Thread wound golf ball

Abstract: The present invention provides a thread wound golf ball having an excellent shot feel, which is obtained by winding a thread rubber around a solid rubber center to form a thread rubber layer and covering the thread rubber layer with a cover layer. The surface hardness (JIS-A) of the rubber center is not more than 60 and the deformation on 500 g loading of the rubber center is not less than 0.5 mm.

Description: The present invention relates to a thread wound golf ball. A thread wound golf ball is obtained by winding a thread rubber around a solid or liquid rubber center to form a rubber layer and covering the thread rubber layer with a cover material (e.g. an ionomer resin, balata. etc). A vulcanized rubber of butadiene is conventionally used as the solid center, and has a high hardness and low compression deformation. In a golf ball using such a conventional center, the spin formation is large and the launch angle is small and, therefore, it is disadvantageous in view of the flight distance. Furthermore, the curving of the ball is too large and it is sometimes hard to control. On the other hand, a liquid center has a high compression deformation. I a golf ball using a liquid center, the spin formation is small and the launch angle is large and, therefore, it is advantageous in view of the flight distance in comparison with a ball with a conventional solid center. The production process of golf balls with a liquid centre is complicated. Also, there is a safety problem, for example, when the ball is cut by a knife or a cutter, since a liquid is sprayed out, which may result in a loss of or damage to the eyesight. GB-A-2134798 describes a golf ball comprising a cover and a wound core and having a diameter of not less than 41.148mm and a weight of not more than 45.92g, said wound core having a weight of not more than 34g and comprising a thread-like material and a center having a diameter of 30 to 38mm, a specific gravity of not more than 1.10 and a compressive strain of 1.0 to 2.0mm. We have found that, by using a flexible vulcanized rubber as the solid center of a thread wound golf ball, the spin formation is suppressed and the launch angle is increased, whereby, an exceptionally long flight distance can be obtained. The main object of the present invention is to provide a thread wound golf ball which is superior in flight distance and shot feel. According to the present invention, there is provided a thread wound golf ball comprising a solid rubber center, a thread rubber layer on the solid rubber center and a cover layer on the thread rubber layer, characterised in that the solid rubber center has a surface hardness (JIS-A) of not more than 60 and a deformation on 500 g loading of not less than 0.5mm. The load is a compressive load. The rubber center used in the present invention has a surface hardness (JIS-A) of not more than 60, preferably 10 to 45, and a deformation (500 g loading) of not less than 0.5 mm. When the surface hardness (JIS-A) of the rubber center is larger than the above range, the spin formation on hitting becomes large and the impact strength is large, which results n an inferior shot feel. Furthermore, when the deformation (500 g loading) is smaller than the above range, the spin formation also becomes large and the shot feel becomes inferior. The outer diameter of the rubber center is preferably 23 to 34 mm, more preferably 26 to 32 mm. When the outer diameter is smaller than 23 mm, the spin formation becomes large and the launch angle becomes small. On the other hand, when the outer diameter is larger than 34 mm, the thread rubber layer becomes thin and golf ball having a predetermined hardness can not be obtained. When the rubber center does not have a suitable impact resilience, the initial velocity on hitting becomes small, which results in a bad influence on the rubber center. The impact resilience is represented by the rebound height of the rubber center which is measured by dropping it on a rigid surface such as concrete block