US3723124A

US3723124A - Dye imbibition images

Info

Publication number: US3723124A
Application number: US00123085A
Authority: US
Inventors: R Jones; W Thompson
Original assignee: Tate and Lyle Ingredients Americas LLC
Current assignee: Staley Continental Inc; Primary Products Ingredients Americas LLC
Priority date: 1969-02-05
Filing date: 1971-03-10
Publication date: 1973-03-27
Anticipated expiration: 1990-03-27

Abstract

THE PROCESS FOR FORMING MOLECURLARLY DISPERSED DYE IMBIBITION IMAGES OF IMPROVED TONAL QUALITIES AND HANDLING PROPERTIES WHICH COMPRISES (1) TREATING A SUBSTRATE BEARING A SOLID, ORGANIC LAYER HOLDING A MONOLAYER OF POWDER PARTICLES IN IMAGE-WISE CONFIGURATION, SAID POWDER PARTICLES COMPRISING A DYE, WITH VAPORS OF A MATERIAL WHICH IS A SOLVENT FOR SAID DYE AND CAPABLE OF SWELLING THE SURFACE OF SAID SUBSTRATE, MOLECULARLY SAID SOLID, ORGANIC LAYER SAID SUBSTRATE, AND (2) REMOVING SAID SOLID, ORGANIC LAYER WITH A METERIAL WHICH IS A SOLVENT FOR SAID SOLID, ORGANIC LAYER AND A POOR SOLVENT FOR THE SURFACE OF THE SUBSTRATE.

Description

" United States Patent US. Cl. 96-48 42 Claims ABSTRACT OF THE DISCLOSURE The process for forming molecularly dispersed dye imbibition images of improved tonal qualities and handling properties which comprises (1) treating a substrate bearing a solid, organic layer holding a monolayer of powder particles in image-wise configuration, said powder particles comprising a dye, with vapors of a material which is a solvent for said dye and capable of swelling the surface of said substrate, molecularly imbibing said dye into said substrate, and (2) removing said solid, organic layer with a material which is a solvent for said solid, organic layer and a poor solvent for the surface of the substrate.

This application is a continuation-in-part of copending applications Ser. Nos. 796,897, filed Feb. 5, 1969, now abandoned, 833,771, filed June 16, 1969, now Pat. No. 3,677,759 and 849,520, filed Aug. 12, 1969 now abandoned.

This invention relates to a method of improving the tonal qualities and handling properties of molecularly dispersed dye images. More particularly, this invention relates to a method of forming direct-reading, positive, molecularly dispersed dye deformation images of improved tonal qualities and handling properties wherein the deformation image is developed by mechanically embedding particles comprising a dye into a stratum at the surface of a powder-receptive, solid, light-sensitive organic layer supported on a substrate, molecularly imbibing dye into the substrate in image-wise configuration by treating the particles embedded in said organic layer with vapors of a material which is a solvent for said dye and capable of swelling said substrate, and treating the element with a solvent for the solid, light-sensitive organic layer.

In our copending application Ser. No. 796,897 now abandoned, we have disclosed a process of forming dyeimbibition deformation images wherein powder particles comprising adye, held in image-wise configuration in particulate form in or on a substrate, are treated with vapors of a material (preferably water) which is a solvent for said dye and capable of swelling the surface of said substrate molecularly imbibing said dye in said substrate. As pointed out in our copending application, the process of molecularly imbibing the particulate dye into the substrate converts the dye particles from a particulate form into a molecularly dispersed form providing an aesthetically more pleasing monochromatic saturated image. Other things being equal, the particulate dye image changes from a pale color to a brilliant, saturated, more pleasing hue. However, the residual light-sensitive, solid organic layer and/ or residual carrier for the dye remaining on the surface of the dye imbibition image tend to screen the dye imbibition image to some extent and accordingly, the dye imbibition image does not exhibit maximum brilliance and saturation. Further, these reproductions have certain minor aesthetic drawbacks. For example, the background areas of dye imbibition deformation images are easily fingerprinted, apparently due to the exudation of oil or moisture from peoples fingers, particularly on hot, humid days. In addition, the image areas of dye imbibition deformation images produced with some developing powders have a gritty, aesthetically undesirable texture, much like extremely fine sandpaper. Generally this occurs when the carrier component of the developing powder is incapable of swelling, fusing or dissolving in vapors of the material which is the solvent for the dye during the dye imbibition step.

The general object of this invention is to provide a method of improving the brilliance, saturation and handling properties of dye imbibition deformation images. Other objects will appear hereinafter.

In the description that follows, the phase powderreceptive, solid, light-sensitive organic layer is used to describe an organic layer which is capable of developing a predetermined contrast or reflection density (R upon exposure to actinic light and embedment of black-powder particles of a predetermined size in a single stratum at the surface of said organic layer. While explained in greater detail below, the R of a light-sensitive layer is a photometric measurement of the difference in degree of blackness of undeveloped areas and black-powder developed areas. The terms physically embedded or physical force are used to indicate that the powder particle is subjected to an external force other than, or in addition to, either electrostatic force or gravitational force resulting from dusting or sprinkling powder particles on a substate. The terms mechanically embedded or mechanical force are used to indicate that the powder particle is subjected to a manual or machine force, such as a lateral to-and-fro or circular rubbing or scrubbing action. The term embedded is used to indicate that the powder particle displaces at least a portion of the light-sensitive layer and is held in the depression so created, i.e. at least a portion of each particle is below the surface of the light-sensitive layer.

We have now found that it is possible to produce improved dye imbibition deformation images by treating the images after dye imbibition with a material which is a good solvent for the original solid, light-sensitive organic layer and a relatively poor solvent for the surface of the substrate. After treatment in this manner, the dye imbibition deformation image has enhanced brilliance and saturation. Electron microscope studies have shown that the preferred solid, light-sensitive, organic layers, such as the hydrogenated rosin esters and acids, which tend to puddle during the dye imbibition step, are removed by the solvent treatment. Further, fingerprinting in the background areas is eliminated. We have also found that the grittiness of the image areas of dye imbibition images produced with developing powders containing a carrier component, which is incapable of swelling or dissolving during the dye imbibition step, can be eliminated by treating the dye imbibition image with a solvent for the carrier. Typically the same solvent can be used to remove the originally light-sensitive organic layer and carrier. In order to facilitate a complete understanding of the present invention, there is also disclosed the various parameters necessary for obtaining dye imbibition deformation images in accordance with Ser. No. 796,897 now abandoned, which is hereby incorporated by reference.

In its preferred aspect, this invention makes use of the discoveries that (1) thin layers of many solid organic materials, some in substantially their naturally occurring or manufactured forms and others, including additives to,

control their powder receptivity and/or sensitivity to actinic radiation, can have surface properties that can be varied with a critical range by exposure to actinic radiation between a particle-receptive condition and a particlenon-receptive condition such that, by the methods of the present invention, continuous-tone images of high quality can be formed as well as line images and half-tones; (2) if said particles comprises a dye, the dye can be imbibed into the surface of the substrate for said thin layer by treating the thin layer with vapors of a material which is a solvent for the dye and a swelling agent for the surface of said substrate; and (3) the light-sensitive layer can be removed after the dye imbibition step with a material which is a solvent for the light-sensitive, organic filmformer and a poor solvent for the surface of the substrate. As explained below, the particle receptivity and particle non-receptivity of the solid thin layers are dependent on the size of the particles, the thickness of the solid thin layer and the development conditions, such as layer temperature.

Broadly speaking, the deformation imaging aspect of the present invention differs from known processes in various subtle and unobvious ways. For example, the particles that form an image are not merely dusted on, but instead are applied against the surface of the light-sensitive thin layer under moderate physical force. The relatively soft or particle-receptive nature of the light-sensitive layer is such that substantially a monolayer of particles, or isolated small agglomerates of a predetermined size, are at least partially embedded in a stratum at the surface of the light-sensitive layer by moderate physical force. The surface condition in the particle-receptive areas is at most only slightly soft but not fluid, as in prior processes. The relatively hard or particle-non-receptive condition of the light-sensitive surface in the non-image areas is such that when particles of a predetermined size are applied under the same moderate physical force, few, if any, are embedded sufliciently to resist removal by moderate dislodging action such as blowing air against the surface.

The ease with which continuous-tone deformation images are producedby the process of this invention is significant. In various preferred forms of this invention, the light-sensitive organic layer is sensitized to actinic radiation in such manner that a determinable quantity of actinic radiation changes the surface of the film from the particle-receptive condition to the non-receptive condition. The unexposed areas accept a maximum concentration of particles while fully exposed areas accept no particles. In others, the light-sensitive organic layer is sensitive to actinic radiation in the opposite way, such that a determinable quantity of such radiation changes the surface of the film from the particle-non-receptive condition to the receptive condition. In both types of layers, the sensitivity typically is such that smaller quantities of actinic radiation provide proportionately smaller changes in the surface of the layer to provide a continuous range of particle-receptive conditions between fully receptive and non-receptive conditions. Thus, the desired image may include intermediate light-values, as are typically produced by actinic radiation through a continuous-tone transparency. While the continuous nature of images produced by the method of this invention cannot be fully explained from a technical standpoint, microscopic studies have established that the range of R (reflection density) obtainable is attributable to the number of particles embedded per unit area. Since only a monolayer of particles is embedded, the light-sensitive layer can be viewed functionally as an ultra-fine screen yielding continuous-tone images. No such results have been reported in prior powder-imaging methods, even those using some of the same materials but in different modes from those of the present invention. This is probably due to the fact that prior powder-imaging processes rely on electrostatics or liquefaction of the unexposed areas, which lead to the formation of multilayers of powder particles, precluding the formation of continuous-tone images.

