Method for preparing silicon nitride ceramic by lifting type LCD (Liquid Crystal Display) photocuring technology 3D (Three-Dimensional) printing

Abstract

The invention belongs to the technical field of silicon nitride ceramic preparation, and particularly relates to a method for preparing silicon nitride ceramic through lifting type LCD photocuring technology 3D printing, and the method comprises the following steps: carrying out oxidation pretreatment on silicon nitride powder; mixing a sintering aid silicon nitride powder to obtain mixed powder; mixing the mixed resin, a reactive diluent, a photoinitiator and a coloring agent to obtain photosensitive resin; mixing and ball-milling a dispersing agent, the mixed powder and photosensitive resin to obtain light-cured ceramic slurry; 3D printing is conducted on the photocuring ceramic slurry through a lifting type LCD photocuring technology, and a ceramic green body is obtained; dumping the ceramic body to obtain a ceramic green body; sintering the ceramic green body to obtain the silicon nitride ceramic. Compared with the prior art, the problems of low curing depth, curing efficiency and precision of the silicon nitride ceramic slurry formed by photocuring in the prior art are solved. According to the scheme, the silicon nitride ceramic is formed by using the lifting type LCD printing technology, so that the performance of the ceramic is ensured, the production efficiency is improved, and the production cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of silicon nitride ceramic preparation, and particularly relates to a method for preparing silicon nitride ceramics by 3D printing using a lifting type LCD photocuring technology. Background Art

[0002] Silicon nitride ceramic materials have excellent properties such as high hardness, good wear resistance, high temperature resistance, and corrosion resistance, and have become one of the indispensable materials. With the development of science and technology and the increasingly strict requirements of production applications, the structural requirements for high-performance silicon nitride ceramics are also higher. How to obtain the required components through near-net shape forming technology and reduce or avoid subsequent machining poses requirements for ceramic forming processes and slurry preparation. Traditional forming methods include slip casting, gel casting, and isostatic pressing, etc. Such methods all require the aid of supporting molds, and also have the disadvantages of long development cycles and high costs. Moreover, it is difficult to form complex components, and the yield is low. In the face of today's complex, precise, miniaturized, and personalized ceramic product market, traditional preparation methods have been difficult to meet its needs. Therefore, it is of crucial significance to conduct research on new silicon nitride ceramic forming technologies.

[0003] In recent years, researchers at home and abroad have combined 3D printing technology with ceramic forming technology, and used light sources with specific wavelengths to irradiate silicon nitride ceramic slurries mixed with photosensitive resins, so that the resins wrapping the ceramic particles are cured, and at this time the green body has cohesion during forming. Currently, according to the pattern formation principle and the characteristics of printing technology, photocuring forming is mainly divided into stereolithography (SLA), digital light processing (DLP), and liquid crystal display (LCD) projection technology. The forming process of SLA is to control the laser scanning by computer, from point to line, from line to surface, and layer by layer output to form a three-dimensional structure, and its printing efficiency is relatively low. The principle of DLP is to use surface projection and layer-by-layer scanning light exposure forming. Although it can greatly improve the forming efficiency, the cost of its core components is expensive. The principle of LCD is to use a liquid crystal panel to expose different patterns, so as to realize the curing of the position of each layer of pattern. It has the advantages of fast printing speed, small size, and low price of the equipment, and has extremely high development prospects in the field of 3D printing, but at the same time has very high requirements for the fluidity of the slurry.

[0004] In addition, the silicon nitride ceramic slurries used for photocuring forming have the following technical difficulties: (1) The refractive index of silicon nitride powder is high, and the refractive index difference between it and the photosensitive resin is large, resulting in a decrease in the curing depth; (2) The silicon nitride powder presents dark gray, and its light absorption coefficient is large, resulting in a large loss of ultraviolet light energy, which greatly affects the curing efficiency and accuracy of the green body; (3) Photocuring ceramic slurries generally have very poor fluidity and even cannot self-level, which limits their photocuring forming methods and also reduces the printing accuracy.

[0005] As disclosed in Chinese Patent CN114524676A, a photocurable silicon nitride ceramic slurry and a preparation method of silicon nitride ceramic are provided. By using a high refractive index resin, the difference in refractive index between the silicon nitride powder and the resin is reduced, and the curing depth of the silicon nitride ceramic slurry is increased. However, the effect of only selecting a high refractive index resin to increase the curing depth of the slurry is very limited.

