One problem with the Laser discharge - electrostatic toner process is
that the characteristics of the phototconducter do not assure a uniform
density over large solid areas. I don't know the details so I will not
speculate as to any remedies. Simply copying the image to an inkjet at a
higher contrast level might serve your needs if you are not doing toner
transfer. Also, it would seem to me that a 2x copy from a laser
printer reduced to correct size on an inkjet might eliminate the voids.
Of course that brings its own problems like wet ink wrinkles and
tracking in the inkjet. After a while it may turn out that accepting
the quality you have is not so bad!
My experience is from many years of field service with IBM equipment. I
learned long ago that I should pay attention to what a new operator had
to say about today's problems. Frequently the newbie's fresh view led
the way to a better process!
Don't give up fixing the problem!
--- In Homebrew_PCBs@yahoogroups.com, Emil Johnsen <emil123@...> wrote:
>
> Hi.
>
> I have been printing artwork for making PCB's using negative photo
resist. The first problem I ran into was the lack of opacity of the
toner. It looks nice and dark until I hold it up to a light, then it's
easy to see how translucent it really is.
>
> I tried using the whiteboard marker method mentioned on this list
before, but had problems getting it to work consistently. Usually I
can't removed the marker from the clear part of the foil without also
removing some of the toner.
>
> I have tried dipping the foil in acetone or xylene. The toner looks
much better, but is only marginally more opaque.
>
> Heating the foil gives basically the same result as the solvents, but
somewhat more opaque.
>
> I tried spraying the foil with clear paint. Doesn't help at all, but
it looks very nice. Might be useful for other purposes like panels.
>
> The method I found to work best us to bond an opaque powder to the
toner.
>
> I used a very fine cerium oxide powder, normally used for polishing
telescope mirrors. I will try aluminium oxide when I remember where I
put it. I also tried powdered graphite, but it did not work nearly as
well as the cerium oxide.
>
> I put a clothes iron upside down and the put the foil on top of it,
with the non-printed side touching the iron. I then brush CeO2 powder on
it until no more powder will stick. After it has cooled for a few
seconds I wash it with water and detergent. The result looks gray but is
very opaque. It took some experimenting to find the correct temperature
setting so that the toner would bond to the powder while not shrinking,
but there seems to be a wide range that works.
>
> I also tried mixing the CeO2 with xylene and dip the foil in it before
leaving it to dry. After it was dry I washed off the excess powder. This
works, but the result was less consistent and not as opaque as the
melting method.
>
>
> Emil
>