KR20250004477A - Slurry Composition For Digital Light Processing 3D Printer And Manufacturing Method Of Zirconia Sintered Body Using The Same - Google Patents

Abstract

The zirconia slurry composition for 3D printing of the present invention has the advantage of maximizing the content of ceramic components while optimizing dispersibility and viscosity to facilitate DLP 3D printing, and optimizing the type and content of resin components so that the resin components are efficiently removed during debinding and sintering of a 3D output, and the strength of the ceramic product is not reduced even after the resin components are removed.
In addition, the digital light processing 3D printer of the present invention has a temperature control device to maintain the temperature of the slurry composition tank at 30 to 40°C, so that it is easy to form a film on a molding plate using the zirconia slurry composition for 3D printing, and since the roughness of the molding plate is adjusted to 30 to 90 degrees, there is an advantage that the 3D output is not damaged when the output is detached.
Therefore, when a zirconia sintered body is manufactured using the zirconia slurry composition for 3D printing of the present invention and a digital light processing 3D printer, not only can a 3D zirconia molded body of a complex shape be manufactured without restrictions, but there is also an advantage in that gradual debinding and sintering are performed according to temperature, so that cracks do not occur in the sintered body.

Description

Slurry composition for digital light processing 3D printer and manufacturing method of zirconia sintered body using the same {Slurry Composition For Digital Light Processing 3D Printer And Manufacturing Method Of Zirconia Sintered Body Using The Same}

The present invention relates to a slurry composition for a digital light processing 3D printer and a method for manufacturing a zirconia sintered body using the same.

Zirconia ceramics exhibit high toughness and strength at room temperature and are utilized in various industries due to their excellent chemical durability. Yttria-stabilized zirconia (YSZ), which is prepared by dissolving 2 to 3 mole% of yttria (Y ₂ O ₃ ) in zirconia (ZrO ₂ ), is used for special cutting tools, nozzles, pump parts, precision screws, and various precision fixtures in the textile industry, and is also widely used in artificial teeth for implants due to its aesthetic properties. However, teeth have different shapes for each person and are asymmetrical and complex in shape, making them difficult to manufacture using conventional molding and sintering methods. Conventionally, a method was mainly used to make a dental block sintered with zirconia and then cut and process it using CAD, but this had the problem that the processing time was too long and productivity was low.

Recently, ceramic 3D printing technology has been studied to overcome the above-mentioned shortcomings. Ceramic 3D printing technology has the advantage of shortening the conventional ceramic molding process and enabling flexible manufacturing according to characteristics, so that multiple parts can be produced in one run. In particular, since the production of press molds is unnecessary when using ceramic 3D printing technology, it has a very advantageous advantage in terms of cost.

Ceramic 3D printing is classified into slurry-based ceramic 3D printing, powder-based ceramic 3D printing, and bulk material-based ceramic 3D printing depending on the material. In the case of powder-based ceramic 3D printing, a powder bed is laid out, a binder is sprayed to a certain part, hardened, and then this is repeated in layers. However, it is not easy to thinly spread the powder to a certain thickness, and even after the finished product is manufactured, the strength is weak and the shape may be distorted or collapsed. In addition, in the case of bulk material-based ceramic 3D printing, a high-viscosity ceramic paste is stacked layer by layer like squeezing toothpaste. In order to precisely control the high-viscosity ceramic paste, a very precise nozzle with high spraying pressure is required. However, there is a disadvantage that precise control is difficult due to limitations in the nozzle hole size. In contrast, slurry-based ceramic 3D printing is a method in which a slurry containing ceramic powder, liquid monomer, and photoinitiator is manufactured, and the slurry is photopolymerized using light with a wavelength in the ultraviolet range, solidified, and stacked to form a molded body with a precise structure and high strength. As such, much research and development is being conducted on this method.

3D printing methods using photocuring are divided into the stereolithography (SL) process, which scans a two-dimensional plane analogically with a laser by irradiating light having a wavelength in the ultraviolet range, and the digital light processing (DLP) process, which irradiates ultraviolet rays to digitalized pixels using micro mirrors. The DLP process has the advantage of being faster than the SL process, greatly reducing the process time, and has the advantage of being able to obtain excellent resolutions reaching several micrometers.

Conventional 3D printing technology using ceramic materials has been mainly developed for alumina. Therefore, if a 3D printing technology using zirconia slurry is developed, it is expected that not only artificial teeth for implants using zirconia, but also various complex-shaped industrial parts will be manufactured.

The patent documents and references mentioned in this specification are incorporated by reference into this specification to the same extent as if each document was individually and specifically designated by reference.

