Golf balls

Abstract

SOLUTION: To provide a golf ball in which a core is covered with a single layer or a plurality of layers of covers, at least one layer of the cover is formed of a resin composition which includes: (I) a thermoplastic polyurethane resin using as a polyol component, PTMG in which Mn is 1900-2100, (II) a thermoplastic polyurethane resin using as a polyol component, PTMG in which Mn is 900-1100, and (III) an aromatic vinyl based elastomer, in which a blending ratio of the component (I) and component (II) is set to a specific range, and Martens hardness HMb[N / mm2] of the cover layer formed by the resin composition including the components (I)-(III), and an elastic work recovery ratio ηItb[%] of the cover layer satisfy a specific formula.EFFECT: A golf ball of the invention does not reduce a carry in driver shot, is excellent in control properties in approach shot, and comprises preferable scratch resistance and molding ability.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a two- or more-piece multi-layer golf ball having a core and a cover, and more particularly to a golf ball which has excellent spin performance on approach shots, as well as excellent abrasion resistance and moldability. [Background technology]

[0002] The main characteristic required for a golf ball is an increase in flight distance, but other characteristics include the ability to stop the ball well on approach shots and abrasion resistance. That is, up until now, many golf balls have been developed that fly well on driver shots and generate a good amount of backspin on approach shots. Furthermore, materials for the cover of golf balls that have high resilience and good abrasion resistance have been developed.

[0003] Many of these cover materials, particularly for professionals and advanced players, use urethane resin materials instead of ionomer resin materials. However, professionals and advanced players are demanding golf balls that are easier to control when approaching, and more specifically, they are demanding golf balls that are excellent in operability and more delicately controllable with short irons such as sand wedges (SW) around the green. For this reason, there is a demand for further improvements in cover materials that use urethane resin materials as the base resin.

[0004] Several polymer blend cover materials have been proposed, in which a urethane resin material is used as the base resin and other resin materials are mixed in. For example, Japanese Patent Application Laid-Open No. 11-9721 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.

[0005] Recently, the physical properties of thermoplastic urethane elastomers have been improved, one of which is their improved abrasion resistance. Therefore, when blending with other resin materials, it is desirable to appropriately adjust the type and amount of the resin to prevent the inherent abrasion resistance of the thermoplastic urethane elastomer from decreasing.

[0006] Furthermore, when a urethane resin material is blended with other resin materials to reduce hardness, it is desirable to avoid changes in impact resilience and deterioration of moldability as much as possible.

[0007] Furthermore, JP 2010-238 A proposes using a multimodal polyol having a multimodal molecular weight distribution as a polyol component constituting polyurethane. However, this golf ball technology does not take into consideration the cover hardness, resilience, and moldability, and it is expected that the controllability and moldability at the time of approach will be insufficient. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 11-9721 [Patent Document 2] JP 2010-238 A Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in consideration of the above circumstances, and has as its object to provide a golf ball which has excellent controllability on approach shots without reducing the flight distance on driver shots, and which also has good abrasion resistance and moldability. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to achieve the above object, and as a result, have found that in order to further improve a resin material using thermoplastic polyurethane as the main component for the cover of a golf ball having a core and a cover, a relatively low number average molecular weight is used as the polyol component constituting the thermoplastic polyurethane, specifically, two types of urethane resins are used in a predetermined blend ratio: a thermoplastic polyurethane resin using polytetramethylene glycol having a number average molecular weight (Mn) of 1900 to 2100 as the polyol component, and a thermoplastic polyurethane resin using polytetramethylene glycol (PTMG) having a number average molecular weight (Mn) of 900 to 1100 as the polyol component. Furthermore, a cover resin composition is prepared by blending an aromatic vinyl elastomer with the above two types of urethane resin, and the Martens hardness of the cover layer formed from this resin composition is measured to be HMb [N / mm 2 ], and the elastic work recovery rate of the cover layer is ηItb [%], HMb and ηItb are expressed by the following formula (1): 2.00≦ηItb / HMb≦7.50 (1) The inventors have produced a golf ball that satisfies the above requirements, and have found that this golf ball has a high spin rate on approach, excellent controllability, and also maintains good abrasion resistance and moldability, which has led to the creation of the present invention.

[0011] That is, when the cover layer is formed from a resin composition using polyurethane as a main component, the softer the polyurethane resin used, the better the spin performance under approach conditions, but the higher the initial velocity, which tends to make it difficult to control the ball on the approach. However, it has been found that adding an aromatic vinyl elastomer in any amount can improve the initial velocity controllability (keep the initial velocity low and maintain good controllability on the approach) while maintaining the spin rate and abrasion resistance. However, if the amount of aromatic vinyl elastomer is excessively increased, the abrasion resistance deteriorates. Therefore, the present inventors have focused on the compounding design of the polyurethane resin itself used and have studied how to achieve further low resilience while maintaining good abrasion resistance. Therefore, when a high molecular weight polyol component is used as the polyurethane, the crystallinity of the urethane increases and the resilience improves. However, by adding a urethane resin of a relatively low molecular weight polyol component in a predetermined range to such a conventionally used polyurethane resin, the crystallinity is reduced and the urethane itself is made low resilient. Furthermore, in order to maintain good moldability of the cover layer, the ratio of the relatively low molecular weight polyol component to the total urethane resin is set within a specific range, and the Martens hardness and elastic work recovery rate of such a low resilience cover layer are specified as above, thereby leading to the completion of the present invention.

