A non-oriented silicon steel insulating coating liquid suitable for motor core bonding and gluing process, and its preparation method and application

Abstract

The invention discloses a non-oriented silicon steel insulating coating liquid suitable for a motor core bonding and gluing process. The non-oriented silicon steel insulating coating liquid comprises an inorganic component, an acrylic emulsion, a water-soluble modified epoxy resin, a microcapsule epoxy curing agent, a film-forming aid, a silane coupling agent, a defoaming agent, and water in a mass ratio of (30-60):(10-30):(5-10):(0.1-0.8):(1-3):(0.2-0.6):(0.1-0.3):(60-120); the inorganic component comprises aluminum dihydrogen phosphate, ammonium molybdate, boric acid, and deionized water; the acrylic emulsion is prepared using methyl methacrylate, ethyl acrylate, N-hydroxyethyl acrylamide, and acrylic acid as monomers; and the water-soluble modified epoxy resin is prepared using epoxy resin E44, propylene glycol methyl ether, diethanolamine, diethyltetramethylimidazole, and ethylene glycol diglycidyl ether as main raw materials. The coating formed by the insulating coating has good adhesion to the silicon steel sheet substrate, excellent insulation and rust resistance, and is compatible with the dispensing process of different resin systems used for the motor core, ensuring a firm bonding and dispensing effect on the core.

Description

Technical Field

[0001] The invention relates to a cold-rolled silicon steel sheet coating, in particular to a non-oriented silicon steel insulating coating liquid suitable for a motor core bonding and gluing process, and a preparation method and application thereof. Background Art

[0002] Cold-rolled non-oriented silicon steel sheets, as an excellent soft magnetic alloy, are primarily used in the manufacture of various electric motors. Traditionally, motors are primarily manufactured by stamping non-oriented silicon steel into a core, which is then laminated together by riveting or welding. The insulating coating applied to the non-oriented silicon steel is a semi-inorganic / semi-organic coating of phosphate or chromate-organic resin, primarily for insulation and rust prevention.

[0003] With the rapid expansion of new energy vehicle production capacity in recent years, demand for new energy vehicle drive motors has increased significantly, with a simultaneous trend toward higher power, higher efficiency, and smaller size. Manufacturers of cores for new energy vehicle motors are actively developing core bonding and gluing processes. By applying glue to the surface coating of non-oriented silicon steel sheets, the cores are bonded and laminated under heat and pressure. This helps further increase the motor's power density, reduce noise, vibration, and lower temperature rise.

[0004] The glue dispensing process involves extracting a predetermined amount of glue and transferring it to a designated location on the surface of the silicon steel sheets to be bonded. The sheets are then laminated into an iron core and subjected to heat and pressure to solidify the glue, bonding the core together. Currently, mainstream glue compositions are primarily solvent-based epoxy or polyurethane resins. The organic resin component of the insulating coating applied to non-oriented silicon steel sheets is primarily water-based acrylic resin, with a small amount of water-based epoxy resin. Furthermore, the monomer structures of the same resins can vary significantly. Therefore, glue formulations are specifically designed based on the type and characteristics of the resin to ensure strong chemical bonding with the insulating coating during the curing process, enhancing the adhesive's bonding performance. However, this also leads to interdependence and compatibility issues between the glue dispensing process and the insulating coating. Once core manufacturers have finalized their glue formula, they are reluctant to change the process easily, creating a technical barrier for later entrants. As mainstream steel mills, they must ensure that their insulating coatings are adaptable to a variety of glue dispensing processes to enhance their product competitiveness. Therefore, it is particularly necessary to develop a non-oriented silicon steel insulating coating that is highly compatible with various dispensing processes for bonding motor cores.

[0005] Several coatings or liquids for non-oriented silicon steel exist in the prior art. For example, CN110283480A discloses a semi-organic-semi-inorganic silicon steel sheet coating for welding. The coating comprises an inorganic component, a silicone-modified acrylic emulsion, a silane polymer, a polyol, and a defoamer in a mass ratio of (8-24):1:(0.1-0.8):0.1-1):(0.01-0.05). The inorganic component comprises, by mass, 1-8 parts magnesium oxide, 14-29 parts chromic anhydride, 0.1-0.8 parts boric acid, and 50-95 parts water. The organic resin in this formulation is a silicone-modified acrylic emulsion. By increasing the network crosslink density of the organic resin, it contains Si-O bonds that are resistant to high temperature breakage. Furthermore, the addition of a high-temperature-resistant silane polymer to the coating reduces the organic component content in the coating. The resulting coating exhibits uniform, dense film formation and high surface energy, but is less suitable for the spreading and wetting of dispensing glue.

[0006] CN110885571A discloses an energy-saving non-oriented silicon steel coating solution, its preparation method, and application. The solution comprises an inorganic component, an epoxy acrylate composite emulsion, a silane polymer, a polyol, and a defoamer in a mass ratio of (6-22):1:(0.1-1.0):(0.1-1.0):(0.01-0.05). The inorganic component comprises, by mass, 15-30 parts of silica sol, 14-28 parts of aluminum dihydrogen phosphate, 10-20 parts of chromium dihydrogen phosphate, 0.1-0.8 parts of boric acid, and 40-100 parts of water. The organic resin in this formulation is an epoxy acrylate composite emulsion with a core-shell structure, comprising an outer shell of hydrophilic carboxyl-containing acrylic groups and an inner core of epoxy groups. The shell groups physically encapsulate the core epoxy resin. Although the resin structure contains epoxy functional groups, it is covered by a shell structure and can only undergo self-crosslinking reactions, but cannot undergo crosslinking reactions with functional groups outside the shell. This also makes the component unsuitable for the motor core bonding and dispensing process.

