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Discussion Starter · #1 ·
Hi, I've been on this forum for a while and never joined until now!

I've been having problems with screen printing for several months now and have learned a lot along the way.

Every time I burn a screen and I proceed to wash out the image the edges around the text of my image starts to peel off. Everything will look really great washing it out and then all of a sudden the edges start to peel and the image is now ruined. I use a fairly low pressure hose that's on my kitchen sink. I start over and get the same result.

If anyone can explain what the problem could be I would appreciate it very much.

Here are the specifications of my setup and what I've been doing.

Emulsion: Ecotex Tex Red HV Emulsion
Emulsion Remover: Ecotex Emulsion Remover (Diluted as instructed and has worked well)
Screens: 20 x 24 inch screen with a decent mesh count? (I'm not sure it is very tight and has an aluminum frame with white mesh)
Film that I use for burning: Vellum (I print my image on Vellum using a Brother Laser Printer)

My Procedure:
  • I lay a light layer of Ecotex Tex Red HV Emulsion on both sides of the screen and remove excess until it is smooth and not thick. (I do this in a dark room)
  • I usually lay the screens in a dark room overnight to dry but I also found that putting in front of a fan for 2 hours also works very well.
  • I print my design that's separated by color and each color is grayscale to be just black for vellum. (I print my image on the highest dpi straight from Photoshop.)
  • After the emulsion is dry I have a DIY station that has two halogen lights that are both 250W and about 1.7 feet from the platform. The platform is completely painted black and I have a pad underneath where the screen goes that is painted black as well.
  • I put my dry screen on the station with the ink side facing down so the print side is up.
  • I put my vellum image on the print side (the image is already reversed so the ink side will be the correct orientation)
  • I have a large piece of glass that I put on the screen to keep the vellum and the screen tightly sealed together so light cannot go underneath the vellum.
  • As the instructions state on the Ecotex Tex Red HV Emulsion container, I burn the image for 7.5 to 8 minutes. 7.5 usually works pretty well.
  • After the image is burned I spray the screen with water and I let is sit for a little bit (not to the point to where its dry)
  • Then I washout the screen which leads me to the beginning where the text edges start to peel. For example if there is an M or N the emulsion that fills those triangles in the letter would peel back a little or peel off completely, leaving a shadow behind.
Once this happens, I wash out the screen with the emulsion remover getting rid of most of the emulsion. Then I use a pressure washer to remove the rest of the emulsion. Afterwards I degrease the screen if I put ink through it. Afterwards I pressure wash again just to get the ink and degreaser out. Then I let the screen dry and I repeat "My Procedure" Again.

Hopefully that was very detailed to see where the problem lies. If anyone can explain what the problem could be I would appreciate it very much :cry:
 

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Well, UV light is what hardens emulsion, so it would seem yours is not getting enough light.

I'll toss out a few things here, and maybe some of them will be of help.

With the halogen lights, are they bare naked, no glass in front of them? The glass in worklight fixtures, and the like, filter out some of the UV, so want to take the glass out of the fixture if there is any.

How thick is the glass you lay over the screen? Regular glass absorbs a good bit of the UV, not a huge issue, but does increase your exposure time a bit. If it is an insanely thick piece of glass, like 3/4" plate, I would get something else. Low Iron glass is what I use. The pure clear name brand glasses are a bit pricey for the marginal gain over using Low Iron. Mentioned for completeness, as more exposure time will probably fix your issue on its own.

Yellow "Bug Lights" are a safelight for this process. Not sure if you were working in a literally dark room or not, so just mentioning that total darkness is not needed, as just need to avoid UV and the blue end of the spectrum.

As to exposure time, see the link in my sig. Everyone's DIY equipment is different, so need to test and dial in exposure for your exact combination of transparency opaqueness, UV intensity, emulsion type and thickness etc. Can probably get it dialed in with one test screen (containing 8 or 10 tests itself).