The quality of the deformation images obtained by the process of this invention is superior to that of prior powder-imaging processes. Line images free of background, having good density and high resolution (better than 40 line pairs per mm.) are readily obtained. As explained below, half-tone reproductions and continuoustone images are also provided readily. Images obtainable by the process of this invention compare favorably with silver halide photographs. Full color reproductions of excellent photographic quantity, both half-tone and continuous-tone, are provided simply by repeating basic processes and applying suitable powders of cyan, magenta and yellow hues in any sequence. Black may be added where desired for further detail. Each developed light-sensitive layer can form the substrate for the next light-sensitive layer and particles of a different color can be applied against the surface of each layer.

For use in this invention, the solid, light-sensitive, organic layer, which can be an organic material in its naturally occurring or manufactured form or a mixture of said organic material with plasticizers and/or photoactivators for adjusting the powder receptivity and sensitivity to actinic radiation, must be capable of developing a predetermined contrast or R using a suitable black developing powder under the conditions of development. The powder-receptive areas of the layer (unexposed areas of a positive-acting, light-sensitive material or the exposed areas of a negative-acting, light-sensitive material) must have a softness such that suitable particles can be embedded into a stratum at the surface of the light-sensitive layer by mild physical forces. However, the layer should be sufficiently hard and non-sticky that film transparencies can be pressed against the surface, as in a vacuum frame, without the surfaces sticking together or being damaged even when heated slightly under high intensity light radiation. The film should also have a degree of toughness so that it maintains its integrity during development. If the R of the light-sensitive layer is below about 0.2, the light-sensitive layer is too hard to accept a suitable concentration of powder particles. On the other hand, if the R is above about 2.2, the light-sensitive layer is so soft that it is diflicult to maintain film integrity during physical development and the layer tends to adhere to transparencies precluding the use of vacuum frame expose equipment. Further, if the R is above 2.2, the lightsensitive layer is so soft that more than one layer of powder particles may be deposited with attendant loss of continuous-tone quality and image fidelity and the layer may be displaced by mechanical forces resulting in distortion or destruction of the image. Accordingly, for use in this invention the light-sensitive layer must be capable of developing a R within the range of 0.2 to 2.2 or preferably 0.4 to 2.0 using a suitable black developing powder under the conditions of development.

The R of a positive-acting light-sensitive layer, which is called R is a photometric measurement of the refiection density of a black-powder-developed, lightsensitive layer after a positive-acting, light-sensitive layer has been exposed to suflicient actinic radiation to convert the exposed areas (or most exposed areas, when a continuoustone transparency is used) into a substantially powdernon-receptive state (clear the background). The R of a negative-acting, light-sensitive layer, which is called R is a photometric measurement of the reflection density of a black-powder-developed area, after a negative-acting, light-sensitive layer has been exposed to suflicient actinic radiation to convert the exposed area into a powder-receptive area.

In somewhat greater detail, the reflection density of a solid, positive-acting, light-sensitive layer (R is determined by coating the light-sensitive layer on a white substrate, exposing the light-sensitive layer to suflicient actinic radiation imagewise to clear the background of the solid positive-acting, light-sensitive layer, applying a black powder (prepared from 77% Pliolite VTL and 23% Neo Spectra carbon black in the manner described below) to the exposed layer, physically embedding said black powder under the conditions of development as a monolayer in a stratum at the surface of said light-sensitive layer and removing the non-embedded particles from said lightsensitive layer. The developed organic layer containing black image areas and substantially power-free non-image areas is placed in a standard photometer having a scale reading from to 100% reflection of incident light or an equivalent density scale, such as on Model 500 A photometer of the Photovolt Corporation. The instrument is zeroed (0 density; 100% reflectance) on a powder-free, non-image area of the light-sensitive organic layer and an average R reading is determined from the powder-developed area of line and half-tone images. With COIltlDlJ.

ous-tone images the R reading is determined on the black:

est powder-developed area. The reflection density is a measure of the degree of blackness of the developed. surface which is relatable to the concentration of particles per unit area. The reflection density of a solid, negativeating, light-sensitive layer (R is determined in the same manner except that the negative-acting, light-sensitive layer is exposed to suflicient actinic radiation to convert the exposed area into a powder-receptive area. If the R under the conditions of development is between 0.2 (63.1% reflectance) and 2.2 (0.63%) reflectance), or preferably between 0.4 (39.8% reflectance) and 2.0 (1.0% recflectance), the solid, light-sensitive, organic material deposited in a layer is suitable for use in this invention.

Although the R of all light-sensitive layers is determined-by using the aforesaid black developing powder and a white substrate, the R is only a measure of the suitability of a light-sensitive layer for use in this invention.

Since the R of any light-sensitive layer is dependent on numerous factors other than the chemical constitution of the light-sensitive layer, the light-sensitive layer is best defined in terms of its R under the development conditions of intended use. The positive-acting, solid, lightsensitive, organic layers useful in this invention must be powder-receptive in the sense that the aforesaid black developing powder can be embedded as a mono-particle layer into a stratum at the surface of the unexposed layer to yield a R of 0.2 to 2.2 (0.4 to 2.0 preferably) under the predetermined conditions of development. In other words, the positive-acting, light-sensitive layer must contain a certain inherent powder receptivity and light-sensitivity. The surface of positive-acting, light-sensitive layers containing no terminal conjugated ethylenic unsaturation is apparently hardened and converted into the powdernon-receptive state by a light-catalyzed hardening action, such as photocrosslinking, photooxidation, etc. However, the exposed positive-acting, light-sensitive layers containing no terminal conjugated ethylenic unsaturation can be removed with a solvent. If the light-sensitive layers c o n; tain organic materials having conjugated. terminal ethylenic unsaturation, the exposed areas may be crosslinked and be incapable of removal, particularly when a polyunsaturated compound containing two or more vinylidene groups is present.

The negative-acting, solid, light-sensitive, organic layers useful in this invention must be light-sensitive in the sense that, upon exposure to actinic radiation, them ost exposed areas of the light-sensitive layer are converted from a non-powder-receptive state under the predetermined conditions of development to a powder-receptive state under the predetermined conditions of development. In other words, the negative-acting, light-sensitive layer must have a certain minimum light-sensitivity and potential powder receptivity. The negative-acting, light-sensitive layers are apparently converted intothe powder-receptive state by a light-catalyzed softening action, such as photodepolymerization and are readily solvent-removable.

In general, the positive-acting, solid, light-sensitive layers useful in this invention comprise'a film-forming organic material in its naturally occurring or manufactured form or a mixture of said organic material with plasticizers and/ or photoactivators for adjusting powder receptivity and sensitivity to actinic radiation. Suitable positiveacting, film-forming organic materials include internally ethylenically unsaturated acids, such as abietic acid, rosin acids, partially hydrogenated rosin acids, such as those sold under the name Staybelite resin, etc.; esters of internally ethylenically unsaturated acids, methylol amides of maleated oils such as described in application Ser. No. 643,367 filed June 5, 1967; now Pat. No. 3,471,466, phosphatides of the class described in application Ser. No. 796,- 841 filed on Feb. 5, 1969, now Pat. No. 3,585,031, in the name of Hayes, such as soybean lecithin, partially hydrogenated lecithin, dilinolenyl-alpha-lecithin, etc., partially hydrogenated rosin acid esters, such as those sold under the name Staybelite esters, rosin modified alkyds, etc.; polymers of ethylenically unsaturated monomers, such as vinyltoluene-alpha methyl styrene copolymers, polyvinyl cinnamate, polyethyl methacrylate, vinyl acetate-vinyl stearate copolymers, polyvinyl pyrrolidone, etc.; coal tar resins, such as coumarone-indene resins, etc.; halogenated hydrocarbons, such as chlorinated waxes, chlorinated polyethylene, etc.

Although numerous positive-acting, film-forming organic materials have the requisite light-sensitivity and powder receptivity at predetermined development temperatures, it is generally preferable to compound the filmforming organic material with photoactivator(s) and/or plasticizer(s) to impart optimum powder receptivity and lightsensitivity to the lightsensitive layer. In most cases, the lightsensitivity of an element can be increased many fold by incorporation of a suitable photoactivator capable of producing free radicals which catalyze the lightsensitive reaction and reduce the amount of photons necessary to yield the desired physical change. For example, the nearultarviolet light sensitivity of soybean lecithin layers can be increased by a factor of 2,000 by the addition of a small concentration of ferric chloride. Whereas it may take eight minutes to clear the background of a lightsensitive lecithin element devoid of photoactivators using near-ultraviolet radiation, lecthin elements containing from about 1-.15% by weight ferric chloride base on the weight of the lecithin are so light-sensitive that they must be handled under yellow safety lights much like silver halide emulsions. The ferric chloride-photoactivated lecithin is about 10 times slower than silver halide printing papers but faster than commercial diazo material. Ferric chloride also advantageously increases the toughness and integrity of phosphatide layers.

Other suitable photoactivators capable of producing free-radicals include benzil, benzoin, Michlers ketone, diacetyl, phenanthraquinone, p-dimethylaminobenzoin, 7,8- benzoflavone, trinitrofiuorenone, desoxybenzoin, 2,3-pentanedione, dibenzylketone, nitroisatin, di(6-dimethylamino-3-pyridyl)methane, metal naphthenates, N-methyl- N-phenylbenzylamine, pyridil, 5-7 dichloroisatin, azodiisobutyronitrile, trinitroanisole, chlorophyll, isatin, bromoisatin, etc. These compounds can be used in a concentration of .001 to 2 times the weight of the film-forming organic material (.1%-200% the weight of film-former). As in most catalytic systems, the best photoactivator and optimum concentration thereof is dependent upon the filmforming organic material. Some photoactivators respond better with one type of film-former and may be useful over rather narrow concentration ranges whereas others are useful with substantially all-film-formers in wide concentration ranges.

