DE1808146C3 - Electrographic printing process and pigment for its implementation - Google Patents

Description

The invention relates to a printing method for printing a symbol to be mapped on, in particular leaf-shaped receiver, by means of a pulse-shaped applied electrical field, which in its shape corresponds to the symbol to be printed and with its help movable pigment particles of the surface of a pigment donor are directly transferable to the recipient, the pigment donor and the receiver is located between the electrodes for generating the electric field, and pigment donors for its implementation.

Processes of this type have become known, for example through US Patents 3,145,156 and 3,257,222, in which print particles (toner) are first distributed on a donor sheet, after which the part of the particles which represents the print symbol is transferred by the application of an electrostatic field. Two steps are carried out, of which the first step is a pre-charging of the particles on the donor sheet and the second step is the application of an electrostatic field to develop the forces necessary for the transfer of the charged particles to a receiver sheet.
The path taken according to the second publication shows a variant in such a way that the printed image

j5 is determined by the shape of the electrode used in the first step. A dry toner is used on the donor sheet. In the first-mentioned patent, on the other hand, the print image is determined by the shape of the electrode used in the second step, in which a stencil over a so. '. ^% he electrode can be placed. In this process, mobile, charged particles are used in a liquid phase. In both known methods, printing particles are first distributed over a donor sheet, as is the case with carbon on conventional carbon paper; both methods are characterized by the use of electrodes shaped according to the characters to be printed.

Other methods use a sheet that is selectively charged according to the character shape to be printed is then fed to a source of pre-charged print particles (toner), the latter being a Spray rain.less particles can resemble. In this case, an accumulation of the Particles. Such procedures work with two or three different steps. Usually it is like that charged sheet is only an interleaf and forms part of the printing device itself; but with that three steps are carried out-

1. the selective charging of the interleaf,
2 the cascade development (or correspondingly a loop development, powder dust development, brush development or magnetic development) and

3. The transfer of the particles on the interleaf to a receiver sheet.
In a simplified arrangement, the last step is eliminated by adding a paper receiver sheet

Interleaf replaced.

US Patent 2,951,443 teaches a three step process indicated in which in the first step the photoconductivity of an interleaf used to create a latent image from electrical charges> will. This is exposed through optical projection. US patent 3093039 is similar to the latter process, however, uses contact pressure. The US patent 2953470 shows the variant that in a first Step the interleaf is covered with a template representing the print image, whereupon a Spray discharge over the intermediate sheet covered by the stencil a corresponding to the print image Generated charge image.

The disadvantage of the above-described method belonging to the prior art is that several successive steps are required to generate an image, which requires a great deal of equipment and limits the printing speed. m

From DE-PS 1253941 a rapid printing device is also known in which a flowable marking compound in a plurality of in one. Marking carrier formed depressions is contained, and in which also pole shoes are provided, each of which is located essentially above the surface of an associated depression, so that by actuation of the pole shoes the transfer of the flowable marking mass to a between the marking mass carrier and the magneto-motor «> Actuatable pole pieces located recording medium can be done. It should also be noted that the transfer of the marking compound can optionally also take place electrostatically. r>

A disadvantage of this known high-speed printing process and the device for carrying it out is that the transfer of the marking mass onto the recording medium using electrostatic Forces working with extremely high voltages, since the electrical When applying low voltages, field largely to the higher parts of the marking mass carrier is deflected. In addition, in the known method, each character is made up of numerous 4-, Points built up, which allow a very precise processing of the wet marking carrier and the. make these corresponding electrodes necessary, while at the same time a relatively complex control is required when working with reasonably high pressure speeds would like to.

Proceeding from the state of the art, the invention is based on the object of specifying a simplified printing process which, due to the low expenditure on equipment, is more trouble-free and, due to the generation of the image in just one single step, is faster and cheaper than the previously known.1 process. this object is achieved according to the invention in that one uses a pigment encoder with _b0 an irregular surface structure on which distributes the bewegliehen pigment part away and spaced high through a medium electrical resistance is separated which is essentially a balance of the electric potential between the individual points of the Surface of the pigment donor and thus a destruction of the contours of the electric field qn this surface is prevented, and that electrically conductive Pjgmentteilchen is used.

The invention has the advantage that a contactless printing of directly from one Computer supplied data as well as facsimile transmission and the generation of other images can be carried out quickly, cheaply and with little maintenance. The advantages of the previously known electrostatic printing methods such as high fidelity, uniform high print density and the possible uses of cheap paper are complemented by the advantages of relative simplicity and higher Speed.

Printing is carried out by applying a correspondingly shaped electric field in the form of a short-lasting impulse between a donor sheet and a receiver sheet located close to it. Included there are electrically conductive particles of a printing material or on the surface of the donor sheet Pigments that are dispersed in or on a high-resistance medium. The electric field is now causing a flow of charge to the print major, whereby the latter becomes the receiver sheet in the electric field moved towards. The print particles moved in this way adhere to the receiver sheet, along with their arrangement corresponds to the print image, which is determined by the corresponding shaping of the electric field became.

The invention describes a simple, one-step process for rapid, contactless printing through selective charging of image-defining pigment particles on a donor sheet and its transfer to a recipient sheet. Typical for that The method is that the same field pulse charges the particles and simultaneously from the donor sheet to the receiver sheet moved there. It is also characteristic that the pulse has an extremely short duration. In the end may be a device for preventing field collapse or a discharge between donor sheet and receiver sheet can be provided, as a Such a field collapse still entails a charge transport, but no longer any pigment movement could cause.

Further details and features of the invention can be found in the claims and / or the following description can be taken from the explanation of the embodiments shown in the drawing serves the invention. It shows

1 shows a schematic sectional illustration of a simplified arrangement of electrodes and pigment donors and receiver sheet as a first embodiment of the invention,

FIG. 2 shows a variant of FIG. 1 without a gap or insulator,

Fig. I the representation of a further variant of Fig. 1, in which closely adjacent characters are printed,

4 shows the representation of a variant of FIG. 1, in which a character is printed on two recipient sheets at the same time we printed ^.

5 shows a sectional illustration of a possible embodiment of a pigment dispenser, and FIG

6 shows a sectional illustration of a possible embodiment of one to be depicted Icon shaped electrode.

All drawings are schematic and in some Respect enlarged representations. The arrangements shown are therefore not to scale. So can-

If a pigment donor and receiver sheet are more or less close together, d. H. touch each other or with a small space between them, as well as the ratio from electrodes to these sheets can vary within limits. It is generally believed that a Air or vacuum gap between electrodes and sheets as between the sheets themselves. Likewise, the representation of a pulse as a square pulse is only intended to be an example, since it is due to function devices according to the invention does not depend on the shape of the pulses.

An embodiment of the invention is shown in simplified form by FIG. Between A pair of mutually facing metallic electrodes 12 and 14 has a leaf assembly 16. This is composed of three sheets, namely a back part or sheet-shaped insulator 18 for Discharge suppression, usually as a film made of polyester film based on ethylene glycol and Terephthalic acid, a polyethylene terephthalate resin and the like, further made of a sheet-shaped pigment donor 20, which can consist of a tissue carrier with movable particles impregnated with a resinous insulating binder or a matrix of insulating material or can be coated, in which electrically conductive pigment particles are incorporated, and finally from a Receiver sheet 22, which is normally ordinary paper, e.g. B. made of rag or a newspaper. Paper with a smooth, hard surface should preferably not be used because it offers the particles too little opportunity to adhere.

The electrode 14 has a smooth, flat surface, which touches the sheet-shaped insulator 18. The electrode 12 forming a print head is in this embodiment shaped according to the symbol to be depicted and bears a relief mark 24 of the symbol to be printed; the sign 24 faces the recipient sheet 22. A gap 26 can be the sign 24 separate from the receiver sheet 22, but it is preferably chosen to be only as wide as absolutely necessary necessary to avoid a collapse of the electric field when an electric pressure pulse is applied 28 to prevent connections 30 and 32.

