Matting by means of a tranfer process

Abstract

Method for applying a matting fluid layer (9) to a printing substrate (6) via a printing form (3), wherein the matting fluid layer (9) on the printing form (3) is dried before being applied to the printing substrate (6), which is characterized in that the degree of mattness of the applied fluid layer (9) is modified via parameters of the drying process and the condition of the surface of the printing form (3).

Description

[0001] The present invention discloses a method for applying a thin matting fluid layer to a printing substrate via a printing form with targeted mattness control.

[0002] The invention lies in the technical field of printing, in particular packaging and commercial printing.

[0003] When printing using the film transfer process, certain phenomena occur, particularly the matting of gloss varnishes during film transfer. The matting of gloss varnishes is independent of the substrate used and can vary in severity and intensity depending on the process parameters.

[0004] Matt varnishing with water-based coatings, particularly in packaging and commercial printing, is currently achieved using two approaches. One variant involves the addition of matting agents, i.e., additives that, for example, roughen the surface. This alters the printability, in the form of the viscosity of the coating, and therefore requires adjustment each time. The other is the volume addition of matting agent, which limits the degree of matting.

[0005] Another option is the use of printing plates that achieve a matting finish on the coating through their surface structure / screening. In this case, the achievable matting is dependent on the form and partly dependent on the printing plate's manufacturing process, so that a targeted adjustment of the matting effect is only possible to a limited extent. However, particularly good matte coatings are subject to certain optical requirements, which can be achieved primarily through a defined surface roughness / matting.

[0006] However, when fillers / additives, such as matting agents, are added, the viscosity of the coating composition changes, so it must be adjusted for printing. Depending on the printing process, further measures may also be required, such as selecting a suitable anilox roller with regard to scoop volume, cell type, and cell size, or constantly circulating the coating to prevent the matting agents from settling.

[0007] DE 10 2006 051 275 A1 describes a process for finishing and protecting a substrate surface in a printing press. A varnish is applied to a plate, dried there, and then transferred to a substrate. The plate can be textured to create a matte or textured effect.

[0008] The object of the present invention is therefore to find a method for the targeted modification of the matting effect in various printing processes.

[0009] This object is achieved by a method according to claim 1, namely a method for applying a matting fluid layer to a printing substrate via a printing form, wherein the matting fluid layer on the printing form is dried before application to the printing substrate, wherein the degree of mattness of the applied fluid layer is modified via parameters of the drying process and the nature of the surface of the printing form, which is characterized in that an overdrying of the applied fluid layer is carried out, wherein the applied fluid layer on the printing form is dried more intensively before application to the printing substrate than would be necessary to achieve an essentially completely dried fluid layer on the printing form, namely by drying at an elevated temperature, a longer drying time, a more focused hot air supply and combinations of these measures.

[0010] Advantageous and therefore preferred developments of the method according to the invention emerge from the associated subclaims and from the description with the associated drawings.

[0011] In a preferred embodiment, the matting fluid layer is a lacquer or paint layer. In a particularly preferred embodiment, the matting fluid layer is a dispersion lacquer layer. In a very particularly preferred embodiment, the matting fluid layer is a dispersion lacquer layer of a gloss lacquer.

[0012] A further preferred development of the method according to the invention is that the parameters of the drying process include the drying performance achieved by hot air supply. Drying performance is the most important parameter. This is preferably achieved and quantified by a hot air supply. In a preferred embodiment, the hot air supply is highly focused, particularly by means of a slotted nozzle. Important parameters are the increased air flow rate and the increased air temperature.

[0013] The method according to the invention modifies the degree of mattness of the applied fluid layer. According to the invention, the matting fluid layer is dried on the printing form before being applied to the printing substrate. According to the invention, the applied fluid layer is overdried to modify the degree of mattness. This means that the applied fluid layer is dried more thoroughly than would normally be necessary. Suitable measures for this purpose according to the invention include drying at an elevated temperature, a longer drying time, a more focused hot air supply, and combinations of these measures.

[0014] It has been shown that a more intense drying than the drying that would be necessary to achieve a substantially completely dried fluid layer on the printing form is essential for the process according to the invention.

[0015] In a preferred embodiment, the matting fluid layer on the printing form is dried at a temperature above the drying temperature of the fluid used before application to the printing substrate. This allows the degree of matting to be adjusted particularly advantageously.

[0016] The drying temperature range is preferably in the range from 30 to 300 °C, particularly preferably in the range from 50 to 100 °C.

