COMPOSITION

Description

TECHNICAL FIELD

[0001] The present invention relates to compositions which are particularly suitable for bonding sheet metal. BACKGROUND OF THE INVENTION

[0002] Bonded metal parts, such as sheet metal parts, are used in a wide variety of technical fields. Primarily in the construction of generators, electric motors, transformers, and other electrical machines, stacks of bonded electrical sheet metal parts are used as the starting material for magnetic cores. Sheet metal parts to be bonded are usually coated on one or both sides with a special adhesive layer, preferably a cross-linkable hot-melt adhesive, a so-called "baking varnish." Coatings made of baking varnish have the advantage that, once applied to the surface of a metal, especially a sheet metal (e.g., a sheet metal strip), they do not develop an adhesive effect. Only during the bonding process is the adhesive layer activated, for example, by the application of thermal energy. This activation makes the coating adhesive, allowing adjacent metals to be bonded.At the same time, the adhesive layer is hardened and becomes a heat-resistant thermoset.

[0003] The production of sheet metal parts or sheet metal slats bonded with self-adhesive varnish has the following advantages, among others: a) Retention of magnetic properties by preserving the microstructure in the steel structure through the use of moderate joining temperatures and pressures; b) Compact lamination packs with tight manufacturing tolerances improve the dissipation of waste heat generated during operation. Cooling arrangements can thus be minimized; c) The viscoelastic bonding layers between the individual laminations exhibit pronounced damping properties against sound transmission; d) Thin, stable adhesive layers, with no adhesive leakage at the outer edges, enable high design freedom while utilizing the tightest tolerances; e) Prevention of corrosion problems (interlamellar corrosion) through a highly stable, heat-resistant, hydrolysis-resistant full-surface bond; and f) Good insulation against electrical short circuits, which can increase the efficiency of transformers, for example.

[0004] Crosslinkable hot melt adhesives are sufficiently described in the prior art. For example, WO 2006 / 049935 discloses an adhesive composition comprising an epoxy resin, fumed silica particles, and a selection of curing agents, such as phenolic resins, carboxylic acids, anhydrides, isocyanates, and especially dicyandiamide, which is used as the sole curing agent in all application examples. This self-adhesive coating is applied to electrical steel sheets and dried at a temperature between 230°C and 260°C. Strips, punched from the coated electrical steel sheets, are placed on top of one another and bonded together for a period of 60 to 120 minutes at a temperature between 100°C and 300°C and at elevated pressure.

[0005] Adhesive compositions as described in WO 2006 / 049935, which essentially comprise bisphenol A or bisphenol F epoxy resins and mixtures thereof (but without any information regarding equivalent weights, functionalities, etc.), fumed silica as a filler and reinforcing agent, and a hardener such as a Lewis acid, are problematic to handle, since Lewis acids in particular are largely harmful and toxic. EP3460019A1 discloses one-component, heat-curing epoxy resin adhesives and their use, particularly in vehicle construction and sandwich panel construction.

[0006] WO 2017 / 050892 also describes thermally activatable adhesive compositions comprising an epoxy resin, an activatable hardener, and an activatable accelerator. These adhesive compositions are cured on the surface of metal sheets at a temperature above 100°C. Sheet metal laminations are then punched out, stacked on top of each other, and bonded together by activating the adhesive on the surfaces at a temperature of approximately 200°C. The activation time of such adhesives is 0.5 to 1 second, and the curing time is a maximum of 5 seconds.

[0007] The rapid curing of the adhesive layer, namely the catalytically accelerated reaction of dicyandiamide, as a hardener, with epoxy resin, is achieved in WO 2017 / 050892 by adding specific accelerators, in particular by adding Lewis acids, which are usually harmful and toxic. Nonspecific and rapid chemical reactions lead to very high crosslinking densities, which lead to brittleness and reduced durability of the adhesive layer. Furthermore, there is a risk of premature partial crosslinking in the liquid state, which manifests itself in a significant increase in viscosity and reduced storage life.

[0008] WO 2020 / 233840 teaches, in particular, that tempering of the punched and thus already coated laminations is necessary to minimize electrical losses in the finished product (a machine comprising bonded lamination stacks). Such an additional energy-intensive process step renders processes for producing laminated cores inefficient.

