Coating for forming pressure-resistant adhesive-overflow-free self-bonding coating layer, silicon steel and motor iron core

Abstract

The present invention relates to a coating for forming a pressure-resistant adhesive-overflow-free self-bonding coating layer. In the coating, water serves as a solvent, and active ingredients of the coating comprise an organic component and an inorganic particulate component. The organic component comprises an epoxy resin and an epoxy resin curing agent. The epoxy resin comprises a macromolecular epoxy resin and a micromolecular epoxy resin. The inorganic particulate component comprises nano-scale gas-phase oxide particles and nano-scale silicon dioxide particles. The mass percentage content of the organic component in the active ingredients is 90-99%. The present invention further relates to silicon steel, comprising a silicon steel substrate and a coating layer formed on the surface of the silicon steel substrate from the coating. The present invention further relates to a high-bonding-strength motor core with a high stacking factor, which is made of the silicon steel.

Description

A coating for forming a pressure-resistant and glue-overflow-free self-bonding coating, silicon steel and motor core TECHNICAL FIELD

[0001] The present disclosure relates to a coating, silicon steel and motor core, in particular to a coating for a self-bonding coating, silicon steel and motor core. BACKGROUND

[0002] The self-bonding laminated core has a problem of glue overflow during the hot-pressing curing process, especially under the following process conditions: large coating film thickness, high curing pressure, high temperature and / or long pressure holding time.

[0003] The thickness of the silicon steel substrate suitable for the self-bonding coating used in the current batch production is generally between 0.35 and 0.65 mm, while the thickness of the high-grade silicon steel substrate is usually less than or equal to 0.30 mm, and the thickness of the silicon steel substrate for driving motor is generally between 0.20 and 0.27 mm. Under the condition that other process parameters are approximately the same, the thinner the substrate, the higher the proportion of the coating in the core per unit, and the more likely to cause glue overflow during the hot-pressing forming process. Therefore, it is necessary to optimize the coating formula and its production process, and to strengthen the glue-overflow-free performance of the coating product.

[0004] In addition, in order to improve the operating efficiency of the motor, the silicon steel laminated core usually needs to achieve a high stacking coefficient during the manufacturing process. However, the thinner the silicon steel substrate, the higher the required coating thickness, which often leads to a decrease in the stacking coefficient.

[0005] In the prior art, the common way to increase the stacking coefficient is to increase the curing pressure. After the core is once hot-pressed and cured, the axial size will shrink to a certain extent, which is usually small and controllable, and can be compensated by setting the height or total weight of the sheet stack in advance to meet the final size requirements.

[0006] However, the axial ends of some flat wire motor cores still need to be treated with paint dripping after hot-pressing and curing in order to enhance the end face insulation performance. The curing process of the paint dripping usually requires heating at 150-200℃ for 30-60min, which is equivalent to a second heating of the core.

[0007] Since no pressure is applied to the axial ends of the core during the second heating process and no limiting constraint is provided, the core is prone to axial size expansion. The expansion degree will be aggravated with the greater first hot-pressing pressure, the thinner substrate and the thicker coating, and at the same time, it also leads to difficulty in controlling the size consistency between different batches, thereby affecting the performance of the core.

[0008] The reason for this phenomenon is that the self-bonding coating absorbs part of the pressure as an elastomer material during the first hot pressing process, and the whole body shrinks after achieving the physical adhesion between the sheets and completing the curing reaction. When the core is heated again without pressure constraint, the residual stress in the coating is released, causing the axial size of the core to expand elastically. SUMMARY

[0009] One of the purposes of the present disclosure is to provide an improved coating that enhances the rigidity of the coating and reduces the elasticity of the coating by introducing effective inorganic particulate matter into the traditional pure organic system of self-bonding coating, achieving pressure-resistant no overflow of the product, and ensuring excellent bonding strength and coating processing performance. The coating of the present invention is particularly suitable for forming a self-bonding coating with pressure-resistant no overflow performance.

