JP2001112889A - Multilayer golf ball - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain increase a good feeling of hitting ball by an increase in carry of a ball. SOLUTION: In the multilayer golf ball, two or more cover layers are formed over a core 2, a large number of recesses are formed on the inner side layer of the two cover layers 11, which are adjacent to each other, while protrusions are formed on the outer side layer thereof so that each protrusion penetrates into corresponding recess. A great circular ridgeline 12 having the same length as the outer circumference of the inner side layer, not in contact with the recesses, is formed. At least two arcuate redgelines 13, each of which intersects the great circular ridgeline 12 at right angles and has a length of at least one- fourth the outer circumference of the inner side layer, are formed on one of semispheres 11a between a pole 14 and the above great circular ridgeline. Each ridgeline 13 is not in contact with the recesses between the great circular ridgeline 12 and a point circumferentially offset by 30 deg. from a pole, while the recesses are disposed in a region defined by the arcuate ridgelines symmetrically with respect to the arcuate redgeline 13 on each of semispherical parts divided by the great circular ridgeline 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-layer golf ball having a core having two or more coating layers formed on a core, and more particularly, to a concave part in two inner layers adjacent to each other and an outer layer in the above-mentioned coating layers. The present invention relates to a multi-layered golf ball provided with a convex portion corresponding to the concave portion and penetrating into the concave portion.

[0002]

2. Description of the Related Art Conventionally, various studies and proposals have been made in order to achieve both an increase in the flight distance of a golf ball and good feeling performance. In a solid golf ball having a cover, it is common practice to form a core and a cover in multiple layers and adjust the hardness, size (diameter, thickness), and the like.

For example, Japanese Patent No. 2616385 proposes a three-piece golf ball having a core, an inner cover and an outer cover, in which the outer cover is formed harder than the inner cover.

On the other hand, the surface shape of each layer constituting a golf ball is mainly a smooth spherical surface, but US Pat.
JP-A-82,567 discloses a technique for suppressing the eccentricity of the core when the cover is injected around the core.
A golf ball having a projection on a core has been proposed.

However, the projection of the golf ball is intended to substitute for a support pin at the time of injection molding, and it has not been attempted to utilize the shape effect of the support pin projection positively.

Recently, there has been proposed a golf ball in which unevenness is provided between a solid core and a cover of a two-piece ball, an adjacent layer of a multilayer solid core, and a multilayer cover (Japanese Patent Application Laid-Open No. 9-285565, and the like). 10-3
37340, 11-89970). This golf ball can give a different hit feeling to a player depending on the direction of an external force applied to the ball when hit.

However, although the golf ball has an improved hit feeling, it is not sufficient in terms of improved flight performance, durability, and uniformity depending on the position of the hit point, and there is room for further improvement. Had left.

The present invention has been made in order to improve the above circumstances, and an object of the present invention is to provide a multi-layered golf ball having a long flight distance, a small variation, and a good shot feeling.

[0009]

Means for Solving the Problems and Embodiments of the Invention The inventor of the present invention has made it clear that two or more coating layers are formed on a core, of which two inner layers adjacent to each other have a concave portion, and the outer layer has the concave portion. As a result of intensive studies on a multi-layered golf ball with a convex portion that penetrates into the structure, in the case of a structure that includes an uneven shape, a structural design was anticipated that the unevenness itself would be used for golf ball performance. On the other hand, it has been found that the effect of the uneven shape may vary depending on the hitting surface. The greater the effect of unevenness on performance, the more uniform the array itself becomes. In view of this point, the present inventor has proceeded with various studies and can form one great circular ridge line having the same length as the outer periphery of the inner layer that does not come into contact with the concave portion, and intersect this great circular ridge line at a right angle. An arc-shaped ridge line having a length of at least 1/4 of the inner layer outer peripheral length is provided between the pole and the great circular ridge line.
Between the great circular ridge and a position 30 degrees from the pole, at least two semi-hemispheres can be formed on each side without contacting at least the concave portion, and each hemispherical part divided by the great circular ridge In the case where the concave portion is arranged in a region defined by the arc-shaped ridge line symmetrically with respect to the arc-shaped ridge line, a flight distance is large, and a golf ball having a good appearance can be obtained. It has been found that a golf ball that is easy to produce stably and has little variation in performance itself can be obtained. That is, since it is necessary to form a concave portion on the surface of the inner layer, an undercut occurs at the time of mold release after molding, and it is difficult to achieve this only by the conventional injection molding technology. Although there is a means for forming the inner layer in advance without forming the concave portion and additionally forming the concave portion therefrom, in order to make the inner layer relatively stable and inexpensive, it is desirable to solve the problem by a mold technique. In the present invention, the mold is divided and formed as a split mold, which can be formed in the category of the conventional injection molding, and a more uniform performance can be obtained by using an arrangement method in consideration of a dividing line which is a restriction on arrangement. It was designed like this.

