Patent Application
20250108266
This non-provisional application claims priority under 35 U.S.C. § 119 (a) on Patent Application No. 2023-166822 filed in Japan on Sep. 28, 2023, the entire contents of which are hereby incorporated by reference.
The present invention relates to a golf ball having a core of at least one layer and a cover of at least one layer.
The property most desired in a golf ball is increased distance, but other desirable properties include the ability for the ball to stop well on approach shots and a good scuff resistance. Many golf balls have hitherto been developed that exhibit a good flight performance on shots with a driver and are suitably receptive to backspin on approach shots. Recently, in golf balls for professional golfers and skilled amateurs, urethane resin materials are often used in place of ionomer resin materials as the cover material.
A number of cover materials that are polymer blends obtained by mixing a urethane resin as the base resin with other resin materials have been described in the art. I have earlier described, in JP-A 2019-107401, including an acrylic or methacrylic resin in a urethane resin-based polymer blend and using this blend as the chief material of the cover. This prior art does provide a golf ball which enables a higher initial velocity to be achieved on driver shots and also enables a lower initial velocity to be achieved on approach shots, but because acrylic resins and methacrylic resins are basically hard resin materials, a sufficient degree of controllability on approach shots cannot be obtained. The maneuverability of the club on approach shots is a key factor in ball controllability on approach shots, and the level of club maneuverability is influenced by the ball rate of spin and also the length of contact (contact time) between the ball and the clubface owing to a low rebound. Such maneuverability improves when the contact time is long and worsens when it is short. A golf ball having even better controllability on approach shots than the golf ball of JP-A 2019-107401 has thus been desired.
In the cover-forming resin material of JP-A 2019-107401, the melt viscosity of the urethane resin material rises with the admixture of an acrylic resin, worsening the flowability and making it necessary to increase the molding temperature. As a result, after molding, defects such as scorching of the overall cover surface may arise. Hence, there remains room for improvement in the moldability and scuff resistance of the golf ball.
JP-A 2019-97573 and JP-A 2020-191906 disclose, as polymer blends that are urethane resin materials, cover-forming resin compositions which include a styrene resin or an aromatic vinyl elastomer, but there remains room for improvement in the feel at impact on approach shots.
JP-A 2019-88770 and U.S. Pat. Nos. 10,124,214 and 10,150,008 do disclose resin materials for golf balls which are formed of mixtures containing a thermoplastic polymer and an acrylic copolymer (MMA copolymer). However, because this literature is silent on whether the ball controllability on approach shots is sufficiently good and the scuff resistance and moldability also are excellent, one would be hard-pressed to say that this is art capable of resolving the above challenges.
It is therefore an object of the present invention to provide a golf ball which, compared with golf balls having a conventional urethane cover, is endowed with an excellent controllability on approach shots and possesses a good scuff resistance and a good feel at impact.
As a result of intensive investigations, I have discovered that by formulating, as the cover material for a golf ball having a core and a cover, a polymer blend that is a resin material composed primarily of polyurethane or polyurea and includes less than a specific amount of a core-shell polymer in which the core is a crosslinked acrylic rubber particle and the shell is made of an acrylic polymer, and producing a golf ball in which a molding of this resin material serves as the cover such that the CS1 value calculated by formula (1) below
(wherein CV50 is the ball coefficient of restitution (COR) at an incident velocity of 50.0 m/s and CV 12 is the ball COR at an incident velocity of 12.0 m/s) is larger than −4.08×10−3, the golf ball has an excellent controllability on approach shots, a good feel at impact on approach shots and a good scuff resistance.
I have also found that by including less than a specific amount of a core-shell polymer in which the core is a crosslinked acrylic rubber particle and the shell is made of an acrylic polymer, the COR of the golf ball decreases at a low initial velocity but does not decrease at a high initial velocity, making this effective for achieving good ball controllability on approach shots. In particular, a urethane resin composition containing a core-shell polymer in which the core is a crosslinked acrylic rubber particle and the shell is made of an acrylic polymer has a good compatibility with urethane resin materials and moreover does not require the use of a plasticizer. As a result, plasticizer vaporization due to shearing heat does not occur during molding and so the golf ball properties, including hardness and rebound resilience, are stable and the ball incurs substantially no adverse effects upon the spin performance on approach shots.
Accordingly, the invention provides a golf ball having a rubber core of at least one layer and a cover of at least one layer encasing the core, wherein at least one layer of the cover is formed of a resin composition which includes:
In a preferred embodiment of the golf ball of the invention, the CS2 value calculated by formula (2) below
(wherein CV12/45 is the coefficient of restitution at an incident velocity of 12.0 m/s when the coefficient of restitution at an incident velocity of 45.0 m/s is set to 1.0) is larger than −5.23×10−3.
