EP1245385A2 - Wet-offset printing form with photo-thermally convertible material, process and apparatus for creating and/or erasing the image of the wet-offset printing form - Google Patents

Abstract

Wet offset printing plate comprises a top layer of a material that can be photocatalytically converted to a hydrophilic state by irradiation with light and converted to a hydrophobic state by heating, where the layer includes absorption centers for radiation, especially near infrared (NIR) laser radiation, such that the layer can be heated imagewise. Independent claims are also included for the following: (1) a process for writing such a plate, comprising imagewise heating of the plate; (2) a process for erasing such a plate, comprising irradiating the plate with UV light while supplying water; and (3) apparatus for repeatedly writing such a plate, comprising a writing device for imagewise heating, an erasing device comprising one or more daylight and/or UV light sources, and a humidifying chamber for generating and maintaining a predetermined air humidity on the plate.

Description

The invention relates to a wet offset printing form with a surface that with a Print image is imageable or illustrated, this surface of a material is formed, which is a photocatalytically and thermally changeable material as part of contains even distribution or consists solely of such a material. Under a Photocatalytically and thermally changeable material is used in the sense of the invention Material understood that by irradiation with light photocatalytically into a hydrophilic State and thermally, namely by heating, can be brought into a lipophilic state is. The invention further relates to a method for generating the printed image, i.e. to Imaging, a method for deleting a printed image, a device for Imaging and a device for deleting a printed image of a wet offset printing form of the type mentioned. The invention particularly preferably relates to a method and a device for imaging and erasing a printing form, for example for a Repeated imaging of the same printing form with different printing images. The printing form, the method and the device are preferably used in Wet offset web-fed rotary printing, especially in newspaper printing.

In the following, an image is understood to mean a process in which the Printing form is acted on at the points that form the pixels, so that a latent Image is generated on the printing form. A deletion is within the meaning of the invention understood a process in which the printing form is preferably not image-dependent but is treated over the whole area in such a way that the image information applied during the imaging, i.e. the printed image is eliminated. The influence on the imaging is preferably an image-based heating, but in principle can also be image-based Be irradiated with UV light.

Newspapers are mainly produced using wet offset. Printing machines like the invention it preferably concerns, typically contain printing units with blanket cylinders, Plate cylinders, inking units and dampening units. One on a printing form cylinder stretched printing form has a surface mostly in the form of an upper layer, the in the illustrated state, hydrophilic (water-friendly) and lipophilic (water-repellent) Areas. The printing form is usually formed by a printing plate, which is clamped on a plate cylinder designed as a plate cylinder. The printing form has imagewise applied lipophilic areas. The non-image areas are hydrophilic and bind water more strongly than color. The lipophilic areas repel water and therefore look color-friendly. In principle, any surface can be used for the offset process can be used, which can be divided into hydrophilic and lipophilic areas.

A large number of methods and devices are used to produce printing forms known using appropriate printing forms. You can, for example, with irradiate a printing form imagewise with a laser and then develop it chemically. Printing forms can also be produced by laser ablation. Doing so either lipophilic areas under a hydrophilic layer or hydrophilic areas under a lipophilic layer exposed. The exposure process relevant for image generation can be done either in a separate system or within the press, as the invention prefers. For exposure or imaging in the printing press the outer drum principle is known. Mostly come so-called process-free Printing forms that do not require chemical development are used.

Printing forms used today are used only once. From economic and for ecological reasons it is desirable to use the same printing form several times to be able to use.

EP 0 911 155 A1 describes the imaging of a printing form by a photocatalytic one Known reaction. The hydrophilic non-image areas are used to generate the printed image irradiated with UV laser light. The printing form exposed in this way and thereby illustrated becomes extinguished by heating. The printing form must reach a high temperature. Of There is also a cleaning process for deleting the printed image after using the printing form with a cleaning device required to remove the paint residue from the Remove printing form. Without cleaning, heating the printing form would result in erasure cause burnt-in ink residues in the printing plate surface of the print image, which would make the printing form unusable.

EP 0 911 154 A1 describes the imaging by image-wise heating and the Deletion by UV radiation. Further details are given in EP 1 020 304 A2 described.

It is an object of the invention to provide a wet offset printing form of the type mentioned create that enables the creation of a printed image with good image sharpness. Preferably, the printing form does not have to be used specifically for deleting the Print image to be cleaned. The illustration of a printing form and / or the deletion of a printed image of a printing form should or should be facilitated, preferably in one Wet offset press.

The object is solved by the subject matter of the independent claims. advantageous Further developments are described by the subclaims.

In a preferred embodiment, the invention is based on the idea of local Wetting behavior, i.e. the hydrophilic or lipophilic behavior of a printing form, thereby achieving that the atoms or molecules of a photocatalytic and thermal changeable material, which is the imageable or illustrated surface of the printing form from an excited state in which they are normally through the Imaging can be converted into a low-energy state. When deleting Conversely, the atoms or molecules from the low energy into the transferred excited state. The printing form is thus before performing a Imaging process or after performing a deletion process in one initial hydrophilic state, characterized by a local, imagewise, preferred temporary, heating of the photocatalytically and thermally changeable material in the lipophilic and hydrophilic usage state is transferred according to the image.

