screen printing > Separations

Ellipse Vrs Dot shape benefit "example attached"

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DraginInk:
On the dot note... I use an angle of 26 (22.5 was my angle of choice for a long time... to be honest I forget why I changed it) for all screens and for the last 5 or so years have been outputting at 45 dpi. It works for MOST things that pass through my shop. I still keep some 305 mesh around for the occasional  "high end" stuff that rolls my way. I find with a little larger dot, a little lower mesh count and the elimination of process inks (for the most part) things seem to be less of a challenge for my press operators (me a lot of the time) to produce great images. And side by side I have found the customers just really can't tell the difference. The easier it is for me, the better ;)   

squeezee:

--- Quote from: Dottonedan on April 06, 2011, 01:54:08 PM ---Tossing in the added variables of aligning "different' screen angles hoping that you don't get any moire is just compounding your potential problems.
--- End quote ---
I think you'll agree that using a single angle is OK, but get one of the screens slightly misaligned and the moire is horrible.  Rosettes are more robust to misregistration.  In addition, I think that the colours are more consistent with rosettes, it's less sensitive to which screen is printed first because the colours aren't on top of one another.  Are you printing shirts?  They tend to be more tolerant of same angles, don't try it with graphics printing!
JMHO

Dottonedan:
Most all of us here are shirt printers. We love other types of printing as well but 99% of us are talking about printing shirt. With that said,


--- Quote ---I think you'll agree that using a single angle is OK, but get one of the screens slightly misaligned and the moire is horrible.
--- End quote ---
No actually, I don't really agree. I hhope I'm not sounding bold or arrogant, but speaking specifically in terms of printing on apparel, I don't get moire in my prints from angles (at all). when ever I've received any feedback from customers about moire, it's been due to screen mesh distortion, emulsion thickness, RIP processing etc. Never any moire from screen angles. I know this from first hand experience. I've done allot of printing 4 color process and sim process in both different angle and all same angles over the last 24+ years.

For me, all the same works best. no question. Now, keep in mind, I don't just do this for myself. I am a separator. I separate jobs out for about 5 shops a day on average. About 3 out of 10 jobs are for process printing and I set the files up for all same angles. Now, for you...and what you do with file prep and/or your color separation techniques. It may work best for you using the rosette patterns and then some just like the look of the pretty rosette pattern. :)

yorkie:
I disagree with everything which has been said.  ;D

In screen printing, it is the knit of the fabric which causes the greatest moire. This has nothing to do with dot shape, but a simple interaction of dots printed on a textile. As dots cross the textured field of the textile, fine dots will fall into the valley between the threads of the  knit, where the ink has no fabric to print. Or the dot will hit the summit of a knot in the textile and print 110%!

In printing a "dot" is the smallest reproducible shape which the washout process can hold. The "ellipse" tends to cross the valley of the textile knit, by bridging a gap unidirectionally.

Angles like 0%, 90%, 180% OR 270% is just asking for a problem with the alignment of the halftone to the alignment of the knit.

My favorite spot function starts as a dot as small as is reproducible, then grows into an ellipse, then grow into a uni-directional "line screen". A line screen as opposed to a halftone dot, does not moire. Dots based halftones do moire. The spot which starts as a dot, should grown into an ellipse, which transforms into a line.

Beyond theory, a 45 LPI "line" halftone is just easier to print than a 45 LPI "round dot" or "ellipse dot" halftone. A line screen at anything other then inline with the shirts knit will not moire, not in 1 color, not in full color.

Dottonedan:
Haha.  I was just telling Pierre that I think The Duke is in town. ;)  lol.  Good to see you here. Stay clean, brush your teeth and we will all have fun.

As usual, your way with words and how you so eloquently dance around the language and science of printing is very inspiring. While I am often impressed by your wisdom, I do not agree with "all" of what you say.


--- Quote ---A line screen as opposed to a halftone dot, does not moire.
--- End quote ---
I am not 100% sure that what I am seeing as a 'line screen" is the same as what you are referring to.  Please, if you will, maybe post up a snap shot example. I double Yorkie Dog dare ya.

Line screens, halftone patterns, be it ellipse or round can create moire.  The simple fact of taking any repetitive line element and crossing that with another repetitive line element at an angle can cause moire. Take a wide open mesh like the screen you put on your screen door. Lay another that is identical in mesh count across it and it too will dance with moire patterns. It's a "line" pattern. The mesh threads are lines that weave in and out, yet still form a line. Thats a simple example.

I do agree that I have seen where the mesh of a garment can interfere with the halftone pattern. It's actually pretty rare and not easily achieved but can happen it you try hard enough. I mean, you have to be pushing the envelope pretty hard in order to have the weave cause issues.  I've seen in happen in high line counts like 70lpi in small percentages like 5% halftone or something. When that happens, just adjust the screen angle a tad or decrease the line count a few degrees can it goes away.

I do remember you mentioning this same issue before. I believe you were suggestion that it make snot benefit to print a 60 line screen on apparel as the dots in the highlight areas are too small for the hills and valleys of the apparel thread weave. I disagree here as well. Especially with everyone printing films out on these digital printers. The dots of a 60lpi are not 100% accurate. Close, and some farther away from close but still usable. Who cares if it's really a 5% of a 60 lpi.  AS long as it works. Pierre for example has been printing 65 line screen sim princess all at the same screen angle of 22.5 with no mesh interference and not garment weave interference. I do remember one job we did where in a 65 line screen we were pushing it with black ink on a white ground printing over top of some very light blues. Those stood out a tad more and did show some "unwanted patterns" in the highlight areas of the print. At that point, we could tell for sure if it was the weave or the mesh. Pierre has increases his mesh quality greatly since then. No issues with 65lpi on 330 mesh.

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