Golf ball

Abstract: The present invention provides a golf ball having an excellent shot feel and control as well as an excellent flight performance and cut resistance, which comprises a core and a cover for covering the core, wherein a heated mixture of an ionomer resin and a polymer containing a glycidyl group is used as a main component of the base resin for the cover.

Description: The present invention relates to a golf ball with a cover, wherein the shot feel and control are improved. As a base resin for a cover of a golf ball, an ionomer resin has widely been used (e.g. Japanese Patent Kokai No. 49-49727), heretofore. Particularly, in almost all of two piece golf balls using a solid core, an ionomer resin is used. The reason is that the ionomer resin is superior in durability, cut resistance and impact resilience and is easily processed and, further, it is cheap in comparison with other base resins for the cover. However, the ionomer resin is inferior in shot feeling and control (ease of spinning) in comparison with balata (transpolyisoprene) which is used as the cover of a thread wound golf ball, because of its considerably high hardness and stiffness. Therefore, attempts have been made to improve the shot feel and control by softening the ionomer resin by various means but, however, satisfactory results have not been obtained. We have intensively studied base resins for the cover. As a result, it has been found that a golf ball having an excellent shot feel and control, as well as an excellent flight performance and cut resistance can be obtained, by using a heated mixture composed of an ionomer resin and a polymer containing a glycidyl group as the main component of a base resin for the cover. The main object of the present invention is to provide a golf ball having improved shot feel and control. According to the present invention, there is provided a golf ball comprising a core and a cover for covering the core, a base resin of the cover being composed of a heated mixture of an ionomer resin and a polymer containing a glycidyl group as a main component, wherein the heated mixture is obtained by mixing the ionomer resin with the polymer containing a glycidyl group with heating at a resin temperature of from 150 to 280°C. A polymer containing a glycidyl group has an elastomeric property and, therefore, when the polymer containing the glycidyl group is mixed with an ionomer resin with heating, the ionomer resin is softened and the shot feel and control are improved and, furthermore, a deterioration of the flight performance and cut resistance are prevented and are suitably maintained. In the present invention, the ionomer resin may be any one which is used for the cover of the golf ball, and one or more ionomer resins can be used in combination. As the ionomer resin used for the cover, for example, there is a resin of a copolymer comprising 10 to 20 % by weight of α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and 80 to 90 % by weight of α-olefin, some of the carboxyl groups in the copolymer being neutralized with metal ions. Examples of the ionic ethylene-methacrylic acid copolymer based ionomer resin include HI-MILAN 1605 (of the type neutralized by sodium ion), HI-MILAN 1706 (of the type neutralized by zinc ion), HI-MILAN 1707 (of the type neutralized by sodium ion), HI-MILAN 1705 (of the type neutralized by zinc ion) which are manufactured by Mitsui DuPont Polychemicals Co.; SURLIN 7930 (of the type neutralized by lithium ion) and SURLIN 7940 (of the type neutralized by lithium ion) which are manufactured by E.I. DuPont de Nemours & Co. Examples of the ionic ethylene-acrylic acid copolymer based ionomer resin include one that is commercially available from EXXON Co. under the trade name of Iotek. As the polymer containing the glycidyl group, for example, there are terpolymers of olefins with vinyl compounds and unsaturated epoxy compounds and bipolymers of olefins with unsaturated epoxy compounds. Examples of the olefins include ethylene, propylene, butene-1, iso-butylene, pentene-1, hexene-1, heptene-1, octene-1, dodecene-1 and 4-methyl-pentene-1. Examples of the vinyl compound include vinyl acetate, styrene-methylmethacrylate, methyl acrylate, acrylic acid, ethyl acrylate, vinyl chloride, α-methylstyrene, divinylbenzene, tetrafluoroethylene, vinylidene chloride, acrylonitrile and acrylic amide. As the unsaturated epoxy compound, for example, there are unsaturated glycidyl esters, unsaturated glycidyl ethers, epoxyalkenes and p-glycidylstyrenes. Examples thereof include glycidyl methacrylate, glycidyl acrylate, glycidyl itaconates, butenecarboxylates, allylglycidyl ether, 2-methylallylglycidyl ether, 3,4-epoxybutene, 3,4-epoxy-3-methyl-1-butene, 3,4-epoxy-1-pentene, 3,4-epoxy-3-methylpentene, 5,6-epoxy-1-hexene, vinylcyclohexene monooxide and p-glycidylstyrene. Preferred examples of the polymer containing the glycidyl group include ethylene-vinyl acetate-glycidyl methacrylate terpolymer, ethylene-methyl acrylate-glycidyl methacrylate terpolymer, ethylene-glycidyl methacrylate bipolymer and mixtures thereof. In these terpolymers and bipolymers, the amount