TWI806320B - Method for preparing ceramic slurry that can be used for three-dimensional printing - Google Patents

Abstract

The main purpose of the present invention is to provide a method for preparing ceramic slurry that can be used for three-dimensional printing. Polyvinyl alcohol is used as an adhesive in the composition of the ceramic slurry. After three-dimensional printing, the process of freezing and thawing is added to promote water-based dispersion. The crystallization of polyvinyl alcohol in the liquid produces green embryos with better structural strength, making the embryos less likely to break during the subsequent drying and sintering processes. The present invention overcomes the problems of low strength of general 3D-printed ceramic green bodies, which are prone to cracks during the drying and sintering process, and support materials are needed when printing objects with complex structures. In addition, the present invention can achieve the goals of high solid content, high green strength, three-dimensional printing, and sample post-shaping while using non-toxic water-based slurry, which is conducive to customizing industrial samples with complex structures and high-value semiconductor equipment. on the ceramic fixture.

Description

Method for preparing ceramic slurry that can be used for three-dimensional printing

The present invention proposes a method for making ceramic slurry for three-dimensional printing. This technology uses the crystallization produced after polyvinyl alcohol is frozen to gel the printed sample, and solve the problem of cracking and sintering during the drying and sintering process. Objects with more complex structures require simultaneous printing of a large number of support materials to ensure the formation of the structure and the difficulty of printing, especially for the 3D printing process of ceramic materials.

In recent years, 3D printing, also known as additive manufacturing, is a technology that has gradually attracted the attention of the industry and academia. The basic mode of operation is to slice the 3D graphic files drawn by the computer layer by layer, and then the printer creates the appearance of the model in the graphic files in a stacked and layered manner. 3D printing can be used to manufacture complex structures that are difficult to achieve with traditional material processes, and can be designed according to customized needs. At present, the materials that can be used for 3D printing are mainly polymers and metals. Ceramic materials require extreme heat treatment processes, and the difficulty of 3D printing is higher than the above two. However, the high heat resistance, acid and alkali resistance, and high mechanical strength of ceramic materials are widely used in various engineering fields. For example, in Taiwan's semiconductor industry, wafers need to be converted by robotic arms in different processes. Considering the The high temperature and corrosive environment in the process, the robotic arm mainly made of ceramic materials Arm jigs are preferred. However, traditional ceramic preparation still requires procedures such as molds and cutting, and the cost of time and money is quite high in the testing of different fixtures. If ceramic fixtures can be prepared by 3D printing, the functions of different designs can be quickly tested, saving manpower and material resources.

At present, the development of 3D printing process for ceramic materials can be roughly divided into binder jetting, stereolithography and direct ink writing. In the binder jetting method, the nozzle of the printing machine sprays the adhesive on the cylinder loaded with ceramic powder, and the three-dimensional shape can be gradually drawn by the movement of the nozzle and the cylinder. The final bonded green embryo is removed from the powder and sintered. In the stereolithography method, ceramic powder or ceramic precursors are first dispersed in a polymer monomer-based adhesive, and then the printer projects a light source on the ink to control the light source pattern in each layer of the structure. After the molecular monomers are polymerized according to the specified shape, the green embryo can be obtained. The advantages of stereolithography lie in smaller layer thickness and higher fineness. However, the photocuring process requires the use of a high proportion of polymer monomer binders. In the subsequent sintering process of ceramic materials, it is easy to cause the binder to volatilize. cause cracking of the sample. Therefore, only a few ceramic materials can be printed in this way, and the application range of materials is relatively narrow. In the direct writing method, the slurry of ceramic powder is mainly extruded through a nozzle and stacked into a green body of a specified three-dimensional shape. Compared with the above two methods, this method is easier to apply to a variety of different ceramic materials, and can be simultaneously Perform 3D printing of various materials. The main disadvantage of the direct writing method is that the fineness is low, and the nozzle is easy to block. How to control the dispersion of ceramic powder in slurry The extent and the rheological behavior of the paste are the main challenges of direct writing.

