Golf Ball

Abstract

Disclosed is a golf ball including a center portion, at least two intermediate tiers sequentially surrounding the center portion, and an outer tier surrounding the intermediate tiers, which comprises: said outer tier having a thickness in a range of 0.8.about.1.4 mm, and an a hardness (Shore D) in a range of 40.about.50; among the intermediate tiers, said first intermediate tier formed just below the outer tier, having a thickness in a range of 1.0.about.2.0 mm and a hardness (Shore D) in a range of 50.about.65; each intermediate tier formed just below the first intermediate tier having a thickness in a range of 1.3.about.1.5 mm, and a hardness (Shore D) in range of 30.about.70; the radius of the center portion is in a range of 5.about.18 mm, and a hardness (Shore D) in a range of 30.about.70; and a moment of inertia value of the golf ball is less than 83 gcm.sup.2. According to the golf ball of the present invention, an iron spin force is excellent as compared to a conventional golf ball for a match, and the flying distance is almost same.

Description

CROSS REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority to Korean Application No. 10-2010-0053604, filed on Jun. 7, 2010, in the Korean Intellectual Property Office, which is incorporated herein by reference in its entirety as if set forth in full.

BACKGROUND

[0002] Various embodiments relate to a golf ball, and in particular to a golf ball which is easy to land on a green with the aid of a better spin in an approach shot within 100 yards, and has less elasticity due to lesser spin in a driver shot which serves to increase a run, thus increasing the total flying distance.

[0003] According to a new regulation, R&A of Great Britain and USGA of the USA have prohibited the use of a conventional square type of groove (club face groove) of irons (fifth iron to wedge) of equal to or more than 25 degrees from Jan. 1, 2010. The value obtained by dividing the total cross sectional area of the groove with the pitch of the groove (Pitch=width+interval) is limited to 0.003 square inches (0.0762 square mm), and the sharpness of the groove edge of the groove is limited to 0.010 inches (0.254 mm).

[0004] A U-shaped groove club, compared to a conventional V-shaped groove club, serves to significantly increase spin in a rough, so the difference of spin between a fairway shot and a rough shot is almost similar, thus decreasing accuracy, which has been shown by many researches.

[0005] The purpose of the regulation regarding the club groove can be seen as to increase the benefits of accurate shots, especially due to high technique required in a rough shot, by increasing the difference of the spin between a fairway shot and a rough shot.

[0006] The main focus of the changed regulation regarding the club is to make a spin more difficult, so the development of a ball with better spin is urgently needed. Currently available products for professional golfers have a cover having a hardness of above 50 (units: Shore D). When a golf ball with such hardness is struck with an iron satisfying the changed regulations, it is hard to give the ball enough spin, so it is difficult to hit the ball to a desired position.

[0007] It is possible to produce a desired spin by using a golf ball having a cover of a lower hardness material. But in such a case, a spin can be increased properly, but over-spin occurs with impact by a driver and the forward flying force is dispersed by a reverse rotation force, so generation of over-lifting force causes an increase in elasticity, which leads to an increase of an angle of falling, which decreases a run, and a flying distance is significantly decreased.

[0008] Finally, it is urgently needed to develop a new golf ball which serves to increase a flying distance when impacted by a driver while it is easy to make a spin when impacted by an iron.

SUMMARY

[0009] Accordingly, it is an object of the present invention to provide a golf ball which serves to satisfy the above demands and is easy to fly to a green with the aid of a good spin at an approach shot by providing a smooth cover (outer layer). At the same time, spins can be reduced at a driver impact by limiting the value of a moment of inertia, and an elasticity can be reduced since an over lifting force is inhibited, and an angle of falling to the ground can be decreased, thus enhancing a run, which consequently results in increasing a total flying distance.

[0010] To achieve the above objects, there is provided a golf ball including a center portion, at least two intermediate tiers sequentially surrounding the center portion, and an outer tier surrounding the intermediate tiers, comprising the outer tier having a thickness in a range of 0.8.about.1.4 mm, and a hardness (Shore D) in a range of 40.about.50; a first intermediate tier formed just below the outer tier among the intermediate tier having a thickness in a range of 1.0.about.2.0 mm and a hardness (Shore D) in a range of 50.about.65; each intermediate tier formed just below the first intermediate tier having a thickness in a range of 1.3.about.1.5 mm, and a hardness (Shore D) in range of 30.about.70; the length of a radius of the center portion is in a range of 5-18 mm, and a hardness (Shore D) in a range of 30.about.70; and a moment of inertia value of the golf ball is less than 83 gcm.sup.2 value.

