Techniques for Rapidly Curing and Coating Parts Produced by Additive Manufacturing

Abstract

A method for curing and / or modifying the surface of a three-dimensional (3D) printed part is described, comprising immersing the 3D-printed part, which contains reactive moieties, in a liquid bath at an elevated temperature to effect polymerization of the reactive moieties of the 3D-printed part, resulting in a cured 3D-printed part. The liquid bath may further contain reactive molecules that can react with the surface of the 3D-printed part to produce a coating that alters the surface properties of the 3D-printed part.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This PCT application claims the benefit of priority to U.S. Provisional Patent Application No. 62 / 831,537, filed April 9, 2019, and entitled “METHODOLOGIES TO RAPIDLY CURE AND COAT PARTS PRODUCED BY ADDITIVE MANUFACTURING,” the contents of which are incorporated by reference in their entirety, including, but not limited to, aspects related to 3D printing, additive manufacturing.

[0002] The present disclosure relates generally to hardening and / or modifying the surface of three-dimensional (3D) printed parts. [Background technology]

[0003] Traditionally, the stereolithography approach (SLA) for additive manufacturing presents unique possibilities and technological opportunities over competing technologies because SLA can provide high printing speeds while producing objects from a range of robust materials.

[0004] However, the rapid construction of three-dimensional (3D) parts using such approaches does have certain drawbacks. One drawback of SLA is that the part is not fully cured by the time the printing process is completed; that is, the chemical reactions necessary to solidify the liquid resin used as the raw material have not reacted until 100% conversion. This can result in the 3D part being "sticky" and the possibility of deformation of the 3D part, since the "curing" is not completed during the initial forming process. In this state, the part is often referred to as being "green," analogous to ceramics, where there are "green" unfired parts and parts with a variety of properties after firing.

[0005] In addition, after a 3D part is formed by an SLA process, the 3D part must be washed multiple times with various solvents to remove any uncured materials, decomposition products, and / or process by-products remaining on the 3D part, which introduces expense, increased manufacturing time, and the cumbersome need to properly dispose of the washing solutions.

[0006] Some SLA press manufacturers have attempted to address these process challenges by using post-washing stations (e.g., Carbon's Smart Part Washer, FormLab's Form Wash station) that are intended to automate and reduce the labor of the process. After this post-wash, the parts must be "cured" in a light box (FormLab's Form Cure station) or in a convection oven (Carbon does not currently have an independent production line and outsources its work to customers using third-party light box and oven manufacturers).

[0007] Therefore, there is a need to overcome one or more of the current deficiencies discussed above. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] U.S. Patent No. 8,232,043 [Patent Document 2] U.S. Patent No. 8,119,214 [Patent Document 3] U.S. Patent No. 7,935,476 [Patent Document 4] U.S. Patent No. 7,767,728 [Patent Document 5] U.S. Patent No. 7,649,029 [Patent Document 6] International Publication No. 2012129968 [Patent Document 7] CN102715751 [Patent Document 8] JP2012210408 [Patent Document 9] U.S. Patent No. 7,824,839 [Patent Document 10] U.S. Patent No. 7,550,246 [Patent Document 11] U.S. Patent No. 7,534,844 [Patent Document 12] U.S. Patent No. 6,692,891 [Patent Document 13] U.S. Patent No. 5,374,500 [Patent Document 14] U.S. Patent No. 5,017,461 [Patent Document 15] U.S. Patent No. 7,919,162 [Patent Document 16] U.S. Patent No. 6,932,930 [Patent Document 17] U.S. Patent No. 4,337,130 [Patent Document 18] U.S. Patent No. 7,507,784 [Patent Document 19] U.S. Patent No. 6,939,940 [Patent Document 20] U.S. Patent No. 4,765,818 [Patent Document 21] U.S. Patent No. 7,709,597 [Patent Document 22] U.S. Patent No. 7,108,947 [Patent Document 23] U.S. Patent No. 8,242,299 [Patent Document 24] U.S. Patent No. 8,147,918 [Patent Document 25] U.S. Patent No. 7,368,514 [Patent Document 26] U.S. Patent No. 7,651,683 [Patent Document 27] U.S. Patent No. 7,651,682 [Patent Document 28] U.S. Patent No. 7,556,490 [Patent Document 29] U.S. Patent No. 6,602,975 [Patent Document 30] U.S. Patent No. 5,836,313 [Non-patent literature]

[0009] [Non-Patent Document 1] Photoacid Generator Selection Guide for the electronics industry and energy curable coatings(BASF 2010) Summary of the Invention [Problem to be solved by the invention]

[0010] The present disclosure surprisingly provides methods for preparing three-dimensionally printed ("3D") parts that reduce the need for cleaning of the parts, as well as methods for providing 3D parts having surfaces that are hardened and / or treated to result in surface modification of the 3D parts. [Means for solving the problem]

[0011] For example, in one embodiment, a method for curing and / or modifying a surface of a three-dimensional (3D) printed part includes immersing a "green" three-dimensional (3D) printed part containing reactive moieties in a liquid bath at an elevated temperature to achieve a degree of polymerization of the reactive moieties in the 3D printed part resulting in a cured 3D printed part. In another embodiment, the liquid bath may contain molecules having reactive moieties capable of reacting with the surface of the 3D printed part. For example, radical initiated polymerization may occur between the reactive moieties of the 3D printed part and the reactive molecules. Generally, initiators or other reactive groups are present in and / or at the surface of the 3D printed part that are responsible for additional curing processes and reactivity with reactive molecules dispersed on the part surface. The initiator may be a photoinitiator or a thermal initiator. Initiation may be from a thermally activated catalyst. Initiation may occur from thermally cleavable groups or products of a decomposition mechanism. In some aspects, initiators remaining within the bulk of the part and / or on the surface of the part may be referred to as residual initiators.

[0012] Thus, by way of example, disclosed herein is the rapid curing of parts produced by 3D printing techniques using either photo- or thermally initiated polymerization reactions. The methods disclosed herein help reduce surface tack (number of dangling bonds) of the resulting 3D parts, and can be used to add additional chemical coatings that modify the feel and / or texture of the final parts.

