HK1048852A - Stabilized phenylenediamine color developer compositions - Google Patents

Description

Stable phenylenediamine color developer compositions

Introduction to the word

The present invention relates to a process for the stabilization of p-phenylenediamine color developers and to the stabilized compositions obtained thereby. More particularly, the present invention relates to a method for stabilizing dry, solid N, N-dialkyl-p-phenylenediamine color developers by intimately mixing such developers with an alkali metal bisulfite or sulfite. The invention also relates to substantially dry stable compositions provided by such methods.

The developer solution is used to develop the exposed photographic film, thereby producing a latent image on the exposed film. One of the components of the color photographic developing solution is an N, N-dialkyl-p-phenylenediamine color developer. Another component present in the developer solution is typically a sulfite salt such as sodium sulfite. The sulfite functions as a preservative and a scavenger for excess oxidized form of the developer in the developer solution that would otherwise undergo multiple self-condensation reactions, causing staining. See, for example, Kirk-Othmer, encyclopedia of chemical technology 6,965, 4 th edition (1993) for a discussion of "color photography".

It has recently been observed that certain N, N-dialkyl-p-phenylenediamine color developers, in dry or substantially anhydrous form, undergo discoloration upon prolonged storage, particularly at higher temperatures as in tropical regions. This discoloration, presumably due to oxidation, is judged by the solid N, N-dialkyl-p-phenylenediamine compound having a tan or gray color rather than a normal white appearance.

Summary of The Invention

It has now been found that the discoloration of solid N, N-dialkyl-p-phenylenediamine compounds can be greatly reduced by the addition thereto of an alkali metal metabisulfite, bisulfite or sulfite. Accordingly, the present invention provides a relatively stable, substantially anhydrous composition comprising: an N, N-dialkyl-p-phenylenediamine color developer which is susceptible to oxidative discoloration, present in finely divided form, such as a powder or pellet, and a stabilizing amount of an alkali metal metabisulfite, bisulfite or sulfite. Another embodiment of the present invention is directed to a process for preparing a stable, substantially anhydrous composition comprising an N, N-dialkyl-p-phenylenediamine color developer susceptible to oxidative discoloration in finely divided form, comprising the steps of: (1) drying a water-wet N, N-dialkyl-p-phenylenediamine color developer in a chemical dryer, (2) adding a stabilizing amount of an alkali metal metabisulfite or sulfite to the N, N-dialkyl-p-phenylenediamine color developer dried in the dryer such that the alkali metal metabisulfite, bisulfite or sulfite is intimately mixed with the N, N-dialkyl-p-phenylenediamine color developer, and (3) removing from the dryer a substantially anhydrous composition comprising the N, N-dialkyl-p-phenylenediamine color developer which exhibits improved stability against oxidative discoloration.

Detailed Description

The alkali metal metabisulphite, bisulphite or sulphite used in the present invention is preferably potassium, especially sodium metabisulphite or sulphite. The stabilizing metabisulfite or sulfite salt will generally be used in an amount of at least 0.05 weight percent and not more than 1.0 weight percent of the total weight of the stabilized composition. The concentration of bisulfite in the color stable compositions of the invention is preferably from 0.1 to 0.25 wt.%.

The N, N-dialkyl-p-phenylenediamine color developers which can be stabilized in accordance with the present invention are known compounds for use in color photography. Each alkyl group of the N, N-dialkyl moiety of the color developer may contain up to 8 carbon atoms, preferably up to 4 carbon atoms, and may be unsubstituted or substituted. Examples of such substituents include alkylsulfonamido and hydroxy. The p-phenylene moiety of the color developer can be unsubstituted or, preferably, substituted, for example with an alkyl group, such as methyl. The N, N-dialkyl-p-phenylenediamine color developer is preferably selected from the group consisting of N, N-dialkyl-4-amino-3-methylanilines in which the alkyl group is selected from the group consisting of ethyl, 2-hydroxyethyl, and 2-methanesulfonylaminoethyl. As is known to those skilled in the art, the N, N-dialkyl-p-phenylenediamine color developers used in the present invention and in photographic developer solutions are in the form of acid addition salts, for example, hydrohalides such as hydrochlorides, sulfates or bisulfates. N, N-diethyl-4-amino-3-methylaniline hydrochloride (CD-2 CAS No.002051-79-8), N- (2-methanesulfonamidoethyl) -N-ethyl-4-amino-3-methylaniline sulfate (CD-3 CAS No.025646-71-3) and N-ethyl-N- (2-hydroxyethyl) -4-amino-3-methylaniline (CD-4 CAS No.025646-77-9) are specific examples of colour developers which can be stabilised according to the invention.

The stabilized compositions of the present invention are dry or substantially anhydrous, that is, the compositions are substantially free of water, that is, the compositions contain less than 0.6 wt% of volatile materials.

In the process of the present invention, a water-wet N, N-dialkyl-p-phenylenediamine color developer is charged or placed into a chemical dryer and drying is initiated at a temperature of, for example, 70 to 75 ℃ and under reduced pressure, for example, at a pressure of less than 10mm Hg, and then a stabilizing amount of an alkali metal metabisulfite, bisulfite or sulfite is added to the dried color developer during the drying operation to obtain a stabilized composition against oxidative discoloration which comprises the color developer in finely dispersed form, for example, as a powder or pellets, in which an effective amount of the stabilizer is intimately dispersed.

