JP2003117025A - Golf ball - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a golf ball 1 capable of providing the good hitting feeling in a case of being hit by a golfer of a slow head speed, and providing long carry. SOLUTION: This golf ball 1 is provided with a core 2, an intermediate layer 3 and a cover 4. A ratio (Ds/Dc) is 0.90 or more and 0.98 or less, and a value of (Y-0.5X) is 0.20 or more and 0.37 or less, when D is a compression deformation amount of the core 2, Ds is a compression deformation amount of a ball body including the core 2 and the intermediate layer 3, X is a ratio of the sum of an area of a region surrounded by an edge of a dimple 5 of a virtual spherical face to a surface area of the virtual spherical face, Vb is the sum of a volume of a space surrounded by a plane including the edge of the dimple 5 and a surface of the dimple 5, Vt is the sum of the volume of a space surrounded by the plane including the edge of the dimple 5 and the virtual spherical face, and Y is a ratio (Vt/Vb) of Vt to Vb.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a golf ball, and more particularly to a solid golf ball having an intermediate layer made of a synthetic resin composition.

[0002]

2. Description of the Related Art Golf balls used for playing on a golf course are roughly classified into a thread-wound golf ball having a core in which a thread rubber is wound and a solid golf ball having a core made of solid rubber. Thread-wound golf balls have been used for a long time, and in the past, almost all first-class golf balls were thread-wound golf balls. However, since solid golf balls developed thereafter are easy to manufacture and can be obtained at low cost, more solid golf balls have been supplied to the market than wound golf balls in recent years. Solid golf balls are generally
It has the drawback that the shot feeling is harder than that of a thread-wound golf ball. On the other hand, general solid golf balls are superior to wound golf balls in terms of flight distance.

A solid golf ball provided with an intermediate layer made of a synthetic resin composition between a core and a cover has been proposed for the purpose of improving the shot feeling or further improving the flight performance (Japanese Patent Laid-Open No. 11- 114094, JP 2000-
70412, JP 2000-296187 A and JP 2001-95947 A).

A golf ball has dimples on its surface. The role of the dimples is to promote the turbulent transition of the boundary layer by disturbing the flow of air around the golf ball during flight of the golf ball to cause turbulent flow separation (hereinafter also referred to as "dimple effect"). . By promoting the turbulent transition, the separation point of the air from the golf ball is lowered to the rear, and the pressure resistance is reduced. Also,
By promoting the turbulent transition, the difference in the separation point between the upper side and the lower side of the golf ball due to backspin is promoted,
The lift acting on the golf ball is increased. By reducing the pressure resistance and improving the lift, the flight distance of the golf ball is increased. The dimples that facilitate the turbulent transition, that is, the dimples that can better disturb the air flow, are more aerodynamically superior.

Various attempts have been made to optimize the combination of the structure and material of the golf ball and the dimple specifications. Such techniques are disclosed in JP-A-11-57067, JP-A-2000-70414, and JP-A-2000-
It is disclosed in Japanese Patent No. 225209.

[0006]

When a golf ball is hit with a golf club, deformation occurs. When the head speed is high, the cover, the intermediate layer and the core are largely deformed. When the head speed is low, the core is not deformed so much, and mainly the cover and the intermediate layer are deformed. The shot feeling for a golfer with a slow head speed largely depends on the material of the intermediate layer. When a golf ball having an intermediate layer made of a synthetic resin composition is hit by a golfer having a slow head speed, it tends to feel hard.

If a soft material is used for the intermediate layer, the shot feeling is improved. However, the soft intermediate layer causes an increase in the amount of backspin. If the amount of backspin is large, the trajectory will hop and the flight distance will be reduced. The reality is that a golf ball that satisfies both the shot feeling and the flight distance of a golfer with a slow head speed has not yet been obtained.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a golf ball which has a good shot feeling when hit by a golfer having a slow head speed, and can obtain a large flight distance. It is what

[0009]

The invention made to achieve the above-mentioned object is to provide a core, an intermediate layer made of a synthetic resin composition and located outside the core, and an intermediate layer located outside the intermediate layer. A golf ball having a large number of dimples formed on the surface of the cover, wherein the compression deformation amount of the core is Dc, and the compression deformation amount of the sphere including the core and the intermediate layer is Ds. And the ratio of the total area of the region surrounded by the dimple edges to the virtual spherical surface is X, and the volume of the space surrounded by the plane including the dimple edges and the dimple surface. Is Vb, and the total volume of the space surrounded by the plane including the dimple edge and the virtual spherical surface is Vt, and the ratio of Vt to Vb (Vt / V
When b) is Y, the ratio (Ds / Dc) is 0.90 or more and 0.98 or less, and the value of (Y-0.5X) is 0.2.
A golf ball, which is 0 or more and 0.37 or less.

