Golf ball

Abstract

To provide a golf ball which extremely reduces displacement of the center of gravity of a ball, enhances rolling (straightness) of a ball at putting with a putter, and is excellent in controllability at approach shot, abrasion resistance and moldability.SOLUTION: A golf ball in which one or more intermediate layers are formed between a core and a cover is configured such that: a standard deviation of a specific gravity of each layer of the core, the intermediate layer and the cover is within 0.07; the cover is formed from a resin composition containing the following (I) and (II) components of (I) polyurethane and (II) a (meth)acrylic block copolymer; and the golf ball satisfies the following formula (1) 0.10≤VRL×VRH≤0.26 ...(1) (in the formula, VRL represents a ratio of a viscosity at 210°C to a viscosity at 200°C at a predetermined shear rate, and VRH represents a ratio of a viscosity η3 at 230°C to a viscosity at 220°C at the predetermined shear rate).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a golf ball in which at least one intermediate layer is formed between a core and a cover. More specifically, the present invention relates to a golf ball that can exhibit good performance in putting with a putter by optimizing the specific gravity of each layer.

Background Art

[0002] Regarding the cover layer and the mantle layer, which are components of a golf ball, in terms of feel and low spin, technologies for reducing the thickness using injection molding or compression molding and for producing multiple layers have advanced. Along with such multi-layer formation and thin gauge, gauge non-uniformity (eccentricity) has become a problem. A non-uniform ball has a changed center of gravity position, and for example, affects the rolling (straightness) of the ball during putting with a putter.

[0003] As conventionally proposed technologies, several patent documents of golf balls with a high moment of inertia can be cited. For example, the following Patent Documents 1 to 3 can be cited. These provide a golf ball with a high moment of inertia, a high spin retention rate, and good ball rolling in putting by appropriately blending a specific gravity adjusting material or the like in the outer layer of the golf ball to set the specific gravity of the outer layer higher than that of the inner layer.

[0004] However, in the above-proposed golf ball, although there is a large difference in the specific gravity of each layer, when there is a shift (eccentricity) in each layer during manufacturing, the shift of the center of gravity position of the ball from the center becomes large. As a result, the ball becomes more likely to curve and the rolling becomes unstable.

[0005] Recently, for professional and advanced players, many golf ball cover materials mainly made of urethane resin have emerged. Among them, some cover materials of polymer blends have been proposed, which are based on urethane resin materials and mixed with other resin materials. Patent Document 4 describes the use of acrylic resin or methacrylic resin as a polymer blend of urethane resin material and as the main material of the cover. This technology provides a golf ball that can achieve a high initial velocity at the driver shot and a low initial velocity at the approach shot. However, since acrylic resin or methacrylic resin is basically a hard resin material, it cannot be said that it can fully satisfy the approach controllability. Approach controllability is one of the factors related to the operability of the club at the approach shot. The quality of the club operability is affected by the length of the contact time between the ball and the club face due to low resilience, in addition to the amount of spin of the ball. When the contact time is long, the operability is good, and when it is short, the operability is poor. That is, it has been desired to improve a golf ball that is further superior in approach controllability than the golf ball described in Patent Document 4.

[0006] Moreover, in the resin material of the cover described in Patent Document 4, since the urethane resin material increases the melt viscosity and deteriorates the fluidity due to the mixing of the acrylic resin, it is necessary to raise the molding temperature. For this reason, after molding, there is a risk that defects such as burning may occur on the entire cover surface, and there is room for improvement in terms of the moldability and scratch resistance of the golf ball.

[0007] Patent Document 5 discloses a resin material for a golf ball formed from a mixture having a thermoplastic polymer and an acrylic copolymer (MMA copolymer). However, the acrylic copolymer described in Patent Document 5 is a polymer having a special core-shell type chemical structure. When this acrylic copolymer is blended with a urethane resin material, Patent Document 5 does not disclose that the approach controllability is sufficiently excellent, and the scratch resistance and moldability are also excellent. It is difficult to say that it is a technology that can solve the above problems of the present invention.

Prior Art Documents

Patent Document

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention has been made in view of the above circumstances, and an object thereof is to provide a golf ball in which the deviation of the center of gravity of the ball is extremely small, the rolling (straightness) of the ball during putting with a putter is enhanced, and the controllability, scratch resistance, and moldability during an approach shot are excellent.

Means for Solving the Problems

[0010] As a result of intensive studies to achieve the above object, the present inventors have set the standard deviation of the specific gravity of each layer of the core, the intermediate layer, and the cover to be within 0.07 for a golf ball in which at least one intermediate layer is formed between the core and the cover, and the cover is made of the following components (I) and (II) (I) Polyurethane (II) (Meth)acrylic block copolymer formed of a resin composition containing, and the following formula (1) 0.10 ≦ VR L × VR H ≦ 0.26 ··· (1) 〔In the above formula, VR Lrepresents the ratio (η1 / η0) of the viscosity η1 at 210 °C to the viscosity η0 at 200 °C at a predetermined shear rate, and VR H represents the ratio (η3 / η2) of the viscosity η3 at 230 °C to the viscosity η2 at 220 °C at the above shear rate. When designing a golf ball so as to satisfy the following, it has been found that the deviation of the center of gravity of the ball becomes extremely small, the rolling (straightness) of the ball during putting with a putter is enhanced, and the controllability, scratch resistance, and moldability during an approach shot are excellent, and the present invention has been achieved.

