Method and printing apparatus for affecting the optical properties of a lacquer layer to be deposited on a printed recording medium.

Abstract

To provide a method and a printing device for influencing optical properties of a lacquer layer to be applied onto a printed recording medium.SOLUTION: Before printing at least one color separation component of a print image on a recording medium 12, a coating material is applied onto the recording medium 12 by digital printing. The quantity of the coating material applied per unit area by digital printing is adjusted depending on desired optical properties of a lacquer layer 34 to be applied later.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for influencing the optical properties of a lacquer layer to be applied to a printed recording carrier on which a printed image has been printed using a printing device, particularly an inkjet printing device. Before printing at least one color separation component of a printed image onto a recording carrier, a coating material is applied to the recording carrier by digital printing. Furthermore, the present invention relates to a printing device for printing on a recording carrier, which is adapted to influence the optical properties of a lacquer layer to be applied to a printed recording carrier on which a printed image has been printed using a printing device, particularly an inkjet printing device.

[0002] The present invention is particularly used in digital printing. Digital printing is also referred to internationally as "Direct Digital Printing" (DDP) or "Computer-to-Print". Digital printing represents a group of printing methods in which a printed image is transferred directly from a data file or a computer's print data flow to a printing device without the use of a static printing plate. When a printed image is formed using a digital printing device, printing dots are formed in rows and columns in relation to the print data. The printing dots formed in the form of row rasters and column rasters are also referred to as "raster dots", "pixels" or "picture elements". To form raster dots of a desired color, the color dots of the individual color separation components are printed in this raster so that at least for an observer, one mixed color can be formed visually. Thus, the row raster and the column raster define a pixel area within which the pixels are then formed on the recording carrier.

[0003] So-called analog lacquering equipment is known that forms a solid lacquer layer over the entire surface of a printed medium. The gloss of the formed lacquer layer is obtained depending on the amount and type of lacquer and the medium used for application. This gloss is uniform and consistent across the entire lacquered surface. Partial surfaces of the recording medium can be excluded from lacquering by cutting out or removing the contact areas of the plate or printing cylinder used for lacquering. In this case, multiple areas of the plate or printing cylinder are cut out so that the plate or printing cylinder does not contact the recording medium in these areas. The resulting lacquer image will be the same on any printed page based on the static configuration of the plate or printing cylinder and can only be changed when the plate or printing cylinder is replaced with a different one. Changing the gloss of the lacquer in different areas of the recording medium is only possible by a second analog lacquering method. In this case, a different amount, a different type of lacquer, or a different medium is used for lacquering.

[0004] Analog lacquer application equipment forms a solid lacquer layer over the entire surface of a printed image or packaging. Such lacquer application equipment includes, for example, commercially available flexographic printing presses or conventional offset printing presses. Such a flexographic printing press may include a flexographic plate, a chambered doctor, and an anilox roller. In this case, the lacquer is applied to the flexographic plate, printing roller, or printing blanket by the chambered doctor and the anilox roller. The doctor then removes the lacquer from the anilox roller again to the extent that a uniformly measured, single amount of lacquer remains on the anilox roller downstream of the doctor. The amount of lacquer is then determined by the volume of the anilox cells (tiny indentations) or the structure of the anilox roller. The lacquer is then transferred to the printing cylinder, printing blanket, or flexographic plate. In this case, a first separation process of the lacquer layer present on the flexographic plate, printing cylinder, or printing blanket takes place. Next, the printing cylinder or printing blanket transfers the lacquer to the recording carrier, such as paper or cardboard for cartons, during which a second lacquer separation process takes place. The recording carrier is then completely covered with a uniform lacquer layer.

