Coating composition, its manufacturing method and application

Abstract

The present invention discloses a composition of heat-expandable microspheres with a wall thickness of at least 60% of the microspheres ≦5 μm, a method for producing a coating composition containing a water-based thermoplastic resin, a water-based thermosetting resin, and a heat-meltable filling resin, and its application. The coating composition of the present invention quickly softens and destroys the thin-shelled spheres in a short time during the heat expansion process, and as the organic solvent evaporates, it crosslinks with the resin matrix in the coating layer on the surface and inside of the coating layer to form a network structure crosslinked with each other, thereby strengthening the gap support of the coating layer, thereby enabling the coating layer to expand stepwise, and after expansion, some of the polymer material wraps the airbag and hardens to form a stable hollow structure. As a result, the coating layer after expansion has a stable structure, relatively high heat shrinkage resistance, relatively high mechanical strength and adhesive strength, can be applied to fix high-temperature resistant parts, and can maintain adhesive stability even when placed in a high-temperature environment (140°C to 180°C) for a long time.

Description

Detailed Description of the Invention

[0001] This application claims priority from a prior application bearing patent application number 202110362416.8 and entitled "Coating composition, manufacturing method thereof, and application thereof," filed with the State Intellectual Property Office of the People's Republic of China on April 2, 2021. The prior application is incorporated herein by reference in its entirety.

[0002] [Technical Field] The present invention belongs to the technical field of coating compositions, and in particular to a coating composition and its manufacturing method and application.

[0003] [Background technology] With the development of the automotive industry, high-temperature resistant adhesives have been widely used in engine manufacturing, and special solvent-based adhesives are often used to bond and fasten engine parts, and the adhesive is applied by injection or dispensing. However, this method has drawbacks such as high material costs, high requirements for equipment and processes, low processing precision, and a tendency for the adhesive to overflow, contaminate the workpiece, and cause uneven adhesive application.

[0004] In recent years, with the rapid development of the new energy vehicle industry, the assembly of magnetic sheets for motors has become one of the main processes in engine manufacturing. In addition to continuing to use the traditional adhesive injection method, major automakers are seeking efficient solutions for fixing magnetic materials in the assembly of new energy vehicle engines.

[0005] At present, epoxy resin powder coatings are widely used in automobile parts. For example, in the patent document JP1993148429A, in order to improve the impact resistance of the film, a powder composition of an organic foaming agent is added to the epoxy resin, thereby obtaining a cured material containing bubbles therein, so that the coating layer has better mechanical impact resistance and thermal shock resistance.

[0006] Furthermore, for example, in Patent Document US20090270533A1, in order to solve the problem of poor chipping resistance and corrosion resistance of the coating layer due to the formation of a large number of bubbles at the contact surface between the cured material and the substrate during film formation, a thermosetting powder coating composition is disclosed that uses a resin having a crosslinkable functional group, thermally expandable resin particles, a curing agent, and a fibrous filler, thereby providing a coating film with excellent long-term corrosion resistance, chipping resistance, flexibility, and adhesiveness.

[0007] Thermally expandable resin particles, or expanded microspheres, are hollow thermoplastic polymer microspheres composed of a thermoplastic shell and an enclosed liquid alkane gas. When heated, the gas pressure inside the microsphere's shell increases, softening the thermoplastic shell and significantly increasing the microsphere's expansion volume. Expanded microsphere paints fabricated according to the above principle are widely used in fields such as plastics, wallpaper, adhesives, inks, and printing. Among these, thermosetting powder paints containing expanded microspheres are typically applied to the underside of automobiles to reduce the impact of stones suddenly flying up while driving.

