A chromium-free environment-friendly coating for non-oriented silicon steel of type C5 and a preparation method thereof

Abstract

The application provides a C5 type chromium-free environment-friendly coating for non-oriented silicon steel and a preparation method thereof, and the components of the application include acrylic resin, phosphoric acid, octyl phosphonic acid, glycerol, polyether modified silicone oil, water and modified functional filler, wherein the modified functional filler is a blend of aluminum hydroxide and modified nano silicon dioxide; the modified nano silicon dioxide is obtained by grafting reaction of polyacrylic acid, citric acid and hydroxylated nano silicon dioxide, and can inhibit nano silicon dioxide agglomeration and improve coating dispersibility and leveling property; after drying and curing of the coating of the application, the phosphoric acid, octyl phosphonic acid and aluminum hydroxide form an inorganic aluminum phosphate / organic aluminum phosphonate composite three-dimensional network matrix, the nano silicon dioxide is uniformly distributed and fills the pores, realizing micro densification and inorganic reinforcement of the coating, and the obtained organic / inorganic composite coating structure is uniform and dense, has high hardness, good insulation, strong adhesion, and good heat resistance and chemical stability; and the application is chromium-free and has environmental protection and practicality.

Description

Technical Field

[0001] This invention relates to the field of coatings, specifically to a non-oriented silicon steel C5 type chromium-free environmentally friendly coating and its preparation method. Background Technology

[0002] With the global power industry transitioning towards high efficiency, energy conservation, and green low-carbon development, non-oriented silicon steel, as a key core material for core power equipment such as motors, transformers, and drive motors for new energy vehicles, directly determines the energy efficiency and service reliability of these devices. Among them, C5 type non-oriented silicon steel, with its excellent characteristics of high magnetic induction and low iron loss, has become the preferred core material for high-end energy-saving power equipment. This places stringent requirements on the matching surface coating: it must possess excellent electrical insulation to reduce iron loss, strong adhesion to the silicon steel substrate to resist mechanical forces during processing and use, excellent high-temperature resistance to adapt to the multi-stage high-temperature processing steps in production, and must also meet the mandatory requirement of being chromium-free and environmentally friendly to avoid the harm of harmful substances to the environment and human health.

[0003] With increasingly stringent environmental regulations restricting chromium-containing pollutant emissions, traditional chromium-containing silicon steel coatings have been restricted or phased out by many countries due to the high toxicity and environmental accumulation of chromium. Chromium-free coatings have become an inevitable development direction for the silicon steel coating industry. Current research and development of chromium-free environmentally friendly coatings for non-oriented silicon steel mainly revolves around two core directions: resin matrix optimization and functional filler formulation. In terms of resin selection, acrylic resin has become the mainstream matrix material due to its good film-forming properties and controllable cost. The industry often balances film density and high-temperature resistance by adjusting its key performance parameters. Regarding functional fillers, inorganic fillers such as aluminum hydroxide and nano-silica are commonly used, leveraging their high insulation and high-temperature resistance to enhance the coating's protective effect. Some solutions involve simple surface treatment of nano-silica to improve its dispersibility in the resin. Simultaneously, various auxiliary components are added to the formulation to enhance the adhesion between the coating and the substrate, adjust the coating's flexibility, and optimize its leveling properties during application, thereby improving the overall performance of the coating.

[0004] However, existing chromium-free environmentally friendly coatings still face several insurmountable technical bottlenecks when adapting to the high-end application requirements of C5 type non-oriented silicon steel: First, the poor dispersibility of nano-silica makes it difficult for traditional surface treatment methods to fundamentally solve the problem of its strong surface polarity and easy agglomeration in organic resins, resulting in the formation of pores and structural defects inside the coating, which seriously affects the uniformity and mechanical stability of insulation performance; Second, the weak bonding between fillers and resin interfaces, with inorganic fillers and resins mostly being simple physical mixtures lacking strong interaction, easily generating internal stress due to differences in thermal expansion coefficients during high-temperature processing, causing coating cracking and peeling, ultimately leading to protective failure; Third, it is difficult to balance environmental protection and practical performance. Some solutions excessively add inorganic fillers to improve high-temperature resistance, resulting in increased coating brittleness, poor leveling during construction, or the introduction of potentially harmful auxiliary components, which neither meets the environmental protection requirements of high-end power equipment nor can it be adapted to industrial production and actual use scenarios, seriously restricting the application expansion of C5 type non-oriented silicon steel in the field of high-end power equipment.

