EP3976881A1

EP3976881A1 - Method for varnishing substrates, and varnished substrates

Info

Publication number: EP3976881A1
Application number: EP20728713.7A
Authority: EP
Inventors: Peter Eladio LUDWIG; Roland Rüedi; Dieter WYLER; Dirk Schlatterbeck
Original assignee: Actega Schmid Rhyner AG
Current assignee: Actega Schmid Rhyner AG
Priority date: 2019-05-28
Filing date: 2020-05-25
Publication date: 2022-04-06
Anticipated expiration: 2040-05-25
Also published as: US20220266615A1; ZA202110226B; AU2020286082A1; CN114026288A; EP3976881B1; BR112021022884A2; DE102019114277A1; WO2020239692A1

Abstract

The invention relates to a method for producing a printed product, wherein a preparation for producing a first layer as a sealing layer is applied to the substrate, and the preparation comprises at least one monomer, oligomer or prepolymer with at least one crosslinkable, functional group. Subsequently, the first layer is cured, and a second layer is applied at least in regions to the first layer, wherein the second layer has a closed surface in the printed regions. Furthermore, the invention relates to a printed product comprising a substrate, a first layer and a second layer, wherein the first layer and the second layer comprise an organic, crosslinked varnish and have a closed surface, and wherein the first layer is transparent and has a layer thickness in the range from 1 to 10 µm. The second layer is applied at least in regions to the first layer (9) such that the first layer is arranged between the substrate and the second layer.

Description

Process for painting substrates and painted substrates

description

Field of invention

The invention generally relates to a method for painting substrates for producing coatings with high surface qualities, and substrates that are painted accordingly. In particular, the invention relates to a method for painting substrates with surfaces that are not completely closed by means of an ink-jet method, as well as correspondingly painted substrates.

State of the art

Printed products are often provided with one or more layers of lacquer. The

Layers of lacquer ensure a high-quality visual and haptic impression. A large part of the printed products, for example in the form of print media or packaging, have graphic paper or cardboard as substrates.

Papers are made from textile and plant fibers, possibly by additional glueing. The fibers absorb liquids (e.g. ink). Gluing reduces the absorbency but does not completely prevent it. Paper can therefore absorb liquids, including printing ink, to a certain extent. This has a disadvantageous effect on the quality of the print image of a corresponding print. To get the color into the

To reduce the surface of a paper or cardboard to be printed, so-called coated substrates are therefore used in high-quality prints, for example in the case of picture printing paper.

Coated substrates are understood here as meaning papers or cardboard, their

The surface can be provided with a highly filled binder layer. This coating, also referred to as a line, can have one or more layers and reduces the penetration of the printing ink into the surface of the substrate and smoothes the surface of the paper or cardboard by filling the depressions between the fibers. The The coating slip contains inorganic particles as fillers in an organic binder. Due to the high degree of filling of the paper coating, the particles in the layer are not completely covered by binder. Due to the drying and the associated reduction in volume of the line, the particles can protrude far from the surface. With matt-coated substrates, the proportion of protruding particles is greater than with glossy-coated types. The most glossy ones are so-called cast-coated papers or cardboard. Here the binder itself is very shiny. Nevertheless, even with cast-coated papers, the particles on the surface are not all completely covered.

In the case of coated substrates, due to the particulate structure of the coating, so-called undercuts can form, in which the particle surface is not completely surrounded by binder. The undercuts thus form flea spaces within the layer, viewed vertically from above. Furthermore, cavities can be formed due to incomplete covering of substrate pores. These flea spaces are used in pressure and

Painting processes not completely filled with paint or varnish. Instead, they are completely or partially covered by layers of paint or varnish during application. When drying, they can partially open again due to the decrease in volume of the binder in the paint or varnish or simply by tearing open the layer. In principle, as with paper coating, there is no production of a completely pore-free layer in any printing process, so that the cavities mentioned are to be expected in principle.

The result of these cavities is that when coated paper or cardboard is coated using inkjet printing, depending on the amount of paint applied, small craters appear on the surface. These are formed by the fact that, in the inkjet process, tiny droplets are thrown onto the substrate surface, which tend to hit the

Substrate surface to reduce their surface tension. Unless the

If there is already a liquid film of the same liquid on the substrate surface, the film is torn upwards by the approaching droplet at the first contact between the droplet and the film, ie away from the substrate surface, before the droplet finally accommodates on the surface. If the undercuts described above are below the point of impact of the droplet, then when approaching the droplet, this can also happen Material is pulled upwards so far that a channel to the trapped air is formed in the cavity of the undercut, which remains open to the surface of the liquid. These channels to the undercuts are referred to below as pinholes. The pinholes remain in the paint layer when the paint hardens and are visually noticeable imperfections in the paintwork. The surface tension of the liquid lacquer causes the pinholes to have an ever larger diameter as the layer thickness increases. Although the number of pinholes decreases with increasing layer thickness, they are more and more visible due to the larger diameter. The pinholes described represent a serious problem in inkjet printing, especially with UV-curing inks.

