Post-cure method for 3D printed output and transparent orthodontic device manufactured thereby

Abstract

The present invention relates to a post-curing method of a 3D printing output and a transparent orthodontic device manufactured according to the method, removing resin remaining on an output manufactured by a 3D printer, improving the curing speed through a post-curing process, and manufacturing an output with a shortened curing time, enhanced strength, and increased transparency. In addition, in the manufacture of a transparent orthodontic device, through the post-curing process, not only the resin on the surface can be removed, but also the strength can be enhanced, the transparency can be excellent, unreacted monomers can be removed, and a shape memory characteristic of returning to the initial printing shape of the transparent orthodontic device upon receiving heat can be exhibited.

Description

Technical Field

[0001] This invention relates to a post-curing method for 3D printed outputs and a transparent orthodontic device manufactured by the same method. Specifically, it relates to a post-curing method that can improve product quality by post-curing 3D printed outputs and a transparent orthodontic device manufactured by the same method. Background Technology

[0002] Generally speaking, in order to manufacture molded products with 3D shapes, there are two methods: mock-up making based on drawings and manual operation, and CNC automated manufacturing using CNC lathes.

[0003] However, the mock-up method is done by hand, which makes it difficult to process intricate shapes and requires a lot of time. While the CNC machine tool method can perform precise numerical control, it is limited in the shapes that can be processed due to tool interference.

[0004] Therefore, 3D printers have recently emerged, which use computers storing 3D design data created by product designers or designers using 3D modeling tools to produce 3D shaped molded products.

[0005] The advantages of using a 3D printer are that it can significantly reduce production costs and shorten production time, enable customized production, and easily create complex three-dimensional shapes.

[0006] The 3D printer employs various methods, including stereolithography (SLA), which solidifies the irradiated part by irradiating the photocurable resin composition with a laser; digital light processing (DLP), which solidifies the resin composition by irradiating the lower part of the storage tank; laser cladding deposition (LCD), which uses a UV light source and an LCD panel to stack resin on the upper part of the build plate to form the product; selective laser sintering (SLS), which uses functional polymers or metal powders for sintering; fused deposition modeling (FDM), which forms the product by extruding molten resin; laser-aided direct metal tooling (DMT), which directly forms metal using a high-power laser beam; and laminated object manufacturing (LOM), which is a mechanical bonding forming method.

[0007] In SLA, DLP, and LCD processes using photocurable composite resins, the molded product needs to be washed after manufacturing and then undergo a separate curing process to obtain the required strength and color.

[0008] The equipment used in the post-curing process is generally called a "post-curing machine," which includes ultraviolet (UV) post-curing machines, ultraviolet light-emitting diode (UV LED) post-curing machines, etc.

[0009] When the output is cured naturally without the use of a post-curing machine, problems such as dimensional deformation or reduced strength of the output may occur.

[0010] In addition, when a 3D printer uses only the printer light source to cure the output, many problems may occur, such as dimensional deformation or reduced strength of the output, and the output becoming sticky after washing due to unreacted light-cured resin.

[0011] Post-curing machines are used to prevent this problem, but when only simple UV curing is performed, there is a problem that the strength and transparency of the output cannot be improved.

[0012] In addition, there is the tedious problem that users need to manually remove the detergent residue on the output before using the post-curing machine in order to perform the post-curing process.

[0013] To prevent this problem, new technologies related to post-processing are needed.

[0014] Existing technical documents

[0015] Patent documents

[0016] Patent Document 1: KR10-2019-0054856A1 Summary of the Invention

[0017] The problem the invention aims to solve

[0018] The purpose of this invention is to provide a post-curing method for 3D printed outputs and a transparent orthodontic device manufactured by the method.

[0019] Another objective of this invention is to provide a post-curing process and apparatus for 3D printed outputs, which can remove residual resin on the outputs manufactured by the 3D printer, and can improve the curing speed through the post-curing process to produce outputs with shorter curing time, increased strength, and increased transparency.

[0020] Another object of the present invention is to provide a transparent orthodontic device, which, during the manufacture of the transparent orthodontic device, uses a post-curing process to not only remove surface resin but also enhance strength and improve transparency. It can also remove unreacted monomers and exhibit shape memory characteristics that allow the device to recover to its initial printed shape by receiving heat.

[0021] means for solving problems

[0022] To achieve the aforementioned objective, a post-curing method for 3D printed outputs according to an embodiment of the present invention may include: a first step of washing the 3D printed outputs in a rotator; a second step of performing a first post-curing on the washed outputs in an inert gas environment; a third step of immersing the first post-cured outputs in an oily substance and then performing a second post-curing; and a fourth step of treating the second post-cured outputs with hot water.

