golf ball

Abstract

The objective is to improve the moldability of golf ball covers containing polyurethane as a resin component, while suppressing a decrease in the scratch resistance of the cover, thereby increasing the productivity of golf balls. [Solution] The golf ball is a golf ball having a spherical core and a cover covering the spherical core, wherein the cover is formed from a cover composition containing (A) thermoplastic polyurethane and (B) a carboxylic acid with a molecular weight of 1000 or less as resin components.

Description

[Technical Field]

[0001] This invention relates to golf balls, and more particularly to improving the moldability of polyurethane covers. [Background technology]

[0002] Traditionally, ionomer resins and polyurethanes have been used as resin components for golf ball covers. Covers made with ionomer resins tend to have superior rebound, durability, and processability. Covers made with polyurethanes tend to improve feel and spin performance. Cover materials combining these ionomer resins and polyurethanes have also been proposed.

[0003] For example, Patent Document 1 describes a multi-piece solid golf ball comprising a solid core and a two-layer cover consisting of an inner layer and an outer layer, wherein the inner layer cover is mainly made of an ionomer resin containing at least 15% by weight of α,β-unsaturated carboxylic acid, and the outer layer cover is mainly made of a thermoplastic elastomer that does not contain an ionomer resin, and an adhesive mainly made of thermoplastic resin is blended into at least one of the inner layer cover and the outer layer cover (see Patent Document 1 (Tables 1 and 2)).

[0004] Furthermore, Patent Document 2 describes a golf ball comprising a core layer and a cover layer, wherein at least one of the layers comprises a polytrimethylene ether glycol composition (see Patent Document 2 (paragraphs 0052, 0061)). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-137726 [Patent Document 2] Special Publication No. 2007-537014 [Overview of the project] [Problems that the invention aims to solve]

[0006] When polyurethane is used as the main resin component in a cover composition, the fluidity of the cover composition tends to decrease, making it difficult to mold the cover. Adding ionomer resin to a polyurethane-containing cover composition can improve its fluidity. However, adding ionomer resin to polyurethane presents a problem: it reduces the scratch resistance of the resulting cover.

[0007] This invention has been made in view of the above circumstances, and aims to improve the moldability of a golf ball cover containing polyurethane as a resin component, while suppressing a decrease in the scratch resistance of the cover, thereby increasing the productivity of golf balls. [Means for solving the problem]

[0008] The golf ball of the present invention, which has been able to solve the above problems, is a golf ball having a spherical core and a cover covering the spherical core, wherein the cover is formed from a cover composition containing (A) thermoplastic polyurethane and (B) a carboxylic acid with a molecular weight of 1000 or less as a resin component. [Effects of the Invention]

[0009] According to the present invention, for golf balls having a cover containing polyurethane as a resin component, it is possible to improve the moldability of the cover while suppressing a decrease in the scratch resistance of the cover, thereby increasing the productivity of golf balls. [Brief explanation of the drawing]

[0010] [Figure 1] A partially cutaway cross-sectional view showing a golf ball according to one embodiment of the present invention. [Modes for carrying out the invention]

[0011] The golf ball of the present invention is a golf ball having a spherical core and a cover covering the spherical core, wherein the cover is formed from a cover composition containing, as a resin component, (A) thermoplastic polyurethane and (B) a carboxylic acid with a molecular weight of 1000 or less (hereinafter sometimes simply referred to as "(B) carboxylic acid").

[0012] By blending (A) thermoplastic polyurethane with (B) carboxylic acid, the melt viscosity of the cover composition can be lowered, thereby improving the moldability of the cover composition. Furthermore, (B) carboxylic acid does not impair the flexibility of (A) thermoplastic polyurethane, thus suppressing a decrease in the scratch resistance of the resulting cover.

[0013] [Composition for covering] The cover composition used in the present invention will now be described. The cover composition contains (A) thermoplastic polyurethane and (B) carboxylic acid as resin components.

[0014] ((A) Thermoplastic polyurethane) The aforementioned cover composition contains (A) thermoplastic polyurethane as a resin component. The thermoplastic polyurethane (A) described above has multiple urethane bonds within its molecule and exhibits thermoplasticity. Thermoplastic polyurethane is a polyurethane that exhibits plasticity upon heating, and generally refers to a polyurethane having a linear structure with a relatively high molecular weight. An example of the thermoplastic polyurethane (A) described above is a product formed by reacting a polyisocyanate with a polyol, in which urethane bonds are formed within the molecule.

[0015] The polyisocyanate constituting the above-mentioned (A) thermoplastic polyurethane is not particularly limited as long as it is a compound having two or more isocyanate groups in the molecule. The polyisocyanate may be used alone or in combination of two or more. The polyisocyanate is preferably a diisocyanate having two isocyanate groups in the molecule.

[0016] Examples of the polyisocyanate include aromatic polyisocyanates such as 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, a mixture of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI), 3,3'-bitolylene-4,4'-diisocyanate (TODI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), and paraphenylene diisocyanate (PPDI); alicyclic polyisocyanates or aliphatic polyisocyanates such as 4,4'-dicyclohexylmethane diisocyanate (H 12 MDI), 1,3-bis(isocyanatomethyl)cyclohexane (H6XDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), trans-1,4-cyclohexane diisocyanate (CHDI), and norbornene diisocyanate (NBDI). Among these, as the polyisocyanate, alicyclic diisocyanate and / or aromatic diisocyanate are preferable. By using alicyclic diisocyanate and / or aromatic diisocyanate, the mechanical properties of the obtained polyurethane are improved, and the scratch resistance of the obtained cover is further improved.

