ELECTRICAL STEEL STRIP OR SHEET, METHOD FOR PRODUCING SUCH AN ELECTRICAL STEEL STRIP OR SHEET, AND LAMINATION STACK MADE THEREFROM

Abstract

An electrical steel strip or sheet with at least one thermo-hardenable, water-based hot-melt adhesive varnish layer provided on one of its flat sides, a method for producing such an electric steel strip or sheet, and a lamination stack made therefrom are disclosed. In order to be able to have an increased melt viscosity during the baking process, it is proposed that the thermo-hardenable, water-based hot-melt adhesive varnish layer also have a pre-cross-linking agent that bonds with the epoxy resin or with a mixture of epoxy resins, the pre-cross-linking agent being an organic amine with three amino groups, namely an organic triamine or a mixture of such organic amines.

Claims

1. An electrical steel strip or sheet comprising: at least one thermo-hardenable, water-based hot-melt adhesive varnish layer provided on one flat side of the electrical steel strip or sheet, wherein the at least one thermo-hardenable, water-based hot-melt adhesive varnish layer comprises an epoxy resin or a mixture of epoxy resins, at least one hardener, and a pre-cross-linking agent that bonds with the epoxy resin or with the mixture of epoxy resins, and wherein the pre-cross-linking agent is an organic amine with three amino groups.

2. The electrical steel strip or sheet according to claim 1, wherein the three amino groups of the pre-cross-linking agent are each primary amino groups.

3. The electrical steel strip or sheet according to claim 1, wherein percentages by weight of the pre-cross-linking agent and the epoxy resin or mixture of epoxy resins in the water-based, thermo-hardenable hot-melt adhesive varnish layer satisfy the following relation: $\mathrm{Percentage}\mathrm{by}\mathrm{weight}\mathrm{of}\mathrm{pre}\text{-}\mathrm{cross}\text{-}\mathrm{linking}\mathrm{agent}=\frac{\begin{array}{c}\begin{array}{c}\mathrm{Percentage}\mathrm{by}\mathrm{weight}\mathrm{of}\\ \mathrm{the}\mathrm{epoxy}\mathrm{resin}\mathrm{or}\end{array}\\ \mathrm{mixture}\mathrm{of}\mathrm{epoxy}\mathrm{resins}\end{array}}{\begin{array}{c}\mathrm{average}M\mathrm{of}\mathrm{the}\mathrm{epoxy}\mathrm{resin}\mathrm{or}\\ \mathrm{mixture}\mathrm{of}\mathrm{epoxy}\mathrm{resins}\end{array}}*\frac{\begin{array}{c}\mathrm{average}M\mathrm{of}\mathrm{the}\\ \mathrm{pre}\text{-}\mathrm{cross}\text{-}\mathrm{linking}\mathrm{agent}\end{array}}{\begin{array}{c}\begin{array}{c}X*\mathrm{average}\mathrm{number}\mathrm{of}\\ \mathrm{amino}\mathrm{groups}\mathrm{of}\mathrm{the}\end{array}\\ \mathrm{pre}\text{-}\mathrm{cross}\text{-}\mathrm{linking}\mathrm{agent}\mathrm{molecules}\end{array}}$ where X stands for a number from 1.9 to 28.9, and M stands for molar mass.

4. The electrical steel strip or sheet according to claim 1, wherein the pre-cross-linking agent is a polyether triamine.

5. The electrical steel strip or sheet according to claim 4, wherein at least one amino group of the polyether triamine is bonded to secondary carbon atoms of terminal ether groups.

6. The electrical steel strip or sheet according to claim 1, wherein the epoxy resin or the mixture of epoxy resins is bisphenol A-based.

7. The electrical steel strip or sheet according to claim 1, wherein the thermo-hardenable hot-melt adhesive varnish layer has a cyanamide-based hardener that is latent at room temperature.

8. The electrical steel strip or sheet according to claim 1, wherein the thermo-hardenable, water-based hot-melt adhesive varnish layer contains: 35 to 55% by weight of an epoxy resin or mixture of epoxy resins with an average molar mass of 1500 to 2000 g/mol; and 0.1 to 2% by weight of triamine as a pre-cross-linking agent with an average molar mass of 350 to 550 g/mol.

