When print designers of the past thought of adding value to the printing for a product, they thought about plate screens, color combinations and fineness of print. For many years, added value also meant hot-foil stamping, cold foil, couponing or some other downstream enhancement.
Today, 4-color process—and to a large degree 7-color process—have become well-established, widely adopted and standard fare on packaging found on the store shelves. With consistency an ever-present challenge, it comes down to execution to achieve contrast to the untrained eye.
Even at the greatest possible resolutions of dot structure, at some point it just doesn’t matter how fine the print becomes to the consumer. When print designers look for added value these days, they look to specialty coatings!
Catch the Eye
Specialty coatings must catch the eye or the feel of the consumer. These coatings may not be readily apparent, like the thermochromatic coating on a can changing temperature to reveal a message. Sometimes the success of the print in the packaging design is a simple matter of catching light in just the right way, to distinguish itself from the other offerings on the shelf.
Many of these coatings rely on texturing for the desired effect, the most common being tactile. Tactile was once a simple contrast of height to the substrate surface, but can be now expanded to texturings like sandpaper and rubber. Tactile is also being used to create more of a three-dimensional effect, like over a printed water droplet image to feign the presence of actual water. While matte coatings have been around for years, they now provide a contrast to the surrounding substrate or pairing with a gloss coating.
In order to be successful in printing these coatings, you must first understand that they can be complex in procedure. Since desired results are in the eye of the beholder, a true target may not be available without research and development. In any setup, you want a complete transfer of particles in a controlled distribution of coating and at a curable or dryable run speed.
Rules for Success
Get a printed sample of the specialty coating from your supplier and determine if the effect is what you are looking for at their tested specifications. I have given samples of tactile at 70 bcm, only to have customers decide they wanted less and use a 50 bcm or 30 bcm, even only 10 bcm!
All photos courtesy of Harper Corporation of America
As you can imagine, that is quite a swing in personal preference. For particulate coatings, you do not have this kind of latitude because you must accommodate the particle and let it work, so a broad range of volumes and geometries will have drastic impacts on transfer and actual performance. This doesn’t mean that testing needs not to be done, but begin with seeking guidance.
Start with a clean anilox with cell opening, geometry and volume that accommodates the particle shape, size and flow. If you have particles that collect to themselves, called agglomeration, the particle size may be much larger than advertised in a distribution. The cell opening, geometry and volume are determined in the following ways:
- The most accurate determination is testing that has already been provided by the ink supplier. This would include the anilox selection, blading requirements, base coating, the percent of the specialty particles, instructions for mixing and maintaining the mixture in press, and finally run speed expectations
- If you are forging your own specifications because the ink supplier does not have them yet, or you are looking to modify their results to suit your own needs, you really will have to consider a banded anilox
Keep the following in mind:
- Most effect coatings start at 15 percent load and the base is typically a tactile varnish. You may go as low as 10 percent or as high as 25 percent for the particle addition to the formula
- Pay attention to how much you add, so you don’t end up choking the cells or clumping the media
- When mixing, don’t dump it all in at once. Add the dry particles to the varnish slowly. The particles don’t wet—this isn’t a cake recipe. Use an actual rotary mixing blade on a drill—a blend like this requires it
- Pouring together and letting your ink pump do the work is not going to give you the effect you need in the time you need it, and it may never get there fully. Blend before going to press
- As far as varnishes go, tactiles are a superior way to sustain suspension of the effect pigments and promote distribution
- Remember what you are trying to do with a particle. For glitter and pearlescent, it is to distribute evenly. For sandpaper, matte and rubber, you want these particles on the surface for the feel or proper reflectivity. If you drown the particles, you don’t get the matte or feel. If you don’t have enough, then you may keep particles from getting through the blading
You may think at this point that an unbladed setup is a tempting way to go, but you will have no control over the film, distribution and effect. You need a banded roll for these applications, or at the very minimum, a tested specification and setup from the ink supplier.
For any of these coatings, make sure you stir them properly, keep them stirred/in solution and use them within their prescribed shelf life. If the particles settle immediately, then you are not going to see the results you want.
Use one pump to circulate and second for pumping. Impeller pumps fare well for mixing and peristaltics work well for sending the coatings to the deck. If you choose not to pump, keeping the particles in suspension becomes much more difficult. Shelf life is also very important. Some of these inks have very short windows for use and will not perform at all due to reactions in the jug and the breaking down of components. No amount of stirring will fix that issue.
Test to Target
In terms of commonalities for recommendations, matte varnishes are very particular when it comes to volume. You want to test to the target. An increase of 1 bcm or 2 bcm may well drown out the particles, and too little volume will inhibit distribution and the action of the matte particle to the surface.
For pearlescents, these particles are robust, three-dimensional chips that can be abrasive, so they need room to move. Keep the linescreens open and the volumes can range from 4 bcm to 15 bcm with a range of particle sizes from 5-μm. to 125-μm.
Glitter is somewhat similar: To get the effect, you need good distribution. Glitter is typically flat and ribbon-like; only a few microns thick while perhaps a hundred microns or more in length and width. Glitter may clump, so slow blending is a must. Glitter has the best transfer with an unbladed setup, but that is not always practical or possible. Skimming is always a concern.
Thermochromatics are also sensitive to volume and very sensitive to shelf life. Typically ran with a channel at 15 bcm to 20 bcm, if the performance isn’t occurring in the prescribed window by the supplier, the coating is not stirred or it may be stale and will never work. I have seen situations where 15 bcm or 20 bcm didn’t work at all, due to the souring of the ink. Use the recommended volume from the supplier and also use the recommended run speeds.
For scratch-and-sniff, it is about getting the encapsulations throughout the printing process with as little damage as possible. A channel is a must here, and if possible don’t run a blade. Understand the encapsulation size and discuss the proper volume with the ink supplier on how much you need. A higher volume can increase the longevity of the effect. You want the “sniff” effect relegated to the printed product, not the air in the pressroom. These applications can range from 8 bcm to 40 bcm, with the lower volumes for film substrates and higher volumes for paper.
Always have a clear understanding of how a specialty coating works to get the performance. Success is always subjective. Printed samples from ink suppliers help you decide specifications in general, but testing will always make the specifications to your liking.
It may be in your best interest to work with preformulated coatings instead of coming up with your own custom blend. Be mindful of the blending process and how to maintain the particles in suspension during use. Settled particles do not print. Use a banded anilox when appropriate to dial in your specifications. Follow these rules and you will soon be adding unique value to your printed product!
About the Author
Teufler was recognized as Harper’s Technical Representative of the Year seven years in a row from 2005 through 2011. He is a former FTA President’s Award recipient and a FIRST Certified Implementation Specialist. Teufler has chaired two Fall Conferences (2012 and 2016), is a frequent presenter at Forum and is a member of the FTA Excellence in Flexography Awards Committee.
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