golf balls

Abstract

To provide a golf ball increasing a spin rate on approach shots without reducing flight distance performance of driver (W#1) hits and having a favorable feeling.SOLUTION: A golf ball comprises a single- or multi-layer core, an intermediate layer and a cover. The cover consists of two layers of an inner cover layer and an outer cover layer, where the material hardness of the inner cover layer is 20 to 40 in Shore D hardness, the material hardness of the outer cover layer is 35 to 55 in Shore D hardness, and the total thicknesses of the two layers is 0.6-1.2 mm. When rebound resilience (%) of the material of the inner cover layer based on JIS-K 6255 is (A) and a rebound resilience (%) of a material of an outer cover layer based on JIS-K 6255 is (B), the golf ball satisfies 0<(A)-(B)<18.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a golf ball having a multi-layer structure including a single-layer or multi-layer core, an intermediate layer, and a two-layer cover consisting of an inner cover layer and an outer cover layer. [Background technology]

[0002] While the primary characteristic required for a golf ball is increased flight distance, another required characteristic is the ability to stop the ball well on approach shots. To achieve these characteristics, urethane resin materials have recently been increasingly used as golf ball cover materials. In particular, thermoplastic urethane elastomers have become increasingly popular as urethane resin materials, and their physical properties are being improved year by year. Several techniques have been proposed to further improve the physical properties of cover resin compositions by blending other resins and additives with thermoplastic urethane elastomers as the base resin.

[0003] For example, Patent Document 1 proposes using a blend of thermoplastic polyurethane and a styrene-based block copolymer as the main material of the cover in order to improve the abrasion resistance of the cover material. However, this blend cover was insufficient in terms of rebound resilience and abrasion resistance. Furthermore, Patent Document 2 discloses a golf ball in which a plasticizer is blended into a resin composition based on a urethane resin to soften the resin composition. However, this merely softens the resin composition, and is insufficient to improve the spin rate on approach shots.

[0004] Furthermore, when blending a urethane resin material with other resin materials to reduce hardness, it is desirable to avoid changes in impact resilience and deterioration in moldability as much as possible. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-9721 [Patent Document 2] Japanese Patent Application Publication No. 2017-12737 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide a golf ball that increases the amount of spin on approach shots and provides a good feel without compromising the distance performance on driver (W#1) shots. [Means for solving the problem]

[0007] As a result of extensive research into achieving the above-mentioned object, the inventors have discovered that in a golf ball having a core, an intermediate layer, and a cover (outermost layer), in order to improve controllability on approach shots, rather than using the conventional method of blending various other polymers and additives into a urethane resin material, a relatively thin layer such as a film can be formed on the inside of the cover (outermost layer) of the golf ball, and a material having a specific range of rebound resilience and hardness can be selected for this thin layer, or the relationship between the rebound resilience of this thin layer and the cover (outermost layer) can be specified. This finding led to the completion of the present invention.

[0008] Accordingly, the present invention provides the following golf balls. 1. A golf ball having a core of one or more layers, an intermediate layer, and a cover, wherein the cover is made of two layers: an inner cover layer and an outer cover layer, the inner cover layer having a material hardness of 20 to 40 Shore D hardness, the outer cover layer having a material hardness of 35 to 55 Shore D hardness, the total thickness of these two layers being 0.6 to 1.2 mm, and wherein the rebound resilience (%) of the inner cover layer material based on JIS-K 6255 is (A), and the rebound resilience (%) of the outer cover layer material based on JIS-K 6255 is (B), the relationship of 0<(A)-(B)<18 is satisfied. 2. The golf ball according to 1 above, wherein the resin component of the material for the outer cover layer is a thermoplastic polyurethane elastomer. 3. The golf ball according to 1 or 2 above, wherein the resin component of the material for the inner cover layer is a thermoplastic elastomer. 4. The golf ball according to 1 or 2 above, wherein the resin component of the material of the inner cover layer is a multicomponent copolymer having conjugated diene units, non-conjugated olefin units, and aromatic vinyl units, wherein the conjugated diene units include butadiene units, the non-conjugated olefin units include units selected from the group consisting of ethylene units, propylene units, and 1-butene units, and the aromatic vinyl units include styrene units, and the content of the conjugated diene units in the multicomponent copolymer is 5% by mass or more. 5. The golf ball according to 4 above, wherein the content of the conjugated diene units in the multicomponent copolymer is 10% by mass or more. 6. The golf ball according to 4 above, wherein the content of the non-conjugated olefin units in the multicomponent copolymer is 90% by mass or less. 7. The golf ball according to 4 above, wherein the content of the aromatic vinyl units in the multicomponent copolymer is 30% by mass or less. 8. The golf ball according to 4 above, wherein the non-conjugated olefin units are ethylene units. 9. The golf ball according to 4 above, wherein the multi-component copolymer is a copolymer polymerized with a gadolinium metallocene complex catalyst. 10. The golf ball according to 1 or 2 above, wherein the inner cover layer has a thickness of 0.1 to 0.5 mm. 11. The thickness relationship between the intermediate layer, inner cover layer, and outer cover layer is expressed by the following formula: Midlayer thickness > Inner cover thickness < Outer cover thickness 3. The golf ball according to 1 or 2 above, which satisfies the above. 12. The golf ball according to 1 or 2 above, wherein the ratio of the thickness (a) of the inner cover layer to the thickness (b) of the outer cover layer is (a) / (b)=0.10 to 0.60. [Effects of the Invention]

[0009] The golf ball of the present invention increases the spin rate on approach shots without compromising the distance performance on driver (W#1) shots, and also provides a good feel. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view of a golf ball according to one embodiment of the present invention.

