JP2004016677A - Method for manufacturing golf ball - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a golf ball decreasing faults in the appearance by restraining an oxidation reaction of a melted resin. <P>SOLUTION: Pellets 18 inside a feed part 15 are melted and bit into a cylinder 10 by rotating a screw 11 of an injection molding machine 6 clockwise while retreating. A shutter 16 is closed. An inert gas is fed into the cylinder 10 from a gas generator 7 via the feed part 15. The melted resin is stored inside the cylinder 10 and in the front of the screw 11. The screw 11 advances, and the melted resin is injected into a mold 8 from a recess part 9 to be molded into a cover. No entrance of air into the cylinder 10 restrains the oxidation reaction of the melted resin, preventing a color change. Nitrogen is preferable as the inert gas. <P>COPYRIGHT: (C)2004,JPO

Description

【００４７】
表１において、比較例１及び２の製造方法では、カバーの変色（焼けを含む）が発生している。これに対し、各実施例の製造方法では、カバーの変色が見られない。この評価結果より、本発明の優位性は明らかである。
【００４８】
以上の説明ではツーピースゴルフボールのカバーが成形される場合が一例とされたが、スリーピースゴルフボールの内側カバー及び外側カバーの成形にも本発明の製造方法が適用されうる。さらに、３以上のカバー層を備えるゴルフボールの各カバーの成形にも、本発明の製造方法が適用されうる。
【００４９】
【発明の効果】
以上説明されたように、本発明のゴルフボール製造方法により外観不良が低減される。この製造方法は、ゴルフボールの品質向上及び生産性向上に寄与する。
【図面の簡単な説明】
【図１】図１は、本発明の一実施形態に係る製造方法によって得られたゴルフボールが示された一部切り欠き断面図である。
【図２】図２は、図１のゴルフボールの製造装置が示された一部切り欠き断面図である。
【図３】図３は、図２の製造装置の成形型の一部が示された断面図である。
【符号の説明】
１・・・ゴルフボール
２・・・コア
３・・・カバー
４・・・ディンプル
５・・・製造装置
６・・・射出成形機
７・・・ガス発生装置
８・・・成形型
９・・・凹陥部
１０・・・シリンダー
１１・・・スクリュー
１２・・・ホッパー
１３・・・ノズル
１４・・・本体
１５・・・供給部
１６・・・シャッター
１９・・・パイプ
２０・・・上型
２１・・・下型
２２・・・保持ピン
２３・・・ベントピン
２４・・・保持ピン孔
２５・・・ベントピン孔
２６・・・キャビティ面[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a golf ball, and more particularly to an improvement in an injection molding method for molding a cover.
[0002]
[Prior art]
A two-piece golf ball has a core and a cover. This cover is made of a thermoplastic resin composition. This cover is generally formed by an injection molding method. In the injection molding method, first, a core (that is, a sphere) is put into a mold having a spherical cavity. This mold has a holding pin that can move forward and backward with respect to the cavity, and a vent pin for communicating the cavity with the outside air. The core is held at the center of the cavity by the advancing holding pin. Next, the resin composition is supplied to the cylinder, melted, and injected toward the cavity. The molten resin fills the gap between the cavity surface and the core. This molten resin coats around the core and eventually solidifies to form a cover.
[0003]
Even in a three-piece golf ball including a core, an inner cover (also referred to as an intermediate layer), and an outer cover, the inner cover and the outer cover are often formed by an injection molding method. Also in the case of molding the inner cover of a three-piece golf ball, a core (that is, a sphere) is put into a mold having a spherical cavity, and a molten resin is injected around the core. In the case of molding the outer cover of a three-piece golf ball, a sphere composed of a core and an inner cover is put into a mold having a spherical cavity, and a molten resin is injected around the sphere.
[0004]
At the stage when the sphere is held by the holding pin, air exists in the gap between the cavity surface and the sphere. As the molten resin flows into the cavity, the air in the cavity is discharged to the outside. The discharge is performed from the clearance of the holding pin and the vent pin.
