US2375366A - Photosensitive materials - Google Patents

Description

Patented May 8, 1945 PHOTOSENS ITIIVE MATERIALS David D. J acobus, Glen Ridge, N. J and John R. Bose, Woodhaven, N. Y., assignors to Keufl'el 8; Essex- Company, Hobokcn, N. 1., a corporation of New Jersey v NoDi-awing. Application October 16, 1941,

Serial No. 415,210 7 3 Claims.

This invention relates to photo reproduction processes and materials and, more particularly, to the procedure which involves a two-component type of light-sensitive surface that after exposure to light undera suitable pattern can be developed by a reagent which permits a reaction between the two components originally forming the lightsensitive surface.

More particularly, the invention is directed to the provision of a light-sensitive sheet comprising certain diazo compounds which are subject to decomposition when exposed to light which sheets also contain what is known as a coupling agent. Reaction between the diazo compound and the coupling agent is prevented before exposure by the presence of a reagent which inhibits such reaction. Usually this is obtained by the provision of an acid medium later neutralized by subjects ing the sheet, after exposure, to an atmosphere of a volatile alkali, usually ammonia.

Many light-sensitive diazo compounds have been known heretofore and have been used in two-component, papers of the type above decoupling during storage resulted in inferior sheets with poor contrast between the exposed and unexposed areas.

' It is an object of the present invention to provide certain new combinations of diazo compounds and coupling compounds which may be applied in a single solution to the surface of a suitable support such as a paper sheet, stored as is necessary in the commercial handling of such sheets and then, after exposure through a pattern, be developed by subjectin the sheet to an alkaline atmosphere and produce a print with permanent dense colored areas and clear backgrounds relatively free from residual color which causes the colored areas to stand out in sharp contrast with the background.

It is another object of the invention to provide prints which have high stability to aging and in which the background will not rapidly yellow with age or with prolonged exposure to light.

p-Aminodiphenylamines as such or carrying various substituents, aminobenzenes with a tertiary nitrogen group para to the amino group,

and various aminonaphthols or aminophenols have been diazotized to yield diazonium salts that can beused in two-component papers. The various members of this large variety of difl'erent diazonium salts have different stabilities and different coupling energies, and coupling components have to be selected that are suited to the particular diazonium salt that is used. For commercially acceptable prints the developed color must be vivid and the background clean and stable against discoloration. The backgrounds of all of the finished prints secured from diazotized paminodiphenylamines, aminobenzenes with a tertiary nitrogen group para to the amino group, and various aminonaphthols or aminophenols tend to be relatively unstable against discoloration on prolonged exposure to light.

The diazonium compounds secured by diazotizing 1-amino-2,5-dialkoxy-4-amino substitutedbenzenes have been widely used to produce the one-component type of light-sensitive papers as is described in U. ,8. Patents 2,198,827. 2,063,832 and 1,816,989 and also in British Patents 489,214 and 454,665. Diazotype prints that are secured from amines of this type as a group have the advantage that the backgrounds of the prints tend to be extremely stable against discoloration by light. On the other hand, the coupling energy of most of these compounds as a class tends to be so great that they have not been used or proposed for use in two-component papers.

We havediscovered that certain N-(4-amino- 25-dialkoxy-phenyl)-alkyl-carbamates, in combination with a restricted class of coupling components, have coupling energies that are low enough to permit them to be used in a two-component paper. The alkoxy groups which form the 2.5 substitutions in the diazotizedbenzene nucleus may be methoxy, ethoxy, or propoxy. If a butoxy or higher alkoxy group is used in these positions, the diazonium salt is precipitated out of the coating solution by the preferred coupling components. The alkyl group which is in the side chain opposite the diazotized amine may be an unsubstituted alkyl group such as ethyl, methyl, propyl, iso-propyl, butyl, or amyl, or an alkyl group having an aryl substitution such as benzyl, xylyl, or chlorobenzyl.

We have found that it is ossible to combine with the diazonium chloride salt of N- 4-amino-.

2,5-diethoxyphenyl)-methyl-carbamate certain limited classes of coupling components to secure useful two-component light-sensitive papers. Most types of coupling components cannot be used if stable papers are desired. For example,

premature coupling results if the known phenolic type coupling agents, phloroglucinol, resorcinol, B-naphthol, or 1,5-dihydroxynaphthalene, are used, since it is impossible to stabilize the coating solutions with either the mild reducing agents or acid buffers that are commonly used in an effort to prevent premature coupling. Aminonaphthol-sulfonic acids as a class give very vivid prints, as do also the acetyl-amino-naphthol-sulionic acids, but the backgrounds of the prints are generally discolored, or if initially clean, they yellow very rapidly on light exposure. This group of coupling components includes 1-amino-8- naphthol-3,6-disulfonic acid (Hi-acid), l-amino- 8-naphthol-4-sulfonic acid (S-acid), l-amino-2- naphthol-i-sulfonic acid, 1-amino-8-naphthol- 2,4-disul'fonic acid, 2-amino-8-naphthol-6-sul ionic acid (gamma acid), 2-amino-5-naphthol- 7-sulfonic acid (J acid), acetyl-H acid and acetyl-gamma acid.

