JPH11262544A - Method for manufacturing rubber ball for golf ball, and two-piece solid golf ball using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a golf ball with an improved productivity using an injection molding machine without reducing the carry and durability of the ball. SOLUTION: The method of manufacturing this rubber ball for golf ball includes a step of preparation of a rubber composition containing a base rubber, a co-crosslinking agent, an organic sulfer compound and/or a metal salt thereof and a crosslinking agent, and a step of injection molding and vulcanization of the rubber composition. Preferably, the contained organic sulfer compound and/or metal salt thereof is 0.1-3.0 parts by weight against the base rubber 100 parts by weight. And injection molding and vulcanization are carried out at the injection speed of 5-300 cc/sec. at a metal mold temperature of 130-190 deg.C for the vulcanization period of 0.5-10 minutes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a golf ball having improved productivity by enabling production of a rubber ball for a golf ball by an injection molding machine without impairing flight performance and durability. .

[0002]

2. Description of the Related Art In general, vulcanization molding of rubber balls for golf balls such as cores of golf balls is carried out by using a base rubber such as polybutadiene rubber, a zinc salt or ester of acrylic acid or methacrylic acid as a co-crosslinking agent, and a crosslinking agent as a crosslinking agent. It is performed by compression molding a rubber composition containing a peroxide or the like. However, in this method, (a) variation in the charged weight of the rubber composition charged into the mold, (b) time and effort for charging the rubber composition into the mold, (c) heating of the rubber composition charged However, there is a problem that the temperature rise is slow and it is difficult to shorten the vulcanization time because the heat conduction from the mold is used.

In order to solve these problems, it has been proposed to use an injection molding machine for manufacturing a core of a golf ball. In general, most injection molding machines are for thermoplastic resins, but injection molding machines are also used for molding rubber and thermosetting resins. Compared to thermoplastic resin, injection molding machines for rubber and thermosetting resin can vulcanize or cure rubber and resin in the mold after injection into the mold, and lower the temperature of the heating cylinder. However, there is a slight difference in the heating method of the cylinder, the shape of the screw, and the like because it is necessary to prevent the rubber and resin from hardening in the cylinder.
However, a method using an injection molding machine for manufacturing a core of a golf ball is effective as a laboratory method, but has the following problems in industrial use. (i) In the rubber injection molding, the rubber composition is heated using heat generated by the internal friction of the rubber composition itself in the flow path. Therefore, the heating time can be significantly reduced as compared with the compression molding, and the cycle time can be reduced. It is characterized by excellent productivity. However, since the rubber composition for the core of the golf ball has a very high initial vulcanization rate as compared with a general rubber composition, so that the vulcanization does not start in the middle of the flow path of the rubber injection molding machine, It is necessary to suppress the heat generation of the rubber composition itself. This suppression of heat generation makes it difficult to shorten the vulcanization time. (ii) When the mold is opened after the rubber composition for a core of a golf ball is injection-molded, cracks occur near the gate on the parting surface of the core. The cracks significantly reduce the durability of the obtained golf ball. This is because the rubber composition for the core of a golf ball has very poor mold release properties,
It is considered that excessive force is applied to the molded product in the vicinity of a particularly thin gate when the mold is opened.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the conventional method for manufacturing a golf ball, and makes it possible to manufacture a core by an injection molding machine. It is an object of the present invention to provide a method for producing a golf ball which is excellent in productivity and flight performance and durability.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, using a rubber composition containing a specific amount of an organic sulfur compound and / or a metal salt thereof in a core, It has been found that by performing injection molding with the injection speed, mold temperature, and vulcanization time specified in specific ranges, rubber balls for golf balls having excellent productivity, excellent flight performance and durability can be obtained. The invention has been completed.

That is, the present invention provides (a) a step of preparing a rubber composition containing a base rubber, a co-crosslinking agent, an organic sulfur compound and / or a metal salt thereof, and a cross-linking agent;
(b) a step of injection molding and vulcanizing the rubber composition. The rubber ball obtained here can be made into a one-piece solid golf ball by changing the shape of a molding die.

[0007] The present invention further provides a two-piece solid golf ball in which a rubber ball obtained by the above manufacturing method is used as a core and a cover is formed on the core.

As described above, the rubber ball for a golf ball of the present invention may be used as a one-piece solid golf ball by itself, or may be used as a multi-piece solid golf ball such as a two-piece solid golf ball or a three-piece solid golf ball. Can also be used as a core or centrosome. Hereinafter, for the sake of simplicity, the description will focus on the use of a two-piece solid golf ball as a core.