[0007] CN114031997A discloses a coating solution suitable for coating the surface of ultra-thin non-oriented silicon steel strips. The coating solution comprises a water-soluble propylene resin, a film-forming aid, a salt-spray resistant agent, a leveling agent, nano-zirconium hydroxide, a defoamer, and water in a mass ratio of 100:(2-8):(1-3):(1-5):(0-1):(0.1-0.5):(70-130). The organic resin in this formulation is obtained by polymerizing and neutralizing various propylene monomers to form salts that are dispersed in water. This resin, in conjunction with a high-boiling-point film-forming aid such as an alcohol ether, forms a thin coating with excellent film quality on the surface of the ultra-thin strip. This coating formulation utilizes the self-crosslinking of propylene functional monomers containing side chain functional groups of varying lengths, resulting in a dense film with a smooth surface, which hinders the spreading and wetting of dispensing glue.

[0008] CN115595010A discloses a non-oriented silicon steel insulating coating suitable for improving secondary electrophoretic paint coating. The coating comprises an acetic acid propylene glycol emulsion, a film-forming aid, a rheological agent, boric acid, a polyol, a defoamer, and deionized water in a mass ratio of 100:(1-10):(2-7):(0.1-0.8):(0.1-1):(0.1-0.5):(60-150). This formulation leverages the low crosslinking density of the acetic acid propylene glycol emulsion to form a film that easily desorbs from the steel substrate during electrophoretic processing, thereby increasing the current density of the electrophoretic process. However, this coating is only suitable for electrophoretic processes. If applied to conventional steel plates, the insulation resistance is low and the steel plates are susceptible to rust. It is also unsuitable for use in motor core adhesive dispensing processes. Summary of the Invention

[0009] The present invention addresses the shortcomings of the prior art by providing a non-oriented silicon steel insulating coating liquid and preparation method suitable for the bonding and gluing process of motor cores. The coating formed by this insulating coating liquid exhibits excellent adhesion to the silicon steel substrate, superior insulation and rust resistance, and is compatible with gluing processes using different resin systems for motor cores, ensuring a secure bonding and gluing effect.

[0010] The technical solution adopted by the present invention to solve the above-mentioned problems is:

[0011] A non-oriented silicon steel insulating coating liquid suitable for a motor core bonding and gluing process comprises an inorganic component, an acrylic emulsion, a water-soluble modified epoxy resin, a microcapsule epoxy curing agent, a film-forming aid, a silane coupling agent, a defoaming agent, and deionized water in a mass ratio of (30-60):(10-30):(5-10):(0.1-0.8):(1-3):(0.2-0.6):(0.1-0.3):(60-120).

[0012] Furthermore, the above-mentioned non-oriented silicon steel insulating coating is preferably composed of inorganic components, acrylic emulsion, modified epoxy resin, microcapsule epoxy curing agent, film-forming aid, silane coupling agent, defoaming agent, and deionized water in a mass ratio of (40-50):(15-25):(6.5-8.5):(0.3-0.6):(1.5-2.5):(0.3-0.5):(0.15-0.25):(75-105).

[0013] According to the above scheme, the inorganic component is composed of aluminum dihydrogen phosphate, ammonium molybdate, boric acid and deionized water in a mass ratio of (30-70): (4-12): (1-4): (40-80). Preferably, the mass ratio of aluminum dihydrogen phosphate, ammonium molybdate, boric acid and deionized water is (40-60): (6-10): (2-3): (50-70). Furthermore, the inorganic component is prepared according to the following steps: adding boric acid to deionized water and stirring at a high speed of 150-250 r / min for 1.5-2.5 hours; adding ammonium molybdate and continuing stirring for 0.3-1.0 hour; adding aluminum dihydrogen phosphate and continuing stirring for 0.5-1.5 hours; filtering the residue with an 80-120 mesh filter to obtain the inorganic component. Furthermore, the aluminum dihydrogen phosphate is a liquid with a solid content of 50±1.0%, a P2O5 mass fraction of 33±1.0%, an Al2O3 mass fraction of 8.5±0.5%, a specific gravity (25°C) of 1.452-1.478, and an appearance of a clear, transparent aqueous solution.

[0014] According to the above scheme, the acrylic emulsion is prepared using methyl methacrylate, ethyl acrylate, N-hydroxyethyl acrylamide, and acrylic acid as monomers in the presence of an initiator, a chain transfer agent, a composite emulsifier, sodium bicarbonate, and water. The mass ratio of methyl methacrylate, ethyl acrylate, N-hydroxyethyl acrylamide, acrylic acid, initiator, chain transfer agent, composite emulsifier, sodium bicarbonate, and water is (80-140):(30-70):(10-30):(5-11):(2-10):(2-8):(0.5-4.5):(0.5-1.5):(110-190). Preferably, the acrylic emulsion is prepared from methyl methacrylate, ethyl acrylate, N-hydroxyethyl acrylamide, acrylic acid, an initiator, a chain transfer agent, a composite emulsifier, sodium bicarbonate, and water in a mass ratio of (95-125):(40-60):(15-25):(6.5-9.5):(4-8):(3.5-6.5):(1.5-3.5):(0.75-1.25):(130-170).

[0015] According to the above scheme, the preparation method of the acrylic emulsion comprises the following steps:

[0016] 1) Methyl methacrylate, ethyl acrylate, N-hydroxyethyl acrylamide and acrylic acid are uniformly mixed to obtain a premixed monomer for standby use;

[0017] 2) Add 20-30% of the premixed monomers, 30-35% of the initiator, 30-35% of the chain transfer agent, a composite emulsifier, and sodium bicarbonate to water, pass nitrogen protection, heat in a water bath to 75-85° C. under stirring, and start timing to carry out the polymerization reaction;

[0018] 3) After the polymerization reaction has completed 1.5 to 2.5 hours, the remaining premixed monomers, initiator, and chain transfer agent are added to the reaction system slowly and continuously by dropwise addition at a uniform rate, and the polymerization reaction is continued for 3.5 to 4.5 hours with stirring. The temperature is then raised to 85 to 95° C. and maintained for 1 to 2 hours. Stirring is stopped and the temperature is lowered to below 35 to 45° C. The pH value of the system is neutralized to 8 to 10 with aqueous ammonia before discharging the material to obtain the acrylic emulsion of the present invention.

