Ball

Abstract

To provide a ball with excellent durability, wear resistance, grip, or control, particularly, a ball suitable for water polo.SOLUTION: A ball according to the present invention is a ball that is hot-vulcanized in one piece, having a tube, a fiber-reinforced layer covering the tube, and a surface layer covering the fiber-reinforced layer, wherein the surface layer comprises a foam rubber having a coefficient of static friction from 0.35 to 0.7 and a coefficient of dynamic friction from 0.35 to 0.7. The coefficients of static and dynamic friction herein are based on ball-on-disk friction testing using a sample silicon sphere immersed in water.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a hand-operated pneumatic ball, and in particular to a ball suitable for use in water polo. [Background technology]

[0002] Pneumatic balls that are operated by hand include volleyballs, basketballs, handballs, water polo balls, etc. These balls are required to have cushioning, controllability, grip, etc., and balls used in competitive sports are also required to have wear resistance and durability that will allow these properties to be maintained.

[0003] In response to such demands, Patent Document 1 proposes a volleyball that includes a spherical hollow rubber tube (1) that encloses compressed air, a wound reinforcing layer (2) in which filament thread is evenly wound around the surface of the rubber tube (1), a closed-cell sponge layer (3) on the wound reinforcing layer (2), and leather attached to the closed-cell sponge layer (3), in which the closed-cell sponge permeates into the wound reinforcing layer (2) when the closed-cell sponge layer (3) is formed, and the closed-cell sponge layer (3) and the wound reinforcing layer (2) are integrated together. A typical structure of a conventional volleyball is one in which the wound reinforcing layer 2 in which nylon thread or polyester thread is evenly wound is formed on the surface of the spherical hollow rubber tube 1 that encloses compressed air, an unvulcanized rubber sheet 6 made of natural rubber, polybutadiene rubber, or the like is attached on the reinforcing layer 2, and natural leather 4 or artificial leather 4 is bonded to the surface of the vulcanized rubber sheet 6. In contrast to such conventional balls, the ball of the present invention is said to have excellent ball stability and durability similar to conventional balls, while also having excellent shock absorption and resilience.

[0004] Patent Document 2 proposes a ball for sports such as handball, volleyball, beach volleyball, and basketball that allows the fingers to hook when gripping, making it easier to grip and aiding in accurate play. That is, the proposed ball has a surface formed from a plurality of panels, the surface having a plurality of panel surfaces, and at least one panel surface is divided by a through joint that separates adjacent panel surfaces. It is said that the surface of this ball is preferably made of a porous polyurethane resin to prevent the hand from slipping when gripping the ball.

[0005] Patent Document 3 proposes a sports or leisure ball made of polyurethane or polyurethane-polyurea foam, having an outer layer composed of a compact skin layer and a layer of a microporous region, the outer layer having a total thickness of 1.5 to 5 mm, and the compact skin layer having a thickness of 0.5 to 2 mm. This ball is said to have excellent grip, very little water capture, a good smooth surface, and properties such as very high abrasion resistance, excellent durability, impact resistance, and shock resistance.

[0006] Patent Document 4 discloses a method for producing a fiber substrate having a surface on which a polymer elastomer coating layer is laminated, and continuous convex portions and discontinuous concave portions are formed on the surface of the coating layer, the discontinuous concave portions being formed at an average interval of 0.5 to 3 mm, the concave portions having a depth of 50 to 500 μm, and the vertical projection area of ​​each concave portion being 1 to 5 mm. 2 A volleyball or beach volleyball ball has been proposed, which is made of a sheet-like material characterized in that the ratio of the total vertical projected area of ​​each recess to the surface area of ​​the coating layer is 3 to 30%. The fiber base material of this ball can be any of various fiber base materials such as natural leather, leather-like sheets, knitted or woven fabrics, or nonwoven fabrics, and the polymeric elastomer that forms the coating layer can be synthetic rubber, polyester elastomer, polyvinyl chloride, polyurethane resin, or the like. When the coating layer is polyurethane, it is said that the polyurethane can be solidified into a porous state by immersing the ball in a treatment bath containing a poor solvent. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2000-5345 A [Patent Document 2] JP 2018-192216 A [Patent Document 3] Patent No. 3173776 [Patent Document 4] JP 2008-49147 A Summary of the Invention [Problem to be solved by the invention]

