golf ball

Abstract

To provide a golf ball that does not require the installation of an inspection device such as an X-ray image instrument and allows a worker to easily confirm eccentricity of a core with the visual recognition during the production process of the golf ball.SOLUTION: There is provided a golf ball in which at least one intermediate layer is formed between a core and a cover, the L value (brightness) in Lab display based on JIS Z 8722 of the core is equal to or less than 85, the L value (brightness) in Lab display based on JIS Z 8722 of the sphere (intermediate layer covering sphere) in which the core is covered by the intermediate layer is equal to or greater than 75, the total light transmittance at the thickness of 1.0 mm of the intermediate layer is between 1 and 50%, and a color difference ΔE of the core and the intermediate layer covering sphere is equal to or greater than 10.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a golf ball having at least one intermediate layer formed between a core and a cover, and more specifically, to a golf ball that allows easy identification of core eccentricity by comprising a low-brightness core and an intermediate layer having constant transparency.

Background Art

[0002] In recent golf balls, the cover (outermost layer) covering the core and the intermediate coating layer have been increasingly multi-layered and thinned by injection molding or compression molding from the perspectives of ball feel and low spin. As the technology for forming multi-layered coating layers and manufacturing thin gauges advances, non-uniformity in the gauge of the coating layer, that is, occurrence of eccentricity, has become an issue. Non-uniform golf balls have altered center of gravity positions, which greatly affects the straight traveling performance of the ball.

[0003] As methods for inspecting eccentricity without destroying the ball, generally, methods of measuring thickness with ultrasonic waves and inspections of visualizing the inside of the ball with X-rays are performed. For example, Patent Document 1 proposes a technique of using a polymer material doped with barium or bismuth, and confirming the eccentricity of the ball by irradiating X-rays with an X-ray imaging device. Similarly, Patent Document 2 and Patent Document 3 describe methods for performing eccentricity inspection of golf balls using X-rays. Further, Patent Documents 4 to 6 propose a method of irradiating a two-piece golf ball with terahertz waves instead of X-rays to calculate the eccentricity of the core in the golf ball.

[0004] However, the eccentricity inspections described in these patent documents require large capital investment costs for equipment such as X-ray imaging devices, and providing such an inspection process reduces productivity in the golf ball manufacturing process. Therefore, it is desired to improve the internal structure of the golf ball so that workers manufacturing golf balls can easily check eccentricity just by visually inspecting the ball or intermediate products such as intermediate-layer-coated spheres.

Prior Art Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2001-259083 [Patent Document 2] U.S. Patent Application Publication No. 2004 / 0042586 [Patent Document 3] U.S. Patent Application Publication No. 2004 / 0196956 [Patent Document 4] Japanese Patent Publication No. 2016-65749 [Patent Document 5] Japanese Patent Publication No. 2019-132863 [Patent Document 6] Japanese Patent Publication No. 2021-63821 [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention has been made in view of the above circumstances, and aims to provide a golf ball in which the eccentricity of the core can be easily confirmed by visual inspection by workers during the golf ball production process, without the need to install inspection equipment such as X-ray imaging equipment. [Means for solving the problem]

[0007] The inventors of the present invention have conducted diligent studies to achieve the above objectives and have found that by adjusting the relationship between the material and color tone of both the core and the adjacent intermediate layer in a golf ball in which an intermediate layer is formed between the core and the cover, specifically by setting the surface color of the core to a low L value (brightness) of 85 or less in Lab notation, finishing the intermediate layer to be semi-transparent with a total light transmittance of 1-50%, and setting the surface color of the sphere (intermediate layer-coated sphere) covering the core to a high L value (brightness) of 75 or more in Lab notation, and making the color difference ΔE between the core and the intermediate layer-coated sphere larger than a certain amount, the eccentricity of the core can be easily determined by a worker's visual inspection alone, and as a result, golf balls without eccentricity can be reliably manufactured without the use of expensive inspection equipment such as X-ray imaging devices, leading to the present invention.

