JP2002263221A - Golf ball and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a golf ball and its manufacturing method for coating a core surface with a thermoplastic resin cover. SOLUTION: In this manufacturing method for this golf ball, a thermoplastic resin cover is manufactured by forming its half sections separately. One half shell previously molded of a covering resin into a semispherical shell shape is hot-pressed in an upper die and put over the cover, and then, the upper die is reversed to be used as a lower die. The other half shell is formed by hot- pressing in the flowing upper die. In this way, excellent productivity is provided, and the abutting face area between the two cover sections is increased for improving adhesion strength in the cover joint part, so that excellent durability is provided for the golf ball.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a golf ball and a method for manufacturing the same, and more particularly to a golf ball having a core covered with a cover made of a thermoplastic resin and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, golf balls have been multi-layered in order to have multiple functions and high performance, and the cover has also been multi-layered. However, since the resin used for the cover material has inferior resilience performance as compared with the core material, it is necessary to reduce the cover thickness as compared with a conventional golf ball.

Hitherto, as a method of covering the core with the cover, press molding in which a half shell in which a resin for the cover is formed into a hemispherical shell in advance and the core is heated and compressed, and the core is held in a metal mold. And injection molding for injection molding a cover resin.

[0004] In press molding, the core sinks into the molten resin for the cover due to its own weight, and the thickness of the cover of the lower mold tends to be small, and there has been a problem that the core tends to be eccentric. This problem becomes more conspicuous as the cover thickness decreases, and the defective production rate increases, resulting in a decrease in productivity. Also,
If the cover resin is pressed in an incompletely molten state to prevent such eccentricity, the eccentricity is improved, but the joint between the upper mold and the lower mold half shell is incomplete, and Occasionally, durability problems such as tearing at the parting line occur. This problem also becomes conspicuous because the joining area of the half shell decreases as the cover thickness decreases.

In the injection molding, as the cover thickness becomes smaller, the gap into which the resin for the cover enters becomes smaller. In particular, since the outermost layer of the golf ball has dimples on the surface, the gap becomes smaller and the injection pressure becomes higher. However, there has been a problem that the eccentricity is apt to occur, the production defect rate is increased, and the productivity is reduced.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the conventional golf ball and the method for manufacturing the same, and provides a golf ball having excellent productivity and durability and a method for manufacturing the golf ball. The purpose is to do.

[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 golf ball obtained by manufacturing a cover made of a thermoplastic resin almost in half has been prepared. One of the half shells, which is formed into a hemispherical shell shape, is heated and pressed in the upper mold to cover the cover, and the upper mold is inverted and installed as a lower mold, and the other half shell is formed. Has excellent productivity by manufacturing by hot pressing in the next upper mold,
Further, the present invention has found that a golf ball having excellent durability and a method for manufacturing the same can be obtained by increasing the area of the joint surface between the two cover portions and improving the adhesive force at the joint portion of the covers. Was completed.

That is, the present invention provides a core comprising one or more layers.
(1) A cover made of a thermoplastic resin composition for covering the core
(2) A method for producing a golf ball comprising: (a)
Forming a spherical core (1), (b) injection molding a thermoplastic resin composition for a cover, and forming a half shell (6) having a thickness set so that the cover has a desired thickness. (C) (i) a third half mold having a hemispherical cavity having a diameter set to the diameter of the core (1).
(3) The core is disposed and covered with the half shell (6), the golf ball has a hemispherical cavity having a diameter set to have a desired diameter, and dimples are formed on the surface of the golf ball. Placing a first half mold (4) having a plurality of projections in the cavity upward so as to be arranged, (i.
i) Lowering the first half mold (4) to lower the first half mold (4)
And the third mold half (3),
Heating the half mold (4), (iii) opening the mold, and
(1) forming a golf ball intermediate molded product in which half of the surface of the golf ball is covered with a first cover part (7); (iv) the first cover of the golf ball intermediate molded product obtained in the step (iii); Department (7)
In a state where the portion coated with is settled in the cavity of the first half mold (4), the first half mold (4) is turned over and placed below, and the same as in the step (i) Placing the half shell (6) on the core (1) and placing the second half mold (5) upward; (v) lowering the second half mold (5) to 1st mold
(4) and the second half mold (5) are centered and clamped,
Heating the second mold half (5) to cover the other half of the surface of the core (1) with the second cover part (8); and (vi) after cooling, opening the mold to form a molded product. And a method for manufacturing a golf ball, comprising the step of taking out a golf ball.