[0011] Therefore, the present invention provides the following golf ball. 1. In a golf ball in which at least one intermediate layer is formed between a core and a cover, the standard deviation of the specific gravity of each of the core, intermediate layer, and cover is within 0.07, and the cover contains the following components (I) and (II) (I) Polyurethane (II) (Meth)acrylic block copolymer is formed of a resin composition containing the same, and the following formula (1) 0.10 ≦ VR L × VR H ≦ 0.26 ···(1) In the above formula, VR L represents the ratio (η1 / η0) of the viscosity η1 (dPa·s) at 210 °C to the viscosity η0 (dPa·s) at 200 °C at a shear rate of 1216 (1 / sec), and VR H represents the ratio (η3 / η2) of the viscosity η3 (dPa·s) at 230 °C to the viscosity η2 (dPa·s) at 220 °C at a shear rate of 1216 (1 / sec). A golf ball characterized by satisfying the above. 2. The golf ball according to the above 1, wherein the blending amount of the component (II) is 20 parts by mass or less with respect to 100 parts by mass of the component (I). 3. The golf ball according to the above 1 or 2, wherein the material hardness of the component (II) is 40 or less in Shore D hardness. 4. The golf ball according to the above 1 or 2, wherein the resilience of the component (II) is 40% or less in the measurement according to JIS-K 6255 standard. 5. The golf ball according to 1 or 2 above, wherein the melt flow rate (MFR) value of the component (II) is 20 g / 10 min or more under the measurement conditions (ISO 1133) of 230 °C and a load of 2.16 kgf. 6. The golf ball according to 1 or 2 above, wherein in the block copolymer of the component (II), the hard segment is mainly composed of methyl methacrylate units, and the soft segment is mainly composed of n-butyl acrylate units or n-butyl acrylate / 2-ethylhexyl acrylate units. 7. The golf ball according to 6 above, wherein the content of methyl methacrylate units in the block copolymer of the component (II) is 20 to 50% by mass. 8. Let the specific gravity of the core be CM, the specific gravity of the intermediate layer be MM, the specific gravity of the cover be FM, the initial velocity (m / s) of the core be CV, the initial velocity (m / s) of the sphere with the intermediate layer coated on the core (intermediate layer-coated sphere) be MV, the initial velocity (m / s) of the sphere with the cover coated on the intermediate layer-coated sphere (ball) be FV, and the deflection amount (mm) 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) be FC. Then, the following formula (2) (CM × CV)+(MM × MV)+(FM × FV / FC)>200 ···(2) 〔However, the initial velocities of the core and the intermediate layer-coated sphere are measured values obtained by measuring each target sphere using an initial velocity measuring device of the same type as the USGA drum rotation type initial velocity meter, and the initial velocity of the ball is measured using a COR type initial velocity meter of the same type as R&A.〕 The golf ball according to 1 or 2 above that satisfies the above. 9. The golf ball according to 1 or 2 above, wherein the moment of inertia of the ball is 82.5 to 85.0 g·cm 2 2. 10. Let the specific gravity of the core be CM, the specific gravity of the intermediate layer be MM, the specific gravity of the cover be FM, the initial velocity (m / s) of the core be CV, the initial velocity (m / s) of the sphere with the intermediate layer coated on the core (intermediate layer-coated sphere) be MV, the initial velocity (m / s) of the sphere with the cover coated on the intermediate layer-coated sphere (ball) be FV, and the moment of inertia of the ball be MOI. Then, the following formula (3) (CM × CV / MOI) + (MM × MV) + (FM × FV / FC) > 110 ···(3) The golf ball according to the above 1 or 2, which satisfies the following condition 11. The golf ball according to the above 1 or 2, wherein the specific gravity of all layers of the core, the intermediate layer and the cover is 1.10 to 1.13 g / cm 3 12. The golf ball according to the above 1 or 2, wherein the relationship between the specific gravities of the intermediate layer and the cover satisfies the following formula -0.03 ≤ (specific gravity of intermediate layer - specific gravity of cover) ≤ 0.03 13. The golf ball according to the above 1 or 2, wherein the material of the intermediate layer contains barium sulfate as a specific gravity adjusting material 14. The golf ball according to the above 1 or 2, wherein the material hardness of the cover is 40 to 52 in Shore D hardness 15. The golf ball according to the above 1 or 2, wherein the amount of deflection (mm) 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 2.8 mm or less

Advantages of the Invention

[0012] The golf ball of the present invention is excellent in controllability during approach, and has little lateral deviation and distance variation during putting, and is a golf ball that achieves both improvement in approach controllability and putting accuracy. Further, the golf ball of the present invention is excellent in scratch resistance and moldability

Brief Description of the Drawings

[0013]

Figure 1

Embodiments for Carrying Out the Invention

[0014] Hereinafter, the present invention will be described in more detail The golf ball of the present invention includes a core, a cover, and an intermediate layer formed between them. Hereinafter, each of the above layers will be described in detail ​

[0015] The core can be formed not only in a single layer but also in multiple layers. As the material of the core, known rubber materials and various resin materials can be used as the base material. When the core is formed of a rubber material, as the base rubber, known base rubbers of natural rubber or synthetic rubber can be used. More specifically, it is recommended to mainly use polybutadiene, especially cis-1,4-polybutadiene having at least 40% or more of the cis structure. Further, in the base rubber, if desired, natural rubber, polyisoprene rubber, styrene-butadiene rubber, etc. can be used in combination with the above-mentioned polybutadiene. Also, polybutadiene can be synthesized by Ziegler catalysts such as titanium-based, cobalt-based, nickel-based, neodymium-based catalysts, and metal catalysts such as cobalt and nickel.

[0016] To the above base rubber, co-crosslinking agents such as unsaturated carboxylic acids and their metal salts, inorganic fillers such as zinc oxide, barium sulfate, calcium carbonate, and organic peroxides such as dicumyl peroxide and 1,1-bis(t-butylperoxy)cyclohexane can be blended. Also, if necessary, commercially available anti-aging agents and the like can be appropriately added.

[0017] The above core can be manufactured by heat-curing a rubber composition containing the above components. For example, kneading is performed using a kneader such as a Banbury mixer or a roll, and compression molding or injection molding is performed using a mold for the core. The molded body is heated appropriately under the conditions of 100 to 200 °C, preferably 140 to 180 °C, for 10 to 40 minutes, which is a temperature sufficient for the organic peroxide and the co-crosslinking agent to act, to cure the molded body and manufacture it.

[0018] Regarding the specific gravity of the above core, there is no particular limitation, but it is preferably 1.00 or more, more preferably 1.03 or more, still more preferably 1.06 or more. As the upper limit, it is preferably 1.20 or less, more preferably 1.17 or less, still more preferably 1.14 or less. In order to ensure good flight distance performance during driver hitting, it is necessary to make the mass of the ball about 45.0 to 45.6 g. In such a case, if the specific gravity of the core is smaller than the above range, it is necessary to increase the specific gravity of the intermediate layer and the cover layer. Therefore, by adding a specific gravity adjusting material, the spin performance of the ball may be impaired. On the other hand, if the specific gravity of the core is too large, the moment of inertia may become too small and the rolling on the putter may deteriorate.

[0019] Around the above core, at least one intermediate layer and a cover can be formed as members covering the core. Also, when the intermediate layer consists of two layers, each layer may be referred to as an inner intermediate layer and an outer intermediate layer in order from the inside. The inner intermediate layer may also be referred to as an enveloping layer.

[0020] The intermediate layer is formed of a resin composition. Examples of such a resin composition include resin compositions mainly composed of resins conventionally used as materials for golf balls. Examples of the base resin of the resin composition include ionomer resins, polyester resins, polyurethane resins, polyamide resins, polyolefin resins, olefin-based thermoplastic elastomers, and styrene-based thermoplastic elastomers. In particular, from the viewpoints of resilience and moldability, ionomer resins are suitable.

[0021] Various fillers can also be blended as specific gravity adjusting materials in the above intermediate layer material. As such fillers, for example, zinc oxide, titanium oxide, barium sulfate, calcium carbonate, potassium titanate, calcium oxide, magnesium oxide, silica, ferrite, etc. can be preferably used. These may be used alone or in combination of two or more.