[0012] Accordingly, the present invention provides the following golf ball. 1. A golf ball having a core made of at least one layer and covered with a single-layer or multi-layer cover, wherein at least one layer of the cover comprises the following components (I) to (III): (I) A thermoplastic polyurethane resin using polytetramethylene glycol (PTMG) having a number average molecular weight (Mn) of 1900 to 2100 as a polyol component, (II) A thermoplastic polyurethane resin using polytetramethylene glycol (PTMG) having a number average molecular weight (Mn) of 900 to 1100 as a polyol component, and (III) Aromatic vinyl elastomers and the cover layer is formed from a resin composition containing the components (I) to (II) in a weight ratio of (II) / (I) of 0.01 to 1.10, and the Martens hardness of the cover layer formed from the resin composition containing the components (I) to (III) is HMb [N / mm 2 ], and the elastic work recovery rate of the cover layer is ηItb [%], HMb and ηItb are expressed by the following formula (1): 2.00≦ηItb / HMb≦7.50 (1) Satisfied The Martens hardness of the thermoplastic polyurethane resin material consisting of the above component (I) and the above component (II) is HMa [N / mm 2 ], 1.005≦HMa / HMb≦1.450 (2) Satisfied A golf ball characterized by: 2. The golf ball according to the above 1, wherein the lower limit of formula (1) is 2.50 and the upper limit is 6.50. 3. The golf ball according to 1 or 2 above, wherein the blending ratio (mass ratio) of component (I) to component (II) is (II) / (I)=0.05 to 0.8. 4 The amount of the component (III) to be blended is 50 parts by mass or less per 100 parts by mass of the total of the components (I) and (II). 3 2. The golf ball according to claim 1 . 5 The composition according to any one of the above 1 to 4, wherein the component (III) is a hydrogenated aromatic vinyl elastomer. 4 2. The golf ball according to claim 1 . 6 The above-mentioned 1 to 3, wherein the component (III) is an elastomer obtained by hydrogenating a polymer consisting of a polymer block mainly composed of an aromatic vinyl compound and a random copolymer block of an aromatic vinyl compound and a conjugated diene compound. 5 2. The golf ball according to claim 1 . 7The above-mentioned 1 to 3, wherein the component (III) is a hydrogenated aromatic vinyl elastomer obtained by hydrogenating a polymer comprising a polymer block of styrene and a random copolymer block of styrene and butadiene, and having a polymer block of styrene at both ends and a random copolymer block in the middle. 6 2. The golf ball according to claim 1 . 8. The melt viscosity of the above resin composition at 200°C and a shear rate of 243 (1 / sec) is 0.2×10 4 ~2.5×10 4 (dPa s) above 1~ 7 2. The golf ball according to claim 1 . Effect of the Invention

[0013] The golf ball of the present invention exhibits excellent controllability during approach shots and also maintains good abrasion resistance and moldability. [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic cross-sectional view of a golf ball according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The present invention will now be described in further detail. The golf ball of the present invention is a golf ball in which a core consisting of at least one layer is covered with a single-layer or multi-layer cover. For example, as shown in FIG. 1, there is a multi-piece solid golf ball G having a core 1, an intermediate layer (inner cover layer) 2 covering the core 1, and an outermost layer (outer cover layer) 3 covering the intermediate layer. The cover layer (outermost layer) 3 is the outermost layer in the layer structure of the golf ball, excluding the paint layer. A large number of dimples D are usually formed on the surface of the cover layer (outermost layer) 3 to improve aerodynamic characteristics. Although not shown in the figure, a paint layer is usually formed on the surface of the cover 3.

[0016] The core can be formed using a known rubber material as a base material. Known base rubbers such as natural rubber or synthetic rubber can be used as the base rubber, and more specifically, it is recommended to mainly use polybutadiene, particularly cis-1,4-polybutadiene having at least 40% or more of a cis structure. Furthermore, natural rubber, polyisoprene rubber, styrene butadiene rubber, etc. can be used in combination with the above-mentioned polybutadiene in the base rubber as desired.

[0017] Polybutadiene can also be synthesized using metal catalysts such as rare earth element catalysts such as Nd catalysts, cobalt catalysts, and nickel catalysts.

[0018] The above base rubber may be blended with 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, etc. Also, commercially available antioxidants and the like may be added as necessary.

[0019] The core can be produced by vulcanizing and curing a rubber composition containing the above-mentioned components. For example, the rubber composition is kneaded using a kneading machine such as a Banbury mixer or a roll, compression molded or injection molded using a core mold, and the molded body is appropriately heated at a temperature sufficient for the organic peroxide and co-crosslinking agent to act, that is, 100 to 200°C, preferably 140 to 180°C, for 10 to 40 minutes, to cure the molded body.

[0020] In the present invention, at least one layer of the cover comprises the following components (I) to (III): (I) A thermoplastic polyurethane resin using polytetramethylene glycol (PTMG) having a number average molecular weight (Mn) of 1900 to 2100 as a polyol component, (II) A thermoplastic polyurethane resin using polytetramethylene glycol (PTMG) having a number average molecular weight (Mn) of 900 to 1100 as a polyol component, and (III) Aromatic vinyl elastomers The resin composition is formed from a resin composition containing the following. Components (I), (II) and (III) are described in detail below.

