GB2081461A - Double-sided silver halide material - Google Patents

Abstract

A double-sided silver halide material comprises a substrate 13 (e.g. of glass) carrying light sensitive silver halide emulsion layers 21, 23 on opposed parallel major surfaces. The substrate 13 may be transparent or opaque, and the emulsion is a fine grain emulsion with a grain size generally less than 0.05 microns. In a modification, the substrate comprises two layers bonded together. <IMAGE>

Description

SPECIFICATION Double-sided silver halide material This invention relates to photographic materials and in particular to a photographic stock material. Recently, it has been discovered that silver halide emulsions may be processed to make reflective optical data storage and laser recording surfaces. The present invention addresses the need for a stock material suitable for recording information on both sides of the record medium.

Previously, double-sided laser recording and data storage media have been manufactured and described.

However, most prior art media were formed by laminating plastic discs, resembling records.

Recently, various novel methods for the manufacture of data storage and laser recording media from silver halide emulsions have been proposed. In each case, however, reflective silver particles are produced at the upper surface of a silver halide emulsion.

In the manufacture of X-ray film, there is a need to maximize the extent of emulsion on a substrate in order to capture images produced by X-rays. In order to do this, it is frequently the practice to coat a transparent substrate on both sides with an X-ray-sensitive silver halide emulsion, as described in United States patent No 4,130,438 to Van Doorselaer. Such emulsions are characterized by coarse silver halide grains typically greater than 2 microns so that a low dose of X-rays will be absorbed to produce a visible exposure. In X-ray film, the substrates are usually made of thin transparent plastics material so that the two emulsions will be relatively closely spaced in order that focus within the two emulsions can be simultaneously maintained.

The present invention is not to be confused with stripping films wherein a silver halide emulsion may be peeled from a substrate, as in United States patent No. 3,844,789. In stripping films, the emulsion coatings usually perform different functions. In the present invention both emulsions firmly adhere to their substrate and the two emulsion coatings are fine grained and perform similar functions.

An object of the present invention is to produce a photographic stock material suitable for making double-sided laser recording and data storage media.

With this object in view, the present invention provides a light-sensitive material comprising a substrate having two parallel opposed major surfaces, each major surface having a fine grain, light sensitive silver halide emulsion thereon, wherein grain size is generally less than 0.05 microns.

The material of the invention is therefore, a light-sensitive stock material which features a unitary substrate, which may be either transparent or opaque. The substrate has parallel opposed, substantially flat major surfaces which each bear a fine-grain photosensitive silver halide emulsion. The fine grain size yields high resolution of small spots which can be recorded in the emulsion before or after processing. Such processing converts the emulsion to a developed state wherein the upper surface of the emulsion is reflective, suitable for use as a reflective laser recording and data storage medium.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which :- Figures la and 1b are cross-sectional views illustrating two different embodiments of the two sided silver halide light-sensitive material of the present invention; Figure2 is a plan view illustrating a substrate in preparation for making a laser recording and data storage medium; Figure 3 is a perspective view illustrating a fixture for use in applying the two sided silver halide coatings; and Figure 4 is enlarged cross-sectional view illustrating a further embodiment of the two sided silver halide, light-sensitive material of the invention, this comprising separate substrates bonded together.

With reference to Figure la, stock material 11 is shown in cross section. This comprises a glass substrate 13 having opposed, parallel major surfaces 15 and 17. These major surfaces should be substantially flat in order to define a focal plane in an emulsion disposed on the major surfaces. The substrate 13 may be optically clear glass having a thickness of the order of 2 mm; however, the thickness of the substrate is not critical.

The substrate 13 is coated on both sides with a fine-grain silver halide emulsion of the type used in making photomasks for semiconductor integrated circuits. One such emulsion is sold under the Agfa-Gevaert trademark "HD Millimask". The composition of such a fine-grain emulsion is described in United States patent No. 4,004,925 at column 6, lines 27 to 68 and column 7, lines 1 to 26. Other similar fine-grain emulsions may be used. These emulsions are characterized by grain size below 0.1 microns and preferably with grain sizes primarily less than 0.05 micron. The emulsions are for black and clear development, although light-attenuating dyes or screening agents may be used where exposure is by means of light, as opposed to a chemical exposure, such as by a fogging agent, like borohydride. Where a light exposure is to be used, it is desirable to expose only one emulsion at a time.This may be done either by providing an opaque substrate, or in the event that a transparent substrate is used, by providing a light absorbing dye which will rapidly attenuate light. Attenuating dyes are well known in the photographic industry. In the present application, an attenuating dye would be used to absorb light which would otherwise penetrate through the substrate 13 and activate photosensitive silver halide on the other side of the substrate. Since most photosensitive silver halide emulsions are sensitive to ultraviolet, blue and green light, a red attenuating dye is preferred. In addition, attenuating dyes will prevent halation caused by specular reflection at the emulsion-substrate interface.

