EP1728124A2 - Method for printing on a recording medium using a liquid developer fixed by cross-linking - Google Patents

Abstract

According to the invention, in order to print on a recording medium (402), potential images of the images to be printed are produced on a potential image recording medium. Said potential images are developed on the potential image recording medium in order to form an image film, by means of a liquid developer consisting of a polymerisable carrier liquid containing suspended toner particles. The image film is than transferred to the recording medium (402) and fixed by the cross-linking of the carrier liquid. The toner particles are not melted.

Description

Method for printing on a recording medium using a liquid developer fixed by crosslinking

For single or multi-color printing on a recording medium e.g. a single sheet or a tape-shaped recording medium made of various materials, e.g. Plastic, paper or thin metal foils, it is known on a potential image carrier, e.g. a photoconductor to generate potential images (charge images) depending on the image, to color them in a developer station (inking station) and to print the image thus developed onto the recording medium.

Either dry toner or liquid developer can be used to develop the potential images.

A method for electrophoretic liquid development (electrographic development) in digital printing systems is e.g. known from EP 0 756 213 Bl or EP 0 727 720 Bl. The process described there is also known under the name HVT (High Viscosity Technology). A carrier liquid containing silicone oil with color particles (toner particles) dispersed therein is used as the developer liquid. The toner particles typically have a particle size of less than 1 icon. Further details can be found in EP 0 756 213 B1 or EP 0 727 720 B1, which form part of the disclosure of the present application. There are described electrophoretic liquid development processes of the type mentioned with silicone oil as carrier liquid with toner particles dispersed therein and also a developer station comprising one or more application rollers for wetting the potential image carrier with liquid developer in accordance with the potential images on the potential image carrier. The developed potential image is then transferred to the recording medium via one or more transfer rollers.

In order to fix the toner images in the recording medium, they are fixed there. Previous liquid developer processes Ren are based on a high-resistance carrier liquid and suspended in it solid particles (toner particles) with a preferred charge.

- When using a volatile carrier liquid, the fixation takes place by evaporation of the carrier liquid and simultaneous melting of the toner particles under the action of heat. The resin of the toner particles sticks together and to the recording medium.

- When using a non-volatile carrier liquid, e.g. Silicone oil, the fixation takes place by reducing the carrier liquid on the surface of the recording medium and by simultaneously melting the toner particles under the action of heat. The carrier fluid is reduced, among other things. by sucking away into the record carrier and / or over conditioning rollers that run on the unfixed print image and thereby remove carrier liquid.

The problem to be solved by the invention consists in specifying a method with which the fixation with liquid developer is largely independent of the properties of the recording medium. Furthermore, the fixation should also be independent of the carrier of the color pigment (toner particles).

This problem is solved according to the features of claim 1.

The invention specifies a novel fixing method for an electrographic printing or copying device. The device contains an image-generating system, which generates an electronic potential image (charge image) on a first potential image carrier (e.g. a photoconductor), which is made visible by means of a developer station (coloring station) through charged dye particles (toner particles) and then, if necessary about other intermediate image carriers, such as Transfer rollers, transfer belt, transferred to a recording medium (e.g. paper) and fixed on it.

Further developments of the invention result from the dependent claims.

In order to be able to carry out a fixation using the method according to the invention, the use of a liquid developer consisting of a high-resistance carrier liquid and toner particles is advantageous. The carrier liquid can have a resistance of preferably> = 10 ¹⁰ Ohm * cm and a boiling point of> 100 ° C. A carrier liquid that meets these requirements can be based on silicone oil, for example

The silicone oil can have polydimethylsiloxane (PDMS) molecules,

• The silicone oil can consist of molecules derived from polydimethylsiloxane (PDMS), which can have functional groups.

The liquid developer should preferably have a weight fraction of toner particles of 10 to 55%.

