Making a color coating formula
1. Dispersion formula
a. Select a coupler and a solvent (such as di-n ethyl lauramide) and an auxiliary solvent such as ethyl acetate (ETOAC). Mix the aux solvent and the solvent together and heat to near boiling of the ethyl acetate, then add the coupler and dissolve. (add more ETOAC as needed to keep in solution when cooled) (NOTE: sometimes, this coupler may be a mix of 2 - 4 couplers, some colorless and some colored, along with DIR and DIAR couplers to control image structure and color, it may also include an antioxidant)(NOTE: the coupler solvent and the amount used can be a curve shape modifier itself as noted below - the engineer is expected to use it as such in the design phase)
b. Prepare 10% gelatin (or whatever gel % your final coating is going to be made at + a small amount extra say to 12% total) and add a suitable surfactant.
c. Mix a + b and run immediately through a colloid mill. Keep running repeatedly until the mixture shows no oily residue and the dispersion looks like milk. Clean the mill with an appropriate solvent.
d. By an appropriate means, clear the ETOAC out of the dispersion so that all that remains is surfactant, coupler and gelatin in water. Dilute dispersion with water to the appropriate gelatin level to match the coating to be made.
2. Prepare emulsion formula
a. Mix 1a and 1a from emulsion formula together and use in prepping the coating formula.
b. Add curve shape moderators to mixture to adjust the ratio of dye formation to silver development to optimize curve shape. It is rare that the dye curve is the same as the silver curve, and it is even rarer that all couplers give matched curve shapes with even the same emulsion due to reactivity rates, therefore the amounts of coupler used, along with moderators force all 3 layers to give a neutral image rather than crossover. This is an exacting science. Otherwise you get a poor image. This is too broad a subject to discuss here.
3. Coat as before.
This description is for chromogenic color materials and does not include interlayers and overcoats for color, nor does it include Fischer type coupler coatings or dye bleach (Ilfochrome) color materials. Names are, for the most part, left out to protect the innocent.
For specific information, see the article by Rodgers and Kapecki in the Kirk Othmer encyclopedia on photography, full details posted elsewhere on APUG, or the relevant patents available free from the US Patent office - online.
In color negative films, up to 4 couplers are used in the C, M and Y layers in some products, with different coupler solvents in each layer, and there are 9 different emulsion formulas, so this makes a total of many many emulsion and dispersion formulas coming together at the same time, particularly in cases where the 4 couplers cannot be mixed as in 1a above. That would make 12 coupler formulas and 9 emulsion formulas plus interlayer formulas, and the overcoat formula. Each interlayer is different, and the overcoat is different than any of these. By my count, some color formulas can take up to nearly 30 different items as I've shown here and in the last post to be properly prepared prior to coating.
A given film or paper may use one or two of these in common, but may contain dozens of differences to get the final desired result. The differences involve curve shape modifiers, emulsion used, etc. Therefore, NC, VC and UC Portra 160 films may use the same emulsions and couplers, but have different amounts of ingredients to achieve the differences in saturation but retain the same color characteristics and speeds.
PE