Further, the present invention provides a core comprising one or more layers.
(1) and a cover (2) made of a thermoplastic resin for covering the core, wherein the cover is formed by joining a hemispherical shell-shaped first cover portion and a hemispherical shell-shaped second cover portion at a ring-shaped joint surface. In the golf ball having the following formula, the following formula is used at the bonding surface: (S ₁ / S ₀ )> 1 (where S ₁ is the bonding area (mm ² ) of the entire bonding surface,
S ₀ is the relationship expressed by the area (mm ² ) of the reference bonding surface where the cover layer intersects with the plane passing through the bonding boundary line on the golf ball surface and the center of the golf ball among the bonding surfaces. The present invention relates to a golf ball characterized by satisfying.

Further, in order to preferably carry out the present invention, the third half mold (3) is provided at the joint surface between the first cover part and the second cover part by the following formula: (S ₁ / S ₀₎ )> 1 (where S ₁ is the joint area (mm ² ) of the entire joint surface;
S ₀ is the relationship expressed by the area (mm ² ) of the reference bonding surface where the cover layer intersects with the plane passing through the bonding boundary line on the golf ball surface and the center of the golf ball among the bonding surfaces. The cross-sectional shape of the joint surface between the first cover part and the second cover part is straight,
And an annular projection having a wedge-shaped cross-section at least at an upper end is formed on an inner peripheral portion of a joining surface of either the first cover portion or the second cover portion, which is inclined from a horizontal line passing through the center of the golf ball. Is preferred.

Hereinafter, the golf ball of the present invention will be described with reference to FIG. FIG. 1 is a schematic sectional view of one embodiment of the golf ball of the present invention. As shown in FIG. 1, the golf ball of the present invention comprises one or more layers of a core (1) and a cover (2) made of a thermoplastic resin formed on the core. The golf ball of the present invention may be a thread-wound golf ball or a solid golf ball such as a two-piece golf ball or a three-piece golf ball.

The core (thread-wound core) used in the thread-wound golf ball may be a conventionally used core, and a center and a thread rubber layer formed by winding thread rubber around the center in a stretched state. Consisting of As the center, either a liquid center (liquid center) or a rubber center (solid center) may be used.
The thread rubber wound on the center may be the same as that conventionally used for the wound layer of the thread-wound golf ball. For example, sulfur, vulcanization of natural rubber or natural rubber and synthetic polyisoprene may be used. A rubber composition obtained by vulcanizing a rubber composition containing an auxiliary, a vulcanization accelerator, an antioxidant and the like may be used. The rubber thread is stretched about 10 times on the center and wound to form a wound core.

Further, the core (solid core) used for the solid golf ball may be a conventionally used core. For example, acrylic acid, methacrylic acid and methacrylic acid are added to 100 parts by weight of a base rubber such as polybutadiene rubber. Vulcanization comprising an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms such as an acid or a monovalent or divalent metal salt thereof such as zinc or magnesium, or a functional monomer such as trimethylolpropane trimethacrylate. 10 to 60 parts by weight of an agent (crosslinking agent) alone or in total, 0.5 to 5 parts by weight of a co-crosslinking initiator such as an organic peroxide, and 10 to 30 parts by weight of a filler such as zinc oxide and barium sulfate. Then, the rubber composition containing an antioxidant and the like is uniformly kneaded using an appropriate kneading machine such as a normal kneading roll, and vulcanized in a mold to obtain a spherical core (1). thing It can be. The conditions at this time are not particularly limited, but usually 130 to 240 ° C. and pressure 2.9 to 240 ° C.
Performed at 11.8 MPa for 15 to 60 minutes. The surface of the obtained core (1) is preferably buff-polished in order to improve the adhesion to the cover (2) coated therearound. Furthermore, even if the solid core has a single-layer structure,
It may have a multilayer structure of two or more layers. However, these solid cores and thread-wound cores are merely examples, and the present invention is not limited thereto.

