GB1565043A

GB1565043A - Dry processing type recording elemnts

Info

Publication number: GB1565043A
Application number: GB1279278A
Authority: GB
Original assignee: Fuji Photo Film Co Ltd
Current assignee: Fujifilm Holdings Corp
Priority date: 1977-04-05
Filing date: 1978-03-31
Publication date: 1980-04-16
Also published as: DE2814732A1; JPS53123918A

Description

(54) DRY PROCESSING TYPE RECORDING ELEMENTS (71) We, FUJI PHOTO FILM CO., LTD., a Japanese Company, of No.

210, Nakanuma, Minami Ashigara-Shi, Kanagawa, Japan, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a dry processing type recording element, and more particularly to a technique for improving the whiteness in non-image areas and for preventing the deterioration of whiteness in non-image areas with the passage of time after heat development processing of a thermally-developable dry processing type recording element containing an organic silver salt and a reducing agent for the organic silver salt or a thermally-developable dry processing type recording element rendered light-sensitive by the addition of a photocatalyst together with the above described organic silver salt and reducing agent (usually designated a thermally-developable light-sensitive element).

Dry processing type recording methods in which a sheet containing an organic silver salt such as silver behenate or silver saccharin and a compound capable of reducing the organic silver salt when heated (a reducing agent) is partially heated using a heat pen or infrared radiation to form a silver image as the result of an oxidation-reduction reaction only at the heated area and dry processing type recording elements therefor are known.

The above described sheet can also be used as an image receiving sheet in combination with a light-sensitive sheet containing a light-sensitive reducing agent which is photoactive. That is, when the light-sensitive sheet containing such a reducing agent is imagewise exposed and heated in contact with an image receiving sheet containing an organic silver salt and a reducing agent described above, the light-sensitive reducing agent in the light-sensitive sheet is thermally transferred depending on the presence or absence of the exposure and accelerates the reduction of the organic silver salt in the transfer area to form a silver image as described in U.S. Patents 3,094,417; 3,526,506 and 3,674,479.

Further, a photocatalyst (a light-sensitive heavy metal salt such as a silver halide) is added to the above described sheet containing an organic silver salt and a reducing agent such that the photocatalyst is in contact with the organic silver salt to prepare a light-sensitive and heat-sensitive recording element as described in U.S.

Patents 3,152,904 and 3,457,075. Such a light-sensitive and heat-sensitive recording element is usually designated a thermally developable light-sensitive element or Dry Silver (tradename, produced by 3M Co.) and this element is stable at normal temperature. However, silver is produced in the light-sensitive layer, when heated usually to 800C or higher, more preferably to 100 C or higher after imagewise exposure to light, due to an oxidation-reduction reaction between the organic silver salt as an oxidizing agent and the reducing agent in the light-sensitive layer caused by the catalytic action of metallic nuclei formed by the exposed photocatalyst in proximity to the oxidizing agent and the reducing agent therein. As a result, the exposed areas of the light-sensitive and heat-sensitive layer are rapidly blackened by the production of silver which results in an image being formed due to the difference in the contrast between the exposed areas and the unexposed areas (background) thereof.

In this light-sensitive system, the silver halide remaining in the light sensitive element following development is not stabilized against light but is allowed to discolor in the presence of light In spite of the discoloration, the system provides the same effects as those obtained in a system where silver halide is stabilized against light The reason is because the silver salt present in the light sensitive element comprises a minor amount of silver halide and a major amount of a white or slightly colored organic silver salt which is relatively stable to light and is not thereby discolored, and even if a minor amount of silver halide is discolored by light, the light-sensitive layer remains white or only slightly colored overall, so that the minor amount of discoloration scarcely adversely affects the visual appearance.

However, such a dry processing type recording element containing at least an organic silver salt and a reducing agent or a light sensitive dry processing type recording element (a thermally-developable light-sensitive element) has an undesirable characteristic in that coloration frequently occurs in the non-image areas.

This coloration of the non-image areas is not only based on factors which are inherent in view of the production of these recording materials, for example, the original color of the support (conventionally a paper) or the color of additives which are optionally used such as sensitizing dyes, but also due to a thermal reaction between the organic silver salt and the reducing agent by heat which is inadvertently applied or a print-out of the photo-catalyst on storage or after the development processing (which can be substantially ignored under usual conditions but becomes visible after a long period of tirade or under severe conditions).

Various means which are effective for preventing the coloration of non-image areas are known. Of these means, the technique in which a layer containing a fluorescent whitening agent is applied to a support in order to improve the whiteness is known in the field of conventional gelatino-silver halide photographic lightsensitive elements. The fluorescent whitening agents used in the field of gelatin- silver halide photographic light-sensitive elements are appropriately selected from a wide range of types of compounds, for example, dinminostilbenedisuffonic acids, imidazoles, coumarins, etc. This is because the interactions between the silver halide or other additives remaining in the photographic layer and the fluorescent whitening agent can be substantially ignored since a gelatino-silver halide photographic lightsensitive element is exposed and developed and then the unexposed silver halide is stabilized or fixed. Therefore, a main requirement in selecting a fluorescent whitening agent for use in the field of gelatino-silver halide photographic light-sensitive elements is that the fluorescent whitening agent does not interact with a developing agent present in a developer solution. This requirement also is not very strict since the developing agent is washed out from the light-sensitive layer or inactivated after development in most cases.

On the contrary, in the field of dry processing type recording elements containing at least an organic silver salt and a reducing agent to which the present invention relates, the interaction between the reducing agent and the fluorescent whitening agent is an inevitable problem because the reducing agent is neither removed from the recording element nor inactivated after development. In addition, the presence of the organic silver salt is a more serious problem. Since the organic silver salt remains in the recording element after development, the organic silver salt may interact with the fluorescent whitening agent and decrease the effects of the fluorescent whitening agent. Further, the fluorescent whitening agent may be act on the organic silver salt on storage before development resulting in a deterioration of the photographic properties.

In fact, typical fluorescent whitening agents used in gelatino-silver halide photographic light-sensitive elements are not effective in or even adversely affect dry processing type recording elements such as those of the present invention as illusstrated in the comparative examples hereinafter.

Therefore, when a fluorescent whitening agent used in the dry processing type recording elements such as those of the present invention is selected, particular atten tion must be given to two points: that the fluorescent whitening agent is not affected, not only by the reducing agent but also by the organic silver salt, and that the fluorescent whitening agent does not affect either the reducing agent or the organic silver salt. Thus, the idea that fluorescent whitening agents which can be used in conventional gelatino-silver halide photographic light-sensitive elements would also simply be usable dry processing type recording elements is not correct.

Since fluorescent whitening agents which can be used in dry processing type recording elements according to the present invention must meet these severe requirements described above, a fluorescent whitening agent which satisfactorily fulfills these requirements has not been known hitherto.

It is also known that titanium dioxide can be used in order to increase the whiteness of non-image areas. However, in dry processing type recording elements, such as those of the present invention, it is not desirable to use titanium dioxide foi the purpose of increasing in the whiteness although it may be used as a photocatalyst.

The reason is because titanium dioxide releases an electron upon irradiation and results in the formation of fog due to light.

Accordingly, a first object of the present invention is to provide a dry processing type recording element in which the whiteness in the non-image areas is improved.

A second object of the present invention is to provide a dry processing type recording element in which the deterioration of whiteness in the non-image areas on storage or with the passage of time after processing is prevented.

A third object of the present invention is to provide a light-sensitive dry processing type recording element in which the whiteness in the non-image areas is improved.

A fourth object of the present invention is to provide a dry processing type recording element which has both superior photographic properties and improved whiteness.

Another object of the present invention is to provide a fluorescent whitening agent suitable for use in a dry processing type recording element containing at least an organic silver salt and a reducing agent.

The objects are attained according to the present invention.

One embodiment of this invention provides a dry processing type recording element comprising a support having, directly or indirectly, thereon one or more layers containing at least (a) an organic silver salt and (b) a reducing agent, wherein (c) at least one compound represented by the following general formula (I)

wherein A represents a

group, a

group or a

group and R represents the atoms necessary to form a 2-benzoxazolyl group which may be substituted with one or more substituents which do not hinder the fluorescent whitening function of the compound represented by the general formula (I) is present in the support or in at least one layer on the support: In another embodiment the present invention provides a dry processing type recording element as described above in which the recording element further contains (d) a photocatalyst in proximity with the organic silver salt (a).

The fluorescent whitening agent, component (c), in the present invention is more specifically illustrated by the following general formula (it), (III) or (IV):

wherein R1 and R2 which may be the same or different, each represents a hydrogen atom or a substituent which does not hinder the fluorescent whitening function of the compound. Most preferred examples of such substituents include an alkyl group having 1 to 5 carbon atoms such as a methyl group, an ethyl group, a propyl group, a butyl group, a t-butyl group or an amyl group, an allyl group, a phenyl group and a naphthyl group.

Specific examples of particularly preferred compounds of the general formula (I) above are illustrated below.

