KR20240074077A - Ceramic slurry composition for 3d printing and manufacturing method high-strength ceramic structure using the same - Google Patents

Abstract

An object of the present invention is to provide a ceramic slurry composition that can be used for 3D printing and has excellent strength, and a method for manufacturing a high-strength ceramic structure using the same. A ceramic slurry composition for 3D printing comprises: 60 to 80 parts by weight of ceramic particles coated with an inorganic binder precursor solution including sodium (Na); 15 to 35 parts by weight of a photocurable resin; and 0.1 to 5 parts by weight of a dispersant, wherein the photocurable resin includes 80 to 90 parts by weight of a photopolymerizable monomer, 1 to 10 parts by weight of a photoinitiator, and other additives.

Description

Ceramic slurry composition for 3D printing and method of manufacturing a high-strength ceramic structure using the same {CERAMIC SLURRY COMPOSITION FOR 3D PRINTING AND MANUFACTURING METHOD HIGH-STRENGTH CERAMIC STRUCTURE USING THE SAME}

The present invention relates to a ceramic slurry composition for 3D printing and a method of manufacturing a high-strength ceramic structure using the same.

Ceramic products have been produced through manufacturing processes such as injection molding, tape casting, and die pressing, and are applied in various fields due to their excellent thermal and mechanical properties. In particular, in application fields of advanced ceramic materials such as aerospace, bio, and energy fields, geometric design and structural complexity of ceramics are required to improve product performance. However, the existing manufacturing process for ceramic products has technical limitations due to low productivity and high production costs due to the use of molds. Therefore, recently, three-dimensional (3D) printing technology has been proposed that can produce products of complex shapes without using molds.

In various 3D printing technologies, ceramic products are typically made from powder or slurry. Methods for using powder include selective laser sintering (SLS) and selective laser melt (SLM) technologies. This method of using powder consumes a lot of energy because it uses an energy source such as a laser beam to selectively bind the particles by melting the ceramic or the binder coated on the ceramic particles. Additionally, this equipment is very expensive because it must have a function to prevent shrinkage and deformation that occurs during lamination.

The method of using ceramic slurry as a raw material is to produce slurry by mixing thermoplastic or photocurable resin and ceramic, and material extrusion (material extrusion) uses thermoplastic resin to produce a green body by laminating materials extruded through a nozzle. extrusion (ME) method, photocurable resin projection (Digital light processing, DLP) and photocurable resin layered modeling (Stereolithography apparatus, SLA) method that creates a three-dimensional shape by selectively irradiating light to a photocurable slurry. There is also a composite 3D printing method using a light-curable material extrusion method that extrudes a photo-curable slurry through a nozzle, stacks the material, and then cures it by irradiating light.

Among 3D printing technologies using ceramic slurry, DLP and SLA printing methods have high precision and can be widely used to create complex geometric structures. The ceramic slurry used is mixed with ceramic particles, a photocurable resin containing an initiator and other additives, and a dispersant. However, in DLP and SLA printing, volumetric shrinkage occurs as monomers form cross-linked polymers, and cracks and warping may occur during the sintering process to obtain dense ceramics. These problems make accurate implementation of complex dimensions impossible.

In order to obtain green and sintered bodies with high dimensional stability in a general ceramic product manufacturing process, the solid content of the ceramic must be as high as possible. However, in order to apply it to DLP and SLA methods, it is necessary to manufacture ceramic slurry with appropriate fluidity and viscosity. This is because it is closely related to preventing particle agglomeration and uniformly applying the slurry to the stacked surface.

As such, ceramic slurry manufacturing technology is a key technology for successful DLP and SLA printing, and many researchers are conducting research on new photopolymerizable ceramic slurries suitable for DLP and SLA 3D printing. However, as product shapes become more complex, Ceramic slurry manufacturing technology for 3D printing with suitable physical properties is still required.

Republic of Korea Patent No. 10-0533627 (announced on December 6, 2005)

The purpose of the present invention is to provide a ceramic slurry composition that can be used in 3D printing and has excellent strength, and a method of manufacturing a high-strength ceramic structure using the same.

In order to achieve the above object, the present invention includes 60 to 80 parts by weight of ceramic particles coated with an inorganic binder precursor solution containing sodium (Na); 15 to 35 parts by weight of photocurable resin; and 0.1 to 5 parts by weight of a dispersant, wherein the photocurable resin consists of 80 to 90 parts by weight of a photopolymerizable monomer, 1 to 10 parts by weight of a photoinitiator, and other additives, and photopolymerization is performed by irradiating light to the composition. Afterwards, a ceramic slurry composition for 3D printing is provided, characterized in that the strength is improved by aging at 50 to 200° C. for 1 to 3 hours.

