Photographic Element Containing A Light Sensitive Photobleachant And A Colored Stable 2-amino-aryl-7-oxyl-3-oxide-2-imidazoline Free Radical

Abstract

Direct-positive photographic compositions are disclosed, the compositions including a radiation-sensitive photobleachant and a colored, stable 2-amino-aryl-1-oxyl-3-oxide-2-imidazoline free radical. When the compositions are exposed to activating radiation for the photobleachant, the colored stable-free radical is bleached or decolorized such that the exposed areas of the composition exhibit lower density and/or different coloring than the unexposed areas. Direct positive images are produced thereby. These compositions can be carried on a support to prepare photographic elements.

Description

FIELD OF THE INVENTION

The present invention relates to photography and particularly to direct-positive photographic compositions and elements including a colored, stable-free radical and a photobleachant.

PRIOR ART

General reference to the use of stable-free radicals in single component imaging systems has been made in papers presented by W. R. Bard at SPSE 2nd Symposium on Unconventional Photographic Systems, Washington, D. C. Oct. 21-28, 1967 and at the Society of Plastics Engineers, Mid-hudson Section November, 1967.

The use of stable-free radicals as sensitizers to increase the photoresponsive characteristics of photoconductive insulating compositions and photohardenable polymer compositions is described in U. S. Pat. No. 3,434,833 to Fox issued Mar. 25, 1969.

Negative working direct imaging systems, i.e. those which are based on the formation of increased color or density in exposed areas, which systems relate to combinations of a color generator with a photooxidant are described in, for example, British Pat. No. 1,047,796; U. S. Pat. Nos. 3,359,109; 3,360,370; 3,395,018; 3,445,233; 3,445,234; and Canadian Pat. No. 798,260.

Furthermore, Canadian Pat. No. 822,049 discloses the use of light-sensitive free radicals which upon exposure to actinic radiation react with a color forming compound to produce areas of density in a negative system, and in a positive system a colored compound which is bleached to provide less density in the exposed areas.

Although many of these systems, as already described, make use of photo-imaging systems comprising a photo-active compound and a color producing compound which reacts with the photoactivator upon exposure to light, no systems have been disclosed which utilize 2-aminoaryl-1-oxyl-3-oxide-2-imidazoline colored stable-free radicals to produde a direct positive and photo-bleachant image. Other patents, describing the use of colored free radicals in combination with photobleachants are U. S. Pat. No. 3,600,168 and its corresponding patent, Canadian Pat. No. 874,372 and British Pat. No. 1,213,823.

A system such as the one described herein overcomes many of the disadvantages exhibited by conventional materials of this type which include relatively high cost, instability of images, generation of offensive odors or poisonous vapors making them difficult to handle, low speed, poor contrast and insufficient resolution. Furthermore, in many known systems, the use of halogenated organic photoactivators which are generally extremely volatile and poisonous is required.

Accordingly, it is an object of this invention to provide novel direct-positive photographic compositions and elements.

Another object of this invention is to provide new direct positive photographic processes.

Still other objects and advantages of the present invention will become apparent from a reading of the following specification and appended claims.

STATEMENT OF THE INVENTION

The objects of this invention are accomplished with direct-positive photographic compositions including a radiation-sensitive photobleachant, (i.e., a compound that when exposed to activating rays forms a species that can react with a colored, stable free radical to lower the density or change the color of the free radical) and a colored, stable free radical are provided. They are non-toxic, efficient and produce positive images on exposure. These compositions can be used in conjunction with a support material to prepare photographic elements. The photographic compositions can be coated on a support as a layer or imbibed into a porous support material.

DESCRIPTION OF PREFERRED EMBODIMENT(S)

Direct-positive (i.e. producing a positive image directly on exposure) photographic compositions of the present type include a radiation-sensitive photobleachant and a colored, stable free radical having the formula: ##SPC1##

wherein:

a. each of R.sup.1, R.sup.2, R.sup.3 and R.sup.4 independently represents one of alkyl group, an alkoxy group or an aryl group, and

b. R.sup.5 represents an aminoaryl group having from six to 14 atoms in a mono- or polycyclic aromatic nucleus, with the amino moiety having the formula ##SPC2## wherein each of R.sup.6 and R.sup.7 independently represents one of an alkyl group or an aryl group (preferably phenyl). In one preferred embodiment, R.sup.6 and R.sup.7 are alike.

As used herein, the term alkyl group includes straight or branched chain aliphatic groups having from one to eight carbon atoms in the carbon chain used to define the group nomenclature, such as methyl, ethyl, 2-chloroethyl, isopropyl, butyl, pentyl, heptyl, n-octyl, 7-methyloctyl and the like alkyl groups. Lower alkyl groups having one to four carbon atoms are preferred. The term alkoxy group refers to etherified alkyl groups, also designated alkyloxide groups, and include an alkyl moiety such as those described herein chemically bonded to an oxygen atom, for example, methoxy, ethoxy, propoxy, isobutoxy, pentyloxy, n-octyloxy, etc. Lower alkoxy groups having from one to four carbon atoms are preferred. The term aryl group, as used herein, refers to and includes aromatic groups derived from mono- and polycyclic carbocyclic nuclei and having from six to 14 atoms in a mono- or polycyclic nucleus, such as phenyl, p-tolyl, naphthyl, anthryl, etc.

