waves in a half tone

[the-shirt-guy]

I am printing at 50%on a large area and I am getting waves in the area that is printed I am printing with 230 mesh 50 lpi and have tried many different andgles but i am still getting a wave patern in the print. any sugestions.

[blue moon]

I am printing at 50%on a large area and I am getting waves in the area that is printed I am printing with 230 mesh 50 lpi and have tried many different andgles but i am still getting a wave patern in the print. any sugestions.

there are several reasons for this ad you'll have to figure out if it's the screens or the garment. Try few different shirts and see if it happens on all  of them. Make sure you use different weight (6.1oz and 5.3oz for example and see if you can find a 50/50). If any of them print fine, the issue is in the weave and you will have to change the angle of the halftone to get rid of the moire. You can do this by loading the garment at an angle and printing for inspection. you'll need to go through several trials until you find something that prints OK. Then figure that angle and use the difference from normal to adjust it on the film.

The other possibility is that the issue is with the screen. Start with 22.5 degrees and go down to 40lpi. See if that solves it. if screens turnn out to be the issue, post more details and we'll try to help. We'll need info on the screens (statics, rollers, tension, mesh thickness, emulsion, coating procedure . . .). The more you post, better we can help.

pierre

p.s. welcome to the TSB!

[blue moon]

p.s. the absolute worst I've seen it was on a white 50/50

[Frog]

Besides the possibility of the fabric pattern being the cuprilt, I still always look at the mesh and lpi combination. When possible, I go one better that the usually fine 4.5:1 ratio, and shoot for 5:1, in your case, on a 230, 45.

And welcome from me as well.

[aauusa]

I would almost bet that is was a mesh and halftone conflict.  I use 230 count mesh all the time and I print halftones at 55lpi  with and 22.5 angle.  Pic below is a 200 count mesh screen on top and a 230 mesh on bottom with the halftones printing at 55lpi /22.5 angle on both screens.

you can see the moire

[blue moon]

it is possible that it is the mesh, but my thinking is that it's the shirt. He is printing 50% dot at 50lpi. That is very large dot! Also with the gradient being uniform 50% rather than photo style image, if most other things are under control, it should be the shirt. If the screens are lose, the emulsion is old, bad vacuum or any other similar issue are good, what's left is the shirt. Now if those things are not in order, it is a different story!

pierre

[Dottonedan]

Everything Pierre has said is correct but would come after a few things first.




First, I'd avoid a straight 50% halftone to begin with. It is the middle point of where the dots transition between a circle or oval dot shape and transform into a diamond shape as you reach 50%, then reverses on the other side of a 50%. So your shapes become very odd at 50%. The lower the line screen, the more pronounced this add shape becomes. I try to stay away of large coverages of anything between 47 and 53% tones.




2nd, Have you actually looked into the films to see if the pattern is in the there before even burning a screen? Sometimes the film output device can cause this.


3rd, Large areas of a single % tone will for sure, show up any imperfections of your screen issues. Lets say, that you did not stretch (or your supplier) did not stretch the screen (100%) true.  When you have a consistent halftone like that of 50% across the board, it will show a variance or a difference from one end to the other. It's almost NEVER that you find a perfectly stretched mesh without (any) flaws) when dealing with such a large area of halftones. So, requiring a large area of lets say 12x12  of a 50% tone.... (without flaws in the print) is way too much to be asking from your standard mesh. Great care in your stretching process needs to go into that in order to handle that scenario well. Many of us use a 50% tone all the time, but not in a just a large open space as you've indicated. It's not just the mesh that show these imperfections when printing large consistent areas of halftone. If you have a bend in your squeegee blade or a nick, it shows as a streak or a heavier halftone (ink) deposit. That is why they tell you to make sure you use sharp clean squeegees when printing 4 color process as you are dealing with mostly halftones across the image.


When you look at the screen, somewhere in the middle, can be a slight arc or something like a rainbow. You may also see it on the outsides near the corners as well.


You can do two things. 1, you can re-burn the screen in an attempt t get a better screen (but highly unlikely. As I've mentioned, it's a bit too much to ask of a screen to be perfect all across the max imprint area.


2, Begins the area of what Pierre posted. You start to look at changing your dot size, (don't go smaller). Go bigger. then line screen angle and shirt type. This pattern can be hidden depending on if you use a larger dot and if you re-output film and change your angle.

[Dottonedan]

AAUUSA\'s example is a great one for showing that it's the mesh stretchign process that can cause this before everything else.


A 50% tone on a 55lpi halftone at 22.5 degrees (WILL WORK) great.  It will even work better on a 50lpi.
Clearly the issue in the photo example is in the stretching. Both normally work and are identical processes except the stretching in unique to each screen.


For a mesh of a tee to cause this, it would need to be a VERY LARGE thread and weave. Probably more so than on a sweat shirt. More like a knitted sweater. I have some some issues come up tho from standard sweat shirts and large areas of halftone as in Pierre's example.

[Dottonedan]

When you see halftones dropping out of low end fades causing a saw toothed jagged effect, yet it looks great in the 15-30-40% ranges, THAT is an example of not having the proper halftone count to mesh ratio.


When you see bowing, arcs or rainbows (in the higher % of halftones like 15-30, 40%, it's more of a mesh stretching issue.

