Patent Application
20250195957
This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2023-213979 filed in Japan on Dec. 19, 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. That is, up until now, many golf balls have 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, polyurethane resins are often used in place of ionomer resin materials.
When a polyurethane having a relatively low hardness is used, many problems are encountered in the overall production process, including the steps of molding a low-hardness polyurethane resin as a cover encasing the ball core, handling the molded cover, and trimming the surface of the cover. Such problems include the difficulty of molding itself, external damage to the cover during and after molding, and the difficulty of trimming work. Also, it is known that when a filler is added to the resin material, the flowability of the resin decreases; when a fibrous filler in particular is used, the decline in flowability is large. As a result, the rate of discharge of the molded resin material also decreases and so there is a need to increase the discharge by elevating the speed of extruder rotation or the injection speed.
JP-A 2007-159996 discloses art that blends a thermoplastic polyurethane and titanium oxide to prepare a cover material and then uses this cover material to mold a cover. In this art, the durability, scuff resistance and appearance of the resulting cover are improved by setting the melt viscosity ratio between the thermoplastic polyurethane used as the raw material and the cover material formulated with this raw material within a fixed range. JP-A 2007-159996 also mentions that, by using titanium oxide having a moisture content of 0.60 wt % or less, the melt viscosity ratio falls within a fixed range. This art explains the influence on the viscosity of the moisture content of titanium oxide and indicates that using titanium oxide having a low moisture content is preferred. Also, a lower titanium oxide content results in a lower viscosity, and increasing the titanium oxide content worsens the flowability. In other words, it appears that, generally, when a filler is added to the resin material, the flowability decreases. There is no finding in JP-A 2007-159996 to the effect that adding titanium oxide to the thermoplastic urethane used in the outer layer of a golf ball enhances the flowability and trimmability.
It is therefore an object of the present invention to provide a golf ball which, even when a low-hardness polyurethane resin having a high level of production difficulty is used as the cover resin material, has a high productivity due to improvements in the flowability of the cover resin material when molded and in the trimmability after molding.
As a result of intensive investigations, I have discovered that in a golf ball having a core and a cover, by using a resin composition containing a thermoplastic polyurethane and an inorganic filler such as titanium oxide as the cover material and by preparing the resin composition such that, setting the wear volume of this resin composition after 1,000 rotations in a Taber abrasion test according to JIS-K 7311 to more than 0.003 cm3 and, letting the Shore D hardness of the resin composition be H and the 210° C. and 220° C. melt viscosities (Pa·s) at a shear rate of 6,080 sec−1 when measured with a capillary rheometer in accordance with ISO 11443: 1995 be respectively η1 and η2, the composition satisfies formula (1) below
Accordingly, the present 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 that includes components (I) and (II) below:
In a preferred embodiment of the golf ball of the invention, the resin composition has a Shore D hardness of less than 50.
In another preferred embodiment of the inventive golf ball, component (II) is titanium oxide. The titanium oxide preferably has an average particle size of at least 0.21 μm.
In yet another preferred embodiment, melt viscosity η1 is 200 Pa·s or less.
In still another preferred embodiment, melt viscosity η2 is 150 Pa·s or less.
During molding of the urethane cover in the inventive golf ball, the cover resin material has a good flowability and excellent moldability. Also, in trimming work on the cover surface after molding, the material has an increased trimmability, enhancing the golf ball productivity.
The objects, features and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the appended diagrams.
The golf ball of the invention has a core of at least one layer and a cover of at least one layer, i.e., 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 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 can 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, a resin composition that includes components (I) and (II) below:
The polyurethane is a substance which can serve as the chief material, or base resin, of the above cover material (resin composition). 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-K 1557.
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 as Pandex® from DIC Covestro Polymer, Ltd. and those available under the trade name RESAMINE from Dainichiseika Color & Chemicals Mfg. Co., Ltd.
Component (I) has a material hardness expressed in terms of the Shore D hardness which, from the standpoint of the spin properties and scuff resistance obtained as a golf ball, is preferably 52 or less, more preferably 50 or less, and even more preferably 48 or less. The lower limit value in the Shore D hardness, from the standpoint of moldability, is preferably 38 or more, and more preferably 40 or more.
Component (I) has a rebound resilience which, from the standpoint of the overall performance of the golf ball, 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) above is the base resin of the resin composition. In order to fully impart the scuff resistance of the 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 below into above component (I), the flowability of the cover resin material during molding and the trimmability are improved, enabling golf balls having a high productivity to be obtained.
