golf ball

Abstract

To provide a golf ball capable of improving a carry in a sure manner with a configuration in which bottom surfaces of dimples are curved convexly toward an outside direction of the golf ball.SOLUTION: A golf ball of the present invention includes a core and a cover positioned outside the core having a plurality of dimples 10 on a surface. A bottom surface 14 of the dimple has a shape curved convexly toward an outside direction of the golf ball. The convex part 15 has a spherical crown shape with a curvature radius R of 20-50 mm. A depth d in a central convex part of the bottom surface of the dimple is a vertical distance to the highest point of the convex part with a line S connecting both ends 12 of an outer peripheral edge of the dimple as a reference. A volume occupancy ratio VR of the dimples is less than 0.75. Relationships between Shore D hardness H of a cover material and the depth d (unit: mm) satisfy a following formula 1: (H-78) / (-300)>d.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a golf ball.

Background Art

[0002] It is well known that when a golf ball is struck, backspin is applied to the golf ball. If too much backspin is applied in a driver shot, the ball tends to balloon, so in order to increase the flight distance, it is generally required to reduce the amount of backspin. In order to reduce the amount of backspin, golf balls have been proposed that can increase the frictional force with the face during a driver shot.

[0003] For example, in Japanese Patent Application Laid-Open No. 2017-006555, the shape of a plurality of dimples formed on the surface of a golf ball is such that the bottom surface of the dimple is curved convexly toward the outside of the golf ball, and the deflection amount H of the golf ball when a predetermined load is applied to the golf ball, the virtual plane area S when there are no dimples on the golf ball surface, and the relationship between the pressurized area PS, which is the area of the golf ball in contact with the plane when a predetermined load is applied, satisfy a predetermined formula. A golf ball is described.

[0004] Also, in Japanese Patent Application Laid-Open No. 2017-079905, a golf ball includes a core, a cover, and at least one intermediate layer between them. The value obtained by subtracting the surface hardness of the intermediate layer-coated sphere from the surface hardness of the ball, and the value obtained by subtracting the core surface hardness from the surface hardness of the intermediate layer-coated sphere are each within a predetermined range. In the core hardness distribution, the hardness at the core center, the hardness at a position 5 mm from the core center, the hardness at a position 10 mm from the core center, the hardness at a position 15 mm from the core center, and the hardness of the core surface are each within a predetermined range. The value obtained by subtracting the core center hardness from the core surface hardness is within a predetermined range, and a golf ball in which the relationship V / H between the initial ball velocity V and the deflection amount H of the golf ball when a predetermined load is applied to the golf ball is within a predetermined range is described.

[0005] Furthermore, Japanese Patent Publication No. 2017-086579 describes a golf ball comprising a two-layer core consisting of an inner layer and an outer layer, a cover, at least one intermediate layer between them, and a coating layer on the surface of the cover, wherein the core hardness distribution satisfies two predetermined formulas, with the hardness Cc at the center of the inner core, the hardness C10 at a position 10 mm from the center of the inner core, the hardness Cs on the surface of the inner core, and the hardness Css on the surface of the outer core, and furthermore, the surface hardness of the sphere with the intermediate layer covering the core being higher than the surface hardness of the ball. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2017-006555 [Patent Document 2] Japanese Patent Publication No. 2017-079905 [Patent Document 3] Japanese Patent Publication No. 2017-086579 [Overview of the project] [Problems that the invention aims to solve]

[0007] All three of the above-mentioned Japanese Patent Publications No. 2017-006555, 2017-079905, and 2017-086579 describe the arrangement of dimples having a shape in which the bottom surface of the dimple is curved convexly toward the outside of the golf ball. However, the inventors have found that such dimples, due to the aerodynamic disadvantage of the convex shape, may not necessarily contribute to an improvement in actual flight distance even if the frictional force increases and the amount of backspin decreases due to the convex shape. Furthermore, the frictional force of such dimples with a convex bottom surface toward the golf club is affected by the material hardness of the cover, but this is not specifically mentioned in the above-mentioned documents.

[0008] Therefore, the present invention aims to provide a golf ball that can reliably improve flight distance by having a configuration in which the bottom surface of the dimples is curved in a convex shape toward the outside of the golf ball. [Means for solving the problem]

[0009] To achieve the above objective, the present invention provides a golf ball comprising a core and a cover located outside the core and having a plurality of dimples on its surface, wherein the bottom surface of the dimples has a portion that is curved in a convex shape toward the outward direction of the golf ball, and this convex portion is a spherical cap shape with a radius of curvature R of 20 to 50 mm, the depth d of the convex portion of the bottom surface of the dimple is the vertical distance from the line S connecting both ends of the outer edge of the dimple to the highest point of the convex portion, the volume occupancy VR of the dimple is less than 0.75, and the relationship between the Shore D hardness H of the cover material and the depth d (unit: mm) is given by the following formula 1: (H-78) / (-300)>d (Formula 1) It satisfies the following conditions.

[0010] The Shore D hardness of the cover material may be set to 50-60.

