Aqueous dispersion for the repair coating of non-polar surfaces and method for the repair coating

Abstract

The present invention relates to the repair coating of non-polar surfaces, in particular lacquered metal surfaces, by means of an aqueous dispersion of a polyurethane resin applied by spraying. The aqueous dispersion according to the invention has optimal wetting properties and good sprayability, so that its use for repair coating is ensured even with large quantities and a consistently high throughput. For this purpose, the dispersion according to the invention contains a polyurethane resin comprising acid groups, a non-ionic or anionic organic surfactant and a substrate wetting agent. In a further aspect, the invention also relates to a method for repair coating using the aqueous dispersion.

Description

New PCT applicationValspar Industries GmbH;SYNTHOPOL CHEMIE Dr. rer. pol. Koch GmbH & CO. KG Vossius Ref.: AK1688 PCTAQUEOUS DISPERSION FOR THE REPAIR COATING OF NON-POLAR SURFACES AND METHOD FOR THE REPAIR COATING

[0001] The present invention relates to the repair coating of non-polar surfaces, 5 in particular lacquered metal surfaces, by means of an aqueous dispersion of a polyurethane resin applied by spraying. The aqueous dispersion according to the invention has optimal wetting properties and good sprayability, so that its use for repair coating is ensured even with large quantities and a consistently high throughput. For this purpose, the dispersion according to the invention contains a 10 polyurethane resin comprising acid groups, a non-ionic or anionic organic surfactant and a substrate wetting agent. In a further aspect, the invention also relates to a method for repair coating using the aqueous dispersion.

[0002] Lacquered sheet metal containers are used in a variety of ways in the 15 food packaging end consumer industries. A material that is used almost ubiquitously for food packaging is tinplate, i.e., tinned sheet steel, and tin free steel. While the inner surfaces of a tinplate packaging that come into direct contact with the food are lacquered to preserve the food's typical aroma, the outer surfaces are given a printable lacquer to allow the packaging to be 20 designed according to the food manufacturer's wishes. Both the inner and outer coating must be capable of regular sterilization, i.e., they must have sufficient adhesion to the metallic packaging material under the selected sterilization conditions because otherwise undesirable changes in the taste of the food will occur and corrosive processes will cause tarnishing of the surface 25 and adversely affect the aesthetically high-quality impression of the packaged goods. Many current packaging coatings contain mobile or bound bisphenol A ("BPA") or aromatic glycidyl ether compounds or PVC compounds. Although the balance of scientific evidence available to date indicates that the small trace amounts of these compounds that might be released from 30 existing coatings does not pose any health risks to humans, some of these compounds are nevertheless perceived by some people as being potentially harmful to human health. From the foregoing, it will be appreciated that whatis needed in the art is a packaging container (e.g., a food or beverage can) that is coated with a composition that does not contain extractible quantities of such compounds.

[0003] To increase convenience for the end consumer, metal packaging with pre-cut openings has now become established in the trade, making it much easier for the consumer to remove the food. For this purpose, cans often have a circular notch in the lid, which is connected to the can cylinder by flanging, said notch running close to the flanging, along which notch the can lid sheet can be easily and completely removed with the help of a tear-off tab. Industrially, the can lid material is manufactured from pre-coated strip material by punching and pressing, with the pre-stamped opening being created in the process, so that at the notch point the sheet thickness of the tear-off can lid is reduced as desired, but at the same time the coating with the can lid lacquer is damaged. This in turn requires post-treatment of the tinplate cans, during which, for cost reasons, a new coat of lacquer is ideally only applied in the region of the notch. Without a repair coating, the can lid lacquer in the region of the notch on the tinplate would be corroded after the sterilization treatment and the aesthetic impression would be impaired to an extent that would be unacceptable to the end consumer.

[0004] In the prior art, the repair coating is carried out by applying a solventbased or solvent-containing lacquer in the region of the can lid notch and, due to the required high throughput in terms of unit numbers, this is almost exclusively done by spray application. The essential property of the lacquer is therefore its sprayability. Likewise, for a uniform film formation of the repair lacquer in the baking stage during the production of such can lids, it is essential that the repair lacquer completely wets the can lid surface, particularly in the region of the notch, immediately after the lacquer has been applied; i.e. , by spreading the liquid drops applied by spraying, a continuous film of the repair lacquer is formed in fractions of a second, which lacquer also penetrates as completely as possible into the region of the lacquer defect to be repaired. When curing the repair lacquer applied to the can lid,it is also important to keep energy consumption low and to achieve a low baking temperature for film formation and curing of the repair lacquer. Low baking temperatures are specifically required in order to not damage the can sealant which in most cases is already applied into the channel of the can lid and is typically sensitive to higher temperatures such as 150°C. In the prior art, such lacquer properties have so far been set by a suitable selection of volatile solvents and hardeners for the mostly epoxy-based binder system. The rapid curing is then achieved by means of hardeners that crosslink sufficiently with the binder system at the lowest possible curing temperatures already mentioned. Binders and hardeners of a repair lacquer, if already mixed for application, therefore have only a short processing time, which must be taken into account when the plant is down and then requires immediate cleaning of the application equipment, for example spray nozzles. An additional common function of the repair coating for some applications is to further cover and protect potential coating damages at the rivet of the tab. Therefore, the spray coating is typically sprayed at a wider range to also cover the full rivet. Moreover, the repair coating needs to be transparent after application so that the decoration of can end lids are not damaged.

[0005] Compared to the prior art, the present invention has the task of establishing a water-based and largely solvent-free repair lacquer, which nevertheless has high wetting properties, has a comparatively long processing time, and can nevertheless be fully cured at the usually desired baking temperatures of less than 160°C, ideally less than 130°C. Although water-based coatings usually show low tendency to wet non-polar surfaces, the repair lacquer must be able to penetrate into and completely fill the defect region, which in the aforementioned tear-open can lid production preferably represents a groove-shaped depression, usually less than 1 millimeter wide, in the lacquered metal surface.Moreover, the inventive aqueous dispersion for example used as a repair coating also exhibits good adhesion to a variety of external coatingchemistries, including after processing conditions (e.g., elevated temperature and pressure sterilization procedures) which packed food cans are routinely subject to. The adhesion to not only metal but the exterior coating that is being “repaired” is important. And, moreover, it needs to exhibit such adhesion across a wide variety of different exterior coating chemistries that may be utilized (e.g., epoxy, acrylic, polyester, etc.).

[0006] Brief description of the drawingFigure 1 is a schematic drawing showing a cross-sectional view of a substrate (1 ), such as a can lid, comprising a non-polar surface (2), such as a lacquered metal surface. In Figure 1 , a defect region in the form of a score line (3) in the non-polar surface (2) and the substrate (1 ) is shown. The repair lacquer shown as a drop (4) needs to penetrate into and completely fill the defect region. Figure 1 shows the situation prior to completely filling the defect region.

[0007] The present invention solves this problem by providing an aqueous dispersion for the repair coating of non-polar surfaces in spray methods (hereinafter also referred to as “repair lacquer”), which dispersion has a solids content according to DIN EN ISO 3251 of at least 10.0 wt.% and contains(A) at least one water-dispersed polyurethane resin selected from polyurethane resins having an acid number of at least 5 mg KOH per gram,(B) at least one hardener dissolved in water selected from organic compounds having at least one carbodiimide group,(C) at least one non-ionic or anionic surfactant, preferably an anionic surfactant, selected from organic compounds having a molecular weight of less than 1000 g / mol, and(D) at least one substrate wetting agent which is not an organic compound according to component (C).