An advantage of this type of imaging is that the unimaged printing form is easy to use Daylight can be handled. The deletion of the printed image and not that Imaging takes place through the action of natural or artificial daylight or UV light, preferably on the surface having the printed image the whole area. On the other hand, the loss of an image in the installed state is Printing form unlikely, since the printing machine no longer has daylight on the Printing form that would fear deletion to a relevant extent. Yet an advantage lies in the self-cleaning properties of the photocatalytic and thermally changeable material formed surface, which in the deletion of the image comes into play. The surface of the printing form is not only hydrophilic but also organic residues are also catalytically oxidized. Compared to the deletion process by means of full-surface heating is therefore a cleaning of the printing form for the purpose of Deletion not required. A full-surface heating to the required high Temperatures can only be achieved with much greater effort within the printing press as an irradiation with daylight or UV light. In particular natural daylight has short-wave, ultraviolet (UV) light, which the Normally existing hydrophilicity of the photocatalytically and thermally changeable Material causes.

By imaging the printing form by image-wise local radiation, preferably Laser irradiation, not the entire printing form, but only a near surface Depth area of the printing form locally warmed briefly. The printing form as a whole remains to ambient temperature, which generally corresponds to the usual room temperature.

A printing form according to the invention has in an upper layer, on the surface of which Print image is generated, absorption centers for radiation to pass through absorption to generate heat from this radiation in the upper layer. The absorption centers become formed by particles of a material that absorbs light, preferably infrared light (IR), which extends into the visible range, i.e. into the near infrared range (NIR) can extend. The absorbent material is in fine particles in the photocatalytic and thermally changeable material evenly dispersed. With the particles of the Absorbent material is preferably nanoparticles, i.e. around particles, whose maximum spatial extension is in the nano range.

Due to the even, fine distribution of the absorption centers in the photocatalytic and thermally changeable material is already in a single layer of material Photo-catalytically and photothermally changeable material created. The well-known namely, photocatalytic materials are transparent. The transparency is immediate Follow the band structure of the material. In fact, there is a band gap of more than 3 eV required to excite the photocatalytic material into a state effect in the binding of OH groups to the surface of the concerned Material is possible. At this bandgap energy, i.e. Band gap energy, however an interaction with low-energy, long-wave photons is not possible. The known photocatalytic semiconductors are therefore transparent in the visible range. A photothermal effect and change of the photocatalytic material can therefore can only be brought about indirectly. The invention creates a photocatalytic and photothermally changeable material due to the fine distribution of the absorption centers in the photo-catalytically and thermally changeable material. Semiconductors are special preferred examples of materials for forming the absorption centers.

The upper layer, which forms the surface to be imaged or already imaged, comprises thus a material that interacts photocatalytically with light and the absorption centers, those in the photo-catalytically interacting material, hereinafter also simply as called photocatalytic material, are finely divided. The photocatalytic material interacts with light whose wavelength is less than the wavelength or the Wavelength range of radiation absorbed and absorbed by the absorption centers Heat is converted. Due to its band gap energy of at least 3 eV the photocatalytic material only interacts with light whose wavelength is less than Is 400 nm. The material that forms the absorption centers interacts accordingly Radiation, the wavelength of which is 400 nm or greater, preferably absorbs light the IR wavelength range.

The invention creates a new material that is both photocatalytic also has absorbent properties. One advantage is that the coating of one Carrier material can be simplified because both interactions, namely the Photocatalysis and absorption take place in a single layer and therefore one only the absorption layer used for absorption can be saved. Furthermore, the thickness of the layer is photocatalytically and photothermally changeable Material less critical. While in a multi-layer system, the thickness of the photothermally changeable upper layer can have a great influence on the heating more uniform heating can be achieved within a single layer, if the absorption centers are distributed homogeneously in this layer. Furthermore, the heat-generating absorption centers closer to the imageable or already illustrated Surface, so that sharper temperature gradients in the surface are possible.

Particularly sharp temperature gradients can be generated on the surface particularly advantageous for preferred imaging by image-based heating, because the sharpness of the printed image is improved. The printing form according to the invention is in principle, however, also advantageous for an imaging process in which the Imaging by image-wise hydrophilization of the surface and the deletion by full-surface hydrophobization can be brought about.

A printing form, also according to the invention, has underneath an upper layer, on the other Surface of the printed image is generated, an absorption layer. The Absorption layer becomes correspondingly local by brief, local radiation warmed, i.e. it is warmed up in accordance with the image with locally warm and in contrast to it cold spots. The absorption layer should be even for image-based heating be thin to the heat in the first place normal to the absorption layer to the preferably immediately above top layer with the photocatalytic and deliver thermally changeable material and a heat balance within the Absorption layer in the tangential direction between the locally warm and to prevent cold spots of the absorption layer. The locally generated heat in the absorption layer is via heat conduction from the absorption layer into the Upper layer transferred so that the lipophilic sites on the surface of the upper layer of the printed image. The two layers are thermally conductive with one another over the entire surface connected. The absorption layer preferably borders directly on the top layer. Each of the two layers interacts with radiation from a specific one Wavelength range, the top layer containing radiation that is particularly strong Dimensions is absorbed by the absorption layer, interacts little or not at all, i.e. is transparent to this radiation. The upper layer interacts photocatalytically with light from the UV range while the absorption layer interacts with Radiation from a different wavelength range, preferably from the IR range is let through by the upper layer, is heated. The upper class is through Heat conduction from the absorption layer heated in accordance with the image also correspondingly warms up imagewise and forms the lipophilic surface on its surface due to this heating Image areas.

