Patent Application
20250186841
This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2023-207898 filed in Japan on Dec. 8, 2023, the entire contents of which are hereby incorporated by reference.
The present invention relates to a golf ball in which at least one intermediate layer is formed between a core and a cover, and more specifically, to a golf ball that may exhibit good performance in putting with a putter by optimizing a specific gravity of each layer.
For a cover layer and a mantle layer, which are constituent members of a golf ball, a technique of reducing a thickness by injection molding or compression molding and making the layers multilayered is progressing from the viewpoint of a feel at impact and low spin. With such multilayering and thinning of a gauge, non-uniformity (eccentricity) of the gauge is a problem. A position of a center of gravity of a non-uniform ball changes, and affects, for example, a rolling (straightness) of the ball at a time of putting with a putter.
As a conventionally proposed technique, there are several patent documents of golf balls in which a moment of inertia is set high. For example, the following Patent Documents 1 to 3 may be cited. These patent documents are intended to provide a golf ball in which a specific gravity adjusting material or the like is appropriately blended in an outer layer of the golf ball to set a specific gravity of the outer layer to be higher than that of an inner layer, thereby increasing the moment of inertia, increasing a spin retention rate, and allowing the ball to roll well with a putter.
However, in the proposed golf ball, there is a large difference in the specific gravity of each layer, but in a case where a deviation (eccentricity) of each layer occurs at a time of manufacturing, the deviation of the center of gravity position of the ball from a center of the ball becomes large, and as a result, the problem that the ball easily swerves and rolling becomes unstable occurs.
In addition, recently, as a cover material for golf balls for professionals and advanced players, those having a urethane resin as a chief material have increased, and among them, some cover materials of polymer blends in which a urethane resin material is used as a base resin and another resin material is mixed have been proposed. Patent Document 4 cites that an acrylic resin or a methacrylic resin is employed as a polymer blend of a urethane resin material and is used as the chief material of the cover. This technique provides a golf ball that may achieve a high initial velocity on shots with a driver and a low initial velocity on approach shots, but since an acrylic resin or a methacrylic resin is basically a hard resin material, it cannot be said that controllability on approach shots may be sufficiently satisfied. One of the factors of controllability on approach shots is an operability of the club at the time of an approach shot, and a quality of the operability of the club is affected by a length of contact time between the ball and a club face due to low rebound in addition to a spin rate of the ball. If the contact time is long, operability is improved, and if the contact time is short, operability is worsened. That is, it has been desired to improve a golf ball more excellent in controllability on approach shots than the golf ball described in Patent Document 4.
In addition, in the resin material of the cover described in Patent Document 4, since a melt viscosity of the urethane resin material increases due to mixing of the acrylic resin and a fluidity worsens, it is necessary to increase a molding temperature. For this reason, there is a possibility that defects such as burning may occur on an entire surface of the cover after molding, and there is room for improvement in terms of moldability and scuff resistance of the golf ball.
Patent Document 5 discloses a resin material for golf balls formed from a mixture containing a thermoplastic polymer and an acrylic copolymer (MMA copolymer). However, the acrylic copolymer described in Patent Document 5 is a polymer having a core-shell type special chemical structure, and if this acrylic copolymer is blended with a urethane resin material, controllability on approach shots is sufficiently excellent, and scuff resistance and moldability are also excellent. This is not disclosed by Patent Document 5, and it is hard to say that this is a technique capable of solving the above problems to be addressed by the present invention.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a golf ball in which a deviation of a center of gravity of the ball is extremely reduced, rolling (straightness) of the ball is enhanced at a time of putting with a putter, and controllability on approach shots, scuff resistance, and moldability are excellent.
As a result of intensive studies to achieve the above object, the present inventors have set a standard deviation of a specific gravity of each layer of a core, an intermediate layer, and a cover to be uniform within 0.07 for a golf ball in which at least one intermediate layer is formed between the core and the cover, the cover being formed of a resin composition that includes the following components (I) and (II):
The inventors have found that if the golf ball is designed so as to satisfy the above condition, a deviation of a center of gravity of the ball is extremely reduced, a rolling (straightness) of the ball is enhanced at a time of putting with a putter, and a controllability on approach shots, a scuff resistance, and a moldability are excellent, and thus have completed the present invention.
Accordingly, the present invention provides a golf ball including
In a preferred embodiment of the golf ball according to the invention, a compounding amount of the component (II) is not more than 20 parts by weight per 100 parts by weight of the component (I).
In another preferred embodiment of the inventive golf ball, a material hardness of the component (II) is not more than 40 on the Shore D hardness scale.
In yet another preferred embodiment, the component (II) has a rebound elasticity of not more than 40% as measured by the JIS-K 6255 standard.
In still another preferred embodiment, a melt flow rate (MFR) value of the component (II) is at least 20 g/10 min under measurement conditions of 230° C. and a load of 2.16 kgf (ISO 1133).
In a further preferred embodiment, in the block copolymer of the component (II), a hard segment is mainly composed of a methyl methacrylate unit, and a soft segment is mainly composed of an n-butyl acrylate unit or an n-butyl acrylate/2-ethylhexyl acrylate unit.
In a yet further preferred embodiment, a content of the methyl methacrylate unit in the block copolymer of the component (II) is from 20 to 50 wt %.