[0023] The 3D printer uses either DLP or SLA technology.

[0024] The first step is to remove residual resin from the output.

[0025] The inert gas in the second step can be selected from the group consisting of nitrogen, argon, helium, krypton, neon, and mixtures thereof.

[0026] The oily substance in the third step can be selected from the group consisting of glycerol, edible oil, castor oil, non-reactive silicone oil, and mixtures thereof.

[0027] The fourth step can be performed using hot water at 80 to 100°C.

[0028] According to another embodiment of the present invention, a transparent orthodontic device can be manufactured by a post-curing method of the 3D printed output.

[0029] Invention Effects

[0030] This invention can remove residual resin from outputs manufactured by 3D printers and improve curing speed through a post-curing process to produce outputs with shorter curing time, increased strength, and increased transparency.

[0031] Furthermore, when manufacturing clear aligners, the post-curing process not only removes surface resin but also enhances strength and transparency. It also removes unreacted monomers and exhibits shape memory properties, allowing the clear aligner to recover its initial printed shape by receiving heat. Attached Figure Description

[0032] Figure 1 These are the results of a comparative experiment on the transparency of a transparent orthodontic device according to an embodiment of the present invention.

[0033] Figure 2 These are experimental results regarding the generation of air bubbles in a transparent orthodontic device according to an embodiment of the present invention.

[0034] Figure 3 This is the result of the wear / storage modulus change of a transparent orthodontic device according to an embodiment of the present invention.

[0035] Figure 4 The results are from a methyl methacrylate (MMA) dissolution test of a transparent orthodontic device according to an embodiment of the present invention.

[0036] Figure 5 This is the GC analysis result of the detection of unreacted organic matter in a transparent orthodontic device according to an embodiment of the present invention. Detailed Implementation

[0037] This invention relates to a post-curing method for 3D printed outputs, comprising: a first step of washing the 3D printed output in a rotator; a second step of performing a first post-curing on the washed output in an inert gas environment; a third step of immersing the first post-cured output in an oily substance and performing a second post-curing; and a fourth step of treating the second post-cured output with hot water. Specific Implementation

[0039] The embodiments of the present invention will now be described in detail to enable those skilled in the art to readily implement them. However, the present invention can be implemented in many different forms and should not be limited to the embodiments set forth herein.

[0040] The Digital Light Processing (DLP) method of the present invention utilizes the principle of curing only the light-irradiated part by irradiating the lower part of a storage tank containing photocurable resin with light, while the Stereo Lithography Apparatus (SLA) method utilizes the principle of curing the irradiated part by irradiating the photocurable resin with a laser.

[0041] In the cases of DLP and SLA methods, light is irradiated onto the photocurable polymer to cure the photocurable polymer resin, thereby producing the output product.

[0042] Since the output is manufactured by curing a light-curing polymer resin, if a 3D printer is used to manufacture the output, resin residue will remain on the surface of the output, and there will be raised surfaces, etc. Therefore, additional post-processing is required to make the surface smooth and clean.

[0043] In the past, in order to perform this post-processing, users would use tools to directly remove the protruding surfaces, while using solvents to remove the resin.

[0044] This process itself is tedious and troublesome because the user has to do it himself, and it is difficult to achieve perfection.

[0045] Furthermore, the output obtained by curing photocurable polymer resins includes unreacted polymer resins that were not fully cured during the manufacturing process, thus resulting in deterioration of physical properties or reduced transparency. To mitigate these issues, a post-curing process is necessary.

[0046] Previous post-curing methods only involved users using tools to remove protruding surfaces or using solvents to remove the resin.

[0047] In other words, no separate post-curing method was introduced to enhance the physical properties of the output or improve its transparency.

[0048] A post-curing method for 3D printed outputs according to an embodiment of the present invention may include: a first step) washing the 3D printed outputs in a rotator; a second step) performing a first post-curing on the washed outputs in an inert gas environment; a third step) immersing the first post-cured outputs in an oily substance and then performing a second post-curing; and a fourth step) subjecting the second post-cured outputs to hot water treatment.

[0049] The first step is to remove any protruding surfaces or residual resin from the surface of the output material.

[0050] Specifically, it is placed in a cylindrical rotator for a residual resin removal process. The cylindrical rotator, more specifically, is a dryer, but is not limited to the example described; any device that can remove residual resin from the output through rotational force can be used.

[0051] Using the apparatus described above for the washing process, not only can resin be easily removed, but also protrusions formed on the surface can be easily removed.

[0052] A dewatering machine is a device that includes a cylindrical dewatering section. When the dewatering section rotates in a certain direction, the output material inside can have resin removed by the centrifugal force generated by the rotation of the dewatering section.