[0006] As disclosed in Chinese Patent CN114105650A, a method for preparing silicon nitride ceramic by 3D printing with a sunken DLP photocuring technology is provided. Combining the characteristics of low viscosity and certain viscosity of the sol, a sol coating layer with a certain thickness is coated on the surface of the silicon nitride powder, so that the silicon nitride powder has the characteristics of an oxide sintering aid sol. However, the photocuring forming equipment adopted by this method is expensive and not conducive to large-scale production.

[0007] In view of the above problems, it is necessary to develop a method for 3D printing silicon nitride ceramic with low cost and high efficiency. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for preparing silicon nitride ceramic by 3D printing with a lifting type LCD photocuring technology to solve at least one of the above problems, so as to solve the problems in the prior art of photocurable silicon nitride ceramic slurry, due to: (1) the high refractive index of the silicon nitride powder and the large refractive index difference between the silicon nitride powder and the photosensitive resin, resulting in a low curing depth; (2) the silicon nitride powder presents dark gray and has a large light absorption coefficient, resulting in a large loss of ultraviolet light energy, greatly affecting the curing efficiency and accuracy of the green body; (3) the photocurable ceramic slurry has very poor fluidity and cannot self-level, restricting its photocuring forming method and also reducing the printing accuracy. This solution uses the lifting type LCD printing technology to form silicon nitride ceramic, which not only ensures the performance of the ceramic, improves the production efficiency, but also reduces the production cost.

[0009] The purpose of the present invention is achieved through the following technical solutions:

[0010] A method for preparing silicon nitride ceramic by 3D printing with a lifting type LCD photocuring technology includes the following steps:

[0011] S1: Oxidatively pretreat the silicon nitride powder to form a silicon dioxide layer on the surface of the silicon nitride powder, and then perform ball milling, drying and sieving;

[0012] S2: Ball mill and disperse the sintering aid and the pretreated silicon nitride powder to obtain a mixed powder; mix the mixed resin, active diluent, photoinitiator and colorant to obtain a photosensitive resin; finally, mix the dispersant, mixed powder and photosensitive resin and ball mill to obtain a photocurable ceramic slurry;

[0013] S4: Perform 3D printing on the photocurable ceramic slurry through the pulling type (pull-up type) LCD photocuring technology to obtain a ceramic green body;

[0014] S5: Debind the ceramic green body to obtain a ceramic green compact; sinter the ceramic green compact to obtain silicon nitride ceramics.

[0015] Preferably, in step S1, one or more of the following are included:

[0016] The oxidation pretreatment is: placing the silicon nitride powder at 1100 - 1350 °C for heat preservation for 1 hour;

[0017] The particle size of the silicon nitride powder is 0.5 - 1 μm.

[0018] Preferably, in step S2, one or more of the following are included:

[0019] The sintering aid is one or more of yttrium oxide, magnesium oxide, and aluminum oxide;

[0020] The sintering aid accounts for 3 - 5 wt% of the pretreated silicon nitride powder

[0021] Preferably, in step S2, one or more of the following are included:

[0022] The mixed resin is two or more of trimethylolpropane triacrylate, 1,6 - hexanediol diacrylate, and tripropylene glycol diacrylate;

[0023] The reactive diluent is one or more of 4 - acryloylmorpholine and 2 - hydroxyethyl methacrylate;

[0024] The photoinitiator is one or more of 2,4,6 - trimethylbenzoyl - diphenylphosphine oxide (TPO) and BASF 819 (photoinitiator 819);

[0025] The mass ratio of the mixed resin to the reactive diluent is 4:6 - 7:3;

[0026] The dosage of the photoinitiator is 2 - 3 wt% of the mixed resin.

[0027] Preferably, in step S2, one or more of the following are included:

[0028] The dispersant is one or more of BYK - 110, BYK - 111, and Solsperse AC7590;

[0029] The total dosage of the colorant and the dispersant is 1 - 5 wt% of the mixed powder, and the dosage of the dispersant is 1 - 2 wt% of the mixed powder;

[0030] The mixed powder accounts for 47-55 vol% of the photocurable ceramic slurry, and the photosensitive resin accounts for 45-53 vol% of the photocurable ceramic slurry;

[0031] The mixed powder is added in batches at intervals during the ball milling process. Specifically, the mixed powder is divided into 5 portions and added to the ball milling tank in batches, with an interval of 10 minutes each time. After all the powder is added, continue to grind for 2 hours. The addition of the mixed powder in batches at intervals can further achieve a more uniform mixing. At the same time, it can avoid the phenomenon of agglomeration of the mixed powder caused by heat accumulation.

