US3389995A - Two-component heat developable diazotypes containing amidine compounds - Google Patents

Description

United States Patent 3,389,995 TWO-COMPONENT HEAT DEVELOPABLE DIAZOTYPES CONTAINING AMID IN E COMPOUNDS Bert E. Tripp, Binghamton, Walter J. Welch, Port Dickinson, and Theodore Panasik, Vestal, N.Y., assignors to General Aniline & Film Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Sept. 15, 1964, Ser. No. 396,715 Claims. (Cl. 96-91) ABSTRACT OF THE DISCLOSURE Two-component diazotype photoprinting material, and a sensitizing composition for its preparation, comprising a surface having thereon a light-sensitive layer containing an azo coupling component, a light-sensitive diazonium compound, an acid stabilizer and at least one amidine compound selected from the group consisting of acetamidine, propionamidine, butyramidine, dicyandiamidine, guanyl thiourea and salts thereof.

This invention relates to two-component diazotype photoprinting material susceptible to development on heating, wherein said light-sensitive two-component diazotype layer comprises an amidine compound characterized by the formula wherein X is selected from the group consisting of methyl, ethyl, propyl, NH--CN, NHCONH and NH-CSNH Two-component diazotype photoprinting material comprises a supporting sheet, such as paper or film, having in a surface coating or layer, an azo coupling component and a light-sensitive diazonium compound stabilized against premature coupling by inclusion of an acid stabilizer. On exposure of such coating to actinic light under an opaque pattern on a translucent background the light-sensitive diazonium compound is destroyed in the light-struck areas and on subsequent exposure to an alkaline development medium, such as gaseous ammonia, the acid stabilizer is neutralized and the residual diazonium compound couples with the coupling component to form an azo dye image in the areas corresponding to the opaque portions of the original pattern. Photoprinting materials of this type have met with various objections, such as the inconvenience associated with alkaline development and the need for special equipment to avoid obnoxious ammonia odors.

It has been proposed to include in a two-component light-sensitive diazotype layer of the aforesaid nature, one or more reagents having an acid to neutral reaction which, on heating, are converted or decomposed to yield an alkaline reacting compound. Diazotype photoprinting materials containing such reagents can be developed after exposure to light under a pattern as mentioned above by heating at a temperature causing the aforesaid modification or decomposition. The alkaline reaction product thereby formed neutralizes the acid stabilizer and causes image-wise coupling of the residual diazonium compound with the azo coupling component. Premature coupling of the diazonium compound during storage has tended to destroy the desired contrast in many cases.

Numerous attempts have been made in the prior art 3,389,995 Patented June 25, 1968 ice to obviate some of the problems associated with these processes. Thus, it has been proposed to prepare and apply the individual diazotype and coupling materials to photographic sheets in such a manner that they will form azo dyes under heat alone. An example is contained in U.S.P. 2,418,623. This patent proposed to use a biguanidine salt of a diazo compound which would decompose under the influence of heat to yield ammonia as a developing agent. In U.S.P. 2,178,771 separate layers were pro posed and development by use of steam was suggested. Various other patents have suggested other processes involving heat.

A number of other prior art investigators have suggested that the diazonium salts and couplers might be developed by heat, provided they are applied in separate layers or coatings, the application of the separate coatin'gs to be such as to avoid premature reaction between them. U.S.P. 3,046,128 discloses a typical heat developing two-component diazotype of this type wherein a lightsensitive diazonium layer is applied to one side of a paper base and an alkali generating layer is applied to the opposite side of the paper. The alkali generating layer contains materials having low vapor pressure at room temperature or slightly above room temperature and substantial vapor pressure at temperatures of about to 200 C. The alkaline material either breaks down and passes as a vapor through the paper or merely passes through the paper without any chemical breakdown. Various materials such as urea, guanidine, alkyl substituted ureas, ammonium salts of weak acids, volatile organic bases (ethylenediamine) are suggested. While this method has certain advantages it is relatively diflicult to package several sheets of this material without a reasonable chance of premature development of the diazotype layer. FIGURE 3 of this patent discloses the use of a vapor barrier film as a top coat for the diazo layer. This layer tends to minimize this disadvantage. However this increases the cost of the final product unduly. Further, care must be exercised in the coating operations to preclude premature coupling.

It has also been suggested in some instances that the alkaline material be physically separated in some manner and only brought together later for development purposes. U.S.P. 3,076,707 discloses forming a non-reactive crystalline complex of a basic material such as an amine, and a phenolic compound or urea. This crystalline complex is decomposed after exposure of the diazotype material by the influence of heat.

