US3038803A

US3038803A - Photosensitive material

Info

Publication number: US3038803A
Application number: US713807A
Authority: US
Inventors: Kosar Jaromir
Original assignee: Keuffel and Esser Co
Current assignee: Keuffel and Esser Co
Priority date: 1958-02-07
Filing date: 1958-02-07
Publication date: 1962-06-12
Anticipated expiration: 1979-06-12

Description

United States Patent Jersey No Drawing. Filed Feb. 7, 1958, Ser. No. 713,807 14 Claims. (Cl. 96-92) This invention relates to brownprint paper. Brownprint paper or Van Dyke paper as known in the art has conventionally been produced by sensitizing a paper with a Water solution of silver nitrate and a ferric salt.

It has been the practice in making engineering reproductions to use a brownprint as an intermediate negative. For example if it is desired to make a duplicate of a tracing of an engir ieering drawing, a brownprint negative is made from the tracing and a duplicate of the tracing is then produced on any suitable photosensitive material on a transparent base. The duplicate tracing can then be used for making additional blueprints, diazo types and the like. The negative brownprint material is usually though not always on so called transparent base material such as tr-ansparentized paper, cloth, film or the like.

The usual brownprint material known in the art is generally made by coating onto a high rag content paper, usually transparentized, a solution containing a watersoluble salt of silver, namely, silver nitrate, together with a complex ferric salt. The ferric salt may be either a complex salt of an inorganic acid such as ferric ammonium sulphate or a complex salt of an organic carboxylic acid. The organic acid may be a mono-, di-, or polycarboxylic acid, which advantageously contains one or more hydroxyl groups. For example ferric ammonium citrate and ferric ammonium oxalate have been used.

When brownprint material is exposed to light through a tracing or other original, the ferric salts are reduced to ferrous salts in the areas that are struck by light. Subsequently, when the print is developed in the presence of water, the ferrous salts in the light struck areas reduce the silver" salt in those areas to form the brown image. The ferrous salts that are formed by the action of light as well as the ferric salts and silver salt in the unexposed areas are removed by the developing solution. In order to help remove the exposed ferrous salts an alkali salt of a polycarboxylic acid such as the sodium potassium or ammonium salts of oxalic acid may be present in the developing solution. In order to prevent the formation of iron hydroxides the pH of the brownprint sensitizing solution must be on the acid side. Preferably this pH should be between 2 and 3. While certain of the complex ferric salts used themselves exhibit an acid reaction, it may in other cases be necessary or advantageous in order to impart the acid reaction to the sensitizing solution to add free acid such as citric acid, tartaric acid or oxalic acid. After the development of a brownprint, it is customary to fix the print with a solution of hypo to dissolve any remaining unexposed silver salts and then give it a final water wash to remove the fixing salts and any iron and silver salts dissolved thereby.

Prior art brownprint reproduction materials have several disadvantages. One of these is poor keeping quality of the light sensitive layer. It is believed that this is due to the fact that upon mixing and coating and during storage nitrogen pentoxide is formed in this layer. This affects not only the photosensitive layer but may also contribute to the destruction of the base material which may be an impregnated paper, cloth or the like. When brownprint sensitizing solutions are coated onto tracing cloth, it is customary to first waterproof the tracing cloth by means of a waterproof lacquer coating. The

3,038,803 Patented June 12, 1962 presence of nitrate in the brownprint sensitizing compo sition has a tendency to cause yellowing and brittleness of this waterproof lacquer coating, which is another disadvantage of the prior art brownprint sensitizers.

It has now been found that the above described disadvantages of the prior art brownprint materials may be overcome by substituting for the silver nitrate commonly used, a silver salt which is ordinarily considered insoluble in water. Silver salts such as silver carbonate, silver citrate and silver tartrate have been found to work satisfactorily in the new brownprint sensitizing compositions. Generally speaking an improvement in the keeping quality of brownprint material can be achieved by replacing the silver nitrate with any silver salt of a nonoxidizing inorganic or organic acid which has an ionization constant no more than that of another anion which appears in the formulation. Theoretically, in order to dissolve the silver salt, the ionization constant of the acid of the anion which appears in the silver salt should be less than the ionization constant of the acid of another anion which appears in the formulation and this other anion should be present in at least equal stoichiometric proportions with the silver salt. It is believed that the fact that a silver salt of a nonoxidizing acid is used according to the present invention instead of the water soluble silver salt, namely silver nitrate used in all prior art brownprint processes accounts for a basic difference in the present process and unexpected advantages over the prior art.

The following specific examples illustrate brownprint materials made up according to the present invention:

Example I Paper is coated in any known manner with the following solution:

Water cc 1000.0 Ferric ammonium citrate gm 127.0 Tartaric acid gm 21.0 Silver carbonate gm 56.0

Days of Aginm O 5 10 15 20 Directions... 0 M O M C M O M G M Standard- AgNO; 331 320 10 58 3 22 2 8 1 1 Experimental Ag CO 346 396 102 121 106 43 101 39 77 In the Schappers test the higher is the averaged figure, the greater is the resistance to tearing. The table clearly shows that the tendency of transparent brownprint paper to become brittle is reduced by the use of silver carbonate.

The success of the brownprint process depends also upon washing out the solution from the unexposed areas. This process is slow and oftentimes incomplete so that there is discoloration in areas which should be the color of the base sheet. These discolorations result in poor reproductions when prints are subsequently made. Since silver carbonate or the other salts used according to this invention do not act upon the fibers of the paper, they do not adversely affect the keeping quality of the material and can be successfully washed off the unexposed areas '2 at even on material which has been aged much longer than would be possible with the prior art material.