[0008] For example, in patent document DE102014214381A1, a thermosetting powder coating is applied to a magnetic sheet for an automobile motor during assembly to provide a coating layer for the magnetic sheet. The coating layer is composed of a thermosetting resin substrate with heat-expandable microspheres embedded in the substrate. The softening temperature of the substrate is lower than the reaction temperature of the heat-expandable microspheres, and the volume of the microspheres increases irreversibly at temperatures higher than the reaction temperature of the microspheres. When the magnetic sheet coated with the coating layer is heated above the reaction temperature of the expandable microspheres, the resin substrate softens first, followed by the expansion of the microspheres. The softened substrate no longer has resistance to expansion, increasing the total thickness of the coating layer on the magnetic sheet, filling the gap between the magnetic sheet and the rotor groove and fixing the magnetic sheet in the rotor groove. Using a thermosetting powder as a coating layer to fix the rotor during motor assembly improves assembly efficiency and processing accuracy. However, the powder spraying process of powder coating has problems of operational safety and environmental pollution in actual operation, and the motor operating environment is harsh. The magnetic sheet must maintain stability and adhesion in high temperature, high humidity, and high speed rotation environments, and must also have relatively high corrosion resistance.

[0009] Summary of the Invention To solve the above technical problems, the present invention provides a coating composition comprising a composition of heat-expandable microspheres in which at least 60%, such as 60%, 70%, 75%, or 80%, of the microspheres have a wall thickness of ≦5 μm, for example, the wall thickness of the microspheres is ≦5 μm, for example, the wall thickness of the microspheres is 5 μm, 4.5 μm, 3 μm, 2 μm, 1 μm, or 0.5 μm.

[0010] According to an embodiment of the present invention, in the composition, the weight percentage of the heat-expandable microspheres is 20% or less, illustratively 15%, 10%, 8%, or 6%.

[0011] According to an embodiment of the present invention, the initial thermal expansion temperature T1 of the heat-expandable microspheres is 100°C≦T1≦200°C, for example, T1 is 125°C≦T1≦180°C, illustratively 120°C, 130°C, 150°C, 160°C, 170°C, 190°C, or any value between the recited temperature points.

[0012] According to an embodiment of the present invention, the heat-expandable microspheres have a maximum heat-resistant temperature T2 of 145°C≦T2≦215°C, for example, T2 is 150°C≦T2≦205°C, illustratively 155°C, 160°C, 165°C, 175°C, 185°C, 195°C, 200°C, or any value between the recited temperature points.

[0013] Those skilled in the art will understand that the initial thermal expansion temperature T1 is equal to or less than the maximum heat-resistant temperature T2.

[0014] According to an embodiment of the present invention, the weight ratio of heat-expandable microspheres having a particle size of 8 μm≦D≦20 μm is 60% or more, for example, 60%, 65%, 70%, 80%, 90%, or 100%, of the total weight of the heat-expandable microspheres. Preferably, the weight ratio of heat-expandable microspheres having a particle size of 10 μm≦D≦15 μm is 50% or more, for example 55%, 60%, or 70%, of the total weight of the heat-expandable microspheres.

[0015] According to an embodiment of the present invention, the heat-expandable microspheres comprise a thermoplastic polymer shell and a liquid alkane encapsulated by the thermoplastic polymer shell.

[0016] For example, the thermoplastic polymer shell may be made of a heat-melting material or a material that cracks upon thermal expansion, such as a copolymer of vinylidene chloride and acrylonitrile, polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate, polyacrylonitrile, polyvinylidene chloride, polysulfone, vinylidene chloride homopolymer, a random terpolymer of vinylidene chloride, acrylonitrile, and divinylbenzene, polystyrene, or polyvinyl chloride.

[0017] According to an embodiment of the present invention, the liquid alkane may be one, two or more selected from ethane, propane, isobutane, n-pentane and isopentane.

[0018] According to an embodiment of the present invention, the heat-expandable microsphere composition may optionally further contain a solvent containing at least one organic solvent having a boiling point of 220°C or higher, for example, the organic solvent having a boiling point of 220°C or higher may be selected from lauryl alcohol esters.

[0019] According to an embodiment of the present invention, the solvent may include at least one organic solvent having a boiling point of 220°C or higher, and may further include one or two of ethylene glycol butyl ether and dipropylene glycol butyl ether.

