Aqueous coating is a fast-drying, water-based, vegetable cellulose product used as a protective coating which is applied in-line on press. It is biodegradable and recyclable. This clear coating is used for any project that requires a more durable finish, providing a high gloss surface which protects the surface from fingerprints, dirt, smudges, and scratches. Aqueous coating improves postcards durability as they go through mail or inserted in pockets. It is also applied on brochures, catalog covers, fliers and other visual aids.
Aqueous coatings are applied to the printed sheet immediately after the inks.
Directly after the coating is applied, the sheets are sent through a heated air system that quickly dries the coating. The printed sheets can progress to the finishing department in a matter of minutes, as opposed to traditional varnishes which may need hours or even days to dry.
This type of coating provides marvelous rub and scuff resistance. They give protection that far exceeds standard varnishes. It protects the product from harmful elements from the shipment through to end use. Available in gloss, dull and satin finish, it is applied during the print run, making it a more cost-effective option than varnish, since it doesn’t require an additional pass through the press.
How Aqueous affects the environment
Aqueous is generally considered to be one of the most sustainable coating options because the formulas are nontoxic in the pressroom, and treated paper can be recycled in standard municipal systems without emitting harmful byproducts. The cleanup process does not require toxic cleaning detergents nor does it necessitate high temperatures (e.g. added energy) for drying. Other sustainable alternatives include clear vegetable-based ink in place of any coating.
UV coating is applied like ink to paper and dried by ultraviolet light. It can be used as an overall “flood” protective coating or “spot” applied to a specific graphic to accent the printed piece, although lacking the precision of a varnish. 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. Some drawbacks to UV, 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.
How UV affects the environment
The process of UV coating emits no toxic byproducts. However, the clean-up process from UV coatings requires utilizing dangerous chemicals that necessitate strict safety measures and could be hazardous to workers’ health if not handled properly. In addition, the UV coating process requires high energy use due to UV drying lamps and air conditioning requirements.
The ability to recycle paper with heavy UV coverage may be limited. Too much of this coating in a batch may contaminate the pulp which prevents the paper from being used to make recycled paper products.
Think of varnish as ink without pigment, requiring its own printing unit on press. This coating comes in gloss, dull and satin finishes. It can be wet-trapped (printed in-line at the same time other inks are laid down), or dry-trapped (run as an additional pass through the press after the initial ink coating has dried). Dry trapping will give a higher gloss finish.
Varnishes require the use of printers’ offset spray powder to keep the printed sheets from sticking together before the varnish is completely cured. The powder that is left behind can affect the look and feel of the finished piece, an especially important concern to many designers.
Depending on the reason you are adding a finish, which is typically either protection or aesthetics, varnish does not give you adequate protection. From an artistic standpoint, you can play a dull-varnished portion of the sheet against a portion without varnish or with a gloss varnish. This contrast can give emphasis to certain areas and/or give the impression of depth. Varnish can have a subtle effect adding to the visual design and may be the right choice for you.
In addition to providing relatively little protection, varnishes have other drawbacks too. One problem is that over time, they tend to yellow. Yellowing is not a big concern when the varnish is used over process colors, but it is noticeable when the varnish is applied over unprinted paper, especially today’s high-brightness blue-white papers. And for some reason, silk, dull and matte coated papers tend to reveal yellowed varnish much more than their gloss-coated counterparts. In an attempt to counteract the yellowing, some printers will add a small amount of opaque optical whitener to the varnish that will be applied over white paper, but it is a less than perfect solution.
How Varnish affects the environment
Varnishes recycle more easily than the UV coated stock. However, they emit harmful volatile organic compounds (VOCs) during the coating process which can cause eye, nose, and throat irritation, headaches, loss of coordination, nausea, as well as damage to the liver, kidneys, and the central nervous system. VOCs are also suspected to cause cancer in humans.
Alternatives to Liquid Coatings
Film laminates are usually applied by finishers or converters that also offer die-cutting, embossing, foil stamping and other finishing 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 press the film and paper together. Either way, the entire sheet is generally laminated. There is no practical way to spot laminate a project.
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 mils, are used on items that are rolled or folded. Heavier films, of up to 10 mils, leave a heavy plastic coating on the sheet that can stand up to almost anything. 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.
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