JPH0449426B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to golf balls. More specifically, the cover material contains a specific α-olefin and α,β.
- A golf ball having high rebound resilience, excellent flight performance, and good durability by using a copolymer ionomer with an ethylenically unsaturated monocarboxylic acid. [Conventional technology] Ionomers, which are commercially available under trade names such as Surlyn and Himilan, have traditionally been used for golf ball covers because they have excellent impact resistance, cut resistance, and flight performance. (For example, Japanese Patent Application Laid-open No. 82768/1982). [Problems to be solved by the invention] However, there is still room for improvement in golf balls using ionomer as a cover material in terms of rebound, flight distance, and feel at impact, especially for users who want to further increase flight distance. In response to these demands, there is a desire for a golf ball with even higher repulsion and superior flight performance. [Means for solving the problem] The ionomer consists of α-olefin,
α, β-ethylenically unsaturated carboxylic acid and α,
Three components of β-ethylenically unsaturated carboxylic acid metal salt or α-olefin, α,β-ethylenically unsaturated carboxylic acid, α,β-ethylenically unsaturated carboxylic acid metal salt, and α,β-ethylenically unsaturated It is an ionic ethylene copolymer consisting of four components of carboxylic acid ester, and various ionomers are known. However, the only ionomer actually used as a cover material is an ethylene-methacrylic acid copolymer ionomer.
There are no examples of cover materials using ionomers containing other α-olefin components and α,β-ethylenically unsaturated carboxylic acid components. In view of the above circumstances, the present inventors have conducted various studies focusing on ionomers, and when using an alkali metal salt ionomer of ethylene-acrylic acid copolymer as a cover material for golf balls, conventional ionomer covers are used. It has been found that a golf ball can be obtained that has higher repulsion resiliency and superior flight performance than the golf balls that have been used. However, the alkali metal salt ionomer of the ethylene-acrylic acid copolymer has poor durability and therefore lacks practicality. Therefore, as a result of further research, the present inventors found that an alkali metal salt ionomer of ethylene-acrylic acid copolymer and a divalent metal salt ionomer of ethylene-acrylic acid copolymer or ethylene-methacrylic acid copolymer When blending (mixing) or neutralizing the carboxylic acid of the ethylene-acrylic acid copolymer with alkali metal ions and divalent metal ions, the alkali metal salt ionomer of the ethylene-acrylic acid copolymer The present inventors have discovered that it is possible to obtain a golf ball that has improved durability while maintaining high repulsion, and has excellent flight performance and good durability, and has now completed the present invention. In the present invention, the golf ball cover is made of a blend of an alkali metal salt ionomer of an ethylene-acrylic acid copolymer and a divalent metal salt ionomer of an ethylene-acrylic acid copolymer or an ethylene-methacrylic acid copolymer; Alternatively, it is formed from a composition whose main component is an ethylene-acrylic acid copolymer ionomer obtained by neutralizing the carboxylic acid of an ethylene-acrylic acid copolymer with an alkali metal ion and a divalent metal ion. As mentioned above, as the alkali metal salt ionomer of the ethylene-acrylic acid copolymer to be blended with the divalent metal salt ionomer, one having a degree of neutralization with alkali metal ions of 25% or more is used. This is due to the degree of neutralization by alkali metal ions.
This is because if the content is less than 25%, sufficient impact resilience cannot be obtained when blended with the divalent metal salt ionomer. Ethylene blended with the alkali metal salt ionomer of the above ethylene-acrylic acid copolymer.