As mentioned previously, the processing of the silver halide emulsions is intended to provide a reflective data storage and laser recording surface distal to the substrate. In some instances, it is desirable photographically to pre-record information in the emulsions prior to making them reflective. This is done by exposure of information to be pre-recorded to light and ordinary chemical development, thereby creating portions of the emulsion which contain pre-recorded indicia. Photographic development of these areas will create black and clear areas, the clear areas being depleted of silver and hence not available for becoming shiny reflective surfaces. Emulsion areas which do not contain pre-recorded information are protected from light exposure so that the silver in these protected areas may be used to form the shiny reflective surfaces for data storage and laser recording.

The emulsions 21 and 23 are adhered to the substrate 13 in a conventional manner, such as by use of subbing layers, so that the emulsions form a tenacious coating with respect to the substrate. The thickness of the emulsion layers is not critical, but thin layers are preferred, i.e. within a three to six micron range.

Subbing layers are extremely thin coatings and for this reason none is shown in the drawings.

The emulsions 21 and 23 should have substantially the same grain size. The thickness of the two emulsions is preferably substantially the same, but need not be the same. The amount of silver halide in the emulsions is more critical than the thickness, and the amount of silver halide in the two emulsions is preferably substantially the same.

The emulsions may each have a surface nuclei layer which is pre-manufactured or stimulated by a fogging agent such as borohydride. Manufactured silver precipitating nuclei are described in United States patent No. 4,204,869 to Bvers et al., as well as elsewhere. Nuclei can also be formed by exposure to light. Nuclei near the surface of the emulsion, distal to the substrate, are essential for forming a reflective surface in one of the chemical treatment methods described below. In these chemical methods, a silver diffusion transfer process is used to cause silver ions from the emulsion to be reduced and precipitated at the nuclei so that non-filamentary silver particles are produced. However, in another processing method, the entire unexposed portion of the emulsion is developed to blackness and then heated to form a reflective surface.

The embodiment of Figure 1 b is similar to that of Figure la, except that the substrate 33 is of a plastics material, rather than glass. The plastics substrate may be any common photographic film base material which is dimensionally stable. The most common photographic film bases are polyester, polyterephthalate, polycarbonate, and cellulose triacetate. While these film base materials are usually optically transparent, opaque plastics may also be used.

With reference to Figure 2, a glass substrate 13' is shown in plan. The substrate illustrated in this figure is adapted for use as a disc medium. For this application, a rectangular glass sheet, indicated by the dashed line 41, is cut to an annular shape with an outer peripheral edge 43 and an inner peripheral edge 45. The size of the annular disc may be any size desired for laser recording. Typically, sizes range from a disc diameter of a few centimetres to diameters of approximately 50 cm. The precise size is not critical. The substrate may be converted to an annular shape as indicated by the solid lines 43 and 45, either prior to or after coating.

When a rectangular sheet is coated on both sides with an emulsion it may be done in one step or in two sequential steps. Coating of the high resolution emulsion may take place in a sodium lighted room. Fogging by actinic radiation is somewhat less critical then for emulsion photomask materials. A hole ground through the glass prior to emulsion coating can simplify handling of the plate during subsequent operations of converting it into a disc.

In order to coat the substrate 13', the substrate is placed in a fixture 45. This fixture has a lower lip 47 which supports the underside of the substrate during the coating process. Transparent or opaque corner support material, shown at 48a, 48b, 48c and 48d, fills in the space between the disc and at the same surface as disc 13' to present a uniform edge and top surface to the emulsion coating trough. The upper side of the substrate 13' and corner material 48a, 48b, 48c and 48d project slightly above the upright wall of the fixture.