[0011] An intermediate layer may be further provided between the core and the cover, and the Shore D hardness of the material of the intermediate layer may be 55 or higher.

[0012] The Shore D hardness of the intermediate layer material may be higher than that of the cover material.

[0013] A coating layer located on the outside of the cover may be further provided, and the coating layer may contain matte particles, and the average surface roughness Ra of the coating layer may be 0.5 to 1.0.

[0014] The dimples having a spherical crown shape with a radius of curvature R of 20 to 50 mm may account for 50% or more of the total number of dimples on the cover surface.

[0015] In addition to the dimples having a convex spherical cap portion with a radius of curvature R of 20 to 50 mm, dimples having a convex spherical cap portion with a radius of curvature R of 12 mm or less may be arranged, and the dimples having a convex spherical cap portion with a radius of curvature R of 12 mm or less may be 1 to 10% of the total number of dimples on the cover surface.

Effect of the Invention

[0016] According to the present invention, when the bottom surface of the dimple is convexly curved in the outward direction of the golf ball and this convex portion has a spherical cap shape with a radius of curvature R of 20 to 50 mm, by defining the relationship between the depth d of the convex portion at the bottom of the dimple and the material hardness of the cover as in the above formula 1, the contact area with the club face in a full shot (shots from a driver to a middle iron) can be increased, and the amount of backspin can be reduced. Further, such a shape in which the bottom surface of the dimple is convexly curved is disadvantageous in terms of aerodynamic characteristics, and although it is not possible to achieve an improvement in the flight distance of the golf ball only by reducing such an amount of backspin, by reducing the volume occupancy rate VR of the dimple to less than 0.75, the trajectory of the golf ball rises and an improvement in the flight distance can be achieved.

Brief Description of the Drawings

[0017] [Figure 1] It is a perspective view showing an embodiment of a golf ball according to the present invention. [Figure 2] It is an enlarged cross-sectional view of one dimple of the golf ball shown in FIG. 1. [Figure 3] It is a perspective view showing an example of a golf ball of Comparative Example 5. [Figure 4] It is an enlarged cross-sectional view of one dimple of the golf ball shown in FIG. 3. [Figure 5] It is a photograph showing the dimples of the golf ball of Example 1. [Figure 6] It is a photograph showing the dimples of the golf ball of Comparative Example 5.

Best Mode for Carrying Out the Invention

[0018] Hereinafter, referring to the accompanying drawings, an embodiment of a golf ball according to the present invention will be described, but the present invention is not limited thereto.

[0019] As an embodiment of the golf ball according to the present invention, as shown in FIG. 1, it includes a core (not shown) and a cover located outside the core and having a plurality of dimples 10 on its surface. Among the surface of the golf ball 1, the portion between the plurality of dimples 10 is usually called the land portion 20. The land portion 20 constitutes the spherical surface of the golf ball 1, and thus the land portion 20 has a curved surface.

[0020] The planar shape of the dimple 10 formed on the surface of the golf ball 1 (that is, the shape of the outer peripheral edge 12 of the dimple 10 or the boundary line between the dimple 10 and the land portion 20 as viewed directly above the dimple) may be a circular shape, a polygonal shape (for example, a regular hexagon), a non-circular shape, etc. In this embodiment, the planar shape is a polygonal shape (substantially regular hexagon). The diameter of a circular dimple and, in the case of a polygonal dimple, the diameter of its circumscribed circle are preferably within the range of 2 to 5 mm. It is not necessary for the diameters of all the dimples formed on the surface of the golf ball to be the same, and they may be different as long as they are within the range of 2 to 5 mm. For example, it is preferable to arrange at least three types of dimples having different sizes, whereby the dimples can be arranged uniformly without gaps on the spherical surface of the golf ball.

[0021] Furthermore, the dimple 10 in this embodiment has a shape in which a part of its bottom surface is curved convexly toward the outside of the ball. A cross-sectional view of the dimple 10 along its diameter is shown in Figure 2. As shown in Figure 2, the dimple 10 has a curved bottom surface 14 that connects from one end to the other of its outer peripheral edge 12. This bottom surface 14 has a central region that is curved convexly toward the outside of the ball, i.e., a central convex portion 15, and an annular region on its outer circumference that is curved concavely toward the outside of the ball.

[0022] The central convex portion 15 has a spherical cap shape (the surface shape of the portion obtained by cutting a sphere with a single plane) at its apex, and this spherical cap shape has a radius of curvature R of 20 to 50 mm. If the radius of curvature R of the spherical cap shape of the central convex portion 15 exceeds 50 mm, even if the depth d of the central convex portion 15, which will be described later, is set to a predetermined depth, the central part of the central convex portion 15 cannot make sufficient contact with the clubface during a full shot, similar to the case where the apex of the central convex portion 35 is flat as shown in Figure 3. On the other hand, if the radius of curvature R is less than 20 mm, the part of the central convex portion 15 other than the central part cannot make sufficient contact with the clubface. By making the central convex portion 15 a spherical cap shape with a radius of curvature R of 20 to 50 mm, the entire central convex portion 15 can make sufficient contact with the clubface during a full shot, thereby reducing the amount of backspin on the golf ball and improving distance. The upper limit of the radius of curvature R is preferably 45 mm or less, and more preferably 40 mm or less. The lower limit of the radius of curvature is preferably 25 mm or more, and more preferably 30 mm or more.

