Bis-pyridinium Salt And A Phenyl Boranate As Photosensitive Combination

Abstract

Dark colored images are obtained by imagewise exposure of light-sensitive layers containing bis-pyridinium compounds and organic boran compounds as explained below.

Description

The invention relates to light-sensitive materials which contain, as light-sensitive substances, bis-pyridinium compounds which are converted into dark colored substances by the action of light.

Numerous processes in which light-sensitive organic substances are used for recording images are known. Some of these processes are based on photochemical rearrangements or on reactions of organic compounds which result in a color change. Such photochemical reactions of organic compounds have been comprehensively described e.g. in "Praparative organische Photochemie" (A. Schonberg, Springer-Verlag 1958 ) and in "Light-Sensitive Systems" (J. Kosar, John Wiley and Sons, New York, 1965).

These reactions include e.g. the formation of monomethine dyes by the photolysis of trihalomethyl compounds in UV light in the presence of aromatic or heterocyclic compounds which by virtue of their constitution have CH ring members which are highly reactive in condensation or diazo coupling reactions.

In these processes, these layers are either initially light-sensitive or the reactive components for the photochemical reaction must be added before exposure. The systems previously known are only of limited utility because their sensitivity to light is generally too low.

A certain improvement has been provided by the light-sensitive materials described in French Pat. specification No. 1,526,496. These materials contain cyclic imides of aryl polycarboxylic acids in which the imide nitrogen is substituted with olefinically unsaturated linear or cyclic aliphatic groups.

Even these last mentioned substances do not have sufficient light sensitivity for certain practical purposes. Moreover, they cannot be used for the special recording materials required for computers and oscillographs, which are not only required to have a relatively high sensitivity to light but in which the color forming reaction should be reversible, i.e., the image formed should be able to be extinguished so that the recording material can be used again.

It is among the objects of the invention to provide light-sensitive materials which are free from silver halides, which materials have sufficient sensitivity to light and yield sufficiently deeply colored reaction products.

Another object of the invention lies in the production of photographic recording materials in which the image produced on exposure can be extinguished either spontaneously or by additional measures so that the material can be used again.

I now have found that photographic materials which contain a light-sensitive composition of phenyl boranates and bis-pyridinium salts are suitable for recording images. Suitable compounds may be represented by the following formulas: ##SPC1##

In which

R represents (I) an aliphatic group containing up to 18 carbon atoms, preferably up to five carbon atoms, which may be saturated or unsaturated and may contain further substituents, e.g., phenyl, halogen such as fluorine, chlorine or bromine, hydroxyl which may be esterified, in particular with short chain aliphatic carboxylic acids containing up to six carbon atoms, carboxyl, esterified carboxyl in which short chain aliphatic alcohols are particularly suitable for the ester component, acyl, especially acyl radicals derived from short chain aliphatic carboxylic acids, sulfonamide in which the amide group may be substituted with alkyl, aryl, especially phenyl, acyl which is advantageously derived from short chain aliphatic carboxylic acids or benzene carboxylic acids, or another sulfonamide group, (II) a cycloalkyl group, e.g., cyclopentyl or cyclohexyl, or (III) an aryl group, in particular a radical of the phenyl or naphthyl series which may be substituted in the same way as the aliphatic radical mentioned under (I);

R.sup.i represents an aryl group such as phenyl or naphthyl, in particular a radical of the phenyl series; these rings may also be interconnected and this radical may carry other substituents, e.g., alkyl, preferably containing up to five carbon atoms, halogen such as chlorine or bromine, hydroxyl, alkoxy, carboxyl, esterified carboxyl, nitro, nitrile, carbamoyl, sulfonic acid, sulfonamide or sulfonic acid ester groups;

R.sup.ii represents a nitrile or R.sup.I group;

n is 0 or 1.

The nature of the anion or cation is not critical. It will depend mainly on the method of preparation used for the above components. Suitable anions are, e.g., halide ions, especially chloride or bromide, sulfate ions, sulphonate ions such as toluene sulfonate and methane sulfonate, etc.

Suitable cations are protons or cations of the alkali metals, depending on the pH of the solution of the components or the pH of the layer. Cations of the alkaline earth metals or ammonium ions which may carry organic substituents may, of course, also be used. The only essential condition for the light sensitivity of the material according to the invention is the simultaneous presence of bis-pyridinium ions and phenyl boranate ions.

The following are examples of suitable compounds:

Bis-pyridinium cations: ##SPC2##

Phenyl boranates: ##SPC3##

The above compounds are prepared by known methods. For the bis-pyridinium compounds, reference may be made, for example, to the publication by E. Weitz, Zeitschrift fur Ang. Chemie, 1954, page 657 et seq and for the phenyl boranates to the publication by G. Wittig, Ann. 563 (1949) page 114.

The bis-pyridinium compounds and phenyl boranates need not be present in stoichiometric quantities in the light-sensitive material. It is sufficient if one of the components is present in an amount of about 10 to 90 percent by weight based on the total weight of the components. The mixture of compounds preferably contains about 40 to 60 percent by weight of one of the compounds.

