US3754916A

US3754916A - Heat developable diazo type sheets

Info

Publication number: US3754916A
Application number: US00203011A
Authority: US
Inventors: J Winslow; B Sagawa
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1968-04-22
Filing date: 1971-11-29
Publication date: 1973-08-28
Anticipated expiration: 1990-08-28
Also published as: FR2006670A1; DE1920196A1; DE1920196B2; GB1271713A; NL6905657A; DE1920196C3; AT300553B; CH529367A

Abstract

A heat-developable diazo type sheet containing an acidstabilized diazonium salt in one layer thereof and an acidneutralizing component in another layer thereof is shown wherein at least half of the basic equivalents of the acid-neutralizing component are provided by at least one weakly basic benzimidazole acid-neutralizer compound.

Description

United States Patent i191 Winslow et a1.

[ ]Aug. 28, 1973 HEAT DEVELOPABLE DIAZO TYPE SHEETS [73] Assignee: Minnesota Mining and Manufacturing Company, St. Paul, Minn.

[22] Filed: Nov. 29, 1971 [21] Appl. No.: 203,011

Related U.S. Application Data [63] Continuation of Ser. No. 723,263, April 22, 1968.

[52] U.S. Cl. 96/75, 96/49.91 R, 250/65 T, 117/368, 117/369 [51] int. C1 G03C l/60 [58] Field of Search 96/49.75, 91; 250/65 T; 117/368, 36.9

[56] References Cited UNITED STATES PATENTS 2,548,845 4/1951 Neumann 96/91 R 2,566,167 8/1951 Carroll et al 96/104 3,199,982 10/1965 Kashiwabara..... 96/91 R X 3,248,220 4/1966 Van Rhijn 96/91 R 3,284,201 11/1966 Meijs et al. 96/75 3,294,542 12/1966 Sus et a1.... 96/91 R 3,294,534 12/1966 Halperia 96/49 3,353,984 ll/1967 Landau 96/75 X 3,380,830 4/1968 Schaefi'er 96/75 3,386,828 6/1968 Slimowicz..... 96/91 R 3,520,691 7/1970 Scheler 96/75 FOREIGN PATENTS ,OR APPLICATIONS 983,665 2/1965 Great Britain 96/91 R 1,032,508 6/1966 Great Britain 96/75 OTHER PUBLICATIONS Dietzgen, J. E., Reproductions Review, 2/1962, p. 14, 15, 22 and 26.

Primary Examiner-Charles L. Bowers, Jr. Attorney-Alexander, Sell, Steldt & Delahunt [57] ABSTRACT 8 Claims, No Drawings HEAT DEVELOPABLE DIAZO TYPE SHEETS This is a continuation of application Ser. No. 723,263, filed Apr. 22, 1968.

Heat-developable diazotype sheets commonly employ diazonium salts, acidic compounds for inhibiting premature coupling or self-coupling reactions, and acid-neutralizing components for neutralizing the acidic compounds, thereby allowing coupling to occur. The acid-neutralizing compounds commonly are made available for neutralization by the application of heat to the diazotype sheets; e.g., heat may cause evolution of acid-neutralizing components, as taught by U. S. Pat. No. 2,732,299; or may permit migration of acidneutralizing components into other components of diazotype sheets by heat-softening of hinder or barrier materials as taught by British Pat. No. 1,032,508.

Few heat-developable diazotype sheets which exhibit good storage properties are also capable of development by exposure to reasonable temperatures for short periods of time. Conversely, diazotype sheets which are capable of development by exposure to reasonable temperatures for short periods of time commonly exhibit relatively poor storage properties. Poor storage properties are evidenced by pre-reaction between diazonium salts and 'azo-couplei' compounds to form dy'es prior to light exposure or by self-coupling of diazonium salt compounds, causing the development of background fog and reducing contrast between the image and background. These phenomena are frequently attributable to highly basic acid-neutralizer components which are normally required to overcome the acidstabilization of diazonium salts and to provide rapid coupling reaction rates. The use of less highly basic components commonly necessitates an undesirable increase in the severity of development conditions to compensate for reduced coupling reaction rates. The rate of the coupling reaction is highly dependent upon the basicity of the coupling reaction environment, e.g., highly basic environments .favor rapid coupling reaction rates as shown in J. Kosar, Light Sensitive Systems, pages 216-217, John Wiley and Sons, New York, 1965. On pages 263-277 of this reference are described various unsatisfactory attempts which have been made to provide diazotype sheets having reasonable storage properties which utilize highly basic acid-neutralizing components to provide rapid coupling reaction rates. Highly basic acid-neutralizing components or precursors of such compounds commonly are physically separated from diazonium salts in diazotype sheets to achieve storage properties, but this physical separation causes an undesirable reduction in coupling reaction rates. Reduction of the degree of separation between components, however, adversely affects the storage properties of such sheets.

