Two-step glue discharging method for DLP-3D printing of silicon nitride ceramics

Abstract

The invention discloses a two-step glue discharging method for DLP-3D printing of silicon nitride ceramics. Firstly, silicon nitride mixed powder is mixed with resin, a dispersing agent and a photoinitiator to obtain organic mixed liquid, and the organic mixed liquid is subjected to ball milling to obtain silicon nitride ceramic slurry; a silicon nitride biscuit is degummed by adopting a two-step method, in the first step, the inert atmosphere is used for degumming, and the inert atmosphere can effectively prevent oxidation reaction, so that the pyrolytic reaction and vaporization rate of various organic matters in the biscuit at high temperature can be greatly reduced; and the defects of cracking, bubbling and the like caused by larger pressure difference between the inside and the outside of the blank can be effectively avoided. In the second-step glue discharging process, the temperature is raised in the air atmosphere, so that residual organic matters such as carbon residues in the first-step glue discharging can be removed through oxidation reaction, the organic matters in the silicon nitride biscuit are completely removed, and the mechanical property of the finally sintered silicon nitride ceramic is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of DLP-3D printing, and in particular to a two-step debinding method for DLP-3D printing of silicon nitride ceramics. Background Art

[0002] Silicon nitride (Si3N4) ceramics are one of the most excellent ceramics in comprehensive performance among advanced ceramics. They have the advantages of high strength, high fracture toughness, high temperature resistance, oxidation resistance, small thermal expansion coefficient, low dielectric constant and dielectric loss, high thermal conductivity, etc. They are widely used in defense, machinery, semiconductor devices and other fields, and have become an indispensable material in the development of modern science and technology. The huge application prospects and possible economic benefits make nitride ceramic materials a research hotspot worldwide, thus attracting the attention of domestic and foreign material researchers. However, ceramic materials usually need to be processed before they can be applied to the industry after they are prepared, and the processing technology of ceramic materials is cumbersome, especially for complex structures and integrated structures. Although a variety of processing technologies have emerged, they are inefficient, costly, and difficult to guarantee processing quality, and have become a bottleneck restricting their widespread application.

[0003] 3D printing technology, also known as additive manufacturing (AM), is a manufacturing process that creates three-dimensional objects by adding materials layer by layer. Compared with traditional subtractive manufacturing (such as cutting, milling, etc.), 3D printing technology has the characteristics of high design freedom, customizable production, high material utilization, and shortened production cycle. Digital light processing (DLP) technology is a 3D printing technology that has emerged in recent years. Compared with the point-line-layer point-by-point molding printing of stereolithography (SLA) technology, DLP-3D printing technology solidifies and prints by projecting the image of the entire layer at one time. Compared with other types of rapid prototyping technologies, DLP technology will not change the molding speed regardless of the size of the workpiece perimeter within the effective processing size of the equipment, especially in batch production. The efficiency is more obvious, thereby achieving rapid printing and improving the preparation speed of the product. Moreover, since the micro-mirrors used in DLP-3D printing technology have a higher resolution, compared with other 3D printing technologies, its processing accuracy can reach 20-30μm, and it can print more delicate and complex geometric shapes.

[0004] Although DLP-3D printing technology has obvious advantages, it is difficult to prepare silicon nitride ceramics using conventional slurries due to the high absorbance and high refractive index of silicon nitride powder. It is usually necessary to add a large amount of organic additives such as photosensitive resins and photoinitiators to play a role in bonding and curing during printing, so that the sintered ceramic products have higher density and good mechanical properties. However, the organic components that play a bonding role should be discharged to the outside of the green body as much as possible during the debinding stage. If they are not fully removed before the subsequent sintering treatment, the final sintering performance of the ceramic will be affected. Therefore, the debinding process system has a great impact on the final performance of silicon nitride ceramics after sintering. Summary of the invention

[0005] In view of this, the present invention provides a two-step debinding method for DLP-3D printing of silicon nitride ceramics to solve the above technical problems.

