Remember the days when peanuts were sold in cellophane bags with a label boldly proclaiming “Peanuts” in black ink? Remember when boxes and jars had splashy, creative labels identifying the contents that called to the consumer from shop shelves? Remember the days when labels were the connection between the consumer and the product?
While those days are not over, the market is evolving to the point where the flexible package containing the product has become the label. In light of that change, many label printers are now considering venturing into the world of flexible packaging. One key transitional element for those going from label printer to flexible package maker, while using existing presses, is in the selection of print and lamination substrates. This requires an understanding of each component of the package and some knowledge of what is available.
Flexible Packaging Substrate Selection
Substrates selected for any flexible package are more than just wrapping for product. By using inks, artwork and other embellishments, packaging material can enhance appeal and be enticing to the consumer. A matte film brings a subtle tone, while a glossy look can capture attention with even a quick glance.
Additionally, films can have a certain feel or touch to mask the sterility of “plastic,” adding warmth to the package. Flexible packaging substrates provide functionality by regulating oxygen flow, moisture permeation and light transmission. The product is protected and shelf life is enhanced. The substrates can also provide rigidity in a standup pouch or flexibility in a bag of candy. The bag can be easy to peel apart or sealed so it is opened only at a place designed into the structure. Substrate selection can be as important as the artwork of a package and should be considered during initial package design.
Consistency & Growth
In what markets are overlamination films mostly used? What makes certain markets a good fit for using these materials? Are there any overlamination markets or areas of usage growing in particular?
Tom DuPont: Overlaminate films are used in a wide range of markets-everywhere from health and beauty to industrial, pharmaceutical, pet food and
even aeronautics. The ease of use and consistency of self-wound overlaminates over UV varnishes or press-applied films greatly benefits the label converter by helping to ensure the first label looks like the last. It also frees up a print station and reduces non-productive time spent dialing in the varnish or adhesive and cleanup.
One area of exceptional growth we’re seeing is in the flexible packaging market. Not surprisingly, digital printing technology continues to expand in the label and flexible packaging market. With this, the demand is growing for a wide range of robust, self-wound overlaminates designed to work specifically with these printers and finishers. Digital printing has evolved beyond short runs and personalization-High-end graphic capabilities, flexibility and low-cost setup have elevated it to assist brand owners to expand and achieve more customized marketing strategies.
To read the full Q&A with Tom DuPont, see “Overlaminates: Trends, Benefits & Market Outlook.”
A flexible package starts with a roll of printed material that is formed, sealed and filled. The forming process involves folding and cutting to a desired shape and function. The design itself can be a simple bag or something more complex with the inclusion of gussets, bottom folds, side panels, spouts, handles, etc. Edges are sealed most commonly with heat and pressure.
Along with having a material that heat seals to itself, the substrates selected for the entire package should be able to withstand the heat applied during the sealing process and any additional processes like the insertion of an olefin “zipper.” The film’s seal initiation temperature (SIT) and seal strength are part of the decision process, along with how the seal performs in the presence of contamination like tiny food particles or salt (caulkability). Typical films used for sealing include:
- Polyethylene (PE)
- Biaxially oriented polypropylene (BOPP)
- Cast polypropylene (CPP) blends
- Multilayer extrusions
Film suppliers can help with the different blends and extrusions to dial in specific seal initiation temperature and bond strength.
Heat sealing is not the only way to construct a package. Some products are compromised by heat, while other packages are designed for easy opening along sealed edges. In these cases, an adhesive can be used to seal the edges. This adhesive is normally non-tacky when dried, bonds to itself with pressure and is commonly known as a cold seal adhesive or cohesive. These can be used with a number of different substrates and allow package designers options to optimize costs by not having to consider film constructions with a heat seal layer. Obviously, cold seal adhesives are applicable for a specific segment and not to be considered for universal packaging designs.
Controlling oxygen, moisture and light transmission to the product is another important consideration for substrate selection. Oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) are usually derived from testing and analysis, and directly impact shelf life. Light transmission is generally regulated by opacity while barrier mechanisms to oxygen and moisture transmission can be layered into the film, surface metalized or coated. OTR and WVTR requirements can be dictated by the product manufacturer or can even be derived by analyzing existing packaging. Ultimately, package designs must be tested under anticipated conditions to determine suitability.