Further advantageous properties of the carrier liquid can be:

- The developer liquid can have a concentration of dispersion stabilizers in the range from 0.5 to 5%, preferably> 1% (there is a significantly increased concentration compared to conventional liquid developers which are <1%). - The toner particles can have a reduced proportion of the carrier (conventionally resin) to bind the color pigments. - The incorporation of the color pigments can be optimized for stable and uniform chargeability without the low melting temperature of the binder (resin) required for heat fixation. If the liquid developer has these properties, the toner images can be fixed on the recording medium by crosslinking the carrier liquid without the toner particles having to be melted. This is done by polymerizing the carrier liquid and / or by adding an auxiliary and / or by the action of a low auxiliary energy. Since only the carrier liquid is used for fixing, the properties of the recording medium for fixing are irrelevant.

Furthermore, the polymerization reaction has progressed so far in process-relevant time (<1 sec) that the toner image is securely connected to the recording medium and the recording medium can be further processed directly.

The polymerization reaction can be controlled so that the properties of the toner image can be adapted to different requirements, e.g. Hardness, gloss can be adjusted.

The fixing according to the method according to the invention is thus characterized by the following special features: the fixing of the toner image on / on the recording medium takes place solely by crosslinking the carrier liquid; • The excess carrier liquid not required for fixing the toner image can be removed from the potential image carrier or intermediate carrier and / or recording medium; • The carrier liquid is transparent on the recording medium in the cross-linked state; By crosslinking the carrier liquid, the toner particles are embedded in a solid polymer matrix, wherein the carrier liquid firmly connects to the recording medium; In the non-image areas, the carrier liquid is solidified into a transparent film; • The carrier liquid can be cross-linked by: - reaction of radicals with the methyl groups of the PDMS; - Polymerization: assembly of the carrier liquid molecules into polymeric macromolecules by start reaction, chain growth and chain termination reaction; Polycondensation: connection of the carrier liquid molecules by reaction with various functional groups by elimination of by-products; - Polyaddition: Continuous addition of two different types of molecules without splitting off by-products.

Furthermore, the crosslinking reaction of the carrier liquid can be started or accelerated by one or more additional components and / or its continuation can be made possible:

• The effect of radiation or radiant energy can represent an additional component.

• The radiation energy can be supplied in the form of heat.

• Free radicals can be created as a result of corona radiation.

The additional component can be in a gas, e.g. Ozone, which acts on the developer liquid; - The gas can be combined with one of the above-mentioned radiation energies, especially the corona radiation.

• The additional component can be an increased humidity; - The increased humidity can be generated by vaporization, a spray bar, etc.; - The increased air humidity can be used in conjunction with a condensation-curing carrier liquid; - The increased humidity can be combined with one of the radiation effects mentioned above.

• The additional component can be a solid or a liquid; - This solid or liquid can act as a reactant; - A catalyst can also be integrated into the component; the catalyst can combine with e.g. Contain platinum, tin, titanium; - This solid or liquid can be combined with one of the radiation effects mentioned above; - The effect of the reaction partner can only be generated by the combination with one of the radiation effects mentioned above.

• The addition or action of a component can take place at various points in the printing process; the addition of the abovementioned radiation effects can take place after the imagewise development of a toner image, preferably after the transfer to the recording medium; - The action of increased air humidity can take place after the imagewise development of a toner image, preferably after transfer to the recording medium; - A reaction partner can be added to the developer liquid circuit in the developer station; - The addition of a reaction partner can take place after the transfer to the record carrier (for example behind each printing module) - through a spray bar; - by a roller application unit.

• If the component is a solid or a liquid, the recording medium can be coated with it. This can be done: - offline to the printing process; - Inline to the printing process before the toner image is transferred to the recording medium.

The invention is further explained on the basis of an exemplary embodiment which is shown in the figures.

Show it

1 shows a basic illustration of a printing or copying device with which the method can be carried out;

2 shows the fixing of toner images in a basic representation;

Fig. 3 shows another way of fixing toner images.