The inorganic binder precursor solution may include a sodium precursor, a silica precursor, and a solvent.

The composition can be used in a 3D printer using a photocurable resin projection (digital light processing, DLP) method or a photocurable resin lamination apparatus (SLA) method.

The present invention includes the steps of immersing ceramic powder particles in an inorganic binder precursor solution and coating the ceramic powder particles with the inorganic binder precursor; Preparing a slurry by mixing the ceramic powder particles coated with the inorganic binder precursor with a photopolymerizable monomer, a photoinitiator, and a dispersant; Manufacturing a molded body by irradiating light to the prepared slurry; Aging the manufactured molded body; and heat-treating the aged molded body to produce a sintered body.

The inorganic binder precursor solution may include 50 to 60 parts by weight of a sodium precursor, 30 to 40 parts by weight of a silica precursor, and the remaining solvent.

The aging step may be performed at 50 to 200°C for 1 to 3 hours.

The step of manufacturing the fired body may be performed by heat treating the aged molded body at 900 to 1,100° C. for 1 to 3 hours.

Additionally, the present invention provides a high-strength ceramic structure manufactured according to the above manufacturing method.

The high-strength ceramic structure can have improved forming strength and plastic strength.

The high-strength ceramic structure can be manufactured using a 3D printer.

The ceramic slurry composition according to the present invention has high strength by using ceramic particles modified with an inorganic binder instead of the conventional sintering process and can minimize deformation that may occur during heat treatment, making ceramics of complex shapes in 3D printing using light polymerization. It can be usefully used to produce products.

The inorganic binder is environmentally friendly as it does not emit harmful substances, and can have high-temperature strength by creating a glass phase without decomposing even after heat treatment.

In addition, the method for manufacturing a high-strength ceramic structure according to the present invention can have high green strength by improving condensation efficiency by applying an aging process of the inorganic binder before the conventional firing process, and ceramic particles are formed during the firing process. By increasing the glass conversion efficiency, excellent firing strength can be obtained.

Figure 1 schematically shows a process for manufacturing a ceramic slurry, a ceramic molded body, and a fired body according to an embodiment of the present invention.
Figure 2 shows the mechanism by which an inorganic binder is coated on silica.
Figure 3 is a differential scanning calorimetry (DSC) spectrum of fused silica coated with an inorganic binder (blue line) and raw fused silica (red line).
4 is a thermogravimetric differential temperature analyzer of fused silica with an inorganic binder aged at 200°C (bottom), fused silica coated with an inorganic binder (middle), and pristine fused silica coating (top). , TG-DTA) spectrum.
Figure 5 shows the forming and firing strength depending on whether the inorganic binder is coated and the aging temperature.
Figure 6 is a scanning electron microscope (SEM) image of the fracture surface microstructure of the molded body according to aging temperature, where A is uncoated fused silica and B is fused silica coated with an inorganic binder.
Figure 7 is a microstructure SEM image of the fractured surface of a sintered body manufactured using fused silica coated with an inorganic binder and the fractured surface of a sintered body manufactured using raw fused silica.
Figure 8 is a Fourier transform infrared spectroscopy (FT-IR) spectrum of a molded body according to aging temperature. (a) is a molded body manufactured using raw fused silica, and (b) is a molded body manufactured using fused silica coated with an inorganic binder. This is a manufactured molded body.
Figure 9 is an .
Figure 10 is a schematic diagram of the inorganic binder binding mechanism for each stage of the molded body and the fired body.
Figure 11 shows the shape after sintering of a sample manufactured using fused silica coated with an inorganic binder depending on aging, and the shape after sintering of a sample made from raw fused silica.

Hereinafter, the present invention will be described in detail.

The present inventor prepared a photocurable slurry to produce ceramic products of complex shapes using 3D printing using photopolymerization, and completed the present invention by confirming that its strength was further improved and deformation that may occur during heat treatment was minimized. did.

The present invention provides a ceramic slurry composition for 3D printing.

More specifically, the ceramic slurry composition for 3D printing includes 60 to 80 parts by weight of ceramic particles coated with an inorganic binder precursor solution containing sodium (Na); 15 to 35 parts by weight of photocurable resin; and 0.1 to 5 parts by weight of a dispersant.

The ceramic particles may include silica, alumina, zirconia, magnesia, mullite, titania, or mixtures thereof, and are preferably fused silica with an average particle diameter of 5 to 10 μm, but are not limited thereto.