[0006] A two-step debinding method for silicon nitride ceramic DLP-3D printing, comprising the following steps:

[0007] Step S1: placing silicon nitride mixed powder and anhydrous ethanol into a ball mill for wet ball milling, placing the treated powder in an oven for drying and sieving with a sieve to finally obtain treated silicon nitride mixed powder;

[0008] Step S2: mixing the resin, the dispersant and the photoinitiator to obtain an organic mixed liquid, and ball-milling the silicon nitride mixed powder and the organic mixed liquid processed in step S1 to obtain silicon nitride ceramic slurry;

[0009] Step S3: adding silicon nitride ceramic slurry into the DLP-3D printing device and printing according to the processed slice information;

[0010] Step S4: Debinding the silicon nitride blank by a two-step method, wherein the first debinding process is heating the temperature to 150-400° C. in an inert atmosphere and keeping the temperature, and the second debinding process is heating the temperature to 300-700° C. in an air atmosphere and keeping the temperature;

[0011] Step S5: The silicon nitride ceramic blank that has undergone the debinding treatment is subjected to air pressure sintering in a nitrogen atmosphere to finally obtain DLP-3D printed silicon nitride ceramics.

[0012] Furthermore, in the above step S1, the treated powder is placed in an oven at 80-100° C. for drying for 6-12 hours, and sieved using a 60-100 mesh sieve.

[0013] Furthermore, in the above step S1, the silicon nitride mixed powder is Si3N4, Al2O3, and Y2O3, wherein the initial particle size of Si3N4 is 0.5-1 μm, the initial particle size of Al2O3 is 0.2-0.7 μm, and the initial particle size of Y2O3 is 0.2-1.5 μm.

[0014] Further, in the above step S2, the resin is one or a combination of 1,6-hexanediol diacrylate (HDDA), trimethylolpropane triacrylate (TMPTA), pentaerythritol tri- and tetraacrylate (PET3A), pentaerythritol tetraacrylate (PET4A), and polydipentaerythritol hexaacrylate (DPHA); the dispersant is one or a combination of modified polyolefin solution, acrylic copolymer solution, and phosphate solution; the photoinitiator is one or a combination of trimethylbenzoyl-diphenylphosphine oxide (TPO), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, benzophenone, and 2-methyl-1-(4-methylthiophenyl)-2-morpholine-1-propanone; and the raw materials are 40 to 50 parts by volume of silicon nitride mixed powder, 30 to 50 parts of photosensitive resin, 5 to 10 parts of dispersant, and 0.5 to 2 parts of photoinitiator.

[0015] Furthermore, in the above step S3, the printing parameters are that the time for each layer of silicon nitride ceramic slurry is 3 to 12 seconds, and the exposure intensity of each layer is 100 to 500 mj / cm 2 .

[0016] Furthermore, in the above step S4, the heating rate of the first step is 0.1-1°C / min, and the insulation time is 1-12h, and the heating rate of the second step is 0.1-1°C / min, and the insulation time is 1-12h.

[0017] Furthermore, in the above step S4, the first step of inert atmosphere debinding can be preferably carried out in multiple stages. In the first stage, the temperature is raised to 150-250°C in an inert atmosphere at a heating rate of 0.1-1°C / min and a holding time of 3-8h. In the second stage, the temperature is raised to 250-400°C in an inert atmosphere at a heating rate of 0.1-1°C / min and a holding time of 1-10h for debinding.

[0018] Furthermore, in the above step S5, the pressure of the nitrogen atmosphere is 0.5-2 MPa, the sintering temperature is 1700-1800° C., and the holding time is 1-4 h.

[0019] Furthermore, the inert atmosphere is nitrogen.

[0020] Compared with the prior art, the two-step debinding method for silicon nitride ceramic DLP-3D printing provided by the present invention effectively prevents the occurrence of oxidation reaction by debinding in an inert atmosphere in the first step, so that the pyrolysis reaction and vaporization rate of various organic substances inside the blank at high temperature will be greatly reduced, and the cracking, bubbling and other defects caused by the large pressure difference between the inside and outside of the blank can be effectively avoided. In air debinding, the organic substances such as carbon residues remaining in the first step of debinding can be removed through oxidation reaction, ensuring that the organic substances in the silicon nitride blank are cleanly removed and defects such as cracking and bulging are avoided, so that the mechanical properties of the finally sintered silicon nitride ceramics are significantly improved. Compared with the silicon nitride ceramics prepared by air debinding in the past, the relative density of the silicon nitride ceramics prepared by the two-step debinding method is increased from 90.16% to 96.86%, and the flexural strength is increased from 281.52MPa to 590.39MPa, and the mechanical properties are significantly improved. The silicon nitride ceramics prepared by this method not only have performance close to that of silicon nitride ceramics prepared by traditional preparation methods, but also combine the great advantages of DLP-3D printing technology in complex structure molding, which greatly expands the application scope of silicon nitride ceramics and enables silicon nitride ceramics to be further applied in more fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A flow chart of a two-step debinding method for DLP-3D printing of silicon nitride ceramics provided by the present invention. DETAILED DESCRIPTION

[0022] The specific embodiments of the present invention are further described in detail below. It should be understood that the description of the embodiments of the present invention herein is not intended to limit the protection scope of the present invention.

