EP0277273A1

EP0277273A1 - Diazotype compositions

Info

Publication number: EP0277273A1
Application number: EP87112341A
Authority: EP
Inventors: Peter Muller; Henry Mustacchi; George Schmitz
Original assignee: Andrews Paper and Chemical Co Inc
Current assignee: Andrews Paper and Chemical Co Inc
Priority date: 1987-01-08
Filing date: 1987-08-25
Publication date: 1988-08-10

Abstract

Solution compatibility of diazotype sensitizing solutions, print color, shade control, and shelf life of diazotypes are improved with the presence of monovalent cation salts of sulfonated hydroxy benzoic acids.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to diazotype compositions and their use in diazotype.

BRIEF DESCRIPTION OF THE PRIOR ART

The diazotype reproduction process is well known to the art and is described in great detail in "Light Sensitive Systems" by Jaromir Kosar, John Wiley & Sons, Inc., N.Y. 1965, and in "Reproduction Coating" by E. Jahoda, 4th Edition, Andrews Paper & Chemical Co., Inc., Port Washington, New York.
In general, diazotype reproduction prints are obtained by an imagewise exposure of a light-sensitive diazo material to ultraviolet light followed by development of the exposed diazotype material. There are several different methods availabel to develop the latent image imposed on the light -sensitive diazo material by the light exposure including ammonia development, amine development, thermal development and moist (liquid) development.
The light-sensitive diazo material generally comprises a light-sensitive diazo composition affixed to a support base such as paper or film such as polyethylene terephthalate film, cellulose acetate, or a polymeric resin coated, like base support. The light-sensitive diazo composition may comprise a light-sensitive diazonium salt compound in admixture with diazo enhancing compounds. Upon exposure of the light-sensitive diazonium compound to ultraviolet light through a translucent original having opaque image portions, the unmasked portions of the diazonium salt are decomposed by the ultrviolet radiation whereas the masked portions are left undecomposed. The latent image created by the image-wise exposure may then be developed by the methods described above.
In the so-called "dry development" process, the light-sensitive diazo composition will contain, in addition to the light-sensitive diazonium salt, an azo coupling agent or color former and an acidic coupling inhibitor. Development of the latent azo dye image is accomplished by placing the exposed diazo material in an alkaline atmosphere which neutralizes the acidic inhibitor, allowing the undecomposed diazonium salt and coupler to react. The latent image is thereby developed.
In the moist development process (also called the one-component process) the light sensitive diazo composition contains essentially the diazonium salt compound. After image-wise exposure, development of the latent azo dye image is accomplished in a pH adjusted solution containing at least one coupler to react with the undecomposed diazonium salt.
It is of great importance in the above described processes that the print development is obtained rapidly and that a minimum of premature development and other deterioration of diazotype materials occur during the time between their manufacture and their use.
Unfortunately, most diazo compounds have low stability and tend to decompose quickly. The coupling reaction unavoidably begins and continues at a very slow rate, immediately after the manufacture of the diazotype materials (i.e., precoupling). Consequently, their shelf life is very limited unless efficient stabilizers are added to delay or block such reactions. In addition to acidic stabilizers, the diazotype compositions generally contain other stabilizing salts, antioxidants for improved print stability, development accelerators and solubilizing compounds for adequate compatability of all active components in the sensitizing solution. As appreciated by those skilled in the art, the wide diversity of compounds desirably present as active ingredients of a diazotype composition, can often lead to problems in incompatability, i.e.; interactions of two or more ingredients may lead to the formation of undesirable complexes, solution incompatibilities or the like.
The commonly used diazo compounds are benzene diazonium salts with various substitutions in the benzene ring and they are more or less ionized into the diazonium cation and the anion of the acid of the salt.
The commonly used diazo couplers are aromatic compounds with enolic character or are compounds with active methylene groups. The couplers, depending on radicals substitution in their molecule, may have anionic or cationic character. Diazos and couplers in the sensitizing solution, dpending on their ionic character and radicals substitutions may form salts and/or complex compounds of different degrees of solubility.
The most widely used antioxidizer is thiourea which is also known to form complex compounds asnd thus afffects dye shade. Development accelerators are often various glycols, allylhydroxethylthiourea and substituted ureas. These compounds of polaric character easily complex azo (print) dyes thereby affecting dye shade.
Highly active solubilizing compounds which mostly increase solubility of diazo-coupler complexes that exhibit poor solubility, are xanthane derivatives such as caffeine. Caffeine is also a solubilizer for may azo dies and probably because of its complexing action, affects the dye shade.
Solution compatibility is or prime importance for the diazotype coating process since it is the basis for obtaining an even coating application in the preparation of the base support.
The effect of each additive to the sensitizing solution on the print dye shade upon development is of particular importance for blackline diazotypes with two or more couplers and which develop to deep black full tones and neutral grey intermediate tones.
Additives for other specific purposes such as improvement of solution stability, shelf life of sensitized paper and rate of development, often affect the print shade in a highly unsatisfactory manner, shifting blackline print colors all the way between blue and brown containing substantial reddish components.
The above-described difficulty in obtaining a balance of diazotype blackline compositions is a serious shortcoming for the diazotype process when such prints are to be used together with xerographic or lithographic prints and desirably are to look alike.
The present invention overcomes the shortcomings described above.
We have found that a specific class of compounds, when used in diazotype sensitizing solutions, greatly improve solution compatibility, lead to blackline diazotype prints with deep black full tones and neutral grey intermediate tones and contribute to good shelf life without negatively affecting the rate of development or hurting waterfastness of the print dye.
We have found that the class of compounds used in this invention function as a solubilizer and as a stabilizer to replace all or at least a substantial portion of the otherwise necessary stabilizing acids such as citric-, sulfosalicylic-, and sulfuric acids and commonly used solubilizers, such as for example caffeine, theophyllin, dialkylureas and alkyl-hydroxy-ethyl thiourea. As such, the compositions of the invention add to the range and choice of useful diazo compositions available to the art, reducing to some extent costs.