The photochemical reaction of the above mentioned compounds will take place both in solution and in the solid phase. In practice, these substances are applied to any layer support either singly or mixed or as mixtures of several bis-pyridinium compounds or phenyl boranates, dissolved or finely divided, with or without binder. The substances are applied by known methods consisting of application or spraying of solutions or casting from solutions or suspensions with layer forming natural colloids or synthetic resins. Suitable for this purpose are gelatine, cellulose, cellulose esters, cellulose ethers, polycarbonates, especially those based on bis-phenylol alkanes, polyesters, especially those based on polyethylene terephthalate, polyamides, polyurethanes and various film-forming polymers or copolymers of olefinically unsaturated monomers such as vinyl chloride, vinyl acetate, styrene, olefinically unsaturated carboxylic acids, their esters or other derivatives such as maleic acid anhydride, acrylic acid or methacrylic acid and their derivatives, as well as polyethylene or polyvinylidene chloride, e.g., in the form of their aqueous dispersions.

The bis-pyridinium compounds may also be contained in a separate layer and the boron compounds may be contained in a second layer which is in contact with the first.

The usual materials are suitable as layer supports, e.g., paper, glass or natural or synthetic materials such as cellulose esters, especially cellulose acetate or cellulose acetobutyrates, polyesters, especially those based on polyethylene terephthalate, polycarbonates, particularly those derived from bis-phenylol alkanes, polystyrene or the like. The layer supports may be transparent or contain pigments such as titanium dioxide, barium sulphate, etc. The surface of the layer support may be smooth or profiled.

The substances for use according to the invention may, of course, be added directly to the layer support. In the case of a layer support of paper, it is sufficient, e.g., to simply to bathe the support material in a solution of the components.

The light-sensitive compound for use according to the invention may also be applied in self-supporting layers. Layer binders of the type mentioned above are also suitable for this purpose. In principle, it is immaterial which layer binder is used and a suitable layer binder can easily be chosen by simple tests from the wide variety of known natural or synthetic hydrophilic or hydrophobic layer forming substances.

Suitable solvents for the compounds for use according to the invention are, e.g., water, short chain aliphatic alcohols such as methanol or ethanol, acetone, dimethyl formamide or the like.

The concentration of the light-sensitive substances in the binder may be varied within any limits. The gradation or maximum density can be influenced by varying the concentration as well as the application. When using binders which swell in water, e.g., gelatine, the pH may be varied within the limits at which no significant change takes place in the binder, such as degradation in the case of gelatine. The substances are advantageously used in quantities of 1 to 80 percent, based on the dry layer.

Casting additives, e.g., wetting agents or compounds which improve the mechanical properties (e.g., hardness) may be added to the layers.

On exposure to light, the light-sensitive compounds used in the materials according to the invention yield colored products which are stable for several hours to several days, depending on the nature of the reactants and the structure of the light-sensitive layer.

These products formed in the exposed areas may be stabilized by the addition of certain compounds so that they remain visible for some time. Hydroxyl-substituted aromatic compounds, particularly those of the phenyl or naphthyl series, e.g., hydroquinone, pyrocatechol, naphthols and the like, are suitable for this purpose. The same effect is achieved with heterocyclic compounds which contain nitrogen, e.g., pyrrolidones, especially N-methyl pyrrolidone, or acid amides such as dimethyl formamide. A particular advantage of the layers according to the invention is that the images produced in them can be extinguished. This can be done very simply by moistening the layers with water. Corrections can thus be made very easily on the image or the whole material can be rapidly regenerated. Reversion of the colored image substance to the original colorless light-sensitive form can be accelerated by heating. The light-sensitive material remains completely suitable for use and can immediately be exposed again when dry.

For these reasons, the materials according to the invention are particularly important for processes in which extinction of the image and reuse of the material are required.

The photographic images obtained in this way can be fixed by rendering the compounds in the unexposed parts of the layer insensitive to light. This can be achieved, e.g., by means of reagents which react with one of the components to form stable colorless products. Separation of exposed and unexposed parts in the layer can also be achieved by selectively dissolving out one of the components with suitable solvents.

The layers according to the invention are generally pale yellow in color. The are sensitive to UV light, including the longer wavelength end of the range, so that in principle they can be exposed with ordinary artificial light. They are particularly suitable for exposure with nitraphot lamps, neon tubes and laser light. The exposure time depends, of course, on the intensity of the source of light, the distance of the layer from the source of light and the sensitivity of the layer. Exposure times of a few seconds to several minutes are generally sufficient.

The two salts may, if desired, be exposed in two separate layers so that the light-sensitive compound is only formed subsequently by diffusion. One may, of course, apply a protective layer by casting or bonding; the half-life time of the image can thus be increased to practically any value.

It is especially unexpected and advantageous that the layers according to the invention can be spectrally sensitized.

The usual compounds used in silver halide photography may be used as sensitizers. Suitable sensitizers are, e.g., cyanine dyes, xanthylium dyes, acridinium dyes or the like. The sensitizing dyes are added in quantities of about 1/500 to 1/10,000 of the weight of the phenyl boranate. Sensitized layers are additionally sensitive to the visible range of the spectrum.