In operation, the fixture is placed on a belt which passes beneath a V-shaped trough having a small aperture in the bottom of the trough. A slight bead forms in the aperture and the bead is brought into contact with the substrate 13' so that the bead wets the substrate directly, or wets a subbing agent which has been previously applied to the substrate for the purpose of causing the emulsion to adhere. As the fixture is drawn past the trough, a thin layer of emulsion is applied to the upper major surface of the substrate. This step may be repeated to coat the second layer. This fixture permits the coating of a glass disc without subsequent glass scribing and breaking that can distribute small glass chips on the emulsion.

With reference to Figure 4, a two-sided silver halide emulsion 51 is shown having a first emulsion coating 53 on one side and a second silver halide emulsion coating 55 on the opposite side. The coatings of Figure 4 are similar to the silver halide emulsion coatings described with reference to Figures 1a and lb. In Figure 4, the substrate 57 is formed by bonding two separate substrate members 63 and 65 together for permanent contact. Such bonding may be effected by use of an epoxy resin. A dye may be mixed with the epoxy resin to filter any light transmitted through the silver halide, rather than applying the dye to the silver halide itself.

There should be no reflection from the bonding layer, in order to avoid halation. Bonding should be accomplished in a manner such that the opposite exposed surfaces of the substrate are parallel to each other. The substrate material should have flat sides on major surfaces. Presently available unexposed photoplates, such as the previously-mentioned Agfa-Gevaert "HD Millimask" material on thin glass substrates may be adhered together, back to back, to form the article of Figure 4. In other words, in the article of Figure 4, the silver halide emulsion 53 may be applied to substrate 63 and the silver halide emulsion 55 may be applied to substrate 65 before the two substrates are joined together at the bonding layer 67. Care must be taken in manipulating the silver halide emulsions so as to maintain the upper surfaces of these emulsions in flat parallel planes.While the use of two laminar substrate members is described with reference to Figure 4, there is nothing to preclude use of more tnan two substrate laminar members, especially where beneficial optical or mechanical properties for the substrate will occur.

The material of the present invention is used for making a double-sided reflective laser recording medium.

The processing of the silver halide emulsion is described with reference to the following examples: Example A In United States patent application serial No. 131,280, a laser-recording medium is produced by heating a silver halide emulsion-coated substrate which was previously exposed to light and developed black. Heating continues until a reflective surface appears on the surface of the emulsion. The substrate is either transparent or absorptive and capable of withstanding temperatures of at least 280 up to 3400C without thermal deformation.

Pre-recorded data base and control information can be applied to the medium by photographic techniques prior to black development Then the entire medium is either exposed to actinic radiation or a fogging agent and developed to produce a black surface on the emulsion. This is followed by heating the recording medium at approximately 270"C to 3400C in air or oxygen until a shiny reflective component appears at the upper surface. Gelatin in the emulsion is partially pyrolyzedwhich increases the absorptivity of the gelatin, thus requiring less laser power.

Example B In United States patent application serial No. 72,908, a reflective data storage medium is produced from a silver halide emulsion in three steps. First, a silver halide emulsion-coated substrate is exposed to actinic radiation or treated with a fogging agent such as hydrazine or potassium borohydride to produce silver precipitating nuclei or alternatively a layer of such nuclei would be included in the original manufacture of the silver halide photographic plate or film. Secondly, the exposed or activated film is then contacted with a monobath to develop the surface latent image and to form soluble complex silver ions and by silver diffusion transfer then to the neclei of the developing latent image or layer containing nuclei where the silver is precipitated and reduced to form a reflective silver image.The silver diffusion transfer process is described below with reference to Example C. The only difference between this Example and Example C is the following annealing step.

Thirdly, the resultant reflective silver image is then thermally annealed at approximately 2500C to 360"C, preferable in an oxygen atmosphere, to increase the reflective layer and shrinkthe gelatin layer thereby increasing gelatin absorptivity resulting in higher laser recording sensitivity. The heating methods may include an air convection oven, a contacting hot source, or radiant heating.

The substrate of the photoplate may be transparent or absorptive and must withstand the temperature used in the thermal annealing step. Pre-recorded data and control indicia may be applied by photographic techniques prior to the treatment described above.

