composition

Abstract

The invention relates to a composition, preferably for bonding metal sheets together, comprising: a. 1 mole fraction of at least one linear epoxy resin having an average epoxy equivalent weight of 600 to 5000 g / mol and an epoxy functionality of 2, b. 0.4 to 0.8 mole fraction 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 mole fraction of at least one basic curing agent comprising at least two free amine-bonded hydrogen atoms, and d. 0.9 to 1.2 mole fraction of at least one crosslinker comprising at least two blocked isocyanate groups.

Description

Technical Field

[0001] This invention relates to compositions particularly suitable for bonding metal sheets together. Background Technology

[0002] Bonded metal components, such as sheet metal components, are used in a wide variety of technical fields. Particularly in the construction of generators, motors, transformers, and other electrical systems, stacks of bonded electrical sheet metal components serve as raw materials for magnetic cores. The sheet metal components to be bonded typically have a special adhesive layer on one or both sides, preferably a cross-linkable hot-melt adhesive, known as an "adhesive varnish." The advantage of coatings made from adhesive varnishes is that they do not produce any adhesive effect after being applied to the surface of metal, especially sheet metal (e.g., metal strips). The adhesive layer is activated only during the bonding process, for example, by providing heat. Due to this activation, the coating becomes adhesive, allowing the metal parts to bond together. Simultaneously, the adhesive layer cures and becomes a heat-resistant thermosetting plastic.

[0003] The production of sheet metal components or sheets of metal bonded together with adhesive varnish has the following advantages:

[0004] a) Maintaining magnetism by applying appropriate bonding temperatures and pressures to preserve the microstructure within the steel structure;

[0005] b) The compact, thin-sheet package with tight manufacturing tolerances improves the dissipation of waste heat generated during operation. This minimizes the need for cooling components.

[0006] c) The viscoelastic bonding layer between individual thin sheets exhibits significant damping behavior for sound transmission;

[0007] d) A thin and stable adhesive layer with no adhesive leakage at the outer edges allows for a high degree of design freedom while using the narrowest possible tolerances;

[0008] e) Corrosion problems (interlayer corrosion) are avoided through highly stable, heat-resistant, and hydrolysis-resistant full-surface bonding; and

[0009] f) Good insulation effect against electrical short circuits, which can result in, for example, improved transformer efficiency.

[0010] Crosslinkable hot melt adhesives have been well described in the prior art. For example, WO 2006 / 049935 discloses an adhesive composition comprising an epoxy resin, fumed silica particles, and a selected curing agent, such as a phenolic resin, a carboxylic acid, an anhydride, an isocyanate, and particularly dicyandiamide, which is used as the sole curing agent in all examples of use. This self-adhesive coating is applied to an electrical board and dried at a temperature between 230°C and 260°C. Sheets punched from the coated electrical board are stacked one on top of the other and bonded together at a temperature between 100°C and 300°C and under increased pressure for 60 to 120 minutes.

[0011] The adhesive composition described in WO 2006 / 049935 essentially comprises bisphenol A or bisphenol F epoxy resin and mixtures thereof (but without any indication of equivalents, functionality, etc.), fumed silica as a filler and reinforcing agent, and a curing agent, such as Lewis acid, which is particularly difficult to handle due to its high health hazards and toxicity in most cases.

[0012] WO 2017 / 050892 also describes a heat-activated adhesive composition comprising an epoxy resin, an activatable curing agent, and an activatable accelerator. These adhesive compositions are cured on a metal sheet surface at temperatures above 100°C. Subsequently, metal sheet sheets are punched out, stacked one on top of the other, and bonded together by activating the adhesive on the surface at approximately 200°C. The activation time of this adhesive is 0.5 to 1 second, with a maximum curing time of 5 seconds.

[0013] In WO 2017 / 050892, the rapid curing of the adhesive layer, i.e., the catalytically accelerated reaction between dicyandiamide as a curing agent and epoxy resin, is achieved by adding specific accelerators, particularly Lewis acids which are generally harmful to health and toxic. This non-specific and rapid chemical reaction results in a very high crosslinking density, leading to brittleness and reduced durability of the adhesive layer. Furthermore, there is a risk of premature partial crosslinking in the liquid delivery state, which manifests as a significant increase in viscosity and a shortened shelf life.