Between the absorption layer and a printing form carrier there is preferably a thermal one Insulation layer is provided to minimize heat loss to the carrier. is an absorption layer does not exist, so a thermal insulation layer nevertheless be formed between the top layer and the carrier.

If a thin absorption layer is formed below the top layer, Absorption centers in the upper layer can be dispensed with. The applicant reserves it propose to claim this separately. On the other hand, the absorption layer and the absorption centers in the upper layer are also advantageously formed in combination his.

The formation of a printing form according to the invention by means of the absorption layer is also possible also advantageous for an imaging process in which the imaging by irradiation with UV light and the extinction caused by heating.

A diffusion barrier can advantageously be provided between the carrier and the top layer in order to prevent diffusion of atoms of the carrier, in particular of Fe or Al atoms. The diffusion barrier can be formed, for example, by an SiO ₂ quartz layer. A layer that acts as a diffusion barrier should be at most 1 μm thick, such a layer preferably has a uniform thickness of 100 nm or less. A gradual diffusion of, for example, Fe and / or A1 atoms into the top layer could disturb the semiconductor effect used according to the invention, since the electron band structure of the top layer could change adversely during the operation of the printing form due to such diffusion effects. The diffusion barrier can also be designed as a thermal insulation layer. A diffusion barrier can likewise be formed by a layer provided specifically for this purpose, which can in principle be arranged between each of the layers mentioned in a printing form according to the invention. In preferred embodiments, a layer provided specifically as a diffusion barrier is formed between the carrier and the absorption layer if an absorption layer is provided. If a thermal insulation layer is present, the diffusion barrier can be provided between the carrier and the insulation layer or between the insulation layer and the absorption layer which may be present. Such a layer acting as a diffusion barrier can particularly preferably be arranged directly under the top layer. In this case, foreign atoms, which may not only originate from a carrier but also from another functional layer, can be most safely prevented from diffusing into the upper layer.

The printing form is erased by irradiating the surface with UV light. According to the invention, it is ensured during the deletion process that the to activating surface of the printing form for a high supporting the deletion process Moisture is taken care of. If the activated surface lacks moisture, this leads to a recombination of the electron-hole pairs generated by UV radiation, so that a permanent hydrophilization of the surface is not achieved. The surface preferably becomes water during the extinguishing process supplied that a high humidity is set on the surface. The Increasing the humidity compared to the environment can be caused in particular by Supply of water vapor can be effected or by means of a dampening system Printing machine, which in this case is a device for atomizing water is assigned. The moisture is on and near the surface preferably such that the air adjacent there is saturated with moisture.

However, high air humidity is generally not desirable in the printing unit. So For example, condensation can form, which can form on the cylinders drips and causes disturbances in the printed image. The offset process can also progress a production can be adversely affected if due to a moisture-saturated Ambient air makes the evaporation of surface water on the Printing form surface or when splitting a color film on the surface of the Ink arrives.

In a development of the invention, moisturizing is therefore preferred also a temperature maintenance, i.e. an air conditioning of the printing unit in this way made that a high during the hydrophilization by means of UV radiation Humidity of more than 60%, more preferably of more than 80%, and for that Hydrophobization of the surface set a significantly lower humidity becomes. Furthermore, a significantly lower humidity is also during the Printing process and preferably at all times outside of the hydrophilization adjusted by moisturizing, preferably air conditioning. An encapsulation of the Printing unit simplifies the setting and maintenance of the desired moisture values and preferably also the temperature in the printing unit and in particular at the Printing form. Furthermore, the humidity or the climate can be determined by the arrangement of Humidity sensors and preferably also be monitored by temperature sensors.

Figur 1a

eine UV-hydrophile Oberfläche,

Figur 1b

eine Benetzung der Oberfläche,

Figur 1c

einen Belichtungsvorgang zur lokalen Aufhebung der Hydrophilie der Oberfläche,

Figur 1d

die Benetzung der Oberfläche nach dem Belichtungsvorgang,

Figur 2a

eine Druckform nach einem ersten Ausführungsbeispiel in einem Querschnitt,

Figur 2b

eine Druckform nach einem zweiten Ausführungsbeispiel in einem Querschnitt,

Figur 2c

eine Druckform nach einem dritten Ausführungsbeispiel in einem Querschnitt,

Figur 2d

eine Druckform nach einem vierten Ausführungsbeispiel in einem Querschnitt und

Figur 3

ein Druckwerk einer Nassoffset-Rotationsdruckmaschine.

