US 3844780 A
An imaging method wherein an imaging member comprising an imaging layer, structurally fracturable in response to the combined effects of electromagnetic radiation to which it is sensitive and applied electric field sandwiched between a donor sheet and a receiver sheet is subjected to a first electric field. Such field is then modified as by reducing, grounding or reversing the field. After such modification the first field is substantially restored across the imaging layer prior to imagewise exposure of the imaging layer to electromagnetic radiation to which it is sensitive. The imaging layer is then exposed to appropriate electromagnetic radiation and the sandwich separated whereupon the imaging layer fractures in imagewise configuration providing a positive image on one of the donor and receiver sheets and a negative image on the other sheet.
Description (OCR text may contain errors)
United States Patent [191 Nelson et al.
[451 Oct. 29, 1974 IMAGING PROCESS  Assignee: Xerox Corporation, Stamford,
22 Filed: Nov.,28, 1972 211 App]. No.: 310,041
Primary ExaminerR0nald H. Smith Assistant Examiner-John L. Goodrow [5 7] ABSTRACT An imaging method wherein an imaging member comprising an imaging layer, structurally fracturable in response to the combined effects of electromagnetic radiation to which it is sensitive and applied electric field sandwiched between a donor sheet and a receiver sheet is subjected to a first electric field. Such field is then modified as by reducing, grounding or reversing the field. After such modification the first field is substantially restored across the imaging layer prior to imagewise exposure of the imaging layer to electromagnetic radiation to which it is sensitive. The imaging layer is then exposed to appropriate electromagnetic radiation and the sandwich separated whereupon the imaging layer fractures in imagewise configuration providing a positive image on one of the donor and receiver sheets and a negative image on the other sheet.
13 Claims, 4 Drawing Figures ACTIVATE MODIFY FIELD EXPOSE SEPARATE IMAGING PROCESS BACKGROUND OF THE INVENTION This invention relates in general to imaging and more particularly to layer transfer imaging and improvements therein.
The manifold imaging system has been known as an imaging technique based upon the transfer of an imaging layer comprising a cohesively weak or structurally fracturable electrically photosensitive material sandwiched between a pair of sheets. Under the influence of electromagnetic radiation to which the imaging layer is sensitive and an applied electric field, the imaging layer fractures in imagewise configuration when the sandwich is separated under an electrical field. In the most common embodiment of this imaging technique, a layer of electrically photosensitive imaging material is provided residing on a substrate. This substrate is commonly called a donor. In one form the imaging layer comprises photosensitive material such as metalfree phthalocyanine dispersed in a binder. An electrical field is applied across this imaging layer and the imaging layer is exposed to a pattern of light and shadow representative of the image to be reproduced. With a receiver sheet in place over the imaging layer and the electrical field extending across the sandwich, the donor and receiver sheets are separated whereupon the imaging layer fractures along the lines defined by the pattern of light and shadow to which the imaging layer has been exposed. Part of the imaging layer is transferred to one of the sheets while the remainder is retained on the other sheet so that a positive image, that is, a duplicate of the original, is produced on one sheet while a negative image is produced on the other. A more complete explanation of such an imaging process is contained in copending U.S. application Ser. No. 708,380 filed Feb. 26, 1968 in the U.S. Patent Office now U.S. Pat. No. 3,707,368 hereby incorporated by reference.
The above described manifold imaging process is known as a high gamma system, that is, one in which the slope of the density versus the log of the exposure curve is very large in that portion of the curve where the imaging layer responds. Another way of characterizing the system is that it is essentially a go or no-go system, so that the imaging layer either adheres to the donor substrate or transfers to the receiver sheet. These properties rendered the imaging method highly useful, many purposes such as in the manufacture of printing plates or resist patterns for printed circuits, etc.
Of course the electric field has been employed in all cases of manifold imaging. In the past, the location of the positive and negative images on the donor and receiver sheets was desirably controlled by the operator of the process. An example of such investigation is described in U.S. Pat. No. 3,655,372 to Krohn et al. wherein this result was achieved by modifying the electric field across the imaging layer subsequent to imagewise exposure of the imaging layer. The result achieved by such modification is the reversal of the image sense obtained upon separation of the manifold sandwich. That is, the positive image and negative image would reside upon the substrate opposite that it would have otherwise resided had the field not been modified. Thus, if a particular imaging layer nonnally provided a positive image residing on the donor sheet and one desired to have such imaging layer provide a positive image on the receiver sheet the use of field modification subsequent to the exposure step produced the desired positive image on the receiver layer while the negative image would reside on the donor layer.