[0021] (I) Thermoplastic polyurethane resin The polyurethane structure is composed of a soft segment made of a long-chain polyol, i.e., a polymeric polyol (polymeric glycol), and a hard segment made of a chain extender and a polyisocyanate. As described above, at least two types of thermoplastic polyurethane resins (I) and (II) are used in the present invention.

[0022] The polymer polyol used is polytetramethylene glycol (PTMG) having a number average molecular weight (Mn) of 1900 to 2100. Such PTMG is a polyurethane resin with high crystallinity, which has been widely used as a polyurethane resin for the cover layer of golf balls and can impart low resilience, spin performance during approach, and abrasion resistance.

[0023] 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, it is possible to reliably obtain a golf ball made of a polyurethane composition having various excellent properties such as the above-mentioned resilience and productivity. 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.

[0024] The number average molecular weight is calculated based on the hydroxyl value measured in accordance with JIS-K1557 (hereinafter the same).

[0025] The chain extender can be suitably used in conventional polyurethane-related techniques, 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 can be used, and among them, an aliphatic diol having 2 to 12 carbon atoms can be suitably 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, and among them, 1,4-butylene glycol can be suitably used.

[0026] The polyisocyanate may be suitably used in conventional polyurethane-related techniques, 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, tetramethyl xylene 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, some isocyanate species may be difficult to control the crosslinking reaction during injection molding.

[0027] In addition, the mixing 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 each component in a ratio such that the isocyanate groups contained in the polyisocyanate compound are 0.95 to 1.05 moles per mole of active hydrogen atoms possessed by the long-chain polyol and the chain extender.

[0028] The method for producing polyurethane is not particularly limited, and polyurethane may be produced by any of the prepolymer method and the one-shot method using a long-chain polyol, a chain extender and a polyisocyanate compound and utilizing a known urethane reaction. Among these, it is preferable to carry out melt polymerization substantially in the absence of a solvent, and it is particularly preferable to carry out the production by continuous melt polymerization using a multi-screw extruder.

[0029] The polyurethane is preferably an ether-based thermoplastic polyurethane material. As the thermoplastic polyurethane material, commercially available products can be preferably used, such as "Pandex" (trade name) manufactured by DIC Covestropolymer Co., Ltd. and "Rezamin" (trade name) manufactured by Dainichiseika Color & Chemicals Co., Ltd.

[0030] (II) Thermoplastic polyurethane resin

[0031] The polymer polyol used is polytetramethylene glycol (PTMG) with a number average molecular weight (Mn) of 900 to 1100. By using this polyurethane resin of PTMG with a relatively low molecular weight in combination with the above component (I), it is possible to impart low resilience, spin properties during approach, and abrasion resistance.

[0032] The explanation of the thermoplastic polyurethane resin other than the polymer polyol is the same as that of the (I) thermoplastic polyurethane resin.

[0033] In the present invention, the blending ratio of the above-mentioned (I) component to the above-mentioned (II) component is adjusted so that the mass ratio is (II) / (I)=0.01 to 1.10, and the preferred range is 0.05 to 0.8. If the blending amount of the above-mentioned (II) component is excessive and exceeds the above range, the solidification property of the resin material during molding of the cover layer may deteriorate, and molding defects may occur. Also, if the blending amount is below the above range, the blending amount of the above-mentioned (II) component is too small, so that the resin itself does not achieve a sufficient low resilience, and controllability on approach may be lacking.

[0034] The thermoplastic polyurethane resins of the above components (I) and (II) are the main components of the resin composition, and the thermoplastic polyurethane resins account for 50% by mass or more of the abrasion-resistant resin composition, preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and most preferably 90% by mass or more.

[0035] (III) Aromatic vinyl elastomers Next, (III) the aromatic vinyl elastomer will be described. Aromatic vinyl elastomers are polymers (elastomers) consisting of a polymer block mainly made of an aromatic vinyl compound and a random copolymer block of an aromatic vinyl compound and a conjugated diene compound. That is, aromatic vinyl elastomers, as typified by SEBS, generally have blocks of aromatic vinyl compound components at both ends as hard segments, and a block of conjugated diene compound components as soft segments in the middle. Recent research has also reported polymers in which aromatic vinyl components are randomly incorporated into the middle block in addition to conjugated diene compound components. The hardness of aromatic vinyl elastomers generally decreases as the aromatic vinyl content, which is the hard segment, decreases, and the soft segment components increase, resulting in an increase in resilience. On the other hand, when aromatic vinyl components are randomly incorporated into the soft components of the middle block, the hardness does not increase much, but the resilience decreases. The same effect can also be obtained by using a conjugated diene compound with a high Tg instead of the aromatic vinyl compound randomly incorporated into the middle block. In particular, in the present invention, in order to fully exert the above-mentioned functions and effects, it is preferable to use, as component (III), the above-mentioned polymer (elastomer) which has been subjected to a hydrogenation treatment.

[0036] Examples of the aromatic vinyl compound in the polymer include styrene, α-methylstyrene, p-methylstyrene, divinylbenzene, 1,1-diphenylethylene, N,N-dimethyl-p-aminoethylstyrene, and N,N-diethyl-p-aminoethylstyrene. These may be used alone or in combination of two or more. Among these, styrene is preferred.

[0037] Examples of the conjugated diene compound in the polymer include butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-pentadiene, and 1,3-hexadiene. These may be used alone or in combination of two or more. Among these groups, butadiene and isoprene are preferred, and butadiene is more preferred.