[0020] In the present invention, the "initial particle size" refers to the median particle size D of the heat-expandable microspheres before thermal expansion. 50 The "thickness" refers to the thickness of the shell wall of the heat-expandable microspheres before thermal expansion.

[0021] The particle size is a volume average diameter, and the diameter of unexpanded heat-expandable microspheres and the thickness of the shell wall of unexpanded heat-expandable microspheres can be measured by any method known in the art.

[0022] According to an embodiment of the present invention, the weight ratio of the heat-expandable microspheres to the solvent is (4-40):1, preferably (5-20):1, and examples thereof include 4:1, 5:1, 6:1, 8:1.2, 7:1, 8:1, 9:1, 10:1, 15:1, and 18:1.

[0023] According to an embodiment of the present invention, the heat-expandable microsphere composition may optionally further contain inorganic fibers. For example, the inorganic fibers may be fibrous or flake-like (e.g., sheet-like). For example, the inorganic fibers may be one, two, or more fibers selected from nanoaluminum silicate fibers, carbon fibers, and boron fibers. After the heat-expandable microsphere composition expands, the inorganic fibers infiltrate with the resin in the subsequent coating layer, supporting the framework of the subsequent coating layer and increasing its strength, thereby improving the strength and shrinkage resistance of the expanded coating layer.

[0024] According to an embodiment of the present invention, the weight ratio of the inorganic fibers to the solvent is (0-2):1, for example (0.5-1.5):1, illustratively 0.5:1, 3:5, 0.7:1, 0.85:1, 0.9:1, 1:1, or 1.2:1.

[0025] According to an embodiment of the present invention, the expansion ratio of the composition of heat-expandable microspheres is 150% to 300%, for example, 180% to 250%.

[0026] According to an exemplary embodiment of the present invention, the composition of the heat-expandable microspheres includes heat-expandable microspheres, a solvent, and inorganic fibers, among which: (1) The weight ratio of heat-expandable microspheres having a particle size of 8 μm≦D≦20 μm to the total weight of the heat-expandable microspheres is 60% or more, for example, 60%, 65%, 70%, 80%, 90%, or 100%; the weight ratio of heat-expandable microspheres having a particle size of 10 μm≦D≦15 μm is 50% or more, for example, 55%, 60%, or 70%, of the total weight of the heat-expandable microspheres; (2) At least 60% of the heat-expandable microspheres have a wall thickness of 3 μm or less; (3) The solvent contains at least a lauryl alcohol ester, the weight ratio of the heat-expandable microspheres to the solvent is (5 to 20):1; (4) The inorganic fibers are nano-aluminum silicate fibers, and the weight ratio of the inorganic fibers to the solvent is (0.5-1.5:1).

[0027] According to an embodiment of the present invention, the composition of heat-expandable microspheres is prepared by mixing raw materials including heat-expandable microspheres, a solvent, and optionally added or unadded inorganic fibers.

[0028] According to an embodiment of the present invention, the coating composition further contains a water-based thermoplastic resin, which has a glass transition temperature of -20°C to 60°C. For example, the weight percentage of the water-based thermoplastic resin in the composition may be 10% to 30%, e.g., 15%, 20%, 25%, or 30%.

[0029] Preferably, the water-based thermoplastic resin is at least one selected from a water-based acrylic resin and a polyurethane resin.

[0030] According to an embodiment of the present invention, the coating composition further contains a water-based thermosetting resin. For example, the weight percentage of the water-based thermosetting resin in the composition may be 10% to 40%, e.g., 15%, 20%, 25%, or 30%.

[0031] Preferably, the water-based thermosetting resin is at least one selected from a water-based epoxy resin and a hydroxyacrylic acid.

[0032] According to an embodiment of the present invention, the coating composition further contains a heat-meltable filler resin. For example, the weight percentage of the heat-meltable filler resin in the composition may be 10% to 35%, e.g., 10%, 15%, 20%, 25%, or 30%.