[0032] Preferably, between step S2 and step S4, step S3 is also carried out: degassing the photocurable ceramic slurry.

[0033] Preferably, in step S3, the degassing treatment is: vacuum degassing for 10-15 min.

[0034] Preferably, in step S4: the parameter settings of the pull-type LCD photocuring technology are: the light source wavelength is 350-450 nm, the exposure time of the bottom layer (bottom) is 60-120 s, the layer thickness of each layer is set to 20-40 μm, the exposure time of each layer (non-bottom layer) is 5-20 s, and the upward separation speed is 1-5 mm / s.

[0035] Preferably, in step S5: the debinding is as follows: under a nitrogen atmosphere, heat up to 172-400 °C at a rate of 0.2-0.4 °C / min and hold for 1-3 h, then heat up to 500-580 °C at a rate of 0.3-0.8 °C / min and hold for 3-5 h, and finally cool naturally.

[0036] Preferably, in step S5: the sintering is as follows: under a nitrogen protection of 5-8 MPa, heat up to 1600-1900 °C at a rate of 4-10 °C / min, and hold for 2-4 h, and silicon nitride ceramics are obtained after cooling.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) During the preparation of the photocurable ceramic slurry in the present invention, the surface of the silicon nitride powder is subjected to oxidation pretreatment. This method uses a high-temperature oxidation process under flowing air to generate a thin layer of silicon dioxide on the powder surface, significantly reducing the refractive index of the powder surface and increasing the curing depth of the green body; as the thickness of the silicon dioxide on the surface of the oxidized silicon nitride particles increases, the number of bisulfate ions ionized on the surface also increases, resulting in the surface of the silicon nitride presenting a negative charge. This negative charge can, on the one hand, inhibit the agglomeration between particles, and on the other hand, help improve the fluidity of the slurry. This well solves the problems of large refractive index and difficult dispersion of the silicon nitride powder.

[0039] (2) The present invention adopts a method of combining monofunctional monomers and polyfunctional monomers, which effectively improves the reaction activity of the system, increases the printing speed, and enhances the strength of the green body. In addition, a colorant is added to modify the color of the silicon nitride slurry, effectively improving the light propagation and energy distribution in the slurry. Through a series of measures such as powder oxidation pretreatment, mixing of multiple types of photosensitive resins, and coloring treatment, the present invention effectively reduces the viscosity of the silicon nitride slurry and increases the curing depth. The prepared silicon nitride ceramic has the advantages of stronger mechanical properties and higher forming accuracy.

[0040] (3) Compared with most expensive and complex stereolithography ceramic forming machines, the silicon nitride ceramic prepared by the present invention can be printed and formed by a lifting type LCD forming machine, breaking through the technical barriers of the traditional stereolithography silicon nitride ceramic forming method, and having a series of advantages such as low cost, high efficiency, and high precision. Description of the Drawings

[0041] Figure 1 It is a cross-sectional morphology diagram of the formed green body in Example 1 of the present invention.

[0042] Figure 2 It is an SEM diagram of the sintered ceramic in Example 1 of the present invention. Detailed Embodiments

[0043] The present invention will be described in detail below with reference to the drawings and specific embodiments. The described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments.

[0044] It should be noted that the materials and instruments used in the following embodiments are all commercially available.

[0045] A method for 3D printing silicon nitride ceramics by a lifting type LCD stereolithography technology, comprising the following steps:

[0046] Step 1: Put the silicon nitride powder into a high-temperature sintering furnace for pretreatment, perform high-temperature oxidation treatment at 1100 - 1350 °C for 1 hour; form a silicon dioxide layer on the surface of the silicon nitride powder, and then perform ball milling, drying, and sieving to obtain the silicon nitride powder after high-temperature oxidation treatment (the silicon nitride powder after pretreatment);