[0019] In the preparation of the above-mentioned acrylic emulsion, methyl methacrylate is used as a hard monomer to ensure the hardness of the coating, ethyl acrylate is used as a soft monomer to help improve the flexibility of the coating, and N-hydroxyethyl acrylamide is used as a cross-linking monomer to help increase the cross-linking density of the resin after thermal curing; acrylic acid is used as a cross-linking monomer to help improve the water solubility of the silicon steel insulation coating and increase the adhesion of the coating. At the same time, through cross-linking reaction with the epoxy resin epoxy group in the formula of the non-oriented silicon steel insulation coating, the acrylic resin and the epoxy resin in the coating undergo cross-linking reaction with each other, thereby improving the film-forming quality of the coating.

[0020] Preferably, the composite emulsifier is a mixture of sodium dodecylbenzenesulfonate (SDBS) and sodium 3-allyloxy-1-hydroxy-1-propanesulfonate (COPS-1), wherein sodium 3-allyloxy-1-hydroxy-1-propanesulfonate (COPS-1) as a reactive emulsifier not only further improves the monomer emulsification effect, but more importantly, participates in the polymerization reaction of the acrylic emulsion through double bonds and hydroxyl groups, thereby improving the film-forming quality of the acrylic resin. More preferably, the composite emulsifier is a mixture of sodium dodecylbenzenesulfonate (SDBS) and sodium 3-allyloxy-1-hydroxy-1-propanesulfonate (COPS-1) in a mass ratio of 1:(1 to 3); the initiator is azobisisobutyronitrile (AIBN); and the chain transfer agent is tert-butyl ester (V-10).

[0021] According to the above scheme, the water-soluble modified epoxy resin is prepared from epoxy resin E44, propylene glycol methyl ether, diethanolamine, diethyltetramethylimidazole, and ethylene glycol diglycidyl ether as main raw materials. Preferably, the molar ratio of epoxy resin E44, propylene glycol methyl ether, diethanolamine, diethyltetramethylimidazole, and ethylene glycol diglycidyl ether is 1:(0.04-0.08):(0.1-0.3):(0.1-0.4):(0.05-0.15). Preferably, the modified epoxy resin is prepared from epoxy resin E44, propylene glycol methyl ether, diethanolamine, diethyltetramethylimidazole, and ethylene glycol diglycidyl ether in a molar ratio of 1:(0.05-0.07):(0.15-0.25):(0.175-0.325):(0.075-0.125).

[0022] According to the above scheme, the preparation method of the water-soluble modified epoxy resin comprises the following steps:

[0023] (1) Resin premixing: Mix epoxy resin E44, propylene glycol methyl ether and ethylene glycol diglycidyl ether evenly, pass nitrogen protection, and heat in a water bath to 85-95°C under stirring to fully dissolve;

[0024] (2) Modified emulsification: diethanolamine is added to the reaction system obtained in step (1) slowly and continuously by dripping at a uniform speed, and stirring is continued for 1.5 to 2.5 hours, and the temperature is raised to 120° C. and kept warm for 4 to 5 hours to obtain a modified epoxy resin;

[0025] (3) Water-based preparation: The modified epoxy resin obtained in step (2) is placed in a vacuum drying oven, kept at 40-50°C for 1 hour to remove the solvent, and then re-placed in a container and placed in a water bath at 60-70°C. Anhydrous acetic acid is slowly added dropwise to adjust the pH value to 6.5-7.5 (neutralization to form a salt), and stirred for 1-2 hours to prepare a water-soluble modified epoxy resin with a solid content of 30-40%.

[0026] The water-soluble modified epoxy resin prepared according to the above method and raw material ratio can be miscible with the above acrylic emulsion below 50°C and exist stably, and the storage period can reach 6 to 12 months. During the preparation process of the water-soluble modified epoxy resin, propylene glycol methyl ether is used as a diluent for the water-based modification of the epoxy resin; ethylene glycol diglycidyl ether is used as an active diluent for the water-based modification of the epoxy resin, which helps to reduce the room temperature activity of the epoxy resin and increase the storage period through a cross-linking reaction between the epoxy group and the epoxy resin; and the epoxy resin is modified by introducing hydrophilic hydroxyl and amino groups by the diethanolamine. The modified epoxy resin obtained by the reaction has strong hydrophilicity and can be uniformly and stably dispersed in water; the diethyltetramethylimidazole is used as a latent curing agent for the epoxy resin, which can not undergo a cross-linking reaction with the epoxy resin at room temperature, while ensuring that a cross-linking reaction occurs with the epoxy resin during the high-temperature baking process of the silicon steel insulation coating.

[0027] According to the above scheme, the overall appearance of the microcapsule epoxy curing agent is a translucent white powder, with 2-undecyl imidazoline and methyl hexahydrophthalic anhydride as the capsule core, polymethyl methacrylate as the capsule wall, and the mass ratio of the capsule wall to the capsule core is 1:(5-10); wherein, the capsule core is 2-undecyl imidazoline and methyl hexahydrophthalic anhydride compounded in a mass ratio of 1:(0.8-1.2).

[0028] According to the above scheme, the microcapsule epoxy curing agent is an excellent latent curing agent, which can withstand high temperatures of 220 to 300°C in a short period of 30 to 90 seconds, ensuring its stable existence during the curing process of the non-oriented silicon steel insulation coating liquid; at the same time, under the conditions of 1 to 3 MPa pressure and 100 to 200°C heating and pressurization, 2-undecyl imidazoline and methyl hexahydrophthalic anhydride gradually seep out from the capsule wall within 6 to 10 hours, and in the subsequent iron core bonding and dispensing process, promotes the cross-linking reaction between the epoxy groups and hydroxyl groups in the coating formed by the non-oriented silicon steel insulation coating liquid and the glue film-forming material at the interface, thereby greatly improving the iron core dispensing bonding strength.

[0029] According to the above scheme, the film-forming aid is one or two of ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, etc.; the defoaming agent is polyoxyethylene polyoxypropylene pentaerythritol ether or polyoxyethylene polyoxypropanolamine ether, etc.

