Coatings are applied to print projects for a number of reasons, but generally they are used as a protective layer to guard against document wear and tear or as a means to strengthen colors and sharpen graphics. There are a variety of different materials that are used as coatings for digitally printed applications (as well as for applications printed conventionally). Among the most popular coatings for printed products are overprint varnishes, aqueous coatings, UV coatings, and EB coatings.

If the printing device is equipped with a means for applying coatings, then the application can be accomplished as an online process, which saves time and expense, otherwise the coating must be applied as an off-line procedure. However, it is often beneficial to apply coatings off-line for various applications (especially some applications that are printed with conventional processes or are printed on certain substrates) because a bold effect is created when the print product is coated after the ink has completely dried.

Coatings are also applied to a wide range of substrates prior to printing. Among these coatings are clay coatings that add strength and gloss to paper; whitewash coatings, which are used as a finish coat for such items as Kraft paper; and grease resistant coatings, which are used on applications for industrial and scientific uses.

Applied during the printing process or as an off-line process, overprint varnish is much like a solvent-based ink. The varieties of overprint varnish are usually colorless, but sometimes they are tinted to achieve a desired effect. Varnish can be applied as an all-over coat or in spots to highlight a specific area of a printed piece.

Overprint varnish is available in glossy, dull, or satin finishes. Gloss varnish creates a smooth surface over the paper, filling in any voids or irregularities that may be on the surface. Dull varnish fills in irregularities to form a smooth surface, but it diffuses light that reflects back to the eyes, which creates a dull appearance. A nearly 3-D effect can be created when applying dull or satin varnish to the background and gloss varnish over the subject. The subject will appear to jump off the page. In addition to applying varnish as a solid coat, it can also be printed as a halftone (series of dots) in order to provide subtle effects and to provide printed objects with an increased dimensional appearance. The effects that can be achieved are endless when using different combinations of varnish, paper, and ink.

Artwork Coated
with Overprint Varnish

Besides design effects, another important aspect of varnish is the protection it provides. A coating of varnish over a printed piece protects it from the wear and tear that results from everyday handling. The varnish coating allows the document to remain intact for a longer period. An all-over coat of satin varnish will protect the printed surface without drawing attention to the fact that varnish was used for protection purposes.

A disadvantage of varnish is that many of them are solvent-based. Solvent-based materials emit VOCs (Volatile Organic Compounds) during the application process, which can be a health hazard for the press operator unless the proper safety precautions are followed. Another disadvantage is that varnishes tend to yellow over time if they are formulated with tung or linseed oil. Varnishes with alkyd formulations will not yellow, but they are not as glossy or as hard as tung or linseed oil.

The use of varnishes on print applications should be planned early in the design process. They should not be applied as an afterthought in an effort to improve the appearance of a printed product in which the incorrect paper or ink have been chosen.

UV coatings come in liquid or paste forms and remain as a liquid or paste until exposed to ultraviolet light. When the printed page is covered with the UV coating and is then exposed to the UV light, photoinitiators within the coating react immediately, creating a hard protective finish on the printed product. Ingredients called monomers provide gloss and hardness characteristics to the UV coating. UV coatings, which are also known as energy curable coatings, provide the best surface properties and offer the best protection for printed surfaces. Some of the benefits of UV coatings include:

• Greater opacity
• Color stability
• Deeper and more vibrant colors and color tones
• Sharper graphics
• Higher gloss
• Uniform surface to give labels a more vibrant look
• Scuff resistance
• Instantaneous curing
• Allows for in-line die cutting
• Chemical resistance
• Better outdoor endurance
• Environmentally safe: no VOCs (Volatile Organic Compounds) are produced