EP0631209B1 - Printing method with at least one image and press for executing this method - Google Patents

Description

The invention relates to a new printing process and the press for implementing this process.

The process of the invention is a hybrid process combining in a way the techniques and advantages of current magnetography with the techniques of magnetolithography as they were exposed in the French patent application entitled "Printing process and press for the implementation "filed on 14.01.93 under the number 93 00301 by the company NIPSON (EP-A-0 607 081) and electrostatography techniques.

It is known from the patent of the United States of America issued under the number US 5,129,321 in the name of the Rockwell International Corporation, a lithographic printing system which makes it possible to dispense with the use of an engraved plate and therefore positioning and timing thereof, but which has the drawback of not being perfectly suited to large print runs.

Indeed, in this lithographic printing system, the invention consists in replacing for printing with a conventional ink (oleaginous) the assembly constituted by the engraved plate and the plate-carrying cylinder by a simple cylinder on the periphery of which each time a new pattern is to be printed, is deposited a layer forming a substrate of powdery oleophobic material, uniform layer on which is produced, using an oleophilic curable material, an image corresponding to the patterns to print. The intermediate transfer element therefore consists of the substrate of oleophobic material and the zones of oleophilic material carried by this layer.

Preferably, the oleophobic material is magnetic, and the cylinder is magnetizable, so that the layer of this material is maintained at the periphery of the cylinder by magnetizing the latter.

The deposition of the oleophilic material, in a configuration corresponding to the patterns to be printed, is carried out using an electronic, electromechanical or electromagnetic transfer device, data representative of the patterns to be carried on the layer of oleophobic material which are contained in an electronic memory. These data are used so that the transfer device deposits oleophilic material only at the necessary locations on the layer of oleophobic material. In an implementation described in this patent, the oleophilic material used is a magnetic and fusible material; its deposition on the oleophobic material substrate is effected by magneto-deposition on the cylinder, in the manner of the deposition of magnetic toner in magneto-graphic printers. To this end, magnetic heads are arranged near the cylinder, which make it possible to create, on the substrate, zones with magnetization making it possible to attract the particles of oleophilic material.

After its deposition, the oleophilic material is fused which makes it possible to harden it on the one hand to prevent the patterns from being deformed, and on the other hand to give it a certain cohesion with the substrate in oleophobic material, the particles of oleophilic material s 'hanging on those of oleophobic material. To this end, the system described in this patent further comprises, near the periphery of the cylinder, a melting device for fixing the oleophilic material.

Printing is carried out as on a conventional press: the cylinder, after having been coated with the substrate layer and patterns, is rotated, then wetted and inked, so that the ink is distributed over the patterns and the wetting product on the oleophobic zones, then the ink is transferred to the printing medium (paper or other) via a blanket.

When the desired printout of an image is reached, the cylinder is demagnetized, so that the substrate layer spontaneously detaches from the cylinder, carrying with it the hardened patterns, of oleophilic material, which it carries. If the printing of another image is desired, then a new substrate is produced, on which are worn then hardened new patterns. The constitution of the patterns corresponding to an image, as well as their removal, are therefore very rapid and less costly than with conventional presses.

This device lends itself to full color printing, insofar as the positioning of the patterns is carried out automatically, by an electronic device.

However, it requires the deposition of two types of material: that constituting the substrate and that constituting the patterns. However, the deposition of the substrate has the function of allowing easy subsequent removal of the oleophilic patterns by forced detachment of this substrate and of preventing the ink from being deposited on the parts of the cylinder not provided with oleophilic material.

In addition, it is not entirely suitable for large print runs because the substrate tends to come off spontaneously, at least in certain places, during the rotation of the carrier cylinder during the printing phases, since it is simply held magnetically. We must therefore monitor the copies that come out and sometimes reconstruct the image (substrate and patterns) at the periphery of the cylinder during printing.

Similarly, it is known from the American patent application issued under the number 3,804,511 in the name of Pelorex Corporation, a device and method for printing an image by transfer of at least one dye vehicle between an intermediate transfer element and a printing medium, comprising at least one phase of automatic production of the intermediate transfer element by developing zones on the intermediate element each having a different affinity with the coloring vehicle. The different affinity of the zones is obtained by developing an electrostatic image of the graphic information by exposure of an endless band whose upper layer consists of zinc oxide. Magnetic toner particles are then applied to this surface and adhere according to the electrostatic image developed on the zinc oxide layer. Portions of this surface are magnetized to form a magnetic image corresponding to the electrostatic image. Then the toner particles are transferred by pressure to a copy medium such as paper, while the magnetic image is retained on the surface of the tape. New magnetic particles can then be applied to the magnetic image for the production of additional copies.