[0030] The present invention also provides a method for preparing the above-mentioned non-oriented silicon steel insulating coating liquid suitable for the bonding and gluing process of the motor core. The specific process is: according to the dosage ratio of the above-mentioned raw materials, deionized water, acrylic emulsion, inorganic component, water-soluble modified epoxy resin and defoaming agent are added to the reaction container in sequence, and after each component is added, stirring is carried out for 1 to 1.5 hours; film-forming aid, silane coupling agent and microcapsule epoxy curing agent are continuously added, and stirring is carried out for 1 to 1.5 hours; after the coating liquid is prepared, it is allowed to stand for 20 to 30 minutes, and the residual particles in the coating liquid are filtered with a filter screen with a mesh size of 80 to 150 to obtain the required non-oriented silicon steel insulating coating liquid suitable for the bonding and gluing process of the motor core.

[0031] On the basis of the above, the present invention further provides a method for applying the non-oriented silicon steel insulating coating liquid of the present invention to a motor core bonding and gluing process, the specific steps of which are as follows:

[0032] S1. The non-oriented silicon steel insulating coating liquid of the present invention is controlled to have a specific gravity in the range of 1.10 to 1.30, preferably 1.15 to 1.25, by adding water. The coating liquid is then applied to the surface of the non-oriented silicon steel sheet. The coating liquid is then placed in a drying furnace and dried and solidified at a certain temperature to form an insulating coating having a thickness of 0.3 to 0.8 μm. At this point, the non-oriented silicon steel sheet with the insulating coating has good magnetic and mechanical properties, and the surface insulating coating has good adhesion, insulation and rust resistance.

[0033] S2. The non-oriented silicon steel sheet with insulation coating obtained in S1 is divided into strips, and then a single die is used to punch out a single-piece motor core. Each piece of the motor core is glued and then cured by high-temperature heating to obtain a glued core; wherein the motor core includes a rotor, a stator, etc.

[0034] Furthermore, in the application method, the glue used for dispensing is mainly solvent-based epoxy system glue or polyurethane system glue, and the dispensing nozzle is used to perform multi-point and uniform spraying on the surface of the iron core (stator or rotor single piece) to ensure that the glue covers a sufficient spraying area of the iron core single piece. At the same time, the iron cores that have completed the spraying are neatly stacked by the fixing rod and the mold pressing plate, and sent to the curing furnace for dispensing heat curing treatment. The heat curing process used is the iron core reinforcement pressure of 1 to 3 MPa, the heating temperature of 100 to 200 ° C, and the heating cycle of 6 to 24 hours. After cooling in the furnace, it is taken out of the furnace to obtain the finished iron core bonded by the dispensing process.

[0035] Furthermore, in the application method, the non-oriented silicon steel is a cold-rolled non-oriented silicon steel plate, which is obtained by pickling a non-oriented silicon steel hot-rolled plate with a thickness of 1.8 to 2.8 mm and a silicon content of 0.4% to 3.0% to remove surface iron oxide scale. The rolling mill rolls the steel plate to a target thickness of 0.20 to 0.65 mm, and then passes the plate through a continuous annealing unit at a high speed to complete decarburization annealing and grain recovery annealing. Before applying the coating liquid, the surface of the steel plate must be clean, dry and free of foreign matter.

[0036] Furthermore, in the application method, the coating liquid is applied using an active four-roller coating machine, and the coating film thickness is mainly controlled by the roller speed ratio between the steel strip A, the coating machine coating roller B, and the dipping roller C. Preferably, the roller speed ratio between the steel strip A and the coating machine coating roller B is 0.5 to 0.8; and the roller speed ratio between the coating machine coating roller B and the dipping roller C is 0.2 to 0.4.

[0037] Furthermore, in the application method, the curing plate temperature (PMT) of the dried and cured steel plate substrate is: 220-280°C / 20-60S, preferably 240-260°C / 35-45S.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1) The present invention prepares a specific acrylic emulsion and performs water-soluble modification on epoxy resin, thereby combining the respective advantages of acrylic resin and epoxy resin, adding inorganic components for synergistic combination, introducing a microcapsule epoxy curing agent, and supplementing with other additives to obtain a non-oriented silicon steel insulating coating liquid for forming an insulating coating with good adhesion, insulation and rust resistance on the surface of a non-oriented silicon steel sheet, which is easy to achieve bonding and curing effect with iron core glue, and overcomes the problems of poor compatibility of traditional silicon steel chromate or phosphate semi-inorganic and semi-organic coatings with motor cores and weak iron core bonding and gluing effect.

[0040] 2) The present invention provides a coating liquid formulation that combines the advantages of both propylene resin and epoxy resin. The two emulsions can be mixed with each other at room temperature and can be stored stably for a long time. During the thermal curing process of the coating liquid by baking at a certain temperature, the two resins can not only undergo cross-linking reactions themselves, but the epoxy resin, under the action of a latent curing agent, further undergoes cross-linking reactions with the hydroxyl, carboxyl and amide groups of the propylene resin through epoxy groups and ether bonds, and simultaneously reacts with phosphates to form phosphate esters and reacts with molybdates to form complex heteropolyacids. The two resin film-forming materials and the inorganic components are entangled and interpenetrated, further increasing the film density of the semi-inorganic and semi-organic coating cross-linking system, while also combining the high gloss and adhesion of the propylene resin with the good electrical insulation and corrosion resistance of the epoxy resin.

[0041] 3) In the process of designing the epoxy resin formula, the present invention uses active diluents and diethanolamine to modify the epoxy resin, appropriately reducing the activity of the epoxy resin. At the same time, a milder latent curing agent is selected to ensure that a large number of epoxy groups and hydroxyl groups are still present in the epoxy resin after the coating is baked and cured. In the subsequent thermal curing process of the iron core bonding glue, the microcapsule epoxy curing agent can undergo cross-linking reaction at the interface, thereby greatly improving the bonding strength of the iron core glue.

[0042] 4) The microcapsule epoxy curing agent selected in the present invention has the ability to withstand short-term high-temperature baking. At the same time, under heating and pressurizing conditions and within a certain period of time, the core curing agent gradually seeps out from the capsule wall, helping the epoxy resin in the insulating coating to participate in the thermal curing cross-linking reaction of the glue in the iron core gluing process, thereby increasing the bonding strength of the iron core. The delayed effect of the core curing agent is fully utilized in the present invention. DETAILED DESCRIPTION

[0043] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with examples, but the present invention is not limited to the following examples.