[0023] Example 1

[0024] A two-step debinding method for silicon nitride ceramic DLP-3D printing, comprising the following steps:

[0025] Step S1: Put the silicon nitride mixed powder and anhydrous ethanol into a ball mill, perform wet ball milling, place the treated powder in an oven at 80-100°C for 6-12 hours, and sieve it with a 60-100 mesh screen to finally obtain the treated silicon nitride mixed powder. Specifically, in this embodiment, the treated powder is placed in an oven at 80°C for 6 hours, sieved with a 60-mesh screen, and finally obtains the treated silicon nitride mixed powder, wherein the silicon nitride mixed powder is Si3N4, Al2O3, and Y2O3, wherein the initial particle size of Si3N4 is 0.5-1μm, the initial particle size of Al2O3 is 0.2-0.7μm, and the initial particle size of Y2O3 is 0.2-1.5μm.

[0026] Step S2: Mixing resin, dispersant and photoinitiator to obtain an organic mixed liquid. The resin is one or more combinations of 1,6-hexanediol diacrylate (HDDA), trimethylolpropane triacrylate (TMPTA), pentaerythritol tri- and tetraacrylate (PET3A), pentaerythritol tetraacrylate (PET4A), and polydipentaerythritol hexaacrylate (DPHA); the dispersant is one or more combinations of modified polyolefin solution, acrylic copolymer solution, and phosphate solution; the photoinitiator is one or more combinations of trimethylbenzoyl-diphenylphosphine oxide (TPO), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, benzophenone and 2-methyl-1-(4-methylthiophenyl)-2-morpholine-1-propanone; and the raw materials are 40 to 50 parts of silicon nitride mixed powder, 30 to 50 parts of photosensitive resin, 5 to 10 parts of dispersant, and 0.5 to 2 parts of photoinitiator by volume. Specifically, in this embodiment, the resin is a mixture of PET4A, HDDA and TMPTA, the volume ratio of the three resins is 1:1:1, the dispersant is an acrylic copolymer solution, the amount of the dispersant added is 4% of the powder mass, the photoinitiator is TPO, and the amount of the photoinitiator added is 2% of the resin mass. The silicon nitride mixed powder and the organic mixed liquid treated in step S1 are ball-milled using a planetary ball mill to obtain silicon nitride ceramic slurry.

[0027] Step S3: Add silicon nitride ceramic slurry to the DLP-3D printing device and print according to the processed slice information. The printing parameters are that the time for each layer of silicon nitride ceramic slurry is 3 to 12 seconds, and the exposure intensity of each layer is 100 to 500 mj / cm 2 Specifically, in this embodiment, the exposure time of each layer is 5s, and the total exposure intensity of each layer is 300mj / cm 2 , to print the silicon nitride blank.

[0028] Step S4: Debinding the silicon nitride blank by a two-step method. In the first step, the temperature is raised to 150-400°C in an inert atmosphere for debinding, the heating rate is 0.1-1°C / min, and the holding time is 1-12h. In the second step, the debinding process is heated to 300-700°C at a heating rate of 0.1-1°C / min in an air atmosphere and kept warm for 1-12h. The inert atmosphere is preferably nitrogen. Specifically, in this embodiment, the first step is to place the DLP-3D printed silicon nitride blank in a debinding furnace and pass an inert gas, and continue to heat it to 300°C in an inert atmosphere at a heating rate of 0.1°C / min for 4h; the second step of the debinding process is to heat it to 500°C at a heating rate of 1°C / min in an air atmosphere and keep it warm for 1h.

[0029] Due to the printing characteristics of DLP-3D printing, it is necessary to add a lot of organic matter such as resin. Therefore, compared with other molding methods, DLP-3D printing has more organic matter in the green body. These organic matter affect the final quality of sintering, so they should be removed as much as possible before sintering. Direct debinding in the air will cause the air to react with a variety of different organic matter, resulting in a too fast reaction rate. Therefore, the inert atmosphere can effectively prevent the occurrence of oxidation reaction, which belongs to the debinding with a small amount of occurrence and slowness, so that the pyrolysis reaction and vaporization rate of various organic matter inside the green body at high temperature will be greatly reduced, and the cracking, bubbling and other defects caused by the large pressure difference between the inside and outside of the green body can be effectively avoided. The second step of debinding in the air atmosphere can remove the organic matter such as carbon residue remaining in the first step of debinding through oxidation reaction, ensuring that the organic matter in the silicon nitride green body is cleanly removed and defects such as cracking and bulging are avoided, so that the mechanical properties of the silicon nitride ceramics sintered in the end are significantly improved.

