Multi-piece solid golf ball

Abstract

To provide a golf ball in which carry is considered seriously and which can achieve a dominant carry when performing full shot by a driver (W#1) and by an iron.SOLUTION: A multi-piece solid golf ball G comprises a core 1, a surrounding layer 2, an intermediate layer 3, and a cover 4. The core is formed of a single or multilayer rubber composition, the surrounding layer, the intermediate layer, and the cover are respectively formed of a single-layer resin material. A hardness relation of respective layers satisfies following two formulae: material hardness of the cover>material hardness of the intermediate layer; and material hardness of the surrounding layer≥surface hardness of the core (where the hardness in the formulae indicates Shore C hardness), and satisfies a following formula: a thickness (mm) of the surrounding layer×material hardness (Shore D hardness) of the surrounding layer≥a thickness (mm) of the cover×material hardness (Shore D hardness) of the cover, and a flexibility amount of the core and the ball in a specific load application state, is made proper.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a multi-piece solid golf ball comprising four or more layers, including a core, a surrounding layer, an intermediate layer, and a cover. [Background technology]

[0002] Many innovations have been made in designing golf balls with a multi-layered structure, resulting in the development of many balls that satisfy not only professional golfers but also amateur golfers ranging from beginners to advanced players. For example, functional multi-piece solid golf balls with optimized material hardness and surface hardness for each layer—the core, surrounding layer, intermediate layer, and cover (outermost layer)—have become widespread. Furthermore, several technologies have been proposed that focus on the hardness distribution of the core, which occupies the majority of the ball's volume, and provide high-performance golf balls by designing various configurations of internal core hardness.

[0003] Examples of such technical documents include the following Patent Documents 1 to 13. These golf balls are multi-layered golf balls with four or more layers, and are designed to prioritize distance (distance type) golf balls with a harder cover (outermost layer) than the intermediate layers.

[0004] However, the proposed golf ball still has room for improvement in optimizing the core hardness distribution and the thickness relationship between each layer. In other words, the proposed golf ball made it difficult for amateur users, especially those with lower swing speeds, to achieve a sufficiently satisfactory distance. While the proposed golf ball provided satisfactory distance when hit with a driver, it did not offer superior distance performance when hitting full shots with an iron. Therefore, there was still room for improvement in the proposed distance-focused golf ball in terms of pursuing distance when hitting full shots with a driver (W#1) and an iron. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2000-061002 [Patent Document 2] Japanese Patent Publication No. 2000-061000 [Patent Document 3] Japanese Patent Publication No. 2001-218872 [Patent Document 4] Japanese Patent Publication No. 2005-218859 [Patent Document 5] Japanese Patent Publication No. 2010-253268 [Patent Document 6] Japanese Patent Publication No. 2014-132955 [Patent Document 7] Japanese Patent Publication No. 2016-016117 [Patent Document 8] Japanese Patent Publication No. 2016-179052 [Patent Document 9] Japanese Patent Publication No. 2019-198467 [Patent Document 10] Japanese Patent Publication No. 2021-087743 [Patent Document 11] Japanese Patent Application Publication No. 10-295852 [Patent Document 12] Japanese Patent Publication No. 2000-140160 [Patent Document 13] Japanese Patent Publication No. 2013-244129 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] This invention has been made in view of the above circumstances, and aims to provide a golf ball that prioritizes distance (distance type) and can achieve superior distance when taking a full shot with a driver (W#1) and an iron. [Means for solving the problem]

[0007] The inventors, after diligent research to achieve the above objective, have determined that for a multi-piece solid golf ball comprising a core, a surrounding layer, an intermediate layer, and a cover, the core is formed from a rubber composition, and the surrounding layer, intermediate layer, and cover are each formed from a resin material, and the relationship between the Shore C hardness of each layer is given by the following two formulas Cover material hardness > Intermediate layer material hardness, and Material hardness of the surrounding layer ≥ Surface hardness of the core Satisfying the following equation The thickness of the surrounding layer (mm) × the material hardness of the surrounding layer (Shore D hardness) ≥ the thickness of the cover (mm) × the material hardness of the cover (Shore D hardness) By satisfying the above conditions and constructing a golf ball such that the value of CB is 1.00 mm or more, when C (mm) is the amount of deflection when an initial load of 98 N (10 kgf) is applied to the core and a final load of 1,275 N (130 kgf) is applied to the ball and the amount of deflection when an initial load of 98 N (10 kgf) is applied and a final load of 1,275 N (130 kgf) is applied to the ball, we found that this configuration not only provides superior distance when taking a full shot with a driver (W#1), but also provides superior distance when taking a full shot with an iron, leading to the present invention.

[0008] In other words, the golf ball of the present invention has a ball structure in which three coating layers (surrounding layer, intermediate layer, and cover) surrounding the core are all made of resin material, and the cover is made harder than the intermediate layer. This golf ball has superior distance performance when hitting a full shot with a driver (W#1) and also superior distance performance when hitting a full shot with an iron, and is a ball that satisfies the performance requirements of the average amateur golfer. Furthermore, the golf ball of the present invention satisfies a soft and good feel and has excellent crack resistance when repeatedly hit.

