Handling Flexible Substrates: Not All Materials Are Created Equal

According to Richard Black, VP business development, All Printing Resources — a supplier of flexographic supplies, equipment and training — web handling needs to be a large part of the focus when working with flexible substrates because not all materials are created equal.

“What might be fine for a 60-lb. label stock,” he says, “just can’t handle it when you get into some of the really thin films and pressure-sensitive materials.”

Process printing press fingerprint run on 18gsm spunbond nonwoven at Web Industries. Image courtesy of Web Industries.

Maintain Tension, Eliminate Variables

One of the most important considerations when working with flexible substrates is to maintain tension during printing and converting. Carl DuCharme, products and applications leader at Paper Converting Machine Co. (PCMC), a flexographic press manufacturer, explains that there are many aspects of the converting process that “may affect tension outside of the abilities of the components to manage and control tension.” Some of those variables can include moisture, heat and the treatment of the material itself. In order to combat this issue, DuCharme suggests implementing a system with sufficient programming that will read the properties of the substrate and adjust heating and air flow patterns accordingly.

“The closer you can get to the machine being able to automatically adjust,” he says, “it will help to eliminate a lot of the variability that the substrates bring into the process.”

Ken Sheets, technical manager, health and hygiene at Web Industries, which specializes in outsource converting and end-product contract manufacturing, stresses the importance of maintaining consistency with plates.

“We’ve learned that you need to go with one print plate supplier,” he says. “You need to partner with one graphics house that has your fingerprint and will use consistent plate material in order to have consistent quality.”

Challenges with Nonwoven Substrates

When it comes to working with nonwoven substrates, the challenges and solutions are slightly different.

“Your challenges in nonwoven are processing the nonwoven under low tension so that you don’t neck-in the material and stretch it, deform it or have excessive print repeat variation,” Sheets explains.

Not only do nonwovens have to be processed under lower tension, they are very porous materials. Sheets explains that if trying to print high ink density designs on nonwovens, ink can pass through the material and coat the impression roll.

SMS nonwoven under magnification, comparing printed with unprinted surfaces, showing the surface irregularity challenges with printing on nonwoven. Image courtesy of Web Industries.

“If that happens, you won’t run very long before you start to have quality defects because your impression roll starts to get coated with ink,” he says. “Then you’re no longer printing on a nice, smooth metal surface, you’re printing on dried ink.”

When the ink strikes through the material, Sheets adds, it can also cause ink transfer on the back of the sheet, which will necessitate downtime as the roll is cleaned.

Nonwoven fibers may also pull off during the printing process and become stuck on the plates and create ink spots on the final product. Sheets stresses the importance of keeping the print cylinder clean by using an on-line plate cleaner or by shutting down frequently to clean the plates. Another way to prevent print defects is by using a web cleaner on the nonwoven prior to the print station to remove excess fibers.

Ensure Color Control

When assessing color control on flexible substrates, DuCharme explains the key is identifying what variable needs to be controlled. Sheets recommends the converter or ink supplier test any substrate introduced to a facility to develop a better understanding of its unique properties.

“They can do rollouts or drawdowns of the desired ink formulation on that substrate. … Every substrate has different properties and color, so you have to adjust the pigments in your ink to get the exact color a customer wants to see once the ink is applied,” he says.

Perform Tests Prior to Production

Sheets says rub testing and ink adhesion checks can also be done before going on press to ensure that the substrate will perform as intended. Having the flexibility to run either water-based or solvent-based ink on nonwoven allows the converter to choose the best ink system to match the customer’s performance requirements.

Black recommends printers review the Flexographic Technical Association (FTA) FIRST specifications and running fingerprint optimization to ensure the right screening, anilox and solid ink density.

Black explains that All Printing Resources is new to the process of working with flexible packaging substrates on its narrow-web equipment, but that there are a lot of educational resources out there that can assist in the learning process. He suggests turning to organizations, such as FTA or TLMI, or even vendors, to get a better understanding of how equipment and substrates should be handled.

“I’ve been in flexo 11 years,” he says, “and 11 years ago, there weren’t a lot of resources. Eleven years later, there are, but some people don’t know that.”