[0008] Therefore, the present invention provides the following golf ball. 1. A golf ball in which at least one intermediate layer is formed between the core and the cover, wherein the core has a Lab value (brightness) of 85 or less according to JIS Z 8722, the sphere (intermediate layer-covered sphere) covered with the intermediate layer has a Lab value (brightness) of 75 or more according to JIS Z 8722, the total light transmittance at an intermediate layer thickness of 1.0 mm is 1 to 50%, and the color difference ΔE between the core and the intermediate layer-covered sphere is 10 or more. 2. The golf ball described in item 1 above, wherein the thickness of the intermediate layer is 0.8 to 1.5 mm. 3. A golf ball as described in 1 or 2 above, wherein the L value (brightness) of the core is 80 or less. 4. The golf ball according to claim 1 or 2 above, wherein the color difference ΔE between the core and the intermediate layer covering sphere is 20 or more. 5. A golf ball according to item 1 or 2 above, wherein the total light transmittance at a thickness of 1.0 mm of the intermediate layer is 25% or more. 6. The golf ball according to claim 1 or 2 above, wherein the intermediate layer contains barium sulfate. 7. The golf ball according to item 6 above, wherein the barium sulfate content is 8 to 20% by mass of the total amount of the intermediate layer material. [Effects of the Invention]

[0009] According to the golf ball of the present invention, during the manufacturing process of the golf ball, the eccentricity of the core can be easily determined by visual inspection by a worker, and golf balls without eccentricity can be reliably obtained with good workability without the need for inspection equipment. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram illustrating the eccentricity of the core in an intermediate layer-coated sphere.

[0011] The present invention will be described in more detail below. The golf ball of the present invention comprises a core, a cover, and an intermediate layer formed between them. Each of these layers will be described in detail below.

[0012] The core can be formed as a single layer or in multiple layers. As the core material, known rubber materials and various resin materials can be used as the base material. When the core is formed from rubber, known base rubbers such as natural rubber or synthetic rubber can be used as the base rubber. More specifically, it is recommended to mainly use polybutadiene, particularly cis-1,4-polybutadiene having at least 40% cis structure. Furthermore, in the base rubber, natural rubber, polyisoprene rubber, styrene-butadiene rubber, etc., can be used in combination with the aforementioned polybutadiene, if desired. Polybutadiene can also be synthesized using Ziegler catalysts such as titanium-based, cobalt-based, nickel-based, and neodymium-based catalysts, as well as metal catalysts such as cobalt and nickel.

[0013] The above-mentioned base rubber can be compounded with co-crosslinking agents such as unsaturated carboxylic acids and their metal salts, inorganic fillers such as zinc oxide, barium sulfate, and calcium carbonate, and organic peroxides such as dicumyl peroxide and 1,1-bis(t-butylperoxy)cyclohexane. Furthermore, commercially available antioxidants may be added as needed.

[0014] Further, as will be described later, various pigments can be blended into the above base rubber so that the surface color of the core has a constant low lightness. As the pigment, inorganic pigments such as graphite and titanium oxide, and organic pigments such as quinacrine red, phthalocyanine blue and isoindoline yellow can be used.

[0015] The blending amount of the above pigment is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, still more preferably 0.2 parts by mass or more, relative to 100 parts by mass of the base rubber. Further, even if the blending amount of the pigment is more than 1.0 part by mass, the effect of bringing the surface color of the core to a constant low lightness is hardly obtained.

[0016] The above core can be produced by heat-curing a rubber composition containing each of the above components. For example, the core can be produced by kneading the components using a kneader such as a Banbury mixer or a roll, performing compression molding or injection molding using a core mold, and appropriately heating the molded product under the conditions of a temperature sufficient for an organic peroxide or a co-crosslinking agent to act, specifically 100 to 200°C, preferably 140 to 180°C, for 10 to 40 minutes, thereby curing the molded product.

[0017] Further, when no pigment is blended into the rubber composition, after the rubber composition is heat-cured to obtain a core, a pigment may be coated on the surface of the core.

[0018] The L value (lightness) of the core is 85 or less, preferably 80 or less, more preferably 70 or less. If this value is too small, the core appears dark, making it difficult to identify whether the core is eccentric. When the core is formed into a plurality of layers, the L value of the core is the L value of the outer core.

