Varnish having a microstructure

Abstract

The present invention relates to a waterborne paint composition, comprising a non-film-forming poly(styrene acrylate) having a glass transition temperature (T.sub.G) of at least 80 C., a poly(styrene acrylate) resin having a weight average molecular weight (M.sub.W) of up to 20 000 g/mol, and water. Such a paint composition is suitable as an overprint varnish or primer for substrates such as paper, paperboard and sheets. Due to its surface structure having micro-cracks the applied paint film can advantageously be printed by inkjet printing.

Claims

1. A waterborne paint composition, comprising: 45 to 65 wt.-% of a non-film-forming poly(styrene acrylate) having a glass transition temperature (T.sub.G) of at least 100 C. in the form of an aqueous dispersion, 8 to 12 wt.-% of a polystyrene acrylate) resin having a weight average molecular weight (M.sub.W) of up to 5 000 g/mol in the form of a neutralized solid, 10-14 wt.-% of a hydrophobic dispersing agent, 5 to 7 wt.-% of an inorganic cross-linking agent in solution, 4 to 7% wt-% of an emulsion of polyethylene wax having an amount of 32 wt.-% solids content, 1 to 3 wt.-% of glycerol, 0.1 to 2 wt.-% of surfactant or wetting agent, 0.1 to 1 wt.-% of a silicone defoamer, ammonia, and water, wherein the percentages add to a total of 100 wt.-%.

2. The waterborne paint composition of claim 1, wherein the ratio of non-film-forming poly(styrene acrylate) to poly(styrene acrylate) resin, each based on the weight of solids, is in the range of from 4:1 to 1.2:1, and wherein when said paint composition is applied to a substrate, a microstructured paint film is formed on said substrate.

3. The waterborne paint composition according to claim 2, wherein the microstructured paint film has numerous cracks having a width of at most 2 m.

4. The waterborne paint composition according to claim 1, wherein the ratio of the non-film-forming poly(styrene acrylate) to the poly(styrene acrylate) resin, each based on the weight of solids, is in the range of from 3:1 to 1.5:1.

5. The waterborne paint composition according to claim 1, wherein the ratio of the non-film-forming poly(styrene acrylate) to the poly(styrene acrylate) resin, each based on the weight of solids, is about 2:1.

6. The waterborne paint composition according to claim 1, wherein the poly(styrene acrylate) resin has a weight average molecular weight (M.sub.W) of up to 2 000 g/mol.

7. The waterborne paint composition according to claim 1, wherein the poly(styrene acrylate) resin has a glass transition temperature (T.sub.G) of at least 55 C.

8. The waterborne paint composition according to claim 1, wherein the poly(styrene acrylate) resin has an acid number of from 200 to 300.

9. The waterborne paint composition according to claim 1, wherein the hydrophobic dispersing agent comprises a salt of a polycarboxylic acid.

10. The waterborne paint composition according to claim 9, wherein the hydrophobic dispersing agent comprises an ammonium salt of a polycarboxylic acid.

11. The waterborne paint composition according to claim 1, wherein the inorganic cross-linking agent comprises ammonium zinc carbonate.

12. The waterborne paint composition according to claim 1, having a minimum film forming temperature of at least 50 C.

13. A method of preparing a microstructured paint film on a substrate, comprising applying the waterborne paint composition according to claim 1 to said substrate.

14. The method of claim 13, wherein the microstructured paint film has numerous cracks having a width of at most 2 m.

15. The method of claim 13 wherein said waterborne composition is applied as a primer and/or overprint varnish to a substrate selected from the group consisting of paper, cardboard, paperboard, and sheet.

16. The method according to claim 13, further comprising printing with a solvent containing gravure printing ink on the microstructured paint film, thereby obtaining a coated substrate.

17. The method according to claim 16, wherein the coated substrate has a gloss of from 40 gloss points to 60 gloss points.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF TI-IE DRAWINGS

(1) FIG. 1 depicts a photomicrograph of a paint film of the present invention (Example 1) in a 500-fold magnitude.

(2) FIG. 2 depicts a photomicrograph of a paint film of the present invention (Example 1) in a 2,000-fold magnitude.

(3) FIG. 3 illustrates that when printing on a paint film, prepared according to Example 1, the ink penetrates into the cracks and thus allows for a uniform inking of the surface.