[0010] To achieve the above-mentioned purpose, the present disclosure provides a coating whose solvent is water, and the effective components of the coating include an organic component and an inorganic particulate component, the organic component includes an epoxy resin and an epoxy resin curing agent, the epoxy resin includes a macromolecular epoxy resin and a small molecular epoxy resin, the inorganic particulate component includes nanoscale fumed oxide particles and nanoscale silica particles, the mass percentage of the organic component in the effective components is 86-99%, preferably 90-99%, more preferably 94%-99%, and most preferably 96%-99%.

[0011] Preferably, the effective components of the coating of the present disclosure consist of the above-mentioned organic component and the above-mentioned inorganic particulate component.

[0012] In the present disclosure, the macromolecular epoxy resin refers to an epoxy resin with an epoxy equivalent weight of 1500-10000 g / eq.

[0013] In the present disclosure, the small molecular epoxy resin refers to an epoxy resin with an epoxy equivalent weight of 100-1000 g / eq.

[0014] In the present disclosure, the macromolecular epoxy resin undergoes endothermic stretching during the heating process through its chain groups, and shrinks during the cooling process, thereby forming effective physical entanglement between the sheet layers and enhancing the bonding force; the small molecular epoxy resin undergoes exothermic reaction during film formation, and forms secondary crosslinking structure with the macromolecular epoxy resin, improving the rigidity and bonding strength of the coating. In addition, the epoxy groups combine with the functional groups in the curing agent in the ring-opening reaction, enhancing the mechanical strength and corrosion resistance of the coating.

[0015] In addition, in the coating of the present disclosure, there are a large number of active hydroxyl groups on the surface of the nanoscale fumed oxide particles in the inorganic particulate component. These particles can form a three-dimensional flocculation network structure with the organic film-forming substances containing polar groups such as amine groups and hydroxyl groups in the coating through hydrogen bonds and van der Waals forces, thereby enhancing the cohesive toughness and structural stability of the coating, and helping to inhibit the overflow phenomenon during hot-pressing curing. However, the introduction of such particles can also cause a decrease in the compatibility of the coating system, resulting in an increase in the viscosity of the coating and the problem of easy skinning on the surface. If commercially available fumed oxide powder is directly used and dispersed in the coating, it can be difficult to improve the cohesive strength of the self-bonding coating, and it can also cause obvious instability phenomena such as coating skinning and precipitation.

[0016] To overcome the above problems, nanoscale silica particles are further introduced into the coating of the present disclosure. Such particles can fill the intermolecular voids in the coating, improve the density and stiffness of the coating, and the long carbon chains of the modifier can form steric hindrance, thereby improving the compatibility and stability of the inorganic dispersion and the coating system, significantly reducing the viscosity of the coating, increasing the wettability of the coating on the silicon steel substrate, and improving the coating processing performance.

[0017] Preferably, in the coating of the present disclosure, the epoxy equivalent weight of the macromolecular epoxy resin is 1500-10000 g / eq.

[0018] Preferably, in the coating of the present disclosure, the epoxy equivalent weight of the small molecule epoxy resin is 100-1000 g / eq.

[0019] Preferably, in the coating of the present disclosure, the mass percentage content of the small molecule epoxy resin in the organic component is 15-30%.

[0020] Preferably, in the coating of the present disclosure, the mass percentage content of the epoxy resin curing agent in the organic component is 2-8%.

[0021] In the coating of the present disclosure, one type of epoxy resin can be used, such as bisphenol A, bisphenol F or phenolic epoxy resin, preferably two or more selected from bisphenol A, bisphenol F and phenolic epoxy resin.

[0022] Preferably, in the coating of the present disclosure, the fumed oxide particles can be selected from at least one of SiO2, Al2O3, TiO2, ZnO, ZrO2.

[0023] Preferably, in the coating of the present disclosure, the epoxy resin curing agent is selected from one or more of amine, acid anhydride and resin curing agents.

[0024] Preferably, in the coating of the present disclosure, the median particle size D50 of the fumed oxide particles is 7-40 nm, and the specific surface area is 50-300 m2 / g.

