Pad Print Thinners and Hardeners
Pad printing’s smooth transfer of an image from the inked cliché to the subtrates is facilitated by additives used in the ink’s mix. Pad Print thinners and hardeners are additives critical in handling ink adjustments for better adhesion and extending image life.
Transferring pad printing inks requires that a percentage of thinner be mixed into the ink. Thinners are volatiles; that is, they evaporate quickly (“flash off”) to dry out the ink mixture so it becomes “tacky.”
This “tackiness” is what enables the silicone pad to pick up an image/ink and transfer it to the part.
Ink manufacturers provide special, chemically-formulated thinners to work with their inks. They usually provide thinners in different.” The “speeds” refers to how fast the thinner evaporates. Typically, you’ll find fast, medium and slow (sometimes referred to as “retarder”) options.
As you may know, there are different ink “series” that adhere best to specific substrates. Manufacturers will provide charts that cross-reference different substrates and which inks work best with them. Each of these inks may utilize one (or many) different thinners, depending on the application. Here is a link to the Ink & Materials Table from the website.
Another important function of a pad printing thinner is it also cross-links the ink/pigment to the surface of the part while the thinner is evaporating, also aiding adhesion. Some substrates are more porous than others, which makes it easier for ink to bond, so the cross-linking happens quickly. Other substrates require more time, so you’ll use a “slower” thinner. In any case, once the ink transfer (print cycle) is complete, the thinner continues to evaporate and perform its cross-link duties simultaneously, eventually leading up to a “cured” image.
Images pad printed with solvent-based inks are usually “dry to the touch” in a matter of seconds, which means you can handle the parts relatively quickly. However, most pad print inks don’t achieve a full cure until at least 24 hours, sometimes longer.
Where do hardeners fit into this, you may ask? They have very little effect on ink adhesion, but have a huge influence on image durability.
Again, ink manufacturers provide hardeners that are formulated specifically to their inks. Some hardeners work with more than one ink series. This formulation also includes different ink-to-hardener ratios. Some are 4:1 (ink-to-hardener), some are 10:1 and others as much as 20:1. Technical data sheets on inks will detail all of that for you.
Hardeners are always added for inks used on metal, glass and ceramics, as well as parts (regardless of substrate) that may face exposure to abrasives, chemicals, sterilization procedures, etc.
The good thing about hardeners is they enhance image durability. The bad thing about hardeners is that they decrease the “pot life” in an ink cup (normally 8–10 hours max). The important thing is your customer gets a quality, long-lasting image.
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