[0019] The L values ​​mentioned above refer to the Lab values ​​based on the JIS Z8722 standard. The L value (lightness) indicates the degree of brightness of a color and does not contain any information about hue. A high L value (lightness) indicates a bright color, while a low L value indicates a dark or dull color. These values ​​can be measured using a known colorimeter, such as the MSC-IS-2DH (manufactured by Suga Test Instruments Co., Ltd.). In this specification, all L values ​​have the meaning described above.

[0020] Around the core described above, at least one intermediate layer and a cover can be formed as a covering material for the core. If the intermediate layer consists of two layers, they may be referred to as the surrounding layer, the intermediate layer, and the outermost layer, in order from the inside out. Furthermore, the intermediate layer may consist of three or more layers, in which case they may be referred to as the inner surrounding layer, the outer surrounding layer, the intermediate layer, and the outermost layer, in order from the inside out.

[0021] The intermediate layer is formed from a resin composition. Examples of this resin composition include resins that have been conventionally used as materials for golf balls. Examples of resins include ionomer resins, polyester resins, polyurethane resins, polyamide resins, polyolefin resins, olefin-based thermoplastic elastomers, and styrene-based thermoplastic elastomers. In particular, ionomer resins are preferred in terms of resilience and moldability.

[0022] The above resin composition may preferably contain substances such as titanium dioxide, various pigments, barium sulfate, and calcium carbonate. By incorporating these substances into the resin composition, the intermediate layer can be made semi-transparent. Of these substances, barium sulfate is preferred in terms of durability and transparency of the intermediate layer-coated sphere.

[0023] When using barium sulfate, the amount of barium sulfate added is preferably in the range of 8 to 20% by mass relative to 100% by mass of the total amount of the resin composition. If the amount is greater than this range, the color of the intermediate layer may become cloudy, making it difficult to maintain translucency. On the other hand, if the amount is less than this range, the transparency of the intermediate layer will increase, making it difficult to detect eccentricity by color difference. In general, when the core is eccentric, the durability of the thin portion of the intermediate layer covering the core deteriorates. Therefore, in addition to adding barium sulfate to adjust the transmittance of the intermediate layer material, the reduction in durability can be prevented by incorporating barium sulfate into the intermediate layer even if the above-mentioned eccentricity occurs. Furthermore, for the purpose of coloring the resin, inorganic pigments such as graphite and titanium dioxide, or organic pigments such as quinacrine red, phthalocyanine blue, and isoindoline yellow can be used as pigments.

[0024] The thickness of the intermediate layer is preferably 0.8 mm or more, more preferably 1.0 mm or more, and even more preferably 1.2 mm or more, with an upper limit of preferably 2.0 mm or less, more preferably 1.5 mm or less, and even more preferably 1.3 mm or less. If the intermediate layer is too thick, the transmittance of the intermediate layer will be low, and the color of the core itself inside the intermediate layer-coated sphere may become difficult to see. On the other hand, if the intermediate layer is too thin, the transparency will be high, and in either case, it will be difficult to detect eccentricity due to color difference.

[0025] The L value (brightness) of a sphere with an intermediate layer covering a core (intermediate-layer-covered sphere) is 75 or higher, preferably 80 or higher, and more preferably 85 or higher. If this value is smaller than the above range, it becomes difficult to clearly distinguish the boundary between the intermediate layer and the core, which may reduce the accuracy of the eccentricity inspection.

[0026] Furthermore, in order to make the intermediate layer semi-transparent, the total light transmittance of the intermediate layer at a thickness of 1.0 mm must be between 1% and 50%. If this value exceeds 50%, the transparency of the intermediate layer itself increases, causing the entire surface to appear the same color, making it difficult to detect eccentricity. This total light transmittance is the value measured according to JIS K-7361. For example, the total light transmittance can be measured using the product name "NDH5000" manufactured by Nippon Denshoku Industries Co., Ltd. The preferred lower limit for the total light transmittance of the intermediate layer is 25% or higher, and more preferably 30% or higher.

[0027] Furthermore, the color difference ΔE between the core and the sphere coated with an intermediate layer (intermediate layer coated sphere) must be 10 or more, preferably 15 or more, and more preferably 20 or more. The larger this value, the easier it is to detect eccentricity. The above color difference is calculated based on the JIS Z8722 standard, where ΔE = [(ΔL)] 2 +(Δa) 2 +(Δb) 2 ] 1 / 2 It can be calculated by [method]. As mentioned above, L represents brightness. Also, a and b above represent color, with a representing the red-green direction and b representing the yellow-blue direction. Therefore, a larger a value tends to result in a stronger reddish tint, a smaller a value intensifies the greenish tint, a larger b value intensifies the yellowish tint, and a smaller b value intensifies the blueish tint.

