WO2016020034A1

WO2016020034A1 - Printing method

Info

Publication number: WO2016020034A1
Application number: PCT/EP2015/001433
Authority: WO
Inventors: Johannes Tasch; Andreas Becker
Original assignee: Merck Patent Gmbh
Priority date: 2014-08-05
Filing date: 2015-07-13
Publication date: 2016-02-11
Also published as: DE112015003607A5

Abstract

The present invention relates to a printing method for applying effect-pigment-containing coatings to a printing material, to a coated printing material produced according to said method, and to the use of said printing material, in particular in the field of packaging.

Description

printing process

The present invention relates to a printing method for applying effect pigment-containing coatings to a printing substrate, a coated substrate produced by the method mentioned and the use thereof, in particular in the packaging sector.

The various common printing methods are generally used for printing different substrates with a visible, black, white or colored ink, which is applied to the substrate in the form of characters, patterns and / or symbols. Depending on requirements, however, partial areas or the entire area to be printed on the printing substrate can be completely coated with printing ink.

It is known that different printing methods are preferred for different fields of application, because the quality requirements for the print images available in each case are just as different depending on the application spectrum of the printed material as the printing qualities achievable with the individual methods.

For many years now, flexographic printing has been used as a further development of the previously used letterpress printing process for printed materials that are mass-produced and do not meet the highest quality standards. The flexographic printing process, due to the flexible high-pressure molds that can be produced in comparatively inconvenient and cost-effective processes, can be used for many substrates of varying quality, ranging from films to cartons to fabrics. This makes it particularly interesting for packaging printing. Flexographic printing units are today used in the actual flexographic printing as well as in the offset coating. In addition to printing various substrates with conventional

Printing inks which contain absorbing organic or inorganic color pigments, for example in four-color printing, are now also applied with effect pigment-containing layers to corresponding substrates by means of printing processes, for example to obtain iridescent color effects, optically variable effects or metallic-like imprints.

In order to be able to obtain the desired optical effects uniformly over the entire coated surface, a specific layer thickness of the respective printing layer is generally necessary. Therefore, for that

Applying effect pigment-containing layers selected such printing processes that can provide the required layer thicknesses because of the peculiarities of the respective printing technology. Preference is given here to the usual intaglio or screen printing processes used, with which, depending on the viscosity of the ink comparatively high layer thicknesses can be obtained.

In addition to the layer thickness, however, it should also be noted that the effect pigments to be used usually have a platelet shape, which, in addition to the materials used, contributes significantly to the achievement of interference effects as well as gloss and glitter effects.

In particular, in printing processes in which the ink is transferred to the substrate by means of wells, such as in a flexographic printing, it is important to note both the size and the platelet shape of the effect pigments, so that the effect pigments do not clog the cells and ensures good cell emptying is.

At the same time, a homogeneous print image and a high surface area of effect pigments on the printing substrate is desired, so that the desired optical effects also come into their own. Especially with very absorbent substrates such as cardboard, corrugated cardboard, uncoated paper or nonwovens, it proves to be very complicated to obtain a print over the entire printed surface visually appealing, interference effects, optically variable effects or metallic effects exhibiting printed image with the help of a single printing process, because In these substrates, the solvent quickly strikes away and the platelet-shaped effect pigments can thereby align insufficiently on the surface of the printing material. However, a quasi-parallel alignment of the platelet-shaped effect pigments on the surface of the printing material is required in order to be able to achieve the optical effects possible with these pigments.

The object of the present invention is therefore to provide a printing process, in particular a printing process which can be used in a flexographic printing process, with the aid of which various printing materials, in particular those having a rough, absorbent surface, are coated with an effect pigment-containing coating in a single working step can be provided, which has no defects, has a sufficiently high layer thickness and leads to a visually appealing print image with intense coloristic effects over the entire printed area.

Another object of the invention is to provide a printing material with an effect pigment-containing coating, which is produced by the said method.

In addition, it is an object of the invention to show the use of such coated with effect pigment-containing layers printing materials.