EXAMPLE 1

The following solution is cast on a layer support of baryta paper:

0.4 g of compound II,2 are dissolved in 10 ml of water and mixed with 30 ml of 10 percent gelatine. A solution of 0.45 g of compound I,1 in 10 ml of water, 20 ml of a 10 percent aqueous gelatine solution and 10 ml of a 10 percent aqueous solution of polyvinyl pyrrolidine are added to this mixture at 40.degree. C.

The thickness of the dry layer is 16 mm. It is exposed imagewise to a nitraphot lamp at a distance of 10 cm for 2 minutes. A deep blue image is obtained on the slightly yellowish layer.

The image persists for several hours and disappears completely within a few days. It can also be made to disappear within seconds by moistening with water. After drying, the layer is again light sensitive.

EXAMPLE 2

If in the casting solution for the above layer the polyvinyl pyrrolidone is replaced, e.g., by 1 g of hydroquinone dissolved in 10 ml of water, the image obtained after suitable processing is deep blue and persists for much longer, about 2 days. If a protective layer containing 5 percent of gelatine is cast on this light-sensitive layer, the image persists for over a week.

The above mentioned layer can be spectrally sensitized. If, for example, 0.01 g of 5,6-benzo-benzothiazole purple dissolved in 10 ml of methanol is added to the casting solution, a pale pink layer is obtained which is sensitive to green light. The exposure time when using a halogen lamp is 30 seconds. The distance from the source of light was again 10 cm. The pale pink layer turns violet on exposure.

Sensitization to red light can be achieved by the addition of 0.001 g of pinacyanol to the above casting solution. The layer is exposed to a halogen lamp for 45 seconds. A deep blue negative image of the original is obtained.

EXAMPLE 3

The following solution is cast on a layer support of baryta paper:

0.85 g of compound II,2 are dissolved in 50 ml of 5 percent aqueous gelatine and added to a solution of 1.2 g of compound I,2 in 50 ml of 5 percent aqueous gelatine with vigorous stirring.

A pale yellow layer is obtained. Upon processing as in Example 1, a reddish violet negative image of the original is obtained.

EXAMPLE 4

The following casting solution is cast on a layer support of baryta paper:

0.85 g of compound II,2 are dissolved in 50 ml of 5 percent aqueous gelatine and mixed with a solution of 1.6 g of compound I,3 in 50 ml of 5 percent aqueous gelatine and 1 g of polyvinyl pyrrolidone.

A light yellow layer is obtained which when exposed as in Example 1 yields a reddish violet image.

EXAMPLE 5

The following casting solution is cast on a layer support of baryta paper:

0.85 g of compound II,2 dissolved in 50 ml of 5 percent aqueous gelatine are poured into a solution of 0.9 g of compound I,1 with stirring and 1 ml of m-cresol is added.

The layer is then processed as described in Example 1. A blueish violet negative image of the original is obtained.

If exposure is carried out at elevated temperature, e.g., between 50.degree. and 70.degree. C the color change is to a distinctly darker color. Alternatively the exposure time can be reduced to obtain the same color change.

EXAMPLE 6

The following casting solution is cast on a layer support of baryta paper:

0.85 g of compound II,2 dissolved in 50 ml of a 1 percent aqueous solution of sodium alginate are poured into a solution of 0.9 g of compound I,1, also in aqueous sodium alginate, with stirring.

The layer is then processed as described in Example 1. A greyish violet image of the original is obtained.

If compound I,1 is dissolved in 50 ml of a 5 percent aqueous gelatine solution instead of 50 ml of sodium alginate solution, a violet gray image of the original is obtained.

EXAMPLE 7

A solution of 0.67 g of compound I,1 in 50 ml of a 5 percent aqueous gelatine solution which contains 1 ml of polyvinyl pyrrolidone and 1.5 ml of a 10 percent aqueous saponin solution is applied to a layer support of cellulose triacetate. When this first layer has partly dried, a solution of 0.75 g of compound II,2 in 50 ml of 5 percent gelatine solution which contains 1 ml of polyvinyl pyrrolidone and 1.5 ml of saponin solution is applied to it. When the layer is completely dry, an almost colorless light-sensitive material is obtained on which a dark blue image is obtained on exposure as described in Example 1.

Claims

I claim:

1. A silver halide free photosensitive material containing a light-sensitive combination of a bis-pyridinium salt component of the following formula ##SPC4##

and a phenyl boranate component of the following formula

in which formulae

R = (i) an aliphatic group having up to 18 carbon atoms, (II) cycloalkyl, (III) aryl;

R.sup.i = aryl or

R.sup.ii = nitrile or aryl;

n = 0 or 1, said bis-pyridinium salt component being present in an amount of from about 10 percent to 90 percent by weight of said combination.

2. A photosensitive material as claimed in claim 1, wherein the bis-pyridinium salt component is ##SPC5##

and the phenyl boranate is

3. A photosensitive material as claimed in claim 1 wherein the bis-pyridinium salt component is ##SPC6## and the phenyl boranate component is

4. A photosensitive material as claimed in claim 1 wherein the bis-pyridinium salt component is ##SPC7## and the phenyl boranate component is