After the injection molding process, plastic housing components are often subjected to secondary operations, such as painting, coating, or being bonded to a foam. DirectCoating and DirectSkining (DC/DS) has proven to be effective at producing premium quality surfaces or reducing manufacturing steps by combining multiple operations into an efficient, single step within the mold. The technique leverages the ability to overmold injection-molded polycarbonate (PC) parts with a polyurethane foam or coating inside the tool. The outcome is a rigid substrate (either PC or alloy) with an outer surface that can be soft, ultraviolet-stabilized, and scratch- and chemical-resistant through an aliphatic polyurethane self-skinning foam, solid polyurethane skin or polyurethane coating.
With DC/DS, the coating or skin is molded onto the first shot plastic substrate using well-known Reaction Injection Molding (RIM) of urethane-based materials. With a single shuttle mold, the core between an injection molding cavity (first shot) and a RIM cavity (second shot) can be alternated to continuously produce finished parts, such as coated equipment housings, without a time-consuming painting process. DC/DS might be a more cost-effective solution for device manufacturers looking to achieve a design based on the assembly of multiple materials or a high-end aesthetic, only achievable with secondary operations. For example, the manufacturing of a pump housing that includes a secondary painting step or a drug delivery device that includes a textured finish demonstrates how DC/DS technology may simplify manufacturing and lower costs. Using DC/DS also allows for design flexibility and freedom with a wide range of customizable colors, textures and softness. The same tool can produce a product with a surface that is hard or soft to the touch.
DirectSkinning is a cost-effective process for finishing parts with colored, decorative polyurethane surfaces, including those with multiple colors, variable softness or tactile textures (Figure 1). Most notably, the process avoids the use of cut-to-order skin components and saves time by eliminating the need to apply adhesives. A typical coating or skinning process could be expensive, labor-intensive, and require several steps to produce finished parts. Conventionally, manufacturers first mold the hard substrate and then move the part to a fixture or other operation to apply the coating or skin. This often requires the storage, transportation, cleaning and pretreatment of the part, which is susceptible to contamination or damage. Other disadvantages include long production time, complex logistics, and high investment costs and energy consumption.
The DirectCoating process is an inherently efficient process to apply colored coatings or clear-coats, including high-gloss surfaces onto rigid substrates. The ultra-low VOC (volatile organic compound) process also eliminates the need for painting and the associated overspray common in traditional painting operations. Utilizing DirectCoating over standard coating can reduce production time from hours to 90 seconds per part.
DC/DS offers many advantages to molders as it provides an opportunity to expand on existing capabilities. Conventional injection molding equipment can be used with the addition of a fitted RIM unit modified to run the DC/DS process. The ability to run two different molding processes in a single tool is more efficient, resulting in cost savings and a higher-value finished product. While manufacturers benefit from improved efficiencies, OEMs might also benefit from simpler supply chains and enhanced products with superior appearance, feel and performance.
When building a tool for DC/DS, it is important to keep in mind that the process relies on a shuttle or rotary-type mold design. This typically requires either multiple cores or cavities, and tooling costs can be expected to be 20 to 30 percent higher than for a conventional multi-cavity injection mold. However, both the injection molding and RIM processes will be integrated into the single tool.
OEMs looking to improve the aesthetics of their parts and increase production efficiency should consider DC/DS. Enhanced surface quality, accelerated cycle time, and reduced scrap and labor costs are among the potential benefits of DC/DS. These advantages, combined with a low capital investment, make DC/DS an attractive option for OEMs seeking to produce quality plastic parts for diverse markets and applications.
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