[0017] The polyisocyanate of the above-mentioned (A) thermoplastic polyurethane is 4,4'-dicyclohexylmethane diisocyanate (H 12At least one diisocyanate selected from the group consisting of 1,3-bis(isocyanatomethyl)cyclohexane (H6XDI), isophorone diisocyanate (IPDI), trans-1,4-cyclohexane diisocyanate (CHDI), 4,4'-diphenylmethane diisocyanate (MDI), and toluene diisocyanate (TDI) is preferred, and 4,4'-dicyclohexylmethane diisocyanate (H 12 MDI) or 4,4'-diphenylmethane diisocyanate (MDI) is particularly preferred. By using these diisocyanates, the mechanical properties of the obtained polyurethane are improved, and the scratch resistance of the obtained cover is further improved.

[0018] Also, from the perspective of improving the weather resistance of the cover, as the polyisocyanate of (A) thermoplastic polyurethane, a non-yellowing polyisocyanate (TMXDI, XDI, HDI, H6XDI, IPDI, H 12 MDI, NBDI, etc.) is preferably used, and more preferably 4,4'-dicyclohexylmethane diisocyanate (H 12 MDI) is used. 4,4'-dicyclohexylmethane diisocyanate (H 12 MDI) has a rigid structure, and the mechanical properties of the obtained polyurethane are further improved.

[0019] The polyol constituting the (A) thermoplastic polyurethane is not particularly limited as long as it is a compound having two or more hydroxy groups in the molecule. For example, high molecular weight polyols can be mentioned. The high molecular weight polyol may be used alone or in combination of two or more. As the polyol, a diol having two hydroxy groups in the molecule is preferred.

[0020] Examples of the high molecular weight polyols include polyether polyols such as polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), polytrimethylene ether glycol (PO3G), and polyoxytetramethylene glycol (PTMG); condensed polyester polyols such as polyethylene adipate (PEA), polybutylene adipate (PBA), and polyhexamethylene adipate (PHMA); lactone-based polyester polyols such as poly-ε-caprolactone (PCL); polycarbonate polyols such as polyhexamethylene carbonate; and acrylic polyols. The high molecular weight polyols may be derived from petroleum resources or from biomass resources.

[0021] The number-average molecular weight of the high molecular weight polyol is not particularly limited, but is preferably 400 or more, more preferably 1,000 or more, 10,000 or less, and more preferably 8,000 or less.

[0022] The thermoplastic polyurethane (A) may contain a chain extender as a component. Low molecular weight polyols, low molecular weight polyamines, and the like can be used as the chain extender component.

[0023] Examples of the low molecular weight polyols include ethylene glycol, diethylene glycol, triethylene glycol, propanediols (e.g., 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, etc.), dipropylene glycol, butanediols (e.g., 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2,3-dimethyl-2,3-butanediol, etc.), neopentyl glycol, pentanediol, hexanediol, heptanediol, octanediol, 1,6-cyclohexanedimethylol, aniline diols, bisphenol A diols, and other diols; triols such as glycerin, trimethylolpropane, and hexanetriol; and tetraols or hexaols such as pentaerythritol and sorbitol.

[0024] The low molecular weight polyamine used as a chain extender component is not particularly limited as long as it has at least two amino groups. Examples of such polyamines include aliphatic polyamines such as ethylenediamine, propylenediamine, butylenediamine, and hexamethylenediamine; alicyclic polyamines such as isophoronediamine and piperazine; and aromatic polyamines.

[0025] 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, indirect bonding means that the amino groups are bonded to the aromatic ring, for example, via lower alkylene groups. 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 a polycyclic aromatic polyamine containing two or more aminophenyl groups in which at least one amino group is bonded to one aromatic ring.

[0026] Examples of the monocyclic aromatic polyamines include types in which the amino group is directly bonded to the aromatic ring, such as phenylenediamine, toluenediamine, diethyltoluenediamine, and dimethylthiotoluenediamine; and types in which the amino group is bonded to the aromatic ring via a lower alkylene group, such as xylylenediamine. Furthermore, the polycyclic aromatic polyamine may be a poly(aminobenzene) in which at least two aminophenyl groups are directly bonded, or it may be a poly(aminobenzene) in which at least two aminophenyl groups are bonded via a lower alkylene group or an alkylene oxide group. 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.

[0027] The molecular weight of the chain extender is preferably less than 400, more preferably 350 or less, even more preferably 200 or less, preferably 30 or more, more preferably 40 or more, and even more preferably 45 or more.

[0028] The constituent configuration of the thermoplastic polyurethane (A) is not particularly limited, but examples include a configuration composed of polyisocyanate and a high molecular weight polyol; a configuration composed of polyisocyanate, a high molecular weight polyol and a low molecular weight polyol; a configuration composed of polyisocyanate, a high molecular weight polyol and a low molecular weight polyol and a polyamine; and a configuration composed of polyisocyanate, a high molecular weight polyol and a polyamine. In particular, a configuration composed of diisocyanate and a diol is preferred for the constituent configuration of the thermoplastic polyurethane (A), and a configuration composed of diisocyanate, a high molecular weight diol and a low molecular weight diol is more preferred.

[0029] The polyol content in 100% by mass of the thermoplastic polyurethane (A) is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less. The polyisocyanate content in 100% by mass of the thermoplastic polyurethane (A) is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less.

[0030] The slab hardness of the thermoplastic polyurethane (A) is preferably 25 or higher on the Shore D scale, more preferably 26 or higher, even more preferably 28 or higher, preferably 40 or lower, more preferably 39 or lower, and even more preferably 38 or lower. If the hardness of the thermoplastic polyurethane (A) is 25 or higher on the Shore D scale, the amount of spin in driver shots can be reduced, and if it is 40 or lower, the amount of spin in approach shots can be increased.

