Water-based self-adhesive coating as well as preparation method and application thereof

Abstract

The invention provides a water-based self-adhesive coating as well as a preparation method and application thereof. The water-based self-adhesive coating comprises the following components in parts by weight: 35-38 parts by weight of BPA epoxy resin; 8 to 10 parts by weight of a modified epoxy resin; 6 to 8 parts by weight of an emulsifier; 5 to 8 parts by weight of a latent curing agent; from 5 to 10 parts by weight of 1-methoxy-2-propanol; and the balance of water. The water-based self-adhesive coating solves the problem of hydrophobicity of the epoxy resin by adding the modified epoxy resin and the emulsifier, and normal-temperature storage stability and hot-pressing curing reliability can be realized by adding the curing agent. And meanwhile, water is used as a main solvent and is matched with low-toxicity auxiliaries such as 1-methoxy-2-propanol, so that the insulating property and the bonding strength of the coating are ensured, and meanwhile, the environment-friendly requirement is met.

Description

Technical Field

[0001] The present invention relates to the technical field of water-based coatings, and in particular to a water-based self-adhesive coating and a preparation method and application thereof. Background Art

[0002] Silicon steel sheets are used in motor and transformer cores. To reduce the eddy current loss of the core and enhance its rust and corrosion resistance, the silicon steel sheets need to be coated with insulating paint. Traditionally, the stators or rotors of motors made of silicon steel sheets are made by using sheets coated with silicon steel sheet paint. After being stamped into the designed specifications, they are pressed into one piece using welding, riveting, bolting, etc. This traditional process has the following characteristics: (1) The silicon steel sheets must be pre-coated with silicon steel sheet paint. The preparation process requires the use of silicon steel sheet paint, and then goes through processes such as painting and baking; (2) After the silicon steel sheets are stamped and formed, they need to be welded and other complex processes. Only after these two processes are completed can they be made into stator or rotor cores. The epoxy coating bonding process simplifies two steps: first, a water-based epoxy self-bonding coating is roll-coated on the surface of the silicon steel sheet and then baked at high temperature for a short period of time to form a pre-cured coating for easy transportation and storage. Second, the pre-coated silicon steel sheet is stamped and then directly fixed in a fixture and baked to fully cure, forming a bonded stator or rotor core. This simple and efficient process avoids complex steps such as welding and riveting, saving labor costs and conserving resources and energy. Among the many coatings used to bond silicon steel sheets, epoxy resins are widely used in anti-corrosion coatings, automotive coatings, metal can coatings, electrical appliances, medical devices, and other fields due to their excellent chemical stability, strong adhesion, excellent electrical insulation properties, and high mechanical strength. However, most epoxy resin coatings are oil-based systems, requiring the use of large amounts of various diluents to reduce viscosity for good application performance. Oil-based systems also have a significant impact on the environment and are gradually being replaced by water-based systems. At present, with the gradual improvement of customer product usage requirements, the bonding performance and adhesion effect between the coating formed by the existing silicon steel sheet bonding coating and the silicon steel sheet after application can no longer meet the bonding requirements of high-performance silicon steel sheets. Summary of the Invention

[0003] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. The present invention provides a water-based self-bonding coating with good stability and strong peeling force, which can be used to coat silicon steel sheets and thus can be used in the field of motors. Conventional epoxy emulsions use common liquid epoxy or solid epoxy resins. The cohesion of the polymer itself is insufficient, and it is difficult to obtain good bonding peel strength. Moreover, most of the curing agents use traditional modified amine curing agents, which have limited storage life and stability. The present invention uses modified epoxy resins, which can extend the molecular weight of the resin, increase the cohesion of the resin, and increase the peel strength. With latent curing agents, the emulsion can be made into a stable single component that does not sink to the bottom or stratify.

[0004] Specifically, the present invention provides the following technical solutions: A first aspect of the present invention provides a water-based self-bonding coating comprising, in parts by weight: 35 to 38 parts by weight of BPA epoxy resin; 8 to 10 parts by weight of a modified epoxy resin; 6 to 8 parts by weight of an emulsifier; 5 to 8 parts by weight of a latent curing agent; 5 to 10 parts by weight of 1-methoxy-2-propanol; and the balance water.