[0025] In the present disclosure, the fumed oxide particles are mixed with the organic components in the coating, and play a role similar to rivets in the process of manufacturing motor iron cores, thereby enhancing the toughness and adhesion of the coating. In order to ensure its enhancing effect, the particle size and specific surface area of the fumed oxide particles need to be reasonably controlled. When the median particle size D50 of the fumed oxide particles is too small, the specific surface area thereof is significantly increased, the surface charges of the particles attract each other to cause agglomeration, the surface energy is reduced, the thermal motion of the molecular chains of the colloidal particles is inhibited, the formation of the network structure of the organic film-forming substances is hindered, and the adhesion strength of the coating is reduced. On the contrary, when the median particle size D50 of the fumed oxide particles is too large, the volume shrinkage of the coating film is easily caused, the wetting and spreading property of the coating is poor, and finally the round spot-shaped defects are unevenly distributed on the surface of the coating steel plate. Therefore, in the coating of the present application, the median particle size D50 of the fumed oxide particles is preferably controlled in the range of 7-40 nm, and the specific surface area is controlled in the range of 50-300 m 2 / g.

[0026] In addition, in order to further improve the structural stability of the coating and the coating processing performance, preferably, in the coating of the present application, the particle size of the silica particles is 8-12 nm.

[0027] In the present disclosure, if the SiO2sol particles contained in the coating are too small, a large amount of micro-bubbles is introduced in the high-speed dispersion process, and in the subsequent coating and heat treatment process, the breakage of the bubbles will cause burr-shaped protrusions on the surface of the sample, increase the brittleness of the coating, and thus deteriorate the adhesion strength of the coating. On the contrary, if the SiO2sol particles contained in the coating are too large, the specific surface area is reduced, so that the modifier cannot fully contact with the particle surface to form an adherent layer, and at the same time, with the increase of the particle size, the total potential energy is reduced, and the Brownian motion between the particles will make the particles spontaneously form a gel, so that the coating is prone to precipitation and sedimentation. Therefore, in the coating of the present application, the particle size of the silica particles is controlled to be 8-12 nm.

[0028] In the coating of the present application, the mass percentage content of the fumed oxide particles in the inorganic particulate component is not particularly limited, and is preferably 12.5-75.0%, more preferably 20-50%, even more preferably 35.0-50%, and most preferably 35.0-42.5%.

[0029] In the present disclosure, the higher the mass percentage content of the fumed oxide particles in the inorganic particulate component, the better the effect of improving the adhesion performance of the coating. However, too high content will cause the storage stability of the coating to be reduced, the coating processing performance to be deteriorated, and the coating defects to be easily caused. Therefore, in the coating of the present application, the mass percentage content of the fumed oxide particles in the inorganic particulate component is preferably controlled to be 12.5-75.0%, and more preferably controlled to be 20-50%.

[0030] In the coating of the present application, the median particle size D50 of the inorganic particulate component is not particularly limited, and is preferably 11-53 μm, more preferably 25-45 μm, and the coarse end particle size D90 is not particularly limited, and is preferably 45-134 μm, more preferably 60-100 μm.

[0031] In the present disclosure, the smaller the median particle size D50 of the inorganic particulate component, the finer the particle size in the coating, the better the surface gloss of the coating, the stronger the scratch resistance and chemical resistance, but the worse the adhesion performance; the larger the coarse end particle size D90 of the inorganic particulate component, the coarser the particle size in the coating, the greater the probability of defects such as point-line leakage, scratching and uneven coating of the coating, and the worse the adhesion performance.

[0032] Another object of the present disclosure is to provide a silicon steel which, on the basis of ensuring the basic performance of the self-adhesive coating such as adhesion strength and insulation, can also withstand a relatively high pressure during hot press forming of the laminated core and has no overflow, and can manufacture a high-efficiency core with a high lamination coefficient.

[0033] To achieve the above object, the present disclosure provides a silicon steel comprising a silicon steel substrate and a coating formed by the above-mentioned coating and coated on the surface of the silicon steel substrate, which can be formed by coating the surface of the silicon steel substrate with the coating of the present application and baking and heating the coated silicon steel substrate.

[0034] Preferably, in the silicon steel of the present application, the thickness of the silicon steel substrate is ≤0.65 mm.