9. The electrical steel strip or sheet according to claim 8, wherein the thermo-hardenable, water-based hot-melt adhesive varnish layer contains 2 to 10% by weight of a latent cyanamide-based hardener.

10. The electrical steel strip or sheet according to claim 9, wherein the thermo-hardenable, water-based hot-melt adhesive varnish layer contains a remainder of water and 4 to 20% by weight of a cosolvent.

11. The electrical steel strip or sheet according to claim 1, wherein the thermo-hardenable hot-melt adhesive varnish layer is dried.

12. The electrical steel strip or sheet according to claim 11, wherein the dried thermo-hardenable hot-melt adhesive varnish layer contains: 75 to 92.8% by weight of an epoxy resin or mixture of epoxy resins with an average molar mass of 1500 to 2000 g/mol, 4 to 24.8% by weight of a hardener, and 0.2 to 4% by weight of triamine as a pre-cross-linking agent with an average molar mass of 350 to 550 g/mol.

13. A method for producing an electrical steel strip or sheet according to claim 1, comprising using a roller application or spray application of the thermo-hardenable, water-based hot-melt adhesive varnish onto the at least one flat side of the electrical steel strip or sheet.

14. A method for producing a lamination stack with an electrical steel strip or sheet according to claim 13, comprising: drying the hot-melt adhesive varnish layer at a strip temperature of 180 to 280° C., detaching sheet-metal parts from the electrical steel strip or sheet, stacking the sheet-metal parts to form a lamination stack, gluing the lamination stack through thermal activation of the hot-melt adhesive varnish layer.

15. A lamination stack produced with the method according to claim 14.

16. A lamination stack composed of an electrical steel strip or sheet, whose thermo-hardenable hot-melt adhesive varnish layer is produced with a method according to claim 14, wherein the hot-melt adhesive varnish layer is dried and hardened.

17. The electrical steel strip or sheet according to claim 1, wherein the pre-cross-linking agent is an organic triamine or a mixture of organic amines.

18. The electrical steel strip or sheet according to claim 1, wherein the pre-cross-linking agent is a polyoxypropylene triamine.

19. The electrical steel strip or sheet according to claim 1, wherein the thermo-hardenable hot-melt adhesive varnish layer has a cyanamide-based hardener that consists of dicyandiamide.

20. The electrical steel strip or sheet according to claim 10, wherein the cosolvent is 1-methoxy-propanol.

Description

WAYS TO IMPLEMENT THE INVENTION

[0037] The invention will be explained by way of example below based on an embodiment variant.

Exemplary Embodiment 1

[0038] The relation for achieving an optimal pre-cross-linking that is improved according to the invention can among other things enable a particularly advantageous balancing of storage stability, ease of use, and leakproofness of the hot-melt adhesive varnish layer. The greater the value of X is, the lower the mass of the pre-cross-linking agent is in relation to the epoxy resin or mixture of epoxy resins. Excessively low values of X—and thus in the relation an excessively high percentage by weight of the pre-cross-linking agent—can result in lower storage stability because of the risk that a hot-melt adhesive varnish could already gel before use, which would simply make it more difficult to apply the hot-melt adhesive varnish. Excessively high values of X—and thus in the relation an excessively low percentage by weight of the pre-cross-linking agent—can among other things result in an excessively low degree of pre-cross-linking being achieved and in the hot-melt adhesive varnish having an excessively low viscosity and therefore being no longer leakage-stable.

[0039] In a preferred exemplary embodiment 1, an electric steel strip or sheet is coated with a thermo-hardenable, water-based hot-melt adhesive varnish layer, 100 grams of which hot-melt adhesive varnish layer contains: [0040] 50 grams of an epoxy resin with an average molar mass of 2000 g/mol, [0041] 5.0 grams of dicyandiamide as a latent hardener, [0042] 1.0 grams of triamine as a pre-cross-linking agent with an average molar mass of 440 g/mol, namely a polyoxypropylene triamine of the following structural formula with three primary amino groups, which are bonded to secondary carbon atoms of terminal ether groups,

##STR00001## [0043] 10 grams of 1-methoxy-propanol as a copolymer, and a remainder of water.