[0023] The diameter of the spherical cap-shaped region of the central convex portion 15, that is, the distance W between its two ends 17, is preferably in the range of 35 to 65, more preferably in the range of 40 to 60, and even more preferably in the range of 45 to 55, where the distance from the outer edge 12 of the dimple to the central point 16 is 100.

[0024] The depth d of the central convex portion 15 of the dimple 10 is the vertical distance from the line S connecting the two ends of the outer edge 12 of the dimple to the highest point (center point 16) of the central convex portion 15. The relationship between the depth d (unit: mm) of the central convex portion 15 and the Shore D hardness H of the material forming the cover, described later, is given by the following equation 1: (H-78) / (-300)>d (Formula 1) The following conditions must be met. That is, if the depth d is deeper than the value of (H-78) / (-300), the contact area with the face of the golf club will not be sufficient, and the frictional force cannot be improved. The value of (H-78) / (-300)-d is preferably 0.002 or more, and more preferably 0.005 or more. By setting the depth d to such a value, excellent frictional force can be reliably obtained depending on the hardness of the cover material. There is no particular upper limit to the value of (H-78) / (-300)-d, but it is preferably 0.030 or less, and more preferably 0.025 or less.

[0025] The depth is greatest at the deepest points 18 located on both sides of the central convex portion 15, and the bottom surface between these points and the land portion 20 has a convex shape that curves outward from the ball. The position of the deepest point 18 on the plane is preferably in the range of 20 to 45, more preferably in the range of 25 to 40, and even more preferably in the range of 30 to 35, where the distance from the outer edge 12 of the dimple to the central point 16 is 100.

[0026] The depth D of the dimple 10 varies depending on the depth d of the central convex portion 15. For example, it is preferable to make the dimple 10 at least 0.025 mm deeper than the depth d of the central convex portion 15, and more preferably at least 0.030 mm deeper. The upper limit of the depth D of the dimple 10 is not particularly limited, but it is preferable to make it at least 0.200 mm deeper than the depth d of the central convex portion 15, and more preferably at least 0.150 mm deeper.

[0027] Not all dimples formed on the surface of a golf ball need to have a central convex portion with a spherical cap shape having a radius of curvature R of 20 to 50 mm. Preferably, 50% or more of the dimples have a predetermined central convex portion, more preferably 70% or more, even more preferably 80% or more, and most preferably 90% or more. Of course, all dimples may also have this portion. From the viewpoint of exhibiting excellent aerodynamic isotropy and air resistance, it is preferable that dimples with such central convex portions be evenly distributed across the entire golf ball.

[0028] Furthermore, it is not necessary for all dimples with a spherical, centrally convex portion to have the same radius of curvature R; they may have different radii of curvature R within the range of 20 to 50 mm. For example, the total number of dimples formed on the surface of a golf ball could be configured such that 1-10% have a radius of curvature R of 20 mm or more and less than 30 mm, 20-40% have a radius of curvature R of 30 mm or more and less than 40 mm, and 30-50% have a radius of curvature R of 40 mm or more and 50 mm or less. Also, when arranging dimples of different diameters on the surface of a golf ball, in order to achieve the same effect as above for the smaller diameter dimples, a centrally convex portion with a spherical shape and a radius of curvature R smaller than that of the above, for example, 2 to 12 mm, can be formed on the bottom surface of these smaller dimples. In other words, the surface of a golf ball may have dimples with a spherical, centrally convex portion with a radius of curvature R of 20 to 50 mm, as well as dimples with a spherical, centrally convex portion with a radius of curvature R of 2 to 12 mm. For example, the total number of dimples formed on the surface of a golf ball may be such that 1 to 10% of them have a radius of curvature R of 2 to 12 mm.

[0029] The upper limit of the total number of dimples is not limited to this, but is preferably 500 or less, and more preferably 450 or less. The lower limit of the total number of dimples is not limited to this, but is preferably 250 or more, and more preferably 300 or more.

[0030] The dimple volume occupancy ratio VR (i.e., the ratio of the total dimple volume formed below the plane surrounded by the edges of the dimples to the virtual spherical volume of a golf ball assuming no dimples) is less than 0.75%. As mentioned above, if the dimples have a centrally convex shape, it is disadvantageous in terms of aerodynamic characteristics. By setting the dimple volume occupancy ratio VR to less than 0.75%, the trajectory of the golf ball can be raised and the distance can be improved. The dimple volume occupancy ratio VR is preferably 0.73% or less, and more preferably 0.70% or less. The lower limit of the dimple volume occupancy ratio VR is not particularly limited, but for example, it is preferably 0.65% or more, and more preferably 0.68% or more.

