Dissolvable 3d printed silicon nitride dental ceramic and method of making

Abstract

The application belongs to the technical field of dental ceramic materials, and particularly relates to a DIW 3D printing silicon nitride dental ceramic and a preparation method thereof. The preparation method comprises the following steps: (1) adding a crosslinking agent and a dispersing agent into polysiloxane to obtain a mixed base liquid; (2) adding an organic solvent into the mixed base liquid, and then adding silicon nitride ceramic powder after ultrasonic dispersion to obtain a printing slurry; (3) adopting a DIW process to perform 3D printing on the printing slurry to obtain a silicon nitride ceramic body; and (4) sequentially performing heat curing and heat pyrolysis treatment on the silicon nitride ceramic body to obtain the DIW 3D printing silicon nitride dental ceramic. By selecting polysiloxane as a binder, the polysiloxane can be used in cooperation with an additive and silicon nitride powder to form a stable slurry suitable for the DIW printing process in a normal temperature environment. After subsequent heat curing and heat pyrolysis treatment, the organic phase of the polysiloxane is gradually converted into an inorganic phase, and the density and mechanical properties of the silicon nitride dental ceramic can be effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of dental ceramic materials technology, specifically relating to DIW 3D printing of silicon nitride dental ceramics and its preparation method. Background Technology

[0002] Silicon nitride ceramics (Si3N4) have significant applications in dentistry. Their color closely resembles natural teeth, allowing them to blend seamlessly with surrounding teeth for aesthetically pleasing restorations. Furthermore, silicon nitride ceramics exhibit excellent wear resistance and corrosion resistance, effectively resisting mechanical wear during daily chewing and the erosion from acids and alkalis in the oral environment. Based on these characteristics, silicon nitride ceramics have become an important choice for dental restorations such as crowns and bridges.

[0003] Ceramic 3D printing technology, based on the core concept of layer-by-layer material stacking, possesses irreplaceable advantages in the flexible fabrication of three-dimensional structures. Theoretically, it can form structures of arbitrary shapes without the need for molds, which is difficult to achieve with traditional manufacturing methods. Ceramic 3D printing technologies mainly include stereolithography, digital light processing, two-photon polymerization, binder jetting, direct-write (DIW) printing, and selective laser sintering. Compared with other methods, direct-write 3D printing (DIW 3D printing) technology has advantages such as high solids content, high efficiency, and low cost.

[0004] Chinese patent CN113372114A discloses a method for preparing an extrusion 3D printing material for zirconia ceramics. This method involves mixing zirconia powder, a dispersant, a binder, and a plasticizer to prepare a slurry suitable for extrusion 3D printing of zirconia ceramics. This material can manufacture zirconia ceramic products with excellent mechanical properties and biocompatibility, saving mold costs, shortening production time, and improving economic efficiency. Chinese patent CN109133908A discloses a slurry for bio-based calcium phosphate 3D printing ceramics and its preparation method. This method utilizes DIW 3D printing technology to print the bio-based ceramic slurry and then sintersects it at high temperatures, ultimately obtaining a ceramic body with high precision, good elastic modulus, and good flexural strength. However, most of the aforementioned 3D printing ceramic slurries use traditional organic binders that are not heat-resistant to mix with ceramic powder, and then the slurry is prepared, printed, degreased, and sintered. During this process, the organic binder network gradually disintegrates, and the remaining ceramic particles form a porous green body skeleton due to the lack of effective bonding force. The density of the sample decreases, and objectively, a higher sintering temperature threshold is needed to overcome the diffusion mass transfer resistance caused by the increased porosity, which significantly increases the production cost of the product.

[0005] Unlike traditional organic binders, organosilicon precursor binders are organic macromolecules containing target elements. After curing and low-temperature pyrolysis, the organic phase can be transformed into an inorganic ceramic phase, which can improve the density of the final ceramic material and reduce its shrinkage rate. Therefore, higher sintering temperatures are not required, significantly reducing costs. Furthermore, current research shows that organosilicon precursors can be uniformly mixed with dispersants and fillers to achieve stable printing of the slurry.

