JPH064103B2 - Two-piece solid golf ball - Google Patents

Description

TECHNICAL FIELD The present invention relates to a two-piece solid golf ball having an inner core and a cover.

(Prior Art and Its Problems) Generally, a two-piece solid golf ball has a drawback that it has a long flight distance but is hard to be spun, and its characteristic trajectory with a low landing angle makes it difficult to stop on an iron shot. Therefore, in order to improve the spin performance at present, the compression deformation of the ball is performed by a method such as reducing the thickness of the cover, lowering the bending elastic modulus of the cover (that is, softening the cover hardness), and further increasing the hardness of the inner core. This is dealt with by reducing the amount.

However, when the cover is softened using, for example, a soft ionomer or a soft polyurethane as a material, or using a mixture of a soft polyester and an aonomer resin,
Although the spin performance is improved, the initial velocity of the ball is reduced and the flight distance becomes shorter. In addition, since the amount of compressive deformation of the ball is reduced, the feeling at the time of hitting the ball also deteriorates,
At this stage, a two-piece solid golf ball having satisfactory performance has not been obtained (for example, JP-A-60-163673, JP-A-61-149178, and JP-A-61-149178).
7-34874).

(Means for Solving Problems) In order to improve the spin performance of a two-piece solid golf ball without reducing the initial velocity of the two-piece solid golf ball and reducing the amount of compressive deformation of the ball, a two-piece solid golf ball is provided. It was completed by focusing on the hardness distribution of the inner core and various performances of the cover. That is, the present invention provides a two-piece solid golf ball having an inner core and a cover, the inner core having a surface hardness of 55 to 7 measured by a JIS-C type hardness meter.
5, having a cross-sectional hardness of 75 to 90 excluding the surface layer, the cover has a thickness of 0.7 to 2.2 mm, and a flexural modulus of 3500 to 600.
A two-piece solid golf ball having 0 kg / cm ² and having a compressive deformation amount of 2.2 to 3.0 mm when an initial load of 10 kg and a final load of 130 kg is applied. .

The golf ball of the present invention is designed so that the inner core surface is softened and a thin cover is covered. The golf ball designed in this way has a large area in contact with the club at the time of hitting the ball, and when the cover hardness is hard, it eliminates the drawback of slipping on the grab surface and reducing spin performance. It takes a lot of spin even if it is hard. Moreover, since the inner core surface is soft, it has been found that a golf ball that absorbs impact and has a soft feeling can be obtained.

The inner core used in the two-piece solid golf ball of the present invention can be obtained by a conventional method by adjusting the vulcanization conditions, the compounding ratio and the like.

Usually, the compounding of the inner core includes a base rubber, a crosslinking agent, a co-crosslinking agent, an inert filler and the like.

As the base rubber, an appropriate natural rubber and / or synthetic rubber conventionally used in two-piece solid rubber can be used. In the present invention, 1,4-polybutadiene having a cis structure of at least 40% or more is used. Is particularly preferable, and if desired, natural rubber, polyisoprene rubber, styrene-butadiene rubber, etc. may be appropriately blended with the polybutadiene.

Examples of the cross-linking agent include organic peroxides such as dicumyl peroxide and di-t-butyl peroxide, but dicumyl peroxide is particularly preferable.

The compounding amount of the crosslinking agent is usually 0.5 to 3.0 parts by weight, preferably 1.0 to 2.5 parts by weight, based on 100 parts by weight of the base rubber.

The co-crosslinking agent is not particularly limited, and examples thereof include metal salts of unsaturated fatty acids, and particularly zinc salts and magnesium salts of unsaturated fatty acids having 3 to 8 carbon atoms (eg acrylic acid, methacrylic acid, etc.). However, zinc acrylate is particularly preferable, and the compounding amount is 30 with respect to 100 parts by weight of the base rubber.
˜38 parts by weight, preferably 32-36 parts by weight.

Examples of the inert filler include zinc oxide, barium sulfate, silica, calcium carbonate and zinc carbonate,
Zinc oxide is common, and its content is the specific gravity of the inner core and outer skin,
Depending on the weight standard of the ball, etc., it is not particularly limited,
Usually, it is 10 to 60 parts by weight with respect to 100 parts by weight of the base rubber.

The composition for the inner core obtained by blending the above components is kneaded using a conventional kneading machine, for example, a Banbury mixer or a roll, and is compressed or injection-molded into a mold for the inner core, and the molded body is cross-linked and co-cross-linked. At a temperature sufficient for the action of, for example, dicumyl peroxide as the cross-linking agent and about 130 to 170 when zinc acrylate is used as the co-crosslinking agent.
Approximately 3 when heat-cured at ℃) and the diameter is large.
8.5 to about 41.4 mm, about 3 for small size
Adjust the inner core from 6.9 to about 39.9 mm.