[0005] The provided water-based self-bonding coating uses BPA epoxy resin as the primary film-forming substance, providing the coating's adhesion and insulation properties. Its epoxy groups are highly reactive and can cross-link with the curing agent to form a dense network structure, imparting mechanical strength and temperature resistance to the coating. The addition of a modified epoxy resin can enhance its water solubility, thereby improving the dispersibility of the water-based self-bonding coating. The addition of an emulsifier can reduce the surface tension of the epoxy resin, thereby enhancing its emulsification and dispersion in water; it can also form a stable aqueous emulsion, preventing stratification or precipitation. The addition of a latent curing agent can achieve room-temperature storage stability and rapid high-temperature curing without sinking or stratification. 1-Methoxy-2-propanol, as a cosolvent / diluent, can reduce system aging and assist in film formation. The water-based self-bonding coating provided by the present invention achieves optimized water solubility, for example, by combining the addition of a modified epoxy resin with an emulsifier to address the hydrophobicity of the epoxy resin. Furthermore, the addition of a curing agent ensures compatibility with the water-based epoxy, achieving room-temperature storage stability and hot-press curing reliability. At the same time, water is used as the main solvent in combination with low-toxic additives such as 1-methoxy-2-propanol to ensure the insulation and bonding strength of the coating while meeting environmental protection requirements.

[0006] According to an embodiment of the present invention, the modified epoxy resin is a PU-modified epoxy resin. PU-modified epoxy resin serves as the primary film-forming material for coatings, providing essential adhesion, insulation, and mechanical strength. Epoxy resins possess excellent chemical stability, electrical insulation, and bond strength, making them suitable for the insulation and bonding requirements of silicon steel sheets. Water-based modification (e.g., by introducing hydrophilic groups) renders them water-soluble, reducing environmental pollution.

[0007] According to an embodiment of the present invention, the emulsifier is GL8661. Emulsifiers can enhance water solubility, for example, by making epoxy resin hydrophilic, allowing it to be stably dispersed in water. Alternatively, they can improve compatibility, enhancing the compatibility of epoxy resin with water and ensuring coating stability.

[0008] According to an embodiment of the present invention, the latent curing agent is 2E4MZ latent curing agent. As a latent curing agent, 2E4MZ latent curing agent can achieve room temperature storage stability and high temperature rapid curing, and is suitable for the process chain of silicon steel sheet pre-curing, stamping, and secondary curing.

[0009] The second aspect of the present invention provides a method for preparing the water-based self-bonding coating according to any one of the first aspects, comprising: Mixing BPA epoxy resin, modified epoxy resin and 1-methoxy-2-propanol, and stirring at a first predetermined temperature until the resin is completely dissolved; Cooling to a second predetermined temperature, adding an emulsifier while stirring, stirring evenly, and adding water for the first emulsification; The temperature is lowered to a third predetermined temperature, mixed with a latent curing agent, and subjected to a second emulsification. The water-based self-bonding coating is obtained after the temperature is lowered.

[0010] According to an embodiment of the present invention, the first predetermined temperature is 120 to 140°C; The second predetermined temperature is 80 to 90° C.; The third predetermined temperature is below 70°C.

[0011] According to an embodiment of the present invention, the first emulsification time is 5 to 7 hours; The second emulsification time is 3 to 4 hours.

[0012] According to an embodiment of the present invention, step (2) performs a second emulsification until the particle size of the mixture is 1 to 2 microns.

[0013] The third aspect of the present invention provides use of the water-based self-bonding coating described in the first aspect in silicon steel sheets.

[0014] The present invention achieves at least the following beneficial effects: the water-based self-bonding coating provided by the present invention optimizes water solubility, for example, by adding a modified epoxy resin to address the low cohesive strength of conventional epoxy resins. Furthermore, the addition of a latent curing agent enables compatibility with the water-based epoxy, achieving room-temperature storage stability and hot-press curing reliability. Furthermore, using water as the primary solvent in combination with low-toxic additives such as 1-methoxy-2-propanol ensures the coating's insulation and bonding strength while meeting environmental requirements. DETAILED DESCRIPTION

[0015] The following describes in detail embodiments of the present invention. The embodiments are exemplary and intended to explain the present invention, but are not to be construed as limiting the present invention.