According to the present invention, component (c) described above is incorporated into the support or at least one layer applied to the support. The layer in which component (c) is incorporated can be a subbing layer on the support, a recording layer or an over-coating layer. Particularly preferred results are obtained when component (c) is incorporated into the support or a subbing layer. In particular, when component (c) is incorporated into a subbing layer, markedly superior results are obtained.

The amount of the component (c) used can be best determined routinely by trial and error. Where the amount of component (c) used is too small, the effects of increasing the whiteness are reduced. On the other hand, where component (c) is used in an excess amount, some problems occur because of the color of the com- ponent (c) itself and because yellowing occurs. Accordingly, where component (c) is incorporated into a layer other than a recording layer or a support, component (c) is used in an amount of from about 1 mg to about 400 mg, preferably from 5 mg to 50 mg, per m2 of the support. Where component (c) is incorporated into a recording layer, component (c) is employed in an amount of from about 0.01 g to about 100 g, preferably from 0.1 g to 20 g, per mole of the organic silver salt (a). Where component (c) is incorporated into the support a suitable amount ranges from about 1 mg to about 400 mg per m2 of the support for either a porous support material or a non-porous support material.

In order to incorporate component (c) into a support, where the support is a porous material such as a paper, a cloth or a synthetic paper, several methods, for example, sizing, spraying a solution containing component (c) onto the support or immersing the support in a solution containing component (c), can be employed.

Where the support is not a porous material, such as a synthetic resin films component (c) is incorporated into a solution of the synthetic resin during production of the synthetic resin film.

In order to incorporate component (c) into a layer on a support, component (c) can be added to a coating solution for that layer. The addition is preferably carried out in the form of a solution or dispersion of component (c).

The term "recording layer" is used in the present invention to describe a layer containing component (a) and component (b), each described in detail hereinafter, or layers which contain these components separately and which are coated on a support directly or on a subbing layer which was previously coated on a support (referred to as a "heat-sensitive layer" hereinafter).

The term "recording layer" as used in the present invention also includes a layer containing a photocatalyst, component (d), in proximity with component (a) in addition to component (a) and component (b) in the same manner as described above (referred to as a light-sensitive and heat-sensitive layer hereinafter).

The organic silver salt, which is used as component (a) in the present invention, can be a colorless, white or slightly colored silver salt, capable of reacting with a reducing agent, imagewise or in the presence of an exposed photocatalyst, on heating at a temperature of about 80C or higher, preferably 100 C or higher, and then forming silver (image). Suitable organic silver salts which can be used include silver salts of organic compounds containing an imino group, a mercapto group or a thione group, or a carboxyl group. Specific examples of suitable organic silver salts which can be used as component (a) in the present invention include the following compounds: (1) Silver salts of organic compounds containing an imino group: For example, silver salts as disclosed in Japanese Patent Application (OPI) 22431/1976 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application".), e.g., silver benzotriazole, silver saccharin, silver phthalazinone, and silver phthalimide, etc.; (2) Silver salts of compounds containing a mercapto group or a thione group: For example, silver salts as disclosed in Japanese Patent Application (OPI) 22431/1976. U.S. Patents 3,933,507, and 3,785,830, e.g., silver 2-mercaptobenzoxazole, silver mercaptooxadiazole, silver 2-mercaptobenzothiazole, silver 2mercaptobenzimidazole and silver 3-mercapto-4-phenyl-1,2,4-triazole, etc; (3) Silver salts of organic compounds containing a carboxyl group: For example: (A) Silver salts of aliphatic carboxylic acids; silver salts as disclosed in Japanese Patent Application (OPI) 22431/1976, U.S. Patent 3,457,075 and Japanese Patent Application (OPI) 99719/1975, e.g., silver laurate, silver myristate, silver palmitate, silver stearate, silver arachidonate, silver behenate, silver salts of aliphatic carboxylic acids having 23 or more carbon atoms, silver adipate, silver sebacate, and silver hydroxystearate, etc.; (B) Silver salts of aromatic carboxylic acids; silver salts as disclosed in Japanese Patent Applications (OPI) 22431/1976 and 99719/1975, e.g., silver benzoate, silver phthalate, silver phenylacetate, and silver 4'-n-octadecyloxydiphenyl4-carboxylate, etc.; (4) Other silver salts: For example, silver salts as disclosed in Japanese Patent Applications (OPI) 22431/1976 and 93139/1970, e.g., silver 4-hydroxy-4-methyl- 1,3,3a,7-tetrazaindene, and silver 5-methyl-7-hydroxy-1 ,2,3,4,6-pentazalndene.

These organic silver salts can be prepared using various methods, e.g., as described in U.S. Patents 3,457,075, 3,458,544, 3,700,458, and 3,839,049, British Patents 1,405,867 and 1,173,426, and 1,408,123, Japanese Patent Applications (OPI) 22431/1976, 116024/1975, 134421/1975, 122011/1976 and 57111/1977. These organic silver salts can be easily prepared according to these methods.

Of these organic silver salts thus prepared, an organic silver salt having a grain size of from about 10 microns to about 0.01 micron and more particularly, from about 5 microns to about 0.1 micron, in length is preferred.

Of the above-described organic silver salts, an organic silver salt which is relatively stable to exposure to light is suitable. Even further, of these silver salts, a silver salt of a long-chain aliphatic carboxylic acid having 10 to 40 carbon atoms, more preferably 18 to 33 carbon atoms, is preferred. Specific examples of these organic silver salts include silver salts of carboxylic acids of the formula CH3(CH2)nCOOH where n ranges from 16 to 31. In addition, a mixture of organic silver salts can be used, if desired.

The amount of the organic silver salt (a) used generally ranges from about 0.1 g to about 4 g of silver, preferably from about 0.2 g to about 2.5 g of silver, per m2 of the support. When the amount of the organic silver salt used is less than about 0.1 g/m2, the image density obtained is too low. On the other hand, even if an amount greater than about 4 g/m2 is used, the image density obtained does not increase, and thus use of an excess amount results in a high cost due to an increased amount of silver used with no attendant advantages accruing.

The reducing agent, which is used as component (b) in the present invention, is a compound which is capable of reducing the organic silver salts [component (a)j upon imagewise heating or heating in the presence of an exposed photocatalyst (d) on heating at a temperature of about 800C or higher, more preferably 1000C or higher. Although component (b) is most preferably incorporated into a layer in which the component (a) is present, component (b) can be occasionally incorporated into a layer adjacent a layer in which component (a) is present. In the latter case the recording layer is divided into two layers.

Examples of reducing agents suitable for use in the present invention as component (b) include mono-, bis-, tris- or tetrakis-phenols; mono- or bis-naphthols; di- or poly-hydroxynaphthalenes; di- or poly-hydroxybenzenes; hydroxymonoethers; ascorbic acids; 3-pyrazolidones; pyrazolines; pyrazolones; reducing saccharides, phenylenediamines, hydroxylamines; reductones; hydroxyoxaminic acids; hydrazides; amidoximes; and N-hydroxyureas. Specific examples of these reducing agents are described in detail in, e.g., Japanese Patent Application (OPI) 22431/1976, U.S.

Patents 3,615,533, 3,679,426, 3,672,904, 3,751,252, 3,751,255, 3,782,949, 3,801,321, 3794,488 and 3,893,863, Belgian Patent 786,086, U.S. Patents 3,770,448, 3,819,382, 3,773,512, 3,928,686, 3,839,048 and 3,887,378, Japanese Patent Applications (OPI) 15541/1975 and 36143/1975, U.S. Patent 3,827,889, Japanese Patent Applications (OPI) 36110/1975, 116023/1975, 117711/1975 and 23721/1976, U.S. Patent 4,021,249 and Japanese Patent Applications (OPI) 51933/1976. A suitable reducing agent for use can be selected from these reducing agents, taking into account the kinds and properties of the organic silver salts employed in combination therewith.

Polyphenols, suffonamidophenols and naphthols, of these compounds, are particularly preferred as reducing agents.

Preferred examples of polyphenols are 2,4-dialkyl-substituted ortho-bisphenols, 2,6dialkyl-substituted para-bisphenols or mixtures thereof. Specific examples of such compounds include 1, 1-bis(2-hydroxy-3,5-dimethylphenyl)-3,5,5-trimethylhexane, 1,1 -bis(2-hydroxy-3-t-butyl-5-methylphenyl)methane, 1, 1-bis(2-hydroxy-3 ,5-di-t- butylphenyl)methane, 6-methylenebis(2-hydroxy-3 -t-butyl-5-methylphenyl)-4-methyl- phenol, 6,6'-benzylidene-bis(2,4-di-t-butylphenol), 6,6'-benzylidenebis(2-t-butyl-4- methylphenol), 6,6'-benzylidene-bis(2,4-dimethylphenol), 1, 1-bis(2-hydroxy-3,5-di- methylphenyl)-2-methylpropane, 1,1,5,5-tetrakis(2-hydroxy-3,5-dimethylphenyl)-2,4- ethylpentane, 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, 2,2-bis(4-hydroxy-3 rnethyl-5-t-butylphenyl)-propane and 2,2-bis(4-hydroxy-3,5-di-t-butylphenyl)propane.

