Emulsion Problems

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cdc
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Emulsion Problems

Post by cdc »

I am using Ulano QTX emulsion. I have had problems getting all the emulsion out, or too much comes out. I am using what I like to refer to as the ghetto exposure unit which consists of 1/4" plexiglass with 6 28" flourescent blacklights. I was exposing at 15 minutes with the lights about 7 inches from the glass, but now I'm exposing at 5 minutes with the bulbs nearly touching the glass.

The 5 minute exposure time seems to be exposing the screens correctly, however when I wash them out I have problems. Last night was my best attempt, 3 out of 4 small designs came out great.

I am also using a scoop coater, but I'm putting on thin coats as I have yet been able to get the hang of using it.

Also, for my positives, I am using transparencies I have made from Kinkos. I have heard of another option where you can get vinyl graphics made and put them on clear acetate, but that's an expensive option and I don't think I have the skill to turn the art I am printing from raster to vector format. That is a huge pain.

I don't have a way to print on films. I don't even know where to get films from. I have seen films come out completely opaque though, and I was impressed. I also know that QTX needs a very opaque image to burn, mine currently you can see through if you hold it up to light. That's as good as kinkos can do unfortunately.

Also, I am using a red safe light when working with the QTX. Is this bad? I couldn't find a yellow one. I heard yellow bug lights work with that emulsion fine though. I just need some clarification here.

Glad I got some good stencil reclaimer! ha.

And I'm using 20x24" 110, 125, 160 mesh screens (110 = wood, 125 & 160 = aluminum) if that matters.. I get the same results with all of them.

Am I exposing to long? To short? Are my positives screwing it up? Do I need a lot of water pressure?

Any help would be greatly appreciated before I waste all of this emulsion!
staticwear
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Post by staticwear »

First you want to make sure you positives are nice and dark. I dont know for clear transp. if toner aid would help but when i use vellum transp. i have to use toner aid to darken my films up. Possibly you could take with printers in your area, for a fee, you could get them to print out your films for you.

Red lights bulbs are fine, as well as yellow bug lights.

Since you keep change the variable of distance from the glass to the light source, its going to be hard for you to pin-point the correct time. My suggestion is to set it at one distance and keep it there. Then experiment with times. If the light source is 7" away and you burn for 15 mins and its hard to was out, take your exposure time down to 12 mins and see what happens. If its still hard to washout, take it down another 2 mins and so on. Some would suggest a step test, i never did that. I knew what the emulsion i used was capable of doing, then i took the manufacture recommendation and split the time in half to start with. I just guessed at my times and it only took me 3 screens to figure out my exposure time.

As far as pressure goes, i use a 1600psi pressure washer from 3' away to wash out my screens. So i am not sure what you are doing there, your distanace and pressure.
cdc
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Post by cdc »

staticwear wrote:First you want to make sure you positives are nice and dark. I dont know for clear transp. if toner aid would help but when i use vellum transp. i have to use toner aid to darken my films up. Possibly you could take with printers in your area, for a fee, you could get them to print out your films for you.

Red lights bulbs are fine, as well as yellow bug lights.

Since you keep change the variable of distance from the glass to the light source, its going to be hard for you to pin-point the correct time. My suggestion is to set it at one distance and keep it there. Then experiment with times. If the light source is 7" away and you burn for 15 mins and its hard to was out, take your exposure time down to 12 mins and see what happens. If its still hard to washout, take it down another 2 mins and so on. Some would suggest a step test, i never did that. I knew what the emulsion i used was capable of doing, then i took the manufacture recommendation and split the time in half to start with. I just guessed at my times and it only took me 3 screens to figure out my exposure time.

As far as pressure goes, i use a 1600psi pressure washer from 3' away to wash out my screens. So i am not sure what you are doing there, your distanace and pressure.
Right now, just an ordinary garden hose. I'm doing this in my garage. My problem is, the detail is not coming out very clearly. I'll check into getting films printed somewhere locally. Where can you get the films and toner darkener?
staticwear
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Post by staticwear »

because i dont know where you are located, i dont know if it will help. but for my laser printer, i get toner aid and my vellum from performance screen supply located here in NJ. for my epson 2200 i get the films and ink from usscreen.com
Roger Jennings
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understanding exposure of emulsion

Post by Roger Jennings »

Start by going to www.youtube.com and watching the video "Screen Printing's Best Exposure Unit" and then contacting me with questions at roger@rjennings.com
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Post by d fleming »

You can get a water based desktop inkjet that prints 11x17 fairly cheap, epson makes some nice ones, possibly able to print a little larger too. Then chromaline makes film that is pretty opaque through the printer. I have a large format printer from epson that uses rolls of film, so it's been a while since I used the Chromaline sheets, but when I did it worked fine. Possibly get a version of corel to design in, you can get older versions real cheap on ebay, I may even have an old licensed version of 9 laying around myself. Try rlx instead of qtx on your exposure at 11 minutes with light up close. Do a step wedge test if necessary. If you are having problems with detail, you may want to check to see that your art is firmly against emulsion at time of exposure. I usually scoop coat each side of frame doing the inside of frame last to leave a thick deposit on the outside to aid in thickness of stencil for max ink laydown at print. Using flourescent lights, you run the risk of undercutting due to length of exposure. I don't recommend using this light source for halftones, it just never seems to work out. That should keep you in trouble for a while hope it helped.};-)
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Post by Hex Screen »

I use a hand held shower head with warm water, but cold or warm should work. High pressure hoses tend to blow pin holes, in my experience, A correct exposure should only need low pressure.
Good quality films and emulsion, If you heard your emulsion needs good quality seps, change emulsion, something that is more forgiving in regards to art and exposure time. What type of mesh is it yellow, white, orange? each has their own pros and cons in regrds to exposure time.
make sure your art is printed right reading up so when you flip it over for exposing there is less chance of under cutting in the detailed areas, you may have to drop the expsoure time for detailed art, wash out very softly and then dry in the sun. Are you using a vacuum to keep the film in contact with the screen, this would help.

Thats My opinion


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Post by X_Autotype_#1 »

The darkness of your positives doesn't have any bearing on the quality of your positives, but the UV DENSITY is THE IMPORTANT FACTOR. Your problem is being caused by a number of factors regarding your exposure dicipline.

1. Undercutting could be a factor. The best exposure is gained from a point light source. Think of how sharp your shadow would be if we had 5 suns! A single source is always preferred (in fact, you may see improvement by using the sun instead of you homemade lightsource). Moving your screen closer to the bank of lights is worse as far as undercutting than moving it back. The closer to the bank of lights, the more undercutting you will get.

2. Your emulsion is only sensitive to UV light rays. The density of your positive is only relevent in terms of its UV density. In fact, many films are transparent (such as amber masking film) and can be totally see through, but have a very high UV density. Check your positives for their UV density. A minimum density of 3.5 is my recommendation. I'll bet your positives are well under 2.

3. Be sure that your emulsion is completely dry. This time of year when the humidity is high can cause lots of problems with wash out of emulsions. Also, don't store the coated screens in too warm of an area.

4. Get your exposures under control by purchasing or borrowing an Exposure Calculator. You Ulano supplier can talk to you about these.

5. Colored mesh will add about .5 to 1 x the exposure of white mesh. You will get better image quality from colored mesh, but you need to compensate your exposure to the UV density of the mesh.

6. Are you coating both sides of the mesh? Make sure that you put at least one scoop on the back side of your mesh, then make sure that it doesn't wash out from the back side when you process the sencil. You need to fully encapsulate the mesh for proper exposure and durability.

Think about these things when you are processing your next screen.

GOOD LUCK!
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