# Exposure and screenprinting issues unexplained (so far)



## monubigina (Apr 9, 2010)

I am having an entire host of issues I haven't had in the past. I have taken detialed pictures to help get the answers no one can seem to answer, I hope that some experts here on the forums can help out as no one in town can quite explain my problems.

I have had very successful prints in the past and am still a moderate novice so I am having difficulty troubleshooting my issues. All links directed to relevant picture

My transparencies seem just fine 

But my screens are terrible now! I use Ulano QX-1 and have for a while. I thought that the emulsion was going bad so I opened up a new container and I am still having the same problems. I have even increased and decreased exposure times incrementally to very extreme. Though I do not have the exposure time dialed in EXACTLY there is still some mystery as to what is happening. Such as image detail washing out immediately and not at all - in the same areas of the screen.

I degrease every screen and allow emulsion to dry overnight.

Granted, the exposure unit is handmade, but there is a very close contact between the positive and the screen during exposure. I have even added an obscene amount of weight evenly distributed across the screen to try and avoid ANY light leaking.The unit contains 8 X 20W UV bulbs (lamps).

Another example of detail washout and retainment.

I wash these out by gently spraying with cold water, letting sit for a minute, and rinsing with very light pressure there forth.

I am using a mesh count of 123 and 156.


Now on to printing issues - 

From an acceptable screen I moved forward to do around of printing. This didn't turn out so well...

I had a significant amount of line drop out on my shirts.

Another example

This is what is going on witht he screen in those areas.

I am using triangle plastisol, Batman Black, to be specific.

I am also printing off contact flood method with even pressure across the garment, my plattens are clean the shirts are laid flat, I have tried 60, 70, and 80 durometer squeegees, different stroke paths, varying pressures - still have this problem. I cleaned the ink out of the screen and tried again - with the same problem. The mesh on this screen is 123.

I am also getting different deposits of ink on the garment, thicker in some places than the rest.

Print on different textile

I appreciate any help anyone is willing to offer. I hope that my descriptions and pictures are helpful in offering some answers. I will gladly trade artwork for some great help if anyone is interested! OF course free help isn't unwelcome either - ( I understand that many of you are already artists and my offer may be not so desirable)!! (= 

tl;dr
detail BOTH washing out and burning in: screens degreased, emulsion dry overnight, positive FLAT against screen during exposure, shower head wash out cold water.

line drop out on garments while on press, calibrated (balanced) press, clean plattens, flat shirt, triangle ink, off contact flood stroke.

Setup: Epson 1400, AccuRIP, light tight exposure unit 8 X 20W UV bulbs(lamps), Shower Head sprayer, Riley Hopkins 4x4, Seiki Flash, Oddessey Flash


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## cortezoid (Oct 15, 2010)

Could it be the film positive is reversed when exposing the screen. You want the ink side of the film contacting the emulsion side of the screen. 

Also , a multipattern garden hose sprayer as a big improvement over a showerhead.


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## monubigina (Apr 9, 2010)

I will definitely get the garden hose, but first I need to make sure that my image isn't coming off so easily first! As for the direction of my positive, I will have to be more aware next time as I couldn't tell you if it were right or wrong last time. I really appreciate your suggestions - they sound very good!


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## Flagrant-T (Nov 11, 2009)

There are a bunch of threads on here about calculating exposure time and doing exposure test that explain it better than I ever could, so search for those...they've helped me a ton. 

The other suggestion I have is to use a pressure washer. If you don't have one, a lot of people go to car washes. Some of those edges look washed out and it might be a function of taking too long to wash it out with a shower head. With a pressure washer, you lightly spray it (like it sounds like you are already doing) wait about 45 seconds and blast away. Your image will be cleaned out in a couple seconds. Less water on it means less chance of edge degradation.

If it takes longer than a few seconds to wash out, chances are you are over exposing.

The parts that didn't print in your example are from the under-exposed emulsion flowing into the cleaned out stencil. When cleaning out your design, don't over wet the squegee side. This will cut it down. You can also blot the squeqee side carefully with newsprint (blot, don't rub). Sometimes you can clean this muck out with screen cleaner after the screen is dried, but it is obviously best to avoid it. Proper exposure time and a pressure washer will cut this down.

Good luck!
Nick


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## evo noche (Dec 11, 2008)

Best to take this one step at a time, because that's how good screens are made.

1) Prep - what degreaser are you using? A good quality commercial degreaser made for screenprinting is a good start. Degrease the ENTIRE screen, including the frame. DO NOT use an abrasive pad, just a very clean sponge or soft brush. Use this brush or sponge ONLY for degreasing. (set it aside in it's own container and keep it rinsed clean) Gently flood rinse the screen thoroughly from top to bottom and set to dry in a dust free environment. (air filter in your screen room is a great idea)

2) Coat screens with fresh emulsion in a dust free, DRY room. It doesn't have to be hot or even very warm - low humidity is the key here. A cheap small dehumidifier from Sears or better yet Goodwill will keep the humidity down. You will notice a drastic improvement in screen drying time.