of ethylene, vinyl acetate or methyl acrylate and glycidyl methacrylate are preferably 60 to 90 % by weight, 0 to 35 % by weight, 1 to 15 % by weight, respectively. Examples of the marketed product of the ethylene-vinyl acetate-glycidyl methacrylate terpolymer include Bondfast 7B (trade name) manufactured by Sumitomo Chemical Co, examples of the marketing product of the ethylene-glycidylmethacrylate bipolymer include Bondfast E (trade name) manufactured by Sumitomo Chemical Co., and examples of the marketing product of the ethylene-methyl acrylate-glycidyl methacrylate terpolymer include Bondfast 7L (trade name) manufactured by Sumitomo Chemical Co. The polymer containing the glycidyl group has an elastomeric property and is superior in processability, heat stability and compatibility with an ionomer resin. The polymer softens the ionomer resin, whereby, the resulting mixture becomes flexible. Since the polymer containing the glycidyl group is used for the purpose of softening the ionomer resin as described above, it is preferred that the polymer has a lower stiffness modulus than that of a conventional ionomer resin. For example, those having a stiffness modulus of not more than 2,000 kgf/cm 2 , particularly 20 to 1,000 kgf/cm 2 are preferred. When the stiffness modulus of the polymer containing the glycidyl group exceeds 2,000 kgf/cm 2 , it becomes equal to that of a normal ionomer resin (i.e. 2,500 to 4,000 kgf/cm 2 ), and it becomes impossible to soften the ionomer resin, completely. In a heated mixture which constitutes the base resin for the cover, the mixing ratio (weight ratio) of the ionomer resin (A) to the polymer (B) containing the glycidyl group is preferably in the range of 99:1 to 50:50, particularly 98:2 to 80:20. When the mixing ratio of the ionomer resin (A) is larger than the above range, since the amount of the polymer (B) containing the glycidyl group is small, the heated mixture can not be sufficiently softened, whereby, a sufficient improvement of shot feel and control of the golf ball can not be obtained. When the amount of the ionomer resin (A) is smaller than the above range, the properties of the ionomer resin (e.g. impact resilience, cut resistance, etc.) deteriorate , which results in a deterioration of the flight performance and cut resistance of the golf ball. In the present invention, a heated mixture of the ionomer resin and polymer containing the glycidyl group is used as the main component of the base resin for the cover. To the heated mixture, if necessary, various additives such as pigments, dispersants, antioxidants, UV absorbers and UV stabilizers can be added. Further, in the present invention, the fact that the heated mixture of the ionomer resin and polymer containing the glycidyl group is used as the main component of the base resin for the cover means the case that the base resin for the cover is only composed of the heated mixture, or the case that the base resin for the cover is composed of the heated mixture, to which other resins are added in an amount within the range which does not affect properties of the heated mixture (normally, in the range of not more than 20 % by weight based on the total weight of the heated mixture). Further, in the present specification, there is a wording "heated mixture of the ionomer resin and polymer containing the glycidyl group", but the "heated mixture" means that the mixture is produced by mixing components with heating and it does not mean that the mixture is used for the cover of the golf ball in the heated state. The heated mixture is obtained by mixing the ionomer resin with polymer containing the glycidyl group with heating at a resin temperature of 150 to 280°C, using an extruder for plastic or an internal mixer such as plastomill, Banbury mixer. Among the above mixers, a twin-screw extruder is most suitable for mixing efficiently. Then, a cover composition which is composed of the heated mixture as the main component of the base resin for the cover is coated on the core to obtain a golf ball. In that case, any of solid core and thread wound core can be used. The solid core is obtained by vulcanizing (crosslinking) a rubber composition mainly composed of a rubber followed by integral molding. The thread wound core is obtained by winding a thread rubber on a central core material. According to the present invention, a golf ball having excellent hit feeling and control property as well as excellent flying performance and cut resistance can be obtained. EXAMPLES The following Examples further illustrate the present invention in detail but are not to be construed to limit the scope thereof. Examples 1 to 3 and Comparative Examples 1 to 3 (1) Preparation of core A rubber composition wherein 35 parts by weight of zinc acrylate, 20 parts by weight of zinc oxide, 1 part of dicumyl peroxide and 0.5 parts by weight of antioxidant [Yoshinox 425 (trade name), manufactured by Yoshitomi Seiyaku Co.] are formulated based on 100 parts by weight of polybutadiene rubber [BR-11 (trade name), manufactured by Nippon Gosei Gomu Co.] was vulcanized at 165°C for 20 minutes to obtain a solid core. An average