A special coating for electrical steel

Abstract

This invention discloses a coating specifically for electrical steel, comprising an inorganic salt solution, an organic resin, a small amount of additives, and water. The mass ratio of the components is as follows: 100 parts organic resin, 80-350 parts inorganic salt solution, 0.02-5 parts additives, and the remainder is water. The solid content of the coating is 15-40%. This invention belongs to the technical field of protective coatings for non-oriented electrical steel, specifically referring to a coating specifically for electrical steel that improves the rust-preventive performance of environmentally friendly non-oriented electrical steel coatings.

Description

Technical Field

[0001] This invention belongs to the technical field of protective coating liquid for non-oriented electrical steel, specifically referring to a special coating for electrical steel. Background Technology

[0002] Electrical steel is mainly used to manufacture the cores of various motors, transformers, etc. A very thin (0.3–10 μm) insulating coating must be applied to its surface to give it a certain surface resistivity, reduce iron loss, and prevent corrosion from various corrosive media during storage, transportation, and use. General requirements for electrical steel coatings include: good adhesion and processing performance; the coating should not peel or powder during post-processing, and it should cause minimal wear on molds; good surface mechanical properties, chemical resistance, and corrosion resistance; good heat resistance; good weldability without blistering during welding; and maintaining high surface resistivity after heat treatment at ≥750℃.

[0003] Based on published articles and patents, electrical steel coatings are mainly classified into three categories: inorganic coatings, organic coatings, and inorganic / organic mixed coatings. Currently, inorganic / organic mixed coatings are more commonly used. Early coatings commonly used hexavalent chromium coatings (such as US 3793073, US 4618377, CN 1229454C), resulting in coatings with excellent overall performance. However, these coatings caused serious environmental pollution and harmed the health of operators. Furthermore, the recycling of chromium-coated electrical steel products could lead to secondary chromium pollution. Therefore, chromium-coated coatings are currently banned in developed countries such as Europe, the United States, and Japan. Research in this area is essential to promote the upgrading of related products.

[0004] Since the 1990s, various countries have strengthened their research on environmentally friendly silicon steel coatings. For example, JP 7268641 invented a phosphate-organic resin insulating coating; Armocol Corporation of the United States applied for a patent (CN 1161434) for an inorganic / organic mixed coating for electrical steel, the main components of which are aluminum dihydrogen phosphate, inorganic silicate particles, acrylic resin and appropriate amounts of organic solvents; Chinese patent CN 1151212C discloses that the main components of a chromium-free silicon steel sheet coating are acrylic resin, amino resin, phosphates and silicates; CN101168642A discloses that the main components of an environmentally friendly insulating coating for non-oriented electrical steel include phosphates, molybdates, organic resins, silane coupling agents, glycerol, etc.; CN101486866A discloses a chromium-free water-based non-oriented silicon steel sheet insulating coating, which can improve the coating's high-temperature annealing resistance.

[0005] From a domestic perspective, although there are numerous research reports and patent applications for environmentally friendly coatings, their actual use is limited. The main reasons are twofold: 1) While relatively inexpensive, the price difference is not significant, and large-scale adoption could reduce costs; 2) Performance deficiencies. Currently available environmentally friendly coatings, both domestically and internationally, can generally meet the needs of electrical steel, but certain properties require further improvement, particularly rust prevention. Rust prevention is a crucial indicator, as electrical steel is exposed to air during storage, transportation, processing, and use. Poor rust prevention makes it prone to rusting, affecting performance. Insufficient rust prevention is a pressing issue hindering the widespread adoption of environmentally friendly electrical steel coatings. Summary of the Invention

[0006] To address the aforementioned challenges, this invention provides a special coating for electrical steel that improves the rust-preventive properties of environmentally friendly non-oriented electrical steel coating liquid.

[0007] To achieve the above functions, the technical solution adopted by the present invention is as follows: a special coating for electrical steel, the main components of which include inorganic salt solution, organic resin, a small amount of additives and water; the mass composition ratio of the above components is: 100 parts of organic resin, 80-350 parts of inorganic salt solution, 0.02-5 parts of additives, the remainder being water, and the solid content of the coating is 15-40%.

[0008] Preferably, the inorganic salt solution mainly consists of water-soluble phosphates, including one or a mixture of several of aluminum dihydrogen phosphate, magnesium dihydrogen phosphate, zinc dihydrogen phosphate, and calcium dihydrogen phosphate. These phosphates can be purchased externally or obtained by reacting metal oxides or hydroxides with phosphoric acid. Before use, they are prepared into an aqueous solution of a certain concentration for convenient application.