The diameter of the core (1) is not particularly limited, but is 39.6-41.8 mm, preferably 40.4-4.
1.4 mm. When it is smaller than 36.8 mm, a normal cover molding method can be used. 41.8
If it is larger than mm, the cover thickness becomes too small, and the durability decreases.

Next, a cover (2) is coated on the core (1). The golf ball of the present invention, the cover and the first cover portion of the hemispherical and hemispherical second cover portion made by joining a ring-shaped bonding surface, the following expression in the junction surface: (S ₁ / S ₀ )> 1 (where S ₁ is the joint area (mm ² ) of the entire joint surface;
S ₀ is the relationship expressed by the area (mm ² ) of the reference bonding surface where the cover layer intersects with the plane passing through the bonding boundary line on the golf ball surface and the center of the golf ball among the bonding surfaces. It is preferable to satisfy. When the value (S ₁ / S ₀ ) is 1 or less, the bonding area becomes small, and the effect of the present invention for improving the durability cannot be sufficiently obtained. In addition, the above value (S ₁
If (/ S ₀ ) is too large, the bonding strength of the bonding surface is improved, but the shape of the bonding part becomes too complicated, which leads to an increase in the manufacturing cost of the device and the like and a reduction in productivity. Thus, the value _(S 1 / S ₀₎ is preferably 1.1 to
It is 3.0, more preferably 1.2 to 2.8, most preferably 1.3 to 2.5.

In the golf ball of the present invention, the shape of the joint of the cover is not particularly limited as long as it satisfies the above expression, but the cross-sectional shape of the joint surface is straight and inclined from a horizontal line passing through the center of the golf ball. An annular projection having a wedge-shaped cross section at least at the upper end is provided on the inner peripheral portion of the joining surface of either the first cover portion or the second cover portion. The formed shape, for example, the shape as shown in FIG. Although a convex shape is illustrated in the above-described drawings, a concave shape may be used. The angle of inclination is not particularly limited, but is preferably 10 degrees or more when the cross-sectional shape of the joint surface is a straight line.

The bonding area S ₁ (mm ² ) of the entire bonding surface
Varies depending on the thickness of the cover,
m ² , preferably 80 to 350 mm ² , more preferably 90 to 300 mm ² . The above value S ₁
If it is less than 70 mm ^2, the adhesive strength of the joint tends to be insufficient, and if it exceeds 400 mm ² , the physical properties and durability of the golf ball obtained by the cover being too thick are reduced, and the shape of the joint is complicated. This leads to an increase in manufacturing cost of the device and the like and a decrease in productivity.

It is preferable that the joining boundary line be within one plane, particularly a circle, so that the cost of the mold is reduced and the productivity is improved. Further, it is preferable that the joining boundary line is near the equator of the golf ball, particularly on the equator. Specifically, when the distance between the joining boundary line and the equatorial plane including the equator is H and the diameter of the golf ball is P, the value of (H / P) is 0 to 0.2, preferably 0 to 0. .1, more preferably H = 0. As a result, the productivity is improved, for example, the golf ball is easily removed from the mold after the cover is formed.