Example C In United States patent application serial number 55,270, a reflective data storage medium is made by silver diffusion transfer similar to the process used for the above-described application serial No. 72,908 without the thermal annealing step. The substrate may be a common photographic film base such as polyester polyterephthalate, polycabonate or cellulose triacetate since no heat treatment is used. The substrate may be either transparent or absorptive depending upon the wavelength of the recording beam or reading beam used. A silver halide emulsion coating is applied to the substrate. Fine grain silver emulsions are preferred for laser recording materials since they permit recording and reading of smaller holes.Surface latent images are formed by exposure of the emulsion to actinic radiation or created by a fogging agent or alternatively a silver precipitating nuclei layer is included near the emulsion surface during the manufacturing process.

Silver Diffusion Transfer Process for Making Reflective Surfaces from Silver Halide Emulsions A very thin, highly reflective, silver surface may be formed by the diffusion transfer of appropriate complexed silver ions to a layer of silver precipitating nuclei. This reflective layer is electrically non-conducting and has low thermal conductivity and may be patterned photographically, these latter two properties being highly desirable for laser recording media. The complexed silver ions are created by reaction of an appropriate chemical and the silver halide used in conventional silver halide emulsions. A developing or reducing agent must be included in this solution to permit the complexed silver ions to be precipitated on the nuclei layer. This combination of developing agent and silver compexing solvent in one solution is called a monobath solution.Preferred monobath formulations for highly reflective surfaces include a developing agent which may be characterized as having low activity. The specific type of developing agent selected appears to be less critical than the activity level as determined by developer concentration and pH.

The developing agent should have a redox potential sufficient for causing silver ion reduction and adsorption or agglomeration on silver nuclei. The concentration of the developing agent and the pH of the monobath should not cause filamentary silver growth which gives a black low reflectivity appearance. The developed silver particles should have a geometric shape, such as a spherical or hexagonal shape which when concentrated form a good reflectivity surface.

Developing agents having the preferred characteristics are well known in the art and almost any photographic developing agent can be made to work by selection of concentration, pH and silver complexing agent, such that there is no chemical reaction between the developing agent and complexing agent. It is well known that photographic developing agents require an antioxidant to preserve them. The following developing agent"anti-oxidant combinations produced the typical indicated reflectivities for exposed and monobath developed Agfa-Gevaert "HD Millimask" photoplates.

For Monobaths using Na (SCN) as a Solvent and Silver Complexing Agent Developing Agent Antioxidant Approximate Maximum Reflectivity p-methylaminophenol Ascorbic Acid 46% p-methylaminophenol Sulphite 37% Ascorbic Acid - 10% p-Phenylenediamine Ascorbic Acid 24% Hydroquinone Sulphite 10% Catechol Sulphite 60% For Monobaths using NH OH as a Solvent and Silver Compexing Agent Developing Agent Antioxidant Typical Reflectivity Hydroquinone Sulphite 25% Catechol Sulphite 30% The preferred solvents/silver complexing agents, which must be compative with the developing agent, are mixed therewith, in proportions promoting the complete diffusion transfer process within reasonably short times, such as a few minutes.Such silver complexing agents, in practical volume concentrations, should be able to dissolve essentially all of the silver halide of a fine grain emulsion in just a few minutes. The solvent should not react with the developing silver grains to dissolve them or to form silver sulphide since this tends to create non-reflective silver. The solvent should be such that the specific rate of reduction of its silver complex at the silver nuclei layer is adequately fast even in the presence of developers of low activity, which are preferred to avoid the creation of low-reflectivity black filamentary silver in the initial developent of the surface latent image.

The following chemicals act as silver halide solvents and silver complexing agents in solution physical development. They are grouped approximately according to their rate of solution physical development; that is, the amount of silver deposited per unit time on precipitating nuclei, when used with a p-methylaminophenol-ascorbic acid developing agent.