[0011] The present invention will be described in more detail below. As shown in Figure 1, the golf ball of the present invention is a golf ball G having a core 1, an intermediate layer 2 enclosing the core, an outer cover layer 4 enclosing the intermediate layer, and a thin inner cover layer 3 inside the outer cover layer 4. The core 1 and the intermediate layer 2 can each be formed as a single layer or multiple layers. The surface of the outer cover layer 4 usually has numerous dimples D formed thereon, and is usually coated with a paint layer 5.

[0012] The core can be formed using a known rubber material as the base material. Known natural or synthetic rubbers can be used as the base rubber. More specifically, polybutadiene, particularly cis-1,4-polybutadiene having at least 40% or more cis structure, is recommended as the primary base material. Furthermore, natural rubber, polyisoprene rubber, styrene-butadiene rubber, etc. can be used in combination with the polybutadiene, as desired, in the base rubber.

[0013] Polybutadiene can also be synthesized using a metal catalyst such as a rare earth element catalyst such as a Nd catalyst, a cobalt catalyst, or a nickel catalyst.

[0014] The base rubber may contain co-crosslinking agents such as unsaturated carboxylic acids and their metal salts, inorganic fillers such as zinc oxide, barium sulfate, and calcium carbonate, and organic peroxides such as dicumyl peroxide and 1,1-bis(t-butylperoxy)cyclohexane. Commercially available antioxidants may also be added as needed.

[0015] The diameter of the core is not particularly limited, but is preferably 20 mm or more, more preferably 25 mm or more, and even more preferably 30 mm or more, with the upper limit being preferably 41 mm or less, and more preferably 40 mm or less.

[0016] The material hardness of the intermediate layer is not particularly limited, but can be set to a Shore D hardness of 55 or more, preferably 60 or more, and more preferably 65 or more. There is also no particular upper limit, but it can be set to preferably 70 or less.

[0017] The thickness of the intermediate layer is not particularly limited, but is preferably 0.5 mm or more, more preferably 0.6 mm or more, and even more preferably 0.7 mm or more, and the upper limit is preferably 1.8 mm or less, more preferably 1.7 mm or less, and even more preferably 1.6 mm or less.

[0018] The material for the intermediate layer is not particularly limited, but known thermoplastic resins and thermoplastic elastomers can be used, and it is particularly preferable to use an ionomer material. Specifically, it is preferable to use a commercially available ionomer resin or a resin mixture containing the following components (i) to (iv). (i-1) an olefin-unsaturated carboxylic acid binary random copolymer and / or a metal ion-neutralized product of an olefin-unsaturated carboxylic acid binary random copolymer; (ii-2) 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 in a mass ratio of 100:0 to 0:100 (i) a base resin and (ii) a non-ionomer thermoplastic elastomer in a mass ratio of 100:0 to 50:50, (iii) 5 to 80 parts by mass of a fatty acid and / or a derivative thereof having a molecular weight of 228 to 1500; (ix) 0.1 to 17 parts by mass of a basic inorganic metal compound capable of neutralizing unneutralized acid groups in the above components (i) and (iii). In particular, when using a mixed material of the above components (i) to (ix), it is preferable to use one in which 70% or more of the acid groups have been neutralized.

[0019] In the present invention, an inner cover layer is formed adjacent to the inside of the outer cover layer, which will be described later. This layer is as thin as a film and has appropriate resilience.

[0020] The thickness of the inner cover layer is preferably 0.1 mm or more, more preferably 0.2 mm or more, with an upper limit of preferably 0.5 mm or less, more preferably 0.4 mm or less. If the thickness is less than this range, the spin rate may not be high when hitting with a club such as a sand wedge (SW) on an approach shot. On the other hand, if the thickness is greater than this range, the spin rate may increase when hitting with a driver (W#1), resulting in a limited distance and a poor feel.

[0021] The material hardness of the inner cover layer is 20 or more, preferably 24 or more, and more preferably 28 or more, in Shore D hardness. The upper limit is 40 or less, preferably 38 or less, and more preferably 36 or less. If the material hardness of this inner cover layer is lower than the above range, the spin rate upon impact with a driver (W#1) increases, making it impossible to increase the distance. On the other hand, if the material hardness of this inner cover layer is higher than the above range, the spin rate upon approach shots with a club such as a sand wedge (SW) is not high, and the feel upon impact is poor.

[0022] The rebound resilience of the material for the inner cover layer, as measured according to JIS-K 6255, is preferably 50% or more, more preferably 55% or more, with the upper limit being preferably 75% or less, more preferably 70% or less. If the rebound resilience is too low, the spin rate on approach shots will be high, but the distance on driver shots may be reduced. If the rebound resilience is too high, the desired high spin rate on approach shots may not be achieved. The rebound resilience of the material for the inner cover layer is always set higher than the rebound resilience of the material for the outer cover layer, which will be described later.

