CA1147462A - Reflective data storage medium made by silver diffusion transfer - Google Patents

Abstract

Abstract A reflective laser recording and data storage medium, for direct reading after writing, formed from a photosensitive silver-halide emulsion wherein a sur-face latent image exposure on the recording area forms a depthwise gradient of silver nuclei. A single step negative silver diffusion transfer process is used to develop silver nuclei of the latent image and dissolve unexposed silver halide elsewhere, forming silver ion complexes. These complexes are transported by diffusion transfer to the developing silver nuclei sites where silver is precipitated and adsorbed to form a high con-centration of non-filamentary particles at a surface of a low melting temperature dielectric matrix which is highly reflective of light and electrically non-conducting.

Description

REFLECTIVE DAT~ STORAGE MEDIUM
MADE BY SILVER DIFF'USION TRANSFER

The invention relates to laser recording media, and more particularly to a reflective silver data recording and storage medium useful for reading laser recordings im-mediately after laser writing which is made from a sil-ver-halide photosensitive e~ulsion by diffusion transfer.

Previously, many types of optical recording media have been developed for laser writing. Some of these media require post write processing before they can be read, and some can be read immediately after laser writing.
The media of interest herein are for "direct read after write" capability, commonly known as "DRAW" media.
Presently known laser DRAW media are thin metal films in which holes may be melted, composite shiny films whose reflectivity at a spot may be reduced by evapor-ation, thin films of dyes or other coatings which canbe ablated at a spot, and dielectric materials whose refractive-index may ~e changed at a point, causing a scattering of light when scanned with a read laser.

The most common DRAW media are thin metal films, usually on a glass substrate. Thin metal films have several advantages. First, they can be produced easily in small quantities with commercially available sputtering equip-ment. Second, they can be read either by reflection or by transmission. Third, films of tellurium and bismuth 25 nave relatively high recording sensitivies. -Fortunately, for all of these reasons, metal films have enabled a large amount of research to be conducted and progress to be made in the design of optical data ~.

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storage systems. To date, tellurium has evolved as the most widely used of the metal films. However, tellurium must be manufactured by an expensive, batch-type, vacuum sputtering technique; it does not form a tenacious coat-ing; and it introduces manufacturing and environmentalcomplications because of its to~icity and since it rapidly oxidizes in air it must be encapsulated in an airtight system in order for it to achieve an acceptable archival life.

What is particularly desirable about tellurium is that it has a low melting temperature for a metal, 450C, and also a very low thermal conductivity of 2.4 watts per meter per degree Kelvin at 573K. In comparison, silver metal has a melting temperature of 960C and a thermal conductivity of 407 watts per meter per degree Kelvin at the same elevated temperature. When these two metals are considered for laser recording with short pulses of laser power, the tellurium is far superior from a recording sensitivity standpoint since the low thermal conductivity keeps the heat generated by the laser beam confined to a small area and the lower melt-ing temperature facilitiates the melting of the hole.
Conversely, silver metal, because of its high thermal conductivity, about 170 times that of tellurium, would not normally be considered suitable for laser recording.

Although it is possible to produce reflective metallic coatings of many types on substrates by vacuum sputter-ing or evaporation, silver is relatively unique in that - it can also be created by photographic techniques and, in particular, by si.ver diffusio~ ransfer. In U.S.

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patent 3,464,822 Blake discloses a silver diffusion transfer reversal process for creating electrically conducting silver images for the fabrication of printed circuit boards. That invention, in turn, is based upon silver diffusion transfer process inventions of the reversal type, leading to black non-reflective and non-conductive images~ one example being U.S. patent

2,500,421 by Dr. E. H. Land. The silver diffusion transfer reversal process forms the basis of direct positives by the Polaroid Land process of Polaroid Corporation and the Gevacopy and Copyrapid processes of Agfa-Gevaert. These reversal processes should be distinguished from the silver diffu$ion negative pro-cess. One such process leading to black non-reflecting and non-conducting images, is described in U.S. patent

3,179,517 by Tregillus. A silver diffusion transfer negative process is used in the present invention.

It is well known that if very small, high electrical conductivity metal spheres or spherical particles are distributed through a dielectric medium, the effective dielectric constant or refractive index will rise owing to the added induced dipoles of the metal particles.

Previously, a re~lective silver laser recording medium was the subject of a prior invention wherein a processed black silver emulsion was converted to a reflective recording medium by heating-at least to 250C until a shiney reflective appearance is achieved.

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The present invention provides a method for making a reflec-tiver electrically non-conducting data storage medium com-prising, defining at least one data storage field in an unexposed photosensitive silver-halide emulsion, forming an areawise surface laten-t image layer of silver precipitating nuclei in the data storage field of the emul-sion by chemical fogging or by exposure to actinic radiation, said layer having a maximum nuclei volume concentration at one surface of the emulsion and a gradient in the depthwise direction of decreasing concentration, and depositing non-filamentary silver on said nuclei by negative silver diffusion transfer from said emulsion, said silver adsorbed on the nuclei to a degree that the emulsion forms an areawise reflective data storage field which is electri-cally non-conducting, said negative silver diffusion transfer process employing a weak silver-halide developing agent for chemical development of the surface latent image layer of silver precipitating nuclei and a silver-halide complexing solvent for reactin~ with unexposed and undeveloped silver halide to form soluble silver ion complexes which are trans-ported by diffusion transfer to said chemically developed silver-precipitating nuclei of said latent image where silver of said silver ion comp:lexes is precipitated and adsorbed on said chemically developed nuclei in the presence of said developer acting as:a reducing agent, thereby forming a re- ~ :
flective electrically non-conducting layer of aggregated and individual silver particles in said areas for data storage.

The present invention further provides a reflective data , -.

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- 4a -storage medium comprising, a low melting temperature colloid matrix supported on a substrate, and a surface layer of non-filamentary individual silver particles, disposed in said matrix, having maximum particle dimensions primarily under .05 microns, some of which are aggregated with similar par-ticles, and having a volume concentration of silver particles greater at said surface than in the interior of said matrix, said surface having an areawise substantially uniform reflec-tivity to visible light, said uniform reflectivity being between 1~% and 75% and being electrically non-conductive.

The present invention further provides a monobath developer for the formation of a highly reflective layer of electri- :
cally non-conducting, non-filamentary silver in a silver-halide emulsion having latent images of silver precipitating nuclei comprising, a weak silver-halide developing agent for partial chemical development of latent images o~ silver pre-cipitating nuclei in a silver-halide emulsion and a rapid-acting, silver-halide complexing solvent for reacting with unexposed and undeveloped silver halide to form soluble ~ ~
20 silver ion complexes, which are transported by diffusion :
transfer to said silver precipitating nuclei where silver of :`~-. -said silver ion complexes is precipitated and adsorbed on said nuclei in the presence of said developer acting as a reducing agent, thereby forming an electrically non-conduct-ing layer of aggregated and individual silver particles exhibiting high reflectivity, where the activity of the com-plexing so:lvent is sufficientl.y low to permit partial chemical development of the surface latent image by the weak chemical developing agent before all of the undeveloped and 30 unexposed silver halide is dissolved and where the chemical ;~
developing agent is su~ic.iently weak to insure the chemical development primarily of non-filamentary silver nuclei. :~

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- -- 4_ -Among the advantages of the preferred embodiments of the invention are the fact that it may be manufactured without the use of a vacuum system and on a continuous basis and which may be used to record low-reflective spots in a reflective field with relatively low energy laser pulses. Control indicia and certain data base data may be pre-recorded by photographic means to facilitate the use of discs or plates in both the re-cording apparatus and the playback apparatus. Repli-cation of optically recorded media is permitted byphotographic contact printing on a rigid or flexible substrate that can be read in reflection or transmis-sion. The laser recording and data storage medium disclosed herein can be fabricated from commercially available photoplates and films or minor modifications thereto, to achieve low cost. A high temperature pro-cessing step is not required and therefore the use of ordinary, low-cost photographic plastic film bases or other available plastics as substrate materials is permitted thus allowing fabrication of recording discs with center holes by a low-cost stamping operation.
Also disclosed herein is a single-step silver diffusion transfer photographic process which could produce a highly reflective electrically non-conducting surface layer having a thickness of 1 micron or less contained almost entirely within the gelatin or colloidal carrier.

It has been discovered that the silver in a photosensi-tive, silver-halide emulsion of a photoplate or film can be brought to a surface of the emulsion in a pre-exposed pattern to form a reflective laser recordingand storage medium by a novel single step silver diffu-sion transfer negative photographic process. First a volume concentration gradient of silver precipitating nuclei is created at one surface of the emulsion by actinic radiation or other methods, with the gradient :: , :
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of decreasing concentration in the depthwise direction,and this is followed by a single step monoba-th silver diffusion transfer development process that is primar-ily a solution physical development process which is used to build up the volume concentration of silver at the surface containing the precipitating nuclei until the surface becomes reflective.