The object of the present invention is achieved by a printing method for applying a coating to a printing material (12), wherein in A filling step on a rotating screen roller (3) arranged wells (6) are filled with an ink (4) and subsequently in a wetting step, the ink (4) from the wells (6) of the anilox roller (3) end faces (13) of grid points ( 10) wetted, wherein the grid points (10) the end faces (13) and adjoining lateral surfaces (14) and on a flexible, on a rotating forme cylinder (8) fixed, printing plate (9) are arranged, and wherein in a transfer step ungsschritt the printing material (12) is pressed radially onto the printing form (9) by a rotating printing cylinder (11) and the printing ink (4) is transferred to the printing material (12), the printing ink containing platelet-shaped effect pigments and at least 50 percent of the screen dots ( 10) on the printing form (9) during the wetting step in the wells (6) of the anilox roller (3), wherein in addition to the end faces (13) and the lateral surfaces (14) of the Ra wetting points (10) with the printing ink (4).

The object of the present invention is also achieved by a printing material with effect pigment-containing coating, which is prepared by the aforementioned printing process.

In addition, the object of the present invention is also achieved by the use of a printing material produced in this way with effect pigment-containing coating, in particular in packaging materials, labels, or decorative materials.

The present invention accordingly provides a printing method according to claim 1.

The printing method according to the invention is a

Rotary printing process, in which usually one or more flexographic printing units are used. In particular, it is a Flexographic printing process in the true sense or an offset coating process.

A conventional flexographic printing process according to the prior art, with the aid of which a color pigment-containing coating is to be applied to a printing substrate, is generally carried out according to the following

steps:

In a filling step, cups (6) arranged on a rotating screen roller (3) are filled with a pigment-containing printing ink (4) and the supernatant ink is stripped off by means of a doctor blade (7).

Subsequently wetted in a wetting step, the ink (4) from the wells (6) of the anilox roller (3) the end faces (13) of grid points (10) on a flexible, on a rotating forme cylinder (8) fixed, printing plate (9) are arranged. The grid points (10) have in addition to the end faces (13) and adjacent thereto lateral surfaces (14). In the ink transfer step, the printing material (12) is then pressed radially onto the printing form (9) by a rotating printing cylinder (11) and the printing ink (4) is transferred from the end faces (13) onto the printing material (12). Subsequently, the ink is dried or otherwise solidified.

The functional principle of a conventional flexographic printing process is described in FIG. Correspondingly, in principle, the rotary printing process according to the present invention also proceeds. The arrows indicate the direction of rotation of the respective rollers. Cutouts of a printing form with halftone dots are shown in FIG.

The wetting of halftone dot end faces with ink by means of an anilox roller according to the prior art are shown in FIGS. 4 and 5. In general, for flexographic printing, regardless of whether the substrate is to be printed over the entire surface or with characters and / or patterns, the rule of thumb that the screen frequency of the anilox roller should be at least 5.5 times greater than the screen frequency of the printing plate , so that defects in the coloring and / or moire phenomena are avoided, and that the Schöpfvolumen the anilox roller should be about twice the desired ink application on the substrate (see H. Kippan, eds., Handbook of print media, Springer Verlag Berlin, 2000 , P. 416).

These rules of thumb are the prerequisites for achieving a high-quality print result.

Following these rules, the color of the screen dots from the wells (4) of the anilox roller (3) as shown in Figures 4 and 5, namely on an exclusive wetting of the end faces (13) of the screen dots, of which the ink (4) later is transferred directly to the substrate (12). These rules are still valid for printing on various substrates containing coloring layers containing common organic or inorganic absorption pigments.

However, it has been found that compliance with the abovementioned rules when applying coatings containing flaky effect pigments by means of a rotary printing process with flexographic printing does not lead entirely to the desired success, since in particular in absorbent substrates such as cardboard of all kinds and printing inks contain platelet-shaped effect pigments, the layer thickness of the printing layer applied to the printing substrate and the concentration and orientation of the effect pigments in this printing layer are insufficient to achieve the desired optical effects and to be able to uniformly maintain over the entire printed surface area. It has now surprisingly been found that the printing of substrates containing platelet-shaped effect pigments facilitates layers and the optical quality of the layers obtained can be significantly improved if the rules of thumb mentioned above are violated and the dot size and thus the screen frequency of the Pressure roller is designed so that in addition to the