[0009] Therefore, the present invention provides the following multi-piece solid golf ball. 1. A multi-piece solid golf ball comprising a core, a surrounding layer, an intermediate layer, and a cover, wherein the core is formed of a single-layer or multi-layer rubber composition, and the surrounding layer, the intermediate layer, and the cover are each formed of a single-layer resin material, and the hardness relationship between the layers satisfies the following two formulas Hardness of the cover material > Hardness of the intermediate layer material, and, Hardness of the surrounding layer material ≧ Surface hardness of the core (However, the hardness in the above formulas means Shore C hardness.) while also satisfying the following formula Thickness of the surrounding layer (mm) × Hardness of the surrounding layer material (Shore D hardness) ≧ Thickness of the cover (mm) × Hardness of the cover material (Shore D hardness) and, when the deflection amount when a load is applied to the core from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is C (mm), and the deflection amount when a load is applied to the ball from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is B (mm), the value of C - B is 1.00 mm or more Furthermore, [Core volume (mm 3 The value of Core·vh is calculated as [Core surface Shore C hardness + Core center Shore C hardness] / 2, and [Volume of the surrounding layer material (mm³] 3 ) × Shore C hardness of the surrounding layer material] value is E·vh, [Volume of the intermediate layer material portion (mm³) 3 When the value of [Shore C hardness of the intermediate layer material] is I·vh, the following formula 1.10≦(E·vh + I·vh) / Core·vh ≦1.46 satisfies A multi-piece solid golf ball characterized by the above. 2. Further, the following formula Thickness of the surrounding layer (mm) × Hardness of the surrounding layer material (Shore D hardness) ≧ Thickness of the intermediate layer (mm) × Hardness of the intermediate layer material (Shore D hardness) The multi-piece solid golf ball according to claim 1, which satisfies the above. 3. The thickness relationship between the layers satisfies the following formula (Cover thickness + Intermediate layer thickness) < Surrounding layer thickness The multi-piece solid golf ball according to claim 1 or 2, which satisfies the above. 4. The hardness relationship between the layers satisfies the following formula Hardness of the cover material > Hardness of the intermediate layer material > Hardness of the surrounding layer material ≧ Surface hardness of the core (However, the hardness in the above formula refers to Shore C hardness.) A multi-piece solid golf ball as described in 1 or 2 above, which satisfies the requirements. 5. The resin material of either or both of the surrounding layer and the intermediate layer consists of the following components (A) to (D): (a-1) A binary random copolymer of olefin-unsaturated carboxylic acid and / or a metal ion neutralized product of a binary random copolymer of olefin-unsaturated carboxylic acid, (a-2) A ternary random copolymer of olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester and / or a metal ion neutralized product of the ternary random copolymer of olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester, (A) base resin formulated in a mass ratio of 100:0 to 0:100, (B) A resin component blended with a non-ionomer thermoplastic elastomer in a mass ratio of 100:0 to 50:50, for 100 parts by mass (C) 5 to 120 parts by mass of fatty acids and / or derivatives thereof having a molecular weight of 228 to 1500, (D) 0.1 to 17 parts by mass of a basic inorganic metal compound capable of neutralizing the unneutralized acid groups in components (A) and (C) above. A multi-piece solid golf ball according to claim 1 or 2 above, which is a highly neutralizing resin material comprising the above as essential components. 6. The multi-piece solid golf ball according to item 5, wherein both the surrounding layer and the intermediate layer are made of different types of highly neutralizing resin materials, each containing components (A) to (D) as essential components. 7. The relationship between the thicknesses of each layer is given by the following formula Encircling layer thickness / (cover thickness + interlayer thickness) ≥ 1.2 A multi-piece solid golf ball as described in 1 or 2 above, which satisfies the requirements. 8. The relationship between the core diameter and the ball diameter is given by the following formula. 0.65 ≤ (core diameter) / (ball diameter) ≤ 0.78 A multi-piece solid golf ball as described in 1 or 2 above, which satisfies the requirements. 9. [Core volume (mm²)] 3The value of Core·vh is calculated as [Core surface Shore C hardness + Core center Shore C hardness] / 2, and [Volume of the surrounding layer material (mm³] 3 ) × Shore C hardness of the surrounding layer material] value is E·vh, [Volume of the intermediate layer material portion (mm³) 3 When the value of [Shore C hardness of the intermediate layer material] is I·vh, the following formula 0.80≦(E·vh + I·vh) / Core·vh ≦2.00 A multi-piece solid golf ball as described in 1 or 2 above, which satisfies the requirements. [Effects of the Invention]

[0010] The golf ball of this invention offers superior distance performance when hitting full shots with a driver (W#1) and irons, provides a soft and pleasant feel, and exhibits excellent crack resistance during repeated impacts. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view of the multi-piece solid golf ball (4-layer structure) of the present invention. [Figure 2] These are plan views showing the dimple patterns common to each embodiment and comparative example. Figure 2(A) shows a plan view of the dimples as seen from directly above, centered on the pole of the ball, while Figure 2(B) shows a plan view of the dimples as seen from diagonally above, shifted upwards from Figure 2(A). [Modes for carrying out the invention]

[0012] The present invention will be described in more detail below. The multi-piece solid golf ball of the present invention, as shown in Figure 1, is a golf ball G having four or more layers, comprising a core 1, a surrounding layer 2 covering the core, an intermediate layer 3 covering the surrounding layer, and a cover 4 covering the intermediate layer. The surface of the cover 4 typically has numerous dimples D formed thereon. Although not specifically shown, the surface of the cover 4 typically also has a coating layer formed by paint. Excluding the coating layer, the cover 4 is the outermost layer in the layer structure of the golf ball. The core 1 is not limited to a single layer but can be formed in two or more layers, while the surrounding layer 2, intermediate layer 3, or cover 4 are formed as single layers.

[0013] The above core is obtained by vulcanizing a rubber composition mainly composed of rubber material. This rubber composition typically consists mainly of a base rubber, to which co-crosslinking agents, crosslinking initiators, inert fillers, organic sulfur compounds, etc., are blended to obtain the rubber composition.

[0014] It is preferable to use polybutadiene as the base rubber. Commercially available polybutadienes can be used, such as BR01, BR51, and BR730 (manufactured by JSR Corporation). The proportion of polybutadiene in the base rubber is preferably 60% by mass or more, and more preferably 80% by mass or more. In addition to the above polybutadiene, other rubber components may be blended into the base rubber in a range that does not impair the effects of the present invention. Examples of rubber components other than the above polybutadiene include other polybutadienes, other diene rubbers, such as styrene-butadiene rubber, natural rubber, isoprene rubber, and ethylene-propylene-diene rubber.

[0015] The cocrosslinking agent is an α,β-unsaturated carboxylic acid and / or its metal salt. Specific examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, and fumaric acid, with acrylic acid and methacrylic acid being particularly preferred. The metal salt of the unsaturated carboxylic acid is not particularly limited, but examples include those obtained by neutralizing the above-mentioned unsaturated carboxylic acid with a desired metal ion. Specifically, examples include zinc salts and magnesium salts of methacrylic acid, acrylic acid, etc., with zinc acrylate being particularly preferred.

[0016] The above-mentioned unsaturated carboxylic acid and / or its metal salt are usually blended in an amount of 5 parts by mass or more, preferably 9 parts by mass or more, more preferably 13 parts by mass or more, with an upper limit of 60 parts by mass or less, preferably 50 parts by mass or less, and more preferably 40 parts by mass or less, per 100 parts by mass of the base rubber. If the blending amount is too high, it may become too hard and the feel of hitting it may become unbearable, and if the blending amount is too low, the rebound may decrease.

[0017] Organic peroxides are preferably used as crosslinking initiators. Specifically, commercially available organic peroxides can be used, such as Parkmill D (manufactured by Nippon Oil & Fats Co., Ltd.), Perhexa C-40, Perhexa 3M (manufactured by Nippon Oil & Fats Co., Ltd.), and Luperco 231XL (manufactured by Atochem). These may be used individually or in combination of two or more. The amount of organic peroxide to be blended is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 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 4 parts by mass or less, even more preferably 3 parts by mass or less, and most preferably 2.5 parts by mass or less. If the blending amount is too high or too low, it may not be possible to obtain a suitable feel, durability, and rebound properties.

[0018] 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, per 100 parts by mass of the base rubber. The upper limit of the amount added is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and even more preferably 100 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.

[0019] As an anti-aging agent, commercially available products such as Nocrack NS-6, NS-30, NS-200, and MB (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) can be used. These may be used individually or in combination of two or more.

[0020] There are no particular restrictions on the amount of antioxidant 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 0.5 parts by mass or less, per 100 parts by mass of 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 the desired rebound properties, durability, and low spin effect during full shots may not be obtained.

[0021] Furthermore, organic sulfur compounds can be added to the above rubber composition to impart excellent resilience. Specifically, it is recommended to add thiophenol, thionaphthol, halogenated thiophenol, or metal salts thereof. More specifically, examples include zinc salts of pentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol, parachlorothiophenol, pentachlorothiophenol, diphenyl polysulfide, dibenzyl polysulfide, dibenzoyl polysulfide, dibenzothiazoyl polysulfide, and dithiobenzoyl polysulfide, with 2 to 4 sulfur atoms. In particular, zinc salts of pentachlorothiophenol and diphenyl disulfide can be preferably used.