1 shows a basic illustration of an electrographic printing device. First, a potential image carrier 101, for example a photoconductor drum, is exposed to an erasure exposure 102. The potential image carrier is then charged in a station 103. Potential images of images to be printed are generated on the potential image carrier 101 by imagewise exposure in the station 104. These potential images are developed in a developer station 200 by a liquid developer with the properties mentioned above. For this purpose, liquid developer is taken from a developer supply 203 and fed to an application roller 202. The application roller 202 promotes the liquid Winder to an applicator roller 201 and this to the potential image carrier 101. The applicator roller 201 is then cleaned in the cleaning station 204.

During the development of the potential images on the potential image carrier 101, carrier liquid with toner particles passes over to the potential image carrier 101 in the image regions and is deposited there, in the non-image regions carrier liquid is transferred to the potential image carrier 101. A film is thus formed on the potential image carrier 101 which contains carrier liquid with toner particles in the image regions and carrier liquid in the non-image regions.

The film is transferred to a recording medium 402 in a transfer printing station with an intermediate carrier 301. A back pressure roller 401 is also used for this. The intermediate carrier

301 can also be cleaned with the help of an intermediate carrier

302 can be cleaned.

The record carrier 402 is finally fed to a fixing station 500, in which the fixing takes place according to the method described above. 2 shows the course of the fixation. The fixing station 500 has a radiation source 501, which emits radiation 502 as auxiliary energy. The radiation 502 is directed onto the recording medium 402 and strikes there on the film 503 which contains the printed images. The film 503 has the toner particles 504 and the carrier liquid 505. The radiation 502 connects the film 503 to the recording medium 402 according to the method described above, i.e. Carrier liquid 505 is crosslinked, but toner particles 504 are not melted.

In a second implementation according to FIG. 3, corona radiation is used as auxiliary energy. The fixing station 500 here has a corona radiation source 506, the radiation of which is directed onto the recording medium 402. With help the radiation, the carrier liquid 505 is crosslinked and solidified, as a result of which the toner images 504 are fixed on the recording medium 402. The toner particles 504 are not melted in the process.

The development of the potential pictures is summarized as follows:

- The charged toner particles dispersed in the carrier liquid pass completely (or almost completely) onto the potential image carrier in the area of the developer gap between the potential image carrier and applicator roller and are deposited there.

- After leaving the developer gap, no (or almost no) toner particles remain on the potential image carrier in the non-image areas.

- The transfer from the potential image carrier via possibly additional intermediate carriers (e.g. transfer roller, transfer belt) to the recording medium takes place by mechanical contact and / or by electrostatic support.

- With each transfer step, the carrier liquid is split proportionally between the potential image carrier and possibly subsequent intermediate carriers (applies to the recording medium), the splitting taking place into image and non-image areas.

If excess carrier liquid on the record carrier or an intermediate carrier is to be removed, this can be done in the following way:

by a conditioning roller that is in contact with the intermediate carrier and / or recording medium,

by a conditioning roller • which is connected to potential in such a way that the charged toner particles are repelled by it and only the carrier liquid is split up; - The carrier liquid transferred to a non-absorbent conditioning roller can be removed, for example, by a doctor blade;

if the roller has an absorbent coating, the transferred carrier liquid can e.g. be removed by a squeeze bar.

The networking of silicone oil-based carrier liquids can be done in the following ways:

- By using radicals: the radicals react with the methyl groups of the PDMS, so that crosslinking is created by oxidation with peroxy compounds.

- Through the formation of silicone rubber (rubber): through wide-meshed crosslinking of the organic side groups of the silicone chains due to chemical bonds.

- By polymerization: acid-catalyzed or by KOH; Absence of chain-terminating substances (Me3SiO-) or cross-linking groups [MeSi (-0-) 3], strengthened by pyrogenic silicon dioxide.

- By oxidative cross-linking (vulcanization): • by benzyl peroxide and heating; • at room temperature through small controlled amounts of Si-H groups, which can be added catalytically to previously added Si-CH = CH2 groups; • by crosslinking one-component silicone rubber with acetoxy groups by exposure to moisture at room temperature.