Examples of divalent metal salt ionomers of acrylic acid copolymers or ethylene-methacrylic acid copolymers include zinc salt ionomers of ethylene-acrylic acid copolymers with a degree of neutralization with zinc ions of 25% or more, and alkali metals. Degree of neutralization by metal ions is 25%
Neutralization with the zinc salt ionomer of the ethylene-methacrylic acid copolymer having a neutralization degree of 25% or more with the alkali metal salt ionomer of the above ethylene-acrylic acid copolymer and alkali metal ion At least one selected from the group consisting of alkali metal salt ionomers of ethylene-methacrylic acid copolymers having a concentration of 25% or more is used. In these divalent metal salt ionomers, the degree of neutralization by zinc ions and neutralization by alkali metal ions is set at 25% or more because the degree of neutralization by these divalent metal ions is less than 25%. This is because sufficient durability cannot be imparted when the ethylene-acrylic acid copolymer is blended with an alkali metal salt ionomer. In the present invention, the blend ratio of the ethylene-acrylic acid copolymer alkali metal salt ionomer and the above divalent metal salt ionomer is 80/20 to 40/
60 (weight ratio), particularly preferably a range of 70/30 to 40/60 (weight ratio). If the content of the divalent metal salt ionomer in the blend is less than 20% by weight, the effect of improving durability will be small, while if it exceeds 60% by weight, the impact resilience will decrease and the intended purpose will not be achieved. Examples of the alkali metal in the alkali metal salt ionomer of the ethylene-acrylic acid copolymer include lithium, sodium, potassium, and cesium. Further, examples of the alkali metal in the alkali metal salt ionomer include beryllium, magnesium, calcium, strontium, barium, and the like. In particular, magnesium is preferred because it has a great effect on improving durability. The alkali metal salt ionomer of the ethylene-acrylic acid copolymer used in the present invention is ethylene. It can be obtained by reacting an acrylic acid copolymer with an alkali metal compound such as a hydroxide, acetate, oxide, carbonate, etc. by a known method. For example, an ethylene-acrylic acid copolymer is dissolved in an organic solvent such as toluene under heating, an aqueous solution of an alkali metal compound such as sodium hydroxide or sodium acetate is added to the resulting solution, and then the solution is dissolved under reflux of the solvent. The reaction mixture is stirred and mixed for about 4 to 6 hours, and then the reaction mixture is dried to remove the solvent, and then maintained at a high temperature to complete the reaction. Alternatively, an ethylene-acrylic acid copolymer and an alkali metal compound can be combined at 120%
It can also be obtained by mixing in a mixer or extruder such as a roll mill or internal mixer at a high temperature of ~250°C; for example, by kneading an ethylene-acrylic acid copolymer at a roll temperature of 120 to 150°C,
140-190 after adding a predetermined amount of acrylic metal compound
It is carried out by kneading for 15-60 minutes at a temperature of °C. Such a reaction on a roll mill or the like may be performed when preparing a cover composition for forming a cover. Alkali metals include lithium, sodium, potassium and cesium.
Alkali metal compounds may be used alone or in combination of two or more. The ethylene-acrylic acid copolymer used as a base resin for the synthesis of an alkali metal salt-based ionomer of ethylene-acrylic acid copolymer has an acrylic acid content of 5 to 30% by weight and a melt index of 60 to 1000 g/ 10 min is preferable. If the acrylic acid content is less than 5% by weight, the rigidity will be low and the cut resistance will be poor, and the acrylic acid content will be 30% by weight.
If it is larger, the rigidity will increase and the feel at the time of impact will deteriorate, which is not preferable. In addition, if the melt index is less than 60g/10min, moldability is poor, and if the melt index is less than 1000g/10min,
If it is larger, the molecular weight will be low, and the rebound and impact resistance will deteriorate, which is not preferable. In addition, even without blending, by neutralizing the carboxylic acid of the ethylene-acrylic acid copolymer with alkali metal ions and divalent metal ions, excellent repulsion based on neutralization with alkali metal ions can be achieved. Durability can be improved while maintaining elasticity. Therefore, in the present invention, instead of the blend, it is possible to use an ethylene-acrylic acid copolymer ionomer in which the carboxylic acid of the ethylene-acrylic acid copolymer is neutralized with an alkali metal ion and a divalent metal ion. can. An ionomer obtained by neutralizing the carboxylic acid of such an ethylene-acrylic acid copolymer with an alkali metal ion and a divalent metal ion is ethylene-acrylic acid copolymer.
