JPH0544305B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a solid golf ball for water practice. [Prior Art] Driving range golf balls are generally classified into two types depending on their use. One of them is a ball normally used on land, and the other is a water practice ball used in ponds, lakes, etc. The performance requirements placed on these two types of practice golf balls are firstly durability, and secondly a feel at impact that is equal to or close to that of a round ball. but,
In the case of water practice golf balls, the most important characteristic is that they must float on water, that is, the specific gravity of the ball must be less than 1 (however, this does not apply in the ocean or lakes containing salt water). . In order to satisfy this characteristic, golf balls have been proposed in which the specific gravity is reduced by incorporating cork as a filler. [Problems to be Solved by the Invention] However, golf balls containing cork to have a specific gravity of less than 1 as described above have a problem in that the feel at impact is significantly worse than that of golf balls for rounds or practice balls for track and field. It was hot. In addition, water practice golf balls have been proposed that contain polyolefin, ABS resin, etc. to give them a hardness and feel similar to those of round balls and land practice balls, but these balls are extremely durable. The problem is that it's bad. [Means for Solving the Problems] The present invention solves the problems of the prior art described above.
- A base rubber whose essential component is polybutadiene rubber (hereinafter referred to as VCR) containing 40 to 95% by weight of polybutadiene, ultra-high molecular weight polyolefin in the form of fine particles with an average particle diameter of 10 to 50 μm, an inorganic filler, and a crosslinking monomer. A golf ball is produced from a rubber composition containing an initiator, or a golf ball is produced by covering an inner core produced from the above rubber composition with an outer skin using an ionomer resin or transpolyisoprene as a base material. As a result, a solid golf ball is provided which is suitable for practice on water and has good shot feel and sound, and is also excellent in durability. In the present invention, VCR is used as an essential component of the base rubber because VCR contains syndiotactic-1,2-polybutadiene with high crystallinity and high melting point, and has appropriate hardness and strength by itself. This allows golf balls to have a suitable hardness (ball compression ), giving a suitable feel and sound at impact, and improving durability. The amount of syndiotactic-1,2-polybutadiene in VCR is 5-30% by weight;
If the amount of syndiotactic-1,2-polybutadiene in VCR is less than this, the ball will become soft and the durability will decrease. As a result, the specific gravity increases and it becomes impossible to float on water, making it impossible to use it as a water practice golf ball.
- This is because if the amount of polybutadiene exceeds the above range, the rebound resilience will decrease and a suitable shot feel and sound will not be produced. In addition, cis-1,4-polybutadiene in VCR must be at least 40% by weight;
If the amount of polybutadiene is less than this, the rebound properties will be lowered and a suitable shot feel and sound will not be produced.
The upper limit of the amount of cis-1,4-polybutadiene in VCR is 95% by weight since the minimum amount of syndiotactic-1,2-polybutadiene is 5% by weight. Such a VCR can be obtained, for example, by carrying out conventional cis polymerization of butadiene and then carrying out 1,2-syndiotactic polymerization in the same system. As a specific example of such a VCR, for example, UBEPOL- manufactured by Ube Industries, Ltd.
VCR309 (Product name, composition: Syndiotactic
9% by weight of 1,2-polybutadiene, cis-1,4
-89% by weight of polybutadiene, trans-1,4-
Polybutadiene 2% by weight), UBEPOL-VCR412
(Product name, composition: Syndiotactic-1, 2-
There are commercially available products such as polybutadiene (12% by weight), cis-1,4-polybutadiene (86% by weight), and trans-1,4-polybutadiene (2% by weight), which are preferably used in the present invention. these
As is clear from the explanation of the manufacturing method that VCR can be obtained by performing the above-mentioned conventional cis polymerization of butadiene and then performing 1,2-syndiotactic polymerization in the same system, VCR is a single polymer. The composition of a typical example is, for example, 9% by weight of syndiotactic-1,2-polybutadiene, 89% by weight of cis-1,4-polybutadiene, and 2% by weight of trans-1,4-polybutadiene.
Although each component is labeled as a polymer, it is not a mixture of multiple polymers. In the present invention, VCR is an essential rubber component, and the more VCR is contained in the base rubber, the better the physical properties of the golf ball will be obtained. Therefore, it is possible to use only this VCR as the base rubber, and from the viewpoint of processability and price,
Natural rubber, cis-1,4-polybutadiene, styrene-butadiene rubber, etc. may be blended with VCR using this VCR as an essential component. As described above
When a base rubber is prepared by blending natural rubber, cis-1,4-polybutadiene, styrene-butadiene rubber, etc. with VCR, it is preferable that the amount of VCR in the base rubber is 30% by weight or more. That is, in the present invention, it is preferable that VCR occupies 30 to 100% by weight of the base rubber. Microparticulate ultra-high molecular weight polyolefin with an average particle diameter of 50 μm or less plays the role of a low specific gravity reinforcing filler, increasing the hardness and durability of golf balls, and improving the feel and sound of the ball at impact. . Such fine particulate ultra-high molecular weight polyolefins can be made somewhat smaller in particle size because they exhibit the above-mentioned effects more effectively due to their small particle size, but if the particle size becomes too small, they may scatter during handling. When handling is considered, particles with an average particle size of up to 10 μm are suitable for practical use. As such a fine particulate ultra-high molecular weight polyolefin, for example, Miperon (trade name, average particle diameter) manufactured by Mitsui Petrochemical Industries, Ltd.
