Insulating medium slurry and preparation method thereof

Abstract

This invention relates to the field of electronic paste technology, and discloses an insulating dielectric paste and its preparation method. The insulating dielectric paste comprises the following components by mass percentage: 60%–80% glass powder; 5%–15% boron nitride nanotube dispersion; and 15%–35% organic carrier. The base materials used to prepare the boron nitride nanotube dispersion include boron nitride nanotubes, a first dispersant, and a first solvent. This invention improves the bending resistance and overall strength of the insulating layer after film formation by adding a pre-prepared boron nitride nanotube dispersion to the insulating dielectric paste, resulting in a uniformly dispersed network structure of the boron nitride nanotubes. The method for preparing the insulating dielectric paste of this invention involves pre-dispersing boron nitride nanotubes uniformly to form a boron nitride nanotube dispersion, then mixing and grinding it with an organic carrier and glass powder, which reduces the viscosity of the insulating dielectric paste and improves its film-forming properties.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic pastes, and in particular to an insulating medium paste and a preparation method thereof. Background Art

[0002] Thick film heaters convert electrical energy into thermal energy through heating plates. According to the conversion method, they are usually divided into resistance heating, induction heating, arc heating, electron beam heating, infrared heating and dielectric heating. Thick film heaters have the advantages of high power density, fast heating speed, high mechanical strength, small size, energy saving, environmental protection and high safety performance. They are widely used in white appliances such as electric kettles, electric water heaters, disinfection cabinets, and rice cookers.

[0003] Electronic paste is the basic material for manufacturing thick film heaters. It can be divided into insulating dielectric paste, resistor paste and conductor paste according to its use. Among them, the insulating dielectric paste needs to be close to the expansion coefficient of the substrate and have strong bonding force, and it must be able to withstand multiple sintering while maintaining unchanged performance. With the diversification of the shapes of thick film heaters (such as special-shaped tubes), the insulating layer formed by the insulating dielectric paste is required to have good bending resistance, otherwise it will directly affect the service life of the product. In addition, in order to ensure the performance of the insulating layer, the insulating dielectric paste needs to be covered on a large area on the substrate, and the thickness must reach more than 80μm. Compared with the amount of resistor paste and conductor paste, it is very large, which leads to an increase in production costs.

[0004] Boron nitride nanotubes are similar in structure to carbon nanotubes, but have better high temperature and high pressure resistance than carbon nanotubes, especially in high temperature areas, they show better elastic modulus performance. However, since boron nitride nanotubes are not easy to disperse and have high viscosity, which is not conducive to grinding, the application of boron nitride nanotubes is limited. Summary of the invention

[0005] Aiming at the problems in the prior art that the insulating medium slurry has poor bending resistance and that boron nitride nanotubes are difficult to disperse, the present invention provides an insulating medium slurry and a preparation method thereof.

[0006] In a first aspect, the present invention provides an insulating medium slurry comprising the following components in percentage by mass:

[0007] Glass powder 60%~80%;

[0008] Boron nitride nanotube dispersion 5% to 15%;

[0009] Organic carrier 15% to 35%;

[0010] The basic materials used to prepare the boron nitride nanotube dispersion include boron nitride nanotubes, a first dispersant and a first solvent.

[0011] In a second aspect, the present invention provides a method for preparing an insulating medium slurry, which is used to prepare the insulating medium slurry of the first aspect, comprising:

[0012] Pretreating the boron nitride nanotubes, the first dispersant and the first solvent to obtain a boron nitride nanotube dispersion;

[0013] Mixing the second solvent, the resin and the auxiliary agent according to a preset mass percentage to obtain an organic carrier;

[0014] The organic carrier, the boron nitride nanotube dispersion and the glass powder are uniformly mixed by a planetary homogenizer to obtain an insulating medium mixture;

[0015] The insulating medium mixture is ground a preset number of times by a three-roll grinding device to obtain the insulating medium slurry.