[0031] The surface area ratio SR of the dimples (i.e., the ratio of the total surface area of ​​the dimples to the total surface area of ​​the hypothetical sphere of the golf ball assuming there are no dimples) is preferably 70% or more, more preferably 75% or more, and even more preferably 80% or more. The upper limit of the surface area ratio SR of the dimples is not particularly limited, but it is preferably 99% or less.

[0032] The materials used to form the cover are not limited to those listed above, but can include ionomer resins, polyurethane-based thermoplastic elastomers, thermosetting polyurethanes, or mixtures thereof. In addition to the main components mentioned above, other thermoplastic elastomers, polyisocyanate compounds, fatty acids or their derivatives, basic inorganic metal compounds, fillers, etc., can be added to the cover.

[0033] The Shore D hardness H of the material forming the cover satisfies Equation 1, as described above. Therefore, although it depends on the depth d of the central convex portion of the dimple, the Shore D hardness H of the material forming the cover is preferably 50 or higher, and more preferably 53 or higher. Furthermore, the Shore D hardness H of the material forming the cover is preferably 65 or lower, more preferably 62 or lower, and even more preferably 60 or lower. By setting the value within this range, the appropriate amount of spin can be achieved for shots from the driver to the mid-irons.

[0034] The lower limit of the cover thickness is not limited to this, but is preferably 0.2 mm or more, and more preferably 0.4 mm or more. The upper limit of the cover thickness is preferably 4 mm or less, more preferably 3 mm or less, and even more preferably 2 mm or less.

[0035] The core can be formed from a rubber composition containing rubber as its main component. This main component rubber (base rubber) can be a wide range of synthetic and natural rubbers, but is not limited to these. Examples include polybutadiene rubber (BR), styrene-butadiene rubber (SBR), natural rubber (NR), polyisoprene rubber (IR), polyurethane rubber (PU), butyl rubber (IIR), vinyl-polybutadiene rubber (VBR), ethylene-propylene rubber (EPDM), nitrile rubber (NBR), and silicone rubber. For example, 1,2-polybutadiene and cis-1,4-polybutadiene can be used as polybutadiene rubber (BR).

[0036] In addition to the base rubber, the core may optionally contain, for example, co-crosslinking agents, crosslinking initiators, fillers, antioxidants, isomerizers, compounding accelerators, sulfur, and organic sulfur compounds. Furthermore, instead of rubber, a resin may be used as the main component; for example, a thermoplastic elastomer, an ionomer resin, or a mixture thereof may be used.

[0037] The co-crosslinking material is not limited to the above, but it is preferable to use, for example, an α,β-unsaturated carboxylic acid or its metal salt. Examples of α,β-unsaturated carboxylic acids or their metal salts include acrylic acid, methacrylic acid, and their zinc salts, magnesium salts, and calcium salts. The blending of the co-crosslinking material is not limited to the above, but for example, with 100 parts by weight of the base rubber, it is preferably about 5 parts by weight or more, and more preferably about 10 parts by weight or more. Furthermore, the blending of the co-crosslinking material is preferably about 70 parts by weight or less, and more preferably about 50 parts by weight or less.

[0038] While not limited to these, organic peroxides are preferred as crosslinking initiators, examples include dicumyl peroxide, t-butyl peroxybenzoate, di-t-butyl peroxide, and 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane. The amount of crosslinking initiator is not limited, but for example, based on 100 parts by weight of the base rubber, it is preferably about 0.10 parts by weight or more, more preferably about 0.15 parts by weight or more, and even more preferably about 0.30 parts by weight or more. Furthermore, the amount of crosslinking initiator is preferably about 8 parts by weight or less, and more preferably about 6 parts by weight or less.

[0039] The filler can be, but is not limited to, silver, gold, cobalt, chromium, copper, iron, germanium, manganese, molybdenum, nickel, lead, platinum, tin, titanium, tungsten, zinc, zirconium, barium sulfate, zinc oxide, manganese oxide, etc. The filler is preferably in powder form. The composition of the filler is not limited to, but for example, with 100 parts by weight of the base rubber, it is preferably about 1 part by weight or more, more preferably about 2 parts by weight or more, and even more preferably about 3 parts by weight or more. Furthermore, the composition of the filler is preferably about 100 parts by weight or less, more preferably about 80 parts by weight or less, and even more preferably about 70 parts by weight or less.

[0040] While not limited to these, commercially available products such as Nocrack NS-6 (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) can be used as the antioxidant. While not limited to these, the amount of the antioxidant is preferably about 0.1 parts by weight or more, and more preferably about 0.15 parts by weight or more, per 100 parts by weight of the base rubber. Furthermore, the amount of the antioxidant is preferably about 1.0 part by mass or less, and more preferably about 0.7 parts by mass or less.

[0041] The resilience of Core 40 can be improved by adding an organic sulfur compound (anti-corrosion agent). The organic sulfur compound is selected from thiophenols, thiocarboxylic acids, and their metal salts. Examples of thiophenols and thiocarboxylic acids include thiophenols such as pentachlorothiophenol, 4-t-butyl-o-thiophenol, 4-t-butylthiophenol, and 2-benzamidothiophenol, and thiocarboxylic acids such as thiobenzoic acid. Zinc salts are preferred as metal salts of these compounds. The amount of organic sulfur compound added is not limited to this, but is preferably about 0.5 parts by weight or more, and more preferably about 1 part by weight or more, based on 100 parts by weight of the base rubber. Furthermore, the amount of organic sulfur compound added is preferably about 3 parts by weight or less, and more preferably about 2 parts by weight or less.