A microparticulate ultra-high molecular weight polyolefin (with a diameter of 20 μm and a molecular weight of 2 million or more) is commercially available and is preferably used in the present invention. The amount of ultra-high molecular weight polyolefin in the form of fine particles having an average particle diameter of 10 to 50 μm is usually preferably 10 to 40 parts by weight based on 100 parts by weight of the base rubber. Examples of inorganic fillers include zinc oxide (ZnO),
Silicon oxide (SiO ₂ ), calcium carbonate, aluminum silicate, etc. are used. The main role of these is to increase the hardness and impact strength of the golf ball, increase the durability of the golf ball, and improve the feel and sound of the ball. - It also has the role of reacting with monoethylenically unsaturated carboxylic acids to become metal salts of those acids and serving as a crosslinking monomer to enable the rubber composition to be crosslinked. If a large amount of these inorganic fillers is blended, the hardness and impact strength will increase, but the specific gravity will increase and it will not float on water, so the amount of these inorganic fillers blended is usually 5 parts by weight per 100 parts by weight of the base rubber. Preferably, the amount is ~20 parts by weight. Crosslinking monomers crosslink rubber compositions to exhibit rebound resilience, etc., and give golf balls hardness, durability, and suitable shot feel and sound. , for example, α,β-monoethylenically unsaturated carboxylic acids or metal salts thereof such as methacrylic acid and acrylic acid, polyfunctional methacrylic acid esters such as trimethylolpropane trimethacrylate, and polyfunctional acrylic acid esters such as trimethylolpropane triacrylate. The amount of these crosslinking monomers is usually 5 to 25 parts by weight based on 100 parts by weight of the base rubber. The initiator is used to initiate the polymerization of the crosslinking monomer to crosslink the rubber composition, and examples of such initiators include dicumyl peroxide, 2,2'-di( Peroxides such as tert-butylperoxy)butane and tert-butyl perbenzoate are used, and the amount of these is usually preferably 0.5 to 5 parts by weight per 100 parts by weight of the base rubber. In the present invention, the rubber composition for producing the one-piece golf ball and inner core includes the above-mentioned rubber compositions.
In addition to the base rubber containing VCR as an essential component, ultra-high molecular weight polyolefin in the form of fine particles, inorganic fillers, crosslinking monomers, initiators, etc., we also use materials for the purpose of making the ball even harder or reducing its specific gravity. High styrene resin, polyolefin, microballoon, cork powder, etc. may be blended as appropriate. [Example] Next, the present invention will be explained in more detail with reference to Examples. Examples 1 to 5 and Comparative Examples 1 to 6 Rubber compositions having the formulations shown in Table 1 were prepared, and the obtained rubber compositions were placed in a ball mold and heated under pressure to crosslink, and the diameter was 42.8. mm one-piece solid golf balls were produced (Examples 1, 3,
5 and Comparative Examples 1 to 6). In addition, the above rubber composition was placed in a mold for forming an inner core and heated under pressure to crosslink it to produce an inner core with a diameter of 38.3 mm, and then titanium oxide (TiO ₂ ) was added to the inner core based on 100 parts by weight of the ionomer resin. An outer skin is applied to the inner core by coating it with an outer skin composition containing 2 parts by weight of
A 42.8 mm two-piece solid golf ball was prepared (Examples 2 and 4). The specific gravity, ball compression, durability, shot feel, and shot sound of the resulting golf balls were examined, and the results are shown in Table 1. Note that the blended parts of each material shown in Table 1 are based on parts by weight. Further, the methods for measuring ball compression and durability, the methods for determining feel at impact and sound at impact, and the evaluation criteria thereof are as follows. Ball compression: The amount of deformation of the golf ball from when an initial load of 3.8 kg is applied to when a load of 45.4 kg is applied (the amount of deformation is 1/1000
(compression 1 in inches). Durability: Continuously the same impact on the golf ball (hitting the ball against a flat iron plate at a speed of 45 m/sec)
The number of impacts until the ball breaks is expressed as an index, and the larger the value, the better the durability. Shot feel and sound: Judgment will be based on actual hits with a Utsudo No. 1 club by a total of 10 people, including 5 professional golfers and 5 amateur golfers (single players). Evaluation criteria: ◎: Very good ○: Good △: Slightly poor ×: Poor

【table】

〔Effect of the invention〕

As explained above, according to the present invention, it was possible to provide a solid golf ball for water practice that has a low specific gravity and is suitable for water practice and is excellent in durability, shot feel, and sound.

Claims (1)

[Scope of Claims] 1. A base rubber whose essential components are polybutadiene rubber containing 5 to 30% by weight of syndiotactic-1,2-polybutadiene and 40 to 95% by weight of cis-1,4-polybutadiene; , the average particle size is 10
~50 μm fine particulate ultra high molecular weight polyolefin,
A one-piece solid golf ball for water practice obtained by crosslinking a rubber composition containing an inorganic filler, a crosslinkable monomer, and an initiator. 2 Syndiotactic - A base rubber whose essential components are polybutadiene rubber containing 5 to 30% by weight of 1,2-polybutadiene and 40 to 95% by weight of cis-1,4-polybutadiene, and a base rubber having an average particle size of 10% by weight.
An inner core obtained by crosslinking a rubber composition containing ultra-high molecular weight polyolefin in the form of fine particles of ~50 μm, an inorganic filler, a crosslinking monomer, and an initiator is made of an ionomer resin or transpolyisoprene as a base material. A two-piece solid golf ball for water practice with an outer skin.