US 3784398 A
The invention relates to a method of and means for transferring recorded signals and latent electrostatic images before development. The insulating medium which is placed over the photoconductor surface is so constructed that the dielectric constant or permittivity on one side is lower than the dielectric constant on the other side. This can be achieved by forming the insulating medium of a laminate of two differing materials of differing dielectric constants.
Claims available in
Description (OCR text may contain errors)
United States Patent 11 1 Metcalfe et al.
[ Jan. 8, 1974 TRANSFERRING RECORDED SIGNALS  References Cited AND LATENT ELECTROSTATIC IMAGES UNlTED STATES PATENTS BEFORE DEVELOPMENT 3,666,458 5/1972 7 Arneth et al 96/1 R  Inventors: Kenneth A. Metcalfe, Lockleys; 3,551,146 12/1970 Gundlach 96/1 R 1 Spencer Clements Largs Bay Cal'lSQn both of Australia 3,672,930 6/1972 Trachtenberg. 117/37 LE  Assignee: The Commonwealth of Australia, Primary Examiner Murray Katz care of the secretary Department 9 Assistant Examiner-M. Sofocleous Supply Parkes Canberra Austral Attorney-Eric H. Waters etal. 221 Filed: Aug. 16, 1971 211 Appl. No.: 172,085 [571 ABSTRACT The invention relates to a method of and means for transferring recorded signals and latent electrostatic  Forelgn Apphcamfn pnomy Dam images before development. The insulating medium Aug. 17, 1970 Australia 2214/70 which is placed over the photoconductor Surface i so constructed that the dielectric constant or permittivity  117/175 96/1 96/1 on one side is lower than the dielectric constant on the 96/14, 7/37 LE other side. This can be achieved by forming the insu-  G033 1 603g 13/10 003g 13/16 lating medium of a laminate of two differing materials  Field of Search 96/1 R, 1.3, 1.4;
Baa/by of differing dielectric constants.
3 Claims, 8 Drawing Figures 6 4 Trans/fer /Vemb TRANSFERRING RECORDED SIGNALS AND LATENT ELECTROSTATIC IMAGES BEFORE DEVELOPMENT FIELD OF THE INVENTION This invention relates to a method of and means for transferring recorded signals and latent electrostatic images before development.
STATE OF THE ART In the past the method of transferring and the means for transferring latent electrostatic images and recorded signals from a receiving surface to another surface prior to development has been sought for some considerable time in the field of electrophotography and facsimile recording particularly for the purpose of replication of the information and re-use of the recording sheet or layer.
In the Carlson inventions the use of an electrostatic printing member which could be re-used after development was introduced, but this and subsequent methods involved the development of the actual receiving surface and entailed the cleaning of the surface before reuse.
According to a method recently developed in a photocopier, the photoconductive surface is itself of a very high grade and highly expensive and to avoid the need of applying developer to this sensitive surface that process utilizes an insulating web which is placed over the photoconductive surface and the latent image so induced in the insulating web is then developed and the developed image is transferred to ordinary paper.
Certain complications exist in the transfer of the image to the insulator web and the development of this web; and an object of the present invention therefore, is to provide a better method of and means for transferring latent electrostatic images and recorded signals while retaining a highlyeffective form of transfer to a medium on which the image can then be developed at the final medium as the developed image transferred to a further receiving member.
SUMMARY OF INVENTION From intensive research carried out-by us we have come to the conclusion that problems which have been encountered in this type of transfer of the latent image have occurred chiefly because of the type of insulator medium which wasused for the transfer, it being common to use a material such as that known under the trade mark Mylar thecharacteristic of which is such that the potentials which are built up in effecting transfer. may be many orders different from the picture potentials produced on the photoconductive medium and therefore there is atendency to swamp the image potentials.
We have found that this difficulty can be overcome by use of an insulating medium which is so constructed that the dielectric constant or permittivity on one side isvlower than the dielectric constant on the other side.
much higher dielectric constant, for example 3, carried on a backing of still higher dielectric constant, say 6, andflas examples of materials we have found that a combination sheet comprising polyvinylidene chloride on a cellulosic carrier sheet forms an effective medium.
The principle underlying the invention is the attainment of a satisfactory gradient between the image recciving surface and the back of the insulator sheet according to which there is a change in polarization of the molecules through the sheet so that the good insulator surface at the receiving face holds the charge transferred to it without substantial leakage, while the layer near the other face serves to hold the charge against lateral transfer because of the enhanced polarization caused through the material having a greater dielectric constant or permittivity. In support of this, attention is directed to the dependence of dielectric effects or permittivity on polarization in an applied field, the applied field in this case being the latent image field which thus effects high level polarization in the area of the more distant layer because of the higher permittivity of this layer.