[0022] The organic sulfur compound is blended in an amount of 5 parts by mass or less, preferably 4 parts by mass or less, more preferably 3 parts by mass or less, and most preferably 2 parts by mass or less, per 100 parts by mass of the base rubber. If the blending amount is too high, the hardness will become too soft, and if it is too low, improvement in rebound properties may not be achieved.

[0023] The above-mentioned core can be manufactured by vulcanizing and curing a rubber composition containing the above-mentioned components. For example, it can be manufactured by kneading using a kneader such as a Banbury mixer or roll, compression molding or injection molding using a core mold, and then curing the molded body by appropriately heating it at a temperature of 100 to 200°C, preferably 140 to 180°C, for 10 to 40 minutes, which is sufficient for the organic peroxide and co-crosslinking agent to act.

[0024] In this invention, the core is formed in a single layer or multiple layers. When a core is made of multiple layers of rubber, if there is a large difference in hardness at the interface between these rubber layers, delamination may occur at the interface when repeatedly struck, and a loss of initial ball velocity may occur when a full shot is made.

[0025] The core diameter is preferably 27.5 mm or larger, more preferably 28.5 mm or larger, and even more preferably 29.5 mm or larger. The upper limit of this diameter is preferably 33.5 mm or smaller, more preferably 32.5 mm or smaller, and even more preferably 32.0 mm or smaller. If the diameter deviates from the above range, it becomes difficult to achieve both low spin on full shots and high initial ball speed, and the desired distance may not be achieved.

[0026] The amount of deflection (mm) of the core when an initial load of 98N (10kgf) is applied to a final load of 1,275N (130kgf) is not particularly limited, but is preferably 3.3mm or more, more preferably 3.5mm or more, and even more preferably 3.7mm or more, with an upper limit of preferably 6.0mm or less, more preferably 5.0mm or less, and even more preferably 4.5mm or less. If the amount of deflection of the core is too small, i.e., the core is too hard, the amount of spin on the ball may increase too much, causing it to not fly far, or the feel of the ball may become too hard. On the other hand, if the amount of deflection of the core is too large, i.e., the core is too soft, the rebound of the ball may decrease too much, causing it to not fly far, or the feel of the ball may become too soft, or the durability against cracking during repeated impacts may be poor.

[0027] Next, the hardness distribution of the core described above will be explained. Note that the hardness of the core described below refers to Shore C hardness. This Shore C hardness is the hardness value measured using a Shore C hardness tester compliant with the ASTM D2240 standard.

[0028] The core's central hardness (Cc) is preferably 50 or higher, more preferably 55 or higher, and even more preferably 60 or higher, with an upper limit of preferably 66 or lower, more preferably 65 or lower, and even more preferably 64 or lower. If this value is too high, the feel of the ball may become too hard, or the amount of spin on a full shot may increase, resulting in a loss of the desired distance. On the other hand, if the above value is too low, the rebound effect may decrease, resulting in less distance, or the resistance to cracking after repeated impacts may worsen.

[0029] The surface hardness (Cs) of the core described above is preferably 68 or higher, more preferably 70 or higher, and even more preferably 72 or higher, with an upper limit of preferably 83 or lower, more preferably 80 or lower, and even more preferably 78 or lower. If these hardness values ​​are exceeded, unfavorable consequences similar to those described for the core's central hardness (Cc) may occur.

[0030] The difference between the core's surface hardness (Cs) and its core's core hardness (Cc) is preferably 8 or more, more preferably 10 or more, and even more preferably 12 or more, with an upper limit of preferably 25 or less, more preferably 20 or less, and even more preferably 16 or less. If this value is too small, the low-spin effect during full shots may be insufficient, resulting in reduced distance. On the other hand, if the above difference is too large, the actual initial ball speed may decrease, resulting in reduced distance, and the durability against cracking due to repeated impacts may worsen.

[0031] Next, I will explain the besieging layers. The material hardness of the surrounding layer is not particularly limited, but is preferably 36 or higher on the Shore D scale, more preferably 41 or higher, and even more preferably 46 or higher, with an upper limit of preferably 58 or lower, more preferably 56 or lower, and even more preferably 54 or lower.

[0032] The material hardness of the surrounding layer, expressed as Shore C hardness, is preferably 58 or higher, more preferably 64 or higher, and even more preferably 71 or higher, with an upper limit of preferably 87 or lower, more preferably 84 or lower, and even more preferably 82 or lower. If the material hardness of the surrounding layer is too soft compared to the above range, the amount of spin may increase during a full shot, or the initial velocity may decrease, resulting in a loss of the desired distance. On the other hand, if the material hardness is too hard, the amount of spin may increase during a full shot, resulting in a loss of the desired distance, or the feel of the shot may become too hard.

[0033] The thickness of the surrounding layer is preferably 2.1 mm or more, more preferably 2.5 mm or more, and even more preferably 2.8 mm or more. On the other hand, the upper limit of the thickness of the surrounding layer is preferably 4.8 mm or less, more preferably 4.4 mm or less, and even more preferably 4.2 mm or less. If the thickness of the surrounding layer is too thick or too thin, it becomes difficult to achieve both low spin and high initial ball speed during a full shot, and the desired distance may not be achieved.

[0034] Furthermore, in this invention, the thickness relationship of each layer is given by the following formula (Cover thickness + Intermediate layer thickness) < Encircling layer thickness It is necessary to satisfy the following conditions.

[0035] The material of the surrounding layer described above consists of a resin material, and various thermoplastic resin materials can be suitably used. Examples of resin materials for the surrounding layer include ionomer resins and the following components (A) to (D). (a-1) A binary random copolymer of olefin-unsaturated carboxylic acid and / or a metal ion neutralized product of a binary random copolymer of olefin-unsaturated carboxylic acid, (a-2) Olefin-unsaturated carboxylic acid-unsaturated carboxylic acid terranandic copolymer and / or metal ion neutralized product of olefin-unsaturated carboxylic acid-unsaturated carboxylic acid terranandic copolymer (A) base resin formulated in a mass ratio of 100:0 to 0:100, (B) A resin component blended with a non-ionomer thermoplastic elastomer in a mass ratio of 100:0 to 50:50, for 100 parts by mass (C) 5 to 120 parts by mass of fatty acids and / or derivatives thereof having a molecular weight of 228 to 1500, (D) 0.1 to 17 parts by mass of a basic inorganic metal compound capable of neutralizing the unneutralized acid groups in components (A) and (C) above. It is preferable to use a resin composition that contains the following as essential components.

[0036] For the above components (A) to (D), for example, the intermediate layer resin materials (A) to (D) described in Japanese Patent Publication No. 2010-253268 can be suitably used.

[0037] Examples of the non-ionomer thermoplastic elastomers mentioned above include polyolefin-based elastomers (including polyolefins and metallocene polyolefins), polystyrene-based elastomers, diene-based polymers, polyacrylate-based polymers, polyamide-based elastomers, polyurethane-based elastomers, polyester-based elastomers, and polyacetals, with thermoplastic polyether ester elastomers, such as thermoplastic polyether ester elastomers, being particularly noteworthy.

[0038] The above resin material can be appropriately blended with various additives depending on the application. For example, various additives such as pigments, dispersants, antioxidants, UV absorbers, and light stabilizers can be added.