[0044] In the following examples, the aluminum dihydrogen phosphate is a liquid having a solid content of 50±1.0%, a P2O5 mass fraction of 33±1.0%, an Al2O3 mass fraction of 8.5±0.5%, a specific gravity (25°C) of 1.452 to 1.478, and an appearance of a clear, transparent aqueous solution; the ammonium molybdate is a white powder with a purity of 99%; and the boric acid is a white powder with a purity of 99.5%.

[0045] In the following embodiments, the preparation method of the microcapsule epoxy curing agent specifically includes the following steps:

[0046] (1) Liquid paraffin, sodium dodecylbenzenesulfonate (SDBS), and deionized water were mixed and stirred in a mass ratio of 1:1:3 to prepare an emulsion, 2-undecyl imidazoline and methyl hexahydrophthalic anhydride were added in a mass ratio of 5% to the emulsion (the mass ratio of 2-undecyl imidazoline to methyl hexahydrophthalic anhydride was 1:1, and the total amount of the two was about 5% of the emulsion), and the mixture was stirred at a high speed of 2000 to 3000 rpm for 20 to 50 minutes to prepare a core material emulsion;

[0047] (2) ultrasonically dispersing polymethyl methacrylate and liquid paraffin in a mass ratio of 1:2 for 15 to 30 minutes to obtain a capsule wall emulsion;

[0048] (3) The capsule wall emulsion is added to the core material emulsion at a mass ratio of 2%, and the mixture is continuously stirred at a high speed of 2000 to 3000 rpm for 20 to 50 minutes. The mixture is then poured into a sealed container, and water is removed by vacuum distillation at 70 to 90° C. for 2.5 to 3.5 hours. The mixture is then centrifuged, washed with petroleum ether, and vacuum dried to obtain a microcapsule epoxy curing agent.

[0049] In the following embodiments, the epoxy resin E44 is a bisphenol A epoxy resin having a softening point of 15 to 23° C., an average epoxy value of 0.44 mol / 100 g, a transparent liquid, and a molecular weight of 300 to 1000; the propylene glycol methyl ether is a colorless transparent liquid with a purity of 99%; and the silane coupling agent is KH-550 or KH-570.

[0050] Examples 1 to 5

[0051] The non-oriented silicon steel insulating coating liquid suitable for the bonding and gluing process of the motor core provided by each embodiment of the present invention is composed of an inorganic component, an acrylic emulsion, a modified epoxy resin, a microcapsule epoxy curing agent, a film-forming aid, a silane coupling agent, a defoaming agent, and deionized water in a mass ratio of (30-60):(10-30):(5-10):(0.1-0.8):(1-3):(0.2-0.6):(0.1-0.3):(60-120). The specific ratios of each embodiment are shown in Table 1;

[0052] The inorganic component is composed of aluminum dihydrogen phosphate, ammonium molybdate, boric acid and deionized water in a mass ratio of (30-70): (4-12): (1-4): (40-80). The specific ratios of each embodiment are shown in Table 2.

[0053] The acrylic emulsion is prepared from methyl methacrylate, ethyl acrylate, N-hydroxyethyl acrylamide, acrylic acid, an initiator, a chain transfer agent, a composite emulsifier, sodium bicarbonate, and water in a mass ratio of (80-140):(30-70):(10-30):(5-11):(2-10):(2-8):(0.5-4.5):(0.5-1.5):(110-190). The specific ratios of each embodiment are shown in Table 3.

[0054] The water-soluble modified epoxy resin is prepared from epoxy resin E44, propylene glycol methyl ether, diethanolamine, diethyltetramethylimidazole, and ethylene glycol diglycidyl ether in a molar ratio of 1:(0.04-0.08):(0.1-0.3):(0.1-0.4):(0.05-0.15). The specific ratios of each embodiment are shown in Table 4.

[0055] Table 1 Overall composition and ratio

[0056] Components Example 1 Example 2 Example 3 Example 4 Example 5 Inorganic components 30 40 45 50 60 Acrylic emulsion 10 15 20 25 30 Water-soluble modified epoxy resin 5 6.5 7.5 8.5 10 Microcapsule epoxy curing agent 0.1 0.3 0.45 0.6 0.8 Coal-forming aids 1 1.5 2 2.5 3 Silane coupling agent 0.2 0.3 0.4 0.5 0.6 defoaming agent 0.1 0.15 0.2 0.25 0.3 Deionized water 60 75 90 105 120

[0057] Table 2 Inorganic components and ratios

[0058] Components Example 1 Example 2 Example 3 Example 4 Example 5 Aluminum dihydrogen phosphate 30 40 50 60 70 Ammonium molybdate 4 6 8 10 12 Boric acid 1 2 2.5 3 4 Deionized water 40 50 60 70 80

[0059] Table 3 Composition and ratio of acrylic emulsion

[0060] Components Example 1 Example 2 Example 3 Example 4 Example 5 Methyl methacrylate 80 95 110 125 140 Ethyl acrylate 30 40 50 60 70 N-Hydroxyethyl acrylamide 10 15 20 25 30 acrylic acid 5 6.5 8 9.5 11 initiator 2 4 6 8 10 Chain transfer agent 2 3.5 5 6.5 8 Composite emulsifier 0.5 1.5 2.5 3.5 4.5 Sodium bicarbonate 0.5 0.75 1 1.25 1.5 water 110 130 150 170 190

[0061] In the above tables, the units of each component are parts by mass. Unit parts by mass represent the same mass in the same table and different masses in different tables.