The primary object of this invention is to provide a heat-developable diazotype sheet which exhibits excellent storage properties and is capable of development by exposure to reasonable temperatures for short periods of time.

Another object of this invention is to provide a heatdevelopable diazotype sheet capable of utilizing a great variety of diazonium salts.

Briefly, the present invention relates to a heatreactive diazotype sheet having at least two layers. One of the layers comprises an acid-stabilized diazonium salt capable of reacting with an azo-coupler compound to form a dye. Another of the layers comprises an acidneutralizer component capable of providing basic equivalents in an amount at least sufficient to render the acid-stabilized diazonium salt reactive with the azocoupler compound. At least one weakly basic benzimidazole acid-neutralizer compound contributes at least half of the basic equivalents provided by the acidneutralizer component. Minor amounts of basic ingredients other than weakly basic benzimidazoles may often be advantageously incorporated into the diazotype sheet of the present invention. Preferably, how ever, such other ingredients provide less than 25 percent of the basic equivalence required to render the acid-stabilized diazonium salt reactive with the azocoupler compound. In the most preferred embodiment, a weakly-basic benzimidazole compound is the sole acid-neutralizer component of the diazotype sheet. The diazotype sheet of the present invention may additionally contain azo-coupler compounds although the azocoupler may be contained in a separate sheet or may be brought into contact with the diazotype sheet.

It is essential that benzimidazole compounds and diazonium salts be kept in separate layers prior to heatdevelopment of the diazotype sheets of the present in vention because of the deleterious effect of benzimid azole compounds upon the storage properties of diazonium salts. Acidic compounds may often be advantageously incorporated in layers containing diazonium salts to prevent premature coupling or self-coupling. Diazonium compounds which are acid-salts or to which acid compounds have been added are herein referred to as acidstabilized.

Benzimidazole compounds have heretofore been utilized in heat-developable diazotype sheets to enhance dye colors, as taught by British Pat. Nos. 967,899 and 1,032,508. Such diazotype sheets, however, have always utilized such strongly basic compounds as ammonia or other organic, non-aromatic amines or salts of such amines as acid-neutralizer components. Benzimidazole compounds in general are but weakly basic in comparison to such amines and to other basic compounds commonly used in diazo processes. In fact, benzimidazole and many of its derivatives exhibit pseudoacidic characteristics, reflected by their ability to form salts with metals. It is consequently surprising that benzimidazole compounds are useful as acidneutralizers without significantly increasing the severity of development conditions normally required for diazotype sheets. Perhaps the greatest advantage realized from the utilization of benzimidazole compounds as the predominant, and preferably the sole acid-neutralizer components of such diazotype sheets is the heretofore seldom attainable excellent storage properties now obtained with the present invention without significant sacrifice in coupling reaction rates during heatdevelopment.

The weakly basic nature of benzimidazole compounds is explained and exemplified in Hofmann, The Chemistry of Heterocyclic Compounds, Part 1, pp. 248-252, lnterscience Pub. N.Y., 1953. The weakly basic benzimidazole compounds of the present invention are defined as benzimidazole compounds which are sufficiently basic to neutralize acids but which are less basic than imidazole. Such benzimidazole compounds include the following: benzimidazole; 6-

nitrobenzimidazole; 2-chlorobenzimidazole; 2- methylbenzimidazole; Z-ethylbenzimidazole; 2-npropylbenzimidazole; Z-n-butylbenzimidazole;

2-hydroxymethylbenzimidazole; 2-( l '-hydroxyethyl)- benzimidazole; 2-(2'-hydroxyethyl)benzimidazole; 2- (l '-hydroxypropyl)benzimidazole; 2-(2'- hydroxypropyl benzimidazole; 2-(3'-hydroxypropyl)- benzimidazole; 2-(1'-hydroxypentylbenzimidazole; 2-

