A three-dimensional printing method

Abstract

A method for three-dimensional printing of an object having different degrees of transmittance to light along an axis of the object is provided, the method comprising the steps of: (a) providing a liquefied polymer resin having a plurality of particles therein, the particles being distributed in the liquefied polymer resin according to the density of the particles; and (b) polymerizing the liquefied polymer resin under certain conditions to form the object layer by layer. A formulation for three-dimensional printing and a three-dimensional printed object are also provided.

Description

Technical Field

[0001] The present invention generally relates to a method for three-dimensional printing of an object. The present invention also relates to a formulation for three-dimensional printing and a three-dimensional printed object. Background Art

[0002] The dental industry is one of the strongest drivers for the development of new additive manufacturing technologies, including new three-dimensional (3D) printers and printable materials. Since 2015, revenue from dental 3D printing has grown by nearly 12%. Currently, dental 3D printing is widely used to make dental implants, dentures, crowns, and bridges, among others. The global dental 3D printing market is expected to be worth $3,427.1 million by the end of 2025. The dental 3D printing market can be divided into three major segments, such as metal, polymer resin, and ceramic. Polymer resins account for the largest market for dental 3D printing, with a market share of 58.0% in 2016, due to the emergence of new technologies for the development of cost-effective polymer materials.

[0003] Generally speaking, clinical dentistry focuses on aesthetics (about 50%), and the rest involves materials, mechanical properties, and others. Dental aesthetics has become increasingly important over the past few decades. The ability to control the color of artificial teeth or to match the shade of artificial teeth with the color of the patient's natural teeth is absolutely important for the future dental industry. When artificial teeth are printed, it is very important to maintain aesthetics by producing artificial teeth with a color as similar as possible to natural teeth. In traditional dental treatment, color plates have been widely used to make artificial teeth have a better color match with natural teeth. However, conventional composite materials are generally monochromatic. For natural teeth, the tooth color from the neck to the incisor is gradual, forming a gradient of color / shade in the tooth. This is because the chromaticity of natural teeth mainly comes from the dentin, and the thickness and opacity of the overlying enamel determine how much the chromaticity of the dentin affects.

[0004] Although attempts to form artificial teeth with gradient colors that best match natural teeth have been reported, the development of dental printing with gradient color changes has not been reported.

[0005] For gradient composites, two main types of gradient structures have been proposed, the first being a continuous structure and the second being a stepped structure. For a continuous gradient structure, the changes in composition and microstructure occur continuously as the position changes. On the other hand, for a stepped gradient structure, the microstructural features change in a step-like manner. Based on the gradient type, gradient composites can also be divided into chemical composition gradient materials, porosity gradient materials, and microstructural gradient materials.

[0006] The manufacturing process of gradient materials can be divided into gradient film coating technology and bulk gradient material technology. The technology for manufacturing gradient thin films includes physical vapor deposition process, chemical vapor deposition process and self-propagating high temperature synthesis (SHS) process, or a combination of some of these processes. The technology used to produce bulk gradient materials includes powder metallurgy, centrifugal casting, slip casting and tape casting.

[0007] When using powder metallurgy, powder materials are first mixed together, then the powder is processed, subjected to a forming operation, and sintered or pressure-assisted thermal consolidation. Although the powder metallurgy process is cheaper than other technologies, the strength of the materials produced by this process is limited, highly complex parts cannot be produced using this process, and it is also complicated to use.

[0008] Recently, with the development of additive manufacturing technology, many additive manufacturing techniques have been tried to develop gradient material printing. However, so far, only four types of additive manufacturing techniques such as material extrusion, powder bed fusion, directed energy deposition, and sheet lamination have been successfully used to manufacture parts with gradient materials.

[0009] According to the literature, gradient materials have been fabricated using fused deposition modeling (FDM) and frozen extrusion fabrication (FEF) techniques. In the FDM process, the FDM process parameters are matched to the material properties of the produced acrylonitrile-butadiene-styrene material, which is then used to develop gradient material samples. This shows the possibility of developing gradient materials using different loading conditions through FDM technology. FEF has also been used to fabricate functional gradient parts, which uses a mechanism of three extruders, each containing a material paste. It uses a static mixer to mix the different material pastes into a homogeneous paste. The advantages of the material extrusion process are cost savings and ease of use. The main disadvantages are that the quality of the part is limited by the nozzle radius, the accuracy is poor compared to other printing technologies, and the process is slow.

[0010] Powder Bed Fusion (PBF) processes are a class of additive manufacturing technologies where powdered materials (metals, polymers, ceramics) are laid on a build platform and sintered with a laser beam or electron beam to form two-dimensional layers from sliced ​​3D CAD files. Numerous additive manufacturing technologies fall into the PBF category, such as Selective Laser Sintering (SLS), Selective Laser Melting (SLM), Selective Heat Sintering (SHS) and Electron Beam Melting (EBM). The main disadvantage of using PBF technology is the need for vacuum and high temperatures in an inert environment.