[0039] Next, I will explain the middle class. The hardness of the intermediate layer material is not particularly limited, but is preferably 40 or higher, more preferably 45 or higher, and even more preferably 50 or higher on the Shore D hardness scale, with an upper limit of preferably 62 or lower, more preferably 60 or lower, and even more preferably 58 or lower. On the Shore C hardness scale, it is preferably 63 or higher, more preferably 70 or higher, and even more preferably 76 or higher, with an upper limit of preferably 92 or lower, more preferably 89 or lower, and even more preferably 87 or lower. If the hardness of the intermediate layer material is too soft compared to the above range, the amount of spin during a full shot may increase too much, resulting in a loss of distance, and the durability against cracking due to repeated impacts may be poor. On the other hand, if the hardness of the intermediate layer material is too hard compared to the above range, the durability against cracking due to repeated impacts may be poor, and the feel of the shot may be poor.

[0040] The thickness of the intermediate layer is preferably 0.7 mm or more, more preferably 0.9 mm or more, and even more preferably 1.1 mm or more. On the other hand, the upper limit of the intermediate layer thickness is preferably 1.5 mm or less, more preferably 1.4 mm or less, and even more preferably 1.3 mm or less. If the intermediate layer is too thin, the durability against cracking due to repeated impacts will be poor, or the feel of the ball may be poor. Also, if the intermediate layer is too thick, the amount of spin during a full shot may increase, resulting in a loss of distance.

[0041] For the intermediate layer material, various thermoplastic resins used as golf ball materials are preferred, particularly ionomer resins, as they achieve superior flight distance by reducing spin during full shots. More preferably, a highly neutralizing resin material containing components (A) to (D) described for the surrounding layer material is used. However, if both the surrounding layer and the intermediate layer use highly neutralizing resin materials, they must be of different types.

[0042] The intermediate layer material can be appropriately blended with any additives depending on the application. For example, various additives such as pigments, dispersants, antioxidants, UV absorbers, and light stabilizers can be added. When these additives are blended, the amount blended is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and preferably 10 parts by mass or less, and more preferably 4 parts by mass or less, per 100 parts by mass of the base resin.

[0043] Next, I will explain the cover (outermost layer). The hardness of the cover material is not particularly limited, but it is preferably 55 or higher on the Shore D hardness scale, more preferably 59 or higher, even more preferably 61 or higher, with an upper limit of preferably 70 or lower, more preferably 68 or lower, and even more preferably 65 or lower. On the Shore C hardness scale, it is preferably 83 or higher, more preferably 88 or higher, even more preferably 91 or higher, with an upper limit of preferably 100 or lower, more preferably 98 or lower, and even more preferably 96 or lower. If the hardness of the cover material is too soft compared to the above range, the amount of spin will increase and the initial ball speed will decrease when hitting with a driver (W#1), resulting in a loss of distance. On the other hand, if the hardness of the cover material is too hard, the crack resistance during repeated impacts may be poor.

[0044] The thickness of the cover is preferably 0.6 mm or more, more preferably 0.8 mm or more, and even more preferably 1.1 mm or more. On the other hand, the upper limit of the cover thickness is 1.7 mm or less, preferably 1.5 mm or less, and even more preferably 1.3 mm or less. If the cover is too thin, its resistance to cracking during repeated impacts may be poor. On the other hand, if the cover is too thick, the amount of spin when hitting with a driver (W#1) may be too high, resulting in a loss of distance, or the feel of the short game and putter may become too hard.

[0045] As for the material of the cover mentioned above, various thermoplastic resins used as golf ball materials are preferred, and in particular, ionomer resin is preferable because it achieves superior flight distance by reducing spin during full shots.

[0046] The cover material can be appropriately blended with any additives depending on the application. For example, various additives such as pigments, dispersants, antioxidants, UV absorbers, and light stabilizers can be added. When these additives are blended, the amount blended is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and preferably 10 parts by mass or less, and more preferably 4 parts by mass or less, per 100 parts by mass of the base resin.

[0047] A multi-piece solid golf ball formed by laminating the core, surrounding layer, intermediate layer, and cover (outermost layer) described above can be manufactured by conventional methods such as known injection molding. For example, a multi-piece golf ball can be obtained by sequentially injecting the materials for the surrounding layer and intermediate layer around the core using respective injection molding dies to obtain each covered sphere, and finally, by injection molding the material for the outermost cover layer. Alternatively, a golf ball can be manufactured by wrapping each covered sphere with two pre-formed hemispherical half-cups and then heat-pressure molding them together.

[0048] When a golf ball is subjected to an initial load of 98N (10kgf) and a final load of 1,275N (130kgf), the amount of deflection (mm) is preferably 2.5mm or more, more preferably 2.6mm or more, and even more preferably 2.7mm or more. On the other hand, the upper limit of the above deflection is preferably 3.5mm or less, more preferably 3.3mm or less, and even more preferably 3.1mm or less. If the amount of deflection of the golf ball is too small, i.e., too hard, the amount of spin may increase too much, resulting in a loss of distance, or the feel may become too hard. On the other hand, if the above deflection is too large, i.e., the sphere may become too soft, the rebound of the ball may become too low, resulting in a loss of distance, or the feel may become too soft, or the durability against cracking during repeated impacts may be poor.

[0049] When the deflection amount of the core is C (mm) when an initial load of 98N (10kgf) is applied to a final load of 1,275N (130kgf), and the deflection amount of the ball is B (mm) when an initial load of 98N (10kgf) is applied to a final load of 1,275N (130kgf), the value of CB is preferably 1.00mm or more, more preferably 1.05mm or more, and even more preferably 1.10mm or more, with an upper limit of preferably 1.60mm or less, more preferably 1.50mm or less, and even more preferably 1.40mm or less. If the above value is too small, the amount of spin when taking a full shot will be large, and the target distance may not be achieved. On the other hand, if the above value is too large, the actual initial velocity when taking a full shot will be low, and the target distance may not be achieved.

[0050] [ Hardness relationship of each layer ] In this invention, the hardness relationship of each layer is given by the following formula Cover material hardness > Intermediate layer material hardness, and Material hardness of the surrounding layer ≥ Surface hardness of the core (However, the hardness in the above formula refers to Shore C hardness.) The following conditions must be met, preferably, Cover material hardness > Interlayer material hardness > Enveloping layer material hardness ≥ Core surface hardness The condition is that it satisfies the requirements.

[0051] The difference between the hardness of the cover material and the hardness of the intermediate layer material is greater than 0 in Shore C hardness, preferably 3 or higher, more preferably 7 or higher, with an upper limit of preferably 25 or lower, more preferably 18 or lower, and even more preferably 12 or lower. If the above value is too low, the amount of spin when taking a full shot will increase, and the target distance may not be achieved. On the other hand, if the above value is too high, the actual initial velocity when taking a full shot will decrease, and the target distance may not be achieved, or the durability against cracking when repeatedly struck may be poor.

[0052] The value obtained by subtracting the material hardness of the surrounding layer from the material hardness of the intermediate layer is greater than 0 in Shore C hardness, preferably 2 or more, more preferably 5 or more, and the upper limit is preferably 20 or less, more preferably 15 or less, and even more preferably 10 or less. If the above value is too small, the amount of spin when taking a full shot will increase, and the target distance may not be achieved. On the other hand, if the above value is too large, the actual initial velocity when taking a full shot will decrease, and the target distance may not be achieved, or the crack resistance when repeatedly struck may be poor.

