Golf ball

Abstract

SOLUTION: In a golf ball having a rubber core and at least one layer of a cover covering the core, at least one layer of the cover is made of a resin composition that contains the following components (I) and (II): (I) thermoplastic polyurethane; and (II) inorganic filler; wherein the content of the ingredient (II) is 5 parts by mass or more with respect to 100 parts by mass of the ingredient (I), in the resin composition, the abrasion volume in a Taber abrasion test in accordance with JIS-K 7311 is larger than 0.003 cm3, and when the Shore D hardness is H, the melt viscosity at 210°C at a shear rate of 6080 (1 / sec) in accordance with ISO 11443:1995 is η1 (Pa s), and the melt viscosity at 220°C is η2 (Pa s), the following formula (1) is satisfied. 7.0×10-4>(η1-η2) / H3 (1)EFFECT: In the golf ball of the present invention, it is possible to improve the fluidity and the abrasiveness of the cover resin material when molding the cover.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a golf ball having at least one layer of core and at least one layer of cover.

Background Art

[0002] The required characteristics of a golf ball are mainly an increase in flight distance. In addition, there are performance such as the ball stopping well during approach shots and abrasion resistance. That is, until now, many golf balls that fly well when hit with a driver and have suitable backspin during approach shots have been developed. Recently, for professionals and advanced players, many have adopted polyurethane resin as an alternative to ionomer resin materials.

[0003] When using a relatively soft and hard polyurethane among polyurethane resins, when a low-hardness polyurethane resin is coated and molded as a cover, and in processes such as handling after molding and polishing the cover surface, there are many inconveniences in the entire production process, such as the difficulty of molding, damage to the cover during and after molding, and the difficulty of polishing work. Also, generally, it is known that adding a filler to a resin material reduces the fluidity of the resin, and in particular, when using a fibrous filler, the fluidity is significantly reduced. For this reason, the discharge amount of the resin molded product also decreases, and it becomes necessary to increase the discharge by increasing the extrusion rotation speed or injection speed.

[0004] Patent Document 1 discloses a technique of once preparing a cover material by blending a thermoplastic polyurethane and titanium oxide, and then molding a cover using this cover material. At this time, by setting the ratio of the melt viscosity of the thermoplastic polyurethane used as the raw material and the cover material obtained by blending the raw materials within a certain range, the durability, scratch resistance, and appearance of the obtained cover are improved. And Patent Document 1 describes that by using titanium oxide with a water content of 0.60 mass% or less, the melt viscosity ratio becomes within a certain range. However, Patent Document 1 only explains the influence of the water content of titanium oxide on the viscosity, and it is described that it is preferable to use titanium oxide with a low water content. And when the blending amount of titanium oxide is less, the viscosity becomes lower, and when the blending amount of titanium oxide is increased, the fluidity deteriorates. That is, generally, it is considered that when a filler is added to a resin material, the fluidity decreases. Patent Document 1 has not found that the fluidity and abrasiveness are improved by adding titanium oxide to the thermoplastic urethane used for the outer layer of a golf ball.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a golf ball with high productivity by improving the fluidity and abrasiveness of the cover resin material during molding even when a low-hardness polyurethane resin with high production difficulty is used as the cover resin material.

Means for Solving the Problems

[0007] In order to achieve the above object, the present inventor uses, as the material of the cover, a resin composition containing a thermoplastic polyurethane and an inorganic filler such as titanium oxide in a golf ball having a core and a cover, and the wear volume after 1000 rotations in the Taber abrasion test according to JIS-K 7311 of this resin composition is 0.003 cm 3 Furthermore, in accordance with ISO 11443:1995, when measured with a capillary rheometer, the melt viscosity at 210 °C at a shear rate of 6080 (1 / sec) is η1 (Pa·s), and the melt viscosity at 220 °C is η2 (Pa·s). When the Shore D hardness of this resin composition is H, the following formula (1) 7.0×10 -4 >(η1 - η2) / H 3 ···(1) When the above resin composition was prepared so as to satisfy the above conditions, in the manufacturing process of the golf ball, the fluidity of the polyurethane resin material during urethane cover molding and the abrasiveness during the polishing operation of the cover surface after cover molding were good. In particular, it was found that the fluidity and abrasiveness can be improved when using a polyurethane resin material with a soft hardness that is easily damaged and difficult to polish, and thus the present invention was completed.