Preferred exemplary embodiments of the invention are described below with reference to figures. Features which become apparent from the exemplary embodiments advantageously form the subjects of the claims individually and in each combination of features. This also applies to combinations of features that are only described explicitly in different exemplary embodiments, provided that the combination of such features does not lead to contradictions that cannot be resolved. Show it:

Figure 1a

a UV-hydrophilic surface,

Figure 1b

wetting the surface,

Figure 1c

an exposure process to locally cancel the hydrophilicity of the surface,

Figure 1d

the wetting of the surface after the exposure process,

Figure 2a

a printing form according to a first embodiment in a cross section,

Figure 2b

a printing form according to a second embodiment in a cross section,

Figure 2c

a printing form according to a third embodiment in a cross section,

Figure 2d

a printing form according to a fourth embodiment in a cross section and

Figure 3

a printing unit of a wet offset rotary printing press.

FIG. 1a shows a surface that is hydrophilic due to irradiation with light from the UV range 130 of a wet offset printing form 31, which is also referred to below as UV-hydrophilic Surface is called. The surface 130 is covered by an upper layer 11 of the printing form 31 formed, which contains a photocatalytically and thermally changeable material or consists entirely of such a material. The excited one that normally exists Condition results for example from the irradiation with natural or artificial Daylight. If the layer 11 is irradiated by a light source, the UV light emits at least as part of its spectrum, preferably a daylight source and / or a UV light source 12, the layer 11 is irradiated with high energetic photons 17, so that in the vicinity of the surface 130 of the layer 11 Electrons from the valence band of the photocatalytically and thermally changeable Material into the conduction band. The electrons missing in the valence band leave positive holes h +. Is the electrical potential of the holes h + sufficient high, so can the photocatalytically and thermally changeable material Water molecules 14 react such that a hydroxyl radical · OH is formed which the atoms or molecules of the photocatalytically and thermally changeable material binds. With increasing number of OH groups bound to the surface 130 the hydrophilic character of surface 130 increases. In particular, water molecules can 14 bind to the OH groups via hydrogen bonds, which in turn bind to the positive holes h + the top layer 11 are bound.

FIG. 1b illustrates the wetting of the UV-hydrophilic surface 130 of the layer 11 with a water drop 140. The acute contact angle that the edge of the water drop 140 with the surface 130 is a measure of the hydrophilicity of the surface 130th

A preferred photocatalytically and thermally changeable material for the upper layer 11 of the printing form 31 is titanium oxide TiO ₂ in the anatase crystal structure. In the anatase structure, the excitation energy from the valence band to the conduction band is approximately 3.2 eV, which corresponds to a wavelength of 387 nm. The action of ultraviolet light, the wavelength of which is not greater than 387 nm, excites valence electrons of the TiO ₂ in the conduction band of the semiconductor. This creates a positive hole h + in the valence band. The excited electron is prevented from falling back onto the positive hole h + if a chemical bond of another substance to the activated semiconductor surface takes place beforehand. With anatase titanium oxide and certain other semiconductors, for example, this is possible if water is present. The hydrophilic state can persist even if UV light no longer acts on the photothermally changeable material.

The material, which is photocatalytically and thermally changeable in the sense of the invention, should have a valence band energy and a conduction band energy, measured in each case on the two mutually facing edges of the energy bands, which are suitable for the reduction and oxidation of water. The conduction band energy should therefore be at least as negative as the energy required to reduce water (0.0 V in acid solution), and the valence band energy should be at least as positive as the energy required to oxidize water (+1.23 V). A top layer forming the surface, which is formed by or at least to a large extent from the photothermally changeable material, has a band gap energy which is preferably at least 3.2 eV. The band-gap energy is the energy required to excite electrons from the valence band into the conduction band. The positive holes of the valence band created by the excitation in this case have an advantageously large potential in order to form highly reactive · OH radicals in connection with water. Particularly preferred materials are the anatase-TiO ₂ already mentioned and other materials with a suitable electronic structure in order to bind hydroxyl groups to the material surface by excitation with UV light in the manner described. Examples of such, likewise suitable materials are zinc oxide, ZrO ₂ , SrTiO ₃ , KTaO ₃ or KTa _0.77 Nb _0.23 O ₃ , which like TiO _2, the photocatalytically and thermally changeable material, either alone or in a material combination of at least two of the mentioned materials including TiO ₂ form. The printing form 31 preferably has at least 40% by weight of the photocatalytically and thermally changeable material in the depth range relevant for the UV-hydrophilic surface, measured on the total weight of the material of the printing form which forms this area. If the photocatalytically and catalytically and thermally changeable material is formed by a combination of materials, a combination of TiO ₂ and SiO _{2 is} a particularly preferred material. SiO ₂ can advantageously also form a material in combination with another or more of the materials mentioned which contains photocatalytically and thermally changeable material.

The hydrophilicity of anatase titanium oxide as an effect of a photocatalytic reaction is known and is used, for example, for self-cleaning surfaces on buildings and anti-fog glass, for example in the automotive sector.

Another advantageous property of titanium oxide layers is self-cleaning to act because organic particles on the surface decompose photocatalytically over time become. This also applies to the other materials mentioned.