The acyloin and vicinal di'ketone photoactivators, particularly benzil and benzoin are preferred. Benzoin and benzil are effective over wide concentration ranges with substantially all film-forming, light-sensitive, organic materials. Although slightly inferior to ferric chloride as photoactivators for lecithin, they are capable of increasing the light-sensitivity of the ethanol-insoluble fraction of lecithin to nearly the level of ferric chloride-sensitized lecithin. Benzoin and benzil have the additional advantage that they have a plasticizing or softening effect on film-forming, light-sensitive layers, thereby increasing the powder receptivity of the light-sensitive layers. When employed as a photoctivator, benzil should preferably comprise at least 1% by weight of the film-forming organic material (0.1 times the film-former weight).

Dyes, optical brightners and light absorbers can be used alone or preferably in conjunction with the aforesaid free-radical producing photoactivators (primary photoactivators) to increase the light-sensitivity of the lightsensitive layers of this invention by converting the light rays into light rays of longer lengths. For convenience, these secondary photoactivators (dyes, optical brighteners and light absorbers) are called superphotoactivators. Suitable dyes, optical brighteners and light absorbers include 4-methyl7-dimethylaminocoumarin, Calcoftuor yellow HEB (preparation described in -U.S. Pat. 2,415,373), Calcofluor white SB super 30080, Calcofluor, Uvitex W conc., Uvitex TXS conc., Uvitex RS (described in Textil- Rundschau 8 [1953], 339), Uvitex WGS conc., Uvitex K, Uvitex CF conc., Uvitex W (described in Textil-Rundschau 8, [1953], 340), Aclarat 8678, Blancophor OS, Tenopol UNPL, MDAC 8-8844, Uvinul 400, thioflavin TG N conc., analine yellowfi'S (low conc.), Setofiavine T 5506-140, Auramine O, Calcozine yellow OX, Calcofiuor RW, Calcofiuor GAC, Acetosol yellow 2 RLSPHF, eosine bluish, Chinoline yellowP conc., Ceniline yellow S (high conc.), anthracene blue violet fluorescence, Calcofiuor white MR, Tenopol PCR, Uvitex GS, acid-yellow- T-supra, Acetosol yellow 5 GLS, Calcoid Or Y. Ex. conc., diphenyl brilliant fiavine 7 OFF, Resoform fiuorescent yel. 3 GPI, eosine yellowish, thiazole fiuorescor G, Pyrazolone orange YB-3 and National FD&C yellow. Individual superphotoactivators may respond better with one type of light-sensitive organic film former and photoactivator than with others. Further, some photoactivators function better with certain classes of brighteners, dyes and light absorbers. For the most part, the most advantageous combinations of these materials and proportions can be determined by simple experimentation.

\As indicated above, plasticizers can be used to impart optimum powder receptivity to the light-sensitive layer. With the exception of lecithin, most of the film-forming, light-sensitive, organic materials useful in this invention are not powder-receptive at room temperature but are powder-receptive above room temperature. Accordingly, it is desirable to add sufiicient plasticizer to impart room temperature to 30 C.) or ambient temperature powder receptivity to the light-sensitive layers and/ or broaden the R range of the light-sensitive layers. Plasticizers are particularly useful in continuous-tone reproduction systems, where the light-sensitive layer must have a R of at least 0.5 and preferably 0.72.0. If the R is less than 0.5, the developed image lacks the tonal contrast necessary for aesthetically pleasing continuous-tone reproductions.

While various softening agents, such as dimethyl siloxanes, dimethyl phthalate, glycerol, vegetable oils, etc. can be used as plasticizers, benzil and benzoin are preferred since, as pointed out above, these materials have the additional advantage that they increase the light-sensitivity of the film-forming organic materials. As plasticizer-photoactivators, benzoin and benzil are preferably used in a concentration of 1% to 80% by weight of the film-forming solid organic material.

The preferred positive-acting, light-sensitive film-formers containing no conjugated terminal ethylenic unsaturation include the esters and acids of internally ethylenically unsaturated acids, particularly the phosphatides, rosin acids, partially hydrogenated rosin acids and the partially hydrogenated rosin esters. These materials, when compounded with suitable photoactivators, preferably acyloins or vicinal diketones together with superphotoactivators, or ferric chloride in the case of lecithin, require less than 2 minutes exposure to clear the background of light sensitive layers and yield excellent continuous-tone reproductions having a R of at least 0.5 as well as line image and half-tone reproductions.

In general, the negative-acting, light-sensitive layers useful in this invention comprise a film-forming organic material in its naturally occurring or manufactured form, or a mixture of said organic material with plasticizers and/or photoactivators for adjusting powder receptivity and sensitivity to actinic radiation. Suitable negative-acting, film-forming organic materials include n-benzyl linoleamide, dilinoleyl-alpha-lecithin, castor wax (glycerol 12- hydroxy-stearate), ethylene glycol monohydroxystearate, polyisobutylene, polyvinyl stearate, etc. Of these, castor wax and other hydrogenated ricinoleic acid esters (hydroxystearates) are preferred. These materials can be compounded with plasticizers and/or photoactivators in the same manner as the positive-acting, light-sensitive, film-forming organic materials.

Surprisingly, some solid, light-sensitive organic film formers can be used to prepare either positive-or negativeacting light-sensitive layers. For example, a poly(n-butyl methacrylate) layer containing 20 percent benzoin (20 parts by weight benzoin per parts by weight polymer) yields good positive-acting images. Increasing the benzoin level to 100 percent converts the poly(n-butyl methacrylate) layer into a good negative-acting system.

The light-sensitive elements useful in this invention are formed by applying a thin layer of solid, light-sensitive film-forming organic material having a potential R, of 0.2 to 2.2. (i.e. capable of developing a D or R of 0.2 to 2.2) to a suitable substrate by any suitable means dictated by the nature of the material (hot-melt draw down, spray, roller coating or air knife, flow or dip coating from solvent solution, curtain coating, etc.) so as to produce a reasonably smooth, homogeneous layer of from about 0.1 to 40 microns thick. The light-sensitive layer must be at least 0.1 micron thick and preferably at least 0.4 micron in order to hold suitable powders during development. If the light-sensitive layer is less than 0.1 micron, or the developing powder diameter is more than 25 times layer thickness, the light-sensitive layer does not hold powder with the tenacity necessary to form a permanent record. In general, as layer thickness increases, the light-sensitive layer is capable of holding larger particles. However, as the light-sensitive layer thickness increases, it becomes increasingly ditficult to maintain film integrity during development. Accordingly, the light-sensitive layer must be from 0.1 to 40 microns, preferably from 0.4 to 10 microns, with 0.5 to 2.5 microns being best.

The preferred method of applying light-sensitive layers of predetermined thickness to a substrate comprises flow coating a solution in organic solvent vehicle (hydrocarbon, such as hexane, heptane, benzene, etc.; halogenated hydrocarbon, such as chloroform, carbon tetrachloride, 1,1,1-trichloroethane, trichloroethylene, etc.; alcohols, such as ethanol, methanol, propanol, etc.; ketones, such as acetone, methyl ethyl ketone, etc.) of the light-sensitive, organic film-former alone or together with dissolved or suspended photoactivators and/ or plasticizers onto a substrate. The hydrocarbons and halohydrocarbons, which are excellent solvents for the preferred positive-acting, lightsensitive film-formers containing no terminal conjugated ethylenic unsaturation, are the preferred vehicles because of their high volatility and low cost. Typically solutions prepared with these vehicles can be applied to a substrate and air dried to a continuous clear film in less than one minute. In general, the halohydrocarbons have the advantages that they are non-flammable and can be used without danger of flash fires. However, many of these, such as chlorofrom and carbon tetrachloride, must be handled with care due to the toxicity of their vapors. Of all these solvents, 1,1,1-trichloroethane is preferred since it has low toxicity, is non-flammable and low-cost and has high volatility. In general, the thickness of the light-sensitive layer can be varied as a function of the concentration of the solids dissolved in the solvent vehicle.

' The substrates for the light-sensitive elements should be smooth and uniform in order to facilitate obtaining a smooth coating. The supportscan be opaque or transparent. Suitable substrates include metals, such as steel and aluminum plates, sheets and foils, glass, paper, cellulose esters, such as cellulose acetate, cellulose propionate, cellulose butyrate, etc., polyethylene terephthalate, nylon, polystyrene, polyethylene, corona discharge-treated polyethylene, polypropylene, Tedlar PVF (polyvinyl fluoride), polyvinyl alcohol, amylose, etc. The supports or bases can be subbed with various hydrophobic polymers such as cellulose acetate, cellulose propionate, cellulose butyrate, polyethylene terephthalate, polystyrene, polyethylene, polypropylene, polyvinyl fluoride, etc., or hydrophilic layers such as polyvinyl alcohol, hardened gelatin, amylose, polyacrylic acid, etc., in order to provide the support or substrates with a surface having the desired hydrophilic or hydrophobic properties. In generalit is prefererd to apply a subbing layer to paper substrates to slow down the penetration of organic solvent solutions, and, other things being equal, a subbing layer facilitates the formation of thicker light-sensitive layers. It is, of course, understood that the selection of substrate or subbing layer for the substrate is dependent on the solubility characteristics of the particulate dye employed in the developer, i.e. the surface of the substrate should be swellable in vapors of the material which is a solvent for the dye. For example, water-soluble dyes should be employed with substrates having a hydrophilic surface such as polyvinyl alcohol, amylose, paper subbed with a hydrophilic layer such as hardened gelatin, polyvinyl alcohol, etc. If a hydrocarbonor halohydrocarbon-soluble dye is employed, the surface of the substrate should be capable of swelling in vapors of a hydrocarbon or halohydrocarbon. Generally the hydrocarbon or halohydrocarbon soluble dyes are employed with substrates having an oleophilic surface. However, polyvinyl pyrrolidone can be used advantageously as a subbing layer to receive water-soluble dyes or halohydrocarbon-soluble-dyes.

