US2244304A - Photographic process - Google Patents

Description

June 3, 1941- A. MARRIAGE HAL 2,244,304-I PHoToGRAPHIc PROCESS Filed Feb. 8. 1940* 2- /ZrL-EMULS/GN 2\ sf-zr? :z: LIGHT DIFFUSING LAYEP 5 COLOUR EN 17725 TR M 4 ,dwg/*3x5 mfifl y Y EMws/ON y PPO Fig. 4.

LIGHT DIFFUSING STE/PPING LAYE? Fig. 5.

Inventors Patented June 3, 1941 l PHOTOGEAPHIC PBCESS Anthony Marriage, Raymond Frank William Seld Guy William Willis Stevens, Wealdstone, Harrow, England, asslgnors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application Februarys, 1940, serum. 317,920 In creat Britain February" 4, 193s (ci. sis-s) 2'Claims.

This invention relates to photographic processes and light-sensitive elements therefor and more particularly to photographic reflex copying processes and to light-sensitive elements adapted to be used in such processes. f

In the so-called reflex copying process which is particularly of value in copying documients and the like it is usual to place in contact with the matter to be copied a light-sensitive layer carried by a paper support and to expose through the paper. On development in any of the usual developers a. negative image is obtained. This process, however, cannot be advantageously applied to material comprising the usual transparent supports suchl as glass or iilm. On the other hand, paper may produce a mottled effect in the image.

may consist in a silver halide emulsion, such as silver bromide or chloro-bromide or iodobromide, having a gamma as high as possible and the density at which the straight line portion of its characteristic curve is reached should be as low as possible. Preferably the major portion of the characteristic curve should be very steep, i. `e. the curve should have a small toe," but an emulsion with a long toe may be use d if One object of the present invention is to prolayer and an emulsion layer, and causing the light to be reiiected from the matter .to beprinted.

The invention also includes light-sensitive photographic elements foruse in the above defined process.

In the accompanying drawing, Figs. 1-5 are enlarged sectional views of elements according to the invention.

The diffusing layer should comprise a photographically innocuous material preferably having the highest possible reiiecting power but the layer may not be opaque. Further, the material of the layer should not blacken appreciably under vthe exposure and subsequent treatment used in the process. The layer preferably consists in a colloid binding material, such as gelatine, containing a iinely divided pigment or other reflecting material uniformly coated on a support. By a photographically innocuous material is meant a. material not having any deleterious eii'ect on the image: lfor example it must not produce excessive fog on development, nor unduly affect theproperties of the image-forming' layer by diffusion of the constituents.

The image-forming emulsion layer is preferably as transparent as possible to light of the' colour to which it is to be exposed consistent with the desired photographic properties. `In the preferred form of the invention the layer the toe is either very low or very steep. We prefer to use an emulsion which, when coated at the usual coating Weight, e. g'. 4-5 g. per 1/2 plate and when developed in a process developer such as that herein described gives a gamma vof-at least 3.5, or better 5, but preferably at least above 7, and especially good results are obtained when the gamma is above 8.

Alternatively the emulsion should be one having a characteristic curverwhich using a process developer such as that herein described is such that over a log exposure range of 0.35 chosen so that the minimum! density is only 0.4 the avera'ge slope of the curve is at least 2.5. Better results are obtained if the average slope over the above-defined range is at least 3, but it is preferably at least 5, and especially good results are obtained when the slope-'is greater than 6.

When the emulsion is treated with a sensitizing dye in, order to modify its spectral sensitivity it is advisable to use a-smaller .quantity `of dye than that giving the maximum sensitivity in orderto ensure a high transparency of the layer to the printing light. By using a suitable low concetnration of a sensitizing dye or mixture of dyes, it is possible 'to use a wider wavelength bandof eiective exposing light-than when using an insensitive layer. Thus the speed of the layer to normal light sources can be greatly increased without detriment to the resulting reflect copies. In some cases the amount may 'be very 4small since as little as'0.005% or less of the optimum hasbeen found satisfactory.-

vIIhe diffusingvlayer and the image-forming.

diffusing layer! over which is coated an imageforming emulsion layer 3.

In Fig. 2 of the drawing is shown a modification of the invention in which the diffusing layer 2 and theimage-forming emrulsion layer 3 are `forni of the invention it is desirable that the support be as thin as is consistent with the necessary strength to support the layers in order to obtain the smallest possible separation of the two `layers.

