Golf ball

Abstract: In a golf ball having dimples (1) and lands (2,3) formed on the surface thereof, dimples (1) are arranged so that there are provided less than 40 lands (2a,2b,2c) containing a rectangle (10) having a short side greater than 0.4mm and an area greater than 0.8mm² and not including a part of the dimple (1) or the whole thereof. A land (2c) having the greatest area of all lands (2,3) is so small that a dimple having an area greater than the average area of all dimples cannot be formed therein.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a golf ball as defined in the preamble portion of claim 1, and more particularly to a golf ball having an improved flight performance because of dimples densely arranged on the surface thereof. Description of the Related Arts Normally, a golf ball has 280 to 540 dimples on its surface. Dimples make air flow turbulent, thereby improving the aerodynamic characteristic of the golf ball during its flight. Thus, the golf ball flies a long distance. In view of the role of the dimple, the more densely dimples are arranged on the surface of the golf ball, the more turbulent air flow becomes and thus the golf ball has a longer flight distance. From this standpoint, various proposals of dimple arrangement have been made. For example, the present applicant made a proposal in Japanese Patent Laid-Open Publication No. 62-192181. According to the proposal, a land does not allow the formation of dimples having an area greater than the average area of dimples on the surface of the golf ball. It is to be noted that the land is a region of the surface of the golf ball other than the region of entire dimples arranged thereon. That is, the area of the land is reduced, i.e., dimples are densely arranged on the surface of the golf ball to increase the aerodynamic characteristic thereof. The golf ball having the above-described dimple arrangement is available on the market and popular among golfers because of its superiority of its flight performance. There is a growing demand for a golf ball having a favorable flight performance partly because feminine golfers who are inferior in muscular strength to male golfers are rapidly increasing in recent years. GB-A-2 203 954 discloses a golf ball having a dimple arrangement designed to reduce the total area of lands to less than 22% of the ball surface. One embodiment shown in Fig. 4 of the document achieves this by providing triangular dimples separated by lands of uniform width. Triangular dimples may cause anisotropy of the aerodynamic properties of the golf ball. The present invention is concerned with a golf ball having conventional circular dimples. SUMMARY OF THE INVENTION It is an essential object of the present invention to provide a golf ball having a long flight distance by making the area of lands smaller and arranging dimples densely on the surface thereof. In accomplishing this and other objects of the present invention, there is provided a golf ball as defined in Claim 1. Preferably the area of any land is less than 1/5 of the average area of dimples. More specifically, in a golf ball having dimples and lands, dimples are arranged on the surface thereof so that the number of lands having a comparatively large area does not exceed 40. These are lands satisfying the following conditions: 1. The short side of a rectangle is greater than 0.4mm. 2. The area thereof is greater than 0.8mm². 3. The rectangle does not contain a part of a dimple or the whole thereof. The number of lands allowing the formation of the rectangle satisfying the above three conditions is set to less than 40 and other lands have a smaller area than the land satisfying the above conditions. Most of the lands allowing the formation of the rectangle satisfying the above three conditions contain a rectangle having a short side of approximately 0.4mm and an area of approximately 0.8mm². Even a land having the greatest area is so small that a dimple having an area greater than the average area of all dimples cannot be formed therein. A land containing a plurality of rectangles satisfying the above-described conditions or a land containing rectangles overlapping with each other is counted as well. In shaping the golf ball, a great circle path having no dimples thereon is formed on a parting line corresponding to the connecting portion of a pair of semispherical molds. Therefore, many lands containing the rectangle satisfying the above-described conditions are formed in the vicinity of the great circle path. According to the present invention, a land in which a rectangle intersecting with the great circle path is formed is not counted. A golf ball having no great circle path thereon can be manufactured by a method, for example, a method as described by the