GB2072866A

GB2072866A - Photographic Surveillance Film

Info

Publication number: GB2072866A
Application number: GB8011179A
Authority: GB
Original assignee: Ciba Geigy AG
Current assignee: Novartis AG
Priority date: 1980-04-02
Filing date: 1980-04-02
Publication date: 1981-10-07

Abstract

A surveillance film is described which has an optically transparent support base which is coated on both sides with a silver halide emulsion layer. There is between the emulsion layers on opposite sides of the support base either one anti-halation underlayer on one side of the base or two anti-halation underlayers, one on each side of the support base. The density of the anti-halation underlayer(s) is sufficient to prevent light which exposes the silver halide emulsion layer on one side of the support base from exposing the silver halide emulsion layer on the other side of the support base. The anti-halation dyes are readily dischargeable by alkali metal sulphite. Since large lengths of film are used in surveillance work of which only an occasional frame needs to be developed, the use of the above design of film assembly reduces the use of expensive film base by half. The silver is easily recoverable.

Description

SPECIFICATION Photographic Film Material This invention relates to photographic film material and in particular to surveillance film.

Surveillance films are used to monitor offices, stores, banks and the like, long lengths of film being fed through a cinematographic camera and one frame being exposed every minute, for example.

For the most part no incident occurs during the time the film is being exposed and therefore it is not necessary that the film be developed. However on those rare instances when there is an incident during the period the film is exposed, for example an intruder or a bank raid, it is required that a very clear photographic reproduction of the incident is obtained because such a reproduction could be used as evidence in subsequent court proceedings. It is for this reason that surveillance film material is preferred to video tape for surveillance purposes because a very clear reproduction of the incident on video tape is difficult.Nevertheless, because of the increasing price of silver and the consequent increase in price of silver halide based photographic materials and the increasing price of oil-based materials such as photographic film base, ways are being sought to minimise the cost of silver-based photographic film materials.

We have discovered a way of making maximum use of photographic film material of use for surveillance purposes.

According to the present invention there is provided photographic silver halide film material which comprises an optically transparent support base having coated on each side thereof at least one photographic silver halide emulsion layer, there being present between the silver halide emulsion layers(s) on opposite sides of the support base either one anti-halation underlayer on one side of the support base or two anti-halation underlayers one on each side of the support base, the density of the anti-halation underlayer(s) being sufficient to prevent light which exposes the silver halide emulsion layer on one side of the support base from exposing the silver halide emulsion layer(s) on the other side of the support base.

By anti-halation underlayer is meant a layer which lies between the photosensitive layer and the support base in photographic material and which comprises light absorbing dyes or pigments which absorb light over the spectral region to which the associated photosensitive layer is sensitive, the dyes or pigments either being uniformly readily bleachable or dischargeable. Anti-halation underlayers contain no photosensitive material therein. Thus after the photosensitive layer has been processed or during the processing thereof the dyes or pigments in the anti-halation underlayer are either bleached or washed out of the layer leaving a clear transparent layer between the support base and the silver image in the photosensitive layer.

In the photographic material of the present invention preferably the combined optical density of the anti-halation underlayer(s) is not less than 4.0. This is sufficient to prevent light which exposes one silver halide emulsion layer on one face of the photographic material from exposing the silver halide emulsion layer on the opposite side of the support base.

It is necessary that anti-halation underlayers can be processed to leave a completely clear layer and no stain. Thus preferably the dyes or pigments which comprise the anti-halation material are bleached rather than rendered dischargeable as some stain is prone to remain in the anti-halation layer or in another layer of the photographic material. Thus most anti-halation underlayers comprise dyes which are readily bleached in photographic processing solutions, such as silver halide developing and fixing solutions, especially those which comprise an alkali metal sulphite.

Thus the preferred anti-halation underlayer for use in the photographic material of the present invention is an underlayer which comprises a dye which is bleached in an aqueous solution of an alkali metal sulphite.

However other types of bleachable anti-halation underlayers have been described, for example the anti-halation underlayers described in U.S. reissue patent 29168 in which the dyed layer is decolourised by the action of heat. In U.S.P. 411699 anti-halation underlayers are described which contain a photobleachable dye, the dye being bleached in an overall strong exposure to light after imagewise exposure and processing of the photographic material. Both these types of anti-halation underlayer may be used in the photographic material of the present invention.

