FR2484119A1 - Reproduction of video discs - by projecting image of video master onto silver halide emulsion and processing to give reflective silver particle surface layer - Google Patents

Abstract

In a process for producing copies of optically recorded data, a master record comprising an opaque medium into which the data is recorded as zones which permit the passage of light is mounted in a parallel plane to a fine grain silver halide material. The reproducing material is exposed imagewise to actinic radiation projected through the master to form a latent image. The material is then chemically developed to form black silver in the form of filaments in the exposed areas. A superficial layer of silver pptn. nuclei is then formed on the top surface of the silver halide emulsion in the unexposed and undeveloped zone of the emulsion. The filamentary silver is then deposited on the nuclei by diffusion of silver from the unexposed and undeveloped zone, the silver being absorbed by the nuclei to form a superficial reflective layer. Process allows relatively simple reproduction of video discs to give a prod. which can be read directly by laser beam playback appts.

Description

 The present invention relates to the reproduction of optical data storage medium information comprising recorded information by means of transparent areas in an opaque layer. According to the invention, a copy of the information to be reproduced is formed on a high resolution silver halide emulsion, which is transformed into a high reflectivity optical data storage medium having patterns with areas of low reflectivity.

 The principle on which the optical data storage is based and which in fact is the basis of data storage in general, lies in the presence or absence of a signal. If the data storage is effected by optical means, this signal may consist of light transmission by the medium, reflection or scattering of light from this medium, absorption by this medium or any combination of these means.

The optical storage medium may include some data that has been recorded directly on that medium with the aid of a laser beam, or it may contain data that has been previously recorded on a prototype using a laser beam, then transferred to the intended medium. to make a copy. The reproduction, or formation of copies, of optical data storage discs (video discs) is carried out in various ways, for example matrix pressing (as in the case of phonograph records), normal black-and-white photography. silver halide, diazow photography or photo-lithography of the photoresist type.

 Optical data storage media for reproduction are used for immediate reproduction to analog or digital data. Such media may be in the form of circular discs that rotate under a laser beam, or rectangular plates that are scanned with a laser beam.

The most common optical disc is the video disc used
in the immediate reproduction video installation
manufactured by Magnovox Corporation, a subsidiary
from North American Philips. This disc stores
information in the form of holes or depressions
on a plastic disc. that we cover with a
aluminum layer. A laser beam is used to
read the rotating disk, detecting the phase changes of the reflected signal as the laser beam passes over the holes. The copies of video discs are made by injection molding or a pressing process analogous to the method used for making phonograph records. The copies have the same plastic base as the discs. The mold for making copies is obtained by covering a disc in a polished greenhouse with a thin layer. of metal, which is in turn covered with a layer of photoresist. A laser beam exposes this photosensitive resin with the video signal.

After development of the photosensitive resin and the chemical etching of the metal layer, a method is generally applied. of electrolytic reproduction for forming the pressing mold. By this means, one can
-fabriquerides thousands of copies of video discs from
of a matrix. After forming a disk copy, it is covered with a thin layer of aluminum under vacuum.

We read this copy by means of a reflection light
on the aluminum surface which constitutes a mirror;
reading can not be done using light
crossing the middle.

Another method of making copies from
prototypesconsist video discs to use photographic film film. of reproduction
diazo. Such a process has been developed by society
ARDEV, a subsidiary of Atlantic Richfield Corporation.

According to this method, a prototype video disk is produced
by exposing a rotating disc of photographic film
unexposed, to a modulated laser beam. Then, we develop
photographically this. prototype in black, so that light absorption zones are formed by exposure to the laser. By contact printing, the images of the prototype disk are transferred to a diazo disk by traversing this prototype by actinic radiation. Finally, the diazo disk is photographically developed using ammonia vapors and a copy is obtained.

This copy is read by transmission of light and not by light reflection as in the case of the Magnavox system mentioned above. For light transmission reading, the disk is focused on the light provided by a light source while the disk rotates, and a photodetector on the opposite side of the disk detects the light variations caused by the images of the diazo disk at as it scrolls past this light source. We can therefore say that the diazo copy is obtained by photography. The diazo disk is not reflective and can only be read by transmission.

 The photographic prototype used to produce this diazo video copy could very well be used to make a thin-chromium optical disc by photo-lithography, in a similar way to the operations that are carried out to make chromium caches in the semiconductor industry. Such a method consists in particular of covering a support with a thin metal layer in a vacuum installation, this thin layer being in turn coated with a layer of photoresist. The photographic prototype is brought into contact with the photosensitive resin and actinic radiation is used to expose this photoresist in the mass of the photographic prototype, which has the effect of transferring the images to the resin. The photosensitive resin is then developed to form small openings through which the metal coating can be etched. After such a chemical etching of the metal coating, the photosensitive resin is torn off, and it remains the replica of the prototype video disk. One can read this replica, or copy, by reflection of light on the surface of this disc which constitutes a mirror or by transmission of light through this disc, of course on the condition that the support is transparent.

At the Congress on the Display, Processing and Storage of Optical Data, organized under the patronage of the Society of Photographic Scientists and
Engineers, and held from 23 to 26 January 1979 at
Orlando, Florida, USA, DG Howe and colleagues made a presentation describing a method of contact printing storage medium reproduction. More specifically, this article describes the use of a photoactivated dye otr of diazo type devices, to form light absorption points in the diazo layer which covers an aluminum-coated support, reflecting like a mirror. This disc can be read in reflected light but not in transmitted light.

