JP2000157647A - Multipiece golf ball - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve hit feeling and to increase a driving distance by using a cover superior in softness and impact resilience. SOLUTION: This golf ball comprises at least one layer of core, and at least one layer of cover formed on the core. One this occasion, M>=1.085D-34.25 is satisfied when the slab hardness of at least one layer of cover is D, a flexural rigidity ratio is N (kg/cm2), and N/D=M.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-piece golf ball having a good feel at impact and an improved flight distance by using a cover having flexibility and excellent rebound resilience.

[0002]

2. Description of the Related Art In recent years, ionomer resins have been widely used as base resins for golf ball covers.
In particular, in a two-piece solid golf ball using a solid core, an ionomer resin is almost always used as a base resin for a cover. This is because the ionomer resin has excellent durability, cut resistance, and resilience, and is easy to process.

However, this ionomer resin is
Balata (trans-polyisoprene), which is used as a base resin for covers of thread-wound golf balls of a multilayer structure having a thread rubber layer because it has considerably high hardness and rigidity
It is inferior to the shot feeling and controllability (easiness of spinning) in comparison with. In order to improve them, attempts have been made to soften the ionomer resin by various methods.

For example, JP-A-1-308577 and JP-A-5-308577
No. 3931 discloses an ionomer resin, α-olefin and acrylic acid, by mixing sodium ion or zinc ion neutralized soft ionomer of a terpolymer of an unsaturated carboxylic acid such as methacrylic acid and an acrylate ester, It has been proposed to soften a high-rigidity ionomer resin to improve shot feeling and controllability.
However, when a mixture of such a soft ionomer resin is used, the flexural rigidity decreases with a decrease in cover hardness. As a result, the resilience performance and flight distance of the golf ball are reduced.

JP-A-6-299052 describes that by adding a thermoplastic elastomer and a specific graft-modified product or its ionomer to an ionomer, flexibility and resilience can be improved. There is
JP-A-9-176429 describes that by blending a thermoplastic elastomer and an epoxydiene-based block copolymer with an ionomer, flexibility and resilience can be improved. However, it was not satisfactory in terms of flexibility, rebound resilience, and compatibility between the thermoplastic elastomer and the ionomer resin, and further improvement was required.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the conventional golf balls, and provides a multi-piece golf ball having a good feel at impact and an improved flight distance. The purpose is to provide.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, a multi-piece comprising one or more layers of a core and one or more layers of a cover formed on the core. In a golf ball, the slab hardness of the cover is represented by D, the flexural rigidity is represented by N (kg / cm ² ), and N
When / D is represented by M, when M and D are on a straight line represented by M = 1.085D-34.25 or in a higher M region than the straight line, a cover having excellent flexibility and resilience can be obtained. Can be
As a result, they have found that a multi-piece golf ball having a good feel at the time of hitting and an improved flight distance can be obtained, and based on this, the present invention has been completed.

That is, according to the present invention, in a multi-piece golf ball comprising one or more layers of a core and one or more layers of a cover formed on the core, the slab hardness of the one or more layers of the cover is represented by D, The rigidity is expressed in N (kg / cm ² )
The present invention relates to a multi-piece golf ball characterized in that when / D is represented by M, the relationship between M and D is represented by the following formula: M ≧ 1.085D−34.25.

Further, as a preferred embodiment, the present invention relates to
In a multi-piece golf ball comprising at least one layer of a core and at least one layer of a cover formed on the core, the slab hardness of the at least one layer of the cover is represented by D, and the flexural rigidity is represented by N (k
g / cm ² ) and N / D is represented by M, M and D
And a relationship represented by the following formula: M ≧ 1.085D−25.90.

[0010] The term "cover slab hardness" as used herein refers to the hardness of only a cover material obtained by forming a cover composition into a slab, that is, a flat plate. The hardness is measured by using a Shore D hardness tester after storing a 2 mm hot press molded sheet at 23 ° C. for 2 weeks, stacking three or more sheets according to ASTM-2240. The hardness of the cover material includes the slab hardness described above and the cover hardness when formed into a golf ball. However, the cover hardness is affected by the hardness of the core. It is preferable to use

The cover of the golf ball of the present invention has a slab hardness of 35 to 61, preferably 40 to 58, more preferably 45 to 55.
It is necessary to have If the slab hardness is less than 35, the resilience is too soft and the rebound is reduced, and the shot feeling becomes heavy and deteriorates. If the slab hardness is more than 61, the slab becomes too hard and the impact becomes large and the shot feeling becomes worse.