(4) FIG. 4 depicts (90-fold magnitude) a section of a QR-Code, printed on a conventional overprint varnish by inkjet printing, wherein no uniform coverage of color on the surface is achieved.

(5) FIG. 5 depicts a section of a printing image of a QR code printed by inkjet printing on a paint film according to Example 1, showing uniform coverage of the surface with the inkjet ink and a better legibility of the printed QR code 15 image.

DISCLOSURE OF THE INVENTION

(6) Therefore, there is a continuous demand for a paint composition, which is suitable as an overprint varnish in the application on printed substrates or as a primer, and which simultaneously allows for a further printing or overprint by inkjet printing in an industrial process and for the use in the packaging industry.

(7) Thus, the object of the present invention is to overcome the above mentioned disadvantages and difficulties and to provide a waterborne paint composition which enables plane area painting and simultaneously has not the problems of conventional waterborne paints.

(8) It has been surprisingly found that the object can be achieved by a waterborne paint composition according to claim 1.

(9) Preferred embodiments have been defined in the dependent claims.

(10) A first aspect of the present application relates to a waterborne paint composition, comprising: a non-film-forming poly(styrene acrylate) having a glass transition temperature (T.sub.G) of at least 80 C. a poly(styrene acrylate) resin having a weight average molecular weight (M.sub.W) of up to 20 000 g/mol, and water.

(11) A further aspect of the present invention relates to the use of a paint composition according to the first aspect for the preparation of a microstructured paint film on a substrate.

(12) The paint composition of the present invention comprises at least a non-film-forming poly(styrene acrylate) having a glass transition temperature (T.sub.G) of at least 80 C., a poly(styrene acrylate) resin having a weight average molecular weight (M.sub.W) of up to 20 000 g/mol, and water.

(13) The basic idea of the invention is based on the provision of a paint composition, whichif applied on a substrateresults in a microstructured paint film after drying of the paint composition.

(14) The paint film is structured in such a manner that numerous small cracks are formed. In a preferred embodiment, these cracks are at most 2 m, more preferably at most 1 m, in width. More preferably the cracks can have a width of from 0.5 to 1 m. The length of the cracks is preferably of from 5 to 50 m. If such a formed paint film is printed by a water-based ink, the cracks will be filled with ink and a major part of ink has access to the below substrate.

(15) Without being bound to any theory, it is believed that these purposively generated cracks fulfill several functions. On the one hand, the cracks can conduct the applied ink to the surface of the substrate. At the surface of the substrate the ink can be absorbed into the substrate by capillary action. Moreover, further ink will be absorbed by the cracks themselves. By rapid embedding of the ink into a solid paint matrixbut not on the surface of a continuous paint filma dry surface can be formed. The rapid evaporation of the ink's solvent, which is required in the conventional application on a continuous paint film surface, is no longer necessary. An additional advantage of the paint film as formed by the present paint composition is that the inkjet ink partially undercuts the paint film and, therefore, is protected by the paint film. As a result, a prompt influence of mechanical forces on the printed image is possible.

(16) In order to generate a continuous paint film on the optionally printed surface of the substrate, the paint composition has to be a film forming paint composition. In a preferred embodiment, the minimum film temperature (MFT, also called minimum film forming temperature, MFFT) is at least 50 C. preferably at least 60 C., more preferably at least 65 C., and in particular the MFT is in the range of from 67 C. to 85 C.

(17) The minimum film temperature (MFT) is the lowest temperature at which a thin layer of a resin dispersion just dries to from a continuous film. For the purpose of the present application, the MFT is determined by the so-called MFT-Bank according to DIN ISO 2155 (edition of April 2001).

(18) A further important parameter of the used polymer dispersions, polymer resins, and the (dried) paint composition according to the present invention is the glass transition temperature (T.sub.G). The glass transition or softening temperature (T.sub.G) is the temperature, at which a substance (glass) has the highest alteration of the ability for deformation. For the purpose of the present application, the T.sub.6 has been determined in accordance with DIN 51007 (edition of June 1994).

(19) In the present invention the poly(styrene acrylate) resin is characterized by the weight average molecular weight (M.sub.W). For the purpose of the present application, the weight average molecular weight (M.sub.W) can be determined by gel permeation chromatography (GPC) according to ISO 16014-4 2003.