Preferred examples of naphthols include 2,2'-dihydroxy-1,1'-binaphthyl, 6,6' dibromo-2,2'-dihydroxy-1,1'-binaphthyl, 6,6'-dinitro-2,2 '-dihydroxy- 1,1 '-binaphthyl, bis(2-hydroxy-1-naphthyl)methane and 4,4'-dimethoxy-1,1'-dihydroxy-2,2'-binaphthyl.

Preferred examples of sulfonamidophenols include 4-benzenesulfonamidophenol, 2-benzenesulfonamidophenol, 2,6-dichloroA-benzenesulfonamidophenol and the like.

Of these reducing agents, mono-, bis-, - tris- or tetrakisphenols having at least one alkyl group as a substituent, such as a methyl group, an ethyl group, a propyl group, an isopropyl group or a butyl group, or an acyl group as a substituent at a position adjacent the position substituted with a hydroxy group, where the hydroxy group is connected to a carbon atom in the aromatic nucleus, for instance, a 2,6-di-t-butylphenol group, are particularly advantageous, since they are stable to light and, therefore, only a slight coloration occurs.

In addition, reducing agents of the kind which undergo photolysis and are rendered inert to light, as disclosed in U.S. Patent 3,827,889 have the advantage in that coloration can be prevented from occurring because the decomposition or the inactivation of such reducing agents by light occurs when the light-sensitive element is allowed to stand under normal room illumination after development and no further progress of the reduction occurs. Examples of photolytic reducing agents which can be used in this invention include ascorbic acid or derivatives thereof, furoin, benzoin, dihydroxyacetone, glyceraldehyde, tetrahydroxyquinone rhodizonate, 4-methoxy-1- naphthol and aromatic polysulfur compounds as disclosed in Japanese Patent Application (OPI) 99719/1975. Direct positive images can be produced when thermally developable light-sensitive elements are prepared using such photolytic reducing agents and, then are imagewise exposed to light to destroy the reducing agents as disclosed in U.S. Patents 3,827,889 and 3,756,829. Further, compounds accelerating the photolytic decomposition of the reducing agents can be used in combination with such reducing agent.

A suitable reducing agent is selected by taking into account the kind (oxidizability) of the organic silver salt [component (a)] employed in combination therewith. For instance, reducing agents having a strong reducing activity are suitable for use with silver salts which are comparatively difficult to reduce, such as silver benzotriazole and silver behenate. On the other hand, for relatively easily reducible organic silver salts such as silver caprate and silver laurate, comparatively weak reducing agents are suitable. Specific examples of appropriate reducing agents for silver benzotriazole include 1-phenyl-3-pyrazolidones, ascorbic acid, ascorbic acid monocarboxylic acid esters, and naphthols such as 4-methoxy-1-naphthols. Suitable reducing agents for silver behenate are o-bisphenols of the bis-(hydroxyphenyl)methane system, hydroquinone and other various kinds of reducing agents. Suitable examples of reducing agents for silver caprate and silver laurate are substituted tetrakisphenols, o-bisphenols of the bis(hydroxyphenyl)alkane system, p-bisphenols such as substituted compounds of bisphenol A and pphenylphenol.

The simplest method for choosing a suitable reducing agent by one skilled in the art is by trial and error, wherein light-sensitive materials are prepared, e.g., as described in the examples hereinafter, and the photographic characteristics are examined. The suitability or lack of suitability of the reducing agents used is determined by the results obtained.

The amount of the reducing agent employed will vary depending upon the kind of organic silver salt and the reducing agent used, and the presence of other additives. However, in general, amounts of about 0.05 to about 10 mol, and preferably about 0.1 to 3 mol, per mol of the organic silver salt (a) are suitable.

The above-described, various types of reducing agents may be used individually or as a combination thereof, if desired.

The above-described component (a) and component (b) are preferably dispersed in a solution of at least one polymer as a binder and coated on a support to prepare a heat-sensitive layer. Preferred binders are generally hydrophobic, however, hydrophilic binders may be used. These binders are preferably transparent or semitransparent, with examples including natural polymers, e.g., proteins such as gelatin, cellulose derivatives; polysaccharides such as dextran; and gum arabic, and synthetic polymers. Particularly suitable binders can be selected from those described in Japanese Patent Application (OPI) 22431/1976. Of these binders, polyvinyl butyral, polyvinyy acetate, ethyl cellulose, polymethyl methacrylate, cellulose acetate buryrate, gelatin and polyvinyl alcohol are illustrated as particularly preferred binders. Two or more of these binders can be optionally used in combination, if desired. The weight ratio of the binder used generally ranges from about 10:1 to about 1: 10, preferably from about 4:1 to about 1:4, to the weight of the organic silver salt, component (a).

The photocatalyst, component (d), which is used in the second embodiment of the present invention wherein the dry processing type recording element of the present invention is employed for a thermally developable light-sensitive element is a heavy metal salt capable of releasing a metal nucleus on exposure to light which is capable of being a catalyst for the silver image forming oxidation-reduction reaction of the above-described component (a) and component (b), or an organic compound, such as a silver dye complex, having a similar stability. By incorporating the photocatalyst into a heat-sensitive layer so that the photocatalyst is in contact with the above-described organic silver salt in the heat-sensitive layer, the heat-sensitive layer is rendered light-sensitive and a light-sensitive and heat-sensitive layer is obtained.

Of these photocatalysts, a light-sensitive silver halide (silver chloride, silver bromide, silver iodide, silver chloroiodobromide, silver chlorobromide, silver iodochloride silver iodobromide or a mixture thereof) is preferred since it has the highest sensitivity.

Of these light-sensitive silver halides, a silver halide having an average grain size of from about 0.001 micron to about 2 microns, more particularly from 0.01 micron to 0.5 microns, is preferred.

The amount of silver halide which can be employed as component (d) ranges from about 0.001 mol to about 0.7 mol, preferably from about 0.01 to abo

(1) Inorganic halides, e.g., represented by the formula: MXn wherein M represents H, NH4, or a metal atom, X represents Cl, Br or I, and n is 1 when M is H or NH,, or the valence of M when M is a metal atom. Specific examples of metals M in such halides include lithium, sodium, potassium, cesium, magnesium, calcium, strontium, barium, zinc, cadmium, mercury, tin, antimony, chromium, manganese, iron, cobalt, nickel, rhodium, cerium, and so on.

(2) Onium halides, specific examples of which include trimethylphenylammonium bromide, cetylethyldimethylammonium bromide, trimethylbenzylammonium bromide and other quaternary ammonium halides; quaternary phosphonium halides such as tetraethylphosphonium bromide; and tertiary sulfonium halides such as trimethylsulfonium iodide.

(3) Halogenated hydrocarbons, specific examples of which include iodoform, bromoform, carbon tetrabromide, 2-bromo-2-methylpropane.

(4) N-halo compounds, specific examples of which include N-chlorosuccinimide, N-bromosuccinimide, N-bromophthalimide, N-bromoacetamide, N-iodosuccinimide, N-bromophthalazone, N-bromooxazolinone, N-chlorophthalazone, N-bromoacetanilide, N,N-dibromobenzenesulfonamide, N-bromo-N-methylbenzenesulfonamide, 1,3dibromo-4,4-dimethylhydantoin and N-bromourazole.

(5) Other halogen-containing compounds such as triphenylmethyl chloride, triphenylmethyl bromide, 2-bromobutyric acid, 2-bromoethanol, benzophenone dichloride or triphenyl bromide.

In the above-described halidation processes, the silver halide-forming components can be used individually or as a combination thereof. A suitable amount of the silver halide-forming component ranges from about 0.001 mol to about 0.7 mol, and preferably about 0.01 mol to about 0.5 mol, per mol of the organic silver salt used as component (a). Use of an amount less than about 0.001 mol results in a low sensitivity, while use of a larger amount than about 0.7 mol causes an undesirable coloration in the background of the processed light-sensitive material when the material is allowed to stand for a long time, as they are, exposed to normal room illumination. The optimum conditions for the halidation method depend to a very great extent upon the desired average grain size of the silver halide and the type of organic silver salt used. Accordingly, the optimum conditions for the halidation method must be determined experimentally. However, the procedures for determin ing these conditions are routine and can be easily conducted by one skilled in the art.

The silver halide produced using any of the methods above can be sensitized with, for example, a sulfur-containing compound, a gold compound, a platinum compound, a palladium compound, a silver compound, a tin compound, or a mixture thereof. Sensitization is described in detail in, for example, Japanese Patent Applica tion (OPI) Nos. 41519/1876, 49023)1976, 69628/1976, 88216/1976, 120715/1976 and 4821/1977.

An improvement in the sensitivity of the silver halide can be attained, for example, usmg a method which comprises forming a silver halide in the presence of a portion of the binder, precipitating the silver salt by means of, for example, a centrifuge, and then re-dispersing the silver salt into the remaining portion of the binder, in other words by use of the flocculation method ordinarily used in producing a gelatin silver halide photographic emulsion as described in, for example, Japanese Patent Application (OPI) 35623/1977.

