golf ball

Abstract

The objective is to provide a golf ball that excels in initial ball speed and low spin, and has a good appearance with minimal visible surface damage. [Solution] A golf ball comprising a core, an intermediate layer, and a cover, wherein the cover surface has a plurality of dimples and land areas surrounded by the plurality of dimples, wherein the core is formed from a heat-molded product of a rubber composition containing a base rubber and an organic peroxide with a half-life temperature of 165°C or higher for one minute, and the land areas are composed of a plurality of land area pieces, each land area piece having a shape with at least three vertices, and including a land area piece of a specific shape in which the land area piece is substantially connected to an adjacent land area piece by a point at the vertices, the outer edge of the land area piece of the specific shape is composed of a plurality of edge elements, and the proportion of the number of land area pieces of a unique shape in which all of the edge elements are formed by a predetermined curve is adjusted to a predetermined range.

Description

[Technical Field]

[0001] The present invention relates to a multi-piece solid golf ball with a three-layer structure or more, comprising a core, a cover, and at least one intermediate layer sandwiched between them. [Background technology]

[0002] Recently, two-piece and three-piece solid golf balls have become the mainstream. These golf balls typically have a rubber core covered with a single or multiple layers of various resin materials. The core occupies the majority of the golf ball's volume and greatly influences various physical properties such as rebound, feel, and durability. Recently, various technologies have been proposed to achieve unique core hardness gradients by appropriately adjusting the cross-sectional hardness of the core, thereby optimizing spin characteristics during full shots with drivers and irons and improving distance.

[0003] In core compounding, the type and amount of organic peroxide selected as a crosslinking initiator for the base rubber, such as polybutadiene, may be appropriately selected based on the temperature of its 1-minute half-life, taking into consideration the types and amounts of other core components, desired core characteristics, and molding conditions. The core obtained by heat-molding a rubber composition using the above organic peroxide will have a unique hardness gradient shape from the center to the outer surface, and this shape will affect the ball characteristics.

[0004] Examples of technologies focusing on the organic peroxides contained in the core include the following Patent Documents 1 to 3. Patent Document 1 proposes that the core be given a certain level of resilience by including two or more types of organic peroxides in the rubber composition that forms the core and specifying the ratio of their half-lives. Patent Document 2 proposes a technology that improves the resilience and productivity of the core by including two or more types of organic peroxides in the rubber composition, with half-life temperatures of 145 to 185°C and 110 to 135°C. Patent Document 3 proposes a technology that reduces the spin of a ball equipped with a core by including two types of organic peroxides with different half-life temperatures, namely (i) diacyl peroxides, (ii) dialkyl peroxides and / or peroxyketals, in the rubber composition.

[0005] However, by designing the hardness so that the hardness gradient from the center to the surface of the core has a unique shape unlike anything before, it is expected that the core's resilience and durability can be further improved.

[0006] On the other hand, in golf balls, it is well known that for a ball to travel a long distance after being launched, the high rebound properties inherent in the ball itself and the reduction of air resistance during flight due to dimples placed on the ball's surface are important. Various methods have been proposed to arrange the dimples on the ball's surface as densely and evenly as possible in order to reduce air resistance.

[0007] Typically, golf ball dimples are designed by placing one or more dimples of a predetermined shape on the ball's surface. However, with this method of placing dimples of a predetermined shape, if the surface coverage of the dimples becomes very high, it becomes difficult to evenly distribute the dimples because the surface of the golf ball is spherical. This often results in uneven spacing between dimples, where some areas are wider and others narrower. Uneven spacing between dimples can lead to extremely poor aerodynamic performance of the golf ball, even if the surface coverage of the dimples is high.

[0008] For example, Patent Document 4 describes a method of forming ridge-like protrusions on the surface of a golf ball, which is completely different from the conventional concept of forming numerous dimples on the surface of a golf ball. It is described that by forming these ridge-like protrusions, the area occupied by the parts without protrusions, which corresponds to the surface area occupied by conventional dimples, can be easily increased, thereby improving aerodynamic performance.

[0009] Furthermore, Patent Document 5 proposes a golf ball comprising a plurality of dimples and a land area surrounded by the plurality of dimples, wherein the land area has a shape having at least one vertex, the land area substantially touches at a point with at least two or more adjacent land areas, and the area of ​​the land area is within a predetermined range. In other words, by making the shape of the land area a specific shape, the above golf ball can maintain a uniform gap between dimples even if the surface coverage of the dimples is high, thereby improving aerodynamic performance and increasing flight distance.

[0010] However, there is a need for a golf ball with a novel surface shape combining land area and dimples that can further improve aerodynamic performance through dimples compared to the golf ball proposed above, and potentially increase flight distance.

[0011] Furthermore, most conventional dimple shapes are circular, elliptical, teardrop-shaped, polygonal, or other indentations created by carving into a sphere, and they do not offer much novelty in terms of appearance. Moreover, ball surfaces with such indentations tend to show scratches from club grooves during golf play, which is not good for the ball's appearance. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Japanese Patent Publication No. 2004-024851 [Patent Document 2] Japanese Patent Publication No. 2012-132004 [Patent Document 3] Japanese Patent Publication No. 2023-105273 [Patent Document 4] Japanese Patent Publication No. 2004-105200 [Patent Document 5] Japanese Patent Publication No. 2011-031043 [Overview of the Initiative] [Problems that the invention aims to solve]

[0013] This invention has been made in view of the above circumstances, and aims to provide a golf ball in which the hardness gradient from the center of the core to the surface is unique, the dimples and land area formed on the ball surface are novel, the ball is excellent in initial velocity and low spin, and the ball has a good appearance with scratches on the ball surface not being noticeable. [Means for solving the problem]

[0014] As a result of intensive studies to achieve the above object, the inventors of the present invention focused on the shape of the land portions on the outer surface of the golf ball rather than the dimples, and optimized the shape, resulting in the completion of the present invention. That is, in addition to the configuration of the core formed of the rubber composition containing the above (a) to (d) as essential components, in the shape of the land portion piece which is the minimum unit of the land portion on the outer surface of the ball, it has a shape having at least three vertices, and at these vertices, the land portion piece is substantially in point contact with and connected to other adjacent land portion pieces. The land portion piece having a specific shape includes a plurality of edge elements on its outer peripheral edge, and all of the edge elements are formed by curves with a curvature of 0.40 or less. By configuring the land portion pieces such that the ratio of the number of the specific-shaped land portion pieces is 25% or more of the total number of all the land portion pieces constituting the land portion, it has been found that the combination of the core formulation and the ball surface shape can solve the above problems of the present invention, and thus the present invention has been accomplished.

