JP2007159996A - Golf ball having urethane cover and method of manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a golf ball which is excellent in durability, abrasion resistance, and an appearance. <P>SOLUTION: The method of manufacturing the golf ball having an urethane cover includes a step of: blending thermoplastic polyurethane and titanium oxide to prepare a cover material; and forming the cover using the cover material. The melt viscosity ratio of the thermoplastic polyurethane and the cover material (the cover material/the thermoplastic polyurethane) is 0.8-2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a golf ball having a urethane cover and a method for producing the same, and more particularly to improvement of a urethane cover using thermoplastic polyurethane as a base resin.

As the base resin constituting the cover of the golf ball, ionomer resin or polyurethane is used. Covers made of ionomer resin are widely used because of their excellent resilience, durability, and workability. However, they have a high rigidity and hardness, resulting in poor shot feel and sufficient spin performance. Has been pointed out, such as poor control and poor control. On the other hand, a thermoplastic polyurethane is used as a base resin constituting the cover because the shot feeling and spin characteristics are improved as compared with ionomer resins. However, it cannot be said that the scratch resistance of the cover using thermoplastic polyurethane is satisfactory. In order to solve such a problem, for example, Patent Document 1 discloses a golf ball using a mixture of a thermoplastic polyurethane elastomer and a thermoplastic polyamide-based elastomer as a base resin constituting the cover.
JP 2002-360740 A

  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 having a urethane cover excellent in durability, scratch resistance and appearance, and a method for producing the same.

  The method for producing a golf ball having a urethane cover according to the present invention that has solved the above-described problems includes a step of preparing a cover material by blending thermoplastic polyurethane and titanium oxide, and forming a cover using the cover material. And the melt viscosity ratio (cover material / thermoplastic polyurethane) of the thermoplastic polyurethane and the cover material is 0.8-2. That is, in the present invention, a cover material is once prepared by blending thermoplastic polyurethane and titanium oxide, and then a cover is formed using this cover material. At this time, a thermoplastic polyurethane used as a raw material, It has been found that the durability, scuff resistance, and appearance of the obtained cover are improved by setting the ratio of the melt viscosity to the cover material obtained by blending the raw materials within a certain range. In order to adjust the melt viscosity ratio to 0.8 or more and 2 or less, for example, it is preferable to use a titanium oxide compounded in the thermoplastic polyurethane having a water content of 0.60% by mass or less. Details of the reason why the melt viscosity ratio is in the above range by using titanium oxide having a moisture content of 0.60% by mass or less are unknown, but if the moisture content is too high, It is presumed that a trace amount of isocyanate groups remaining in the thermoplastic polyurethane react with each other to form a urea bond, a burette bond, and the like, thereby increasing the melt viscosity of the cover material.

  Moreover, 1-10 mass parts is suitable for content of the said titanium oxide with respect to 100 mass parts of thermoplastic polyurethanes, for example. As a preferable method of forming a cover from the cover material, a method of forming a cover by forming a hollow shell-like shell from the cover material, covering the core with a plurality of shells, and compressing and forming the cover is exemplified. it can.

  The golf ball having the urethane cover of the present invention is a golf ball having a core and a urethane cover covering the core, and the urethane cover has a thermoplastic polyurethane as a base resin and a water content of 0.60% by mass. It consists of the cover material containing the following titanium oxides, It is characterized by the above-mentioned.

  The golf ball of the present invention is excellent in scuff resistance, durability, and appearance.

  A method for producing a golf ball having a urethane cover according to the present invention includes a step of preparing a cover material by blending thermoplastic polyurethane and titanium oxide, and a step of forming a cover using the cover material, The melt viscosity ratio of the thermoplastic polyurethane and the cover material (cover material / thermoplastic polyurethane) is 0.8 to 2.

  In the production method of the present invention, a cover material is prepared by blending thermoplastic polyurethane and titanium oxide. The method for preparing the cover material is not particularly limited. For example, it is preferable to mix thermoplastic polyurethane and titanium oxide using a kneader such as a double-arm kneader or a twin screw kneader. The heating temperature by the kneader may be appropriately set according to the flow start temperature of the thermoplastic polyurethane to be blended, but is usually preferably 130 ° C or higher, more preferably 150 ° C or higher, and preferably 230 ° C or lower. More preferably, it is 210 degrees C or less. By setting the heating temperature to 130 ° C. or higher, the thermoplastic polyurethane and titanium oxide can be blended uniformly. On the other hand, if the heating temperature is higher than 230 ° C., the thermoplastic polyurethane is likely to be thermally decomposed, and the durability and scuff resistance of the obtained cover may be lowered.

  As the kneader, a twin-screw extrusion kneader is preferable. For example, a screw having a screw diameter of 20 mm to 60 mm and a screw L / D of 20 to 50 can be used. Moreover, as a screw rotation speed, 50 rpm-500 rpm are suitable.

  The shape of the prepared cover material is preferably in the form of a pellet. For example, the cover material softened with a twin screw extruder kneader is taken out into a filament, cooled, and cut into a pellet. it can.