[0033] Preferably, the heat-meltable filling resin is at least one selected from modified chlorinated polyvinyl chloride, polyester resin, polyurethane, polyamide, polyethersulfone, epoxy, and polymethyl methacrylate.

[0034] In the coating composition of the present invention, the content of the aqueous thermoplastic resin must be lower than the content of the aqueous thermosetting resin, and the dosage ratio of the aqueous thermoplastic resin to the aqueous thermosetting resin is preferably 1:1 to 1:2, e.g., 1:1, 1.5:1, or 1:2.

[0035] In the present invention, if the amount of the thermoplastic resin is too low, the expansion ratio of the coating composition will be insufficient to achieve the expansion effect, while if the amount of the thermoplastic resin is too high, the coating layer will shrink severely after curing, failing to meet the application requirements of motor assembly.The glass transition temperature of the heat-melting filling resin can be heated to a high temperature of 60°C or higher, preferably 130°C or higher, to form a translucent or transparent molten resin, so that when the coating composition is used as an expansion adhesive, it can bond the coating layer to the contact surface and provide support.

[0036] Preferably, the mass ratio of the sum of the masses of the thermoplastic resin and the thermosetting resin to the heat-meltable filling resin is 1.5:1 to 2.5:1, for example, 1.5:1, 2:1, or 2.5:1.

[0037] According to an embodiment of the present invention, the coating composition may optionally further include other conventional coating additives, preferably in an amount of 0% to 15% by weight of the total coating composition, more preferably 1% to 10% by weight of the total coating composition, e.g., 1%, 2%, 2.5%, 3%, 4%, or 5%.

[0038] According to one embodiment of the present invention, the other conventional paint additives may be selected from, for example, curing agents, dispersants, antifoaming agents, fillers, crosslinking agents, thickeners, colorants, and the like.

[0039] For example, the coating composition may optionally contain 0.2 to 1.5% of a dispersant. For example, the dispersant may be one selected from nonionic, anionic, and cationic dispersants so that the coating composition forms a stable emulsion. Preferably, the dispersant may be one, two, or more selected from amine salts, quaternary ammonium salts, pyridinium salts, ethylene glycol, and acrylic ester polymer dispersants.

[0040] For example, the coating composition may optionally contain 1% to 3% of a filler to improve the crystallization tendency and solubility of the coating composition, so as to increase the glass transition temperature and hardness of the expanded coating layer and reduce the shrinkage rate of the expanded coating layer. Preferably, the filler may be one, two or more selected from insulating carbon black, calcium carbonate, and talc powder.

[0041] According to an embodiment of the present invention, the coating composition further comprises water.

[0042] According to an embodiment of the present invention, the sum of the weight percentages of the components in the coating composition is 100%.

[0043] The present invention further provides a method for producing the above coating composition, which comprises mixing a composition of heat-expandable microspheres, a water-based thermoplastic resin, a water-based thermosetting resin, a heat-meltable filling resin, and optionally other conventional coating additives in the above-mentioned blending ratio.

[0044] The present invention further provides a method for improving the stability of a thermally expandable coating layer, comprising applying the above-mentioned coating composition to a body of a substrate and then heating the body of the substrate to obtain a thermally expandable coating layer.

[0045] According to an embodiment of the present invention, the main body of the substrate is a magnetic material, such as a magnetic sheet for motors used in the manufacture and production of motors, preferably a neodymium-iron-boron magnet.

[0046] According to an embodiment of the present invention, the application may be selected from methods of applying the coating composition to the surface of the body of the substrate by means known in the art, such as spraying, rolling, brushing, painting, electroplating, dipping, roller coating, etc.

[0047] According to an embodiment of the present invention, the method further comprises the step of drying or allowing the body of the substrate to which the coating composition has been applied.

[0048] According to an embodiment of the present invention, the dry thickness of the thermally expandable coating layer is 100 μm to 300 μm, e.g., 100 μm, 150 μm, 200 μm, or 300 μm.

