JP4047261B2 - Golf ball - Google Patents

Description

  The present invention relates to a golf ball. More specifically, the present invention relates to a golf ball that includes a core and a cover and in which dimples are formed on the cover.

  Except for those manufactured for driving ranges, general golf balls have a core and a cover. The core includes a single solid rubber layer, two or more solid rubber layers, and a solid rubber layer and a synthetic resin layer.

  A large number of dimples are formed on the surface of the cover. The role of the dimples is to promote the turbulent transition of the boundary layer by disturbing the air flow around the golf ball when flying, thereby causing turbulent separation. By promoting the turbulent transition, the separation point of air from the golf ball is shifted backward, the drag coefficient (Cd) is decreased, and the flight distance of the golf ball is increased. Further, by promoting the turbulent transition, the difference between the peeling points on the upper side and the lower side of the golf ball due to backspin is promoted, and the lift force acting on the golf ball is increased.

  Various golf balls with improved dimple patterns intended to improve flight performance have been proposed. For example, Japanese Examined Patent Publication No. 58-50744 discloses a golf ball in which dimples are closely arranged so that the pitch between the dimples is as small as 1.62 mm or less. Japanese Patent Application Laid-Open No. 62-192181 discloses a golf ball in which dimples are closely arranged so that a new dimple having an area larger than the average area cannot be formed on a land portion other than the dimple. Is disclosed. Further, JP-A-4-347177 discloses a golf ball in which dimples are arranged very densely so that the number of land portions on which a rectangle having a predetermined size can be drawn is 40 or less.

  All of the golf balls disclosed in these known documents have densely arranged dimples. In other words, the surface area occupation ratio of the dimples is increased. One skilled in the art recognizes that one of the important factors affecting the dimple effect is the surface area occupancy.

  As the performance of a golf ball that is regarded as important as the flight distance, spin performance can be cited. When the backspin rate is high, the run (the distance from the point where the golf ball dropped to the point where it stopped) is also small. In other words, for golfers, golf balls that are susceptible to backspin are easy to rest at a target point. When the side spin rate is high, the golf ball tends to bend. In other words, for golfers, golf balls that are susceptible to side spin are intentionally bendable. A golf ball excellent in spin performance is excellent in control performance. Advanced golfers place emphasis on the control performance when hitting with a short iron.

  In general golf balls, an ionomer resin is used for a cover. The ionomer resin is excellent in durability and resilience performance. However, ionomer resins are generally high in hardness. A golf ball provided with a cover made of an ionomer resin is inferior in control performance. In order to improve control performance, a cover in which a hard ionomer resin and a ternary copolymer soft ionomer resin are used in combination has been proposed. In addition, a cover in which an ionomer resin and a thermoplastic elastomer are used in combination has been proposed. Furthermore, a cover made of a thermosetting polyurethane elastomer or a thermoplastic polyurethane elastomer has also been proposed.

Japanese Patent Publication No. 58-50744 JP-A-62-192181 JP-A-4-347177

  The flight distance and control performance, which are important performance requirements for golf balls, are contradictory performances. A golf ball that is sufficiently satisfied by golfers has not yet been obtained. The present invention has been made in view of such a situation, and an object thereof is to provide a golf ball excellent in both flight performance and control performance.

The golf ball of the present invention includes a core, a cover, and a large number of dimples formed on the surface of the cover. The base polymer of this cover is mainly composed of a polyurethane-based thermoplastic elastomer. The Shore D hardness of this cover is 30 or more and 55 or less. The surface area occupation ratio Y of these dimples is 75% or more. Golf ratio of the diameter _{d max} of the largest dimples to the diameter D of the ball R1 is less 18.0% 11.0% or more.

  Preferably, the ratio R2 of the number of dimples having a diameter d that is 11.0% or more and 18.0% or less with respect to the diameter D of the golf ball to the total number N of dimples is 20% or more.

  Preferably, the average occupation ratio y is 0.22% or more. This golf ball has a large number of dimples having a large size as a comparative example. The average occupation ratio y is a value obtained by dividing the surface area occupation ratio Y by the total number N of dimples.

Preferably, the sum total (total contour length) X of the contour length x of the dimple and the surface area occupation ratio Y satisfy the relationship represented by the following formula (1).
X ≦ 38.82 × Y + 1495 −−− (1)
This golf ball has a dimple pattern having a small total contour length X instead of the surface area occupation ratio Y.

  The present invention has a remarkable effect in a golf ball in which the core includes a center and an intermediate layer, and the difference (Hm−Hc) between the Shore D hardness Hm of the intermediate layer and the Shore D hardness Hc of the cover is 5 or more. To demonstrate.