In another preferred embodiment of the inventive golf ball, component (II) does not include a plasticizer.
In yet another preferred embodiment, component (II) has a melt flow rate (MFR), as measured at 230° C. and under a load of 2.16 kgf (ISO 1133), which is 18 g/10 min or less.
In still another preferred embodiment, component (II) has a rebound resilience of 22% or less.
In a further embodiment, component (II) has a Shore D hardness of from 22 to 40.
Compared with conventional golf balls having a urethane cover, the golf ball of the invention exhibits a superior controllability on approach shots, in addition to which it has a good feel at impact on approach shots and also is able to maintain a good scuff resistance.
The FIGURE is a graph showing the relationship between the incident velocity and the coefficient of resilience (COR) in golf balls according to the invention and conventional golf balls.
The objects, features and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the appended diagram.
It is critical for the golf ball of the invention to have a CS1 value calculated according to formula (1) below which is larger than −4.08×10−3
(wherein CV50 is the coefficient of restitution at an incident velocity of 50.0 m/s and CV12 is the coefficient of restitution at an incident velocity of 12.0 m/s).
As shown in the FIGURE, at a fast incident velocity, the golf ball of the invention has a COR which does not differ much from that of conventional golf balls, but at slower incident velocities, the COR becomes lower and the slope of the straight-line graph becomes smaller. CS1=(CV50−CV12)/38 signifies the slope of this straight-line graph. That is, when the value of CS1 is larger than −4.08×10−3, the COR decreases in the low initial velocity range, but does not decrease in the high initial velocity range, which is effective for ball controllability on approach shots. In above formula (1), using CV12 (incident velocity, 12.0 m/s) corresponds to striking conditions on a 15-yard approach shot at a head speed (HS) of about 11 to 13 m/s, and using CV50 (incident velocity, 50.0 m/s) corresponds to striking conditions with a driver (W #1) by a topflight professional golfer or a skilled amateur.
In addition, the golf ball of the invention preferably has a CS2 value calculated according to the following formula (2)
(wherein CV12/45 is the coefficient of restitution at an incident velocity of 12.0 m/s when the coefficient of restitution at an incident velocity of 45.0 m/s is set to 1.0) which is larger than −5.23×10−3.
In formula (2), the reason for using CV12 (incident velocity, 12.0 m/s) is that this corresponds to the striking conditions on a 15-yard approach shot at a head speed (HS) of about 11 to 13 m/s, and the reason for using CV45 (incident velocity, 45.0 m/s) as the reference is that this corresponds to the striking conditions with a driver (W #1) by an ordinary male amateur golfer.
The golf ball of the invention has a core of at least one layer and a cover of at least one layer—that is, a single-layer or multilayer cover—that encases the core.
The core may be formed using a known rubber material as the base material. A known base rubber such as a natural rubber or a synthetic rubber may be used as the base rubber. More specifically, it is recommended that polybutadiene, especially cis-1,4-polybutadiene having a cis structure content of at least 40%, be chiefly used. If desired, natural rubber, polyisoprene rubber, styrene-butadiene rubber or the like may be used together with the foregoing polybutadiene in the base rubber.
The polybutadiene may be synthesized with a metal catalyst, such as a neodymium or other rare-earth catalyst, a cobalt catalyst or a nickel catalyst.
Co-crosslinking agents such as unsaturated carboxylic acids and metal salts thereof, inorganic fillers such as zinc oxide, barium sulfate and calcium carbonate, and organic peroxides such as dicumyl peroxide and 1,1-bis(t-butylperoxy)cyclohexane may be included in the base rubber. If necessary, commercial antioxidants and the like may be suitably added.
The core may be produced by vulcanizing/curing the rubber composition containing the above ingredients. For example, production may be carried out by kneading the composition using a mixer such as a Banbury mixer or a roll mill, compression molding or injection molding the kneaded composition using a core mold, and curing the molded body by suitably heating it at a temperature sufficient for the organic peroxide and the co-crosslinking agent to act, i.e., from 100° C. to 200° C., preferably from 140 to 180° C., for a period of between 10 and 40 minutes.
In the golf ball of the invention, the core is encased by a single-layer or multilayer cover. Such a golf ball may take the form of, for example, a golf ball having a single-layer cover over a core, or a golf ball having a core, an intermediate layer encasing the core, and an outermost layer encasing the intermediate layer.