[0022] The blending amount of the above specific gravity adjusting material (filling material) is not particularly limited, but it is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, still more preferably 15 parts by mass or more, based on 100 parts by mass of the base resin of the above intermediate layer. Also, the upper limit of this blending amount is not particularly limited, but it can be preferably 40 parts by mass or less, more preferably 30 parts by mass or less, still more preferably 25 parts by mass or less, based on 100 parts by mass of the base resin. If the blending amount is too large or too small, an appropriate specific gravity cannot be obtained, and the desired effects of the present invention may not be achieved.

[0023] The thickness of the intermediate layer is preferably 0.6 mm or more, more preferably 0.8 mm or more, still more preferably 1.0 mm or more, and the upper limit value is preferably 2.0 mm or less, more preferably 1.5 mm or less, still more preferably 1.3 mm or less. If the intermediate layer is too thin, the amount of spin of the ball at full shot may increase, and the desired flight distance may not be achieved. On the other hand, if the intermediate layer is too thick, the resilience of the ball may decrease.

[0024] The material hardness of the intermediate layer is not particularly limited, but in terms of Shore D hardness, it is preferably 60 or more, more preferably 65 or more, still more preferably 67 or more, and as the upper limit value, it is preferably 75 or less, more preferably 73 or less. The harder the above hardness, the greater the increase in flight distance due to low spin during an iron (I#6) full shot can be achieved, but if it is too hard, the crack durability due to repeated impacts may decrease.

[0025] The specific gravity of the intermediate layer is preferably 1.05 or more, more preferably 1.07 or more, still more preferably 1.09 or more, and the upper limit value is preferably 1.25 or less, more preferably 1.20 or less, still more preferably 1.15 or less. If the specific gravity of the intermediate layer is too small, the crack durability due to repeated impacts may deteriorate. On the other hand, if the specific gravity of the intermediate layer is too large, the resilience of the ball may decrease, or the amount of spin of the ball at full shot may increase, and the desired flight distance may not be achieved.

[0026] Incidentally, it is desirable that the relationship between the specific gravities of the intermediate layer and the cover satisfy the following formula. -0.03 ≦ (specific gravity of intermediate layer - specific gravity of cover) ≦ 0.03 The reason is that the difference in specific gravity between the layers causes variations in the rolling (front-back, left-right) of the pattern. Therefore, it is set within the above range in order to suppress this variation as much as possible.

[0027] The cover is formed of a resin composition. As this resin composition, the following components (I) and (II) (I) Polyurethane (II) (Meth)acrylic block copolymer are contained and formed of the resin composition.

[0028] (I) Polyurethane Polyurethane can be the main material or the base resin of the above cover material (resin composition). The details of this component, polyurethane, are as follows.

[0029] The structure of the polyurethane consists of a soft segment made of a high molecular weight polyol (polymeric glycol) which is a long-chain polyol, and a chain extender and a polyisocyanate that constitute the hard segment. Here, as the high molecular weight polyol used as a raw material, any of those conventionally used in technologies related to polyurethane materials can be used, and there is no particular limitation. For example, polyester polyols, polyether polyols, polycarbonate polyols, polyester polycarbonate polyols, polyolefin polyols, conjugated diene polymerization polyols, castor oil polyols, silicone polyols, vinyl polymerization polyols, etc. can be mentioned. As the polyester polyol, specifically, adipate polyols such as polyethylene adipate glycol, polypropylene adipate glycol, polybutadiene adipate glycol, polyhexamethylene adipate glycol, and lactone polyols such as polycaprolactone polyol can be adopted. Examples of the polyether polyol include poly(ethylene glycol), poly(propylene glycol), poly(tetramethylene glycol), poly(methyltetramethylene glycol), etc. These may be used alone or in combination of two or more.

[0030] As the above high molecular weight polyol, it is preferable to use a polyether polyol.

[0031] The number average molecular weight of the above long-chain polyol is preferably in the range of 1,000 to 5,000. By using a long-chain polyol having such a number average molecular weight, a golf ball made of a polyurethane composition excellent in various properties such as the above-mentioned resilience and productivity can be surely obtained. The number average molecular weight of the long-chain polyol is more preferably in the range of 1,500 to 4,000, and still more preferably in the range of 1,700 to 3,500.

[0032] In addition, the above number average molecular weight is the number average molecular weight calculated based on the hydroxyl value measured in accordance with JIS-K1557 (hereinafter the same).

[0033] As the chain extender, those used in the prior art related to polyurethanes can be preferably used, and there is no particular limitation. In the present invention, a low molecular weight compound having two or more active hydrogen atoms capable of reacting with isocyanate groups in the molecule and having a molecular weight of 2,000 or less can be used. Among them, aliphatic diols having 2 to 12 carbon atoms can be preferably used. Specifically, 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, etc. can be mentioned. Among them, 1,4-butylene glycol can be particularly preferably used.

[0034] As the polyisocyanate, those used in the prior art related to polyurethanes can be preferably used, and there is no particular limitation. Specifically, one or more selected from the group consisting of 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, naphthylene 1,5-diisocyanate, tetramethylxylylene diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylene diisocyanate, 1,4-bis(isocyanatomethyl)cyclohexane, and dimer acid diisocyanate can be used. However, depending on the isocyanate species, it may be difficult to control the crosslinking reaction during injection molding.

[0035] In addition, the mixing ratio of the active hydrogen atoms to the isocyanate groups in the polyurethane-forming reaction can be adjusted as appropriate within a preferable range. Specifically, when producing polyurethane by reacting the above-mentioned long-chain polyol, polyisocyanate compound, and chain extender, it is preferable to use each component at a ratio such that the isocyanate groups contained in the polyisocyanate compound are 0.95 to 1.05 moles per 1 mole of the active hydrogen atoms possessed by the long-chain polyol and the chain extender.

[0036] The method for producing the polyurethane is not particularly limited, and it may be produced by any of the prepolymer method and the one-shot method using a known urethanization reaction with a long-chain polyol, a chain extender, and a polyisocyanate compound. Among them, it is preferable to carry out melt polymerization substantially in the absence of a solvent, and particularly preferably to produce it by continuous melt polymerization using a multi-screw type extruder.

[0037] As the above-mentioned polyurethane, it is preferable to use a thermoplastic polyurethane material, and particularly preferably an ether-based thermoplastic polyurethane material. As the thermoplastic polyurethane material, commercially available products can be preferably used, and examples thereof include the product name "Pandex" manufactured by DIC Covestro Polymer GmbH and the product name "Resamin" manufactured by Dainichi Seika Kogyo Co., Ltd.

[0038] Regarding the material hardness of the above-mentioned component (I), from the viewpoints of the spin characteristics and scratch resistance obtained as a golf ball, it is preferably 52 or less in Shore D hardness, more preferably 50 or less in Shore D hardness, and still more preferably 48 or less. Also, as the lower limit value, from the viewpoint of moldability, it is preferably 38 or more in Shore D hardness, and more preferably 40 or more in Shore D hardness.