[0023] The inner cover layer may be made of a resin component selected from various thermoplastic elastomers, or may be made of a multicomponent copolymer containing conjugated diene units, non-conjugated olefin units, and aromatic vinyl units. This multicomponent copolymer is described in Japanese Patent No. 6780827 and has optimal impact resilience and other properties for the present invention. This multicomponent copolymer is described as follows:

[0024] <Conjugated diene unit> The multicomponent copolymer contains conjugated diene units. The conjugated diene units are structural units derived from a conjugated diene compound as a monomer. Because the multicomponent copolymer can be polymerized using a conjugated diene compound as a monomer, it has superior crosslinking properties compared to copolymers polymerized using a non-conjugated diene compound such as the well-known EPDM. The conjugated diene compounds include butadiene units. The butadiene units are structural units derived from butadiene compounds, and specific examples of butadiene compounds include 1,3-butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. Furthermore, the conjugated diene units in the multicomponent copolymer preferably contain 1,3-butadiene units, and more preferably consist solely of 1,3-butadiene units.

[0025] Furthermore, the multicomponent copolymer preferably has a cis-1,4 bond content of 50% or more, more preferably 70% or more, even more preferably 80% or more, and particularly preferably 90% or more, based on all the conjugated diene units. Such a multicomponent copolymer having a high cis-1,4 bond content of all the conjugated diene units can be obtained by using a conjugated diene compound, a non-conjugated olefin compound, and an aromatic vinyl compound as monomers. Meanwhile, the vinyl bond (1,2 vinyl bond, 3,4 vinyl bond, etc.) content of all the conjugated diene units is preferably 30% or less, more preferably 15% or less, even more preferably 10% or less, and particularly preferably 6% or less. Furthermore, the trans-1,4 bond content of all the conjugated diene units is preferably 30% or less, more preferably 15% or less, and even more preferably 10% or less. The contents of cis-1,4 bonds, trans-1,4 bonds, and vinyl bonds can be determined from the integral ratios of the results of 1H-NMR and 13C-NMR measurements.

[0026] The conjugated diene compound may be used alone or in combination of two or more. That is, the multicomponent copolymer may contain one type of conjugated diene unit alone or two or more types. The content of the conjugated diene unit is preferably 10% by mass or more, more preferably 15% by mass or more, of the entire multicomponent copolymer. Furthermore, the content of the conjugated diene unit is preferably 80% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less, of the entire multicomponent copolymer.

[0027] <Non-conjugated olefin unit> The multicomponent copolymer contains non-conjugated olefin units. The non-conjugated olefin units are structural units derived from a non-conjugated olefin compound as a monomer. The non-conjugated olefin compound is selected from the group consisting of ethylene, propylene, and 1-butene. In particular, in order to impart sufficient impact resilience and softness to the golf ball material, it is preferable that the non-conjugated olefin units be ethylene units.

[0028] The non-conjugated olefin compound may be used alone or in combination of two or more. That is, the multicomponent copolymer may contain one non-conjugated olefin unit alone or two or more non-conjugated olefin units. The content of the non-conjugated olefin unit is preferably more than 20% by mass and less than 90% by mass of the entire multicomponent copolymer, more preferably 30 to 85% by mass, even more preferably 40 to 80% by mass, and most preferably 45 to 75% by mass.

[0029] <Aromatic vinyl unit> The above-mentioned multicomponent copolymer contains an aromatic vinyl unit. The aromatic vinyl unit is a structural unit derived from an aromatic vinyl compound as a monomer. Examples of the aromatic vinyl compound include styrene compounds, specifically styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, o-ethylstyrene, m-ethylstyrene, p-ethylstyrene, etc. The aromatic vinyl unit in the above-mentioned multicomponent copolymer contains a styrene unit, and more preferably consists of only a styrene unit. Note that the aromatic ring in the aromatic vinyl unit is not included in the main chain of the copolymer unless it is bonded to an adjacent unit.

[0030] The aromatic vinyl compounds may be used alone or in combination of two or more. That is, the multicomponent copolymer may contain one type of aromatic vinyl unit alone or two or more types. The content of the aromatic vinyl unit is 3 to 30% by mass of the entire multicomponent copolymer. If the content of the aromatic vinyl unit is less than 3% by mass or more than 30% by mass, the length of the non-conjugated olefin portion of the copolymer cannot be suppressed, and the durability improvement derived from the non-conjugated olefin crystals is not achieved. The content of the aromatic vinyl unit is preferably 3 to 30% by mass of the entire multicomponent copolymer, more preferably 5 to 25% by mass, and even more preferably 10 to 20% by mass.

[0031] The number of types of monomers in the multicomponent copolymer is not particularly limited as long as the multicomponent copolymer contains conjugated diene units, non-conjugated olefin units, and aromatic vinyl units. The multicomponent copolymer may contain other structural units in addition to the conjugated diene units, non-conjugated olefin units, and aromatic vinyl units. From the viewpoint of achieving the desired effect, the content of the other structural units is preferably 30% by mass or less of the entire multicomponent copolymer, more preferably 20% by mass or less, and even more preferably 10% by mass or less. It is particularly preferable that the other structural units are not contained, i.e., the content is 0% by mass.

