Insulation coating composition for electrical steel sheet, electrical steel sheet, and method for manufacturing same

Abstract

An insulation coating composition for an electrical steel sheet according to an embodiment of the present invention comprises as solids: 30 to 45 wt % of an organic resin; 30 to 45 wt % of a metal phosphate; 1 to 8 wt % of a silane resin; and 8 to 17 wt % of a nitrate.

Description

Electrical steel sheet insulation film composition, electrical steel sheet, and method of manufacturing the same

[0001] One embodiment of the present invention relates to an electrical steel sheet insulating film composition, an electrical steel sheet, and a method for manufacturing the same. Specifically, it relates to an electrical steel sheet insulating film composition, an electrical steel sheet, and a method for manufacturing the same that improves weather resistance and bonding properties between steel sheets.

[0002] Electrical steel sheets are products used as materials for transformers, motors, and electrical equipment. Unlike general carbon steel, which prioritizes processability such as mechanical properties, electrical steel is a functional product that places importance on electrical characteristics. Required electrical properties include low iron loss and high magnetic flux density, permeability, and stacking density.

[0003] Electrical steel sheets are further classified into oriented electrical steel sheets and non-oriented electrical steel sheets. Oriented electrical steel sheets utilize an abnormal grain growth phenomenon called secondary recrystallization to form a Goss texture ({110} <001> It is an electrical steel sheet with excellent magnetic properties in the rolling direction, formed by creating a texture throughout the entire sheet. Non-oriented electrical steel is an electrical steel sheet in which magnetic properties are uniform in all directions on the rolled sheet.

[0004] Electrical steel sheets are used in two forms: one that requires stress relief annealing (SRA) to improve magnetic properties after stamping, and another that omits SRA when the cost loss due to heat treatment outweighs the effect on magnetic properties provided by SRA.

[0005] Meanwhile, the formation of an insulating film is a process corresponding to the final manufacturing process of a product. In addition to electrical properties that suppress the generation of eddy currents, it typically requires continuous stamping processability to suppress mold wear when multiple sheets are stacked to form a core after stamping into a predetermined shape, as well as anti-sticking properties and surface adhesion to prevent adhesion between core sheets after the SRA process, which removes processing stress from the steel sheets and restores magnetic properties. In addition to these basic properties, excellent application workability of the coating solution and solution stability that allows for long-term use after mixing are also required. Coating solutions used for this purpose include chromium coatings based on chromic acid and phosphate coatings based on phosphate.

[0006] Insulating films are primarily intended for interlayer insulation between laminated steel plates. However, with the expansion of small electric motors, film performance that is advantageous for processability, weldability, and corrosion resistance, in addition to insulation, has come to be evaluated as a major physical property. Recently, as the surface quality of the steel plates also affects usage characteristics, there has been a demand for electrical steel plates with excellent surface quality.

[0007] As mentioned earlier, non-oriented electrical steel is currently riding the wave of premiumization driven by the development of high-efficiency motors in line with the government's low-carbon policy. As premiumization progresses, the surface of the electrical steel requires high functionality (high insulation, high heat resistance, and high corrosion resistance). In particular, excellent insulation, which can maximize motor performance by minimizing eddy current loss, is an essential requirement. The most common method to secure excellent insulation is to increase the coating thickness. However, increasing the coating thickness has the disadvantage of degrading required characteristics such as weather resistance and inter-sheet fastening.

[0008] One embodiment of the present invention provides an electrical steel sheet insulating film composition, an electrical steel sheet, and a method for manufacturing the same. Specifically, it provides an electrical steel sheet insulating film composition, an electrical steel sheet, and a method for manufacturing the same that improve weather resistance and bonding between steel sheets.

[0009] An insulating film composition for electrical steel sheets according to one embodiment of the present invention comprises, as solid content, 30 to 45 weight% organic resin, 30 to 45 weight% metal phosphate, 1 to 8 weight% silane resin, and 8 to 17 weight% nitrate.

[0010] The organic resin may include one or more of epoxy resins, ester resins, acrylic resins, styrene resins, urethane resins, and ethylene resins.

[0011] Organic resins may include emulsion resins.

[0012] Metal phosphates may include one or more of Mg, Ca, Ba, Sr, Zn, and Al.

[0013] The silane resin may include one or more of methoxypolyethylene glycol-silane (mPEG-Silane), trimethyl(propargyl)silane, trimethoxy(octyl)silane, tris(2-methoxyethoxy)(vinyl)silane, trimethoxy(octadecyl)silane, triacetoxy(methyl)silane, and tris(dimethylamino)silane.

