WO2002024802A1

WO2002024802A1 - Golf ball cover and method of manufacture

Info

Publication number: WO2002024802A1
Application number: PCT/US2001/029440
Authority: WO
Inventors: Hyun Jin Kim
Original assignee: Taylor Made Golf Company, Inc.
Priority date: 2000-09-22
Filing date: 2001-09-19
Publication date: 2002-03-28
Also published as: JP2004509675A

Abstract

A golf ball cover incorporates ionomer and a specified block copolymer in specified weight ratio ranges. Also, a method includes a step of a blending ionomer and the specified block copolymer within a specified weight ratio for preparing a golf ball cover composition. The specified weight ratios define compositions outside the scope of those previously considered suitable for ball covers. The ball covers provide for improved ball performance with respect to spin rate, feel, and durability.

Description

GOLF BALL COVER AND METHOD OF MANUFACTURE

BACKGROUND OF THE INVENTION

This invention relates generally to golf ball covers and, more particularly, to golf ball covers made from a composition that optimizes ball performance, and it also relates to methods of manufacture of such ball covers.

Golf balls generally include a core and at least one cover layer surrounding the core. Balls can be classified as two-piece, multi-layer, or wound balls. Two-piece balls include a spherical inner core and an outer cover layer. Multi-layer balls include a core, a cover layer, and one or more intermediate layers. Wound balls include a core, a rubber thread wound under tension around the core to a desired diameter, and a cover layer, typically of balata material.

Generally, two-piece balls have good durability and ball distance when hit, but poor "feel"-the overall sensation transmitted to the golfer while hitting the ball-and low spin rate, which results in poor ball control. Wound balls having balata covers generally have high spin rate, leading to good control, and good feel, but they have short distance and poor durability in comparison to two- piece balls. Multi-layer balls generally have performance characteristics between those of two-piece and wound balls; that is, multi-layer balls exhibit distance and durability inferior to two-piece balls but superior to wound balata balls, and they exhibit feel and spin rate inferior to wound balata balls but superior to two-piece balls.

Material characteristics of the compositions used in the core, cover, and any intermediate layers are among the important factors that determine the performance of the resulting golf balls. In particular, the composition of the cover layer is important in determining the ball's durability, scuff resistance, speed, shear resistance, spin rate, "click" (the sound made by a golf club head when it hits the ball), and feel. Various materials having different physical properties are used to make cover layers to create a ball having the most desirable performance possible. For example, many modern cover layers are made using soft or hard ionomeric resins, elastomeric resins, or blends of these. Ionomeric resins used generally are ionic copolymers of an olefin and a metal salt of a unsaturated carboxylic acid, or ionomeric terpolymers having a co-monomer within its structure. These resins vary in resiliency, flexural modulus, and hardness. Examples of these resins include those marketed under the name SURLYN manufactured by E.I. DuPont de

Nemours & Company of Wilmington, Delaware, and IOTEK manufactured by Exxon Mobil Corporation of Irving, Texas. Elastomeric resins used in golf ball covers include a variety of thermoplastic or thermoset elastomers available.

Each of the materials discussed above has particular characteristics that can lead to good golf ball properties when used in a ball cover. However, one material generally cannot optimize all of the important properties of a golf ball cover. Properties such as feel, spin rate, resilience, and durability all are of importance, but improvement of one of these properties by use of a particular material often can lead to worsening of another. For example, ideally, a golf ball cover should have low hardness, high spin rate, and good feel, without sacrificing ball speed, distance, or durability. Such a cover would be difficult to make using only an ionomer resin having a high flexural modulus, because the resulting cover, while having good distance and durability, also will have poor feel and low spin rate, leading to reduced controllability of the ball.

Therefore, to improve golf ball properties, some of the materials discussed above can be blended to produce improved cover layers. As discussed above, ideally a golf ball cover should provide high spin rate and good feel, without sacrificing the ball's distance and durability. Therefore, an ionomer having a high flexural modulus often is combined in a cover composition with another ionomer or an elastomer having a low flexural modulus. The resulting intermediate-modulus blend will have acceptable hardness, spin, and durability. In addition to the above materials, golf ball compositions also can include various fillers, fibers, colorants, and processing aids to impart additional desirable mechanical or cosmetic properties to the golf ball.

However, even with blending of materials to improve properties, use of the materials discussed above is not completely satisfactory. Improving one characteristic can lead to worsening another. For example, blending an ionomer having a high flexural modulus with an ionomer having a low flexural modulus can lead to reduced resilience and durability compared to use of the high-modulus ionomer alone. In general, it is difficult to make a material for a golf ball cover layer that has low hardness, good feel, high speed, high resilience, and good shear disability.