[0016] The water-based self-bonding coating mentioned in this article refers to a specialty insulating coating using water as the dispersion medium. Designed specifically for the surface treatment of silicon steel sheets, it can bond silicon steel sheets together under heat or pressure while maintaining insulation, corrosion resistance, and punchability.

[0017] The latent curing agent mentioned herein is a curing agent that has a certain storage stability at room temperature, but can rapidly undergo a curing reaction under conditions such as heating, light, and moisture. This type of curing agent uses physical and chemical methods to block or passivate the activity of ordinary curing agents, thereby maintaining stability during storage, and activating its reaction activity under specific conditions during use to achieve rapid curing. The present invention provides a method for preparing a water-based self-bonding coating, comprising: (1) Add 1-methoxy-2-propanol, BPA epoxy resin, and PU modified epoxy resin into a high shear emulsifier, heat to 120 to 140°C, and stir until the resin is completely dissolved; (2) Cool down to 80 to 90°C, add emulsifier while stirring, stir evenly, then add water dropwise, and continue emulsification for 5 to 7 hours after addition; (3) After the emulsification reaches a particle size of 1 to 2 microns, the temperature is lowered to 70°C, a latent curing agent is added, and the emulsification is continued for 3 to 4 hours. The temperature is lowered to below 40°C to obtain a water-based self-bonding coating.

[0018] According to a specific embodiment, the invention comprises, in parts by weight: 35 to 38 parts by weight of BPA epoxy resin; 8 to 10 parts by weight of modified epoxy resin; 6 to 8 parts by weight of emulsifier; 5 to 8 parts by weight of latent curing agent; 5 to 10 parts by weight of 1-methoxy-2-propanol; and the balance of water.

[0019] During the research, it was found that increasing the BPA epoxy resin content can lead to excessively high system viscosity, affecting workability and leveling. Reducing the BPA epoxy resin content can reduce the hardness and durability of water-based self-bonding coatings, potentially affecting the coating's self-bonding properties. Modified epoxy resins are commonly used to improve the emulsification and stability of water-based epoxy resins while also providing a certain degree of crosslinking capacity. They work synergistically with BPA epoxy resins to form a more stable curing system. An appropriate amount of modified epoxy resin can improve emulsion stability, reduce flocculation and delamination, and potentially improve the coating's water resistance and weatherability. However, too little modified epoxy resin can lead to decreased emulsion stability, making flocculation, delamination, or gelation more likely, impacting the coating's performance. Emulsifiers disperse epoxy resins in water, forming a stable emulsion system and helping to improve the coating's leveling and workability. However, excessive amounts of emulsifiers can lead to excessively high system viscosity, impacting workability, while too little can destabilize the emulsion, making flocculation, delamination, or gelation more likely, impacting the coating's performance. The addition of a latent curing agent can improve the long-term stability of the system, but excessive amounts can lead to premature curing, affecting application time. Excessive amounts can slow the curing reaction, prolong application time, and even affect the performance of the final coating. 1-Methoxy-2-propanol is a commonly used solvent and plasticizer used to adjust the viscosity and fluidity of coatings, while also having a certain emulsifying effect. However, excessive use of 1-methoxy-2-propanol can reduce the coating's water and chemical resistance. Reducing the 1-methoxy-2-propanol content can result in excessively high coating viscosity, affecting application and leveling properties.

[0020] The modified epoxy resin used is PU modified epoxy resin. The PU modified epoxy resin mentioned refers to a composite material in which epoxy resin is toughened and modified by polyurethane (PU), which can improve the inherent brittleness and poor impact resistance of epoxy resin.

[0021] According to a specific embodiment, the emulsifier used is GL8661.

[0022] According to a specific embodiment, the latent curing agent used is 2E4MZ latent curing agent.

[0023] The technical solutions of the present invention are described below by way of specific examples. It should be noted that these examples are intended only to facilitate the understanding of those skilled in the art and should not be considered as limiting the scope of the present invention. Unless otherwise specified, the reagents used in the examples can all be commercially available.