[0047] Step 2: Add the silicon nitride powder after high-temperature oxidation treatment and the sintering aid according to the set ratio of the formula (the sintering aid accounts for 3 - 5 wt% of the silicon nitride powder after pretreatment), use anhydrous ethanol as the ball milling solvent and silicon nitride grinding balls as the grinding medium, and use a planetary ball mill to ball mill and disperse at a speed of 400 rpm for 6 hours to obtain a mixed powder. The drying method is vacuum drying, and the drying temperature is 70 - 90 °C;

[0048] Step 3: Stir and mix the mixed resin, reactive diluent, photoinitiator, and colorant to obtain a photosensitive resin; among them, the photoinitiator accounts for 2-3 wt% of the mixed resin; finally, mix the dispersant, mixed powder, and photosensitive resin and ball-mill them to obtain a photocurable ceramic slurry; among them, the colorant and dispersant account for 1-5 wt% of the mixed powder;

[0049] Step 4: Add the fully mixed photosensitive resin into the ball-mill tank, divide the mixed powder into 5 portions and add them into the ball-mill tank in batches, with an interval of 10 minutes each time. After all are added, continue to grind for 2 hours; among them, the mixed powder accounts for 47-55 vol% of the ceramic slurry, and the photosensitive resin accounts for 45-53 vol% of the ceramic slurry.

[0050] Step 5: Pour the ball-milled photocurable ceramic slurry into the trough of a pull-type LCD photocuring rapid prototyping machine for light printing to obtain a ceramic green body;

[0051] Step 6: Place the photocured ceramic green body into a debinding furnace and pass nitrogen for debinding treatment to obtain a debound ceramic green body;

[0052] Step 7: Place the debound ceramic green body into a gas pressure sintering furnace for sintering.

[0053] Preferably, the particle size of the silicon nitride powder in the silicon nitride slurry described in Step 1 is 0.5-1 μm.

[0054] Preferably, the sintering aid described in Step 2 is one or more of yttrium oxide, magnesium oxide, and aluminum oxide.

[0055] Preferably, the mixed resin described in Step 3 is two or more of trimethylolpropane triacrylate, 1,6-hexanediol diacrylate, and tripropylene glycol diacrylate.

[0056] Preferably, the reactive diluent described in Step 3 is one or more of acryloylmorpholine and 2-hydroxyethyl methacrylate.

[0057] Preferably, the photoinitiator described in Step 3 is one or more of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and BASF 819.

[0058] Preferably, the dispersant described in Step 3 is one or more of BYK-110, BYK-111, and Solsperse AC7590.

[0059] Preferably, the dosage ratio of the mixed resin to the reactive diluent described in Step 3 is 4:6-7:3.

[0060] Preferably, the dosage of the dispersant described in Step 3 is 1-2 wt% of the mixed powder.

[0061] Preferably, the light source wavelength for the stereolithography in Step 5 is 350 - 450 nm, the exposure time for the bottom layer is 60 - 120 s, the layer thickness is set to 20 - 40 μm, and the upward separation speed is 1 - 5 mm / s.

[0062] Preferably, the specific process of debinding in Step 6 is as follows: heating to 172 - 300 °C at a rate of 0.2 - 0.4 °C / min and holding for 1 - 3 h, then heating to 500 - 580 °C at a rate of 0.3 - 0.8 °C / min and holding for 3 - 5 h, and finally cooling naturally.

[0063] Preferably, the sintering process of the ceramic green body in Step 7 is as follows: heating to 1600 - 1900 °C at a rate of 4 - 10 °C / min and holding for 2 - 4 h, and obtaining silicon nitride ceramics after cooling.

[0064] Example 1

[0065] The method for preparing silicon nitride ceramics by 3D printing with the pull - type LCD stereolithography technology described in the present invention includes the following steps:

[0066] Step 1: Put silicon nitride powder into a high - temperature sintering furnace, perform high - temperature oxidation treatment at 1100 °C, then ball - mill for 6 h with a planetary ball mill, put it into a vacuum drying oven and dry at 60 °C, and grind and sieve after drying.

[0067] Step 2: Add the oxidized silicon nitride powder and sintering aids to an ethanol solution and put them into a planetary ball mill for mixing and dispersion. The particle size of the silicon nitride powder is 0.5 - 1 μm, the sintering aids are yttrium oxide and alumina, and their mass ratio is 1:1.

