Multi-piece solid golf ball

Abstract

To provide a multi-piece solid golf ball of a distance system emphasizing a carry, which achieves a satisfactory distance in hitting with a driver (W#1) and an iron by an amateur user, and has good durability on repeated impact and soft feel.SOLUTION: A multi-piece solid golf ball includes a core 1, an intermediate layer 2, and a cover 3. The core is formed of a rubber composition of a single layer or plural layers. The intermediate layer is formed by using an ionomer resin as a main material. The intermediate layer and the cover are made of a single layer, and respectively contain an inorganic granular filler. The multi-piece solid golf ball satisfies the following three expressions: surface hardness of the ball>surface hardness of a sphere (an intermediate layer covering sphere) where the core is covered with the intermediate layer; surface hardness of the ball (Shore D)-center hardness (Shore D) of the core≥37; and specific gravity of the cover>specific gravity of the intermediate layer.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Conventionally, for the purpose of softening a golf ball, that is, improving resilience and feel, a method of softening the core in terms of feel and covering the core with a hard cover to compensate for resilience around the core has been generally used. However, according to this method, although the resilience is improved, there is a problem that the cover cracks due to repeated impacts.

[0003] On the other hand, many techniques have been proposed for adding an inorganic filler to a cover material. For example, the main focus is on increasing the moment of inertia of the ball by increasing the specific gravity of the cover and improving the flight distance performance. However, there is a problem that if too much inorganic filler is added, the resilience and crack durability of the ball are impaired. In addition, a technique has been proposed to obtain a solid golf ball in which the crack durability of the cover under repeated impacts is significantly improved by adding a predetermined amount of an inorganic filler having a certain specific gravity as a reinforcing material to the cover material. In addition, in a multi-piece solid golf ball including a core, an intermediate layer, and a cover, in Patent Documents 1 to 23 below, many techniques have been proposed to obtain a golf ball having a balance of flight distance, feel, and crack durability by blending a granular inorganic filler into the intermediate layer or the cover.

[0004] However, it is difficult to say that these proposed golf balls are excellent in flight performance, soft in feel, have a good hitting feeling, and are excellent in crack durability during repeated impacts when used by amateur golfers whose head speed (HS) is not as high as that for professionals or advanced players. Therefore, a problem remains in this regard.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2000-5341 [Patent Document 2] Japanese Patent Publication No. 2000-51396 [Patent Document 3] Japanese Patent Publication No. 2000-51397 [Patent Document 4] Japanese Patent Publication No. 2000-51398 [Patent Document 5] Japanese Patent Publication No. 2002-355343 [Patent Document 6] Japanese Patent Publication No. 2002-355344 [Patent Document 7] Japanese Patent Publication No. 2000-60997 [Patent Document 8] Japanese Patent Publication No. 2000-60999 [Patent Document 9] Japanese Patent Publication No. 2000-70409 [Patent Document 10] Japanese Patent Publication No. 2000-70411 [Patent Document 11] Japanese Patent Publication No. 2001-79116 [Patent Document 12] Japanese Patent Publication No. 2001-340494 [Patent Document 13] Japanese Patent Publication No. 2003-759 [Patent Document 14] Japanese Patent Publication No. 2003-760 [Patent Document 15] Japanese Patent Publication No. 2003-761 [Patent Document 16] Japanese Patent Publication No. 2003-762 [Patent Document 17] Japanese Patent Publication No. 2003-126298 [Patent Document 18] Japanese Patent Publication No. 2004-97802 [Patent Document 19] Japanese Patent Publication No. 2008-194521 [Patent Document 20] Japanese Patent Publication No. 2008-194524 [Patent Document 21] Japanese Patent Publication No. 2011-92708 [Patent Document 22] Japanese Patent Publication No. 2012-148072 [Patent Document 23] Japanese Patent Publication No. 2003-250931 [Overview of the project] [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 offers good distance when hit with a driver (W#1) and an iron when used by an amateur user, has good durability for repeated impacts, and furthermore has a soft feel. [Means for solving the problem]

[0007] The inventors of the present invention have conducted diligent studies to achieve the above objectives and have found that, in a multi-piece solid golf ball comprising a core, an intermediate layer, and a cover, the ball comprises a core formed from a single or multiple layers of rubber composition, an intermediate layer mainly composed of ionomer resin, and a cover, wherein the intermediate layer and the cover each contain an inorganic granular filler, and the surface hardness of the ball is set higher than the surface hardness of a sphere with the intermediate layer covering the core (intermediate layer-covered sphere). This results in a distance-oriented ball characteristic that prioritizes distance without considering spin performance in the short game, and by setting the specific gravity of the cover higher than the specific gravity of the intermediate layer, good flight performance and durability for repeated impacts when used by amateur users with a driver (W#1) and irons are obtained, leading to the present invention.

[0008] That is, the golf ball of the present invention is a distance-based multi-piece solid golf ball that emphasizes flight distance without considering the spin performance in short games. It has a hard cover, an intermediate layer mainly made of ionomer softer than the cover, and a ball structure composed of a single-layer or multi-layer rubber core. As described above, the relationship between the intermediate layer specific gravity and the cover specific gravity is specified. When an amateur user hits it, it satisfies the excellent flight distance performance during a full shot with a driver (W#1) and the excellent flight distance performance during a full shot with an iron. Preferably, by adding an inorganic granular filler to the cover and the intermediate layer, the reinforcing effect of these layers is enhanced, and the cracking durability due to repeated hitting is enhanced.

