Golf ball

Abstract

A one-piece solid golf ball including a matrix containing one or more rubber components in which butadiene rubber is a predominant component, and pulverized rubber obtained by pulverizing a one-piece solid golf ball predominantly containing butadiene rubber, wherein the pulverized rubber is incorporated in amount of 1-30 parts by mass on the basis of 100 parts by mass of the rubber components of the matrix. Also disclosed is a multi-piece golf ball including a core and one or more cover layers, the core including a matrix and pulverized rubber obtained by pulverizing a one-piece solid golf ball, the matrix containing one or more rubber components, wherein the pulverized rubber is incorporated in amount of 1-30 parts by mass on the basis of 100 parts by mass of the rubber components of the matrix.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a one-piece solid golf ball and a multi-piece solid golf ball which have suppressed restitution and attain a short carrying distance, making them suitable for use on golf practice ranges.

[0003] 2. Description of the Related Art

[0004] In many cases, one-piece solid golf balls (hereinafter may be referred to as simply “one-piece balls”) are used on golf practice ranges (hereinafter the expression “balls used on golf practice ranges” will be simplified to “practice golf balls”), although the golf balls may be used as course balls (i.e., balls used on golf courses). In Japan, where most golf practice ranges are small, one-piece balls are designed so as to attain a short carrying distance and have durability against repeated hitting in view of production costs. Customary practice golf balls are designed so as to have a hardness slightly higher than that of course balls (i.e., balls used on golf courses).

[0005] In recent years, the carrying distance of golf balls has been increased considerably in association with improvement of golf clubs. As a result, in Japan, where most golf practice ranges are small, there arises the problem that hit golf balls tend to fly outside the practice ranges. Therefore, demand has increased for one-piece balls of suppressed restitution and short carrying distance which are suited for use as practice golf balls.

[0006] In connection with this demand, conventionally, there has been disclosed a one-piece ball of short carrying distance, which contains base rubber (100 parts by weight) and acrylonitrile-butadiene rubber (3-40 parts by weight) (Japanese Patent Application Laid-Open (kokal) No. 7-24087).

[0007] However, the one-piece ball disclosed in Japanese Patent Application Laid-Open (kokai) No. 7-24087 involves a problem in terms of production.

[0008] Specifically, since rubber materials having different properties must be kneaded during the production process, a method for feeding the materials during the kneading step must be controlled and an optimum kneading temperature must be determined, rendering the overall production techniques complicated.

[0009] Meanwhile, among golf practice range owners, there has been demand for use of multi-piece golf balls, such as two-piece solid golf balls and three-piece solid golf balls, which are used on golf courses, so as to distinguish their businesses from other golf practice ranges.

[0010] From golfers' viewpoints, golfers have complained about conventional practice golf balls, in that they cannot acquire a distance sensation regardless of how much they practice with the practice balls, due to the difference in carrying distance between the practice balls and course balls. Also, golfers complain that they cannot practice in an effective way with customary practice golf balls, because of the difference in ball trajectory for an approach shot (shot angle; i.e., the height of shot ball) between the practice balls and course balls, the difference being attributed to the difference in hardness between the practice balls and course balls.

[0011] However, conventional multi-piece golf balls cannot be used as practice golf balls, since the balls have a very long carrying distance, and they may fly outside golf practice ranges upon being hit. For example, when a conventional practice one-piece golf ball is shot at 1,376 rpm, the initial velocity of the ball is about 74 m/s as measured by use of a USGA-type initial velocity meter, whereas when a commercially available multi-piece golf ball is shot at 1,376 rpm, the initial velocity of the ball is about 77 m/s as measured by use of the meter. When the difference in carrying distance between the one-piece golf ball and the multi-piece golf ball is estimated on the sole basis of the difference in initial velocity; i.e., when differences attributed to dimples and other factors are neglected, the difference in carrying distance is about 20-30m.

[0012] Therefore, in order to realize multi-piece golf balls which are suitable as practice golf balls, the carrying distance of the multi-piece balls must be reduced. However, in view that conventional multi-piece golf balls—having a core coated with one or more covers—have been developed as course balls so as to increase the carrying distance, no practical means have ever been proposed for realizing use of such multi-piece golf balls as practice golf balls of short carrying distance and low cost.