Korean Registered Patent 10-1551255 Korean registered patent 10-0808954

The purpose of the present invention is to provide a zirconia slurry composition for 3D printing, which maximizes the content of ceramic components while optimizing dispersibility and viscosity to facilitate DLP 3D printing, and optimizes the type and content of resin components so that the resin components are efficiently removed during debinding and sintering of a 3D output, and the strength of the ceramic product is not reduced even after the resin components are removed, and a method for manufacturing a zirconia sintered body using the slurry composition and a 3D printer.

Other objects and technical features of the present invention are more specifically presented in the detailed description of the invention, the claims and the drawings below.

The present invention provides a method for manufacturing a zirconia sintered body using a 3D printer, the method comprising: a first step of manufacturing a zirconia slurry composition for 3D printing, the composition including zirconia powder and a light-transmitting monomer mixture having a pyrolysis temperature of 150 to 600°C; a second step of manufacturing a zirconia molded body using a digital light processing 3D printer equipped with the zirconia slurry composition for 3D printing, a slurry composition tank equipped with a temperature control device, and a roughened molding plate; and a third step of heat-treating the zirconia molded body by heating it from 20°C to 1000 to 1500°C at a heating rate of 0.3 to 0.7°C per minute, thereby manufacturing a zirconia sintered body.

The above zirconia slurry composition for 3D printing is characterized by having a pH of 6 to 8, and the light-transmitting monomer mixture is a mixture of 2 to 6 kinds of light-transmitting monomers having a thermal decomposition temperature of 150 to 520°C, and the light-transmitting monomers are characterized by having a thermal decomposition temperature difference of 40 to 370°C.

Specifically, the zirconia slurry composition for 3D printing is characterized by having a pH of 6.5 to 7.5, and the light-transmitting monomer mixture is characterized by being a mixture of two or more light-transmitting monomer resins selected from the group consisting of a light-transmitting monomer resin having a thermal decomposition temperature of 150 to 190°C; a light-transmitting monomer resin having a thermal decomposition temperature of 300 to 340°C; a light-transmitting monomer resin having a thermal decomposition temperature of 380 to 420°C; and a light-transmitting monomer resin having a thermal decomposition temperature of 480 to 520°C.

In addition, the above-mentioned light-transmitting monomer mixture is characterized by being transparent to ultraviolet rays and having a viscosity of 350 to 450 cps.

The temperature control device of the above digital light processing 3D printer is characterized by maintaining the temperature of the slurry composition tank at 30 to 40°C, and the build plate of the above digital light processing 3D printer is characterized by having a roughness of 30 to 90.

The above zirconia molded body is characterized in that, during the process of heat treatment by increasing the temperature, the light-transmitting monomer included in the light-transmitting monomer mixture is gradually degreased according to the thermal decomposition temperature, so that cracks do not occur in the zirconia sintered body.

The zirconia slurry composition for 3D printing of the present invention has the advantage of maximizing the content of ceramic components while optimizing dispersibility and viscosity to facilitate DLP 3D printing, and optimizing the type and content of resin components so that the resin components are efficiently removed during debinding and sintering of a 3D output, and the strength of the ceramic product is not reduced even after the resin components are removed.

In addition, the digital light processing 3D printer of the present invention has a temperature control device to maintain the temperature of the slurry composition tank at 30 to 40°C, so that it is easy to form a film on a molding plate using the zirconia slurry composition for 3D printing, and since the roughness of the molding plate is adjusted to 30 to 90 degrees, there is an advantage that the 3D output is not damaged when the output is detached.

Therefore, when a zirconia sintered body is manufactured using the zirconia slurry composition for 3D printing of the present invention and a digital light processing 3D printer, not only can a 3D zirconia molded body of a complex shape be manufactured without restrictions, but there is also an advantage in that gradual debinding and sintering are performed according to temperature, so that cracks do not occur in the sintered body.

Figure 1 shows a DLP-type 3D printer of the present invention.
Figure 2 shows an optimized molding plate of the present invention.
Figure 3 shows a DLP 3D printer of the present invention equipped with a temperature maintenance device.
Figure 4 shows the results of analyzing the thermal decomposition behavior of a 3D printed object manufactured using the zirconia slurry composition for 3D printing of the present invention.

The present invention provides a method for manufacturing a zirconia sintered body using a 3D printer, the method comprising: a first step of manufacturing a zirconia slurry composition for 3D printing, the composition including zirconia powder and a light-transmitting monomer mixture having a pyrolysis temperature of 150 to 600°C; a second step of manufacturing a zirconia molded body using a digital light processing 3D printer equipped with the zirconia slurry composition for 3D printing, a slurry composition tank equipped with a temperature control device, and a roughened molding plate; and a third step of heat-treating the zirconia molded body by heating it from 20°C to 1000 to 1500°C at a heating rate of 0.3 to 0.7°C per minute, thereby manufacturing a zirconia sintered body.

The present invention manufactures a molded body by 3D printing a slurry composition containing ceramic through a ceramic 3D printing process, and then manufactures a product (sintered body) containing only ceramic components through a debinding and sintering process.

