US3394002A - Charge transfer with liquid layers - Google Patents

Description

July 23, 1968 J. T. BlCKMoRg 3,394,002

CHARGE TRANSFER WITH LIQIIJID LAYERS Filed OC'C. 2l, 1964 2 Sheets-$heet l JOHN T. BICKMQRE '9W w `uw Me.;

ATTORNEYS July 23, 1968 J. T. BlcKMoRE 3,394,002

CHARGE TRANSFER WITH LIQUID LAYERS Filed Oct. 21, 1964 2 sheets-Sheet 2 40 45 l 4l l 42 y/ 46 I A \/f d I l I %I// H150 '/49 1| I I if.)

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ATTORNEYS United States Patent 3 394 602 CHARGE TRANSFR WITH LlQUll) LAYERS John T. Biclonore, Rochester, N.Y., assigner to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed @et Z1, 1964, Ser. No. 405,469 14 Claims. (Cl. 96-1) ABSTRACT 0F THE DISCLOSURE This application relates to a method of applying charge onto an electrically insulating surface utilizing a liquid of high resistivity across Which an electrostatic image is transferred, said liquid Vbeing suitably doped to reduce its resistivity to the desired range in a controlled reproducible manner.

This invention relates to improvements in electrical charge transfer characteristics of liquid materials utilized in various electrostatic imaging systems. More particularly, the invention relates to the chemical doping of such liquids whereby the electrical charge transfer characteristics thereof are controlled for effecting image charge transfer between juxtaposed surfaces of different imaging materials separated thereby.

The advantages to transferring electrostatic charge patterns has been recognized for a lar-ge number of applications in the fields of xerography and allied electrostatic printing methods. In the usual process of' xerography, for example, as disclosed in Carlson Patent 2,297,691, issued Oct. 6, 1942, a xerographic plate comprising a layer of photoconductive insulating material on a conductive backing is given a uniform electric charge over its surface and is then exposed to the subject matter to be reproduced, usually by conventional projection techniques. This exposure discharges the plate areas in accordance with the radiation intensity that reaches them, and thereby creates an electrostatic latent image on or in the photoconductive layer. Development of the latent image is effected with an electrostatically charged, finely divided material such as an electroscopic powder that is brought into surface contact with the photoconductive layer and is held thereon electrostatically in a pattern corresponding to the electrostatic latent image. Thereafter, the developed xerographic powder image is usually transferred to a support surface to which it may be fixed by any suitable means. By transferring charge from the xerographic plate to a suitable dielectric surface it becomes possible to develop the electrostatic image on the dielectric surface thus avoiding any possibility of damage to the photoconductive surface or need for its cleaning as a substantially enhance its recycling life expectancy.

ln another application, there has recently been discovered a novel image forming process capable of continuous-tone reproduction known as thermoplastic recording and disclosed in copending application Ser. No. 193,277 in the name of Gunther et al., now U.S. Patent No. 3,196,011. As disclosed therein, a charged thermoplastic layer overlying a photoconductor can be optically exposed to image conguration to deform imagewise when subsequently developed by softening. Softening is effected by the application of heat or solvent thereto causing the thermoplastic to take on a microscopically uneven surface which can be described as rippled, strippled, reticulated, wrinkled or frosted. This local deformation has a milky appearance in proportion to the amount of illumination received in different areas being generally comprised of alternating ridges and valleys that recur at substantially uniform spacing with -recurrently variable width and/or height. A distinctly different type of deformation may also occur, depending upon operating conditions and caused by fringing fields existing solely at the edge or boundary separating charged and uncharged areas. These latter fields a-re likewise capable of deforming a thermoplastic layer to form a relief pattern at such boundaries only. Such patterns may have utility per se or can generally be eliminated or minimized by softening the deformable material just long enough to the frost pattern to appear. Once produced, the image thus formed can be utilized in a variety of different ways for optical projection or reflection. Subsequently, the image can be erased by the reapplication of heat or solvent, usually in the presence of light uniformly applied, and generally of greater intensity or duration than that employed for developing.