SUMMARY OF THE INVENTION

[0013] In view of the foregoing, a first object of the present invention is to provide, through a simple production process, a one-piece ball of suppressed restitution so as to attain a short carrying distance.

[0014] A second object of the present invention is to provide a multi-piece golf ball of low restitution so as to attain a short carrying distance.

[0015] In order to achieve the first object, the present inventors have performed extensive studies, and have found that when a one-piece ball predominantly containing butadiene rubber contains a pulverized product of a similar one-piece ball in a predetermined amount, the resilience of the one-piece ball is reduced, the initial velocity of the ball upon being hit is lowered appropriately, and the carrying distance of the ball is reduced.

[0016] The present invention has been accomplished on the basis of the above findings. Accordingly, in a first aspect of the present invention, there is provided a one-piece solid golf ball comprising a matrix containing one or more rubber components in which butadiene rubber is a predominant component, and pulverized rubber obtained by pulverizing a one-piece solid golf ball predominantly containing butadiene rubber, wherein the pulverized rubber is incorporated in an amount of 1-30 parts by mass on the basis of 100 parts by mass of the rubber components of the matrix.

[0017] In order to achieve the second object, the present inventors have performed extensive studies, and have found that when a multi-piece golf ball containing a core and one or more cover layers contains a predetermined amount of a pulverized one-piece ball in the matrix of the core, the resilience of the multi-piece ball is reduced, the initial velocity of the ball upon being hit is appropriately lowered, and the carrying distance of the ball is reduced.

[0018] The present invention has been accomplished on the basis of the above findings. Accordingly, in a second aspect of the present invention, there is provided a multi-piece golf ball comprising a core and one or more cover layers, the core comprising a matrix and pulverized rubber obtained by pulverizing a one-piece solid golf ball, the matrix containing one or more rubber components, wherein the pulverized rubber is incorporated in an amount of 1-30 parts by mass on the basis of 100 parts by mass of the rubber components of the matrix.

DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

[0019] The present invention will next be described in detail. In the first aspect of the present invention, pulverized rubber obtained by pulverizing a one-piece ball predominantly containing butadiene rubber is incorporated into the matrix of a one-piece ball predominantly containing butadiene rubber.

[0020] Typical examples of the butadiene rubber include 1,4-cis-polybutadiene. As used in connection with the first aspect of the present invention, the term “matrix” refers to a rubber composition serving as a rubber base material of the one-piece ball.

[0021] In the second aspect of the present invention, pulverized rubber obtained by pulverizing a one-piece ball is incorporated into the matrix of the core of a multi-piece golf ball. As used in connection with the second aspect of the present invention, the term “matrix” refers to a rubber composition serving as a rubber base material of the core. Examples of the matrix of the core of the multi-piece golf ball include a composition predominantly containing butadiene rubber, such as 1,4-cis-polybutadiene, which is cross-linked by a cross-linking agent predominantly containing zinc acrylate. Examples of the one-piece ball from which the pulverized rubber is obtained include a one-piece ball predominantly containing butadiene rubber, such as 1,4-cis-polybutadiene, which is cross-linked by a cross-linking agent predominantly containing methacrylic acid and zinc.

[0022] In the first and second aspects of the present invention, preferably, the pulverized rubber is prepared so as to contain rubber particles having an average size of more than 0.80 mm in an amount of about 30%, and rubber particles having an average size of 0.80 mm or less in an amount of about 70%. The average particle size is determined by averaging the diameters of 100 rubber particles which are randomly selected from the pulverized rubber particles, each particle being regarded as a sphere.

[0023] The pulverized rubber may be obtained by pulverizing a one-piece ball after the surface coating of the ball is removed, or may be obtained by pulverizing a one-piece ball having a surface coating. In the latter case, a step of removing the surface coating can be omitted during production of the pulverized rubber. In general, surface coating of a one-piece ball is performed as follows: the surface of the ball is covered with white coating after the ball is formed through vulcanization; a marking for discernment (e.g., brand name or logo) is printed on the surface; and the resultant surface is subjected to clear coating for reinforcing the surface.