[0016] The present invention provides an insulating medium slurry, by adding a pre-prepared boron nitride nanotube dispersion liquid into the insulating medium slurry, on the basis of the elastic modulus performance of the boron nitride nanotubes themselves, the boron nitride nanotubes are evenly dispersed to form a network structure, and the bending resistance and overall strength of the insulating layer after the insulating medium slurry is formed into a film are further improved. The present invention also provides a method for preparing an insulating medium slurry, in which the boron nitride nanotubes are evenly dispersed in advance to form a boron nitride nanotube dispersion liquid, and then mixed with an organic carrier and glass powder for grinding, thereby reducing the viscosity of the slurry, making the distribution of the boron nitride nanotubes in the insulating medium slurry more uniform, and improving the film-forming performance of the insulating medium slurry. DETAILED DESCRIPTION

[0017] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0018] In a first aspect, an embodiment of the present invention discloses an insulating medium slurry, comprising the following components in percentage by mass:

[0019] Glass powder 60%~80%;

[0020] Boron nitride nanotube dispersion 5% to 15%;

[0021] Organic carrier 15% to 35%;

[0022] The basic materials used to prepare the boron nitride nanotube dispersion include boron nitride nanotubes, a first dispersant and a first solvent.

[0023] Further, the first dispersant is a dispersant used when the boron nitride nanotube dispersion is prepared in advance according to the boron nitride nanotubes, and the first solvent is an organic solvent used when the boron nanotube dispersion is prepared in advance. According to the different compositions of the dispersant, it can be divided into inorganic dispersants, organic dispersants, high molecular polymer dispersants and composite dispersants. The dispersant can reduce the interfacial tension between the solid phase boron nitride nanotubes and the liquid phase solvent, effectively wet the solid phase particles, and avoid the formation of solid phase particle agglomeration. The components of the insulating dielectric slurry include glass powder, boron nitride nanotube dispersion and organic carrier, and the insulating dielectric slurry is printed on the substrate to form an insulating layer. The glass powder is used to form a bonding phase as a bonding agent to bond the insulating layer to the substrate; the boron nitride nanotube dispersion is used to form a functional phase, and the properties of boron nitride are used to improve the performance of the insulating layer; the organic carrier is a carrier of the functional phase and the bonding phase particles, and is used to control the rheological properties of the insulating dielectric slurry for screen printing. Boron nitride nanotubes exhibit excellent elastic modulus performance in high temperature areas, but since boron nitride nanotubes are not easy to disperse, this embodiment does not directly add boron nitride nanotubes to the insulating medium slurry, but instead adds a boron nitride nanotube dispersion prepared in advance from boron nitride nanotubes, a first dispersant and a first solvent.

[0024] In this embodiment, the boron nitride nanotube dispersion prepared in advance is added to the insulating medium slurry, and the boron nitride nanotubes are evenly dispersed on the basis of utilizing the elastic modulus performance of the boron nitride nanotubes themselves, thereby further improving the bending resistance of the insulating layer. The insulating medium slurry of this embodiment can be widely used in application fields requiring high bending resistance, such as tubular heaters and curved heaters.

[0025] Optionally, the boron nitride nanotubes include at least one of single-walled boron nitride nanotubes, double-walled boron nitride nanotubes and multi-walled boron nitride nanotubes, the first dispersant includes at least one of polyether ester acid amine salts and polyester amide salts, and the first solvent includes at least one of pineneol, N-methylpyrrolidone and diethylene glycol butyl ether acetate.

[0026] Optionally, the diameter of the boron nitride nanotube is 2 to 100 nm; and / or,

[0027] The length of the boron nitride nanotube is 5 to 30 μm.

[0028] Optionally, the components of the boron nitride nanotube dispersion include 1% to 10% of boron nitride nanotubes, 1% to 5% of a first dispersant, and 85% to 97% of a first solvent in terms of mass percentage.

[0029] Further, the preparation methods of boron nitride nanotubes mainly include arc discharge method, laser ablation method, mechanical ball milling method, carbon nanotube replacement method, chemical vapor deposition method and solvent thermal method. Boron nitride nanotubes are cylinders with nanometer-level diameter and micrometer-level length. According to the number of layers of the tube wall, they can be divided into single-wall, double-wall and multi-wall structures. Preferably, the diameter of the boron nitride nanotube is 2 to 100 nm, and the length of the boron nitride nanotube is 5 to 30 μm.