[0039] The rebound resilience rate of the above-mentioned component (I) is preferably 55% or more, more preferably 57% or more, and still more preferably 59% or more from the comprehensive viewpoints as a golf ball such as the initial velocity performance and spin performance at the time of hitting. The above-mentioned rebound resilience rate is measured based on the JIS-K 6255:2013 standard.

[0040] The above component (I) is the main material of the resin composition. From the viewpoint of sufficiently imparting the scratch resistance of the urethane resin, it is 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, and most preferably 90% by mass or more of the resin composition.

[0041] In the present invention, by blending the following component (II) with the above component (I), it is excellent in controllability, scratch resistance, and moldability during approach shot.

[0042] (II) (Meth)acrylic block copolymer

[0043] In this specification, the term “(meth)acrylic block copolymer” is used to mean both acrylic block copolymers and methacrylic block copolymers.

[0044] The (meth)acrylic block copolymer of component (II) is preferably a block copolymer having two or more blocks constituting the hard segment and one or more blocks constituting the soft segment. That is, the (meth)acrylic block copolymer used in the present invention is a polymer containing block polymers A and B, and can be represented by a chemical structure of A-B or A-B-A. In addition, the (meth)acrylic block copolymer used in the present invention has a chemical structure different from that of a general core-shell type acrylic copolymer as described in Patent Document 5.

[0045] Block polymer A is a site that constitutes the hard segment. Specifically, as monomer units, there are methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, phenyl methacrylate, 2-hydroxyethyl methacrylate and other methacrylic acid esters. It is preferably used mainly with methyl methacrylate (MMA). Block polymer A can be composed of one or more of the above monomer units used alone or in combination.

[0046] On the other hand, block polymer B is a site that constitutes the soft segment. Specifically, as monomer units, there are methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, pentadecyl acrylate, dodecyl acrylate, benzyl acrylate, phenoxyethyl acrylate, 2-methoxyethyl acrylate and other acrylic acid esters. It is preferably used mainly with n-butyl acrylate (nBA). Block polymer B can be composed of one or more of the above monomer units used alone or in combination.

[0047] The glass transition temperature (Tg) of the above block polymer A indicating the hard segment is preferably 80 to 140 °C, more preferably 100 to 120 °C. On the other hand, the glass transition temperature (Tg) of the above block polymer B indicating the soft segment is preferably -80 to -20 °C, more preferably -60 to -40 °C 100 to 120 °C.

[0048] In the above-mentioned (meth)acrylic block copolymer, the content ratio of the hard segment to the soft segment is preferably 5:95 to 40:60, more preferably 10:90 to 30:70, by mass ratio. As the proportion of the soft segment increases, it can be expected that the resin composition will be softened to obtain the desired approach controllability. However, if the proportion of the hard segment is too small, the compatibility with the base polyurethane resin or the like will decrease, and the moldability may deteriorate.

[0049] When the hard segment is mainly composed of methyl methacrylate units, the content of methyl methacrylate units in the block copolymer of the above-mentioned component (II) is preferably 20 to 50% by mass. If this value is too low, the fluidity will become extremely high and it will not be suitable as a molding material. On the other hand, if this value is too high, the resulting molded product may become too hard.

[0050] (Meth)acrylic block copolymers can be obtained by polymerizing the above monomer units. Examples of the polymerization method include radical polymerization, living anionic polymerization, living radical polymerization, etc. Examples of the polymerization form include solution polymerization, emulsion polymerization, suspension polymerization, bulk polymerization, etc.

[0051] (Meth)acrylic block copolymer's weight average molecular weight is not particularly limited, but is preferably 10,000 or more, more preferably 30,000 or more, still more preferably 45,000 or more. The upper limit is preferably 200,000 or less, more preferably 150,000 or less, still more preferably 100,000 or less. The higher this weight average molecular weight, the more it has the effect of low resilience, and the spin amount also increases, making it excellent in controllability during approach shot. This weight average molecular weight can be measured by gel permeation chromatography (GPC).

[0052] As the (meth)acrylic block copolymer used in the present invention, it is preferable that the hard segment is mainly composed of methyl methacrylate units and the soft segment is mainly composed of n-butyl acrylate units. Such a (meth)acrylic block copolymer can be a commercially available product. For example, "Clarity" manufactured by Kuraray Co., Ltd. can be mentioned. Specifically, product names such as "Clarity LA2114", "Clarity LA2140", "Clarity LA2250", "Clarity LA2270", "Clarity LA2330", and "Clarity LA4285" can be exemplified.

[0053] Regarding the material hardness of the above-mentioned component (II), from the viewpoint of improving the approach spin amount, it is preferably 40 or less in Shore D hardness, more preferably 38 or less in Shore D hardness, still more preferably 35 or less, and most preferably 32 or less. Also, as the lower limit value, it is preferably 7 or more in Shore D hardness, more preferably 15 or more, and still more preferably 20 or more.

[0054] The rebound resilience of the component (II) is preferably 40% or less, more preferably 35% or less, and still more preferably 30% or less, from the viewpoint of maintaining the approach spin amount and suppressing the rebound property during approach to obtain controllability. Also, the lower limit value of the above-mentioned rebound resilience is preferably 10% or more, more preferably 15% or more, and still more preferably 20% or more. The above-mentioned rebound resilience is measured based on the JIS-K 6255:2013 standard.

[0055] By setting the melt flow rate (MFR) of the component (II) to a high value, the fluidity of the polyurethane resin material can be improved, the molding temperature during molding can be lowered, the cleavage and deterioration of urethane molecules can be suppressed, and furthermore, the scratch resistance can be improved. Specifically, it is a measured value under the conditions of the ISO1133 standard, a test temperature of 230°C, and a test load of 21.18 N (2.16 kgf), and is preferably 2 g / 10 min or more, more preferably 50 g / 10 min or more, still more preferably 100 g / 10 min or more, and most preferably 200 g / 10 min or more.

[0056] (II) The blending amount is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and still more preferably 10 parts by mass or less with respect to 100 parts by mass of the above (I) component. If this value exceeds, there is a risk of deterioration in abrasion resistance. The lower limit value of the above blending amount is 0.5 parts by mass or more, preferably 1 part by mass or more, and more preferably 2 parts by mass or more with respect to 100 parts by mass of the above (I) component.

[0057] In the resin composition containing the above (I) and (II), other resin materials may be blended in addition to the resin components described above. The purpose is from the viewpoints of further improving the fluidity, enhancing various physical properties such as resilience and crack durability of the resin composition for golf balls.

[0058] The above resin composition can be obtained, for example, by mixing the above-described components using various kneaders such as a kneading type (single-screw or) twin-screw extruder, Banbury mixer, and kneader.

[0059] Regarding the resilience modulus of the above resin composition, for the purpose of low resilience and improvement of the approach spin amount, it is required to be 48% or more as measured according to JIS-K 6255:2013 standard, preferably 50% or more, and still more preferably 52% or more, and the upper limit value is 72% or less, preferably 70% or less, and more preferably 68% or less.