In a still further preferred embodiment, when the specific gravity of the core is denoted by CM, the specific gravity of the intermediate layer is denoted by MM, the specific gravity of the cover is denoted by FM, an initial velocity (m/s) of the core is denoted by CV, an initial velocity (m/s) of a sphere (intermediate layer-encased sphere) obtained by encasing the core with the intermediate layer is denoted by MV, an initial velocity (m/s) of a sphere (ball) obtained by encasing the intermediate layer-encased sphere with the cover is denoted by FV, and a deflection (mm) when the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is denoted by FC, the following condition (2) is satisfied:
In another preferred embodiment, the ball has a moment of inertia of from 82.5 to 85.0 g·cm2.
In yet another preferred embodiment, when the specific gravity of the core is denoted by CM, the specific gravity of the intermediate layer is denoted by MM, the specific gravity of the cover is denoted by FM, an initial velocity (m/s) of the core is denoted by CV, an initial velocity (m/s) of the sphere (intermediate layer-encased sphere) obtained by encasing the core with the intermediate layer is denoted by MV, an initial velocity (m/s) of the sphere (ball) obtained by encasing the intermediate layer-encased sphere with the cover is denoted by FV, and a moment of inertia of the ball is denoted by MOI, the following condition (3) is satisfied.
In still another preferred embodiment, all the layers of the core, the intermediate layer, and the cover have a specific gravity of from 1.10 to 1.13 g/cm3.
In a further preferred embodiment, a relationship between the specific gravities of the intermediate layer and the cover satisfies the following condition:
−0.03≤(specific gravity of intermediate layer−specific gravity of cover)≤0.03.
In a yet further preferred embodiment, a material of the intermediate layer contains barium sulfate as a specific gravity adjusting material.
In a still further preferred embodiment, a material hardness of the cover is from 40 to 52 on the Shore D hardness scale.
In another preferred embodiment, a deflection (mm) when the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is not more than 2.8 mm.
According to the golf ball of the present invention, the golf ball has excellent controllability on approach shots, has little lateral swing and variation in distance at the time of putting, and has both controllability on approach shots and improved putting accuracy. In addition, the golf ball of the present invention has excellent scuff resistance and moldability.
The FIGURE is a schematic view for explaining a putting test.
Hereinafter, the present invention is described in more detail.
A golf ball of the present invention includes a core, a cover, and an intermediate layer formed therebetween. Hereinafter, each of the above layers is described in detail.
The core may be formed in a single layer or a plurality of layers. As a material of the core, a known rubber material or various resin materials may be used as a substrate. If the core is formed of a rubber material, a known base rubber such as a natural rubber or a synthetic rubber may be used as the base rubber, and more specifically, it is recommended to mainly use polybutadiene, particularly cis-1,4-polybutadiene having at least 40% or more of a cis structure. In addition, in the base rubber, a natural rubber, a polyisoprene rubber, a styrene butadiene rubber, and the like may be used in combination with the above-described polybutadiene as desired. The polybutadiene may be synthesized by a Ziegler-type catalyst such as a titanium-based catalyst, a cobalt-based catalyst, a nickel-based catalyst, or a neodymium-based catalyst, or by a metal catalyst such as cobalt or nickel.
In the base rubber, a co-crosslinking agent such as an unsaturated carboxylic acid and a metal salt thereof, an inorganic filler such as zinc oxide, barium sulfate, or calcium carbonate, an organic peroxide such as dicumyl peroxide or 1,1-bis(t-butylperoxy)cyclohexane, or the like may be blended. If necessary, a commercially available antioxidant or the like may be appropriately added.
The core may be manufactured by thermally curing a rubber composition containing the above components. For example, a molded body can be manufactured by intensively mixing the rubber composition using a mixing apparatus such as a Banbury mixer or a roll mill, subsequently compression molding or injection molding the mixture using a core mold, and curing the resulting molded body by appropriately heating it at a temperature sufficient for the organic peroxide or the co-crosslinking agent to act, such as at a temperature of from 100 to 200° C., and preferably at a temperature of from 140 to 180° C., for 10 to 40 minutes.
The core has a specific gravity which, although not particularly limited, is preferably at least 1.00, more preferably at least 1.03, and even more preferably at least 1.06. The upper limit is preferably not more than 1.20, more preferably not more than 1.17, and even more preferably not more than 1.14. It is necessary to set a weight of the ball to about 45.0 to 45.6 g in order to ensure good distance performance on shots with a driver, and in such a case, if the specific gravity of the core is smaller than the above range, it is necessary to increase the specific gravities of the intermediate layer and the cover layer, and thus there is a possibility that a spin performance of the ball is impaired by adding a specific gravity adjusting material. On the other hand, if the specific gravity of the core is too large, a moment of inertia becomes too small, and rolling with a putter may worsen.
At least one intermediate layer and one cover may be formed around the core as a member encasing the core. If the intermediate layer includes two layers, the layers may be referred to in order from the inner side as an inner intermediate layer and an outer intermediate layer. The inner intermediate layer may also be referred to as a surrounding layer.
The intermediate layer is formed of a resin composition. Examples of the resin composition include a resin composition whose chief material is a resin conventionally employed as a material for golf balls. Examples of a base resin of the resin composition include an ionomer-based resin, a polyester resin, a polyurethane resin, a polyamide resin, a polyolefin resin, an olefin-based thermoplastic elastomer, and a styrene-based thermoplastic elastomer. In particular, an ionomer-based resin is preferable from the viewpoints of rebound and moldability.