[0006] Although organosilicon precursors have shown unique advantages in the field of high-temperature ceramic precursors, their application in DIW 3D printing technology is still in the exploratory stage. The related rheological behavior regulation, printing process adaptability, and structure-property correlation mechanisms are not yet clear. This research gap directly restricts the application and development of this type of material in the fields of high-precision complex ceramic component manufacturing and medical applications, and it is urgent to break through the technical bottleneck through systematic process-performance synergistic optimization research. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a DIW 3D printed silicon nitride dental ceramic. By selecting polysiloxane as a binder, it can synergistically form a stable slurry adapted to the DIW printing process with additives and silicon nitride powder at room temperature. Subsequently, through thermosetting and thermal decomposition treatment, the organic phase of polysiloxane is gradually transformed into an inorganic phase, which can effectively improve the density and mechanical properties of silicon nitride dental ceramic.

[0008] Another object of the present invention is to provide a method for preparing DIW 3D printed silicon nitride dental ceramics.

[0009] The method for preparing DIW 3D printed silicon nitride dental ceramics according to the present invention includes the following steps:

[0010] (1) Add crosslinking agent and dispersant to polysiloxane, and stir evenly using a vacuum homogenizer to obtain a mixed base liquid;

[0011] (2) Add organic solvent to the mixed base liquid, disperse it by ultrasonication, add silicon nitride ceramic powder, and stir it evenly with a vacuum homogenizer to obtain printing paste;

[0012] (3) The printing paste is 3D printed using the DIW process. First, the printing paste is introduced into the paste tank, then the printing model is imported into the DIW equipment, and the printing parameters of the instrument are adjusted. Finally, the model is sliced ​​using slicing software, and then printed layer by layer by the equipment to obtain the silicon nitride ceramic blank.

[0013] (4) The silicon nitride ceramic blank is subjected to thermal curing and thermal pyrolysis treatment in sequence to obtain DIW 3D printed silicon nitride dental ceramic.

[0014] The polysiloxane is prepared by reacting tetramethylcyclotetrasiloxane and tetramethyltetravinylcyclotetrasiloxane in the presence of a caster catalyst, specifically including the following steps:

[0015] At room temperature and pressure, tetramethylcyclotetrasiloxane and tetramethyltetravinylcyclotetrasiloxane in a molar ratio of (0.8-1.2):1 are mixed and stirred continuously until a uniform and transparent solution is formed. Castella catalyst (0.5-2 wt.% of the total amount of tetramethylcyclotetrasiloxane and tetramethyltetravinylcyclotetrasiloxane) is added and stirred for 8-12 hours to obtain polysiloxane.

[0016] The crosslinking agent is dicumyl peroxide; the dispersant is KOS 110.

[0017] The organic solvent is tetrahydrofuran; the D50 particle size of the silicon nitride ceramic powder is 0.5-1 μm.

[0018] The amount of crosslinking agent added is 2.5-5 wt. of polysiloxane; the amount of dispersant added is 10-20 wt. of silicon nitride ceramic powder.

[0019] The amount of organic solvent added is 20-30 wt. of polysiloxane; the amount of silicon nitride ceramic powder added is 65-70 wt. of the total amount of polysiloxane, organic solvent and silicon nitride ceramic powder.

[0020] The 3D printing speed is 20-35 mm / s, the printing nozzle diameter is 0.35-0.5 mm, and the printing pressure is 0.2-0.5 kPa.

[0021] In step (1), the speed of the vacuum homogenizer is 300-500 rpm and the stirring time is 9-30 min; in step (2), the speed of the vacuum homogenizer is 1500-2000 rpm and the stirring time is 4-6 min.

[0022] The thermosetting process is as follows: the temperature is raised to 95-105℃, 115-125℃, 135-145℃, 155-165℃, and 175-185℃ respectively, and the temperature is maintained at each temperature for 2.5-3 hours.

[0023] The thermal pyrolysis temperature is 1000-1100℃, the thermal pyrolysis time is 1-2h, the heating rate is 2℃ / min, and the cooling rate is 5℃ / min.