(20) It is believed that the formation of cracks of the paint film is based on the ratio and type of the polymer resin and polymer dispersion, in particular on the used polymer dispersions and mixtures thereof.

(21) In the paint composition according to the present application, a non-film-forming poly(styrene acrylate) is used. It is preferably a water-based dispersion of a non-film-forming poly(styrene acrylate). The poly(styrene acrylate)s used according to the present invention are formed by copolymerization or graft polymerization of styrene or -methyl-styrene with acrylic acid or methacrylic acid and/or the respective esters, such as methyl or ethyl esters of acrylic acid. Styrene or -methyl-styrene can be used alone or as a mixture. Likewise acrylic acid, methacrylic acid, and the respective ester can be used alone or as a mixture. Alternatively, or additionally to acrylic acid also maleic acid or maleic anhydride may be used. Such polymer dispersions can be produced by several polymerization processes (e.g., emulsion polymerization, suspension polymerization) directly from the monomers or also through the dispersion of polymers.

(22) According to a preferred embodiment of the first aspect, the non-film-forming poly(styrene acrylate) has a glass transition temperature (T.sub.G) of at least 80 C., preferably of at least 90 C., more preferably of at least 95 C., and in particular of at least 100 C.

(23) A further essential component of the paint composition of the present invention is a poly(styrene acrylate) resin. Preferred is a resin having such a molecular weight M.sub.W that the resin, optionally after neutralization, for instance with a base such as ammonia, amines, KOH, NaOH, and similar bases, can be dissolved in water. The poly(styrene acrylate) resin can be prepared by a bulk polymerization from styrene and acrylic acid, and subsequently can be optionally neutralized. Apart from styrene also -methyl-styrene with acrylic acid or methacrylic acid and the respective esters, such as methyl or ethyl esters of acrylic acid, can be polymerized to obtain a poly(styrene acrylate) resin. Styrene or -methyl-styrene can be used alone or as a mixture. Likewise, acrylic acid, methacrylic acid and the respective esters can be used alone or as a mixture. Alternatively or additionally to acrylic acid, also maleic acid or maleic anhydride can be used. The poly(styrene acrylate) resin of the present invention, e.g., can have an acid number in the range of from 200 to 300, preferably of from 210 to 250. The acid number indicates the amount of potassium hydroxide in mg, being necessary in order to neutralize the free fatty acids contained in 1 g of poly(styrene acrylate) resin. The acid number is a measure of the number of carboxylic acid groups within the poly(styrene acrylate) resin.

(24) In a preferred embodiment of the first aspect of the present invention, the poly(styrene acrylate) resin has a weight average molecular weight (M.sub.W) of up to 10 000 g/mol, preferably of up to 5 000 g/mol, in particular of up to 2 000 g/mol.

(25) According to another preferred embodiment of the first aspect, the poly(styrene acrylate) resin has a glass transition temperature (To) of at least 55 C.

(26) The ratio of the two main components of the composition according to the invention is freely adjustable. According to a preferred embodiment of the first aspect, the ratio of non-film-forming poly(styrene acrylate) to poly(styrene acrylate) resin, each based on the weight of solids, is in the range of from 5:1 to 1:1, preferably in the range of from 4:1 to 1.2:1, more preferably in the range of from 3:1 to 1.5:1, and in particular, the ratio is about 3:1 or about 2:1.

(27) Apart from both polymeric main components of a non-film-forming poly(styrene acrylate) and a poly(styrene acrylate) resin, the waterborne paint composition of the present invention can also contain a cross-linking agent, preferably an inorganic cross-linking agent. Preferably the cross-linking agent is added as a solution, for instance as an aqueous solution. The concentration of the cross-linking agent in the solution can preferably be in the range of from 10 to 50 wt.-%, more preferably in the range of from 15 to 30 wt.-%, in particular at about 20 wt.-%. The amount of cross-linking agent in the paint composition can preferably be in the range of from 0.1 to 5, more preferably in the range of from 0.5 to 2 wt.-%, each based on the total weight of the water-based paint composition.

(28) In a preferred embodiment of the present invention, the cross-linking agent comprises ammonium zinc carbonate.