[0028] The cover is formed from a resin composition. While the resin composition is not particularly limited, it can be formed using ionomer resins, polyurethane-based thermoplastic elastomers, thermosetting polyurethanes, or mixtures thereof as the main components. In addition to the main components, other thermoplastic elastomers, polyisocyanate compounds, fatty acids or their derivatives, basic inorganic metal compounds, fillers, etc., may be added to the cover.

[0029] The above resin composition can be obtained, for example, by mixing the above-mentioned components using various kneaders such as a kneading-type (single-screw or) twin-screw extruder, a Banbury, or a kneader.

[0030] The surface of the cover can typically have one or more types of dimples formed on it, and the shape, diameter, depth, number, and occupied surface area of ​​these dimples are selected as appropriate.

[0031] The method for manufacturing a golf ball is not particularly limited, and it can be obtained by molding using known molding methods such as injection molding and compression molding. For example, a core can be set in the mold of an injection molding machine, and the above-mentioned intermediate layer resin composition can be supplied to produce a coated sphere (intermediate layer coated sphere) with the intermediate layer covering the core. Then, the intermediate layer coated sphere can be set in the mold of another injection molding machine, and a cover resin composition can be injected to produce a golf ball with a cover.

[0032] Furthermore, a paint layer can be formed on the surface of the cover. In this case, the paint layer is formed using a paint composition. There are no particular restrictions on the base resin of this paint composition, but examples include polyurethane resin, epoxy resin, polyester resin, acrylic resin, and cellulose resin. From the viewpoint of durability of the paint layer, it is preferable to use a two-component curable polyurethane resin. In addition, various additives such as antioxidants, ultraviolet absorbers, light stabilizers, fluorescent agents, and fluorescent whitening agents can be added to the paint composition in appropriate amounts as needed.

[0033] There are no particular restrictions on the method of applying the above-mentioned paint to the surface of the cover; known methods can be used, such as electrostatic painting, spray gun painting, or brush painting.

[0034] The specifications of the golf ball of this invention, such as its mass and diameter, can be set appropriately in accordance with the rules of golf. [Examples]

[0035] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0036] [Examples 1-3, Comparative Examples 1-6] As a core common to each of the examples and comparative examples, a core composition was prepared using the rubber compound shown in Table 1 below, and then vulcanized at 153°C for 19 minutes to produce nine types of cores with a diameter of 38.7 mm.

[0037] [Table 1]

[0038] Details regarding the above formulation are as follows: • Polybutadiene: Product name "BR01" (manufactured by JSR Corporation) • Organic peroxide: Dicumyl peroxide, trade name "Perkmyl D" (manufactured by NOF Corporation) • Zinc oxide: Product name "Triple Zinc Oxide" (manufactured by Sakai Chemical Industry Co., Ltd.) • Zinc acrylate: Product name "ZN-DA85S" (manufactured by Nippon Shokubai Co., Ltd.) • Water: Pure water (manufactured by Masaki Pharmaceutical Co., Ltd.) • Pentachlorothiophenol zinc salt: Manufactured by Wako Pure Chemical Industries, Ltd. • Product name: "Resino Yellow GL-6-B" (yellow), manufactured by Resino Color Industries Co., Ltd. (Pigment used: disazo yellow) • Product name: "Regino Red K" (red), manufactured by Regino Color Industries Co., Ltd. (Pigment used: Lake Red) • Product name: "Regino Blue KP-25" (blue), manufactured by Regino Color Industries Co., Ltd. (Pigment used: phthalocyanine blue)

[0039] Formation of an intermediate layer covering sphere Next, using an injection molding die for forming the intermediate layer, the resin materials A to F for the intermediate layer shown in Table 2 are injection molded around the core surface. This injection molding die has a cavity diameter of 41.1 mm such that when a core with a diameter of 38.7 mm is placed in the center of the cavity, an intermediate layer with a thickness of 1.2 mm is formed. However, in this embodiment, the core is offset from the center of the cavity, and as shown in Figure 1, the core C is positioned such that the cavity forming the intermediate layer has a thickness of 1.7 mm on one side T1 and 0.7 mm on the other side T2, thereby creating an eccentric intermediate layer-covered sphere M.