[0008] As shown in Patent Document 1, the material for the outer skin of a pneumatic ball such as a volleyball that is operated by hand is generally natural leather or artificial leather. Meanwhile, as shown in Patent Documents 2 to 4, foamed resin or foamed rubber is used as the material for the outer skin of the ball, and foamed urethane is particularly preferred. However, there is a demand for further improvements in durability, abrasion resistance, grip, and controllability.

[0009] In addition, for water polo balls, which are always used in moist and humid environments, the ball surface is buffed to ensure grip and control. This processing is performed along the longitudinal direction of each panel surface formed by the grooves that divide the ball surface, and the buff finishing direction is vertical and horizontal when viewed from the entire surface of the ball. This allows the ball to be manipulated by gripping the parts with different buff finishing directions. However, such balls are not only labor-intensive to process, but also have the problem of generating a large amount of processing waste.

[0010] In view of the demands and problems associated with conventional pneumatic balls that are operated by hand, the present invention aims to provide a ball that is excellent in durability, wear resistance, gripping ability, and controllability, and is particularly suitable for use as a water polo ball. [Means for solving the problem]

[0011] The ball according to the present invention has a tube, a fiber-reinforced layer covering the tube, and a skin layer covering the fiber-reinforced layer, which are thermally vulcanized together, and the skin layer is made of foamed rubber having a static friction coefficient of 0.35 to 0.7 and a kinetic friction coefficient of 0.35 to 0.7, where the static and kinetic friction coefficients are based on a ball-on-disk friction test using a sample silicon ball immersed in water.

[0012] In the above invention, the foaming ratio of the foamed rubber is preferably 1.1 to 2.5 times, where the foaming ratio (times) is the specific gravity of unfoamed rubber / specific gravity of foamed rubber.

[0013] The surface roughness of the skin layer is preferably Ra=5 to 30 (μm).

[0014] The ball according to the present invention has a tube, a fiber reinforcement layer covering the tube, and a skin layer covering the fiber reinforcement layer, which are thermally vulcanized together, and the skin layer can be made of foamed rubber with an expansion ratio of 1.1 to 2.5, where the expansion ratio (times) is defined as: expansion ratio = specific gravity of unfoamed rubber / specific gravity of foamed rubber.

[0015] The ball according to the present invention may comprise a tube, a fiber reinforcement layer covering the tube, and a skin layer covering the fiber reinforcement layer, which are thermally vulcanized together, and the skin layer may be made of foamed rubber having a rubber hardness of ASKER C 55 to 65. The rubber hardness is measured using a spring-type ASKER C type (SRIS 0101). Effect of the Invention

[0016] The ball according to the present invention is an air-filled ball that is operated by hand and has excellent durability, abrasion resistance, grip and controllability. The present invention is particularly suitable for use in water polo balls. [Brief description of the drawings]

[0017] [Figure 1] 1 is a schematic diagram, partially in cross section, showing the configuration of a ball according to the present invention. [Diagram 2] 1 is a schematic diagram showing the front of a conventional water polo ball. [Diagram 3] 1 is a schematic diagram showing a partial cross section of a conventional water polo ball. [Figure 4] 2 is a graph showing the relationship between the coefficient of friction and the sensory score for a water polo ball having the surface layer of FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The ball according to the present invention is a ball having a tube, a fiber reinforcement layer covering the tube, and a skin layer covering the fiber reinforcement layer, which are thermally vulcanized together. That is, as shown in FIG. 1, the present ball 10 has a tube 15, fiber reinforcement layer 13, and skin layer 11, which have a known configuration, but are molded together by thermal vulcanization. The material of skin layer 11 is a foamed rubber having a predetermined friction coefficient in water. That is, skin layer 11 has a static friction coefficient of 0.35 to 0.7 and a dynamic friction coefficient of 0.35 to 0.7 based on a ball-on-disk friction test using a sample silicon ball immersed in water.