Most Active Thiocyanates (ammonium, potassium, sodium, etc.) Thiosulphates (ammonium, potassium, sodium, etc.) Ammonium hydroxide Moderately Active a picolinium - ss phenylethyl bromide Ethylenediamine 2-Aminophenol furane n-Butylamine 2-Aminophenol thiophene Isopropylamine Much LessActive Hydroxylamine sulphate Potassium chloride Potassium bromide Triethylamine Sodium sulphite From the above it can be seen that the thiocyanates and ammonium hydroxide are amongst the most active solvents/complexing agents. While almost all developers suitable for solution physical development can be made to work in the silver diffusion transfer process of the present invention with the proper concentration and pH, not all solvents/complexing agents will work within the desired short development time or in the proper manner.For example, the thiosulphate salts, the most common silver halide solvent used in photography and in Polaroid-Lane black and white instant photography's diffusion transfer process, does not work in this process for two reasons. Its complexed silver ions are so stable that it requires a strong reducing agent to precipitate the silver on the nuclei, and this strong reducing or developing agent would have the undesirable effect of developing low reflective black filamentary silver. It has another undesirable effect, also exhibited by the solvent thiourea; namely, that it forms black, low reflecting silver sulphide with the developing silver grains. On the other hand in the black and white Polaroid-Land process black silver is a desirable result.Sodium cyanide is not recommended, even though it is an excellent silver halide solvent, because it is also an excellent solvent of metallic silver and would thus etch away the forming image. It is also about 50 times as toxic as sodium thiocyanate, which is a common photographic reagent.

The process chemicals can be applied by a variety of methods, such as by immersion, doctor blades, capillary applicators, spin-spray processors and the like. The amount of processing chemicals and temperature thereof should be controlled to control reflectivity. Preferably, the molar weight of the developing agent is less than 7% of the molar weight of the solvent since higher concentrations of developing agent can lead to low reflective filamentary silver growth, exceptions to this ratio being found among p-phenylenediamine and its N, N-dialkyl derivatives having a half-wave potential between 170 mv and 240 mv at a pH of 11.0, which have lower development rates and require higher concentrations, i.e., up to 15 grams per litre and minimum of about 2 grams per litre.These derivatives and their half-wave potentials are listed in Table 13.4 of the book entitled "The Theory of the Photographic Process," 3rd edition Macmillan Company (1966). The concentration of the solvent in the form of a soluble thiocyanate or ammonium hydroxide should be more than 10 grams per litre but less than 45 grams per litre. If the concentration is too low the solvent would not be able to convert the halide to a silver complex within a short process time and if the solvent concentration is too great the latent image will not be adequately developed into the necessary silver precipitating nuclei causing much of the silver complex to stay in solution rather than be precipitated. The process by which the silver complex is reduced at the silver precipitating nuclei and builds up the size of the nuclei is called solution physical development.

It is important to note that in solution physical development, as used herein, the silver particles do not grow as filamentary silver as in direct or chemical development, but instead grow roughly equally in all directions, resulting in a developed image composed of compact, rounded particles. As the particles grow, a transition to a hexagonal form is often observed. If the emulsion being developed has an extremely high density of silver nuclei to build upon and there is sufficient silver halide material to be dissolved, then eventually the spheres will grow until some contact other spheres forming aggregates of several spheres or hexagons. As this process takes place the light transmitted through this medium initially takes on a yellowish appearance when the grains are very small.This changes to a red appearance as the particles build up in size Xand eventually will take on a metal-like reflectivity as the aggregates form.

In ' In summary, silver precipitating nuclei are formed on one ofthe surfaces of a silver halide emulsion either in the emulsion manufacturing process, by actinic radiation, or by a fogging agent; and if this emulsion is then developed in a monobath solution containing a weak developer and a very fast solvent which forms complexed silver ions which are readily precipitated by catalytic action of silver nuclei; and if the solvent does not form silver sulphide; then a reflective coating is developed on one of the emulsion surfaces thereby creating a medium for data storage and laser recording. Any of the common developing agents will work whereas only a small number of solvents/complexing agents have all of the desired properties, the most successful of these being the soluble thiocyanates and ammonium hydroxide.

In a common version of the black and white silver diffusion transfer process the silver in the unused silver halide in the negative image will diffuse to a second separatable layer containing precipitating nuclei for reducing the silver and thereby creating a positive image. In the diffusion transfer process, a volume concentration of silver precipitating nuclei may be created on an emulsion surface without use of a separate layer containing nuclei. When actinic radiation or fogging chemicals are used to create these nuclei in the data recording areas, the desired reflective layer appears where the emulsion surface was exposed or activated so this process may be considered a negative-type process as compared to the positive-type process of the conventional silver diffusion transfer. After the concentrating gradient of silver nuclei is created, a monobath processing step follows.The developing agent-solvent monobath performs several functions; it develops and thus enlarges the silver nuclei of the latent images, dissolves the silver halide within the body, creates complexed silver ions and provides the reducing agent necessary for the solution physical development process, that is, the reduction and precipitation of the complexed silver ions on the silver precipitating nuclei of the developing latent image.