[0031] The content of thermoplastic polyurethane (A) in the resin component is preferably 50% by mass or more, more preferably 55% by mass or more, even more preferably 60% by mass or more, particularly preferably 70% by mass or more, most preferably 80% by mass or more, preferably 99.9% by mass or less, more preferably 99.5% by mass or less, and even more preferably 99.0% by mass or less. If the content of component (A) is 50% by mass or more, the scratch resistance of the cover will be better, and if it is 99.9% by mass or less, the moldability of the cover composition will be better.

[0032] ((B) Carboxylic acid) The aforementioned cover composition contains (B) a carboxylic acid with a molecular weight of 1000 or less as a resin component. The (B) carboxylic acid is a compound having at least one carboxyl group in its molecule. The (B) carboxylic acid may be used alone or in combination of two or more types.

[0033] (A) By blending thermoplastic polyurethane with (B) carboxylic acid, which has a low molecular weight, the melt viscosity of the cover composition can be lowered, thereby improving the moldability of the cover composition. Furthermore, since (B) carboxylic acid has a carboxyl group, it has the effect of relaxing the hydrogen bonds of (A) thermoplastic polyurethane during melt molding at high temperatures, thus minimizing the loss of the flexibility of (A) thermoplastic polyurethane and suppressing a decrease in the scratch resistance of the resulting cover.

[0034] For example, the thermoplastic polyurethane (A) may contain 4,4'-dicyclohexylmethane diisocyanate (H) as a polyisocyanate. 12 If MDI is included, (B) by incorporating a carboxylic acid, the moldability of the cover can be improved while suppressing a decrease in the scratch resistance of the cover.

[0035] Furthermore, for example, if the thermoplastic polyurethane (A) contains 4,4'-diphenylmethane diisocyanate (MDI) as a polyisocyanate, the addition of carboxylic acid (B) can improve not only the moldability of the cover but also its scratch resistance. The reason why this improves not only the moldability but also the scratch resistance of the cover is not entirely clear, but it is thought to have effects such as promoting the recombination of the thermoplastic polyurethane (A) after thermal decomposition.

[0036] The molecular weight of the (B) carboxylic acid is preferably 50 or more, more preferably 80 or more, even more preferably 100 or more, preferably 1000 or less, more preferably 950 or less, and even more preferably 900 or less. If the molecular weight of the (B) carboxylic acid is 50 or more, the volatilization of the carboxylic acid is suppressed when the cover composition is melted, and if it is 1000 or less, a small amount of addition can be used to improve the scratch resistance of the cover.

[0037] The number of carboxyl groups in the molecule of the carboxylic acid (B) is 1 or more, preferably 2 or more, preferably 10 or less, more preferably 8 or less, and even more preferably 5 or less. If the number of carboxyl groups in the molecule of the carboxylic acid (B) is 2 or more, the effect of relaxing hydrogen bonds in the thermoplastic polyurethane (A) during melt molding at high temperatures will be greater, and if it is 10 or less, the dispersibility in the thermoplastic polyurethane (A) will be higher.

[0038] The amount of carboxyl groups per unit mass of the (B) carboxylic acid is preferably 1 mmol / g or more, more preferably 2 mmol / g or more, even more preferably 3 mmol / g or more, preferably 30 mmol / g or less, more preferably 25 mmol / g or less, and even more preferably 20 mmol / g or less. If the amount of carboxyl groups per unit mass of the (B) carboxylic acid is 1 mmol / g or more, the moldability of the cover composition is further improved, and if it is 30 mmol / g or less, the compatibility with the (A) thermoplastic polyurethane is good.

[0039] The (B) carboxylic acid may have functional groups other than a carboxyl group. Examples of such functional groups include a hydroxyl group, a carbonyl group, and an ester group.

[0040] It is also preferable to use a hydroxy acid as the (B) carboxylic acid. The hydroxy acid is a compound having at least one carboxyl group and at least one hydroxyl group in its molecule. The number of hydroxyl groups in the molecule of the hydroxy acid is one or more, preferably 10 or less, more preferably 9 or less, and even more preferably 8 or less. If the number of hydroxyl groups in the molecule of the hydroxy acid is 10 or less, the dispersibility in (A) thermoplastic polyurethane is improved.

[0041] Examples of the carboxylic acid include aliphatic carboxylic acids, aromatic carboxylic acids, aliphatic hydroxy acids, and aromatic hydroxy acids.

[0042] As the aliphatic carboxylic acid, either a saturated aliphatic carboxylic acid or an unsaturated aliphatic carboxylic acid can be used. Examples of the saturated aliphatic carboxylic acids include butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, pentadecyl acid, palmitic acid, margaric acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid, and melissic acid; saturated aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, corticic acid, azelaic acid, sebacic acid, and dodecanedioic acid; and saturated aliphatic tricarboxylic acids such as tricarbaryl acid. Examples of the aforementioned unsaturated aliphatic carboxylic acids include unsaturated aliphatic monocarboxylic acids such as myristoleic acid, palmitoleic acid, oleic acid, elaidic acid, vaccenic acid, gadrenic acid, eicosenoic acid, erucic acid, nervonic acid, linoleic acid, linolenic acid, and arachidonic acid; and unsaturated aliphatic dicarboxylic acids such as maleic acid, fumaric acid, citraconic acid, and mesaconic acid.

