US3351467A - Method of fixing photographically exposed oxygen-sensitive free radical photosensitive film - Google Patents

Description

3,351,467 Patented Nov. 7, 1967 fiFice METHGD F FIXHNG PHOTOGRAPHICALLY E"- PQSED @XYGEN SENSHTHVE FREE RADHJAL PHOTUSENSHTHVE FiLM Robert E. Sprague, Chagrin Fails, John A. Stewart, Parma, and James M. Lewis, Cleveland, Ohio, assignors to Horizons Incorporated, Cleveland, Ohio, :1 corporation of New .lersey No Drawing. Filed Get. 10, 1363, Ser. No. 315,357

8 Claims. (Ci. 96--48) This invention relates to free radical photography of the type described in any of the following United States patents and in other patents nad pending patent applications directed to photographic processes of a similar nature:

US. Patent 3,082,086, issued Mar. 19, 1963 US. Patent 3,102,027, issued Aug. 27, 1963 US. Patent 3,102,810, issued Sept. 3, 1963 US. Patent 3,104,973, issued Sept. 24, 1963 More particularly, it relates to improvements in the fixing of the image-bearing film resulting when free radical compositions such as those described in said patents are photographically exposed.

As described in the above noted patents and in articles published in Photographic Science and Engineering, two methods of fixing the exposed image-bearing free radical films have previously been utilized. In one, the film has been heated after exposure, the amount of heat being sufficient to drive off at least one essential reactive constituent from the film. This method has proven effective with com-positions based on diphenylamine and carbon tetrabromide such as those described in Photographic Science and Engineering, vol. 5, No. 2, pp. 98-l03, March-April 1961, and in United States Patent 3,042,515 or with compositions based on N-vinylcarbazole and carbon tetrabromide such as those described in United States Patent 3,042,517 and also with compositions such as those described in United States Patent No. 3,121,632, in which a ketone or an organic acid is used to activate certain types of leuco compounds such as leuco Opal Blue, but it has not been found useful with some other types of compositions, particularly those which exhibit a marked tendency to fog in the unexposed areas when subjected to heat.

The second method of fixing described in the above disclosures involves the application of a solvent rinse which extracts the unexposed color-producing reactants from the film composition and leaves the image dye in the film. Although this method is satisfactory for fixing images such as those produced by the processes described in United States Patents 3,095,303 and 3,096,144 and others wherein the dye forming component is colored, the solvent rinse procedure has the disadvantage that it is a wet process and that in order to have a clean background it is often necessary to perform several rinses which adds to the expense and time required for processmg.

The present invention is directed to an entirely different method of fixing and resides in the discovery that certain free radical photographic systems were found to require the presence of oxygen as an essential reactant in the propagation steps of the dye forming chain reaction. The fixing method of the present invention consists of the application of a solution containing a plastic film-former and an agent which penetrates into the photosensitive layer and which destroys or inhibits the effect of any oxygen already present in the photosensitive film and which produces a barrier which effectively prevents the diffusion of oxygen into the photosensitive film. The agent will be designated as an inhibitor in the description which follows but it is not intended that the use of this term shall be construed as a limitation on the invention.

The solution of film-forming plastic: and inhibitor may be sprayed onto the photosensitive layer or it may be applied thereto by an applicator bar or by a doctor-knife blade as in any of a number of commercially available film coating or processing machines. Since volatile solvents may be used for the fixing overcoat-solution, the applied coating dries very quickly and for all practical purposes is effectively a dry process for fixing.