[0013] Currently, most 3D printing techniques use extensive solvent washes to help minimize surface sticking of 3D printed parts, followed by long bake times in high intensity light boxes or thermal ovens to cure. Embodiments of the present invention reduce the need for many solvent washes, allowing for higher throughput in the processing of "green" (not fully cured / polymerized) 3D printed parts, while also allowing for novel coating applications (i.e., anti-adhesion, paint adhesion promoters, electrodeposition promoters, etc.).

[0014] While multiple embodiments are disclosed, still other embodiments of the present disclosure will become apparent to those skilled in the art from the following detailed description. As will become apparent, the present disclosure is capable of modification in various obvious aspects, all without departing from the spirit and scope of the present disclosure. Accordingly, the detailed description is to be regarded as illustrative in nature, and not restrictive. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram illustrating an example of a conventional SLA post-processing. [Diagram 2] FIG. 2 illustrates an example of a novel SLA post-processing approach disclosed herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] As used herein and in the claims, the terms "including" and "comprising" are open-ended terms and should be construed to mean "including, but not limited to." These terms encompass the more restrictive terms "consisting essentially of" and "consisting of."

[0017] It should be noted that, as used herein and in the claims, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Similarly, the terms "a" (or "an"), "one or more," and "at least one" can be used interchangeably herein. It should also be noted that the terms "comprising," "including," "characterized by," and "having" can also be used interchangeably.

[0018] Unless otherwise indicated, all technical and scientific terms herein have the same meaning as commonly understood by one skilled in the art to which this disclosure belongs. All publications and patents detailed herein are incorporated by reference in their entirety for all purposes, including to describe and disclose the chemistry, apparatus, statistical analysis, and techniques reported in the publications that may be used in connection with this disclosure. All references cited herein should be taken as indicative of the level of skill in the art. Nothing herein should be construed as an admission that the present disclosure is not entitled to antedate such disclosure by reason of prior disclosure.

[0019] The phrases "reactive moiety" and / or "reactive moieties" refer to a polymer resin that retains some unreacted portion of a monomer used to prepare the polymer resin, or the remaining monomer itself. That is, the polymer resin that forms the 3D printed part does not fully cure 100% of all potentially possible reactive sites, e.g., acrylate groups, methacrylate groups, vinyl groups, olefin groups, etc. Thus, there is a percentage of reactive sites that remain within and / or on the surface of the polymer resin that forms the 3D printed part. These "reactive moieties" (potentially curable functional groups within the polymer resin) can further react with another reactive molecule that also has a reactive site under appropriate conditions (e.g., heat and / or UV light) and in the presence of an initiator that is present in the reactive moieties within the polymer resin or in or on the surface of the 3D printed part.

[0020] The phrases "reactive molecules" or "small reactive molecules" or "small molecules" refer to monomeric or oligomeric materials that can react with the surface of a 3D printed part that is partially or fully cured. As an example, residual initiators found in or on the surface of the 3D printed part can contribute to a reaction between the residual reactive moieties present on and / or at the surface of the 3D printed part. There are other chemical mechanisms by which such reactions can occur, but the primary aspect is that there are moieties in or on the bulk 3D printed part that would otherwise be unreacted in the absence of "small reactive molecules". The reaction can result in a coating of the surface of the 3D printed part that can impart unique physical properties to the surface, such as slipperiness, hydrophobicity, chemical resistance, hydrophilicity, biocompatibility, etc.

[0021] The term "initiator" is known in the art. Two types of initiators can be included in the polymer resin formulation used in the method of preparing 3D printed parts described herein. Radical initiators include photoinitiators and thermal initiators. The term is used broadly to include other initiation processes and initiators, such as cationic initiators, photoacid generators, thermally activated catalysts, or any other chemical species that can contribute to initiating further polymerization in the bulk of the 3D print or to attaching small molecules to the surface of the print. Initiators that remain in the bulk of the polymerized part and / or on the surface of the part are referred to as "residual initiators."

[0022] Suitable photoinitiators include, but are not limited to, benzoin ethers (e.g., benzoin methyl ether or benzoin isopropyl ether) or substituted benzoin ethers (e.g., anisoin methyl ether). Other exemplary photoinitiators are substituted acetophenones, such as 2,2-diethoxyacetophenone or 2,2-dimethoxy-2-phenylacetophenone (available commercially under the trade name IRGACURE 651 from BASF Corp., Florham Park, NJ, USA, or under the trade name ESACURE KB-1 from Sartomer, Exton, Pa., USA). Still other exemplary photoinitiators are substituted alpha-ketols, such as 2-methyl-2-hydroxypropiophenone, aromatic sulfonyl chlorides, such as 2-naphthalenesulfonyl chloride, and photoactive oximes, such as 1-phenyl-1,2-propanedione-2-(O-ethoxycarbonyl)oxime. Other suitable photoinitiators include, for example, 1-hydroxycyclohexyl phenyl ketone (commercially available under the trade name IRGACURE 184), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (commercially available under the trade name IRGACURE 819), 2,4,6-trimethylbenzoylphenylphosphinic acid ethyl ester (commercially available under the trade name IRGACURE 184), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (commercially available under the trade name IRGACURE 184), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (commercially available under the trade name IRGACURE 1819), bis(2,4,6-trimethylbenzoyl)phenylphosphine acid ethyl ester (commercially available under the trade name IRGACURE 184), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (commercially available under the trade name IRGACURE 1819 ... TPO-L), 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one (commercially available under the trade name IRGACURE 2959), 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone (commercially available under the trade name IRGACURE 369), 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one (commercially available under the trade name IRGACURE 907), and 2-hydroxy-2-methyl-1-phenylpropan-1-one (commercially available under the trade name DAROCUR 1173 from Ciba Specialty Chemicals Corp., Tarrytown, NY, USA). Other suitable photoinitiators (types I and II) include those listed in the table below.

