US3642483A

US3642483A - Thermally developable diazotype copying materials

Info

Publication number: US3642483A
Application number: US678183A
Authority: US
Inventors: Keishi Kubo; Sadao Matsumura
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 1966-11-07
Filing date: 1967-10-26
Publication date: 1972-02-15
Anticipated expiration: 1989-02-15
Also published as: DE1597625A1; NL136527C; GB1212358A; DE1597625B2; NL6715040A

Abstract

A thermally developable diazotype copying material is manufactured which comprises a supporting sheet and a lightsensitive copying layer coated on said supporting sheet, said layer consisting of a water soluble light-sensitive diazo compound, a water soluble heat fugitive acidic salt (base generating agent) and a water insoluble coupler. Another thermally developable diazotype copying material is also obtained, which is of a similar structure but said copying layer further contains an additional component consisting of an agent for lowering the melting point of said coupler besides said diazo compound, said salt and said coupler.

Description

O United States Patent 1151 3,642,483 Kubo et a1. Feb. 15, 1972 [54] THERMALLY DEVELOPABLE 3,326,686 6/1967 Randall et a1. ..96/49 X DIAZOTYPE COPYING MATERIALS 3,360,369 11/1967 Amariti eta1.. ..96/75 3,389,995 6/ 1968 Tripp et al. ..96/49 X [72] Inventors: Keishi Kubo, Tokyo; Sadao Matsumura,

[73] Assignee: v Kabushiki Kaisha Ricoh, Tokyo, Japan 1,045,714 10/1966 Great Britain ..96/49 907,724 10/1962 Great Britain ...96l49 1 09L 1967 642,613 5/1964 Belgium ...96/75 21 A LN J 7 1 3 1,041,022 9/1966 Great Britain. ...96/75 1 pp 0 1,376,709 9/1964 ,France ...96/75 6,404,164 10/1964 Netherlands... ...96/75 [30] Foreign Application Priority Data 800,956 12/1968 Canada ..96/91 Nov. 7, 1966 Japan ..41/72900 Nov. 18, 1966 Japan ..41/75823 OTHER PUBLICATIONS D' .,R ,F .196, s2] u.s.c| ..96/75,96/49,96/91 1 ,i i i 5 epmducm Rev'ew eb 2 pp [51] lnt.Cl G03cl/60,G03c1/54,G03c1/58 & E n v 1 5 4 1961 58] Field 61 Search ..96/49, 75,91; 117/367, 36.8; 2 32;"

Primary Examiner-Charles L. Bowers, Jr. [561 Reierems Attorney-Woodhams, Blanchard and Flynn UNITED STATES PATENTS 57] ABSTRACT gfi j i 42 A thermally developable diazotype copying material is manu- 3064049 1 1,1962 C m e a [91 x factured which comprises a supporting sheet and a light-sensi- 5398 1 196 96 75 x tive copying layer coated on said supporting sheet, said layer 4 1 I a1 4 91 consisting of a water soluble light-sensitive diazo compound,a 5991 6/ l 0 euge ouer et I water soluble heat fugitive acidic salt (base generating agent) 2239'704 4/1941 de et "96/9l x and a water insoluble coupler. Another thermally developable 3,199,982 8,1965 Kash'wabara'm diazotype copying material is also obtained, which is of a 3,202,510 8/1965 Hollmann ..96/91 Similar Structure but Said copying layer further contains an 33551007 6/1966 K053: "96/91 X ditional component consisting of an agent for lowering the 3,255,011 6/1966 Welch .....96/91 X melting point of said coupler besides said diazo compound, 3,271,155 9/1966 Aebi .96/91 X said salt and said coupler. 3,301,679 1/1967 Halperin et al. ..96/91 X 2 Claims, No Drawings THERMALLY DEVELOPABLE DIAZOTYPE COPYING MATERIALS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is concerned with thermally developable diazotype copying materials having features which are represented particularly by the markedly improved color developing ability and shelf life, which are manufactured by forming, on the supporting sheet, a light-sensitive layer containing a light-sensitive diazo compound, a base generating agent consisting of a water soluble heat fugitive acidic salt and a coupler, or by the provision of a light-sensitive layer containing said respective components and additional agent for lowering the melting point of said coupler.