[0032] The multicomponent copolymer is a multicomponent copolymer containing at least one conjugated diene unit, one non-conjugated olefin unit, and one aromatic vinyl unit. From the viewpoint of obtaining favorable breaking properties, the multicomponent copolymer is preferably a polymer obtained by polymerizing at least one conjugated diene compound, one non-conjugated olefin compound, and one aromatic vinyl compound as monomers. The multicomponent copolymer is more preferably a terpolymer consisting of only one type of conjugated diene unit, one type of non-conjugated olefin unit, and one type of aromatic vinyl unit, and even more preferably a terpolymer consisting of only 1,3-butadiene units, ethylene units, and styrene units. Here, "one type of conjugated diene unit" encompasses conjugated diene units with different bonding modes.

[0033] Multicomponent copolymers contain conjugated diene units, non-conjugated olefin units, and aromatic vinyl units, and one of their major characteristics is that their main chains are composed exclusively of acyclic structures. A cyclic main chain reduces fracture properties (especially elongation at break). NMR is the primary measurement method used to confirm whether the main chain of a multicomponent copolymer has a cyclic structure. Specifically, if peaks attributable to cyclic structures present in the main chain (e.g., peaks appearing at 10 to 24 ppm for three- to five-membered rings) are not observed, this indicates that the main chain of the multicomponent copolymer is composed exclusively of acyclic structures. Furthermore, as described below, multicomponent copolymers can be synthesized in a single reaction vessel, i.e., one-pot synthesis, allowing for simplified production.

[0034] The multicomponent copolymer preferably has a polystyrene-equivalent weight-average molecular weight (Mw) of 10,000 to 10,000,000, more preferably 100,000 to 9,000,000, and even more preferably 150,000 to 8,000,000. A multicomponent copolymer with an Mw of 10,000 or greater ensures sufficient strength as a golf ball material, while an Mw of 10,000,000 or less ensures high workability. The weight-average molecular weight and molecular weight distribution are determined by gel permeation chromatography (GPC) using polystyrene as a standard.

[0035] The chain structure of the multicomponent copolymer is not particularly limited and can be appropriately selected depending on the purpose. For example, where A is a conjugated diene unit, B is a non-conjugated olefin unit, and C is an aromatic vinyl unit, the multicomponent copolymer may have a structure such as Ax-By-Cz (x, y, and z are integers of 1 or greater), a random copolymer in which A, B, and C are randomly arranged, a tapered copolymer consisting of a mixture of the random copolymer and the block copolymer, or an alternating copolymer having a structure such as (ABC)w (w is an integer of 1 or greater). The multicomponent copolymer may have a structure in which the conjugated diene unit, the non-conjugated olefin unit, and the aromatic vinyl unit are linearly linked (linear structure), or a structure in which at least one of the conjugated diene unit, the non-conjugated olefin unit, and the aromatic vinyl unit is linked by forming a branched chain (branched structure). When the multicomponent copolymer has a branched structure, the branched chain can also be bicomponent or multicomponent (i.e., the branched chain can contain at least two of the conjugated diene unit, the non-conjugated olefin unit, and the aromatic vinyl unit). Therefore, among multicomponent copolymers, multicomponent copolymers having a branched structure with two or more branched chains can be clearly distinguished from conventional graft copolymers in which the backbone chain and the side chains are formed of a single type of unit that is different from each other.

[0036] The production method, polymerization process, and production conditions such as the polymerization catalyst to be used for the multicomponent copolymer can be those described in Japanese Patent No. 6780827. Preferably, the multicomponent copolymer is one polymerized using a gadolinium metallocene complex catalyst.

[0037] The material hardness of the outer cover layer is at least 35, preferably at least 40, and more preferably at least 42, in Shore D hardness. The upper limit is not more than 55, preferably not more than 52, and more preferably not more than 50. If the material hardness of the outer cover layer deviates from the above range, it may be impossible to sufficiently achieve low spin on full shots with a driver (W#1), or it may be impossible to obtain high controllability due to a high spin rate on approaches.

[0038] There are no particular restrictions on the thickness of the outer cover layer, but it is preferably at least 0.4 mm, more preferably at least 0.5 mm, and the upper limit is preferably at most 1.0 mm, more preferably at most 0.9 mm.

[0039] In the present invention, the thickness relationship between the intermediate layer, the inner cover layer, and the outer cover layer is expressed by the following formula: Midlayer thickness > Inner cover thickness < Outer cover thickness Furthermore, the ratio of the thickness (a) of the inner cover layer to the thickness (b) of the outer cover layer, expressed as (a) / (b), is preferably 0.10 or greater, more preferably 0.20 or greater, with the upper limit being preferably 0.60 or less, more preferably 0.50 or less. If the ratio is outside the above range, the spin rate upon impact with a driver (W#1) may increase, resulting in a poorer distance or a worsening feel.

[0040] The sum of the thickness (a) of the inner cover layer and the thickness (b) of the outer cover layer, (a) + (b), is 0.6 mm or more, and preferably 0.7 mm or more. The upper limit is 1.2 mm or less, and preferably 1.0 mm or less. If the sum of the thicknesses falls outside the specified range, the spin rate may not be high when approaching with a club such as a sand wedge (SW), or the spin rate may increase when hitting with a driver (W#1), resulting in a decrease in flight distance.

[0041] The rebound resilience of the outer cover layer material, as measured according to JIS-K 6255, is preferably 40% or more, more preferably 45% or more, with the upper limit being preferably 60% or less, more preferably 55% or less. If the rebound resilience is too low, the spin rate on driver shots may increase, resulting in reduced distance, and the spin rate on approach shots may also decrease. On the other hand, if the rebound resilience is too high, the desired high spin rate on approach shots may not be achieved.