In the material for the intermediate layer, various fillers may be blended as a specific gravity adjusting material. As such a filler, for example, zinc oxide, titanium oxide, barium sulfate, calcium carbonate, potassium titanate, calcium oxide, magnesium oxide, silica, ferrite, and the like may be suitably used. These may be used singly, or two or more may be used in combination.
The compounding amount of the specific gravity adjusting material (filler) is not particularly limited, although the compounding amount may be set to preferably at least 5 parts by weight, more preferably at least 10 parts by weight, and even more preferably at least 15 parts by weight per 100 parts by weight of the base resin of the intermediate layer. In addition, an upper limit of the compounding amount is not particularly limited, although the upper limit may be set to preferably not more than 40 parts by weight, more preferably not more than 30 parts by weight, and even more preferably not more than 25 parts by weight per 100 parts by weight of the base resin. If the compounding amount is too large or too small, an appropriate specific gravity cannot be obtained, and a desired effect of the present invention may not be obtained.
A thickness of the intermediate layer is preferably at least 0.6 mm, more preferably at least 0.8 mm, and even more preferably at least 1.0 mm, and the upper limit thereof is preferably not more than 2.0 mm, more preferably not more than 1.5 mm, and even more preferably not more than 1.3 mm. If the intermediate layer is too thin, the spin rate of the ball may rise on full shots, and an intended distance may not be attainable. On the other hand, if the intermediate layer is too thick, the rebound of the ball may be lowered.
The intermediate layer has a material hardness on the Shore D hardness scale which, although not particularly limited, is preferably at least 60, more preferably at least 65, and even more preferably at least 67, and the upper limit thereof is preferably not more than 75, and more preferably not more than 73. The harder the hardness, the more the distance may be increased due to low spin on full shots with an iron (I #6), but if the hardness is too hard, there is a possibility that a durability to cracking on repeated impact is reduced.
A specific gravity of the intermediate layer is preferably 1.05 or more, more preferably 1.07 or more, and even more preferably 1.09 or more, and the upper limit value thereof is preferably 1.25 or less, more preferably 1.20 or less, and even more preferably 1.15 or less. If the specific gravity of the intermediate layer is too small, the durability to cracking on repeated impact may worsen. On the other hand, if the specific gravity of the intermediate layer is too large, the ball rebound becomes low, or the spin rate of the ball on full shots rises, and the intended distance may not be attained.
A relationship between the specific gravities of the intermediate layer and the cover desirably satisfies the following condition.
−0.03≤(specific gravity of intermediate layer−specific gravity of cover)≤0.03.
The reason for this is that a difference in specific gravity between the respective layers causes a variation in rolling (forward, backward, left, and right) with a putter. Therefore, in order to suppress this variation as much as possible, the relationship is set within the above range.
The cover is formed of a resin composition. The resin composition includes the following components (I) and (II):
The polyurethane may be a chief material of the cover material (resin composition) or a base resin. Details of the polyurethane as this component are as follows.
The structure of polyurethane is composed of a soft segment composed of a polymer polyol (polymeric glycol), which is a long-chain polyol, and a hard segment composed of a chain extender and a polyisocyanate. Here, as the polymer polyol as a raw material, any polymer polyol that is conventionally used in a technique related to a polyurethane material may be used, and is not particularly limited. Examples thereof may include polyester-based polyol, polyether-based polyol, polycarbonate polyol, polyester polycarbonate polyol, polyolefin-based polyol, conjugated diene polymer-based polyol, castor oil-based polyol, silicone-based polyol, and vinyl polymer-based polyol. Specific examples of the polyester-based polyol may include adipate-based polyols such as polyethylene adipate glycol, polypropylene adipate glycol, polybutadiene adipate glycol, and polyhexamethylene adipate glycol, and lactone-based polyols such as polycaprolactone polyol. Examples of the polyether polyol include poly(ethylene glycol), poly(propylene glycol), poly(tetramethylene glycol), and poly(methyltetramethylene glycol). These may be used singly, or at least two may be used in combination.
As the polymer polyol, a polyether-based polyol is preferably used.
A numerical average molecular weight of the long-chain polyol is preferably within a range of from 1,000 to 5,000. By using a long-chain polyol having such a numerical average molecular weight, it is possible to reliably obtain a golf ball made of a polyurethane composition excellent in various properties such as productivity and the above-mentioned rebound. The numerical average molecular weight of the long-chain polyol is more preferably within the range of from 1,500 to 4,000, and even more preferably within the range of from 1,700 to 3,500.
The numerical average molecular weight is a numerical average molecular weight calculated based on a hydroxyl value measured in accordance with JIS-K 1557 (the same applies hereinafter.).
As the chain extender, those used in conventional techniques related to polyurethanes may be suitably used, and the chain extender is not particularly limited. In the present invention, a low molecular weight compound having at least two active hydrogen atoms capable of reacting with an isocyanate group in the molecule and having a molecular weight of not more than 2,000 may be used, and among low molecular weight compounds, an aliphatic diol having 2 to 12 carbon atoms may be suitably used. Specific examples thereof include 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, and among the specific examples, 1,4-butylene glycol may be particularly suitably used.
