EP1787169B1 - Method for uv curing toner images applied to an image support in an electrographic printing or copying device - Google Patents

Description

For single or multi-color printing of a final image carrier, e.g. a single sheet or a tape-shaped recording medium made of various materials, e.g. Paper or thin plastic or metal foils, it is known, on a potential image carrier, e.g. a photoconductor, image-dependent to generate potential images (charge images), which correspond to the images to be printed, consisting of areas to be inked and non-inked. The areas of the potential images to be inked are made visible by toner as a toner image with a developer station (inking station). Subsequently, the toner images are printed directly or with the interposition of an intermediate image carrier on the end image carrier and fixed there.

For dyeing the potential images, either dry toner or toner-containing liquid developer can be used.

The applied on the final image carrier and fixed toner images (in the following end images called) should have abrasion resistance, be temperature resistant and their gloss should meet the requirements. In addition, a sticking together of opposite end images (blocking) should be avoided.

Dry toner layers may be formed in a conventional manner during or after the fusing process, e.g. by means of cold or heated rollers, under pressure, whereby the gloss can be increased and the tendency for mechanical abrasion can be reduced.

Out DE 100 64 560 A1 or DE 100 64 552 A1 It is known to fix toner images in electrographic printers and to provide a luster that the toner image is melted by infrared light and then cured by UV irradiation, whereby the viscosity increases. For this purpose, a toner is used which has at least one polymer.

US 5,888,689 describes a method in which toner images are fixed on a support by chemical reaction of the toner with a layer on the support. The fixation is supported by heating (eg infrared radiation), in addition, the toner image can be cured by UV irradiation.

In EP 1 437 628 A1 UV-curable toner particles and developers containing them are described. The toner images are fixed by heat (IR irradiation) and cured by UV irradiation.

DE 694 26 920 T2 discloses toner for developing electrostatic toner images using as a binder resin a polyester resin, a combination of a non-linear polyester resin and a linear polyester resin. Accordingly, the polyester resins can be subjected to a crosslinking reaction.

US 2002/0118986 A1 describes a printer in which the fixation of toner images by irradiation in the range of UV to IR wavelengths takes place. For this purpose, a radiation source is proposed.

Out DE 101 35 865 B4 results in an image recording method in which the toner images are melted and fixed by electromagnetic radiation. The wavelength of the radiation is in the range of 0.8 .mu.m to 10 .mu.m, preferably 0.8 to 3 .mu.m.

at DE 100 64 563 A1 the fixation of toner images with electromagnetic radiation takes place. At multicolor printing will be the colors are arranged one above the other and the wave range is chosen according to the color. For yellow toner, a wavelength range of 420 to 460 nm is selected, for magenta 510 to 550 nm, for cyan 630-670 nm. In this way, the superimposed color toner images can be fixed separately.

DE 100 64 566 A1 describes a method for controlling the gloss of a toner image. The toner image is fixed by heating and then heated again according to the desired toner image gloss (in the UV range).

Out EP 1 341 048 A1 The result is a method according to which toner images are first fixed (by conventional methods) and then cured with UV radiation.

US 2003/0165766 A1 describes an electrophotographic printer in which the toner images are first fixed and then cured. It is fixed by crosslinking, cured by polymerization by UV or IR radiation. The UV radiation is in the range of 200 nm to 250 nm.

The problem to be solved by the invention is to provide a method which can be used to adjustably modify the properties of toner images on an image carrier, e.g. their abrasion resistance, temperature resistance, gloss, viscosity.

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

The invention solves the above problem by UV-IR irradiation of the toner images on the image carrier, such as an intermediate image carrier or a final image carrier, wherein a toner material is selected which contains UV-curable components. This may include, for example, linear or branched polyester resins or other resins that are not very strong three-dimensional are cross-linked or otherwise suitable for UV curing. The intensity of photopolymerization in the toner material achieved by UV irradiation can be enhanced by the addition of photoinitiators.

Advantageously, the method can be used to adapt already fixed on a final image carrier (recording medium) final images according to the specific requirements of the required properties of the printed matter or to the special load conditions of certain printing Nachverarbeitungsoder shipping conditions. Furthermore, the method can be used to facilitate or facilitate the transfer process of toner images from an image carrier to a final image carrier, in particular a thick final image carrier.

The method can be used advantageously both when dry toner is used to develop the potential images and when liquid developer is used.

Further developments of the invention will become apparent from the dependent claims.

According to the invention, the chemical properties of the toner material and the spectral distribution and power density of the irradiation are matched to one another. The process of UV curing is optimized by the correct spectral distribution and the correct power density of the radiation.