Various techniques are known for charging the thermoplastic layer in order to effect deformation and subsequent utility including the use of a liquid charge transfer layer 'between the thermoplastic and the photoconductor as disclosed in the Gunther application supra. The advantages of the charge transfer technique are many including the possibility of utilizing opaque or colored photoconductors in imaging systems where the final image is to be reviewed by projection without the resulting loss in the capability to project White light images at high efficiency. A further advantage is that charge transfer methods make possible the use of photoconductors that are otherwise unusable because of high spontaneous dark discharge rates. A still further advantage is that the con-- ductive substrate of a suitable charge receptive dielectric, such as a thermoplastic layer, can be used to impose a field on the photoconductor during exposure and thus eliminate the requirement for prior photoconductor charging as 4by a corona. This also reduces the magnitude of potentials required to carry out the process by eliminating the high voltages normally associated with corona discharge.

Charge transfer between surfaces utilizing a thin air gap as the transfer medium is described in Walkup U.S. Patent 2,937,943. Charge transfer through air or other gaseous gaps is a useful technique but suffers from several disadvantages. The first of these is that charge transfer across the gap does not occur unless a critical threshold potential of several hundred volts is exceeded. Provided the potentials required are readily obtainable, this does not pose serious problems when relatively lange amounts of charge are to be transferred if the exact amount of charge transferred is not critical. However, in imaging applications requiring high image quality, as in continuous tone, it is exceedingly difficult to accurately control fine gradations in transferred charge that ultimately is to represent fine gradations of image density. This is generally attributed to gaseous breakdown which tends to be imprecise in that the gap potential necessary for charge transfer is critically dependent upon the gap spacing. Uniform spacings on the order of about 10 microns are necessary before charge transfer can occur, which is difficult to obtain because of surface smoothness and liatness irregularities in the different materials. In Fotland and Mayer U.S. Patent 2,975,052, it is disclosed that a thin layer of liquid can serve as a chargetransfer medium` and that it is capable of giving higher transfer resolution than can generally be obtained in a comparable air or gas transfer system. It has been found that characteristics of charge-transfer liquids are critical and must be matched to particular applications. Thus, whatever the charging arrangement, the charge transfer liquid forms a coupling between adjacent surfaces and must be characterized electrically in its ability to transport suliicient charge between the adjacent surfaces. When used for transporting image charge to a deformable thermoplastic material, electrical control has well defined limits of criticality. Specifically, it has been found, that with the type of imaging described herein insufficient electrical resistivity `of the liquid results i-n loss of resolution on the imaging member. At the same time, where the resistivity is too high incomplete charge transfer is ef- `fected between the adjacent surfaces resulting in no image or a poorly defined image on the thermoplastic layer. Accordingly, the liquid must be possessed of the critical range of electrical properties necessary to transfer charge sufficient to effect image deformation in the `manner described. In addition, for obvious reasons, the employed liquids should be chemically compatible iwith the adjacent materials it is to couple.

It has heretofore been found that certain materials marketed commercially, such as types of silicone oil described, for example, in the Fotland patent supra, are sometimes capable of effecting the desired charge-transfer results. However, it is generally not possible to fi-nd a range of commercially available liquids with the desired physical properties -which can be obtained in the optimum resistivity range. Moreover, such liquids are not known to be presently available for the specific purpose of charge-transfer applications. Hence, no attempt has been made in the manufacture thereof to assure that electrical properties are maintained consistent from batch to batch in a range optimally suited for a particular chargetransfer application. It should be explained that the range of resistivity required in these charge-transfer liquids is extremely high by ordinary standards and that small variations in the concentrations of unknown contaminants which vary between manufactured batches might be expected and it might further be expected that such variations would cause undesirable changes in the resistivity of these liquids if used for charge-transfer purposes. Now, in accordance rwith the invention hereof, it has been discovered that charge-transfer liquids can be composed f a liquid of high resistivity with appropriate doping which reduces the liquid resistivity to an optimum range in a controllable, reliable, and reproducible manner.