This reflective surface layer is typically less than 1 micron thick; has a reflectivity of 15~ to 50%; is electrically a non-conductor and thermally a poor con-ductor since the matrix is typically ge~atin, which holds the high concentration of tiny particles and ag-glomerates of silver particles which are separated and isolated from each other by the gelatin matrix. Thus, although the layer reflects light like a metal, it melts easily like a plastic, with the result that its recording sensitivity is in the class of bismith and tellurium and at least an order of magnitude more sensi-tive than that of a thin, continuous silver metal layer.

A principal step in the process is an exposure or sur-face activation of the area to be used for data record-ing or alternatively non-data recording, which affects mainly the silver-halide grains close to one of the surfaces of the emulsion. Such an exposure or activa-tion creates a surface latent image having a depthwiseexposure gradient, with a concentration of exposed silver-halide which is greatest at the one surface and least in the interior of the emulsion. The surface of greatest concentration may be either the surface distal to the substrate or proximate thereto, depending on where laser writing will initially impinge on the medium.

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_ 7 _ For example, if laser writing is on the upper surface, the emulsion surface distal to the substrate has the greatest concentration of exposed silver-halide.

The surface latent image may include images in the photographic recording sense or may cover the entire surface, but is always located primarily at a surface of a photographic emulsion, which also contains some unexposed silver halide, in the interior of thc emul-sion. Such a surface latent image may be made by light itself, i.e., by intentionally e~posing one surface or the other of the photosensitive emulsion to light where data recording will occur, the remaining area bein~
masked. Alternatively the surface treatment may be made by a surface activating chemical, namely a fogging agent, such as hydrazine or a borohydride salt such as potassium borohydride, which,performs a surface latent image activation on silver-halide emulsions similar to a light exposure. Alternatively during the original manufacture of the silver-halide photographic plate or film a very thin gelatin layer containi~g silver-pre-cipitating nuclei would be included at the surface distal to or the~surface proximate to the substrate, which would be the basis for creating a reflective sur-face at either of these two surfaces.

The second principal step of the process involves con-; tacting the exposed or activated and~unexposed silver-halide with a monobath containing a silver-halide de-veloping agent for developing the surface latent image created in the exposure or activation step. Simultane-ously a silver-halide solvent in the monobath, prefer- ~ ;
ably a soluble thiocyanate or ammonium hydroxide, : :

reacts rapidly with unexposed and undeveloped silver-halid~ to fo~m soluble compl~xed si]ver :ions which .Ire transported by diffusion transfer to nuclei of -the de-veloping latent image or in the alternative case to the layer containing nuclei, where the silver in the com-plexed silver ions is precipitated in the presence of the silver halide developing agent. This process forms a reflective silver image which is a negative of the light exposed or surfaee activated latent image, Re-eording is aeeomplished by puncturing through the re-fleetive eomponent with a laser beam so as to create a hole in the refleetive component which may later be detected by a variety of means such as reduced reflec-tion of the hole; scattering of light from the hole;
inereased light transmission through the hole; and, if the reeording is done on the surfaee distal to the sub-strate, detection may be aecomplished by means of mech-anieally probing the surfaee relief image of the hole.

An advantage of the above method for making a refleetive reeording medium is that it allows a low-eost manufae-turing proeess to create a preeise very thin patterned reflective silver layer on the medium which eould be used for laser recording without resorting to high- :~
temperature proeesses which couId limit the selection of :~
substrate materials.: Several embodimen~s of the present method may be earried out by continuous manufacturing operations, as opposed to bateh operations, but batch procédures may al50~00 used.

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Figure 1 is a top plan view of the recording medium of the present invention;

Figure 2 is a side sectional view of the recording medium of Figure 1, taken along lines 2-2;

Figures 3-8 are detail views of the recording medium of Figure 1 showing the results of different combinations of photographic processing steps for making the finished recording medium;

Figures 9-11 are side sectional views of three versions of the recording medium of Figure 1 showing methods of laser reading or writing;

Figure 12 is a plot of relative contrast ratio versus laser power for two materials; and Figure 13 is a plot of percent reflectivity versus ex-posure for two materials.
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The reflective laser recording medium of the present :~
invention is made in t~o principaI steps: one step in-volving formation of a~surface latent image, the other -~
step involving silver diffusion transfer~

I. Surface Latent Image Formation : -Surface latent image formation for a laser recording ~;; : medium is achieved by exposing a region of unexposed photographic emulslon to light or to a fogging agent :

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over the area where laser writing is to be done. Alter-natively during the original manufacture of the silver~
halide photographic plate or film a very thin gelatin layer containiny silver-precipitating nuclei would be included at the surface distal to or the surface proxi-mate to the substrate, which would be the basis for creating a reflective surface at either of these two surfaces. To record control in~dicia on the medium, part of the emulsion may be masked or alternatively may have been exposed and chemically developed prior to this surface latent image formation step. Typically such a medium is a disc, as illustrated in Figure l; however it could be a plate or film strip.

Figure 1 shows a ;disc 11 having an inner periphery 13 and an outer periphery 15. The interior of the inner periphery 13 is void so that a centering collar may be used to hold disc 11 on a spindle for high speed rota-tion. While the recording medium of the present inven-tion is described as a disc, a disc configuration is not èssential for operating of the recording medium.
For example, the recording medium may be a flat sheet-like material which could be square and with a central hub rather than a hole. It could also be a non-rotating rectangular plate. However, rotating discs are prefer-red for fast random access to medium amounts of data`andnon-rotating rectangular plates in stacks are preferred to provide intermediate speed random access to large amounts of data by mechanically selecting a plate and scanning it by mechanical and electro-optical means.

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The aisc o~ Figure 1 is photographically partitioned into recording and non-recording areas. For example, a first annular recording zone 17 could be spaced Erom a second annular recording zone 1~ by an annular guard zone 21. The func-tion of the guard zone may be to sepa-rate different recording fields, to carry control infor~
mation, such as timing signals and to provide space for data read-write transducers to reside when not over re-cording areas. While such guara bands are preferable, they are not essential to the operation of the present invention. It should be noted that the recording fields are for data and control signal recording, while the guard band is not for data recording, but may have control signal recording thereon. The recording field 19 is shown to have a plurality of concentric, circum-ferentially-spaced servo guides 23 thereon. Such servo guides are thin lines which define the spaces between -circular paths wherein data are written. The pattern for such lines is applied photographically as explained below with reference to Figures 3-8.

Figure 2 shows a slde sectional view of the recording medium of Figure l~ The medium consists of a substrate 27 which is a sheet-like layer which may be transparent or translucent, preferably a dimensionally stable ma-terial, like glass or plastics used for photographicfilm bases. - Opaque, light-absorptive materials will work in those applications of the present invention where light transmission through the substrate is not desirea~ Transparency or absorptivity of the substrate 30 lS desired so that when the light beam of the reflective ' ' ' :~ ~

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playback apparatus impinges upon a recorded spot, it either passes through -the substrate or is absorbed by it with minimum reflection. If the substrate is ah-sorptive, it may be absorptive at the wavelengths of the recording beam or the reading beam, or preferably both. The most common photographic film bases are poly-ester polyterephthalate, polycarbonate, or cellulose triacetate.

For the case where the substrate is transparent, re-cording and reflective reading of the data can be done through the substrate as shown in Figures 10 and 11, or from the side distal to the substrate as shown in Figure 9. For transmissive read, the configurations of Figures 10 and 11-may be used. If the substrate is absorptive then~reflective read is the only possibility and the configuration OL Figure 9 would be used.

The thickness of the substrate is not critical when the laser beam is directed onto the surface as shown in Figure 9, but it should have sufficient thickness to provide strength for resistance against breakage. If the laser beam is directed through a transparent sub-strate, as in Figures 10 and 11, then in order to main-tain focus of the beam the thickness of the transparent substrate would have to be very uniform (for example, as obtainable from float glass or selected high quality drawn glass). Also, the thickness of the substrate may depend on the overall size of the recording medium be-ing used. For a 12-inch disc, a thickness of 1/8 inch may be suitable.
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. . , The purpose of substrate 27 is to support a silver-halide emulsion coating 29, which is uniformly applied to the substrate in a conventional manner and which is converted by surface latent image formation and silver diffusion transfer into components 32 and 33 in Figures 9, 10 and ll. This process for creating the reflective layer 32 does no-t require any chemical constituent with-in the emulsion other than a conventional silver-halide held in a suitable colloid carrier, preferably gelatin.
They may also contain optical and chemical sensitizers, anti-fogging agents, stabilizing compounds, emulsion hardeners and wetting agents. However, when commercial photoplates or films are used, they may contain certain physical characteristics or added chemical ingredients which could lead to favorable or unfavorable results.