As the polyisocyanate, those hitherto used in the art related to polyurethane may be suitably used, and are not particularly limited. Specifically, one or more selected from the group consisting of 4,4′-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, 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 may be used. However, it may be difficult to control a crosslinking reaction during injection molding depending on the type of isocyanate.
In addition, the blending ratio of active hydrogen atoms:isocyanate groups in the polyurethane forming reaction may be appropriately adjusted within a preferable range. Specifically, when the long-chain polyol, the polyisocyanate compound, and the chain extender are reacted to produce a polyurethane, it is preferable to use each component at a ratio such that the isocyanate group contained in the polyisocyanate compound is from 0.95 to 1.05 mol, based on 1 mol of active hydrogen atoms of the long-chain polyol and the chain extender.
The method for producing the polyurethane is not particularly limited, and the polyurethane may be produced by either a prepolymer method or a one-shot method using the long-chain polyol, the chain extender, and the polyisocyanate compound by utilizing a known urethanization reaction. Among the methods, it is preferable to perform melt polymerization substantially in the absence of a solvent, and it is particularly preferable to perform production by continuous melt polymerization using a multi-screw extruder.
As the polyurethane described above, it is preferable to use a thermoplastic polyurethane material, and it is particularly preferable to use an ether-based thermoplastic polyurethane material. As the thermoplastic polyurethane material, a commercially available product may be suitably used, and examples thereof include “Pandex” (trade name) manufactured by DIC Covestro Polymer, Ltd., and “Rezamin” (trade name) manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.
A material hardness of the component (I) on the Shore D hardness scale is preferably not more than 52, more preferably not more than 50, and even more preferably not more than 48 in view of spin characteristics and scuff resistance obtained as a golf ball. A lower limit thereof on the Shore D hardness scale is preferably at least 38, and more preferably at least 40 from the viewpoint of moldability.
A rebound elastic modulus of the component (I) is preferably at least 55%, more preferably at least 57%, and even more preferably at least 59% from a comprehensive viewpoint as a golf ball such as initial velocity performance and spin performance at the time of striking. The rebound elastic modulus is measured based on the JIS-K 6255: 2013 standard.
The component (I) is the chief material of the resin composition, and is 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 from the viewpoint of sufficiently imparting the scuff resistance of the urethane resin.
In the present invention, by blending the component (II) described in detail below into the component (I), controllability on approach shots, scuff resistance, and moldability are excellent.
In the present specification, the term “(meth)acrylic block copolymer” is used to mean both an acrylic block copolymer and a methacrylic block copolymer.
The (meth)acrylic block copolymer as the component (II) is preferably a block copolymer having at least two blocks constituting the hard segment and at least one block constituting the soft segment. That is, the (meth)acrylic block copolymer used in the present invention is a polymer containing block polymers A and B, and may be represented by a chemical structure of A-B or A-B-A. The (meth)acrylic block copolymer used in the present invention is different in chemical structure from an acrylic copolymer having a general core-shell type as described in Patent Document 5.
The block polymer A is a site constituting the hard segment, and specific examples of a monomer unit include methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, phenyl methacrylate, and 2-hydroxyethyl methacrylate, and methyl methacrylate (MMA) is preferably used as a chief component. The block polymer A may be composed of one of the above-mentioned monomer units or at least two of the above-mentioned monomer units in combination.
On the other hand, the block polymer B is a site constituting the soft segment, and specific examples of the monomer unit include acrylic acid esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, pentadecyl acrylate, dodecyl acrylate, benzyl acrylate, phenoxyethyl acrylate, and 2-methoxyethyl acrylate, and it is preferable to use n-butyl acrylate (nBA) as the chief component. The block polymer B may be composed of one of the above-mentioned monomer units or at least two of the above-mentioned monomer units in combination.
The glass transition temperature (Tg) of the block polymer A showing the hard segment is preferably from 80 to 140° C., and more preferably from 100 to 120° C. On the other hand, the glass transition temperature (Tg) of the block polymer B showing the soft segment is preferably from −80 to −20° C., more preferably from −60 to −40° C.
In the (meth)acrylic block copolymer, a content ratio of the hard segment and the soft segment is preferably 5:95 to 40:60, and more preferably 10:90 to 30:70 in weight ratio. As the ratio of the soft segment increases, it may be expected that the resin composition is softened to obtain a desired controllability on approach shots. However, if the ratio of the hard segment is too small, compatibility with a polyurethane resin or the like as a substrate decreases, and moldability may deteriorate.
If the hard segment is composed mainly of a methyl methacrylate unit, a content of the methyl methacrylate unit in the block copolymer of the component (II) is preferably from 20 to 50 wt %. If this value is too low, a fluidity becomes very high and it is not suitable as a molding material. On the other hand, if this value is too high, the resulting molded product may become too hard.
The (meth)acrylic block copolymer may be obtained by polymerizing each monomer unit described above, and examples of a polymerization method include a radical polymerization method, a living anion polymerization method, and a living radical polymerization method. Examples of a polymerization form may include a solution polymerization method, an emulsion polymerization method, a suspension polymerization method, and a bulk polymerization method.