Up to now, in the graphics industry, painting has mostly been done with painting processes in which the paint is transferred to the substrate by roller application. Alternatively, it can also be painted with screen or pad printing. In the process described, the paint is transferred in a touching manner. The undercuts described above are almost completely covered with the paint. The tool (the roller, the sieve, etc.) is lifted from the substrate during the process. The liquid film between the tool and the substrate is separated and corresponding structures appear on the surface. Even if the imperfections inherent in the substrate are not completely covered, these structures mean that pinholes that may arise do not stand out so clearly in the layer. Only with high layer thicknesses and sufficiently slow process speeds, e.g. in the case of screen printing, these structures can run again and a very smooth surface is formed. If only a partial, laterally structured coating of the substrate surface is desired, correspondingly structured printing forms must be used.

Another method of applying a layer of lacquer to coated substrates provides for lamination of the substrate with a plastic film. This will make the

Undercuts are largely covered and a surface coating is produced that is largely free of visually noticeable defects. If pores remain between the film and the substrate or if larger particles are built into the adhesive layer below the film, these defects are clearly visible even when the film is laminated. In addition, a special laminating device is required for film lamination. Another disadvantage consists in that the applied film typically has a thickness of at least 10 mhi. The comparatively thick coating produced with these films has a strong influence on the properties of the substrate, in particular its haptic properties.

Another possibility of producing a defect-free lacquer layer without pinholes on coated substrates is described in patent application DE 102 007 034 877 A1. Here, a coating compound is first applied to the substrate by means of inkjet printing and the coated surface is then treated with an air knife. As a result, the coating compound is deflected minimally laterally. This leads to the fact that the air hose of the crater tears off at the existing pinholes and the crater moves with it from below

Coating compound fills. Thus the pinholes are closed. After the pinholes have been removed, the coating compound is then cured to form the paint. However, a special device is required for this.

Object of the invention

The invention is thus based on the object of providing a method which enables painting, in particular painting by means of inkjet printing, of a substrate for producing coatings with a high surface quality, regardless of its surface structure and nature. Furthermore, a further object of the invention is to provide a preparation and a correspondingly lacquered printed product with a high surface quality.

Brief description

The object of the invention is already through the subject of the independent

Patent claims solved. Advantageous refinements and developments are the subject of the dependent claims.

The invention relates to a method for producing a printed product with at least the following method steps a) to d)

a) Provision of a print substrate that may have already been printed, b) applying a first layer to at least one surface of the substrate, the layer having organic, functional groups,

c) curing of the layer applied in step b) by thermal or UV crosslinking of the functional groups to produce the sealing layer, the cured first layer having a layer thickness in the range from 1 to 10 mhi, d) application of a second layer to the surface the first layer.

The layer hardened in step e) has a layer thickness in the range from 1 to 10 mhi. This layer thickness ensures that the coating is sufficiently thick so that

Undercuts and pores are covered and not transferred to the lacquer layer applied in the subsequent step d). Other properties of the substrate or the substrate surface that are disadvantageous during painting, for example a great roughness, high porosity or too high a surface tension, can also be compensated or neutralized by the layer cured in step e), so that the layer cured in step d) The coating is not influenced by the specific surface properties of the substrate. The original coating processes are therefore used for the coating process taking place in step d)

Substrate properties replaced by the corresponding properties of the sealing layer. This enables reproducible results regardless of the respective substrate

Coating properties. The first layer cured in step c) is therefore in the

Also referred to below as the sealing layer.

According to a development of the invention, the substrate provided with the first layer is printed before step d). One embodiment of this development provides that the printing on the cured first layer, i.e. after step c) takes place. Alternatively, the substrate can also be printed after step b). In this embodiment, the first layer is cured in step c) after the printing. In this way, the first layer and the printing layer can be cured together.

The second layer is preferably applied by means of inkjet printing in step d).

Due to the layer thickness according to the invention and the mechanical stability and strength of the sealing layer, structures such as pores and undercuts, as they occur, for example, in coated paper and cardboard, are covered in such a way that No or at least almost no pinholes are formed in the ink jet printing that takes place in step d). The second printing step applied in step d) thus has a closed surface. In this context, a closed surface within the meaning of the invention is understood to mean in particular a surface which has a pinhole density of less than 10 pinholes per dm ² , preferably a maximum of 2 pinholes per dm ² , particularly preferably a maximum of 1 pinhole per dm ² To be recognized by the eye and otherwise disturb the print image considerably. For a really high-quality print, as is expected in the area of luxury packaging, for example, no defects should be recognizable on the lacquered surfaces.

The number of pinholes depends on the substrate and the layer thickness. When painted substrates are painted without the sealing layer according to the invention, the number of pinholes decreases with the thickness of the paint layer. However, a decrease in the pinholes is not always associated with an improvement in the visual impression, since the diameter of the pinholes also influences their visibility. In the range up to approx. 4 mhi layer thickness, the diameter of the pinholes is very small. They visually convey the impression of no particles, which makes the resulting layer appear somewhat matt. Between 6-12mhi, the pinholes are very clearly visible. Although the number of pinholes decreases towards higher layer thicknesses, the enlargement of the craters at higher layer thicknesses means that the remaining pinholes disturb the appearance much more. The pinholes only disappear completely from a layer thickness of around 20 mhi (depending on the substrate).