[0068] Step 3: Mix and stir the mixed resin, reactive diluent, photoinitiator, and colorant; among them, the mixed resin is 1,6 - hexanediol diacrylate (HDDA) and trimethylolpropane triacrylate (TMPTA); the reactive diluent is 4 - acryloylmorpholine (ACMO); the photoinitiator is 2,4,6 - trimethylbenzoyl - diphenylphosphine oxide; the colorant uses 0.2 g (1 wt%) of yellow pigment; among them, the mass ratio of HDDA, TMPTA, and the reactive diluent is 3:1:6, and the photoinitiator accounts for 3 wt% of the mixed resin.

[0069] Step 4: Add the treated silicon nitride powder, dispersant, and mixed resin to a ball - milling tank, and the rotation speed of the planetary ball mill is 400 r / min; among them, the powder is divided into 5 portions in total, added to the ball - milling tank in batches and ball - milled for 10 min each time, and ball - milled for 3 h after all the powder is added; the silicon nitride powder accounts for about 47 vol% of the slurry; the dispersant is selected as BYK - 111; the dispersant accounts for 1 - 2 wt% of the silicon nitride powder.

[0070] Step Five: Pour the ball-milled photocurable ceramic slurry into a clean container and place it in a vacuum degassing device for vacuum degassing treatment; among them, the degassing time is 10 min.

[0071] Step Six: Use a lifting type LCD photocuring device to 3D print silicon nitride ceramic slurry; among them, the light source wavelength of the device is 405 nm, the bottom exposure time is 60 s, the printing thickness of each layer is 20 μm, the exposure time of each layer is 10 s, and the upward separation speed is 1 mm / s.

[0072] Step Seven: Place the formed green body in a debinding furnace and perform debinding treatment under a nitrogen atmosphere. Heat it up to 172 °C at a rate of 0.2 °C / min and hold for 1.5 h, then heat it up to 500 °C at a rate of 0.3 °C / min and hold for 3 h, and finally cool it naturally.

[0073] Step Eight: Put the debound green body into a gas pressure sintering furnace and sinter it in the temperature range of 1600 °C under the protection of 5 MPa nitrogen, and the holding time is 4 hours.

[0074] The cross-sectional morphology and SEM of the above-mentioned silicon nitride ceramic slurry are as Figure 1 、 2 shown, and its performance is shown in Table 1.

[0075] Table 1 Performance test results of silicon nitride ceramics prepared in Example 1

[0076] Curing depth / μm Viscosity / mPa·s Settling rate / % Relative density of sintered body 95 637 ≤10%, standing for 30 days 98.86％

[0077] The performance tests in Table 1 are carried out by the following methods (the same hereinafter):

[0078] The curing depth is measured by using a vernier caliper to measure the single-layer curing thickness of the green body.

[0079] The viscosity of the slurry is measured by an NDJ-8T type rotational viscometer.

[0080] The sedimentation rate is carried out through a static sedimentation experiment using a 15 mL test tube. The proportion of the supernatant liquid in the total liquid level height is defined as the sedimentation rate, and the sedimentation situation of the slurry is recorded for 30 days.

[0081] The relative density of the sintered body is measured by using the Archimedes drainage method at room temperature to measure the relative density of the sintered sample.

[0082] Example 2

[0083] The method for 3D printing silicon nitride ceramics by using the lifting type LCD photocuring technology described in the present invention includes the following steps:

[0084] Step 1: Put silicon nitride powder into a high-temperature sintering furnace, conduct high-temperature oxidation treatment at 1200 °C, then ball mill it for 4 h with a planetary ball mill, put it into a vacuum drying oven and dry it at 60 °C after ball milling, and grind and sieve it after drying.

[0085] Step 2: Add the oxidized silicon nitride powder and sintering aids to an ethanol solution and put them into a planetary ball mill for mixing and dispersion. The particle size of the silicon nitride powder is 0.5 - 1 μm, the sintering aids are yttrium oxide and magnesium oxide, and their mass ratio is 1:1.

[0086] Step 3: Mix and stir the mixed resin, reactive diluent, photoinitiator, and colorant; among them, the mixed resin is 1,6 - hexanediol diacrylate (HDDA) and trimethylolpropane triacrylate (TMPTA); the reactive diluent is 4 - acryloylmorpholine (ACMO); the photoinitiator is 2,4,6 - trimethylbenzoyl - diphenylphosphine oxide; the colorant uses 1.2 wt% yellow pigment; among them, the mass ratio of HDDA, TMPTA, and the reactive diluent is 6:1:3, and the photoinitiator accounts for 3 wt% of the mixed resin.