A gap at this point is practically necessary in those devices in which the corresponding to the The symbol-shaped electrode 12 to be depicted is arranged on a rapidly rotating drum, as would be required with high-speed printers. Likewise, between the electrode 14 and the leaf-shaped insulator 18 and a gap between the two leaves.

In Fig. 6, a modified printhead 12a is shown which is also suitable for such purposes; it is shown as it appears when viewed from the receiver sheet 22. The letter C is as metallic Relief image visible on an electrode body united with it. A layer of insulating material 33 fills the relief space and is level with the relief image surface. You can by uniform Covering the electrode with an insulating plastic material can be produced according to its Solidification ground down so far from its surface is until the surface of the metallic relief mark is exposed. This modified form for a printhead can be used in any of the below Execution methods can be used.

In a preferred embodiment, the sheet-like pigment donor 20 has a relatively high level Resistance value and is made as follows:

Composition 1:

carbon
Polystyrene

black Iosol dye
yellow Iosol dye
red Iosol dye
toluene

Weight percent

6%

3%

0.8%

0.8%

0.8%

88.6%

100%

However, the above composition is only intended to serve as an example. The carbon is in a solution of the resin and the dyes dispersed, namely by Bfnui / .uiig dci known sand mill technology. The resulting slurry is dried and the residue ground. With the granules the ground particles are impregnated into a nylon woven fabric sheet in a sand mill. The sheet impregnated in this way can take the form of a color

2 ^r > cloth, ribbon or other suitable shape.

The resistivity of the sheet-shaped pigment 20 is usually measured so that the Isolator 18 and the receiver sheet 22 are removed

jo and against the pigment generator 20 a pair of test electrodes are placed in order to reduce the DC resistance of the pigment donor path between to measure the electrodes; the opposing, identical test electrodes are round with a flat surface about 6 mm in diameter. This resistance value can be changed by changing the ratio of the conductive dye to the insulating resin can be varied. The polystyrene resin is known as an insulating material, but in the application in question it is slightly conductive due to the Presence of dyes dissolved or dispersed in the resin. It should be noted that the at Toners generally used in earlier electrostatic printing processes had insufficient conductivity for use in the method according to the invention.

If one uses the embodiment according to the composition in the arrangement of FIG. 1, where the Pigment donor 20 has a resistance value of 2 -10 "

so ohm cm, with a gap 26 of approximately 50 μ and with an insulator 18 made of polyester film .ün 8 μ Thickness, an image of the character 24 is obtained as a print on the receiver sheet 22 by applying it a pulse 28 of 1300 volts over a period of 150 nanoseconds. This extraordinarily short one Time interval is characteristic of the high printing speed of the method according to the invention. The applied voltage pulse causes two phenomena in the material of the pigment donor 20: firstly in the presence of the electric field a current through the matrix of the high-resistance binder, what an electrical charge of the coloring and carbon-containing granules on or near the surface of the pigment donor, and secondly, the detachment of a sufficient number of those charged in this way Granule particles from the pigment donor 20 and their migration to the receiver sheet 22.

The now adhering to the sheet-shaped receiver 22

Granules can - if desired or necessary - be fixed there, for example by action by heat, if the particles are fusible, or by means of solvents, lacquers or other appropriate way. >

The method discussed according to FIG. 1 can now be expanded or changed in several points. For example, the tissue of the pigment transmitter 20 may be made of a different material or be replaced by another material such as ^{|. (>} By paper or a plastic film, it may be partly or entirely the high-impedance medium contained in the dispersing the marking particles or are bonded and through which the current flows. Known techniques for coloring and coating of color cloths can also be used. The high-resistance matrix which contains the conductive particles can be used as an impregnation as well as a surface coating

Plastic film carrier sheet 34 made of a material ho- ^ v hen electrical resistance, coated or impregnated with a resinous binder or a matrix 36 made of insulating material, in which movable and electrically conductive pigment particles 38 are dispersed.