[0015] Therefore, the present invention provides the following golf balls. 1. A golf ball having at least one intermediate layer interposed between a core and a cover, and a plurality of dimples and lands surrounded by the plurality of dimples formed on the surface of the cover, wherein the core comprises the following components (a) to (d): (a) A base rubber (b) As a co-crosslinking agent, an α,β-unsaturated carboxylic acid and / or its metal salt (c) An organic peroxide (d) As an antioxidant, a benzimidazole represented by the following general formula and / or its metal salt [Chemical formula] (However, in the formula, R is a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, m is an integer of 1 to 4, and when m is 2 or more, these may be the same or different from each other.) It contains , and the component (c) is formed by a heat-molded product of a rubber composition consisting only of an organic peroxide having a half-life temperature of 165°C or higher for 1 minute. The land portion is composed of a number of land pieces. One land piece has a shape having at least three vertices, and at these vertices, the land piece is connected in substantial point contact with other adjacent land pieces to form a land piece of a specific shape. The outer peripheral edge of the land piece of the specific shape is composed of a plurality of edge elements, and the ratio of the number of land pieces of the specific shape formed by curves with a curvature of 0.40 or less for all of the edge elements is 25% or more of the total number of land pieces constituting the land portion. A golf ball characterized by this. 2. The golf ball according to item 1 above, wherein the component (d) is 2-mercaptobenzimidazole. 3. The golf ball according to item 1 or 2 above, wherein the blending amount of the component (d) is 0.1 part by mass or more with respect to 100 parts by mass of the component (a). 4. In the core hardness distribution, when the JIS-C hardness at the core center is O, the JIS-C hardness at a position 10 mm from the core center is A, and the JIS-C hardness at the core surface is S, the following three formulas 0≦A - O≦10 10≦S - A≦20 15≦S - O≦25 The golf ball according to item 1 or 2 above that satisfies. 5. The intermediate layer is the following (A) to (C), (A) An ionic or non-ionic olefin-unsaturated carboxylic acid copolymer and / or an ionic or non-ionic olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester copolymer, (B) An organic acid or its metal salt, (C) A basic inorganic metal compound for neutralizing 80 mol% or more of the acid groups in the components (A) and (B) The golf ball according to item 1 or 2 above formed by a resin composition containing. 6. The golf ball according to claim 1 or 2 above, wherein the cover is formed from a resin composition containing at least one copolymer from the group consisting of an ionic or nonionic olefin-unsaturated carboxylic acid copolymer and an ionic or nonionic olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester copolymer. 7. The golf ball according to item 5, wherein in the copolymer of the intermediate layer, the unsaturated carboxylic acid is acrylic acid or methacrylic acid. 8. The golf ball according to 6 above, wherein in the copolymer of the cover, the unsaturated carboxylic acid is acrylic acid or methacrylic acid. 9. The golf ball according to item 1 or 2 above, wherein the material hardness of the intermediate layer is 45 to 60 on the Shore D scale, and the material hardness of the cover is 55 to 65 on the Shore D scale. 10. The golf ball according to claim 1 or 2 above, wherein the land portion is formed by connecting 4,000 or more curved edge elements. 11. The golf ball according to item 1 or 2 above, wherein the proportion of edge elements with a curvature of 0.40 or less among the curved edge elements forming the above land portion is 70% or more. 12. A golf ball as described in 1 or 2 above, wherein the area coverage ratio of the dimples is 80-95%. [Effects of the Invention]

[0016] According to the golf ball of the present invention, the hardness gradient from the center of the core to the surface is unique, and the shape of the dimples and land area formed on the ball surface is novel. The combination of these configurations results in excellent initial ball speed and low spin, less noticeable surface scratches, and a good ball appearance. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic cross-sectional view showing the internal structure of a golf ball, which is an example of the present invention. [Figure 2] This graph shows the core hardness distribution for Examples 1 and 3 and Comparative Example 1. [Figure 3]This is a schematic diagram showing the ball surface of Examples 1 to 4, which are embodiments of the present invention. [Figure 4] (A) is a magnified view of the ball surface shown in Figure 3, and (B) is a schematic diagram showing only the land portion of (A). [Figure 5] This is a schematic diagram showing a golf ball in Comparative Example 2. [Figure 6] (A) is a magnified view of the ball surface shown in Figure 5, and (B) is a schematic diagram showing only the land portion of (A). [Modes for carrying out the invention]

[0018] The present invention will be described in more detail below. The golf ball of the present invention is a multi-piece solid golf ball with a three-layer structure or more, having a core, an intermediate layer, and a cover from the inside out. For example, an example is shown in Figure 1. The golf ball G shown in Figure 1 has a single-layer core 1 and a single-layer cover 3, and further has a single-layer intermediate layer 2 between them. The cover 3, excluding the paint layer, is located in the outermost layer of the golf ball's layer structure. The core is formed as a single layer as shown in Figure 1, and the cover is also formed as a single layer as shown in Figure 1. Furthermore, a surrounding layer made of a single or multiple layers of resin may be included between the intermediate layer and the core. The surface of the cover (outermost layer) 3 usually has many dimples D formed on it to improve aerodynamic properties. In addition, although not specifically shown, a paint layer is usually formed on the surface of the cover 3. The above layers will be described in detail below.