Such a device has the disadvantage of preferably using a zinc oxide strip which is a first generation photoconductor having a very short service life.

On the other hand, so that such a band does not die in fatigue, the cycle time between the exposure of an image and the resetting of the band to change the image must be very long, that is to say of the order of a second. This therefore requires very long strips and generates a high cost for the material.

Document EP-A-0 097 954 discloses an electrostatic printing process by transfer of a coloring vehicle between an intermediate element obtained by magnetic imaging and a substrate or printing medium. The magnetic image on the intermediate element is produced, in a first imaging device, by the fusion of magnetic toner on the intermediate element to form an image of insulating toner. The intermediate element is removed from the imaging device and then placed in a press where the insulating toner is electrostatically charged to develop areas having different affinities with the coloring vehicle. Then, the coloring vehicle is deposited on the loaded image, the coloring vehicle consisting of toner particles comprising a coloring agent and a binding agent such as a thermoplastic polymer. Finally, the coloring vehicle is transferred to the printing medium either by electrostatic means, or by pressure means, or by heating means associated with pressure means. After the print medium has passed through the last print station, the toner is fused to the medium by heating means.

However, this process is not suitable for large print runs because of the complexity of the processing it requires. In fact, in the imaging device, a first decorating roller creates the magnetic image on a second magnetic roller. Then, the magnetic toner image of the second roller is transferred to the intermediate member or conductive roller. In addition, throughout the process, numerous corona devices as well as suction means neutralize and eliminate the toner which is not correctly transferred from one roll to another. This complexity, also due to the need to manipulate the intermediate element between the imaging device and the press, significantly increases its cost.

The main object of the present invention therefore is to overcome the drawbacks of the prior art by proposing a simple printing process which is low in cost while allowing constant quality and the possibilities of monochrome and full color lithographic printing, whatever the envisaged print, without requiring the etching of a plate, without using materials requiring oleophilic or oleophobic qualities to solve the wetting problems, or with a blanket.

• le matériau isolant et durcissable est durci et soumis à une charge électrostatique par tout dispositif susceptible de le charger en surface afin de conférer aux zones représentatives de l'image l'affinité avec le véhicule colorant;
• le véhicule colorant ayant des propriétés électrostatiques est déposé sur les parties du matériau durci chargées électrostatiquement et enfin le transfert du véhicule colorant sur le support d'impression est effectué par contact direct avec l'élément intermédiaire de transfert.

This object is achieved by the fact that the process of printing at least one image, at a determined print, using a press, by transfer of a coloring vehicle between an intermediate transfer element obtained by imaging magnetic and a printing medium, comprising at least one phase of automatic production of the intermediate transfer element in the press by developing on a substrate zones each having a different affinity with the coloring vehicle, some of which correspond to the image to print, is characterized in that a material, insulating and curable, is fixed on the substrate to constitute these zones with different affinities,

• the insulating and curable material is hardened and subjected to an electrostatic charge by any device capable of charging it on the surface in order to give the areas representative of the image affinity with the coloring vehicle;
• the coloring vehicle having electrostatic properties is deposited on the parts of the hardened material electrostatically charged and finally the transfer of the coloring vehicle on the printing medium is carried out by direct contact with the intermediate transfer element.

In another feature, the method includes a step of cleaning the transfer member by removing the curable material when a new image is to be printed.

According to another particular feature, the coloring vehicle is previously charged with electrostatic charges of opposite polarity to the charge of the curable material.

According to another particularity, the hardenable material is fusible, and the determined operation of the withdrawal phase consists of a fusion of the hardenable material on the substrate, the substrate having a low thermal inertia, so that immediately after the fusion and the withdrawal , the substrate regains the temperature it had before this phase, allowing without delay the creation of a new transfer element.

According to another particularity, the hardenable material is chemically attackable, and the determined operation of the withdrawal phase consists of a chemical attack of this hardenable material on the substrate, the press substrate being formed so as not to be reached by this attack.

According to another particular feature, the substrate cannot be dismantled from the press and formed so as to have a low thermal inertia, so that the consequences of an increase in its temperature, due to chemical attack, are quickly blurred to allow the almost immediate creation of a new intermediate transfer element after removal of the hardenable material.