[0008] In a further aspect, the present invention then relates to a method for the repair coating of a lacquered metal surface which, in at least one region of the lacquering, has a defect which consists in the fact that the lacquer layerthickness is at least reduced compared to the lacquer layer thickness realized outside this defect region, in which method, in order to increase the lacquer layer thickness in the defect region, an aqueous dispersion according to the invention is applied at least there as a wet film and then dried (hereinafter also referred to as “repair coating method”). The repair lacquers preferred according to the invention, which are specified in more detail below, represent analogously preferred embodiments in the repair coating method according to the invention using these repair lacquers.

[0009] The solids content of the repair lacquer according to the invention in accordance with DIN EN ISO 3251 is at least 10.0 wt.%, preferably at least 15.0 wt.%, more preferably at least 18.0 wt.%, based on the repair lacquer, for a sufficient layer weight in the defect region to be repaired after film formation and curing of the lacquer film. Because the repair lacquer is preferably to be applied by spraying, as is usual in the production of tear-off can lids, and the high throughput rates required in this case require that a volume of liquid sufficient for the repair must be sprayed onto the can lid within fractions of a second, it is advantageous and therefore preferred if the viscosity of the lacquer is kept low and the solids content of the repair lacquer is below 30.0 wt.%, particularly preferably below 25.0 wt.%, especially preferably below 20.0 wt.%. In this context, it is advantageous and therefore preferred if the repair lacquer has a dynamic viscosity below 200 mPas’1, particularly preferably below 120 mPas’1, particularly preferably below 80 mPas-1, each measured according to Brookfield with spindle 2 at a shear rate of 60 rpm (rounds per minute).

[0010] According to the invention, the repair lacquer is provided as an aqueous dispersion. The term “aqueous (or water-based) dispersion” means that the dispersion contains water as major component. The dispersion contains preferably more than 50 wt.% water, more preferably at least 55 wt.% water and still more preferably at least 58 wt.% water. Such a dispersion is present when the solids content of the lacquer, in particular the polyurethane resin according tocomponent (A), is at least partially dispersed in the continuous water-based phase. In this context, it has proven advantageous for a good film formation of the resin components and for the penetration of said components into the defect region of the lacquered metal surface to be healed if the aqueous dispersion, preferably the polyurethane resin dispersed in water according to component (A), has a D90 value of less than 1.00 pm, particularly preferably less than 0.50 pm, especially preferably less than 0.25 pm. In the context of the present invention, the D90 value refers to the particle diameter which 90 vol.% of the particulate components contained in the aqueous dispersion do not exceed. The D90 value can be determined according to ISO 13320:2009 by means of light scattering analysis according to the Mie theory from volume-weighted cumulative particle size distributions immediately after dilution of the dispersion to a solids content of 1 .0 wt.% with an appropriate amount of deionized water (K < 1 pScnr1) at 20°C, assuming spherical particles.

[0011] The repair lacquer according to the invention is preferably adjusted via the amount of the at least one substrate wetting agent according to component (D) which is not a surfactant in the sense of component (C) such that the repair lacquer has a static surface tension of less than 30.0 mNnr1, particularly preferably less than 25.0 mNnr1, most preferably less than 22.0 mNnr1, measured by the platinum ring method at 20°C. For this purpose, the amount of at least one non-ionic surfactant according to component (C) in the aqueous dispersion is preferably above its critical micelle formation concentration. This allows all non-polar surfaces to be sufficiently wetted and, in the context of the repair coating method, ensures that a lacquered metal surface, or in particular a coated tinplate can lid, can be successfully recoated in the defect region or in the region of the tear notch.

[0012] The repair lacquer according to the invention is preferably adjusted via the amount of at least one surfactant according to component (C) which is not a substrate wetting agent in the sense of component (D) such that the repair lacquer has a dynamic surface tension of less than 45.0 mNnr1,particularly preferably less than 40.0 mNm-1, particularly preferably less than 35.0 mNm’1, measured by bubble pressure tensiometer at 20°C and a surface age of 0.030 seconds. In this way, it is achieved that a liquid film of the repair lacquer applied by spraying experiences its maximum spreading, determined by the static surface tension and the lacquered metal surface, in fractions of a second, so that penetration of the repair lacquer in its original composition into the defect region to be healed is ensured before the thermal treatment of the lacquered metal surface provided with the repair lacquer.

[0013] In the following, preferred embodiments of the repair lacquer according to the invention are explained and introduced with reference to the individual mandatory components (A)-(D).Component (A) - polyurethane resin

[0014] As already mentioned, the solid content of the repair lacquer is at least 10 wt.%. This solids content is essentially carried by components (A) and (B), wherein for a sufficient amount of the binder consisting of the polyurethane resins according to component (A), these are preferably contained in the repair lacquer in a proportion of at least 4 wt.%, preferably at least 8 wt.%, particularly preferably at least 12 wt.%, based on said repair lacquer. For the reasons already mentioned here of the need to provide sprayable repair lacquers with high stability compared to agglomeration of the particulate components, preferred upper limits of preferably 30 wt.% and particularly preferably 20 wt.%, in each case based on the repair lacquer, also result for the proportion of polyurethane resins in component (A).

[0015] According to the invention, the polyurethane resin present in dispersed form in the repair lacquer has an acid number of at least 5 mg KOH per gram of resin. On the one hand, the acid groups are necessary for good dispersibility and thus stability of the repair lacquer and, on the other hand, the acid groups allow crosslinking with the hardener comprising carbodiimide groups and thus thecuring of the repair lacquer applied to the defect region and already formed as a film during the baking process. In order to further improve the stability of the lacquer and to further support its rapid curing, it is preferred if the polyurethane resin has an acid number of at least 8 mg KOH per gram, preferably of at least 10 mg KOH per gram, in each case based on the resin. Higher acid numbers can be detrimental to the barrier properties of the cured repair lacquer, which in turn allows the migration of corrosive salts dissolved in water into the repair lacquer and the transport thereof to the metal surface in the actually healed defect region of the lacquered metal surface, so that corrosion phenomena, such as discoloration of the metal surface, can occur there despite the repair lacquer coating. Consequently, the proportion of acid groups is advantageously reduced to the required level and it is therefore preferred if the at least one polyurethane resin of the repair lacquer according to the invention has an acid number not above 30 mg KOH per gram, particularly preferably not above 24 mg KOH per gram, especially preferably not above 24 mg KOH per gram, in each case based on the resin. The acid number is determined according to DIN EN ISO 2114.

[0016] The main field of application of the repair lacquers according to the invention is in the food packaging market segment. In this context, for food hygiene reasons, it is preferable to avoid polyurethanes made from aromatic isocyanates or aromatic polyols. According to the invention, it is therefore preferred if the dispersed polyurethane resin is selected from aliphatic polyurethane resins, in turn preferably from those aliphatic polyurethane resins which are available on the basis of aliphatic polyether polyols, aliphatic polyester polyols, aliphatic polycarbonate diols and / or aliphatic polyoxyalkylene-modified alkane diols, particularly preferably on the basis of aliphatic polycarbonate diols by addition reaction with aliphatic isocyanates.