[0053] The resin is a residual polymer that adheres to the surface and can be easily removed, even on protruding surfaces, by rubbing against the dehydration section.

[0054] This process allows for easy resin removal and surface finishing.

[0055] The first step is followed by a post-curing step, which is performed in the order of the first post-curing step and the second post-curing step.

[0056] Specifically, the second step of post-curing in an inert gas environment can promote curing by irradiating the 3D printed output with UV light to prevent deformation of the output and enhance its strength to prevent damage caused by external forces.

[0057] If the curing process is carried out in an inert gas environment, not only will the curing speed of the 3D printed output be increased, but its strength will also be enhanced, so that it will not easily deform even under high-level impact.

[0058] In other words, compared to simply curing with UV light, curing with UV light in an inert gas environment accelerates the curing process and increases the strength of the output. Furthermore, if a post-curing process is performed in an inert gas environment, the transparency of the output will be further improved.

[0059] If a DLP or SLA 3D printer is used to manufacture the output, and a dye-free photocurable polymer resin is used, a transparent output can be obtained.

[0060] *As mentioned earlier, when using a DLP or SLA 3D printer to manufacture output materials, unreacted polymer resin remains within the output material. This unreacted polymer resin is in a state requiring further curing, thus necessitating a post-curing process. However, during this post-curing process, when the output material is exposed to the atmosphere, the photoinitiator within the output material comes into contact with oxygen, generating free radicals. The elimination effect of these free radicals inhibits photocuring.

[0061] In other words, it is necessary to prevent the output from coming into contact with oxygen. To this end, in the first post-curing process of this invention, post-curing is performed by irradiating with UV light in an inert gas environment to block contact with oxygen.

[0062] When the transparent output material undergoes the post-curing process, it will turn pale yellow, so it can be said that it is difficult to manufacture a completely transparent output material.

[0063] In particular, in the case of orthodontic appliances worn on teeth (such as clear aligners), transparency must be excellent to avoid having a significant impact on appearance.

[0064] When the transparent orthodontic device is manufactured into a customized output using a 3D printer and used as an orthodontic device, if the transparency is poor and a slight yellow tint appears, it may be mistaken for poor tooth condition, negatively impacting the user's appearance.

[0065] To prevent this problem, the 3D printed output itself must be completely transparent.

[0066] When outputs are manufactured using traditional DLP or SLA printers and then processed into products through a post-curing process, some differences may occur depending on the type of photocurable polymer resin, but the color is usually yellow, making it impossible to provide a completely transparent corrector.

[0067] Conversely, in the case of the present invention, when UV is irradiated in an inert environment during the post-curing process, the curing speed can be increased, the lightness can be enhanced, and the transparency of the output can be improved due to UV irradiation.

[0068] In other words, the post-curing process of this invention can provide a completely transparent corrective device.

[0069] This is because when UV is used for post-curing in an inert gas environment, the curing speed is increased, which increases the production speed of the final product. Furthermore, due to its excellent strength, it is not easy to deform due to external forces.

[0070] The inert gas in the second step is selected from the group consisting of nitrogen, argon, helium, krypton, neon and mixtures thereof, preferably nitrogen, but not limited to the examples described, and any inert gas that can block the output from contacting oxygen can be used without restriction.

[0071] The present invention is characterized in that a second post-curing process is performed after the first post-curing process.

[0072] Specifically, in the second post-curing process, the output material that has undergone the first post-curing process is completely immersed in an oily substance and then irradiated with UV light for post-curing.

[0073] Even without the second post-curing process, if the first post-curing process is performed at room temperature in an inert gas environment, the output will not exhibit shape memory properties.

[0074] As described later, the present invention is characterized in that when an output is manufactured using the photocurable composition of the present invention and subjected to a post-curing process according to the steps described, the output exhibits shape memory characteristics that restore it to its initial printed shape when heat above 60°C is supplied.

[0075] However, this shape memory property is achieved through the post-curing process of the present invention. Therefore, if the first post-curing process is performed without the second post-curing process or if the order is changed by performing the second post-curing process first and then the first post-curing process, the characteristics of the output cannot be achieved.

[0076] In the second post-curing process of the present invention, the output material that has undergone the first post-curing process is completely immersed in an oily substance and irradiated with UV light to perform the post-curing process.

[0077] As mentioned above, when the output material is immersed in an oily substance and irradiated with UV light, a high curing density can be achieved through a post-curing process, and sufficient heat energy can be supplied to the output material.

