Mattifying by means of transfer process

Abstract

The invention relates to a method for applying a matting fluid layer (9) to a printing substrate (6) by means of a stamp (3), wherein the matting fluid layer (9) is dried on the stamp (3) before being applied to the printing substrate (6), characterized in that the degree of matting of the applied fluid layer (9) is modified by means of parameters of the drying process and by means of the surface properties of the stamp (3).

Description

Technical Field

[0001] The present invention discloses a method for applying a thin matte fluid layer to a printing substrate via a stamp in a targeted matte-controlled manner.

[0002] The invention belongs to the technical field of printing (especially packaging printing and small batch printing). Background Art

[0003] When printing using film transfer processes, certain phenomena can occur, in particular the matting of gloss varnishes during film transfer. The matting of the gloss varnish is independent of the substrate used and can (depending on the process parameters) take on different forms and vary in intensity.

[0004] Matt varnishing (mattlack varnishing) with water-based varnish (particularly in packaging printing and in short-run printing) is currently carried out using two approaches. One variant involves the addition of matting agents (i.e. additives) which, for example, roughen the surface. This, on the one hand, changes the printability (in the form of the varnish viscosity) and therefore has to be adjusted accordingly, and on the other hand, the volume addition of matting agent and, therefore, the degree of matting, is limited.

[0005] Another alternative is to use molds that achieve a matt finish through their surface structure / texture. The achievable matt finish is limited by the form and partially depends on the mold production method, so that a targeted adjustment of the matt effect is only possible under certain conditions. However, a particularly good matt finish must meet certain optical requirements, which can be achieved primarily through a defined surface roughness / matt.

[0006] However, when fillers / additives (i.e., matting agents) are added, the viscosity of the varnish composition changes, so that it must be adjusted for printing. Furthermore, depending on the printing method, further measures may be taken, such as selecting a suitable anilox roller (e.g., with regard to the pick-up volume, mesh type and size) and continuous circulation of the varnish in order to prevent matting agent deposits. Summary of the Invention

[0007] The object of the present invention is therefore to find a method for selectively varying the matte effect in various printing methods.

[0008] This object is achieved by a method for applying a matt fluid layer to a printing substrate via a stamp, wherein the matt fluid layer is dried on the stamp before being applied to the printing substrate. The method is characterized in that the mattness of the applied fluid layer is varied by means of parameters of the drying process and the surface properties of the stamp. By specifically combining these two modification options—drying parameters and stamp surface—the desired mattness can be adjusted more precisely than with existing methods.

[0009] Advantageous and therefore preferred developments of the method according to the invention emerge from the associated subsequent description and the description with the associated figures.

[0010] In a preferred embodiment, the matt fluid layer is a varnish layer or a pigment layer. In a particularly preferred embodiment, the matt fluid layer is a diffused varnish layer. In a particularly preferred embodiment, the matt fluid layer is a diffused varnish layer of a glossy varnish.

[0011] Another preferred development of the method according to the invention is that the parameters of the drying process include the drying power caused by the hot air supply. The drying power is the most important parameter. Preferably, the drying power is achieved and quantified by the hot air supply. In a preferred embodiment, the hot air supply is achieved in a highly concentrated manner (especially by means of slot nozzles). The important parameters here are the increased volume flow rate of the air and the increased temperature of the air.

[0012] The method according to the present invention changes the mattness of an applied fluid layer. According to the present invention, the matt fluid layer is dried on a stamp before being applied to the printing substrate. Overdrying the applied fluid layer has been shown to be particularly advantageous for changing the mattness. This means drying the applied fluid layer more intensively than would normally be necessary. Suitable measures for this purpose include, in particular, drying at elevated temperatures, longer drying times, a more concentrated hot air supply, and combinations of these measures.

[0013] It has been shown that more intensive drying than is necessary to achieve a substantially completely dried-out fluid layer on the stamp is particularly advantageous for the method according to the invention.

[0014] In a preferred embodiment, the matt fluid layer is dried on the stamp before being applied to the printing substrate at a temperature that is above the drying temperature of the fluid used. This makes it possible to adjust the mattness particularly advantageously.

[0015] The drying temperature range is preferably in the range of 30°C to 300°C, particularly preferably in the range of 50°C to 100°C.

[0016] A further preferred embodiment of the method according to the invention is that the applied fluid layer is dried on the stamp by heat input, and the final drying of the fluid film after transfer to the printing substrate takes place without further heat input. Since partial drying is already performed before transfer to the printing substrate, the remaining final drying after transfer does not require a further active heat source.

[0017] A further preferred embodiment of the method according to the invention is that the variable roughness and / or fullness of the stamp surface or dot-shaped The surface properties of the stamp can be modified by the choice of the form and / or material of the stamp. The choice of variant depends on the desired properties. The combination of these three variants increases the accuracy of the desired mattness.

