It is known that the printers quality is given by their DPI specification (and not only). Reading out what DPI means and how it is applied to printers, a question arise in my mind. If printers do many dots on the paper, it is possible to print overlapped dots in order to achieve solid continuous colors?

The practical meaning for this question: Let's say that I want to print an UV mask using an inkjet printer, but in the end it will have some holes in the lines provided, so the final product will have bad artifacts.

  • 2
    I honestly have no idea what you are asking. End user color printers do "overlap dots" that's how you get green... by overlapping Cyan and Yellow dots... purple from overlapping Cyan and Magenta dots... etc... – Scott Jun 9 '20 at 7:32
  • Do you ask how to print one color that would be, well, solid? So in a matrix 2x2 filling each cell with a black dot you think it would leave an empty, non covered by paint space? – SZCZERZO KŁY Jun 9 '20 at 8:05
  • You will have gaps. The normal inks arent really meant for uv ranges. So more ink does not linearily translate to more uv coverage. For this reason hobbyists use two separate films of laserprinted mask as 2 films ensure enough uv coverage. The black is most covering technically the other inks would be transparent in uv ranges (although they arent). Then there is the problem of ink drying you cant just put too much ink in or it will flood. In pactice if you want repeatable results you should measure your uv opacity with a suitable densiometer and (not or) use ink meant for uv masks. – joojaa Jun 9 '20 at 9:45
  • Note that the ink we use, on a printer designed for this is quite suprising. somewhat transparent to human eyes blocks UV well. When we adjusted the printer so that your eyes see it as less transparent it is then supprisingly nolonger entirely UV blocking. So you cant really reason on ranges you dont see effectively – joojaa Jun 9 '20 at 9:51
  • @SZCZERZOKŁY Yes, that is bothering me, if the printer can draw dots in a matrix manner, that means in the center there will be an empty gap. – Ursescu Ionut Jun 9 '20 at 11:01

I have had the same problem while preparing silkscreen screens. Here are two solutions that have worked for me:

  1. As @SZCZERZO KŁY mentioned, adjust the raster angle when printing your template, to achieve maximum coverage. Additionally I have printed the same template on two sheets of transparent foil and placed them on top of each other during the UV-exposure to achieve better opacity.

  2. Have your Templates developed by a local screen printing company. They have professional film-printing equipment and will often do your template along for very little money if you ask them nicely.

  • Yeah in my experience the two sheet method is best you can do for nondedicated hardware. Thankfully we actually have an uv mask printer at work with special film and special ink. – joojaa Jun 9 '20 at 13:31
  • @joojaa, nice! lucky you ;) – dom Jun 9 '20 at 13:38
  • Still thats fine for screenprinting but only adequate for pcb making or metal etchforming. Ideally id like to have some optical reduction for the masking process. – joojaa Jun 9 '20 at 13:43

The easiest solution would be either do two run prints, one along biggest DPI density and then with 90 degrees turn OR one run normal and then second with same picture but moved X:Y amount so second run overlap the empty spaces.

You could also use CMYK printer where every "Color" is your UV so you can control raster angle and get the most coverage. Then you might have an issue with "more than 100%" saturation but that depend on the medium if it's something you should worry about. That might require you to override some printer drivers so YOU decide what you send for printing and not the internal RIP of a printer.

For your particular need that might be a lot of trial and error to match proper set of "colors" with your machine dots density.

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