[0035] Preferably, in the silicon steel of the present application, the thickness of the silicon steel substrate is 0.15-0.3 mm.

[0036] Preferably, in the silicon steel of the present application, the single-side dry film thickness of the coating is 0.5-5.0 μm.

[0037] Still another object of the present disclosure is to provide a high-adhesion motor core with a high lamination coefficient, which has no overflow of the coating when subjected to hot press forming at a pressure of 0.5-10 MPa, and has a high adhesion strength of ≥2 N / mm.

[0038] To achieve the above object, the present disclosure provides a motor core made of the silicon steel of the present application.

[0039] Preferably, the lamination coefficient F% of the motor core of the present application is (98-0.06×h / H+0.23×P)%; wherein P represents the pressure between the laminated silicon steel sheets (inter-sheet pressure), in MPa; H represents the thickness of the silicon steel substrate, in mm; and h represents the sum of the double-side dry film thicknesses of each silicon steel sheet, in μm.

[0040] Preferably, the lamination coefficient of the motor core of the present application is ≥97%.

[0041] Preferably, the motor core of the present application has no overflow when subjected to hot-pressing at 0.5-10 MPa.

[0042] More preferably, the motor core of the present application has a coating with a bonding strength ≥ 2 N / mm, preferably ≥ 3 N / mm, when subjected to hot-pressing at 0.5-10 MPa.

[0043] Compared with the prior art, the coating, silicon steel and motor core of the present application have the following advantages and beneficial effects:

[0044] The coating of the present application can be used to form a self-bonding coating on the surface of silicon steel sheets, and has good pressure resistance and overflow control ability on the basis of ensuring the basic properties of the self-bonding coating such as bonding strength and insulation. The coating can withstand high pressure without overflow during hot-pressing of the laminated core, and can produce a high-efficiency core with a high stacking factor, which has significant practical value.

[0045] The motor core of the present application has no overflow of the coating when subjected to hot-pressing at 0.5-10 MPa, and more preferably can exhibit a high bonding strength ≥ 2 N / mm.

[0046] Under the suitable solidification and molding process of a total coating thickness of 1-10 μm and a pressure ≥ 1 MPa, the coating silicon steel laminated core formed by the coating of the present application can stably achieve a stacking factor ≥ 97%. It is particularly suitable for a self-bonding coating product with high viscosity, no overflow and high stacking factor for thin-gauge silicon steel substrates, and can better manufacture and exhibit the application advantages of high-efficiency motor cores. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 shows the trend relationship of the bonding strength of the coating of the motor core of the present application with the content ratio of organic or inorganic components in the coating.

[0048] Figure 2 shows the trend relationship of the bonding strength of the coating of the motor core of the present application with the content of gas-phase oxide particles in the coating.

[0049] Figure 3 shows the change trend of the stacking factor F of the motor core of the present application under different silicon steel sheet inter-pressure conditions. DETAILED DESCRIPTION

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0051] In this context, the "effective ingredients" of the coating refer to substance ingredients that directly participate in the formation of the coating and impart functionality to the coating in the formula, as distinguished from solvents, dispersion media or other inert substances.

[0052] In the present disclosure, the epoxy equivalent weight can be determined by conventional methods in the art, such as according to GB / T 4612-2008.

[0053] In the present disclosure, the median particle size D50 refers to the particle size value corresponding to a cumulative distribution percentage of 50% in the particle size distribution, which can be determined by conventional methods in the art, such as laser particle size analysis.

[0054] In the present disclosure, the coarse end particle size D90 refers to the particle size value corresponding to a cumulative distribution percentage of 90% in the particle size distribution, which can be determined by conventional methods in the art, such as laser particle size analysis.

[0055] In the present disclosure, the single-sided dry film thickness of the coating refers to the thickness of the coating formed on a single surface after drying or curing.

[0056] In the present disclosure, the stacking factor F of the motor core refers to the ratio between the actual core height after pressing and the sum of the theoretical full metal thickness, which is determined according to GB / T 19289 (or IEC 60404-13) standard.

