Gc electronics used to make both positive and negative photo resist. I have used both ,only problem I had sometimes with the positive is getting it to adhere good to the board while etching it.
From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com]
Sent: Thursday, March 02, 2017 10:25 AM
To: Homebrew_PCBs@yahoogroups.com
Subject: [Homebrew_PCBs] Re: uv resin for a photoresist substitute
Yes and no, with regards to using a UV resin for a photoresist. The original popular photoresist was KPR (Kodak PhotoResist):
https://en.wikipedia.org/wiki/KPR
That photoresist is UV sensitive, and will harden when exposed to UV light. Then, it is developed with KPR-developer, a rather nasty mix of volatile and toxic materials (Xylene?) (although I think I remember that safer, alternative developers were available at one point).
The largest problem with KPR is that it is a "negative type" photoresist, in that you need to UV expose the areas which are going to leave Copper. The world has been searching for an effective "positive type" photoresist for decades.
Now, I haven't tried to obtain any KPR for about 35 years. I know that, at least at one time, it became quite difficult to obtain. I'm not sure of the availability now, though.
Dave