The inorganic filler is blended in a given amount with the base resin (component (I)) so as to increase the flowability of the thermoplastic polyurethane resin serving as the base resin and improve the trimmability of the resin composition. Examples of the inorganic filler include titanium oxide, zinc oxide, alumina, magnesium oxide, barium sulfate, aluminum nitride, boron nitride, barium titanate, talc, kaolin, calcium carbonate, silica, glass beads and powdered glass. From the standpoint of lowering the melt viscosity during injection molding and obtaining a high trimmability for the resin molding, it is preferable in particular to use titanium oxide. Titanium oxide can be produced by the sulfate process or the chloride process; rutile or anatase may be used. In addition, composite particles composed of titanium oxide that has been surface treated with aluminum oxide, a silane coupling agent (polysiloxane) or the like may be used.
The inorganic filler has, in the particle size distribution measured by laser diffractometry, a mean particle size D50 at which the cumulative weight from the fine particle side is 50 wt % of preferably at least 0.10 μm, more preferably at least 0.15 μm, and even more preferably at least 0.20 μm. Although there is no particular upper limit, this value is preferably not more than 1.0 μm.
The component (II) content is at least 5 parts by weight, preferably at least 6 parts by weight, and more preferably at least 7 parts by weight, per 100 parts by weight of component (I). The upper limit is preferably not more than 30 parts by weight, and more preferably not more than 25 parts by weight.
In addition to components (I) and (II), the resin composition may also include other resin materials. The purposes for doing so include further enhancing the flowability of the golf ball resin composition and increasing such golf ball properties as the rebound and durability to cracking.
Examples of other resin materials include polyamide elastomers, ionomer resins, ethylene-ethylene/butylene-ethylene block copolymers and modified forms thereof, polyacetals, polyethylene, nylon resins, styrene 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.
The resin composition may additionally include an isocyanate compound having activity. This active isocyanate compound reacts with the polyurethane serving as the chief component and can further increase the scuff resistance of the overall resin composition. In addition, the plasticizing effect of isocyanate can enhance the flowability and thus improve the moldability.
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 terminal isocyanate groups 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 polyurethane 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, optional additives may be suitably included in the above resin composition in accordance with the intended use thereof. For example, in cases where the golf ball material of the invention is to be used as a cover material, various additives such as 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 included 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 provide the golf ball with a low rebound and increase the spin rate 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 50 or less, more preferably 48 or less, and even more preferably 45 or less. In terms of the moldability, the lower limit in the material hardness on the Shore D hardness scale is preferably at least 30, and more preferably at least 35.
One characteristic of the resin composition in this invention is that the abrasion volume after 1,000 rotations in a Taber abrasion test according to JIS-K 7311 is larger than 0.003 cm3. When the content of inorganic filler in the resin composition is increased, the abrasion wear increases, resulting in an excellent trimmability and thus enabling trimming work after molding of the cover to be carried out smoothly. Particularly in cases where a thermoplastic polyurethane having a relatively soft hardness is used as the base resin, difficulties with the trimming work that are attributable to the softness of the cover surface are ameliorated, enabling the cover surface during trimming to be uniformly and properly trimmed. The abrasion volume is preferably 0.005 cm3 or more, more preferably 0.007 cm3 or more, even more preferably 0.01 cm3 or more, and most preferably 0.02 cm3 or more.
Another characteristic of the resin composition in this invention is that, letting H be the Shore D hardness of the resin composition and η1 and η2 be respectively the 210° C. and 220° C. melt viscosities (Pa·s) at a shear rate of 6,080 sec−1 when measured with a capillary rheometer in accordance with ISO 11443: 1995, the composition satisfies formula (1) below
In other words, the value obtained by dividing the difference between the 210° C. viscosity and the 220° C. viscosity of the resin composition at a specific shear rate by the Shore D hardness of the resin raised to the third power is smaller than 7.0×104. The specific technical meaning here is that, as shown in
The melt viscosity η1 is preferably 200 Pa·s or less, more preferably 180 Pa·s or less, even more preferably 150 Pa·s or less, and most preferably 100 Pa·s or less. The melt viscosity η2 is preferably 150 Pa·s or less, more preferably 120 Pa·s or less, even more preferably 100 Pa·s or less, and most preferably 60 Pa·s or less.