One of the advantages of gelatin is that it has a rela-tively low melting temperature, less than 400C, which - aids laser recording. Such low melting temperature carriers are preferred in the present invention.

If a screening dye is used within the emulsion to create an exposure gradient in conjunction with actinic radia-tion exposure, the dye should be selected so that it is not trapped within layer 32 so as to cause a streaked surface of non-uniform reflectivity.

Emulsion thickness of 3 to 6 microns are adequate to contain sufficient silver-halide emulsion to build up the reflective layer by the complexing and difEusion ~` transfer steps. If thicker commercial emulsions are used along with long processing times, the reflective layer may become too thick or too thermally conducting to permit recording with low-power lasers. The thicker :
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~ ~ ~7~3 coating requires a higher laser beam power to penetrate it and a higher thermal conductivity leads to faster heat flow away from the spot being recorded, also lead-ing to higher recording powers.

If a hardened emulsion is desired it may be preferable to harden or cross link the gelatin aEter forming re-flective layer 32. If the emulsion is hardened initial-ly, then it will swell to a reduced extend during mono-bath processing thereby reducing the rate at ~hich the silver-halide is dissolved and complexed, thus extending the process time.

Small silver-halide grains typically found in commer-cially available high resolution or high definition photoplates used in photomask making, holography and high-resolution recording are excellent for producing reflective laser-recording materials. These emulsions typically have mean grain sizes of .05 micron and a spread of about .007 micron. One type, the Agfa-Gevaert Millimask HD photoplate, has a mean grain size of .035 micron and a spread of .0063 micron. The finer grains result in minimizing the micro variations or granular-ity in reflectivity ànd thickness of the reflective component and thereby permit recording and reading of smaller holes than for coarse grain emulsions. ~he finer grain emulsions also dissolve faster owing to their greater surface-to-volume ratio which leads to a shorter process time.

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High resolution emulsion coated glass pl~tes having these characteristics are commercially available and are known as photoplates which are used to make photo-masks for the manufacture of semiconductor integrated circuits. For example, emulsion coated photoplates suitable for use herein are manufactured by Agfa-Gevaert of Belgium, Konishiroku Photo Industries Co., Ltd. of Japan and the Eastman Kodak Company.

The shiny reflective component 32 in Figures 9, 10 and 11 result from the photographic monobath processing de-scribed herein but the silver is present initially as silver-halide and reflectivity does not initially exist in -the emulsion. Thus at the inception the silver of reflective component 32 is found in the photographic emulsion 29, which is uniform in its composition. An inert subbing layer, not shown, is usually used to attach the substrate 27 to,the emulsion 29. Following the photographic conversion of the present invention the emulsion 29 of Figure'2 produces a reflective com-ponent 32 at the emulsion surface shown in Figure 9,with a low-reflective underlayer 33 beneath it. The reflective layer 32 is,more sharply defined in thickness when nuclei are included during manufacturing or when a fogging agent is used for surface ac*ivation. Thus, although Figures 9, 10 and 11 depict a~sharp boundary for reflective component 32, if light exposure is used such is not the case but actually the concentration falls off and continues into underlayer 33.

Thus when light exposure is used underlayer 33, while not completely depleted of silver, contains much less ~: ;

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silver than reflective component 32. Optically, under-layer 33 is either clear or reddish in color which is transmissive to red light having wavelengths of 630 nanometers and longer. Underlayer 33 tends to be clear or slightly yellow if the silver-halide therein is not subject to latent image formation. Underlayer 33 tends to be amber or red if latent image formation occurs in the underlayer. As described hereinafter, better defi-nition of the reflective component occurs where a fog-ging agent is used for surface latent image formation.Since the depth of penetration of the fogging agent can be controlled, for example by the length of time of - emulsion dipping into the fogging agent, the unfogged silver-halide below this penetration depth forms under-layer 33. Since the silver in the unfogged silver-halide region subsequently goes into solution as a sil-ver complex, some of which is deposited on silver nuclei in reflective component 32, the underlayer 33 becomes substantially clear and is essentially gelatin.

On the other hand, if surface laten-t image treatment is achieved by means of exposure to light, the depth of treatment is more difficult to control, but is made easièr with screening dyes. The purpose of the screen-ing dye is to attenuate actinic radiation through the depth of the emulsion so that there is surface latent image formation through only a fraction of the depth of the emulsion. Screening dyes are usually of narrow bandwidth to absorb either blue or green light, but not both. Thus if this type of dye is used the actinic radiation must also be narrow band or filtered accord-ingly, otherwise unwanted actinic radiation will pene- , trate the emulsion. Thus, in g~neral, actinic radiation -. '~ .

-exposure does not leave a clear boundary between re-gions of surface latent image EGrmation and regions oE
no surface latent image formation. Ra-ther, there is a gradient with good surface latent image formation closest to the light source where there is strongest exposure and weak latent image Eormatlon further away where there is weakest exposure. In this case the monobath develops the weak latent image in the under-layer 33 which thereby forms a nuclei base for further silver deposits from the silver complex with the result that the underlayer has a red or amber color.

Either method of surface latent image treatment creates an exposure gradient with a greater concentration of exposed silver-halide near the surface of the emulsion lS where the exposure is greatest. Portions of the exposed and partially developed silver-halide grains become sil-ver nuclei where silver will be reduced from silver ion complexes during diffusion transfer. When the densest concentration of exposed silver-halide grains is desired at the emulsion surface distal to the substrate, either method of surface latent image treatment may be used.
However, when the surface having the highest exposed silver-halide concentration is desired proximate to the substrate, then either nuclei are included in manufac-turing or actinic radiation exposure through the trans-parent substrate is necessary to create the surface latent image. An emulsion heavily dyed with a screen-ing dye is necessary in this case to create a surface latent image concentration proximate to the substrate.
A short photographic development cycle before monobath development may be used to help create the required :` :
' ~ - 18 -silver precipitating nuclei prior to the creation of the silver complex and thus enhance diffusion transfer and reflectivity proximate to -the substrate. Owing to the dielectric constant of the glass a much higher vol-ume concentration of silver is necessary to give thesame reflectivity as compared to an emulsion side re-flective layer. The required layer of high concentra-tion silver precipitating nucle:i at the substrate or distal to the substrate can also be incorporated during the film or photoplate manufacturing process.
, Once craters are created penetrating reflective com-ponent 32, the data contained in the craters may be read by changes in reflectivity of the shiny reflective com-ponent throughout the visible spectrum and into the near infrared where it is ultimately limited in its usability as reflective component 32 becomes more and more trans-parent and therefore less reflective. The craters also may be detected by transmission of red light, provided that the opacity of the reflective layer is sufficiently great at the selected wavelength to permit detection of the craters through differences in light transmission.

It should be noted that both the recording areas 17, 19 and the non-recording guard band 21 of Figure l initially have silver-halide emulsion covering a substrate. Thus, 25 the designation of recording and non-recording areas is `
arbitrary and the entire surface could be used for re-cording if desired. However, as a matter of convenience, it is preferable to designate areas as non-recording areas. The boundaries between recording and non-record-ing areas may be defined by concentric lines, just as ' . .

: ' .--vz the servo guides 23 oE Fiyure 1, which have been greatly enlarged in the Figure, may be defined by lines. Typi-cally, servo guides are closely spaced concentric circles or adjacent lines of a spiral, with data being written on or between the lines. Such servo guide lines, as well as line boundaries for non-recording areas, may be photographically rec~rded on the recording medium prior to any data recording. Moreover, other alphanumeric information or data base information which is to be a permanent part of the recording medium also may be ap-plied to the recording medium photographically at an early time in the processing cycle since it becomes a permanent part of the recording medium.

- One of the advantages of the present invention is that the permanent information to be pre-recorded on the recording medium of the present invention may be applied by photographic techniques since the starting material for the recording medium is an unexposed commercially available photoplate used in the manufacture of semi-conductor in-tegrated circuits or film-based materials of similar quality. A principal characteristic of silver-halide emulsion photosensitive materials for use in the present invention is fine grain size so that the reflectivity granularity is minimized and very small holes can exhibit measurable changes in reflectivity.
Large grain sizes would lead to greater granularity which would tend to mask changes in reflection created by small holes. Pre-recording of information may be achieved by masking off areas as described herein.
After photographic processing, this pre-recorded in-formation may be read in reflection since the pre-recording areas ~ill consist of either highly reflective : : .

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The photographic techniques which may be used to pre-record data base and control information are closely related to the fabrication of emulsion photomasks in the semiconductor industry. Lines having a thickness of one micron may be made using these photomask manufacturing techniques. Some procedures for creating a pre-recorded line pattern are illustrated in Figures 3-8.