[0008] Therefore, the present invention provides the following golf ball. 1. In a golf ball comprising at least one layer of a rubber core and at least one layer of a cover covering the core, at least one layer of the cover is composed of a resin composition containing the following components (I) and (II) (I) Thermoplastic polyurethane (II) Inorganic filler The blending amount of the component (II) is 5 parts by mass or more with respect to 100 parts by mass of the component (I), and in the above resin composition, the wear volume after 1000 rotations in the Taber abrasion test according to JIS-K 7311 is 0.003 cm 3Larger, in accordance with ISO 11443:1995, when measured with a capillary rheometer, the melt viscosity at a shear rate of 6080 (1 / sec) at 210 °C is η1 (Pa·s), the melt viscosity at 220 °C is η2 (Pa·s), and the Shore D hardness is H. When the following formula (1) 7.0×10 -4 >(η1 - η2) / H 3 ···(1) A golf ball characterized by satisfying the above. 2. The golf ball according to item 1 above, wherein the Shore D hardness of the resin composition is less than 50. 3. The golf ball according to item 1 or 2 above, wherein the component (II) is titanium oxide. 4. The golf ball according to item 3 above, wherein the average particle size of titanium oxide is 0.21 μm or more. 5. The golf ball according to item 1 or 2 above, wherein the melt viscosity η1 is 200 Pa·s or less. 6. The golf ball according to item 1 or 2 above, wherein the melt viscosity η2 is 150 Pa·s or less.

Advantages of the Invention

[0009] The golf ball of the present invention has good fluidity of the cover resin material during urethane cover molding, excellent moldability, and enhanced abrasion resistance during the polishing operation of the cover surface after molding, and can improve the productivity of the golf ball.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0011] Hereinafter, the present invention will be described in more detail. The golf ball of the present invention has a ball structure in which at least one layer of a cover, that is, a single-layer or multi-layer cover, is coated on a core composed of at least one layer.

[0012] The above core can be formed using a known rubber material as a base material. As the base rubber, a known base rubber of natural rubber or synthetic rubber can be used. More specifically, it is recommended to mainly use polybutadiene, especially cis-1,4-polybutadiene having at least 40% or more of a cis structure. Further, in the base rubber, natural rubber, polyisoprene rubber, styrene-butadiene rubber, etc. can be used in combination with the above-mentioned polybutadiene as desired.

[0013] Also, polybutadiene can be synthesized by metal catalysts such as rare earth element-based catalysts of Nd catalysts, cobalt catalysts, and nickel catalysts.

[0014] To the above base rubber, co-crosslinking agents such as unsaturated carboxylic acids and their metal salts, inorganic fillers such as zinc oxide, barium sulfate, and calcium carbonate, organic peroxides such as dicumyl peroxide and 1,1-bis(t-butylperoxy)cyclohexane, etc. can be blended. Further, if necessary, commercially available anti-aging agents, etc. can be appropriately added.

[0015] The above core can be manufactured by vulcanizing and curing a rubber composition containing the above components. For example, kneading is performed using a kneader such as a Banbury mixer or a roll, compression molding or injection molding is performed using a core mold, and the molded body is appropriately heated under conditions of 100 to 200 ° C, preferably 140 to 180 ° C, and 10 to 40 minutes, which is a temperature sufficient for the organic peroxide and the co-crosslinking agent to act, to cure the molded body and manufacture it.

[0016] The golf ball of the present invention has a core covered with a single-layer or multiple-layer cover. Examples of such golf ball embodiments include a golf ball having a single-layer cover on the core, and a golf ball having a core, an intermediate layer covering the core, and an outermost layer covering the intermediate layer.

[0017] In the present invention, as the resin material of at least one layer of the cover, the following components (I) and (II) (I) Polyurethane (II) Inorganic filler A resin composition containing the same is used.