The layer thickness of the sealing layer, on the other hand, is so small that the haptic

Properties of the substrate not or at least not significantly due to the

Sealing layer are affected. For example, a substrate coated with a sealing layer according to the invention can still be haptically identified as paper. In contrast to this, the haptic properties of the plastic coating usually dominate with appropriately laminated paper. A layer thickness of the sealing layer in the range from 1 to 5 mhi and in particular from 2 to 3 mhi has proven to be particularly advantageous.

According to a variant, the sealing layer can also be designed to be inconspicuous not only haptically but also visually. The sealing layer has according to one Embodiment a high transparency and little or no inherent color. In particular, no or only a very small amount occurs due to the sealing layer

Shift of the color locus of the underlying substrate, so that the optical appearance of the substrate is not influenced by the sealing layer or is only influenced to a very small extent. This can be particularly in embodiments in which the second layer is designed as a transparent lacquer layer and / or in embodiments in which the second layer is structured laterally and thus only on partial areas of the

Sealing layer provided substrate is applied, be advantageous.

However, if the substrate quality is such that the above-described coating quality cannot be achieved with the layer thicknesses mentioned, it may also be necessary to increase the layer thickness of the sealing layer. Economically, this can still mean a clear advantage over lamination, since poorer substrate qualities are accessible to high-quality finishing, even if the haptic properties of the substrate, in particular when using radiation-curing sealing layers, are significantly changed.

One embodiment of the invention provides that in a step preceding step a) a line is applied to at least one surface of the printing substrate provided in step a). Here, a line is understood to mean a coating compound with a high proportion of inorganic, particulate fillers in an organic binder. In particular, the substrate provided in step a) is a coated paper or a coated cardboard.

In an alternative embodiment, the substrate provided in step a) is an uncoated paper or an uncoated cardboard. Such substrates have open surfaces. These are characterized by a high porosity and can therefore absorb liquids to a certain extent. As a result, uncoated papers and cardboard, for example, are only suitable to a limited extent as substrates for inkjet printing processes, especially with UV-curable printing inks. By contrast, the sealing layer according to the invention completely covers the pores and thus closes the surface. The sealing layer also provides a surface with homogeneous surface properties such as a homogeneous surface tension. This enables, for example, homogeneous flow properties of inks or coating agents applied with inkjet printing. If, for example, a substrate is printed with offset printing inks, the areas with the hydrophobic offset printing inks have a completely different surface tension than the unprinted substrate. If the transition between the unprinted and the printed area is used for painting, in particular using the inkjet method, the course of the paint on the unprinted substrate will differ from that on the printing ink

differ, which results in a step in the paint finish in the transition. This effect can worsen the painting results even on surfaces that are already closed. The method according to the invention is therefore also suitable for coating substrates with closed surfaces such as, for example, plastics. Here the required layer thickness is significantly smaller and can be less than 1 mhi, since no structures on the substrate surface, such as pores or undercuts, have to be covered and closed by the sealing layer.

The curing or crosslinking of the first layer in step c) takes place according to a

Embodiment of the invention by UV radiation or electron beam. The advantage of radiation-curing formulations is that they can do without solvents. Therefore, in the case of radiation-curing formulations, the first layer shows only a very low volume shrinkage during curing. The volume reduction is only due to the

Polymerization shrinkage due to crosslinking. Due to the small volume or mass loss due to the hardening process taking place in step c), the

method according to the invention thus not or not significantly reduced the layer thickness of the first layer applied in step b). This ensures that the undercuts covered by the first layer applied in step b) during the

Hardening process cannot be reopened.

By means of the method according to the invention, the substrate is provided with a cured first layer as a sealing layer before the painting step d), which the

Undercuts and pores in substrates covered. In addition, the

Sealing layer provided a closed surface, which due to their Layer properties such as roughness, homogeneity, surface tension or polarity can be printed very well. Thus, with the method according to the invention, independently of the substrate provided in step a) or its surface properties, it can be coated by means of inkjet printing. The hardened first layer “neutralizes” the surface of the substrate, so to speak. Thus, substrates, for example inexpensive substrates or substrates that are less suitable for painting, can also differ due to their

Surface properties, in particular due to their high surface roughness, cannot be over-lacquered, or can only be lacquered over poorly, or can be lacquered or printed with the known processes. A further development of the invention provides that the first layer or sealing layer is applied in a laterally structured manner to the surface of the substrate provided in step a). This is understood in particular to mean that only partial areas of the substrate surface are coated with the sealing layer. According to this development, in step d) the second layer is only applied to partial areas of the sealing layer.

The formulation applied in step d) is preferably applied to the first layer by means of inkjet printing. Inkjet printing is a flexible and inexpensive one

Coating method. For example, in step d), the applied preparation can be applied in a laterally structured manner and thus the substrate can only be coated in certain surface areas without special printing forms being necessary for this. The preparation here preferably contains monomers, oligomers and / or prepolymers with at least one crosslinkable group. Acrylates, methacrylates or epoxides have proven to be particularly advantageous as crosslinkable groups. Vinyl esters are also suitable for this application.

The crosslinking of the crosslinkable groups and thus the crosslinking of the second layer preferably takes place in a step subsequent to step d). In particular, the crosslinking of the second layer by UV radiation, electron beam or thermal

Treatment. The cured second layer represents the lacquer layer. The lacquer layer can be designed as a matt lacquer or gloss lacquer.