In yet another form of element according to the invention as shown in Fig. 3, a homogeneous layer of a suitable silver halide emulsion is coated on a support to a thickness greater than usual and immersed in a bath of a sensitizing dyestuif, such as a cyanine dye, for a suiilcient period to sensitize'only the outer stratum "of the emulsion. The element may .then be used for reiiex'copying according to the invention by exposing to light of such colour that only lthe colour sensitized outer stratum is affected by the light whilst the unsensitized stratum acts as a diffusing layer.

A sectional view of such a photographic element is shown in Fig. 3 in which the transparent support I carries a thick emulsion layer the outer stratum of which has been treated with a sensitizlng dye and is denoted by the numeral 5. The remaining stratum of silver halide emulsion which has not been penetrated by the sensitizing dye is denoted by the numeral 4. This inner layer 4 acts as the diffusing layer and does not record any appreciable image when the element is exposed according to the invention to light o! such spectral composition that the stratum I is` relatively insensitive but stratum 5 is sensitive thereto.

Alternatively this surface colour sensitization may be achieved by supercoating the insensitive emulsion layer with gelatine or other layer, this thin supercoat to have incorporated in it a limited amount of colour sensitizer.

ifi' further form of element according to the present. invention is shown in Fig. 4,the diiusing layer being completely removable, and the element being constructed in the manner used for any of the known wet or dry stripping processes. After exposure with the support in contact with the matter to be 'copied the diffusing layer may be stripped oi at any convenient stage of the processing treatment. The diiusing layer may be carried by a separate support and stripped off therewith or the layer may consist in.a material such as that usuallyused for lm 'supports but containing a flnely dispersed pigment or other scattering material which need not be capable of removal by a solvent. In such form of element it is desirable that thesupport carrying the sensitive layer should be as thin as conveniently possible.

In .the example shown in Fig. 4 the support I carries the image-forming emulsion layer 6 and over this a stripping layer l consisting in a layer coated on opposite sides of the support l. In this colloid being one which is easily soluble in water or one of the processing baths, such as the developer, or even a special bath for .the purpose. The colloid may conveniently be one of the wellknown materials used for anti-halation layers or other soluble protective layers which dissolve in the developer provided it does not possess a -colour whichwill interfere .with the printing and also does not damage the surfaces oi' anyv documents or objects with which it may be placed in contact during exposure. In this form of element it is again desirable that the support b as thin -as conveniently possible since the element must be placed with the support in contact with the document to be copied and the exposure made so that the light passes through the diffusing layer first, then through the sensitive layer and the support.

In cases where maximum definition and contrast are desired those forms of the invention not having the image-forming layer appreciably separated from the matter to be copied or from the diiusing layer are preferred.

of lm support material having a nely divided pigment uniformly dispersed therein. The layer 1 is held to the emulsion 6 by a suitable adhesive and may be strippedl from the film at any convenient' stage after exposure. Obviously the element can also be constructed with the stripping layer of light-diiusing material attached to the opposite side of the support instead of to the emulsion layer or 'the emulsion layer may A be strippedA from .the diffusing layer whiclnmay or may not be carried on a support.

In yet a further form of element according Ato the present invention shown in Fig. 5 the element comprises a sensitive emulsion layer B coated on a thin support I and over this is coated a layer 9 of a colloid binding material having a finely-divided pigment dispersed therein, the

Various other forms of the invention will be apparent and the above are given by way of illustration only, In using photographic elements in accordance with the process ofthe present invention the element is placed in contact with the matter to be copied, such as a document, and with the image-forming emulsion layer nearest thereto, exposed by a suitable light so that the rays pass iirst through the diiusing layer, then through the emulsion layer on to the document. Light is reflected from the bright parts of the document and this again traverses the emulsion and meets the diffusing layer where a proportion of the lightis again reflected down to the surface of the document through the sensitive emulsion and so on. Hence the maximum photographic effect is obtained from the reflected light.

The light used for the exposure is dependent on the type of element. If the diffusing layer is not light-sensitive the colour of the light used may be varied according to the emulsion and/or according to the colour of the matter to be copied following the well-known principles of the photographic art. If the light-diiusing layer comprises one or more light-sensitive materials as hereinafter described it may be desirable to expose through a filter whichabsorbs some or all of the wavelengths to which the diffusing layer is sensitive. In order to ensure maximum transparency of the layers to the printing light it is desirable to use light of such a wavelength that it is not too strongly absorbed by the layers. In the case of image-forming layers not specially colour-sensitized it is often advantageous to work on the longer wavelength side of the maximum 1 of the spectral sensitivity curve of the emulsion, for example light of wavelengthl longer than 520 ma has been found useful. On the other hand, when the difference in speed between the emulsion and diiusing layers is very great such a filter is not essential and it may even be desirable in this case to use a filter transmitting light of the shorter wavelengths.4

The filters desirable for use with any particular elements may with advantage be incorporated in the elements either in the form oi a dyestufl uniformly dispersed in one or more of the layers or in a special layer of colloid, such as gelatine,

coated on the element. The lter dyestui is preferably1 one which can be decolourized by the the purpose but not by theprinting light. Suitable dyestuirs and the methods of incorporating them in layers or emulsions are well-known. In addition there may be used other light-absorbing substances in the filter layers, such as colloidally dispersed solids, e. g. colloidal silver, where the colour is suitable.

