Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-07-25
2004-07-27
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S095000, C524S099000, C524S104000, C524S236000, C525S256000, C525S259000, C525S274000, C473S354000, C473S371000, C473S374000, C473S377000, C473S378000
Reexamination Certificate
active
06767940
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to golf balls, and, in particular, to a composition of golf ball cores and covers comprising stable free radicals.
BACKGROUND OF THE INVENTION
Solid core golf balls are well known in the art. Typically, the core is made from polybutadiene rubber material, which provides the primary source of resiliency for the golf ball. A known processing difficulty of polybutadiene cores cross-linked with peroxide initiators is the rapid increase in viscosity during cross-linking due to increase in polymer molecular weight. When the viscosity becomes too high, the partially cross-linked polymer cannot flow rapidly and does not completely fill the mold containing it. This phenomenon, known as scorch, results from premature cross-linking which may occur during compounding or manufacturing.
Scorch is accentuated by processing conditions that include high temperatures and/or high shear rates. For example, in an injection molding process, the elastomeric polymer and peroxide composition must be exposed to high shear rates and high temperatures to keep the composition fluid as it flows rapidly through the injection nozzle, runners and gates to the mold. If scorch occurs, the surface of the resulting molded golf ball core will be irregular and the composition may solidify in the runners leading to the mold, thereby unfavorably impacting the efficiency, scrap rate and safety of the process. High shear rates combined with high temperatures also occur in other common golf ball composition processing methods, such as in roll milling and extrusion.
A short scorch time (time between start of reaction and onset of crosslinking) further increases the occurrence of backrinding, the undesirable torn or gouged appearance of cross-linked articles at a mold parting line. Backrinding is caused by the continuing thermal expansion of the elastomeric polymer after cross-linking occurs, and is most severe for a spherical object, such as the outermost layers or portions of a golf ball core, where the surface area to mass ratio is at a minimum. Physical manifestations of backrinding are thought to contribute to premature failure of golf balls by making the golf ball less uniform, causing a focal stress at the gouge, and initiating cracks. Thus, it is desirable to reduce backrinding by increasing the scorch time in the cores to enhance golf ball durability.
One way to increase the scorch time is to decrease the decomposition rate of the peroxide initiator by lowering reaction temperature, resulting in a long half-life for the peroxide initiator. However, this approach is generally unsatisfactory, since a long half-life tends to result in a slow cross-linking rate and a long cure time. Recently, so-called scorch retarding or scorch resistant peroxides have become available. Exemplary applications of scorch retarding peroxides in golf balls are described in U.S. Pat. No. 6,339,119, the disclosure of which is incorporated herein by reference in its entirety. The scorch retarding peroxides slow the onset of scorch through free radical “scavengers” that react with the peroxide radicals and prevent them from immediately initiating cross-linking. However, these peroxides are only available in pre-mixed packages, which lack the flexibility of controlling the peroxide and the scavenger levels independently. Furthermore, existing systems, such as Varox® 802-40KE-HP available from R. T. Vanderbilt, do not significantly alter the cure state, unlike the compositions disclosed in the present invention.
Stable free radicals such as Tempo® have long been known to moderate the state of cure and extend the scorch time of elastomers by ways of reversibly quenching, scavenging and/or trapping early unstable free radicals formed during decomposition. Stable free radicals may further serve as a free radical capping additive or an antioxidant to prevent reaction of undesirable free radicals generated upon wear to the base rubber. It is therefore advantageous to incorporate stable free radicals in golf ball compositions, particularly in core and intermediate layers, in order to prolong scorch time for ease and flexibility of processing, as well as to impart durability and resilience to golf balls.