(l',2'-dihydroxyethyl)benzimidazole; 2- phenylbenzimidazole; 2-benzylbenzimidazole; 2- aminomethylbenzimidazole; 2- chloromethylbenzimidazole; 2-

cyanomethylbenzimidazole; zimidazole; 2-meth'yl-5-chlorobenzimidazole; 2- methyl-S,6-dimethylbenzimidazole; 2-(1'-hydroxy) ethyl-S ,6-dimethylbenzimidazole; 2-( 1 '-hydroxy-l methyl)ethyl-S,6-dimethylbenzimidazole; 1,2-bis-(benzimidazolyl-2 )ethanol; 1,2-bis-(benzimidazolyl- 2)glycol and l,3-bis-(benzimidazolyl-2) propanol-l. The benzimidazole compounds used in the present invention preferably are non-coupling. The preferred benzimidazole compounds are benzimidazole, 2- methylbenzimidazole, Z-phenylbenzimidazole and 5,6- dimethylbenzimidazole. Of these compounds, benzimidazole is especially preferred.

Although the following explanation should not be construed as binding on applicant, it is believed that weakly basic benzimidazole compounds contained within a diazotype sheet tend to readily migrate within the sheet during heat-development, thereby neutralizing reaction-inhibiting acidic compounds and providing a weakly basic environment within which coupling of the diazonium salts with azo-coupler compounds may occur. The apparent reactivity of a benzimidazole compound consequently depends not only upon its basicity but also upon the ease with which it can migrate within a diazotype sheet under the influence of heat. Many benzimidazole and bis-benzimidazole compounds are less preferable in the present invention than benzimidazole itself even though they are more strongly basic than benzimidazole.

it is desirable that the weakly basic benzimidazole compounds be separated from the diazonium salts in the present invention, since benzimidazole compounds generally have an unfavorable influence on the storage properties of diazonium salt. This unfavorable influence can often be obviated by including acidic compounds such as tartaric or oxalic acids within the layer containing the benzimidazole compound and the diazonium salts. Difficulty is then often experienced, however, in promoting the coupling reaction, e.g., an unusually large amount of benzimidazole compound is required. Separation of the benzimidazole compounds from the diazonium salts may be effected by incorporating these compounds in different layers or by introducing a barrier layer between layers containing these compounds.

Diazonium salts which find utility in this invention are those which are capable of coupling with azocoupler compounds in weakly basic environments to form dyes. Of the many diazonium salts which may be used in this invention, the following have given good results: p-amino-N-benzyl-N-ethylbenzenediazonium chlorostannate, p-amino-N-benzyl-N- ethylbenzenediazonium chloro-zincate, 3chloro-4- diethylaminobenzenediazonium chlorozincate, pdiethylaminobenzenediazonium fluoroborate, pdiethylamino-2-ethoxybenzenediazonium chlorozincate, 4-diethylamino-2-methylbenzenediazonium chlorozincate, p-morpholinobenzenediazonium fluorobo- 2-methylcarbonylbenrate, p-diazo-N-methyl-N-hydroxyethylaniline zinc chloride, p-diazo-N-ethyl-o-toluidine zinc chloride, pdiazo-N-diethyl-m-phenetidine zinc chloride, pdiazomorpholino-2,5-diethoxybenzene zinc chloride, p-diazomorpholino-2,S-dibutoxybenzene boro fluoride, p-diazo(4-toluyl)mercapto-2,5- dimethoxybenzene zinc chloride, 4-diazo-l,2,5- triethoxydiphenyloxalate, p-diazomorpholino-2,5-dibutoxybenzene zinc sulfate, p-diazodimethyl aniline 1/l-ZnCl p-diazo diethyl aniline zinc chloride, pdiazo-N-hydroxyethyl-N-ethylanilinel /2 zinc chloride, p-diazo-N-ethyl-N-benzylaniline zinc chloride, 4-diazophenylmorpholine zinc chloride, 1 -diazo-4- benzoylamino-2,S-diethoxybenzene zinc chloride. Preferred diazonium salts include: p-diazomorpholino-2,5- dibutoxybenzene borofluoride,p-diazomorpholino-2,5- dibutoxybenzene zinc sulfate, 4-diazophenylmorpholine zinc chloride. Light-sensitive diazonium salts are preferably used.