With reference of Figure 3, fine grain silver-halide emulsion medium 11 is exposed to actinic radiation in the areas for data recording but the line pattern con-sisting of the circular lines 23a, 23b and 23c is masked from the radiation. This procedure creates a surface - 15 latent image formation in the data recording areas.
The masked areas are then unmasked and the emulsion is subjected to the monobath processing described herein which creates the reflective surface for laser recording on 11 in Figure 4. If the recording areas are to be activated by actinic radiation, it is preferable that the emulsion contain a screening dye which is absorptive to the actinic radiation so that the latent image of the silver nuclei is concentrated on the ~urface. Al-though a screening dye is preferred~ it is not essential to creating a reflective surface. Without a screening dye the silver concentration gradient will not fall off as rapidly from the surface into the body and a higher power laser beam may be required for recording. ;

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There are two principal reasons -that the silver can be concentrated at the surface distal to the substrate without use of a screening dye. Firstly, the photons irradiating the surface are absorbed by the silver-halide as they create silver atoms; thus, there is agreater exposure at the emulsion surface than at the body. Secondly, when the emulsion is dipped into the monobath the surface silver nuclei begin to grow by chemical development more rapidly than the inner silver nuclei since they contact the d~eveloper first. Thus, when the solution physical development part of the mono-bath development begins, more of the complexed silver ions will precipitate on the surface where the silver nuclei will be larger and more numerous. Also it is known that it requires four silver atoms per silver-halide grain for the grain to participate in chemical development. Thus, any absorption by the silver-halide will result in a higher probability of silver-halide grains on the surface having the four atoms of reduced silver than for internal grains. Commercially avail-able photoplates containing screening dyes include East-man Kodak's High Resolution Plate - Type II, and three Agfa-Gevaert photoplates: Millimask Negative, Millimask Reversal, and Millimask Precision Flat HD. Denser screening dyes than these are necessary to create the desirable reflectivity at the surface proximate to the substrate.
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The circular lines 23a, 23b, and 23c which were masked represent low reflectivity servo guides which would pro-vide informatlon as to whether the recording laser isrecording on the data track or has moved off the edge , .
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.. , of the da-ta track. To provide additional information to the servo system, the servo guides could contain a reflective and non-reflective pattern shown in Figure 5, which would provide information as to whether the correction requires a movement to the right or left.
Note that the right and lef-t servo guides would provide different frequency signals to the playback system.
The dashed pattern shown could be created in the master by means of a photomask or by interrupting a laser photo-graphic recording beam.

For the servo guides or any other indicia markings tobe in the form of low reflective black silver, as op-posed to clear gelatin markings discussed above, the servo guides themselves could be exposed through a mask or by means of a continuous or interrupted laser beam.
Figure 6 illustrates the making of such indicia where actinic radiation is used first to expose servo guides 43a, 43b, 43c and the remaining area 41 would be shield-ed. Then a normal chemical or direct development would be used to create a black low reflectivity pattern as shown in Figure 7. No fixing would be used since the silver-halide in region 41 would be used in the subse-quent monobath processing to create reflective areas.
Also note that the lines 43a, 43b, and 43c could have ~5 been broken into a pattern such as those shown in Figure 5. With the track guides and possibly other indicia recorded in black silver, the next step would be to ex-pose the surface latent image in the remaining areas for laser recording.

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Surface latent image formation is done in the recording area 41 of Figure 8, as well as recording area 11 oE
Figure 4 previously mentioned, in either of three ways:
first, by exposure o~ the unexposed silver-halide emul-sion data recording area to actinic radiation such asby mercury arc lamp, incandescent lamp, xenon flash lamp onto an emulsion containing a screening dye for the entire bandwidth of the actinic radiation or second-ly, by means of a surface activation o~ a fogging agent such as hydrazine in aqueous solution or in gaseous state, or for example, potassium borohydride in aqueous solution, or thirdly, by including a silver-precipita-ting nuclei layer near the emulsion surface where the surface latent image is desired. Surface latent image formation would be followed by processing as described below.

When the surface latent images are created by a fogging agent, it is of no consequence that the screening dye may have been washed out in the earlier development process. The surface activation of the emulsion could take place either by a few-second dip in a fogging agent, such as an aqueous carrier containing hydrazine or by exposure to hydrazine gas for a period of minutes.
Penetration of the fogging agent to the interior of the emulsion can be minimized by starting with a dry emul-sion. ~fter monobath development, the finished laser recording medium would have th~ appearance shown in Fig-ures 5 or 8. Note~that the pre-recorded black control indicia 43 of Figure 8 would be low refle~tive black compar~d to the shiny sllver rerording areas o~ 41.

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Use of a fogging agent creates nuclei where silver in silver ion complexes may be reduced and absorbed. As an alternative to use of a fogging agent, preformed silver-precipitating nuclei may be disposed in the un-exposed silver-halide emulsion, for example in the manu-facturing process. The commercially available instant photographic films o the Polaroid-Land photograhic system have such nuclei layers in contact with the silver-halide emulsion. Note that the use of silver-precipitating nuclei layers incorporated in the emul-sion does not preclude the possibility of pre-recorded control indicia. The non-data recording areas may be exposed first and chemically developed to low reflec-tivity black silver and not fixed. The entire plate is then given a monobath development to create reflective data recording areas.

An alternate method of surface latent image formation is by means of actinic radiation exposure of the data recording area. It is desirable for the medium to con-tain a screening dye to limit the exposure primarilyto the surface, but this dye may be washed out if the medium was previously processed as for example in pro-ducing black silver control indicia. This problem can be overcome by a dyeing process after the chemical de-~7elopment process is completed or by utilization of apermanent, non-soluble screening dye in the initial manufacture of the emulsion, which does not cause non-uniform xeflectivity. The monobath processing may be carried out in the same manner as was described in the case of the fogging agent activation. ~lso, if desired, the black silver areas created by the initial exposure and development could be bleached out before monobath processing.
.

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The surface latent image formation methods crea-te a depthwise exposure gradient, with a concentration of exposed silver-halide which is greatest at one emulsion surface where exposure was greatest. That concentration falls off in the depthwise direction, rather abruptly in the case of fogging agents, such that the concen-tration of exposed silver-halide is low throughout the body of the emulsion. In the case of actinic radiation exposure the volume concentration of latent image ~or~
mation falls continually from the exposed surface and is lowest at or near the opposite emulsion surface.
The unexposed silver-halide exists in concentrations inversely related to the exposure concentration. After monobath processing, the volume concentration of reflec-tive siiver particles at the reflective surface distalto the substrate will exceed the lowest concentration in the body of the emulsion by a ratio typically ex-ceeding 5~

The reflective component 32 of Figures 9-ll is thus de-rived from the silver in the silver-halide emulsion.
While this reflective silver component may appear at either of the two emulsion surfaces and is concentrated there, the thickness of the reflective component is not well defined when created by actinic radiation exposure because some radiation penetrates below the surface of the emulsion and a silver latent image is created. An advantage of using a fogging agent for surface latent image formation as compared to actinic radiation ex-posure is that it creates a better defined reflective layer and a lower silver concentration wi-thin the body ::

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of the emulsion. With both of -these processes, silver~
halide in a commercially available photographic emul-sion is the starting material for crea-ting the laser-recording medium in the present invention, and the finished product may be considexed to be silver parti-cles in a gelatin dielectric matrix, the halide being removed in the monobath process:ing.

To use the laser recording medium of the present inven-tion, laser light is focused on a spot on the reflective component either from the side distal to the substrate or through a transparent substrate. For laser record-ing as opposed to data storage applica-tions the reflec-tivity of the reflective layer preferably ranges between 15~ and 50%; thus, the remaining percentage of incident lS radiation of 85% to 50% is either absorbed by the re-flective component or partly passes through it. The absorbed power distorts or melts the gelatin supporting the reflective component so as to reduce the reflectivity at the spot and create an adequate contrast in reflec-tive reading of the recorded data. For data storageapplications, i.e., laser reading but not recording the reflectivity may be as high as possible and the thickness of the reflective layer is not critical. The reflective component 32 is located on the underlayer as shown in Figure 9 and Figure 11 and adjacent to the substrate as shown in Figure 10. In all three cases a reflective read procedure can be used - for example, as described in U.S. Patent 3,657,707. In the cases shown, the re-cording laser beam need only affect the reflective com-ponent, and further penetration into component 33 isnot needed.