[0024] For example, emulsifier GL8661 was purchased from Haian Petrochemical Plant, Jiangsu Province; 2E4MZ latent curing agent was purchased from Ajinomoto Co., Ltd. BPA epoxy resin was purchased from Jiangsu Sanmu Group Co., Ltd.; PU modified epoxy resin was purchased from Dow Chemical, model number DER791.

[0025] Example 1 Example 1 A water-based self-bonding coating was prepared by the following method, comprising: Add 5 parts of 1-methoxy-2-propanol, 35 parts of BPA epoxy resin, and 8 parts of PU-modified epoxy resin to a high-shear emulsifier. Raise the temperature to 120°C and stir until the resin is completely dissolved. Cool to 80°C and add 6 parts of emulsifier (GL8661) while stirring. Stir evenly, then add water dropwise. Continue emulsifying for 5 hours. After emulsification to a particle size of 1 to 2 microns, cool to 70°C and add 5 parts of 2E4MZ latent curing agent. Continue emulsifying for 3 hours, then cool to below 40°C and discharge to obtain a water-based self-bonding coating.

[0026] Example 2 Example 2 A water-based self-bonding coating was prepared by the following method, comprising: Add 8 parts of 1-methoxy-2-propanol, 38 parts of BPA epoxy resin, and 10 parts of PU-modified epoxy resin to a high-shear emulsifier. Raise the temperature to 130°C and stir until the resin is completely dissolved. Cool to 90°C and add 8 parts of emulsifier (GL8661) while stirring. Stir evenly, then add water dropwise. Continue emulsifying for 5 hours. After emulsification to a particle size of 1 to 2 microns, cool to 70°C and add 6 parts of 2E4MZ latent curing agent. Continue emulsifying for 4 hours, then cool to below 40°C and discharge to obtain a water-based self-bonding coating.

[0027] Example 3 Example 3 A water-based self-bonding coating was prepared by the following method, comprising: Add 10 parts 1-methoxy-2-propanol, 38 parts BPA epoxy resin, and 10 parts PU-modified epoxy resin to a high-shear emulsifier. Raise the temperature to 130°C and stir until the resin is completely dissolved. Cool to 90°C and add 7 parts emulsifier (GL8661) while stirring. Stir evenly, then add water dropwise. Continue emulsifying for 5 hours. After emulsification to a particle size of 1 to 2 microns, cool to 70°C and add 7 parts 2E4MZ latent curing agent. Continue emulsifying for 4 hours, then cool to below 40°C and discharge to obtain a water-based self-bonding coating.

[0028] Example 4 Example 4 A water-based self-bonding coating was prepared by the following method, comprising: Add 9 parts of 1-methoxy-2-propanol, 37 parts of BPA epoxy resin, and 10 parts of PU-modified epoxy resin to a high-shear emulsifier. Raise the temperature to 125°C and stir until the resin is completely dissolved. Cool to 85°C and add 8 parts of emulsifier (GL8661) while stirring. Stir evenly, then add water dropwise. Continue emulsifying for 5 hours. After emulsification to a particle size of 1 to 2 microns, cool to 70°C and add 8 parts of 2E4MZ latent curing agent. Continue emulsifying for 4 hours, then cool to below 40°C before discharging.

[0029] Comparative Example 1 Comparative Example 1: A water-based self-bonding coating was prepared by the following method: Add 5 parts of 1-methoxy-2-propanol, 35 parts of BPA epoxy resin, and 8 parts of PU-modified epoxy resin to a high-shear emulsifier. Raise the temperature to 120°C and stir until the resin is completely dissolved. Cool to 80°C and add OP-10 emulsifier while stirring. Stir evenly, then add water dropwise. Continue emulsifying for 5 hours. After emulsification to a particle size of 1 to 2 microns, cool to 70°C, add 5 parts of curing agent, and continue emulsifying for 3 hours. Cool to below 40°C and discharge to obtain a water-based self-bonding coating.

[0030] Comparative Example 2 Comparative Example 2: A water-based self-bonding coating was prepared by the following method, comprising: Add 5 parts of 1-methoxy-2-propanol, 35 parts of BPA epoxy resin, and 5 parts of PU-modified epoxy resin to a high-shear emulsifier. Raise the temperature to 120°C and stir until the resin is completely dissolved. Cool to 80°C and add 6 parts of emulsifier (GL8661) while stirring. Stir evenly, then add water dropwise. Continue emulsifying for 5 hours. After emulsification to a particle size of 1 to 2 microns, cool to 70°C and add 5 parts of 2E4MZ latent curing agent. Continue emulsifying for 3 hours, then cool to below 40°C and discharge to obtain a water-based self-bonding coating.