Development may be eiected in a developer giving a maximum contrast or gamma with the sensitive emulsion used.

In a very advantageous form of the invention the diffusing layer is such that it or the reiecting material contained therein may be removed from the element after exposure either by a special treatment bath for the purpose, or, preferably,

by one of the usual processingvrbaths such as that for developing or fixing. The pigment should have a high reflecting power, (when dispersed in gelatine), especially for light of the wavelengths to which the sensitive layer is exposed. Suitable pigments are for example zinc oxide, cadmium carbonate, or lead oxalate, in a finely divided form. Lead oxalate dissolves in neutral fixing baths whilst lzinc oxide and cadmium carbonate require an acid xing bath. The pigments may be uniformly dispersed in the colloid binding material, such as gelatine, by lgrindingor milling, if necessary, or they may be deposited therein by chemical precipitation in known manner (followed by washing to remove soluble subhalide emulsion not supplying any appreciable part of the nal silver image. This layer is preferably coated between the support and the image-forming layer and may consist in any silver halide relatively insensitive to the light used for exposing the sensitive layer. For example,

b the support may be coated with a not specially colour sensitized silver halide emulsion and over this may be coated a. more rapid unsensitized silver halide emulsion. Alternatively, the support vmay be coated with a not specially colour sensitized emulsion of silver halide such as silver bromide, and over this there maybe coated a layer of an emulsion sensitized to light having substantially no eiect on the lower layer. 'I'he exposure is then made through a iilter transmitting light such that only the extral colour sensitivity of the topmost stratim is used. This may be carried out by using a filter on the printing light or by incorporatinga filter layer in the photographic element between the light and the image-forming layer, such. lter being decolourisable ifdesired. p

'I'he speeds and contrasts of the two emulsions should be so' related that the ratio oi the speed of the top-coat (i. e. the image-forming layer) to the speed of the under-coat (i. e. the diffusing layer) is preferably not less than 20, but if this ratio is less than then the product obtained by multiplying the ratio of the speed of the top-coat to the speed of the undercoat by the ratio of the gamma of the top-coat to thegamma of the under-coat shouldnot be less than 20. Best results are obtained when the above values are not less Athan 30. 'I'he values of speed and gamma for the purpose of this definition should be those obtained by measyused for making the reex copies.

emulsion was coated at a weight of 440 grams urement on the emulsionscoated separately and developed in a normal caustic hydroquinone developer.

The invention is illustrated by the following examples. l. Example 1 Glass plates were coated with a layer of an insensitive gelatino silver bromide emulsion having a speed oi' 0.49 and a. gamma of 0.50 measured as given below. The coating weight, was 375 grams of emulsion per square metre, i. e. 7.5 grams of emulsion (containing 0.25 .gram of silver) per half-plate. 'I'liis layer was allowed todry and over it was coated a layer of a contrasty gelatino silver chloro-bromide process emulsion having a speed of 3.55 and a gamma of 6.35, measured as given below. This layer had a very high sensitivity compared with the bromide undercoat emulsion with respect to the light 'I'his latter ofemulsion per' square metre, i. e. 9.0 grams (containing 0.174 grams of silver) per half-plate.

When exposed with thel sensitive surface in contact with a white enamelled surface carrying a line drawing through a lter screen effectively absorbing all photographically active light o1' wave length shorter than about 520 ma, these plates required approximately 30 seconds exposure at one metre from a 250 watt Photoilood lamp. 0n developing in the caustic hydroqui` none developergiven below at '70 F. for a period of 31A minutes a negative of rhigh reex contrast was obtained.

The speed and gamma of the undercoat and 4topcoat emulsions, when measured by normal methods. i. e. exposed in a time-scale sensitometer to light, having an intensity of 30 candle metres, from an incandescent filament lamp run at a colour temperature of 2,700 K., and developed under conditions of maximum Vagitation for six minutes at 20 C. in a standard metolhydroquinone developer were:

'Speed Gamma Top-coat .Q .l 3. 55 6. 35 Under-coat 0. 49 0. 50

The speed was defined as Stock solution A Hydroquinone grams-- 25 lPotassium metabisulphite do 25 Potassium bromide do 25 Water to .cubic centimeters-- 1000 Stock solution B Caustic potash grams.- 50 Water to cubic centimeters-- 1000 For use take equal parts of solutions A and B.