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~ . . . --~2 In Figure 9, the substrate could be either transmissive or opaque if reflective read is used, but must be trans-missive to the read laser beam if transmissive read is used. The component 33 would consist of a red or amber silver gelatin complex if a soluble screening dye and actinic exposure were used to create component 32, but would be essentially clear gelatin if fogging agent surface activation were used or if the emuIsion had been manufactured with a silver precipitating nuclei layer included. The color of component 33 would have little effect on reflective read methods but would affect trans-missive read methods. ~f component 33 is red in color, transmissive reading can be accomplished to a limited extent by use of a`red or near infrared laser beam pro-vided that the opacity of the undisturbed reflectivecoating blocks about 90~ of the light and the recorded craters permit transmission of at least about 50~ of the light. If component 33 is essentially clear gelatin it would permit transmissive reading with a green or blue laser as well; and since the reflective component is more opaque at these wavelengths, a higher contrast would be achieved than in the case of a red or infrared laser being used for transmissive read.
~ ' Figure 10 illustrates a configuration which could have been produced by photographic exposure using narrow band blue or green actinic radiation through a transparent ` substrate 27 onto an emulsion heavily dyed to attenuate the selected narrow band actinic radiation. Commerciall~
available soluble screening dyes with adequate absorption properties can accomplish the task. Dyes contained in commercial photoplates are not adequate to achieve the :: ;

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k~J2 desired reflec-tivity. After final processing the com-ponent 33 would be red or amber in color. Recording and reflective reading would be achieved through the substrate. Transmissive read could be accomplished to a limited extent by use of a red or near infrared laser beam such that the opacity of the reflective coating blocks 90% of the read-beam radiation and the recorded craters permit trapsmission of at least 50% of the light. If this configuration were produced by use of an emulsion which had been manufactured with a silver precipitating nuclei layer incIuded, component 33 would be essentially clear gelatin and transmissive read also could be accomplished in blue and green as described in the previous paragraph.

15 Figure 11 illustrates a configuration where both the , substrate and the underlayer are transmissive tc visible and near infrared radiation. It has the advantage that -layer 32 can be coated with a non-optical flat protec-tive layer which would serve to encapsulate layer 32.
This type of protective layer could~not be used in the configuration of Figure 9 because lt would be in the optical path. The configuration of;Figure 11 also offers an advantage ovér the configuration of Figure 10 in that higher reflectLvities are more easily attain-~
able by use of the herein described process. The es-~sentially clear~gelatin component 33 would be~created by fogging agent surface activation or actinic radia-. tlon exposure~dlstal~to~the~sub~strate~of~an emulslonheavily dyed with a~screening-dye so that almost no 30 silver latent images in the body of the emuIsion are -~
reduced during monobath development. Thls conflguration ~ ~%

can also be produced by use of an emulsion which had been manufactured wi-th a silver precipitating nuclei layer included at the location of layer 32. In this case in addition to reflective read at visible wave-lengths and near infrared, the component 33 also permitstransmissive read at these wavelengths by laser light transversing substrate 27 for transmission through the essentially clear gelatin component 33 and through crater 30 in component 32.
.
Figures 9, 10 and 11 show emulsion coating 29 on sub-strate 27 covered by shiny component 32 having a crater 30 damaging the shiny component created by means of laser light indicated by the rays 31. The size of the craters is kept at a minimum, preferably about one mic-ron in diameter but no larger than a few microns indiameter to achieve high data densities. Data written by means of laser light are recorded in the recording areas 17, 19 shown in Figure l, designated by the letter R. As mentioned previously, these recording areas may also contain pre-recorded data base data and control indicia which may be`disposed over essentially the en-tire area of the medium. No data is recorded in the guard band 21, designated by the letter G, although this region may have control indicia written therein.
Control indicia in either of the areas may be written by means of photographic techniques or by pyrographic methods such as laser writing.

, .

Thus, the recording medium of the present invention may contain a mix of pre-recorded data and control indicia which has been applied to the recording medium by photo-graphic techniques, as well as subsequently written data applied to the recording medium by laser pyrographic writing. There need be no data storage distinction be- -tween the photographically pre-recorded non-reflective spots and non-reflective spots made by laser writing.
In the recording mode the pre-recorded control infor-mation is used to determine the location of the data craters being recorded.

II. Silver Diffusion Transfer We have found that a very thin, highly reflective, sil-ver surface may be formed by the diffusion transfer of appropriate complexed silver ions to a layer of silver precipitating nuclei. This reflective layer is electri-cally 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 reac-tion of an appropriate chemical and the silver-halide used in conventional silver-halide emulsions. A develop-ing 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 complexing solvent in one solution is called a monobath solution. Preferred monobath formu-lations for highly reflective surfaces include a develop-ing agent which may be characterized as having low ac-tivity. The specific type of developing agent selected appears to be less critical than the activity level as determined by developer concentration and pH. ~

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The developing agent should have a redox potential sufficient for causing silver ion reduction and ab-sorption or agglomeration on silver nuclei, The con-centration 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 rleflectivity 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 develop-ing agent and complexing agent. It is well known thatphotographic 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 Millimask HD photoplates.

For Monobaths Usinq Na(SCN~ As a Solvent And Silve~ plexing A~ent ApproximateDevelo~in~ Agent Antioxidant Maxim m Raflectivit~
p-methylaminophenol Ascorbic Acid 46%
25 p-methylaminophenol Sulfite 37%
- Ascorbic Acid 10%
p-Phenylenediamine Ascorbic Acid 24%
Hydroquinone Sulfite 10%
Catechol Sulfite 60 For Monobaths Using NH 0~ As a Solvent

4 - _ And Silver Complexing Agent Developing Agent Antioxidant Typical Reflectivit~
Hydroquinone Sulfite 25%

5 Catechol Sulfite 30%

The preferred solvents/silver complexing agents, which must be compatible with the developing agent, are mixed therewith, in proportions promoting the complete dif-fusion 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 sulfide 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 oE low activity, which are preferred to avoid the creation of low-reflec-tivity black filamentary silver in the initial develop-ment of the surface latent image.

The following chemicals act as silver-ha~llde solvents and silver complexing agents in solution physical develop-ment. They are grouped approximately according to theirrate of solution physical development; that isj the amount of silver deposited per unit time on precipitating nuclei, when used with a p-methylaminophenol-ascorbic acid developing agent.
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Most Active Thiocyanates ~ammonium, potassium, sodiu~, etc.) Thiosulphates (ammonium, potassium, sodium, etc.) Ammonium hydroxide Moderately Active ~ picolinium - ~ phenylethyl bromide Ethylenediamine 2-Aminophenol Furane n-Butylamine 2-Aminophenol thiophene Isopropylamine Much Less Active Hydroxylamine sulfate Potassium chloride Potassium bromide Triethylamine Sodium sulfite ' From the above it can be seen that the thiocyanates and ammonium h~droxide are amongst the most active solvents/
complexing agents. While almost all deve~lopers 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 ~anner. For example, the thiosulfate salts,;the most common silver~
halide solvent used in photography and in Polaroid-Land black and~white instant photography'~diffusion transfer ; process, does~not work in this process for two reasons. ;~

t Its complexed silver ions are so stable that it re-quires a strong reducing agent to precipitate the sil-ver on the nuclei, and this strong reducing or develop-ing agent would have the undesirable effect of develop-ing low reflective black filamentary silver. It hasanother undesirable effect, also exhibited by the sol-vent thiourea; namely, it forms black, low reflecting silver sulfide 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 ex-cellent 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 photo-graphic 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 shoula be controlled to control reflectivity. Prefer-ably, 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 re-flective filamentary silver growth, excpetions to thisratio being found among p-phenylenediamIne and its N, N-dialkyl derivatives having a half-wave potential be-tween 170 mv and 240 mv at a pH of 11.0, which have lower development rates and require higher concentra-tions, i.e., up to l5 grams per liter and minimum ofabout 2 grams per liter. These derivatives and their , ~A, , ~

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half-wave potentials are listed in Table 13.4 of the book entitled The Theory of the Photographic Process, 3rd ed., 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 liter but less than 45 grams per liter. If the concen- `
tration 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 de-velopment, as used herein, the silver particles do not grow as filamentary silver as in direct or chemical de-velopment, but instead grow roughly equally in all di-rections, 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 suf-ficient 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 trans-mitted through this medium initially takes on a yellow-ish appearance when the grains are very small. ~his ., - .
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changes to a red appearance as the par-ticles build up in size and eventually will take on a metallic-like reflec-tivity as the aggregates form.

In summary, it was discovered that if silver precipita-ting nuclei are formed on one of the surfaces of a sil-ver-halide emulsion either in the emulsion manufacturing process, by actinic radiation, or by a fo~ging agent;
and if this emulsion is then developed in a monobath solution containing a weak developer and a very ~ast solvent which forms complexed silver ions which are readily precipitated by catalytic action of silver nuclei; and if the solvent does not form silver sulfide;
then a reflective coating is developed on one of the emulsion~surfaces thereby creating a medium for data storage and laser recording. It was also discovered that 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 dif-fusion transfer process the silver in the unused silver-halide in the negative image will diffuse to a second separatable layer containing precipi~atlng nuclei for reducing the silver and thereby creating a positive image. In the diffusion transfer process of this in-vention, a volume concentration of silver precipitating nuclei may be created on an emulsion surface without use of a separate layer containing nuclei. When actinic ~,, - ::
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7g~:2 radiation or fogging chemicals are used to create these nuclei in the data recording areas, the desired reflec-tive layer appears where the emulsion surface was ex-posed 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 de-veloping agent-solvent monobath performs several func-tions; it develops and thus enlarges the silver nucleiof the latent images, dissolves the silver-halide with-in the body, creates complexed silver ions and provides the reducing agent necessary for the solution physical development process, that is, the reduction and pre-cipitation of the complexed silver ions on the silverprecipitating nuc,lei of the developing latent image.
.
Thus, the key steps in the present invention involve creating a surface latent image or concentration gradient of silver-precipitating nuclei in the data recording - 20 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 tsle silver in the surface latent image area until it becomes adequately re~lective.
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 nu~lei :

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which is then exposed to light in the non-data-record-ing 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 reflec-tive. 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 of the present inven-tion 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 I presents 14 experimental examples to illustrate some of the variations of the individual steps that may be used and to present an overview oE
t~o principal steps necessary to create a laser record-ing media of adequate reflectivity.