Rice and his associates have found that contact impressions of the size of a few microns could be obtained without a serious diminution of resolving power, provided that mitigation is taken care of (Newton's rings). ) at the interface of the emulsion (see article titled An Experimental
Television Recording and Playback System Using Photographic
Discs, by Rice and others, J. SMPTE, Vol. 79, November 1970, page 997). This is achieved by using a thin film of liquid having the approximate refractive index between the two faces of the interface. The use of liquids for contact printing has been studied extensively.

The article Printing MRtion can be consulted on this subject.
Picture Films Immersed in Liquid, by Stoll and Miscellaneous,
J. SMPTE, Vol. 70, October 1957, page 607, as well as the article Printing Motion Picture Films Immersed in a
Liquid: Evaluation of Liquids, by Delwiche and others,
J. SMPTE, Vol. 67, October 1958, page 678.

 French Patent Application No. 8014996 filed July 4, 1980 discloses a photographic method for forming data images in a reflecting medium for recording and storing data. Contact and exposure projection methods through a cover are used in the semiconductor industry for the construction of high resolution black silver emulsion caches. Such caches are 12.5 cm squares and contain images of two microns or more. For comparison, in the optical data storage industry, the prototype medium and the photosensitive reproduction medium are much larger, that is, they are up to 30 cm in diameter and the images are smaller, one micron or less. In this case, the conventional contact printing according to which the prototype is in direct contact with the photosensitive reproduction medium can no longer be suitable, due to the existence of small invertible gaps containing air between the prototype and the material. of reproduction. These small air gaps prevent the smallest forms from forming and cause the formation of parasitic images of Newton's rings. In addition, the permanent contact of the prototype with the reproduction material finally has the consequence of damaging this prototype. It would therefore be advantageous to be able to expose the reproduction medium by means of a prototype but without direct contact.

 The following description relates to a simple and inexpensive method of making reflective optical recording copies of data on a prototype, without the use of expensive metal coatings, formed by evaporation or sputtering.

This simple method of reproduction makes it possible to obtain an optical data storage disk that can be read both in reflected light and in transmitted light, without the need for vacuum deposition or chemical etching of the metal. . In addition, the following description relates to an optical disk (or video disk) reproduction method on a high resolution reproduction reproduction medium, obtained from high resolution resolution silver halide emulsions. , available on the market. In this way, reflective copies up to 30 cm in diameter containing data images of one micron or less in size can be obtained. The silver halide reproduction medium can be exposed without direct contact with the prototype.

 More specifically, the subject of the invention is a method for reproducing, or de-making copies, of a prototype constituting an optical data storage medium, characterized in that it consists in orienting a main face of a fine-grain silver halide photosensitive medium in a reference plane, providing a prototype constituting an opaque memory storage medium having light-transmitting areas in a plane parallel to said main face of the medium photo-sensitive, in a disposition that allows the projection1 to project an actinic radiation through said zones of the prototype allowing the light to pass, so as to constitute, in the photo-sensitive medium, latent image zones corresponding to said zones allowing the light, to chemically develop said latent image zones of the photosensitive medium, so as to constitute zones of black silver to the state of filaments, to constitute a surface layer of silver precipitation nuclei on the main surface of the silver halide emulsion, in the unexposed and undeveloped zone of the photosensitive emulsion, and depositing silver in the non-filamentous state on said nuclei by diffusion diffusion of silver from said unexposed and undeveloped area, said silver particles being adsorbed onto the cores, thus constituting a reflective surface field.

 In accordance with the preferred embodiment, actinic radiation is transmitted through the light transmitting regions of an opaque prototype constituting an optical data storage medium constituting latent images in an unexposed photoresensitive medium. This exposure can be carried out with the prototype and the photosensitive medium in direct contact or, on the contrary, at a certain distance from each other. The photosensitive medium should consist of a black-and-white emulsion of fine-grained silver halide, the main face being parallel to the prototype. The actinic radiation which passes through the prototype light transmission zones causes the formation of latent images in the silver halide emulsion immediately opposite the light transmitting regions.

The photosensitive medium is removed and photographically developed so that the latent images give gray or black spots. However, the developed medium is not chemically fixed, since the remaining silver halide will have to be used for subsequent processing operations.

 Then, the surface of the photosensitive medium is activated so as to form a layer of latent images of silver precipitation nuclei. This activation can be provided by chemical veiling or by exposure to light.

Subsequently, the partially developed silver halide emulsion superficially veiled or exposed to actinic radiation is immersed in a single bath consisting of a silver halide solvent and a silver halide developer. , which ensures a light chemical development of the latent image layer of precipitation nuclei. At the same time, the silver halide solvent of the single bath reacts rapidly with the unexposed and undeveloped silver halide. to form soluble complexed silver ions, which are transported by diffusion transfer on the latent image layer under development of the silver nuclei, the silver of the complexed silver ions
precipitating on silver nuclei having undergone partial chemical development, in the presence of the silver halide developer acting as a reducing agent.

The size of the silver nuclei is increased by this silver diffusion transfer or physical development operation and, since there is a high concentration of non-filamentous reflective silver particles, the surface takes on a very reflective appearance. . Neighboring black areas of data remain gray or black.

Since the exposure of the photosensitive medium through the light-transparent prototype is extensive exposure and the chemical development that follows this exposure is a complete development, there are only negligible amounts of halide halide. money in gray or black areas. In this way, the density of the latent images of the silver precipitation nuclei in the gray and black zones is low, and in these areas there is very little silver halide remaining to form silver ion complexes. . As a result, these black and gray areas retain their low reflectivity. By these operations, the transparent zones of the prototype disk correspond to the gray or black areas of the copy, these zones having a reflectivity significantly less than 5%. The opaque areas of the prototype disk correspond to zones that have a reflectivity that is clearly greater than 25%. in the copy. Therefore, the contrast ratio of the prototype may exceed 5/1.