[0030] The dispersant has the functions of wetting, dispersing and suspending and stabilizing. After the dispersant is added to the dispersion of boron nitride nanotubes, the boron nitride nanotubes are partially or completely covered by the dispersant due to the adsorption of the dispersant on the surface of the boron nitride nanotubes, which hinders the aggregation of particles, improves the suspension and stability of the boron nitride nanotubes, and is beneficial to the dispersion of the boron nitride nanotubes. The solvent adopts a polar organic solvent, which can provide polar groups, can adjust the viscosity of the boron nitride nanotube dispersion, and is beneficial to the dispersion of the boron nitride nanotubes. Preferably, the first dispersant includes at least one of polyether ester acid amine salt and polyester amide salt, and the first solvent includes at least one of pineneol, N-methylpyrrolidone and diethylene glycol butyl ether acetate.

[0031] Boron nitride nanotubes are insoluble in most known organic solvents. When the content of boron nitride nanotubes, dispersant and solvent is a specific ratio, boron nitride nanotubes can be uniformly dispersed in the solvent to form a boron nitride nanotube dispersion. When the content of boron nitride nanotubes, dispersant and solvent is not enough to make the boron nitride nanotubes dispersed evenly, each boron nitride nanotube cannot form real mutual contact and interaction, and the film-forming performance of the insulating medium slurry is poor. When the content of boron nitride nanotubes, dispersant and solvent is sufficient to make the boron nitride nanotubes dispersed evenly, each boron nitride nanotube can reach mutual contact and interaction, and a chain-like or mesh-like structure is formed in the whole system, which can effectively improve the bending resistance and strength performance of the insulating layer after the insulating medium slurry is formed. Preferably, the components of the boron nitride nanotube dispersion include 1% to 10% of boron nitride nanotubes, 1% to 5% of the first dispersant and 85% to 95% of the first solvent by mass percentage.

[0032] In this embodiment, the type and size of the boron nitride nanotubes are limited, and the content of the boron nitride nanotubes, the first dispersant and the first solvent is used to form a boron nitride nanotube dispersion, which is beneficial to the pre-dispersion treatment of the boron nitride nanotubes and allows the boron nitride nanotubes to be evenly dispersed while forming a network structure, further improving the bending resistance and overall strength of the insulating layer.

[0033] Optionally, the glass powder has a median particle size of 3 to 6 μm, a softening temperature of 600 to 950° C., and a thermal expansion coefficient of 7.5 to 9.5 ppm / ° C.

[0034] Furthermore, the particle size of the glass powder will affect the performance of the insulating medium slurry. The maximum particle size of the glass powder used in the insulating medium slurry is generally not more than 15 μm. The smaller the particle size, the finer the glass powder, so that the insulating medium slurry has good dispersibility, can improve the surface roughness, and reduce the sintering temperature. Preferably, the median particle size of the glass powder is 3 to 6 μm.

[0035] The softening temperature refers to the temperature at which the glass begins to soften but has not yet completely melted. At the softening temperature, the molecules of the glass begin to become more active, and the bond structure begins to become unstable, causing the glass to begin to deform. At this point, if the heating continues, the glass will soften further and eventually become liquid. The softening temperature of the glass powder is related to the working temperature of the insulating layer. When the softening temperature is lower than the working temperature, the insulating layer will degrade in performance or even fall off due to the deformation of the glass powder. Preferably, the softening temperature is 600-950°C.

[0036] The thermal expansion coefficient is the degree to which an object expands or contracts as the temperature changes. When the thermal expansion coefficients of the glass powder and the substrate do not match, the thermal expansion and contraction of the substrate and the insulating layer are not synchronized, resulting in a large thermal stress between the insulating layer and the substrate. Excessive thermal stress causes severe deformation of the substrate, resulting in cracks in the insulating layer and even peeling off the surface of the substrate. When the thermal expansion coefficients of the glass powder and the substrate match, the insulating layer can maintain stable performance under high temperature conditions. Preferably, the thermal expansion coefficient of the glass powder is 7.5 to 9.5 ppm / °C.

[0037] This embodiment further improves the dispersibility of the insulating medium slurry by limiting the particle size of the glass powder. This embodiment ensures the stability of the insulating medium slurry during use by limiting the softening temperature and thermal expansion coefficient of the glass powder.

[0038] Optionally, the components of the organic carrier include a second solvent, a resin and an auxiliary agent; wherein the second solvent includes pineol, diethylene glycol butyl ether, diethylene glycol butyl ether acetate, alcohol ester dodecahydrate, tributyl citrate and N-methylpyrrolidone, the resin includes ethyl cellulose and acrylate resin, and the auxiliary agent includes a second dispersant, a thixotropic agent and a leveling agent.

