By Dianna Brodine, vice president, editorial, Plastics Decorating

As demand grows for premium packaging, production efficiency and recyclable solutions, in-mold labeling (IML) continues to evolve as one of the most versatile decorating technologies in plastics manufacturing. Yet achieving success with IML requires far more than selecting a label. From project planning and print method selection to troubleshooting molding issues, optimizing static pinning and evaluating emerging PCR materials, every stage of the process demands collaboration among molders, printers, brand owners and automation experts.

Bob Travis, president, InkWorks Printing, and Adam Boehlke, IML product manager for Inland, answered questions about in-mold labels during a recent In-Mold Meet-Up for the In-Mold Decorating Association (IMDA). They discussed the critical questions that should be asked at the start of every project, the advantages and limitations of various printing technologies, common troubleshooting approaches, the impact of recycled-content substrates and best practices for static management. Their perspectives highlight a common theme: The earlier the right partners are involved and the more information shared throughout the process, the greater the opportunity to deliver a successful IML solution.

When a new IML project comes in, what initial questions are asked?
Boehlke: One of the first questions I ask a molder or brand owner is, “What do you want to prioritize?”

IML does two things very effectively: It creates efficiencies, and it creates a higher-end decoration method. Sometimes, molders and brand owners want to create efficiencies; sometimes, they are focused on the decorative possibilities; and ideally, some see the best path is to focus on both. For example, there’s too many folks out there that still utilize a clear label to showcase the resin color when they could be fully encompassing the decorated part with a fully beautifully decorated IML label. Most of those folks are going for efficiencies over higher decoration.

The second thing that I’ll ask a new customer is whether they’re open to optimization. Optimization is very important upfront in communication with OEMs and brand owners and especially the molders themselves. Optimization can come in a multitude of ways, but as an example: Too often, the mold has already been designed, a system has already been bought, a footprint has already been established, and then a label printer is selected. At that point, it’s too late to optimize by looking at a different label size that doesn’t change the marketing capabilities of the package or the container and could have saved 20% to 30%.

Travis: When we’re called in on a project, the first question is, “How are you decorating today? What are you hoping to gain by doing IML?” If the current decoration method is heat transfer or pad printing, the question becomes, “Are you happy with what you’re doing today?” Because if you are, there’s probably not a real reason to switch to IML.

There needs to be an additional benefit that you’re looking to achieve. If the current method is pad printing and the product doesn’t meet the customer’s needs, now we have a reason to look at IML. It’s finding that other functionality, that other benefit, that’s so important.

And, Adam’s spot on – hopefully, we’re being involved early in the whole process. It’s a lot easier to design an entire system with all the right people around from the beginning rather than launching into something secondarily. So, while we can go into a lot of existing molds and make an IML work, making it work or designing it to work are really two different things. We’d much rather design it to work. We get a ton of calls from brand owners or consumer packaging companies – they’re novice to IML and don’t understand the relationships that need to be orchestrated. Having key folks involved right up front allows everyone to talk and a project to run smoothly.

What should be considered when determining the best printing method fit for an application?
Travis: Almost any printing method can be carried into in-mold decoration, and it really comes down to the end case for the label itself after it’s been molded in. So, whether it’s screen printing, flexo, offset or digital, if the label provider is familiar with the art and science of in-mold decoration, they can make an IML label that will work in most of the solutions that are out there.

The use case does make a difference. Screen printing is the most appropriate when you’re looking for very heavy, specialized laydowns. The best example of that is in the appliance industry or automotive industry, where the longevity of the inks is key, and that’s where screen printing has its place. You would not take screen printing into the decoration of a food package, unless you weren’t looking too closely at the appearance and dot quality. The basics of the printing methodology gets to the durability of the inks and what we’re asking the in-mold label to do after it’s been molded and in the final product.

Boehlke: At Inland, we have digital, flexo, offset and gravure capabilities. And, as we review the print processes for project applicability, the capabilities and limitations help decide which method is most appropriate.

For example, digital print probably gives you the widest window of substrates and decorative options, but you’re limited on volume. Flexo offers a wide array of capabilities, including the ability to venture into more durable labels with laminations. Offset has traditionally dominated the packaging space with consumer goods and food products. And then, gravure is still specialized in some areas, such as roll-to-roll, because it’s more difficult to sheet. The process decision comes down to understanding the print capabilities of each and having a clear picture of the requirements for your final part.