  In the golf ball according to the present invention, since the base polymer of the cover is mainly composed of a polyurethane-based thermoplastic elastomer and the cover has a Shore D hardness of 30 to 55, this golf ball has excellent control performance. This golf ball also has excellent flight performance. The reason why the flight performance of this golf ball is excellent is unknown in detail, but the maximum dimple contributes to the reduction of the drag coefficient (Cd), particularly in the high speed region immediately after hitting. Presumed to be because.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing a golf ball 1 according to an embodiment of the present invention. The golf ball 1 includes a spherical core 2 and a cover 3. The core 2 includes a spherical center 4 and an intermediate layer 5. A large number of dimples 6 are formed on the surface of the cover 3. A portion of the surface of the cover 3 other than the dimple 6 is a land 7. The golf ball 1 includes a paint layer and a mark layer on the outside of the cover 3, but these layers are not shown. The diameter of the golf ball 1 is usually 40 mm to 45 mm, and further 42 mm to 44 mm. From the viewpoint of reducing air resistance within a range that satisfies the standards of the US Golf Association (USGA), the diameter is particularly preferably 42.67 mm or greater and 42.80 mm or less. The weight of the golf ball 1 is usually 40 g or more and 50 g or less, and further 44 g or more and 47 g or less. From the viewpoint of increasing the inertia within a range that satisfies the standards of the American Golf Association, the mass is particularly preferably 45.00 g or more and 45.93 g or less.

  In this specification, the cover 3 means the outermost layer excluding the paint layer and the mark layer. There is a golf ball whose cover is referred to as having a two-layer structure. In this case, the outer layer corresponds to the cover 3 in this specification.

  The base polymer of the cover 3 is a polyurethane thermoplastic elastomer. A general polyurethane-based thermoplastic elastomer includes a polyurethane component as a hard segment and a polyester component or a polyether component as a soft segment. The polyurethane-based thermoplastic elastomer contributes to the control performance of the golf ball 1. Furthermore, the polyurethane-based thermoplastic elastomer also contributes to the scuff resistance of the cover 3.

  Examples of the curing agent for the polyurethane component include alicyclic diisocyanate, aromatic diisocyanate and aliphatic diisocyanate. In particular, alicyclic diisocyanates are preferred. Since the alicyclic diisocyanate has no double bond in the main chain, yellowing of the cover 3 is suppressed. In addition, since the alicyclic diisocyanate is excellent in strength, the cover 3 is prevented from being damaged. Two or more diisocyanates may be used in combination.

Examples of the alicyclic diisocyanate include 4,4′-dicyclohexylmethane diisocyanate (H ₁₂ MDI), which is a hydrogenated product of 4,4′-diphenylmethane diisocyanate, and 1,3-bis (isocyanate), which is a hydrogenated product of xylylene diisocyanate. Examples are natomethyl) cyclohexane (H ₆ XDI), isophorone diisocyanate (IPDI) and trans-1,4-cyclohexane diisocyanate (CHDI). From the viewpoint of versatility and workability, H ₁₂ MDI is preferable. Specific examples of the polyurethane-based thermoplastic elastomer whose H ₁₂ MDI is a constituent component include BASF Polyurethane Elastomers trade name “Elastollan XNY90A”, trade name “Elastollan XNY97A” and trade name “Elastollan XNY585”. It is done.

  Aromatic diisocyanates include 4,4'-diphenylmethane diisocyanate (MDI) and toluene diisocyanate (TDI). As the aliphatic diisocyanate, hexamethylene diisocyanate (HDI) is exemplified.

  As the base polymer of the cover 3, other synthetic resins may be used together with the polyurethane-based thermoplastic elastomer. When the polyurethane-based thermoplastic elastomer is used in combination with another synthetic resin, the polyurethane-based thermoplastic elastomer is the main component from the viewpoint of control performance. The ratio of the polyurethane-based thermoplastic elastomer to the total base polymer is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more.

  Examples of synthetic resins that can be used include polyamide-based thermoplastic elastomers, polyester-based thermoplastic elastomers, polyolefin-based thermoplastic elastomers, and ionomer resins. A synthetic resin having a polar group such as a carboxyl group, a glycidyl group, a sulfone group, or an epoxy group may be used. In particular, a polyamide-based thermoplastic elastomer is preferable. The polyamide-based thermoplastic elastomer is excellent in compatibility with the polyurethane-based thermoplastic elastomer. The polyamide-based thermoplastic elastomer also contributes to the resilience performance of the golf ball 1. When the polyurethane-based thermoplastic elastomer and the polyamide-based thermoplastic elastomer are used in combination, the mass ratio between the two is preferably 70/30 or more and 95/5 or less.

