ELECTRICAL STEEL STRIP OR SHEET, METHOD FOR PRODUCING SUCH AN ELECTRICAL STEEL STRIP OR SHEET, AND LAMINATED CORE MADE THEREFROM

Abstract

An electrical steel strip or sheet with a thermosetting water-based hot-melt adhesive varnish layer provided on at least one of its flat sides, a method for producing such an electrical steel strip or sheet, and a laminated core made therefrom are disclosed. In order to produce a particularly storable and aging-stable thermosetting hot-melt adhesive varnish layer on the electrical steel strip or sheet in the B state, it is proposed for the stoichiometric ratio of the epoxy groups of the epoxy resin or epoxy resins relative to the hydrogen atoms of the at least two amino groups of the hardener that is latent at room temperature to lie in the range from 1.33:1 to 5:1.

Claims

1. An electrical steel strip or sheet with a thermosetting water-based hot-melt adhesive varnish layer provided on at least one of its flat sides, comprising: an epoxy resin or a mixture of different epoxy resins; and a hardener that is latent at room temperature and has at least two amino groups, which are primary and/or secondary amino groups, wherein a stoichiometric ratio of epoxy groups of the epoxy resin or epoxy resins relative to hydrogen atoms of the at least two amino groups of the latent hardener is in a range from 1.33:1 to 5:1.

2. The electrical steel strip or sheet according to claim 1, wherein the stoichiometric ratio is in a range from 2.0:1 to 2.7:1.

3. The electrical steel strip or sheet according to claim 1, wherein the stoichiometric ratio is in a range from 2.0:1 to 4:1.

4. The electrical steel strip or sheet according to claim 1, wherein epoxy resin molecules of the epoxy resin have on average 1 to 3 epoxy groups per 1000 g of their molar mass or the epoxy resin molecules of the mixture of different epoxy resins have on average 1 to 3 epoxy groups per 1000 g of their average molar mass.

5. The electrical steel strip or sheet according to claim 1, wherein the epoxy resin is based on bisphenol.

6. The electrical steel strip or sheet according to claim 1, wherein epoxy groups of the epoxy resin molecules are terminally positioned on the epoxy resin molecules.

7. The electrical steel strip or sheet according to claim 1, wherein the latent hardener has exactly two primary amino groups.

8. The electrical steel strip or sheet according to claim 1, wherein the latent hardener is based on cyanamide.

9. The electrical steel strip or sheet according to claim 1, wherein the thermosetting water-based hot-melt adhesive varnish layer has 35 to 55 wt % of the epoxy resin or of the mixture of different epoxy resins with an average molar mass of 1000 to 2000 g/mol and 0.15 to 1.0 wt % of the latent hardener.

10. The electrical steel strip or sheet according to claim 1, wherein the hot-melt adhesive varnish layer also has an organic triamine as a pre-crosslinking agent that bonds with epoxy resin at room temperature.

11. The electrical steel strip or sheet according to claim 10, wherein the thermosetting water-based hot-melt adhesive varnish layer has 35 to 55 wt % of the epoxy resin or of the mixture of different epoxy resins with an average molar mass of 1000 to 2000 g/mol, 0.1 to 2 wt % of triamine as a pre-crosslinking agent with an average molar mass of 350 to 550 g/mol, and 0.15 to 1.0 wt % of the latent hardener.

12. The electrical steel strip or sheet according to claim 1, wherein the thermosetting water-based hot-melt adhesive varnish layer optionally has a filler, which filler is a metal carbonate, metal sulfate, metal sulfide, metal silicate, or metal phosphate, or an arbitrary mixture thereof and has an average grain size of 0.6 to 3 μm.

13. The electrical steel strip or sheet according to claim 1, wherein the thermosetting water-based hot-melt adhesive varnish layer has a residue of water and a cosolvent in the form of 1-methoxy-propanol.

14. The electrical steel strip or sheet according to claim 1, wherein the thermosetting hot-melt adhesive varnish layer dried at a strip temperature of 180 to 280° C.