SUMMARY OF THE INVENTION

The invention comprises the use of compounds of the formulae:-
wherein X represents the cation of a metal or the cation formed by the addition of a proton to the nitrogen atom of an amine base selected from the group consisting of ammonia, urea, a dialkylurea, an organic alkylamine, a mono-, di-, or trialkanolamine, an aralkylamine or a heterocyclic nitrogen base amine; and
wherein Y represents the multivalent cation of an alkylene diamine or piperazine; as solubilizers and stabilizers in diazotype reproduction materials asnd diazotype materials.
The invention also comprises the method of using the compounds (I) and (II) in diazotype reproduction materials (compositions) of the invention.
The term "metal" as used herein to describe salts of the 5-sulfosalicylic acid is embracive of alkali metals such as lithium, sodium, potassium, and the like.
The term "alkylene" is used herein to mean the divalent moiety obtained upon removal of two hydrogen atoms from a parent hydrocarbon. Representatives of alkylene are alkylene of 1 to 6 carbon atoms, inclusive, such as methylene, ethylene, propylene, butylene, pentylene, hexylene and the like.
The above-described acidic salts of formulae (I) and (II) may be used alone or in admixture with salts of 5-sulfosalicylic acid in which both the sulfonic radical and the carboxylic radical, are neutralized. The sulfosalicylic acid salts of the formulae (I) and (II) are easy to prepare at a low cost and their use results in a cost saving when compared with the more expensive caffeine, theophyllin and alkyl hydroxyethyl thiourea together with the acid stabilizers which they replace in the compositions of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The compounds of the formulae (I) and (II) given above are well known salts of 5-sulfosalicylic acid, as are the methods of their preparation. In general, the compounds of the formula (I) wherein X represents the cation of an alkali metal may be prepared by reacting stoichiometric proportions of 5-sulfosalicylic acid with a salt of the metal.
These copounds of the formula (I) and (II) wherein X and Y represent the cation of an amine base may be prepared by reaction of 5-sulfosalicyclic acid with equivalent proportions of the amine base, in an aqueous media.
The above-described reactions to obtain the compounds (I) and (II) may be carried out over a broad range of temperatures and pressures, neither being a critical parameter of the reaction. Advantageously the reaction is carried out at a temperature within the range of from about 0°C to about 100°C, preferably at room temperature (circa 26°C) and under atmospheric pressures.
The reactions are generally complete within minutes and are indicated by precipitation of the desired product compounds of the formulae (I) and (II) given above, in the reaction mixture. Precipitation usually occurs without further treatment of the solution, although under certain conditions, it may be desirable to initiate precipitation of the product salts by cooling the reaction mixtures, seeding the solution or adding some sodium chloride or like salt to reduce the solubility of the product salts in the reaction mixture. Following precipitation, the desired salts of the formulae (I) or (II) are readily separated from the reaction mixture by conventional technique such as by filtering, washing and recrystallization.