from a height of 254 cm (100 inches) at 23/C. The impact resilience is preferably 90 cm or more. When it is smaller than 90 cm, the initial velocity of the golf ball becomes too small and the effect of the center is hardly obtained. The rubber for the rubber center is not specifically limited, and examples thereof include butadiene rubber (BR), natural rubber (NR), ethylene-propylene-diene copolymer (EPDM), polynorbornene rubber, and silicone rubber. Polynorbornene rubber and silicone rubber are particularly preferred. Polynorbornene rubber can contain a large amount of oil and easily obtain flexibility. The polynorbornene rubber can also be controlled to a suitable impact resilience by selecting the oil. In order to prevent deformation of the center during winding the thread rubber around the center, it is necessary to freeze the center in advance. It is therefore preferred that the rubber is solidified at a low temperature (e.g. -30 to -50°C). Polynorbornene rubber is solidified over the above range even if it contains a large amount of oil. In order to reduce the hardness and to obtain a suitable impact resilience, an oil is added. Non-limited examples thereof include alkylbenzene oil, naphthenic oil, paraffinic oil, aromatic oil, or an ester plasticizer (e.g. dioctyl adipate (DOA), dioctyl phthalate (DOP), etc.). Of these naphthenic oil or an alkylbenzene oil which hardly cause blooming even if large amounts are added and which provide high impact resilience, are particularly preferred. The rubber center is normally obtained by kneading 100 parts by weight of the rubber, 100 to 500 parts by weight of oil, 0.5 to 5 parts by weight of sulfur, 3 to 10 parts by weight of a vulcanization auxiliary, 1 to 5 parts by weight of a vulcanization accelerator and an optional amount of a modifier by a Banbury mixer or a roll and vulcanizing the mixture at 150 to 170°C for 10 to 20 minutes. Examples of the silicone rubber are heat vulcanization types and room temperature vulcanization types. In general, a heat vulcanization type silicone rubber obtained by copolymerizing dimethylsiloxane as the main component with a small amount of a methyl vinyl siloxane is preferred because of its good impact resilience. As the vulcanization method of the silicone rubber, for example, there is a vulcanization method using an organic peroxide, aliphatic azo compound or radiation. In general, an organic peroxide is used. 0.5 to 5 Parts by weight of vulcanizing agent and an optional amount of weight modifier (based on 100 parts by weight of silicone rubber) are kneaded using a Banbury mixer or a roll and the resulting mixture is vulcanized at 150 to 170°C for 10 to 20 minutes to obtain a vulcanized silicone rubber. By using a flexible vulcanized silicone rubber as a solid ball center for a thread wound core, the formation of spin is suppressed and the launch angle is increased. Furthermore, an exceptionally long flight distance can be obtained by the high impact resilience of the silicone rubber. The above vulcanization auxiliary, vulcanization accelerator and weight modifier may be any which are normally used. As the weight modifiers, those having a large specific gravity are preferred in order to obtain a low hardness by increasing the rubber fraction of the rubber center. Examples thereof include barium sulfate, calcium carbonate, a clay filler or a silica filler. Then, a thread rubber is wound around the rubber center whilst applying a stretching force to the thread rubber. The thread rubber may be any which is normally used as a thread rubber for golf balls. The method for covering the rubber center with a cover (ionomer resin or balata) is not specifically limited. Normally, the rubber center is covered with two semi-spherical shaped covers which have been molded in advance, followed by compression molding. Furthermore, the rubber center may be covered by subjecting a cover composition to injection molding. As described above, according to the present invention, there is provided a thread wound golf ball superior