Replacement from VOCs to solvents with no vapor pressure

Abstract

The present invention relates to a method for printing a carrier by a digital printing method, the method comprising the steps of: a) providing a carrier; and b) printing the carrier by a digital printing method using a composition, the composition comprising: i) 50 to 98 wt. % of water, ii) 1 to 49 wt. % of an ionic liquid, and iii) 1 to 30 wt. % of a pigment, dye, or mixture thereof, each relative to the total weight of the composition, wherein the carrier is a plastic film and the digital printing method is an inkjet printing method.

Description

[Technical Field]

[0001] The present invention relates to an (ink) composition and its use as an ink in an ink jet printing process. [Background technology]

[0002] For printing on plastic films, printing methods associated with printing plates (especially flexography, intaglio, and offset printing) and increasingly digital printing methods, in which the printing ink is applied to the film without the use of a printing plate, for example by ink jet methods (inkjet methods), are used. All printing methods can also use water-soluble printing inks, which is particularly advantageous when printing on food packaging.

[0003] Plastic films, for example made from polypropylene (PP) or polyethylene (PE), have essentially non-polar properties that make them difficult to print with water-soluble, and therefore polar, inks. In some cases, applying a primer (a so-called "primer") to the film surface prior to printing can improve the adhesion and drying of water-soluble inks. However, even with the primer, the subsequent final drying of water-based inks often requires significant effort to remove volatile components from the ink by evaporation or convection.

[0004] In addition to water, prior art water-based inks also contain significant amounts of low-boiling organic solvents (VOCs, volatile organic compounds), typically in amounts of about 20-50% by weight. These VOCs are released during printing or during drying of the ink following the printing process. This results in, for example, the following problems:

[0005] For one thing, VOCs are often harmful to health. Therefore, high VOC emissions in the workplace can cause problems, especially in mass production. Furthermore, VOC emissions can lead to the formation of explosive and / or flammable mixtures. Similarly, known VOC-containing ink systems often have unfavorable drying characteristics, especially when using radiation drying systems, which often result in the optical properties of the printed substrate needing improvement, particularly in terms of gloss and color space. Consequently, there is a need to improve the adhesion and chemical resistance of correspondingly printed products. Summary of the Invention [Problem to be solved by the invention]

[0006] It is therefore an object of the present invention to provide an ink composition which overcomes the drawbacks of the prior art, and which has a reduced amount of VOC or is VOC-free, in particular for ink jet printing processes. [Means for solving the problem]

[0007] The above problem is solved by the subject matter of the independent claims. Preferred embodiments emerge from the dependent claims.

[0008] The problem underlying the present invention is solved by a composition comprising: a) 50 to 98% by weight of water, b) 1 to 49% by weight of an ionic liquid, and c) 1 to 30% by weight of a pigment, dye, or mixture thereof, each relative to the total weight of the composition.

[0009] The present inventors have surprisingly found that low-boiling organic solvents (VOCs) in ink compositions for use in digital printing processes can be partially or completely replaced with ionic liquids. It has been found that the use of ionic liquids instead of VOCs not only solves the problems associated with VOC emissions, but also achieves other advantages. In particular, it has been found that the compositions according to the invention enable the production of prints with improved ink adhesion and chemical resistance. Advantages have also been achieved in terms of additive solubility, pigment and polymer dispersibility, and improved optical properties of the prints.

[0010] The composition according to the present invention is an aqueous ink composition. The ink composition can be used in inkjet printing. The aqueous ink composition contains at least 50% by weight of water, based on the total weight of the composition. Alternatively, the aqueous ink composition may contain at least 60% by weight, or at least 70% by weight, or at least 80% by weight of water, each based on the total weight of the composition. Alternatively, the composition may contain up to 95% by weight, or up to 90% by weight, or up to 85% by weight of water, each based on the total weight of the composition.

[0011] It is contemplated that the ionic liquid will be present in the composition in an amount of at least 2% by weight, alternatively at least 3% by weight, alternatively at least 4% by weight, alternatively at least 5% by weight, alternatively greater than 5% by weight, or alternatively at least 5.5% by weight. It is also contemplated that the ionic liquid will be present in the composition in an amount of up to 45% by weight, alternatively at most 40% by weight, alternatively at most 30% by weight, alternatively at most 20% by weight, alternatively at most 10% by weight, or alternatively at most 8% by weight. Each percentage is based on the total weight of the composition.