In.illustration of the degree of reflex contrast obtainable with these plates the following' table gives the values obtained by using a series of exposures to give various line densities. In the column headed Line density is given the vdensity in the reflex negative opposite the lines or dark portions of the original document. I n the columnsheaded Reilex contrast are given the difference of densities between the lines or light portions and background or dark portions of a line negative using plates coated with the sensitive silver chloro-'bromide emulsion only at the same coating weight as above and with plates having an undercoat of insensitive silver bromide emulsion as described above.

Reflex contrast Line density Without With underunder-coat coat Example 2 was allowed to set and then over it was coated a Y layer of contrasty process emulsion having a sensitivity curve with a more gradual cut-off from about 480 to 550 ma. This was coated at a weight of 125 g. per square metre, i. e. 2.5 g. per halfplate and containing 0.0635 g. of. silver, mainly in the form o bromide. This latter contrasty emulsion was one which, when coated at usual weight of 4-5 g. per half-plate and developed in the caustic hydroquinone developer used in Example 1 `gave a maximum gamma of about 9.

Reex copies were then made from a line drawing under the same conditions as in Example 1 and the plates were developed in high contrast developer for 31/2 minutes at 70 F. and Xed.

With the object of obtaining a comparison, glass plates were also coated with one layer only of the above contrasty emulsion atthe same coating weight, i. e. 125 g. per square metre. The values of the reiiex contrast for diierent values of the line density with various exposures are given below:

Reilex contrast Line densit y Without With underunder-coat coat Example 3 25o-500 grams of suspension per square metre, i. e. at 5-10 grams per half-plate. This 111m was placed with its sensitive side in contact with a line drawing as in Example 1 and exposed and developed under the same conditions to produce a negative of high reex contrast.

The values of the reilex contrast for diierent Reflex contrast Line dem@ without titawith uuinium dioxide nium dioxide coating coating Example 4 Glass plates were coated heavily with a layer of a contrasty gelatine silver chloro-bromide process emulsion as used in Example 1. The coating was at 600 grams of emulsion per square metre, i. e. 12 grams per half-plate (containing 0.36 gram of silver). These plates were then colour sensitized by bathing for two minutes at 70 F. in a solution containingone part of dibenzoxacarbocyanine 2.2'diethyl 3.4:3.4' iodide in 20,000 parts of 50% vethyl alcohol.

This element was placed with its sensitive surface in contact with aline drawing as in Example 1 and v'exposed through the support to light passing through a selenium glass lter cutting of! light of shorter wavelengths than 620 ma. On development for three minutes at 70 F. in the caustic hydroquinone developer used in Example .1 a heavy density was produced in the surface layer ot the emulsion but no development appeared to have occurred in the lower layer.

In illustration of the reflex contrast obtainable with the plates of this example comparative tests were carried out with similar heavily coated plates which had not been colour sensitized. These unsensitized plates were exposed through lthe support with a tliter cutting off at 520 ma whilst the sensitized plates were exposed as before through a filter cutting oi at 620 mp. The following table gives the values of reflex contrast obtained on both sets of plates for various values of the line density obtained by varying the exposure. These values show that the sensitized plate gave considerable improvement in the reflex contrast compared with the unsensitized plate and this must be due to the fact that the lower stratum of the emulsion layer which was not sensitized by the bathing treatment was acting as an inert scattering or diffusing layer.

Reflex contrast Line density S mz d ens e plates Having thus described ourinv'ention and the preferred embodiments thereof, we wish to point out that it is not limited to the specific examples shown, but is of the scope of the appended claims.

What we claim and desire to secure by Letters Patent of the United States is:

1. Process of forming a photographic image by reex printing which comprises passing the light in succession 'through a light diiusing layer comprising a nely divided, unfogged, silver halide of relatively low sensitivity compared with the lightsensitive layer, said light being of such intensity that said diiusing layer is not exposed and then through a silver halide light sensitive lay'er and causing the light to be reflected from the matter to be printed onto the last mentioned light-sensitive layer, immersing said layers in a develop1 ing bath and then xing said layers to remove substantially all of the silver halide from the diffusing layer and the unexposed silver halide from the light-sensitive layer.

2. Process of forming a photographic image which comprises passing the light in succession through a filter layer transmitting light to which a silver halide image-forming layer is sensitive but to which an unfogged silver halide layer is relatively insensitive, through said silverhalide

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