[0024] The DIW 3D printed silicon nitride dental ceramics are prepared using the aforementioned method for preparing DIW 3D printed silicon nitride dental ceramics.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) This invention uses an organosilicon precursor—polysiloxane—as a key material component. This precursor exhibits a molecular structure and processability similar to conventional polymers at room temperature, and therefore can be prepared using common molding processes such as 3D printing. During high-temperature heat treatment, the precursor undergoes a decomposition reaction, gradually transforming from an organic polymer into an inorganic ceramic phase. This transformation process achieves an integrated structural evolution from organic to inorganic, enabling the material to possess both the easy processing of organic materials and the high-performance characteristics of inorganic ceramics.

[0027] (2) The organosilicon precursor used in this invention forms in-situ ceramics during the ceramicization process. This process helps to fill the micropores inside the material, thereby promoting densification. In addition, by designing the molecular structure of the organosilicon precursor, the volume change of the material under high temperature environment can be limited, thereby reducing the deformation risk during molding and sintering. With its unique conversion mechanism, the density of silicon nitride ceramics prepared by it is significantly improved, while the overall shrinkage rate is effectively controlled.

[0028] (3) The silicon nitride ceramics prepared by this invention can achieve densification and performance optimization at relatively low sintering temperatures, without relying on excessively high sintering temperatures. This characteristic not only reduces the requirements for preparation equipment and energy consumption, but also reduces the dependence on high-temperature environment control, ultimately significantly reducing the preparation cost. Therefore, this invention achieves high-performance silicon nitride ceramic preparation while also possessing good economic efficiency and process feasibility;

[0029] (4) Traditional silicon nitride ceramic manufacturing typically involves multiple separate processes such as "forming, debinding, sintering, and post-treatment and bonding," resulting in complex processes, low efficiency, weak interfacial bonding, and susceptibility to defects. This invention, through integrated innovation of "materials, processes, and structure," enables simultaneous morphological shaping and material functionalization prototype construction during a single printing process, effectively breaking through the traditional technical barriers of "step-by-step preparation + post-bonding." This innovation not only avoids performance loss and interfacial problems caused by multiple processing steps but also significantly shortens the manufacturing cycle, improves the integrity and reliability of components, and provides a new technical path for the efficient preparation of high-performance, personalized ceramic restorations in the dental field. Detailed Implementation

[0030] The present invention will be further described below with reference to the embodiments.

[0031] Unless otherwise specified, the raw materials used in the examples and comparative examples are all commercially available materials, and the process methods used in the examples and comparative examples are all conventional methods in the art.

[0032] The following is a description of some of the raw materials used in the examples and comparative examples:

[0033] KOS 110, purchased from Guangzhou Kangou Shuang Trading Co., Ltd.

[0034] The polysiloxane has a weight-average molecular weight of 600 g / mol and a number-average molecular weight of 580 g / mol. Its preparation method is as follows:

[0035] At room temperature and pressure, equimolar amounts of tetramethylcyclotetrasiloxane and tetramethyltetravinylcyclotetrasiloxane were introduced into a flask and stirred continuously until a homogeneous and transparent solution was formed. A caster catalyst (1 wt.% of the total amount of tetramethylcyclotetrasiloxane and tetramethyltetravinylcyclotetrasiloxane) was then added, and the mixture was stirred for 12 hours to obtain polysiloxane. The polysiloxane is a viscous, transparent liquid.

[0036] Polycarbosilane, purchased from Suzhou Sailife Ceramic Fiber Co., Ltd.

[0037] Silicon nitride ceramic powder, D 50 The particle size is 1 μm.

[0038] Example 1

[0039] The method for preparing DIW 3D printed silicon nitride dental ceramics includes the following steps:

[0040] (1) At room temperature, add 0.25g of dicumyl peroxide and 2.7g of KOS 110 to 10g of polysiloxane, and stir three times with a vacuum homogenizer for 3 minutes each time at a speed of 500 rpm to obtain a mixed base liquid.

