Primer for an aluminium surface

Abstract

A solvent-based priming varnish for application to an aluminium surface for subsequent application of a printed image with water-based inks by inkjet technology. In order to achieve a good printed image, it is envisaged that this contains i) amino resin, preferably of the amino-imino type, having methylol groups, etherified methylol groups and amino groups, ii) a mixture of a. a non-reactive polyester, b. a reactive polyester containing hydroxyl groups, iii) optionally a flatting agent, iv) optionally a surface additive, v) optionally a catalyst that catalyses the reaction of hydroxyl groups with methylol groups, etherified methylol groups and amino groups, or a mixture of such catalysts, vi) a mixture of solvents from the group of esters and ketones, viii) optionally a pigment, preferably a white pigment, based on TiO2.

Description

[0001] Primer for an aluminum surface

[0002] The disclosure described below relates to a printing primer for an aluminum surface and specifically to the problems that arise when water-soluble ink is applied to an aluminum surface using an inkjet printer. These problems particularly concern the ink running on the substrate and the resulting impossibility of obtaining a clean and neat print image. Such applications are increasingly in demand in the packaging sector, especially for food products.

[0003] The state of the art, mostly from the time before the invention of inkjet printing, includes the following:

[0004] From 1954, GB 800,479 discloses that, for printing on aluminum, a primer containing, among other ingredients, chromic acid, phosphoric acid, polyvinyl butyral, various alcohols, and citric acid should first be applied. A specific application for this primer is aluminum foil that has only been partially deoiled, requiring a certain degree of aggressiveness and degreasing. This primer is completely unsuitable for the purposes stated above.

[0005] US Pat. No. 2,889,233 from 1957 describes applying a vinyl resin to the surface of aluminum, and then applying a print with a vinyl resin-based ink to this vinyl resin coating, which at least partially dissolves the lower vinyl resin layer and achieves a particularly close bond between the print and the substrate. The final product is then cured in an oven. Due to the complexity and nature of the products, this process and the products used are unsuitable for use, for example, in printing aluminum foil for the food industry, especially for circuit boards.

[0006] The proposal from US Pat. No. 3,123,516 to use a coating consisting essentially of vinyl chloride, acetate copolymer, and a monolaurate as a primer for aluminum dates back to 1962. The cost and nature of the application make its use in connection with foodstuffs inadvisable. In 1963, DE 1 444 621 disclosed a reactive dye containing at least two chromogens without a water-soluble radical, at least two reactive radicals, and at least one soluble or dispersible radical. The complexity, cost, and the chemicals used make its use in the intended application impossible.

[0007] From 1965, GB 999,061 discloses an emulsion which is essentially based on a vinyl chloride resin and which is applied directly to the aluminium, apparently combining priming properties and printing properties at the same time.

[0008] Dating back to 1972, US Pat. No. 3,904,790 discloses a special polyamide that is particularly suitable as a primer for aluminum foil used with food. Since the application takes place in the form of a solution, the absolutely necessary subsequent drying step is costly in terms of space, energy, time, and thus money, and is not readily feasible. In addition, the resulting resin has a softening point of approximately 100°C, thus causing problems during sealing.

[0009] In 1974, GB 1,503,384, published in Great Britain in 1978, was introduced. It deals with a coating on aluminum that is supposed to exhibit particularly high reflectivity and corrosion resistance. The solution is the use of primarily a terpolymer of vinyl chloride, vinyl acetate, and maleic acid, with the addition of alkyl methacrylate and some other components that are unsuitable for the intended purpose in terms of price, processing, and properties.

[0010] In 1984, BASF's DE 34 22 216 specified a special coating agent, specifically a suitable binder, which consists of water-insoluble polycondensates (of phenols and aldehydes, or essentially contains them), whereby the polycondensation can be specifically controlled. This agent, too, is not suitable for use in the intended field due to costs and the nature of the components. EP 795 418, published in 1997, discloses a primer specifically for aluminum foil for blister packaging, which consists of conventional lacquers with an addition of 0.3 to 20 wt. % "fine-grained components," preferably highly dispersed silica. The claims describe the fine-grained component exclusively. This addition improves adhesion, even for laser-printing-like processes with low thermal energy.This is irrelevant for inkjet printing and the silica is not a practical component for the intended purpose due to its water solubility.