[0011] Directed energy deposition (DED) is a class of additive manufacturing processes used to produce 3D objects from 3D CAD models, using energy (such as laser, electron beam or plasma arc) to create a molten pool on a substrate. Laser-metal deposition (UM) is a typical DED technology and is widely used for the repair of high-value parts. The laser-direct metal deposition (LDMD) process has been used to form thin-walled gradient structures of 316L steel and 718 chromium-nickel-iron alloy (Inconel 718). The results show that gradient materials can be continuously produced using the LDMD process; and the properties of the functional gradient materials produced can be controlled by controlling the processing parameters.

[0012] Sheet lamination type additive manufacturing processes include ultrasonic additive manufacturing (UAM) and laminated object manufacturing (LOM). It has been reported that gradient materials have been successfully manufactured using sheet lamination technology by using an ultrasonic consolidation process. Three sheet materials including stainless steel foil, aluminum foil and copper foil were used in this study, and the formation of gradient structures was demonstrated. The main disadvantage of lamination technology is that the achievable surface finish is heavily dependent on the material used and requires long post-processing to achieve the desired surface finish.

[0013] Although the above four techniques have been successfully demonstrated to fabricate functional gradient materials, they all have their own drawbacks and have not yet been used for dental printing with gradient color changes.

[0014] It is necessary to provide a 3D printing method for functional gradient materials that overcomes or at least improves one or more of the above-mentioned disadvantages.

[0015] Overview

[0016] A method for three-dimensionally printing an object having different degrees of transmittance to light along an axis of the object is provided, the method comprising the following steps: (a) providing a liquefied polymer resin having a plurality of particles therein, wherein the particles are distributed in the liquefied polymer resin according to the density of the particles; and (b) polymerizing the liquefied polymer resin under certain conditions to form the object layer by layer.

[0017] In a first aspect, the present disclosure relates to a method for three-dimensionally printing an object having different degrees of transmittance to light along an axis of the object, the method comprising the steps of: (a) providing a liquefied polymer resin having a plurality of particles therein, wherein the particles have a density of about 3 g / cm 3 Up to 12g / cm 3 the particles are distributed in the liquefied polymer resin according to the density of the particles; and (b) polymerizing the liquefied polymer resin under certain conditions to form the object layer by layer.

[0018] The method may involve vat photopolymerization technology. Printing technologies based on vat photopolymerization include laser-based stereolithography (SLA) and digital light processing (DLP) 3D printing. Both technologies can provide high printing resolution and high surface smoothness, making them ideal technologies for bio-related printing, such as dental and bone 3D printing.

[0019] Advantageously, the method can be used to print artificial teeth with natural gradient color changes. Therefore, the method provides a 3D printing solution to the problem of single-color dental restoration composites, whereby the method can be used to produce functionally graded artificial teeth with a color gradient from the bottom of the tooth to the top of the tooth. This allows the artificial teeth to be similar in color and shade to natural teeth.

[0020] In another aspect, the present disclosure relates to a formulation for three-dimensional printing, comprising, based on the weight of the formulation: (i) 60 to 95 wt% of a liquefied polymer resin; (ii) 5 to 40 wt% of particles; (iii) 0.1 to 5 wt% of a photoinitiator; and (iv) 0 to 0.2 wt% of a photoadditive; wherein the particles include a plurality of particles having different density values; and wherein the particles have a density of 3 g / cm 3 Up to 12g / cm 3 Density within the range.

[0021] A three-dimensional printed object is provided, the object having different degrees of transmittance to light along an axis of the object.

[0022] In another aspect, the present disclosure relates to a three-dimensional printed object having different degrees of transmittance to light along an axis of the object; wherein along the axis, the transparency of the object gradually changes from opaque or partially opaque at one end to translucent or transparent at the other end.

[0023] definition

[0024] As used herein, the following words and terms shall have the meanings indicated.

[0025] The word "substantially" does not exclude "completely", for example, a composition "substantially free" of Y may be completely free of Y. If necessary, the word "substantially" may be omitted from the definition of the present invention.

[0026] Unless otherwise stated, the terms "comprising" and "comprise" and grammatical variations thereof are intended to represent "open" or "inclusive" language such that they include the elements stated but also permit the inclusion of additional, unrecited elements.

[0027] As used herein, the term "about", in the context of formulation ingredient concentrations, typically refers to + / - 5% of the stated value, more typically refers to + / - 4% of the stated value, more typically refers to + / - 3% of the stated value, more typically refers to + / - 2% of the stated value, even more typically refers to + / - 1% of the stated value, and even more typically refers to + / - 0.5% of the stated value.

[0028] In the present disclosure, certain embodiments may be disclosed in the form of ranges. It should be understood that the description in the form of ranges is only for convenience and brevity and should not be construed as a hard limit to the disclosed range. Therefore, the description of a range should be deemed to have specifically disclosed all possible subranges and each numerical value within the range. For example, a description of a range such as from 1 to 6 should be deemed to specifically disclose subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and each number within the range, such as 1, 2, 3, 4, 5 and 6. This applies regardless of the breadth of the range.

[0029] Certain embodiments may also be described broadly and generically herein. Each of the narrower classes and subgeneric groupings falling within the generic disclosure also form part of this disclosure. This includes the generic description of the embodiments with a proviso or negative limitation removing any subject matter from the generic, regardless of whether the removed material is specifically recited herein. DETAILED DESCRIPTION

[0030] An exemplary, non-limiting embodiment of a method of three-dimensionally printing an object will now be disclosed.