[0009] Therefore, the present invention provides the following multi-piece solid golf ball. 1. A multi-piece solid golf ball comprising a core, an intermediate layer, and a cover, wherein the core is formed of a single-layer or multi-layer rubber composition, the intermediate layer is formed mainly of an ionomer resin, both the intermediate layer and the cover are single layers, and each contains an inorganic granular filler. The following three formulas Surface hardness of the ball > Surface hardness of the sphere with the intermediate layer covering the core (intermediate layer-covered sphere) Surface hardness of the ball (Shore D) - Core center hardness (Shore D) ≥ 41 Specific gravity of the cover > Specific gravity of the intermediate layer are satisfied Furthermore, when the Shore C hardness of the core surface is Cs and the Shore C hardness of the core center is Cs, the value of Cs-Cc is 20 or less. A multi-piece solid golf ball characterized by this. 2. The main material of the cover is an ionomer resin, and the main material of the intermediate layer is the following components (a) to (d), (a) An olefin-unsaturated carboxylic acid binary random copolymer and / or a metal ion neutralized product of an olefin-unsaturated carboxylic acid binary random copolymer, and (b) An olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary random copolymer and / or a metal ion neutralized product of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary random copolymer, and a base resin in which the blending ratio of component (a) and component (b) is 100:0 to 0:100 by mass ratio, (c) Fatty acids having a molecular weight of 228 or more and 1500 or less or derivatives thereof, (d) A basic inorganic metal compound capable of neutralizing the acid groups in the above base resin and component (c) An ionomer resin composition containing the above, and in which 50 mol% or more of the acid groups contained in the above base resin and component (c) are neutralized in The multi-piece solid golf ball according to the above item 1. 3. The multi-piece solid golf ball according to the above item 1 or 2, wherein the surface hardness of the ball is 65 or more in Shore D hardness. 4. The multi-piece solid golf ball according to any one of the above items 1 to 3, wherein the specific gravity of the cover is 1.10 or more and the specific gravity of the intermediate layer is 1.05 or more. 5. the above The multi-piece solid golf ball according to any one of the above items 1 to 4, wherein the value of Cs - Cc is 12 or more and 20 or less. 6. In the relationship between the surface hardness (Cs) of the core, the core center hardness (Cc), and the hardness (Cm) at the midpoint between the core surface and the core center ( However, all of these hardness values ​​are Shore C hardness values. ), in the following formula (Cs - Cm) / (Cm - Cc) ≧ 1.2 The multi-piece solid golf ball according to any one of the above items 1 to 5 that satisfies. 7. A multi-piece solid golf ball including a core, an intermediate layer, and a cover, wherein the core is formed of a single-layer or multiple-layer rubber composition, the intermediate layer is formed mainly of an ionomer resin, and the following three formulas The surface hardness of the ball > the surface hardness of the sphere with the intermediate layer covering the core (intermediate layer-covered sphere) The surface hardness of the ball (Shore D) - the core center hardness (Shore D) ≧ 41 The specific gravity of the cover > the specific gravity of the intermediate layer (However, the specific gravity of the intermediate layer ≧ 1.05, the specific gravity of the cover ≧ 1.10) Satisfy, and When the Shore C hardness of the core surface is Cs and the Shore C hardness of the core center is Cs, the value of Cs-Cc is 20 or less. A multi-piece solid golf ball characterized by this. 8. The main material of the cover is an ionomer resin, and the main material of the intermediate layer is the following components (a) to (d), (a) 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, (b) A base resin comprising an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester terranandic copolymer and / or a metal ion neutralized product of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester terranandic copolymer, wherein the blending ratio of component (a) to component (b) is 100:0 to 0:100 by mass, (c) Fatty acids or derivatives thereof with a molecular weight of 228 or more and 1500 or less, (d) Basic inorganic metal compounds that can neutralize the acidic groups in the base resin and component (c) above. An ionomer resin composition containing the above base resin and component (c), wherein 50 mol% or more of the acid groups contained in the base resin and component (c) are neutralized. in A multi-piece solid golf ball as described in item 7 above. 9. The intermediate layer and cover each contain an inorganic granular filler, as described in 7 or 8 above, for the multi-piece solid golf ball. 10. A multi-piece solid golf ball as described in any of items 7-9 above, wherein the surface hardness of the ball is 65 or higher on the Shore D scale. 11. the above A multi-piece solid golf ball as described in any of items 7-10 above, wherein the Cs-Cc value is between 12 and 20. 12. Core surface hardness (Cs), core center hardness (Cc), and hardness at the midpoint between the core surface and the core center (Cm) However, all of these hardness values ​​are Shore C hardness values. In relation to ), the following formula (Cs-Cm) / (Cm-Cc) ≥ 1.2 A multi-piece solid golf ball as described in any of the above 7-11, which satisfies the requirements.

[0010] In this specification, "amateur golfer" refers to a golfer whose head speed (HS) when hitting with a driver (W#1) is in the medium to low head speed range of approximately 30 to 43 m / s. [Effects of the Invention]

[0011] According to the golf ball of the present invention, amateur users can achieve superior distance performance when hitting with a driver (W#1) full shot, as well as superior distance performance when hitting with an iron full shot. Furthermore, the golf ball of the present invention has good crack resistance from repeated impacts and also provides a soft and pleasant feel. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic cross-sectional view of a golf ball, which is one embodiment of the present invention.

[0013] 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 a core 1, an intermediate layer 2 covering the core, and a cover 3 covering the intermediate layer. The intermediate layer 2 is formed as a single layer and contains an inorganic granular filler 2a. The cover 3 is formed as a single layer, and usually has numerous dimples D formed on its surface, as well as a paint layer 4 formed by coating. The cover 3, excluding the paint layer, is located as 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 as two or more layers.

[0014] The core diameter is preferably 35.9 mm or more, more preferably 36.7 mm or more, and more preferably 37.0 mm or more, with an upper limit of preferably 39.5 mm or less, more preferably 38.3 mm or less, and even more preferably 37.6 mm or less. If the core diameter is too small, the amount of spin will increase when hitting with a driver (W#1), which may prevent golfers with slower swing speeds from achieving their desired distance. On the other hand, if the core diameter is too large, the durability against repeated impacts may be poor.

[0015] 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 3.8mm or more, more preferably 4.0mm or more, and even more preferably 4.2mm or more, with an upper limit of preferably 5.5mm or less, more preferably 5.0mm or less, and even more preferably 4.8mm 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.

[0016] The core described above consists of one or more layers of vulcanized molded products of a rubber composition mainly composed of rubber material, preferably formed as a single layer. If the core material is not rubber, the rebound may be low and the ball may not fly far. Also, if multiple layers are used, cracks may easily occur at the interface, and initial velocity loss may occur when a full shot is made, so care must be taken to avoid large differences in hardness at the interface.

[0017] The rubber composition for the core described above 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.

[0018] 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.

[0019] 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.

[0020] The above-mentioned unsaturated carboxylic acid and / or its metal salt are usually blended in an amount of 8 parts by mass or more, preferably 12 parts by mass or more, more preferably 17 parts by mass or more, with an upper limit of 50 parts by mass or less, preferably 40 parts by mass or less, and more preferably 30 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.

[0021] 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.

[0022] 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 4 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 7 parts by mass or more, per 100 parts by mass of the base rubber. The upper limit of this amount is preferably 100 parts by mass or less, more preferably 75 parts by mass or less, and even more preferably 50 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.

[0023] 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.

[0024] There are no particular restrictions on the amount of 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 0.5 parts by mass or less, per 100 parts by mass of base rubber. If this amount is too high or too low, 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.

[0025] 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.

[0026] The organic sulfur compound is added in an amount of 0.03 parts by mass or more, preferably 0.05 parts by mass or more, more preferably 0.07 parts by mass or more, with an upper limit 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 amount added is too high, the hardness will become too soft, and if it is too low, improvement in rebound properties cannot be expected.

[0027] 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.

[0028] Next, the hardness distribution of the core described above will be explained. Note that the core hardness described below primarily 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.

[0029] The core's central hardness (Cc) is preferably 50 or higher, more preferably 55 or higher, and even more preferably 58 or higher, with an upper limit of preferably 66 or lower, more preferably 64 or lower, and even more preferably 62 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 durability against cracking after repeated impacts may worsen.

[0030] 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.

[0031] Furthermore, when the core's central hardness (Cc) is expressed in Shore D, its hardness value (Dc) is preferably 18 or higher, more preferably 22 or higher, and even more preferably 25 or higher, with an upper limit of preferably 32 or lower, more preferably 30 or lower, and even more preferably 28 or lower. Also, when the core's surface hardness (Cs) is expressed in Shore D, its hardness value (Ds) is preferably 34 or higher, more preferably 36 or higher, and even more preferably 38 or higher, with an upper limit of preferably 48 or lower, more preferably 45 or lower, and even more preferably 43 or lower.

[0032] The hardness (Cm) at the midpoint between the core surface and the core center is preferably 55 or higher, more preferably 60 or higher, and even more preferably 63 or higher, with an upper limit of preferably 72 or lower, more preferably 70 or lower, and even more preferably 68 or lower. Deviating from these hardness values ​​may lead to unfavorable consequences similar to those described for the core's central hardness (Cc).

[0033] The difference between the core's surface hardness (Cs) and its core's core hardness (Cc) is preferably 12 or more, more preferably 13 or more, and even more preferably 14 or more, with an upper limit of preferably 24 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 this value is too large, the actual initial ball speed may decrease, resulting in reduced distance, or the resistance to cracking due to repeated impacts may worsen.

[0034] The ratio of the slope of the hardness distribution of the surface portion to the center portion of the core, i.e., (Cs-Cm) / (Cm-Cc), is preferably 1.2 or more, more preferably 1.4 or more, and even more preferably 1.6 or more, with an upper limit of preferably 3.0 or less, more preferably 2.4 or less, and even more preferably 1.8 or less. If this ratio is too small, the low-spin effect during full shots may be insufficient, resulting in a loss of the target distance. On the other hand, if this ratio is too large, the actual initial ball speed during full shots may be low, resulting in a loss of the target distance, or the durability against cracking after repeated impacts may be poor.

[0035] Next, I will explain the middle class. The material hardness of the intermediate layer is not particularly limited, but is preferably 40 or higher on the Shore D scale, more preferably 44 or higher, and even more preferably 48 or higher, with an upper limit of preferably 60 or lower, more preferably 58 or lower, and even more preferably 55 or lower. The surface hardness of the sphere (intermediate layer-coated sphere) with the core covered by the intermediate layer is preferably 46 or higher on the Shore D scale, more preferably 50 or higher, and even more preferably 54 or higher, with an upper limit of preferably 66 or lower, more preferably 64 or lower, and even more preferably 61 or lower. If the material hardness and surface hardness of these intermediate layers are 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 resistance to cracking due to repeated impacts may worsen. On the other hand, if the material hardness and surface hardness of the intermediate layer are too hard compared to the above range, the resistance to cracking due to repeated impacts may worsen, and the feel of the shot may deteriorate.

[0036] The material hardness of the intermediate layer, expressed as Shore C hardness, is preferably 63 or higher, more preferably 68 or higher, and even more preferably 74 or higher, with an upper limit of preferably 89 or lower, more preferably 87 or lower, and even more preferably 83 or lower.

[0037] The thickness of the intermediate layer is preferably 0.9 to 2.4 mm, more preferably 1.2 to 2.1 mm, and even more preferably 1.3 to 1.6 mm. If the thickness of the intermediate layer deviates from the above range, the low-spin effect may be insufficient during driver (W#1) shots, resulting in reduced distance.

[0038] For the intermediate layer material, an ionomer resin composition is used. In particular, to achieve superior distance by reducing spin during full shots with a driver (W#1) when hit by an amateur user, it is preferable to use the highly neutralized ionomer resin composition described later.

[0039] As a highly neutralizing ionomer resin material, a material can be suitably used that contains a base resin as an essential component, which is a mixture of (a) a metal ion neutralized product of an olefin-unsaturated carboxylic acid binary random copolymer and / or an olefin-unsaturated carboxylic acid binary random copolymer and (b) a metal ion neutralized product of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester terrandom copolymer and / or an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester terrandom copolymer.