The weight average molecular weight of the (meth)acrylic block copolymer is not particularly limited, although the weight average molecular weight is preferably at least 10,000, more preferably at least 30,000, and even more preferably at least 45,000, and the upper limit thereof is preferably not more than 200,000, more preferably not more than 150,000, and even more preferably not more than 100,000. As the weight average molecular weight becomes higher, an effect of low rebound is exhibited, and the spin rate is also increased, so that controllability on approach shots is excellent. This weight average molecular weight may be measured by gel permeation chromatography (GPC).
The (meth)acrylic block copolymer used in the present invention is preferably a polymer composed mainly of the methyl methacrylate unit in the hard segment and composed mainly of an n-butyl acrylate unit in the soft segment. As such a (meth)acrylic block copolymer, a commercially available product may be employed, and examples thereof include “KURARITY” manufactured by Kuraray Co., Ltd., and specific examples thereof include trade names “KURARITY LA2114”, “KURARITY LA2140”, “KURARITY LA2250”, “KURARITY LA2270”, “KURARITY LA2330”, and “KURARITY LA4285”.
The material hardness of the component (II) on the Shore D hardness scale is preferably not more than 40, more preferably not more than 38, even more preferably not more than 35, and most preferably not more than 32 from the viewpoint of improving the spin rate on approach shots. The lower limit thereof on the Shore D hardness scale is preferably at least 7, more preferably at least 15, and even more preferably at least 20.
The rebound elastic modulus of the component (II) is preferably not more than 40%, more preferably not more than 35%, and even more preferably not more than 30% from the viewpoint of maintaining the spin rate on approach shots and suppressing the rebound on approach shots to be low to obtain controllability. The lower limit of the rebound elastic modulus is preferably at least 10%, more preferably at least 15%, and even more preferably at least 20%. The rebound elastic modulus is measured based on the JIS-K 6255: 2013 standard.
By setting a melt flow rate (MFR) of the component (II) to a high value, a fluidity of the polyurethane resin material may be improved, the molding temperature during molding may be lowered, cutting and deterioration of urethane molecules may be suppressed, and scuff resistance may be further improved. Specifically, the melt flow rate is preferably at least 2 g/10 min, more preferably at least 50 g/10 min, even more preferably at least 100 g/10 min, and most preferably at least 200 g/10 min as a measured value under the ISO 1133 standard, a test temperature of 230° C., and a test load of 21.18 N (2.16 kgf).
The compounding amount of the component (II) is preferably not more than 20 parts by weight, more preferably not more than 15 parts by weight, and even more preferably not more than 10 parts by weight per 100 parts by weight of the component (I). If the compounding amount exceeds this value, the scuff resistance may be deteriorated. The lower limit of the compounding amount is at least 0.5 parts by weight, preferably at least 1 parts by weight, and more preferably at least 2 parts by weight per 100 parts by weight of the component (I).
In the resin composition containing the above (I) and (II), other resin materials may be blended in addition to the resin components described above. The purpose of this is to further improve the fluidity of the resin composition for golf balls and improve various physical properties such as rebound and durability to cracking.
The resin composition may be obtained, for example, by mixing the above-described components using various kneaders such as a knead-type twin-screw (or single-screw) extruder, a Banbury mixer, or a kneader.
For low rebound and improvement of the spin rate on approach shots, the rebound elastic modulus of the resin composition is required to be at least 48%, preferably at least 50%, and even more preferably at least 52%, and the upper limit thereof is not more than 72%, preferably not more than 70%, and more preferably not more than 68% in measurement according to the JIS-K 6255: 2013 standard.
In addition, the material hardness of the resin composition on the Shore D hardness scale is preferably not more than 50, more preferably not more than 48, and even more preferably not more than 45 from the viewpoint of scuff resistance and application of an appropriate spin rate on approach shots. The lower limit thereof is preferably at least 30, more preferably at least 35, and even more preferably at least 37 on the Shore D hardness scale from the viewpoint of moldability.
In the present invention, in the resin composition, if a ratio (η1/η0) of a viscosity η1l (dPa·s) at 210° C. and a viscosity η0 (dPa·s) at 200° C. at a shear rate of 1,216 (1/sec) is denoted by VRL and a ratio (η3/η2) of a viscosity η3 (dPa·s) at 230° C. and a viscosity η2 (dPa·s) at 220° C. at the shear rate of 1,216 (1/sec) is denoted by VRH, a value of VRL×VRH is at least 0.10, and preferably at least 0.12, and the upper limit is not more than 0.26, preferably not more than 0.23, and more preferably not more than 0.20. That is, since the fluidity of the cover resin material at 200° C. is lower than the fluidity at 210° C., solidifiability may be improved, and molding defects such as pin butting during molding may be reduced. In addition, since the fluidity of the cover resin material at 230° C. is higher than the fluidity at 220° C., the fluidity changes sufficiently sensitively to the temperature even in a molding temperature range, and it is not necessary to excessively increase the molding temperature in order to improve the fluidity. As a result, it is possible to reduce deterioration of a resin state and a burden on a mechanical device such as a molding machine, which might occur at the time of molding the cover.
The thickness of the cover formed of the resin composition is preferably at least 0.4 mm, more preferably at least 0.5 mm, and even more preferably at least 0.6 mm, and the upper limit thereof is preferably not more than 3.0 mm, and more preferably not more than 2.0 mm. If the cover is too thin, the scuff resistance of the ball on shots with a wedge may worsen. On the other hand, if the cover is too thick, the spin of the ball may be excessively increased, and a desired distance may not be obtained.