[0030] The first step of inert atmosphere debinding can be divided into multiple stages. The first stage is heated to 150-250℃ with an inert atmosphere, the heating rate is 0.1-1℃ / min, and the insulation time is 3-8h. The second stage continues to use inert atmosphere to debind and heat up to 250-400℃, the heating rate is 0.1-1℃ / min, and the insulation time is 1-10h. Then the second step of debinding process in air atmosphere is carried out. In this way, the multi-stage inert atmosphere can effectively prevent the occurrence of oxidation reaction, which is a debinding with a small amount of occurrence and slow, so that the thermal decomposition reaction and vaporization rate of various organic substances inside the blank at high temperature will be greatly reduced. At the same time, by determining the reaction temperature points of different organic substances, a staged heating method is adopted, and the heat preservation treatment is carried out at the temperature point where the decomposition reaction is intense, so that the silicon nitride blank has enough reaction time to eliminate the decomposable organic substances in the blank at the current temperature, and avoid the defects such as cracking of the silicon nitride blank caused by the intense decomposition of organic substances due to the continued heating, which leads to more organic substances participating in the reaction.

[0031] Step S5: The silicon nitride ceramic blank after the binder removal treatment is subjected to air pressure sintering in a nitrogen atmosphere, the pressure of the nitrogen atmosphere is 0.5-2MPa, the sintering temperature is 1700-1800°C, and the holding time is 1-4h, and finally a DLP-3D printed silicon nitride ceramic with high density and high mechanical strength is obtained. Specifically, in this embodiment, the sintering system is kept at 1700°C / 1MPa for 4h.

[0032] Example 2

[0033] A two-step debinding method for silicon nitride ceramic DLP-3D printing, comprising the following steps:

[0034] Step S1: Put the silicon nitride mixed powder and anhydrous ethanol into a ball mill and perform wet ball milling. The treated powder is placed in an oven at 80° C. for 10 hours and sieved with a 70-mesh sieve to finally obtain the treated silicon nitride mixed powder.

[0035] Step S2: Mix the resin, dispersant and photoinitiator to obtain an organic mixed liquid, wherein the resin is a mixture of PET4A, PET3A and TMPTA, the volume ratio of the three resins is 1:2:1, the dispersant is an acrylic copolymer solution, the amount of the dispersant added is 4% of the powder mass, the photoinitiator is TPO, and the amount of the photoinitiator added is 3% of the resin mass, and the silicon nitride mixed powder and the organic mixed liquid processed in step S1 are ball-milled using a planetary ball mill to obtain silicon nitride ceramic slurry.

[0036] Step S3: Add silicon nitride ceramic slurry to the DLP-3D printing device and print according to the processed slice information. The exposure time for each layer is 8s and the total exposure intensity for each layer is 400mj / cm 2 , to print the silicon nitride blank.

[0037] Step S4: Debinding the silicon nitride blank in two steps: the first step is heating the temperature to 400°C at a rate of 0.5°C / min in a nitrogen atmosphere and keeping the temperature for 7 hours; the second step is heating the temperature to 500°C at a rate of 1°C / min in an air atmosphere and keeping the temperature for 5 hours.

[0038] Step S5: The silicon nitride ceramic blank after the binder removal treatment is subjected to air pressure sintering in a nitrogen atmosphere and kept at 1700°C / 1MPa for 4 hours, thereby finally obtaining a DLP-3D printed silicon nitride ceramic with high density and high mechanical strength.

[0039] Example 3

[0040] A two-step debinding method for silicon nitride ceramic DLP-3D printing, comprising the following steps:

[0041] Step S1: Put the silicon nitride mixed powder and anhydrous ethanol into a ball mill, perform wet ball milling, place the treated powder in an oven at 80° C. for 8 hours, and sieve it with a 80-mesh sieve to finally obtain the treated silicon nitride mixed powder;

[0042] Step S2: Resin, dispersant and photoinitiator are mixed to obtain an organic mixed liquid, wherein the resin is a mixture of PET4A, HDDA and TMPTA, the volume ratio of the three resins is 3:2:1, the dispersant is an acrylic copolymer solution, the amount of the dispersant added is 4% of the powder mass, the photoinitiator is bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and the amount of the photoinitiator added is 3% of the resin mass. The silicon nitride mixed powder and the organic mixed liquid treated in step S1 are ball-milled using a planetary ball mill to obtain silicon nitride ceramic slurry.