In another instance of research on the manifold imaging process there was seen a need for improved quality of images when such images were produced from an imaging layer exposed through the receiver sheets or from an imaging layer which has been subjected to the image reversal process as described above. The investigation to improve the quality of such images resulted in the discovery that improved images in such processes were obtained when the electrical field across the imaging layer was reversed prior to the exposure step. This process is more fully described in copending application Ser. No. 829,963 filed June 3, l969 now U.S. Pat. No. 3,718,462.
In both of the above instances the results obtained, whether in the nature of a reversed image sense or improved image quality, did not change the fundamental nature of the manifoldimaging process as mentioned above. That is the imaging process produced high gamma images and was generally known as a go, no-go layer transfer imaging process.
There is now a desire to have the convenience of a layer transfer imaging process while at the same time providing low gamma, low contrast images. Such a process would have a wider application particularly if the contrast density or gamma of the image could be selectively controlled by imaging process conditions. Accordingly there is desired a method whereby the manifold layer transfer imaging process can provide images of greater density variation and increased resolution.
SUMMARY OF THE INVENTION It is, therefore an object of this invention to provide a layer transfer imaging method overcoming the above noted deficiencies. 1
Another object of this invention is to provide a layer transfer imaging method which allows the operator to determine the image contrast.
Another object of this invention is to provide a layer transfer imaging method providing images of improved resolution.
In accordance with this invention images can be pro duced by the manifold layer transfer imaging process having lower contrast and more density variation by means of oscillating the electric field across the imaging layer prior to exposing the imaging layer to actinic electromagnetic radiation. More particularly the imaging layer of the manifold imaging process is subjected to a first electric field as in the usual case for exposure purposes and then modified as by reversing, grounding or reducing the field to an extent further defined below. Subsequent to such alteration the field is then substantially restored and is maintained at a value considered suitable for exposure purposes as previously known in the art for such imaging layer. That is, while the restored field need not be of the same magnitude as the first field it is one which provides imaging conditions and preferably is slightly higher in potential than the first field. The restored field is sufficient to provide selective adhesion of the imaging layer to the donor and receiver sheets in accordance with the pattern of light and shadow to which it is exposed under said field.
DETAILED DESCRIPTION OF THE INVENTION The manifold layer transfer imaging process is practiced in accordance with this invention by inserting field oscillation into the process at any point prior to exposure of the imaging layer to suitable electromagnetic radiation. Basically the field manipulation involves first raising the potential across the imaging layer to provide a first electrical'field. The field is then modified by reversing, grounding or reducing it. Finally the field is again altered or modified by raising the potential across the imaging layer typically to the extent of substantially restoring the original or first electric field across the imaging layer. Of course the actual values of field strength are dependent upon the nature of the imaging layer and the donor and receiver layers residing in the electrical field.
The strength of the electrical potential applied initially in the first electrical field across the imaging layer depends as stated on the structure of the manifold sandwich or set and the materials employed therein. The potential strength required may however be easily determined. If too large a potential is applied electrical breakdown of the manifold sandwich will occur allowing arcing between the electrodes. If too little potential is applied the imaging layer will not fracture in imagewise configuration should be imaging layer be exposed to suitable electromagnetic radiation at that time and sandwich opened. The preferred potential across the manifold sandwich is, however, in the range of from about 2,000 volts per mil. to about 7,000 volts per mil. of insulating material in the field. Since relatively high potentials are utilized it is desirable to insert a resistor in the circuit to limit the flow of current. Resistors on the order of from about 1 megohm to about 20,000 megohms are conveniently employed. While the potential across the imaging layer is not varied during the exposure step of the imaging process, alternating current can be employed prior to such exposure step. Thus direct current or alternating current can be employed prior to the imagewise exposure step of the process. Direct current is preferred due to the relatively high potential employed and appropriate circuitry for alternating current would be necessary if the operator of the process desired to employ this type of electrical power source.