The rubber composition for a rubber ball of the present invention has an extremely high initial vulcanization rate as compared with a general rubber composition.
When manufacturing by injection molding, it is necessary to suppress heat generation of the rubber composition itself so that vulcanization does not start in the flow path of the injection molding machine. For this purpose, a method using a compound capable of capturing a radical generated during the vulcanization reaction is considered. Such a compound is industrially an organic oxygen-containing compound, an organic nitrogen compound, or an organic sulfur compound.
However, when an organic oxygen-containing compound and an organic nitrogen compound are used, cracks are generated near the gate on the parting surface of the core during injection molding, thereby lowering the durability of the golf ball obtained. Therefore, an organic sulfur compound is preferable.

The golf ball of the present invention is formed by covering a cover on a core obtained by injection molding and vulcanizing a rubber composition. The method for manufacturing the core of the golf ball of the present invention will be described in detail with reference to FIG. FIG. 1 is a schematic sectional view of an injection molding machine illustrating one embodiment of a method for manufacturing a core of a golf ball of the present invention. The core of the present invention is a rubber composition containing polybutadiene, a co-crosslinking agent, an organic sulfur compound and / or a metal salt thereof, a crosslinking agent, a filler, if necessary, an antioxidant, and the like, using an injection molding machine. It is obtained by injection molding vulcanization.

In FIG. 1- (a), the above rubber composition is mixed and put into a hopper (1), and the rubber composition is plasticized by rotation of a screw (2) by a driving motor (6). The screw (2) itself moves to inject the composition into the mold (4). The rubber composition is preferably preheated by a heater (3) for ease of injection, stable vulcanization, and the like. Preheating temperature is 40-120 ° C, preferably 60-100 ° C
It is. If the preheating temperature is lower than 40 ° C., the viscosity of the rubber composition is high and injection is not performed smoothly. If the preheating temperature is higher than 120 ° C., vulcanization is completed in the injection section. Injection speed is 5-300cc /
Seconds, preferably 10-100 cc / sec, more preferably 20-60 cc
Per second. If the injection speed is less than 5 cc / sec, it takes too much time to fill the rubber composition into the cavity (5) of the mold (4), and the vulcanization of the previously filled rubber composition proceeds first. However, uniformity of the degree of vulcanization in the core cannot be maintained. 300cc /
If the time exceeds seconds, the heat generation due to the internal friction of the rubber composition itself in the flow channel becomes too large, and vulcanization occurs in the flow channel.

In FIG. 1- (b), the screw (2) reaches the forefront, and the cavity (5) of the mold (4) of the rubber composition is used.
The vulcanization is performed immediately after the filling into the inside. Mold temperature
130-190 ° C, preferably 140-185 ° C, more preferably 16
0-180 ° C. If the mold temperature is lower than 130 ° C, the vulcanization will be too slow and the production time will be long.If the mold temperature is higher than 190 ° C, the vulcanization will be too fast, and the vulcanization of the previously filled rubber composition will be too fast. It progresses and uniformity in the core cannot be maintained. The vulcanization time is 0.5 to 10 minutes, preferably 1 to 8 minutes, more preferably 1.5 to 5 minutes. Vulcanization time 0.5
If it is less than one minute, the vulcanization is insufficient, and if it exceeds ten minutes, it becomes over-vulcanized.

In FIG. 1- (c), the screw (2) is retracted to the last position while rotating, the mold is opened, and the vulcanized molded product is opened.
Remove (7). This completes the injection molding cycle.
In the conventional rubber composition for a core of a golf ball, cracks occur near the gate on the parting surface of the core when the mold is opened, so that the durability of the obtained golf ball is significantly reduced. However, in the golf ball of the present invention using a rubber composition containing a specific amount of an organic sulfur compound and / or a metal salt thereof in the core, the injection speed, the mold temperature, and the vulcanization time are specified in the above-described specific ranges. By molding, a golf ball having excellent productivity, which is a feature inherent in injection molding, and excellent flight performance and durability can be obtained. The core of the present invention is also applicable to a multilayer core.

The base rubber used in the rubber composition for the core of the golf ball of the present invention is a cis-1,4-bond 90%
Polybutadiene rubber having the above is preferred. Cis-1,4
-If the bond is less than 90%, the resilience performance is poor. If desired, the polybutadiene rubber may be blended with natural rubber, polyisoprene rubber, styrene polybutadiene rubber, ethylene-propylene-diene rubber (EPDM), or the like.