[0019] The above core is characterized by being formed from a heat-molded product of a rubber composition containing the following components (a) to (d). (a) Base rubber, (b) As a cocrosslinking agent, α,β-unsaturated carboxylic acids and / or metal salts thereof (c) organic peroxide; (d) Benzimidazole and / or its metal salts, represented by a specific formula, as an antioxidant.

[0020] The base rubber of component (a) above is not particularly limited, but polybutadiene is particularly preferred.

[0021] The polybutadiene described above preferably has 60% or more, preferably 80% or more, more preferably 90% or more, and most preferably 95% or more, cis-1,4-bonds in its polymer chain. If the proportion of cis-1,4-bonds in the polybutadiene molecule is too low, the repulsive properties may decrease.

[0022] Furthermore, the 1,2-vinyl bond content in the polybutadiene is typically 2% or less, preferably 1.7% or less, and more preferably 1.5% or less in the polymer chain. If the 1,2-vinyl bond content is too high, the resilience may decrease.

[0023] The above polybutadiene is (ML 1+4 The temperature (at 100°C) is preferably 20 or higher, more preferably 30 or higher, and the upper limit is preferably 120 or lower, more preferably 100 or lower, and even more preferably 80 or lower.

[0024] In this invention, Mooney viscosity refers to an industrial viscosity index (JIS K 6300) measured by a Mooney viscometer, a type of rotational plasticity meter, and is expressed in units of ML. 1+4 (100°C) is used. Also, M is Mooney viscosity, L is large rotor (L type), 1+4 indicates a preheating time of 1 minute and a rotor rotation time of 4 minutes, and indicates that the measurement was taken under conditions of 100°C.

[0025] The polybutadiene described above can be synthesized using rare earth element catalysts or group VIII metal compound catalysts.

[0026] Furthermore, the base rubber may contain polybutadiene rubber synthesized with a catalyst different from the lanthanum series rare earth element compounds mentioned above. In addition, styrene-butadiene rubber (SBR), natural rubber, polyisoprene rubber, ethylene propylene diene rubber (EPDM), etc., may be blended, either individually or in combination of two or more.

[0027] The proportion of the above-mentioned polybutadiene in the total rubber is preferably 60% by mass or more, more preferably 70% by mass or more, and most preferably 90% by mass or more. Alternatively, 100% by mass of the base rubber, i.e., the entire base rubber, may be the above-mentioned polybutadiene.

[0028] Next, component (b) is a co-crosslinking agent, which is an α,β-unsaturated carboxylic acid and / or its metal salt. The number of carbon atoms in this unsaturated carboxylic acid is preferably 3 to 8, and specific examples include acrylic acid, methacrylic acid, maleic acid, and fumaric acid. Specific examples of the metal in the above unsaturated carboxylic acid include zinc, sodium, magnesium, calcium, and aluminum, with zinc being particularly preferred. Therefore, zinc acrylate is the most preferred co-crosslinking agent.

[0029] (b) The amount of component (b) blended is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 20 parts by mass or more, per 100 parts by mass of the base rubber of component (a), with an upper limit of preferably 65 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 55 parts by mass or less. If the blending amount is less than the above range, it will become too soft and have poor rebound properties, and if it is more than the above range, it will become too hard and have a poor feel when hitting the ball, as well as be brittle and have poor durability.

[0030] (b) The co-crosslinking agent of component (b) preferably has an average particle size of 3 to 30 μm, more preferably 5 to 25 μm, and even more preferably 8 to 15 μm. If the average particle size of the co-crosslinking agent is less than 3 μm, it tends to aggregate in the rubber composition, increasing the reactivity between the acrylic acids and decreasing the reactivity between the base rubbers, which may result in insufficient rebound performance of the golf ball. If the average particle size of the co-crosslinking agent exceeds 30 μm, the co-crosslinking agent particles become too large, leading to greater variation in the properties of the resulting golf ball.

[0031] (c) Component is an organic peroxide, and in this invention, only organic peroxides with a 1-minute half-life temperature of 165°C or higher are used. That is, in this invention, no organic peroxides with a 1-minute half-life temperature of less than 165°C are blended into the rubber composition. Examples of such organic peroxides include dicumyl peroxide (NOF Co., Ltd. "Permyl D"), 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (NOF Co., Ltd. "Perhexa 25B"), di(2-t-butylperoxyisopropyl)benzene (NOF Co., Ltd. "Perbutyl P"), di-t-butyl peroxide (NOF Co., Ltd. "Perbutyl D"), t-butyl-cumyl peroxide (NOF Co., Ltd. "Perbutyl C"), di-t-hexyl peroxide (NOF Co., Ltd. "Perhexyl D"), etc., and dicumyl peroxide can be used particularly suitably.

[0032] In this invention, by using only organic peroxides with a 1-minute half-life temperature of 165°C or higher as the organic peroxide, the hardness gradient from the core center to a certain distance is not very large, and the hardness gradient from that certain distance to the outer surface of the core becomes large. For example, the hardness morphology is as shown in the core hardness distribution of Examples 1 and 3 in Figure 2. Furthermore, by blending the above organic peroxides, the difference in hardness between the core center and the outer surface of the core can be made relatively small. As a result, the initial velocity of the core and the ball can be improved, and the spin of the ball can be controlled.

[0033] (c) The amount of component blended is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, per 100 parts by mass of base rubber, with an upper limit of preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less.

