The present invention relates to multilayer golf balls and to systems and methods for manufacturing multilayer golf balls, and more particularly, to golf ball manufacturing systems and methods that mold small particles into a golf ball substrate, which may then be removed to form voids in the substrate, including the outer surface and interior of the substrate.
Most conventional golf balls are constructed of at least two layers of material. These multilayer golf balls come in two principal varieties: wound golf balls and solid golf balls. Wound golf balls typically have at least three layers, including a center core, a wound layer surrounding the core, and a cover surrounding the wound layer. Multilayer solid golf balls have a solid core and one or more layers surrounding the core. Multilayer solid golf balls having a single solid core and a single cover layer are the most popular commercial products and are generally referred to as “two-piece” golf balls.
In multilayer golf balls, individual outer layers may be formed by molding them around an underlying substrate, such as an intermediate layer (sometimes referred to as a mantle layer) or core. The outer layers may be formed by, for example, injection molding, compression molding, and casting the outer layer material around the underlying substrate. To provide optimal performance requirements, an outer layer is preferably strongly bonded to its adjacent underlying substrate.
With wound balls, the inter-layer adhesion may be facilitated between an outer layer (e.g., cover) and its underlying wound layer due to the uneven surfaces and texture provided by the thread windings of the wound layer. The material of the outer layer flows into and around these surfaces and texture when the outer layer is molded around the wound layer, resulting in improved adhesion. In contrast, between even layers that are not wound, in either wound or solid golf balls, adhesion between the layers may be greatly reduced due to the smooth interfaces between the layers.
Improper inter-layer adhesion may significantly detract from the durability and play characteristics of a golf ball. For example, poor adhesion may cause empty cavities and other weaknesses between layers, resulting in delamination when a golf ball is subjected to impacts, such as from golf clubs or other hard surfaces. The delamination may detract from the aesthetics and playability of a golf ball. In addition, when the cover of a golf ball is cut or otherwise damaged, improper inter-layer adhesion may cause pieces of the cover to separate from the inner layer and fall off, leading to further disintegration of the golf ball.
Improper inter-layer adhesion may also adversely impact the spin characteristics of a golf ball. For example, improper inter-layer adhesion may cause a loss in shear stress generated in the ball, which may hinder a player's ability to apply a desired spin to the ball with a club having a large loft angle. This tendency toward a decreased spin due to loss in shear stress may be especially critical at the interface between the cover layer and its adjacent underlying substrate, where spinning characteristics are most affected.
Golf ball manufacturers have attempted to improve adhesion between layers by forming texture or other surface features in substrates. Those manufacturing techniques have included molding a golf ball layer with a mold cavity having a roughened surface, or forming surface features in the surface of an already formed substrate using low pressure plasma treatment, a corona discharge treatment, chemical etching, or shot blast finishing. These techniques, however, often require additional time, tooling, and manufacturing equipment, which may increase the costs and duration of production.
Accordingly, there remains a need for more efficiently manufacturing multilayer golf balls having strong inter-layer bonds, and for multilayer golf balls having improved inter-layer bonds.