[0011] From JP 2012 / 04,1373 it is known to apply an acrylic resin to aluminum and fire it on; the resulting sandwich structure can subsequently be heavily deformed (embossed), which is irrelevant for the intended purpose.

[0012] Since 2013, a process has been disclosed in US 2013 / 0150509 in which various TSSS and TI SS-Be coatings are applied to copper or aluminum to obtain very specific reflection spectra. This, too, does not represent a model for the intended use.

[0013] WO / 2018030089, dating back to 2016, proposes a non-aqueous primer containing a chlorinated polyolefin resin and a ketone resin for non-absorbent substrates, which is largely unsuitable for the intended use.

[0014] EP 3 498 793, dating back to 2017, describes a primer generally for non-absorbent substrates. It contains a chlorinated polyolefin resin and a ketone resin, which must meet various constraints. The cost and composition make this product unsuitable for its intended purpose.

[0015] With a priority of 2019, US 2022 / 0025196 was published in 2022. It discloses an aqueous primer composition specifically designed for inkjet printing. The primer consists of a polyvalent metal salt contained in an aqueous solution and an amino-functionalized copolymer dispersed as an emulsion in the aqueous solution. This composition is also unsuitable for the intended application due to cost and the materials used.

[0016] There is therefore a need for a primer that enables aluminum surfaces to be printed using inkjet technology and achieve a visually flawless print image.

[0017] One solution to this problem is to use a solvent-based primer containing: i) amino resin, preferably as amino-imino type, which contains methylol groups, etherified methylol groups and amino groups ii) a mixture of a. a non-reactive polyester b. a hydroxyl-containing, reactive polyester iii) optionally a matting agent iv) optionally a surface additive v) optionally a catalyst which catalyzes the reaction of hydroxyl groups with methylol groups, etherified methylol groups and amino groups, or a mixture of such catalysts vi) a mixture of solvents from the group of esters and ketones vii) optionally a pigment, preferably a white pigment, based on TiO2.

[0018] A coating formulation is thus proposed that is based on at least one mixture of polyesters with an amino resin in organic solvents, preferably a mixture of esters and ketones. The binders are a mixture of a low- to medium- and high-molecular-weight polyester. The preferred amino resin is an amino-imino type, as listed below.

[0019] The amino resin acts as a crosslinker for the polyester binder. Both self-crosslinking and external crosslinking reactions occur. The former occur between the free NH groups and the methylol groups and etherified methylol groups of the neighboring amino resin molecules, releasing water or alcohol. External crosslinking occurs between the free hydroxy groups of the polyester blend and the methylol groups and etherified methylol groups, sometimes with the release of water or alcohol. This amino-imino resin type offers the possibility of formulating a low-formaldehyde coating. Other components that may be included are catalysts, surface additives, pigments, and matting agents.

[0020] A coating formulated in this way can be applied to an untreated aluminum surface using standard industrial coating processes with excellent adhesion properties. In contrast to untreated aluminum surfaces and those treated with other common technologies, the resulting surface is optimized for water-based ink applied using the inkjet process. The surface properties are largely determined by the combination of matting agent and surface additive.

[0021] For example, very good results are achieved with a pigment-free pre-print varnish formulation based on

[0022] 62.7% solvent,

[0023] 25.5% polyester binder,

[0024] 5% amino resin,

[0025] 4% surface additive,

[0026] 1.5% matting agent and

[0027] 1.3% catalyst all values ​​±2% achieved.

[0028] In the case of a pigmented paint formulation, the composition changes as follows:

[0029] 55.8% solvent,

[0030] 22.9% polyester binder,

[0031] 10% white pigment here TiÜ2,

[0032] 4.5% amino resin,

[0033] 4% surface additive,

[0034] 1.5% matting agent and

[0035] 1.3% catalyst, all values ​​±2%. In principle, the limits of the composition can be specified, with the limits included in each case:

[0036] Amino resin in the amount of 4-6%,

[0037] Mixture of polyesters in total in the amount of 22.5-28%,

[0038] Matting agents in the amount of 1-7%,

[0039] Surface additive in the amount of 0-4.5%,

[0040] Catalyst in the amount of 1-1.5%,

[0041] Solvents in total amount of 55-66% and

[0042] Pigment in the range of 0-14%

[0043] Lacquer I: colorless formulation

[0044] A solvent mixture, preferably consisting of ethyl acetate and methyl ethyl ketone, is placed in a container at room temperature in a ratio of approximately 0.54 (22% EA and 40.7% MEK; yields 0.54). Then, 12.5% ​​of a high-molecular-weight polyester, for example, Skybon ES 120 from IMCD Deutschland GmbH with a molecular weight of 28,000 g / mol, is added. Mixing the high-molecular-weight polyester into the solvent mixture has proven advantageous. The process then continues in the following order with continuous stirring: Add 13% of a medium-molecular-weight polyester, for example, Dynapol LH 826-05 / A from Evonik Operations GmbH, with a molecular weight of 6,000 g / mol. This is followed by the addition of 5% of an amino resin, for example, Maprenal MF 988 / 80B from Prefere Melamines GmbH. The polyether macromer-modified polyacrylate as a surface additive, for example Byk 3560 from Byk-Chemie GmbH, is added at 4%.Next, 1.5% of a matting agent is added, for example, Syloid 244 from Grace GmbH with a d50 value of 3 lpm and an oil absorption of 300g / 100g. Finally, 1.3% of a catalyst solution, for example, Cycat 600 from Allnex Austria GmbH, is added. The values ​​are given in percent by weight.

[0045] Lacquer II: pigmented formulation

[0046] A solvent mixture of preferably ethyl acetate and methyl ethyl ketone is placed in a container at room temperature in a ratio of approximately 0.6 (21% EA and 34.8% MEK; yields 0.6). Then, 11.5% of a high-molecular-weight polyester, such as Skybon ES 120 from IMCD Deutschland GmbH with a molecular weight of 28,000 g / mol, is added. Mixing the high-molecular-weight polyester into the solvent mixture has proven advantageous. The white pigment, such as Kronos 2066 from Kronos International, Inc., is then added and ground to a grain size of less than 10 μm and greater than 5 μm. The temperature should not exceed 60°C. The process then continues in the following sequence with continuous stirring: Addition of 11.4% of the medium molecular weight polyester, for example Dynapol LH 826-05 / A from Evonik Operations GmbH, with a molecular weight of 6000 g / mol.Next, 4.5% of the amino resin, Maprenal MF 988 / 80B from Prefere Melamines GmbH, is added. A polyether macromer-modified polyacrylate surface additive, such as Byk 3560 from Byk-Chemie GmbH, is added at 4%. A 1.5% matting agent, such as Syloid 244 from Grace GmbH with a d50 value of 3 lpm and an oil absorption of 300g / 100g, is added. 1.3% of the catalyst solution, such as Cycat 600 from Allnex Austria GmbH, is added. The values ​​are given in percent by weight.

[0047] The described paints can be applied in an even layer to aluminum using a roller application. The colorless paint with a grammage of 2.5g / m 2 ± 0.7g / m 2 and the pigmented varnish with 2.5g / m 2 ± 0.5g / m 2The applied colorless or pigmented coating film is preferably processed at a baking temperature of 100°C and a belt speed of 180 m / s.

[0048] Examples are listed in the two tables below. The percentages given are by mass and are accurate to ±2%. The right-hand side of the first column indicates the assignment to the above list, from i) to vi) or vii).

[0049] General:

[0050] The high-molecular-weight polyester should expediently have a hydroxyl number of 0-6 mg KOH / g, preferably 3 mg KOH / g. The average molar mass of the high-molecular-weight polyester should be between 15,000 and 35,000 g / mol, preferably between 20,000 and 30,000 g / mol, and particularly preferably between 25,000 and 28,000 g / mol. The glass transition temperature Tg should be between 60-80°C and preferably between 65-70°C. The low- to medium-molecular-weight polyester should expediently have a hydroxyl number of 15-40 mg KOH / g, preferably 20-35 mg KOH / g. The average molar mass of the low- to medium-molecular-weight polyester should be between 3,000-9,000 g / mol, and particularly preferably between 4,000 and 6,000 g / mol. The glass transition temperature Tg should be between 20-40°C and preferably 30°C.