[0062] Table 4 Composition and ratio of water-soluble modified epoxy resin (units are all molar ratios)

[0063] Components Example 1 Example 2 Example 3 Example 4 Example 5 Propylene glycol methyl ether / epoxy resin E44 0.04 0.05 0.06 0.07 0.08 Diethanolamine / Epoxy Resin E44 0.1 0.15 0.2 0.25 0.3 Diethyltetramethylimidazole / epoxy resin E44 0.1 0.175 0.25 0.325 0.4 Ethylene glycol diglycidyl ether / epoxy resin E44 0.05 0.075 0.1 0.125 0.15

[0064] The preparation method and use method of the non-oriented silicon steel insulating coating liquid suitable for the motor core bonding and gluing process described in each embodiment are as follows:

[0065] 1. Preparation of Inorganic Components in Each Example

[0066] In each example, boric acid was added to deionized water according to the ratio in Table 2, and the mixture was stirred at a high speed of 200 r / min for 2 hours; ammonium molybdate was added, and stirring was continued for 0.5 hours; aluminum dihydrogen phosphate was added, and stirring was continued for 1 hour; and the residue was filtered through a 100-mesh filter to obtain the inorganic components required by the example.

[0067] 2. Preparation of acrylic emulsions in various embodiments

[0068] (1) In each embodiment, methyl methacrylate, ethyl acrylate, N-hydroxyethyl acrylamide, and acrylic acid were mixed uniformly according to the ratio in Table 3 to obtain a premixed monomer;

[0069] (2) 1 / 4 of the premixed monomer, composite emulsifier, 1 / 3 of the initiator, 1 / 3 of the chain transfer agent, and sodium bicarbonate were added to water, mixed evenly in a reactor, and nitrogen was passed through. The temperature was raised to 80° C. in a water bath under stirring conditions, and the polymerization reaction was started and timed;

[0070] (3) After 2 hours of polymerization, the remaining premixed monomers, initiator and chain transfer agent were added to the reactor slowly and continuously by dropwise addition at a uniform rate and the polymerization was continued for 4 hours. The temperature was raised to 90° C. and kept at this temperature for 1.5 hours. Stirring was stopped and the temperature was lowered to below 40° C. The material was neutralized to pH 10 with aqueous ammonia and discharged to obtain the acrylic emulsion required in the embodiment.

[0071] Among them, the initiator of each embodiment is azobisisobutyronitrile (AIBN), the chain transfer agent is versatate (V-10), and the composite emulsifier is a mixture of sodium dodecylbenzenesulfonate SDBS and 3-allyloxy-1-hydroxy-1-propanesulfonic acid sodium salt (COPS-1) in a mass ratio of 1:3.

[0072] 3. Preparation of water-soluble modified epoxy resins in various embodiments

[0073] (1) Resin premixing: According to the proportions in Table 4, epoxy resin E44, propylene glycol methyl ether and ethylene glycol diglycidyl ether were mixed uniformly in a reactor, protected by nitrogen, and heated in a water bath to 90° C. under stirring to pre-dissolve;

[0074] (2) Modified emulsification: diethanolamine was added to the reactor of step (1) slowly and continuously by dripping at a uniform speed and continued to stir for 2 hours, and the temperature was raised to 120° C. and kept warm for 4.5 hours to obtain a modified epoxy resin;

[0075] (3) Water-based preparation: The modified epoxy resin obtained in step (2) was placed in a vacuum drying oven, kept warm at 45°C for 1 hour to remove the solvent, and then re-placed in a container. Anhydrous acetic acid was slowly added dropwise in a 65°C water bath to adjust the pH value to 6.5-7.5 to neutralize the salt. The mixture was stirred for 1.5 hours to prepare a water-soluble modified epoxy resin with a solid content of 35%.

[0076] 4. Preparation of non-oriented silicon steel insulation coating suitable for motor core bonding and dispensing process

[0077] In each embodiment, deionized water, acrylic emulsion, inorganic component, water-soluble modified epoxy resin and defoamer were added to the reaction container in sequence according to the ratio in Table 1. After each component was added, stirring was performed for 1 hour. Film-forming aid, silane coupling agent and microcapsule epoxy curing agent were continuously added and stirred for 1.5 hours. After the coating solution was prepared, it was allowed to stand for 25 minutes and the residual particles in the coating solution were filtered through a 100-mesh filter to obtain the desired non-oriented silicon steel insulating coating solution.

[0078] The film-forming aid in each embodiment is ethylene glycol monomethyl ether, the silane coupling agent is KH-550, and the defoaming agent is polyoxyethylene polyoxypropylene pentaerythritol ether, with a relative molecular weight of 4000.

[0079] 5. The application method of the above non-oriented silicon steel insulating coating liquid in the bonding and dispensing process of the motor core is as follows:

[0080] Step 1: Take a finished non-oriented silicon steel sheet with a thickness of 0.30mm and a silicon content of 2.85%. The non-oriented silicon steel sheet is obtained by pickling and rolling a non-oriented silicon steel hot-rolled plate with a thickness of 2.1mm, and then passing the plate through a continuous annealing unit at high speed to complete decarburization annealing and grain recovery annealing. The surface must be clean, dry and free of foreign matter.

[0081] Step 2: Add water to the non-oriented silicon steel insulating coating prepared in each embodiment to control the specific gravity in the range of 1.10 to 1.30, and then apply it to the surface of the non-oriented silicon steel sheet selected in step 1, place it in a drying furnace, and dry and solidify it at a certain temperature to form an insulating coating. At this time, a non-oriented silicon steel sheet with an insulating coating is obtained, and the coating thickness is 0.3 to 0.5 μm; wherein, the coating liquid coating method adopts an active four-roll roller coating machine, and the coating film thickness control is mainly achieved by the roller speed ratio between the strip A, the coating roller B of the coating machine, and the dipping roller C, wherein the A / B ratio is 0.7 and the B / C ratio is 0.3; the curing plate temperature (PMT) of the drying and curing silicon steel sheet substrate is: 220 to 280°C / 20 to 60S. The specific process parameters of this step in each embodiment are shown in Table 5.

[0082] Table 5 Coating curing parameters of various examples

[0083]

[0084] Step 3: The non-oriented silicon steel sheet with insulating coating obtained in step 2 is divided into strips, and a single-piece rotor and stator punching sheet is punched out using a single die. Each rotor and stator punching sheet is glued and cured by high-temperature heating to obtain a rotor viscose core and a stator viscose core.

