A THREE-DIMENSIONAL PRINTING METHOD

Abstract

A method of three-dimensional printing an object having a varying degree of transmissivity 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, the particles being distributed in the liquefied polymer resin based on the density of the particles; and (b) polymerizing the liquefied polymer resin under conditions to form the object layer-by-layer. There is also provided a formulation for three-dimensional printing and a three-dimensional printed object.

Claims

1. A method of three-dimensional printing an object having a varying degree of transmissivity to light along an axis of said object, the method comprising the steps of: (a) providing a liquefied polymer resin having a plurality of particles therein, said particles being distributed in said liquefied polymer resin based on the density of said particles; and (b) polymerizing said liquefied polymer resin under conditions to form said object layer-by-layer.

2. The method according to claim 1, further comprising, before said providing step (a), the steps of: (a1) providing a homogenous suspension of said particles within said liquefied polymer resin; and (a2) allowing the particles to distribute within said liquefied polymer resin based on their density values after a period of time.

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

4. The method according to any one of the preceding claims, wherein said liquefied polymer resin further comprises a photoadditive selected from a photoabsorber or a photostabilizer.

5. The method according to any one of the preceding claims, wherein said polymerizing step (b) comprises the step of: (b1) exposing each layer to light.

6. The method according to any one of the preceding claims, further comprising the step of: (c) post-treating the formed object.

7. A formulation for three-dimensional printing comprising: (i) a liquefied polymer resin; (ii) a plurality of particles having various density values; (iii) a photoinitiator; and (iv) optionally a photoadditive.

8. The formulation according to claim 7, wherein said formulation comprises: (i) 60 to 95 wt % liquefied polymer resin; (ii) 5 to 40 wt % particles; (iii) 0.1 to 5 wt % photoinitiator; and (iv) 0 to 0.2 wt % photoadditive, based on the weight of the formulation.

9. The formulation according to claim 7 or 8, wherein said particles have densities in the range of 3 g/cm.sup.3 to 12 g/cm.sup.3.

10. The formulation according to any one of claims 7 to 9, wherein said particles have a particle size in the range of 50 nm to 50 microns

11. The formulation according to any one of claims 7 to 10, wherein said particles have a shape that is selected from the group consisting of spheres, rods, fibers, plates and star-shaped.

12. The formulation according to any one of claims 7 to 11, wherein said liquefied polymer resin comprises an acrylate.

13. The formulation according to claim 12, wherein said 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 glycerolate diacrylate, Bisphenol A ethoxylate diacrylate, Bisphenol A ethoxylate dimethacrylate (oligo), Bisphenol F ethoxylate diacrylate (oligo), Poly(ethylene glycol) diacrylate, Di(ethylene glycol) diacrylate, Tetra(ethylene glycol) diacrylate, 1,4-Butanediol diacrylate, Hydroxy ethylmethacrylate, 3,4-epoxy-cyclohexyl-methyl methacrylate (METHB), triethylene glycol dimethacrylate (TEGDMA), Tertiobutyl cyclohexanol methacrylate, 1,6-bis[2-(methacryloyloxy) ethoxycarbonylamino]-2,4,4-trimethylhexane (UDMA), 3,3,5-trimethyl cyclohexanol methacrylate, Dipentaerythritol penta-/hexa-acrylate and mixtures thereof.

14. The formulation according to any one of claims 7 to 13, wherein said particles are selected from the group consisting of metal oxides, metal nitrides, metal carbides, metalloid oxides, metalloid nitrides and metalloid carbides.

15. The formulation according to claim 14, wherein the metal or metalloid of said metal oxides, metal nitrides, metal carbides, metalloid oxides, metalloid nitrides or metalloid carbides 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.

16. The formulation according to claim 15, wherein said particles are selected from the group consisting of zinc oxide, Silicon carbide, Silicon nitride, Gallium nitride, Aluminium 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.

17. The formulation according to any one of claims 7 to 16, wherein said photoinitiator is a type I or type II photoinitiator.

18. The formulation according to claim 17, wherein said photoinitiator is selected from the group consisting of bis(2,4,6-trimethyl benzoyl)phenylphosphine oxide (IRGACURE 819), Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO), 2,4,6-trimethylbenzoyl diphenyl phosphine (TPO), 2-hydroxy-2-methyl-1-phenyl-1-propane (DAROCUR 1173) and benzophenone (BP).

19. The formulation according to any one of claims 7 to 18, wherein said photoadditive is a photoabsorber selected from the group consisting of Sudan I-IV, 2,5-Bis(5-tert-butyl-benzoxazol-2-yl)thiophene, 4-methoxyphenol and butylated hyrdorxytoluene.

20. A three-dimensional printed object having a varying degree of transmissivity to light along an axis of said object.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0060] The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

[0061] FIG. 1 is a schematic diagram showing an embodiment of the disclosed three-dimensional printing method.