The simplest choice for a narrow web printer is a substrate combining sealing, barrier and aesthetics in a single web. This is done by combining different substrates (films, foils, paper, etc.) into a single roll product commonly known as a pre-laminate. The converter simply prints onto the pre-laminate using an existing press and then seals the print with a varnish or overlaminate film. It is a direct print process not unlike printing directly on label stock. The finished roll is then taken to a pouch-making machine to be formed into the flexible package. No new equipment is required and training could be as simple as learning a different label stock.
Other Film Options for Narrow Web Printers to Evaluate
A narrow web printer can also reverse print on a barrier film and laminate a self-wound, adhesive-coated sealing web inline on the press. The reverse-printed film is the outer layer of the package and the print is buried between the layers.
This option again uses existing equipment with a process that is not much different from printing labels. A barrier film is used instead of label stock and a self-wound sealing web is used instead of the film overlamination. The sealing web can be clear, white, metalized or even colored for a special effect. The lamination process is the same as with making labels but no die cutting/matrix stripping is required. The laminating adhesive in this case would probably be a pressure-sensitive (PS) adhesive, so end use applications should not include harsh environments like boil-in-bag or microwave. Once again, the finished roll is now ready to go to the pouch machine.
What has changed in the overlaminate market in the last five to 10 years, and what can printers expect to change in the next five to 10 years?
Tom DuPont: Concurrent with the commoditization of overlaminates has been the increased performance demand from innovative printers and end users. Innovation from printers with designs, materials, inks, etc. should drive innovations from overlaminate suppliers. The rate of innovation has increased with the advent of digital and hybrid presses. Overlaminate innovation should keep pace with-or in some cases even drive-some of these innovations. Customer regulatory requirements have also changed in the past five to 10 years. The overlaminate is no longer just a tag-along piece, but must meet requirements imposed on the rest of the product from toys to foods. Customer quality management systems have also improved, with expectations passed on to suppliers.
To read the full Q&A with Tom DuPont, see “Overlaminates: Trends, Benefits & Market Outlook.”
Another possibility for narrow web printers is one which is the same for the majority of wide web flexible packaging converters. In this case, a web is printed and then taken to another machine to be laminated to a sealing web. The laminating adhesive can now be water-based, solvent-based, solventless or even polyolefin extrusion. Notably, this option requires a second machine that a narrow web label producer may not have. Substrates for this option are generally unlimited and can be sourced from a number of different suppliers. This option can use pre-laminate structures, as well as single-layer substrates, depending on application, costs, design considerations, etc.
Substrate Made from Recycled Materials
A more recent consideration with flexible packaging substrates has gained prominence alongside the increasing awareness of the growing volume of waste. As flexible packaging becomes more popular, glass, metal and paper use decrease. Historically, recycled packages are being replaced by materials that might take many years to decompose. The plastic island in the Pacific Ocean compels designers to now more than ever consider recycling and reuse options.
One issue with current substrates is the mixture of plastics, for example using a PE sealing web and polyethylene terephthalate (PET or polyester) outside web. One solution being considered is having PE as both the sealing and print webs. Another being considered is a CPP sealing web with a BOPP print web. One could even conceive of a pure PET construction, once a suitable sealing solution is found. The recycling channels for these are not readily available or established, but there are efforts underway to identify and establish viable avenues to keep bags and pouches out of landfills and oceans.
The transformation from printing labels to creating flexible packages can be intimidating. Along with new regulations and product safety requirements comes a new array of materials and properties to consider. A new vocabulary with terms such as OTR, WVTR, seal strength, SIT and caulkability must be developed. The customer base is expanded with new questions to master. With all the changes, it is good to know that some packaging is manageable using existing equipment and operator skills. Using pre-laminate structures or self-wound sealing webs, one can start providing packaging solutions as the transformation happens.
About the Author: Tom DuPont is the corporate R&D director for acpo Ltd and is based in Oak Harbor, OH. acpo has been manufacturing pressure-sensitive, adhesive-coated films to the narrow web printing and converting market for more than 30 years. acpo films can be found on labels and flexible packaging products from the health and beauty industry to pharmaceuticals and pet foods. Recognizing the industry’s desire for innovative solutions, acpo’s R&D team continuously is developing new, innovative products for labels and flexible packaging. acpo truly lives up to its tagline, “Films with Technology. Products with Purpose.”