[0017] A further preferred development of the method according to the invention is that the applied fluid layer on the printing form is initially dried by heat input, and final drying of the fluid layer after transfer to the printing substrate takes place without further heat input. Because the partial drying is already carried out before transfer to the printing substrate, no further active heat source is required for the remaining final drying after transfer.

[0018] A further preferred development of the method according to the invention is that the quality of the surface of the printing form is modified by varying the roughness and / or a full-surface or spot-like surface shape and / or the selection of the printing form material. Which variant is chosen depends on the desired quality. A combination of the three variants increases the accuracy of achieving the desired degree of mattness.

[0019] A further preferred development of the method according to the invention involves integrating a control strip consisting of various microstructures into the printing form to control the drying process parameters and the surface quality of the printing form. These microstructures provide printed information about the current process and the achievable print quality. This control strip then also releases a "print image" of fluid onto the printing substrate and can be evaluated in a similar way to a color control strip.

[0020] A further preferred development of the method according to the invention is that the matting fluid layer is applied to the printing form by a varnish dosing unit, in particular an anilox roller, or a digital printing system, in particular an inkjet print head. This distinction is not synonymous with the use of a corresponding printing press. It is certainly possible, although not always advantageous, to use an inkjet dosing unit to apply the fluid in an offset printing press, and vice versa, a varnish dosing unit with an anilox roller in an inkjet printing press.

[0021] The invention as such, as well as structurally and / or functionally advantageous developments of the invention, are described in more detail below with reference to the accompanying drawings using at least one preferred embodiment. In the drawings, corresponding elements are provided with the same reference numerals.

[0022] The drawings show: Figure 1: the schematic structure when applying the fluid using an anilox roller Figure 2: the schematic structure when applying the fluid using an inkjet unit Figure 3: the sequence of the method according to the invention

[0023] Figure 3 shows the sequence of the method according to the invention schematically. In a first step, the fluid 9, usually varnish or ink, is metered onto a printing form 3, which can be full-surface or spot-formed, whereby the metering can be carried out conventionally or digitally. The fluid 9 applied to the printing form 3 is dried by heat input before being transferred to the substrate 6. The resulting fluid layer 9 is then transferred to the substrate 6 in an already solidified state.

[0024] The achievable mattness of the applied varnish layer can be influenced or adjusted during the printing process via two variables. Firstly, the achievable mattness can be adjusted by the degree of initial drying before film transfer, i.e., by the selection of the drying parameters. Secondly, the mattness of the varnish layer can be further influenced by using a printing form 3, which is either full-surface or spot-shaped, with a rough surface. The rough surface conditions the fluid layer 9 during initial drying in such a way that a matting effect occurs on the printed product 10. The aforementioned control variables can also be combined as desired.

[0025] To continuously monitor the process with regard to the achievable quality of the matte effect and to adjust the process parameters, a control strip, similar to the print control strip, is integrated into printing form 3. This is composed of various microstructures that provide printed information about the current process and the achievable print quality. The production of a printing form 3 with microstructures, which serve as a control element in the matting process, can be based on printing forms 3 known from the prior art, such as the printing form 3 described in DE 10 2014 222 677 A1.

[0026] The described procedural steps can also be divided into three phases: Phase 1: Fluid 9 is dosed onto a printing form 3, e.g., using an anilox roller 1 as in flexographic printing. Phase 2: The applied fluid 9 is dried on the printing form 3 by applying heat, preferably hot air via a drying nozzle. Phase 3: The dried fluid layer 9 is transferred to the substrate 6.

[0027] The final drying of the fluid layer 9 on the substrate 6 preferably takes place without any additional energy input. The printing form 3 is made of a suitable material, e.g., silicone, and has a rough surface that directly influences the degree of matting. Furthermore, a control element is integrated into the printing form 3, which serves as a quality assurance measure. Figure 1shows schematically the structure of the system when applying the fluid 9 by means of an anilox roller 1. Further components of the system include the inking unit 2, the drying unit 4, the drive for the web transport 5 of the printing substrate 6 and a cleaning unit 7.

[0028] The preferred application is graphic use as a finishing process in packaging and commercial printing, e.g. matt-gloss, frost effect, etc.

[0029] An alternative approach involves using a different varnish dosing unit 11 instead of the anilox roller 1. In particular, the use of a digital printing system 11, such as an inkjet print head 11, for applying the fluid 9 is one possibility. This means that a transparent ink is used as the varnish, which is transferred in its matt state to a substrate, such as a graphic printing substrate 6 or a technical surface, via the transfer process described above using a textured transfer form in conjunction with an intermediate thermal treatment. Figure 2 shows the application of the fluid 9 by means of an inkjet unit 11.