Another embodiment of this invention includes both types of electrical fields. That is one may oscillate the field across the imaging layer by subjecting the layer to a field of alternating current. After such treatment, the imaging layer is then subjected to direct current of imaging intensity and the process completed as described below. For example, high voltage 60 cycle AC current of about 3,000 volts, per mil. of insulating material in the field is applied across the imaging layer for about 1 second. The field is discontinued and a DC field of about the same strength is applied while the imaging layer is exposed to actinic radiation and the manifold sandwich subsequently separated. In this embodiment a transformer is preferably employed with the AC field to provide an output to the electrodes of high voltage and low current.
The extent to which the potential must be reduced to achieve effective field modification across the imaging layer varies greatly and is dependent upon the original potential across the manifold set V,,, the original potential across the imaging layer V the dielectric constant of the receiver sheet K that of the donor sheet K that of the imaging layer K and the thickness of the donor sheet (d,,, the receiver sheet d and the imaging layer d The maximum reduced potential V can be calculated for any particular manifold set by the formula! VR 0 J 'H L/ L) D/ D R/ RH In most instances reduction of the potential to a value below about one-half to about one-third of the original potential is sufficient to achieve the desired results in the process of this invention. Of course the manipulations required for reversing or grounding the first electrical field are well known to those skilled in the art.
Subsequent to the alteration of the first electrical field across the imaging layer as described above the altered or modified field is then again modified so as to restore the electrostatic charges initially induced into the imaging layer by the first electrical field. This is easily accomplished by subjecting the imaging layer to a second electric field of the same polarity and typically of substantially the same potential as first employed, As mentioned above potentials slightly higher than that first employed is preferred in most instances.
Subsequent to the field alteration step the imaging layer is exposed to electromagnetic radiation to which it is sensitive. The usual procedures and materials employed in the manifold imaging art are practiced in concert with the field alteration step employed in accordance with this invention. Thus the electrical field is applied by the usual means as is known in the art. The electrically photosensitive materials are well known and need no special treatment for use in the process of this invention. Organic electrically photosensitive materials are preferred because of their color and availability although inorganic materials can be employed. The x-form phthalocyanine is preferred because of its excellent photosensitivity although any suitable form of phthalocyanine can be employed.
The binder material in the heterogenous imaging layer may be any material which are or can be rendered cohesively weak by the conventional activators. Of course, the binder material is coordinated with the activator so as to produce the frangible or structurally fracturable condition required of the imaging layer. Typical binders such as the microcrystalline waxes, polyethylenes, polystyrenes and modified polystyrenes, styrenevinyltoluene copolymers and polyproylenes are suitable as mixtures thereof. Examples of the above are paraffin waxes such as Sunoco 5512 from the Sun Oil Company; microcrystalline waxes such as Paraflint R. G. from the Moore and Munger Company; polyethylenes such as Union Carbides DYJT, DYLT and DYDT; modified styrenes such as Pennsylvania Industrial Chemicals Piccotex 75, and I20 and resins such as E. I. DuPont de Nemours and Co. Inc. Elvax resins 210, 310 and 420.
A typical preferred activator is Odorless Solvent 3440, an aliphatic (kerosene) hydrocarbon fraction available from The Standard Oil Co., and others include petroleum ether, halogenated hydrocarbons such as chloroform, methylene chloride, trichloroethylene, perchloro-ethylene; ethers such as diethyl ether and diisopropyl ether.
Other suitable materials useful in the manifold imaging process of this invention including donor and receiver sheets, electrically photosensitive materials, binders and activators are found in copending application Ser. No. 708,380 filed Feb. 26, 1968 now US. Pat.
No. 3,707,368 all of which is incorporated herein by reference. A particularly preferred method of activating and preferred activators are thermosolvents as described in US. Pat. No. 3,598,581 to Reinis also incorporated herein by reference. In one embodiment of this invention, the thermosolvent, preferably a low-melting wax is first saturated with a reactive hydrocarbon described in copending application Ser. No. 301,563 filed Oct. 27, 1972, said copending application being hereby incorporated herein by reference, and then coated on the imaging layer. For storage purposes the manifold sandwich is kept sealed so as to prevent the premature oxidation of the reactive hydrocarbon.
BRIEF DESCRIPTION OF THE DRAWINGS The advantages of this improved method of imaging will become apparent upon consideration of the detailed disclosure of the invention especially when taken in conjunction with the accompanying drawings wherein:
FIG. I is a side sectional view of a photosensitive imaging manifold set for use in the invention.