[0087] Step 4: Add the treated silicon nitride powder, dispersant, and mixed resin to a ball milling tank, and the rotational speed of the planetary ball mill is 600 r / min; among them, divide the powder into 5 portions in total, add them to the ball milling tank in batches and ball mill for 10 min each time, and ball mill for 2 h after all the powder is added; the silicon nitride powder accounts for 50 vol% of the slurry; the dispersant is selected as SolsperseAC7590; the dispersant accounts for 1.2 wt% of the silicon nitride powder.

[0088] Step 5: Pour the ball - milled photocurable ceramic slurry into a clean container and put it into a vacuum degassing device for vacuum degassing treatment; among them, the degassing time is 15 min.

[0089] Step 6: Use a pull - type LCD photocuring device to 3D print the silicon nitride ceramic slurry; among them, the light source wavelength of the device is 405 nm, the bottom exposure time is 100 s, the printing thickness of each layer is 30 μm, the exposure time of each layer is 5 s, and the up - pull separation speed is 2 mm / s.

[0090] Step 7: Put the formed green body into a debinding furnace, conduct debinding treatment in a nitrogen atmosphere, heat it up to 172 °C at a rate of 0.4 °C / min and hold for 2 h, then heat it up to 540 °C at a rate of 0.2 °C / min and hold for 3 h, and finally cool it naturally.

[0091] Step 8: Put the debound green body into a gas - pressure sintering furnace, sinter it in a nitrogen protection of 8 MPa within a temperature range of 1700 °C, and the holding time is 2 hours.

[0092] The properties of the above-mentioned silicon nitride ceramic slurry are shown in Table 2.

[0093] Table 2 Performance test results of the silicon nitride ceramic prepared in Example 2

[0094] Curing depth / μm Viscosity / mPa·s Settling rate / % Relative density of sintered body 71 1358 ≤10%, standing for 30 days 99.52％

[0095] Example 3

[0096] The method for preparing silicon nitride ceramics by 3D printing using the lift-type LCD photocuring technology of the present invention comprises the following steps:

[0097] Step 1: Put silicon nitride powder into a high-temperature sintering furnace, perform high-temperature oxidation treatment at 1350 °C, then ball-mill for 6 h with a planetary ball mill, put it into a vacuum drying oven and dry at 60 °C, and after drying, grind and sieve.

[0098] Step 2: Add the oxidized silicon nitride powder and sintering aids to an ethanol solution and put them into a planetary ball mill for mixing and dispersion. The particle size of the silicon nitride powder is 0.5 - 1 μm, and the sintering aids are yttrium oxide and magnesium oxide, and their mass ratio is 1:1.

[0099] Step 3: Mix and stir the mixed resin, active diluent, photoinitiator, and colorant; wherein the mixed resin is 1,6-hexanediol diacrylate (HDDA) and trimethylolpropane triacrylate (TMPTA); the active diluent is 4-acryloylmorpholine (ACMO); the photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide; the colorant uses 1.2 wt% green pigment; wherein, the mass ratio of HDDA, TMPTA, and the active diluent is 3:3:4, and the photoinitiator accounts for 3 wt% of the mixed resin.

[0100] Step 4: Add the treated silicon nitride powder, dispersant, and mixed resin to a ball mill tank, and the rotational speed of the planetary ball mill is 800 r / min; wherein, the powder is divided into 5 portions in total, added to the ball mill tank in batches and ball-milled for 20 min each time, and after all the powder is added, ball-mill for 3 h; the silicon nitride powder accounts for 55 vol% of the slurry; the dispersant is Solsperse AC7590; the dispersant accounts for 1.8 wt% of the mass of the silicon nitride powder.

[0101] Step 5: Pour the ball-milled photocurable ceramic slurry into a clean container and put it into a vacuum degassing device for vacuum degassing treatment; wherein, the degassing time is 10 min.

[0102] Step 6: Use a lift-type LCD photocuring device to 3D print the silicon nitride ceramic slurry; wherein, the light source wavelength of the device is 405 nm, the bottom exposure time is 120 s, the printing thickness of each layer is 40 μm, the exposure time of each layer is 20 s, and the upward separation speed is 3 mm / s.