[0014] WO 2020 / 233840 specifically teaches that temperature control must be applied to the punched and thus coated sheets to minimize electrical losses in the finished product (including the machines that bond the sheets together). The process of producing laminated magnetic cores becomes inefficient due to this additional energy-intensive process step.

[0015] The common thread in all three papers discussed here is that the curing of dicyandiamide with epoxy resin is essentially shortened by so-called catalytic accelerators. Related problems, such as precise temperature control, excessively short and difficult-to-control crosslinking times during production, over-crosslinking and associated embrittlement, and the toxicity of the accelerators, are well-established.

[0016] The object of this invention is to provide a water-dilutable composition that allows metal parts, such as metal sheets, to be bonded together in the shortest possible time. Significant cost savings can be achieved by reducing the time required for the bonding process. Furthermore, the composition should not have the disadvantages of the prior art, particularly WO 2006 / 049935, WO 2017 / 050892, and WO 2020 / 233840.

[0017] Another object of the present invention is to provide a composition that is stable for storage for at least six months. Metals coated with this composition should remain adhesive even after storage exceeding six months, without limitation. Summary of the Invention

[0018] This invention relates to a composition, preferably used for bonding metal sheets together, comprising:

[0019] a. 1 mole part of at least one linear epoxy resin having an average epoxy equivalent of 600 to 5000 g / mol and an epoxy functionality of 2.

[0020] b. 0.4 to 0.8 molar parts of at least one nonlinear epoxy resin having an average epoxy equivalent of 180 to 350 g / mol and an average epoxy functionality of at least 3.

[0021] c. 0.8 to 1.3 moles of at least one alkaline curing agent containing at least two free amine-bonded hydrogen atoms, and

[0022] d. 0.9 to 1.2 moles of at least one (pre)crosslinking agent containing at least two capped isocyanate groups.

[0023] The compositions according to the invention can be used as single-component materials for coating and subsequent bonding of metals, particularly metal sheets, metal plate components, or metal sheet flakes. Surprisingly, it has been shown that the compositions according to the invention preferably exhibit high storage stability at room temperature, making the compositions usable for coating and subsequent bonding of metals, particularly metal plates, even after several months, i.e., at least six months, preferably at least eight months, more preferably at least twelve months, without any loss of quality.

[0024] If a metal, particularly a sheet of metal or a sheet of metal component, is coated with the composition according to the invention, it can bond to a second metal that has optionally been coated, even after at least six months. Therefore, the coated metal can be stored for a longer period and can be processed and bonded as needed.

[0025] The composition according to the invention has the advantage of using a lower temperature than similar compositions in the prior art, which allows for rapid drying and simultaneous pre-crosslinking on the metal surface (within less than two minutes). Therefore, the coating process can be optimized and shortened. In particular, since the metal sheet can be rerolled in a very short time after coating, typically immediately after the rolling and coating processes, the coating of metal sheets that are usually stored in a rolled-up state is significantly simplified and optimized.

[0026] Another advantage of this invention is that additional temperature control of the coated, stamped, and optionally layered metal sheets is no longer required before final bonding and curing, although this is common practice according to the prior art (see, for example, WO2020 / 233840), because the curing parameters can be set so precisely that a wide application window (time and temperature gradient) can be omitted. This results in additional energy savings and increased efficiency when using the compositions according to the invention.

[0027] Compared to other compositions in the prior art, the “activation and final curing” of the pre-crosslinked coating on the metal, as well as the subsequent bonding with another metal, can also be carried out in a shorter time (less than two minutes).

[0028] The compositions according to the invention are particularly advantageous because they eliminate the need for health-damaging Lewis acids, such as those taught in the literature, used in crosslinking components. Furthermore, the compositions according to the invention can be provided essentially water-based, thus largely eliminating the need for organic solvents. Using water as the basis of the composition has both safety-related advantages and health-related advantages, as vapors / exhaust gases from organic solvents can be avoided and / or minimized, for example.

[0029] By providing an alkaline curing agent and a crosslinking agent in the composition according to the invention, the (pre)crosslinking and final curing of the resin and its adhesion to the metal surface can be controlled more advantageously than in the adhesive compositions previously described in the prior art.