[0078] In other words, when immersed in oily substances, the oil can absorb the heat energy of UV rays and evenly transfer it to the output material while blocking oxygen. Due to these properties, the output material can be transferred to a uniform temperature during the second post-curing process, exhibiting the flowability characteristics of the output material.

[0079] The order of the first and second post-curing processes is crucial. Changing the order can lead to air bubbles forming on the surface of the output material due to oily substances, causing curing defects. To prevent this problem, it is preferable to perform the post-curing processes according to the sequence of the present invention.

[0080] The oily substance in the third step is selected from the group consisting of glycerol, edible oil, castor oil, non-reactive silicone oil, and mixtures thereof, with glycerol being preferred, but not limited to the examples described. Any oily substance that exhibits non-reactivity with the output, blocks contact with oxygen, and can absorb heat and uniformly transfer it to the output can be used without limitation.

[0081] Following the post-curing process, a hot water treatment process is performed. In this fourth step, the product is treated with hot water at 80 to 100°C to remove any remaining unreacted monomers.

[0082] According to another embodiment of the present invention, a transparent orthodontic device is manufactured by a post-curing method of the 3D printed output.

[0083] The transparent orthodontic appliance is used to correct teeth to the desired position by fitting over the patient's teeth.

[0084] The transparent orthodontic device of the present invention is manufactured by the aforementioned post-curing method, thus exhibiting excellent transparency, excellent physical properties, and shape memory characteristics that can be restored to the initial printed shape by heat.

[0085] The transparent orthodontic device is manufactured by printing it with a 3D printer using a light-curing composition described later, and then subjecting it to a post-curing process.

[0086] A photocurable composition for 3D printers according to an embodiment of the present invention includes: a photocurable oligomer; a reactive monomer; a photoinitiator; and nanoclay, wherein the nanoclay can enhance the mechanical properties of the output material produced by 3D printing based on the interaction of electro-attraction with the reactive monomer.

[0087] The nanoclay is characterized in that it is sepiolite; however, the nanoclay is not limited to sepiolite, and any nanoclay that can enhance mechanical properties by being included in a photocurable composition for 3D printers can be used without limitation.

[0088] To overcome the limitations of mechanical strength in 3D printing materials, polymer composite technology can be applied. However, several problems remain when using these composite materials in 3D printing. The most significant issue is the size of the additives used in the composite material. As the size of the additives increases, the size of the printing gap also increases, potentially leading to a decrease in printing resolution.

[0089] To prevent the aforementioned problems, nanoscale materials can be used as additives. However, for known traditional nanoscale materials such as graphene and carbon nanotubes (CNTs), price competitiveness may be an issue. In contrast, nanoclays offer a reasonable price and are more suitable for industrial applications. Among nanoclays, sepiolite is a type with Mg8Si... 12 O 30 Magnesium silicate hydrate is given by the half-unit cell formula of (OH)4·12H2O.

[0090] The sepiolite has the following properties: Figure 2 The cross-sectional chemical structure shown and as Figure 3 The lattice shape shown is more specifically, a needle-like or fibrous shape composed of multiple blocks and tunnels parallel to the fiber direction. Each structural block contains a central octahedral magnesium (MgOH6) sheet sandwiching two tetrahedral silica (SiO4) sheets. Individual sepiolite fibers are 0.2 to 4 μm in length, 10 to 30 nm in width, and 5 to 10 nm in thickness.

[0091] When sepiolite is included as nano-clay, the photocurable composition can maintain a viscosity suitable for 3D printing, and the printed output can exhibit high mechanical strength.

[0092] In other words, when a large amount of nano-clay is included, the viscosity of the photocurable composition increases. When the viscosity increases, the composition cannot be manufactured into an output object using a 3D printer. While including a certain amount of nano-clay can increase the mechanical strength of the output object, the high viscosity of the composition cannot be used for 3D printing. Therefore, preferably, the viscosity of the photocurable composition must be within a certain range.

[0093] Therefore, relative to 100 parts by weight of UV resin, the photocurable composition may contain 0.5 to 5 parts by weight of nano-clay and 1 part by weight of photoinitiator. The UV resin comprises photocurable oligomers and reactive oligomers. When used in combination within the range described, not only can outputs be manufactured using a 3D printer, but the manufactured outputs also exhibit excellent mechanical strength. More specifically, the 3D printer is a DLP-based 3D printer.

[0094] The photocurable oligomer can be a compound represented by the following chemical formula 1:

[0095] Chemical Formula 1

[0096]

[0097] Chemical formula 2

[0098]

[0099] Chemical formula 3

[0100]

[0101] in,

[0102] n is an integer from 1 to 1000.

[0103] A is a compound represented by chemical formula 2 or chemical formula 3.