In step b) the first layer is carried out according to one embodiment of the invention

Deposit of a preparation obtained. The preparation for producing the first layer contains at least one monomer, oligomer or prepolymer with at least one ok

crosslinkable, functional group and a reactiwerd (inner. Monomer, oligomer and prepolymers each contain at least one crosslinkable, functional group, which are crosslinked in step c).

With the help of the reactive diluent, the viscosity of the preparation can be adjusted to the coating process used in step b). For example, the preparation in step b) can be applied in particular by a flexographic printing process, a screen printing process, by gravure printing, with a roller or by knife-coating. In step b) the preparation is applied evenly to the surface of the substrate. The entire surface of the substrate is preferably provided with the coating in step b). For example, surface structures such as undercuts in the substrate are removed from the

Coating preparation completely covered.

Since the first layer deposited in step b) according to this embodiment has a

Contains reactive diluent as a solvent, which is incorporated into the polymer network and thus, unlike a conventional solvent, remains in the layer, there is only a very slight reduction in volume during crosslinking. This ensures that, even after curing, the entire surface of the substrate coated in step b) is covered with the cured sealing layer. In particular, by using a reactive diluent, i. E. a solvent that is bound in the polymer network during curing and thus remains in the layer, cracking or renewed exposure of the undercuts can be avoided.

According to one embodiment, the layer deposited in step b) can also be compacted and smoothed by a calendering process. In this embodiment, a thermoplastic lacquer system is applied to the substrate surface in step b), hardened by drying and then compacted with a polished stainless steel calender. The lacquer optionally also contains a crosslinkable group, so that in step c) of the method according to the invention, even in this variant of the invention, the first layer deposited in step b) is hardened. This reduces the thermoplasticity of the layer. The lacquer systems used to produce the lacquer layer calendered in step b) can contain organic solvents or water or be radiation-curing. The use of hybrid paints, also referred to as dual-cure paints, has proven to be particularly advantageous here. These paint systems are water-based, but also contain binders with unsaturated, crosslinkable acrylate groups. To one

To produce calenderable lacquer, step b) after the application of the

Coating compound removed from this by drying water and volatile solvents. The lacquer obtained has a high thermoplasticity and can therefore be calendered well in step b). In step c), UV curing then takes place by crosslinking the acrylate groups. This leads to high mechanical stability and a reduction in the thermoplasticity of the cured sealing layer. However points in this

Embodiment, the first deposited layer has a sufficiently high mechanical stability even before the UV curing, so that it can be printed by means of an inkjet process without the undercuts opening during the printing process. Intermediate UV drying before a further coating step is therefore not absolutely necessary. According to a further development of this embodiment, the UV curing of the first deposited layer can therefore take place together with the curing of the second deposited layer. In this development, step d) takes place before step c).

Substrates with calender varnishes as a sealing layer have particularly smooth surfaces. According to one embodiment of the invention, the surface of the substrates treated in this way is so smooth that when the surface is mirrored, the mirror image of the viewer is easily recognizable and is not too strongly distorted by surface undulation. Correspondingly coated substrates are therefore particularly suitable for applying coatings in the form of paints or lacquers, where particularly sharp contours and a high level of brilliance are important. One embodiment of the invention therefore provides that the second layer deposited in step d) so-called VMP colors, i.e. Colors based on

vacuum metallized pigments. This can be, for example, a printing ink that develops a high metallic luster after printing. In these colors, the pigments are in the form of flakes. A uniform alignment of the platelets leads to a high brilliance of the surface created with the color. The uniform alignment of the pigments is promoted by a very smooth surface. According to a further development, the in Step d) deposited layer has a mirror effect. The correspondingly coated substrates are suitable, for example, as a replacement for vacuum-metallized foils, in which a high metallic luster is achieved. Will be the same ink on one only with one on top

If the sealing layer described is applied without calendering, the substrate unevenness results in a glossy but uneven layer in which the mirror image is slightly distorted. When silver printing inks of the type described are applied to uncoated substrates, the lack of alignment of the pigments and the partial absorption of the printing ink produce a gray color layer. Also digital foil embossing, in which the layer deposited in step d) represents an adhesive which, upon subsequent calendering with a suitable embossing foil, is given a shiny metallic surface.

A further development provides that in step b) a hybrid lacquer is deposited as the first layer with the aid of a slot nozzle or a so-called Mayer bar. Alternatively, the hybrid lacquer can also be applied to the substrate provided in step a) using a roller doctor blade method. In this way, too, extremely smooth surfaces are produced.

Alternatively, the preparation applied in step b) can comprise isocyanate-crosslinking systems, polyurethanes, epoxy systems, acrylates, methacrylates, polyvinyl ethers, polyesters based on maleic and fumaric acid, styrene compounds or silicone acrylates.

In step b), the preparation for setting the first layer can in particular by a flexographic printing process, a screen printing process, by gravure printing, with a roller, by doctoring, with a Mayer bar, with a slot nozzle or by means of curtain casting onto the in step a) provided substrate can be applied. Alternatively, the layer deposited in step b) can also be a full-area roller coating.