[0011] Meanwhile, the outer tier is made of an ionomer resin, and the ionomer resin is made by neutralizing mono-olefin containing at least a part of unsaturated carbonic acid with the number of 3.about.8 carbon atoms and the ester of carbonic acid with a 1- or 2-metal.

[0012] Meanwhile, the outer tier is a polyurethane containing at least one among an ester type polyurethane, ether type polyurethane or ether ester copolymer type polyurethane. It is formed of a poly urethane elastomer made by polymerizing polyol, disocianate, crosslinker, etc. or is formed of a 2-liquid type polyurethane mixed in the course of forming polyol and pole isocianate.

[0013] In addition, the first intermediate tier is formed of an ionomer resin, the ionomer resin being made by neutralizing mono-olefin containing at least a part of unsaturated carbonic acid with the number of 3.about.8 carbon atoms and the ester of carbonic acid with a 1- or 2-metal.

[0014] In the golf ball according to the present invention, a spin force by an iron is excellent as compared to a conventional golf ball used in competition, and a driver flying distance is almost the same as a conventional golf ball used in competition.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0016] FIG. 1 is a schematic cross sectional view of a golf ball according to an embodiment of the present invention; and

[0017] FIG. 2 is a schematic cross sectional view of a golf ball according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] The present invention is basically characterized in that when assuming the center portion of the golf ball as a first tier, the entire construction is formed of four tiers (called a 4-piece ball) or five or more tiers, thus forming a multi-tier golf ball. Various moment of inertia values are obtained by adjusting a thickness and density of each tier, and a spin degree and a flying distance are measured and analyzed using a swing robot and a flying performance measurement device, thus developing a golf ball which satisfies a spin degree and a flying distance.

[0019] Through the above experiments, the value of the moment of inertia of a golf ball needed to be less than 83 gcm.sup.2, and optimum conditions on the thickness and hardness of the outer tier, the first intermediate tier and second intermediate tier and the following tiers are found. When the following conditions are satisfied, the moment of inertia value of a golf ball is less than 83 gcm.sup.2 while obtaining a desired spin amount.

[0020] A golf ball according to the present invention is characterized in that the thickness of the outer tier (cover of outer-most side) is 0.8-1.4 mm, and the hardness (Shore D) is 40.about.50, and the thickness of the first intermediate tier (second tier from the outer most tier) is 1.0.about.3.0 mm, and the hardness (Shore D) is 50.about.65, and the thickness of each tier from the second intermediate tier (third tier from outer most tier) is 1.3.about.15 mm, and the hardness (Shore D) is 30.about.70. The length of the radius of the center is 5-18 mm, and the hardness (Shore D) is 30.about.70.

[0021] A golf ball according to the present invention is characterized in having the moment of inertia value of less than 83 gcm.sup.2.

[0022] When the thickness of the outer tier is less than 0.8 mm, the difference of the flying distance between when a ball is hit on a portion with a dimple and the portion without a dimple is large. When the thickness of the outer tier is more than 1.4 mm, the loss of the flying distance increases greatly and is undesirable.

[0023] When the cover hardness (Shore D) of the outer tier is more than 50, the spin generation force of an iron decreases and might result in failing to achieve the objective of the present invention. When the cover hardness is less than 40, the flying distance significantly decreases, which keep consumers from selecting the product.

[0024] When the thickness of the first intermediate tier is less than 1.0 mm, the flying distance is decreased, and when above 3.0 mm, the impact does not feel good. When the hardness (Shore D) of the first intermediate tier is less than 50, the flying distance decreases, and when more than 65, the impact feels bad.

[0025] It is preferred that the thickness of each tier from the second intermediate tier is in a range of 1.3.about.15 mm, and it is determined considering the thicknesses of the other tiers, the radius of the center portion, and the entire diameter of the golf ball. The radius of the center portion is determined to be in a range of 5-18 mm, considering the thicknesses of the other tiers and the entire diameter of the golf ball.