In the direct writing printing method, the preparation method of the ceramic slurry and the ratio of each component are the key to the printing effect. In order to avoid shrinkage and cracking of the finished product after sintering, the proportion of solid powder in the slurry is generally high, about 30 to 50vol%, and a small amount of adhesive is used. In the slurry with a high solid ratio, appropriate dispersants such as polyacids and polymer electrolytes are needed to strengthen the charge force on the surface of the particles to reduce the aggregation and precipitation between particles. In addition, such a high-concentration slurry needs to have proper rheological behavior for printing. Generally, the slurry needs to have shear-thinning viscoelastic properties, and the viscosity needs to decrease with the increase of the shear rate. This allows ink to be extruded using lower pressures in the high shear rate environment of direct writing. In addition, the slurry also needs to have a high storage modulus (G') and a high yield stress (yield stress), so that the liquid ink can quickly return to the elastic behavior close to the solid state after extrusion, and maintain the structure without being affected by gravity. collapse.

In view of the above-mentioned shortcomings of the conventional technology, the main purpose of the present invention is to provide a method for preparing ceramic slurry that can be used for three-dimensional printing. This technology uses the crystallization produced after freezing polyvinyl alcohol to gel the printed sample , to solve the problems of cracks in the drying and sintering process and objects with more complex structures that need to print a large number of supports simultaneously to ensure the formation of the structure and the difficulty of printing.

According to the idea of the present invention, there is provided a three-dimensional printing The preparation method of the ceramic slurry, the preparation steps include: providing a plasticizer and a dispersant, mixing uniformly, then mixing with an adhesive, and finally adding a yttrium stabilized zirconia powder for sufficient stirring and defoaming , to prepare the ceramic slurry that can be used for three-dimensional printing.

In the composition of the ceramic slurry proposed in the above steps, the plasticizer is polyethylene glycol (PEG-400), wherein the weight ratio of the yttrium stabilized zirconia powder to the plasticizer is 1: 0.05-0.2.

In the ceramic slurry composition proposed in the above steps, the dispersant is a mixture of citric acid and sodium hydroxide, wherein the weight ratio of the yttrium stabilized zirconia powder to the dispersant is 1:0.01-0.05.

In the ceramic slurry composition proposed in the above steps, the adhesive is polyvinyl alcohol (PVA; molecular weight 88,000~97,000), wherein the weight ratio of the yttrium stabilized zirconia powder to the adhesive is 1: 0.05-0.2.

A method for preparing ceramic slurry that can be used for three-dimensional printing proposed by the present invention further includes a step of preparing a plastic green body: the ceramic slurry after three-dimensional printing is placed in a freezer for a freezing process to promote the crystallization of PVA , and then thawed at room temperature to form a plastic embryo with a gel structure. The temperature range of the freezing process is 0~-40°C, and the freezing process is a cycle of freezing for two hours and thawing for half an hour.

A method for preparing ceramic slurry that can be used for three-dimensional printing proposed by the present invention further includes a high-temperature sintering step: placing the green body In a high-temperature furnace fed with argon gas, the temperature is raised to 600°C at a rate of 1°C/min and maintained for two hours, then raised to 1450°C and maintained for two hours to form a ceramic body.

A method for preparing ceramic slurry that can be used for three-dimensional printing proposed by the present invention further includes a carbon removal step: put the sintered ceramic body into a high-temperature furnace and bake it at 600°C for two hours to form a Ceramic material without carbon residue.

The above overview, the following detailed description and the accompanying drawings are all for further explaining the ways, means and effects of the present invention to achieve the intended purpose. Other purposes and advantages of the present invention will be described in the subsequent description and drawings.

S101-S104: Steps

The first figure is a flow chart of the trial production process of the ceramic jig for the ceramic slurry that can be used for 3D printing proposed by the present invention.

The second figure is the (a) boundary potential diagram and (b) particle size distribution diagram of the yttrium-stabilized zirconia powder of the ceramic paste that can be used for three-dimensional printing proposed by the present invention under different pH values.