Accordingly, it is an object of the invention to apply doping agents to high dielectric strength liquids 'whereby the charge-transfer characteristics of these liquids are i-mproved and made reproducibly reliable.

It is a further object of the invention to provide dependably reliable charge-transfer liquids to transfer charge from metal surfaces to dielectric layers.

It is a further object of the invention to provide dependably reliable charge-transfer liquids employable as a coupling layer between a photoconductor and a chargereceiving layer.

It is a further object of the invention to provide dependably reliable charge-transfer liquids employable as a coupling layer between a photoconductor and an imagedeformable thermoplastic layer.

It is a still further object of the invention to produce liquid materials having controlled conductivity characteristics for use in charge transfer systems.

The various features, advantages, and limitations of the invention will become apparent from the following description and drawings in which:

FIGURE 1 is a schematic showing the transfer of charge in image configuration from a metallic surface containing the image in the form of a relief pattern to a dielectric charge-receiving layer;

FIGURE Z is a schematic showing the transfer of charge from an electrostatic image-bearing dielectric surface to a dielectric receiving layer;

FIGURE 3 is a schematic showing an arrangement for transferring charge from a photoconductor to a thermoplastic image-deformable layer;

FIGURE 4 is a series of curves showing the relationship between the resolution obtainable with various charge transfer liquids and the length of delay between the charge transfer operation and the development of the electrostatic image.

Referring now to FIGURE l, there is illustrated an arrangement for applying an image charge onto a dielectric layer utilizing charge transfer liquids in accordance with the invention hereof. As shown, the various elements are maintained in an electrically coupled sandwich arrangement that includes a charge-receiving layer 10 on an optional conductive layer 11 (required when the support 1t) is a dielectric) and a dielectric layer 12 supported |by means of an intervening layer 13 of charge-transfer liquid in electrical contact with the conducting or semiconducting member 14 containing a pre-formed image relief pattern 15. The charge-transfer liquid is shown as occupying only the upper or raised portions of the image relief whereat it has been found that suitable liquids having limited conductivity transfer selectively from the raised portions eve-n where the intervening space is completely filled -with liquid. A switch 18 connects a suitable source of potential 19 in series between the relief member 14 and the conductive layer 11.

Suitable for use in the above are a metallic substrate 14 as aluminum or the like with raised image portions 15 opposite a charge-receiving member consisting of a 3-mil Mylar support 10 coated lby a thin layer 11 of aluminized Mylar in turn coated with a Z-micron layer of Velsicol X-37 sold by the Velsicol Chemical Corporation `and being a complex terpolymer containing ethylenic unsaturation (60 grams) dissolved in 125 ml. diethyl ether. Filling the intervening space between the relief member and the charge-receiving member is a charge transfer liquid consisting of about 0.5 percent triuoroacetate dissolved in a fluorocarbon liquid manufactured by Minnesota Mining Manufacturing Company, and designated FC- and comprising a mixture of completely fiuorinated cyclic ethers with the empirical formula CBFlGO. With relief member 14 connected to the negative pole of the potential source 19 negative charges are transferred to the surface of layer 12 in areas corresponding to the raised portions of the relief. After transfer substrate 15 is removed and the charges of layer 12 can be processed as by conventional techniques. It has been shown that potentials as low as volts result in charge transfer that is developable by conventional xerographic developing methods such as cascade development. By contrast, if the charge-transfer liquid is omitted, no perceptible charge appears on the charge-receiving member with 100 volts applied although at potentials on the order of 200 volts and above a faint image can be detected due to air breakdown effects. The improved uniformity of the electrostatic image created by charge transfer through the specified liquid becomes immediately obvious.