  In the production method of the present invention, the melt viscosity ratio of the cover material obtained by blending and the melt viscosity ratio of the thermoplastic polyurethane used as the raw material (cover material / thermoplastic polyurethane) is 0.8 or more, more preferably 0. .85 or more, more preferably 0.9 or more, even more preferably 1.0 or more, and 2 or less, more preferably 1.75 or less, and still more preferably 1.5 or less. By setting the melt viscosity ratio in the range of 0.8 to 2, durability, abrasion resistance, and appearance of the obtained golf ball are improved. Here, the melt viscosity of the cover material is the melt viscosity immediately after kneading obtained by blending thermoplastic polyurethane and titanium oxide (if the cover material further contains a pigment, the melt viscosity measured in the state containing the pigment) The melt viscosity of the thermoplastic polyurethane is the melt viscosity of the thermoplastic polyurethane itself used as a raw material before kneading.

  In the present invention, in order to adjust the melt viscosity ratio to 0.8 or more and 2 or less, for example, the titanium oxide blended in the thermoplastic polyurethane has a water content of 0.60 mass% or less, more preferably 0.5 mass. % Or less, more preferably 0.4% by mass or less is suitable. Details of the reason why the melt viscosity ratio is in the above range by using titanium oxide having a moisture content of 0.60% by mass or less are unknown, but if the moisture content is too high, It is presumed that a trace amount of isocyanate groups remaining in the thermoplastic polyurethane react with each other to form a urea bond, a burette bond, and the like, thereby increasing the melt viscosity of the cover material.

  Examples of the titanium oxide used in the present invention include titanium monoxide, titanium dioxide, dititanium trioxide and the like, but it is preferable to use titanium dioxide because it is used as a white pigment for the cover. The crystal form of the titanium oxide is not particularly limited, and examples thereof include an anatase type, a rutile type, and a brookite type. The titanium oxide may be titanium oxide in which oxides such as aluminum, silicon, zinc, zirconium, tin, and cerium and / or hydrated oxides exist on the surface in addition to titanium oxide alone. Titanium oxide is inherently hydrophilic and contains moisture that is physically adsorbed, or in the case of titanium oxide that has been surface-treated with a hydrous oxide, there is crystal water in the hydrous oxide. In addition, when heated and mixed with the thermoplastic polyurethane, the hydroxyl groups present on the titanium oxide surface may undergo a dehydration reaction to generate moisture.

  The titanium oxide having a water content of 0.60% by mass or less (preferably 0.40% by mass or less) suitably used in the present invention is not particularly limited as long as the water content is 0.60% by mass or less. For example, what fixed the hydroxyl group which exists on the surface of titanium oxide by surface treatment can be mentioned. Examples of the surface treatment applied to the surface of titanium oxide include surface treatments described in Japanese Patent No. 3854293 and Japanese Patent Application Laid-Open No. 2001-2417. In the present invention, for example, titanium oxide surface-treated with a calcium salt or a silane coupling agent can be suitably used, and it is more preferable to use titanium oxide surface-treated with a silane coupling agent.

  The silane coupling agent is not particularly limited, and examples thereof include alkyl alkoxysilanes such as methyltrimethoxysilane, dimethyldimethoxysilane, and dimethyldiethoxysilane; vinylsilanes such as vinyltrimethoxysilane and vinyltriethoxysilane. Aminosilanes such as γ-aminopropyltriethoxysilane, N- (β-aminoethyl) -γ-aminopropyltrimethoxysilane, N- (β-aminoethyl) -γ-aminopropylmethyldimethoxysilane; γ-glycid Epoxy silanes such as xylpropyltrimethoxysilane and β-glycidoxypropylmethyldimethoxysilane; methacryloxysilanes such as γ-methacryloxypropyltrimethoxysilane and γ-methacryloxypropylmethyldimethoxysilane; γ Such as mercaptosilane such as mercaptopropyltrimethoxysilane (3-mercaptopropyltrimethoxysilane) can be exemplified.

  The compounding amount of the titanium oxide in the cover material is 1 part by mass or more, more preferably 2 parts by mass or more, further preferably 3 parts by mass or more, and 10 parts by mass or less with respect to 100 parts by mass of the thermoplastic polyurethane. More preferably, it is 9 parts by mass or less, and further preferably 8 parts by mass or less. When the compounding amount of titanium oxide is less than 1 part by mass, the concealability is lowered, the cover has a sense of transparency, and the resulting golf ball has a poor appearance. On the other hand, if the amount of titanium oxide exceeds 10 parts by mass, the resilience of the resulting golf ball may be reduced.

  The thermoplastic polyurethane used in the present invention is not particularly limited as long as it has a plurality of polyurethane bonds in the molecule and exhibits thermoplasticity. For example, by reacting a polyisocyanate and a polyol, the urethane bond becomes a molecule. The product formed inside is obtained by further reacting with a polyamine or the like, if necessary.

The polyisocyanate component constituting the thermoplastic polyurethane is not particularly limited as long as it has two or more isocyanate groups. For example, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 2,4-toluene diisocyanate and Mixture of 2,6-toluene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI), 3,3′-vitrylene-4,4′-diisocyanate (TODI) , xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), aromatic polyisocyanates such as p-phenylene diisocyanate (PPDI); 4,4'-dicyclohexylmethane diisocyanate _(H 12 MDI), water Xylylene diisocyanate _(H 6 XDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 1 kind of cycloaliphatic polyisocyanates or aliphatic polyisocyanates such as norbornene diisocyanate (NBDI), or, 2 A mixture of seeds or more.