[0005] As already mentioned, individual areas of the lacquered surface can also be excluded from the coating. To achieve this, multiple areas are removed from the printing cylinder or printing blanket, so that lacquer cannot be transferred from the printing cylinder or printing blanket to the recording medium in these areas. As a result, areas with a lacquered layer and areas without a lacquered layer are created. The glossiness of the lacquered layer thus applied is the same at all points in the lacquered layer. Deviations can only occur due to uneven application or lacquer transfer and defects in the recording medium. Therefore, conventional lacquering equipment can either apply a lacquered layer at specified, unchanging locations (100%) or not (0%). In many use cases, a full-surface lacquered layer is formed, and in the case of a full-surface lacquered layer, the printing blanket or printing cylinder does not have any notches that are excluded from the coating, so the surface of the recording medium is fully lacquered, i.e., 100% lacquered. Therefore, areas with a lacquered layer have a constant, equal amount of lacquer and the same glossiness. To form a recording medium with various glossy areas, two or more lacquering processes are required. It is impossible to individually control the glossiness of individual areas on different printed pages. On the contrary, since the formed lacquer layer and the glossy image of the lacquer layer are identical in the printed images that are lacquered sequentially, a copy of the lacquer layer is formed on all printed pages that are printed sequentially.

[0006] In digital printing, particularly digital inkjet printing or ink jet printing, a coating material, or so-called primer, is applied to the recording medium before printing the color separation components of the print image. This coating material is applied digitally, preferably using a primer inkjet printing unit, or so-called primer inkjet station, as a uniform layer across the entire print area of ​​the recording medium. The primer may be, for example, an aqueous saline solution, which reacts with the color inks in the inkjet station to prevent ink aggregation or bleeding, so that the ink adheres directly to the recording medium during printing. Furthermore, the primer prevents the inks of different color separation components from bleeding into each other. Such a primer is generally colorless, or invisible or undetectable when printed on the recording medium. Thus, it does not have any undesirable effect on the printed image. Such primer application is known, for example, based on German Patent Application Publication No. 102017101527. This primer enables the achievement of extremely sharp printed images.

[0007] Furthermore, a polyurethane-based primer is publicly known, based on International Publication No. 2013 / 126869.

[0008] The object of the present invention is to provide a method and a printing apparatus for influencing the optical properties of a lacquer layer to be deposited on a printed recording carrier.

[0009] This problem is solved by a method having the features described in claim 1 and a printing apparatus having the features described in claim 10. Each of the dependent claims describes an advantageous improvement.

[0010] The method having the features described in claim 1 achieves that the coating material applied before the application of the color separation component is applied to the recording medium not as a uniform layer, but in varying amounts per unit area in relation to the desired optical properties of the lacquer layer to be applied later. This allows for the formation of different gloss characteristics of the lacquer layer to be applied later, individually for each printed image. The lacquer layer itself can then be applied to the printed recording medium conventionally as a uniform lacquer layer. Different gloss levels of the lacquer layer to be applied can be achieved based on different optical properties. Furthermore, matte surfaces are suitable for adhesive bonding due to their roughness. In this case, these areas do not need to be excluded from the coating during the formation of the lacquer layer, unlike in the known prior art.

[0011] Different amounts of coating material applied per unit area by digital printing create surface regions with different surface energies, which in turn produce different roughnesses in the lacquer layer subsequently applied. In this context, surface energy is the amount of energy required to break chemical bonds when a new surface of a liquid or solid is formed. Surface energy is defined as the energy that must be consumed per unit area to form the surface.

[0012] A digitally printed image can be formed by digital printing on the coating material. This digitally printed image then becomes visible as a glossy image after the lacquer layer is applied.

[0013] The printed image of the coating material, like the printing of color separation components, can be digitally controlled to vary from page to page along a web-like recording medium, or from sheet to sheet in the case of a sheet-like recording medium. The printing unit, in particular a print bar with multiple print heads for printing the coating material, can be controlled in the same way as the printing unit or print bar for printing color separation components. This allows the amount of coating material applied per unit area to be easily determined within a range of 0% (no coating material applied) to 100% (the maximum amount of coating material that can be applied per unit area using the printing unit). Since the coating material is applied using the print heads of the print bar, in particular using inkjet print heads, any pattern possible within the resolution range of the print heads can be formed. This allows the image of the coating material to be printed at a resolution of 600 dpi for a print head with a resolution of 600 dpi, and at a resolution of 1200 dpi for a print head with a resolution of 1200 dpi, respectively. The applied coating material is used both as a primer to prevent the color separation of the applied color components, particularly the bleeding of the applied ink, and to form the desired optical properties of the lacquer layer to be applied to various surface areas in a subsequent analog lacquer coating process. In this case, the analog lacquer coating process refers to applying a uniform lacquer layer using an offset printing machine or a flexographic printing machine. In an alternative embodiment, the lacquer layer may also be applied by a spraying process.