End faces of the grid points and the immediately adjacent to the end faces lateral surfaces of the grid points in the contact of the

Printing form with the anilox roller (the wetting step) are wetted with the ink. This is ensured (for 50 percent of the halftone dots) by having at least 50 percent of the halftone dots of such small dimensions relative to the wells of the anilox roll that they dip into the wells of the anilox roll during the wetting step. Depending on the depth of immersion and the progression of the printing process, the lateral surfaces of the dipping grid points are wetted with the printing ink partially or completely (10 to 100% of the respective lateral surface). This additional wetting of the lateral surfaces of the halftone dots causes a complete emptying of the cups during the wetting process, so that the ink in the cups is emptied to more than the otherwise usual about 50 percent of the scoop volume and the color split is shifted in favor of the applied print layer. With the same scoop volume of the wells, therefore, a higher layer thickness compared to the prior art can be transferred to the printing material.

While such an increased layer thickness in the conventional color printing process, which contains inorganic or organic absorption color pigments in the printing ink that do not have a specific particle shape, would lead to over-coloration or color-overlapping effects, it will result in the application of platelet-shaped effect pigments

Layers ensure that print layers with sufficient layer thickness, the are contiguous over the entire printed area, have no defects and have a visually appealing appearance at all points of the printed area, can be applied. This is particularly advantageous for highly absorbent substrates such as paper (coated or uncoated), cardboard, kraft paper, Kraftliner and various other cardboard and fabrics and nonwovens, in which the solvent usually present in the printing ink often very quickly wegschlag into the substrate and thereby a convergence of the individual pressure points is difficult to flat layers. If the printing inks have platelet-shaped effect pigments, increased layer thickness application means that the concentration of the effect pigments per unit area is sufficiently high and in particular their parallel orientation relative to the surface of the printing material is particularly good, in order to achieve the desired optical quality of the total printing layer at each point of the layer to be able to guarantee. In a flexographic printing, which is carried out with the usual parameters, this can because of the technologically limited pigment volume concentration in the ink and the anyway in a

Flexo printing process very small layer thicknesses in the range of a few microns (2-5 pm, preferably 2-3 pm) can not be consistently ensured.

Without it being confirmed by more detailed investigations, it is assumed that in addition to an increased quantitative transfer of platelet-shaped effect pigments by immersing the screen dots in the wells also for the transfer of a larger amount of ink vehicle (binder, solvent and auxiliary agents and additives) on the substrate comes. This increases the volume of liquid in which the platelet-shaped effect pigments can align parallel to the surface of the printing substrate. The increased application volume of liquid volume also requires a longer period of time until the solvent has been blown off the substrate. This lengthens the period of time available to the platelet-shaped pigments for parallel alignment relative to the surface of the substrate.

Advantageously, according to the invention, at least 70 percent of the screen dots of the printing form dive into the printing process during the wetting process

Well of the anilox roller, so that their lateral surfaces are wetted in addition to the end faces with ink.

It goes without saying that either with the same cliché raster (grid of the printing form) the size of the wells of the anilox roll is adjusted according to the invention so that at least 50% of the screen dots of the printing form can dip into the wells, or that, with a constant grid of Anilox roller, the grid of the printing form is adjusted accordingly. To reduce the dot size at a given screen frequency of the printing form, it is often sufficient to reduce the area coverage of the screen dots so that the screen dots can dive into the wells of the anilox roller. In accordance with the present invention, regions having the same or less than 50% areal coverage of the halftone dots at a given screen frequency of the printing form have proven to be particularly advantageous. Particularly preferred is the

Area coverage in the range of 15 to 50%, in particular in the range of 20 to 30%. The percent area coverage is defined as the ratio of the area of the halftone dots to the total area of the printing form that is provided with the halftone screen.

The above information applies to the standard in packaging printing screen frequencies of the printing plate in the range of 34 L / cm to 60 L / cm.