The cover used for the golf ball of the present invention
The requirement (2) is to use a thermoplastic resin. Examples of the thermoplastic resin include an ionomer resin which is generally used for a cover of a golf ball. Examples of the ionomer resin include those obtained by neutralizing at least a part of the carboxyl groups in a copolymer of ethylene and α, β-unsaturated carboxylic acid with metal ions, or ethylene and α, β-unsaturated carboxylic acid. It is obtained by neutralizing at least a part of carboxyl groups in a terpolymer with an α, β-unsaturated carboxylic acid ester with a metal ion. Examples of the α, β-unsaturated carboxylic acid include acrylic acid, methacrylic acid, fumaric acid, maleic acid, crotonic acid and the like, 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, fumaric acid,
Methyl, ethyl, propyl, n-butyl, isobutyl esters and the like such as maleic acid are used, and acrylic esters and methacrylic esters are particularly preferable. 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 Examples of metal ions that neutralize at least a part of sodium, potassium, lithium, magnesium, calcium, zinc, barium, aluminum, tin, zirconium, cadmium ions, etc., and particularly sodium, zinc, and magnesium ions are repelled. Often used and preferred from the viewpoints of properties and durability.

Specific examples of the above ionomer resin include:
Without limitation, Hi-mil
an) 1555, High Milan 1557, High Milan 16
05, High Milan 1652, High Milan 1702, High Milan 1705, High Milan 1706, High Milan 17
07, Himilan 1855, Himilan 1856 (manufactured by DuPont-Mitsui Polychemicals), Surlyn
8945, Surlyn 9945, Surlyn AD8511,
Surlyn AD8512, Surlyn AD8542 (manufactured by DuPont), Iotek 7010, 80
00 (manufactured by Exxon) and the like. As these ionomers, the above-mentioned examples may be used alone or as a mixture of two or more.

Further, as an example of a preferable material of the cover (3) of the present invention, the above-mentioned ionomer resin alone may be used, but the ionomer resin and the thermoplastic elastomer or diene block copolymer may be used. You may use in combination with more than one kind. Specific examples of the thermoplastic elastomer include, for example, a polyamide thermoplastic elastomer commercially available from Toray Industries, Inc. under the trade name “Pebax” (eg, “Pebax 2533”) and a trade name “Hytrel from Toray Dupont Co., Ltd. (E.g., "Hytrel 3548", "Hytrel 4047") polyester-based thermoplastic elastomer, commercially available from BASF Polyurethane Elastomers Co., Ltd. under the trade name "Elastolane" (e.g., "Elastolane"). ET880 ”) a polyurethane-based thermoplastic elastomer, commercially available from Mitsubishi Chemical Corporation under the trade name“ Thermolan ”(for example,“ Thermolan 3981N ”); an olefin-based thermoplastic elastomer; a trade name“ Sumitomo Chemical Co., Ltd. TPE ”(for example,“ Sumitomo TP 3682 ",
"Sumitomo TPE9455") polyolefin-based thermoplastic elastomer, commercially available from Asahi Kasei Kogyo Co., Ltd. under the trade name "ToughTech" (for example, "ToughTech H105").
1)) Styrene-based thermoplastic elastomers and the like.

The diene-based block copolymer has a double bond derived from a conjugated diene compound of a block copolymer or a partially hydrogenated block copolymer. The base block copolymer is a block copolymer comprising at least one polymer block A mainly composed of a vinyl aromatic compound and at least one polymer block B mainly composed of a conjugated diene compound. It is. In addition, the partially hydrogenated block copolymer is obtained by hydrogenating the above block copolymer. Examples of the vinyl aromatic compound constituting the block copolymer include styrene,
One or more of α-methylstyrene, vinyltoluene, pt-butylstyrene, 1,1-diphenylstyrene and the like can be selected, and styrene is preferred. Further, as the conjugated diene compound, for example, one or more kinds of butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene and the like can be selected, butadiene, isoprene And combinations thereof. Specific examples of the diene-based block copolymer, for example, Daicel Chemical Industries, Ltd.
Available from Kuraray Co., Ltd. under the trade name “Septon” (eg, “Septon HG-252”) and the like. No. Examples of other thermoplastic resins include those commercially available from Mitsui DuPont Polychemicals Co., Ltd. under the trade name “Nucrel” (eg, “Nucrel AN4213C”), an ethylene-methacrylic acid copolymer, and the like.