[0014] By individually controlling the amount of coating material to be applied per unit area, a digital printed image of the coating material is formed on the recording medium, and this printed image is invisible to the observer. In this way, image information is imprinted on the recording medium in an invisible form. This information is memorized by various amounts of coating material per unit area, and then, in the subsequently applied lacquer layer, various optical properties are produced. That is, even with a lacquer layer applied to the entire surface, a visually visible image is produced in the lacquer layer due to the various optical properties of the lacquer layer related to the amount of coating material applied per unit area.

[0015] Therefore, image information becomes visible in the lacquer layer that is later applied. Different degrees of gloss are produced depending on the amount of coating material applied per unit area. In areas with a large amount of coating material, a rough, uneven lacquer structure is created. As a result, light rays are scattered at the lacquer surface; that is, diffuse reflection occurs. The image appears matte. In image areas without coating material or with only a small amount of coating material per unit area, the lacquer layer has a smoother surface, and as a result, light rays are not scattered at the surface, or are only scattered slightly, thus forming a high gloss. Therefore, the gloss of the lacquer layer can change the optical properties or optical impression of the printed product as if it were an additional color. In this case, glossy and matte areas or areas with different reflective properties are formed. This can be arbitrarily changed from page to page or from sheet to sheet, as is common in digital printing. That is, peripheral effects can be particularly emphasized, or matte and glossy areas can be formed in a way that is comparable to a watermark. This makes additional background information visible. This can be particularly useful as a safety feature of the resulting printed product, because the formation of various optical properties in the lacquer layer cannot be imitated by simple copying systems.

[0016] By intentionally altering the surface structure of the lacquer layer, it is possible to intentionally improve the adhesive properties of printed products in specific areas. This is achieved, in particular, by using rougher surfaces, because rough surfaces have a larger surface area than smooth surfaces. This increases the mechanical adhesion.

[0017] In the prior art, such areas often require the laborious process of cutting out the corresponding parts by changing the printing cylinder, plate, or printing blanket. This requires a particularly large printing cylinder or blanket, the circumference of which must correspond to the length of one printed page. According to the present invention, the surface to be bonded may be intentionally coated with a coating in an amount such that the lacquer layer to be subsequently applied has a rough surface.

[0018] By forming a printed image of the coating material, the gloss information of the lacquer layer to be formed can be permanently memorized before the lacquer layer is applied. Therefore, the lacquer layer can be applied at a considerably later point in time, and especially at a different location. Consequently, the lacquer coating process can be carried out at any point after printing.

[0019] The lacquer layer can be applied using a commercially available flexographic printing apparatus. This purely analog lacquer coating / flexographic printing apparatus provides a uniform lacquer layer, which is then applied to the recording medium, forming gloss in relation to the printed image of the coating. Thus, the information contained in the printed image of the coating is "developed." Very inexpensive standard lacquers can be used to form the lacquer layer. For this purpose, special printable lacquers that can be printed onto pre-printed recording mediums, particularly using an inkjet printing unit, are not required.

[0020] The amount of coating material applied alters the energy state of the phase boundary between the recording medium and the liquid lacquer. The application of the coating material, particularly the application of a high amount, increases the surface energy, altering the wettability of the recording medium's surface and the separation of the lacquer layer during transfer from the printing roller or blanket to the printed recording medium. The lacquer dries within a short time after application. For this purpose, drying equipment, especially heating units and / or fans, may be used, so the lacquer forms as a solid layer.

[0021] The surface structure of the lacquer is related to the amount of coating material applied per unit area and is maintained after drying. The greater the amount of coating material applied, the higher the surface roughness of the applied lacquer layer. Subsequently, the surface of the lacquer layer is given a high roughness or corrugated structure upon drying of the lacquer layer into the solid phase. This high roughness results in diffuse light reflection, making it appear matte to the observer. Optical gloss can be increased by reducing the amount of coating material applied. The highest degree of gloss was achieved in experiments in areas without coating material.

