JPH0375186B2 - - Google Patents

Description

[Detailed description of the invention]

Technical Field This invention relates to a solid golf ball, particularly a two-piece solid golf ball consisting of a core and a cover. By lowering the crosslinking density of the base rubber constituting the rubbery composition that becomes the core and increasing the specific gravity of the composition, the distribution of specific gravity is concentrated mainly in the inner core, and the hardness is lowered to increase the density of the entire ball. Reduce the moment of inertia of and make the run smaller.
By increasing the crosslinking density of the base rubber that makes up the rubber composition that forms the outer core, and by lowering the specific gravity of the composition, it is possible to lightly increase hardness and improve repulsion, extending flight distance and making it softer. The design is designed to provide a comfortable hitting feel. Prior Art and Its Disadvantages Recently, two-piece solid golf balls have become widely used. This two-piece solid golf ball has a spherical core made of a butadiene rubber composition and covered with a cover made of an ionomer resin. However, although this two-piece solid golf ball provides a long flight distance for amateur golfers, it has the drawbacks of a long run (the rolling distance after landing), difficulty in controlling it, and a hard feel when hit. In addition, if the compression, which corresponds to the pressure required to elastically deform the diameter of the ball by a certain amount, is reduced to obtain a softer hitting feeling, the drawback is that the repulsion is reduced and the flight distance is not achieved. be. It is also known that in order to improve these drawbacks, the structure of the ball is divided into two or three or more layers from the inner layer to the outer layer, and the hardness is gradually increased toward the outside, and the weight distribution is lower toward the outside. However, (Japanese Patent Application Laid-Open No. 51-49840), this is a simple improvement on the characteristics of the so-called thread-wound ball, which is formed by enclosing a liquid in the core and wrapping an elongated rubber thread around it. This is only a qualitative and abstract expression, and there is no disclosure of a specific manufacturing method for manufacturing a golf ball with such a characteristic structure, and there is still no solution yet. It has not been. Purpose of the Invention The present invention was made in view of the above circumstances, and an object of the present invention is to provide a solid golf ball having a multilayer structure that provides a small run, a large distance, and a soft feel when hit. That is. Structure of the Invention The solid golf ball of the present invention has a core divided into an inner core and an outer core, the inner core is made of a crosslinked rubber composition with a specific gravity of 1.6 to 2.4 and a hardness of 50 to 70, and the outer core is made of a crosslinked rubber composition with a specific gravity of 1.0 to 1.2. , hardness 70~90
The present invention provides a specific structure and composition for constructing the crosslinked rubber composition. DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows an example of the solid golf ball of the present invention. Reference numeral 1 in the figure is a golf ball according to the present invention, and this golf ball 1
The core is divided into two parts: an inner core 2 at the center and an outer core 3 at the outer side. This double-structured core 4 is entirely covered with a cover 5. The inner core 2 is spherical and has a diameter of 20 to 30 mm for both the small ball and the large ball. The outer core 3 has a hollow spherical shape, and its outer diameter is 36 to 38 mm for a small ball and ^37.5 to ^39.5 mm for a large ball. Inner core 2 has a specific gravity of 1.6 to 2.4,
Hardness (all hardness referred to in this invention is JIS-K-
This is a value measured at 20°C using a JIS C type rubber hardness tester specified in 6301. ) 50 to 70, and the outer core 3 has a specific gravity of 1.0.
~1.2, and is composed of a crosslinked rubber composition with a hardness of 70-90. If the specific gravity of the inner core 2 is less than 1.6, it becomes virtually impossible to concentrate most of the weight of the entire ball 1 here, and the specific gravity distribution spreads too much, making it impossible to achieve the effect of reducing the run described below. , exceeding 2.4, the amount of filler blended becomes very large, making blending difficult and causing manufacturing inconveniences. Further, if the hardness of the inner core 2 is less than 50, it will be too soft and the rebound will be low, and if it exceeds 70, the hardness of the core 4 as a whole will be too high and will not be different from a conventional two-piece ball, causing inconvenience. The specific gravity of the outer core 3 cannot be less than 1.0 due to its composition; if it exceeds 1.2, a considerable amount of filler must be added, making it impossible to reduce tanδ, which will be described later. . Also,