[0018] (I) Polyurethane Polyurethane can be the main material or the base resin of the above cover material (resin composition). The details of this component are as follows.

[0019] The structure of polyurethane consists of a soft segment made of a high molecular polyol (polymeric glycol) which is a long-chain polyol, and a chain extender and a polyisocyanate that constitute the hard segment. Here, as the high molecular polyol used as a raw material, any of those conventionally used in technologies related to polyurethane materials can be used, and there is no particular limitation. For example, polyester polyols, polyether polyols, polycarbonate polyols, polyester polycarbonate polyols, polyolefin polyols, conjugated diene polymerization polyols, castor oil polyols, silicone polyols, vinyl polymerization polyols, etc. can be mentioned. As the polyester polyol, specifically, adipate polyols such as polyethylene adipate glycol, polypropylene adipate glycol, polybutadiene adipate glycol, polyhexamethylene adipate glycol, and lactone polyols such as polycaprolactone polyol can be adopted. Examples of the polyether polyol include poly(ethylene glycol), poly(propylene glycol), poly(tetramethylene glycol), poly(methyltetramethylene glycol), etc. These may be used alone or in combination of two or more.

[0020] As the above-mentioned high molecular polyol, it is preferable to use a polyether polyol.

[0021] The number average molecular weight of the above-mentioned long-chain polyol is preferably in the range of 1,000 to 5,000. By using a long-chain polyol having such a number average molecular weight, a golf ball made of a polyurethane composition excellent in various properties such as the above-mentioned resilience and productivity can be surely obtained. The number average molecular weight of the long-chain polyol is more preferably in the range of 1,500 to 4,000, and even more preferably in the range of 1,700 to 3,500.

[0022] In addition, the above-mentioned number average molecular weight is the number average molecular weight calculated based on the hydroxyl value measured in accordance with JIS-K1557 (hereinafter the same).

[0023] As the chain extender, those used in the prior art related to polyurethane can be preferably used, and there is no particular limitation. In the present invention, a low molecular compound having two or more active hydrogen atoms capable of reacting with isocyanate groups in the molecule and having a molecular weight of 2,000 or less can be used. Among them, aliphatic diols having 2 to 12 carbon atoms can be preferably used. Specifically, 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, etc. can be mentioned. Among them, 1,4-butylene glycol can be particularly preferably used.

[0024] As the polyisocyanate, those used in the prior art related to polyurethane can be preferably used, and there is no particular limitation. Specifically, one or more selected from the group consisting of 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, naphthylene 1,5-diisocyanate, tetramethylxylylene diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylene diisocyanate, 1,4-bis(isocyanatomethyl)cyclohexane, and dimer acid diisocyanate can be used. However, depending on the isocyanate species, it may be difficult to control the cross-linking reaction during injection molding.

[0025] In addition, the mixing ratio of active hydrogen atoms to isocyanate groups in the polyurethane-forming reaction can be adjusted as appropriate within a preferable range. Specifically, when producing polyurethane by reacting the above-mentioned long-chain polyol, polyisocyanate compound, and chain extender, it is preferable to use each component at a ratio such that the isocyanate groups contained in the polyisocyanate compound are 0.95 to 1.05 moles per 1 mole of active hydrogen atoms possessed by the long-chain polyol and the chain extender.

[0026] The method for producing the polyurethane is not particularly limited, and it may be produced by any of the prepolymer method and the one-shot method using a known urethanization reaction using a long-chain polyol, a chain extender, and a polyisocyanate compound. Among them, it is preferable to perform melt polymerization substantially in the absence of a solvent, and particularly preferably to produce it by continuous melt polymerization using a multi-screw type extruder.

[0027] As the above-mentioned polyurethane, it is preferable to use a thermoplastic polyurethane material, and particularly preferably an ether-based thermoplastic polyurethane material. As the thermoplastic polyurethane material, commercially available products can be preferably used, and examples thereof include the product name "Pandex" manufactured by DIC Covestro Polymer Co., Ltd. and the product name "Resamin" manufactured by Dainichi Seika Kogyo Co., Ltd.