The use of alkali generating agents, such as urea or trichloroacetic acid (sodium trichloroacetate in an acidic system) for coupling also has been proposed in the prior art. A reaction would take place subsequently on heating. However, urea decomposes at moderate storage temperature and even at normal room temperature. Furthermore, relatively large amounts of urea are required for satisfactory development. For example U.S.P. 3,046,128 sug gests using up to 3,000 grams of urea per one thousand square feet of diazotype paper. It is difficult to store materials of this type and maintain proper quantities over moderate periods of time. The trichloroacetic acid sodium trichloroacetate system has not been satisfactory, in general, because the excess trichloroacetic acid usually causes severe degeneration of the paper. In addition, the sodium trichloroacetate itself tends to cause the diazonium salt to decompose prematurely,

Degeneration of cellulosic bases is not a problem peculiar to the use of trichloroacetic acid heat development. All two-component diazotypes present this problem with more or less severity. Decomposition is due to the acidic nature of the materials used to prevent premature coupling.

The object of this invention is to provide a new source of alkaline generating material which can be included in a sensitized composition of heat developable diazotype material. Anotherobject of this invention is to provide heat developable light-sensitive diazotype material containing an alkali generating material which is stable for extended periods of storage. A further object is to provide twocomponent diazotype materials which have a much smaller tendency to degrade the paper base.

We have now found that the objects of our invention are accomplished by employing an amidine compound characterized by the structure and salts thereof as the alkali generating material. In the above formula X represents methyl, propyl, ethyl,

Typical compounds of this class are acetamidine, propionamidine, butyramidine, dicyandiamide, dicyandiamidinc, guanyl thiourea, etc. All of these compounds are used as salts except for dicyandiamide which is essentially neutral. Suitable salts include the hydrochloride, carbonate, sulfate, etc. The amidine compound can be added to the sensitizer as a salt or the salt formed in situ by adding suitable acid.

Diazotypes of this invention are unexpectedly stable. This is contrary to what one would expect from the disclosure of U.S.P. 3,046,128 where the basic material is applied to the opposite side of the sheet of paper bearing a heat-sensitive diazotype layer and U.S.P. 3,076,707 which complexes tetramethylguanidine with 4,4-'butylidene-bis-(6-tertiary butyl-rn-cresol). Further, the amidine compound acts as a stabilizer preventing undue degradation of the paper base.

The quantity of amidine compound employed in accordance with this invention advantageously ranges from 1 to about 15% by weight of the diazotype sensitizing solution, and constitutes from about 3 to about 40% by weight of the non-volatile components of the sensitizing composition and of the resultant light-sensitive layer. In general the amidine compound comprises from about 1 to 25 parts by weight per part by weight of diazonium compound. Best results have been obtained using about to parts of amidine compound per part by weight of diazonium compound.

The sensitizing compositions of this invention may contain as light-sensitive stable diazonium compounds, those listed in U.S. Patent 2,501,874 and in the article by Van der Grinten in Photographic Journal, volume 92 (B), page 46. They are especially diazonium compounds derived from N-monoor N-di-substituted p-phenylenediamines, e.g., diazotization products of:

N,N-dimethyl-p-phenylenediamine N,N-diethyl-p-phenylenediamine N-benzyl-N-ethyl-p-phenylenediamine N-ethyl-para-phenylenediamine N,N-diethyl-2-ethoxy-p-phenylenediamine N,N-'bis-hydroxyethyl-p-phenylenediamine N-ethyl-2-methyl-p-phenylenediamine N-beta-hydroxyethyl-Nnnethyl-p-phenylenediamine 4-morpholinophenylamine These compounds are preferably stabilized in the form of their double salts with zinc chloride, tin chloride, cadmium chloride and the like.

A coupling components which can be incorporated in the materials of the invention are for example:

2-(m-hydroxyphenoxy)ethanol 2,3-dihydroxynaphthalene 1,8-dihydroxynaphthalene Phloroglucinol Resorcinol Octylresorcinal Alpha-resorcylamid 3-methyl-l-phenyl-S-pyrazolone Acetoacetanilide H-acid 2,3-dihydroxynaphthalene-o-sulfonic acid 2,5-xylenol Z-methyl resorcinol Acid stabilizers such as citric acid, tartaric acid, boric acid, acetic acid and similar acid reacting compounds are used to prevent premature coupling of the diazonium salt and azo coupling component.

In addition to the foregoing materials there can also be included reagents commonly employed in diazotype photoprinting materials, as for example, intensifiers such as ammonium sulfate, zinc chloride or nickel sulfate; stabilizing agents such as thiourea, a-thiosinamine', accelerators such as 1-allyl-3-beta-hydroxyethyl-thiourea or l-allyl-thiourea; hygroscopic agents such as glycol or glycerin; and wetting agents such as saponin, lauryl sulfate, keryl benzene sulfonate or oleyl-N-methyltaurine.