[0023] [Table 1A]

[0024] [Table 1B]

[0025] [Table 2A]

[0026] [Table 2B]

[0027] Chemical initiators include, for example, those set forth in the table below.

[0028] [Table 3A]

[0029] [Table 3B]

[0030] [Table 3C]

[0031] The catalysts described herein are used in concentrations ranging from about 0.05 to about 5.0%, from about 0.1 to about 2.0%, or from about 0.2 to about 1.0% (by weight, based on the weight of the composition).

[0032] Suitable thermal initiators include, but are not limited to, suitable peroxides ("ROOR"), where R is H or an organic moiety. Peroxide catalysts include, for example, hydrogen peroxide and any organic peroxide, such as benzoyl peroxide, methyl ethyl ketone peroxide, 1-butyl hydroperoxide, and derivatives, and combinations thereof. Peroxide catalysts are generally used at concentrations ranging from about 0.1 to about 5% or more of the total weight of the composition. More specifically, peroxide catalysts are used at concentrations ranging from about 0.05 to about 5.0%, about 0.1 to about 2.0%, or about 0.2 to about 1.0% (by weight, relative to the weight of the composition). For example, methyl ethyl ketone peroxide (0.1% solution in toluene) can be used.

[0033] Suitable thermal initiators also include various azo compounds, such as those commercially available under the trade name VAZO from EIDuPont de Nemours Co., Wilmington, Del., USA, such as VAZO 67, 2,2'-azobis(2-methylbutanenitrile), VAZO 64, 2,2'-azobis(isobutyronitrile), VAZO 52, (2,2'-azobis(2,4-dimethylpentanenitrile), and VAZO 88, 1,1'-azobis(cyclohexanecarbonitrile); various peroxides, such as benzoyl peroxide (BPO, CAS No. 94-36-0), cyclohexane peroxide, lauroyl peroxide, di-tert-amyl peroxide, tert-butyl peroxybenzoate, di-cumyl peroxide, and the like, as well as various peroxides commercially available from Atofina Chemicals, Inc., Philadelphia, PA, USA, such as VAZO 67, 2,2'-azobis(isobutyronitrile), VAZO 52, (2,2'-azobis(2,4-dimethylpentanenitrile), and VAZO 88, 1,1'-azobis(cyclohexanecarbonitrile); Also included are peroxides commercially available from Merck KGaA under the trade name LUPEROX (e.g., LUPEROX 101 (CAS No. 78-63-7), which is 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, LUPEROX 130, which is 2,5-dimethyl-2,5-di-(tert-butylperoxy)-3-hexyne, and LUPEROX 531 (CAS No. 15677-10-4), which is 1,1-di-(t-amylperoxy)cyclohexane); various hydroperoxides, such as tert-amyl hydroperoxide and tert-butyl hydroperoxide; and mixtures thereof.

[0034] Additional thermal initiators include, but are not limited to, p-toluenesulfonic acid (CAS No. 104-15-4), dibutyltin dilaurate (CAS No. 77-58-7), n-butylaminopropyltrimethoxysilane (CAS No. 31024-56-3), and zinc alkylamine carboxylate (K-Kat 670).

[0035] Another example of a peroxide is urea peroxide, which is often supplied as one weight percent in solution.

[0036] Amine synergists / catalysts may also be used. The following table provides examples of suitable amine synergists / catalysts:

[0037] [Table 4]

[0038] Cationic photoinitiators can also be used in the methods described herein. Suitable examples are set out in the table below.

[0039] [Table 5]

[0040] In another embodiment, a photoacid generator can be used as the initiator. Suitable examples are shown in the table below.

[0041] [Table 6]

[0042] Surface adhesion promoters may also be used in the methods described herein. Examples of suitable surface adhesion promoters include those in the table below.

[0043] [Table 7]

[0044] The present disclosure provides embodiments for preparing three-dimensionally printed ("3D") parts with reduced need for cleaning of the parts, as well as 3D parts having as their surfaces cured and / or treated to provide surface modifications to the 3D parts.

[0045] For example, in one embodiment, a method for curing and / or modifying a surface of a three-dimensional (3D) printed part includes immersing a three-dimensional (3D) printed part containing reactive moieties in a liquid bath at an elevated temperature in the presence of a residual initiator to effect polymerization of the reactive moieties of the 3D printed part to result in a cured 3D printed part. In another embodiment, the liquid bath may contain reactive molecules. The reactive molecules include functional groups that can react with the bulk and / or surface of the 3D printed part that includes the reactive moieties. For example, radical initiated polymerization may occur between the reactive moieties of the 3D printed part and the reactive molecules. Generally, an initiator, e.g., a residual initiator, is present in the bulk and / or surface of the 3D printed part. The initiator may be a photoinitiator or a thermal initiator.

[0046] Rather than curing "green" parts (parts that are not fully cured / polymerized, i.e., the chemical reactions are pushed to 100% completion after printing) in a light box or thermal oven, embodiments of the present invention use a hot liquid bath to cure the 3D printed parts, which offers advantages over traditional light boxes or thermal ovens.

[0047] Without being limited by theory, one advantage provided by embodiments of the present invention is a result of the liquid and polymer resin being incompatible (low surface energy, high contact angle of the liquid at the part surface). At the surface of the solidified 3D part, the dangling oligomer chains break down and are forced back against the part surface as opposed to spreading out in the liquid. In other words, the dangling polymer chains are in a theta solvent condition (above the theta point, in poor solvent form) where they are insoluble and contract / coil back against the part surface rather than spreading out in the liquid. As the temperature increases for this liquid, the dangling oligomers continue to react and reattach to the bulk surface of the part, preventing the spreading of the dangling oligomers when the poor solvent / oil is removed. With the final reaction occurring with the polymer strands in the broken configuration, the surface tack of the part is substantially reduced for the end use application.