[0041] (2) Add 2.5g of tetrahydrofuran to the mixed base liquid, ultrasonically disperse it for 30min under 300W, then add 26.6g of silicon nitride ceramic powder, and stir it three times with a vacuum homogenizer for 100s each time at a speed of 1800rpm to obtain the printing paste.

[0042] (3) Set the printing nozzle diameter of the DIW equipment to 0.45 mm, the printing speed to 30 mm / s, and the printing pressure to 0.3 kPa. On the alumina ceramic substrate coated with Vaseline, the printing paste is 3D printed using the DIW process according to the preset printing path to obtain a silicon nitride ceramic blank. After drying at 60°C for 3 hours, it is taken out.

[0043] (4) The dried silicon nitride ceramic blank is placed in a vacuum curing oven for thermal curing. The thermal curing process is as follows: the temperature is raised to 100℃, 120℃, 140℃, 160℃ and 180℃ respectively, and held at each temperature for 3h. The thermally cured sample is placed in a tube furnace for thermal pyrolysis. Under air atmosphere, the temperature is raised from room temperature to 1100℃ at a heating rate of 2℃ / min and held for 1h. Then the sample is cooled to room temperature at a cooling rate of 5℃ / min to obtain DIW 3D printed silicon nitride dental ceramic.

[0044] Example 2

[0045] The method for preparing DIW 3D printed silicon nitride dental ceramics includes the following steps:

[0046] (1) At room temperature, add 0.25g of dicumyl peroxide and 2.4g of KOS 110 to 5g of polysiloxane, and stir three times with a vacuum homogenizer for 10 minutes each time at a speed of 300 rpm to obtain a mixed base liquid.

[0047] (2) Add 1.5g of tetrahydrofuran to the mixed base liquid, ultrasonically disperse it for 30min under 300W, then add 13.2g of silicon nitride ceramic powder, and stir it three times with a vacuum homogenizer for 120s each time at a speed of 1800rpm to obtain the printing paste.

[0048] (3) Set the printing nozzle diameter of the DIW equipment to 0.5 mm, the printing speed to 35 mm / s, and the printing pressure to 0.2 kPa. On the alumina ceramic substrate coated with Vaseline, the printing paste is 3D printed using the DIW process according to the preset printing path to obtain a silicon nitride ceramic blank. After drying at 70°C for 3 hours, it is taken out.

[0049] (4) The dried silicon nitride ceramic blank is placed in a vacuum curing oven for thermal curing. The thermal curing process is as follows: the temperature is raised to 100℃, 120℃, 140℃, 160℃ and 180℃ respectively, and held at each temperature for 3h. The thermally cured sample is placed in a tube furnace for thermal pyrolysis. Under air atmosphere, the temperature is raised from room temperature to 1100℃ at a heating rate of 2℃ / min and held for 1h. Then the sample is cooled to room temperature at a cooling rate of 5℃ / min to obtain DIW 3D printed silicon nitride dental ceramic.

[0050] Example 3

[0051] The method for preparing DIW 3D printed silicon nitride dental ceramics includes the following steps:

[0052] (1) At room temperature, add 0.4g of dicumyl peroxide and 3.8g of KOS 110 to 10g of polysiloxane, and stir three times with a vacuum homogenizer for 8 minutes each time at a speed of 400 rpm to obtain a mixed base liquid.

[0053] (2) Add 2.5g of tetrahydrofuran to the mixed base liquid, ultrasonically disperse it for 30min under 300W, then add 25.4g of silicon nitride ceramic powder, stir it three times with a vacuum homogenizer for 120s each time, and the speed is 1800rpm to obtain the printing paste.

[0054] (3) Set the printing nozzle diameter of the DIW equipment to 0.35 mm, the printing speed to 20 mm / s, and the printing pressure to 0.5 kPa. On the alumina ceramic substrate coated with Vaseline, the printing paste is 3D printed using the DIW process according to the preset printing path to obtain a silicon nitride ceramic blank. After drying at 70°C for 3 hours, it is taken out.