In this invention, at least one layer of the cover is formed of a resin composition containing components (I) and (II) below:
The polyurethane or polyurea is a substance which can serve as the chief material, or base resin, of the above cover material (resin composition). The polyurethane (I-a) or polyurea (I-b) used as this component is described in detail below.
The polyurethane has a structure which includes soft segments composed of a polymeric polyol (polymeric glycol) that is a long-chain polyol and hard segments composed of a chain extender and a polyisocyanate. Here, the polymeric polyol serving as a starting material may be any that has hitherto been used in the art relating to polyurethane materials, and is not particularly limited. It is exemplified by polyester polyols, polyether polyols, polycarbonate polyols, polyester polycarbonate polyols, polyolefin polyols, conjugated diene polymer-based polyols, castor oil-based polyols, silicone-based polyols and vinyl polymer-based polyols. Specific examples of polyester polyols that may be used include adipate-type polyols such as polyethylene adipate glycol, polypropylene adipate glycol, polybutadiene adipate glycol and polyhexamethylene adipate glycol; and lactone-type polyols such as polycaprolactone polyol. Examples of polyether polyols include poly(ethylene glycol), poly(propylene glycol), poly(tetramethylene glycol) and poly(methyltetramethylene glycol). These polyols may be used singly, or two or more may be used in combination.
It is preferable to use a polyether polyol as the polymeric polyol.
The long-chain polyol has a number-average molecular weight that is preferably in the range of 1,000 to 5,000. By using a long-chain polyol having a number-average molecular weight in this range, golf balls that are made with polyurethane compositions and have excellent properties, including a good rebound and good productivity, can be reliably obtained. The number-average molecular weight of the long-chain polyol is more preferably in the range of 1,500 to 4,000, and even more preferably in the range of 1,700 to 3,500.
Here and below, “number-average molecular weight” refers to the number-average molecular weight calculated based on the hydroxyl value measured in accordance with JIS-K1557.
The chain extender is not particularly limited; any chain extender that has hitherto been employed in the art relating to polyurethanes may be suitably used. In this invention, low-molecular-weight compounds with a molecular weight of 2,000 or less which have on the molecule two or more active hydrogen atoms capable of reacting with isocyanate groups may be used. Of these, preferred use can be made of aliphatic diols having from 2 to 12 carbon atoms. Specific examples include 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol and 2,2-dimethyl-1,3-propanediol. The use of 1,4-butylene glycol is especially preferred.
Any polyisocyanate hitherto employed in the art relating to polyurethanes may be suitably used without particular limitation as the polyisocyanate. For example, use can be made of one or more selected from the group consisting of 4,4′-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, 1,5-naphthylene diisocyanate, tetramethylxylene diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylene diisocyanate, 1,4-bis(isocyanatomethyl)cyclohexane and dimer acid diisocyanate. However, depending on the type of isocyanate, crosslinking reactions during injection molding may be difficult to control.
The ratio of active hydrogen atoms to isocyanate groups in the polyurethane-forming reaction may be suitably adjusted within a preferred range. Specifically, in preparing a polyurethane by reacting the above long-chain polyol, polyisocyanate and chain extender, it is preferable to use the respective components in proportions such that the amount of isocyanate groups included in the polyisocyanate per mole of active hydrogen atoms on the long-chain polyol and the chain extender is from 0.95 to 1.05 moles.
The method of preparing the polyurethane is not particularly limited. Preparation using the long-chain polyol, chain extender and polyisocyanate may be carried out by either a prepolymer process or a one-shot process via a known urethane-forming reaction. Of these, melt polymerization in the substantial absence of solvent is preferred. Production by continuous melt polymerization using a multiple screw extruder is especially preferred.
It is preferable to use a thermoplastic polyurethane material as the polyurethane, with an ether-based thermoplastic polyurethane material being especially preferred. The thermoplastic polyurethane material may be a commercial product, illustrative examples of which include those available under the registered trademark PANDEX from DIC Covestro Polymer, Ltd. and those available under the trade name RESAMINE from Dainichiseika Color & Chemicals Mfg. Co., Ltd.
The polyurea is a resin composition composed primarily of urea linkages formed by reacting (i) an isocyanate with (ii) an amine-terminated compound. This resin composition is described in detail below.
The isocyanate is not particularly limited, but is preferably one that has hitherto been used in the prior art relating to polyurethanes. Use can be made of isocyanates similar to those mentioned above in connection with the polyurethane material.
The amine-terminated compound is a compound having an amino group at the end of the molecular chain. The long-chain polyamines and/or amine curing agents indicated below may be used in this invention.