When used, the amount of the thermoplastic elastomer or diene-based block copolymer is 1 to 60 parts by weight, preferably 1 to 35 parts by weight, per 100 parts by weight of the base resin for the cover. is there. If the amount is less than 1 part by weight, the effect of lowering the impact at the time of hitting by mixing them becomes insufficient, and if the amount is more than 60 parts by weight, the cover becomes too soft and the resilience decreases, or the compatibility with the ionomer is reduced. And the durability tends to decrease.

To the cover used in the present invention, if necessary, various additives other than the above resins, for example, pigments such as titanium dioxide, dispersants, antioxidants, ultraviolet absorbers, light stabilizers and the like are added. May be.

Next, the method for producing a golf ball of the present invention will be described in detail below. The method for manufacturing a golf ball of the present invention can be roughly divided into the steps of (a) forming the core (1), (b) forming the half shell, and
(c) three steps of covering the core (1) with the cover (2). The step (b) is not particularly limited, and a known method such as a method of injection molding a thermoplastic resin composition for a cover or a method of hot pressing using a mold having a hemispherical shell-shaped cavity and a core mold. The method can be performed using the method described above.

The manufacturing process (c) will be described in detail with reference to FIGS. Figures 2 and 3 show the cover on the core (1)
It is a route figure showing typically manufacturing process (c) which coats (2). As shown in FIG. 2, first (i) a third having a hemispherical cavity having a diameter set to the diameter of the core (1).
The above-mentioned core is arranged on a half mold (3) and covered with a half shell (6) made of thermoplastic resin for a cover, and the obtained golf ball has a diameter set so as to have a desired diameter as described above. A first half mold (4) having a hemispherical cavity and having a plurality of protrusions in the cavity is disposed above so as to arrange dimples on the surface of the golf ball.

(Ii) Lower the first half mold (4),
The first half mold (4) and the third half mold (3) are centered and clamped, and the first half mold (4) is heated. The heating temperature of the first half mold (4) is 100 to 200 ° C, preferably 1 to 200 ° C.
20-180 ° C. If the temperature is lower than 100 ° C., the flowability of the resin composition for a cover is poor, and the core is eccentric and molding cannot be performed well. If the temperature exceeds 200 ° C., the core is thermally degraded (the resin composition for the cover is also degraded), and the resilience performance is lowered. The heating time is 10 seconds to 10 minutes, preferably 0.5
~ 5 minutes. If the time is shorter than 10 seconds, the flowability of the resin composition for a cover is deteriorated. If the time exceeds 10 minutes, the core is deteriorated or the molding time is prolonged, and the productivity is reduced.

In addition, unlike a solid core, a wound core has irregularities and a difference in winding density. Therefore, stress is applied to the core when it is strongly suctioned as described above, and the center of the held wound core is likely to shift. There was a problem. In the present invention, the stress is not applied only to the wound core located in the hemispherical cavity of the third half mold (3) arranged on the lower side, and such a problem cannot occur. Further, in the present invention, since the wound core is held by the entire hemispherical cavity having a diameter set to the diameter of the core of the third half mold, there is no eccentricity of the core, and the thickness of the cover to be covered is small. Becomes uniform.

(Iii) The mold is opened to form a golf ball intermediate molded product in which half of the surface of the core (1) is covered with the first cover (7).

As shown in FIG. 3, (iv) the portion of the golf ball intermediate molded product obtained in the above step (iii) which covers the first cover portion (7) is located inside the cavity of the first half mold (4). The first half mold (4) is turned upside down while being settled, and the half shell (6) is placed on the core (1) in the same manner as in the above step (i).
And put the second half mold (5) upward. If necessary, a step of cooling the first half mold (4) may be further included after the step (ii) and before the step (v).

