Moiré on screens - CTS printed

[Rockers]

No matter what we quite frequently get a slight moiré pattern when printing bigger areas of the same percentage halftone. Just did a coup@le of screens where the background of an image prints in 75% halftone over a bigger area. It`s screened 53 lpi, elliptical dot on a 225-40 mesh yellow. Wax printer
Not sure how to avoid this?

[BP]

What is your halftone angle?

[Rockers]

What is your halftone angle?

22.5

[BP]

If you take the 53lpi X 4.5 you come up with 238.5 mininum mesh count. So I would try a higher mesh.

[Colin]

that moire look can happen if the wax print head is to far from the screen.  I have seen 55 lpi printed on 150/157 thin thread with zero visible issues many many times. 

I would contact the manufacturer and see if they can help with settings adjustments.

Or it could be something else

[cbjamel]

I would try 25 degrees i see less problems with that angle on all my screens except cmyk and any special screens.
Shane

Sent from my SAMSUNG-SM-G890A using Tapatalk

[Dottonedan]

No matter what we quite frequently get a slight moiré pattern when printing bigger areas of the same percentage halftone. Just did a coup@le of screens where the background of an image prints in 75% halftone over a bigger area. It`s screened 53 lpi, elliptical dot on a 225-40 mesh yellow. Wax printer
Not sure how to avoid this?

As you can see in my post after yours in this section. I'm getting the same thing.  I also state, that I think much of this issue we are talking about, stems more from mesh alignment (via panel frames or static frames) than it does our angles and shop parameters.   I've seen it in a lot of shops that use the panel frames and the Static frames (where most people are not stretching themselves).


Nowadays, in most cases, shops are not stretching their. own frames. Therefore, there has been an increase in the purchase of pre stretched and re-stretching businesses. This higher demand apply pressured on this type of business. Like any business, as you grow, there are some pains. One of those pains is accommodating the need for faster pace production and therefore, less attention to detail. This is my guess and it all seems logical.


You typically don't see these issues until you happen to use an LPI and % fill that doesn't jive right with the slight offer angle". IN sim process, you might not get to see it but maybe it's there. With larger areas of the same %, you see it very clearly. I happen to have ran 5 jobs all together that were of this nature.  Not seeing it every day, makes you think this is something rare, but I'm thinking it's not as rare as we believe.
I also use 22.5 and have never seen an issue for the last 4 months.


So the problem for us now days, is how do we address this new variable of screen mesh not coming into our shop straight?    The answer is I guess, is to increase dot size or halftone % of the fill. This can work only some of times since...the off angle issue is not consistent either.




Back to the CTS factor.
Due to not having film and the ink or wax laying on the film flat, you can sometimes see a visual interference as the light hits it a certain way to where some angled dots get picked dup by light and some do not.


With DTS, Wax or wet ink, You can see more of the dots laying down into the valleys of the mesh...a mesh that is not coated think enough to lay smooth.  This is the RZ value that most people seem to avoid getting well. We typically want easy coating process with less coats, less emulsion to hold more detail. The best RZ values can come after drying a 1"1 and coming back and hitting the face with another coat to finish it off and smooth it out. (More time and labor). Lesser RZ values allows the mesh thread to also become (more of) a factor...as well as, when the emulsion dries, it takes form of the mesh threads causing what looks similar to a waffle texture (more exaggerated on Lower mesh).  Then the ink and wax, can hit a valley and the side of a mesh thread and seem angled.  (This is what is seen before washout).  Typically, it's not visible in the print.


Since most times, this visual issue (pre washout) with DTS does not show up in the print...it brings me back to a mesh angle issue.


I have been seeing this angle issue in the areas of 15-30% in the highlights and in the 70-85 areas...but nowhere else in the halftones.  You can use a LPI and angle that you know works on a specific mesh and still see it. Like 55lpi on a 305 mesh at 22.5 degree angle.  I can do 20 screens this way that turn out great, and come to # 21 and it happens on 22, 23, 24, 25 and then gone again. That also tells me it's more of a production thing at the mesh shops.

[Rockers]

No matter what we quite frequently get a slight moiré pattern when printing bigger areas of the same percentage halftone. Just did a coup@le of screens where the background of an image prints in 75% halftone over a bigger area. It`s screened 53 lpi, elliptical dot on a 225-40 mesh yellow. Wax printer
Not sure how to avoid this?

As you can see in my post after yours in this section. I'm getting the same thing.  I also state, that I think much of this issue we are talking about, stems more from mesh alignment (via panel frames or static frames) than it does our angles and shop parameters.   I've seen it in a lot of shops that use the panel frames and the Static frames (where most people are not stretching themselves).


Nowadays, in most cases, shops are not stretching their. own frames. Therefore, there has been an increase in the purchase of pre stretched and re-stretching businesses. This higher demand apply pressured on this type of business. Like any business, as you grow, there are some pains. One of those pains is accommodating the need for faster pace production and therefore, less attention to detail. This is my guess and it all seems logical.