A long-chain polyamine is an amine compound which has on the molecule two or more amino groups capable of reacting with isocyanate groups and which has a number-average molecular weight of from 1,000 to 5,000. In this invention, the number-average molecular weight is more preferably from 1,500 to 4,000, and even more preferably from 1,900 to 3,000. Examples of such long-chain polyamines include, but are not limited to, amine-terminated hydrocarbons, amine-terminated polyethers, amine-terminated polyesters, amine-terminated polycarbonates, amine-terminated polycaprolactones, and mixtures thereof. These long-chain polyamines may be used singly, or two or more may be used in combination.
The amine curing agent is an amine compound which has on the molecule two or more amino groups capable of reacting with isocyanate groups and which has a number-average molecular weight of less than 1,000. In this invention, the number-average molecular weight is more preferably less than 800, and even more preferably less than 600. Specific examples of such amine curing agents include, but are not limited to, ethylenediamine, hexamethylenediamine, 1-methyl-2,6-cyclohexyldiamine, tetrahydroxypropylene ethylenediamine, 2,2,4- and 2,4,4-trimethyl-1,6-hexanediamine, 4,4′-bis(sec-butylamino)dicyclohexylmethane, 1,4-bis(sec-butylamino)cyclohexane, 1,2-bis(sec-butylamino)cyclohexane, derivatives of 4,4′-bis(sec-butylamino)dicyclohexylmethane, 4,4′-dicyclohexylmethanediamine, 1,4-cyclohexane bis(methylamine), 1,3-cyclohexane bis(methylamine), diethylene glycol di(aminopropyl) ether, 2-methylpentamethylenediamine, diaminocyclohexane, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, propylenediamine, 1,3-diaminopropane, dimethylaminopropylamine, diethylaminopropylamine, dipropylenetriamine, imidobis(propylamine), monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, isophoronediamine, 4,4′-methylenebis(2-chloroaniline), 3,5-dimethylthio-2,4-toluenediamine, 3,5-dimethylthio-2,6-toluenediamine, 3,5-diethylthio-2,4-toluenediamine, 3,5-diethylthio-2,6-toluenediamine, 4,4′-bis(sec-butylamino)diphenylmethane and derivatives thereof, 1,4-bis(sec-butylamino)benzene, 1,2-bis(sec-butylamino)benzene, N,N′-dialkylaminodiphenylmethane, N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine, trimethylene glycol di-p-aminobenzoate, polytetramethylene oxide di-p-aminobenzoate, 4,4′-methylenebis(3-chloro-2,6-diethyleneaniline), 4,4′-methylenebis(2,6-diethylaniline), m-phenylenediamine, p-phenylenediamine and mixtures thereof. These amine curing agents may be used singly or two or more may be used in combination.
(iii) Polyol
Although not an essential ingredient, in addition to above components (i) and (ii), a polyol may also be included in the polyurea. The polyol is not particularly limited, but is preferably one that has hitherto been used in the art relating to polyurethanes. Specific examples include the long-chain polyols and/or polyol curing agents indicated below.
The long-chain polyol may be any that has hitherto been used in the art relating to polyurethanes. Examples include, but are not limited to, polyester polyols, polyether polyols, polycarbonate polyols, polyester polycarbonate polyols, polyolefin-based polyols, conjugated diene polymer-based polyols, castor oil-based polyols, silicone-based polyols and vinyl polymer-based polyols. These long-chain polyols may be used singly or two or more may be used in combination.
The long-chain polyol has a number-average molecular weight of preferably from 1,000 to 5,000, and more preferably from 1,700 to 3,500. In this average molecular weight range, an even better rebound and productivity are obtained.
The polyol curing agent is preferably one that has hitherto been used in the art relating to polyurethanes, but is not particularly limited. In this invention, use may be made of a low-molecular-weight compound having on the molecule two or more active hydrogen atoms capable of reacting with isocyanate groups and having a molecular weight of less than 1,000. Of these, the use of aliphatic diols having from 2 to 12 carbon atoms is preferred. Specific examples include 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol and 2,2-dimethyl-1,3-propanediol. The use of 1,4-butylene glycol is especially preferred. The polyol curing agent has a number-average molecular weight that is preferably less than 800, and more preferably less than 600.
A known method may be used to produce the polyurea. A prepolymer process, a one-shot process or some other known method may be suitably selected for this purpose.
Component (I) has a material hardness on the Shore D hardness scale which, from the standpoint of the spin properties and scuff resistance that can be obtained in the golf ball, is preferably 52 or less, more preferably 50 or less, and even more preferably 48 or less. From the standpoint of the moldability, the lower limit in the material hardness on the Shore D scale is preferably 38 or more, and more preferably 40 or more.