[0009] Preferably, the organic resin is a mixture of α,ω-N-hydroxymethylamide polyetheramine and water-soluble amino resin in a ratio of 50-70:30-50, and the resin is cured during the drying and sintering of the coating solution.

[0010] Preferably, the α,ω-N-hydroxymethylamide-based polyetheramine is obtained by reacting a polyetheramine with hydroxymethylacrylamide; the polyetheramine is a terminal amino-based polypropylene oxide ether, or a terminal amino-based polytetrahydrofuran ether, or a mixture of both, with an average molecular weight of 500-2000. This polyetheramine is obtained by mixing it with hydroxymethylacrylamide in a certain proportion and reacting it at room temperature to 80°C.

[0011] Preferably, the water-soluble amino resin is Cymex CYMEL325 or CYMEL327.

[0012] Preferably, the small amount of additives are defoamers and leveling agents, which suppress foam generation when used in the coating liquid and can quickly level the surface of electrical steel.

[0013] The present invention also discloses a method for preparing a special coating for electrical steel, comprising the following steps: 1) preparing an aqueous solution of a certain concentration of the above inorganic salt; 2) adding the above organic resin to a certain mass of water, adding phosphoric acid to adjust the pH value to about 2.5, and stirring until dissolved; 3) gradually adding the organic resin aqueous solution to the prepared inorganic salt aqueous solution under stirring, and stirring evenly; 4) adding a small amount of additives to the above mixture solution under stirring, and adding water to adjust the solid content of the material.

[0014] The beneficial effects of the above-mentioned structure of the present invention are as follows: a specific organic resin is used, which can coexist with dihydrogen phosphate in water to obtain a stable coating solution. The two organic resins used can self-polymerize or cross-link with each other through condensation polymerization, resulting in good corrosion resistance and rust prevention performance of the electrical steel coating. Secondly, the electrical steel coating of the present invention is an environmentally friendly coating solution, which does not contain organic solvents and hexavalent chromium salts, and the coating film has excellent comprehensive performance. Attached Figure Description

[0015] Figure 1 This is a product spectrum of a special coating for electrical steel according to the present invention. Detailed Implementation

[0016] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1

[0018] Preparation of self-crosslinking polymer resin: 50.0 g of terminal amine polyoxypropylene ether with a molecular weight of 2000, 10.1 g of N-hydroxymethylacrylamide, and 20 ml of methanol were added to a 250 ml four-necked flask. A reflux condenser was attached, and the mixture was stirred at 50 °C for 3 h with a magnetic stirrer. Then, the temperature was raised to reflux and stirred for 4 h to stop the reaction. The methanol was then removed under vacuum using a rotary evaporator to obtain 60.0 g of viscous liquid, which was named SCR-PPO-2000.

[0019] The product was subjected to FTIR, and the spectrum is attached. Figure 1 .

[0020] Example 2

[0021] 25.0 g of terminal amine polyoxypropylene ether with a molecular weight of 500, 20.2 g of N-hydroxymethylacrylamide, and 30 ml of methanol were added to a 250 ml round-bottom flask. The mixture was stirred at room temperature for 7 days with a magnetic stirrer. The methanol was then removed under vacuum using a rotary evaporator to obtain 50.1 g of viscous liquid, which was named SCR-PPO-500.

[0022] Example 3

[0023] 25.0 g of amine-terminated polytetrahydrofuran with a molecular weight of 1000, 10.1 g of N-hydroxymethylacrylamide, and 30 ml of anhydrous ethanol were added to a 250 ml round-bottom flask. The mixture was stirred at 50 °C for 12 h with a magnetic stirrer, and then heated to reflux (80 °C) and stirred for another 2 h to stop the reaction. The ethanol was then removed under vacuum using a rotary evaporator to obtain 34.8 g of a viscous liquid, which was named SCR-PTHF-1000.

[0024] Example 4

[0025] The amino-terminated polypropylene oxide ether in Example 1 was replaced with an amino-terminated polytetrahydrofuran ether with a molecular weight of 2000. All other raw materials and amounts remained unchanged. The reaction was carried out under the same conditions to obtain 60.0 g of product, which was named SCR-PTHF-2000.

[0026] Example 5

[0027] Preparation of coating solution: Add 0.7g SCR-PPO-2000, 0.3g CYMEL 325 and 4.8g water to a 100ml beaker, adjust the pH to 2.5 with phosphoric acid, then add the resulting solution to 12g of 20% aluminum dihydrogen phosphate solution, then add 0.005g Momentive L-77 leveling agent and 0.003g Haian Petrochemical AEO-3, and stir until homogeneous.

[0028] Examples 6-10

[0029] The preparation method is the same as in Example 5, and the raw materials are listed in Appendix 1.

