I use a HP4101 printer and the transparencies are also speckled. I go over them completely with a black, dry erase marker (Expo brand) on the toner side. Let them dry, they wipe off with soft tissue like Kleenex. The black pigment is retained only in the speckles.
I wrote a more detailed procedure a few months ago, but that is the gist of it.
John
----- Original Message -----
From: tda7000
To: Homebrew_PCBs@yahoogroups.com
Sent: Wednesday, February 22, 2012 12:10 AM
Subject: [Homebrew_PCBs] Re: Printers not making pattern opaque enough for UV process
--- In Homebrew_PCBs@yahoogroups.com, DJ Delorie <dj@...> wrote:
>
>
> In cases like this, you really should consider buying a transmission
> step wedge. I got a stouffer 21-step wedge for $7 plus s&h and it
> REALLY tells you how well (and accurately) your process is. For
> example, my inkjet gives me an 8-step range, but my laser printer only
> gives a 3-step range. Even the worst inkjet film I can print is going
> to be better than the laser printer.
>
> I found that using "standard" software and films won't give you truly
> opaque prints. I ended up writing my own printer driver just for films,
> and buying Jetstar films (perhaps anything with "ultra fast drying" in
> the name should work, but YMMV). The specially coated films let me put
> much more ink than standard software would, resulting in a much darker
> film.
>
I didn't mention it before but I did a rudimentary test by covering the board with a credit card and exposing a little bit every minute for 7 minutes (chose that time as I saw a site where someone who made a UV box with LEDs say 7 minutes was the maximum they could go before overexposure)
It seemed that 1-3 minutes or so was underexposed, anything over that was good but had the speckling problem.
I tried putting the printer control panel on darkest. It didn't seem to make any difference. The film is designed for inkjets and appears to have a special coating.
A custom printer-driver sounds great, I don't suppose yours is available and is for Canons?
I wonder though if I somehow could force the printer to print black by mixing the colour cartridge it would be like getting 3 layers of artwork, from the 3 different inks. Not sure how to do that though.
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