2. Description of the Prior Art Among the conventional, thermally developable diazotype copying materials, it is known to use those having the structure which comprises (1) a support sheet carrying thereon a light-sensitive copying layer containing a water soluble lightsensitive diazo compound, a water soluble coupler and a base generating agent consisting of a nitrogen-bearing compound, and those having the structure wherein (2) a mixture of a water insoluble or hardly soluble light-sensitive diazo compound, a coupler having an insoluble or hardly soluble nature and an alkaline component all of which are in the form of fine particles and constitute a light-sensitive layer dispersed in a binder which is adapted to unite the light-sensitive layer to the supporting sheet. However, the first-mentioned copying materials had the shortcoming that, during storage, the base generating agent became dispersed and was transferred into the supporting sheet even at normal temperature, resulting in a reduction in the developing ability (or color developing ability). Accordingly, when prior art copying materials which had undergone such degenerating changes of the copying layers were exposed to actinic light under originals and were then subjected to heat development, the result of their development was often found to be poor in quality so that it was impossible to obtain prints having a satisfactory image density. This shortcoming of the prior art copying materials was compensated for either by increasing the base generating agent content of the light-sensitive layer or by conducting the development at a temperature slightly higher than the proper development temperature for these copying materials. However, the inclusion of the base generating agent in the lightsensitive layer to an extent more than the necessary amount led to the formation of a large amount of products resulting from thermal decomposition, during the process of heat development, hampering the proper development of the transferred image. Not only that, but also such an inclusion of an excess amount of a base generating agent caused these heat decomposition products to adhere to the face of the portions of the sheet carrying the printed image, which stained the print. Furthermore, when the development was conducted at such an elevated temperature, a part of the light-sensitive diazo compound tended to decompose and, as a result, the print did not have a satisfactory image density. The secondmentioned prior art copying materials carrying a light-sensitive layer consisting of fine particle components had the shortcoming that the coupling velocity (or the color developing velocity) of the light-sensitive diazo compound and the coupler contained in the light-sensitive layer was somewhat smaller than that of said first-mentioned copying materials having their light-sensitive layers made with a water-soluble light-sensitive component, and involved a difficulty in forming a clear image on the print.

SUMMARY OF THE INVENTION It is, therefore, the primary object of the present invention to eliminate the aforesaid shortcomings of the prior art and to provide thermally developable diazotype copying materials having superior copying ability, by forming a light-sensitive layer with the principal components consisting of a combination of a water soluble light-sensitive diazo compound, a water insoluble coupler with or without an agent for lowering the melting point of said coupler, and a base generating agent consisting of a water soluble heat fugitive acidic salt.

Another object of the present invention is to provide thermally developable diazotype copying materials which permit the color development at an increased velocity during the development process and which permit the formation of clear images on the prints and which are of a markedly improved shelf life.

The water soluble light-sensitive diazo compounds which are used in the present invention are double salts of zinc chlorides or cadmium chlorides and the compounds which include, for example:

P-dimethyl-aminobenzene-diazonium chloride,

P-diethyl-aminobenzene-diazonium chloride,

P-methyl-hydroxyethyl-aminobenzene-diazonium chloride,

and P-ethyl-hydroxyethyl-aminobenzene-diazonium chloride. The water insoluble couplers which are used in the present invention include, for example, 2,3-dihydroxy-naphthalene, 2,3-dihydroxy-6-sulfonamide-naphthalene, 2,3-dihydroxy-6- dihydroxyethyl sulfonamide-naphthalene, l-carboxy-2,3- dihydroxy-naphthalene, 1 ,4-dichloro-2 ,3-dihydroxynaphthalene, and 3,3'-dihydroxy-Z-naphthanilide. These water insoluble couplers are used in the form of fine particles or powder.

The water soluble heat fugitive acidic salts include, for example, such water soluble salts which are the compounds formed with the substances of the following two groups: (1) water soluble heat fugitive acids which are represented, for example, by halogenoacetic acids such as monochloroacetic acid, dichloroacetic acid and trichloroacetic acid; derivatives of acetic acid, such as cyanoacetic acid and halogenomalonic acid such as dichloromalonic acid, and (2) alkali metals such as sodium and potassium, or basic components such as ammonia, ethanolamine and isopropylamine. According to the present invention, these salts are added to said diazo compound in an amount preferably ranging from 4 parts by weight to 7 parts by weight per part by weight of such a diazo compound.