The golf ball cover of the present invention has a flexural rigidity of 500 to 2,500 kg / cm ² , preferably 700 to 2,300 kg / cm ² ,
More preferably, it has 900 to 2,000 kg / cm ² . If the flexural rigidity is less than 500 kg / cm ² , the rebound decreases, and if it is greater than 2,500 kg / cm ^2, the ball becomes too hard and the impact on the shot feeling becomes large, resulting in poor impact. The flexural rigidity of the cover is measured according to JIS K-7106 after storing a hot-pressed sheet having a thickness of about 2 mm prepared from the cover composition at 23 ° C. for 2 weeks.

In the present invention, when the slab hardness of the cover determined as described above is represented by D, the flexural rigidity is represented by N (kg / cm ² ), and N / D is represented by M, D is on a straight line represented by M = 1.085D−34.25 (I) or in a region higher than the straight line by M,
Preferably, when M is on the straight line represented by M = 1.085D-25.90 (II) or in a region higher than the straight line, a cover having excellent resilience and flexibility can be obtained.
As a result, a multi-piece golf ball having a good feeling at the time of hitting and an improved flight distance can be obtained. Further, for reasons of material production, the relationship between M and D can be further defined as represented by the following formula: M ≦ 1.085D + 1.5.

Hereinafter, the present invention will be described in more detail. The golf ball of the present invention comprises one or more layers of a core and one or more layers of a cover. The core may be either a solid golf ball core (solid core) made entirely of vulcanized rubber, or a wound core having a rubber thread layer with a rubber thread wound on a center.

The solid core is not necessarily required to be uniform and integral, but may have a multilayer structure of two or more layers. These are all known. Hereinafter, a two-piece ball using a uniform and integrated solid core will be described for simplification of the description. The solid core is obtained by vulcanizing and molding a rubber composition used for an ordinary two-piece golf ball core. The rubber composition usually contains a base rubber, a co-crosslinking agent, an organic peroxide, a filler and the like.

As the base rubber, natural rubber and / or synthetic rubber conventionally used for solid golf balls are used, particularly having at least 40%, preferably at least 80% of cis-1,4-bonds. So-called high cis polybutadiene rubber is preferred, and natural rubber, polyisoprene rubber, styrene polybutadiene rubber, ethylene-propylene-diene rubber (EPDM), or the like may be blended with the polybutadiene rubber, if desired.

Examples of the co-crosslinking agent include α, β-unsaturated carboxylic acids having 3 to 8 carbon atoms, such as acrylic acid and methacrylic acid, and monovalent or divalent metal salts thereof such as zinc and magnesium salts. And functional monomers such as trimethylolpropane trimethacrylate, and mixtures thereof. Of these, zinc acrylate which imparts high resilience is preferred. The amount is 15 parts by weight based on 100 parts by weight of the base rubber.
6060 parts by weight, preferably 20-40 parts by weight. If the amount is more than 60 parts by weight, it becomes too hard and the feel when hitting becomes poor.If the amount is less than 15 parts by weight, the amount of organic peroxide must be increased in order to obtain an appropriate hardness, and the resilience becomes poor, resulting in poor flight performance. Distance decreases.

Examples of the organic peroxide include dicumyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-
Trimethylcyclohexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, t-butyl peroxide and the like are mentioned, and dicumyl peroxide is preferred. The compounding amount is 0.3 to 5.0 parts by weight, preferably 0.5 to 3.0 parts by weight based on 100 parts by weight of the base rubber. If the amount is less than 0.3 part by weight, the vulcanized rubber will not be sufficiently vulcanized. If the amount exceeds 5.0 parts by weight, the vulcanized rubber will be too hard and the shot feeling will be poor.

The filler may be any one which is usually blended in the core of a solid golf ball, and examples thereof include inorganic fillers, specifically, zinc oxide, barium sulfate, calcium carbonate and the like. It may be used in combination with a filler, for example, tungsten powder, molybdenum powder and the like, and a mixture thereof. The compounding amount is 3 to 30 parts by weight, preferably 5 to 20 parts by weight based on 100 parts by weight of the base rubber. If the amount is less than 3 parts by weight, it is difficult to adjust the weight. If the amount exceeds 30 parts by weight, the weight fraction of rubber becomes small and the rebound becomes too low.