[0028] Regarding the material hardness of the above-mentioned component (I), from the viewpoints of spin characteristics and scratch resistance obtained as a golf ball, it is preferably 52 or less in Shore D hardness, more preferably 50 or less in Shore D hardness, and still more preferably 48 or less. Also, as the lower limit value, from the viewpoint of moldability, it is preferably 38 or more in Shore D hardness, more preferably 40 or more in Shore D hardness.

[0029] The resilience modulus of the above-mentioned component (I) is preferably 55% or more, more preferably 57% or more, and still more preferably 59% or more from the comprehensive viewpoints as a golf ball such as initial velocity performance and spin performance during hitting. The above-mentioned resilience modulus is measured based on the JIS-K 6255:2013 standard.

[0030] The above-mentioned component (I) is the main material of the resin composition. From the viewpoint of sufficiently imparting the scratch resistance of the urethane resin, it is 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, and most preferably 90% by mass or more of the resin composition.

[0031] In the present invention, by blending the component (II) described in detail below with the above-mentioned component (I), the fluidity and polishability of the cover resin material during molding can be improved, and a golf ball with high productivity can be obtained.

[0032] (II) Inorganic filler The inorganic filler is blended for the purpose of improving the fluidity of the thermoplastic polyurethane resin as the base resin and the polishability of the resin composition by blending a predetermined amount with respect to the base resin of the above-mentioned component (I). Examples of the inorganic filler include titanium oxide, zinc oxide, alumina, magnesium oxide, barium sulfate, aluminum nitride, boron nitride, barium titanate, talc, kaolin, calcium carbonate, silica, glass beads, and powdered glass. In particular, it is preferable to use titanium oxide from the viewpoint of reducing the melt viscosity during injection molding and obtaining high polishability of the resin molded product. Titanium oxide can be produced by the sulfuric acid method or the chlorine method, and the rutile type or anatase type can be used. Furthermore, composite particles obtained by surface-treating the surface of titanium oxide with aluminum oxide or a silane coupling agent (polysiloxane) can also be used.

[0033] Regarding the above-mentioned inorganic filler, in the particle size distribution measured by the laser diffraction scattering method, the average particle diameter D50 at which the cumulative amount from the fine particle side reaches 50% by mass is preferably 0.10 μm or more, more preferably 0.15 μm or more, preferably 0.20 μm or more, and the upper limit value is not particularly limited, but is preferably 1.0 μm or less.

[0034] (II) The compounding amount is 5 parts by mass or more, preferably 6 parts by mass or more, more preferably 7 parts by mass or more, based on 100 parts by mass of the above (I) component. The upper limit is preferably 30 parts by mass or less, more preferably 25 parts by mass or less.

[0035] In the resin composition containing the above (I) and (II), other resin materials may be blended in addition to the above-described components. The purpose is to improve the fluidity, resilience, crack durability and other physical properties of the resin composition for golf balls.

[0036] Specific examples of other resin materials include polyamide elastomers, ionomer resins, ethylene-ethylene / butylene-ethylene block copolymers or modified products thereof, polyacetals, polyethylenes, nylon resins, styrene resins, polyvinyl chlorides, polycarbonates, polyphenylene ethers, polyarylates, polysulfones, polyethersulfones, polyetherimides and polyamideimides. One or more of them can be used.

[0037] In addition, the above resin composition can further contain an active isocyanate compound. This active isocyanate compound can react with the main components, polyurethane or polyurea, to further improve the scratch resistance of the entire resin composition. In addition, the plasticizing effect of isocyanate can improve the fluidity and thus the moldability.

[0038] As the above isocyanate compound, any isocyanate compound that is normally used in polyurethane can be used without particular limitation. For example, as aromatic isocyanate compounds, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate or a mixture of both, 4,4-diphenylmethane diisocyanate, m-phenylene diisocyanate, 4,4'-biphenyl diisocyanate, etc. can be mentioned. Hydrogenated products of these aromatic isocyanate compounds, such as dicyclohexylmethane diisocyanate, etc. can also be used. Further, aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), octamethylene diisocyanate, and alicyclic diisocyanates such as xylene diisocyanate can be mentioned. Furthermore, blocked isocyanate compounds obtained by reacting the isocyanate groups of a compound having two or more isocyanate groups at the terminal with a compound having active hydrogen, uretdione bodies formed by dimerization of isocyanates, etc. can be mentioned.