  A general polyamide-based thermoplastic elastomer includes a polyamide component as a hard segment and a polyester component or a polyether component as a soft segment. A preferred soft segment is a polyether component. Specific examples of suitable polyamide-based thermoplastic elastomers include trade names “Pebax 5533” and “Pebax 4033” from Atofina Japan.

  If necessary, the cover 3 contains a suitable amount of a colorant such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, and a fluorescent brightening agent. The For the purpose of adjusting the specific gravity, the cover 3 may be mixed with powder of a high specific gravity metal such as tungsten or molybdenum.

  The cover 3 has a Shore D hardness Hc of 30 or more and 55 or less. In other words, the cover 3 is soft. By adopting the soft cover 3, the contact time and the contact area between the club face and the golf ball 1 when hit with a golf club are increased. Thereby, the spin performance of the golf ball 1 is improved and the control performance is improved. From this viewpoint, the hardness Hc of the cover 3 is more preferably 50 or less. If the cover 3 has a hardness Hc that is too low, the resilience performance of the golf ball 1 will be insufficient, so the hardness Hc is more preferably 35 or more, and particularly preferably 40 or more.

  The thickness of the cover 3 is preferably 0.2 mm or greater and 2.0 mm or less. When the thickness is less than the above range, the control performance and durability of the golf ball 1 may be insufficient. In this respect, the thickness is more preferably equal to or greater than 0.3 mm, and particularly preferably equal to or greater than 0.5 mm. If the thickness exceeds the above range, the resilience performance and flight performance of the golf ball 1 may be insufficient. In this respect, the thickness is more preferably equal to or less than 1.8 mm, and particularly preferably equal to or less than 1.5 mm.

  FIG. 2 is an enlarged plan view showing the golf ball 1 of FIG. 1, and FIG. 3 is a front view thereof. This golf ball 1 has an A dimple having a circular planar shape and a diameter of 5.60 mm, a B dimple having a circular planar shape and a diameter of 5.10 mm, and a circular planar shape and a diameter of 4. A C dimple having a diameter of 85 mm, a D dimple having a circular planar shape and a diameter of 4.50 mm, an E dimple having a circular planar shape and a diameter of 4.25 mm, and a circular planar shape having a diameter of 3 F dimple having a diameter of 90 mm and a G dimple having a circular planar shape and a diameter of 2.75 mm. The number of A dimples is 18, the number of B dimples is 102, the number of C dimples is 24, the number of D dimples is 18, and the number of E dimples is 72, The number of F dimples is 36, and the number of G dimples is 24. The total number N of dimples of this golf ball 1 is 294.

In this specification, the maximum dimple means a dimple having the largest diameter. In the case of a non-circular dimple, a circular dimple having the same area as the non-circular dimple is assumed, and the diameter of the circular dimple is the diameter of the non-circular dimple. The maximum dimple of the golf ball 1 shown in FIGS. 2 and 3 is an A dimple. In other words, the maximum dimple has a diameter d _max of 5.60 mm. The ratio R1 of the diameter D of the golf ball 1 diameter _{d max} of the maximum dimple for (42.70 mm in this example) (5.60 mm in this example) is 13.1%.

  In this golf ball 1, the ratio R <b> 1 is larger than that of the conventional golf ball 1. In other words, the maximum dimple is extremely large. This maximum dimple contributes to the aerodynamic characteristics and imparts excellent flight performance to the golf ball 1. In the golf ball 1, both flight performance and control performance are achieved. From the viewpoint of aerodynamic characteristics, the ratio R1 is set to 11.0% or more. The ratio R1 is more preferably 12.0% or more, and particularly preferably 13.0% or more. If the ratio R1 is too large, the original characteristic of the golf ball 1 that is a substantially spherical body may be impaired, resulting in a decrease in flight performance or the golf ball 1 being difficult to roll on the green. From this viewpoint, the ratio R1 is set to 18.0% or less. The ratio R1 is more preferably 17.0% or less, and particularly preferably 16.0% or less.

  The dimple 6 having a diameter d that is 11.0% or more and 18.0% or less with respect to the diameter D of the golf ball 1 contributes to the improvement of the aerodynamic characteristics of the golf ball 1. The ratio R2 of the number of dimples 6 having a diameter d that is 11.0% or more and 18.0% or less with respect to the diameter D of the golf ball 1 to the total number N of dimples is preferably 20% or more. The golf ball 1 having the ratio R2 of 20% or more has excellent flight performance. In this respect, the ratio R2 is more preferably equal to or greater than 22%, and particularly preferably equal to or greater than 30%. The ratio R2 is ideally 100%.