[0055] (4) The dried silicon nitride ceramic blank is placed in a vacuum curing oven for thermal curing. The thermal curing process is as follows: the temperature is raised to 100℃, 120℃, 140℃, 160℃ and 180℃ respectively, and held at each temperature for 3h. The thermally cured sample is placed in a tube furnace for thermal pyrolysis. Under air atmosphere, the temperature is raised from room temperature to 1100℃ at a heating rate of 2℃ / min and held for 1h. Then the sample is cooled to room temperature at a cooling rate of 5℃ / min to obtain DIW 3D printed silicon nitride dental ceramic.

[0056] Comparative Example 1

[0057] The difference from Example 1 is that in step (1), dicumyl peroxide and KOS 110 are not added, but otherwise the same as in Example 1.

[0058] Comparative Example 2

[0059] The difference from Example 1 is that in step (3), the diameter of the printing nozzle is 0.6 mm, and the rest is the same as in Example 1.

[0060] Comparative Example 3

[0061] The difference from Example 1 is that step (4) is as follows: the dried silicon nitride ceramic blank is placed in a tube furnace for thermal pyrolysis, heated from room temperature to 1100°C at a heating rate of 2°C / min in an air atmosphere, held for 1 hour, and then cooled to room temperature at a cooling rate of 5°C / min to obtain DIW 3D printed silicon nitride dental ceramic.

[0062] Comparative Example 4

[0063] The difference from Example 1 is that in step (1), polysiloxane is replaced with polycarbosilane in equal amounts, while the rest is the same as in Example 1.

[0064] The performance of the silicon nitride dental ceramics prepared in the examples and comparative examples was tested, and the test methods are as follows:

[0065] Vickers hardness: Tested according to GB / T 16534-2009;

[0066] Density, porosity, and water absorption were tested using the Archimedes method of water displacement.

[0067] Bending strength: Tested in accordance with ISO 14704:2016;

[0068] Impact resistance: The impact resistance of the samples was tested using a CHAPY IZOD pendulum impact testing machine from Beijing Chuangcheng Zhijia Technology Co., Ltd. 55mm×10mm×10mm specimens were selected, with a support span of 15mm and an impact rate of 5mm / min. The experimental results are the average of 3-5 specimens.

[0069] The test results are shown in Table 1.

[0070] Table 1 Performance Test Results

[0071]

[0072] As shown in Table 1, when the mass percentages of each component (including DCP crosslinking agent, polysiloxane, silicon nitride ceramic powder, tetrahydrofuran, and KOS 110) are within the range defined in this invention, the silicon nitride ceramic samples prepared by DIW 3D printing technology exhibit complete morphology and uniform structure. After high-temperature pyrolysis, the resulting composite ceramic skeleton demonstrates excellent mechanical strength and comprehensive physical properties. This is due to the synergistic effect of the thermosetting and pyrolysis processes: during the thermosetting stage, the system is heated and held at different temperatures in stages, causing the polysiloxane to undergo gradual physicochemical changes. In the low-temperature range (95-105℃), small molecule volatiles are released. As the temperature rises to the medium-temperature range (135-145℃ and above), the polysiloxane molecular chains break and recombine, and the oligomers further decompose and volatilize. Entering the pyrolysis stage (1000-1100℃), the precursor undergoes a ceramic transformation, and the molecules are reconstructed through chemical bonds (forming Si-O covalent bonds, CN bonds, etc.), constructing a dense and stable ceramic phase structure. This chemical bonding and microstructure optimization significantly improves the mechanical and physical properties of the material, ultimately endowing silicon nitride dental ceramics with excellent overall performance.