[0017] Preferred aliphatic isocyanates are di- and / or triisocyanates, particularly preferably aliphatic diisocyanates having 4 to 15 carbon atoms in the aliphatic functional group, which in turn are preferably selected from 1 ,6-hexamethylene diisocyanate, 1 ,4-diisocyanatocyclohexane or 1 -isocyanato- 3,5,5-trimethyl-5-isocyanatomethylcyclohexane.

[0018] Preferred aliphatic polycarbonatediols are obtainable by reacting di- and / or trihydric alcohols having 2 to 24, in particular 3 to 10 carbon atoms, typically 1 ,6-hexanediol, neopentyl glycol, 1 ,4-dimethanol-cyclohexane or mixtures thereof, with dimethyl carbonate (DMC). Polyester or polyether carbonate diols are also suitable. Here, low molecular weight linear aliphatic polyester polyols or polyether polyols are used as starters and subjected to the above reaction. Alternatively, aliphatic polycarbonate diols can also be obtained directly from carbon dioxide and an aliphatic di- or trihydric alcohol.

[0019] In order to provide good barrier properties of the cured repair lacquer, it is particularly preferred if polyurethane prepolymers (hereinafter referred to as “pre-PU”) with an excess of isocyanate groups are first formed from the aforementioned reactants, i.e., isocyanates and polyols, which are then reacted with alcohols that additionally have an acid function to form the polyurethane resin. In this way, the number of acid groups in the polyurethane resin can be reduced to the amount necessary for crosslinking and stabilization. According to the invention, therefore, the polyurethane resins preferred as component (A) are those which are obtainable by reacting an aliphatic prepolymer comprising free isocyanate groups (hereinafter also called “ali-pre-PU”) with an aliphatic alcohol which comprises at least one carboxyl and / or sulfonate group and is preferably selected from dimethylol-C2- to C6-alkanoic acids and particularly preferably selected from dimethylolpropionic acid. The prepolymer ali-pre-PU mentioned in this context, which comprises free isocyanate groups, is in turn preferably obtainable by reacting at least one aliphatic di- or triisocyanate, preferably aliphatic diisocyanate, having at least one polyhydric alcohol selected from aliphatic polyether polyols, aliphatic polyester polyols, aliphatic polycarbonate diols and / or aliphatic polyoxyalkylene-modified alkanediols, particularly preferably aliphatic polycarbonate diols, wherein the reaction has to take place in such aratio that the sum of the isocyanates used and the sum of the alcohols used results in a molar NCO / OH ratio of greater than 1.1 :1 , but preferably not greater than 2.5:1. In a particular embodiment, the prepolymer ali-pre-PU comprising free isocyanate groups is obtainable by reacting at least one aliphatic di- or triisocyanate, preferably aliphatic diisocyanate, having at least two aliphatic polyhydric alcohols, wherein at least one polyhydric alcohol is selected from the group consisting of aliphatic polyether polyols, aliphatic polyester polyols and / or aliphatic polycarbonate diols, particularly preferably from aliphatic polycarbonate diols, and at least one further polyhydric alcohol is selected from aliphatic polyoxyalkylene-modified alkanediols, wherein the reaction has to be carried out in such a ratio that the sum of the isocyanates used and the sum of the alcohols used results in a molar NCO / OH ratio of greater than 1.1 :1 , but preferably not greater than 2.5:1 .

[0020] The polyurethane resins modified with acid groups, which are obtainable from the pre-PUs in the manner described, can be further crosslinked after dispersion in water, which in turn is advantageous for the barrier effect of the repair lacquer, provided that the stability of the dispersion is still maintained. For this purpose, the reaction of the pre-PU with the aliphatic alcohol, which has at least one carboxyl and / or sulfonate group, is initially carried out substoichiometrically, so that free isocyanate groups remain in the reacted pre-PU, which is then chain- extended to form a polyurethane resin according to component (A) with at least partial to complete reaction of the isocyanate groups.

[0021] In a particularly preferred embodiment, the at least one polyurethane resin according to component (A) is therefore obtainable by chain extension of an aliphatic-acid-group-modified polyurethane prepolymer (hereinafter also referred to as “ali-sPre-PU”), which is obtainable by reacting at least one aliphatic diisocyanate with both at least one aliphatic polycarbonate polyol and at least one aliphatic alcohol which has at least one carboxyl and / or sulfonate group, wherein the NCO / OH ratio of the sum of the isocyanates and the sum of the alcohols is in the range from 1.1 :1 to 2.5:1 , and wherein the chain extension is preferablycarried out after dispersing the at least partially neutralized ali-sPre-PU in the aqueous phase by adding an amount of one or more di- and polyfunctional water- soluble alcohols, amines and amino alcohols, preferably by adding an amount of a diamine, such as ethylenediamine, and / or a triamine, such as ethylenetriamine.

[0022] As already mentioned, the dispersed polyurethane resin(s) according to component (A) crosslink with the hardener according to component (B) via the acid groups, and the polyurethane resins are therefore preferably provided in such a way that a total of less than 0.20 wt.%, preferably less than 0.05 wt.% of free NCO groups — determined according to DIN 53185 and in each case based on the resin component according to component (A) of the repair lacquer — is contained.Component (B) - hardener

[0023] For the good crosslinking of the repair lacquer consisting of the polyurethane resins described in detail above, which are dispersed in water, and in order to be able to achieve low baking temperatures, organic compounds from the carbodiimide group are essential as hardeners and are therefore mandatory according to the invention.

[0024] Polycarbodiimides having two or more carbodiimide groups are suitable for this purpose and are therefore preferred hardeners for the repair lacquer. Such polycarbodiimides are in turn preferably obtainable from diisocyanates, preferably from aliphatic diisocyanates, and at least one amine, preferably aliphatic amine, and / or a polyether, preferably a polyalkylene glycol, particularly preferably a polyethylene glycol. The use of aliphatic polycarbodiimides is preferred to ensure food hygiene regulations in the context of the present invention; therefore, the aforementioned starting products of the polycarbodiimides according to component (B) are also preferably aliphatic.

[0025] Hardeners according to component (B) which have proven particularly advantageous in the context of the present invention are those selected from carbodiimides having a carbodiimide equivalent weight of less than 500 grams per mole of carbodiimide groups, but preferably at least 200 grams, particularly preferably at least 300 grams per mole of carbodiimide groups, wherein the carbodiimides additionally preferably have a number-average molar mass of at least 1 ,500 g / mol, but preferably below 50,000 g / mol. Such compounds are able to crosslink the repair lacquer even at temperatures significantly below the boiling point of water, so that in the repair coating method according to the invention, curing in solution already begins in the drying phase of the wet film, which promotes the formation of a repair coating that is as homogeneous as possible and well crosslinked.

