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Publication numberUS2911299 A
Publication typeGrant
Publication dateNov 3, 1959
Filing dateJul 22, 1952
Priority dateJul 22, 1952
Publication numberUS 2911299 A, US 2911299A, US-A-2911299, US2911299 A, US2911299A
InventorsBaril Jr Albert, De Barbieris Irvin H, Nieset Robert T, Thornton Stearns
Original AssigneeKalvar Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
System of photographic reproduction
US 2911299 A
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Description  (OCR text may contain errors)

Nov. 3, 1959 A. BARIL, JR., ETAL 2,911,299


f ffy/a ifa Nov. 3, 1959 Filed July 22, 1952 fff lll/OHRA 7 E iff/$762 E A. BARIL, JR., ErAL SYSTEM oF PHOTOGRAPHIC REPRODUCTION 3 Shececs-SheetI 3 www@ /PEZXED [4579/62 E @@ll @@@lll OOOOO OOOOO United States Patent O SYSTEM F PHOTOGRAPHIC REPRODUCTION Albert Baril, Jr., Irvin H. De Barbieris, and Robert T.

Nieset, New Orleans, La., and Thornton Stearns, Winchester, Mass., assignors, by mesne assignments, to Kalva'r Corporation, New Orleans, La., a corporation of Louisiana Application July 22, 1952, Serial No. 300,282

1 Claim. (Cl. 96-49) The present invention relates to a process of forming copies of records such as printed matter or microlms by means of compounds which produce gas upon irradiation, and also to material wherein such copies can be formed, and to the copies themselves.

It is a principal object of the invention to provide photographic reproductions according to a technique which is extremely simple and inexpensive and yet fully satisfactory particularly for use in oiiices, libraries, drafting rooms and similar establishments where it is desirable to copy record material with a minimum of effort, with unskilled labor, and in minimum time.

Another object is to provide such a technique which employs material that is comparatively inexpensive, stands up well through reasonably rough routine handling, and produces exact and permanent copies.

Further objects are to provide a reproduction technique which is dry throughout and does not require chemical treatment or rinsing baths, and to provide such a technique which optionally permits the direct printing of either negative or positive copies, -with the same material, apparatus, and general procedure.

In accordance with the invention, an essentially stable photographic record is produced in a vehicle of adjust- :able rigidity containing a sensitizing substance capable of liberating -gas upon exposure to radiation, in the form of gas sources or units that are essentially invisible upon generation and while the vehicle remains indurated but 'which are capable of expanding into visible bubbles With- ;'in the relaxed vehicle, by exposing a layer of the vehicle,

in either indurated or relaxed condition to a radiation :image thus forming therein a record in terms of gas'units, fby relaxing or indurating, respectively, the vehicle to bring fit into the other condition with image selected units exjpanding into bubbles to form a nal visible record, and vby rendering ineiective the sensitizer which might remain `Within the vehicle in portions which are not occupied by '-,the bubbles which form the final record, thus xing the :record against further exposure; in an important embodiment the xed 4vehicle is in irreversibly hardened indurated condition.

In a practically important aspect of the invention, a Elayer of the vehicle is exposedin indurated condition to iform therein a record in terms of gas units, the vehicle lis then relaxed to form a record in terms of bubbles, and.

the sensitizer which after exposure remains within the vehicle is rendered ineffective and the copy fixed by Auniformly exposing it and by diffusing the gas units thus iformed from the indurated vehicle, or fixation is accomgas units, the gas is then permitted substantially to diuse from the vehicle, an overall exposure is applied to gen- Verate gas sources from the remaining sensitizer, the vehicle relaxed to expand the gas units resulting `from the Ffice 2 Y overall exposure to form a record in terms of bubblesgand a fixation step vis applied. v -v ln an additional aspect, `a layer of the vehicle is exposed in indurated condition yto form a record'in terms of gas units, the gas is dilused from the vehicle, the vehicle is relaxed, and an essentially uniform exposure is applied to generate gas units from the remaining sensitizer which units expand into record dening bubbles; fixation follows.

ln a further aspect, a layer of the vehicle is exposedv in relaxed condition to form a record in terms of gas bubbles, the vehicle is then suiciently indurated essentially to prohibit further bubble formation while permitting diffusion of gas, a substantially uniform overall exposure is applied to generate gas from the remaining sensitizer, and the remaining gas is permitted to diffuse.

Reproduction material according to the invention comprises a layer of vehicle material of adjustable rigidity and permeability incorporating an amount of sensitizing substance .capable of generating sufficient gas to form a visible record in terms of gas bubbles upon exposure to radiation and expansion of the gas, the vehicle being characterized by a rigidity which is adjustable between optimal degrees, one of higher rigidity preventing substantial bubble formation but of sutlcient permeability to permit gas unit formation and if desired gas diffusion from the vehicle, and the other of lower rigidity permitting gas bubble formation with permeability permitting escape of gas from the vehicle. In an important embodiment the vehicle is of the gelatin type, suiciently indurated at ordinary temperatures to prohibit bubble formation, suciently relaxed at moderately elevated temperature to permit bubble formation, and becoming irreversibly hardened to a highly indurated condition upon heating to a further ele-v vated temperature.