(29) In another preferred embodiment of the present invention the paint composition according to the first aspect comprises a hydrophobic dispersing agent. In particular, the hydrophobic dispersing agent comprises the salt of a polycarboxylic acid, preferably an ammonium salt. The dispersing agent can preferably be used as a solution. The concentration of the dispersing agents in the solution is in the range of from 10 to 50 wt.-%, preferably in the range of from 15 to 30 wt.-%, in particular at about 20 wt.-%. The amount of the dispersing agent in the paint composition can preferably be in the range of from 0.1 to 5, more preferably in the range of from 2 to 3 wt.-%, each based on the total weight of the water-based paint composition.

(30) The amount of further salts, such as inorganic salts, in particular inorganic metal salts, in the paint composition of the present invention is preferably less than 10 wt.-%, more preferably less than 5 wt.-%, and in particular less than 2 wt.-%, each based on the total weight of the water-based paint composition.

(31) Moreover, the paint composition of the present invention can contain other usual additives. In a preferred embodiment of the present invention, the paint composition further comprises at least an additive selected from wax, surfactant or wetting agent, defoamer, base, retarder, and coalescing agent.

(32) For instance, the minimum film temperature of a paint composition can be reduced by addition of coalescing agents, such as, e.g., glycol ether, or a surfactant or wetting agent. The abrasion resistance of the dried paint film can be influenced, e.g., by addition of a wax. Drying of the paint film in the unit can be influenced by retarders, such as glycerol.

(33) The gloss of an applied paint film can be controlled by the addition of matting agents. Thus, in a preferred embodiment, the paint composition of the present invention comprises as a further component a matting agent, such as silica. The matting agent can be used in the paint composition preferably in an amount of up to 10 wt.-%, more preferably in the range of from 1 to 4 wt.-%, each based on the total weight of the water-based paint composition.

(34) The level of matting can also be influenced by the addition of a polyurethane dispersion. Turbidity is developed on the surface of the paint. Preferably a polyurethane dispersion is used up to at most 20% (preferably up to 10%). As the polyurethane dispersion, for instance, Neorez 1010 up to at most 20% (preferably up to 10%) can be used.

(35) The waterborne paint composition of the present invention can be used as a graphic overprint varnish (Overprint Varnish, OPV). However the paint compositions of the present invention can also be used as a primer (base coat) before applying a printing ink, whereby they basically can be used in very different printing techniques (flexo printing, gravure printing, roll-/sheet offset printing, and the like). Thus, the waterborne paint systems according to the present invention may also be advantageously usedapart from the mentioned conventional printing processesin digital printing, for instance in inkjet printing processes, both as overprint varnish and also as a primer.

(36) A preferred paint composition according to the first aspect of the present invention comprises: 45 to 65 wt.-% of the non-film-forming poly(styrene acrylate) having a glass transition temperature (T.sub.G) of at least 100 C. (DSC) in the form of an aqueous dispersion, 8 to 12 wt.-% of the poly(styrene acrylate) resin having a weight average molecular weight (M.sub.W) of up to 5 000 g/mol in the form of a neutralized solid, 5 to 7 wt.-% of the inorganic cross-linking agents in solution, 4 to 7 wt.-% of an emulsion of polyethylene wax with 32 wt.-% solids content, 1 to 3 wt.-% of glycerol, 0.1 to 2 wt.-% of a surfactant or wetting agent, 0.1 to 1 wt.-% of a silicone defoamer, ammonia, and water, wherein the percentages add to a total of 100 wt.-%.

(37) A more preferable paint composition according to the first aspect of the present invention comprises: 45 to 65 wt.-% of the non-film-forming poly(styrene acrylate) having a glass transition temperature (T.sub.G) of at least 100 C. (DSC) in the form of an aqueous dispersion, 8 to 12 wt.-% of the poly(styrene acrylate) resin having a weight average molecular weight (M.sub.W) of up to 5 000 g/mol in the form of a neutralized solid, 8 to 14 wt.-%, preferably 10 to 14 wt.-% of a hydrophobic dispersing agent, 5 to 7 wt.-% of the inorganic cross-linking agents in solution, 4 to 7 wt.-% of a emulsion of polyethylene wax with 32 wt.-% solids content, 1 to 3 wt.-% of glycerol, 0.1 to 2 wt.-% of a surfactant or wetting agent, 0.1 to 1 wt.-% of a silicone defoamer, ammonia, and water, wherein the percentages add to a total of 100 wt.-%.