See Table I which follows.

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Note that the fourteen examples include creation of sur-face latent images by actinic radiation, a~ueous and gaseous fogging by hydrazine and aqueous fogging by potassium borohydride. A key step is creation of sur-face latent images in the data recording area if anuclei 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 sur-face. This invention is not limited to the use of gel-atin-based emulsions. Other film-forming colloids may be used as carriers. A variety of commercially avail-able high-resolution films and plates manufactured by three different companies were used to illustrate the general nature of the process. 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 I lists four different developing ager.ts, three different solvents/
complexing agents, five different emulsions and four different surface activation procedures. The reflec-tivities achieved range between 15% and 75%. ~;

Example 1 A photoplate coated with a commercial Agfa-Gevaert HD
emulsion 4.5 microns thick and containing a screening dye was exposed to sunlight for several minutes and then -~ immersed for five minutes at 23C in a monobath which contained the following formulation: p-phenylenediamine, . : ~.
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5.4 grams; 1-ascorbic acid, 5.0 grams; KBr, 0.5 grams;
and NaSCN, 10.0 grams; with water added to bring volume up to 1 liter; and wi-th a pH = 11 achieved by adding NaOH. After drying, samples exhibited a range of reflec-tives of 20~ to 24~ at 633 nanometers and a range of op-tical densities measured in the red with a commercial densitometer of 1.0 to 1.2.

Laser recording was then accomplished with an argon laser using the green line at 5:L4 nanometers. The beam diameter was approximately 0.8 micron at the media sur-face, and pulse lengths of 100 nanoseconds were used.
Tests were conducte~ to determine how the reflective contrast ratio varied with laser-beam power. Measure-ments were made starting at beam powers of 28 milliwatts and down to under 5 milliwatts. The results of those tests for two samples are shown as curves "A" and "B"
in Figure 12. The ratio of reflected power from the unrecorded surface to that of the hole at 24 milliwatts was in the range of 7:1 or 8`1. At each measured power level, the contrast was measured at 32 points and aver-aged.

Example 2 A photoplate coated with a commercial Agfa-Gevaert Milli- ~ ;~
mask HD emulsion 4.5 microns thick and containing a screening dye was exposed in an exposure box through a stepped wedge stepped in optical density units of 0.1 `
to produce ten exposure levels. Four sequential expo-; sures were used, after which the plate was developed for , . ~' , - ~3 -five minutes at 23C in a monobath cons:isting oE p-methylaminophenol sulfate, 0.28 grams; l-ascorbic acid, 2,8 grams; KBR~ 1 . O grams; NaOH, 2 grams; NaSCN, 22.0 grams; in a volume of 1 liter after adding water. The pH was 11. After drying, the reflectivïty measured at 633 nanometers as a function of log exposure is shown in Figure 13 as curve "C".

Example 3 A photoplate coated with a commercial ~onishiroku ST
emulsion 3 microns thick containing no screening dye and with the backing removed was exposed in an exposure box through a stepped wedge stepped in optical density units of 0.1 to produce ten exposure levels. Three plates were used. The first plate was exposed to one flash of actinic radiation; the second, to four; and the third, to sixteen. The plates were then developed in the mono-bath described in Example 2. The processing time was 5 minutes at 23C. After drying, the reflectivity measure-ments were made on the ten reflective steps on each of the three plates at 633 nanometers as a function of log exposure and are shown in Figure 13 as curve "Di'. The curve covers a much greater range of log exposure than curve "C" because "D" interconnects the data taken from the three plates subject to different exposures, while "C" represents only one plate.

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- ~4 -Example 4 A strip of Agfa-Gevaert lOE75 film was exposed to room light for several minutes~ then developed in a monobath, as described in Example 2, for 2 minutes at 23C. After drying, it did not appear reflective. It was concluded that the gelatin overcoat was reducing ~he overall re-flectivity. The strip was immersed in a 0.5% Protease WT solution at 35C for 4 minutes. The reflectivity was in the range of 40% to 43% and the optical density in the red was 2.5 to 2.7. Protease WT is a mixture of enzymes and is a trademark of GB Fermentation Industries, Inc., of West Germany.

Example 5 A commercially available Eastman Kodak SO 173 film was etched with a Protease WT 0.5% solution for 5 minutes at 35C in a darkroom to remove the gelatin overcoat. The , film was then immersed in a hydrazine 68% aqueous solu-tion for 2 seconds to create the developable surface latent image. It was then developed in a monobath as described in Example 2, for 5 minutes. After drying, it exhibited a reflectivity of 32% and a red density of 1.9 to 2Ø

Example 6 An unexposed commercially available Agfa-Gevaert Milli-mask HD photoplate was dipped into a 68% aqueous solu-tion of hydrazine for several seconds to create a de-velopable surface latent image. It was then developed :': ~
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in monobath as described in Example 2 for 5 minutes at 23C and then dried. Samples exhibited reflectivities ranging between 39% and 41~ at the emulsion surface and reflectivities of 17% to 18% when measured through the glass substrate. The gelatin under the reflective silver coating was so clear that the silver coating was visually reflective through the glass substrate. Opti-cal densities in the red ranged between 0.8 and 1Ø

Example 7 A commercially available photoplate manufactured by Konishiroku Photo Industries, of Japan, called a KR SN
photoplate, has a 6-micron-thick emuIsion which does not contain a screening dye but does contain an anti-halation backing coated on the back of the glass sub-strate. This photoplate was dipped into a 68% aqueous solution of hydrazine for a few seconds and then devel- ~--oped for 5 minutes at 23C in monobath as described in Example 2 and then dried. It exhibited a reflectivity from the emulsion side of 23% and an optical density in the red of 1.5.

Example 8 .

A commercially available Agfa-Gevaert Millimask ~D photo-plate had latent images created on its surface by means of gaseous hydrazine. The photoplate was placed in a chamber which is exhausted of air down to 13 mm of mer-cury, after which hydrazine is evaporated into the cham~er. The photoplate is exposed to this gas for 10 :
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minutes in darkness and then developed in monobath, as described in Example 2, for 5 minutes at 23C. After drying, the plate exhibited a reflectivity of 22~ and an optical density in the red of 2Ø

~xample~9 A commercially available Agfa-Gevaert Millimask HD
photoplate having a 4.5 micron thick emulsion and con-taining a screening dye was immersed in a water solu-tion consisting of 5 grams/liter of potassium boro-hydride (KsH4) for 2 seconds to fog the surface andcreate silver nuclei for silver diffusion transfer.
After it was washed well, the photoplate was developed in the monobath described in Example 2 for five minutes at 23C. When washed and dried, the plate exhibited a reflectivity of 75%.

_ample 10 A commercially available Agfa-Gevaert Millimask HD
photoplate having a 4.5 micron thick emulsion and con-taining a screening dye was exposed to room light for :
several minutes and then developed for 2 hours in a monobath developer having the following constituents:
p-methylaminophenol sulfate, 0.25 grams; ascorbic acid, :
2.5 grams; sodium hydroxide, 2.0 grams; hydroxylamine hydrochloride (HO-NH2-HCL~, 5 grams; in a volume of one :
liter after adding water. After the photoplate was washed and dried, its reflectivity was measured at 18.5%.

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- ~7 -Example 11 A commercially available Agfa-Gevaert Millimask HD
photoplate having a 4.5 micron thick emulsion and con-taining a screening dye was exposed to room light for several minutes and then immersed for five minutes at 23C in a monobath developer having the following con-stituents: catechol, l gram; sodium sulfite, 10 grams;
sodium hydroxide, 2 grams; sodium thiocyanate, 25 grams;
in a volume of one liter after adding water. After the photoplate was washed and dried, it exhibited a reflec-tivity of 56%.