Alatent image is formed in the light-sensitive elements of this invention by exposing theelement to actinic radiation in image-receiving manner for a time sufiicient to provide a potential R of 0.2 to 2.2. (clear the background of the positive-acting, light-sensitive layers or establish a potential R of 0.2 to 2.2 with negative-acting, light-sensitive layers). The light-sensitive elements can be exposed to actinic light through a photographic positive or nega tive, Which may be line, half-tone or continuous-tone, etc.

As indicated, the latent images are produced from positive-acting, light-sensitive layers by exposing the element in image-receiving manner for a time sufficient to clear the background, i.e. render the exposed areas nonpowder-receptive. As explained below, the amount of actinic radiation necessary to clear the background varies to some extent with developer powder size and development conditions. Due to these variations, it is often desirable to slightly overexpose line and half-tone images in order to assure complete clearing of the background. Slightly more care is necessary in continuous-tone work since overexposure tends to decrease the tonal range of the developed image. In general overexposure is preferred with negative-acting, light-sensitive elements in order to provide maximum contrast.

After the light-sensitive element is exposed to actinic radiation for a time sufficient to clear the background of a positive-acting, light-sensitive layer or establish a potential R of 0.2 to 2.2., a suitable developing powder having a diameter'or dimension along one axis of at least 0.3 micron is applied physically with a'suitable force, preferably mechanically, to embed the'powder in the lightsensitive layer.

The developing powders suitable for use in the present invention comprise a suitable dye or dyes. Preferably the dye or dyes are on a solid carrier in order to control the particle size of the developing powder and to control the intensity of the final dye image. As explained above, the dye must be selected so that it is soluble in the material whose vapors act as a swelling agent for the surface of the substrate. The dye can be ball-milled with carrier in order to coat the carrier with dye or, if desired, dye can be blended above the melting point of fusible or resinous carriers, and the blend ground to a suitable size and classified. In some cases, it is advantageous to dissolve dye and carrier in a mutual solvent, dry and grind to suitable size. Usually the developing powder contains from about 0.1 to 50 percent by weight dye and correspondingly 99.9 to 50 percent by weight carrier.

The black developing powder for determining the R of a light-sensitive layer is formed by heating about 77% Pliolite VTL (vinyltoluene-butadiene copolymer) and 23% Neo Spectra carbon black at a temperature above the melting point of the resinous carrier, blending on a rubber mill for fifteen minutes and then grinding in a Mikro-atomizer. Commercially available powders such as XEROX 9'14 Toner give substantially similar results although tending toward slightly lower R values.

Suitable carriers for the dyes include hydrophilic polymeric carriers, such as polyvinyl alcohol, granular starches (preferably corn or rice), animal glue, gelatin, gum arabic, gum tragacanth, carboxypolymethylene, polyvinyl pyrrolidone, Carbowaves, etc.; hydrophilic monomeric materials, such as sorbitol, mannitol, dextrose, tartaric acid, urea, etc., hydrophobic carriers, such as polystyrene, Pliolite VTL (butadiene-styrene copolymer), polymethyl methylacrylate, etc.

Suitable water-soluble dyes include Alphazurine 2G, Calcocid Phloxine 2G, tartrazine, acid chrome blue 3BA conc., acid magenta 0., Ex. Conc., acid violet l0BN, Calcocid Rubine XX Conc., Carmoisine BA Ex. Conc., neptune blue BRA Conc., Nigrosine Jet Conc., patent blue AF Ex. Conc., Pontacyl light red 4BL Conc. percent, etc. Suitable oil-soluble dyes include oil blue AV, oil red N-l700, etc.

In somewhat greater detail the water-soluble dyes can be employed with hydrophilic polymeric carriers, hydrophilic monomeric carriers, hydrophobic polymeric carriers, etc. The hydrophobic carriers, particularly those soluble in hydrocarbon and halohydrocarbon, have the advantage (using water-soluble dyes) that they can be removed at a later stage in the processing with a suitable solvent, when employed in conjunction with the preferred halohydrocarbon-solulnle or hydrocarbon-soluble lightsensitive materials, as explained below. Further, dye imbibition images produced with hydrophobic carriers tend to be glossy. On the other hand, the polymeric hydrophilic carriers tend to partially dissolve and imbibe into the surface of the hydrophilic substrate during the dye imbibition step, leading to a somewhat matte finish. Accordingly, the particular carrier employed can be varied to obtain either a glossy or matte finish. Likewise, oil-soluble dyes can be used with hydrophilic polymeric carriers, etc. and imbibed into the surface of substrates having a suitable surface, which is oil-swellable, hydrocarbon-swellable, halohydrocarbon-swellable, etc.

The developing powders useful in this invention con tain particles having a diameter or dimension along at le t one axis from 0.3 to 40 microns, preferably from 0.5 to 10 microns with powders of the order of l to 7 microns being best for light-sensitive layers of 0.4 to 10 microns. Maximum particle size is dependent on the thickness of light-sensitive layer while minimum particle size is independent of layer thickness. Electron microscope studies have shown that developing powders having a diameter 25 times the thickness of the light-sensitive layer cannot be permanently embedded into lightsensitive layers and, generally speaking, best results are obtained where the diameter of the powder particle is less than about 10 times the thickness of the light-sensitive layer. For the most part, particles over 40 microns are not detrimental to image development provided the developing powder contains a reasonable concentration of powder particles under 40 microns, and less than 25 times, preferably less than 10 times, the light-sensitive layer thickness. However, other things being equal, the larger the development-powder particles (above 10 microns), the lower the R of the developed image. For example, when XEROX 9 14 Toner, classified to contain (a) all particles under 1 micron, (b) 1 to 3 micron particles, (c) 3 to 10 micron particles, ((1) 10 to 18 microns and (e) all particles over 18 microns, was used to develop positive-acting, l-micron thick lecithin light-sensitive elements after the same exposure, the images had a R of (a) 0.83, (b) 0.95, (c) 0.97, (d) 0.32, and (e) 0.24 respectively.

Although particles over 40 microns are not detrimental to image development, the presence of particles under 0.3 micron diameter along all axes can be detrimental to proper image formation. In general, it is preferable to employ developing powders having substantially all powders having a diameter along at least one axis not less than 0.3 micron, preferably more than 0.5 micron, since particles less than 0.3 micron tend to embed in non-image areas. For examplt, mechanical development with commercial carbon blacks: .008 micron Neo Spectra Mark I, .020 micron Peerless, 0.25 micron Raven Bead, 0.041 micron Statex B, .055 micron Statex R and 0.073 micron Molacco all resulted in substantially equal powder embedment in image and non-image areas with a positiveacting, light-sensitive lecithin element. Substantially less background or non-image area powder embedment occurred using 03 0.4 micron iron oxide IRN-351, 0.4 micron iron oxide BK-247 and BK250, 0.55X0.08 micron iron oxide IRN 100 and 0.50X0.08 micron IRN 110 with the same positive-acting, light-sensitive lecithin element.

As the particle size of the smallest powder in the developer increases, less exposure to actinic radiation is required to clear the background. -For example, when XEROX 914 Toner, classified to contain (a) all particles under 1 micron, (b) 1 to 3 micron particles, (c) 3 to 10 micron particles, '(d) 10 to 18 micron particles and (e) over 18 micron particles, was used to develop the light-exposed portions of positive-acting 1 micron thick lecithin light-sensitive elements, the exposed portions had a R of (a) 0.26, (b) 0.23, (c) 0.10, (d) and (e) 0 after equal exposures. By suitably increasing the exposure time, the R of the non-image areas was reduced to substantially zero with particles (a), (b) and (c).

In general, somewhat more deposition of powder particles into non-image areas can be tolerated when using a black developing powder than a colored powder, since the human eye is less offended by gray background or non-image areas than by the deposition of colored particles in non-image areas. Therefore, the concentration of particles under 0.3 micron and the size of the developing powder is more critical when using a colored powder such as cyan, magenta or yellow. For best results, the developing powder should have substantially all particles (at least 95% by weight) over 1 micron in diameter along one axis and preferably from 1 to 7 microns for use with light-sensitive layers of from 0.4 to 10 microns. In this way, powder embedment in image areas is maximum and relatively little powder is embedded into nonimage areas. Accordingly, rice starch granules, which are 5 to 6 microns, are particularly useful as carriers for dyes of different hues.