[0060] Also, regarding the material hardness of the above resin composition, from the viewpoints of scratch resistance and imparting an appropriate approach spin amount, it is preferably 50 or less in Shore D hardness, more preferably 48 or less, and still more preferably 45 or less in Shore D hardness. As the lower limit value, from the viewpoint of moldability, it is preferably 30 or more in Shore D hardness, more preferably 35 or more, and still more preferably 37 or more.

[0061] In the present invention, for the above resin composition, the ratio (η1 / η0) of the viscosity η1 (dPa·s) at 210 °C to the viscosity η0 (dPa·s) at 200 °C at a shear rate of 1216 (1 / sec) is VRL Let the ratio (η3 / η2) of the viscosity η3 (dPa·s) at 230°C to the viscosity η2 (dPa·s) at 220°C at a shearing speed of 1216 (1 / sec) be VR. H When this is done, VR L ×VR H has a value of 0.10 or more, preferably 0.12 or more, and the upper limit value is 0.26 or less, preferably 0.23 or less, more preferably 0.20 or less. That is, by making the fluidity of the cover resin material at 200°C lower than that at 210°C, the solidifying property can be improved, and molding defects such as pin punching during molding can be reduced. Also, by making the fluidity of the cover resin material at 230°C higher than that at 220°C, the fluidity changes sufficiently sensitively with respect to temperature even in the molding temperature range, and it becomes unnecessary to excessively raise the molding temperature in order to improve the fluidity. As a result, deterioration of the resin state during molding of the cover and the burden on mechanical devices such as molding machines can be reduced.

[0062] The thickness of the cover formed by the above resin composition is preferably 0.4 mm or more, more preferably 0.5 mm or more, still more preferably 0.6 mm or more, and as the upper limit, preferably 3.0 mm or less, more preferably 2.0 mm or less. If the cover is too thin, the scratch resistance of the ball struck with a wedge may deteriorate. On the other hand, if the cover is too thick, the spin of the ball may increase too much and the desired flying distance may not be obtained.

[0063] Regarding the specific gravity of the cover, there are no particular restrictions, but it is preferably 1.00 or more, more preferably 1.03 or more, still more preferably 1.06 or more, and as the upper limit, preferably 1.20 or less, more preferably 1.17 or less, still more preferably 1.14 or less. If the specific gravity of the cover is smaller than the above range, the scratch resistance may deteriorate due to the blend ratio of the resin used for specific gravity adjustment. On the other hand, if the specific gravity of the cover is too large, the addition amount of the filler increases, and the repulsion becomes too low, and the aimed flying distance may not be obtained.

[0064] In addition, it is preferable that the specific gravity of all of the core, intermediate layer, and cover described above is 1.10 or more and 1.13 or less. By setting the specific gravity of all the layers within such a numerical range, a golf ball conforming to golf rules is obtained, and since the specific gravity difference between the respective layers is minimized, there is an advantage that the variation in rolling in the front-back and left-right putts is reduced.

[0065] The material hardness of the cover is not particularly limited, but in terms of Shore D hardness, it is preferably 52 or less, more preferably 50 or less, still more preferably 48 or less, and as the lower limit value, it is preferably 40 or more, more preferably 43 or more. By setting the hardness relatively low, it becomes difficult for the initial ball speed during putting to increase, and the variation in putting distance is reduced. Also, within the above range, the harder the hardness, the more the flight distance can be increased by reducing the spin during a full shot with an iron (I#6).

[0066] For the golf ball, the amount of deflection (mm) when a load is applied from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is preferably 3.0 mm or less, more preferably 2.9 mm or less, still more preferably 2.8 mm or less. By setting the amount of deflection relatively small in this way, the variation in the distance of the ball during putting is reduced. Note that the lower limit value of the amount of deflection is preferably 2.2 mm or more, more preferably 2.3 mm or more.

[0067] The moment of inertia of the golf ball of the present invention is preferably 82.5 kg·cm 2 or more, more preferably 83.0 kg·cm 2 or more, and as the upper limit value, it is preferably 85.0 kg·cm 2 or less. Here, the moment of inertia adopted in the present invention can be calculated by the following formula.

[0068] M=(n / 5880000)×{(r1-r2)×D1 5 +(r2-r3)×D2 5 +r3×D3 5} M: Moment of inertia r1: Core specific gravity D1: Core diameter r2: Intermediate layer specific gravity D2: (Core + Intermediate layer) diameter r3: Cover specific gravity D3: Ball diameter

[0069] That is, the moment of inertia is a calculated value obtained from the diameter (thickness) and specific gravity of each layer, and can be obtained by regarding the ball as a perfect sphere. The moment of inertia of a golf ball can be measured using a moment of inertia measuring machine, for example, "M01 - 005" manufactured by INERTIA DYNAMICS INC.

[0070] In the present invention, it is required that the standard deviation of the specific gravity of each layer of the core, intermediate layer, and cover, which are components of the golf ball, be within 0.07.

[0071] The above standard deviation is a generally calculated standard deviation, which is the positive square root obtained by summing the squares of the differences between the data values and the average value and dividing by the total number of data. The difference between the data value and the average value means the deviation, the mean square value of the deviation means the variance, and therefore, the standard deviation means the positive square root of the variance.

[0072]

Equation

[0073] For example, in Example 1 of Table 4, the specific gravity of the core is 1.13, the specific gravity of the intermediate layer is 1.08, and the specific gravity of the cover is 1.07. The average value of these three data is (1.13 + 1.08 + 1.07) / 3 ≈ 1.0933. Substituting into the above formula, σ = {1 / 3×(1.13 - 1.0933) 2 + 1 / 3×(1.08 - 1.0933) 2 + 1 / 3×(1.07 - 1.0933) 2} 1 / 2 ≈ 0.03.

[0074] The standard deviation of the specific gravity of each of the above core, intermediate layer, and cover is within 0.07, preferably 0.05 or less, and more preferably 0.03 or less. By setting the standard deviation within 0.07, the lateral deviation width of the ball during padding becomes smaller, and stable padding can be provided.

[0075] In the present invention, the specific gravity of the core is CM, the specific gravity of the intermediate layer is MM, the specific gravity of the cover is FM, the initial velocity (m / s) of the core is CV, the initial velocity (m / s) of the sphere with the intermediate layer covering the core (intermediate layer-covered sphere) is MV, the initial velocity (m / s) of the sphere with the cover covering the intermediate layer-covered sphere (ball) is FV, and the deflection amount (mm) 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 FC. Then, the following formula (2) (CM × CV) + (MM × MV) + (FM × FV / FC) > 200 ···(2) 〔However, the above initial velocity is a measured value obtained by measuring each target sphere using an initial velocity measuring device of the same method as the drum rotation type initial velocity meter of the USGA.〕 It is preferable to satisfy the above. The value of (CM × CV) + (MM × MV) + (FM × FV / FC) is preferably greater than 200, more preferably 203 or more, and still more preferably 206 or more. By setting the value of the above formula to be greater than 200 in this way, the variation in the distance of the ball during padding becomes smaller.