Final copies according to the invention comprise an in durated layer of plastic material of essentially uniform thickness which contains in substantially uniform distribution chemically unchanged photolytic decomposition products of a radiation sensitive substance, and essentially bubble shaped cavities distributed in a record V forming pattern, the configuration of the individual bubbles as well as their distribution being fixed by therigidity ofthe indurated vehicle. In an important embodimentA the vehicle consists of irreversibly hardened gelatin.

Other objects, aspects and features will appear, in ad- Figs. 7 and 8 are diagrams illustrating the rigidityad justrnent according to the invention; and f Figs. 9 to 12 are diagrams illustrating four respective embodiments of the process according to the invention.

The following description presents first the general operational principles of the most important aspects ofl the invention with regard to the properties of vehicle and sensitizing substance, and then supplies speciic examples of materials as well as of process sequences which incorporate these principles for various practical purposes.

'I'he photographic reproduction system according to the invention is based on the possibility of determining a record pattern in terms of transmission, absorption, re-

flection and scattering 'of the incident light by the con-l trolled formation of a structure of gas bubblesV within a vehicle, coated on suit-able sheet stock or Self-supporting.

The primary photochemical, reaction releases gas in a pattern determined by a radiation image, in proportion to the amount of radiant energy absorbed by a sensitizing substance.

The term record as herein .used denotes `any picture. or indicia patternl in terms of eectively tangible characteristics of a body, such as texture or grain distribution., A record should be distinguished from a radiation image as dened by a beam that is modulated by an original record, in direct contact with the copying surface or related thereto through the intermediary of an image forming system. The term original is used for any object that modulates the radiation to which the sensitive substance is exposed; it can be a scene, anV original picture or print, or a photographically or otherwise produced positivev or negative copy. The term radiation as herein used includes electromagnetic radiation suchl as light Vwithin and on either side of the visible spectrum, as well as particle impingement.

The material which is used in the present system has two essential components in intimate cooperation, namely the vehicle and the sensitizing substance. A vehicle is the carrier or binder material for sensitizing substances and for the gas released therefrom upon photolysis, which gas occurs in the form of initial sources or units, and as record forming bubbles. A sensitzing substance or sensitizer for short, is radiation sensitive material incorporated in the vehicle which generates gas by decomposition upon irradiation.

The vehicle must have two properties in order to be usable for purposes of the invention, namely, permeability and adjustable rigidity.

The permeability has two important aspects, namely, the internal permeability or rate of diffusion of gas within the vehicle itself and the escape permeability, that is the rate at which gas can escape entirely from the vehicle.

The rate of diffusion of the gas within the vehicle itself (internal permeability) varies between an upper and lower limit. TheV lower limit of diffusion is determined by the need for gas to move with suflicient freedom to obey Boyles and Charles laws. relating the volume to pressure and temperature, respectively, after the release of what is herein referred to as gas sources, from the irradiated sensitizing substance. These sources can. be conceived as single gas molecules or groups thereof, but at any rate they do not yet form units of a true. gas. If these sources were trapped within the vehicle upon release by photolysis, they could not form the smallest units with the above characteristics of a true. gas, which units might also be referred to as latent bubbles or bubble nuclei. These sources and units constitute an invisible latent record of the image defining radiation pattern which causes their release from the sens'itizer within the vehicle. The gas contents of the unitsl or latent, bubbles varies to a degree which can be controlled by way of the internal permeability. The upper limit of internal permeability is determined by the spatial resolution required in the finished product, and hence by the size of the ultimate record forming bubbles. For example a microfilm print intended for projection use requires but a very small bubble. On the other hand' reproduction for example of large size prints by contact exposure permits considerably larger bubbles. For a resolution of one thousand lines per inch, bubbles of approximately 2 microns are needed, and such a bubble would contain approximately 2x10-13 moles of gas. Accordingly, for applications requiring resolution of this fineness, the diffusion of the gas and hence the interna permeability of the vehicle has to be so adjusted that units containing substantially more than this amount of gas'do not occur. Furthermore, the internal permeabllity has to be so regulated that the gas does not diffuse away from the exposed' areas into unexposed areas Where 1t might later cause general background foggn.

This property of the vehicle, providing for optimal internal diffusion of the gas, is illustrated in Fig. l where dots m represent molecules of the sensitizer which is dispersed in the vehicle v. In Fig. 2 crossed dots s represent sources of gas, generatedrbyV irradiation with a radiation image pattern z'. At this stage the molecules released in photolysis cannot truly behave as a gas and, therefore, no bubble record can be formed if internal diffusion is so restricted that the partial volumes are small, containing only one or Very few gas molecules.

The operative situation is represented in Fig. 3. Here the partial volumes are sufficiently large so that great numbers of the gas molecules can act together, behaving in units zz asV an ideal gas, and forming under high pressure the latent bubble agglomerates indicated as crosses which can expand to a maximum size determined by the rigidity of the vehicle, as will be discussed below. Fig. 3 also indicates how the record detail can be obscured or even expanded into the unexposed background, thus creating a fogged area, if diffusion 'is very great and marginal units um form beyond the actually exposed area.