[0019] The material of the skin layer 11 may be natural rubber, butyl rubber, or a mixed rubber thereof, and is foamed during thermal vulcanization to have isolated fine bubbles 11b. When thermal vulcanization is performed in a mold, the surface 11a of the skin layer 11 can be made to have a predetermined surface roughness by providing irregularities on the mold surface. The surface roughness is preferably Ra=5 to 30 (μm).

[0020] Tube 15 and fiber reinforcement layer 13 of the ball according to the present invention can be made of known materials and have known structures. The thickness of each component constituting the ball according to the present invention can be, for example, as follows: tube 15: 0.7 to 1.2 (mm), fiber reinforcement layer 13: 0.7 to 1.1 (mm), and skin layer 11: 1.1 to 2.0 (mm).

[0021] On the other hand, a water polo ball is shown in Fig. 2 as a conventional ball. The surface of this ball 10 is covered with multiple panels 10a separated by grooves 10b, and each panel is buffed to have stripe-like grooves 10c running along the length of the panel. The stripe-like grooves 10c run vertically and horizontally across the ball as a whole.

[0022] The structure of this conventional water polo ball is shown in Figure 3. As shown in Figure 3, ball 10 has tube 15, fiber reinforcement layer 13, and skin layer 11. Surface 11a of skin layer 11 has significantly greater irregularities than ball 10 according to the present invention shown in Figure 1, making it difficult to measure the surface roughness (Ra).

[0023] The surface roughness measurement was carried out as follows. First, two foamed test pieces (foamed) and two foamed and uneven test pieces (foamed + uneven) were prepared from the material forming the skin layer 15. The vulcanization was carried out at 155°C for 300 seconds, and the foaming ratio was 1.1 to 2.5 times. After compounding the test pieces, they were stabilized for 24 hours or more before vulcanization, and the surface roughness was measured after 24 hours or more had passed since vulcanization.

[0024] The surface roughness was measured using a measuring instrument (SJ-500: manufactured by Mitutoyo Corporation), and the median value of measurements taken at five random locations was taken as the surface roughness Ra (JIS B 0601-2001). The surface roughness was Ra = 4.07 (μm) for foamed and Ra = 7.42 (μm) for foamed + uneven. The surface and cross section of the test piece were observed with a digital microscope (VHX-5000: manufactured by Keyence Corporation).

[0025] The above-mentioned coefficient of friction was determined by a friction test. The above-mentioned test piece (foamed) and test piece (foamed + uneven) (invention examples) and a test piece (comparative example) made of the same material as the surface layer of a water polo ball were prepared. A ball-on-disk friction test was performed on these test pieces using a friction wear tester (HEIDON Type 20, manufactured by Shinto Scientific Co., Ltd.) that was modified for this measurement. A load of 500 g was applied to the silicon ball (hardness 50), the rotation speed was 50 rpm x 5 rotations, and five measurements were performed. The maximum value between 0 and 1500 (s) was taken as the static friction coefficient, and the average value between 1500 and 3500 (s) was taken as the dynamic friction coefficient. Before the first test of each sample, a break-in run of one rotation was performed, and the three measured values ​​excluding the maximum and minimum values ​​were taken as the representative values. In the table, "wet" refers to the case where the test piece was immersed in water and the friction test was performed, and "dry" refers to the case where the friction test was performed in air (dry type). Incidentally, the conventional water polo ball is a water polo ball whose surface has been buffed.

[0026] The results of the measurement of the friction coefficient are shown in Table 1. In addition, a sensory test was conducted to evaluate the operability and grip of the actual balls using a water polo ball (invention example) having the same shape as a conventional water polo ball having a surface layer according to this invention example, and a conventional water polo ball (comparative example). In the sensory test, the hands were dipped in water before the test to familiarize the balls, and then the balls were gripped and rotated from side to side to evaluate the grip of the balls. The evaluation method was a relative evaluation in which the comparative example was given a sensory score of 3.0 and the maximum sensory score was 5.0. The results of the sensory test are shown in Table 2.