15. The electrical steel strip or sheet according to claim 14, wherein the thermosetting hot-melt adhesive varnish layer has: 75 to 92.8 wt % of the epoxy resin or of the mixture of different epoxy resins with an average molar mass of 1000 to 2000 g/mol, 0.3 to 2 wt % of the latent hardener, and a residue of water and cosolvent.

16. The electrical steel strip or sheet according to claim 10, wherein the thermosetting hot-melt adhesive varnish layer is dried at a strip temperature of 180 to 280° C., and has: 75 to 92.8 wt % of the epoxy resin or of the mixture of different epoxy resins with an average molar mass of 1000 to 2000 g/mol, 0.2 to 4 wt % triamine as a pre-crosslinking agent with an average molar mass of 350 to 550 g/mol, 0.3 to 2 wt % of the latent hardener, and a residue of water and cosolvent.

17. The electrical steel strip or sheet according to claim 12, wherein the thermosetting hot-melt adhesive varnish layer is dried at a strip temperature of 180 to 280° C., and has: 50 to 82.8 wt % of the epoxy resin or of the mixture of different epoxy resins with an average molar mass of 1000 to 2000 g/mol, 10 to 25 wt % of the filler, 0.3 to 2 wt % of the latent hardener, optionally 0.2 to 4 wt % of triamine as a pre-crosslinking agent with an average molar mass of 350 to 550 g/mol, and a residue of water and a cosolvent.

18. The electrical steel strip or sheet according to claim 14, wherein the thermosetting hot-melt adhesive varnish layer is free of water and cosolvents.

19. A method for producing the electrical steel strip or sheet according to claim 1, comprising a roller application or a spray application of the thermosetting water-based hot-melt adhesive varnish carried out on at least one flat side of the electrical steel strip or sheet.

20. The method for producing a laminated core with sheet metal parts of an electrical steel strip or sheet according to claim 19, including the steps: 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 laminated core, bonding the laminated core by thermal activation of the hot-melt adhesive varnish layer.

21. A laminated core produced with the method according to claim 20.

22. A laminated core produced from an electrical steel strip or sheet according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0067] In the following, the invention will be demonstrated by way of example based on a plurality of embodiments:

[0068] FIG. 1 shows the comparison of the invention to an exemplary embodiment from the prior art

[0069] FIG. 2 shows the comparison of the effects according to the invention based on two additional examples.

WAY TO IMPLEMENT THE INVENTION

Exemplary Embodiment 1 (EE1)

[0070] Exemplary embodiment 1 relates to a silicon-alloyed (for example 3% Si) electrical steel strip with a thermosetting water-based hot-melt adhesive varnish layer provided on one of its flat sides, which was applied by roller application in a layer thickness of 5 μm—which hot-melt adhesive varnish layer has:

40.0 wt % epoxy resin with an average molar mass of 1000 g/mol
1.00 wt % dicyandiamide
9.00 wt % 1-methoxy-propanol
and a residue of water. Exemplary embodiment EE1 therefore does not contain other ingredients such as fillers. Also, no accelerants are provided.

[0071] In 100 grams of the recipe according to EE1, there are thus 40.0 grams of the epoxy resin with an average molar mass of 1000 g/mol—and thus 0.0400 mol of epoxy resin molecules, which epoxy resin molecules each have two epoxy groups.

[0072] These 100 grams of the recipe according to EE1 also contain 1.00 gram of dicyandiamide with a molar mass of 84.08 g/mol—consequently this example has 0.0119 mol of dicyandiamide molecules, with a total of 4 hydrogen atoms of the amino groups per dicyandiamide molecule.

[0073] In exemplary embodiment 1, the stoichiometric ratio of the epoxy groups of the epoxy resin to the hydrogen atoms of the amino groups of the dicyandiamide as a latent hardener is therefore 0.0800:0.0476, i.e. 1.68:1. This is within the stoichiometric ratio of claim 1, namely within the range of from 1.33:1 to 5:1.

[0074] In addition, the requirement of claim 4 is satisfied: The 0.0400 mol of epoxy resin molecules, which in exemplary embodiment EE1 have a molar mass of 1000 g/mol, have 0.0800 mol of epoxy groups—this yields an average of 2 epoxy groups per 1000 g of the molar mass of the epoxy resin.