[0018] A further preferred development of the method according to the invention is that, in order to adjust the parameters of the drying process and the surface properties of the stamp, a test strip consisting of different microstructures is integrated into the stamp. These different microstructures provide information about the current process and the achievable print quality in printed form. Similarly, this test strip outputs a "print image" of the fluid onto the printing substrate and can be evaluated similarly to a color test strip.

[0019] A further preferred embodiment of the method according to the invention provides for the matting fluid layer to be applied to the stamp by a varnish metering unit (in particular an anilox roller) or a digital printing system (in particular an inkjet print head). This distinction does not necessarily equate to the use of corresponding printing presses. Although not always advantageous, it is entirely possible to use an inkjet metering unit for applying the fluid in an offset printing press and, vice versa, to use a varnish metering unit with an anilox roller in an inkjet printing press. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The invention itself and advantageous structural and / or functional developments of the invention will be described in more detail below with reference to the accompanying drawings based on at least one preferred embodiment. In the drawings, corresponding elements are provided with the same reference numerals. The drawings show:

[0021] Figure 1 shows a schematic configuration when applying a fluid by means of an anilox roller,

[0022] Figure 2 shows a schematic configuration when applying a fluid by means of an inkjet unit,

[0023] Figure 3 The flow of the method according to the present invention is shown. DETAILED DESCRIPTION

[0024] Figure 3 The flow of the method according to the invention is schematically shown. In a first step, a fluid 9 (mostly varnish or pigment) is metered onto the stamp 3, either over the entire surface or in spots. This metering can be done conventionally or digitally. The fluid 9 applied to the stamp 3 is dried by heat input before being transferred to the substrate 6. The resulting fluid film 9 is then transferred to the substrate 6 in a solidified state.

[0025] The achievable mattness of the applied varnish layer can be influenced (or adjusted) during the printing process by two parameters. On the one hand, the achievable mattness can be adjusted by the degree of drying before the film transfer (i.e., by selecting the drying parameters). On the other hand, the mattness of the varnish layer can be further influenced by using a stamp 3 with a roughened surface, either solid or dotted. This roughened surface conditions the fluid film 9 during drying in such a way that a matt effect appears on the printed product 10. The aforementioned adjustment parameters can also be combined as desired.

[0026] To continuously monitor the process with respect to the achievable quality of the matting effect and to coordinate process parameters, a test strip (similar to a printed test strip) is integrated into the stamp 3. This test strip is composed of a combination of different microstructures that provide information about the current process and the achievable print quality in printed form. These microstructures serve as test elements in the matting method. The production of a stamp 3 having such microstructures can be based on stamps 3 known from the prior art, such as the stamp 3 described in DE 10 2014 222 677 A1.

[0027] The method steps described in the present invention can also be divided into three stages:

[0028] Phase 1: Metering of the fluid 9 onto the die 3, for example with the aid of an anilox roller 1, as in flexographic printing,

[0029] Phase 2: The applied fluid 9 is dried on the stamp 3 by heat input, preferably by hot air supply via drying nozzles,

[0030] Phase 3: Transferring the dried fluid film 9 to the substrate 6 .

[0031] The final drying of the fluid film 9 on the substrate 6 preferably takes place without further energy supply. The stamp 3 is made of a suitable material (e.g., silicone) and has a rough surface, which has a direct influence on the mattness. In addition, a test element is integrated into the stamp 3, which serves to ensure quality. Figure 1 The configuration of the system is schematically shown when applying a fluid 9 by means of an anilox roller 1 . Further components of the system include a coloring unit 2 , a drying unit 4 , a drive 5 for web transport of a printing substrate 6 , and a cleaning unit 7 .

[0032] The preferred application of the present invention is as a finishing method for graphics in packaging printing and small-batch printing, such as matte-finishing, frosting effects, etc.

[0033] An alternative method according to the invention involves using an additional varnish metering unit 11 instead of the anilox roller 1. In particular, a digital printing system 11 (e.g., an inkjet print head 11) can be used to apply the fluid 9. That is, a transparent ink is used as the varnish, which is transferred to the carrier material (e.g., graphic substrate 6) or the technical surface in terms of its mattness by means of the transfer process described above, using a textured transfer mold in combination with an intermediate heat treatment. For this purpose, Figure 2 The application of the fluid 9 by means of an inkjet unit 11 is shown.

[0034] Further alternative embodiments according to the present invention relate in particular to alternative applications of such a clear coat, for example:

[0035] Producing a porous layer in order to utilize it, for example, as an absorbent which can absorb moisture in pores close to the surface. In the case of a high heat input, bubbles are partially formed in the varnish, which thereby create porosity.