While not wishing to be bound by any specific theoretical reasoning, it appears that this method of fixing is applicable only to those free radical photosystems which depend on the presence of oxygen in the color-forming chain reaction. The single exception to this generalization appears to be those photosensitive compositions in which a leucoxanthene compound is activated by carbon tetrabromide. Such compositions are effectively fixed by the application of the inhibitor-plastic as hereinafter described, although the photographic operability of these compositions presently is believed to be insensitive to oxygen. However, this generalization excludes the method of fixing herein-after described from use in such free radical photosystems as the diphenylamine/CBn; system described in US. 3,042,515, the styryl dye base/CBn; system described in US. Patent 3,095,303 and the cyanine dye base/CBr, system described in US. Patent 3,100,703. Furthermore, the method of fixing which constitutes the present invention cannot be used in the latent image photosysterns utilizing N-vinylcarbazole and CBr for example, wherein the visible image is developed by means of heat as described in United States Patent 3,042,517.

The compositions found to be effective for the purposes of this invention consist of three essential constituents, namely:

(1) An inhibitor,

(2) A film-forming plastic, and

(3) A solvent for the inhibitor and the film-forming plastic.

It is to be understood that more than a single inhibitor may be used, and that either the solvent or the film-forming plastic may consist of more than a single d. compo 1) INHIBITOR In the fixing overcoatings of this invention following compounds have been found to be effective as inhibitors:

Hydroquinone Benzoquinone Ascorbic acid l-phenyl-3-pyrazolidone 2,6-di-t-butyl-p-cresol 2,6-di-t-butylphenol N,N-diphenyl-p-phenylenediamine Ferric chloride Cobalt chloride Cobalt naphthenate Cobaltous thiocyanate (2) FILM-FORMING BINDER Any film-forming binders may be used as the basis of the fixing overcoat, it merely being necessary that the binder does not react chemically with the inhibitor, for which it is to serve as a physical support, and further that a relatively volatile solvent or mixture of such solvents be available for placing the binder and the inhibitor in solution.

Film-forming binders which have been found useful in the practice of this invention include the following:

Polystyrene, Polyvinyl chloride,

Polyvinylidene chloride, Methyl methacrylate, Half-second cellulose acetate, Butyrate,

Cellulose nitrate, and Polycarbonates.

(3) PROPORTIONS The relative proportions of solvent, film-forming binder and inhibitor in the fixing coating solution do not. appear to be critical except that the amount of inhibitor present in the coating after the solvent has evaporated or has been otherwise dissipated, must suflice for the desired fixing of the photosensitive composition beneath the fixing layer. While this may depend in some measure on the specific constituents in the photosensitive layer, it has been found that inhibitor concentration between 0.1% and 50% by weight in the dried overcoating film provide satisfactory protection against subsequent fogging.

The photosensitive compositions to which the instant invention has been found to be particularly applicable include those based on at least one leuco compound of the type illustrated in list A which follows and at least one activator of the type listed in list B which follows.

LIST A wherein each R represents a monovalent radical selected from the group consisting of diethyl N-, dimethyl N-, methyl ethyl N- and similar di-lower alkyl N-groups; Z

is a member selected from and 8; Q is a member selected from the group and N-H and wherein R represents a monovalent radical selected from the group consisting of methyl, ethyl, n-propyl,

when Z is oxygen and Q represents a member selected from the group consisting of NH and CH when Z is sulfur.

LIST B Z-mercaptobenzothiazole 2-mercapto-4-phenylthiazole 2-mercapto-fi-naphthothiazole mercaptobenzoic acid ot-mercaptoacetaniline Rhodanine 1,3 -diphenylpyrazolone 1-phenyl-5-mercaptotetrazole The following examples are intended to illustrate the practice of this invention and are not to be construed as limiting the same. In the examples all percentages are by Weight unless otherwise specified.

(31. Example 1 A light-sensitive film was prepared by coating a mixture of 50 milligrams of 3,6-tetramethyldiamino-9-(pdimethylaminophenyl)xanthene and mg. 2-mercaptobenzothiazole in 2 cc. acetone plus 2 cc. of 10% polystyrene in benzene. This mixture was coated 0.0015- inch wet thickness on polyester film, using the drawdown Bird applicator, and allowed to dry. A projection print was made on the film through a silver microfilm negative in a SOO-watt slide projector with an exposure of 15 seconds at a distance of 45 inches. The exposure produced an intense red print out image in the light-struck areas against a nearly colorless background in the unexposed part of the film.