[0005] In conclusion, a new technical solution is urgently needed to address the problems existing in the current technology. Summary of the Invention

[0006] To address the shortcomings and deficiencies of the existing technology, this invention provides a chromium-free environmentally friendly coating for non-oriented silicon steel (C5 type) and its preparation method. The coating preparation method provided by this invention is simple and easy to apply. The coating formed on the surface of non-oriented silicon steel exhibits excellent insulation properties, adhesion, and high-temperature resistance, and can improve the corrosion resistance of the metal substrate. This product solves the environmental pollution problem caused by hexavalent chromium compounds and is environmentally friendly and beneficial to human health.

[0007] The first objective of this invention is to provide a chromium-free environmentally friendly coating for non-oriented silicon steel C5 type, wherein the non-oriented silicon steel C5 type chromium-free environmentally friendly coating comprises the following components in parts by weight: 15-25 parts acrylic resin 15-20 parts of phosphoric acid 5-10 parts of octylphosphonic acid 4-6 parts of glycerol 0.1-0.5 parts of polyether-modified silicone oil 100-120 parts water 30-40 parts of modified functional filler; The modified functional filler is a mixture formed by blending aluminum hydroxide and modified nano-silica. The modified nano-silica is a product obtained by hydroxylating nano-silica and then grafting it with a mixed solution of polyacrylic acid and citric acid.

[0008] Furthermore, the mass ratio of the aluminum hydroxide to the modified nano-silica is 1:(1-3).

[0009] Furthermore, the molecular weight of the acrylic resin is 30,000-80,000.

[0010] Furthermore, the molecular weight of the polyacrylic acid is 1000-5000.

[0011] The second objective of this invention is to provide a method for preparing the non-oriented silicon steel C5 type chromium-free environmentally friendly coating, the method comprising the following steps: S1. Hydroxylation treatment of nano-silica to obtain hydroxylated nano-silica; S2. The hydroxylated nano-silica, polyacrylic acid and citric acid are mixed and heated and stirred to react, thereby obtaining modified nano-silica; S3. The modified nano-silica is blended with aluminum hydroxide to obtain a modified functional filler. S4. The modified functional filler is blended with the remaining components to obtain a non-oriented silicon steel C5 type chromium-free environmentally friendly coating.

[0012] Further, in step S2, the mass ratio of the hydroxylated nano silica, polyacrylic acid and citric acid is 10:(1-3):(0.1-1).

[0013] Furthermore, in step S2, the heating temperature is 60-80℃.

[0014] The present invention has the following beneficial effects: This invention provides a chromium-free environmentally friendly coating for non-oriented silicon steel C5 type. The coating comprises: acrylic resin, phosphoric acid, octylphosphonic acid, glycerol, polyether-modified silicone oil, water, and modified functional filler. The modified functional filler is a mixture formed by blending aluminum hydroxide and modified nano-silica. The modified nano-silica is obtained by grafting hydroxylated nano-silica with polyacrylic acid and citric acid. The hydroxylated nano-silica has a surface rich in hydroxyl groups, which can undergo esterification-like reactions with the carboxyl groups of polyacrylic acid and citric acid to form stable covalent bonds. This allows polyacrylic acid and citric acid to be grafted onto the surface of the nano-silica, forming a stable star-shaped structure with nano-silica particles as the core. Grafting of nano-silica with polyacrylic acid and citric acid significantly improves its compatibility with acrylic resin, allowing the modified nano-silica to be uniformly dispersed in the acrylic resin system, preventing coating layering and sedimentation, and ensuring leveling properties during coating application.

[0015] The C5 type chromium-free environmentally friendly coating of this invention, after drying and curing, forms an inorganic aluminum phosphate / organic aluminum phosphonate composite three-dimensional network matrix with phosphoric acid, octylphosphonic acid, and aluminum hydroxide. Nano-silica is uniformly distributed and fills the pores, achieving micro-densification and inorganic reinforcement of the coating. The resulting organic / inorganic composite coating has a uniform and dense structure, high hardness, good insulation, and strong adhesion, while also possessing good heat resistance and chemical stability. Furthermore, octylphosphonic acid enhances corrosion resistance; its participation in forming the three-dimensional network structure optimizes the coating's shielding and protective effect, further improving its corrosion resistance. This invention is chromium-free, combining environmental friendliness and practicality. Detailed Implementation

[0016] To more clearly illustrate the technical solution of the present invention, the following embodiments are provided. Unless otherwise stated, the raw materials, reactions, and post-processing methods appearing in the embodiments are all commercially available raw materials and technical methods well known to those skilled in the art.

[0017] The terms "preferred," "more preferably," and "more suitable" used in this invention refer to embodiments of the invention that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this invention.

[0018] It should be understood that, except in any operational instance or otherwise indicated, the amounts or all figures representing ingredients used, for example, in the specification and claims, should be understood to be modified by the term "about" in all cases. Therefore, unless otherwise stated, the numerical parameters set forth in the following specification and appended claims are approximate values ​​varying according to the desired performance to be obtained according to the invention.