According to another particular feature, the method consists in constituting the intermediate transfer element by depositing on the non-dismantable substrate of the press a magnetic curable material using a magnetic transfer device comprising means for removing the curable material from a reservoir and means for placing the hardenable material at determined locations on the substrate, so as to constitute there an image corresponding to the patterns to be printed.

In another feature, the material is curable by polymerization.

According to another particularity, the material is curable by fusion.

Another object of the invention is to provide a press allowing the implementation of the method according to the invention.

This object is achieved by the fact that the printing press comprises means for depositing a material in determined locations representative of an image on an endless band carried by rollers allowing its movement, the endless band is metallic , the deposited material is hardenable and the press comprises at least one station for electrostatically charging the hardened material and a station delivering a coloring vehicle having electrostatic properties to adhere to the hardened material after it has hardened in order to constitute the patterns to be transferred to print media.

According to another particular feature, the press includes means for removing and cleaning the hardened material.

According to another particular feature, the press comprises the means for electrostatically charging the hardened material with a charge of given polarity.

According to another particular feature, the electrostatic charge of the hardened material is obtained by a corona device.

According to another particular feature, the press includes means for loading the coloring vehicle with a polarity opposite to that of the hardened material.

According to another particular feature, the charge of the coloring vehicle is triboelectric and the press comprises in the means for delivering the coloring vehicle a device ensuring the mixing of the coloring vehicle so as to cause the charging of the particles by friction.

According to another particular feature, the material is curable by making it heat, then cool, the press comprising heating means opposite the tone of the width, and of a small part of the length, of the strip.

According to another particular feature, at least two heating means are arranged opposite one another, on either side of the two main faces of the strip.

According to another particular feature, the hardened material can be removed by melting, the withdrawal means being constituted by heating means, for remelting the hardened material, associated with means for cleaning the remelted material.

According to another particularity, the curable material is polymerizable by exposing it to radiation, such as ultraviolet radiation, the press comprising means making it possible to emit such radiation towards the entire width, and of a small part of the length, of the strip.

According to another particular feature, the hardened material can be removed by chemical attack, the press comprising means making it possible to spray a chemical agent on the hardened material, associated with means for cleaning the remelted material.

According to another particularity, the cleaning means, such as scrapers or scrapers, are arranged on the one hand so that the recasting or the chemical attack of the material is initiated before this material comes into contact with the cleaning means, in order to facilitate their action and, on the other hand, so that their action is facilitated by natural gravity.

According to another particular feature, the strip is metallic, the press comprises means for transferring a curable magnetic material between a reservoir and determined locations of the metallic strip.

According to another particularity, the strip is made of magnetic material, and the means for transferring the magnetic material comprise on the one hand, on the side of the face of the strip on which the material is to be deposited, and in the vicinity thereof, an outlet opening for the material from the reservoir, and on the other hand, opposite the opening, on the side of the opposite face, a set of magnetic heads, for selectively magnetizing certain points of the strip and attracting material on these points.

According to another particular feature, the set of magnetic heads is displaceable relative to the strip, in order to compensate for the spacing between the heads and to constitute on the strip patterns of high print quality.

• à proximité de la bande, un nombre n de stations pour appliquer chaque véhicule colorant électrostatique sur le matériau après son durcissement, équivalent au nombre de couleurs de base nécessitées pour l'impression, chaque station contenant une couleur de base différente d'une autre ;
• une longueur développée de la bande au moins égale à n fois la longueur du plus grand document susceptible d'être imprimé par la presse;
• des moyens d'asservissement et de commande agencés pour qu'une seule des stations d'application du véhicule colorant soit active à la fois.

According to another particular feature, the press intended for the full color printing of documents, in particular of sheet-by-sheet documents, comprises:

• near the strip, a number n of stations for applying each electrostatic coloring vehicle to the material after it has hardened, equivalent to the number of base colors required for printing, each station containing a base color different from another;
• a developed length of the strip at least equal to n times the length of the largest document capable of being printed by the press;
• servo and control means arranged so that only one of the application stations of the coloring vehicle is active at a time.

According to another particular feature, the press comprises means for applying the printing medium against the strip, consisting of a sheet feed device, a sheet cylinder in contact in rotation with the strip and d 'A device for recovering printed sheets, the servo and control means being arranged so that the sheet cylinder performs n rotations to completely print a sheet.