Component (I) has a rebound resilience which, in terms of the overall ball performance, such as the initial velocity performance and spin performance when struck, is preferably 55% or more, more preferably 57% or more, and even more preferably 59% or more. The rebound resilience is measured based on JIS-K 6255:2013.
Component (I) serves as the base resin of the resin composition. To fully confer the scuff resistance of a urethane resin, it accounts for at least 50 wt %, preferably at least 60 wt %, more preferably at least 70 wt %, even more preferably at least 80 wt %, and most preferably at least 90 wt %, of the resin composition.
In this invention, by blending component (II) described in detail below with above component (I), a golf ball of excellent controllability on approach shots and scuff resistance can be obtained.
[(II) Core-Shell Polymer in which Core is Acrylic Crosslinked Rubber Particle and Shell Consists of Acrylic Polymer]
Next, the core-shell polymer serving as component (II) is described.
Core-shell polymers generally have a structure consisting of an inner core and an outer shell. By having the core and the shell made of different materials, the compatibility with a matrix resin can be improved and the physical properties otherwise enhanced depending on the respective glass transition points (Tg) and viscoelasticities.
The core refers to a center portion which consists of a crosslinked acrylic rubber particle. Specific examples include crosslinked rubber particles obtained by polymerizing a monomer mixture composed of 30 to 99.9 wt % of at least one type of alkyl acrylate having an alkyl group of 1 to 12 carbon atoms, 0 to 70 wt % of at least one type of alkyl methacrylate having an alkyl group of 1 to 8 carbon atoms, 0 to 30 wt % of an unsaturated monomer which is copolymerizable with these, and 0.1 to 10 wt % of a polyfunctional crosslinkable monomer and/or a polyfunctional graft monomer.
The shell is an outer polymer layer obtained by polymerizing a monomer mixture composed of 30 to 99 wt % of at least one type of alkyl acrylate having an alkyl group of 1 to 12 carbon atoms, 1 to 70 wt % of at least one type of alkyl methacrylate having an alkyl group of 1 to 8 carbon atoms and 0 to 30 wt % of an unsaturated monomer which is copolymerizable with these.
Specific examples of alkyl acrylates which can be used in the core-shell polymer include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, cyclohexyl acrylate and benzyl acrylate. One of these may be used alone or two or more may be used together. Ethyl acrylate, butyl acrylate and 2-ethylhexyl acrylate are especially preferred. Specific examples of alkyl methacrylates include methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate and benzyl methacrylate. One of these may be used alone or two or more may be used together. Methyl methacrylate is especially preferred. Examples of unsaturated monomers that are copolymerizable with these include butadiene, isoprene, styrene, α-methylstyrene, vinyltoluene, acrylonitrile, methacrylonitrile, N-cyclohexylmaleimide, N-ethylmaleimide, N-t-butylmaleimide, N-phenylmaleimide and N-o-chlorophenylmaleimide. Examples of polyfunctional crosslinkable monomers include ethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate and divinylbenzene. Examples of polyfunctional graft monomers include allyl methacrylate, allyl acrylate, allyl malate, allyl fumarate, diallyl fumarate and triallyl cyanurate. The respective above monomers may each be used singly or two or more may be used together.
The core-shell polymer can be produced by a known emulsion polymerization process. For example, the monomer for obtaining the polymer which makes up the core can be emulsion polymerized to obtain seed particles, and the monomer for obtaining the polymer which makes up the shell can be seed emulsion polymerized in the presence of these seed particles. A known emulsifying agent such as an anionic surfactant, a cationic surfactant or a nonionic surfactant may be used as the emulsifying agent in emulsion polymerization. An anionic surfactant is especially preferred. The polymerization initiator used in emulsion polymerization is not particularly limited; for example, a persulfate-type or redox-type initiator may be used. In addition, where necessary, a chain transfer agent such as an alkyl mercaptan may be used.
Primary particles of the core-shell polymer have a volume mean particle which, although not particularly limited, is from 0.05 to 0.5 μm.
The above acrylic-based core-shell type polymer and the resin composition containing this polymer generally have a good moldability and are rendered into an injection-molding material or directly extruded as, for example, sheet, film, tubing or the like with an extruder. Injection-molded articles and shapes such as sheet, film or tubing obtained from the resin composition have a good flexibility and flexural durability at normal temperatures, good transparency and excellent weather resistance.
A commercial product may be used as the core-shell polymer serving as component (II). Examples of such commercial products include the Parapet™ Series from Kuraray Co., Ltd.