Further, the core of the golf ball of the present invention may appropriately contain an antioxidant, a peptizer, an organic sulfur compound, and other components which can be generally used for producing a core of a solid golf ball. However, the amount of the antioxidant is 0.1 to
It is preferably 1.0 part by weight.

The rubber composition for a core is press-vulcanized (cross-linked), for example, heated and compressed at a temperature of 140 to 170 ° C. for 10 to 40 minutes to form a spherical vulcanizate to be used as a solid core. it can. Solid core diameter is 34.5
441.0 mm, preferably 34.7-40.7 mm. If it is less than 34.5 mm, the cover becomes too thick and the impact on the shot feeling tends to increase, and if it is more than 41.0 mm, the cover becomes thin and the durability tends to decrease. In the case of a multilayer core,
The overall diameter of the multilayer core is preferably 34.5 to 41.0 mm, more preferably 34.7 to 40.7 mm for the same reason.

The thread-wound core comprises a center and a thread rubber wound on the center.
Either a liquid center or a solid center can be used. As the solid center, those obtained by vulcanizing and molding the same rubber composition as the above-mentioned solid core can be used. The rubber thread wound on the center may be the same as that conventionally used for the thread rubber layer of the thread-wound golf ball. For example, natural rubber or natural rubber and synthetic polyisoprene may be sulfur-cured or vulcanized. A rubber composition obtained by vulcanizing a rubber composition containing an agent, a vulcanization accelerator, an antioxidant and the like may be used. The thread rubber layer can be wound on a solid center by a method for manufacturing a thread wound core of a conventional thread wound golf ball. The thickness of the rubber thread layer is 1.0 to 5.0 mm, preferably 1.5 to 4.0 mm. When the thickness is less than 1.0 mm, the impact relaxation at the time of hitting is not utilized, and the shot feeling is deteriorated. When the thickness is more than 5.0 mm, the spin rate at the time of hitting increases and the flight distance decreases.

However, these solid cores and wound cores are merely examples, and the present invention is not limited to these examples.

Next, a cover is coated on the core. This cover is not limited to one layer, and may have a multilayer structure of two or more layers. The cover of the present invention comprises a mixture of (a) an ionomer resin, (b) a thermoplastic elastomer selected from the group consisting of polyamide-based, polyester-based and polyurethane-based thermoplastic elastomers, and (c) a diene-based block copolymer. Become.

The above ionomer resin (a) is obtained by neutralizing at least a part of carboxyl groups in a copolymer of ethylene and α, β-unsaturated carboxylic acid with a metal ion;
Alternatively, at least a part of carboxyl groups in a terpolymer of ethylene, α, β-unsaturated carboxylic acid and α, β-unsaturated carboxylic acid ester is neutralized with a metal ion. As the above α, β-unsaturated carboxylic acid, for example, acrylic acid, methacrylic acid, fumaric acid, maleic acid,
Crotonic acid and the like are mentioned, and acrylic acid and methacrylic acid are particularly preferable. Further, as the α, β-unsaturated carboxylic acid ester metal salt, for example, acrylic acid, methacrylic acid,
Methyl, ethyl, propyl such as fumaric acid and maleic acid,
N-butyl, isobutyl ester and the like are used, and acrylate and methacrylate are particularly preferred.
Carboxyl groups in the above-mentioned copolymers of ethylene and α, β-unsaturated carboxylic acid or in terpolymers of ethylene, α, β-unsaturated carboxylic acid and α, β-unsaturated carboxylic acid ester As the metal ion that neutralizes at least a part of, sodium, potassium, lithium, magnesium,
Calcium, zinc, barium, aluminum, tin, zirconium, cadmium salts and the like can be mentioned, and sodium, zinc and magnesium salts are particularly preferable.

A specific example of the above ionomer resin (a) is exemplified by a trade name. For example, Mitsui Dupont Polychemical Co., Ltd.
Himilan 1555 (Na), 1557 (Zn), commercially available from
1601 (Na), 1605 (Na), 1705 (Zn), 1706 (Zn), 1707
(Na), AM7311 (Mg), AM7315 (Zn), AM7317 (Zn), AM73
18 (Na), MK7320 (K), and Himilan 1855 (Zn), 1856 (Na), and Himilan AM7316 (Zn) as terpolymer ionomer resins. AD8920 (Na), AD8940 (Na), AD89
45 (Na), AD9910 (Zn), AD9945 (Zn), AD7930 (Li), AD
7940 (Li) and Surlyn AD8265 (Na), AD8269 (Na), and AD8542 (Mg) as terpolymer ionomers, and Iotech (IOTEC) 7010 commercially available from Exxon Chemical Company. (Zn) and 8000 (Na). In addition, Na, Zn, K, Li, Mg, etc. described in parentheses () after the trade name of the ionomer resin indicate neutralizing metal ion species thereof. As these ionomers, the above-mentioned examples may be used alone or as a mixture of two or more. The above ionomer resin (a)
Assuming that the total amount of resin for the cover is 100 parts by weight,
0 to 98 parts by weight, preferably 50 to 95 parts by weight. If the amount is less than 40 parts by weight, the resilience tends to decrease. If the amount is more than 98 parts by weight, the impact becomes large and the shot feeling tends to decrease.