[0043] Step S3: Add silicon nitride ceramic slurry to the DLP-3D printing device and print according to the processed slice information. The exposure time for each layer is 8s and the total exposure intensity for each layer is 400mj / cm 2 , printing of silicon nitride blank;

[0044] Step S4: Debinding the silicon nitride blank by a two-step method, wherein the first step is heating the temperature to 350°C at a heating rate of 0.4°C / min in a nitrogen atmosphere and keeping the temperature for 4 hours; the second step of the debinding process is heating the temperature to 550°C at a heating rate of 1°C / min in an air atmosphere and keeping the temperature for 1 hour;

[0045] Step S5: The silicon nitride ceramic blank after the debinding treatment is subjected to air pressure sintering in a nitrogen atmosphere, and kept at 1750°C / .0.6MPa for 4 hours. Finally, a DLP-3D printed silicon nitride ceramic with high density and high mechanical strength is obtained.

[0046] Example 4

[0047] A two-step debinding method for silicon nitride ceramic DLP-3D printing, comprising the following steps:

[0048] Step S1: Put the silicon nitride mixed powder and anhydrous ethanol into a ball mill, perform wet ball milling, place the treated powder in an oven at 100° C. for 8 hours, and sieve it with a 80-mesh sieve to finally obtain the treated silicon nitride mixed powder;

[0049] Step S2: Mix the resin, dispersant and photoinitiator to obtain an organic mixed liquid, wherein the resin is a mixture of PET4A, HDDA and TMPTA, the volume ratio of the three resins is 4:2:5, the dispersant is an acrylic copolymer solution, the amount of the dispersant added is 5% of the powder mass, the photoinitiator is bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and the amount of the photoinitiator added is 4% of the resin mass. The silicon nitride mixed powder and the organic mixed liquid treated in step S1 are ball-milled using a planetary ball mill to obtain silicon nitride ceramic slurry.

[0050] Step S3: Add silicon nitride ceramic slurry to the DLP-3D printing device and print according to the processed slice information. The exposure time for each layer is 6s and the total exposure intensity for each layer is 350mj / cm 2 , to print the silicon nitride blank.

[0051] Step S4: Debinding the silicon nitride blank in two steps: the first step is heating the temperature to 400°C at a heating rate of 0.2°C / min in a nitrogen atmosphere and keeping the temperature for 2 hours; the second step is heating the temperature to 600°C at a heating rate of 1°C / min in an air atmosphere and keeping the temperature for 3 hours.

[0052] Step S5: The silicon nitride ceramic blank after the debinding treatment is subjected to air pressure sintering in a nitrogen atmosphere, and kept at 1800°C / .0.6MPa for 4 hours, so as to finally obtain DLP-3D printed silicon nitride ceramics with high density and high mechanical strength.

[0053] Example 5

[0054] A two-step debinding method for silicon nitride ceramic DLP-3D printing, comprising the following steps:

[0055] Step S1: Put the silicon nitride mixed powder and anhydrous ethanol into a ball mill, perform wet ball milling, place the treated powder in an oven at 100° C. for 8 hours, and sieve it with a 80-mesh sieve to finally obtain the treated silicon nitride mixed powder;

[0056] Step S2: Mix the resin, dispersant and photoinitiator to obtain an organic mixed liquid, wherein the resin is a mixture of PET3A, HDDA and TMPTA, the volume ratio of the three resins is 3:2:3, the dispersant is an acrylic copolymer solution, the amount of the dispersant added is 5% of the powder mass, the photoinitiator is TPO, and the amount of the photoinitiator added is 2% of the resin mass, and the silicon nitride mixed powder and the organic mixed liquid processed in step S1 are ball-milled using a planetary ball mill to obtain silicon nitride ceramic slurry.

[0057] Step S3: Add silicon nitride ceramic slurry to the DLP-3D printing device and print according to the processed slice information. The exposure time for each layer is 6s and the total exposure intensity for each layer is 350mj / cm 2 , printing of silicon nitride blank;

[0058] Step S4: Debinding the silicon nitride blank by a two-step method, wherein the first step is heating the temperature to 300°C at a rate of 0.1°C / min in a nitrogen atmosphere and keeping the temperature for 5 hours; the second step is heating the temperature to 450°C at a rate of 0.8°C / min in an air atmosphere and keeping the temperature for 5 hours;

[0059] Step S5: The silicon nitride ceramic blank after the debinding treatment is subjected to air pressure sintering in a nitrogen atmosphere, and kept at 1800°C / 1MPa for 2 hours, thereby finally obtaining a DLP-3D printed silicon nitride ceramic with high density and high mechanical strength.