From the viewpoint of improving the scratch resistance, it is preferable to use an aromatic polyisocyanate as the polyisocyanate component of the polyurethane. By using the aromatic polyisocyanate, the mechanical properties of the resulting polyurethane are improved, and a cover having excellent scratch resistance can be obtained. From the viewpoint of improving weather resistance, non-yellowing polyisocyanates (TMXDI, XDI, HDI, H ₆ XDI, IPDI, H ₁₂ MDI, NBDI, etc.) may be used as the polyisocyanate component of polyurethane. Preferably, more preferably 4,4′-dicyclohexylmethane diisocyanate (H ₁₂ MDI) is used. This is because 4,4′-dicyclohexylmethane diisocyanate (H ₁₂ MDI) has a rigid structure, the mechanical properties of the resulting polyurethane are improved, and a cover having excellent scratch resistance can be obtained.

  The polyol component constituting the thermoplastic polyurethane is not particularly limited as long as it has a plurality of hydroxyl groups, and examples thereof include a low molecular weight polyol and a high molecular weight polyol. Examples of the low molecular weight polyol include diols such as ethylene glycol, diethylene glycol, triethylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol; glycerin, trimethylol Examples include triols such as propane and hexanetriol. Examples of the high molecular weight polyol include polyether polyols such as polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), and polyoxytetramethylene glycol (PTMG); polyethylene adipate (PEA), polybutylene adipate (PBA), condensation-type polyester polyols such as polyhexamethylene adipate (PHMA); lactone-type polyester polyols such as poly-ε-caprolactone (PCL); polycarbonate polyols such as polyhexamethylene carbonate; and acrylic polyols A mixture of at least two of the above-described polyols may be used.

  Although the average molecular weight of a high molecular weight polyol is not specifically limited, For example, it is preferable that it is 400 or more, More preferably, it is 1,000 or more. This is because if the average molecular weight of the high molecular weight polyol becomes too small, the resulting polyurethane becomes hard and the feel at impact of the golf ball decreases. The upper limit of the average molecular weight of the high molecular weight polyol is not particularly limited, but is 10,000 or less, more preferably 8,000 or less.

  Moreover, the polyamine which comprises the said thermoplastic polyurethane as needed is not specifically limited if it has at least 2 or more amino groups. Examples of the polyamine include aliphatic polyamines such as ethylenediamine, propylenediamine, butylenediamine and hexamethylenediamine, alicyclic polyamines such as isophoronediamine and piperazine, and aromatic polyamines.

  The aromatic polyamine is not particularly limited as long as at least two amino groups are directly or indirectly bonded to the aromatic ring. Here, being indirectly bonded means that the amino group is bonded to the aromatic ring via, for example, a lower alkylene group. The aromatic polyamine may be, for example, a monocyclic aromatic polyamine in which two or more amino groups are bonded to one aromatic ring, or an amino in which at least one amino group is bonded to one aromatic ring. It may be a polycyclic aromatic polyamine containing two or more phenyl groups.

  Examples of the monocyclic aromatic polyamine include a type in which an amino group such as phenylenediamine, toluenediamine, diethyltoluenediamine, and dimethylthiotoluenediamine is directly bonded to an aromatic ring; and an amino group such as xylylenediamine. Examples include a type bonded to an aromatic ring via a lower alkylene group. The polycyclic aromatic polyamine may be poly (aminobenzene) in which at least two aminophenyl groups are directly bonded, or at least two aminophenyl groups intervene with a lower alkylene group or an alkylene oxide group. May be combined. Of these, diaminodiphenylalkanes in which two aminophenyl groups are bonded via a lower alkylene group are preferred, and 4,4′-diaminodiphenylmethane and its derivatives are particularly preferred.

  Although it does not specifically limit as a structural aspect of the said thermoplastic polyurethane, For example, the aspect comprised by the polyisocyanate component and the high molecular weight polyol component; By the polyisocyanate component, the high molecular weight polyol component, and the low molecular weight polyol component An embodiment constituted by a polyisocyanate component, a high molecular weight polyol component, a low molecular weight polyol component and a polyamine component; an embodiment constituted by a polyisocyanate component, a high molecular weight polyol component and a polyamine component, etc. Can be mentioned. Specific examples of the thermoplastic polyurethane include “Elastolan XNY90A”, “Elastolan XNY97A”, and “Elastolan XNY585” commercially available from BASF Japan.

  In the present invention, the cover material is not particularly limited as long as it contains the thermoplastic polyurethane as a base resin component, and the content of the thermoplastic polyurethane in the resin component constituting the cover material is: It is desirable that the content be 50 mass% or more, more preferably 70 mass% or more, and still more preferably 90 mass% or more. Furthermore, it is also a preferable aspect that the resin component constituting the cover material is substantially made of only thermoplastic polyurethane.

  In the present invention, as the cover material, in addition to the thermoplastic polyurethane, examples of resin components that can be further used include thermoplastic resins, thermoplastic elastomers, and diene block copolymers. Examples of the thermoplastic resin include an ionomer resin. Examples of the ionomer resin include at least a carboxyl group in a copolymer of ethylene and an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms. Some of the carboxyl groups in a terpolymer of a part of which is neutralized with a metal ion, ethylene, an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and an α, β-unsaturated carboxylic acid ester The thing which neutralized at least one part with the metal ion, or a mixture thereof can be mentioned. Specific examples of the ionomer resin include Hi Milan, which is commercially available from Mitsui DuPont Polychemical Co., Ltd., Surlyn, which is commercially available from DuPont, and Iotech, which is commercially available from ExxonMobil Chemical Co., Ltd. be able to.