One material that can be used in golf ball compositions is a block polymer having at least one polymer block comprising an aromatic vinyl compound and at least one polymer block comprising a conjugated diene compound, and having a hydroxyl group at a block copolymer, or its hydrogenated product. The hydroxyl group can be at the terminal block copolymer or elsewhere in the block copolymer structure. An example of this block copolymer having a hydroxyl group at the terminal block copolymer is sold under the trade name HG-252 by Kuraray Company of Kurashiki, Japan. Use of this material in golf ball compositions has been previously disclosed. For example, U.S. Patent No. 5,693,711 to Akiba et al. discloses and claims golf ball cover compositions incorporating the block copolymer and a specified ionomer, with the weight ratio of ionomer to block polymer ranging from 98:2 to 50:50. The disclosed cover composition provides flexibility and toughness to the ball cover. The Akiba et al. patent specifies that the block copolymer must not be used in an amount greater than the specified ratio range, because of the worsening of the durability and oil resistance of the resulting ball cover. The composition disclosed in the Akiba et al. patent, though suited for use in making golf ball covers, is not completely satisfactory in providing optimal ball cover properties.

In view of the above, it is apparent that golf ball covers are needed that allow the optimization of many ball performance properties without the worsening of other properties. The ball covers also should provide little or no processing and preparation difficulties over existing covers. The present invention fulfills this need and other needs, and provides further related advantages.

SUMMARY OF THE INVENTION

The present invention resides in a golf ball cover made from an ionomer and a block copolymer, the block copolymer incorporating a first polymer block having an aromatic vinyl compound, a second polymer block having a conjugated diene compound, and a hydroxyl group located at a block copolymer, or its hydrogenation product, in which the ratio of block copolymer to ionomer ranges from 51:49 to 95:5 by weight, more preferably from about 55:45 to about 80:20 by weight, more preferably from about 55:45 to about 70:30 by weight, and most preferably from about 60:40 to about 70:30 by weight. Additional preferred ranges of the ratio of block copolymer to ionomer ranges include from 51:49 to about 80:20 by weight and from 51:49 to about 70:30 by weight. The ball cover also can include fillers, stabilizers, colorants, processing aids, or antioxidants.

The golf ball cover can be incorporated into a golf ball having a core and one or more layers situated between the core and the cover, including, for example, a layer of rubber thread. The core may comprise multiple layers and may comprise a liquid. The ionomer preferably is a copolymer of an α-olefin and an unsaturated carboxylic acid, or a teipolymer of an α-olefin, an unsaturated carboxylic acid, and a softening comonomer, or a mixture of these.

The present invention also is embodied in a golf ball cover incorporating a high-acid, magnesium-neutralized, high flexural modulus copolymer of an α-olefin and an unsaturated carboxylic acid and a block copolymer incorporating a first polymer block having an aromatic vinyl compound, a second polymer block having a conjugated diene compound, and a hydroxyl group located at a terminal block copolymer, or its hydrogenation product, wherein the ratio of block copolymer to copolymer ranges from 60:40 to 90: 10 by weight.

Additionally, the present invention is embodied in a method for making a composition for use in golf ball covers, comprising blending an ionomer and a block copolymer incorporating a first polymer block having an aromatic vinyl compound, a second polymer block having a conjugated diene compound, and a hydroxyl group located at a block copolymer, or its hydrogenation product, wherein the ratio of block copolymer to ionomer ranges from 51 :49 to about 95:5 by weight.

Other features and advantages of the present invention should become apparent from the following detailed description of the preferred embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is embodied in a golf ball cover that includes an ionomer and the block copolymer discussed above. The invention also is embodied in a method of manufacture of such a ball cover. The cover provides for excellent golf ball cover properties without introducing processing difficulties. In view of the prior disclosures discussing use of the specified block copolymer in ball covers, it has been surprisingly found that including this block copolymer in cover compositions in higher weight ratios than that previously thought suitable produces golf ball covers that are both soft and durable. Preparation and analysis of cover compositions incorporating the block copolymer and ionomers commonly used in golf ball covers show unexpected material characteristics of the blends. Specifically, it is observed that increasing the ratio of block copolymer to ionomer in the cover composition from 2:98 up to 50:50 results in increased spin rate of the ball and decreased hardness and durability of the cover as measured by observed shear resistance. However, upon increasing the ratio of block copolymer to ionomer in the cover composition beyond 50:50, it is surprisingly observed that while spin rate continues to increase and hardness continues to decrease, the shear resistance of the ball begins to increase. That is, at higher percentages of block copolymer in the cover blend, both spin rate and durability increase, while hardness decreases. This performance of the blend is in opposition to the prior understanding of blending these materials.