[0026] A golf ball according to the present invention, in the case of a four-piece golf ball, the thicknesses of the outer tier and the first intermediate tier and the hardness are determined to meet the above conditions. The thickness of the second intermediate tier is in a range of 1.3.about.15 mm, and the radius of the center portion is in a range of 5.about.18 mm. The thickness of the second intermediate tier and the size of the center portion are determined considering the entire diameter of the golf ball.

[0027] When the thickness of the second intermediate tier becomes thicker, the radius of the center portion becomes relatively shorter, so the diameter of the golf ball can be in the desired range. The diameter of the golf ball used in competition is regulated to be longer than 42.67 mm. However, since having shorter diameters in most golf balls provide advantageous flying distances, it is preferred that most golf balls are slightly longer than 42.6 mm. The diameters of golf balls according to the first and second embodiments of the present invention are 42.7 mm, respectively.

[0028] In the case of a five-piece golf ball, it is constituted to have the thickness and hardness of the outer tier and the first intermediate tier as described above, and the thicknesses of the second intermediate tier and the third intermediate tier are determined to be in a range of 1.3.about.15 mm, and the length of the radius of the center portion is in a range of 5.about.18 mm. The thicknesses of the second and third intermediate tiers and the size of the center portion must be properly adjusted to obtain a desired size in the entire diameter of the golf ball.

[0029] In case of the six-piece or seven-piece golf ball, the thicknesses of the outer tier and the first intermediate tier are determined to meet the above conditions, and the thicknesses of the second, third and fourth or fifth intermediate tiers are determined to be in a range of 1.3.about.15 mm in consideration of the diameter of the entire golf ball, and the radius of the center portion is in a range of 5.about.18 mm.

[0030] In the second and subsequent intermediate tiers, it cannot affect a moment of inertia when the respective thickness is less than 1.3 mm, and when the thickness is above 15 mm, it is impossible to obtain an enough thickness in other tiers in relation with the other tiers.

[0031] In the second and subsequent intermediate tiers and the center part, the flying distance becomes significantly decreased when each tier is less than 30 in its hardness (Shore D), and provides a bad impact feeling when each tier is more than 70 in its hardness, so it is preferred to use the material having a hardness in a range of 30.about.70.

[0032] FIG. 1 is a cross sectional view illustrating a golf ball according to a first embodiment of the present invention.

[0033] The golf ball 1 of the first embodiment is a four-piece golf ball. The golf ball 1 is formed of an outer tier 10, a first intermediate tier 20, a second intermediate tier 22, and a center part 30.

[0034] The outer tier 10 has a thickness of 1.325 mm, and the hardness (Shored D) is 48. According to another embodiment of the present invention, the thickness may be in a range of 0.8-1.4 mm, and the hardness in a range of 40.about.50.

[0035] The outer tier 10 is formed of an ionomer resin, and the ionomer resin is made by neutralizing mono-olefin containing at least a part of unsaturated carbonic acid with a number of 3.about.8 carbon atoms and an ester of carbonic acid with a 1- or 2-metal.

[0036] According to another embodiment of the present invention, the outer tier is made of polyurethane containing at least one of ester type polyurethane, ether type polyurethane or ether ester copolymer type polyurethane.

[0037] The polyurethane may be formed of polyurethane elastomer made by polymerizing polyol, disocianate, crosslinker, etc. or may be formed of 2-liquid type polyurethane mixed in the course of forming polyol and pole isocianate.

[0038] The first intermediate tier 20 has a thickness of 1.45 mm and a hardness (Shore D) of 45. According to another embodiment of the present invention, the thickness may be in a range of 1.0.about.2.0 mm, and the hardness in a range of 50.about.65.

[0039] The first intermediate tier 20 is formed of ionomer resin, and the ionomer resin is made by neutralizing mono-olefin with a 1- or 2-metal, the mono-olefin containing at least a part of unsaturated carbonic acid of 3.about.8 carbon atoms and an ester of the carbonic acid.

[0040] The second intermediate tier 22 has a thickness of 6.55 mm and hardness of (Shore D) of 45. According to another embodiment of the present invention, the thickness may be in a range of 1.3.about.15 mm, and the hardness in a range of 30.about.70.

[0041] The radius of the center portion 30 is 12.05 mm, and the hardness (Shore D) is 52. According to another embodiment of the present invention, the thickness may be in a range of 5.about.8, and the hardness in a range of 30.about.70.