  Specific examples of the thermoplastic elastomer include thermoplastic polyamide elastomer commercially available from Arkema Co., Ltd. under the trade name “Pebax (eg,“ Pebax 2533 ”), and trade name“ Hytrel ”from Toray DuPont Co., Ltd. (For example, “Hytrel 3548”, “Hytrel 4047”) ”, a thermoplastic polyester elastomer commercially available under the trade name“ Lavalon ”from Mitsubishi Chemical Corporation, and the like. Of these, thermoplastic polystyrene elastomer is preferred. Examples of the thermoplastic polystyrene elastomer include a polystyrene-diene block copolymer having a polystyrene block component as a hard segment and a diene block component such as polybutadiene, isoprene, hydrogenated polybutadiene, and hydrogenated polyisoprene as a soft segment. be able to. The polystyrene-diene block copolymer has a double bond derived from a conjugated diene compound of a block copolymer or a partially hydrogenated block copolymer. Examples of the polystyrene-diene block copolymer include a block copolymer having an SBS (styrene-butadiene-styrene) structure having a polybutadiene block, or a block copolymer having an SIS (styrene-isoprene-styrene) structure. Is mentioned.

  The golf ball cover material of the present invention includes the above-described thermoplastic polyurethane and titanium oxide, pigment components such as blue pigments, specific gravity adjusting agents such as calcium carbonate and barium sulfate, dispersants, anti-aging agents, ultraviolet absorbers, You may contain a light stabilizer, a fluorescent material, a fluorescent whitening agent, etc. in the range which does not impair the performance of a cover.

In the present invention, the change rate of the weight average molecular weight of the cover material with respect to the weight average molecular weight of the thermoplastic polyurethane used as a raw material (when the cover material includes other resin components, the thermoplastic polyurethane and other resin components) is Small is preferable. The change rate of the weight average molecular weight [= 100 × (weight average molecular weight of cover material−weight average molecular weight of thermoplastic polyurethane) / weight average molecular weight of thermoplastic polyurethane] is −30% or more, and more preferably − It is 20% or more, more preferably -10% or more, 20% or less, more preferably 10% or less, still more preferably 5% or less. When the rate of change of the weight average molecular weight is too small, the scuff resistance of the resulting cover tends to decrease, and when the rate of change is too large, the durability of the obtained cover tends to decrease. The weight average molecular weight is measured by gel permeation chromatography of tetrahydrofuran-soluble matter. The measurement conditions are as follows.
Model: HLC-8120 manufactured by Tosoh Corporation
Column: TSK-GEL SUPER HM-M
Detector: UV-8020U
Solvent: Tetrahydrofuran Injection volume: 100 μl
Temperature: 40 ° C
Flow rate: 0.6 ml / min Standard: Polystyrene

  In the present invention, as a method of forming a cover using the cover material, for example, a method of forming a hollow shell-like shell from the cover material, and covering and compressing the core with a plurality of shells (preferably, A method in which a hollow shell-shaped half shell is formed from the cover material, the core is covered with two half shells and compression-molded), and the cover material is directly injection-molded on the core. Adopts compression molding method. This is because by employing the compression molding method, the scuff resistance and durability of the obtained cover are further improved.

  The half shell can be molded by either compression molding or injection molding, but compression molding is preferred. For example, FIG. 1 is an explanatory view schematically illustrating a method of forming a half shell by a compression molding method. The half shell molding die 1 includes an upper die 3 and a lower die 5. The upper die 3 is provided with a flat portion 7 and a hemispherical convex portion 9, and the lower die has a flat portion 11 and a hemispherical concave portion. 13 is provided. The compression molding of the half shell can be performed by putting the pellet-shaped cover material 15 into the recess of the lower mold and clamping the upper mold 3 and the lower mold 5 using a press machine or the like. At this time, a plurality of pellets may be put into the recess of the lower mold, but when a plurality of pellets are put, a joint line (weld line) between the pellets is generated in the obtained half shell. Since the weld line may reduce the durability of the obtained cover, it is preferable that the number of pellets to be put into the recess of the lower mold is one. From such a viewpoint, the mass per pellet is preferably 1.4 g or more and 2.0 g or less. One half shell can be shape | molded from one pellet by setting it as 1.4 g or more and 2.0 g or less. Further, when the number of pellets to be put into one concave portion is one, the throwing operation becomes easy.

  The pressure for compressing and forming the cover material into the half shell is, for example, 1 MPa or more, preferably 2 MPa or more, and 20 MPa or less, preferably 15 MPa or less. By setting the molding pressure to 1 MPa or more and 20 MPa or less, a half shell having a uniform thickness can be molded.