  From the viewpoint of flight performance, the diameter d of all the dimples 6 is preferably 5.0% or more, more preferably 5.5% or more, and particularly 5.8% or more of the diameter D of the golf ball 1.

  FIG. 4 is a schematic enlarged cross-sectional view showing a part of the golf ball 1 shown in FIG. In this figure, a cross section passing through the deepest part of the dimple 6 is shown. In this figure, the diameter of the dimple 6 is indicated by a double arrow d. The diameter d is a distance between both contacts when a common tangent is drawn at both ends of the dimple 6. Further, the volume of the portion surrounded by the phantom sphere of the golf ball 1 (the sphere when it is assumed that the dimple 6 does not exist and is indicated by a two-dot chain line in FIG. 4) and the surface of the dimple 6 is , Dimple 6 volume.

The area of the dimple 6 is an area of a region surrounded by the outline of the dimple 6 when the center of the golf ball 1 is viewed from infinity (that is, an area of a planar shape). In the case of the circular dimple 6, the area s is calculated by the following mathematical formula.
s = (d / 2) ² × π

In the golf ball 1 shown in FIGS. 2 and 3, the area s of the A dimple is 24.63 mm ² , the area s of the B dimple is 20.43 mm ² , and the area s of the C dimple is 18.47 mm ^2. The area s of the D dimple is 15.90 mm ² , the area s of the E dimple is 14.19 mm ² , the area s of the F dimple is 11.95 mm ² , and the area s of the G dimple is 5. 94 mm ² . Therefore, the sum total (total area) S of the dimple areas is 4850.7 mm ² . The ratio of the total area S to the surface area of the phantom sphere is the surface area occupation ratio Y. In this golf ball 1, the surface area occupation ratio Y is 84.68%. By dividing the surface area occupation ratio Y by the total number of dimples, the average occupation ratio y is calculated. In this golf ball 1, the average occupation ratio y is 0.288%. The average occupation ratio y means an area ratio of the dimple 6 having an average area to the spherical surface of the phantom sphere.

  The surface area occupation ratio Y is 75% or more. If the surface area occupation ratio Y is less than the above range, the lift of the golf ball 1 in flight may be insufficient. In this respect, the surface area occupation ratio Y is more preferably equal to or greater than 78%, and particularly preferably equal to or greater than 80%. A general golf ball 1 has a surface area occupation ratio Y of 88% or less.

  When the designer intends to design a dimple pattern having a large surface area occupation ratio Y, there is means for increasing the total surface area N of the dimples to achieve the surface area occupation ratio Y, and increasing the diameter d of the dimple 6 to increase the surface area. There is also a means for achieving the occupancy Y. When the designer mainly employs means for increasing the diameter d of the dimple 6 to achieve the surface area occupation ratio Y, the golf ball 1 having an average occupation ratio y of 0.22% or more is obtained.

  If the average occupancy y is less than 0.22%, the drag coefficient (Cd) in a region where the flight speed in the ballistic trajectory is large is increased, and the flight distance of the golf ball 1 may be insufficient. In this respect, the average occupation ratio y is more preferably 0.24% or more, further preferably 0.26% or more, and particularly preferably 0.28% or more. In the golf ball 1 having an extremely large average occupancy y, the original characteristic of the golf ball 1 that is substantially a sphere is not maintained, so the average occupancy y of the normal golf ball 1 is 0.40 or less.

  The total number N of the dimples 6 is preferably 320 or less. If the total number N exceeds the above range, the individual dimples 6 become small, and the flight performance of the golf ball 1 may be insufficient. In this respect, the total number N is more preferably 310 or less, and particularly preferably 295 or less. In light of maintaining the surface area occupation ratio Y of 75% or more and maintaining the golf ball 1 to be substantially spherical, the total number N is preferably 210 or more, particularly 230 or more.

  In the golf ball 1 shown in FIG. 2, the contour length x of the A dimple is 17.59 mm, the contour length x of the B dimple is 16.02 mm, and the contour length x of the C dimple is 15. The contour length x of the D dimple is 14.14 mm, the contour length x of the E dimple is 13.35 mm, the contour length x of the F dimple is 12.25 mm, and the contour of the G dimple The length x is 8.64 mm. In this golf ball 1, the total contour length X, which is the sum of the contour lengths x, is 4180.8 mm.