While, as above discussed, the vehicle` should be of suflicient internal permeability to allow the optimum diffusion of gas once formed therewithin, it should have a reasonably impervious surface so that gas is not completely lost from the emulsion during exposure, thereby reducing the cfiiciency and hence the sensitivity of the emulsion or the film. Efficiency is here defined as the ratio of the actual volume of gas confined in light scattering bubbles, to the amount released at standard conditions of pressure and temperature. This efiiciency is affected by the above loss of gas and by the flow characteristics of the vehicle to be discussed below. Low efiiciency means low sensitivity because it requires more energy to activate sufiicient sensitive material to give a required contrast. The loss in sensitivity due to low efficiency cannot be compensated for by increased concentration of sensitizer because, if the concentration exceeds a certain rather critical value, then the gas units are initially too large and impair the resolution. A high efficiency therefore enhances sensitivity as well as detail resolution. The efficiency is also affected by the duration of those periods of the record forming technique during which the vehicle permits escape of gas.

The escape permeability of the vehicle furthermore aects the permanence of the final record which will be further discussed below. If after record formation the permeability of the vehicle is so changed that any fur` ther gas released by photolysis can escape quickly without forming bubbles, then the record is xed against subsequent exposure. Thus, while it is in the interests of efficiency desirable to have a low rate of gas escape prior to record formation, it is desirable to have a high rate of gas escape thereafter. However, fixation is promoted by this gas escape only if the gas previously Iconfined in the bubbles is no longer required to preserve the bubble structure. This, in turn, depends upon the rigidity characteristics of the vehicle which will now be discussed.

The rigidity characteristics of the vehicle have to conform to certain requirements during the principal steps of the present technique, namely, exposure, development, and fixation.

During exposure for the purpose of providing a latent record the vehicle, in addition to the above discussed internal permeability permitting formation of gas units, must have suflicient rigidity or resistance to fiow to prevent the formation of expanded units or bubbles during exposure. Such bubbles would scatter light in the highlighted areas, thus cutting ofi further photolysis in these regions, causing insufficient exposure and reducing coutrast. 'These considerations apply to exposure leading to formation of bubbles which constitute a final record, while. they do not apply for purposes of preliminary,

5. although pattern determining, exposure of a relaxed vehicle, as will be pointed out below with reference to a practical example of this type, illustrated in Fig. 1l.

To convert or develop the record in terms of gas units or latent bubbles produced during exposure, into a visible record, the vehicle is relaxed in such rfashion that the latent bubbles can expand to cross sections which will produce the maximum light-scattering effect consistent with the required resolution. Fig. 4 indicates this stage of bubble formation. The circles b which surround units u represent bubbles of desirable relative proportions. Fig. 5 indicates the record structure upon diffusion of gas from now empty bubbles be. These diagrams do not indicate possibilities of removing the remaining sensitizer m, which will be discussed below. In a practical and satisfactory embodiment, the average diameter for good resolution is about 2 microns, bubbles above 5 microns in diameter being undesirable. a

In accordance with the present invention, the ratio of the cross section of the gas unit formed during exposure can be controlled for purposes of optimal utilization of the photosensitive material during exposure, and of increasing the overall efficiency of the whole photographic process. This ratio is therefore `an amplification factor and will be so referred to herein.

Of equal importance to unit formation by internal diffusion is the increase Iin overall quantum eiliciency that can be obtained by utilizing the ygas amplification principle. The pressure under which the gas is released during exposure is a function of the concentrationof the sensitive material, the primary quantum eiciency of decomposition of the photosensitive material upon irradiation, and the rigidity of the vehicle Vagainst which the gas -must expand. In accordancewith the invention these three variables are adjusted Yto limit the size during exposure to negligible light-scattering cross sections. We found that the gas amplification factor increases the overall quantum eficiency beyond that which can be obtained by coupling the decomposed material with a dye.

Fig. 6 indicates the undesirable condition where internal diffusion has been too rapid kor relaxation gone too far so that large bubbles bl have formed which obscure the detail.

Development by relaxing the vehicle accomplishes the above discussed amplification by purely physical means. If the vehicle -is a thermoplastic, the requisite conditions of plastic ow during development can be brought about by the amplification of heat by conduction, convection or radiation. The physical means for applying heat to obtain regulated relaxation and induration consistent with a large gas amplification factor can be quite simple, which is a primary advantage of the invention.

Fixation has the purpose of making the record stable and permanent in general use. The record must not disappear or be reduced incontrast or sharpness subsequent to development by losingits light scattering properties, it must be stable against fogging or accidental re-exposure, and it must be mechanically stable, that is sufficiently hard to withstand ordinary handling, including damage by scratching or softening under the heat of a projector lamp.

Preservation of the record proper can be accomplished by hardening the vehicle after the bubbles have been alloWedtheir maximum expansion during development. This freezing of the bubble structure brings about fixation by sealing up each individual bubble to confine the gas therewithin, and by making the walls of each bubble sufficiently rigid so that even though the gas subsequently escapes, the wall remains, forming a light scattering cellular structure which is mechanically strong enough to maintain itself against ordinary use. It is this second aspect that is especially important since it preserves the record regardless of gas diffusion from the vehicles. This nal hardening is especially beneficial because irreversible and of a high degree, if the vehicle is of the gelatin`V type, as will be discussed more in detail below.