[0039] The blending amount of the above isocyanate compound is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, based on 100 parts by mass of the polyurethane or polyurea resin as the component (I). Also, as the upper limit value, it is preferably 30 parts by mass or less, more preferably 20 parts by mass or less. If this blending amount is too small, a sufficient cross-linking reaction may not be obtained, and improvement in physical properties may not be observed in some cases. On the other hand, if this blending amount is too large, discoloration over time, by heat or ultraviolet rays may increase, or problems such as loss of thermoplasticity or decrease in resilience may occur.

[0040] Furthermore, optional additives can be appropriately blended into the above resin composition according to the application. For example, when using the golf ball material of the present invention as a cover material, various additives such as organic short fibers, reinforcing agents, crosslinking agents, pigments, dispersants, antioxidants, ultraviolet absorbers, and light stabilizers can be added to the above components. When blending these additives, the blending amount is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, and the upper limit is preferably 10 parts by mass or less, more preferably 4 parts by mass or less, based on 100 parts by mass of the base resin.

[0041] Regarding the rebound elastic modulus of the above resin composition, in order to achieve low rebound and improve the amount of approach spin, it is required to be 48% or more as measured according to JIS-K 6255:2013 standard, preferably 50% or more, more preferably 52% or more, and the upper limit value is 72% or less, preferably 70% or less, more preferably 68% or less.

[0042] Also, regarding the material hardness of the above resin composition, from the viewpoints of scratch resistance and imparting an appropriate amount of approach spin, it is preferably less than 50 in Shore D hardness, more preferably 48 or less, and more preferably 45 or less in Shore D hardness. As the lower limit value, from the viewpoint of moldability, it is preferably 30 or more in Shore D hardness, more preferably 35 or more.

[0043] In the present invention, in the above resin composition, the wear volume after 1000 rotations in the Taber abrasion test according to JIS-K 7311 is 0.003 cm 3 One of the characteristics is that it is larger. When increasing the blending amount of the inorganic filler in the above resin composition, the amount of wear will be large and it will be excellent in abrasiveness, and the polishing operation after cover molding can be carried out smoothly. In particular, when using a relatively soft thermoplastic polyurethane as the resin base material, it is possible to improve the problems of the polishing operation caused by the softness of the cover surface and to polish the cover surface uniformly and well during polishing. The preferable amount of the above wear volume is preferably 0.005 cm 3 or more, more preferably 0.007 cm 3 or more, and even more preferably 0.01 cm3 Above, most preferably 0.02 cm 3 or more.

[0044] In addition, in the present invention, in the above resin composition, when measured with a capillary rheometer in accordance with ISO 11443:1995, when the melt viscosity at 210 °C at a shear rate of 6080 (1 / sec) is η1 (Pa·s) and the melt viscosity at 220 °C is η2 (Pa·s), and the Shore D hardness is H, the following formula (1) 7.0×10 -4 (η1 - η2) / H 3 ···(1) is one of the features. That is, for the above resin composition, the value obtained by dividing the difference between the viscosity at 210 °C and the viscosity at 220 °C at a specific shear rate by the cube of its resin hardness (Shore D hardness) is 7.0×10 -4 or less. Specifically, this technical meaning means that, as shown in FIG. 3, when the difference between the viscosity at 210 °C and the viscosity at 220 °C is taken, when a large amount of titanium oxide is blended, the difference in the above viscosity per a certain resin hardness becomes small. For this reason, the temperature dependence of the viscosity becomes small, and the higher the amount of the (II) inorganic filler such as titanium oxide is blended, the higher the fluidity independent of temperature is obtained, and the workability during molding becomes good. Also, the value of the above (η1 - η2) / H 3 is preferably 6.5×10 -4 or less, more preferably 6.0×10 -4 or less, still more preferably 5.5×10 -4 or less.