A further development of the invention provides that the preparation for setting up the first layer additionally contains organic or inorganic particles. The preparation has in particular a solids content in the range from 2 to 40% by weight, preferably in the range from 5 to 25% by weight. According to one embodiment, the preparation contains polymer particles made from polyolefins, polyacrylates, polyamides and the like, talc particles, silicate particles and / or carbonate particles, in particular talc particles. The particles have a matting effect Effect so that the sealing layer produced from the corresponding has a low degree of gloss. In addition, the corresponding sealing layers have a particularly homogeneous and closed surface. This is achieved in particular through the interaction of inorganic particles and the liquid, UV-curable components of the preparation. The inorganic particles in the preparation lead to an increase in the structural viscosity. In particular, it is assumed that the particles increase the cohesive forces within the preparation. This leads to the preparation forming a closed, liquid film. The closed surface of the film is no longer opened, or only opened to a small extent, in the course of the application process. Accordingly, surface defects and undercuts on the substrate surface are almost completely covered. Since preparations with inorganic particles form particularly stable films, the function of the sealing layer according to the invention is ensured even with very small layer thicknesses. Due to the increased intrinsic viscosity, the corresponding preparations are also particularly suitable for application processes in which the film is exposed to high adhesive forces, such as the flexographic printing process, for example.

The invention further relates to a printed product comprising a substrate with a first and a second layer, the first and the second layer comprising an organic, crosslinked lacquer and having a closed surface. The first layer, hereinafter also referred to as the sealing layer, is transparent and preferably colorless. Thus it is optically inconspicuous and does not affect the visual appearance or only to a small extent

Appearance of the substrate. The layer thickness of the sealing layer is in the range from 1 to 10 mhi. As a result, unevenness is at least partially leveled and

Undercuts or pores of the substrate covered or covered by the material of the sealing layer and thus compensated. At the same time, the haptic ones remain

Properties of the substrate largely preserved. According to a preferred embodiment, the cured sealing layer has a layer thickness in the range from 1 to 5 mhi, particularly preferably in the range from 2 to 3 mhi.

The second layer is applied to the sealing layer so that the second layer is separated from the substrate surface by the sealing layer. The second layer therefore has no contact with the substrate surface. Here, the second layer can be the entire Cover the surface of the sealing layer. Alternatively, the second layer can also be arranged on the surface of the sealing layer only in regions, ie in a laterally structured manner.

One embodiment of the invention provides that the first layer is a polymer layer crosslinked by radiation curing, an isocyanate crosslinking system, a polyurethane, an epoxy system, an acrylate, a methacrylate, a polyvinyl ether, a polyester on maleic and

Contains fumaric acid, styrene compounds and / or silicone acrylates.

According to one embodiment, the second layer is a digital print applied by means of an inkjet method. The second layer preferably has a defect-free surface, whereby a defect-free surface is understood to mean in particular a surface with a pinhole density of less than 10 pinholes per dm ² , preferably at most 2 pinholes per dm ² and particularly preferably at most 1 pinhole per dm ² . The pinholes can be seen with the naked eye and otherwise disrupt the print image considerably. For a really high-quality print, as is expected in the area of luxury packaging, for example, no defects should be recognizable on the lacquered surfaces.

According to a further embodiment of the invention, the first and the second layer are applied laterally structured on the substrate, the second layer being arranged on the entire surface of the sealing layer. According to one embodiment of the invention, the second layer forms at least on a portion of the with the

Sealing layer provided substrate with a contiguous area

closed surface, wherein preferably at least 50%, particularly preferably at least 70% of the total surface areas covered with the second layer form a common, contiguous area.

Alternatively, the second layer is applied in a laterally structured manner to partial areas of the first layer. The second layer can thus be applied to the first layer in the form of lines, letters and / or symbols. The corresponding print image of the second layer preferably has a minimum line width of more than 1 mm, preferably more than 2 mm. Another embodiment provides that the second layer is arranged laterally structured on the first layer and the first and the second layer differ in their degree of gloss. This allows gloss and matt effects on individual areas of the

Printed product can be achieved. Both variants are common here. Either the first layer has a higher degree of gloss than the second or vice versa.

According to one embodiment of the invention, the substrate has a binder-containing, particulate coating on at least one surface and the first layer is applied to the binder-containing particulate coating. In this embodiment, the substrate preferably comprises a coated paper or a coated cardboard.

Alternatively, the substrate is an uncoated paper or an uncoated cardboard.

Detailed description of the invention

The invention is explained in more detail below using exemplary embodiments and using the

Figures 1 to 14 described in more detail. Show it:

1 shows a schematic representation of the surface of a coated paper,

FIG. 2 shows a schematic representation of a primer layer applied to the in FIG. 1

represented paper,

3 shows a schematic representation of the applied primer layer shown in FIG. 2 after the drying process,

FIG. 4 shows a schematic representation of a lacquer layer applied by means of an inkjet method in the coated paper shown in FIG. 3,

FIG. 5 shows a schematic representation of a lacquer layer applied by means of an inkjet method in the coated paper shown in FIG. 2, 6 shows a schematic representation of an exemplary embodiment of the invention with a coated paper as the substrate,

7 shows a schematic representation of a lacquer layer applied to an uncoated paper,