[0026] The total proportion of hardeners dissolved in water should be adjusted to the amount of polyurethane resin according to component (A) in such a way that very over- or under-stoichiometric proportions are avoided, because otherwise a lower hardness and protective effect of the repair coating is achieved due to the excess of hardener or resin. Typically, and therefore preferably, the total proportion of hardeners according to component (B) dissolved in water in repair lacquers according to the invention is at least 0.50 wt. %, particularly preferably at least 1.00 wt. %, especially preferably at least 1 .50 wt. %, but the total proportion is preferably not above 5.0 wt. %, particularly preferably not above 3.0 wt. %, especially preferably not above 2.50 wt. %, in each case based on the repair lacquer.Component (C) - surfactant

[0027] The repair lacquer according to the invention must completely wet the defect region of a lacquered metal surface to be repaired almost instantly after its application, ideally at least before the wet film begins to dry, in order to ensure that the repair lacquer penetrates into all areas of the lacquering that are to be healed and that this defect region is thus completely covered by therepair lacquer. Only in this way will the original lacquering actually heal where it is damaged, i.e. , torn, worn or thinned, after the repair lacquer has dried and baked on. As mentioned at the outset, the dynamic surface tension of the water-based repair lacquer must be reduced accordingly, if possible below 45.0 rnNm-1, so that according to the invention the presence of at least one non-ionic or anionic surfactant, preferably an anionic surfactant, is mandatory, which at the same time comprises an organic compound having a molecular weight of less than 1 ,000 g / mol.

[0028] The surfactants used should preferably be those with non-foaming or defoaming properties, otherwise spray application of the repair lacquer would not be possible. Suitable preferred non-ionic surfactants are fatty amine alkoxylates and / or fatty alcohol alkoxylates. Even-numbered fatty alcohols are preferred because of their better biodegradability. The fatty alcohol may be a C6 to C22 fatty alcohol, preferably a C6 to C18 fatty alcohol, particularly preferably a C6 to C12 fatty alcohol. The fatty alcohol can be branched or linear, with the hydrophobic functional group preferably being branched. The fatty alcohol can be saturated, monounsaturated or polyunsaturated, with fully saturated functional groups being preferred. The fatty alcohol can be selected from the group consisting of 1 -hexanol, 1 -heptanol, 1 -octanol, 1 - decanol, 1 -dodecanol, 1 -tetradecanol, 1 -hexadecanol, 1 -heptadecanol, 1- octadecanol, 1-eicosanol, 1 -docosanol and combinations thereof.

[0029] However, surfactants preferably used as component (C) are anionic surfactants and, in turn, preferably those which have at least one sulfonate and / or sulfate group and particularly preferably exclusively aliphatic functional groups, wherein, in turn, the sum of the carbon atoms of all aliphatic functional groups is preferably at least 6, preferably at least 8. This surfactant group is able to reduce the dynamic surface tension to a particularly high degree. Surprisingly, it was further found that, insofar as substrate wetting agents based on siloxanes are included according to component (D), particularly good wetting of non-polar surfaces with the repair lacquer is achieved and this canbe achieved in fractions of a second if the aforementioned anionic surfactants which have sulfonate and / or sulfate groups are used. In this context and more generally in the context of the lacquer according to the invention, particular emphasis should be given to those anionic surfactants which are selected from organic compounds of the general structural formula (I) and the water-soluble salts thereof, preferably alkali and / or alkaline earth metal salts:(I)where Y and Z represent aliphatic functional groups each having at least 4 carbon atoms, preferably each having at least 6 carbon atoms, but each not more than 14 carbon atoms, preferably each not more than 10 carbon atoms, which can each be branched or unbranched and can be selected independently of one another. Most preferably, the sulfosuccinic acid bis(2- ethylhexyl) ester and the water-soluble salts thereof, preferably alkali and / or alkaline earth metal salts, are selected as surfactant according to component (C) of the repair lacquer. Anionic surfactants according to the general structural formula (I) reliably reduce the dynamic surface tension of the repair lacquer to values below 40.0 mNnr1, wherein, in the presence of siloxanes as substrate wetting agents according to component (D), a further reduction to less than 30.0 mNnr1can be achieved, in each case determined at 20°C using a bubble tensiometer at a surface age of 0.030 seconds.

[0030] In order to achieve the desired effect, which consists in the rapid wetting of non-polar surfaces by the repair lacquer, it is advantageous if at least one surfactant according to component (C) above its micelle formation concentration is used, particularly preferably the proportion of the surfactant according to component (C) in the repair lacquer is at least 0.10 wt. %, preferably at least 0.20 wt. %, particularly preferably at least 0.40 wt. %, but preferably does not exceed 2.00 wt. %, particularly preferably does not exceed 1 .50 wt. %, in each case based on the repair lacquer.Component (D) - substrate wetting agent

[0031] The repair lacquer according to the invention must ensure sufficient wetting of non-polar surfaces as intended. Preferably, the non-polar surface is a lacquered metal surface, where the metal is preferably tin-free steel, steel, tinplate or aluminum, more preferably tin-free steel or tinplate, still more preferably tin-free steel. A non-polar surface in the context of the present invention is present if it has a polar surface energy component measured at 20°C using the static method and calculated using the OWRK method (Owens-Wendt-Rabel-Kaelble) according to DIN EN ISO 19403-2 of less than 5.0 mJrrr2. As mentioned at the outset, the static surface tension of the water-based repair lacquer must be reduced accordingly, if possible below 30.0 mNrrr1, so that according to the invention the presence of at least one substrate wetting agent according to component (D) of the repair lacquer is mandatory.

[0032] The substrate wetting agents used in addition to the surfactants according to component (C) are not restricted in any way and can be any compounds that are suitable for reducing the static surface tension. However, it has been found that siloxanes have a particularly positive influence on the wetting properties of the repair lacquer, especially in combination with the anionic surfactants according to component (C), which contain sulfonate and / or sulfate groups. In a preferred embodiment of the repair lacquer, the at least one substratewetting agent is therefore selected from siloxanes, wherein the siloxanes are in turn preferably selected from trisiloxanes and / or polysiloxanes and particularly preferably comprise at least one [-Si(CH3)2-O] structural unit. The siloxanes are most preferably selected from polyether-modified siloxanes, preferably from polyoxoalkylated, particularly preferably from polyethoxylated siloxanes.

[0033] In order to achieve the desired effect, which consists in the most complete and / or rapid wetting of non-polar surfaces by the repair lacquer, it is advantageous if the proportion of substrate wetting agents, preferably the proportion of siloxanes, particularly preferably the proportion of polyether- modified siloxanes, is at least 0.05 wt.%, particularly preferably at least 0.10 wt.%, especially preferably at least 0.20 wt.%, but preferably not above 1.00 wt.%, particularly preferably not above 0.80 wt.%, especially preferably not above 0.70 wt.%, more preferably not above 0.6 wt%, in each case based on the repair lacquer. For example, preferred substrate wetting agents are polyether-modified polydimethylsiloxanes, which are commercially available under the tradename BYK-3455, Byk 3450, Byk 3480 or Byk 3756.Solvent

[0034] The presence of organic solvents in the aqueous dispersion of the repair lacquer can provide particular advantages in the crosslinking of the polyurethane- based binder, as rapid drying of the applied repair lacquer is achieved when the repair-coated components are heated, for example during transfer to the baking oven, and the curing of the binder thus begins in an already concentrated dispersion, which in turn results in faster and more complete crosslinking. In this respect, it is preferred according to the invention if the repair lacquer contains a total of at least 2.0 wt.%, preferably a total of at least 4.0 wt.% of the solvents acetone, methyl ethyl ketone, dimethyl sulfoxide and / or N,N‘-dimethylformamide, wherein methyl ethyl ketone is preferably selected as the solvent.

