JP2001246018A - Golf ball and method for production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a golf ball and a method for production thereof which achieve excellent flying characteristic and ball hitting touch. SOLUTION: In the golf ball comprising a core, an intermediate layer and a cover, the intermediate layer and the cover are connected with a mesh-like protruded rib penetrating into the intermediate layer from the internal surface of the cover. The core has a hardness enough to cause a distortion ranging 3.0-7.0 mm under a load of 981N, and the intermediate layer is made softer than the cover but has a Shore D hardness of 10-55 while the cover has a bending rigidity of 100-450 MPa. In the golf ball production method, the core is set at the center part of the cavity of a die which includes a protrusion for forming the mesh-like protruded rib on the inner wall surface during the forming of the intermediate layer and is provided with a plurality of gates for the injection of a resin on the circumferences at high latitudinal positions in proximity to a split face part corresponding to the equator and both poles thereof and the intermediate layer is formed at a void formed between the core and the inner wall surface of the die by forcing a resin material through the gates.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid golf ball comprising an elastic core, an intermediate layer and a cover, and a method of manufacturing the same. More specifically, the present invention relates to a solid golf ball at a boundary between the intermediate layer and the cover. The present invention relates to a golf ball provided with a convex rib on an inner surface of a cover, which intrudes into an intermediate layer, and a method of manufacturing the golf ball.

[0002]

2. Description of the Related Art Various studies and proposals have been made to achieve both an increase in the flight distance of a golf ball and good feeling characteristics.
In particular, in a golf ball including a solid core and a cover, it is generally practiced to adjust the hardness and size (diameter, thickness) of the core and the cover.

For example, US Pat. No. 5,439,227 discloses a solid core, an inner cover and an outer cover.
Among three-piece golf balls, there has been proposed a golf ball in which an outer cover is formed harder than an inner cover. Also, US Pat. No. 5,490,674 proposes a three-piece golf ball in which a cover is covered with a solid core composed of an inner layer and an outer layer, in which the inner layer core is formed harder than the outer layer core.

[0004] Generally, a boundary surface of each layer constituting a golf ball as described above is a smooth spherical surface without irregularities. However, US Pat. No. 5,692,973 discloses a cover around a solid core. When performing injection molding,
In order to suppress the eccentricity of the core, a golf ball having a plurality of protrusions on the surface of the core has been proposed.

[0005] However, the projections on the core surface of the golf ball described above are intended as substitutes for injection molding, and no attempt has been made to actively utilize the shape effect of the support pin-like projections. That is, the proposal relates to a technique for suppressing the eccentricity of the solid core and preventing a material of a different material from entering the cover, and relates to a core surface made of the same material as the cover so that the cover layer has a uniform thickness. By forming the projections on the cover, the projections and the cover are integrated, and the projections themselves do not contribute to the ball performance.

Recently, golf balls have been proposed in which unevenness is provided between a solid core and a cover of a two-piece golf ball, an adjacent layer of a multilayer solid core, an adjacent layer of a multilayer cover, and the like. (JP-A-9-285,565). 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.

[0007] However, although the golf ball has been improved in terms of feel at impact, it is not sufficient in terms of flight performance, durability and the like, leaving room for further improvement.

[0008] The present invention has been made in view of the above circumstances,
At the boundary between the intermediate layer and the cover, a mesh structure of convex ribs, part of which penetrates from the inner surface of the cover into the intermediate layer, has an excellent flight distance and good hit feeling that are not present in conventional solid golf balls. And a method for producing the same.

[0009]

SUMMARY OF THE INVENTION The present invention comprises an elastic core, an intermediate layer, and a cover. A boundary portion between the intermediate layer and the cover is partially formed from the inner surface of the cover into the intermediate layer. In the golf ball joined by the penetrating mesh-like convex ribs, the core is 981 N (100 kgf).
And a hardness of 3.0 to 7.0 mm when a load is applied, and the intermediate layer is more flexible than the cover,
With a Shore D hardness of
A golf ball having a bending rigidity of 450 MPa.