The co-crosslinking agent is not particularly limited, but may be a C3-C8 α, β- such as acrylic acid or methacrylic acid.
Examples thereof include monovalent or divalent metal salts of unsaturated carboxylic acids such as zinc and magnesium, and zinc or magnesium metal salts of acrylic acid or methacrylic acid are preferred. The amount is 5 to 60 parts by weight, preferably 15 to 40 parts by weight, based on 100 parts by weight of the base rubber. If the amount is less than 5 parts by weight, it becomes too soft and rebound is deteriorated, and the flight distance is reduced. If the amount is more than 60 parts by weight, it becomes too hard and a favorable feeling at impact cannot be obtained.

As the crosslinking agent, an organic peroxide such as dicumyl peroxide, 1,1-bis (t-butylperoxy)
-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-
Di (t-butylperoxy) hexane and di-t-butyl peroxide are exemplified, and dicumyl peroxide is preferred. The compounding amount is 0.5 to 3.
0 parts by weight, preferably 0.7 to 2.5 parts by weight. If it is less than 0.5 parts by weight, it becomes too soft and rebound becomes worse, resulting in a shorter flight distance. If it exceeds 3.0 parts by weight, it will be too hard, and the feel when hitting will be poor.

The core of the golf ball of the present invention contains an organic sulfur compound and / or a metal salt thereof in addition to the above components. Examples of the organic sulfur compound include pentachlorothiophenol, pentafluorothiophenol, 4-chlorothiophenol, 4-bromothiophenol, 4-fluorothiophenol, 4-t-butyl-o-thiophenol, and 4-t-
Butylthiophenol, 2,3-dichlorothiophenol,
2,4-dichlorothiophenol, 2,5-dichlorothiophenol, 2,6-dichlorothiophenol, 3,4-dichlorothiophenol, 3,5-dichlorothiophenol, 2,4,5-trichlorothiophenol, Thiosalicylic acid, methylthiosalicylic acid, o-toluenethiol, m-toluenethiol, p-toluenethiol, 3-aminothiophenol, 4
-Aminothiophenol, 3-methoxythiophenol, 4
Thiophenols such as -methoxythiophenol, 4-mercaptophenyl sulfide and 2-benzamide thiophenol; thiocarboxylic acids such as thioacetic acid and thiobenzoic acid; diphenyl disulfide and bis (2-aminophenyl)
Disulfide, bis (4-aminophenyl) disulfide,
Bis (4-hydroxyphenyl) disulfide, bis (4-methylphenyl) disulfide, bis (4-t-butylphenyl) disulfide, bis (2-benzamidophenyl) disulfide, dixylyldisulfide, di (o-benzamidophenyl) disulfide , Dimorpholino disulfide, bis (4-chlorophenyl) disulfide, bis (2,5-
Dichlorophenyl) disulfide, bis (3,5-dichlorophenyl) disulfide, bis (2,4,5-trichlorophenyl) disulfide, bis (2-cyanophenyl) disulfide, bis (2-nitrophenyl) disulfide, bis (4-nitro (Phenyl) disulfide, bis (2,4-dinitrophenyl) disulfide, 2,2-dithiodibenzoic acid, 5,5-dithiobis (2-nitrobenzoic acid), bis (pentafluorophenyl) disulfide, dibenzyldisulfide, di- t-dodecyl disulfide, diallyl disulfide, difurryl disulfide, 2,2'-dibenzothiazolyl disulfide, bis (2-naphthyl) disulfide, bis (4-mercaptophenyl) sulfide, 4- (2-benzothiazolyldithio ) Morpholine, 2,2-dipyridinyl disulfide, 2,2-
Dithiobis (5-nitropyridine), 2,2-dithiodianiline, 4,4-dithiodianiline, 2,4-dinitrophenylsulfenyl chloride, dithiodiglycolic acid, 4,4′-dithiomorpholine, L-cystine Disulfides such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetramethylthiuram monosulfide, N, N'-dimethyl-
Thiurams such as N, N'-diphenylthiuram disulfide and dipentamethylenethiuram tetrasulfide; 2-mercaptobenzothiazole, 2-mercaptobenzothiazole sodium salt, 2-mercaptobenzothiazole zinc salt, 2-mercaptobenzothiazole dicyclohexylamine salt , 2- (N, N-diethylthiocarbamoylthio) benzothiazole, 2- (4'-morpholinodithio) benzothiazole, 2,5-dimercapto-1,3,4-thiadiazole, bismuthiol I, bismuthiol II, 2- Thiazoles such as amino-5-mercapto-1,3,4-thiadiazole and trithiocyanuric acid; sulfenamides; thioureas; and dithiocarbamates. Examples of the metal salt include a sodium salt and a zinc salt, and a zinc salt is preferable from the viewpoint of resilience performance. The amount is 0.1 to 3.0 parts by weight, preferably 0.2 to 2.5 parts by weight, more preferably 0.3 to 1.5 parts by weight, based on 100 parts by weight of the base rubber. If the amount is less than 0.1 part by weight, the compounding amount is too small, and the effect of the organic sulfur compound and / or the metal salt thereof cannot be exerted. If the amount exceeds 3.0 parts by weight, the vulcanization rate becomes too low and the vulcanization time becomes long. .