The contour length x of the dimple 6 is a length actually measured along the contour of the dimple 6. For example, in the case of the dimple 6 whose plane shape is a triangle, the total length of three sides is the contour length x. Since this side exists on a spherical surface, strictly speaking, it is not a straight line but an arc shape. The length of this arc is the side length. In the case of the circular dimple 6, the contour length x is calculated by the following mathematical formula.
x = d × π

The surface area occupation ratio Y and the total contour length X preferably satisfy the relationship represented by the following mathematical formula (1).
X ≦ 38.82 × Y + 1495 −−− (1)
In the golf ball 1, the total contour length X is small for the surface area occupation ratio Y. In this golf ball 1, the drag coefficient (Cd) at the time of flight is small. This golf ball 1 is excellent in flight performance. As far as the present inventor is aware, there is no golf ball that satisfies the formula (1).

From the viewpoint of reducing the drag coefficient (Cd), the total contour length X and the surface area occupation ratio Y preferably satisfy the following formula (2), more preferably satisfy the following formula (3), and the following formula (4) It is particularly preferable to satisfy
X ≦ 38.82 × Y + 1445 −−− (2)
X ≦ 38.82 × Y + 1335 −−− (3)
X ≦ 38.82 × Y + 1085 −−− (4)
In order to maintain the original characteristic of the golf ball 1 that is a substantially spherical body, the total contour length X and the surface area occupation ratio Y need to satisfy the relationship of the following mathematical formula (5).
X ≧ 38.82 × Y + 95 −−− (5)

  The total contour length X is appropriately determined from the relationship with the surface area occupation ratio Y in a range satisfying the above mathematical formula (1), but is usually 2800 mm or more and 5000 mm or less, particularly 3100 mm or more and 4700 mm or less.

  From the viewpoint of reducing the drag coefficient (Cd), the number of dimples 6 whose contour length x is 10.5 mm or more is preferably 91% or more of the total number of dimples, and particularly preferably 95% or more. This ratio is ideally 100%.

  The depth of the dimple 6 (the distance between the phantom spherical surface and the deepest part of the dimple 6) is preferably 0.05 mm or greater and 1.00 mm or less. If the depth is less than the above range, turbulent transition is unlikely to occur. In this respect, the depth is more preferably 0.10 mm or more, and particularly preferably 0.15 mm or more. If the depth exceeds the above range, the dimple 6 is likely to be clogged with soil. In this respect, the depth is more preferably equal to or less than 0.85 mm, and particularly preferably equal to or less than 0.70 mm.

  Although only one type of dimple 6 may be formed, it is preferable that two or more types, particularly three or more types of dimples 6 having different diameters or depths are formed from the viewpoint of flight performance. Instead of the circular dimple 6, or together with the circular dimple 6, a non-circular dimple (a dimple whose planar shape is not a circle) may be formed. Specific examples of non-circular dimples include polygonal dimples, elliptical dimples, oval dimples, oval dimples, and the like.

The total dimple volume (total volume) is preferably 400 mm ³ or more and 800 mm ³ or less. If the total volume is less than the above range, a hopping trajectory may occur. In this respect, the total volume is more preferably 450 mm ³ or more, 500 mm ³ or more is particularly preferable. If the total dimple volume exceeds the above range, the trajectory may drop. In this respect, the total volume is more preferably 770 mm ³ or less, 750 mm ³ or less is particularly preferred.

  The golf ball 1 preferably has no great circle path. The great circle passage means a great circle that does not intersect the dimple 6 at all. In forming the golf ball 1, a forming die composed of an upper die and a lower die each having a hemispherical cavity is used. By using a molding die in which the parting line between the upper die and the lower die is uneven, the golf ball 1 having no great circle path can be formed.

  The center 4 is usually obtained by crosslinking the rubber composition. For the base rubber of the rubber composition, polybutadiene, polyisoprene, styrene-butadiene copolymer, ethylene-propylene-diene copolymer, natural rubber and the like are suitable. Two or more of these rubbers may be used in combination. From the viewpoint of resilience performance, polybutadiene is preferred. When polybutadiene and other rubber are used in combination, it is preferable that polybutadiene is a main component. Specifically, the proportion of polybutadiene in the total base rubber is preferably 50% by mass or more, particularly 80% by mass or more. Polybutadiene having a cis-1,4 bond ratio of 40% or more, particularly 80% or more is particularly preferred.