[0005]
At the beginning of injection, gas is exhausted from both the holding pin clearance and the vent pin clearance. When the molten resin flows to some extent, the clearance of the holding pin is closed by the molten resin. Thereafter, gas is discharged only from the clearance of the vent pin. If the clearance of the vent pin is too small, the discharge of gas becomes insufficient, and if the clearance is too large, the molten resin flows into the clearance. From the viewpoint of preventing these inconveniences, the clearance of the vent pin is set to 50 μm to 100 μm.
[0006]
Japanese Patent Application Laid-Open No. 2000-37480 discloses a technique in which a pin is formed from a porous material to enhance gas exhaustability. This pin can cause clogging of the hole with repeated use. This pin is expensive. Moreover, this pin is fragile and easily breaks. Pins made of porous materials are not practical.
[0007]
[Problems to be solved by the invention]
Some air enters the cylinder as the resin composition is supplied. Occasionally, oxygen contained in air reacts with the molten resin due to shear heat generated when the molten resin is injected into the cavity, and the molten resin is oxidized. Oxidation leads to discoloration of the molten resin. Significant discoloration is called "burn". Discoloration reduces the appearance of the golf ball. Further, the product of the oxidation reaction may turn into a gas and evaporate from the molten resin. The product adheres to the cavity surface and causes the golf ball to become dirty.
[0008]
The product also adheres to the inner peripheral surface of the vent pin hole, causing the vent pin clearance to be blocked. If the clearance is closed, the air will not be sufficiently exhausted from here. The air remaining in the cavity is likely to cause an oxidation reaction with the molten resin, thereby generating a new reaction product. That is, a vicious cycle occurs in which the molten resin is oxidized by the air entering the cylinder, and the air located in the gap between the cavity surface and the sphere is also oxidized by the influence of the product generated by the oxidation. Further, clogging of the vent pin clearance causes air to enter into the cover, and causes weld marks (line-like marks generated at joints between resins) and bears (spaces due to residual gas).
[0009]
In recent years, golf balls provided with a thin cover (this cover also includes an intermediate layer) have been developed for high performance, and are commercially available. In molding a thin cover, the gap between the sphere and the cavity surface is narrow, so that the molten resin does not easily flow. In order to enhance the fluidity of the molten resin, the temperature of the molten resin is often set to a higher temperature when molding a thin cover. Thereby, the reaction between the molten resin and the air is promoted. In molding a thin cover, poor appearance due to discoloration of the molten resin is a major problem.
[0010]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a golf ball manufacturing method in which an oxidation reaction of a molten resin is suppressed and appearance defects are reduced.
[0011]
[Means for Solving the Problems]
The golf ball manufacturing method according to the present invention includes:
(A) A melting step in which a thermoplastic resin is supplied to a cylinder and heated to obtain a molten resin.
(B) an injection step of injecting the molten resin around a sphere arranged in a mold having a spherical cavity.
as well as,
(C) a solidification step of solidifying the molten resin to form a cover.
including. In this melting step, an inert gas is supplied into the cylinder.
[0012]
In this production method, the oxidation reaction of the molten resin is suppressed by supplying the inert gas. This prevents the appearance defect due to the discoloration of the molten resin, prevents the golf ball from being stained by the reaction product, and also prevents the clearance from clogging due to the reaction product.
[0013]
Preferably, the relative humidity of the inert gas supplied in the melting step is 40% or less. As a result, the amount of gas generated from the molten resin due to the evaporation of water is reduced, and poor appearance of the golf ball due to the remaining gas is suppressed. In addition, it is possible to prevent the durability of the golf ball from decreasing due to the cover containing moisture. From the viewpoint of economy, a preferred inert gas is nitrogen gas.