You typically don't see these issues until you happen to use an LPI and % fill that doesn't jive right with the slight offer angle". IN sim process, you might not get to see it but maybe it's there. With larger areas of the same %, you see it very clearly. I happen to have ran 5 jobs all together that were of this nature.  Not seeing it every day, makes you think this is something rare, but I'm thinking it's not as rare as we believe.
I also use 22.5 and have never seen an issue for the last 4 months.


So the problem for us now days, is how do we address this new variable of screen mesh not coming into our shop straight?    The answer is I guess, is to increase dot size or halftone % of the fill. This can work only some of times since...the off angle issue is not consistent either.




Back to the CTS factor.
Due to not having film and the ink or wax laying on the film flat, you can sometimes see a visual interference as the light hits it a certain way to where some angled dots get picked dup by light and some do not.


With DTS, Wax or wet ink, You can see more of the dots laying down into the valleys of the mesh...a mesh that is not coated think enough to lay smooth.  This is the RZ value that most people seem to avoid getting well. We typically want easy coating process with less coats, less emulsion to hold more detail. The best RZ values can come after drying a 1"1 and coming back and hitting the face with another coat to finish it off and smooth it out. (More time and labor). Lesser RZ values allows the mesh thread to also become (more of) a factor...as well as, when the emulsion dries, it takes form of the mesh threads causing what looks similar to a waffle texture (more exaggerated on Lower mesh).  Then the ink and wax, can hit a valley and the side of a mesh thread and seem angled.  (This is what is seen before washout).  Typically, it's not visible in the print.


Since most times, this visual issue (pre washout) with DTS does not show up in the print...it brings me back to a mesh angle issue.


I have been seeing this angle issue in the areas of 15-30% in the highlights and in the 70-85 areas...but nowhere else in the halftones.  You can use a LPI and angle that you know works on a specific mesh and still see it. Like 55lpi on a 305 mesh at 22.5 degree angle.  I can do 20 screens this way that turn out great, and come to # 21 and it happens on 22, 23, 24, 25 and then gone again. That also tells me it's more of a production thing at the mesh shops.

I got the following reply by Exile

Now I don`t understand all of it...

"First you need to confirm it is moire and not something else… is the pattern at an angle or is it running at 0 or 90 degrees?

If it is at an offset angle (not 0 or 90) and it is not being caused bu a mesh clash then the other possibility is that the clash is between the lip (screen ruling) and the dpi (I assume you run the SPYDER at 600dpi).

53lpi on a 600dpi output device is designed to minimise moire caused by ’Screen clash’ whereby the halftone dot is cut off on some rows because of the screen mask (dpi versus dpi).
This is a mathematical rounding issue due to the masking process which causes some halftone dots to be bigger and some smaller when they should all be the same size.

Usually this can be fixed by modifying the PrePress settings.. for example: different dot shape, different Angle or different screen ruling.

Best thing is to isolate what tint value(s) is/are causing the patterning and then try different settings in the RIP to eliminate the problem."

[tbarnes]

No matter what we quite frequently get a slight moiré pattern when printing bigger areas of the same percentage halftone. Just did a coup@le of screens where the background of an image prints in 75% halftone over a bigger area. It`s screened 53 lpi, elliptical dot on a 225-40 mesh yellow. Wax printer
Not sure how to avoid this?

Dan makes a great point about the mesh not being fully encapsulated. If your stencil is not thick enough, the knuckles of the mesh are going to create a bit of a moire pattern. Personally, I would start experimenting there before adjusting the print head and everything else. Coat it a bit thicker and see if that pattern disappears. I use 225-40 mesh on 55 LPI all day with no issues, EOM at about 20% with a full exposure.

What brand and model is your machine? If it is a reliable brand that hasn't had this problem in other shops, then odds are it is some variable within your shop. If they have had this issue in other shops, they should know how to adjust and fix it already.

[Rockers]

No matter what we quite frequently get a slight moiré pattern when printing bigger areas of the same percentage halftone. Just did a coup@le of screens where the background of an image prints in 75% halftone over a bigger area. It`s screened 53 lpi, elliptical dot on a 225-40 mesh yellow. Wax printer
Not sure how to avoid this?

Dan makes a great point about the mesh not being fully encapsulated. If your stencil is not thick enough, the knuckles of the mesh are going to create a bit of a moire pattern. Personally, I would start experimenting there before adjusting the print head and everything else. Coat it a bit thicker and see if that pattern disappears. I use 225-40 mesh on 55 LPI all day with no issues, EOM at about 20% with a full exposure.

What brand and model is your machine? If it is a reliable brand that hasn't had this problem in other shops, then odds are it is some variable within your shop. If they have had this issue in other shops, they should know how to adjust and fix it already.

We use an Exile Spyder II. I did already coat this batch of screens thicker then what we used to. I might try go even a bit thicker with the next lot. I`m sure print head distance plays as well a big role in all this. Too bad that the last engineer set the print head so that it is at over 3mm distance to the mesh at a dial setting of 4 . 8 is the closest you can get so that leaves me not with . alot to bring the head any closer to the mesh.