[0031] The method may include the steps of: (a) providing a liquefied polymer resin having a plurality of particles therein, the particles being distributed in the liquefied polymer resin according to the density of the particles; and (b) polymerizing the liquefied polymer resin under conditions to form an object layer by layer.

[0032] The object may be an object having different degrees of transmittance to light along an axis of the object. The axis may be in the direction of three-dimensional printing, with the zero position of the axis being where the first layer begins to print and moving forward in the direction of further printing of the object. The axis may be considered a "Z-axis" and is therefore orthogonal to the XY plane (where the XY plane is typically a substrate or support on which a three-dimensional object is printed or forms the basis for the layer-by-layer printing of a three-dimensional object). Thus, the object may be an object having different degrees of transmittance to light along its Z-axis.

[0033] Different degrees of transmittance to light can be such that the lowest transmittance to light occurs at the bottom of the object (i.e., the zero point position of the above-mentioned axis), while the maximum transmittance occurs at the top of the object, away from the zero point position of the above-mentioned axis (or the highest possible positive value of the above-mentioned axis).

[0034] The portion of the object with the lowest transmittance to light is considered to be opaque or partially opaque to the passage of light through the object, while the portion of the object with the highest transmittance to light does not mean that this portion of the object is completely transparent, but rather that this portion of the object allows more light to pass through (and is therefore less opaque, or more translucent) than the portion of the object with the lowest transmittance to light. Along the above-mentioned axis, the lowest transmittance to light occurs at the zero point of the axis and increases along the axis so that the maximum transmittance occurs at the highest possible positive value on the axis. Different degrees of transmittance can be a transmittance that varies randomly along the axis (that is, as long as the maximum transmittance occurs at the highest possible positive value of the axis, the transmittance can be higher or lower than another point along the axis). Different degrees of transmittance can be a transmittance that gradually increases along the axis, so that a point on the object with a higher positive value on the axis always has a greater transmittance than a point on the axis with a lower positive value.

[0035] It is understandable that the above situation can also be viewed in reverse, that is, different degrees of transmittance to light can be such transmittance: the lowest transmittance to light appears at the top of the object (i.e., the highest possible positive value of the above axis), and the maximum transmittance appears at the bottom of the object (i.e., the zero point position of the above axis). Therefore, the maximum transmittance to light appears at the zero point position of the axis and decreases along the axis, so that the lowest transmittance appears at the highest possible positive value on the axis.

[0036] The varying degrees of transmittance along an object may appear as a color variation or color gradient that can be observed when viewing the outer surface of the object. The color can be thought of as being "darker" or having a darker hue at points where the object has lower transmittance, and "lighter" or having a lighter hue at points where the object has higher transmittance.

[0037] The transmittance to light may be considered as the transmittance to visible light having a wavelength in the range of about 380 to about 740 nanometers.

[0038] The method may further include, prior to providing step (a), the following steps: (a1) providing a homogenous suspension of particles in a liquefied polymer resin; and (a2) distributing the particles in the liquefied polymer resin according to their density values ​​after a period of time. The particles may be mixed in the liquefied polymer resin for a period of time. The particles may be mixed by subjecting the mixture to shear forces, mixing forces, or ultrasonic mixing. The mixing may be performed for a period of at least 1 hour, at least 2 hours, at least 3 hours, or at least 4 hours. The liquefied polymer resin may then be allowed to stand for a period of time ranging from a few minutes to an hour or about 5 minutes to 30 minutes to allow sedimentation to occur, thereby allowing the particles in the liquefied polymer resin to separate under the action of gravity according to differences in density, resin viscosity, particle size, and / or particle shape. Due to the use of different types of particles with different density values, or the use of particles of the same type (i.e., particles of the same material) but with different shapes / sizes that result in different density values, particles with the same density value will settle in the same area of ​​the liquefied polymer resin, so that the type of particles will change when moving from the bottom of the liquefied polymer resin to the top of the liquefied polymer resin. Particles with the largest or greater density values ​​will settle at the bottom of the liquefied polymer resin, while particles with smaller density values ​​will settle in the upper regions, resulting in a distribution of particles within the liquefied polymer resin based on particle density. Due to this distribution of particles within the liquefied polymer resin, this will determine the light transmittance of the final printed object, as portions of the printed object with more particles will have lower transmittance to light, while portions of the printed object with fewer particles will have higher transmittance to light. Particles can be colored, thus contributing to color variations or color gradients along the object.

[0039] The liquefied polymer resin may further include a photoinitiator and an optional light additive selected from a light absorber or a light stabilizer. The photoinitiator and the optional light additive may be added to the liquefied polymer resin containing the particles and mixed to form a uniform suspension. In order to avoid premature polymerization of the polymer resin, mixing is carried out in the absence of light. Any suitable mixing technique can be used to stir the mixture for a suitable period of time. For example, when the mixing technique used is magnetic stirring, mechanical stirring or shaking, the mixing time can be about 8 hours to about 24 hours, about 8 hours to about 12 hours, about 8 hours to about 18 hours, about 12 hours to about 24 hours, or about 18 hours to about 24 hours to form a uniform suspension. When the mixing technique is homogenization and / or ultrasonic treatment, the mixing time can be about 10 minutes to about 15 minutes, about 10 minutes to about 30 minutes, about 10 minutes to about 45 minutes, about 10 minutes to about 60 minutes, about 10 minutes to about 75 minutes, about 10 minutes to about 90 minutes, about 10 minutes to about 105 minutes, about 15 minutes to about 2 hours, about 30 minutes to about 2 hours, about 45 minutes to about 2 hours, about 60 minutes to about 2 hours, about 75 minutes to about 2 hours, about 90 minutes to about 2 hours, or about 105 minutes to about 2 hours.