present applicant in Japanese Patent Laid-Open Publication No. 2-337564. Preferably, this kind of golf ball has less than 40 lands in which the rectangle satisfying the above-described conditions can be formed. According to the present invention, the configuration of the land is defined by a rectangle although the sides of the rectangle are spherical. According to the above dimple arrangement, the minimum area of a dimple is approximately 5mm² because normally, the diameter of the dimple ranges from 2.50mm to 4.50mm. The area of each of the lands not exceeding 40 pieces is 0.8mm² which is less than 1/5 of the dimple having the minimum area. Other lands formed on the surface of the golf ball have smaller areas and consequently, dimples are densely arranged on the surface thereof. In the land which is comparatively large enough to form the rectangle satisfying the above-described conditions and smooth in spherical configuration, dimple effect of improving aerodynamic characteristic by making air flow turbulent is reduced. According to the present invention, the number of the lands are reduced and the areas of most of lands are small in such an extent as not to deteriorate dimple effect. Consequently, dimples are densely arranged on the surface of the golf ball. Thus, aerodynamic characteristic can be improved during the flight of the golf ball and therefore, the golf ball flies a long distance. BRIEF DESCRIPTION OF THE DRAWINGS These and other object and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which: Fig. 1 is a front view showing a golf ball according to a first embodiment of the present invention; Fig. 2 is a plan view showing the golf ball according to the first embodiment of the present invention; Fig. 3 is a schematic view showing the relationship between dimples and a land; Fig. 4 is a schematic view showing the relationship between dimples and a land; Fig. 5 is a schematic view showing the relationship between dimples and a land; Fig. 6 is a schematic view showing the relationship between dimples and a land; Fig. 7 is a schematic view showing the relationship between dimples and a land; Fig. 8 is a view showing the specification of a dimple; Fig. 9 is a front view showing a golf ball according to a second embodiment of the present invention; Fig. 10 is a plan view showing the golf ball according to the second embodiment of the present invention; Fig. 11 is a front view showing a golf ball according to a first comparison; Fig. 12 is a plan view showing a golf ball according to the first comparison; Fig. 13 is a front view showing a golf ball according to the second comparison; Fig. 14 is a plan view showing a golf ball according to the second comparison; Fig. 15 is a front view showing a golf ball according to a third comparison; Fig. 16 is a plan view showing a golf ball according to the third comparison; Fig. 17 is a front view showing a golf ball according to a fourth comparison; and Fig. 18 is a plan view showing a golf ball according to the fourth comparison. DETAILED DESCRIPTION OF THE INVENTION Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings, in which; Embodiments of the present invention will be described below with reference to the accompanied drawings. Golf balls having the specification shown in Table 1 according to a first embodiment and a second embodiment of the present invention are described below with reference to Fig. 1 through 8. Dimple specification of embodiments and comparisons 1 2 (mm) 3 (mm) 4 (mm³) 5 (mm³) 6 7 (mm²) 1st Embodi. 432 A 30 4.30 0.13 0.97 315 20 14.5 B 130 4.00 0.13 0.84 12.6 C 180 3.70 0.13 0.72 10.8 D 60 3.40 0.13 0.61 9.1 E 32 2.70 0.13 0.38 5.7 2nd Embodi. 420 A 30 4.30 0.14 0.98 316 32 14.5 B 130 4.00 0.14 0.85 12.6 C 180 3.70 0.14 0.73 10.8 D 60 3.40 0.14 0.61 9.1 E 20 2.80 0.14 0.42 6.2 1st Compar. 432 A 132 4.00 0.14 0.92 314 80 12.6 B 180 3.50 0.14 0.70 9.6 C 60 3.30 0.14 0.62 8.6 D 60 3.10 0.13 0.51 7.5 2nd Compar. 420 A 180 4.00 0.15 0.96 315 182 12.6 B 60 3.80 0.14 0.81 11.3 C 60 3.30 0.14 0.61 8.6 D 120 3.00 0.13 0.47 7.1 3rd Compar. 392 A 392 3.60 0.16 0.81 316 220 10.2 4th Compar. 