[0024] In consideration of kneadability and durability, the amount of the pulverized rubber to be incorporated is 1-30 parts by mass, preferably 5-20 parts by mass, on the basis of 100 parts by mass of rubber components of the aforementioned matrix. When the amount is less than one part by mass, the resilience of the resultant ball cannot be effectively reduced, resulting in failure to reduce the initial velocity of the ball, whereas when the incorporation amount exceeds 30 parts by mass, the pulverized rubber cannot be fed into a rotor of a kneader during a kneading process, resulting in considerably poor workability of kneading.

[0025] When the one-piece ball of the first aspect of the present invention is hit by a driver, preferably, the total carrying distance of the ball having a reduced initial velocity is about 4-5 m shorter than that of a conventional one-piece ball.

[0026] The one-piece ball of the first aspect of the present invention can be recycled repeatedly. Furthermore, a conventional one-piece ball exhibiting excellent durability—specifically, in a durability test in which the one-piece ball is repeatedly hit by use of a driver at a head speed of 45 m/s, the ball is not broken until when the ball is hit 1,500 times—is pulverized and incorporated into the one-piece ball of the first aspect of the present invention, and thus durability of the one-piece ball is lowered by a very small amount. Therefore, according to the first aspect of the present invention, recycling of the one-piece ball containing pulverized rubber can be repeated; i.e., pulverized rubber can be obtained from the one-piece ball repeatedly.

EXAMPLES

[0027] (First Aspect of the Present Invention)

[0028] A commercially available one-piece ball was pulverized by use of a pulverizer, to thereby produce pulverized rubber. The composition of the matrix of the one-piece ball is shown in Table 1. 1 TABLE 1 Component Amount (parts by mass) 1,4-Cis-polybutadiene 100 Methacrylic acid 20.0 Zinc oxide 23.0 Dicumyl peroxide 1.5

[0029] Subsequently, the resultant pulverized rubber was kneaded into the matrix of a one-piece ball predominantly containing butadiene rubber, to thereby produce a one-piece ball (Examples 1 through 3). In Comparative Example 1, a conventional one-piece ball predominantly containing butadiene rubber was produced. Table 2 shows the compositions of the one-piece balls of Examples 1 through 3 and Comparative Example 1. In each of Examples 1 through 3 and Comparative Example 1, predetermined vulcanization, removal of burrs, and coating were carried out, to thereby complete formation of a one-piece ball. Thereafter, the resultant one-piece ball was subjected to measurement of outer diameter, weight, hardness, initial velocity, and durability against hitting by means of the below-described methods. Kneadability of the pulverized rubber was evaluated during production of the one-piece ball. The results are shown in Table 2.

[0030] Outer Diameter

[0031] The outer diameter of the one-piece ball was measured at 15 points by use of a dial gauge.

[0032] Hardness

[0033] The hardness of the one-piece ball was measured at 10-130 kg by use of a &mgr; hardness meter (N=30).

[0034] Initial Velocity

[0035] The initial velocity of the one-piece ball shot at 1,376 rpm was measured by use of a USGA-type initial velocity meter.

[0036] Durability Against Hitting

[0037] The one-piece ball was repeatedly hit at a head speed of 45 m/s by use of a driver (No. 1 wood) (N=10), to thereby measure the smallest number of hits at which the ball began to crack (the number of hits at which cracking started), as well as the average number of hits at which the ball began to crack (the average number of hits at which cracking started).

[0038] Kneadability

[0039] Kneadability of the pulverized rubber was evaluated according to the following criteria.

[0040] ∘: Good

[0041] &Dgr;: Slightly poor 2 TABLE 2 Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 1 Composition 1,4-Cis-polybutadiene 100 100 100 100 (parts by mass) Methacrylic acid 20.0 20.0 20.0 20.0 Zinc oxide 23.0 23.0 23.0 23.0 Dicumyl peroxide 1.5 1.5 1.5 1.5 Pulverized rubber 10 20 30 0 Product Outer diameter (mm) 42.64 42.66 42.66 42.65 Weight (g) 45.57 45.55 45.62 45.60 Hardness (mm) 2.67 2.66 2.68 2.66 Initial velocity (m/s) 73.42 73.35 73.22 73.50 Durability The number of hits at 1156 1121 1020 1208 against which cracking started hitting The average number of 1187 1153 1130 1251 hits at which cracking started Kneadability O O O˜&Dgr; —