The DLP 3D printer used in the ceramic 3D printing process of the present invention forms a cured layer by thinly applying a slurry composition to a build plate, irradiating ultraviolet rays at a specific location, and repeating this process to stack cured layers to output a 3D output (molded object). Therefore, the slurry composition for DLP 3D printing should have an appropriate viscosity so that it can be applied to a build plate at a constant thickness to form a film, and should have excellent light transmittance to ultraviolet rays so that it can be cured over the entire film layer, and in particular, adhesion between cured layers should be easy.

The zirconia slurry composition for 3D printing of the present invention comprises domestically produced zirconia powder as a ceramic component; comprises four kinds of light-transmitting monomer resins having different thermal decomposition temperatures as a resin component; and comprises a photoinitiator.

The content and degree of dispersion of the ceramic component included in the zirconia slurry composition for 3D printing of the present invention; and the type and content of the resin component determine the DLP 3D printing result and the debinding and sintering result of the DLP 3D output product. For example, if the ceramic content is too high, the dispersibility of the slurry deteriorates, resulting in a decrease in the ultraviolet ray transmittance; or if the viscosity of the slurry is too high, making it difficult to evenly apply the slurry composition to the build plate, resulting in a problem of a decrease in the quality of DLP 3D printing. In addition, if the resin component is increased to correct the above problem, the problem occurring during DLP 3D printing can be solved, but during the debinding and sintering of the output product, a large amount of the resin component is removed, and the space remains as a void, which causes a decrease in the strength of the ceramic product (sintered body).

The present invention provides a zirconia slurry composition for 3D printing in which the content of ceramic components is maximized while dispersibility and viscosity are optimized to facilitate DLP 3D printing, and the type and content of resin components are optimized so that the resin components are efficiently removed during debinding and sintering of a 3D output, and the strength of the ceramic product is not reduced even after the resin components are removed.

According to an embodiment, the zirconia slurry composition for 3D printing of the present invention comprises 50 to 73 wt% of domestically produced zirconia powder, 47 to 22 wt% of a light-transmitting monomer resin mixture, and 2 to 5 wt% of a photoinitiator. Preferably, it comprises 70 wt% of domestically produced zirconia powder, 26 wt% of a light-transmitting monomer resin mixture, and 4 wt% of a photoinitiator.

The domestically produced zirconia, which is a ceramic component of the present invention, has an average diameter of about 0.4 μm, a white color, and an isoelectric point of around pH 5. In the present invention, in order to improve the dispersibility of the ceramic component, the pH of the zirconia slurry composition for 3D printing can be adjusted to a level of 6 to 8. Preferably, the pH of the zirconia slurry composition for 3D printing can be adjusted to 6.7 to 6.9. If the pH is less than 6, the dispersibility of the domestically produced zirconia deteriorates, and ultraviolet rays do not penetrate, so that the hardening of the output product during 3D printing may be irregular, resulting in deterioration in quality.

If the content of the domestically produced zirconia of the present invention is excessively high or the degree of dispersion is low, the viscosity increases, which hinders the formation of a film and causes a deterioration in the quality of a 3D output. According to an embodiment of the present invention, it is preferable that the viscosity of the light-transmitting monomer resin mixture is 350 to 450 cps.

The present invention comprises a mixture of 2 to 6 kinds of light-transmitting monomer resins having different pyrolysis temperatures, and by optimizing the content of the light-transmitting monomer resin mixture, cracks are prevented from occurring due to heat treatment by being gradually degreased during the heating process. The light-transmitting monomer resin mixture of the present invention is a mixture of 2 to 6 kinds of light-transmitting monomers having pyrolysis temperatures of 150 to 520°C, and is characterized in that the light-transmitting monomers have a difference in pyrolysis temperatures of 40 to 370°C. Preferably, the light-transmitting monomer resin mixture of the present invention comprises a light-transmitting monomer resin (first light-transmitting monomer resin) having a pyrolysis temperature of 150 to 190°C; a light-transmitting monomer resin (second light-transmitting monomer resin) having a pyrolysis temperature of 300 to 340°C; A mixture of a light-transmitting monomer resin having a thermal decomposition temperature of 380 to 420°C (third light-transmitting monomer resin); and a light-transmitting monomer resin having a thermal decomposition temperature of 480 to 520°C (fourth light-transmitting monomer resin), more preferably a mixture of a light-transmitting monomer resin having a thermal decomposition temperature of 170°C (first light-transmitting monomer resin); a light-transmitting monomer resin having a thermal decomposition temperature of 320°C (second light-transmitting monomer resin); a light-transmitting monomer resin having a thermal decomposition temperature of 400°C (third light-transmitting monomer resin); and a light-transmitting monomer resin having a thermal decomposition temperature of 500°C (fourth light-transmitting monomer resin).