A fixing solution composed of 50 mg. of ferric chloride dissolved in 2 cc. of acetone plus 2 cc. of a 10% solution of half-second cellulose acetate butyrate in acetone was applied to the exposed film by a drawdown technique, using the same Bird applicator which had been used for the original coating.

Half of the exposed film was covered with the fixing solution in the this fashion, the other half was left unprotected. After drying, the whole sheet was re-exposed for 5 minutes to the light of one reflector photoflood lamp at 12 inches distance; in the area protected by the ferric chloride plastic overcoat very little fogging occurred, while the unprotected area was turned dark purple, with no trace of the image remaining.

Example 2 A light-sensitive film was prepared and exposed in the same fashion as in Example 1, and a protective overcoat was applied, consisting of 50 mg. of hydroquinone dissolved in 2 cc. of acetone plus 2 cc. of 10% halfsecond cellulose acetate butyrate. The protected print was stable on re-exposure for one minute to a photoflood lamp at 12 inches distance, but fogged somewhat on 5- minutes exposure.

Example 3 A light-sensitive film was prepared by coating 2. mixture of 25 mg. of 2-mercaptobenzothiazole, 25 mg. of omercaptobenzoic acid and 100 mg. of 2,6-tetramethyldiamino-9-(p-dimethylaminophenyl)xanthene in 2 cc. acetone plus 2 cc. of 10% polystyrene in benzene, 0.0015- inch wet thickness on polyester film.

The dried film was exposed for 3 seconds through a silver microfilm negative in a SOO-watt slide projector at a distance of 45 inches, and half of the exposed film was topcoated 0.0015-inch wet thickness with a solution of 50 mg. ferric chloride in 2 cc. acetone plus 2 cc. of 10% half-second cellulose acetate butyrate in acetone.

The topcoated area was only slightly fogged on reexposed for 5 minutes to one reflector photoflood lamp at 12 inches distance, while the unprotected area was completely fogged.

Example 4 A photosensitive film was prepared by coating a mixture of 100 mg. of 3,6-bis(tetraethyldiamino)-9-(m-nitrophenyl)xanthene and 100 mg. of Z-mercaptobenzothiazole 1n 2 cc. of acetone plus 2 cc. of 10% polystyrene in benzene, 0.0015-inch wet thickness on baryta-coated paper. A projection print was made on this paper through a silver microfilm negative in a SOO-Watt slide projector at a distance of 45 inches with an exposure time of 30 seconds.

Part of the exposed sheet was topcoated 0.0015-inch wet thickness with a solution of 50 mg. of ferric chloride in 2 cc. of acetone plus 2 cc. of half-second cellulose acetate butyrate (10% in acetone). The entire sheet was then re-exposed for 5' minutes to a photoflood lamp at a distance of 12 inches. The topcoated area was only slightly fogged by this re-exposure, while the unprotected area was changed to a deep purple-blue color which completely obscured the image.

Example 5 A photosensitive film was prepared in the same fashion as in Example 4 except that the leucoxanthene compound was replaced by 100 mg. of leuco Opal Blue (tris-panilinotriphenylmethane). The dried film was exposed for one minute to a silver negative to the light from one reflector photoflood lamp at 12 inches distance. Half of the print prepared in this manner was topcoated with the stabilizing solution composed of 50 mg. of ferric chloride dissolved in 2 cc. acetone plus 2 cc. of 5% polystyrene in benzene. The coating was applied 0.0015-inch wet thickness, and the film was allowed to dry.

The topcoated area showed very little fog on re-exposure for 5 minutes to one photoflood lamp at 12 inches distance, while the uncoated, unprotected area was completely fogged.