Preferably the photographic material of the present invention comprises in order a gelatin supercoat layer, a gelatino silver halide emulsion layer, a gelatin based anti-halation underlayer comprising a dye bleachable in alkali metal sulphite solution and having an optical density of substantially 2.0, and optically clear support base, a second gelatin-based anti-halation underlayercomprising a dye bleachable in an alkali-metal sulphite solution and having an optical density of substantially 2.0, a second gelatino silver halide emulsion layer and a second gelatin supercoat layer.

It is preferred to have an anti-halation underlayer on each side of the support base because it is not easy to bleach completely a heavily dyed layer in alkali metal sulphite solution and because of the better photographic reproduction obtained when an anti-halation underlayer is present.

According to another aspect of the present invention there is provided a process for the production of a photographic image using the photographic material of the present invention which comprises imagewise exposing at least one side of the photographic film material and then applying, to that side of the photographic film which was being exposed at the time at which an incident occurred a photographic record of which is required, a silver halide developing solution, then after development of the silver images on one side of the photographic material, fixing out the undeveloped silver halide on both sides of the photographic film material using a photographic silver halide fixing solution and simultaneously with the photographic processing or subsequent thereto clearing the anti-halation underlayer or layers of dye or pigment.

When the preferred photographic material of the present invention is employed preferably both the silver halide developing solution and the silver halide fixing solution contain an alkali metal sulphite, usually sodium sulphite.

The dissolved silver in the used fixing solution can be removed to recover the silver.

Most usually virtually all the silver is recovered from the exposed surveillance film of the material as it is not developed. However by use of the photographic film material of the present invention the amount of support base used is halved compared with the usual survellance film material, thus resulting in a considerable saving in cost of the material.

The support base used in the photographic material of the present invention may be any of the support bases used for the production of photographic film, for example cellulose triacetate, cellulose acetate-butyrate or polyethylene terephthalate. The thickness of the support base is usually about 0.1 mm.

For the preferred film material of the present invention any of the readily bleachable anti-halation dyes which have been proposed to be used in anti-halation underlayers may be usde. Examples of suitable dyes are described for example in German published patent applications No. 2835074 and No.

283554 and published British patent application No. 2014598. The silver halide emulsion of the surveillance film material is sometimes not optically sensitised and in this case is sensitive to blue light only. A single anti-halation dye is usually sufficient in this case to act as a sufficient light barrier in the anti-halation underlayer(s) of the photographic material of the present invention. If however the silver halide emulsions are ortho-chromatically or panchromatically sensitised it is preferred to use a combination of anti-halation dyes in the anti-halation underlayer(s) of the photographic film material of the present invention to provide a complete light barrier between the emulsion layers on opposite sides of the support base. Suitable combinations of anti-halation dyes are described for example in published British patent application No. 2002916A.

The format of the photographic film material of the present invention is preferably 16 mm or 35 mm cine film. Most preferably the film material is single perforated. This is to help prevent exposing the same side of the film material twice. Most preferably the film material of the present invention is exposed in a cine camera which works on one perforation line and the camera is adapted to or capable of reversing the direction of wind on the take-up. For example, if the camera is presented with film wound so that emulsion A is facing in and emulsion B is facing out, then, after exposure, the film should preferably be wound on the take-up so that emulsion A is facing out and emulsion B is facing in. When the take-up reel is transferred to the feed position in the camera the unexposed side of the film material will be presented for exposure.Preferably the camera operator cuts a mark on the leader of the film when threading up tha film for the first pass. This is to prevent the film being passed accidentally through the camera for a third pass.

If it is required to process the film material to obtain a photographic reproduction of an incident which occurred when the film was being exposed, the film material is removed from the take-up position in the camera and fed to a processor which applies a silver halide developing solution to the side of the film last exposed. The silver halide developing solution must be applied only to the last exposed side which contains the frames which are required to be developed to obtain a reproduction of the incident.

The silver halide developing solution can be applied to the correct side of the film material only by, for example, a roller coated with the developing solution, a spray coating apparatus or a slot applicator device.

Examples of suitable applicator devices are described in British patent specification 814080.

Webs soaked in suitable processing solutions can also be used. Examples of such web processing are given in British patent specifications 352012 and 964514.

Furthermore the use of processing solutions rendered viscous makes the application of the processing solution to the correct side of the film easier. Examples of the use of viscous processing liquids are given in U.S. patent specification 3190205, 2948209, 3574618 and 3157103.

The following Example will serve to illustrate the invention.

Example Cine film of 16 mm size and perforated was prepared having the following layers in order: 1 st supercoat layer-gelatin at a coating weight of 1.0 g/m2 emulsion.