If the hardness of the outer core 2 is less than 70, the deformation during high-speed impact as a repulsion layer will be too large, resulting in poor repulsion characteristics, while if it exceeds 90, it will be too hard, which will adversely affect the feel of impact, resulting in inconvenience. In order to manufacture the structure of a golf ball having the above-mentioned physical properties, a large amount of filler is blended into the rubber base material in the inner core 2, and a relatively small amount of a crosslinking agent is blended to reduce the crosslinking density, and also in the outer core. 3 can be realized by adding almost no filler to the rubber base material and adding a large amount of crosslinking agent to increase the crosslinking density. Specifically, as a formulation that satisfies these physical properties, in the inner core 2 using cis-1,4-polybutadiene rubber as the rubber base material, cis-1,4-polybutadiene rubber is used.
For 100 parts by weight, 2 to 8 parts by weight of unsaturated fatty acids such as zinc acrylate or some or all metal salts thereof, 100 to 150 parts by weight of zinc oxide, and 0.5 to 3 parts by weight of dicumyl peroxide. , outer core 3 uses cis 1,4-polybutadiene rubber 100
40 to 70 parts by weight of unsaturated fatty acids such as zinc acrylate or some or all metal salts thereof,
Zinc oxide 0-10 parts by weight, dicumyl peroxide
The amount is 0.5 to 3 parts by weight. In this case, it is preferable to use 100% cis-1,4-polybutadiene as the rubber base material, but it is also preferable to use 100% cis-1,4-polybutadiene.
% or more as a main component, and in addition, styrene-butadiene rubber, natural rubber, high styrene resin, etc. may be added to the rubber base material in an appropriate amount as necessary so as to obtain the above physical property values. In addition to zinc acrylate, metal salts of unsaturated fatty acids such as magnesium acrylate, zinc methacrylate, and magnesium methacrylate are used, and fillers such as barium sulfate, calcium carbonate, and silica are added to zinc oxide. Can be used. moreover,
In place of dicumyl peroxide, it is possible to use peroxides such as benzoyl peroxide and azo compounds such as azobisisobutylnitrile. The cover 5 is made of a common paratha rubber composition, an ionomer resin composition, etc., and an ionomer resin composition is preferable in terms of cut-proof effect, repulsion, etc. Function In the golf ball 1 of the present invention having the above structure and composition, by increasing the specific gravity of the inner core 2 and concentrating most of the weight of the entire ball 1 on the inner core 2, the entire ball 1 is The moment of inertia becomes smaller, which results in a smaller run and better stopping power. That is, the weight of the inner core 2 is M ₁ (g), the density is ρ ₁ and the radius α ₁ (cm), the weight of the outer core 3 is M ₂ and the density is ρ ₂ , the outer radius α ₂ , and the weight of the cover 5 is Assuming that M ₃ is the density, ρ ₃ and the outer radius α ₃ , the moment of inertia () of the entire ball 1 can be obtained by the following equation. I=2/5 (M ₁・α ² ₁ +M ₂ α ² ₂ +M ₃ α ² ₃ ) −8/15α ⁵ ₁ ρ ₂ minπ−8/15α ⁵ ₂ ρ ₃・π From this relational expression, the ball of this invention 1 and the conventional ball inertia moment (g・cm ² ) are as follows: Ball of the present invention I = 67 to 70 g・cm ² Wound ball I = ^66.3 to 67 g・cm ² Two-piece solid ball I = 72 ~74g・cm ² One-piece solid ball I = ^76.9 g・cm ² . (However, all values are for small balls.) In this way, the golf ball 1 of the present invention
It can be seen that the moment of inertia is smaller than that of a conventional solid ball, comparable to that of a wound ball, and that the run is small and stops well. Further, by adding almost no filler to the outer core 3 and reducing its specific gravity, the repulsion characteristics of the outer core 3 are improved and the flight distance of the ball 1 is extended. Generally, when a filler is added to crosslinked rubber, the elastic modulus E ₁ increases due to the volume effect, but at the same time the loss modulus E ₂ also increases significantly.
As a result, tan δ, which is the ratio of these elastic moduli E ₂ /E ₁ , increases. Tan δ is an index of energy loss in which mechanical energy applied to a viscoelastic body is lost as heat, and as this value increases, the loss of externally applied mechanical energy in the form of heat increases. Therefore, by reducing tan δ, the loss of mechanical energy will be reduced, the pressure against the applied external force will be increased, and the repulsion characteristics of the ball will be improved. The graph in FIG. 2 shows this relationship. The graph in Figure 2 is
It shows the relationship between the restitution coefficient E and tanδ of a viscoelastic body. This graph also shows that it is necessary for tan δ to be small in order to obtain high repulsion characteristics.
Note that this repulsion coefficient E is defined as follows. E=e ^-tan 〓 ⁽ 〓 ^-2 〓 ⁾ However