The zirconia slurry composition for 3D printing of the present invention uses a photoinitiator suitable for a wavelength of 405 nm, preferably bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide.

The zirconia slurry composition for 3D printing of the present invention is manufactured by mixing domestically produced zirconia powder, a light-transmitting monomer mixture, and a photoinitiator by a ball milling method, and has a pH adjusted to 6 to 8, so that it has a high light transmittance to ultraviolet rays. Therefore, when the zirconia slurry composition for 3D printing of the present invention is used, ultraviolet rays are well transmitted, so that curing occurs well at the boundary between the building plate of a DLP 3D printer and a film formed thereon, or between the film and a film additionally formed thereon, so that a 3D output having excellent strength can be manufactured.

The Digital Light Processing 3D printer of the present invention is characterized in that it is optimized for 3D printing using the zirconia slurry composition for 3D printing of the present invention by having a temperature control device and a method of controlling the roughness of a building plate. The temperature control device has the characteristic of maintaining the temperature of the slurry composition tank at 30 to 40°C, thereby facilitating film formation, and the building plate has the advantage of providing a roughness of 30 to 90 degrees, thereby facilitating detachment of a 3D output.

Therefore, when a zirconia sintered body is manufactured using the zirconia slurry composition for 3D printing of the present invention and a digital light processing 3D printer, not only can a 3D zirconia molded body of a complex shape be manufactured without restrictions, but there is also an advantage in that gradual debinding and sintering are performed according to temperature, so that cracks do not occur in the sintered body.

The present invention is described in detail below through examples.

Example

1. Zirconia slurry composition for 3D printing

1) Optimization of zirconia slurry composition for 3D printing

The present invention optimizes the zirconia content of a zirconia slurry composition for 3D printing through various embodiments. First, domestically produced zirconia powder, a light-transmitting monomer resin mixture, and a photoinitiator (bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide)) were mixed, and then the pH was adjusted to 6.78. The mixture thus prepared was mixed with zirconia balls (ball size 2.5Ø) at a weight ratio of 1:4, and then ball milling was performed at a speed of 100 rpm for 12 hours to prepare a zirconia slurry composition for 3D printing (see Table 1). Using the zirconia slurry composition for 3D printing thus prepared, DLP 3D printing was performed, and the output was evaluated. The above DLP 3D printing was performed under the conditions of a temperature of 35°C and a thickness of 0.025 mm.

Ceramic slurry composition for 3D printing Ball milling time result Domestic zirconia powder Light-transmitting monomer mixture Photon initiator Example 1 61wt% 35wt% 4wt% 6 hours success Example 2 65wt% 31wt% 4wt% 12 hours success Example 3 69wt% 27wt% 4wt% 18 hours success Example 4 73wt% 23wt% 4wt% 24 hours success Example 5 77wt% 19wt% 4wt% 24 hours failure

The experimental results confirmed that the content of domestically produced zirconia powder corresponding to the solid content in the slurry during the 3D printing process affects the output results. It is determined that when the solid content increases to 75 wt% or more, the solid content in the slurry prevents light from penetrating and prevents it from attaching to the build plate of the DLP 3D printer. If the solid content is excessively low, the properties of the ceramic product manufactured after debinding and sintering deteriorate. Therefore, it is determined that it is desirable to adjust the solid content of the present invention to a range of 67 to 73 wt%.

Based on the above results, a zirconia slurry composition (pH 6.78) for 3D printing containing 70 wt% of domestic zirconia powder was manufactured, and the ball milling conditions were optimized (see Table 2). The light-transmitting monomer mixture of the present invention used four kinds of light-transmitting monomers having different thermal decomposition temperatures. The thermal decomposition temperatures of the four kinds of light-transmitting monomers are 170°C for light-transmitting monomer 1; 320°C for light-transmitting monomer 2; 400°C for light-transmitting monomer 3; and 500°C for light-transmitting monomer 4.

Ceramic slurry composition for 3D printing Ball milling time result Domestic zirconia powder Optically transparent monomer 1 Optically transparent monomer 2 Optically transparent monomer 3 Optically transparent monomer 4 Photon initiator Example 6 70wt% 12wt% 6wt% 5wt% 3wt% 4wt% 6 hours Inappropriate Example 7 70wt% 12wt% 6wt% 5wt% 3wt% 4wt% 12 hours Inappropriate Example 8 70wt% 12wt% 6wt% 5wt% 3wt% 4wt% 18 hours fitness Example 9 70wt% 12wt% 6wt% 5wt% 3wt% 4wt% 24 hours fitness

When the ball milling time was 6 hours and 12 hours, respectively (Examples 6 and 7), the dispersion of the zirconia slurry composition for 3D printing was very low, so that sedimentation occurred quickly, making it unsuitable for use in 3D printing. When the ball milling time was 18 hours and 24 hours, respectively (Examples 8 and 9), the dispersion of the zirconia slurry composition for 3D printing was good, so that it was suitable for use with a DLP 3D printer. Additionally, it was confirmed that the zirconia slurry composition for 3D printing of Examples 8 and 9 did not exhibit sedimentation for 6 hours or more.