[0043] The aromatic carboxylic acid is not particularly limited as long as it is a compound having an aromatic ring and a carboxyl group. Examples of the aromatic carboxylic acid include aromatic monocarboxylic acids such as benzoic acid, toluic acid, xylylic acid, prenicylic acid, γ-isojurylic acid, jurylic acid, β-isojurylic acid, α-isojurylic acid, cumic acid, α-toluic acid, hydroatropic acid, and hydrocinnamic acid; aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, diphenic acid, and ubitic acid; aromatic tricarboxylic acids such as hememiritic acid, trimellitic acid, and trimesic acid; aromatic tetracarboxylic acids such as merophanic acid and pyromellitic acid; and aromatic hexacarboxylic acids such as meritolic acid.

[0044] Examples of the aforementioned aliphatic hydroxy acids include aliphatic hydroxy acids having one carboxyl group, such as glycolic acid, lactic acid, glyceric acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid, 3-hydroxyisobutyric acid, γ-hydroxybutyric acid, leucic acid, mevalonic acid, pantoic acid, ricinoleic acid, ricineradicic acid, quinic acid, shikimic acid, 3-hydroxypropionic acid, γ-hydroxyvaleric acid, 3-hydroxyisovaleric acid, and dimethylolbutanoic acid; aliphatic hydroxy acids having two carboxyl groups, such as tartaronic acid, malic acid, tartaric acid, and citramalic acid; and aliphatic hydroxy acids having three carboxyl groups, such as citric acid, hydroxycitric acid, and isocitric acid.

[0045] Examples of the aforementioned aromatic hydroxy acids include salicylic acid, 3-hydroxybenzoic acid, 4-hydroxybenzoic acid, vanillic acid, syringic acid, protocatechuic acid, gentisic acid, orceric acid, gallic acid, mandelic acid, 4-hydroxymandelic acid, benzyl acid, floretic acid, coumaric acid, caffeic acid, ferulic acid, and synapic acid, which are aromatic hydroxy acids having one carboxyl group.

[0046] The content of (B) carboxylic acid in the resin component is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1.0% by mass or more, preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less. If the content of component (B) is 0.1% by mass or more, the moldability of the cover composition is further improved, and if it is 30% by mass or less, the decrease in the scratch resistance of the resulting cover can be further suppressed.

[0047] The mass ratio ((A) / (B)) of the thermoplastic polyurethane (A) and the carboxylic acid (B) in the resin component is preferably 70 / 30 or more, more preferably 80 / 20 or more, even more preferably 90 / 10 or more, preferably 99.9 / 0.1 or less, more preferably 99.5 / 0.5 or less, and even more preferably 99.0 / 1.0 or less. If the mass ratio ((A) / (B)) is 70 / 30 or more, the decrease in scratch resistance of the resulting cover can be further suppressed, and if it is 99.9 / 0.1 or less, the moldability of the cover composition can be further improved.

[0048] The molar amount of (B) carboxylic acid in 100g of the resin component is preferably 0.1 mmol or more, more preferably 0.2 mmol or more, even more preferably 0.3 mmol or more, preferably 60 mmol or less, more preferably 55 mmol or less, and even more preferably 50 mmol or less. If the molar amount of component (B) is 0.1 mmol or more, the moldability of the cover composition is further improved, and if it is 60 mmol or less, the compatibility with (A) thermoplastic polyurethane is good.

[0049] The molar amount of carboxyl groups derived from (B) carboxylic acid in 100 g of the resin component is preferably 0.1 mmol or more, more preferably 0.3 mmol or more, even more preferably 0.5 mmol or more, preferably 100 mmol or less, more preferably 95 mmol or less, and even more preferably 90 mmol or less. If the molar amount of carboxyl groups derived from component (B) is 0.1 mmol or more, the moldability of the cover composition is further improved, and if it is 100 mmol or less, the compatibility with (A) thermoplastic polyurethane is good.

[0050] (Other resin components) The cover composition may contain only (A) thermoplastic polyurethane and (B) carboxylic acid as resin components, but may also contain other resin components in addition to these.

[0051] Other resin components include thermoplastic elastomers and the like.

[0052] Specific examples of the aforementioned thermoplastic elastomers include, for example, thermoplastic polyamide elastomers such as Arkema's "Pebax® (e.g., "Pebax 2533")", thermoplastic polyester elastomers such as Toray Celanese's "Hytrel® (e.g., "Hytrel 3548", "Hytrel 4047")", and thermoplastic polystyrene elastomers such as Mitsubishi Chemical's "Tefablock®".

[0053] When resin components other than components (A) and (B) are blended as the aforementioned resin component, the total content of components (A) and (B) in the resin component is preferably 85% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0054] (Additives) The cover composition may further contain additives such as pigment components like titanium dioxide or blue pigment, weight modifiers like calcium carbonate or barium sulfate, dispersants, antioxidants, ultraviolet absorbers, light stabilizers, fluorescent materials, or fluorescent whitening agents, to the extent that they do not impair the cover performance. The content of the resin component in the cover composition is preferably 90% by mass or more, more preferably 92% by mass or more, and even more preferably 94% by mass or more.

[0055] The content of the white pigment (titanium dioxide) is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, even more preferably 1.5 parts by mass or more, preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 6 parts by mass or less, per 100 parts by mass of the resin component. If the content of the white pigment is 0.5 parts by mass or more, the cover can be given opacity, and if it is 10 parts by mass or less, the decrease in the durability of the cover can be suppressed.