[0048] For example, a liquid that solvates dangling polymer chains from the bulk surface and does not itself promote the collapse of the dangling polymer chains is considered a good solvent. A liquid that by itself causes the collapse of dangling polymer chains at the bulk surface is considered a poor solvent (i.e., no solvent). Solvent / poor solvent combinations can be used to vary the percentage of polymer chains that will collapse and survive at the bulk surface of the part.

[0049] To further elaborate the methods described herein, Figure 1 depicts one example of a conventional SLA post-processing. First, most of the residual photoactive resin (red haze) is removed by solvent washing. Multiple washing stations are used in sequence to remove any traces of unbound reactive oligomers (red strands). The object is then cured using light or heat to convert the reactive groups to a non-reactive state (black strands). These strands do not necessarily bond with the surface of the bulk part, leaving a residual tackiness.

[0050] The phrases "solvent wash", "washing solvent", "solvent washing", or "washing with a solvent" refer to a solvent used to clean / remove unreacted polymer resin, decomposition products, and / or by-products left on the surface of a 3D printed part. Suitable solvents include, but are not limited to, isopropyl alcohol, acetone, propylene glycol, propylene glycol ethers, such as dipropylene glycol monomethyl ether (DPM) and tripropylene glycol monomethyl ether (TPM), methanol, decafluoropentane, fluoroethers, hexane, ethyl acetate, dichloromethane, chloroform, and mixtures thereof.

[0051] Typically, current methods of manufacturing 3D printed shapes require three washes or two to about five washes to remove residual polymer resin or by-products or decomposition products from the 3D printing process.

[0052] Some 3D printing companies "soak" their 3D printed parts in the solvent for 15-30 minutes, which can be a disadvantage in that the part may swell with the solvent and become weaker.

[0053] In contrast, embodiments of the present invention require only a single wash or two washes, thus saving the use of solvents and time to prepare the surface of the 3D printed part for additional modification. The methods of the present invention described herein do not require the 3D printed part to be "soaked" for any length of time (15-30 minutes). This eliminates the possibility of swelling of the 3D printed part, reducing production time.

[0054] A second advantage represented by embodiments of the present invention is that parts can be coated or derivatized with a layer of small reactive molecules that bind to the surface. The reactive molecules can be added to a liquid bath and the surface energy induces a part-liquid interface (i.e., the reactive molecules act as surfactants). The reactive groups of these small molecules, e.g., vinyl groups, acrylate or methacrylate groups, olefin groups, or thiols, can react with the surface of the 3D printed part and chemically link to the surface. These small molecules can be used to change important properties, e.g., chemical resistance, hydrophobicity, hydrophilicity, biocompatibility, or the feel of the surface. In addition, chemical accelerators can be linked to the part to promote adhesion of a second coating material (e.g., accelerators for auto body paint adhesion, accelerators for metal deposition by electroless metal plating). Importantly, these small reactive molecules do not react with each other and do not polymerize when dispersed in the bulk liquid phase, since the process that initiates the chemical reaction is only in the bulk or on the surface of the 3D printed part. They can only react when in close proximity to a 3D printed part that contains the necessary initiator.

[0055] FIG. 2 depicts one example of the inventive SLA post-treatment approach disclosed herein. First, most of the residual photoactive resin (red haze) is removed by solvent washing. Limiting the washing steps to one bath leaves behind residual strands. Any residual reactive oligomers (red strands) that are not removed by these washing steps are disrupted at the surface of the part by immersion in an incompatible liquid. The object is then cured using light or heat to bond these oligomers to the bulk surface while simultaneously causing them to go from a disrupted state to a non-reactive state (black strands). Alternatively, small reactive molecules can be added to the liquid (blue-red strands) to coat the surface of the object. When heated, these molecules react with the still reactive oligomers on the surface of the part, resulting in a coating (pendant blue chains). The reaction can be driven by leaving residual initiator molecules in the bulk and / or on the surface of the cured object.

[0056] One example of a class of hydrophobic molecules (reactive small molecules) is (meth)acrylate-containing siloxane monomers. (Meth)acrylate-containing siloxane monomers may be monofunctional, difunctional, or may include a combination of monofunctional and difunctional acrylate-containing siloxane monomers. In the example where the acrylate-containing siloxane monomer is composed of one or more monofunctional acrylate-containing siloxane monomers (i.e., it does not contain any multifunctional acrylate-containing siloxane monomers), the polymerizable composition will typically further include an acrylate-containing crosslinker, which will be further described below. In one specific example, the acrylate-containing siloxane monomer has one or more polymerizable methacrylate groups. Various non-limiting examples of suitable (meth)acrylate-containing siloxane monomers include 3-[tris(trimethylsiloxy)silyl]propyl methacrylate ("TRIS"), 3-methacryloxy-2-hydroxypropyloxy)propyl bis(trimethylsiloxy)methylsilane ("SiGMA"), methyldi(trimethylsiloxy)silylpropyl glycerol ethyl methacrylate ("SiGEMA"), and monomethacryloxypropyl functional polydimethylsiloxanes such as MCR-M07 and MCS-M11, all available from Gelest, Inc. (Morrisville, Pa., USA).

[0057] Examples of hydrophobic vinyl-containing monomers (reactive small molecules) include, but are not limited to, tetrafluoroethylene (TFE), hexafluoropropylene, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, perfluoroalkyl vinyl ethers, and mixtures thereof.

[0058] Examples of hydrophobic (meth)acrylate-containing monomers (reactive small molecules) include, but are not limited to, fluorinated alkyl (meth)acrylates and fluorinated (meth)acrylate siloxanes, such as monomethacryloxypropyl-terminated poly(dimethylsiloxane).

[0059] Examples of hydrophilic vinyl-containing monomers include hydrophilic monomers having one vinyl ether, vinyl ester, allyl ester, or vinyl amide polymerizable group. Exemplary hydrophilic vinyl-containing monomers include N-vinyl-N-methylacetamide (VMA), N-vinylpyrrolidone (NVP), 1,4-butanediol vinyl ether (BVE), ethylene glycol vinyl ether (EGVE), diethylene glycol vinyl ether (DEGVE), and combinations thereof.