[0012] It is also contemplated that the pigment / dye will be present in the composition in an amount of at least 2%, alternatively at least 3%, alternatively at least 4%, alternatively at least 5% by weight. It is also contemplated that the pigment / dye will be present in the composition in an amount of up to 25%, alternatively at most 20%, alternatively at most 15%, alternatively at most 10%, alternatively at most 8% by weight, where each percentage is based on the total weight of the composition.

[0013] Ionic liquids are ionic compounds (salts) comprising one or more anions and one or more cations, in particular anions and cations, which are liquid at temperatures below 200°C, in particular below 150°C, more preferably below 100°C, where the salt is not dissolved in a solvent such as water. According to the invention, it is possible for the ionic liquid to have a melting point above 60°C. Ionic liquids are completely miscible with water. Ionic liquids have no (measurable) vapor pressure, i.e., they are not released into the gas phase even at high temperatures.

[0014] Exemplary cations that may be included in the ionic liquid according to the invention are 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 more complex ions such as, for example, tetrafluoroborate, trifluoroacetate, triflate, hexafluorophosphate, phosphinate and tosylate. Organic anions such as, for example, imide or amide may 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 which case the imidazolium may be considered to be a dialkylimidazolium of the following formula: [ka] where R 1 and R 2 are independently selected from the group consisting of C1-C8 alkyl, in particular C1-C6 alkyl, especially C1-C4 alkyl, particularly preferably C1-C3 alkyl, most preferably C1-C2 alkyl.

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

[0018] Another embodiment contemplates that the ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate.

[0019] The pigment according to the present invention can be an inorganic pigment or an organic pigment. Commonly used corresponding pigments are known to those skilled in the art. Suitable inorganic pigments include, inter alia, titanium dioxide, red iron oxide, antimony(V) sulfide, cadmium yellow, cobalt blue, ultramarine blue, Prussian blue, carbon black, graphite, or other color pigments, as well as calcium carbonate, kaolin, clay, barium sulfite, aluminum hydroxide, talc, etc.

[0020] Suitable organic pigments are, for example, azo pigments, copper phthalocyanine pigments, condensed polycyclic pigments, etc. In principle, all dyes are suitable as dyes which have sufficient solubility in the aqueous systems according to the invention.

[0021] In another embodiment, the composition may be designed to include one or more additives independently selected from the group consisting of binders, fillers, rheological additives, stabilizers, surfactants, preservatives, and humectants.

[0022] In this case, the total amount of the additives may be contemplated to be 0.1 to 10% by weight relative to the total weight of the composition.

[0023] In another embodiment, it is contemplated that the composition further comprises a polymer, a precursor thereof, or a mixture of a polymer and a precursor.

[0024] The polymers contained in the composition according to the present invention or produced by polymerization of a precursor / by reaction of a precursor with a polymer are used as fixative resins to fix pigments / dyes to substrates. Fixative resins can be acrylic resins, styrene-acrylic resins, rosin-modified resins, phenolic resins, terpene resins, polyester resins, polyamide resins, epoxy resins, vinyl acetate resins, vinyl chloride resins, or cellulose acetate butyrate resins. Precursors are compounds suitable for producing the above resins, such as their monomers or corresponding oligomers. In this context, the polymers (fixative resins) and / or precursors in the composition may be present in a total amount of 0.05% to 15% by weight, especially 1% to 10% by weight, and particularly preferably 5% to 7% by weight, based on the total weight of the composition.

[0025] In one embodiment, it is contemplated that the polymer is a polyacrylate. In this embodiment, it may be contemplated that the precursor is an acrylate monomer or an acrylate oligomer.

[0026] Furthermore, according to the present invention, in embodiments in which the composition comprises a polymer and / or a precursor thereof, it can be envisaged that the composition further comprises a cross-linking agent suitable for cross-linking the polymer.