[0034] (d) The component is benzimidazole and / or its metal salt, represented by the following general formula, and is used as an anti-aging agent. [ka]

[0035] In formula (1) above, R is a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, and m is an integer from 1 to 4. When m is 2 or greater, these may be the same or different from each other. Examples of benzimidazoles having formula (1) above include 2-mercaptobenzimidazole, 2-mercaptomethylbenzimidazole, and their metal salts, with zinc salt being preferred as the metal salt.

[0036] The amount of benzimidazole and / or its metal salt represented by the above specific formula in component (d) is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, per 100 parts by mass of the base rubber, with an upper limit of preferably 5 parts by mass or less, more preferably 3 parts by mass or less. By keeping the amount of component (d) within the above range, the hardness difference between the inside and outside of the core can be increased. If the amount of component (d) is too small, the crosslinking reaction near the core surface will not be efficiently promoted, the crosslinking density will not be sufficiently large, a hard layer will not be sufficiently formed, the hardness difference between the core surface and the core center will not be sufficiently large, and sufficient impact resistance may not be obtained. On the other hand, even if the amount of component (d) is increased unnecessarily, the effect obtained will not change beyond the above-mentioned preferred amount.

[0037] In addition to the components (a) to (d) described above, various additives such as fillers, organic sulfur compounds, water, and processing aids may be added, as long as they do not interfere with the effects of the present invention.

[0038] Suitable fillers include, for example, zinc oxide, barium sulfate, and calcium carbonate. These may be used individually or in combination of two or more. The amount of filler added is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the base rubber. The upper limit of this addition is preferably 100 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 40 parts by mass or less, per 100 parts by mass of the base rubber. If the amount added is too much or too little, it may not be possible to obtain the appropriate mass and suitable rebound properties.

[0039] There are no particular restrictions on the organic sulfur compounds, but examples include thiophenols, thionaphthols, diphenyl polysulfides, halogenated thiophenols, or their metal salts. Specifically, examples include zinc salts of pentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol, parachlorothiophenol, etc., diphenyl polysulfides with 2 to 4 sulfur atoms, dibenzyl polysulfides, dibenzoyl polysulfides, dibenzothiazoyl polysulfides, dithiobenzoyl polysulfides, 2-thionaphthol, etc. These may be used individually or in combination of two or more. Among these, zinc salts of pentachlorothiophenol and / or diphenyl disulfides can be preferably used.

[0040] The amount of organic sulfur compound added is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.2 parts by mass or more, per 100 parts by mass of the base rubber, with an upper limit of preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and even more preferably 1 part by mass or less. If the amount of organic sulfur compound added is too high, the hardness of the heat-molded product of the rubber composition may become too soft, while if it is too low, improvement in rebound properties may not be expected.

[0041] As processing aids, higher fatty acids and their metal salts can be suitably used. Examples of higher fatty acids include stearic acid, palmitic acid, oleic acid, linoleic acid, linolenic acid, and myristic acid, with stearic acid being particularly preferred. Examples of metal salts of higher fatty acids include lithium salts, sodium salts, potassium salts, copper salts, magnesium salts, calcium salts, strontium salts, barium salts, tin salts, cobalt salts, nickel salts, zinc salts, and aluminum salts, with zinc stearate being particularly preferred. The amount of processing aid added can be preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the base rubber. Furthermore, the upper limit of this amount can be preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less, per 100 parts by mass of the base rubber. If the amount is too high, sufficient hardness and resilience cannot be obtained, and if it is too low, the added chemicals may not be sufficiently dispersed, and the expected physical properties may not be obtained. Regarding the method of adding the processing aid, there are several methods, but they are not limited to the above. These include adding it to the mixer at the same time as other chemicals, pre-mixing it with other chemicals such as component (b) above and then adding it, coating it on the surface of other chemicals such as component (b) above and then adding it, or preparing a masterbatch in advance together with component (a) above and then adding it.

[0042] In the present invention, a specific anti-aging agent is used as component (d) above, but it may contain an anti-aging agent different from component (d). Specifically, examples of hindered phenol-based anti-aging agents include 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 1,3,5-tris(3',5'-di-t-butyl-4-hydroxybenzyl)isocyanuric acid. Commercially available products include Nocrac 200, Nocrac M-17 (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.), IRGANOX 1010 (manufactured by BASF), and Adekastab AO-20 (manufactured by ADEKA). These may be used individually or in combination of two or more. There are no particular restrictions on the amount of this anti-aging agent added, but it is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, with an upper limit of preferably 1.0 part by mass or less, more preferably 0.7 parts by mass or less, and even more preferably 0.4 parts by mass or less, per 100 parts by mass of the base rubber. If the amount added is too much or too little, it may not be possible to obtain an appropriate core hardness gradient, and it may not be possible to obtain the desired rebound properties, durability, and low spin effect during full shots.

[0043] The core described above is a vulcanized molded product obtained by vulcanizing and curing the rubber composition described above. The core may be a single layer or multiple layers, and the vulcanized molded product can be used for all or part of a single-layer or multiple-layer core. For example, a core, which is a vulcanized molded product, can be produced by kneading using a kneader such as a Banbury mixer or roll, compression molding or injection molding using a core mold, and then appropriately heating the molded body at a temperature of about 100 to 200°C for 10 to 40 minutes, which is sufficient for the organic peroxide and co-crosslinking agent to act, thereby curing the molded body.

[0044] There are no particular restrictions on the core diameter, and it depends on the layer structure of the golf ball being manufactured, but it is preferably 33 mm or more, more preferably 35 mm or more, with an upper limit of preferably 41 mm or less, more preferably 40 mm or less. If the core diameter deviates from this range, the initial velocity of the ball may be low, or the appropriate spin characteristics may not be obtained.