[0103] Step Seven: Put the formed green body into a debinding furnace, and conduct debinding treatment under a nitrogen atmosphere. Heat it at a rate of 0.2 °C / min to 172 °C and hold for 1.5 h, then heat it at a rate of 0.2 °C / min to 550 °C and hold for 1.5 h, and finally cool it naturally.

[0104] Step Eight: Put the debound green body into a gas pressure sintering furnace, and sinter it within the temperature range of 1900 °C under the protection of 8 MPa nitrogen for 2 h of holding time.

[0105] The properties of the above-mentioned silicon nitride ceramic slurry are shown in Table 3.

[0106] Table 3 Performance test results of the silicon nitride ceramic prepared in Example 3

[0107] Curing depth / μm Viscosity / mPa·s Settling rate / % Relative density of sintered body 64 6371 ≤10%, standing for 30 days 98.74％

[0108] Comparative Example

[0109] The present invention also provides a comparative example. The comparative example uses a commercially available photosensitive resin product (Anycubic standard resin) to prepare the photosensitive silicon nitride ceramic slurry. The preparation of this silicon nitride ceramic includes the following steps:

[0110] Step One: Put silicon nitride powder into a high-temperature sintering furnace, conduct high-temperature oxidation treatment at 1200 °C, then ball mill it with a planetary ball mill for 4 h, put it into a vacuum drying oven and dry it at 60 °C, and after drying, grind and sieve it.

[0111] Step Two: Add the oxidized silicon nitride powder and sintering aids to an ethanol solution and put them into a planetary ball mill for mixing and dispersion. The particle size of the silicon nitride powder is 0.5 - 1 μm, and the sintering aids are yttrium oxide and alumina, and their mass ratio is 1:1.

[0112] Step Three: Add the treated silicon nitride powder, dispersant and commercially available photosensitive resin product to a ball milling tank, and the rotational speed of the planetary ball mill is 400 r / min; among them, divide the powder into 5 portions in total, add them to the ball milling tank in batches and ball mill for 10 min each time, and ball mill for 3 h after all the powder is added; the silicon nitride powder accounts for about 47 vol% of the slurry; the dispersant is selected as BYK-111; the dispersant accounts for 1.5 wt% of the silicon nitride powder.

[0113] Step Four: Pour the ball-milled photosensitive ceramic slurry into a clean container, and put it into a vacuum degassing device for vacuum degassing treatment; among them, the degassing time is 10 min.

[0114] Step 5: Use a lifting type LCD photocuring device to perform 3D printing of silicon nitride ceramic slurry; wherein, the light source wavelength of the device is 405 nm, the bottom exposure time is 60 s, the printing thickness of each layer is 20 μm, the exposure time of each layer is 10 s, and the upward separation speed is 1 mm / s.

[0115] Step 6: Place the formed green body into a debinding furnace and perform debinding treatment under a nitrogen atmosphere. Heat it at a rate of 0.2 °C / min to 172 °C and hold for 1.5 h, then heat it at a rate of 0.3 °C / min to 500 °C and hold for 3 h, and finally cool it naturally.

[0116] Step 7: Place the debound green body into a gas pressure sintering furnace and sinter it within a temperature range of 1600 °C under 5 MPa of nitrogen protection for a holding time of 4 hours.

[0117] The properties of the above silicon nitride ceramic slurry are shown in Table 4.

[0118] Table 4 Performance test results of silicon nitride ceramics prepared in the comparative examples

[0119] Curing depth / μm Viscosity / mPa·s Settling rate / % Relative density of sintered body 25 15383 34%, standing for 30 days 97.74％

[0120] It can be seen from Examples 1-3 and the comparative examples that through the combination and synergy of a series of methods such as oxidation pretreatment of silicon nitride powder, formulation of photosensitive resin components, and coloring treatment of the slurry, the present invention not only improves the solid content of the silicon nitride ceramic slurry, but also increases the single-layer curing thickness of the printed green body. Using the lifting type LCD technology for printing and forming, it breaks through the technical methods of the traditional photocuring silicon nitride ceramic forming method, and has a series of advantages such as low cost, high efficiency, and high precision.