  The molding temperature for compression molding the cover material into a half shell can be set as appropriate according to the flow start temperature of the cover material to be used. The temperature is preferably −10 ° C. or higher, 70 ° C. or lower, preferably 60 ° C. or lower, more preferably 50 ° C. or lower. By setting the molding temperature to 70 ° C. or less with respect to the flow start temperature of the cover material, the durability and scuff resistance of the obtained cover are improved. Moreover, a moldability improves by making molding temperature into -20 degreeC or more with respect to the flow start temperature of a cover material.

The molding temperature means the maximum temperature that the surface of the concave portion of the lower mold reaches between the mold clamping and the mold opening. Moreover, the flow start temperature of a cover material can measure a pellet-shaped cover material on condition of the following using "FLOWSTER CFT-500" of Shimadzu Corporation.
Plunger area: 1 cm ²
DIE LENGTH: 1mm
DIE DIA: 1mm
Load: 588.399N
Starting temperature: 30 ° C
Temperature increase rate: 3 ° C / min

  The molding time for compression molding the cover material into a half shell is preferably 30 minutes or less, more preferably 20 minutes or less, further preferably 10 minutes or less, and particularly preferably 5 minutes or less. This is because if the molding time is long, the thermal decomposition of the thermoplastic polyurethane proceeds, and the durability and scratch resistance of the resulting cover may be reduced. The molding time is preferably 1 minute or longer, and more preferably 2 minutes or longer. This is because in a molding time of about 1 minute, the pellet-shaped cover material flows in the mold and the half shell can be molded. The molding time is the time from mold clamping to mold opening.

  In the present invention, the half shell can be formed by injection molding. The injection molding of the half shell can be performed by injecting and cooling the heated cover material into the upper and lower molds for half shell molding that are clamped at a pressure of 3 MPa to 10 MPa. The molding temperature at the time of injection molding can be appropriately set according to the flow start temperature of the cover material to be used, and is −20 ° C. or higher, more preferably −10 ° C. or higher with respect to the flow start temperature of the cover material. More preferably, it is 0 ° C. or higher, 70 ° C. or lower, more preferably 60 ° C. or lower, and further preferably 50 ° C. or lower. By setting the molding temperature to 70 ° C. or less with respect to the flow start temperature of the cover material, the durability and scuff resistance of the obtained cover are improved. Moreover, a moldability improves by making molding temperature into -20 degreeC or more with respect to the flow start temperature of a cover material. The molding temperature is the maximum temperature that the cover material reaches after the pellet-shaped cover material is charged into the cylinder of the injection molding machine until the molding is completed. The molding time when the half shell is injection molded is not particularly limited, but is preferably 20 minutes or less, and more preferably 15 minutes or less. This is because when the molding time is long, the molecular chain of thermoplastic polyurethane is broken and dissociated, and the durability and scuff resistance of the resulting cover are lowered. The molding time is the time from when the pellet-shaped cover material is introduced into the cylinder of the injection molding machine until it is injected into the mold cavity.

  As a method for forming a cover using the half shell obtained as described above, for example, a method in which a core is covered with two half shells and compression-molded can be mentioned. FIG. 2 is an explanatory view schematically illustrating a method of compression molding by covering a core with two half shells using a mold. The cover molding die (compression molding) 21 includes an upper mold 23 and a lower mold 25, and each of the upper mold 23 and the lower mold 25 includes a large number of cavity surfaces 27, and the cavity surfaces 27 are hemispherical. The cavities are formed. After covering the core 29 with the two half shells 31, the cover can be formed by placing the resulting covering in a lower mold cavity and clamping with a press or the like. In the example shown in FIG. 2, the half shells 31 are connected by a flat portion 33 made of a cover material. Although not shown, a large number of pimples are formed on the cavity surface, and dimples having a shape in which the pimples are inverted are formed on the surface of the cover.

  The molding temperature for compression molding the half shell into the cover is −20 ° C. or higher, preferably −10 ° C. or higher and 70 ° C. or lower, preferably 60 ° C. or lower, relative to the flow start temperature of the cover material. More preferably, it is 50 ° C. or less. By setting the molding temperature to 70 ° C. or less with respect to the flow start temperature of the cover material, the durability and scuff resistance of the obtained cover are improved. Further, the moldability is improved by setting the molding temperature to −20 ° C. or higher with respect to the flow start temperature of the cover material.

  The pressure for compression-molding the half shell into the cover is, for example, 0.5 MPa or more, preferably 1 MPa or more, and 25 MPa or less, preferably 15 MPa or less. By setting the molding pressure to 0.5 MPa or more and 25 MPa or less, a golf ball cover having a uniform cover thickness can be molded.

  The molding time for compression molding the half shell into the cover is preferably 30 minutes or less, more preferably 20 minutes or less, further preferably 10 minutes or less, and particularly preferably 5 minutes or less. This is because if the molding time is long, the thermal decomposition of the thermoplastic polyurethane proceeds, and the durability and scratch resistance of the resulting cover may be reduced. The molding time is preferably 1 minute or longer, and more preferably 2 minutes or longer. This is because the cover can be molded from the half shell in a molding time of about 1 to 2 minutes. The molding time is the time from mold clamping to mold opening.

  In the present invention, the cover can also be formed by injection molding the cover material directly onto the core. In this case, as the upper and lower molds for molding the cover, it is preferable to use a cover having a hemispherical cavity, with pimples and also serving as a hold pin in which a part of the pimples can be advanced and retracted. The cover can be formed by injection molding by projecting the hold pin, inserting and holding the core, injecting the cover material, and cooling the cover, for example, a pressure of 9 MPa to 15 MPa. The cover material heated to 200 ° C. to 250 is poured into the mold clamped in step 0.5 to 5 seconds, cooled for 10 to 60 seconds, and opened.