The agents for lowering the melting points of the couplers, which are used in the present invention, include guanidine-tartaric acid salt (having a melting point of 164 C.) and the derivatives of guanidine which include, for example:

Aminoguanidine-hydrochloric acid salt (melting point being 163 C.),

Cyanoguanidine (melting point being 208 C.),

Ethylbiguanide-hydrochloric acid salt (melting point being Dimethylbiguanide-hydrochloric acid salt (melting point being 216 C.),

3-methoxy benzoguanidine (melting point being 204 C.

l-butyl-B-nitroguanidine (melting point being 84 C. and

2-guanyl phthalic acid amide (melting point being 166 C.

Said agents further include acid amides such as acetamide (melting point being 82 C.), acrylamide (melting point being 85 C.), propionamide (melting point being 79 C.), butylamide (melting point being 116 C.) and malonamide (melting point being C.). The aforesaid agents for lowering the melting points of the couplers are invariable water soluble.

The present invention is concerned, therefore, with copying materials which are formed by providing, on a supporting sheet such as paper, precoated paper and plastic foil, a lightsensitive layer which consists of an appropriate combination of the aforesaid respective components constituting a lightsensitive layer.

Next, description will be directed to one example of the present invention to explain in detail the ability and the effect accruing therefrom of the copying materials of the present invention. Said one example of the present invention is represented by a thermally developable diazotype copying material having a structure wherein a supporting sheet carries thereon a light-sensitive layer containing the following three components, i.e., one of the aforesaid diazo compounds, one of the aforesaid couplers and one of the aforesaid water soluble salts. This coping material is featured by an extremely increased development velocity which is displayed when the exposed copying material is subjected to the development process, as compared with conventional copying materials. This difference can be explained by the following facts. The conventional copying materials employing, as the base generating agent in general, a nitrogen-bearing compound such as urea or the derivatives thereof present impaired color developing ability at the time of heat development for the reasons that have been stated previously, with the result that the obtained prints do not have a satisfactory color density. In contrast to this, the base generating agent of the present invention employs a water soluble heat fugitive acidic salt such as monochloroacetic acid, dichloracetic acid and trichloroacetic acid, so that the color development velocity of the copying material of the present invention containing such a base generating agent increases, and accordingly, a print bearing a satisfactory image density is obtained.

However, these heat fugitive acidic salts have a tendency to cause the occurrence of a premature coupling phenomenon which is represented by the coupling between the light-sensitive diazo compound and the coupler both of which are contained in the light-sensitive layer, which takes place at normal temperature, leading to the fog phenomenon which impairs the shelflife of the copying materials. Therefore, when it is intended to use a nitrogen-bearing compound as the base generating agent, it is necessary to explore the color development agents to improve the color development ability which is to be displayed at the time heat development is conducted. Contrariwise, when it is intended to use heat fugitive acidic salts, it is necessary to use a color development suppressing agent for preventing the occurrence of this fog phenomenon. As a means for suppressing the color development, it is considered useful to form an intermediate layer consisting of a waxlike substance for being interposed between the light-sensitive diazo compound and the coupler. However, the formation of such an intermediate layer will impair satisfactory coupling between the light-sensitive diazo compound and the coupler at the time of the heat treatment, resulting in a marked deterioration in the color development of the obtained image on the print.

According to the present invention, however, the occurrence of the aforesaid premature coupling phenomenon is arrested by the particular use ofthe water insoluble couplers. By virtue of the use of these water insoluble couplers, there hardly takes place a coupling between the light-sensitive diazo compounds and the couplers at normal temperature even where the water soluble heat fugitive acidic salts have undergone decomposition to some extent, so that, as a result, there occurs no impairment of the color development in the image formed on the print obtained. Instead, the coupler gains its coupling activity for the first time from the heat development, and the coupler is allowed, by this heat treatment, to be united with the water soluble light-sensitive diazo compound to quickly form a dye image. The adoption of the water insoluble couplers in the present invention thus contributes to the provision of thermally developable copying materials which are of superior color developing ability and an improved shelf life.