[0042] The upper limit of the Shore D hardness of the core material is preferably 60 or less, more preferably 50 or less, and even more preferably 40 or less. On the other hand, the lower limit of the Shore D hardness of the core material is not limited to these limits, but is preferably 20 or more, and more preferably 30 or more. By setting the core material hardness within this range, the feel of the golf ball can be improved.

[0043] The lower limit of the core thickness is 4.5 mm or more, and more preferably 10 mm or more, in order to impart a predetermined rebound force to the golf ball. On the other hand, the upper limit of the core thickness is not particularly limited, but is preferably 25 mm or less, and more preferably 20 mm or less. Furthermore, the core is not limited to a single layer, and may consist of multiple layers, for example. In this case, it is preferable that the hardness of each layer of the core increases from the inside to the outside of the golf ball.

[0044] An intermediate layer (not shown) may be optionally provided between the core and the cover. By providing an intermediate layer, the appropriate amount of spin can be achieved for shots from the driver to the mid-irons.

[0045] While not limited to the materials listed below, it is preferable to use the following heated mixtures as the main material for the intermediate layer. By using this material for the intermediate layer, it is possible to reduce spin during impact and obtain a greater flight distance. (a) a binary random copolymer of olefin-unsaturated carboxylic acid and / or a metal ion neutralized product of a binary random copolymer of olefin-unsaturated carboxylic acid, (b) Olefin-unsaturated carboxylic acid-unsaturated carboxylic acid terranandic copolymer and / or metal ion neutralized product of olefin-unsaturated carboxylic acid-unsaturated carboxylic acid terranandic copolymer A base resin formulated so that the weight ratio is 100:0 to 0:100, (e) A non-ionomer thermoplastic elastomer blended with this base resin in a weight ratio of 100:0 to 50:50, For 100 parts by weight of the resin component containing the base resin and component (e), (c) 5 to 150 parts by weight of fatty acids and / or derivatives thereof having a molecular weight of 228 to 1500, (d) 0.1 to 17 parts by weight of a basic inorganic metal compound capable of neutralizing unneutralized acid groups in the base resin and component (c).

[0046] Furthermore, "main material" refers to material that accounts for 50% or more by weight, preferably 60% or more by weight, and more preferably 70% or more by weight, of the total weight of the intermediate layer.

[0047] The Shore D hardness of the material forming the intermediate layer is preferably 55 or higher, and more preferably 57 or higher. The Shore D hardness of the intermediate layer material is preferably higher than that of the cover material. This allows for an appropriate amount of spin in shots from the driver to the mid-irons. The upper limit of the Shore D hardness of the intermediate layer material is not particularly limited, but is preferably 65 or lower, and more preferably 63 or lower.

[0048] The thickness of the intermediate layer is not limited to this, but is preferably 0.5 mm or more, and more preferably 1 mm or more. Furthermore, the thickness of the intermediate layer 20 is preferably 10 mm or less, more preferably 5 mm or less, and even more preferably 3 mm or less.

[0049] A coating layer (also called a paint layer) (not shown) may be optionally provided on the surface of the cover. The coating layer is formed from a paint composition. The paint composition may also contain matte particles. The paint composition is not particularly limited, but for example, a urethane-based paint is preferred. Due to the need to withstand the harsh operating environment of golf balls, a two-component curing type urethane paint, in particular a non-yellowing urethane paint, is more preferable.

[0050] In the case of two-component curing urethane paints, it is preferable to use various polyols such as saturated polyester polyols, acrylic polyols, and polycarbonate polyols as the main component. As the curing agent, isocyanate, it is preferable to use non-yellowing polyisocyanates, such as adducts, burettes, or isocyanurates of hexamethylene diisocyanate, isophorone diisocyanate, or hydrogenated xylylene diisocyanate, or mixtures thereof.

[0051] Examples of matte particles include silica-based, melamine-based, and acrylic-based particles. Specifically, examples include silica, polymethyl methacrylate, polybutyl methacrylate, polystyrene, and polybutyl acrylate. Both organic and inorganic materials are acceptable, but silica is particularly preferred.

[0052] While the inclusion of such matte particles in the coating layer negatively impacts aerodynamic performance, in this embodiment, the dimple volume occupancy rate (VR) is less than 0.75, allowing the trajectory to rise and thus maintaining distance. When matte particles are included in the coating layer, the dimple volume occupancy rate (VR) may be set to less than 0.70. This further increases the trajectory and improves distance.