[Formula] FIG. 3 is a graph showing the relationship between filler content and tan δ. It can be seen from this graph that tan δ becomes smaller as the amount of filler is reduced. The results shown in the graph in Figure 3 were obtained by thermally crosslinking a rubber composition with the formulation shown in Table 1 to form a sphere with a diameter of 37.2 mm, and measuring the dynamic viscoelasticity using this sphere as a sample. It is something that

[Table] Dynamic viscoelasticity was measured in a region where the amount of deformation was large due to compressive deformation, assuming that the ball would be hit by the head of a golf ball. Static load 420Kg, dynamic load ±60Kg,
The measurement was carried out at a vibration frequency of 11 Hz and a temperature of 25°C using a viscoelastic spectrometer (Tokyo Testing Machine). From this, it is understood that the outer core 3 has good repulsion characteristics and contributes to extending the flight distance of the ball because it contains almost no filler and has a low specific gravity. Furthermore, since the hardness of the inner core 2 is low and the hardness of the outer core 3 is high, the impact at the time of hitting is received by the hard outer core 3 and the soft inner core 2, so whether the club head speed is fast or slow. You can also get a soft hitting feeling. Manufacturing Method Next, a method for manufacturing a golf ball using the composition of the present invention will be described. Compounds using cis-1,4-polybutadiene rubber as a rubber base are prepared for inner core and outer core, respectively.
These blends are kneaded using a Banbury mixer, rolls, etc., and molded into chips using an extruder. The mold is filled with chips for the outer core, and a hemispherical shell-shaped primary molded product is heated at a temperature of 85 to 100°C for 3 hours.
Mold in ~4 minutes. Meanwhile, chips for the inner core are filled into a mold, and the spherical primary molded body is heated to about
Mold at 150℃ for 30 minutes. The two hemispherical primary molded bodies that will become the outer core are wrapped around the spherical primary molded body of the inner core, and heated at approximately 150°C for 30 minutes to form the core. This core is centerless polished to make it a perfect sphere. Next, the golf ball 1 of the present invention can be obtained by molding a resin composition prepared by adding a pigment such as titanium dioxide to an ionomer resin as a cover over the core by injection molding. In addition, when the rubber base material and various compounding agents are changed, the above-mentioned molding temperature and time may be changed as appropriate. Examples Hereinafter, the effects of this invention will be clarified by showing examples. Solid golf balls (small balls) having the formulations and dimensions shown in Table 2 were manufactured by the above manufacturing method, and their various properties were evaluated. The results are shown in Table 3.