According to another particular feature, the press for full-color printing of documents using n basic colors, in particular continuous printing, comprises n presses each having a single station for application of a coloring vehicle, each station containing a color different base from another, the press being arranged so that the print medium passes successively in front of each of these presses.

• la figure 1 illustre un premier mode de réalisation d'une presse permettant une impression monochrome selon le procédé de l'invention ;
• la figure 2 illustre un autre mode de réalisation d'une presse permettant une impression polychrome ;
• la figure 3 illustre le principe d'impression mis en oeuvre dans le procédé selon l'invention.

Other characteristics and advantages of the invention will appear on reading the description, of embodiments of the invention given by way of illustration but not limitation, made with reference to FIGS. 1 to 3, in which:

• FIG. 1 illustrates a first embodiment of a press allowing monochrome printing according to the method of the invention;
• FIG. 2 illustrates another embodiment of a press allowing full color printing;
• FIG. 3 illustrates the printing principle implemented in the method according to the invention.

The press shown in FIG. 1 allows the deposition of a fusible material (1) on an endless metal strip (2), in order to constitute the intermediate element supporting the patterns corresponding to an image to be printed on a printing medium. (3) such as continuously fed paper. The endless belt, carried by supporting rollers (4, 5, 6, 7, 8) is in contact with printing support, such as paper (3), using a pressure roller (90) .

In the example illustrated, the fusible material (1) is pulverulent and magnetic, and is contained in a reservoir (210) before it is deposited on the endless strip (2). A device (21) for magnetically transferring the fusible material (1) from the reservoir to the strip is provided and allows the curable material (1) used to be a magnetic material, curable by melting, polymerization, or other process. The substrate, formed by the endless band is a material itself magnetizable. A device (21) for placing the material (1), at the appropriate locations on the strip (2), is composed on the one hand of a reservoir (210) of material provided with an outlet opening and placed on the side of the face of the strip (2) which is in contact with the printing medium (3), and on the other hand of an excitation device (211) with magnetic heads, placed on the other side of the strip, that is to say inside the space delimited by the endless strip. This excitation device makes it possible to selectively excite determined points of the strip to magnetize it and to attract at these points the material (1) contained in the reservoir, in order to form zones there where it is possible to develop an affinity with the coloring vehicle (ink) used.

The magnetic head assembly (211) is movable relative to the strip to compensate for the location between the heads and to provide high print quality patterns on the strip.

The dimensions of the endless strip 2 should make it possible to reproduce therein the largest image intended to be printed with the press, that is to say that, for example, the developed length and the width of the strip 2 are respectively at least equal to those of this image.

The material 1, after having been transferred to the metal strip 2, is fixed firmly on the latter. As already indicated, this operation makes it possible to avoid dismantling the patterns during printing.

In the embodiment, illustrated by this FIG. 1, this fixing is carried out by heating, then allowing to cool, the material. For this, at least one heating member 14 is provided in the vicinity of the strip 2, taking account of the direction of travel (illustrated by arrows) thereof, so that the material can be fixed immediately after being deposited, and acts on the entire width of the strip, and on a small length portion thereof.

Preferably, this member 14 is arranged opposite the surface of the strip which receives the fusible material 1, so that its action is as effective as possible. However, as illustrated by this figure, in order for the heating to be even more efficient and rapid, it is conceivable to have at least one other heating member 15, facing the first 14, and facing the surface of the strip opposite to that which receives the material. Of course, due to the low thermal inertia of the strip, a heated part of it cools as soon as it leaves the zone, of short length, heated by the means 14, 15, so that the hardening is very fast. In this way, the material adheres to the substrate (strip) by the bonding forces, the magnetic forces only intervening during the development of the magnetic image.

In a variant, the material used is hardenable and fixable by natural or forced polymerization, for example by exposing it to ultraviolet radiation. In this case, the member 14, that is to say the one disposed opposite the surface of the strip which receives the fusible material 1, would be replaced by an appropriate radiation source. No source corresponding to the member 15 would be provided opposite, since the radiation would be stopped by the band 2.

Of course, the magnetic transfer device (211) and the heating members (14, 15) are only put into operation when it is necessary to constitute areas representative of the image on the thin strip (2).