From the above it will be realized that the side of the insulating medium which contacts the actual latent image is a good insulator with a lower dielectric constant than the other side, so that there is a gradient between them and thus for instance a machine can be produced which has a drum coated with a photoconductive medium, which can be of a relatively expensive type because it is merely used to produce a latent image and does not have to be contacted by a developer, but this drum is in turn in contact with a drum which has on its surface a medium of high insulating value but in the form of a laminate in which the outer layer has a lower dielectric constant or permittivity than the inner layer, whereupon it will be found that as the one drum rolls on the other, the image will be transferred to the transfer drum and can be developed thereon by a developer roller or the like in contact with the drum and the developed image can then be immediately transferred to paper or the like which passes between the transfer drum and a loading roller which presses the paper onto the drum and between which and the transfer drum a potential may be applied if this is thought desirable.
We have also discovered that the effectiveness of transfer of electrostatic images is very dependent on the quality of the surface of the recording member, for example the photoconductive drum or plate. It is possible according to this invention to use a cheap and expendable electrostatically coated drum as the photoconductive member and to have a suitable laminated drum or an insulator belt or sheet associated with this drum for the reception and retention of the latent transfer image, or alternatively instead of using the drum or belt or medium with the laminate construction to which the latent image is transferred, the image may be transferred to the paper itself provided the paper has on it a layer of polyvinyl-chloride or the like so that a smooth surface exists which is a good insulator with a relatively low dielectric constant and which is in contact with the photoconductive drum, enabling the transfer to be effected before development because of the better surface and because of the suitable dielectric properties.
In this case of course the surface is developed after the transfer of the image.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 demonstrates the principle of the invention and shows how image transfer from a photoconductor sheet to an insulator sheet can be effected,
FIGS. 2A-2E diagrammatically show the steps of the invention,
FIG. 3 shows schematically a machine embodying the invention, and
FIG. 4 shows schematically how a transfer sheet which itself is a laminate may be processed to receive the latent image and the image can then be developed on this laminate.
PREFERRED EMBODIMENTS Referring first to FIG. 1 therein is seen a photoconductor sheet 1 which consists of a backing 2 with a photoconductor surface 3 there-on. This is the recording member.
This photoconductor surface has an image formed on it in any suitable manner such as by first charging the surface and then projecting a light image thereon and this latent electrostatic image is then transferred to transfer sheet 4 which forms an intermediate between the photoconductor sheet and the final copy sheet. This sheet 4 is thus the transfer member.
This transfer sheet is a composite sheet having a good insulator 5 on one side with a relatively low dielectric constant, and an insulator 6 on the other side with a higher dielectric constant, the purpose of this being to provide a potential gradient between the two insulator membranes.
It is preferred to use materials in which, for instance, the insulator on the image receiving side has a dielectric constant of perhaps 2 while the other side has a dielectric constant of about 4, measured at 10 C.P.S.
In this way, the latent electrostatic image is removed from the photoconductor sheet and is held on the transfer sheet where it can then be developed by means of any of the normal xerographic methods.
FIGS. 2A-2E demonstrate the actual steps of a pro- I 1 now placed beneath a projector 14 which projects a light image onto it, the photoconductor sheet 1 being of course placed on a suitable support which is of a conductive nature, unless the photoconductor sheet backing is itself conductive, and the light then bleeds away the image at those areas where the light strikes the photoconductor sheetv which of course is maintained under dark room conditions from the time it is charged to the time the image has been formed and developed.
FIG. 2C shows the photoconductor sheet now turned over and placed onto a transfer sheet 4 which as shown in FIG. 1 is a composite sheet of good insulator properties, but of a lower dielectric constant on one side and a higher dielectric constant on the other, the lower dielectric surface being placed into contact with the photoconductor sheet, which action then transfers the latent electrostatic image from the photoconductor sheet 1 to the transfer sheet 4.
FIG. 2D shows a developer roller is now run over the transfer sheet to apply developer to the image according to where the developer is attracted to the sheet, and this transfer sheet 4 as shown in FIG. 2B is now brought into contact with a final copy sheet 17 or receiving member by the application of pressure or a potential which will ensure transfer of the developed image from the transfer sheet to the final copy sheet.
The developer roller 16 can of course be replaced by any convenient developer mechanism and development could be either by means of marking particles used in dry form or suspended in a carrier liquid of high electrical insulating characteristic so that during development it does not destroy the latent image on the transfer sheet.