[0030] Therefore, the crosslinking of the resin with the composition according to the invention is carried out in two chemically distinct and easily controlled sub-steps.

[0031] In the first sub-step, the pre-crosslinking of the composition coated on the metal surface occurs at a temperature and time suitable for the reaction of secondary hydroxyl groups of a linear bifunctional (epoxy functionality 2) and preferably long-chain epoxy resin with a polyfunctional, preferably difunctional or trifunctional isocyanate, to form a large-mesh elastic polyurethane matrix. In this first step, the epoxy groups are temporarily retained. The isocyanate present in the composition according to the invention is delivered in an amine-terminated form and is capable of addition polymerization without being terminated by only moderate temperature influence. Surprisingly, the amines present in this process do not escape into the environment but instead add to the ethylene oxide groups of the epoxy resin to form tertiary amines. These, in turn, accelerate the formation of the polyurethane (isocyanate addition to hydroxyl groups), making the crosslinking in the first sub-step very rapid and complete, and the resulting adhesive layer remains thermoplastic, thus perfectly suited as a hot melt adhesive for the second step.

[0032] By selecting the isocyanate, its spacer length, the capped amine, and optimal crosslinking parameters, those skilled in the art can set the desired properties in a reproducible manner. Surprisingly, it has also been shown that an NCO equivalent (i.e., isocyanate equivalent) of 0.2 to 1.0, preferably 0.3 to 0.8, more preferably 0.3 to 0.6 per OH equivalent produces a particularly suitable pre-crosslinking.

[0033] To achieve thermosetting and therefore heat-resistant complete crosslinking in the second sub-step, further addition reactions of at least one basic curing agent with at least two amine-bonded hydrogen atoms per molecule and a large number of thermally reactive epoxy groups in the composition are necessary. It has been shown that this can be achieved, for example, by guanidine-based amine curing agents and by using at least trifunctional nonlinear epoxy resins, preferably hydroxyl-free, such as phenolic varnish epoxy resins (i.e., epoxy resins with an average epoxy functionality of at least 3).

[0034] The average functionality (i.e., the number of epoxy groups per resin molecule) of the epoxy resin mixture in the composition according to the invention is preferably 2.3 to 5.0, more preferably 2.4 to 3.5. This functionality allows for optimal results in terms of heat resistance, adhesion, and peel strength.

[0035] Furthermore, it has been shown that the ratio of ethylene oxide to NH groups in the compositions according to the invention should preferably be 0.8 to 1.3, more preferably 0.9 to 1.1.

[0036] In summary, the NCO and ethylene oxide groups thus react, although in a hierarchical order of the crosslinking steps described above, in each case forming a thermosetting, sufficiently elastic material for connecting electrical panels through addition reactions with OH and NH groups.

[0037] Another aspect of the invention relates to coated metals, preferably coated metal plates, which can be prepared by coating the composition of the invention onto a solid, preferably a metal plate.

[0038] Another aspect of the invention relates to a method for coating metal sheets and optionally bonding them together, comprising the following steps:

[0039] - The composition according to the invention is coated onto the surface of a metal plate.

[0040] - The composition is dried at a temperature of 150 to 200°C, preferably 170 to 190°C, on the surface of a pre-crosslinked metal plate for 10 seconds to 2 minutes, preferably 20 to 30 seconds.

[0041] -Optionally punch metal sheets out of the metal plate,

[0042] -Optional stacking of punched metal sheet components, and

[0043] - Optionally, the stamped metal sheet components are bonded together and cured at a temperature of 220 to 260°C for 5 seconds to 2 minutes, preferably 10 to 30 seconds.

[0044] Another aspect of the invention relates to laminated magnetic cores or component parts including laminated magnetic cores, particularly component parts for motors and / or transformers, wherein the laminated magnetic core comprises at least two metal plates bonded together by the composition of the invention. Detailed Implementation

[0045] The compositions of the present invention are prepared by mixing the following:

[0046] a. 1 mole part of at least one linear epoxy resin having an average epoxy equivalent of 600 to 5000 g / mol and an epoxy functionality of 2.

[0047] b. 0.4 to 0.8 molar parts of at least one nonlinear epoxy resin having an average epoxy equivalent of 180 to 350 g / mol and an average epoxy functionality of at least 3.

