Use of Ionic Liquids in Primer Compositions

Abstract

The present invention relates to a primer composition comprising: a) 50 to 97.5 wt. % of water; b) 1 to 48.5 wt. % of an ionic liquid; c) 1 to 30 wt. % of an inorganic oxide, a polymeric compound, or a mixture of two or more thereof; and d) 0.5 to 10 wt. % of a polar organic compound, each of which is based on the total weight of the primer composition; and its use for preparing a carrier for a digital printing process.

Description

Technical Field

[0001] The present invention relates to a primer composition and its use in the production of a primer layer on a carrier for the preparation of a digital printing method.

Background Art

[0002] For printing plastic films, in addition to printing methods associated with printing plates (especially flexographic printing, gravure printing, and offset printing), digital printing methods in which printing ink is applied to the film without using a printing plate, for example, by an inkjet method, are becoming increasingly established. Water-soluble printing ink can also be used in all printing methods, which is particularly advantageous when printing on food packaging.

[0003] For example, plastic films made of polypropylene (PP) or polyethylene (PE) basically have non-polar properties, which makes it difficult to print with water-soluble, and thus polar, inks. In some cases, the adhesion and drying of water-soluble ink can be improved by applying an application layer (so-called "primer") to the film surface prior to printing. However, in many cases, even with the use of a primer, a significant amount of effort is required to finally dry the water-based ink later to remove volatile components by evaporation or convection from the ink.

[0004] Conventional primers, i.e., water-based primer compositions for producing an application layer, contain, in addition to water, a significant amount of usually about 20 to 50% by weight of low-boiling organic solvents (VOCs, volatile organic compounds). During the production of the primer layer or subsequent drying, these VOCs are released. As a result, for example, the following problems occur.

[0005] First, in many cases, VOCs are harmful to health. Therefore, especially in the case of mass production, problems occur due to a large amount of VOC emissions in the workplace. Furthermore, the release of VOCs can lead to the formation of explosive and / or flammable mixtures. Ultimately, it is necessary to improve the corresponding products containing the corresponding primer layer with respect to adhesion and chemical resistance. Summary of the Invention Problems to be Solved by the Invention

[0006] Therefore, an object of the present invention is to provide a primer composition that overcomes the drawbacks of the prior art, and to provide a primer composition with a reduced amount of VOCs or no VOCs, particularly for the preparation of the inkjet printing method. Means for Solving the Problems

[0007] The above problems are solved by the subject matter of the independent claims. Preferred embodiments will become apparent from the dependent claims.

[0008] The problem underlying the present invention is, in particular, a primer composition comprising, with respect to the total weight of the primer composition: a) 50 to 97.5% by weight of water, b) 1 to 48.5% by weight of an ionic liquid, c) 1 to 30% by weight of an inorganic oxide, a polymer compound, or a mixture of two or more thereof, and d) 0.5 to 10% by weight of a polar organic compound.

[0009] Surprisingly, the inventors have confirmed that the low-boiling organic solvents (VOCs) in the primer composition for the preparation of digital printing methods can be partially or completely replaced by ionic liquids. In this case, it has been confirmed that by using ionic liquids instead of VOCs, not only can the problems associated with VOC emissions be solved, but also other advantages can be achieved. In particular, it has been confirmed that the composition according to the present invention enables the production of prints with improved adhesion and chemical resistance of the primer layer.

[0010] The primer composition according to the present invention is an aqueous primer composition. This primer composition can be used for the preparation of digital printing methods. In this context, there is a preparation for digital printing methods, in particular the placement of a primer layer on a carrier, in order to facilitate the printing of a carrier in a digital printing method, for example an inkjet printing method using a suitable ink composition, and in particular to improve the adhesion of the ink on the carrier. The aqueous primer composition contains at least 50% by weight of water based on the total weight of the composition. Alternatively, it may be contemplated that the aqueous primer composition contains at least 60% by weight, or at least 70% by weight of water, respectively based on the total weight of the composition. It may be contemplated that the primer composition contains water in an amount of up to 95% by weight, or up to 90% by weight, or up to 85% by weight, or up to 80% by weight, respectively based on the total weight of the primer composition.

[0011] The ionic liquid may be contemplated to be contained in the primer composition in an amount of at least 2% by weight, or at least 3% by weight, or at least 4% by weight, or at least 5% by weight. The ionic liquid may also be contemplated to be contained in the primer composition in an amount of up to 45% by weight, or up to 40% by weight, or up to 30% by weight, or up to 20% by weight, or up to 10% by weight, or up to 8% by weight. The percentage is based on the total weight of the primer composition respectively.

