AU701846B2 - Golf ball and method of manufacturing the same - Google Patents

Description

P:\OPER\MJC5219I-93. DIV -6/&97 -1A- GOLF BALL AND METHOD OF MANUFACTURING THE SAME This invention is a divisional of 52198/93, the entire contents of which is incorporated herein by reference.

This invention relates to a golf ball which can stably elicit carrying or flight properties of dimples and a method of manufacturing the same.

A golf ball has its surface covered with a coat formed of both enamel paint and clear paint, or clear paint alone, so that the ball may be kept clean in its outer appearance and prevented from dirt depositing thereon.

The golf ball is formed on its surface with depressions, called dimples, which are intended to help produce a certain carry.

However, in order to stably elicit carrying properties of which dimples are possessed, it is necessary that the coat of paint which covers the surface of the golf ball must be uniformly distributed. With air gun painting, for example, that is one of the painting techniques commonly used in the art, it is impractical to arrange that the interior of each dimple is uniformly coated. In particular, where the paint is applied thick through a few times of painting, the edge portion of each dimple is, in effect, coated relatively thin; further, the resulting coat involves considerable variations in thickness from part to part of the ball.

P.\OPER\MJC\24779-97.338 4/12/98 -2- Instead of the above discussed air gun painting, attempts have been made to coat the surface of a golf ball by electrostatic painting. However, with the electrostatic painting method employed so far, it has been not possible to positively elicit carrying properties of dimples, because the method can only produce a coat of paint which is excessively thick.

According to the present invention there is provided a golf ball comprising a surface covered with a coat of paint formed by electrostatic painting having a thickness of 5 to S. the ratio of maximum to minimum thickness of the coat being 1 to 2.

According to a second aspect of the invention there is provided a method of preparing a coated golf ball including the step of coating the surface of a golf ball with an atomized 0 paint by supplying a paint to which a voltage of from 50,000 V to 120,000 V is applied to a disk revolving at a velocity of from 15,000 rpm to 35,000 rpm for atomization.

o o •o 0 0: S 15 The golf ball produced as a surface covered with a coat of paint which is within a 0 thickness range of 5 to 60ptm, the ratio of maximum to minimum coat thickness being 1 to 2 so that carrying properties of dimples can be advantageously stabilized.

P:\OPER\M)C\5219393jJDV 6/6/97 -2A- First, the thickness and thickness uniformity of the coat of paint covering the surface of the golf ball will be discussed. When the thickness of the coat is less than the coat may lack durability and its gloss may be lost as a result of several strokes given to the ball. When the coat thickness is more than 60 I/m, even if coating is uniformly effected, the dimples may lose their pre-coat configuration with the result that their carrying properties will change. Therefore, the thickness of the coat is advantageously within the range of 5 to 60 m, especially preferably within the range of to 30 pm.

10 The ratio of maximum to minimum coat thickness (maximum coat thickness minimum coat thickness) represents the degree of uniformity of the coat. When the ratio is greater than 2, the uniformity of the coat may be lost, and dimples may lose their prei coat configuration, which results in changes in the carrying properties of dimples.

a o e it -3- Nextly, methods for coat formation will be discussed. Air gun painting is known as a painting method for forming a coat of paint. In order to form such a coat by air gun painting, however, it is necessary that a few coats of paint, each of 2 to 3 p/m in thickness, must be applied, which results in level degradation and unsightly appearance.

Where the conventional electrostatic painting method is employed, it is impractical to run a disk at a rotational speed of more than 10,000 rpm. Therefore, paint atomization by the coating machine does not provide paint particles of sufficiently fine size. Consequently, the

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960702&p:\Oper\hdd.5219&9. .spe.3 4 paint coat at the edge portion of each dimple is thinner than that at other portion of the dimple, no uniform coat being obtainable within the thickness range of 5 to 60 pm, with respect to the edge portion.

Hence, according to the invention, a paint to which has been applied a voltage of more than 50,000 V is supplied to a disk revolving at a speed of more than 15,000 rpm for atomization, and the atomized paint is coated on the surface of the golf ball to form a paint coat.

0 In other words, since the paint is supplied to the disk which is in rotation at such a high velocity as W4** more than 15,000 rpm for atomization of the paint, fine paint particles can be obtained, so that the coat at the edge portion of each dimple can be formed to a thickness similar to that at other portion of the dimple. Thus, it is possible to obtain a uniform coat that is within a thickness range of 5 to 60 pm, with the ratio of maximum to minimum coat thickness being less than 2.

According to the present invention, in carrying out electrostatic coating, the voltage applied to the paint is more than 50,000 V, preferably more than 80,000 V, especially preferably 90,000 to 120,000 V. The speed of rotation of the disk is preferably more than 15,000 rpm, especially preferably 25,000 to 35,000 rpm.

It is preferable that the surface of the golf ball to which a paint coat is to be applied is previously coated with an electroconductive agent so as to readily enable the ball to adsorb charged paint particles. For such conductive agent, quaternary amine or the like is preferred which will absorb airborne moisture after it is coated on the golf ball.

Preferably, charged paint particles are applied so as for them to enclose the golf ball; and it is especially preferable that they are applied from the lower portion of the ball. Also, it is preferable that the golf ball is kept in rotation during the process of coating.

According to the invention, it is possible to uniformize the paint coat covering the "surface of the golf ball, thereby to stably elicit carrying properties of which dimples o, possess.

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~Fig. 1 is a view schematically illustrating a dimple and its periphery on the 15 surface of the golf ball of the invention.

.,o o To further illustrate the invention, the following examples are given together with comparison examples but are not meant to limit the scope of the claims in any way.

Examples 1 to 4, and Comparison Examples 1 to 8 Golf balls were formed on their respective surfaces with dimples according to the following specifications and were subjected to surface coating. Evaluation was made with respect to their characteristics.

1. Golf balls used: 9 6 O7O2,p:\oper\&d.S2198-9 3 6 Two-piece golf balls each comprising a core formed by vulcanizing a rubber composition, and a cover formed principally of an ionomer rubber, the core being covered with the cover.

2. Number of dimples formed on each golf ball: Dimples were formed in either of the following two ways, with respect to their number.

A 432 B 342 3. Coating methods: *C electrostatic painting; disk diameter 80 mm D electrostatic painting; disk diameter 200 mm E air gun painting, 1 time coat F air gun painting, 2 time coat G electrostatic painting; disk diameter 200 mm In electrostatic painting C, D and G, the voltage applied to the paint was 90,000 V, and speed ranges of disk rotation were C: 25,000 to 35,000 rpm; D: 7,000 to 9,000 rpm; and G: 7,000 to 9,000, as shown in Table 1 given hereinafter.

The speed of ball rotation during the process of electrostatic painting was 50 rpm. After painting, each ball was dried at a temperature of less than 50 for 24 hours. In cases C, D and G, for the purpose of electrostatic painting, the surface of the ball was previously coated with Plaslac Electroconductive Agent NC (trade name available 7 from Cashew Co.) that had been diluted with isopropyl alcohol to a concentration of 1 In cases E and F for air gun painting, the pressure applied during the painting process was 2 kg/cm 2 4. Paint Clear paint only was used.

Coating amounts on sample balls were: 200 mg one minute after coat application, in each of cases C to E; 100 mg in case F; and 500 mg in case G.

i 5. Manner of Evaluation Evaluation was made on four items: appearance, coat thickness, maximum coat thickness minimum coat thickness, and carrying property or flight performance.

Appearance: For each example, 12 golf balls were visually observed in respect of their appearance.

."-Observation results are expressed on the basis of the following evaluation criteria: 0: generally uniform in color and dimples are clearly contoured; a: dimple edge portion is slightly lighter in color than other portion, but dimples are clearly contoured; and x: dimple edge portion is noticeably different in color from other portion, or dimples are not clearly contoured.

8 Coat thickness: Using 12 golf balls as samples, measurements were made with three portions of each golf ball, at four positions designated H, I, J and K in Fig. 1; and with respect to each measured portion, the average of coat thickness values measured at the four positions was taken as the coat thickness of that particular portion.

On the basis of the measurements was 10 determined the average for each golf ball.

Then, an average was determined for the 12 golf balls. Evaluation results are shown in overall average values and R (difference between maximum value and minimum value) values.

Referring to Fig. i, there is schematically shown a portion of a golf ball including a dimple and its periphery on the surface of the ball. In the drawing, H, I, J, K represent the following positions.

H: dimple center, or deepmost portion of the dimple; I: edge portion of the dimple; j: midportion between the dimple center and the edge portion; and K: peripheral surface portion of the dimple.

Max. coat thickness min. coat thickness: Calculated on the basis of the measurements of coat thickness in above. The results are shown 9 in both average and R values.

Carrying property: In each example, 12 golf balls were used as samples, which were tested by employing a swing robot of True Temper's make in such a way that each ball was hit by a No. 1 wood club at a head speed of 45 m/s.