  For the crosslinking of the center 4, a co-crosslinking agent is usually used. A preferred co-crosslinking agent from the viewpoint of resilience performance is a monovalent or divalent metal salt of an α, β-unsaturated carboxylic acid having 2 to 8 carbon atoms. Specific examples of preferred co-crosslinking agents include zinc acrylate, magnesium acrylate, zinc methacrylate and magnesium methacrylate. Zinc acrylate and zinc methacrylate are particularly preferable because of high resilience performance.

  As a co-crosslinking agent, an α, β-unsaturated carboxylic acid having 2 to 8 carbon atoms and a metal oxide may be blended. Both react in the rubber composition to obtain a salt. This salt functions as a co-crosslinking agent. Preferred α, β-unsaturated carboxylic acids include acrylic acid and methacrylic acid. Preferred metal oxides include zinc oxide and magnesium oxide.

  The compounding amount of the co-crosslinking agent is preferably 10 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the base rubber. When the blending amount is less than the above range, the resilience performance of the golf ball 1 may be insufficient. In this respect, the amount to be blended is more preferably equal to or greater than 15 parts by weight. If the blending amount exceeds the above range, the feel at impact of the golf ball 1 may become hard. In this respect, the amount to be blended is more preferably equal to or less than 45 parts by weight.

  The rubber composition used for the center 4 is preferably blended with an organic peroxide together with a co-crosslinking agent. The organic peroxide contributes to the crosslinking reaction. By blending the organic peroxide, the resilience performance of the golf ball 1 is increased. Suitable organic peroxides include dicumyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di (t- Butyl peroxy) hexane and di-t-butyl peroxide. A particularly versatile organic peroxide is dicumyl peroxide.

  The compounding amount of the organic peroxide is preferably 0.1 parts by mass or more and 3.0 parts by mass or less with respect to 100 parts by mass of the base rubber. When the blending amount is less than the above range, the resilience performance of the golf ball 1 may be insufficient. In this respect, the amount is more preferably equal to or greater than 0.3 parts by weight, and particularly preferably equal to or greater than 0.5 parts by weight. If the blending amount exceeds the above range, the feel at impact of the golf ball 1 may become hard. In this respect, the amount is particularly preferably equal to or less than 2.5 parts by mass.

  The center 4 may be blended with a filler for the purpose of adjusting specific gravity and the like. Suitable fillers include zinc oxide, barium sulfate, calcium carbonate and magnesium carbonate. As a filler, a powder made of a high specific gravity metal may be blended. Specific examples of the high specific gravity metal include tungsten and molybdenum. The blending amount of the filler is appropriately determined so that the intended specific gravity of the center 4 is achieved. A particularly preferred filler is zinc oxide. Zinc oxide functions not only as a specific gravity adjuster but also as a crosslinking aid. In the center 4, various additives such as sulfur, an antioxidant, a colorant, a plasticizer, and a dispersant may be blended in appropriate amounts as necessary. The center 4 may further contain a crosslinked rubber powder or a synthetic resin powder.

  The diameter of the general center 4 is 25 mm or more and 41 mm or less, and particularly 27 mm or more and 40 mm or less. The crosslinking temperature of the center 4 is usually 140 ° C. or higher and 180 ° C. or lower. The crosslinking time of the center 4 is usually 10 minutes or longer and 60 minutes or shorter.

  The mid layer 5 may be composed of a crosslinked rubber or a resin composition. The base rubber in the case of being composed of a crosslinked rubber is equivalent to the base rubber of the center 4. Further, the same co-crosslinking agent and organic peroxide as in the case of the center 4 can be blended. The compounding amount of the co-crosslinking agent is preferably 15 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the base rubber. When the blending amount is less than the above range, the resilience performance of the golf ball 1 may be insufficient. In this respect, the amount to be blended is more preferably equal to or greater than 20 parts by weight. When the amount exceeds the above range, the feel at impact of the golf ball 1 may be deteriorated. In this respect, the amount to be blended is more preferably equal to or less than 45 parts by weight, and particularly preferably equal to or less than 40 parts by weight.

  The compounding amount of the organic peroxide in the mid layer 5 is preferably 0.1 parts by mass or more and 6.0 parts by mass or less with respect to 100 parts by mass of the base rubber. When the blending amount is less than the above range, the resilience performance of the golf ball 1 may be insufficient. In this respect, the amount is more preferably equal to or greater than 0.3 parts by weight, and particularly preferably equal to or greater than 0.5 parts by weight. If the blending amount exceeds the above range, the feel at impact of the golf ball 1 may become hard. In this respect, the amount is more preferably equal to or less than 5.0 parts by weight, and particularly preferably equal to or less than 4.0 parts by weight. The intermediate layer 5 can also contain the same fillers and various additives as the center 4.