[0056] The cover composition can be obtained, for example, by dry blending component (A), component (B), and other additives as needed. Alternatively, the dry-blended mixture may be extruded to form pellets. For dry blending, it is preferable to use a mixer capable of blending pelletized raw materials, and more preferably a tumbler-type mixer. For extrusion, known extruders such as single-screw extruders, twin-screw extruders, and twin-screw single-screw extruders can be used.

[0057] The slab hardness of the cover composition is preferably 25 or higher on the Shore D scale, more preferably 26 or higher, even more preferably 28 or higher, preferably 40 or lower, more preferably 39 or lower, and even more preferably 38 or lower. If the slab hardness is 25 or higher on the Shore D scale, the amount of spin in driver shots can be reduced, and if it is 40 or lower, the amount of spin in approach shots can be increased.

[0058] [Golf balls] The golf ball of the present invention has a spherical core and a cover that covers the spherical core, and the cover is formed from the cover composition. The cover constitutes the outermost layer of the golf ball body. The present invention relates to the moldability and scratch resistance of the cover, and the structure of the spherical core is not limited.

[0059] (Spherical core) Examples of the spherical core include a single-layer spherical core, a spherical core consisting of a center and one intermediate layer covering the center, and a spherical core consisting of a center and two or more intermediate layers covering the center.

[0060] A known rubber composition (hereinafter sometimes simply referred to as "rubber composition for core") can be used for the spherical core or center. For example, a rubber composition containing a base rubber, a co-crosslinking agent, and a crosslinking initiator can be molded by heating and pressing.

[0061] As the base rubber, it is preferable to use high-cis polybutadiene containing 40% by mass or more, preferably 70% by mass or more, and more preferably 90% by mass or more, cis bonds which are advantageous for rebound.

[0062] The cocrosslinking agent is preferably an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms or a metal salt thereof, more preferably an acrylic acid or a metal salt thereof, or a methacrylic acid or a metal salt thereof. The metal of the metal salt is preferably zinc, magnesium, calcium, aluminum, or sodium, more preferably zinc. The amount of cocrosslinking agent used is preferably 20 to 50 parts by mass per 100 parts by mass of the base rubber. When using an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms as the cocrosslinking agent, it is preferable to incorporate a metal compound (e.g., magnesium oxide).

[0063] Organic peroxides are preferably used as crosslinking initiators. Specifically, examples of organic peroxides include dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide, of which dicumyl peroxide is preferably used. The amount of crosslinking initiator blended is preferably 0.2 parts by mass or more, more preferably 0.3 parts by mass or more, even more preferably 0.4 parts by mass or more, preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less, per 100 parts by mass of base rubber.

[0064] Furthermore, the core rubber composition may also contain an organic sulfur compound. Suitable organic sulfur compounds include diphenyl disulfides, thiophenols, and thionaphthols. The amount of organic sulfur compound is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, even more preferably 0.5 parts by mass or more, preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 2.0 parts by mass or less, per 100 parts by mass of the base rubber.

[0065] The core rubber composition may further contain a carboxylic acid and / or its salt. Preferably, the carboxylic acid and / or its salt has 1 to 30 carbon atoms. The carboxylic acid can be either an aliphatic carboxylic acid or an aromatic carboxylic acid (such as benzoic acid). The amount of carboxylic acid and / or its salt added is 1 part by mass or more and 40 parts by mass or less per 100 parts by mass of the base rubber.

[0066] In addition to the base rubber, co-crosslinking agent, crosslinking initiator, and organic sulfur compound, the core rubber composition may also contain, as appropriate, weight adjusters such as zinc oxide and barium sulfate, antioxidants, colorants, and the like.

[0067] The heating and pressing conditions for the core rubber composition can be set appropriately according to the rubber composition, but it is generally preferable to heat at 130°C to 200°C for 10 to 60 minutes, or to heat at 130°C to 150°C for 20 to 40 minutes, followed by two-stage heating at 160°C to 180°C for 5 to 15 minutes.

[0068] When the spherical core has an intermediate layer, examples of intermediate layer materials include thermoplastic resins such as polyurethane resin, ionomer resin, polyamide resin, and polyethylene; thermoplastic elastomers such as styrene elastomer, polyolefin elastomer, polyurethane elastomer, polyamide elastomer, and polyester elastomer; and cured rubber compositions. Here, examples of ionomer resins include those in which at least a portion of the carboxyl groups in a copolymer of ethylene and an α,β-unsaturated carboxylic acid are neutralized with metal ions, or those in which at least a portion of the carboxyl groups in a terpolymer of ethylene, an α,β-unsaturated carboxylic acid, and an α,β-unsaturated carboxylic acid ester are neutralized with metal ions. The intermediate layer may further contain weight adjusters such as barium sulfate and tungsten, antioxidants, pigments, etc.

[0069] The method for forming the intermediate layer is not particularly limited, but examples include a method in which the intermediate layer composition is pre-formed into a hemispherical half-shell, two of these are used to enclose a sphere, and then pressure-molded, or a method in which the intermediate layer composition is directly injection-molded onto a sphere to enclose the sphere.

[0070] When forming an intermediate layer by injection molding an intermediate layer composition onto a sphere, it is preferable to use upper and lower molds having hemispherical cavities. The intermediate layer can be formed by injection molding by extending a holding pin, inserting and holding the coated sphere, injecting the heated and melted intermediate layer composition, and then cooling it.