Fig. 8 is a schematic representation of an embodiment of the invention with a

uncoated paper as substrate,

9 shows a schematic representation of an embodiment of the invention

Sealing layer in which the sealing layer has been calendered,

10 shows a schematic representation of an embodiment in which a lacquer layer has been applied to a calendered sealing layer,

Fig. 11 is a schematic representation of an embodiment with a calendered

Sealing layer and a lacquer layer with VMP color pigments,

12 shows a micrograph using the coaxial incident light of a coated paper varnished by means of inkjet printing,

13 shows a micrograph using the coaxial incident light of a coated paper varnished by means of inkjet printing as an exemplary embodiment with a 2.5 mm thick sealing layer and FIG

14 shows a micrograph using the coaxial incident light of a coated paper varnished by means of inkjet printing as an exemplary embodiment with a 4.5 mm thick sealing layer.

In Fig. 1, the surface of a coated paper 1 is shown schematically. The

Paper surface 2 is coated with a so-called line 3. The line 3 includes here Particulate, inorganic fillers 4 which are deposited on the paper surface 2 and are held together by an organic binder layer 5. The paper surface 2 is not smooth here, but rather has unevenness. In addition, due to the irregular shape of the inorganic fillers 4, so-called undercuts 6 are formed, which likewise cannot be filled with the binder 5.

FIG. 2 schematically shows the coated paper shown in FIG. 1, which has been provided with a primer coating compound 15. This can be done, for example, by a flexographic printing process, a screen printing process, by gravure printing, with a roller, or by doctoring or curtain casting. Alternatively, the coating can also be a slot nozzle coating or a Mayer bar coating. The primer layer 15 has not yet dried and consists of a formulation which experiences a certain volume shrinkage during drying / curing. The not yet dried layer covers the

Undercuts 6.

FIG. 3 shows the corresponding primer layer 14 which was obtained by drying the coating compound 15 shown in FIG. Due to the drying process and the associated loss in volume of the coating compound 15, the substrate surface is no longer completely covered by the primer 14 obtained by drying the coating compound 15. Furthermore, the drying process also reduces the layer thickness of the primer layer 14 over the undercuts 6, as a result of which the film no longer completely covers the undercuts.

If a corresponding, coated paper 1 is coated with a layer of lacquer 7 by means of an inkjet process, channels to these imperfections arise at undercuts and cavities due to the impact of the inkjet droplets. This is shown schematically in FIG. 4 and in addition to the fact that craters, so-called pinholes 8, are formed in the deposited lacquer layer 7. These represent visually conspicuous defects in the lacquer layer 7, so that the substrate 1 is not suitable for surface refinement by means of inkjet coating.

The same effect occurs when the substrate from FIG. 1 has been provided with a primer coating material as shown in FIG. 2, which after drying has some Has undercuts, as shown in FIG. After coating with a layer of lacquer by means of an inkjet process, this also leads to the formation of craters (so-called pinholes) as shown in FIG.

5 shows a coated paper 1 which has been provided with a primer layer 14 and then a lacquer layer 7 has been applied by means of an ink-jet process. In the

Primer layer 14 can be, for example, an aqueous primer. During the drying process, previously covered defects (cf. FIG. 2) were opened up again due to volume shrinkage. These flaws produce pinholes 8 as flaws in the lacquer layer 7 applied over the primer layer.

In Fig. 6, a substrate coated according to the invention is shown schematically first

Embodiment shown. Here the lacquer layer 7 was also applied by means of inkjet printing, but the surface of the coated paper 1 is completely covered by a sealing layer 9. The sealing layer 9 thus separates the surface of the coated paper 1 from the lacquer layer 7 and covers the cavities in the coated paper which are formed by undercuts 6. Because the undercuts are completely covered, no channels can arise on undercuts during the inkjet coating of the sealing layer 9. The lacquer layer 7 thus has no craters or pinholes and is suitable for surface finishing.

To produce the embodiment of the invention shown in FIG. 6, the provided, coated substrate 1 is first provided with a coating compound. This can be done, for example, by a flexographic printing process, a screen printing process, by gravure printing, with a roller or by doctoring or curtain casting. Alternatively, the coating can also be a slot nozzle coating or a Mayer bar coating. The coating compound contains crosslinkable functional groups. After the coating compound has been applied to the surface of the substrate 1, the crosslinking or curing of the coating compound takes place via the crosslinkable functional groups.

The crosslinkable groups here are preferably radiation-curing, so that the crosslinking can take place with the aid of a UV lamp in step c). There is only a very slight reduction in volume of the coating during crosslinking, which is mainly due to the Polymerization shrinkage is due. As a result of the only slight reduction in volume during curing, unlike, for example, with water-based primers (see FIG. 3), there is no tearing of the layer above undercuts that are not completely filled by the primer liquid, and the cured sealing layer 9 therefore has a closed surface. The cured sealing layer 9 thus represents an ideal surface for the inkjet printing process for depositing the lacquer layer 7.