That is, the present invention provides the following multi-layer golf ball. Claim 1: Two or more coating layers are formed on the core, and a large number of concave portions are formed in two inner layers adjacent to each other among the coating layers, and the convex portions penetrate into these concave portions corresponding to the concave portions in the outer layer. A multi-layered golf ball having a portion formed therein, wherein one great circular ridge line having the same length as the outer periphery of the inner layer not in contact with the concave portion can be formed, and intersects the great circular ridge line at right angles, An arc-shaped ridge line having a length of at least 1/4 of the inner layer outer peripheral length is provided between the pole and the great circle ridge, and between the great circle ridge and a position 30 degrees from the pole. At least two of each can be formed in one hemisphere without being in contact with the concave portion, and in each hemispherical portion divided by the great circular ridge line, the concave portion is formed in an area defined by the arc-shaped ridge line. Arranged line-symmetrically on the arcuate ridge Multi-layer structure golf ball, characterized in that was. Claim 2: The arc-shaped ridge line is 2 to 10 in one hemisphere.
2. The golf ball according to claim 1, wherein the arc-shaped ridges can be formed, and the arc-shaped ridges are suspended toward the great-circle ridge at equal angles at the poles. Claim 3: The golf ball of claim 1 or 2, wherein the interface between the two adjacent layers is at a position of 0.5 to 8 mm from the ball surface. Claim 4: Sn (mm ² ) is the imaginary sphere surface area of the inner layer where no recess is formed in the inner layer, and Sb is the sum of the surface-side opening areas of the recesses formed in the inner layer.
(Mm ² ), the ratio Sb / Sn is 0.02
4. The golf ball according to claim 1, wherein the concave portion is formed such that ≤Sb / Sn≤0.6. In a preferred embodiment, the difference in Shore D hardness between the inner layer and the outer layer adjacent to each other is 20 or more and 60 or less, and the outer layer is hard. Golf ball. Claim 6: When the diameter of the sphere in the state in which the inner layer is formed is Dn (mm), and the sum of the surface-side opening areas of the concave portions formed in the inner layer is Sb (mm ² ), 1
The golf ball according to claim 1, wherein the concave portion is formed so as to satisfy a relationship of 5-0.3 × Dn ≦ Sb ≦ 60−0.3 × Dn. In another preferred embodiment, the two adjacent layers are an inner cover and an outer cover. In a preferred embodiment, the golf ball has a surrounding layer formed over the core, and at least two cover layers formed over the surrounding layer, wherein the two adjacent layers are closest to the surrounding layer. The golf ball according to any one of claims 1 to 6, which is an inner cover.

The golf ball of the present invention is characterized in that in any of the adjacent inner and outer layers of the multilayer structure, a concave portion is formed in the inner layer and a convex portion corresponding to the concave portion is formed in the outer layer. However, in the present invention, by using the above-described arrangement method for the arrangement of the concave portions and the convex portions, variations in various performances can be reduced.

Further, by providing unevenness in two adjacent layers, it is possible to obtain an effect of mixing the material characteristics of the layer forming the concave portion and the material characteristics of the layer forming the convex portion. In the present invention, in particular, the inner layer is configured to be 20 to 60 softer in Shore D hardness than the outer layer, and when irregularities are arranged in a regular polyhedron, the spherical surface is divided into regular polyhedrons, and the basic unit is a basic unit of the regular polyhedron. The unevenness is arranged on the divided surfaces. At this time, if the arrangement is such that the unevenness arranged on the adjacent divided surfaces is line-symmetrical at the boundary line between the adjacent divided surfaces, furthermore, The effect can be exerted evenly. The basic unit of the regular polyhedron is, for example, a regular tetrahedron, a regular octahedron, a regular icosahedron a triangle, a regular hexahedron a square, and a regular dodecahedron a regular pentagon. Furthermore, when the area ratio of the concave portion on the inner layer surface forming the concave portion is in the range of 2 to 60%, the effect is further promoted.