A golf ball comprising an elastic core, an intermediate layer and a cover, wherein a boundary portion between the intermediate layer and the cover is joined by mesh-shaped convex ribs in which a part of the cover enters the intermediate layer from the inner surface of the cover. In molding the intermediate layer, a plurality of split molds having a spherical cavity formed therein and having the mesh-shaped convex rib mold projection on the inner wall surface, and having a dividing surface at a position corresponding to the equator of the cavity,
A plurality of resin injection gates are provided on the periphery along the cavity at the mold dividing surface position and on the periphery at a high latitude position close to both poles. Between the elastic core and the mold wall set at the center of the cavity of the mold. A method of manufacturing a golf ball, characterized in that an intermediate layer is formed in a cavity formed by press-fitting a resin material through the gate.

In the golf ball of the present invention, the convex rib extending from the inner surface of the cover has a width of 0.5 to 2.0 mm, preferably 0.8 to 1.8 mm, and a thickness of the intermediate layer of 10 to 9 mm.
It has a height corresponding to 0%, preferably 40-80%.

[0012] The mold used in the golf ball manufacturing method of the present invention includes, in addition to the position corresponding to the equator, the divided surface,
The high-latitude gate position also has a division plane along the latitude,
Thereby, a metal mold | die can be comprised by a pair of equatorial side 1st part, and a pair of both pole side 2nd part.

The first part of the mold can be divided into a plurality of segments by providing a dividing surface in the longitudinal direction. In addition, a submarine gate that communicates with a runner extending from the equator-corresponding division surface side can be provided in the first portion of the mold.

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a plan view of a golf ball, and FIGS. 2 and 3 schematically show one embodiment of a golf ball according to the present invention. FIG. 2 is a partial cross section of the golf ball taken along a line AA 'in FIG. FIG. 3 and FIG. 3 are plan views of the inner surface of the cover.

The golf ball 1 of the present invention comprises an elastic core 3, an intermediate layer 4, and a cover 5 having a large number of dimples 2 arranged on the outer surface.
A part of the cover 5 is joined by a mesh-like convex rib 6 which partially enters the intermediate layer 4 from the inner surface. And in this case,
The core has a hardness that causes a strain of 3.0 to 7.0 mm when a load of 981 N (100 kgf) is applied.
Is softer than the cover 5, but has a Shore D hardness of 10 to 55, and the cover has a bending rigidity of 100 to 450 MPa (megapascal). The cover 5 is composed of a layer having dimples 2 and an inner layer having different physical properties inside thereof.
When it is formed of a plurality of layers, mesh-shaped convex ribs are provided on the inner surface of the innermost layer in contact with the intermediate layer.

Although the strain of the core 3 under the load of 981N (100 kgf) is in the range of 3.0 to 7.0 mm as described above, if the strain is less than 3.0 mm, the ball becomes too hard,
A blow-up of the hit ball occurs, thereby reducing the flight distance. On the other hand, if the distortion exceeds 7.0 mm, the ball becomes too soft and the resilience of the ball decreases. A preferred range of the distortion under load is 3.5 to 6.0 mm. The mid layer 4 is softer than the cover from which the ribs protrude, and has a Shore D hardness of 10 to 55, but if it is less than 10, the ball becomes too soft and the resilience of the ball decreases. On the other hand, if the hardness exceeds 55, the ball becomes too hard and the feel at impact of the ball deteriorates. The bending rigidity of the cover 5 is 10
Although it is 0 to 450 MPa, when it is less than 100 MPa, the rib becomes too soft, and the expected effect of bonding to the intermediate layer cannot be obtained. Conversely, if it exceeds 450 MPa, the cover becomes too hard and the hit feeling becomes poor. Therefore, a more preferable bending rigidity is 120 to 400 MPa.

In the embodiment shown in FIG. 2, the whole ball 1 is a core.
3, a middle layer 4, and a cover 5 having a three-layer structure. Cover 5
A convex rib 6 part of which enters the intermediate layer 4 from the inner surface of the
In FIG. 3, as an example of a mesh arrangement, convex ribs 6 are arranged vertically and horizontally, and a notch 7 is formed at a position corresponding to a knot of the mesh where the vertical and horizontal ribs 6 should cross.

Referring to FIGS. 2 and 3, in the golf ball of the present invention, the convex rib extending from the inner surface of the cover is 0.1.
A width a of 5 to 2.0 mm, preferably 0.8 to 1.8 mm;
10 to 90% of the thickness d of the intermediate layer, preferably 40 to 80%
Has a height c corresponding to And the length b of the rib is 3.0.
１５15.0 mm, and preferably 4.0 to 10.0 mm.