(38) A second aspect of the present invention relates to the use of a paint composition according to the first aspect of the present invention for the preparation of a microstructured paint film on a substrate.

(39) As a substrate, inter alia, paper, paperboard and card board, such as coated and non-coated or printed paper or card board, or sheets or films are suitable. Preferably, printed or unprinted paper or printed or unprinted paperboard is used as a substrate.

(40) In particular, all materials for the manufacture of paperboard packaging and flexible packaging, all materials for the manufacture of job printing (leaflets, promotion), folded boxes, labels, bag or sack packaging, round boxes, covering boxes or secondary packaging, sleeves, decal labels, and composite and layer materials are suitable.

(41) In a preferred embodiment of the second aspect, the microstructured paint film has numerous cracks having a width of at most 2 m.

(42) In another preferred embodiment of the second aspect, the paint composition is used as a primer (base coat) and/or overprint varnish on substrates such as paper or paperboard.

(43) In particular, the non-film-forming dispersion has a T.sub.G of at least 80 C. This dispersion is modified by admixing other raw materials, so that the resulting MFT in the paint film is reduced in such a manner, that an approach of the polymers becomes basically possible, but that an even and total coalescence via a development of spatially separated islands is excluded to a significant amount by crack formation. By the modification a good flow behavior in the coater is ensured and the final minimum water resistance is guaranteed.

(44) The paint composition of the present invention offers numerous advantages. If, for instance, the paint composition is applied on non-coated papers, in particular inkjet inks having an intensive color are rapidly absorbed. A type of blotter effect arises, and the printing ink bleeds through.

(45) However, if a coated paperboard is coated with a paint composition according to the invention andafter dryingis subsequently printed with solvent containing gravure printing inks having a low viscosity, the gloss is enhanced, e.g. from about 40 gloss points to 60 gloss points. The printing ink is maintained in the paint matrix and is abrasion resistant.

(46) By the use of the paint composition according to the present invention, new application techniques will be developed. Thus, for instance, folded boxes may be painted over the full area with the paint composition according to the present invention and may subsequently be printed e.g. by gravure printing and may also be glued together without any problems. Due to the properties of the paint film, omissions for printing areas or glue areas are no longer necessary. The preparation and exchange of varnish printing plates is no longer necessary which results in savings of material and setup time in offset printing. The area for a print, for instance a code, may be selected freely at any time. It is not necessary, as is normally usual, to select an area for printing beforehand.

(47) The paint composition according to the invention also allows for primers or base coats on substrates, whereby, for instance, by means of the above mentioned blotter effect, safety signs, such as water marks, may subsequently be applied.

(48) By the use of the paint composition according to the present invention as primer or base coat, surfaces of substrates may be improved in their quality, whereby the subsequent printing has a more brilliant appearance and is higher resistant to abrasion.

(49) Thus, a paint being applied as primer already before the printing process is enabled to act as an OPV and to achieve the respective characteristics for the final product, although no further coating is applied after the application of the printing agent.

(50) In the following, the present invention as described above is further illustrated by the accompanying examples.

Example 1

(51) The following components have been stirred together in their respective amounts.

(52) TABLE-US-00001 component amount (wt.-%) Induprint SE 385 ex Indulor Chemie GmbH 60 (non-film-forming dispersion, T.sub.G 107 C.) Joncryl 678 ex BASF SE 10 (M.sub.W about 8500 g/mol/acid number 216/T.sub.G 101 C.) ammonia 2.4 ammonium zinc carbonate solution (20%) 6 Ultralube E 842 D (PE-wax emulsion, 32%) 6 Aerosol OT-85 AE ex Cytec 1 (surfactant or wetting agent) Glycerol (retarder) 2.84 BYK 019 ex Byk Chemie (silicone defoamer) 0.34 water 11.42

(53) With the selected formulation, a dried paint film having a crack structure is obtained, as is also apparent from FIGS. 1 and 2. The above formulations could be processed in a coating unit without any problems.

(54) FIGS. 1 and 2, respectively, depict a photomicrograph of a paint film of the present invention (Example 1) in a 500-fold (FIG. 1) and a 2 000-fold (FIG. 2) magnitude. The formation of a crack structure on the surface is evident. The cracks have an average length of about 5 to 50 m and an average width in the range of from 0.5 to 1 m.