Azo-coupling compounds which find utility in this invention are those which will couple with diazonium salts in weakly basic environments to form dyes. Such couplers include: 2,3-dihydroxy naphthalene, 2,3- dihydroxynaphthalene-6-sulfonic acid sodium salt, 2,7-dihydroxynaphthalene, l,7-dihydroxynaphthalene, phloretin, acetoacetanilide, aceto-ace't-o-ansidide, 3- methyl-p-sulfophenyl-S-pyrazolone, aceto-acet-2,5- dimethoxyanilide, aceto-acet-p-toluidide, aceto-acet- 2,4-xylidide, 2,6-dihydroxy toluene, 3-methyl-l-phenyl-S-pyrazolone, 2-chloroacetanilide, ethylenediaminebisacetoacetamide, N,N- ethylenebisacetoacetamide, 'y-naphtol, B-naphtol,

spectral absorption characteristics. For example, in a.

preferred embodiment, the dyes resulting from the coupling of p-diazomorpholino 2,5-dibutoxy boro fluoride with acetoacetanilide, 2,7-dihydroxy-naphthalene, and 3-hydroxy-Z-naphtho-o-toluidide are yellow, reddishpurple, and cyan, respectively, and together form substantially black images.

it is often desirable to incorporate acidic compounds, such as oxalic acid, in diazotype sheets which contain highly-reactive diazonium salts for the purpose of inhibiting self-coupling reactions. Diazotype sheets which contain less highly-reactive diazonium salts generally require proportionately reduced amounts of acidic compounds, and many diazonium acid-salts exhibit sufficient stability without the addition of other acidic compounds.

A binder material, normally polymeric, is preferably used to contain the reactive components in layers in the diazotype sheets of the present invention. The binder materials and barrier materials are preferably thermoplastic and soften sufficiently at reasonable development temperatures to permit benzimidazole compounds to readily migrate therethrough. Thermoplastic binder materials in addition should be sufficiently rigid at normal storage temperatures to hinder such migration. It is desirable that the binder materials used in the present invention be capable of forming continuous films. Examples of such polymeric binder materials include polyvinyl chloride acetate, polystyrene, polymethylmethacrylate, etc. Such binder materials are preferably chosen to be compatible with the components incorporated therein, i.e., capable of forming a single phase system with such components, and permit the ready migration of benzimidazole compounds therethrough upon heating. However, polymeric binder materials which are incompatible with the components contained therein, such as polymeric latices, may often be advantageously utilized. Non-thermoplastic and non-continuous binder materials such as paper and cloth may also be used in this invention to yield desirable results. Binder materials which permit the migration therethrough of chemical compounds such as benzimidazole compounds, couplers, and the like are generally known to the art, and the selection therefrom is not critical to the present invention.

The supporting substrates for the layers of the present invention may be of any suitable material such as plastic film, glass, paper, metal, cloth, wood, etc. Plastic films, such as polyester and cellulose triacetate, are preferred. The substrates desirably should have a heatdistortion temperature sufficiently high to permit reasonable development temperatures to be used without damage thereto. It is contemplated, however, that substrates having lower heat-distortion temperatures may be desirable, as, for example, when a wrinkled design pattern is desired. It is further contemplated that a separate supporting layer may be advantageously eliminated in some cases, as when at least one of the binder materials is a self-supporting film.

The diazotype sheets of the present invention may be prepared by a variety of methods, such as consecutively coating polymer emulsions containing reactive components upon a substrate to form layers; laminating together reactive component-containing layers, etc. Preferably, however, the reactive components and polymeric binder material for each layer are combined in a solution which is coated and dried to form a layer. The solvent for each solution is preferably a nonsolvent for the binder material of the preceding layer, thereby avoiding the migration which might otherwise occur should a solvent be capable of dissolving the binder material of the preceding layer to liberate the reactive components contained therein.

In the following examples the densities of the lightstruck background (D,,,,,,) and the non-light-struck imaged areas (D,,,,,,) of diazotype sheets of the present invention were measured with a MacBeth Quantalog Densitometer Model OT20 using the green filter (Mac- Beth Corporation).

The following examples are presented for illustrative purposes only and should not be construed as limiting the spirit or scope of the present invention.

EXAMPLE 1 A solution of:

25 g. polyvinyl chloride acetate copolymer (Bakelite VYHH, Union Carbide Corp.)

2.2 g. benzimidazole 53 g. acetone 22 g. methyl ethyl ketone was prepared and was coated onto the surface of polyester film. After drying for 2 minutes at 96 C., a layer having a dry coating weight of 15.1 g./m was obtained.

Over this dry layer was coated a solution of:

10 g. alcohol-soluble cellulose acetate butyrate polymer (Eastman EASB) 1.0 g. 3-hydroxy-2-naphtho-o-phenetidide 1.4 g. p-diazomorpholino-Z,S-dibutoxybenzene boro 10 g. butanol g. methanol Upon drying for 2 minutes at 49 C., a layer of 5.38 g./m coat-ing weight was obtained.