[0027] [Table 1]

[0028] [Table 2]

[0029] FIG. 4 shows the evaluation results of the operability and grip of the water polo ball having the skin layer 15 according to the present invention. The horizontal axis shows the coefficient of friction, and the vertical axis shows the value obtained by dividing the total sensory score from the sensory test results by 24 (sensory score / 24). FIG. 4 shows that the static friction coefficient curve and the kinetic friction coefficient curve have very similar shapes. In both friction coefficient curves, the friction coefficient and the sensory score are almost proportional to each other when the friction coefficient is about 0.35 to 0.4 or 0.45. However, it can be seen that the friction coefficient curve shows that the rate of increase in the sensory score relative to the friction coefficient gradually decreases when the friction coefficient exceeds 0.4 or 0.45, and becomes almost horizontal (saturated) at a friction coefficient of about 0.7. In other words, the balls of the invention (balls used in water polo and other balls in a moist or humid environment) have higher coefficients of kinetic friction and static friction (coefficient of friction) than conventional water polo balls, and the balls of the invention, which have coefficients of friction of 0.35 to 0.4 or 0.45, are understood to have improved maneuverability and grip by approximately 20%. The starting point of the friction coefficient curve is the sensory score of the conventional water polo ball / 24=1.

[0030] Furthermore, with respect to the ball of the present invention, when the coefficient of friction exceeds 0.4 or 0.45, the controllability and grip do not increase in proportion to the increase in the coefficient of friction, and when the coefficient of friction exceeds about 0.7, it is believed that a saturation state is reached where the controllability and grip do not improve even with an increase in the coefficient of friction.

[0031] Table 3 shows the results of rubber hardness tests on the skin layer 11 of the ball according to the present invention. The rubber hardness is ASKER C hardness measured using a spring-type ASKER C type (SRIS 0101). In Table 3, the average values ​​indicate the ratio (%) of the average rubber hardness of the inventive examples to the rubber hardness of the comparative example. The inventive examples are based on the above test piece (foamed + uneven), while the comparative example is based on a test piece (comparative example) made of the same material as the skin layer of the water polo ball. According to Table 3, the hardness of the inventive examples is about 80% of that of the comparative example, making them softer. The minimum rubber hardness of the inventive examples is 55, and the maximum rubber hardness is 65.

[0032] [Table 3] [Explanation of symbols]

[0033] 10 Ball 11 Tube 13 Fiber reinforcement layer 15 Epidermal layer

Claims

1. A ball having a tube, a fiber reinforcement layer covering the tube, and a skin layer covering the fiber reinforcement layer, the ball being integrally thermally vulcanized, The surface layer of the ball is made of foamed rubber having a static friction coefficient of 0.35 to 0.7 and a kinetic friction coefficient of 0.35 to 0.

7. Here, the static and kinetic friction coefficients are based on a ball-on-disk friction test using a silicon ball of the sample immersed in water.

2. 2. The ball according to claim 1, wherein the foamed rubber has a foaming ratio of 1.1 to 2.

5. Here, the foaming ratio (times) is expressed as follows: Foaming ratio = specific gravity of unfoamed rubber / specific gravity of foamed rubber.

3. 3. The ball according to claim 1, wherein the surface roughness of the skin layer is Ra = 5 to 30 (μm).

4. A ball having a tube, a fiber reinforcement layer covering the tube, and a skin layer covering the fiber reinforcement layer, the ball being integrally thermally vulcanized, The surface layer of the ball is made of foamed rubber having a foaming ratio of 1.1 to 2.

5. Here, the foaming ratio (times) is expressed as follows: Foaming ratio = specific gravity of unfoamed rubber / specific gravity of foamed rubber.

5. A ball having a tube, a fiber reinforcement layer covering the tube, and a skin layer covering the fiber reinforcement layer, the ball being integrally thermally vulcanized, The surface layer of the ball is made of foamed rubber having a rubber hardness of ASKER C 55 to 65. Here, the rubber hardness is measured by a spring type Asker C type (SRIS 0101).

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