Run water over both sides of the screen, but mostly on the shirt side, as that is the thicker side. The unexposed areas should change color. After 30 seconds or a minute, the emulsion should be softened enough to easily spray out.

A common thing that can go wrong is laying down the emulsion too thickly and it not drying all the way through--but sounds like you avoided that. In any case, make sure the emulsion has had time dry all the way through. You cannot get it dryer than your local humidity level without using heat and/or a dehumidifier--a potential issue depending on where you live. You want it under 50%. I got a $10 humidistat from Home Depot, so I know when my drying box gets there (heat and dehumidifier).

Degrease before coating, doesn't matter if the screen is brand new or has just been reclaimed. Simple Green, or the like, works fine for this (just saying that you don't need a screen-printing-specific cleaner).

All that said, it probably comes down to too little UV, so more time and/or more UV.
 

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Discussion Starter · #5 ·
My emulsion states that it takes 7.5 - 8 mins to expose and I have photopolymer emulsion. I did one wedge test that went to 10 minutes, then I did another wedge test that went to 15 minutes. Every one of the peeled. The more cooked parts peeled less but the image is still ruined.
 

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My emulsion states that it takes 7.5 - 8 mins to expose and I have photopolymer emulsion. I did one wedge test that went to 10 minutes, then I did another wedge test that went to 15 minutes. Every one of the peeled. The more cooked parts peeled less but the image is still ruined.
It takes 7.5 - 8 minutes if you use the exact same equipment in the exact same way as they did to establish that time. Else it just serves as a point of reference to deviate from. It would take 20 or 30 seconds on my exposure unit (assuming similar sensitivity to other photopolymers).

Does your emulsion bucket have a date of manufacture or expiration date on it? If kept reasonably cool, photopolymer should last quite a while. Mine is three years old, but a different brand. Generally they say it lasts a year from the date it was made, if it doesn't get too warm.

Can you post some photos of:
  • The printed transparancy
  • A coated screen
  • An exposed and washed screen showing the peeling (if you still have one)
Also, is it humid where you are?
 

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Discussion Starter · #7 ·
I know I haven't replied in a while but I figured it out.

For anyone else having the same problem, I'm not going to just leave (I hate that).

My halogen lights are not strong enough to pierce through my vellum very well so for me it takes 11 mins instead of 7.5 to 8 mins to expose the emulsion.

Second, because my halogen lights are this way I used an alternative of sprayaway toner and heavily sprayed my vellum until the blacks got blacker and the vellum got almost transparent. Then I took that vellum and applied it directly to the glass, smoothing out the air bubbles as I go.

The main problem was the air bubbles and the size of the glass. My glass was bigger than the screen so it didn't properly lay on the emulsion right and there where apparent wrinkles to the vellum. When I spray the vellum and make it transparent and wet; sticking it to the glass gets rid of the air bubbles since I can smooth them out.

Afterwards I place the glass with the stuck paper onto the screen and expose for 11 mins. Afterwards I spray the screen with some water and let it sit for 5 mins.

This is also an important step for me. Make sure the water pressure of whatever you are using to washout your screen is high enough. If not, you could be putting so much water on it till eventually the text will start to peel. I used my garden hose which worked fine and exposing for 11 mins produced a clear image that could also withstand the power of my garden hose.

After that, my screen is done and I let it dry.

The next steps I am going to take is to just buy transparent paper to make it easier on my lights and also get diazo emulsion instead of photopolymer emulsion. Photopolymer emulsion requires pretty exact times and my home DIY rig can make that frustrating. I've had better experience with diazo due to the times being more lenient (10% window).

Also, I missed one key detail as well. I degreased my screens very well and I also applied 2 coats of emulsion on print side and one coat of emulsion on the ink side. Makes it thicker and less able to peel off, like text.