[0051] The amino resin should preferably have a reactivity of 4 per molecular unit and preferably have methylol groups etherified with butanol.

[0052] The matting agent should have a suitable average particle size d50 of 3-12 μm, preferably 3-6 μm, and particularly preferably 3 μm. The oil absorption should suitably be between 10-400 g / 100 g, preferably 200-300 g / 100 g, and particularly preferably 300 g / 100 g.

[0053] The mass ratio in the mixture of the non-reactive polyester to the hydroxyl group-containing, reactive polyester is preferably from 0.8 to 1.2.

[0054] The mass ratio in the mixture of ester to ketone is preferably from 0.5 to 0.85.

[0055] Regarding the surface additive and catalyst, it can be said that, with knowledge of the disclosure, it is easy for the person skilled in the art to make the appropriate selection from the range on offer.

[0056] All percentages stated in the disclosure, tables, and claims are by mass unless otherwise stated and are accurate to ±2%. For values ​​such as 12.3%±2%, this does not mean 10.3-14.3%, but rather 12.054-12.546%. Table I: Colorless formulations Table II: pigmented formulations

[0057] Compound A: Dynapol LH 826-05 / A, medium molecular weight 6000 g / mol

[0058] Compound B: Dynapol LH 773, low molecular weight, 4000 g / mol

[0059] Compound C: Byk 3560

[0060] Compound D: Byk 3440

[0061] The following applies to amino resins in principle:

[0062] Maprenal MF988 / 80B is described in the English data sheet as “Imino type, highly reactive n-butylated benzoguanamine-formaldehyde resin”, with the structural formula For the purposes of disclosure and the protection sought when using this resin, the structure specified in the data sheet is the one to be applied.

[0063] Other suitable amino resins are CYMEL 659 resin or CYMEL 5010 resin, which, according to the English data sheet, are "partly n-butylated benzoguanamine resin(s)." The structure is not specified, but it can be assumed that they also have an amino-imino structure.

[0064] If necessary, further additives can be added to the composition, in particular pigments / pigment mixtures with other colors. Those skilled in the art of printing technology and priming, with knowledge of the invention and the respective applications / requirements, will readily be able to make the appropriate selection from the state of the art for such additives.

[0065] The disclosure also relates to an aluminum surface which is provided with a primer of the type described and on which a printed image made of water-based inks has been applied by means of ink-jet technology.

[0066] Effect:

[0067] The present disclosure offers the solution of modifying / coating an aluminum surface so that it can be printed with water-based inks using the inkjet process. The print quality meets standard market requirements and even exceeds the print quality of the commonly used gravure printing process. Furthermore, the present disclosure can easily meet the required level of technical properties.

Claims

Patent claims:

1. Solvent-based printing pre-coat for application to an aluminum surface, characterized in that it contains i) amino resin, preferably of the amino-imino type, which has methylol groups, etherified methylol groups and amino groups, ii) a mixture of a. a non-reactive polyester b. a hydroxyl-containing reactive polyester iii) optionally a matting agent iv) optionally a surface additive v) optionally a catalyst which catalyzes the reaction of hydroxyl groups with methylol groups, etherified methylol groups and amino groups, or a mixture of such catalysts, vi) a mixture of solvents from the group of esters and ketones vii) optionally a pigment, preferably a white pigment based on TiO2.

2. Printing undercoat according to claim 1, characterized in that it contains, based on the total mass, i) to the extent of 4-6%, ii) in total to the extent of 22.5-28%, iii) to the extent of 1-7%, iv) to the extent of 0-4.5%, v) to the extent of 1-1.5%, vi) in total to the extent of 55-66% and vii) to the extent of 0-14%, the limit values ​​in each case included.

3. Printing pre-lacquer according to claim 1 or 2, characterized in that the mass ratio in the mixture ii) of the non-reactive polyester to the hydroxyl group-containing, reactive polyester is from 0.8 to 1.

2.

4. Printing undercoat according to one of claims 1 to 3, characterized in that the mass ratio in the mixture vi) of the ester to the ketone is from 0.5 to 0.

85.

5. An aluminium surface on which a printing undercoat according to one of claims 1 to 4 is applied, characterized in that a print image made of water-based Colors were applied using ink-jet technology.

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