[0040] The components (a) and (b) described above may be commercially available products. For example, as random copolymers of component (a), Nucrel N1560, N1214, N1035, and AN4221C (all manufactured by Mitsui Dow Polychemicals) can be used, and as random copolymers of component (b), for example, Nucrel AN4311, AN4318, and AN4319 (all manufactured by Mitsui Dow Polychemicals) can be used.

[0041] Furthermore, examples of metal ion neutralized products of the random copolymer of component (a) include Hymiran 1554, 1557, 1601, 1605, 1706, and AM7311 (all manufactured by Mitsui Dow Polychemicals), and Surlyn 7930 (manufactured by The Dow Chemical Company), etc., and examples of metal ion neutralized products of the random copolymer of component (b) include Hymiran 1855, 1856, and AM7316 (all manufactured by Mitsui Dow Polychemicals), and Surlyn 6320, 8320, 9320, and 8120 (all manufactured by The Dow Chemical Company), etc. Suitable sodium-neutralized ionomer resins for the metal ion neutralized products of the above random copolymers include Hymiran 1605, 1601, and 1555, etc.

[0042] When preparing the above base resin, the blending ratio of component (a) to component (b) can usually be 100:0 to 0:100 by mass. Furthermore, the proportion of component (a) to the total amount of component (a) and component (b) can preferably be 50% by mass or more, more preferably 75% by mass or more, and most preferably 100% by mass.

[0043] To further improve the feel and rebound properties during impact, (e) a non-ionomer thermoplastic elastomer may be added to the above base resin. Specific examples of this (e) component include olefin-based elastomers, styrene-based elastomers, polyester-based elastomers, urethane-based elastomers, and polyamide-based elastomers. In the present invention, polyester-based elastomers, olefin-based elastomers, and especially olefin-based elastomers consisting of thermoplastic block copolymers containing crystalline polyethylene blocks as hard segments can be suitably used because they can further enhance rebound properties.

[0044] The above component (e) may be a commercially available product, specifically, Dynalon (manufactured by JSR Corporation) and, as a polyester elastomer, Hytrel (manufactured by Toray DuPont Corporation), etc.

[0045] The amount of component (e) can be 0 parts by mass or more. There is no particular upper limit to the amount, but preferably it can be 100 parts by mass or less, more preferably 60 parts by mass or less, even more preferably 50 parts by mass or less, and most preferably 40 parts by mass or less, per 100 parts by mass of the base resin. If the amount of component (e) is too high, the compatibility of the mixture will decrease, which may significantly reduce the durability of the golf ball.

[0046] Next, a fatty acid or its derivative having a molecular weight of 228 to 1500 can be added to the base resin as component (c). This component (c) has an extremely small molecular weight compared to the base resin and appropriately adjusts the melt viscosity of the mixture, contributing particularly to improved fluidity. Furthermore, component (c) contains a relatively high content of acid groups (derivatives), which can suppress excessive loss of resilience.

[0047] The amount of component (c) can be 5 parts by mass or more, preferably 20 parts by mass or more, more preferably 50 parts by mass or more, and even more preferably 70 parts by mass or more, per 100 parts by mass of the resin component obtained by appropriately blending components (a), (b), and (e). The upper limit of this blending amount can be 150 parts by mass or less, preferably 120 parts by mass or less, more preferably 110 parts by mass or less, and even more preferably 100 parts by mass or less. If the amount of component (c) is too low, the melt viscosity may decrease and the processability may decrease, and if it is too high, the durability may decrease.

[0048] (d) A basic inorganic metal compound that can neutralize the acidic groups in the base resin and component (c) can be added as component (d). By incorporating component (d), the acidic groups in the base resin and component (c) are neutralized, and the synergistic effect of these component combinations increases the thermal stability of the resin composition, while simultaneously providing good moldability and improving the resilience of the molded product.

[0049] The amount of component (d) can be 0.1 parts by mass or more, preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more, per 100 parts by mass of the resin component. The upper limit of the amount can be 17 parts by mass or less, preferably 15 parts by mass or less, more preferably 13 parts by mass or less, and even more preferably 10 parts by mass or less. If the amount of component (d) is too low, no improvement in thermal stability or rebound properties will be observed, and if it is too high, the heat resistance of the golf ball material may actually decrease due to the excess basic inorganic metal compound.

[0050] As described above, by blending predetermined amounts of components (c) and (d) with a base resin containing predetermined amounts of components (a) and (b), and a resin component containing an optional component (e), it is possible to create a material with excellent thermal stability, fluidity, and moldability, and furthermore, the resilience of the molded product can be dramatically improved.

[0051] The material containing predetermined amounts of the resin component, component (c), and component (d) described above is recommended to have a high degree of neutralization (highly neutralized). Specifically, it is recommended that 50 mol% or more, preferably 60 mol% or more, more preferably 70 mol% or more, and even more preferably 80 mol% or more of the acid groups in the material are neutralized. By highly neutralizing the acid groups in the material, the exchange reaction that is problematic when using only the base resin and fatty acid (derivative) of the conventional technology described above can be suppressed more reliably, preventing the generation of fatty acids. Furthermore, thermal stability is significantly improved, moldability is good, and molded products with extremely superior resilience compared to conventional ionomer resins can be obtained.

[0052] Here, the degree of neutralization refers to the degree of neutralization of acid groups contained in the mixture of the base resin and the fatty acid (derivative) of component (c), and is different from the degree of neutralization of the ionomer resin itself when ionomer resin is used as the metal ion neutralizer of the random copolymer in the base resin. When comparing a mixture with the same degree of neutralization to ionomer resin alone with the same degree of neutralization, the mixture of the present invention contains a very large number of metal ions due to the inclusion of component (d), resulting in a higher density of ion crosslinks that contribute to improved resilience, and thus providing excellent resilience to the molded product.