2) Evaluation of storage properties of zirconia slurry composition for 3D printing

A zirconia slurry composition for 3D printing must maintain stable dispersion without precipitation for a long period of time to be able to be stored for a long period of time. When a zirconia slurry composition for 3D printing containing 70 wt% of the domestically produced zirconia powder of the present invention was stored in an oven at 60° C. for 48 hours, it was confirmed that no hardening or evaporation due to heat occurred.

The DLP 3D printer of the present invention uses light corresponding to an ultraviolet wavelength to harden the slurry. Therefore, when the ceramic slurry composition for 3D printing is exposed to light and hardened, the dispersibility is reduced, thereby reducing the marketability. Accordingly, in the present invention, the exposure hardening time according to the solid content (zirconia) of the zirconia slurry composition for 3D printing was analyzed to evaluate the storability (see Table 3).

Ceramic slurry composition for 3D printing Curing time result Domestic zirconia powder Optically transparent monomer 1 Optically transparent monomer 2 Optically transparent monomer 3 Optically transparent monomer 4 Photon initiator Example 10 60wt% 16.6wt% 8.3wt% 6.9wt% 4.2wt% 4wt% 24 hours Inappropriate Example 11 67wt% 13.4 wt% 6.7wt% 5.6wt% 3.3wt% 4wt% 34 hours Inappropriate Example 12 73wt% 10.6 wt% 5.3wt% 4.4wt% 2.7wt% 4wt% 46 hours fitness

The experimental results showed that as the solid content (domestic zirconia powder) increases, the resin content decreases relatively, so it takes a long time for curing due to exposure. This means that if exposure to light is unavoidable during the process, curing can occur more easily when the solid content is low. In the case of storage, it is considered important to block light as much as possible to prevent curing due to exposure, as curing does not occur if not exposed to light.

In summary, the optimized zirconia slurry composition for 3D printing of the present invention comprises 70 wt% of domestically produced zirconia powder, 26 wt% of a light-transmitting monomer resin mixture, and 4 wt% of a photoinitiator. Preferably, the optimized zirconia slurry composition for 3D printing of the present invention comprises 70 wt% of domestically produced zirconia powder, 12 wt% of a light-transmitting monomer resin 1, 6 wt% of a light-transmitting monomer resin 2, 5 wt% of a light-transmitting monomer resin 3, 3 wt% of a light-transmitting monomer resin 4, and 4 wt% of a photoinitiator (compositions of Examples 6 to 9).

2. Optimization of 3D printing process

1) DLP 3D printer for zirconia slurry composition for 3D printing

The DLP-type 3D printer of the present invention contacts a slurry composition with a build platform descending from the top, and then uses a micro mirror to irradiate ultraviolet rays in units of digitalized pixels only to specific areas to harden and produce an output.

FIG. 1 shows a DLP-type 3D printer of the present invention. Panel A schematically shows a DLP-type 3D printer of the present invention; and panel B shows the appearance of the DLP-type 3D printer of the present invention. A DLP-type 3D printer has the advantage of being able to stably manufacture 3D outputs with a short process time and excellent resolution of up to several micrometers. The 3D printer of the present invention uses an IMC model of Carima, but some parts are modified and optimized so that a zirconia slurry composition can be smoothly introduced to manufacture a 3D output. The build size of the DLP 3D printer of the present invention is 110 × 61 × 130 mm; the light source is 365 to 405 nm; the resolution is 30 to 57 ㎛; the single layer thickness is 25 to 100 ㎛; the VAT method is a transparent urethane film method; and the UV engine output is 150 to 850 mW/cm ² .

(1) Optimization of the formative plate

The build plate of a conventional DLP 3D printer has a smooth surface. According to a previous study of the present invention, if the surface of the build plate is smooth, it was confirmed that a 3D output manufactured using a zirconia slurry composition for 3D printing was not easily separated from the build plate during the process of detaching it, resulting in damage. Accordingly, the present invention solved the above problem by providing roughness to the surface of the build plate.

Fig. 2 shows an optimized building plate of the present invention. ① shows a 40-room building plate of the present invention, and ② shows an 80-room building plate of the present invention. In the present invention, particles were introduced onto the surface of the building plate to manufacture a 40-room to 80-room building plate. The building plate was precisely manufactured into a 40-room to 80-room building plate through electric discharge machining, sand blast polishing, and computerized numerical control. As a result of manufacturing a 3D output using a DLP 3D printer equipped with the optimized zirconia slurry composition for 3D printing of the present invention and the building plate with the roughness introduced thereto, it was confirmed that the output was easily detached from the building plate and that the output was not damaged during the detachment process.

