Pad printing ink hardener is a catalyst that is sometimes used in different ink series to increase adhesion and abrasion resistance. But how do we know when its time to use it?
A pad printing ink hardener is a catalyst added to various ink mixtures. It works as a curing agent. The hardener makes the ink more durable, withstand abrasion, increases adhesion to some substrates, and in some circumstances, can be used to protect prints from outdoors/weather. Hardener also helps the print withstand certain chemicals such as cleaning agents. It is important to check the correct mixing ratio of hardener to ink, it will vary depending upon ink series and hardener type.
The use of hardener will also aid in the adhesion of ink. Items that are higher density may require hardener in order to increase adhesion. High-density parts, such as hard plastics, are known to be difficult substrates when it comes to adhesion.
The good thing about pad printing ink 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).
There are also heat activated hardeners whereby the catalyst will polymerize or cure only when the decoration is heated to a certain temperature. This is a great advantage if pot-life is a consideration.
All hardeners are sensitive to humidity. Therefore, the drying process must take place at the lowest possible ambient humidity in the first 24 hours, otherwise, parts of the hardener will react with the water instead of the ink. During storage of the hardener any contact with humidity must also be strictly avoided (containers must always be completely closed after use!). Furthermore, the degree of cross-linking of hardener and ink, subsequently the chemical and mechanical resistance of the printed 2 component ink, is highly dependent on the temperature. By a forced drying of the ink at 140°C-150°C for 20-30 min. directly after printing, the best possible cross-linking and thus the highest resistances will be achieved. ink systems can also be dried at room temperature; the complete cross-linking will, however, take up to 7 days and may have a reduced resistance. On difficult substrates such as glass, some metals, thermosetting plastics, and high requirements, (e.g. dishwasher-resistance), forced drying of the ink in the oven may be essential.
First and foremost it is important to check with the ink manufacturer about how much pad printing ink hardener you should add. Pad printing ink series vary by one-component (does not require the use of hardener) or two-component (does require the use of hardener). Most ink series would be considered both a one-or-two-component ink, meaning you can use hardener if you desire.
The use of hardener is dependant on the end-users need. Do they request that the print have a higher abrasion resistance or is it fine without the hardener?
A hardener is sometimes requested to be left out of ink mixtures because it will affect flexibility. While pad printing ink series, such as our Sapphire® SB Series Ink, are flexible and can generally stretch and bend with the part without damage, and added hardener could make the print more rigid and less flexible. Causing the print to crack if bent or stretched too much.
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