[0040] The liquefied polymer resin may have a viscosity ranging from about 100 to about 1000 cps, about 100 to about 900 cps, about 100 to about 800 cps, about 100 to about 700 cps, about 100 to about 600 cps, about 100 to about 500 cps, about 100 to about 400 cps, about 100 to about 300 cps, about 100 to about 200 cps, about 200 to about 1000 cps, about 300 to about 1000 cps, about 400 to about 1000 cps, about 500 to about 1000 cps, about 600 to about 1000 cps, about 700 to about 1000 cps, about 800 to about 1000 cps, or about 900 to about 1000 cps. Depending on the viscosity of the resin, this will affect the light transmittance in the formed object, thereby affecting the optical effect of the formed object. Generally speaking, the liquefied polymer resin can have a uniform viscosity, which will affect the dispersibility of the particles. If particles with a large density are used, a liquefied polymer resin with a large viscosity will be selected. Similarly, if particles with a low density are used, a liquefied polymer resin with a low density will be selected.

[0041] The liquefied polymer resin may then be polymerized to form the object layer by layer. This may involve the use of vat photopolymerization, where the liquefied polymer resin is placed in a vat and a support arm is moved within the vat to allow a thin layer of the liquefied polymer resin to be exposed to a light source close to the surface of the liquefied polymer to initiate polymerization of that layer. Once one layer is polymerized, the support arm is moved to expose another thin layer of the liquefied polymer resin to the light source again to polymerize the subsequent layer. This is repeated until the object is formed. The light source may be ultraviolet light, a laser, or any suitable light source capable of exciting the photoinitiator present in the liquefied polymer resin to initiate the polymerization process.

[0042] The formed object may be post-processed, such as washed, dried, and further cured. Thus, the formed object may be washed with an organic solvent (such as isopropyl alcohol) to remove any excess liquefied polymer resin and then dried. To complete the curing process, the formed object may be placed in a UV oven.

[0043] The method can be used with any conventional 3D printer with any conventional 3D printing software.

[0044] Exemplary, non-limiting embodiments of formulations for three-dimensional printing will now be disclosed.

[0045] Agents used for 3D printing include:

[0046] (i) liquefying a polymer resin;

[0047] (ii) multiple particles with different density values;

[0048] (iii) a photoinitiator; and

[0049] (iv) Optional photoadditives.

[0050] The various ingredients may be present in the formulation in the following amounts based on the weight of the formulation:

[0051] (i) 60 to 95 wt% of a liquefied polymer resin;

[0052] (ii) 0.5 to 40 wt% of particles;

[0053] (iii) 0.1 to 5 wt % of a photoinitiator; and

[0054] (iv) 0 to 0.2 wt% of a photoadditive.

[0055] The liquefied polymer resin may include an acrylate. It should be understood that any acrylate suitable for three-dimensional printing can be used here. Exemplarily, the acrylate can be a monomer or oligomer selected from the group consisting of: bisphenol A dimethacrylate (Bis-DMA), bisphenol A diglycidyl ether methacrylate (Bis-GMA), ethoxylated bisphenol A dimethacrylate (Bis-EMA), tricyclo[5.2.1.02,6]decanedimethanol diacrylate, bisphenol A glycerol diacrylate, bisphenol A ethoxylate diacrylate, bisphenol A ethoxylate dimethacrylate (oligomer), bisphenol F ethoxylate diacrylate (oligomer), poly(ethylene glycol) diacrylate Acrylates, di(ethylene glycol) diacrylate, tetra(ethylene glycol) diacrylate, 1,4-butanediol diacrylate, hydroxyethyl methacrylate, 3,4-epoxy-cyclohexyl-methyl methacrylate (METHB), triethylene glycol dimethacrylate (TEGDMA), tert-butyl cyclohexanol methacrylate, 1,6-bis[2-(methacryloyloxy)ethoxycarbonylamino]-2,4,4-trimethylhexane (UDMA), 3,3,5-trimethylcyclohexanol methacrylate, dipentaerythritol penta / hexaacrylate and mixtures thereof.