diameter of the resulting solid core was 38.4 mm. (2) Preparation of cover composition Formulation components shown in Table 1 were mixed and extruded by a twin-screw extruder to obtain a pellet-like cover composition. The extrusion was conducted under the condition of a screw diameter of 45 mm, a screw revolution speed of 200 rpm and a screw L/D of 35. A composition temperature was 220 to 260°C. Cover composition No. 1 2 3 4 5 6 HI-MILAN 1605 90 90 100 100 50 50 BONDFAST 7B 10 - - - - - BONDFAST E - 10 10 - - - SURLIN AD8265 - - - - 50 - SURLIN AD8269 - - - - - 50 Titanium dioxide 1.0 1.0 1.0 1.0 1.0 1.0 (3) Preparation of golf ball The core obtained in the above process (1) was coated with the cover obtained in the above process (2) by a injection molding method to prepare a golf ball. A ball weight, a ball compression and a flying distance and a kind of a cover composition used in the preparation of a golf ball are shown in Table 2. A golf ball of Comparative Example 1 is a golf ball wherein an ionomer resin is used alone as a resin component of the cover and it is a criterion for comparison. As shown in Table 2, regarding the golf balls of Examples 1 to 3, the flying distance is 206 to 208 m (225 to 227 yard) and is almost the same as that of the golf ball of Comparative Example 1. To the contrary, regarding the golf balls of Comparative Examples 2 and 3, the flying distance is shorter than that of the golf ball of the Comparative Example 1 by about 4.5 to 5.5 m (5 to 6 yards). Regarding the golf balls of Examples 1 to 3 and Comparative Examples 1 to 3, professional golfers were asked to hit the golf balls and their evaluation about hit feeling, control property and flying distance were asked. As a result, regarding the golf balls of Examples 1 to 3, the hit feeling and control property are almost the same as those of the thread wound golf ball coated with the cover containing transpolyisoprene (balata) as a main component and the flying distance is also good. On the contrary, regarding the golf ball of Comparative Example 1, the hit feeling is hard and spinning is hardly obtained and, further, the control property is inferior. Regarding the golf balls of Comparative Examples 2 and 3, the hit feeling and control property are good, but the flying resistance is inferior. In order to examine the cut resistance of the golf balls of Examples 1 to 3 and Comparative Examples 1 to 3, the head part of the golf balls were hit at a speed of 30 m/second by a swing-robbot provided with a pitching wedge (manufactured by True Temper Co.) to examine whether a cut mark is arisen or not. As a result, regarding the golf balls of Examples 1 to 3, no cut mark was arisen. To the contrary, regarding the golf balls of Comparative Examples 2 and 3, a small cut mark was arisen. Further, the cut resistance of the thread wound golf ball coated with the cover containing transpolyisoprene (balata) as a main component was also examined under the same condition. As a result, considerably large cut mark was arisen in the thread wound golf ball.

Claims: A golf ball comprising a core and a cover for covering the core, a base resin of the cover being composed of a heated mixture of an ionomer resin and a polymer containing a glycidyl group as a main component, wherein the heated mixture is obtained by mixing the ionomer resin with the polymer containing a glycidyl group with heating at a resin temperature of from 150 to 280°C. A golf ball as claimed in Claim 1 wherein the polymer containing a glycidyl group is an ethylene-vinyl acetate-glycidyl methacrylate terpolymer, ethylene-methyl acrylate-glycidyl methacrylate terpolymer, ethylene-glycidyl methacrylate bipolymer or a mixture thereof. A golf ball as claimed in Claim 2 wherein ethylene is contained in an amount of from 60 to 90% by weight based on the total polymer weight. A golf ball as claimed in Claim 2 wherein vinyl acetate or methyl acrylate is contained in an amount of from 0 to 35% by weight based on the total polymer weight. A golf ball as claimed in Claim 2 wherein glycidyl methacrylate is contained in an amount of from 1 to 15% by weight based on the total polymer weight. A golf ball as claimed in any one of the preceding claims wherein the polymer containing a glycidyl group has a stiffness of not more than 2,000 Kgf/cm 2 . A golf ball as claimed in any one of the preceding claims wherein the mixing ratio of the ionomer resin to the polymer containing glycidyl group is within the range of from 99:1 to 50:50. A golf ball as claimed in any one of the preceding claims wherein the cover further contains a pigment, dispersant, antioxidant, UV absorber, UV stabilizer or a mixture thereof. A golf ball as claimed in any one of the preceding claims wherein the core is either a solid core obtained by vulcanizing a rubber composition or a thread wound core obtained by winding thread rubber of a central core.

Inventors: HAMADA AKIHIKO, HORIUCHI KUNIYASU, KATO AKIRA, HAMADA, AKIHIKO, HORIUCHI, KUNIYASU, KATO, AKIRA
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES, LTD.
Application year: 1993
Main classification: C08L23
IPC codes: C08L23, A63B37