(V) The second half mold (5) is lowered, and the first half mold (4) and the second half mold (5) are centered and clamped. 2 Heat the half mold (5)
The other half of the surface of (1) is covered with the second cover part (8).
The heating temperature of the second half mold (5) is 100 to 200 ° C,
Preferably it is 120-180 degreeC. If the temperature is lower than 100 ° C., sufficient flowability cannot be obtained due to poor flowability of the resin and eccentricity. If the temperature exceeds 200 ° C., the resilience performance is reduced, and the molded resin composition for the cover in the lower mold flows to eccentric the core. Heating time is 10 seconds to 10 minutes,
Preferably, it is 0.5 to 5 minutes. If it is shorter than 10 seconds, the flowability of the resin composition for a cover will be poor. If the time exceeds 10 minutes, the resilience performance decreases, and the resin composition for the cover after molding in the lower mold flows to eccentric the core. In the method for manufacturing a golf ball of the present invention, the above-described steps
As shown in (ii) and (v), when the upper mold is heated when the mold is clamped, only the cover resin composition in the upper mold becomes a molten state. Therefore, the core does not sink into the cover, and the core is hardly eccentric.

(Vi) After cooling to room temperature, the second half mold (5)
To open the mold and take out the molded product.

It is desirable that the cover (2) of the golf ball of the present invention has a thickness of 0.5 to 1.6 mm, preferably 0.7 to 1.2 mm. If the thickness is smaller than 0.5 mm, the durability is reduced. If the thickness is larger than 1.6 mm, a normal molding method is sufficient.

The golf ball cover (2) of the present invention desirably has a Shore D hardness of 30 to 70, preferably 40 to 60. If the cover hardness is less than 30, the scratch resistance and the resilience performance decrease, and if it is greater than 70, the shot feeling is hard and poor. In the present specification, the cover hardness means a hardness measured on the surface of a golf ball obtained by coating a cover on a core.

In the golf ball of the present invention, after the cover is formed, a paint finish, a marking stamp, and the like can be applied as necessary. The golf ball of the present invention is formed to have a diameter of not less than 42.67 mm (preferably 42.67 to 42.82 mm) and a weight of not more than 45.93 g based on the golf ball rules.

[0036]

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

(A) Preparation of core A rubber composition having the composition shown in Table 1 below was mixed and kneaded.
3 at 160 ° C in upper and lower molds with hemispherical cavity
By hot pressing for 0 minutes, a spherical core having a diameter of 40.8 mm was produced.

[0038]

[Table 1]

(Note 1) Trade name “BR01” from JSR Corporation
High cis polybutadiene rubber (cis-1,4-
(Polybutadiene content: 96%) (Note 2) Zinc acrylate commercially available under the trade name “ZNDA90S” from Nippon Distillery Co., Ltd. (Note 3) Oxidation commercially available under the trade name “Zinc Hua No. 1” manufactured by Toho Zinc Co., Ltd. Zinc (Note 4) Dicumyl peroxide commercially available from NOF Corporation under the trade name “Parkmill D”

(B) Preparation of composition for cover Materials having the composition shown in Table 2 below were mixed and extruded by a single screw extruder, and a pellet-shaped cover composition was prepared using a pelletizer. Using the obtained composition for a cover, a half shell having an inner diameter of 41 mm and a thickness of 1.2 mm was produced by injection molding.

[0041]

[Table 2]

(Note 5) A sodium ion neutralized ethylene-methacrylic acid copolymer ionomer resin commercially available under the trade name “Himilan 1605” from Mitsui Dupont Polychemicals. "Ionomer resin, zinc-neutralized ethylene-methacrylic acid copolymer, commercially available under the trade name" * 7 "Titanium dioxide commercially available under the trade name" A220 "from Ishihara Sangyo Co., Ltd.