The reflecting surface is obtained entirely with the silver contained in the silver halide of the emulsion of the photosensitive medium.

 If it is desired that the copy can be read by transmission of light, it is possible to erase the gray or black areas using a conventional product, immediately after the initial chemical development and before the operation of the devoilage of the area. The resulting copy has reflective and transparent areas and could be read in both transmission and reflection; however, it should be noted that the reflection contrast is not as good as in the previous case.

 One advantage of the invention is that reflective copies of given optical storage having high resolving power can be obtained from prototypes of large diameters using photosensitive silver halide materials. available on the market and applied on glass or plastic supports, these copies can be read as well by reflection as by transmission.

 Another advantage of the invention lies in the fact that any material wear of the prototype can be eliminated and that the quality of the images of the data can be improved by means of projection and exposure-free printing devices. This is a commercially available contact for obtaining copies of small prototypes, and finally improving the quality of the data images and increasing the resolving power. prototypes of large dimensions than prototypes of small dimensions, by printing through a non-aqueous liquid.

 Other features and advantages of the invention will emerge from the description which follows, made with reference to the accompanying drawings and giving, by way of explanation but not limited to, various forms of implementation of the method according to the invention.

On these drawings,
Figure 1 is a side elevational view in section showing silver halide emulsion exposure on a plastic support, in accordance with the process of the invention.
Figure 2 is a side sectional view showing the operation of photographic development and superficial chemical fogging of the photosensitive medium of FIG.
Figure 1, according to the method of the invention;
Figure 3 is a side view in section of the reflecting copy obtained according to the method of the invention;
Figure 4 is a sectional side view showing an exposure operation according to a variant of the method of the invention;
FIG. 5 is a sectional view in section of the photosensitive medium, photographically developed, erased and having undergone superficial chemical fogging, obtained according to a variant of the process according to the invention;
Figure 6 is a side view and in section of the reflecting copy obtained according to a variant of the method according to the invention.
Figure 7 is a side view in section of the photosensitive medium developed photographically and veiled by deep penetration, obtained according to another form of implementation of the invention;
Figure 8 is a side view in section of the reflecting copy obtained by deep penetration veiling according to a variant embodiment of the method according to the invention.

 The method of reproducing or making copies, according to the invention comprises three successive operations. First, an unexposed silver halide emulsion is exposed through an opaque prototype and exposed areas are developed in black but not fixed. The surface of the remaining silver halide emulsion is then veiled to form the latent images of silver precipitation nuclei. Finally, the so-called medium is exposed to a single bath which ensures a partial chemical development of the latent images and renders the silver halide soluble to give silver complexes, then transports these soluble silver complexes by transfer by diffusion on silver precipitation nuclei, the silver being reduced on nuclei by physical development by forming a reflective surface of silver in the vicinity of a low reflectivity data area. By these operations, areas of low reflectivity data are formed in the reflective field.

A. EXHIBITION OF FICTION AND DEVELOPMENT
The first stage of the process according to the invention consists in exposing a fine-grained silver halide emulsion photosensitive medium to actinic radiation through an opaque prototype, which constitutes a latent image pattern. In the present description, the term "actinic radiation" is a generic term which refers to any exposure forming a latent image in the photosensitive medium.The term "latent image" refers to the activation of the unexposed silver halide. opaque prototype is an optical data storage medium, constituting either an original or a fabricated copy, on which data has been coded in the form of light-transmitting areas, generally of the order of magnitude. one micron, in an opaque material. This opaque material can be applied to a transparent support, which is generally made of glass or plastic. The holes for the passage of light may be round or oval, depending on whether it is a digital or analog data record. The prototype may consist of a disk, but this is not obligatory.

 The photosensitive silver halide medium exhibits may be a black-and-white photo-plate commercially available or a black-and-white film. The finer the grains of the halide emulsion, the higher the resolution of the images on the final article resulting from the implementation of the process according to the invention.

If we want to obtain very good results, it is necessary that the grains of the emulsion have a dimension less than 10%, and even at 5% of the size of the holes of the prototype. The high resolution silver halide emulsion photo-plates used for the fabrication of semiconductor integrated circuits have grains less than 0.05 micron in size and are suitable for the process according to the invention. invention. The silver halide contained in these plates is retained in a matrix consisting of a colloid, generally gelatin, but of course the invention does not require the use of such photo-plates. photosensitive fine-grain silver halide emulsion can be used for carrying out the process according to the invention; for example, the medium may consist of a silver halide emulsion coated with a thin transparent layer permeable to water.

 As shown in FIG. 1, a silver halide emulsion 21, applied on a support 19, is applied against the transparent zones of the operating prototype 13. These holes are the holes 14a, 14b and 14c pierced in the opaque layer 15. of the prtotype. This opaque layer is applied to a support 17, which is generally made of glass or transparent plastic.

 Reflective copies can be obtained from a prototype which is either in direct contact with the phtosensitive silver halide medium or at a distance from a prototype which is separated by the photosensitive medium. In the case of prototypes and copies of small dimensions, for example with a diameter of 15 cm or less and if the number of copies is small, for example 100 or less, direct contact reproduction may be satisfactory for many applications. . One of the main drawbacks of such a method is that the repeated contacts of the copies with the prototype cause the material wear of this prototype, resulting in the introduction of errors on the data recorded in the memory copies. of data.

 In the case of prototype disks having a diameter of up to 12.5 cm and data images having a size of 1 micron or more, a projection exposure device employing optical reflection may be used to expose the photosensitive medium of silver halide while eliminating the risk of material wear of the prototype. In this case, the prototype and the reproduction means may be at least 10 centimeters apart or more.

 in the case of prototype disks up to 12.5 cm in diameter and data images having a size of 3 microns or more! a contactless printer can be used in which the prototype and the cover are separated by several tens of microns. As has been pointed out, such a provision can only be appropriate in the case of large data images.