The present inventor further paid attention to the deformation of the golf ball, and studied repeatedly in consideration of the deformation at the time of hitting. As a result, the golf ball differs depending on the compression set. Approximately 3.5-6cm
Has a contact area of about ² and deformation in the compression direction is 3-6m
m. Therefore, it has been found that the effect of the uneven structure is more effective when set within a range of 0.5 to 8 mm from the golf ball surface. In addition, the position of the interface between the inner and outer layers where irregularities are formed in consideration of the deformation as described above is defined.In the present invention, the size of the inner layer sphere and the concept of the occupation rate of the concave portion forming surface are taken into consideration. By defining the relationship as an upper limit (60-0.3 × diameter of inner sphere) and a lower limit as (15-0.3 × diameter of inner sphere), a more effective range is found. It is a thing.

Hereinafter, the present invention will be described in more detail. The golf ball of the present invention has a core in which two or more coating layers are formed, and the core may be a solid core or a wound core. The covering layer can be an envelope layer covering the core, and one or more cover layers covering the core directly or via the envelope layer.

FIG. 1 is a schematic sectional view showing one embodiment of a multi-layer golf ball of the present invention. This multi-layer golf ball 1 has a solid core 2, an envelope layer 3 covering the core 2, and a solid core 2. An inner cover 4 covers the surrounding layer 3 and an outer cover 5 covers the inner cover 4. in this case,
The surrounding layer 3 can be omitted.

The solid core is formed from a rubber composition mainly composed of a base rubber composed mainly of polybutadiene rubber. As the polybutadiene, 1,4-cis polybutadiene having a cis structure of at least 40% or more is preferable. In the base rubber, natural rubber, polyisoprene rubber, styrene butadiene rubber, and the like can be appropriately compounded with the polybutadiene, if desired. However, in order to maintain the resilience of the golf ball, other than these polybutadienes are used. The rubber component is polybutadiene 10
It is preferable that the content be 10 parts by weight or less with respect to 0 parts by weight.

The rubber composition may contain, as a crosslinking agent, zinc compounds of unsaturated fatty acids such as zinc methacrylate and zinc acrylate, magnesium salts, and ester compounds such as trimethylpropane methacrylate in addition to the rubber component. Particularly, zinc acrylate can be suitably used because of its high resilience. The compounding amount of these crosslinkers is preferably 15 to 40 parts by weight based on 100 parts by weight of the base rubber.

The compounding amount of the vulcanizing agent is 100%
It can be 0.1 to 5 parts by weight based on parts by weight.

The rubber composition may further contain, if necessary, an antioxidant or a filler for adjusting specific gravity, such as zinc oxide or barium sulfate. It can be 5 to 130 parts by weight based on parts by weight.

Preferred embodiments of the rubber composition for a solid core are as follows. Cis-1,4-polybutadiene 100 parts by weight Zinc oxide 5 to 40 parts by weight Zinc acrylate 15 to 40 parts by weight Barium sulfate 0 to 40 parts by weight Peroxide 0.1 to 5.0 parts by weight Vulcanization conditions: preferably 150 5-20 at ± 10 ° C
Vulcanize for a minute.

The above-mentioned rubber composition for a core is prepared by using a conventional kneader (for example, a Banbury mixer, a kneader or a roll).
And the resulting compound can be formed by injection molding or compression molding using a core mold.

The solid core thus obtained is:
Its diameter is preferably at least 27 mm, particularly at least 29 mm, and is preferably at most 41 mm, especially at most 40 mm.

The amount of deformation of the core under a load of 100 kg is preferably 2.5 to 7.0 mm, more preferably 3.0 to 6.0 mm. Weight is usually 12-40g
It is about.

The core may have a single-layer structure made of one kind of material.
It may be a multilayer structure composed of layers or more.

The envelope layer can be formed using a polyester resin, a polyester elastomer, an ionomer resin, a styrene-based elastomer, a polyurethane elastomer, a hydrogenated butadiene resin, and a mixture thereof, and a thermoplastic polyester elastomer is particularly preferable. Specifically, commercially available products such as Hytrel (manufactured by Toray DuPont) can be used.

The Shore D hardness of the envelope layer is 15 or more, especially 20 or more, and can be 55 or less, especially 50 or less. The thickness is 0.5 mm or more, especially 1.
5 mm or more, and may be 6 mm or less, particularly 5 mm or less.

The cover material used for forming the cover (inner cover, outer cover) is not particularly limited, and known cover materials can be used. Examples thereof include ionomer resins, polyurethane resins, polyester resins, polyester elastomers, and styrene elastomers. , A polyurethane elastomer, a hydrogenated butadiene resin, a balata rubber, and the like, but an ionomer resin is particularly preferable. Specifically, commercially available products such as “Surlyn” (manufactured by Dupont) and “Himilan” (manufactured by Dupont Mitsui Polychemicals) can be used.