[0045] Regarding the hardness distribution of the core described above, it is preferable that the hardness is equal to or increases from the center of the core toward the surface, and does not decrease. When the JIS-C hardness at the core center is O, the JIS-C hardness at a position 10 mm from the core center is A, and the JIS-C hardness at the core surface is S, the following three equations apply. 0 ≤ AO ≤ 10 10 ≤ SA ≤ 20 15 ≤ SO ≤ 25 It is preferable that the following conditions be met. If the hardness difference values ​​in each of the above formulas are smaller than the lower limit, the low-spin effect when hitting with a driver (W#1) may be insufficient, resulting in reduced distance. On the other hand, if the hardness difference values ​​in each of the above formulas are larger than the upper limit, the initial ball speed when actually hitting the golf ball may be low, resulting in reduced distance, or the durability against cracking due to repeated impacts may be poor. Here, the above-mentioned central hardness refers to the hardness measured at the center of the cross-section obtained by cutting the core in half (through the center), and the surface hardness refers to the hardness measured on the surface (spherical surface) of the above-mentioned core. Furthermore, JIS-C hardness refers to the hardness measured with a spring-type hardness tester (JIS-C type) specified in JIS K 6301-1975.

[0046] The core's central hardness O is preferably 45 or higher, more preferably 50 or higher, on the JIS-C hardness scale, with an upper limit of preferably 70 or lower, and more preferably 65 or lower. If the core's central hardness deviates from the above range, the feel of the ball may deteriorate or its durability may decrease. If it falls below the above range, it may indicate insufficient vulcanization of the core, making it difficult to obtain the desired ball performance.

[0047] For positional hardness A at 10 mm from the core center, the JIS-C hardness is preferably 50 or higher, more preferably 52 or higher, with an upper limit of preferably 65 or lower, more preferably 60 or lower. If the positional hardness of the core deviates from the above range, the feel of the ball may deteriorate.

[0048] The core surface hardness S is preferably 60 or higher, more preferably 65 or higher, on the JIS-C hardness scale, with an upper limit of preferably 90 or lower, and more preferably 85 or lower. If the core surface hardness is lower than the above range, the ball's rebound will decrease, and it will be difficult to obtain a sufficient low-spin effect, which may result in insufficient distance. On the other hand, if the core surface hardness is higher than the above range, the feel of the ball may become too hard, and the resistance to cracking due to repeated impacts may be poor.

[0049] The hardness distribution of the core in the present invention that satisfies the three equations described above is characterized by a hardness gradient that increases from a point 10 mm away from the core center to the core surface, as shown in Figure 2 (Examples 1 and 3).

[0050] At least one intermediate layer is provided between the core and the cover (outermost layer).

[0051] There are no particular restrictions on the resin material for the intermediate layer, but known thermoplastic resin materials such as various ionomer resins used in golf balls can be used.

[0052] Furthermore, to further reduce the spin rate of the ball, it is particularly preferable to use a highly neutralized ionomer material as the intermediate layer material. Specifically, it is preferable to use a material containing the following components (A) to (C). (A) Ionic or nonionic olefin-unsaturated carboxylic acid copolymers, and / or ionic or nonionic olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester copolymers, (B) Organic acids or their metal salts, (C) A basic inorganic metal compound for neutralizing 80 mol% or more of the acid groups in the above (A) and (B) components A resin composition containing the same.

[0053] As the olefin component of the (A) component, it is preferably a compound having 2 to 6 carbon atoms, and ethylene is particularly preferred. Further, as the unsaturated carboxylic acid of the (A) component, it is preferable to adopt either acrylic acid or methacrylic acid. As the unsaturated carboxylic acid ester of the (A) component, a lower alkyl ester is preferable, and particularly, butyl acrylate (n-butyl acrylate, butyl acrylate) is preferable.

[0054] Specific examples of the (A) component include the "IOTEK" series manufactured by ExxonMobil, the "HIMILAN" series manufactured by Mitsui Dow Chemical, the ionomer resin manufactured by THE DOW CHEMICAL COMPANY, and the "Surlyn" series.

[0055] The (B) component is an organic acid and its metal salt, and the type thereof is not particularly limited, but particularly, it is preferable to adopt a metal stearate or a metal oleate. Examples of the metal stearate include magnesium stearate, calcium stearate, zinc stearate, sodium stearate, etc. Among these, it is particularly preferable to use magnesium stearate.

[0056] The (C) component is a basic inorganic metal compound, and examples of the type thereof include Na + , K + , Li + , Zn 2+ , Ca 2+ , Mg 2+ , Cu 2+ , Co 2+ , etc. Particularly preferred are Na + , Zn 2+ , Ca 2+ , Mg 2+ , and more preferably Mg 2+These metal salts can be introduced into resin compositions using formate, acetate, nitrate, carbonate, bicarbonate, oxide, hydroxide, and the like.

[0057] Component (C) neutralizes 80 mol% or more of the acidic groups in components (A) and (B) above, preferably in an appropriate amount to neutralize 83 mol% or more of the acidic groups, more preferably 85 mol% or more. The specific amount to be added is 0.5 to 4.0 parts by mass, preferably 0.75 to 3.5 parts by mass, per 100 parts by mass of the resin of components (A) and (B).

[0058] The resin composition containing the above components (A) to (C) may be appropriately blended with any additives depending on the application, and various additives such as pigments, dispersants, antioxidants, UV absorbers, and light stabilizers may be added.

[0059] Furthermore, while known kneading methods can be used to prepare the resin composition containing the above components (A) to (C), and are not particularly limited, a method of kneading using an extruder can be preferably employed. In this case, either a single-screw extruder or a twin-screw extruder can be used, but a twin-screw extruder, which has a higher kneading effect, can be preferably used. In addition, a linked type extruder, which connects multiple extruders, can also be used, for example, a two-stage linked type such as a single-screw extruder-twin-screw extruder or twin-screw extruder-twin-screw extruder.