In somewhat greater detail, the developing powder is applied directly to the light-sensitive layer, while the powder-receptive areas of said layer are in at most only a slightly soft deformable condition and said layer is at a temperature below the melting point of the layer and powder. The powder is distributed over the area to be developed and physically embedded into the stratum at the surface of the light-sensitive layer, preferably mechanically by force having a lateral component, such as to-and-fro and/or circular rubbing or scrubbing action using a soft pad, fine brush or even an inflated ballon. If desired, the powder may be applied separately or contained in the pad or brush. The quantity of powder is not critical provided there is an excess available beyond that required for full development of the area, as the development seems to depend primarily on particle-to-particle interaction rather than brush-to-surface or pad-to-surface forces to embed a layer of powder particles substantially one particle thick (monoparticle layer) into a stratum at the surface of the light-sensitive layer. When viewed under an inverse microscope, spherical powder particles under about 10 microns in diameter enter the powderreceptive areas first and stop dead, embedded substantially as a monolayer. The larger particles seem to travel over the embedded smaller particles which do not rotate or move as a pad or brush is moved back and forth over the developed area. Non-spherical particles, such as platelets, develop like the spherical powders except that the flat side tends to embed. Only a single stratum of powder particles penetrates into the powder-receptive areas of the light-sensitive layer even if the light-sensitive layer is several times thicker than the developer particle diameter.

The minimum amount of powder of the preferred type required to develop an area to its maximum density is about 0.01 gram per square inch of light-sensitive surface. Ten to 20 or more times this minimum range can be used with substantially the same results, a useful range being about 0.02 to 0.2 gram per square inch.

The pad or brush used for development is critical only to the extent that it should not be so stiff as to scratch or scar the film surface when used with moderate pressure with the preferred amount of powder to develop the film. Ordinary absorbent cotton loosely compressed into pad about the size of a baseball, weighing about 3 to 6 grams, is especially suitable. The developing motion and force applied to the pad during development is not critical. A force as low as a few grams applied to the pad when using the preferred amount of powder will develop an area of the film to essentially maximum density, although a suitable material could withstand a developing force of 300 grams with substantially the same density resulting in both instances. A force of 10 to grams is preferred to assure uniformity of results. A slightly longer developing time (30 seconds) may be required at the lower loading while only a few seconds would be required at a higher loading. The speed of the swabbing action also is not critical other than that it affects the time required, rapid movement requiring less time than slow. The preferred mechanical action involved is essentially the lateral action applied in ultrafine finishing of a wood surface by hand sanding or steel wooling.

Hand swabbing is entirely satisfactory, and when performed under the conditions described above, will reproducibly produce the maximum density which the material is capable of achieving. That is, the maximum concentration of particles per unit area will be deposited under the prescribed conditions, dependent upon the physical properties of the material such as softness, resiliency, plasticity, and cohesiveness. Substantially the same results can be achieved using a mechanical device for the power application. A rotating, or rotating and oscillating, cylindrical brush or pad may be used to provide the described brushing action and will produce a substantially similar end result.

After the powder application, excess powder remains on the surface which has not been sufiiciently embedded into, or attached to, the film. This may be removed in any convenient way, as by wiping with a clean pad or brush usually using somewhat more force than employed in mechanical development, by vacuum, by vibrating, or by air doctoring. For simplicity and uniformity of results, the excess powder usually is blown olf using an air gun having an air-line pressure of about 20 to 40 p.s.i. The gun is preferably held at an angle of about 30 to 60 degrees to the surface at a distance of 1 to 12 inches (3 to 8 preferred). The pressure at which the air impinges on the surface is about 0.1 to 3, and preferably about 0.25 to 2, pounds per square inch. Air-cleaning may be applied for several seconds or more until no additional loosely held particles are removed. The remaining powder should be sufiiciently adherent to resist removal by moderately forceful wiping or other reasonable abrasive action.

Under some circumstances, it is possible to develop an image without applying mechanical force, such as by using air pressure or cascade-development techniques, which use large carrier beads as a driving force. However, the image is usually imperfect in the sense that it has lower contrast and the image areas lack uniformity or proper tonal values, when compared to images developed using the prescribed mechanical force. For example, when a light-sensitive Staybelite resin element, capable of yielding a R of 1.9 with the aforementioned preferred black toner (77% Pliolite VTL-23% Neo Spectra carbon black) at room temperature using mechanical force, was dusted at room temperature with the preferred black toner and subjected to air pressure (a non-mechanical, physical force), such as that normally used to remove excess powder particles from non-image areas, a non-uniform image was obtained having a maximum R of 0.67. The nonuniform image was similar to images developed with insufficient developer using mechanical force. When the non-uniform air-developed element was gently swabbed with a clean cotton pad, image uniformity improved somewhat. When the same light-sensitive Staybelite resin element, capable of yielding a R of 0.99 with XEROX 914 Toner at room temperature using mechanical force, was developed by cascade development at room temperature using XEROX 9'14 Toner with large carrier beads as a driving force, air cleaned and wiped with a cotton pad, an image having a R of 0.66 was obtained. Although this image lacked the excellent resolution and uniformity of images developed using mechanical force, it had substantially better image qualities than images developed using air pressure alone or air pressure followed by gentle wiping. While air pressure or cascade development have been used with some success with light-sensitive Staybelite resin elements, not all light-sensitive elements of this invention can be developed in this manner. Attempts to develop light-sensitive lecithin elements using air pressure or cascade development at room temperature have generally resulted in images having a R of less than 0.2.

. The reflection density, and the R in particular, of a light-sensitive layer is also dependent upon the temperature of the light-sensitive layer during physical embedment. In general, the higher the temperature of the lightsensitive layer, the higher the R of the developed image. For example, Staybelite Ester No. 10 alone, which is incapable of forming an image having a R of at least 0.2 from -130 'F., can be developed to a R of about 0.2 at 135 F. and about 0.6 at 165 F. Similarly, soybean lecithin, in its naturally occurring form, which readily develops a R of about 0.7 to 0.9 with a suitable developer at room temperature, yields a R of less than 0.2 at 0 F.

To some extent reproducibility of results and length of exposure are also dependent upon the relative humidity of the development chamber or area. For development at higher relative humidity, sensitized-lecithin elements must be exposed to more actinic radiation to clear the background. For example, other things being equal, an exposed lecithin element, which is non-powder-receptive at 38% RH. (relative humidity) has a background R of 0.16 at 14 48% RH, 0.38 at 56% RM. and 0.61 at 65% RH. On the other hand, rosin derivatives, such as Staybelite Ester No. 10, are much less sensitive to relative humidity.

As explained above, powder particles comprising a dye, held in image-wise configuration in particulate form in or on a substrate, are contacted with vapors of a material which is a solvent for said dye and capable of swelling the surface of the substrate, thereby molecularly imbiding said dye into said substrate. The process of molecularly imbiding the particulate dye into the substrate converts the dye particles in particulate form into a molecularly dispersed form providing an aesthetically more pleasing, saturated image. Other things being equal, the particulate dye image changes from a pale color to a brilliant, saturated, more pleasing hue. In a typical situation, substrates bearing a hydrophilic subbing layer, such as hardened gelatin, polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylic acid, amylose, are employed as dye imbibition receiving layers for water-soluble dyes. A suitable solid, positive-acting or negative-acting, light-sensitive layer is applied to the hydrophilic subbing layer, exposed to actinic radiation in image-receiving manner to form a latent image and developed with developer particles of at least 0.3 micron along at least one axis containing a water- 'soluble dye. At this point, the dye component of the powder particles is separated from the hydrophilic subbing layer or receiving layer by the light-sensitive layer which may be considered as an additional subbing layer. An aesthetically more pleasing image is then produced by treating the developed image with vapors of a material which is a solvent for the dye and capable of swelling the substrate, thereby transferring the previously particulately dispersed dye to the subbing layer in molecularly dispersed form. For example, if the dye is water-soluble, it can be transferred to the subbing layer by Water vapor, aqueous alcohol, etc. Essentially the same results can be obtained using a hydrophobic subbing layer, such as polystyrene or polyvinylidene chloride, a hydrophobic dye and suitable solvent vapors.

The particular solvent employed in the dye imbibition step is also dependent on the physical properties of the exposed light-sensitive layer. Although the transportation of the dye through the solid, organic layer is not completely understood, it is believed that in most cases dye imbibition is due to the weakening of the light-sensitive layer by the powder particles employed during deformation imaging creating potential points of stress in the film surface. Subsequently, when solvent vapors capable of swelling the surface of the substrate (dye imbibition receiving layer) upon which the stressed film is disposed, swell the surface of the substrate, a second stress is placed upon the light-sensitive layer due to the swelling of the receiving layer with the result that the light-sensitive layer fractures and the dye is transported through the lightsensitive layer and imbibed into the surface of the substrate. In other cases dye imbibition may be due to the solvent vapors diffusing the dissolved dye into the lightsensitive layer. In any event, the solvent must be capable of transporting the dye through the original light-sensitive layer.

Experiments have shown that the development of various light-sensitive elements, such as Staybelite Ester #10 and Staybelite resin, with developing powder weakens the film layer. For example, when these light-sensitive elements are developed with undyed developing powder, it is possible to imbibe water-soluble dye into the receiving layer in image-wise configuration by merely dipping the developed light-sensitive element into an aqueous dye bath. In such case the water-soluble dye enters the hydrophilic receiving layer in the areas defined by the undyed powder particles. Accordingly, in such case, it is clear that transportation of the dye through the light-sensitive layer is at least partially due to weakening of the lightsensitive layer by developer particle.