[0060] Examples of hydrophilic (meth)acrylate-containing monomers include, for example, (meth)acrylic acid, hydroxyethyl (meth)acrylate, hydroxypropyl meth(acrylate), and mixtures thereof.

[0061] A third advantage is the speed at which the polymerization reaction occurring within the "green" printed part can be driven to completion. As noted above, a light box or convection oven is typically used to raise the temperature of the part. This is potentially the slowest part of the manufacturing process and can limit throughput. By using a liquid bath as described herein, thermal energy is transferred to the part to raise the internal temperature much more quickly. This allows for the curing of 3D printed parts at a faster rate than conventional techniques.

[0062] The liquid bath used can be any commercially available solvent that can be heated over a range of temperatures. Organic oils, silicone oils, fluorinated oils, aqueous-based oil baths such as water, water / glycol, water / DMSO, DMSO, etc. can function in the liquid bath.

[0063] Fluoro liquids can include, but are not limited to, fluorinated oils. Fluorinated oils generally include liquid perfluoro organic compounds. Examples of fluorinated oils include perfluoro-n-alkanes, perfluoropolyethers, perfluoroalkyl ethers, copolymers of substantially fluorinated molecules, and combinations of the above.

[0064] Organic liquids include, but are not limited to, organic oils, organic solvents, including but not limited to, chlorinated solvents (e.g., dichloromethane, dichloroethane, and chloroform), and organic liquids that are incompatible with aqueous systems. Organic oils include neutral, non-polar organic compounds that are viscous liquids at room temperature and are both hydrophobic and lipophilic. Examples of organic oils include, but are not limited to, higher density hydrocarbon liquids.

[0065] Silicone oils are liquid polymerized siloxanes with organic side chains. Examples of silicone oils include polydimethylsiloxane (PDMS), simethicone, and cyclosiloxane. For example, silicone oils are used in oil baths. Silicone oils are generally polydimethylosiloxane (PDMS) and can have a viscosity range (at room temperature) of about 0.65 cSt to about 2,500,000 cSt. Suitable PDMS oils include Gelest, Available from DMSO, Inc., e.g., DMS-T00 (0.65 cSt), DMS-T01 (1.0 cSt), DMS-T01.5 (1.5 cSt), DMS-T02 (2.0 cSt), DMS-T03 (3.0 cSt), DMS-T05 (5.0 cSt), DMS-T07 (7.0 cSt), DMS-T11 (10 cSt), DMS-T12 (20 cSt), DMS-T15 (50 cSt), DMS-T21 (100 cSt), DMS-T22 (200 cSt), DMS-T23 (350 cSt), DMS-T25 (500 cSt), DMS-T30 (300 cSt), DMS-T31 (300 cSt), DMS-T32 (300 cSt), DMS-T33 (300 cSt), DMS-T34 (300 cSt), DMS-T35 (300 cSt), DMS-T36 (300 cSt), DMS-T37 (300 cSt), DMS-T38 (300 cSt), DMS-T39 (300 cSt), DMS-T40 (300 cSt), DMS-T41 (300 cSt), DMS-T42 (300 cSt), DMS-T43 (300 cSt), DMS-T44 (300 cSt), DMS-T45 (300 cSt), DMS-T46 (300 cSt), DMS-T47 (300 cSt), DMS-T48 (300 cSt), DMS-T49 (300 cSt), DMS-T50 (300 cSt), DMS-T51 (300 cSt), DMS-T52 (300 cSt), DMS-T53 (300 cSt), DMS- DMS-T31 (1000 cSt), DMS-T35 (5,000 cSt), DMS-T41 (10,000 cSt), DMS-T41.2 (12,500 cSt), DMS-T43 (30,000 cSt), DMS-T46 (60,000 cSt), DMS-T51 (100,000 cSt), DMS-T53 (300,000 cSt), DMS-T56 (600,000 cSt), DMS-T61 (1,000,000 cSt), DMS-T63 (2,500,000 cSt), and DMS-T72 (20,000,000 cSt).

[0066] A fourth advantage of the liquid bath system relates to the load deflection of the material used to print the 3D part. For many materials in the 3D printing space, when heated, they can lose their structural strength and bend / deflect under their own mass. Thus, the temperature at which a material substantially changes its material properties is known as the "load deflection temperature." Both the oven and liquid bath methods described herein can be used to bring the material close to its load deflection temperature. One difference in the liquid bath is that due to the buoyant forces acting on the object, there is less gravity acting on the 3D print when submerged in liquid. In short, when an object is freestanding in an oven, it can potentially sag and permanently deform under its own mass. In the embodiments described herein, the effective mass of the object is substantially smaller due to the buoyant forces of the liquid, thereby limiting or eliminating the degree of deformation.

[0067] The choice of solvent in the liquid bath can be dilute so that the density of the liquid is comparable or substantially comparable to the density of the object. By choosing the appropriate liquid for the bath, stresses associated with the part in a typical curing environment, e.g., gravity, are reduced or eliminated so that the object is essentially weightless in the curing bath. Such dilution limits or eliminates the degree of deformation often associated with curing of green objects. Non-limiting examples of 3D printing resins can include densities in the range of about 0.8 to about 1.3 g / mL; suitable oils can range from about 0.7 to about 2.4 g / mL, with non-limiting examples including resin to oil density ratios in the range of about 0.5 to about 1.5. In another embodiment, the green part / object can be coated with oil and subjected to a conventional oven cure to reduce surface tack without immersion in a bath as described herein. The oil coating, followed by a UV cure and / or thermal cure process can act in a similar manner as described above, with the poor solvent layer causing the collapse of dangling surface polymer strands.

[0068] As used herein, "polymerizable liquid" includes any small building blocks that combine to form larger structures, such as monomers / oligomers cross-linked by traditional polymer chemistry, small particles / colloidal materials that bond together, metal ions that deposit to form bulk metals, or any of a number of other chemistries into microscale building blocks. It is understood that the polymerizable liquids described herein can include various additives, and that once polymerized, the polymerizable liquid provides a green object / composition that can be further cured as detailed herein.