[0014] Nitrates may include one or more of iron nitrate (Fe(NO3)3), aluminum nitrate (Al(NO3)3), cobalt nitrate (Co(NO3)2), calcium nitrate (Ca(NO3)2), strontium nitrate (Sr(NO3)2), zinc nitrate (Zn(NO3)2), manganese nitrate (Mn(NO3)2), magnesium nitrate (Mg(NO3)2), and silver nitrate (AgNO3).

[0015] An electrical steel sheet according to one embodiment of the present invention comprises an electrical steel sheet substrate and an insulating film located on the surface of the electrical steel sheet substrate, wherein the insulating film comprises 30 to 45 weight% of an organic resin, 30 to 45 weight% of a metal phosphate, 1 to 8 weight% of a silane resin, and 8 to 17 weight% of a nitrate.

[0016] The organic resin may have an average aspect ratio of 1.3 to 3.5.

[0017] A method for manufacturing an electrical steel sheet according to one embodiment of the present invention comprises the steps of: preparing an electrical steel sheet substrate; applying an insulating film composition to the surface of the electrical steel sheet substrate; and heat-treating the electrical steel sheet substrate, wherein the insulating film composition comprises, as a solid content, 30 to 45 weight% organic resin, 30 to 45 weight% metal phosphate, 1 to 8 weight% silane resin, and 8 to 17 weight% nitrate.

[0018] The heat treatment step can be performed at a temperature of 250 to 550°C for 5 to 100 seconds.

[0019] According to one embodiment of the present invention, an insulating film with excellent weather resistance and, in particular, excellent fastening properties when steel plates are fastened using an adhesive can be obtained.

[0020] FIG. 1 is a schematic diagram showing a cross-section of an electrical steel sheet according to one embodiment of the present invention.

[0021] Figure 2 is a scanning electron microscope (SEM) image of a cross- section of the insulating film prepared in Example 4.

[0022] Figure 3 is a scanning electron microscope (SEM) image of a cross- section of the insulating film prepared in Example 2.

[0023] Figure 4 is a scanning electron microscope (SEM) image of a cross- section of the insulating film prepared in Comparative Example 2.

[0024] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0025] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0026] When it is stated that one part is "on" or "on" another part, it may be directly on or on the other part, or another part may be involved in between. In contrast, when it is stated that one part is "directly on" another part, no other part is interposed in between.

[0027] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0028] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0029]

[0030] An insulating film composition for electrical steel sheets according to one embodiment of the present invention comprises, as solid content, 30 to 45 weight% organic resin, 30 to 45 weight% metal phosphate, 1 to 8 weight% silane resin, and 8 to 17 weight% nitrate.

[0031] Metal phosphates are known as conventional insulating film compositions. However, after coating, unreacted free phosphoric acid precipitates, leading to hygroscopicity or surface deterioration due to the free phosphoric acid and potentially degrading weather resistance. In one embodiment of the present invention, a silane resin is partially introduced instead of a metal phosphate to drastically reduce the amount of precipitated free phosphoric acid and improve weather resistance. Additionally, the bonding strength between steel plates can be strengthened through the silane resin.

[0032]

[0033] Organic resins are added to the insulating film composition to ensure adhesion and insulation properties with the base steel plate of the insulating film. Specifically, the organic resins may include one or more selected from epoxy resins, siloxane resins, acrylic resins, phenolic resins, styrene resins, vinyl resins, ethylene resins, and urethane resins. More specifically, acrylic resins may be included.

[0034] The organic resin may have a weight-average molecular weight of 1,000 to 100,000 and a number-average molecular weight of 1,000 to 40,000. With respect to the weight-average molecular weight and the number-average molecular weight, if they are below each lower limit, the physical properties of the insulating film, such as curability and strength, may be degraded, and if they exceed each upper limit, phase separation within the resin may occur and compatibility with metal phosphates may decrease. More specifically, the resin may have a weight-average molecular weight of 5,000 to 30,000.

[0035] In addition, the softening point (Tg) of the organic resin may be 30 to 150°C, and the solid fraction (content of solids) may be 10 to 50% by weight. If the softening point (Tg) of the organic resin exceeds 150°C, the viscosity of the composition becomes too high, which may reduce the workability of the coating.