[0057] In the present disclosure, the motor core without overflow refers to the phenomenon that the coating does not overflow, flow or overflow to the outside of the core during the manufacturing process of the motor core when hot-pressing.

[0058] In the present disclosure, the adhesion strength of the coating of the motor core is determined according to DIN EN 1464.

[0059] The coating, silicon steel and motor core of the present disclosure will be further explained and described below in conjunction with specific examples, however, the explanation and description do not constitute undue limitation on the technical solutions of the present disclosure.

[0060] Examples 1-13 and Comparative Example 1

[0061] The coating, silicon steel and motor core of Examples 1-13 and Comparative Example 1 were prepared by the following steps:

[0062] (1) The coating was prepared, and Table 1-1, Table 1-2 and Table 1-3 list the mass fraction and mass ratio of each component in the coating used in Examples 1-13 and the comparative coating used in Comparative Example 1.

[0063] Table 1-1.

[0064] In some embodiments, the inorganic particulate component in the coating is a dispersion suspension of nanoparticles of two different types, hydrophilic fumed oxide powder and silica sol, prepared by dispersion processing, and prepared by the following process:

[0065] Step 1: Hydrophilic fumed oxide powder is prepared by high-temperature hydrolysis in a hydrogen-oxygen flame, and the fumed oxide is selected from SiO2, Al2O3, TiO2, ZnO, and ZrO2 metal oxides. In the preparation process, the amount of metal halide additive is adjusted to control the particle size of the fumed oxide, and the ratio of halide to hydrogen and air is in the range of 1:(0.3-1.7):(8-20). The gas flow rate at the nozzle of the synthesizer hydrolysis furnace is 5-15 m / s; the synthesizer furnace temperature is 1000-1800°C; the cooling medium temperature is 70-110°C; and the dispersion solvent can be pure water, or a mixture of two or more of ethylene glycol, glycerol, n-butanol, isobutyl alcohol, isopropyl alcohol, and ethylene glycol methyl ether.

[0066] According to the above process, the fumed oxide particles with a median particle size D50 of 7-40 nm, a specific surface area of 50-300 m 2 / g, and hydrophilic groups such as -OH on the particle surface are prepared.

[0067] Step 2: Silica sol is prepared by sol-gel method. The silicon source tetraethyl orthosilicate, alcohol, and distilled water are added to a flask in a volume ratio of 15:(110-320):10, the oil bath temperature is set to 70°C, and the stirring speed is set to 150 rpm. Then 0.5-3% of a surfactant by volume is added, and the mixture is continuously stirred to obtain a clear microemulsion. Then 10-25% of a basic catalyst by volume is added dropwise to the microemulsion within 5 minutes. After 1.5-2 hours, the emulsion becomes clear and transparent, and the reaction is complete. The product is centrifuged and washed with distilled water, and then the silica sol is surface-modified under ultrasonic conditions using a modifier. Finally, the SiO2 particle size of the silica sol is 10±2 nm.

[0068] The basic catalyst can control the particle size in the sol, and can be selected from amines and ammonia; the alcohol can be selected from methanol, ethanol, propanol, and pentanol; the surfactant can be selected from ammonium chloride and sodium dodecylbenzenesulfonate to inhibit rapid particle growth and obtain nanoscale silica sol; and the modifier can be selected from fatty alcohols, amines, fatty acids, and siloxanes.

[0069] Step 3: The aforementioned fumed oxide powder is added to the SiO2 sol, and if necessary, a certain amount of pure water and additives can be added, and the solid content of the mixture is adjusted to 5-30%. The mixture is dispersed at a shear rate of 7-25 m / s for 60-180 minutes, and the liquid temperature is controlled to be <40°C by ice bath during the process. Finally, the inorganic particulate dispersion suspension is obtained.

[0070] (2) The coating is applied to the surface of a B25AV1300 high-grade silicon steel plate roll by a two- or three-roll coating machine, and the coating is cured by using a direct-fired oven or an infrared drying oven to obtain a silicon steel roll. In some embodiments, the dry film thickness of each side can be preferably controlled to be between 1 and 3 μm. The coating strip steel production speed can be controlled to be between 80 and 200 mpm, the baking heating time is controlled to be 18 to 45 s, and the coating steel plate temperature is controlled to be 210 to 280 °C.

