Patent Application
20080018020
The present invention is directed to a method of making layer or cover components in a golf ball. In particular, the invention is directed to the employment of aspects generally associated with injection molding and creating an improved compression molding process for forming thin layers or covers of thermoset or thermoplastic materials in a golf ball. Thin layer technology can provide an outer cover or a transition between a soft outer cover layer and a hard inner cover layer. This can provide the ball designer a means to tune the spin rate profile for medium to short iron play. Alternatively, as an inner layer, the thin layer can also act to reduce driver spin rates while maintaining wedge spin rates
Traditionally, for separating the molded product and matrix from the mold cavity during a compressor molding process, the industry has relied upon either a permanent or a semi-permanent (sacrificial) mold release agent consisting primarily of either silicon or Teflon based polymer. The permanent agents are generally baked-on at relatively high temperatures of 600° F. to 750° F. Because of the design of conventional compression molds frames, wherein O-rings are employed that cannot tolerate these high temperatures and therefore must be removed before applying the permanent release agent to the cavity, the hydraulic press must be shut down, utilities discontinued, and the entire frame removed from the press. Because of this inconvenience and subsequent production downtime, semi-permanent release agents, which can be sprayed-on at lower temperatures (250° F.-350° F.) are usually the type used. Depending upon the materials molded, the cavities may require an application of the release agent as often as every thirty minutes. While this may create a significant downtime in the manufacturing process, an even greater problem occurs downstream because particles of the release agent can adhere to the surface of the molded product, and thus before the molded product can be printed or painted upon, this release agent must be cleaned off the surface. In addition to avoiding of this problem, the present invention provides a benefit in addition to not requiring a mold release agent, in that plasma or in line corona surface treatment may be then used downstream. The present invention provides a means for capturing the benefits that are inherent with a compression molding process, and by utilizing injection molding principles eliminating some of the maintenance problems associated with compression molding.
A cover material (not shown) is pre-formed into half-shells, and each placed into one of the respective mold cavities 28, 30. The core (not shown) is then placed between the cover material half-shells and the mold 10 is closed. The core and cover combination is then exposed to heat and pressure, which cause the cover half-shells to combine and form a full cover. Compression molding does not require support members for the core or other components for adding materials. For convenience a core as herein described may have a cover or layer placed about it, and may be a ball product at any stage of manufacturing, such as a core with one or more layers already formed thereon. The orientation of knockout pins 56 is variable, but a vertical layout is preferred. The pins 56 are activated by the knockout pin retainer plate 38, which controls movement of pins 56 to engage with the core to forcefully remove the core out of the cavities 28. Knockout retainer plate 38, may be actuated in a variety of manners known within the art, such as electrically, hydraulically or pneumatically. The knockout retainer plate 38, limits the ejection stroke x of the knockout pins 56 to about 0.005 inch to 0.040 inch, and preferably about 0.022 inch injection stroke. Despite that conventional vent pins are configured with primary and secondary vents or porous tips to increase ventilation capacity, ventilation of trapped air and gasses inside the mold often remains a limiting factor in the speed at which material is injected into the mold cavity. If the vent holes are too small, poor ventilation can cause improper or inadequate venting of trapped air and gasses from the mold cavity during injection, which can have a deleterious effect on both the visual quality and durability of the newly formed layer. Conversely, if the vent holes are too large, the injected material flows there into and forms flash on the newly formed layer, thereby requiring substantial additional processing for removal of the flash and surface finishing. If the injection speed of the material is too fast, the speed of evacuating air and gasses out of the mold cavity during the injection process can cause the newly formed layer to scorch or not completely fill the mold cavity.
The present invention employs high pressure air blow, preferably with retractable knockout pins 56 to release molded products during the compression molding process. As shown on
Multiple retractable pins 56 are activated to eject the molded parts and matrix from the retainer plate 24. As previously stated the ejection stroke is about 0.005 inch to about 0.040 inch. The mold frame 20 has a vacuum cap plate 42, which retains the O-rings 54 around the knockout pins 56. The knockout pin retainer plate 38 controls the length of the pin 56 movement.
Just before the mold closes vacuum is added to remove trapped air, while air blow is activated upon the mold opening, Knockout pins 56 may be activated from the upper mold frame 22 and immediately followed by the lower mold frame 20 for a few seconds. Once the mold is fully opened, the pins 56 are retracted and the molded product is unloaded. For use with multiple cavities, a segmented manifold concept can be used with controlled activation of each segment. Manufacturing costs may be substantially reduced by eliminating the need for a mold release agent, as well as improving the efforts for developing simpler surface prep processes and one coat paint systems. Important health considerations are gained by eliminating release agents from compression molding because these agents are normally applied by spray guns which typically have a significant over spray released to the surrounding atmosphere.
The golf ball produced may be a two-piece, multi-layer, or wound ball having cores, intermediate layers, covers and/or coatings. A “cover” or a “core” as these terms are used herein includes a structure comprising either a single mass or one with two or more layers. As used herein, a core described as comprising a single mass means a unitary or one-piece core. The layer thus includes the entire core from the center of the core to its outer periphery. A core, whether formed from a single mass, two or more layers, or a liquid center may serve as a center for a wound ball. An intermediate layer may be incorporated, for example, with a single layer or multi-layer cover, with a single mass or multi-layer core, with both a single layer cover and core, or with both a multi-layer cover and a multi-layer core. A layer may additionally be composed of a tensioned elastomeric material. Intermediate layers of the type described above are sometimes referred to in the art, and, thus, herein as well, as an outer core layer, an inner cover layer, an outer core layer, or a mantle layer.
While the preferred embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not of limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. For example, while the method and apparatus of the present invention have been described above as forming a golf ball product, the present invention can be used to form layers on other objects. Thus the present invention should not be limited by the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