Examples of suitable ionomers for use in the present invention include copolymer-type ionomers having varied acid contents and degrees of acid neutralization, neutralized by monovalent or bivalent cations, and also terpolymeric ionomers having a comonomer in the structure having varied acid contents and degrees of acid neutralization, neutralized by monovalent or bivalent cations. Examples of these include α-olefin/unsaturated carboxylic acid copolymer-type ionomeric resins and terpolymeric resins having a softening comonomer, such as acrylate or methacrylate. The acid moiety is neutralized to form an ionomer by a cation such as lithium, sodium, potassium, magnesium, calcium, barium, lead, tin, zinc, aluminum, or a combination of these. Examples of these resins include those sold under the trade names SURLYN and IOTEK, discussed above. The ball covers of the present invention include blends of the specified polymer material and ionomer with blend ratios of the specified polymer to ionomer ranging from 51:49 to about 95:5, more preferably from about 55:45 to about 80:20, more preferably from about 60:40 to about 80:20, and most preferably from about 60:40 to about 70:30. Covers incorporating these compositions provide superior ball properties, mcluding high spin rates and high durability. In addition to ionomer and the specified polymer, the ball covers also can be comprised of any of the polymer materials commonly used in golf ball compositions, such as ionomeric and elastomeric resins and block copolymers. Any colorants, stabilizers, antioxidants, processing aids, fillers, or mold release agents commonly used in the manufacture of golf balls also can be used in the covers of the present invention. Ball covers of the present invention can be used in a variety of ball designs, including two-piece, multi-layer, and wound balls, and with balls having solid, liquid, or multi-layer cores.

EXAMPLE

Golf ball covers within the scope of the present invention were prepared. Test golf balls were prepared in which the covers comprised from 60% to 90% by weight of the HG-252 material described above, with the rest of the cover comprising SURLYN 6120, a high-acid, low flexural modulus, magnesium- neutralized copolymer of an α-olefϊn and an unsaturated carboxylic acid. The compositions, flexural moduli, and hardnesses of the cover materials are shown below in Table 1.

The test balls each incorporated a core having a PGA compression of 70. Over each core was placed a mantle layer having a hardness of 37 on the Shore D scale, a flexural modulus of 9.7 kpsi, and a tensile elongation of 717%. Over each mantle layer was placed a cover layer as specified in Blend Nos. 1 to 4 in Table 1. The ball cover compositions were manufactured using conventional compounding techniques.

Testing

The balls were tested for spin rate speed, and ball compression when hit with an 8-iron, and they also were tested for surface hardness on the Shore D scale (as distinguished from the cover material hardness shown in Table 1). The balls also were tested for shear resistance by hitting them with a pitching wedge at controlled speed. Three of each type of ball were used for this testing. Each ball was assigned a numerical score from 1 (no visible damage) to 5 (substantial material displaced), and these scores were averaged for each ball type to produce the shear resistance numbers below.

In addition to the balls incorporating the covers of the present invention, several golf balls currently available on the market were tested for the same parameters. These balls included the Titleist Professional, Titleist Tour Balata, and Titleist HP Tour, manufactured by Acushnet Corporation of Fairhaven, Massachusetts and also the InerGel Pro Distance, manufactured by Taylor Made Golf Company of Carlsbad, California. Results of the tests are show below in Table 2.

Results

The test balls demonstrated spin rate and speed comparable to that of the Titleist Tour Balata balls and much higher than that of the Titleist Professional balls. The test balls demonstrated speed comparable to that of the Titleist HP Tour balls, but with much higher spin rate. When compared to the Taylor Made InerGel Pro Distance balls, the test balls demonstrated lower speed, but with much higher spin rate. The test balls also exhibit lower hardness than the marketed balls, leading to enhanced ball feel. As discussed above, high spin rate is desirable because it allows for improved control of the ball when hit. High ball speed is desirable because it leads greater flying distance of the ball, and low cover hardness and PGA compression provide for improved ball feel. The test balls generally demonstrated ball speeds higher than or roughly equal to that of the marketed balls, despite the fact that low ball hardness generally leads to reduced ball speed. Balls incorporating covers within the scope of the present invention, therefore, overcome design limitations previously known in the manufacture of golf balls, i.e., that softer ball covers generally provide reduced ball speeds. These balls provide good spin rate and feel, as well as good distance performance.

