GB2125724A

GB2125724A - Improvements relating to the manufacture of two-piece golf balls

Info

Publication number: GB2125724A
Application number: GB08320543A
Authority: GB
Inventors: Mikio Yamada
Original assignee: Sumitomo Rubber Industries Ltd
Current assignee: Sumitomo Rubber Industries Ltd
Priority date: 1982-07-31
Filing date: 1983-07-29
Publication date: 1984-03-14
Also published as: JPS5945506B2; GB8320543D0; JPS5924648A; GB2125724B

Abstract

A method of moulding a golf ball by covering a core with a pair of half shells made of an ionomer resin and subjecting the assembly to compression moulding characterized by covering the core with the pair of half shells with a clearance of 4 to 10 mm formed between the opposed end faces of the half shells and moulding the resulting assembly by hot pressing with upper and lower dies.

Description

SPECIFICATION Improvements relating to the manufacture of two-piece golf balls The present invention relates to a method of moulding two-piece golf balls comprising a spherical core covered by cover members and also to an improved form of half shell for moulding two-piece golf balls.

Golf balls are moulded by various methods, such as injection moulding, transfer moulding and compression moulding. Among these moulding methods, compression moulding is widely used for moulding two piece-balls which are becoming popular because of its greater carrying distance.

In moulding golf balls by the compression moulding method, a spherical core is covered by a pair of shells for forming a cover member, and the assembly is hot-pressed by upper and lower dies. At this moment, the opposed end faces of the pair of half shells covering the core are in intimate contact with each other and are spaced apart only by a small clearance (up to 3.6 mm) in the conventional compression moulding method.

The half shells are melted by the heat through heated dies, and the said clearance is gradually decreased by means of the clamping force of the upper and lower dies, to form a cover having a uniform wall thickness.

In recent years, ionomer resins which are outstanding in toughness, elasticity, hardness and like properties have been generally used for half shells forming the covers of two-piece balls.

The ionomer resin also has a high flow rate in a molten state, as compared with other resin materials.

When the ionomer resin is subjected to the moulding process, its high melt fluidity or flowability results in the problem of the product having a defective surface with air holes or flashing, because when the half shells are softened and melted by the heat while applying pressure thereto through the inner surface of the die cavity, the molten resin flows into the clearance to join together the dies are closed or shut off. Consequently, the air present between the core and the half shells is trapped and becomes enclosed in the dies. Flashing is also liable to occur because the half shells melt and intimately adhere together more rapidly if the clearance between the opposed open end faces of the pair of half shells is small. Since the ionomer resin is a tough material, flashing thus formed is difficult to remove.

The present invention provides a method of moulding a golf ball by covering a core with a pair of half shells made of an ionomer resin and subjecting the assembly to compression moulding comprising the steps of covering the core with a pair of half shells making a clearance of 4 to 10 mm between the opposed open end faces of the half shells, moulding the resulting assembly by hot pressing with upper and lower dies, so that just before the upper and lower dies are completely closed and sealed off, the said clearance between the open end faces of the half shells still remains, permitting escape of air from inside, and joining the pair of half shells to each other so that the molten resin forms a seam joint substantially simultaneously with the closing of the upper and lower dies.

The present invention also provides a pair of half shells made of an ionomer resin material for use in moulding about a core to form a two-piece ball wherein the distance between the plane of open end face of each half shell and a parallel plane through the centre of curvature of the inner periphery of the half shell is 2 to 5 mm, said inner periphery forming an included angle of less than 180 about said centre of curvature.

The invention will now be described in more detail with reference by way of example to the accompanying drawings in which: Figure 1 is a sectional view illustrating a method of compression moulding according to the present invention; Figure 2 is a sectional view illustrating the shape and dimensions of a half shell; Figure 3 is a sectional view illustrating a covered core; and Figure 4 is a sectional view illustrating conventional compression moulding.

As shown in Fig. 3, a hard rubber core 1 serves as the core of a two-piece ball, and a pair of upper and lower half shells 2, 2 cover the core 1 for forming the cover of the two-piece ball.

The half shell 2 is made of an ionomer resin wherein long-chain molecules are linked by metal ions providing cross-links. A suitable ionomer resin is commercially available under the name Surlyn A.

Referring now to Figures, it is known that hemispherical projection 3 may be provided outwardly at the substantially central portion in the outer periphery of the half shell 2 so that concavity of the die enables the half shell to support the projection 3 with minimized contact areas. Consequently, when the half shell 2 is placed in the die, the outer periphery thereof is less affected by residual heat from the previous moulding operation in the dies.

With reference to Fig. 2, the dimensions of the half shell 2 include radius R1 of the outer periphery, radius R2 of the inner periphery, radius R3 of the projection 3 provided at the centre of the outer peripheral surface, distance H1 between the centre of curvature of the outer periphery and the centre of curvature of the inner periphery, and distance H2 between the plane of the open end face of the half shell 2 and the parallel plane which includes the centre of curvature of the inner periphery.These dimensions are in the following ranges: R1: 20.2-20.9 mm (for a small ball) R2: 18.3-19.7 mm (for a small ball) R1: 21.0-21.7 mm (for a large ball) R2: 18.9-20.5 mm (for a large ball) R3: 0 - 6.0 mm (for both) Hi: 0 - 3.5 mm (for both) H2: 2.0- 5.0 mm (for both) With the half shell 2 thus dimensioned, R1, R2, R3 and H1 are naturally determined according to the diameter of the core 1 since the amount of covering required is dependent on the diameter. The dimension important to the hot-press moulding is therefore H2.When the core 1 is covered with the pair of upper and lower half shells 2, 2 as senn in Fig. 3, the dimension between the opposed open end face of the half shells 2, 2 is set to H2 x 2 = 4 to 10 mm, taking into consideration the property of high melt flowability of the ionomer resin. The significance of the dimensional range will be apparent from the examples described hereinafter.