'Ihe vehicle can be stabilized against exposure and fogging by destroying detrimental sensitizer, by permanent hardening, and by optical screening.

The destruction of remaining lsensitizing material which was not needed for `formation of the final record, can be accomplished in several ways, three of which have proved to be especially important for the process accord ing to the invention.

The first Way is `to make the material thermally unstable such as to prevent it from producing gas. This technique is applicable -to the diazo sensitizer used in an important embodiment of the invention. Such material chemically decomposes at elevated temperatures, but in such a way that the yield of gas from thermal decomposition is much lower than it is for photodecomposition.

Another way of destroying the remaining sensitizer is the diffusion of the released gas such that, as rapidly as the gas is formed by photodecomposition, it escapes completely from the vehicle so that bubbles cannot form. Particularly effective is the combination of optical screening in the manner pointed out below and of slow diffusion of gas released thus destroying the remaining photosensitive material simply by exposure to a lower level of illumination than is required for initial exposure.A

A third means of inactivating the remaining sensitizer is to eliminate a volatile component of the primary photochemical reaction'. In a gelatinous vehicle for example,

this can be accomplished by way of driving olf the waterthat is required for the eficient release of gas by photodecomposition. At temperatures practical for relaxation development and iixation, most of the water is driven off. In the absence of water, the quantum efficiency of the photochemical reaction that remains possible is so much less than the quantum eliciency in the presence of water,v that the sensitivity is greatly reduced. Y

Subsequent to the fixation process proper, the vehicle can be made too hard and resistant for bubbles to form readily under ordinary exposure conditions. Even though small amountsv of gas are released by subsequent exposure it cannot expand into bubbles of significantly light-scattering cross section. This condition is essentially identical with that lmentioned above as required for theprigid preservation of the cellular structure, and it goes hand in hand with the mechanical stability mentioned below which is desirable as a protection against scratching and other mechanical deformation in routine handling of the material. v

Stabilization of the sensitizer is aided by changing the spectral transmission characteristics of the vehicle. The vehicle and sensitive material, before and during exposure, passes radiation of a critical wavelength required for the primary photochemical reaction. After exposure however, the spectral transmission characteristics of the vehicle can in many instances be so changed that it becomes opaque to light of the critical wavelength. This is in effect equivalent to Wrapping up the unexposed parts of the lm in black paper forever after. In the case of gelatinous vehicles carrying certain diazo compounds as sensitizers, for example, this can be accomplished concomitantly with the nal hardening induration which in this instance somewhat tans the surface of the gelatin. This tanning and some coagulation within the emulsion renders the gelatin'less transparent to the ultraviolet light in the general region of 3600 A., so that the actinic spectral region mainly effective for image formation is liltered out.

Mechanical stability is in the mainv provided by the indurating and hardening procedures described above. A

mechanical structure sufficiently rigid to preserve the l bubbles which constitute the record, as well as to prevent the direct expansion of bubbles upon further exposure is sufficiently hard to meet all the usual photographic` needs.

In order to perform the above-outlined functions within the frame work of the invention, the materials employed therein are compounded and selected as follows.

The sensitizing substance must be capable of dispersion within the vehicle suiciently line for purposes of the required definition as further controlled by the abovediscussed permeability and rigidity characteristics of the vehicle. Compounds of the diazo type which upon irradiation liberate nitrogen were found to be especially suitable, but other compounds for example of the type which liberate carbon oxides can be used.

Among the sensitizing substances which liberate nitrogen units upon irradiation, para-diazo dimethyl aniline zinc chloride was found to be especially valuable, but the following substances were also found to be usable.

P-diazo diphenylamine sulfate, p-diazo diethylaniline zinc chloride, p-diazo ethyl hydroxyethylaniline zinc chloride, p-diazo ethyl methyl aniline zinc chloride, p-diazo diethyl methyl aniline zinc chloride, p-diazo ethyl hydroxyethylaniline Zinc chloride, l-diazo-2 oxy naphthalene-4r sul-fonate, p-diethyl amino benzene diazonium chloride ZnCl2, 4-benzoylamino-2-5-diethoxy benzene diazonium chloride, p-chlorobenzene-sulfonate of 4-diazo-lcyclohexylaniline, p-chlorobenzene-sulfonate of 4diazo2 methoxy-l-cyclo-hexylamino benzene, tin chloride double salt of 4-N-nethyl-cyclohexylamino-benzene diazonium chloride, p-acetarnino benzene diazonium chloride, 4-dimethylarnino benzene diazonium chloride, S-methyl 4- diethyl amino benzene diazonium chloride, 4-morpholino benzene diazonium chloride, 4-piperidyl 2-5-diethoxy benzene diazonium chloride, l-dimethyl amino naphthalene-4 diazoniurn chloride, 4-phenyl amino diazo benzene diazonium chloride. A

Substances which liberate carbon oxides upon irradiation and which are useful for purposes of the invention are organic acids such as ferric ammonium citrate and oxalic acid.

