DE1497060A1 - Halftone Xerographic Reproduction - Google Patents

Description

HlNK XEROX LIMITBD, 37-41 Mor * "er Stritt,!," Do "V. 1., lnglind

Xerographic halftone reproductions S.

Dr. Extl.

The invention relates to xerography and in particular new electrostatic processes for generating visible patterns corresponding to optical images.

With the usual forms of xerography, the joint action of an electric field and a "lent pattern on a photoconductive, insulating layer creates a latent" electrostatic image generated. The latent image will be later or immediately thereafter, or in some cases, evenly transformed into a visible image with the help of τοη electirtral attraction, repulsion or redistribution in image form »sound fine * er divided, solid or liquid particles.

Various xerographic methods are known which generally correspond to the description above and the tith enjoy a widespread commercial solution and in various patents or other publications ..eehri.be » and Terfeurs are also known, in which tin IUd trtrtstatically as surface formations of a similar surface of a substance is reproduced, but this terfahren erftrdti * Hochvakuurüeinrichtungen for image generation and miss the opportunity, continuously tinted images and great

To reproduce surfaces.

A modified Viedergab.verfahren for an electrottatic -sches deformation image is already proposed at de., an electrostatic image pattern in the air from a üeliektm xerographic plate or the like on a layer

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deformable, insulating material is transferred, in which then Surface deformations arise in accordance with the transferred charge pattern. The transfer of charge emus tern over eohaale Between the two is known as TESI (transfer of electrostatic Images) and the main features of such! Are experienced in U.S. Patent 2,937 * 943, referring to those relating to Operating Conditions ii.i referenced for electrostatic image transfer. The aforementioned driving is suitable for photo-accurate reproductions and does not require a Yakuuaeystea, however, it is not able to reproduce full areas or continuously tinted images. This defect is not in that Charge transfer mechanism establishes "" another Ib of the kind " how a surface becomes old as a result of the electroetatieehen ladtoge * deformed on it. Sohon different torsos are confessed been to overcome these shortcomings * u »but the ·· require ii.i general particularly complicated construction et eile or similar. The present invention relates to an improved and simplified method for the presentation of continuous tones and full surface areas of a xerographic deformation image system Charge pattern with continuous tint on one surface otformed into a halftone charge pattern on the adjacent surface. These and other fictional features go from the following description and claims in conjunction with the drawings, in which *

Fi ₀ . 1 is a schematic representation of a device which is suitable for carrying out various inventive methods, and

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Τ ± £. 2 different forms of the inventive image carrier.

It seems appropriate to discuss halftone printing here as it is involved in certain features of the invention. the Ordinary printing processes, such as letterpress and lithographic printing, can only print black and white and are therefore unable to produce gray shades to reproduce. There are also other printing processes, such as intaglio, which only roll small black areas and no stretched η can print black areas. These problems have been solved in printing technology by using halftoning techniques in which the image is resolved into a series of closely spaced points, the size of which differs from that to be simulated

Degree of blackening depends. These points are generally very good

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small and close together, since the radio distance has a lower limit for the playback of image tails eetst. In general, but not necessarily, the points are evenly spaced and can be round, diamond-shaped or any other shape. For closely related types of printing, an image may have a continuous tint can be represented by a pattern of lines, which are straight or can be curved and their dioke changes along their length according to the degree of blackness of the original. As part of According to the present invention, all of these processes are referred to as halftoning processes, regardless of whether they are concerned with Reproduction of a gray tint by means of a pattern of points, lines or other shaped elements is

The xei-ographic procedures in which a charge meter is made visible through the mechanical deformation of a surface, resemble the printing process in which lines and Fun to be reproduced well, but no gray nuances

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and no large full areas. It's already suggested to make use of the knowledge of printing technology by using large values or large volume areas as a continuous Pattern reproduces surface deformations. It is proposed It has been envisaged to do this by using the mechanical. Properties of the deformable layer changed from point to point, but this has become complicated and unsatisfactory Results. ·, Led. It is also already proposed been to use a halftone screen or similar during the exposure phase. According to the invention, however, are constructions and methods are provided in which the halftone effects are impressed on the transferred charge oyster during the charge transfer itself will.