[0075] After being applied in accordance with claim 14, the hot-melt adhesive varnish layer is dried at a strip temperature (PMT—peak metal temperature) of 220° C. This yields an electrical steel strip in the B state, which is coated with an essentially wa-ter-free and cosolvent-free thermosetting hot-melt adhesive varnish layer.

Prior Art (PA1):

[0076] The known example PA1 is a silicon-alloyed (for example 3% Si) electrical steel strip with a thermosetting water-based hot-melt adhesive varnish layer provided on one of its flat sides, which was applied by roller application in a layer thickness of 5 μm—which hot-melt adhesive varnish layer has:

40.0 wt % epoxy resin with an average molar mass of 1000 g/mol
2.00 wt % dicyandiamide
9.00 wt % 1-methoxy-propanol
and a residue of water.

[0077] In 100 grams of the recipe according to PA1 there are thus 40.0 grams of the epoxy resin with an average molar mass of 1000 g/mol—and thus 0.0400 mol of epoxy resin molecules, which epoxy resin molecules each have two epoxy groups. These 100 grams of the recipe according to PA1 also contain 2.00 grams of dicyandiamide with a molar mass of 84.08 g/mol—consequently this example has 0.0240 mol of dicyandiamide molecules, with a total of 4 hydrogen atoms of the amino groups per dicyandiamide molecule.

[0078] In PA1, the stoichiometric ratio of the epoxy groups of the epoxy resin to the hydrogen atoms of the amino groups of the dicyandiamide as a latent hardener is therefore 0.0800:0.0960, i.e. 0.83 to 1. This is not within the stoichiometric ratio of claim 1, namely within the range of from 1.33:1 to 5:1.

[0079] After being applied, the hot-melt adhesive varnish layer is likewise dried at a strip temperature (PMT—peak metal temperature) of 220° C. This yields an electrical steel strip in the B state, which is coated with an essentially water-free and cosol-vent-free thermosetting hot-melt adhesive varnish layer.

Comparison of Exemplary Embodiment 1 (EE1) to the Prior Art (PA1):

[0080] FIG. 1 shows the roller peel force of exemplary embodiment 1 (EE1) according to the invention compared to that of the prior art (PA1).

[0081] For this purpose, the electrical steel strips EE1 and PA1, which had been dried as mentioned above, were stored for 4 days at a strip temperature of 60° C. and were then cooled to room temperature. Then a hardening of the hot-melt adhesive varnish layer was carried out by means of thermal activation at 130° C. for 4 hours and with a mechanical pressure of 1 megapascal. The subsequent determination of the roller peel force was performed using the method according to the standard EN 1464.2010-02. The value 100 in FIG. 1 stands for the roller peel force of the electrical steel strips EE1 and PA1, which have been dried as mentioned above and then hardened as mentioned above—but without being stored above room temperature in the B state.

[0082] According to FIG. 1, there is a clear increase in the roller peel force for EE1—which means that the invention achieves a significantly smaller adverse effect on the adhesion force due to an elevated storage temperature.

Exemplary Embodiment 2 (EE2)

[0083] Exemplary embodiment 2 relates to a silicon-alloyed (for example 3% Si) electrical steel strip with a thermosetting water-based hot-melt adhesive varnish layer provided on one of its flat sides, which was applied by roller application in a layer thickness of 5 μm—which hot-melt adhesive varnish layer has: [0084] 40.00 wt % epoxy resin with an average molar mass of 1000 g/mol [0085] 0.75 wt % dicyandiamide [0086] 0.75 wt % polyether triamine as a pre-crosslinking agent with the following struc-tural formula (brand name Jeffamine® T-403)

##STR00001## [0087] 9.0 wt % 1-methoxy-propanol
and a residue of water. Other ingredients such as fillers are conceivable, but accelerants are avoided.