[0009] What all three publications discussed here have in common is that the curing time of resins, primarily dicyandiamide with epoxy resin, is to be accelerated by so-called catalytic accelerators. The associated problems, such as precise temperature control, excessively short curing times that are difficult to manage in production, over-curing and the resulting embrittlement, and the toxicity of accelerators, are accepted.

[0010] The object of the present invention is to provide a water-dilutable composition that enables metal parts, such as sheet metal, to be bonded together in the shortest possible time. By reducing the time required for the bonding process, significant cost savings are possible. Furthermore, the composition should not exhibit the disadvantages of the prior art, in particular WO 2006 / 049935, WO 2017 / 050892, and WO 2020 / 233840.

[0011] A further object of the present invention is to provide a composition that is storage-stable for a period of at least six months. Metals coated with such a composition should also be fully bondable even after storage for more than six months. SUMMARY OF THE INVENTION

[0012] The present invention relates to a composition, preferably for bonding metal sheets, comprising: a. 1 mol part of at least one linear epoxy resin having an average epoxy equivalent weight of 600 to 5,000 g / mol and an epoxy functionality of 2, b. 0.4 to 0.8 mol parts of at least one non-linear epoxy resin having an average epoxy equivalent weight of 180 to 350 g / mol and an average epoxy functionality of at least 3. c. 0.8 to 1.3 mol parts of at least one basic hardener comprising at least two free amine-bonded hydrogen atoms, and d. 0.9 to 1.2 mol parts of at least one (pre-)crosslinker comprising at least two blocked isocyanate groups.

[0013] The composition according to the invention can be used as a one-component material for coating and subsequently bonding metals, in particular sheet metal, sheet metal parts, or sheet metal laminations. It has surprisingly been found that the composition according to the invention has a high storage stability, preferably at room temperature, so that the composition can be used for coating and subsequently bonding metals, in particular sheet metal, even after several months, i.e., at least six, preferably at least eight, and even more preferably at least twelve, months without any loss of quality.

[0014] If a metal, in particular a sheet metal or sheet metal part, is coated with the composition according to the invention, it can be bonded to a second, optionally coated metal even after a period of at least six months. This makes it possible to store coated metals for an extended period and to process and bond them as needed.

[0015] The composition according to the invention has the advantage that it can be dried on the surface of a metal quickly and at lower temperatures than comparable prior art compositions, and simultaneously pre-crosslinked (in less than two minutes). This allows coating processes to be optimized and shortened. In particular, the coating of sheet metal, which is usually stored rolled, is significantly simplified and optimized, as the sheets can be re-rolled very quickly after coating, usually immediately after the rolling and coating process.

[0016] A further advantage of the present invention is that additional tempering of the coated, punched, and optionally layered sheets prior to final bonding and curing is no longer necessary, although this is often practiced according to the prior art (see, for example, WO 2020 / 233840), since the curing parameters can be adjusted so precisely that broad application windows (time and temperature gradients) are eliminated. This leads to additional energy savings and increased efficiency when using the composition according to the invention.

[0017] The "activation and final curing" of the pre-crosslinked coating on the metal and the subsequent bonding to another metal can also be carried out in a shorter time (in less than two minutes) compared to other prior art compositions.

[0018] The composition according to the invention is particularly advantageous because, for example, harmful Lewis acids—as suggested in the literature—for crosslinking the components can be dispensed with. Furthermore, the composition according to the invention can be provided essentially water-based, thus largely eliminating the need for organic solvents. The use of water as the basis of the compositions offers safety advantages on the one hand, and health benefits on the other, since, for example, vapors / offgases from organic solvents can be prevented and / or minimized.

[0019] By providing a basic hardener and a crosslinker in the composition according to the invention, it is possible to control both the (pre-)crosslinking and the final curing of the resins and their bonding to a metallic surface more advantageously than adhesive compositions previously described in the prior art.

[0020] The crosslinking of the resins with the composition according to the invention thus takes place in two chemically different and easily controllable sub-steps.