Pig. 1 shows a device which allows the invention to be carried out in several ways. It comprises a Xerographieehe plate 10 in Tonn a drum which is rotatable by means of a not shown drive about its axis · The drum consists of a mechanical support layer 11, which is preferably electrically conductive and contains various metals, such as aluminum or the like. It can also consist of glass or some other permeable substance to which an electrically conductive layer, preferably a transparent conductive layer such as tin oxide or copper iodide, is applied. The carrier layer 11 is covered with a photoconductive insulating layer 12, which consists of one of the photoconductive insulating substances known in xerographic technology. These substances are general. characterized in that it insulates sufficiently in the dark to hold an electrostatic charge above a useful one

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To be able to hold on for a period of time, but that they become sufficiently conductive if they are exposed to light or other activating radiation in order to allow the charge to flow away. Photoconductive insulators can contain vitreous substances, of which selenium is widely used, or they can be dispersions of photoconductive pigments, of which 2lbkoxide is currently used, which are diapered in an electrically iaolated4am ₍ a film-forming binder) .Bine spray charging device 1; Apply plate 10 as is customary in xerographic practice.

A projector 1f is arranged which projects an image on the plate 10 after it has been charged by the spray charge device 13, thereby creating an electro-static charge pattern on the plate 10. Preferably, the projector 15 projects a moving image moving in synchronism with the movement of the plate 10. The plate 10 first runs through a contact position with a band of deformable transfer material 16, which is guided by a supply roll 17 and is in close contact with the plate 10 with the help of an electrically conductive transfer roll 18, which is fed from the heating source 1Q is held. The transmission material 16 can be any in _# . an insulating material that is easily softened by the use of heat or solvent vapor or the like. Polystyrene is a particularly suitable material, but most natural and man-made resins, yachts or the like are suitable. The transmission material 16 can also be used

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icht include a traverse, which is not shown in this drawing, which provides a mechanical support for the deformable Layer forms. This carrier material is preferably flexible, but can also be stiff in some cases) it should be an electrical insulator and its mechanical properties under the necessary to soften the deformable material Maintaining conditions · Various substances are suitable, among which polyethylene terephthalate due to its excellent properties electrical properties, its strength and great resistance to heat and all common solvents excels. The potential which is impressed on the transfer roller 18 by the energy source 19 generates a strong electrical field between the roller 18 and the plate 10. 91. the plate 10 is preferably earthed in this embodiment and this can be done via the energy source 20, which is connected to the plate connected and grounded. It is noteworthy that the desired tension between the plate 10 and the roller 18 arises when either one of the two energy sources 19 and? 0 or both deliver a potential

The potential difference between the roller 18 and the plate 10 is superimposed on that on the plate 10 from the charge nut formed field a uniform electrical field, whereby the charge roughened previously on the plate 10 on the Transfer material 16 passes, so that on this one Facsimile of the original charge pattern. Invention·" however, the transfer roller 18 has a smooth cylindrical surface, but instead bears a pattern of grooves and depressions so that the surface of the roller 18 covers the

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The bearing is touched by 16 in a pattern that contains several points, parallel lines, crossed lines, or the like. By applying an electric field sufficient for image transmission, a transmission occurs that changes according to the raised planes and depressions of the surface. Accordingly, the charge transferred onto the transfer material 16 contains a Hulbtonmueter superimposed on the continuously toned pattern originally formed on the plate 10. The deformable material 16 then passes through an oven 21 where it is softened and where the electrostatic charge pattern creates a deformation pattern in the softened material. The size of an individual deformation area will of course depend on the amount of charge transferred to the respective area, which creates a continuous tone effect. Itfsnvö good one can also use a steam chamber which is filled with vapors of a solvent for the transfer material 16. After it has passed through the furnace, the material cools down, solidifies and can then be projected by means of streak optics or the like or wound onto a take-up roll 22 for later use.

In a further embodiment according to the invention the spray charging device 13 and the projector 15 are not used and the carrier layer 11 is used for this duroheiohtige front covered by a conductive layer described above. A projector 23 is disposed inside the drum 10 and projects through the carrier layer 11 through to the photoconductive, insulating ' Layer 12 an image in the area where the photoconductive insulating layer 12 faces the transfer roller 18.

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Between the plate 10 and the roller 18 is one or both Energy sources 19 and 20 applied an electric field that the causes transfer of the charge pattern from the plate 10 to the / transfer material 16 in the configuration of the image and although simultaneously with the exposure of the plate 10 with the image pattern. Again, the fields acting on the transmission medium 16 are only there sufficiently strong around a charge transition to cause where the transmission material 16 is in real contact with the transmitted sun roll 18 and again a hue pattern is superimposed on the transmitted charge.

The invention is described on the basis of a rotating cylindrical forex raphic plate and a transfer roller 18 but of course the same can be experienced even if you have an intermittent one flat forex raphic plate and a flat conductive plate used instead of transfer roller 18 ..