Where it is desired to transfer positive charges to the same charge receiving member, the FC-75 liquid just described gives extremely weak images when the contact time is of the order of one second or less, Accordingly, for positive charge transfer a preferred liquid consists of about 9.2 percent triuoroacetic acid dissolved in hexamethyl disiloxane which is a 0.65 centistoke viscosity silicone liquid obtainable from Dow Chemical Company or the General Electric Company. This liquid produces irnages of positive charges on the charge-receiving medium as readily as the preceding liquid produced images with negative charges. Both liquids described in connection with FIG. 1 are composed of a base liquid of high initial resistivity that can be doped to produce the proper range of conductivity for a certain sign charge carrier. In addition, each is readily evapo-rable so that the electrostaticy images resulting from charge transfer can be developed almost immediately following the charge transfer operation by dry powders or other means without interference from a liquid layer.

It should be clear to those skilled in the art that instead of transferring charge in relation to the height of a relief pattern it is possible by the system described to transfer charge uniformly from a planar conductive surface when desired for example, to sensitize a xerographic photoconductor.

FIG. 2 illustrates another embodiment in which charge is transferred from one dielectric surface to another. As illustrated, there is shown a charge-receiving laye-r consisting of `support 25, conductive layer 26 and dielectric layer 27, being rolled by means of roller 28 against chargebearing dielectric member 29 containing a film of charge transfer liquid 30 `and supported on conductive substrate 3l. Although in no way limited to this use, charge-bearing dielectric 29 may consist of a photoconductor upon which a charge pattern can be formed by uniformly charging and exposing to an optical image to obtain a pattern of image charges. The charge transfer liquid layer 30 can be applied either before or after charging layer 29. The charge-receiving dielectric 27 may consist of a deformable layer for subsequent deformation development, if desired. Alternatively, it can be a nondeformable layer for use with powder development or some other form of electrostatic image utilization.

It has been found most convenient to form the liquid layer 30 by applying an excess thereof to the chargebearing surface 29, after the electrostatic image is formed and then roll the charge-receiving layer 27 at one edge to 'the layer 29 to sweep out excess liquid and form a uniform film. Applicator means other than a roller could obviously be employed, as for example a Teflon blade approximating the width of the charge-receiving layer. Forming the liquid layer in this manner serves to prevent the formation of voids and bubbles. The thickness of the liquid layer is determined to a large extent by the pressu-re and number of sweeps of the applicator as well as the liexibility of support layer 25. When the latter is comprised of 3-mil Mylar moderate hand pressure with a Tefion blade wiper results in an average liquid film thickness in the range of 1-2 microns. With continued `wiping or thinner substrates thicknesses, less than l micron film thickness can be readily achieved and by contrast lm Referring now to FIG. 3, there is illustrated an arrangement for applying an image charge onto an image deformable layer utilizing charge transfer liquids in accordance with the invention hereof. As before, the various elements are maintained in an electrically coupled sandwich arrangement that includes a thermoplastic layer 4d supported in contact with -a conductive layer 4l in turn supported on a fiexible substrate 42. Opposite the thermoplastic layer and separated therefrom by a liquid coupling layer 43 is a photoconductive layer dal supported on a conductive substrate 45.

It will be appreciated that the system to be described has a number of advantages which should be apparent to those skilled in the art including no need for a separate charging step and the abilities to utilize photoconductors with relatively high dark currents; utilize photoconductors that require a capacitive coupling to their free surfaces; obtain high quantum efficiencies by maintaining relatively large fields across the photoreceptor during exposure; collect relatively larger quantities of charge than those which can be stored on the photoreceptor; and add or subtract uniform charges for sensitometric purposes.

Deformable layer dit comprises a thin layer of material which is generally normally hard and electrically insulating but which may be temporarily softened by the application of heat or solvent. Layer may be opaque when viewed by refiection only; otherwise, it should be and normally is transparent as is exemplified by the system illustrated herein. For illustration purposes only, layer 4l) may be considered a uniformly thick layer of thermoplastic resin of approximately 2 to 5 microns in thickness and having a smooth surface. For relief imaging, material requirements are not as critical as for frost imaging and generally includes a wide choice of materials having electrically insulating properties and which can be softened in set. Table I below is a partial list of materials usable for frost and/ or relief image deformation.

