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 http://silvergrain.org
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