In this golf ball, the ratio (Ds / Dc)
Is 0.90 or more and 0.98 or less, in other words, since the intermediate layer is relatively soft, the shot feeling for a golfer with a slow head speed is soft. Moreover, (Y-0.5
Since the dimple specifications are determined so that the value of (X) is 0.20 or more and 0.37 or less, the hop of the golf ball is suppressed even when the backspin amount is large, and a large flight distance can be obtained. In this golf ball, the intermediate layer contributes to a good shot feeling, and the dimples complement the reduction in flight distance caused by the intermediate layer.

Preferably, the compression deformation amount Dc of the core is 3.
It is 5 mm or more and 7.0 mm or less, and the amount of compressive deformation Ds of the sphere consisting of the core and the intermediate layer is 3.0 mm or more and 6.5 mm.
It is the following. This golf ball provides a better shot feeling.

[0012] Preferably, the Shore D hardness of the intermediate layer is 3
5 and less than Shore D hardness of the core surface. This golf ball provides a better shot feeling.

The thickness of the intermediate layer is preferably 1.0 mm or more and 2.5 mm or less. This golf ball has a good shot feeling and excellent resilience performance.

Preferably, the base polymer of the intermediate layer contains an ionomer resin as a main component, and particularly contains the ionomer resin and the thermoplastic elastomer in a mass ratio of 50/50 or more and 95/5 or less. This intermediate layer contributes to improved shot feeling, durability and resilience performance.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, with reference to the drawings,
The present invention will be explained in detail based on the preferred embodiments.

FIG. 1 is a sectional view showing a golf ball 1 according to one embodiment of the present invention. This golf ball 1 includes a core 2, an intermediate layer 3, and a cover 4. Many dimples 5 are formed on the surface of the cover 4. The golf ball 1 is provided with a paint layer and a mark layer on the outer side of the cover 4, but these are not shown. The diameter of this golf ball 1 is 40 mm
The length is 45 mm or less, and particularly 42 mm or more and 44 mm or less. The diameter is 4 from the viewpoint of reducing the air resistance within the range that meets the standards of the US Golf Association (USGA).
It is preferably set to 2.67 mm or more and 42.80 mm or less. The mass of this golf ball 1 is 44 g or more and 46 g or more.
The following is particularly set to 45.00 g or more and 45.93 g or less.

The core 2 is formed by crosslinking a rubber composition. The base rubber of the rubber composition includes polybutadiene, polyisoprene, styrene-butadiene copolymer, ethylene-propylene-diene copolymer (E
PDM), natural rubber and the like are suitable. 2 of these rubbers
One or more species may be used in combination. From the viewpoint of resilience performance, polybutadiene is preferable. Even when polybutadiene and other rubbers are used in combination, it is preferable that polybutadiene is the main component. Specifically, the proportion of polybutadiene in the total base rubber is 50% by mass or more, and particularly 80% by mass.
The above is preferable. Among polybutadienes, the ratio of cis-1,4 bonds is 40% or more, and particularly 80
High cis polybutadiene having a content of at least 100% is preferable.

The cross-linking form of the rubber composition is not particularly limited, but from the viewpoint of resilience performance, an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms or a metal salt thereof is used as a co-crosslinking agent. It is preferable to use a monovalent or divalent metal salt. Specific examples of preferred co-crosslinking agents include:
Examples include zinc acrylate, magnesium acrylate, zinc methacrylate and magnesium methacrylate. In particular, zinc acrylate, which can obtain high resilience performance, is preferable.

The content of the co-crosslinking agent is preferably 10 parts or more and 50 parts or less with respect to 100 parts of the base rubber. If the blending amount is less than the above range, the core 2 may be soft and the resilience performance may be insufficient. From this viewpoint, the compounding amount is 15
More preferably, it is 20 parts or more. If the blending amount exceeds the above range, the core 2 may become hard and the shot feeling may not be soft. From this viewpoint, the blending amount is more preferably 45 parts or less, and particularly preferably 35 parts or less. The term "parts" used in the present specification means a mass ratio (parts weight).

The rubber composition used for the core 2 preferably contains an organic peroxide. The organic peroxide is
It functions as a crosslinking agent together with the aforementioned α, β-unsaturated carboxylic acid metal salt, and also as a curing agent. By blending the organic peroxide, the resilience performance of the core 2 is enhanced. Suitable organic peroxides include dicumyl peroxide,
1,1-bis (t-butylperoxy) -3,3,5-
Trimethylcyclohexane, 2,5-dimethyl-2,5
-Di (t-butylperoxy) hexane and di-t-butylperoxide. A particularly versatile organic peroxide is dicumyl peroxide.

The amount of the organic peroxide compounded is 100
It is preferably 0.1 part or more and 3.0 parts or less with respect to parts. If the blending amount is less than the above range, the core 2 may be soft and the resilience performance may be insufficient. From this viewpoint, the content is more preferably 0.2 parts or more, and particularly preferably 0.5 parts or more. If the blending amount exceeds the above range, the core 2 may become hard and the shot feeling may not be soft. From this viewpoint, the blending amount is more preferably 2.8 parts or less, and particularly preferably 2.5 parts or less.