[0073] In Comparative Example 1, the lack of dicumyl peroxide and KOS 110 resulted in insufficient compatibility and dispersion uniformity of the components within the slurry. During subsequent heat treatment, the insufficiently cross-linked system failed to effectively bind small molecules, causing them to escape prematurely during the heating phase. This not only reduced the ceramic yield of the precursor but also disrupted the continuity of the material structure, ultimately leading to a significant decrease in the physical and chemical properties of the resulting sample. In Comparative Example 2, increasing the printing nozzle diameter resulted in an excessively large nozzle diameter, increasing the width of the printed lines and reducing the dimensional accuracy and shape resolution of the printed components. Furthermore, due to the increased gaps between the printing paths, the small molecules encapsulated within the slurry failed to fully release at low temperatures and rapidly vaporized and escaped during high-temperature heat treatment, generating significant internal stress, causing micro-cracks and structural defects, thus impairing the overall performance of the final product. In Comparative Example 3, the sample underwent a slow, gradual curing process after molding and was directly subjected to high-temperature heat treatment. Under these conditions, the migration and diffusion of small organic molecules within the sample are insufficient, failing to achieve orderly release. This results in the generation of a large amount of gas in a short period during the high-temperature pyrolysis stage, causing sample expansion, cracking, and even local collapse, severely affecting ceramic yield and material density. In Comparative Example 4, the sample was subjected to pyrolysis treatment in an air atmosphere. The carbon component in polycarbosilane is largely lost in gaseous forms such as CO or CO2 in the high-temperature oxidizing environment, causing an imbalance in elemental composition and exacerbating mass loss. In contrast, polysiloxane can form a more stable Si-O network during air pyrolysis, resulting in a higher ceramic yield. Therefore, the polycarbosilane sample suffers from a looser structure and reduced density due to carbon loss, ultimately leading to significantly inferior physicochemical properties compared to the polysiloxane system.

Claims

1. A method for preparing DIW 3D printed silicon nitride dental ceramics, characterized in that, Includes the following steps: (1) Add crosslinking agent and dispersant to polysiloxane, stir evenly to obtain mixed base liquid; the preparation method of polysiloxane is as follows: under normal temperature and pressure, introduce equimolar amounts of tetramethylcyclotetrasiloxane and tetramethyltetravinylcyclotetrasiloxane into a flask, stir continuously until a uniform and transparent solution is formed, add caster catalyst, the amount of caster catalyst added is 1 wt.% of the total amount of tetramethylcyclotetrasiloxane and tetramethyltetravinylcyclotetrasiloxane, stir for 12 h to obtain polysiloxane; the crosslinking agent is dicumyl peroxide; the dispersant is KOS 110; (2) Add organic solvent to the mixed base liquid, disperse it ultrasonically, add silicon nitride ceramic powder, stir evenly, and obtain printing paste; (3) The printing paste is 3D printed using the DIW process to obtain a silicon nitride ceramic blank; wherein the printing nozzle diameter is 0.35-0.5mm, the printing speed is 20-35mm / s, and the printing pressure is 0.2-0.5KPa; (4) The silicon nitride ceramic blank is subjected to thermal curing and thermal decomposition treatment in sequence to obtain DIW 3D printed silicon nitride dental ceramic; wherein, the thermal curing process is as follows: the temperature is raised to 95-105℃, 115-125℃, 135-145℃, 155-165℃ and 175-185℃ respectively, and the temperature is held for 2.5-3h at each temperature point; the thermal decomposition temperature is 1000-1100℃ and the thermal decomposition time is 1-2h.

2. The method for preparing DIW 3D printed silicon nitride dental ceramics according to claim 1, characterized in that, The organic solvent is tetrahydrofuran; the D50 particle size of the silicon nitride ceramic powder is 0.5-1 μm.

3. The method for preparing DIW 3D printed silicon nitride dental ceramics according to claim 1, characterized in that, The amount of crosslinking agent added is 2.5-5 wt. of polysiloxane; the amount of dispersant added is 10-20 wt. of silicon nitride ceramic powder.

4. The method for preparing DIW 3D printed silicon nitride dental ceramics according to claim 1, characterized in that, The amount of organic solvent added is 20-30 wt. of polysiloxane; the amount of silicon nitride ceramic powder added is 65-70 wt. of the total amount of polysiloxane, organic solvent and silicon nitride ceramic powder.

5. A DIW 3D printed silicon nitride dental ceramic, characterized in that, It is prepared by the method for preparing DIW3D printed silicon nitride dental ceramics according to any one of claims 1-4.

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