[0031] Comparative Example 3 Comparative Example 3: A water-based self-bonding coating was prepared by the following method, comprising: Add 5 parts of 1-methoxy-2-propanol, 35 parts of BPA epoxy resin, and 9 parts of PU-modified epoxy resin to a high-shear emulsifier. Raise the temperature to 120°C and stir until the resin is completely dissolved. Cool to 60°C and add the emulsifier while stirring. Stir evenly, then add water dropwise. Continue emulsifying for 5 hours. After emulsification to a particle size of 1 to 2 microns, cool to 50°C and add 5 parts of curing agent. Continue emulsifying for 3 hours, then cool to below 40°C before discharging.

[0032] The water-based self-adhesive coatings prepared in the above examples and comparative examples were characterized, wherein the rolling peel strength was determined in accordance with the national standard GB / T 1457-2022.

[0033] The results are shown in Table 1 below: Table 1 Characterization results of waterborne self-bonding coatings

[0034] Comparative Example 1 differs from Example 1 in that the emulsifier used in Example 1 is GL8661, a reactive emulsifier that provides good system cohesion, resulting in an emulsion with good stability and excellent peel strength. However, the OP-10 used in Comparative Example 1 is a common non-reactive emulsifier, which affects system stability and peel strength.

[0035] Compared with Example 1, Comparative Example 2 used less PU modified epoxy resin. The results showed that the prepared water-based self-bonding coating had insufficient cohesion and low peel strength.

[0036] Comparative Example 3 used a lower emulsification temperature during emulsification. The low emulsification temperature resulted in poor emulsification effect, sedimentation and stratification of the emulsion, and lower peeling strength.

[0037] The peel strength of the water-based self-adhesive coatings obtained in Examples 1 to 4 of the present invention is higher, and the stability of the obtained emulsions is very high.

[0038] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A water-based self-bonding coating, characterized in that: In parts by weight, it comprises: 35 to 38 parts by weight of BPA epoxy resin; 8 to 10 parts by weight of a modified epoxy resin; 6 to 8 parts by weight of an emulsifier; 5 to 8 parts by weight of a latent curing agent; 5 to 10 parts by weight of 1-methoxy-2-propanol; and the balance water.

2. The water-based self-bonding coating according to claim 1, characterized in that The modified epoxy resin is PU modified epoxy resin.

3. The water-based self-bonding coating according to claim 1, characterized in that The emulsifier is GL8661.

4. The water-based self-bonding coating according to claim 1, characterized in that The latent curing agent is 2E4MZ latent curing agent.

5. A method for preparing a water-based self-bonding coating according to any one of claims 1 to 4, characterized in that: include: Mixing BPA epoxy resin, modified epoxy resin and 1-methoxy-2-propanol, and stirring at a first predetermined temperature until the resin is completely dissolved; Cooling to a second predetermined temperature, adding an emulsifier while stirring, stirring evenly, and adding water for the first emulsification; The temperature is lowered to a third predetermined temperature, mixed with a latent curing agent, and subjected to a second emulsification. The water-based self-bonding coating is obtained after the temperature is lowered.

6. The preparation method according to claim 5, characterized in that The first predetermined temperature is 120 to 140° C.; The second predetermined temperature is 80 to 90° C.; The third predetermined temperature is below 70°C.

7. The preparation method according to claim 5, characterized in that The first emulsification time is 5 to 7 hours; The second emulsification time is 3 to 4 hours.

8. The preparation method according to claim 5, characterized in that Step (2) performs a second emulsification until the particle size of the mixture is 1 to 2 microns.

9. A silicon steel sheet, characterized in that: The surface of the silicon steel sheet is coated with the water-based self-bonding coating according to any one of claims 1 to 4.

10. Use of the water-based self-bonding coating according to any one of claims 1 to 4 or the silicon steel sheet according to claim 9 in the field of motors.

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