Further, the sensitivity of the silver halide can be increased using a method in which a silver halide forming agent is reacted with an organic silver salt in the presence of an amido compound or an imido compound as described in U.K. Patent Application 35179/77 (Serial No. 1,547,323) and U.S. Patent 3,980,482.

Other photocatalysts can be used in this invention instead of the silver halide.

For instance, a light-sensitive complex of silver and a dye as described in Japanese Patent Publication 25498/1974, Japanese Patent Application (OPI) 4728/1971 and U.S. Patent 3,933,507 can be employed as a photocatalyst. Also, an organic silver salt having a relatively high light-sensitivity and an organic silver salt having a relatively low light-sensitivity can be used in combination as an organic silver salt as described in Japanese Patent Application (OPI) 8522/1975. In addition, a metal diazosulfonate and a salt of sulfinic acid as described in U.S. Patent 3,152,904 can be used as a photocatalyst. Further, a photoconductive material such as zinc oxide and titanium dioxide can be used. However, where a highly sensitive thermally-developable light-sensitive element is required, a silver halide is preferred as a photocatalyst.

Some optical sensitizing dyes which are effective for gelatin-silver halide emulsions can also be used to achieve a sensitizing effect with the thermally developable light-sensitive elements of the present invention and thus they can be used to increase the sensitivity of component (d).

Examples of effective, optical sensitizing dyes include cyanine, merocyanine, rhodacyanine, complex (tri- or tetra-nuclear) cyanine or merocyanine, holopolar cyanine, styryl, hemicyanine, oxonol, hemioxonol and xanthene dyes. Those cyanine dyes which contain basic nuclei such as thiazoline, oxazoline, pyroline, pyridine, oxazole, thiazole, selenazole and imidazole nuclei are particularly preferred. Cyanine dyes containing imino groups or carboxy groups are particularly effective. Merocyanine dyes may contain acidic nuclei such as thiohydantoin, rhodanine, oxazolidinedione, thiazolizinedione, barbituric acid, thiazolinone, malononitrile and pyrazolone nuclei, in addition the the above-described basic nuclei. Merocyanine dyes containing imino or carboxy groups are particularly effective. Specific examples of particularly effective sensitizing dyes for the thermally developable light-sensitive materials of the present invention include merocyanine dyes containing rhodanine, thiohydantoin or 2-thio-2,4-oxazolidinedione nuclei, e.g., as disclosed in U.S. Patent 3,761,279, Japanese Patent Applications (OPI) 105127/1975 and 104637/1975.

Further, examples of other sensitizing dyes which may be employed in the present invention include trinuclear merocyanine dyes as disclosed in U.S. Patent 3,719,495; sensitizing dves mainly effective for silver iodide as disclosed in Japanese Patent Application (OPI) 17719/1974; dyes of the styrylquinoline system as disclosed in British Patent 1,409,009; rhodacyanine dyes as disclosed in U.S. Patent 3,877,943; acidic dyes such as 2',7'-dichlorofluorescein dye as disclosed in Japanese Patent Applications (OPI) 96717/1974 and 102328/1974, and British Patent 1,417,382; and merocyanine dyes as disclosed in Japanese Patent applications (OPI) 156424/1975 and 27924/1976.

A suitable amount of these sensitizing dyes is about 10 i mol to about 1 mol, per mol of the silver halide or the silver halide-forming component, component (d).

The component (c) of the present invention can be incorporated into a coating solution for an overcoat layer which is provided on the above-described heat-sensitive layer or light-sensitive and heat-sensitive layer, if desired. A suitable thickness of the overcoat layer ranges from about 1 micron to about 20 microns. Examples of polymers suitable for use in the overcoat polymer layer are those described in Japanese Patent Application (OPI) 6917/1974. Specific examples are, for example, polyvinyl chloride, polyvinyl acetate, a copolymer of vinyl chloride and vinyl acetate, polystyrene, polyrr.ethyl methacrylate, methyl cellulose, ethyl cellulose, celluose acetate butyrate, cellulose acetate, polyvinylidene chloride, cellulose propionate, cellulose acetate phthalate, polycarbonate, cellulose, acetate propionate, polyvinyl pyrrolidone, polystyrene, polyvinyl toluene, nitrocellulose, a copolymer of styrene and isobutylene, gelatin, a polymer latex such as 2-acetocetoxyethyl methacrylate, a carboxy polyester, and so on. The overcoat polymer layer may also contain a carrier, for example, titanium dioxide, kaolin, zinc oxide, silica, alumina, a polysaccharide such as starch, etc. in order to enable the recording element to be written upon using an inked stamp, a ball-point pen, a pencil or the like. The overcoat layer may further contain an antihalation dye, a filter dye, an ultraviolet light absorbing agent, an acid stabilizer such as a higher fatty acid or a toning agent such as a phthalazinone.

Even when component (c) is incorporated into a layer other than the overcoat layer or a support, it is preferred to provide the above-described overcoat layer on a recording layer because of the advantages of increasing the transparency of the heatsensitive layer or light-sensitive and heat-sensitive layer and of improving the storage stability of the fresh element.

Component (c) of the present invention can be incorporated into a subbing layer which is provided between a support and a heat-sensitive layer or between a support and a light-sensitive and heat-sensitive layer. In such a case the most marked effects in improving whiteness are achieved.

Suitable binders which can be employed in the above-described subbing layer are thermoplastic resins. Examples of suitable thermoplastic resins include homopolymers or copolymers of polyolefinic type resins, polystyrene type resins, polyvinyl chloride tyDe resins, polyvinylidene chloride type resins, polyacrylate type resins, saturated polyester type resins, polycarbonate type resins, etc. or a mixture thereof. Of these thermoplastic resins, polyvinyl chloride type resins and polyvinylidene chloride type resins are preferred since they have the ability to improve the storage stability of the fresh dry processing type recording elements. Various polyvinyl chloride type resins and polyvinylidene chloride type resins can be used. Examples include polyvinyl chloride, a copolymer of a vinyl ester and vinyl chloride, a copolymer of an acrylate and vinyl chloride, a copolymer of a maleate and vinyl chloride, a copolymer of a fumarate and vinyl chloride, a copolymer of acrylonitrile and vinyl chloride, a copolymer of a vinyl alkyl ether and vinyl chloride, a copolymer of vinyl chloride and vinylidene chloride, polyvinylidene chloride, a copolymer of acrylonitrile and vinylidene chloride, and a copolymer of a vinyl ester and vinylidene chloride.

Suitable acids for the vinyl ester include carboxylic acids and sulfonic acids each having from 1 to 22 carbon atoms. Specific examples of vinyl esters which can be used include vinyl acetate, vinyl stearate, vinyl butyrate, vinyl propionate, vinyl (diethylphosphono)acetate, and vinyl butylsulfonate.

Suitable alcohols for the acrylate and the methacrylate, the maleate or the fumarate esters, include alcohols having 1 to 22 carbon atoms. Specific examples of suitable alcohols include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, lauryl alcohol, stearyl alcohol, and 2,3-epoxypropanol.

The amount of the vinyl chloride or the vinylidene chloride to the other monomer or monomers copolymerized therewith in copolymers can be varied over a wide range.

Preferably the copolymers used contain 50 mole percent or higher of vinyl chloride or vinylidene chloride. More preferably the copolymers used contain 70 mole percent or higher of vinyl chloride or vinylidene chloride.

Where a copolymer of vinyl chloride and vinylidene chloride is employed, a copolymer containing about 50 to about 98 mole percent of vinylidene chloride is preferred.

The degree of polymerization of the polymers can be also varied widely. Generally, at least one polymer selected from a vinyl chloride type polymer or a vinylidene chloride type polymer each having a degree of polymerization of about 30 or greater can be used. Preferably, at least one polymer selected from a vinyl chloride type polymer or a vinylidene chloride type polymer each having a degree of polymerization of from about 50 to 50,000 can be used.

Specific examples of vinyl chloride type polymers and vinylidene chloride type polymers which can be used include a copolymer of vinyl acetate and vinyl chloride, a copolymer of vinyl stearate and vinyl chloride, a copolymer of vinyl butyrate and vinyl chloride, a copolymer of vinyl propionate and vinyl chloride, a copolymer of vinyl (diethylphosphono)acetate and vinyl chloride, a copolymer of vinyl butylsulfonate and vinyl chloride, a copolymer of methyl acrylate and vinyl chloride, a copolymer of ethyl acrylate and vinyl chloride, a copolymer of lauryl acrylate and vinyl chloride, a copolymer of 2,3-epoxypropyl methacrylate and vinyl chloride, a copolymer of diethyl fumarate and vinyl chloride, a copolymer of diethyl maleate and vinyl chloride, a copolymer of dibutyl maleate and vinyl chloride, a copolymer of vinyl isobutyl ether and vinyl chloride, a copolymer of allyl 2,3-epoxpropyl ether and vinyl chloride, a copolymer of chlorobutadiene and vinyl chloride, a copolymer of methyl acrylate and vinylidene chloride, and a copolymer of ethyl methacrylate and vinylidene chloride.