  The golf ball formed with the cover is preferably removed from the mold and subjected to surface treatment such as deburring, washing, and sand blasting as necessary. Moreover, a paint layer and a mark can also be formed if desired.

  The present invention provides a golf ball having a core and a urethane cover covering the core, wherein the urethane cover includes a thermoplastic polyurethane as a base resin and titanium oxide having a water content of 0.60% or less. A golf ball having a urethane cover comprising the cover material contained therein is included, and preferably a golf ball having a urethane cover obtained by the production method of the present invention described above. As the thermoplastic polyurethane used in the golf ball of the present invention and titanium oxide having a water content of 0.60% or less, the same ones as described above can be used.

  In the present invention, the thickness of the urethane cover of the golf ball is preferably 1.0 mm or less, more preferably 0.6 mm or less, and further preferably 0.5 mm or less. This is because by setting the thickness to 1.0 mm or less, the resilience of the golf ball is increased and the total flight distance is increased. Although the minimum of the thickness of a urethane cover is not specifically limited, For example, it is 0.3 mm. This is because if it is less than 0.3 mm, it may be difficult to mold the urethane cover.

  The slab hardness of the urethane cover is Shore D hardness, preferably 20 or more, more preferably 30 or more, preferably 70 or less, and more preferably 60 or less. This is because if the cover hardness is less than 20, the resilience of the golf ball may decrease and the flight distance may decrease. On the other hand, if the cover hardness exceeds 70, the durability of the resulting golf ball may be reduced.

  In the present invention, the structure of the golf ball is not particularly limited as long as it has a core and a urethane cover, and may be a two-piece golf ball, a multi-piece golf ball more than a three-piece golf ball, or a thread wound golf ball. . This is because the present invention can be preferably applied in any case. The core in the case where the golf ball of the present invention has a core like a thread wound golf ball, a two-piece golf ball, and a multi-piece golf ball will be described. For the core, a conventionally known rubber composition (hereinafter sometimes simply referred to as “core rubber composition”) may be employed. For example, a diene rubber as a base rubber, a co-crosslinking agent, And a rubber composition containing a crosslinking initiator can be molded by hot pressing.

  As the diene rubber, it is particularly preferable to use a high-cis polybutadiene having a cis bond advantageous for rebound of 40% or more, preferably 70% or more, more preferably 90% or more. The co-crosslinking agent is an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms or a metal salt thereof, preferably a metal salt of acrylic acid or methacrylic acid, and the metals include zinc, magnesium and calcium. Aluminum and sodium are preferably used, and zinc is more preferably used. The amount of the co-crosslinking agent used is preferably 20 to 50 parts by mass per 100 parts by mass of the base rubber. As the crosslinking initiator, an organic peroxide is preferably used. Specifically, dicumyl peroxide, 1,1-bis (t-butylperoxy) -3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, Examples thereof include organic peroxides such as di-t-butyl peroxide, among which dicumyl peroxide is preferably used. The compounding amount of the organic peroxide is preferably 0.2 parts by mass or more, more preferably 0.3 parts by mass or more, and preferably 1.5 parts by mass or less with respect to 100 parts by mass of the base rubber. More preferably, it is 1.0 mass part or less. Moreover, the rubber composition for a core may further contain diphenyl disulfides. The compounding amount of diphenyl disulfides is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and preferably 5.0 parts by mass or less, with respect to 100 parts by mass of the base rubber. Preferably it is 3.0 mass parts or less.

  In addition to the base rubber, co-crosslinking agent, cross-linking initiator, diphenyl disulfides, the core rubber composition further includes specific gravity adjusters such as zinc oxide and barium sulfate, anti-aging agents, and color powders as appropriate. Can be blended. The hot-press molding conditions for the core rubber composition may be appropriately set according to the rubber composition, but are usually heated at 130 to 200 ° C. for 10 to 60 minutes, or at 130 to 150 ° C. for 20 to 40 minutes. After heating, it is preferable to perform two-step heating at 160 to 180 ° C. for 5 to 15 minutes.

  When the golf ball of the present invention is a three-piece or more multi-piece golf ball, a multilayer core having at least two layers can be employed. The multilayer core has an inner layer and an outer layer, and the inner layer core is preferably formed by hot pressing the above-described rubber composition for core. Examples of the outer layer of the multilayer core include thermoplastic resins such as polyurethane resins, ionomer resins, nylon, and polyethylene; thermoplastic elastomers such as polystyrene elastomers, polyolefin elastomers, polyurethane elastomers, and polyester elastomers. Here, as the ionomer resin, for example, a resin obtained by neutralizing at least a part of a carboxyl group in a copolymer of ethylene and an α, β-unsaturated carboxylic acid with a metal ion, or ethylene and an α, β-unsaturated resin. What neutralized at least one part of the carboxyl group in the ternary copolymer of saturated carboxylic acid and (alpha), (beta)-unsaturated carboxylic acid ester with a metal ion is mentioned. The outer layer may further contain a specific gravity adjusting agent such as barium sulfate or tungsten, an anti-aging agent, or a pigment.