- By means of hot-curing (addition-curing) silicones: these consist of 1 or 2-component systems with, for example, platinum as a catalyst, the reaction proceeding without elimination of by-products; the vulcanization time for 1-component and 2-component systems is dependent on the temperature , - Condensation-curing silicone: They consist of 1 or 2-component systems with, for example, tin as a catalyst and air humidity for crosslinking. By-products are generated during the reaction. The vulcanization time in 2-component systems depends on the catalyst (hardener) and in 1-component systems on the air humidity, thickness of the layer and the temperature.

- Through the formation of silicone resins: it is achieved by spatial networking of the siloxane framework.

- By polycondensation: by hydrolysis of phenyl-substituted dichlorosilanes or trichlorosilanes in toluene; Removal of HCl with water and partially controlled polymerization. Final connection to 3-dimensional siloxane frameworks is achieved by heating in the presence of a heavy metal or quaternary ammonium catalyst and condensation of the silanol group.

Reference character list

101 potential image carrier 102 erasure exposure 103 charging 104 image-wise exposure 105 cleaning of the potential image carrier 200 developer station 201 applicator roller 202 feed roller 203 liquid developer conveying 204 cleaning of the applicator roller 301 intermediate carrier 302 cleaning of the intermediate carrier 401 counterpressure roller 402 recording medium 500 fixing station 501 radiation source 502 radiation 503 print image 504 source liquid corona particles 505 solid particles 505