The inorganic binder precursor solution may include a sodium precursor, a silica precursor, and a solvent. The solution may consist of 50 to 60 parts by weight of a sodium precursor, 30 to 40 parts by weight of a silica precursor, and the remaining solvent, but is not limited thereto.

The sodium precursor may be one or more selected from the group consisting of sodium methoxide, sodium ethoxide, and sodium hydroxide, and is preferably sodium methoxide (NaOMe), but is not limited thereto.

The sodium precursor in the above weight range adjusts the network structure of the ceramic particles, enabling excellent strength to be achieved even after firing through a vitrification reaction.

The silica precursor is tetraethylorthosilicate, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, tetraisopropoxysilane, methoxytriethoxysilane, dimethoxydiethoxysilane, Toxytrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diethyldiethoxysilane, tetramethoxymethylsilane, tetramethoxyethyl It may be selected from the group consisting of silane, tetraethoxymethylsilane, and combinations thereof, and is preferably tetraethyl orthosilicate (TEOS), but is not limited thereto.

The solvent may include an organic solvent, for example, selected from the group consisting of methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol, hexyl alcohol, cyclohexyl alcohol, and combinations thereof. It may be, but is not limited to this.

The inorganic binder precursor solution can be prepared in a liquid state for solubility, and is made of an organic-inorganic hybrid material, so it can have both the advantages of an inorganic material with excellent mechanical strength and an organic material with advantageous flexibility and moldability.

The photocurable resin may include 80 to 90 parts by weight of a photopolymerizable monomer, 1 to 10 parts by weight of a photoinitiator, and other additives.

The photopolymerizable monomer may include an acrylate-based monomer, and the acrylate-based monomer is, for example, ethylene glycol di(meth)acrylate, 1,2-propylene glycol di(meth)acrylate, 1,3 -Butylene glycol di(meth)acrylate, 1,4-butylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, dipropylene Selected from the group consisting of glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, and trimethylolpropane triacrylate. There may be one or more, preferably trimethylolpropane triacrylate (TMPTA), but is not limited thereto.

The photoinitiator is not particularly limited as long as it can cause a photopolymerization reaction when irradiated with light (e.g., UV), and may include, for example, a ketone-based photopolymerization initiator, an organic peroxide-based photopolymerization initiator, an azo-based photopolymerization initiator, or a combination thereof. It may be one or more selected from the group consisting of, and preferably may be a ketone-based photopolymerization initiator, but is not limited thereto.

The ketone photopolymerization initiator is, for example, 2,2-dimethoxy-2-phenyl acetophenone, 2-methyl-1-[4-(methylthio)phenyl-2-morpholino]propan-1-one , 2-benzyl-2N,N-dimethylamino-1-(4-morpholinophenyl)-1-butanone, isopropylthioxanthone, camphorquinone, [4-(4-methylphenylthio)phenyl]phenyl Ketone, 4-phenylbenzophenone, 2-ethylanthraquinone, di-iodobutoxyfluorone, diphenyl ketone, diethoxyacetophenone, 1-hydroxy cyclohexyl phenyl ketone, 2-hydroxy-2-methyl- 1-phenyl-propane-1-one, benzoin ether, benzoin, benzoin alkyl ether, acetophenone, aminoacetophenone, anthraquinone, thioxanthone, ketal, benzophenone, xanthone or 2,4,6 - It may be selected from the group consisting of trimethylbenzoyl diphenyl phosphine oxide, preferably 1-hydroxy cyclohexyl phenyl ketone (HPCK), but is not limited thereto.

Preferably, the photoinitiator may be included in an amount of 2 to 10 parts by weight, more preferably 3 to 5 parts by weight, based on 100 parts by weight of the total photopolymerizable monomer, but is not limited thereto.

The other additives may be one or more selected from UV stabilizers, UV absorbers, antioxidants, adhesion enhancers, low shrinkage agents, brighteners, antifoaming agents, pigment wetting agents, thickeners, or water repellent additives, but are not limited thereto.

The dispersant is not particularly limited as long as it is a material that allows the ceramic particles coated with the inorganic binder precursor solution to be well dispersed in the photocurable resin, for example, DISPERBYK-111, NTI-TERRA-210, SMD-13, SMD May include, but is not limited to -33S, SMD-53N, Gendisper-201, Gendisper-202, Gendisper-601, Targon 886, Targon 1128, KH56, or LSPERSE 39000.

Preferably, the dispersant may be included in an amount of 0.5 to 3 parts by weight, more preferably 1 to 2 parts by weight, based on 100 parts by weight of the total photopolymerizable monomer, but is not limited thereto.