According to the present invention, the copying materials may be made by first applying a coupler onto the supporting sheet and then applying a mixture ofa diazo compound and a water soluble heat fugitive acidic salt to the resulting first layer to form a light-sensitive layer on the supporting sheet. Or, alternatively, the light-sensitive layer may be formed by applying a mixture of the aforesaid three components onto the supporting sheet. However, the former copying material of the present invention which carries a light-sensitive layer consisting of the aforesaid two layers, i.e., a first layer of coupler and a second layer consisting of said mixture is somewhat superior in shelf life to the latter copying material which is a single layer type. In each of these two types of copying materials, however, the water insoluble coupler is provided in the form of a solution such that the coupler is dispersed in a vinyl acetate emulsion.

According to the present invention, the aforesaid series of agents adapted for lowering the melting point of the couplers are provided as one of the components constituting the lightsensitive layer in order to further improve the color developing ability of the coping materials during the development process.

Now, the inclusion, in the light-sensitive layer, of a water soluble agent, such as guanidine, its derivatives and acid amides, adapted for lowering the melting point of the coupler jointly with the other components constituting the light-sensitive layer, or the inclusion of such an agent in the layer of the aforesaid water insoluble coupler, leads to a markedly lowered eutectic point of the water insoluble coupler by virtue of the multiplying action effected by the coupler and the agent, with the result that the velocity of coupling (or the color development velocity) between the light-sensitive diazo compound and the coupler at the time of heat development is further increased, leading to an improved color developing ability as well as the materialization of high density images on the prints obtained. This improved color developing ability of copying materials permits a reduction in the contacting time of the heated rollers. This reduced contacting time of the heated rollers, in turn, leads to the advantages that not only the manufacture of copying apparatuses is economized by the simplified developing mechanism which is incorporated in such apparatuses, but also the production of copying apparatuses of compact size becomes possible.

Next, some examples of the eutectic points resulting from the addition of the aforesaid compounds which give an eutectic effect to the water insoluble couplers are shown in the following t a ble.

As is clear also from the above table, it is desirous that the agent for lowering the melting point of the coupler be admixed to the coupler inan amount which is represented by the eutectic ratio by weight. Ordinarily, however, the agent is added in an amount ranging from 0.14 parts by weight to 0.25 parts by weight per part by weight of the coupler used.

As has been understood from the foregoing description, the present invention is concerned with thermally developable diazotype copying materials which thoroughly satisfy various requirements, such as the instantaneously effected coupling at a low temperature and the improved shelf life, which are demanded of thermally developable diazotype copying materials.

DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE 1 To said solution (A) containing a light-sensitive diazo compound was added said solution (B) prepared by dispersing a water-insoluble coupler in a vinyl acetate emulsion. The lightsensitive solution which was obtained from thoroughly dispersing (B) in (A) was applied to a supporting sheet and was dried. As a result, a thermally developable diazotype copying material was obtained.

An original was placed on the copying material thus obtained and the resulting assembly was exposed to actinic light by irradiating ultraviolet rays thereto. Thereafter, the exposed sheet was subjected to heat development by passing it over a roller heated to a temperature ranging from 140 to 160 C. for 2 to 3 seconds, and a print bearing a clear blue image was obtained.

A comparison of shelf life between the copying material of the present invention and a conventional copying material (whose light-sensitive layer contains a water soluble coupler and 2,3-dihydroxy-naphthalene-fi-sodium sulphate) was conducted by subjecting these two copying materials to coercive ageing by preserving them under the conditions consisting of a temperature which was 50 C. and a relative humidity which was 20 percent. More specifically, these two copying materials which have undergone coercive ageing for a predetermined period of time were exposed and developed in a manner as described above. It was confirmed that the copying material of the present invention showed an improved shelf life which was two to three times longer than that of the conventional copying material.

EXAMPLE 2 Solution (A):

Water 80 cc. P-dimethyl-aminobenzene diazonium chloride-zinc chloride double salt l.0 g. Trietha nolamine trichloroacetate 6.0 g. Tartaric acid 0.6 g. Solution (B):

Water 20 cc. 2,3-dihydroxy-6-sulfonamide-naphthalene 3.0 g.