A wide variety of amine bases may be employed to prepare the compounds of the formulae (I) and (II) described above. When ammonia or an ammonium compound is used, X in the formula (I) will be the ammonium cation. When urea or a dialkylurea are used, the X will represent the corresponding cation of the base. The term "dialkylurea" is used herein to mean urea wherein a hydrogen atom on each of the two nitrogen atoms is replaced with an alkyl group.
The term "alkyl" is used throughout the specification and claims as meaning the monovalent moiety obtained by removal of a hydrogen atom from a parent alkane, which latter for example, contains 1 to 12 carbon atoms. Illustrative of such moieties are alkyl of 1 to 12 carbon atoms, inclusive, such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl and isomeric forms thereof.
Representative of dialkylureas are dimethylurea, dibutylurea, dihexylurea and the like.
Alkylamines employed to prepare the compounds of formula (I) given above are compounds of the formula:-
H₂N-R (III)
wherein R represents alkyl as defined above. Representative of alkylamines are methylamine, propylamine, butylamine, hexylamine and the like. The aralkylamine bases are compounds of the formula (III) given above wherein R represents aralkyl. The term "aralkyl" is used to mean the monovalent moiety obtained upon removal of a hydrogen atom from the alkyl portion of an alkyl-substituted aromatic hydrocarbon. Representative of aralkyl are benzyl, phenethyl, phenpropyl, phenbutyl and the like.
Heterocyclic nitrogen base amines are generally well known compounds, represented by morpholine and piperidine.
The alkylene diamines are also generally well known compounds and include ethylene diamine, propylene diamine, hexylene diamine and the like. Preferably the alkylene diamines employed to prepare the compounds of formula (II) will have 1 to 6 carbon atoms, inclusive.
The mono-, di- and tri-alkanolamines are also a well known class of compounds as are methods of their preparation. Representative of the class of compounds are ethanolamine, 2-amino-l-propanol, 3-hydroxypropylamine, diethanolamine, triethanolamine and the like.
As is well known in the art, diazo compositions for the two-component diazotype process comprise at least one light-sensitive diazonium compound, at least one azo coupler and acidic stabilizers which are necessary to obtain a diazotype copy. The term "light-sensitive" as used herein means the compound or material undergoes photolytic decomposition. In the diazotype coating compositions of the present invention, any of the conventionally employed, light-sensitive diazonium compounds may be employed. Aromatic para amino and para mercapto substituted diazo compounds of more or less pronounced yellow color and which absorb ultraviolet light to undergo a photolyitic decomposition to colorless products are advantageously used. Such diazonium compounds and the method of their preparation are well known in the art. Representative of diazonium compounds used in the invention are:

1. Derivatives of 1-diazo-4-amino benzene with or without alkyl, oxyalkyl or halogen substitutions in the benzene ring and with alkyl or dialkyl or acyl or acyl-alkyl or aryl substitution on the amino nitrogen or with the amino nitrogen forming a member of a heterocyclic ring with or without a second hetero atom of oxygen or nitrogen.
2. Derivatives of 1-diazo-4-phenyl benzene with and without substitution in the phenyl and in the benzene rings.
3. 2-diazo-1-hydroxy-naphthalene-5-sulfonic acid, and the like.