(2) Optimization of temperature control device

In the present invention, a temperature control device is installed inside the DLP 3D printer so that the temperature of the zirconia slurry composition for 3D printing can be appropriately controlled and maintained (see Fig. 3). The fluidity of the slurry composition is very important in 3D printing using the DLP method. The DLP 3D printer manufactures a 3D output by repeatedly curing and laminating the slurry composition by introducing the slurry composition onto the build plate, irradiating it with ultraviolet rays, and then introducing the slurry composition thereon again and irradiating it with ultraviolet rays. Therefore, the zirconia slurry composition for 3D printing of the present invention must exist in a state of forming an appropriate oil film in the tank so that it can be introduced homogeneously without empty space when in contact with the build plate, thereby enabling precise output. If the viscosity of the zirconia slurry composition for 3D printing is high, it is difficult to form an oil film, which may result in output failure. In particular, if the temperature of the ceramic slurry for 3D printing is low, the viscosity increases even if the amount of ceramic solids in the slurry is appropriate, so an appropriate oil film is not formed, making precise printing difficult.

In order to solve the above problem, in the present invention, a temperature control device is installed at the bottom of a zirconia slurry composition tank for 3D printing. Fig. 3 shows a DLP 3D printer having a temperature maintenance device of the present invention installed. By using the temperature control device, the temperature of the zirconia slurry composition for 3D printing can be appropriately controlled and maintained, so that the viscosity of the slurry is controlled to secure optimal fluidity, which leads to optimal film formation and enables precise output. In addition, by controlling the temperature, the film formation time can be controlled, which has the effect of shortening the process time.

Table 4 shows the results of analyzing the film formation time according to the temperature control using a temperature control device for the optimized zirconia slurry composition for 3D printing of the present invention.

Preheating and slurry holding temperature Oil film formation time Example 13 20℃ 43 seconds Example 14 24℃ 34 seconds Example 15 26℃ 26 seconds Example 16 28℃ 20 seconds Example 17 30℃ less than 20 seconds

As a result of the experiment, it was confirmed that the formation of the oil film was accelerated as the maintenance temperature of the zirconia slurry for 3D printing (the composition of Examples 8 to 9) increased. In particular, when the temperature was increased to 30°C or higher, the oil film formation time was confirmed to be less than 20 seconds, and it is judged that utilizing this can shorten the 3D printing process time. However, even if the maintenance temperature of the zirconia slurry for 3D printing exceeds 30°C, the oil film formation time was confirmed to be almost the same at less than 20 seconds, and when the temperature of the zirconia slurry for 3D printing rises to 40°C or higher, there is a possibility that the acrylic monomer included in the zirconia slurry composition for 3D printing will deteriorate, and therefore it was confirmed that it is desirable to control it to below that.

2) Optimization of DLP 3D printer process using zirconia slurry for 3D printing

In order to proceed with DLP 3D printing, various process conditions must be optimized. Since the success or failure of the output and the process time are determined based on the above process conditions, it is important to establish the optimal conditions that enable 3D printing while requiring the shortest process time.

(1) Establishment of first exposure stage conditions

The first exposure step is a process of stably attaching and curing the zirconia slurry composition for 3D printing to the build plate by irradiating the UV of the DLP 3D printer at maximum output. If the first exposure step is performed for a long time, the UV engine of the DLP 3D printer may be overloaded, so it is necessary to optimize it. The first exposure cured layer formed through the first exposure step is composed of two or more cured layers, and the conditions can be optimized by adjusting the number of cured layers and the exposure time. If the exposure time of the first exposure step is set shorter than the necessary level, the output may not be smoothly attached to the build plate, which may cause problems in 3D printing. Table 5 shows the results of organizing the 3D printing results according to the conditions of the first exposure step of the present invention. The zirconia slurry composition for 3D printing used in the results of Table 5 is the composition of Examples 8 to 9. The temperature of the exposure step was set to 30° C., and the thickness of the cured layer was set to 0.025 mm.

First exposure stage Output Results Exposure time UV century Number of hardened layers Example 18 80 seconds 850 mW/cm ² 11 pieces failure Example 19 100 seconds 850 mW/cm ² 11 pieces failure Example 20 120 seconds 850 mW/cm ² 11 pieces failure Example 21 150 seconds 850 mW/cm ² 11 pieces success

For the first exposure step, it is important to optimize the number of curing layers and the exposure time. In the present invention, the number of first exposure curing layers was set to 11, and then tests were conducted by changing the exposure time. In the cases of Examples 18 to 20 where the exposure time of the first exposure step was 120 seconds or less, it was confirmed that the first exposure curing layer was not properly formed on the building plate, resulting in a failure in printing. In contrast, in the case of Example 21 where the exposure time of the first exposure step was 150 seconds, it was confirmed that the first exposure curing layer was properly formed on the building plate, resulting in a successful 3D printing since the output was well attached. In summary, it was confirmed that the first exposure curing layer requires an average exposure time of 13.6 seconds per curing layer. Therefore, in the present invention, it is determined that the condition for forming the optimal first exposure curing layer without straining the UV engine is to irradiate (expose) ultraviolet rays for an average of 13 to 15 seconds per curing layer.

