US20110300968A1

US20110300968A1 - Golf ball

Info

Publication number: US20110300968A1
Application number: US13/118,909
Authority: US
Inventors: Hui Tak RYU; Jeong Su Kim; Gyu Tak Lee; Chan Rae Kim; Jae Ho Lee; Gi Min Ryu; Gyeong An Moon
Original assignee: Volvik Inc
Current assignee: Volvik Inc
Priority date: 2010-06-07
Filing date: 2011-05-31
Publication date: 2011-12-08
Also published as: CN102294110A; KR100995019B1; JP2011255172A

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˜1.4 mm, and an a hardness (Shore D) in a range of 40˜50; among the intermediate tiers, said first intermediate tier formed just below the outer tier, having a thickness in a range of 1.0˜2.0 mm and a hardness (Shore D) in a range of 50˜65; each intermediate tier formed just below the first intermediate tier having a thickness in a range of 1.3˜1.5 mm, and a hardness (Shore D) in range of 30˜70; the radius of the center portion is in a range of 5˜18 mm, and a hardness (Shore D) in a range of 30˜70; and a moment of inertia value of the golf ball is less than 83 g·cm². 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

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

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.
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).
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.
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.
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.
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.
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

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.
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˜1.4 mm, and a hardness (Shore D) in a range of 40˜50; a first intermediate tier formed just below the outer tier among the intermediate tier having a thickness in a range of 1.0˜2.0 mm and a hardness (Shore D) in a range of 50˜65; each intermediate tier formed just below the first intermediate tier having a thickness in a range of 1.3˜1.5 mm, and a hardness (Shore D) in range of 30˜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˜70; and a moment of inertia value of the golf ball is less than 83 g·cm²value.
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˜8 carbon atoms and the ester of carbonic acid with a 1- or 2-metal.
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.
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˜8 carbon atoms and the ester of carbonic acid with a 1- or 2-metal.
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

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.

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

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

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.
Through the above experiments, the value of the moment of inertia of a golf ball needed to be less than 83 g·cm², 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 g·cm²while obtaining a desired spin amount.
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˜50, and the thickness of the first intermediate tier (second tier from the outer most tier) is 1.0˜3.0 mm, and the hardness (Shore D) is 50˜65, and the thickness of each tier from the second intermediate tier (third tier from outer most tier) is 1.3˜15 mm, and the hardness (Shore D) is 30˜70. The length of the radius of the center is 5-18 mm, and the hardness (Shore D) is 30˜70.
A golf ball according to the present invention is characterized in having the moment of inertia value of less than 83 g·cm².
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.
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.
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.
It is preferred that the thickness of each tier from the second intermediate tier is in a range of 1.3˜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.
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˜15 mm, and the radius of the center portion is in a range of 5˜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.
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.
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˜15 mm, and the length of the radius of the center portion is in a range of 5˜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.
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˜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˜18 mm.
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.
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˜70.
FIG. 1 is a cross sectional view illustrating a golf ball according to a first embodiment of the present invention.
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.
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˜50.
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˜8 carbon atoms and an ester of carbonic acid with a 1- or 2-metal.
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.
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.
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˜2.0 mm, and the hardness in a range of 50˜65.
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˜8 carbon atoms and an ester of the carbonic acid.
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˜15 mm, and the hardness in a range of 30˜70.
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˜8, and the hardness in a range of 30˜70.
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.
The moment of inertia of the golf ball 1 according to an embodiment of the present invention is 83 g·cm², the computation of which will be described later.
FIG. 2 is a schematic cross sectional view of a golf ball according to a second embodiment of the present invention.
The golf ball 1 a of the second embodiment of the present invention is a five-piece golf ball. The golf ball 1 a 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.
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.
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.
The following table also shows the comparisons between comparisons 1, 2, 3 and 4 and the embodiments of the present invention.


		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

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


				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

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


	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

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”.
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_i, and the density of each tier is ρ_i.
The moment of inertia (I) is,
$\int r^{2} \partial m = \frac{8}{15} {πρ}_{1} r_{1}^{5} + \frac{8}{15} {πρ}_{2} (r_{2}^{5} - r_{1}^{5}) + \frac{8}{15} {πρ}_{3} (r_{3}^{5} - r_{2}^{5}) + \frac{8}{15} {πρ}_{4} (r_{4}^{5} - r_{3}^{5})$
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 g·cm², the lengths in the above table is converted into the values by the units of cm.


	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/cm³)	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/cm³)	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/cm³)	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/cm³)	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/cm³)	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/cm³)	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/cm³)	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/cm³)	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/cm³)	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/cm³)	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/cm³)	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

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°, and the test place was R&D center of the applicant of the present invention.


Moment of	Spin			Total flying
inertia	amount	carry	Run	distance
(g -cm²)	(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)

The following results are obtained from the above tables.
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.
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.
Third, the second to fourth embodiments (all 5PC) have the moment of inertias of less than 83 g·cm², and the fifth to seventh comparisons (all 5PCs) have the moment of inertias of above 83 g·cm², 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.
The terminologies used in the detailed descriptions of the present invention are described as follows.
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.
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˜1.4 mm, and an a hardness (Shore D) in a range of 40˜50;

among the intermediate tiers, said first intermediate tier formed just below the outer tier, having a thickness in a range of 1.0˜2.0 mm and a hardness (Shore D) in a range of 50˜65;

each intermediate tier formed just below the first intermediate tier having a thickness in a range of 1.3˜1.5 mm, and a hardness (Shore D) in range of 30˜70;

the radius of the center portion is in a range of 5˜18 mm, and a hardness (Shore D) in a range of 30˜70; and

a moment of inertia value of the golf ball is less than 83 g·cm².

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˜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˜8 carbon atoms and an ester of carbonic acid with a 1- or 2-metal.