[0088] In 100 grams of the recipe according to EE2, there are thus 40.00 grams of the epoxy resin with an average molar mass of 1000 g/mol—and thus 0.0400 mol of epoxy resin molecules, which epoxy resin molecules each have two epoxy groups. These 100 grams of the recipe according to EE2 also contain 0.75 grams of dicyandiamide with a molar mass of 84.08 g/mol—consequently this example has 0.0089 mol of dicyandiamide molecules, with a total of 4 hydrogen atoms of the amino groups per dicyandiamide molecule.

[0089] Without taking into account the other ingredients of the recipe from EE2, the stoichiometric ratio of the epoxy groups of the epoxy resin to the hydrogen atoms of the amino groups of the dicyandiamide as a latent hardener is therefore 0.0800:0.0357, i.e. 2.24:1. This is within the stoichiometric ratio of claim 1, namely within the range of from 1.33:1 to 5:1—and is within the preferred ranges of claims 2 and 3.

[0090] In 100 g of the recipe according to EE2 there are 0.75 g of Jeffamine® T-403. Jeffamine® T-403 has a molar mass of 440 g/mol—in exemplary embodiment EE2, the 6 hydrogen atoms of the primary amino groups per pre-crosslinking agent molecule of Jeffamine® T-403 yield 0.0102 mol of hydrogen atoms. On the assumption that all 0.0102 mol of the hydrogen atoms of the primary amino groups of the pre-crosslinking agent Jeffamine® T-403 react with epoxy groups of the epoxy resin in the A state or B state of the hot-melt adhesive varnish layer, i.e. in the thermosetting water-based hot-melt adhesive varnish layer or in the thermosetting dried hot-melt adhesive varnish layer, the number of the epoxy groups of the epoxy resin is reduced by the total number of hydrogen atoms of the primary amino groups of the pre-crosslinking agent. Taking into account the pre-crosslinking agent contained, 0.0698 mol of epoxy groups of the epoxy resin would still be present after this in exemplary embodiment EE2. This means that a stoichiometric ratio of the epoxy groups of the epoxy resin to the hydrogen atoms of the amino groups of the dicyandiamide as a latent hardener of 1.96:1 would still be present—the stoichiometric ratio of claim 1 is thus still satisfied.

[0091] Based on this assumption, the feature of claim 4 is likewise still satisfied: The 0.0400 mol of epoxy resin molecules, which in the exemplary embodiment have a molar mass of 1000 g/mol, have 0.0698 mol of epoxy groups—this yields an average of 1.745 epoxy groups per 1000 g of the molar mass of the epoxy resin.

[0092] The subsequent drying of exemplary embodiment 2 takes place in accordance with exemplary embodiment 1.

[0093] The same comparison test with regard to the roller peel force of EE2 was carried out as mentioned above—namely EE2 instead of EE1 in comparison to the prior art PA1.

[0094] Essentially the same result is apparent for EE2 as for EE1 in FIG. 1—which among other things demonstrates that the stoichiometric ratio according to the invention can be used even if a pre-crosslinking agent is present and more precisely, a pre-crosslinking agent does not exhibit any adverse effects on the above-mentioned advantages of the stoichiometric ratio.

Exemplary Embodiment 3 (EE3)

[0095] Exemplary embodiment 3 relates to a silicon-alloyed (for example 3% Si) electrical steel strip with a thermosetting water-based hot-melt adhesive varnish layer provided on one of its flat sides, which was applied by roller application in a layer thickness of 5 μm—which hot-melt adhesive varnish layer has: [0096] 40.0 wt % epoxy resin with an average molar mass of 1000 g/mol, the epoxy resin molecules each having an average of two epoxy groups, [0097] 1.00 wt % dicyandiamide [0098] 1.25 wt % of the polyether triamine mentioned in EE2 as a pre-crosslinking agent (brand name Jeffamine® T-403) [0099] 9.00 wt % 1-methoxy-propanol
and a residue of water. Other ingredients such as fillers are conceivable, but accelerants are avoided.

[0100] The recipe therefore corresponds to that of exemplary embodiment 1 (EE1)—but also contains the indicated pre-crosslinking agent.

[0101] The epoxy resin molecules in the recipe of EE3, as mentioned above, have an average molar mass of 1000 g/mol. They also have an average of 2 epoxy groups each, which in this exemplary embodiment 3 therefore yields 2 epoxy groups per 1000 g of the average molar mass of the epoxy resin molecules.