Free radical precursors from which free radicals of the present type can be prepared are themselves able to be prepared by the reaction of an ortho bis(hydroxylamino) alkane with an appropriate arylamino benzaldehyde in an organic solvent. Depending on the particular substituents represented by R.sup.1, R.sup.2, R.sup.3 and R.sup.4, the ortho bis(hydroxylamino) alkane can be substituted with alkyl, alkoxy or aryl groups. As an example, when each of R.sup.1, R.sup.2, R.sup.3 and R.sup.4 is a methyl radical, the alkane is 2,3-bis(hydroxylamino)-2,3-dimethylbutane. Other precursors useful in preparing stable free radical precursors and stable free radicals described herein include such compounds as 2,3-bis(hydroxylamino)-2,3-dimethoxybutane, etc.

The stable free radicals of the present type are prepared by treatment of the appropriate stable free radical precursor with a suitable oxidation catalyst, for example active lead dioxide in benzene solution, or any other similar oxidation catalyst well known to those skilled in the art.

As mentioned herein, the colored, stable free radical is used in conjunction with a light-activatable photobleachant. When exposed to activating rays, e.g. ultraviolet light, other actinic rays visible light or the like, the photobleachants useful herein are capable of reacting with the free radical. It is theorized that this capability may be the result of the photogeneration of a reactive species such as a radical, radical ion, ion or hydrogen atom. Amplification factors may be introduced in some instances since two or more reactive species may be formed upon absorption of a single photon.

Exemplary photobleachants that may be utilized herein include the following: ##SPC3##

Generally, any one or more of the above-described photobleachants may be used in combination with the aforementioned stable-free radicals so that upon exposure to light, a reaction occurs which bleaches the colored free radical and produces a decrease in color density in exposed regions, thereby producing desired direct positive image. Generally, the mole ratio of free radical to photobleachant ranges from about 1:1 to about 1:10 and preferably between from about 1:1 to about 1:5.

To prepare a composite photographic composition, the colored free radical and the photobleachant can be included in a coating solution, optionally containing a polymer suitable support or cast or extruded into a self-supporting film and dried. Coating can be accomplished by dipping, flow coating, hopper coating, doctor blade coating, etc. It is desirable that the polymer binder for the free radical and the photobleachant as well as the solvent therefor and the support upon which the coating solution may be applied do not react with either the stable-free radical or the photobleachant. Among the polymeric binders which have been found useful herein are cellulose esters such as for example, cellulose acetate, cellulose acetate butyrate and cellulose acetate propionate; polyester materials, especially poly(ethylene therephthalate), polyvinyl and poly-.alpha.-olefin resins, all of which may be codissolved with the photoreactants using conventional solvents such as the alcohols, acetone, methylene chloride, naphtha and a wide variety of other materials. When a binder is used, the concentration of the combined free radical and photo-bleachant generally range from about 1 weight percent to about 90 weight percent, based on the total weight of the composition, with a preferred range occurring from about 2 weight percent to about 60 weight percent. However, the concentration of photo-reactants would be 100 percent in the case where a binder is not used and the active components are, for example, imbibed into a porous support.

If a support is utilized to prepare a photographic element. Useful materials include conventional photo-graphic support like glass, metal, paper or the resinous supports, e.g., cellulose acetate, poly(ethylene terephthalate), poly-.alpha.-olefins, polystyrenes, etc., which are well known in the photographic arts, may be used.

Once prepared, the photographic compositions or elements of the present type can be exposed to actuating rays for the photobleachant and image formation occurs directly on exposures. It is theorized that the reaction which occurs upon exposure of the photosensitive compositions of the present invention to activating rays may be described generically and most simply as follows: ##SPC4##

The following examples are included for a further understanding of the invention.

EXAMPLE I

A photographic composition of the present type is prepared by dissolving 0.03 g. of 1-oxyl-2-[4-dimethyl-amino phenyl]-4,4,5,5-tetramethyldehydroimidazole-3-oxide and .131 g. of 4-diethylaminobenzenediazonium tetra-fluoroborate along with 10 g. of cellulose acetate butyrate, in 25 mls. of 2-methoxyethanol plus 75 mls. of methylene chloride. The coating solution is coated on a paper support at a wet thickness of 0.005 inches. When dry, a portion of the photographic element is imagewise exposed to ultraviolet rays in the exposure in a Filmsort 086 unit of a diazo printer which contains a mercury arc source. The coating bleached to nearly colorless in the exposed area, while it remains unchanged in unexposed areas. Color change is from blue to colorless in exposed areas. A control coating is prepared in the same manner, except that the diazonium salt photobleachant is omitted. This coating is then exposed in the same manner, in a Filmsort 086 Diazo printer. After a period of 10 minutes, the element is removed, and shows no visible signs of bleaching in the exposed areas. No differential density between the exposed and unexposed areas can be detected thereby indicating that the free-radical exhibits high stability.