For incorporating sensitizers in vehicles used for purposes of the invention, two techniques are feasible.

The sensitizing compound can be dissolved and in that state mixed with a solution of the plastic, and the mixture dried in the form of a film applied to a support. This technique is particularly applicable to gelatinous vehicles. Up to certain concentration-s which depend on the particular gelatin, such vehicles contain the sensitizer most likely in molecular dispersion dissolved in the gelatin water. Above such concentrations the sensitizer is probably also dispersed in precipitated form, as will be discussed below with reference to the vehicle structure.

The sensitizing substance can also be incorporated in vehicles which are made from organosols which can be kfused at temperatures below, although rather close to the decomposition temperature of the sensitizing substance, which condition must be taken into account in preparing such material.

The vehicle material plays a very important role within the framework of the present invention. It must lend itself easily to quick, positively controllable and reversible transformation from relaxed or amplifying condition into indurated condition, and vice versa, and in an important modification also to irreversible transformation into highly' hardened condition. In either state, permeability is to be preserved, but in iinal irreversible induration or hardening the escape of gas can be excluded if desired.

In accordance with the invention, this transformation is accomplished by the purely physical expedients principally of temperature, and sometimes of moisture, or both. For most purposes dry heat is sufficient, with the ensuing practical advantages. The vehicle is for practical purposes of such a nature that it softens if the temperature is raised during the development process. As it softens, the gas units and bubbles are allowed to expand as above explained. After the bubbles have reached their optimum diameter, another change in temperature leads again to induration, either of the reversible, or at choice of the hardening or final type. This cycle can be carried out for certaingelatin emulsions such as herein described. As theV temperature is raised, gelatin of selected types softens somewhere between and 200 F. allowing the bubbles to expand. As the temperature goes above 200 F., the gelatin tans on the surface somewhere between 200 and 250 F., and, in general, assumes a. hard, rigid and irreversibly coagulated structure, which then provides the above discussed mechanical rigidity which freezes the bubble walls and preserves .the structure even though the gas may subsequently escape. Vehicles of the Bakelite type are somewhat similar. They become plastic at an inter-mediate temperature of about 200 F., the approximate temperature required for expansion of the bubbles, and at a higher temperature of about 250 or 300 F., polymerize irreversibly.

Other vehicle characteristics can be utilized With slight modification of procedure. For example, a completely ythermoplastic vehicle can be used which, when warmed to about 200 F. flows quitefreely, thus providing the characteristics necessary for development by bubble amplication. Such a material need not have thermo-setting properties if it can be indurated by cooling it rather rapidly after development has taken place. Such reversibly controllable materials can be re-exposed and re-developed by proper sequences of heat and light application, but can 'oe rendered stable against the application of heat alone or light alone as might be encountered in subsequent use. Still another type of vehicle material can be cooled rapidly'enough after development to assume an irreversible structure or degree of hardness that rerquires the application of extremely high temperatures to plasticize it again, being in this respect somewhat analogous to the rst mentioned type.

For any'particular material, the optimum temperatures on either side of the transition points between relaxed and indurated conditions depend to some extent upon the technique of printing. The vehicle has to be chosen with regard to the relation between bubble gas pressure, rigidity, permeability, and to some extent also withregard to the record characteristics required, which may vary according to emphasis on line grain, density, or other properties.

Figs. 7 and 8 illustrate the above-described temperature determined rigidity characteristics, which are a principal expedient within the process according to the invention.

Fig. 7 relates to vehicle material of the gelatin or bakelite type, which exhibits upon increase in temperature three distinct regions of induration. The low temperature range marked Arepresents an indurated yet permeable phase which is mainly employed during exposure of the areas of the final record. is relaxed permitting bubble expansion or development. In range C, the Ivehicle indurates permanently and to a higher degree. This cycle is reversible so far as ranges A and B are concerned but irreversible from range C.'

It will appear hereinbelow that the invention can be carried out within the reversible transformations between A and B, without reaching C, although use of the latter con-l stitutes an important aspect of the invention.

In the case of gelatin vehicles, the function of range C is particularly assured through the tanning and hardening of the surface layer of gelatin, which acts somewhat as a barrier for the re-entrance or re-absorption of water. Such vehicles are as hard and stable mechanically as. ordinary photographic emulsion.

Fig. 8 illustrates another cycle which can be carried out with .thermoplastic vehicles which do not have a permanently indurated phase, but also with vehicles of the gelatin type if range C is not used.

Expedients other than heatcan be used alone or in cooperation with a temperature cycle.V Such an expedient is'moisture, especially for gelatinous vehicles. Another in range B the vehicle expedient isthe above mentioned optical fixation by way y of changing the light transmittingcharacteristic of the vehicle in range C. In the case of gelatin the tanning effect which vaccompanies the hardening induration can be utilized for this purpose. Y

The internal structurel of the vehicle is as important a characteristic as the ,rigidity itself. The ideal structure is a porous one, in which each little pore forms a completely lsealed cell Within which gas units can form during exposure.` These cells-should have negligible light-scattering properties, andhence bevery small in relation to the final bubble size. In the gelatin type vehicles, the small cells actually contain water, namely the water of emulsification of the gelatin. This water contains the sensitizer in` solution, whereas precipitated sensitizer formsk on the cell walls. It is within these small cells that the gas is released and collected during exposure. In other vehicle types the cells are formed by plastic walls and contain only such gas as is entrapped during the compounding of the vehicle.