[0014]
Even when a cover having a thickness of 1.7 mm or less is formed by the supply of the inert gas, the defective rate due to the oxidation of the molten resin is reduced.
[0015]
By supplying the inert gas, even when a mold having a clearance between the vent pin hole and the vent pin of 50 μm or less is used, a defective rate due to oxidation of the molten resin is reduced. By using this mold, burrs caused by the flow of the molten resin into the clearance are suppressed. With a golf ball obtained with this molding die, the work of removing burrs is easy.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the drawings as appropriate.
[0017]
FIG. 1 is a partially cutaway sectional view showing a golf ball 1 obtained by a manufacturing method according to an embodiment of the present invention. The golf ball 1 has a two-piece structure and includes a core 2 as a sphere and a cover 3. The core 2 is formed by crosslinking a rubber composition. The cover 3 is made of a resin composition containing a thermoplastic resin as a main component. Many dimples 4 are formed on the surface of the cover 3. The golf ball 1 has a paint layer and a mark layer on the outside of the cover 3, but these are not shown. The diameter of the golf ball 1 is usually 40 mm to 45 mm, particularly 42 mm to 44 mm. The diameter is preferably 42.67 mm or more and 42.80 mm or less from the viewpoint that air resistance is reduced within a range satisfying the standards of the United States Golf Association (USGA). The mass of the golf ball 1 is usually 40 g or more and 50 g or less, particularly 44 g or more and 47 g or less. The weight is preferably 45.00 g or more and 45.93 g or less from the viewpoint that the inertia can be increased within a range satisfying the standards of the United States Golf Association.
[0018]
FIG. 2 is a partially cutaway sectional view showing the manufacturing device 5 of the golf ball 1 of FIG. In this figure, an injection molding machine 6, a gas generator 7, and a molding die 8 are shown. In this figure, the injection molding machine 6 is separated from the mold 8. The injection molding machine 6 is movable in the left-right direction in the figure. When the injection molding machine 6 moves to the left, the tip of the injection molding machine 6 comes into contact with the concave portion 9 of the molding die 8.
[0019]
The injection molding machine 6 includes a cylinder 10, a screw 11, and a hopper 12. The tip of the cylinder 10 is a nozzle 13. The screw 11 is housed in the cylinder 10. The hopper 12 includes a main body 14, a supply unit 15, and a shutter 16. The shutter 16 is configured to be openable and closable. When the shutter 16 is open, the main body 14 and the supply unit 15 communicate with each other. When the shutter 16 is closed, the main body 14 and the supply unit 15 are shut off. The supply unit 15 is inserted into an opening 17 formed on the upper surface of the cylinder 10. The hopper 12 stores pellets 18 (granular thermoplastic resin composition).
[0020]
The gas generator 7 generates nitrogen gas. The gas generator 7 is connected to the hopper 12 via a pipe 19. The tip of the pipe 19 reaches the supply section 15 of the hopper 12. Nitrogen gas is sent from the gas generator 7 to the hopper 12 through the pipe 19.
[0021]
FIG. 3 is a sectional view showing a part of the molding die 8 of the manufacturing apparatus 5 of FIG. The molding die 8 includes an upper die 20, a lower die 21, a plurality of holding pins 22, and two vent pins 23. The holding pin 22 is located at an equal distance from the pole in each of the upper mold 20 and the lower mold 21. In each of the upper die 20 and the lower die 21, three to eight holding pins 22, particularly three to six holding pins 22, are provided. FIG. 3 illustrates two holding pins 22 in each of the upper mold 20 and the lower mold 21. The holding pins 22 pass through the holding pin holes 24. The vent pins 23 are located at the extreme points of the upper mold 20 and the lower mold 21. The vent pin 23 is inserted into the vent pin hole 25. The tips of the holding pin 22 and the vent pin 23 protrude. The dimples 4 are formed on the golf ball 1 by the protruding portions. When the tips of the pins 22 and 23 come into contact with the lands (the surface of the golf ball 1 other than the dimples 4), the tips of the pins 22 and 23 are flat.