[0012] It may also be contemplated that an inorganic oxide, a polymer compound, or a mixture of two or more of them is contained in the primer composition in a total amount of at least 2% by weight, or at least 4% by weight, or at least 8% by weight, or at least 10% by weight. It may also be contemplated that an inorganic oxide, a polymer compound, or a mixture of two or more of them is contained in the primer composition in a total amount of up to 25% by weight, or up to 20% by weight, or up to 17.5% by weight, or up to 15% by weight. In this case, the percentage is based on the total weight of the primer composition respectively.

[0013] An ionic liquid is an ionic compound (salt) that contains one or more anions and one or more cations, particularly an anion and a cation, and is liquid at a temperature of 200 °C or lower, particularly 150 °C or lower, more preferably 100 °C or lower, and at this time the salt is not dissolved in a solvent such as water. According to the present invention, it is contemplated that the ionic liquid may have a melting point exceeding 60 °C. The ionic liquid is completely miscible with water. The ionic liquid has no (measurable) vapor pressure, that is, it is not released into the gas phase even at high temperatures.

[0014] According to the present invention, exemplary cations that may be contained in the ionic liquid are particularly imidazolium, pyridinium, pyrrolidinium, phosphonium, ammonium, guanidinium, uronium or thiouronium. In particular, these cations are alkylated cations.

[0015] Anions according to the present invention are, for example, halides and relatively complex ions such as tetrafluoroborate, trifluoroacetate, triflate, hexafluorophosphate, phosphinate and tosylate. Organic anions such as imide or amide can also be contemplated. Preferred anions are I - , Cl - , Br - , SCN - , BF4 - , PF6 - , ClO4-, SbF6 - (CF3SO2)2N - , (CF3CF2SO2)2N - , Ph4B - , (C2H4O2)2B - , (CF3SO2)3C - , CF3COO - , CF3SO3 - , C6F5SO3 - and MeO(EtO)2SO3-.

[0016] In one embodiment, the ionic liquid is an imidazonium salt. In this case, it is contemplated that the imidazolium is a dialkylimidazolium of the following formula. [Chemical] Here, R 1 and R 2 are independently selected from the group consisting of C1-C8 alkyl, particularly C1-C6 alkyl, particularly C1-C4 alkyl, most preferably C1-C3 alkyl, and most preferably C1-C2 alkyl.

[0017] In one embodiment, the cation of the ionic liquid is intended to be 1-ethyl-3-methylimidazolium (R 1 = methyl, and R 2 = ethyl).

[0018] In another embodiment, it is contemplated that the ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate.

[0019] The inorganic oxide may be contemplated to be a colloidal inorganic oxide. It may also be contemplated that the polymer compound is in the form of a colloid. In the sense of the present disclosure, a colloid is a finely dispersed substance in the form of discrete particles. According to the present invention, it may be contemplated that the inorganic oxide or the polymer compound is in the form of particles. In this case, the BET surface area of the particles determined in accordance with DIN ISO5794 / 1 Annex D by N2 is 10 to 550 m 2 / g, particularly 25 to 350 m 2 / g. It may also be contemplated that the average particle diameter of the inorganic oxide / polymer compound particles is 2 to 20 μm, particularly 5 to 20 μm. In this case, the average particle diameter determined and calculated by Coulter Counter, Model TA II of Coulter Electronics is referred to. A 100 μm capillary is used.

[0020] In one embodiment, the inorganic oxide is selected from the group consisting of silicon dioxide, titanium dioxide, zinc oxide, tin oxide, aluminum oxide, indium oxide, magnesium oxide, barium oxide, molybdenum oxide, tungsten oxide, vanadium oxide, and mixtures of two or more thereof, and in particular may be contemplated as being silicon dioxide.

[0021] It is particularly preferred that the inorganic oxide is precipitated silicic acid, i.e., precipitated silicic acid. Precipitated silicic acid (precipitated silicon dioxide) is an amorphous form of silicon dioxide in the form of a white powdery substance obtained by precipitation from a silicate-containing solution. The precipitated silicic acid is produced in particular by condensing silicic acid from a dilute alkali silicate solution.

[0022] The polymer compound can in particular be a colloidal polymer material. It may be contemplated that this is a hydrophilic colloidal material containing a water-soluble polymer. According to the present invention, the polymer compound, which can be in the form of a colloidal material, can be one or more selected from polyvinyl compounds such as polyvinyl alcohol, polyacrylamide, polymethacrylamide, poly(N,N-dimethylacrylamide), poly(n-isopropylacrylamide), poly(vinylpyrrolidone), poly(vinyl acetate), polyacrylate, polyurethane, gelatin, dextran, rubber, etc.