When the width a, height c, and length b of these ribs 6 are less than the lower limit values of 0.5 mm, 10%, and 3.0 mm, the distance between the cover 5 and the intermediate layer 4 is reduced. The expected reinforcing effect cannot be obtained, while if each exceeds the upper limit, the feeling at the time of hitting may be reduced and the symmetry of the ball may be impaired.

The notches 7 (FIGS. 2 and 3) are provided for the purpose of improving the fluidity of the intermediate layer molding material in the mold at the time of ball production. By providing the notches 7, the height c of the rib can be increased. It can be set relatively high in the numerical range. Notch width h is 0.5-10.0m
m, preferably 2.0 to 8.0 mm. Mid layer 4 thickness
d and the thickness g of the cover 5 are 1.0 to 5.0 mm, respectively.
And ranges from 0.5 to 4.0 can be applied.

Although there is no particular limitation on the mode in which the ribs are arranged in a mesh shape, the following modes can be adopted from the viewpoint of ensuring symmetry and simplicity of molding. That is, the vertex of each spherical triangle 20 assuming a regular octahedron on the inner surface of the cover 5 in which the rib 6 is formed in FIG. 4 is point A, the center (inner center: the center of the inscribed circle) is point B, and each side is Is the point C, the center point of the line connecting the center B and each vertex A is point D, and the line connecting the points D and A is 2
1. In this embodiment, the ribs 6 are arranged along a line 22 connecting the points D and B, and along a line 23 connecting the points D and C. FIG. 5 shows a specific example of this. FIG. 5 shows a configuration in which a concave portion 8 corresponding to the rib 6 on the inner surface of the cover 5 is formed on the outer surface of the intermediate layer 4.

FIGS. 6 to 9 show another embodiment relating to the formation of the mesh-shaped convex ribs. 6 is a partial cross-sectional view of the golf ball at the position BB 'in FIG. 7, FIG. 7 is a plan view of the inner surface of the cover, and FIG. 8 is a partial layout of protrusions on the inner surface of the cover 5 assuming a regular octahedron. FIG. 9 is a plan view of an intermediate layer in which a rib-corresponding concave portion is shown, showing a specific example of a regular octahedron arrangement.

The feature of this embodiment is that a notch (FIG. 2) formed at a position corresponding to the mesh node of the rib in the previous embodiment.
The point is that the columnar projection 9 is arranged in place of 3). Columnar protrusion 9
Is not necessarily limited, but it is desirable that the height e is substantially equal to the thickness d of the intermediate layer 4 into which the protrusion 9 enters (e = d). As the maximum diameter or the maximum width of the columnar projection, the numerical range given for the notch width h in the previous embodiment can be applied. Also, the width a of the rib in this embodiment,
For the length b and the height c, the numerical ranges given for the previous embodiment can be applied.

FIG. 10 is a sectional view of a mold for forming an intermediate layer which can be suitably used in the golf ball manufacturing method of the present invention. FIG. 11 is a sectional view of a mold for forming a cover portion of the ball. is there. In FIG.
Has a spherical cavity 31 inside, and a mold dividing surface 32 along the equator at a position corresponding to the cavity. In addition to the dividing surface 32, dividing surfaces 33 and 34 are provided along the latitude at a high latitude position close to the both poles, so that the mold can be paired with a pair of equatorial first portions 35 and 36 and a bipolar second portion. 37, 38
Is divided into And further, the first mold parts 35, 36
Although not shown, is divided into a plurality of segments along the longitude. In this embodiment, longitude 0 ° 90
Divided surfaces are provided at 180 ° and 270 ° positions and subdivided into four segments.

Reference numeral 39 denotes a runner provided so as to surround the cavity at the position of the dividing surface 32, and reference numerals 40 and 41 denote runners similarly provided at the positions of the dividing surfaces 33 and 34, respectively. A plurality of gates 42 opening to the cavity 31 are connected to the runner 39, and are arranged at equal intervals on the periphery (on the equator). Runners 40 and 41 also have multiple gates 43 and 44, respectively.
Are connected at equal intervals on the circumference and open to the cavity 31. The diameter of these gates 42, 43, 44 and 45 is 0.5
A range of .about.1.5 mm is preferred. In this embodiment, each gate is 1.0 mm.