Example 12 A commercially available Agfa-Gevaert Millimask HD
photoplate having a 4.5 micron thick emulsion and con-taining a screening dye was exposed through a photomaskcontaining one micron serpentine lines for 8 seconds using an Ultratech contact printer and then immersed for five minutes at 23C in a monobath developer having the following constituents: catechol, 1/2 gram; sodium sulfite, 10 grams; sodium hydroxide, 2 grams; sodium thiocyanate, 25 grams; in a volume of one liter after adding water. After the photoplate was washed and dried, its reflectivity was approximately 35%. This reflective serpentine pattern of one micron lines and one micron spaces was of excellent image quality and demonstrated the ability of this process of pre-record data and control indicia having image sizes of one micron.

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Example 13 A commercially available Agfa-Gevaert Millimask ~ID
photoplate having a 4.5 micron thick emulsion and con-taining a screening dye was exposed to room light for several minutes and then immersed for five minutes at 23C in a monobath developer having the following con-stituents: catecholl 1/2 gram,; sodium sulfite, 10 grams; sodium hydroxide, 2 grams; 58% solution of am-monium hydroxide, 50 milliliters; in a volume of one liter after adding water. After the photoplate was washed and dried, its reflectivity was approximately 30%.

Example 14 i A commercially available Agfa-Gevaert Millimask HD
photoplate having a ~.5 micron thick emulsion and con-taining a screening dye was exposed to room light-for several minutes and then immersed for five minutes at 23C in a monobath developer having the following con-stituents: hydroquinone, 1/2 gram; sodium sulfite, 10 grams; sodium hydroxide, 2 grams; 58% solution of am-monium hydroxide, 50 milliliters; in a volume of one liter after adding water. After the photoplate was washed and dried, its reflectivity was approximately 25%.

The appearance of the surface of the finished record-ing medium varies with the degree of reflectivity. At reflectivities of 50~ or more it has a silver-like appearance. In the 35% to 45% range its color is like white gold, and in the 17% to 30% range it looks like yellow golc. Below about 12% reflectivity it has a - . ~ . .

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reflective black appearance similar to black patent leather.

One of the principal differences between the single step diffusion transfer process of the present inven-tion and the prior art is that in the present inventionthe unexposed and undeveloped silver halide is put into solution quickly so that the silver ion complex forming reaction takes place at a more rapid rate than the chemical development of photographically exposed silver halide. In the prior art the development of the nega-tive black image must be essentially completed before the remaining silver-halide is complexed and transfer-red; otherwise, the positive image would in essence be fogged. Thus, in the prior art a very high concentra-tion of developing agent is used to rapidly completethe chemical development process. The initial chemical development process of the present invention only slightly develops the latent image before the complex forming reaction takes places since the principal ob-jective is the physical development of the latent imageto produce a reflec-tive image of it, not the chemical development of the latent image to permit the remain-ing silver-halide to produce a reversal image as in the prior art.

Nothing limits the silver diffusion transfer process of the present invention to use as a data storage med-ium. The process may be used to make other articles where high reflectivity is needed in conjunction with various types of information imaging.
.

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In the broadest sense, the invention comprises disper-sing high eleetrical eonduetivity tiny metal spheres or spherieal particles in a dielectric medium of low thermal conductivity and low melting temperature to form a laser recording medium. If these small parti-cles are of very high volume concentration, e.g. be-tween 20% to 70% of the volume of the reflective sur-face layer, the medium can exh:ibit very high refleetives in the visible speetrum even though the'reflective sur-face would have no measurable eleetrieal conductivity.
Such a dielectrically based electrically non-conducting reflective medium is desirable for laser recording.

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Claims (38)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for making a reflective, electrically non-conducting data storage medium comprising, defining at least one data storage field in an unex-posed photosensitive silver-halide emulsion, forming an areawise surface latent image layer of silver precipitating nuclei in the data storage field of the emul-sion by chemical fogging or by exposure to actinic radiation, said layer having a maximum nuclei volume concentration at one surface of the emulsion and a gradient in the depthwise direction of decreasing concentration, and depositing non-filamentary silver on said nuclei by negative silver diffusion transfer from said emulsion, said silver adsorbed on the nuclei to a degree that the emulsion forms an areawise reflective data storage field which is electrically non-conducting, said negative silver diffusion transfer process employing a weak silver-halide developing agent for chemical development of the surface latent image layer of silver precipitating nuclei and a silver-halide complexing solvent for reacting with unexposed and undevel-oped silver halide to form soluble silver ion complexes which are transported by diffusion transfer to said chemi-cally developed-silver-precipitating nuclei of said latent image where silver of said silver ion complexes is precipi-tated and adsorbed on said chemically developed nuclei in the presence of said developer acting as a reducing agent, thereby forming a reflective electrically non-conducting layer of aggregated and individual silver particles in said areas for data storage.

2. The process of claim 1 wherein said layer of silver precipitating nuclei is enhanced by the step of providing, in said emulsion, a screening dye attenuating said actinic radiation.

3. A negative silver diffusion transfer process for making a reflective electrically non-conducting data storage medium from a photosensitive silver-halide emulsion compris-ing, defining at least one recording field in a photosensi-tive silver-halide emulsion, forming an areawise surface latent image layer of silver precipitating nuclei by means of contacting the recording field of the photosensitive silver-halide emulsion with a fogging agent, said layer having a maximum nuclei volume concentration at one surface of the emulsion and a gradient in the depthwise direction of decreasing concentration, contacting said photosensitive silver-halide emulsion with a reagent comprising a weak silver-halide developing agent for chemical development of said surface latent image layer of silver precipitating nuclei and a rapid-acting, silver-halide complexing solvent for reacting with unexposed and undeveloped silver halide to form soluble silver ion complexes which are transported by diffusion transfer to said chemically developed silver pre-cipitating nuclei where silver of said silver ion complexes is precipitated and adsorbed on said chemically developed nuclei in the presence of said developing agent acting as a reducing agent, thereby forming a reflective, electrically non-conducting layer of aggregated and individual silver particles in the recording fields, the activity of solvent permitting chemical development of said surface latent image by the weak developing agent while simultaneously all of the undeveloped and unexposed silver halide is dissolved by the complexing agent.

4. The process of claim 3 wherein said fogging agent is selected from the group consisting of hydrazine and non-reacting cations of borohydride.

5. The method of claim 3 further defined by the step of photographically defining a pattern of indicia in said recording field of the silver-halide emulsion prior to forming said latent image exposure, said step comprising, masking the area of a silver-halide emulsion, said masking defining desired indicia images, photographically exposing the desired indicia images in the silver-halide emulsion, and chemically developing said desired indicia images to achieve black low reflective indicia images in the silver-halide emulsion.

6. A negative silver diffusion transfer process for making a reflective electrically non-conducting data stor-age medium from a photosensitive silver-halide emulsion comprising, defining at least one recording field in a photosensitive silver-halide emulsion layer, forming an areawise latent image layer of silver precipitating nuclei by means of an actinic radiation exposure in the recording field of said photosensitive silver-halide emulsion layer, said silver precipitating nuclei having a gradient of de-creasing volume concentration through the depth of the emulsion, said emulsion having unexposed photosensitive silver-halide remaining therein in concentrations inversely related to said nuclei concentration, contacting said photosensitive silver-halide emulsion layer with a reagent comprising a weak silver-halide developing agent for chemi-cal development of said surface latent image layer of silver precipitating nuclei and a rapid-acting silver-halide complexing solvent for reacting with unexposed and undeveloped silver halide to form soluble silver ion com-plexes which are transported by diffusion transfer to the chemically developed silver-precipitating nuclei of said latent image where silver of said silver ion complexes is precipitated and adsorbed on said chemically developed nuclei in the presence of said developer acting as a reducing agent, thereby forming a reflective electrically non-conducting layer of aggregated and individual silver particles in said recording field, the activity of solvent permitting chemical development of said surface latent image by the weak developing agent while simultaneously all of the undeveloped and unexposed silver halide is dissolved by the complexing agent.

7. The method of claim 6 wherein said layer of silver precipitating nuclei is enhanced by the step of providing, in said emulsion, a screening dye attenuating said actinic radiation.

8. The method of claim 6 further defined by the step of photographically defining a control indicia pattern in said recording field of the silver-halide emulsion prior to forming said latent image exposure, said step comprising masking said control indicia pattern on the surface of said emulsion to be exposed by latent image exposure, then form-ing said areawise latent image exposure through a mask, and then unmasking said control indicia pattern.

9. The method of claim 6 further defined by the step of photographically defining a pattern of indicia in said recording field of the silver-halide emulsion prior to forming said latent image exposure, said step comprising, masking the area of a silver-halide emulsion, said masking defining desired indicia images, photographically exposing the desired indicia images in the silver-halide emulsion, and chemically developing said desired indicia images to achieve black low-reflective indicia images in the silver-halide emulsion.

10. The method of claim 5 or 9 further defined by.
bleaching out the developed black control indicia pattern prior to creating the layer of silver precipitating nuclei on the surface of the remaining silver halide.