[0060] Example 6

[0061] A two-step debinding method for silicon nitride ceramic DLP-3D printing, comprising the following steps:

[0062] Step S1: Put the silicon nitride mixed powder and anhydrous ethanol into a ball mill, perform wet ball milling, place the treated powder in an oven at 100° C. for 8 hours, and sieve it with a 80-mesh sieve to finally obtain the treated silicon nitride mixed powder;

[0063] Step S2: Mix the resin, dispersant and photoinitiator to obtain an organic mixed liquid, wherein the resin is a mixture of PET3A, HDDA and TMPTA, the volume ratio of the three resins is 3:2:3, the dispersant is an acrylic copolymer solution, the amount of the dispersant added is 5% of the powder mass, the photoinitiator is bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and the amount of the photoinitiator added is 2% of the resin mass, and the silicon nitride mixed powder and the organic mixed liquid treated in step S1 are ball-milled using a planetary ball mill to obtain silicon nitride ceramic slurry.

[0064] Step S3: Add silicon nitride ceramic slurry to the DLP-3D printing device and print according to the processed slice information. The exposure time for each layer is 6s and the total exposure intensity for each layer is 350mj / cm 2 , printing of silicon nitride blank;

[0065] Step S4: Debinding the silicon nitride blank by a two-step method, wherein the first step is heating the temperature to 200°C at a heating rate of 0.5°C / min in a nitrogen atmosphere and keeping the temperature for 10 hours; the second step is heating the temperature to 600°C at a heating rate of 1°C / min in an air atmosphere and keeping the temperature for 2 hours;

[0066] Step S5: The silicon nitride ceramic blank after the debinding treatment is subjected to air pressure sintering in a nitrogen atmosphere, and kept at 1800°C / 1MPa for 2 hours, thereby finally obtaining a DLP-3D printed silicon nitride ceramic with high density and high mechanical strength.

[0067] Example 7

[0068] A two-step debinding method for silicon nitride ceramic DLP-3D printing, comprising the following steps:

[0069] Step S1: Put the silicon nitride mixed powder and anhydrous ethanol into a ball mill, perform wet ball milling, place the treated powder in an oven at 100° C. for 8 hours, and sieve it with a 80-mesh sieve to finally obtain the treated silicon nitride mixed powder;

[0070] Step S2: Mix the resin, dispersant and photoinitiator to obtain an organic mixed liquid, wherein the resin is a mixture of PET3A, HDDA and TMPTA, and the volume ratio of the three resins is 1:2:3; the dispersant is an acrylic copolymer solution, and the dispersant addition amount is 2% of the powder mass; the photoinitiator is TPO, and the photoinitiator addition amount is 2% of the resin mass; the silicon nitride mixed powder and the organic mixed liquid processed in step S1 are ball-milled using a planetary ball mill to obtain silicon nitride ceramic slurry.

[0071] Step S3: Add silicon nitride ceramic slurry to the DLP-3D printing device and print according to the processed slice information. The exposure time for each layer is 5s and the total exposure intensity for each layer is 200mj / cm 2 , printing of silicon nitride blank;

[0072] Step S4: Debinding the silicon nitride blank by a two-step method, wherein the first step is heating the temperature to 260°C at a heating rate of 0.5°C / min in a nitrogen atmosphere and keeping the temperature for 5 hours; the second step of the debinding process is heating the temperature to 510°C at a heating rate of 0.6°C / min in an air atmosphere and keeping the temperature for 2 hours;

[0073] Step S5: The silicon nitride ceramic blank after the debinding treatment is subjected to air pressure sintering in a nitrogen atmosphere, and kept at 1800°C / 2MPa for 3 hours, so as to finally obtain a DLP-3D printed silicon nitride ceramic with high density and high mechanical strength.