Submarine gates 45 extending from the runner 39 are arranged at equal intervals on the circumference of the cavity 31 like the other gates in the first mold sections 35 and 36 (the first mold section 35).
The illustration of the submarine gate is omitted). Runner 39, 4
0, 41 are connected to the intermediate layer 4 molding material supply source (not shown),
Press-fit into cavity 31 through each gate. Gate
The positions of 43 and 44 are preferably 50 to 70 degrees each in the south and north latitudes. In this embodiment, they are provided at the positions of 60 ° each of latitude and longitude. In this case, as in the case of the equatorial position, the runner / gate position and the dividing plane are made to coincide with each other (see FIG. 10).
41 and a gate 44 are preferably disposed). The submarine gate 45 is preferably arranged at a latitude of 25 to 45 degrees each of latitudes north and south.

On the inner wall surface 46 of the cavity, a concave portion 8 is formed in the intermediate layer 4.
Although projections for molding (FIGS. 5 and 9) are arranged in a mesh pattern, they are not shown. The number of the gates 42 at the position of the division surface 32 is preferably 6 to 16 evenly around the circumference, and in this embodiment, eight gates 42 are arranged at intervals of 45 °. The gates at the dividing planes 33 and 34 are preferably arranged similarly at 8 to 20 gates on the circumference, and in this embodiment, 12 gates are arranged at intervals of 30 °. It is preferable that 6 to 16 submarine gates 45 provided in the first portions 35 and 36 of the mold are similarly arranged on the circumference. In this embodiment, eight submarine gates 45 are arranged on the circumference at intervals of 45 °.

As described above, since the dividing surface and the gate of the mold are provided at the high latitude position close to both poles in addition to the position corresponding to the equator of the spherical cavity, the mesh-like concave portion 8 (FIGS. ) Even if the mold projections are provided on the inner wall surface of the cavity, the core 3 and the cavity wall surface 46 may be pressed when the molding material is pressed.
There is no hindrance to the even flow of the press-fitting material between them. Although illustration of support pins and degassing means for holding the core 3 at the center position of the cavity 31 is omitted in FIG. 10, an example in a cover molding die described later can be applied.

The cover part forming die 50 shown in FIG. 11 comprises an upper die 51 and a lower die 52, and has a spherical cavity 53 inside. The cavity has a dividing surface 54 at a position corresponding to the equator. A projection or ridge for molding the dimple 2 (FIG. 1) is provided on the inner wall surface 55 of the cavity, but is not shown. At the center of the cavity 53, a core 3 with an intermediate layer 4 molded using the mold 30 (FIG. 10) is set, and a runner 57 arranged to surround the cavity at the position of the equator or the dividing surface 54. And a plurality of gates 58 leading from this runner to the cavity 53
(In this embodiment, eight on the circumference equally). Cover 5
In the molding, a cover material supply source (not shown) is pressed into the cavity 53 through the runner 57 and the gate 58.

The in-cavity set of the intermediate layer coated core is:
This is performed by support pins 56 arranged near the co-polarity of the upper mold 51 and the lower mold 52 in a direction orthogonal to the division surface 54. These support pins 56 are usually arranged on four concentric circles centered on the poles, and are arranged at equal intervals in this embodiment so as to be able to advance and retreat toward the cavity 53. In addition
Numeral 59 denotes degassing pins provided at both pole positions. Also for the intermediate layer forming die 30, the support pins and the gas release pins can be arranged according to the cover forming die.

Next, the components of each layer constituting the golf ball of the present invention will be described. As a material of the core (solid type) 3 in the present invention, as a base rubber, for example, 1,4-cis polybutadiene, polyisoprene, natural rubber, silicone rubber or the like can be exemplified as a main component. In particular, it is recommended to use 1,4-cis polybutadiene as a main component in order to improve resilience.

In addition to the rubber component, zinc salts of unsaturated fatty acids such as zinc methacrylate and zinc acrylate as crosslinking agents;
Magnesium salts and ester compounds such as trimethylpropane methacrylate may be blended. In particular, zinc acrylate can be suitably used because of its high resilience. The compounding amount of these crosslinking agents is preferably 15 to 40 parts by weight based on 100 parts by weight of the base rubber. The amount of the cross-linking agent is 0.1 to 100 parts by weight of the rubber.
It can be 1 to 5 parts by weight.