The method described can be carried out in all the variants listed here both in a vacuum, for example below 4 × 10 ^s Torr, as well as at atmospheric pressure and in air or in the presence of other gases. J0

P_r gap 26 serves, together with the sheet-shaped insulator 18, to prevent an arc discharge or partial or shunt discharge of the amount of charge on pigment particles 38; through such a partial discharge, the electric field could not be used to transport the particles 38 to develop the receiver sheet 22 required forces. However, under certain conditions the gap 26 or the insulator 18 or both are omitted. In Fig. 2 both are omitted, with one Pulse 40 has a lower amplitude than pulse 28, which in this case triggers the printing process enough. Here a sheet-shaped pigment donor 42 of relatively low resistance is used; it has the following composition:

Composition 2:

Weight percent

Carbon 5%

Alcohol 95%

100%

The carbon is dispersed in the alcohol, and the dispersion becomes a nylon cloth in a sand mill impregnated as a carrier. The color cloth is dried and its surface mechanically in one Sand mill partially removed. Here the fibrous carrier forms instead of a plastic coating the high-resistance matrix material in which the carbon particles are charged when a current flows through it.

When using the composition 2, in which ω of the sheet-shaped pigment donor 42 has a resistance value of 5 X 10 ^ft ohms cm, with the device according to FIG a voltage of 250 volts of pulse 40. Even without a gap, satisfactory results were obtained with 40 nanosecond pulse duration and 250 volts.

With an ink sheet of 5 Χ l0 ^c 'Erm · cm resistance value can without insulator 18 with higher pulse amplitudes are worked, if a gap is used similarly to the FIG. 1. For example, printing is possible with a 25 μ gap, with a pulse amplitude of 500 volts and a pulse duration of 40 nanoseconds.

3 shows a basic arrangement for printing out a character 44 and an adjacent one Character 46 shown on the recipient sheet 22. Both relief-like characters are on an electrode 48, opposite of which is a flat electrode 50 and a further electrode 52 of the same type are attached. A space 58 of 50 μ is provided between the latter. A leaf-shaped insulator 54 is also used here. A selective printing of the characters 44 or 46 can be carried out by An electrical pulse 56 is applied to lines 30, 32 and 30, 31, respectively. With a gap 58

44 and 46 on the one hand and the receiver sheet 22 on the other hand, with a pigment generator 20 with a resistance value of 1.8 X 10 '"ohm · cm and a A 1000 volt pulse with a duration of 150 nanoseconds enables selective printing to be carried out successfully will; likewise with a pigment generator of 2 X 10 "ohm · cm resistance value and a pulse of 1300 volts at 150 nanoseconds duration.

The same success was achieved with lower voltages (750 volts) and a pigment donor of 4 x 10 ^s ohm cm; the gap 58 and the leaf-shaped insulator 54 were omitted.

Fig. 4 shows a further embodiment. Here, printing is carried out on two receiver sheets 22a and 22b at the same time. In the embodiment shown, the sheet-like pigment dispenser 42 has a relatively low resistance; on the lines 30 and 32 is a pulse 60 with an amplitude of 400 volts and a pulse width of 110 nanoseconds. By applying the pulse, the pressure granules in or near the upper surface of the sheet-shaped pigment donor 42 are charged with one polarity and moved towards the receiver sheet 22a, while at the same time the granules in or near the lower surface of the pigment donor are charged with the opposite polarity and to the receiver 22b to be led.

As suggested in FIG. 4, it is also possible in the embodiments of FIGS. 1 to 3 that the Relief symbols 24, 44, 46 are located on one of the two electrodes; that means the printhead may be due to the pigment donor or receiver sheet; in any case it must break the electric field the character to be printed. Which side is chosen is simply decided by the Print quality of the achieved print image. The application of a relief mark on each of the two electrodes a pair of electrodes is therefore also possible. Otherwise, the surfaces of each other opposing electrodes should be flat, with the printed character then outlining the electrode surface equals.