408 A 18 4.50 0.13 1.02 316 60 15.9 B 216 4.10 0.13 0.87 13.2 C 96 3.80 0.13 0.73 11.3 D 36 3.50 0.13 0.62 9.6 E 42 2.90 0.13 0.42 6.6 1; number of dimples, 2; diameter, 3; depth, 4;volume, 5;total volume, 6; number of rectangles, 7; area of dimple Figs. 1 and 2 show a golf ball according to the first embodiment. Fig. 1 is a front view of the golf ball. Fig. 2 is a plan view thereof. The golf ball has 432 dimples consisting of five kinds of dimples A, B, C, D, and E on the surface thereof as shown in Table 1. The diameters of the dimples 1 are set to 4.30mm to 2.70mm. The areas of the dimples 1 are set to 5.7mm² to 14.5mm². Other dimple specifications are as shown in Table 1. Referring to Fig. 2, the spherical surface of the golf ball is divided into 20 units. According to the present invention, a black-pained rectangle 10 contained in one unit has a short side greater than 0.4mm and an area greater than 0.8mm². The rectangle 10 does not include any dimples. According to the first embodiment, the rectangle 10 has a short side of 0.7mm and an area of 1.9mm² which is approximately 1/7 as small as the area (14.5mm²) of the dimple 1. As shown in Fig. 2, the dimples 1 are arranged so that one rectangle 10 having a short side of more than 0.4mm and an area greater than 0.8mm² can be formed in one unit and there is only one land 2 which does not have an area greater than the average area of dimples 1. Since 20 units have the same dimple arrangement, the golf ball has 20 (= 1 x 20) lands 2 on the surface thereof. Other lands 3 of one unit have an area smaller than the area of the land 2 having the above-described rectangle 10 therein and therefore, do not have an area greater than the average area of the dimples 1, either. Fig. 3 shows a rectangle 10 not including a part of a dimple or the whole thereof. Fig. 4 shows a rectangle 10' including a part of a dimple. Fig. 5 shows a rectangle 10'' including the whole of a dimple. According to the present invention, the following lands 2 are also counted: The land 2 containing two rectangles 10 or more having a short side greater than 0.4mm and an area greater than 0.8mm² and including neither a part of a dimple nor the whole thereof; and the land 2 in which the rectangles 10 overlap with each other as shown in Fig. 7. Neither the area of the land 2 shown in Fig. 6 nor the land 2 shown in Fig. 7 has an area greater than the average area of dimples. The golf ball according to the first embodiment, dimples cannot be formed on the parting line formed on the surface thereon in producing it by a semispherical mold. Thus, a great circle path 5 not intersecting with dimples is formed on the surface of the golf ball. Therefore, in the vicinity of the great circle path 5, there are many lands 2 containing rectangles having a short side more than 0.4mm and an area more than 0.8mm² and not including a part of a dimple or the whole thereof. According to the present invention, a land in which a rectangle intersecting with the great circle path 5 is formed is not counted. According to the present invention, in the golf ball having no great circle path 5 formed thereon, there are less than 40 lands 2, on the surface thereof, allowing the formation of a rectangle having a short side more than 0.4mm and an area more than 0.8mm² and not including a part of a dimple or the whole thereof. Referring to Table 1, diameter is the distance between contacts (a) and (b) of a common tangent (L) drawn from one end of the dimple 1 shown in Fig. 8 to the other end thereof. Depth is the distance between the midpoint of the common tangent (L) and the deepest point of the dimple 1, namely, the distance between points (c) and (d). Area is counted based on the above-described diameter. Volume is the volume of a space represented by diagonal lines. Total volume is the sum of the volumes of all dimples. A second embodiment of the present invention is described below with reference to Fig. 9 which is a front view showing a golf ball according to the second embodiment and Fig. 10 which is a plan view showing the golf ball according to the second embodiment. The dimple specification is as shown in Table 1. The golf ball has 432 dimples 1 formed on the surface thereof. As shown in Table 1, dimples consist of five kinds, namely, A, B, C, D, and E. The diameters of the dimples 1 are set to 4.30mm to 2.80mm. The areas of the dimples 1 are set to 6.2mm² to 14.5mm². Similarly to Fig. 2 showing the first embodiment, Fig. 10 shows one of 20 units. Each of black-pained rectangles 10 contained in one unit has a short side greater than 0.4mm and an area greater than 0.8mm². The rectangles 10 do not contain any dimples. As shown in Fig. 10, the number of lands 2 which allows the formation of a rectangle satisfying the above-described condition is 1.6 in one unit. The rectangle satisfying the above-described condition means a rectangle having a short side more than 0.4mm and an area more than 0.8mm² and not including a part of a dimple or the whole thereof. That is, 1 x (2-a) + 1/2 x (2-b) + 1/10 x (2-c) , namely, 1+1/2+1/10 = 1.6. Therefore, there are 32 (= 1.6 x 20 units) lands 2 which allows the formation of the rectangle satisfying the above-described condition on the surface of the golf ball. The length of the short sides of the lands (2-a), (2-b), and (2-c) and the area thereof are as shown below. short side (mm) area (mm²) land 2-a 0.4 0.8 land 2-b 1.0 2.2 land 2-c 1.0 2.2 Comparison