[0071] When forming an intermediate layer by compression molding, the half-shell can be formed by either compression molding or injection molding, but compression molding is preferred. Conditions for compressing the intermediate layer composition to form a half-shell include, for example, a pressure of 1 MPa or more and 20 MPa or less, and a molding temperature of -20°C or more and +70°C or less relative to the flow start temperature of the intermediate layer composition. By using these molding conditions, a half-shell with a uniform thickness can be formed. As a method for forming an intermediate layer using a half-shell, for example, a method of covering a sphere with two half-shells and compress molding them can be used. Conditions for compressing the half-shell to form an intermediate layer include, for example, a molding pressure of 0.5 MPa or more and 25 MPa or less, and a molding temperature of -20°C or more and +70°C or less relative to the flow start temperature of the intermediate layer composition. By using these molding conditions, an intermediate layer with a uniform thickness can be formed.

[0072] The molding temperature refers to the highest temperature reached by the surface of the recess in the lower mold between mold clamping and mold opening. The flow start temperature of the composition was determined using Shimadzu Corporation's "Flow Tester CFT-500" with a pelletized thermoplastic resin composition and a plunger area of ​​1 cm². 2Measurements can be taken under the following conditions: DIE LENGTH: 1mm, DIE DIA: 1mm, Load: 588.399N, Starting temperature: 30℃, Heating rate: 3℃ / min.

[0073] The diameter of the spherical core is preferably 34.8 mm or more, more preferably 35.7 mm or more, even more preferably 36.6 mm or more, preferably 42.2 mm or less, more preferably 41.8 mm or less, even more preferably 41.2 mm or less, and most preferably 40.8 mm or less. If the diameter of the spherical core is 34.8 mm or more, the thickness of the cover will not become too thick, and the resilience will be better. On the other hand, if the diameter of the spherical core is 42.2 mm or less, the cover will not become too thin, and the function of the cover will be better performed.

[0074] (The structure of a golf ball) The structure of the golf ball is not particularly limited as long as it has a spherical core and a cover that covers the spherical core. Examples of golf ball structures include a two-piece golf ball having a single-layer spherical core and a cover that covers the spherical core; a three-piece golf ball having a spherical core consisting of a center and one intermediate layer covering the center and a cover that covers the spherical core; and a multi-piece golf ball having a spherical core consisting of a center and two or more intermediate layers covering the center and a cover that covers the spherical core.

[0075] The method of forming the cover using the cover composition is not particularly limited, but examples include directly injection molding the cover composition onto a spherical core, or forming a hollow shell from the cover composition and then compression molding the spherical core with multiple shells (preferably, forming a hollow half-shell from the cover composition and then compression molding the spherical core with two half-shells). The golf ball body with the molded cover is removed from the mold and, if necessary, undergoes surface treatment such as deburring, cleaning, and sandblasting. A mark can also be formed if desired.

[0076] The thickness of the cover is preferably 0.3 mm or more, more preferably 0.4 mm or more, even more preferably 0.5 mm or more, preferably 2.0 mm or less, more preferably 1.8 mm or less, and even more preferably 1.6 mm or less. If the cover thickness is 0.3 mm or more, the cover is easier to mold, and if it is 2.0 mm or less, the diameter of the core can be relatively increased, thus improving the rebound performance of the golf ball.

[0077] The total number of dimples formed on the cover is preferably between 200 and 500. If the total number of dimples is less than 200, the effect of the dimples is difficult to obtain. Also, if the total number of dimples exceeds 500, the size of each dimple becomes smaller, making it difficult to obtain the effect of the dimples. The shape of the formed dimples (planar view shape) is not particularly limited, and may be a circle; a polygon such as a roughly triangular, roughly square, roughly pentagon, roughly hexagon; or other irregular shapes; used individually or in combination of two or more types.

[0078] The golf balls with molded covers are removed from the mold and, if necessary, subjected to surface treatments such as deburring, cleaning, and sandblasting. A coating or mark can also be formed as desired. The thickness of the coating is not particularly limited, but is preferably 5 μm or more, more preferably 7 μm or more, even more preferably 9 μm or more, preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. A thickness of 5 μm or more ensures that the coating is less likely to wear away even with continuous use, while a thickness of 50 μm or less allows the dimple effect to be fully realized.

[0079] The diameter of the golf ball is preferably 40 mm to 45 mm. From the viewpoint of meeting the standards of the United States Golf Association (USGA), a diameter of 42.67 mm or more is particularly preferred. From the viewpoint of suppressing air resistance, a diameter of 44.00 mm or less is more preferred, and 42.80 mm or less is particularly preferred. The mass of the golf ball is preferably 40 g to 50 g. From the viewpoint of obtaining a large inertia, a mass of 44.00 g or more is more preferred, and 45.00 g or more is particularly preferred. From the viewpoint of meeting the standards of the USGA, a mass of 45.93 g or less is particularly preferred.

[0080] In the golf ball of the present invention, when the diameter is 40 mm to 45 mm, the amount of compression deformation (the amount the golf ball shrinks in the compression direction) when an initial load of 98 N is applied and a final load of 1275 N is applied is preferably 2.0 mm or more, more preferably 2.4 mm or more, even more preferably 2.5 mm or more, preferably 5.0 mm or less, more preferably 4.5 mm or less, and even more preferably 4.0 mm or less. A golf ball with a compression deformation of 2.0 mm or more is not too hard and has a good feel when hit. On the other hand, by making the compression deformation amount 5.0 mm or less, the rebound performance is increased.

[0081] Figure 1 shows an example of a golf ball according to the present invention. Figure 1 is a partially cutaway cross-sectional view showing a golf ball 1 according to one embodiment of the present invention. The golf ball 1 has a spherical core 2 composed of a center 21 and an intermediate layer 22 covering the center 21, and a cover 3 covering the spherical core 2. Numerous dimples 31 are formed on the surface of the cover 3. The portion of the surface of the golf ball other than the dimples 31 is a land 32. The golf ball 1 has a paint layer and a mark layer on the outside of the cover 3, but these layers are not shown in the illustration. [Examples]

[0082] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples, and any modifications and embodiments that do not depart from the spirit of the present invention are all included within the scope of the present invention.