Component (II) has a material hardness on the Shore D hardness scale which, in order to increase the spin rate of the golf ball on approach shots, is 40 or less, preferably 35 or less, more preferably 30 or less, and even more preferably 22 or less. The lower limit is preferably at least 5.
Component (II) has a rebound resilience which, from the standpoint of maintaining the spin rate of the ball on approach shots, keeping the ball rebound on approach shots low and thus achieving a good controllability, is preferably not more than 40%, more preferably not more than 38%, even more preferably not more than 36%, and most preferably not more than 30%. By thus keeping the rebound resilience low, a small amount of addition will not have an adverse effect on the golf ball properties, enabling a decrease in the ball initial velocity on approach shots to be achieved. To minimize influences leading to a decrease in rebound and a reduction in distance on shots with a driver, the lower limit of the rebound resilience is preferably at least 5%, more preferably at least 8%, even more preferably at least 10%, and most preferably at least 15%. This rebound resilience is measured in accordance with JIS-K 6255:2013.
The content of component (II) per 100 parts by weight of component (I) is less than 15 parts by weight, and is preferably 10 parts by weight or less. The lower limit in this content is preferably at least 1 part by weight, and more preferably at least 2 parts by weight. When the content of component (II) is too high, the scuff resistance and moldability may worsen. On the other hand, when the content of component (II) is too low, a good controllability and a good feel on approach shots may not be obtained.
Component (II) has a melt flow rate (MFR) which is preferably 20 g/10 min or less, and more preferably 18 g/10 min or less. The lower limit is at least 1.0 g/10 min. Because the MFR is low (meaning the flowability is poor) in this way, the dispersed state of component (II) within the matrix can be well maintained to some extent, making it easier for the golf ball cover to manifest a low rebound performance. This MFR value is measured in accordance with ISO 1133-1:2011 at a test temperature of 230° C. and a test load of 21.18 N (2.16 kgf).
It is preferable for component (II) to not include any plasticizer. When a plasticizer is included in the cover-forming resin composition, the plasticizer vaporizes due to shearing heat during molding. As a result, defects such as air bubbles arise during molding, in addition to which the plasticizer has an adverse influence on the hardness and rebound resilience of the molded cover, and also has an adverse influence on the spin performance of the ball on approach shots.
In addition to the above resin ingredients, other resin materials may be included in the resin composition containing components (I) and (II). The purposes for doing so are, for example, to further improve the flowability of the golf ball resin composition and to enhance such ball properties as the rebound and durability.
Specific examples of other resin materials that may be used include polyester elastomers, polyamide elastomers, ionomer resins, ethylene-ethylene/butylene-ethylene block copolymers and modified forms thereof, polyacetals, polyethylenes, nylon resins, methacrylic resins, polyvinyl chlorides, polycarbonates, polyphenylene ethers, polyarylates, polysulfones, polyethersulfones, polyetherimides and polyamideimides. These may be used singly or two or more may be used together.
In addition, an active isocyanate compound may be included in the above resin composition. This active isocyanate compound reacts with the polyurethane or polyurea serving as the chief ingredient, enabling the scuff resistance of the overall resin composition to be further enhanced. Moreover, the isocyanate has a plasticizing effect which increases the flowability of the resin composition, enabling the moldability to be improved.
Any isocyanate compound employed in ordinary polyurethanes may be used without particular limitation as the above isocyanate compound. Aromatic isocyanate compounds that may be used include, for example, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate and mixtures of both, 4,4-diphenylmethane diisocyanate, m-phenylene diisocyanate and 4,4′-biphenyl diisocyanate. Use can also be made of the hydrogenated forms of these aromatic isocyanate compounds, such as dicyclohexylmethane diisocyanate. Other isocyanate compounds that may be used include aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate (HDI) and octamethylene diisocyanate; and alicyclic diisocyanates such as xylene diisocyanate. Further examples of isocyanate compounds that may be used include blocked isocyanate compounds obtained by reacting the isocyanate groups on a compound having two or more isocyanate groups on the ends with a compound having active hydrogens, and uretdiones obtained by the dimerization of isocyanate.
The amount of the above isocyanate compounds included per 100 parts by weight of the polyurethane or polyurea resin serving as component (I) is preferably at least 0.1 part by weight, and more preferably at least 0.5 part by weight. The upper limit is preferably not more than 30 parts by weight, and more preferably not more than 20 parts by weight. When too little is included, a sufficient crosslinking reaction may not be obtained and improvements in the physical properties may not be observable. On the other hand, when too much is included, discoloration over time due to heat and ultraviolet light may increase, or problems such as a loss of thermoplasticity or a decline in resilience may arise.