[0030] Performance of the coating liquid

[0031] Examples 5-10 were coated onto 50W500 electrical steel sheets (please modify according to the company's situation, Mr. Tang), cured at the set temperature, and then the performance was tested. The results are shown in Appendix Table 2.

[0032] Appendix 1: Formulations for Examples 6-10

[0033] Raw materials and dosage Example 6 Example 7 Example 8 Example 9 Example 10 SCR-PPO-2000 / g 0.30 SCR-PPO-500 / g 0.30 0.20 SCR-PTHF-2000 / g 0.30 0.40 0.65 SCR-PTHF-1000 / g 0.60 0.20 CYMEL327 0.30 0.40 CYMEL325 0.40 0.35 0.60 Aluminum dihydrogen phosphate / g 2.00 2.10 1.25 2.30 2.60 Magnesium dihydrogen phosphate / g 0.20 0.20 0.10 Zinc dihydrogen phosphate / g 0.10 0.10 0.10 0.20 calcium dihydrogen phosphate / g 0.20 0.10 0.20 L-77 / g 0.005 0.002 0.0025 0.02 0.02 AEO-3 / g 0.002 0.010 0.001 0.01 0.02 Water / g 11.00 19.8 12.6 11.4 5.40

[0034] Appendix 2: Curing conditions and properties of Examples 5-10

[0035] Example sequence number Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Coating roller model Webster9# Webster7# Webster14# Webster7# Webster7# Webster5# Curing conditions / s / ℃ 50 / 350 21 / 480 20 / 480 20 / 530 18 / 550 50 / 350 Adhesion O O O 0 0 A <![CDATA[Surface resistance / Ωmm 2 > 986 1053 1328 1360 1285 837 NSS Experiment No rust No rust No rust No rust No rust <2％

[0036] Application method of the coating liquid: Apply the coating liquid at a rate of 1-5 g / m2 to the silicon steel sheet that has been derusted and degreased, and bake it at 350-550℃ for curing. The reference curing time is: 45-55s / 350℃, 18-25s / 480℃, or 15-20s / 550℃.

[0037] The main test methods and standards related to this invention are as follows: Adhesion and insulation are determined according to the national standard GB / T2522-2007 "Test Method for Insulation Resistance and Coating Adhesion of Electrical Steel Sheets (Strips)"; Neutral Salt Spray Test (NSS Test) is determined according to GB / T10125-1997 "Artificial Atmosphere Corrosion Test Salt Spray Test", with a test time of 8 hours; Copper Sulfate Solution Resistance Test: Saturated copper sulfate solution is dropped onto the coated electrical steel surface at room temperature, left to stand for 30 minutes, and then the corrosion of the electrical steel surface is observed.

[0038] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A coating specifically for electrical steel, characterized in that: The main components include an inorganic salt solution, an organic resin, a small amount of additives, and water. The mass ratio of the above components is as follows: 100 parts organic resin, 80-350 parts inorganic salt solution, 0.02-5 parts additives, and the remainder is water. The solid content of the coating is 15-40%. The organic resin is a mixture of α,ω-N-hydroxymethylamide polyetheramine and water-soluble amino resin in a ratio of 50-70:30-50. The α,ω-N-hydroxymethylamide polyetheramine is obtained by reacting polyetheramine with hydroxymethylacrylamide. The polyetheramine is terminal amino polyoxypropylene ether, or terminal amino polytetrahydrofuran ether, or a mixture of both, with an average molecular weight of 500-2000. This polyetheramine is mixed with hydroxymethylacrylamide in a certain proportion and reacted at room temperature to 80°C.

2. The coating for electrical steel according to claim 1, characterized in that: The inorganic salt solution mainly consists of water-soluble phosphates, including one or a mixture of several of aluminum dihydrogen phosphate, magnesium dihydrogen phosphate, zinc dihydrogen phosphate, and calcium dihydrogen phosphate.

3. The coating for electrical steel according to claim 1, characterized in that: The water-soluble amino resin is either Cymex CYMEL325 or CYMEL327.

4. The coating for electrical steel according to claim 1, characterized in that: The small amount of additives mentioned are defoamers and leveling agents.

5. A method for preparing the special coating for electrical steel according to claim 1, characterized in that: The process includes the following steps: 1) Prepare an aqueous solution of inorganic salts at a certain concentration; 2) Add organic resin to a certain mass of water, add phosphoric acid to adjust the pH to about 2.5, and stir until dissolved; 3) While stirring, gradually add the organic resin aqueous solution to the prepared inorganic salt aqueous solution in proportion, and stir evenly; 4) While stirring, add a small amount of additives to the mixture solution, and add water to adjust the solid content of the material.

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