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The problem that arises is due to the fact that the temperature required for these laminates to bond may cause many ink jet prints to what we call "outgas." That is to say that you will see areas on the laminated print where the ink has bubbled away from the print itself. This has happened because the inks, whose water content has not fully evaporated, have basically been boiled.

Because of the water content in most ink jet inks, it is inevitable that if there is any moisture in/on your print, and this moisture is exposed to the high temperature required for these adhesives to "flow," the moisture in/on your print will boil and want to escape. The steam that is created as a by-product cannot escape upwards through the laminate, thereby forcing the laminate away from the print and creating what can best be termed as bubbles in the finished product.

There is another problem that you may face when printing this type of output and using high temperature thermal laminates. When you print onto coated papers as opposed to standard bond papers, what happens is that your ink jet inks actually rest on top of the paper instead of being absorbed into the paper (as is the case with bond paper). The end results can sometimes spell disaster when attempting to apply a thermal overlaminate. Why? Well, there are a number of reasons, the first being that polyethylene adhesives (copolymers) are not as aggressive as acrylic or thermoplastic adhesives. What happens is that they bond to the top layer of inks that are resting on the top of the paper, as opposed to bonding to the actual paper itself. The outcome of this is that the laminate may peel away from the paper, taking some of the inks along with it.

If you feel that you would like to continue using these products because of their relatively low price, there are ways to circumvent the obstacles that thermal overlaminates sometimes present. The first being that you can switch your media from coated paper to a more absorbent alternative like bond, presentation bond, or matte paper. Another way to overcome these problems is to be sure that your ink jet prints are in fact dry before lamination. One can sometimes be deceived by a print that both looks and feels dry, but if it has heavy ink coverage (i.e., a lot of dark colors), then there will be a very high risk that outgassing will occur. On high ink coverage, ink jet prints, this could mean waiting as long as a day or two for the print to dry.

Another ink jet-specific problem that you may face with thermal laminates is that many ink jet inks have glycerin added to their makeup, so that the inks can be fired through the nozzles. The problem you face at the finishing station is due to the fact that the polyethylene (copolymer) adhesives cannot bond through these glycerin particles (acrylic and thermoplastic adhesives will). That is why it can be so easy to peel away a thermal laminate from an ink jet print printed onto a coated paper.

If you encapsulate the print (i.e., if you apply a laminate to both sides of the print bonding with a 1" seal around the edges), you should be able to overcome this problem. If encapsulation is not really an option for your specific application, try leaving a white border of unprinted paper around the periphery of the print. The laminate will then be able to bond directly to the paper around the edge of the print, greatly reducing the chance of having the laminate peel away.

Another drawback when using these materials is that they are not compatible with vinyl substrates and/or media. While they will bond to vinyl for some short-term applications, if the print is designed for medium to long-term use, the polyester will not expand and contract with the vinyl materials when they are exposed to extreme heat or cold. The end result is a cockling of the print that will at best leave cracks on the print. At worst, the laminate will have buckled away from the substrate altogether.

One more thing to remember is thermal laminates do not bond while heating, they bond while cooling. What this means to you is that you must have steady uniform tension (and a cooling apparatus for thicker films) to ensure that you do not get waves or wrinkles in the output. If the laminate is not perfectly straight and flat while cooling, it will not be perfectly straight when you give it to your customer.

Low-Temperature Thermal Laminates
These laminates are relatively new to the large-format graphics scene, and being used as a thermal laminate replacement, due to the problems faced when laminating ink jet output with high ink coverage. Like standard thermal laminates, these new low-temperature versions are predominantly polyester with a polyethylene (copolymer) adhesive. What has been done, however, is that the manufacturers of these films have manipulated the chemical makeup of the adhesive so that it will begin to "flow" (or get sticky) at a lower temperature (approximately 185-210ºF, depending upon the manufacturer).

Because these products have only recently been introduced, they are a little more expensive than standard thermal laminates. Their price should decrease somewhat once they have replaced standard thermal laminates on a permanent basis, as is expected.

Just because these laminates now bond at a lower temperature does not necessarily mean that they have become the overnight cure-all for the problems faced when laminating ink jet prints. Like standard thermal laminating films, low-temperature thermal films have a polyethylene (copolymer) adhesive. Hence, the problem of having the adhesive bond to the top layer of ink (in photoglossy paper applications) as opposed to the paper still exists. To overcome this problem if you are faced with it, either switch the type of paper you are printing on, or encapsulate the print leaving a "lip" of sealed laminate around the edges.