[0042] The present invention is characterized in that, where the rebound resilience (%) of the inner cover layer material based on JIS-K 6255 is (A) and the rebound resilience (%) of the outer cover layer material based on JIS-K 6255 is (B), the relationship 0<(A)-(B)<18 is satisfied. By consistently setting the rebound resilience of the inner cover layer material higher than that of the outer cover layer material and setting the difference in rebound resilience between the two within a specific range, the desired effects of the present invention can be achieved, such as increased spin rate and improved feel on approach shots without compromising distance performance on driver (W#1) shots. The lower limit of the difference in rebound resilience between the two, i.e., (A)-(B), is preferably 3% or more, more preferably 5% or more, and even more preferably 7% or more, with the upper limit preferably 17% or less. If the value of (A)-(B) is outside the above range, the ball will not spin sufficiently on approach shots, preventing the desired high spin rate from being achieved.

[0043] The resin material for the outer cover layer is not particularly limited, but it is preferable to use a polyurethane resin material, the details of which are as follows:

[0044] The polyurethane structure consists of a soft segment made of a long-chain polyol (polymeric glycol), and a hard segment made of a chain extender and polyisocyanate. The polymeric polyol used as the raw material can be any of those conventionally used in polyurethane material technology, and is not particularly limited. Examples include polyester polyols, polyether polyols, polycarbonate polyols, polyester polycarbonate polyols, polyolefin polyols, conjugated diene polymer polyols, castor oil polyols, silicone polyols, and vinyl polymer polyols. Specific examples of polyester polyols include adipate polyols such as polyethylene adipate glycol, polypropylene adipate glycol, polybutadiene adipate glycol, and polyhexamethylene adipate glycol, as well as lactone polyols such as polycaprolactone polyols. Examples of polyether polyols include poly(ethylene glycol), poly(propylene glycol), poly(tetramethylene glycol), and poly(methyltetramethylene glycol). These may be used alone or in combination of two or more.

[0045] As the polymer polyol, it is preferable to use a polyether polyol.

[0046] The number-average molecular weight of the long-chain polyol is preferably within the range of 1,000 to 5,000. By using a long-chain polyol having such a number-average molecular weight, golf balls made from polyurethane compositions having various excellent properties such as the above-mentioned resilience and productivity can be reliably obtained. The number-average molecular weight of the long-chain polyol is more preferably within the range of 1,500 to 4,000, and even more preferably within the range of 1,700 to 3,500.

[0047] The number average molecular weight mentioned above is a number average molecular weight calculated based on the hydroxyl value measured in accordance with JIS-K1557 (the same applies hereinafter).

[0048] The chain extender may be any of those used in conventional polyurethane-related technologies, and is not particularly limited. In the present invention, a low-molecular-weight compound having two or more active hydrogen atoms in the molecule that can react with an isocyanate group and a molecular weight of 2,000 or less may be used, and among these, an aliphatic diol having 2 to 12 carbon atoms may be preferably used. Specific examples include 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, and 2,2-dimethyl-1,3-propanediol, and among these, 1,4-butylene glycol may be particularly preferably used.

[0049] The polyisocyanate may be any of those used in conventional polyurethane-related technologies, and is not particularly limited. 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, tetramethylxylene 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 may be used. However, depending on the isocyanate, it may be difficult to control the crosslinking reaction during injection molding.

[0050] The ratio of active hydrogen atoms to isocyanate groups in the polyurethane-forming reaction can be adjusted within a suitable range. Specifically, when the long-chain polyol, polyisocyanate compound, and chain extender are reacted to produce polyurethane, it is preferable to use the components in such a ratio that the amount of isocyanate groups contained in the polyisocyanate compound is 0.95 to 1.05 moles per mole of active hydrogen atoms contained in the long-chain polyol and chain extender.

[0051] The method for producing polyurethane is not particularly limited, and polyurethane may be produced by either a prepolymer method or a one-shot method using a long-chain polyol, a chain extender, and a polyisocyanate compound, utilizing a known urethane reaction. Among these methods, melt polymerization in the substantial absence of a solvent is preferred, and production by continuous melt polymerization using a multi-screw extruder is particularly preferred.

[0052] As the polyurethane, it is preferable to use a thermoplastic polyurethane material, and particularly an ether-based thermoplastic polyurethane material. As the thermoplastic polyurethane material, commercially available products can be suitably used, such as "Pandex" manufactured by DIC Covestropolymer Co., Ltd. and "Rezamin" manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.

[0053] The resin materials for the intermediate layer, inner cover layer, and outer cover layer described above can be blended with various additives as needed, such as pigments, dispersants, antioxidants, light stabilizers, UV absorbers, and release agents. Each of the resin materials described above can be obtained by mixing the components described above using various kneading machines, such as a kneading-type (single-screw or) twin-screw extruder, a Banbury mixer, or a kneader.

[0054] In the present invention, a sphere (unpainted golf ball) having the above-described core, intermediate layer, inner cover layer, and outer cover layer can be manufactured by conventional methods such as injection molding or hot-press molding. For example, the materials for the intermediate layer and inner cover layer can be sequentially injected around the core using respective injection molds to obtain each coated sphere, and finally, the material for the outer cover layer, which is the outermost layer, can be injection molded to obtain a multi-layered golf ball. Alternatively, a golf ball can be manufactured by encasing the coated sphere in two half-cups previously molded into a spherical half-shell and then hot-press molding the coated sphere to form each coating layer.