[0053] In terms of the specific surface area of ​​matte particles, considering quenching properties and applicability, the BET specific surface area should be 200-400 m². 2 It is preferable that the amount be / g, and 250-350m 2 A value of / g is more preferable. Furthermore, the average primary particle diameter of the matte particles is preferably 1.0 to 3.0 μm, and more preferably 2.0 to 2.8 μm, from the viewpoint of spin performance and quenching effect. If the average primary particle diameter exceeds 3.0 μm, the ball surface becomes rough, which may adversely affect the spin performance of the golf ball and reduce spin performance. On the other hand, if the average primary particle diameter is too small, the quenching effect may be reduced.

[0054] The amount of matte particles added is preferably 5 to 10 parts by mass per 100 parts by mass of the main component (total amount of resin component and solvent) of the coating layer's paint composition. If the amount is too high, the viscosity of the paint composition tends to increase, making it difficult to apply, and if it is too low, the quenching effect may be reduced. The average surface roughness Ra of the coating layer is preferably 0.5 to 1.0, from the viewpoint of balancing the amount of ball spin during approach and quenching. This surface roughness Ra of the coating film refers to the arithmetic mean roughness according to JIS B0601 (1994). [Examples]

[0055] A golf ball was manufactured with the configuration shown in Example 1 of Table 1. The core composition is shown in Table 3, the intermediate layer and cover composition is shown in Table 4, and the coating layer composition is shown in Table 5. All units are parts by weight. The dimple arrangement was the pattern shown in Figure 1. As shown in Figure 2, the shape of the bottom of the dimple was curved in a convex shape toward the outside of the ball in the central region, and this central convex portion was a spherical cap shape with a radius of curvature R in the range of 25 to 45 mm. More detailed specifications of the dimple are shown in Table 6.

[0056] [Table 1]

[0057] [Table 2]

[0058] [Table 3]

[0059] In Table 3, the polybutadiene is manufactured by JSR Corporation, trade name "BR01," and the zinc acrylate is manufactured by Nippon Shokubai Co., Ltd. Organic peroxide A is manufactured by NOF Corporation, trade name "Perkmill D," and organic peroxide B is manufactured by NOF Corporation, trade name "Peroxa C-40." The antioxidant is 2,2-methylenebis(4-methyl-6-butylphenol), manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "Nocrack NS-6." Zinc oxide is manufactured by Sakai Chemical Industry Co., Ltd., trade name "Zinc Oxide 3 Types." Pentachlorothiophenol zinc salt is manufactured by ZHEJIANG CHO&FU CHEMICAL.

[0060] [Table 4]

[0061] In Table 4, "HPF1000" is an ionomer resin manufactured by THE DOW CHEMICAL COMPANY. "Hymilan 1605" is an ionomer resin manufactured by Mitsui Dow Polychemicals. "AM7329" is an ionomer resin manufactured by Mitsui Dow Polychemicals. "Sarlyn 9320" is an ionomer resin manufactured by THE DOW CHEMICAL COMPANY.

[0062] [Table 5]

[0063] For the "polyol" main component in Table 5, a polyester polyol synthesized by the following method was used. First, 140 parts by mass of trimethylolpropane, 95 parts by mass of ethylene glycol, 157 parts by mass of adipic acid, and 58 parts by mass of 1,4-cyclohexanedimethanol were charged into a reaction apparatus equipped with a reflux condenser, dropping funnel, gas inlet tube, and thermometer. The mixture was heated to 200-240°C while stirring and heated (reacted) for 5 hours. Subsequently, a polyester polyol with an acid value of 4, a hydroxyl value of 170, and a weight-average molecular weight (Mw) of 28,000 was obtained. For the "matte particles," "Finesil X-35" manufactured by Maruo Calcium Co., Ltd. was used.

[0064] For the curing agent, we used "Isocyanate," a nurate (isocyanurate) form of hexamethylene diisocyanate (HMDI), specifically Asahi Kasei's product name Duranate TPA-100 (NCO content 23.1%, non-volatile content 100%). For both the main component and the curing agent, we used butyl acetate as the solvent. Using the above-described two-component curing urethane paint, we applied the paint to the surface of the dimpled cover using an air spray gun to form a paint layer.

[0065] [Table 6]

[0066] In Table 6, the dimples of types A to F all have a depth d in the central convex portion that is the same as the depth d value shown in Table 1, but the diameter of the dimple (the diameter of the circumscribed circle of the roughly hexagonal shape) differs depending on the radius of curvature R of the convex portion. The size of the dimples is smallest for type A, and increases sequentially from type B to type F. The dimple of type G is a conventional dimple formed by a support pin.

[0067] Tests were conducted to evaluate the spin rate and flight distance of a golf ball with the configuration described in Example 1. First, a driver club (Bridgestone Sports' "TourB XD-5" (W#1) (loft angle 9.5°)) was attached to a golf hitting robot, and a sample golf ball was struck at a head speed of 45 m / s to measure the backspin rate and flight distance. Next, a middle iron club (Bridgestone Sports' "TourB X-CB" (I#6)) was attached to the golf hitting robot, and a sample golf ball was struck at a head speed of 42 m / s to measure the backspin rate. The results are shown in Table 1.

