What sort of things are critical to long run pre-prints?
The first concern should always be the compatibility of the plate resin and ink. If this isn’t the case, the resin plate will swell during printing causing the lines and halftone dots to become thicker, leaving dot stains and fatter lines. Therefore, it’s important to plan ahead when selecting your ink and plate material.
How many lines should I use for pre-printing?
A commonly accepted method is to consider the ratio between desired print lines compared to the number of lines on the anilox roll. Our recommendation for stable printing – even across long runs – is to print at one-fifth the density of your anilox roll. (ex. printing 70 lines with a 350 line anilox)
However, if you want to print a design with a higher density then a ration one-third is also possible.
What things should I keep in mind when using low-grade paper?
Recently there has been a trend among pre-printing to reduce the chosen paper weight, which can cause various difficulties during production. The reduced surface smoothness of this paper makes applying consistent strength and tension needed for proper printing.
This can lead to haloing which makes it difficult to align registration marks. Since these alignments (distortion, dot gain, trapping) must be aligned based on real printed results so the ability to observe accurate markings is vital.
What is causing my uneven printing?
First, check the compatibility of the plate resin and printing ink.
Next, check that there is no unintended unevenness of the resin plate. Make sure that the printer and anilox roll are not applying more pressure than necessary. If excess pressure is being applied then the ink will not spread evenly across the plate surface leaving excess ink on the plate. Over multiple cycles this excess ink will build up causing unevenness, so it is vital that all ink is transferred from the plate to the substrate. As a contingency against this problem, microcells can be added to the plate surface to improve the transfer of ink.
Another possible culprit could be mechanical vibrations from the press itself, causing the plate to “bounce”. Some of these problems can be solved with proper double-sided tape or resin plate guides.
What should I do to get excellent print quality at high speeds?
Adequate print and anilox roll pressure are of primary concern. Additionally, it is important to select an ink and resin plate design for high-speed printing. Applying ink to a plate, slapping it on a page, and letting that dry seems simple in theory but is actually quite a technical challenge. In this situation it is important to use a resin plate with an extremely smooth surface which requires less printing and anilox pressure, allowing it to make proper contact at high speeds. To achieve this, recent techniques such as flat top halftone dots and fine lines have been developed to further increase plate smoothness.
Why is the ink for my half-tone dots entangled?
First ensure that your anilox roll has the correct number of lines compared to your desired number of print lines.
We recommend printing at less than one-fifth the lines of your anilox roll. If problems persist then check that your ink and resin plate are compatible. This problem can sometimes be resolved by changing the resin plate.
An uneven plate can also lead to ink contamination.
This poses a challenge to all but the most technically accomplished of platemakers of how to produce halftone dots and linework on a resin plate without introducing unevenness through small measurement errors.
I want to reduce fringing. What can I do?
In recent years certain industry trends, such as use of lower grade substrates and high-speed printing, have increased the likelihood of fringing. The best way to counteract this is to make sure that your paper, ink, plate, and printing machine are all compatible with one another.
In recent years the materials and platemaking methods to produce halftone dots, lines, and solids has become increasingly technical.
In addition to print pressure, anilox pressure can also contribute to fringing so it is important to diligent inspect and adjust the pressure.
Post-print (Direct Print)
Is there generally any difference in lines and solids when performing direct (post-printing) on cardboard using flexo (resin) plates?
Flexo plates designed for process printing often us a resin that is 30 degrees harder than the material used for a more general purpose flexo plate.
Does process printing require any changes to the resin plate?
Printing direct to corrugated is characterized by significant fringing, so to combat this we control the surface size of the halftone dots with the assumption that they will generate fringing.
This process is referred to as dot gain control (DGC) and the experience gained over our lengthy history of successful projects we can design our plates to fit your exact printing circumstances. If these considerations are neglected, large fringing will occur, increasing print density, and rendering the process printing run unsuccessful. These specific settings will change depending on the press, ink, paper quality, resin material, and design.
The colors are different at the beginning and end of a long run of process printing. Is there any solution for this?
In process printing, whether the beginning, middle, or end of a long run, it is important to produce consistent colors. We sometimes hear from customers that print density increases during printing. Though it may result from the condition and environment of the printing press, it is most likely that the flexo plate has swollen for some reason.
In this case it is necessary to review the material of the flexo plate.
Changing to a plate produced with the conditions of your print facility in mind should eliminate any print density issues.
Is there anything to be aware of when direct process (post-) printing?
To start, you should make sure that you are using a flexo plate that is compatible with process printing. Next is to remember that the density of colors will change in accordance with the print and anilox pressure. In principle, you want to focus on printing with a kiss impression Also, it’s important to remember that your cardboard should be as smooth as possible. Finally, as a general rule, use ink that has been selected specifically with process printing in mind.