[0022]
The upper mold 20 and the lower mold 21 have a hemispherical cavity surface 26. When the molding die 8 is tightened, a spherical cavity is formed by the cavity surface 26 of the upper die 20 and the cavity surface 26 of the lower die 21 as shown in FIG. Although not shown, a large number of protrusions are formed on the cavity surface 26. When the cover 3 is formed, the dimple 4 having a shape inverted from the shape of the protrusion is formed by the protrusion. When the mold 8 is tightened, the runner 27, the gate 28, and the recess 9 are formed. The cross-sectional shapes of the runner 27 and the gate 28 are circular. The recess 9 is hemispherical.
[0023]
The holding pin 22 is configured to be able to move forward and backward. FIG. 3 shows a state in which the holding pin 22 has moved forward, in other words, a state in which the tip of the holding pin 22 has approached the center of the cavity. The holding pin 22 holds the core 2 at the center of the cavity.
[0024]
When the golf ball 1 is molded by the manufacturing apparatus 5, first, the screw 11 of the injection molding machine 6 rotates while retreating rightward. Due to the rotation, the pellets 18 in the supply unit 15 are bitten into the cylinder 10. Since the cylinder 10 is heated by a heating means (not shown), the pellet 18 gradually melts in accordance with the biting. At this time, the shutter 16 is closed. The nitrogen gas is supplied to the supply unit 15 by the operation of the gas generator 7, whereby the vicinity of the supply unit 15 in the cylinder 10 is also placed under a nitrogen gas atmosphere. Although a small amount of atmospheric gas enters the cylinder 10 due to the melting of the pellets 18, the atmosphere is nitrogen gas as described above, so that air can be prevented from entering the cylinder 10. The molten resin is stored in the cylinder 10 and in front of the screw 11.
[0025]
On the other hand, the core 2 is put into the cavity of the lower mold 21 and the mold is clamped. Almost simultaneously with the mold clamping, the holding pin 22 advances, and the core 2 is held at the center of the cavity as shown in FIG.
[0026]
Next, the injection molding machine 6 advances to the left, and the nozzle 13 is pressed against the recess 9. Next, the screw 11 advances with respect to the cylinder 10, and the molten resin is injected from the recess 9 toward the mold 8. The molten resin passes through the runner 27 and the gate 28 and is injected into the cavity. With the injection, the air in the cavity is gradually discharged outside through the clearance between the holding pin 22 and the holding pin hole 24 and the clearance between the vent pin 23 and the vent pin hole 25. Immediately before the injection of the molten resin is completed, the holding pin 22 is retracted. Due to the retreat, the tip of the holding pin 22 substantially coincides with the cavity surface 26. Although the holding pin 22 is separated from the core 2, the core 2 hardly moves thereafter because the molten resin exists between the core 2 and the cavity surface 26. Even after the holding pin 22 has receded, a small amount of molten resin is injected into the cavity, and the entire outer peripheral surface of the core 2 is covered with the molten resin. The molten resin is cooled and solidified to form the cover 3.
[0027]
The molten resin in the cylinder 10 is at a high temperature (for example, 200 ° C.). At the time of injection, the temperature of the molten resin is further increased by the heat generated by shearing when passing through the gate 28. Since the entry of air into the cylinder 10 is prevented as described above, the reaction of the molten resin at a high temperature with oxygen is prevented. In this manufacturing method, discoloration of the cover is suppressed. This manufacturing method reduces poor appearance of the golf ball. In this manufacturing method, the product of the oxidation reaction is suppressed from adhering to the cavity surface 26, which also reduces the poor appearance of the golf ball. Further, in this production method, the product is also prevented from blocking the clearance.