The carry of the ball and the height of its flight trajectory were measured. The results are shown in both average and R values. Tests were carried out under the conditions of no wind and 24°C.

C.The height of the flight trajectory of each hit ball is expressed by the angle which a straight line connecting between the highest point of the trajectory and the point of hitting makes with the e CC horizontal.

The appearance evaluation results, coat thickness measurement results, and maximum coat thickness minimum coat thickness ratios are shown in Table 1, and the carrying property measurement results are shown in Table 2.

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9 9 9 9 999 99 9 9 9 9*9 9 9 99 Table 1: r~ No. No. of dimples Coating Appearance Coat thickness (Pm) Max. coat thickness Min coat thickness Method Rotary speed (rpm) Aver. Aver.

A I 4. 1 t t Example 25, 000 000 35,000 000 18.5 19.3 18. 1 19.5 2.1 1.4 1.9 1.7 1.53 1.31 1.61 1 .40 0.24 0.20 0.31 0.26 I t I I i Comparison example 2 3 4 6 7 8 7,000 9,000 9,000 18.6 18.9 19.4 18.8 19. 1 19. 6 18.9 65.3 4.5 3.0 2.3 10.9 11.2 8.3 7.8 20.0 4.80 2 .30 2.40 7.80 8.80 2.60 2.50 1.50 1.80 0.60 0.60 3.50 3.20 0.80 0.70 0.21 9,000 .1 9** C CCC C CCC C

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No N.of Crrig rpet No.

dimples trrying property Carry (yard) Height of flight trajectory() Aver Aver.

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.1 I r 231.3 1.2 13.8 0.20 Example Comparison example 2 3 4 1 2 3 4 6 7 8

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231.7 231.0 230. 8 1.1 1.1 1.6 13.7 13 .8 13.4 0.20 0.10 0.20 230.5 3.0 14.0 0.50 230.9 229.3 228. 1 226.4 230.3 228. 5 210.5 2.1 2.2 3.9 4.1 2.5 4.7 1.7 13. 8 13.6 14.9 14.6 14. 1 13.9 17. 5 0.40 0.40 0.80 0.80 0.50 0.60 0.21 j I .1 12- As may be appreciated from Table 1, balls of Examples 1 to 4 are all satisfactory in appearance and within a coat thickness range of 5 to 60 lum, with a maximum coat thickness minimum coat thickness ratio registered lower than 2, which shows good uniformity of coat thickness. Therefore, as Table 2 shows, balls of Examples 1 to 4 exhibited a greater carry than balls of comparison examples having corresponding numbers of dimples, stably eliciting the potential flight performance of dimples.

In contrast to this, balls of Comparison Examples 1 to 8 are all unsatisfactory in appearance and, although balls of Comparison Examples 1 to 7 are within a coat thickness range of 5 to 60 anyhow, they have a maximum to minimum coat ratio ot' greater than 2, showing lack of coat thickness uniformity. In Comparison Example 8, •in which the coat thickness is particularly large, dimples of each ball have lost their precoat configuration and, therefore, the flight performance or carrying property of the ball is rather low as shown in Table 2.

~Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

960702,p:\oper\add,52198-9 3 .spe.

1 2 P:\OPER\MJC\24779-97.339 -4112/98 -13- THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A golf ball comprising a surface covered with a coat of paint formed by electrostatic painting having a thickness of 5 to 6 0 the ratio of maximum to minimum thickness of the coat being 1 to 2.

2. The golf ball according to claim 1 wherein said coat of paint has a thickness of 10 to 3. A method of manufacturing a golf ball according to claim 1 or claim 2 including the 10 step of coating the surface of a golf ball with an atomized paint by supplying a paint to which a voltage of from 50,000 V to 120,000 V is applied to a disk revolving at a velocity of from 15,000 rpm to 35,000 rpm for atomization.

o 4. A method according to claim 3 wherein the applied voltage is more than 80,000 V.

5. A method according to claim 3 wherein the applied voltage is 90,000 to 120,000 V.

6. A method according to claim 3 wherein the disk is revolved at a velocity of 25,000 to 35,000 rpm.

7. A method according to claim 3 wherein said golf ball is pretreated with an electroconductive agent.

8. A method according to claim 7 wherein the electroconductive agent is a quaternary amine.

9. A golf ball according to claim 1 substantially as hereinbefore described with reference to any one of the examples or drawings.

DATED this 4th day of December, 1998 Sumitomo Rubber Industries, Ltd.

By DAVIES COLLISON CAVE Patent Attorneys for the Applicant