In preferred compositions of the invention, azo couplers are mixed with the diazonium compounds in an acid environment to prevent precoupling. When changing the pH from an acid to an alkaline pH, the coupling reaction occurs to produce an azo dye as is known in the art. Azo couplers are generally aromatic compouds with phenolic hydroxyl group~with or without other substituent groups. The couplers are generally colorless. Representative of azo couplers are:

1. resorcinol and its halogen and alkyl derivatives and ethers;
2. resorcyclic acids with or without halogen substitution in the ring and their amides and substituted amides;
3. dihydroxy naphthalene mono sulfonic acids and disulfonic acids;
4. dihydroxy naphthalenes;
5. beta and alpha-hydroxy naphthoic acid amides and substituted amides;
6. compounds with active methylene groups such as aceto-acet derivatives and cyano-acet derivatives;
7. mono and poly hydroxy biphenyls;
8. polyhydroxy biphenyl sulfides;
9. pyrazolone derivatives;
10. amino phenol derivatives; and the like.

The proportions of the various components of the compsitions of the invention described above may be those proportions conventionally used in their use prior to this invention, in the preparation of prior art diazo light-sensitive compositions (where they were so used). These proportions are well known to those skilled in the art; see for example the disclosure of Kopsar, supra and of U.S. Patents 3,923,518 and 3,996,056. In general, the aqueous diazo coating compositions contain from about 0.1 to about 10 percent by weight of the light-sensitive diazonium compound and sufficient coupler to react with and couple the diazonium compound upon development.
A necessary ingredient of the diazo coating compositions of the invention, is a stabilizing proportion of a compound of the formulae (I) and/or (II) given above. A stabilizing proportion is one which will maintain the desired acid pH of the diazo coating until development occurs. In general, a stabilizing proportion of the compounds as represented by those of the formulae (I) and (II) given above, will be within the range of from about 5 gms to 200 gms (preferably 20 gms to 70 gms) for each liter of aqueous diazo coating composition to be stabilized. Preferably the proportion of the compounds (I) and (II) is one within the range of from 1 to 5 parts by weight for each part by weight of the light-sensitive diazonium compound. The compounds (I) and/or (II) may be used as the sole stabilizer, or they may be used in conjunction with reduced conventional proportions of previously known acid stabilizers employed in diazotypy. Representative of such prior art acid stabilizers are citric acid, tartaric acid, hydrochloric acid, sulfuric acid, boric acid, mixtures thereof and the like.
The light-sensitive diazo coating compositions of the invention may contain any number of additional ingredients conventionally used in the preparation of prior art lightsensitive diazo coating compositions such as, for example,

1. development accelerators such as glycerol, polypropylene glycol, urea and the like to minimize the necessary ammonia or amine concentration in the developing environment;
2. antioxidants such as thiourea, glucose and the like to stabilize diazotype prints against discoloration under daylight exposure;
3. contrast controlling compounds; and
4. solubilizers such as caffein which improve the compatibility of the various components in the sensitizing solution.

Sometimes such components fulfill more than one of these functions.
The diazo compositions of the invention may be prepared by bringing the ingredients together in a suitable vessel. Preferably the diazo compositions of the invention are prepared in an aqueous media for use as an aqueous coating mixture to prepare diazotype reproduction materials of the invention. In case of precoating it is possible to add one or more components to a precoat preparation and at least one of the remaining components of the compositions of this invention to a secondary coating preparation.
The diazotype reproduction materials of the invention may be prepared by coating aqueous mixtures of the diazo compositions of the invention on a suitable base support material, using conventional diazo coating apparatus. The techniques are well known; see for example U.S. Patents 3,923,518 and 3,996,056. Representative of suitable base supports are opaque paper, translucent papers, polymeric resin films, and like supports. Preferred are the commercially avilable diazobase papers.
The following examples describe the manner and method of making and using the invention and set forth the best mode contemplated by the inventors but are not to be construed as limiting. All parts specified are by weight unless otherwise stated.
Where specified, accelerated aging test results were obtained by the following procedures:
Diazotype sheets are exposed for 24 hours at 50°C to an atmosphere of 50% and/or 75% relative humidity. This is done by suspending sample sheets of sensitized diazotypes in a closed box over a supersaturated solution of potassium carbonate (50% R.H.) and in another closed box over a supersa turated solution of sodium chloride (for 75% R.H.); and the boxes being placed inside an oven at 50°C. Thereafter they are half covered with a black opaque sheet and exposed to UV light in the printing section of a diazo copying machine, sufficiently to decompose all diazo in the non- covered area. The sheets are then fully developed with ammonia by passing the diazotype sheet through the developing section of a diazotype copying machine. A fresh sheet of the same diazotype paper is also half covered with a black opaque sheet and printed and developed in the same manner. The resulting prints are then compared as to their loss of full tone print color density and discoloration of their print background brightness in the light exposed areas. The loss of print color and the degree of print background discoloration are an indication of their useful shelf life. The aging test with a 50 percent relative humidity (R,H.) atmosphere, in general, reflects a normal shelf life of 3 months. The aging test with a 75 percent R.H. atmosphere reflects behaviour under extremely adverse conditions.