[0053] 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, based on 100 parts by mass of the total sum of components (a) to (e) above.

[0054] The intermediate layer material may contain an inorganic granular filler. While the inorganic granular filler is not particularly limited, zinc oxide, barium sulfate, titanium dioxide, etc., can be used as appropriate. Barium sulfate, and particularly preferably precipitated barium sulfate, is preferable due to its excellent resistance to cracking from repeated impacts.

[0055] The average particle size of the inorganic granular filler described above is not particularly limited, but is preferably 0.01 to 100 μm, and more preferably 0.1 to 10 μm. If the average particle size of the inorganic granular filler is too small or too large, the dispersibility during material preparation may deteriorate. The average particle size described above refers to the particle size measured by a particle size distribution analyzer when dispersed in an aqueous solution with a suitable dispersant.

[0056] The amount of the inorganic granular filler described above is not particularly limited, but it is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, per 100 parts by mass of the base resin of the intermediate layer material. There is also no particular upper limit, but it is 45 parts by mass or less, preferably 35 parts by mass or less, and even more preferably 25 parts by mass or less. If the amount of inorganic granular filler is too low, the crack resistance due to repeated impact may be poor. On the other hand, if the amount of inorganic granular filler is too high, the rebound of the ball may be too low, resulting in a loss of distance.

[0057] The specific gravity of the intermediate layer is preferably 1.05 or higher, more preferably 1.07 or higher, and even more preferably 1.08 or higher, with an upper limit of preferably 1.20 or lower, more preferably 1.15 or lower, and even more preferably 1.10 or lower. If the specific gravity of the intermediate layer is too low, the durability against cracking due to repeated impacts may be poor. On the other hand, if the specific gravity of the intermediate layer is too high, the rebound of the ball may be too low, resulting in a loss of distance.

[0058] Next, I will explain the cover. The hardness of the cover material is not particularly limited, but is preferably 59 or higher on the Shore D scale, more preferably 60 or higher, and 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. The surface hardness of the sphere covered with the cover (ball surface hardness) is preferably 65 or higher on the Shore D scale, more preferably 66 or higher, and even more preferably 67 or higher, with an upper limit of preferably 76 or lower, more preferably 74 or lower, and even more preferably 71 or lower. If the hardness of the cover material and the ball surface hardness are 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), and the distance may be reduced. On the other hand, if the hardness of the cover material and the ball surface hardness are too hard compared to the above range, the crack resistance when repeatedly hitting the ball may be poor.

[0059] The hardness of the cover material, expressed as Shore C hardness, is preferably 88 or higher, more preferably 89 or higher, and 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.

[0060] The thickness of the cover is preferably 0.8 mm or more, more preferably 1.1 mm or more, and even more preferably 1.3 mm or more. On the other hand, the upper limit of the cover thickness is preferably 1.7 mm or less, more preferably 1.5 mm or less, and even more preferably 1.4 mm or less. If the cover is too thick, the amount of spin when hitting with a driver (W#1) may increase too much, resulting in a loss of distance, and the feel of the short game and putter may become too hard. On the other hand, if the cover is too thin, its durability against cracking due to repeated impacts may be poor.

[0061] The main material for the cover can be the same or a different type of resin material as the intermediate layer material mentioned above, but ionomer resin is preferable. Using ionomer resin for the cover material makes it possible to achieve both high rebound of the ball and low spin during full shots. On the other hand, if urethane or rubber material is used as the cover material, the cover hardness will be lower, the amount of spin during full shots will increase, and it will be difficult to achieve long distances.

[0062] The cover material may include inorganic granular fillers. The type and particle size of the inorganic granular fillers are the same as those used in the intermediate layer material described above.

[0063] The amount of the inorganic granular filler described above is not particularly limited, but it 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 resin of the cover material. There is also no particular upper limit, but it is preferably 50 parts by mass or less, preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less. If the amount of inorganic granular filler is too low, the crack resistance due to repeated impact may be poor. On the other hand, if the amount of inorganic granular filler is too high, the rebound of the ball may be too low, resulting in a loss of distance.

[0064] The specific gravity of the cover is preferably 1.10 or higher, more preferably 1.12 or higher, and even more preferably 1.14 or higher, with an upper limit of preferably 1.25 or lower, more preferably 1.20 or lower, and even more preferably 1.16 or lower. If the specific gravity of the cover is too low, its resistance to cracking due to repeated impacts may be poor. On the other hand, if the specific gravity of the cover is too high, the rebound of the ball may be too low, resulting in a loss of distance.

[0065] The amount of deflection (mm) of the ball when an initial load of 98N (10kgf) is applied to it, up to a final load of 1,275N (130kgf), is not particularly limited, but is preferably 3.0mm or more, more preferably 3.2mm or more, and even more preferably 3.4mm or more. The upper limit is preferably 4.5mm or less, more preferably 4.2mm or less, and even more preferably 4.0mm or less. If the amount of deflection of the ball is too small, that is, if the ball as a whole 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 to become too hard. On the other hand, if the amount of deflection of the ball is too large, that is, if the ball as a whole is too soft, the rebound of the ball may become too low, causing it to not fly far, or the feel of the ball to become too soft, or the durability against cracking during repeated impacts may be poor.

[0066] In this invention, regarding the relationship between the surface hardness of the ball and the surface hardness of a sphere coated with an intermediate layer on a core (intermediate layer coated sphere), the surface hardness of the ball is higher than that of the intermediate layer coated sphere. The value obtained by subtracting the surface hardness of the intermediate layer coated sphere from the surface hardness of the ball is a Shore D hardness that is greater than 0, preferably 5 or more, more preferably 10 or more, and the upper limit is preferably 25 or less, more preferably 20 or less, and even more preferably 15 or less. If the above value is too small, the amount of spin may increase during full shots with a driver (W#1) and irons, and the target distance may not be achieved. On the other hand, if the above value is too large, the crack resistance when repeatedly struck may be poor.

