Aqueous Coatings create Special Effects
Many different special effects may be obtained using aqueous coatings that are formulated to provide various levels of gloss. This range in gloss can extend from a very flat matte (reflecting only 15% of light) to very high gloss coatings that are able to reflect as high as 90% + of light beamed from a 60° angle. Satin and semi-gloss formulations are available that will produce gloss results in between these extremes.
Matte finishes, or course, can actually lower the gloss of glossy paper or plastic substrates. Gloss coatings can raise the gloss of most substrates, or in the case of very glossy plastic substrates, equal or sometimes lower the gloss.
Testing for Glossiness
The gloss of any surface is dependent on the smoothness and the ability to reflect. The glossmeters that are commonly used to measure gloss measure the percentage of illumination beamed at an angle onto a sample that is reflected. The higher the value (% light that is reflected), the glossier the surface is said to be in its’ ability to reflect a high percentage of light, as a mirror does.
Matteness on the other hand is the result of a surface’s ability to scatter light and not reflect efficiently.
Printers have routinely used gloss and matte press varnishes to produce creative graphics with contrasting gloss and matte areas. This same type of creative result can be achieved using aqueous coatings, but additionally, they can be used together to create a wider variety of effects. Both of these techniques – press varnishing and aqueous coating – can be used to overall or pattern (spot) finish. Because a high gloss aqueous coating will uniformly add gloss, one can spot matte overprint press varnish, and then overall aqueous coat. The net result is total rub and scuff protection while creating a contrasting finish that plays gloss against flatter (less glossy) areas. Other times a dull ink might be used in a given area to produce a similar result where a gloss print area is contrasted against a flat printed area.
Spot Coating
Coating equipment offers the capability to overall coat or spot coat through the use of special plates and/or blanket techniques.
Spot coating has been done using:
- Raised magnesium plates
- Photopolymer plates
- Cut blankets
- Packed blankets
- Sticky back plastic sheeting
Raised magnesium plates have been used with coater/dampeners to selectively transfer coating to a blanket for application to a substrate.
Photopolymer plates have been used similarly and also with blanket coaters where they are blanket cylinder mounted to effectively spot coat. Benefits are superior registration, coating transfer, long impression runs, and very fine line intricate design spot coating.
Blankets have been routinely cut, or selectively packed to allow the spot locating of coating. While not as precise as photopolymer plates and capable of fewer impressions, the time-consuming cutting technique is popular and is used to relieve areas of coating for economy or functionality, i.e., in glue flap and trim areas.
Sticky back plastic sheeting has also been used to either create a raised blanket or plate to selectively spot coat, or an entire sheet is cut so that areas not to be coated are removed.
Plotters are also being used to accurately locate where packing materials and blankets are to be cut so that more accurate spot coating can be done.
Combine Aqueous Coatings – Get Creative
Whatever the technique, which is somewhat dictated by the coating equipment employed, printers are able to produce a wide variety of creative effects. Utilizing the availability of gloss and flat coatings, as well as conventional overprint press varnishes, graphic designers creatively contrast gloss and flat areas of a print for award-winning effects.
The acceptable application of matte and satin aqueous coatings is dependent upon proper coating techniques being employed. When using these coatings, it is essential to use a KISS impression! Use the lightest possible KISS impression that effectively transfers an adequate amount of aqueous coating to the sheet being coated.
Although a satin coating is less affected by low film weight than a matte coating, adequate coat weight is required in either case for acceptable results. If too little coating is applied, the result is likely to be an undesirable, non-uniform mottled appearance with adjacent gloss/dull areas. In contrast to this, if too much coating is transferred, excessive slinging and edge bead formation is likely to compromise the results.
Use your imagination and discover that the range of creative effects is boundless using aqueous coatings. ADD VALUE to graphics with the creative application of aqueous coatings!