(C) Production of Golf Ball (Examples 1 and 2) (i) The core (1) obtained in the above (a) was placed in the hemispherical cavity of the third half mold (3), The half shell (6) obtained in (b) above was put on, and the first half mold (4) with dimples was placed above. (ii) Lower the first half mold (4) to make the first half mold
(4) and the third half mold (3) were centered and clamped, and the first half mold (4) was heated at 150 ° C. for 1 minute. (iii) The mold was opened to form a golf ball intermediate molded product in which half of the surface of the core (1) was covered with the first cover (7). (iv) While the portion of the golf ball intermediate molded product obtained in the above step (iii) covering the first cover portion (7) is accommodated in the cavity of the first half mold (4), the first half is formed. The mold (4) is turned upside down and placed in the same manner as in the step (i), a half shell (6) is put on the core (1), and the second half mold (5) is placed upward. installed. (v) The second half mold (5) is lowered to the first half mold (4).
And the second half mold (5) are centered and clamped, the second half mold (5) is heated at 150 ° C. for 1 minute, and the other half of the surface of the core (1) is subjected to the second half mold. It was covered with a cover part (8). (vi) After being cooled to room temperature, the mold was opened and the molded product was taken out, deburred, and then subjected to clear paint on the surface, with a diameter of 42.8 mm and a weight of 45.2 to 45.7 g.
Was obtained.

As shown in FIG. 5, the cross-sectional shape of the joint surface between the first cover portion and the second cover portion is (i) a wedge shape (α = 45).
(Degree, m = 1.0 mm), and (ii) horizontal ones were referred to as Examples 1 and 2, respectively. As can be seen from FIGS. 4 and 5, the cross-sectional shape can be obtained by a similar process only by changing the cavity structure of the third half mold (3).

(Comparative Example 1) Press molding: Using two half shells obtained in (b) above, wrapping the core obtained in (a) above, and hot-pressing at 150 ° C for 2 minutes. The cross-sectional shape of the joint of the cover is horizontal (FIG. 5 (ii)). After cooling to room temperature, the mold was opened and the molded product was taken out. After deburring, clear paint was applied to the surface, and the diameter was 42.
A golf ball having a diameter of 8 mm and a weight of 45.2 to 45.7 g was obtained.

Comparative Example 2 Injection molding: The above
The cover composition obtained in (b) was directly injection-molded on the core obtained in (a), and after deburring, a clear paint was applied to the surface to obtain a diameter of 42.8 mm and a weight of 4%.
A golf ball having 5.2 to 45.7 g was obtained.

The obtained golf ball was disassembled, and the cover thickness of a portion having no dimple was measured at 12 points at random.
Table 3 shows the maximum value and the minimum value. The difference between the two is shown in the same table as the eccentricity. Further, the durability of each of the obtained golf balls was evaluated and the results are shown in Table 3. The test method was performed as follows.

(Test Method) Durability A Wood No. 1 club (W # 1, driver) was attached to a swing robot manufactured by True Temper Co., and the golf ball was repeatedly hit at a head speed of 50 m / sec. The number of hits before tearing occurred was measured.

[0049]

[Table 3]

S ₁ : bonding area of the entire bonding surface (mm ² ) S ₀ : plane passing through the bonding boundary line on the surface of the golf ball of the bonding surface and the center of the golf ball, and reference bonding where the cover layer intersects Area of surface (mm ² ) H: distance between joining boundary line and equatorial plane including equator P: diameter of golf ball

The golf balls of Examples 1 and 2 using the production method of the present invention have excellent eccentricity of the core as compared with Comparative Examples 1 and 2 produced by conventional press molding and injection molding, respectively. It was found to have properties. Further, it was found that Example 1 in which the area of the joint surface between the first cover portion and the second cover portion was increased ((S ₁ / S ₀ )> 1) had extremely excellent durability.

[0052]

According to the present invention, in a golf ball obtained by manufacturing a cover made of a thermoplastic resin substantially in half at a time, one half shell in which a cover resin is formed in a hemispherical shell shape in advance is used as an upper mold. By heating and pressing in the cover on the cover, inverting the upper mold and installing it as a lower mold, the other half shell is manufactured by hot pressing in the next upper mold, A golf ball having excellent durability and a method of manufacturing the golf ball having excellent durability by increasing the area of the joint surface between the two cover portions and improving the adhesive force at the joint portion of the covers. provide.