[0022] In systems where a lacquer layer is formed using an inkjet printing unit, a special lacquer for the inkjet head is required, which must meet specific requirements regarding viscosity, solid content, and / or pH value. Such lacquers are UV-curable, often containing photoinitiators, and are typically cured using mercury vapor lamps or LED systems. This also necessitates special measures for worker safety. Forming a lacquer layer on a pre-printed recording medium in this manner is relatively expensive, especially when applying a lacquer layer to a large surface. However, such systems can also be used to apply lacquer in varying amounts.

[0023] In contrast, an inexpensive water-based lacquer can be used by analog lacquer application using a printing roller, printing blanket, or flexographic printing apparatus. Such lacquers can be dried with hot air or an infrared radiator. The method according to claim 1 allows for stepless adjustment of gloss, in particular, by the amount of coating material applied per unit area. The most matte finish is achieved at the maximum possible amount of coating material per unit area. The maximum amount per unit area is predetermined by the print head that applies the coating material when using an inkjet printing unit. The coating material exists on the recording carrier in a dried solid form, together with the visible printed image, after printing and drying. As already described, a lacquer layer may then be applied immediately thereafter, or separately in terms of time and space. The recording carrier may be paper web or cardboard, such as corrugated cardboard.

[0024] A second aspect of the present invention relates to a printing apparatus, particularly an inkjet printing apparatus, for influencing the optical properties of a lacquer layer to be deposited on a printed recording medium on which a printed image has been printed. A first digital printing unit deposits a coating onto the recording medium. A second digital printing unit prints at least one color separation component of the printed image to be formed on the recording medium.

[0025] The amount of coating material applied per unit area using the first printing unit is adjusted or controlled, in particular, by a control unit, in relation to the desired optical properties of the lacquer layer to be applied later.

[0026] This printing apparatus is suitable for implementing a method having the features described in claim 1 or an improved form of this method as described in each of the dependent claims, particularly in dependent form. In this case, since the control unit controls the printing unit accordingly, the printed image of the coating material is printed in different amounts of the coating material per unit area for each region. When a uniform lacquer layer is subsequently applied, this lacquer layer has different optical properties in relation to the amount applied per unit area of the coating material applied by digital printing using the first printing unit.

[0027] The coating material is particularly a primer, and the primer reduces or avoids the bleeding of the dyes of the different color separation components of the printed image to be printed or the bleeding of the applied dyes of the individual color separation components on the recording carrier. The coating material may contain an aqueous salt solution or be an aqueous salt solution. The aqueous salt solution particularly contains magnesium nitrate or magnesium sulfate. In an alternative or additional embodiment, the coating material may contain polyurethane or be a coating material mainly composed of polyurethane. The coating material forms a colorless layer on the recording carrier.

[0028] Examples will be described below with reference to the drawings.

Brief Description of the Drawings

[0029] [Figure 1] It is a diagram schematically showing a printing apparatus for printing a printed image on a recording carrier according to the first embodiment, and subsequently an apparatus for applying a lacquer layer to the printed recording carrier. [Figure 2] It is a partial cross-sectional view schematically showing an apparatus for applying a lacquer layer to a printed recording carrier according to the second embodiment. [Figure 3] It is a cross-sectional view of a printed recording carrier provided with a lacquer layer applied after printing. [Figure 4] It is a cross-sectional view showing a section of a printed recording carrier provided with a lacquer layer having a low optical gloss applied after printing. [Figure 5]This is a cross-sectional view showing a section of a printed recording carrier, which has a lacquer layer with high optical gloss that has been applied after printing. [Figure 6] This figure schematically illustrates the diffuse reflection of light rays on the surface of a low-gloss lacquer layer. [Figure 7] This diagram has curves that show the relationship between the gloss of the surface of a first recording medium with a lacquer layer, the gloss of the surface of a second recording medium, and the amount of coating material applied to the recording medium before printing.

[0030] Figure 1 shows a schematic diagram of a printing apparatus 10 for printing a printable image onto a recording medium 12, and a subsequent apparatus 32 for applying a lacquer layer 34 to the printed recording medium 12, according to the first embodiment. The printing apparatus 10 has a plurality of digital printing units 22 to 30, which in this embodiment are formed as inkjet printing units 22 to 30. In another embodiment, the digital printing units may operate by a different printing principle.