[0023] It may be contemplated that the polar organic compound contains from 2 to 18 carbon atoms, in particular from 2 to 10 carbon atoms, more preferably from 2 to 6 carbon atoms, and particularly preferably 4 carbon atoms.

[0024] Furthermore, it may be contemplated that the polar inorganic compound contains at least one carboxyl group.

[0025] It may also be contemplated that the polar organic compound contains two carboxyl groups.

[0026] Furthermore, it may be contemplated that the polar organic compound further contains an additional polar functional group, particularly selected from -OH, -NH2, -C(=O)H, -C(=O)R, -SH, etc.

[0027] Furthermore, it may be contemplated that the polar organic compound is preferably tartaric acid.

[0028] In another embodiment, it may be contemplated that the organic solvent is contained in the primer composition in an amount of 10% by weight or less based on the total weight of the primer composition.

[0029] In another embodiment, it may be contemplated that the primer composition contains an organic solvent in an amount of 5% by weight or less.

[0030] The organic solvent in the meaning of the present invention is particularly volatile organic compounds (VOCs) and very volatile organic compounds (VVOCs). The organic solvent in the meaning of the present invention is particularly a polar organic solvent, i.e., a solvent soluble in water. The organic solvent in the meaning of the present invention (i.e., particularly a solvent that is not contained in the composition or is contained only in a small amount, i.e., in an amount of 5% by weight or less) particularly includes DMSO, monoalcohols, polyalcohols, polyalcohol lower alkyl ethers, ketones, ethers, esters, nitrogen-containing solvents, etc.

[0031] In another embodiment, it is contemplated that the primer composition according to the present invention does not contain an organic solvent or contains only an amount of 5% by weight or less based on the total weight, and the ionic liquid is contained in an amount of at least 5% by weight based on the total weight of the composition.

[0032] The above problem is further solved by a method of printing a carrier by digital printing, including: a) providing a carrier; b) providing a primer layer on at least one surface of the carrier using the primer composition according to any one of the preceding claims; and c) printing the carrier by digital printing on at least one surface coated with the primer layer.

[0033] In this case, as the carrier according to the present invention, in particular, a plastic film can be contemplated. In one embodiment, the plastic film is polyethylene, polypropylene, or a mixture thereof.

[0034] The digital printing method used in the method according to the present invention, and the method in which the composition according to the present invention is used as the ink can be any digital printing method known from the prior art, for example, an inkjet printing method.

[0035] Furthermore, the above problem is solved by using the primer composition according to the present invention for producing a primer layer on a carrier for the preparation of a digital printing method.

Examples

[0036] Hereinafter, the present invention will be described based on specific examples. Of course, the scope of protection is not limited to the specific examples.

[0037] Comparative Example A primer composition according to the prior art was produced by mixing the following components. Water 74.5% by mass DMSO 10% by mass Precipitated silica 12.5% by mass 2,3-Dihydroxybutanedioic acid 3% by mass 1,2-Benzisothiazolin-3-one 0.2% by mass

[0038] Example A primer composition according to the present invention was produced by mixing the following components. Water 74.5% by mass DMSO 5% by mass Ethylmethylimidazole BF4 (emimbf4) 5% by mass Precipitated silica 12.5% by mass 2,3-Dihydroxybutanedioic acid 3% by mass 1,2-Benzisothiazolin-3-one 0.2% by mass

[0039] The primer composition (Example) according to the present invention is different from the primer composition (Comparative Example) according to the prior art in that the organic solvent (DMSO), which is used in large amounts according to the prior art, is partially replaced by an ionic liquid (1-ethyl-3-methylimidazolium tetrafluoroborate).

[0040] The primer compositions according to the Examples and Comparative Examples were applied to a plastic film for the preparation of inkjet printing and subsequently tested for their adhesion and chemical resistance.

[0041] The determination was carried out on the following scale. 5 = 100% = No damage to the coating 4 = 75% = Slight damage to the coating 3 = 50% = Obvious damage to the coating 2 = 25% = Severe damage to the coating 1 = 0% = Complete peeling of the coating

[0042] For the various tests conducted, the following results were obtained.

Table 1

[0043] As can be seen from Table 1, the (partial) replacement of VOCs in the primer composition for the preparation of digital printing with ionic liquids results in a significant improvement in adhesion of up to 40%. An improvement in chemical resistance can also be achieved.

[0044] Furthermore, a reduction of about 15% in the energy consumption for drying was confirmed by the inventors.