A filler may be added to the rubber composition for the purpose of adjusting specific gravity and the like. Suitable fillers include powders made of inorganic salts such as zinc oxide, barium sulfate and calcium carbonate, and high specific gravity metals such as tungsten and molybdenum. The blending amount of the filler is appropriately determined so that the intended specific gravity of the core 2 is achieved. Because it functions not only as a specific gravity adjustment but also as a crosslinking aid,
The preferred filler is zinc oxide.

Various additives such as an antioxidant, a colorant, a plasticizer and a dispersant may be added to the rubber composition in an appropriate amount, if necessary.

For molding the core 2, known molding methods such as compression molding and injection molding can be applied. Usually, the rubber composition is put into the spherical cavity of the mold and heated while being pressurized to mold the core 2. A cross-linking reaction occurs by heating and the rubber composition is cured. Typical heating time is 10 minutes or more and 60 minutes or less, and heating temperature is 140 ° C.
It is above 180 ° C. Particularly, it is preferable that the crosslinking temperature is 160 ° C. or higher because the hardness difference of the core 2 becomes large. The hardness difference is a value obtained by subtracting the minimum value from the maximum value in the distribution of hardness (JIS-C hardness) from the center of the core 2 to the surface.

The specific gravity of the general core 2 is 1.05 or more and 1.25 or less. The diameter of the core 2 is 30 mm or more 4
It is preferably 1 mm or less. If the diameter is less than the above range,
The resilience performance and shot feeling of the golf ball 1 may be insufficient. From this viewpoint, the diameter is more preferably 32 mm or more, particularly preferably 36 mm or more. If the diameter exceeds the above range, the durability of the golf ball 1 may be insufficient. From this viewpoint, the diameter is particularly preferably 40 mm or less. The core 2 may be composed of two or more layers.

The surface hardness (Shore D) of the core 2 is preferably 30 or more and 60 or less. If the surface hardness is less than the above range, the resilience performance of the golf ball 1 may be insufficient. From this viewpoint, the surface hardness is particularly preferably 35 or more. If the surface hardness exceeds the above range, the shot feeling of the golf ball 1 may be insufficient. From this viewpoint, the surface hardness is more preferably 55 or less, and particularly preferably 50 or less.

The core 2 has a center hardness (JIS-C) of 45.
It is preferably 75 or more and 75 or less. If the central hardness is less than the above range, the resilience performance of the golf ball 1 may be insufficient. From this viewpoint, the central hardness is particularly preferably 50 or more. When the central hardness exceeds the above range, the shot feeling of the golf ball 1 may be insufficient. From this viewpoint, the central hardness is more preferably 70 or less, and particularly preferably 65 or less.

The cover 4 is usually made of a synthetic resin composition. Examples of the base polymer of the synthetic resin composition include ionomer resins, polyesters, polyurethanes, polyethylenes, polypropylenes and thermoplastic elastomers. From the viewpoints of shot feeling, durability and resilience performance, ionomer resins, thermoplastic elastomers and mixtures thereof are preferable.

Among the ionomer resins, those in which a part of the carboxylic acid in the copolymer of the α-olefin and the α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms are neutralized with metal ions are preferable. Is. Ethylene and propylene are preferable as the α-olefin. Acrylic acid and methacrylic acid are preferable as the α, β-unsaturated carboxylic acid. Examples of metal ions for neutralization include alkali metal ions such as sodium ions, potassium ions and lithium ions; divalent metal ions such as zinc ions, calcium ions and magnesium ions; trivalent metal ions such as aluminum ions and neodymium ions. Etc. Neutralization may be done with more than one metal ion.
Particularly suitable metal ions from the viewpoint of resilience performance and durability of the golf ball 1 are sodium ion, zinc ion, lithium ion and magnesium ion.

Specific examples of suitable ionomer resins include "HIMIRAN 1555", "HIMIRAN 1557", and "HIMIRAN 1" manufactured by DuPont Mitsui Polychemical Co., Ltd.
"601", "High Milan 1605", "High Milan 16
52 "," High Milan 1705 "," High Milan 170
6 ”,“ High Milan 1707 ”,“ High Milan 185
5 "," Himilan 1856 "; trade name" Duron 9945 "," Cirrin 8945 "," Cirrin AD8511 "," Cirrin AD8512 "; trade name" IOTEK7010 "," IOTEK "of Exxon
8000 ”and the like. Two or more ionomer resins may be used in combination.

Preferred thermoplastic elastomers include
Examples thereof include polyurethane-based thermoplastic elastomers, polyamide-based thermoplastic elastomers, polyester-based thermoplastic elastomers, styrene-based thermoplastic elastomers, and thermoplastic elastomers having OH groups at the ends. Two or more thermoplastic elastomers may be used in combination. From the viewpoint of resilience performance of the golf ball 1, polyester-based thermoplastic elastomers and styrene-based thermoplastic elastomers are particularly suitable.

