[2020 PrintWorks]

Can anyone tell me why I would be getting moire from a 40lpi halftone burned on a 280 mesh screen?

 

[Omni]

There are a variety of possibilities: If the moire is not showing up on your screen, but showing up on the print of your shirt, then it could be caused by the halftones interacting with the weave of the shirt.....another possibility may be undercutting of halftones during your screen exposure, rendering certain halftones closed up, depending on where they fall relative to the mesh......another possibility may be that your mesh 280 which is divided by 40 renders a whole number (7).....Generally you want the numbers to fall at a number plus 1/2 or so.......ie: mesh count used should be 3 1/2 to 5 1/2 times your halftone line count.....another possibility may be the angle of your halftone relative to the screen mesh..... These are just a few of many possibilities......Research and experimentation is what I would recommend

 

[20vK]

^^^^ all great points. nicely covered.

As an example of the shirt, I got moire on Gildan G5000, but not g2000

 

[2020 PrintWorks]

I actually use G5000 also. Undercutting is definitely a possibility. I'm just using a home made unit with 4 black lights. Also I never knew about the line count ending in halves when divided. Thank you!

 

[ShirlandDesign]

What is the rotation of the halftone?

 

[2020 PrintWorks]

The angle is 22.5 and the dots are ellipse. I don't use a rip or anything. I just print straight from photoshop. Not sure if that has any bearing.

 

[Omni]

Halftone angle is a tough one in some instances and the contemporary practice, as well as default angle set on Accurip is 22.5.....I prefer 45 degrees for a variety of reasons......but these all assume that your mesh is stretched accurately and squarely at 90 degree angles with your frame.....any variance in how the mesh is stretched can add to moire issues, as well........There are tons of articles with different theories as to what halftone angles to use and that can even get more complicated when it comes to multi-color process printing.....This is why experimentation and experience is so important......I hope you figure it out.......Generally a point light source is the best source of light for halftone burning......I get great results with a 400 watt Metal Halide bulb......Cheap bulb, but requires an initial investment in a balast, however, and my exposure times are a bit longer than other, more powerful light sources out there, but with the time I take in my screen making, ie, coating etc, I get excellent results.

 

[ShirlandDesign]

Also the weave of the shirt can moire a half tone. I usually print on pellon to see the print on something without a weave first. Come to think of it stencils with a little emulsion scum can moire for the first few prints before the stencil opens up, so I'm assuming an under exposed stencil might as well. Please let us know how you work it out.

 

[Omni]

Also the weave of the shirt can moire a half tone. I usually print on pellon to see the print on something without a weave first. Come to think of it stencils with a little emulsion scum can moire for the first few prints before the stencil opens up, so I'm assuming an under exposed stencil might as well. Please let us know how you work it out.

I tend to overexpose my screens.....With the emulsions available today, exposure latitude is a good thing, and I prefer to deal with a screen that will not leave scum during the washout - drying phase, particularly with basic line art.....I also use multiple, thin coats of emulsion, both front and back of screen, which also requires longer exposure times.....but longer exposure times do allow me to get a more thorough washout, with more water pressure, without the worry of totally blasting the emulsion off the screen....This gives me a great stopedge, with razor sharp lines on the finished screen. I can carry 5% to 90% halftones, but prefer to work with 10% up through 70%, due to on press printing issues.....Proper knowledge of your inks and mesh selection come into play here, expecially if you are printing on a manual press....

 

[sben763]

Everything here mention can cause the moire. If you think its weave interference take a shirt and load at a angle. Setting just 5-10 degrees can let you know if its a weave interface. Another thing you can do is load a shirt and put the film on the shirt. You should be able to see if its a weave interface problem. This also works for checking a screen mesh interface by putting film on a non coated screen. If you see moire just turn the film till it disappears. Take the angle it disappeared at and add to the printed angle the reprint film with the added together angle. . If you have a underbase. Never use the same mesh as you top coats. The probability of a mesh to mesh interface problem becomes very high.

Photoshop CS6 seems to be creating a lot of moire patterns. I just sepped a design and I can see the moire patterns on the screen. Printed and they were on the films. Ran though rip and no problem. Then I ran though simple seps in Corel again no problem.

Another thing I find is going under the 4.5 divided by the mesh can cause issues. On a 280 I would have been at 50-55 LPI minimum. I actually try to go over a little. So on a 205 it would be 45 LPI. I use 50 LPI. Or drop down to a 166 for 40-45 LPI.

There are many factors that cause this. The film to shirt and screen testing is fast and the most probable cause. To check for moire from photoshop just Veiw at 100% and look for the moire.

 

[InnerLoop]

Hey guys. Sorry to revive this old thread. I do a lot of halftone prints and have had mostly success. But I have a question regarding LPI and mesh count because I usually work with 230 or 280 mesh screens doing anywhere between a 45-55 LPI halftone. However, the shop right up the street from my house now carries screens which could possibly make my life a lot easier for when I want a screen at the last minute and don't feel like washing out a new one or waiting in the mail for something that will cost me a bit of shipping. If I'm buying just one screen it's actually cheaper because of shipping too. So anyway, the highest mesh they carry in stock is 200. Otherwise they have to order it which I might as well do myself if I need a higher mesh. Do you think I can get away doing a 45 LPI halftone on a 200 mesh screen? I tried making one of my designs 40 LPI to see how I'd like it and the 45 LPI seems to be significantly better to my eye. The difference to me is much bigger than the difference between 45 and 55 LPI. Basically I was hoping you guys might have some experience with trying 45 LPI on a 200 mesh. I will include a pic of one of my music project's t-shirts that I designed and printed using a 280 mesh (I can't remember if the halftone lpi was 45 or 55). The background lighting in the design have a moire pattern I guess, but the shirts still look pretty damn cool.

 

[Ripcord]

Do you think I can get away doing a 45 LPI halftone on a 200 mesh screen?

Heck yeah, I do 45 lpi halftones on 156 mesh all the time and it makes printing the solid areas of the design way easier.

For years we've all been told that you need finer mesh for halftones but in my experience this is for the most part a myth. Much more important than the thread count is the emulsion layer. It needs to be on the shirt side of the mesh, achieved by doing your last coat stroke on the squeegee side, (hopefully everybody already knows this...) and it needs to be fairly thick. This gives the ink a chance to "regroup" after the mesh cuts it up into thousands of tiny pieces. So by the time it gets to the print surface it's printing the stencil image without interference from the mesh.

Also it's important that your mesh is square on the frame and that your film is square as well. 22.5° is the screen angle many, if not most of us use.

 

[InnerLoop]

Ok, great. I'm gonna go pick up a 200 today and try it then. So you are saying I should double coat the print side with emulsion right? And then coat the ink side once after that? I usually do one coat on each side. 22.5 is the angle that I always use.

 

[Ripcord]

It's not so much the number of strokes so much as the amount of emulsion you lay down. I coat twice on both sides. You'll know it's a good coat when the shirt side of the screen has a thick shiny coating.

 

[Biverson]

I do 1 coat on the shirt side and 2 on the squeegee and can do 45 LPI on a 200. I'm using Saati PHU and try and use high tension screens when I have them in. Get them from Spot Color Supply. I also find that yellow mesh is so much better when washing out. I got some 156's with yellow and I can notice a big difference when washing out. I could burn the same design on a white and yellow, expose the same time and the yellow washes out sooooo much nicer. I'll also lay down my screen with the shirt side facing up and spray it with water, rub it in lightly, and let it sit for 2 minutes before I do my final wash out. This helps with halftones. Sben actually soaks his in a dip tank to help with washout.

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