Compiled by Erin La Row, editor, Plastics Decorating
In-mold labeling (IML) is a decorating technique where a preprinted label is placed directly into the mold, becoming part of the packaging during the molding process. This process has advantages including increased quality and durability, recyclability, shorter production time, and reduced costs. IML also happens to be one of the fastest growing packaging decoration methods in the marketplace today. There are several processes involved in a successful IML application. It starts with the production of the IML label itself.
Plastics Decorating got insight from Kim Hill, R&D director – liquid solvent technology at INX International Ink, Co., and Adam Boehlke, product growth manager – IML at Inland Packaging, about substrates and inks used in the IML process, as well as questions producers should be asking.
What are the most common substrates used in the production of in-mold labels? Are there specific challenges with working with these?
Boehlke: When it comes to IML, specific to packaging, there are typically three common varieties of label materials – cavitated white, solid white and clear – that offer different options within and are all of a BOPP variety. The most frequently used label substrate is cavitated white, more commonly known as “orange peel” for its orange peel-like matte molded finish. This option comes in a wide variety of gauges determined by specific need(s), and/or appearance. Cavitated whites are mostly found in refrigerated grocery aisles, commonly used by consumer packaged goods (CPG) companies. The second, less widely used substrate, is solid white. This substrate offers more of a sheen or semi-gloss finish and is often preferred in the box or hardware stores – items such as containers, pails and multi-use applications. The third most commonly used substrate is a clear BOPP material. This is preferred where the end user or brand owner prefers a window to the product or a unique design option. Clears are used in all different areas of the market to offer these unique options, however, they are often limited in vibrancy, or opacity of colors, when compared to the other white film options so appropriate planning and expectations are required when using a clear substrate.
Overall, IML can be a challenging, but extremely rewarding and efficient, labeling technique. With that said, knowledge relating to substrates is a large key to success. For example, lower-density film options like cavitated materials can be more challenging on larger label applications, while solid, or higher-density films, offer more rigidity that may help lower scrap rates and mold larger parts. The key to successful and quick-to-market IML packaging is to work upfront with the chosen parties – molder, label printer, mold makers, automation/robotics, etc. – to understand any limitations, suggestions or concerns for the project. Having the proper technical resources and upfront discussions lead to an extremely efficient and dialed in product that will yield strong advantages for years to come.
Other considerations with substrate variations may also include artwork design, label handling, speeds/cycle times, scrap management, mold flow and temperatures, and resin color for end containers, among other items. All of these items can and should be discussed with the partner companies upfront.
What special formulations of inks are needed for the printing of in-mold labels? Are there any special coatings or curings that must be incorporated in the production of inks for in-mold applications?
Hill: There are several key attributes when formulating inks and coatings for in-mold labels, beginning with heat resistance. The resin used in the molding process is hot so the inks and coatings need to withstand these temperatures.
Coefficient of friction (COF) and curl are important factors. When the label is placed in the mold, COF helps prevent it from moving or sliding around when the resin is injected and helps ensure the label is placed correctly on the containers. The in-mold label film is very thin and adding inks and coatings can make it more rigid. The label edges can curl if it becomes too rigid, and if the label isn’t flat and smooth the mold won’t stay in place.
There are resistivity and static dissipation considerations as well. Labels are often held in place in the mold with static. The inks and coatings must be formulated to keep the label in place during the injection mold process. Many in-mold containers are household cleaners and detergents, so often there is a product resistance requirement of the ink and coating when working with these types of products as well.
Are adhesives involved in the manufacturing of in-mold labels or used when applied to plastic products?
Boehlke: One of the major upsides to standard IML packaging is not having a need for adhesive. Adhesives will add an extra layer of variability and challenge to any label type, so to avoid this (as the label “adheres” naturally to the liquid resin during the molding process) is a large positive to this type of cut and stack label.
In some cases, applications will require a more robust label option which may require the base BOPP label film to be laminated or adhered to another label film – for protection and/or appearance. In this case, an adhesive is often necessary; however, this should not affect the molding process as long as the laminated material still maintains the same static properties during the molding and handling processes.
Is registration in the printing and diecutting of in-mold labels an issue? If so, what precautions need to be taken to ensure accurate registration?
Boehlke: Registration in the printing and diecutting of in-mold labels is critical, more so than most other types of labels used in the market. IML label tolerances are some of the tightest in the packaging industry due to the requirements of equipment for precision high-speed molding. In order to maintain these tolerances, specialized diecutting equipment, specific for thin gauge film substrates, have been developed and are necessary for precision diecutting.
With diecutting tolerances being as tight as they are, print registration is often critical as well, given the detailed graphics often incorporated within IML packaging. Unique and customized shapes often present a unique challenge to maintain the, also extremely tight, print-to-cut tolerances – or the movement of print allowed within the die line/cut of the label. Similar to the actual cutting of the label, specific print technology has been developed to monitor print and press movements to take these tight tolerances into account and maintain the needs of IML.
What types of questions should be asked by a producer of in-mold labels to ensure a quality product for the in-mold labeling process?
Hill: For new inquiries from printer or converter customers, we definitely need to know the in-mold label substrate. The films vary in the market and ink recommendations need to be validated for the exact substrate. The film plays a key role in the testing of the inks and coatings, and the film itself is not chosen by the in-mold producer. This is generally decided by the in-mold label printer. It also is important to know about the product or end-use to determine if product resistance will be a factor.
What types of limitations from a printing and production standpoint are there with in-mold labels compared to more conventional label applications?
Boehlke: From a purely IML packaging perspective, respective of IMD or more durable applications, most of the world’s leading IML label producers are printing offset/lithograph. This type of printing offers a wider sheet layout than traditional flexo, while offering a more competitive platform than the latest digital technologies. Because of this, producers should understand the capabilities and technologies of offset printing. Personally, I would put world-class offset print technology up against any of the various print technologies, relative to print quality, clarity and graphics quality. Options and availability in print partners, raw materials and technologies when it comes to more traditional pressure-sensitive or shrink-sleeve decoration methods are more plentiful at this time than those of IML.
While one can create a wider variety of options to fit various packaging types, shapes and sizes than traditional label decoration, it is important to understand the IML label options and embellishment abilities of the molder and supply chain partners. When it comes to packaging, there are several notably strong raw material suppliers, equipment and original equipment manufacturer (OEM) partners. Utilizing these strong supply partners, it is critical to ensure needs and capabilities are discussed up front by all parties – printer, molder, mold maker, automation/robotics, brand owner, etc. to ensure expectations are clear on how to accomplish the desired look and feel of the end package.
Plastics Decorating would like to thank Kim Hill at INX International Ink, Co. and Adam Boehlke at Inland Packaging, for their assistance with this article. Learn more about INX at www.inxinternational.com and Inland Packaging at www.inlandpackaging.com.