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Coatings & Laminates Explained

The right protective coating or laminate can keep your printing project looking professional.

Even though protection may be necessary on a marketing piece it is often overlooked. While a great deal of thought may have gone into a project for the printing press, much less attention has been paid to preserving the artwork after it leaves the printer. Aside from using a varnish to highlight a photo, most print shops, not including xgraphix, often give little thought to the use of protective coatings or laminates, and you the client may not ask about them at all.

Film laminates are usually applied by finishers or converters that also offer die cutting, embossing, foil stamping and other such services. The film may be applied using either a wet method, which relies on solvents, water or both, or the more environmentally friendly thermal method, which uses heat to iron the film and paper together. Either way, the entire sheet is generally laminated there is no practical way to spot laminate a project.

offset machine roll foil laminator detail

Lamination films are available in a variety of tints and textures, and there's even a lenticular film designed to help create a holographic effect. The films are classified by thickness, which is measured in mils, or thousandths of an inch. The thinnest films, typically around 1.2 mm, are used on items that are rolled or folded. Heavier films, of up to 10 mm, leave a heavy plastic coating on the sheet that can stand up to anything short of a small but determined Rottweiler. The laminates can be applied on one side or both sides of the paper, and with a sealed edge, which makes the sheet virtually waterproof.

Film laminates offer much more protection than liquid coatings in exchange for longer production times and higher costs. Heavily textured stocks, however, may be difficult to laminate because the film cannot reach down into the valleys of the paper.

Liquid coatings can be applied in-line by the printer as part of the printing process or off-line after the project leaves the press. Some coatings, such as varnish, can be spot applied to a precise point or points on the page such as just to the photos, for example. Other coatings, including aqueous coatings, are usually flooded across the entire sheet. Different coatings are available in different finishes, tints, textures and thicknesses, which may be used to adjust the level of protection or achieve different visual effects. Areas that are heavily covered with black ink or other dark colors often receive a protective coating to guard against fingerprints, which stand out against a dark background. Coatings are also used on magazine and report covers and on other publications that are subject to rough or frequent handling.

Liquid coatings are by far the most common way to protect small print publications. They provide light to medium protection at a relatively low cost. Three major types of coatings are used:

 

Aqueous Coating

Low cost water based aqueous coatings are among the most commonly used coatings available today and provide good protection from fingerprints and other blemishes. Aqueous coatings are applied in-line on press, and they are shiny and smooth, have high abrasion and rub resistance, are less likely to yellow and are more environmentally friendly.

Available in gloss or dull finishes, water based coatings offer other advantages as well. Because they seal the ink from exposture to the air they can help prevent metallic inks from tarnishing. Specially formulated aqueous coatings can be written on with a number two pencil, or overprinted using a laser jet printer, a key consideration in mass mail projects.

Since they are less likely to yellow, aqueous coatings provide a good alternative to varnish, especially when it comes to protecting projects that feature large amounts of white space. However, it is difficult to apply a spot aqueous coating with the same degree of precision that is possible with a varnish, which is why aqueous coatings typically are flooded across the entire sheet. Because the coatings are typically applied over the entire sheet and are water based, most experts recommend using 80# text weight or heavier paper stocks to keep the paper from becoming curled or wrinkled. Aqueous coatings can be used in conjunction with either varnish or UV coatings, but doing so can be costly, and unless production is managed carefully, the coatings may not dry or lay right.

Aqueous coatings and UV coatings are also susceptible to chemical burning. In a very small percentage of projects, for reasons not fully understood, certain reds, blues and yellows, such as Reflex Blue, Rhodamine Violet, Purple and PMS Warm Red, have been known to change color, bleed or burn out. Heat, exposure to light, and the passage of time can all contribute to the problem of these fugitive colors, which may change at any point from immediately after the job leaves the press to months or years later. Light tints of colors, made using a 25% screen or less, are especially prone to burning.

To help combat the problem, ink companies now offer more stable, substitute inks that are close in color to ones that tend to burn, and these inks are often used to print light tints or bright colors. Even so, burning can still occur and dramatically affect the look of the project.

UV Coating

Extremely high gloss UV, or ultraviolet, coatings offer more protection than either varnish or aqueous coatings. UV coatings are applied in-line by printers or, more frequently, off-line by printers, finishers or converters. UV coatings are applied as a liquid, using a roller, screen or blanket, and then exposed to ultraviolet light to polymerize and harden the coating, with zero emissions. The coatings can either be applied across the entire page or, while lacking the precision of a varnish, on a spot basis. The coatings are available in a high gloss as well as matte, satin and a wide variety of specialty finishes, including glitter and tints, and even different scents.

When first introduced, UV coatings were often perceived as murky and yellow. Those problems have been corrected, but the coatings still have other drawbacks. Like aqueous coatings, UV coatings are susceptible to chemical burning. UV coatings also are more likely to show fingerprints than either aqueous coatings or varnish, and some UV coatings can make paper difficult to fold. Dwell time, viscosity, temperature, the intensity of the UV light source and the interaction between the coating and the paper can all cause problems too. If conditions aren't right, the coating will not have a chance to spread evenly across the page before the coating is cured, and the finish can develop an "orange peel" look.

UV coatings also tend to accentuate the roughness of, or any defects in, the surface of the paper. Some printers insist that UV coatings require the use of coated paper stocks because uncoated papers allow the coating to sink into the sheet, leaving little of it on the surface. And in the past, most printers said that UV coatings should be used in conjunction with UV inks and that if conventional inks were used, they had to be wax free and allowed to dry completely before the coating was applied. However, new hybrid inks help reduce the potential for drying and surface problems.

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