[0068] For comparison, golf balls of Comparative Examples 2-4, shown in Table 2, were manufactured with the same configuration as Example 1, except that the material hardness of the cover, the volume occupancy rate (VR) of the dimples, and the depth d of the central convex portion of the dimples were appropriately changed to make them not satisfy the conditions of Equation 1. The spin rate and flight distance were evaluated in the same manner as in Example 1. The results are shown in Table 2. Note that the dimples of Comparative Examples 2-4 also had the same specifications as in Table 6, and in each example, the diameter of the A-G type dimples remained unchanged, while the depth d of the central convex portion was changed (the same applies to Examples 2-6 and Comparative Example 1, which will be described later).

[0069] As shown in Tables 1 and 2, the golf ball of Example 1, which had a dimple volume occupancy ratio VR of less than 0.75 and satisfied the condition (H-78) / (-300)>d in Equation 1, showed less backspin on driver shots and improved distance compared to Comparative Examples 2 and 3, which did not satisfy the condition in Equation 1 despite having a dimple volume occupancy ratio VR of less than 0.75. Furthermore, the backspin on mid-iron shots was also lower in Example 1 compared to Comparative Examples 2 and 3. Therefore, it is considered that distance on mid-iron shots can also be improved.

[0070] Furthermore, while the conditions of Equation 1 were met, Example 1 and Comparative Example 4 had nearly the same amount of backspin on driver shots compared to Comparative Example 4, where the volume occupancy ratio VR was 0.75 or higher. However, Example 1, with a volume occupancy ratio VR of 0.70, was able to improve the distance. Also, the amount of backspin on mid-irons was nearly the same for Example 1 as for Comparative Example 4. Therefore, it is considered that Example 1, with a volume occupancy ratio VR of 0.70, can also improve the distance on mid-irons.

[0071] Furthermore, golf balls of Examples 2 and 3, shown in Table 1, were manufactured with the same configuration as Example 1, except that the hardness of the cover material was the same as that of Comparative Examples 2 and 3, and the volume occupancy rate VR of the dimples and the depth d of the central convex portion of the dimples were changed to satisfy the conditions of Equation 1. Tests were then conducted to evaluate their spin rate and flight distance in the same manner as Example 1. The results are shown in Table 1.

[0072] As shown in Tables 1 and 2, Examples 2 and 3 showed less backspin on driver shots and improved distance compared to Comparative Examples 2 and 3, which did not satisfy the conditions of Equation 1. Furthermore, the amount of backspin on mid-iron shots was also lower in Examples 2 and 3 compared to Comparative Examples 2 and 3. Therefore, it is considered that distance with mid-iron shots can also be improved.

[0073] Table 2 shows a golf ball of Comparative Example 1 with the same configuration as Example 1, except that the hardness of the cover material is the same as in Example 1, and the volume occupancy rate VR of the dimples and the depth d of the central convex portion of the dimples are changed so that the conditions of Equation 1 are not met. In a simulation that takes the above test results into account, as shown in Table 2, Comparative Example 1 has a depth d of the convex portion that is too deep, resulting in a smaller contact area with the club, more backspin on driver shots and a decrease in distance compared to Example 1. The amount of backspin on mid-iron shots is also greater in Comparative Example 1 than in Example 1, so it is thought that the distance will also decrease.

[0074] Furthermore, a golf ball of Comparative Example 5 was manufactured with the same configuration as Example 1, except that the depth d of the central convex portion of the dimple was kept the same as that of Example 1, while the apex of the central convex portion 35 was made flat, as shown in Figures 3 and 4. More specifically, the bottom surface 34 of the outer peripheral edge 32 of the dimple 30, which connects from one end to the other, has a central convex portion 35 formed in its central region, which curves convexly toward the outside of the ball, but its apex is flat. The distance W between the two ends 37 of this flat region is equivalent to the distance W between the two ends 17 of the spherical cap-shaped region shown in Figure 2. Also, the depth d of the flat region of the central convex portion 35 is based on the line S connecting the two ends of the outer peripheral edge 32 of the dimple, as in Figure 2. In the regions on both sides of the central convex portion 35, the curve is such that the depth D is maximized at its deepest point 38.

[0075] Table 7 shows more detailed specifications of the dimples. The H-M type dimples in Table 7 correspond to the A-F type dimples in Table 6, respectively, and have similar dimple diameters. The N type dimple is a conventional dimple formed by a support pin. Then, tests were conducted to evaluate the spin rate and flight distance, as in Example 1. The results are shown in Table 2.

[0076] [Table 7]

[0077] Furthermore, Figure 5 shows a photograph of the dimples formed when the golf ball of Example 1 was launched at a speed of 35 m / s and struck a transparent plate, and Figure 6 shows a photograph of the dimples formed when the golf ball of Comparative Example 5 was struck a transparent plate under similar conditions.