The strength of the ceramic slurry composition for 3D printing according to the present invention can be improved by photopolymerization by irradiation with light and then aging at 50 to 200° C. for 1 to 3 hours.

Additionally, the ceramic slurry composition for 3D printing can be used in a 3D printer using a photocurable resin projection (digital light processing, DLP) or photocurable resin lamination apparatus (SLA) method.

The present invention provides a method of manufacturing a high-strength ceramic structure using the above ceramic slurry composition.

The method for manufacturing a high-strength ceramic structure according to the present invention includes the steps of immersing ceramic powder particles in an inorganic binder precursor solution and coating the ceramic powder particles with the inorganic binder precursor; Preparing a slurry by mixing the ceramic powder particles coated with the inorganic binder precursor with a photopolymerizable monomer, a photoinitiator, and a dispersant; Manufacturing a molded body by irradiating light to the prepared slurry; Aging the manufactured molded body; And it may include producing a fired body by heat treating the aged molded body.

In the manufacturing method according to the present invention, the step of coating the ceramic powder particles with an inorganic binder precursor may be performed by immersing the ceramic powder particles in an inorganic binder precursor solution.

More specifically, the ceramic powder particles are immersed in an inorganic binder precursor solution at 20 to 30°C for 1 to 3 hours, then filtered to separate only the ceramic powder particles, and then the particles are incubated at 70 to 90°C for 5 to 15 hours. This can be done by allowing time to dry.

The ceramic particles may include silica, alumina, zirconia, magnesia, mullite, titania, or mixtures thereof, and are preferably fused silica with an average particle diameter of 5 to 10 μm, but are not limited thereto.

The inorganic binder precursor solution may include a sodium precursor, a silica precursor, and a solvent. The solution may consist of 50 to 60 parts by weight of a sodium precursor, 30 to 40 parts by weight of a silica precursor, and the remaining solvent, but is not limited thereto.

Corresponding features may be substituted for the parts described above.

In the manufacturing method according to the present invention, the step of preparing the slurry may be performed by mixing ceramic powder particles coated with the inorganic binder precursor with a photopolymerizable monomer, a photoinitiator, and a dispersant.

More specifically, it can be performed by mixing ceramic powder particles coated with the inorganic binder precursor, photopolymerizable monomer, photoinitiator, and dispersant and mixing at 1000 to 2000 rpm for 5 to 15 minutes.

Corresponding features may be substituted for the parts described above.

In the manufacturing method according to the present invention, the step of manufacturing the molded body may be performed by irradiating light to the prepared slurry.

More specifically, after putting the fluid slurry into a glass mold, a molded body can be manufactured through a photopolymerization reaction by light irradiation.

In the manufacturing method according to the present invention, the step of aging the manufactured molded body may be performed at 50 to 200° C. for 1 to 3 hours.

Due to the aging process, a sol-gel reaction of the inorganic binder precursor coated on the ceramic powder particles forms a network between the ceramic powder particles, thereby improving inter-particle adhesion, thereby improving green strength.

In this specification, the "sol-gel method" refers to a process of making an inorganic material such as ceramics starting from a liquid, passing through a sol containing fine particles, and then passing through a gel containing liquid etc. in the gaps between the solid skeleton. This means that a product with high chemical uniformity can be obtained.

According to an experimental example of the present invention, it was confirmed that as the aging temperature increased to 200° C., the inter-particle network was further strengthened and the molding strength was improved. In addition, strengthening of this network can improve vitrification efficiency by increasing the necking area between particles during the subsequent firing process.

In the manufacturing method according to the present invention, the step of manufacturing the fired body may be performed by heat treating the aged molded body. More specifically, the inorganic binder precursor may be vitrified by heat treatment at 900 to 1,100° C. for 1 to 3 hours.

According to an experimental example of the present invention, it was confirmed that the glass conversion efficiency and firing strength were improved by subjecting the fired body to an aging process before heat treatment.

In addition, it was confirmed that even if the polymer polymerized through a high temperature (1000°C) heat treatment process below the sintering point decomposes, the molten inorganic binder can bind the particles and maintain their shape and size.

That is, the inorganic binder precursor coated on the ceramic particle powder according to the present invention can be converted into a glass phase through a sol-gel reaction and vitrification to exhibit excellent firing strength and have high shape and dimensional stability. A fired body can be obtained.

The manufacturing method according to the present invention can be performed using a 3D printer, but is not limited thereto.

Additionally, the present invention provides a high-strength ceramic structure manufactured according to the above manufacturing method.