[0038] In addition, the units derived from the above conjugated diene compounds, for example, units derived from butadiene, become ethylene units or butylene units when subjected to hydrogenation treatment. For example, styrene-butadiene-styrene block copolymer (SBS) becomes styrene-ethylene-butylene-styrene block copolymer (SEBS) when subjected to hydrogenation treatment.

[0039] As described above, it is preferable to adopt an aromatic vinyl elastomer that has been subjected to hydrogenation treatment, i.e., a hydrogenated aromatic vinyl elastomer, as the aromatic vinyl elastomer, which is the component (III). As the hydrogenated aromatic vinyl elastomer, an elastomer obtained by hydrogenating a polymer consisting of a polymer block mainly made of an aromatic vinyl compound and a random copolymer block of an aromatic vinyl compound and a conjugated diene compound is preferable, an elastomer obtained by hydrogenating a polymer consisting of a polymer block mainly made of styrene and a random copolymer block of styrene and butadiene is more preferable, and an elastomer obtained by hydrogenating a polymer consisting of a polymer block mainly made of styrene and a random copolymer block of styrene and butadiene, and in particular, an elastomer obtained by hydrogenating a polymer having a polymer block mainly made of styrene at both ends (particularly a polymer block made of only styrene at both ends) and a random copolymer block in the middle is preferable. By using a copolymer having this structure, it is considered that the copolymer has both low hardness and low resilience, has a fast solidification speed after molding, has little tack, and has excellent compatibility with the thermoplastic polyurethane, which is the main component, so that the deterioration of physical properties due to blending can be minimized.

[0040] Specific examples of the hydrogenated aromatic vinyl elastomer include styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-isobutylene-styrene block copolymer (SIBS), styrene-isoprene-styrene block copolymer (SIS), styrene-isobutylene block copolymer (SIB), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS), styrene-butadiene-butylene-styrene block copolymer (SBBS), and styrene-ethylene-propylene block copolymer (SEP).

[0041] In the aromatic vinyl elastomer, the ratio of the units derived from aromatic vinyl compounds in the copolymer (i.e., the aromatic vinyl compound content, preferably the styrene content) is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and most preferably 60% by mass or more. In this way, by setting the aromatic vinyl compound content, preferably the styrene content, to a high level, compatibility with the thermoplastic polyurethane resins, which are components (I) and (II), is improved, and deterioration of the desired hardness and moldability can be prevented. The content of the units derived from the aromatic vinyl compound (preferably the styrene content) is measured by a H 1 - It can be calculated by NMR measurement.

[0042] Furthermore, the aromatic vinyl elastomer preferably has a glass transition temperature (Tg) indicated by the tan δ peak temperature obtained by dynamic mechanical analysis (DMA) of −20 to 50° C., more preferably at least 0° C., and even more preferably at least 5° C. In other words, by having the tan δ peak temperature in the vicinity of the temperature range at which golf balls are normally used, it is believed that the rebound resilience of the entire resin composition can be kept low in the temperature range at which golf balls are normally used, thereby enhancing the desired effects of the present invention.

[0043] As the aromatic vinyl elastomer, which is component (III), a commercially available product can be used. Examples of commercially available products include "SOE (trade name)", "Tuftec", and "Tufprene" manufactured by Asahi Kasei Corporation, and "Dicstyrene" manufactured by DIC Corporation.

[0044] The rebound resilience of component (III) is preferably 40% or less, more preferably 30% or less, and even more preferably 25% or less, as measured according to JIS-K 6255. By keeping the rebound resilience very low in this way, a small amount of the component can be added without adversely affecting the physical properties of the golf ball, and the initial velocity of the ball can be reduced during approach shots. However, the lower limit of the rebound resilience is preferably 20% or more in order to minimize the effect on the rebound reduction and the reduction in flight distance during driver shots.

[0045] The amount of the (III) component is preferably 50 parts by weight or less per 100 parts by weight of the total of the (I) and (II) components. The lower limit of the amount is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, and even more preferably 0.5 parts by weight or more. If the amount of the (III) component is too large, the abrasion resistance and moldability may deteriorate. On the other hand, if the amount of the (III) component is too small, the cover resin material may not have low hardness and desired resilience, and the effect of reducing the initial velocity of the ball during approach shots may also be reduced.

[0046] The resin composition containing the above components (I) to (III) may contain other resin materials in addition to the resin components described above in order to further improve the flowability of the resin composition for golf balls and to enhance various physical properties such as resilience and abrasion resistance.

[0047] The other resin material may be specifically selected from polyester elastomers, polyamide elastomers, ionomer resins, ethylene-ethylene-butylene-ethylene block copolymers or modified products thereof, polyacetal, polyethylene, nylon resins, methacrylic resins, polyvinyl chloride, polycarbonate, polyphenylene ether, polyarylate, polysulfone, polyethersulfone, polyetherimide, and polyamideimide, and one or more of these may be used.

[0048] The resin composition may further contain an active isocyanate compound, which reacts with the polyurethane, the main component, to further improve the abrasion resistance of the entire resin composition, and also improves the flowability and moldability due to the plasticizing effect of the isocyanate.

[0049] The isocyanate compound may be any isocyanate compound used in ordinary polyurethanes without any particular limitations. For example, aromatic isocyanate compounds include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, or a mixture of these two, 4,4-diphenylmethane diisocyanate, m-phenylene diisocyanate, 4,4'-biphenyl diisocyanate, etc., and hydrogenated products of these aromatic isocyanate compounds, such as dicyclohexylmethane diisocyanate, etc., may also be used. In addition, aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), octamethylene diisocyanate, etc., and alicyclic diisocyanates such as xylene diisocyanate, etc. may also be used. In addition, blocked isocyanate compounds obtained by reacting an isocyanate group of a compound having two or more isocyanate groups at the terminal with a compound having active hydrogen, and uretidione bodies obtained by dimerization of isocyanates may also be used.