[0056] The particles in the formulation may have a particle size of about 3.00 g / cm 3 To about 12.00g / cm 3 , about 3.00g / cm 3 To about 4.00g / cm 3 , about 3.00g / cm 3 To about 5.00g / cm 3 , about 3.00g / cm 3 To about 6.00g / cm 3 , about 3.00g / cm 3 To about 7.00g / cm 3 , about 3.00g / cm 3 To about 8.00g / cm 3 , about 3.00g / cm 3 To about 9.00g / cm 3 , about 3.00g / cm 3 To about 10.00g / cm 3 , about 3.00g / cm 3 To about 11.00g / cm 3 , about 4.00g / cm 3 To about 12.00g / cm 3 , about 5.00g / cm 3 To about 12.00g / cm 3 , about 6.00g / cm 3To about 12.00g / cm 3 , about 7.00g / cm 3 To about 12.00g / cm 3 , about 8.00g / cm 3 To about 12.00g / cm 3 , about 9.00g / cm 3 To about 12.00g / cm 3 , about 10.00g / cm 3 To about 12.00g / cm 3 , or about 11.00g / cm 3 To about 12.00g / cm 3 As described above, depending on the density value, the particles will settle or distribute in the liquefied polymer resin, forming a particle gradient based on the particle density value in the liquefied polymer resin, wherein particles with higher density values ​​will settle at the bottom of the liquefied polymer resin due to gravity, while particles with lower density values ​​will exist in the area above the particles with higher density.

[0057] The particles can have a particle size in the nanometer or micrometer range. The particle size can be between about 50 nanometers and about 50 micrometers, about 50 nanometers and about 100 nanometers, about 50 nanometers and about 200 nanometers, about 50 nanometers and about 500 nanometers, about 50 nanometers and about 1 micrometer, about 50 nanometers and about 5 micrometers, about 50 nanometers and about 10 micrometers, about 50 nanometers and about 15 micrometers, about 50 nanometers and about 20 micrometers, about 50 nanometers and about 25 micrometers, about 50 nanometers and about 30 micrometers, about 50 nanometers and about 35 micrometers, about 50 nanometers and about 40 micrometers, about 50 nanometers and about 50 micrometers. In the range of about 45 microns, about 100 nanometers to about 50 microns, about 200 nanometers to about 50 microns, about 500 nanometers to about 50 microns, about 1 micron to about 50 microns, about 5 microns to about 50 microns, about 10 microns to about 50 microns, about 15 microns to about 50 microns, about 20 microns to about 50 microns, about 25 microns to about 50 microns, about 30 microns to about 50 microns, about 35 microns to about 50 microns, about 40 microns to about 50 microns, or about 45 microns to about 50 microns.

[0058] The shape of the particles is not particularly limited and may be spherical, rod-like, fibrous, plate-like or star-like.

[0059] The particles that can be used in the method may not be particularly limited, as long as they have a density value within the above range. For example, the particles may be selected from the group consisting of metal oxides, metal nitrides, metal carbides, metalloid oxides, metalloid nitrides, and metalloid carbides. The metal or metalloid in the metal oxide, metal nitride, metal carbide, metalloid oxide, metalloid nitride, or metalloid carbide may be selected from Group 2, Group 3, Group 4, Group 5, Group 6, Group 8, Group 11, Group 12, Group 13, Group 14, or the lanthanide series of the periodic table. The particles may be selected from zinc oxide (5.61 g / cm 3 ), silicon carbide (3.21g / cm 3 )、Silicon nitride (3.44g / cm 3 ), GaN (6.15 g / cm 3 ), aluminum oxide (3.95 g / cm 3 ), titanium dioxide (4.23 g / cm 3 ), zirconium dioxide (5.68g / cm 3 ), tin dioxide (5.61g / cm 3 ), iron(III) oxide (5.24 g / cm 3 ), magnesium oxide (3.58 g / cm 3 ), indium(III) oxide (7.18 g / cm 3 ), tungsten trioxide (7.16g / cm 3 ), tungsten(IV) oxide (10.8 g / cm 3 ), silver oxide (7.14 g / cm 3 ), vanadium(V) oxide (3.36 g / cm 3 ), vanadium(IV) oxide (4.57 g / cm 3 ), molybdenum trioxide (4.69 g / cm 3 ), yttrium(III) oxide (5.01 g / cm 3 ), cerium (IV) oxide (7.22 g / cm 3 ) and copper(II) oxide (6.31 g / cm 3 A mixture of different types of particles with different density values ​​may be used, as well as particles of the same type (i.e. all particles are from the same material) but of different shapes / sizes may be used in order to form a plurality of particles with different density values.

[0060] The photoinitiator used in the formulation may not be particularly limited and may depend on the type of acrylate used. The photoinitiator may be a Type I or Type II photoinitiator. For example, the photoinitiator may be selected from the group consisting of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (IRGACURE 819), phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO), 2,4,6-trimethylbenzoyldiphenylphosphine (TPO), 2-hydroxy-2-methyl-1-phenyl-1-propane (DAROCUR 1173) and benzophenone (BP).

[0061] The light additive used in the formulation may not be particularly limited, and may be a light absorber. Exemplary light absorbers may be selected from the group consisting of Sudan I-IV, 2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene, 4-methoxyphenol, and butylhydroxytoluene.

[0062] Exemplary, non-limiting embodiments of three-dimensionally printing an object will now be disclosed.

[0063] The 3D printed object may have different degrees of transmittance to light along the axis of the object. The different degrees of transmittance to light may be along the Z axis of the object.

[0064] The 3D printed object can be considered to have a functional color gradient along an axis. The 3D printed object can be a tooth or an implant for a human or animal body. When the 3D printed object is used as a surgical or biological product, it is important to note that the components of the formulation forming the 3D printed object may not be toxic or harmful to the recipient.