The degree of neutralization of the acrylic acid copolymer with alkali metal ions is 7.5% or more, preferably 10% or more, and neutralization with at least one divalent metal ion selected from the group consisting of zinc ions and alkali metal ions. degree is 5% or more, preferably 7.5% or more,
An ethylene-acrylic acid copolymer ionomer having a total degree of neutralization by metal ions of 25% or more is used. This indicates that the degree of neutralization by alkali metal ions is
If the degree of neutralization by divalent metal ions is less than 5%, the durability will be poor, and if the total degree of neutralization by metal ions is less than 25%, the rebound will be low. This is because impact resistance also deteriorates. Alkali metal ion and 2 in the molecule as above
The introduction of divalent metal ions into the ethylene-acrylic acid copolymer to obtain the ethylene-acrylic acid copolymer having valent metal ions is carried out in the same manner as in the case of the alkali metal salt-based ionomer. This is carried out by reacting the acid copolymer with at least one of the hydroxides, acetates, oxides, and carbonates of zinc or an alkali metal. The alkali metal ions and the divalent metal ions may be introduced at the same time; in this case, if at least one alkali metal compound and at least one divalent metal compound are reacted with the ethylene-acrylic acid copolymer, good. As the alkali metal or alkali metal to obtain such an ionomer having two or more different metal ions in the molecule, the same ones as in the case of the blend described above are used. The golf ball cover of the present invention has an ethylene-
A blend of an acrylic acid copolymer alkali metal salt ionomer and the above-mentioned divalent metal salt ionomer, or ethylene prepared by neutralizing the carboxylic acid of an ethylene-acrylic acid copolymer with an alkali metal ion and a divalent metal ion. - acrylic acid copolymer-based ionomers, but other ionomers, such as alkali metal salt-based ionomers of ethylene-methacrylic acid copolymers, polyolefins,
Other resins such as polyester elastomers and polyamides, pigments, fillers as specific gravity adjusters, and commonly used additives such as dispersants, antioxidants, and ultraviolet absorbers can also be appropriately added and blended. In addition, almost the same result can be obtained when an ethylene-acrylic acid copolymer ionomer in which the carboxylic acid of the ethylene-acrylic acid copolymer is neutralized with an alkali metal ion and a divalent metal ion is blended with a divalent metal salt ionomer. You can expect good results. Covers according to the present invention can be used to cover both solid golf ball cores and wound golf ball cores. Both the solid core and the thread-wound core may be those commonly used, and the solid core may not only be a core for a two-piece ball, but also a core for a so-called multilayer solid golf ball having a multilayer structure of two or more layers. Good too. For example, the solid core is made by combining polybutadiene with co-crosslinking agents such as α,β-monoethylenically unsaturated carboxylic acids such as acrylic acid and methacrylic acid or metal salts thereof, functional monomers such as trimethylolpropane trimethacrylate, zinc oxide, and oxidized By vulcanizing a composition containing metal oxides such as magnesium and peroxides such as dicumyl peroxide, and, if necessary, weight adjusters such as barium sulfate, calcium carbonate, and silica. can get. The ratio of the ingredients in such a solid core composition varies depending on whether a large-sized core or a small-sized core is made, but an example of a preferable composition is, for example, polybutadiene.
100 parts (by weight, same below), 10 to 60 parts of metal acrylate or metal methacrylate, 10 to 60 parts of zinc oxide
60 parts and 0.5 to 5 parts of a peroxide such as dicumyl peroxide. The thread-wound core consists of a center and a rubber thread wound around it, and the center can be either liquid or rubber-based, and the rubber-based center can be, for example, a rubber composition using the same formulation as the solid core. Those obtained by vulcanizing can be used. The thread rubber used is one that has been used conventionally, for example, one obtained by vulcanizing natural rubber or a rubber composition containing natural rubber and polyisoprene with anti-aging agents, vulcanization accelerators, sulfur, etc. It will be done. However, these solid cores and thread-wound cores are merely examples, and the present invention is not limited to these examples. The method of covering the core with the cover is not particularly limited and may be carried out by a conventional method. For example, a cover-forming composition containing the above-mentioned specific ionomer or other components as needed is formed in advance into a hemispherical shell shape called a half-shell, and two pieces of it are used to wrap the core. 170
A method is employed in which pressure molding is performed at 1 to 5 minutes at a temperature of 1 to 5 minutes, or a method in which the cover-forming composition is injection molded to wrap the core. The thickness of the cover is usually about 1.0 to 3.0 mm. When the cover is molded, dimples are formed on the surface of the ball or yering is performed as necessary, and the resulting ball is finished with paint as necessary. [Example] Next, the present invention will be explained in more detail with reference to Examples. Examples 1 to 4 and Comparative Example 1 A rubber composition prepared by adding and kneading 30 parts of zinc acrylate, 20 parts of zinc oxide, and 1 part of dicumyl peroxide to 100 parts of cis-1,4-polybutadiene was heated to 150 parts in a mold. Pressure molded at ℃ and diameter approx. 38.4
A solid core of mm was obtained. The sodium salt ionomer of ethylene-acrylic acid copolymer (EAA-Na) shown in Table 1 was synthesized as follows. Ethylene-acrylic acid copolymer (manufactured by Mitsubishi Yuka Co., Ltd., trade name Yucalon AW-500, acrylic acid content 20% by weight, melt index 300g/
10min) 400g was dissolved in toluene 1 at 80°C. 36.75 g of sodium acetate was made into an aqueous solution and dropped into the solution over about 20 minutes, and reacted by stirring and kneading at about 85° C. for 5 hours to neutralize 40% of the carboxylic acid with sodium ions. After the reaction was completed, the reaction mixture was air-dried to remove toluene. After vacuum drying at 70°C for 2 days and nights, the mixture was left under reduced pressure at 170°C for 4 hours to remove water and toluene and complete the reaction. The infrared absorption spectrum of the reaction product was measured, and it was confirmed that a sodium salt of ethylene-acrylic acid copolymer was formed. The zinc salt ionomer of ethylene-acrylic acid copolymer (EAA-Zn) was produced by reacting the ethylene-acrylic acid copolymer with zinc acetate dihydrate and achieving a neutralization degree of 30% with zinc ions. It was synthesized in almost the same way. The obtained EAA-Na was mixed in the weight proportion shown in Table 1.