The third figure shows the viscosity, storage and loss modulus results of the yttrium stabilized zirconia slurry, which can be used for 3D printing ceramic slurry, at three different solid contents of 30, 35 and 37.5vol%.

The fourth picture is the SEM picture of the yttrium-stabilized zirconia semi-finished product after the 600°C degreasing process of the ceramic slurry that can be used for 3D printing proposed by the present invention.

The fifth picture is the SEM picture of the finished ceramic paste that can be used for 3D printing proposed by the present invention after sintering at 1450°C.

Figure 6 shows the (a) flexural strength test and (b) Archimedes method density test of the yttrium stabilized zirconia sintered product proposed by the present invention that can be used for 3D printing ceramic slurry.

The implementation of the present invention is described below through specific examples, and those skilled in the art can easily understand the advantages and effects of the present invention from the content disclosed in this specification. However, the implementation of this case cannot be limited by the following implementation cases.

Embodiment of the present invention: first measure the Zeta potential of yttrium stabilized zirconia ceramic powder at different pH and different dispersant concentrations, and understand the surface charge of the ceramic powder and the change of the surface charge of the powder by the dispersant According to the measurement results of Jieda potential, we first mix polyethylene glycol (Polyethylene glycol, PEG-400) plasticizer with citric acid and sodium hydroxide dispersant after pH adjustment, and then pour Put it into a volumetric flask filled with polyvinyl alcohol (PVA) adhesive and mix it evenly again. Finally, add yttrium stabilized zirconia powder and use a mixer to fully stir and defoam to prepare ceramics suitable for 3D printing. slurry.

Please refer to the first figure, which is a flow chart of the method for preparing a three-dimensional printing ceramic material. The steps include: Step S101 is to provide a plasticizer and a dispersant, and the plasticizer is polyethylene glycol (Polyethylene glycol, PEG-400), the dispersant is a mixed solution of citric acid and sodium hydroxide, mix the aforementioned plasticizer and dispersant evenly, and then mix with an adhesive, the adhesive is polyvinyl alcohol (Polyvinyl alcohol, PVA ; molecular weight is 88,000~97,000), wherein the weight ratio of yttrium stabilized zirconia powder to plasticizer is 1:0.05-0.2, the weight ratio of yttrium stabilized zirconia powder to dispersant is 1:0.01-0.05, yttrium stabilized zirconia powder to dispersant is 1:0.01-0.05, The weight ratio of the stabilized zirconia powder to the binder is 1:0.05-0.2, and finally add a yttrium stabilized zirconia powder for sufficient stirring and defoaming to prepare a ceramic slurry that can be used for 3D printing; step S102 After three-dimensional printing of the ceramic slurry, the printed sample is then placed in a -20°C freezer for several hours to promote the crystallization of polyvinyl alcohol, and then thawed at room temperature to form a gel structure. The green embryo can be shaped, the PVA gel structure formed by this process has a high green strength, so that the embryo body is not easy to break in the subsequent drying and sintering process, and can be further shaped into a specified shape according to the external force; step S103 will After the green embryo is dried at room temperature to remove excess water, it can be placed in a high-temperature furnace for sintering process. First, the temperature is raised to 600°C at a heating rate of 1°C/min and heated for 2 hours to remove organic matter, and then heated to 1450°C for several hours. Further, the sintered ceramic body is further placed; step S104 , the sintered ceramic body is placed in a high-temperature furnace and baked at 600° C. for two hours to form a carbon-free ceramic material.

Please refer to the second picture, which is yttrium stabilized zirconia powder in different (a) Jieda potential diagram under pH value; (b) Particle size distribution diagram. The results show that when the pH value exceeds 5, the Jieda potential remains at -60 to -70mV without much change. According to the deduction from the results, under this negative potential, it is enough to make it difficult for the yttrium-stabilized zirconia powders to repel each other due to Coulomb repulsion. At the same time, it is also pointed out that adding citric acid as a dispersant can indeed make the powder more uniformly dispersed in water. With the adjustment of pH value, the average particle size and distribution of yttrium stabilized zirconia powder are larger than those without dispersant. Yttrium-stabilized zirconia powder may settle during the measurement process due to the density relationship, and the particle size measurement time is about 20 minutes, resulting in the opposite phenomenon. However, based on the results of Jieda potential, it can be judged that the pH value of 5 is sufficient to allow citric acid to adsorb on the surface of yttrium stabilized zirconia.