The core of the golf ball of the present invention may further contain a filler (for example, zinc oxide, barium sulfate,
Calcium carbonate, etc., high specific gravity metal powder (for example, tungsten powder, molybdenum powder, etc.), an antioxidant or a peptizer, and other components that can be generally used for the production of solid golf ball cores may be appropriately compounded. The antioxidant is preferably used in an amount of 0.2 to 0.5 part by weight based on 100 parts by weight of the base rubber. Further, the core of the golf ball of the present invention,
It may have a multilayer structure of two or more layers.

A cover is then coated on the core obtained as described above. The material used for the cover of the present invention can be formed of a thermoplastic resin such as an ionomer resin or a balata usually used as a cover material of a solid golf ball, but is formed of an ionomer resin to achieve high resilience. Is preferred. As the ionomer resin, a resin obtained by neutralizing a part of carboxylic acid in a copolymer of ethylene- (meth) acrylic acid with metal ions or a mixture thereof is used. Examples of the neutralizing metal ion include alkali metal ions such as Na ion, K ion, and Li ion; divalent metal ions such as Zn ion, Ca ion, and Mg ion; trivalent metal ions such as Al ion; Nd ions and the like; and mixtures thereof, of which Na ions, Zn ions, and Li ions are often used because of their resilience, durability and the like. Specific examples of the ionomer resin include, but are not limited to, Himilan 1555, 1557, 1605, 1652, 1705, 1706, 1707, 18
55, 1856 (Mitsui DuPont Polychemical), Surlyn AM
7317, AM7318 (Dupont, USA), IOTEC 7010, 8000
(Manufactured by Exxon) and the like.

In the present invention, in addition to the above-mentioned resin as a main component, the above-mentioned cover composition may contain, if necessary,
Fillers such as barium sulfate and calcium carbonate, coloring agents such as titanium dioxide, and other additives such as dispersants, anti-aging agents, ultraviolet absorbers, light stabilizers, fluorescent materials or fluorescent brighteners, etc. Although it may be contained in a range that does not impair the desired properties of the ball cover, usually, the amount of the coloring agent is 0.1 to 0.5 with respect to 100 parts by weight of the cover resin.
Parts by weight are preferred.

The cover of the present invention can be formed by using a generally known method used for forming a cover of a golf ball, and is not particularly limited. The cover composition is previously formed into a hemispherical shell-like half shell,
A method may be used in which a solid core is wrapped and pressure-formed using a single sheet, or the core is wrapped by directly injection-molding the cover composition onto the core. Further, the cover of the golf ball of the present invention may have a multilayer structure of two or more layers.
When molding the cover, a large number of depressions called dimples are formed on the surface as necessary. The golf ball of the present invention is usually put on the market after being subjected to a paint finish, a marking stamp, or the like, in order to enhance aesthetic appearance and commercial value.

[0022]

EXAMPLES The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Preparation of core (Examples 1 to 3 and Comparative examples 2 to 4) A rubber composition for a core having the composition shown in Table 1 below was preheated at 70 ° C.
Injection molding was performed at cc / sec, at a mold temperature of 170 ° C. and for the vulcanization time shown in the same table, to obtain a spherical core. The obtained core was visually inspected for the presence or absence of cracks, and the results are shown in Table 3.

Comparative Example 1 A rubber composition for a core having the composition shown in Table 1 below was kneaded with a kneading roll, and heated and pressed at 150 ° C. for the vulcanization time shown in the table to form a spherical core. Obtained. The obtained core was visually inspected for the presence or absence of cracks, and the results are shown in Table 3.

[0025]

(Table 1) (parts by weight) Example Comparative example Core composition 1 2 3 1 2 3 4 BR01 (Note 1) 100 100 100 100 100 100 100 Zinc acrylate 30 30 −30 30 30 30 30 Magnesium methacrylate − − 30 − ---Zinc oxide 10 10-10 10 10 10 Magnesium oxide--10----Dicumyl peroxide 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Diphenyl disulfide 1.5--1.5 0.05--Zinc diphenyl disulfide salt-2.0--- − −Thiobenzoic acid − − 1.8 − − 5.0 − Molding method Injection Injection Injection Press Injection Injection Injection Vulcanization time (min) 1.0 1.5 1.0 30 1.0 15 1.0 (Note 1) Polybutadiene rubber (Nippon Synthetic Rubber Co., Ltd.) (Content of -1,4-bond: 97%)

Preparation of Cover Composition The materials having the compositions shown in Table 2 below were mixed by a twin-screw kneading extruder to prepare a pellet-like intermediate layer and a cover composition. Extrusion conditions are screw diameter 45mm,
The screw speed was 200 rpm, the screw L / D = 35, and the blend was heated to 200-260 ° C. at the die position of the extruder.

