Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-10-23
2003-09-02
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S274000, C473S354000, C473S357000, C473S372000, C473S373000, C473S374000, C473S377000
Reexamination Certificate
active
06613842
ABSTRACT:
FIELD OF INVENTION
The present invention is directed toward novel golf ball core compositions and golf balls comprising such compositions, and to a method for forming golf balls containing such core compositions, particularly golf balls having dual cores. Golf balls of the invention have at least one core layer comprising at least one Low Modulus Ionomer (“LMI”) or corresponding acid terpolymer and a highly-neutralized polymer.
BACKGROUND OF THE INVENTION
Three-piece, wound golf balls with balata covers are preferred by most expert golfers. These balls provide a combination of distance, high spin rate, and control that is not available with other types of golf balls. However, balata is easily damaged in normal play, and, thus, lacks the durability required by the average golfer. Therefore, most amateur golfers typically prefer a solid, two-piece ball with an ionomer cover, which provides a combination of distance and durability. Because of the hard ionomer cover, these balls are almost impossible to cut, but also have a very hard “feel,” which many golfers find unacceptable, and a lower spin rate, making these balls more difficult to draw or fade. The differences in the spin rate can be attributed to the differences in the composition and construction of both the cover and the core.
Recently, multilayer golf balls have become available, in an effort to overcome some of the undesirable aspects of conventional two-piece balls, such as their hard feel, while maintaining the positive attributes of these balls such as their increased initial velocity and distance. Multilayer golf balls typically comprise at least one of multiple core layers, a single or multiple intermediate or mantle layer, and/or multiple cover layers. Ideally, multilayer balls have “feel” and spin characteristics approaching those of wound balls. However, the use of at least one mantle or intermediate layer or of multiple core layers has, in some cases, adversely affected the durability of the core.
A number of elastomers such as polybutadiene, natural rubber, styrene butadiene rubber, and isoprene rubber, have been used in the manufacture of golf ball cores. However, golf ball cores are now predominantly made from compositions comprising polybutadiene. In order to obtain the desired physical properties for golf balls, manufacturers have added cross-linking agents, such as metallic salts of an unsaturated carboxylic acid to the polybutadiene, typically in an amount of about 20 to 50 pph of polybutadiene. Typically, either zinc diacrylate or zinc dimethacrylate is used as the cross-linking agent, with zinc diacrylate providing a higher initial velocity than zinc dimethacrylate.
Typically, about 5 to 50 pph of zinc oxide (“ZnO”) is also added to the composition, as both a filler and an activation agent for the zinc diacrylate/peroxide cure system. The zinc diacrylate/peroxide cure system, which is well known in the art, cross-links the polybutadiene during the core molding process. In addition to acting as an activation agent, zinc oxide has a high specific gravity (5.6 g/cm
3
) that allows the weight of the golf ball to be adjusted.
Regardless of the form of the ball, players generally seek a golf ball that delivers maximum distance, which requires a high initial velocity upon impact. Therefore, in an effort to meet the demands of the marketplace, manufacturers strive to produce golf balls with initial velocities in the United States Golf Association (“USGA”) test that approach the USGA maximum of 250 ft/s plus 2 percent test tolerance or total of 255 ft/s as closely as possible.
To meet the needs of golfers having varying levels of skill and swing speeds, golf ball manufacturers frequently vary the compression of the ball, which is a measurement of the deformation of a golf ball or core in inches under a fixed load. Often, to maximize the initial velocity of a golf ball, the hardness of the core has been increased, which increases the compression of the golf ball. However, in general, the results of durability tests show that hard cores, particularly hard outer cores in dual core golf balls, are less durable than softer cores. Attempts to improve the durability of hard cores by the addition of impact modifiers, such as copolymers of ethylene and glycidyl acrylate, to standard core compositions have resulted in golf balls having a reduced initial velocity, thereby adversely affecting the overall performance of the ball.
Therefore, a need remains for a golf ball core composition containing an impact modifier that provides a golf ball core having improved toughness and impact strength with the initial velocity of prior art golf ball cores that lack an impact modifier. The present invention provides such a core composition for golf balls.
SUMMARY OF THE INVENTION
The present invention is directed to a golf ball comprising a core and a cover, the cover having a thickness of less than about 0.08 inches, the core having a compression of less than about 90 and is formed from a composition comprising a base rubber, a metal salt acrylate or diacrylate, an initiator, a highly-neutralized polymer, and at least one of a low modulus ionomer or an acid terpolymer of the formula:
having a dynamic shear storage modulus at 23° C. of at least about 104 dynes/cm
2
and a loss tangent of no more than about 1 at a frequency of about 1 Hz, wherein R
1
, R
2
, and R
3
are hydrogen or CH
3
; R
4
is linear or branched alkyl of formula C
n
H
2n+1
, where n is an integer; M
+
is H
+
, Li
+
, Zn
2+
, Ca
2+
, Ti
2+
, Mg
2+
, Na
+
, W
3+
, or Zr
2+
; and x ranges from about 20 to about 85 weight percent of the polymer, y ranges from about 1 to about 50 weight percent of the polymer, and z ranges from about 1 to about 30 weight percent of the polymer; wherein the low modulus ionomer or acid terpolymer is present in an amount sufficient to improve the durability of the core.
In one embodiment, the cover has a thickness between about 0.02 to about 0.08 inches but the cover may have a thickness between about 0.02 inches and about 0.05 inches. The highly-neutralized polymer includes ionomeric copolymers and terpolymers, ionomer precursors, thermoplastics, polyamides, polycarbonates, polyesters, polyurethanes, polyureas, thermoplastic elastomers, polybutadiene rubber, balata, grafted metallocene-catalyzed polymers, non-grafted metallocene-catalyzed polymers, single-site polymers, high-crystalline acid polymers, cationic ionomers, and mixtures thereof.
In a preferred embodiment, the highly-neutralized polymer comprises an E/X/Y copolymers where E is ethylene, X is an &agr;,&bgr;-ethylenically unsaturated carboxylic acid, and Y is a softening comonomer. X can be acrylic or methacrylic acid and Y can be a C
1-8
alkyl acrylate or methacrylate ester. X is typically present in an amount from about 1 to about 35 weight percent of the polymer and Y is typically present in an amount from about 0 to about 50 weight percent of the polymer. X can be present in an amount from about 5 to about 30 weight percent of the polymer and Y can be present in an amount from about 5 to about 25 weight percent of the polymer. Ideally, X is present in an amount from about 10 to about 20 weight percent of the polymer and Y is present in an amount from about 10 to about 20 weight percent of the polymer.
The golf ball may further include an intermediate layer disposed between the core and the cover and, if so, the intermediate layer may include a tensioned elastomeric material. In one embodiment, the core comprises an outer core layer formed of the core composition.
The low modulus ionomer or acid terpolymer present in the core blend is preferably in an amount of up to about 50 pph based on the weight of the elastomer. The low modulus ionomer or acid terpolymer has a flexural modulus of from about 500 to about 35,000 psi and a material hardness of from about 40 Shore A to about 40 Shore D and, if desired, the low modulus ionomer or acid terpolymer is present in the blend in an amount of about 5 to about 45 pph based o
Acushnet Company
Buttner David J.
Lacy William B.
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