Dome coating of decorative, novelty items such as pens, lapel pins, name plates, and logo stickers is common. The coating forms a protective layer over the items, but generally, the main purpose is the glossy, raised appearance which can magnify the image below it. In other applications, the coating is primarily protective, and the appearance is of less concern.
The coating selection process is similar for both protective and decorative coatings. The main points to consider in selecting a dome coating are:
Processing choices – Today, there are a variety of processing choices available including: a) two component reactive systems, b) solvent based systems, and c) UV Curable systems. Two component reactive systems require mixing, followed by de-airing. Solvent based systems can create difficulties with health and safety and workplace handling.
UV Curable dome coating requires UV cure equipment which can be costly. However, equipment choices have expanded and become less costly due to developments in dome coating chemistry. Historically, fairly high intensity UV light was required to cure the surface of the coating to a tack free dry surface. Recent advances in UV curable dome coating materials now offer a tack free finished appearance with low intensity UV light (which also helps minimize shrinkage and overheating during cure).
These advances expand the selection of lamps that are appropriate for coating. Tailor the curing process by choosing a lamp that provides the optimal time vs. intensity cure model for the coating.
Parts –What are the substrates? A common dome coating application is dome coating a logo. The logo may be a screen printed paint or a sticker… so consider what material does the coating need to bond to? This will help to determine a product with good adhesion to the substrate. Will the coating material in its liquid form attack the ink or artwork?
Is the part flexible? If the end item requires flexing, the coating should be flexible to increase durability. If the end item is very thin or very flexible, consider the dome depth, shrinkage, and hardness of the coating. This is to ensure the part doesn’t curl up on the edges.
Purpose – Like all scientists, adhesive manufacturers like to hear the numbers. What are the temperature requirements, chemical exposure times & concentrations, etc… But, it is generally best to begin the conversation with the purpose – the purpose of your assembly provides so much more information. For example, will it be exposed to the elements outdoors on a vehicle badge, going through a dishwasher, or even more extreme in a subsea application?
For further help and advice, please contact Permabond.