TABLE I Trade Name Chemical Type Manufacturer Piccotex Pennsylvania Industrial Chemicals Co. Piecolyte Terpene res1n D0. Staybelite 5-... ROSID esten... Hercules Powder Co. Stayhelite l0- d0 Do. Piccoumaron Coumarone. Pennsylvania Industrial Chemicals Co. Piccolastic D150 styrene Do. Piccoex 100A. Polyvmyl chloride. D0. Neville Rl3 Coumarone indene Neville Chemical Co. Nevillac soit Phenol modified coumaron dene o. Piccolastie E125-.. styrene Penns lvania Industrial Chemicals Co. Piceolastie D125 do D0, Picco 75 Indene D0, Piccopale 70 Hydrocarbon (unsaturated) Do. Piecolastie A- styrene De. Piceolastic A-75 d0 Do.

thicknesses on the order of 5 microns can be achieved by the use of reduced pressure. Because charge transfer is not critically related t0 liquid film thickness, thickness of the latter is generally not itself regarded as critical.

When conductive substrates 25 and 31 are electrically connected via switch 32, the charge residing on layer 29 is divided in such a way that on subsequent separation of the layer the potentials on layers 26 and 29 are approximately equal. The nature of the charge transfer liquid 30 suitable for use in the configuration of FIG. 2 depends upon the conductivity required and other physical att-ributes. When the liquid layer is to be evaporable, as described in connection with FIG. 1, the same liquids can be used. As little as 0.001% trifluoroacetic acid in FC-75 is sufficient to give required conductivity for negative charge transfer although somewhat larger quantities are requi-red if positive charges are to be transported readily. Other suitable dopants for these liquids include glacial acetic acid, trifluoroethanol, m-arninobenzotriiiuoride, and methyl trifluoroacetate. Mixtures of the aforementioned dopants are also suitable.

For the system shown, layer 4l comprises a thin conductive layer which is also transparent and may, for example, comprise copper iodide, aluminum, chromium or Inconel usually on the order of approximately to 800 angstroms in thickness. Layer 42 comprises a material having sufficient strength for the supporting of the layers thereon and may conveniently comprise Mylar, or Kodar polyester films or other suitable fiexible transparent materials as is known in the art.

Support member 45 is generally a material which is relatively conductive when compared to photoconductive insulating layer 44 and may comprise, in accordance with conventional xerographic usage, such materials as aluminum, brass or other materials, including paper or glass with a transparent or other conductive coating or the like known layers.

To place an image deformable charge on the surface of the thermoplastic layer an image source 46 is supported at the object plane for optical projection through an objective lens 47 and a shutter mechanism 48 onto the surface of photoconductive material 44. Operation is effected'under control of a switch 49 which when closed trips the shutter 48 and simultaneously connects a source of potential 50 between the conductive layers 41 and 45 of the `Sandwich arrangement. Those portions of the photoconductive layer 44 which are subjected to radiation from the image source 46 become conductive in response to the radiation permitting charge to migrate from the conductive support to the surface of layer 44 and then across through the liquid coupling layer 43 to the surface of the image deformable thermoplastic layer 40. With the charge thus transferred to the layer of the thermoplastic material it may be removed from the sandwich arrangement and softened to effect image deformation as by heating or solvent vapor in the manner described above.

It should be appreciated, therefore, whether charge transfer is effected through the liquid layer 43 by the means just described or by any other means known in the art, as for example, described in the above copending Gunther application supra, that the electrical charge transfer characteristics of the liquid layer is to a large degree critical. If the liquid layer is excessively insulating in its characteristics, incomplete charge transfer will take place and subsequent development of the thermoplastic layer will not result in an adequate and suitable image deformation. By the same token, where the liquid layer is excessively conductive, Iuncontrolled transfer including lat` eral transfer takes place substantially reducing the resolution of the ultimately produced and developed image deformation. Accordingly, it has been found that the cornpressed thickness of the liquid layer in the sandwich of the type described should preferably be approximately 0.1 to 0.5 micron usually about 0.2 micron since thicknesses below this range usually result in non-uniform transfer whereas greater thicknesses make necessary the need for higher potentials to effect transfer. The actual mechanism may be more complicated from that described, but the latter is considered adequate for the present discussion.