[0102] The 100 grams of the recipe according to EE3 also contain 1.00 gram of dicyandiamide with a molar mass of 84.08 g/mol—consequently, this example has 0.0119 mol of dicyandiamide molecules, with a total of 4 hydrogen atoms of the amino groups per dicyandiamide molecule.

[0103] Without taking into account the other ingredients of the recipe from EE3, the stoichiometric ratio of the epoxy groups of the epoxy resin to the hydrogen atoms of the amino groups of the dicyandiamide as a latent hardener is therefore 0.0800:0.0476, i.e. 1.68:1. This is within the stoichiometric ratio of claim 1.

[0104] In the 100 g of the recipe according to EE2, however, there are also 1.25 grams of Jeffamine® T-403. Jeffamine® T-403 has a molar mass of 440 g/mol—in exemplary embodiment EE2, the 6 hydrogen atoms of the primary amino groups per pre-crosslinking agent molecule of Jeffamine® T-403 yield 0.0170 mol of hydrogen atoms.

[0105] On the assumption that all 0.0170 mol of the hydrogen atoms of the primary amino groups of the pre-crosslinking agent Jeffamine® T-403 react with epoxy groups of the epoxy resin in the A state or B state of the hot-melt adhesive varnish layer, i.e. in the thermosetting water-based hot-melt adhesive varnish layer or in the thermosetting dried hot-melt adhesive varnish layer, the number of the epoxy groups of the epoxy resin is reduced by the total number of hydrogen atoms of the primary amino groups of the pre-crosslinking agent. In other words, 0.0630 mol of epoxy groups of the epoxy resin would still be present after this in exemplary embodiment EE2. This means that based on this assumption, a stoichiometric ratio of the epoxy groups of the epoxy resin to the hydrogen atoms of the amino groups of the dicyandiamide as a latent hardener of 1.32:1 is still present—based on this assumption, the stoichiometric ratio of claim 1 is no longer satisfied.

[0106] Based on this assumption, the feature of claim 4 is still satisfied: The 0.0400 mol of epoxy resin molecules, which in the exemplary embodiment have a molar mass of 1000 g/mol, have 0.0630 mol of epoxy groups—this yields an average of 1.575 epoxy groups per 1000 g of the molar mass of the epoxy resin.

[0107] The subsequent drying of exemplary embodiment 2 takes place in accordance with exemplary embodiment 1 (EE1).

[0108] After being applied in accordance with claim 14, the hot-melt adhesive varnish layer is dried at a strip temperature (PMT—peak metal temperature) of 220° C. An electrical steel strip in the B state, which is coated with an essentially water-free and cosolvent-free thermosetting hot-melt adhesive varnish layer, is thus obtained—this means that under the indicated drying conditions only residual water that has not escaped and cosolvent that has not escaped are still found in the thermosetting hot-melt adhesive varnish layer.

FIG. 2:

[0109] FIG. 2 shows the comparison of the roller peel force of exemplary embodiment 2 (EE2) according to the invention and exemplary embodiment 3 (EE3).

[0110] For this purpose, the electrical steel strips EE2 and EE3, which had been dried as mentioned above, were stored for 7 days at a strip temperature of 60° C. and were then cooled to room temperature. Then a hardening of the hot-melt adhesive varnish layer was carried out by means of thermal activation at 130° C. for 4 hours and with a mechanical pressure of 1 megapascal. The subsequent determination of the roller peel force was performed using the method according to the standard EN 1464.2010-02.

[0111] The value 100 in FIG. 2 stands for the roller peel force of the electrical steel strips EE2 and EE3, which have been dried as mentioned above and then hardened as mentioned above—but without being stored for 7 days at the strip temperature of 60° C. in the B state.

[0112] According to FIG. 2, it is clear for EE2, which likewise has a pre-crosslinking agent, that its roller peel force is reduced to a less significant degree than that of EE3—which means that the invention achieves a significantly smaller adverse effect on the adhesion force due to an elevated storage temperature.