An uncoated paper 2 which has been provided with a lacquer layer 7 is shown schematically in FIG. The surface of the uncoated paper 2 is uneven and porous. This porosity means that part of the coating composition for producing the lacquer layer is absorbed by the paper in the period from application to curing of the coating composition through crosslinking or solvent depletion. As a result, the layer on the surface of the substrate becomes increasingly thinner. Since the substrate surface is locally different

Has absorption properties, the coating compound is absorbed to different degrees in the different areas of the substrate surface, so that the

Coating thickness varies across the substrate surface and the coating appears spotty. The substrate 2 is therefore not suitable for surface finishing by means of an inkjet process.

FIG. 8 shows a second exemplary embodiment of a printed product according to the invention, the substrate being an uncoated paper 6 as in FIG. Here, too, there is a sealing layer 9 between the lacquer layer 7 and the paper surface, which the

Sealed paper surface and has a closed, homogeneous surface. The lacquer layer 7 thus also has a low roughness and a homogeneous, closed surface.

In the figures 9 to 11 are schematic embodiments with particularly smooth

Sealing layers 13 shown. These sealing layers 17 are applied here analogously to the sealing layers 9 shown in FIGS. 6 and 8. However, the coating compositions applied in this way have greater layer thicknesses. Furthermore, in these embodiments, the coating compound comprises so-called dual-cure coating preparations in one embodiment. These coating preparations are water-based and additionally contain radiation-curable functional groups. After the order of the In this development of the invention, a drying step takes place in preparation for the coating on the substrate 1. The layer obtained in this way is thermoplastic and here, like the sealing layer 9 shown in FIG. 6, at least partially reproduces the unevenness of the substrate surface. In order to still obtain a dense layer with low surface roughness for the inkjet printing process, the dried layer is compacted and smoothed by calendering. For this purpose, the layer is compacted with a polished stainless steel calender.

The calendered layer 13 obtained in this way thus has a closed surface with a low surface roughness and a sufficiently high mechanical stability for the subsequent finishing even without further crosslinking of the functional groups.

The lacquer layer 7 shown in FIG. 10 was applied by means of inkjet to the layer 13, which was very smooth as a result of the calendering. The surface quality obtained in this way is characterized by the fact that the unevenness of the substrate is almost completely compensated by the calendering, which results in an extremely smooth paint surface. As a result of the curing of the lacquer layer 7 by UV radiation, the uncrosslinked radiation-curable functional groups remaining in the calendered layer 13 are also crosslinked

11 shows an embodiment in which the lacquer layer 16 contains platelet-shaped metal pigments (VMP inks). Due to the very smooth surface of the calendered sealing layer 13, these can be aligned parallel or at least largely parallel to the substrate surface, so that a very good mirror effect without distortions due to the

Substrate unevenness can be achieved.

FIGS. 12 to 14 are microscope recordings with 12 times magnification with coaxial incident light of various two-dimensional images applied with inkjet varnishing

Coating samples on cardboard substrates. The samples shown in FIGS. 12 to 13 have the same substrate 1 and the same composition of the lacquer layer 7 and differ in the pretreatment of the substrate prior to the inkjet lacquering to produce the lacquer layer 7.

The lacquer layer 7 was applied in a laterally structured manner so that the area 17 shows the untreated (FIG. 12) or pretreated (FIGS. 13 to 14) substrate without lacquer layer 7. The samples shown in FIGS. 12 and 13 represent comparison samples, the substrate 1 in FIG. 12 not having been pretreated before the painting process. The samples shown in FIG. 13 and FIG. 14 are two exemplary embodiments of the

printed product according to the invention. In both cases, a sealing layer 9 was applied before the painting process. The sample shown in FIG. 12 here has a sealing layer 9 with a layer thickness of 2.5 mhi, the layer thickness of

Sealing layer of the sample shown in Fig. 13 is 4.5 mhi.

While the areas 17 shown in FIG. 12 have a high surface roughness, the surface is smoothed by the sealing layer of the samples shown in FIGS. 13 and 14. Furthermore, FIGS. 11 to 14 show the influence of a sealing layer on the pinhole density in the lacquer layer. The pinholes 8 can be seen in the figures as dark, point-like defects. The pinhole density, that is to say the average number of pinholes 8 per cm ^{2 of} coating area, decreases steadily from FIG. 11 to FIG. 14. The highest pinhole density of approx. 2000 / cm ² has that which is applied directly to the untreated substrate 1

Lacquer layer 7 (Fig. 11) on (with a layer thickness of 8 g / n). The pinholes 8 are generated by not covering or opening undercuts and pores during the inkjet printing process. Even a primer layer 18, which was produced by applying a corresponding aqueous coating preparation to the substrate 1 (layer thickness approx. 1 g / n dry), cannot effectively prevent the formation of pinholes 8, because the high volume or mass loss of the coating material during Drying process the

Undercuts and pores are partially exposed again. In contrast to this, the exemplary embodiments shown in FIGS. 12 and 13 have significantly lower pinhole densities of 25 / cm ² (FIG. 12) and <1 / cm ² (FIG. 13). This is due to the inventive

Lead back sealing layer 9 through the undercuts and pores of the

Substrates 1 are permanently covered. This advantageous effect of the sealing layer 9 is dependent on its layer thickness and increases with increasing layer thickness. Reference number

1 substrate

2 paper

3 lines

4 inorganic filler

5 binders

6 undercut 7 lacquer layer 8 pinhole

9 sealing layer

13 calendered layer

14 aqueous primer

15 Coating compound 16 Color with VM pigments

17 uncoated area

Claims

1. A method for producing a printed matter comprising at least the following

Process steps a) to d)

a) providing a printing substrate (1, 2),

b) applying a preparation for producing a first layer as

Sealing layer (9) on at least one surface of the substrate (1, 2), the preparation for producing the first layer containing at least one monomer, oligomer or prepolymer with at least one crosslinkable, functional group, c) curing of the layer applied in step b) (1 1) wherein the cured first layer (9) has a layer thickness in the range from 1 to 10 mhi and

d) applying a second layer (7) to the surface of the first layer (9) produced in step c), the second layer (7) applied in step d) having a closed surface in the printed areas.