EXAMPLE 1

On a diazotype coating machine, equipped with three air knife coating stations and three dryer passes, one after each coating, an opaque base paper with a basis weight of 73 g/m² is coated and dried in sequence with the following preparations:

1. first coat on front side (precoat):

water 9,000 ml
silica (1 micron particle size) 500 g
Aqueous dispersion of polyvinylacetate (50% solids) 750 ml
antifoam agent 5 g
ammonia 10 ml

2. second coating on front side (sensitizing):

water 10,000 ml
sodium sulfosalicylate 400 g
thiourea 400 g
2,7-dihydroxy naphthalene-3-disulfonic acid, sodium salt 75 g
2,3-dihydroxy naphthalene-6-sulfonic acid, sodium salt 30 g
2,4-dihydroxy benzyl aminemethanesulfonate 100 g
isopropyl alcohol 100 ml
1-diazo-4-dimethyl aminobenzene-iso-phthalic sulfonate 200 g
zinc chloride 450 g
(The sensitizing solution was clear and exhibited no crystallization nor precipitation even after standing 24 hours.)

3. third coating on back side (anticurl coating):

water 10,000 ml
zinc chloride 200 g
A flat diazotype paper with no loss of physical strength characteristics was obtained. Image-wise exposure and ammonia development in commercial diazo copying machines with hot development at 105°C and in developing machines at room temperature resulted in copies with deep black lines in full tones and neutral grey lines in intermediate tones on a white background.
Accelerated aging tests at 50°C and 50% R.H. as well as 75% R.H. for 24 hours indicate that the shelf life of the paper is better than one year.
The rate of development of the test paper was highly satisfactory.
Comparative tests in which the sodium sulfosalicylate was replaced by the lithium, potassium, and ammonium salts of the same acid, respectively, gave very similar results.
When an equimolaric amount of the free sulfosalicylic acid was used to replace the sodium sulfosalicylate, a clear and stable sensitizing solution was also obtained. However, the print color, in particular of the intermediate tones, turned reddish upon dissipation of the ammonia and sensitized paper upon accelerated aging lost strength and exhibited brittleness.
When an equimolaric acmount of the zinc salt of sulfosalicylic acid was used to replace the sodium sulfosalicylate, a reddish print color in full and intermediate tones was obtained.
Brownish shades were obtained when the aluminum salt of sulfosalicylic acid was used to replace the sodium salt of sulfosalicylic acid.
When citric acid was used insteasd of sodium sulfosalicylate, the sensitizing solution became turbid and some crystallization occurred within 24 hours. In order to obtain a clear and stable sensitizing solution with citric acid, it was necessary to add at least 10g/l theophylline and 15g/l allyl-hydroxy ethyl thiourea as solubilizers. The print color of the test paper with citric acid developed to a more reddish-black and the shade turned brownish after full dissipation of excessive ammonia.

EXAMPLE 2

The following two blueline diazotype solutions A and B were prepared by dissolving the specified compounds under mechanical stirring in water.
After the solutions wee allowed to cool down to room temperature and left standing for 4 hours, solution "A" showed substantial crystallization while solution "B" stayed entirely clear without crystallization. When the citric acid in solution "A" was replaced by tartaric acid or p- toluene sulfonic acid, crystallization occurred to a very similar degree.
When the freshly prepared solutions "A" and "B" were applied to a precoated paper in a conventional diazotype coating machine, diazotype paper was obtained which, when image-wise exposed and developed with ammonia, resulted in blueline prints of equally good print contrast and print background brightness. Accelerated aging test of the sensitized papers from solutions "A" and "B" indicate a better shelf life for paper coated with solution "B".
When solutions "A" and "B" after standing for 4 hours, were applied to precoated paper in an identical manner, diazotypes from solution "A" resulted in prints with reduced print dye density indicating that the crystal separation contained diazo compound.
The results of Example 2 show that the sodium sulfosalicylate not only replaces conventional acids such as citric-, tartaric- or p-toluenesulfonic-acid as a stabilizer for shelf life, but also acts as an active solubilizer for solution compatability of the various diazotype components.

