Pad printing on polypropylene can be challenging. When it comes to pad printing on Polyethylene and other substrates, the team at Liberty Clark are subject matter experts. Pad printing on polypropylene requires a unique process to achieve successful ink adhesion.

What Makes Pad Printing On Polypropylene Different?

Without the proper pretreatment process, in most instances, pad printing ink will scratch off very easily even after the ink fully cures. This is because polypropylene and other substrates have a surface tension that is below the minimum requirement for pad printing. Surface tension is measured in Dyne units, and pad printing inks generally require a surface tension of at least 42 Dyne. Untreated polypropylene is often well below 42 Dyne.

We also pad print on the following substrates:

  • Acetal (homopolymer)
  • Acetal (copolymer)
  • ABS (acrylonitrile butadiene styrene)
  • Acrylic
  • Copolyester
  • Fluorosilicone
  • Nylon (polyamide)
  • PC-ABS
  • PC + Amorphous Polyster
  • Polycarbonate (PC)
  • Polyethylene
  • Polypropylene
  • Polyarylamide
  • Polyetherimide (PEI)
  • Polyurethane
  • PVC (polyvinyl chloride, rigid)
  • Rigid Polyurethane (3D printed)
  • Silicone
  • Steel (powder coated)
  • Steel (303 stainless)
  • Thermoplastic Elastomer (TPE)
  • And More

Pad Printing Pretreatment

It’s possible to raise the surface tension of polypropylene to a level at or above 42 Dyne with a flame or corona pretreatment process. Flame pretreatment involves a torch and is used when preferred methods are not possible. Corona pretreatment is the preferred method as flame pretreatment is more difficult to control, hazardous, and can easily damage components. Corona pretreatment is a low frequency plasma discharge process that is controllable, repeatable, less hazardous, and is a proven process to improve pad printing ink adhesion on polypropylene.

Testing Polypropylene Dyne Levels

Once the polypropylene has been corona treated, Liberty Clark will measure the surface tension with a Dyne ink pen to confirm the minimum surface tension has been achieved prior to printing. Our process involves pad printing the same day as the corona process occurs. Testing is required for every component and substrate. Not all polypropylene is the same.

Several pad printing ink manufacturers offer ink systems with claims of ink adhesion onto polypropylene without a pretreatment process. If durable ink adhesion isn’t critical then expectations may be met with these systems. For medical syringes barrels, on the other hand, ink adhesion may be critical.

Corona treatment also raises the surface tension of additional substrates. For substrates that require more power than Corona pretreatment, the use of a high frequency plasma discharge machine should be considered.