The device of FIG. 3 utilizes an image producing station 20 which charges and light bleeds the photoconductor drum 21 in any convenient manner, the drum 21 being coated with selenium or any other suitable type of photoconductor, and obviously as it does not have developer applied to it, the initial costs of such a photoconductor drum is not a vital consideration as it is were an image is developed on same and much more expensive but more suitable photoconductors can be used for this purpose.
The drum 22 which is in contact with the photoconductor drum 21 has on it a compound insulator surface consisting of a lower dielectric constant material 23 which forms the outer part of the drum, and a higher dielectric material 24 which forms the inner part of the drum, so that here again there is a transfer member which has a dielectric gradient characteristic between the surface 23 and 24.
This arrangement will transfer any latent electrostatic image formed on the photoconductor drum to the transfer drum at the point of contact 25 between the drums, and this drum 22 then has the image developer on it at a developer station 26 where a developer roller 27 which dips into developer 28 in the tank 29 is brought into contact with the transfer drum 22.
As the surface of the transfer drum 22 preferably moves towards the roller 27 at the developer station 26, a developer liquid nip 30 is formed forwardly of the point of contact between the transfer drum 22 and the developer roller 27 this ensuring that there is a high degree of turbulence at this point and a constant replenishing of the developer, but as the developer roller is in firm contact with the transfer drum 22, excess developer is removed from the drum and only the image is left on the transfer drum after it passes the developer station, with very little dampness due to the liquid developer.
A second transfer station 32 now transfers the developed image to a paper or other web 33, which is taken from a roll 34 and passes over a pressure roller 35 which urges the paper or similar member into contact with the transfer drum 22, and at this stage the still damp developed image is accepted by the paper web or the like and the final transfer is achieved.
A cleaning station 37 is disposed between the second transfer station 32 and the first transfer station 25, so that the sequence is that a latent image is formed at the image station 20, on the photoconductor drum 21, which is then transferred at the transfer station 25 as a latent electrostatic image, to the transfer roller 22, but
on the roller 22 the latent electrostatic image is developed so that the image is now changed from a latent electrostatic image to a developed image which leaves this station in a state so that at the second transfer sta tion the now developed image will be transferred to the paper web 33 or other convenient medium.
In the machine shown in FIG. 4 the photoconductor drum 40 has an image forming station 41 associated with it, and the latent image is transferred to a member 42 comprising a paper or other backing layer 43 having a layer 44 on it which receives the latent electrostatic image and which is of lower dielectric constant than the backing layer 43, the image being developed by the developer roller 45. Rollers 46 and 47 press the member 42 against the photoconductor drum 40 and the developer roller 45 respectively.
The novel feature of the devices illustrated is the use of an intermediate transfer member having specific characteristic layers as described earlier herein, namely a layer which is a laminate of a relatively high insulating outer layer with a low dielectric constant and an insulating layer with a higher dielectric constant immediately beneath which receives the latent image as opposed to receiving a developed image.
While in the foregoing the general description has been made with reference to latent electrostatic images produced by charging and light bleeding, it will be obvious that the image producing stations or 41 could consist of a series of stylii 50 (FIG. 4) to which the necessary signals are applied, and obviously whiledrums have been shown in the illustration, these members could be in the nature of belts or the like.
EXAMPLES OF MATERIALS ing or treating with an Na-l solution if necessary to give the necessary dielectric constant.
Polymer Dielectric D.C.
Constant Resistivity l0 CPS. OHM. -CM.
Instead of paper the backing layer could be:
Melamine Formaldehyde 7.2-8.4 lO IO" Phenol Formaldehyde 4.0-7.0 lO"-l0"" Polyester (Styrene-alkyd) But the selection must be made to ensure that the backing layer is of a higher dielectric constant than the receiving layer.
1. A method of transferring latent electrostatic images from a recording member to a receiving member, said method comprising contacting the recording member with a transfer member to transfer the information thereon to the transfer member, said transfer member being formed as a Iaminateof two insulator layers, one being an image receiving layer having a relatively low dielectric constant, the other being a backing layer having ahigher dielectric constant, said image receiving layer being brought into contact with the recording member during said transfer of information, said image receiving layer being selected from the group consisting of polyvinyl chloride, vinyl chloride acetate copolymer, cellulose acetate butyrate, methylmethacrylate, epoxy, polyethylene and silicones, said backing layer being selected from the group consisting of melamine formaldehyde, phenol formaldehyde and styrene alkyd polyesters, developing the image on the transfer member, and transferring the thusly developed image from the transfer member to the receiving member.
2. The method of claim I wherein the two layers have a dielectric constant difference substantially in the ratio of l to 2.
3. The method -of claim 1 wherein the image receiving layer has a dielectric constant between 2 and 4 and the backing layer has a dielectric constant of approximately twice that of the image receiving layer.