Also, the test balls demonstrated low PGA compressions, within the range of 73 to 76, far better than the Titleist Professional and Taylor Made Pro Distance balls, and comparable to the Titleist Tour Balata and HP Tour balls. The low PGA compressions of the test balls allow for better feel of the ball when hit. The feel and controllability of the test balls is similar to a ball having a wound core and a balata cover. Additionally, the test balls demonstrated shear resistance, and therefore durability, either comparable to or far superior to that of the marketed balls. In particular, Type # 2 and #3 balls exhibited durability comparable to the Titleist HP Tour and Taylor Made InerGel Pro Distance, and Type #1 balls exhibited durability comparable to the Titleist Professional balls. All of the test balls demonstrated shear resistance far better than that of the Titleist Tour Balata balls.

In general, even though low cover hardness typically leads to poor shear resistance, the low hardness test balls generally exhibited durability equal to or better than the harder marketed balls. As mentioned above, the test balls provide for ball feel comparable to that of wound balata balls, but with far superior durability. Overall, the test results for shear resistance indicate that balls mcorporating cover compositions within the scope of the present invention provide for a combination of low cover hardness and high shear resistance in comparison to balls currently available.

Generally, it is difficult to produce golf balls having high spin rate, long distance when hit, low PGA compression, soft feel, and good durability. The test balls incorporating ball covers within the scope of the present invention exhibited all of these. As discussed above, these performance results contradict the prior understanding of the effect of increasing percentages of the specified block copolymer on ball cover durability. The performance of the test balls demonstrates the utility of the ball covers of the present invention in maximizing desirable ball properties.

Although the invention has been disclosed in detail with reference only to the preferred embodiments, those skilled in the art will appreciate that additional golf ball covers can be made without departing from the scope of the invention.

Claims

I claim:

1. A golf ball cover comprising an ionomer and a block copolymer, the block copolymer comprising a first polymer block comprising an aromatic vinyl compound, a second polymer block comprising a conjugated diene compound, and a hydroxyl group located at a block copolymer, or its hydrogenation product, wherein the ratio of block copolymer to ionomer ranges from 51:49 to about 95:5 by weight.

2. A golf ball cover as defined in claim 1, wherein the ratio of block copolymer to ionomer ranges from about 55:45 to about 80:20 by weight.

3. A golf ball cover as defined in claim 1, wherein the ratio of block copolymer to ionomer ranges from about 55:45 to about 70:30 by weight.

4. A golf ball cover as defined in claim 1, wherein the ratio of block copolymer to ionomer ranges from about 60:40 to about 70:30 by weight.

5. A golf ball cover as defined in claim 1, wherein the ratio of block copolymer to ionomer ranges from 51:49 to about 80:20 by weight.

6. A golf ball cover as defined in claim 1, wherein the ratio of block copolymer to ionomer ranges from 51:49 to about 70:30 by weight.

7. A golf ball cover as defined in claim 1, further comprising fillers, stabilizers, colorants, processing aids, antioxidants, or mixtures thereof.

8. A golf ball comprising a core and a cover as defined in claim 1 encasing the core.

9. A golf ball as defined in claim 8, wherein the core comprises an inner core and one or more outer cores encasing the inner core.

10. A golf ball as defined in claim 8, wherein the core comprises liquid.

11. A golf ball as defined in claim 8, further comprising one or more layers situated between the core and the cover.

12. A golf ball as defined in claim 8, further comprising a layer of rubber thread situated between the core and the cover.

13. A golf ball cover as defined in claim 1, wherein the ionomer is selected from the group consisting of: a copolymeric ionomer comprised of an α-olefin and an unsaturated carboxylic acid; and, a terpolymeric ionomer comprised of an α-olefin, an unsaturated carboxylic acid, and a softening comonomer; or mixtures thereof.

14. A golf ball cover comprising an ionomer and a block copolymer, wherein: the ionomer is a high-acid, low flexural modulus copolymer comprised of an α-olefin and an unsaturated carboxylic acid, wherein a portion of the carboxylic acid groups is neutralized by magnesium; the block copolymer comprises a first polymer block comprising an aromatic vinyl compound, a second polymer block comprising a conjugated diene compound, and a hydroxyl group located at a terminal block copolymer, or its hydrogenation product; and the ratio of block copolymer to ionomer ranges from 60:40 to 90:10 by weight.

15. A method for making a composition for use in golf ball covers, comprising a step of blending into the composition an ionomer and a block copolymer, the block copolymer comprising a first polymer block comprising an aromatic vinyl compound, a second polymer block comprising a conjugated diene compound, and a hydroxyl group located at a block copolymer, or its hydrogenation product, wherein the ratio of block copolymer to ionomer ranges from 51:49 to 95:5 by weight.