When projects aren’t quite going right, what does the troubleshooting process look like?
Boehlke: The label is showing the visual defect, but that doesn’t always mean the label is the reason for the defect. We preach it time and time again: Pictures – and videos – tell a thousand words. Videos help us see things that are happening in the process, in the automation or in the mold itself rather than speculating about what might be going on. Then we can come to the table to discuss the things that could be affecting the end product. Too often, I think customers believe we’ve seen it all, but the one thing about IML – and anyone involved with IML would probably agree – if you think you’ve seen it all, you’re wrong.

It’s more about trying to create consistency. If you’re seeing something that’s consistent and frequent in a cavity or on a specific machine, and it’s reoccurring in the same fashion on an in-mold label, chances are it’s more of a mechanical-led issue. If you’re seeing something that’s occurring randomly and inconsistently, those are label-related issues. To create that consistency, we can look at alternative film options, die line changes and a multitude of different options to help improve the finished part.

Travis: Diagnosing the problem often starts before we get involved, and that can cause delays in finding the true problem. If we hear, “The label is melting through, so we need a thicker label,” the problem has been diagnosed, but the solution is almost never going to be a thicker label. If a label melts through, it’s because the tooling component is not cooling the label sufficiently to prevent the melt-through – so, a thinner label actually solves the problem. But when diagnosis occurs prior to us understanding where that failure mode is occurring, without us seeing samples, we end up chasing ideas instead of finding solutions. It serves us well to get samples and video of the failure mode and a description of how it occurs. It’s about gathering information before we start diagnosing solutions.

How should static pinning be optimized in the IML process?
Travis: Static pinning requires thinking about the mold flow across the IML and then selecting the areas to pin the label down. It’s not necessary to pin the entire label to be perfectly flat against the tool surface – in fact, in a lot of cases, that will compound the problem of how well the label will mold. The label needs to have some freedom to move along with the flow front. The key is to pin the leading edge of the label down tightly, so when the injection flow encounters the label, that edge is flat against the tool. After that, the flow itself will iron the label out.

In a lot of cases, people go overboard with the number of pins they’re putting on their end-of-arm tooling and imparting far too much static. More is not better from a charging standpoint.

Boehlke: Our mantra’s always been that less is more from a static standpoint. And it sometimes requires a trial-and-error period to find those perfect pin spots. To Bob’s point, it doesn’t have to be perfection, and it doesn’t have to be overdone.

The other side of static optimization is that delivery of the label into the tool surface is critical, and getting the labels out of the nest one at a time is the most critical piece. What we often see with automation design is, if the label shape is a rectangle, the instinct is to grab the label by the four corners. But, when you’re picking up two surfaces that want to stick together, whether it’s inherent static within the materials or van der Waals forces, it’s better to move those section cups in so that the label drapes a bit. This helps break the static forces when picking the label out of the stack, which gives you a better chance of getting the label into the mold correctly.

Do PCR (post-consumer recycled) resins add or detract from the IML process?
Travis: The films that are available right now with PCR tend to be ethylenes, and those films are used in the flexible packaging industry. But we have also used those for IML products, and they’ve gotten better in a very short period. The initial PCR films were full of gels and imperfections from the recycling process. That has been alleviated, and the films we now receive look quite good. When it comes to polypropylenes, we haven’t seen a whole lot with PCR content, but in the world of engineered plastics, the resins we use for ABS can carry a lot of PCR content and it doesn’t impact performance.

Boehlke: If you’re talking ABS or other types of materials specific to high-speed IML and large-scale packaging, the print surface is the most important part – specifically, the whiteness, opacity and consistency when we’re setting up our presses and press profiles to meet customer standards and specifications.

From a PCR standpoint, the same issues exist today that existed 10 to 15 years ago when PCR first became a hot thing in the paper field. The challenge always was to maintain a consistent sheet. And, it’s a higher-cost material. When using a mix of virgin and post-consumer content, it can be questionable as to where the post-consumer is coming from. Making a mix that creates a consistent white sheet that matches the printer’s profiles is extremely difficult at the end of the day. In the network that I work in, there haven’t been many requests for this yet on the food packaging side within the polypropylene space.

Overall, the large BOPP film suppliers are heavily exploring this area, likely waiting on demand to swing in North America to adopt a viable and repeatable commercial grade. Assuming demand and interest continues in our marketspace, options and development will be proposed.

For more information, visit www.inkworks.com and www.inlandpackaging.com. To join future In-Mold Meet-Ups, register at www.imdameetups.com/meet-up-event-dates.