Please refer to the third figure, which shows the results of viscosity, storage and loss modulus of yttrium-stabilized zirconia slurries with three different solid contents of 30, 35 and 37.5vol%. In the third figure (a), it is found that the viscosities of the three pastes all show a linear decrease trend with the increase of the shear rate, which is in line with the shear thinning properties required for 3D printing. In the third picture (b), it is found that the yield stress value of 30vol% yttrium stabilized zirconia slurry is only about 100, and it can be expected that there will be problems of collapse and skew of semi-finished products; although 37.5vol% slurry has the best yield stress value, and it is also the slurry with the highest viscosity. At such a high viscosity, there will be problems such as pumps are difficult to extrude, and the extrusion rate is unstable. After comprehensive consideration of the above factors, the final choice is to use a slurry with a yield stress value of about 580Pa and 35vol% for 3D printing.

With 35vol% yttrium stabilized zirconia powder solid content and 0.5wt% citric acid as dispersant, 2.5wt% polyvinyl alcohol as adhesive and 2.5wt% PEG-400 is used as a plasticizer for printing. Considering the problem of moisture evaporation and severe shrinkage after sintering of the slurry, the printing speed is selected at a printing speed of 35mm/s, and the extrusion ratio (Extrusion ratio) is 60% and the filling of the sample The ratio is 85%. At this printing speed, the situation is generally good, the lines are arranged neatly, the stacking effect between layers is good, and basically no obvious printing defects are observed, indicating that this paste does have suitable storage modulus and yield stress , which can be used for direct writing printing.

Due to the difference in drying rate, warpage and cracks will occur when the printed product is placed in the air. Put the sample into a -20°C refrigerator. While freezing the water, it also promotes the formation of PVA crystallization. After the sample is thawed to room temperature, the overall plasticity of the green embryo increases, and it can be deformed by external force. The characteristic of deformability can make the finished product restrain warpage after being subjected to gravity.

Please refer to the fourth picture, which is the SEM picture of the semi-finished yttrium stabilized zirconia after degreasing at 600°C. Please refer to the fifth picture, which is the SEM picture of the finished product after sintering at 1450°C. The experimental results show that the morphology of the yttrium-stabilized zirconia powder has changed. In the fourth figure, there are still obvious gaps between the powders before degreasing, and the yttrium stabilized zirconia powders have not been completely densified. But in the fifth picture, it can be found that most of the powders are successfully fused and bonded together. The SEM results show some blemishes, as circled in red. These small holes may be caused by air bubbles left in the printing process, or the anisotropic shrinkage of the sample during the drying and sintering process. It is expected that if the sintering time is further extended, Such defects should be reduced.

For the mechanical strength of the sample after sintering, we use the ASTM C 1161 standard to test. The flexural strength of yttrium stabilized zirconia was measured by three-point bending mode. The test results are shown in Figure 6 (a). The results show that the average flexural strength of yttrium stabilized zirconia is about 400MPa, and the lowest data is 392MPa, which can be It can be seen that most of the finished products of yttrium stabilized zirconia have sufficiently high flexural strength, and it has also been verified that the yttrium stabilized zirconia samples have indeed been successfully sintered.

Use the Archimedes method to test the density of yttrium-stabilized zirconia sintered products. Please refer to Figure 6 (b) for the measurement results. The theoretical densities of zirconia are 6.00g/cm ³ , and the results show that the average density is about 5.88 g/cm ³ is 97.93% of the theoretical density. The measurement results show that the density of the yttrium-stabilized zirconia sample has indeed reached the original predetermined standard, indicating that the sintering process can be successfully completed under the condition of holding the temperature at 1450°C for two hours. This result is also consistent with the SEM image of the yttrium-stabilized zirconia sample. The yttrium-stabilized zirconia crystals are closely arranged inside the finished product with few voids, which verifies that the yttrium-stabilized zirconia slurry has been sintered.