[0060] The material hardness of the above-mentioned intermediate layer is preferably 45 or higher on the Shore D scale, and more preferably 48 or higher. While there is no particular upper limit, it is preferably 60 or lower, and more preferably 55 or lower.

[0061] The thickness of the intermediate layer described above is set to 2.0 mm or less, preferably 1.8 mm or less, and more preferably 1.5 mm or less. There is no particular lower limit, but it is preferably 0.8 mm or more, more preferably 1.0 mm or more, and even more preferably 1.2 mm or more. If the thickness of the intermediate layer deviates from the above numerical range, the low-spin effect of the driver (W#1) may be insufficient, and the distance may be reduced.

[0062] Next, the cover in this invention will be described. There are no particular restrictions on the resin material of the cover, but it can be the same or different ionomer resin or highly neutralizing resin material as the intermediate layer material mentioned above, or a polyurethane resin such as a thermoplastic polyurethane elastomer as the main material. In particular, it is preferable that the cover be formed from a resin composition containing at least one of the copolymers consisting of ionic or nonionic olefin-unsaturated carboxylic acid copolymers and ionic or nonionic olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester copolymers.

[0063] The material hardness of the cover described above is preferably 55 or higher on the Shore D scale, and more preferably 58 or higher. While there is no particular upper limit, it is preferably 65 or lower, and more preferably 63 or lower.

[0064] The thickness of the cover described above should be set to 2.0 mm or less, preferably 1.8 mm or less, and more preferably 1.5 mm or less. There is no particular lower limit, but it is preferably 0.8 mm or more, more preferably 1.0 mm or more, and even more preferably 1.2 mm or more. If the thickness of the cover described above deviates from the above numerical range, the low-spin effect of the driver (W#1) may be insufficient, and the distance may be reduced. Also, if the thickness of the cover described above is too small, the durability may deteriorate.

[0065] The manufacturing method for a golf ball formed by laminating the core, intermediate layer, and cover (outermost layer) described above can be carried out by conventional methods such as known injection molding. For example, an intermediate layer material can be injected around the core using an injection molding die to obtain each coated sphere, and then the material for the outermost cover can be injection molded to obtain a golf ball. Alternatively, a golf ball can be manufactured by wrapping each coated sphere with two pre-formed hemispherical half-cups and then heat-pressure molding them.

[0066] In this invention, the surface of the cover (outermost layer) is provided with a plurality of dimples and a land area surrounded by the plurality of dimples. This land area refers to the portion of the surface of the outermost layer in which no dimples are formed. The boundary line between the land area and the dimples corresponds to the outer edge of the land area or the outer edge of the dimples, and in this invention, it is referred to as an edge or edge element.

[0067] The above-mentioned land portion is composed of numerous land portion pieces. For example, Figure 3 shows a plan view of golf balls according to embodiments 1 to 3 of the present invention, which have numerous dimples D and a land portion L. Figure 4(A) is an enlarged view of region T, and shows that numerous land portion pieces 10, which are the smallest units of the land portion L, are formed therein. That is, six land portion pieces 10 are formed around one dimple D. As a result, the shape of the outer edge of the dimple D is approximately dodecagonal. The edges between the vertices of this approximately dodecagon are not straight but curved.

[0068] Furthermore, as shown in Figures 4(A) and (B), the land segment 10 has a tridentate shape (a shape with three radial extensions spaced approximately 120 degrees apart), and each radially extending portion gradually narrows outward, with a pointed tip. This pointed portion is the vertex 1a, meaning that one land segment 10 has three vertices 10b, and at these vertices, it substantially touches another adjacent land segment at a single point. In addition, the outer edge of one land segment 10 consists of six edge elements 10a. In other words, the land segment takes on the tridentate shape described above by the connection of these six edge elements.

[0069] The shape of the land segment described above is not limited to the three-pronged shape, but can be any specific shape having at least three vertices, such as a Y-shape, T-shape, or star shape, where adjacent land segments are substantially connected at points at these vertices. Furthermore, the land segment is not limited to just one type, but can be two or more types with different sizes or shapes.

[0070] In the present invention, it is preferable that the edge elements of the land portion are formed with a curve of curvature of 0.40 or less. In the present invention, by using a curve with a curvature of 0.40 or less as the edge element, the novelty of the ball surface (appearance) and the optimal shape for aerodynamic performance are configured, thereby increasing the flight distance. The curvature of the edge element is preferably 0.40 or less, more preferably 0.35 or less, and even more preferably 0.30 or less. In this way, the curvature of each edge element is set to be as small as described above in order to avoid as much as possible shapes that create air resistance on the inner circumferential side surface (edge) of the dimple.

[0071] The proportion of land segments in which all of the above edge elements are formed with a curve of curvature 0.40 or less is 25% or more of the total number of land segments constituting the land, preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more.

[0072] Furthermore, in this invention, it is preferable that the total number of curves forming the edge elements is 4000 or more. And, among the curved edge elements forming the land portion, the proportion of edge elements with a curvature of 0.40 or less is preferably 70% or more, and more preferably 75% or more. By increasing the proportion of curves with a predetermined curvature or less in this way, air resistance on the ball surface can be reduced, thereby further increasing the flight distance.

[0073] In this way, by arranging land pieces having a predetermined shape on a golf ball to design dimples on the ball's surface, and by arranging multiple land pieces so that adjacent land pieces touch at virtually points, it is possible to increase the proportion of the dimple surface area on the virtual spherical surface of the golf ball, i.e., the surface coverage ratio of the dimples, while maintaining uniform gaps between the dimples. Consequently, the aerodynamic performance of the golf ball is significantly improved, resulting in longer flight distances. Furthermore, the surface coverage ratio of the dimples can be easily controlled by changing the shape of the land pieces.