Of these polymers, a copolymer of vinyl acetate and vinyl chloride and a copolymer of vinyl chloride and vinylidene chloride are most preferred for use in the present invention.

A suitable amount of the polymer employed is an amount of from 0.1 g to 20 g, more preferably from 0.2 g to 10 g, per m2 of the support.

The subbing layer can contain various types of compounds. For instance, a matting agent such as calcium carbonate, starch, titanium dioxide, zinc oxide, silica, dextrin, barium sulfate, alumina, kaolin, clay, and diatomaceous earth can be incorporated into the subbing layer.

Even when component (c) is incorporated into a layer other than the subbing layer or the support, it is preferred to provide the above-described subbing layer on a support because of the improvement in the storage stability of the fresh dry processing type recording elements.

The dry processing type recording elements of the present invention can contain the following various types of additives.

A toning agent can be used as one of such additives. A toning agent is advantageously used where a dark, particularly black, image is desired. The amount of the toning agent used ranges from about 0.0001 mole to about 2 mol, preferably from about 0.0005 mol to about 1 mol, per mol of the organic silver salt (a). Effective toning agents are determined by taking the types of the organic silver salt (a) and the reducing agent (b) used into account.

Phthalazinones, oxazinediones, cyclic imides, urazoles, 2-pyrazoline-5-one and the derivatives thereof can be used as suitable toning agents. Specific examples of toning agents which can be used are described in detail in U.S. Patents 3,846,136, 3,782,941, 3,844,797, 3,832,186, 3,881,938 and 3,885,967, British Patent 1,380,795, Japanese Patent Applications (OPI) 151138/1975, 91215/1974, 67132/1975, 67641/1975, 114217/1975, 32927/1975, 22431/1976 and 99813/1977. Some specific examples of toning agents include phthalazinone, N-acetylphthalazinone, N-hydroxyethylphthalazinone, phthalimide, N-hydroxyphthalimide, benzoxadinedione, uracil and the like.

A thermal fog preventing agent is also one of the additives optionally used. One example of a thermal fog preventing agent is a mercury compound as disclosed in U.S. Patent 3,589,903. Preferred mercury compounds are mercury bromide, mercury iodide and mercury acetate. A second example of a compound for preventing thermal fog is an N-halo compound such as an N-halosuccinimide and an N-haloacetamide as disclosed in Japanese Patent Applications (OPI) 10724/1974, 97613/1974, 90118/ 1974 and 22431/1976. Other examples of compounds for preventing thermal fog are those described in U.S. Patent 3,885,968, Japanese Patent Applications (OPI) 101019/1975, 116024/1975, 123331/1975 and 134421/1975, Japanese Patent Application (OPI) Nos. 47419/1976, 42529/1976, 51323/1976, 57435/1976, 78227/1976, 104338/1976 and 24520/1977, with specific examples including a lithium salt, a peroxide, a persulfate, a rhodium salt, a cobalt salt, a palladium compound, a cerium compound, sulfinic acids, thiosulfonic acids, disulfides, rhodinic acid and a polymer having acidic group(s). Particularly preferred compounds which can be used are sodium benzenesulfinate, sodium ptoluenesulfinate, sodium benzenethiosulfonate, cerium compounds (e.g., cerium nitrate, cerium bromide, etc.), a palladium-acetylacetone complex, a rhodium-acetylacetone complex, a fatty acid, and the like. Other specific examples of preferred compounds are described in Japanese Patent Application (OPI) 22431/1976.

A compound effective to prevent further light discoloration of processed dry processing type recording elements (the phenomenon which gradually occurs resulting in discoloration at the unexposed areas of the light-sensitive elements when the processed dry processing type recording element is exposed to normal room illumination following the development processing) is another example of the additives which can be optionally used. Suitable examples of this type of compound include, for example, a precursor of a stabilizing agent such as an azolethioether and the blocked azolethiones as disclosed in U.S. Patent 3,839,041, a tetrazolylthio compound as disclosed in U.S. Patent 3,700,457, a halogencontaining light-sensitive organic oxidizing agent as disclosed in U.S. Patent 3,707,377, a halogencontaining compound as disclosed in Japanese Patent Application (OPI) 119624/1975 and U.S. Patent 3,874,946, a 1-carbarnoyl-2-tetrazolin-5-thione as disclosed in U.S.

Patent 3,893,859, and sulfur as disclosed in Japanese Patent Application (OPI) 26019/1976.

In addition to the above-described additives, various types of additives which are known in the field of thermally developable light-sensitive elements can also be employed. Such additives can be incorporated in at least one of a support, a subbing layer, a heat-sensitive or a light-sensitive and heat-sensitive layer and an overcoat layer, described hereinbefore.

The dry processing type recording elements of the present invention can also have, in addition to the above-described layers, a deposited metal layer as disclosed in U.S. Patent 3,748,137, a backing layer as disclosed in Japanese Patent Application (OPI) 43130/1976, and a magnetic material layer as disclosed in Japanese Patent Application (OPI) 136099/1975.

The layer(s) containing the respective components to be used in the dry proc cessing type recording element of the present invention and other layers can be coated on various supports selected from various types of materials. Suitable supports include those of any shape but, since flexible supports are preferred for handling as information-recording materials, film- or sheet-shaped supports, rollshaped supports or ribbon-shaped supports are usually used.

Suitable materials for the support include synthetic resin films, and sheets, glasses, wool, cotton cloth, paper, metals such as aluminum, and the like. Examples of suitable synthetic resin films include cellulose acetate films, polyester films such as polyethylene terephthalate films, polyamide films, polyimide films, cellulose triacetate films, polycarbonate films etc. Also, as a support paper, in addition to general papers, photographic papers, printing papers (e.g., coated papers, art papers, etc.), baryta papers, resin,coated papers, water-proof papers, papers subjected to a sizing with a polysaccharide or the like as described in Belgian Patent 784,615, pigmentcontaining papers such as those containing titanium dioxide, or the like, papers coated with an a-olefin polymer (e.g., polyethylene, polypropylene, an ethylene-butene copolymer, etc.), papers previously processed with polyvinyl alcohol, and the like, can be used.

As described hereinbefore, the dry processing type recording element of the present invention includes two embodiments, i.e., a first embodiment comprising a support and a heat-sensitive layer (heat-sensitive paper) and a second embodiment comprising a support and a light-sensitive and heat-sensitive layer (thermally developable light-sensitive element).

A dry processing type recording element comprising a support having thereon a subbing layer containing component (c) and a heat-sensitive layer containing component (a) and component (b) is a particularly preferred example of the first embodiment described above. Particularly, the use of a copolymer of vinyl chloride and vinylidene chloride or a copolymer of vinyl chloride and vinyl acetate as a binder of the subbing layer leads to best results.

A dry processing type recording element comprising a support having thereon a subbing layer containing component (c) and a light-sensitive and heat-sensitive layer containing component (a), component (b) and component (d) is a particularly preferred embodiment of the second embodiment described above. Particularly, the use of a copolymer of vinyl chloride and vinylidene chloride or a copolymer of vinyl chloride and vinyl acetate as a binder of the subbing layer leads to best results.

A suitable process for producing the dry processing type recording element of the present invention which includes the first embodiment and the second embodiment described above is outlined as follows. That is, an organic silver salt is prepared by reacting an organic silver salt forming agent and a silver ion-providing agent such as silver nitrate using one of the various known methods. The thus-prepared organic silver salt is washed with water or an alcohol, etc., if desired, and then dispersed in a binder for an emulsion. A colloid mill, a mixer, a ball mill, or the like can be used for the dispersion. Alternatively, an organic silver salt can be prepared in a binder.

Then, a variety of additives, other than a photocatalyst, component (d), such as a reducing agent, a toning agent, etc. is added, preferably in the form of a solution to the thus-prepared polymer dispersion of the organic silver salt, which results in the production of a coating solution for a heat-sensitive layer.

On the other hand, a previously prepared photocatalyst is added to the abovedescribed polymer dispersion of the organic silver salt, or a silver halide-forming agent is added to the polymer dispersion and then a portion of the organic silver salt is converted to silver halide. After that, a variety of additives such as a sensitizing dye, a reducing agent, a toning agent, etc., is added, which results in the production of a coating solution for a light-sensitive and heat-sensitive layer.

Each coating solution thus prepared is coated on an appropriate support, directly or through a subbing layer, without drying. An overcoat polymer layer, a subbing layer, a backing layer and other layers can be formed by preparing coating solutions thereof, respectively, and coating, in sequence, using various coating processes such as a dipcoating process, an air knife-coating process, a curtain coating process or a hopper coating process. If desired, two or more layers can be coated at the same time according to the process as described in U.S Patent 2,761,791 and British Patent 837,095.