[0049] The present invention further provides a substrate comprising a coating layer prepared from the above coating composition and the body of the substrate.

[0050] According to an embodiment of the present invention, the thickness of the coating layer is 100 μm to 300 μm, for example, 100 μm, 150 μm, 200 μm, or 300 μm.

[0051] According to an embodiment of the present invention, the coating layer is located on the surface of the body of the substrate.

[0052] Preferably, the body of said substrate has the meaning described above.

[0053] Preferably, the coating composition has the meaning described above.

[0054] [Beneficial Effects of the Present Invention] (1) During the thermal expansion process, the coating composition of the present invention rapidly softens and destroys the thin-shelled spheres in a short time, and as the organic solvent evaporates, it crosslinks with the resin matrix in the coating layer on the surface and inside of the coating layer, forming a crosslinked network structure, strengthening the gap support of the coating layer and enabling gradual expansion of the coating layer. After expansion, some of the polymer material envelops the airbag and hardens to form a stable hollow structure. As a result, the expanded coating layer has a stable structure, relatively high thermal shrinkage resistance, relatively high mechanical strength and adhesive strength, making it suitable for fixing high-temperature-resistant parts, and can maintain adhesive stability even when left in a high-temperature environment (140°C to 180°C) for a long time.

[0055] (2) The high-boiling point solvent in the coating composition of the present invention can further lower the softening temperature and film-forming temperature of the resin in the coating composition, thereby improving resin compatibility. Furthermore, the thermally expandable coating layer produced thereby has relatively high thermal shrinkage resistance, relatively high mechanical strength, and adhesive strength after thermal expansion, making it suitable for fixing high-temperature-resistant components, and maintaining adhesive stability even when placed in a high-temperature environment (140°C to 180°C) for a long period of time.

[0056] (3) The water-based high-temperature thermal expansion resistant adhesive coating of the present invention can reduce the problems of VOC emissions and environmental damage caused by solvent-based adhesives.

[0057] (4) The present invention improves the film-forming properties of coating layers at medium to low temperatures by using an emulsion or dispersion (a fluid liquid) of a water-based thermoplastic resin with a glass transition temperature of -20°C to 60°C, which allows the coating layer to self-dry at room temperature (15°C to 35°C) or to form a complete coating layer under baking conditions at medium to low temperatures (35°C to 90°C). Furthermore, after baking at 150°C for 96 hours, there is no or slight yellowing, the artificial aging resistance exceeds 360 hours, and the powdering of the coating layer is at least grade 1.

[0058] (5) The present invention adds a small amount of a hot-melt filler resin that has a particle size of 800 mesh or more, a glass transition temperature of 60°C or more, and can form a translucent or transparent molten state when heated at a high temperature of 130°C or more, and has a certain degree of fluidity and adhesive strength, and can improve the compatibility between components at high temperatures.The resulting coating layer has sufficient fineness and uniform density after drying at medium to low temperatures.In addition, the color of the coating layer does not essentially turn yellow even when baked at a high temperature of 150°C or more for 96 hours or more, thereby improving the high-temperature resistance and service life of the coating layer.

[0059] (6) The present invention uses inorganic materials with a fibrous or sheet-like structure (nanoaluminum silicate fibers, ultrafine calcined mica powder) or silicone resin reinforcing agents with high hardness and high temperature resistance. These materials infiltrate with the resin after the coating film expands, supporting the skeleton of the coating layer and increasing its strength, thereby improving the strength and shrinkage resistance of the expanded coating layer. [Brief explanation of the drawings]

[0060] [Figure 1] 1 is a photograph of the coating layer of Example 7 in an unexpanded state (scale 100 μm, 500x magnification). [Figure 2] 1 is a photograph (scale 100 μm, 500x magnification) of the coating layer of Example 7 after expansion. [Figure 3] The magnet with the expanded coating layer is assembled into a motor rotor assembly. In the figure: 1, expanded coating layer; 2, sintered magnet; 3, pre-gap; 4, motor assembly. [Figure 4] 1 is a comparison of the infrared spectrum results of the expansion coating layer of Example 7 before and after foaming.

