The printing business uses many different substrates -- some better than others.
Popular substrates today include rigid vinyl PVC, polypropylene and / or BOPP, and polyester (PET). The advantage of these plastic substrates over traditional ones is their durability. Plastics are resistant to damage by water or chemicals and can be a more budget-friendly option for many applications.
Plastic substrates produce high-quality prints if you know how to print on plastic film. High-quality prints are vibrant and full of life, which will increase your sales by attracting an audience.
Flexography is one of the most foolproof methods used to print on plastic film substrates. Here’s how it’s done:
Opt for Flexography
Some quick background: Flexography printing shares its origin with traditional printing methods. Before we jump into the nuances of printing on plastic film substrates, it’s important to understand the basis of the flexo process.
To print on plastic film, you apply ink on an anilox roller, which works with the doctor blade. This controls the process of producing an even layer of ink. The roller surface has small cells placed at a particular angle to transfer ink onto the image carrier.
Next, the anilox rollers deposit the ink to the surface of an image carrier wrapped around a rotating cylinder. The plastic substrate is on a backup roll or CI drum and the image carrier transfers ink, and thus your print, evenly onto the substrate.
As the name insinuates, flexo printing is flexible when it comes to applications. It produces prints at high speed, reducing press downtime and thus longer print runs.
How to Print on Plastic Film: 6 Factors to Keep in Mind
There are several factors to consider when printing on clear plastic film.
1. Surface Tension
Surface tension is a force in liquids that allows them to act as if surrounded by an elastic membrane. It occurs when the molecules of the liquid adhere to one another, causing a beading effect.
Surface tension affects the wettability of ink on the surface and is expressed in dynes/cm. For a successful print, the surface tension of the ink must be lower than the image carrier’s to allow it to transfer from the anilox to the surface of the image carrier properly.
2. Surface Energy
Surface energy is the surplus energy at the surface of the plastic substrate compared to its size. It’s measured in joules/sq. meter.
As you select the type of plastic substrate needed for your end packaging to use while flexo printing, it’s important to know its surface energy to avoid ending up with costly and time consuming printing defects.
Most plastic substrates tend to be very treatable in order to raise the surface energy, to ensure it is above the ink’s - allowing for the ink to “stick” to it and proper transfer to occur.
This is the ability of ink to wet the surface on which you’re printing. It’s affected by the ink’s surface tension and the substrate’s surface energy. This can also be affected by the polar quality of your image carrier.
Overall, wettability affects how well your ink lays / spreads out on your surface.
It’s vital to have good ink-substrate interaction to ensure high-quality prints when printing on clear plastic film. This results in smoother coverage, less pinholes, and overall less printing defects.
4. Ink Selection
Choose inks with surface tension that’s 10 dynes lower than the surface energy of the plastic film. This allows the image carrier to easily fall in between.
There are some actions you can take to affect the surface tension of the ink - such as adding alcohol or other treatments. However, it is much easier and more effective to treat your plastic film when possible, as noted above.
This will ensure good wettability and high-quality prints.
When flexo printing, you can accomplish zero distortion by choosing in-the-round flexo sleeves that are engraved at 100% on size.
Elastomer blend sleeves can be built to be more durable than photopolymer plates and are more flexible on substrates.
6. Time and Money
For large-scale industrial printing, working efficiently is the key to maximizing profits.
You’ll need to make proper calculations so you don't have to go back and restep because something was disproportionate. Exact stepping on plastic film is easy to accomplish with a well-made elastomer sleeve.
Get Started With Beautiful Prints on Plastic Film
Every substrate is different. Understanding the considerations specific to your project is crucial for an impressive final print.
Interested in learning about flexo printing on a variety of substrates? Check out our substrate troubleshooting printing guide here: