CN115246214A

CN115246214A - Method for photocuring 3D printing of transparent object

Info

Publication number: CN115246214A
Application number: CN202110378274.4A
Authority: CN
Inventors: 高杰; 胡梦龙; 卢伊丝; 朱光
Original assignee: Qingfeng Beijing Technology Co Ltd
Current assignee: Luxcreo Beijing Inc
Priority date: 2021-04-08
Filing date: 2021-04-08
Publication date: 2022-10-28

Abstract

Embodiments of the present invention disclose a method for photocuring 3D printed transparent objects that uses excess photoinitiator to reduce the transmission depth of the liquid resin used for photocuring printing, thereby avoiding excessive curing that affects printing accuracy. After the printing is completed, the printed matter containing the unreacted photoinitiator is irradiated with light to react the unreacted photoinitiator, thereby completing the printing process of the transparent object.

Description

Method for photocuring 3D printing of transparent object

Technical Field

The application relates to the technical field of 3D printing, in particular to a method for photocuring 3D printing of transparent objects.

Background

Generally, the additive manufacturing or 3D printing technology is based on the technical principle of layering a three-dimensional model of an object constructed by Computer Aided Design (CAD) software, then obtaining contour information or image information of each layer, and using a bondable material such as powdered metal or resin to complete the manufacturing of the three-dimensional object in a layer-by-layer printing manner. In one type of additive manufacturing technology, the photocuring 3D printing technology mainly uses liquid resin as a raw material, and completes the printing process by utilizing the characteristic that the liquid resin printing raw material is cured under the irradiation of light with specific wavelength and intensity. The specific steps of photocuring 3D printing are typically: the three-dimensional model is layered in one direction, so that outline information or image information of each layer is obtained, then a light pattern of each layer is irradiated onto printing raw materials, the printing raw materials in the raw materials are irradiated by light, a curing reaction is carried out to form a cured layer, the cured layer can be adhered and attached to a forming table (or adhered and attached to an upper cured layer), after the light pattern of the layer is cured, the forming table drives the cured layer to move a certain distance in a direction away from a light source, then the next layer of curing is carried out, iteration is repeated, and finally a complete printed part (namely the three-dimensional model) is formed.

Printing transparent three-dimensional objects using conventional light-curable 3D printing techniques is challenging, especially when transparent or translucent resins are used, and it is more difficult to precisely control the transmission of light and the depth of cure, during which printing incident light in the ultraviolet or visible wavelength range not only irradiates the liquid resin of the current cured layer to form the current cured layer, but also transmits through the liquid resin of the current cured layer to the previous cured layer, resulting in undesired curing. This situation can cause a reduction in resolution in the Z-axis direction (i.e., the direction perpendicular to the stereolithographic surface), which can affect the transparency of the printed article.

One approach to improving the resolution of prints of transparent resins using uv absorbers to solve the problem of excessive unwanted photocuring is disclosed in US patent application US 2020/0024381 "creating transparent objects by additive manufacturing", but the uv absorbers disclosed in this patent application may not be suitable for many of the wavelengths of light used for photocuring 3D printing, nor for some transparent resins. For example, in the specification of this patent application, it is mentioned that, although Mayzo OB + which is an ultraviolet absorber is used, it is due to inclusion in the resin systemUndesirable curing of the amine compounds is still observed. Only after removal of the amine compound, the undesired curing is reduced (example 1). In addition, the presence of UV absorbers in the resin system may have undesirable effects on the printed matter, for example when UV absorbers are used

When this was observed, the printed material was observed to be significantly yellowish. Therefore, how to print the transparent object more effectively still remains a technical problem to be solved urgently in the field.

Disclosure of Invention

One embodiment of the present invention provides a method for photocuring a 3D printed transparent object, the method including the steps of: providing a photocurable liquid resin comprising: (1) At least one of a photocurable resin monomer, oligomer, or prepolymer; (2) excess photoinitiator; b, performing photocuring 3D printing by using photocuring 3D printing equipment and the photocuring liquid resin to obtain a printed piece, wherein the printed piece contains an unreacted photoinitiator; c, optionally cleaning the printed piece after the step b; and D, illuminating the printed part to enable at least part of the unreacted photoinitiator in the printed part to be initiated to react to obtain the required 3D printing transparent object.

In some embodiments, the weight% of the excess photoinitiator is no less than 2% of the total weight of the liquid resin.

In some embodiments, the illumination time in step d is 20 to 120 minutes.

In some embodiments, the illumination wavelength in step D is the same as the photocuring 3D printing wavelength in step b.

In some embodiments, the illumination wavelength in step D and the photocuring 3D printing wavelength in step b are both 405nm.

In some embodiments, the photoinitiator is an acylphosphine oxide; in some embodiments, the photoinitiator is phenyl bis (2,4,6-trimethylbenzoyl) phosphine oxide.

In some embodiments, the photocurable liquid resin further comprises an amine or imine-based compound; the method further includes a post-curing step, which may be one or more of heating, microwave irradiation, humidification, etc., of the printed article.

In some embodiments, the depth of transmission of the photocurable liquid resin is no greater than 3 times the thickness of the cured layer of each layer in the photocurable 3D printing step.

Drawings

The present application will be further explained by way of exemplary embodiments, which will be described in detail by way of the accompanying drawings. These embodiments are not intended to be limiting, and in these embodiments like numerals are used to indicate like structures, wherein:

fig. 1 is a transparency comparison of a transparent orthodontic mouthpiece printed according to the disclosed photocured 3D printing method and an orthodontic mouthpiece made in a hot-pressed form with a commercially available PTMG material according to some embodiments of the present invention.

Detailed Description

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings used in the description of the embodiments will be briefly described below. It is obvious that the drawings in the following description are only examples or embodiments of the application, from which the application can also be applied to other similar scenarios without inventive effort for a person skilled in the art. Unless otherwise apparent from the context, or stated otherwise, like reference numbers in the figures refer to the same structure or operation.

It should be understood that "system", "apparatus", "unit" and/or "module" as used herein is a method for distinguishing different components, elements, parts, portions or assemblies at different levels. However, other words may be substituted by other expressions if they accomplish the same purpose.

As used in this application and the appended claims, the terms "a," "an," "the," and/or "the" are not intended to be inclusive in the singular, but rather are intended to be inclusive in the plural unless the context clearly dictates otherwise. In general, the terms "comprises" and "comprising" merely indicate that steps and elements are included which are explicitly identified, that the steps and elements do not form an exclusive list, and that a method or apparatus may include other steps or elements.

As used herein, the term "and/or" refers to any and all possible combinations of one or more of the listed components, as well as combinations lacking any of the components. For example, "a, B, and/or C" means all possibilities: a alone, B alone, C alone, A and B, A and C, B and C, A, B and C. "

The term used in the present invention, the critical exposure (Ec) is the lowest energy at which the photocurable resin changes from liquid to solid upon curing; the transmission depth (Dp) is the depth at which the optical energy density decays to 1/E of the incident energy density E.

One aspect of the present invention provides a method for photocuring 3D printed transparent objects, characterized in that the method comprises the steps of:

providing a photocurable liquid resin comprising:

(1) At least one of a photocurable resin monomer, oligomer, or prepolymer;

(2) An excess of photoinitiator;

b, performing photocuring 3D printing by using photocuring 3D printing equipment and the photocuring liquid resin to obtain a printed piece, wherein the printed piece contains an unreacted photoinitiator;

c, optionally cleaning the printed piece after the step b;

and D, illuminating the printed part to enable at least part of the unreacted photoinitiator in the printed part to be initiated to react to obtain the required 3D printing transparent object.

In some embodiments, examples of photocurable resin monomers, oligomers, or prepolymers may include, but are not limited to: acrylates, methacrylates, olefins, N-vinyls, acrylamides, methacrylamides, styrenics, epoxies, thiols, 1,3-diene, halogenated vinyls, acrylonitriles, vinyl esters, maleimides, vinyl ethers, olefins (such as methoxyethylenes, 4-methoxystyrenes, styrenes, 2 methylprop-1-ene, 1,3-butadiene, and the like), vinyl ethers, N-vinylcarbazoles, lactones, lactams, cyclic ethers (e.g., epoxides), cyclic acetals, cyclosiloxanes, and oligomers and/or prepolymers comprising one or more of the foregoing monomers.

In some embodiments, the photocurable liquid resin may be a resin material having multiple components and multiple curing mechanisms, the resin material comprising a second component in addition to a first component comprising a photocurable resin monomer, oligomer, or prepolymer, the second component may or may not participate in a photocuring reaction, but the second component participates in a post-curing reaction, wherein post-curing may be one or more means of illumination, heating, microblogging radiation, humidification, or otherwise providing energy required for post-curing. The resin material may be a resin material having a dual component dual cure mechanism as disclosed in U.S. Pat. No. 9,598,606,9,453,142,9,982,164,9,676,963, the disclosure of which is incorporated herein by reference. In some embodiments, the first component is a reactive end-capped polyurethane prepolymer and the second component comprises groups that are reactive with isocyanate groups in the polyurethane prepolymer, thereby allowing the first component to undergo a chain extension reaction during the post-cure reaction. Examples of the second component may include, but are not limited to, one of a diol, a polyol, a diamine, a polyamine, and an imine. In some preferred embodiments, the second component is an imine based compound, such as a resin material with a dual component dual cure mechanism as disclosed in PCT/CN2020/095715, the disclosure of which is incorporated herein by reference. Because the structure of the amine compound has substituent groups which can aggravate the yellowing of the photoinitiator, the imine compound can relieve the yellowing of the photoinitiator.

In some embodiments, examples of photoinitiators can include, but are not limited to: benzoin ethers, dialkyl acetophenones, hydroxyalkyl ketones, acyl phosphine oxides, amino ketones, benzophenones, thioxanthones, 1,2 dione, 1,7,7-trimethyl-bicyclo [2.2.1] heptane-2,3-dione, bis 2,6-difluoro-3-pyrrolylphenyltitanocene. In some embodiments, the photoinitiators used in the present invention are benzoylphosphine oxides, including TPO, 819, TEPO, 819DW. In other embodiments, examples of photoinitiators that can initiate the photocuring reaction can include, but are not limited to: onium salts, halonium salts, oxyiodonium salts, selenium salts, sulfonium salts, sulfoxonium salts, diazonium salts, metallocene salts, isoquinoline salts, phosphonium salts, clockwork salts, cycloheptatriene cation salts (tropylium salt), dialkyl phenacylsulfonium salts, thiopyrylium salts, diaryl iodonium salts, triaryl sulfonium salts, sulfonium antimonate salts, ferrocene, bis (cyclopentadienyl iron) arenium compounds, pyridinium salts, and mixtures comprising one or more of the foregoing photoinitiators. In some preferred embodiments, if light having a wavelength of over 400nm is used to initiate photocuring, a wavelength of 405nm is preferred because 819 photoinitiators have a stronger absorption in the long wavelength UV range in the phosphine oxide photoinitiator family.

In some embodiments, the photocurable liquid resin may further include a diluent, and in some embodiments, the diluent may be a reactive diluent, which may be a photocurable monomer or oligomer having a photocurable group. In some embodiments, the photocurable group can be a group that can undergo free radical polymerization. In other embodiments, the photocurable group may be a group that can undergo cationic polymerization. In some embodiments, the photocurable monomer or oligomer can comprise an acrylate, a methacrylate, an olefin, an N-vinyl, a vinyl amide, a vinyl ether, a vinyl ester, an acrylamide, a methacrylamide, a styrene, an acrylic acid, an epoxy, a thio, a 1,3-diene, a vinyl halide, an acrylonitrile, a vinyl ester, a maleimide, a vinyl ether, and a combination of two or more of the foregoing. In some embodiments, the photocurable monomer or oligomer may comprise epoxy/amine, epoxy/hydroxyl, oxetane/amine, oxetane/alcohol. The reactive diluent reduces the viscosity of the photocurable polymer network and copolymerizes with the photocurable components of the polymerizable liquid.

In some embodiments, the reactive diluent may have one or more functionalities. Examples of reactive diluents may include, but are not limited to, 1,3-propanediol diacrylate and 1,3-propanediol dimethacrylate, 1,4-butanediol diacrylate and 1,4-butanediol dimethacrylate, 1,5-pentanediol diacrylate and 1,5-pentanediol dimethacrylate, 1,6-hexanediol diacrylate and 1,6-hexanediol dimethacrylate, 1,7-heptanediol diacrylate and 1,7-heptanediol dimethacrylate, 1,8-octanediol diacrylate and 1,8-octanediol dimethacrylate, trimethylolpropane triol triacrylate and trimethylolpropane triol trimethacrylate, ethoxylated trimethylolpropane triol triacrylate and ethoxylated trimethylolpropane triol trimethacrylate, neopentyl glycol diacrylate and dimethacrylate, tripropylene glycol diacrylate and tripropylene glycol dimethacrylate, pentaerythritol and pentaerythritol trimethacrylate, and similar compounds. In some embodiments, selection of certain reactive diluents or certain combinations of reactive diluents may increase the solubility of the photoinitiators used in the present invention. In a preferred embodiment, monomers with low functionality are suitable for increasing the solubility of photoinitiators having a powder form. In some embodiments, if the photoinitiator 819 is selected to be a solid powder under normal temperature and pressure conditions, selecting a low functionality monomer as a diluent can increase the solubility of the powdered photoinitiator in the liquid resin.

In some embodiments, the weight percentage of photocurable resin monomers, oligomers, or prepolymers in the photocurable liquid resin may range from 10% to 95%; or 20% -80%; or 30% -70%; or 40% -60%. In some embodiments, when the photocurable liquid resin includes a resin material having multiple components and multiple curing mechanisms, the weight percent of the first component may range from 10% to 90%, alternatively from 20% to 80%, alternatively from 30% to 70%, alternatively from 40% to 60%; the weight percent of the second component may range from 10% to 90%, alternatively from 20% to 80%, alternatively from 30% to 70%, alternatively from 40% to 60%. In some embodiments, the weight percentage of diluent in the photocurable liquid resin ranges from 10% to 60%, alternatively from 20% to 50%, alternatively from 30% to 40%.

In some embodiments, the weight percent of excess photoinitiator in the photocurable liquid resin is no less than 2% of the total weight of the liquid resin; in some embodiments, the weight percentage of excess photoinitiator in the photocurable liquid resin ranges from 2% to 5%; in some embodiments, the weight percent of excess photoinitiator in the photocurable liquid resin ranges from 2.3% to 4%; in some embodiments, the weight percentage of excess photoinitiator in the photocurable liquid resin ranges from 2.5% to 3%.

In some embodiments, an excess of photoinitiator is used such that the transmission depth of the photocurable liquid resin is no greater than 3 times the thickness of each cured layer when photocured printing is performed using the liquid resin; in some embodiments, the liquid resin has a transmission depth of no more than 2 times the thickness of each cured layer when photocured printing is performed using the liquid resin; in some embodiments, the liquid resin has a transmission depth of no more than 1.5 times the thickness of each cured layer when photocured printing is performed using the liquid resin. In some embodiments, it is possible to use a higher cured layer thickness at the initial stage of photocuring 3D printing than at the later stages of printing, and in such embodiments, the disclosed relationship of liquid resin transmission depth to cured layer thickness for each layer during printing uses the maximum cured layer thickness used during printing.

The absorption of the liquid photocurable resin to ultraviolet light generally follows Beer Lambert's theorem, and the ultraviolet laser irradiated on the liquid surface of the photocurable resin conforms to the Beer Lambert's theorem, namely the energy of the ultraviolet laser also becomes negative exponential attenuation along the irradiation depth, namely E (Z) = Eexp (-Z/Dp), wherein E is the energy density of the ultraviolet laser irradiated on the liquid surface, and E (Z) is the energy density of the laser penetrating to the depth Z; dp is the transmission depth and represents the strength of the resin to the ultraviolet laser absorption performance, wherein the smaller the Dp value is, the stronger the resin to the ultraviolet laser absorption is, namely the smaller the depth that the ultraviolet laser can penetrate through the resin is; when E exceeds the critical exposure Ec, namely Eexp (-Z/Dp) > Ec, the resin in liquid state changes phase and changes from liquid state to solid state, when Z < DpLn (E/Ec), the curing depth Cd = DpLn (E/Ec), namely Cd = DpLn E-DpLn Ec. The formula is the light curing equation of the light-curable resin irradiated by the ultraviolet laser. And (3) plotting the natural logarithm of the exposure energy E to the curing depth Cd to obtain a straight line which takes LnE as an X axis and Cd as a Y axis, wherein the slope of the straight line is Dp, and the intersection point of the straight line and the X axis is DpLnE. Therefore, the Dp value can be obtained by actually measuring a series of curing depths and exposure amounts.

When a transparent three-dimensional object is printed by photo-curing using a transparent or translucent resin, it becomes more difficult to precisely control the transmission of light and the curing depth, and during the printing process, light not only irradiates the liquid resin of the current cured layer to form the current cured layer but also transmits through the liquid resin of the current cured layer to the previous cured layer, resulting in undesired curing. This situation can cause a reduction in resolution in the Z-axis direction (i.e., the direction perpendicular to the stereolithographic surface), which can affect the transparency of the printed article. In the prior art, the dosage of the photoinitiator cannot be too high, because excessive initiator causes a large amount of unreacted initiator to remain in a printed part, and the initiator is degraded after being exposed to UV light at the later stage, so that the printed part is yellowed; in addition, excessive initiator causes light attenuation, so that the polymerization depth is limited; furthermore, the use of an excess of initiator can affect the storage stability of the resin material. The method disclosed by the invention uses a reasonable excessive photoinitiator, reduces the transmission depth of the whole resin material by utilizing the influence of the excessive photoinitiator on the transmission depth of the liquid resin, adjusts the transmission depth of the liquid resin to be in a reasonable proportion to the thickness of a cured layer used in photocuring 3D printing, reduces the undesired curing of an unprecedented cured layer, improves the precision of a printed product in a Z axis, and further improves the transparency of the printed product.

The method for photocuring printing of the transparent object disclosed by the invention uses excessive photoinitiator to increase the precision of the printing piece in the Z axis so as to improve the transparency of the printing piece, so that the printing piece contains unreacted photoinitiator after printing is finished, and the printing piece needs to be irradiated in a post-treatment process so that at least part of the unreacted photoinitiator in the printing piece is initiated to react to obtain the required 3D printing transparent object. In some embodiments, the post-processing illumination step uses the same wavelength as that used for photocuring 3D printing; in some preferred embodiments, the post-processing illumination step uses a wavelength of 405nm for both photocuring 3D printing. In some embodiments, the post-treatment illumination step has an illumination time in the range of 20 to 120 minutes, or 30 to 80 minutes, or 40 to 60 minutes. In some embodiments, the post-treatment illumination step may be heated simultaneously.

In some embodiments, the photocurable liquid resin may be a resin material with multiple components and multiple curing mechanisms, wherein the first component is a blocked or reaction-blocked polyurethane prepolymer and the second component is a chain extender. The liquid resin further comprises an excess of photoinitiator and optionally a reactive diluent. The linkages between the end-capping groups of the first component used to block the polyurethane prepolymer and the isocyanate groups (-NCO) of the polyurethane are thermally or otherwise unstable, and under unstable conditions such linkages will break to expose the isocyanate groups (-NCO) and allow subsequent reaction with the other components to occur freely. Examples of NCO blocking groups include, but are not limited to: phenols, nonylphenols, pyridinol, oximes, thiophenols, thiols, amides, cyclic amides, imides, imidazoles, imidazolines, methyl Ethyl Ketoxime (MEKO), alcohols, epsilon-caprolactam, pyrazoles, triazoles, amidines, hydroxy acid esters, and the like. In a preferred embodiment, the NCO blocking group is 2-methyl-2-propenoic acid-2- [ (1,1-dimethylethyl) amino ] ethyl ester (t-BAEMA). The second component contains groups that react with isocyanate groups in the polyurethane prepolymer, thereby allowing the first component to undergo a chain extension reaction during the post-cure step. Examples of the second component may include, but are not limited to, one of a diol, a polyol, a diamine, a polyamine, and an imine. In some embodiments, the second component is an imine compound, which may be formed by the polycondensation of an amine compound, such as an aldehyde or ketone.

When the method disclosed by the invention is used for carrying out photocuring 3D printing on the transparent object by using the resin material with multiple components and multiple curing mechanisms, the method can comprise the following steps:

providing a photocurable liquid resin comprising:

(1) A photocurable first component resin;

(2) A second component resin capable of causing the first component to undergo a chain extension reaction in a post-curing step;

(3) An excess of photoinitiator;

b, performing photocuring 3D printing by using photocuring 3D printing equipment and the photocuring liquid resin to obtain a printed piece, wherein the printed piece contains an unreacted photoinitiator; the printed matter also comprises a second component resin;

c, optionally cleaning the printed piece after the step b;

d, post-curing the printed piece, wherein the post-curing step can be one or more of heating, microwave radiation, humidification and the like on the printed piece; the second component resin reacts with the first component resin in post-curing reaction to further form a three-dimensional crosslinking network;

e, illuminating the printed part to enable at least part of the unreacted photoinitiator in the printed part to be initiated to react to obtain the required 3D printing transparent object. The order of step d and step e is not limited, and may be determined according to the specific resin material used.

EXAMPLES printing of transparent orthodontic braces Using excess photoinitiator

Three orthodontic braces were printed on a TP02 printer of LuxCreo corporation using the photo-curable liquid resins of different formulations listed in table 1 according to the printing parameters listed in table 2, respectively, and after printing was completed, the braces were first removed from the forming table, and ultrasonic cleaning was performed using an isopropyl alcohol solvent at an ultrasonic intensity of 50Hz for 300 seconds. And (3) carrying out post-treatment illumination on the cleaned orthodontic braces by using a U102H (Cure-M) LED curing box, wherein the post-treatment illumination has the wavelength of 405nm and the light intensity of 300mw/cm ² And the illumination time is 30 minutes. Photographs of 3 orthodontic braces after post-treatment illumination are shown in fig. 1. For clarity comparison, a commercially available orthodontic mouthpiece made from Poly (tetramethylene ether) PTMG material in a heat and pressure format is included in fig. 1 as a comparison. The 3 photo-cured 3D printed orthodontic braces shown in fig. 1 have different transparencies, with example 3 having the highest transparency.

Table 1 material formulations for three orthodontic mouthpiece printing examples

TABLE 2 printing parameters for the three orthodontic mouthpiece embodiments described above

Wavelength (nm)	405
		Thickness of the solidified layer (mm)	0.1
Light intensity (mw/cm) ² )	2.0
		Temperature (. Degree.C.) of liquid resin for printing	40

Having thus described the basic concept, it will be apparent to those skilled in the art that the foregoing detailed disclosure is to be considered merely illustrative and not restrictive of the broad application. Various modifications, improvements and adaptations to the present application may occur to those skilled in the art, although not explicitly described herein. Such modifications, improvements and adaptations are proposed in the present application and thus fall within the spirit and scope of the exemplary embodiments of the present application.

Also, this application uses specific language to describe embodiments of the application. Reference throughout this specification to "one embodiment," "an embodiment," and/or "some embodiments" means that a particular feature, structure, or characteristic described in connection with at least one embodiment of the present application is included in at least one embodiment of the present application. Therefore, it is emphasized and should be appreciated that two or more references to "an embodiment" or "one embodiment" or "an alternative embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, certain features, structures, or characteristics may be combined as suitable in one or more embodiments of the application.

Additionally, the order in which elements and sequences of the processes described herein are processed, the use of alphanumeric characters, or the use of other designations, is not intended to limit the order of the processes and methods described herein, unless explicitly claimed. While various presently contemplated embodiments of the invention have been discussed in the foregoing disclosure by way of example, it is to be understood that such detail is solely for that purpose and that the appended claims are not limited to the disclosed embodiments, but, on the contrary, are intended to cover all modifications and equivalent arrangements that are within the spirit and scope of the embodiments herein. For example, although the system components described above may be implemented by hardware devices, they may also be implemented by software-only solutions, such as installing the described system on an existing server or mobile device.

Similarly, it should be noted that in the preceding description of embodiments of the application, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure aiding in the understanding of one or more of the embodiments. This method of disclosure, however, is not intended to require more features than are expressly recited in the claims. Indeed, the embodiments may be characterized as having less than all of the features of a single embodiment disclosed above.

Numerals describing the number of components, attributes, etc. are used in some embodiments, it being understood that such numerals used in the description of the embodiments are modified in some instances by the use of the modifier "about", "approximately" or "substantially". Unless otherwise indicated, "about", "approximately" or "substantially" indicates that the number allows a variation of ± 20%. Accordingly, in some embodiments, the numerical parameters set forth in the specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameter should take into account the specified significant digits and employ a general digit-preserving approach. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the range are approximations, in the specific examples, such numerical values are set forth as precisely as possible within the scope of the application.

The entire contents of each patent, patent application publication, and other material cited in this application, such as articles, books, specifications, publications, documents, and the like, are hereby incorporated by reference into this application. Except where the application is filed in a manner inconsistent or contrary to the present disclosure, and except where the claim is filed in its broadest scope (whether present or later appended to the application) as well. It is noted that the descriptions, definitions and/or use of terms in this application shall control if they are inconsistent or contrary to the statements and/or uses of the present application in the material attached to this application.

Finally, it should be understood that the embodiments described herein are merely illustrative of the principles of the embodiments of the present application. Other variations are also possible within the scope of the present application. Thus, by way of example, and not limitation, alternative configurations of the embodiments of the present application can be viewed as being consistent with the teachings of the present application. Accordingly, the embodiments of the present application are not limited to only those embodiments explicitly described and depicted herein.

Claims

1. A method for photocuring 3D printed transparency, the method comprising the steps of:

providing a photocurable liquid resin comprising:

(1) At least one of a photocurable resin monomer, oligomer, or prepolymer;

(2) An excess of photoinitiator;

c, optionally cleaning the printed piece after the step b;

2. The method for photocuring 3D printing of transparent objects according to claim 1 wherein the weight% of excess photoinitiator is not less than 2% of the total weight of the liquid resin.

3. The method for photocuring 3D printing of transparent objects according to claim 1, wherein the illumination time in step D is from 20 to 120 minutes.

4. The method for photocuring 3D printing of transparent objects as defined in claim 1 wherein the illumination wavelength in step D is the same as the photocuring 3D printing wavelength in step b.

5. The method for photocuring 3D printing of transparent objects as defined in claim 5 wherein the illumination wavelength in step D and the photocuring 3D printing wavelength in step b are both 405nm.

6. The method for photocuring 3D printing of transparent objects according to claim 1 wherein the photoinitiator is an acylphosphine oxide.

7. The method for photocuring 3D printing of transparent objects according to claim 6, characterized in that the photoinitiator is phenyl bis (2,4,6-trimethylbenzoyl) phosphine oxide.

8. The method for photocuring 3D printing of transparent objects as recited in claim 1 wherein the photocurable liquid resin further comprises an amine or imine based compound; the method further includes a post-curing step, which may be one or more of heating, microwave irradiation, humidification, etc., of the printed article.

9. The method for photocuring 3D printing of transparent objects as recited in claim 1, wherein the depth of transmission of the photocurable liquid resin is no more than 3 times the thickness of the cured layer per layer in the photocuring 3D printing step.