[0031] In this embodiment, each printing unit 22-30 includes a single printing bar equipped with multiple inkjet print heads. These inkjet print heads are positioned so that the printing bar and the print heads can print on the recording medium 12 across the entire printing width. To perform printing using the printing units 22-30, the recording medium 12 is guided past the printing units 22-30 in the direction of arrow P1, and then transported through the printing apparatus 10 via guide rollers 14, 16, and 18. In this case, the recording medium 12, on which the print image has been printed and which has been coated with a lacquer layer 34, is then wound onto the roll 20. Each printing unit 24, 26, 28, and 30 forms a raster image of one color separation component on the recording medium. In this case, the printing units 24, 26, 28, and 30 are controlled by a control unit (not shown) which includes a raster image processor.

[0032] In this case, printing unit 24 can print the color separation component of the color "yellow", printing unit 26 can print the color separation component of the color "magenta", printing unit 28 can print the color separation component of the color "cyan", and printing unit 30 can print the color separation component of the color "black". The color order described herein can also be arranged in a different order. Printing unit 22 is used to apply a coating material. In this embodiment, this coating material is a primer, which reduces or prevents the pigments of the color separation components printed by printing units 24-30 of the print image to be printed from bleeding into each other, or the pigments of the individual color separation components on the recording carrier 12 from bleeding.

[0033] The coating material may contain or be a saline solution. The saline solution particularly contains magnesium nitrate or magnesium sulfate. In alternative or additional embodiments, the coating material may contain polyurethane or be a polyurethane-based coating material.

[0034] The coating material forms a colorless layer on the recording carrier 12. The printing unit 22 for applying the coating material is also controlled by a control unit, which controls the printing unit 22 so that the ratio of the amount of coating material to be applied per unit area can be adjusted between 0% and 100%, depending on the desired optical properties of the lacquer layer 34 to be applied using the device 32 for subsequently applying the lacquer layer 34. In this case, 100% is the maximum amount of coating material that can be applied per unit area using the printing unit 22. Thus, the printing unit 22 forms a raster image of the coating material, which is still not visually detectable by an observer. However, this raster image affects the glossiness of the lacquer layer 34 in each surface area after application, in relation to the amount of coating material applied per unit area.

[0035] The apparatus 32 for applying the lacquer layer 34 includes a lacquer storage section 42 for applying lacquer to the anilox roller 40. A doctor (not shown) limits the amount of lacquer layer applied to the anilox roller 40, so that a uniform lacquer layer is present on the anilox roller 40 in the contact region between the anilox roller 40 and the printing roller 38. As a result, a uniform lacquer layer is formed on the outer surface of the printing roller 38. The lacquer layer is then transferred from the printing roller 38 to the printed recording carrier 12. In the transfer region, a pressing roller 36 is positioned opposite the printing roller 38.

[0036] As already mentioned, the glossiness of the lacquer layer 34 is related to the amount of coating material applied per unit area using the printing unit 22. The resolution of the printing unit 22 is preferably the same as the printing resolution of the printing units 24-30. In another embodiment, the printing unit 22 may have a lower resolution than the printing units 24-30. In particular, the printing unit 22 may have a resolution of 300 dpi, 600 dpi, or 1200 dpi. This allows the use of a printing unit that has proven advantageous for applying the coating material.

[0037] Figure 2 shows a schematic partial cross-sectional view of an apparatus 50 for applying a lacquer layer to a printed recording carrier 12 according to a second embodiment. In this second embodiment, unlike the first embodiment shown in Figure 1, the lacquer layer is applied to the underside of the printed recording carrier. In particular, the apparatus 50 is a separate apparatus spatially independent of the printing units 22-30, and the lacquer layer 34 can be applied to the printed recording carrier 12 afterwards using this apparatus 50. In the embodiment shown in Figure 2, different amounts of coating material are printed in regions 52 and 54 of the recording carrier 12. In contrast, no coating material is printed in region 56 of the recording carrier 12. The coating material is etched onto the underside of the recording carrier 12, in which case approximately 30% of the maximum amount of coating material is applied in region 52, and the maximum amount of coating material is applied in region 54. Similar to the apparatus 32 shown in Figure 1, apparatus 50 has an anilox roller 40, which is lacquered by a lacquer storage unit 42. In this case, the thickness of the lacquer layer applied to the anilox roller 40 is limited by a doctor 44. The lacquer scraped off by the doctor 44 is collected by a collection container 46 and supplied back to the lacquer storage unit 42 by a pump 48.