[0039] Furthermore, the second solvent refers to the organic solvent in the organic carrier, and the second dispersant refers to the auxiliary chemical used to improve the dispersion performance in the organic carrier. The organic carrier is mainly composed of organic solvents, resins and additives, which are used to disperse and wet the glass powder bonding phase and functional phase in the insulating medium slurry, control the rheological properties of the insulating medium slurry, and facilitate the printing of the insulating medium slurry. By adjusting the composition and content of the organic carrier, the viscosity, volatility, thixotropy and wettability of the insulating medium slurry can be changed, so that the insulating medium slurry has good fluidity during printing. The volatility of the organic solvent determines the volatility of the organic carrier, and the volatility of the organic carrier directly determines the quality of the insulating layer. If the organic solvent evaporates too quickly, the viscosity of the insulating medium slurry will increase during printing and block the screen, and it is easy to form defects such as holes and microcracks on the surface of the insulating layer after drying and sintering. If the solvent evaporates too slowly, it is not easy to dry after screen printing, resulting in defects after sintering. At the same time, the volatility of the organic carrier is also an important factor affecting the stability and storage time of the insulating medium slurry. The resin is also a film-forming carrier of the insulating medium slurry, which can ensure the continuity and viscosity of the slurry. The moderate viscosity can ensure the fluidity of the insulating medium slurry to be suitable for screen printing. Adding additives makes the insulating medium slurry have good thixotropy and wettability. Good thixotropy can keep the insulating medium slurry in a good shape after printing, and wettability can ensure uniform dispersion of the bonding phase and the functional phase without agglomeration and precipitation. Preferably, the additives include a second dispersant, a thixotropic agent and a leveling agent. The second dispersant can be the same as the first dispersant or different.

[0040] In this embodiment, by using a specific type of organic solvent, resin and additive to form an organic carrier, the rheological properties of the insulating medium slurry are improved, which is helpful for the film formation of the insulating medium slurry.

[0041] In a second aspect, an embodiment of the present invention further discloses a method for preparing an insulating medium slurry, which is used to prepare the insulating medium slurry of the first aspect, comprising:

[0042] Pretreating the boron nitride nanotubes, the first dispersant and the first solvent to obtain a boron nitride nanotube dispersion;

[0043] Mixing the second solvent, the resin and the auxiliary agent according to a preset mass percentage to obtain an organic carrier;

[0044] The organic carrier, the boron nitride nanotube dispersion and the glass powder are uniformly mixed by a planetary homogenizer to obtain an insulating medium mixture;

[0045] The insulating medium mixture is ground a preset number of times by a three-roll grinding device to obtain the insulating medium slurry.

[0046] Further, the preset mass percentage is the percentage content of each component in the preset organic carrier. Preferably, the preset mass percentage includes: 30% to 50% of pineol, 10% to 20% of diethylene glycol butyl ether, 20% to 30% of diethylene glycol butyl ether acetate, 6% to 15% of ethyl cellulose, 0% to 10% of acrylic resin, 1% to 5% of dispersant, 1% to 5% of thixotropic agent and 1% to 5% of leveling agent. The planetary homogenizer can make the liquid of the organic carrier and the liquid of the boron nitride nanotube dispersion liquid mix evenly, and can also make the liquid and the solid of the glass powder mix evenly to form an insulating medium mixture. In this embodiment, a three-roller grinder is used to grind the insulating medium mixture formed by the organic carrier, the boron nitride nanotube dispersion liquid and the glass powder to prepare an insulating medium slurry. The grinding effect is achieved by the mutual extrusion of the surfaces of the three horizontal rollers and the friction at different speeds. The fineness of the insulating medium slurry is less than 10μm. The three-roller mill is suitable for the manufacture of slurries such as paints, inks and pigments, and is especially suitable for the effective grinding and dispersion of high-viscosity materials. The preset number is the preset number of three-roller grinding times, which can also be adjusted according to actual needs. For example, the default setting is 3 times, which can be manually adjusted to 5 times when used.

[0047] In this embodiment, the boron nitride nanotubes are dispersed uniformly in advance to form a boron nitride nanotube dispersion, which is then mixed with an organic carrier and glass powder for grinding to prepare an insulating medium slurry. The viscosity of the slurry is reduced after multiple grindings, making the distribution of the boron nitride nanotubes in the insulating medium slurry more uniform.