Hope this helps and for all the people that replied if there is something in this process that could be improved please let me know. I am just ecstatic that I finally figured it out after so many retries. I used like a pint of emulsion in 2 days 😔
 

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Thicker is more likely to peel than thinner, as it is lack of exposure, not lack of emulsion, that leads to the peeling. The thicker the emulsion, the more exposure it requires, and the harder it is to get it to dry all the way through.

There are transparencies made specifically for screen printing. Fixxons is a commonly used brand, but that is all for inkjet, I believe. Not sure what is best for using a laser printer, other than not using a laser printer.

To make better contact between your screen and transparency, cut a piece of foam to fit inside your screen, but with the foam thicker than the depth of the screen. That pressure will make some marginal difference in how well the two meet.

Note, Diazo has more exposure latitude because it is slow--not something you need more of when your burns already take way over 5 minutes.

Weak light and poor films, the trial by (dim) fire that most of us go through at first. If you eventually upgrade both of those, it will be like ceasing to hit yourself in the head with a hammer :) . I had good films to start with, but a relatively slow DIY 4-tube UV unit and slow Diazo emulsion. Switching to 1000 w metal halide and photo-polymer was a revelation, and a relief.
 

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Discussion Starter · #9 ·
Thicker is more likely to peel than thinner, as it is lack of exposure, not lack of emulsion, that leads to the peeling. The thicker the emulsion, the more exposure it requires, and the harder it is to get it to dry all the way through.

There are transparencies made specifically for screen printing. Fixxons is a commonly used brand, but that is all for inkjet, I believe. Not sure what is best for using a laser printer, other than not using a laser printer.

To make better contact between your screen and transparency, cut a piece of foam to fit inside your screen, but with the foam thicker than the depth of the screen. That pressure will make some marginal difference in how well the two meet.

Note, Diazo has more exposure latitude because it is slow--not something you need more of when your burns already take way over 5 minutes.

Weak light and poor films, the trial by (dim) fire that most of us go through at first. If you eventually upgrade both of those, it will be like ceasing to hit yourself in the head with a hammer :) . I had good films to start with, but a relatively slow DIY 4-tube UV unit and slow Diazo emulsion. Switching to 1000 w metal halide and photo-polymer was a revelation, and a relief.
Thanks for the info, I assumed the peeling was also due to how my emulsion was way too thin. Also that does make sense about Diazo. Where did you get your metal halide bulb? I see some on amazon but I was just wondering.
 

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Thanks for the info, I assumed the peeling was also due to how my emulsion was way too thin. Also that does make sense about Diazo. Where did you get your metal halide bulb? I see some on amazon but I was just wondering.
A place online called 1000bulbs. That was some years ago. Note, you don't just get one of these bulbs and screw it into a socket :eek: They require a special socket and a transformer/ballast thing of their own. For our purpose, we need the type of bulb that does not filter out the UV. This type of bulb has a bump in its base that requires a special socket different from the filtered type of halide bulbs. That is because these bulbs put out a dangerous amount of UV light and are intended for use only inside of light fixtures that filter out the UV. Bulbs like this are used in warehouses, sports stadiums, and the like. They are about 18" long and 10" or so wide. You need to build an enclosed exposure unit to block any stray UV, as well as to block the 120,000 candle power of the bulb. Way too bright to want in your eyes at close range--remember, these are intended to be like 50 or more feet up in the air shining down like a distant sun.

There are also ones intended as grow lights for pot farms. I'm not sure of the relative merits of the halide bulbs available at this time.

All that said, UV LEDs are probably the smart choice now. But need to make sure that they put out the correct bit of the UV spectrum to work with emulsion. A lot less waste heat produced, and likely will last a lot longer too. That's what I would look into if I were starting now. There are some good threads on this topic, so poke around with the Search feature if you are curious abut what others have done. Either approach requires some DIY skills, including playing with wiring/electricity ... though perhaps there are some decent plug-n-play LED UV bulb options now. The old CFL UV bulbs were not very strong.
 
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