[0067] The value obtained by subtracting the core surface hardness from the ball's surface hardness is preferably 16 or higher, more preferably 20 or higher, and even more preferably 24 or higher on the Shore D hardness scale. The upper limit is preferably 36 or lower, more preferably 32 or lower, and even more preferably 28 or lower. If the above value is too low, the amount of spin may increase during full shots with a driver (W#1) and irons, and the desired distance may not be achieved. On the other hand, if the above value is too high, the durability against cracking when repeatedly struck may be poor.

[0068] The value obtained by subtracting the core hardness from the surface hardness of the ball is preferably 37 or higher, more preferably 38 or higher, and even more preferably 39 or higher on the Shore D scale, with an upper limit of preferably 46 or lower, more preferably 44 or lower, and even more preferably 42 or lower. A Shore D hardness of 37 or higher for the difference between the surface hardness and the core hardness of the ball means that the ball has a relatively hard cover and a relatively soft core compared to a typical distance golf ball. If the above value is too low, the amount of spin may increase during full shots with a driver (W#1) and irons, and the desired distance may not be achieved. On the other hand, if the above value is too high, the crack resistance when repeatedly struck may be poor.

[0069] Ratio of weight between cover and middle layer This invention relates to a multi-piece golf ball designed for maximum distance, with a cover density greater than that of the intermediate layer. When inorganic granular fillers are not added to the intermediate layer and cover, the harder cover material is more likely to crack after repeated impacts. Therefore, it is preferable to add a slightly larger amount of inorganic granular filler to the more easily cracked cover material, thereby providing a reinforcing effect on the cover. On the other hand, it is preferable to add a slightly smaller amount of inorganic granular filler to the intermediate layer than to the cover material. If too much inorganic granular filler is added to both the intermediate layer and the cover, the ball's rebound may decrease, or the amount of spin on a full shot may increase, resulting in reduced distance. If too little inorganic granular filler is added, the crack resistance after repeated impacts may decrease.

[0070] The difference between the cover specific gravity and the intermediate layer specific gravity, i.e., the value obtained by subtracting the intermediate layer specific gravity from the cover specific gravity, is greater than 0, preferably 0.02 or more, more preferably 0.04 or more, and the upper limit is preferably 0.20 or less, more preferably 0.15 or less, and even more preferably 0.10 or less. If the above value falls outside the above range, the crack resistance when repeatedly struck may deteriorate.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] A paint layer (coating layer) can be formed on the cover surface. This paint layer can be applied using various paints, and as the paint, it is preferable to use a paint composition mainly composed of a urethane paint consisting of polyol and polyisocyanate, given the need to withstand the harsh conditions of use of golf balls.

[0075] There are no particular restrictions on the thickness of the paint layer made from the above paint composition, but it is usually 5 to 40 μm, preferably 10 to 20 μm. The paint layer thickness referred to here is the average thickness of the paint film measured at three locations: the center of the dimple and two locations between the center of the dimple and the dimple edge.

[0076] When using the above-described paint composition, the paint composition of the present invention can be prepared during painting on a golf ball manufactured by a known method, applied to the surface using a normal painting process, and a paint layer can be formed on the ball surface after a drying process. In this case, spray painting, electrostatic painting, dipping, etc., can be suitably used as the painting method, and there are no particular limitations.

[0077] 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]

[0078] 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.

[0079] [Examples 1-4, Comparative Examples 1-7] Core formation For Example 1 and Comparative Examples 1-3, solid cores were produced by preparing the rubber compositions shown in Table 1 and then vulcanizing them under the vulcanization conditions shown in Table 1.

[0080] For Examples 2-4 and Comparative Examples 4-7, cores were prepared based on the formulations shown in Table 1, in the same manner as described above.

[0081] [Table 1]

[0082] Details regarding the above formulation are as follows: • Polybutadiene rubber: Product name "BR01" (manufactured by JSR Corporation) • Zinc acrylate: Product name "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 "Peroxa C-40" (manufactured by NOF Corporation) • Zinc stearate: Product name "Zinc Stearate G" (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.) • Barium sulfate: Product name "Varico #300W" (manufactured by Hakusui Tech Co., Ltd.) • Pentachlorothiophenol zinc salt: Manufactured by Wako Pure Chemical Industries, Ltd.

[0083] Formation of the intermediate layer and cover (outermost layer) Next, for Example 1 and Comparative Examples 1-3, an intermediate layer was formed by injection molding using an injection mold with the intermediate layer resin material No. 1 or No. 2 shown in Table 2 around the core surface. Then, using a different injection mold, a cover was formed by injection molding using the cover (outermost layer) resin material No. 3 or No. 4 shown in Table 2 around the intermediate layer-covered sphere.

[0084] For Examples 2-4 and Comparative Examples 4-7, an intermediate layer is formed by injection molding of the intermediate layer resin material No. 1 or No. 2 shown in Table 2 around the core surface using an injection molding die. Then, using another injection molding die, a cover is formed by injection molding of the cover (outermost layer) resin material No. 3, No. 5, or No. 6 shown in Table 2 around the intermediate layer-covered sphere.

[0085] [Table 2]

[0086] The details of the ingredients listed in the table above are as follows: • "Nucrel AN4319" is a terpolymer manufactured by Mitsui Dow Polychemicals. • "Hymilan 1555", "Hymilan 1557", "Hymilan 1601", "Hymilan 1605", and "Hymilan 1706" are ionomer resins manufactured by Mitsui Dow Polychemicals. • "AM7329" and "AM7327" are ionomer resins manufactured by Mitsui Dow Polychemicals. • "Sarlyn 8320" Ionomer resin manufactured by The Dow Chemical Company • "Magnesium stearate" manufactured by NOF Corporation, "Magnesium Stearate G" • Magnesium oxide, manufactured by Kyowa Chemical Industry Co., Ltd., "Kyowa Mag MF150" • "Barium Sulfate" - "Precipitating Barium Sulfate 300" manufactured by Sakai Chemical Industry Co., Ltd. • Titanium dioxide, manufactured by Ishihara Sangyo Co., Ltd., "Typeque R550"

[0087] For each golf ball obtained, various physical properties such as the hardness of the core surface and center, the outer diameter of the core and each coated sphere, the thickness and material hardness of each layer, and the surface hardness of each coated sphere were evaluated using the method described below and are shown in Table 3.

