Hi Jeff,
If you are not having any luck with Elmers's glue, try casein (see patent 4237210). Elmer's glue by the way, is an emulsion of PVA/PVac. The most explicit recipe for PVac and PVA that I could find was in patent 5556735, but you will never be able to make it without a high speed mixing mill which is why I turned to Elmer's glue. Another factor that might be causing problems is your UV source. 5556735 is applying an energy deposition of 800 mJoules/cm∗∗2. There is a relationsip between the rate and the required total energy to crosslink; generally the fastest rate possible. The range of Riston dry film is 35-150 mJoules/cm∗∗2 depending upon the product line. I have a 150 watt metal halide source that is providing 14 mW/cm∗∗2 at 6 inches. Most DIY black light setups are putting out much less than this. My exposure time was of the order of 60 sec.
I am satisfied with toner transfer for PCBs. My original quest was for a DIY solder mask so that it was only necessary to mask the pads. The PVac provides toughness to the coating in this case and it is only necessary rub off (yes, I did have to rub it off under water) the coating on small areas after exposure. For traces, PVA might work just fine. You can buy it here,
http://www.ebay.com/itm/Polyvinyl-Alcohol-PVA-One-Pound-Lab-Chemical-/250983683335?pt=LH_DefaultDomain_0&hash=item3a6fcb1507and,
http://shop.chemicalstore.com/navigation/detail.asp?MySessionID=167-920303619&CatID=30&id=PVOH7130Baxter
--- In Homebrew_PCBs@yahoogroups.com, "Jeff Heiss" <jeff.heiss@...> wrote:
>
> Hi Baxter,
>
>
>
> I am trying the recipe of ammonium dichromate mixed with Elmers glue and I
> am finding two things. First, the Elmers glue does not dissolve in water
> without physical agitation. Take plain, unmixed Elmers strait from the
> bottle, spread it on something, and let it dry. Once dry, immerse it in
> water. The glue does not dissolve in the water unless rubbed lightly with
> your finger. No rubbing, no dissolving. I left the glue in water over
> night and all was still there the next day.
>
>
>
> Second, the glue hardened from UV exposure does not stick to the copper well
> enough to avoid coming off during the agitation required to remove the
> unexposed glue. If the unexposed glue could dissolve on it's own in the
> water, I don't think this would matter. I would try real PVA polyvinyl
> alcohol to see if it dissolves in water without agitation but I don't have
> PVA. I read that Elmers is polyvinyl acetate, not polyvinyl alcohol and
> they are two different things.
>
>
>
> Jeff
>