The diazotype sheet thus prepared was exposed for 16 seconds through a test negative having a density gradient ranging from D,,,,,, of 0. 10 to D of 2.16 to radiation from a 250 watt mercury-vapor lamp positioned 3.18 cm. from the recording element. The exposed sheet was developed by exposure for 30 seconds to a temperature of 121 C. A bluish-purple image exhibiting a D of 1.20 was obtained. The D of the lightstruck background areas was 0.06.

EXAMLE 2 Upon the surface of a polyester film was coated a solution of:

25 g. polyvinyl chloride acetate copolymer (Bakelite VYHH, Union Carbide Corp.) 2.2 g. benzimidazole 0.6 g. aceto-acet-o-anisidide A coating weight of 15.1 g./m was obtained upon drying this layer for 2 minutes at 96 C.

Upon this dry layer was coated the following solution:

10 g. alcohol-soluble cellulose acetate butyrate polymer (Eastman EASB) 2.0 g. p-diazomorpholino-2,S-dibutoxybenzene boro fluoride 0.80 g. 4-diazophenylmorpholine zinc chloride 0.80 g. 3-hydroxy-2-naphtho-o-phenetidide 0.80 g. 3-hydroxy-2-naphtho-o-toluidide 0.12 g. 2,3-dihydroxy naphthalene 0.40 g. oxalic acid 10.0 g. butanol 80.0 g. methanol. After drying for 2 minutes at 49 C., a dry layer having a coating weight of 15.1 g./m was obtained. 4

The diazotype sheet thus prepared was exposed and developed as in Example 1. The resulting reddish-black image exhibited a D of 1.70. The D of the lightstruck background was 0.06. A sample of the unexposed was aged for 6 months at 23 C., 50 percent R.H., and was then exposed and developed as above, yielding a D, value of 0.11 and a D of 1.30.

EXAMPLE 3 A solution of: 25 g. polyvinyl chloride acetate copolymer (Bakelite VYHH, Union Carbide Corp.)

2.2 g. benzimidazole 0.60 g. aceto-acet-2,4-xylidide 0.80 g. 3-hydroxy-2-naphtho-o-phenetidide 53 g. acetone 22 g. methyl ethyl ketone was coated upon the surface of 80 lb SP-l paper (Lee Shoeller Company) and was dried for 2 minutes at 96 C. to yield a dry layer having a coating weight of 15.1 g./m

Upon this dry layer was coated a solution of g. alcohol-soluble cellulose acetate butyrate polymer (Eastman EASB) 2.0 g. p-diethylaminobenzene diazonium fluoroborate 0.60 g. oxalic acid which, upon drying for 2 minutes at 49 C., yielded a dry layer having a coating weight of 5.38 g./m

The diazotype sheet thus prepared was exposed and developed as in Example 1. A green image was obtained having a D of 1.30. The background exhibited a D of 0.14.

EXAMPLE 4 A solution of: 10 g. polyamide resin (Elvanol 8061, E. l. DuPont de Nemours) 2.2 g. benzimidazole 0.60 g. aceto-acet-p-toluidide 10 g. butanol 80 g. methanol was coated on the surface of polyester film. The coating weight of this layer after drying for 2 minutes at 96 C. was 6.46 g./m

Upon this dry layer was coated a solution of:

5.0 g. cellulose acetate (N-200, Dow Chem. Co.)

2.0 g. p-diazomorpholino-2,5-dibutoxy-benzene boro 0.80 g. 4-diazophenylmorpholine zinc chloride 0.80 g. 3-hydroxy-2-naphtho-ophenetidide 0.80 g. 3-hydroxy-2-naphtho-o-toluidide 0.12 g. 2,3-dihydroxynaphthaline 0.40 g. oxalic acid 10 g. methyl ethyl ketone 85 g. acetone After drying for 2 minutes at 49 C., the coating weight of this layer was found to be 5.38 g./m

The diazotype sheet thus prepared was exposed for 16 seconds through a suitable negative to radiation from a 140 ampere carbon are positioned 0.915 m from the element. The sheet was then developed as in Example l, yielding a reddish-black image having a D of 1.65. The D of the background was 0.07.

EXAMPLE 5 A solution of:

Upon exposure and development as in Example 4, a cyan image was obtained which exhibited a B of 1.00. The D of the background was 0.08.