[0069] In the embodiments described herein, the polymerizable liquid may include a monomer or oligomer, particularly a photopolymerizable and / or free radical polymerizable monomer and oligomer, and a suitable initiator, such as a free radical initiator. Examples include, but are not limited to, acrylic, methacrylic, acrylamide, styrene, olefin, halogenated olefin, cyclic alkene, maleic anhydride, alkene, alkyne, carbon monoxide, functional oligomer, multifunctional cure site monomer, functional PEG, and the like, including combinations thereof. Examples of liquid resins, monomers, and initiators include, but are not limited to, those shown in U.S. Pat. No. 8,232,043; U.S. Pat. No. 8,119,214; U.S. Pat. No. 7,935,476; U.S. Pat. No. 7,767,728; U.S. Pat. No. 7,649,029; WO2012129968; CN102715751; JP2012210408.

[0070] In the embodiments described herein, the polymerizable liquid comprises a monomer or oligomer selected from the group consisting of acrylic, methacrylic, urethane, acrylic ester, polyester, cyanoester, acrylamide, maleic anhydride, functional PEG, dimethacrylate oligomer, or combinations thereof.

[0071] In other embodiments described herein, the polymerizable liquid comprises a monomer or oligomer selected from the group consisting of olefins, halogenated olefins, cyclic alkenes, alkenes, alkynes, and combinations thereof. In embodiments, the organic polymerizable liquid is selected from the group consisting of 1,6-hexanediol diacrylate (HDDA), pentaerythritol triacrylate, trimethylolpropane triacrylate (TMPTA), isobornyl acrylate (IBOA), tripropylene glycol diacrylate (TPGDA), (hydroxyethyl) methacrylate (HEMA), and combinations thereof.

[0072] Acid-catalyzed polymerizable liquids. While various embodiments above provide polymerizable liquids that include free radically polymerizable liquids, in other embodiments, the polymerizable liquids include acid-catalyzed or cationic polymerization polymerizable liquids. In such embodiments, the polymerizable liquids include monomers containing groups suitable for acid catalysis, such as epoxide groups, vinyl ether groups, and the like. Thus, suitable monomers include olefins, such as methoxyethene, 4-methoxystyrene, styrene, 2-methylprop-1-ene, 1,3-butadiene, and the like; heterocyclic monomers (including lactones, lactams, and cyclic amines), such as oxiranes, thietanes, tetrahydrofurans, oxazolines, 1,3,dioxepanes, oxetan-2-ones, and the like, and combinations thereof. Suitable (generally ionic or non-ionic) photoacid generators (PAGs) may be included in the acid-catalyzed polymerizable liquid, examples of which include, but are not limited to, onium salts, sulfonium salts, and iodonium salts, such as diphenyl iodide hexafluorophosphate, diphenyl iodide hexafluoroarsenate, diphenyl iodide hexafluoroantimonate, diphenyl p-methoxyphenyl triflate, diphenyl p-toluenyl triflate, diphenyl p-isobutylphenyl triflate, diphenyl p-tert-butylphenyl triflate, triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroarsenate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium triflate, dibutylnaphthylsulfonium triflate, and the like, including mixtures thereof. See, for example, U.S. Patent No. 7,824,839; U.S. Patent No. 7,550,246; U.S. Patent No. 7,534,844; U.S. Patent No. 6,692,891; U.S. Patent No. 5,374,500; and U.S. Patent No. 5,017,461; see also Photoacid Generator Selection Guide for the electronics industry and energy curable coatings (BASF 2010).

[0073] Base-catalyzed polymerizable liquid. In some embodiments, the polymerizable liquid comprises a base-catalyzed polymerizable liquid. Suitable base-catalyzed polymerizable liquids include, but are not limited to, malachite green carbinol base, which produces hydroxide when irradiated with green light.

[0074] Hydrogels. In some embodiments, suitable polymerizable liquids include photocurable hydrogels such as poly(ethylene glycol) (PEG) and gelatin. PEG hydrogels have been used to deliver a variety of biopharmaceuticals, such as growth factors, but a major challenge for PEG hydrogels crosslinked by chain-growth polymerization is the potential for irreversible protein damage. Maximum release of biopharmaceuticals from photopolymerized PEG diacrylate hydrogels can be enhanced by including affinity binding peptide sequences in the monomer resin solution, allowing sustained delivery prior to photopolymerization. Gelatin is a biopolymer frequently used in the food, cosmetic, pharmaceutical, and photographic industries. Gelatin is obtained by thermal denaturation or chemical and physical degradation of collagen. There are three types of gelatin, including those found in animals, fish, and humans. Gelatin from cold-water fish skin is considered safe for use in pharmaceutical applications. Modified gelatin can be appropriately crosslinked using UV or visible light. Methods for crosslinking gelatin include curing derivatives from dyes such as Rose Bengal.

[0075] Silicone resin. Suitable polymerizable liquids include silicones. Silicones can be photocurable or can be solidified via a Michael reaction between thiol and vinyl residues using a radical photoinitiator. Suitable photoinitiators include, but are not limited to, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, vinylmethoxysiloxane homopolymer, and (mercaptopropyl)methylsiloxane homopolymer.

[0076] Biodegradable resins. Biodegradable polymerizable liquids are particularly important in temporary performance applications, such as implantable devices for drug delivery or biodegradable screws and stents (U.S. Patent No. 7,919,162; U.S. Patent No. 6,932,930). Biodegradable copolymers of lactic and glycolic acid (PLGA) can be dissolved in PEG dimethacrylate to yield transparent resins suitable for use. Polycaprolactone and PLGA oligomers can be functionalized with acrylic or methacrylic groups to make them effective resins for use.