[0044] Other additives and/or adjuvants are also conceivable.

[0045] In addition, the percentages by weight of the pre-cross-linking agent and the epoxy resin or mixture of epoxy resins in the thermo-hardenable hot-melt adhesive varnish layer satisfy the relation:

[00002]$\mathrm{Percentage}\mathrm{by}\mathrm{weight}\mathrm{of}\mathrm{pre}\text{-}\mathrm{cross}\text{-}\mathrm{linking}\mathrm{agent}=\frac{\begin{array}{c}\begin{array}{c}\mathrm{Percentage}\mathrm{by}\mathrm{weight}\mathrm{of}\\ \mathrm{the}\mathrm{epoxy}\mathrm{resin}\mathrm{or}\end{array}\\ \mathrm{mixture}\mathrm{of}\mathrm{epoxy}\mathrm{resins}\end{array}}{\begin{array}{c}\mathrm{average}M\mathrm{of}\mathrm{the}\mathrm{epoxy}\mathrm{resin}\mathrm{or}\\ \mathrm{mixture}\mathrm{of}\mathrm{epoxy}\mathrm{resins}\end{array}}*\frac{\begin{array}{c}\mathrm{average}M\mathrm{of}\mathrm{the}\\ \mathrm{pre}\text{-}\mathrm{cross}\text{-}\mathrm{linking}\mathrm{agent}\end{array}}{\begin{array}{c}\begin{array}{c}X*\mathrm{average}\mathrm{number}\mathrm{of}\\ \mathrm{amino}\mathrm{groups}\mathrm{of}\mathrm{the}\end{array}\\ \mathrm{pre}\text{-}\mathrm{cross}\text{-}\mathrm{linking}\mathrm{agent}\mathrm{molecules}\end{array}}$

where M stands for molar mass. In exemplary embodiment 1, X turns out to have the value 3.67—which value also falls within the particularly preferably claimed range of 2.9 to 7.2.

[0046] Conventional layer thicknesses for steel strips have a thickness of 4 μm to 16 μm for the wet varnish; this is equivalent to approximately 2 μm to 8 μm in the dried state. For example, approximately 10 g/m.sup.2/strip side corresponds to a layer thickness of 5 μm in the dried state (i.e. approximately 10 μm of wet varnish thickness).

[0047] This composition can be used to adjust a particular state of the hot-melt adhesive varnish layer. The primary amino groups of the triamine react—at least at room temperature—with reactive epoxy groups of the epoxy resin to form secondary and tertiary amines. This therefore yields comparatively voluminous compounds in the thermo-hardenable, water-based hot-melt adhesive varnish layer and results in an increase in the molar mass.

[0048] The ratio of amino groups and epoxy groups according to the invention is also ideal for achieving a degree of pre-cross-linking that is ample enough to not cause a gelling of the water-based hot-melt adhesive varnish layer.

[0049] A hot-melt adhesive varnish of this kind has a high storage stability at room temperature without negatively affecting its properties with regard to adhesiveness and adhesive strength relative to the electric steel strip or sheet. For example, it can easily achieve a shelf life of 6 months. The water-based, thermo-hardenable hot-melt adhesive varnish layer is therefore easy to use.

[0050] The pre-cross-linking agent of the exemplary embodiment 1 exhibits another advantageous property, namely a steric hindrance at the carbon atom that carries the amino group. This results in the fact that the amino group of the polyether triamine is bonded to a secondary carbon atom of a terminal ether group. This influences the reactivity of the amino group. In particular, it reduces the tendency of a secondary amino group of the pre-cross-linking agent—i.e. an amino group that has already undergone a bonding with an epoxy resin molecule—to react with a second epoxy resin molecule to form a tertiary amino group. Thus not only can the degree of pre-cross-linking be adjusted with particular ease, but also the hot-melt adhesive varnish layer is also comparatively storage-stable. It can be stored at room temperature, even for a period of six months.