[0048] c. 0.8 to 1.3 moles of at least one alkaline curing agent containing at least two free amine-bonded hydrogen atoms, and

[0049] d. 0.9 to 1.2 moles of at least one crosslinking agent containing at least two end-capped isocyanate groups.

[0050] As used herein, “molar parts” refers to the molar ratio of the components present in the composition. For example, a composition according to the invention comprises 0.4 to 0.8 molar parts of at least one nonlinear epoxy resin / at least one molar part of at least one linear epoxy resin.

[0051] According to a preferred embodiment of the invention, the composition comprises water and / or an organic solvent and is provided as a solution, emulsion, or dispersion.

[0052] The compositions according to the invention may preferably contain water and / or an organic solvent, for example derived from a starting component 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 compositions according to the invention.

[0053] According to a further preferred embodiment of the present invention, the average epoxy equivalent of at least one linear epoxy resin is 1500 to 2500 g / mol.

[0054] It has been shown that bisphenol-based linear epoxy resins, namely so-called bisphenol (di) glycidyl ethers, have particularly advantageous properties. Therefore, 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 bisphenol A-based resins being particularly preferred.

[0055] According to a preferred embodiment of the present invention, at least one linear epoxy resin comprises at least three bisphenol units per molecule.

[0056] According to a further preferred embodiment of the present invention, 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.

[0057] Free hydroxyl groups in linear epoxy resins are essential for the (pre-)crosslinking of the resin. For this reason, at least one linear epoxy resin preferably contains hydroxyl groups, wherein the linear epoxy resin molecule has at least one, preferably at least two hydroxyl groups.

[0058] According to another preferred embodiment of the invention, at least one linear epoxy resin contains 2 to 14, preferably 3, 6 or 8, secondary hydroxyl groups per molecule.

[0059] According to a preferred embodiment of the present invention, 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.

[0060] According to a particularly preferred embodiment of the present invention, the average epoxy equivalent of at least one nonlinear epoxy resin is 190 to 280 g / mol.

[0061] Preferably, at least one nonlinear epoxy resin is at least one phenolic varnish epoxy resin.

[0062] Phenolic varnishes are phenolic resins with a formaldehyde / phenol ratio of less than 1:1, obtained through the acidic condensation of reactants. Phenolic varnishes are particularly useful in the compositions of this invention because they have low ethylene oxide equivalents and high functionality, making them especially suitable for controlled curing. Due to the absence of hydroxyl groups, they only participate in the processing cascade during the final curing process (i.e., during bonding).

[0063] According to a preferred embodiment of the present invention, at least one phenolic varnish epoxy resin comprises phenol and / or cresol units, and at least one phenolic varnish epoxy resin comprises 3 to 8, preferably 3 to 6, epoxy groups per molecule of epoxy resin.

[0064] According to another preferred embodiment of the invention, the mixture of at least one linear epoxy resin and at least one nonlinear epoxy resin together contains an average of 2.3 to 5.0, preferably 2.4 to 3.5 epoxy groups per molecule of epoxy resin.

[0065] According to a preferred embodiment of the present invention, at least one alkaline curing agent containing at least two free amine-bonded hydrogen atoms is a guanidine derivative, preferably selected from the group consisting of dicyandiamide, amidourea, aminoguanidine, creatine, creatine anhydride, arginine, aliphatic biguanide, aromatic biguanide, 2-aminopyrimidine, 3-amino-1,2,4-triazole, 5-amino-1H-tetrazole, 1,3-di-o-tolylguanidine, and 2-cyanoimino-1H,5-alkyl-1,3,5-triazine.

[0066] As previously stated, in the compositions according to the invention, the ratio of ethylene oxide to NH groups is preferably 0.8 to 1.3, more preferably 0.9 to 1.1. If some of the guanidine derivatives listed herein have more than two free amine-bonded hydrogen atoms, which typically react in different ways, then in the calculations and relevance to the invention, only the minimum value of two is considered in each case.

[0067] To promote additional cross-linking in the pre-crosslinked polyurethane matrix during the final curing process, an alkaline curing agent containing free amino groups is added to the composition according to the invention. Therefore, the alkaline curing agent is responsible for curing the composition according to the invention during the bonding process to form a high-strength, thermally stable thermosetting plastic.