[0042] As is clear from Table 2, the initial velocity of the one-piece ball of the first aspect of the present invention is lower than that of the conventional one-piece ball of Comparative Example 1, although the one-piece ball of the first aspect of the present invention is nearly identical with the conventional one-piece ball in terms of outer diameter, weight, and hardness. The results also show that the one-piece ball of the first aspect of the present invention exhibits sufficient durability to serve as a practice golf ball, although the durability against hitting becomes slightly poor as the incorporation amount of the pulverized rubber increases. Note: in the case of a typical course ball (game ball), which is not a one-piece ball, the average number of hits at which cracking starts is about 300.

[0043] (Second Aspect of the Present Invention)

[0044] A commercially available one-piece ball was pulverized by use of a pulverizer, to thereby produce pulverized rubber. The matrix formulation of the one-piece ball is shown in Table 1.

[0045] Subsequently, the resultant pulverized rubber was kneaded into the matrix of the core of a two-piece sold golf ball (two-piece ball) predominantly containing butadiene rubber, to thereby produce a two-piece ball (Examples 4 and 5). In Comparative Example 2, a conventional two-piece ball was produced. Table 3 shows the compositions of the two-piece balls of Examples 4 and 5 and Comparative Example 2. In each of Examples 4 and 5 and Comparative Example 2, predetermined vulcanization, removal of burrs, cover formation, and coating were carried out, to thereby complete formation of a two-piece ball. Thereafter, the resultant two-piece ball was subjected to measurement of outer diameter, weight, hardness, initial velocity, and durability against hitting by means of the below-described methods. Kneadability of the pulverized rubber was evaluated during production of the two-piece ball. The results are shown in Table 3. When the pulverized rubber was incorporated in an amount of 50 parts by mass on the basis of 100 parts by mass of the rubber component of the matrix of the core, the pulverized rubber could not be satisfactorily fed to a rotor of a kneader, resulting in failure to produce a two-piece ball.

[0046] Outer Diameter

[0047] The outer diameter of the two-piece ball was measured at 15 points by use of a dial gauge.

[0048] Hardness

[0049] The hardness of the two-piece ball was measured at 10-130 kg by use of a &mgr; hardness meter (N=30).

[0050] Initial Velocity

[0051] The initial velocity of the two-piece ball shot at 1,376 rpm was measured by use of a USGA-type initial velocity meter.

[0052] Durability Against Hitting

[0053] The two-piece ball was repeatedly hit at a head speed of 45 m/s by use of a driver (No. 1 wood) (N=10), to thereby measure the smallest number of hits at which the ball began to crack (the number of hits at which cracking started), as well as the average number of hits at which the ball began to crack (the average number of hits at which cracking started).

[0054] Kneadability

[0055] Kneadability of the pulverized rubber was evaluated according to the following criteria.

[0056] ∘: Good

[0057] &Dgr;: Slightly poor 3 TABLE 3 Comp. Ex. 4 Ex. 5 Ex. 2 Compo- 1,4-Cis-polybutadiene 100 100 100 sition Zinc acrylate 25.0 25.0 25.0 *1 Zinc oxide 30.0 30.0 30.0 (parts Aging preventive agent 0.1 0.1 0.1 by Dicumyl peroxide 0.6 0.6 0.6 mass) Pulverized rubber 10 30 0 Product Outer diameter (mm) 42.71 42.71 42.72 Weight (g) 45.16 45.05 45.23 Hardness (mm) 3.03 3.23 2.92 Initial velocity (m/s) 77.10 76.90 77.30 Durability The number of hits at 342 333 350 against which cracking started hitting The average number of hits at which cracking 403 393 412 started Kneadability &ogr; &ogr;˜&Dgr; — *1: Composition of the core of the two-piece ball

[0058] As is clear from Table 3, the initial velocity of the two-piece ball of the second aspect of the present invention decreases as the incorporation amount of the pulverized rubber increases, and the initial velocity of the two-piece ball is lower than that of the conventional two-piece ball of Comparative Example 2, although the two-piece ball of the second aspect of the present invention is nearly identical with the conventional one-piece ball in terms of outer diameter, weight, hardness, and durability. Therefore, the great difference in carrying distance between a course ball (two-piece ball) and a practice golf ball (one-piece ball) can be reduced to about 3-10 mn.