It has also been found that the above light-sensitive materials have a tendency to puddle up in the exposed areas in image-wise configuration when merely exposed to light and treated with water vapors. Accordingly, dye imbibition of water-soluble dyes through these materials is also partially due to the ability of moist warm air to disrupt the unexposed areas of the light-sensitive layer. In other cases, such as in the case of phosphatide lightsensitive elements, the exposed areas of the light-sensitive layer are converted into a more water-soluble condition than the unexposed areas as explained in copending application, Ser. No. 796,841 of "Hayes, filed Feb. 5, 1969, now US. Pat. 3,585,031. In such case, water vapor tends to transport the dye image through the exposed areas of the light-sensitive element with the result that the original positive powder image changes into a negative dye imbibition image. In still other cases, it has been possible to prevent passage of water-soluble dye into the dye imbibition receiving layer by adding various hydrophobic agents, such as silicone oils, in a concentration of 200 parts per million to various light-sensitive layers, such as those based on Staybelite resins and esters. The silicone tends to act as a waterproofing agent in this environment and no dye imbibition with water vapor is possible since water vapor is incapable of transporting the dye through the light-sensitive layer. Dye imbibition of water-soluble dye through light-sensitive layers based on poly(n-butyl methacrylate) and other high molecular weight hydrophobic polymers, is relatively difficult due to the extreme hydrophobic nature of these film-formers. Accordingly, routine experimentation may be carried out to determine which solvents are best for transporting specific dyes through particular light-sensitive elements.

After the dye imbibition step, the light-sensitive, solid organic layer, which preferably contains no conjugated terminal ethylenic unsaturation, is removed by flushing or rinsing the element with a material which is a good solvent for the light-sensitive film-former or layer and a poor solvent for the surface of the substrate. This treatment removes the light-sensitive organic layer and most of the carrier for the original developer particle, embedded in the light-sensitive layer, resulting in a more brilliant pure color by eliminating the extraneous lightsensitive layer and carrier particles. Further, the developed image has improved handling properties in the sense that the background areas have a reduced tendency to pick up fingerprints under humid conditions. In addition, by suitable choice of solid carrier particle and solvent, the grittiness of certain image areas can be eliminated.

In the preferred methods of employing this invention, one of the prefered hydrocarbon-soluble or halohydrocarbon-soluble, light-sensitive, film-formers is deposited on a hydrophilic subbing layer from a hydrocarbon or halohydrocarbon solvent or vehicle. The light-sensitive element is exposed to actinic radiation in image-receiving manner to form a latent image and developed with developer particles of at least 0.3 micron along at least one axis containing a water-soluble dye. An aesthetically more pleasing image is then produced by treating the developed image with vapors of a material which is a solvent for the dye (preferably water vapor) and capable of swelling the substrate, thereby molecularly imbibing the dye into the hydrophilic subbing layer. The dye imbibition image is then flushed and rubbed, if desired, with a hydrocarbon or halohydrocarbon solvent, typically the one employed as the vehicle for applying the lightsensitive organic layer, thereby removing the lightsensitive organic layer in both the exposed and unexposed areas. In this way, the handling properties and tonal qualities of the molecularly dispersed dye image are markedly improved. If the developer powder solid carrier is soluble in the hydrocarbon or halohydrocarbon solvent, it is also removed when the light-sensitive organic layer is removed in the solvent flush. For example, Pliolite VTL, polystyrene, and polyvinyl pyrrolidone can be removed in this manner. If the carrier is very watersoluble, it tends to imbibe into the substrate during the dye imbibition step. Typical carriers of this type include urea, tartaric acid, polyvinyl alcohol, etc. On the other hand, less water-soluble hydrophilic carriers, such as granular starches, tend to be removed during the solvent flush since they are no longer held on the surface of the substrate by the original light-sensitive organic layer.

Suitable organic solvents for removing the original light-sensitive organic layer include hydrocarbons, such as hexane, heptane, benzene, etc.; halogenated hydrocarbons such as chloroform, carbon tetrachloride, 1,1,1- trichloroethane, trichloroethylene, etc.; alcohols, such as ethanol, methanol, propanol, etc.; ketones such as acetone, methyl ethyl ketone, etc.

Removal of the original light-sensitive organic material has the additional advantage that the element can be recoated with a smooth second light-sensitive organic layer more readily for use in multi-color work, since the developed image no longer contains the residual lightsensitive organic layer and carrier particles.

The following examples are merely illustrative and should not be construed as limiting the scope of our invention.

EXAMPLE I One and one-quarter grams Staybelite resin (partially hydrogenated rosin acids), 0.1 gram benzil and .3125 gram 4-methyl-7-dimethylaminocoumarin, dissolved in 100 mls. Chlorothene (1,1,1-trichloroethane) was applied to the gelatin side of a hardened-gelatin-coated paper by flow coating the solution over the substrate supported at about a 60 angle with the horizontal. After air drying for approximately 1 minute, the light-sensitive layer was approximately 2.25 microns thick. The light-sensitive element was placed in a vacuum frame in contact with continuous-tone, half-tone and line positive transparencies and exposed to a carbon are for about 60 seconds. The light-sensitive element was removed from the vacuum frame and developed in a room maintained at 75 F. and 50% relative humidity by rubbing a cotton pad containing an Alphazurine 2G-Pliolite VTL (cyan) developing powder of from about 1 to 40 microns diameter along the largest axis, prepared in the manner described below, across the element. The cyan developing powder was embedded into the unexposed areas of the light-sensitive layer by rubbing a loosely compressed absorbent cotton pad about the size of a baseball, weighing about 3 to 6 grams, back and forth over the light-sensitive layer using essentially the same force used in ultrafine finishing of wood surfaces by sanding or steel wooling. The excess powder was removed from the light-sensitive layer by impinging air at an angle of about 30 to the surface until the surface was substantially free of particles. The reproduction was then wiped with a fresh cotton pad resulting in excellent continuous-tone, half-tone and line reproductions of the positive transparencies. The scanning electron microscope showed that a monolayer of particles was embedded in the image areas. The developed image was placed over a breaker of boiling water for about 15 seconds, during which time the pale blue dye image was imbibed and molecularly dispersed in image-wise configuration into the hardened gelatin layer. The molecularly dispersed image changed from a pale blue to a brilliant, saturated, aesthetically more pleasing cyan hue. Photomicrographs of the powder image before and after dye imbibition imaging showed (1) that the light-sensitive layer puddled up when contacted with steam, (2) of the embedded particles did not move during steaming, and (3) about 10% of the particles, those having the least surface area per volume (largest particles), moved slightly.

The dye imbibition deformation image tended to pick up fingerprints in the background areas when touched with oily fingers, and the image areas had a rough sandpaper-like texture due to the roughness of the Pliolite VTL particles which did not swell during the dye imbibition step. The light-sensitive layer was then washed with Chlorothene by flushing the substrate held at about a 60 angle with the horizontal. Initially the liquid flowing down the sheet had a cyan hue due to the liberation of no-n imbibed dye particles from the Pliolite VTL carrier. Flushing was continued until the liquid contained no residual cyan color. After the dye imbibition image dried, the fingerprint-s in the background areas disappeared, and the element did not pick up fingerprints. The image areas had the same smooth texture as the background areas and the dye imbibition image had a more brilliant, pure color. The scanning electron microscope showed that there was no residual Pliolite VTL developing powder or Staybelite resin.

The Alphazurine 2G-Pliolite VTL developer powder was prepared by milling 200 gramsof micronized Pliolite VTL and 25 grams Alphazurine 26 on a ball mill with porcelain balls for 64 hours.

Essentially the same results were obtained by replacing the Pliolite VTL in the developing powder with Piccolastic D 125 (styrene polymer) and poly(isobutyl methacrylate).

Essentially the same results were obtained by replacing the Alphazurine 2G in the developing powder with tartrazine (yellow) except that the yellow did not run during the Chlorothene wash.

Essentially the same results were obtained by replacing the Alphazurine 2G in the developing powder with Calcocid Phloxine 2G (magenta) which was washed until there was no magenta in the wash 01f.

Example II This example illustrates the use of a water-soluble carrier in the developing powder. One and one-quarter grams Staybelite Ester No. (partially hydrogen rosin acid ester of glycerol), .25 gram benzil and .25 gram 4-methyl-7-dimethylaminocoumarin, dissolved in 100 mls. Chlorothene, was applied to the gelatin side of a hardenedgelatin-coated paper by flow coating the solution over the substrate supported at about a 60 angle with the horizontal. The light-sensitive layer was exposed to light through a half-tone positive transparency in the manner described in Example I and developed with an Alphazurine 2G-polyvinyl alcohol developing powder, described below, in the. manner described in Example I. The excellent half-tone pale blue reproduction was imbibed and molecularly dispersed in image-wise configuration by holding the embedded reproduction over boiling water for seconds. The molecularly dispersed image changed from a pale blue to a brilliant, saturated, aesthetically more pleasing cyan hue.

The developed image, which had a smoother texture in the image areas than the dye imbibition images prepared with the Pliolite VTL, Piccolastic D 125 or poly(isobutyl methacrylate) developing powder, was flushed with Chlorothene in the manner described in Example 1. However, no cyan or blue color was liberated during the wash since substantially all of the dye was either imbibed into the surface of the hardened gelatin or molecularly dispersed into the polyvinyl alcohol carrier, which in turn was fused to the surface of the hardened-gelatineoated paper. After drying, the dye imbibition image did not pick up fingerprints under humid conditions and the reproduction had a more brilliant color. The scanning electron microscope showed that the Staybelite Ester No. 10-had been completely removed by the Chlorothene wash.

The developing powder employed in this example was prepared by tumbling 1 part by weight of Alphazurine 2G with 10 parts by weight polyvinyl alcohol fines with porcelain balls for 15 minutes.

Essentially the same results were obtained by replacing the hardened-gelatin-coated paper with polyvinyl-alcoholsubbed paper.

Example III Example I was repeated except that the Pliolite VTL was replaced with polyvinyl pyrrolidone with essentially the same results. All of the Staybelite resin layer and substantially all of the polyvinyl pyrrolidone was removed during the Chlorothene wash.

