What Pad Printing Ink Sticks to This?
Our print lab technicians are asked this question every day. Finding the answer is like scientific research. There are so many variable factors in matching pad printing inks to substrates that narrowing them down to a single formula for a specific application requires experience and experimentation. Here are typical questions we ask to find the most compatible ink to use on a new application.
First: Determine Substrate To Be Pad Printed
The single most important factor that helps us decide which pad printing ink to use on an application is the material of the substrate to be pad printed. Because the chemistry of each ink is formulated to adhere to a limited range of materials, by knowing the specific substrate we can focus on inks that we have successfully used on similar applications in the past.
Does the part show mold markings of codes that indicate material (i.e., ABS, PS, PET, PVC .etc. )?
This information may also be shown on the bill of materials or the lot label. The original molder or manufacturer should certainly identify the substrate.
If the origin of the material is still unknown you may be able to identify it by its characteristics. The specific color, texture, flexibility, sound, weight or density may be similar to a known sample. This is a good start for narrowing down the possibilities.
What are Performance Expectations?
Because each printing ink is formulated with certain performance features, the function of the printed part also helps determine which ink to select. What are the conditions in which it will be used? Is it in an environment with extremes of temperature and humidity? Does it need to endure constant wear and bending? Are quality aesthetics or visual appeal a high priority? These choices will influence the proper ink selection as well. For example with an application in which maximum durability is required, a two part epoxy pad printing ink such as Type B or Type W may be recommended.
Pre-Treating May Be Needed Before Pad Printing
Some plastics substrates, especially olefins, are inherently slippery (technically referred to as having low surface energy or “poor wettability”.) Most liquids, Including inks have difficulty adhering to olefins (polypropylene, polyethylene, etc,) unless the printing surface is pre-treated to change the surface energy. Typically this is done using an electrical corona discharge or flame treating.
Pad Printing Ink That Is Dry To Touch Is Not Cured
Another consideration in pad printing ink selection is whether curing is required. An image transfer may be successful and even feel dry to the touch, but in order to fully adhere to certain substrates, the ink may need to cure for hours, even up to several days. However, this time may be shortened with heat curing (thermodiffusion or infrared units). This ensures the ink will achieve maximum hardness with permanent adhesion to the surface within the shortest possible time.
For specific ink type recommendations, always ask your ITW Trans Tech support team.