[0076] Furthermore, in the present invention, when the moment of inertia of the ball is MOI, the following formula (3) (CM × CV / MOI) + (MM × MV) + (FM × FV / FC) > 110 ···(3) 〔However, the above initial velocity is a measured value obtained by measuring each target sphere using an initial velocity measuring device of the same method as the drum rotation type initial velocity meter of the USGA.〕 It is preferable to satisfy. The value of (CM×CV / MOI)+(MM×MV)+(FM×FV / FC) described above is preferably greater than 110, more preferably 113 or more, and even more preferably 115 or more. By setting the value of the above formula to be greater than 110 in this way, the variation in the distance of the ball during padding becomes smaller.

[0077] Regarding the initial velocity of each sphere Regarding these relationships of the initial velocity (CM) of the core, the initial velocity (MV) of the intermediate layer coated sphere, and the initial velocity (FV) of the ball, it is preferable to set them within the following ranges respectively. Incidentally, the initial velocity of the core and the initial velocity of the intermediate layer coated sphere can be measured using an initial velocity measuring device of the same method as the USGA drum rotation type initial velocity meter, which is a device approved by the R&A. Specifically, test in a room at a room temperature of 23.9±2°C, strike the ball at a striking speed of 143.8 ft / s (43.83 m / s) using a 250-pound (113.4 kg) head (striking mass), measure the time taken to pass through a distance of 6.28 ft (1.91 m), and calculate the initial velocity (m / s). In this case, the ball to be measured is temperature-adjusted at a temperature of 23.9±1°C for 3 hours or more. On the other hand, the initial velocity of the ball is a value measured by a COR type initial velocity meter of the same type as the R&A. Specifically, a COR type initial velocity device manufactured by Hye Precision in the United States is used. As a condition, during measurement, the air pressure is changed in four stages for measurement, a relational expression between the incident velocity and the COR is constructed, and from this relational expression, the initial velocity at an incident velocity of 43.83 m / s is obtained. Regarding the measurement environment of the above COR type initial velocity device, a ball temperature-adjusted in a constant temperature bath adjusted to 23.9±1°C for 3 hours or more is used, and when measuring, it is measured at a room temperature of 23.9±2°C. Also, the barrel diameter is selected such that the clearance on one side between the outer diameter of the measurement object is between 0.2 and 2.0 mm.

[0078] ​​The initial velocity (CM) of the core is preferably 77.50 m / s or more, more preferably 77.60 m / s or more, still more preferably 77.70 m / s or more, and the upper limit is preferably 78.10 m / s or less, more preferably 77.90 m / s or less.

[0079] The initial velocity (MV) of the intermediate layer-coated sphere is preferably 77.70 m / s or more, more preferably 77.80 m / s or more, still more preferably 77.90 m / s or more, and the upper limit is preferably 78.30 m / s or less, more preferably 78.10 m / s or less.

[0080] The initial velocity (FM) of the ball is preferably 77.00 m / s or more, more preferably 77.10 m / s or more, still more preferably 77.20 m / s or more, and the upper limit is preferably 77.70 m / s or less, more preferably 77.60 m / s or less.

[0081] If these initial velocities deviate from the above ranges, the vertical variation when hit with a putter may increase.

[0082] On the surface of the cover, usually, one or more than two kinds of a large number of dimples can be formed, and the shape, diameter, depth, number, occupied surface area, etc. of the dimples are appropriately selected.

[0083] The method for producing a golf ball is not particularly limited, and it can be obtained by molding by known molding methods such as injection molding and compression molding. For example, with the core set in the mold of an injection molding machine, the above-described resin composition for the intermediate layer is supplied to coat the core with an intermediate layer to produce a coated sphere (intermediate layer-coated sphere), and then, with the intermediate layer-coated sphere set in the mold of another injection molding machine, a golf ball coated with a cover can be produced by injecting the resin composition for the cover.

[0084] In addition, a paint layer can be formed on the surface of the cover. In this case, the paint layer is formed from a paint composition. There are no particular restrictions on the base resin of this paint composition, but examples thereof include polyurethane resins, epoxy resins, polyester resins, acrylic resins, and cellulose resins. From the viewpoint of the durability of the paint layer, it is preferable to use a two-component curable polyurethane resin. In addition, various additives such as antioxidants, ultraviolet absorbers, light stabilizers, fluorescent agents, and fluorescent brighteners can be blended in appropriate amounts as necessary in the paint composition.

[0085] As a method for applying the above paint to the surface of the cover, there are no particular restrictions, and known methods can be used, such as electrostatic painting, spray gun painting, and brush painting.

[0086] The ball specifications such as the mass and diameter of the golf ball of the present invention can be appropriately set according to the golf rules.

Examples

[0087] Hereinafter, examples and comparative examples will be shown to specifically explain the present invention, but the present invention is not limited to the following examples.

[0088] 〔Examples 1 to 8, Comparative Examples 1 to 8〕 The core composition was adjusted by the rubber formulation shown in Table 1 common to each of the examples and comparative examples, vulcanized, and a core with a diameter of 38.7 mm was produced. For zinc oxide and zinc acrylate, appropriate amounts were blended so that the specific gravity and amount of deflection shown in Table 4 described later would match, and four types, A, A', B, and B', were produced.

[0089]

Table 1

[0090] The details of the above formulation are as follows. · Polybutadiene: Trade name "BR 01" (manufactured by ENEOS MATERIALS Co., Ltd.) · Organic peroxide: Dicumyl peroxide, trade name "PERKEMIL D" (manufactured by NOF Corporation) · Zinc oxide: Trade name "Three Types of Zinc Oxide" (manufactured by Sakai Chemical Industry Co., Ltd.) · Zinc acrylate: Trade name "ZN-DA85S" (manufactured by Nippon Shokubai Co., Ltd.)

[0091] Formation of the intermediate layer and the cover (outermost layer) Next, for each example and comparative example, using the following injection mold, around the above core surface, injection molding is performed with the resin materials C and D of the intermediate layer shown in Table 2 to form an intermediate layer with a thickness of 1.20 mm and a Shore D hardness of 66 - 68.

[0092]

Table 2

[0093] The details of the compounding components in the above table are as follows. · "Hymilan AM7318": Ionomer resin manufactured by Mitsui Dow Chemical Co., Ltd. · "Hymirene 1706": Ionomer resin manufactured by Mitsui Dow Chemical Co., Ltd. · "Trimethylolpropane": Manufactured by Tokyo Chemical Industry Co., Ltd. · "Barium sulfate": Trade name "Precipitated Barium Sulfate 300" of Sakai Chemical Industry Co., Ltd.