[0021] In a first sub-step, the composition applied to a metallic surface undergoes pre-crosslinking at temperatures and times adapted to production requirements through a reaction of secondary hydroxyl groups from the linear, difunctional (epoxy functionality of 2), and preferably long-chain epoxy resins with multifunctional, preferably di- or trifunctional, isocyanates to form a wide-mesh, elastic polyurethane matrix. In this first step, the epoxy groups are initially retained. The isocyanates present in the composition according to the invention are in amine-blocked form as delivered and are only unblocked and enabled for polyaddition upon moderate temperature influence. The amines formed simultaneously do not escape into the environment, but are added to the oxirane groups of the epoxy resins to form tertiary amines.These in turn accelerate the polyurethane formation (addition of the isocyanates to the hydroxyl groups), so that this first step of crosslinking takes place very quickly and completely, whereby the resulting adhesive layer still remains thermoplastic and is therefore ideally suited for a second step as a hot-melt adhesive.

[0022] By selecting the isocyanates, their spacer length, the blocking amines, and the optimal crosslinking parameters, the desired properties can be reproducibly adjusted by the skilled person. Surprisingly, it has also been shown that 0.2 to 1.0, preferably 0.3 to 0.8, and even more preferably 0.3 to 0.6, NCO equivalents (i.e., isocyanate equivalents) per OH equivalent result in a particularly suitable precrosslinking.

[0023] To achieve a thermosetting and thus heat-resistant full crosslinking in a second step, a further addition reaction of at least one basic hardener with at least two amine-bonded hydrogen atoms per molecule and sufficient thermally reactive epoxy groups in the composition is required. It has been shown that this can be achieved with amine hardeners based on guanidines, for example, and the use of preferably hydroxyl-free, at least trifunctional non-linear epoxy resins, such as novolak epoxy resins (i.e., epoxy resins with an average epoxy functionality of at least 3).

[0024] The average functionality of the epoxy resin mixture (ie, the number of epoxy groups per resin molecule) in the composition according to the invention is preferably 2.3 to 5.0, more preferably 2.4 to 3.5. With such a functionality, the best results in terms of heat resistance, adhesion, and peel strength can be achieved.

[0025] It has also been shown that the ratio of oxirane to NH groups in the composition according to the invention should preferably be in the range of 0.8 to 1.3, even more preferably 0.9 to 1.1.

[0026] In summary, NCO and oxirane groups react, albeit in the gradual order of the above crosslinking steps, by addition reactions with OH and NH groups to form a thermosetting, sufficiently elastic material for joining electrical sheets.

[0027] A further aspect of the present invention relates to a coated metal, preferably coated sheet, producible by applying a composition according to the invention to a solid body, preferably to a sheet.

[0028] Yet another aspect of the present invention relates to a method for coating and optionally bonding metal sheets, comprising the steps Applying a composition according to the invention to the surface of a sheet, drying and simultaneous pre-crosslinking of the composition on the surface of the sheet at a temperature of 150 to 200°C, preferably 170-190°C, for a duration of 10 seconds to 2 minutes, preferably 20 to 30 seconds, optionally punching out sheet pieces from the sheet, optionally stacking the punched-out sheet pieces and optionally bonding and curing the punched-out sheet pieces at a temperature of 220 to 260°C, for a duration of 5 seconds to 2 minutes, preferably 10 to 30 seconds.

[0029] A further aspect of the present invention relates to a laminated core or component comprising a laminated core, in particular a component for electrical machines and / or transformers, wherein the laminated core comprises at least two sheets bonded together with a composition according to the invention. DESCRIPTION OF THE EMBODIMENTS

[0030] The composition according to the invention is prepared by mixing a. 1 mol part of at least one linear epoxy resin having an average epoxy equivalent weight of 600 to 5,000 g / mol and an epoxy functionality of 2, b. 0.4 to 0.8 mol parts of at least one non-linear epoxy resin having an average epoxy equivalent weight of 180 to 350 g / mol and an average epoxy functionality of at least 3, c. 0.8 to 1.3 mol parts of at least one basic hardener comprising at least two free amine-bonded hydrogen atoms, and d. 0.9 to 1.2 mol parts of at least one crosslinker comprising at least two blocked isocyanate groups.