[0071] (3) The silicon steel is cut and punched to form a core, and the core is obtained after heat pressing and curing in a tooling fixture. In the curing process of the core heat pressing, the interlaminar pressure load can be controlled to be between 0.5 and 10 MPa, and the temperature is maintained at 160 to 250 °C for 10 to 240 min. In addition, to stably produce a high-bonding motor core with a high stacking factor, the interlaminar pressure P (MPa) of the laminated silicon steel, the silicon steel substrate H (mm), and the sum of the dry film thickness h (μm) of the double-sided coating of each silicon steel sheet need to satisfy the following formula relationship: Stacking factor F% = (98-0.06xh / H+0.23xP)%.

[0072] Table 2 lists the relevant process parameters of the motor cores of Examples 1-13 and the comparative motor core of Comparative Example 1 in the above manufacturing process.

[0073] Table 2.

[0074] The motor cores of Examples 1-13 and the comparative motor core of Comparative Example 1 are tested for performance, including testing the bonding strength of the coating, the stacking factor, and the glue overflow during heat pressing and forming, and the test results are listed in Table 3. The test methods are as follows:

[0075] Bonding strength of the coating: The bonding strength of the motor cores of Examples 1-13 and the comparative motor core of Comparative Example 1 is tested according to DIN EN 1464.

[0076] Glue overflow test: Whether the motor core overflows glue during heat pressing and forming at 0.5 to 10 MPa is observed.

[0077] Stacking factor: The stacking factor is determined according to the GB / T 19289 (or IEC 60404-13) standard. Stacking factor F% = (98-0.06xh / H+0.23xP)%; wherein P represents the pressure between the laminated silicon steel sheets, in MPa; H represents the thickness of the silicon steel substrate, in mm; and h represents the sum of the dry film thickness of the double-sided coating of each silicon steel sheet, in μm.

[0078] Table 3 lists the results of relevant performance tests of the motor cores of Examples 1-13 and the comparative motor core of Comparative Example 1.

[0079] Table 3.

[0080] Figure 1 shows the trend of the adhesive strength of the coating of the motor core of the present application with the proportion of the content of the organic component or the inorganic component in the coating.

[0081] Figure 1 shows that, when the proportion of the organic component in the coating is ≥ 90%, the coating has a certain adhesive strength, and the adhesive strength is the highest when the proportion of the organic component is 96%; considering the adhesive strength and the overflow of the coating, the proportion of the organic component in the coating is preferably 90-99%.

[0082] As can be seen from Table 3, the motor cores prepared in Examples 1-13 do not overflow when subjected to hot pressing at a pressure of 0.5-10 MPa.

[0083] Figure 2 shows the trend of the adhesive strength of the coating of the motor core of the present application with the content of the fumed oxide particles in the coating.

[0084] As can be seen from Figure 2, the adhesive strength of the coating gradually increases with the increase of the mass percentage of the fumed oxide particles in the inorganic particulate component, and therefore, in the more preferred embodiments, the mass percentage of the fumed oxide particles in the inorganic particulate component is controlled to be 20-50%. The mass percentage of the fumed oxide particles in the inorganic particulate component in Example 12 of the present disclosure is lower than the range, and therefore, the adhesive strength is slightly lower than that of Examples 1-10. The mass percentage of the fumed oxide particles in the inorganic particulate component in Example 13 is higher than the range, and a too high content of the fumed oxide particles may deteriorate the storage stability of the coating.

[0085] In addition, the particle size of the inorganic particulate of Example 11 does not meet the preferred scheme of the present disclosure, and the adhesive strength is slightly lower than that of Examples 1-10.

[0086] Figure 3 shows the trend of the stacking factor F of the motor core of the application under different interlaminar pressures of the silicon steel sheets.

[0087] As can be seen from Figure 3, the thinner the base plate, the smaller the stacking factor of the laminated steel block. When the double dry film thickness is ≤6μm and the interlaminar pressure is ≥3MPa, the laminated core can achieve a high stacking factor of ≥97%.