[0053] The value obtained by subtracting the core surface hardness from the material hardness of the surrounding layer is 0 or greater on the Shore C hardness scale, preferably 1 or greater, more preferably 2 or greater, with an upper limit of preferably 17 or less, more preferably 12 or less, and even more preferably 7 or less. If the above value is too small, the amount of spin when taking a full shot will increase, and the target distance may not be achieved. On the other hand, if the above value is too large, the actual initial velocity when taking a full shot will decrease, and the target distance may not be achieved, or the crack resistance when repeatedly struck may worsen.

[0054] [ Relationship between the thickness of each layer and the material hardness value ] In this invention, the value of "material hardness × thickness" between the surrounding layer and the cover is given by the following formula The thickness of the surrounding layer (mm) × the material hardness of the surrounding layer (Shore D hardness) ≥ the thickness of the cover (mm) × the material hardness of the cover (Shore D hardness) The following conditions must be met. The value of {thickness of the surrounding layer (mm) × material hardness of the surrounding layer (Shore D hardness) - thickness of the cover (mm) × material hardness of the cover (Shore D hardness)} is usually 0 or greater, preferably 20 or greater, more preferably 50 or greater, and the upper limit is usually 250 or less, preferably 200 or less, more preferably 120 or less. If the above value deviates from the above range, it becomes difficult to achieve both low spin and high initial ball speed when taking a full shot, and the desired distance may not be achieved.

[0055] Furthermore, in the present invention, the following formula The thickness of the surrounding layer (mm) × the material hardness of the surrounding layer (Shore D hardness) ≥ the thickness of the intermediate layer (mm) × the material hardness of the intermediate layer (Shore D hardness) It is preferable that the following conditions be met. The value of {thickness of the surrounding layer (mm) × material hardness of the surrounding layer (Shore D hardness) - thickness of the intermediate layer (mm) × material hardness of the intermediate layer (Shore D hardness)} is usually 0 or greater, preferably 30 or greater, more preferably 60 or greater, and the upper limit is usually 260 or less, preferably 210 or less, more preferably 130 or less. If the above value deviates from the above range, it becomes difficult to achieve both low spin and high initial ball speed when taking a full shot, and the desired distance may not be achieved.

[0056] [ Thickness relationship of each layer ] In this invention, the thickness relationship of each layer is given by the following formula (Cover thickness + Intermediate layer thickness) < Encircling layer thickness The following conditions must be met. Specifically, the value of surrounding layer thickness / (cover thickness + intermediate layer thickness) is greater than 1.0, preferably 1.1 or more, more preferably 1.2 or more, and the upper limit is preferably 2.0 or less, more preferably 1.8 or less, and even more preferably 1.6 or less. Furthermore, the value obtained by subtracting the total thickness of the cover thickness and intermediate layer thickness from the surrounding layer thickness is greater than 0, preferably 0.2 or more, more preferably 0.4 or more, and the upper limit is preferably 2.1 or less, more preferably 1.8 or less, and even more preferably 1.5 or less. If the values ​​deviate from the above range, it becomes difficult to achieve both low spin on full shots and high initial ball speed, and the desired distance may not be achieved.

[0057] The value obtained by subtracting the intermediate layer thickness from the surrounding layer thickness is preferably 1.00 mm or more, more preferably 1.30 mm or more, and even more preferably 1.60 mm or more, with an upper limit of preferably 3.20 mm or less, more preferably 3.00 mm or less, and even more preferably 2.80 mm or less. If the above value deviates from the above range, it becomes difficult to achieve both low spin and high initial ball speed during full shots, and the desired distance may not be achieved.

[0058] Relationship between volume and hardness of each layer [(Core volume (mm 3 )) × (Shore C hardness of core surface + Shore C hardness of core center) / 2] is defined as Core·vh, [(Volume of the surrounding layer material portion (mm 3 )) × Shore C hardness of the surrounding layer material] is defined as E·vh, [(Volume of the intermediate layer material portion (mm 3 )) × Shore C hardness of the intermediate layer material] is defined as I·vh, when the following formula 0.80 ≤ (E·vh + I·vh) / Core·vh ≤ 2.00 is preferably satisfied. Specifically, the value of (E·vh + I·vh) / Core·vh is preferably 0.80 or more, more preferably 1.00 or more, still more preferably 1.10 or more, and the upper limit value is preferably 2.00 or less, more preferably 1.90 or less, still more preferably 1.80 or less. If it deviates from the above range, it becomes difficult to achieve both low spin at full shot and high initial hitting speed, and the desired flying distance may not be obtained.

[0059] The value of Core·vh is preferably 700 or more, more preferably 800 or more, still more preferably 900 or more, and the upper limit value is preferably 1600 or less, more preferably 1400 or less, still more preferably 1200 or less. If the above value is too large, the spin amount may increase and it may not fly, or the hitting feeling may become too hard. On the other hand, if the above value is too small, the resilience may become too low and it may not fly, or the hitting feeling may become too soft, or the crack durability when repeatedly hitting may deteriorate.

[0060] The value of E·vh is preferably 650 or more, more preferably 750 or more, still more preferably 850 or more, and the upper limit value is preferably 1600 or less, more preferably 1400 or less, still more preferably 1200 or less. If the above value deviates from the above range, the spin amount at full shot may increase and the desired flying distance may not be obtained.

[0061] ​​The value of I·vh is preferably 260 or higher, more preferably 360 or higher, and even more preferably 460 or higher, with an upper limit of preferably 850 or lower, more preferably 700 or lower, and even more preferably 560 or lower. If the above value deviates from the above range, the amount of spin when taking a full shot will increase, and the desired distance may not be achieved.

[0062] Numerous dimples can be formed on the outer surface of the cover described above. There are no particular restrictions on the number of dimples arranged on the cover surface, but preferably there are 250 or more, more preferably 300 or more, and even more preferably 320 or more, with an upper limit of preferably 440 or less, more preferably 400 or less, and even more preferably 360 or less. If the number of dimples exceeds the above range, the ball's trajectory may become lower and the flight distance may decrease. Conversely, if the number of dimples is too low, the ball's trajectory may become higher and the flight distance may not increase. Furthermore, the arrangement of these dimples may have symmetry according to a tetrahedron, octahedron, icosahedron, or other polyhedron, or rotational symmetry along the axis connecting the poles.

[0063] Regarding the types of dimples, it is preferable to form two or more types of dimples with different diameters and / or depths, and more preferably three or more types. Regarding the planar shape of the dimples, one or more types, such as circular, various polygons, dewdrop shapes, and other elliptical shapes, can be used as appropriate. For example, when using circular dimples, the diameter can be approximately 2.5 mm to 6.5 mm, and the depth can be 0.07 mm to 0.30 mm. Regarding the cross-sectional shape of the dimples, one or more types, such as arcs, cones, pan bottoms, and curves expressed by various functions, can be defined in combination, and may have multiple inflection points other than near the edges.