[0104] * refers to the bonded portion.

[0105] R1 to R6 may be the same as or different from each other, and are independently selected from hydrogen, deuterium, cyano, nitro, halogen, hydroxyl, substituted or unsubstituted alkyl with 1 to 30 carbon atoms, substituted or unsubstituted cycloalkyl with 1 to 20 carbon atoms, substituted or unsubstituted alkenyl with 2 to 30 carbon atoms, substituted or unsubstituted alkynyl with 2 to 24 carbon atoms, substituted or unsubstituted aralkyl with 7 to 30 carbon atoms, substituted or unsubstituted aryl with 6 to 30 carbon atoms, substituted or unsubstituted heteroaryl with 5 to 60 carbon atoms, and substituted or unsubstituted carbon 6... The group consisting of heteroarylalkyl groups of 1 to 30, substituted or unsubstituted alkoxy groups of 1 to 30 carbon atoms, substituted or unsubstituted alkylamino groups of 1 to 30 carbon atoms, substituted or unsubstituted arylamino groups of 6 to 30 carbon atoms, substituted or unsubstituted arylalkylamino groups of 6 to 30 carbon atoms, substituted or unsubstituted heteroarylamino groups of 2 to 24 carbon atoms, substituted or unsubstituted alkylsilyl groups of 1 to 30 carbon atoms, substituted or unsubstituted arylsilyl groups of 6 to 30 carbon atoms, and substituted or unsubstituted aryloxy groups of 6 to 30 carbon atoms.

[0106] The substituted alkylene, substituted arylene, substituted heteroarylene, substituted cycloalkylene, substituted alkyl, substituted cycloalkyl, substituted alkenyl, substituted alkynyl, substituted aryl, substituted heteroaryl, substituted heteroarylalkyl, substituted alkoxy, substituted alkylamino, substituted arylamino, substituted arylalkylamino, substituted heteroarylamino, substituted alkylsilyl, substituted arylsilyl, and substituted aryloxy are selected from hydrogen, deuterium, cyano, nitro, halogen, hydroxyl, alkyl with 1 to 30 carbon atoms, cycloalkyl with 1 to 20 carbon atoms, alkenyl with 2 to 30 carbon atoms, and carbon atoms. The substituent is one or more of the following groups: alkynyl group numbering 2 to 24, aralkyl group numbering 7 to 30, aryl group numbering 6 to 30, heteroaryl group numbering 5 to 60, heteroarylalkyl group numbering 6 to 30, alkoxy group numbering 1 to 30, alkylamino group numbering 1 to 30, arylamino group numbering 6 to 30, arylalkylamino group numbering 6 to 30, heteroarylamino group numbering 2 to 24, alkylsilyl group numbering 1 to 30, arylsilyl group numbering 6 to 30, and aryloxy group numbering 6 to 30, wherein when substituted by multiple substituents, they are the same as or different from each other.

[0107] Specifically, R1 to R6 may be the same as or different from each other, and may be independently selected from the group consisting of hydrogen, deuterium, hydroxyl and alkyl groups having 1 to 30 carbon atoms.

[0108] More specifically, the photocurable oligomer is a compound represented by the chemical formula 1, and includes compounds whose A is selected from chemical formula 2 and compounds whose A is selected from chemical formula 3.

[0109] More specifically, it is a polymer compound with photocuring functional groups incorporated for UV curing, including a carbon-carbon double bond structure, through which the photocuring effect can be exhibited.

[0110] Furthermore, the photocurable oligomer is characterized in that it contains a polyurethane structure as the main chain, the polyurethane structure is incorporating photocurable functional groups, and the compound contains both soft functional groups and hard functional groups.

[0111] The output exhibits flexibility due to the soft functional groups contained in the photocurable composition, and can also exhibit heat resistance due to the hard functional groups.

[0112] In other words, by incorporating photocurable functional groups into photocurable oligomers and using both soft and hard functional groups, it is possible not only to achieve a flexible effect using a carbon skeleton that is soft at room temperature, but also to exhibit heat resistance using a carbon skeleton that is hard at room temperature.

[0113] Because the photocurable oligomer contains a carbon skeleton with rigid properties, it can produce 3D printed outputs with excellent physical properties (such as thermal properties, strength, elastic modulus and tensile elongation) and can be thermally restored to their original shape.

[0114] Furthermore, since photocurable oligomers contain a carbon skeleton with flexible properties, their shape can be deformed by external force after being supplied with heat.

[0115] Generally speaking, the composition used in 3D printers only contains a carbon skeleton with rigid properties to increase the physical properties of the output. While this can increase the physical properties of the output, conversely, when the shape is deformed due to use, the shape cannot be restored, thus posing a problem of not being able to be used multiple times.