EXAMPLE 6 Upon the surface of polyester film was coated a solution of:

25 g. polyvinyl chloride acetate copolymer (Bakelite VYHl-l, Union Carbide Corp.)

2.2 g. benzimidazole 53 g. acetone 22 g. methyl ethyl ketone which yielded a layer having a coating weight of 15.1 g./m upon drying for 2 minutes at 96 C.

Over this dry layer was coated a solution of:

20 g. polystyrene (Dow Chemical Co. No. 700) 40 g. toluene 40 g. acetone to form, after drying for 2 minutes at 96 C., a second layer having a coating weight of 5.38 g./m

Upon the dry second layer was coated a solution of:

10 g. alcohol-soluble cellulose acetate butyrate polymer (Eastman EASB) 2.4 g. p-diazomorpholino-2,5-dibutoxybenzene boro 1.0 g. 2,3-dihydroxynaphthalene 1.0 g. oxalic acid to form, after drying for 2 minutes at 49 C., a third layer having a coating weight of 5.38 g./m

The diazotype sheet thus produced was exposed and developed as in Example 1, yielding a bluish-purple image having a D of 0.07. The background exhibited a D of 1.30. A sample of the unexposed diazotype sheet was aged for 6 months at 23 C., 50 percent R.l-l., and then was exposed and developed as above. D and D,,,,, values of 0.15 and 1.00 respectively were obtained.

EXAMPLE 7 A solution of:

25 g. polyvinyl chloride acetate (Bakelite VYHH,

Union Carbide Corp.)

2.2 g. benzimidazole 53 g. acetone 22 g. methyl ethyl ketone was coated onthe surface of 80 lb. SP-l paper (Lee 10 g. polyvinyl alcohol (Gelvatol, Shawinigan Chem. 50

Shoeller,,Company). After drying for 2 minutes at 96 C., the coating weight of this layer was 15.1 g./m

Upon this dry layer was coated a solution of: 20 g. polystyrene-acrylonitrile copolymer (Tyril 770,

Dow Chemical Co.) 0.60 g. aceto-acet-o-anisidide g. acetone to form a second layer having a coating weight of 7.55 g./m after drying for 2 minutes at 96 C.

Upon the dry second layer thus formed was coated a solution of:

5 g. alcohol-soluble cellulose acetate butyrate polymer (Eastman EASB) 5 g. polyvinyl acetate (Gelva V-l00, Dow Chem.

Co.) 2.4 g. p-diazomorpholino-2,S-dibutoxybenzene boro fluoride 0.12 g. 2,3-dihydroxy naphthalene 0.08 g. 2,7-dihydroxy naphthalene 0.80 g. 3-hydroxy 2-naphtho-o-phenetidide 0.80 g. 3-hydroxy-Z-naphtho-o-toluidide 0.40 g. oxalic acid 10 g. butanol 80 g. methanol to form a third layer which, after drying for 2 minutes at 49 C., exhibited a coating weight of 5.38 g./m

The diazotype sheet thus obtained was exposed and developed according to Example 1, yielding a bluishblack image having a D of 1.20. The 1),, of the non-imaged areas was 0.15.

EXAMPLE 8 A sheet of paper (80 lb. SP-l, Lee Schoeller Company) was saturated with a solution of:

3 g. 3-hydroxy-2-naphtho-o-phenetidide 3 g. p-diazomorpholino-2,S-dibutoxybenzene 0.4 g. oxalic acid 94 g. methanol A coating weight of 2.25 g./m was obtained upon drying for 2 minutes at 96 C. The coated paper was imaged as in Example 1 and was divided into identical portions A, B and C.

A second paper substrate (80 lb. SP-l Lee Schoeller Company) was divided into two portions X and Y which were treated as follows:

Portion X was saturated with a solution of 4.0 grams of benzimidazole in 96 ml. of methanol. Upon drying for 2 minutes at 49 C., a coating weight of 1.65 grams (0.0014 g. moles) of benzimidazole per square meter was obtained.

Portion Y was saturated with a solution of 2.61 grams of ammonium acetate in 97.4 ml. of methanol to give a coating weight of 0.065 gram (0.00845 g. moles) of ammonium acetate per square meter upon drying for 2 minutes at 49 C.

lmaged portions A, B and C were developed as follows:

Portion A was placed in facing contact with portion X (containing benzimidazole) and was heated at 121 C. for 10 minutes. Similarly, portion B was placed in facing contact with portion Y (containing ammonium acetate) and was heated at 121 C. for 10 minutes. Portion C was exposed to a saturated atmosphere of ammonia at 60 C. for 10 minutes in a commercial diazo developing unit (Uniprinter 086, Model No. 49BG, Minnesota Mining and Manufacturing Co.).