  When the intermediate layer 5 is made of a resin composition, suitable base polymers include ionomer resins, polyester-based thermoplastic elastomers, polyamide-based thermoplastic elastomers, polyurethane-based thermoplastic elastomers, polyolefin-based thermoplastic elastomers, and polystyrene-based thermoplastics. An elastomer is mentioned. Two or more synthetic resins may be used in combination.

  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 is neutralized with a metal ion are preferable. Preferred α-olefins are ethylene and propylene. Preferred α, β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. Examples of the metal ions for neutralization include sodium ions, potassium ions, lithium ions, zinc ions, calcium ions, magnesium ions, aluminum ions, and neodymium ions. Neutralization may be performed with two or more metal ions. Particularly suitable metal ions from the viewpoint of the resilience performance and durability of the golf ball 1 are sodium ions, zinc ions, lithium ions and magnesium ions.

  The intermediate layer 5 may be blended with a filler for the purpose of adjusting specific gravity and the like. Suitable fillers include zinc oxide, barium sulfate, calcium carbonate and magnesium carbonate. As a filler, a powder made of a high specific gravity metal may be blended. Specific examples of the high specific gravity metal include tungsten and molybdenum. The blending amount of the filler is appropriately determined so that the intended specific gravity of the mid layer 5 is achieved. The intermediate layer 5 may be blended with a colorant, a crosslinked rubber powder, or a synthetic resin powder.

  The thickness of the mid layer 5 is preferably 0.5 mm or greater and 4.0 mm or less. When the thickness is less than the above range, the resilience performance of the golf ball 1 may be insufficient. In this respect, the thickness is more preferably equal to or greater than 0.7 mm. If the thickness exceeds the above range, the feel at impact of the golf ball 1 may be insufficient. In this respect, the thickness is more preferably equal to or less than 3.0 mm, and particularly preferably equal to or less than 2.0 mm.

  The Shore D hardness Hm of the mid layer 5 is preferably 55 or more. Thereby, the resilience performance of the golf ball 1 is improved. In this respect, the hardness Hm is more preferably equal to or greater than 58, and particularly preferably equal to or greater than 60. When the hardness Hm is extremely large, the feel at impact of the golf ball 1 becomes insufficient. In this respect, the hardness Hm is preferably equal to or less than 70, and more preferably equal to or less than 65.

  The difference (Hm−Hc) between the Shore D hardness Hm of the mid layer 5 and the Shore D hardness Hc of the cover 3 is preferably 5 or more. Thereby, the resilience performance of the golf ball 1 is improved. In this respect, the hardness difference (Hm−Hc) is more preferably 8 or greater and particularly preferably 10 or greater. When the hardness difference (Hm−Hc) is extremely large, the golf ball 1 has a poor feel at impact. In this respect, the hardness difference (Hm−Hc) is preferably 40 or less, more preferably 35 or less, and particularly preferably 30 or less. The Shore D hardness of the cover 3 and the intermediate layer 5 is measured by a spring type hardness meter Shore D type in accordance with the provisions of “ASTM-D 2240-68”. When the measurement target (the cover 3 or the intermediate layer 5) is made of a resin composition, the hardness is measured by a slab molded from the resin composition. When the measurement object is formed by crosslinking a rubber composition, the hardness is measured by a slab obtained by crosslinking the rubber composition under the same conditions as the measurement object.

  The center 4 of the golf ball 1 shown in FIG. 1 is composed of a single layer, but a center composed of two or more layers may be used. Another intermediate layer may be provided between the center 4 and the intermediate layer 5, and another intermediate layer may be provided between the intermediate layer 5 and the cover 3. A core composed of a single layer without the intermediate layer 5 may be used. In the golf ball 1 having two or more intermediate layers, the Shore D hardness Hm of at least one intermediate layer is preferably 5 or more larger than the Shore D hardness Hc of the cover 3. The hardness is preferably 55 or more.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

  Golf balls of Examples 1 to 8 and Comparative Examples 1 to 5 were obtained with the specifications of the core, cover, and dimple as shown in Table 1 below. These golf balls have a diameter of 42.7 mm. Details of the blending of the center, intermediate layer and cover are shown in Table 2, and details of the dimple specifications are shown in Tables 3 and 4.

[Measurement of compression deformation]
First, the golf ball was placed on a metal rigid plate. Next, the metal cylinder was gradually lowered toward the golf ball, and the golf ball sandwiched between the bottom surface of the cylinder and the rigid plate was deformed. And the movement distance of the cylinder from the state where the initial load of 98N was applied to the golf ball to the state where the final load of 1274N was applied was measured. The results are shown in Table 5 below.