[PixelPimp]

Hi all! i was about to start a new thread and then saw this one that maybe the same issue.
slight moiree pattern appearing when printed.
Checked the films (halftones 55lpi @ 21degrees on 305 mesh), the screens and a test print on paper, the pattern is not there. A slight moiree appears when printed on the fabric and it appears to be the weave causing it. I didn't get a chance to ask them to print on a different material to test before they took it down.
here's the pics

[Dottonedan]

Can't see by the images all that well. You can post larger images in here to view if you like.


As it is, the fade you show, looks really good. Many people would love to maintain that level of dot.


What that looks like to me, (from that bottom pic) is an example of losing the 1-2 % dots and is standard in a fade of most any fine halftones fades out (to nothing or to shirt color).


As it drops out, it's got to have a point where it holds and it doesn't hold. So, you see that slight unwanted pattern. It's not moire, but rather mesh interference. It looks so subtle because it's right at the lowest end of the gradations.

[inkman996]

I would almost bet that is was a mesh and halftone conflict.  I use 230 count mesh all the time and I print halftones at 55lpi  with and 22.5 angle.  Pic below is a 200 count mesh screen on top and a 230 mesh on bottom with the halftones printing at 55lpi /22.5 angle on both screens.

you can see the moire

I think this above is an awesome example of what a few less or extra thread count can do to a half tom,e pattern, Dan I do not  think this has anything to do with a bad stretched screen at all AA was simply showing that mesh count and angle can conflict.

[PixelPimp]

here's a larger pic (i had to retake it as i must have deleted the previous one)

[Dottonedan]

PixelPimp,


Many people would lOVE to print that good. You do not have a garment weave issue my friend. You have "outer limits" syndrome. The desire to extend beyond the physical limitations of your boundaries.  LOL.


Thats about as good a halftone result as one can wish for.  If we were to really nit pick, we could evaluate where the slight jump comes from. It's more of a small hop. The slight jump near the center of the halftone drop off where we go from probably 7% fading to the shirt and then seems to jump in a lighter tone to 4% or something. (guessing on that of course).  To me, if I had to guess, I'd say this is where the dots are holding, but not 100% and is where the ink will just pass through barley enough to make a color difference. As if they just kiss the shirt...and don't really adhere well and maybe stick partially in the screen.  (splitting hairs).


Good stuff.

[Dottonedan]

Inkman,


That is a good guess.  It's an incorrect one I am almost sure of, but a good one none the less. Very common.


The above image (in AA's photo example) would be an extreme and very rare occasion of thread interference. You would need the weave of a thick wide weave in the worse case scenario of a sweat shirt...versus the below image of a smooth tight tight weave of a tee shirt.


Angle can conflict....due to the parameters in your shops workings ...no matter your garment weave, mesh or line count.  The angle conflict has nothing to do with what mesh you use, but has much to do with how popper you've coated your emulsion, and aligned and stretched your mesh. All other issues only enhance or dilute the visibility of said issues.


You can have angle conflict on 60 mesh,  110, 156, 200, 230, 305, 330, 350 etc.   You can have angle conflict on halftones of 10, 25lpi, 45lpi, 65lpi, whatever.  It is not directly related to any of the mesh or halftone combinations.


What is seen in AA's example, is a CLEAR result of mesh miss alignment issues. Had this been aligned straight, you would not see these bands at all, even if the halftone count would be too high for the mesh. If it were just a halftone issue of (too high for the mesh), you would ONLY  see that the small dots were faded out and have jaggie zig zags edges in the gradations of the 3-4% range as those dots would be too low to handle on that mesh for sure.


This is not to say it came from him or his shop. He may have bought the stretched screen that way and even if not, It's a manual process that can result in human error. We are all capable of doing it.




His issue in the picture stems from two directions and neither are garment weave (that I can see form this picture).


1, As he recognized later as a cure, he needed to go up in mesh to a 230 matching that 55lpi halftone....or, gone down on line screen to 40-45 lpi and maxing out at 50 lpi.


For a 50 line screen, we should use a 200 mesh. At the smallest, a 50lpi halftone. (200 divided by 4 = 50lpi)   and at the largest, (pertaining to halftone dots), he would want to use no larger than a 40 lpi halftone. (200 divided by 5 = 40 lpi.




2, The other issue is that you can see a bend or arc in the mesh. This is not achieved by angle conflict. This is achieved by inconsistency tension at various points of the mesh. This makes a pinch on the square shape and effects the results (and can interfere with the image results) as seen.


# 1 above, will result in the lower end dots being obliterated from using a halftone that is too small) for that mesh. (i.e.) 55lpi on a 200 mesh as apposed to 50lpi on the 200 mesh.  Even at 50 lpi, that is still pushing it. I prefer to use at least 4.5 and often 5 to help make sure I hold all small dots.


#2, compounds this. I would have normally just left it alone and said it was not the correct lpi for the mesh....had I not seen the arc/bending in the mesh.


The answer, is that it is a combination of the two and has nothing to do with garment weave (that we can see by any evidence) visually in these pictures.  What is present in these pictures is evidence of #2 and what we are told by the poster in #1.  Garment weave issues do exist, but not here in these pics.