Because there is always a certain amount of ultraviolet light in a normal working environment is one of a photocatalytically and thermally changeable material surface is always stimulating, it can be assumed that such Surface is normally hydrophilic. The printing form can by natural or artificial daylight can be extinguished. The deletion can be supported by a additional UV source. One for extinguishing alone or in combination with daylight UV lamps used should have a spectrum with a sufficient amount of UV light with a wavelength of 387 nm and smaller. The peak is preferably of the emitted spectrum at a wavelength of 387 nm, corresponding to a band gap energy of 3.2 eV, or a shorter wavelength. It's the spectral one Distribution of the radiation preferably predominantly below 387 nm. In particular A UV laser or UV laser system can be used as the UV lamp. On a Focusing optics for the laser or lasers are preferably dispensed with.

The UV-hydrophilic surface is localized by irradiation with (IR) infrared laser light made color friendly. The printing form is not significantly heated overall. It remains at the temperature normally prevailing in a printing press Range from 10 ° C to 40 ° C.

FIG. 1c illustrates the removal of the hydrophilicity of the UV-hydrophilic surface 130. This is done by locally heating the top layer 11 according to the image. The exposure or imaging is carried out by irradiation with laser light 18. The wavelength of the laser light 18 can be in the visible range up to the near infrared (NIR), ie between approximately 400 and 3000 nm. Laser light from the range from 700 nm to 3000 nm and particularly preferably from the range from 800 nm to 1100 nm is preferably used for imaging. Due to the local action of the laser light 18, a lipophilic surface area 131 corresponding to the laser spot on the surface is generated on the surface 130. The heat transfer to the atoms or molecules to which the OH groups are attached causes the bonds to split. Then there is a recombination of electrons from the conduction band of the photocatalytically and thermally changeable material of layer 11 with the positive holes h +. As a result, the hydrophilicity decreases and the printing form 31 becomes lipophilic in the irradiated surface region 131, while the hydrophilic state is retained in the surface region 130 not irradiated with the laser light. During the imaging, local surface elements, each corresponding to a pixel, of, for example, 50 × 50 μm ^{2 are} heated to a temperature of 400 ° C. to 600 ° C. for a period of 1 μs to 100 μs, while the other regions 130 of layer 11 stay at ambient temperature. After the imaging, a latent image is present on the wet offset printing form 31 which is retained during the printing. The lipophilic pixels 131 transmit the color during the printing process.

Figure 1d illustrates the wetting of layer 11 by water in the non-irradiated Surface area 130 and the irradiated surface area 131. In the irradiated and thereby heated material in the surface area 131 is water wetting low. The contact angle formed in the surface area 131 between the surface area 131 and the water drop 141 is large, and the layer 11 is lipophilic in this surface area 131. To prevent that from the time from the beginning of the exposure to the end of a printing process UV light from the Environment for a new stimulation of the photocatalytically and thermally changeable Material, it is sufficient that the printing form is in the shade. This is in Usually given after installing the printing form in a printing press.

FIGS. 2a to 2d show advantageous exemplary embodiments for a layered structure Printing form 31, which is preferably designed as a printing plate and on a Printing form cylinder can be clamped or is already clamped.

The printing form 31 of FIG. 2a has a two-layer structure with a carrier layer 21 and a single top layer 24, applied directly to the carrier layer 21, on the other free surface the print image is generated or in the case of an illustrated printing form 31 already exists. Layer 24 contains a photocatalytic and thermal changeable material 24a in a sufficiently large proportion to a pixel-wise fine To enable imaging. The case is to be included that the layer 24 exclusively from a photo-catalytically and thermally changeable material 24a consists.

As in the further exemplary embodiments, the carrier layer 21 is made of one flexible steel plate or aluminum plate formed and subsequently simply as Carrier designated.

From the electron band structure of a photocatalytically and thermally changeable Material that forms a hydrophilic surface due to UV radiation can be closed be such a material in the visible region of the spectrum and in the near Infrared (NIR) is transparent. There is therefore no interaction with laser light from the visible range of the spectrum and the NIR or even longer-wave light. In order to nevertheless generate the heat required for the imaging, the Upper layer of the printing form advantageously absorption centers for laser light in the NIR or the entire IR range. This leads to an indirect one Heating of the photocatalytically and thermally changeable material of the upper layer through heat conduction.

The upper layer 24 is a dispersion from the photocatalytic in the exemplary embodiment and thermally changeable material 24a and absorbent particles contained in the material 24a are dispersed in a fine, uniform distribution. The absorption particles are nanoparticles of a semiconductor material that emit radiation from the IR wavelength range absorbed, converted into heat and transferred to the surrounding, outputs photocatalytically and thermally changeable material 24a. The absorption particles form the absorption centers 24b for the radiation used for heating. It can also particles of several semiconductor materials that form absorption centers 24b.

So that there is not too much heat in the lateral direction within the upper layer of the printing form 31 diffuses, can obtain a lower layer immediately adjacent to the upper layer be that it absorbs heat. As a material for such an underlayer, that too directly by a printing form support such as the support layer 21 can be suitable materials that enable high heat conduction and a large heat capacity have. Because a printing form carrier has a high mechanical strength should, in order to enable permanent installation within the printing press such a carrier consist of steel or aluminum, for example.