The styrene-based thermoplastic elastomer (thermoplastic elastomer containing a styrene block) includes a styrene-butadiene-styrene block copolymer (SB
S), styrene-isoprene-styrene block copolymer (SIS), styrene-isoprene-butadiene-styrene block copolymer (SIBS), hydrogenated SBS, hydrogenated SIS and hydrogenated SIBS. Be done.
Examples of hydrogenated products of SBS include styrene-ethylene-butylene-styrene block copolymer (SEBS). Examples of hydrogenated products of SIS include styrene-ethylene-propylene-styrene block copolymer (SEPS). Examples of hydrogenated products of SIBS include styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS).

Specific examples of the thermoplastic polyurethane elastomer include "Elastolan", trade name of BASF Polyurethane Elastomers Co., Ltd., and more specifically, "Elastolan ET880". A specific example of the polyamide-based thermoplastic elastomer is "Pebax", a trade name of Toray Company, and more specifically, "Pebax 25".
33 ”. Specific examples of the polyester-based thermoplastic elastomer include "Hytrel", a trade name of Toray-Dupont, and more specifically, "Hytrel 354".
8 "and" Hytrel 4047 ". Specific examples of the styrene-based thermoplastic elastomer include Mitsubishi Chemical Co., Ltd.'s trade name "Lavalon", and in detail, "Lavalon SR04", "Lavalon SJ4400N", "Lavalon SJ5400N", "Lavalon SJ6400N",
"Lavalon SJ7400N", "Lavalon SJ8400
N ”and“ Lavalon SJ9400N ”.

The cover 4 may be blended with a diene block copolymer. The diene-based block copolymer has at least one polymer block mainly containing a vinyl aromatic compound and at least one polymer block mainly containing a conjugated diene compound. The diene-based block copolymer has a double bond derived from a conjugated diene compound. A diene-based block copolymer in which hydrogen is added to a part of the polymer block can also be preferably used.

As the vinyl aromatic compound constituting the diene block copolymer, styrene, α-methylstyrene, vinyltoluene, pt-butylstyrene and 1,
1-diphenylstyrene can be mentioned, and among these, 1
One kind or two or more kinds are selected. Styrene is particularly preferred. Examples of the conjugated diene compound include butadiene, isoprene, 1,3-pentadiene and 2,3-dimethyl-
1,3-Butadiene may be mentioned, and one or two or more thereof are selected from these. Particularly preferred are butadiene and isoprene, and combinations thereof.

Preferred diene block copolymers have an SBS (styrene-butadiene-styrene) structure having a polybutadiene block containing an epoxy group, and SIS (styrene-isoprene block having a polyisoprene block containing an epoxy group). -Styrene)
The thing of a structure is mentioned. Specific examples of the diene-based block copolymer include Daicel Chemical Company's trade name “Epofriend” (specifically, “Epofriend A1010”) and Kuraray's trade name “Septon” (specifically, “Septon HG
-252).

A filler may be added to the cover 4 if necessary. Suitable fillers include inorganic salts such as zinc oxide, barium sulfate and calcium carbonate, and powders of high specific gravity metals such as tungsten and molybdenum. Two
One or more fillers may be used in combination. A colorant such as titanium dioxide, a dispersant, an antiaging agent, an ultraviolet absorber, a light stabilizer, a fluorescent agent, an optical brightener and the like may be added to the cover 4 in an appropriate amount, if necessary.

The cover 4 is usually molded by an injection molding method. In the injection molding method, the synthetic resin composition is injected into a cavity in which a sphere composed of the core 2 and the intermediate layer 3 is held at the center. The synthetic resin composition filled in the gap between the sphere and the cavity surface is solidified to form a cover. The cover 4 may be molded by a compression molding method using a half shell made of a synthetic resin composition. The specific gravity of the cover 4 is usually 0.9 or more and 1.4 or less.

The cover 4 has a thickness of 1.0 mm or more and 2.5.
mm or less is preferable. The cover 4 having a thickness less than the above range is difficult to be molded, and further, the durability and the resilience performance of the golf ball 1 may be deteriorated. From this viewpoint, the thickness is more preferably 1.3 mm or more, and 1.5 m
m or more is particularly preferable. If the thickness exceeds the above range, the shot feeling may deteriorate. From this viewpoint, the thickness is 2.
It is more preferably 3 mm or less, and particularly preferably 2.0 mm or less. The cover 4 may be composed of two or more layers.

The hardness (Shore D) of the cover 4 is preferably 55 or more and 70 or less. If the hardness is less than the above range, the shot feeling may be heavy. From this viewpoint, the hardness is 57
The above is more preferable, and 59 or more is particularly preferable. If the hardness exceeds the above range, the shot feeling may become hard. From this viewpoint, the hardness is particularly preferably 67 or less. The hardness is
It is measured by a spring hardness meter (Shore D type). For convenience, a sheet having a thickness of 2.0 mm formed by hot pressing from the same resin composition as the cover 4 is used for the measurement. This sheet is kept in an environment of 23 ° C. for 2 weeks, three sheets are stacked, and hardness is measured.