In addition, depending on the intended use, optional additives may be suitably included in the above resin composition. For example, in cases where the golf ball material of the invention is to be used as a cover material, various additives such as fillers (inorganic fillers), organic staple fibers, reinforcing agents, crosslinking agents, pigments, dispersants, antioxidants, ultraviolet absorbers and light stabilizers may be added to the above ingredients. When including such additives, the amount thereof per 100 parts by weight of the base resin is preferably at least 0.1 part by weight, and more preferably at least 0.5 part by weight; the upper limit is preferably not more than 10 parts by weight, and more preferably not more than 4 parts by weight.
In order to achieve a suitable rebound and a suitable spin performance on approach shots, the above resin composition has a rebound resilience, as measured according to JIS-K 6255:2013, which is preferably at least 48%, more preferably at least 50%, and even more preferably at least 52%. The upper limit is preferably not more than 72%, more preferably not more than 70%, and even more preferably not more than 68%.
The resin composition has a material hardness on the Shore D hardness scale which, from the standpoint of the scuff resistance and to impart a suitable spin rate on approach shots, is preferably not more than 50, more preferably not more than 48, and even more preferably not more than 45. In terms of the moldability, the lower limit in the material hardness on the Shore D hardness scale is preferably at least 30, more preferably at least 35, and even more preferably at least 37.
The above resin composition may be prepared by mixing together the ingredients using any of various types of mixers, such as a kneading-type single-screw or twin-screw extruder, a Banbury mixer, a kneader or a Labo Plastomill. Alternatively, the ingredients may be mixed together by dry blending when the resin composition is to be injection-molded. In addition, when an active isocyanate compound is used, it may be incorporated at the time of resin mixture using various types of mixers, or a resin masterbatch already containing the active isocyanate compound and other ingredients may be separately prepared and the various components mixed together by dry blending when the resin composition is to be injection molded.
The method of molding the cover from the above resin composition may involve, for example, feeding the resin composition into an injection molding machine and molding the cover by injecting the molten resin composition over the core. In this case, the molding temperature differs according to the type of polyurethane or polyurea (I) serving as the chief ingredient, but is typically in the range of 150° C. to 270° C.
The cover has a thickness which is preferably 0.4 mm or more, more preferably 0.5 mm or more, and even more preferably 0.6 mm or more. The upper limit is preferably not more than 3.0 mm, and more preferably not more than 2.0 mm.
In cases where at least one intermediate layer is interposed between the above core and the above cover, various types of thermoplastic resins used in golf ball cover materials, especially ionomer resins, may be used as the intermediate layer material. Commercial products may be used as the ionomer resins. In such a case, the thickness of the intermediate layer may be set within the same range as the above cover thickness.
In the golf ball of the invention, numerous dimples are provided on the surface of the outermost layer for reasons having to do with the aerodynamic performance. The number of dimples formed on the surface of the outermost layer is not particularly limited. However, to enhance the aerodynamic performance and increase the distance traveled by the ball, this number is preferably at least 250, more preferably at least 270, even more preferably at least 290, and most preferably at least 300. The upper limit is preferably not more than 400, more preferably not more than 380, and even more preferably not more than 360.
A coating layer may be formed on the surface of the cover in the golf ball of the invention. A two-part curable urethane coating may be suitably used as the coating that forms this coating layer. Specifically, in this case, the two-part curable urethane coating is one that includes a base resin composed primarily of a polyol resin and a curing agent composed primarily of a polyisocyanate.
A known method may be used without particular limitation as the method for applying this coating onto the cover surface and forming a coating layer. Use can be made of a desired method such as air gun painting or electrostatic painting.
The thickness of the coating layer, although not particularly limited, is typically from 8 to 22 μm, and preferably from 10 to 20 μm.
The golf ball of the invention can be made to conform to the Rules of Golf for play. The inventive ball may be formed to a diameter which is such that the ball does not pass through a ring having an inner diameter of 42.672 mm and is not more than 42.80 mm, and to a weight which is preferably between 45.0 and 45.93 g.
The following Examples and Comparative Examples are provided to illustrate the invention, and are not intended to limit the scope thereof.
A core-forming rubber composition formulated as shown in Table 1 and common to all of the Examples was prepared and then molded/vulcanized to produce a 38.6 mm diameter core.
Details on the above core material are given below.
An intermediate layer-forming resin material was injection-molded over the 38.6 mm diameter core, thereby producing an intermediate layer-encased sphere having a 1.25 mm thick intermediate layer. This intermediate layer-forming resin material, which was a resin blend common to all of the examples, consisted of 50 parts by weight of the sodium neutralization product of an ethylene-unsaturated carboxylic acid copolymer having an acid content of 18 wt % and 50 parts by weight of the zinc neutralization product of an ethylene-unsaturated carboxylic acid copolymer having an acid content of 15 wt %, for a total of 100 parts by weight.