[0048] Optionally, the boron nitride nanotubes, the first dispersant and the first solvent are pretreated to obtain a boron nitride nanotube dispersion, comprising:

[0049] Adding the first dispersant and the first solvent into a mixing device and stirring at a first speed for a first time to obtain a first mixture;

[0050] Adding the boron nitride nanotubes to the first mixture, controlling the mixing device to stir at a second speed for a second time, and then stirring at a third speed for a third time, to obtain a second mixture;

[0051] The second mixture is added into a grinding device, and ground at a fourth rotation speed for a fourth time to obtain the boron nitride nanotube dispersion.

[0052] Optionally, the first speed is 380-420rpm, and the first time length is 5-15 minutes; the second speed is 550-600rpm, and the second time length is 25-35 minutes; the third speed is 1300-1400rpm, and the third time length is 25-35 minutes; the fourth speed is 1500-2000rpm, and the fourth time length is 85-95 minutes.

[0053] Furthermore, the mixing device in this embodiment can adopt a high-speed disperser, set multiple sets of parameters to adjust the speed and duration of stirring, and achieve full mixing and pre-dispersion treatment by adjusting the speed from low to high and the duration from short to long by using multiple sets of parameters. The grinding device in this embodiment can adopt a sand mill, which uses a material pump to input the solid-liquid phase mixture material after pre-dispersion treatment into the cylinder, and the material and the grinding medium in the cylinder are stirred together by a high-speed rotating disperser, so that the boron nitride nanotube solid particles in the material and the grinding medium produce strong collision, friction, and shearing effects with each other, so as to accelerate the grinding of particles and disperse aggregates, and prepare boron nitride nanotube dispersion.

[0054] In this embodiment, the rotation speed is set from low to high and the time is set from short to long, and multiple groups of parameters are used to achieve full mixing and pre-dispersion processing, and a sand mill is used to accelerate the grinding of particles and disperse aggregates, so that the solid particles of boron nitride nanotubes are evenly dispersed to obtain a boron nitride nanotube dispersion.

[0055] Optionally, before uniformly mixing the organic carrier, the boron nitride nanotube dispersion and the glass powder by a planetary homogenizer, the process further comprises:

[0056] 30% to 40% of CaO, 30% to 40% of SiO2, 5% to 10% of B2O3 and 10% to 20% of Al2O3 are uniformly mixed to obtain a third mixture;

[0057] After the third mixture is melted at 1300-1500° C. for 1-3 hours, the melted second mixture is sequentially subjected to water quenching and ball milling to obtain the glass powder.

[0058] Furthermore, after mixing the raw materials of the glass powder, the raw materials are kept at high temperature for a period of time to ensure that the mixed raw materials are fully melted. The molten liquid glass body is poured into water to quickly cool down to form glass slag, avoiding partial crystallization due to too slow cooling, thereby affecting the softening temperature of the glass powder. Ball milling the glass slag after water quenching can ensure that the particle size of the glass powder meets the requirements.

[0059] In this embodiment, the glass powder is prepared by molten water quenching method, and the particle size of the glass powder is ensured to be fine and uniform through ball milling to meet the requirements of preparing insulating medium slurry.

[0060] The specific embodiments and comparative examples of the insulating medium slurry of the present invention are as follows:

[0061] Example 1

[0062] Preparation of Boron Nitride Nanotube Dispersion:

[0063] 1% polyester amide salt as a first dispersant and 97% pineol as a first solvent are added into a high-speed disperser and stirred at 400 rpm for 5 minutes to obtain a first mixture;

[0064] 2% of multi-walled boron nitride nanotubes were added to the first mixture, and the high-speed disperser was controlled to stir at 600 rpm for 30 minutes and then at 1400 rpm for 30 minutes for pre-dispersion treatment to obtain a second mixture;

[0065] The second mixture was added to a sand mill and ground at 1500 rpm for 90 minutes to obtain a boron nitride nanotube dispersion.

[0066] Preparation of organic carrier:

[0067] An organic carrier is obtained by mixing 40% of terpineol, 15% of diethylene glycol butyl ether, 20% of diethylene glycol butyl ether acetate, 10% of ethyl cellulose, 5% of a dispersant, 5% of a thixotropic agent and 5% of a leveling agent.