The high-strength ceramic structure may have improved forming strength and plastic strength.

The high-strength ceramic structure can be manufactured using a 3D printer.

Hereinafter, the present invention will be described in detail through examples to aid understanding. However, the following examples only illustrate the content of the present invention and the scope of the present invention is not limited to the following examples. Examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

<Example 1> Preparation of photocurable slurry type resin

The photocurable slurry-type resin consisted of modified fused silica, acrylate monomer, dispersant, and photoinitiator. Trimethylolpropane triacrylate (TMPTA) and 1-hydroxy cyclohexyl phenyl ketone (HPCK) are each photocured by photoradical polymerization of acrylate monomers under ultraviolet (UV) irradiation. It was used as an acrylate monomer and photoinitiator to prepare the polymer. TMPTA and HPCK were purchased from Sigma-Aldrich (Germany). DISPERBYK-111 (BYK, Wesel, Germany) was used as a dispersant for homogeneous mixtures. The mixing ratios of HPCK and BYK-111 in the mixture were 4% by weight and 1% by weight, respectively, based on the weight of TMPTA.

Table 1 below shows the composition (weight ratio) of the photocurable ceramic slurry.

photocurable resin
(monomer + photoinitiator) modified fused silica dispersant 30 70 0.3

In this example, fused silica (Sibleco, Korea) with an average particle size of 9.51 μm was used as the ceramic material. In order to improve the mechanical strength of the ceramic body after heat treatment, modified fused silica containing an inorganic binder was manufactured through the following process.

First, silica as a starting powder was immersed in an inorganic binder solution at ~25°C for 1 hour. The solution consisted of tetraethyl orthosilicate (TEOS), sodium methoxide (NaOMe), and isobutyl alcohol (i-BuOH). The weight ratios of TEOS, NaOMe, and i-BuOH were 38, 56, and 6 wt%, respectively. TEOS, NaOMe, and i-BuOH were purchased from Sigma-Aldrich (Germany). Silica beads were immersed in this solution and filtered using a filter (Advantec, Toyo, #5A) to separate the immersion solution from the silica beads. Wet silica beads were dried at 80°C for 10 hours.

Silica particles coated with an inorganic binder and photocurable resin were uniformly mixed using a paste mixer (HanTech, Korea) at 1200 rpm for 5 minutes.

In order to compare the effect of the inorganic binder coating, a slurry was additionally prepared using fused silica without an inorganic binder coating as a raw material and a photocurable resin of the same composition and same process.

<Example 2> Production of green body and fired body

To manufacture the molded body, two types of slurries were molded into a rectangular parallelepiped shape of 50 mm × 6 mm × 1 mm to measure fracture strength. To prevent surface oxygen reactivity of radical polymerization, the molded slurry was covered with a slice of glass. UV light with a dominant wavelength of 365 nm was irradiated for 5 minutes for photoradical polymerization. Afterwards, the front and back sides of each sample were re-irradiated with UV light for 5 minutes to limit the UV penetration depth and to ensure uniform polymerization on the front and back sides of the sample. To increase the strength limit of green and fired samples, an aging process was applied for an additional hour before heat treatment to the existing process. Additionally, to evaluate the condensation reaction efficiency according to aging temperature, it was performed at 50, 100, and 200°C, respectively. Fabricated samples were heat treated at 1000°C for 1 hour (Figure 1).

<Experimental Example 1> Characteristic analysis of modified fused silica and ceramic body

1. Experimental method

The condensation behavior of the modified fused silica was characterized by differential scanning calorimetry (DSC, DSC4000, PerkinElmer, USA). Samples were placed in aluminum pans for analysis. Displacements were measured from -50°C to 400°C with a heating rate of 1°C·min ^-1 .

The fracture strength of the molded body was measured in three-point bending mode at a speed of 0.5 mm·min ^-1 and a limiting load of 10,500 N using a universal testing machine (Instron 5566, Instron Corp, USA). The test was conducted five times at room temperature and the average value was obtained.

After measuring the fracture strength of the molded body and the fired body, the fracture surface of the fractured specimen was analyzed using a scanning electron microscope (SEM, JSM-5610, Jeol, Japan) to analyze the microstructure and shape.

The loss of hydroxyl groups (-OH) in the molded body according to the aging temperature was analyzed using Fourier transform infrared (FT-IR) spectroscopy (FT-IR, FT/IR-6300; JASCO, Japan). All measurements were performed in the range of 4000 to 500 cm ^-1 with a resolution of 4 cm ^-1 .