EAA-Zn, EMAA-Na (product name Hymilan)
1605, Mitsui Dupont Polychemical Co., Ltd. Ethylene
Methacrylic acid copolymer sodium salt ionomer, methacrylic acid content 15% by weight, degree of neutralization with sodium ions 29%), EMAA-Zn (trade name Himilan 1706, ethylene-methacrylic acid copolymer zinc manufactured by Mitsui DuPont Polychemical Co., Ltd.) Salt-based ionomer, methacrylic acid content 15% by weight, degree of neutralization with zinc ions 58%) or EMAA-NaMg (ionomer made by further neutralizing the free carboxylic acid of Himilan 1605 with magnesium ions, degree of neutralization with sodium ions 29%) , the degree of neutralization by magnesium ions is 15%), and these ionomers are mixed with
2 parts of titanium oxide (TiO ₂ ) was added to 98 parts and kneaded to prepare a cover composition. The obtained cover composition was press-molded at 150° C. for 3 minutes to produce a cup-shaped half shell.
The resulting pair of half shells were placed over the solid core and molded into a mold for large size golf balls.
Compression molding was carried out at ℃ for 1 minute, and the resulting ball was coated with paint to produce a large size two-piece solid golf ball with a diameter of 42.7 mm. The restitution coefficient and flight performance of the resulting golf ball were measured, and the durability at room temperature (25°C) and low temperature (-10°C) was also examined. The results are shown in Table 1. In addition, in order to clarify the difference from the conventionally used ionomer, we used the same method as above except that only an ethylene-methacrylic acid copolymer-based ionomer was used instead of the ethylene-acrylic acid copolymer-based ionomer. A large size two-piece solid golf ball of Comparative Example 1 was prepared. The restitution coefficient, flight performance, and durability of this ball were also examined, and the results are shown in Table 1. The methods for measuring the repulsion coefficient, flight performance (flight test), and durability are as follows. Repulsion coefficient: Calculated from the ball speed when a cylindrical object weighing 198.4 g collided with the ball at a speed of 45 m/sec, and from the results. Flight test (flight performance): Using a golf ball hitting test machine (Swing Robot, manufactured by True Temper), the ball was hit with a No. 1 wood club at a head speed of 45 m/sec for measurement. Durability: The ball is kept at a specified temperature (room temperature (25℃), low temperature (-
After storing it at 10℃), use an air gun to attach it to a metal plate.
This was done by colliding at a speed of 45 m/sec and visually inspecting for cracks in the cover.

[Table] As shown in Table 1, EAA-Na (ethylene-
The golf balls of Examples 1 to 4 in which an acrylic acid copolymer (sodium salt ionomer) was blended with a divalent metal salt ionomer and used for the cover were:
Compared to the golf ball of Comparative Example 1, which used only the conventional EMAA-based (ethylene-methacrylic acid copolymer-based) ionomer for the cover, the restitution coefficient was higher;
It had excellent flight performance. Further, the golf balls of Examples 1 to 4 had good durability both at room temperature and low temperature, had excellent flight performance, and had good durability. Examples 5 to 6 and Comparative Examples 2 to 7 Sodium salt ionomers of ethylene-acrylic acid copolymers having the degrees of neutralization shown in Table 2 were synthesized as shown below. Ethylene-acrylic acid copolymer (manufactured by Dow Chemical Japan Co., Ltd., trade name Primacol 5980, acrylic acid content 20% by weight, melt index 300g/
10min) 250g was dissolved in 1 part of toluene at 80°C. A predetermined amount of aqueous sodium hydroxide solution was added dropwise thereto over about 20 minutes, and the mixture was stirred and kneaded at about 85° C. for 5 hours to react. After the reaction was completed, the reaction mixture was air-dried to remove toluene. After vacuum drying at 70°C for two days and nights, the mixture was left under reduced pressure at 170°C for 4 hours to remove water and toluene and complete the reaction. The infrared absorption spectrum of the reaction product was measured, and it was confirmed that a sodium salt of ethylene-acrylic acid copolymer was formed. The zinc salt ionomer of ethylene-acrylic acid copolymer was synthesized in substantially the same manner as above except that the ethylene-acrylic acid copolymer was reacted with zinc acetate dihydrate. Further, an ionomer having two types of metal ions, sodium and zinc, was synthesized as shown below. 250 g of ethylene-acrylic acid copolymer was dissolved in toluene 1 at 80°C, a predetermined amount of aqueous sodium hydroxide solution was added dropwise thereto over about 20 minutes, and the mixture was stirred and kneaded at about 85°C for 5 hours to react. Next, an aqueous solution of zinc acetate dihydrate was added dropwise over about 20 minutes.