Example IV This example illustrates the use of a negative-acting, light-sensitive layer and the use of paper as the receiving layer for the dye imbition image. A sheet of white, lb. Lusterkote Cover CIS paper was flow coated with a solution of 1.5 grams Paricin 15 (ethylene glycol monohydroxy stearate), 0.2 gram benzil and 0.2 gram 4- methyl-7-dimethylaminocoumarin dissolved in mls. of Chlorothene. The light-sensitive layer was exposed to light through a half-tone negative transparency in the manner described in Example I and developed with an Alphazurine 2G-Pliolite VTL developing powder in the manner described in Example I. The excellent half-tone positive pale blue reproduction was imbibed and molecularly dispersed in the paper substrate in image-wise configuration by holding the embedded reproduction over boiling water for 15 seconds. The molecularly dispersed image changed from a pale blue to a brilliant, saturated, aesthetically more pleasing cyan hue. The developed image was then flushed with Chlorothene until the liquid flowing olf the sheet contained no residual cyan color. After the image dried, the background areas did not pick up fingerprints under hot, humid conditions and the image areas had the same texture as the background areas. Further, the dye-imbibition image had a more brilliant, pure color.

EXAMPLE V Example I was repeated with essentially the same results except that the light-sensitive layer was formed by flow coating 10 grams of lecithin and 1 gram of ferric chloride dispersed in 100 mls. of Chlorothene. In this case the positive image was converted to a negative dye-imbibition image.

EXAMPLE VI This example illustrates the use of a hydrophobic dye and hydrophobic subbing layer. A Baryta paper bearing a /3 mil polyethylene subbing layer was flow coated with a composition consisting of 1.25 gram Staybelite resin, 0.10 gram benzil and 0.316 gram 4-methyl-7-dimethylaminocoumarin dissolved in 100 mls. of Chlorothene. The light-sensitive element was exposed through a metal stencil mask for 60 seconds to a 275 watt sunlamp and developed with rice starch bearing an oil-soluble blue dye prepared in the manner described below. The element was placed in a chamber of saturated Chlorothene vapors at room temperature for about 20 esconds, molecularly imbibing the dye particles into the polyethylene layer. The Staybelite resin light-sensitive layer and substantially all of the embedded rice starch particles were removed from the substrate by flushing the developed image with ethanol.

The developing powder used in this example was prepared by blending 0.2 gram American Cyanamid oil blue AV and 1.80 grams rice starch suspended in Chlorothene, evaporating to dryness on a hot plate at 50 C. and grinding with a mortar and pestle.

Essentially the same results were obtained replacing the blue dye in the developing powder with 0.2 gram American Cyanamid oil red N-1700.

EXAMPLE VII Example I was repeated with essentially the same results except that the light-sensitive layer was formed by flow coating 1.25 grams Chlorowax 70 LMP, .3 gram benzil and .3125 gram 4-methyl-7-dimethylaminocon marin, dissolved in 100 ml. Chlorothene, onto the gelatin side of a hardened-gelatin-coated paper.

19 EXAMPLE VIII Example II was repeated with essentially the same results except that the Staybelite Ester No. 10 layer was removed with (a) hexane, (b) chloroform, carbon tetrachloride and (d) methanol.

While this invention is directed primarily to a method of improving the tonal qualities and handling properties of molecularly dispersed dye imbibition images, the subject process can also be used advantageously to improve the handling properties of molecularly dispersed dye images of the type described in our parent application Ser. No. 833,771 filed June 16, 1969, now US. Pat. 3,677,759, which is hereby incorporated by reference. In Serial No. 833,771, we disclosed a process of forming molecularly dispersed dye images wherein powder particles comprise a dye and a carrier, held in image-wise configuration on a substrate, are contacted with vapors of a material (preferably water), which is a solvent for said dye, capable of swelling the surface of the carrier for the dye and incapable of swelling the surface of said substrate, thereby molecularly dispersing said dye into the carrier. As pointed out in this application, the process of molecularly dispersing the particle dye into the carrier converts the dye particles from a particulate form into a molecularly dispersed form providing an aesthetically more pleasing, monochromatic, saturated image. Other things being equal, the particulate dye image changes from a pale color to a brilliant, saturated, more pleasing hue. However, these reproductions have a minor aesthetic drawback in that the background areas of the molecularly dispersed dye images are easily fingerprinted, apparently due to the exudation of oil or moisture from peoples fingers, particularly on hot, humid days. We have found that it is possible to improve the handling properties of the molecularly dispersed dye images of Ser. No. 833,771 by treating the developed image with a material which is a good solvent for the original solid, light-sensitive, organic layer and a relatively poor solvent for the components of the molecularly dispersed dye images. However, whereas the dye imbibition images can be rubbed vigorously during the solvent wash without any detrimental effect, the dye images molecularly disperesd in the carrier should not be rubbed during the solvent wash or flush, since force of this nature has a tendency to alter the adhesion of the fused carrier particle to the surface of the substrate.

EXAMPLE IX A solution of 0.64 gram Staybelite Ester No. 10, 0.16 gram benzil and 0.096 gram 4-methyl-7-dimethylcoumarin, dissolved in 100 mls. Chlorothene, was flow coated over a polyethylene terephthalate film supported at about a 60 angle with the horizontal. After air drying, the light-sensitive element was placed in a vacuum frame in contact with continuous-tone and half-tone transparency and exposed to a carbon arc for about 60 seconds. The light-sensitive element was removed from the vacuum and developed in a room maintained at 75 F. and 50% relative humidity with an Alphazurine 2G (cyan) polyvinyl alcohol toner of from 1 to microns diameter along the largest axis in the manner described in Example 1. After the unembedded excess cyan developing powder was removed, the developed image was placed over a beaker of boiling water for about seconds, during which time the pale blue dye image was molecularly dispersed in the polyvinyl alcohol carrier in continuous-tone and halftone configuration onto the polyethylene terephthalate substrate. The molecularly dispersed image changed from a pale blue to a brilliant, saturated, aesthetically more pleasing cyan blue. The image, which had a tendency to pick up fingerprints in the background areas when touched with oily fingers, was washed with Chlorothene by flushing the substrate held at about a 60 angle with the horizontal. After the meleeula y di p y image 20 dried, the background areas did not tend to pick up fingerprints.

The developing powder used in this example was prepared in the manner described in Example II.

EXAMPLE X Example II was repeated with essentially the same results except that the Staybelite Ester #10 light-sensitive solution was replaced with a solution comprising 1 gram Piccotex 75 (alpha-methyl styrene-viuyltoluene copolymer), .2 gram benzil and .15 gram 4-methyl-7-dimethylaminocoumarin dissolved in mls. Chlorothene.

EXAMPLE XI Example II was repeated with essentially the same results except that the Staybelite Ester solution was replaced with a solution comprising .8 gram Dimerex (resin dimer), .6 gram benzil and .6 gram 4-methyl-7-dimethylaminocoumarin, dissolved in 100 mls. Chlorothene and using a four minute exposure was used.

Since many embodiments of this invention may be made and since many changes may be made in the embodiments described, the foregoing is to be interpreted as illustrative only and our invntion is defined by the claims appended hereafter.

What is claimed is:

1. The process for forming moleculaly dispersed dye imbibition images of improved tonal qualities and handling properties which comprises (1) contacting a substrate bearing a light-sensitive, solid, organic layer of from 0.1 to 10 microns thick holding a monolayer of powder particles comprising a solid carrier and dye, held in image-Wise configuration in particulate form, said powder particles displacing at least a portion of said solid, organic layer, with vapors of a material and transporting said dye through said solid, organic layer, molecularly imbibing said dye into said substrate, wherein said material is a solvent for said dye, capable of swelling the surface of said substrate and transporting said dye through said solid, organic layer, and (2) removing said solid, organic layer with a material which is a solvent for said solid, organic layer and a poor solvent for the surface of the substrate.

2. The process of claim 1, wherein said solid, organic layer contains no conjugated terminal ethylenic unsaturatron.

3. The process of claim 1, wherein said solid, organic layer is alcohol-soluble and said solid, organic layer is removed in step (2) with an alcohol.

4. The process of claim 3, wherein said alcohol is ethanol.

5. The process of claim 1, wherein said solid, organic layer is hydrocarbon-soluble and said solid, organic layer is removed in step (2) with a hydrocarbon.

6. The process of claim 5, wherein said hydrocarbon is hexane.

7. The process of claim 1, wherein said solid, organic layer is halohydrocarbon-soluble and said solid, organic layer is removed in step (2) with a halohydrocarbon.

8. The process of claim 7, wherein said halohydrocarbon is 1,1,1-trichloroethane.

9. The process of claim 1, wherein said solid, organic layer and said solid carrier are both hydrocarbon-soluble and said solid, organic layer and solid carrier are removed in step (2) with a hydrocarbon.

10. The process of claim 1, wherein said solid, organic layer and said solid carrier are both halohydrocarbonsoluble and said solid, organic layer and solid carrier are removed in step (2) with a halohydrocarbon.

11. The process of claim 1, wherein said solid, organic layer comprises an internally ethylenically unsaturated acid.

12. The process of claim 11, wherein said solid, organic layer comprises a partially hydrogenated rosin acid.

1 3. The process of claim 1, wherein said solid, organic layer comprises an ester of an internally ethylenically unsaturated acid.

14. The process of claim 13, wherein said ester comprises a partially hydrogenated rosin ester.

15. The process of claim 13, wherein said ester comprises a phosphatide.

16. The process of claim 1, wherein said solid, organic layer comprises a halogenated hydrocarbon.

17. The process ofclaim 1, wherein-said solid, organic layer comprises a hydrogenated ester of ricinoleic acid.

18. The process of claim 1, wherein the substrate comprises a base bearing a hydrophilic subbing layer and the dye is water-soluble.