[0116] Because the 3D printer composition according to the present invention comprises a rigid carbon skeleton and a flexible carbon skeleton, it not only possesses excellent physical properties (such as thermal properties, strength, elastic modulus, and tensile elongation), but also achieves shape recovery by utilizing the flexible properties of the soft functional groups. This shape recovery refers to the ability to be fixed in its deformed shape when subjected to heat and altered by external force, and then restored to its original shape upon further exposure to heat.

[0117] As described below, the photocurable composition for 3D printers of the present invention can be used as a clear orthodontic appliance for correcting teeth to the desired position by fitting them onto the patient's teeth. Therefore, the clear orthodontic appliance printed by a 3D printer must exhibit physical properties that will not be damaged by resistance from the current position of the patient's teeth, and should also provide the force to move the teeth to the corrected position. The corrective effect and principle of the clear orthodontic appliance of the present invention will be described below. Regarding the photocurable composition for 3D printers of the present invention, the photocurable oligomer contains both soft and hard functional groups, thus exhibiting excellent physical properties. Furthermore, due to its property (it can change shape when heated) it can be restored to its original shape by heating, thus enabling the manufacture of a clear orthodontic appliance with excellent corrective force.

[0118] Furthermore, as previously mentioned, the photocurable composition may additionally contain nano-clay, thus supplementing its physical properties and enabling it to exhibit high corrective force.

[0119] The reactive monomer is an acrylate monomer.

[0120] More specifically, the acrylate monomers may be selected from compounds represented by Chemical Formula 4 below, compounds represented by Chemical Formula 5 below, and mixtures thereof.

[0121] Chemical Formula 4

[0122]

[0123] Chemical formula 5

[0124]

[0125] A transparent orthodontic device according to another embodiment of the present invention may include the light-curing composition for 3D printing.

[0126] The transparent orthodontic device of the present invention is produced by 3D printing using a light-curing composition. Unlike traditional transparent orthodontic devices, it can even accurately reproduce the curvature of the teeth and has excellent orthodontic effect due to its strong adhesion to the teeth.

[0127] The transparent orthodontic device of the present invention is manufactured by acquiring data of the patient's tooth structure and printing it. It can be manufactured with a deviation of 50 to 80 μm from the tooth structure (almost no difference), while the traditional transparent orthodontic device has a deviation of 200 to 300 μm from the patient's teeth, which leads to a decrease in orthodontic force due to the inability to fit closely.

[0128] The transparent orthodontic device of the present invention is heated to above 40°C and then placed on the patient's teeth to fix its shape in a state of close fit to the teeth. The transparent orthodontic device that fits the teeth in a close fit can return to its original shape due to body temperature, thereby correcting the teeth.

[0129] The transparent orthodontic device of the present invention can deform its shape when immersed in heated water and then removed. When heated, it becomes soft for a certain period of time, thus allowing it to deform. Therefore, this property can be utilized to immerse the transparent orthodontic device in water at 60 to 100°C before placing it on the patient's teeth. After removal and placement on the teeth, a simple press with the hand is sufficient to achieve a close fit to the shape of the teeth and deform its form.

[0130] Afterwards, when the body temperature inside the mouth provides heat to the transparent orthodontic appliance, it will return to the original printed shape.

[0131] In other words, after immersing the transparent orthodontic device of the present invention in water at 60 to 100°C, it is then placed on the teeth and deformed to the same shape as the teeth. The transparent orthodontic device changes shape to adapt to the current dental structure of the patient. Then, when heat is provided by body temperature, it gradually returns to the initial printed state. At this time, the transparent orthodontic device moves the teeth to the position to be corrected by the force required to restore the original shape.

[0132] In other words, traditional orthodontic appliances are manufactured step-by-step based on information obtained from the patient's tooth structure. After being fitted onto the teeth according to the position of the teeth to be corrected, the appliances move the teeth according to the properties of the rigid material. As mentioned earlier, traditional clear aligners move the teeth based on the material's properties, thus failing to provide uniform force within the teeth, resulting in reduced orthodontic effectiveness.

[0133] Conversely, as mentioned above, the transparent orthodontic device of the present invention is deformed into the same state as the tooth structure when it is first used. However, when heat is provided by body temperature, the transparent orthodontic device returns to its original shape and transmits force to the tooth. The force transmitted to the tooth does not come from the material of the orthodontic device, but from the force generated and transmitted when the shape is restored. Therefore, it provides a uniform force to the entire tooth and allows the tooth to move as a whole.