 If the diameter of the prototype disk is less than a value between 12.5 and 30 cm and the images have dimensions between half a micron and several microns, it is possible to proceed in a different way to avoid contact. too protracted material of the prototype and faithfully reproduce small data images. This method consists in using a non-aqueous liquid between the prototype and the reproduction material, this liquid having a refractive index of the order of 1.5 and having the advantage of making less use a high compression contact between the prototype and the reproduction material.

 The process according to the invention can be carried out by applying at least four different known types of exposure to actinic radiation. In the direct contact printing, the trapped air is expelled between the prototype and the pumped reproduction mat, resulting in the pressure of the outside air strongly applying the two surfaces to each other, thus ensuring their intimate contact. In the case of prototypes up to 15 cm, there are commercially available contact printers which are used in the semiconductor industry for making cache copies, on silver halide emulsions of the type used for the manufacture of reflective media for storing data. Therefore, the same apparatus can be used for making reflective copies from prototypes; such a device can be cited as the Ultratech CP 210 printer.

If a projection up to 12.5 cm diameter with 1 micron images or more is to be projected by projection, the projection splash exposure device can be used. type
Perkin-Elmer Microalign 500. This device allows to expose 125 copies per hour and has a resolving power of 1 micron. The prototype and the copy are several centimeters apart and a reflection optical system is used to project the image of the prototype onto the reproduction material. This machine has been designed to expose photosensitive resin-coated silicon wafers, but can also be used to expose photosensitive silver halide media. The main feature of this machine is the use of a system. with optical reflection for orienting the prototype in a plane parallel to the main surface of the silver halide photosensitive medium in a position which provides orientation accuracy of. 1/4 micron.

 If the prototype contains images that are not. less than 3 or 5 microns and not more than 12.5 cm, we can then use, to obtain copies of the prototype contactless printers found on the market. Such machines are manufactured by the Cobilt division of Computervision Corporation.

These machines make it possible to print as well by direct and soft contact, as without contact. In such a machine, the prototype and the reproducing means may be several tens of microns apart.

 According to another form of implementation of the method according to the invention, before bringing the prototype against the photosensitive medium; the transparent face is coated with the prototype light and the photosensitive face of the photosensitive medium with a non-aqueous liquid. This coating (20> is chosen essentially according to its refractive index which must correspond to the refractive index of the photosensitive emulsion, so as to reduce as much as possible the reflections between the prototype and this photosensitive medium. the refractive index of the gelatin at the temperature of 200C is about 1.5, it is preferable to use liquids having a refractive index, at the temperature of 200C, close to 1.5. The coating must not react with the support which is under the photosensitive emulsion layer, nor dissolve in its support.An advantageous characteristic lies in the high volatility, so that when separating the photosensitive medium from the prototype, the liquid can evaporate rapidly Trichlorethylene is an excellent coating liquid to be applied to either photo-plates or photographic film. As a non-limiting example, a list of other coating liquids. Numerous liquids can be used to cover the prototype and the photosensitive medium, the criteria that must determine the choice between these various liquids are as follows: Compatibility of the refractive indices and high volatility in order to reduce the drying time as much as possible.

TABLE 1
COATING FLUIDS
POSSIBLE TO BE USED
Refractive index
at 200 C
1,461 Carbon tetrachloride
1,467 Ethyl thioacetate
1,475 Decalin Solvent
1,478 Trichlorethylene
1,483 1,1,1, 2-tetrachloroethane
1.485 Furfuryl alcohol
1,489 1-bromo-2-chlorethane
1,491 Sulphide d1ally) e
1,494 1,1,2,2,2-tetrachloroethane
1,496 Toluene
1,501 Benzene
After having the appropriate liquid on the surface of the opaque prototype and on the surface of the emulsion of the photosensitive medium, the surfaces are brought into intimate contact with each other.It is necessary to drive out all the air bubbles which The thin layer of coating (20) between the prototype and the photosensitive medium can be formed in the coating layer, resulting in a zone having a substantially constant refractive index. As a result, the actinic radiation from the source 11 undergoes no reflection at the boundary between the prototype and the photosensitive medium. The presence of the coating layer prevents the formation of an interference spectrum, consisting of Newton's rings. It is known that Newton's rings are concentric rings, which in general are not perfectly circular and which form when a plane surface is maintained in contact with another, by interference between the light passing directly through the media. and light that is reflected many times between layers that are not perfectly in contact.

 The exposure or formation of latent images in the photosensitive medium constitutes a high exposure, this expression meaning that almost all the silver halide grains of the zones 23a, 23b, 23c are activated so as to constitute latent images which faithfully preserve the images of the prototype. Therefore, the unexposed areas contain only non-activated silver halide, whereas the exposed areas essentially contain activated silver halide.

 In order to prevent the formation of parasitic latent images, the photosensitive medium must not be exposed to actinic radiation during the exposure process. Therefore, this exposure must be in the absence of actinic radiation or with a safelight. After exposure, the photosensitive medium is physically developed, but it is not fixed.

The development operation transforms the latent images formed during the exposure into dark gray or black areas. The development to be carried out should advantageously be that recommended by the manufacturer of the photosensitive emulsion. This development must also be carried out without light or at least under an inactinic light.

 After development, and in order to obtain very good results, the photosensitive medium is dried before proceeding to the next operation.