[0068] According to a further preferred embodiment of the invention, at least one (pre)crosslinking agent is an aliphatic or alicyclic diisocyanate or triisocyanate, wherein the isocyanate group of the aliphatic or alicyclic diisocyanate or triisocyanate is C4 to C4, which serve as spacers. 10 Alkyl groups are separated.

[0069] According to a preferred embodiment of the present invention, at least one crosslinking agent comprising at least two isocyanate groups is a diisocyanate, preferably selected from the group consisting of hexamethylene diisocyanate, 2-methyl-hexamethylene diisocyanate, 2,2,4(2,4,4)-trimethylhexamethylene diisocyanate (TMDI), 1,12-dodecane diisocyanate, ω,ω-diisocyanate dipropyl ether, 1,4-cyclohexane diisocyanate, 1,4-methylcyclohexane diisocyanate, isophorone diisocyanate and / or isocyanurate trimers thereof.

[0070] According to a particularly preferred embodiment of the invention, at least one crosslinking agent comprising at least two isocyanate groups is hexamethylene diisocyanate, isophorone diisocyanate and / or an isocyanurate trimer.

[0071] According to a further preferred embodiment of the invention, the isocyanate group is capped by an amine, preferably by a heterocyclic amine containing at least two nitrogen atoms.

[0072] Free isocyanates, due to their reactivity, can only exist in anhydrous systems. Therefore, a (pre)crosslinking agent added to the composition according to the invention is used to cap the composition to achieve an aqueous formulation, thereby achieving a long shelf life. In aqueous compositions, free isocyanates cause a reaction with the hydroxyl groups of the linear epoxy resin (pre-crosslinking), which is undesirable at this point in time, i.e., when it is already in a deliverable form. Therefore, a less practical two-component approach is needed, which also has a short pot life when mixed. The end result is certainly comparable to those according to the invention, but the object of the invention is to provide a single-component formulation that can be stored on an aqueous basis. In a coating process in which the metal and coating are heated together, the capping groups are removed so that the linear epoxy resin can crosslink to form a still thermoplastic matrix.

[0073] According to a preferred embodiment of the present invention, the amine is a pyrazole, imidazole, benzimidazole, 1,2,3-triazole, preferably benzotriazole, 1,2,4-triazole, triazabicyclodecene, or N-monosubstituted piperazine.

[0074] According to a preferred embodiment of the present invention, the amine is a pyrazole, preferably 3,4-dimethylpyrazole or 3,5-dimethylpyrazole.

[0075] According to a preferred embodiment of the invention, at least one organic solvent is a water-miscible solvent and is selected from the group consisting of monoalkyl-(C2-C4)-ethers of C3-C6 ketones, C2-C4 alcohols, C1-C4 diols, di- and / or triethylene glycol and / or propylene glycol, dioxanes, tetrahydrofurans and C4 to C8 lactones.

[0076] Another aspect of the invention relates to coated metals, which can be prepared by coating a composition according to the invention onto a solid, preferably a metal plate.

[0077] The compositions according to the invention can be applied to metal surfaces using known methods (e.g., by dipping, spraying, roller coating, blade coating, or brush coating). After applying the composition, the coating is pre-crosslinked by heating. The metal can then be stored for further processing and / or transportation.

[0078] Another aspect of the invention relates to a method for coating metal sheets and optionally bonding them together, comprising the following steps:

[0079] - Coat the surface of a metal plate with the composition of the present invention.

[0080] - The composition on the surface of the metal plate is dried at a temperature of 150 to 200°C, preferably 170 to 190°C, for 10 seconds to 2 minutes, preferably 20 to 30 seconds, while simultaneously pre-crosslinking it.

[0081] -Optionally punch metal sheets out of the metal plate,

[0082] - Optionally, the stamped metal sheet components are bonded together at a temperature of 220 to 260°C for 5 seconds to 2 minutes, preferably 10 to 30 seconds.

[0083] Surprisingly, the compositions according to the invention can cure and bond together in a particularly short, but technically controllable and adjustable, time. Furthermore, the temperature used for this is lower than that employed in compositions known in the prior art. Therefore, industrial processes can be designed and accelerated in a more cost-effective manner.