[0031] "Molar part," as used herein, represents the molar ratio of the components in the composition to one another. For example, the composition according to the invention comprises 0.4 to 0.8 molar parts of the at least one non-linear epoxy resin per molar part of the at least one linear epoxy resin.

[0032] According to a preferred embodiment of the present invention, the composition comprises water and / or an organic solvent and is in the form of a solution, emulsion or dispersion.

[0033] The composition according to the invention may preferably comprise water and / or an organic solvent, which may, for example, be derived from the starting components dissolved or suspended in water or an organic solvent. Furthermore, water and / or an organic solvent may be added to adjust the viscosity of the composition according to the invention.

[0034] According to a further preferred embodiment of the present invention, the at least one linear epoxy resin has an average epoxy equivalent weight of 1,500 to 2,500 g / mol.

[0035] It has been shown that linear epoxy resins based on bisphenols, so-called bisphenol (di)glycidyl ethers, have particularly advantageous properties. Accordingly, the at least one linear epoxy resin is preferably a bisphenol epoxy resin, preferably a bisphenol A epoxy resin, a bisphenol F epoxy resin, a bisphenol S epoxy resin, or a bisphenol Z epoxy resin, with resins based on bisphenol A being particularly preferred.

[0036] According to a preferred embodiment of the present invention, the at least one linear epoxy resin comprises at least three bisphenol units per molecule.

[0037] According to a further preferred embodiment of the present invention, the at least one linear epoxy resin is a bisphenol A epoxy resin having 3 to 15, preferably 4, 7 or 9, bisphenol A units per molecule.

[0038] The free hydroxyl groups in the linear epoxy resin are essential for the (pre-)crosslinking of the resins. For this reason, the at least one linear epoxy resin preferably comprises hydroxyl groups, with a linear epoxy resin molecule having at least one, preferably at least two, hydroxyl groups.

[0039] According to yet another preferred embodiment of the present invention, the at least one linear epoxy resin comprises two to 14, preferably three, six or eight secondary hydroxyl groups per molecule.

[0040] According to a preferred embodiment of the present invention, the at least one linear epoxy resin comprises a bisphenol A epoxy resin having 2 to 14, preferably 3, 6 or 8 hydroxyl groups per molecule.

[0041] According to a particularly preferred embodiment of the present invention, the at least one non-linear epoxy resin has an average epoxy equivalent weight of 190 to 280 g / mol.

[0042] Preferably, the at least one non-linear epoxy resin is at least one novolak epoxy resin.

[0043] Novolaks are phenolic resins with a formaldehyde-to-phenol ratio of less than 1:1, obtained by acid condensation of the reactants. Novolaks are particularly well-suited for the composition of the present invention because they have low oxirane equivalent weights and high functionality, making them particularly suitable for controlled curing. Due to the absence of hydroxyl groups, they only enter the processing cascade during the final curing step (i.e., during bonding).

[0044] According to a preferred embodiment of the present invention, the at least one novolak epoxy resin comprises phenol and / or cresol units, wherein the at least one novolak epoxy resin comprises three to eight, preferably three to six, epoxy groups per molecule of the epoxy resin.

[0045] According to yet another preferred embodiment of the present invention, the mixture of the at least one linear epoxy resin and the at least one non-linear epoxy resin together comprises on average 2.3 to 5.0, preferably 2.4 to 3.5, epoxy groups per molecule of the epoxy resin.

[0046] According to a preferred embodiment of the present invention, the at least one basic hardener comprising at least two free amine-bonded hydrogen atoms is a guanidine derivative, preferably selected from the group consisting of dicyandiamide, dicyandiamidine, aminoguanidine, creatine, creatinine, arginine, aliphatic biguanide, aromatic biguanide, 2-aminopyridimine, 3-amino-1,2,4-triazole, 5-amino-1H-tetrazole, 1,3-di-o-tolylguanidine and 2-cyanimino-1H,5-alkyl-1,3,5-triazine.

[0047] As previously stated, the ratio of oxirane to NH groups in the composition according to the invention is preferably in the range of 0.8 to 1.3, even more preferably 0.9 to 1.1. If individual guanidine derivatives listed here have more than two free amine-bonded hydrogen atoms, which generally have different reactivity, only the minimum value of two is taken into account in the calculations and correlations relevant to the invention.