[0028]
When the amount of the pellet 18 in the supply unit 15 becomes small, the shutter 16 is opened. Thereby, the pellets 18 stored in the main body 14 fall to the supply unit 15. After a predetermined amount of the pellets 18 have fallen, the shutter 16 is closed. While the shutter 16 is open, the nitrogen gas leaks from the supply unit 15 toward the main body 14, but the time during which the shutter 16 is open is short (for example, several seconds to several tens of seconds), and therefore has little adverse effect. The shutter 16 may not be provided, and the entire inside of the hopper 12 may be in a nitrogen gas atmosphere.
[0029]
In the manufacturing apparatus of FIG. 2, the nitrogen gas is supplied to the cylinder 10 via the supply unit 15, but the nitrogen gas may be directly supplied to the cylinder 10.
[0030]
An inert gas other than nitrogen may be supplied to the cylinder 10. Examples of other inert gases include helium gas, neon gas, and argon gas. Two or more inert gases may be mixed and supplied to the cylinder 10. From the viewpoint of economy, nitrogen gas is preferred.
[0031]
The relative humidity of the inert gas is preferably 40% or less. Thereby, the moisture content of the molten resin is reduced, and the amount of gas generated from the molten resin due to evaporation of the moisture is reduced. By reducing the gas amount, the load on the vent pin clearance is reduced, and poor appearance of the golf ball 1 due to residual gas is prevented. Further, the moisture content of the cover 3 is reduced by the specification of the inert gas having a low relative humidity. The cover 3 having a small moisture content has excellent durability. In these respects, the relative humidity is more preferably equal to or less than 35% and particularly preferably equal to or less than 30%.
[0032]
From the viewpoint of reducing the defective rate, the purity of the inert gas is preferably 90% or more, more preferably 95% or more, and particularly preferably 99% or more. The supply amount of the inert gas is appropriately determined in consideration of the capacity of the cylinder 10. In the case of a general cylinder 10 used for manufacturing the golf ball 1, the supply amount per minute is preferably about 1 liter to 50 liters.
[0033]
The pressure of the supplied inert gas is preferably 1.5 kgf / cm ² (0.147 MPa) or more. If the pressure is less than the above range, the supply of the inert gas to the cylinder 10 may be insufficient. In this respect, the pressure is more preferably 2.0 kgf / cm ² or more, 2.5 kgf / cm ² or more is particularly preferable. If the pressure is too high, the effect will level off and the economy will be uneconomical, so the pressure is preferably 10 kgf / cm ² (0.981 MPa) or less.
[0034]
This manufacturing apparatus 5 is suitable for molding the cover 3 having a thickness of 1.7 mm or less, that is, the thin cover 3. In molding the thin cover 3, the gap between the core 2 and the cavity surface 26 is narrow, so it is necessary to inject a low-viscosity molten resin (in other words, a high-temperature molten resin). The high-temperature molten resin easily reacts with oxygen. However, in the manufacturing method of the present invention, the entry of oxygen into the cylinder 10 is prevented. The manufacturing method of the present invention is particularly suitable for forming the cover 3 having a thickness of 1.5 mm or less. It is difficult to form the cover 3 that is too thin by injection molding. The thickness of the normal cover 3 is 0.5 mm or more.
[0035]
According to this manufacturing method, since the product of the oxidation reaction does not block the clearance of the vent pin 23, even when the clearance of the vent pin 23 is small, a failure hardly occurs. By using a mold having a small clearance, the size of a burr generated due to the flow of the molten resin into the clearance is reduced. The small burrs do not deteriorate the appearance of the golf ball 1 even if they are not removed in a later step. Even when burrs are removed, the removal operation is simple because the size is small. This manufacturing method also contributes to improving the appearance or productivity of the golf ball 1. In this respect, the clearance of the vent pin 23 is preferably equal to or less than 50 μm, more preferably equal to or less than 20 μm, and particularly preferably equal to or less than 10 μm. If the clearance is too small, the discharge of air becomes insufficient, so the clearance is preferably 5 μm or more.