[0064] The dimple occupancy rate (SR value) (%), which is the ratio of the total area of ​​the virtual spherical surface surrounded by the edges of each dimple to the total area of ​​the dimple surface, is preferably between 70% and 90% in order to fully utilize aerodynamic properties. Furthermore, the cylindrical volume ratio V0, which is the value obtained by dividing the spatial volume of the dimples below the plane surrounded by the edges of each dimple by the cylindrical volume with the plane as the base and the maximum depth of the dimple from this base as the height, is preferably between 0.35 and 0.80 in order to optimize the ball's trajectory. Moreover, the VR value, which is the ratio of the total dimple volume formed below the plane surrounded by the edges of the dimples to the ball's spherical volume assuming no dimples exist, is preferably between 0.6% and 1.0%. If the above values ​​deviate from their respective ranges, the trajectory may not yield a good flight distance, and the ball may not achieve a sufficiently satisfactory flight distance. Furthermore, in order to satisfy the rules regarding the symmetry of ball flight distance, the dimple volume near the poles may be smaller and the dimple volume near the equator may be larger compared to the dimple volume near the poles and equator.

[0065] A coating layer can be formed on the cover surface. This coating layer can be applied using various paints, and as the paint, it is preferable to use a paint composition mainly composed of urethane paint made of polyol and polyisocyanate, given the need to withstand the harsh conditions of use of golf balls.

[0066] Examples of the polyol components mentioned above include acrylic polyols and polyester polyols. These polyols may also contain modified polyols, and other polyols can be added to further improve workability.

[0067] It is preferable to use two types of polyester polyols in combination as the polyol component. In this case, if the two types of polyester polyols are component (a) and component (b), the polyester polyol of component (a) can be a polyester polyol in which a cyclic structure has been introduced into the resin backbone. Examples include polyester polyols obtained by polycondensation of a polyol having an alicyclic structure such as cyclohexanedimethanol with a polybasic acid, or by polycondensation of a polyol having an alicyclic structure with diols or triols with a polybasic acid. On the other hand, the polyester polyol of component (b) can be a polyester polyol having a multi-branched structure. Examples include polyester polyols having a branched structure such as "NIPPOLAN 800" manufactured by Tosoh Corporation.

[0068] On the other hand, there are no particular restrictions on the polyisocyanates used; commonly used aromatic, aliphatic, and alicyclic polyisocyanates are acceptable. Specifically, examples include tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, 1,4-cyclohexylene diisocyanate, naphthalene diisocyanate, trimethylhexamethylene diisocyanate, dicyclohexylmethane diisocyanate, and 1-isocyanato-3,3,5-trimethyl-4-isocyanatomethylcyclohexane. These can be used individually or in combination.

[0069] Depending on the painting conditions, various organic solvents can be mixed into the paint composition. Examples of such organic solvents include aromatic solvents such as toluene, xylene, and ethylbenzene; ester solvents such as ethyl acetate, butyl acetate, propylene glycol methyl ether acetate, and propylene glycol methyl ether propionate; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ether solvents such as diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and dipropylene glycol dimethyl ether; alicyclic hydrocarbon solvents such as cyclohexane, methylcyclohexane, and ethylcyclohexane; and petroleum hydrocarbon solvents such as mineral spirits.

[0070] There are no particular restrictions on the thickness of the coating layer made from the above-mentioned paint composition, but it is usually 5 to 40 μm, preferably 10 to 20 μm. The thickness of the coating layer referred to here means the average thickness of the coating layer measured at three locations: the center of the dimple and two locations between the center of the dimple and the dimple edge.

[0071] In this invention, the elastic work recovery rate of the coating layer made of the above-mentioned paint composition must be 60% or more, preferably 80% or more. If the elastic work recovery rate of the coating layer is within this range, the coating layer has high elasticity, resulting in high self-healing function and excellent abrasion resistance. Furthermore, the various performance characteristics of golf balls coated with the above-mentioned paint composition can be improved. The method for measuring the above-mentioned elastic work recovery rate is as follows.

[0072] The elastic work recovery rate is an ultra-microhardness testing method that controls the indentation load on the order of micronewtons (μN) and tracks the indenter depth during indentation with nanometer (nm) precision. It is one parameter of the nanoindentation method used to evaluate the physical properties of coating layers. Conventional methods could only measure the size of the deformation mark (plastic deformation mark) corresponding to the maximum load, but the nanoindentation method allows for automatic and continuous measurement, enabling the relationship between the indentation load and the indentation depth to be obtained. Therefore, it is considered that the physical properties of the coating layer can be evaluated with high accuracy, without the individual differences that exist when visually measuring deformation marks with an optical microscope as in conventional methods. Since the coating layer on the surface of a golf ball is greatly affected by impacts from drivers and various clubs, and the influence of the coating layer on the physical properties of a golf ball is not insignificant, measuring the coating layer with an ultra-microhardness testing method and performing the test with higher precision than conventional methods is a very effective evaluation method.

[0073] Furthermore, the hardness of the coating layer is preferably 40 or higher, more preferably 60 or higher, with an upper limit of preferably 95 or lower, more preferably 85 or lower. This Shore M hardness conforms to ASTM D2240. Furthermore, the hardness of the coating layer is preferably 40 or higher, more preferably 50 or higher, with an upper limit of preferably 80 or lower, more preferably 70 or lower. This Shore C hardness conforms to ASTM D2240. If the coating layer is too hard, the coating may become brittle when repeatedly struck, and may not be able to protect the cover layer. If the coating layer is too hard, the ball surface may be easily scratched when it hits a hard object, which is undesirable.

[0074] When using the above-described coating composition, the coating composition of the present invention can be prepared during painting of a golf ball manufactured by a known method, applied to the surface using a normal painting process, and a coating layer can be formed on the ball surface after a drying process. In this case, suitable painting methods include spray painting, electrostatic painting, dipping, etc., and there are no particular limitations.

[0075] Furthermore, the multi-piece solid golf ball of the present invention can be used in competition and comply with the rules of golf. The outer diameter of the ball is such that it does not pass through a ring with an inner diameter of 42.672 mm, and the mass can preferably be formed to 45.0 to 45.93 g. [Examples]

[0076] 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.

[0077] [Examples 1-5, Comparative Examples 1-8] Core formation After preparing the rubber compositions of Examples 1-4 and Comparative Examples 1-7 shown in Table 1, solid cores were produced by vulcanization molding according to the vulcanization conditions for each example shown in Table 1.

[0078] However, for Example 5 and Comparative Example 8, the cores were prepared based on the formulations shown in Table 1, in the same manner as described above.

[0079] [Table 1]

[0080] The details of each component listed in Table 1 are as follows: • Polybutadiene A: Manufactured by JSR Corporation, product name "BR01" • Polybutadiene B: Manufactured by JSR Corporation, product name "BR51" • Zinc acrylate: "ZN-DA85S" (manufactured by Nippon Shokubai Co., Ltd.) • Organic peroxide (1): Dicumyl peroxide, trade name "Perkmyl D" (manufactured by NOF Corporation) • Organic peroxide (2): A mixture of 1,1-di(t-butylperoxy)cyclohexane and silica, trade name "Perhexa C-40" (manufactured by NOF Corporation) • Anti-aging agent: 2,2-methylenebis(4-methyl-6-butylphenol), trade name "Nocrac NS-6" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) • Zinc oxide: Product name "Triple Zinc Oxide" (manufactured by Sakai Chemical Industry Co., Ltd.)