1 st photosensitive silver halide layer-silver iodobromide comprising 95% bromide and 5% iodide at a silver coating weight of 6.0 g/m2 in a gelatin binder having a coating weight of 10 g/m2, silver halide panchromatically sensitised by use of a dye of the formula:~

1 st antihaltion layers layer containing a mixture of 1.5 g/m2 of the dye of the formula~

and 1.5 g/m2 of the dye of the formula~

in gelatin binder having a coating weight of 5 g/m2.

Support base 0.1 mm biaxially oriented polyethylene terephthalate base optically clear and subbed on both surfaces.

2nd antihalation layers 1 sot antihalation layer.

2nd photosensitive silver halide emulsion layers 1 st silver halide emulsion layer.

2nd supercoat layers 1 st supercoat layer.

A sample of this material was tested and found to have a density of 4.

This cine fim material was wound onto a spool and loaded into a 16 mm cine camera. Purely for test purposes the length of film was exposed to a scene which included a man performing a manual operation. After exposure of the first side the film was taken off the take-up spool and rewound insideout on another spool and the spool placed in the 16 mm cine camera again. This side was exposed to another scene which included a second manual operation.

After the film length had been exposed on the reverse side the side which had last been exposed was processed by manually coating on this side a viscous developing solution having the following formulation:~ Metol 2g sodium sulphite 100 g hydroquinone 8g sodium carbonate 38 g potassium bromide 2 g carboxy methyl cellulose 15g water to 3 litres at 200C for 5 minutes.

The whole of the length of film was then washed in an acid water (pH 2) at 300C for 5 minutes with agitation to remove the viscous developer and to prevent the first exposed side of the film materia from being developed.

The unexposed silver halide was fixed out by placing the length of film in a fixing bath at 250C for 10 minutes and the remaining antihalation dye was bleached.

Fixing/dye bleaching bath: ammonium thiosulphate 20 g sodium metabisulphite 20 g sodium sulphite 40 g water to 1 litre Finally the length of film material was washed in running water for 10 minutes and air dried.

The length of film was then projected in a cine projector and a very clear image of the second manual operation was obtained. No sign of the image of the first manual operation was visible.

The density of the exposed and processed film in the highlight areas was 0.1.

Claims

1. Photographic silver halide film material which comprises an optically transparent support base having coated on each side thereof at least one photographic silver halide emulsion layer, there being present between the silver halide emulsion layer(s) on opposite sides of the support base either one anti-halation underlayer on one side of the support base or two anti-halation underlayers one on each side of the support base, the density of the anti-halation underlayer(s) being sufficient to prevent light which exposes the silver halide emulsion layer(s) on one side of the support base from exposing the silver halide emulsion layer(s) on the other side of the support base.

2. Photographic film material according to claim 1 wherein the combined optical density of the anti-halation underlayer(s) is not less than 4.0 in the waveband(s) to which the photographic silver halide emulsion layer(s) is/are sensitive.

3. Photographic film material according to claim 1 which comprises in order a gelatin supercoat layer, 2 gelatino silver halide emulsion layer, a gelatin based anti-halation underlayer comprising a dye bleachable in alkali metal sulphite colution and having an optical density of substantially 2.0, an optically clear support base, a second gelatin-based anti-halation underlayer comprising a dye bleachable in an alkali metal sulphite solution and having an optical density of substantially 2.0, a second gelatino silver halide emulsion layer and a second gelatin supercoat layer.

4. Photographic film material according to any one of claims 1 to 3 wherein the format of the film material is 35 mm or 1 6 mm cine film.

5. Photographic film material according to claim 4 wherein the 35 mm or 16 mm cine film is perforated along one edge only.

6. A process for the production of a photographic image using the photographic material as claimed in claim 1 which comprises imagewise exposing at least one side of the photographic film material and then applying to that side of the photographic film material which was being exposed at the time at which an incident occurred a photographic record of which is required, a silver halide developing solution, then after development of the silver images on one side of the photographic material, fixing out the undeveloped silver halide on both sides of the photographic film material using a photographic silver halide fixing solution and simultaneously with the photographic processing or subsequent thereto clearing the anti-halation underlayer or layers of dye or pigment.

7. A process according to claim 6 wherein the photographic material used is the material of claim 3 and there is present both in the silver halide developing solution and in the silver halide fixing solution an alkali metal sulphite.

8. Photographic silver halide material according to claim 1 substantially as hereinbefore described with reference to the accompanying Example.