[0055] The golf ball of the present invention has a large number of dimples on the surface of the outermost layer from the viewpoint of aerodynamic performance. There are no particular restrictions on the number of dimples formed on the surface of the outermost layer, but from the viewpoint of improving aerodynamic performance and increasing flight distance, the number is preferably at least 250, more preferably at least 270, even more preferably at least 290, and most preferably at least 300, with the upper limit being preferably at most 400, more preferably at most 380, and even more preferably at most 360.

[0056] In the present invention, a paint layer is formed on the surface of the cover. As the paint for forming this paint layer, a two-component curing urethane paint is preferably used. Specifically, in this case, the two-component curing urethane paint contains a base agent whose main component is a polyol resin and a curing agent whose main component is polyisocyanate.

[0057] The method for applying the above-mentioned paint to the cover surface to form a paint layer is not particularly limited, and any known method can be used, such as air gun painting or electrostatic painting, as desired.

[0058] There are no particular restrictions on the thickness of the paint layer, but it is usually 8 to 22 μm, preferably 10 to 20 μm.

[0059] The golf ball of the present invention can be made to conform to the Rules of Golf for competitive use, and can be formed to have an outer diameter of 42.80 mm or less so as not to pass through a ring with an inner diameter of 42.672 mm, and a mass of preferably 45.0 to 45.93 g. [Example]

[0060] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0061] [Examples 1 to 5, Comparative Examples 1 to 11] A rubber composition for the core common to all examples was prepared using the formulation shown in Table 1, and then vulcanized and molded to produce a core with a diameter of 38.7 mm.

[0062] [Table 1]

[0063] Details of the core material are as follows: "cis-1,4-Polybutadiene" manufactured by JSR Corporation, product name "BR01" "Zinc acrylate" manufactured by Nippon Shokubai Co., Ltd. Zinc oxide, manufactured by Sakai Chemical Industry Co., Ltd. "Barium sulfate" manufactured by Sakai Chemical Industry Co., Ltd. "Anti-aging agent" product name "Nocrac NS6" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) "Organic peroxide (1)" Dicumyl peroxide, trade name "Percumyl D" (manufactured by NOF Corporation) "Organic peroxide (2)": A mixture of 1,1-di(tert-butylperoxy)cyclohexane and silica, trade name "Perhexa C-40" (manufactured by NOF Corporation) "Zinc stearate" manufactured by NOF Corporation

[0064] middle class The resin material for the intermediate layer was injection molded around a core with a diameter of 38.7 mm to produce an intermediate-layer-coated sphere with an intermediate layer thickness of 1.0 mm, 1.2 mm, or 1.4 mm. The resin material for the intermediate layer was a resin formulation common to all examples: a blend of 50 parts by weight of sodium-neutralized ethylene-unsaturated carboxylic acid copolymer with an acid content of 18% by weight and 50 parts by weight of zinc-neutralized ethylene-unsaturated carboxylic acid copolymer with an acid content of 15% by weight, totaling 100 parts by weight.

[0065] Inner cover layer Next, an inner cover layer was formed around the mid layer-covered sphere of each example using resin materials No. 1 to No. 8 shown in Table 2 (Examples 1 to 5 and Comparative Examples 1 to 3) and Table 3 (Comparative Examples 4 to 11). This formation method involves first molding a pair of hemispherical half cups from the inner cover layer material, and then encasing the mid layer in these half cups and molding them under heat and pressure.

[0066] Details of the components contained in the compositions shown in Tables 2 and 3 below are as follows. No.1 "Multicomponent copolymer A" Details below No.2 "Multicomponent copolymer B" Details below No. 3: Hytrel 3001, a thermoplastic polyether ester elastomer manufactured by Toray DuPont No. 4: Hytrel 2401, a thermoplastic polyether ester elastomer manufactured by Toray DuPont No. 5 "HPF2000" manufactured by The Dow Chemical Company No.6 "AN4319" Mitsui Dow Polychemicals "Nucrel" No. 7: "AN42012" Nucrel manufactured by Mitsui Dow Polychemicals. No. 8: "SOES1611" Styrene-ethylene-butylene-styrene block copolymer (SEBS) manufactured by Asahi Kasei.

[0067] Multi-component copolymer A 80 g of styrene and 600 mL of toluene are added to a thoroughly dried 1,000 mL pressure-resistant stainless steel reactor. In a glove box under a nitrogen atmosphere, 0.25 mmol of mono(bis(1,3-tert-butyldimethylsilyl)indenyl)bis(bis(dimethylsilyl)amide) gadolinium complex (1,3-[(t-Bu)MeSi]CHGd[N(SiHMe)]), 0.275 mmol of dimethylanilinium tetrakis(pentafluorophenyl)borate [MeNHPhB(CF)], and 1.1 mmol of diisobutylaluminum hydride were placed in a glass vessel, and 40 mL of toluene was added to prepare a catalyst solution. The catalyst solution is added to the pressure-resistant stainless steel reactor and heated to 70°C. Next, ethylene is charged into the pressure-resistant stainless steel reactor at a pressure of 1.5 MPa, and then 80 mL of a toluene solution containing 20 g of 1,3-butadiene is charged into the pressure-resistant stainless steel reactor over 8 hours, and copolymerization is carried out at 70°C for a total of 8.5 hours. Next, 1 mL of a 5% by mass solution of 2,2'-methylene-bis(4-ethyl-6-t-butylphenol) (NS-5) in isopropanol is added to the pressure-resistant stainless steel reactor to stop the reaction. Next, the copolymer is separated using a large amount of methanol and dried in vacuum at 50°C to obtain copolymer A.