The cover has a specific gravity which, although not particularly limited, is preferably at least 1.00, more preferably at least 1.03, and even more preferably at least 1.06. The upper limit is preferably not more than 1.20, more preferably not more than 1.17, and even more preferably not more than 1.14. If the specific gravity of the cover is less than the above range, the scuff resistance may worsen due to the blend ratio of the resin used for adjusting the specific gravity. On the other hand, when the cover specific gravity is too high, the amount of filler added is high and the rebound may become too low, as a result of which the intended distance may be unattainable.
It is preferable that the specific gravities of all of the core, the intermediate layer, and the cover described above are at least 1.10 and not more than 1.13. By setting the specific gravities of all the layers within such a numerical range, there are advantages that a golf ball conforming to the Rules of Golf is obtained, and the difference in specific gravity between the respective layers is minimized, so that the variation in rolling forward, backward, left, and right with the putter is reduced.
The cover has a material hardness on the Shore D hardness scale which, although not particularly limited, is preferably not more than 52, more preferably not more than 50, and even more preferably not more than 48, and the lower limit is preferably at least 40, and more preferably at least 43. By setting the hardness relatively low, the initial velocity of the ball at the time of putting is less likely to be fast, and a variation in a putting distance is reduced. In addition, within the above range, the harder the hardness, the more it is possible to increase the distance due to low spin on full shots with an iron (I #6).
The golf ball has a deflection (mm) when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) which is preferably not more than 3.0 mm, more preferably not more than 2.9 mm, and even more preferably not more than 2.8 mm. By setting a relatively small deflection in this manner, the variation in the distance of the ball at the time of putting is reduced. The lower limit of the deflection is preferably at least 2.2 mm, and more preferably at least 2.3 mm.
The moment of inertia of the golf ball of the present invention is preferably at least 82.5 kg·cm2, and more preferably at least 83.0 kg·cm2, and the upper limit thereof is preferably not more than 85.0 kg·cm2. Here, the moment of inertia employed in the present invention may be calculated by the following condition.
M=(n/5,880,000)×{(r1−r2)×D15+(r2−r3)×D25+r3×D35}
That is, the moment of inertia is a calculated value obtained from the diameter (thickness) and specific gravity of each layer, and may be obtained by regarding the ball as a complete sphere. The moment of inertia of the golf ball may be measured using a moment of inertia measuring device, for example, “M01-005” manufactured by Inertia Dynamics, Inc.
In the present invention, the specific gravity of each layer of the core, the intermediate layer, and the cover, which are constituent members of the golf ball, is required to have a standard deviation within 0.07.
The above standard deviation is a standard deviation that is generally calculated, and is a positive square root obtained by summing the square of a difference between a data value and a mean value and dividing the sum by a total number of data. The difference between the data value and the mean value means a deviation, a root mean square value of the deviation means a variance, and therefore the standard deviation means the positive square root of the variance.
(In the above formula, a is the standard deviation, Xi is the data value, Xo is the mean value, and n is the total number of data.)
For example, in Example 1 in Table 4, the specific gravity of the core is 1.13, the specific gravity of the intermediate layer is 1.08, and the specific gravity of the cover is 1.07. A mean value of the three pieces of data is (1.13+1.08+1.07)/3≈1.0933. When applied to the above formula, σ={1/3×(1.13−1.0933)2+1/3×(1.08−1.0933)2+1/3×(1.07−1.0933)2}1/2≈0.03.
The standard deviation of the specific gravity of each layer of the core, the intermediate layer, and the cover is within 0.07, preferably not more than 0.05, and more preferably not more than 0.03. By setting the standard deviation within 0.07, the width of lateral swing of the ball at the time of putting is reduced, and stable putting may be provided.
In the present invention, when the specific gravity of the core is denoted by CM, the specific gravity of the intermediate layer is denoted by MM, the specific gravity of the cover is denoted by FM, the initial velocity (m/s) of the core is denoted by CV, the initial velocity (m/s) of the sphere (intermediate layer-encased sphere) obtained by encasing the core with the intermediate layer is denoted by MV, the initial velocity (m/s) of the sphere (ball) obtained by encasing the intermediate layer-encased sphere with the cover is denoted by FV, and the deflection (mm) when the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is denoted by FC, the following condition (2) is preferably satisfied:
Further, in the present invention, when the moment of inertia of the ball is denoted by MOI, the following condition (3) is preferably satisfied:
Relationships among the initial velocity of the core (CM), the initial velocity of the intermediate layer-encased sphere (MV), and the initial velocity of the ball (FV) are preferably set to the following ranges.
The initial velocity of the core and the initial velocity of the intermediate layer-encased sphere may be measured using an initial velocity measuring instrument of the same method as the drum rotation type initial velocity meter of the USGA, which is a device approved by the R&A. Specifically, a test is performed in a room having a room temperature of 23.9±2° C., the ball is struck at a striking speed of 143.8 ft/s (43.83 m/s) using a head (striking mass) of 250 pounds (113.4 kg), a time for passing through 6.28 ft (1.91 m) is measured, and the initial velocity (m/s) is calculated. In this case, the temperature of the ball to be measured is adjusted by a temperature of 23.9±1° C. for at least three hours.
