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UV Flexo + Labels = A Perfect Match

By Web Administrator on April 01, 1999

Flexo printers that have made the transition from solvent inks to waterbased inks will likely remember that the process wasn't an easy one. It required changing the way everything was done, from purchasing habits to daily attitudes. Waterbased was an unknown technology at the time, one that presented many challenges. However, I'm willing to bet that after tackling the learning curve and realizing benefits such as the environmental friendliness of the inks and quicker cleanup, you would never think of going back to using solvents. The same case could be made for any new or developing technology, including UV flexographic printing. At first, the transition may be daunting, but with careful planning, the adoption of UV-flexo technology allows you to provide a higher quality product for your customers and thus make you a more successful supplier. In this article, I'll explore some of the ways UV flexo is being put to outstanding use here at New York Label.

"No-Label" Look
An increasing application for UV is the "no-label" look, which allows the flexo printer to provide a product comparable to rotary silkscreen at a much lower price. As an example, consider the shampoo bottles where the product shows through the clear label. Some also have an attractive four-color-process image reverse-printed on the back label so that it shows through the product, with copy on the opposite side. In the past, the front label was always done by more expensive processes, such as rotary silkscreen, while the back was a difficult process for flexography because you had to print on clear, then marry white stock to it, then print on the white stock.

By printing UV inks on clear stock, you can achieve an ink film with an opacity similar to that produced by other processes. Also, in the case of the back label, the same look can be achieved by printing process in mirror image, which, by the way, also requires reversing the order of the ink. For example, if you run yellow, magenta, cyan then black, just reverse that sequence. Next, you print a flood coat of white on top of that, then print your line copy as a positive. The end result is a product that is very close to that produced by other printing disciplines, but at a substantially lower cost. One reason for the lower cost is a reduction in the amount of press time required to complete the job. Rotary silkscreen, for example, has to be run a lot slower than flexo. Keep in mind that the advantages gained by the opacity can also be applied to other stocks, such as foil.

Better Dot Structure/Reduced Gain
The viscosities of UV inks tend to be higher than those of waterbased inks. This ultimately results in sharper, crisper dots and reduced dot gain, especially in the highlight areas. If you're used to printing 10-percent highlights, a highlight of 3 or 4 percent will be a welcomed improvement. The tendency for the infamous "halo" dot is also nearly eliminated. Overall, you will be producing a halftone with sharper edges than that of even offset. The reduced fluctuation in the printed product, combined with markedly less on-press maintenance, allows you to have greater control of your process. Better still, UV inks will not evaporate, meaning you won't have to kick in as many additives to maintain the inks on press. Not only does that reduce cost, but any time you eliminate variables such as the addition of water, ammonia or other additives, you increase reliability and consistency. Now a word or two about consistency. . .

Consistency is what we all hope to achieve in our printing. Consistency leads to a more cost-effective operation and is a word we can sell to our customers. And it is a fact that greater consistency can be achieved through UV inks. Why? Fewer variables! There is no evaporation on press, and no false body when off press and on the shelf. No pH adjustments are necessary, which means you can get rid of those ammonia additives. Finally, you will not need to make viscosity adjustments due to instability from evaporation or press heat. To prove these benefits, monitor a long run on a spot-color job. You'll be amazed at the results. These benefits are even more appealing on a process run, where you have four colors to worry about. In short, color shifts can easily occur as a result of myriad variables, including impression, doctor blade, evaporation, pH, viscosity and press speed. And as we all know, with flexo, the more variables that can be eliminated, the better.

Process versus Spot Colors
Many UV-ink manufacturers are able to produce process colors that can run on aniloxes with higher screen counts; ranging from 700 to 1200. In the case of UV spot colors, the manufacturers have so far only been able to provide color strength on lower aniloxes, ranging from 200 to 500. This has a lot to do with the need for photoinitiators in the ink and available room for pigments.

Now, because your spot colors have to run on lower-line aniloxes, your halftone line screen is limited. All things considered, you're probably better off running your spot colors with waterbased inks. When possible, try running your process colors as UV, with your spot colors as water. You can then run higher screens for both inks.