in flight distance and shot feel, which has no safety problem. Furthermore, the production process can be simplified. EXAMPLES The following Examples further illustrate the present invention in detail but are not to be construed as limiting the scope thereof. Examples 1 to 7 and Comparative Examples 1 to 3 A formulation shown in Table 1 was mixed and then vulcanized at 155°C for 20 minutes to make a rubber center having a diameter of 30 mm. A thread rubber which was stretched about 10 times was wound around the rubber center. Then, the rubber center was covered with an ionomer resin by injection molding to make a thread wound golf ball with an ionomer cover. The flight performance of the resulting golf ball was evaluated by a conventional method. The results are shown in Table 2. Component Ex.1 Ex.2 Ex.3 Ex.4 Ex.5 Ex.6 Ex.7 Comp. Ex. 1 Comp. Ex.2 Comp. Ex.3 Norsolex NAl5 250 250 250 - - 250 250 - - - BRll - - - 100 70 - - 10 0 100 - NR - - - - 30 - - - - - NSll6 - - - - - - - - - 100 Sunthene 255ZJ - 50 150 50 50 50 150 - - - Sulfur 2 2 2 2 2 2 2 1 0 10 2 Zinc oxide 5 5 5 5 5 5 5 5 5 5 Stearic acid 2 2 2 2 2 2 2 2 2 2 Barium sulfate 190 240 320 150 150 300 400 7 5 95 75 Noxelar CZ - - - 1.5 1.5 - - 1. 5 1.5 1.5 Noxelar TT 0.8 0.8 0.8 0.2 0.2 0.8 0.8 0. 2 0.2 0.2 Noxelar M 0.8 0.8 0.8 - - 0.8 0.8 - - - Noxelar TBT-N 1.2 1.2 1.2 - - 1.2 1.2 - - - Sunselar TE-G 0.4 0.4 0.4 - - 0.4 0.4 - - - As is apparent from Table 2, regarding the golf balls of Examples 1 to 7, the flying distance was 4 to 6 yards longer than that of Comparative Examples 1 and 2. Further, as the hardness of the rubber center becomes small and the outer diameter of the rubber center becomes larger, spin was reduced and launch angle was enhanced. Regarding Comparative Example 3, the hardness of the center is small but the elasticity is extremely low and, therefore, long flying distance can not be obtained. Professional golfers were asked to hit the golf balls and their evaluations were asked. As a result, the golf balls of Examples 1 to 7 using a flexible rubber as the center had excellent hit feeling in comparison with Comparative Examples 1 to 3. The flying distance of the golf balls of Examples 1 to 7 was almost the same as that of a two piece golf ball. Examples 8 to 10 and Comparative Example 4 According to the same manner as that described in Examples 1 to 7, a thread wound golf ball with a balata cover was made, respectively, using a formulation shown in Table 3. The flight performances of the resulting golf ball was evaluated by a conventional method. The results are shown in Table 4. Component Ex.8 Ex.9 Ex.10 Comp. Ex.4 Norsolex Nal5 250 250 250 - Sunthene 255ZJ 50 100 150 - BRll - - - 100 Sulfur 2 2 2 10 Zinc oxide 5 5 5 5 Stearic acid 2 2 2 2 Barium sulfate 230 272 313 75 Noxelar CZ - - - 1.5 Noxelar TT 0.8 0.8 0.8 0.2 Noxelar M 0.8 0.8 0.8 - Noxelar TBT-N 1.2 1.2 1.2 - Sunselar TE-G 0.4 0.4 0.4 - Ex.8 Ex.9 Ex.10 Comp. Ex.4 Ball center Outer diameter (mm) 28.4 28.4 28.4 28.4 Weight (g) 17.0 17.0 17.0 17.0 Compression deformation(mm) 1.2 1.9 2.4 0.3 JIS-A hardness 30 24 15 76 Impact resilience (cm) 125 123 120 220 Ball Weight (g) 45.4 45.3 45.3 45.3 Compression 90 90 91 90 Flight performances 1 Launch angle (°) 10.8 11.0 11.2 10.0 Spin (rpm) 3200 3100 3050 3900 Carry (yard) 218 218 217 213 Total (yard) 224 225 224 219 Flight performances 2 Launch angle (°) 14.3 14.5 14.6 13.0 Spin (rpm) 4400 4300 4250 6000 Carry (yard) 171 172 172 166 Total (yard) 174 174 175 168 Examples 11 to 14 and Comparative Examples 5 and 6 According to the same manner as that described in Examples 1 to 7, a thread wound golf ball with an ionomer cover was made, respectively, using a formulation shown in Table 5. The flight performances of the resulting golf ball was evaluated by a conventional method. The results are shown in Table 6. Component Ex.11 Ex.12 Ex.13 Ex.14 Comp. Ex.5 Comp. Ex.6 KE520-U 100 - - 100 - - KE530-U - 100 - - - - KE540-U - - 100 - - - BRll - - - - 100 100 Barium sulfate 52 50 43 70 75 95 Zinc oxide - - - - 5 5 Stearic acid - - - - 2 2 C-8 2 - - 2 - - C-4 - 4 4 - - - Sulfur - - - - 10 10 Noxelar CZ - - - - 1.5 1.5 Noxelar TT - - - - 0.2 0.2 Ex.11 Ex.12 Ex.13 Ex.14 Comp. Ex.5 Comp. Ex.6 Ball center Outer diameter (mm) 30.3 30.3 30.3 28.4 30.3 28.4 Weight (g) 20.9 20.5 20.3 18.5 20.5 20.5 Compression deformation (mm) 2.6 1.5 1.1 2.4 0.4 0.3 JIS-A hardness 25 36 43 17 75 75 Ball Weight (g) 45.5 45.3 45.2 45.3 45.3 45.3 Compression 78 78 77 79 78 79 Flight performances 1 Launch angle (°) 11.8 11.7 11.4 11.6 10.7 10.5 Spin (rpm) 2850 2940 3100 2900 3300 3350 Carry(yard) 224.5 223.5 223.0 223.0 219.5 219.0 Total (yard) 228.0 225.5 226.0 225.5 222.0 221.5 Flight performances 2 Launch angle (°) 15.3 15.1 14.8 15.1 14.0 13.9 Spin (rpm) 3650 3720 3850 3750 4010 4400 Carry(yard) 177.0 176.5 178.0 177.0 172.5 172.0 Total(yard) 183.5 184.0 184.0 183.0 180.0 179.0 Examples 15 to 17 and Comparative Examples 7 According to the same manner as that described in Examples 8 to 10, a thread wound golf ball with a balata cover was made, respectively, using a formulation shown in Table 7. The flight performances of the resulting golf ball was evaluated by a conventional method. The results are shown in Table 8. Component Ex.15 Ex.16 Ex.17 Comp. Ex.7 KE520-U 100 - - - KE530-U - 100 - - KE540-U - - 100 - BRll - - - 100 Barium sulfate 45 37 32 70 Zinc oxide - - - 5 Stearic acid - - - 2 C-8 2 - - - C-4 - 4 4 - Sulfur - - - 10 Noxelar CZ - - - 1.5 Noxelar TT - - - 0.2 Ex.15 Ex.16 Ex.17 Comp. Ex.7 Ball center Outer diameter (mm) 28.4 28.4 28.4 28.4 Weight (g) 17.1 17.0 17.0 17.0 Compression deformation (mm) 2.5 1.4 1.0 0.3 JIS-A hardness 24 35 43 75 Ball Weight (g) 45.4 45.3 45.3 45.4 Compression 90 91 90 90 Flight performances 1 Launch angle (°) 11.3 10.9 10.3 9.5 Spin (rpm) 3100 3250 3380 3950 Carry (yard) 219 219 218 214 Total (yard) 223 222 221 217 Flight performances 2 Launch angle (°) 15.1 15.0 14.8 13.5 Spin (rpm) 4150 4200 4300 5900 Carry (yard) 172 173 172 167 Total (yard) 174 175 175 168 As is apparent from Table 6, regarding the golf balls of Examples 11 to 14, the flying distance was 3 to 5 yards longer than that of Comparative Examples 5 and 6. Further, as the hardness of the rubber center becomes smaller than that of Examples 11 to 13 and Comparative Example 5 and the outer diameter of the rubber center becomes larger than that of Examples 11 and 14 and Comparative Examples 5 and 6, spin was reduced and launch angle was enhanced. In a golf ball with a balata cover as shown in Table 8, regarding the balls of Examples 15 to 17, the flying distance was 4 to 6 yards longer than that of Comparative Example 7. Professional golfers were asked to hit the golf balls and their evaluations were asked. As a result, the golf balls of Examples 11 to 14 using a vulcanized silicone rubber as the center had excellent hit feeling in comparison with Comparative Examples 5 to 7. The flying distance of the golf balls of Examples 11 to 14 was almost the same as that of a two piece golf ball.

Claims: A thread wound golf ball comprising a solid rubber center, a thread rubber layer on the solid rubber center and a cover layer on the thread rubber layer, characterized in that the solid rubber center has a surface hardness (JIS-A) of not more than 60 and a deformation on 500 g loading of not less than 0.5 mm A thread wound golf ball as claimed in claim 1 wherein the solid rubber center is made of a silicone rubber. A thread wound golf ball as claimed in claim 1 or claim 2, wherein the solid rubber center has an impact resilience of not less than 90 cm. A thread wound golf ball as claimed in any one of the preceding claims wherein the solid rubber center has an outer diameter of 23 to 34 mm. A thread wound golf ball as claimed in any one of the preceding claims wherein the surface hardness is in the range of from 10 to 45.

Inventors: KATO AKIRA, MORIYAMA KEIJI, KATO, AKIRA, MORIYAMA, KEIJI
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES, LTD.
Application year: 1993
Main classification: A63B37
IPC codes: B29K19, A63B37, B32B25, B29K83, B29D99