If there is a selection of anilox rollers and printing plates in different screenings, only the corresponding ones can be used

Rolls in their respective grid matched to each other according to the invention are used. On the other hand have corresponding rollers or New forms of printing plates are recommended, the new production of a suitably adapted printing form is recommended because the flexible printing plates for a flexographic printing process are much easier and cheaper to produce than the corresponding anilox rollers.

Although it is not absolutely necessary for carrying out the method according to the invention, it proves advantageous if the cells of the anilox roller have the same shape and size over the entire surface of the anilox roller. It is irrelevant with which of the usual manufacturing process the wells are engraved. All of the anilox rolls produced using conventional methods, that is to say by etching engraving, mechanical engraving or laser engraving or laser direct engraving, have proven suitable. The available form of the cups is different in each case. While mechanically engraved wells have the shape of an upside down pyramid, see Figure 3, etched and laser engraved wells have a round cross section. The latter can also, due to their cylinder-like shape, a total of a larger Schöpfvolumen and a higher penetration depth of the grid points and are therefore preferably used for the inventive method.

According to the invention, the well width, which is determined from the diameter of round wells or the smallest side edge length of mechanically engraved wells, is designated as W.

Similar to the wells of the anilox roller, it is advantageous for the screen dots of the printing form used according to the invention if the size and the shape of the screen dots over the entire screened surface of the printing plate are the same. As a result, the immersion of a plurality of grid points in the wells of the anilox roller is facilitated. The grid points regularly have a round cross-section. The size of the grid points, which corresponds to the diameter of the face, is designated G according to the invention. It is possible to use all flexographic printing plates produced in accordance with the customary processes, which can be constructed in one or more layers and can consist of different materials (rubber, elastomers, photopolymers).

According to the invention, the ratio G / W (dot size of the

Printing form / cell width of the anilox roller) has a value in the range of 0.10 to 0.50, preferably a value in the range of 0.15 to 0.30. This means that the size of the screen dots is according to the invention only in the range of 10 to 50%, preferably 15 to 30%, of the pot width. This allows the immersion of a large number of existing on the printing form grid points in the wells of the anilox roller. Depending on the nature and intended use of the decorative coating desired in each case, the proportion of the printed area on the printing material can be different relative to the total printable area of the printing material. Depending on the proportion of the area to be printed on the substrate, the screening on the printing form is selected. If only partial surfaces of the printing material to be provided with the effect pigment-containing coating, only a partial area screening on the printing plate is required.

Therefore, the proportion of the screened surface of the printing form is usually between 5 and 100 percent of the total surface, preferably between 30 and 100 percent. In particular, in some embodiments of the present invention, the portion of the rasterized surface of the printing form is 100 percent of the surface of the printing form, i. the printing form is on its entire

Surface provided with grid points. As already mentioned above, the area coverage of the screen dots on the printing form according to the invention is between 15 and 50%, preferably between 20 and 30%. The printing plates used in the method according to the invention as well as the anilox rollers used independently of one another preferably have a screen frequency in the range from 34 lines / cm (34 L / cm) to 60 lines / cm (60 L / cm). In one embodiment of the present invention

Invention, the printing plate and the anilox roller also each have the same screen frequency.

The printing ink used in the printing process according to the invention contains platelet-shaped effect pigments. Platelet-shaped effect pigments are platelet-shaped pearlescent pigments, predominantly transparent or semitransparent interference pigments and metallic effect pigments. Also, liquid crystal pigments, so-called LCPs (Liquid Crystal Pigments), or structured polymer platelets, so-called holographic pigments, include this. Of these, interference pigments and metallic effect pigments are preferred. The above-mentioned platelet-shaped effect pigments are composed of one or more layers of at least partially different materials.

Pearlescent pigments consist of transparent platelets with high

Refractive index and show in parallel orientation by multiple reflection a characteristic pearlescence. Such pearlescent pigments, which additionally show interference colors, are referred to as interference pigments.

Although naturally also classic pearlescent pigments such as TiO 2 flakes, basic lead carbonate, BiOCl pigments or fish silver pigments are suitable in principle, as platelet-shaped effect pigments within the meaning of the invention it is preferable to use interference pigments or metallic effect pigments. used, which comprises on an inorganic platelet-shaped support at least one coating of a metal, metal oxide, metal oxide hydrate or mixtures thereof, a mixed metal oxide,

Metal suboxide, metal oxynitride, metal fluoride, BiOCl or a polymer.

