Ilfotec DD-X
From Silvergrain Labs
The DD-X Patent
Fielding (1993), US Patent 5210010 discloses a PQ photographic developer concentrate employing 300 to 500 g/l of potassium sulfite as the preservative, with its pH buffered with an agent other than alkanolamine. The concentrate contains an organic solvent other than alkanolamine.
This author speculate that the formula given in the columb B of the example of this patent to be identical or very similar to Ilfotec DD-X.
The Examble B is:
| US Patent 5210010 Example B | |
|---|---|
| potassium sulfite, 65% | 548 ml |
| diethylene glycol | 45 ml |
| hydroquinone | 44 g |
| Dimezone S | 1.2 g |
| DAPTA (1,3-diamino-2-propanol-tetraacetic acid) | 4.8 g |
| borax | 23.5 g |
| water | 380ml |
The develoepr is used at 1+4 dilution. pH is 8.5 at 25C when diluted 1+4.
Note that, assuming Ilford continued to pay the patent maintenance fee in full, this patent is in effect until 2010.
Remark
In the background section (column 1), Fielding discussed the prior art in making concentrated developer using alkanolamine, particularly diethanolamine (DEA). Fielding argued that DEA accelerated chemical development. I agree with this assesment. However, Fielding proceeds to argue that DEA reduced relative contribution of physical development, leading to more grainy image. I disagree with this view.
When a large quantity of secondary amine is added to an active developer such as the one in Example A, the amine will act as a silver halide solvent and it accelerates both chemical and physical development. Indeed, grainy image resulted from Example A is most likely due to greater contribution of physical development. In the developer A, the developed film may also have dichroic fog due to high degree of silver halide solvency.
One way to reduce this disadvantage is to N-substitute the hydrogen atom to make it a tertiary amine. The hydrogen may be substituted with a suitable alkyl or alkanol group, among other possibilities, to make a buffering agent of desired pH. Tertiary amines generally have less silver halide solvency, and they rarely cause dichroic fog problem. This is a very clean solution, and it may be utilized together with elements of the invention disclosed in this patent. That is, substituted alkanolamine may be used in place of buffering agent and organic solvent in this invention to make a very effectively concentrated developer.
Another way to reduce this disadvantage is to add an agent that suppresses physical development. 1-phenyl-5-mercaptotetrazole and perhaps some other antifoggants are capable of this function, although they also retard development.