[0027]

[Table 2] Cover composition parts by weight Himilan 1605 (Note 2) 50 Himilan 1706 (Note 3) 50 Titanium oxide 2 (Note 2) Sodium ion neutralized ethylene-methacrylic acid copolymer ionomer resin manufactured by Mitsui DuPont Polychemicals (Note) 3) Zinc ion neutralized ethylene-methacrylic acid copolymerized ionomer resin manufactured by Mitsui DuPont Polychemicals, Ltd.

Preparation of Golf Ball The above cover composition was injection molded on the obtained core. Next, deburring, paint pretreatment, paint and the like are performed to finish the same processing as a normal golf ball,
A golf ball having a size of 42.7 mm was obtained. The flight distance and durability of the obtained golf ball were evaluated, and the results are similarly shown in Table 3. The test method was performed as described below.

(Test Method) Flying Distance A Wood No. 1 club (W # 1, driver) was attached to a swing robot manufactured by True Temper, and a golf ball was hit at a head speed of 45 m / sec. Distance) was measured. Endurance A ball was hit against a metal plate at a speed of 45 m / sec, and the number of times until cracking occurred was examined. The results are shown by an index when the number of times until cracking of Example 1 is set to 100.

(Test results)

(Table 3) (parts by weight) Example Comparative Example Test Item 1 2 3 1 2 3 4 Crack of core No No No No No Yes No Yes Carry (yard) 235 230 233 225 220 222 219 Durability 100 95 100 90
70 95 65

From the above results, it can be seen that the golf balls of Examples 1 to 3 of the present invention are excellent in both flight distance and durability as compared with the golf balls of Comparative Examples 1 to 4. In addition, the golf ball of Example 1 has a vulcanization time of 30 minutes of Comparative Example 1 when compared with the golf ball of Comparative Example 1 manufactured by a hot press without injection molding vulcanization of the core with the same composition. The result was greatly reduced to one minute, and both the flight distance and the durability were excellent.

In the golf ball of Comparative Example 2, since the amount of the organic sulfur compound in the rubber composition for the core was small, cracks occurred during the injection molding of the core, and the durability of the obtained golf ball was reduced. . In the golf ball of Comparative Example 3, since the amount of the organic sulfur compound in the rubber composition for the core was large, the vulcanization rate was low and the vulcanization time was very long. Since the golf ball of Comparative Example 4 does not contain an organic sulfur compound in the rubber composition for the core, cracks occur during the injection molding of the core, and the durability of the obtained golf ball is greatly reduced.

[0033]

The golf ball of the present invention uses a rubber composition containing a specific amount of an organic sulfur compound and / or a metal salt thereof for the production of the core, and controls the injection speed, mold temperature and vulcanization time in a specific range. Injection molding specified in
It is excellent in productivity and improved in flight performance and durability.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of an injection molding machine illustrating a method of manufacturing a core of a golf ball of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Hopper 2 ... Screw 3 ... Heater 4 ... Mold 5 ... Cavity 6 ... Drive motor 7 ... Molded product

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29L 31:54

Claims (5)

[Claims] 1. A step of preparing a rubber composition containing (a) a base rubber, a co-crosslinking agent, an organic sulfur compound and / or a metal salt thereof, and a crosslinking agent; and (b) injecting the rubber composition. A method for producing a rubber ball for a golf ball, comprising a step of molding and vulcanizing. 2. The injection molding vulcanization is performed at an injection speed of 5 to 300 c.
The method for producing a rubber ball for a golf ball according to claim 1, wherein the method is performed at c / sec, a mold temperature of 130 to 190 ° C and a vulcanization time of 0.5 to 10 minutes. 3. The method for producing a rubber ball for a golf ball according to claim 1, wherein the amount of the organic sulfur compound and / or the metal salt thereof is 0.1 to 3.0 parts by weight based on 100 parts by weight of the base rubber. 4. The method according to claim 1, wherein the obtained rubber ball for a golf ball is a one-piece solid golf ball. 5. A two-piece solid golf ball in which a rubber ball obtained by the production method according to claim 1 is used as a core, and a cover is formed on the core.