[0083] [Evaluation Method] (1) Slab hardness (Shore D hardness) Using the intermediate layer composition, thermoplastic polyurethane, and cover composition, sheets approximately 2 mm thick were fabricated by injection molding and stored at 23°C for two weeks. Three or more of these sheets were stacked to avoid interference from the measurement substrate, and their hardness was measured using an automated hardness tester (H. Barleys, DigiTest II). A "Shore D" detector was used.

[0084] (2) Melt viscosity, flow initiation temperature The melt viscosity and flow onset temperature were measured on pelletized samples using a flow characteristics evaluation device (Shimadzu Corporation, Flow Tester CFT-500D) and evaluated according to the following evaluation criteria. The measurement conditions were: die length: 10 mm, die bore diameter: 1 mm, cylinder pressure: 3 MPa, temperature: 190 °C. The melt viscosity and flow onset temperature are shown as indexed values ​​with the measured values ​​of the formulation without component (B) set to 100. Tables 3 and 4 show the melt viscosity and flow onset temperature of cover composition No. 7, indexed to 100. Table 5 shows the melt viscosity and flow onset temperature of cover composition No. 21, indexed to 100.

[0085] (3) Scratch resistance A commercially available pitching wedge was attached to a swing robot, and it struck two different spots on a golf ball once each at a head speed of 36 m / s. The two impact points were visually observed and evaluated on a 5-point scale based on the following criteria, with the worse of the two being used as the final evaluation result. 5 points: No damage is practically visible. 4 points: No visible damage was observed, but slight scratches were found upon close inspection. 3 points: There are visible scratches. Points 2: There are noticeable scratches. 1 point: It has damage that makes it unusable.

[0086] [Golf ball manufacturing] (1) Preparation of rubber composition Each raw material was kneaded with a kneading roll so as to have the formulation shown in Table 1, and a rubber composition was obtained.

[0087]

Table 1

[0088] The materials used in Table 1 are as follows. BR730: Manufactured by ENEOS MATERIALS, high cis-polybutadiene rubber (cis-1,4-bond content = 95% by mass, 1,2-vinyl bond content = 1.3% by mass, Mooney viscosity (ML 1+4 (100 °C)) = 55, molecular weight distribution (Mw / Mn) = 3) ZN-DA90S: Manufactured by Nisso Techno Fine Chemical, zinc acrylate (containing 10% zinc stearate) Zinc oxide: Manufactured by Toho Zinc, "Ginrei R" Barium sulfate: Manufactured by Sakai Chemical Industry, "Barium Sulfate BD" PBDS: Manufactured by Kawaguchi Chemical Industry, bis(pentabromophenyl) disulfide Dicumyl peroxide: Manufactured by Tokyo Chemical Industry

[0089] (2) Preparation of the intermediate layer composition The raw materials were extruded with a twin-screw kneading extruder so as to have the formulation shown in Table 2, and a pelletized intermediate layer composition was prepared.

[0090]

Table 2

[0091] (3) Preparation of the cover composition Thermoplastic polyurethane No. 1 Thermoplastic polyurethane No. 1 was synthesized as follows: Dicyclohexylmethane diisocyanate (H) heated to 80°C 12 Polytetramethylene ether glycol (PTMG (number average molecular weight 1400)) heated to 80°C is added to MDI), and further, raw materials (H 12 After adding 0.005% by mass of dibutylthin dilaurate (MDI, PTMG, and BD), the mixture was stirred at 80°C for 2 hours under a nitrogen atmosphere. Subsequently, butanediol (BD) heated to 80°C was added under a nitrogen atmosphere, and the mixture was stirred at 80°C for 1 minute. After that, the reaction mixture was cooled and degassed by reducing the pressure at room temperature for 1 minute. The degassed reaction mixture was spread in a container and stored under a nitrogen atmosphere at 110°C for 6 hours to carry out the urethane reaction and obtain thermoplastic polyurethane No. 1. Note that PTMG, H 12 The molar ratio of MDI to BD is PTMG:H 12 The ratio of MDI to BD was set to 1:3.81:2.81. The resulting thermoplastic polyurethane No. 1 slab hardness was 31 on the Shore D hardness scale.

[0092] Thermoplastic polyurethane No. 2 As thermoplastic polyurethane No. 2, thermoplastic polyurethane (BASF-manufactured, Elastolane® 1195ATR) was used. The aforementioned thermoplastic polyurethane No. 2 contains 4,4'-diphenylmethane diisocyanate (MDI) as the polyisocyanate constituting the polyurethane, and its slab hardness is 35 on the Shore D scale.

[0093] Next, using the thermoplastic polyurethane No. 1 obtained above, the raw materials were extruded using a twin-screw kneading extruder to prepare pellet-shaped cover compositions according to the formulations shown in Tables 3 to 5.

[0094] (4) Making golf balls Golf balls No. 1-21 A center with a diameter of 38.5 mm was obtained by heating and pressing the rubber composition in upper and lower molds having hemispherical cavities. Barium sulfate was added in an appropriate amount so that the mass of the resulting golf ball was 45.6 g. The aforementioned intermediate layer composition was injection molded onto a center to obtain a spherical core. The thickness of the intermediate layer was 1.6 mm. The obtained spherical core was placed into a final mold having numerous dimples on the cavity surface. Half shells were obtained from the cover composition by compression molding. Two half shells were placed on a spherical core in a final mold to obtain a golf ball in which numerous dimples, the shape of which is the reverse of the pimples on the cavity surface, were formed on the cover. The results of the evaluation of the obtained golf balls are shown in Tables 3 to 5.