[0085] In step 3, the glue used is primarily a solvent-based epoxy or polyurethane adhesive. A dispensing nozzle is used to evenly spray the stator or rotor core at multiple locations, ensuring sufficient coverage. The cores are then stacked neatly using a fixed rod and mold platen. The cores are then placed in a curing oven for heat curing. The heat curing process employs a core reinforcement pressure of 1-3 MPa, a heating temperature of 100-200°C, and a heating cycle of 6-24 hours. The cores cool and are then removed from the oven. The finished stator and rotor cores are bonded together using the dispensing process. Specific resin types and curing processes are shown in Table 6.

[0086] Table 6 Dispensing formula resin types and curing processes of different manufacturers

[0087]

[0088] Comparative Example 1

[0089] For comparison, a coating formulation of an acetic acid acrylic emulsion was used, consisting of an acetic acid acrylic emulsion, a film-forming aid, a rheological agent, boric acid, a polyol, a defoamer, and deionized water in a mass ratio of 100:5.5:4:0.3:0.5:0.3:90. The acetic acid acrylic emulsion was prepared from four monomers: vinyl acetate, butyl acrylate, acrylic acid, and hydroxyethyl methacrylate; a composite emulsifier (SDS and TX-9 mixed in a mass ratio of 1:2); and an initiator, ammonium persulfate, in a mass ratio of 55:40:9:5:3:3. The film-forming aid was ethylene glycol monomethyl ether, the rheological agent was polyether-modified tetrasiloxane, and the defoamer was polyoxyethylene polyoxypropylene pentaerythritol ether.

[0090] Comparative Example 2

[0091] The microcapsule epoxy curing agent in Example 3 was removed, and the remaining steps remained unchanged.

[0092] Comparative Example 3

[0093] The water-soluble modified epoxy resin in Example 3 is replaced with conventional epoxy resin E44, a bisphenol A epoxy resin with a softening point of 15-23°C, an average epoxy value of 0.44 mol / 100g, a liquid transparent state, and a molecular weight of 300-1000. The remaining steps remain unchanged.

[0094] Test Case

[0095] The coating properties of the coatings prepared in the examples and comparative examples, the interlayer resistance, glossiness and salt spray resistance of the non-oriented silicon steel with insulating coatings were tested, and the results are listed in Table 7. The coating test methods used are as follows:

[0096] 1) Interlayer resistance: Tested with an interlayer resistance tester in accordance with GB / T2522-2007.

[0097] 2) Gloss test: Use a gloss meter to test in accordance with GB9754-2007.

[0098] 3) Salt spray resistance: The neutral salt spray resistance test was carried out according to the method in GB2423.17-93.

[0099] 4) Pull-out strength test of coating after core glue treatment: The core stator and rotor bonded by the glue treatment were tested for pull-out strength using an electronic universal material testing machine, specifically a Dyna double-arm DN-WD5KN.

[0100] Table 7 Performance test results of various embodiments and comparative examples

[0101]

[0102] Table 7 Performance test results of various embodiments and comparative examples (continued)

[0103]

[0104] As can be seen from Table 7: Comparative Example 1 is a non-oriented silicon steel insulating coating suitable for improving the secondary coating of electrophoretic paint. The experimental results show that the coating can well adapt to the dispensing process of manufacturer B. However, the core pull-out force test of manufacturers A and C after the dispensing process is very low, and loose pieces appear; Comparative Examples 2 and 3 are respectively Example 3 without the microcapsule epoxy curing agent and the water-based modified epoxy resin is replaced with conventional epoxy resin E44. The test results show that the core pull-out force test of Comparative Examples 2 and 3 after the dispensing process of the three manufacturers is very low, and loose pieces, warping and cracking defects appear.

[0105] The non-oriented silicon steel with insulating coatings prepared in Examples 1-5 of the present invention has a good surface, excellent insulation performance and rust resistance, and is particularly suitable for downstream motor core glue bonding processes and can be adapted to different manufacturers. Among them, Example 3 has a good coating surface gloss, and the insulation resistance and rust resistance of the coating are optimized. At the same time, the pull-out force test of different motor core glue bonding process manufacturers can reach a good level. The stator and rotor pull-out force of the other examples except Example 3 also has very good performance. Although there are slight cracks or a few warped pieces, they all meet user requirements as a whole, and are greatly improved compared to Comparative Examples 1-3, achieving the purpose of optimizing the coating formula.

[0106] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this field, several improvements and changes can be made without departing from the creative concept of the present invention, which all fall within the scope of protection of the present invention.

Claims

1. A non-oriented silicon steel insulating coating liquid suitable for the bonding and gluing process of motor cores, characterized in that: The main raw materials of the non-oriented silicon steel insulating coating liquid include inorganic components, acrylic emulsion, water-soluble modified epoxy resin, microcapsule epoxy curing agent, film-forming aid, silane coupling agent, defoaming agent, and water; wherein the mass ratio of the inorganic components, acrylic emulsion, water-soluble modified epoxy resin, microcapsule epoxy curing agent, film-forming aid, silane coupling agent, defoaming agent, and water is (30-60):(10-30):(5-10):(0.1-0.8):(1-3):(0.2-0.6):(0.1-0.3):(60-120); The inorganic component is composed of aluminum dihydrogen phosphate, ammonium molybdate, boric acid and deionized water in a mass ratio of (30-70):(4-12):(1-4):(40-80); the acrylic emulsion is prepared using methyl methacrylate, ethyl acrylate, N-hydroxyethyl acrylamide and acrylic acid as monomers in the presence of an initiator, a chain transfer agent, an emulsifier, sodium bicarbonate and water; and the water-soluble modified epoxy resin is prepared using epoxy resin E44, propylene glycol methyl ether, diethanolamine, diethyltetramethylimidazole and ethylene glycol diglycidyl ether as main raw materials.