The support can be of any suitable material, which will be transparent if the exposure takes place therethrough or the reproduction is intended to be a diapositive.` Glass, acetate film and'similar substances are satisfactory, provided they withstand the operational temperatures required. v

.Opaque supports will generally be fiexible such as paper or synthetic sheet material. These supports can be of any desirable color. Depending on the refiection characteristics of the backing or support, the diffusing bubble record will appear thereon lighter or darker; this must be taken into consideration in describing the photographic sign of the record as will be pointed out below.

Example I 100 g. of high grade dry gelatin such vas sold under the tradedesignation Kodak Peabody Gelatin is soaked for two hours in 1900 ml. distilled water of 30 C. To this is added 8 gjcitric acid C.P., and l0 g. of the sensitizing substance sold under the trade designation Edwal Compound #8, which is a zinc salt of para diazo dimethylaniline. This is then diluted to vmake 2000 ml. This emulsion is coated by conventional means on glass plates or cellulose film of the types used for purposes of commercial photography, to a thickness of about 2 mils to 0.6 mil., rather, less than more, depending on process control details and record requirements. This material, coated on a commercial cellulose film, is for example exposed 4to an original film in conventional contact or projection printing apparatus for copying microfilm, such as a blower cooled standard 35 mm. film projector modified.

for use as a contact printer with the film stage which consists of -two spring loaded glass rectangles, holding the original film to -be copied and the film to be exposed in a plane perpendicular to the optical axis.

The exposure time depends upon the output of the exposure flamp in the range of spectral sensitivity of the material (here within a band between about 3000 A. to 4200 A.), upon the density of the original, and upon the efiiciency-of thelight gathering system used. Exposure timesranging from one second to-several minutes have been successfully used for the above material.

The -gas is then allowed to diffuse for about 30 minutes 10 plied, in the manner described above for the developing procedure within the reversible ranges A, B of Figs. 7 and 8.`

Example II The record forming exposure should be of fairly high intensity in View of the facts that most sensitizing substances at disposal for present purposes are only moderately sensitive,and that prolonged exposures are not only undesirable from ythe point of view of shop or ofiice practice but might introduce temperature changes within the vehicle which cannot be easily controlled or prevented. It is possible to utilize an illumination source for heating the copying material, but the control of such heating complicates the printing setup. Short time high intensity exposure such as by way of arc lamps with efficient reectors, placed fairly close to the printing material, was

' found to be quite satisfactory, permitting exposure times or less, depending on ythe thickness of the vehicle layer;

5 minutes is the average for thin films. The lm is then relaxed by heating it for a few seconds to about 200 F., between two .metal plates which are electrically heated and'thermostatically controlled, or by infrared radiation. Thisy is a heating within the reversible range discussed above with reference to Figs. 7 and 8. An overall exposure is thenlapplied, of an intensity and duration which are about the same as required for the above exposure through the original.

1If it is desired to harden the vehicle irreversibly, in region C of Fig. 7, a temperature of about 250 F. is apof a few seconds which order of magnitude can be easily managed by comparatively unskilled operators. This is important since the prescribed exposure time is fairly closely tied to the properties of original and copying material and should be rather carefully adhered to.

Conventional contact or projection printing apparatus can be used for purposes of the invention. In an installation for copying microfilm, a blower cooled standard 35 mm. film projector has been modified for use as a contact printer. 'I'he projection lens can be used to observe the films during exposure. The condenser system efficiently collects the projector lamp light to channel a maximum proportion thereof through the film to be exposed, and to permit the use of smaller light sources. For other purposes, exposures have been made directly by General Electric AH-6 mercury are lights, by photoflood lamps,-and by projection lamps alone, in the film stage of microfilm readers. W

The rate of gas diffusion from -the exposed areasyof a particular vehicle sets an upper limit on the length f exposure. Underexposure results in lack of record, or in thin records of inadequate contrast. Overexposure rresults in fogging at the edges of records due to sensitizer decomposition or bubble expansion beyond the record contours. Unless the sensitive material is purposely exposed in relaxed condition, care must be taken not to have the film so close to the light source as to permit heat to cause relaxation and hence development during exposure. Forced cooling can be used. f

The emission spectrum of the source of radiation should be chosen with a view to the particularr sensitivity of the' sensitive substance. A preferred embodiment using Edwal #8 in gelatin asy above described, is sensitive to radiation within the wavelength band of 4200 A. down to 3000 A.; this permits the use of ordinary orange room light for handling.

Overall fixing and developing exposures such as will be described below are less critical. For most fixing purposes overexposure is harmless since complete exhaustion of sensitizing substance is desirable. Suitably diffused sources including daylight, are practical for this purpose. Overall reversal exposures are generally speaking similar to fixing exposures.

Rigiditycontrol of the vehicle for purposes of development aswell as fixation can becarried out in various ways as indicated above, mainly by application of heat or moisvrture orboth.