[0094] Next, using another injection mold, around the above intermediate layer-coated sphere, injection molding is performed with 12 types of urethane resin compositions C1 - C12 shown in Table 3 to form a cover (outermost layer) with a thickness of 0.8 mm and a Shore D hardness of 43 - 50.

[0095]

Table 3

[0096] In the above table, the details of the compounding components are as follows. · "TPU1": Trade name "Pandex", ether-type thermoplastic polyurethane, material hardness (Shore D) "47", manufactured by DIC Covestro Polymer GmbH · "TPU2": The product name "Pandex" manufactured by DIC Covestro, an ether-type thermoplastic polyurethane, with a material hardness (Shore D) of "43" · "TPU3": The product name "Pandex" manufactured by DIC Covestro, an ether-type thermoplastic polyurethane, with a material hardness (Shore D) of "50" · "LA2140", "LA2250", and "LA2270" are all (meth)acrylic block copolymers (hard segment PMMA / soft segment PBA) of the "Clarity LA" series with the product name of Kuraray Co., Ltd. · "S.O.E.S1611": A hydrogenated aromatic vinyl elastomer (styrene content 60% by mass) manufactured by Asahi Kasei Corporation

[0097] The rebound resilience rates described in the above table are the rebound resilience rates of each resin component measured based on the JIS-K 6255:2013 standard, and the fluidity (MFR) is the MFR (g / 10 min) measured under the measurement conditions (ISO1133) of 230°C and a load of 2.16 kgf.

[0098] Viscosity of the cover at a predetermined shear rate (200 °C, 210 °C, 220 °C, 230 °C) In accordance with ISO 11443:1995, it is measured using the product name "Capillograph 1C" manufactured by Toyo Seiki Seisaku-sho, Ltd. As for the measurement conditions, the capillary conditions are set at L / D = 10.0 / 1.0 mm, and the melt viscosity (dPa·s) of the sample at a shear rate (1216 (1 / sec)) at a piston speed of 100 mm / min is measured. In the above measurement, the melt viscosity at a temperature condition of 200°C is η0 (dPa·s), the melt viscosity at 210°C is η1 (dPa·s), the melt viscosity at 220°C is η2 (dPa·s), and the melt viscosity at 230°C is η3 (dPa·s).

[0099] For each golf ball obtained, the VR of the cover L ×VR H, calculate the difference in specific gravity between each layer, the standard deviation of specific gravity, the following formulas (2) and (3), the initial velocity of each coated sphere, the amount of deflection of each coated sphere, and the moment of inertia of the ball. At the same time, evaluate the putting test, approach controllability, hitting feeling, scratch resistance, and moldability of the balls in each example by the following methods. The results are shown in Table 4.

[0100] Deflection amount of the core, the intermediate layer-coated sphere, and the ball Place each target coated sphere on a hard board, and measure the amount of deflection when the load is increased from an initial load of 98 N (10 kgf) to a final load of 1275 N (130 kgf). The above amount of deflection is a measured value measured at a temperature of 23.9 ± 1 °C in a thermostatic bath for at least 3 hours or more and measured in a room at 23.9 ± 2 °C. The measuring instrument uses a high-load compression tester manufactured by Miyu Seiki Co., Ltd., and the downward speed of the pressurizing head that compresses the core, the coated sphere of each layer, or the ball is 10 mm / s.

[0101] Initial velocity of the core, the intermediate layer-coated sphere, and the ball The initial velocity is measured using an initial velocity measuring instrument of the same method as the drum rotation type initial velocity meter of the USGA, which is an apparatus approved by the R&A. Adjust the temperature of the core, the intermediate layer, and each coated sphere of the ball at 23 ± 1 °C for 3 hours or more, and test in a room at room temperature of 23 ± 2 °C. Hit each of 20 cores, the intermediate layer, and each coated sphere of the ball twice, measure the time taken to pass through 6.28 ft (1.91 m), and calculate the initial velocity. Perform this cycle in about 15 minutes.

[0102] Moment of inertia The measurement of the moment of inertia of the golf ball is performed using a moment of inertia measuring machine ("M01-005" manufactured by INERTIA DYNAMICS INC). This measuring machine calculates the moment of inertia of the golf ball based on the difference between the vibration period when the golf ball is placed on the jig of the measuring machine and the vibration period when the golf ball is not placed.

[0103] Difference and standard deviation of the specific gravity of each layer, calculation of formulas (1) and (2) The specific gravity of each layer is calculated from the member mass and member volume of the material of each layer by measuring the outer diameter and weight before and after injection molding. Note that Equation (1) in Table 4 means (CM×CV)+(MM×MV)+(FM×FV / FC), and Equation (2) means (CM×CV / MOI)+(MM×MV)+(FM×FV / FC). (CM represents the specific gravity of the core, MM represents the specific gravity of the intermediate layer, FM represents the specific gravity of the cover, CV represents the initial velocity of the core, MV represents the initial velocity of the intermediate layer-coated sphere, FV represents the initial velocity of the ball, FC represents the amount of deflection when a predetermined load is applied to the ball, and MOI represents the moment of inertia of the ball.)

[0104] Putting measurement method Adjust and fix the swing width of the putter robot so that the rolling distance is about 5 m, and strike the ball for each example. At the same target distance, measure the average initial velocity, rolling distance X, and left-right variation Y when measured 10 times each, and use X(σ) and Y(σ), which are the standard deviations of X and Y, as the fluctuations in the rolling distance (vertical) and left-right direction (horizontal), respectively. Figure 1 shows a schematic diagram explaining the putting test. The symbol T indicates the area of the bent grass, O indicates the hitting point of the putter robot, P indicates the target point, X indicates the rolling distance, and Y indicates the left-right deviation width. The conditions of each test device are as follows. (Test device) · Head speed of the putter robot during putting: 1.35 m / s · Rolling speed of the artificial grass: Set the rolling speed to 12 feet on the horizontally laid surface · Type of putter: Pintype putter (prototype) manufactured by Bridgestone Sports Co., Ltd.

[0105] Molding temperature difference Examine the temperature difference of the molding temperature during cover injection molding with Comparative Example 1 as a reference. Since the lower the temperature is with Comparative Example 1 as a reference, the lower the molding temperature is, it is evaluated that the productivity is good.

[0106] Evaluation of moldability (demolding property) Evaluate the demolding property of the ball for each example from the mold after cover injection molding according to the following criteria. ○ ··· No trauma such as runner breakage or pins during demolding, and the ball diameter can be easily adjusted. △ ··· Trauma such as runner breakage or pins occurs during demolding, or a large temperature change is required to adjust the ball diameter. × ··· Trauma such as runner breakage or pins occurs during demolding, and a large temperature change is required to adjust the ball diameter.

