WO2021110210A1 - Use of ionic liquids in primer composition - Google Patents

Abstract

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

Description

Use of ionic liquids in primer composition

Field of invention

The present invention relates to a primer composition and the use thereof in the production of a primer layer on a carrier in preparation for a digital printing process.

Background of the invention

For printing on plastic films, digital printing processes have become increasingly established in addition to printing form-related printing processes (in particular flexographic printing, gravure and offset printing), in which the printing ink is applied to the film without a printing form - for example using the inkjet process. Water-soluble printing inks can also be used in all printing processes, as is particularly advantageous when printing food packaging.

Plastic films, for example made of polypropylene (PP) or polyethylene (PE), basically have a non-polar property, which makes printing with water-soluble and therefore polar ink difficult. Primer ”) on the film surface can be improved. Even with a primer, however, it is often necessary to subsequently dry the water-based ink afterwards, in order to remove the volatile constituents from the ink by means of evaporation or convection. Prior art water-based primer compositions for the production of primers, ie communication layers, comprise not only water but also substantial amounts of low-boiling organic solvents (VOC, volatile organic compounds), usually in amounts of about 20-50% by weight. These VOCs are released during the production of the primer layer or the subsequent drying. The following problems arise, for example.

For one thing, VOCs are often harmful to health. In particular in mass production, this results in problems due to high VOC emissions at the workplace. In addition, the release of VOCs can lead to the formation of explosive and / or flammable mixtures. Finally, there is a need for improvement of corresponding products that comprise a corresponding primer layer with regard to adhesion and chemical resistance.

It is therefore the object of the present invention to provide a primer composition which overcomes the disadvantages of the prior art, in particular to provide a primer composition for the preparation of an inkjet printing process in which the amount of VOCs is reduced or which is VOC-free.

Overview of the invention

This problem is solved by the subject matter of the independent claims. Preferred embodiments emerge from the subclaims.

The object on which the invention is based is achieved in particular by a primer composition comprising: a) 50-97.5% by weight of water; b) 1-48.5% by weight of an ionic liquid; c) 1-30% by weight of an inorganic oxide, a polymer compound, or a mixture of 2 or more thereof; and d) 0.5-10% by weight of a polar organic compound; each based on the total weight of the primer composition.

Surprisingly, it was found by the inventors that low-boiling organic solvents (VOCs) in primer compositions for the preparation of a digital printing process can be partially or completely replaced by ionic liquids. It was found that the use of ionic liquids instead of VOCs not only solves problems associated with the emission of VOCs, but that further advantages can also be achieved. In particular, it was found that the composition according to the invention allows the production of printed products with improved adhesion and chemical resistance of the primer layer.

The primer composition according to the invention is an aqueous primer composition. The primer composition can be used in preparation for a digital printing process. In this context, the preparation of a digital printing process is in particular the application of a primer layer to a carrier in order to facilitate the printing of the carrier in the digital printing process, e.g. in the inkjet printing process using a suitable ink composition, in particular to improve the adhesion of the ink to the carrier. The aqueous primer composition comprises at least 50% by weight of water, based on the total weight of the composition. Alternatively, it can be provided that the aqueous primer composition contains at least 60% by weight of water, alternatively at least 70% by weight, in each case with regard to the total weight of the composition. It can be provided that the primer composition contains water in an amount of at most 95% by weight, alternatively at most 90% by weight, alternatively at most 85% by weight, alternatively at most 80% by weight, each based on the total weight of the Primer composition contains.

It can be provided that the ionic liquid is present 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 is contained in the primer composition It can also be provided that the ionic liquid in the primer composition is at most 45% by weight, alternatively at most 40% by weight, alternatively at most 30% by weight , alternatively a maximum of 20% by weight, alternatively a maximum of 10% by weight, alternatively a maximum of 8% by weight. The percentages relate in each case to the total weight of the primer composition.

It can also be provided that the inorganic oxide, the polymer compound or the mixture of two or more thereof in a total amount of at least 2% by weight, alternatively at least 4% by weight, alternatively at least 8% by weight, alternatively at least 10% by weight % By weight is contained in the primer composition. It can also be provided that the inorganic oxide, the polymer compound or the mixture of two or more thereof in a total amount of at most 25% by weight, alternatively at most 20% by weight, alternatively at most 17.5% by weight, alternatively at most 15% by weight is contained in the primer composition. The percentages here relate in each case to the total weight of the primer composition.

An ionic liquid is an ionic compound (salt) comprising one or more anions and one or more cations, preferably an anion and a cation, which is preferably at a temperature of 200 ° C. or less, preferably 150 ° C. or less, moreover 100 ° C or less, is liquid without the salt being dissolved in a solvent such as water. According to the invention, it can be provided here that the ionic liquid has a melting point which is above 60 ° C. Ionic liquids are completely miscible with water. Ionic liquids have no (measurable) vapor pressure, so they are not released into the gas phase even at high temperatures.