B. SUPEBICIEL CHEMICAL JAIL
After exposure and development, the silver halide photosensitive medium is subjected to a veiling operation. Veiling or nucleation is the operation of forming silver precipitation nuclei as latent images in the remaining silver halide emulsion. According to the invention, these latent image cores essentially form the surface of the emulsion, where the silver of the ion complexes can be reduced to the metallic silver state by forming a reflective surface layer. Some nuclei are found in the bulk of the emulsion, but usually at a lower concentration than at the surface. The veiling operation essentially causes the formation of zones where the transported silver complexes can be reduced to state of reflective money. The latent image cores obtained by fogging are indicated by crosses (+) in FIGS. 2, 5 and 7,
The photographic plates generally do not contain a coating layer or gelatin layer over the emulsion. On the other hand, photographic films almost always carry. a coating and it is necessary to carry out operations a little different depending on the case. In the case of an uncoated photographic medium, the photosensitive emulsion layer 21 is lightly penetrated by the fogging agent, forming a very thin surface layer of cores, generally for photosensitive halide materials. silver gelatin is used as a colloidal suspension medium of the argept halide. Consequently, in order to form a very thin layer of silver precipitation nuclei on the surface of the medium, the gelatin must pass only slightly. It is well known that, when gelatin absorbs water, it swells, which results in a rapid and deep penetration of any solution containing water. However, in the case of a superficial curtain, it The Applicant has found that if a water-miscible alcohol (eg, methanol) is used, the inflation and deep penetration are almost completely suppressed. which therefore leads to the formation of a layer of very thin and thin latent image cores, and this layer, after the development operation in a single bath, can constitute the desired medium, thin and highly reflective, of recording of data.

 If, on the other hand, the photographic medium bears a thin coating of gelatin, as is the case for a photographic film, the penetration must be deeper in order to reach the silver halide so as to constitute the nuclei of silver precipitation. As a result, in the case where the silver halide emulsion is coated with a thick layer, a voiding agent containing water may be more useful than a water miscible alcohol. When water-containing fogging agents are used, the duration of the fogging should be adjusted so as not to penetrate too deeply into the photosensitive emulsion and to form a thick surface coating having low reflectivity.

 The article obtained according to the invention has a very thin reflective silver superficial layer with a thickness of one micron or even less.

The areas of low reflectivity formed during previous exposure and development operations are surrounded by this reflective surface. This reflective silver surface is obtained by passing the silver ion complexes of the silver halide from the emulsion into the lightly developed silver precipitation nuclei contained in the super fine top layer. and then reducing the silver complexes formed in these nuclei in the state of non-filamentous and reflective silver particles. It is certain that it is the surface of the silver halide emulsion which is the most efficient place for silver pre-citing nuclei.

 In order to obtain a very high reflectivity, it is necessary to limit the penetration of the fogging agent so that it exceeds as little as possible the surface of the photosensitive medium. In this respect, methanol or any other water-miscible alcohol is particularly suitable. However, any aqueous solution of a reducing agent penetrates the gelatin of most commercially available photosensitive materials, which causes a decrease in the depth direction of the concentration of the silver precipitation nuclei. In general, for photography, the fogging agents are used in a bath and penetrate throughout the mass of the medium. However, in the process according to the invention, the duration of the fogging and the penetration power of the fogging solution are used to regulate the depth of penetration. It is very important that the emulsion have a uniform state of dryness before immersing in the fogging agent, in order to prevent the depth of penetration of this fogging agent from being everywhere the same.

 A fogging agent is a very powerful reducer. Any one of the hundreds of photographic developers that exist is a reductant that could at least theoretically be made sufficiently active to obscure the silver halide, with proper regulation of the concentration, pH and of duration. Borohydride is an example of a compound that can advantageously be used to carry out the process according to the invention, since it is a very powerful body for reducing the silver halide, that it does not oxidize at all. and is not a silver halide solvent. It is advantageous to use lithium, sodium, potassium, cesium or rubidium borohydride.

 In accordance with the above limits, the deep penetration of the voiding agent is maintained at a low value, less than one micron. The factors constituted by the penetration and the duration of the exposure to the fogging agent, combine to determine the factors of the veiling operation, If one limits the deep penetration of the fogging agent or formation of cores, the final layer of reflective silver has a thickness of less than one micron, the silver being concentrated almost entirely in the 1/10 of the upper micron of this layer. The underlayer contains a number of cores, on which a certain amount of complementary silver is deposited during the diffusion transfer operation. Normally, the thickness of photosensitive emulsion medium is 6 microns or less.

 The superficial chemical warping or nucleation operation can be suppressed by adding a thin layer of a nucleating agent to the surface of the silver halide emulsion for precipitation of silver. . This is commonly done in money transfer deferral operations. In Chapter 16, entitled "Diffusion Transfer and Monobaths", from The Theory of the Photographic Process, fourth edition of THJames, are cited several types of efficient core-forming materials, added to a layer of silver precipitation these materials include copper, silver, silver sulphide, selenium, cacmeum sulphide, lead sulphide and mercuric sulphide used to form black silver. When it is a reflective surface and not a black surface that it wants to obtain, it is essential to cause the growth of silver crystals of round shape and not crystals in the state of filaments that would lead to a black surface . Pure round-shaped silver particles are preferable for this core-forming layer since the sulfides tend to give silver in the filament state, with consequent low reflectivity surface.

C. SILVER DISSEMINATION OVER CORES
As a result of the operation of forming a thin layer of latent images of silver precipitation nuclei on the surface of the photosensitive silver halide emulsion, the last stages of the process according to the invention comprise a light photographic development of these nuclei of latent images, then the transfer of the silver halide on these nuclei developed with silver complexes to reduce the money of these nuclei.On performs this operation by arranging the copy of veiled medium in a single bath. This bath contains both a silver halide solvent and a silver reducer. This operation also takes place in the dark or under safelight until the transfer by silver diffusion is total. The two elements of this unique bath, namely a silver halide solvent and a reducing agent money, are constituted by a photographic developer and a system of transfer by diffusion of money and reduction. This bath of developer and reducer plays several roles: it develops slightly and consequently enlarges the silver nuclei of the latent images; it dissolves the silver halide contained in the mass, gives rise to complexed silver ions and provides the reducing agent necessary for the physical development operation of the solution, namely the reduction and the precipitation of the silver ions. The silver complexes are transported in the mass of the photosensitive emulsion to the surface of this emulsion.