[0088] All publications, patent applications, patents, and other references mentioned in this disclosure are incorporated by reference in their entirety.

[0089] Although the present disclosure has been illustrated and described with reference to certain preferred embodiments thereof, it should be understood by those skilled in the art that the foregoing is a detailed description of only a few of the many possible embodiments of the disclosure. Various modifications in form and detail can be made to the disclosure without departing from the spirit and scope of the disclosure.

Claims

1. A coating, whose solvent is water, and whose effective component comprises an organic component and an inorganic particulate component, wherein: the organic component comprises an epoxy resin and an epoxy resin curing agent, the epoxy resin comprises a macromolecular epoxy resin and a small molecular epoxy resin; the inorganic particulate component comprises nano-sized fumed oxide particles and nano-sized silica particles; the mass percentage of the organic component in the effective component is 86-99%, preferably 90-99%. The effective component is composed of the organic component and the inorganic particulate component. The epoxy equivalent weight of the macromolecular epoxy resin is 1500-10000 g / eq. The epoxy equivalent weight of the small molecular epoxy resin is 100-1000 g / eq.

2. The coating of claim 1, wherein, The mass percentage of the small molecular epoxy resin in the organic component is 15-30%, and the mass percentage of the epoxy resin curing agent in the organic component is 2-8%.

3. The coating of claim 1 or 2, wherein, The epoxy resin is selected from two or more of bisphenol A, bisphenol F, and phenolic epoxy resin.

4. The coating of any one of claims 1 to 3, wherein, The fumed oxide particles are selected from at least one of SiO2, Al2O3, TiO2, ZnO, and ZrO2.

5. The coating of any one of claims 1 to 4, wherein, The epoxy resin curing agent is selected from at least one of amine, acid anhydride, and resin curing agents.

6. The coating of any one of claims 1 to 5, wherein, The particle size of the silica particles is 8-12 nm.

7. The coating of any one of claims 1 to 6, wherein, The mass percentage of the fumed oxide particles in the inorganic particulate component is 20-50%.

8. The coating of any one of claims 1 to 7, wherein, The median particle size D50 of the inorganic particulate component is 25-45 μm, and the coarse end particle size D90 is 60-100 μm.

9. The coating of any one of claims 1 to 8, wherein, The median particle size D50 of the gas phase oxide particles is 7 to 40 nm, and the specific surface area is 50 to 300 m 2 / g.

10. The coating of any one of claims 1 to 9, wherein, 13. A silicon steel comprising a silicon steel substrate and a coating layer formed by the coating of any one of claims 1-12 coated on the surface of the silicon steel substrate.

11. The coating of any one of claims 1 to 10, wherein, The thickness of the silicon steel substrate is ≤0.65 mm.

12. The coating of any one of claims 1 to 11, wherein, The thickness of the silicon steel substrate is 0.15-0.3 mm. The single-side dry film thickness of the coating layer is 0.5-5.0 μm.

14. The silicon steel of claim 13, wherein, The motor core is made of the silicon steel of any one of claims 13-16.

15. The silicon steel of claim 13 or 14, wherein, The stacking factor F% of the motor core is (98-0.06xh / H+0.23xP)%, wherein P represents the pressure between the stacked silicon steel sheets, in MPa; H represents the thickness of the silicon steel substrate, in mm; and h represents the sum of the double-side dry film thickness of each silicon steel, in μm.

16. The silicon steel of any one of claims 13-15, wherein, The stacking factor F is ≥97%.

17. An electrical machine core wherein, The motor core does not overflow when subjected to hot pressing forming at 0.5-10 MPa.

18. The motor core of claim 17, wherein, The motor core has a coating layer with a bonding strength ≥2 N / mm, preferably ≥3 N / mm, when subjected to hot pressing forming at 0.5-10 MPa. ​ 19. The motor core of claim 18, wherein, ​ 20. The electrical machine core of any one of claims 17 to 19, wherein, ​ 21. The electrical machine core of any one of claims 17 to 20, wherein, ​

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