[0074] Example 8

[0075] A two-step debinding method for silicon nitride ceramic DLP-3D printing, comprising the following steps:

[0076] Step S1: Put the silicon nitride mixed powder and anhydrous ethanol into a ball mill, perform wet ball milling, place the treated powder in an oven at 80° C. for 8 hours, and sieve it with a 80-mesh sieve to finally obtain the treated silicon nitride mixed powder;

[0077] Step S2: Mix the resin, dispersant and photoinitiator to obtain an organic mixed liquid, wherein the resin is a mixture of PET4A, DPHA and TMPTA, and the volume ratio of the three resins is 1:1:3; the dispersant is an acrylic copolymer solution, and the dispersant addition amount is 3% of the powder mass; the photoinitiator is TPO, and the photoinitiator addition amount is 2% of the resin mass; the silicon nitride mixed powder and the organic mixed liquid processed in step S1 are ball-milled using a planetary ball mill to obtain silicon nitride ceramic slurry.

[0078] Step S3: Add silicon nitride ceramic slurry to the DLP-3D printing device and print according to the processed slice information. The exposure time for each layer is 5s and the total exposure intensity for each layer is 200mj / cm 2 , printing of silicon nitride blank;

[0079] Step S4: Debinding the silicon nitride blank by a two-step method, wherein the first step is heating the temperature to 230°C at a heating rate of 0.5°C / min in a nitrogen atmosphere and keeping the temperature for 4 hours; the second step is heating the temperature to 500°C at a heating rate of 1°C / min in an air atmosphere and keeping the temperature for 8 hours;

[0080] Step S5: The silicon nitride ceramic blank after the debinding treatment is subjected to air pressure sintering in a nitrogen atmosphere, and kept at 1700°C / 2MPa for 3 hours, so as to finally obtain a DLP-3D printed silicon nitride ceramic with high density and high mechanical strength.

[0081] Example 9

[0082] A two-step debinding method for silicon nitride ceramic DLP-3D printing, comprising the following steps:

[0083] Step S1: Put the silicon nitride mixed powder and anhydrous ethanol into a ball mill, perform wet ball milling, place the treated powder in an oven at 80° C. for 8 hours, and sieve it with a 80-mesh sieve to finally obtain the treated silicon nitride mixed powder;

[0084] Step S2: Mix the resin, dispersant and photoinitiator to obtain an organic mixed liquid, wherein the resin is a mixture of PET4A, DPHA and TMPTA, the volume ratio of the three resins is 2:1:3, the dispersant is an acrylic copolymer solution, the amount of the dispersant added is 4% of the powder mass, the photoinitiator is bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and the amount of the photoinitiator added is 4% of the resin mass, and the silicon nitride mixed powder and the organic mixed liquid treated in step S1 are ball-milled using a planetary ball mill to obtain silicon nitride ceramic slurry.

[0085] Step S3: Add silicon nitride ceramic slurry to the DLP-3D printing device and print according to the processed slice information. The exposure time for each layer is 8s and the total exposure intensity for each layer is 500mj / cm 2 , printing of silicon nitride blank;

[0086] Step S4: Debinding the silicon nitride blank by a two-step method, wherein the first step is heating the temperature to 200°C at a rate of 0.5°C / min in a nitrogen atmosphere and keeping the temperature for 6 hours; the second step is heating the temperature to 500°C at a rate of 1°C / min in an air atmosphere and keeping the temperature for 6 hours;

[0087] Step S5: The silicon nitride ceramic blank after the binder removal treatment is subjected to air pressure sintering in a nitrogen atmosphere and kept at 1700°C / 1MPa for 2 hours, thereby finally obtaining a DLP-3D printed silicon nitride ceramic with high density and high mechanical strength.

[0088] Compared with the prior art, the two-step debinding method for silicon nitride ceramic DLP-3D printing provided by the present invention effectively prevents the occurrence of oxidation reaction by debinding in an inert atmosphere in the first step, so that the pyrolysis reaction and vaporization rate of various organic substances inside the blank at high temperature will be greatly reduced, and the cracking, bubbling and other defects caused by the large pressure difference between the inside and outside of the blank can be effectively avoided. In air debinding, the organic substances such as carbon residues remaining in the first step of debinding can be removed through oxidation reaction, ensuring that the organic substances in the silicon nitride blank are cleanly removed and defects such as cracking and bulging are avoided, so that the mechanical properties of the finally sintered silicon nitride ceramics are significantly improved. Compared with the silicon nitride ceramics prepared by air debinding in the past, the relative density of the silicon nitride ceramics prepared by the two-step debinding method is increased from 90.16% to 96.86%, and the flexural strength is increased from 281.52MPa to 590.39MPa, and the mechanical properties are significantly improved. The silicon nitride ceramics prepared by this method not only have performance close to that of silicon nitride ceramics prepared by traditional preparation methods, but also combine the great advantages of DLP-3D printing technology in complex structure molding, which greatly expands the application scope of silicon nitride ceramics and enables silicon nitride ceramics to be further applied in more fields.