The intensities (D,,,,,,) of the images formed on portions A, B and C were measured as a function of time, yielding the following values:

seconds seconds seconds Portion A, D 0.66 0.74 0.85 Portion B, D. 0.60 0.72 0.74 Portion C, D 0.79 0.84 0.87

These data show the surprising efficiency of benzimidazole as an acid-neutralizing compound in comparison to the efficiency of the highly basic, often-used acidneutralizer, ammonia.

EXAMPLE 9 A solution of:

25 g. polyvinyl chloride acetate copolymer (Bakelite VYHH, Union Carbide Corp.)

2.5 g. Z-aminobenzimidazole 53 g. acetone 22 g. methyl ethyl ketone 5 10 g. alcohol-soluble cellulose acetate butyrate polymer (Eastman EASB) 1.2 g. 2,3-dihydroxynaphthalene 2.0 g. p-diazomorpholino-2,5-dibutoxybenzene boro fluoride 10 0.2 g. oxalic acid 80 g. methanol 10 g. butanol to yield a layer which exhibited a coating weight of 5.38 g./m after drying for 2 minutes at 49 C.

Upon exposure and heat-development as in Example 1, a light-blue image upon a clear background was obtained.

EXAMPLES 10-13 Example 9 was repeated, except that the 2- aminobenzimidazole was replaced by 2.5 g. of the following benzimidazole compounds:

Example 10: Z-methylbenzimidazole Example 11: 2-phenylbenzimidazole Example 12: 5,6-dimethylbenzimidazole Example 13: Z-hydroxybenzimidazole In each case, a light-blue image upon a clear background was obtained.

Various other embodiments of the present invention will be apparent to those skilled in the art without departing from the scope thereof.

What is claimed is:

l. A heat reactive diazotype sheet having at least two layers, one of said layers comprising a heat-softenable component capable of providing basic equivalents in an amount at least sufficient to neutralize said acid stabilization of said diazonium salt, to provide a weakly basic environment for the diazonium salt in the sheet, and to render said acid-stabilized diazonium salt reactive with said azo-coupler compound, at least one of said layers containing an azo-coupler, and greater than percent of said basic equivalents being provided by at least one weakly-basic benzimidazole acid-neutralizer compound.

2. A heat reactive diazotype sheet having at least three layers, one of said layers comprising a heatsoftenable binder material and an acid-stabilized diazonium salt capable of reacting with an azo-coupler compound to form a dye, another of said layers comprising 5 a heat-softenable binder material and an acidneutralizer component capable of providing basic equivalents in an amount at least sufficient to neutralize said acid stabilization of said diazonium salt to render said diazonium salt reactive with said azo-coupler compound by providing a weakly basic environment for the diazonium salt in the sheet, greater than 75% of said basic equivalents being provided by benzimidazole, at least one of said heat softenable binder layers additionally including an azo-coupler compound, and between said diazonium salt containing layer and said benzimidazole-containing layer a barrier layer, permeable, upon heating, to benzimidazole.

3. A light-sensitive, storage-stable diazotype sheet capable of rapid heat development, said sheet comprising a support bearing at least two layers, one of said layers comprising a heat-softenable polymeric binder and a dye-forming composition including an azo-coupler compound and a light-sensitive acid-stabilized diazonium salt capable of reacting with said coupler compound to form a dye, and another of said layers comprising a heat-softenable polymeric binder and an acid neutralizer capable of neutralizing said acid stabilization of said acid-stabilized diazonium salt in sufficient quantity to provide a weakly basic environment for the diazonium salt in the sheet, and to render said diazonium salt reactive with said coupler compound, greater than 75 percent of the basic equivalents of said acid neutralizer being provided by benzimidazole.

4. The sheet of claim 3 wherein said dye-forming composition comprises p-diazomorpholino-2,5- dibutoxy benzene borofluoride, acetoacetanilide, 2,7-dihydroxynaphthalene and 3-hydroxy-2-naphthoo-toluidine.