[0107] Approach controllability The sensory evaluation of the controllability of the ball during the approach shot is carried out by the following method. The club used is the same sand wedge (SW) product name "Bridgestone Tour Stage TW-03 (loft angle 57°)" as above, and it is evaluated according to the following criteria when the golfer actually hits. 〔Judgment evaluation〕 ◎ ··· Extremely excellent in operability. ○ ··· Excellent in operability. × ··· Slightly inferior in operability.

[0108] Evaluation of scratch resistance Keep the ball at 23°C, and use a swing robot machine. Use a pitching wedge (PW) for the club and hit each ball 5 times at a head speed of 33 m / s. Visually evaluate the impact damage according to the following criteria. ◎ ··· No damage or almost no visible damage. ○ ··· Slightly damaged but hardly noticeable. △ ··· The surface is slightly fluffy. × ··· The surface is fluffy or the dimples are chipped.

[0109] Feeling of impact The approach sensory evaluation regarding the hitting feeling is carried out as follows. The club used is the same sand wedge (SW) as above. 〔Judgment evaluation〕 ○ ··· No clicking sound and good hitting feeling. △ ··· Since it makes a slightly clicky sound, a slightly uncomfortable hitting feeling is felt. × ··· Since it makes a clicky sound, an uncomfortable hitting feeling is felt.

[0110]

Table 4

[0111] As shown in Table 4, the golf balls of Examples 1 to 8 are excellent in approach controllability, hitting feeling, scratch resistance, and moldability, and the standard deviation of the specific gravity of each layer is small, and the deviation of the vertical distance and the horizontal distance is small, and the variation of the vertical and horizontal distances is small. On the other hand, Comparative Examples 1 to 8 are as follows. In Comparative Example 1, the cover does not contain the (II) component and the formula (I) is large, so the moldability and approach controllability are inferior. In Comparative Example 2, the cover does not contain the (II) component and the formula (I) is large, so the approach controllability is inferior. In Comparative Example 3, the cover does not contain the (II) component and the formula (I) is large, so the moldability and hitting feeling are inferior. In Comparative Example 4, the cover does not contain the (II) component and the formula (I) is large, so the moldability, scratch resistance, and hitting feeling are inferior. In Comparative Example 5, the cover does not contain the (II) component and the formula (I) is large, so the moldability and approach controllability are inferior. In Comparative Example 6, since the standard deviation of the specific gravity of each layer is large, the variation of the horizontal distance (left - right deviation) is large. In Comparative Example 7, since the standard deviation of the specific gravity of each layer is large, the variation of the horizontal distance (left - right deviation) is large. In Comparative Example 8, since the standard deviation of the specific gravity of each layer is large, the variation of the horizontal distance (left - right deviation) is large.

Claims

1. In a golf ball in which at least one intermediate layer is formed between a core and a cover, the standard deviation of the specific gravity of each of the core, the intermediate layer, and the cover is within 0.07, and the cover is composed of the following components (I) and (II): (I) Polyurethane (II) (Meth)acrylic block copolymer It is formed of a resin composition containing the above, and the following formula (1): 0.10 ≤ VR L × VR H ≤ 0.26... (1) [In the above formula, VR L represents the ratio (η1 / η0) of the viscosity η1 (dPa·s) at 210°C to the viscosity η0 (dPa·s) at 200°C at a shear rate of 1216 (1 / sec), and VR H represents the ratio (η3 / η2) of the viscosity η3 (dPa·s) at 230°C to the viscosity η2 (dPa·s) at 220°C at a shear rate of 1216 (1 / sec).] A golf ball characterized by satisfying the above.

2. The golf ball according to claim 1, wherein the blending amount of the above component (II) is 20 parts by mass or less with respect to 100 parts by mass of the above component (I).

3. The golf ball according to claim 1 or 2, wherein the material hardness of the above component (II) is 40 or less in Shore D hardness.

4. The golf ball according to claim 1 or 2, wherein the rebound resilience of the above component (II) is 40% or less as measured according to the JIS-K 6255 standard.

5. The golf ball according to claim 1 or 2, wherein the melt flow rate (MFR) value of the above component (II) is 20 g / 10 min or more under the measurement conditions (ISO 1133) of 230°C and a load of 2.16 kgf.

6. In the block copolymer of the above component (II), the hard segment is mainly composed of methyl methacrylate units, and the soft segment is mainly composed of n-butyl acrylate units or n-butyl acrylate / 2-ethylhexyl acrylate units. The golf ball according to claim 1 or 2.

7. The golf ball according to claim 6, wherein the content of methyl methacrylate units in the block copolymer of the above component (II) is 20 to 50% by mass.

8. Let the specific gravity of the above core be CM, the specific gravity of the above intermediate layer be MM, the specific gravity of the above cover be FM, the initial velocity (m / s) of the above core be CV, the initial velocity (m / s) of the sphere (intermediate layer-coated sphere) obtained by coating the above intermediate layer on the above core be MV, the initial velocity (m / s) of the sphere (ball) obtained by coating the above cover on the above intermediate layer-coated sphere be FV, and the deflection amount (mm) 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) be FC. Then, the following formula (2) (CM × CV) + (MM × MV) + (FM × FV / FC) > 200... (2) [However, the initial velocities of the core and the intermediate layer-coated sphere are measured values obtained by measuring each target sphere using an initial velocity measuring device of the same type as the USGA drum rotation type initial velocity meter, and the initial velocity of the ball is measured using a COR type initial velocity meter of the same type as R&A.] The golf ball according to claim 1 or 2, which satisfies the above.

9. The moment of inertia of the above ball is 82.5 to 85.0 g·cm 2 The golf ball according to claim 1 or 2.

10. Let the specific gravity of the above core be CM, the specific gravity of the above intermediate layer be MM, the specific gravity of the above cover be FM, the initial velocity (m / s) of the above core be CV, the initial velocity (m / s) of the sphere (intermediate layer-coated sphere) obtained by coating the above intermediate layer on the above core be MV, the initial velocity (m / s) of the sphere (ball) obtained by coating the above cover on the above intermediate layer-coated sphere be FV, and the moment of inertia of the above ball be MOI. Then, the following formula (3) (CM × CV / MOI) + (MM × MV) + (FM × FV / FC) > 110... (3) The golf ball according to claim 1 or 2, which satisfies the above condition.

11. The golf ball according to claim 1 or 2, wherein the specific gravity of all layers of the core, the intermediate layer, and the cover is 1.10 to 1.13 g / cm 3

12. The golf ball according to claim 1 or 2, wherein the relationship between the specific gravities of the intermediate layer and the cover satisfies the following formula. -0.03 ≤ (specific gravity of the intermediate layer - specific gravity of the cover) ≤ 0.03

13. The golf ball according to claim 1 or 2, wherein the material of the intermediate layer contains barium sulfate as a specific gravity adjusting material.

14. The golf ball according to claim 1 or 2, wherein the hardness of the material of the cover is 40 to 52 in Shore D hardness.

15. The golf ball according to claim 1 or 2, wherein the deflection amount (mm) 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 2.8 mm or less.​

Images