[Flight distance test]
A driver with a metal head was attached to a golf laboratory swing machine. The machine conditions were set so that the head speed was 45 m / sec, the golf ball was hit, and the flight distance (distance from the launch point to the stationary point) was measured. The average value of five measurements is shown in Table 5 below.

[Abrasion resistance]
A pitching wedge was attached to the aforementioned swing machine. The machine conditions were set so that the head speed was 36 m / sec, and a golf ball was hit. The surface condition of the golf ball after hitting was visually observed and evaluated according to the following criteria.
A: There are some scratches, but they are not noticeable. B: There are scratches and fuzz. C: The surface of the cover is scraped off, and the fuzz is conspicuous.

[Evaluation of control performance]
Ten senior golfers were given a pitching wedge to hit a golf ball and evaluated the control performance. The case where spin was easily applied and excellent in control performance was designated as “A”, the case where spin was difficult and poor in control performance was designated as “C”, and the intermediate product between them was designated as “B”. The results of the most concentrated evaluation are shown in Table 5 below.

  As can be seen from Table 5, the golf balls of the examples are excellent in all of flight performance, scratch resistance and control performance. From this evaluation result, the superiority of the present invention is clear.

  The golf ball of the present invention is excellent in flight performance and control performance. This golf ball gives a refreshing feeling to a golfer who hits the golf ball and contributes to an improvement in score.

FIG. 1 is a schematic cross-sectional view showing a golf ball according to an embodiment of the present invention. FIG. 2 is an enlarged plan view showing the golf ball of FIG. FIG. 3 is a front view showing the golf ball of FIG. FIG. 4 is a schematic enlarged cross-sectional view showing a part of the golf ball of FIG. FIG. 5 is a plan view showing a golf ball having a type II dimple pattern. FIG. 6 is a front view showing the golf ball of FIG. FIG. 7 is a plan view showing a golf ball having a type III dimple pattern. FIG. 8 is a front view showing the golf ball of FIG. FIG. 9 is a plan view showing a golf ball having a type IV dimple pattern. FIG. 10 is a front view showing the golf ball of FIG. FIG. 11 is a plan view showing a golf ball having a type V dimple pattern. FIG. 12 is a front view showing the golf ball of FIG. FIG. 13 is a plan view showing a golf ball having a type VI dimple pattern. 14 is a front view showing the golf ball of FIG. FIG. 15 is a plan view showing a golf ball having a dimple pattern of type VII. FIG. 16 is a front view showing the golf ball of FIG. FIG. 17 is a plan view showing a golf ball having a dimple pattern of type VIII. FIG. 18 is a front view showing the golf ball of FIG. FIG. 19 is a plan view showing a golf ball having a dimple pattern of type IX. FIG. 20 is a front view showing the golf ball of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Golf ball 2 ... Core 3 ... Cover 4 ... Center 5 ... Intermediate layer 6 ... Dimple 7 ... Land

Claims (5)

A golf ball comprising a core, a cover, and a large number of dimples formed on the surface of the cover,
The base polymer of this cover is mainly composed of polyurethane thermoplastic elastomer,
The Shore D hardness of this cover is 30 or more and 55 or less,
The surface area occupation ratio Y of these dimples is 75% or more,
The ratio R1 of the maximum dimple diameter d _max to the diameter D of this golf ball is 13.0% or more and 18.0% or less,
A golf ball in which the ratio R2 of the number of dimples having a diameter d that is 11.0% or more and 18.0% or less with respect to the diameter D to the total number N of dimples is 22.9% or more.   The golf ball according to claim 1, wherein an average occupation ratio y, which is a value obtained by dividing the surface area occupation ratio Y by the total number N of dimples, is 0.22% or more. The golf ball according to claim 1, wherein a total X (mm) of the contour length x of the dimple and a surface area occupation ratio Y (%) satisfy a relationship represented by the following mathematical formula (1).
X ≦ 38.82 × Y + 1495 −−− (1)   The core includes a center and an intermediate layer, and when the Shore D hardness of the intermediate layer is Hm and the Shore D hardness of the cover is Hc, the value of (Hm-Hc) is 5 or more. 4. The golf ball according to any one of items 1 to 3. The ratio R2 of the number of dimples having a diameter d that is 11.0% to 18.0% with respect to the diameter D to the total number N of dimples is 49.0% or more. 2. A golf ball according to item 1.

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