These silver complexes then undergo a reduction, thanks to the presence of the reducing agent, which gives silver silver on the silver nuclei. This phenomenon is indicated by a mass of points in the reflective layer 27 of
Figures 3, 6 and 8.

 The complexed silver ions are produced by reaction of a suitable silver solvent with the unactivated silver halide contained in the emulsion. A developer or reducer must be added to this solution so that the silver ions in complex can precipitate on the layer of nuclei. This combination of a developer and a solvent of the silver complexes in the same solution constitutes a so-called "single-bath" solution. The preferred single baths for obtaining highly reflective surfaces comprise a developer characterized by low activity. The choice of one developer over another is less important than the level of activity provided by the concentration of this developer and its pH.

 The developing agent must have a high enough oxidation-reduction potential to cause reduction of silver ions and absorption or agglomeration on silver precipitation nuclei. The concentration of the developer and the pH of the single bath should be chosen so as not to cause silver development in the filament state, which would give a black appearance, with low reflectivity. The silver particles developed should have a geometric shape, for example a spherical or hexagonal shape which can after concentration form a highly reflective surface.

 The developers possessing the best characteristics are well known to those skilled in the art and any photographic developer can be advantageously used, provided that the concentration, pH and silver complexing agent are suitably chosen so that that there is no chemical reaction between the developer and the complex-forming agent. It is well known that an antioxidant is necessary to preserve photographic reducers. The following are combinations of developer and antioxidant that can be used in combination with a complex forming agent and sodium thiocyanate (NaSCN) as a solvent.

REVELATORS ANTI-OXIDANTS CONVENING
Has a unique bath using
Na (SCN) AS A SOLVENT AND
A TRAINING AGENT FROM. SILVER COMPLEXES
Developer Antioxidant p-methylaminophenol Ascorbic acid p-methylaminophenol Sulfite
Ascorbic acid p-phenylenediamine Ascorbic acid
Hydroquinone Sulphite
Catechol Sulphite
The preferred mixtures of solvent and silver complexing agent, which must be compatible with the developer, are mixed with the developer in proportions intended to facilitate the complete transfer by diffusion in a relatively short time, for example A few minutes. Such silver complex forming agents must, under suitable volume concentrations, be able to dissolve in a few minutes almost all of the silver halide contained in a fine-grained emulsion. The solvent should not react with the developing silver grains, which would dissolve or form silver sulphide, as this would tend to give non-reflective silver The solvent must be chosen in such a way that the rate of reduction of its silver complex in the precipitation nucleus layer is quite high even in the presence of low activity developers, the latter being preferred because they prevent formation of black silver filaments with low reflectivity at the beginning of the development of the superficial latent image.

 The following chemicals are suitable as silver halide solvents and as silver complexing agents for the physical development of solutions. These bodies were grouped approximately according to their physical development rate, that is to say as a function of the amount of silver deposited per unit time on the precipitation nuclei, when the developer is used as a developer. p-methylaminophenol-ascorbic acid mixture.

Most powerful bodies
Thiocyanates (ammonium, potassium, sodium, etc.)
Thiosulfates (ammonium, potassium, sodium, etc., ..)
Ammonium hydroxide.

Moderately strong bodies
-Picolinium bromide - (3-phenylethyl) ethylenediamine 2-Aminophenol furan n-Butylamine 2-Aminophenol thiophene isopropylamine
Much less powerful bodies
Hydroxylamine sulphate
Potassium chloride
Potassium bromide
triethylamine
Sodium sulphite
This table shows that thiocyanates and ammonium hydroxide are among the most active pairs of solvents and agents. complex training.

 Virtually all of the developers suitable for the physical development of solutions can advantageously be used in the silver diffusion transfer method according to the invention at a suitable concentration and pH, but, on the other hand, the solvent / agent-forming pairs of not all of them act during the short duration of development or do not act as they should.

For example, thiosulfates, which are the most commonly used silver halide solvents in photography and Polaroid-Land's black-and-white instantaneous photo-diffusion transfer method, are not suitable. not for the process according to the invention for two reasons. The silver ions in complex of a thiosulphate are so stable that a powerful reducer must be used to precipitate the silver on the nuclei outside, such a powerful reducer or developer would have the mowing effect of giving by developing the In the case of thiourea used as a solvent, a thiosulphate also has the disadvantage of forming black silver sulphide with low reflectivity with silver grains in the form of black filaments with low reflectivity. development course. On the contrary, in the Polarold-Land process in black and white, the formation of black silver is advantageous. Sodium cyanide is not recommended although it is an excellent solvent for silver halide, because it is also an excellent solvent for silver in the metallic state so that it may erase the silver. image in formation by chemical attack. In addition, sodium cyanide is about 50 times more toxic than sodium thiocyanate, which is a reagent commonly used in photography.

 In addition, if the solvent concentration is too low, the solvent is not able to rapidly convert the silver halide into a silver complex and if the reducer is too weak, the halide developed and unexposed circumvents the silver precipitation nuclei, so that a large proportion of the silver complex passes into the solution instead of precipitating. The method according to which the silver complex is reduced in the arsenic precipitation nuclei.

and gives nuclei their dimension, is called "physical development in solution". Since p-phenylenediamine is both a chemical developer and a silver complexing agent, one can
use in a single bath to play both roles.