(2) Establishment of second exposure stage conditions

The second exposure step refers to a step of introducing a zirconia slurry composition for 3D printing into the first exposure cured layer formed through the first exposure step and then curing it to form an additional cured layer (second exposure cured layer). Table 6 shows the results of organizing the output results according to the conditions of the second exposure step of the present invention. The temperature of the exposure step was set to 30°C and the thickness of the cured layer was set to 0.025 mm.

First exposure stage Second exposure stage Output Results Exposure time UV century Number of hardened layers Exposure time UV century Number of hardened layers Example 22 150 seconds 850 mW/cm ² 11 pieces 8 seconds 450 mW/cm ² 1 piece failure Example 23 150 seconds 850 mW/cm ² 11 pieces 10 seconds 450 mW/cm ² 1 piece failure Example 24 150 seconds 850 mW/cm ² 11 pieces 12 seconds 450 mW/cm ² 1 piece failure Example 25 150 seconds 850 mW/cm ² 11 pieces 14 seconds 450 mW/cm ² 1 piece success Example 26 150 seconds 850 mW/cm ² 11 pieces 14 seconds 650 mW/cm ² 1 piece Partial failure Example 27 150 seconds 850 mW/cm ² 11 pieces 14 seconds 550 mW/cm ² 1 piece Partial failure Example 28 150 seconds 850 mW/cm ² 11 pieces 14 seconds 250 mW/cm ² 1 piece failure Example 29 150 seconds 850 mW/cm ² 11 pieces 14 seconds 300 mW/cm ² 1 piece success Example 30 150 seconds 850 mW/cm ² 11 pieces 14 seconds 450 mW/cm ² 1 piece success

For the first exposure time, it refers to the time to irradiate ultraviolet rays per curing layer, and since it is a condition for the curing time of tens to hundreds of layers depending on the design, it has a great influence on the process. Examples 17 to 20 were analyzed by fixing the UV intensity of the second exposure step to 450 mW/cm ² and adjusting the second exposure time for one curing layer. In the case of Example 23, it was confirmed that only the first exposure curing layer was confirmed on the building plate and the output (second exposure curing layer) was not formed, indicating a failure in printing. In the cases of Examples 23 and 24, the second exposure curing layer was formed on the first exposure curing layer, but the thickness of the second exposure curing layer was confirmed to be insufficient compared to the designed level. It is believed that this is because the curing of the second exposure curing layer was incomplete. In contrast, in the case of Example 25, it was confirmed that the thickness of the printed second exposure cured layer was the same as the designed level, and since no traces of the second exposure cured layer being separated were found, it was judged to have been printed successfully. Based on the results of the above Examples 22 to 25, it was judged that it is desirable to set the basic exposure time to 14 seconds or more when irradiating with UV at an intensity of 450 mW/cm ² .

Examples 26 and 27 were performed by setting the exposure time of the second exposure step to 14 seconds and the UV intensity to 650 mW/cm ² and 550 mW/cm ^{2 ,} respectively. As a result of the experiment, the second exposure cured layers of Examples 26 and 27 were output in a state of being attached to the second exposure cured layer, but the UV intensity was too strong, so that curing exceeding the design level was observed. If the curing of the cured layer is excessive, the molding precision deteriorates, which poses a problem in that the designed 3D output cannot be manufactured.

Example 28 was performed by setting the exposure time of the second exposure step to 14 seconds and the UV intensity to 250 mW/cm ² . As a result, it was confirmed that the curing of the second exposure cured layer was incomplete and separated from the first exposure cured layer.

Examples 29 and 30 were performed with the exposure time of the second exposure step set to 14 seconds and the UV intensity set to 300 mW/cm ² and 450 mW/cm ^{2 ,} respectively. As a result, it was confirmed that the cured layer was formed well as set.

(3) Establishment of exposure conditions according to the thickness of the hardening layer

Since the DLP 3D printing of the present invention is a method in which a cured layer is attached to a building plate by irradiating UV from the bottom of the device, it is very important that the irradiated UV penetrates the zirconia slurry composition for 3D printing and stably reaches the building plate to harden it.

In the case of the thickness of the hardened layer, it is a factor that greatly affects the penetration as well as the dispersibility of the zirconia slurry composition for 3D printing, and so a proper thickness must be selected according to the printing conditions for successful 3D printing.