Moreover, there can be included, finely divided or colloidal silica or alumina, and/or aqueous dispersions of colloidal solutions of organic film-forming binders, such as colloidal water-soluble polyvinylalcohol, hydroxyethylcellulose, methylcellulose, gelatin or the like, or latex-like dispersions of polyvinyl chloride-acetate, polyvinylene chloride, polyacrylonitrile or polymethylmethacrylate.

The components of the sensitizing composition are preferably incorporated in a single solution or suspension, and applied in a single coating step to the base. The latter may be paper, or film such as regenerated cellulose, cellulose acetate or other plastic films. However, the various components of the sensitizing composition can be applied, if desired, in two successive coatingone containing, for example, the diazonium salt, and another the alkali generating heat-sensitive reagent, the azo coupling component being incorporated in either of the two layers.

The material coated in accordance with this invention is developed after exposure under an opaque pattern on a translucent background, by heating at temperatures between and 200 C., and preferably between 180 C., at which temperature the amidine compound is converted to an alkaline material. This promotes coupling of the residual diazonium compound with the azo coupling component in the areas corresponding to the opaque pattern to form an azo dye image.

The following examples are merely illustrative and should not be construed as limiting the scope of this invention. In the examples that follow, parts and percent ages are by weight unless otherwise indicated.

EXAMPLE I A paper base was sensitized with the following heatdeveloping composition:

Parts by weight The paper was dried and exposed to light under a translucent original. The exposed paper was developed by passing it through a heated chamber having temperatures of 121 to 177 C. A blue dye was formed in the image areas of the heat-developed print. If the acetamidine compound is replaced by dicyandiamide, or a salt of dicyandiamidine or guanyl thiourea, a like result is obtained. If the amidine compound is omitted from the sensitizing composition, no dye image of consequence results of the heat-developing coating.

EXAMPLE 'II A paper base was sensitized with the following heatdeveloping composition:

Parts by weigh Citric acid 0.5 Sodium 6,7-dihydroxynaphthalene-Z-sulfonate 2-methyl resorcinol Resorcinol Magnesium chloride Dicyandiamide 4 N,N dimethylaminobenzenediazonium chlorozincate 0.6 Polyvinyl alcohol, fully hydrolyzed 4.0 Silica 4.0 Polyvinyl acetate emulsion 5.0 Water 100.0

The base was dried and exposed to light under a translucent original. The exposed paper was developed by passing it through a heated chamber having temperatures of 121 to 177 C. A black dye image was formed in the image areas of the print. Essentially the same results are obtained by substituting the amidine compounds of this invention for the dicyandiamidine. If no amidine compound is used there is little or no dye image formation upon development.

EXAMPLE HI A transparent, light-weight rag paper was sensitized with the following heat-developing composition:

The paper was dried and exposed to light under a translucent original. The exposed paper was developed by passing it through a heated chamber having temperatures of 121 to 177 C. A brown sepia-like image was formed in the image areas of the heat-developed print and the actinic opacity of the image was adequate for use of the heat developed print as an intermediate for reprinting onto standard blue or blackline heat developed papers. A formulation having no amidine compound yielded dye images that were very weak or non-existent.

EXAMPLE IV This example illustrates the improved strength of the paper base when using an amidine compound of this invention in a sensitizing composition. The paper base material was coated uniformly with the following sensitizing composition:

Parts of weight Citric acid 3.0 Sodium 6,7-dihydroxynaphthalene-Z-sulfonate 4.0 Zinc chloride 7.0 Thiourea 5.0 4-dimethylamiuobenzenediazonium chlorozinate 2.0 Silica 5.0 Polyvinyl acetate emulsion 5.0 Dicyandiamide 5.0 Water 10010 The same paper base material was coated with the same sensitizing composition having no dicyandiamide. The papers were dried to 3 /2% moisture and subjected to forced aging tests. The results are as follows where L stands for with the grain and C for across the grain:

No Dicyandiamide Forced Aging Dicyandiamide Conditions Tear 54 190 5 hours, 150 F.

14 171 72 hours, 120 F.

The above table illustrates that the amidine compounds of this invention effectively stabilize cellulosic paper base materials against degradation resulting from the acidic components and acidic salt components of two-component diazotype printing materials. The above composition can be used to prepare two-component heat-developing diazotypes or the more conventional-two-component ammonia developing diazotypes.