[0036]
The clearance C of the vent pin 23 is calculated by the following formula when the inner diameter of the vent pin hole 25 is D and the outer diameter of the vent pin 23 is d.
C = (D−d) / 2
[0037]
The cover 3 to which this manufacturing method is applied mainly contains a thermoplastic resin. Preferred thermoplastic resins include ionomer resins and thermoplastic elastomers. Specific examples of the thermoplastic elastomer include a styrene-based thermoplastic elastomer, a polyurethane-based thermoplastic elastomer, a polyamide-based thermoplastic elastomer, and a polyester-based thermoplastic elastomer. Particularly preferred thermoplastic elastomers are styrenic thermoplastic elastomers (thermoplastic elastomers containing styrene blocks). Styrene-based thermoplastic elastomers include styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-isoprene-butadiene-styrene block copolymer (SIBS), SBS Hydrogenated product, SIS hydrogenated product and SIBS hydrogenated product. Examples of hydrogenated SBS include styrene-ethylene-butylene-styrene block copolymer (SEBS). Examples of hydrogenated SIS include styrene-ethylene-propylene-styrene block copolymer (SEPS). Examples of hydrogenated SIBS include styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS).
[0038]
【Example】
Hereinafter, the effects of the present invention will be clarified by examples, but the present invention should not be construed as being limited based on the description of the examples.
[0039]
[Example 1]
100 parts by mass of polybutadiene (trade name “BR01” of JSR Corporation), 22.5 parts by mass of zinc acrylate, 8 parts by mass of zinc oxide, 0.8 parts by mass of dicumyl peroxide and an appropriate amount of barium sulfate are kneaded with a kneader, A rubber composition was obtained. The rubber composition was charged into a mold and heated to cause a crosslinking reaction in the rubber, thereby obtaining a spherical core having a diameter of 40.5 mm. The crosslinking temperature was 160 ° C. and the crosslinking time was 23 minutes.
On the other hand, 50 parts by mass of an ionomer resin (trade name "Surlyn 8945" of DuPont), 50 parts by mass of another ionomer resin (trade name of "Surlyn 9945") and 2 parts by mass of titanium dioxide are kneaded with a twin-screw extruder. Thus, a pellet-shaped resin composition was obtained.
Next, the manufacturing apparatus shown in FIG. 2 was prepared, and a cover having a thickness of 1.1 mm was formed around the core using the pellets. At this time, the room temperature was 35 ° C., and the relative humidity in the room was 76%. During molding, nitrogen gas was supplied to the cylinder using a gas generator. The purity of the nitrogen gas was 98%, the relative humidity was 20%, and the pressure was 1.8 kgf / cm ² . The vent pin clearance of the mold of this manufacturing apparatus is 10 μm.
[0040]
[Comparative Example 1]
A cover was formed in the same manner as in Example 1 except that no nitrogen gas was supplied.
[0041]
[Example 2]
100 parts by mass of polybutadiene (the above-mentioned trade name "BR01"), 22.5 parts by mass of zinc acrylate, 8 parts by mass of zinc oxide, 0.8 parts by mass of dicumyl peroxide and an appropriate amount of barium sulfate are kneaded with a kneader, and a rubber composition is prepared. I got something. The rubber composition was charged into a mold and heated to cause a crosslinking reaction in the rubber, thereby obtaining a spherical core having a diameter of 39.3 mm. The crosslinking temperature was 160 ° C. and the crosslinking time was 23 minutes.
On the other hand, 100 parts by mass of a polyurethane-based thermoplastic elastomer (trade name “Elastollan ET880” of BASF Polyurethane Elastomers) and 2 parts by mass of titanium dioxide were kneaded with a twin-screw extruder to obtain a pellet-shaped resin composition.