[0050] The amount of the isocyanate compound is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and the upper limit is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, based on 100 parts by mass of the thermoplastic polyurethane resin, which is the main material. If the amount is too small, sufficient crosslinking reaction may not be obtained, and improvement in physical properties may not be observed. On the other hand, if the amount is too large, discoloration due to heat or ultraviolet rays may increase over time, or thermoplasticity may be lost, or problems such as a decrease in resilience may occur.

[0051] Furthermore, any additives can be appropriately blended into the resin composition according to the application. For example, when the golf ball material of the present invention is used as a cover material, various additives such as fillers (inorganic fillers), organic short fibers, reinforcing agents, crosslinking agents, pigments, dispersants, antioxidants, UV absorbers, and light stabilizers can be added to the above components. When these additives are blended, the blending amount is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and the upper limit is preferably 10 parts by mass or less, more preferably 4 parts by mass or less, per 100 parts by mass of the base resin.

[0052] The resilience modulus of the resin composition is preferably 65% ​​or less as measured according to JIS-K 6255 standard, since if this value is too high, there is an effect of increasing the flight distance during driver shots, but the initial velocity of the ball during approach shots also becomes high and difficult to control. However, the lower limit of the resilience modulus is preferably 30% or more in order to suppress as much as possible the decrease in resilience and the reduction in flight distance during driver shots.

[0053] From the viewpoint of spin characteristics and abrasion resistance of the resulting golf ball, the material hardness of the resin composition is preferably not more than 55 in Shore D hardness, more preferably not more than 50, even more preferably not more than 48, and most preferably not more than 45. From the viewpoint of moldability, the lower limit is preferably not less than 20 in Shore D hardness, and more preferably not less than 30 in Shore D hardness.

[0054] Regarding the method of preparing each component of the above resin composition, for example, they can be mixed using various kneading machines such as a kneading type (single screw or) twin screw extruder, a Banbury, a kneader, a lab plastomill, etc., or each component may be mixed by dry blending at the time of injection molding of the resin composition. Furthermore, when the above active isocyanate compound is used, it may be included at the time of resin mixing using various kneading machines, or a master batch containing the active isocyanate compound and other components may be separately prepared in advance, and each component may be mixed by dry blending at the time of injection molding of the resin composition.

[0055] For example, the method for molding the cover layer with the above-mentioned resin composition may be, for example, to supply the above-mentioned resin composition to an injection molding machine and inject the molten resin composition around the core to mold the cover layer. In this case, the molding temperature varies depending on the types of thermoplastic polyurethane resins (I) and (II) that are the main components, but is usually in the range of 150 to 270°C.

[0056] In the present invention, the Martens hardness of the cover layer formed from the resin composition containing the above components (I) to (III) is HMb [N / mm 2 ], and the elastic work recovery rate of the cover layer is ηItb [%], HMb and ηItb are expressed by the following formula (1): 2.00≦ηItb / HMb≦7.50 (1) It is necessary to satisfy the following.

[0057] The lower limit of the above formula (1) is 2.00 or more, preferably 2.50 or more, more preferably 2.70 or more, and the lower limit is 7.50 or less, preferably 6.50 or less, more preferably 6.30 or less. If the value of the above formula (1) is too large, the mold release property during molding may be poor or the resilience may be high, and if the value is too small, the abrasion resistance may be deteriorated.

[0058] The Martens hardness HMb of the cover layer formed from the resin composition containing the above components (I) to (III) is preferably 8.00 N / mm 2 More preferably, it is 9.00N / mm 2 The upper limit is preferably 28.00 N / mm 2 Less than or equal to 23.00N / mm 2 The following is the result.

[0059] The elastic work recovery rate ηItb of the cover layer is preferably 50% or more as a lower limit, more preferably 55% or more as an upper limit, and is preferably 85% or less, more preferably 80% or less.

[0060] The Martens hardness of the thermoplastic polyurethane resin material consisting of the above component (I) and the above component (II) is expressed as HMa [N / mm 2 ], in order to improve the control performance at the time of approach while maintaining good abrasion resistance and moldability, it is preferable that the following formula (1) is satisfied. 1.005≦HMa / HMb≦1.450 (2)

[0061] The lower limit of the above formula (2) is preferably 1.005 or more, more preferably 1.007 or more, and even more preferably 1.009 or more, and the upper limit is preferably 1.450 or less, more preferably 1.400 or less, and even more preferably 1.350 or less. If the value of the above formula (2) is too large, the abrasion resistance and moldability will deteriorate, while if the value of the above formula (2) is too small, the approach controllability may deteriorate.

[0062] The Martens hardness HMa has a lower limit of preferably 10.00 N / mm 2 More preferably, it is 11.00 N / mm 2 The upper limit is preferably 30.00 N / mm 2 Less than or equal to 25.00 N / mm 2 The following is the result.