The intermediate layer 3 is made of a synthetic resin composition. As the base polymer of the mid layer 3, the same base polymer as that of the cover 4 described above can be used. In particular, it is preferable that the ionomer resin is the main component. The ratio of the ionomer resin to the total amount of the base polymer is preferably 50% by mass or more, and particularly preferably 55% by mass or more.

It is especially preferred that a thermoplastic elastomer is used with the ionomer resin. In this case, the mass ratio of the ionomer resin and the thermoplastic elastomer is 5
It is preferably 0/50 or more and 95/5 or less. If the mass ratio is less than the above range, the resilience performance of the golf ball 1 may be insufficient. From this viewpoint, the mass ratio is 55/45.
The above is particularly preferable. If the mass ratio exceeds the above range, the shot feeling may be insufficient. From this viewpoint, the mass ratio is more preferably 90/10 or less, and particularly preferably 80/20 or less.

A filler may be added to the intermediate layer 3 if necessary. Suitable fillers include inorganic salts such as zinc oxide, barium sulfate and calcium carbonate, and powders of high specific gravity metals such as tungsten and molybdenum. Two
One or more fillers may be used in combination.

The intermediate layer 3 is usually formed by an injection molding method. In the injection molding method, the synthetic resin composition is injected into the cavity in which the core 2 is held at the center. Core 2
The synthetic resin composition filled in the space between the cavity surface and the cavity surface is solidified to form the intermediate layer 3. The intermediate layer 3 may be molded by a compression molding method using a half shell made of a synthetic resin composition.

The specific gravity of the intermediate layer 3 is usually 0.9 or more.
It is 4 or less. The thickness of the mid layer 3 is 1.3 mm or more.2.
It is preferably 5 mm or less. When the thickness is less than the above range,
The shot feeling may be insufficient. From this viewpoint, the thickness is more preferably 1.3 mm or more, and particularly preferably 1.5 mm or more. When the thickness exceeds the above range, the resilience performance of the golf ball 1 may be insufficient. From this viewpoint, the thickness is more preferably 2.3 mm or less, and 2.0 mm
The following are particularly preferred. The intermediate layer 3 may be composed of two or more layers.

The hardness (Shore D) of the mid layer 3 is preferably 35 or more. When the hardness is less than the above range, the resilience performance of the golf ball 1 may be insufficient. From this viewpoint, the hardness is more preferably 37 or higher, and particularly preferably 38 or higher. From the viewpoint of shot feeling, the hardness of the mid layer 3 is preferably smaller than the surface hardness of the core 2. Specifically, the hardness is preferably 50 or less, more preferably 45 or less, and 42
The following are particularly preferred.

The amount of compressive deformation Dc of the core 2 is preferably 3.5 mm or more and 7.0 mm or less. When the amount of compressive deformation Dc is less than the above range, the shot feeling may be deteriorated. From this viewpoint, the amount of compressive deformation Dc is more preferably 3.7 mm or more, and particularly preferably 4.0 mm or more. When the amount of compressive deformation Dc exceeds the above range, the resilience performance may be insufficient. From this viewpoint, the amount of compressive deformation Dc is more preferably 6.5 mm or less, and particularly preferably 5.5 mm or less. The amount of compressive deformation in this specification refers to a sphere that is a measurement target.
It means the amount of deformation of this sphere from the state where an initial load of N is applied to the state where a final load of 1274N is applied.

The amount of compressive deformation Ds of the spherical body composed of the core 2 and the mid layer 3 (in other words, the spherical body obtained by removing the cover 4 from the golf ball 1) is preferably 3.0 mm or more and 6.5 mm or less. If the amount of compressive deformation Ds is less than the above range, the shot feeling may deteriorate. From this viewpoint, the compression deformation amount Ds
Is more preferably 3.2 mm or more, and particularly preferably 3.7 mm or more. When the amount of compressive deformation Ds exceeds the above range, the resilience performance may be insufficient. From this viewpoint, the amount of compressive deformation Ds is more preferably 6.0 mm or less and 5.5 m
m or less is particularly preferable.

The core 2 with respect to the compression deformation amount Dc of the core 2
Of the compression deformation amount Ds of the sphere composed of the intermediate layer 3 and the intermediate layer 3 (Ds
/ Dc) is 0.90 or more and 0.98 or less. Ratio (D
When s / Dc) is less than the above range, the amount of deformation of the mid layer 3 is smaller than the amount of deformation of the core 2 at the time of hitting, and the shot feeling may be insufficient. From this viewpoint, the ratio (Ds /
Dc) is particularly preferably 0.91 or more. Ratio (Ds / D
When c) exceeds the above range, the backspin amount is large and the flight distance may be insufficient. From this viewpoint, the ratio (D
The s / Dc) is more preferably 0.96 or less, and particularly preferably 0.95 or less.

The amount of compressive deformation Db of the golf ball 1 is 2.
It is preferably 8 mm or more and 4.5 mm or less. Compressive deformation amount Db
Is less than the above range, the shot feeling may be insufficient. From this viewpoint, the amount of compressive deformation Db is more preferably 2.9 or more, and particularly preferably 3.0 or more. Compressive deformation amount D
When b exceeds the above range, the resilience performance may be insufficient. From this viewpoint, the amount of compressive deformation Db is more preferably 4.2 mm or less, and particularly preferably 4.0 mm or less.