[0062] FIG. 2a is a photo of a side view of a printed plate made in accordance to Example 1 below. [FIG. 2b] is a graph showing the transparency change as a function of the position of the printed plate.

[0063] FIG. 3a is a photo of a side view of a printed plate made in accordance to Example 2 below. [FIG. 3b] is a graph showing the transparency change as a function of the position of the printed plate.

[0064] FIG. 4 is an image showing the cross-section of a printed tooth made in accordance to Example 3 below.

[0065] FIG. 5 is an image showing the cross-section of a printed tooth made in accordance to Example 3 below.

[0066] FIG. 6 is a photograph showing a number of prototypes of the artificial teeth made in accordance with Example 4 below.

DETAILED DESCRIPTION OF DRAWINGS

[0067] Referring to FIG. 1, there is provided a schematic diagram showing an embodiment of the disclosed three-dimensional printing method which is based on digital light processing. In FIG. 1(l), a liquefied polymer resin 2 is first provided in a vat 6. The liquefied polymer resin 2 is as described above. When the liquefied polymer resin 2 is left to settle under the influence of gravity, sedimentation potential occurs. The high density particles present in the liquefied polymer resin 2 are suspended or sediment at rates that depend on the following factors: difference in density, fluid viscosity, particle sizes and particle shape. Therefore, when high density particles are blended with Vat polymers for the liquid resin based three-dimensional printing, the high density particles will form a sedimentation gradient in the tank under the influence of gravity (FIG. 1(I)). When the platform 4 is lowered down to print, the solidified materials at the starting layers will have higher content particles due to particles sedimentation. With continue printing processing, more and more particles are solidified into the polymers resin, and the concentration of particles in the liquid polymer resin will drop correspondingly. As shown in FIG. 1, the particles concentration is continually decreased with the printing process (moving from FIG. 1(I), to FIG. 1(II), to FIG. 1(III) to FIG. 1(IV)), and finally there are limited particles left in the resin and thus a more and more transparent solid is formed. In this way, the printed structures will show a gradient color change from the bottom to top, and also the transparency will show a similar gradient change. With this method, it is possible to produce one dimensional gradient of component materials content in the printed structure. Due to sedimentation process, the highest filler content is expected in the lowest printed layer.

EXAMPLES

[0068] Non-limiting examples of the invention be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Example 1

Resin Formulation

[0069] The base resin and the particles (all chemicals from Aldrich Sigma of St. Louis of Missouri of the United States of America) (Table 1) were weighed into a flask and ultrasonicated in an ultrasonic bath for at least 2 hours. Then the photoinitiators and photstabilizer were added into the mixture and stirred in the absence of light for 8 to 24 hrs until a homogeneous suspension was obtained.

TABLE-US-00001 TABLE 1 formulation of resin 1 Ingredient Percentages (wt %) Bisphenol A ethoxylate diacrylate (average 35 Mn ~468) Di(ethylene glycol) dimethacrylate (Aldrich) 60 zinc oxide (particles sizes < 5 μm) 4.4 Phenylbis(2,4,6-trimethylbenzoyl)phosphine 0.5 oxide 4-methoxyphenol 0.1
Printing of the Structures with Gradient Optical Properties Change

[0070] To demonstrate the possibility of gradient color printing, a rectangle plate was printed on a DLP printer (LittleRP with build volume 60 mm (X) 40 mm (Y) 100 mm (Z), which uses dynamic light processing projector with a resolution of 1024×768 (Brand & model: Acer P128) as light source and Creation Workshop as controlling software.) Printing was carried out with slice thickness of 50 μm. Exposure time per layer was 6 seconds. After printing, the printed part was washed thoroughly with iso-propanol, air dried and placed inside UV oven for further curing. The printed structure with gradient colour change is shown in FIG. 2a. In addition, the gradient change in transparency was evaluated by using UV-vis spectrometer. The difference in transparency was measured at different position and the results were plotted in FIG. 2b.

Example 2

Resin Formulation

[0071] The base resin and the particles (Table 2) were weighed into a flask and ultrasonicated in an ultrasonic bath for at least 2 hours. Then the photoinitiators and photstabilizer were added into the mixture and stirred in the absence of light for 8 to 24 hrs until a homogeneous suspension was obtained.

TABLE-US-00002 TABLE 2 formulation of resin 2 Ingredient Percentages (wt %) Bisphenol A ethoxylate diacrylate (average 23 Mn ~468) Di(ethylene glycol) dimethacrylate 70 Zirconium dioxide (325 mesh) 6.4 Phenylbis(2,4,6-trimethylbenzoyl)phosphine 0.5 oxide 4-methoxyphenol 0.1
Printing of the Structures with Gradient Optical Properties Change

[0072] To demonstrate the possibility of gradient color printing, a rectangle plate was printed on a DLP printer (LittleRP with build volume 60 mm (X) 40 mm (Y) 100 mm (Z), which uses dynamic light processing projector with a resolution of 1024×768 (Brand & model: Acer P128) as light source and Creation Workshop as controlling software.) Printing was carried out with slice thickness of 50 μm. Exposure time per layer was 6 seconds. After printing, the printed part was washed thoroughly with iso-propanol, air dried and placed inside UV oven for further curing. The printed structure with gradient colour change is shown in FIG. 3a. In addition, the gradient change in transparency was evaluated by using UV-vis spectrometer. The difference in transparency was measured at different position and the results were plotted in FIG. 3b.