[0045] It is preferable that the above melt viscosity η1 is 200 Pa·s or less, more preferably 180 Pa·s or less, still more preferably 150 Pa·s or less, and most preferably 100 Pa·s or less. Also, it is preferable that the above melt viscosity η2 is 150 Pa·s or less, more preferably 120 Pa·s or less, still more preferably 100 Pa·s or less, and most preferably 60 Pa·s or less.

[0046] Note that, for the above resin composition, the higher the blending amount of the inorganic filler, the lower the moisture absorption amount of the resin molded article, and thus, the change over time due to moisture absorption of the golf ball and the deterioration of the ball physical properties can be suppressed. Specifically, in a wetting test where the mass of the ball at 23°C is taken as the initial mass, the ball is placed in a desiccator filled with water at the bottom so as not to come into direct contact with the water, sealed, left standing at 23°C, and after 3 weeks, the ball is taken out of the desiccator and the increase amount from the initial weight of the ball is measured. It is preferable that the increase amount of the ball is 0.0085 g or less, more preferably 0.0083 g or less, and still more preferably 0.0080 g or less.

[0047] Regarding the preparation method of each component of the above resin composition, for example, it can be mixed using various kneading machines such as a kneading type (single-screw or) twin-screw extruder, Banbury mixer, kneader, and lab plastomill, or each component may be mixed by dry blending during the injection molding of the resin composition. Further, when using the above active isocyanate compound, it may be contained during resin mixing using various kneading machines, or a masterbatch containing the active isocyanate compound and other components may be separately prepared in advance and dry blended during the injection molding of the resin composition to mix each component.

[0048] For example, as a method of molding a cover with the above resin composition, for example, the above resin composition can be supplied to an injection molding machine, and the cover can be molded by injecting the molten resin composition around the core. In this case, the molding temperature varies depending on the type of the main component (I) such as polyurethane or polyurea, but is usually in the range of 150 to 270°C.

[0049] The thickness of the cover is preferably 0.4 mm or more, more preferably 0.5 mm or more, still more preferably 0.6 mm or more, and as the upper limit, it is preferably 3.0 mm or less, more preferably 2.0 mm or less.

[0050] When at least one intermediate layer is interposed between the core and the cover, it is preferable to employ various thermoplastic resins used as cover materials for golf balls, particularly ionomer resins, as the material for the intermediate layer, and commercially available products can be used as the ionomer resin. In this case, the thickness of the intermediate layer can be set within the same range as the thickness of the cover.

[0051] From the viewpoint of aerodynamic performance, a large number of dimples are provided on the surface of the outermost layer of the golf ball of the present invention. There is no particular limitation on the number of dimples formed on the surface of the outermost layer, but from the point of enhancing aerodynamic performance and increasing the flight distance, it is preferably 250 or more, more preferably 270 or more, still more preferably 290 or more, and most preferably 300 or more. As the upper limit value, it is preferably 400 or less, more preferably 380 or less, and still more preferably 360 or less.

[0052] In the present invention, a coating film layer is formed on the cover surface. It is preferable to employ a two-component curable urethane paint as the paint for forming this coating film layer. Specifically, in this case, the two-component curable urethane paint contains a main agent mainly composed of a polyol resin and a curing agent mainly composed of a polyisocyanate.

[0053] There is no particular limitation on the method of forming the coating film layer by applying the above paint on the cover surface, and known methods can be used, and a desired method such as an air gun coating method or an electrostatic coating method can be used.

[0054] There is no particular limitation on the thickness of the coating film layer, but it is usually 8 to 22 μm, preferably 10 to 20 μm.

[0055] In addition, the golf ball of the present invention can conform to golf rules for competitive use, and the ball outer diameter can be made such that it does not pass through a ring with an inner diameter of 42.672 mm and is 42.80 mm or less, and the mass can preferably be formed to be 45.0 to 45.93 g.

Examples

[0056] Hereinafter, examples and comparative examples will be shown to specifically describe the present invention, but the present invention is not limited to the following examples.

[0057] 〔Examples 1 to 8, Comparative Examples 1 to 4〕 Common core By preparing and vulcanizing and molding a rubber composition for the core common to all examples according to the formulation shown in Table 1, a core with a diameter of 38.6 mm was produced.