5. A light-sensitive, storage-stable diazotype sheet capable of rapid heat development comprising a support bearing at least two layers, one of said layers comprising a first heat-softenable polymeric binder containing a dye-forming composition including an azo coupler compound and a light-sensitive acid-stablized diazonium salt capable of reacting therewith to form a dye, and another of said layers comprising a second heatsoftenable polymeric binder which contains, as the sole acid neutralizer component of said sheet, a sufficient quantity of benzimidazole to neutralize said acid stabilization of said diazonium salt and to render said diazonium salt reactive with said azo coupler compound, by providing a weakly basic environment for the diazonium salt in the sheet.

6. The sheet of claim 5 wherein said second heatsoftenable polymeric binder is soluble in a non-solvent for said first polymeric binder.

7. A heat-reactive diazotype sheet having at least two layers, one of said layers comprising a heat-softenable binder material and an acid-stabilized diazonium salt capable of reacting with an azo-coupler compound to form a dye, and another of said layers comprising a heat-softenable binder material and an acid-neutralizer component capable of providing basic equivalents in an amount at least sufficient to neutralize said acid stabilization of said diazonium salt and to render said diazonium salt reactive with said azo-coupler compound by providing a weakly basic environment for the diazonium salt in the sheet, greater than of said basic equivalents being provided by benzimidazole, at least one of said layers additionally including an azo-coupler compound.

8. Thesheet of claim 7 additionally comprising, in said layer containing said diazonium salt, an acid stabilizing compound.

Claims

2. A heat reactive diazotype sheet having at least three layers, one of said layers comprising a heat-softenable binder material and an acid-stabilized diazonium salt capable of reacting with an azo-coupler compound to form a dye, another of said layers comprising a heat-softenable binder material and an acid-neutralizer component capable of providing basic equivalents in an amount at least sufficient to neutralize said acid stabilization of said diazonium salt to render said diazonium salt reactive with said azo-coupler compound by providing a weakly basic environment for the diazonium salt in the sheet, greater than 75% of said basic equivalents being provided by benzimidazole, at least one of said heat softenable binder layers additionally including an azo-coupler compound, and between said diazonium salt containing layer and said benzimidazole-containing layer a barrier layer, permeable, upon heating, to benzimidazole.
3. A light-sensitive, storage-stable diazotype sheet capable of rapid heat development, said sheet comprising a support bearing at least two layers, one of said layers comprising a heat-softenable polymeric binder and a dye-forming composition including an azo-coupler compound and a light-sensitive acid-stabilized diazonium salt capable of reacting with said coupler compound to form a dye, and another of said layers comprising a heat-softenable polymeric binder and an acid neutralizer capable of neutralizing said acid stabilization of said acid-stabilized diazonium salt in sufficient quantity to provide a weakly basic environment for the diazonium salt in the sheet, and to render said dia-zonium salt reactive with said coupler compound, greater than 75 percent of the basic equivalents of said acid neutralizer being provided by benzimidazole.
4. The sheet of claim 3 wherein said dye-forming composition comprises p-diazomorpholino-2,5-dibutoxy benzene borofluoride, acetoacetanilide, 2,7-dihydroxynaphthalene and 3-hydroxy-2-naphtho-o-toluidine.
5. A light-sensitive, storage-stable diazotype sheet capable of rapid heat development comprising a support bearing at least two layers, one of said layers comprising a first heat-softenable polymeric binder containing a dye-forming composition including an azo coupler compound and a light-sensitive acid-stablized diazonium salt capable of reacting therewith to form a dye, and another of said layers comprising a second heat-softenable polymeric binder which contains, as the sole acid neutralizer component of said sheet, a sufficient quantity of benzimidazole to neutralize said acid stabilization of said diazonium salt and to render said diazonium salt reactive with said azo coupler compound, by providing a weakly basic environment for the diazonium salt in the sheet.
6. The sheet of claim 5 wherein said second heat-softenable polymeric binder is soluble in a non-solvent for said first polymeric binder.
7. A heat-reactive diazotype sheet having at least two layers, one of said layers comprising a heat-softenable binder material and an acid-stabilized diazonium salt capable of reacting with an azo-coupler compound to form a dye, and another of said layers comprising a heat-softenable binder material and an acid-neutralizer component capable of providing basic equivalents in an amount at least sufficient to neutralize said acid stabilization of said diazonium salt and to render said diazonium salt reactive with said azo-coupler compound by providing a weakly basic environment for the diazonium salt in the sheet, greater than 75% of said basic equivalents being provided by benzimidazole, at least one of said layers additionally including an azo-coupler compound.
8. The sheet of claim 7 additionally comprising, in said layer containing said diazonium salt, an acid stabilizing compound.