In general, a radiation source can be used, which is a combination of ultraviolet light (wavelength: 200 to 400 nm, abbreviation: UV), visible light (wavelength: 400 to 700 nm, abbreviation: VIS) and infrared heat radiation (wavelength: 700 nm to 10μm, abbreviation: IR) radiates. In this case, the relative proportion of these spectral ranges is selected so that in adaptation to the chemical composition of the photopolymerizable toner material, the IR / VIS components for the activation the bonds required for the photopolymerization (heating) are used and the UV component is used for the actual curing of the photopolymerizable toner material. Both the relative proportions of the spectral regions and the absolute power density of the radiation must be adapted to the chemical properties of the substances involved, to the thickness of the layer to be polymerized and to the process speed of the printing and fixing process or the post-processing process. In addition, by a sufficiently strong IR irradiation, which preferably contains strong portions in the frequency range of the main absorption of the toner material used, an additional or stronger heating of the toner material are generated, in turn, a better connection of the toner particles with each other and the image carrier and possibly a higher Gloss of the surface causes.

• Durch gezielten Einsatz bestimmter UV-Wellenlängenbereiche können die Fixierqualität, der Glanz und die Abriebfestigkeit des Endbildes und/ oder der Klebewirkung bei erhöhten Temperaturen entsprechend der gewünschten Eigenschaften des Endbildes und der in einer bestimmten Nachverarbeitungslinie zu erwartenden Belastung des Endbildes angepasst werden.
• Die UV-A Strahlung (Wellenlänge: 320 bis 400 nm) hat eine größere Eindringtiefe und bewirkt eine stärkere Volumenwirkung, d.h. eine Polymerisation des gesamten Schichtvolumens des Endbildes.
• Die UV-B Strahlung (Wellenlänge: 280 bis 320 nm) bewirkt infolge geringerer Eindringtiefe eine stärke Härtung des Materials an der Oberfläche als im Inneren des Endbildträgers.
• Die UV-C Strahlung (Wellenlänge: 200 bis 280 nm) wird zur Oberflächenhärtung eingesetzt.
• Der Einsatz von Schutzgas (z.B. Stickstoff) führt zu verstärkter Oberflächenhärtung des Endbildes bzw. zu einem geringerem Anteil an Photoinitiatoren im Tonerharz.
• Eine Koronabestrahlung vor und/oder während der UV-Härtung führt zu verringerter Oberflächenpolymerisation des Endbildträgers, was z.B. zur Vermeidung einer zu starken Sprödigkeit der Oberfläche und zu besserer Elastizität in der Nachverarbeitung eingesetzt werden kann.
• Durch die geeignete Kombination von Korona-Einwirkung und starker IR- Bestrahlung vor der UV- Härtung kann ein gutes Verfließen bzw. Verkleben des Tonerbildes sowie eine gute Verbindung des Tonerbildes mit der Oberfläche des Endbildträgers bei hohem Oberflächenglanz erzielt werden. Dies kann insbesondere bei schlecht haftenden Endbildträgern wie nicht gut mit dem Toner verträglichen Papieren sowie glatten Polymerfolien oder Metallfolien erforderlich sein. Wird eine besonders harte Oberfläche gewünscht, kann mit UV-C nachgehärtet werden.
• Wenn die Elastizität des Tonerbildes erhalten bleiben soll (gute Knickbeständigkeit) ist reines Oberflächenhärten mit UV-C zweckmäßig.

The following measures are advantageous for effecting a fine grading of the curing process, influencing the gloss and the abrasion resistance, for example of the final image on a final image carrier, and the adhesive action at elevated temperatures:

• Through targeted use of certain UV wavelength ranges, the fixing quality, the gloss and the abrasion resistance of the final image and / or the adhesive effect at elevated temperatures can be adjusted according to the desired properties of the final image and the expected in a given Nachverarbeitungslinie load of the final image.
• The UV-A radiation (wavelength: 320 to 400 nm) has a greater penetration depth and causes a greater volume effect, ie a polymerization of the entire layer volume of the final image.
• The UV-B radiation (wavelength: 280 to 320 nm) causes due to lower penetration depth a stronger hardening of the material at the surface than in the interior of the final image carrier.
• The UV-C radiation (wavelength: 200 to 280 nm) is used for surface hardening.
• The use of inert gas (eg nitrogen) leads to increased surface hardening of the final image or to a lower proportion of photoinitiators in the toner resin.
• A corona irradiation before and / or during the UV curing leads to reduced surface polymerization of the final image carrier, which can be used, for example, to avoid excessive brittleness of the surface and better elasticity in the post-processing.
• Due to the suitable combination of corona action and strong IR irradiation before the UV curing, good adhesion or adhesion of the toner image and good bonding of the toner image with the surface of the final image carrier can be achieved with high surface gloss. This may be necessary in particular for poorly adhering final image carriers, such as papers that are not well tolerated by the toner, as well as smooth polymer films or metal foils. If a particularly hard surface is desired, can be postcured with UV-C.
• If the elasticity of the toner image is to be retained (good kink resistance), pure surface hardening with UV-C is expedient.