Titanium dioxide, barium sulfate and the like can be added to the cover material if desired to adjust the specific gravity and the like. Furthermore, if necessary, a UV absorber, an antioxidant, a dispersant such as metal soap, and the like can be added.
The cover may have a single-layer structure made of one kind of material, or may have a multilayer structure of two or more layers in which layers made of different kinds of materials are stacked.

The total thickness of the cover is 0.5 mm or more, especially 1.0 mm or more, and can be 8 mm or less, especially 7 mm or less. In the case of a two-layer structure of the inner cover and the outer cover, the thickness of the inner cover is 0.3 mm or more, particularly 1.0 mm or more, and 7 mm or less, particularly 6 mm or less, and the outer cover is 0.5 mm or more, particularly 1.0
mm or more, and preferably 6 mm or less, particularly 4 mm or less.

The hardness of the cover is usually selected from the range of 15 to 80 as Shore D hardness. In the case of forming a two-layer structure of the inner cover and the outer cover, either of them may be hard.

According to the present invention, there is provided a golf ball having a multi-layer structure in which at least two coating layers are formed.
Among the above-mentioned coating layers, two adjacent layers, for example, in the golf ball of FIG. 1, a large number of recesses are formed in the inner layer of the inner layer cover and the outer layer cover or the inner layer of the surrounding layer and the inner layer cover, and Projections are formed corresponding to the depressions and penetrate these depressions. FIG. 1 shows a state in which a concave portion 4a is formed in the inner layer cover, and the convex portion of the outer layer cover has entered the concave portion 4a.

In this case, the number of concave portions (convex portions) is 50 or more, preferably 70 or more, more preferably 120 or more, and 500 or less, preferably 460 or less, more preferably 410 or less. It is recommended that If the amount is too small, it is difficult to obtain the function and effect, and the variation increases.
If the amount is too large, it is difficult to obtain the function and effect, and there is no great difference from the conventional multilayer golf ball.

The depth of the concave portion corresponds to the thickness of the inner layer, but is not less than 1/2 of the thickness of the inner layer, more preferably 2 /
It is preferable to form three or more, more preferably through the inner layer. Although the shape of the concave portion is not particularly limited, the concave portion can be formed in an appropriate shape such as a cylinder, a cone, a prism, a pyramid, a truncated cone, and a truncated pyramid. When the concave portion is formed in a state penetrating the inner layer, the penetrated state includes a state in which the concave portion converges in a dot shape on the inner surface of the inner layer, and most preferably a state in which the concave portion is opened on the inner surface of the inner layer. This is preferable in order to increase the reinforcing effect of the convex portion, that is, to obtain a sufficient effect.

The dimension (size; diameter in the case of a plane circle, longest side in the case of a triangle, longest diagonal in the case of a square or the like) in the outer surface of the inner layer of the recess is 0.5 mm or more, preferably Is 1.0 mm or more,
It is good to be 5.0 mm or less, preferably 4.0 mm or less.

Further, the surface area of the virtual sphere in the state where no concave portion is formed in the inner layer is defined as Sn (m).
m ² ), where Sb (mm ² ) is the sum of the surface-side opening areas of the concave portions formed in the inner layer, and the ratio Sb /
The recess so that Sn is 0.02 or more, more preferably 0.03 or more, further preferably 0.04 or more, 0.6 or less, more preferably 0.5 or less, and still more preferably 0.45 or less. Is preferably formed.

The outer surface of the inner layer (the interface between the inner layer and the outer layer) is 0.5 to 8 mm, particularly 1 to 6 mm from the surface of the golf ball (the portion where no dimple is formed).
The diameter of the sphere in the state where the inner layer is formed is Dn (mm), and the sum of the surface-side opening areas of the concave portions formed in the inner layer is Sb (m
m ² ), it is preferable to form the concave portion so as to satisfy the following relationship: 15−0.3 × Dn ≦ Sb ≦ 60−0.3 × Dn.

Here, when the concave portions are arranged on the outer surface of the inner layer, one large circular ridge line having the same length as the outer periphery of the inner layer which does not contact the concave portion can be formed. Intersect at right angles and at least 1/4 of the inner layer perimeter
The arc-shaped ridge of length is between the pole and the great circle ridge, and between the great circle ridge and the position 30 degrees from the pole, without contacting at least the concave portion, the one-sided hemisphere In each of the hemispherical portions divided by the great circular ridge line, the concave portions are arranged in a region defined by the circular ridge line symmetrically with respect to the circular ridge line.