[0061] [Mode for Carrying Out the Invention] The technical solutions of the present invention will be described in more detail below with reference to specific examples. It should be understood that the following examples are merely for illustrative purposes and should not be construed as limiting the scope of the claims of the present invention. Any technology realized based on the above content of the present invention is included within the scope of the claims of the present invention.

[0062] Unless otherwise specified, all raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0063] The heat-expandable microspheres used in the present invention can be purchased from the market, and are, for example, two or more compositions selected from AKZO-Nobel's Expancel series, including 920DU80, 920DU20, 909DU80, 920DU40, and 461DU40.

[0064] The table below shows the main parameters of five types of heat-expandable microspheres from AKZO-Nobel's Expancel series. [Table 1]

[0065] Examples 1 to 5 The weight ratio of expanded microspheres, lauryl alcohol ester and inorganic fiber in the composition of heat-expandable microspheres was 8:1.2:0.8, that is, the weight percentage of each component was 8 wt% expanded microspheres, 1.2 wt% lauryl alcohol ester and 0.8 wt% inorganic fiber.

[0066] The composition of the heat-expandable microspheres shown in Table 1 comprises heat-expandable microspheres:

[0067] Using a combination of different heat-expandable microspheres from the Expancel series manufactured by AKZO-Nobel, model numbers 920DU80 and 461DU40 were uniformly mixed at a weight ratio of 1:2. Test results from the BFS-MAGIC test conducted by Sympatec, Germany, showed that the heat-expandable microspheres had an initial particle size of 15.50 μm, an average wall thickness of 2 μm, and 90% of the microspheres had a wall thickness of ≦5 μm (Examples 1 to 5).

[0068] The method for making the coating compositions described in Examples 1-5 includes the following steps:

[0069] First, the expanded microspheres, lauryl alcohol ester, and nano-aluminum silicate fibers are mixed to prepare a composition of heat-expandable microspheres. Then, the composition of heat-expandable microspheres and other coating additives (insulating carbon black as a filler, ethylene glycol as a dispersant) are added to a water-based coating resin under low shear stirring.

[0070] Samples 1 to 5 of the above coating composition were prepared according to the ratios in Table 1 below. [Table 2]

[0071] Examples 6 to 11 In the present invention, the content, particle size, and wall thickness of expandable microspheres in the composition of heat-expandable microspheres, as well as the content of high-boiling-point solvents, affect the performance of the expandable coating layer. The amounts of expandable microspheres, solvents, and inorganic fibers in the composition of heat-expandable microspheres also affect the performance of the coating composition, which in turn affects the performance of the expandable coating layer produced from the coating composition.

[0072] In Examples 6 to 11, coating composition samples 6 to 11 were prepared by adjusting the composition of the heat-expandable microspheres.

[0073] A combination of different heat-expandable microspheres was used in the Expancel series of AKZO-Nobel. Model numbers 920DU80 and 461DU40 were mixed at a weight ratio of 1:2 to obtain a combination of heat-expandable microspheres with an initial particle size of 15.50 μm (Example 6).

[0074] Microspheres of model numbers 920DU80, 920DU20, and 920DU40 were mixed in a weight ratio of 1:1:1 to obtain a combination of heat-expandable microspheres with an initial particle size of 13.10 μm (Examples 7, 8, 9, and 10).

[0075] Microspheres of model numbers 920DU80, 909DU80, and 920DU40 were mixed in a weight ratio of 1:1:1 to obtain a combination of heat-expandable microspheres with an initial particle size of 17.30 μm (Example 11).

[0076] Coating composition samples 6 to 11 differed in the following points: water-based polyurethane resin 25 wt%, water-based epoxy resin 35 wt%, polyurethane resin 15 wt%, polymethyl methacrylate 10 wt%, water-based silicone resin 1 wt%, ethylene glycol as a dispersant 1 wt%, insulating carbon black as a filler 2 wt%, acrylic acid as a thickener 0.5 wt%, polydimethylsiloxane as an antifoaming agent; and the composition of heat-expandable microspheres shown in Table 2 below.