[0036] A matte or porous layer is applied to a film substrate, wherein the applied layer can perform the function of an optical diffuser in combination with a transparent film ("frosted glass").

[0037] The technical application of matt layers to transparent substrates (for example films) for so-called light trapping (application of functional layers) in the field of optical systems (especially photovoltaics).

[0038] Alternative fluid / varnish systems:

[0039] Hybrid solution: A hybrid varnish is used in order to produce the matt finish in a first step by evaporation of the aqueous component, which is then fixed during the UV curing process and a matt-gloss effect is established.

[0040] The options for use in the machine mainly involve:

[0041] -sheet printing presses,

[0042] - web printing presses,

[0043] -Coating machine.

[0044] The method according to the invention for applying a thin matting fluid layer 9 to a substrate 6 offers various advantages. In this method, fluid transfer refers to the transfer of an already solidified fluid to the substrate 6. This method is particularly stable for applying thin layers because it requires less drying power. If used in conjunction with a stamp 3 for the matting effect, no additional energy input is even required within the printing press.

[0045] The present invention enables the application of particularly thin layers, either over a full surface or in spots, and achieves targeted matting without the addition of matting additives or fillers. This process is achieved by metering a fluid film 9 onto the stamp 3, drying it in a second step on the stamp 3 by a drying unit 4 using a defined heat input, and transferring it to the substrate 6 in a third step. The degree of matting can be adjusted using two independent process parameters: drying power and stamp design. If matting 10 is primarily achieved via the stamp 3, different (possibly spot-applied) matting effects 10 can also be achieved on the page.

[0046] Compared to the prior art DE 10 2014 222 677, the present invention does not involve a conventional / specialized casting process of the surface of the stamp 3, but rather a more general transfer printing with changes caused in particular by drying (thermal) parameters, which bring about a change in the matting effect of the varnish.

[0047] Naturally, the rough surface texture of the stamp 3 also has an influence on the matte 10 , but the surface texture influences the matte only indirectly.

[0048] Reference Signs List

[0049] 1 unit of measurement

[0050] 2 Shading Units

[0051] 3 Impression

[0052] 4 Drying units

[0053] 5 Drives for web transport

[0054] 6 Printing substrate

[0055] 7 Cleaning Unit

[0056] 8 Anilox roller

[0057] 9 Fluid

[0058] 10 Matte printed products

[0059] 11 Digital metering unit (inkjet)

Claims

1. A method for applying a matt fluid layer (9) to a printing substrate (6) by means of a stamp (3), in, The matte fluid layer (9) is dried on the stamp (3) before being applied to the printing substrate (6), It is characterized by: The mattness of the applied matt fluid layer (9) is modified by the parameters of the drying process and by the surface properties of the stamp (3), wherein the applied matt fluid layer (9) is overdried, wherein the applied matt fluid layer (9) is dried more strongly on the stamp (3) before being applied to the printing substrate (6) than is required in order to achieve a completely dried fluid layer on the stamp (3).

2. The method according to claim 1, It is characterized by: The matt fluid layer (9) is dried on the stamp (3) at a temperature higher than the drying temperature of the fluid used before being applied to the printing substrate (6).

3. The method according to claim 1 or 2, It is characterized by: The matt fluid layer (9) is a bright oil layer or a pigment layer.

4. The method according to claim 1 or 2, It is characterized by: The matt fluid layer (9) is a diffusion type bright oil layer.

5. The method according to claim 1 or 2, It is characterized by: The matt fluid layer (9) is a diffusion type varnish layer of gloss varnish.

6. The method according to claim 1 or 2, It is characterized by: The parameters of the drying process include the drying power caused by the hot air supply.

7. The method according to claim 1 or 2, It is characterized by: The applied matting fluid layer (9) is dried on the stamp (3) by heat input, and Final drying of the matt fluid layer (9) on the printing substrate (6) after transfer is achieved without further heat input.

8. The method according to claim 1 or 2, It is characterized by: The surface properties of the stamp (3) are varied by a variable roughness and / or a solid or punctiform form of the stamp surface and / or by the choice of the material of the stamp (3).

9. The method according to claim 1 or 2, It is characterized by: In order to adjust the parameters of the drying process and the surface properties of the stamp (3), a test strip consisting of different microstructures is integrated into the stamp (3), which provide information about the current process and the achievable printing quality in printed form.

10. The method according to claim 1 or 2, It is characterized by: The matting fluid layer (9) is applied to the printing substrate (6) by a varnish metering unit or by a digital printing system.

11. The method according to claim 10, It is characterized by: The varnish metering unit is an anilox roller.

12. The method according to claim 10, It is characterized by: The digital printing system is an inkjet print head.

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