The metallic effect pigments preferably have at least one metal layer. The inorganic plate-shaped carrier is preferably made of natural or synthetic mica, kaolin or others

Phyllosilicates, of glass, S1O2, T1O2, Al2O3, Fe203, polymer platelets, graphite platelets or metal flakes, such as

Aluminum, titanium, bronze, silver, copper, gold, steel or various

Metal alloys.

Particular preference is given to supports made of mica, glass, graphite, S1O2, T1O2 and Al2O3 or mixtures thereof or metal supports of aluminum or aluminum alloys. Preferably, a coating applied to the carrier consists of metals, metal oxides, metal mixed oxides, metal suboxides or

Metal fluorides and in particular of a colorless or colored metal oxide selected from TiO 2, titanium suboxides, titanium oxynitrides, Fe 2 O 3, Fe 3 O 4, SnO 2, Sb ₂ O 3, SiO ₂ , Al ₂ O 3, ZrO ₂ , B ₂ O 3, Cr ₂ O 3, ZnO, CuO, NiO or mixtures thereof.

Coatings of metals are preferably made of aluminum, titanium, chromium, nickel, silver, zinc, molybdenum, tantalum, tungsten, palladium, copper, gold, platinum or alloys containing them.

The metal fluoride used is preferably MgF.sub.2. As platelet-shaped effect pigments, multilayer effect pigments are particularly preferably used. These have on a platelet-shaped carrier several layers, which preferably consist of the aforementioned materials and have different refractive indices in such a way that in each case at least two layers of different refractive index are alternately on the carrier, wherein the refractive indices in the individual layers differ by at least 0.1 and preferably by at least 0.3. In this case, the layers located on the support can be both almost transparent as well as colored or semitransparent.

Likewise, the so-called LCPs, which consist of crosslinked, oriented, cholesteric liquid crystals, or else also known as holographic pigments structured polymer platelets can be used as platelet-shaped effect pigments.

The platelet-shaped effect pigments described above may be present individually or in a mixture in the printing ink used in the printing process according to the invention.

In one embodiment of the present invention, which may be preferred depending on the intended use of the printed materials, a platelet-shaped effect pigment is used which leaves a different visually perceptible color and / or brightness impression at different illumination and / or viewing angles. For different color impressions, this property is called a color flop. In particular, pigments which have a Farbflopp, produce in the printing layers produced conspicuous, optically interesting color and gloss impressions, which in particular for

Packaging and decoration purposes can be highly attractive. Pigments of this type are also referred to as optically variable. Such optically variable platelet-shaped effect pigments preferably have three optically clearly distinguishable discrete colors under at least two different illumination or viewing angles at least two and at most four, but preferably at two different illumination or viewing angles two or three different illumination or viewing angles.

In order to be able to develop their full optical effect, it is advantageous if platelet-shaped effect pigments are present in the medium containing them in an oriented form, i. in the present case, if they are aligned almost parallel to the surface of the printing material provided with the coating produced according to the invention. However, such an alignment already takes place by means of the printing process used according to the invention in the shear forces acting on the process and the increased layer thickness, so that it can be assumed that the platelet-shaped effect pigments used in the coating produced by the printing process according to the invention on a substrate in the desired aligned form available. As platelet-shaped effect pigments, for example, the commercially available interference pigments, which under the names

Iriodin®, Colorstream®, Xirallic®, Meoxal®, Xirona®, Colorcrypt® and Securalic® from Merck KGaA, Mearlin® from Mearl, metallic effect pigments from Eckhard and goniochromic (optically variable) effect pigments such as Variochrom ® from BASF, Chromafflair® from Flex Products Inc., Helicone® from Wacker or holographic pigments from Spectratec and other similar commercially available pigments. However, this list is to be considered as illustrative and not restrictive. The size (longest dimension in one dimension, ie greatest length or largest diameter) of the platelet-shaped effect pigments is not critical per se, but must be matched to the anilox roll used. The expansion of the pigments in length or width is usually from 1 to 200 μm, in particular from 5 to 125 μm, preferably from 1 to 60 μm, and very particularly preferably from 1 to 25 μm. The thickness of the pigments is in the range of 0.01 to 5 μηι, in particular between 0.05 and 4.5 μηη and particularly preferably between 0.1 and 1 μηπ.