[0048] To enable additional cross-links in the pre-crosslinked polyurethane matrix during final curing, a basic hardener containing free amino groups is added to the composition according to the invention. The basic hardener is thus responsible for the curing of the composition according to the invention to form a high-strength, thermostable thermoset during the bonding process.

[0049] According to a further preferred embodiment of the present invention, the at least one (pre-)crosslinker is an aliphatic or cycloaliphatic diisocyanate or triisocyanate, wherein the isocyanate groups of the aliphatic or cycloaliphatic diisocyanate or triisocyanate are separated by a C 4 to C 10 alkyl radical as a spacer.

[0050] According to a preferred embodiment of the present invention, the at least one crosslinker comprising at least two isocyanate groups is a diisocyanate, preferably selected from the group consisting of hexamethylene diisocyanate, 2-methylhexamethylene diisocyanate, 2,2,4(2,4,4)-trimethylhexamethylene diisocyanate (TMDI), 1,12-dodecane diisocyanate, omega,omega-diisocyanatodipropyl ether, 1,4-cyclohexane diisocyanate, 1,4-diisocyanatomethylcyclohexane, isophorone diisocyanate, and / or their isocyanurate trimers.

[0051] According to a particularly preferred embodiment of the present invention, the at least one crosslinker comprising at least two isocyanate groups is hexamethylene diisocyanate, isophorone diisocyanate and / or their isocyanurate trimers.

[0052] According to a further preferred embodiment of the present invention, the isocyanate groups are blocked with an amine, preferably with a heterocyclic amine comprising at least two nitrogen heteroatoms.

[0053] The (pre-)crosslinker added to the composition according to the invention is blocked to enable a water-based formulation and thus a long shelf life of the composition, since free isocyanates, due to their reactivity, can only exist in anhydrous systems. In a water-based composition, free isocyanates would lead to an undesirable reaction (pre-crosslinking) with the hydroxyl groups of the linear epoxy resins, i.e., already in the delivered form. One solution would therefore be a less practical two-component solution with additionally short pot lives after mixing. The end results would likely be comparable to those of the invention, but the purpose of the present invention is to provide a storable, one-component, water-based formulation.During the coating process, in which the metal with the coating is heated, the blocking groups are removed to enable cross-linking of the linear epoxy resins to form a still thermoplastic matrix.

[0054] According to a preferred embodiment of the present invention, the amine is a pyrazole, an imidazole, a benzimidazole, a 1,2,3-triazole, preferably a benzotriazole, a 1,2,4-triazole, a triazabicyclodecene or an N-monosubstituted piperazine.

[0055] According to a further preferred embodiment of the present invention, the amine is a pyrazole, preferably 3,4-dimethylpyrazole or 3,5-dimethylpyrazole.

[0056] According to a preferred embodiment of the present invention, the at least one organic solvent is a water-miscible solvent and is selected from the group consisting of a C 3 -C 6 ketone, a C 2 -C 4 alcohol, a monoalkyl (C 2 -C 4 ) ether of C 1 -C 4 glycols, a di- and / or triethylene and / or propylene glycol, dioxane, tetrahydrofuran and C 4 to C 8 lactone.

[0057] A further aspect of the present invention relates to a coated metal producible by applying a composition according to the invention to a solid body, preferably to a sheet.

[0058] The composition according to the invention can be applied to a metallic surface using known methods (e.g., by dipping, spraying, rolling, knife coating, or brushing). After application of the composition, the coating is pre-crosslinked by heating. The metal can then be stored and / or transported for further processing.

[0059] A further aspect of the present invention relates to a method for coating and optionally bonding metal sheets comprising the steps Applying a composition according to the invention to the surface of a sheet, drying the composition on the surface of the sheet and simultaneous pre-crosslinking at a temperature of 150 to 200°C, preferably 170 to 190°C, for a duration of 10 seconds to 2 minutes, preferably 20 to 30 seconds, optionally punching out sheet pieces from the sheet, optionally stacking the punched-out sheet pieces and optionally bonding the punched-out sheet pieces at a temperature of 220 to 260°C, for a duration of 5 seconds to 2 minutes, preferably 10 to 30 seconds.