[0045] The features of the present invention disclosed in the above description and claims may be essential for realizing the present invention in its various embodiments both individually and in any combination. The present specification includes the following aspects. Item 1. A primer composition, For each, relative to the total weight of the primer composition a) 50 to 97.5% by weight of water, b) 1 to 48.5% by weight of an ionic liquid, c) 1 to 30% by weight of an inorganic oxide, a polymer compound, or a mixture of two or more thereof, and d) 0.5 to 10% by weight of a polar organic compound, wherein the polar organic compound contains two carboxyl groups and a further polar functional group selected in particular from -OH, -NH2, -C(=O)H, -C(=O)R, -SH, A primer composition. Item 2. The primer composition according to item 1, wherein the ionic liquid is an imidazolium salt. Item 3. The primer composition according to item 1 or 2, wherein the ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate. Item 4. The primer composition according to any one of items 1 to 3, wherein the inorganic oxide is a colloidal inorganic oxide. Item 5. The primer composition according to any one of items 1 to 4, wherein the inorganic oxide is selected from the group consisting of silicon dioxide, titanium dioxide, zinc oxide, tin oxide, aluminum oxide, indium oxide, magnesium oxide, barium oxide, molybdenum oxide, tungsten oxide, vanadium oxide, and mixtures of two or more thereof. Item 6. The primer composition according to any one of items 1 to 5, wherein the inorganic oxide is precipitated silicic acid. Item 7. The primer composition according to any one of items 1 to 6, wherein the polar organic compound is tartaric acid. Item 8. Use of the composition according to any one of items 1 to 7 as a primer coating on a carrier for the preparation of a digital printing method. Item 9. A method of printing a carrier by a digital printing method, comprising a) a step of providing a carrier, and b) providing a primer layer on at least one surface of the carrier using a primer composition, wherein the primer composition comprises i) 50 to 97.5% by weight of water, ii) 1 to 48.5% by weight of an ionic liquid, iii) 1 to 30% by weight of an inorganic oxide, a polymer compound, or a mixture of two or more thereof, and iv) 0.5 to 10% by weight of a polar organic compound, each based on the total weight of the primer composition; and c) printing the carrier by digital printing on the at least one surface coated with the primer layer. A method comprising the steps of: Item 10. The method according to item 9, wherein the ionic liquid is an imidazolium salt. Item 11. The method according to item 9 or 10, wherein the ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate. Item 12. The method according to any one of items 9 to 11, wherein the inorganic oxide is a colloidal inorganic oxide. Item 13. The method according to any one of items 9 to 12, wherein the inorganic oxide is selected from the group consisting of silicon dioxide, titanium dioxide, zinc oxide, tin oxide, aluminum oxide, indium oxide, magnesium oxide, barium oxide, molybdenum oxide, tungsten oxide, vanadium oxide, and mixtures of two or more thereof. Item 14. The method according to any one of items 9 to 13, wherein the inorganic oxide is precipitated silica. Item 15. The method according to any one of items 9 to 14, wherein the polar inorganic compound contains at least one carboxyl group. Item 16. The method according to any one of items 9 to 15, wherein the polar organic compound is tartaric acid.​

Claims

1. A method of printing a carrier by a digital printing method, comprising: a) providing a carrier, wherein the carrier is a plastic film; b) providing a primer layer on at least one surface of the carrier using a primer composition, wherein the primer composition comprises: i) 50 to 97.5% by weight of water, ii) 1 to 48.5% by weight of an ionic liquid, iii) 1 to 30% by weight of an inorganic oxide, and iv) 0.5 to 10% by weight of a polar organic compound, each based on the total weight of the primer composition; c) printing the carrier by a digital printing method on the at least one surface coated with the primer layer. A method comprising the steps of.

2. The method according to claim 1, wherein the ionic liquid is an imidazolium salt.

3. The method according to claim 1 or 2, wherein the ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate.

4. The method according to any one of claims 1 to 3, wherein the inorganic oxide is a colloidal inorganic oxide.

5. The method according to any one of claims 1 to 4, wherein the inorganic oxide is selected from the group consisting of silicon dioxide, titanium dioxide, zinc oxide, tin oxide, aluminum oxide, indium oxide, magnesium oxide, barium oxide, molybdenum oxide, tungsten oxide, vanadium oxide, and mixtures of two or more thereof.

6. The method according to any one of claims 1 to 5, wherein the inorganic oxide is precipitated silicic acid.

7. The method according to any one of claims 1 to 6, wherein the polar organic compound contains at least one carboxyl group.

8. The method according to any one of claims 1 to 7, wherein the polar organic compound is tartaric acid. ​

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