[0035] On the other hand, it is precisely a desired characteristic of the repair lacquer that it can be formulated largely solvent-free, as this significantly reduces CO2 equivalent emissions in high-volume production, such as in the repair coating of tear-open can lids. This requirement for the repair lacquer is also met in the form of the aqueous dispersion provided according to the invention, without prejudice to the previously mentioned usefulness of a certain solvent content. Consequently, for environmental hygiene reasons, the repair lacquer preferably contains a total of less than 10.0 wt.%, particularly preferably a total of less than 8.0 wt.%, especially preferably a total of less than 6.0 wt.% of the solvents acetone, methyl ethyl ketone, dimethyl sulfoxide and / or N,N‘-dimethylformamide, and preferably a total of less than 10.0 wt.%, particularly preferably a total of less than 8.0 wt.%, especially preferably a total of less than 6.0 wt.% of organic compounds having a boiling point below 160°C at atmospheric pressure (1013 mbar).

[0036] In a particularly preferred embodiment, the repair lacquer contains at least 2.0 wt.%, particularly preferably at least 4.0 wt.% of methyl ethyl ketone, but a total of less than 10.0 wt.%, preferably a total of less than 8.0 wt.%, particularly preferably a total of less than 6.0 wt.% of organic compounds having a boiling point below 160°C at atmospheric pressure (1013 mbar), in each case based on the repair lacquer.Other optional components

[0037] The repair lacquer according to the invention may contain further lacquer-typical additives. Of particular note here are UV tracers to control complete wetting of the repair lacquer in the defect region, defoamers (such as polyether siloxane) to prevent foam formation when applying the repair lacquer using airless spraying, adhesion promoters, such as silanes, which in particular improve the adhesion of the repair lacquer to the lacquered metal surface, and skin extenders, such as butyldiglycol, to extend the open time when baking the repair lacquer and to avoid skin bubbles, reduce nozzle drying and improvewetting. In preferred embodiments, the repair lacquer according to the invention may contain a rheology control additive, such as a silica-based rheology control additive, to improve wetting, sprayability (less nozzle blocking) and crosslinking for sterilization resistance.

[0038] The repair lacquer according to the invention may contain one or more additives selected from the group consisting of UV tracers, defoamers, adhesion promoters, crosslinkers, skin extenders and rheology control additives. Preferably, the repair lacquer may contain a UV tracer in an amount of at least 0.001 wt. %, preferably at least 0.005 wt. %, particularly preferably at least 0.01 wt. %, but preferably does not exceed 0.03 wt. %, particularly preferably does not exceed 0.02 wt. %, in each case based on the repair lacquer. Suitable UV tracers include 4,4’-bis(2-sulfostyryl)-biphenyl disodium salt (Tinopal NFW 10 liquid) and 2,5-thiophenediylbis(5-tert-butyl-1 ,3- benzoxazole) (Tinopal OB CO, Benetex OB, Omnistab OB). Preferably, the repair lacquer may contain an adhesion promoter including silanes in an amount of at least 0.1 wt. %, preferably at least 0.3 wt. %, particularly preferably at least 0.5 wt. %, but preferably does not exceed 2.0 wt. %, particularly preferably does not exceed 0.8 wt. %, in each case based on the repair lacquer. Suitable adhesion promoters include N-2-aminoethyl-3- aminopropyltrimethoxysilane (Dynasylan DAMO, GENIOSIL® GF 91 ), N-(2- aminoethyl)-3-aminopropylmethyldimethoxysilane (GENIOSIL® DAPDM). Preferably, the repair lacquer may contain a defoamer including polyether siloxane in an amount of at least 0.005 wt. %, preferably at least 0.02 wt. %, particularly preferably at least 0.04 wt. %, but preferably does not exceed 0.18 wt. %, particularly preferably does not exceed 0.12 wt. %, in each case based on the repair lacquer. Suitable defoamers include a polyether siloxane copolymers or modified polyether modified siloxanes containing silica (TEGO Foamex 8420, TEGO Foamex 822, BRB Siloen® DA 291 , AgeSin® DF-A5062 (Sinocure) or TEGO Airex 901 W). Preferably, the repair lacquer may contain a skin extender in an amount of at least 1 wt. %, preferably at least 2.5 wt. %, particularly preferably at least 4 wt. %, but preferably does not exceed20 wt. %, particularly preferably does not exceed 10 wt. %, in each case based on the repair lacquer. Suitable skin extenders include butyldiglycol, n- butylglycol, n-butanol, 1 -methoxy propan-2-ol or dipropylene glycol mono methyl ether. Preferably, the repair lacquer may contain a rheology control additive in an amount of at least 0.1 wt. %, preferably at least 0.2 wt. %, particularly preferably at least 0.4 wt. %, but preferably does not exceed 1.0 wt. %, particularly preferably does not exceed 0.7 wt. %, in each case based on the repair lacquer. Suitable rheology control additives include a silica- based rheology control additive (Aerosil E 972, Cab-O-Sil TS-720; Aerolsil R 974). The repair lacquer may further contain a crosslinker. Suitable crosslinkers include blocked isocyanates, isocyanates, aziridines, triazine compounds, and / or carbodiimides.

[0039] A particularly preferred embodiment of the repair lacquer according to the invention contains:(A) 4 - 30 wt.% of at least one water-dispersed polyurethane resin selected from polyurethane resins having an acid number of at least 5 mg KOH per gram,(B) 0.50 - 5.0 wt.% of at least one hardener dissolved in water selected from organic compounds having at least one carbodiimide group,(C) at least one anionic surfactant having a molecular weight of less than 1000 g / mol selected from organic compounds according to the general structural formula (I) and the water-soluble salts thereof, preferably alkali and / or alkaline earth metal salts:where Y and Z represent aliphatic functional groups each having at least 4 carbon atoms, preferably each having at least 6 carbon atoms, but each not more than 14 carbon atoms, preferably each not more than 10 carbon atoms, which can each be branched or unbranched and can be selected independently of one another,(D) at least one siloxane, preferably selected from polyether-modified siloxanes, particularly preferably from polyoxoalkylated, especially preferably from polyethoxylated siloxanes, and(E) at least 2 wt.% of methyl ether ketone, wherein the repair lacquer has a solids content according to DIN EN ISO 3251 of at least 10.0 wt.%, but contains a total of less than 10 wt.% of organic compounds with a boiling point below 160°C at normal pressure (1013 mbar), in each case based on the repair lacquer.

[0040] In a further aspect, the present invention relates to the repair coating method described at the outset. The repair lacquer according to the present invention and as described herein is preferably applied in the repair coating method. In the following, preferred embodiments of such a method according to the invention are therefore explained and introduced with reference to selected aspects.

[0041] Within the scope of the repair coating method according to the invention, the lacquered metal surfaces are considered non-polar if their polar surface energy content measured at 20°C using the static method and calculated using the OWRK method according to DIN EN ISO 19403-2 is less than 5.0 mJrrr2, preferably less than 2.0 mJrrr2, particularly preferably less than 1.0 mJrrr2. Such surfaces are usually realized using conventional lacquers that contain appropriate additives, for example waxes. Lacquered metal surfaces preferably treated in the method according to the invention have a lacquering with an organic binder system, particularly preferablyselected from epoxides, acrylates, polyesters, polyurethanes and / or polyolefins, very particularly preferably selected from epoxides.

[0042] The type of defect region that experiences an increase in the lacquer layer thickness during the repair coating method is irrelevant for the suitability of the method for healing the defect. Thus, point defects as well as flat or linear defect regions can be successfully repaired or healed by applying a repair lacquer according to the invention. However, the properties of the repair lacquer are such that particularly narrow depressions or cracks in the original lacquering of the metallic substrate are easily accessible by the repair lacquer due to its excellent wetting properties and can be effectively repair coated.