The core 1 is covered with the half shells 2, 2 thus formed, and the assembly is placed into the cavities of upper and lower dies 4, 5 for moulding the cover of a two-piece ball. With application of heat and pressure under usual moulding conditions, the half shells 2, 2 are thereafter melted and moulded into a cover having a surface shaped in conformity with the cavity surfaces of the upper and lower dies 4, 5.

At this moment, the half shells, 2, 2 are melted at a temperature in the range 140 to 150 C by heated dies, while the clearance between the opposed opening end faces is gradually decreased by the clamping force of the upper and lower dies 4, 5. However, immediately before the upper and lower dies 4, 5 are completely closed and sealed off, the clearance still remains between the opening end faces of the half shells 2, 2, permitting escape of air from inside.

Substantially simultaneously with the closing of the upper and lower dies 4, 5, the half shells 2, 2 join to each other in the form of molten resin to form a seam joint.

For comparison, Table 1 and Table 2 respectively show balls prepared with use of half shells for two-piece balls according to the present invention and those obtained with use of conventional half shells for two-piece balls. The balls were produced by the usual compression moulding process.

The half shells are made of an ionomer resin.

Table 1 Example Example Example Example Example 1 2 3 4 5 RI (mm) 20.8 20.9 20.5 20.6 21.5 R2 (mm) 19.0 19.6 18.3 18.4 19.4 R3 (mm) 4.0 6.0 2.0 2.2 4.0 Hi (mm) 1.5 2.0 3.5 3.5 1.5 H2 (mm) 3.5 2.0 5.0 5.0 4.0 H2 X 2 7.0 4.0 10.0 10.0 8.0 Core diam. (mm) 37.4 38.1 36.6 36.6 38.3 Press Temp. ( C) 150 145 150 140 150 Pressure (tons) 100 100 100 100 100 Appearance good good good good good Table 2 Example Example Example Example Example 6 7 8 9 10 Ri (mm) 20.8 20.8 20.9 20.9 21.5 R2 (mm) 19.0 19.0 18.3 18.3 19.4 R3 (mm) 4.0 4.0 6.0 6.0 4.0 Hi (mm) 1.5 1.5 2.0 2.0 1.5 H2 (mm) 1.8 1.8 0 0 0 H2 x 2 (mm) 3.6 3.6 0 0 0 Core diam. (mm) 37.4 37.4 36.6 36.6 38.3 Press Temp. ( C) 150 120 150 120 150 Pressure (tons) 100 40 100 40 100 Appearance Poor, Faulty Air Air Air Air seam, trapped trapped trapped trapped air trapped Example Nos. 1 to 5, as prepared according to the molding method of the present invention, give good appearance free from air trapped or faulty seams, while examples Nos. 6 to 10 as prepared according to the conventional moulding method give poor appearance by trapping air or by faulty of seam.

Since the clearance of 4 to 10 mm is provided between the open end faces of the pair of half shells, the molten resin of the opposed half shells subjected to heat and pressure by the upper and lower dies will not join together just before the dies are to be closed, leaving a small clearance for the interior air to escape therethrough effectively. This eliminates trapping of air to provide a two-piece ball having a satisfactory appearance.

Furthermore, a two-piece ball can be moulded almost without any fin or flashing. This is advantageous for moulding a two-piece ball made of ionomer resin material as a cover member, because flashing of the said ionomer resin, having great toughness, is difficult to remove if it occurs.

Thus, covers made of ionomer resin and giving outstanding properties to two-piece balls can be moulded without producing faulty products. The method is therefore suited to the mass production of excellent product.

Claims

1. A method of moulding a golf ball by covering a core with a pair of half shells made of an ionomer resin and subjecting the assembly to compression moulding comprising the steps of covering the core with the pair of half shells making a clearance of 4 to 10 mm between the opposed open end faces of the half shells, moulding the resulting assembly by hot pressing with upper and lower dies, so that just before the upper and lower dies are completely closed and sealed off, the said clearance between the open end faces of the half shells still remains, permitting escape of air from inside, and joining the pair of half shells to each other so that the molten resin forms a seam joint substantially simultaneously with the closing of the upper and lower dies.

2. A pair of half shells made of an ionomer resin material for use in moulding about a core to form a two-piece ball wherein the distance between the plane of open end face of each half shell and a parallel plane through the centre of curvature of the inner periphery of the half shell is 2 to 5 mm, said inner periphery forming an included angle of less than 1 80' about said centre of curvature.

3. A method as claimed in claim 1 of moulding a golf ball which method is substantially as hereinbefore described with reference to and as illustrated in Figs. 1 to 4 of the accompanying drawings.

4. A golf ball when moulded by a method as claimed in claim 1 or claim 3.