Exemplary cations that can be contained in the ionic liquid according to the invention are in particular imidazolium, pyridinium, pyrrolidinium, phosphonium, ammonium, guanidinium, uronium or thiouronium. These cations are preferably alkylated cations. Anions according to the invention are, for example, halides and more complex ions such as tetralfluoroborates, trifluoroacetate, triflate, hexafluorophosphate, phosphinate and tosylate. Organic anions, for example imides or amides, can also be provided. Preferred anions are I-, Cl-, Br-, SCN-, BF ₄ -, PF ₆ -, ClO ₄ -, SbF ₆ - (CF ₃ S0 ₂ ) ₂ N-, (CF ₃ CF ₂ S0 _a ) _z N -, Ph ₄ B-, (C ₂ H ₄ O ₂ B-, (CF ₃ SO ₂ ) ₃ C-, CF ₃ COO-, CF ₃ SO ₃ -. C ₆ F ₅ SO ₃ - and MeO (EtO) ₂ SO ₃ -.

wobei R¹ und R² unabhängig voneinander ausgewählt sind aus der Gruppe bestehend aus C₁-C₈-Alkyl, vorzugsweise C₁-C₆-Alkyl, vorzugsweise C₁-C₄-Alkyl, besonders bevorzugt C₁-C₃-Alkyl am meisten bevorzugt C₁-C₂-Alkyl. In one embodiment the ionic liquid is an imidazonium salt. It can be provided here that the imidazolium is a dialkylimidazolium of the following formula

where R ¹ and R ^{2 are} independently selected from the group consisting of C ₁ -C ₈ -alkyl, preferably C ₁ -C ₆ -alkyl, preferably C ₁ -C ₄ -alkyl, particularly preferably C ₁ -C ₃ -alkyl most preferably C ₁ -C ₂ alkyl.

In one embodiment it is provided that the cation of the ionic liquid is 1-ethyl-3-methylimidazolium (R ¹ = methyl and R ⁸ = ethyl).

In a further embodiment it is provided that the ionic liquid is 1-ethyl-3-methylimidazoUum tetrafluoroborate. It can be provided that the inorganic oxide is a colloidal inorganic oxide. It can also be provided that the polymer compound is in the form of a colloid. For the purposes of the present disclosure, a colloid is a finely divided substance that is in the form of discrete particles. According to the invention it can be provided that the inorganic oxide or the polymer compound is present in the form of particles. It can be provided here that the BET surface area of the particles, determined in accordance with DIN ISO 5794/1 Annex D with Na, is from 10 to 550 m ² / g, preferably 25 to 350 m ² / g. It can also be provided that the particles of the inorganic oxide / polymer compound have an average particle diameter of from 2 to 20 μm, preferably from 5 to 20 μm. Reference is made here to an average particle diameter determined by means of a Coulter Counter, Model TA Π from Coulter Electronics, determined using the 100 μm capillary.

In one embodiment it can be provided that 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 a mixture of two or more thereof, preferably Silicon dioxide.

It is particularly preferred that the inorganic oxide is precipitated silica, i.e. precipitated silica is precipitated silica (precipitated silicon dioxide) is an amorphous form of silicon dioxide in the form of a white, powdery material, obtainable by precipitation from a solution containing silicate. Precipitated silica is produced in particular by condensation of silica from dilute alkali silicate solutions

The polymer compound can in particular be a colloidal polymer material. It can be provided that this is a hydrophilic colloidal material that comprises a water-soluble polymer. According to the invention it can be provided that the polymer compound, which can be present in the form of a colloidal material, is one or more selected from polyvinyl compounds, some polyvinyl alcohol, polyacrylamide, Polymethacrylamide, poly (N, N-dimethylacrylamide), poly (n-isopropylacrylamide),

Poly (vinylpyrrolidone), poly (vinyl acetate), polyacrylate, polyurethane, gelatin, dextran, rubber etc.

It can be provided that the polar organic compound comprises two to 18 carbon atoms, preferably two to ten carbon atoms, more preferably two to six carbon atoms, particularly preferably 4 carbon atoms.

It can further be provided that the polar inorganic compound comprises at least one carboxyl group.

It can also be provided that the polar organic compound comprises two carboxyl groups.

Furthermore, it can be provided that the polar organic compound _{comprises further polar functional groups, preferably selected from -OH, -NH 2} , -C (= O) H, -C (= O) R, -SH, etc.

In addition, it can preferably be provided that the polar organic compound is tartaric acid.

In a further embodiment it can be provided that the primer composition contains an organic solvent in an amount of 10% by weight or less, based on the total weight of the primer composition. In a further embodiment it can be provided that the primer composition comprises organic solvent in an amount of 5% by weight or less.

Organic solvents in the context of the invention are in particular volatile organic compounds (VOC) and very volatile organic compounds (VVOC). Organic solvents for the purposes of the present invention are, in particular, polar organic solvents, i.e. solvents that are soluble in water. Organic solvents within the meaning of the present invention (i.e. solvents which are preferably not contained in the composition or only in small amounts, ie in an amount of 5% by weight or less) include in particular DMSO, monoalcohols, polyalcohols, polyalcohols of lower alkyl ethers , Ketones, ethers, esters, nitrogen-containing solvents etc.