11. A method of making a reflective laser recording medium from an unexposed photosensitive silver-halide emulsion layer incorporating a surface layer of high volume concentration silver precipitating nuclei having a size primarily less than five hundredths of a micron therein, the emulsion being disposed on a substrate with the nuclei layer disposed in said emulsion comprising, defining laser recording areas in the silver-halide emulsion, contacting the unexposed and undeveloped photosensitive silver-halide emulsion layer incorporating the surface layer of silver precipitating nuclei with an aqueous monobath comprising a weak silver-halide developing agent and a rapid-acting silver-halide solvent for reacting with unexposed and un-developed silver halide to form soluble silver ion complexes which are transported by diffusion transfer to the silver precipitating nuclei within said emulsion layer where the silver of said silver ion complexes is precipitated and adsorbed on said nuclei in the presence of said developer acting as a reducing agent, to the extent that a layer of aggregate and individual silver particles is formed exhib-iting reflectivity of at least 15%.

12. A reflective data storage medium comprising, a low melting temperature colloid matrix supported on a sub-strate, and a surface layer of non-filamentary individual silver particles, disposed in said matrix, having maximum particle dimensions primarily under .05 microns, some of which are aggregated with similar particles, and having a volume concentration of silver particles greater at said surface than in the interior of said matrix, said surface having an areawise substantially uniform reflectivity to visible light, said uniform reflectivity being between 15%

and 75% and being electrically non-conductive.

13. The data storage medium of claim 12 wherein the volume concentration at said reflective surface layer ex-ceeds the lowest silver volume concentration within the interior of said colloid matrix layer by a ratio of at least 5:1.

14. The data storage medium of claim 12 wherein said reflective surface layer is less than one micron thick.

15. The data storage medium of claim 12, wherein said volume concentration of silver particles in said reflective layer is a minimum of 20% and a maximum of 70%.

16. The data storage medium of claim 12, wherein said colloid matrix layer is photographic gelatin used in the manufacture of silver-halide emulsions.

17. The data storage medium of claim 12, wherein said reflective surface layer is derived from a photographic emulsion.

18. The data storage medium of claim 17, wherein said reflective surface layer contains pre-recorded information indicia therein.

19. The data storage medium of claim 18 wherein said pre-recorded information indicia comprises a photographic image.

20. The data storage medium of claim 18 wherein said pre-recorded information indicia comprises a pattern of laser writing.

21. The data storage medium of claim 18 wherein said pre-recorded information indicia comprises a photographic image and a pattern of laser writing.

22. The data storage medium of claim 12 wherein the colloid matrix forms an underlayer component beneath said reflective layer which is transmissive of visible light.

23. The data storage medium of claim 12 wherein the colloid matrix forms an underlayer component beneath said reflective layer which is absorptive of green and blue light.

24. The data storage medium of claim 12 wherein said reflective layer of said matrix layer is distal to said sub-strate.

25. The data storage medium of claim 12 wherein said reflective surface layer of said matrix layer is proximate to said substrate.

26. The data storage medium of claim 12 wherein said reflective surface layer includes interspersed regions of essentially clear colloid matrix material.

27. The data storage medium of claim 12 wherein said reflective surface layer includes interspersed black regions consisting of black filamentary silver particles.

28. The data storage medium of claim 12 wherein the thickness of the colloid matrix layer is lass than 15 microns.

29. A monobath developer for the formation of a highly reflective layer of electrically non-conducting, non-filamen-tary silver in a silver-halide emulsion having latent images of silver precipitating nuclei comprising, a weak silver-halide developing agent for partial chemical development of latent images of silver precipitating nuclei in a silver-halide emulsion and a rapid-acting, silver-halide complexing solvent for reacting with unexposed and undeveloped silver halide to form soluble silver ion complexes, which are transported by diffusion transfer to said silver precipi-tating nuclei where silver of said silver ion complexes is precipitated and adsorbed on said nuclei in the presence of said developer acting as a reducing agent, thereby forming an electrically non-conducting layer of aggregated and in-dividual silver particles exhibiting high reflectivity, where the activity of the complexing solvent is sufficiently low to permit partial chemical development of the surface latent image by the weak chemical developing agent before all of the undeveloped and unexposed silver halide is dis-solved and where the chemical developing agent is suffi-ciently weak to insure the chemical development primarily of non-filamentary silver nuclei.

30. The monobath developer of claim 29 wherein said complexing solvent consists of a water soluble thiocyanate or ammonium hydroxide having a concentration of between 10 to 45 grams per liter.

31. The monobath developer of claim 29 wherein said developing agent has a concentration of between 0.25 and 15 grams per liter.

32. The monobath developer of claim 29, 30 or 31 wherein said developing agent is selected from a group con-sisting of p-phenylenediamine and its N, N-dialkyl deriva-tives having a half-wave potential of between 170 mv and 240 mv at a pH of 11Ø

33. A monobath developer comprising a developing agent selected from a group consisting of 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 and a rapid-acting silver-halide solvent selected from the group consisting of soluble thiocyanates having non-reactive cations and ammonium hydroxide, said solvent for reacting with unexposed and un-developed silver halide to form soluble silver ion complexes, which are transported by diffusion transfer to said silver precipitating nuclei where silver of said silver ion com-plexes is precipitated and adsorbed on said nuclei in the presence of said developer acting as a reducing agent, thereby forming a layer of aggregated and individual silver particles exhibiting reflectivity, the developing agent being present in an amount between 2 and 15 grams and the concentration of said solvent is less than 45 grams per liter.

34. A negative silver diffusion transfer process for making a reflective electrically non-conducting data storage medium from a photosensitive silver-halide emulsion compris-ing, photographically defining data storage fields in a photosensitive silver-halide emulsion, masking a pattern of data images in said data storage fields, forming an areawise surface latent image layer of silver precipitating nuclei by means of actinic radiation exposure in the unexposed and un-developed recording fields of the photosensitive silver-halide emulsion layer, said silver precipitating nuclei having a gradient of decreasing volume concentration through the depth of the emulsion, said emulsion having unexposed photosensitive silver halide remaining therein in concentra-tions inversely related to said nuclei concentration, un-masking said pattern of data images in said data storage fields, and contacting said photosensitive silver-halide emulsion layer with a reagent comprising a weak silver-halide developing agent for chemical development of said surface latent image layer of silver precipitating nuclei and a rapid-acting silver-halide complexing solvent for reacting with unexposed and undeveloped silver halide to form soluble silver ion complexes which are transported by diffusion transfer to said silver-precipitating chemically developed nuclei of said latent image where silver of said silver ion complexes is precipitated and adsorbed on said chemically developed nuclei in the presence of said developer acting as a reducing agent, thereby forming a reflective electrically non-conducting layer of aggregated and individual silver particles in said areas for data storage, the activity of said solvent permitting chemical development of the surface latent image by the weak developing agent while simultaneously all of the undeveloped and unexposed silver halide is dis-solved by the complexing agent.

35. A negative silver diffusion transfer process for making a reflective electrically non-conducting data storage medium from a photosensitive silver-halide emulsion compris-ing, photographically defining data storage fields in a photosensitive silver-halide emulsion and further defining a pattern of indicia in these recording fields, photographi-cally exposing and chemically developing said pattern to form low reflectivity data images while leaving the remain-der of the silver-halide emulsion unexposed and undeveloped, forming an areawise surface latent image layer of silver precipitating nuclei in the unexposed and undeveloped record-ing fields of the photosensitive silver-halide emulsion layer, said latent image layer of silver precipitating nuclei having a gradient of decreasing volume concentration through the depth of the emulsion, said emulsion having unexposed photosensitive silver halide remaining therein in concentra-tions inversely related to said latent image concentration, contacting said unexposed photosensitive silver-halide emulsion layer with a reagent comprising a weak silver-halide developing agent for partial chemical development of said surface latent image layer of silver precipitating nuclei and a rapid-acting silver-halide complexing solvent for reacting with unexposed and undeveloped silver halide to form soluble silver ion complexes which are transported by diffusion transfer to said chemically developed silver-precipitating nuclei of said latent image where silver of said silver ion complexes is precipitated and adsorbed on said chemically developed nuclei in the presence of said developer acting as a reducing agent ! thereby forming a reflective electrically non-conducting layer of aggregated and individual silver particles in said areas for data storage, the activity of said solvent permitting chemical development of the surface latent image by the weak develop-ing agent while simultaneously all of the undeveloped and unexposed silver halide is dissolved by the complexing agent.

36. A method of making a reflective laser recording medium comprising, dispersing electrically conductive metal particles having a size primarily less than five hundredths of a micron in a surface layer of low melting temperature dielectric material so as to produce a reflective electri-cally non-conductive recording medium.

.37. The process of claim 36 wherein said low melting temperature dielectric comprises a gelatin.

38. The process of claim 36 or 37 wherein said electrically conductive metal particles are silver.