[0058]

Table 1

[0059] The details of the above core material are as follows. · "cis-1,4-polybutadiene" manufactured by ENEOS MATERIALS Co., Ltd., 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. · "Antioxidant" product name "No Crack NS6" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) · "Organic peroxide (1)" dicumyl peroxide, product name "Perk Mill D" (manufactured by NOF Corporation) · "Organic peroxide (2)" mixture of 1,1-di(tert-butylperoxy)cyclohexane and silica, product name "Perhexa C-40" (manufactured by NOF Corporation) · "Zinc stearate" manufactured by NOF Corporation

[0060] Common intermediate layer An intermediate layer-coated sphere having an intermediate layer with a thickness of 1.25 mm was produced by injection molding a resin material for the intermediate layer around the core with a diameter of 38.6 mm. This resin material for the intermediate layer is a blend of a total of 100 parts by mass of 50 parts by mass of the sodium neutralized product of an ethylene-unsaturated carboxylic acid copolymer with an acid content of 18% by mass and 50 parts by mass of the zinc neutralized product of an ethylene-unsaturated carboxylic acid copolymer with an acid content of 15% by mass, which is a resin formulation common to all examples.

[0061] Resin composition of the cover (outermost layer) For the resin composition of each cover example, using another injection mold, the urethane resin compositions shown in Tables 2 and 3 were injection molded around the above-mentioned intermediate layer-coated spheres to form a cover (outermost layer) with a thickness of 0.8 mm. At this time, although not particularly shown in the drawings, common dimples were formed on the cover surfaces of each example and comparative example.

[0062] In Table 3 above, the details of the compounding components are as follows. · "TPU1" The product name "Pandex" manufactured by DIC Covestro, thermoplastic polyurethane, material hardness (Shore D) "40" · "TPU2" The product name "Pandex" manufactured by DIC Covestro, thermoplastic polyurethane, material hardness (Shore D) "50" · "Titanium oxide" The product name "Typepeck R-550" manufactured by Ishihara Sangyo Co., Ltd., sulfuric acid process titanium oxide rutile type (average particle diameter 0.24 μm, water content 0.35 wt%)

[0063] Physical properties of the resin composition The contents of the Shore D hardness, wet test, Taber abrasion test, and viscosity measurement of the above cover resin composition are as follows.

[0064] (1) Shore D hardness Each of the above resins was molded into a sheet with a thickness of 2 mm and left for 2 weeks at a temperature of 23 ± 2°C. At the time of measurement, three sheets were overlapped. The material hardness of the resin was measured with a Shore D hardness tester conforming to ASTM D2240 standard. For the hardness measurement, an automatic rubber hardness tester "P2" manufactured by Kobunshi Keiki Co., Ltd. equipped with a Shore D type hardness tester was used.

[0065] (2) Taber abrasion test In accordance with JIS K 7311, a resin sheet obtained by molding each of the above resins to a thickness of 2 mm and a diameter of 100 mm or more was subjected to a Taber abrasion test using a Taber abrasion tester (manufactured by Yasuda Seiki Seisakusho, Taber type abrasion tester) under the conditions of a load of 1 kg, an abrasion wheel H-22, a rotation speed of 60 rpm, and 1000 rotations to measure the abrasion volume (cm 3 ). A graph showing the relationship between the difference in the abrasion volume of each example and Comparative Examples 1 and 3 (examples without titanium oxide) and the amount of titanium oxide added is shown in FIG. 1.

[0066] (3) Moisture test The mass of the ball at 23 °C was measured as the initial mass. The ball was placed in a desiccator filled with water at the bottom so as not to come into direct contact with water, sealed, left standing at 23 °C, and after 3 weeks, the ball was taken out of the desiccator and the increase in weight from the initial weight of the ball (moisture absorption) was measured. A graph showing the relationship between the difference in the moisture absorption of each example and Comparative Examples 1 and 3 (examples without titanium oxide) and the amount of titanium oxide added is shown in FIG. 2.