[0042] The detailed materials of the second intermediate tier and the center portion are shown in the following table, provided that the materials may be properly selected depending on the hardness, density, etc.

[0043] The moment of inertia of the golf ball 1 according to an embodiment of the present invention is 83 gcm.sup.2, the computation of which will be described later.

[0044] FIG. 2 is a schematic cross sectional view of a golf ball according to a second embodiment of the present invention.

[0045] The golf ball 1a of the second embodiment of the present invention is a five-piece golf ball. The golf ball 1a is formed of an outer tier 10, a first intermediate tier 20, a second intermediate tier 22, a third intermediate tier 24, and a center part 30. The description of each element is the same as or similar to the description of the first embodiment.

[0046] As further embodiments of the present invention, there are third and fourth embodiments which are each five-piece golf balls. Golf balls according to the third and fourth embodiments of the present invention, as compared to the second embodiment, each comprise a five-piece ball as does the second embodiment, but the value of the physical properties of each tier and the center part are different. In case of the third and fourth embodiments, the entire appearance is similar with the second embodiment, so drawings are not separately provided.

[0047] The diameters, weights and hardness of the outer tier, the intermediate tier and the center part of each golf ball according to the first, second, third and fourth embodiments of the present invention are shown in the table below.

[0048] The following table also shows the comparisons between comparisons 1, 2, 3 and 4 and the embodiments of the present invention.

TABLE-US-00001 third second first physical intermediate intermediate intermediate property center tier tier tier outer tier comparison1 diameter (mm) 40.1 42.75 (2PC) weight (g) 38.936 45.508 hardness 43 48 comparison2 diameter (mm) 29.8 40.1 42.75 (3PC) weight (g) 15.184 38.680 45.452 hardness 52 43 48 comparison3 diameter (mm) 29.62 40.1 42.75 (3PC) weight (g) 13.037 38.705 45.540 Hardness 47 45 48 first diameter (mm) 24.1 37.2 40.1 42.75 embodiment weight (g) 7.965 32.412 38.937 45.621 (4PC) Hardness 52 45 45 48 comparison4 diameter (mm) 29.55 37.1 40.1 42.75 (4PC) weight (g) 12.945 32.072 38.951 45.699 Hardness 47 50 45 48 second diameter (mm) 29.9 34.1 37.1 40.1 42.75 embodiment weight (g) 15.295 24.952 32.070 38.868 45.604 (5PC) Hardness 52 48 43 45 48 comparison5 diameter (mm) 29.4 34.2 37.2 40.1 42.75 (5PC) weight (g) 12.564 23.433 32.247 38.997 45.746 Hardness 55 43 49 45 48 comparison6 diameter (mm) 29.4 35.2 37 40.1 42.75 (5PC) weight (g) 12.664 23.851 29.461 38.448 45.264 Hardness 55 44 46 44 48 comparison7 diameter (mm) 29.9 34.1 37.1 40.1 42.75 (5PC) weight (g) 15.241 22.900 31.753 38.959 45.516 Hardness 49 43 45 45 48 third diameter (mm) 29.9 34 37 40.1 42.75 embodiment weight (g) 15.235 23.611 31.931 38.762 45.521 (5PC) Hardness 49 42 48 45 48 fourth diameter (mm) 29.9 34 37 40.1 42.75 embodiment weight (g) 15.257 25.435 31.935 38.770 45.503 (5PC) Hardness 49 50 40 45 48

[0049] The following table shows the specific mixing ratios of the first embodiment and the first to fourth comparisons.

TABLE-US-00002 First comparison1 comparison2 comparison3 embodiment comparison4 Mixed chemicals 2PC 3PC 3PC 4PC 4PC center cis-1,4-poly butadiene 100 100 100 rubber 2,2'-methylenebis(4-ethyl- 0.5 0.5 0.5 6-tertiarybutyl phenol) zinc oxide 16.6 7 7 Sub-creamic acid zinc 30 31 31 dicumyl peroxide (40%) 3 3 3 surlyn HPF2000(product 100 100 name of ionomer resin) second cis-1.4-poly butadiene 100 100 100 100 intermediate rubber tier 2,2'-methylenebis(4-ethyl- 0.5 0.5 0.5 0.5 6-tertiarybutyl phenol) zinc oxide 22.8 38.9 29.8 67.4 Sub-creamic acid zinc 30 30 30 30 dicumyl peroxide (40%) 3 3 3 3 first surlyn HPF1000(product 100 100 intermediate name of ionomer resin) tier zinc oxide 5 5 outer surlyn #8320(product name 73 73 73 73 73 tier of ionomer resin) surlyn #9910(product name 27 27 27 27 27 of ionomer resin) titanium oxide(Rutile type) 2 2 2 2 2 zirconium oxide 3 3 3 3 3

[0050] The following shows the mixing ratios of the second to forth embodiments and the fifth to seventh comparisons.