Temperature control is the principal expedient for adjusting rigidity according to the invention. It can be effected by way of convection such as treatment in an oven or air stream, or by conduction such as by way of heat controlled plates or baths, or by radiation such as infrared rays. Combinations of such temperature control methods are possible and in use.

One practical method of heat treatment is to place the material after exposure in range A (Figs. 7 and 8) between two metal plates which are electrically heated and thermostatically controlled within the range of 180 F. to 235 F. This has been a thoroughly satisfactory development method for gelatin type vehicles. A few seconds suflice for development in range B, and an additional to 2O seconds lead to range C and fixation through irreversible hardening of the vehicle.

For heating gelatin vehicles to range C, irradiation with infrared energy has also been found satisfactory. It' properly controlled, this induces fixation through irreversible hardening of the vehicle and optical screening.

A method frequently used for developing gelatin vehicles is to combine temperature and moisture control by passing exposed material rapidly through an atmosphere or jet of low pressure steam. The warmth of the steam cloud or low pressure jet, somewhat below 212 F; and thus within the desired temperature range B, together with the moisture serve to develop out the latent record. It will be understood that these conveniently adjustable temperature and moisture controls are materially dependent upon 4initial and thereafter unchangeable selection of other factors, such as thickness and inherent porosity and plasticity properties of the vehicle material.

'Ihe relaxation time required for development is generally not ver] critical; between 2 and 5 seconds suce in most instances for satisfactory development. For ixation there is no particular time limit.

Several methods for fixation of vehicle and record are practical and will now be described. As will become apparent from the practical examples, they can be used individuallyor combined, according to circumstances.

Application of hea-t for changing from relaxed condition in range B to indurated condition in range C or A (Figs. 7 and 8) is the principal fixation expedient. This change from relaxed developing to indurated nondeveloping condition involves mainly controlled and fairly rapid application of heat or quick cooling. The expedients used for changing from range A to B can be used such las hot plates, -air blast devices and heat radiators, and temperature control is -accomplished with conventional thermostats. In the case of gelatin vehicles, satisfactory xation is accomplished by keeping the material between controlled temperature hot plates, beyond the required development time. A time of 5 to 20 seconds, depending on the temperature gradient, has been found to be adequate, leading to a great degree of permanence. Another technique is `application of infrared light continued beyond the required development time.

Gasdilusion is another important fixation expedient. After development, the entire film surface can be exposed to light of intensitysufcient to cause pho-tolysis. if the vehicle is then not placed again in development condition the released gas does not form bubbles but diffuses out of the film. Sutiicient fixation exposure to destroy all photosensi-tive material not originally imaged exposed and developed has been `achieved in times generally about the same as required for exposure of the record proper. After such exposure, the diffusion process requires from 2 minutes to 30 minutes, the time depending on the thickness ofthe vehicle layer.

Because yof the availability of the diffusion method of fixation, it is not always necessary to introduce lixation as a definite step in theV process. The developed mate-rial if put to routine use is in some cases necessarily exposed to suicient light to complete photolysis in the previously unexposed areas. Thereafter, in ordinary storage, the released gas diffuses out and leaves the non-record areas clear and incapable of further change. It will however be understood that fixation according to the invention is in many cases an important and indispensable step.

Four different practical embodiments, some of them with optional variations will now be described by way of example. Since the underlying theoretical considerations and the procedural details which are selectively used in these examples `are su'ciently described above, they will not now be repeated, unless specic circumstances call for one or the other detailed directions.

Due to the adaptability of the present system, it is very Y easy, by way of minor procedural changes, to make copies of the same as well as opposite photographic sign. As herein understood, the term photographic sign describes the general gradation relation of original and copyV so that any reference herein to printing with the same sign means making a positive from a positive as well as a negative from a negative, and printing with opposite sign means the making of negatives from positives as well as of positives from negatives, the term positive and negative being used in a relative sense to express mutually complementary record patterns, independently of the character of the support which lfor this purpose is assumed to be transparent.

The `adaptability of the present system is similary advantageous with regard to the fixation procedure which can be easily modified for any practical purpose.

In Figs. 9 -to 12, only the coatings C are mainly shown, for the sake of simplicity. The various phases undergone by Ithe sensitizer are indicated in the same manner as in Figs. 1 to 6. The three vehicle conditions are indicated by single, double 4and triple contours, corresponding to temperature ranges A, B and C respectively.

Fig. 9 shows at a9 an ioriginal O directly superimposed upon a film F which consists of a coating C and a support S. The coating C comprises a vehicle v and a sensitizing substance indicated by dots m. The original O can for example be a microlm and the two elements O and F can be exposed in the above-mentioned modified projector. Assuming that the coating is of the type described `above in material Example I, the vehicle is at room temperature and hence in indurated condition corresponding to range A of Fig. 7. Upon exposure the original O irnpresses its record upon the beam L of collimated light, establishing a radiation image in terms of sources s. As indicated at b9, this exposure produces a record pattern composed of units u.