[0077] The method for producing the coating composition includes the following steps:

[0078] First, the expanded microspheres, lauryl alcohol ester, and nanoaluminum silicate fibers are mixed to prepare a composition of heat-expandable microspheres. Then, the composition of heat-expandable microspheres and other coating additives (insulating carbon black as a filler, acrylic acid as a thickener, polydimethylsiloxane as a defoamer, and ethylene glycol as a dispersant) are added to a water-based coating resin under low shear stirring. [Table 3]

[0079] Samples of the coating compositions of Examples 1 to 11 were applied to the surface of a magnetic sheet by roller brushing, and the surface coating layer was dried and cured at room temperature. The cured coating layer exhibited a certain degree of corrosion resistance, facilitating transportation and protection of the magnetic sheet. The magnetic sheet was transported to a workshop, e.g., a motor rotor assembly site, where it was assembled and inserted into the motor rotor's locking groove. The motor rotor with the expanded coating layer assembled was then placed in a high-temperature oven, heated to 180°C, and heated for 10 minutes. The thermally expandable coating layer was applied to the magnet surface, and the coating layer softened and expanded after heating. The expandable microspheres were first heated and expanded. The high-boiling point solvent then softened and ruptured the shells of the expandable microspheres, crosslinking with the resin matrix in the coating layer and forming a stable coating layer structure.

[0080] As can be seen from Figures 1 and 2, the coating composition of Example 7 was applied to the surface of a sintered neodymium-iron-boron magnet and cured at room temperature to obtain a magnet coated with an expandable coating layer, the results of which are shown in Figure 1. The magnet with the expandable coating layer was then heated at a high temperature of 190°C for 10 minutes, causing the coating layer to expand and resulting in a cross-linked coating layer structure (see Figure 2).

[0081] As shown in Figure 3, 1 is the expansion coating layer, 2 is the sintered magnet, 3 is the motor assembly gap, and 4 is the motor assembly. The sintered magnet 2 (of which the sintered magnet measures 40mm x 15mm x 5mm) with the expansion coating layer 1 was assembled into the motor assembly 4. The motor assembly gap was 250μm, and the thickness of one side of the expansion coating layer was 110μm. The assembly was performed at the expansion temperature. The coating layer expanded upon heating, filling the motor gap and tightly fixing the magnet within the motor assembly. Under these conditions, the adhesive thrust of the magnet in the motor assembly was measured at room temperature and at a high temperature of 170°C.

[0082] FIG. 4 shows the infrared spectrum of the coating layer of Example 7 before and after expansion and foaming. As can be seen from the figure, after the coating layer expanded, -1 and wavelength 725.74 cm -1 The peak intensity of the characteristic peak at 1000 kJ / cm2 increased significantly, which may be due to the fact that the resin in the coating layer reacted again during the high-temperature expansion of the coating layer to form a crosslinked coating layer structure, which provided stable support. [Table 4]

[0083] As can be seen from the results in Table 3, the adhesive force of the cured coating layer was affected by varying the dosage ratio between the water-based thermoplastic resin and the water-based thermosetting resin, and / or the ratio between the total mass of the water-based thermoplastic resin and the water-based thermosetting resin and the hot-melt resin. The present invention unexpectedly found that by rationally optimizing the dosage ratios of the resins, when the dosage ratio between the water-based thermoplastic resin and the water-based thermosetting resin was 1:1 to 1:2 and the dosage ratio between the total mass of the water-based thermoplastic resin and the water-based thermosetting resin and the hot-melt resin was 1.5:1 to 2.5:1, the adhesive force of the coating layer at room temperature, especially after expansion at high temperatures, was improved, thereby meeting the requirements for motor use under high-temperature operating conditions.