3) Keep UV light, moisure and excessive heat off the screens until they are dry. It doesn't matter if you dry them over night, if the room is humid the screens are just sitting there soaking up the moisture. If it is too warm the screens might be polymerizing before they are exposed.

4) The UV lights in you exposure unit degrade over time. The only way to track the degradation is by regular exposure calculations. Ulano makes an excellent one-step calculator film, or you can you a step-wedge technique.
Here's a good example: How to Determine correct screen exposure times using Vellum
Don't get the exposure in the "ballpark", make sure you nail it down and then re-check every few months or more. Make a chart for each mesh count, mesh color, number of emulsion coats, etc and record the correct exposure for each.

Some notes here about exposure: you want the black areas in your films to be dense and smooth (no graininess or streaks in the printed black) but that is half the battle. The key is to hit the emulsion with as much UV energy in as little time as possible. The shorter the exposure, the less time light has to scatter and leak into the areas of the stencil that you do not want exposed. You can even have films that are less than perfectly black and still get good results if you are nailing the emulsion with enough UV light energy. This is accomplished by:
UV lamps, as high a wattage that can be obtained, that are producing light in the correct spectrum. (330-430 Nanometer). One solution for a home made machine is take your current design and double the number of installed lamps, and make them higher wattage, and the correct lamp type.
Info:
Low pressure & medium pressure UV lamps for industrial curing | Light Sources
[media]http://www.light-sources.com/sites/default/files/images/IndustrialCuring_SDI_Lamps_Specifications.pdf[/media]
_Low iron, optically clear glass!_ Cheap, standard glass can increase exposure times drastically, as it will block or reflect much of the UV energy. Ask about low-iron glass at the local supplier, a few extra bucks here makes a huge difference.

Your post-exposure routine seems fine, gently flood the image from both sides, wait a minute or two and then wash out thoroughly from the print side.

As far as the print problems it looks like there is partially cured emulsion haze clogging up your finer lines. If the screen is rinsed thoroughly during development and the emulsion is exposed properly, that issue should resolve itself. (unless there is something else going on like excessive flash cure heat fusing the ink in the mesh...that's another ball of wax...)


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## evo noche (Dec 11, 2008)

Flagrant-T said:


> The other suggestion I have is to use a pressure washer. If you don't have one, a lot of people go to car washes. Some of those edges look washed out and it might be a function of taking too long to wash it out with a shower head. With a pressure washer, you lightly spray it (like it sounds like you are already doing) wait about 45 seconds and blast away. Your image will be cleaned out in a couple seconds. Less water on it means less chance of edge degradation.


If the exposure is correct and the emulsion is properly exposed all the way through (think: cooked burger - no red in the middle) then a pressure washer is way overkill. Only time I turn mine on is when reclaiming and de-hazing. 

One of those mult-selector garden sprayer pistols work great. Shower style for rinsing and fan or jet spray for washing out the image. My favorite one I've found is the Dramm "Revolver", very well made and stands up to daily use. (all the important parts are brass or cast metal)
Dramm Hand Held Watering Tools


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## monubigina (Apr 9, 2010)

Excessive flash cure heat clogging up the mesh? I don't see what oyu are saying. The way this is worded it sounds like you are saying the screen is being flashed. The only other thing I can imagine is that you are referring to the room temp due to the flash being on... Is this right?


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## monubigina (Apr 9, 2010)

Flagrant - The example picture does not show underexposed seeping or flowing emulsion in the print area - I hope I don't sound argumentative, I'm not trying to. I gave up trying to rinse out the stencil after too much time and took the picture. It is slightly exposed emulson that we are seeing in the stencil area. I only say this to seek the correct method of fixing my problem! Thanks btw!!


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## monubigina (Apr 9, 2010)

Evo - To answer :

1. I am using professional grade degreaser.
2. I live in the middle of a desert - we have no humidity, my house isn't even humid.
3. Screens are at a nominal 75 degrees at all times
4. I understand the importance of step wedge, I am waiting on an order of amber and rubylith to arrive currently. I replaced my lamps recently as well. I currently measure my lights with a candela meter and light temp meter from work. As for doubling the number of lamps - that wouldn't be very efficient as I already have 8 and I would have to build an exposure unit the size of a kitchen table to house 16! (= 

As for wavelength My lamps are spot on in the spectrum. I took particular care in choosing the lamps as professional lighting is my day trade. The bell envelope is 350 -410 with the apex at 360.

Print Problem - It may just be emulsion haze, I have been having an awful time with my new container of emulsion staining the living daylights out of my screens - BADLY. I completely totaled a screen today because of one exposure staining it so badly. This is WAY before reclaimer even comes into the picture so I know it isn't that which is setting the emulsion in.

I really appreciate the response. Thanks!!!