The amount of compressive deformation Db of the golf ball 1 and the core 2
(Db + Dc) together with the amount of compressive deformation Dc of 7.0 m
It is preferably m or more and 10.0 mm or less. When (Db + Dc) is less than the above range, the shot feeling may be insufficient. From this viewpoint, (Db + Dc) is more preferably 7.1 mm or more, and particularly preferably 7.2 mm or more. (Db
If + Dc) exceeds the above range, the resilience performance may be insufficient. From this viewpoint, (Db + Dc) is 9.5.
mm or less is more preferable, and 9.0 mm or less is particularly preferable.

FIG. 2 is a front view showing the golf ball 1 of FIG. 1, and FIG. 3 is a plan view showing the golf ball 1 of FIG. As is clear from these figures, this golf ball 1 has four kinds of dimples 5, namely, A dimples, B dimples, C dimples and D dimples. All the dimples 5 are circular dimples. A
The dimples have a diameter of 4.085 mm, the B dimples have a diameter of 3.815 mm, the C dimples have a diameter of 3.450 mm, and the D dimples have a diameter of 2.6.
It is 00 mm. 2 and 3, what is indicated by the symbol L is a great circle that divides the surface of the golf ball 1 into eight spherical triangles. 2 and 3, the type of the dimple 5 is shown for one spherical triangle. The dimple 5 pattern identical to this dimple 5 pattern is also provided for the other seven spherical triangles.

FIG. 4 is an enlarged sectional view showing a part of the golf ball 1 shown in FIG. In this figure, the vicinity of the dimple 5 is shown. The dimple surface Sd is recessed from the virtual spherical surface Sp (the surface of the golf ball 1 when it is assumed that the dimple 5 does not exist). Reference numeral T in FIG.
A straight line is drawn so as to contact both sides of the dimple 5. The contact point P is a point on the dimple edge (outline of the dimple 5). The distance between the contacts P and P is the diameter Di of the dimple 5. In FIG. 4, a plane which is a plane perpendicular to the paper surface and which includes the straight line T is
It is a plane including the edges of the dimples 5.

The distance between the deepest part of the dimple surface Sd and the plane including the edge of the dimple 5 is the depth d1. The maximum distance between the virtual spherical surface Sp and the plane including the edge of the dimple 5 is the depth d2. The sum of the depth d1 and the depth d2 is the total depth de. The volume of the space surrounded by the plane including the edge of the dimple 5 and the dimple surface Sd is the volume vb. The volume of the space surrounded by the plane including the edge of the dimple 5 and the virtual spherical surface Sp is the volume vt. The total sum of the volumes vb of all the dimples 5 is Vb. The total sum of the volumes vt of all the dimples 5 is Vt. Ratio of Vt to Vb (Vt / V
b) is Y.

The ratio of the total area of the region surrounded by the edge of the dimple 5 on the virtual spherical surface to the surface area of the virtual spherical surface is X. As shown in FIG. 4, when the edge of the dimple 5 does not exist on the virtual spherical surface, the total area of the region surrounded by the portion immediately above the edge of the dimple 5 (the portion including the point P ′) on the virtual spherical surface is , X.

The value of (Y-0.5X) is 0.20 or more and 0.37 or less. As a result, the trajectory of the golf ball 1 is optimized and the reduction in flight distance is suppressed, even though the mid layer 3 is relatively soft. (Y-0.
If the value of 5X) is less than the above range, the trajectory may be too low and the flight distance may be insufficient. From this viewpoint, (Y-
The value of (0.5X) is more preferably 0.21 or more, 0.2
Particularly preferred is 3 or more. If the value of (Y-0.5X) exceeds the above range, the trajectory may be blown up and the flight distance may be insufficient. From this viewpoint, the value of (Y-0.5X) is more preferably 0.35 or less, and particularly preferably 0.33 or less.

The diameter Di of the dimple 5 is usually 2.0 m.
It is set in the range of m or more and 6.0 mm or less. If the diameter Di is less than the above range, the dimple effect may be insufficient. From this viewpoint, the diameter Di is more preferably 2.2 mm or more, and particularly preferably 2.3 mm or more. If the diameter Di exceeds the above range, not only the appearance of the golf ball 1 may be deteriorated, but also the golf ball 1 may be hard to roll straight. From this viewpoint, the diameter Di is more preferably 5.5 mm or less, and particularly preferably 5.0 mm or less. Dimple 5
Has a total depth de of 0.10 mm or more and 0.40 mm or less,
Further, it is 0.12 mm or more and 0.35 mm or less, and particularly 0.13 mm or more and 0.33 mm or less.

From the viewpoint of improving flight distance by promoting turbulent transition, it is preferable to provide two or more kinds of dimples 5 having different diameters Di or depth de from each other. Here, “different in diameter” means a state in which the diameter difference is 0.15 mm or more. “Different total depth” means that the difference in total depth is 0.
It means a state of 005 mm or more. The number of types of dimples 5 is usually 10 or less.