[0084] Another aspect of the invention relates to laminated magnetic cores or component parts including laminated magnetic cores, particularly component parts for motors and / or transformers, wherein the laminated magnetic core comprises at least two metal plates bonded together by the composition of the invention.

[0085] Laminated magnetic cores can be produced in a simple and rapid manner using the method and composition according to the invention. Laminated magnetic cores are used in various fields, with generators, transformers, and electric motors being the most important applications.

[0086] Another aspect of the invention relates to laminated magnetic cores or component parts including laminated magnetic cores that are obtainable by the method according to the invention, particularly component parts for motors and / or transformers.

[0087] Example

[0088] Example 1: Aqueous Composition I

[0089] The following components were mixed with water to form a dispersion with a total solids content of 53%:

[0090] A linear epoxy resin (based on bisphenol A) with an epoxy functionality of 2 and an average epoxy equivalent of 1750 g / mol is provided as a 53% dispersion in water / methoxypropanol (3:1).

[0091] -0.8 mol of nonlinear epoxy resin with an epoxy functionality of 3.6 and an average epoxy equivalent of 194 g / mol (based on phenolic varnish), provided as a 58% dispersion in water.

[0092] -1.1 mol of dicyandiamide (DCDA) with a functionality of 2 and an equivalent of 42 g / mol, provided as a 30% methoxypropanol solution, and

[0093] -1.12 mol of hexamethylene diisocyanate (HMDI) with a functionality of 2, capped by 3,5-dimethylpyrazole (DMP), is provided in a 38% aqueous solution.

[0094] After mixing, heat the dispersion to 60°C and hold for 15 minutes, then cool to room temperature. The viscosity of the dispersion is 60 to 80 s (flow time according to DIN EN ISO 2431:2011).

[0095] According to the present invention, composition I exhibits the following parameters:

[0096]

[0097] Composition I exhibits an average epoxy functionality of 2.71 for both linear and nonlinear epoxy resins. The ratio of NCO to OH groups is 0.37, the ratio of ethylene oxide to NH groups is 1.10, and the ratio of NCO and ethylene oxide groups to OH and NH groups is 0.68.

[0098] Composition I can be stored at room temperature for more than 6 months without affecting its beneficial properties. During this period, no significant separation of components was observed.

[0099] It was found that after being coated onto a metal plate, Composition I could dry and pre-crosslink at 195°C within 20 seconds. Two metal plates, one of which was coated with Composition I, could be bonded together at 210°C within 15 seconds.

[0100] To rule out the possibility that this was not a pure catalytic effect of the amine (DMP) as a DCDA / ethylene oxide reaction promoter, an equimolar amount of DMP was used instead of the blocked (terminated) amine in another experiment. After the composition was coated onto the metal plate, it became reactive, causing the reactive groups of the composition to undergo almost complete cross-linking on the metal surface within a very short time. Due to this rapid cross-linking, the coated composition exhibited thermosetting properties and could not be thermally bonded together.

[0101] To demonstrate the necessity of the NCO specification required for this invention, the simplest prototype of a capped isocyanate, namely urea, was used instead of the HMDI compound. This comparative composition cured at room temperature for 14 hours and was no longer suitable for further processing, therefore it was not storable.

[0102] In further comparative tests, it became clear that common crosslinking agents that replace DCDA, such as hexamethylenetetramine or hexamethylolmelamine, also resulted in a significant reduction in batch lifespan and curing after only a few hours.

[0103] Example 2: Solvent-based comparative composition II

[0104] Composition II differs from Composition I (see Example 1) in that the linear epoxy resin is added in a 75% solution of methyl ethyl ketone (MEK), while the non-linear epoxy resin is added as a liquid resin. Furthermore, the end-capped hexamethylene diisocyanate is added in a 50% MEK / MP (methoxypropanol) (1:1) solution. The total solids content is adjusted to 40% using MP.

[0105] After mixing, the composition is heated to 60°C and held for 15 minutes, then cooled to room temperature. The viscosity of the dispersion is 60 s (flow time according to DIN EN ISO 2431:2011).

[0106] The parameters and relationships are similar to those in Example 1.

[0107] When the composition was stored at room temperature, gelation was observed to begin after 10 weeks.

[0108] Shelf life: 10 weeks, then it begins to gel.