[0038] Similar to the apparatus 32 shown in Figure 1, the lacquer layer is transferred from the anilox roller 40 to the printing roller 38, and then from the printing roller 38 to the printed recording carrier 12. At least the printed image of the coating material is printed on the recording carrier 12. In the section of the recording carrier 12 shown in Figure 2, there are no color separation components of the printed image.

[0039] In the region of the recording carrier 12 that has already passed through the apparatus 50, a lacquer layer 64 with an uneven surface is formed on the section 54 which has 100% coating material. This uneven surface causes diffuse reflection of incoming light rays, so this layer 64 later appears matte. In region 56, there is no coating material between the recording carrier 12 and the lacquer layer 34, so the lacquer layer 34 has an extremely smooth surface in this region 66, and the diffuse reflection of incoming light rays due to the lacquer layer 34 in this region 66 is less than that of the lacquer layer 34 in region 64. Therefore, region 66 has high gloss. The lacquer layer 34 applied to the subsequent region 52 has a gloss in region 62 that is intermediate between that of region 64 and region 66.

[0040] Figure 3 shows a cross-sectional view of a printed recording carrier 12 having a lacquer layer 34 applied by the apparatus 32 or 50 after printing. In this case, a printed image is printed on several areas of the recording carrier 12 with the coating, and in this case, the printed image formed or printed by multiple color separation components is indicated by reference numeral 60. Area 52 of the recording carrier 12 has a first amount of coating per unit area. Area 54 of the recording carrier 12 has a second amount of coating per unit area, and area 56 of the recording carrier is uncoated. Area 62 of the lacquer layer 34 has a first gloss characteristic, area 64 of the lacquer layer 34 has a second gloss characteristic, and area 66 of the lacquer layer has a third gloss characteristic. Region 64 has strong diffuse reflectance, region 62 has moderate diffuse reflectance, and region 66 has weak diffuse reflectance. Therefore, region 66 is perceived as glossy by the observer, region 64 is perceived as matte, and region 62 is perceived as being in an intermediate stage between matte and glossy.

[0041] Figure 4 shows a cross-sectional view of a section of the printed recording carrier 12, which is fitted with a lacquer layer 34 having low optical gloss after printing.

[0042] Figure 5 shows a cross-sectional view of a section of the printed recording carrier 12, which is fitted with a lacquer layer 34 having high optical gloss after printing.

[0043] Figure 6 shows a schematic diagram of the optical path 68. The incident light beam 67 undergoes diffuse reflection of light rays on the surface of the lacquer layer 34 in the low-gloss region 64, so that the reflected light beam 69 is directed in various directions.

[0044] Figure 7 shows a diagram with curve 70 showing the relationship between the gloss of the surface of a first recording medium having a lacquer layer 34 and the amount of coating material applied to the recording medium 12 before printing, and curve 72 showing the relationship between the gloss of the surface of a second recording medium having a lacquer layer 34 and the amount of coating material applied to the recording medium 12 before printing. In this case, the x-axis represents the amount of coating material applied (g / m²). 2 The graph shows the glossiness measured at a set angle of 60° on the measuring device. Both the recording carrier 12 of curve 70 and the recording carrier 12 of curve 72 are coated paper, but have different characteristics. In both papers, the glossiness of the coated lacquer layer 34 decreases as the amount of coated material increases, so the glossiness of the surface of the lacquer layer 34 can be easily and intentionally changed and controlled by the application of a corresponding amount of coating material before the lacquer layer is applied, especially before the printed image is applied to the recording carrier 12.

[0045] A water-based lacquer, which is particularly convenient, may be used as the lacquer for forming the lacquer layer 34. The lacquer layer is applied, in particular, after the coated covering has dried and / or after the color separation components have been printed onto the recording carrier 12. The lacquer layer 34 may be dried, in particular, using an infrared heating unit and / or a fan. The recording carrier 12 may be a web-like recording carrier or a sheet-like (sheet-fed) recording carrier. The sheet-like recording carrier may be cardboard, particularly corrugated cardboard.