EXAMPLE 3

The following four blueline diazotype solutions "C", "D", "E" and "F" were prepared by dissolving the specified compounds under mechanical stirring:
The solutions after cooling down to room temperature had the following properties.
Solutions "C" and "D" has to be reheated to 40-45°C to redissolve the crystals.
Solutions "C", "D", "E" and "F" were applied to a precoated paper in a conventional diazotype coating machine. Diazotype papers were obtained which when image wise exposed and developed with ammonia resulted in blueline prints on white background. The background on the diazotype from solution "C", however, exhibited a slight bluish discoloration.
Results from accelerated aging tests at 50°C and 75% R.H. for 24 hours indicated that diazotypes from solutions "D", "E" and "F" have a substantially better shelf life than diazotypes from solution "C".
The results of Example 3 show that the use of sodium sulfosalicylate with or without citric acid in the diazotype sensitizing solution instead of citric acid alone improves solution compatibility and allows the use of sensitizing solutions at room temperature and avoids the need for heating solutions during the coating operation.
The advantageous use of the sulfosalicylic acid salts of the invention does not exclude their appliction in conjuction with conventional stabilizing acids or solubilizing compounds, in particular if some special effects from such compounds are useful for the particular application.

EXAMPLE 4

The following two blackline diazotype solutios G and H were prepared by dissolving the specified compounds under mechancal stirring.
It was found that complete dissolution of all the chemicals took place at room temperature in the case of solution H whereas it was necessaray to warm the solution up to 55°C to achieve the same result with solution G.
When the clear solutions G and H were applied to a precoated paper in a conventional diazotype coating machine, diazotype paper was obtained which, when image-wise exposed and developed; with ammonia, resulted in blackline prints of equally good print contrast and brightness, although the paper obtained with solution H had more grey neutral half tones than the paper obtained with Solution G which exhibited more reddish half tones.
On standing overnight at room temperature, solution G crystallized whereas solution H remained clear.

Claims

1. A light sensitive diazo coating composition, which comprises:
a light-sensitive diazo compound, sufficient of an azo dye coupler to couple the diazo compound and a stabilizing proportion of a compound selected from those of the formulae:-

wherein X represents the cation of an alkali metal or the cation formed by the addition of a proton to the nitrogen atom of an amine base selected from the group consisting of ammonia, urea, a dialkylurea, an organic alkylamine, a mono-, di or trialkanolamine, an aralkylamine or a heterocyclic nitrogen base amine; and

wherein Y represents the multivalent cation of an alkylene diamine or piperazine.

2. The composition of claim 1 wherein the compound selected is sodium sulfosalicylate.

3. The composition of claim 1 wherein the compound selected is lithium sulfosalicylate.

4. The composition of claim 1 wherein the compound selected is potassium sulfosalicylate.

5. The composition of claim 1 wherein the compound selected is ammonium sulfosalicylate.

6. The composition of claim 1 wherein the compound selected is ethylene diamine-disulfosalicylate.

7. The composition of claim 1 in which the stabilizer is contained at a ratio of between 1 and 5 parts by weight for 1 part by weight of the light-sensitive diazo compound.

8. A method for improving diazotype materials having a light-sensitive coating, which comprises:
admixing in said coating a stabilizing proportion of a compound selected from those of the formulae:-

wherein X represents the cation of an alkali metal or the cation formed by the addition of a proton to the nitrogen atom of an amine base selected freom the group consisting of ammonia, urea, a dialkylurea, an organic alkylamine, a mono-, di- or trialkanolamine, an aralkylamine or a heterocyclic nitrogen base amine; and