 It should be noted that, in the physical solution development as practiced in the present application, the silver particles do not eventually give silver filaments as in the case of direct or chemical development, but on the contrary, grow to in the same way in all directions, giving a developed image of packed round particles. As the particles grow, the transition to the hexagonal form is often noted. If the solution developed has a very high density of silver nuclei, and there is sufficient silver halide to dissolve, the spheres grow larger and finally some of them come into contact with other spheres forming aq # regencies of spheres or hexagons. When the chemical development is partial, or weak as in the case of the development of latent images or precipitating nuclei, it means that the chemical development only continued until the development nuclei have approximately the spherical shape or hexagonal. Complete chemical development leads to silver filaments and the formation of gray or black areas.

 After exposing the photosensitive medium # to the single bath, it is washed with water and dried. This has the effect of stopping the reduction of 11 silver and sta skew this photosensitive medium.

 Since this diffusion transfer operation transports only the non-activated silver halide, the areas developed in black during the first stage of the invention do not yield silver complexes. If too thick emulsions are used, the amount of complex silver entering the solution may be large and the reflective silver may be deposited on all areas including black areas. . This is unfortunate as some images may be distorted or lost. The reflective areas constitute a background or background for the non-reflective spots. The article that one wishes to obtain consists of an optical data storage medium having a reflective background, with small points with low reflectivity that encode the data. recorded.

As a variant of the method, using a prototype with opaque images of small dimensions, one would obtain an article having reflective points in an opaque field.

D. OTHER METHODS
According to a variant of the process according to the invention, all the operations indicated above are carried out, but another operation is added. The first stage of this variant of the process is shown in FIG. 4. A source (31) of uniform actinic radiation ensures the exposure of the silver halide emulsion 41 through the holes 33 of the prototype 37. exposed, are developed in black, as shown in Figure 2, but after development, they are erased to form transparent areas # 5a, 45b and 45c), using to erase a photographic product of conventional type. Therefore, in places where there is black money developed on the
Figure 2, Figure 5 indicates the absence of silver or activated silver halide in areas 45a, 45b and 45c.

 Of course, the product used to erase removes only the black silver filaments, without having any action on the silver halide contained in the unexposed areas.

The remaining halide emulsion is then subjected to a veiling operation, as described above, which causes the formation of silver precipitation nuclei on the surface of the photosensitive medium where the halide remains. As explained above, the depth of penetration of the fogging agent is of great importance. If the photosensitive medium is covered with too thick a layer, water or a water-miscible alcohol may be preferable. If the photosensitive medium is not coated with a very thick layer, it can advantageously be used as a voiding agent methanol. On the
5, the + signs indicate that the nuclei only form on the emulsion surface 41. After the veiling operation, the emulsion is brought into contact with a single bath in order to carry out a light chemical development. followed by physical development. The silver halide dissolves in the soluble silver complexes that are transported on the silver precipitation nuclei. Soluble silver complexes are reduced in these silver-reflecting cores by forming a glossy surface layer of reflective silver, as shown in Figure 6, in which the black dots 47 represent the bright particles of silver. reflective money.

Since there is no silver halide in the transparent areas 45a, 45b and 45c, no amount of halide is transferred to the surface or reduced, since There are no silver nuclei in these areas. Therefore, these transparent areas are only slightly reflected and moreover, they let the light. This variant of the method according to the invention therefore provides an optical data storage medium that can be read in both reflected light and transmitted light.

 Figures 7 and 8 show variants of the method according to the invention shown in Figures 2 and 3. In Figures 7 and 8, the emulsion 41 'is subjected to a veiling operation, as indicated above, but at a greater depth. This operation is provided either by actinic radiation or by a powerful curtaining agent. The voiding agent penetrates the emulsion throughout its thickness, but with a power that varies along a gradient in the direction of the depth, with a larger amount of nuclei 46 'of latent images on the upper face of the emulsion. emulsion only in the mass of this emulsion. When actinic radiation is used, it is preferable that at least 50% of the latent image cores are less than 2 microns away from the face furthest from the support.After voiling, the emulsion is in contact with a single bath to ensure partial chemical development, and a very advanced physical development As previously explained; the silver halide of the emulsion is made soluble and silver complexes are formed which are transported to the nuclei, where the silver is reduced and absorbed on the partially developed silver nuclei.

This phenomenon is represented in FIG. 8, in which the + signs have been replaced by black dots 47 ', these dots representing nuclei comprising silver particles. These black dots in Figure 8 are in fact reflective glossy particles with the highest volume concentration on the upper surface and; the weaker as we descend into the mass. On the surface, there are also aggregates of silver particles.

Example 1
This example illustrates the process according to the invention as applied to silver halide emulsions which are not covered with a very thick layer. Starting from a 6.25 cm by 6.25 cm photo plate coated with a commercially available 3 micron Konishiroku ST emulsion, having an anti-halo coating but no filter dye; This ## exposes this photo-plate through a pattern containing sinuous lines of 1 and 2 microns, on a printer Ultratech CP 210, for 5 seconds, with a power of 1.15 L / dm2. This photograph is then exposed for 4 minutes in a developer having the following composition: 7.9 g of hydroquinone; 36.9 g of sodium sulfite; 0.52 g of phenidone; 7.9 g of potassium hydroxide; 2.7 g of potassium bromide: 0.07 g of benzoltriazole. Water is added up to one liter. This plate is removed from the developer bath, washed well and dried in a stream of nitrogen.

 After washing and drying this plate. thus developed, it is immersed in a veiling bath containing 0.5 g of RBH4 and 0.6 g of NaOCH3, adding methanol up to one liter. This immersion lasts 30 seconds, after which the plate is washed well.