[0036] The organic resin may be included as a solid component in an insulating film composition in an amount of 30 to 45 weight percent. If the organic resin is included in too little, problems may arise regarding stamping resistance, corrosion resistance, weather resistance, and bonding strength with adhesives. If the organic resin is included in too much, problems may arise regarding surface characteristics after heat treatment. More specifically, the organic resin may be included in an amount of 35 to 43 weight percent. In one embodiment of the present invention, the solid component refers to the weight when each component is dried in a state free of volatile components such as solvents. Specifically, assuming a heat treatment process during the formation of an insulating film, it refers to the weight remaining after heat treatment.

[0037] Organic resins may include emulsion resins. Emulsion resins are advantageous compared to dispulsion resins in terms of reaction with hydrophobic adhesives because they can secure hydrophobic groups. In one embodiment of the present invention, emulsion resins and dispulsion resins can be distinguished by whether the solution phase is cloudy (emulsion resin) or translucent (dispulsion resin), or by whether C-enriched particles are detected in the TEM-EDS cross-sectional analysis of the insulating coating layer.

[0038] Metal phosphates ensure heat resistance within the insulating film composition. The insulating film composition contains 30 to 45 weight percent of metal phosphates as a solid content. If the metal phosphate is not included in an appropriate amount, surface properties may deteriorate after heat treatment. If a large amount of metal phosphate is added, the amount of precipitated free phosphoric acid increases and weather resistance may be compromised. More specifically, it may contain 35 to 45 weight percent of metal phosphates.

[0039] Metal phosphates can be produced by a manufacturing process in which a metal oxide is added to pure phosphoric acid (H3PO4) and reacted. To improve the adhesion of the metal phosphate, a condensation reaction between the metal phosphate and boric acid can be induced by additionally adding boric acid during the reaction process and maintaining it for at least 3 hours, and it is also possible to use this condensation product instead of the metal phosphate. In one embodiment of the present invention, the metal phosphate includes not only the metal phosphate but also the condensation product of the metal phosphate and boric acid. The produced metal phosphate is strongly acidic.

[0040] Metal phosphates can be added to the composition using a solution having a solid content of 50 to 70 weight%. At this time, if the solid content in the solution is too low, the amount of free phosphoric acid in the metal phosphate increases, which may cause surface moisture absorption after the production of the metal phosphate; if the solid content is too high, the excess of solid content relative to pure phosphoric acid may result in poor reaction and precipitation.

[0041] Metal phosphates and metal oxides may include various metals without limitation. Specifically, the metals of the metal phosphates and metal oxides may include one or more of Mg, Ca, Ba, Sr, Zn, and Al. More specifically, the metal phosphate may include one or more of magnesium diphosphate (Mg(H2PO4)2) and aluminum diphosphate (Al(H2PO4)3). More specifically, it may include magnesium diphosphate (Mg(H2PO4)2) and aluminum diphosphate (Al(H2PO4)3). In this case, the metal phosphate may include 10 to 40 parts by weight of aluminum diphosphate and 60 to 90 parts by weight of magnesium diphosphate, based on 100 parts by weight of the total metal phosphate. If too little aluminum diphosphate is included, the tensile strength enhancement effect due to the addition of aluminum diphosphate may not be sufficient. If too much aluminum diphosphate is added, the Al component may increase the crystallization of silica, causing cracks in the insulating film. Specifically, the metal phosphate may comprise 15 to 35 parts by weight of aluminum diphosphate and 65 to 85 parts by weight of magnesium diphosphate based on 100 parts by weight of the total metal phosphate, and more specifically, may comprise 20 to 30 parts by weight of aluminum diphosphate and 70 to 80 parts by weight of magnesium diphosphate.

[0042] In one embodiment of the present invention, the fastening force between steel plates resulting from the reduction of metal phosphate can be supplemented by adding silane resin. An insulating film composition according to one embodiment of the present invention contains 1 to 8 weight percent of silane resin as a solid content. If too little silane resin is included, it is difficult to sufficiently secure the fastening force between steel plates. More specifically, 2 to 7 weight percent of silane resin may be included.

[0043] The silane resin may include one or more of methoxypolyethylene glycol-silane (mPEG-Silane), trimethyl(propargyl)silane, trimethoxy(octyl)silane, tris(2-methoxyethoxy)(vinyl)silane, trimethoxy(octadecyl)silane, triacetoxy(methyl)silane, and tris(dimethylamino)silane.