[0088] Outer diameter of each sphere in the core and intermediate layer covering spheres The spheres to be measured are conditioned in a constant temperature bath adjusted to 23.9±1℃ for at least 3 hours, and then measured in a room at 23.9±2℃. Five arbitrary points on the surface are measured, and the average value is taken as the measurement value for each sphere. The average value for all 10 measured spheres is then calculated.

[0089] Ball diameter The balls to be measured are conditioned in a constant temperature chamber set to 23.9±1℃ for at least 3 hours, and then measured in a room at 23.9±2℃. 15 measurements are taken at arbitrary points on the ball without dimples, and the average value is taken as the measurement value for one ball. The average value for 10 balls is then calculated.

[0090] Core and ball deflection The core or ball to be measured is temperature-controlled in a constant-temperature chamber adjusted to 23.9±1℃ for at least 3 hours, and then measured in a room at 23.9±2℃. The target coated sphere of the core or ball is placed on a hard plate, and the amount of deflection is measured from the initial load of 98N (10kgf) to the final load of 1275N (130kgf). The pressure rate of the head used to compress the core or ball is set to 10mm / s.

[0091] Core hardness distribution The core surface is spherical, and the hardness Cs is measured using the Shore C hardness scale according to ASTM D2240 by setting the needle of the hardness tester nearly perpendicular to the spherical surface. For the core's central hardness Cc and the hardness Cm at the midpoint between the core's center and the core surface, the core is cut into a hemispherical shape to create a flat cross-section, and the hardness tester needle is pressed perpendicularly against the central portion and predetermined positions to measure the hardness. The hardness at the center and the aforementioned midpoint is expressed as a Shore C hardness value. For hardness measurement, an automatic rubber hardness tester "P2" manufactured by Polymer Instruments Co., Ltd., equipped with a Shore C hardness tester, is used. The maximum value is read. All measurements are performed in an environment of 23±2℃. Note that the values ​​in Table 3 are Shore C hardness values.

[0092] Material hardness of the intermediate layer and cover Each layer of resin material is molded into a 2mm thick sheet and left for two weeks. Afterward, Shore D and Shore C hardness are measured according to the ASTM D2240 standard. A P2 automatic rubber hardness tester manufactured by Polymer Instruments Co., Ltd. is used for hardness measurement. The Shore D and Shore C hardness attachments are fitted, and the respective hardnesses are measured. The maximum value is read. All measurements are performed under conditions of 23±2℃.

[0093] Surface hardness of each sphere in the intermediate layer coated sphere and the ball The hardness of each sphere is measured by pressing the needle perpendicularly against its surface. The surface hardness of the ball (cover) is measured on the land portion of the ball surface where no dimples are formed. Shore D hardness is measured according to the ASTM D2240 standard. An automatic rubber hardness tester "P2" manufactured by Polymer Instruments Co., Ltd. is used for hardness measurement. The maximum value is read. All measurements are performed in an environment of 23±2℃.

[0094] [Table 3]

[0095] The flight distance (W#1)(I#6) and durability under repeated impact were evaluated for each golf ball using the following method. The results are shown in Table 4.

[0096] Flight evaluation (W#1) A golf swing robot will be fitted with a driver (W#1) and the spin rate and total distance will be measured when it hits the ball at head speeds (HS) of 40 m / s and 35 m / s. The club used will be the "JGR 2016 model" (loft angle 9.5°) manufactured by Bridgestone Sports. The evaluation criteria are as follows:

[0097] [Judgment criteria based on a head speed (HS) of 40 m / s] Total distance of 203.0m or more ··· ○ Total distance less than 203.0m ··· ×

[0098] [Judgment criteria based on a head speed (HS) of 35 m / s] Total distance of 168.0m or more ··· ○ Total distance less than 168.0m ··· ×

[0099] Flight evaluation (I#6) A golf swing robot will be fitted with a 6-iron (I#6) and struck at a head speed (HS) of 35 m / s. The spin rate and total distance will be measured and judged according to the following criteria. The club used will be the "JGR Forged 2016 model" manufactured by Bridgestone Sports. 〔Judgment criteria〕 Total distance of 145.8m or more ··· ○ Total distance less than 145.8m ··· ×

[0100] Crack resistance from repeated impacts The durability of the golf ball was evaluated using the ADC Ball COR Durability Tester manufactured by Automated Design Corporation, USA. After launching a golf ball using air pressure, it was repeatedly struck against two parallel metal plates. Durability was defined as the average number of shots required for the ball to break. In this case, the average value was calculated by preparing three identical balls, launching each ball, and averaging the number of shots required for each ball to break. The test machine type was a horizontal COR, and the incident velocity on the metal plates was set to 43 m / s. 〔Judgment criteria〕 ○ ··· Average value 130 times or more × ··· Average value less than 130 times

[0101] [Table 4]

