U of S | Mailing List Archive | alt-photo-process-l | Re: I have a question

Re: I have a question

From: Richard Knoppow <dickburk@ix.netcom.com>
Subject: Re: I have a question
Date: Sat, 20 Oct 2007 14:29:07 -0700

>     Please give an example.

You can get hundreds of examples by looking up US Patent
5391466. Iron (III) complex of some of the the compounds
derived from Formula (II) in this patent, used alone, in a
weakly acidic buffer, are an excellent b&w bleach with
superior biodegradability. As usual of Konica patents it
includes a ridiculously long list of many compounds taht can
be potentially used, but one just has to think about which
ones are easy, fast and cheap to make and the list immediately
becomes much shorter. Fujifilm and AGFA also came up with
different compounds that may be used similarly. Perhaps the
compound (I) disclosed in US Patent 5149618 (assigned to AGFA)
is related to the former patent's Formula II, although this
compound is, of course, excluded from it. The best compound in
the Konica patent is more biodegradable than the AGFA one.

Bleaching agents that are one generation older, such as iron
(III) EDTA or iron(III) DTPA bleach is poorly biodegradable
but these are still much more preferrable to ferricyanide in
terms of environmental damage.

These compounds are also usable in mixture with thiosulfate as
a stable print reducer, but generally speaking, you can get
stronger bleaching action when bleach is used alone (oxidation
potential is 100-200mV higher without fixer mixed in).
Ryuji Suzuki