The chemical bonding state of the constituent elements was measured with an X-ray photoelectron spectrometer (XPS, AXIS ultra-delayed line detector equipped with an Al Kα

2. Experiment results

2-1. Condensation of inorganic binders on silica and confirmation of their thermal behavior

TEOS, a precursor of silica, absorbs moisture from the atmosphere and decomposes into orthosililic acid and alcohol (hydrolysis reaction). The produced orthosilicylic acid is coated by hydrogen bonding while condensing with the hydroxyl group (-OH) on the surface of the fused silica, which is the starting particle. Through this polycondensation reaction, oxide fine particles with a skeleton formed of -O-Si-O-(siloxane) bonds are created, which are connected to form a dense film on the surface of silica when the solution is gelled and dried. NaOMe undergoes a hydrolysis reaction to produce NaOH, which is coated on the surface of fused silica (Figure 2).

The thermal behavior of silica coated by hydrolysis and condensation reactions of an inorganic binder precursor with respect to raw fused silica was comparatively analyzed.

First, referring to Figure 3, which shows differential scanning calorimetry (DSC) spectra in the low temperature region of raw fused silica and fused silica coated with an inorganic binder, fused silica coated with an inorganic binder starts at 20°C and goes up to 140°C. The reaction proceeded. This reaction is an exothermic reaction caused by the sol-gel reaction of the inorganic binder and the dehydration of physically adsorbed moisture. On the other hand, fused silica not coated with an inorganic binder did not show an exothermic peak as the temperature increased, and no thermal peak was observed. This means that the raw fused silica does not react in the low temperature region.

To confirm the aging effect of raw silica, silica coated with an inorganic binder, and inorganic binder, thermogravimetric-differential thermal analysis (TG-DTA) was performed on molded bodies aged at 200°C for 1 hour with silica coated with an inorganic binder. As a result, referring to Figure 4, the weight reduction in section (a) can be seen only in the specimen coated with the inorganic binder. In this temperature range (~400°C), the silanol group (Si-OH) changes into a siloxane group (Si-O-Si) by dehydration of the -OH group in the sol-gel reaction of the inorganic binder. And this peak due to dehydration has a higher intensity in the aged sample, which means that the aged sample has a higher dehydration effect, i.e. a higher conversion rate to siloxane.

Next, in section (b), it can be seen that the weight of the sample decreases as the organic matter (photocurable polymer) is removed due to decomposition. Additionally, an exothermic peak in the DTA spectrum can be observed in this part. The exothermic peak due to decomposition proceeded in two stages. When silica coated with an inorganic binder was used, the rate of organic matter decomposition was faster than when raw silica was used.

In section (c), liquefaction and melting of the inorganic binder occurs. Therefore, a broad endothermic peak was observed in the sample prepared using an inorganic binder in section (d).

Silica does not originally liquefy at 1000°C, but when sodium is added, the network structure of silica is broken and it begins to liquefy, creating a glassy substance due to capillary forces between particles. Therefore, samples to which an inorganic binder is applied can develop fracture strength even after firing through a sol-gel reaction, dehydration reaction, and vitrification reaction during each process. On the other hand, samples that are not coated with an inorganic binder cannot have plastic strength because no reaction occurs other than vaporization of the organic binder.

2-2. Check the fracture strength of ceramic molded bodies and fired bodies

Referring to Figure 5, the fracture strength of a green body manufactured using silica coated with an inorganic binder as a starting particle was found to be higher than that of a green body manufactured with raw silica. This promotes the condensation reaction of the inorganic binder by the UV lamp and the heat generated during the photopolymerization process, thereby increasing the density of the molded body, thereby improving strength without a separate aging process. After aging, the sol-gel reaction of the inorganic binder coated on the silica surface forms a network between the fused silica particles, improving the bonding between particles, thereby improving green strength. As previously shown in Figure 3, the molding strength increased even after aging at 50°C because the condensation reaction due to the inorganic binder occurred even in the low temperature range. And as the aging temperature increased, the molding strength depending on the starting particle increased.

On the other hand, samples using raw silica showed little difference in molding strength even when the aging temperature increased. Rather, the molding strength was found to slightly decrease after aging at 200°C. This is because the weak bonds of the organic binder are broken, weakening the organic binder network. This is also the reason why the aging process was not applied at a temperature of 200°C or higher in one embodiment of the present invention. Despite this bond loss, when silica coated with an inorganic binder was used as the starting particle, the molded strength of the samples increased with increasing aging temperature. This is because the network between silica particles is strengthened by aging of the inorganic binder.

