GB2134798A

GB2134798A - Wound golf ball

Info

Publication number: GB2134798A
Application number: GB8400167A
Authority: GB
Inventors: Mikio Yamada
Original assignee: Sumitomo Rubber Industries Ltd
Current assignee: Sumitomo Rubber Industries Ltd
Priority date: 1983-01-12
Filing date: 1984-01-05
Publication date: 1984-08-22
Also published as: GB8400167D0; JPS59129072A; GB2134798B

Abstract

A wound golf ball having improved flight characteristics comprises a cover, and a wound core having a weight of not more than 34 g., the center of the wound core having a diameter of 30 to 38 mm., a specific gravity of not more than 1.10 and a compressive strain of 1.0 to 2.0 mm.

Description

SPECIFICATION Wound golf ball The present invention relates to a wound golf ball, and more particularly to a wound golf ball having improved flight characteristics.

Wound golf balls have a high impact resilience and are very good in strike feeling, and accordingly have hitherto been widely employed. In these wound golf balls, the moment of inertia of the ball is made small, that is to say, the specific gravity of the center of the ball is made large, so that the ball is easy to spin, because back spin caused at the time of striking the ball provides the lift to the bali, whereby the flight distance is increased. However, the relationship between the number of spins and the flight distance of a wound golf ball has not been made clear, and also the diameter of the center of the wound golf ball is oniy experiencialiy determined as 25 to 29 mm. Conventional wound golf balls have a small moment of inertia, thus are subject to back spin, but in practice, the flight distance has not increased as one wishes.

It is an object of the present invention to provide a wound golf ball having improved flight characteristics.

This and other objects of the present invention will become apparent from the description hereinafter.

The present inventor made a study on the relationship between the structure of a wound golf ball and the aerodynamic characteristics of the ball in flight, and has found that although conventional wound golf balls are made so as to be subject to back spin, the number of spins remarkably decreases in flight and the number of spins in the vicinity over the point of reaching the maximum height which is important in increasing the flight distance becomes very smaller than the initial number of spins at the time of driving the ball, and that the flight characteristics of a wound golf bail can be remarkably increased by making the diameter of the center large and making the specific gravity of the center small to change the weight distribution from a conventional center high specific gravity type to a cover high specific gravity type, thereby making the moment of inertia of the ball large.When such a weight distribution of the cover high specific gravity type is adopted, the large decrease in the number of spins in the vicinity over the maximum height point is avoided, thus the aerodynamic characteristics of the ball are maintained relatively constant from driving to falling of the ball.

In accordance with the present invention, there is provided a wound golf ball comprising a cover and a wound core and having a diameter of not less than 41.148 mm and a weight of not more than 45.92 g, said wound core having a weight of not more than 34 g and comprising a thread-like material an a center having a diameter of 30 to 38 mm, a specific gravity of not more than 1.10 and a compressive strain of 1.0 to 2.0 mm.

The term "compressive strain" as used herein indicates the value obtained by subtracting the compressive strain when a load 3.8 kg is applied from the compressive strain when a load 45.4 kg is applied. The smaller the compressive strain, the harder the center.

In the present invention, the center is made of a solid rubber, and the diameter thereof is from 30 to 38 mm. When the diameter of the center is more than 38 mm, winding of a thread-like material such as an elastomeric thread is completed before a tension is applied to the thread, and accordingly no effect of winding the thread around the center is obtained. Also, when the diameter of the center is less than 30 mm, it approaches the diameter of the center of conventional wound golf balls which is usually from 25 to 29 mm and the effects of the present invention are not sufficiently exhibited.

Also, it is necessary that the center has a specific gravity of not more than 1.10 and a compressive strain of 1.0 to 2.0 mm. When the specific gravity is more than 1.1 0, the moment of inertia of the ball becomes small like conventional wound golf balls, thus resulting in lowering of the flight characteristics. When the compressive strain is less than 1.0 mm, the ball becomes too hard and the feeling becomes bad because the ball gives a feeling such that there is a core. On the other hand, when the compressive strain is more than 2.0 mm, the ball becomes too soft, thus resulting in lowering of the flight characteristics.

The center having a diameter of 30 to 38 mm, a specific gravity of not more than 1.10 and a compressive strain of 1.0 to 2.0 mm can be obtained by curing a rubber composition containing a rubber material such as butadiene rubber or isoprene rubber and usual rubber additives such as a curing agent and a filter in a usual manner. For instance, the center is obtained by subjecting to heat pressure molding a rubber composition containing a butadiene rubber, 10 to 40 parts by weight of a metal salt of acrylic or methacrylic acid, 2 to 10 parts by weight of zinc oxide and 0.5 to 5 parts by weight of a peroxide such as dicumyl peroxide, respectively, per 100 parts by weight of the rubber.

Any of conventionally used thread-like materials can be used in the present invention. For instance, a rubber thread to be wound around the center is prepared by curing a rubber composition containing natural rubber or a mixture of natural rubber and synthetic isoprene rubber, an antioxidant, a curing accelerator and a curing agent such as sulfur in a usual manner.

In the present invention, it is also necessary that the weight of the wound core obtained by winding the thread-like material around the center is not more than 34 g. The reason is that if the weight of the wound core is more than 34 g, the specific gravity of the cover side portion does not become high and consequently it is difficult to make the moment of inertia of the ball large.

Also, the wound golf ball of the present invention must have a diameter of not less than 41.148 mm and a weight of not more than 45.92 g to satisfy the PGA and R Ek A standards.