The up-front costs for a switch to UV will undoubtedly be high. Aside from investing in UV lamps, you will I also need improved airflow systems in your pressroom. Suffice it to say, your electric bill will also be much higher. But these costs can be recouped once production begins. As discussed earlier, you don't have to worry about evaporation with UV inks. Thus, you can leave the inks in the press overnight. This benefit alone will probably save you one or two hours in setup and cleanup. Imagine the savings you can realize with an extra hour or two of uptime each day. And while per-pound ink costs for UV inks are greater than waterbased inks, the extended mileage achieved from the UV inks will again offset the additional expense. Ultimately, the quality improvements and reduced usage and labor over the long run will more than outweigh the initial cash investment.

Hit the Books!
One way to cut down on the conversion costs is to do some research. Talk to suppliers to make sure you purchase the right equipment for your needs. Every press manufacturer will tout its UV press as the best on the market, but you may want to inspect the ink pans. Some UV inks are very viscous and require pans of special shapes. One press manufacturer provides pans that angle down where the anilox reaches the bottom. This improves flow and is a must when using thick ink. You may also want to choose a press with stations that can be set up with either UV or drying units. This would provide the versatility to switch back and forth between waterbased and UV.

Selecting the proper anilox is also a tricky issue. UV spot colors lack the color strength to run on higher-line aniloxes, such as those in the range of 600 to 700. On the other hand, UV process can run on aniloxes up to 1200 and still have strength. Keep in mind that you need more volume in your aniloxes for UV than for water inks, because of the high photoinitiator component. So, with anilox volumes, the higher screen count you use, the less volume is available. For example, if you are using a 900-linescreen anilox, you are limited in volume, since there is only enough room for pigment and photo-initiator. This is why you lack color strength on spot colors and have to go to a lowerscreen/higher-volume anilox. Now, if you're running spot colors with line screens of 133, for example, multiply that by four to determine minimal anilox screen, and you would need an anilox of about 550-600 lpi to keep the screen open and reduce dot gain. Unfortunately, UV inks cannot match color strength on most spot colors when using higher-line aniloxes. Indeed, to achieve color on UV spot colors, New York Label has had to use 360 and 440 lpi aniloxes. As a rule of thumb, UV anilox volumes will probably have to be about 30 to 40 percent greater than comparable waterbased aniloxes to achieve similar densities. As a note of reference, remember to use your UV aniloxes solely for UV applications - do not alternate between water and uv. The ammines in the waterbased ink tend to react with the UV in the cells, potentially destroying the anilox.

Watch Your Stock!
Dust will become a problem when using paper stocks with UV Every paper stock has some amount of paper dust associated with it. There is also a certain degree of dust present in the air. With waterbased inks, you're able to hide or cover the dust as you print. This is much more difficult to do with uv, and may require investment in a vacuum system and/or a more effective airflow system. To cut down on the expense involved in solving the dust problem, you may opt to set up your UV presses in a room of their own.

Another concern is making sure your plates and inks are compatible. The easiest way to ensure this is to send a sample of the ink to your plate manufacturer. Alternatively, you could also do a 24-hour soak test. Simply take an exposed plate and soak it in the ink for 24 hours. Remove the plate and measure it with a micrometer to see if it has swelled. If it has, it's probably incompatible and will result in dirty printing and increased dot gain.

Finally, you must absolutely remember to make sure that all lights in your pressroom are fitted with UV ftlters. Failure to do so could lead to the inks curing right in the pans, or worse, in the cells of your anilox, which could easily destroy the rolls. It's also a good idea to cover your ink pans when they're not in use to keep out dust and outside lights.

A transition to UV flexo is not without its bumps, the largest of which will be the startup cost. However, with careful planning, communication, and a wise spending plan, you have the ability to place your company on the leading edge of this rapidly improving process. You'll be able to provide a better product, enjoy greater long-term profitability and advance the technology of the flexo industry. Speaking from experience, the results we've achieved using UV in our work at New York Label have been nothing short of fantastic. If you're not into UV yet, I would highly recommend giving it serious consideration.

This article originally appeared in the April 1999 issue of Flexo Magazine

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