By Lou Piffer, consultant, Extrusion Training Solutions

Extrusion coating and adhesive lamination both coat and laminate substrates to create more complex structures. Although the methods have similarities and often can be used to make the same structure, converters have opinions on which asset to use for a given end product. This article is the result of surveying a number of those converters, noting when they lean toward adhesive lamination and where they prefer extrusion coating.

The following is the third paper in my series of articles comparing extrusion coating to adhesive lamination. The first two articles, “Extrusion Coating in an Adhesive Lamination World” and “Extrusion Coating vs. Adhesive Lamination – A Comparative Study,” can be found in Converting Quarterly Quarter 2, 2015, and Quarter 3, 2022.

Factors that affect the decision (leaning to adhesive lamination)

The following factors help determine whether to use extrusion coating or adhesive lamination, with a nod to adhesive lamination as the most likely choice.

Volume: When I wrote the first paper in this series, the simplest reason to go with one process vs. the other was “long runs go extrusion coating, short runs go adhesive lamination.” This wisdom still applies, with one converter saying, “When we get a non-legacy product, all things being equal, we first look at adhesive lamination.” Extrusion coating has a greater scrap rate of 5% to 9% compared to adhesive lamination, which can be less than half that amount. The extrusion coating scrap rate reduces as larger volumes are processed. On average, converters want a run of at least 10,000 lbs of product for extrusion coating to be considered.

Retort: Retort temperatures need to withstand temperatures of 250° to 275° F. The weak link in the extrusion process is whether the process requires a primer. An extrusion primer able to withstand those temperatures would be solvent-based, difficult to apply and require an exceptionally large dryer. Traditionally, this product is made via adhesive lamination.

Fitments: Fitments are HDPE buttons or spouts added to a pouch (see Figure 1). Higher temperatures are required to melt the grooves on the fitments for installation. These temperatures could liquefy LDPE, resulting in a lack of support for the other layers in the structure and flex cracking.

Curl: Asymmetrical structures, when subjected to extrusion coating temperatures, can curl due to differences in cooling rates. The effect may not be acceptable for certain structures that require tight print repeats or require stacking during the filling process, such as lidding stock.

Mono Materials and Sustainability: Once again, the temperature utilized in extrusion coating can invalidate it as a process. Replacing a thermally stable preprinted substrate, such as PET, with a less thermally stable polyolefin substrate can lead to stretching of the film, resulting in inconsistent registration. Work is being done in this area to anticipate this stretching while maintaining registration, but it adds complexity to using extrusion coating.

Extrusion coating can win the day if a thin product is considered, such as a chip bag. The thinner the product, the higher the percentage taken up by the adhesive or extrudate. This can be an issue in adhesive lamination because adhesive lamination uses a non-plastic adhesive. If the percentage of that non-plastic component is over about 10%, the product may not be considered a mono material, depending on the laws in the area. This can reduce the market for and value of both the end product and the trim that will be generated.

Extrusion coating also has the environmental advantage of being able to extrude a biopolymer.

Sealant films: In my discussions with converters, in general, the thicker the sealant film used, the greater the chance that adhesive lamination is the process employed. Specifically, if the sealant film is over 1 mil and if the blown sealant film must impart stiffness to the end product, adhesive lamination is used. For sealant films less than 1 mil where stiffness is obtained through other layers, extrusion coating can be a candidate.

Eliminating the blown sealant film by replacing it with an extrudate can be a great way to minimize costs, but before you do that, you need to see what you may be losing with the loss of the blown film, such as strength and low seal-initiation temperatures.

Chemical resistance: When trying to contain water, alcohol-based materials or extremely acidic products (strong spices, hot sauce, cleaning chemicals), solvent primers normally are required instead of water-based primers. US converters prefer to keep their extrusion coating lines solvent-free, leaving adhesive lamination as the process to package these materials.