The mixture was stirred and kneaded at about 85° C. for 5 hours to react. After the reaction was completed, the reaction mixture was air-dried to remove toluene. Then, after vacuum drying at 70℃ for 2 days and nights, it was dried at 170℃.
The reaction mixture was left under vacuum for 4 hours to remove water and toluene and complete the reaction. The infrared absorption spectrum of the reaction product was measured, and it was confirmed using an X-ray microanalyzer that sodium salt and zinc salt of the ethylene-acrylic acid copolymer were formed. A large size two-piece solid golf ball was prepared in the same manner as in Example 1 except that the ionomer thus obtained was used. The restitution coefficient and flight performance of the obtained golf balls were measured, and the durability was also examined. The results are shown in Table 2. These measurement methods are as described in Example 1 above.
The same is true for . In addition, in order to clarify the difference from conventionally used ionomers, in Comparative Example 7, Hymilan 1605 (trade name, ethylene-methacrylic acid copolymer manufactured by Mitsui DuPont Polychemicals Co., Ltd.) was used instead of an ethylene-acrylic acid copolymer ionomer. Polymeric sodium salt ionomer, methacrylic acid content 15% by weight, degree of neutralization with sodium ions 29%) and Himilan
1706 (trade name, Mitsui DuPont Polychemical Co., Ltd. ethylene-methacrylic acid copolymer zinc salt ionomer, methacrylic acid content 15% by weight, degree of neutralization with zinc ions 58%) at a weight ratio of 50/50 was used. Other than that, the test was conducted in the same manner as above. The results are also shown in Table 2. Note that the melt index in Table 2 is the melt index of the ionomer.

〔Effect of the invention〕

As explained above, in the present invention, ethylene-
An acrylic acid copolymer alkali metal salt ionomer and a divalent metal salt ionomer may be blended to form the cover, or the carboxylic acid of the ethylene-acrylic acid copolymer may be blended with an alkali metal ion and divalent metal ionomer.
By using an ethylene-acrylic acid copolymer ionomer neutralized with valent metal ions for the cover, it was possible to provide a golf ball with excellent flight performance and good durability.

Claims (1)

[Scope of Claims] 1 Comprising a core and a cover covering the core, the cover containing a copolymer ionomer of α-olefin and α,β-ethylenically unsaturated monocarboxylic acid as a main component. 1. A golf ball using a resin, wherein the ionomer is the following (A) or (B). (A) Alkali metal salt ionomer of ethylene-acrylic acid copolymer with a degree of neutralization by alkali metal ions of 25% or more and zinc of ethylene-acrylic acid copolymer with a degree of neutralization by zinc ions of 25% or more Salt-based ionomer, ethylene with a degree of neutralization of 25% or more with alkali metal ions.
The degree of neutralization with alkali metal salt ionomer of acrylic acid copolymer and zinc ion is 25% or more.The degree of neutralization with zinc salt ionomer and alkali metal ion of ethylene-methacrylic acid copolymer is 25% or more. Blend ratio of the above ethylene-methacrylic acid copolymer with at least one divalent metal salt ionomer selected from the group consisting of alkali metal salt ionomers: 80/
20-40/60 (weight ratio) blend (B) The degree of neutralization of the ethylene-acrylic acid copolymer with alkali metal ions is 7.5% or more, selected from the group consisting of zinc ions and alkali metal ions. Ethylene-acrylic acid copolymer ionomer 2 having a degree of neutralization by at least one type of divalent metal ion of 5% or more and a total degree of neutralization by metal ions of 25% or more. 2. The golf ball according to claim 1, wherein the golf ball is at least one selected from the group consisting of , potassium, and cesium. 3. The golf ball according to claim 1 or 2, wherein the alkali metal of the alkali metal ion is magnesium.