2. The method according to claim 1, wherein in a step preceding step a) a line (3) is applied to at least one surface of the printing substrate (2) provided in step a).

3. The method according to claim 2, wherein the substrate (1) provided in step a) is a coated paper or a coated cardboard.

4. The method according to claim 1, wherein the substrate (2) provided in step a) is an uncoated paper or an uncoated cardboard.

5. The method according to any one of the preceding claims, wherein the first layer (7) has a thickness in the range from 1 to 5 mhi, preferably from 2 to 3 mhi.

6. The method according to any one of the preceding claims, wherein the preparation for producing the first layer contains at least one monomer, oligomer or prepolymer with a crosslinkable group and in step c) the sealing layer through Crosslinking of the functional groups is obtained.

7. The method according to the preceding claim, wherein in step c) the deposited layer is crosslinked by UV radiation, electron beam or thermal treatment and / or the preparation applied in step b) contains a reactive diluent as solvent.

8. The method according to any one of the preceding claims 6 and 7, wherein the layer deposited in step b) is hardened and is subsequently calendered before step d), the hardened layer being thermoplastic.

9. The method according to the preceding claim, wherein step c) takes place after step d) and in step c) the calendered layer (13) is crosslinked together with the layer deposited in step d).

10. The method according to any one of the preceding claims, wherein in step b) the

Preparation for the production of the first layer by a flexographic printing process, a screen printing process, by gravure printing, with a roller, by doctoring, with a Mayer bar, with a slot nozzle or by means of curtain casting onto the substrate (1, 2) provided in step a) ) is applied or the layer deposited in step b) is a full-area roller coating.

1 1. The method according to any one of the preceding claims, wherein in step d) a

Preparation is applied to the first layer (9) by means of ink-jet printing, which layer contains monomers, oligomers and / or prepolymers with at least one crosslinkable group.

12. The method according to any one of the preceding claims, wherein the layer deposited in step d) is crosslinked in a step following step d).

13. The method according to any one of the preceding claims, wherein the second layer (7) is a matt or gloss lacquer.

14. Printed product comprising a substrate (1, 2), a first layer (9) and a second layer (8), the first layer (9) and the second layer (7) comprising an organic, crosslinked lacquer and a closed surface have, and wherein the first layer (9) is transparent and has a layer thickness in the range of 1 to 10 mhi, and wherein the second layer (7) is applied at least in some areas to the first layer (9) so that the first layer ( 9) is arranged between the substrate (1, 2) and the second layer (7), the second layer (7) being a digital print, preferably applied by means of an inkjet process, and the second layer (8) through the first layer (9) is separated from the substrate surface (1, 2) so that the second layer (7) has no contact with the substrate material.

15. Printed product according to claim 14, wherein the substrate (1, 2) has a binder-containing, particulate coating (3) on at least one surface and the first layer (9) is applied to the binder-containing, particulate coating (3).

16. The printed product according to claim 15, wherein the substrate (1) comprises a coated paper or a coated cardboard.

17. Printed product according to one of claims 14 to 16, wherein the first layer (9) has a layer thickness in the range from 1 to 5 mhi, preferably from 2 to 3 mhi.

18. Printed product according to one of claims 14 to 17, wherein the first layer (7) comprises a polymer layer of acrylates crosslinked by radiation curing.

19. Printed product according to one of claims 14 to 18, wherein the first layer (7) crosslinked by polymerization coating agent of the group with the elements isocyanate-crosslinking systems, polyurethanes, epoxy systems, acrylates, methacrylates, polyvinyl ethers, polyesters based on maleic and fumaric acid, and styrene compounds Includes silicone acrylates.

20. Printed product according to one of claims 14 to 19, wherein the second layer (7) is applied laterally structured on the first layer (9).

21. Printed product according to one of claims 14 to 20, wherein the second layer (7) has a closed and homogeneous surface.

22. Printed product according to one of claims 14 to 21, wherein the printed product has a pinhole density <30 / cm ² , preferably <1 / cm ² .

23. Printed product according to one of claims 14 to 22, wherein the second layer (7) is crosslinked.

24. Printed product according to one of the preceding claims 14 to 23, characterized

characterized in that the first layer (9) and the second layer (7) differ in their degree of gloss, the second layer (8) preferably having a higher degree of gloss than the first layer (9).

25. Printed product according to the preceding claim, characterized in that the first layer (9) contains inorganic or organic particles.

26. Printed product according to one of the preceding claims 14 to 25, wherein the first layer (9) comprises a calender varnish.