The pad printing process transfers a two-dimensional (2-D) image onto a three-dimensional (3-D) object. This printing process uses a silicone pad to transfer an image from a printing plate (cliché) onto the object or substrate. This method of printing has gained popularity for printing onto odd-shaped objects. To print, you need an image. A printing plate (cliché) gets etched with an image. It is this image that the printing pad transfers to an object or the part by a silicone pad (tampon). Next, a cup filled with printing ink floods and removes the excess pad printing ink from the image. Then, a printing pad made of silicone picks up the image and transfers it onto the object. All these parts must be properly configured on the pad printing machine.
Hardener is not only responsible for adhesion and physical resistance, but it is also responsible for enhancing the printed image. Like with our solvents, different hardeners work with different ink series. Also different applications require different ink-to-hardener ratio. This can vary from 0% (not adding hardener at all) to adding up to 25% of the inks weight. Note; that the hardener reduces the pot life of the ink. The higher the hardener ratio, the lower the inks pot-life.
Specifications are requirements by the end user that pad printing inks have specific characteristics and meet certain standards. For example, Military (MIL-Spec)/Aerospace Qualified Ink-Military spec to MIL-I-43553 and AA56032. When properly applied and cured, the ink has excellent adhesion to metal, glass, and hard plastics. The ink is resistant to acids, alkalies, solvents, salt spray, and thermal shock. The Natron MG Series ink for glass, metals, ceramics, and hard plastics meets military spec for MIL-I-43553 and AA56032. This printing ink is a permanent, two-component, epoxy-based printing ink. Use the i-240x hardener, which cures at elevated and/or at room temperatures. For room temperature curing, perform adhesion testing 18–36 hours after printing. This wait time enables the ink to cross-link to the substrate. In some cases, the printed product can take up to 6 days to achieve full cure.
Choosing the right pad printing ink is the key to successfully completing a pad printing job. To buy the right printing ink, you ought to consider several factors. But first, let us explore the components of pad printing ink.
Ink pigment: This is usually in the form of a powder. The pigment gives the ink color and controls the ink’s opacity.
Resin is essential to an ink’s functionality. It impacts the ink characteristics of a finished ink. This includes gloss, adhesion, ink flow, and can also help disperse pigment.
Solvent: A dissolving vehicle for resin and pigment. The solvent also controls the ink’s viscosity and aids in the transport and drying of the ink. The solvent eventually evaporates, leaving the ink solids as the print. The solvent is also added during printing to alter the ink’s viscosity. The speed of the added solvent additionally impacts the ink pot life.
Substrate. Prior to printing, understanding and knowing the substrate is the most important factor. This will determine which type of ink to use. Different inks adhere onto different substrates. Choosing the wrong ink will almost certainly guarantee a filed print.
Resistance (Chemical and abrasion) and specifications. Different products get used for different applications and environments. A printed product will need to withstand the products use specifications. For example, if a product must withstand abrasion resistance, the ink must meet this requirement. If an ink will be cleaned with alcohol, then ink used must withstand this. Pad ink for glass must withstand dishwasher, hot-water, and detergents. Mil-spec prints must use Mil-spec inks. Tagless pad printing inks must pass Oeko tex and RSL certifications. Therefore, it is important to determine the type of resistance and specifications for the printed product.
Some applications call for a matte finish, while others call for a glossy finish. The SE silicone inks have a high gloss finish. This is not the case with ST Series inks for tagless printing and other rubber applications. The ST pad printing inks have a matte finish. Natron inks for glass, on the other hand, can be changed from a gloss to a satin to a matte finish.