[0065] BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The accompanying drawings illustrate the disclosed embodiments and are used to explain the principles of the disclosed embodiments. However, it should be understood that the accompanying drawings are designed only for illustration purposes and not as a definition of the limits of the present invention.

[0067] Figure 1

[0068] [ Figure 1 ] is a schematic diagram showing an implementation of the disclosed three-dimensional printing method.

[0069] Figure 2

[0070] [ Figure 2 a] is a side view photograph of a printing plate made according to the following Example 1. [ Figure 2 b] is a graph showing the variation of transparency with plate position.

[0071] Figure 3

[0072] [ Figure 3 a] is a side view photograph of a printing plate made according to the following Example 2. [ Figure 3 b] is a graph showing the variation of transparency with plate position.

[0073] Figure 4

[0074] [ Figure 4 ] is an image showing a cross-section of a printed tooth produced according to Example 3 below.

[0075] Figure 5

[0076] [ Figure 5 ] is an image showing a cross-section of a printed tooth produced according to Example 3 below.

[0077] Figure 6

[0078] [ Figure 6 ] is a photograph showing prototypes of some artificial teeth made according to Example 4 below.

[0079] Detailed description with drawings

[0080] Reference Figure 1 , provides a schematic diagram showing an embodiment of the disclosed three-dimensional printing method based on digital light processing. Figure 1 In (I), first, a liquefied polymer resin 2 is provided in a vat 6, and the liquefied polymer resin 2 is as described above. When the liquefied polymer resin 2 settles under the action of gravity, a sedimentation potential is generated. The high-density particles present in the liquefied polymer resin 2 are suspended or settled at a rate that depends on the following factors: density difference, fluid viscosity, particle size and particle shape. Therefore, when the high-density particles are mixed with a vat of polymer for liquid resin-based 3D printing, the high-density particles will form a sedimentation gradient ( Figure 1 (I)). When the platform 4 is lowered for printing, the solidified material of the initial layer will have a higher particle content due to the sedimentation of the particles. As the printing process continues, more and more particles are solidified into the polymer resin, and the particle concentration in the liquid polymer resin will decrease accordingly. Figure 1 As shown in Figure 2, the particle concentration decreases as the printing process progresses (from Figure 1 (I) to Figure 1 (II), to Figure 1 (III) to Figure 1(IV)), and finally a limited number of particles remain in the resin, resulting in an increasingly transparent solid. In this way, the printed structure will show a gradient color change from bottom to top, and a similar gradient change in transparency. In this way, a one-dimensional gradient of the component material content can be generated in the printed structure. Due to the sedimentation process, the highest filler content is expected in the lowest printed layers.

[0081] Example

[0082] Non-limiting embodiments of the present invention are described in further detail by reference to specific examples, which should not be construed as limiting the scope of the present invention in any way.

[0083] Example 1

[0084] Resin preparation

[0085] The base resin and particles (all chemicals were from Aldrich Sigma, St. Louis, MO, USA) (Table 1) were weighed into a flask and sonicated in an ultrasonic bath for at least 2 h. The photoinitiator and light stabilizer were then added to the mixture and stirred in the absence of light for 8 to 24 h until a homogeneous suspension was obtained.

[0086] Table 1 - Resin Formulation 1

[0087] Element Percentage (wt%) Bisphenol A ethoxylate diacrylate (average Mn~468) 35 Di(ethylene glycol) dimethacrylate (Aldrich) 60 Zinc oxide (particle size <5μm) 4.4 Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide 0.5 4-Methoxyphenol 0.1

[0088] Printing structures with gradient optical property changes

[0089] To demonstrate the possibility of gradient color printing, a rectangular plate was printed on a DLP printer (LittleRP, build volume 60mm (X) 40mm (Y) 100mm (Z), using a dynamic light processing projector (brand and model: Acer P128) with a resolution of 1024×768 as the light source, and Creation Workshop as the control software). Printing was performed with a layer thickness of 50μm. The exposure time for each layer was 6 seconds. After printing, the printed parts were thoroughly cleaned with isopropyl alcohol, air-dried and placed in a UV oven for further curing. Figure 2 A printed structure with gradient color change is shown in a. In addition, the gradient change of transparency is evaluated by using UV-visible spectrometry. The difference in transparency is measured at different positions and the results are plotted in Figure 2 b.

[0090] Example 2

[0091] Resin preparation

[0092] The base resin and particles (Table 2) were weighed into a flask and sonicated in an ultrasonic bath for at least 2 hours. The photoinitiator and light stabilizer were then added to the mixture and stirred in the absence of light for 8 to 24 hours until a homogeneous suspension was obtained.

[0093] Table 2 - Resin Formulation 2

[0094] Element Percentage (wt%) Bisphenol A ethoxylate diacrylate (average Mn~468) 23 Di(ethylene glycol) dimethacrylate 70 Zirconium dioxide (325 mesh) 6.4 Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide 0.5 4-Methoxyphenol 0.1

[0095] Printing structures with gradient optical property changes

[0096] To demonstrate the possibility of gradient color printing, a rectangular plate was printed on a DLP printer (LittleRP, build volume 60mm (X) 40mm (Y) 100mm (Z), using a dynamic light processing projector (brand and model: Acer P128) with a resolution of 1024×768 as the light source, and Creation Workshop as the control software). Printing was performed with a layer thickness of 50μm. The exposure time for each layer was 6 seconds. After printing, the printed parts were thoroughly cleaned with isopropyl alcohol, air-dried and placed in a UV oven for further curing. Figure 3 a shows a printed structure with gradient color change. In addition, the gradient change of transparency was evaluated by using UV-visible spectrometer. The difference in transparency was measured at different positions and the results are plotted in Figure 3 b.