[0046] Generally, the amount of coating material applied can affect the roughness of the lacquer layer 34 that is applied later, so that areas with relatively rough surfaces and areas with relatively smooth surfaces can be formed. These areas have different optical properties based on their different surfaces. The printed image with the coating material can then be used as an invisible security feature. This security feature becomes visible when the lacquer layer 34 is applied during document inspection. This makes it easy to form an invisible security feature. [Explanation of symbols]

[0047] 10 Printing device 12 Recording Carrier 14, 16, 18 Guide elements 20 rolls 22 Digital printing unit covering material 24, 26, 28, 30 Digital printing unit Color separation components 32.50 Printing equipment for lacquer layers 34 Lacquer Layer 36 Pressure rollers 38 Printing Rollers 40 Anilox Slora 42 Lacquer Storage 44 Doctor 46 Collection container 48 pumps 52 Region of a recording carrier having a first amount of covering material per unit area 54 Region of a recording carrier having a second amount of covering material per unit area 56 Area of ​​recording carrier without coating 60 Printed Images 62 Region of the lacquer layer having the first glossy property 64 Region of the lacquer layer having a second glossy property 66 Region of the lacquer layer having a third glossy property 67 Incident light beam 68 Light path 69 Reflected light beam 70,72 curve P1 Conveying direction

Claims

1. A method for influencing the optical properties of a lacquer layer (34) applied to a printed recording carrier (12) on which a printed image has been printed using a printing device (24-30), Before printing at least one color separation component of the printed image (60) onto the recording carrier (12), a coating material is applied to the recording carrier (12) by digital printing. The amount of the coating material applied per unit area by digital printing is adjusted in relation to the desired optical properties of the lacquer layer (34) to be applied later. A method wherein the coating material is a primer that reduces the mutual bleeding of pigments of various color separation components of a printed image (60) printed on the recording carrier (12).

2. The method according to claim 1, characterized in that the coating material is applied to the recording carrier (12) in a liquid state.

3. The method according to claim 2, characterized in that, in relation to the amount of the coating material applied to the recording carrier (12), at least a pixel region having a first surface energy and a pixel region having a second surface energy can be formed.

4. The method according to any one of claims 1 to 3, characterized in that the unit area corresponds to the printable pixel area of ​​a digital printing unit (22) for applying the coating material.

5. By digital printing, a first amount of the covering material is applied to the first surface area (54) of the recording carrier (12), and a second amount of the covering material is applied to the second surface area (56) of the recording carrier (12). The method according to any one of claims 1 to 4, characterized in that the lacquer layer (34) subsequently applied to the first surface region (54) has a first optical property, and the lacquer layer (34) subsequently applied to the second surface region (56) has a second optical property.

6. The method according to claim 5, characterized in that the first optical property and the second optical property are the reflective properties of the lacquer layer (34) applied to the first surface region (54) and the second surface region (56).

7. The coating material contains or is a saline solution, and / or The coating material is a coating material mainly composed of polyurethane, and / or The method according to any one of claims 1 to 6, characterized in that the covering material forms a colorless layer on the recording carrier.

8. The method according to any one of claims 1 to 7, characterized in that a lacquer layer (34) is formed on the printed recording carrier (12) with a uniform thickness, and / or the lacquer layer (34) is formed on the printed recording carrier by a lacquer layer (34) that is applied to the outer circumferential surface of the recording carrier (12) with a uniform lacquer layer thickness in the contact area with the recording carrier (12), and / or the lacquer layer is formed on the printed recording carrier (12) with a uniform lacquer layer thickness during the spraying process.

9. To form a print data for creating a visible image of the covering material, The method according to any one of claims 1 to 8, characterized in that the print data is processed by a control unit, and the control unit controls a digital printing unit (22) to print the covering material image.

10. A printing device, A digital first printing unit (22) for applying a coating material to the recording carrier (12), At least one digital second printing unit (24-30) for printing at least one color separation component of a printed image formed on the recording carrier (12) Equipped with, The amount of the coating material applied per unit area by the first printing unit (22) is adjustable in relation to the desired optical properties of the lacquer layer (34) that can be applied later. The coating material is a primer that reduces the mutual bleeding of pigments of various color separation components of the printed image (60) printed on the recording carrier (12). Printing device.

Images