DISPERSED IN HIGH-CIS POLYBUTADIENE

This invention relates to a dispersion of zinc diacrylate in polybutadiene for use in golf balls and the production thereof, wherein a first and a second processing promoter is employed in the production of the dispersion and being incorporated therein.

US Patent No. 7,135,514 provides for a dispersion of zinc diacrylate in polybutadiene commonly used by golf ball manufacturers, in which processing promoters are included to achieve the dispersion. The '514 processing promoters are selected from the group of low molecular weight polyethylene, fatty acids, zinc salts of fatty acids and mixtures thereof.

It has now be found that further improvements to the zinc diacrylate in polybutadiene dispersions commonly used by golf ball manufacturers can be achieved via the addition of a second processing promoter to those first promoters as described in the '514 patent, in which this second processing promoter is a metal oxide.

In general, metal oxides have been employed heretofore as activators in curing systems or fillers. Surprisingly, however, it has now been found that the use of a metal oxide as a second processing promoter in the production of zinc diacrylate in polybutadiene dispersions results in improvements to both the extrusion flow properties (throughput rate) of the product and in the quality of peptization, for example, in an improved pellet-size uniformity for the

manufactured dispersion. If not otherwise stated herein, it is to be assumed that all patents, patent applications, patent publications and other publications mentioned and cited herein are hereby fully incorporated by reference herein as if set forth in their entirety herein.

There is broadly contemplated, in accordance with at least one

embodiment of the present invention, a rubber dispersion composition which comprises a mixture of i) from about 12 to 50 parts by weight of a polybutadiene; ii) from about 50 to 85 parts by weight of zinc diacrylate; iii) from about 0.5 to 5 parts by weight of a first processing promoter selected from the group of low molecular weight polyethylene, fatty acids, zinc salts of fatty acids and mixtures thereof; and iv) from about 0.5 to 5 parts by weight of a secondary processing promoter, wherein said secondary processing promoter is a metal oxide, and wherein said parts by weight are all based on the total weight of the dispersion. It being understood, the aforementioned parts by weight of each component being selected so as to result in a sum total of 100 parts by weight. In another embodiment of the present invention there is a process for the production of a rubber dispersion composition comprising the steps of a) mixing i) from about 12 to 50 parts by weight of a polybutadiene; ii) from about 50 to 85 parts by weight of zinc diacrylate; iii) from about 0.5 to 5 parts by weight of a first processing promoter selected from the group of low molecular weight

polyethylene, fatty acids, zinc salts of fatty acids and mixtures thereof; and iv) from about 0.5 to 5 parts by weight of a second processing promoter, thereby forming a mixture; b) extruding the mixture, thereby forming an extruded mixture; and pelletizing or slabbing said extruded mixture, and wherein said parts by weight are all based on the total weight of the dispersion. It being understood, the aforementioned parts by weight of each component being selected so as to result in a sum total of 100 parts by weight.

In another embodiment of the present invention, the metal oxide of the dispersion and process above is a zinc oxide, magnesium oxide, calcium oxide or a mixture thereof. In another embodiment of the present invention the metal oxide is zinc oxide.

For a better understanding of the present invention, together with other and further features and advantages thereof, reference is made to the following description.

The present invention provides for a dispersion of zinc diacrylate in polybutadiene and the process by which it is made. In one embodiment, the polybutadiene is a special high-cis grade of polybutadiene commonly used by golf ball manufacturers. The preferred high-cis polybutadiene is neodymium catalyzed and has a cis- ,4 content of above about 90% and more preferably above about 96%. However, any grade of polybutadiene can be used by compensating for the molecular weight differences, using more or less processing promoters. In one example grades of polybutadiene accepted by the various golf ball manufacturers are Buna CB 1220, 1221 and Taktene 221 from LANXESS Corporation.

If desired, the polybutadiene can also be mixed with other elastomers known in the art, such as natural rubber, styrene butadiene, and/or isoprene in order to further modify the properties of the core. When a mixture of elastomers is used, the amounts of other constituents in the core composition are generally based on 100 parts by weight of the total elastomer mixture.

Zinc diacrylate is a co-agent preferred for use in golf balls because it provides golf balls with a high initial velocity in the USGA test. The zinc diacrylate of the present invention can be of various grades of purity. Typical grades contain about 90% ZDA and 10% zinc stearate, which is either incorporated in-situ or post added. Suitable, commercially available zinc diacrylates can be obtained from Sartomer Company.

The preferred concentrations of the commercially available zinc diacrylate grades that can be used in this invention are from about 86 to 92 percent by weight zinc diacrylate and 8 to 14 percent zinc salts of fatty acids, preferably zinc stearate.

The combination of adding both a first and a second processing promoter of the present invention enable improved extrusion and pelletizing rates of the dispersion formed, as well as functioning as a separant to greatly minimize, if not totally eliminate, massing of the pelletized product. The resulting dust-free pelletized product, which can optionally be supplied in slab form, is capable of use for direct addition to golf-ball formulations for golf-ball manufacturing. Preferred first processing promoters of an embodiment of the present invention are low molecular weight polyethylenes (MW approximately 800 - 2500); and fatty acids (preferably saturated fatty acids), zinc salts of fatty acids and combinations thereof. Oleic acid and zinc salts of oleic acid may also be used in the manufacture of the ZDA dispersion.

The preferred concentrations of first processing promoters that can be used are from 0.5 to 5 parts by weight based on the total weight of the said dispersion.

Preferred secondary processing promoters of an embodiment of the present invention are metal oxides such as zinc oxide, magnesium oxide, calcium oxide and mixtures thereof.

The preferred concentrations of secondary processing promoters that can be used are from 0.5 to 5 parts by weight based on the total weight of the said dispersion. In one embodiment, the ZDA dispersion of the present invention is made in an internal mixer into which is first added the total amount of polymer, e.g., polybutadiene rubber, optionally some dispersion from a previous batch, all of the first and secondary processing promoters, and all of the ZDA powder. The mixed batch is discharged preferably at a mixer temperature of 200°F (93°C). The temperature of the batch obtained using a thermocouple is generally about 20°F higher. The mix temperature is a compromise between being high enough to melt the first processing promoters and optionally to melt and disperse low-melt bags if desired, and low enough to minimize odor, undesired reactions and even decompositions.

Since ZD A poses a dust explosion hazard, all appropriate precautions are taken in the mixing area to minimize such hazard risks. Following the mixing operation, the homogeneous mixture is then pelletized using, for example, a dry- face-cutter-head on an extruder. Although pellets are the preferred form for automatic weighing, a slabbed version is also available by using a slot-die on the extruder. The mixing and forming processes used to make this product is known to the skilled artisan, but the process of mixing all the ingredients at once and the inclusion of previously mixed material is a material improvement to the process that shortens the total mixing time of the product.

Although the preferred embodiment of the present invention has been described herein, it is to be understood that the invention is not limited to that precise embodiment, and that various other changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention.