EP0401208B1 - Process and device for printing by inking a latent image - Google Patents

Abstract

Printing device comprising a temperature-control device (A) by means of which an image support (10) guided by a motor through the printing device is controlled approximately uniformly at a predetermined temperature, a thermal lettering device (B) which produces a latent character image on the image support (10) by means of local supply of heat controlled in function of the character, and a developing device (C) in which the latent character image is developed by condensation of an ink vapour or by application of ink.

Description

The invention relates to a method and an apparatus for printing by coloring a latent thermal image.

Non-mechanical printing processes which are based on the electrophotographic or magnetographic principle are generally known and have been used successfully. Such a printing process, which works on the principle of electrophotography, is e.g. known from US-PS 4,311,723. A latent charge image is generated on an electrostatically charged photoconductive material, be it a photoconductor drum or a photoconductor belt, by selective discharge using an imagewise modulated light source. This charge image is then colored in a developer station by electrically charged color particles (toner) and then in a transfer station on a recording medium, e.g. transfer a continuous paper tape or a single sheet.

Such a charge pattern is developed either by applying dry toner or liquid toner.

During dry toner development, the charge of the color particles is generated triboelectrically, by friction on so-called carrier particles, usually iron, steel or ferrite, which also ensure transport close to the charge pattern due to their magnetic adhesion to a rotating magnetic roller.

The color particles can also be charged by other methods, e.g. Corona charge or generated by the polarization of the toner particles in the electric field of the latent charge image itself. In order to obtain an acceptable ratio between the undesirable adhesive forces of the toner particles to the photoconductor, carrier or transport device and the desired electrical switching forces, it is customary to use a toner particle size of approximately 5 to 10 μm.

With the liquid processes, e.g. by chemical charge separation electrically charged toner particles in an insulating organic carrier liquid, e.g. Isopar (trademark of Exxon). The color particles can be much smaller since undesirable adhesive forces are better balanced.

During dry toner development, the required particle size creates a certain granularity of the image with negative effects on very fine characters and the transition area between image patterns and background (edge sharpness). In addition, local electrical development fields in these transition areas result in a particularly high particle application, which can lead to visible image disturbances (over-toning) and, consequently, to poorer adhesion of the toner to the recording medium.

Disadvantages of liquid development processes are the discharge of the carrier liquid from the printing device together with the recording medium and the very high sensitivity of the particle application to fluctuations in the toner concentration in the carrier liquid.

The magnetographic principle is based on the generation of a latent magnetic image on a permanently magnetizable carrier medium. A certain amount of iron allows the one-component toner powder to adhere to the imagewise magnetized carrier medium. Transfer printing is carried out with pressure or magnetic field support.

As with electrophotographic processes, the granularity of the toner powder is disadvantageous. The iron / ferrite additive also complicates the production of brilliant colors.

An electrostatic copying device is known from US Pat. No. 4,514,744, in which a light-tight thin layer is first applied to a band-shaped photoconductor. With the help of a thermal labeling device, this layer is then removed depending on the character, e.g. by evaporation. After exposure of the photoconductor, the photoconductor is colored with toner and transferred onto a recording medium. The light-tight layer is then removed from the photoconductor.

A printing device is also known from US Pat. No. 4,718,340, in which a monomolecular layer of hydrophilic or oleophilic material is applied to a roller with an application element. This layer is made dependent on the character with the help of a thermal printing element, e.g. a laser can be detached. With the help of another application element, an aqueous solution is then applied and the layer, which is structured as a function of the character, is colored with the aid of a color application element. The image is then transferred to a recording medium.

The object of the invention is to provide a non-mechanical printing method and a printing device which makes it possible to produce a print image of high resolution and high color saturation on a recording medium at a high printing speed, be it continuous paper or single sheets.

This object is achieved according to the patent claims. Advantageous embodiments of the invention are characterized by the subclaims.

According to one embodiment of the invention, on a movably guided, thermally stabilized carrier in a printer, by means of a character-dependent controlled thermal labeling device, e.g. can contain a laser or Peltier elements, generates a latent thermal drawing image. This latent thermal character image is then exposed to steam. According to the temperature distribution of the character image, the steam condenses on the image areas of the character image that have a temperature below the dew point of the steam. Colored steam or colorless steam can be used as steam. In the following, under 'colored steam', both pure color steam, i.e. evaporated paint, as well as colorant vapor i.e. Vapor of a carrier liquid understood with color particles floating in it.

The condensate deposited on the support, which is either colored as pure color steam condensate itself or has color particles as colorant steam condensate, is then printed onto a recording medium.

In this way, a transfer printing which is little influenced by the properties of the recording medium and the color to be transferred is achieved.

The condensation process does not result in a different application of paint in points and edges and in extensive areas, and the submicroscopic size of the vapor particles completely avoids a granularity of the image.

In a further embodiment of the invention, an oleophilic or hydrophilic thin liquid film is applied to a support set at an approximately uniform temperature. A latent thermal cell image is then generated by selective evaporation of the liquid film on the carrier by means of a character-dependent controlled thermal labeling device. This latent character image is then developed in a developer station by condensing a colored vapor. The developing drawing image is then transferred to single sheets or continuous paper in a transfer printing station.

As a carrier for the latent thermal character image, it is advantageous if it consists of an elastic composite material that has a surface layer with a high thermal conductivity perpendicular to the surface and a low thermal conductivity in the surface direction, and if the surface layer is arranged on a heat-insulating carrier layer.

A composite material of this type can produce a latent thermal character image that is stable over a longer period of time without the latent thermal tick image flowing through heat transfer. Furthermore, the condensation heat released during the condensation is reliably dissipated from the image surface and thus enables a safe condensation.

In a further embodiment, the character image generated by condensation can also be colored separately using a paint atomizer.

If the latent thermal character image is colored with the aid of a condensation device, it is furthermore advantageous to guide the carrier through a development space through which steam flows and which is connected to a steam cycle system. In this steam cycle system, the excess steam discharged from the development space is condensed and fed again to an evaporator device that generates the steam.

Particularly favorable coloring conditions with regard to the latent thermal character image result when the steam and the carrier move in the opposite direction in the development space (countercurrent principle).

In the following, the term recording medium means both paper and any other printable material. This material can also be a textile tape or a plastic tape, for example.

• FIG 1 eine schematische Schnittdarstellung einer Druckvorrichtung mit einer Kondensations-Entwicklereinrichtung.
• FIG 2 eine schematische Schnittdarstellung einer Aufzeichnungsträgerstruktur aus Verbundwerkstoff und
• FIG 3 eine schematische Schnittdarstellung einer Druckvorrichtung mit einer Befeuchtungseinrichtung mit der auf einen Zwischenträger ein oleophiler oder hydrophiler molekularer Flüssigkeitsfilm aufgebracht wird und bei der Umdruck mit Hilfe einer Farbwalze erfolgt.

Embodiments of the invention are shown in the drawings and are described in more detail below, for example. Show it

• 1 shows a schematic sectional view of a printing device with a condensation developer device.
• 2 shows a schematic sectional illustration of a record carrier structure made of composite material and
• 3 shows a schematic sectional view of a printing device with a moistening device with which an oleophilic or hydrophilic molecular liquid film is applied to an intermediate carrier and is carried out during transfer printing with the aid of an ink roller.

A printing device shown only schematically here contains a band-shaped carrier (intermediate carrier 10) made of composite material, which is driven by an electric motor and is guided over deflection rollers 11. However, a correspondingly dimensioned roller is also possible. The intermediate carrier 10 is designed as an endlessly circulating band and consists of an elastic composite material, the structure of which will be described later. The various units of the printer are grouped around this intermediate carrier 10. They essentially consist of a cooling device A, with which the intermediate carrier is brought to a defined temperature; a thermal inscription device B for generating a latent thermal character image; a developer device C for coloring the latent thermal character image; a transfer printing device D for transferring the colored latent thermal drawing image to a recording medium 26, for example a paper web, and a cleaning device E which cleans the recording medium 10 of color residues.

The structure and function of these units is described below using the various process steps of the printing process.

Cooling device

In a first method step, the intermediate carrier moved in the printer with the aid of deflection rollers 11 driven by an electric motor is brought to a uniform temperature by means of the cooling device A. When water is used as the color carrier liquid, this temperature is preferably between 10 and 15 ° C. between 0 and 20 ° C. The cooling device consists of one to three cooled pressure roller pairs 13, which ensure a uniform recording medium temperature. However, the cooling is also contact-free e.g. possible through an air flow.

Thermal labeling device

The image areas not to be colored are heated to a temperature between 60 to 120 ° C., preferably 80 to 100 ° C., by means of a thermal inscription device. For labeling, i.e. The local heating of the areas not to be colored in the image is suitable for high-energy electromagnetic radiation, which is absorbed as completely as possible by the material of the belt. This can e.g. be provided by CO2 waveguide lasers or high-temperature lamps. In the case of laser use, e.g. uses the deflection and focusing optics known from laser printers to generate the image pattern, as used e.g. in U.S. Patent 4,311,723. With high temperature lamps e.g. a PLZT switching optics makes sense, the structure of which can be found in DE-OS 36 23 487. However, the labeling device can also consist of laser diode arrays, microwave elements or pin electrode arrays.

With all these elements, a latent thermal drawing image is created, which consists of individual heat points, wherein the thermal labeling device can be controlled via a conventional character generator, not shown here, as can be seen, for example, from US Pat. No. 4,311,723.

It is also possible to generate the thermal character image with the aid of a contact made of Peltier elements which rest on the intermediate carrier 10 and selectively cool or heat it depending on the character in accordance with the principle customary in thermal transfer processes.

Developing device

The latent thermal character image embossed on the intermediate carrier 10 is developed within the developing device in that colored steam is guided past the intermediate carrier 10 in the countercurrent principle. For this purpose, the developing device has a closed steam cycle system. This consists of a liquid vapor container 14 with a heating device 15 for evaporating the color liquid 16 into a temperature-controlled steam buffer space 17. The colored steam flows under the action of a radial fan 18 into a development space 19 through which the intermediate carrier 10 is guided in a vapor-tight manner. The band-shaped intermediate carrier 10 forms a side wall of the development space. With the aid of a further radial blower 20 arranged at the other end of the development space 19, the colored steam, after it has been guided past the direction of movement of the intermediate carrier, is transported into the return condensation unit 21 and condensed there. The condensate then drops back into the liquid vapor container 14 under the effect of gravity. This liquid vapor container 14 is connected to a liquid storage container 23 via a control valve 22.

In the event of a pressure interruption, electromagnetic is arranged at the entrance area of the development space 19 Actuatable valve flap 24 completed the development space and at the same time opened the connection to a shunt tube 25 connecting the outlet of the radial blower to the liquid vapor container 14, so that the paint vapor flows back into the liquid vapor container 14.

The colored steam flowing into the development space 19 is kept at a temperature of approximately 5 ° Celsius below the temperature of the non-image areas of the thermal drawing image on the intermediate carrier 10 in order to avoid condensation in these areas.

The amount of paint applied to the intermediate carrier 10 is mainly dependent on the relative speed between the intermediate carrier 10 and the steam flow, on the temperature difference between the steam and image area, on the thermal capacity of the ribbon and on the thermal conductivity of the ribbon and liquid.

At temperature differences of 70 to 80 ° Celsius and relative speeds of the belt steam flow of 2 to 4 m / sec. layers of color from 5 to 20 µm are produced. This enables a very flexible design of the printing device for printing speeds between 0.1 to 1 m / s, since a color application of only 2 to 4 µm is required for a good print image.

It should be pointed out, however, that the image can be produced using either the positive or the negative method, which means that the characters consist either of the non-colored parts or of the colored parts of the thermal drawing image.

In an embodiment not shown here, the paint is applied in color powder atomization only after the condensation of the carrier liquid. In this exemplary embodiment, another color powder atomizing device follows the actual developing device at. The structure of this paint powder atomization device corresponds to that of conventional paint powder atomization systems known from powder coating technology.

Transfer printing device

The transfer of the colored thermal drawing image takes place within the transfer printing station D. The continuous paper 26 or the textile tape is continuously guided past a deflection roller 27 at the speed of the intermediate carrier 10 with slight pressure.

When using water as the carrier liquid, both continuous paper and individually transported paper sheets, or e.g. Textiles with appropriate absorbency. If suitable liquids are used, plastics and metal foils can also be printed.

Cleaning facility

The intermediate carrier 10 is cleaned after transfer printing in the cleaning device E by means of a scraper blade 28 and a cleaning brush 29, at the same time the intermediate carrier 10 is rinsed with carrier liquid.

The cleaning and the cooling of the intermediate carrier 10 to a uniform temperature can be combined, wherein in an embodiment of the invention, not shown here, the tape is immersed in a bath of carrier liquid brought to the desired preparation temperature during the cleaning.

After cleaning, the described recording cycle begins anew.

In order to be able to reliably generate the latent thermal character image on the carrier 10, this exists according to the illustration in FIG. 2, expediently made of an elastic composite material with a high thermal conductivity perpendicular to the surface and a low thermal conductivity in the surface direction. This thermal conductivity can be generated, for example, by applying a surface layer 31 with a layer thickness between 30 to 300 µm, preferably 70 to 130 µm, on a heat-insulating plastic carrier material, for example made of Mylar, with a thickness of 100 to 500 µm. The surface layer 31 can contain, for example, a large number of thin fibers made of metal or other thermally conductive materials. These fibers, which run perpendicular to the surface layer 31, are embedded in corresponding heat-insulating plastic, for example made of Mylar.

In one embodiment of the invention shown in FIG. 3, the thinnest possible liquid film made of an oleophilic or hydrophilic liquid is applied to the intermediate carrier with the aid of a liquid application device 33. This liquid application device can consist of a container 34 which holds the liquid 35 and which has at its lower end a roller 36 which transfers the liquid to the intermediate carrier. The oleophilic or hydrophilic, very thin liquid film is then selectively evaporated by means of the thermal inscription device B already described, and a latent character image is thereby generated with the liquid film. The latent character image is now developed either with the aid of a steam condensation development device according to FIG. 1 or by applying paint using an ink roller 37 with an associated storage container 38. The paint used can be either water-based or oil-based. In accordance with the hydrophilic or oleophilic image pattern on the intermediate carrier 10, the color is only recorded in accordance with the image pattern.

The inked character image is then in the usual way in the transfer printing station on a recording medium 26 e.g. Transfer paper 26.

In the exemplary embodiments shown, it has been assumed that the drawing image is first generated on a carrier, referred to as intermediate carrier 10, which consists of an endless belt. With a corresponding construction of the carrier, however, it is also possible, in accordance with an embodiment of the invention, not shown here, to generate the drawing image directly on the carrier, which is then the recording medium itself, and then to color it with the aid of one of the development devices described. The recording medium used could have a structural structure according to FIG. 2.

Reference symbol list

10th

Record carriers, intermediate carriers

11

Reversing rollers

A

Cooling device

B

thermal labeling device

C.

Development facility

O

Transfer printing device

E

Cleaning facility

13

Pinch roller pairs

14

Liquid vapor container

15

Heater

16

Color liquid

17th

Steam buffer room

18th

Radial blower

19th

Development space

20th

Radial blower

21

Feedback condensing unit

22

Control valve

23

Storage container

24th

Valve flap

25th

Shunt tube

26

Continuous paper

27th

Pulley

28

Scraper element, scraper blade

29

Cleaning brush

30th

Plastic carrier material

31

Surface layer

32

Fibers

33

Liquid application device, humidifier

34

container

35

liquid

36

roller

37

Ink roller

38

Storage container

Claims (13)

1. Process for producing a character image by vapour condensation, comprising the following process steps:

a) A carrier (10) movably guided in a printer is brought to a uniform temperature (A),

b) a latent thermal character image is produced on the carrier (10) by means of a thermal inscription device (B) which is controlled in a character-dependent manner, and

c) the latent thermal character image is developed in a developer station (C) by condensation of a coloured vapour or by separate inking after condensation of a vapour, the condensation behaviour of the vapour and the temperature of the carrier (10) being selected so that the vapour is deposited on the carrier (10) in a character-dependent manner.

2) Process for producing a character image by vapour condensation, comprising the following process steps:

a) A carrier (10) movably guided in a printer is brought to a uniform temperature,

b) a liquid film (33) is applied to the carrier (10),

c) a latent character image is produced on the carrier (10) by means of a thermal inscription device (B) controlled in a character-dependent manner, with selective vaporisation of the liquid film, and

d) the latent character image is developed in a developer device (C) by inking, utilising the condensation of a coloured vapour.

3. Process according to one of Claims 1 or 2 comprising the following process step:
The developed character image is transferred to a record carrier (26) in an offset print station (D).

4. Process according to Claim 1, comprising the following process step:
The character image consisting of condensate is separately inked by means of ink powder spraying.

5. Device for producing a character image by vapour condensation, comprising

- a temperature control device (A) for setting a carrier (10) guided through the device to an approximately uniform, predetermined temperature,

- a thermal inscription device (B) for producing a latent thermal character image by local supply of heat, controlled in a character-dependent manner, to the carrier (10) and

- a developer device (C) for developing the latent thermal character image by condensation of a coloured vapour or by separate inking after condensation of a vapour.

6. Device for producing a character image by vapour condensation, comprising

- a temperature control device (A) for setting a carrier (10) guided through the device to an approximately uniform, predetermined temperature,

- a dampening device (33), disposed in front of an inscription device (B) in the direction of movement of the carrier (10), for producing a liquid film on the carrier (10),

- a thermal inscription device (B) for producing a latent character image by local supply of heat, controlled in a character-dependent manner, to the carrier (10) and

- a developer device (C) in which the latent character image is developed by inking, utilising the condensation of a vapour.

7. Device according to one of Claims 5 or 6, comprising an offset print station (D) for transferring the developed character image to a record carrier (26).

8. Device according to one of Claims 5 to 7, comprising a carrier (10) consisting of composite material, which carrier exhibits a surface layer (31) having a high thermal conductivity perpendicular to the surface and a low thermal conductivity in the direction of the surface and a thermally insulating carrier layer (30).

9. Device according to Claim 8, comprising a surface layer (31) having a layer thickness of 30 to 300 µm and a carrier layer (30) having a layer thickness of 100 to 500 µm.

10. Device according to one of Claims 5 to 7, comprising a carrier (10) which is formed as an endless belt or as a roller.

11. Device according to one of Claims 5 to 7, comprising a development space (19) which receives the carrier (10) in the development region and through which vapour flows.

12. Device according to Claim 11, comprising a vapour circulation system, connected to the development space (19), including a vapour container (14), a heating device (15) for vaporising a liquid and a temperature-controlled vapour buffer space (17) and a reflux condensation unit (21) which condenses the vapour guided through the development space (19) and feeds the concentrate to the vapour container (14).

13. Device according to Claim 11, comprising a device which guides the vapour counter to the direction of movement of the carrier (10) through the development space (19).

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