Lamination of Digital Output: Art vs. Science
by Scott Diamond, manager of laminating sales & service
When it comes to testing for bond, the x test still is considered the best method.
A good bond that has penetrated the stock will pull up paper fibers when peeled away.
With the modern trend in digital printing being short-run and quick turn, this can present difficulties in lamination. Too often we are asked the broad question of, what temperature should I laminate at? Or worse, the film manufacturer advertises a temperature for its film. The fact is, the manufacture is just telling you what temperature the adhesive will activate at, and this rarely equates to what temperature you will run your laminator. You have to take into account the thickness of film as well as substrate, the speed at which you want to run, the pressure of your roller, and finally, the biggest modern variables: what print engine it came off of and the amount of coverage, as well as colors. This is why I refer to laminating as an art more than a science.
While there are many different digital-grade laminating adhesives on the market, this is not a simple solution. Different manufactures adhesives work differently on the various outputs, and you also have to take into account what type of laminator you are using. For instance, heavy dark coverage from an Igen 4 will be very difficult to bond to. In this situation, you would ideally want to have your print sit for up to 72 hours after printing, use a good digital adhesive and also run on a high-quality, commercial-grade laminator. I have seen people try to laminate difficult digital output on a sub-$1,000 laminator designed for the educational market – one with no roller pressure control and minimal heat. This equates to putting racing fuel in a Ford Focus – you just dont get that much better performance. The opposite also is true: if you have light coverage (mainly text) and a good commercial laminator with good adjustable roll pressure, you may be able to use a standard grade adhesive, even when printed off the toughest print engines to work with.
In the past, printer manufacturers have not been concerned with what happens after the print is printed. This trend is being reversed, and many of the big print engine manufacturers now have print finishing divisions that are working with the lamination companies to provide solutions for their customers. They are a good source for information.
Here are some basic tips:
- Use a quality commercial laminator.
- Test several digital adhesives to see what works best for your needs.
- Wait 72 hours after printing before laminating.
- Wait 24 hours after laminating before cutting or folding.
- Understand and adhere to the basics of laminating: heat, speed, pressure and tension.
The key is to pre-qualify as often as you can. Most of the film manufacturers are willing to test product for you. It is in your best interest to take advantage of this service, so send in prints – lots of prints!
The basics: heat, pressure, speed, tension
The first variable setting we run into will be heat. The typical thermal adhesive will activate and bond to offset print at temperatures of 212 to 230°F (100 to 110°C). Add 10 to 20 degrees to this for digital prints. There are many factors in the laminating machine that have to be considered. Higher laminating speeds call for higher temperatures, as do thicker stocks and film; consider dwell time and the actual temperature to which the adhesive can be brought. We are talking about the temperature necessary in the adhesive layer to adhere to the print and not the temperature of the roll in contact with the base film. At slow speeds, the temperature setting on the laminating roll may be close to the settings noted above, but laminating thicker films at higher speeds will require an increase in temperature settings to obtain these temperatures in the adhesive layer.
Pressure is another variable to consider: the more pressure you can apply, the better the bond. Be careful, though, as pressure also can increase curl in the product. You can correct curl to some extent using roll tension. If a print is curling down, increase top roll tension and/or decrease bottom roll tension. The opposite is true if the print is curling up. Many single-sided laminators have de-curl devices that will correct curl and allow the film to be run at very high pressure.
You also have to consider the type of film you are using. OPP films are more sensitive to heat, and they can shrink and distort at high temperature. PET- and Nylon-based films are more thermally stable and will allow higher temperatures of the laminating nip roll for higher operating speeds. Even the manufacturer of the film is a variable. No two digital adhesives are identical. All have strengths and weaknesses. While D&K was the first to be successful in the digital adhesive game, others have progressed and developed adhesives with a broader range. Nobelus has worked with several adhesive and film manufacturers to develop a broad spectrum digital adhesive in Ultra Grip, and KDX has made progress with a new generation of All-Stick.
The digital variables: print engine, coverage, color, post-laminating finishing (cutting or folding)
Next, we must take into account the digital variables, the first of which is what digital print engine your prints are coming off of. In general, the newer and more modern the print engine, the larger the obstacles. For instance, an IGen 4 of Indigo 10000 may pose more challenges in finishing than a smaller, older model from the same manufacturer. Also, the amount of coverage and bleed will affect bond, as will color. Darker colors tend to pose more problems. Finally, additional steps in finishing, such as folding or cutting, can affect the lamination. Whenever possible, having the laminated prints sit overnight before the final finishing step can help overcome bonding issues.
Testing for bond
The traditional method of the X test to check for bond still is good standard, although the results need to be interpreted in a different manner for digital prints. The technique involves slitting an X on the print, trying to just penetrate the film layer and not cut into the stock. Next, attempt to peel up the film. In a traditional offset print, a good bond will pull up fibers of the paper as the adhesive has penetrated into the stock. In a digital print, the adhesives may not penetrate the toner or fuser oil so you may not actually pull up fibers of paper; instead, you will actually pull up the ink. In theory, the ink should be well bonded to the paper and your adhesive will be bonded to the ink. Test in several spots, especially dark areas with heavy coverage.
There is no absolute right answer to how you need to laminate your digital prints. It is as much an art as a science, and you need to continually be monitoring what works. Pre-qualify, continually test and keep a log of what worked and what didnt.