On the other hand, the initial velocity of the ball is a numerical value measured by a COR type initial velocity meter of the same type as the R&A. Specifically, a Golf Ball Testing Machine manufactured by Hye Precision USA is used. As a condition, at the time of measurement, an air pressure is changed in four stages and measured, a relational expression between the incident velocity and the COR is constructed, and the initial velocity at an incident velocity of 43.83 m/s is determined from the relational expression. It is noted that for a measurement environment of the Golf Ball Testing Machine, a ball temperature-controlled for three hours or more in a thermostatic bath adjusted to 23.9±1° C. is used, and the measurement is performed at a room temperature of 23.9±2° C. In addition, a barrel diameter is selected such that a clearance on one side with respect to an outer diameter of the object being measured is from 0.2 to 2.0 mm.
The initial velocity of the core (CM) is preferably at least 77.50 m/s, more preferably at least 77.60 m/s, and even more preferably at least 77.70 m/s, and the upper limit thereof is preferably not more than 78.10 m/s, and more preferably not more than 77.90 m/s.
The initial velocity of the intermediate layer-encased sphere (MV) is preferably at least 77.70 m/s, more preferably at least 77.80 m/s, and even more preferably at least 77.90 m/s, and the upper limit thereof is preferably not more than 78.30 m/s, and more preferably not more than 78.10 m/s.
The initial velocity of the ball (FM) is preferably at least 77.00 m/s, more preferably at least 77.10 m/s, and even more preferably at least 77.20 m/s, and the upper limit thereof is preferably not more than 77.70 m/s, and more preferably not more than 77.60 m/s.
If these initial velocities deviate from the above ranges, a variation in the vertical direction when struck with a putter may increase.
One kind or two or more kinds of a large number of dimples may be typically formed on a cover surface, and the shape, diameter, depth, number, occupied surface area, and the like of the dimples are appropriately selected.
A method for producing the golf ball is not particularly limited, and the golf ball may be obtained by molding by a known molding method such as injection molding or compression molding. For example, the resin composition for the intermediate layer described above is supplied in a state where the core is set in a mold of an injection molding machine to produce a layer-encased sphere (intermediate layer-encased sphere) in which the core is encased with the intermediate layer, then the intermediate layer-encased sphere is set in a mold of another injection molding machine, and the resin composition for the cover is injected to produce a golf ball encased with the cover.
In addition, a coating layer may be formed on the cover surface. In this case, the coating layer is formed of a coating composition. A base resin of the coating composition is not particularly limited, although examples thereof include a polyurethane resin, an epoxy resin, a polyester resin, an acrylic resin, and a cellulose resin. From the viewpoint of durability of the coating layer, it is preferable to use a two-liquid curable polyurethane resin. In the coating composition, various additives such as an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, and a fluorescent brightener may be blended in an appropriate amount as necessary.
A method for applying the coating material to the cover surface is not particularly limited, and a known method may be used, and electrostatic coating, spray gun coating, brush coating, or the like may be adopted.
A ball standard such as the weight and the diameter of the golf ball of the present invention may be appropriately set according to the Rules of Golf.
Hereinafter, the present invention is specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.
A core composition is prepared by blending rubber shown in Table 1 common to each of the Examples and Comparative Examples, and vulcanization is performed to prepare a core having a diameter of 38.7 mm. Zinc oxide and zinc acrylate are blended in appropriate amounts so that deflections and specific gravities shown in Table 4 described later match, and four types of A, A′, B, and B′ are prepared.
Details of the above formulations are as follows.
Next, in each of the Examples and Comparative Examples, injection molding is performed around a surface of the core with resin materials C and D of the intermediate layer shown in Table 2 using the following injection mold to form an intermediate layer having a thickness of 1.20 mm and a Shore D hardness of 66 to 68.
Details of the blending components in the above table are as follows.
Next, 12 kinds of urethane resin compositions of C1 to C12 shown in Table 3 are injection molded around the intermediate layer-encased sphere using another injection mold to form a cover (outermost layer) having a thickness of 0.8 mm and a Shore D hardness of 43 to 50.
In the above table, details of the blending components are as follows.
The rebound elastic modulus described in the above table is a rebound elastic modulus of each resin component measured based on the JIS-K 6255: 2013 standard, and the melt flow rate (MFR) is the MFR (g/10 min) measured under measurement conditions of 230° C. and a load of 2.16 kgf (ISO 1133).
Measurement is performed according to ISO 11443: 1995 using trade name “Capilograph 1C” manufactured by Toyo Seiki Seisaku-sho, Ltd. As the measurement conditions, conditions of a capillary are set at L/D=10.0/1.0 mm, and a melt viscosity (dPa·s) of a sample at a shear rate (1,216 (1/sec)) at a piston speed (100 mm/min) is measured. In the above measurement, the melt viscosity at 200° C. is denoted as η0 (dPa·s), the melt viscosity at 210° C. is denoted as η1 (dPa·s), the melt viscosity at 220° C. is denoted as η2 (dPa·s), and the melt viscosity at 230° C. is denoted as η3 (dPa·s).
For the obtained golf ball of each example, VRLλVRH of the cover, the difference in specific gravity of each layer, the standard deviation of the specific gravity of each layer, the following conditions (2) and (3), the initial velocity of each layer-encased sphere, the deflection of each layer-encased sphere, and the moment of inertia of the ball are calculated, and a putting test, the controllability on approach shots, feel at impact, scuff resistance, and moldability of the ball of each example are evaluated by the following methods. The results are shown in Table 4.