[0077] Photocurable polyurethanes. Particularly useful polymerizable liquids are photocurable polyurethanes. Photopolymerizable polyurethane compositions containing (1) polyurethanes based on aliphatic diisocyanates, poly(hexamethylene isophthalate glycol), and optionally 1,4-butanediol; (2) multifunctional acrylic esters; (3) photoinitiators; and (4) antioxidants can be formulated to provide hard, abrasion-resistant, and stain-resistant materials (U.S. Pat. No. 4,337,130). Photocurable thermoplastic polyurethane elastomers incorporate photoreactive diacetylenic diols as chain extenders.

[0078] High performance resin. In some embodiments, the polymerizable liquid comprises a high performance resin. As mentioned above and further described below, such high performance resins may sometimes require the use of a heating process to melt and / or reduce their viscosity. Examples of such resins include, but are not limited to, resins for materials sometimes referred to as liquid crystalline polymers of esters, ester-imide oligomers, and ester-amide oligomers, as described in U.S. Pat. No. 7,507,784; U.S. Pat. No. 6,939,940. Since such resins are sometimes used as high temperature thermosetting resins, they further comprise a suitable photoinitiator, such as a benzophenone initiator, an anthraquinone initiator, and a fluoroenone initiator (including derivatives thereof), for initiating crosslinking upon irradiation, as further described below in this disclosure.

[0079] Additional Exemplary Resins. Particularly useful resins for polymerizable liquids for dental applications include EnvisionTEC's Clear Guide, EnvisionTEC's E-Denstone Material. Particularly useful resins for the hearing aid industry include EnvisionTEC's e-Shell 300 series of resins. Particularly useful resins include EnvisionTEC's HTM140IV High Temperature Mold Material for direct use with vulcanized rubber in molding / casting applications. Particularly useful materials for producing tough and rigid parts include EnvisionTEC's RC31 resin. Particularly useful resins for investment casting include EnvisionTEC's Easy Cast EC500.

[0080] Sol-gel polymerizable liquid. In some embodiments, the polymerizable liquid can include a sol solution or an acid-catalyzed sol. Such solutions generally include metal alkoxides, such as silicon alkoxides and titanium alkoxides, e.g., silicon tetraethoxide (tetraethyl orthosilicate; TEOS), in a suitable solvent. Products can be produced with a variety of different properties, ranging from rubbery materials (e.g., using silane-terminated silicone rubber oligomers) to extremely hard materials (glass using TEOS alone), and properties in between, using various combinations of silane-terminated oligomers and TEOS. Additional components, such as dyes and dopants, can be included in the sol solution, as known in the art, and post-polymerization baking steps can be included, as known in the art. See, for example, U.S. Pat. Nos. 4,765,818; 7,709,597; 7,108,947; 8,242,299; 8,147,918; and 7,368,514.

[0081] Additional resin components. In some embodiments, the polymerizable liquid includes particulate or colloidal materials capable of bonding together. In other embodiments, the polymerizable liquid includes metal ions capable of depositing to form bulk metal. The polymerizable liquid resin or polymerizable liquid material can have solid particles suspended or dispersed therein. Any suitable solid particles can be used depending on the final product to be fabricated. The particles can be metallic, organic / polymeric, inorganic, ceramic, or composite, or mixtures thereof. The particles can be non-conductive, semi-conductive, or conductive (including metallic and non-metallic or polymeric conductors), and the particles can be magnetic, ferromagnetic, paramagnetic, or non-magnetic. The particles can be of any suitable shape, including spherical, ellipsoidal, cylindrical, and the like. The particles can include an active agent, although these can also be provided dissolved and solubilized in the liquid resin, as described below. For example, magnetic or paramagnetic particles or nanoparticles can be used.

[0082] The polymerizable liquid can have additional soluble components, depending on the particular purpose of the product being fabricated, including pigments, dyes, UV blockers (also known as UV inhibitors), active or pharmaceutical compounds, detectable compounds (e.g., fluorescent, phosphorescent, radioactive), etc. Examples of such additional components include, but are not limited to, proteins, peptides, nucleic acids (DNA, RNA), e.g., siRNA, sugars, small organic compounds (drugs and drug-like compounds), etc., including combinations thereof.

[0083] UV blockers / UV inhibitors / UV absorbers (also known as stabilizers, UVA) dissipate the light energy absorbed from UV light as heat by reversible intramolecular proton transfer. UVA can be included in the 3D printing resin formulation, as this technique does not rely solely on UV curing to cure green parts. After printing, the methods described herein allow for the entire part to be fully cured. By using a standard UV-only post-cure, the interior of the part may still be partially uncured and may exhibit different mechanical properties than the surface of the part.

[0084] Suitable UV blocking agents include, but are not limited to, benzophenones, benzotriazoles, aryl esters, oxanilides, acrylic esters, formamide carbon black, hindered amines, nickel quenchers, phenolic antioxidants, metal salts, zinc compounds, hydroxybenzophenones (e.g., 2-hydroxy-4-n-octoxybenzophenone), hydroxybenzotriazines, cyanoacrylates, benzoxazinones (e.g., 2,2'-(1,4-phenylene)bis(4H-3,1-benzoxazin-4-one), available from Solvay under the trade name CYASORB UV-3638), aryl salicylates, hydroxybenzotriazoles (e.g., 2,2'-(1,4-phenylene)bis(4H-3,1-benzoxazin-4-one), available from Solvay under the trade name CYASORB UV-3638, and 2,2'-(1,4-phenylene)bis(4H-3,1-benzoxazin-4-one), available from Solvay under the trade name CYASORB UV-3638. and 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)-phenol), commercially available under the tradename 5411, or a combination comprising at least one of the foregoing UV stabilizers.

[0085] Additional examples of UV absorbers include, but are not limited to, benzotriazole UVAs (e.g., available from BASF / Azelis under the trade names "TINUVIN P213," "TINUVIN P234," "TINUVIN P326," "TINUVIN P327," "TINUVIN P328," and "TINUVIN P329"). P571); hydroxylphenyl triazines, such as mixtures of 2-[4-[(2-hydroxy-3-dodecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine and 2-[4-[(2-hydroxy-3-tridecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, available, for example, under the trade names "TINUVIN 400" and "TINUVIN 405" from BASF / Azelis, and bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate (CAS No. 41556-26-7) and methyl 1,2,2,6,6-pentamethyl-4-piperidylsebacate (CAS No. 41556-26-7) under the trade name "TINUVIN 292" from BASF / Azelis. No. 82919-37-7).