The rubber composition may further contain zinc oxide, barium sulfate or the like as an anti-aging agent or a filler for adjusting specific gravity, if necessary. 5 to 130 parts by weight per part.

Preferred embodiments of the core (solid) rubber composition are as follows. 1,4-cis polybutadiene 100 parts by weight Zinc oxide 5-40 parts by weight Zinc acrylate 15-40 parts by weight Barium sulfate 0-40 parts by weight Peroxide 0.1-5.0 parts by weight Vulcanization conditions: preferably 150 ± 5 to 2 at 10 ° C
Vulcanize for 0 minutes.

The above composition for the core is kneaded using a usual kneader (for example, a Banbury mixer, a kneader and a roll), and the obtained compound is subjected to injection molding or compression using a core mold. It is molded by molding.

The core thus obtained has a diameter of 28 to 38 mm, preferably 30 to 37, and 981
3.0-7.0mm by loading N (100kgf)
The hardness for deformation is increased, while the Shore D hardness is 20 to 50, more preferably 25 to 45. The weight (mass) is in the range of 12 to 35 g.

The material of the intermediate layer is not particularly limited, and may be any of a resin and a rubber material. However, it is preferable to use a resin material excellent in impact resistance in consideration of durability. For example, polyester elastomer, polyurethane resin, ionomer resin, styrene-based elastomer,
Examples thereof include hydrogenated butadiene resins and mixtures thereof. Specifically, Hytrel 3078, 4047, 4767
Commercial products such as (manufactured by Du Pont-Toray Co., Ltd.) can be used, but polyester elastomers and polyurethane resins can be particularly preferably used. In this case, the Shore D hardness of the intermediate layer is 10 to 55, more preferably 15 to 55.
45, which must be smaller than that of the cover described later.

The material of the cover is not particularly limited, and a known cover material can be used. For example, an ionomer resin, a polyurethane resin, a polyester resin, and a balata rubber can be arbitrarily selected. In particular, an ionomer resin is preferable, and 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 to adjust the specific gravity and the like, if desired. Further, 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 a multilayer structure of two or more layers in which layers made of different materials are stacked. The thickness g (FIGS. 2 and 6) of the cover is 0.5 to 4.0 mm, preferably 1.0 to 2.5 mm, and the Shore D hardness is 40 to 7 mm.
0, preferably 50 to 65.

The golf ball thus obtained is
As shown in FIG. 1, a large number of dimples are uniformly formed on the surface, and the surface can be subjected to a finishing treatment such as painting or stamping as necessary. When a load of 981 N (100 kgf) is applied to the entire ball, 2.6
It has a hardness that produces a strain of about 4.0 mm, preferably 2.8 to 3.8 mm. According to the R & A golf rules, the ball diameter and weight are 42.67 mm or more and the weight is 45.93.
g or less.

[0041]

EXAMPLES In order to confirm the performance of the golf ball according to the present invention, a comparison test was conducted between the following three examples and the three comparative examples in terms of flight performance and hit feeling. In making these balls as prototypes, the arrangement of dimples is shown in Fig. 1.
The example shown in Table 2 was applied in common. Examples 1, 2, and 3
It is composed of three layers: a core, an intermediate layer, and a cover. The main feature of these examples is that the rib height c / intermediate layer thickness d is 1.2
mm / 1.7 mm, 1.6 mm / 2.1 mm and 2.4 mm / 3.
On the other hand, Comparative Example 1 has a three-layer structure in which the rib height c / intermediate layer thickness d is 1.6 mm, which is the same as Example 2.
mm / 2.1 mm, the middle layer and the cover have the same hardness, Comparative Example 2 also has three layers but no ribs on the inner surface of the cover, and Comparative Example 3 has a two-layer structure consisting of a core and a cover. It is. Table 1 shows the details of the test balls, and Table 2 shows the structure and test results.

[0042]

[Table 1]

[0043]

[Table 2]

In producing the first to third embodiments,
The mold of the intermediate layer was formed using a mold having the structure shown in FIG. 10, while the mold used for forming the intermediate layer in Comparative Examples 1 to 3 was similar to the mold shown in FIG. A two-part mold that was arranged only in the parting plane was used.