[0060] Surprisingly, it has been shown that the composition according to the invention can be cured and bonded in a particularly short, yet technically manageable and adjustable time. Furthermore, the temperatures used are lower than with compositions known from the prior art. This makes it possible to design and accelerate industrial processes more cost-effectively.

[0061] A further aspect of the present invention relates to a laminated core or component comprising a laminated core, in particular a component for electrical machines and / or transformers, wherein the laminated core comprises at least two sheets bonded together with a composition according to the invention.

[0062] Using the process according to the invention and the composition according to the invention, laminated cores can be produced simply and quickly. Laminated cores are used in a wide variety of applications, with generators, transformers, and electric motors being the most important areas of application.

[0063] A further aspect of the present invention relates to a laminated core or component comprising a laminated core, in particular a component for electrical machines and / or transformers obtainable by a method according to the invention. EXAMPLES Example 1: Composition I water-based

[0064] The following components were mixed with water to form a dispersion with a total solids content of 53%: 1 mol of a linear epoxy resin (based on bisphenol A) with an epoxy functionality of 2 and an average epoxy equivalent weight of 1750 g / mol present as a 53% dispersion in water / methoxypropanol (3:1), 0.8 mol of a non-linear epoxy resin (based on phenol novolak) with an epoxy functionality of 3.6 and an average equivalent weight of 194 g / mol present as a 58% dispersion in water, 1.1 mol of dicyandiamide (DCDA) calculated with a functionality of 2 and an equivalent weight of 42 g / mol present as a 30% solution in methoxypropanol, and 1.12 mol of a 3,5-dimethylpyrazole (DMP)-blocked hexamethylene diisocyanate (HMDI) with a functionality of 2, present as a 38% solution in Water.

[0065] After mixing, the dispersion was heated to 60°C for 15 minutes and then cooled to room temperature. The viscosity of the dispersion was 60 to 80 s (flow time according to DIN EN ISO 2431:2011).

[0066] Composition I showed the following parameters according to the invention: ∑ Equiv.-OH: 6 ∑ Equiv.-NH: 4,45 ∑ Equiv.-NCO: 2,25 ∑ Equiv.-Oxirane: 4,9 ∑ OH+NH: 10,45 ∑ NCO+Oxirane: 7,15

[0067] Composition I had an average epoxy functionality of 2.71 for the linear and nonlinear epoxy resins. The ratios of NCO to OH groups were 0.37, the ratios of oxirane to NH groups were 1.10, and the ratios of NCO and oxirane groups to OH and NH groups were 0.68.

[0068] Composition I could be stored at room temperature for more than 6 months without any impairment of its beneficial properties. During this period, no detectable separation of the components occurred.

[0069] It was shown that Composition I, after being applied to a sheet at 195°C, can be dried and pre-crosslinked in 20 seconds. Two sheets, one of which was coated with Composition I, could be bonded together at 210°C in 15 seconds.

[0070] To rule out the possibility that this was not purely catalytic action of an amine (DMP) as the DCDA / OXIRAN reaction accelerator, an additional test was conducted using an equimolar amount of DMP instead of the capped (blocked) amine. This composition was so reactive after application to a sheet that almost complete cross-linking of the reactive groups of the composition occurred on the metal surface within a very short time. This rapid cross-linking gave the applied composition thermosetting properties and rendered it impossible to bond thermally.

[0071] To confirm the inventive necessity of the required NCO specification, the simplest prototype of a blocked isocyanate, namely urea, was used instead of the HMDI compound. This comparison composition solidified within 14 hours at room temperature and was no longer amenable to further processing and therefore not storable.

[0072] Further comparative tests showed that common crosslinking agents, such as hexamethylenetetramine or hexamethylolmelamine, used as substitutes for DCDA, also led to significantly shortened curing times of the batches and cured after a few hours. Example 2: Composition II Comparison on Solvent Base

[0073] Composition II differs from Composition I (see Example 1) in that the linear epoxy resin is added as a 75% solution in methyl ethyl ketone (MEK) and the nonlinear epoxy resin is added as a liquid resin. In addition, the blocked hexamethylene diisocyanate is added as a 50% solution in MEK / MP (methoxypropanol) (1:1). The total solids content is adjusted to 40% with MP.