  When the golf ball of the present invention is a thread wound golf ball, a thread wound core may be used as the core. In such a case, as the thread wound core, for example, a thread core composed of a center formed by curing the core rubber composition described above and a thread rubber layer formed by winding the thread rubber around the center in a stretched state is used. do it. The thread rubber wound on the center may be the same as that conventionally used for the thread wound layer of a thread wound golf ball, for example, natural rubber or natural rubber and synthetic polyisoprene with sulfur, You may use what was obtained by vulcanizing the rubber composition which mix | blended the vulcanization adjuvant, the vulcanization accelerator, the anti-aging agent, etc. The thread rubber is stretched about 10 times on the center and wound to form a thread wound core.

  Hereinafter, the present invention will be described in detail by way of examples. However, the present invention is not limited to the following examples, and all modifications and embodiments without departing from the gist of the present invention are not limited thereto. Included in range.

[Evaluation methods]
(1) Melt Viscosity of Thermoplastic Polyurethane and Cover Material Using a high-pressure flow tester manufactured by Shimadzu Corporation, the measurement sample was held at 190 ° C. for 4 minutes, and then the viscosity when a load of 294 N was applied was determined. The melt viscosity of the cover material is measured by measuring the melt viscosity of a kneaded thermoplastic polyurethane and titanium oxide (if the pigment is present, kneading the pigment), and the thermoplastic polyurethane is in a state before kneading. Things were measured.

(2) Appearance defect rate (%)
500 golf balls were produced, and the appearance of the buffed golf ball was visually observed to distinguish between buff scratches that could be visually confirmed and those that could not be visually confirmed, and buff scratches could be visually confirmed. It is shown as a percentage of the number of things.

(3) Scratch resistance A commercially available pitching wedge was attached to a swing robot manufactured by Golf Laboratories, and each ball was hit once at a head speed of 36 m / sec. .
Evaluation criteria ○: Slight scratches on the surface of the golf ball.
Δ: The surface of the golf ball is slightly shaved and fluffing occurs.
X: The surface of the golf ball is considerably shaved and the fuzz is conspicuous.

(4) Durability A metal head # W1 driver was attached to a swing robot manufactured by Trutemper, and each golf ball was hit at a head speed of 45 m / sec to collide with a collision plate. This was repeated to measure the number of hits until the golf ball was broken. The durability of each golf ball is determined according to the golf ball no. The number of hits in 2 was taken as 100, and the hit count for each golf ball was shown as an index value. The larger the indexed value, the more excellent the golf ball is.

(5) Cover slab hardness (Shore D hardness)
A sheet having a thickness of about 2 mm was produced by hot press molding using the cover material, and stored at 23 ° C. for 2 weeks. An automatic rubber hardness tester P1 type manufactured by Kobunshi Keiki Co., Ltd. equipped with a spring type hardness tester Shore D type as defined in ASTM-D2240 in a state where three or more sheets are stacked so as not to affect the measurement substrate or the like. It measured using.

(6) Measurement of moisture content of titanium oxide It was measured using a Karl Fischer moisture measuring device (Mitsubishi Kasei Co., Ltd .: moisture measuring device CA-06, moisture vaporizer VA-06, measuring temperature 180 ° C.).

[Production of golf balls]
(1) Production of Multilayer Core A rubber composition for a core having the composition shown in Table 1 was kneaded and heated and pressed at 170 ° C. for 15 minutes in an upper and lower mold having hemispherical cavities to obtain a diameter of 38.5 mm and a mass of 34. 9 g of spherical inner layer core (center) was obtained.

Polybutadiene rubber: BR730 (high cis polybutadiene) manufactured by JSR Corporation
Zinc acrylate: ZNDA-90S manufactured by Nippon Distilled
Zinc Oxide: Toho Zinc Gin R
Dicumyl peroxide: Park Mill D made by NOF
In addition, an appropriate amount of zinc oxide was added so that the mass of the obtained golf ball was 45.4 g.

  Next, as an ionomer resin, 50 parts by mass of “Hi-Milan 1605” manufactured by Mitsui DuPont Polychemical Co., Ltd. and 50 parts by mass of “Surlin 9945” manufactured by DuPont are mixed by a twin-screw kneading extruder to prepare a pellet-shaped outer layer core material. did. Extrusion was performed with a screw diameter of 45 mm, a screw rotation speed of 200 rpm, and a screw L / D = 35, and the outer layer core material was heated to 160 ° C. to 180 ° C. at the die position of the extruder. The obtained material for the outer layer core was directly injection-molded on the inner layer core to produce a multilayer core (diameter 41.7 mm) composed of the inner layer core and the outer layer core.

(2) Preparation of Cover Material The cover material having the composition shown in Table 2 was mixed at a temperature of 160 ° C. to 210 ° C. for 5 minutes with a twin-screw kneading extruder to prepare a pellet-shaped cover material. Extrusion was performed with a screw diameter of 45 mm, a screw speed of 200 rpm, and a screw L / D = 35. The melt viscosity of the obtained pellet-shaped cover material was measured. The measurement results of the melt viscosity are shown in Table 2.