They usually have an aspect ratio (ratio of the average diameter to the mean particle thickness) of at least 2 and preferably of at least 5. The aspect ratio may vary within a wide range and may be up to 250, preferably up to 100.

For the use of the platelet-like effect pigments in the printing process according to the invention, the general principle applies that the methods described in US Pat

Ink selected pigments are selected so that the width W of the wells on the anilox roller is at least equal to 1, 5 to 2 times the longest dimension of the pigments. Otherwise, there would be disturbances in the emptying behavior of the ink from the wells during the wetting step.

The printing ink used according to the invention contains at least one binder in addition to the platelet-shaped effect pigments. Suitable binders are, in general, suitable binders for coating compositions, in particular those based on nitrocellulose, polyamide, acrylic, polyvinyl butyral, PVC, PUR, or suitable mixtures of these. Particular preference is given to UV-curing binders (free-radically or cationically curing). These binders or binder mixtures are preferably transparent after the coating has cured, but may also be translucent. The additional use of a solvent, which may consist of water and / or the usual organic solvents used for printing process or solvent mixtures is partially advantageous, but not mandatory, because many binder systems that can be used in flexographic printing, are radiation-curing and therefore the additional Use of solvents is completely or partially obsolete.

As organic solvents branched or unbranched alcohols, aromatics or alkyl esters, such as ethanol, 1-methoxy-propanol, 1-ethoxy-2-propanol, ethyl acetate, butyl acetate, toluene, etc., or mixtures thereof can be used.

Furthermore, the printing ink used in the printing process according to the invention may contain other auxiliaries and additives customarily used in printing inks, which are absolutely familiar to the person skilled in the art and therefore need not be further explained here.

The concentration of the platelet-shaped effect pigments in the ink containing them is, according to the invention, between 5 and 45 percent, based on the solids content of the printing ink, in particular between 15 and 35 percent. With a pigment content of less than 5 percent, based on the solids content of the printing ink, the desired optical effect of the coating can not be sufficiently ensured. On the other hand, pigment concentrations of more than 45 percent lead to clogging of the wells on the anilox roller as well

Emptying difficulties when wetting the screen dots. This would also affect the printing performance in the printing process. For this reason, pigment concentrations beyond the stated range are not advantageous. The printing material used in the process according to the invention may in principle be any printing material which is accessible to a rotary printing process with flexographic printing, ie papers, cartons and woven fabrics or nonwovens of various types. However, the process according to the invention is particularly advantageous for printing substrates consisting of a cellulose-containing material or having a surface to be printed of cellulose-containing material. These are, in particular, uncoated paper, coated paper, cardboard, kraft paper or Kraftliner. These materials typically have a rough surface and have some absorbency which generally allows for rapid drying or solidification of the printed coating when printed by a conventional flexographic printing process

However, coatings containing effect pigments can lead to the previously mentioned deficiencies. These deficiencies can be reduced or prevented by the printing method according to the invention in an advantageous manner.

The application of the platelet-shaped effect pigments containing coating on the substrate can be done either on the uncoated substrate, as is the case for example with uncoated paper, cardboard or kraftliner, but can also be done on an already pre-treated or precoated substrate (eg coated or color precoated paper). In addition, the printing material which has already been printed according to the invention with the effect pigment-containing coating can, if necessary, be overprinted with further layers, for example with further dyeing or effecting patterns, motifs or the like, for example on a surface of the printing material which is fully coated according to the invention.

The present invention also provides a printing substrate with a coating containing a platelet-like effect pigment which is prepared according to the printing method described above according to the invention.

As already described above, in the context of the present invention, such a printing substrate is substrates of various types printed on a coating comprising a platelet-shaped effect pigment by means of a flexographic printing device, but preferably uncoated paper, coated paper, cardboard, kraft paper or kraft liners. which (s) has a shiny, colored iridescent, metallic and / or optically variable coating, which is based on the optical effect of platelet-shaped effect pigments.