As a specific example of the thermoplastic elastomer (b) used in the present invention, for example, a polyamide-based thermoplastic elastomer is commercially available from Toray Industries, Inc. under the trade name "Pebax" (for example, "Pebax 2533SN00"). ),
Polyester thermoplastic elastomer is DuPont Toray
Available under the trade name "Hytrel 3548" and "Hytrel 4047" from Co., Ltd., and polyurethane thermoplastic elastomer is Takeda Birdish.
Examples include those commercially available from Co., Ltd. under the trade name "Elastollan" (for example, "Elastollan ET880").
The amount of the thermoplastic elastomer (b) is 1 to 30 parts by weight, preferably 5 to 25 parts by weight, based on 100 parts by weight of the resin for the cover. If the amount is less than 1 part by weight, the effect of lowering the impact at the time of hitting the ball by blending the above elastomer becomes insufficient, and if it is more than 30 parts by weight, the cover becomes soft and the rebound resilience is reduced. Have poor compatibility and the durability tends to decrease.

The diene block copolymer (c) used in the present invention has a double bond derived from a conjugated diene compound of a block copolymer or a partially hydrogenated block copolymer. The block copolymer serving as the base is:
A block copolymer comprising a polymer block A mainly composed of at least one vinyl aromatic compound and a polymer block B mainly composed of at least one conjugated diene compound. In addition, the partially hydrogenated block copolymer is obtained by hydrogenating the above block copolymer. As the vinyl aromatic compound constituting the block copolymer, for example, one or more kinds are selected from styrene, α-methylstyrene, vinyltoluene, pt-butylstyrene, 1,1-diphenylstyrene and the like. And styrene is preferred. Further, as the conjugated diene compound, for example, one or more kinds can be selected from butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, and the like. Butadiene, isoprene And combinations thereof. Specific examples of the diene-based block copolymer (c) include, for example, those marketed by Daicel Chemical Industries, Ltd. under the trade name “Epofriend” (eg, “Epofriend A1010”). The blending amount of the diene-based block copolymer (c) is 1 to 20 parts by weight, assuming that the entire cover resin is 100 parts by weight.
Preferably it is 3 to 15 parts by weight. If the amount is less than 1 part by weight, the effect of lowering the impact upon hitting due to the incorporation of the above-mentioned diene-based block copolymer becomes insufficient. Or the compatibility with the ionomer becomes poor, and the durability tends to decrease.

In addition to the above mixture, the cover used in the present invention may contain, if necessary, an inorganic filler such as zinc oxide or barium sulfate, various additives such as a pigment such as titanium dioxide, a dispersant, an antiaging agent. Agents, ultraviolet absorbers, light stabilizers and the like may be added.

The above components are usually heated and mixed at 150 to 250 ° C. for 0.5 to 15 minutes using an internal mixer such as a kneading twin screw extruder, a Banbury or a kneader to prepare a cover composition. .

The method of covering the above-mentioned cover is not particularly limited, and it can be carried out by a method of covering an ordinary golf ball cover. The cover composition is preliminarily formed into a hemispherical shell-like half shell, and two cores are used to wrap the core and pressure-formed at 130 to 170 ° C. for 1 to 5 minutes, or the cover composition is directly cored. A method of wrapping the core by injection molding on it is used. The thickness of the cover is usually 1
４4 mm. Then, when forming the cover, dimples may be formed on the ball surface as necessary, and after the cover is formed, paint finishing, stamping, and the like may be performed as necessary.

In the present invention, without impairing flight performance,
Provided is a golf ball having an excellent feel when hit.

[0033]

Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

Examples 1 to 7 and Comparative Examples 1 to 4
~ 4 golf balls were produced. Preparation of Core A core composition having the composition shown in Table 1 below was vulcanized and molded by heating at 160 ° C. for 15 minutes to obtain a solid core having an average diameter of 39.0 mm.