Changes in the network between starting particles due to the application of inorganic binder and the aging process can also be confirmed in the microstructure of the fracture surface of the specimen.

Referring to Figure 6, all samples without an inorganic binder had a clear boundary between the silica particles and the polymer regardless of the aging temperature, and there was little change in shape.

Meanwhile, it was confirmed that a molded body manufactured using silica coated with an inorganic binder had a coating layer formed on the surface of the silica particles after photopolymerization. This coating layer is an inorganic binder coated on fused silica, and as the aging temperature increases, it sticks to the particles and the boundary with the polymer becomes unclear. The growth of this coating layer strengthened the network between silica particles and improved the fracture strength of the molded body. In addition, strengthening of this network improved vitrification efficiency by increasing the necking area between particles during the firing process.

Therefore, the plastic strength was improved through the aging process of the inorganic binder. Specifically, a fired test piece manufactured by heat-treating a molded body made of silica starting particles coated with an inorganic binder at 1000°C secured a plastic strength that increased as the aging temperature increased. The strength of the sintered body heat-treated at 1000°C without applying the aging process was 26.6 MPa, and the strength of the sintered body heat-treated at 1000°C using the 200°C aging process was 38.8 MPa. This strength improvement of more than 10 MPa means that the conversion efficiency of the glass material between starting particles increases.

In the experimental examples according to the present invention, the plastic strength is expressed by the glass phase that binds the particles. In this glass formation process, the Si-O-Si siloxane bond of silica at 1000°C created by the condensation reaction of the inorganic binder is broken by NaOH (lowering the melting point), and sodium silicate is produced in liquid form. Sodium silicate, which has some fluidity, moves inside the particle by capillary force and moves into the narrow space of the particle. As the temperature decreases after firing, the viscosity of the liquid glass gradually increases to form solid glass. Therefore, the larger the necking point and area between particles before firing, the more glassy is produced and the higher the firing strength can be. As a result, the aging process of the inorganic binder increased the amount of glass created between particles after heat treatment at 1000°C and improved the plastic strength. As shown in Figure 7, this result can also be confirmed through the microstructure of the fracture surface of the sample fired at 1000°C. It was confirmed that as the aging temperature increased, the vitreous bond area between particles increased.

2-3. Confirmation of correlation between aging process and improvement in fracture strength

According to an experimental example of the present invention, it was confirmed that the fracture strength of the molded body and the fired body was improved as the aging process of the inorganic binder was introduced and the aging temperature was increased. This result is due to the strengthened network between particles.

Additionally, FT-IR and XPS were analyzed to determine what type of binding was increased or decreased.

First, referring to Figure 8, silica without an inorganic binder showed little change in the hydroxyl group (-OH) even when the aging temperature was increased, but in the specimen to which a binder was applied, the hydroxyl group (-OH) decreased as the aging temperature increased. appear. This is because the condensation reaction was promoted by the inorganic binder coated on fused silica. TEOS and NaOMe, the inorganic binders used in an experimental example of the present invention, react as follows.

Si(OR) ₄ + 4H ₂ O → Si(OH) ₄ + 4ROH (1)

Si(OH) ₄ → SiO ₂ + 2H ₂ O (2)

RONa + H ₂ O → ROH + NaOH (3)

As shown in the above reaction equations (1) and (3), TEOS and NaOMe react with moisture in the air to form silanol and sodium hydroxide, respectively. At the same time, the generated silanol group is condensed into siloxane to form a skeleton of SiO ₂ (reaction (2)). At this time, when the hydrolysis reaction slows down due to evaporation of water and the condensation reaction becomes dominant, dehydration occurs. As temperature increases, these dehydration and condensation reactions accelerate. Therefore, the silanol group (Si-OH) generated in reaction (1) is converted to a siloxane group, and the hydroxyl group is reduced. These reactions occur only at relatively low temperatures. Specifically, as can be seen from the DSC and TG-DTA results in Figures 3 and 4, dehydration of the -OH group occurs at 20°C to 140°C and to 400°C. Between 20°C and 140°C (up to 170°C according to references), physically adsorbed hydroxyl groups are dehydrated. Additionally, since silanol groups change into siloxane groups around ~400℃, it is assumed that the highest bonding strength was developed when the aging temperature was 200℃.

In addition, the dehydration reaction due to aging can be confirmed through the XPS spectrum in Figure 9.

In the case of the molded body, it can be seen that the siloxane group (Si-O-Si) increases and the silanol group (Si-OH) decreases after aging compared to the non-aged sample. In each case, it was confirmed that the specimens fired at 1000°C and then subjected to an aging process had many Si-O-Si bonds and glassy Si-Na-O bonds. On the other hand, specimens that underwent a sintering process without aging have many Si-O groups and have low bonding efficiency.