FIG. 2 is a process flow diagram of the method steps of the invention.
FIGS. 2A and 2B are side sectional views diagrammatically illustrating the process steps of the invention.
DETAILED DESCRIPTION OF THE DRAWINGS Referring now to FIG. 1 of the drawings, there is seen a supporting donor substrate layer 11 and an imaging layer generally designated 12. In the manufacture of the imaging member, herein referred to as the manifold set, layer 12 is preferably coated on substrate 11 so that it adheres thereto. These layers are collectively referred to as the imaging donor or merely the donor. In this particular illustrative example, layer 12 consists of photoconductive pigment I3 dispersed in a binder 14. Above imaging layer 12 is receiver sheet 16. Sheets 11 and 16 are preferably electrically insulating although either may be conductive. Insulating donor and receiver sheets are preferred because higher fields may be employed and because they allow the use of convenient high strength materials as final image substrates.
Receiver sheet 16 is a separate layer which does not initially adhere to layer 12. Accordingly, although the whole imaging member or manifold set" may be supplied in a convenient three-layer sandwich as shown in FIG. 1, receiver sheet 16 may also be supplied as a separate sheet or roll if desired. On the other hand, in those systems where activation of the imaging layer is not required or where imaging layer 12 has been preactivated, sheet 16 may rest on imaging layer 12. In the particular embodiment of the manifold set shown in FIG. 1, receiver sheet 16 is made up of an electrically conductive material such as cellophane with at least one of them being optically transparent to provide for the exposure of layer 12. In this embodiment of the manifold set, sheet 16 acts as one of the electrodes.
Combinations of the structure described in FIG. 1 may also be used in carrying out the invention with a relatively conductive layer immediately in contact with one side of imaging layer 12 and an electrically insulating sheet on the other side of the imaging layer.
Referring now to the flow diagram of FIG. 2, it is seen that, when required, the activation step is typically the first step in the imaging process. In this stage of the imaging process, the manifold set is opened and the activator is applied to imaging layer 12 following which these layers are closed back together again, as indicated in the second block of the process flow diagram of FIG. 2. Although the activator may be applied by any suitable technique, such as with a brush, with a smooth or rough surfaced roller, by flow coating, by vapor condensation or the like, FIG. 2A which diagrammatically illustrates the first two process steps shows the activator fluid 23 being sprayed on to imaging layer 12 of the manifold set from a container 24. The activator serves to swell or otherwise weaken and thereby lower the cohesive strength of imaging layer 12. The activator should preferably have a high level of resistivity to help prevent electrical breakdown of the manifold set.
It is generally preferable to include an activation step in the imaging process because if this step is included, then a stronger and more permanent imaging layer 12 may be provided which can withstand storage and transportation prior to imaging.
Following the deposition of the activator fluid, the set is closed by a roller 26 which also serves to squeeze out any excess activator fluid which may have been deposited.
Although it is preferred to use a separate electrode, sheet 16 in FIG. 2A and FIG. 2B is shown as a conductive receiver sheet which also acts as an electrode.
Potential source 28 is connected to switch 31, to resistor 30, receiver sheet 16 and transparent conductive electrode 18. A first electrical field is applied across the manifold set and it is exposed to the image 29 to be reproduced. Prior to imagewise exposure the first electric field is modified by changing switch 31 from position A to position B. Modifications may also be achieved by lowering the voltage or grounding the circuit. Subsequent to such modification the original or first electric field is restored by changing switch 31 from position B back to position A. Of course the final field applied need not be exactly the same potential as the first field and is preferably slightly greater. After switch 31 is moved from position B to position A the imaging layer is exposed to an imagewise pattern of electromagnetic radiation to which it is sensitive as indicated to light rays 29. Light rays 29 are drawn to show a variation in density from the original image by varying the length of the arrows. The length is intended to relate to the intensity of light directly. Thus the longer arrows indicate the higher intensity while the shorter arrows indicate the lower intensity. After exposure and upon separation of substrate 17 and receiver sheet 16, imaging layer 12 fractures along the edges of exposed areas. Accordingly, once separation is complete, exposed portions of imaging layer 12 adhere to on one of layer 17 and 16 while unexposed portions are retained on the other layer, resulting in the simultaneous formation of a positive image on one of the sheets and a negative on the other.