Vinyl acetate emulsion (content: 50%) 4.0 g.

The light-sensitive solution (A) containing a light-sensitive diazo compound was admixed with the solution (B) prepared by dispersing a water insoluble coupler in a vinyl acetate emulsion which was then thoroughly dispersed in said solution (A). The resulting light-sensitive solution was applied to a supporting sheet and was dried, and thus, a thermally developable diazotype copying material was obtained.

An original was placed on the face of the light-sensitive layer of the copying material thus obtained and they were exposed to actinic light which was done by the application of ultraviolet rays thereto, and this was followed by heat development conducted by passing the exposed sheet over a roller heated to a temperature ranging from 140 to 160 C. for 2 to 3 seconds. As a result, a print bearing a very clear blue image was obtained.

This copying material showed a shelf life which was in the order similar to that of the copying material of the present invention obtained in Example 1.

EXAMPLE 3 Water I00 cc. 2.3-dihydroxy-fi-sulfonamide-naphthalene 3.5 3. Vinyl acetate emulsion (content: 50%) 4.0 3. Fine powder of silica (grain size: l-5 microns) 2.0 g.

The above solution was applied to the face of a supporting sheet and was dried to form a coupler-bearing layer. Thereafter, a light-sensitive solution containing a light-sensitive diazo compound consisting of:

Water cc P-ethyl-hydroxyethyl-aminobenzene diazonium chloride-zinc chloride double salt l.0 g. Sodium trichloroacerate 6.0 g. Tartaric acid 0.5 g .Saponin 0.l g

was applied to the upper face of the aforesaid coupler-bearing layer and was dried. Thus, a thermally developable diazotype copying material was obtained.

An original was placed on the light-sensitive layer of the copying material thus obtained. The assembly was exposed to actinic light which was done by applying ultraviolet rays thereto. Thereafter, the exposed sheet was subjected to heat development by passing it over a roller heated to -160 C. for 2 to 3 seconds. As a result, a print bearing a very clear blue image was obtained. This copying material was found to be of an improved shelf life which was nearly 20 percent superior to those of the copying materials obtained in Examples 1 and 2.

EXAMPLE 4 Solution (A):

Water 80 cc. P-ethyl-hydroxy-ethyl-aminobenzene diazonium chloridezinc chloride double salt l.0 g. Sodium trichloroacetate 6.0 g. Tartaric acid 0.6 g. Cyanoguanidine 0.5 g. Saponin 0.1 g. Solution (B):

2,3-dihydroxy-naphthalene 2.0 g. Vinyl acetate emulsion (content: 50%) 4.0

To the above solution (A) was added the solution (B) and the resulting solution was thoroughly mixed. This mixture solution was then applied to the upper face of a supporting sheet and was dried, with a result that a thermally developable diazotype copying material was obtained. An original was placed on the face of the light-sensitive layer of the copying material, and ultraviolet rays were irradiated thereto to perform exposure. Thereafter, the exposed sheet was heatdeveloped by passing it over a roller heated to 140-150 C. for 2 to 3 seconds, with the result that a print bearing a very clear blue image was obtained. The color density of this blue image and the color density of the image obtained according to the present invention in Example 1 were measured by the use of a reflection densitometer. It was confirmed that the image density of the present example was 15 to 20 percent superior to that of the latter. Furthermore, the shelf life of the product of this example was measured by means of a coercive ageing in a manner similar to that described in Example l. [t was noted that the inclusion of an agent for lowering the melting point of the coupler in the light-sensitive layer gave rise to no adverse effect.

EXAMPLE 5 Solution (A):

Water 80 cc. P-diethyl-aminobenzene diazonium chloridezinc chloride double salt 1.0 g. Trichloroacetic acid diisopropylarnine 6.0 g. Tartaric acid 0.6 g. Dimethylbiguanide (hydrochloride) 0.4 g.

Saponin 0.l g. Solution (B):

Water 20 cc. 2,3-dihydroxy-6sulfonamide-naphthalene 3.0 g. Vinyl acetate emulsion (content: 50%) 4.0 g.