The hardened material (1) magnetically secured to the strip (2) is brought to a station (16) for corona charging where a corona wire (161) electrostatically charges this material (1). After the station (16) for corona charging, the hardened material or substrate (1), electrostatically charged, is designated in Figures 1 to 3 by the reference numeral (10). As a material (1), a magnetographic toner can be used which, by the magnetic compounds which it contains, has a low colorability potential but, by the polymerizable materials allowing its hardening, is very insulating (resistivity between 1012 and 1014 ohms. cm), which allows it to charge electrostatically without problem while the metal strip (2), which is conductive, will not retain any electrostatic charge. At the exit from this station there is therefore a substrate (2) coated in places with areas covered with a hardened material having a different affinity with the coloring vehicle which is deposited therein at the inking station (17). This coloring vehicle (9) will advantageously consist of an electrostatic toner having a good colorability potential. This toner (9) will deposit on the areas having affinities, that is to say on the areas coated with the hardened material electrostatically charged. The inking station (17) will comprise for example two rollers (171, 172) ensuring an internal mixing of the toner made up largely of polymers to thus charge this toner by triboelectricity, in the case of a solid electrostatic toner then used in conjunction with a carrier (carrier) as is known in the state of the prior art of electrophotography. In a variant, liquid electrostatic toners may be used, the toner consisting of fine coloring particles, the carrier then consisting of a liquid having the required dielectric characteristics, as is also known in the state of the prior art . The charges thus developed in the toner will preferably have the opposite polarity to those developed on the hardened magnetic material (1). On contact with the print media strip (3), the electrostatic toner (9) is transferred on the printing medium (3) and only the hardened magnetic material (1) remains on the substrate (2).

Finally, the press includes a device for removing the material, which is put into service when the drawing of an image is reached, to allow the dismantling of intermediate transfer device without damaging the substrate formed by the surface of the thin strip (2)
In the case of the press illustrated in FIG. 1, adapted to operate with a fusible material (1), the removal device comprises means (18) for recasting the material, such as the heating members, means (19) cleaning equipment such as scrapers or scrapers and, optionally, a material recovery tank (20). The remelting means and those (19) for cleaning are arranged relatively to each other and to the strip so that the areas to be cleaned are heated, so that the material (1) is at least partially remelted, before undergo the action of the cleaning means (19), and so that the recasting continues when the cleaning means are active.
The embodiment of FIG. 1 makes it possible to meet these constraints: the recasting means (18) are arranged facing the surface of the strip opposite to that which receives the material, and the cleaning means (19) are on the side of the surface that supports the material. The cleaning means (19) are opposite only part of the recasting means, so that there is a press area where the zones of the strip to be cleaned undergo the simultaneous action of means (18) for recasting and those (19) for cleaning.
Preferably, the removal device is arranged in such a way that the action of the cleaning means (19) is facilitated by natural gravity. Figure 1 illustrates how this device should be placed for this action to be optimal. The cleaning means are positioned so as to act on a horizontal part of the strip, the surface to be cleaned facing the ground. Thus the material after being remelted, tends to fall spontaneously by gravity into the recovery tank (20) which is then placed below.
Of course, other arrangements of the removal device are possible to allow natural gravity to facilitate cleaning. It is sufficient for the removal device to act on a part of the strip arranged in a more or less significant slope, directed towards the ground.
The low thermal inertia of the metal strip means that, as soon as a part is no longer subjected to the radiation of the device recast, it cools very quickly, allowing the almost immediate constitution of a new intermediate transfer element.

As mentioned above, instead of carrying out a thermal attack, in order to recast the material 1, in order to clean the metal strip 2, with a view to preparing a new intermediate transfer element, it is possible to carry out chemical attack, provided that the agents chosen do not attack the metal strip. It is clear that this operation is much more delicate and that we will prefer thermal attack. The endless belt is still preferable in the case of a chemical attack, since it lends itself more easily to cleaning. In addition, a chemical attack generally generates a release of heat, and the low thermal inertia of a strip still allows its rapid cooling after cleaning using such an attack, and therefore the immediate constitution of a new transfer element.

In a variant, not shown, implementing this method, the means 19, 20 for cleaning and recovery are present, but the recasting means are replaced by means making it possible to spray the chemical agent. These are arranged so that, on the one hand, the chemical attack on the material 1 is initiated before it comes into contact with the cleaning means to facilitate their action and, on the other hand, so that their action is totally effective.

The device shown in Figure 1 allows only monochrome printing, since it only has one press and / or inking station.

The device of Figure 2 allows polychrome printing sheet by sheet that is to say, the printing of a support 3 in the form of independent sheets.

The device of FIG. 2 allows a polychrome sheet-by-sheet printing using for example 3 colors (red, green and blue) in the case of an additive synthesis, generally better suited to the case of solid electrostatic toners, or four colors including three of base (yellow, cyan, magenta) and black in the case of a subtractive synthesis generally better suited to the case of liquid electrostatic toners. This device consists of four inking stations A, B, C, D placed one after the other, and controlled by a single servo and control device (not shown).

In the example, the four inking stations (17A, 17B, 17C, 17D) are identical, and each correspond to that (17) described with reference to FIG. 1, that is to say that they comprise each a device for transferring a coloring vehicle 9 having electrostatic properties on the strip 2 coated with a curable material 1. It is understood that this representation is not limiting, and that the device could contain presses corresponding to those described with reference to Figure 1.

The first station 17A is used for example for printing yellow patterns, the second 17B for printing cyan patterns, the third 17C for printing magenta patterns, the fourth 17D for printing black patterns. For this, the sheets of paper 3 are brought into contact with the transfer roller 26 of this press. The essential differences between the press of FIG. 2 and those of FIG. 1 as regards the supply of paper are as follows: the press is associated with a device 25, known per se and not shown in detail, for feeding cut sheet, a sheet cylinder 26, and a device 27 for recovering printed sheets. The sheet cylinder 26 is in contact with the periphery of the strip 2, so that the rotational movement of the strip is transmitted to the cylinder 26, making it possible to transfer the image to a sheet carried by the cylinder 26. Of course , such a paper feed device could be adapted on the press of Figure 1 without changing the spirit of the invention.

The single control device controls both the magnetic transfer device 21 so that the pattern is correctly positioned and that the final image is of impeccable quality. Likewise, it controls the heating members 14, 15, the electrostatic charge inking device 16, a single inking device at a time 17A to 17D and finally the device 18,19,20 for removing the hardenable material.

In a preferred embodiment, the dimensions of the strip are such that it is possible to successively and adjacent thereto form the basic patterns corresponding to the separation of the colors making it possible to constitute a given image. In fact, the length the developed web should be at least three times the circumference of the sheet cylinder which determines the dimensions of the largest printable image. In this case, control and control means (not shown) of the press make it possible to select and activate synchronously an inking station, for example 17A with the passage of the corresponding basic image. On the other hand, the servo and control means are such that the same sheet remains for at least three turns on the sheet cylinder, so that each turn, one of the basic images can be printed. , so that the final image, which synthesizes at least three colors, appears on the sheet after at least three turns.

These preferred embodiments of the presses, in which the length of the strip is a function of the circumference of the sheet cylinder 26 allow the same image to be printed in large numbers, which is often the case in conventional printing, constituting once on strip 2 all of the patterns (three or four) corresponding to each base color of this image, and keeping this set as it is, until the expected print run of this image is reached , which reduces the number of redesign and cleaning operations, and achieves high printing speeds.

If the length of the strip is not linked to the maximum dimension of the sheets to be printed, but is less than three or four times this dimension, depending on whether the printing is in three or four colors, it is nevertheless possible to perform full color printing, but it is then necessary to clean the strip one or more times when printing each sheet, and to separately constitute the various patterns corresponding to the final image to be obtained, which results in a reduction in speed d 'impression. when it comes to making large prints.

According to another variant, the polychrome document printing device can be produced using n presses of the type of FIG. 1 and each having a single station (17) for applying a coloring vehicle, each station containing a color of base different from another, and in that it is arranged so that the print medium passes successively in front of each of these presses.

The presses according to the invention make it possible to obtain images of very good quality, with a print density comparable to that of lithographic presses.

FIG. 3 represents in more detail the stages of the printing process of the invention by magnetoelectrostatography. This method comprises a first step on which an area of the strip subjected to a magnetic field attracts particles 11 of a powdered magnetographic toner. The second step represents the melting of these powdery toner particles 11 to form a hardened substrate 1 which is held on the strip possibly by the remanent magnetism developed by the latter in the vicinity of the substrate but especially by the bonding forces of the polymers on the metal strip. The third step represents the surface charge of the hardened substrate 1 by electrostatic charges when passing through the corona station. This operation develops electrostatic charges on the surface of the molten substrate 1 which is made up of 60 to 90% polymer, to form the charged substrate 10. The electrostatic charges induced by the corona tube 16 on the metal strip 2 dissipate therein. since the strip is conductive. Finally, the fourth step represents the deposition on the charged substrate 10 of an electrostatic toner 9 charged with a polarity opposite to that of the charge of the cured substrate 10.

The method described provides the advantages of producing a resistant medium by melting the magnetographic toner while eliminating the problems of wetting solution or the presence of the blanket as in the magnetolithography process. In addition, this process by the fact that it uses electrostatic toners makes it possible to have better colorability than with magnetographic toners because these electrostatic toners in principle give access to all the colors.

In addition, the fundamental interest of the magnetographic developer is to reduce this role to a simple imaging intermediary in order to allow the development of a magnetic image on a metallic medium. Cycle times much shorter than those of the prior art are thus obtained. In fact, magnetic toners were used to develop electrostatic images on photoconductive mediums which have very long cycle times requiring very large bands. length and therefore resulting in expensive machines. Finally, the use of a relatively fragile photoconductive medium sensitive to the environment would not allow the toner to be melted or recast.

Furthermore, the step of remelting the magnetographic toner makes it possible to easily change the image on the tape.

Finally, between the different prints, the strip provided with the hardened substrate can be regularly recharged by the corotron (corona tube) at each turn (for each copy) without this requiring a new imaging phase.

So we have a system that can be used very flexibly, either with very long cycle times and electrostatic recharging during the cycle time, or with very short cycle times and reflow before a new phase of imagery.

Claims (27)

1. Method for printing at least one image, with a predetermined print run, using a press, by transferring a colouring vehicle (9) between an intermediate transfer element obtained by magnetic imaging and a print carrier (3), comprising at least: a phase of automatically producing the intermediate transfer element in the press by developing, on a substrate (2), zones that each have a different affinity with the colouring vehicle, some of which correspond to the image to be printed, characterised in that an isolating and hardenable material (1) is fixed to the substrate (2) in order to constitute these zones with different affinities,

   the isolating and hardenable material (1) is hardened and subjected to an electrostatic charge by any device (16) capable of charging it on the surface in order to confer on the zones representing the image the affinity with the colouring vehicle (9);