[0043] In a preferred embodiment of the repair coating method, the defect region therefore runs along a groove-shaped depression in the lacquer, wherein the width of the depression orthogonal to the groove course and to the surface normal is preferably less than 1000 pm, particularly preferably less than 500 pm, but preferably not less than 20 pm. Such defects are typically those that are embossed into the lacquered metallic can lid material during the manufacture of tear-open can lids when the desired opening is created, thus causing the notch and thus the damage in the already lacquered can lid that requires repair. The method according to the invention is therefore particularly suitable for the repair coating of tear-open can lids and is preferably used there, in particular in the food packaging industry, which uses lids made of aluminum, steel, tin free steel (such as electrolytic chromium coated steel (ECCS) and trivalent chromium coating technology (TCCT)) and tinplate for this purpose, whereby the steel, tin- free steel and tinplate are particularly susceptible to the problem of corrosive infiltration in the region of the embossing of the desired opening and thus of discoloration of the lid made of steel or tinplate. The repair coating in the method according to the invention can effectively counteract this.

[0044] In a preferred embodiment of the repair coating method, the lacquered metal surface is therefore a steel, tinplate or aluminum surface, inparticular a tinplate surface, wherein the lacquered metal surface preferably represents the surface of a can lid and a rivet, more preferably represents the surface of a can lid, in particular a tinplate can lid. In another preferred embodiment of the repair coating method, the lacquered metal surface is a tin-free steel surface.

[0045] The method of applying the repair lacquer as a wet film is not restricted in any way in the method according to the invention, and all conventional coating methods, such as dipping, roller application, spin coating etc., are possible, but the repair lacquer is particularly suitable for application by spraying, because especially in the context of can lid production, high throughput rates are typical and require spraying techniques for the dosed application of the repair lacquer, ideally only locally in the region of the defect to be healed by the repair coating.

[0046] In a preferred embodiment of the repair coating method, the repair lacquer is therefore applied by spraying, particularly preferably by atomization, especially preferably by airless atomization, so-called airless spraying methods. The repair lacquer is preferably applied at a spray pressure of at least 10 bar, particularly preferably at least 15 bar, but the spray pressure is preferably below 30 bar in order not to make targeted application more difficult by the formation of a spray mist.

[0047] The drying of the applied wet film of the repair lacquer and its curing takes place in the method according to the invention preferably in a heat treatment stage, at a temperature (PMT = peak metal temperature) of preferably above 60°C, particularly preferably above 80°C, especially preferably above 90°C, but preferably below 160°C, particularly preferably below 130°C and especially preferably below 100°C. The method according to the invention is characterized precisely in that complete curing of the binder can take place at temperatures already below the boiling point of water, so that the repair coating method can be operated with low energy consumption regardless of the fact that the repair lacquer is an aqueous dispersion.

[0048] The repair lacquer according to the present invention may be also used for other applications within metal packaging, including interior foodcontact applications. For example, as an interior and exterior side stripe protection for 3 piece cans to protect the welded unlacquered areas of a 3 piece can (e.g., the weld where the sidewall is joined together to form a cylinder) or other welded non protected surfaces in metal packaging.

[0049] Moreover, the inventive aqueous dispersion for example used as a repair coating also exhibits good adhesion to a variety of external coating chemistries, including after processing conditions (e.g., elevated temperature and pressure sterilization procedures) which packed food cans are routinely subject to. The adhesion to not only metal but the exterior coating that is being “repaired” is important. And, moreover, it needs to exhibit such adhesion across a wide variety of different exterior coating chemistries that may be utilized (e.g., epoxy, acrylic, polyester, etc.).

[0050] The present invention provides, among other things, the following objects:

[0051] 1 . An aqueous dispersion for the repair coating of non-polar surfaces in spray methods, containing(A) at least one water-dispersed polyurethane resin selected from polyurethane resins having an acid number of at least 5 mg KOH per gram,(B) at least one hardener dissolved in water selected from organic compounds having at least one carbodiimide group,(C) at least one non-ionic or anionic surfactant, preferably an anionic surfactant, selected from organic compounds having a molecular weight of less than 1000 g / mol, and(D) at least one substrate wetting agent which is not an organic compound according to component (C),wherein the dispersion has a solids content according to DIN EN ISO 3251 of at least 10.0 wt.%, wherein the non-polar surface is preferably a lacquered metal surface, where the metal is preferably tin-free steel, steel, tinplate or aluminum, more preferably tin-free steel or tinplate, especially preferred tin-free steel.

[0052] 2. The aqueous dispersion according to point 1 , characterized in that the dispersion has a static surface tension of less than 30.0 mNrrr1, preferably less than 25.0 mNrrr1, particularly preferably less than 22.0 mNrrr1, measured by the platinum ring method at 20°C.

[0053] 3. The aqueous dispersion according to one or both of the preceding points, characterized in that the dispersion has a dynamic surface tension of less than 45.0 rnNm-1, preferably less than 40.0 rnNm-1, particularly preferably less than 35.0 rnNm-1, measured by bubble pressure tensiometer at 20°C and a surface age of 0.030 seconds.

[0054] 4. The aqueous dispersion according to one or both of the preceding points, characterized in that the dispersion has a dynamic viscosity below 200 m Pas-1, preferably below 120 m Pas-1, particularly preferably below 80 mPas’1has.

[0055] 5. The aqueous dispersion according to one or more of the preceding points, characterized in that the aqueous dispersion containing the polyurethane resin dispersed in water has a D90 value of less than 1.00 pm, preferably less than 0.50 pm, particularly preferably less than 0.25 pm.

[0056] 6. The aqueous dispersion according to one or more of the preceding points, characterized in that the at least one polyurethane resin dispersed in water has an acid number of at least 8 mg KOH per gram, preferably of at least 10 mg KOH per gram, but preferably not above 30 mg KOH per gram,particularly preferably not above 24 mg KOH per gram, especially preferably not above 24 mg KOH per gram, in each case based on the polyurethane resin.

[0057] 7. The aqueous dispersion according to one or more of the preceding points, characterized in that the proportion of polyurethane resins in the dispersion is at least 4 wt.%, preferably at least 8 wt.%, particularly preferably at least 12 wt.%, but preferably not above 30 wt.%, particularly preferably not above 20 wt.%.

[0058] 8. The aqueous dispersion according to one or more of the preceding points, characterized in that the dispersed polyurethane resin is selected from aliphatic polyurethane resins, preferably based on polyether polyols, polyester polyols, polycarbonate diols and / or polyoxyalkylene-modified alkane diols, particularly preferably based on polycarbonate diols.

[0059] 9. The aqueous dispersion according to one or more of the preceding points, characterized in that the dispersed polyurethane resin is obtainable by reacting an aliphatic prepolymer comprising free isocyanate groups with an aliphatic alcohol which has at least one carboxyl and / or sulfonate group and is preferably selected from dimethylol C2 to C6 alkanoic acids.