 After washing, the photo plate is placed for two minutes in a single developer bath having the following composition: 0.25 g of Kodak Elom developer, 10 g of sodium sulfite; 2 g of soda; 2.5 g of ascorbic acid; 50 g of NaSCN. Water is added up to one liter. After development, this plate is removed from the single bath, washed thoroughly and dried.

The copy of the pattern thus obtained is formed of lines with low reflective power and lines with high reflective power. If one calls "image with low reflectivity", the image of the pattern and "highly reflective image", the field, the reflective powers obtained for various wavelengths are as follows:
633 mm 780 mm 830 mm
Field 36% 23% 20%
Pattern image 3.4% 2198 2.1%
The 1 micron lines of the pattern have satisfactory resolving power and good illumination contrast at the top of the copy. Note that the reflection contrast ratio is at least 8/1.

Example 2:
This new example illustrates the process according to the invention for a photosensitive application coated with a thick layer. We start with a sheet of Kodak SO-343 film 6.25 cm by 6.25 cm; it is exposed through the same pattern as in Example 1, for 5.2 seconds, under a power of 1.12 L / dm2. After exposure, this film is developed for 4 minutes in a developer having the following composition: 7.9. hydroquinone; 36.9 g of sodium sulfite; 7.4 g of potassium hydroxide; 2.7 g of potassium bromide; 0.07 g of benzoltriazole. Water is added up to one liter. This film is carefully washed and dried in an oven at a temperature of 450 for 10 minutes.

 This dry film was then immersed for 5 seconds in a solution containing 0.75 g of KBH4 and 4 g of sodium hydroxide, adding water to 1 liter. Immediately after the veiling operation, this film is immersed in a 5% acetic acid stop bath for 30 seconds. This film is then washed properly and put for 2 minutes in a single developer bath having the following composition: 0.5 g of "Kodak Elon" developer; 10 g of sodium sulphite; 2.0 g of sodium hydroxide; 10 g of sodium thiocyanate. Water is added up to one liter.

After completion of the partial chemical development and physical development step pushed into the single bath, the film is properly washed and fixed. The low reflectivity of the copy pattern images and the high reflectivity of the surrounding field are as follows, for the indicated wavelengths
633 mm 830 mm
Field 26% 35.3%
Pattern image 3.9% 3.5%
This table shows that we have a field / image reflecting power ratio of at least 6/1. The copy therefore has a high contrast ratio.

The two micron images of the patterns have satisfactory resolving power.

Claims (10)

 1 - The method of reproduction, or of making copies, of a prototype constituting an optical data storage medium, characterized in that it consists in orienting a main face of a photosensitive silver halide medium with a fine grain in a reference plane, having a prototype constituting an opaque optical data storage medium comprising light-transmitting regions, in a plane parallel to said main face of the photosensitive medium, in a disposition which allows projection, projecting actinic radiation through said zones of the prototype, allowing the light to pass through so as to constitute, in the photosensitive medium, latent image zones corresponding to said light-transmitting regions chemically developing said latent image zones of the photosensitive medium , so as to constitute zones of black silver in the state of filaments, to constitute a superlative layer of silver precipitation nuclei on the main surface of the silver halide emulsion, in the unexposed and undeveloped zone of the photosensitive emulsion, and to deposit silver in the non-filamentous state on said ar -gent diffusion transfer nuclei from said unexposed and undeveloped area, said silver particles being absorbed onto the cores. thus constituting a reflective surface field.  2 - The method according to claim 1 characterized by the fact that it comprises a complementary operation of putting said dark silver zones in the state of filaments in contact with a product of effacement of silver, before to form a surface layer of silver precipitation nuclei.  3 - The method according to any one of claims 1 and 2 characterized in that one constitutes said core layer by superficially exposing a main surface of the photosensitive medium to actinic radiation, which ensures a concentration of precipitation nuclei of money that goes down in the direction of the depth.  4 - The method according to any one of claims 1 and 2, characterized in that one forms said core layer by subjecting the main surface of the photosensitive medium to chemical fogging.  5 - Process according to any one of claims 1 to 4, characterized in that one further proceeds to this operation of physically removing said opaque prototype of said photosensitive medium of silver halide emulsion, of a distance greater than 2.5 cm.  6 - The method according to any one of claims 1 to 4, characterized in that it is further carried out the operation of physically removing said opaque prototype of said photosensitive medium of silver halide, of a distance of 0.25 mm or less.  7 - Process according to any one of claims 1 to 4, characterized in that it is further carried out the operation of putting said prototype in contact with said photosensitive emulsion of silver halide through a liquid layer.  8 - Process according to any one of claims 1 to 4, characterized in that it is further carried out the operation of putting said opaque prototype in contact with said silver halide emulsion.  9 - Process according to any one of claims 1 to 8, characterized in that one deposits the non-filamentous silver by putting said layer of cores of the photosensitive medium in contact with a reagent constituted by a weak developer of the silver halide used to ensure the partial chemical development of said layer of arpent precipitation nuclei and a fast-acting solvent of the silver halide complexes for reacting with the silver halide unexposed and undeveloped so as to form soluble silver ion complexes which are transported by diffusion transfer on said chemically developed nuclei, the silver of said ion complexes precipitating and being absorbed on said chemically developed nuclei in the presence of said developer which acts as a reducer, which causes the formation of a non-conductive reflective layer of electricity formed of aggregates and particles. the silver particles being separated, the activity of the solvent being sufficiently low that said superficial latent image undergoes a partial chemical development under the action of the weak developer before the whole of the undeveloped and unexposed silver halide is dissolved.  Data storage medium having reproductively applied data according to the method of claim 1.