Factors that affect the decision (leaning to extrusion coating)

The following factors help determine whether to use extrusion coating or adhesive lamination, with a nod to extrusion coating as the most likely choice.

Triangle of death: This colorful term was coined by a major brand owner when describing the effect that can occur when a chip-bag package goes through a form, fill and seal machine.

When a fin seal is formed and then flattened during the bag-making process, there is a hinge point created in the bag where stresses build up. When the clamps release the bag, the fin seal pivots on the hinge point, creating stress at the hinge. The bonding material attempts to normalize those stresses. The thinner, more brittle adhesive does not respond well to the movement of this hinge and creates voids in the product (see Figures 2a and 2b). Extrusion coating is thicker and more flowable, reducing the chance of a void being formed during the creation of the bag (see Figure 3).

Increased sealing speeds: In adhesive lamination, sealing occurs using a blown-film sealant, while in extrusion coating, you have the option of using a blown film or eliminating it and sealing with the extrudate. This last option can save money by having more of the end product come from pellets instead of paying for the conversion cost of the blown-film substrate. Many converters noted that if you seal on an extrudate, you can achieve higher sealing speeds because special lower-MI resins can be used that may not lend themselves to running on a blown-film line.

Sealing on an extrudate instead of a blown film may have its cost advantages, but as mentioned before, you first need to make certain you are not sacrificing toughness, stand-up ability or the need for a lower seal-initiation temperature (SIT).

White background: To make graphics pop, a white background often is needed behind the graphics. In adhesive lamination, those graphics are achieved through a flood coat in a multi-color flexo or gravure coater. Extrusion coating achieves this effect through a white masterbatch blended into the main coating or laminating resin (see Figure 4). The method utilized by extrusion coating saves money. In addition, the background achieved in extrusion coating can be more opaque than the flood coat in adhesive lamination.

Another advantage is that you gain an additional color in the printer, and the dryer can be smaller by eliminating the need to apply and dry the flood coat.

Pet food: When providing food for pets, we need to worry about the packaging as well as the food. Adhesive lamination using solvent coatings may create a package that will be unacceptable to our pets and their much more sensitive noses. Most of the converters I spoke to in the US said that if a package is to contain pet food, they stick with extrusion coating.

Pharmaceutical packaging also often is run solvent-free, which can tip the scales to extrusion coating.

Paper and Board Coating: When coating or laminating a paper or board substrate, adhesive lamination can be an expensive proposition due to the amount of adhesive that will sink into the substrate compared to running a more impervious film or foil. If an adhesive is needed on a paper substrate, like in a backing paper for release coating, extrusion coating can be first applied to the paper to allow the use of a minimal amount of silicone without absorption concerns.

Multi-wall sacks: An extrusion coating laminator can run with a rubber nip roll that creates a “loose nip,” resulting in voids in the extrudate/nip interface. These voids can help improve the resistance of the bag to tearing. A good example of this process is used in industrial French fry bags.

Foil: When you run foil and want to prevent flex cracking, you need to ensure it is well supported during the packaging process. The flowability of extrusion coating can provide that support. I was told by multiple converters that if foil is in the structure, unless it is buried in a tri-lam structure, they first look at extrusion coating. One exception is fitments, where the elevated temperatures employed can liquefy the extrudate, taking away the support for the foil.

In summary, there is no perfect process. Neither extrusion coating nor adhesive lamination will eliminate the other. What is important is to understand better their individual strengths and weaknesses so the optimal asset can be purchased and used for a given application. 

Lou Piffer worked at Davis-Standard for 36 years in Extrusion Coating Sales. He recently retired and started his new company, Extrusion Training Solutions, where he provides consulting and training to the extrusion coating industry. He is a Tappi Leadership and Tappi Technical award winner, as well as a winner of the Davis-Standard President Award. Lou also has taught at the Extrusion Coating Short Course for over 30 years. He can be reached at email: lou@extrustioncoatingtraining.com.