It has now been found that otherwise unsubstituted naphthol-disulfonic acids as a class give line colors of good density, with truly stable backgrounds such as cannot be secured with the It is important that the diazonium salt be se- V cured free of impurities, since nitrous acid or nitrites are particularly damaging. The amine may be diazotized in the usual manner in dilute mineral acid, followed by the addition of sodium nitrite, but we have found that it is advantageous to age these solutions in the presence of urea or sulfamic acid to remove all traces of excess nitrite. In addition to removing excess nitrite, aging of the diazonium solution will tend to throw down other unstable impurities in the form of tars or insoluble precipitates. Additional purification can also be secured by stirring the aged solution with animal charcoal before making the final filtration. We have also discovered a, method of precipitating the diazonium salt in a manner that produces an especially pure product.

The following examples are illustrative of the invention:

Example] 25.4 gm. of N-(4-amino-2,5-diethoxy-phenyl)- methyl-carbamate were suspended in a solutionof 25 cc. of conc. hydrochloric acid in 1000 cc. of water, the whole being vigorously stirred for a period of one (1) hour. A solution of 7.2 gm. of sodium nitrite in 50 cc. of water was then poured directly into the suspension of the amine at 25 C., and stirring was continued for one hour, at the end of which time the solution was filtered free of tars. Excess nitrite was removed by the addition of 2 gm. of sulfamic acid, and the solution was buflered by the addition of 12 gm. diammonium citrate, 15 gm. citric acid, 100 gm. of aluminum sulfate and 40 gm. of cane sugar (sucrose). With compounds of the type herein described, the use of aluminum sulfate is particularly efiective in producing a print with a clear background. The solution was then aged at room temperature for a period of one week and filtered.

30 gm. or the sodium salt of 2--naphthol-3,6-disulfonic acid (R salt) were dissolved in the diazonium filtrate. 15 gm. of animal charcoal were then stirred into the solution for a period of 20 minutes and the solution was filtered.

The filtrate, which we will now term the coating solution, can be applied directly in the form of a thin film to a paper surface, dried, and the dried surface can then be'exposed to light under a suitable pattern. Ammonia fumes will develop the image, which will consist of dense blue-purple lines on a clear white background of excellent stability.

Example II A coating solution was prepared in the manner described in Example I, except that 30 gm. of 1- naphthol-3,8-disulfonic acid (Andresens acid) were used in place of the R salt. An image with dark purple-blue lines on a background of moderately good stability was obtained.

Example III A coating solution was prepared in the manner described in Example I, except that 30 gm. of 2-naphthol-6,8-disulfonic acid (G acid) were used in place of the R salt. An image with red lines on a white background of excellent stability was obtained.

i Example IV continued for one hour, and the solution was then dense yellow precipitate of the diazonium salt.

The precipitate was separated on a Buchner funnel and dried in a vacuum desiccator.

3.5 gm. of the dried diazonium salt, 3 gm. of thiourea, 3 gm. of citric acid, and 4 gm. of R acid were dissolved in cc. of water. A thin layer of this solution was spread over the surface of a sheet of papenthe wetted surface dried, the dried surface exposed to light under a pattern, and the image developed by exposing the sheet to the action of ammonia fumes. An image with blue-purplish lines on a clean white background of excellentstability was secured.

Having described our preferred procedure and materials, we claim: I

1. A reproduction material comprising a base having a photosensitive coating which includes.

the diazonium compound of O I R.

having a photosensitive coating which includesthe diazonium compound of IhN wherein R is an alkyl radical selected from the group consisting of methyl, ethyl, and propyl, and R is a radical selected from the group consisting of alkyl and aralkyl radicals, and 2-naphthol- 3,6-disulfonic acid (R acid).

3. A reproduction material comprising, a base having a photosensitive coating which includes the diazonium compound of wherein R is an alkyl radical selected from the group consisting of methyl, ethyl, and propyl, and R is a radical selected from the group consisting or alkyl and aralkyi radicals, and 2-naphtho1- 6,8-disulfonic acid (G acid).

DAVID D. JACOBUS. JOHN R. BOSE.