[0134] Preparation Example 1

[0135] Monomers represented by Chemical Formulas 4 and 5 were mixed in a 1:1 weight ratio. After adding sepiolite, the mixture was pulverized and dispersed using an ultrasonic probe at 750 W for 1 minute. Then, it was mixed with a photocurable oligomer heated in an oven at 60°C for 12 hours to ensure its flowability. The photocurable oligomer is a chemical represented by Chemical Formula 1, including compounds selected from Chemical Formula 2 and 3, in a 1:1.5 weight ratio. Then, it was mixed with a photoinitiator represented by Chemical Formula 6, and the mixture was mixed and defoamed using a paste mixer.

[0136] Chemical Formula 1

[0137]

[0138] Chemical formula 2

[0139]

[0140] Chemical formula 3

[0141]

[0142] Chemical Formula 4

[0143]

[0144] Chemical formula 5

[0145]

[0146] Chemical Formula 6

[0147]

[0148] in,

[0149] n is an integer from 1 to 1000.

[0150] * refers to the bonded portion.

[0151] R1 to R6 are methyl groups.

[0152] Relative to 100 parts by weight of UV resin, the photocurable composition comprises 1 part by weight of photoinitiator and 2 parts by weight of sepiolite. The UV resin comprises a photocurable oligomer and monomers, and contains, in a weight ratio of 1:1.5:1:1, a compound of formula 1 A selected from formula 2, a compound selected from formula 3, a monomer represented by formula 4, and a monomer represented by formula 5.

[0153] Example 1

[0154] Preparation of transparent orthodontic appliances

[0155] The photocurable composition was placed in a DLP 3D printer and printed into a transparent corrector. The manufactured transparent corrector underwent a post-curing process. Specifically, a washing process using a dehydrator was performed in the same manner to remove residual resin and protruding surfaces.

[0156] Next, the straightening device is placed in a box and subjected to UV irradiation for 25 minutes under a nitrogen atmosphere to completely block oxygen. The device is then immersed in a water bath containing glycerin and subjected to UV irradiation for 25 minutes for a second post-curing process. Finally, the straightening device, after the second post-curing, is treated with hot water at 80 to 100°C to complete the final curing process.

[0157] Comparative Example 1

[0158] Except for using a dehydrator to wash the transparent orthodontic device printed by the DLP 3D printer and exposing the washed transparent orthodontic device to room temperature (20°C to 25°C) for up to 50 minutes, it was manufactured in the same manner as in Example 1.

[0159] Comparative Example 2

[0160] Except for using a dehydrator to wash the transparent correction device printed by the DLP 3D printer, and subjecting the washed transparent correction device to a first UV irradiation for 25 minutes in a nitrogen atmosphere, followed by a second UV irradiation for 25 minutes under the same conditions, the device was manufactured in the same manner as in Example 1.

[0161] Comparative Example 3

[0162] Except for using a dehydrator to wash the transparent orthodontic device printed by the DLP 3D printer, immersing the washed transparent orthodontic device in a water tank containing glycerin, irradiating it with UV for 25 minutes, and then irradiating it with UV for 25 minutes in a nitrogen atmosphere, the manufacturing process was carried out in the same manner as in Example 1.

[0163] Experimental Example 1

[0164] Confirmation of transparency

[0165] The transparent orthodontic appliances manufactured in Example 1, Comparative Example 1, and Comparative Example 2 were immersed in a water bath containing water at 37°C for 24 hours to create conditions similar to the oral cavity environment, and then the degree of transparency was visually confirmed.

[0166] The result, such as Figure 1 As shown. Figure 1 (a) is the transparent orthodontic device of Comparative Example 1, (b) is the transparent orthodontic device of Example 1, and (c) is the transparent orthodontic device of Comparative Example 2.

[0167] like Figure 1 As shown, it can be confirmed that (b) is significantly more transparent.

[0168] Specifically, photocuring in the atmospheric environment (exposed to air) is inhibited by the elimination of oxygen free radicals. For example... Figure 1 As shown, it can be confirmed that the transparency of the correction device cured in an atmospheric environment decreases after immersion for 24 hours. This decrease in transparency is due to the low cross-linking density of the surface, making it sensitive to moisture.

[0169] Furthermore, in Comparative Example 2, two post-curing processes were performed without glycerin immersion. However, when glycerin was used, it absorbed heat energy through UV irradiation and uniformly transferred it into the transparent orthodontic appliance, resulting in high curing density and increased transparency.

[0170] Experiment Example 2

[0171] Are bubbles forming on the surface?

[0172] As described in Comparative Example 3 above, when the second post-curing process is performed before the first post-curing process, in a different order than the post-curing method of the present invention, the experimental results can be obtained through... Figure 2 confirm.