Claims

Expectations 1. A method for printing on a recording medium, - in which potential images of the images to be printed are generated on a potential image carrier (101), - in which the potential images (101) are created by a liquid developer from a polymerizable carrier liquid with dye particles suspended therein on the potential image carrier (101) be developed into an image film, - in which the image film is transferred to the recording medium (402), - in which the image film is fixed on the recording medium (402) by crosslinking the carrier liquid. 2. The method according to claim 1, wherein the crosslinking of the carrier liquid embeds the dye particles of the image areas in a solid polymer matrix and the carrier liquid firmly connects to the recording medium (402). 3. The method of claim 2, wherein the carrier liquid is transparent in the crosslinked state. 4. The method according to claim 2 or 3, wherein the carrier liquid is solidified in the non-image areas to form a transparent film. 5. The method according to any one of the preceding claims, wherein the carrier liquid is based on silicone oil. 6. The method according to claim 5, wherein the silicone oil consists of polydimethylsiloxane. 7. The method according to claim 5, in which the carrier liquid consists of polydimethylsiloxane-derived molecules which have functional groups. 8. The method according to any one of the preceding claims, wherein the liquid developer has a weight fraction of 10 to 50% of dye particles. 9. The method according to any one of the preceding claims, wherein the liquid developer has a concentration of dispersion stabilizers in the range of 0.5 to 5%. 10. The method of claim 9, wherein the concentration is> 1%. 11. The method according to any one of the preceding claims, wherein the incorporation of color pigments in the color particles in the liquid developer requires a reduced proportion of a binder. 12. The method of claim 11, wherein the fixation is independent of the binder of the color pigment. 13. The method according to any one of the preceding claims, wherein the crosslinking of the carrier liquid is carried out by a reaction of radicals with the methyl groups of the polydimethylsiloxane. 14. The method according to claim 13, wherein the crosslinking is formed by oxidation with peroxy compounds. 15. The method according to any one of claims 1 to 12, wherein the crosslinking of the carrier liquid is carried out by polymerization. 16. The method according to claim 15, in which the carrier liquid molecules assemble into polymeric macromolecules by means of a start reaction, chain reaction and / or the chain termination reaction. 17. The method according to claim 16, in which silicone rubber is formed by wide-mesh crosslinking of the organic side groups of the silicone chains as a result of chemical bonds. 18. The method of claim 17, wherein the assembly is acid catalyzed or caused by KOH (potassium hydroxide). 19. The method according to claim 16 or 17, wherein the assembly takes place in the absence of chain-breaking substances (Me3SiO-) or cross-linking groups (MeSi (-0-) 3). 20. The method of claim 19, wherein the assembly is enhanced by pyrogenic silicon dioxide. 21. The method according to any one of claims 1 to 12, in which an oxidative crosslinking (vulcanization) is carried out. 22. The method of claim 21, wherein the vulcanization is carried out by benzyl peroxide and heating. 23. The method according to claim 21, wherein the vulcanization is carried out at room temperature by small amounts of Si-H groups, which can be added catalytically to previously added Si-CH = CH2 groups. 24. The method of claim 21, wherein the one-component silicone rubber with acetoxy groups is crosslinked by the action of moisture at room temperature. 25. The method according to any one of claims 1 to 12, in which for crosslinking hot-crosslinking (addition-crosslinking) silicones consisting of a 1- or 2-component system with e.g. Platinum can be used as a catalyst. 26. The method according to any one of claims 1 to 12, in which for crosslinking a condensation-crosslinking silicone consisting of 1- or 2-component system with e.g. Tin is used as a catalyst and air humidity. 27. The method according to any one of claims 1 to 12, wherein the crosslinking of the carrier liquid is formed by formation of silicone resins with spatial crosslinking of the siloxane framework. 28. The method according to any one of claims 1 to 12, wherein the crosslinking of the carrier liquid is carried out by polycondensation. 29. The method according to claim 28, in which the polycondensation is carried out by hydrolysis of phenyl-substituted dichlorosilane or trichlorosilanes in toluene 30. The method according to any one of claims 1 to 12, in which the carrier liquid is crosslinked by polyaddition, two different types of molecules being added continuously without splitting off by-products. 31. The method according to any one of the preceding claims, in which the crosslinking of the carrier liquid takes place with the addition of an auxiliary and / or auxiliary energy. 32. The method according to claim 31, wherein the crosslinking reaction of the carrier liquid is started, accelerated or extended by at least one component. 33. The method of claim 31 or 32, in which acts on the carrier liquid as a component radiation or radiation energy. 34. The method of claim 33, wherein the radiation energy is supplied in the form of heat. 35. The method of claim 33, wherein the radiation energy acts by corona radiation. 36. The method according to claim 31 or 32, in which as a component a gas, e.g. Ozone that acts on the carrier liquid. 37. The method of claim 31 or 32, in which increased humidity is used as a component. 38. The method of claim 37, wherein the increased humidity is generated by vaporization or a spray bar. 39. The method of claim 37, wherein the increased humidity is used in conjunction with a condensation-crosslinking carrier liquid. 40. The method according to claim 31 or 32, in which a solid or liquid is used as the component, which acts as a reactant. 41. The method according to claim 40, in which a catalyst is additionally incorporated, which contains a compound with e.g. Contains platinum, tin, titanium. 42. The method according to any one of claims 31 to 41, in which the individual components are combined. 43. The method as claimed in one of claims 31 to 42, in which the component acts on the carrier liquid at different points in the printing process. 44. The method according to claim 43, in which the addition of the radiation or the effect of the increased atmospheric humidity takes place after the development of the toner image, preferably after the transfer printing onto the recording medium (402). 45. The method according to claim 43, in which the addition of a reaction partner into the liquid developer takes place in the developer station (200) or takes place after transfer printing onto the recording medium (402) by means of a spray bar or roller application unit. 46. The method according to claim 43, in which the recording medium is precoated with a solid or liquid as a component. 47. The method according to any one of the preceding claims, wherein the excess carrier liquid is removed by a conditioning roller. 48. The method according to claim 47, in which a potential is applied to the conditioning roller such that the dye particles are repelled and the carrier liquid is broken down. 49. The method of claim 47, wherein the conditioning roller has an absorbent coating. 50. The method of claim 47 or 48, wherein the conditioning roller is cleaned by a doctor or squeeze bar from the transferred carrier liquid. 51. Electrographic printing or copying device, in which printed images which have been printed on a recording medium (402) are fixed in accordance with the method according to one of the preceding claims.