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Standard heat-activated polyester films with a co-polymer adhesive tend to stick to the ink and not the paper. The laminate at times lifts off the inkjet paper, especially in those darker color areas with high ink coverage. The problem is most apparent when the laminate is flush trimmed with the print and when darker colors extend all the way to the edges with no white border.

A second problem with laminating the glossy heavy coated papers with this style of laminate is that the ink tends to separate from the paper when exposed to the high heat (210-240ºF) required to activate the adhesive. This problem manifests itself in the form of air bubbles between the print and the laminate; the popular term used is outgassing.

There is no single correct answer to this question, but rather several options that you can choose from, depending on your particular application, inventory of laminates, equipment available and other variables. The options below address multi-heat roller laminator applications.

Option 1
Change the inkjet paper you are printing on, and apply standard heat-activated polyester laminates (activation range 210-240ºF). This sounds overly simplistic, but it has been an effective solution in many cases. A more ink-receptive paper provides a better bonding surface for co-polymer adhesives and since there is less ink on the surface of the paper, there is less likelihood of the ink "bubbling up."

Even bond inkjet paper looks quite glossy when laminated with 3, 5, 7 or 10 mil gloss laminate, and a thicker laminate will make up for any loss in rigidity. Try printing the same image on a variety of papers, laminating all of them with the same laminate, and comparing the results.

What if changing the paper is not an option or if the customer brings in an unfamiliar inkjet print?

Option 2
Use a HeatSet™ (heat-assist) PVC vinyl film. These laminates have a lower activation temperature (160-180ºF) than laminates in Option 1, creating less chance of outgassing. Secondly, the thermo-plastic adhesive is more aggressive, providing a far superior bond, even on high ink coverage applications. PVC vinyls are also more pliable and, when heated, conform even better to the output and are thus less likely to separate from "stiffer" inkjet output.

The fact that these PVC films are used to laminate inkjet output on canvas, with minimal loss of texture, gives some idea of how pliable they are. The films are relatively thin (2-4 mil), so in the case of encapsulation, one may wish to consider using a thicker heat-activated polyester on the back.

Option 3
Cold pressure-sensitive laminates are a third, but more expensive option. Because they are (as the name suggests) applied cold, there is little problem with ink separating from the paper. The most common pressure-sensitive laminates are made up of Polyester, PVC vinyl or polycarbonates, coated with a pressure-sensitive acrylic adhesive that provides an excellent bond to inkjet output. (If applied on a multi-heat roller laminator, one can process the print with a little heat [110-120ºF] which will improve the flow of the adhesive and reduce any silvering*).

As with the heat-activated vinyls, one can use a thicker heat-activated polyester on the back if additional rigidity is required. Their main disadvantage is price, but if you stock this product for heat-sensitive output anyway, it may be a good alternative. If you do not yet have a multi-heat roller laminator but rather a cold pressure-sensitive laminator, it is the only option.

The above options work most of the time, but there will always be exceptions to the rule. The type of laminator, speed, pressure, heat and humidity will all influence the results. If changing the inkjet paper is not an option, paying a little more for heat-activated vinyls or pressure-sensitive laminates may prevent the need for costly reprints.

* Very small air bubbles between print and laminate, usually caused by poor "flow" of adhesive and primarily seen in pressure-sensitive adhesives. This can usually be remedied by increasing roller pressure and applying a little heat.

Marc Oosterhuis is president of Drytac Corporation in the United States, Canada and Europe. For comments and suggestions, he can be contacted by email at marcoosterhuis@drytac.com. You can visit Drytac's web site at www.drytac.com.