HeatSet (Heat-Assist) Films
These films are almost a hybrid between thermal and pressure-sensitive films. They are similar to thermal films in that they require heat to bond (170-195ºF), but are similar to pressure-sensitive films in that they are for the most part vinyl (although Tedlar, polyester, etc. will sometimes compose the films) and have the same, if not better, bonding characteristics. These laminating films come with a release liner as the adhesive on these films are still slightly sticky when cool. These films are also very flexible. If you are unsure of what a HeatSet laminate actually is, or whether you have seen one, just keep the following in mind: if it is a heat-activated overlaminate and comes with a release liner, then it is probably a HeatSet film.

These HeatSet films have a thermoplastic adhesive (that almost always incorporate excellent UV qualities) that is far more aggressive than the adhesive on low-temp and standard thermal films. Unlike standard and low-temp thermal films, these films will bond right through the inks to the paper itself, even on prints with very high ink coverage on photoglossy paper. They can be applied on most laminating equipment, including hardbed and vacuum presses, which the aforementioned laminates cannot (at least not with the same quality).

Another attribute of these films is that they are ideal for use on textured substrates like canvas, because they are very flexible and will conform to the substrate being laminated. An application that has until now been largely ignored is the lamination of banner material. Because these laminates are vinyl, they will allow this material to retain its flexibility. In fact, the vinyl versions of these HeatSet laminates will expand and contract along with this material, so that the print will have a much longer life and will not be returned to you cracked or with the laminate buckled.

There are perhaps only two drawbacks when using these films. The first is that these materials are lacking in rigidity (although I have heard that a 15-mil rigid vinyl with these same adhesive characteristics may be hitting the market in just a few months). The second factor to keep in mind is that they are quite a bit more expensive that thermal laminates.

To overcome the rigidity problem that you may face when using these laminates, apply a thick (approximately 10-15 mil) polyester thermal film to the back of the print. Applying a polyester to the back of a print will not affect the inks on the front, so you can continue to use your standard high-temperature films on the back of any print for rigidity. With regard to the second factor--price--your waste when using HeatSet products can be minimal when compared with thermal films and the possible cost of reprinting an image. And, how much does peace of mind cost?

Liquid Laminates
Although relatively new to the large-format and digital graphics markets, liquid laminates have, in fact, been around for decades. Very few people perceive liquid laminates as a stand-alone method of finishing prints, but rather complementary to laminating films. Their benefits include offering excellent moisture and UV protection, not to mention their low price.

Some companies are presently using liquid laminates to pre-coat their ink jet prints before laminating because they find it easier to laminate their prints afterwards. Plus, users like the added benefits of the UV and moisture protection that it offers their customers. If you would like to mount prints, provide specialty or textured finishes, provide your print with more rigidity, or simply encapsulate a print, then liquid laminate technology will not be the right option for you.

Much like HeatSet laminating films, liquid laminates are also excellent for coating textured materials like canvas or banner material.

The Final Word
The important point to remember is that not every solution is either right or wrong. Your choice will largely depend upon what type of inks and media you will be laminating and the volume being laminated. If you¹re only doing a few prints, or laminating heat-sensitive output, you will have a greater chance of success using a pressure-sensitive or HeatSet laminate. If you are laminating xerographic, offset, electrostatic, or a high volume of prints, then thermal laminates may be best suited for your application.

If you¹re unsure of what laminating material is most appropriate for your output, remember that you can always contact your film vendor for advice. They should be able to assist you with any concerns that you might have.

Educate your customers as to what is available to them. Sometimes they may opt for 3-mil gloss because they’re not sure what the best option is for their output. Let the salesperson in you come alive! I am certain that by showing your customers what finishes are available to them, and by charging them accordingly for a premium finish, your finishing department will continue to be a lucrative profit center for your business.

Hayden Kelley is the General Manager of Drytac Canada Inc. Drytac is a manufacturer and distributor of mounting, laminating and finishing materials and equipment, as well as installation & finishing accessories. Phone: US 800-280-6013 Canada 800-353-2883 or e-mail info@drytac.com. For more information, visit www.drytac.com.