of 4 mm, followed by cutting the flat plate using a dumbbell-shaped type-2 punching die based on JIS K 6251:2017 to obtain a dumbbell-shaped test piece for each of the resin composites. Each of the test pieces was subjected to a tensile test based on JIS K 6251:2017, using an autograph precision universal tester (product name “AG-50kNIS MS” manufactured by Shimadzu Corporation) at 23° C. and at a crosshead speed of 500 mm/min, to thereby measure the tensile strength and the elongation at break of the test piece. Further, the initial elastic modulus of each of the test pieces was measured based on the gradient of the stress/strain curve corresponding to a portion between two strain points of ε1=0% and ε2=5% in the tensile test. The results are shown in Table 3 below.

Measurement of Tear Strength

Each of the elastomer compositions of Comparative Examples 1 to 5 and Examples 1 to 13 was heated at 160° C. for 8 to 12 minutes using a flat plate mold having a thickness of 2 mm to obtain a flat plate-shaped test piece having a thickness of 2 mm. Each of the test pieces was formed into a standard shape using a punching die, and subjected to a tear test based on JIS K 6252:2007 to thereby measure the tensile strength of each of the test pieces. The results are shown in Table 3 below.

Measurement of Abrasion Resistance

A cylindrically-shaped mold having a diameter of 16.0 mm and a thickness of 12 mm was used to obtain a cylindrically-shaped test piece composed of each of the elastomer compositions of Comparative Examples 1 to 5 and Examples 1 to 13. Each of the test pieces was subjected to a DIN abrasion test based on JIS K 6264-2:2005 to thereby measure the abrasion volume of each of the test pieces. The results are shown in Table 3 below.

Friction Test

Each of the elastomer compositions of Comparative Examples 1 to 5 and Examples 1 to 13 was introduced into a molding die having a flat plate shape, and pressed at 160° C. for 8 to 12 minutes (i.e., predetermined appropriate vulcanization time+2 minutes) using a device (name: Ram diameter of 12″ 150 tons (manufactured by Nimei Koki Co., Ltd.)), thereby obtaining a test piece molded into a flat plate shape having a thickness of 2 mm. Each of the obtained test pieces was ultrasonically cleaned with ion-exchanged water three times to thereby remove sodium chloride particles exposed on the surface of each of the test pieces of Examples 1 to 13. FIG. 13 shows a photograph of a part of the surface of the test piece of Example 5 from which the sodium chloride particles exposed on the surface have been removed. It can be confirmed in FIG. 13 that the sodium chloride particles exposed on the surface of the test piece have been eluted to thereby form recesses each having a diameter of about 100 μm on the surface.

Each of the test pieces was made wet with water, and an alumina ball was caused to slide on the test piece to thereby measure the static friction coefficient and the dynamic friction coefficient under the water lubrication condition. Specifically, under the atmospheric temperature of 24° C. and the relative humidity of 75% RH, the surface of the test piece molded into a flat shape was made wet with water, and the alumina ball having a diameter of 9.5 mm was disposed on the surface of the test piece wet with water so as to be in contact with the surface of the test piece. Thereafter, the alumina ball was caused to slide on the surface of the test piece at a vertical load of 4.91 N and a sliding speed of 10.0 mm/s to measure the static friction coefficient and the dynamic friction coefficient at that time. The results are shown in Table 3 below.