After adding the above solution (B) to the solution (A) and thoroughly mixing them together, the resulting mixed solution was applied onto the upper face of a supporting sheet and was dried, with the result that a thermally developable diazotype copying material was obtained. After processing this copying sheet and heat developing the same in a manner similar to that described in Example 4, a print bearing a very clear blue image was obtained. The image density and the shelf life of this copying material were both noted to be in the same order to those of the copying material obtained in Example 4,

EXAMPLE 6 Water 100 cc. 2,3-dihydtoxy-6-sulfonamide-naphthalene 3.5 g. Vinyl acetate cmulsion (content: 50%) 4.0 g. Fine particles nt'silicu (grain size: l-S microns) 2.0 g. Aminoguanidine (hydrochloride) 0.5 g.

The above solution was applied onto a supporting sheet and was dried to form a layer containing a coupler. Thereafter, the upper face of this coupler-bearing layer was coated with a light-sensitive solution consisting of the following components:

Water 100 cc. P-methyl-hydroxyethyl-aminobenzene diazonium chloride zinc chloride double salt 1.0 g. Sodium trichloroacetate 6.0 g. Tartaric acid 0.5 g. Saponin O.l g.

and was dried, with the result that a thermally developable diazotype copying material was obtained. An original was placed on the upper face of the light-sensitive layer of this copying material. Exposure was conducted by irradiating ultraviolet rays onto the assembly. Then heat development was conducted by passing the exposed sheet over a roller heated to l40-l50 C. for 2 to 3 seconds. As the result, a print bearing a very clear blue image was obtained. It was confirmed that this copying material had an image density and a shelf life which were improved by nearly 20 percent over those of the copying materials obtained in Examples 4 and 5.

What is claimed is:

l. A thermally developable diazotype copying material having on one surface of a supporting member a light-sensitive layer comprising a binder resin having dispersed therein a diazonium compound, an azo coupling compound, a base generating agent, an acidic stabilizer and a compound for lowering the melting point of said azo compound, in which a. said diazonium compound is a water-soluble, light-sensitive, diazonium compound selected from the group consisting of zinc chloride and cadmium chloride double salts of p-dimethyl-aminobenzene diazonium chloride, pdiethyl-aminobenzene diazonium chloride, p-methylhydroxyethyl-aminobenzene diazonium chloride and pethylhydroxyethyl-aminobenzene diazonium chloride;

b. said base generating agent is a water-soluble, heat-fugitive, acidic salt selected from the group consisting of a1- kali metal salts, ammonium salts, ethanolamine salts and isopropylamine salts of halogenoacetic acids, cyanoacetic acid and halogenomalonic acids;

c. said azo coupling compound is a water-insoluble azo coupling compound uniformly dispersed in said layer in the form of fine particles, said compound being selected from the group consisting of 2,3-dihydroxy-naphthalene, 2,3-dihydroxy-fi-sulfonamide-naphthalene, 2,3-dihydroxy-G-dihydroxyethyl sulfonamide-naphthalene, l-carboxy- 2,3-dihydroxy naphthalene, l,4-dichloro-2,3-dihydroxy naphthalene and 3,3-dihydroxy-Z-naphthanilide; and

(1. said compound for lowering the melting point of said azo coupling compound is a water-soluble compound selected from the group consisting of guanidine-tartaric acid salt, aminoguanidine-hydrochloric acid salt, cyanoguanidine, ethylbiguanide-hydrochloric acid salt, dimethylbiguanide-h drochloric acid salt, 3-methoxy benzoguanldtne, -butyl-3-nitroguanrdine, Z-guanyl phthalic acid amide, acetamide, acrylamide, propionamide, butylamide and malonamide, the amount of said compound for lowering the melting point being in the range of 0.14 to 0.25 part by weight per one part by weight of said azo coupling compound and forming a eutectic with the azo coupling compound.