To illustrate the effectiveness of the present invention, a production batch of CD-4 was dried in a commercial dryer at about 75 deg.C under reduced pressure. After the color developer dried, sodium metabisulfite was added to the dryer in an amount equivalent to produce a concentration of 0.25 weight percent based on the total weight of CD-4 and sodium metabisulfite. The dry materials are mixed in a dryer to produce an intimate mixture of color developer and stabilizer. The mixture was packaged in plastic bags in an amount of 22.36kg (50 pounds) per serving, sealed and placed in a fiberboard bucket and sealed as well. And (3) subjecting the packaged material to an accelerated degradation discoloration test, and specifically placing the packaged material in an oven which maintains the relative humidity of 95% and the temperature of 100-105 ℃ for 3 months. CD-4 identical packages (control material) without sodium metabisulfite were also subjected to accelerated degradation testing.

Oxidative degradation evaluation of the stabilized and unstabilized CD-4 samples was performed by measuring the absorption coefficient (color) at 540nm using a Perkin-Elmer Lambda 2 (or equivalent) spectrophotometer. The CD-4 sample was dissolved and diluted in a 1.0N aqueous solution of sulfuric acid. The absorbance of the solution at 540nm in a 10cm cell was recorded and the net absorbance was calculated. Molecular spectroscopic terms and symbols are in accordance with the ASTM E131 specifications.

The stabilized and unstabilized materials have an absorption coefficient at 540nm of between 0.17 and 0.20mL/g-cm prior to being subjected to the accelerated degradation test described above. At the end of the 3 month accelerated degradation test, the absorbance of stabilized CD-4 was 0.69mL/g-cm, while the absorbance of unstabilized CD-4 was 1.63.

While the invention has been described in detail with particular reference to preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims (9)

1. A stable, substantially anhydrous composition comprising an easily oxidatively discolored, finely divided form of an N, N-dialkyl-p-phenylenediamine color developer, and a stabilizing amount of an alkali metal metabisulfite, bisulfite or sulfite.

2. The stabilizing composition of claim 1, wherein the alkali metal metabisulfite, bisulfite or sulfite is sodium or potassium metabisulfite, bisulfite or sulfite present in a concentration of at least 0.05 percent by weight of the composition.

3. The stable composition of claim 1, wherein the N, N-dialkyl-p-phenylenediamine color developer is selected from the group consisting of salts of: n, N-diethyl-4-amino-3-methylaniline, N- (2-methanesulfonamidoethyl) -N-ethyl-4-amino-3-methylaniline and N-ethyl-N- (2-hydroxyethyl) -4-amino-3-methylaniline.

4. A stabilising composition according to claim 3, wherein the alkali metal metabisulphite, bisulphite or sulphite is sodium metabisulphite, bisulphite or sulphite and is present in a concentration of at least 0.1 to 0.25% by weight of the composition.

5. The stabilizing composition of claim 4, wherein the N, N-dialkyl-p-phenylenediamine is a salt of N-ethyl-N- (2-hydroxyethyl) -4-amino-3-methylaniline in finely divided form.

6. A process for preparing a stable, substantially anhydrous composition comprising a readily oxidatively color-changing, finely divided form of an N, N-dialkyl-p-phenylenediamine color developer, the process comprising the steps of: (1) drying a water-wet N, N-dialkyl-p-phenylenediamine color developer in a chemical dryer, (2) adding a stabilizing amount of an alkali metal metabisulfite, bisulfite or sulfite to the N, N-dialkyl-p-phenylenediamine color developer dried in the dryer such that the alkali metal metabisulfite, bisulfite or sulfite is intimately mixed with the N, N-dialkyl-p-phenylenediamine color developer, and (3) removing from the dryer a substantially anhydrous composition comprising the N, N-dialkyl-p-phenylenediamine color developer which exhibits improved stability against oxidative discoloration.

7. The method of claim 6 wherein the water-wet N, N-dialkyl-p-phenylenediamine color developer is dried at a temperature of from 70 to 75 ℃ under reduced pressure and the alkali metal metabisulfite, bisulfite or sulfite is a potassium or sodium metabisulfite, bisulfite or sulfite added in an amount to produce a substantially anhydrous composition comprising the N, N-dialkyl-p-phenylenediamine color developer containing at least 0.05 weight percent potassium or sodium metabisulfite, bisulfite or sulfite.

8. The process of claim 6 or 7 wherein the water-wet N, N-dialkyl-p-phenylenediamine color developer is selected from the group consisting of salts of: n, N-diethyl-4-amino-3-methylaniline, N- (2-methanesulfonamidoethyl) -N-ethyl-4-amino-3-methylaniline and N-ethyl-N- (2-hydroxyethyl) -4-amino-3-methylaniline.

9. The process of any of claims 6 to 8 wherein the water-wet N, N-dialkyl-p-phenylenediamine color developer is dried at a temperature of from 70 to 75 ℃ under reduced pressure and the alkali metal metabisulfite is sodium metabisulfite added in an amount to produce a substantially anhydrous composition comprising the N, N-dialkyl-p-phenylenediamine color developer containing at least 0.1 to 0.25 weight percent sodium metabisulfite based on the weight of the composition.