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
2001-02-16
2003-04-22
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...
C525S072000, C525S221000, C473S379000, C473S385000
Reexamination Certificate
active
06552126
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to golf balls, and more particularly to golf balls having covers containing blends of ionomer and plastomer.
BACKGROUND OF THE INVENTION
Traditional golf ball covers were comprised of balata or blends of balata with elastomeric or plastic materials. Balata covered balls provide an experienced golfer with the ability to apply a spin to control the ball in flight. Moreover, the soft balata covers produce a soft ‘feel” to the low handicap player. However, despite the benefits of balata, balata-covered golf balls are easily cut and/or damaged if mis-hit; thus, balata and its synthetic substitutes, trans-polybutadiene and trans-polyisoprene have been essentially replaced by covers made of ionomers.
Ionomers are partial metal salts of acid containing polymers, such as ethylene based polymers. These include the partial metal salts of copolymers of ethylene and an ethylene-copolymerizable unsaturated carboxylic acid, such as acrylic acid, methacrylic acid, or maleic acid. Metal ions, such as sodium, zinc, lithium, magnesium, and the like are used to neutralize a portion of the acidic group in the copolymer resulting in a thermoplastically reversible crosslinked polymer exhibiting enhanced properties, i.e. durability, etc., for golf ball cover construction as compared to balata-covered balls.
Several attempts have been made to match or improve the performance of an ionomer golf ball by adding non-ionic and non-ionizable polymers thereto. For example, U.S. Pat. No. 4,567,219 is directed to a cover composition for golf balls with improved impact resistance. The cover comprises a blend of ionomer resin and 1-15 parts by weight of a linear, low-density polyethylene per 100 parts by weight of the ionomer resin. U.S. Pat. No. 5,019,320 discloses a golf ball composition comprising an ionomer resin and a low molecular weight polyethylene wax. This blend also is alleged to provide improved impact resistance. The polyethylene wax is present in a quantity of 0.1 to 6 parts by weight based upon 100 parts by weight of ionomer resin. It would be useful to develop a golf ball cover containing a blend of an ionomer and a non-ionic or non-ionizable polymer in which substantial quantities of the non-ionic and/or non-ionizable polymers can be used while achieving playability properties comparable to those which are obtained using known ionomeric golf ball cover materials.
SUMMARY OF THE INVENTION
An object of the invention is to provide a golf ball having the playability properties of an ionomeric covered ball while containing reduced quantities of ionomer.
Another object of the invention is to provide a golf ball having a durable cover.
Yet another object of the invention is to provide a golf ball which can be produced in an efficient and economical manner.
A further object of the invention is to provide a method for making a golf ball having the characteristics described above.
Other objects will be in part obvious and in part pointed out more in detail hereafter.
The invention in a preferred form is a golf ball having a core and one or more cover layers, wherein the cover layer contains a blend of ionomer and plastomer. The plastomer is comprised of catalytically polymerized, random copolymers of ethylene and one or more olefin comonomers characterized by a narrow or controlled composition distribution. The plastomer preferably has a dispersion index (M
W
/M
M
), i.e. the ratio of weight average molecular weight to number average molecular weight, of about 1.5 to 4. The olefin comonomer or comonomers are present in amounts of about 10-35 wt % based upon the overall weight of the plastomer.
In a particularly preferred form of the invention, the cover layer contains 10-90, and preferably 20-60, parts of plastomer based upon 100 parts by weight of ionomer. The golf ball has a cut resistance of at least 3 and a Shore D hardness in the range of 40-80.
Another preferred form of the invention is a method of making a golf ball comprising the steps of (1) obtaining a core and (2) forming a cover over the core, the cover comprising a blend of ionomer and plastomer.
The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others and the article possessing the features, properties, and the relation of elements exemplified in the following detailed disclosure.
DETAILED DESCRIPTION OF THE INVENTION
The golf balls of the invention have covers which comprise blends of ionomers, thermoplastic elastomers, and non-ionic and/or non-ionizable olefin copolymers which have a uniform, narrow molecular weight, a high comonomer content, and an even distribution of plastomer. The dispersion index of the plastomers generally is about 1.5-4, preferably 1.5-3.5 and more preferably 1.5-2.4. The density is typically in the range of 0.85-0.93 g/cc it unfoamed and 0.10-0.90 g/cc if foamed. The comonomer content typically is in the range of 10-35%, and preferably 15-30%. The melt index (MI) of the plastomer generally is less than 30 with the lower molt index materials providing blends with better low temperature impact. Accordingly a melt index less than about 20 is typical with a melt index of less than 10 being preferred and one of less than 5 being most preferred. The composition distribution breadth index generally is greater than 30%, preferably is at least 45%, and more preferably is at least 50%. Preferably the golf balls also include a curing agent for the plastomer.
The term “copolymer” includes olefin copolymers made from ethylene and one or other olefin monomers. Examples of olefin monomers include propylene, 1-butene, 1-hexene, 1-octene, 4-methyl pentene-1,1,4-hexadiene, norbornene, norbornadiene, vinyl norbornene, ethylidene norbornene, etc. The compositions of the invention further may include additives and fillers as well as a co-agent that can react with the curing agent to aid in crosslinking the plastomer and/or ionomer or to improve processability. Co-agents which have been used for that purpose include triallyl cyanurates, ethylene glycol di(meth)acrylate, tri(meth)acrylates, divinyl benzene and other multifunctional chemicals.
The “composition distribution breadth index” (CDBI) is defined as the weight percent of the plastomer molecules which have a comonomer content between 50 percent and 125 percent of the median comonomer content (on a mole basis) of the sample. For example the CDBI of a sample which had a butene content of 8 mole percent would be the weight percent of the molecules which had butene contents between 6 and 10 mole percent.
The plastomers employed are polyolefin copolymers developed using metallocene single-site catalyst technology. Polyethylene plastomers generally have better impact resistance than polyethylenes made with Ziegler-Natta catalysts. Plastomers exhibit both thermoplastic and elastomeric characteristics. In addition to being comprised of a polyolefin such as ethylene, plastomers contain up to about 35 wt % comonomer. Plastomers include but are not limited to ethylene-butene copolymers, ethylene-octene copolymers, ethylene-hexene copolymers, and ethylene-hexene-butene terpolymers, as well as mixtures thereof.
The golf ball covers of the invention contain a blend of plastomer and ionomer in a ratio of 10:90 to 90:10, and more preferably 20:80 to 50:50. The golf ball covers may also include a thermoplastic elastomer such as available from Shell Chemical Company under the designation Kraton®. It has been found that the golf ball cover properties of high impact resistance, good durability and playability are particularly favorable when the ratio of plastomer;ionomer is in the range of 10:90 to 50:50. Other additives such as coloring agents, optical brighteners, processing aids and fillers typically are added in an amount of up to about 10 parts by weight based upon 100 parts by weight of the plastomer-ionomer blend.
The plastomers employed in the invention preferably are formed by a single site metallocene catalyst such as those disclosed in EP 29368, U.S.
Domine Joseph
Kaltenbacher Edward J.
Sullivan Michael J.
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