In a further embodiment it is provided that the primer composition according to the invention comprises no organic solvent or only in an amount of 5% by weight or less, based on the total weight, and the ionic liquid in an amount of at least 5% by weight based on the total weight of the composition

The object is also achieved by a method for printing a carrier using the digital printing process, comprising: a) providing the carrier; b) applying a primer layer to at least one surface of the carrier using the primer compositions according to one of the preceding claims; and c) printing the carrier in the digital printing process on the at least one surface which is coated with the primer layer

A plastic film can in particular be provided as the carrier according to the invention. In one embodiment, the plastic film is a film made of polyethylene, polypropylene or mixtures thereof. The digital printing process which is used in the process according to the invention, as well as the process in which the composition according to the invention is used as ink, can be any digital printing process known from the prior art, for example an inkjet printing process.

Finally, the object is achieved by the use of the primer composition according to the invention for producing a primer layer on a carrier for the preparation of a digital printing process.

Working examples

In the following, the invention will be described on the basis of specific exemplary embodiments, the scope of the boot being of course not limited to the specific exemplary embodiments.

Comparative example

A prior art primer composition was prepared by mixing the following ingredients.

Water 74.5 mass%

DMSO 10 mass%

Precipitated silica 12.5% by mass 2,3-dihydroxybutanedioic acid 3% by mass 1,2-benzoisothiazolin-3-one 0.2% by mass example

A primer composition according to the present invention was prepared by mixing the following ingredients.

Water 74.5 mass%

DMSO 5 mass%

Ethylmethylimidazole BF ₄ (emimbf ₄ ) 5% by mass precipitated silica 12.5% by mass 2,3-dihydroxybutanedioic acid 3% by mass 1,2-benzoisothiazolin-3-one 0.2% by mass

The primer composition according to the invention (example) differs from the primer composition according to the prior art (comparative example) in that the organic solvent (DMSO) used in large quantities according to the prior art is partially replaced by an ionic liquid (1-ethyl-3- methylimidazolium tetrafluoroborate) was replaced.

The primer compositions according to the example and according to the comparative example were applied to a plastic film in preparation for an inkjet print and then tested for their adhesion and chemical resistance.

The assessment is based on the following scale:

5 100% no damage to the coating

4 75% minor damage to the coating

3 50% significant damage to the coating

2 25% severe damage to the coating

1 0% complete peeling of the coating

The following results were obtained for the various tests carried out.

Table 1:

As is apparent from Table 1, the resulting (partial) replacement of VOC _s by ionic liquids in primer compositions for the preparation of digital printing to significant improvements in adhesion of up to 40%. An improved chemical resistance can also be achieved. In addition, the inventors found a reduction in the energy consumption of drying of about 15%.

The features of the invention disclosed in the above description and in the claims can be essential both individually and in any combination for the implementation of the invention in its various embodiments.

Claims

Expectations 1. A primer composition comprising: a) 50-97.5 wt% water; b) 1-48.5% by weight of an ionic liquid; c) 1-30% by weight of an inorganic oxide, a polymer compound, or a mixture of 2 or more thereof; and d) 0.5-10% by weight of a polar organic compound, the polar organic compound having two carboxyl groups and further polar functional groups, preferably selected from -OH, -NH ₂ , - C (= O) H, -C (= O) R, -SH, comprises; each based on the total weight of the primer composition. 2. The primer composition of claim 1, wherein the ionic liquid is a.

3. Primer composition according to claim 1 or 2, wherein the ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate 4. Primer composition according to one of the preceding claims, wherein the inorganic oxide is a colloidal inorganic oxide 5- primer composition according to any one of the preceding claims, 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 a mixture of two or more thereof . 6. Primer composition according to one of the preceding claims, wherein the inorganic oxide is precipitated silica 7. Primer composition according to one of the preceding claims, wherein the polar organic compound is tartaric acid 8. Use of a composition according to any one of claims 1 to 7 as a primer coating on a carrier in preparation for a digital printing process. 9. A method for printing a carrier in the digital printing process comprising: a) providing the carrier; b) applying a primer layer to at least one surface of the carrier using a primer composition, wherein the primer composition comprises: i) 50-97.5 wt% water; ii) 1-48.5% by weight of an ionic liquid; iii) 1-30% by weight of an inorganic oxide, a polymer compound, or a mixture of 2 or more thereof; and iv) 0.5-10% by weight of a polar organic compound; each based on the total weight of the primer composition; c) printing of the carrier in the digital printing process on the at least one surface which is coated with the primer layer. 10. The method of claim 9, wherein the ionic liquid is an imidazolium salt. 11. The method according to claim 9 or 10, wherein the ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate. 12. The method according to any one of claims 9 to 11, wherein the inorganic oxide is a colloidal inorganic oxide. 13. The method according to any one of claims 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 a mixture of two or more thereof. 14- The method according to any one of claims 9 to 13, wherein the inorganic oxide is precipitated silica. 15. The method according to any one of claims 9 to 14, wherein the polar inorganic compound comprises at least one carboxyl group. 16. The method according to any one of claims 9 to 15, wherein the polar organic compound is tartaric acid.