[0060] 10. The aqueous dispersion according to point 9, characterized in that the aliphatic prepolymer comprising free isocyanate groups is obtainable by reacting at least one aliphatic di- or triisocyanate, preferably diisocyanate, having at least one polyhydric alcohol selected from polyether polyols, polyester polyols, polycarbonate diols and / or polyoxyalkylene-modified alkanediols, preferably having at least two polyhydric alcohols, wherein at least one polyhydric alcohol is selected from the group consisting of polyether polyols, polyester polyols and / or polycarbonate diols and at least one further polyhydric alcohol is selected from polyoxyalkylene-modified alkanediols, wherein the reaction has to take place in such a ratio that the sum of theisocyanates used and the sum of the alcohols used results in a molar NCO / OH ratio of greater than 1.1 :1 , but preferably not greater than 2.5:1.

[0061] 11. The aqueous dispersion according to one or more of the preceding points, characterized in that the dispersed polyurethane resin has a total of less than 0.20 wt.%, preferably less than 0.05 wt.% of free NCO groups determined according to DIN 53185 and in each case based on the dispersed resin component.

[0062] 12. The aqueous dispersion according to one or more of the preceding points, characterized in that the hardener is selected from polycarbodiimides having two or more carbodiimide groups, preferably obtainable from diisocyanates, preferably from aliphatic diisocyanates, and at least one amine, preferably aliphatic amine, and / or a polyether, preferably polyethylene glycol.

[0063] 13. The aqueous dispersion according to one or more of the preceding points, characterized in that the hardener is selected from carbodiimides having a carbodiimide equivalent weight of less than 500 grams per mole of carbodiimide groups, but preferably at least 200 grams, particularly preferably at least 300 grams per mole of carbodiimide groups, wherein the carbodiimides preferably have a number-average molecular weight of at least 1 ,500 g / mol, but preferably less than 50,000 g / mol.

[0064] 14. The aqueous dispersion according to one or more of the preceding points, characterized in that the proportion of hardener dissolved in water selected from organic compounds having at least one carbodiimide group is at least 0.50 wt.%, preferably at least 1.00 wt.%, particularly preferably at least 1.50 wt.%, but preferably not above 5.0 wt.%, particularly preferably not above 3.0 wt.%, especially preferably not above 2.50 wt.%.

[0065] 15. The aqueous dispersion according to one or more of the preceding points, characterized in that the surfactant is selected from organiccompounds of the general structural formula (I) and the water-soluble salts thereof, preferably alkali and / or alkaline earth metal salts:where Y and Z represent aliphatic functional groups each having at least 4 carbon atoms, preferably each having at least 6 carbon atoms, but each not more than 14 carbon atoms, preferably each not more than 10 carbon atoms, which can each be branched or unbranched and can be selected independently of one another.

[0066] 16. The aqueous dispersion according to one or more of the preceding points, characterized in that the surfactant is selected from sulfosuccinic acid bis(2-ethylhexyl) ester and the water-soluble salts thereof, preferably alkali and / or alkaline earth metal salts.

[0067] 17. The aqueous dispersion according to one or more of the preceding points, characterized in that the proportion of surfactant in the dispersion is at least 0.10 wt.%, preferably at least 0.20 wt.%, particularly preferably at least 0.40 wt.%, but preferably not above 2.00 wt.%, particularly preferably not above 1 .50 wt.%.

[0068] 18. The aqueous dispersion according to one or more of the preceding points, characterized in that the at least one substrate wetting agent is selected from siloxanes, wherein the siloxanes in turn are preferablyselected from trisiloxanes and / or polysiloxanes and particularly preferably comprise at least one [-Si(CH3)2-O] structural unit.

[0069] 19. The aqueous dispersion according to point 18, characterized in that the siloxanes are selected from polyether-modified siloxanes, preferably from polyoxoalkylated, particularly preferably from polyethoxylated siloxanes.

[0070] 20. The aqueous dispersion according to one or more of the preceding points, characterized in that the proportion of polyether-modified siloxanes in the dispersion is at least 0.05 wt.%, preferably at least 0.10 wt.%, particularly preferably at least 0.20 wt.%, but preferably not above 1.00 wt.%, particularly preferably not above 0.8 wt.%, especially preferably not above 0.70 wt.%, more preferably not above 0.6 wt%.

[0071] 21. The aqueous dispersion according to one or more of the preceding points, characterized in that the dispersion contains a total of at least 2.0 wt.%, preferably a total of at least 4.0 wt.% of the solvents acetone, methyl ethyl ketone, dimethyl sulfoxide and / or NN'-dimethylformamide, wherein methyl ethyl ketone is preferably selected as the solvent.

[0072] 22. The aqueous dispersion according to one or more of the preceding points, characterized in that the dispersion contains a total of less than 10.0 wt.%, preferably a total of less than 8.0 wt.%, particularly preferably a total of less than 6.0 wt.% of the solvents acetone, methyl ethyl ketone, dimethyl sulfoxide and / or N,N‘-dimethylformamide, and preferably a total of less than 10.0 wt.%, particularly preferably a total of less than 8.0 wt.%, especially preferably a total of less than 6.0 wt.% of organic compounds, having a boiling point below 160°C at atmospheric pressure (1013 mbar).

[0073] 23. The aqueous dispersion according to one or more of the preceding points, characterized in that the dispersion contains a UV tracer in an amount of at least 0.001 wt. %, preferably at least 0.005 wt. %, particularlypreferably at least 0.01 wt. %, but preferably does not exceed 0.03 wt. %, particularly preferably does not exceed 0.02 wt. %, in each case based on the repair lacquer.

[0074] 24. The aqueous dispersion according to one or more of the preceding points, characterized in that the dispersion contains an adhesion promoter including silanes in an amount of at least 0.1 wt. %, preferably at least 0.3 wt. %, particularly preferably at least 0.5 wt. %, but preferably does not exceed 2.0 wt. %, particularly preferably does not exceed 0.8 wt. %, in each case based on the repair lacquer.

[0075] 25. The aqueous dispersion according to one or more of the preceding points, characterized in that the dispersion contains a defoamer including polyether siloxane in an amount of at least 0.005 wt. %, preferably at least 0.02 wt. %, particularly preferably at least 0.04 wt. %, but preferably does not exceed 0.18 wt. %, particularly preferably does not exceed 0.12 wt. %, in each case based on the repair lacquer.

[0076] 26. The aqueous dispersion according to one or more of the preceding points, characterized in that the dispersion contains a skin extender in an amount of at least 1 wt. %, preferably at least 2.5 wt. %, particularly preferably at least 4 wt. %, but preferably does not exceed 20 wt. %, particularly preferably does not exceed 10 wt. %, in each case based on the repair lacquer.27. The aqueous dispersion according to one or more of the preceding points, characterized in that the dispersion contains a rheology control additive in an amount of at least 0.1 wt. %, preferably at least 0.2 wt. %, particularly preferably at least 0.4 wt. %, but preferably does not exceed 1.0 wt. %, particularly preferably does not exceed 0.7 wt. %, in each case based on the repair lacquer.

[0077] 28. A method for the repair coating of a lacquered metal surface which, in at least one region of the lacquering, has a defect which consists in the fact that the lacquer layer thickness is at least reduced compared to the lacquer layer thickness realized outside this defect region, in which method, in order to increase the lacquer layer thickness in the defect region, an aqueous dispersion is applied at least there as a wet film according to one or more of the previous points and is then dried.

[0078] 29. The method according to point 28, characterized in that the defect region runs along a groove-shaped depression in the lacquer, wherein the width of the depression orthogonal to the groove course and to the surface normal is preferably less than 1000 pm, particularly preferably less than 500 pm, but preferably not less than 20 pm.