Depending on the sensitivity of the top layer, it may be advantageous to give off the heat a carrier to decrease the imaging effect of the top layer locally increase heat generated. For example, between the top layer and the carrier an insulation layer can be provided, which conducts heat to the carrier reduced. The material of the insulation layer should naturally have a low thermal conductivity exhibit.

FIG. 2b shows an embodiment in which an absorption layer is initially on the carrier 21 23 and the top layer 24 are applied thereon. About this three-layer structure is locally imaged by the radiation during the imaging in the absorption layer 23 Generates heat. The heat generated in the absorption layer 23 is transferred via the Contact surface in the upper layer 24, which is the photocatalytic and thermal changeable material 24a contains, transferred and reaches the surface of the top layer 24. As already described, the heat transfer to the atoms or Molecules on the surface to which the OH groups are attached split of these bonds, causing recombinations and a decrease in hydrophilicity comes. A layer thickness of the absorption layer 23 of 1 μm to 5 μm is advantageous.

The upper layer 24 has a special absorption layer 23 uniform thickness from preferably 0.05 µm to 5 µm, particularly preferably from 0.05 µm to 2 µm. Without an absorption layer, such as in the first In the exemplary embodiment, the top layer 24 advantageously has a layer thickness of 1 µm to 30 µm, particularly advantageously between 1 µm to 10 µm.

Figure 2c shows a third preferred embodiment. Here is immediately Over the carrier 21, a thermally insulating intermediate layer 22, on which immediately the upper layer 24 with the photocatalytically and thermally active material 24a is arranged. The thickness of the intermediate layer 22 is preferably between 1 μm and 30 µm. In the top layer 25 are again as in the first embodiment absorption centers 24b evenly distributed. The upper layer 24 has preferably a thickness of 1 µm to 30 µm, particularly preferably a thickness of 1 µm up to 10 µm.

Figure 2d shows a fourth embodiment. In this example is located immediately A thermally insulating intermediate layer 22, the thickness of which is preferably above the substrate 21 is between 1 µm and 30 µm. Immediately on the intermediate layer 22 an absorption layer 23 is provided, the layer thickness of which is preferably between 1 μm and is 5 µm. An upper layer 24 is arranged on the absorption layer 23 the photocatalytically and thermally changeable material 24a contains or exclusively consists of such material and preferably has a thickness of 0.05 µm to 5 µm, particularly preferably from 0.05 μm to 2 μm.

The top layers 24 of the exemplary embodiments in FIGS. 2b and 2d can likewise have dispersed absorption centers, although because of the absorption layer 23 also on the installation of absorption centers in which the photocatalytic and thermal changeable material can be dispensed with. In the embodiment of Figure 2d nevertheless a top layer 24 with dispersed absorption centers 24b is formed.

To apply the top layer and one or more additional layers or Layers are, for example, the sol-gel process and the CVD process (Chemical Vapor deposition). The layer or layers can or can be immediate applied on top of each other, i.e. without mediating layers such as Adhesive layers.

FIG. 3 shows a printing unit with a printing form cylinder 32, an associated one Blanket cylinder 38 and an impression cylinder 39, which with the blanket cylinder 38 forms a printing nip for a web 37 to be printed. On the printing form cylinder 32 two pressure plates 31 are attached in a known manner. However, each of the two printing plates 31 from a printing form according to the invention, for example according to one of the embodiments of Figures 2a to 2d formed. About the scope around the Printing form cylinders 32 distributed, an imaging device are arranged in the printing press 33, two quenching devices 34, inking rollers 35 and a dampening roller 36. A dampening solution film is applied in a known manner via the dampening application roller 36, preferably a film of water, to which printing formes 31 are brought up. Using the paint application rollers 35 becomes imagewise color during printing in a manner also known transferred to the printing forms 31, which of the printing forms 31 initially to the blanket cylinder 38 and is transmitted from this to the web 37. The Impression cylinder 39 can itself be a blanket cylinder of another printing unit for double-sided printing, a steel cylinder for only one printing point or one Steel cylinder of a satellite printing unit, for example a 9 or 10 cylinder printing unit his.

The imaging device 33 is the surface of the printing form 31 to be imaged directly facing and arranged parallel to the axis of rotation of the printing form cylinder 32. The imaging unit 33 has a plurality of along the axis of rotation of the Printing form cylinder 32 lasers arranged side by side. The laser spots of this Lasers are focused on the surface of the printing form 31. The lasers of the Imaging device 33 are preferably side by side to one or more arranged laser arrays summarized. An imaging device in preferred Embodiments are described in DE 199 11 907 A1, which is used as an example is taken.

The two extinguishing devices 34 each have at least one daylight emitter and / or at least one UV lamp. The extinguishers 34 are over the scope of the Printing form cylinder 32 spaced from each other parallel to the axis of rotation of the Printing form cylinder 32 arranged. Basically, a single would Erasing devices 34 are sufficient to close the imaged surfaces of the printing formes 31 delete by using the photothermally modifiable surface Material in relation to the respective print image in the normal hydrophilic state whole-area irradiation with light from the UV range is set back.