2. A thermally developable diazotype copying material having on one surface of a supporting sheet a two-layer light-sensitive coating comprising a diazonium compound, an azo coupling compound, a base generating agent, an acidic stabilizer and a compound for lowering the melting point of said azo coupling compound, in which a. the first layer consists of a binder resin containing a water-insoluble azo coupling compound uniformly dispersed in said binder resin in the form of fine particles and a compound for lowering the melting point of said azo coupling compound, said azo coupling compound being selected from the group consisting of 2,3-dihydroxy-naphthalene, 2,3-dihydroxy-naphthalene-6-sulfonamide-naphthalene, 2,3-dihydroxy-6-dihydroxyethyl-sulfonamide-naphthalene, l-carboxy-2,3-dihydroxynaphthalene, l,4-dichloro-2,3-dihydroxy-naphthalene and 3,3'-dihydroxy-2-naphthanilide; and said compound for lowering the melting point of said azo coupling compound being selected from the group consisting of guanidine-tartaric acid salt, amino-guanidine-hydrochloric acid salt, cyanoguanidine, ethylbiguanide-hydrochloric acid salt, dimethyl-biguanide-hydrochloric acid salt, 3- methoxy benzoguanidine, l-butyl-3-nitroguanidine, 2- guanyl phthalic acid amide, acetamide, acrylamide, propionamide, butylamide and malonamide, the amount of said compound for lowering the melting point being in the range of 0.14 to 0.25 part by weight per one part by weight of said azo coupling compound and forming a eutectic with the azo coupling compound;

b. a second layer containing a water-soluble, light-sensitive diazonium compound, a water-soluble, heat-fugitive, acidic salt as the base generating agent and an acidic stabilizer, said second layer overlying said first layer, said diazonium compound being selected from the group consisting of zinc chloride and cadmium chloride double salts of p-dimethyl-aminobenzene diazonium chloride, pdiethyl-aminobenzene diazonium chloride, p-methylhydroxyethyl-aminobenzene diazonium chloride and pethylhydroxyethyl-aminobenzene diazonium chloride, and said heat-fugitive acidic salt being selected from the group consisting of alkali metal salts, ammonium salts, ethanolamine salts and isopropylamine salts of halogenoacetic acids, cyanoacetic acid and halogenomalonic acids.

Claims

2. A thermally developable diazotype copying material having on one surface of a supporting sheet a two-layer light-sensitive coating comprising a diazonium compound, an azo coupling compound, a base generating agent, an acidic stabilizer and a compound for lowering the melting point of said azo coupling compound, in which a. the first layer consists of a binder resin containing a water-insoluble azo coupling compound uniformly dispersed in said binder resin in the form of fine particles and a compound for lowering the melting point of said azo coupling compound, said azo coupling compound being selected from the group consisting of 2,3-dihydroxy-naphthalene, 2,3-dihydroxy-naphthalene-6-sulfonamide-naphthalene, 2,3-dihydroxy-6-dihydroxyethyl-sulfonamide-naphthalene, 1-carboxy-2,3-dihydroxy-naphthalene, 1,4-dichloro-2,3-dihydroxy-naphthalene and 3,3-dihydroxy-2-naphthanilide; and said compound for lowering the melting point of said azo coupling compound being selected from the group consisting of guanidine-tartaric acid salt, amino-guanidine-hydrochloric acid salt, cyanoguanidine, ethylbiguanide-hydrochloric acid salt, dimethyl-biguanide-hydrochloric acid salt, 3-methoxy benzoguanidine, 1-butyl-3-nitroguanidine, 2-guanyl phthalic acid amide, acetamide, acrylamide, propionamide, butylamide and malonamide, the amount of said compound for lowering the melting point being in the range of 0.14 to 0.25 part by weight per one part by weight of said azo coupling compound and forming a eutectic with the azo coupling compound; b. a second layer containing a water-soluble, light-sensitive diazonium compound, a water-soluble, heat-fugitive, acidic salt as the base generating agent and an acidic stabilizer, said second layer overlying said first layer, said diazonium compound being selected from the group consisting of zinc chloride and cadmium chloride double salts of p-dimethyl-aminobEnzene diazonium chloride, p-diethyl-aminobenzene diazonium chloride, p-methyl-hydroxyethyl-aminobenzene diazonium chloride and p-ethylhydroxyethyl-aminobenzene diazonium chloride, and said heat-fugitive acidic salt being selected from the group consisting of alkali metal salts, ammonium salts, ethanolamine salts and isopropylamine salts of halogenoacetic acids, cyanoacetic acid and halogenomalonic acids.