Each subject layer-encased sphere is placed on a hard plate, and a deflection when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is measured. Note that the deflection in each case is a measurement value measured in a room at a temperature of 23.9±2° C. after temperature adjustment to 23.9±1° C. for at least three hours or more in a thermostatic bath. As a measuring device, a high-load compression tester manufactured by MU Instruments Trading Corp. is used, and a down speed of a pressure head that compresses the core, the layer-encased sphere of each layer, or the ball is set to 10 mm/s.
The initial velocities are measured using an initial velocity measuring instrument of the same method as the drum rotation type initial velocity meter of the USGA, which is a device approved by the R&A. Each layer-encased sphere of the core, the intermediate layer, and the ball is temperature-adjusted at a temperature of 23±1° C. for at least three hours, and tested in a room at a room temperature of 23±2° C. Each layer-encased sphere of the 20 cores, intermediate layers, and balls is struck twice, the time for passing through 6.28 ft (1.91 m) is measured, and the initial velocity is calculated. This cycle is performed in about 15 minutes.
The moment of inertia of the golf ball is measured using a moment of inertia measuring device (“MO1-005” manufactured by Inertia Dynamics, Inc.). This measuring device calculates the moment of inertia of a golf ball based on a difference between a period of vibration when the golf ball is placed on a jig of the measuring device and the period of vibration when the golf ball is not placed on the jig of the measuring device.
The specific gravity of each layer is calculated from a member weight and a member volume of the material of each layer by measuring an outer diameter and a weight before and after injection molding.
Condition (1) in Table 4 means (CM×CV)+(MM×MV)+(FM×FV/FC), and condition (2) means (CM×CV/MOI)+(MM×MV)+(FM×FV/FC).
(CM represents the specific gravity of the core, MM represents the specific gravity of the intermediate layer, FM represents the specific gravity of the cover, CV represents the initial velocity of the core, MV represents the initial velocity of the intermediate layer-encased sphere, FV represents the initial velocity of the ball, FC represents the deflection when a predetermined load is applied to the ball, and MOI represents the moment of inertia of the ball.)
A swing width of a putter robot is adjusted and fixed so as to have a rolling distance of about 5 m, and the ball of each example is struck. An average initial velocity, a rolling distance X, and a lateral variation Y when each measurement is performed 10 times at the same target distance are measured, and X(a) and Y(a), which are standard deviations of X and Y, are taken as the rolling distance (vertical) and the lateral direction (horizontal) swing, respectively. The FIGURE shows a schematic view explaining a putting test. Symbol T indicates an area of artificial turf, symbol O indicates a striking point of the putter robot, symbol P indicates a target point, symbol X indicates the rolling distance, and symbol Y indicates the width of lateral swing. The conditions of the test apparatus are as follows.
Regarding the molding temperature during cover injection molding, a temperature difference is examined with reference to Comparative Example 1. Based on Comparative Example 1, the lower the temperature, the lower the molding temperature, and thus the higher the productivity.
The ball of each example is evaluated for demolding properties from the mold after cover injection molding according to the following criteria.
Sensory evaluation on the controllability of the ball on approach shots is performed by the following method. The club used is a sand wedge (SW), product name “Bridgestone Tour Stage TW-03 (loft angle 57°)”, similar to that described above and is rated according to the following criteria when a golfer actually strikes the ball.
The ball is kept at 23° C. and a swing robot machine is used. The club used is a pitching wedge (PW), each ball is struck five times at a head speed of 33 m/s, and scratches from striking are visually evaluated according to the following criteria.
An approach sensory evaluation related to the feel at impact is performed as follows. The club used is a sand wedge (SW) similar to the above.
As shown in Table 4, the golf balls of Examples 1 to 8 have excellent controllability on approach shots, feel at impact, scuff resistance, and moldability, and have a small standard deviation of the specific gravity of each layer, small swing in vertical distance and horizontal distance, and small variations in vertical and horizontal distance. On the other hand, Comparative Examples 1 to 8 are as follows.
In Comparative Example 1, since the cover does not contain the component (II) and the condition (1) is large, moldability and controllability on approach shots are inferior.
In Comparative Example 2, since the cover does not contain the component (II) and the condition (1) is large, controllability on approach shots is inferior.
In Comparative Example 3, since the cover does not contain the component (II) and the condition (1) is large, moldability and feel at impact are inferior.
In Comparative Example 4, since the cover does not contain the component (II) and the condition (1) is large, moldability, scuff resistance, and feel at impact are inferior.
In Comparative Example 5, since the cover does not contain the component (II) and the condition (1) is large, moldability and controllability on approach shots are inferior.
In Comparative Example 6, since the standard deviation of the specific gravity of each layer is large, a variation in the lateral distance (lateral swing) is large.
In Comparative Example 7, since the standard deviation of the specific gravity of each layer is large, the variation in the lateral distance (lateral swing) is large.
In Comparative Example 8, since the standard deviation of the specific gravity of each layer is large, the variation in the lateral distance (lateral swing) is large.
Japanese Patent Application No. 2023-207898 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 |
|---|---|---|---|
| 2023-207898 | Dec 2023 | JP | national |