[0081] Formation of the besieged layer Next, for Examples 1-4 and Comparative Examples 1 and 2, a surrounding layer was formed around the core by injection molding using a surrounding layer material with the No. 1 formulation shown in Table 2. For Examples 5 and Comparative Example 8, the surrounding layer was prepared in the same manner as above, based on the formulations in Table 2. Note that no surrounding layer was formed for Comparative Examples 3-7.

[0082] Formation of the intermediate layer Next, for Examples 1-4 and Comparative Examples 1 and 2, an intermediate layer was formed around the surrounding layer-covered sphere obtained above by injection molding using the intermediate layer material of formulation No. 2 shown in Table 2. For Comparative Examples 3-7, an intermediate layer was formed around the core obtained above by injection molding using the intermediate layer material of formulation No. 1 or No. 2 shown in Table 2. For Example 5 and Comparative Example 8, the surrounding layer was prepared based on the formulations in Table 2, similar to Examples 1-4 and Comparative Examples 1 and 2.

[0083] Formation of the cover (outermost layer) Next, a cover (outermost layer) was formed around the intermediate layer covering sphere of each of the above examples by injection molding using a cover material with formulation No. 3 of the formulations shown in Table 2. At this time, a predetermined number of dimples common to all examples and comparative examples were formed on the cover surface. For Example 5 and Comparative Example 8, covers with a number of dimples formed on the outer surface were manufactured in the same manner as above.

[0084] [Table 2]

[0085] The main ingredients listed in the table are as follows: "HPF1000" and "HPF2000" are trademarks of THE DOW CHEMICAL COMPANY. "Hymiran 1605," "Hymiran 1706," and "AM7329" are ionomers manufactured by Mitsui Dow Polychemicals. "Sarlyn 7930" and "Sarlyn 6320" are ionomers manufactured by The Dow Chemical Company. "Nucrell 9-1" is a trademark of Dupont. "Low molecular weight polyolefin" Sanyo Chemical Industries, Ltd.'s "Sunwax 161-P" "Magnesium stearate" - "Zinc Stearate G" manufactured by NOF Corporation. "Titanium dioxide" "A-190" manufactured by Sakai Chemical Industry Co., Ltd.

[0086] The dimples common to all embodiments and comparative examples are eight types of circular dimples, the details of which are shown in Table 3 below, and their arrangement is as shown in Figure 2. Figure 2(A) shows a plan view of the dimples as seen from directly above, centered on the pole of the ball, and Figure 2(B) shows a plan view of the dimples as seen from diagonally above, with the pole of the ball shifted upward in the same way as in Figure 2(A). In Figure 2, the symbol D indicates a dimple, and the symbol P indicates the pole portion of the golf ball G.

[0087] [Table 3]

[0088] Definition of a dimple Edge: The highest point in the cross-section passing through the center of the dimple. Diameter: The diameter of the plane surrounded by the rim of the dimple. Depth: Maximum depth of the dimple from the plane surrounded by the edges of the dimple. SR: The ratio of the total dimple area, defined by the plane enclosed by the edges of the dimples, to the ball's surface area assuming no dimples exist. Dimple volume: The volume of the dimple beneath the plane surrounded by the edges of the dimple. Cylinder volume ratio V0: The ratio of the dimple volume to the volume of a cylinder with the same diameter and depth as the dimple. VR: The sum of the dimple volumes formed downward from the plane surrounded by the edges of the dimples is the ball volume assuming no dimples exist.

[0089] For each golf ball obtained, various physical properties such as the surface and core hardness, the outer diameter of the core and each covering sphere, the thickness of each layer, and the material hardness were evaluated using the method described below and are shown in Table 4. In Table 4, "Enclosing layer (thickness × hardness) - Cover (thickness × hardness)" means {thickness of the enclosing layer (mm) × material hardness of the enclosing layer (Shore D hardness) - thickness of the cover (mm) × material hardness of the cover (Shore D hardness)}, and "Enclosing layer (thickness × hardness) - Intermediate layer (thickness × hardness)" means {thickness of the enclosing layer (mm) × material hardness of the enclosing layer (Shore D hardness) - thickness of the intermediate layer (mm) × material hardness of the intermediate layer (Shore D hardness)}.

[0090] Outer diameter of each sphere in the core, surrounding layer covering sphere, and intermediate layer covering sphere The spheres were kept at a constant temperature of 23.9±1℃ for at least 3 hours. Then, in a room at 23.9±2℃, measurements were taken at five arbitrary points on the surface, and the average value was taken as the measurement value for each sphere. The average value for all 10 spheres was then calculated.

[0091] Ball diameter The balls were kept at a constant temperature of 23.9±1℃ for at least 3 hours. Then, in a room at 23.9±2℃, measurements were taken at 15 arbitrary non-dimpled areas, and the average value was taken as the measurement value for one ball. The average value for 10 measured balls was then calculated.

[0092] Core and ball deflection The target coated sphere of the core or ball is placed on a hard plate, and the amount of deflection is measured when an initial load of 98N (10kgf) is applied and then a final load of 1275N (130kgf) is applied. The above deflection amounts were measured in a room at 23.9±2℃ after the temperature was adjusted in a constant temperature chamber at 23.9±1℃ for at least 3 hours. The pressure rate of the head used to compress the core, each layer of coated spheres, or ball is set to 10mm / s.

[0093] Core core and surface hardness The core surface is spherical, and the hardness Cs of the core was measured using the Shore C hardness scale according to ASTM D2240, with the hardness tester needle set approximately perpendicular to the spherical surface. The hardness measurement was performed using the "P2" automatic rubber hardness tester manufactured by Polymer Instruments Co., Ltd., which is equipped with a Shore C hardness tester. The maximum value was read. All measurements were performed under conditions of 23±2℃. The core's central hardness Cc was measured by cutting the core into a hemispherical shape, flattening the cross-section, and pressing the hardness tester needle perpendicularly against the measurement area. The value is expressed as the Shore C hardness scale.

[0094] Material hardness (Shore C hardness, Shore D hardness) of the surrounding layer, intermediate layer, and cover. Each layer of resin material was molded into a 2mm thick sheet and left at a temperature of 23±2℃ for two weeks. Three sheets were stacked together for measurement. Shore C and Shore D hardness were measured using Shore C and Shore D hardness testers compliant with the ASTM D2240 standard. For hardness measurement, an automatic rubber hardness tester "P2" manufactured by Polymer Instruments Co., Ltd., equipped with either a Shore C or Shore D hardness tester, was used. The maximum value was read.

[0095] [Table 4]

[0096] The flight performance (1) to (3) of each golf ball was evaluated as follows. The results are shown in Table 5.