In the present invention, the vulcanization conditions and blending are adjusted so that the surface hardness of the inner core is 55 to 75, preferably 65 to 70, and the cross-sectional hardness excluding the surface portion of the inner core is 75 to 90, preferably 80 to 85. Adjust the ratio etc. appropriately. Both the surface hardness and the cross-section hardness are measured with a JIS-C type hardness meter. The measuring method is JIS K6301. With respect to the surface hardness, the pressing needle of the JIS-C type hardness meter is brought into contact with the pressure surface so as to be perpendicular to the inner core surface, and the scale is immediately read. The cross-sectional hardness is a measured value when the same measurement is performed on the cross section of the inner core. Strictly speaking, since the portion corresponding to the depth of the measuring needle that enters when measuring the surface hardness is measured by the surface hardness even if it is a cross section, the cross section hardness is referred to as the hardness of the cross section excluding the portion of about 2 mm from the surface. When the surface hardness is less than 55, the vulcanization of the inner core is insufficient and an appropriate hardness cannot be obtained, and the initial velocity of the ball decreases. If the surface hardness exceeds 75, the spin performance deteriorates. If the cross-sectional hardness is less than 75, the initial velocity of the ball decreases, and if it exceeds 90, the ball becomes too hard and the feel on impact becomes poor.

The inner core obtained as described above has a thickness of 0.7 to 2.2 m.
It is covered with a cover of m, preferably 1.0-2.0 mm. The cover is mainly composed of an aonomer resin, and if necessary, an inorganic filler (for example, titanium dioxide,
Those containing barium sulfate) are usually used.
The thickness of the cover is usually a point where two points on an arbitrary axis of the ball are not punched out, and about six points near four points on the equator when these two points are the north pole and the south pole are not punched out. The cover was measured with a caliper and the average thereof was calculated. It is not preferable that the thickness of the cover is less than 0.7 mm because the balls are dimpled.
If it exceeds 2.2 mm, it is hard to spin and the feeling is bad.

A preferred aonomer resin is a polymer of a monoolefin and at least one selected from the group consisting of unsaturated mono- or dicarboxylic acids having 3 to 8 carbon atoms and their esters (unsaturated mono- or dicarboxylic acids and / or their It is a thermoplastic resin in which a cross metal bond is added to the ester (containing 4 to 30% by weight). As such an aonomer resin, various "HIMIRAN" commercially available from DuPont Mitsui Polychemical Co., Ltd.
55, 1557, 1707, 1706, 1605, etc. or combinations thereof).

In the present invention, the cover has a bending elastic modulus of 3500 to 6000 kg.
/ Cm ² , preferably 4000-5000 kg / cm ² . Flexural modulus is the value measured by ASTM D-790. Ionomer resins having various flexural moduli are commercially available, and those having a predetermined flexural modulus can be obtained by selecting or mixing them. Flexural modulus of 3500kg / cm if smaller than ² becomes too soft cover, the flight distance is insufficient, too hard and feel of the ball striking in the case greater than 6000kg / cm ^2, not appropriate.

The method of coating the cover on the inner core is sometimes not limited,
Usually, the inner core is wrapped with two covers that have been formed into a hemispherical shell shape in advance, and the mixture is heated and pressed. However, the cover composition may be injection-molded to wrap the inner core.

The amount of compressive deformation of the obtained golf ball also affects the feel at impact and the spin performance. The amount of compressive deformation referred to here is 10 kg from the initial load to 130
This is the amount of deformation of the ball when multiplied by kg, and in the case of the present invention, 2.2 to 3.0 mm is preferable. When the amount of compressive deformation is 2.2 mm or less, the ball is too hard and the feel on impact becomes poor. If it exceeds 3.0 mm, the ball becomes too soft and the spin performance deteriorates, which is not preferable.

The two-piece solid golf ball of the present invention has a suitable combination in various properties of the cover and the amount of compressive deformation of the ball. In particular, cover thickness 1.0 to 1.7 mm, cover bending elastic modulus 4000 to 6000 kg / cm ^2, and ball compression deformation amount 2.2 to 2.8 mm (desirably 2.3 to 2.6 mm).
Is preferred. Further, the cover thickness 1.3 to 2.
0 mm, flexural modulus of 3500 to 5000 kg / cm ² and compressive deformation amount of 2.3 to 3.0 mm (desirably 2.4 to 2.8 mm)
Is preferred.

(Example) The present invention will be described in more detail based on an example.

Example I and Comparative Example I <Preparation of Inner Core> The compounds shown in Table-1 were kneaded using a kneading roll and pressure-molded under the vulcanization conditions shown in Table-1 to obtain five kinds of inner cores (I to V). Prepared. Table 1 shows the hardness distribution measured by the JIS-C type hardness meter.