Solvents which are used in the coating folutions are appropriately selected. Nonflammable solvents as described in British Patent 1,422,145 can also be used. When a subbing layer is employed, it is particularly preferred to use a solvent, which does not dissolve a polymer used in the subbing layer, as a solvent for the coating solution of the recording layer. For instance, when a copolymer of vinyl chloride and vinyl acetate is employed in a subbing layer, preferred results are obtained by using, as a solvent for a coating solution of the recording layer, an alcohol (such as methanol, ethanol, propanol, isopropanol, etc.).

According to the present invention, component (c) is incorporated into a support or at least one layer provided on the support as described above.

The dry processing type recording element thus produced can be stored in the form of sheets or rolls. It is preferred to use a dessiccant (such as silica gel, etc.) as described in Japanese Patent Applications (OPI 2523/1975 and 17247/1976 during storage.

The dry processing type recording element of the present invention can be used in the following manner. That is, the first embodiment of the dry processing type recording element of the present invention can be used to record an image therein by heating in an imagewise fashion, for example, heating the element using a heated pen or by exposure to infrared radiation through an original. Such procedure can be carried out with reference to the disclosures present in U.S. Patents 2,910,377, 3,328,167, 3,028,254, 3,031,329, 3,074,809, 3,080,254, 3,107,174, 3,147,134, 3,212,890, 3,446,648, 3,547,648, 3,682,684 and 3,795,532 and British Patent 943,993.

Also, when the element of the first embodiment according to the present invention is contacted with an original having an image therein and heated, a difference of temperature occurs between image areas and non-image areas of the original and the imagewise record is obtained on the element of the present invention.

Furthermore, the element of the first embodiment according to the present invention can be used to record upon imagewise exposure using in combination therewith a light-sensitive sheet containing a photolytic light-sensitive reducing agent, that is, a thermally transferable light-sensitive element as disclosed in U.S. Patents 3,094,417, 3,526,506, 3,218,166, 3,218,168, 3,460,946, 3,559,478, 3,799,799, 3,094,619, 3,409,348, 3,632,377 and 3,770,442. Japanese Patent Publication 9596/ 1970, British Patents 1,280,593 and 1,296,969, U.S. Patents 3,685,996, 3,664,842, 3,816,139, 3,653,907, 3,798,039 and 3,764,333 and Japanese Patent Application (OPI) 102329/1974. More specifically, the light-sensitive sheet is imagewise exposed and then heated in close contact with a heat-sensitive layer of the dry processing type recording element of the present invention, which results in a heat transfer of reducing agent in the unexposed areas of the light-sensitive sheet to the heatsensitive layer and promoting the function of reducing organic silver salts, which a reducing agent, component (b), present in the heat-sensitive layer possesses, to form a silver image. Similar light-sensitive elements are further disclosed in U.S. Patents 3,674,479, 3,674,480, 3,728,115, 3,734,733, 3,753,395, 3,816,131, 3,764,321, 3,810,760 and 3,839,048 Japanese Patent Publication 35449/1974, German Patent Applications (OLS) 1,926,656, 1,926,658, 2,140,406, 2,329,144 and 2,321,329, Japanese Patent Applications (OPI) 5737/1972, 29298/1974, 91215/1974 and 15540/1975 and Japanese Patent Publications 27074/1969 and 2610/1974. The element of the first embodiment according to the present invention can be applied to such processes.

In the first embodiment of this invention a suitable heating temperature can range from about 80 to about 1800C, preferably about 1000C to about 1500C. The heating time can be optionally selected between about 1 to about 60 seconds or outside this range, if desired. The heating time is dependent upon the heating temperature used.

The dry processing type recording element of the second embodiment according to the present invention, i.e. a thermally developable light-sensitive element, is particularly preferred since image recording can be carried out by heating alone after imagewise exposure of the light-sensitive element. The element may be pre-heated (about 800C to 1400 C), if desired, before exposure. Suitable light sources for the imagewise exposure include light from a tungsten lamp, a fluorescent lamp for copying mainly used for exposing diazo light-sensitive materials, a mercury lamp, an iodine lamp, a xenon lamp, a CRT light source, a laser light source, etc. Photographic images having a gradation may be used, as well as line images of a drawing, as an original for copying. In addition, it is also possible to take a picture of people or scenery using a camera using the element of this inventio ment to achieve substantially the same image density or, alternatively, where all other factors such as components (a) and (b), etc., as well as the heating temperature are the same, a heating time of about two times or longer than that required for the dry processing element of the second embodiment will be used for the dry processing element of the first embodiment to achieve substantially the same image density.

A variety of heating means can be used. For example, the light-sensitive element can be contacted with a simple heated plate or with a heated drum, or alternatively the light-sensitive element can be passed through a heated space. In addition, the light-sensitive element can be heated using high frequency heating or laser beam as disclosed in U.S. Patent 3,811,885. In order to prevent an odor which occurs on heating from being detected, a deodorizing agent can be installed in the processing device. In addition, in order for an odor emitted from the light-sensitive element not to be perceived, certain types of perfumes can be also incorporated in the element.

In order to further stabilize the thus-processed thermally developable lightsensitive elements to heat or light after the processing, various methods as described below may be employed. For example, the method for stabilizing thermally developable light-sensitive elements in which the thermally developable light-sensitive element is treated with a solution containing a thiosulfate, a thiocyanate, triphenylphosphine, a mercapto compound, etc., as described in U.S. Patent 3,617,289 and Japanese Patent Application (OPI) 104826/1976; the method for stabilizing thermally developable light-sensitive elements with an aldehyde compound as described in Japanese Patent Application (OPI) 80226/1976; the method for stabilizing thermally developable light-sensitive elements in which a layer containing a stabilizing agent such as a mercapto compound, a halogen-containing compound, etc. is applied to the thermally developable light-sensitive elements before, during or after the processing, as described in Japanese Patent Applications (OPI) 54329/1975, 77034/1975, 156425/1975, 328/1976 and 121332/1976, are illustrative.

The thermally developable light-sensitive elements according to the present invention are very useful because these elements can be employed in various uses other than usual reproduction of line images or drawings. For example, these elements can be used to record direct positive images as described in U.S. Patents 3,607,282 and 3,589,901; these elements can provide planographic printing plates as described in Japanese Patent Application (OPI) 4659/1972 and U.S. Patents 3,679,414 and 3,811,886; these elements can be used as thermally transferable sheets as described in U.S. Patents 3,767,394 and 3,895,094 and Japanese Patent Publication 13023/ 1976; and these elements can be used as commutation tickets as described in Japanese Patent Applications (OPI) 87318/1975 and 125737/1975 and Japanese Patent Publication 4107/1976.

The dry processing type recording elements of the present invention are extremely useful and provide improved whiteness in the non-image areas and prevent discoloration in the non-image areas due to light or heat after processing produce clear images which can be stored semipermanently.

The present invention is illustrated in greater detail below by reference to the following Examples. Unless otherwise indicated, all parts, percents, ratios and the like are by weight.

In the following Examples and Comparative Examples, the whiteness is shown by using the relative value defined as follows. That is, a sample is placed on a grey colored paper and observed visually under diffuse sunlight at a window, and a relative value of 1 to 10 is assigned based on the whiteness of a standard sample (X) and a standard sample (Y) being 5 and 10, respectively.

Standard Sample (X) is a paper which is prepared by size-pressing a paper support for a pressure-sensitive copying paper with polyvinyl alcohol (1 g/m2).

Standard Sample (Y) is a paper which is prepared by coating the following coating solution on one surface of Standard Sample (X) in a coating thickness of 80 microns just after coating and before drying and dried at 70CC.

Composition of the Coating Solution Vinyl Chloride/Vinyl Acetate Copolymer (90:10 by weight) 7.5 g Compound (1): bis(Benzoxazole)thiophene 50 mg Methyl Ethyl Ketone 100 ml EXAMPLE 1 3.4 g of behenic acid was dissolved in 100 ml of benzene at 600C and the solution was maintained at 600C. To the solution, 100 ml of water was added while stirring with a stirrer to emulsify. An aqueous solution at 100C which was prepared by adding aqueous ammonia to about 80 ml of an aqueous solution containing 1.7 g of silver nitrate to form a silver-ammonium complex salt and adding water to make the total volume of 100 ml was added to the emulsion. Thus, fine crystals of silver behenate were obtained. The solution mixture was allowed to stand at room temperature (250C) for 20 minutes and an aqueous phase and a benzene phase separated. After removing the aqueous phase, 400 ml of water was again added to the benzene phase and the benzene phase was washed by decantation. 400 ml of methanol was added to the benzene phase and the silver behenate was collected using a centrifugal separation.

4 g of spindle-shaped silver behenate crystals having a length of 1 micron and a width of 0.05 microns was obtained.

2.3 g of the thus-prepared silver behenate (about 1/200 mol) was dispersed in 20 ml of an ethanol solution containing 2.5 g of polyvinyl butyral. To the polymer dispersion of the silver behenate, was added at 500C the components illustrated below in the order shown below at intervals of five minutes, to prepare a coating solution for a heat-sensitive layer.