The depth d1 of the dimple type having the smallest diameter (D dimple in the embodiment of FIG. 2) is equal to that of another dimple type (any one of A dimple, B dimple and C dimple in the embodiment of FIG. 2). It is preferably larger than the depth d1. This promotes turbulent transition.

Non-circular dimples may be formed instead of or together with the circular dimples.
Since the edges of non-circular dimples do not lie on a plane,
The volume vb and the volume vt cannot be calculated exactly. In the case of a non-circular dimple, a circle having the same area as that of its planar shape (a contour shape when the dimple is viewed from the normal direction) is assumed, and a circular dimple having this circle as a planar shape is assumed. For convenience, the volume of the region surrounded by the plane including the edge and the virtual spherical surface is the volume vt of the non-circular dimple. In addition, from the volume of the region surrounded by the phantom spherical surface and the surface of the dimple to the volume v
For convenience, the value obtained by subtracting t is the volume vb.

The total value of the volume Vb and the volume Vt is 480
mm ³ or more 620 mm ³ or less. If the total value is less than the above range, the trajectory of the golf ball 1 may be too high and the flight distance may be insufficient. From this perspective,
The total value is more preferably 490 mm ³ or more, 500 mm
Particularly preferred is ³ or more. If the total value exceeds the above range,
The trajectory of the golf ball 1 may be too low and the flight distance may be insufficient. From this viewpoint, the total value is 610 mm.
³ or less is more preferable, and 600 mm ³ or less is particularly preferable.

X is preferably 0.70 or more and 0.90 or less. When X is less than the above range, the effect of the dimple 5 that disturbs the flow of air is small, and the flight performance of the golf ball 1 may be insufficient. From this viewpoint, X is more preferably 0.72 or more, and particularly preferably 0.75 or more. When X exceeds the above range, the trajectory tends to blow up. From this viewpoint, X is more preferably 0.86 or less, and particularly preferably 0.83 or less.

The total number of dimples 5 is 300 or more and 50 or more.
0 or less is preferable. If the total number is less than the above range, X
It may be difficult to make the shape of the golf ball 1 substantially spherical while maintaining the value of (1) in a desired range (that is, the smoothness of the surface of the golf ball 1 is impaired). From this viewpoint, the total number is more preferably 320 or more, and 360 is more preferable.
More than one is particularly preferable. If the total number exceeds the above range, the individual dimples 5 may become small and the effect of disturbing the air flow may be insufficient. From this perspective, the total number is 4
50 or less is more preferable, and 440 or less is particularly preferable.

[0064]

EXAMPLES The effects of the present invention will be clarified below based on Examples, but the present invention should not be construed in a limited way based on the description of the Examples.

Example 1 100 parts of polybutadiene, 26 parts of zinc acrylate, 20 parts of zinc oxide, an appropriate amount of barium sulfate, 0.5 parts of diphenyl disulfide and 0.8 part of dicumyl peroxide were kneaded in a closed kneader. Then, a rubber composition was obtained. This rubber composition was put into a mold having a spherical cavity, heated to 160 ° C. and held for 25 minutes,
A core with a diameter of 36.3 mm was obtained. The compounding amount of barium sulfate was adjusted so that the mass of the golf ball was 45.4 g.

Next, an ionomer resin (HIMILAN 16
05) 27.5 parts, another ionomer resin (Himilan 1706) 27.5 parts and styrene thermoplastic elastomer (Lavalon SR04) 45 parts were kneaded to obtain a resin composition. On the other hand, a core was put into a mold having a spherical cavity, and the resin composition melted by heating was injected around the core to mold an intermediate layer having a thickness of 1.6 mm.

Next, an ionomer resin (HIMILAN 16
05) 47.5 parts, another ionomer resin (Himilan 1706) 47.5 parts, styrene thermoplastic elastomer (Lavalon SR04) 5 parts and titanium oxide 3 parts were kneaded to obtain a resin composition. On the other hand, with a spherical cavity,
A sphere consisting of a core and an intermediate layer is put into a molding die having a large number of protrusions on the cavity surface, and the resin composition melted by heating is injected around the sphere to have a thickness of 1.6 mm.
Molded cover. Simultaneously with the molding of the cover, dimples having a shape in which the shape of the convex portion was reversed were formed. The dimple specifications are I shown in Table 3. The dimple pattern of this specification I is shown in FIGS. 2 and 3. The Shore D hardness of the cover is 61. The golf ball of Example 1 was obtained by applying a coating around this cover.

[Examples 2 to 5 and Comparative Examples 1 to 6] Example 1 except that the core formulation, vulcanization conditions, intermediate layer formulation and dimple specifications were changed as shown in Tables 1 to 4 below. Similarly, golf balls of Examples 2-5 and Comparative Examples 1-6 were obtained. The dimple patterns of specifications II to V and the dimple pattern of specification I have different dimple sizes, but the positions of the dimples are the same.