FIG. 2 shows this, in which 11 is an inner layer, and 12 is the above-mentioned great circle-shaped ridge line which does not come into contact with a concave portion, which is usually an equator line. 13 is a pole 14
Is an arc-shaped ridge line having a length of 1/4 of the outer peripheral length of the inner layer vertically suspended from the great circle-shaped ridge line 12, and the arc-shaped ridge line (1/4 ridge line) 13 is formed into a hemisphere on one side. At least 2
Book, preferably 2 to 10, more preferably 3 to 10
Books, more preferably 3 to 8 books are formed. In this case, it is preferable that these arc-shaped ridge lines 13 are arranged at equal angles to each other at the pole point 14. These arc-shaped ridge lines 13 do not contact the concave portion between the great circular ridge line 12 and the position P 30 degrees from the pole 14, and preferably do not contact the concave portion over the entire length of the ridge line 13. Things.

Although FIG. 2 shows a state in which an arc-shaped ridge line 13 is formed on one hemisphere 11a, an arc-shaped ridge line 13 is similarly formed on another hemisphere 11b. In this case, the shape of the arc-shaped ridge line in the other one-sided hemisphere 11b is the same as the above, but the two hemispheres 11a,
In 11b, the number of arc-shaped ridge lines may be the same or different, but is preferably the same from the viewpoint of uniformity.
Further, the arc-shaped ridge of one hemisphere 11a may be continuous with the arc-shaped ridge of the other hemisphere 11b at the great circular ridge, or may be discontinuous with the arc-shaped ridge of the other hemisphere 11b. You may. In the one hemisphere 11a, two arc-shaped ridges at the extreme point 14
When there is a phase difference of degrees, these two arc-shaped ridges form a semi-circular ridge, and when these two arc-shaped ridges are continuous with the semi-circular ridge in the other hemisphere 11b, they form a great circular ridge. is there.

In addition, the concave portions are disposed in regions (for example, A and B in FIG. 2) defined by the arc-shaped ridges in a line-symmetric manner at the arc-shaped ridges.

When the concave portion is formed in the inner layer and the convex portion is formed in the outer layer as described above, the difference in hardness between adjacent inner and outer layers in Shore D hardness is 20 or more, particularly 25 or more. Yes, it is preferably 60 or less, particularly 55 or less, and the outer layer is preferably hard.

In the present invention, the inner layer can be formed by ordinary injection molding or compression molding. In this case, it is preferable to form a large number of recesses on the surface of the inner layer simultaneously with the molding of the inner layer. Specifically, a number of convex portions corresponding to a number of concave portions are formed on the inner surface of the cavity of the mold for the inner layer, and the inner layer having a number of concave portions on the surface by ordinary injection molding using the mold. Can be formed. In some cases, after forming the inner layer, it is also possible to form a concave portion by hollowing out the surface. Then, corresponding to the formation of these concave portions, convex portions are formed between these concave portions.

In the present invention, the outer layer having a projection in the inner layer is formed by subjecting the outer layer to normal injection molding or compression molding so as to cover the inner layer having a large number of concave portions formed on the surface.

The golf ball of the present invention has a ball diameter and a weight of 42.67 mm in accordance with R & A golf rules.
As described above, it can be formed to a weight of 45.93 g or less.

[0045]

As described above, the multi-layer golf ball of the present invention has a reduced spin performance, thereby reducing extra lifting force during flight of the golf ball, resulting in an increase in the flight distance. Further, with regard to the feel at impact, it is possible to simultaneously satisfy softness, pleasant lightness, light impact sound, and the like, which cannot be achieved by a structure in which only conventional ball planes are in contact with each other. At the same time, by arranging a regular polyhedron, the same shot feeling,
Spin performance and flight distance can be obtained.

[0046]

EXAMPLES The present invention will be described below in detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[Examples and Comparative Examples] The core rubber composition having the composition shown in Table 1 was kneaded with a kneader, and then vulcanized in a core mold at a temperature of 155 ° C for about 15 minutes to obtain a solid. Created the core. Further, the surrounding layer, the inner layer cover, and the outer layer cover having the composition shown in Table 1 were coated around the core by injection molding. In this case, in the molds for the inner layer covers or the surrounding layers of Examples 1 to 7 and Comparative Examples 1, 2, and 4, a large number of convex shapes (columns) are formed on the inner peripheral surface of the cavity, so that the concave portions are formed as shown in Table 2. , And in the mode shown in FIGS. In FIGS. 3 to 10, reference numeral 20 denotes a concave portion.