[0051] It has also surprisingly turned out that a particularly good adhesive strength of the hot-melt adhesive varnish layer according to the invention relative to an electric steel strip or sheet is achieved.

[0052] The hot-melt adhesive varnish layer according to the invention on the electric steel strip or sheet is dried at a strip temperature of 220° C.—as a result, water and the cosolvent, i.e. 1-methoxy-propanol, are driven out of the hot-melt adhesive varnish layer. After this process, the dried thermo-hardenable hot-melt adhesive varnish layer of exemplary embodiment 1 is composed of [0053] 89% by weight epoxy resin, [0054] 8.9% by weight dicyandiamide as a latent hardener, and [0055] 2.1% by weight triamine as a pre-cross-linking agent

[0056] It must presumed that the amino groups of the pre-cross-linking agent each react with at least one epoxy group of different epoxy resin molecules of the epoxy resin.

[0057] According to the invention, an increased drying speed of the hot-melt adhesive varnish layer on the electric steel strip or sheet is observed. This dried thermo-hardenable hot-melt adhesive varnish layer also excels due to a high hardness with very good elasticity at the same time. The improved ductility is of particularly great significance—in combination with the outstanding adhesive strength of the dried thermo-hardenable hot-melt adhesive varnish layer relative to the electric steel strip or sheet, there are substantial improvements with regard to peel resistance.

[0058] As proof of the improvement in the peel resistance, the comparison results of 3 samples are shown.

Sample 1: Prior Art

[0059] The composition of the thermo-hardenable hot-melt adhesive varnish layer of sample 1 corresponds to a conventional commercially available baked varnish.

Sample 2: Prior Art

[0060] The composition of the thermo-hardenable hot-melt adhesive varnish layer from sample 2 corresponds to that of exemplary embodiment 1 (sample 3) according to the invention, but without the addition of the pre-cross-linking agent.

Sample 3: Exemplary Embodiment 1

[0061] The composition of the thermo-hardenable hot-melt adhesive varnish layer corresponds to that of exemplary embodiment 1 according to the invention. This was applied in a layer thickness of 5 μm onto a silicon-alloyed (approx. 3% Si) electric steel strip using roller application and underwent a drying at a strip temperature (PMT—peak metal temperature) of 220° C.

[0062] The peel resistance was determined using the method specified in the standard EN 1464.

[0063] Table 1 shows a clear increase in the peel resistance for sample 3.

[0064] A particular advantage according to the invention lies in the adjustability of the melt viscosity of the dried thermo-hardenable hot-melt adhesive varnish layer during hardening. This is achieved in particular because of the special pre-cross-linking by means of the relation according to the invention of the percentage by weight of the pre-cross-linking agent and the epoxy resin in the thermo-hardenable hot-melt adhesive varnish layer. It is thus possible to reduce the risk of leakage of hot-melt adhesive varnish during the baking process of electric steel strips or sheets coated with hot-melt adhesive varnish according to the invention or the baking of sheet metal parts produced therefrom.

[0065] This is possible without a disadvantageous influence with regard to the stability and dispersion and with regard to the use of the hot-melt adhesive varnish, e.g. during application of the hot-melt adhesive varnish layer. Among other things, this is surprising because—despite an additional hardener that is also latent at room temperature—with the aid of a pre-cross-linking agent, which bonds to resin at room temperature, a high storage stability at room temperature is nevertheless assured and with regard to the further use, there are also no negative effects due to the drying of the thermo-hardenable hot-melt adhesive varnish layer on the electric steel strip or sheet.

[0066] Even percentages by weight of the pre-cross-linking agent that are slightly increased—relative to the limits according to the invention—not only result in a massive reduction in the storage stability of the thermo-hardenable, water-based hot-melt adhesive varnish, but also increase the melt viscosity of the dried thermo-hardenable hot-melt adhesive varnish layer on the electric steel strip or sheet to a degree that decreases its adhesion strength to an unacceptable degree.