Using Silicone Inks for Custom Silicone Molding
Silicone ink is a versatile and reliable product effectively used for custom silicone molding. It is stable at room temperature and lasts an extended period of time over traditional inks. The main way it achieves this is by not having a catalyst added until the ink is needed for production. Ink storage and the mixing room are held to high standards of sanitation. Cleanliness is an important part of the process of mixing inks. All workstations are constantly cleaned of any contaminants. The floors, tools and mixers are kept exceptionally clean. Paperwork is also an essential part of the ink process. Tracking from the receipt of the ink to combining colors to catalyzing is thoroughly recorded.
Procedures for combining silicone inks are strictly followed to achieve a constant result each time it’s used in the custom silicone molding process for keypads and other products. Chemicals are regulated, labeled and stored in approved containers. Silicone inks come in five basic colors and can be combined to create a never ending variety of colors. A very accurate scale is used in the process of combining pigments to make a new color. When a color is achieved for printing on keypads a small amount of it is weighed out with a platinum based catalyst, a cross link and an agent to achieve a proper viscosity.
The next step is to print on a sample silicone part and to cure the ink for 2 to 6 minutes at 400 degrees F. The custom silicone molding part is checked for adhesion, rub resistance and color. If the ink is mixed to become a pigment to be used in the process of molding liquid silicone rubber, a sample of the pigment is combined with the “A” and “B” components of liquid silicone. The part is then compressed and baked at 400 degrees F for 15 minutes to cure.
Once the part is cured and cooled completely it can also be tested for proper color. To test the ink or pigment for color a spectrophotometer is used. It measures intensity as a function of the color, or more specifically, the wavelength of light. Delta-E is a single number that represent the variation between two colors. A measure of variance from a standard color book such as a Pantone color book is measured in delta deviation. This is usually with a plus or minus status (+ or – 2 deltas). A high standard of color match would be a rating of + or – one delta of the controlled color.
Two to three delta variations is the absolute smallest a human eye can decipher the difference in color. When the color is approved, documented and released, production can begin. When released, the pigment for molding needs to be “de-gassed,” or remove the air that was produced while mixing.
Inks can also be made into sprays. Sprays are made by combining ink, a catalyst and a high flash spirit to thin the mixture. Once combined the sprays can be used to touch up molded parts or to color already molded part. A clear molded silicone part, such as custom rubber keypads, can be sprayed any color and then a laser can be used to burn through the color in a specific design to achieve a part that can be backlit.
The health hazard for silicone inks is extremely low under normal working conditions. The primary concerns are the eyes and skin. It may cause eye irritation if directly exposed to the eyes. Prolonged contact with skin may cause irritation or discoloration. Wearing eye protection and gloves are two easy ways to avoid irritation. At room temperature, vapors are minimal and material is not an inhalation hazard.
Silicone inks are versatile for use in many applications, including custom rubber keypads. They are predictable with the use of standard procedures. The inks and pigments are very concentrated. A few grams of ink can produce hundreds of parts. They are very shelf stable and do not lose quality quickly over time. Silicone inks and pigments cure quickly under specific heat conditions, reducing oven time and increasing efficiency. With the proper process in place an array of high quality parts can be produced.