Thus, the key steps for forming reflective silver surfaces involve creating a surface latent image or concentration gradient of silver-precipitating nuclei in the data recording area near a surface of the emulsion and then using a special monobath containing a developing agent and complexing agent to build up the silver grains until they begin to aggregate into groups thereby increasing the volume concentration of the silver in the surface latent image area until it becomes adequately reflective. An alternative procedure is to use a silver halide emulsion which is coated on one side by, or otherwise incorporates a layer of, silver precipitating nuclei which is then exposed to light in the non-data-recording areas assigned to control indicia.This is then followed by a chemical development to produce black control indicia or other pre-recordings and finally a monobath development of the special type previously described is used to build up the silver grains in the data recording area until it becomes adequately reflective. The resulting reflective laser-recording and data storage medium consists of concentrated reflective silver grains near a surface of an essentially clear gelatin matrix.

Some of the key processing steps may be achieved by physical phenomenon, chemical treatments or manufacturing techniques but when these steps are linked together in the proper processing sequence, the result is a reflective laser-recording medium. Table 1 presents 14 experimental examples to illustrate some of the variations of the individual steps that may be used and to present an overview of two principal steps necessary to create a laser recording media of adequate reflectivity.

See Table 1 which follows.

Example Surface Activation Developing Agent Solvent/Complexing Photographic Material Typical Agent Reflectivity Example 1 Light P-Phenylendiamine Sodium Thiocayanate Agfa HD Photoplate;* 20% - 24% Example 2 Light P-Methylaminophenol Sodium Thiocyanate Agfa HD Photoplate; 20% - 35% and Ascorbic Acid Example 3 Light P-Methylaminophenol Sodium thiocyanate Konishiroku St Photo- 15% - 27% and Ascorbic Acid plate; 3 Micron Emulsion Example 4 Light P-methylaminophenol Sodium Thiocyanate Agfa-Gevaert Type 10E75 40% - 43% and Ascorbic Acid Film; 5 Micron Emulsion Example 5 Aqueous Hydrazine; P-Methylaminophenol Sodium Thocyanate Kodak S0173 Film; 32% Surface Fogging and Ascorbic Acid 6 Micron Emulsion Example 6 Aqueous Hydrazine;P-Methylaminophenol Sodium Thocyanate Agfa HD photoplate; 39% - 41% Surface Fogging and Ascorbic Acid 4-1/2 Micron Emulsion Example 7 Aqueous Hydrazine; P-Methylaminophenol Sodium Thiocyanate Konishiroku SN Photo- 23% Surface Fogging and Ascorbic Acid plate; 6 Micron Emulsion Example 8 Gaseous Hydrazine; P-methylaminophenol Sodium Thiocyanate Agfa HD Photoplate; 22% Surface Fogging and Ascorbic Acid 4-1/2 micron Emulsion Example 9 Aqueous Potassium Borohydride;P-Methylaminophenol Sodium Thiocyanate Agfa HD Photoplate; 75% Surface Fogging and Ascorbic Acid 4-1/2 Micron Emulsion Example 10 Light P-Methylaminophenol Hydroxylamine Agfa HD Photoplate; 18% and Ascorbic Acid Hydrochloride 4-1/2 Micron Emulsion Example 11 Light Catechol Sodium Thiocyanate Agfa HD Photoplate; 56% 1 gms./liter 4-1/2 Micron Emulsion TABLE 1 (Continues) Solvent/Complexing Typical Example surface Activation Developing Agent Agent Photographic Material Reflactivity Example 12 Light-Micron Image Catechol Sodlum Thlocyanate Agfa HD Photoplate; 35% 1/2 gm/liter 4-1/2 Micron Emulsion Example 13 Light Catechol Ammonium Hydroxide Agfa HD Photoplate; 30% 1.2 gm/liter 4-1/2 Micron Emulsion Example 14 Light Hydroquinone Ammonium Hydroxide Agfa HD Photoplate; 25% 1/2 gm/liter 4-1/2 Micron Emulsion * Agfa HD is an abbreviation for Agfa-Gevaert Millimask HD Photoplate.