[0089] The above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modification, equivalent substitution or improvement within the spirit of the present invention is included in the scope of the claims of the present invention.

Claims

1. A two-step debinding method for silicon nitride ceramic DLP-3D printing, comprising the following steps: Step S1: placing silicon nitride mixed powder and anhydrous ethanol into a ball mill for wet ball milling, placing the treated powder in an oven for drying and sieving with a sieve to finally obtain treated silicon nitride mixed powder; Step S2: mixing the resin, the dispersant and the photoinitiator to obtain an organic mixed liquid, and ball-milling the silicon nitride mixed powder and the organic mixed liquid processed in step S1 to obtain silicon nitride ceramic slurry; Step S3: adding silicon nitride ceramic slurry into the DLP-3D printing device and printing according to the processed slice information; Step S4: Debinding the silicon nitride blank by a two-step method, wherein the first debinding process is heating the temperature to 150-400° C. in an inert atmosphere and keeping the temperature, and the second debinding process is heating the temperature to 300-700° C. in an air atmosphere and keeping the temperature; Step S5: The silicon nitride ceramic blank that has undergone the debinding treatment is subjected to air pressure sintering in a nitrogen atmosphere to finally obtain DLP-3D printed silicon nitride ceramics.

2. The two-step debinding method for silicon nitride ceramic DLP-3D printing according to claim 1, characterized in that: In the above step S1, the treated powder is placed in an oven at 80-100° C. for drying for 6-12 hours, and sieved using a 60-100 mesh sieve.

3. The two-step debinding method for silicon nitride ceramic DLP-3D printing according to claim 1, characterized in that: In the above step S1, the silicon nitride mixed powder is Si3N4, Al2O3, and Y2O3, wherein the initial particle size of Si3N4 is 0.5-1 μm, the initial particle size of Al2O3 is 0.2-0.7 μm, and the initial particle size of Y2O3 is 0.2-1.5 μm.

4. The two-step debinding method for silicon nitride ceramic DLP-3D printing according to claim 1, characterized in that: In the above step S2, the resin is one or a combination of 1,6-hexanediol diacrylate (HDDA), trimethylolpropane triacrylate (TMPTA), pentaerythritol tri- and tetraacrylates (PET3A), pentaerythritol tetraacrylate (PET4A), and polydipentaerythritol hexaacrylate (DPHA); the dispersant is one or a combination of modified polyolefin solution, acrylic copolymer solution, and phosphate solution; the photoinitiator is one or a combination of trimethylbenzoyl-diphenylphosphine oxide (TPO), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, benzophenone, and 2-methyl-1-(4-methylthiophenyl)-2-morpholine-1-propanone; and the raw materials are 40 to 50 parts by volume of silicon nitride mixed powder, 30 to 50 parts of photosensitive resin, 5 to 10 parts of dispersant, and 0.5 to 2 parts of photoinitiator.

5. The two-step debinding method for silicon nitride ceramic DLP-3D printing according to claim 1, characterized in that: In the above step S3, the printing parameters are as follows: the time for each layer of silicon nitride ceramic slurry is 3 to 12 seconds, and the exposure intensity of each layer is 100 to 500 mj / cm 2 .

6. The two-step debinding method for silicon nitride ceramic DLP-3D printing according to claim 1, characterized in that: In the above step S4, the heating rate of the first step is 0.1-1°C / min, and the insulation time is 1-12h, and the heating rate of the second step is 0.1-1°C / min, and the insulation time is 1-12h.

7. The two-step debinding method for silicon nitride ceramic DLP-3D printing according to claim 1, characterized in that: In the above step S4, the preferred first step of inert atmosphere debinding can be divided into multiple stages. In the first stage, the temperature is raised to 150-250°C in an inert atmosphere at a heating rate of 0.1-1°C / min and a holding time of 3-8h. In the second stage, the temperature is raised to 250-400°C in an inert atmosphere at a heating rate of 0.1-1°C / min and a holding time of 1-10h for debinding.

8. The two-step debinding method for silicon nitride ceramic DLP-3D printing according to claim 1, characterized in that: In the above step S5, the pressure of the nitrogen atmosphere is 0.5-2 MPa, the sintering temperature is 1700-1800° C., and the holding time is 1-4 h.

9. The two-step debinding method for silicon nitride ceramic DLP-3D printing according to claim 1, characterized in that: The inert atmosphere is nitrogen.

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