When charge transferring to a deformable thermoplastic to be developed as a frost image, the quantity of charge required for frost development can be reduced if liquid is allowed to remain on the deformable layer during heat development. For this purpose a non-evaporable liquid is preferable. Of course, liquids chemically compatible with the thermoplastic layer as well as the photoconductor must be used. A suitable liquid for use with Staybelite layers consists of a base layer of polymethylsiloxane silicone liquid, centistokes, plus a dopant consisting of bis (tributyl tin) oxide. This liquid transports charge of either polarity readily yet allows the achievement of moderately high resolutions, and has no deleterious effect on the frostable layer. Other tin compounds can also serve as dopants. However, it is believed that the striking similarity in the structural formulas of Vdimethyl polysiloxane and bis (tributyl tin) oxide is a partial explanation of their solubility and compatibility in this application.

While not completely understood7 modern theories on conduction of charge in dielectric liquids indicate that with the possible exception of extremely pure liquified rare gases, charges move through the liquid attached to molecules. From this view-point, it appears that the function of the dopant is to provide particles that can move readily through the liquid and which are capable of carrying either a positive or a negative charge. Regardless of the exact mechanism, charge is carried from the photoconductor-liquid interface to the charge-receiving layer interface where it becomes immobilized. Separation of the charge-receiving layer then allows utilization of the resulting electrostatic image as, for example, for frost development.

The length of time required for the completion of charge transfer depends upon the effective conductivity of the charge-transfer liquid. Liquids with relatively high conductivity, such as the one containing bis (tributyl tin) oxide mentioned in the previous example, can transport the charge from a photoreceptor to a frostable chargereceiving layer in a fraction of one second. Less conductive liquids may require more time. Charge transfer will usually continue at a diminished rate after exposure has ceased when the substrates are merely electrically connected. Accordingly, it is often advantageous to leave the field applied after the exposure is completed to give more complete charge transfer. Less conductive liquids are sometimes advantageous for charge-transfer purposes since there is a reduced tendency for lateral charge migration, and thus it is possible to achieve higher image resolutions.

FIG. 4 graphically illustrates the relation of image resolution as it depends upon the type of liquid used and the elapsed time interval between the end of exposure and the beginning of thermoplastic heat development. Part of this time interval is utilized for completing the charge transfer step and the balance represents the delay between separation of the thermoplastic layer from the photoconductor and the time of heat development during which lateral charge migration continues to degrade resolution. The charge-transfer liquids all utilized 50 centistoke dimethyl polysiloxane silicone liquid plus the following dopants in order of increasing resolution or decreasing conductivity: bis (tributyl tin) oxide 0.4%, bis (tributyl tin) oxide 0.2%, bis (tributyl tin) oxide 0.08%, and dibutyl tin dilaurate 0.4%. Another tin compound capable of giving relatively low orders of conductivity to silicone liquid is tetrabutyl tin. Curves A and B represent relief image formation while C, D and E represent frost image formation respectively. Mixtures of the aforementioned organotin dopants with the other dopants previously discussed can be utilized in the practice of the invention.

As can be seen for the different liquids shown, resolution in line pairs per millimeter is maximum at less than one minute and decreases generally with increase of charging time. It can be seen that maximum charge transfer with different of the doped insulating liquids peak at approximately 0.2-0.4 second and that maximum resolution is obtained by not permitting pulsing beyond approximately one minute.

As stated previously, it has been found that specific dopant materials were well suited for some of the liquid layers and generally unsuited for others. Generally, it was found that where the dopant formulas `correspond closely to the liquids themselves they were lmore readily dissolved therein and able to enhance charge transfer properties of the recipient liquid. For example, whereas bis (tributyl tin) oxide was effective in S0 cs. silicone fluid, it was found generally ineffective in 0.65 cs. silicone fluid.