The erasure devices 34 are switched off during the imaging. Preferably there are no rollers or cylinders with the printing form cylinder during the imaging 32, in particular the printing forms 31, in order to keep them as quiet as possible To enable rotation of the printing form cylinder 32. After printing is finished the extinguishers 34 turned on. During the deletion, the surfaces of the printing formes 31 is wetted with water in order to previously lipophilic surface areas permanently bound by OH groups to make hydrophilic. In particular, the dampening unit of the printing unit or a Steam generator can be used.

In a further development, the printing unit, the printing form cylinder 32 and the Blanket cylinder 38 includes, encapsulated and conditioned to the environment within the encapsulation 40 the humidity and also the temperature of the particular one To be able to optimally adapt the operating state. So within the encapsulation 40 a uniformly high humidity of at least 60% during the extinguishing process prevail, preferably at least 80%, while for imaging and ongoing Pressure production the humidity should be significantly lower. Preferably encloses the Encapsulation 40 as in the embodiment also the impression cylinder 39. If that Printing unit includes other cylinders, are preferably also to the printing unit belonging further cylinder enclosed by the encapsulation 40. Is it in the printing units of the printing press around rubber / rubber printing units, so encloses the encapsulation 40 preferably each of the two against each other Blanket cylinders and their associated printing form cylinders. It can Encapsulations 40 in the case of printing units formed in this way also for the conventional H or N bridges, i.e. for four blanket cylinders and their plate cylinders, be formed. For satellite printing units with nine or ten cylinder units these units are preferably each of its own encapsulation 40 enclosed.

Although a pure humidification system is already advantageous in order to set the high atmospheric humidity for the UV radiation within the encapsulation 40 and to maintain it during the irradiation, air conditioning with the simultaneous setting and maintenance of a predetermined temperature within the encapsulation 40 is preferred. The a predetermined humidity for adjusting and attitude F _to and a predetermined temperature T _set air conditioner used comprises on the encapsulation 40 and the means for the supply of water, in the embodiment, the dampener roller 36, a humidity and temperature controller 43 and at least one within the Encapsulation 40 arranged moisture sensor 41 and at least one temperature sensor 42 arranged inside the encapsulation 40. The sensors 41 and 42 record the air humidity and the temperature within the encapsulation 40 and give both the air humidity and the temperature depending on the control variable F _ist and T _ist the controller 43. the controller 43 forms the difference between the recorded values of humidity and temperature and the predetermined values _to the respective difference F-F _and T _to T _and forms in dependence on the humidity difference and the temperature difference, the humidity control variable F and the temperature control variable T for the devices acting within the encapsulation 40 for the supply of water and the influencing of the temperature.

Imaging and deletion in the printing press is preferred, especially imaging and deletion on the printing form cylinder on which the printing form is also in the Print production is attached or integrated on the cylinder. Basically you can however, the imaging and erasure are also carried out outside the printing press become. Also performing one of the operations in the press and performing the other of the operations outside the press is not intended to be excluded become.

Claims (31)