[0102] As shown in the results in Table 4, the golf balls of Comparative Examples 1 to 7 are inferior to the present invention (example) in the following respects. Comparative Example 1 does not contain inorganic granular filler in the intermediate layer, and the specific gravity of the intermediate layer is less than 1.05. As a result, the ball flight is poor when hit with a driver (W#1) at a head speed (HS) of 45 m / s, and it also has poor durability against repeated impacts. Comparative Example 2 does not contain inorganic granular filler in the intermediate layer, resulting in an intermediate layer specific gravity of less than 1.05. As a result, the ball flight is poor when struck with a driver (W#1) at a head speed (HS) of 45 m / s, and it also has poor durability against repeated impacts. Comparative Example 3 does not contain inorganic granular filler in the intermediate layer, and the specific gravity of the intermediate layer is less than 1.05. As a result, the ball flight is poor when hit with a driver (W#1) at a head speed (HS) of 45 m / s, and it also has poor durability against repeated impacts. Comparative Example 4 lacks inorganic granular filler in its cover, and its cover's specific gravity is lower than that of the intermediate layer. As a result, it has inferior durability against repeated impacts. Comparative Example 5 lacks inorganic granular fillers in both the cover and the intermediate layer, resulting in an intermediate layer specific gravity below 1.05 and a cover specific gravity below 1.10. Consequently, it exhibits poor durability against repeated impacts. Comparative Example 6 has a Shore D value (surface hardness minus core hardness) of 36, which is less than 37. As a result, it has inferior distance with both the driver (W#1) and irons (I#6). Comparative Example 7 has a lower ball surface hardness than the surface hardness of the intermediate layer coated sphere, and the value obtained by subtracting the core center hardness from the ball surface hardness (Shore D) is 20, which is less than 37. As a result, it is inferior in distance with the driver (W#1) and irons (I#6). [Explanation of Symbols]

[0103] G Golf Balls 1 core 2. Middle Class 2a Inorganic granular filler 3 Cover 4 paint layers D-dimple

Claims

1. A multi-piece solid golf ball comprising a core, an intermediate layer, and a cover, wherein the core is formed from a single or multi-layer rubber composition, the intermediate layer is formed mainly from an ionomer resin, and both the intermediate layer and the cover are single layers, each containing an inorganic granular filler, and the following three formulas Surface hardness of a ball > Surface hardness of a sphere with an intermediate layer covering the core (intermediate layer coated sphere) Ball surface hardness (Shore D) - Core core hardness (Shore D) ≥ 41 Cover specific gravity > Intermediate layer specific gravity A multi-piece solid golf ball that satisfies the following conditions, and is characterized in that, when the Shore C hardness of the core surface is Cs and the Shore C hardness of the core center is Cs, the value of Cs-Cc is 20 or less.

2. The main material of the cover is ionomer resin, and the main material of the intermediate layer is the following components (a) to (d). (a) 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, (b) A base resin comprising an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid terranandic copolymer and / or a metal ion neutralized product of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid terranandic copolymer, wherein the blending ratio of component (a) to component (b) is 100:0 to 0:100 by mass, (c) Fatty acids or derivatives thereof with a molecular weight of 228 or more and 1500 or less, (d) Basic inorganic metal compound capable of neutralizing the acidic groups in the base resin and (c) component. The multi-piece solid golf ball according to claim 1, which is an ionomer resin composition containing the above-mentioned base resin and component (c), wherein 50 mol% or more of the acid groups contained in the base resin and component (c) are neutralized.

3. A multi-piece solid golf ball according to claim 1 or 2, wherein the surface hardness of the ball is 65 or higher on the Shore D scale.

4. A multi-piece solid golf ball according to any one of claims 1 to 3, wherein the specific gravity of the cover is 1.10 or more, and the specific gravity of the intermediate layer is 1.05 or more.

5. The multi-piece solid golf ball according to any one of claims 1 to 4, wherein the Cs-Cc value is 12 or more and 20 or less.

6. The relationship between the core's surface hardness (Cs), core's central hardness (Cc), and the hardness at the midpoint between the core's surface and its center (Cm) (where all of these hardnesses are Shore C hardness values) is given by the following formula: (Cs-Cm) / (Cm-Cc) ≧ 1.2 A multi-piece solid golf ball according to any one of claims 1 to 5 that satisfies the requirements.

7. A multi-piece solid golf ball comprising a core, an intermediate layer and a cover, wherein the core is formed from a single or multiple layers of rubber composition, and the intermediate layer is formed mainly from an ionomer resin, and the following three formulas Surface hardness of a ball > Surface hardness of a sphere with an intermediate layer covering the core (intermediate layer coated sphere) Ball surface hardness (Shore D) - Core core hardness (Shore D) ≥ 41 Cover specific gravity > Intermediate layer specific gravity (However, the specific gravity of the intermediate layer must be ≥ 1.05, and the specific gravity of the cover must be ≥ 1.10) A multi-piece solid golf ball that satisfies the following conditions, and is characterized in that, when the Shore C hardness of the core surface is Cs and the Shore C hardness of the core center is Cs, the value of Cs-Cc is 20 or less.

8. The main material of the cover is ionomer resin, and the main material of the intermediate layer is the following components (a) to (d). (a) 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, (b) A base resin comprising an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid terranandic copolymer and / or a metal ion neutralized product of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid terranandic copolymer, wherein the blending ratio of component (a) to component (b) is 100:0 to 0:100 by mass, (c) Fatty acids or derivatives thereof with a molecular weight of 228 or more and 1500 or less, (d) Basic inorganic metal compound capable of neutralizing the acidic groups in the base resin and (c) component. The multi-piece solid golf ball according to claim 7, which is an ionomer resin composition containing the above-mentioned base resin and component (c), wherein 50 mol% or more of the acid groups contained in the base resin and component (c) are neutralized.

9. The multi-piece solid golf ball according to claim 7 or 8, wherein the intermediate layer and the cover each contain an inorganic granular filler.

10. A multi-piece solid golf ball according to any one of claims 7 to 9, wherein the surface hardness of the ball is 65 or higher on the Shore D hardness scale.

11. The multi-piece solid golf ball according to any one of claims 7 to 10, wherein the value of Cs-Cc is 12 or more and 20 or less.

12. The relationship between the core's surface hardness (Cs), core's central hardness (Cc), and the hardness at the midpoint between the core's surface and its center (Cm) (where all of these hardnesses are Shore C hardness values) is given by the following formula: (Cs-Cm) / (Cm-Cc) ≧ 1.2 A multi-piece solid golf ball according to any one of claims 7 to 11 that satisfies the requirements.

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