[0030] Further alternative embodiments relate in particular to alternative applications of such lacquer layers, such as: The creation of a porous layer to be used, for example, as an absorber that can absorb moisture in the pores close to the surface. With higher heat input, bubbles sometimes form in the paint, thereby creating porosity. The application of a matting or porous layer to a film substrate. In combination with a transparent film, the applied layer can function as an optical diffuser ("ground screen"). Technical application of the matted layer on transparent substrates (e.g., films) for so-called light harvesting (application of a functional layer) in the field of optics, particularly photovoltaics.

[0031] Alternative fluid / paint systems: Hybrid approach: Use of hybrid coatings to create the matting in a first step by evaporating the aqueous portion and then fixing it in the UV curing process to achieve a matt-gloss effect.

[0032] Options for use in a machine mainly concern: Sheet-fed printing presses Web-fed printing presses Coating machines

[0033] The inventive method for applying a thin matting fluid layer 9 to a substrate 6, where fluid transfer in the sense of the method refers to the transfer of an already solidified fluid to the substrate 6, has various advantages. For example, it is particularly stable when applying thin layers, since less drying power is required. No additional energy input within the printing press is even required if a combination with printing plates 3 is used for the matting effect.

[0034] The invention makes it possible to apply particularly thin layers, over the entire surface or as a spot area, and to achieve targeted matting without the addition of matting additives or fillers. The process is carried out by metering a fluid layer 9 onto a printing form 3, drying it on the printing form 3 in a second step using a defined heat input in a drying unit 4, and transferring it to a substrate 6 in a third step. The degree of matting can be adjusted using two independent process parameters: the drying performance and the printing form design. If the matting 10 is primarily achieved using the printing form 3, it is also possible to achieve different matting effects 10, possibly spot-based, across the sheet surface.

[0035] In contrast to DE 10 2014 222 677, this is not a classic / exclusive molding process of the surface of printing form 3, but a more general transfer printing with modification, in particular by the (thermal) drying parameters, which lead to a matting varnish change.

[0036] Of course, the rough surface texture of the printing plate 3 also affects the matting 10, but the surface texture only influences it indirectly. Reference symbol

[0037] 1Dosing unit 2Inking unit 3Printing form 4Drying unit 5Drive for web transport 6Printing substrate 7Cleaning unit 8Anilox roller 9Fluid 10Matted printed product 11Digital dosing unit (inkjet)

Claims

1. Method for applying a matting fluid layer (9) to a printing substrate (6) via a printing form (3), wherein the matting fluid layer (9) on the printing form (3) is dried before application to the printing substrate (6), wherein the degree of mattness of the applied fluid layer (9) is modified via parameters of the drying process and the properties of the surface of the printing form (3), characterized in that overdrying of the applied fluid layer (9) is carried out, wherein the applied fluid layer (9) on the printing form (3) is dried more than would be necessary to achieve a substantially completely dried fluid layer on the printing form (3) before application to the printing substrate (6), namely by drying at an elevated temperature, for a longer drying time, with a more strongly focused hot air supply and combinations of these measures.

2. Method according to claim 1, characterized in that the matting fluid layer (9) on the printing form (3) is dried at a temperature above the drying temperature of the fluid used before application to the printing substrate (6).

3. Method according to one of the preceding claims, characterized in that the matting fluid layer (9) is a coating layer or ink film.

4. Method according to one of the preceding claims, characterized in that the matting fluid layer (9) is a dispersion varnish layer.

5. Method according to one of the preceding claims, characterized in that the matting fluid layer (9) is a dispersion varnish layer of a gloss coating.

6. Method according to one of the preceding claims, characterized in that the parameters of the drying process include the drying capacity through hot air supply.

7. Method according to one of the preceding claims, characterized in that the properties of the surface of the printing form (3) are modified by a variable roughness and / or a full-surface or spot shape of the surface and / or the selection of the material of the printing form (3).

8. Method according to one of the preceding claims, characterized in that a control strip consisting of different microstructures, which provide information in printed form about the current process and the achievable print quality, is integrated into the printing form (3) to control the parameters of the drying process and the properties of the surface of the printing form (3).

9. Method according to one of the preceding claims, characterized in that the matting fluid layer (9) is applied to the printing substrate (6) by a coating metering unit (1, 11), in particular a screen roller (1), or a digital printing system (11), in particular an inkjet print head (11).

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