How to make a coupler disperson
I have had several requests to describe how a coupler dispersion is prepared and used. I just dashed this off, and thought it might be of interest. Your comments would be appreciated.
How to make a disperson
You will need:
Coupler 5.1 g
Coupler solvent 5.1 g
Ethyl Acetate 5.1 g
10% Gelatin solution 51 g
10% surfactant solution 1 ml
You will also need a dispersing device such as a common industrial dispersator or a polytron unit. These should be capable of making dispersions in the range of 0.1 – 10 microns.
The typical coupler solvent could be N, N- Diethyl Lauramide.
The typical surfactant could be Photo Flo 200, TX-200, TX-100, or Saponin.
Mix the coupler solvent and ethyl acetate and warm on a steam bath until the ethyl acetate is just below the boiling point and add the coupler. Stir gently until dissolved.
Melt 51 grams of 10% gelatin and add 38.8 grams of distilled water. Add one drop of the surfactant and dump in the organics at once. Begin milling this mixture at once. The heat generated by the milling will keep the gelatin melted. Rinse the organics beaker out with the milled material to insure no waste.
When there is no longer any visible oil on the surface of the mixture, and the mixture looks like cream, the dispersion is complete. Observation with a microscope will help determine if the dispersion is complete.
Chill set this dispersion and then noodle. Wash first in ice cold 10% Calcium Sulfate solution until the ethyl acetate odor is gone, and then wash in plain ice cold distilled water to remove the calcium salt. This prevents excess swell. The total weight should have been 105.1 grams and after removing all ethyl acetate it should be 100 grams, however there is swell and therefore the weight may be greater. This will affect the ability to form the proper density. However, the ratio of gelatin / coupler / solvent will remain at 1:1:1 and this is the goal in this preparation.
The next step is to test the dispersion.
If you know the epsilon value (molar extinction value) of the dye formed, a small drop of dispersion can be added to color developer solution along with a drop or two of Hydrogen Peroxide. Measurement of the dye density that forms will then allow you to determine the actual concentration of coupler in the dispersion in terms of percentage or grams / gram.
If you do not have a spectrophotometer and/or do not know the epsilon value you can just coat coupler with silver halide on film and develop in a color developer to see what density you achieve.
In most cases, you would use 4 moles of silver / mole of coupler and 2 moles of silver / mole of coupler in order to determine the correct value of the necessary ratio for a 4 equivalent or a 2 equivalent coupler. It is not always clear what type of behavior a coupler conforms to by looking at the chemical structure.
If you maintain a fixed silver/coupler ratio, you should then be able to achieve any dmax you wish along with the concomitant H&D curve in dye. This will NOT work on paper support due to non-linearity. In the latter case, you will have to coat several levels of coupler and silver with different ratios to determine the best level.
Variations in polarity of the main coupler solvent will vary the hue of the dye obtained and will vary the activity of the dye sometimes giving greater or lesser density per unit of coupler coated.
And this is relevant to ?
As you know Ron I have used colour couplers for colour processing of B&W materials in the past, and fully understand the process. I guess here your describing making a single layer of a colour emulsion ?
This is a description of how to make a coupler dispersion for inclusion in a single (or multi) layer coating such as is done for C-41 or E6 products. It will allow a person to understand how to make a substantive coating as opposed to the non-substantive processing you have used and refer to and which is used in Kodachrome.
If you make a C, M and Y disperson and put them into R, G and B sensitive emulsion layers, you make a color product similar to current products.
It is relevant to the fact that I have not seen the procedure described anywhere else and so this is an added effort at preserving things. If you have information on how to make dispersions, please add them. If you are unfamiliar with the process, then consider this a teaching post. It is also relevant to the fact that several people have asked me how this was done in actual practice, as the Agfa method has been previously published widely in the BIOS reports.
Verrrry interesting....another piece of the puzzle falls into place....thanks for sharing this, PE. When you mention a 'common industrial dispersator or a polytron', can you please elaborate on this? Are you referring to a homogenizer or a more conventional mixer, or an addendum delivery method which we might have already discussed? What do you mean by 'milling'?
P.S. Are you going to add this information as an appendix to the book, by any chance?
Last edited by rmazzullo; 07-22-2009 at 07:45 PM. Click to view previous post history.
Reason: fixed typo
A dispersator is a mill in common parlance. A Polytron is an industrial product and they are both on Google.
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