(55) FIG. 3 illustrates that when printing on a paint film, prepared according to above Example 1, the ink penetrates into the cracks and thus allows for a uniform inking of the surface.

(56) This characteristic is further illustrated when compared to a conventional overprint varnish. FIG. 4 depicts (90-fold magnitude) a section of a QR-Code, printed on a conventional overprint varnish by inkjet printing. As shown in FIG. 4, no uniform coverage of color on the surface is achieved. Rather, ink droplets have been formed on the paint film, which then dry in a non-uniform manner. Apart from a longer drying time on a conventional paint film also a non-uniform print arises.

(57) In contrast. FIG. 5 depicts the same section of a printing image of a QR code printed by inkjet printing on a paint film according to Example 1. The more uniform coverage of the surface with the inkjet ink allows for a better legibility of the printed image, and thus of the QR code. This results from the penetration of ink into the cracks on the surface of the paint film and from the penetration of the ink into the underlying substrate, provided that it is absorptive.

Example 2

(58) The following components have been stirred together in the respective amounts.

(59) TABLE-US-00002 amount component (wt.-%) Induprint SE 385 ex Indulor Chemie GmbH 47.0 (non-film-forming dispersion, T.sub.G 107 C.) Indurez SR 10 ex Indulor Chemie GmbH 8.0 (M.sub.W about 6.000-8.000 g/mol/acid number 215-230/T.sub.G 105 C.) ammonia 1.8 ammonium zinc carbonate solution 5.0 (20% ig) Orotan 731 AER ex Rohm & Haas 11.0 (hydrophobic dispersant) Aquacer 3RC 7999 ex Byk Cera 5.0 (PE-wax emulsion, 32%) Aerosol OT-85 AE ex Cytec 1.0 (surfactant or wetting agent) Glycerol (retarder) 2.5 BYK 019 ex Byk Chemie 0.3 (silicone defoamer) water 18.4

(60) With the selected formulation, a dried paint film having a crack structure is obtained, similar to that in FIGS. 1 and 2. The above formulation could be processed in a coating unit without any problems and has subsequently been inkjet-printed in accordance with Example 1.

Example 3

(61) The following components have been stirred together in their respective amounts.

(62) TABLE-US-00003 amount component (wt.-%) Induprint SE 385 ex Indulor Chemie GmbH 53.0 (non-film-foaming dispersion, T.sub.G 107 C.) Indurez SR 10 ex Indulor Chemie GmbH 8.0 (M.sub.W about 6.000-8.000 g/mol/acid number 215-230/T.sub.G 105 C.) ammonia 2.0 ammonium zinc carbonate solution (20%) 6.0 Aquacer 3RC 7999 ex Byk Cera 6.0 (PE-wax emulsion, 32%) Aerosol OT-85 AE ex Cytec 1.0 (surfactant or wetting agent) Glycerol (retarder) 2.8 BYK 019 ex Byk Chemie 0.3 (silicone defoamer) water 20.9

(63) With the selected formulation, a dried paint film having a crack structure is obtained, similar to that in FIGS. 1 and 2. The above formulation could be processed in a coating unit without any problems and has subsequently been inkjet-printed in accordance with Example 1.

Example 4

(64) The following components have been stirred together in their respective amounts.

(65) TABLE-US-00004 amount component (wt.-%) Induprint SE 371 ex Indulor Chemie GmbH 60 (non-film-forming dispersion, T.sub.G 101 C.) Indurez SR 30 ex Indulor Chemie GmbH 8 (M.sub.W about 2.500-3.500 g/mol/acid number 240-260/T.sub.G 72 C.) ammonia 1.8 ammonium zinc carbonate solution (20%) 5.0 Orotan 731 AER ex Rohm&Haas 8.0 (hydrophobic dispersant) Aquacer 3RC 7999 ex Byk Cera 5.0 (PE-wax emulsion, 32%) Aerosol OT-85 AE ex Cytec 1.0 (surfactant or wetting agent) Glycerol (retarder) 1.0 BYK 019 ex Byk Chemie 0.3 (silicone defoamer) water 9.9

(66) With the selected formulation, a dried paint film having a crack structure is obtained, similar to that in FIGS. 1 and 2. The above formulation could be processed in a coating unit without any problems and has subsequently been inkjet-printed in accordance with Example 1.