[0019] In embodiments of the present invention, the following raw materials will be used: The acrylic resin, brand name S-70, was purchased from Yinjie Chemical.

[0020] The polyether-modified silicone oil, brand name P875564, was purchased from Maclean's.

[0021] Nano-silica, grade HL-200, was purchased from Hubei Huifu Nanomaterials Co., Ltd.

[0022] Polyacrylic acid, MW~2000, purchased from Wengjiang Reagent.

[0023] Unless otherwise specified, the water used in the embodiments of this invention refers to deionized water.

[0024] In the embodiments of this invention, "parts" refers to parts by mass.

[0025] Example 1 A chromium-free environmentally friendly coating for non-oriented silicon steel C5 type, wherein the non-oriented silicon steel C5 type chromium-free environmentally friendly coating comprises the following components in parts by weight: 15 parts acrylic resin 15 parts of phosphoric acid 5 parts of octylphosphonic acid 4 parts glycerol 0.1 parts of polyether-modified silicone oil 100 parts water 30 parts of modified functional filler; The preparation method of the non-oriented silicon steel C5 type chromium-free environmentally friendly coating includes the following steps: S1. Soak 1 g of nano-silica in 50 mL of 5 mol / L sodium hydroxide aqueous solution, sonicate for 3 h, filter, wash and dry to obtain hydroxylated nano-silica; S2. Using an ethanol-water mixture (ethanol to water volume ratio of 1:9) as a solvent, the hydroxylated nano silica, polyacrylic acid and citric acid in a mass ratio of 10:1:0.5 were mixed, heated to 70°C, stirred for 2 h, filtered, washed and dried to obtain modified nano silica. S3. The modified nano-silica and aluminum hydroxide are mixed at a mass ratio of 1:2 and stirred evenly to obtain the modified functional filler. S4. According to the above-mentioned mass proportions, the modified functional filler is mixed with the remaining components and stirred evenly to obtain the non-oriented silicon steel C5 type chromium-free environmentally friendly coating.

[0026] Example 2 A chromium-free environmentally friendly coating for non-oriented silicon steel C5 type, wherein the non-oriented silicon steel C5 type chromium-free environmentally friendly coating comprises the following components in parts by weight: 20 parts acrylic resin 18 parts of phosphoric acid 7 parts of octylphosphonic acid 5 parts glycerol 0.3 parts polyether-modified silicone oil 110 parts water 35 parts of modified functional filler; The preparation method of the non-oriented silicon steel C5 type chromium-free environmentally friendly coating includes the following steps: S1. Soak 1 g of nano-silica in 50 mL of 5 mol / L sodium hydroxide aqueous solution, sonicate for 3 h, filter, wash and dry to obtain hydroxylated nano-silica; S2. Using an ethanol-water mixture (ethanol to water volume ratio of 1:9) as a solvent, the hydroxylated nano silica, polyacrylic acid and citric acid in a mass ratio of 10:1.5:0.5 were mixed, heated to 70°C, stirred for 2 h, filtered, washed and dried to obtain modified nano silica. S3. The modified nano-silica and aluminum hydroxide are blended at a mass ratio of 1:2 to obtain a modified functional filler. S4. According to the above-mentioned mass proportions, the modified functional filler is blended with the remaining components to obtain the non-oriented silicon steel C5 type chromium-free environmentally friendly coating.

[0027] Example 3 A chromium-free environmentally friendly coating for non-oriented silicon steel C5 type, wherein the non-oriented silicon steel C5 type chromium-free environmentally friendly coating comprises the following components in parts by weight: 25 parts acrylic resin 20 parts of phosphoric acid 10 parts of octylphosphonic acid 6 parts of glycerol 0.5 parts of polyether-modified silicone oil 110 parts water 40 parts of modified functional filler; The preparation method of the non-oriented silicon steel C5 type chromium-free environmentally friendly coating includes the following steps: S1. Soak 1 g of nano-silica in 50 mL of 5 mol / L sodium hydroxide aqueous solution, sonicate for 3 h, filter, wash and dry to obtain hydroxylated nano-silica; S2. Using an ethanol-water mixture (ethanol to water volume ratio of 1:9) as a solvent, the hydroxylated nano silica, polyacrylic acid and citric acid in a mass ratio of 10:2:0.5 were mixed, heated to 70°C, stirred for 2 h, filtered, washed and dried to obtain modified nano silica. S3. The modified nano-silica and aluminum hydroxide are blended at a mass ratio of 1:2 to obtain a modified functional filler. S4. According to the above-mentioned mass proportions, the modified functional filler is blended with the remaining components to obtain the non-oriented silicon steel C5 type chromium-free environmentally friendly coating.