[0068] Preparation of glass powder:

[0069] 35% of CaO, 40% of SiO2, 10% of B2O3 and 15% of Al2O3 are uniformly mixed to obtain a third mixture;

[0070] After the third mixture was smelted at 1400° C. for 3 hours, it was water quenched and ball-milled to obtain glass powder, and the median particle size of the glass powder was 3 μm.

[0071] Preparation of insulating dielectric slurry:

[0072] 15% of an organic carrier, 5% of a boron nitride nanotube dispersion and 80% of glass powder are uniformly mixed by a planetary homogenizer to obtain an insulating medium mixture;

[0073] The insulating medium mixture was ground three times by a three-roll mill to a fineness of less than 10 μm, thereby obtaining the insulating medium slurry of Example 1.

[0074] Example 2

[0075] Preparation of Boron Nitride Nanotube Dispersion:

[0076] Add 5% of polyester amide salt as a first dispersant and 85% of pineol as a first solvent into a high-speed disperser, and stir at 400 rpm for 15 minutes to obtain a first mixture;

[0077] Add 10% of multi-walled boron nitride nanotubes to the first mixture, control the high-speed disperser to stir at 600 rpm for 30 minutes, and then stir at 1400 rpm for 30 minutes for pre-dispersion treatment to obtain a second mixture;

[0078] The second mixture was added to a sand mill and ground at 2000 rpm for 90 minutes to obtain a boron nitride nanotube dispersion.

[0079] Preparation of organic carrier:

[0080] An organic carrier is obtained by mixing 40% of terpineol, 15% of diethylene glycol butyl ether, 20% of diethylene glycol butyl ether acetate, 10% of ethyl cellulose, 5% of a dispersant, 5% of a thixotropic agent and 5% of a leveling agent.

[0081] Preparation of glass powder:

[0082] 35% of CaO, 40% of SiO2, 10% of B2O3 and 15% of Al2O3 are uniformly mixed to obtain a third mixture;

[0083] After the third mixture was smelted at 1400° C. for 3 hours, it was water quenched and ball-milled to obtain glass powder, and the median particle size of the glass powder was 3 μm.

[0084] Preparation of insulating dielectric slurry:

[0085] 15% of an organic carrier, 10% of a boron nitride nanotube dispersion and 75% of glass powder are uniformly mixed by a planetary homogenizer to obtain an insulating medium mixture;

[0086] The insulating medium mixture was ground 5 times by a three-roll mill to a fineness of less than 10 μm, thereby obtaining the insulating medium slurry of Example 2.

[0087] Example 3

[0088] Preparation of Boron Nitride Nanotube Dispersion:

[0089] Add 3% of polyester amide salt as a first dispersant and 91% of pineol as a first solvent into a high-speed disperser, and stir at 400 rpm for 10 minutes to obtain a first mixture;

[0090] 6% of multi-walled boron nitride nanotubes were added to the first mixture, and the high-speed disperser was controlled to stir at 600 rpm for 30 minutes and then at 1400 rpm for 30 minutes for pre-dispersion treatment to obtain a second mixture;

[0091] The second mixture was added to a sand mill and ground at 1800 rpm for 90 minutes to obtain a boron nitride nanotube dispersion.

[0092] Preparation of organic carrier:

[0093] An organic carrier is obtained by mixing 40% of terpineol, 15% of diethylene glycol butyl ether, 20% of diethylene glycol butyl ether acetate, 10% of ethyl cellulose, 5% of a dispersant, 5% of a thixotropic agent and 5% of a leveling agent.

[0094] Preparation of glass powder:

[0095] 35% of CaO, 40% of SiO2, 10% of B2O3 and 15% of Al2O3 are uniformly mixed to obtain a third mixture;

[0096] After the third mixture was smelted at 1400° C. for 3 hours, it was water quenched and ball-milled to obtain glass powder, and the median particle size of the glass powder was 3 μm.

[0097] Preparation of insulating dielectric slurry:

[0098] 15% of an organic carrier, 10% of a boron nitride nanotube dispersion and 75% of glass powder are uniformly mixed by a planetary homogenizer to obtain an insulating medium mixture;

[0099] The insulating medium mixture was ground four times by a three-roll mill to a fineness of less than 10 μm, thereby obtaining the insulating medium slurry of Example 3.