SUMMARY OF THE INVENTION
The present invention is directed to a golf ball having a core and a cover, particularly to a golf ball core formed from a composition including an elastomeric polymer, a free radical initiator, and at least one stable free radical. The stable free radical is present in an amount sufficient to increase the scorch time of the elastomeric polymer during curing by at least about 10%, preferably by at least about 25%, to substantially prevent backrinding. Preferably, the amount of the stable free radical is also sufficient to decrease the maximum torque of the elastomeric polymer during curing by at least about 5%, more preferably by at least about 10%. Specifically, the amount of the stable free radical is preferably between about 0.01 phr and about 20 phr by weight of the elastomeric polymer, more preferably between about 0.05 phr and about 5 phr, and most preferably between about 0.05 phr and about 1 phr.
Suitable stable free radicals for the present invention include, without limitation, nitroxide radicals; hydrazyl radicals; allyloxyl radicals; trityl radicals; and derivatives thereof having at least one substituent group comprising amino, isocyanate, hydroxyl, carboxyl, oxirane, thiirane; and mixtures thereof. Specific nitroxide radicals include, but are not limited to, 2,2,6,6-tetramethlpiperidinyloxy and derivatives thereof; 2,2,5,5-tetramethyl-1-pyrrolidinyloxy and derivatives thereof; 4,4-dimethyl-3-oxazolinyloxy and derivatives thereof; 2,6-di-t-butyl-&agr;-(3,5-di-t-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-p-tolyloxy and derivatives thereof; di-t-butyl nitroxide and derivatives thereof; and mixtures thereof. The most preferred choice of the stable free radical for the present invention is 2,2,6,6-tetramethlpiperidinyloxy or a derivative thereof.
The elastomeric polymer for the golf ball core of the invention can be one or more natural or synthetic elastomers, including without limitation natural rubbers; balata; gutta-percha; synthetic polyisoprenes; styrene-butadiene rubbers; styrene-propylene-diene rubbers; chloroprene rubbers; acrylonitrile rubbers; acrylonitrile-butadiene rubbers; ethylene-propylene-diene terpolymers; polypropylene resins; ionomer resins; polyamides; polyesters; urethanes; polyureas; thermosetting or thermoplastic elastomers; metallocene catalyzed rubbers; styrene-ethylene block copolymers; maleic anhydride or succinate modified metallocene catalyzed ethylene copolymers; chlorinated polyethylenes; polysulfide rubbers; flurocarbons; and mixtures thereof. Preferably, the elastomeric polymer comprises at least about 40 phr by weight of a polybutadiene having a cis-1,4 content of at least about 40%, a Mooney viscosity of at least about 20, a number molecular weight of at least about 150,000, and a polydispersity of less than about 4.0.
The free radical initiator for the golf ball core may be one or more peroxides; sulfur curing agents; high-energy radiation sources capable of generating free radicals; and mixtures thereof. Suitable peroxides include, but are not limited to, dicumyl peroxide; n-butyl-4,4-di(t-butylperoxy)-valerate; 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane; &agr;,&agr;′-bis(t-butylperoxy)-diisopropylbenzene; 2,5-dimethyl-2,5-di(t-butylperoxy)hexane; di-t-butyl peroxide; di-t-amyl peroxide; di(2-t-butyl-peroxyisopropyl)benzene peroxide; lauryl peroxide; benzoyl peroxide; t-butyl hydroperoxide; and mixtures thereof. Suitable sulfur curing agents include, without limitation, N-oxydiethylene 2-benzothiazole sulfenamide; N,N-di-orthotolyguanidine; bismuth dimethyldithiocarbamate; N-cyclohexyl-2-benzothiazole sulfenamide; N,N-diphenylguanidine; and mixtures thereof. And suitable high-energy radiation sources include electron beams; ultra-violet radiation; gamma radiation; X-ray radiation; infrared radiation; heat;
Bulpett David A.
Voorheis Peter R.
Acushnet Company
Buttner David J.
Lacy William B.
LandOfFree
Golf ball compositions comprising stable free radicals does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Golf ball compositions comprising stable free radicals, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Golf ball compositions comprising stable free radicals will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3213139