The higher the inorganic filler content in the resin composition, the lower the moisture absorption by the molded resin material, making it possible to suppress changes over time due to moisture absorption by the golf ball and decreases in the ball properties. Specifically, in a wetting test which, letting the ball weight at 23° C. be the initial weight, measures the amount of increase from the initial ball weight when the ball is placed and hermetically closed within a desiccator filled at the bottom with water in such a way as not to be in direct contact with the water, left at rest for three weeks at 23° C. and then removed from the desiccator, the amount of increase in the ball weight is set to preferably 0.0085 g or less, more preferably 0.0083 g or less, and even more preferably 0.0080 g or less.
The 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 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 injection molded.
The method of molding the cover from the above resin composition may involve, for example, feeding the resin composition to 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 (I) polyurethane serving as the chief component, 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 core and the cover, various types of thermoplastic resins used in golf ball cover materials, especially ionomer resins, may be used as the intermediate layer material. A commercial product may be used as the ionomer resin. 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.
In the practice of the invention, a paint layer is formed on the surface of the golf ball cover. A two-part curable urethane coating may be suitably used to form this paint layer. The two-part curable urethane coating in this case is one which 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 to apply this coating onto the cover surface and form a paint layer. Use can be made of a desired method such as air gun painting or electrostatic painting.
The thickness of the paint 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 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.
With regard to the cover-forming resin compositions in the respective examples, using a separate injection mold, the urethane resin compositions shown in Tables 2 and 3 were injection-molded over the above-described intermediate layer-encased sphere, thereby forming a 0.8 mm thick cover (outermost layer). Dimples common to all of the examples were formed at this time on the cover surface in each Example and Comparative Example.
Details on the compounding ingredients in Table 3 are given below.
The Shore D hardness, wetting test, Taber abrasion test and viscosity measurements of the above cover-forming resin compositions are described below.
Each of the above resins was formed into 2 mm thick sheets and left to stand for two weeks at a temperature of 23±2° C. Three sheets were stacked together at the time of measurement. The material hardness of the resin was 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 was used for measuring the hardness.
In accordance with JIS-K 7311, resin sheets obtained by molding the respective above resins to a thickness of 2 mm and a diameter of at least 100 mm were tested with a Taber abrader (Taber-type Abrasion Tester, from Yasuda Seiki Seisakusho, Ltd.) and the abrasion volume (cm3) after 1,000 rotations at a rotational speed of 60 rpm under a load of 1 kg and using an H-22 abrasion wheel was measured. The graph in
The weight of the ball at 23° C. was measured as the initial weight. The amount of increase (moisture absorption) from the initial ball weight when the ball was placed and hermetically closed within a desiccator filled at the bottom with water in such a way as not to be in direct contact with the water, left at rest for three weeks at 23° C. and then removed from the desiccator was measured. The graph in
The melt viscosity was measured in accordance with ISO 11443: 1995 using the capillary rheometer available under the trade name Capilograph 1C from Toyo Seiki Seisaku-sho, Ltd. The melt viscosity (Pa·s) of the sample was measured at temperature settings of 210° C. and 220° C., at a capillary condition set to L/D=10.0/1.0 mm and at a piston speed of 500 mm/min and a shear rate of 6,080 sec−1. In these measurements, the values of (η1−η2)/H3, wherein H is the Shore D hardness of the resin and 11 and f2 are the melt viscosities (Pa·s) at respectively 210° C. and 220° C., are presented in Tables 2 and 3. The graph in
The golf balls obtained in the respective examples were evaluated by the following methods for three types of moldability (mold fillability, external damage, trimmability) and for the feel at impact. The results are presented in Tables 2 and 3.
The ability of the molten resin to fill the mold when the cover is injection molded was evaluated based on the following criteria.
The ball was examined for external damage, both during and after injection molding of the cover, and was evaluated based on the following criteria.
The trimmability of the cover in the ball surface (cover surface) trimming work carried out following injection molding of the cover was evaluated based on the following criteria.
The feel of the ball at impact was evaluated as follows using a sand wedge (SW) available from Bridgestone Sports Co., Ltd. under the product name Bridgestone TourStage TW-03 (loft angle, 57°).
Japanese Patent Application No. 2023-213979 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 |
|---|---|---|---|
| 2023-213979 | Dec 2023 | JP | national |