2. The non-oriented silicon steel insulating coating liquid suitable for the motor core bonding and gluing process according to claim 1, characterized in that: The acrylic emulsion is prepared from methyl methacrylate, ethyl acrylate, N-hydroxyethyl acrylamide, acrylic acid, an initiator, a chain transfer agent, an emulsifier, sodium bicarbonate, and water in a mass ratio of (80-140):(30-70):(10-30):(5-11):(2-10):(2-8):(0.5-4.5):(0.5-1.5):(110-190); The molar ratio of the main raw materials of the water-soluble modified epoxy resin, epoxy resin E44, propylene glycol methyl ether, diethanolamine, diethyltetramethylimidazole, and ethylene glycol diglycidyl ether, is 1:(0.04~0.08):(0.1~0.3):(0.1~0.4):(0.05~0.15).

3. The non-oriented silicon steel insulating coating liquid suitable for the motor core bonding and gluing process according to claim 1, characterized in that: The non-oriented silicon steel insulating coating liquid is composed of inorganic components, acrylic emulsion, water-soluble modified epoxy resin, microcapsule epoxy curing agent, film-forming aid, silane coupling agent, defoaming agent, and water in a mass ratio of (40-50):(15-25):(6.5-8.5):(0.3-0.6):(1.5-2.5):(0.3-0.5):(0.15-0.25):(75-105); The inorganic component consists of aluminum dihydrogen phosphate, ammonium molybdate, boric acid and deionized water in a mass ratio of (40-60):(6-10):(2-3):(50-70).

4. The non-oriented silicon steel insulating coating liquid suitable for the motor core bonding and gluing process according to claim 1, characterized in that: The acrylic emulsion is prepared from methyl methacrylate, ethyl acrylate, N-hydroxyethyl acrylamide, acrylic acid, an initiator, a chain transfer agent, an emulsifier, sodium bicarbonate, and water in a mass ratio of (95-125):(40-60):(15-25):(6.5-9.5):(4-8):(3.5-6.5):(1.5-3.5):(0.75-1.25):(130-170); The emulsifier is a mixture of sodium dodecylbenzenesulfonate and sodium salt of 3-allyloxy-1-hydroxy-1-propanesulfonic acid; The water-soluble modified epoxy resin is prepared from epoxy resin E44, propylene glycol methyl ether, diethanolamine, diethyltetramethylimidazole, and ethylene glycol diglycidyl ether in a molar ratio of 1:(0.05-0.07):(0.15-0.25):(0.175-0.325):(0.075-0.125).

5. The non-oriented silicon steel insulating coating liquid suitable for the motor core bonding and gluing process according to claim 1, characterized in that: The preparation method of the acrylic emulsion comprises the steps: 1) Methyl methacrylate, ethyl acrylate, N-hydroxyethyl acrylamide and acrylic acid are uniformly mixed to obtain a premixed monomer for standby use; 2) Add 20-30% of the premixed monomers, 30-35% of the initiator, 30-35% of the chain transfer agent, an emulsifier, and sodium bicarbonate to water, pass nitrogen protection, heat in a water bath to 75-85°C under stirring, and start timing to start the polymerization reaction; 3) After the polymerization reaction has completed for 1.5 to 2.5 hours, the remaining premixed monomers, initiator, and chain transfer agent are added to the reaction system in a dropwise manner at a uniform rate and continuously, and the polymerization reaction is continued for 3.5 to 4.5 hours with stirring. The temperature is then raised to 85 to 95° C. and maintained for 1 to 2 hours. Stirring is stopped and the temperature is lowered to below 45° C. The pH value of the system is neutralized to 8 to 10 with aqueous ammonia, and the material is discharged to obtain the acrylic emulsion.

6. The non-oriented silicon steel insulating coating liquid suitable for the motor core bonding and gluing process according to claim 5, characterized in that: The emulsifier is prepared by mixing sodium dodecylbenzenesulfonate and sodium 3-allyloxy-1-hydroxy-1-propanesulfonic acid in a mass ratio of 1:(1-3); the initiator is azobisisobutyronitrile; and the chain transfer agent is tert-butyl vinyl carbonate.

7. The non-oriented silicon steel insulating coating liquid suitable for the motor core bonding and gluing process according to claim 1, characterized in that: The microcapsule epoxy curing agent uses 2-undecyl imidazoline and methyl hexahydrophthalic anhydride as the capsule core and polymethyl methacrylate as the capsule wall. The mass ratio of the capsule wall to the capsule core is 1:(5-10). The capsule core is prepared by compounding 2-undecyl imidazoline and methyl hexahydrophthalic anhydride in a mass ratio of 1:(0.8-1.2). The film-forming aid is one or two of ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and propylene glycol monomethyl ether; and the defoaming agent is polyoxyethylene polyoxypropylene pentaerythritol ether or polyoxyethylene polyoxypropanolamine ether.

8. The method for preparing the non-oriented silicon steel insulating coating liquid suitable for the motor core bonding and gluing process according to claim 1, characterized in that: According to the mass ratio of the above raw materials, water, acrylic emulsion, inorganic component, water-soluble modified epoxy resin and defoamer are added to the reaction container in sequence, and after each component is added, stirring is carried out for 1 to 1.5 hours; a film-forming aid, a silane coupling agent and a microcapsule epoxy curing agent are continuously added and stirred for 1 to 1.5 hours; after the coating liquid is prepared, it is allowed to stand for 20 to 30 minutes, and residual particles in the coating liquid are filtered through a filter with a mesh size of 80 to 150 to obtain the non-oriented silicon steel insulating coating liquid suitable for the motor core bonding and dispensing process.

9. The method for applying the non-oriented silicon steel insulating coating liquid according to claim 1 to a motor core bonding and gluing process, characterized in that: The specific steps are as follows: S1, the non-oriented silicon steel insulating coating liquid is controlled to have a specific gravity in the range of 1.10-1.30 by adding water, and then applied to the surface of the non-oriented silicon steel sheet, and dried and cured to form an insulating coating with a coating thickness of 0.3-0.8 μm; S2. Slice the non-oriented silicon steel sheet with insulation coating obtained in S1, and then use a single punch die to punch out a single motor core. Apply glue to each motor core and perform heat curing to obtain a glued core.

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