[0097] (1) Flight performance (W#1) A golf swing robot was fitted with a driver (W#1), and the distance of the ball when struck at a head speed of 45 m / s was measured and judged according to the following criteria. The club used was a Bridgestone Sports "TourStage X-Drive 410 (2007 model)" (loft angle: 9.5°). Similarly, the spin rate was measured using an initial condition measurement device immediately after impact. <Judgment criteria> ◎ ··· Total distance 235.0m or more 〇 ··· Total distance between 234.0m and 235.0m × ··· Total distance less than 234.0m

[0098] (2) Flight performance (W#1) A golf swing robot was fitted with a driver (W#1), and the distance of the shot was measured when it was struck at a head speed of 40 m / s. The distance was judged according to the following criteria. The club used was the same as above, a Bridgestone Sports "TourStage X-Drive 410 (2007 model)" (loft angle: 9.5°). Similarly, the spin rate was measured using an initial condition measurement device on the ball immediately after impact. <Judgment criteria> ◎ ··· Total distance 208.0m or more 〇 ··· Total distance between 207.0m and less than 208.0m × ··· Total distance less than 207.0m

[0099] (3) Flight performance (I#6) A golf hitting robot was fitted with an iron (I#6) and the distance of the ball when struck at a head speed of 40 m / s was measured and judged according to the following criteria. The club used was Bridgestone Sports' "J's Classical Edition" (I#6). Similarly, the spin rate was measured using an initial condition measurement device immediately after impact. <Judgment criteria> ◎ ··· Total distance 160.0m or more 〇 ··· Total distance between 158.5m and 160.0m × ··· Total distance less than 158.5m

[0100] [Table 5]

[0101] As shown in the results in Table 5, the golf balls of Comparative Examples 1 to 8 are inferior to the present invention (Example) in the following respects. In Comparative Example 1, the value of (thickness of the surrounding layer × material hardness - thickness of the cover × material hardness) is negative, meaning that the difference between the core deflection and the ball deflection is less than 1.00 mm, and the material hardness of the surrounding layer is softer than the core surface hardness. As a result, for distance (2) and distance (3), the balance between the amount of spin and the actual initial velocity when hitting a full shot is poor, and the desired distance is not achieved. In Comparative Example 2, the value of (thickness of the surrounding layer × material hardness - thickness of the cover × material hardness) is negative, and the difference between the core deflection and the ball deflection is less than 1.00 mm. As a result, for distance (1) and distance (3), the balance between the amount of spin and the actual initial velocity when a full shot is poor, and the desired distance is not achieved. Comparative Example 3 is a three-piece ball structure without a surrounding layer. As a result, the balance between the amount of spin during a full shot and the actual initial ball speed is poor, resulting in a failure to achieve the desired distance (2). Comparative Example 4 is a three-piece ball structure without a surrounding layer. As a result, the balance between the amount of spin during a full shot and the actual initial ball speed is poor for both distance (1) and distance (2), preventing the desired distance from being achieved. Comparative Example 5 is a three-piece ball structure without a surrounding layer, and as a result, the balance between the amount of spin during a full shot and the actual initial velocity is poor, resulting in a failure to achieve the desired distance (2). Comparative Example 6 is a three-piece ball structure without a surrounding layer. As a result, the balance between the amount of spin during a full shot and the actual initial ball speed is poor for both distance (1) and distance (2), resulting in the inability to achieve the desired distance. Comparative Example 7 is a three-piece ball structure without a surrounding layer. As a result, the balance between the amount of spin during a full shot and the actual initial ball speed is poor for both distance (2) and distance (3), resulting in the inability to achieve the desired distance. In comparative example 8, the hardness of the cover material is softer than the hardness of the intermediate layer material, resulting in a large amount of spin when taking a full shot with a driver (W#1), and thus failing to achieve the desired distance.

Claims

1. A multi-piece solid golf ball comprising a core, a surrounding layer, an intermediate layer, and a cover, wherein the core is formed from a single or multiple layers of rubber composition, and the surrounding layer, intermediate layer, and cover are each formed from a single layer of resin material, and the hardness relationship of each layer is given by the following two formulas The hardness of the cover material > the hardness of the intermediate layer, and Material hardness of the surrounding layer ≥ Surface hardness of the core (However, the hardness in the above formula refers to Shore C hardness.) In addition to satisfying the following equation The thickness of the surrounding layer (mm) × the material hardness of the surrounding layer (Shore D hardness) ≥ the thickness of the cover (mm) × the material hardness of the cover (Shore D hardness) If the following conditions are met, and the deflection amount when the core is subjected to an initial load of 98 N (10 kgf) and a final load of 1,275 N (130 kgf) is C (mm), and the deflection amount when the ball is subjected to an initial load of 98 N (10 kgf) and a final load of 1,275 N (130 kgf) is B (mm), then the value of C - B is 1.00 mm or more, and furthermore, if the value of [Core volume (mm³) × (Shore C hardness of core surface + Shore C hardness of core center) / 2] is Core・vh, the value of [Volume of surrounding layer material (mm³) × Shore C hardness of surrounding layer material] is E・vh, and the value of [Volume of intermediate layer material (mm³) × Shore C hardness of intermediate layer material] is I・vh, then the following formula 1.10≦(E・vh + I・vh) / Core・vh ≦1.46 A multi-piece solid golf ball characterized by satisfying the following conditions.

2. Furthermore, the following formula The thickness of the surrounding layer (mm) × the material hardness of the surrounding layer (Shore D hardness) ≥ the thickness of the intermediate layer (mm) × the material hardness of the intermediate layer (Shore D hardness) A multi-piece solid golf ball according to claim 1 that satisfies the requirements.

3. The relationship between the thicknesses of each layer is given by the following formula: (Cover thickness + Intermediate layer thickness) < Surrounding layer thickness A multi-piece solid golf ball according to claim 1 or 2 that satisfies the requirements.

4. The relationship between the hardness of each layer is given by the following formula Cover material hardness > Interlayer material hardness > Surrounding layer material hardness ≥ Core surface hardness (However, the hardness in the above formula refers to Shore C hardness.) A multi-piece solid golf ball according to claim 1 or 2 that satisfies the requirements.

5. The surrounding layer and / or the resin material of the intermediate layer consist of the following components (A) to (D): (a-1) A binary random copolymer of olefin-unsaturated carboxylic acid and / or a metal ion neutralized product of a binary random copolymer of olefin-unsaturated carboxylic acid, (a-2) A ternary random copolymer of olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester and / or a metal ion neutralized product of the ternary random copolymer of olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester, (A) base resin formulated in a mass ratio of 100:0 to 0:100, (B) A resin component blended with a non-ionomer thermoplastic elastomer in a mass ratio of 100:0 to 50:50 for 100 parts by mass, (C) 5 to 120 parts by mass of fatty acids and / or derivatives thereof having a molecular weight of 228 to 1500, (D) 0.1 to 17 parts by mass of a basic inorganic metal compound capable of neutralizing the unneutralized acid groups in components (A) and (C) above. A multi-piece solid golf ball according to claim 1 or 2, which is a highly neutralizing resin material comprising the essential components.

6. The multi-piece solid golf ball according to claim 5, wherein both the surrounding layer and the intermediate layer are resin materials of different types of highly neutralizing resin materials, each containing components (A) to (D) as essential components.

7. The relationship between the thicknesses of each layer is given by the following formula Encircling layer thickness / (cover thickness + interlayer thickness) ≥ 1.2 A multi-piece solid golf ball according to claim 1 or 2 that satisfies the requirements.

8. The relationship between the core diameter and the ball diameter is given by the following formula 0.65 ≤ (core diameter) / (ball diameter) ≤ 0.78 A multi-piece solid golf ball according to claim 1 or 2 that satisfies the requirements.

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