JPS61112619A - Manufacture of golf ball - Google Patents

Abstract

PURPOSE:To shorten the time of drying and hardening a protective layer by forming an outer skin by injection molding on the surface of a uniform-thick protective closely adhered to a yarn rubber-wound core. CONSTITUTION:A yarn rubber-wound core 2 is covered with a film 1 of a thick ness of 10-500mum, formed of one or two or more of thermoplastic materials having a softening point of 30-100 deg.C. The covering operation of the film 1 on the core 2 can be simplified if the film 1 is molded into a tubular form 11 or baggy form with a space enough to sufficiently cover the core 2. Hot air is applied to the film 1 to thermally contract the film 1, thereby forming a protective layer 1a on the periphery of the core 2. The core with the protec tive layer is set in a mold for injection molding and a thermoplastic resin is injected into the mold to form an outer skin in order to obtain a complete golf ball.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing a thread-rubber-wound core golf ball, and more particularly, to a method for manufacturing a golf ball in which a thread-wound core is covered with an outer skin material by injection molding. .

(Prior Art) There are two types of golf ball cores: a rubber thread-wrapped core made of thread rubber wound into a ball shape, and a solid core. Methods for covering the core with an outer skin material include a compression molding method and an injection molding method.

In the compression molding method, a golf ball core is covered with a pair of thick-walled half-shell cups that have been preformed, and then compression molded using a compression mold.

The injection molding method involves insert molding the golf ball core and covering the outer periphery of the core with a skin material, and has higher productivity than the compression molding method.

For solid cores, the two methods mentioned above can be carried out, but for thread-rubber-wound cores, only the compression molding method is carried out.

This is because the rubber thread used for the thread rubber core is close to pure rubber with few additives and is stretched 8 to 10 times in order to emphasize impact resilience. It is extremely sensitive to heat (generally, it is said that it cannot be molded at temperatures of 100°C or higher), as fine scratches often occur on the surface of the rubber thread when it is wound.

Therefore, in an injection molding method in which the outer skin material is plasticized at a temperature of 200° C. or higher and then injected into a mold, the rubber thread core is damaged and cannot be molded.

Cool the rubber thread core, or use heat-resistant rubber thread.
The former has cost issues associated with cooling the core and process problems due to condensation, while the latter sacrifices repulsion by sacrificing the heat resistance of the core. It is not possible to make a ball, and none of these methods have been adopted industrially.

As a method for overcoming the above-mentioned drawbacks and forming the outer skin material of a golf ball by injection molding, as shown in British Patent No. 1.047.254, a spool core is dipped in neoprene latex and then dried. A method in which a resin layer is formed for the purpose of protection against heat and bonding of the thread-wound core and the outer shell material by heating, and then a thermoplastic outer shell material is injection molded on the resin layer.

■ As shown in Japanese Patent Publication No. 49-48014, a thread-wound core is fitted into a mold, liquid synthetic resin is poured around the core, the resin is cured to form a heat-resistant protective layer, and a thermoplastic outer covering material is applied on top of this. How to injection mold.

is proposed.

(Problems to be Solved by the Invention) In the method (2), after the rubber thread-wrapped core is dipped in latex and then dried, the latex drips down, causing variations in the thickness of the coating layer between the upper and lower parts of the core. Also, it takes a long time to dry.

Additionally, neoprene latex itself has low impact resilience, which impairs impact resilience, which is the most important property of a golf ball.

Method (2) involves a complicated process of pouring liquid resin into a mold to form a protective layer, and there are currently no materials for the protective layer that bond well with the outer skin material and have excellent impact resilience. , it is impossible to make a good golf ball.

(Means for solving the problem) The thread rubber core is covered with a thermoplastic film that has high impact resilience and good heat shrinkability, and the film is heat-shrinked to form a material with a substantially uniform thickness that is closely attached to the thread rubber core. A protective layer is formed, and then a skin material is injection molded on the surface of the protective layer.

(Functions and Effects) A protective layer can be easily formed by heating the film wrapped around the thread rubber core, and if the heating is stopped, the resin will solidify in a short time and a protective layer will be formed, making it possible to form a protective layer by heating the film wrapped around the rubber thread core. The time required to dry and solidify the protective layer can be significantly shortened compared to the method of forming the protective layer. Furthermore, there is no dripping of the liquid resin due to the dipping method, and therefore a protective layer having a substantially uniform thickness can be formed over the entire circumference of the core.

(Detailed Description of the Invention) The same thread rubber core as before is used. The film surrounding the rubber thread core is made of a single thermoplastic material or a mixture of two or more thermoplastic materials with a softening point of 30 to 100°C, has a thickness of 10 to 5 (jOμ), and has an area of 25% or more when heated. Shrink.