A cover of covering the wound core is formed from a cover composition prepared in accordance with usual formulations except that a large amount of a filler such as zinc oxide, barium sulfate, and titanium dioxide is used for controlling the weight of the ball, since the specific gravity of the center is made smaller than that of conventional wound golf balls. Representative examples of the cover composition are, for instance, a rubber composition containing balata (main component: transpolyisoprene), pale crepe, zinc oxide, sulfur and a curing accelerator, and a rubber composition containing an ionomer resin (partially ionized copolymers of ethylene and acrylic or methacrylic acid, e.g. those sold under the trademark "Surlyn" by the E. I. DuPont de Nemours Company) and a filler such as barium sulfate or titanium dioxide.

A method for covering the wound core with a cover material is not particularly limited, and known methods are adoptable. Usually, two hemispherical shells are formed from a cover composition, positioned around the wound core and then fused together by curing at a high temperature for a short period of time so as to form a finished golf ball.

The present invention is more specifically described and explained by means of the following Examples, in which all parts are by weight.

It is to be understood that the present invention is not limited to the Examples, and various changes and modifications may be made in the invention without departing from the spirit and scope thereof.

Examples 1 to 3 and Comparative Examples 1 to 3 Six kinds of wound golf balls having a diameter of 41.2 mm were prepared by employing center, thread and cover compositions shown in Table 1.

The curing of the center compositions was carried out at 1 700C for 20 minutes, and the curing of the thread compositions was carried out at 1 500C for 40 minutes. Also, the curing of the cover compositions was carried out at 1400 C for 20 minutes for the trans-polyisoprene cover and at 1 600C for 10 minutes for the Surlyn cover.

The flight test of the balls was made by striking a ball with a wood No. 1 golf club (driver) at a head speed of 45 m/sec by employing a swing machine (swing robot made by True Temper Co., Ltd.).

The results are shown in Table 2.

Table 1 Com. Com. Com.

Ex. 1 Ex. 2 Ex. 3 Ex. 1 Ex. 2 Ex. 3 Center Composition (part) Butadine rubber*1 100 100 100 100 100 100 Zinc diacrylate 30 30 30 30 - 30 Zinc oxide 5 5 5 5 - 5 Barium sulfate - - - - 133 Precipitated calcium carbonate - - - - 43.3 Dicumyl peroxide 2 2 2 2 3.0 2 Thread composition (part) Natural rubber 50 50 50 50 50 50 Polyisoprene rubber 50 50 50 50 50 50 Antioxodant*2 1 1 1 1 1 1 Sulfur 2.5 2.5 2.5 2.5 2.5 2.5 Curing accelerator*3 1 1 1 1 1 1 Cover composition (part) Trans-polyisopropene*4 100 100 - 100 100 100 Pale crepe 30 30 - 30 30 30 Zinc oxide 280 280 - 280 20 20 Sulfur 1.5 1.5 - 1.5 1.5 1.5 Curing accelerator*5 2.0 2.0 - 2.0 2.0 2.0 Surlyn 1601 - - 100 - - Barium sulfate - - 240 - - (Notes) *1: Butadiene rubber comercially available under the commercial name "BRO 1" made by Japan Synthetic Rubber Co., Ltd *2:N-Isopropyl-N'-phenyl-p-phenylenediamine *3: 2-Mercaptobenzothiazole *4: Trans-polyisoprene commercially available under the commercial name "Kuraray TP-301" made by Kuraray Co., Ltd.

*5: N-Cyclohexyl-2-benzothiazylsulfenamide Table 2 Com. Com. Com.

Ex.1 Ex.2 Ex.3 Ex.1 Ex.2 Ex.3 Diameter of center (mm) 36.1 30.9 30.9 29.1 26.4 36.1 Weight of center (g) 28.1 23.5 23.5 21.0 21.8 34.9 Compressive strain of center (mm) 1.4 1.9 1.9 1.4 2.2 1.3 Specific gravity of center 1.04 1.04 1.04 1.03 1.81 1.38 Weight of wound core (g) 30.8 31.3 31.4 31.8 37.3 36-8 Weight of ball (g) 45.4 45.6 45.2 45.6 45.1 45.8 Harndess of ball proper proper proper proper soft proper Initial velocity of ball (m/sec) 65.3 65.2 65.5 65.3 65.7 65.3 Peak angle of delivery (degree) 9.1 9.0 9.1 8.3 8.1 9.0 Carry (m) 204 203 205 198 196 195 Total distance (m) 218 220 222 209 211 214 As shown in Table 2, the flight distance of the wound golf balls of the present invention is large.

In contrast to this, in case of the golf ball of Comparative Example 3, the center has the same diameter as that of the ball of Example 1, but has a higher specific gravity. Accordingly, since the ball of Comparative Example 3 is the center high specific gravity type, the moment of inertia is small and the flight distance is not increased. The ball of Comparative Example 2 which corresponds to a conventional wound golf ball, shows similar results to Comparative Example 3. With respect to the ball of Comparative Example 1 , the diameter of the center is made slightly smaller as compared with the golf balls of the present invention. The flight distance of the ball of Comparative Example 1 is smaller than that of the balls of the present invention. The reason is considered to be that the behavior of the ball at the time of strike is similar to that of the ball of Comparative Example 2 corresponding to a conventional wound golf ball and accordingly the peak angle of delivery is low.

In addition to the ingredients used in the Examples, other ingredients can be used in the Examples as set forth in the specification to obtain substantially the same results.

Claims

1. A wound golf ball comprising a cover and a wound core and having a diameter of not less than 41.148 mm and a weight of not more than 45.92 g, said wound core having a weight of not more than 34 g and comprising a thread-like material and a center having a diameter of 30 to 38 mm, a specific gravity of not more than 1.10 and a compressive strain of 1.0 to 2.0 mm.

2. A wound golf ball substantially as described with reference to any one of the Examples 1 to

3.