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## evo noche (Dec 11, 2008)

monubigina said:


> Excessive flash cure heat clogging up the mesh? I don't see what oyu are saying. The way this is worded it sounds like you are saying the screen is being flashed. The only other thing I can imagine is that you are referring to the room temp due to the flash being on... Is this right?


This would be from printing over a hot shirt that has been flash dried (like the first color) and not allowed to cool slightly. I was grabbing at straws there.


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## evo noche (Dec 11, 2008)

Ok after reading the response and looking at the pics again it is (as far as my guess)

a) Bad emulsion 

or

b) you really need a vacuum frame

or 

c) perhaps the excessive weight you are applying is distorting everything and is counter productive

or

d) all of the above


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## monubigina (Apr 9, 2010)

hmm.. I see what you are saying Evo...

I am going to assume, for now, that my unit is not the problem and wait for the new emulsion and gels. That way I can rule out safely the photopolymer going bad - I ordered Diazo this go around. This just strikes me as funny because I had such a great run (for about 1 year) with the photopolymer and all of a sudden I have crap screens. Though - I haven't tried a lot of detailed prints until recently either. After I nail down the emulsion/exposure time garbage, then I guess I will move forward starting with glass... 

One thing I do not understand is how a vacuum frame would work any differently/better than the foam and weight method. I know their technical differences and how each one's fundamental properties - I just don't see how the outcome could be so different. I mean, the point is, to keep the film as close to the screen as possible right? I (personally) don't see how a vaccuum would get the film closer than the weight of the screen on top of it - however I do understand you opinion of adversely affecting the exposure with too much weight. I think I will leave the warping scenario for last - but we all know that means that this only designates it automatically as the problem!! (=

Again - I really really appreciate the opinions, I am not a professional of even one of seasoned experience. This is a great way to get the help of others who are well versed int heir trades that are also willing to share!! Not the easiest thing to find these days! Especially living in one of the most competitive cities in the world. There aren't many locals who are willing to help!


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## evo noche (Dec 11, 2008)

One option, although it's messy but it might help to eliminate the film-to-emulsion contact issue would be to not use the vacuum OR the weight :

Try this stuff -
3M Spray Mount Artist's Adhesive - BLICK art materials

Spray a light, even coat on the positive, wait about 20 seconds, stick it to the screen and smooth it out making sure it's adhered evenly. Burn the screen as normal with no weight.

The film will peel right off for washout. There will be a residue of adhesive on the film so use an old film you don't care about as a test exposure.

Not the most elegant of solutions but it might help narrow things down a bit.

A shop I worked at years ago burned every screen this way. No vacuum frame. In the sun. (even 4-color process halftones)


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## InkedApparel (Mar 18, 2009)

> I have even added an obscene amount of weight evenly distributed across the screen to try and avoid ANY light leaking


I have to agree with evo......to much weight will bow the glass causing uneven contact between glass and film....when I first built my exposure unit I has thin glass and used to much weight to keep the film tight(or so I thought)to the glass...which cause the image to turn out just like the pictures you posted......after I exposed the screen and washed it out it looked blurry , I thought I was underexposed so I increased the burn time..just made everything worse....how thick is the glass on you exposure unit?

Inked


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## evo noche (Dec 11, 2008)

InkedApparel said:


> I have to agree with evo......to much weight will bow the glass causing uneven contact between glass and film....when I first built my exposure unit I has thin glass and used to much weight to keep the film tight(or so I thought)to the glass...which cause the image to turn out just like the pictures you posted......after I exposed the screen and washed it out it looked blurry , I thought I was underexposed so I increased the burn time..just made everything worse....how thick is the glass on you exposure unit?
> 
> Inked


Hence the advantage of a vacuum, it doesn't push everything together, it _pulls_ it together. You simply can's get the same kind of tight contact without dangerously loading the glass.


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## InkedApparel (Mar 18, 2009)

yes...a vacuum is next on my list 

Inked


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## macmiller (Jul 23, 2007)

You're underexposed, plain and simple. No sense in exploring all these other variables in the problem. If your positives are as dense as you say, it's not going to hurt to overexpose provided you're making good contact with the glass. If you get as much "scum" as that when washing out, you need to burn it longer. The ink side should only have a trace amount of emulsion wash off, the print side should have no emulsion wash out, other than the image. You will get better results w/ a pressure washer, but not until the screen is properly exposed.


"The example picture does not show underexposed seeping or flowing emulsion in the print area"- That's exactly what that is. It's not exposed properly and therefore can't withstand the proper pressure and amount of water needed to clear all of that out, and when dried is keeping it from printing in those areas.

For those fine lines, you also want to move up to higher meshes. You will be able to hold that detail on lower meshes once you get coating and exposures nailed, but it's a lot easier on a finer mesh.


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## sophia747 (Apr 15, 2020)

Hi!
I currently have the same exact issues that you had. 
Where you able to figure out exactly what was causing the issue? In addition I am also using the Epson 1400 to print out my designs. Please let me know when you have a moment.
Sophia


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