(3) Half-shell molding Half-shell compression molding is performed by using the pellet-shaped cover material (mass 1.7 g) obtained as described above for each concave portion of the lower mold of the half-shell molding die. One by one was charged and pressed to form a half shell. The compression molding was performed at a molding temperature of 170 ° C., a molding time of 5 minutes, and a molding pressure of 2.94 MPa.

(4) Molding of the cover The multilayer core obtained in (1) was covered with the two half shells obtained in (3), and the cover was molded by compression molding. Molding was performed at a molding temperature of 140 ° C., a molding time of 2 minutes, and a molding pressure of 9.8 MPa. The surface of the obtained golf ball body is subjected to sand blasting and marking, and then a clear paint is applied, and the paint is dried in an oven at 40 ° C. to obtain a golf ball having a diameter of 42.7 mm and a mass of 45.4 g. Obtained.

  Table 2 shows the results of evaluating the scratch resistance, durability, and appearance of the obtained golf balls.

Titanium dioxide 1: Surface treatment with A-160 manufactured by Sakai Chemical Industry Co., Ltd., anatase type, aluminum oxide, silane coupling agent (polysiloxane) Titanium dioxide 2: CR63 manufactured by Ishihara Sangyo Co., Ltd., rutile type, aluminum oxide, silane coupling agent Surface treatment with (polysiloxane) Titanium dioxide 3: R-11P manufactured by Sakai Chemical Industry Co., Ltd., rutile type, aluminum oxide, surface treatment with silane coupling agent (polysiloxane) Titanium dioxide 4: A-220 manufactured by Ishihara Sangyo Co., Ltd., anatase Type, surface treatment with aluminum oxide Titanium dioxide 5: CR60 manufactured by Ishihara Sangyo Co., Ltd., rutile type, surface treatment with aluminum oxide

  In Table 2, golf ball No. 1-No. 3 and no. 6 is a case where titanium oxide having a water content of 0.60% by mass or less is used, and the melt viscosity ratio (cover material / thermoplastic polyurethane) between the thermoplastic polyurethane as a raw material and the cover material is 0.8-2. It can be seen that all the golf balls are excellent in durability and scratch resistance and have a low appearance defect rate. On the other hand, golf ball No. 4 and no. No. 5 is a case where a titanium oxide having a moisture content exceeding 0.60% by mass was used and the melt viscosity ratio exceeded 2, but both durability and scratch resistance were lowered. Golf ball no. 7 is the case where the melt viscosity ratio is less than 0.8, but the scratch resistance and durability were lowered.

  In Table 2, Remark 1 shows the weight average molecular weight and melt viscosity of the thermoplastic polyurethane (Elastolan XNY97A) before kneading, and Remark 2 shows that only the thermoplastic polyurethane is golf ball no. 1-No. The weight average molecular weight and the melt viscosity after processing under the same conditions as the kneading conditions performed in 3 were shown. From Remarks 1 and Remark 2, when only thermoplastic polyurethane is heated and kneaded, the melt viscosity and molecular weight decrease. 1-No. 5 shows that the weight average molecular weight and melt viscosity of the cover material obtained by kneading titanium oxide with thermoplastic polyurethane are increased. In particular, golf ball No. 1 using titanium oxide having a high moisture content. 4 and no. 5 shows that the weight average molecular weight change rate exceeds 20%. From these results, the moisture contained in titanium oxide reacts with a small amount of isocyanate groups remaining in the thermoplastic polyurethane, resulting in urea bonds, burette bonds, etc., and the melt viscosity of the cover material is increased. Conceivable.

  The golf ball of the present invention is excellent in scuff resistance, durability, and appearance.

Explanatory drawing which illustrates typically the method of shape | molding a half shell. Explanatory drawing which illustrates the method of shape | molding a cover from a half shell.

Explanation of symbols

  1: half-shell molding die, 3: half-shell molding upper die, 5: half-shell molding lower die, 7: flat part, 9: hemispherical convex part, 11: flat part, 13: hemispherical part Recesses 13 and 15: pellet-shaped cover material, 21: mold for cover molding, 23: upper mold for cover molding, 25: lower mold for cover molding, 27: cavity surface, 29: core, 31: half shell, 33: Flat part made of cover material

Claims (5)

A method for manufacturing a golf ball having a urethane cover, the manufacturing method comprising:
A step of preparing a cover material by blending thermoplastic polyurethane and titanium oxide; and a step of forming a cover using the cover material,
A method for producing a golf ball having a urethane cover, wherein the melt viscosity ratio of the thermoplastic polyurethane and the cover material (cover material / thermoplastic polyurethane) is 0.8-2.   The method for producing a golf ball having a urethane cover according to claim 1, wherein the titanium oxide has a moisture content of 0.60% by mass or less.   3. The method for producing a golf ball having a urethane cover according to claim 1, wherein the cover material includes 1 to 10 parts by mass of the titanium oxide based on 100 parts by mass of the thermoplastic polyurethane.   The golf ball having a urethane cover according to any one of claims 1 to 3, wherein a hollow shell-like shell is formed from the cover material, and the cover is formed by compressing and molding the core with a plurality of shells. Manufacturing method. A golf ball having a core and a urethane cover covering the core,
2. The golf ball having a urethane cover, wherein the urethane cover is made of a cover material containing thermoplastic polyurethane as a base resin and titanium oxide having a water content of 0.60% by mass or less.

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