[Table] Cis-1,4-polybutadiene: Japan Synthetic Rubber Co., Ltd.
Manufactured by BR01 Ionomer Resin A; Surlyn manufactured by DuPont
1706 Ionomer resin B; Surlyn manufactured by DuPont
1707 Ionomer resin C; Surlyn manufactured by DuPont
1605

【table】

[Table] Test condition club; outer shell CFRP core foam resin head and
Driver machine consisting of CFRP shaft: Swing robot manufactured by True Temper Head speed: 45±2m/sec Ball temperature: 21±1℃ Air temperature: 21±1℃ From the results in Table 3, it can be seen that the golf ball of this invention is different from the conventional two-piece Compared to solid golf balls, the initial ball speed is higher and the repulsion characteristics are improved.
The distance is longer and there are fewer runs. In addition, despite the long flight distance, a soft hitting feeling can be obtained. Therefore, this golf ball is
It can be seen that this is a well-balanced ball that eliminates the drawbacks of conventional two-piece solid golf balls. Effects of the Invention As explained above, the solid golf ball of the present invention has a core divided into two parts, an inner core and an outer core, and the inner core has a specific gravity of 1.6 to 2.4 and a hardness of 1.6 to 2.4.
A rubber composition with a low crosslinking density of 50 to 70 and a high filler content, making the outer core have a specific gravity of 1.0 to 1.0.
1.2, with a hardness of 70 to 90, a rubber composition with a high crosslink density and a low filler content, so the weight of the entire ball is concentrated in the center of the inner core, and the moment of inertia of the entire ball is reduced. It becomes smaller, has a smaller run, and has a better stop. Furthermore, since the outer core has a low specific gravity and contains almost no filler, the tan δ of this portion is small, the repulsion coefficient is large, and the flight distance is extended. Furthermore, since the inner core is soft and the outer core is hard, the impact of the impact is received by both the hard and soft layers, providing a soft impact feel regardless of the club head speed.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing an example of the solid golf ball of the present invention, Fig. 2 is a graph showing the relationship between tan δ of the viscoelastic body and the coefficient of restitution, and Fig. 3 is a graph showing the relationship between the filler content of the crosslinked rubber and the coefficient of restitution. It is a graph showing the relationship with tanδ. 1...Golf ball, 2...Inner core, 3
...Outer core, 4...Core.

Claims (1)

[Claims] 1. A solid golf ball consisting of a core and a cover covering the core, the core being divided into an inner core and an outer core, and the inner core containing 100 parts by weight (parts by weight, same hereinafter) of base rubber. ) Specific gravity 1.4 obtained by heating and curing a composition containing 2 to 8 parts of unsaturated fatty acids, 100 to 150 parts of zinc oxide, and 0.5 to 3 parts of organic peroxide.
~2.4, hardness 50 to 70, the outer core is a base rubber 100 parts unsaturated fatty acid 40 to 70 parts zinc oxide 0 to 10 parts organic peroxide 0.5 to 3 parts. Specific gravity obtained by adhering to the surface of a crosslinked rubber composition for inner core and heating and curing it.
A solid golf ball comprising a crosslinked rubber composition having a hardness of 1.0 to 1.2 and a hardness of 70 to 90. 2 In a solid golf ball consisting of a core and a cover covering the core, the core is divided into an inner core and an outer core, and the inner core is made of base rubber 100 parts metal salt of some or all of the unsaturated fatty acids 2 Specific gravity 1.4 obtained by heating and curing a composition containing ~8 parts zinc oxide 100-150 parts organic peroxide 0.5-3 parts
~2.4, hardness 50-70 crosslinked rubber composition, outer core is base rubber 100 parts metal salt of some or all unsaturated fatty acids 40-70 parts zinc oxide 0-10 parts organic peroxide 0.5-3 A specific gravity obtained by adhering a composition containing 50% to the surface of the crosslinked rubber composition for inner core and heating and curing the composition.
A solid golf ball comprising a crosslinked rubber composition having a hardness of 1.0 to 1.2 and a hardness of 70 to 90. 3. The solid golf ball according to claim 2, wherein the metal salt of unsaturated fatty acid is zinc acrylate.