The UV curing processes described can also be used for complete fixing of toner images, which were only "fixed" in the actual fixing process.

• Die UV-Bestrahlung kann in den oben beschriebenen Varianten bei Einsatz verringerter Bestrahlungsleistung auch zur Erhöhung der Viskosität des erwärmten Tonerbildes in beliebigen Stufen des Druckprozesses eingesetzt werden.
• Z.B. kann zur Unterstützung des Umdrucks des Tonerbildes auf einen sehr dicken Endbildträger, bei dem auch eine elektrostatische Umdruckunterstützung auf Schwierigkeiten stößt, dessen Viskosität im erwärmten Zustand derart erhöht werden, dass die gesamte Tonerschicht zusammenhängend von einem Zwischenbildträger mit geringer Oberflächenenergie (z.B. Teflon) durch Andruck auf den dicken Endbildträger (z.B. dicker Karton, Holz o.ä.) übertragen werden kann.
• Ein solcher Prozess kann dadurch optimiert werden, dass eine Korona-Vorbehandlung in Kombination mit UV-A Härtung benutzt wird, wodurch ein im Volumen zusammenhängender Tonerbildfilm mit klebriger Oberfläche erzeugt wird, was zu einer geschlossenen Übertragung des Tonerbildes mit Klebewirkung auf den Endbildträger führt.
• Ein UV-A/B-Nachhärten führt zu hinreichender Haftung und Festigkeit des Tonerbildes auf dem Endbildträger.
• Unter anderem kann man auch die MICR- Toner- Abriebfestigkeit erhöhen, wobei die Grundelastizität des Tonerbildes (gute Knickbeständigkeit) erhalten bleibt, indem man nacheinander oder gleichzeitig eine IR- und UV-C Bestrahlung durchführt.

The process of the invention also brings in the intermediate curing or viscosity increase or transfer to very thick final image carrier further advantages:

• The UV irradiation can also be used in the variants described above when using reduced irradiation power to increase the viscosity of the heated toner image in any stages of the printing process.
• For example, in support of the transfer printing of the toner image on a very thick end image carrier, in which also an electrostatic Umdruckunterstützung encounters difficulties whose viscosity is increased in the heated state so that the entire toner layer can be transmitted coherently by a intermediate image carrier with low surface energy (eg Teflon) by pressure on the thick final image carrier (eg thick cardboard, wood, etc.).
• Such a process can be optimized by using a corona pretreatment in combination with UV-A curing, thereby producing a volume-coherent, tacky-surface toner image film, resulting in a closed transfer of the toner image with adhesion to the final image carrier.
• UV-A / B post curing results in adequate adhesion and strength of the toner image on the final image carrier.
• Among other things, one can also increase the MICR toner abrasion resistance, while maintaining the basic elasticity of the toner image (good kink resistance) by successively or simultaneously carrying out an IR and UV-C irradiation.

In the case of multicolor printing, the various color image separations can be generated one after the other on the potential image carrier and transmitted successively either to an intermediate image carrier or to the final image carrier. The color image extracts can also be collected directly on the potential image carrier and then transferred together to the final image carrier or they can be transferred individually from the potential image carrier to the intermediate image carrier, collected thereon and then transferred to the final image carrier.

In this application of the method can be carried out by adapted UV-IR irradiation curing of the existing multiple color separations overall picture.

It is also possible to produce individual color separations with special gloss or Abriebeigenschaften to highlight them in appearance or better distinguishable too by subjecting these color separations to a separate treatment with a sequence of IR irradiation, UV irradiation and / or corona pretreatment.

For example, Image hardening while maintaining the matt properties can be achieved by first applying a UV-C irradiation, then a combined IR-UV-A exposure. An increased gloss can be achieved by first performing a corona treatment of the toner surface, then an IR irradiation or corona treatment with IR irradiation, which causes a sufficient softening with gloss increase (until the toner image flows), followed by UV irradiation to be led. After softening by IR irradiation or by contact with a hot roll or strip surface, a smooth or deliberately matt surface with increased strength and hardness can be achieved by roll embossing with a certain surface roughness and subsequent UV irradiation.

The method can also be used to generate print image elements that can be rubbed off more easily. By a particularly strong UV irradiation, preferably without or with low IR irradiation, an end image or a part of an end image can be embrittled, which is e.g. leads to a noticeably reduced scratch resistance.

With reference to an embodiment, which is illustrated in the figures, the invention will be further explained.