[0044] Nitrates increase ionic strength during the process of forming an insulating film, cause organic resin particles to clump together to increase the aspect ratio of the organic resin within the insulating film, improve the weather resistance of the insulating film, and strengthen the bonding force between steel plates. An insulating film composition according to one embodiment of the present invention contains 8 to 17 weight percent of nitrate as a solid content. If too little nitrate is included, the reaction between the phosphate and the base iron does not occur sufficiently, which may result in inferior weather resistance. If too much nitrate is included, the surface hardness increases due to excessive reaction with the base iron, which may cause a flaking phenomenon. More specifically, it may contain 10 to 15 weight percent.

[0045] The nitrate may include one or more of iron nitrate (Fe(NO3)3), aluminum nitrate (Al(NO3)3), cobalt nitrate (Co(NO3)2), calcium nitrate (Ca(NO3)2), strontium nitrate (Sr(NO3)2), zinc nitrate (Zn(NO3)2), manganese nitrate (Mn(NO3)2), magnesium nitrate (Mg(NO3)2), and silver nitrate (AgNO3). More specifically, the nitrate may include one or more of iron nitrate (Fe(NO3)3), aluminum nitrate (Al(NO3)3), and magnesium nitrate (Mg(NO3)2).

[0046]

[0047] In addition to the aforementioned components, the insulating film composition may include a solvent to facilitate application and to uniformly disperse the components.

[0048]

[0049] FIG. 1 shows a schematic cross-sectional view of an electrical steel sheet (100) according to one embodiment of the present invention. As shown in FIG. 1, the electrical steel sheet (100) according to one embodiment of the present invention includes an electrical steel sheet substrate (10) and an insulating film (20) located on the electrical steel sheet substrate (10).

[0050] The electrical steel substrate (10) can be any general non-oriented or oriented electrical steel without limitation. In one embodiment of the present invention, since the main configuration is to form an insulating film (20) of a special component on the electrical steel substrate (10), a detailed description of the electrical steel substrate (10) is omitted.

[0051] The insulating film (20) comprises 30 to 45 weight% organic resin, 30 to 45 weight% metal phosphate, 1 to 8 weight% silane resin, and 8 to 17 weight% nitrate. Since each component has been described in relation to the aforementioned insulating film composition, a redundant description is omitted. The components and component ratios within the insulating film composition can be maintained during the manufacturing process of the insulating film (20).

[0052] In the insulating film (20), by including nitrates within the insulating film composition components, a phenomenon occurs in which particles clump together and the size of the resin particles increases. Accordingly, the organic resin contained within the insulating film (20) can have an average aspect ratio of 1.3 to 3.5. The aspect ratio can be measured by observing the organic resin particles using a scanning electron microscope on a cross-section including the thickness direction of the insulating film (20). The organic resin particles can be identified as areas with a high C content through cross-sectional TEM-EDS within the insulating film (20), or determined as dark areas on the SEM cross-sectional image. The aspect ratio is the ratio of the longest major axis to the shortest minor axis among the axes of the organic resin particles. The average aspect ratio refers to the average of the number of organic resin particles. In this way, by securing the aspect ratio, the weather resistance and fastening strength of the insulating film (20) can be improved. More specifically, the average aspect ratio can be 1.5 to 3.0.

[0053] A method for manufacturing an electrical steel sheet according to one embodiment of the present invention comprises the steps of: preparing an insulating film composition; applying the insulating film composition to the surface of an electrical steel sheet substrate; and heat-treating the electrical steel sheet substrate.

[0054] As detailed information regarding the insulating film composition has been provided above, redundant explanations are omitted. The method of manufacturing the insulating film composition is not particularly limited and can be manufactured by mixing the aforementioned components.

[0055] In the heat treatment step, the heat treatment temperature may be 250 to 550°C. If the temperature is too low, the reaction between the metal phosphate and the base iron may not occur sufficiently, and weather resistance may be compromised. If the temperature is too high, the fastening force may decrease when fastening the steel plate with the adhesive. More specifically, the heat treatment may be performed at 300 to 500°C. The heat treatment time may be 5 to 100 seconds. More specifically, it may be 10 to 60 seconds.

[0056] The atmosphere during heat treatment may be a nitrogen atmosphere.

[0057]

[0058] Preferred embodiments of the present invention, comparative examples, and evaluation examples thereof are described below. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0059]

[0060] Examples

[0061] A non-oriented electrical steel sheet (150*50 mm) with a thickness of 0.27 mm containing 3.15 wt% silicon (Si) by weight was used as a test specimen, and an insulating film composition having the following solid content ratio was applied to the sheet to a thickness of about 0.7 μm using a bar coater and a roll coater, then heat-treated at 450°C for 20 seconds and slowly cooled in air to form an insulating film on the electrical steel sheet substrate.