<Preparation of Two-Piece Golf Ball> The inner core is wrapped with two hemispherical shell-like covers obtained from a mixture of cover resins shown in Table-2 in a combination shown in Table-3,
A large size two-piece solid golf ball having a diameter of 42.8 mm was manufactured by pressure molding at 155 ° C. for 5 minutes. Table 3 shows various physical properties of the obtained golf ball.

Comparing balls 1, 2, and 3, the higher the bending elastic modulus of the cover, the harder the ball and the faster the initial velocity, but the more difficult it is to spin. Two-piece balls currently on the market use an ionomer resin with a flexural modulus of 2500 to 3500 kg / cm ² , so spin is relatively high in terms of material, but compared to thread-wound golf balls, Not enough. On the other hand, if the bending elastic modulus is high, the feel at the time of hitting is deteriorated, so for a two-piece ball which is considered to be still hard at this time, a material having a higher bending elastic modulus has a higher ball initial velocity ( Inappropriate (without inner core).

Comparing balls 3 and 4, when the cover becomes thinner,
Although it tends to spin, the durability of the ball deteriorates and the feel on hit is improved, but it still feels a little hard. Therefore, from the conventional viewpoint, in order to reduce the thickness of the cover, it is better to make the bending elastic modulus of the cover softer (when the inner core of the present invention is not used).

Comparing the balls 1, 2, 3, 4 and the ball 7 (invention), it was found that the invention has a higher initial ball velocity, better durability and a larger contact area. Therefore, the spin was good and the feeling was good. Even if the cover bending elastic modulus is high, the feeling is not hard, and the deformation at the time of hitting is large, so the area in contact with the club is large and the ball's initial velocity is fast, so the characteristics of the wound ball with good spin are A equipped two-piece solid golf ball was obtained.

Comparing Ball 7 (invention) and Ball 5 (comparative), the hardness of the inner core of Ball 5 is too soft, so the ball hardness becomes too soft, and as a result, the spin amount also becomes small.

Comparing the balls 4 and 6 (comparative) with the ball (invention), the ball 7 was softer than the ball 4 and harder than the ball 6, but the feeling was better than both. This is because the hardness distribution of the inner cores of the balls 4 and 6, particularly the hardness of the surface portion, is too high, resulting in less spin and poor feeling.

Example II and Comparative Example II An inner core was obtained in the same manner as in Example I from the formulation and vulcanization conditions shown in Table 4, and a cover was placed on the inner core to obtain a small size two-piece ball having a diameter of about 41.3 mm. The various characteristics are shown in Table-4.

Looking at the balls 8 to 11, the balls having proper inner core hardness distribution, cover thickness, cover bending elastic modulus, and ball compression deformation amount have a high initial velocity of the ball and a large contact area at the time of impact. It can be seen that it takes a lot of time and feels good when hit.

(Effect of the Invention) According to the present invention, while maintaining the excellent characteristics of the two-piece solid golf ball such as the initial velocity of the ball, the spin performance is enhanced and the controllability of the ball during iron shot is greatly improved.

Claims (9)

[Claims] 1. A two-piece solid golf ball comprising an inner core and a cover, wherein the inner core has a surface hardness of 55 to 75 measured by a JIS-C type hardness meter and a cross-section hardness excluding the surface layer of 75 to 90. Has a thickness of 0.7 to 2.2 mm,
A two-piece solid having a flexural modulus of 3500 to 6000 kg / cm ² and having a compressive deformation amount of 2.2 to 3.0 mm when a two-piece solid golf ball is subjected to an initial load of 10 kg and a final load of 130 kg. Golf ball. 2. A golf ball according to claim 1, wherein the surface hardness of the inner core is 65 to 70. 3. The golf ball of claim 1, wherein the inner core has a sectional hardness of 80 to 85. 4. A golf ball according to claim 1, wherein the cover has a thickness of 1.0 to 2.0 mm. 5. The flexural modulus of the cover is 4000-5000.
The golf ball according to claim 1, wherein the golf ball is kg / cm ² . 6. A cover having a thickness of 1.0 to 1.7 mm, a flexural modulus of the cover of 4000 to 6000 kg / cm ² , and a golf ball having a compressive deformation amount of 2.2 to 2.8 mm. The golf ball according to item 1. 7. A sixth compression deformation amount of 2.3 to 2.6 mm
The golf ball according to the item. 8. The cover has a thickness of 1.3 to 2.0 mm, the cover has a bending elastic modulus of 3500 to 5000 kg / cm ² , and the ball has a compressive deformation amount of 2.3 to 3.0 mm. The golf ball according to item 1. 9. An eighth compression deformation amount of 2.4 to 2.8 mm
The golf ball according to the item.