In practice it turns out to be necessary that the shape of the electric field extends over the entire distance from electrode to electrode, especially in the space between pigment donor and Recipient identical to the character to be printed. Such a requirement can be the choice of material for the Constrict carrier sheet 34 of pigment dispenser 20 in some cases, since too high a conductivity of this carrier

bialts to equalize the electrical potential at points within the carrier sheet and thus to a destruction of the desired field structure. In the embodiments of FIGS. 1 to 3, this point of view need not be paid attention to, since the carrier sheet does not lie in the above-described critical region of the electric field. In the embodiments of FIG. 4, however, this is the case; The carrier sheet of the pigment donor 42 lies between the relief mark 24 and the surface of the receiver sheet 22b, so that a printing process of the latter is only successful if the carrier sheet has a sufficiently high resistance *

The present invention is suitable for from ¹ printing of symbols, such as binary code, as well as from alphänunierischen characters or other configurations; it is also possible to print in the half gate, as well as the printout of blocks and lines.

The conductive paint particles used in the present invention can have various shapes and sizes consist of different material, they can for example consist of powdered metals such as Compose brass, or from metal oxides, such as lead dioxide. Still other types of dyes, However, solutions and resins with high dielectric constants can also be used.

ίο The example of FIG. 4 indicates that a multi-layer arrangement with several sheet-shaped pigment donors and between them located, sheet-shaped receivers in the manner of conventional printing from Dufchschlägen

(5 is possible; it is always assumed that all leaves are sufficiently high resistance so that the shape of the electric field is preserved and no distortion subject.

1 sheet of drawings

Claims (13)

Patent claims: 1. A method for printing a symbol to be imaged on a symbol, in particular in the form of a sheet Receiver, by means of a pulsed electrical field, the shape of which corresponds to the corresponding to the printing symbol and with its help movable pigment particles from the surface a pigment donor are directly transferable to the recipient, the pigment donor and the receiver are located between the electrodes for generating the electric field, characterized in that one uses a pigment donor with an irregular surface structure on which the movable Pigment particles distributed and separated from each other by a medium of high electrical resistance are separated, which essentially balances the electrical potential between the individual points of the surface of the pigment donor and thus a destruction of the Contours of the electric field on this surface prevents, and that one is electrically conductive Pigment particles used. 2. The method according to claim 1, characterized by the use of pigment particles that are essentially uncharged prior to the application of the electric field. 3. The method according to claim 1 or 2, characterized by the use of at least one shaped according to the symbol to be depicted Electrode. 4. The method according to any one of claims 1-3, characterized by the use of an isolator between an electrode and the pigment donor or the receiver. 5. The method according to any one of claims 1-4, characterized in that the electric field is applied across a gap. 6. pigment donor for performing the method according to any one of claims 1-5 with a Carrier sheet made of a material of high electrical resistance, characterized in that the The surface of the carrier sheet carrying pigment particles has an irregular surface structure having. 7. pigment donor according to claim 6, characterized in that the carrier sheet is fibrous is. 8. pigment donor according to claim 6 or 7, characterized in that on the carrier sheet a binding agent of high specific resistance is provided, which in finely divided form the electrically contains conductive pigment particles. 9. pigment donor according to any one of claims 6-8, characterized in that the pigment particles consist essentially of Kolenstoff. 10. Pigment donor according to one of claims 6-8, characterized in that the pigment particles are metallic. 11. Pigment donor according to one of claims 8-10, characterized in that the binder consists of resinous particles. 12. Pigment donor according to one of claims 8-11, characterized by a dye, which is dispersed or dissolved in the binder. 13. Pigment donor according to claim 8, characterized in that the binder is essentially is a dye-impregnated polystyrene material.