[0027] In another embodiment, it is contemplated that the composition further comprises a base. This may be particularly advantageous when a fixing resin containing carboxyl groups is used to neutralize the corresponding acid groups. Suitable basic compounds are, for example, inorganic bases such as sodium hydroxide, potassium hydroxide, or ammonia, or organic bases such as methylamine, ethylamine, ethanolamine, dimethylethanolamine, diethylethanolamine, dibutylethanolamine, diethylanolamine, triethanolamine, morpholine, etc.

[0028] In this case, the amount of base can be considered to be between 0.1 and 5% by weight relative to the total weight of the composition.

[0029] In another embodiment, it may be considered that the composition does not contain organic solvents. Organic solvents in the sense of the present invention are particularly volatile organic compounds (VOCs) and very volatile organic compounds (VVOCs). Organic solvents in the sense of the present invention are particularly polar organic solvents, i.e., solvents that are soluble in water. Organic solvents in the sense of the present invention (i.e., solvents that are not particularly contained in the composition) include, in particular, monoalcohols, polyalcohols, polyalcohols of lower alkyl ethers, ketones, ethers, esters, nitrogen-containing solvents, etc.

[0030] In another embodiment, it is contemplated that the composition according to the present invention does not contain an organic solvent and the ionic liquid is present in an amount greater than 5% by weight, based on the total weight of the composition.

[0031] Another embodiment contemplates that the composition is free of organic solvents and the ionic liquid is included in an amount of 5.5% to 20% by weight, based on the total weight of the composition.

[0032] The above problem is further solved by a method for printing a carrier by a digital printing method, comprising the steps of: a) providing a carrier; and b) printing the carrier by a digital printing method using the composition according to the present invention as an ink.

[0033] In this case, a plastic film may in particular be considered as a carrier according to the invention, 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 invention, and in which the composition according to the invention is used as ink, can be any digital printing method known from the prior art, for example ink jet printing.

[0035] Furthermore, the above problems are solved by using the composition as an ink in a digital printing method. [Example]

[0036] The present invention will be described below based on specific examples, but it goes without saying that the scope of protection is not limited to the specific examples.

[0037] Comparative Example A prior art ink composition was made by mixing the following ingredients: [Table A]

[0038] example An ink composition according to the present invention was prepared by mixing the following ingredients: [Table B]

[0039] The compositions according to the present invention (Examples) differ from the compositions according to the prior art (Comparative Examples) in that the organic solvent used according to the prior art (isopropyl alcohol) has been completely replaced by an ionic liquid (1-ethyl-3-methylimidazolium tetrafluoroborate).

[0040] The ink compositions according to the examples and the comparative examples were applied to plastic films by ink jet printing and subsequently tested for their adhesion and chemical resistance.

[0041] The ratings were made on the following scale: 5 = 100% = No coating damage 4 = 75% = slight coating damage 3 = 50% = obvious damage to the coating 2 = 25% = severe coating damage 1 = 0% = complete removal of coating

[0042] The following results were obtained for the various tests carried out: [Table 1]

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

[0044] Furthermore, the inventors observed a reduction of approximately 15% in the energy consumption of drying.

[0045] The features of the invention disclosed in the above description and in the claims may be essential both alone and in any combination for realizing the invention in various embodiments thereof.

Claims

1. 1. A method for printing a substrate by digital printing, comprising: a) providing a carrier; b) printing a substrate by digital printing using a composition, said composition comprising: each based on the total weight of the composition i) 50 to 98% by weight of water; ii) 1 to 49% by weight of an ionic liquid, and iii) 1 to 30% by weight of a pigment, dye, or mixture thereof; and a step comprising: the carrier is a plastic film, The digital printing method is an ink jet printing method. method.

2. The method of 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. 4. The method of any one of claims 1 to 3, wherein the composition further comprises one or more additives independently selected from the group consisting of binders, fillers, rheological additives, stabilizers, surfactants, preservatives, and humectants.

5. The method of any one of claims 1 to 4, wherein the composition further comprises a polymer, a precursor thereof, or a mixture of the polymer and the precursor.

6. 6. The method of claim 1, wherein the polymer is a polyacrylate.

7. The method of claim 1 , wherein the composition further comprises a base.

8. The method of claim 1 , wherein the composition is free of organic solvents.

9. 9. Use of a composition as defined in any one of claims 1 to 8 as an ink for printing plastic films by ink jet printing.