Example 11 Fine quality tracing cloth Waterproofed by means of a suitable lacquer coating such as a nitrocellulose lacquer coating in known manner is coated by any suitable known method with the following solution:

Ferric ammonium oxalate gm 90.0

Ferric oxalate gm 45.0 Tartaric acid. gm 25.0 Water cc 750.0 Polyvinyl pyrrolidone 20% solution cc 175.0 Sodium hexametaphosphate solution cc 50.0 Silver carbonate gm 45.0

This material is suitable for producing negative prints intended for rough handling or for the reproduction of maps. The sensitizing salts do not cause yellowing or embrittle the waterproof lacquer coating on the backside of this waterproof tracing cloth. The coated material was subjected to forced aging in a hot box at a temperature of 150 F. and 55% relative humidity and there was no evidence of decomposition of the coated layer or the base material.

Example 111 Fine quality tracing paper is coated in known manner with the following solution:

Water cc 500 Ferric ammonium oxalate grams 30 Ferric oxalate c do 32 Tartaric acid do 12 Silver citrate do 26 The ferric salts and tartaric acid are dissolved in water. Then the silver citrate is added in small portions to the solution with constant stirring. When the reaction is complete, the solution is coated on the tracing paper base. The sensitized material so prepared has very good shelflife.

Example IV Instead of the solution described in Example III, tracing paper is coated with the following solution:

Water cc 150 Ferric ammonium oxalate grams 1 1 Ferric oxalate do 12 .Oxalic acid do 5 Silver tartrate do 18 The sensitized material has the same good properties described in Example III.

Having thus described the invention, what is claimed is:

1. A light sensitive material comprising a base sheet coated with a light sensitizing solution including a complex ferric salt containing in addition to ferric ions at least one cation selected from the group consisting of NI-Lf Na+, and K+ and an anion selected from the group consisting of sulphate and organic carboxylates and a silver salt selected from the group consisting of silver carbonate, silver citrate and silver tartrate.

2. A light sensitive material comprising a base sheet coated with a light sensitizing solution including a complex ferric salt containing in addition to ferric ions at least one cation selected from the group consisting of NH Na+, and K+ and an anion selected from the group consisting of anions of dicarboxylic acids and polycarboxylic acids and a silver salt selected from the group consisting of silver carbonate, silver citrate and silver tartrate.

3. A light sensitive material comprising a base sheet coated with a light sensitizing solution including a complex ferric salt containing in addition to ferric ions at least one cation selected from the group consisting of NHJ, Na+, and K and an anion of a polycarboxylic acid containing at least one hydroxyl group and a silver salt selected from the group consisting of silver carbonate, silver citrate and silver tartrate.

4. A light sensitive material comprising a base sheet coated with a light sensitizing solution including ferric ammonium citrate and silver carbonate.

5. A light sensitive material comprising a base sheet coated with a light sensitizing solution including ferric ammonium citrate and silver citrate.

6. A light sensitive material comprising a base sheet coated with a light sensitizing solution including ferric sodium oxalate and silver carbonate.

7. A light sensitive material comprising a base sheet coated with a light sensitizing solution including silver citrate, a complex ferric salt containing in addition to ferric ions at least one cation selected from the group consisting of NHJ, Na and K+ and an anion selected from the group consisting of citrate and oxalate.

8. A light sensitive material comprising a base sheet coated with a light sensitizing solution including silver tartrate, a complex ferric salt containing in addition to ferric ions at least one cation selected from the group consisting of NHJ, Na+ and K+ and an anion selected from the group consisting of citrate and oxalate.

9. A light sensitive material comprising a base sheet coated with a light sensitizing solution including a complex ferric salt containing in addition to ferric ions at least one cation selected from the group consisting of citrate and oxalate, a silver salt selected from the group consisting of silver carbonate, silver citrate and silver tartrate and a free acid selected from the group consisting of citric acid, tartaric acid and oxalic acid.

10. A light sensitive material, comprising a base sheet coated with a light sensitizing solution including ferric ammonium citrate and silver carbonate and being free from silver nitrate.

11. A light sensitive material, comprising a base sheet coated with a light sensitizing solution including ferric ammonium citrate and silver citrate and being free from silver nitrate.

12. A light sensitive material, comprising a base sheet coated with a light sensitizing solution including ferric sodium oxalate and silver carbonate and being free from silver nitrate.

13. A light sensitive material, comprising a base sheet coated with a light sensitizing solution including silver citrate and being free from silver nitrate, and a complex ferric salt containing in addition to ferric ions at least one cation selected from the group consisting of NHfi, Na+ and K+ and an anion selected from the group consisting of citrate and oxalate.

14. A light sensitive material, comprising a base sheet coated with a light sensitizing solution including silver tartrate and being free from silver nitrate, and a complex ferric salt containing in addition to ferric ions at least one cation selected from the group consisting of NI-Ifi, Na and K+ and an anion selected from the group consisting of citrate and oxalate.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Brown: Ferric and Heligraphic Processes, p. 41, 1900, Tennant & Ward, New York.

Claims

1. A LIGHT SENSITIVE SOLUTION INCLUDING A CONCOATED WITH A LIGHT SENSITIZING SOLUTION INCLUDING A COMPLEX FERRIC SALT CONTAINING IN ADDITION TO FERRIC IONS AT LEAST ONE CATION SELECTED FROM THE GROUP CONSISTING OF NH2+NA+, AND K+ AND AN ANION SELECTED FROM THE GROUP CONSISTING OF SULPHATE AND ORGANIC CARBOXYLATES AND A SILVER SALT SELECTED FROM THE GROUP CONSISTING OF SILVER CARBONATE, SILVER CITRATE AND SILVER TARTRATE.