[0097] Example 3 - Dental Printing and Characterization

[0098] Resin preparation

[0099] The base resin and particles (Table 3) were weighed into a flask and sonicated in an ultrasonic bath for at least 2 hours. The photoinitiator and light stabilizer were then added to the mixture and stirred in the absence of light for 8 to 24 hours until a homogeneous suspension was obtained.

[0100] Table 3 - Resin Formulation 3

[0101]

[0102]

[0103] Printing structures with gradient optical property changes

[0104] To demonstrate the possibility of artificial teeth with gradient color changes, tooth structures were printed on a DLP printer (LittleRP, with a build volume of 60 mm (X) 40 mm (Y) 100 mm (Z), using a dynamic light processing projector (brand and model: Acer P128) with a resolution of 1024×768 as the light source and Creation Workshop as the control software). Printing was performed with a layer thickness of 50 μm. The exposure time for each layer was 6 seconds. After printing, the printed parts were thoroughly cleaned with isopropyl alcohol, air-dried and placed in a UV oven for further curing. The printed structure was cut, and the cut image of the cross section is shown in Figure 4 and Figure 5 The cut structures were measured by scanning electron microscopy to confirm the distribution of particles ( Figure 4 ), and confirmed the gradient structure by energy dispersive X-ray spectroscopy measurements ( Figure 5 ).

[0105] refer to Figure 4 , the peripheral photos show that the pigment concentration (white particles in the photos) in the cross-section of the printed tooth increases from top to bottom (the order of the photos from top to bottom is: top left, top right, middle left, bottom right, and bottom left). Therefore, the maximum concentration of pigment is at the bottom of the printed tooth, and the lowest concentration of pigment is at the top of the printed tooth.

[0106] refer to Figure 5 , the peripheral photos show that the abundance of pigment elements in the cross-section of the printed teeth increases from top to bottom (the order of the photos from top to bottom is: upper left, upper right, middle left, lower right and lower left). Figure 4 Similarly, the maximum abundance of the pigment is at the bottom of the printed tooth, while the lowest abundance of the pigment is at the top of the printed tooth.

[0107] Example 4 - Prototype printing

[0108] To demonstrate the application of this technology in dental printing, a set of teeth with gradient color changes were printed on a DLP printer (LittleRP, with a build volume of 60mm (X) 40mm (Y) 100mm (Z), using a dynamic light processing projector (brand and model: AcerP128) with a resolution of 1024×768 as the light source, and Creation Workshop as the control software). The resin used was the same as that described in Example 3. Printing was performed with a layer thickness of 50μm. The exposure time for each layer was 6 seconds. After printing, the printed parts were thoroughly cleaned with isopropyl alcohol, air-dried and placed in a UV oven for further curing. The printed prototype is displayed on Figure 6 In the figure, the gradient color changes of the printed teeth are clearly shown.

[0109] Industrial Applicability

[0110] The disclosed method can be used to 3D print an object having different degrees of transmittance to light along its axis. The 3D printed object can be used as an artificial tooth, wherein the artificial tooth has higher opacity in the neck region and higher translucency in the incisor region.

[0111] The 3D printed object can be used as an implant in the human or animal body, such as an artificial bone. The 3D printed object can be used to form artificial materials that mimic those found in nature, such as wood or bamboo, with functional hierarchies.

[0112] The disclosed methods can be used for engineering device development, whereby materials formed therefrom can have graded combinations of flexibility, elasticity, or rigidity.

[0113] The disclosed method can be used in flame retardant applications, such as forming spacecraft heat shields or heat exchanger tubes.

[0114] The disclosed method can be used in electronic devices or optoelectronic devices, such as optical fibers for high-speed transmission.

[0115] The disclosed method may be used for defense, such as in armor plates or bulletproof vests.

[0116] The disclosed method can be used for thermal barrier coatings, such as in the automotive, aircraft industries, and power plants, to reduce heat losses from engine exhaust systems.

[0117] The disclosed methods can be used in energy applications, such as energy conversion devices.

[0118] Obviously, various other modifications and adaptations of the present invention will be apparent to those skilled in the art after reading the above disclosure without departing from the spirit and scope of the present invention, and all such modifications and adaptations are intended to be within the scope of the appended claims.

Claims

1. A method for three-dimensionally printing an object, wherein the object has different degrees of light transmittance along an axis of the object, the method comprising the following steps: (a) providing a liquefied polymer resin having a plurality of particles therein, wherein the particles have a particle size of 3 g / cm 3 Up to 12g / cm 3 the particles are distributed in the liquefied polymer resin according to the density of the particles; and (b) polymerizing the liquefied polymer resin by exposing each layer to light to form the object layer by layer.

2. The method according to claim 1, further comprising the following steps before step (a): (a1) providing a homogeneous suspension of said particles in said liquefied polymer resin; as well as (a2) After a period of time, the particles are distributed in the liquefied polymer resin according to their density values.