The subject matter of the present invention is also the use of a printing material containing platelet-shaped effect pigments as described above in packaging materials, labels or decorative materials.

The process according to the invention can be used to produce coatings comprising platelet-shaped effect pigments which are continuous with the aid of a simple, adapted flexographic printing process and printing substrates, in particular on substrates with a rough and absorbent surface, in a single process step which has the desired surface area over the entire printed area have optical properties such as shiny, colored iridescent, metallic and / or optically variable properties and show a very uniform, optically dense printed surface without misaligned due to a sufficiently high pigment concentration per unit area printed area and a very good pigment orientation. Such a surface quality can be obtained, in particular on rough, absorbent substrates, with known, conventional flexographic printing processes only with several printing layers one above the other. The inventive method can therefore be advantageous for the Applying different types of substrates with a relatively low-cost flexographic printing process in a single printing step, which is particularly important for long runs in packaging printing and decoration printing is of particular importance. At the same time, the method according to the invention can be incorporated into the customary packaging printing methods without much additional effort, so that additional cost-intensive additional coating processes or complex device conversions can be dispensed with.

The invention will be explained below by means of examples, but not limited to these. The explanation, as already in the descriptive part, is made with the aid of the following drawings: schematic construction of a flexographic printing unit schematic view of a part of a printing form with several grid points schematic view of a part of an anilox roller with several wells (6) (mechanically engraved) and webs (15) schematic view of the wetting of a grid point according to the prior art schematic view of the wetting of a grid point according to the invention

8, 9, 10 are schematic views of wetting and ink transfer according to the invention Example 1 :

As printing material (12) is a kraft liner, which serves as a surface cover for corrugated cardboard used. The viscosity of an aqueous printing ink (4) containing 30% by weight of an interference pigment (Iriodin® 96107 Icy White Lightning), based on platelet-shaped synthetic mica substrates with a coating of ΤΊΟ2 and having a particle size of 5-40 μm (product of the Fa Merck KGaA, Darmstadt), and 70% by weight of an aqueous binder containing Varnishes (Senolith 350147, product of Weilburger), is adjusted with water to 35 sec (4 mm flow cup, according to DIN 53211). This ink is introduced via an inlet device (5) in the inking unit (2) of a flexographic printing machine. The wells (6) of a rotating screen roller (3) are brought into contact with the inking unit and thereby filled with the printing ink (4). Excess ink is stripped off the surface of the anilox roller with the aid of a doctor blade (7).

The anilox roller has a screen frequency of 40 Ucm 60 ° (cell width W 160 pm). A Flexod ruckform (9) with a screen frequency of 60 L / cm (Flint FAC, tape Tesa 52122) is mounted on a plate cylinder and brought into contact with the rotating anilox roller. The grid dot size G of the grid points (10) on the printing form (9) varies in the range of 30 pm to 40 pm (60 L / cm, about 25% area coverage FD). The transfer of the printing ink to the substrate (printing process) takes place at a speed of 50 m / min. The coated substrate is allowed to dry.

On the light brown substrate, a uniform, optically closed, silvery white print layer with high gloss can be observed. Comparative Example 1

Example 1 is repeated with the change that the printing ink is printed with a printing form in which the area coverage is 100% (full area). The other conditions are the same as in Example 1.

The area printed on the kraftliner has a very faint, silvery white sheen and a blotchy appearance. In comparison to the printed substrate according to Example 1, the impression is created visually that in Comparative Example 1 a significantly lower concentration of pigments was used (in fact the same pigment concentration in the printing ink).

Comparative Example 2:

Comparative Example 1 is repeated with the difference that as

Printing ink, an aqueous ink with a commercially available green absorption pigment (FF2 Frontal MD 417 Green HKS 55 Fa. Follmann, blended with Senolith 350147 Fa. Weilburger) is used.

The printed image obtained shows a uniform, green opaque ink application on the substrate.

Comparative Example 3

Example 1 is repeated with the change that the printing ink according to Comparative Example 2 is used as printing ink. The other conditions are the same as in Example 1.