Wrap the thread rubber core with the above film. At this time, care should be taken to minimize the overlap between the films.

As shown in Figure 1, the film (1) is wrapped in a thread rubber core (2
) is formed into a tube body (Ill or bag body) that fits with a slight margin and accommodates the thread-rubber-wound core, the work of covering the core with the film can be done easily without requiring any skill. I can do it.

Next, hot air at a temperature equal to or higher than the softening point of the film is applied to the film to cause the film to shrink. As a result, a protective layer (la) is formed around the outer periphery of the rubber thread-wound core.

Set the core with the protective layer formed on it in an injection mold,
The golf ball is completed by injection molding thermoplastic resin to form the outer skin.

It should be noted that films with a softening point of 30° C. or lower are difficult to handle because they soften near room temperature, and films of 100° C. or higher will damage the thread rubber of the thread-rubber-wound core due to the heating temperature for softening. Considering the thermal effects during handling and heating, the film desirably has a softening point in the range of 50 to 80°C.

Further, if the thickness of the film is less than 10μ, the effect of protecting the rubber thread from heat will be reduced, and if it is thicker than 500μ, the softening property will be reduced.

The thickness of the film is preferably 50 to 200 μm, considering the effect of protecting the rubber thread core from the heat during injection molding of the outer skin material and the fact that it must be brought into close contact with the rubber thread core by exposing it to hot air.

The higher the heat shrinkability of the film, the more closely it can be attached to the thread-rubber-wound core without any gaps, and it is desirable that the film shrinks in area by 40% or more when heated.

Considering the above points comprehensively, trans polyisoprene, ionomer resin, trans polybutadiene, and polycaprolactone are preferable as film materials.

The temperature of the hot air for heat-shrinking the film is set to 120° C. or lower, preferably 100° C. or lower, in consideration of the thermal influence on the thread rubber-wound core.

(Example 1) A rubber thread core (2) with a diameter of 38 threads is made by winding a rubber thread for a standard golf ball around a solid center for a standard golf ball with a diameter of 29 mm.

Tube 01) made of transpolyisoprene film with a softening point of 56℃ and a thickness of 75μ with a circumference of 61m and a total length of 55#.
form. A thread rubber-wrapped core (2
), and hot air at about 70°C is applied from the outside of the tube (11).

As shown in FIG. 2, the tube is immediately heat-shrinked to form a protective layer (1a) in close contact with the thread-rubber-wound core (2). If both ends of the tube are floating from the rubber thread core (2), press the floating portions against the rubber thread core (2) while applying hot air, or immediately after stopping the hot air. let

The rubber thread core (2) on which the protective layer (1a) has been formed is set in a large size two-piece injection mold, and the ionomer outer shell for golf balls is heated and melted at 220°C on the surface of the protective layer (1a). Injection mold the material.

(Example 2) A tube with a circumferential length of 65+s+ and an axial length of 57rMn was made from a transisoprene film with a thickness of 100μ,
A thread-rubber-wound core similar to that in Example 1 was housed in the center of the tube, and the same procedure as in Example 1 was carried out.

(Comparative Example) For comparison with Example 1.2, an ionomer outer skin material was directly injection molded onto the same thread-rubber-wound core as described above. In this case, the bobbin core burns and deteriorates due to heat and is cut, making it impossible to form the core. Even if the product looked like it had been molded, it was not possible to produce a product that was satisfactory because the rubber thread would get caught in the weld line, or the stuck rubber thread would come out and create holes in the outer skin material.

In addition, for Example 1.2 and Comparative Example 1, 6 pieces each of 70
A heat aging test was conducted to examine changes in the appearance of the balls over time by placing them in an open chamber uniformly heated to .degree. C., and no change was observed in the balls of Examples 1 and 2 after 3 months.

In the comparative example, all six pieces were deformed. This is because the stress distribution inside the ball changes over time because the rubber thread is cut during molding of the outer skin material.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of the rubber thread core covered with a tubular film, and FIG. 2 is a sectional view of the film after it has been heat-shrinked. (1)...Film (la)...Protective layer (
2)...Thread rubber-wrapped core

Claims (3)

[Claims] (1) A process of covering a rubber thread core with a rubber thread core wound into a ball shape with a thermoplastic film that has high rebound resilience and good heat shrinkability. A method for manufacturing a golf ball, comprising the steps of forming a protective layer of uniform thickness and injection molding an outer skin material on the surface of the protective layer. (2) The method for manufacturing a golf ball according to claim 1, wherein the film has a thickness of 10 to 500 μm. (3) The method for manufacturing a golf ball according to claim 1 or 2, wherein the softening point of the film is 30 to 100°C.