[0074] The surface coverage of the dimples is preferably 80% or more, and more preferably 85% or more. By setting the surface coverage of the dimples to 80% or more, air resistance can be reduced. On the other hand, the upper limit of the surface coverage of the dimples is preferably 95% or less. Specifically, the surface coverage of the dimples refers to the ratio (SR value) of the total dimple area, defined by the plane edges surrounded by the edges of the dimples, to the ball surface area assuming that no dimples exist.

[0075] The total number of land segments formed on the surface of the golf ball is preferably 434 or more, and more preferably 540 or more. On the other hand, the total number of land segments 12 is preferably 864 or less, and more preferably 756 or less. By setting the total number of land segments within this range, the surface coverage ratio of the dimples on the ball surface can be designed to fall within the above preferred range.

[0076] The total number of dimples formed on the surface of a ball is usually between 200 and 500, but this is determined by the total number of land segments and the relationship between the land segments and the dimples. For example, if the total number of land segments is 434, and 6 land segments form one dimple, the total number of dimples will be 218. Similarly, if 6 land segments form one dimple, then with a total of 540 land segments, the total number of dimples will be 272; with a total of 756 land segments, the total number of dimples will be 380; and with a total of 864 land segments, the total number of dimples will be 434.

[0077] Regarding the shape of the dimples, typically, due to the arrangement of the land fragments described above, the majority will be non-circular dimples, but circular dimples can also be formed. When circular dimples are present, it is preferable that there be two or more circular dimples, more preferably ten or more, and the upper limit is preferably 30 or less. Furthermore, it is preferable that the proportion of circular dimples to the total number of dimples is 10% or less, and more preferably 5% or less. Thus, the dimples formed on the surface of the golf ball according to the present invention are not limited to non-circular dimples, but can also include circular dimples.

[0078] Furthermore, the total volume of the dimples refers to the sum of the volumes of each dimple formed in a single ball, below the plane surrounded by the edges of the dimples. While there are no particular limitations on this total dimple volume, it is preferably 300-600 mm². 3 It is preferable that this be the case. By adjusting within the above range, the ball trajectory after hitting with the driver (W#1) can be optimized and stabilized to achieve the desired distance.

[0079] The golf ball of the present invention can be manufactured using a mold. For the creation of such a mold, a method can be used in which 3D CAD or CAM is used to directly carve the entire surface shape in three dimensions from a reversal master mold, or a method can be used to directly carve the cavity portion of the molding die in three dimensions. By designing the mold so that the parting line passes through the land portion of the golf ball surface, finishing (trimming) can be facilitated. Furthermore, to evenly distribute the land portion pieces across the spherical surface of the golf ball, it is preferable to utilize arrangement methods such as polyhedra (icosahedron, dodecahedron, octahedron, etc.) or 3-fold or 5-fold symmetry. [Examples]

[0080] 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.

[0081] [Examples 1-4, Comparative Examples 1, 2] After preparing the core composition using a rubber compound mainly composed of polybutadiene as shown in Table 1 below, vulcanization is performed at 155°C for 20 minutes, followed by a polishing process of the core surface to produce a core with a diameter of 37.6 mm.

[0082] [Table 1]

[0083] Details regarding the core formulation mentioned above are as follows: • Polybutadiene rubber: Product name "BR730" (manufactured by ENEOS Material Co., Ltd.) • Zinc acrylate: Product name "ZN-DA85S" (manufactured by Nippon Shokubai Co., Ltd.) • Zinc stearate: Product name "Zinc Stearate GP" (manufactured by NOF Corporation) • Organic peroxide (1): Dicumyl peroxide, trade name "Perkmyl D" (manufactured by NOF Corporation), half-life temperature at 1 minute: 175.2°C. • Organic peroxide (2): A mixture of 1,1-di(t-butylperoxy)cyclohexane and silica, trade name "Perhexa C-40" (manufactured by NOF Corporation), half-life temperature at 1 minute: 153.8°C • Anti-aging agent: Product name "Nocrack MB" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) • Zinc oxide: Product name "Zinc Oxide 3 Types" (manufactured by Sakai Chemical Co., Ltd.) • Water: Distilled water • Pentachlorothiophenol zinc salt: Manufactured by ZHEJIANG SHOU&FU CHEM Co., Ltd.

[0084] Next, using an injection molding die, an intermediate layer with a thickness of 1.30 mm and a Shore D hardness of "50" was formed around the core surface by injection molding with the intermediate layer resin material D or E shown in Table 2. Then, using an injection molding die having numerous dimple-forming protrusions in the cavity, a cover (outermost layer) resin material F shown in Table 2 was injected around the intermediate layer-covered sphere to form a cover with a thickness of 1.25 mm and a Shore D hardness of "62".

[0085] [Table 2]

[0086] The details of the ingredients listed in the table above are as follows: • "AM7318" Ionomer resin manufactured by Mitsui Dow Polychemicals. • "AM7327" Ionomer resin manufactured by Mitsui Dow Polychemicals. • "AN4319" Nucrel manufactured by Mitsui Dow Polychemicals • "HPF1000" manufactured by THE DOW CHEMICAL COMPANY • Titanium dioxide manufactured by Sakai Chemical Industry Co., Ltd.

[0087] [Dimples and land areas in each example] As described above, the resin material for the cover is injected using an injection molding die having numerous dimple-forming protrusions within the cavity, thereby forming dimples and land fragments of a predetermined shape on the surface of the cover. Details are shown in Table 3. In addition, a photograph of dimple No. 1 is shown in Figure 3, and a photograph of dimple No. 2 is shown in Figure 5.