TABLE-US-00003 secod Fifth Sixth Seventh third fourth embodiment comparison comparison comparison embodiment embodiment Mixed chemicals 5PC 5PC 5PC 5PC 5PC 5PC center cis-1.4-poly butadiene 100 100 100 100 rubber 2,2'-methylenebis(4-ethyl- 0.5 0.5 0.5 0.5 6-tertiarybutyl phenol) zinc oxide 7 7 7 7 Sub-creamic acid zinc 31 31 31 31 dicumyl peroxide (40%) 3 3 3 3 surlyn HPF{circumflex over ( )}OO(product 100 100 100 name of ionomer resin) Third cis-1.4-poly butadiene 100 100 100 100 100 100 intermediate rubber tier 2,2'-methylenebis(4-ethyl- 0.5 0.5 0.5 0.5 0.5 0.5 6-tertiarybutyl phenol) zinc oxide 63.2 67.8 27.4 14.2 31.4 85.6 Sub-creamic acid zinc 30 30 30 30 30 30 dicumyl peroxide (40%) 3 3 3 3 3 3 second cis-1.4-poly butadiene 100 100 100 100 100 100 intermediate rubber tier 2,2'-methylenebis(4-ethyl- 0.5 0.5 0.5 0.5 0.5 0.5 6-tertiarybutyl phenol) zinc oxide 19.1 69.2 43.2 75.8 53.9 0 Sub-creamic acid zinc 30 30 30 30 30 30 dicumyl peroxide (40%) 3 3 3 3 3 3 first cis-1.4-poly butadiene 100 intermediate rubber tier 2,2'-methylenebis (4-chil- 0.5 6-tertiarybutyl phenol) zinc oxide 45 Sub-creamic acid zinc 30 dicumyl peroxide (40%) 3 surlyn HPFIOOO 100 100 100 100 100 (product name of ionomer resin) zinc oxide 5 5 5 5 5 outer Surlyn #8320 (product 73 73 73 73 73 73 tier name of ionomer resin) surlyn #9910 27 27 27 27 27 27 (product name of ionomer resin) Titanium oxide(Rutile 2 2 2 2 2 2 type) zirconium oxide 3 3 3 3 3 3

[0051] The computations for the moment of inertias are derived from the following two articles "Fundamentals of Physics 7/e by David Halliday, 2006, p 302-p 305" and "Physics for Scientists and Engineers with Modern Physics 6/e by Raymond A. Serway, 2004, p 211-p 217".

[0052] In the common formula, the moment of inertia I of the golf ball of four non-uniform tiers can be computed from the following formula. The radius of each tier from the portion of the outer to the outer side is r.sub.i, and the density of each tier is .rho..sub.i.

[0053] The moment of inertia (I) is,

.intg. r 2 m = 8 15 .pi..rho. 1 r 1 5 + 8 15 .pi..rho. 2 ( r 2 5 - r 1 5 ) + 8 15 .pi..rho. 3 ( r 3 5 - r 2 5 ) + 8 15 .pi..rho. 4 ( r 4 5 - r 3 5 ) ##EQU00001##

[0054] The moment of inertia values of the first to four embodiments and the comparisons are computed using the above formula. In the following formula, since the moment of inertia value I uses the unit of gcm.sup.2, the lengths in the above table is converted into the values by the units of cm.