[0063] The Martens hardness HMa and HMb can be measured using an ultra-microhardness tester based on ISO 14577:2002 "Metallic materials - Instrumented indentation test for hardness and materials parameters." In other words, it is a physical property value obtained by pressing an indenter into a measurement object while applying a load, and is expressed as the ratio of pressing force [N] / area of ​​the pressure receiving part [mm 2 The Martens hardness can be measured using, for example, an ultra-microhardness testing system, trade name "Fischerscope HM2000" (manufactured by Fisher Instruments). This measuring device can measure the hardness of the cover by continuously applying a load in steps, and the setting conditions are room temperature and an applied load of 50 mN for 10 seconds.

[0064] Furthermore, when measuring the surface of the cover, if a coating or the like has been formed on the surface of the cover, it is difficult to identify it. Also, if the hardness is measured deep from the surface of the cover toward the center of the ball, the hardness will be affected by the hardness of the adjacent layers. Therefore, it is desirable to measure the Martens hardness at a position approximately 0.3 mm from the surface of the cover toward the center of the ball, as this provides a stable measurement of the cover's inherent Martens hardness.

[0065] The elastic work recovery rates ηIta and ηItb in the above ranges allow the cover formed on the surface of the golf ball to maintain a certain hardness and elasticity while improving the self-repairing function, which contributes to the excellent durability and abrasion resistance of the ball. Even if the Martens hardness is low, if the elastic work recovery rate is too low, the spin performance during approach is good but the abrasion resistance is poor. The method for measuring the elastic work recovery rate will be described later.

[0066] The elastic work recovery rate is one of the parameters of the nanoindentation method for evaluating the physical properties of a cover, which is an ultra-microhardness test method that controls the indentation load on the order of micronewtons (μN) and tracks the indenter depth at the time of indentation with nanometer (nm) accuracy. In the conventional method, only the size of the deformation mark (plastic deformation mark) corresponding to the maximum load could be measured, but in the nanoindentation method, the relationship between the indentation load and the indentation depth can be obtained by automatic and continuous measurement. Therefore, it is considered that the physical properties of the cover can be evaluated reliably and with high accuracy without individual differences as in the conventional method of visually measuring the deformation mark with an optical microscope. For this reason, since the cover of a golf ball is greatly affected by the impact of a driver or various clubs, and the effect of the cover on various physical properties of the golf ball is not small, measuring the cover with the ultra-microhardness test method with higher accuracy than the conventional method is a very effective evaluation method.

[0067] The resin composition has a melt viscosity of 0.2×10 at 200°C and a shear rate of 243 (1 / sec). 4 ~2.5×10 4 (dPa·s). This melt viscosity provides appropriate fluidity and solidification after molding of the resin composition, and suppresses deterioration of moldability (productivity). This melt viscosity is measured at a shear rate of 243 (1 / sec) when measured with a capillograph at a temperature condition of 200°C in accordance with ISO 11443:1995.

[0068] The thickness of the cover is preferably 0.4 mm or more, more preferably 0.5 mm or more, and even more preferably 0.6 mm or more, and is preferably 3.0 mm or less, and more preferably 2.0 mm or less.

[0069] At least one intermediate layer may be interposed between the core and the core. In this case, the intermediate layer is preferably made of any of the thermoplastic resins used in golf ball cover materials, particularly ionomer resins, and commercially available ionomer resins may be used.

[0070] 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 is no particular restriction on the number of dimples formed on the surface of the outermost layer, but from the viewpoint of improving aerodynamic performance and increasing the flight distance, the number is preferably 250 or more, more preferably 270 or more, even more preferably 290 or more, and most preferably 300 or more, with the upper limit being preferably 400 or less, more preferably 380 or less, and even more preferably 360 or less.

[0071] In the present invention, a coating layer is formed on the cover surface. As the coating material for forming the coating layer, it is preferable to use a two-component curing urethane coating material. Specifically, in this case, the two-component curing urethane coating material contains a base material mainly composed of a polyol resin and a curing agent mainly composed of a polyisocyanate.

[0072] The method for applying the above-mentioned paint to the cover surface to form a coating layer is not particularly limited, and any known method can be used, such as an air gun coating method or an electrostatic coating method.

[0073] The thickness of the coating layer is not particularly limited, but is usually 8 to 22 μm, preferably 10 to 20 μm.

[0074] The golf ball of the present invention can be made for competitive use in accordance with the Rules of Golf, with 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. EXAMPLES

[0075] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples. Note that, although the values ​​in Examples 3 to 5, 8 to 10 and Comparative Examples 1 to 3, 5, and 8 are actually measured values, the values ​​in the exceptions of Examples 1, 2, 6, 7, 11 to 15 and Comparative Examples 4, 6, and 7 are predicted values ​​estimated from Examples 3 to 5, 8 to 10 and Comparative Examples 1 to 3, 5, and 8 under the same conditions.

[0076] [Examples 1 to 15, Comparative Examples 1 to 8] A rubber composition for the core common to all the examples is prepared according to the formulation shown in Table 1, and then vulcanized and molded to produce a core with a diameter of 38.6 mm.

[0077] [Table 1]

[0078] 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

[0079] Next, the intermediate layer resin material common to all the examples is mixed. This intermediate layer resin material is a blend of 50 parts by mass of sodium neutralized ethylene-unsaturated carboxylic acid copolymer with an acid content of 18% by mass and 50 parts by mass of zinc neutralized ethylene-unsaturated carboxylic acid copolymer with an acid content of 15% by mass, totaling 100 parts by mass. This resin material is injection molded around the core with a diameter of 38.6 mm obtained above to produce an intermediate layer-coated sphere with an intermediate layer thickness of 1.25 mm.