[0088] The measurement conditions and methods for the radius of curvature of the edge elements of the land portion formed on the ball surface in each example are as follows. The six or more curves (edge ​​elements) that make up the shape of the land portion of the ball surface are analyzed, and the curvature of each curve is calculated. Each curve that makes up the shape of the land portion is divided into sections by 20 equal plots, and the curvature of the curve is calculated in each section, and the maximum and minimum curvature of each curve is calculated. For circular dimples, the land portion (land portion) sandwiched between each dimple is specified individually, and the maximum and minimum curvature of the arc of each dimple is calculated. This curvature is calculated by analyzing each curve on the drawing using a computer, or by using the equation of the curves that make up the land portion based on the measured dimple shape. The number of curves with a maximum curvature of 0.4 or less is counted, and the ratio to the total number of curves that make up the land portion is calculated.

[0089] [Core hardness distribution] The core surface is spherical, and the hardness S of the core is measured using the JIS-C hardness scale according to the JIS K6301-1975 standard, with the needle of the hardness tester set approximately perpendicular to the spherical surface. For the core's central hardness O and the cross-sectional hardness A at a distance of 10 mm from the core's center, the core is cut into a hemispherical shape, and the cross-section is made flat. The hardness tester needle is then pressed perpendicularly against the measurement area. The values ​​are expressed in JIS-C hardness scale. The measured values ​​are shown in Table 3.

[0090] Furthermore, graphs of the core hardness distribution for Examples 1 and 3 and Comparative Example 1 are shown in Figure 2.

[0091] [Evaluation of flight distance] The flight of the golf ball in each example is evaluated as follows: A golf swing robot was fitted with a driver club, and the initial velocity, spin rate, and distance (carry and total) were measured when the robot struck the ball at head speeds (HS) of 45 m / s and 40 m / s. The results are shown in Table 3. The club used was a Bridgestone Sports "TourB XD-5 Driver (2017 model)" (loft angle 9.5°).

[0092] [Table 3]

[0093] As shown in the results in Table 3, the golf balls of Comparative Examples 1 and 2 are inferior to the present invention (example) in the following respects. Comparative Example 1 contains an organic peroxide in its core formulation with a half-life temperature of less than 165°C per minute, and the flight distance when struck with HS40m / s and HS45m / s drivers (W#1) is inferior to that of each example. Comparative Example 2, although the ball surface contains a unique three-pronged land portion within the land portion, has a very small proportion of such land portions where all of the edge elements of the land portion are formed with a curve of curvature of 0.40 or less. As a result, the flight distance when struck with a driver (W#1) at HS40m / s and HS45m / s is inferior to that of the respective embodiments. [Explanation of symbols]

[0094] G Golf Balls 1 core 2. Middle Class 3 Cover L Land D-dimple 10 land piece 10a Edge element 10b Vertex of the continental portion

Claims

1. A golf ball comprising at least one intermediate layer between the core and the cover, wherein the surface of the cover has a plurality of dimples and land areas surrounded by the plurality of dimples, wherein the core comprises each of the following components (a) to (d): (a) Base rubber, (b) As a cocrosslinking agent, α,β-unsaturated carboxylic acids and / or their metal salts, (c) organic peroxide; (d) Benzimidazole and / or its metal salts represented by the following general formula as an anti-aging agent. 【Chemistry 1】 (However, in the formula, R is a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, and m is an integer from 1 to 4. If m is 2 or greater, these may be the same or different from each other.) A golf ball characterized in that it contains, the above (c) component is formed by a heat-molded product of a rubber composition consisting only of organic peroxides having a half-life temperature of 165°C or higher for one minute, the land portion is composed of a number of land portion pieces, each land portion piece has a shape having at least three vertices, and at the vertices, the land portion is substantially connected to another adjacent land portion by point contact, and the outer edge of the land portion of the land portion is composed of a plurality of edge elements, and the proportion of land portion pieces with a unique shape in which all of the edge elements are formed by curves with a curvature of 0.40 or less is 25% or more of the total number of land portion pieces constituting the land portion.

2. The golf ball according to claim 1, wherein the above component (d) is 2-mercaptobenzimidazole.

3. The golf ball according to claim 1 or 2, wherein the amount of component (d) is 0.1 parts by mass or more per 100 parts by mass of component (a).

4. In the above core hardness distribution, when the JIS-C hardness at the core center is O, the JIS-C hardness at a position 10 mm from the core center is A, and the JIS-C hardness at the core surface is S, the following three equations 0 ≤ A - O ≤ 10 10 ≤ S - A ≤ 20 15 ≤ S - O ≤ 25 A golf ball according to claim 1 or 2 that satisfies the requirements.

5. The above intermediate layer consists of (A) to (C) below. (A) Ionic or nonionic olefin-unsaturated carboxylic acid copolymers, and / or ionic or nonionic olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester copolymers, (B) Organic acids or their metal salts, (C) Basic inorganic metal compound for neutralizing 80 mol% or more of the acidic groups in components (A) and (B) above. A golf ball according to claim 1 or 2, formed from a resin composition containing the following:

6. The golf ball according to claim 1 or 2, wherein the cover is formed from a resin composition containing at least one copolymer from the group consisting of an ionic or nonionic olefin-unsaturated carboxylic acid copolymer and an ionic or nonionic olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester copolymer.

7. The golf ball according to claim 5, wherein the unsaturated carboxylic acid in the copolymer of the intermediate layer is acrylic acid or methacrylic acid.

8. The golf ball according to claim 6, wherein the unsaturated carboxylic acid in the copolymer of the cover is acrylic acid or methacrylic acid.

9. The golf ball according to claim 1 or 2, wherein the material hardness of the intermediate layer is 45 to 60 on the Shore D scale, and the material hardness of the cover is 55 to 65 on the Shore D scale.

10. The golf ball according to claim 1 or 2, wherein the above land portion is formed by connecting 4,000 or more curved edge elements.

11. The golf ball according to claim 1 or 2, wherein, among the curved edge elements forming the above-mentioned land portion, the proportion of edge elements with a curvature of 0.40 or less is 70% or more.

12. The golf ball according to claim 1 or 2, wherein the area coverage ratio of the dimples is 80 to 95%.

Images