[0078] As shown in Figure 5, in Example 1, where the central convex portion of the dimple is spherical, almost the entire convex portion is in contact with the transparent plate. In contrast, as shown in Figure 6, in Comparative Example 5, where the central convex portion of the dimple is flat, the central part of the convex portion is not in sufficient contact with the transparent plate. Therefore, as shown in Table 2, although Comparative Example 5 satisfies Equation 1, which is the relationship between the material hardness of the cover and the depth d of the convex portion, and the volume occupancy rate VR of the dimple was less than 0.75, the contact area with the club face during a full shot was smaller than in Example 1, resulting in more backspin and a shorter distance with driver shots than in Example 1. Furthermore, the amount of backspin with middle irons was also greater in Comparative Example 5 than in Example 1, which is considered to be the reason for the shorter distance.

[0079] Furthermore, as shown in Table 8, golf balls of Reference Examples 1 and 2 were manufactured with dimples having flat convex portions, similar to Comparative Example 5, except that matte particles were incorporated into the coating layer, the conditions of Equation 1 were not met, and the volume occupancy rate VR of the dimples was set to 0.68 and 0.75. Tests were then conducted to evaluate their spin rate and flight distance, similar to Example 1.

[0080] [Table 8]

[0081] Reference Examples 1 and 2, which incorporated matte particles, both showed slightly more backspin on driver shots than Comparative Example 5. However, Reference Example 1, with a low volume occupancy rate (VR) of 0.68, showed improved distance, while Reference Example 2, with a high volume occupancy rate (VR) of 0.75, showed decreased distance. Similarly, while the backspin on middle irons was almost the same for Reference Examples 1 and 2, Reference Example 1, with its low volume occupancy rate (VR) of 0.68, showed improved distance, while Reference Example 2, with its high volume occupancy rate (VR) of 0.75, showed decreased distance.

[0082] Table 1 shows golf balls of Examples 4 and 5, which have the same configuration as Example 1, except that matte particles are incorporated into the coating layer and the volume occupancy ratio VR of the dimples and the depth d of the central convex portion of the dimples are appropriately changed. In a simulation that takes the above test results into account, as shown in Table 1, Examples 4 and 5 have almost the same amount of backspin on driver shots, but Example 4, with a volume occupancy ratio VR of 0.68, can achieve a greater increase in distance than Example 5, which has the same volume occupancy ratio VR as Example 1, which has a volume occupancy ratio VR of 0.72. In addition, the amount of backspin on middle irons was also almost the same for Examples 4 and 5. Therefore, it is considered that Example 4 is superior to Example 5 in terms of the improvement in distance on middle irons.

[0083] Table 1 shows a golf ball of Example 6, which has the same configuration as Example 1 except that the material hardness of the intermediate layer is lower than that of the cover. In a simulation that takes the above test results into account, Example 6, as shown in Table 1, has the same amount of backspin on driver shots as Example 1 and can maintain distance, but the amount of backspin on mid-irons is higher. Therefore, it is considered that the improvement in distance with mid-irons is inferior. [Explanation of Symbols]

[0084] 1. 3 golf balls 10, 30 dimples 12, 32 Outer edge 15, 35 Central convex part 20, 40 Rikubu

Claims

1. A golf ball comprising a core and a cover located outside the core and having a plurality of dimples on its surface, The bottom surface of the dimple has a central convex portion that is curved convexly toward the outside of the golf ball, and an outer convex portion that is curved convexly toward the outside of the golf ball in an annular region on the outer circumference of the central convex portion, from the deepest point of the dimple to the outer edge of the dimple, and the central convex portion has a spherical shape with a radius of curvature R of 20 to 50 mm. The dimples having a central convex portion in a spherical crown shape with a radius of curvature R of 20 to 50 mm account for 50% or more of the total number of dimples on the cover surface. The depth d of the central convex portion on the bottom surface of the dimple is the vertical distance from the line S connecting both ends of the outer edge of the dimple to the highest point of the central convex portion. The volume occupancy rate (VR) of the dimples is less than 0.75%. The relationship between the Shore D hardness H of the cover material and the depth d (unit: mm) is given by the following equation 1: (H-78) / (-300)>d...(Formula 1) A golf ball that meets the requirements.

2. The golf ball according to claim 1, wherein the Shore D hardness of the cover material is 50 to 60.

3. The golf ball according to claim 1, further comprising an intermediate layer between the core and the cover, wherein the Shore D hardness of the material of the intermediate layer is 55 or higher.

4. The golf ball according to claim 3, wherein the Shore D hardness of the intermediate layer material is higher than the Shore D hardness of the cover material.

5. The golf ball according to claim 1, further comprising a coating layer located on the outside of the cover, wherein the coating layer contains matte particles, the average surface roughness Ra of the coating layer is 0.5 to 1.0 μm, and the volume occupancy VR of the dimples is less than 0.70%.

6. The golf ball according to claim 1, wherein the volume occupancy rate (VR) of the dimples is 0.73% or less.

7. The golf ball according to claim 1, wherein, in addition to the dimples having a central convex portion of a spherical crown shape with a radius of curvature R of 20 to 50 mm, dimples having a central convex portion of a spherical crown shape with a radius of curvature R of 12 mm or less are arranged, and the dimples having a central convex portion of a spherical crown shape with a radius of curvature R of 12 mm or less account for 1 to 10% of the total number of dimples on the cover surface.

Images