[0080] Next, the above-mentioned intermediate layer-coated sphere is injection molded with the cover materials shown in Tables 2 and 3 in the amounts shown in the tables to produce three-piece golf balls with a diameter of 42.7 mm and a cover layer (outermost layer) of 0.8 mm thickness. In this process, common dimples are formed on the cover surfaces of the examples and comparative examples, although not shown in the figures.

[0081] Preparation of resin composition for cover (outermost layer) The resin compositions are dry blended with the components and amounts shown in Tables 2 and 3 below, and injection molded at a molding temperature of 210 to 250° C. The compounding numbers in the tables indicate parts by mass.

[0082] Details of the components contained in the compositions in Tables 2 and 3 below are as follows. "TPU1": Trade name "Pandex" manufactured by DIC Covestro Polymer, ether type thermoplastic polyurethane (polyol component: PTMG with number average molecular weight of 2000), Shore D hardness "43" "TPU2": Trade name "Pandex" manufactured by DIC Covestro Polymer, ether type thermoplastic polyurethane (polyol component: PTMG with number average molecular weight of 1000), Shore D hardness "43" "TPU3": Trade name "Pandex" manufactured by DIC Covestro Polymer, ether type thermoplastic polyurethane (polyol component: PTMG with number average molecular weight of 2000), Shore D hardness "47" "TPU4": Trade name "Pandex" manufactured by DIC Covestro Polymer, ether type thermoplastic polyurethane (polyol component: PTMG with number average molecular weight of 1000), Shore D hardness "47" "SOE S1611": Hydrogenated aromatic vinyl elastomer manufactured by Asahi Kasei Corporation (styrene content: 60 wt%, Shore D hardness: 23, and rebound resilience: 20%)

[0083] The Martens hardness (HMa) and elastic work recovery rate (ηIta) of the thermoplastic polyurethane resins ("TPU1" to "TPU4") used in each Example and Comparative Example were measured by the following method. In addition, the Martens hardness (HMb) and elastic work recovery rate (ηItb) of the resin composition of the cover layer (outermost layer) used in each Example and Comparative Example were measured. Next, the following two relational expressions of these parameters were used: Equation (1): ηItb / HMb, and Formula (2): HMa / HMb, These calculated values ​​are shown in Tables 2 and 3.

[0084] Martens hardness (HMb) of the outermost layer (cover layer) For each golf ball, the ball was cut in half, and a point 0.3 mm from the surface of the cover toward the center of the ball was identified on the cross section of the ball. The Martens hardness HMb [N / mm 2 ] is measured using an ultra-microhardness tester, Fischerscope HM2000, manufactured by Fisher Instruments, Inc. The hardness measurement is performed at room temperature under an applied load of 50 mN / 10 s.

[0085] Martens hardness (HMa) of thermoplastic polyurethane resin materials The Martens hardness (HMa) of the thermoplastic polyurethane resin material is measured in the same manner as above. The Martens hardness of each of the thermoplastic polyurethane resins ("TPU1" to "TPU4") is as follows. The measuring device and conditions for the Martens hardness of these resins are the same as those described above. - Martens hardness of TPU1: 14.3N / mm 2 - Martens hardness of TPU2: 13.8N / mm 2 - Martens hardness of TPU3: 22.1N / mm 2 - Martens hardness of TPU4: 22.0N / mm 2

[0086] Elastic work recovery rate of the cover layer (outermost layer) The elastic work recovery rate of the cover layer is measured using an ultra-microhardness tester, Fischerscope HM2000, manufactured by Fisher Instruments. The measurement conditions are room temperature, an applied load of 50 mN / 10 s, and the indentation work W due to the return deformation of the cover. elast (Nm) and mechanical pushing work W total Based on this, the elastic work recovery rate is calculated by the following formula: Elastic work recovery rate = W elast / W total × 100(%)

[0087] Elastic work recovery rate of resin materials The elastic work recovery rate (%) of each of the polyurethane resins ("TPU1" to "TPU4") is as follows. The measuring device and measuring conditions for the elastic work recovery rate of these resins are the same as those described above. Elastic work recovery rate of TPU1: 72% Elastic work recovery rate of TPU2: 71% Elastic work recovery rate of TPU3: 57% Elastic work recovery rate of TPU4: 56%

[0088] Melt Viscosity Tables 2 and 3 show the melt viscosity of each resin composition at a shear rate of 243 (1 / sec) when measured with a capillograph at a temperature condition of 200° C. in accordance with ISO 11443:1995.

[0089] Ball properties during approach shots For each of the obtained golf balls of each Example and Comparative Example, a sand wedge (SW) was attached to a golf hitting robot, and the initial velocity and backspin amount of the ball immediately after hitting with a head speed (HS) of 20 m / s were measured using an initial condition measuring device. These measured values ​​are shown in Tables 2 and 3.

[0090] In addition, a sensory evaluation of the operability of the club during an approach was performed by the following method. The results are shown in Tables 2 and 3. [Judgment and Evaluation] 〇 ··· Extremely easy to operate. △ ··· Excellent operability. ×...Poor operability.

[0091] Evaluation of abrasion resistance The balls were kept warm at 23°C, and five balls of each type were hit at a head speed of 33 m / s using a swing robot machine and a pinching wedge club, and the impact damage was visually evaluated according to the following criteria. The evaluation results are shown in Tables 2 and 3. [Judgment and Evaluation] 〇: Slightly scratched or barely noticeable scratches. △ The surface is slightly fuzzy or the dimples are slightly missing. × The dimple has been completely removed.