The invention can also be achieved through the use of new forms for the transmission material 16 made effective will. It is already known that transfer materials consist, for example, of a construction that has an optional Layer of an insulating carrier material, a thin, protective

wise transparent layer made of a conductive material and a surface layer made of a deformable material contains With such a construction, the transfer roller 18 can be omitted, because they are required for the transfer of the charge pattern Electric fields can be generated by applying controlled potentials to the conductive layer of the transmission material 16 Accordingly, in FIG. 1 there is a further energy source 24

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shown, which are connected to such a conductive layer can.

Fig. 2A shows a Porm dee transfer material · containing a conductive layer and corresponding lat altered the present invention. Ee includes "ine electrically insulating carrier layer _v which in turn aue polyethylene terephthalate or Toggle 'which mechanically tough, there is insulating material, which are resistant to heat or solvent vapor θ or both · 'The carrier layer 25 is coated with a thin electrically conductive layer 26, which is covered with a layer 27 of deformable material. Layer 27 is preferably, but not necessarily, transparent. If it is, the formation of the charge pattern and its transfer can be brought about by the '''a light. ter is projected through the transparent material 16 instead of through the plate 10, and the projection of the image can take place better in transmitted light than in reflected light. In the arrangement shown in FIG Place that the transfer roller 18 occupies. As shown in FIG. 2A, the conductive layer 26 does not form a continuous layer, as has previously been the case with UbIiOh _9, but instead contains a pattern of intersecting lines. If this material is in the device according to fig. 1 or in another apparatus, the electric field created in the deforable layer 27 and on the plate 10 is not a uniform field but changes over the surface of the layer 27 in accordance with the pattern of the layer 26. The charge transfer takes place accordingly from plate 10 to layer 2? as it is controlled by the field, in

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a half-goal oyster. instead of a continuously tinted pattern,

The crossed line pattern in Pig, 2A is not the only suitable pattern for the conductive layer 26. This can also be, for example, a parallel straight line cough, as in I ¹ Ig. 2B, or a Pig zigzag cough. 20 contain, τοrauegetzt, that these lines are electrically connected to each other so that they always remain at the same potential, or even a spiral., As it is shown in flg. 2D. In each pail, these patterns are suitable for generating a locally changing electrical pitch between the transfer material 16 and the plate 10. This is because the face changes along the surface of the transfer material and this change contains a component which corresponds to the conductive layer 26, but will generally also contain a pattern which originates from the exposed original.

The transfer roll 18 can be manufactured using a conventional etching technique. Thus, an originally smooth roll can be coated with a layer of a photohardenable material such as Ohromgelatin or Kodak photoresist available from Eastman Kodak Company, Rochester, New York. This layer is then exposed to a light pattern that corresponds to the desired halftone pattern, and the unexposed material is then washed out. Then the roller 18 is immersed in an acid bath that covers the surface in the areas that are no longer covered by your material? etches away. Finally, the remaining light-curing material is removed and the desired relief pattern remains on the roll 18. Ale. Depressions with a plastic or some other insulator

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be filled in so that a smooth surface is created. Various other methods can still be used to achieve this the roller 13 to form a nut and this as well as the above b · -. written procedures can also be used to find useful Surface oyster on flat plates or other technical To raise equivalents for the transfer roll 18

If the transfer material includes a conductive layer, it can be made of different fabrics in a number of ways. For example, the conductive sleeve 26 can be a Be a metal layer that was applied as a foil, vapor-deposited in a vacuum or chemically deposited or the like if it is sufficiently thin, such a metal layer will be transparent. If the carrier layer 25 is made of glass or a similar Borrowed difficult to melt substance is j a transparent conductive layer of tin oxide can be applied to it by known methods. If the carrier layer 25 made of a plastic or a similar non-heat resistant material that is used for the application of the tin oxide coating cannot withstand the required heat, a transparent, electrically conductive one can be used instead copper iodide coating can be used

The desired pattern can be used on all of these sockets different procedures can be applied. Such a method consists in applying the coating to the carrier layer 25 to apply the applied template through *? in another process is, parts of the layer 26 after it has been applied evenly., was to selectively remove using the same Ätateohnik, Alt in connection with the manufacture of the transfer roller 18 has been described. As is well known, one can also use parts alae »thinÜL.:

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Films, such as the conductive layer 26, by controlled electron beam exposure remove in a high vacuum. After getting the senior If the layer 26 has been applied to the carrier layer 25 in the desired pattern, a layer of deformable material 27 can be used can be added using a conventional coating technique.