[Brief description of the drawings]

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

FIG. 2 is a route diagram schematically showing one embodiment of the golf ball manufacturing process of the present invention.

FIG. 3 is a route diagram schematically showing one embodiment of the golf ball manufacturing process of the present invention.

FIG. 4 is a schematic sectional view showing an aspect of a sectional shape of a joint surface of a cover portion of the golf ball of the present invention.

FIG. 5 is a schematic enlarged sectional view showing an aspect of a sectional shape of a joint surface of a cover portion of the golf ball of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Core 2 ... Cover 3 ... 3rd half mold 4 ... 1st half mold 5 ... 2nd half mold 6 ... Half shell 7 ... 1st cover part 8 ... 2nd cover part

Claims (5)

[Claims] 1. A method of manufacturing a golf ball comprising a core (1) comprising one or more layers and a cover (2) made of a thermoplastic resin composition covering the core, comprising: (a) a spherical core; (B) Injecting the thermoplastic resin composition for a cover to form a half shell (6) having a thickness set so that the cover has a desired thickness. (C) (i) disposing the core in a third half mold (3) having a hemispherical cavity having a diameter set to the diameter of the core (1) and covering the half shell (6); A first half mold having a hemispherical cavity having a diameter set so that the golf ball has a desired diameter, and having a plurality of protrusions in the cavity to arrange dimples on the surface of the golf ball; (4) setting the upper half, (ii) lowering the first half mold (4) and setting the first half mold
(4) and the third half mold (3) are centered and clamped,
Heating the first mold half (4), (iii) opening the mold, and forming a golf ball intermediate molded article in which half of the surface of the core (1) is covered with the first cover portion (7); (iv) The portion of the golf ball intermediate molded product obtained in the step (iii) which covers the first cover part (7) is the first half mold (4).
The first half mold (4) is turned upside down while being settled in the cavity, and the half shell (6) is placed on the core (1) in the same manner as in the step (i). And the second half mold (5)
(V) lowering the second half mold (5) to lower the first half mold (4)
And the second half mold (5) are centered and clamped, the second half mold (5) is heated, and the other half of the surface of the core (1) is covered with a second cover ( 8) A method for producing a golf ball, comprising: a step of coating in step 8); and (vi) a step of opening a mold after cooling and taking out a molded product. Wherein said third half mold (3) is the following formula in the junction surface of the first cover portion and the second cover _{portion: (S 1 / S 0)} > 1 ( wherein, S ₁ is The bonding area (mm ² ) of the entire bonding surface,
S ₀ is the relationship expressed by the area (mm ² ) of the reference bonding surface where the cover layer intersects with the plane passing through the bonding boundary line on the golf ball surface and the center of the golf ball among the bonding surfaces. The method of claim 1, wherein the method is designed to be satisfactory. 3. The golf club according to claim 1, wherein a cross-sectional shape of a joining surface between the first cover portion and the second cover portion is a straight line and is inclined from a horizontal line passing through the center of the golf ball. The manufacturing method of the golf ball of the description. 4. An annular projection having a wedge-shaped cross section at least at an upper end thereof is formed on an inner peripheral portion of a joining surface of either the first cover portion or the second cover portion.
The method for producing a golf ball according to any one of the above items. 5. A core (1) comprising one or more layers and a cover (2) made of a thermoplastic resin for covering the core, the cover comprising a first cover portion having a hemispherical shell shape and a first cover portion having a hemispherical shell shape. 2 In a golf ball formed by joining a cover portion with a ring-shaped joint surface, the following formula is used at the joint surface: (S ₁ / S ₀ )> 1 (where S ₁ is the joint area of the entire joint surface (mm ² ) And
S ₀ is the relationship expressed by the area (mm ² ) of the reference bonding surface where the cover layer intersects with the plane passing through the bonding boundary line on the golf ball surface and the center of the golf ball among the bonding surfaces. A golf ball characterized by satisfying.