   the colouring vehicle (9) having electrostatic properties is deposited on the parts of the hardened material (1) that are electrostatically charged and finally the transfer of the colouring vehicle (9) to the print carrier (3) is effected by direct contact with the intermediate transfer element (2, 1).
2. Method according to Claim 1, characterised in that it comprises a stage of cleaning the transfer element by removing the hardenable material when a new image has to be printed.
3. Method according to Claim 1 or 2, characterised in that the colouring vehicle (9) is first charged with electrostatic charges of opposite polarity to the charge of the hardenable material (1).
4. Method according to Claim 2 or 3, characterised in that the hardenable material (1) is meltable, and the predetermined operation of the removal phase consists in melting the hardenable material (1) on the substrate (2), the substrate having low thermal inertia so that, immediately after melting and removal, the substrate (2) returns to the temperature it had before this phase, permitting the production of a new transfer element without delay.
5. Method according to Claim 2 or 3, characterised in that the hardenable material (1) can be attacked chemically, and the predetermined operation of the removal phase consists in a chemical attack of this hardenable material on the substrate (2), and in that the substrate (2) of the press is constituted so as not to be affected by this attack.
6. Method according to Claim 5, characterised in that the substrate (2) cannot be dismantled from the press and is constituted so as to have low thermal inertia, so that the consequences of an increase in its temperature, as a result of chemical attack, are quickly diffused in order to allow the almost immediate production of a new intermediate transfer element after the removal of the hardenable material (1).
7. Method according to Claim 1, characterised in that it consists in constituting the intermediate transfer element by depositing on the substrate (2), which cannot be dismantled from the press, a magnetic hardenable material (1) with the aid of a magnetic transfer device (21) comprising means (211) for taking the hardenable material (1) from a reservoir (210) and means for placing the hardenable material (1) at predetermined locations of the substrate (2), in order to constitute thereon an image corresponding to the patterns to be printed.
8. Method according to any one of Claims 1 to 7, characterised in that the material (1) is hardenable by polymerisation.
9. Method according to any one of Claims 1 to 7, characterised in that the material (1) is hardenable by melting.
10. Printing press, for implementing the method according to any one of the preceding claims, comprising means for depositing a material at predetermined locations representing an image on an endless belt (2) carried on rollers (4 to 8) allowing it to be set in motion, characterised in that the endless belt is metallic, the material (1) deposited is hardenable and the press comprises at least one station (16) for electrostatically charging the hardened material and at least one station (17) supplying a colouring vehicle (9) having electrostatic properties for adhering to the hardened material (1) after its hardening in order to constitute thereon the patterns to be transferred to the print carrier (3).
11. Press according to Claim 10, characterised in that it comprises means for removing and cleaning the hardened material (1).
12. Press according to Claim 10, characterised in that it comprises means for electrostatically charging the hardened material (1) with a charge of given polarity.
13. Press according to Claim 10, characterised in that the electrostatic charge of the hardened material is obtained by a corona device (16).
14. Press according to Claim 10, characterised in that it comprises means (171, 172) for charging the colouring vehicle (9) with a polarity that is opposite that of the hardened material.
15. Press according to Claim 14, characterised in that the colouring vehicle (9) is charged by triboelectricity, the press comprising, in the means (17) for supplying the colouring vehicle (9), a device (171, 172) ensuring that the colouring vehicle (9) is agitated so as to cause the particles to be charged by friction.
16. Press according to Claim 10, characterised in that the material (1) can be hardened by causing it to be heated, then cooled, the press comprising means (14, 15) for heating with respect to the whole width, and a small part of the length, of the belt (2).
17. Press according to Claim 16, characterised in that at least two heating means (14, 15) are arranged opposite one another, on either side of the two main faces of the belt (2).
18. Press according to one of Claims 10 to 15, characterised in that the hardened material (1) can be removed by melting, the removal means being constituted by heating means (18) for remelting the hardened material (1), associated with means (19) for cleaning the remelted material.
19. Press according to one of Claims 10 to 17, characterised in that the hardenable material (1) can be polymerised by exposing it to radiation, such as ultraviolet radiation, the press comprising means (14) making it possible to emit such radiation in the direction of the whole width, and a small part of the length of the belt (2).
20. Press according to Claim 19, characterised in that the hardened material (1) can be removed by chemical attack, the press comprising means making it possible to project a chemical agent on the hardened material, associated with means (19) for cleaning the remelted material.
21. Press according to one of Claims 18, 19 or 20, characterised in that the cleaning means (19), such as squeegees or scrapers, are arranged on the one hand so that the remelting or chemical attack of the material (1) is started before this material (1) comes into contact with the cleaning means, in order to facilitate their action and, on the other hand, so that their action is facilitated by natural gravity.
22. Press according to Claim 10, characterised in that the belt (2) is metallic, and in that the press comprises means (21) for transferring a hardenable magnetic material (1) between a reservoir (210) and predetermined locations on the metallic belt.
23. Press according to Claim 22, characterised in that the belt (2) is made of a magnetic material, and the means for transferring the magnetic material comprise on the one hand, on the side of the face of the belt on which the material has to be deposited, and close thereto, an opening for the material (1) to leave the reservoir (210) and, on the other hand, opposite the opening, on the side of the opposite face, an assembly (211) of magnetic heads, for selectively magnetising certain points on the belt and attracting material to these points.
24. Press according to Claim 23, characterised in that the assembly (211) of magnetic heads can be displaced relative to the belt (2), in order to compensate the spacing between the heads and to constitute high print-quality patterns on the belt.
25. Press according to Claim 10 or 24, for the multicolour printing of documents, in particular sheet-fed documents, characterised in that it comprises:

    - near the belt (2), a number n of stations (17A, 17B, 17C, 17D) for applying each electrostatic colouring vehicle to the material (1) after its hardening, equivalent to the number of base colours required for the printing, each station containing a different base colour from another;

    - a developed length of the belt (2) that is at least equal to n times the length of the largest document likely to be printed by the press;

    - servo-control means arranged so that just one of the stations (17A, 17B, 17C, 17D) for applying the colouring vehicle is active at any one time.
26. Press according to Claim 25, characterised in that it comprises means (25, 26, 27) for applying the print carrier (3) against the belt, constituted by a sheet-feed supply device (25), a sheet-carrier cylinder (26) in rotating contact with the belt (2) and a device for collecting the printed sheets, and in that the servo-control means are arranged so that the sheet-carrier cylinder (26) effects n rotations in order to print one sheet completely.
27. Press for the multi-colour printing of documents with the aid of n base colours, particularly continuous printing, characterised in that it comprises n presses according to any one of Claims 10 to 26, each having a single station (17) for applying a colouring vehicle, each station containing a different base colour from another, and in that it is arranged so that the print carrier passes successively in front of each of these presses.

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