golf balls 1 through 4 having the dimple specification shown in Table 1 are prepared to check the dimple effect of the golf ball according to the present invention. The golf ball according to the first comparison has 432 dimples on the surface thereof. Fig. 11 is a front view of the golf ball according to the first comparison and Fig. 12 is a plan view of the golf ball according to the first comparison. Similarly to Fig. 2 showing the first embodiment and Fig. 10 showing the second embodiment, Fig. 12 shows one of 20 units. Each of black-painted rectangles 10 contained in one unit has a short side greater than 0.4mm and an area greater than 0.8mm². The rectangles 10 do not contain any dimples. As shown in Fig. 12, there are 4 (= 2 + 1/2 x 4) lands in one unit which allows the formation of the rectangle 10 satisfying the above-described condition. That is, 2 x (2-x) + 4 x 1/2 x (2-y) , namely, 2 + 2 = 4. Therefore, the golf ball has 80 (= 4 x 20) lands 2 on the surface thereof. According to the golf ball of the first comparison, the number of lands satisfying the above-described condition is approximately four times as many as that of the first embodiment and approximately twice as many as that of the second embodiment. The dimple pattern of the golf ball according to the first comparison is disclosed in the fourth embodiment of Japanese Patent Laid-Open Publication No. 62-192181 described previously. The golf ball according to the second comparison has 420 formed on the surface thereof. Fig. 13 is a front view of the golf ball according to the second comparison and Fig. 14 is a plan view of the golf ball according to the second comparison. Fig. 14 shows one of 20 units. Similarly to the first comparison, each of black-painted rectangles 10 contained in one unit has a short side greater than 0.4mm and an area greater than 0.8mm². The rectangles 10 do not contain any dimples. As shown in Fig. 14, there are 9.1 (= 6 + 1/2 x 6 + 1/10) lands 2 in one unit which allows the formation of the rectangle 10 satisfying the above-described condition. That is, 6 x (2-x) + 1/2 x 6 x (2-y) + 1 x 1/10 (2-z) , namely, 6 + 3 + 1/10 = 9.1. Therefore, the golf ball has 182 (= 9.1 x 20) lands 2 on the surface of the golf ball. According to the golf ball according to the second comparison, the number of lands is approximately nine times as many as that of the first embodiment and approximately six times as many as that of the second embodiment. The dimple pattern of the golf ball according to the second comparison is disclosed in the third embodiment of Japanese Patent Laid-Open Publication No. 62-192181 described previously. Since the dimple pattern of the golf balls according to the first comparison and the second comparison are the same as that of Japanese Patent Laid-Open Publication No. 62-192181, the golf balls do not have a land in which a dimple having an area greater than the average area of dimples can be formed. In other words, the golf balls according to the first comparison and the second comparison have dimples densely arranged on the surface thereof, but have lands containing rectangles satisfying the above-described condition several times as many as those of the golf balls according to the first and second embodiments of the present invention. Thus, it cannot be said that the golf balls according to the first comparison and the second comparison have dimples densely arranged on the surface thereof as compared with the golf ball according to the present invention. The golf ball according to the third comparison has 392 dimples on the surface thereof. Fig. 15 is a front view of the golf ball according to the third comparison and Fig. 16 is a plan view of the golf ball according to the third comparison. Fig. 16 shows one of 20 units. Each of black-painted rectangles 10 contained in the unit has a short side greater than 0.4mm and an area greater than 0.8mm². The rectangles 10 do not contain any dimples. As shown in Fig. 16, the number of lands 2 having the rectangle 10 satisfying the above-described condition is 11 (= 10 + 1/2 x 2) in one unit. That is, 10 x (2-x) + 1/2 x 2 x (2-y) , namely, 10 + 1 = 11. Therefore, the golf ball has 220 (= 11 x 20) lands 2 on the surface thereof. According to the golf ball of the third comparison, the number of lands is approximately 11 times as many as that of the first embodiment and approximately seven times as many as that of the second embodiment. The dimple pattern of the golf ball according to the third comparison is known and still popular. The golf ball according to the fourth comparison has 408 dimples on the surface thereof. Fig. 17 is a front view of the golf ball according to the fourth comparison and Fig. 18 is a plan view of the golf ball according to the fourth comparison. Fig. 