[0062] The surface appearance was checked by touching the surface of the insulating film and using 3M tape; if particles were felt or powder came off, it was marked as fine, and if not, it was marked as good.

[0063] Weather resistance was rated as good if the gloss reduction rate before and after storage at RH 85~95% and a temperature of 50~70C was 10% or less, and poor if it was more than that.

[0064] The clamping force was measured using the ISO 4587 (shear strength) method.

[0065] The aspect ratio of the organic resin was calculated using a computer program by observing the cross-section of the insulating film with a scanning electron microscope.

[0066] Organic Resin Silane Resin Metal Phosphate Nitrate Type Content Type Content Type Content Type Content Example 1 Acrylic Emulsion 41 Trimethoxy(octadecyl)silane 5 Al-phosphate 44 Fe-nitrate 10 Example 2 Acrylic Emulsion 38 Trimethoxy(octadecyl)silane 4 Mg-phosphate 43 Fe-nitrate 15 Example 3 Acrylic Emulsion 38 Triacetoxy(methyl)silane 7 Al-phosphate 45 Al-nitrate 10 Example 4 Epoxy Emulsion 41 Tris(2-methoxyethoxy)(vinyl)silane 5 Al-phosphate 44 Fe-nitrate 10 Example 5 Acrylic Emulsion 43 Isobutyl(trimethoxy)silane 2 Al-phosphate 45 Fe-nitrate 10 Example 6 Acrylic Emulsion 38 Trimethoxy(octadecyl)silane 4 Al-phosphate 43 Mg nitrate 15 Comparative Example 1 Acrylic Emulsion 45 -0 Al-phosphate 45 Fe-nitrate 10 Comparative Example 2 Acrylic Emulsion 43 Trimethoxy(octadecyl)silane 5 Al-phosphate 47 Fe-nitrate 5 Comparative Example 3 Acrylic Emulsion 36 Trimethoxy(octadecyl)silane 4 Al-phosphate 40 Fe-nitrate 20 Comparative Example 4 Acrylic Emulsion 36 Trimethoxy(octadecyl)silane 9 Al-phosphate 45 Fe-nitrate 10 Comparative Example 5 Epoxy Dispersion 41 Trimethoxy(octadecyl)silane 5 Al-phosphate 44 Fe-nitrate 10

[0067] Surface Shape Weather Resistance Fastening Strength (MPa) Organic Resin Aspect Ratio Example 1 Good Good 9.5 1.5 Example 2 Good Good 9.8 3.0 Example 3 Good Good 9.7 1.5 Example 4 Good Good 9.2 2.0 Example 5 Good Good 9.3 2.0 Example 6 Good Good 9.0 2.0 Comparative Example 1 Good Good 2.8 2.0 Comparative Example 2 Good Inferior 9.2 1.0 Comparative Example 3 Good 3.6 3.0 Comparative Example 4 Good 8.9 1.5 Comparative Example 5 Good Good 1.8 -

[0068] As shown in Tables 1 and 2, it can be confirmed that Examples 1 to 6, in which the insulating film composition components are appropriately added, exhibit excellent properties of the insulating film, including weather resistance and fastening strength. Additionally, as shown in Figures 2 and 3, it can be confirmed that the shape of the organic resin is also appropriately formed within the insulating film.

[0069] On the other hand, Comparative Examples 1 and 4 contain too little or too much silane component, so it can be confirmed that some characteristics of the insulating film are inferior.

[0070] In addition, it can be confirmed that Comparative Examples 2 and 3 contain too little or too much nitrate component, and thus some properties of the insulating film are inferior. In particular, as shown in FIG. 3, it can be confirmed that Comparative Example 2 contains less nitrate component, so the organic resin particles are formed in a roughly spherical shape.

[0071] Comparative Example 5 includes a dispersion resin, and it can be confirmed that the fastening force is inferior.

[0072]

[0073] The present invention is not limited to the above embodiments and can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without changing the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

[0074] [Explanation of the symbol]

[0075] 100 : Electrical steel sheet 10 : Electrical steel sheet material

[0076] 20: Insulating film

Claims

1. Electrical steel sheet substrate and It includes an insulating film located on the surface of the electrical steel sheet substrate, and The above insulating film is an electrical steel sheet comprising 30 to 45 weight% organic resin, 30 to 45 weight% metal phosphate, 1 to 8 weight% silane resin, and 8 to 17 weight% nitrate.

2. In Paragraph 1, The above organic resin is an electrical steel sheet having an average aspect ratio of 1.3 to 3.5.

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