Golf balls are made in a variety of constructions and compositions. In this regard, each of the golf ball core, intermediate layer, and cover may be single layered or comprise multiple layers. Examples of golf ball materials range from balata to polybutadiene, ionomer resins, polyurethanes, and/or polyureas. Typically, outer layers are formed about the spherical outer surface of an inner golf ball component via compression molding, casting, or injection molding.
Golf ball manufacturers continuously experiment with golf ball constructions and material formulations in order to target and improve aerodynamic and/or inertial properties and achieve desired feel without sacrificing durability. In this regard, sufficient adhesion between golf ball layers is essential in achieving adequate impact durability. Without a satisfactory amount of adhesion between these layers, both the impact durability as well as the shear resistance of the cover can suffer.
This issue typically presents when the materials of adjacent golf ball layers don't bond together well. For example, the bond strength or “adhesive strength” between an ionomeric casing/intermediate layer and a polyurethane cover layer may be unacceptably low.
Poor interlayer bond or adhesive strength can result in layer separation or “delamination” when the golf ball is struck by a club. Layer separation may be visually apparent as “bubbling” or air pockets between the two layers. Delamination detrimentally affects not only the appearance of the golf ball but playability as well. Accordingly, golf ball manufacturers look for cost effective compounds and methods for addressing this problem in order to preserve brand recognition and reputation.
Currently, several different types of adhesion promoting pre-treatment processes exist for addressing cut and shear issues caused by lack of adhesion between layers. Examples of pretreatments include surface roughening; surface energy modifications such as corona, plasma, and flame treatments; adhesives; adhesion promoters and combinations thereof. Adhesives are typically applied via spray or dip and usually require a drying and post cure step. Adhesion promoters are likewise usually applied by dip or spray, followed by rinsing and drying steps.
In this regard, silane adhesion promoter surface pretreatments and tie layers are known to improve interlayer adhesion between adjacent differing mated layers. See, e.g., commonly owned U.S. Pat. No. 6,926,621 of Lutz. et al., hereby incorporated herein in its entirety. With such surface pretreatments, the silane adhesion promoter, either neat (without solvent) or in solution, is exposed to or applied about the outer surface of one layer before mating or otherwise joining it with a second layer. The silane adhesion promoter provides a reactive surface for creating strong bonds between the treated layer and an adjacent different layer. However, silane-containing adhesion promoters have undesirably limited shelf lives once performed/applied and will fail to provide adequate adhesion between those layers unless molding follows within a short specified time window of the surface pretreatment or application of the tie layer.
Silanes have also previously been included within golf ball layers, but as intralayer coupling agents or crosslinking catalysts wherein any free functional groups of the silanes are solely dedicated to facilitating bonding/crosslinking of ingredients inside the layer—for example, between butadiene and fillers.
There is a need, however, for golf balls having the excellent interlayer adhesive strength between adjacent differing layers created by silane-containing surface-pretreatments and tie layers without the need for such additional processing steps or the timing limitations associated therewith. Such golf balls would improve golf ball manufacturing efficiency (e.g., time savings), flexibility and meanwhile reduce the cost of making the golf ball. The present inventive golf ball and method of making same addresses and solves these needs.