The amidine compounds of this invention can be advantageously used in conjunction with alkali metal salts of strong acids, which decomposable on heating. The decomposable alkali metal salts of strong acids tend to reinforce and sharpen the image provided by the amidine compounds. In effect the decomposable alkali metal salts of strong acids are the primary developing agents while the amidine compounds act secondarily as developing agents and primarily as stabilizers to prevent degradation of the cellulosic substrate. Suitable alkali metal salts of strong organic acids which are decomposed on heating to form basic compounds include alkali metal salts (e.g., Na, K) of malonic, oxalic, maleic or benzene sulphinic acids, alkali metal salts of aliphatic monocarboxy acids of 1 to 3 carbon atoms having negative chain substituents such as halogen, ON or N0 in alpha or beta positions; and of these are preferred the alkali metal (e.g., Na, K), ammonium and nitrogen base salts or trichloroacetic acid.

EXAMPLE V This example illustrates the use of dicyandiam'ide with an alkali metal salt of a strong decomposable organic acid. A paper base was sensitized with the following heat developing formulation:

Parts by weight 4 N,N-dimethylaminobenzenediazonium chlorozincate 0.6 Dicyandiamide 5 Sodium trichloroacetate 4 Polyvinyl alcohol, fully hydrolyzed 4 Silica 4 Polyvinyl acetate emulsion 5 Water The base was dried and exposed to light under a translucent original. The exposed paper was developed by passing it through a heated chamber having temperatures 121-177 C. A black dye image of good density and brightness was formed in the image areas of the heat developed print. The dye density and rate of development were better than that obtained without the use of either dicyan- 7 diarnide or sodium trichloroacetate in the sensitizing solution.

Variations and modifications can be made in the procedures, compositions and materials herein described without departing from the scope and spirit of the invention.

We claim:

1. Two-component diazotype photoprinting material susceptible to development on heating, having on a surface of a supporting sheet, a light sensitive layer comprising an azo coupling component, a light-sensitive diazonium compound an acid stabilizer against premature development and at least one amidine compound selected from the group consisting of acetamidine, propionami-de, butyramidine, dicyandiamidine, guanyl thiou-rea and salts thereof.

2. The article of claim 1 wherein said amidine compound comprises from 3 to 40% by weight of the components of said light-sensitive layer.

3. The article of claim 1 wherein said amidine compound comprises from 1 to 25 parts by weight per part by weight of diazonium compound.

4. The article of claim 3 wherein said amidine compound comprises dicyandiarnidine.

5. The article of claim 3 wherein said amidine compound comprises acctamidine.

6. A sensitizing composition for two-component diazotype printing material susceptible to development on heating, comprising an aqueous medium, an azo coupling component, light-sensitive diazonium compound, an acid stabilizer against premature development and at least one amidine compound selected from the group consisting of acetamidine, propionamidine, butyramidine, dicyandiamidine, guanyl thiourea and salts thereof.

7. The composition of claim 6 wherein said amidine compound comprises from 1 to 15% by weight of said sensitizing composition.

8. The composition of claim 6 wherein said amidine compound comprises from 1 to 25 parts by Weight per part by Weight of diazonium compound.

9. The composition of claim 8 wherein said amidine compound comprises acetamidine.

10. The composition of claim 8 wherein said amidine compound comprises dicyandiamidine.

11. Two-component diazotype printing material having on a surface of a support sheet of cellulosic material, a light-sensitive layer comprising an azo coupling component, light-sensitive diazonium compound an acid stabilizer against premature development and at least one amidine compound selected from the group consisting of acetamidine, propionamidine, butyramicline, dicyandiamidine, guanyl thiourea and salts thereof,

12. The article of claim 11 wherein said amidine compound compriscs from 3 to 40% by weight of the components of said light-sensitive layer.

13. The article of claim 11 wherein said amidine compound comprises from 1 to 25 parts by Weight per part by weight of diazonium compound.

14. The article of claim 13 wherein said amidine compound comprises acetamidine.

15. The article of claim 13 wherein said amidine compound comprises dicyandiamidine.

References Cited UNITED STATES PATENTS 2,545,423 2/1949 Duerr 96-75 3,153,592 10/1964 Klimskowski et a1. 96-91 X 3,157,503 11/1964 Kosar 96-75 X 3,199,982 8/1965 Kashiwabara 96-75 X 3,255,007 6/1966 Kosar 96-91 X 3,255,011 6/1966 Welch 96-75 3,271,155 9/1966 Aebi 96-75 3,316,092 4/ 1967 Klimkowski et al 96-75 FOREIGN PATENTS 1,249,913 11/1960 France.

NORMAN G. TORCHIN, Primary Examiner.

C. L. BOWERS, Assistant Examiner.