3. The method according to claim 1 or 2, wherein the liquefied polymer resin further comprises a photoinitiator.

4. The method according to claim 1 or 2, wherein the liquefied polymer resin further comprises a light additive selected from a light absorber and a light stabilizer.

5. The method according to claim 1 or 2, further comprising the following steps: (c) Post-processing the formed object.

6. The method according to claim 3, wherein the liquefied polymer resin further comprises a light additive selected from the group consisting of a light absorber and a light stabilizer, The method further comprises the following steps: (c) Post-processing the formed object.

7. A preparation for three-dimensional printing, comprising, based on the weight of the preparation: (i) 60 to 95 wt% of a liquefied polymer resin; (ii) 5 to 40 wt% of particles; (iii) 0.1 to 5 wt% of a photoinitiator; and (iv) 0 to 0.2 wt % of a photoadditive; wherein the particles include a plurality of particles having different density values; The particles have a g / cm 3 Up to 12g / cm 3 density; and The particles are distributed in the liquefied polymer resin according to the density of the particles.

8. The formulation of claim 7, wherein the particles have a particle size of 50 nanometers to 50 micrometers.

9. The formulation according to claim 7 or 8, wherein the particles have a shape selected from the group consisting of spheres, rods, fibers, plates and stars.

10. The formulation of claim 7 or 8, wherein the liquefied polymer resin comprises an acrylate.

11. The formulation of claim 10, wherein the acrylate is a monomer or oligomer selected from the group consisting of bisphenol A dimethacrylate (Bis-DMA), bisphenol A diglycidyl ether methacrylate (Bis-GMA), ethoxylated bisphenol A dimethacrylate (Bis-EMA), tricyclo[5.2.1.02,6]decanedimethanol diacrylate, bisphenol A glycerol diacrylate, bisphenol A ethoxylate diacrylate, bisphenol A ethoxylate dimethacrylate (oligomer), bisphenol F ethoxylated diacrylate (oligomer), (Ethylene glycol) diacrylate, di(ethylene glycol) diacrylate, tetra(ethylene glycol) diacrylate, 1,4-butanediol diacrylate, hydroxyethyl methacrylate, 3,4-epoxy-cyclohexylmethyl methacrylate (METHB), triethylene glycol dimethacrylate (TEGDMA), tert-butyl cyclohexanol methacrylate, 1,6-bis[2-(methacryloyloxy)ethoxycarbonylamino]-2,4,4-trimethylhexane (UDMA), 3,3,5-trimethylcyclohexanol methacrylate, dipentaerythritol penta / hexaacrylate and mixtures thereof.

12. The formulation of claim 7 or 8, wherein the particles are selected from the group consisting of metal oxides, metal nitrides, metal carbides, metalloid oxides, metalloid nitrides, and metalloid carbides.

13. The formulation of claim 12, wherein the metal or metalloid of the metal oxide, metal nitride, metal carbide, metalloid oxide, metalloid nitride or metalloid carbide is selected from Group 2, Group 3, Group 4, Group 5, Group 6, Group 8, Group 11, Group 12, Group 13, Group 14 or the lanthanide series of the Periodic Table of Elements.

14. The formulation of claim 13, wherein the particles are selected from the group consisting of zinc oxide, silicon carbide, silicon nitride, gallium nitride, aluminum oxide, titanium dioxide, zirconium dioxide, tin dioxide, iron (III) oxide, magnesium oxide, indium (III) oxide, tungsten trioxide, tungsten (IV) oxide, silver oxide, vanadium (V) oxide, vanadium (IV) oxide, molybdenum trioxide, yttrium (III) oxide, cerium (IV) oxide, and copper (II) oxide.

15. The formulation of claim 7 or 8, wherein the photoinitiator is a Type I photoinitiator or a Type II photoinitiator.

16. The formulation of claim 15, wherein the photoinitiator is selected from the group consisting of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (IRGACURE 819), phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO), 2,4,6-trimethylbenzoyldiphenylphosphine (TPO), 2-hydroxy-2-methyl-1-phenyl-1-propane (DAROCUR 1173) and benzophenone (BP).

17. The formulation according to claim 7 or 8, wherein the photoadditive is a light absorber selected from the group consisting of Sudan I-IV, 2,5-bis(5-tert-butylbenzoxazol-2-yl)thiophene, 4-methoxyphenol and butylated hydroxytoluene.

18. The formulation of claim 9, wherein: The liquefied polymer resin includes acrylate, The particles are selected from the group consisting of metal oxides, metal nitrides, metal carbides, metalloid oxides, metalloid nitrides and metalloid carbides, The photoinitiator is a Type I photoinitiator or a Type II photoinitiator, and The photoadditive is a light absorber selected from the group consisting of Sudan I-IV, 2,5-bis(5-tert-butylbenzoxazol-2-yl)thiophene, 4-methoxyphenol and butylated hydroxytoluene.

19. A three-dimensional printed object having different degrees of transmittance to light along an axis of the object; wherein along the axis, the transparency of the object gradually changes from opaque or partially opaque at one end to translucent or transparent at the other end; and wherein the object is formed from the formulation of claim 7 or 8.

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