Table 7 shows the results of confirming the optimal exposure conditions according to the thickness of the curing layer. The thickness of the curing layer refers to the thickness per layer of the first exposure curing layer and the second exposure curing layer. In the case of the DLP 3D printer of the present invention (IMC model of Carima), output is possible by setting the thickness to 0.025 mm, 0.05 mm, and 0.1 mm. As the thickness increases, the output process time decreases, but it is necessary to set the output conditions so that curing proceeds sufficiently.

Thickness of the hardened layer First exposure stage Second exposure stage temperature Output Results Number of hardened layers Exposure time UV century Exposure time UV century Example 31 0.1mm 11 pieces 150 seconds 850 mW/cm ² 14 seconds 350 mW/cm ² 35℃ failure Example 32 0.05mm 11 pieces 150 seconds 850 mW/cm ² 14 seconds 350 mW/cm ² 35℃ failure Example 33 0.025mm 11 pieces 150 seconds 850 mW/cm ² 14 seconds 350 mW/cm ² 35℃ success

In the case of Examples 31 and 32, where the thickness of the hardened layer was set to 0.1 mm or 0.05 mm, it was confirmed that the quality of the 3D printed product was deteriorated due to incomplete hardening, while in the case of Example 33, it was confirmed that the 3D printed product was successfully manufactured.

3) Enumeration analysis of 3D prints

The thermal decomposition behavior of a 3D printed object manufactured using the zirconia slurry composition for 3D printing of the present invention was analyzed while heating up to 1200°C at a heating rate of 0.5°C per minute. Fig. 4 shows the results of analyzing the thermal decomposition behavior of a 3D printed object manufactured using the zirconia slurry composition for 3D printing of the present invention. As a result of analyzing the thermal decomposition behavior, it was confirmed that each resin component was thermally decomposed and degreased at 170°C, 320°C, 400°C, and 500°C, thereby decreasing the thermal weight of the 3D printed object. In addition, it was confirmed that no cracks occurred in the 3D printed object when the binder was removed while maintaining it at each temperature for 1 hour.

The specific embodiments described in this specification are meant to represent preferred embodiments or examples of the present invention, and the scope of the present invention is not limited thereby. It will be apparent to those skilled in the art that modifications and other uses of the present invention do not depart from the scope of the invention described in the claims of this specification.

Claims (7)

A first step of preparing a zirconia slurry composition for 3D printing comprising zirconia powder and a light-transmitting monomer mixture having a pyrolysis temperature of 150 to 600°C;
A second step of manufacturing a zirconia molded body using a digital light processing 3D printer equipped with a slurry composition tank equipped with a temperature control device and a zirconia slurry composition for 3D printing and a roughened molding plate; and
A method for manufacturing a zirconia sintered body using a 3D printer, comprising: a third step of manufacturing a zirconia sintered body by heat-treating the zirconia molded body by heating it from 20° C. to 1000 to 1500° C. at a heating rate of 0.3 to 0.7° C. per minute.
A method for manufacturing a zirconia sintered body using a 3D printer, characterized in that in claim 1, the zirconia slurry composition for 3D printing has a pH of 6 to 8.
A method for manufacturing a zirconia sintered body using a 3D printer, characterized in that in claim 1, the light-transmitting monomer mixture is a mixture of 2 to 6 kinds of light-transmitting monomers having a thermal decomposition temperature of 150 to 520°C, and the light-transmitting monomers have a thermal decomposition temperature difference of 40 to 370°C.
A method for manufacturing a zirconia sintered body using a 3D printer, wherein in the third paragraph, the light-transmitting monomer mixture is a mixture of two or more light-transmitting monomer resins selected from the group consisting of a light-transmitting monomer resin having a thermal decomposition temperature of 150 to 190°C; a light-transmitting monomer resin having a thermal decomposition temperature of 300 to 340°C; a light-transmitting monomer resin having a thermal decomposition temperature of 380 to 420°C; and a light-transmitting monomer resin having a thermal decomposition temperature of 480 to 520°C.
A method for manufacturing a zirconia sintered body using a 3D printer, characterized in that in the third paragraph, the light-transmitting monomer mixture is transparent to ultraviolet rays and has a viscosity of 350 to 450 cps.
A method for manufacturing a zirconia sintered body using a 3D printer, wherein the temperature control device is characterized in that the temperature of the slurry composition tank is maintained at 30 to 40° C., and the forming plate has a roughness of 30 to 90.
A method for manufacturing a zirconia sintered body using a 3D printer, characterized in that in the first paragraph, the zirconia molded body is heat-treated by increasing the temperature, and thus the light-transmitting monomer included in the light-transmitting monomer mixture is gradually degreased according to the thermal decomposition temperature, so that cracks do not occur in the zirconia sintered body.