Although FIG. 2B shows a negative image being formed on the surface of substrate 16 and a positive image on sheet 17, the positions of these images may be reversed depending on the initial polarity of the applied field and the photoconductive materials used. Further, although layer 12 is shown as being exposed from the donor side, the layer may also be exposed from the receiver side. As can be seen in FIG. 2B, the
imaging layer fractures and adheres to the respective sheets in accordance with the amount of exposure received. The amount of light is indicated by the length of arrows 29. That is, the length is proportional to the amount of incident energy on the imaging layer. The field oscillation has enabled the imaging layer to fracture in two dimensions to provide a-continuous tone image. I
If a relatively volatile activator is employed, such as petroleum ether or carbon tetrachloride, fixing occurs almost instantaneously after separation of layers 17 and 16 because the relatively small quantity of activator in the layer of imaging material flashed off very rapidly. With somewhat less volatile activators, such as the Sohio Odorless Solvent 3440' or Freon 214, described above, fixing may be accelerated by flowing air over the images or warming them to about 150F., whereas with the even less volatile activators, such as transformer oil, fixing is accomplished by absorption of the activator into another layer such as a paper substrate to which the image is transferred. Many other fixing techniques and methods for protecting the images such as overcoating, laminating with a transparent thermoplastic sheet and the like will occur to'those skilled in the art. Increased image durability and hardness may also be achieved by treatment with an image material hardening agent or with a hard polymer solution which will wet the image material.
In general, the apparatus for carrying out the imaging procedure described above will employ the elements illustrated in FIGS. 2A and 28 including a source of activator fluid, a squeegee roller to remove excess activator fluid, a power supply with series resistor, a switch and a set of electrodes which may or may not be built into the manifold set. Opening the manifold set for activation, closing the set for exposure and opening again for separation and image formation may be accomplished by any one of a number of techniques which will be obvious to those skilled in the art. However, one straight-forward way to accomplish this result is to supply the imaging materials in the form of long webs which can be entrained over rollers so as to provide opening and closing of the set during the imaging process.
DESCRIPTION OF THE EMBODIMENTS The following examples further specifically illustrate the present invention. The examples below are intended to illustrate various preferred embodiments of the improved imaging method. The parts and percentages are by weight unless otherwise indicated.
EXAMPLE I PRIOR ART alpha phthalocyanine is then salt milled for 6 days and desalted by slurrying in distilled water, vacuum filtering, water washing, and finally methanol washing until the initial filtrate is clear. After vacuum drying to remove residual methanol the X form phthalocyanine thus produced is used to prepare the imaging layer ac- .cording to the following procedure: About 5 grams of the X form phthalocyanine is added to about 5 grams of Algol Yellow GC, l,2,5,6-di-(C,C'-diphenyl) thiazo leanthraquinone, C. I. No. 67300, available from General Dyestuffs, and about 2.8 grams of purified Watchung Red B, l-(4'-methyl-5-chloroazobenzene-2'- sulfonic acid)-2-hydroxy-3-naphthoic acid, C. I. No. l5865, available from E. I. DuPont de Nemours & Co. which is purified as follows: Approximately 240 grams of the Watchung Red B is slurried in about 2400 milliliters of Sohio Odorless Solvent 3440. The slurry is then heated to a temperature of about 65C. and held there for about one-half hour. The slurry is then filtered through a glass sintered filter. The solids are then reslurried with petroleum ether to C.) available from Matheson, Coleman and Bell Division of the Matheson Company, East Rutherford, NJ. and filtered through a glass sintered filter. The solids are then dried in an oven at about 50C. 7
About eight grams of Sunoco Microcrystalline Wax Grade 5825 having an ASTM-D-l27 melting point of 151F. and about two grams Paraflint R. G., a low molecular weight paraffinic material, available from the Moore and Munger Company, New York City and about 320 milliliters of petroleum ether (90 to 120C.) and about 40 milliliters of Sohio Odorless Solvent 3440 are placed with the pigments in a glass jar containing V2 inch flint pebbles. The mixture is then milled by revolving the glass jar at about 70 r.p.m. for about 16 hours. The mixture is then heated for approximately two hours at about 45C. and allowed to cool to room temperature. The mixture is then ready for coating on the donor substrate. The paste-like mixture is then coated in subdued green light on l mil Mylar (a polyester formed by the condensation reaction between ethylene glycol and tetphthalic acid available from E. I. Du- Pont de Nemours & Co., Inc.) with a No. 36 wire wound drawdown rod to produce a coating thickness when dried of approximately 7% microns. The coating and l mil Mylar sheet is then dried in the dark at a temperature of about 33C. for one-half hour. A receiver sheet of aluminum foil is placed over the donor. The receiver sheet is lifted .up and the imaging layer activated by the application of Sohio Odorless Solvent 3440 with a wide camels hair brush saturated with the liquids. The receiver sheet is then lowered back down and a roller is rolled slowly over the closed manifold sandwich with light pressure to remove excess solvent. The manifold sandwich is placed donor side down on the tin oxide surface of a NESA glass plate and a black paper electrode is placed over the receiver. The electrodes are connected to a 6,000 volt DC. power supply in series with a 5,500 megohm resistor with the NESA glass electrode being the positive electrode and the black opaque electrode being the negative electrode. With the voltage applied, a white incandescent light image is projected upward through the NESA glass with an illumination of approximately 1 foot-candle applied for five seconds for a total incident energy of about 1.5 foot-candle seconds. After exposure, the receiver sheet together with the opaque electrode is peeled from the 'set with the potential source still connected. Upon separation the imaging layer fractures in imagewise configuration yielding a pair of images with a duplicate of the original on the donor sheet and a reversal or negative image on the receiver sheet.
EXAMPLE ll The procedure of Example I is repeated with the exception that subsequent to the application of the 6,000 volt D.C. field across the imaging layer and prior to exposing the imaging layer the leads on the power supply are reversed making the NESA glass electrode negative and black paper electrode positive. After application of the reversed field for approximately l seconds the leads on the power supply are again reversed making the NESA electrode positive and the opaque electrode negative. The voltage on the final field is raised to 7,000 volts. With the elevated voltage applied a white incandescent light image is projected as in Example 1. After exposure the receiver sheet together with the black electrode is peeled from the set with the potential source still connected. Upon separation, the imaging layer fractures in imagewise configuration yielding a pair of images having decreased gamma from those obtained in Example I to the extent of about two additional steps in a 2 step wedge.
EXAMPLE lll PRIOR ART An imaging layer comprising electrically photosensitive material dispersed in a binder is first prepared. About 100 parts of Naphthol Red B which is l-(2'- methoxy-5 '-nitro-phenzlao )-2-hydroxy-3 "-nitro-3- naphthanilide, C. I. No. 12355 is dissolved in reagent grade ethylenediamine. The solution is filtered immediately through coarse filter paper, and the filtrate mixed with an equal volume of reagent grade isopropanol. The Naphthol Red B precipitates in the alcohol and is removed by means of a centrifuge. After separating the ethylenediamine and alcohol, the electrically photosensitive material is washed and filtered with successive amounts of isopropanol, a 2:l volume mixture of isopropanol and deionized water and five washings with deionized water until the filtrate is neutral. Finally, the material is washed with dimethylformamide and methanol in succession until the filtrates have a pale yellow color. The Naphthol Red B is then dried at 40C. under vacuum.
A binder material is prepared by combining about 1.5 parts of Paraflint RG, a low molecular weight paraffinic material available from the Moore & Munger Co., about 3 parts of polyethylene DYLT available from Union Carbide Corp.; about 0.5 parts of a vinylacetateethylene copolymer available as Elvax 420 from E. l. DuPont de Nemours Inc., and about 2.5 parts of a modified polystyrene available as Piccotex 100 from Pennsylvania Industrial Chemical Company with about parts of Sohio Odorless Solvent 3440. The mixture is heated until all is dissolved and then cooled. About 45 parts of isopropyl alcohol is added and the mixture is milled in a ball mill for 15 minutes together with about 2.5 parts of Naphthol Red B. The resulting imaging material is then coated on a 1 mil Mylar sheet with a doctor blade set at a gap of 4.4 mils to produce a donor. The donor is dried at a temperature of about 90C. After drying the imaging layer, it is activated with Sohio Odorless Solvent 3440 and incorporated into a manifold sandwich by placing a 1 mil Mylar receiver sheet over the imaging layer. Employing electrodes as in Example I and with 8,000 volts applied across the imaging layer it is exposed to a pattern of white incandescent light as in Example 1. Upon separation of the sandwich there is produced a pair of high gamma red colored images.