[0040] [Table 2]

[0041] The details of the materials in Table 2 are as follows: "AM7318" Ionomer resin manufactured by Mitsui Dow Polychemicals. "Hymilan 1706" is an ionomer resin manufactured by Mitsui Dow Polychemicals.

[0042] Total light transmittance of the intermediate layer material The intermediate layer material was molded to create resin sheets with the thicknesses listed in Table 2 above, and the total light transmittance was measured using a haze meter with the product name "NDH5000" manufactured by Nippon Denshoku Industries Co., Ltd.

[0043] For each example obtained, the core and the sphere coated with an intermediate layer (intermediate-layer coated sphere) were measured for color tone, color difference, and color difference during eccentricity using the method described below.

[0044] tone The color tone of each sphere (core and intermediate layer coated sphere) was measured using a colorimeter (model MSC-IS, manufactured by Suga Test Instruments Co., Ltd.), and the lightness (L value) and saturation (C value) were determined based on the Lab color chart of JIS Z8722. The color difference is calculated as follows, based on the JIS Z8722 standard. ΔE = [(ΔL)] 2 +(Δa)2 +(Δb) 2 ] 1 / 2

[0045] Color difference during eccentricity As shown in Figure 1, the color difference of the intermediate layer-coated sphere M in the eccentric state of core C is determined. This measurement method involves measuring the color tone of the intermediate layer-coated sphere in the direction of arrow P1 in Figure 1 (the side where the thick intermediate layer T1 is located) and the color tone of the intermediate layer-coated sphere in the direction of arrow P2 in Figure 1 (the side where the thin intermediate layer T2 is located). The difference in brightness ΔL and the color difference ΔE between these two locations are recorded as the "color difference during eccentricity" in Tables 3 to 8.

[0046] Eccentricity testing was performed on each of the obtained intermediate layer-coated spheres using the method described below. The composition of each layer (combination of core and intermediate layer) and its eccentricity evaluation are shown in Tables 3 to 8.

[0047] Eccentricity test The evaluation was performed with the core covered by an intermediate layer. As described above, for the eccentricity evaluation, as shown in Figure 1, the intermediate layer material was injection molded with an intentional eccentricity from thickness T(1.2mm) / T(1.2mm) to T1(1.7mm) / T2(0.7mm) when coating the core with a 1.2mm thick intermediate layer. Eccentricity was determined by visual inspection by a worker according to the following criteria. [Judgment criteria] ◎ The eccentricity is clearly visible. ○ The eccentric state can be identified. △ The eccentricity is difficult to discern. × The eccentricity is completely unclear.

[0048] [Table 3]

[0049] [Table 4]

[0050] [Table 5]

[0051] Table 6

[0052] Table 7

[0053] Table 8

Claims

1. A golf ball having at least one intermediate layer formed between the core and the cover, characterized in that the core has an L value (brightness) of 85 or less according to the Lab display based on JIS Z 8722, the sphere (intermediate layer-covered sphere) covered with the intermediate layer has an L value (brightness) of 75 or more according to the Lab display based on JIS Z 8722, the total light transmittance at an intermediate layer thickness of 1.0 mm is 1 to 50%, and the color difference ΔE between the core and the intermediate layer-covered sphere is 10 or more.

2. The golf ball according to claim 1, wherein the thickness of the intermediate layer is 0.8 to 1.5 mm.

3. The golf ball according to claim 1 or 2, wherein the L value (brightness) of the core is 80 or less.

4. The golf ball according to claim 1 or 2, wherein the color difference ΔE between the core and the intermediate layer covering sphere is 20 or more.

5. The golf ball according to claim 1 or 2, wherein the total light transmittance at a thickness of 1.0 mm of the above-mentioned intermediate layer is 25% or more.

6. The golf ball according to claim 1 or 2, wherein the intermediate layer contains barium sulfate.

7. The golf ball according to claim 6, wherein the barium sulfate content is 8 to 20% by mass of the total amount of the intermediate layer material.

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