EXAMPLE II

The procedure described in Example I is used except that the diazonium salt component is replaced by 0.5 g. of polyethylene glycol, average MW 600. This coating is also bleached in the exposed areas from blue to colorless, but remains unchanged in unexposed areas.

EXAMPLE III

The procedure described in Example I is used to prepare another photographic element, except the diazonium salt is replaced by 0.04 g. of benzophenone, and 0.04 g. of benzhydrol were used; and also 2 g. of cellulose acetate butyrate in 5 mls. of 2-methoxyethanol plus 15 mls. of methylene chloride is used. The resultant element bleaches in exposed areas but remains unchanged in unexposed area. Color change is from blue to colorless.

It will be appreciated that the convenient procedures described herein, such as in the Examples, can be used with any stable free radicals and photo-bleachants of the present type. Such variations will be apparent to those skilled in the art.

Other ingredients such as sensitizers, matting agents, plasticizers, etc. may also be added to the imaging systems of the present invention to improve various aspects and characteristics thereof. Fixing and/or stabilization treatments may be used to improve the quality and/or stability of the images formed using the imaging products of the present invention.

For example, in some instances, e.g., when a bis-2,4,5-triarylimidazole is used as the photobleachant, it may be desirable to obtain a degree of fixation such as might be required for use of the image in the presence of ultraviolet light. This can be accomplished by preferentially eliminating the photo-bleachant, e.g., bis-2,4,5-triarylimidazole, from the unexposed areas through the use of solvent washout of the photobleachant or a redox system such as the quinone-polyethylene oxide system which is activated at wavelengths different than the photo-bleachant and on activation deactivates the photobleachant. When a diazonium salt is used as the photobleachant, it may be removed from the non-image areas by incorporating a conventional diazo coupler, for example 2-hydroxynaphthol in the system and coupling the diazonium salt by exposure of the system to a basic medium without generating extensive density in the non-image area.

There has thus been described herein a series of imaging elements which find advantageous use in applications wherein photosensitive elements which react only to, for example, light of short wavelength, e.g., specific wavelengths of ultraviolet light, but have low sensitivity to light of longer wavelengths, e.g., visible light, so that the resulting image is substantially stable under normal conditions of use and does not require additional fixation or stabilization treatments.

The invention has been described in detail with specific reference to preferred embodiments thereof, however, it will be readily recognized that variations and modifications can be made within the spirit and scope of the invention and the same should not be limited except as defined in the appended claims.

Claims

There is claimed:

1. A direct-positive photographic composition comprising a radiation-sensitive photobleachant selected from the group consisting of 4-dialkylaminobenzene diazonium salts, 4-alkoxybenzenediazonium salts, 4-aryloxybenzenediazonium salts, bis-2,4,5-triphenylimidazoles, azobispropionitriles, poly-(ethylene glycols), benzophenones, tetraphenyl pyrroles, benzo-peroxides, cumene hydroperoxides, 1,8-pyrenediones and mixtures thereof and a colored, stable free radical having the formula: ##SPC5##

wherein:

a. each of R.sup.1, R.sup.2, R.sup.3 and R.sup.4 independently represents one of an alkyl group having from one to eight carbon atoms, an alkoxy group or an aryl group having from six to 14 carbon atoms, and

b. R.sup.5 represents an aminoaryl group having from six to 14 atoms in a mono or polycyclic aromatic nucleus, said amino moiety having the formula ##SPC6##

R.sup.6 and R.sup.7 each representing independently one of an alkyl group or an aryl group as described above.

2. A direct-positive photographic composition as described in claim 1 wherein, in the free radical, each of R.sup.1, R.sup.2, R.sup.3 and R.sup.4 is a lower alkyl group and each of R.sup.6 and R.sup.7 are alike and are either a methyl group, and ethyl group or a phenyl group.

3. A direct-positive photographic composition as described in claim 1 wherein said free radical and said photobleachant are included in a molar ratio of from 1:1 to about 1:10.

4. A direct-positive photographic composition as described in claim 1 and further comprising a film-forming polymeric binder.

5. A direct-positive photographic composition as described in claim 4 wherein said binder is cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate or gelatin.

6. A photographic element comprising a support having thereon a direct-positive photographic composition as described in claim 1.

7. A photographic element comprising a support having thereon a direct-positive photographic composition as described in claim 1.

8. A photographic element as described in claim 6 wherein said support comprises a porous material and said direct-positive photographic composition is imbibed into the pores of said support.