EXAMPLE IV The procedure of Example Ill is repeated with the exception that subsequent to the application of the 5,000 volt electrical field across the manifold set and prior to the exposure of the imaging layer the leads of the power supply are reversed making the NESA electrode negative and the paper electrode positive. After about 2 seconds with the voltage set at 5,000 volts the leads are again reversed making the NESA electrode positive and the paper electrode negative. Upon reestablishing the original field the receiver along with the electrode over it is separated from the donor providing an image having decreased gamma and improved resolution.
EXAMPLE V The procedure of Example I is repeated with the exception that after establishing the initial field across the imaging layer the voltage is reduced to 2,000 volts for about 5 seconds and then raised to about 7,000 volts. Upon separation of the donor and receiver layers imaging layer fractures providing a pair of low gamma images having an increased number of density steps than that obtained from the procedure of Example I.
EXAMPLE VI The procedure of Example IV is repeated with the exception that subsequent to establishing the initial electrical field across the manifold set the field is grounded and then reestablished prior to the exposure of the imaging layer. Results similar to that obtained in Example [V are found upon separation of the donor and receiver layers.
Although specific components and proportions have been stated in the above description of preferred embodiments of the invention, other typical materials as listed above, if suitable, may be used with similar results. In addition, other materials may be added to the mixture to synergize, enhance, or otherwise modify the properties of the imaging layer. For example, various dyes, spectral sensitizers or electrical sensitizers such as Lewis acids may be added to the several layers.
Other modifications and ramifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of the invention.
What is claimed is:
l. A method of imaging comprising;
a. providing a manifold set comprising an electrically photosensitive imaging layer sandwiched between the donor sheet and a receiver sheet said layer being structurally fracturable in response to the combined effect of an applied electrical field and exposure to electromagnetic radiation to which said layer is sensitive;
b. subjecting said imaging layer to a first electrical field;
c. modifying said first electrical field wherein said modification involves reversing the potential across said manifold set;
d. subsequent to said modification, substantially restoring said first electrical field across said manifold set;
e. while said imaging layer is subjected to said restored electrical field exposing said imaging layer 1 l to a pattern of actinic electromagnetic radiation, and;
f. separating said receiver sheet from said donor sheet whereby said imaging layer fractures in imagewise configuration forming a positive image on one of the donor and receiver sheets and a negative image on the other said sheet.
2. The method of claim 1 wherein said first electrical field is in the range of from about 2,000 volts per mil to about 7,000 volts per mil.
3. The method of claim 1 wherein said electrically photosensitive material is an organic material.
4. The method of claim 3 wherein said organic material comprises metal-free phthalocyanine.
5. The method of claim 3 wherein said organic electrically photosensitive material is dispersed in an insulating binder.
6. The method of claim 1 wherein the electrically photosensitive imaging layer is initially nonfracturable in response to the combined effects of an applied field and exposure to actinic electromagnetic radiation and further including the step of activating said imaging layer by applying thereto an activating amount of an activator.
7. The method of claim 6 wherein said activator is a thermo solvent.
8. The method of claim 6 wherein the activator is selected from the group consisting of partial solvents, solvents, swelling agent and softening agents for said imaging layer.
9. An imaging method comprising;
a. providing a manifold set comprising an electrically photosensitive imaging layer sandwiched between a donor sheet and a receiver sheet, said layer being structurally fracturable in response to the combined effects of an applied electrical field and exposure to actinic electromagnetic radiation to which the layer is sensitive;
b. subjecting said imaging layer to an electrical field througha power source providing alternating current;
c. terminating said field and applying a second electrical field provided by a power source providing direct current;
d. exposing said imaging layer to actinic electromagnetic radiation while said imaging layer is subjected to said second electrical field;
e. separating said receiver sheet from said donor sheet whereby said imaging layer fractures in imagewise configuration forming a positive image on one of said donor and receiver sheets in a negative image on the other of said sheets.
10. The method of claim 9 wherein the alternating current is 60 cycles per second.
11. The method of claim 10 wherein said first electrical field is applied for about 1 second.
12. The method of claim 9 wherein said electrically photosensitive material comprises organic material dispersed in an insulating binder.
13. The method of claim 12 wherein said electrically photosensitive material comprises phthalocyanine.