[0109] However, it was found that solvent-based composition II could also be pre-crosslinked within 20 seconds at 195°C after being coated onto the metal plates. Two metal plates, one of which was coated with composition II, could be bonded together within 12 seconds at 215°C.

[0110] Example 3: Aqueous Composition III

[0111] Similar to Composition I, Composition III comprises 1 mole of linear epoxy resin. Furthermore, Composition III comprises 0.6 moles of cresol-phenolic varnish resin with an epoxy functionality of 5.5 and an average equivalent of 215 g / mol, provided as a 40% dispersion in water. As for the curing agent, Composition III comprises 1.1 moles of creatine anhydride with a functionality of 2 and an equivalent of 56.5 g / mol, provided as a 30% methoxypropanol solution. Composition III further comprises 1 mole of DMP-terminated trimer HMDI with a functionality of 3, provided as a 40% aqueous solution.

[0112] After mixing, composition III is heated to 60°C and held for 15 minutes, then cooled to room temperature. The viscosity of the dispersion is 60 to 80 s (flow time according to DIN EN ISO 2431:2011).

[0113] According to the present invention, composition III exhibits the following parameters:

[0114]

[0115] Composition III exhibits an average epoxy functionality of 2.97, encompassing both linear and nonlinear epoxy resin functionalities. The ratio of NCO to OH groups is 0.5, the ratio of ethylene oxide to NH groups is 1.06, and the ratio of NCO and ethylene oxide groups to OH and NH groups is 0.75.

[0116] It was found that after being coated onto a metal plate, Composition III could dry within 20 to 30 seconds at 180°C to 195°C. Two metal plates, one of which was coated with Composition III, could be bonded together within 25 seconds at 230°C.

[0117] After one month of storage at room temperature, the viscosity of composition III increased slightly, and the composition began to gel after another two months. However, the resulting thixotropic properties remained acceptable for the next three months.

Claims

1. A composition for bonding metal sheets together, comprising: a. 1 mole part of at least one linear epoxy resin having an average epoxy equivalent of 600 to 5000 g / mol and an epoxy functionality of 2, wherein the linear epoxy resin is a bisphenol epoxy resin. b. 0.4 to 0.8 molar parts of at least one nonlinear epoxy resin having an average epoxy equivalent of 180 to 350 g / mol and an average epoxy functionality of at least 3, wherein the nonlinear epoxy resin is a phenolic varnish epoxy resin. c. 0.8 to 1.3 moles of at least one alkaline curing agent comprising at least two free amine-bonded hydrogen atoms, wherein the alkaline curing agent comprising at least two free amine-bonded hydrogen atoms is a guanidine derivative, and d. 0.9 to 1.2 moles of at least one crosslinking agent containing at least two terminal isocyanate groups, wherein the crosslinking agent containing at least two terminal isocyanate groups is an aliphatic or alicyclic diisocyanate or triisocyanate.

2. The composition according to claim 1, characterized in that, The composition contains water and / or an organic solvent and is provided as a solution, emulsion, or dispersion.

3. The composition according to claim 1 or 2, characterized in that, The average epoxy equivalent of bisphenol epoxy resin is 1500 to 2500 g / mol.

4. The composition according to claim 1 or 2, characterized in that, Bisphenol epoxy resin is bisphenol-A epoxy resin, bisphenol-F epoxy resin, bisphenol-S epoxy resin or bisphenol-Z epoxy resin, and bisphenol epoxy resin contains at least three bisphenol units per molecule.

5. The composition according to claim 4, characterized in that, Bisphenol epoxy resin is a bisphenol-A epoxy resin having 3 to 15 bisphenol A units per molecule.

6. The composition according to claim 4, characterized in that, Bisphenol epoxy resin is a bisphenol-A epoxy resin having 4, 7 or 9 bisphenol A units per molecule.

7. The composition according to claim 5, characterized in that, Bisphenol epoxy resins contain 2 to 14 secondary hydroxyl groups per molecule.

8. The composition according to claim 5, characterized in that, Bisphenol epoxy resins contain 3, 6, or 8 secondary hydroxyl groups per molecule.

9. The composition according to claim 1 or 2, characterized in that, The average epoxy equivalent of phenolic varnish epoxy resin is 190 to 280 g / mol.