Example 6 A light-sensitive film was prepared in the same fashion as in Example 1. The dried film was exposed for 5 seconds to a silver negative on a 500-watt slide projector at 45 inches distance, and part of the exposed film was topcoated 0.0015-inch wet thickness with a solution of one drop of cobalt naphthenate in 2 cc. acetone plus 2 cc. 10% polystyrene in tetrahydrofuran. After re-exposing for 5 minutes to one photofiood lamp at 12 inches distance there was very little fogging in the topcoated area while the unprotected part of the film was completely fogged.

In general, any of the other binders listed previously may be substituted for polystyrene or half-second cellulose acetate butyrate. Ferric chloride and cobalt naphthenate are the preferred inhibitors for use in this method of fixing.

It should be particularly noted that the present invention is not to be confused with the procedure described in Wainer US. Patent 3,042,515 in which the use of certain polyhydric phenols and aminophenols is described in connection with the stabilization of free radical films which are subsequently to be fixed by heat. Although it has been found that some of the phenolic compounds are operable in the instant invention, their effectiveness is significantly lower than the effectiveness of the iron and cobalt compounds hereinbefore described.

We claim:

1. A photographic method which comprises preparing an oxygen sensitive free radical photosensitive film, photographically exposing said film and thereafter applying a protective layer to at least one surface of said imagebearing photographically exposed film, said protective layer consisting essentially of a film-forming plastic and an inhibitor selected from the group consisting of ferric chloride, cobalt chloride, cobalt naphthenate and cobaltous thiocyanate dispersed throughout said film-forming plastic.

2. The method of claim 1 wherein the protective layer is applied as a solution consisting of a film-forming plastic, an inhibitor and a volatile solvent in which said filmforming plastic and said inhibitor are dissolved.

3. The method of claim 2 in which the solution is applied as a wet coating onto a photographically exposed film and the protective layer is formed by elimination of the solvent.

4. The method of claim 2 in which the solution is sprayed ontothe surface of a photographically exposed film.

5. A method of fixing the image in an oxygen-sensitive photographically exposed free radical photosensitive film which consists in applying a protective layer to at least one surface of said image-bearing photographically exposed film said protective layer consisting essentially of a film-forming plastic and an inhibitor selected from the group consisting of ferric chloride, cobalt chloride, cobalt naphthenate and cobaltous thiocyanate dispersed throughout said film-forming plastic.

6. The method of claim 1 wherein the amount of inhibitor present in said layer is about 1 part by weight per 10 parts by weight of film-forming plastic.

7. A laminate comprising an oxygen sensitive, free radical photosensitive composition in the form of a thin layer and a protective coating which prevents the intrusion of oxygen into the photosensitive constituents in said layer, consisting essentially of an inhibitor selected from the group consisting of ferric chloride, cobalt chloride, cobalt naphthenate and cobaltous thiocyanate dispersed in a thin layer of a film-forming binder, said coating being applied to at least one surface of said oxygen-sensitive film.

8. The laminate of claim 7 wherein the photosensitive composition consists essentially of a leuco compound selected from the group consisting of leuco xanthenes, leuco thiazines and leuco triarylmethane dyes and an activator for said leuco compound.

References Cited UNITED STATES PATENTS 3/1960 Ryskiewicz 4/1964 Agruss

Claims (1)

1. A PHOTOGRAPHIC METHOD WHICH COMPRISES PREPARING AN OXYGEN SENSITIVE FREE RADICAL PHOTOSENSITIVE FILM, PHOTOGRAPHICALLY EXPOSING SAID FILM AND THEREAFTER APPLYING A PROTECTIVE LAYER TO AT LEAST ONE SURFACE OF SAID IMAGEBEARING PHOTOGRAPHICALLY EXPOSED FILM, SAID PROTECTIVE LAYER CONSISTING ESSENTIALLY OF A FILM-FORMING PLASTIC AND AN INHIBITOR SELECTED FROM THE GROUP CONSISTING OF FERRIC CHLORIDE, COBALT CHLORIDE, COBALT NAPHTHENATE AND COBALTOUS THIOCYANATE DISPERSED THROUGHOUT SAID FILM-FORMING PLASTIC.