The present invention uses polyvinyl alcohol (PVA) as an adhesive in the ceramic slurry. PVA is a water-soluble macromolecule. In addition to being used as an adhesive, it can also be used to prepare high-strength hydrogel. When the aqueous solution of PVA is frozen, the crystallization of PVA macromolecules can be promoted. This kind of crystallization will not disappear after returning to room temperature, so the PVA crystallization site can be used as a polymer cross-linking site to form a hydrogel. The characteristics of PVA can be used to form a ceramic green body that can be 3D printed and subsequently molded with a relatively simple formula.

The present invention utilizes the crystallization produced after freezing polyvinyl alcohol to gel the printed sample, which can achieve the following two specific advantages: (1) Enhance the green strength: if you want to increase the green strength of ordinary ceramic green embryos, It is often necessary to increase the amount of organic matter and reduce the solid content of ceramics. The green embryo prepared by the present invention has high solid content and strength, which can reduce cracks caused by sample shrinkage when the green embryo is dried. (2) Post-shaping of green blanks: For the forming of complex structures, most 3D printing needs to print a lot of support materials, which is very difficult. However, the green embryo prepared by the present invention has high enough strength and ductility, and can be reshaped through subsequent manufacturing processes. While reducing the support material, the formation of complex structures can be achieved.

The above-mentioned embodiments are only illustrative to illustrate the characteristics and functions of the present invention, and are not intended to limit the scope of the essential technical content of the present invention. Any person familiar with the art can modify and change the above-mentioned embodiments without departing from the spirit and scope of the invention. Therefore, the scope of protection of the rights of the present invention should be listed in the scope of the patent application described later.

S101-S104: Steps

Claims (4)

A method for preparing a ceramic slurry that can be used for three-dimensional printing. The preparation steps include: providing a plasticizer and a dispersant, mixing uniformly, then mixing with an adhesive, and finally adding a yttrium stabilized zirconia powder Thorough stirring and defoaming are carried out to prepare the ceramic slurry which can be used for three-dimensional printing; wherein, the plasticizer is polyethylene glycol (PEG-400), and the dispersant is citric acid and Sodium hydroxide mixed solution, the adhesive is polyvinyl alcohol (PVA; molecular weight 88,000~97,000); wherein, the weight ratio of the yttrium stabilized zirconia powder to the plasticizer is 1:0.05-0.2 , the weight ratio of the yttrium-stabilized zirconia powder to the dispersant is 1:0.01-0.05, the weight ratio of the yttrium-stabilized zirconia powder to the adhesive is 1:0.05-0.2; wherein, it further includes a moldable Embryo preparation steps: After the 3D printing is completed, the ceramic slurry is placed in a freezer for a freezing process to promote the crystallization of polyvinyl alcohol, and then thawed at room temperature to form a plastic green embryo with a gel structure; among them, The temperature range of the freezing process is 0~-40°C. A method for preparing ceramic slurry that can be used for three-dimensional printing as described in item 1 of the patent application, wherein the freezing process is a cycle of freezing for two hours and thawing for half an hour. A method for preparing ceramic slurry that can be used for three-dimensional printing as described in item 1 of the scope of the patent application, further comprising a high-temperature sintering step: placing the green body in a high-temperature furnace filled with argon, and raising the temperature to Raise the temperature to 600°C at a rate of 1°C/min and hold the temperature for two hours, then raise the temperature to 1450°C and hold the temperature for two hours to form a ceramic green body. A method for preparing ceramic slurry that can be used for three-dimensional printing as described in item 3 of the patent application, further includes a carbon removal step: put the sintered ceramic body into a high-temperature furnace again and bake it at 600°C After two hours, a ceramic material without carbon residue is formed.

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