[0095] [Table 3]

[0096] [Table 4]

[0097] [Table 5]

[0098] The materials used in Tables 3-5 are as follows: Malic acid: Manufactured by Tokyo Chemical Industry Co., Ltd. Citric acid: Manufactured by Tokyo Chemical Co., Ltd. Dimethylolbutanoic acid: Manufactured by Tokyo Chemical Industry Co., Ltd. Succinic acid: Manufactured by Tokyo Chemical Industry Co., Ltd. Adipic acid: Manufactured by Tokyo Chemical Industry Co., Ltd. Tricarbaryl acid: Manufactured by Tokyo Chemical Industry Co., Ltd. Benzoic acid: Manufactured by Tokyo Chemical Co., Ltd. Hymiran (registered trademark) 1605: Sodium ion-neutralized ethylene-methacrylic acid copolymer ionomer resin, manufactured by Mitsui Dow Polychemicals. Hymiran AM7329: A zinc ion-neutralized ethylene-methacrylic acid copolymer ionomer resin manufactured by Mitsui Dow Polychemicals. Titanium dioxide: Manufactured by Ishihara Sangyo, A-220

[0099] Golf balls No. 1-6 and 10-20 have covers formed from cover compositions No. 1-6 and 10-20, which contain (A) thermoplastic polyurethane and (B) carboxylic acid as resin components. Golf balls No. 7 and 21 have covers formed from cover compositions No. 7 and 21, which contain (A) thermoplastic polyurethane as a resin component and (B) do not contain carboxylic acid. Golf balls No. 8 and 9 are formed from a cover composition No. 8 or 9 containing (A) thermoplastic polyurethane and an ionomer resin (metal neutralized olefin-unsaturated carboxylic acid copolymer or metal neutralized olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester copolymer).

[0100] The cover compositions No. 1-6 and 10-16, which form the covers of golf balls No. 1-6 and 10-16, have a lower melt viscosity than the cover composition No. 7, which forms the cover of golf ball No. 7. Therefore, the moldability of the covers of these golf balls No. 1-6 and 10-16 is improved. Furthermore, golf balls No. 1-6 and 10-16 have higher scratch resistance to the cover than golf balls No. 8 and 9, and the use of (B) carboxylic acid suppresses the decrease in scratch resistance.

[0101] The cover compositions No. 17-20, which form the covers of golf balls No. 17-20, have a lower melt viscosity than the cover composition No. 21, which forms the cover of golf ball No. 21. Therefore, the moldability of the covers of these golf balls No. 17-20 is improved. Furthermore, golf balls No. 17-20 have higher scratch resistance to the cover than golf ball No. 21, and the use of (B) carboxylic acid improves scratch resistance.

[0102] (Aspects of the present invention) The present invention (1) is a golf ball having a spherical core and a cover covering the spherical core, wherein the cover is formed from a cover composition containing (A) thermoplastic polyurethane and (B) a carboxylic acid with a molecular weight of 1000 or less as a resin component.

[0103] The present invention (2) is a golf ball according to the present invention (1), wherein the mass ratio ((A) / (B)) of the thermoplastic polyurethane (A) and the carboxylic acid (B) in the resin component is 70 / 30 to 99.9 / 0.1.

[0104] The present invention (3) is a golf ball according to the present invention (1) or (2), wherein the thermoplastic polyurethane (A) contains an alicyclic diisocyanate and / or an aromatic diisocyanate as the polyisocyanate constituting the thermoplastic polyurethane (A).

[0105] The present invention (4) is a golf ball according to the present invention (3), wherein the polyisocyanate is at least one diisocyanate selected from the group consisting of 4,4'-dicyclohexylmethane diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, isophorone diisocyanate, trans-1,4-cyclohexane diisocyanate, 4,4'-diphenylmethane diisocyanate, and toluene diisocyanate.

[0106] The present invention (5) is a golf ball according to any one of the present inventions (1) to (4), wherein the (B) carboxylic acid has 2 or more and 10 or fewer carboxyl groups in the molecule. [Explanation of Symbols]

[0107] 1: Golf ball, 2: Spherical core, 21: Center, 22: Middle layer, 3: Cover, 31: Dimple, 32: Land

Claims

1. A golf ball having a spherical core and a cover that covers the spherical core, A golf ball characterized in that the cover is formed from a cover composition containing (A) thermoplastic polyurethane and (B) a carboxylic acid with a molecular weight of 1000 or less as resin components.

2. The golf ball according to claim 1, wherein the mass ratio ((A) / (B)) of the thermoplastic polyurethane (A) to the carboxylic acid (B) in the resin component is 70 / 30 to 99.9 / 0.

1.

3. The golf ball according to claim 1, wherein the thermoplastic polyurethane (A) contains an alicyclic diisocyanate and / or an aromatic diisocyanate as the polyisocyanate constituting the thermoplastic polyurethane (A).

4. The golf ball according to claim 3, wherein the polyisocyanate is at least one diisocyanate selected from the group consisting of 4,4'-dicyclohexylmethane diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, isophorone diisocyanate, trans-1,4-cyclohexane diisocyanate, 4,4'-diphenylmethane diisocyanate, and toluene diisocyanate.

5. The golf ball according to claim 1, wherein the (B) carboxylic acid has two or more and ten or fewer carboxyl groups in its molecule.

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