(i) Behenic Acid (10 ml of a 3 % by weight toluene solution) (ii) 2,2'-Methylenebis(6-tert-butyl-4-methylphenol) [reducing agent] (3 ml of a 2.5 % by weight acetone solution) (iii) Phthalazinone [toning agent] (3 ml of a 2.5% by weight methyl Cellosolve solution) (iv) Fluorescent Whitening Agent-having the following formula:

(1 ml of a 2% by weight toluene solution).

The thus-prepared solution was coated on a coated paper in a silver amount of 0.4 g/m2 to prepare Heat-Sensitive Paper (1r).

For comparison, Heat-Sensitive Paper (,B) was prepared in the same manner as described above except that the fluorescent whitening agent set forth above was not employed.

Heat-Sensitive Papers (a) and tss) were each contacted with an original and heated at 1200C for 10 seconds to produce a black image with a white background.

The whiteness ofthe background and the D max of the image determined with Heat-Sensitive Papers (a) and Gss) were as follows: Heat-Sensitive Paper Whiteness D max (a) 8 1.45 3 3 1.44 From these results it can be seen that while the D max of the images produced in Heat-Sensitive Papers (per) and GR) were the same, a markedly higher contrast between the image and the white background was obtained with Heat-Sensitive Paper (per) of this invention.

EXAMPLE 2 Preparation of a coating solution for a light-sensitive and heat-sensitive layer 100 ml of an aqueous solution containing 1.9 g of sodium hydroxide dissolved therein and 200 ml of a toluene solution containing 12 g of lauric acid dissolved therein were mixed and emulsified with a homomixer. To the emulsion was added 50 ml of an aqueous solution containing 8.5 g of silver nitrate dissolved therein to form silver laurate. After removing the aqueous phase, the toluene phase (containing silver laurate) was dispersed in 180 g of a 1.5 vÓ by weight isopropanol solution of polyvinyl butyral using a homogenizer. To 80 g of the thus-prepared polymer dispersion of the silver salt (about 1/60 mol of the silver salt) was added 4 ml of a 1.1% by weight acetone solution of N-bromoacetamide and the mixture was heated at 50 C for 60 minutes. After adding 20 ml of water, the mixture was centrifuged at 3000 rpm for 30 minutes to collect the precipitate. The precipitate was dispersed in 60 g of a 15% by weight isopropanol solution of polyvinyl butyral using a homogenizer.

To the mixture thus-obtained, maintained at 200C while stirring, was added the components illustrated below, in the order shown below at intervals of five minutes, to prepare a coating solution.

(1) Merocyanine Dye (sensitizing dye)-having the following formula:

(10 ml of a 0.025 . by weight 2-methoxyethanol solution) (2) Phthalazinone (toning agent) (50 ml of a 3% by weight methanol solution) (3) Compound (reducing agent)-having the following formula:

(25 ml of 20% by weight acetone solution) (4) Abietic Acid (fog preventing agent) (16 ml of a 5% by weight toluene solution) (5) Sodium benzenethiosulfonate (25 ml of a 0.02% by weight methanol solution).

Preparation of a thermally developable light-sensitive element Thermally Developable Light-Sensitive Elements (A) to (F) were prepared by coating the thus-prepared coating solution for a light-sensitive and heat-sensitive layer on a support or on a subbing layer provided on a support, designated (A) to (F) hereinafter, in an amount of 0.3 g of silver per square meter of the support (A) Paper support for a pressure-sensitive copying paper which was sized-pressed with polyvinyl alcohol [Standard Sample (X) described above] (B) Paper support which was prepared by coating the following subbing composition on Standard Sample (X) ill an amount of 1 g of the polymer per square meter of the paper support [without fluorescent whitening agent] Vinyl Chloride/Vinyl Acetate Copolymer (90:10 by weight) 15 g Methyl Ethyl Ketone 200 ml (C) Paper support which was prepared by coating the following subbing composition on Standard Sample (X) in an amount of 1 g of the polymer per square meter of the paper support [present invention] Vinyl Chloride/Vinyl Acetate Copolymer (90: 10 by weight) 15 g Fluorescent Whitening Agent-having the following formula:

Methyl Ethyl Ketone 200 ml (D) Paper support which was prepared by coating the following subbing com- position on Standard Sample (X) in an amount of 1 g of the polymer per square meter of the present invention.

(present invention) Vinyl Chloride/Vinylidene Chloride Copolymer (10:90 by weight) 15 g Fluorescent Whitening Agent-having the following formula:

Methyl Ethyl Ketone 200 ml (E) Paper support which was prepared by coating the following subbing cora- position on Standard Sample (X) in an amount of 1 g of the polymer per square meter of the paper support (comparative sample containing a fluorescent whitening agent other than that of the present invention) Polyvinyl Alcohol 5g FluorescentWhitening Agent-having the following formula.

Water 100 ml (F) Paper support which was prepared by coating the following subbing com position on Standard Sample (X) in an amount of 1 g of the polymer per square meter of the paper support (comparative sample) Polyvinyl Alcohol 5 g Titanium White (TiO2) 20 g Water 100 ml Processing of the thermally developable light-sensitive elements and evaluation of the results obtained These thermally developable light-sensitive elements thus prepared were each exposed to light of 103 lux.sec. through an optical wedge and then developed by heating at 1400C for 12 seconds to form a black image.

The reflection density and the whiteness of these samples were measured. The sensitivity was determined using the value of the reciprocal of the exposure amount required to provide a density of 0.1 above fog. The results obtained are shown in Table 1 below.

TABLE 1 Thermally Developable Light-Sensitive Element A B C D E F (present (present Property (control) (control) invention) invention) (comparison) (comparison) Dmax 1.32 1.35 1.36 1.35 1.40 1.40 Admin 0.30 0.28 0.25 0.25 0.35 0.60 Sensitivity 100 150 200 200 150 100 Whiteness 2 2 6 6 7 4* * The value is the whiteness measured before heat development. The whiteness after heat development was 3 and became 1 when the sample was stored under normal room illumination for a short time.

Thermally Developable Light-Sensitive Element (E) was white just after the heat development, but the white area of the element readily discolored to pink or brown (whiteness=2) due to exposure to white light. This means the stability with the pas sage of time after development is inferior. On the contrary, a degradation in whiteness did not occur in Thermally Developable Light-Sensitive Elements (C) and (D) according to the present invention even when these elements were exposed to white light for several days.

Comparative Example 1 A paper support was prepared by coating a subbing layer having the following composition in standard sample (X) and dried Composition of the subbing layer Vinyl Chloride/Vinyl Acetate Copolymer (90:10 by weight) 5 g Fluorescent Whitening Agent (as shown in Table 2 below) (1% by weight dimethylformamide solution) 1 ml Methyl Ethyl Ketone 100 ml The whiteness of the sample was measured just after production and after exposure to sun light for three days. The results obtained are shown in Table 2 below.

TABLE 2

Whiteness After Just after Exposure to Sample No. Fluorescent Whitening Agent Production Sun Light Standard Sample (X) None 5 5 Standard Sample (Y) Compound (1) 10 9 (G) (3NHtNsNHCFCH-CH < NHfN Nt t) 4 ~ C1 SO3N. 503N C1 (H) (lloc2M4)2N+Nr H < tCH"cH9N"g^NrW NtC2H40R)2 6 5 NH OjNJ Sough. NH (I) X Na,,N NH > H"CHÇNHt*N CH2 6 5 SO3N SO3Na (J) Hakkol RN (trade name, manufactured by Showa Chemical Co.) (derivative of 4,4'-diaminostilbene disulfonic acid) 4 (K) Whitex WS (trade name, manufactured by Sumitomo Chemical Co.) (derivative of coumarin) 7 4 (L) Whitex BO conc. (trade name, manufactured by Sumitomo Chemical Co.) (derivative of 4,4'-diamino stilbene disulfonic acid) 7 4 Further, on samples (K) and (L) in which an effect of improving the whiteness was observed (i.e. the whiteness measured just after the production was 7 or above), a coating solution for light-sensitive and heat-sensitive layer as described in Example 2 was coated in an amount of 0.3 g silver per square meter of the paper support and dried to prepare. These elements were heated at 1300C for 8 seconds and then the whiteness thereof was measured. The whiteness in both Thermally Develop able Light-Sensitive Elements (K) and (L) degraded to 3. On the contrary, where the same procedure was carried out using Standard Sample (Y), hardly any degradation of whiteness was observed (whiteness= 6).

Example 3 340 g of behenic acid was added to 5000 ml of water and dissolved on heating at 850C (Solution A). 20 g of sodium hydroxide was dissolved in 500 ml of water to prepare an aqueous solution (Solution B). To Solution A maintained at 850C while stirring, was added Solution B at the rate of 100 ml per minute. A dispersion of a mixture of sodium behenate and behenic acid was obtained (Solution C). Solution C was cooled to 300C and maintained at this temperature while stirring.

