Water Proof Emulsion Question

[Binkspot]

I have been messing around with the CCI WR-25 and Saatichem DW with what I would consider great results. One thing I have noticed with both, a clear residue in the image area random places. I can not see it when the screen is wet and once dried its tougher then nails and usually wont come out until reclaim. I have had to reburn a few screens because of it. Tried screen opener, MEK, thinner etc. The only thing that will take it out is the spot gun which usually freaks up the stencil or worse yet put a hole in the screen.  I activate the emulsion the night before I plan on using it, mix slowly with a drill mixer for about 10-15 min while slowly adding the diazo. Then I will hand mix it before each use about 30 min to an hour before each use. If I rinse the screen after blowing out the image for what I would conside an excisively long time the screen is fine. Is the diazo causing this. Do I just need to rinse a little more. Is this normal. Am I doing something wrong. We have used diazo emulsion before but never had trouble like this.

What are some of the other emulsion shops are using, any recomendations to use with plastisol and discharge?

[ebscreen]

Sounds like underexposure. Diazo needs a lot more light than photopolymer. A lot lot more.

We use Aquasol HV for plastisol and discharge (post hardener long runs. No complaints.

[Homer]

sounds like scumming from underexposure. The emulsion is still left in the image but the color is washed away. is the back of the screen "sudsy" like soap bubbles? try water. should take it right out.

we are back to aquasol hvp. left it for a year or so but it's just too damn good to try anything else.

oop -eb beat me to it

[Mr Tees!!]

..sounds like plain ol scum, usually from the squeegee side and a result of underexposure. I switched to CCI WR25 recently, and yeah , the exposure time can feel painfully long, ESPECIALLY if you are coming from photopolymer use. It is also kinda hard to develop post-burn, making you think even more that perhaps you have overexposed, but thats not the case. Play with your exposure times, its REALLY hard to overexpose that stuff. Also, when developing, I use a pressure wash on the print side, then flip it over for a flood-type rinse with a regular hose on the squeegee side. It helps wash away what little underexposed emulsion you may have left, which is whats causing that scum.

[ZooCity]

Exactly what eb said, beat me too it.  We use nothing but Aquasol HVP for everything we run.

You are experiencing "scumming" from underexposure on the squeegee side of the screen which is microns further away from the light source than the print side is.  You can solve it by:

1. Dialing your exposures in to where you have close to full light penetration of the stencil and are still holding detail.

2. Flood rinsing both sides of the screen very thoroughly after resolving and padding dry with some paper shop towels.

Option 1 is limited in that, if you use the milky wp film, you'll hit a wall where you are losing finer detail in exchange for complete exposure.  A DTS or crystal clear film would solve this.  This option is also limited by the strength of your bulb.  I would struggle to achieve this without our 5k watt setup.   

Some might snark at Option 2 as a "band aid" or newbie thing to do but it's a quick fix and a solution to holding finer detail on thicker stencils.  There are some coating techniques we use that always result in a slightly underexposed squeegee side with wp film. 

In any case, it's not a bad idea to either pat down the stencil, blast it with some clean, compressed air or vacuum it after resolving.  Next, get them horizontal and into a dry box asap so there is no opportunity for the underexposed emulsion scum to run into your image.  Then you are speeding up the drying of the stencil so it could go on press quicker.  It's essential that your wb stencils are completely bone dry before going on press.

[jsheridan]

Unerexposure..

Keep adding time/light until you can no longer see a color change in the emulsion where the film was/wasn't. This line will be very pronounced when underexposed and rinse water in wash tank may appear yellowish as this is diazo washing off.

Once you hit the right exposure, back off to maintain detail on fine line images.

[JBLUE]

You will also have premature breakdown on press with the under exposure so be aware of that. I tried CCI WR25 and I could not get it to work half as well as Aquasol HV.

[jasonl]

KIWO DISCHARGE, I use it for EVERYTHING.  Photopolymer and it exposes for me in 22 ltu.

[Nick Bane]

I have had the same issues before, and like everyone else, its underexposure.  no matter how much you rinse, the scum or leftover wet emulsion mixed w water runs back into the image and drys in the image.

you can see it on the squeegee side of the screen as youre developing, the water rinses off with a yellowish tint to it.

[Binkspot]

Thanks guys. From the effects you are all describing its got to be under exposure, you are right on the money. I was getting a little scared this might just be one of those nature of the beast things. I did two burns with the exposure calculator and added a little but guess I'm still a little off. Back to some test burns.

I am shooting 156 coated 3/2 for 120 ltu on our 3140 (1200w?), clear films. Am I close, yes no maybe. I know everyone will be a little different, just trying to dial it in and make this switch as painless as possible.

[alan802]

KIWO DISCHARGE, I use it for EVERYTHING.  Photopolymer and it exposes for me in 22 ltu.

I still haven't tried any of that.  I've sampled the Kiwo 300WR (I think that's what it's called) and it was fine.  I still haven't had anything work as poorly as the CP Tex and as good as the WR25.  I'm at about 25 light units for our dual cure emulsions which feels like an eternity compared to PP that exposes in 6-8 light units. 

Back in the day when we were underexposing everything and those symptoms you're experiencing were an every single day occurence at our shop.  That's where the compressed air stage came in at our shop.  We were getting the scum in the image area and drying the hell out of it as quickly as possible kept it from happening.  Finally we figured out the real issue and the only time we have to worry about underexposure is if we are trying to or if we're testing new emulsions.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               

[ericheartsu]

we have been using the kiwo discharge for the last 3-4 months and we LOVE it.

It exposes fast. Holds amazing detail. Holds up to waterbase and discharge fantastic. Strips super easy.

we have been blowing through it, and have only had screens wash out, or not expose, because we are still learning how to expose certain meshes and details with our new exposure unit!

but it rules.

[brandon]

Sounds like underexposure. Diazo needs a lot more light than photopolymer. A lot lot more.

We use Aquasol HV for plastisol and discharge (post hardener long runs. No complaints.

Exactly the same here

[Screened Gear]

Who does the white glove test? If you expose your screen and then get it wet in the washout booth you should not have any color from the emulsion come off on a white glove on the squeegee side of the screen. I have never done it but it makes sense. 

[alan802]

Who does the white glove test? If you expose your screen and then get it wet in the washout booth you should not have any color from the emulsion come off on a white glove on the squeegee side of the screen. I have never done it but it makes sense. 

Not with a white glove but my finger.  I will swipe a screen on the squeegee side often to see if it's underexposed.