Referring to FIG. 10 regarding the bonding mechanism between starting particles that changes due to aging of the inorganic binder, (a) is the state before performing the aging process, and before aging, many hydroxyl groups exist on the surface of the inorganic binder. (b) is a low-temperature region during the aging process. In the low-temperature region, hydroxyl groups physically adsorbed on the surface of the inorganic binder are desorbed to form silanol groups. In (c), you can see that the silanol group changes into a siloxane group as the hydroxyl group is chemically desorbed. During the aging process, processes (b) and (c) are performed. The inorganic binder coated on the surface of these particles forms a siloxane bond through a condensation reaction with the inorganic binder coated on other particles. Previously, it was confirmed through FR-IR and XPS analysis in FIGS. 8 and 9 that the amount of siloxane bonds increases as the aging temperature increases. Therefore, as the amount of siloxane groups increased, the molding strength increased. However, this condensation reaction can proceed up to ~400℃, but at temperatures above 200℃, the breaking strength may decrease due to decomposition of organic substances that make up the photopolymer. The increased amount and area of interparticle bonding can increase the conversion efficiency to a glass body during the vitrification process in (d). Therefore, as the amount of siloxane bonds increased, the plastic strength also increased.

Referring to FIG. 11, no changes in shape such as shrinkage or deformation were observed after firing at 1000°C, regardless of whether or not there was aging treatment. This is because, as mentioned above, the liquid inorganic binder is located between the particles, becomes glassy after cooling, and binds between the particles. However, the sintered sample was distorted. This is because shrinkage occurred due to particle-to-particle bonding without the formation of glass.

So far, we have looked at specific embodiments of the present invention. A person skilled in the art to which the present invention pertains will understand that the present invention may be implemented in a modified form without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments should be considered from an illustrative rather than a restrictive perspective. The scope of the present invention is indicated in the claims rather than the foregoing description, and all differences within the equivalent scope should be construed as being included in the present invention.

Claims (10)

60 to 80 parts by weight of ceramic particles coated with an inorganic binder precursor solution containing sodium (Na);
15 to 35 parts by weight of photocurable resin; and
A ceramic slurry composition containing 0.1 to 5 parts by weight of a dispersant,
The photocurable resin consists of 80 to 90 parts by weight of a photopolymerizable monomer, 1 to 10 parts by weight of a photoinitiator, and other additives,
A ceramic slurry composition for 3D printing, characterized in that the strength is improved by photopolymerizing the composition by irradiating light and then aging it at 50 to 200° C. for 1 to 3 hours.
According to claim 1,
The inorganic binder precursor solution is,
A ceramic slurry composition for 3D printing, comprising a sodium precursor, a silica precursor, and a solvent.
According to claim 1,
The composition is,
A ceramic slurry composition for 3D printing, characterized in that it is used in a 3D printer using a photocurable resin projection (Digital light processing, DLP) method or a photocurable resin lamination apparatus (SLA) method.
Coating the ceramic powder particles with the inorganic binder precursor by immersing the ceramic powder particles in an inorganic binder precursor solution;
Preparing a slurry by mixing the ceramic powder particles coated with the inorganic binder precursor with a photopolymerizable monomer, a photoinitiator, and a dispersant;
Manufacturing a molded body by irradiating light to the prepared slurry;
Aging the manufactured molded body; and
A method of manufacturing a high-strength ceramic structure, comprising the step of heat-treating the aged molded body to produce a sintered body.
According to claim 4,
The inorganic binder precursor solution is,
A method for manufacturing a high-strength ceramic structure, comprising 50 to 60 parts by weight of a sodium precursor, 30 to 40 parts by weight of a silica precursor, and the remaining solvent.
According to claim 4,
The aging step is,
A method of manufacturing a high-strength ceramic structure, characterized in that it is carried out at 50 to 200 ° C. for 1 to 3 hours.
According to claim 4,
The step of manufacturing the fired body is,
A method of manufacturing a high-strength ceramic structure, characterized in that it is performed by heat treating the aged molded body at 900 to 1,100° C. for 1 to 3 hours.
A high-strength ceramic structure manufactured according to any one of claims 4 to 7.
According to claim 8,
The high-strength ceramic structure,
A high-strength ceramic structure characterized by improved forming strength and plastic strength.
According to claim 8,
The high-strength ceramic structure,
A high-strength ceramic structure manufactured using a 3D printer.