[0067] Measurement of melt viscosity In accordance with ISO 11443:1995, measurements were made using a product named "Capillograph 1C" manufactured by Toyo Seiki Seisakusho Co., Ltd. The measurement conditions were two set conditions of temperature conditions of 210 °C and 220 °C, the capillary condition was set at L / D = 10.0 / 1.0 mm, and the melt viscosity (Pa·s) of the sample at the shear rate (6080 sec -1 ) at a piston speed of (500 mm / min) was measured. In the above measurement, when the melt viscosity at 210 °C is η1 (Pa·s), the melt viscosity at 220 °C is η2 (Pa·s), and the resin hardness (Shore D hardness) is H, the value of (η1 - η2) / H 3 is shown in Tables 2 and 3, and a graph showing the relationship between the value and the amount of titanium oxide added is shown in FIG. 3.

[0068] For each of the obtained golf balls, three types of moldability (fillability, trauma, grindability) and hitting feeling were evaluated by the following methods. The results are shown in Tables 2 and 3.

[0069] Moldability 1 (fillability) The fillability of the molten resin into the mold during cover injection molding was evaluated according to the following criteria. ◎ No filling defects occur at all. ○ Filling defects rarely occur, and the cover layer may be partially thin, but filling defects hardly occur. △ Filling defects occur, and the cover layer may be partially thin. × Filling defects frequently occur, and the cover layer cannot be successfully molded.

[0070] Moldability 2 (trauma) The damage to the balls during and after cover injection molding was observed and evaluated according to the following criteria. ◎ No damage caused by the pins of the mold during molding or by the device during ball removal occurs. ○ Hardly any damage caused by the pins of the mold during molding or by the device during ball removal occurs. △ Damage caused by the pins of the mold during molding or by the device during ball removal rarely occurs. × Damage caused by the pins of the mold during molding or by the device during ball removal frequently occurs.

[0071] Moldability 3 (abrasiveness) In the polishing operation of the ball surface (cover surface) after cover injection molding, the polishability of the cover was evaluated according to the following criteria. ◎ Almost no traces of polishing remain on the ball surface, and burrs can be removed very easily. ○ The dimples can be polished and burrs can be removed without being deformed. △ Burrs can be removed by polishing, but it is difficult and the dimples may be deformed. × Scratches or deformation of the dimples occur on the ball surface, and polishing cannot be performed.

[0072] Feeling of impact Using the sand wedge (SW) product name "Bridgestone Tour Stage TW-03 (loft angle 57°)" (manufactured by Bridgestone Sports Co., Ltd.), the feel of hitting was evaluated as follows. ◎ It has a very favorable feel of hitting. ○ It has a favorable feel of hitting. △ There is no problem in use, but it has a feel of hitting with no particular characteristics. × It has a less favorable feel of hitting.

[0073]

Table 2

[0074]

Table 3

Claims

1. In a golf ball comprising at least one layer of a rubber core and at least one layer of a cover covering the core, at least one layer of the cover contains the following components (I) and (II): (I) Thermoplastic polyurethane (II) Inorganic filler Formed by a resin composition containing, the blending amount of the component (II) is 5 parts by mass or more with respect to 100 parts by mass of the component (I), and in the resin composition, the wear volume after 1000 rotations in the Taber abrasion test according to JIS-K 7311 is 0.003 cm 3 Larger than, according to ISO 11443:1995, when measured with a capillary rheometer, when the melt viscosity at 210 °C at a shear rate of 6080 (1 / sec) is η1 (Pa·s), the melt viscosity at 220 °C is η2 (Pa·s), and the Shore D hardness is H, the following formula (1) 7.0×10 -4 >(η1 - η2) / H 3 ...(1) The golf ball is characterized in that the above is satisfied.

2. The golf ball according to Claim 1, wherein the Shore D hardness of the above resin composition is less than 50.

3. The golf ball according to Claim 1 or 2, wherein the component (II) is titanium oxide.

4. The golf ball according to Claim 3, wherein the average particle diameter of titanium oxide is 0.21 μm or more.

5. The golf ball according to Claim 1 or 2, wherein the melt viscosity η1 is 200 Pa·s or less.

6. The golf ball according to Claim 1 or 2, wherein the melt viscosity η2 is 150 Pa·s or less.

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