[Measurement of Core Hardness] The surface hardness of the core was measured using a spring type hardness meter (Shore D type). Further, the surface hardness and the internal hardness of the core were measured using a spring hardness meter (JIS-C type), and the hardness difference was calculated.
The results are shown in Table 4 below.

[Measurement of Hardness of Intermediate Layer] A sheet having a thickness of 2.0 mm was formed by hot pressing from the same resin composition as that used for the intermediate layer. This sheet was kept in an environment of 23 ° C. for 2 weeks. Three sheets were stacked and the hardness was measured using a spring type hardness meter (Shore D type).

[Measurement of Repulsion Coefficient] A hollow cylinder made of aluminum having a mass of 200 g was used in a golf ball at 40 m / m.
It collided at a speed of s. Then, the speed of the hollow cylinder before and after the collision and the speed of the golf ball after the collision are measured,
The coefficient of restitution of the golf ball was determined according to the law of conservation of momentum. The index when the coefficient of restitution of the golf ball of Comparative Example 1 is 1.00 is shown in Table 4 below.

[Flying Distance Test] A driver (W1) having a swing machine (manufactured by Trutemper Co., Ltd.) equipped with a metal head.
Was mounted, the machine condition was adjusted so that the head speed was 40 m / s, and the golf ball was hit.
Then, the total flight distance (the distance from the hitting point to the point where the golf ball stopped) was measured. The average values of the total flight distances measured for five golf balls are shown in Table 4 below.

[Evaluation of Shot Feeling] Ten female golfers were made to have a driver with a metal head attached, and hit with a golf ball. Then, the quality of hitting (the degree of impact at the time of hitting) was evaluated. When there are 8 or more golfers who are evaluated as good, "◎", when 6 or more and 7 or less, "○", when 4 or more and 5 or less, "△", when 3 or less Was designated as "x". The results are shown in Table 4 below.

[0074]

[Table 1]

[0075]

[Table 2]

[0076]

[Table 3]

[0077]

[Table 4]

As shown in Table 4, the golf balls of the respective examples are excellent in shot feeling and the flight distance is comparable to that of the golf balls of the comparative examples. From this evaluation result, the superiority of the present invention is clear.

[0079]

As described above, the golf ball of the present invention provides a soft shot feeling by the relatively soft intermediate layer when hit by a golfer having a low head speed. Moreover, in this golf ball, dimples suppress the reduction in flight distance due to the soft mid layer.

[Brief description of drawings]

FIG. 1 is a sectional view showing a golf ball according to an embodiment of the present invention.

FIG. 2 is a front view showing the golf ball of FIG.

FIG. 3 is a plan view showing the golf ball of FIG. 1.

FIG. 4 is an enlarged cross-sectional view showing a part of the golf ball of FIG.

[Explanation of symbols]

1 ... golf ball 2 ... core 3 ... Middle layer 4 ... Cover 5 ... Dimples A ... A dimple B ... B dimple C ... C dimple D ... D dimple E ... E dimple L ... Great circle

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Seiichiro Endo             3-6-9 Wakihama-cho, Chuo-ku, Kobe-shi, Hyogo               Sumitomo Rubber Industries, Ltd.

Claims (6)

[Claims] 1. A core, a middle layer made of a synthetic resin composition and located outside the core, and a cover located outside the middle layer, wherein a large number of dimples are formed on the surface of the cover. In the formed golf ball, the amount of compressive deformation of the core is Dc, the amount of compressive deformation of the sphere including the core and the intermediate layer is Ds, and the dimple edge of the virtual spherical surface with respect to the surface area of the virtual spherical surface is The ratio of the total area of the enclosed area is X, the total volume of the space surrounded by the plane including the dimple edge and the surface of the dimple is Vb, and the plane including the dimple edge and the virtual spherical surface When the total volume of the space surrounded by is Vt and the ratio of Vt to Vb (Vt / Vb) is Y, the ratio (Ds / Dc) is 0.90 or more and 0.98 or less. ,
A golf ball having a value of (Y-0.5X) of 0.20 or more and 0.37 or less. 2. The compression deformation amount Dc of the core is 3.5 mm.
The golf ball according to claim 1, wherein the amount of compressive deformation Ds of the sphere consisting of the core and the mid layer is 3.0 mm or more and 6.5 mm or less. 3. The golf ball according to claim 1, wherein the Shore D hardness of the intermediate layer is larger than 35 and smaller than the Shore D hardness of the core surface. 4. The thickness of the intermediate layer is 1.0 mm or more.2.
The golf ball according to any one of claims 1 to 3, which has a diameter of 5 mm or less. 5. The golf ball according to claim 1, wherein the base polymer of the intermediate layer contains an ionomer resin as a main component. 6. The base polymer of the intermediate layer contains an ionomer resin and a thermoplastic elastomer, and the mass ratio of the ionomer resin to the thermoplastic elastomer is 5%.
The golf ball according to claim 5, which is 0/50 or more and 95/5 or less.