Fig. 1

eine prinzipielle Darstellung einer Druck- oder Kopiereinrichtung, mit der das Verfahren durchgeführt werden kann;

Fig. 2

die Behandlung eines Endbildes in prinzipieller Darstellung.

Show it:

Fig. 1

a schematic representation of a printing or copying device, with which the method can be performed;

Fig. 2

the treatment of a final image in a schematic representation.

Out FIG. 1 results in a schematic representation of an electrographic printing device. First, a potential image carrier 101, eg a photoconductor drum, exposed to a quenching exposure 102. Subsequently, the potential image carrier is charged in the station 103. Potential images of images to be printed are produced on the potential image carrier 101 by imagewise exposure in the station 104. These potential images are developed in a developer station 200 by toner material, eg in a liquid developer. For this purpose, for example, liquid developer is taken from a developer supply 203 and fed via an application roller 202 to an applicator roller 201. The applicator roller 201 conveys the liquid developer to the potential image carrier 101. Subsequently, the applicator roller 201 is cleaned in the cleaning station 204.

In the development of the potential images on the potential image carrier 101, toner is transferred to the potential image carrier 101 in the areas to be inked and deposited there. In the regions which are not to be inked, virtually no toner is transferred to the potential image carrier 101. The toner image thus forms on the potential image carrier 101. In a transfer station, the toner image is transferred to an end image carrier 402 via an intermediate image carrier 301. For this purpose, a counter-pressure roller 401 is used.

The final image carrier 402 is finally fed to a fixing station 500, in which the fixation can take place in a known manner.

Out Fig. 2 In principle, the treatment of the final image 403 on the final image carrier 402 results according to the above-described method. For this purpose, a radiation source 601 is provided, which emits the radiation 602 described above. The radiation 602 is directed onto the final image carrier 402 and impinges there on the final image 403. The radiation 602 selectively hardens or lightens the final image 403 according to the method described above.

LIST OF REFERENCE NUMBERS

101

Potential image carrier

102

erase exposure

103

Charging 104 imagewise exposure

105

Cleaning of the potential image carrier

200

developer station

201

applicator

202

applicator roll

203

Developers stock

204

Cleaning the applicator roller

301

Intermediate image carrier

302

Cleaning of the intermediate image carrier

401

Backing roll

402

final image

403

final image

500

fuser

601

radiation source

602

radiation

Claims (7)

1. A method for modification of properties of toner images applied on an image carrier (301, 402) in an electrographic printing or copying device,

   - in which a toner material comprising UV curable components is used for generation of the toner images,

   - in which the toner images are exposed to a radiation with at least one IR component in order to generate the heat required for polymerization,

   - in which the toner images on an intermediate image carrier (301) or the fused toner images on a final image carrier (402) are exposed to a radiation with a combination of ultraviolet light (UV) and visible light (VIS) as well as infrared heat radiation (IR), as a result whereof the properties of the toner images are set, wherein the toner images are exposed to a UV radiation with UV components,

   • the wavelength of which is set in the range from 320 to 400 nm (UV-A) when a polymerization of the entire layer volume of the toner images should be achieved, and/or

   • the wavelength of which is set in the range from 280 to 320 nm (UV-B) when a stronger curing of the toner images should be achieved on their surface than inside them, and/or

   • the wavelength of which is set in the range from 200 to 280 nm (UV-C) when the toner images should only be cured on their surface.
2. The method according to claim 1,
   in which an IR exposure is used before the transfer printing of the toner images from the intermediate image carrier (301) onto the final image carrier (402) and the UV exposure occurs after the fusing station (500) on the final image carrier (402).
3. The method according to claim 1,
   in which the UV exposure is used to increase the viscosity of the toner images on the intermediate image carrier (301) so that the transfer printing of the toner images onto a final image carrier (402) can occur via contact pressure.
4. The method according to claim 1,
   in which the radiation is adjusted such that the visible light and the IR radiation generates the heat necessary for activation of the polymerization and the UV radiation cures the polymerizable toner material.
5. The method according to one of the preceding claims,
   in which a linear or a branched polyester resin is used as a toner material.
6. An electrographic printing or copying device,
   in which after the fusing station (500) a radiation source (601) is arranged that exposes the toner images (403) transfer-printed and fused onto the final imager carrier (402) to a radiation with a combination of ultraviolet light (UV) and visible light (VIS) as well as infrared heat radiation (IR) according to the method according to one of the preceding claims.
7. An electrographic printing or copying device,
   in which a radiation source (601) is arranged before the transfer printing of the toner image onto the final image carrier, which radiation source exposes the toner images present on the intermediate image carrier (402) to a radiation with at least infrared heat radiation (IR) according to the method according to one of the preceding claims to increase the viscosity of the toner images on an intermediate image carrier (301) such that the transfer printing of the toner images onto a final image carrier (402) occurs via contact pressure only.

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