[0048]

[Table 1]

[0049]

[Table 2]

Next, the flight distance and hit feeling of the obtained golf ball were evaluated as follows. The results are shown in Tables 5 and 6.

Evaluation of Flight Distance A golf club manufactured by Bridgestone Sports (driver (# W1), 23
0 titanium, S shaft, 10.5 degrees of loft), head speed 45 m / sec per ball
30 pieces were hit with c and evaluated by the average value, the maximum value, and the minimum value. Evaluation of feel at impact A total of four people were evaluated, two each for amateurs and professionals. Each was tested by # W1 and # I5, and each ball was appropriately combined and hit at least three by three. The evaluation includes
The relative evaluation with respect to the prior art (Comparative Example 3) was scored and represented by an average value.

[0052]

[Table 3]

[0053]

[Table 4]

[0054]

[Table 5]

[0055]

[Table 6]

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a golf ball according to one embodiment of the present invention.

FIG. 2 is an explanatory view of a ridge line forming aspect of the present invention.

FIG. 3 is a perspective view of a recess arrangement mode I;

FIG. 4 is a perspective view of a recess arrangement mode II.

FIG. 5 is a perspective view of a concave portion arrangement mode III.

FIG. 6 is a perspective view of a recess arrangement mode IV.

FIG. 7 is a perspective view of a recess arrangement mode V;

FIG. 8 is a perspective view of a recess arrangement mode VI.

FIG. 9 is a perspective view of a concave portion arrangement mode VII.

FIG. 10 is a perspective view of a concave portion arrangement mode VIII.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Golf ball 2 Core 3 Surrounding layer 4 Inner layer cover 5 Outer layer cover

Claims (8)

[Claims] 1. A core having two or more coating layers formed on a core, wherein a large number of recesses penetrate into two adjacent inner layers of the coating layer and penetrate into these recesses corresponding to the recesses on the outer layer. A multi-layered golf ball having a convex portion, wherein one large circular ridge line having the same length as the outer periphery of the inner layer not in contact with the concave portion can be formed, and intersects the large circular ridge line at a right angle. An arc-shaped ridge having a length of at least 1/4 of the inner layer outer peripheral length is provided between the pole and the great circle ridge, and between the great circle ridge and a position 30 degrees from the pole. Can be formed at least two in one side hemisphere without contacting at least the concave portion, and in each hemispherical portion divided by the great circular ridge line, the concave portion is formed in a region defined by the arc-shaped ridge line. Arranged line-symmetrically on arc-shaped ridges A golf ball having a multilayer structure. 2. An arc-shaped ridge line having a radius of 2 to 2 in one hemisphere.
2. A golf ball according to claim 1, wherein ten arc-shaped ridges can be formed, and these arc-shaped ridges are suspended toward the great-circle ridge at the same angle at the poles. 3. The golf ball according to claim 1, wherein the interface between the two adjacent layers is at a position of 0.5 to 8 mm from the ball surface. 4. The surface area of the imaginary sphere in a state where no concave portion is formed in the inner layer is Sn (mm ² ), and the sum of the surface-side opening areas of the concave portions formed in the inner layer is Sb (mm). ² ), the ratio Sb / Sn is 0.1.
4. The golf ball according to claim 1, wherein the concave portion is formed so that 02 ≦ Sb / Sn ≦ 0.6. 5. The method according to claim 1, wherein a hardness difference in Shore D hardness between the inner layer and the outer layer adjacent to each other is 20 or more and 60 or less, and the outer layer is hard.
Item 2. The golf ball according to item 1. 6. When the diameter of the sphere in the state where the inner layer is formed is Dn (mm), and the sum of the surface-side opening areas of the concave portions formed in the inner layer is Sb (mm ² ). The golf ball according to claim 1, wherein the concave portion is formed so as to satisfy a relationship of −0.3 × Dn ≦ Sb ≦ 60−0.3 × Dn. 7. The golf ball according to claim 1, wherein the two adjacent layers are an inner cover and an outer cover. 8. A golf ball comprising a core, a surrounding layer formed over the core, and at least two cover layers formed over the surrounding layer, wherein the two adjacent layers are the surrounding layer. 7. An inner cover according to claim 1, wherein said cover is an innermost cover.
Item 2. The golf ball according to item 1.