The resin compositions for the covers in the respective examples were prepared by using as the base resin (component (I)) an aromatic ether-type thermoplastic polyurethane (TPU) having a Shore D hardness of 40 available under the trade name Pandex from DIC Covestro Polymer, Ltd. and suitably compounding therewith component (II) or a corresponding resin ingredient. Details on component (II) are shown below in Table 2.
Details on the resin ingredients in Table 2 are provided below.
Each of the above resins is formed into 2 mm thick sheets and left to stand for two weeks at a temperature of 23±2° C., following which three sheets are stacked together and the material hardness of the resin is measured using a Shore D durometer in accordance with ASTM D2240. The P2 Automatic Rubber Hardness Tester (Kobunshi Keiki Co., Ltd.) equipped with a Shore D durometer is used for measuring the hardness.
The rebound resilience is measured in accordance with JIS-K 6255:2013.
The melt flow rate (g/10 min) is measured in accordance with ISO 1133 at 230° C. and under a load of 2.16 kgf.
Next, the above cover-forming resin composition was injection-molded over the intermediate layer-encased sphere, thereby producing a 42.7 mm diameter three-piece golf ball having a 0.8 mm thick outermost layer. Dimples common to all of the examples were formed at this time on the cover surface in each example according to the invention and each comparative example.
The coefficient of restitution, spin rate on approach shots, controllability on approach shots, feel at impact and scuff resistance of the golf balls produced in each example are evaluated by the following methods. The results are shown in Table 3.
The COR value of the golf ball is measured using the ADC Ball COR Durability Tester manufactured by Automated Design Corporation (U.S.). This tester fires a golf ball pneumatically at an initial velocity of from 12 to 50 m/s. A velocity measurement sensor is located at a distance of about 0.8 meter. When the golf ball strikes a metal plate located at a distance of about 1.2 meters, the golf ball rebounds in such a way as to pass by the velocity measuring sensor. The COR value is the value obtained by dividing the rebound velocity by the initial velocity.
A sand wedge (SW) is mounted onto a golf swing robot and the initial velocity and backspin rate of the ball immediately after being struck at a head speed (HS) of 20 m/s are measured with a launch monitor. The difference between the spin rates in the respective examples of the invention and in Comparative Example 1 is determined based on the backspin rate of the ball on approach shots in Comparative Example 1.
Sensory evaluations of the ball controllability on approach shots are carried out by the following method. The club used is a sand wedge (SW) similar to that mentioned above: the TourStage TW-03 (loft angle, 57°) manufactured by Bridgestone Sports Co., Ltd. The controllability is evaluated based the following criteria when actually hit by golfers.
In addition to the spin rate of the ball, the length of the contact time between the ball and the clubface arising from the low resilience also affects the determination as to whether the controllability is good. When the contact time is long, the controllability is good; when it is short, the controllability worsens. What is being determined here is the controllability, which includes as factors the spin rate and the length of the contact time.
A sensory evaluation on approach shots relating to the feel of the ball at impact is carried out as described below. The club used is the same sand wedge (SW) as that mentioned above.
The golf balls are held isothermally at 23° C. and five balls of each type are hit at a head speed of 33 m/s using as the club a pitching wedge (PW) mounted on a golf swing robot. The damage to the ball from the impact is visually rated according to the following criteria.
As demonstrated by the results in Table 3, the golf balls of Comparative Examples 1 to 4 are inferior in the following respects to the golf balls according to the present invention obtained in Examples 1 to 4.
In Comparative Example 1, component (II) is not included in the resin composition and the CS1 value is small. As a result, the controllability on approach shots is inferior.
In Comparative Example 2, although a hydrogenated aromatic vinyl elastomer is included in the resin composition, compared with the examples according to the invention, the spin rate on approach shots is small and the feel at impact is somewhat unpleasant.
In Comparative Example 3, although a hydrogenated aromatic vinyl elastomer is included in the resin composition, compared with the examples according to the invention, the spin rate on approach shots is small and the feel at impact is somewhat unpleasant.
In Comparative Example 4, a hydrogenated aromatic vinyl elastomer is included in the resin composition, but the amount thereof is high. As a result, the spin rate on approach shots is small, the feel at impact is poor and the scuff resistance falls short of what is desired.
Japanese Patent Application No. 2023-166822 is incorporated herein by reference. Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-166822 | Sep 2023 | JP | national |