[0035]

[Table 1]

Preparation of cover composition The compounding materials having the compositions shown in Tables 2 and 3 below were mixed by a twin-screw kneading extruder to obtain a pellet-shaped cover composition. The amount of each component in the table is expressed in parts by weight,
Details shown by the product name in the table are shown after Table 3. The extrusion conditions were a screw diameter of 45 mm, a screw rotation speed of 200 rpm, and a screw L / D = 35, and the compound was heated to 200 to 260 ° C. at the position of the die of the extruder. The slab hardness and flexural rigidity of the obtained cover were measured, and the results are shown in Table 4 (Example) and Table 5 (Comparative Example). The test method was performed as described below.

Preparation of Golf Ball The cover composition of the above step was directly injection molded on the solid core of the above step to form a cover layer, and the surface was painted with paint to obtain a diameter of 42.7 mm and weight.
A golf ball having a weight of 45.4 g was produced. The slab hardness and flexural rigidity of the obtained cover, the ball compression of the golf ball, the coefficient of restitution, the flight distance (carry) with a driver, and the feel at the time of hitting were evaluated. The results are shown in Table 4 (Example) and The results are shown in Table 5 (Comparative Example). The test method was performed as described below.

[0038]

[Table 2]

[0039]

[Table 3]

(Note 4) Sodium ion neutralized ethylene-methacrylic acid copolymer ionomer resin manufactured by DuPont Mitsui Polychemicals Co., Ltd., Shore D hardness = 57, Flexural rigidity = 2,550 kg / cm ² (Note 5) Mitsui Zinc ion-neutralized ethylene-methacrylic acid copolymer ionomer resin manufactured by DuPont Polychemical Co., Ltd., Shore D hardness = 57, flexural rigidity = 2,550 kg / cm ² (Note 6) Manufactured by Mitsui Dupont Polychemical Co., Ltd. Sodium ion neutralized ethylene-methacrylic acid copolymer ionomer resin, Shore D hardness = 61, flexural rigidity = 3,770 kg / cm
² (Note 7) Zinc ion-neutralized ethylene-methacrylic acid copolymer ionomer resin manufactured by Mitsui Dupont Polychemical Co., Ltd., Shore D hardness = 56, flexural rigidity = 2,350 kg / cm ² (Note 8) Mitsui Dupont Poly Chemical Co., Ltd. ethylene-methacrylic acid-isobutyl acrylate terpolymer copolymer ionomer resin, Shore D hardness = 54, flexural rigidity = 917k
g / cm ² (Note 9) Sodium ion neutralized ethylene-methacrylic acid copolymer ionomer resin manufactured by DuPont, Shore D hardness = 61, Flexural rigidity = 2,775 kg / cm ² (Note 10) Zinc manufactured by DuPont Ion neutralized ethylene-methacrylic acid copolymer ionomer resin, Shore D hardness =
59, Flexural rigidity = 2,255 kg / cm ² (* 11) Magnesium ion neutralized ethylene manufactured by DuPont
-Methacrylic acid-n-butyl acrylate terpolymer ionomer resin, Shore D hardness = 44, flexural rigidity =
357 kg / cm ² (Note 12) Polyether block amide containing polyamide made by Toray Co., Ltd. as a hard component and polyether as a soft component (Note 13) Polybutadiene block containing an epoxy group made by Daicel Chemical Industries, Ltd. Styrene-butadiene with
Styrene block polymer, butadiene / styrene = 60/40 (weight ratio), JIS-A hardness = 67, epoxy content = approx.
1.5-1.7% by weight

(Test Method) Slab Hardness (Shore D Hardness) A hot-pressed sheet having a thickness of about 2 mm produced from each cover composition was stored at 23 ° C. for 2 weeks, and then subjected to the test according to ASTM-D 2240. Three or more sheets are stacked and measured using a Shore D hardness meter. Flexural rigidity A hot-pressed sheet having a thickness of about 2 mm produced from each cover composition is stored at 23 ° C. for 2 weeks, and then measured according to JIS K 7106. Ball compression Measured by the PGA measurement method. Coefficient of restitution A metal cylinder of 198.4 g is made to collide with a golf ball at a speed of 45 m / sec by an R & A initial velocity measuring machine, and the velocities of the cylinder and the golf ball before and after the collision are measured. The coefficient of restitution was calculated. It was represented by an index when Comparative Example 3 was set to 100. Flying distance The No.1 wood club (driver) is attached to a swing robot made by True Temper, and the golf ball is hit at a head speed of 45 m / sec. The flying distance to the drop point (carry)
Was measured. Impact at impact The magnitude of the impact at the time of the impact is evaluated by an actual impact test with a driver by 10 professional and top amateur golfers. The evaluation criteria are as follows. Evaluation criteria 〇 8 to 10 people answered that it was good. Δ: 4 to 7 people answered that it was good. ×: 0 to 3 people answered that it was good.