[0100] Comparative Example 1

[0101] Compared with Example 2, in Comparative Example 1, no boron nitride nanotube dispersion is added during the preparation of the insulating dielectric slurry, and 25% of the organic carrier and 75% of the glass powder are evenly mixed by a planetary homogenizer to obtain an insulating dielectric mixture; the insulating dielectric mixture is ground 5 times by a three-roll grinder to obtain the insulating dielectric slurry of Comparative Example 1.

[0102] Comparative Example 2

[0103] Compared with Example 2, when preparing the boron nitride nanotube dispersion, 5% of the first dispersant, 85% of the first solvent and 10% of the boron nitride nanotubes are directly added to a sand mill and ground at 2000 rpm for 90 minutes without pre-dispersion treatment. Other preparation methods are consistent to obtain the insulating medium slurry of Comparative Example 2.

[0104] Comparative Example 3

[0105] Compared with Example 2, in Comparative Example 3, when preparing the boron nitride nanotube dispersion, 5% of the first dispersant and 85% of the first solvent are added to a high-speed disperser, and stirred at 400 rpm for 15 minutes to obtain a first mixture; 10% of boron nitride nanotubes are added to the first mixture, and the high-speed disperser is controlled to stir at 600 rpm for 30 minutes and then at 1400 rpm for 30 minutes for pre-dispersion treatment. No sanding treatment is performed, and other preparation methods are consistent, to obtain the insulating medium slurry of Comparative Example 3.

[0106] The insulating medium slurry in the embodiment and the comparative example was screen printed onto a 430 stainless steel substrate, dried, sintered, and the sintered film thickness was 45 μm. Finally, the flexible conductor slurry was printed on the insulating medium to obtain a heating plate. The insulating medium slurry was tested for slurry viscosity, and the heating plate was tested for sintered film thickness, breakdown voltage, and bending resistance. The test results are shown in Table 1.

[0107] Slurry viscosity test:

[0108] The viscosity of the insulating medium slurry was tested using a Brookfield SC4-14 model viscometer, with a test speed of 10 rpm and a test temperature of 25°C.

[0109] Breakdown voltage test: Use a withstand voltage tester to perform a breakdown voltage test on the heating plate using a DC voltage.

[0110] Bending test: The heating plate is subjected to a 90° bending test.

[0111] Table 1 Performance test results of insulating medium slurry and heating plate in Examples and Comparative Examples

[0112] Slurry viscosity (Pa.s) Sintered film thickness (μm) Breakdown voltage(V) Bending times Example 1 250 45.2 1500 10 Example 2 280 45.5 1800 15 Example 3 260 45.3 1600 12 Comparative Example 1 210 44.6 900 3 Comparative Example 2 300 46.2 1300 6 Comparative Example 3 350 44.7 1000 5

[0113] It can be seen from the test results in Table 1 that, compared with the comparative example, the insulating medium slurry in the embodiment has a lower slurry viscosity, the sintered film thickness of the heating plate is more uniform and the error is smaller, the heating plate has a higher number of anti-bending times, and in addition, the uniformly distributed boron nitride nanotubes make the heating plate in the embodiment have a higher breakdown voltage. This is because the embodiment adds a boron nitride nanotube dispersion obtained by pre-dispersion treatment to the insulating medium slurry, which reduces the slurry viscosity and has better film-forming performance. At the same time, on the basis of utilizing the elastic modulus performance of the boron nitride nanotubes themselves, the boron nitride nanotubes are uniformly distributed to further improve the bending resistance of the heating plate. Comparing the embodiments, since the boron nitride nanotube dispersion added in Example 1 is the least compared with Examples 2 and 3, although Example 1 has the lowest viscosity compared with Examples 2 and 3, Examples 2 and 3 can effectively improve the breakdown voltage and bending resistance compared with Example 1. Compared with Example 2, Comparative Example 1 does not add boron nitride nanotube dispersion liquid, so the elastic modulus performance of boron nitride nanotubes itself cannot be utilized, resulting in poor bending resistance and the lowest breakdown voltage. Compared with Example 2, Comparative Example 2 adds boron nitride nanotubes, but does not perform pre-dispersion treatment on the boron nitride nanotubes, resulting in high slurry viscosity and uneven distribution of boron nitride nanotubes in the insulating medium slurry. Therefore, although the bending resistance and breakdown voltage performance of the heating plate are higher than those of Comparative Example 1, they are not as good as those of Examples 1, 2 and 3. Compared with Example 2, Comparative Example 3 does not perform sand milling after pre-dispersion treatment, and cannot further grind the solid particles of boron nitride nanotubes and disperse the aggregates. The slurry has high viscosity and uneven distribution of boron nitride nanotubes, which further affects the bending resistance and breakdown voltage performance of the heating plate.