[0059] The one-piece solid golf ball of the first aspect of the present invention has suppressed restitution to thereby attain a reduced carrying distance and is easily produced, with feeling on impact and durability being maintained at the level of a conventional one-piece ball. Also, the one-piece solid golf ball is advantageous in that it can be recycled repeatedly.

[0060] The multi-piece golf ball of the second aspect of the present invention has low restitution and thus attains a short carrying distance, and is suitable for use as a practice golf ball. Specifically, the multi-piece golf ball has the following advantages.

[0061] (1) According to the second aspect of the present invention, when pulverized rubber is incorporated in an appropriate amount into the core of a multi-piece golf ball, the resilience of the core is reduced, resulting in reduction of the initial velocity of the ball upon being hit. As a result, the aforementioned great difference in carrying distance between a course ball and a practice golf ball, which is estimated to 20-30 m, can be reduced to about 3-10 m.

[0062] (2) A conventional practice one-piece golf ball has induced miss shots (i.e., an intended carrying distance of the ball is not obtained) at a golf course, since the trajectory of the one-piece ball differs from that of a course ball, by virtue of the difference in spin amount between these balls, the difference being attributed to the difference in hardness. However, when the multi-piece golf ball is used for golf practice, since the trajectory of the ball is similar to that of a course ball, the aforementioned miss shot can be prevented.

[0063] (3) Since the multi-piece golf ball of the second aspect of the present invention contains pulverized rubber, the material cost of the ball is reduced. Therefore, even when the multi-piece ball is produced as a practice golf ball, the production cost of the ball is maintained at a commercially practicable level.

Claims

1. A one-piece solid golf ball comprising a matrix containing one or more rubber components in which butadiene rubber is a predominant component, and pulverized rubber obtained by pulverizing a one-piece solid golf ball predominantly containing butadiene rubber, wherein the pulverized rubber is incorporated in amount of 1-30 parts by mass on the basis of 100 parts by mass of the rubber components of the matrix.

2. A one-piece solid golf ball according to claim 1, wherein the butadiene rubber is 1,4-cis-polybutadiene.

3. A one-piece solid golf ball according to claim 1, wherein the pulverized rubber is incorporated in an amount of 5-20 parts by mass on the basis of 100 parts by mass of the rubber components of the matrix.

4. A one-piece solid golf ball according to claim 1, wherein the pulverized rubber comprises rubber particles having an average size of more than 0.80 mm and rubber particles having an average size of 0.80 mm or less, in an amount of about 30% and in an amount of about 70%, respectively.

5. A multi-piece golf ball comprising a core and one or more cover layers, the core comprising a matrix and pulverized rubber obtained by pulverizing a one-piece solid golf ball, the matrix containing one or more rubber components, wherein the pulverized rubber is incorporated in an amount of 1-30 parts by mass on the basis of 100 parts by mass of the rubber components of the matrix.

6. A multi-piece golf ball according to claim 5, wherein the matrix of the core predominantly contains butadiene rubber, such as 1,4-cis-polybutadiene, which is cross-linked by use of a cross-linking agent predominantly containing zinc acrylate.

7. A multi-piece golf ball according to claim 5, wherein the one-piece solid golf ball from which the pulverized rubber is obtained predominantly contains butadiene rubber, such as 1,4-cis-polybutadiene, which is cross-linked by use of a cross-linking agent predominantly containing methacrylic acid and zinc.

8. A multi-piece golf ball according to claim 5, wherein the pulverized rubber is incorporated in an amount of 5-20 parts by mass on the basis of 100 parts by mass of the rubber components of the matrix.

9. A multi-piece golf ball according to claim 5, wherein the pulverized rubber comprises rubber particles having an average size of more than 0.80 mm and rubber particles having an average size of 0.80 mm or less, in an amount of about 30% and in an amount of about 70%, respectively.