[0028] Comparative Example 1 A non-oriented silicon steel C5 type chromium-free environmentally friendly coating. The difference between this comparative example and Example 1 is that step S2 is omitted, and the modified nano-silica in step S3 is replaced by hydroxylated nano-silica. The remaining components and amounts remain unchanged.

[0029] Comparative Example 2 A non-oriented silicon steel C5 type chromium-free environmentally friendly coating. The difference between this comparative example and Example 1 is that the octylphosphonic acid is replaced with phosphoric acid by mass, while the other components and amounts remain unchanged.

[0030] Test Example 1 The C5 type chromium-free environmentally friendly coatings for non-oriented silicon steel prepared in Examples 1-3 and Comparative Examples 1-2 were applied to the surface of 0.5 mm thick non-oriented silicon steel sheets using a roller coater, maintaining a coating weight of 1.8 g / m². 2 Then, dry at 80℃ for 30 min, cure at 300℃ for 1 min, and perform performance tests on the coating.

[0031] Interlayer resistance: Refer to GB / T 2522-2007; Adhesion: Refer to GB / T 2522-2007; Pencil hardness: Tested using Mitsubishi pencils in accordance with GB / T 6739-2006; Corrosion area: Salt spray test was conducted in accordance with GB / T 13448-2006 and GB / T 1766-1995, with a test duration of 8 hours; The test results are shown in Table 1.

[0032] Table 1 Performance Test Results As shown in Table 1, the non-oriented silicon steel C5 type chromium-free environmentally friendly coatings prepared in Examples 1-3 of this invention exhibit excellent performance in core properties such as interlayer resistance, adhesion, pencil hardness, and salt spray corrosion protection. In Comparative Example 1, no nano-silica grafting was performed, leading to easy agglomeration of the nano-silica, poor dispersion of the coating system, and numerous pores and structural defects within the formed coating. This resulted in deterioration of the coating's insulation, adhesion, pencil hardness, and other core properties, as well as a decrease in its salt spray corrosion protection. In Comparative Example 2, octylphosphonic acid was replaced with phosphoric acid. The three-dimensional network structure formed by phosphoric acid and aluminum hydroxide lacks organic segments, leading to a decline in various properties.

[0033] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0034] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A chromium-free environmentally friendly coating for non-oriented silicon steel C5 type, characterized in that, The non-oriented silicon steel C5 type chromium-free environmentally friendly coating comprises the following components in parts by weight: 15-25 parts acrylic resin 15-20 parts of phosphoric acid 5-10 parts of octylphosphonic acid 4-6 parts of glycerol 0.1-0.5 parts of polyether-modified silicone oil 100-120 parts water 30-40 parts of modified functional filler; The modified functional filler is a mixture formed by blending aluminum hydroxide and modified nano-silica. The modified nano-silica is a product obtained by hydroxylating nano-silica and then grafting it with a mixed solution of polyacrylic acid and citric acid.

2. The C5 type chromium-free environmentally friendly coating for non-oriented silicon steel according to claim 1, characterized in that, The mass ratio of aluminum hydroxide to modified nano-silica is 1:(1-3).

3. The C5 type chromium-free environmentally friendly coating for non-oriented silicon steel according to claim 1, characterized in that, The molecular weight of the acrylic resin is 30,000-80,000.

4. The C5 type chromium-free environmentally friendly coating for non-oriented silicon steel according to claim 1, characterized in that, The molecular weight of the polyacrylic acid is 1000-5000.

5. The method for preparing the C5 type chromium-free environmentally friendly coating for non-oriented silicon steel according to any one of claims 1-4, characterized in that, The preparation method of the non-oriented silicon steel C5 type chromium-free environmentally friendly coating includes the following steps: S1. Hydroxylation treatment of nano-silica to obtain hydroxylated nano-silica; S2. The hydroxylated nano-silica, polyacrylic acid and citric acid are mixed and heated and stirred to react, thereby obtaining modified nano-silica; S3. The modified nano-silica is blended with aluminum hydroxide to obtain a modified functional filler. S4. The modified functional filler is blended with the remaining components to obtain a non-oriented silicon steel C5 type chromium-free environmentally friendly coating.

6. The method for preparing the C5 type chromium-free environmentally friendly coating for non-oriented silicon steel according to claim 5, characterized in that, In step S2, the mass ratio of the hydroxylated nano silica, polyacrylic acid and citric acid is 10:(1-3):(0.1-1).

7. The method for preparing the C5 type chromium-free environmentally friendly coating for non-oriented silicon steel according to claim 5, characterized in that, In step S2, the heating temperature is 60-80℃.

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