[0173] Figure 2 When the transparent orthodontic appliance in Comparative Example 3 was not cured in a nitrogen atmosphere before being immersed in glycerin for post-curing, it was confirmed that bubbles would form on the surface.

[0174] In other words, nitrogen (N2), in its gaseous state, can act uniformly on the surface of a material. However, oils (such as glycerin) are high-viscosity fluids, and their wettability on the surface of a solidified material is uneven, which can generate bubbles during the immersion process. Figure 2 As shown, air bubbles generated during the immersion process remain as traces on the surface of the finally cured material, which are equivalent to product defects. In contrast, the clear dentistry appliance of Example 1, after being cured for the first time in a nitrogen atmosphere, was then immersed in glycerin for a second curing, confirming that it did not generate air bubbles.

[0175] Experimental Example 3

[0176] Resilience assessment

[0177] For the transparent orthodontic appliance of Example 1, the changes in the loss / storage modulus of the appliance within the temperature range were confirmed using the dynamic mechanical analysis (DMA) mode of the Anton Paar MCR702 rheometer, which is used as a double cantilever fixation device.

[0178] The result, such as Figure 3 As shown.

[0179] At around 60℃, the tgδ value of the correction device reaches its peak, which means that it can exhibit shape memory characteristics that restore it to its original state due to the internal stress generated within the correction device.

[0180] In other words, the transparent orthodontic device of the present invention is printed using the light-curing composition of the present invention and then manufactured through a post-curing process. The orthodontic device manufactured by this method has shape memory characteristics, allowing it to recover its initial printed shape at temperatures above 60°C. This characteristic should be interpreted as the orthodontic device, which is heated by heat generated by a light source during the post-curing process and transferred to the sample, having the ability to return to its initial cured state after printing.

[0181] When glycerin, an oil-based substance, is used in the second curing process, it blocks oxygen while absorbing heat and evenly transferring it to the clear aligner. The aligner manufactured using the process described above exhibits shape memory properties based on heat, a property that plays a significant role in enhancing the corrective force of the clear aligner.

[0182] Experiment Example 4

[0183] Detection of the presence of unreacted organic matter

[0184] The transparent orthodontic device of Example 1 was washed with hot water at 80 to 100°C for 5 minutes to remove unreacted monomers, and the experiment was conducted using gas chromatography-tandem mass spectrometry according to ISO 20798-2.

[0185] Experimental results are as follows Figure 4 and Figure 5 As shown. The standard curve of the sample used is as follows. Figure 4 As shown, no leaching of methyl methacrylate (MMA) was found in the correction device after hot water treatment.

[0186] The preferred embodiments of the present invention have been described in detail above, but the scope of the present invention is not limited thereto. Furthermore, various modifications and improvements made by those skilled in the art using the basic concepts of the present invention, as defined in the claims, also fall within the scope of the present invention.

[0187] Industrial applicability

[0188] This invention relates to a post-curing method for 3D printed outputs and a transparent orthodontic device manufactured by the same method. Specifically, it relates to a post-curing method that can improve product quality by post-curing the outputs of a 3D printer and a transparent orthodontic device manufactured by the same method.

Claims

1. A post-curing method for 3D printed outputs, characterized in that, include: First step: Place the 3D printed output into the rotator for washing; Second step: Perform a first post-curing on the washed output in an inert gas environment; Third step: Immerse the output material that has undergone the first post-curing in an oily substance and then perform the second post-curing; as well as Fourth step: The output material that has undergone the second post-curing process is subjected to hot water treatment. When supplied with heat above 60°C, the output exhibits shape memory properties, recovering to its initial printed shape. The first and second post-curing processes are performed by irradiating with UV light.

2. The post-curing method for 3D printed outputs according to claim 1, characterized in that, The 3D printed output is produced by a 3D printer that uses digital light processing or stereolithography.

3. The post-curing method for 3D printed outputs according to claim 1, characterized in that, The first step removes residual resin from the output.

4. The post-curing method for 3D printed outputs according to claim 1, characterized in that, The inert gas in the second step is selected from nitrogen, argon, helium, krypton, neon, and mixtures thereof.

5. The post-curing method for 3D printed outputs according to claim 1, characterized in that, The oily substance in the third step is selected from the group consisting of glycerol, edible oil, castor oil, non-reactive silicone oil, and mixtures thereof.

6. The post-curing method for 3D printed outputs according to claim 1, characterized in that, The fourth step involves processing with hot water at 80 to 100°C.

7. A transparent orthodontic appliance, characterized in that, It is manufactured by the post-curing method of the 3D printed output as described in any one of claims 1 to 6.

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