Shoulder woes

Hello everybody,

I’m currently on the verge of a mental breakdown during the plate making process.

I can not - for the life of me - get an acceptable amount of “shoulder” from my exposure device. I am using an uv device developed for exposing (circuit) boards, with tubes.
My setup is:
UV Bulbs —> Glass —> 2 layers of diffusion plastic material —> Film —> Plates —> Glass and Foam for pressure —> Lid.

I am already placing the plate in the middle of the device and the distance from the tubes to the plates is about 5 centimetres.

I think my films are fine, they are very very dense with fine and sharp edges. The photopolymer plates (0,94 red material with steel backing) is also holding details very well, but no shoulders whatsoever. I know I maybe expect too much for my basic tools (exposure device and hand washing) but it really bothers me that I seem to be unable to achieve this.

What could cause my problem? Spacing of the tubes? Distance to the plate? The fact that there is glass between the tubes and the film?

I am thankful for any help.

Kind regards!

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One thing I would go back and double check is - how good a seal are you getting in your vacuum when making your exposure. I have found this this a critical step. Any compromise here can cause a lack of detail and quality and can be hard to detect.

Thanks dwallen. I am not using vacuum, the plate is pressed on the film with pressure of foam and another glass layer. I also think I don’t have trouble with fine details, but with the creation of the “shoulder”. I noticed an improvement when doubling the diffusion material, but this also increases exposure times a lot.

The key to getting a shoulder is using kreen plastic, available from Anderson-Vreeland. This is integral to the design of photopolymer plate making, as I understand it.

Increase distance from tubes to 8 CM, remove ‘diffusion’ material, try again with longer exposure time (1.5 length).

Try adding more and more time to several test plates.

Increase distance from tubes to 8 CM, remove ‘diffusion’ material, try again with longer exposure time (1.5 length).

Try adding more and more time to several test plates.

Thank you nyletterpress and Havenpress.

Regarding the “Kreene”… as far as my research has brought me, Kreene is some kind of mylar-sheeting with a diffuse/structured side to diffuse the light. That why I am using translucent diffusion material. I don’t have any “original” Kreene but I think my diffusion sheets give me a similar effect. Is the glass between a problem?

@HavenPress: If I remove the diffusion sheets, which nyletterpress says is crucial, won’t this contradict creating the desired effect?

I will make some modifications to my exposure device to convert it to a vacuum device so I can increase the distance and remove the glass.

I already started experimenting with the exposure times and now, at 25 MINUTES, I noticed I started to get some slight slope. But far from the amount of commercially exposed plates have. Does this mean, I should go on increasing exposure time? And how much is too much? Does too much UV degrade the quality of the photopolymer?
I guess without the diffusion and without the glass, I could at least halve the exposure time.

Thank you and kind regards!

I am assuming your glass has a fully u v transmissive spec.

I think it is plain old window glass… it surely swallows some of the UV.
Todays test plates (at 30 Minutes….) look not bad. Not perfect but not bad.

If you can obtain the instruction sheet for the polymer material that you are using it will tell you the proper exsposure. If you didn’t get thie instructions from whoever you bought it from try looking online at the manufacturer’s website. They want you to have this information to avoid problems with their product. The instruction sheet for the polymer that I use states the proper exposure on a 21 step stouffer grey scale for each of their products and also states times and temperatures for washout, drying and post-exposure.
You might also be able to check the output of the tubes that you are using online and/or fine alternate high-output tubes for your device. Look for the manufacturer and model number and search that information.

I had problems years ago with fine lines getting “wiggly”. I started doing a 10% exposure on the back of the plate prior to removing the protective film. It helped with creating a substantial shoulder. Works like a charm. 25 minutes seems like a pretty long exposure time. See if you can’t find a Stouffer step scale to test with.

Thanks all!

Yes, back exposure would make sense, however, I am using steel backed plates, that makes it a little harder.

So far, I found an exposure between 35-40 Minutes results in what I had in mind. My exposure device is kind of low power (4x15w) and with the glass in between, the exposure time seems to get a little high. But it gives me a great “shoulder” now.

Yesterday, I was able to expose and print a plate with really thin lines and dots (0,1mm), which I thought would not be possible to archieve with hand washing.

Still, it’s time to find some used polymer processor, this long exposure times are really tiring.

Kind regards