[0121] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A method for preparing silicon nitride ceramics by 3D printing using a lifting type LCD photocuring technology, characterized in that, It includes the following steps: S1: Oxidatively pre-treat the silicon nitride powder to form a silica layer on the surface of the silicon nitride powder, and then perform ball milling, drying, and sieving. S2: Ball mill and disperse the sintering aid and the pre-treated silicon nitride powder to obtain a mixed powder; mix the mixed resin, the reactive diluent, the photoinitiator, and the colorant to obtain a photosensitive resin; finally, mix the dispersant, the mixed powder, and the photosensitive resin and perform ball milling to obtain a photocurable ceramic slurry. S4: Perform 3D printing on the photocurable ceramic slurry by the pull-type LCD photocuring technique to obtain a ceramic green body. S5: Debind the ceramic green body to obtain a ceramic green compact; sinter the ceramic green compact to obtain silicon nitride ceramics.

2. The method for preparing silicon nitride ceramics by 3D printing using a pull-type LCD photocuring technology according to claim 1, wherein, In step S1, one or more of the following are included: The oxidative pre-treatment is: placing the silicon nitride powder at 1100 - 1350 °C for 1 hour. The particle size of the silicon nitride powder is 0.5 - 1 μm.

3. A method for preparing silicon nitride ceramics by 3D printing using a lift-type LCD photocuring technology according to claim 1, characterized in that, In step S2, one or more of the following are included: The sintering aid is one or more of yttrium oxide, magnesium oxide, and aluminum oxide. The sintering aid accounts for 3 - 5 wt% of the pre-treated silicon nitride powder.

4. A method for preparing silicon nitride ceramics by 3D printing using a pull-type LCD photocuring technology according to claim 1, characterized in that, In step S2, one or more of the following are included: The mixed resin is two or more of trimethylolpropane triacrylate, 1,6 - hexanediol diacrylate, and tripropylene glycol diacrylate. The reactive diluent is one or more of 4 - acryloylmorpholine and 2 - hydroxyethyl methacrylate. The photoinitiator is one or more of 2,4,6 - trimethylbenzoyl - diphenylphosphine oxide and BASF 819. The mass ratio of the mixed resin to the reactive diluent is 4:6 - 7:

3. The dosage of the photoinitiator is 2 - 3 wt% of the mixed resin.

5. A method for preparing silicon nitride ceramics by 3D printing using a pull-type LCD photocuring technology according to claim 1, characterized in that, In step S2, one or more of the following are included: The dispersant is one or more of BYK - 110, BYK - 111, and Solsperse AC7590. The total dosage of the colorant and the dispersant is 1 - 5 wt% of the mixed powder, and the dosage of the dispersant is 1 - 2 wt% of the mixed powder. The mixed powder accounts for 47 - 55 vol% of the photocurable ceramic slurry, and the photosensitive resin accounts for 45 - 53 vol% of the photocurable ceramic slurry. The mixed powder is added in portions at intervals during the ball milling process.

6. A method for preparing silicon nitride ceramics by 3D printing using a pull-type LCD photocuring technology according to claim 1, characterized in that, Between step S2 and step S4, step S3 is also performed: defoaming the photocurable ceramic slurry.

7. A method for preparing silicon nitride ceramics by 3D printing using a pull-type LCD photocuring technology according to claim 6, characterized in that, In step S3, the defoaming treatment is: vacuum defoaming for 10 - 15 min.

8. A method for preparing silicon nitride ceramics by 3D printing using a pull-type LCD photocuring technology according to claim 1, characterized in that, In step S4: The parameter settings of the pull-type LCD photocuring technique are: the light source wavelength is 350 - 450 nm, the exposure time of the bottom layer is 60 - 120 s, the layer thickness is set to 20 - 40 μm, and the up-pull separation speed is 1 - 5 mm / s.

9. A method for preparing silicon nitride ceramics by 3D printing using a pull-type LCD photocuring technology according to claim 1, characterized in that, In step S5: The debinding is: in a nitrogen atmosphere, heating at a rate of 0.2 - 0.4 °C / min to 172 - 400 °C and holding for 1 - 3 h, then heating at a rate of 0.3 - 0.8 °C / min to 500 - 580 °C and holding for 3 - 5 h, and finally cooling naturally.

10. A method for preparing silicon nitride ceramics by 3D printing using a pull-type LCD photocuring technology according to claim 1, characterized in that, In step S5: The sintering is as follows: Under the protection of nitrogen at 5 - 8 MPa, the temperature is raised to 1600 - 1900 °C at a rate of 4 - 10 °C / min, and held for 2 - 4 h, and silicon nitride ceramics are obtained after cooling.

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