[0092] Evaluation of moldability (removal) The balls of each example were evaluated for ease of demolding from the mold after the cover was injection molded, according to the following criteria. The results are shown in Tables 2 and 3. ○ No external damage such as broken runners or pins sticking occurs when demolding. × When removing from the mold, external damage such as broken runners or pins getting stuck occurs, making molding impossible.

[0093] [Table 2]

[0094] The following points can be considered from the results in Table 2. In Examples 1 to 5, when the amount of component (III) was fixed at 3 parts by mass and the ratio of (II) / (I) was gradually increased, the initial velocity of actual shots on approach shots decreased and the controllability improved while maintaining moldability and abrasion resistance. In Examples 6 to 10, as compared with Examples 1 to 5, the amount of component (III) was increased from 3 parts by mass to 50 parts by mass, thereby improving the controllability. In Comparative Example 1, compared to Example 1, 3 parts by mass of component (III) was blended, but component (II), PTMG having a molecular weight of 1000, was not blended, and therefore controllability in the approach was lacking. Comparative Example 2 is an example in which components (I) and (III) are not blended and only component (II) is used. Although the controllability in approach is good, moldability is poor and productivity is poor. Comparative Example 3 is an example in which components (II) and (III) are not blended and only component (I) is used, and although the moldability and abrasion resistance are good, controllability in the approach is lacking. Comparative Example 4 is an example in which only component (I) was used as the thermoplastic polyurethane resin, and component (III) was blended in excess, and although the controllability on approach was good, the abrasion resistance was significantly deteriorated. In Comparative Example 5, the ratio of (II) / (I) is as large as 3.00, and therefore the controllability in the approach is good, but the moldability is poor, resulting in poor productivity.

[0095] [Table 3]

[0096] The following points can be considered from the results in Table 3. In Examples 11 to 15, the thermoplastic polyurethane resin used has a Shore D hardness of 47, which is harder than the thermoplastic polyurethane resins of Examples 1 to 10 in Table 2. In these Examples, as in Examples 1 to 5, when the component (III) is fixed at 3 parts by mass and the ratio of (II) / (I) is gradually increased, the initial velocity of actual shots on approach shots decreases and controllability improves while maintaining moldability and abrasion resistance. In Comparative Example 6, compared to Example 11, 3 parts by mass of component (III) was blended, but component (II) PTMG having a molecular weight of 1000 was not blended, so that the controllability of the approach was somewhat lacking. Comparative Example 7 is an example in which components (I) and (III) are not blended and only component (II) is used. Although the controllability in approach is good, moldability is poor and productivity is poor. Comparative Example 8 is an example in which components (II) and (III) are not blended and only component (I) is used, and although the moldability and abrasion resistance are good, controllability in the approach is lacking.

Claims

1. A golf ball having a core made of at least one layer and covered with a single-layer or multi-layer cover, wherein at least one layer of the cover comprises the following components (I) to (III): (I) A thermoplastic polyurethane resin using polytetramethylene glycol (PTMG) having a number average molecular weight (Mn) of 1,900 to 2,100 as a polyol component; (II) A thermoplastic polyurethane resin using polytetramethylene glycol (PTMG) having a number average molecular weight (Mn) of 900 to 1100 as a polyol component, and (III) Aromatic vinyl elastomer and the cover layer is formed from a resin composition containing the components (I) to (II) in a weight ratio of (II) / (I) of 0.01 to 1.10, and the Martens hardness of the cover layer formed from the resin composition containing the components (I) to (III) is HMb [N / mm 2 ], and the elastic work recovery rate of the cover layer is ηItb [%], HMb and ηItb are expressed by the following formula (1): 2.00≦η / HM≦7.50 (1) and the Martens hardness of the thermoplastic polyurethane resin material comprising the above component (I) and the above component (II) is expressed as HMa [N / mm 2 ]. 1.005≦HMa / HMb≦1.450 ... (2) A golf ball characterized by satisfying the above.

2. 2. The golf ball of claim 1, wherein the lower limit of formula (1) is 2.50 and the upper limit is 6.

50.

3. 3. The golf ball according to claim 1, wherein the blending ratio (mass ratio) of component (I) to component (II) is (II) / (I)=0.05 to 0.

8.

4. 4. The golf ball according to claim 1, wherein the blending amount of the component (III) is 50 parts by weight or less per 100 parts by weight of the combined total of the components (I) and (II).

5. 5. The golf ball of claim 1, wherein the component (III) is a hydrogenated aromatic vinyl elastomer.

6. 6. The golf ball according to claim 1, wherein the component (III) is an elastomer obtained by hydrogenating a polymer consisting of a polymer block mainly composed of an aromatic vinyl compound and a random copolymer block of an aromatic vinyl compound and a conjugated diene compound.

7. 7. The golf ball according to claim 1, wherein the component (III) is a hydrogenated aromatic vinyl elastomer obtained by hydrogenating a polymer which comprises a polymer block made of styrene and a random copolymer block of styrene and butadiene, and has polymer blocks made of styrene at both ends and a random copolymer block in the middle.

8. The melt viscosity of the resin composition at 200° C. and a shear rate of 243 (1 / sec) is 0.2×10 4 ~2.5 x 10 4 8. The golf ball of claim 1, wherein the viscosity is (dPa·s).

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