10. The composition according to claim 1 or 2, characterized in that, Phenolic varnish epoxy resin contains phenol and / or cresol units, and each molecule of phenolic varnish epoxy resin contains 3 to 8 epoxy groups.

11. The composition according to claim 10, characterized in that, Phenolic varnish epoxy resin contains 3 to 6 epoxy groups per molecule of epoxy resin.

12. The composition according to claim 1 or 2, characterized in that, Bisphenol epoxy resin and phenolic varnish epoxy resin together contain an average of 2.3 to 5.0 epoxy groups per molecule of epoxy resin.

13. The composition according to claim 1 or 2, characterized in that, Bisphenol epoxy resin and phenolic varnish epoxy resin together contain an average of 2.4 to 3.5 epoxy groups per molecule of epoxy resin.

14. The composition according to claim 1 or 2, characterized in that, The guanidine derivatives are selected from the group consisting of dicyandiamide, amidourea, aminoguanidine, creatine, creatine anhydride, arginine, aliphatic biguanides, aromatic biguanides, 2-aminopyrimidine, 3-amino-1,2,4-triazole, 5-amino-1H-tetrazole, 1,3-di-o-tolylguanidine, and 2-cyanoimino-1H,5-alkyl-1,3,5-triazine.

15. The composition according to claim 1 or 2, characterized in that, The isocyanate group of aliphatic or alicyclic diisocyanates or triisocyanates is C4 to C5. 10 Alkyl groups are separated.

16. The composition according to claim 1 or 2, characterized in that, Aliphatic or alicyclic diisocyanates or triisocyanates are selected from the group consisting of hexamethylene diisocyanate, 2-methyl-hexamethylene diisocyanate, 2,2,4(2,4,4)-trimethylhexamethylene diisocyanate (TMDI), 1,12-dodecane diisocyanate, ω,ω-diisocyanate dipropyl ether, 1,4-cyclohexane diisocyanate, 1,4-methylcyclohexane diisocyanate, isophorone diisocyanate and / or isocyanurate trimers thereof.

17. The composition according to claim 15, characterized in that, The isocyanate group is capped by an amine.

18. The composition according to claim 15, characterized in that, The isocyanate group is capped by a heterocyclic amine containing at least two nitrogen atoms.

19. The composition according to claim 18, characterized in that, Heterocyclic amines are selected from the group consisting of pyrazole, 3,4-dimethylpyrazole, 3,5-dimethylpyrazole, imidazole, benzimidazole, 1,2,3-triazole, benzotriazole, 1,2,4-triazole, triazabicyclodecene, or N-monosubstituted piperazine.

20. The composition according to claim 2, characterized in that, At least one organic solvent is a water-miscible solvent and is selected from the group consisting of monoalkyl-(C2-C4)-ethers of C3-C6 ketones, C2-C4 alcohols, C1-C4 diols, di- and / or triethylene glycol and / or propylene glycol, dioxanes, tetrahydrofurans and C4 to C8 lactones.

21. A coated metal, which can be prepared by coating a metal plate with the composition of any one of claims 1 to 20.

22. A method for coating metal sheets and bonding them together, comprising the following steps: - Apply the composition of any one of claims 1 to 20 to the surface of a metal plate. - The composition is dried and applied to the surface of a pre-crosslinked metal plate at a temperature of 150 to 200°C for 10 seconds to 2 minutes. - Metal sheets are punched out from the metal plate. - Stacked stamped metal sheet components, and - Bond the punched metal sheet parts together and harden them at a temperature of 220 to 260°C for 5 seconds to 2 minutes.

23. The method according to claim 22, characterized in that, The composition is dried and applied to the surface of a pre-crosslinked metal plate at a temperature of 170 to 190°C for 20 to 30 seconds.

24. The method according to claim 22, characterized in that, The punched metal sheet components are bonded together and cured at a temperature of 220 to 260°C for 10 to 30 seconds.

25. A laminated magnetic core or an assembly comprising a laminated magnetic core, said laminated magnetic core comprising at least two metal plates bonded together by a composition according to any one of claims 1 to 20.

26. A laminated magnetic core or an assembly comprising a laminated magnetic core may be obtained by the method according to any one of claims 22 to 24.

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