The printed image shows an irregularly printed green

Surface with clearly visible non-printed areas and overall a significantly weaker hiding power than the printed image from Comparative Example 2.

In summary, it can be seen that on the rough, absorbent substrate, here in the form of a kraft liner, printed images are obtained which behave in opposite directions with regard to the printing conditions and the pigments used in the printing ink. While the use of a conventional absorption pigment with Undefined particle shape the full-surface printing leads to a visually appealing, fully opaque imprint and applied by a grid (25% area coverage) coating to an irregular, partially unprinted appearing print of poor quality, occurs when adding a platelet-shaped Effect pigment in the printing ink of the opposite effect, namely an in gloss behavior and color position inadequate surface quality with printed solid surface and a glossy surface with high coverage of the silvery white effect pigment with a coverage of only 25%.

27

List of reference numbers

(1) Rotary printing device

(2) inking unit

(3) Anilox roller

(4) printing ink

(5) Inlet device

(6) wells

(7) squeegee

(8) forme cylinder

(9) printing form

(10) halftone dots

(11) impression cylinder

(12) substrate

(13) Face of the grid point

(14) lateral surface of the grid point

(15) Footbridges

Claims

- 24 - Claims

Printing method for applying a coating to a

Substrate (12), wherein in a filling step on a rotating screen roller (3) arranged cups (6) are filled with a printing ink (4) and subsequently in a wetting step, the printing ink (4) from the wells (6) of the anilox roller (3) Wets faces (13) of grid points (10), wherein the grid points (10) the end faces (13) and adjoining lateral surfaces (14) and are arranged on a flexible, on a rotating forme cylinder (8) fixed pressure mold (9), and wherein in a transfer step, the printing material (12) by a rotating printing cylinder (11) to the printing plate (9) pressed radially and the ink (4) on the

Printing material (12) is transferred,

characterized in that the printing ink contains platelet-shaped effect pigments and that at least 50 percent of the dots (10) on the printing form (9) during the wetting step in the wells (6) of the anilox roller (3) are immersed, wherein in addition to

End surfaces (13) and the lateral surfaces (14) of the grid points (10) with the ink (4) are wetted.

2. Printing method according to claim 1, characterized in that the lateral surfaces (14) of the screen dots (10) are wetted partially or completely with the printing ink (4).

3. Printing method according to claim 1 or 2, characterized in that at least 70 percent of the grid points (10) dive into the wells (6).

4. Printing method according to claims 1 to 3, characterized in that the grid points (10) a grid point size G and the 25

Wells (6) have a width W and the ratio G / W represents a value in the range of 0.10 to 0.50.

5. Printing method according to claim 4, characterized in that the ratio G / W represents a value in the range of 0.15 to 0.30.

6. Printing method according to one or more of claims 1 to 5, characterized in that the printing form and the anilox roller each have a screen frequency in the range of 34 lines / cm to 60

Have lines / cm.

7. Printing method according to one or more of claims 1 to 6, characterized in that the printing form is provided on its entire surface with screen dots.

8. Printing method according to one or more of claims 1 to 7, characterized in that the screen dots on the printing form have a coverage in the range of 15 to 50%.

9. Printing method according to one or more of claims 1 to 8, characterized in that it is the printing material is a cellulose-containing material.

10. Printing method according to claim 9, characterized in that the cellulose-containing material is selected from uncoated paper, coated paper, cardboard, kraft paper or Kraftliner.

11. Printing method according to claim 10, characterized in that the platelet-shaped effect pigments are selected from pearlescent pigments, interference pigments, metallic effect pigments, liquid crystal pigments and structured polymer platelets or mixtures of these. - 26 -

12. printing substrate with platelet-shaped effect pigments containing coating, prepared by a printing process according to one or more of claims 1 to 11.

13. A printing substrate according to claim 12, characterized in that it is uncoated paper, coated paper, cardboard, kraft paper or Kraftliner, which (s) has a color irsierende, metallic and / or optically variable coating.

14. Use of a printing material according to claims 12 and 13 in packaging materials, labels or decorative materials.