Example 3—Dental Printing and Characterization

Resin Formulation

[0073] The base resin and the particles (Table 3) were weighed into a flask and ultrasonicated in an ultrasonic bath for at least 2 hours. Then the photoinitiators and photstabilizer were added into the mixture and stirred in the absence of light for 8 to 24 hrs until a homogeneous suspension was obtained.

TABLE-US-00003 TABLE 3 formulation of resin 3 Ingredient Percentages (wt %) Bisphenol A ethoxylate diacrylate (average 31 Mn ~468) Di(ethylene glycol) dimethacrylate 60 Zirconium dioxide (325 mesh) 8.4 Phenylbis(2,4,6- 0.5 trimethylbenzoyl)phosphine oxide 2,5-Bis(5-tert-butyl-benzoxazol-2- 0.1 yl)thiophene
Printing of the Structures with Gradient Optical Properties Change

[0074] To demonstrate the possibility the artificial tooth with gradient color change, the tooth structure was printed on a DLP printer (LittleRP with build volume 60 mm (X) 40 mm (Y) 100 mm (Z), which uses dynamic light processing projector with a resolution of 1024×768 (Brand & model: Acer P128) as light source and Creation Workshop as controlling software.) Printing was carried out with slice thickness of 50 μm. Exposure time per layer was 6 seconds. After printing, the printed part was washed thoroughly with iso-propanol, air dried and placed inside UV oven for further curing. The printed structure was cut and the cross section cutting image is shown in FIG. 4 and FIG. 5. The cut structure was measured by scanning electron microscopy to identify both the particle distribution (FIG. 4) and the gradient change structure was also confirmed by energy-dispersive X-ray spectroscopy measurement (FIG. 5).

[0075] Referring to FIG. 4, the peripheral photos show that the concentration of the pigments (white particles in the photo) increased in the cross-section of the printed tooth from top to bottom (the sequence of the photos from top to bottom is: left top, right top, left middle, right bottom and left bottom). Therefore, the greatest concentration of the pigments was at the bottom of the printed tooth while the lowest concentration of the pigments was at the top of the printed tooth.

[0076] Referring to FIG. 5, the peripheral photos show that the elemental abundance of pigments increased in the cross-section of the printed tooth from top to bottom (the sequence of the photos from top to bottom is: left top, right top, left middle, right bottom and left bottom). Similar to FIG. 4, the greatest abundance of the pigments was at the bottom of the printed tooth while the lowest abundance of the pigments was at the top of the printed tooth.

Example 4—Prototype Printing

[0077] To demonstrate the application of the present technique in dental printing, a set of teeth with gradient color change was printed on a DLP printer (LittleRP with build volume 60 mm (X) 40 mm (Y) 100 mm (Z), which uses dynamic light processing projector with a resolution of 1024×768 (Brand & model: Acer P128) as light source and Creation Workshop as controlling software.) The resin used is the same as described in Example 3. Printing was carried out with slice thickness of 50 μm. Exposure time per layer was 6 seconds. After printing, the printed part was washed thoroughly with iso-propanol, air dried and placed inside UV oven for further curing. The printed prototype was displayed in FIG. 6, which shows clearly the gradient colour change of the printed teeth.

INDUSTRIAL APPLICABILITY

[0078] The disclosed method can be used to three-dimensional print an object having a varying degree of transmissivity to light along an axis of the object. The three-dimensional printed object may be used as an artificial tooth whereby the artificial tooth has more opacity in the cervical area and more translucency in the incisal area.

[0079] The three-dimensional printed object may be used as an implant in a human or animal body, such as an artificial bone. The three-dimensional printed object may be used to form artificial materials that mimic those found in nature that are functionally graded, such as wood or bamboo.

[0080] The disclosed method may be used in engineering devices development whereby the materials formed may have graded combinations of flexibility, elasticity or rigidity.

[0081] The disclosed method may be used in fire retardant applications such as forming spacecraft heat shields or heat exchanger tubes.

[0082] The disclosed method may be used in electronics or optoelectronics such as in optical fibers for high speed transmission.

[0083] The disclosed method may be used in defense such as in armour plates or bullet-proof vests.

[0084] The disclosed method may be used in thermal barrier coatings such as in automotive, aircraft industries and power plant to reduce heat loss from engine exhaust systems.

[0085] The disclosed method may be used in energy applications such as in energy conversion devices.

[0086] It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.