[0079] 30. The method according to one or both of points 28 and 29, characterized in that the dispersion is applied by spraying, preferably by atomization, particularly preferably by airless atomization.

[0080] 31. The method according to point 30, characterized in that the dispersion is applied at a spray pressure of at least 10 bar, preferably at least 15 bar, but preferably below 30 bar.

[0081] 32. The method according to one or more of the preceding points 28 to 31 , characterized in that the drying takes place at a temperature (PMT) above 60°C, preferably above 80°C, particularly preferably above 90°C, but preferably below 160°C, particularly preferably below 130°C and especially preferably below 100°C.

[0082] 33. The method according to one or more of the preceding points 28 to 31 , characterized in that the lacquered metal surface is a tin-free steel, steel, tinplate or aluminum surface, in particular a tin-free steel or tinplate surface.

[0083] 34. The method according to one or more of the preceding points 28 to 33, characterized in that the lacquered metal surface has a polar surface energy component measured at 20°C according to the static method and calculated according to the OWRK method according to DIN EN ISO 19403-2 of less than 2.0 mJnr2, preferably less than 1 .0 m Jrrr2has.

[0084] 35. The method according to one or more of the preceding points 28 to 34, characterized in that the lacquered metal surface comprises a lacquering with an organic binder system, preferably selected from epoxies, acrylates, polyesters, polyurethanes and / or polyolefins.

[0085] 36. The method according to one or more of the preceding points 28 to 35, characterized in that the lacquered metal surface represents the surface of a can lid and a rivet, preferably represents the surface of a can lid, in particular a tin-free steel or tinplate can lid.

Claims

1. New PCT applicationValspar Industries GmbH;SYNTHOPOL CHEMIE Dr. rer. pol. Koch GmbH & CO. KGVossius Ref.: AK1688 PCTClaims1 . An aqueous dispersion for the repair coating of non-polar surfaces in spray methods, containing5 (A) at least one water-dispersed polyurethane resin selected from polyurethane resins having an acid number of at least 5 mg KOH per gram,(B) at least one hardener dissolved in water selected from organic compounds having at least one carbodiimide group,(C) at least one non-ionic or anionic surfactant selected from organic 10 compounds having a molecular weight of less than 1000 g / mol, and(D) at least one substrate wetting agent which is not an organic compound according to component (C), wherein the dispersion has a solids content according to DIN EN ISO 3251 of at least 10.0 wt.%.

152. The aqueous dispersion according to claim 1 , characterized in that the dispersion has a static surface tension of less than 30.0 mNnr1, preferably less than 25.0 mNnr1, particularly preferably less than 22.0 mNnr1, measured by the platinum ring method at 20°C.

203. The aqueous dispersion according to one or both of the preceding claims, characterized in that the dispersion has a dynamic surface tension of less than 45.0 mNnr1, preferably less than 40.0 mNnr1, particularly preferably less than 35.0 mNnr1, measured by bubble pressure tensiometer25 at 20°C and a surface age of 0.030 seconds.

4. The aqueous dispersion according to one or more of the preceding claims, characterized in that the proportion of polyurethane resins in the dispersion is at least 4 wt.%, preferably at least 8 wt.%, particularly preferably at least 12 wt.%,30 but preferably not above 30 wt.%, particularly preferably not above 20 wt.%.

5. The aqueous dispersion according to one or more of the preceding claims, characterized in that the dispersed polyurethane resin is selected from aliphatic polyurethane resins, preferably based on polyether polyols, polyester polyols, polycarbonate diols and / or polyoxyalkylene-modified alkane diols, particularly preferably based on polycarbonate diols.

6. The aqueous dispersion according to one or more of the preceding claims, characterized in that the dispersed polyurethane resin is obtainable by reacting an aliphatic prepolymer comprising free isocyanate groups with an aliphatic alcohol which comprises at least one carboxyl and / or sulfonate group and is preferably selected from dimethylol C2 to C6 alkanoic acids.

7. The aqueous dispersion according to one or more of the preceding claims, characterized in that the hardener is selected from polycarbodiimides having two or more carbodiimide groups, preferably obtainable from diisocyanates, preferably from aliphatic diisocyanates, and at least one amine, preferably aliphatic amine, and / or a polyether, preferably polyethylene glycol.

8. The aqueous dispersion according to one or more of the preceding claims, characterized in that the hardener is selected from carbodiimides having a carbodiimide equivalent weight of less than 500 grams per mole of carbodiimide groups, but preferably at least 200 grams, particularly preferably at least 300 grams per mole of carbodiimide groups, the carbodiimides preferably having a number-average molecular weight of at least 1 ,500 g / mol.

9. The aqueous dispersion according to one or more of the preceding claims, characterized in that the surfactant is selected from organic compounds of the general structural formula (I) and the water-soluble salts thereof, preferably alkali and / or alkaline earth metal salts:where Y and Z represent aliphatic functional groups each having at least 4 carbon atoms, preferably each having at least 6 carbon atoms, but each not more than 14 carbon atoms, preferably each not more than 10 carbon atoms, which can each be branched or unbranched and can be selected independently of one another, particularly preferably selected from sulfosuccinic acid bis(2-ethylhexyl) ester and the water-soluble salts thereof, preferably alkali and / or alkaline earth metal salts.

10. The aqueous dispersion according to one or more of the preceding claims, characterized in that the at least one substrate wetting agent is selected from siloxanes, wherein the siloxanes are in turn preferably selected from trisiloxanes and / or polysiloxanes and particularly preferably comprise at least one [-Si(CH3)2-O] structural unit.

11. The aqueous dispersion according to claim 17, characterized in that the siloxanes are selected from polyether-modified siloxanes, preferably from polyoxoalkylated, particularly preferably from polyethoxylated siloxanes.

12. The aqueous dispersion according to one or more of the preceding claims, characterized in that the dispersion contains a total of at least 2.0 wt.%, preferably a total of at least 4.0 wt.% of the solvents acetone, methyl ethyl ketone, dimethyl sulfoxide and / or N,N‘-dimethylformamide, wherein methyl ethyl ketone is preferably selected as the solvent.

13. The aqueous dispersion according to one or more of the preceding claims, characterized in that the dispersion contains a total of less than 10.0 wt.%, preferably a total of less than 8.0 wt.%, particularly preferably a total of less than 6.0 wt.% of the solvents acetone, methyl ethyl ketone, dimethyl sulfoxide and / or N,N‘-dimethylformamide, and preferably a total of less than 10.0 wt.%, particularly preferably a total of less than 8.0 wt.%, particularly preferably a total of less than 6.0 wt.% of organic compounds having a boiling point below 160°C at atmospheric pressure (1013 mbar).

14. A repair coating method of a lacquered metal surface which, in at least one region of the lacquering, has a defect which consists in the fact that the lacquer layer thickness is at least reduced compared to the lacquer layer thickness realized outside this defect region, in which in order to increase the lacquer layer thickness in the defect region, an aqueous dispersion according to one or more of the preceding claims is applied at least there as a wet film and then dried.

15. The method according to claim 14, characterized in that the lacquered metal surface is a tin-free steel, steel, tinplate or aluminum surface, preferably a tin-free steel or tinplate surface, more preferably a tin-free steel surface, wherein the lacquered metal surface preferably represents the surface of a can lid and a rivet, more preferably represents the surface of a can lid, in particular a tin free steel or tinplate can lid.

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