TABLE-US-00004 third second first intermediate intermediate intermediate Moment center tier tier tier outer tier of inertia comparison1 Radius (cm) 2.005 2.1375 82.55 density(g/cm.sup.3) 1.153 0.974 volume 33.762 40.508 partialvolume 33.762 6.746 weight 38.936 45.508 partialweight 38.936 6.572 comparison2 Radius (cm) 1.49 2.005 2.1375 83.59 density(g/cm.sup.3) 1.096 1.180 1.004 volume 13.856 33.762 40.508 partialvolume 13.856 19.906 6.746 weight 15.184 38.68 45.452 partialweight 15.184 23.496 6.772 comparison3 Radius (cm) 1.481 2.005 2.1375 86.12 density(g/cm.sup.3) 0.958 1.273 1.013 volume 13.607 33.762 40.508 partialvolume 13.607 20.156 6.746 weight 13.037 38.705 45.54 partialweight 13.037 25.668 6.835 first Radius (cm) 1.205 1.86 2.005 2.1375 82.36 embodiment density(g/cm.sup.3) 1.087 1.246 0.958 0.991 volume 7.329 26.954 33.762 40.508 partialvolume 7.329 19.625 6.808 6.746 weight 7.965 32.412 38.937 45.621 partialweight 7.965 24.447 6.525 6.684 comparison4 Radius (cm) 1.4775 1.855 2.005 2.1375 85.07 density(g/cm.sup.3) 0.958 1.446 0.979 1.000 volume 13.510 26.737 33.762 40.508 partialvolume 13.510 13.227 7.025 6.746 weight 12.945 32.072 38.951 45.699 partialweight 12.945 19.127 6.879 6.748 second Radius (cm) 1.495 1.705 1.855 2.005 2.1375 82.72 embodiment density(g/cm.sup.3) 1.093 1.427 1.191 0.968 0.999 volume 13.996 20.762 26.737 33.762 40.508 Partialvolume 13.996 6.765 5.976 7.025 6.746 weight 15.295 24.952 32.070 38.868 45.604 Partialweight 15.295 9.657 7.118 6.798 6.736 comparison5 Radius (cm) 1.47 1.71 1.86 2.005 2.1375 85.46 density(g/cm.sup.3) 0.944 1.423 1.467 0.991 1.001 volume 13.306 20.945 26.954 33.762 40.508 Partialvolume 13.306 7.639 6.009 6.808 6.746 weight 12.564 23.433 32.247 38.997 45.746 Partialweight 12.564 10.869 8.814 6.750 6.749 comparison6 Radius (cm) 1.47 1.76 1.85 2.005 2.1375 85.86 density(g/cm.sup.3) 0.952 1.174 1.522 1.241 1.010 volume 13.306 22.836 26.522 33.762 40.508 Partialvolume 13.306 9.531 3.686 7.240 6.746 weight 12.664 23.851 29.461 38.448 45.264 Partialweight 12.664 11.187 5.610 8.987 6.816 comparison7 Radius (cm) 1.495 1.705 1.855 2.005 2.1375 83.38 density(g/cm.sup.3) 1.089 1.132 1.481 1.026 0.972 volume 13.996 20.762 26.737 33.762 40.508 Partialvolume 13.996 6.765 5.976 7.025 6.746 weight 15.241 22.900 31.753 38.959 45.516 Partialweight 15.241 7.659 8.853 7.206 6.557 third Radius (cm) 1.495 1.7 1.85 2.005 2.1375 82.97 embodiment density(g/cm.sup.3) 1.089 1.272 1.400 0.943 1.002 volume 13.996 20.580 26.522 33.762 40.508 Partialvolume 13.996 6.583 5.942 7.240 6.746 weight 15.235 23.611 31.931 38.762 45.521 Partialweight 15.235 8.376 8.320 6.831 6.759 fourth Radius (cm) 1.495 1.7 1.85 2.005 2.1375 82.18 embodiment density(g/cm.sup.3) 1.090 1.546 1.094 0.944 0.998 volume 13.996 20.580 26.522 33.762 40.508 Partialvolume 13.996 6.583 5.942 7.240 6.746 weight 15.257 25.435 31.935 38.770 45.503 Partialweight 15.257 10.178 6.500 6.835 6.733

[0055] The following table shows flying performances of the first to fourth embodiments of the present invention and the first to seventh comparisons. The equipment used in the test were the measurement instruments of Iron Byron Robot, Trackman, and the test impacting club was Callaway Driver-`R`SHAFT-10.5.degree., and the test place was R&D center of the applicant of the present invention.