19. The process of claim 18, wherein the vapors of the material which is a solvent for said dye and capable of swelling the surface of said substrate'comprise Water.

20. The process of claim 18, wherein the solid carrier for said dye is hydrophilic.

21. The process for forming molecularly dispersed dye imbibition deformation images of improved tonal qualities and handling properties which comprises:

(1) exposing to actinic radiation in image-receiving manner a substrate bearing a solid, light-sensitive organic layer having a thickness of 0.1 to microns capable of developing a R of 0.2 to 2.2;

(2) continuing the exposure to establish a potential R of 0.2 to 2.2;

(3) applying to said layer of organic material, freeflowing powder particles having a diameter, along at least one axis, of at least about 0.3 micron but less than 25 times the thickness of said organic layer wherein said powder particles comprise 'a solid carrier and dye;

(4) while the layer is at a temperature below the melting points of the powder and the organic layer, mechanically-embedding said powder particles as a monolayer in a stratum at the surface of said lightsensitive layer to yield an image having portions varying in density in proportion to the exposure of each portion;

(5) removing non-embedded particles from said organic layer to develop an image;

(6) transporting said dye through said solid, organic layer molecularly imbibing said dye into said substrate by contacting the particles embedded in said organic layer with vapors of a material which is a solvent for said dye, capable of swelling said substrate and capable of transporting said dye through said solid, organic layer; and

(7) removing said solid, organic layer with a material which is a solvent for said solid, organic layer and a poor solvent for the surface of the substrate.

22. The process of claim 21, wherein said solid, organic layer is alcohol-soluble and said solid, organic layer is removed in step (7) with an alcohol.

23. The process of claim 21, wherein said solid, organic layer contains no conjugated terminal ethylenic unsaturation.

24. The process of claim 21, wherein said solid, organic layer is soluble in a material selected from the group consisting of hydrocarbons and halohydrocarbons and said solid, organic layer is removed in step (7) with a member selected from the group consisting of hydrocarbons and halohydrocarbons.

25. The process of claim 21, wherein said solid, organic layer and said solid carrier are both soluble in a material selected from the group consisting of hydrocarbons and halohydrocarbons and both said solid, organic layer and solid carrier are removed in step (7) with a solvent selected from the group consisting of hydrocarbons and halohydrocarbons.

26. The process of claim 21, wherein said solid, organic layer comprises an internally ethylenically unsaturated acid.

27. The process of claim 21, wherein said solid, organic layer comprises an ester of an internally ethylenically unsaturated acid.

28. The process of claim 21, wherein said solid, organic layer comprises a halogenated hydrocarbon.

29. The process of claim 21, wherein said solid, organic layer comprises a hydrogenated ester of ricinoleic acid.

30. The process for forming molecularly dispersed dye imbibiion deformation images of improved tonal qualities and handling properties which comprises:

(1) exposing the actinic radiation in image-receiving manner a substrate having a hydrophilic surface bearing a solid, light-sensitive organic layer having a thickness of 0.1 to 10 microns capable of developing a R, of 0.2 to 2.2;

(2) continuing the exposure to establish a potential R of 0.2 to 2.2;

(3) applying to said layer of organic material, freetlowing powder particles having a diameter, along at least one axis, of at least about 0.3 micron but less than 25 times the thickness of said organic layer wherein said powder particles comprise a solid carrier and water-soluble dye;

(4) while the layer is at a temperature below the melting points of the powder and the organic layer, mechanically embedding said powder particles as a monolayer in a stratum at the surface of said lightsensitive layer to yield an image having portions varying in density in proportion to the exposure of each portion;

(5 removing non-embedded particles from said organic layer to develop an image;

(6) transporting said dye through said solid, organic layer, molecularly imbibing said dye into said substrate, by contacting the particles embedded in said organic layer with water vapor and imbibing said water-soluble dye into the surface of said substrate; and

(7) removing said solid, organic layer with a material which is a solvent for said solid, organic layer and a poor solvent for the surface of the substrate, said solvent being selected from the group consisting of hydrocarbons and halohydrocarbons.

31. The process of claim 30, wherein said base comprises paper.

32. The process of claim 31, wherein said paper base bears a subbing layer selected from the group consisting of hardened gelatin, polyvinyl alcohol and polyvinyl pyrrolidone.

33. The process of claim 30, wherein said solid, organic laygr comprises an internally ethylenically unsaturated aci 34. The process of claim 30, wherein said solid, organic layer comprises an ester of an internally ethylenically unsaturated acid.

35. The process of claim 30, wherein said solid, organic layer comprises a halogenated hydrocarbon.

36. The process of claim 30, wherein said solid carrier is soluble in a material selected from a group consisting of hy(drocarbons and halohydrocarbons and is removed in step 7).

37. The process of claim 30, wherein substantially all of said solid carrier is hydrocarbon-soluble and is removed in step (7) with said hydrocarbon.

38. The process of claim 30, wherein substantially all of said solid carrier is halohydrocarbon-soluble and is removed in step (7) with said halohydrocarbon.

39. The process of claim 30, wherein said solid carrier is water-soluble and imbibed into the surface of said substrate and is not removed with the material selected from the group consisting of hydrocarbons and halohydrocarbons.

40. The process of forming molecularly dispersed images of improved handling properties which comprises (1) contacting a substrate bearing a solid, light-sensitive,

23 organic layer, holding a monolayer of powder particles comprising a solid carrier and dye, held in imagewise configuration in particulate form, said powder particles displacing at least a portion of said solid, organic layer, with vapors of a material which is a solvent for said dye and capable of swelling the solid carrier and incapable of. swelling the surface of said substrate, molecularly dispersing said dye into said carrier, and (2) removing said solid, organic layer with a material which is a solvent for said solid, organic layer and a poor solvent for the components of the molecularly dispersed dye image.

41. The process of claim 39, wherein said solid, organic layer contains no conjugated terminal ethylenic unsaturation.

42. The process of claim 39, wherein said solid, organic layer is soluble in a material selected from the group con- 24 o sisting of hydrocarbons, halohydrocarbons and alcohols and said solid organic layer is removed with a member selected from the group consisting of hydrocarbons, halohydroc arbons and alcohols.

References Cited UNITED STATES PATENTS 2/1942 Whitehead 8-14 1/1971 Tanno et al. 117--63 I U.S.C1.X.R. 96-2, 13, 115, 119; 117 1.7, 37

Inventor 8011mm 3 fimlumn 4, fiolumn 5, Column 5, Column 5 Column 5, Column Column Column Column Column Column Column fio'iumn (201mm Column Column Column 3011mm Column Qolumn Bolumn ficvlumn Calumn Golumn Column Column Column Column 17, Cwliumn 18 Coiumn 18 @ERTIFICATE 0 Patent No.

March 27, 1973 3,723, 12 Dated line line line line bridging acting--- I line line line line line line line line line line 111m line line line line line line line line line line fine line braid line fine Rexford W. Jones and William 33.. Thompson It is certified that error aypears in the above-identified patent and that said Letters Patent herah y CUETIQC'EEd as shown below:

for for for "quantity" quality b'iack image" read --black annier-embedded imagepower-free read meander-freelines 19 and 20; Ear negative-siting" read ---negative- 00632) reflfictfifiie) read --00637 reflectance) "recflectance) read -ref1ectance) "them osat" read -'--the most-- "'lighcsensitivity read ----light sensitivity--- "lightaensitive" read -=--light sensitive- "lightsensitivity" read ---light sensitivity"- "lightsensitive" read ----light sensitive"- "ultarviolec" read ---u1i:raviolet--- for lecithin read --=-lE:cithin--- for "base" read ---baaed--- for "photoctivator" read ---ph0t0activator-- for "brightnera" read --brighteners--- for "Calcoid" ":ead --Ca1cncid--- for "chlorofrom read ---chloroorm--- 01 prefererd read ---preerred--- for carbowaves read ---Ce1rb0waxes-- for *znethylacwiate read --'methacry1ate--- for *examp'it read '---examp1e--- for "POWEKN read --powder-- for "56% Ram wad ---56"Z. for "ix-abiding z'ead ---imbib:ing--- for "imbiding read --imbibing for "breakefl read beake-r lines 6 and 7; 02 no nimbibing" read ---non-imbibing--- for positive image read "-wositive powder image--- for ascends read --sec0nds for for for for for for for for FORM PO-I050 (10-69) USCOM|M-DC 60376-P69 w us GOVERNMENT Pmrrrms OFFICE: I989 o-366-334,

UNITED S'IIATESV1%13311'1v OFFICE CERTIFICATE OF (CORRECTION Patent No. 3,723,124 Dated March 27, 1973 Ihventofls) Rexford' W. Jones and William E. Thompson It is certified that error appears in the above-identified patent and that said Letters Patent are as @hown below:

PAGE 2 Column 19, line 43; for "dispeyeed" read --=-diepereed--- Column 19, bridging lines 51' and 52; for "dimethyleoumarin" read ---dimethy1aminocoumarin-- Column 19, line 71; for "blue" read ---hue--- Column 22, line 9; for "imbibiion" read ---imbibition--- Column 22, line 11; for "the" read ---to--- Signed and sealed this 1st day of October 1974.v

(SEAL) Attest:

MCCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents OFEM PO-IOEO (IO-69) USCOMM-DC B0376-p59 1 US. GOVERNMENT PRINTING OFFICE: [959 0-366-33L