[0114] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An insulating medium slurry, characterized in that: The following components are included in mass percentage: Glass powder 60%~80%; Boron nitride nanotube dispersion 5%~15%; Organic carrier 15%~35%; Wherein, the basic materials used to prepare the boron nitride nanotube dispersion liquid include boron nitride nanotubes, a first dispersant and a first solvent; The boron nitride nanotubes include at least one of single-walled boron nitride nanotubes, double-walled boron nitride nanotubes and multi-walled boron nitride nanotubes; the first dispersant includes at least one of polyether ester acid amine salt and polyester amide salt; the first solvent includes at least one of terpineol, N-methyl pyrrolidone and diethylene glycol butyl ether acetate; the components of the boron nitride nanotube dispersion liquid include, by mass percentage: 1% to 10% of boron nitride nanotubes, 1% to 5% of the first dispersant and 85% to 97% of the first solvent; The components of the organic carrier include a second solvent, a resin and an auxiliary agent; wherein the second solvent includes at least one of terpineol, diethylene glycol butyl ether, diethylene glycol butyl ether acetate, alcohol ester dodecahydrate, tributyl citrate and N-methylpyrrolidone, the resin includes ethyl cellulose and acrylate resin, and the auxiliary agent includes a second dispersant, a thixotropic agent and a leveling agent; the components of the organic carrier include, by mass percentage: 60% to 100% of the second solvent, 6% to 25% of the resin and 3% to 15% of the auxiliary agent.

2. The insulating medium slurry according to claim 1, characterized in that: The diameter of the boron nitride nanotubes is 2-100 nm; and / or, The length of the boron nitride nanotube is 5-30 μm.

3. The insulating medium slurry according to claim 1, characterized in that: The glass powder has a median particle size of 3-6 μm, a softening temperature of 600-950° C., and a thermal expansion coefficient of 7.5-9.5 ppm / ° C.

4. A method for preparing an insulating medium slurry, characterized in that: The insulating medium slurry preparation method is used to prepare the insulating medium slurry according to any one of claims 1 to 3, and the insulating medium slurry preparation method comprises: Pretreating the boron nitride nanotubes, the first dispersant and the first solvent to obtain a boron nitride nanotube dispersion; Mixing the second solvent, the resin and the auxiliary agent according to a preset mass percentage to obtain an organic carrier; The organic carrier, the boron nitride nanotube dispersion and the glass powder are uniformly mixed by a planetary homogenizer to obtain an insulating medium mixture; The insulating medium mixture is ground a preset number of times by a three-roll grinding device to obtain the insulating medium slurry.

5. The method for preparing insulating medium slurry according to claim 4, characterized in that: The method of pretreating the boron nitride nanotubes, the first dispersant and the first solvent to obtain a boron nitride nanotube dispersion comprises: Adding the first dispersant and the first solvent into a mixing device and stirring at a first speed for a first time to obtain a first mixture; Adding the boron nitride nanotubes to the first mixture, controlling the mixing device to stir at a second speed for a second time, and then stirring at a third speed for a third time, to obtain a second mixture; The second mixture is added into a grinding device, and ground at a fourth rotation speed for a fourth time to obtain the boron nitride nanotube dispersion.

6. The method for preparing insulating medium slurry according to claim 5, characterized in that: The first speed is 380~420rpm, and the first duration is 5~15 minutes; the second speed is 550~600rpm, and the second duration is 25~35 minutes; the third speed is 1300~1400rpm, and the third duration is 25~35 minutes; the fourth speed is 1500~2000rpm, and the fourth duration is 85~95 minutes.

7. The method for preparing insulating medium slurry according to claim 4, characterized in that: Before the organic carrier, the boron nitride nanotube dispersion and the glass powder are uniformly mixed by a planetary homogenizer, the method further comprises: 30% to 40% of CaO, 30% to 40% of SiO2, 5% to 10% of B2O3 and 10% to 20% of Al2O3 are uniformly mixed to obtain a third mixture; After the third mixture is smelted at 1300-1500° C. for 1-3 hours, the smelted third mixture is sequentially subjected to water quenching and ball milling to obtain the glass powder.