85 g of silver nitrate was dissolved in 500 ml of water to prepare an aqueous solution (Solution D). To Solution C, was added Solution D at a rate of 100 ml per minute to prepare Dispersion E containing silver behenate. Dispersion E was stirred at 300C for 90 minutes. To the dispersion, was added Solution F prepared by dissolving 40 g of polyvinyl butyral in 1000 ml of isoamyl acetate and the mixture was stirred at 300C for 10 minutes. After allowing the mixture to stand, the liquid phase separated was removed and the solid phase was centrifuged at 3,000 r.p.m. for 30 minutes. To the precipitate, was added 400 ml of isopropanol and the mixture was stirred for 10 minutes, mixed with a solution prepared by dissolving 270 g of polyvinyl butyral in 1800 ml of isopropanol and dispersed using a homogenizer for 60 minutes. Thus, uniform polymer dispersion containing silver behenate and behenic acid was obtained (Solution G).

To Solution G maintained at 500C while stirring, was added 160 ml of a 4.2% by weight acetone solution of N-bromosuccinimide (silver halide forming agent) and reacted for 60 minutes to form silver bromide catalytically in contact with a part of the silver behenate.

The thus-prepared polymer dispersion of silver behenate-behenic acid-silver bromide (Solution H) was maintained at 300C with stirring, and components illustrated below were added thereto at intervals of five minutes to prepare a coating solution.

(1) Sensitizing Dye-having the following formula:

(200 ml of a 0.025 % by weight methyl ethyl ketone solution) (2) Sodium Benzenethiosulfonate (fog preventing agent) (200 ml of a 0.01% by weight methanol solution) (3) m-Nitrobenzoic Acid (fog preventing agent) (200 ml of a 0.05% by weight ethanol solution) (4) Phthalazinone (toning agent) (500 ml of a 4.5 % by weight ethylene glycol monomethyl ether) (5) Compound (reducing agent)-having the following formula:

(800 ml of a 10% by weight acetone solution).

The thus prepared coating solution for a light-sensitive and heat-sensitive layer was divided into 6 portions and these portions were designated Coating solutions (M), (N), (O), (P), (Q) and (R), respectively.

Coating Solution (M) was directly coated on Standard Sample (X) to prepare Thermally Developable Light-Sensitive Element (M).

Coating Solution (N), to which 240 ml of a 2% by weight toluene solution of Compound (1) of the present invention was added, was indirectly coated on Standard Sample (X) to prepare Thermally Developable Light-Sensitive Element (N).

Coating Solution (0) was directly coated on Standard Sample (X) and dried, and then an overcoat layer having the following composition Composition of Overcoat Layer Cellulose diacetate 5 g Compound (1) (4% by weight toluene solution) 1 ml Acetone 90 ml Methanol 10 ml was coated in an amount of 1 g polymer per square meter thereon to prepare Thermally Developable Light-Sensitive Element (O).

Coating Solutions (P), (Q) and (R) were coated on a subbing layer prepared by coating each of the following subbing layer compositions on Standard Sample (X) in an amount of 1 g polymer per square meter to prepare Thermally developable Light-Sensitive Elements (P), (Q) and (R), respectively.

Compositions of Subbing Layer P: Vinyl Chloride/Vinyl Acetate Copolymer (90:10 by weight) 15 g Methyl Ethyl Ketone 200 ml Q: Vinyl chloride/Vinyl Acetate Copolymer (90: 10 by weight) 15 g Compound (3) of the present invention 150 mg Methyl Ethyl Ketone 200 ml R: Vinyl Chloride/Vinyl Acetate Copolymer (90: 10 by weight) 15 g Compound (6) of the present invention 150 mg Methyl Ethyl Ketone 200 ml In all of the above-described Thermally Developable Light-Sensitive Elements (M) to (R), the light-sensitive and heat-sensitive layer was coated in an amount of 0.4 g silver per square meter.

These Thermally Developable Light-Sensitive Elements (M) to (R) were each exposed to light of 3 X 10 lux.sec. through an optical wedge and then heated for 9 seconds. The photographic properties and the whiteness were measured and the results obtained are shown in Table 3 below.

TABLE 3 Thermally Developable Light-Sensitive Element M N O P Q R Component (c) None Present Present None Present Present Component (c) - Light-sensitive Overcoat - Subbing Subbing Location and heat- layer layer layer sensitive layer D= 1.30 1.32 1.28 1.35 1.40 1.40 Dmjn 0.15 0.17 0.12 0.12 0.08 0.08 Sensitivity 100 180 140 200 240 260 Whiteness 4 8 8 4 9 10 The sensitivity is a relative value of the reciprocal of the exposure amount required to provide a density of 0.1 above fog, assuming that the sensitivity of Thermally Developable Light-Sensitive Element (M) is 100.

WHAT WE CLAIM IS: 1. A dry processing type recording element comprising a support having, thereon directly or indirectly, one or more layers containing at least (a) an organic silver salt and (b) a reducing agent, and wherein (c) at least one compound represented by the following general formula (I):

wherein A represents a

group, a

group or a

group and R represents the atoms necessary to complete a 2-benzoxazolyl group, which may be substituted with one or more substituents which do not hinder the fluorescent whitening ability of the compound represented by the general formula (I), is present in the support or in at least one layer in the support.

2. A dry processing type recording element as claimed in Claim 1, wherein the compound represented by the general formula (I) is a compound represented by the following general formula (it), (III) or (IV):

wherein R, and R2, which may be the same or different, each represents a hydrogen atom or a substituent which does not hinder the fluorescent whitening ability of the compound represented by the general formula (it), (III) or (IV).

3. A dry processing type recording element as claimed in Claim 2, wherein R1

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. (M) to (R), the light-sensitive and heat-sensitive layer was coated in an amount of 0.4 g silver per square meter. These Thermally Developable Light-Sensitive Elements (M) to (R) were each exposed to light of 3 X 10 lux.sec. through an optical wedge and then heated for 9 seconds. The photographic properties and the whiteness were measured and the results obtained are shown in Table 3 below. TABLE 3 Thermally Developable Light-Sensitive Element M N O P Q R Component (c) None Present Present None Present Present Component (c) - Light-sensitive Overcoat - Subbing Subbing Location and heat- layer layer layer sensitive layer D= 1.30 1.32 1.28 1.35 1.40 1.40 Dmjn 0.15 0.17 0.12 0.12 0.08 0.08 Sensitivity 100 180 140 200 240 260 Whiteness 4 8 8 4 9 10 The sensitivity is a relative value of the reciprocal of the exposure amount required to provide a density of 0.1 above fog, assuming that the sensitivity of Thermally Developable Light-Sensitive Element (M) is 100. WHAT WE CLAIM IS:

1. A dry processing type recording element comprising a support having, thereon directly or indirectly, one or more layers containing at least (a) an organic silver salt and (b) a reducing agent, and wherein (c) at least one compound represented by the following general formula (I):

wherein A represents a

group, a

group or a

3. A dry processing type recording element as claimed in Claim 2, wherein R1

or R2 is an alkyl group having 1 to 5 carbon atoms, an allyl group, a phenyl group or a naphthyl group.

4. A dry processing type recording element as claimed in Claim 1, 2 or 3, where the compound represented by the general formula (I) is present in the support, a subbing layer, a recording layer containing said organic silver salt or an overcoat layer.

5. A dry processing type recording element as claimed in Claim 4, wherein the compound represented by the general formula (I) is present in the recording layer and is present in an amount from 0.01 to 100 gram per mole of the organic silver salt (a).

6. A dry processing type recording element as claimed in Claim 4, wherein the compound represented by the general formula (I) is present in the support, a subbing layer or an overcoat layer and is present in an amount of from 1 to 400 milligrams per square metre of the support.

7. A dry processing type recording element as claimed in any preceding claim, wherein the compound represented by the general formula (I) is any of Compounds (1) to (9) shown hereinbefore.

8. A dry processing type recording element as claimed in any preceding claim, which additionally includes, in proximity with said organic silver salt (a) (d) a photocatalyst capable of catalyzing in the presence of light, the reaction of components (a) and (b).

9. A dry processing type recording element as claimed in Claim 8, wherein said photocatalyst is a light-sensitive silver halide.

10. A dry processing type recording element as claimed in any preceding claim, which element comprises a support having thereon, in order, a subbing layer containing component (c) and a heat-sensitive layer containing component (a) and component (b).

11. A dry processing type recording element as claimed in any of Claims 1 to 8, wherein the recording element comprises a support having thereon a subbing layer containing component (c) and a light-sensitive and heat-sensitive layer containing component (a), component (b) and component (d).

12. A dry processing type recording element as claimed in Claim 10 or 11, wherein the subbing layer contains a copolymer of vinyl chloride and vinylidene chloride or a copolymer or vinyl chloride and vinyl acetate as a binder.

13. A dry processing type recording element as claimed in Claim 1, substantially as hereinbefore described with reference to any of the Examples.

14. A photograph made by imagewise exposure and thermal development of a recording element as claimed in any preceding Claim.