[0068] Multi-component copolymer B 65 g of styrene and 600 mL of toluene are added to a thoroughly dried 1,000 mL pressure-resistant stainless steel reactor. In a glove box under a nitrogen atmosphere, 0.26 mmol of mono(bis(1,3-tert-butyldimethylsilyl)indenyl)bis(bis(dimethylsilyl)amido) gadolinium complex (1,3-[(t-Bu)MeSi]CHGd[N(SiHMe)]), 0.283 mmol of dimethylanilinium tetrakis(pentafluorophenyl)borate [MeNHPhB(CF)], and 0.83 mmol of diisobutylaluminum hydride were charged into a glass vessel, and 40 mL of toluene was added to form a catalyst solution. The catalyst solution was then added to the pressure-resistant stainless steel reactor and heated to 70°C. Next, ethylene is charged into the pressure-resistant stainless steel reactor at a pressure of 1.5 MPa, and then 120 mL of a toluene solution containing 24 g of 1,3-butadiene is charged into the pressure-resistant stainless steel reactor over 8 hours, and copolymerization is carried out at 70°C for a total of 8.5 hours. Next, 1 mL of a 5% by mass solution of 2,2'-methylene-bis(4-ethyl-6-t-butylphenol) (NS-5) in isopropanol is added to the pressure-resistant stainless steel reactor to stop the reaction. Next, the copolymer is separated using a large amount of methanol and dried in vacuum at 50°C to obtain copolymer B.

[0069] For each of the "multicomponent copolymer A" and "multicomponent copolymer B," the contents (mass %) of butadiene, ethylene, and styrene are measured and evaluated by the following method. <Butadiene, ethylene, and styrene content> The contents of butadiene, ethylene, and styrene in each copolymer 1 The results are as follows: "Multicomponent copolymer A": Butadiene / ethylene / styrene = 14 / 70 / 16 (mass%), weight average molecular weight (Mw) 273 x 10 3 "Multicomponent copolymer B": Butadiene / ethylene / styrene = 16 / 72 / 12 (mass%) Weight average molecular weight (Mw) 338 x 10 3

[0070] Outer cover layer Next, a urethane resin material common to all examples (trade name "Pandex" manufactured by DIC Covestro Polymer, an ether-type thermoplastic polyurethane with a Shore D hardness of 47) was injection molded around the sphere, resulting in a sphere with an intermediate layer coated with an inner cover layer, to produce golf balls of a predetermined thickness so as to achieve a diameter of 42.7 mm in all examples. While not specifically shown, common dimples were formed on the cover surface of each example and comparative example. Additionally, a common two-component curing polyurethane resin composition was applied to a thickness of 15 μm on the cover surface of each example and comparative example.

[0071] The material hardness and rebound resilience of the cover of the above golf ball were measured as follows, and the values ​​shown in Table 2 (Examples 1 to 5 and Comparative Examples 1 to 3) and Table 3 (Comparative Examples 4 to 11) were obtained.

[0072] Material hardness (Shore D hardness) of the inner and outer cover layers The resin material for each cover layer was molded into a 2mm thick sheet and left for at least two weeks. After that, the Shore D hardness was measured in accordance with the ASTM D2240-95 standard.

[0073] Rebound elasticity The resin material is formed into a 2 mm thick sheet using a press, stacked to a thickness of 4 mm, and the temperature is adjusted to 23 ± 1°C. After that, the rebound resilience is measured using a Tripson type rebound resilience device in accordance with JIS-K 6255 (2013) (note that the drop angle specified in the JIS-K 6255 standard is adjusted to 40 degrees to measure the above rebound resilience).

[0074] The spin performance of each golf ball on driver (W#1) shots and approach shots, and the feel on approach shots were evaluated using the following methods. The results are shown in Table 2 (Examples 1 to 5 and Comparative Examples 1 to 3) and Table 3 (Comparative Examples 4 to 11).

[0075] Spin performance when using a driver A driver (W#1) was attached to the golf hitting robot, and the amount of backspin immediately after hitting the ball at a head speed (HS) of 45 m / s was measured using an initial condition measuring device and evaluated according to the following criteria. The driver (W#1) used was the "Tour B XD-3 (loft angle 9.5°)" manufactured by Bridgestone Sports Co., Ltd. [Judgment evaluation] ◎ Spin rate less than 3000 rpm ○ Spin rate is 3000 rpm or more and less than 3100 rpm △: Spin rate is 3100 rpm or more and less than 3200 rpm × Spin rate is 3200 rpm or more

[0076] Spin performance during approach A sand wedge (SW) was attached to a golf hitting robot, and the amount of backspin immediately after hitting the ball at a head speed (HS) of 10 m / s was measured using an initial condition measuring device and evaluated according to the following criteria. The sand wedge (SW) used was the "Tour B XW-B (loft angle 56°)" manufactured by Bridgestone Sports Co., Ltd. [Judgment evaluation] ◎ Spin rate of 3200 rpm or more ○ Spin rate is 3150 rpm or more and less than 3200 rpm △ Spin rate is 3050 rpm or more and less than 3150 rpm × Spin rate less than 3050 rpm

[0077] Feeling evaluation A sensory evaluation of the feel of the ball when hitting an approach shot is carried out using the following method. The club used is a sand wedge (SW) manufactured by Bridgestone Sports Co., Ltd., product name "TOUR B XW-B" (loft angle 56°), and amateur golfers evaluate the actual shot using the following criteria. [Judgment evaluation] ◎ Very good hitting feel 〇 ··· Good feel × Poor feel The feel of the hit is judged based on the impact (hardness) of the ball hitting the club face, the sound of the ball hitting the club, and how the ball is launched.

