How to Improve Flexo Print Quality with Direct Laser Engraving
We’ve all heard about direct laser engraving and know that DLE is a proven technology.
Direct laser engraving has come a long way from its infancy and now delivers print quality and efficiencies we did not think was possible in flexo. The following is an article written for Flexo magazine that explains how DLE dramatically improves flexo print quality.
Controlling Engraving Parameters Affecting Dot Shape & Support
The role of the flexo plate is pretty simple; to carry or transfer ink from the anilox roll to the substrate. The problem is gaining results from applying pressure to transfer ink from the plate to the substrate. The more pressure that is placed on the substrate, the more ink lays down resulting in a spread.
The solution is to place the smallest image possible on the plate and lay down less ink. In other words, better control of the dot. CTP technology allows for greater control and more consistent manipulation of the dot and image in two dimensions. CTP technology uses a laser to create an image and the laser is either on or off to create black or white. There is no variable control feature.
Direct Laser Engraving – The ability to directly engrave elastomer and polymer plates with laser impacts all three dimensions of the image being reproduced on the printing plate. DLE uses a precision laser to create an image directly onto the plate. The laser determines the value of gray levels by using graduated intensity, which can range from less than 1% (very light areas) to 100% (black), and every tonal value in between. Because of the laser’s variable intensity feature, we have better control over dot size and shape. In essence, we can sculpt the image with the laser beam.
Shoulder Angle – One key advantage of direct laser engraving is the shoulder angle. DLE allows the user to manipulate the shoulder angle to whatever specification is required. The average shoulder on a flexo plate is somewhere from 45 degrees to 60 degrees throughout the plate. With DLE using a polymer plate material, the average shoulder angle is 80 degrees in the highlight and 90 degrees in the shadow.
That’s right, we can create several different shoulder angles on one plate, with sharp shoulders that produce a sharp print. While we want a kiss impression, I believe we also print the shoulder. The wider the angle, the more shoulder we print creating a larger dot. With DLE, we have very narrow shoulders and open where desired, in the shadow area with a smaller dot. Just like an open reverse on a standard flexo plate.
You may ask “How can I hold a 1% dot on the plate? Won’t this break off?” The answer is “No, even with a steep shoulder.” This does not represent the dot. The dot is actually on top of the shoulder and not as deep as the rest. This so-called shoulder is just a base for the dot. This is another advantage of DLE, with no missing dots caused by poor lights or depth.
Depth – How do you control it? Relief depth is controlled by one simple test. A depth calibration test is conducted using the material. This test uses a solid image with shades of gray varying from 1% to 100%. We laser it, measure it, and assign a number to the specific gray, similar to a fingerprint on a press. That’s it. You don’t need to worry about bulb output and for the most part, if you can push a button, you can make a DLE plate just as well as someone with 20 years experience. Now while I say this, it is nice to have someone who understands the test to facilitate the process.
Below surface dots – DLE allows you to control the below surface image. The laser controls image height based on the pressure that is placed on the press. As a result, you can print small and better dots as well as lines. For example, you can print a large solid and a fine UPC on the same plate. The UPC lines are engraved below the large solid area. This allows you to print the solid with heavier pressure that also prints the UPC lines. All of this is controlled by DLE’s gray level outputs.
Direct laser engraving today and tomorrow – With new systems and advanced materials (primarily polymer), we can now achieve print quality and efficiencies we did not think was possible in flexo. With DLE we can create 1% dots at 250 lines per inch. Direct laser engraving has come a long way from its infancy and now delivers plate quality that is converting jobs from rotogravure to flexo.