16 shows one of 12 units. Each of black-painted rectangles 10 included in one unit has a short side greater than 0.4mm and an area greater than 0.8mm². The rectangles 10 do not contain any dimples. As shown in Fig. 18, the golf ball has 5 (= 4 + 1/2 x 2) lands 2 in one unit which allows the formation of the rectangle 10 satisfying the above-described condition. That is, 4 x (2-x) + 1/2 x 2 x (2-y) , namely, 4 + 1 = 5. Therefore, the golf ball has 60 (= 5 x 12) lands 2 on the surface thereof. The golf ball of the fourth comparison has the smallest number of lands of all the golf balls according to the first through fourth comparison. The length of the short side of the land and the area thereof of the first through fourth comparison are as shown in Table 3 below. The golf ball of the first and second embodiments and the first through fourth comparisons has a liquid center wound with thread covered with a balata cover and has the same construction and material-mixing proportion. The outer diameter thereof is all 42.70 ± 0.03mm and compression is all 95 ± 2. Flight tests of the golf balls of the first and second embodiments and the first through fourth comparisons were conducted by using a swing robot manufactured by True Temper Corp. Golf balls were hit by a driver (No. 1 wood) at a head speed of 45m/s. Spin was 3500 ± 300rpm. Ball launching angle was 10 ± 0.5 . The result shown in Table 4 is the average of the result of 20 golf balls. flight distance (yard) trajectory height (DEG) duration of flight (SEC) first embo. 246 13.6 5.9 second embo. 245 13.8 5.9 first compar. 241 13.5 5.6 second compar. 238 13.6 5.5 third compar. 233 13.3 5.4 fourth compar. 242 13.8 5.7 In the above, embodiment is abbreviated as embo. and comparison is abbreviated as compar. In Table 4, flight distance is the distance from a hitting point to a point at which each golf ball stopped. Trajectory height is an angle of elevation viewed from the launching point of each golf ball to the highest point thereof in trajectory. As shown in Table 4, it was confirmed from the test result that the golf balls according to the first and second embodiments of the present invention were longer than those of the first through fourth comparison in duration of flight and flight distance. The golf ball of the fourth comparison having the fewest lands on the surface thereof was superior to those of the first comparison through the third comparison in flight distance, trajectory height, and duration of flight. This is because of the following reason: In the land 2 which is comparatively large enough to form the rectangle 10 and smooth in spherical configuration, dimple effect of improving aerodynamic characteristic obtained by making air flow turbulent is reduced. Thus, the more the lands 2 are formed on the surface of the golf ball, the lower aerodynamic characteristic becomes during the flight of the golf ball while the fewer the lands 2 are formed on the surface of the golf ball, the more aerodynamic characteristic is improved because dimple effect does not deteriorate. Thus, the golf ball flies a long distance. As apparent from the foregoing description, lands are arranged on the surface of the golf ball in a small area and the short side of a rectangle contained in a land of a comparatively large area is greater than 0.4mm and the area of the rectangle is greater than 0.8mm². Further, dimples are densely arranged on the surface of the golf ball so that there are less than 40 lands (less than 1/5 of the average area of dimples) in which a rectangle not including a part of a dimple or the whole thereof can be formed. In addition to the above dimple arrangement, the area of each land of the comparatively large area is smaller than that of the land of a golf ball having the conventional dimple arrangement. Therefore, dimple effect is not deteriorated by the presence of lands and aerodynamic characteristic can be improved. Thus, the golf ball flies a long distance. Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.

Claims: A golf ball having circular dimples (1) and lands (3) between the dimples formed on its surface, characterized in that the number of lands having a size sufficient to allow the formation of a rectangle (10) having a short side greater than 0.4 mm and an area greater than 0.8 mm² and not including any parts of a dimple, is less than 40. A golf ball as claimed in claim 1, wherein the dimples (1) are densely arranged on the surface of the golf ball such that the area of any land (3) having a size as defined in claim 1 is less than 1/5 of the average area of the dimples (1).

Inventors: OKA KENGO, OKA, KENGO
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LIMITED
Application year: 1992
Main classification: A63B37
IPC codes: A63B37