[0084] The performance test results of Samples 6 to 11 showed that changing the dosage ratio of expandable microspheres, solvent, and inorganic fiber in the composition of heat-expandable microspheres affected the adhesive force of the coating layer after high-temperature expansion.

[0085] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the scope of the claims of the present invention without departing from the spirit and principles of the present invention are included within the scope of the claims of the present invention.

Claims

1. A coating composition comprising a composition of heat-expandable microspheres, wherein at least 60% of the microspheres have a wall thickness of ≦5 μm; The coating composition further comprises a water-based thermoplastic resin, a water-based thermosetting resin, a heat-melting filling resin, a solvent, and water; the weight percentage of the heat-expandable microspheres in the composition is 20% or less; The dosage ratio of the water-based thermoplastic resin to the water-based thermosetting resin is 1:1 to 1:2; the mass ratio of the sum of the masses of the waterborne thermoplastic resin and the waterborne thermosetting resin to the heat-melting filling resin is 1.5:1 to 2.5:1; the solvent contains lauryl alcohol ester, which is an organic solvent having a boiling point of 220°C or higher, and the weight ratio of the heat-expandable microspheres to the solvent is (4 to 40):1; The weight percentage of the water-based thermoplastic resin is 10% to 30%; the waterborne thermoplastic resin is at least one selected from a waterborne acrylic resin and a polyurethane resin; The weight percentage of the water-based thermosetting resin is 10% to 40%; the water-based thermosetting resin is a water-based epoxy resin, The weight percentage of the heat-melting filling resin is 10% to 35%; The hot-melt filling resin is at least one selected from polyester resin and polyurethane; The heat-expandable microspheres have an initial thermal expansion temperature T 1 in the range of 100°C≦T 1 ≦200°C; The heat-expandable microspheres have a maximum heat-resistant temperature T2 of 145°C ≤ T2 ≤ 215°C; The composition of the heat-expandable microspheres comprises: heat-expandable microspheres having a particle size of 8 μm≦D≦20 μm, which account for 60% or more of the total weight of the heat-expandable microspheres; and heat-expandable microspheres having a particle size of 10 μm≦D≦15 μm, the weight ratio of which is 50% or more of the total weight of the heat-expandable microspheres, The heat-expandable microspheres comprise a thermoplastic polymer shell and a liquid alkane encapsulated in the thermoplastic polymer shell.

2. 2. The coating composition of claim 1, wherein the liquid alkane is one, two or more liquid alkanes selected from ethane, propane, isobutane, n-pentane and isopentane.

3. The paint composition described in claim 1, wherein the solvent further comprises one or two of ethylene glycol butyl ether and dipropylene glycol butyl ether.

4. The coating composition of claim 1 , wherein the composition of the heat-expandable microspheres further comprises inorganic fibers.

5. the inorganic fibers are one, two or more selected from nanoaluminum silicate fibers, carbon fibers and boron fibers; The coating composition according to claim 4, wherein the weight ratio of the inorganic fibers to the solvent is (0-2):

1.

6. 10. The coating composition of claim 1, wherein the coating composition further comprises another conventional coating additive selected from a curing agent, a dispersant, an antifoaming agent, a filler, a crosslinking agent, a thickener, and a colorant.

7. the conventional paint additives comprise 0% to 15% of the total weight of the paint composition; 7. The coating composition of claim 6, wherein the sum of the weight percentages of said conventional coating additives in said coating composition is 100%.

8. A method for producing the coating composition according to any one of claims 1 to 7, comprising the step of mixing the components defined in any one of claims 1 to 7.

9. A method for producing a thermally expandable coating layer comprising applying the coating composition according to any one of claims 1 to 7 to a body of a substrate and heating the body of the substrate, A method for improving the stability of a thermally expandable coating layer, wherein the body of the substrate is a magnetic material.

10. a substrate body and a coating layer disposed on a surface of the substrate body; The coating layer is prepared from the coating composition according to any one of claims 1 to 7, The substrate, wherein the coating layer has a thickness of 100 μm to 300 μm.

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