There are many steps involved in the process of printing on molded silicone. The first step in the process of printing is to make a screen with the image to be printed. A screen consists of a metal frame that is designed to hold the mesh. A mesh is most commonly made of metal and comes in many sizes. It can also be made of silk or polyester for specific applications. The mesh is attached to the frame and adjusted on all sides to a very specific tension. In the next step, the image to be printed on molded silicone can be transferred to the screen. An image that is to be printed is transferred to the mesh using artwork over film and exposed to UV light for curing.
Voids between the image and the edges of the frame are filled in to avoid ink leaking and transferring onto parts to be printed. Two ways to avoid ink leaking through are use of specialty tapes or Block out, which is a water-soluble liquid that is usually dyed red to see more easily. It is brushed onto the exposed area of the screen and used to fix any defects in the image itself.
When the screen is dry, it is ready to be positioned over a nest. A nest is a rubber cast of the part being printed. The nest is made using a sample part and liquid two-part mixture to create a base that holds the part to be printed. It’s important to line up the screen image over the nest very precisely with the part being printed, and adjust for exact registration of ink. Silicone ink is the next part to consider in the process. The ink used is very versatile and has many advantages over standard ink. Silicone inks come in a variety of colors and can be combined to achieve more colors. Silicone inks do not dry by air alone. When preparing inks for printing, a cross link is added as well as an agent for viscosity and a catalyst for curing under heat. The catalyst is made out of liquid platinum. All of the ingredients need to be weighed with in 1/10th of a gram. Once the ink mixture is complete, it will remain very workable for several hours.
The next step is to secure the molded silicone part or parts in the nest. The ink is applied to the screen above the image using a rubber squeegee. The ink is spread across the image not in contact with the part being printed. This is referred to as flooding the screen. The point in flooding the screen is to have complete coverage of ink onto the first part. At this point, printing can proceed at a very efficient speed with accurate results. After printing the silicone molding part, it can be placed in an oven for as little as 2 to 6 minutes to cure.
There are many efficiencies to take advantage of in the processes of printing with silicone ink. The first is when a screen is no longer needed, it can be cleaned and reused. The inks used can be stored for very long periods of time without curing when they are stored in a cool environment. If a mistake is made while printing and before curing, it can be removed by wiping with high-flash mineral spirits. Printing on silicone molding with silicone-based ink provides a very strong bond, or cross link, which results in a weatherproof, wear resistant product.