[0074] After mixing, the composition was heated to 60°C for 15 minutes and then cooled to room temperature. The viscosity of the dispersion was 60 s (flow time according to DIN EN ISO 2431:2011).

[0075] Parameters and relations were analogous to Example 1.

[0076] When the composition was stored at room temperature, initial gelation was observed after 10 weeks.

[0077] Shelf life: 10 weeks, then gelling begins.

[0078] However, it was shown that solvent-based composition II, after application to a sheet, can also be pre-cured at 195°C in 20 seconds. Two sheets, one of which was coated with composition II, could be bonded together at 215°C in 12 seconds. Example 3: Composition III water-based

[0079] Composition III, analogous to Composition I, comprised 1 mol of the linear epoxy resin. Composition III also contained 0.6 mol of a cresol-based novolak resin with an epoxy functionality of 5.5 and an average equivalent weight of 215 g / mol, present as a 40% dispersion in water. As a hardener, Composition III contained 1.1 mol of creatinine with a functionality of 2 and an equivalent weight of 56.5 g / mol, present as a 30% solution in methoxypropanol. Composition III additionally contained 1 mol of a DMP-blocked trimeric HMDI with a functionality of 3, present as a 40% solution in water.

[0080] After mixing, composition III was heated to 60°C for 15 minutes and then cooled to room temperature. The viscosity of the dispersion was 60 to 80 s (flow time according to DIN EN ISO 2431:2011).

[0081] Composition III showed the following parameters according to the invention: ∑ Equivalents -OH: 6 ∑ Equivalents -NH: 5 ∑ Equivalents -NCO: 3 ∑ Oxirane equivalents: 5,3 ∑ OH + NH: 11 ∑ NCO + Oxirane: 8,3

[0082] Composition III had an average epoxy functionality of 2.97 for the functionalities of the linear and nonlinear epoxy resins. The ratio of NCO to OH groups was 0.5, the ratio of oxirane to NH groups was 1.06, and the ratio of NCO and oxirane groups to OH and NH groups was 0.75.

[0083] It was shown that Composition III, after being applied to a sheet at 180°C to 195°C, can be dried in 20 to 30 seconds. Two sheets, one of which was coated with Composition III, could be bonded together at 230°C in 25 seconds.

[0084] Composition III showed a slight increase in viscosity after one month of storage at room temperature, and after a further two months, the composition began to gel. However, the resulting thixotropic properties remained acceptable for a further three months.

Claims

1. Composition, preferably for bonding metal sheets, comprising: a. 1 molar part of at least one linear epoxy resin with an average epoxy equivalent weight of 600 to 5,000 g / mol and an epoxy functionality of 2, b. 0.4 to 0.8 molar parts of at least one non-linear epoxy resin with an average epoxy equivalent weight of 180 to 350 g / mol and an average epoxy functionality of at least 3, c. 0.8 to 1.3 molar parts of at least one basic hardener comprising at least two free amine-bonded hydrogen atoms, and d. 0.9 to 1.2 molar parts of at least one crosslinker comprising at least two blocked isocyanate groups.

2. Composition according to claim 1, characterized in that the composition comprises water and / or an organic solvent and is present as a solution, emulsion or dispersion.

3. Composition according to claim 1 or 2, characterized in that the at least one linear epoxy resin has an average epoxy equivalent weight of 1,500 to 2,500 g / mol.

4. Composition according to any one of claims 1 to 3, characterized in that the at least one linear epoxy resin is a bisphenol epoxy resin, preferably a bisphenol A epoxy resin, a bisphenol F epoxy resin, a bisphenol S epoxy resin or a bisphenol Z epoxy resin, wherein the at least one linear epoxy resin preferably comprises at least three bisphenol units per molecule.

5. Composition according to any one of claims 1 to 4, characterized in that the at least one linear epoxy resin is a bisphenol A epoxy resin having 3 to 15, preferably 4, 7 or 9, bisphenol A units per molecule.