By the above description, there is disclosed novel techniques and materials for obtaining optimum charge-transfer chracteristics utilizing liquid layers. The effects pro,- duced thereby have rendered the employment of such liquids reliable and dependable for use as charge transfer medias. Whereas specific materials have been named as liquid charge-transfer layers and specific dopants have been named for controlling enhancement of their chargetransfer characteristics, it is intended that the invention not be limited thereby since other insulating liquids and dopants will readily occur to those skilled in the art. Rather, it is the intention of this invention to disclose the technique of utilizing a dielectric liquid with suitable physical properties and a resistivity higher than that which could by itself be used for charge-transfer application. By the addition of a suitable dopant material in proper quantity the resistivity is reduced in a controlled reliable and reproducible manner to the precise level required for a specific charge-transfer application.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. The method of applying charge onto the surface of an electrically insulating charge-receiving layer comprising the step of electrically connecting for a controlled time period a conductive backing of an electrically insulating charge receiving layer and a charge-bearing support layer coupled to said insulating layer by means of a liquid charge transfer layer comprising an insulating liquid selected from the group consisting of silicone oil and a fluorocarbon liquid comprising a mixture of completely fluorinated cyclic ethers with the empirical formula C8F16O and containing a composition selected from the group consisting of glacial acetic acid, trifluoroethanol, m-aminobenzotrifluoride, trifluoroacetic acid, methyl trifluoroacetate, bis (tributyl tin) oxide and mixtures thereof.

2. The method according to claim 1 wherein there is a potential source connected between said connected layers to render said support layer charge-bearing.

3. The method according to claim 1 wherein the charge on said support layer represents a latent image charge pattern and said charge receiving layer is a charge deformable thermoplastic.

4. The method according to claim 3 wherein said support layer comprises a photoconductor.

5. The method according to claim 1 wherein said liquid charge transfer comprises a silicone oil doped with up to about 0.4 percent by weight of bis (tributyl tin) oxide.

6. The method according to claim 1 wherein said liquid charge transfer layer comprises a silicone oil doped with glacial acetic acid.

7. The method according to claim 1 wherein the said liquid charge transfer layer comprises a silicone oil doped with triuoroacetic acid.

8. The method according to claim 7 wherein said silicone oil contains about 0.2% trifluoroacetic acid.

9. The method accordin-g to claim 1 wherein said liquid charge transfer layer comprises said iluorocarbon liquid doped with at least .001 percent -by weight of trilluoroacetic acid.

10. The method according to claim 1 wherein said liquid charge transfer comprises said iluorocarbon liquid doped with trifluoroethanol.

11. The method according to claim 1 wherein said liquid charge transfer layer comprises said iiuorocarbon liquid doped with m-aminobenzotriuoride.

12. The method according to claim 1 wherein said liquid charge transfer layer comprises said uorocarbon liquid doped with methyl triuoracetate.

13. The method according to claim 12 wherein said iluorocarbon liquid contains about 0.5% methyl trifluoro acetate.

14. A method of applying an image charge onto the surface of an electrically insulating layer comprising the steps of:

(a) applying charge from a potential source to a sandwich arrangement of an electrically insulating layer coupled to the surface of a photoconductive material by means of a liquid charge transfer layer comprising an insulating liquid selected from the group consisting of silicone oil and a fluorocarbon liquid comprising a mixture of completely :fluorinated cyclic ethers with the empirical formula CFlsO and containing a composition selected from the group consisting of lglacial acetic acid, trifluoroethanol, rnaminobenzotriuoride, trifluoroacetic acid, methyl tritluoroacetate, bis (tributyl tin) oxide and mixtures thereof; and

(b) exposing the photoconductor to an image source of actinic radiation for a time period until an image char-ge is produced on said insulating layer.

References Cited UNITED STATES PATENTS 2,742,368 4/1956 Rossiter et al 106--10 2,904,431 9/ 1959 Moncrieff-Yeates 96-1 2,975,052 3/1961 Fotland et al 96-1 3,196,013 7/1965 Walkup 96-1 NORMAN G. TORCHIN, Primary Examiner. C. E. VAN HORN, Assistant Examiner.

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