At C9, the vehicle is then relaxed as above described with reference to Fig. 7, by raising the temperature into range B. This induces expansion of the gas units u into gas bubbles b. The coating C now contains a record, corresponding yto the original O, in terms of visible bubbles containing gas, and unexposed sensitizer mc. In order to xate the record, various techniques can be ernployed in accordance with the invention,.as discussed Iabove. Three optional xing procedures will now be explained.

As indicated a-t d9, the coating C can be brought into indurated condition by cooling it to region A which will inhibit expansion of the gas units ud. A uniform exposure is applied and the gas developed during such exposure allowed to diffuse through the vehicle which, it will be remembered, is still permeable. The record defining bubbles b solely remain as shown at e9 of Fig. 9.

An alternative uses the possibility of hardening the vehicle in temperature region C, as indicated a-t i9 of Fig. 9. This arrests with safety any further expansion and it is in this case unnecessary to make certain whether or not an overall ixing exposure is applied and the gas permitted to diffuse.

A further alternative is shown at g9. In this instance the vehicle is rendered opaque for actinic light as indicated by cross hatching of the diagrammatical showing of layer C. As mentioned above, this technique of imparting an optical filter action to the vehicle can be connected with the tanning in accordance wih f9 in which case xation is even more safe, although it will be understood that either procedure f or g is sufficient, and that the respective steps can be separately applied by means which are expedient in any particular environment.

This modification results in a record of opposite photographic sign from that of the original.

As indicated in Fig. 10, the iirst two steps n10 and blO are in this instance identical with steps a9 and b9 of Fig. 9. However, `Where-as according to Fig. 9 the vehicle is relaxed immediately after exposure in indurated condition, the gas is here given suflicient time to diffuse from the Vehicle, as indicated at C10. A negative record in terms of sensitizing substance mc remains. At d10 this is now given an overall exposure that converts the sensitizer molecules into gas units ud. The vehicle is thereupon relaxed, permitting the gas units to expand and form bubbles be as shown at e10. It will be noted that in this instance iixation is unnecessary so far as remaining sensitizer is concerned, but for mechanical reasons another induration can be applied as indicated at f10.

This technique produces a inal record of the same sign as the original.

In the example according to Fig. 11, the iirst two steps are similar to a9 and b9 of Fig. 9, namely exposure and gas unit formation at approximate room temperature. The step cll is similar to step C10, namely the diiusion of the exposed portions, resulting in a negative record in terms of sensitizer molecules mc. The vehicle is thereupon relaxed and an overall exposure applied which results in a negative record in terms of bubbles shown at bd. The vehicle is then indurated or hardened in temperature region A or C, which results in the permanent record indicated at ell. It will be noted that this is the technique according to Example I.

The record ell is of the same photographic sign as the original.

As indicated at a12 of Fig. 12, the vehicle is in this instance in relaxed condition during exposure. As indicated at b12, the irradiated sensitizer molecules immediately expand to form bubbles bb, Whereas in the unexposed portie-ns the sensitizer m is not aiected. As indicated at cl2, an overall exposure is then applied after the Vehicle has been indurated. This preserves the record in terms of gas bubbles whereas the remainder consists of units. This record can then be iixed in any one of the ways described above with reference to Pig. 9. Fig. l2 indicates a preferred embodiment according to which the gas is permitted to diiuse from condition 14 C12, `which provides an indurated vehicle record in terms of empty gas bubbles bf.

The record according to this modification is of opposite sign to the original.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents whichV fall within the scope of the appended claim.

We claim:

A method for producing essentially stable photographic records in terms of substantially purely textural changes of a vehicle whose rigidity varies reversibly within a given temperature range and which contains dispersed therein a .photolytic compound capable of liberating gas upon irradiation which gas does not eiect said textural changes at a low temperature Within said range but eiects such changes at a vehicle relaxing temperature that is comparatively high within said range,

comprising the steps of exposing said vehicle to record defining irradiation in comparatively rigid condition at a temperature that is comparatively low within said range, diffusing said gas as liberated from the unchanged vehicle at said low temperature, and subjecting said vehicle to said high relaxing temperature with application of essentially uniform irradiation, whereby gas is liberated from the previously less irradiated vehicle portions effecting development of said record defining textural changes, thephotolytic compound is essentially eliminated, and the record essentially iixed.

References Cited in the iile of this patent UNITED STATES PATENTS 1,571,103 Sury Jan. 26, 1926 1,594,470 Schwarz Aug. 3, 1926 1,919,194 Bennett July 25, 1933 1,942,872 Murray Jan. 9, 1934 1,944,293 Martinez Jan. 23, 1934 1,952,787 Bennett Mar.` 27, 1934 1,954,325 Martinez Apr. 10, 1934 1,990,925 Bennett Feb. l2, 1935 2,018,657 Bennett Oct. 29, 1935 2,699,392 Herrick et al. Ian. 11, 1955 2,703,756 Herrick et al. Mar. 8, 1955 FOREIGN PATENTS 402,737 Great Britain Mar. 4, 1932 898,391 France July 3, 1944 645,825 Great Britain Nov. 8, 1950

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U.S. Classification430/152, 430/290
International ClassificationG03C5/60
Cooperative ClassificationG03C5/60
European ClassificationG03C5/60