(Test results)

[Table 4]

[0043]

[Table 5]

From the above results, for Examples 1 to 7 and Comparative Examples 1 to 4, slab hardnesses D and M (= flexural rigidity N
FIG. 1 is a graph showing the relationship between the slab hardness and the slab hardness D). As is apparent from the figure, all of Examples 1 to 7 are on the straight line represented by M = 1.085D-34.25 (I) or in the M region higher than the straight line, while Comparative Examples 1 to 4 are on the straight line (I). It is in the lower M region. Furthermore,
Examples other than Examples 5 and 6 are on the straight line represented by M = 1.085D-25.90 (II) or in the M region higher than the straight line. In addition, the graph shown in FIG. 2 is plotted on Examples 1 to 7 and Comparative Examples 1 to 4 with the vertical axis representing the flight distance and the horizontal axis representing compression (the smaller the impact, the smaller the impact upon hitting and the better the feeling). (The numbers next to the plots in Examples and Comparative Examples represent the respective numbers). In other words, the larger the value on the vertical axis and the smaller the value on the horizontal axis (upper left area of the graph), the better the long flight distance and the overall performance of a small impact in feeling at impact.

As can be seen from the results shown in Tables 4 and 5 and FIG. 2, the golf balls of Examples 1 to 7 of the present invention satisfying the relationship of M ≧ 1.085D−34.25 have M ≧ 1.085D.
As compared with Comparative Examples 1 to 4, which did not satisfy the relationship of −34.25, the results were excellent in the coefficient of restitution, the carry (carry), and the overall performance in feeling at impact.

The golf ball of Example 5 has a slightly lower coefficient of restitution and a shorter flight distance than Examples 2 and 7 having the same slab hardness. The golf ball of the sixth embodiment has a lower coefficient of restitution and a longer flight distance than that of the fourth embodiment having the same slab hardness, and also has a lower coefficient of restitution and a longer flight distance than the third embodiment having the same level of slab hardness. Feeling is getting worse.

On the other hand, the golf balls of Comparative Examples 1 to 4 in which the cover composition was composed of only the ionomer resin,
The flexural rigidity is low, the coefficient of restitution is small, and the flight distance is short as compared with the embodiment having the same slab hardness. Comparative Example 4
Golf ball has a worse feeling than the golf ball having the same level of restitution coefficient and flight distance.

[0048]

The multi-piece solid golf ball of the present invention has a good feel at the time of hitting and an improved flight distance by using a cover which is flexible and has excellent rebound resilience.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the slab hardness D of a cover and M (= flexural rigidity M / slab hardness D) for golf balls of Examples and Comparative Examples.

FIG. 2 is a graph showing the relationship between compression and flight distance for the golf balls of Examples and Comparative Examples.

[Explanation of symbols]

 I: Straight line M = 1.085D-34.25 II: Straight line M = 1.085D-25.90

Claims (4)

[Claims] 1. A multi-piece golf ball comprising one or more layers of a core and one or more layers of a cover formed on the core, wherein the slab hardness of the one or more layers of the cover is represented by D,
When the flexural rigidity is represented by N (kg / cm ² ) and N / D is represented by M, the relationship between M and D is represented by the following formula: M ≧ 1.085D−34.25 Multi-piece golf ball. 2. The multi-piece golf ball according to claim 1, wherein the relationship between M and D is represented by the following formula: M ≧ 1.085D−25.90. 3. The method according to claim 1, wherein the at least one cover comprises: (a) an ionomer resin; (b) a thermoplastic elastomer selected from the group consisting of polyamide, polyester and polyurethane thermoplastic elastomers; and (c) a diene-based thermoplastic elastomer. 2. The multi-piece golf ball according to claim 1, comprising a mixture of a block copolymer. 4. The slab hardness is 35 to 61 in Shore D hardness.
The multi-piece golf ball according to claim 1, wherein