Next, the manufacturing apparatus shown in FIG. 2 was prepared, and a cover having a thickness of 1.7 mm was formed around the core using the pellets. At this time, the room temperature was 35 ° C., and the relative humidity in the room was 76%. During molding, nitrogen gas was supplied to the cylinder using a gas generator. The purity of the nitrogen gas was 98%, the relative humidity was 20%, and the pressure was 1.8 kgf / cm ² . The vent pin clearance of the mold of this manufacturing apparatus is 40 μm.
[0042]
[Examples 3 to 6]
A cover was formed in the same manner as in Example 2 except that a mold having a vent pin clearance shown in Table 1 below was used.
[0043]
[Comparative Example 2]
A cover was formed in the same manner as in Example 2 except that no nitrogen gas was supplied.
[0044]
[Reference example]
A cover having a thickness of 2.0 mm was formed in the same manner as in Example 2 except that a core having a diameter of 38.7 mm was used and nitrogen gas was not supplied.
[0045]
[Observation of appearance]
The defect of the obtained cover was visually observed, and the number of golf balls having the defect was counted. The evaluation items are as follows.
Burn: Whether there is severe discoloration on the surface of the cover. Discoloration: Whether there is slight discoloration on the surface of the cover. Poor burr: Whether there is a huge burr at the position corresponding to the vent pin clearance. : Whether or not air has entered the cover. The results are shown in Table 1 below.
[0046]
[Table 1]

[0047]
In Table 1, in the production methods of Comparative Examples 1 and 2, discoloration (including burning) of the cover occurred. On the other hand, in the manufacturing method of each embodiment, no discoloration of the cover is observed. From the evaluation results, the superiority of the present invention is clear.
[0048]
In the above description, the case where the cover of the two-piece golf ball is formed is taken as an example, but the manufacturing method of the present invention can be applied to the formation of the inner cover and the outer cover of the three-piece golf ball. Further, the manufacturing method of the present invention can be applied to molding of each cover of a golf ball having three or more cover layers.
[0049]
【The invention's effect】
As described above, the golf ball manufacturing method of the present invention reduces appearance defects. This manufacturing method contributes to improving the quality and productivity of the golf ball.
[Brief description of the drawings]
FIG. 1 is a partially cutaway sectional view showing a golf ball obtained by a manufacturing method according to an embodiment of the present invention.
FIG. 2 is a partially cutaway sectional view showing the golf ball manufacturing apparatus of FIG. 1;
FIG. 3 is a sectional view showing a part of a mold of the manufacturing apparatus of FIG. 2;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Golf ball 2 ... Core 3 ... Cover 4 ... Dimple 5 ... Manufacturing apparatus 6 ... Injection molding machine 7 ... Gas generator 8 ... Mold 9 ... -Recessed part 10-Cylinder 11-Screw 12-Hopper 13-Nozzle 14-Body 15-Supply unit 16-Shutter 19-Pipe 20-Upper die 21 ... Lower mold 22 ... Holding pin 23 ... Vent pin 24 ... Holding pin hole 25 ... Vent pin hole 26 ... Cavity surface

Claims (5)

A melting step of supplying a thermoplastic resin to a cylinder and heating to obtain a molten resin;
An injection step of injecting the molten resin around a sphere arranged in a mold having a spherical cavity,
A solidification step of solidifying the molten resin to form a cover, a golf ball manufacturing method,
A method for manufacturing a golf ball, wherein an inert gas is supplied into a cylinder in the melting step. The golf ball manufacturing method according to claim 1, wherein the relative humidity of the inert gas supplied in the melting step is 40% or less. 3. The golf ball manufacturing method according to claim 1, wherein the inert gas supplied in the melting step is a nitrogen gas. The golf ball manufacturing method according to any one of claims 1 to 3, wherein the thickness of the cover obtained in the solidification step is 1.7 mm or less. The molding die used in the injection step has a vent pin hole and a vent pin inserted into the vent pin hole, and a clearance between the vent pin hole and the vent pin is 50 μm or less. 13. The method for producing a golf ball according to item 12.

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