Wet offset printing form with a top layer (24), which contains a photocatalytically and thermally changeable material, which can be photocatalytically converted into a hydrophilic state by irradiation with light and into a lipophilic state by heating, and which has an imageable or illustrated surface (130, 131) forms,
characterized in that
the upper layer (24) has absorption centers (24b) for radiation, in particular for laser radiation in the NIR, with which the upper layer (24) is heated in accordance with the image. Wet offset printing form according to claim 1, characterized in that the absorption centers (24b) are dispersed in the photocatalytically and thermally changeable material (24a). Wet offset printing form according to one of the preceding claims, characterized in that the absorption centers (24b) are nanoparticles. Wet offset printing form according to one of the preceding claims, characterized in that the absorption centers (24b) are formed by particles of at least one light-absorbing semiconductor material. Wet offset printing form according to one of the preceding claims, characterized in that the photocatalytically and thermally changeable material (24a) of the upper layer (24) is a semiconductor material with a conduction band energy measured at the lower edge of the conduction band, which is at least as negative as that for the reduction of Water in hydrogen gas requires energy, and a valence band energy appropriate at the top of the valence band that is at least as positive as an energy required to oxidize water to hydrogen gas. Wet offset printing form according to one of the preceding claims, characterized in that the photocatalytically and thermally changeable material (24a) of the upper layer (24) anatase-TiO ₂ or zinc oxide or ZrO ₂ or SrTiO ₃ or KTaO ₃ or KTa _0.77 Nb _{0, 23} O ₃ or a combination of at least two of these materials. Wet offset printing form according to one of the preceding claims, characterized in that a material forming the surface (130, 131) contains the photocatalytically and thermally changeable material (24a) in a proportion of at least 40% by weight. Wet offset printing form according to one of the preceding claims, characterized in that an absorption layer (23) for radiation of a wavelength of 400 nm or greater is arranged below the top layer (24) and is thermally conductively connected to the top layer (24). Wet offset printing form according to the preceding claim, characterized in that the absorption layer (23) borders directly on the top layer (24) for direct thermal contact. Wet offset printing form according to one of the preceding claims, characterized in that a thermally insulating layer (22) is formed below the upper layer (24), preferably below an absorption layer (23) arranged below the upper layer (24). Wet offset printing form according to one of the preceding claims, characterized in that the printing form (31) has a carrier (21) for the upper layer (24), which preferably consists of steel or aluminum. Wet offset printing form according to one of the preceding claims, characterized in that between a printing form support (21) and the upper layer (24) there is provided a layer which acts as a diffusion barrier and can be formed by a thermally insulating layer (22), this layer prevents or hinders diffusion of atoms of the carrier (21) into the upper layer (24). Wet offset printing form according to one of the preceding claims, characterized in that a diffusion barrier is formed by a layer (22) arranged between the top layer (24) and a support (21) of the printing form (31). Process for imaging a wet offset printing form (31) which has a photocatalytically and thermally changeable material on an imageable surface (130), which can be photocatalytically converted into a hydrophilic state by irradiation with light and into a lipophilic state by heating, in which
the printing form (31) is imaged by image-wise heating of the photocatalytically and thermally changeable material,
characterized in that
a printing form (31) according to one of the preceding claims is used. Method according to the preceding claim, characterized in that the printing form (31) is imaged with laser beams, preferably IR laser beams. Method according to the preceding claim, characterized in that laser light with a wavelength between 400 and 3000 nm is used. Method according to the preceding claim, characterized in that laser light with a wavelength of at least 700 nm, preferably at least 800 nm, is used. Method according to one of the preceding claims, characterized in that the printing form (31) is irradiated with daylight and / or UV light in order to delete a print image generated by the image-based heating. Method for deleting or imaging a printed image of a wet offset printing form, which has a photocatalytically and thermally changeable material (24a) on a surface (130, 131) forming the printed image, which is photocatalytically rendered into a hydrophilic state by irradiation with light and heated into one by heating lipophilic state is displaceable, in which a) the printed image is deleted or generated by irradiating the surface (130, 131) with UV radiation, b) and the surface (130, 131) is supplied with water during the irradiation. Method according to the preceding claim, characterized in that a moisture content of at least 60%, preferably of at least 80%, is generated on the surface (130, 131) for the UV radiation and is preferably maintained over the duration of the UV radiation. Method according to the preceding claim, characterized in that a predetermined temperature is set and maintained over the duration of the UV radiation. Method according to one of the four preceding claims, characterized in that the imaged surface (130, 131) of the printing form (31) is irradiated over the entire area for deletion. Device for the repeated imaging of a wet offset printing form, which has a photocatalytically and thermally changeable material (24a) on an imageable or already imaged surface, which can be photocatalytically converted into a hydrophilic state by irradiation with light and into a lipophilic state by heating full: an imaging device (33) for generating a printed image by image-wise heating of the photocatalytically and thermally changeable material (24a) and an erasing device (34) for erasing the printed image, the erasing device (34) having one or more emitters for daylight and / or UV light, characterized in that
the device comprises a humidification system (40, 41, 43), preferably an air conditioning system (40-43), by means of which a predetermined air humidity can be generated and maintained on the printing form (31). Device according to the preceding claim, characterized in that the humidification system (40, 41, 43) has an encapsulation (40) for the wet offset printing form (31) and preferably for a plurality of cylinders (32, 38, 39) of a printing unit, around the generate and maintain predetermined air humidity within the encapsulation (40). Device according to the preceding claim, characterized in that the humidification system (40, 41, 43) comprises at least one moisture sensor (41) arranged within the encapsulation (40) and a controller (43) to which the air humidity picked up by the moisture sensor is supplied as a control variable becomes. Device according to one of the preceding claims, characterized in that the extinguishing device (34) has one or more emitters for irradiation of the entire surface of the surface (130, 131). Device according to one of the preceding claims, characterized in that the radiator (s) of the quenching device (34) emit a high proportion of radiation of a wavelength of at most 387 nm, a wavelength spectrum emitted by the radiator preferably having a peak at a wavelength of 387 nm Or less. Device according to one of the preceding claims, characterized in that the printing form (31) on a printing form cylinder (32) in a wet offset printing machine, in particular web-fed rotary printing press, is arranged detachably or non-releasably and the erasing device (34) is directed at the printing form cylinder (32) and preferably extends so far over the length of the printing form (31) measured parallel to an axis of rotation of the printing form cylinder (32) that uniform irradiation of the printing form (31) can be carried out over the entire surface. Device according to one of the preceding claims, characterized in that the imaging device (33) comprises a plurality of radiators for image-wise irradiation of the printing form (32). Device according to one of the preceding claims, characterized in that the radiators of the imaging device (33) are IR lasers, preferably NIR lasers. Device according to one of the preceding claims, characterized in that the printing form (31) is arranged detachably or non-releasably on a printing form cylinder in a wet offset printing press, in particular web-fed rotary printing press, and the radiators of the imaging device (33) are directed and preferably directed towards the printing form cylinder (32) are arranged side by side parallel to an axis of rotation of the printing form cylinder (32).

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