Question about moire?

[Doug S]

I know this is a crazy question, but now that we are DTS I'm noticing moire when imaging screens.

To start off with, I'm using mainly smart mesh and using their angle guide.  I'm using saati DW textile emulsion that has 41% solid content and coating 1/1 slowly with the round edge.

Not that I'd ever try printing 55 lpi with a 150/48 but imaging 55lpi on a 150/48 with a 22.5 angle "for an exposure test" there is obvious moire so I bumped it down to 45 lpi and it's the same thing.  I've also tried other meshes such as a 200, 225, and a 300 with the same result. 

Now for the crazy question, does emulsion have anything to do with moire?  Or maybe it's the coating method and I should bump it up to 2/1.  I don't have a micron meter but it seems like a decent eom. 

What about linearization?  Would that make a difference?

Thanks

[jsheridan]

are you using a round dot or an elipse dot, that can make a difference.

[Ripcord]

An emulsion layer that is too thin or on the wrong side of the mesh can result in a moire, because a thicker layer of emulsion creates a little more distance between the positive and the mesh. Another reason could be that the screen mesh is on the frame slightly crooked. This can happen with retensionable frames.

[3Deep]

One good way to find out if it's your film is to stack them one at a time on a light table and look for moire patterns, if it's not present in your film then something is off with your mesh.  Kind of doubt your emulsion is causing the problem...Oh chit I just reread your post your DTS none of what I just said helps so I'm betting it's in your DTS settings.  I will say 22.5 does not work with all the screens 100% of the time I've found out.

[Doug S]

I normally use elliptical but I tried both.  It's a little less obvious with the round but still there.  Also, I'm using shurloc frames.

Rip, I was wondering about the emulsion thickness too.  If I went thicker I was thinking I might not notice it when I'm imaging but it might still be there and I wouldn't notice it until the first strike off.  I'm going to have to give that a try though.

I appreciate everyone's input.  I don't do much halftone work, maybe 8 times a year but I want to be ready.

[Dottonedan]

For DTS, a flat or smoother surface is best.  Thin coats will have the print sort of laying in valleys and on top of hills of the mesh thread knuckles.  I've seen this cause mesh interference before on thin mesh.
When they coated another time, it improved.  Film lay up on top of the emulsion away from the mesh so you may not have seen this issue with film that much.  Where it becomes very noticeable, is when you are now holding finer dots like 3-4% and in large areas of that (where interference becomes more visible).

[jsheridan]

I don't do much halftone work, maybe 8 times a year but I want to be ready.

Tell us how you make your halftones as the process you use could lead to it and also what kind of RIP you're using for the CTS as sometimes it can over ride what you did in the art to what prints on screen.

Screen angle, try 25 as I had some amazing results compared to 22 or 22.5

[Alex M]

I don't do much halftone work, maybe 8 times a year but I want to be ready.

Tell us how you make your halftones as the process you use could lead to it and also what kind of RIP you're using for the CTS as sometimes it can over ride what you did in the art to what prints on screen.

Screen angle, try 25 as I had some amazing results compared to 22 or 22.5

^ This, while 22.5 is certainly the most common angle used now it is not always the best. Try to print the same test file with different angles to find the one that works best for you.

[Screen Dan]

We use a wax CTS and have done 55LPI day-in-and-day-out at 61 degrees.  150/48 is excellent at that.  Now, sometimes when developing it appears that there is moire...that just means you've got some tiny little dots in there that you need to finesse out.  Even after developing everything sometimes there is apparent moire in the stencil...but once it goes on press it all looks great.

Since we couldn't get the shop to be a little nicer to our 225/40 we bumped the mesh up to 225/48 and the LPI down to 53...barely any perceptible difference to anyone but the few of us veteran (ex)printers in the 15+ year club and is noticeably easier to deal with on the screen room side.

I would definitely try to get that EOM up first.  Low tension can exacerbate this situation but 150/48 isn't terribly hard to keep in a perfectly usable tension...but I guess you could double check that as well.

[Doug S]

I appreciate everyone's help.  Here is the file I created in illustrator.    I'm fixing to coat some screens 2/1 to see if that makes a difference. 

I'll print the same file in the morning and post the results in case anyone else has this problem.

[jvanick]

that looks like 10% steps to my eye...

you'll want some more variance in your 90-100 range and your 10-0 ranges...

I prefer to do 1% increments from 1-10 and 90-100.

that way you can easily see what's happening in those ranges.

[Doug S]

I just wanted to thank everyone for their input.  The moire in my situation was due to not enough eom as suggested so I went from 1/1 with the round edge to 2/1 with the sharp edge. 

Also, changing the angle suggestion worked also.  Using the 150/48 took a different angle than a 156 to deal with moire as well. 

Any way I wanted to say thanks and have a great weekend

[Frog]

I just wanted to thank everyone for their input.  The moire in my situation was due to not enough eom as suggested so I went from 1/1 with the round edge to 2/1 with the sharp edge. 

The problem of not enough EOM is easily solved by coating with the "glisten" method.
Described here in detail in one of our oldest articles, it explains that rather than counting on number of strokes and a particular edge, one can actually have a visual clue to enough emulsion during the coating process.

[Ripcord]

I've noticed over the years that new mesh will glisten quite nicely, and the more you times you use it the harder it is to achieve that glisten, even though the mesh is still usable. Have you noticed that as well?

[Frog]

Nope, because I think that it's the emulsion that is coming through the mesh that we (are supposed to) see glisten, and not the mesh itself.