Note that the fourteen examples of Table 1 include creation of surface latent images by actinic radiation, aqueous and gaseous fogging by hydrazing and aqueous fogging by potassium borohydride. A key step is creation of surface latent images in the data recording area if a nuclei layer has not been added in the manufacture of the emulsion; or, as previously mentioned, if a nuclei layer is already present and pre-recordings are desired, then surface latent images must be created in the non-data recording areas. It appears that any silver halide emulsion may be used to create a reflective silver surface and is not limited to the use of gelatin-based emulsions. Other film-forming colloids may be used as carriers.It is also shown that the monobath developing-agent-complexing agent can be formulated by use of a variety of developing agents and solvents/silver complexing agents. Table 1 lists four different developing agents, three different solvents/complexing agents, five different emulsions and four different surface activation procedures. The reflectivities achieved range between 15% and 75%.

Example D In United States patent application serial No. 140,136 a broadband reflective laser recording and data storage medium with absorptive underlayer is made by exposing a silver halide emulsion to a series of steps in order to create a partially transmissive mirror-like reflective upper layer over an absorptive underlayer, both of which absorb light energy in the ultraviolet visible and infrared spectra. Recording is accomplished by melting a spot in the gelatin in the reflective layer.

This storage medium is produced by four steps. A silver halide photosensitive medium is exposed to non-saturation actinic radiation to form a latent image which is photographically developed to produce a layer of filamentary silver particles with a grey optical density which will become the absorptive underlayer.

No fixing step is used since the remaining silver halide is used to create the desired reflective surface. The medium is protected from actinic radiation after the initial exposure through the final monobath step.

The surface is then fogged to form a thin surface layer of silver precipitating nuclei. Fogging agents such as the borohydrides of lithium. sodium, potassium, cesiu, and rubidium are useful. Alternately a thin layer of nucleating agent for silver precipitation could be incorporated in the emulsion layer.

After having formed a thin layer of silver precipitating nuclei on the surface of the silver halide photosensitive medium, the final step of the method of the present invention entails transporting the silver in the remaining silver halide to the silver precipitating nuclei and by means of silver complexes there reducing the silver. This procedure is usually accomplished by placing the nucleated photosensitive medium in a monobath. This monobath contains both a silver halide solvent and a silver reducing agent. This step is also done in the dark or using a safe light until silver diffusion transfer is complete.

The two elements of this monobath, a silver halide solvent and a silver reducing agent, comprise a silver diffusion transport and reduction system as described in Example C. The silver halide solvent acts on the silver halide in the photosensitive medium to produce mobile silver ion complexes. These free silver complexes. are transported within the photosensitive medium to and through the surface of the medium.

These silver complexes are then subjected to reduction, producing metallic silver on the silver nuclei and on the filamentary silver at the surface.

Claims (13)

1. A light-sensitive material comprising a substrate having two parallel opposed major surfaces, each major surface having a fine grain, light sensitive silver halide emulsion thereon, wherein grain size is generally less than 0.05 microns.

2. A light-sensitive material as claimed in Claim 1 wherein said substrate is opaque.

3. A light-sensitive material as claimed in Claim 1 wherein said substrate is transparent.

4. A light-sensitive material as claimed in Claim 1,2 or 3 wherein each emulsion contains a light absorbing dye for attenuating light transmitted into the emulsion.

5. A light-sensitive material as claimed in any preceding claim wherein each emulsion contains a nuclei layer dispersed parallel to said major surface of the substrate and having a concentration which is greatest distal to the nearest major surface.

6. A light-sensitive material as claimed in any preceding claim wherein each emulsion has a light sensitive portion and a light insensitive portion, the light insensitive portion containing photographically processed indicia patterns.

7. A light-sensitive material as claimed in any preceding claim wherein said substrate is annular.

8. A light-sensitive material as claimed in any preceding claim wherein said substrate consists of plural members bonded together.

9. A light-sensitive material comprising an opaque substrate having two parallel substantially flat opposed major surfaces, each major surface having a light sensitive silver-halide emulsion adhering thereto.

10. A light-sensitive material as claimed in Claim 9 wherein each emulsion contains a nuclei layer dispersed parallel to said major surface of the substrate and having a concentration which is greatest distal to the nearest major surface.

11. A light-sensitive material as claimed in Claim 9 or 10 wherein each emulsion has a light sensitive portion and a light insensitive portion, the light insensitive portion containing photographically processed indicia patterns.

12. A light sensitive material as claimed in Claim 9, 10 or 11 wherein said substrate is annular.

13. A light-sensitive material substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.