6. Composition according to any one of claims 1 to 5, characterized in that the at least one linear epoxy resin, preferably a bisphenol A epoxy resin, comprises two to 14, preferably three, six or eight secondary hydroxyl groups per molecule.

7. Composition according to any one of claims 1 to 6, characterized in that the at least one non-linear epoxy resin has an average epoxy equivalent weight of 190 to 280 g / mol.

8. Composition according to any one of claims 1 to 7, characterized in that the at least one non-linear epoxy resin is at least one novolak epoxy resin, wherein the at least one novolak epoxy resin preferably comprises phenol and / or cresol units, wherein the at least one novolak epoxy resin comprises three to eight, preferably three to six, epoxy groups per molecule of the epoxy resin.

9. Composition according to any one of claims 1 to 8, characterized in that the at least one linear epoxy resin and the at least one non-linear epoxy resin together comprise on average 2.3 to 5.0, preferably 2.4 to 3.5, epoxy groups per molecule of the epoxy resin.

10. Composition according to any one of claims 1 to 9, characterized in that the at least one basic hardener comprising at least two free amine-bonded hydrogen atoms, a guanidine derivative, preferably selected from the group consisting of dicyandiamide, dicyandiamidine, aminoguanidine, creatine, creatinine, arginine, aliphatic biguanide, aromatic biguanide, 2-aminopyridimine, 3-amino-1,2,4-triazole, 5-amino-1H-tetrazole, 1,3-di-o-tolylguanidine and 2-cyanimino-1H,5-alkyl-1,3,5-triazine.

11. Composition according to any one of claims 1 to 10, characterized in that the at least one crosslinker is an aliphatic or cycloaliphatic diisocyanate or triisocyanate, wherein the isocyanate groups of the aliphatic or cycloaliphatic diisocyanate or triisocyanate are separated by a C4 - to C10 -alkyl radical, preferably selected from the group consisting of hexamethylene diisocyanate, 2-methylhexamethylene diisocyanate, 2,2,4(2,4,4)-trimethylhexamethylene diisocyanate (TMDI), 1,12-dodecane diisocyanate, omega,omega-diisocyanatodipropyl ether, 1,4-cyclohexanediisocyanate, 1,4-diisocyanatomethylcyclohexane, isophorone diisocyanate, and / or their isocyanurate trimers.

12. Composition according to any one of claims 1 to 11, characterized in that the isocyanate groups are blocked with an amine, preferably with a heterocyclic amine comprising at least two nitrogen heteroatoms, wherein the amine is preferably a pyrazole, preferably 3,4-dimethylpyrazole or 3,5-dimethylpyrazole, an imidazole, a benzimidazole, a 1,2,3-triazole, preferably a benzotriazole, a 1,2,4-triazole, a triazabicyclodecene or an N-monosubstituted piperazine.

13. Composition according to any one of claims 2 to 12, characterized in that the at least one organic solvent is a water-miscible solvent and is selected from the group consisting of a C3 -C6 -ketone, a C2 -C4 -alcohol, a monoalkyl (C2 -C4 ) ether of C1 -C4 -glycols, a di- and / or triethylene and / or propylene glycol, dioxane, tetrahydrofuran and C4 to C8 -lactone.

14. Coated metal producible by applying a composition according to any one of claims 1 to 13 to a solid body, preferably to a metal sheet.

15. Process for coating and optionally bonding metal sheets comprising the steps of - Application of a composition according to any one of claims 1 to 13 to the surface of a metal sheet, - Drying and pre-crosslinking of the composition on the surface of the sheet at a temperature of 150 to 200°C, preferably 170 to 190°C, for a period of 10 seconds to 2 minutes, preferably 20 to 30 seconds, - optional punching of sheet metal pieces from the sheet, - optional stacking of the punched sheet metal parts and - optional bonding and hardening of the punched sheet metal parts at a temperature of 220 to 260°C for a period of 5 seconds to 2 minutes, preferably 10 to 30 seconds.

16. Laminated core or component comprising a laminated core, in particular a component for electrical machines and / or transformers, wherein the laminated core comprises at least two sheets bonded together with a composition according to one of claims 1 to 13.

17. Laminated core or component comprising a laminated core, in particular a component for electrical machines and / or transformers obtainable by a method according to claim 15.