[0078] [Table 2]

[0079] [Table 3]

[0080] As shown in Tables 2 and 3, the golf balls of Comparative Examples 1 to 11 are inferior to the products of the present invention (Examples) in the following respects. Comparative Example 1, in which no inner cover layer was formed, had a poor feel on impact and slightly less spin on approach shots. In Comparative Example 2, no inner cover layer was formed, and the spin rate on approach shots was slightly lower. In Comparative Example 3, no inner cover layer is formed, and the spin rate on approach shots is low. In Comparative Example 4, the difference in resilience between the inner cover layer and the outer cover layer exceeds 18%, resulting in a low spin rate on approach shots. In Comparative Example 5, the difference in resilience between the inner cover layer and the outer cover layer exceeds 18%, resulting in a low spin rate on approach shots. In Comparative Example 6, the inner cover layer had a material hardness of over 40 in Shore D hardness, resulting in a poor feel on approach shots. In Comparative Example 7, the inner cover layer had a material hardness of over 40 in Shore D hardness, and the spin rate on approach shots was slightly low. In Comparative Example 8, the material hardness of the inner cover layer exceeded 40 in Shore D hardness, and the difference in resilience between the inner cover layer and the outer cover layer exceeded 18%, resulting in a slightly higher spin rate when hit with a driver (W#1) and a poor feel. In Comparative Example 9, the outer cover layer had a higher rebound resilience than the inner cover layer, resulting in a slightly higher spin rate on driver (W#1) shots and a slightly lower spin rate on approach shots. In Comparative Example 10, the inner cover layer had a material hardness of over 40 Shore D hardness, and the outer cover layer had a higher resilience than the inner cover layer, resulting in low spin rate and poor feel on approach shots. In Comparative Example 11, the outer cover layer had a higher rebound resilience than the inner cover layer, resulting in a slightly lower spin rate on approach shots. [Explanation of symbols]

[0081] G Golf Ball 1 core 2. Middle class 3 Inner cover layer 4 outer cover layer 5 Paint layer D dimple

Claims

1. A golf ball having a core of one or more layers, an intermediate layer, and a cover, wherein the cover is made of two layers, an inner cover layer and an outer cover layer, the inner cover layer having a material hardness of 20 to 40 Shore D hardness, the outer cover layer having a material hardness of 35 to 55 Shore D hardness, the total thickness of these two layers being 0.6 to 1.2 mm, and wherein, where A is the rebound resilience (%) of the material of the inner cover layer based on JIS-K 6255, and B is the rebound resilience (%) of the material of the outer cover layer based on JIS-K 6255, the golf ball satisfies the relationship 0<(A)-(B)<18.

2. 2. The golf ball of claim 1, wherein the resin component of the material for the outer cover layer is a thermoplastic polyurethane elastomer.

3. 3. The golf ball according to claim 1, wherein the resin component of the material for said inner cover layer is a thermoplastic elastomer.

4. 3. The golf ball of claim 1, wherein the resin component of the material of the inner cover layer is a multicomponent copolymer having conjugated diene units, non-conjugated olefin units, and aromatic vinyl units, the conjugated diene units include butadiene units, the non-conjugated olefin units include units selected from the group consisting of ethylene units, propylene units, and 1-butene units, the aromatic vinyl units include styrene units, and the content of the conjugated diene units in the multicomponent copolymer is 5% by mass or greater.

5. 5. The golf ball according to claim 4, wherein the content of the conjugated diene unit in the multicomponent copolymer is 10% by mass or more.

6. 5. The golf ball according to claim 4, wherein the content of the non-conjugated olefin units in the multicomponent copolymer is 90% by mass or less.

7. 5. The golf ball according to claim 4, wherein the content of the aromatic vinyl units in the multi-component copolymer is 30% by mass or less.

8. 5. The golf ball of claim 4, wherein the non-conjugated olefin units are ethylene units.

9. 5. The golf ball of claim 4, wherein the multi-component copolymer is a copolymer polymerized with a gadolinium metallocene complex catalyst.

10. 3. The golf ball according to claim 1, wherein the thickness of the inner cover layer is 0.1 to 0.5 mm.

11. The thickness relationship between the intermediate layer, inner cover layer, and outer cover layer is expressed by the following formula: Mid layer thickness > inner cover thickness < outer cover thickness 3. The golf ball of claim 1, wherein the above formula satisfies the above formula.

12. 3. The golf ball according to claim 1, wherein the ratio of the thickness (a) of the inner cover layer to the thickness (b) of the outer cover layer is (a) / (b)=0.10 to 0.60.

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