In another embodiment of the present invention, the conductive layer 26 may include two superimposed layers, one of which is an extremely thin uniform layer of relatively high electrical resistance and the other is a patterned layer of higher conductivity of the type described above. In this Ausführungeform the changes the Ladun _ö sübergang causing electric field does not abruptly from point to point along the surface of Übertragun ^ smaterialB 16, as happens when the conductive layer 26 Hau ^ Daily departures areas of very high electrical conductivity mixed with areas in which the conductivity is practically zero. Other methods of achieving a halftone pattern by changing the conductivity in the conductive layer 26 are also useful to produce a more gradual local change in the electrical field used to transfer charge. It has been found that such a gradual change in field results in higher resolution in the final Reformation image than can be achieved with very abrupt field changes associated with a conductive layer 26 which is either present or absent at one point.

In some examples it has been found to be advantageous to provide the plate 10 or the overfcra ^ untape 16 with an electrical

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insulating liquid such as silicone oil. For example Ijrp DC-200 silicone oil from Dow Corning can be used will. Such an oil film fills the space between the Plate 10 and the tape 1.6, creates a more even Kontcöct and increases the mobility of the electrical charges between the two limbs. It has been found that through a such oil connections significantly reduce the electrical potential required for TESI transmission.

In the meantime, the invention has been described with reference to specific constructions, methods and applications, but these are only intended to be illustrative and are not intended to limit the invention, which is determined by the scope of the following claims. In particular, the methods described above are useful for achieving a halftone effect in the transfer of electrical charge iriuators, regardless of whether these charge patterns are transferred to a deformable surface or to other types of surfaces for other purposes. '

£ AD ORIGINAL

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Claims (1)

1497066 Claims ^ J ♦ "Terfahre.n for the production of a halftone reproduction of a continuously tinted light pattern in which an electrostatic image is generated on the surface of an insulating photoconductive layer, which corresponds to the light pattern, and the electrostatic image on an adjacent deforaable insulation - The layer is transferred as a charge pattern and a defereible layer τοη of the photoconductive layer is separated and softened so that a relief image is visible on it, characterized in that during the transfer of the charge amount to the deformable layer a location changes The electric field is superimposed in such a way that the charge is only transferred in certain areas in accordance with the changes in force. 2 · Terfahren according to Claim 1, characterized in that _v 4 * 6 dl · Local changes in the superimposed electrical Veldee in the mean • have a distance that is smaller than the smallest beta size of the image pattern to be reproduced ·. 3. Terfahren according to claim 1 or 2, daduroh characterized da0 a) the photoconductive insulating layer (12) is arranged over a conductive carrier layer (11), _u b) at the. An electrical conductor is arranged on the rear side of the deformable layer at least in the area of the image transmission becomes, which is a cough of grooves in the manner of a half-tone raster carries on its surface, 90S828 / 1329 BADORiGINAL c) between the conductive Trä _o erechicV.t (11) and the electrical conductor a sufficient potential difference is applied, wherein charges are transferred in eineui Mu.ter of (3p photoconductive insulating layer on the deformable layer, welohee both de. "electrostatic Charge pattern ale also τοη the pattern of the surface grooves of the electrical conductor is determined. 4. The method nac.'j claim 3, characterized in that the RUcliaeite of the cleformable layer arranged conductors ala the deformable layer was underlaid with an electrically conductive layer is trained. 5. Texfahren according to claim 3, characterized in that the conductor arranged on the rear side of the deformable layer is formed as a transfer member which touches the layer mainly at the point of image transfer. 6. Yerfahren according to claim 5r, characterized in that the transmission member is designed as a role (18). 7. The method according to one of claims 1 to 6, characterized in that the deformable layer is provided with a pattern of surface grooves. 90S828 / 1329 8. The method according to any one of claims 1 bit, 7, characterized in that that-between the photoconductive, insulating layer and the deformable Shift during the transfer of the charge pattern narrow, liquid-filled gap is arranged in which a locally changing electric field is superimposed. 9. The method according to any one of claims 1 to 8, characterized in that that the defor / übaren layer and a conductive base existing transmission material (16) is transparent and that Light pattern through the transfer material onto the photoconductive Layer (12) is projected. 10. The method according to any one of claims 1 to 8, characterized in that • that the arranged on the back of the photoconductive layer (12), conductive carrier layer (11) is transparent and the light pattern is projected through the conductive carrier layer. (1. Carrier for a relief image for performing the method according to one of claims 1 to 10, characterized in that it consists of the following layers:. * · A) a layer of insulating, dimensionally stable material (25),.-B) a files consisting of electrically conductive layer (26) over the layer according to a), ■
. c) a layer of deformable, insulating material (27) over the Layer according to b).
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