The flying performance shown in Table 2 was measured by using a swing robot and measuring HS (head speed, the same applies hereinafter) of 45 m / s by W♯1 (driver) at a loft angle of 11 ° and by W♯1 at a loft angle of 14 °. It is a measured value at HS 35 m / s. The hit feeling is an evaluation of the hit feeling when a test ball is hit by three professional golfers using W♯1.

[0046]

When the golf ball according to the present invention is hit at a high head speed using a club having a small loft angle, for example, a driver, the backspin tends to decrease as shown in Table 2, and therefore the initial speed Although the difference is not so large, it is possible to suppress the undesired blow-up of the hit ball and obtain a large flight distance. On the other hand, it is recognized that the hitting feeling, which tends to occur as a characteristic of this kind of ball, is significantly improved rather than worsening.

[Brief description of the drawings]

FIG. 1 is a plan view of a golf ball.

FIG. 2 is a schematic sectional view showing one embodiment of the golf ball according to the present invention.

FIG. 3 is a plan view schematically showing an inner surface of the cover in the embodiment.

FIG. 4 is a partial plan view of an inner surface of a cover in which ribs are arranged assuming a regular octahedron in the embodiment.

FIG. 5 is a plan view of an intermediate layer in the embodiment shown in FIG.

FIG. 6 is a schematic cross-sectional view of a golf ball according to another embodiment of the present invention.

FIG. 7 is a plan view schematically showing an inner surface of a cover according to the embodiment.

FIG. 8 is a partial plan view of the inner surface of the cover in which ribs are arranged assuming a regular octahedron in the embodiment.

FIG. 9 is a plan view of an intermediate layer related to the embodiment shown in FIG. 8;

FIG. 10 is a mold for forming an intermediate layer that can be suitably used in carrying out the production method according to the present invention.

FIG. 11 is a mold for molding a cover of a golf ball.

[Explanation of symbols]

 Reference Signs List 1 golf ball 3 core 4 intermediate layer 5 cover 6 convex rib 30 mold 31 spherical cavity 32 division surface 42 gate 43, 44 gate 46 cavity inner wall surface

Claims (6)

[Claims] 1. An elastic core, an intermediate layer and a cover,
In a golf ball in which the boundary between the intermediate layer and the cover is joined by mesh-shaped convex ribs in which a part of the cover penetrates into the intermediate layer from the inner surface of the cover, the core is 981N (10
0 kgf) when applied with a load that produces a strain of 3.0 to 7.0 mm.
A golf ball having a Shore D hardness of 0 to 55 and the cover having a flexural rigidity of 100 to 450 MPa. 2. The golf ball according to claim 1, wherein the rib has a width of 0.5 to 2.0 mm and a height corresponding to 10 to 90% of the thickness of the intermediate layer. 3. An elastic core, an intermediate layer and a cover,
The boundary between the intermediate layer and the cover forms a spherical cavity inside when forming the above-mentioned intermediate layer of the golf ball in which a part of the cover is joined from the inner surface of the cover by mesh-like convex ribs penetrating into the intermediate layer. A plurality of split molds having the mesh-shaped convex rib mold projection on a wall surface and having a dividing surface at a position corresponding to the equator of the cavity, the mold being close to the periphery and both poles along the cavity at the mold dividing surface position. A plurality of resin injection gates are provided on the circumference at the high latitude position, and the resin material is pressed into the cavity formed between the elastic core set at the center of the cavity of the mold and the mold wall surface through the gate. A method for manufacturing a golf ball, comprising forming an intermediate layer. 4. The mold has a division surface along the latitude at the high-latitude injection gate position, whereby the mold comprises a pair of equatorial first parts and a pair of bipolar second parts. 4. The method for producing a golf ball according to claim 3, wherein: 5. The method according to claim 1, wherein the first portion of the mold is constituted by a plurality of segments having a division surface in a longitudinal direction.
4. The golf ball manufacturing method according to 4. 6. The method of manufacturing a golf ball according to claim 4, further comprising a submarine gate in the first portion of the mold, the submarine gate being connected to a runner extending from the equator-corresponding dividing surface.