TABLE-US-00005 Moment of Spin Total flying inertia amount carry Run distance (g -cm.sup.2) (rpm) (yd) (yd) (yd) comparison 1(2PC) 82.55 2219 229.6 34.7 264.3 comparison2(3PC) 83.59 1964 231.9 37.5 269.4 comparison3(3PC) 86.12 2486 237.1 31.1 268.2 First 82.36 2001 234.5 37 271.5 embodiment(4PC) comparison4(4PC) 85.07 2277 238.6 32.4 271 Second 82.72 1969 234.1 37.3 271.4 embodiment(5PC) comparison5(5PC) 85.46 2267 237.5 33.4 270.9 comparison6(5PC) 85.86 2646 239.8 28.1 267.9 comparison7(5PC) 83.38 2058 234.7 36.2 270.9 Third 82.97 2024 235.9 36.3 272.2 embodiment(5PC) Fourth 82.18 1961 235.7 37.1 272.8 embodiment(5PC)

[0056] The following results are obtained from the above tables.

[0057] First, comparing the first to third comparisons (2PC, 3PC and 3PC), the spin amount of the second comparison (3PC) is smallest at 1964 and has the longest flying distance. So, it can be shown that when the value of the moment of inertia is small, and the spin amount is small, the flying distance becomes longer. In the case of 2PC and 3PC, since the cover on the core is respectively formed of one tier, the flying distance becomes shorter as compared to 4PC and 5PC, which is not appropriate for a golf ball of the present invention.

[0058] Second, comparing the first (4PC) and the fourth comparisons (4PC), the spin amount of the first embodiment is small at 2001, and the flying distance is longer by 0.5 yards, which shows the effects of the moment of inertias of the present invention.

[0059] Third, the second to fourth embodiments (all 5PC) have the moment of inertias of less than 83 gcm.sup.2, and the fifth to seventh comparisons (all 5PCs) have the moment of inertias of above 83 gcm.sup.2, and the average flying distance of the second to fourth embodiments (all 5PCs) were 2.2 yards longer when compared to the average flying distance of the fifth to seventh comparisons (all 5PCs), which prove the moment of inertia effects of the present invention.

[0060] The terminologies used in the detailed descriptions of the present invention are described as follows.

[0061] A cover means an outer tier of a golf ball made of resin. A spin means a rotation of a golf ball. A driver is a type of club. A run mean a distance that a golf ball rolls. A carry means the distance that a golf ball flies. A iron is a type of club. A groove means a groove formed on the head part of a golf club. A wedge is a type of club. Ionomer means a resin containing metallic ions.

[0062] As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described examples are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the meets and bounds of the claims, or equivalences of such meets and bounds are therefore intended to be embraced by the appended claims.

Claims

1. A golf ball including a center portion, at least two intermediate tiers sequentially surrounding the center portion, and an outer tier surrounding the intermediate tiers, comprising: said outer tier having a thickness in a range of 0.8.about.1.4 mm, and an a hardness (Shore D) in a range of 40.about.50; among the intermediate tiers, said first intermediate tier formed just below the outer tier, having a thickness in a range of 1.0.about.2.0 mm and a hardness (Shore D) in a range of 50.about.65; each intermediate tier formed just below the first intermediate tier having a thickness in a range of 1.3.about.1.5 mm, and a hardness (Shore D) in range of 30.about.70; the radius of the center portion is in a range of 5.about.18 mm, and a hardness (Shore D) in a range of 30.about.70; and a moment of inertia value of the golf ball is less than 83 gcm.sup.2.

2. The golf ball of clam 1, wherein said outer tier is made of an ionomer resin, and said ionomer resin is made by neutralizing mono-olefin containing at least a part of unsaturated carbonic acid with a number of 3.about.8 carbon atoms and an ester of carbonic acid with a 1- or 2-metal.

3. The golf ball of claim 1, wherein said outer tier is a polyurethane containing at least one among an ester type polyurethane, ether type polyurethane or ether ester copolymer type polyurethane, and is formed of a poly urethane elastomer made by polymerizing polyol, disocianate, crosslinker, etc. or is formed of 2-liquid type polyurethane mixed in the course of forming polyol and pole isocianate.

4. The golf ball of claim 1, wherein said first intermediate tier is formed of an ionomer resin, said ionomer resin being made by neutralizing mono-olefin containing at least a part of unsaturated carbonic acid with a number of 3.about.8 carbon atoms and an ester of carbonic acid with a 1- or 2-metal.