[0086] Other suitable UVAs include, but are not limited to, 9-anthracenecarboxaldehyde (CAS No. 642-31-9), anthracene (CAS No. 120-12-7), benzo[b]anthracene (CAS No. 92-24-0), coumarin 6 (CAS No. 38215-36-0), 9-cyanoanthracene (CAS No. 1210-12-4), 9-nitroanthracene (CAS No. 602-60-8), 2-aminoanthracene (CAS No. 613-13-8), 9,10-diphenylanthracene (1499-10-10), 9,10-di(1-naphthyl)anthracene (CAS No. 269-27-1), and 1-methylnaphthalene (90-12-0).

[0087] If used, the amount of UVA in any particular composition can be from about greater than 0 to about 1 wt%, particularly 0.05-0.75 wt%, and more particularly 0.1-0.5 wt%, based on the total weight of the composition.

[0088] The polymerizable liquid may further include one or more additional components dispersed therein, including carbon nanotubes, carbon fibers, and glass filaments.

[0089] Polymerizable liquids carrying living cells. In some embodiments, the polymerizable liquids can carry living cells as "particles" in the liquid. Such polymerizable liquids are generally aqueous, can be oxygenated, and can be thought of as "emulsions" that are separate phases. Suitable living cells can be plant cells (e.g., monocotyledonous, dicotyledonous), animal cells (e.g., mammalian, amphibian, reptile cells), microbial cells (e.g., prokaryote, eukaryote, protozoa, etc.), etc. The cells can be differentiated cells from any type of tissue (e.g., blood, cartilage, bone, muscle, endocrine glands, exocrine glands, epithelium, endothelium, etc.) or corresponding differentiated cells, or can be undifferentiated cells such as stem cells or progenitor cells. In such embodiments, the polymerizable liquid can be one that forms a hydrogel, including but not limited to those described in U.S. Pat. Nos. 7,651,683; 7,651,682; 7,556,490; 6,602,975; and 5,836,313.

[0090] The polymerizable liquid resulting in the polymer resin can include one or more crosslinking agents. The phrase "polyethylenically unsaturated crosslinking agent or polyethylenically unsaturated monomer" is art-recognized and is intended to include crosslinking agents having two or more reactive double bonds present in the monomer backbone. The degree of unsaturation provides the ability to polymerize with other crosslinking agents and ethylenically unsaturated monomers to form a network of polymerized material. A "polyethylenically unsaturated crosslinking agent" can have multiple degrees of unsaturation associated with the agent, for example, di-, tri-, tetra-, or penta.

[0091] A "crosslinker" is any compound having a molecular weight less than about 2,000 that contains two or more ethylenically unsaturated groups. Thus, a crosslinker can react with the functional groups of two or more polymer chains to crosslink one type of polymer to another. An "acrylate-containing crosslinker" has at least two polymerizable acrylate functional groups and no other type of polymerizable functional groups. A "vinyl-containing crosslinker" has at least two polymerizable vinyl groups and no other type of polymerizable functional groups. Non-limiting examples of crosslinkers include trimethylolpropane trimethacrylate (TMPTMA), divinylbenzene, di-epoxy, tri-epoxy, tetra-epoxy, di-vinyl ether, tri-vinyl ether, tetra-vinyl ether, and combinations thereof.

[0092] Suitable acrylate-containing crosslinked materials include, for example, 2-hydroxypropyl-1,3-diacrylate and 2-hydroxypropyl-1,3-dimethacrylate, 3-hydroxypropyl-1,2-diacrylate and 3-hydroxypropyl-1,2-dimethylacrylate, pentaerythritol diacrylate and pentaerythritol dimethacrylate, polyethylene glycol (400) diacrylate and polyethylene glycol (400) dimethacrylate, glycerol dimethacrylate and glycerol diacrylate, and pentaerythritol trimethacrylate. acrylate and pentaerythritol triacrylate, reaction products of pyromellitic dianhydride and glycerol dimethacrylate (PMGDM), addition products of 2-hydroxyethyl (meth)acrylate and pyromellitic dianhydride (PMDM), 2,2'-bis[4-(3-methacryloxy-2-hydroxypropoxy)-phenyl]-propane (bis-GMA), lower alkylene glycol dimethacrylates such as triethylene glycol dimethacrylate (TEGDMA) or ethylene glycol dimethacrylate (EDGMA), and mixtures thereof.

[0093] Additional examples of (meth)acrylate-containing crosslinkers that may be used in the polymerizable compositions disclosed herein include, but are not limited to, lower alkylene glycol di(meth)acrylates, poly(lower alkylene) glycol di(meth)acrylates, lower alkylene di(meth)acrylates, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, bisphenol A di(meth)acrylate, methylene bis(meth)acrylamide, and 1,3-bis(3-methacryloxypropyl)tetramethyldisiloxane.

[0094] Examples of vinyl-containing crosslinkers that may be used in the polymerizable compositions disclosed herein include, but are not limited to, divinyl ether, or divinyl sulfone, or triallyl isocyanurate, and any combination thereof. Exemplary divinyl ethers include diethylene glycol divinyl ether, or triethylene glycol divinyl, or 1,4-butanediol divinyl ether, or 1,4-cyclohexanedimethanol divinyl ether, or any combination thereof.

[0095] Additional examples of vinyl-containing crosslinkers include divinyl ethers such as triethylene glycol divinyl ether (TEGDVE) or diethylene glycol divinyl ether (DEGDVE).Acrylate-containing crosslinkers are lower alkylene glycol dimethacrylates such as triethylene glycol dimethacrylate (TEGDMA) or ethylene glycol dimethacrylate (EDGMA).

[0096] Embodiments of the present invention provide one or more of the following advantages: The liquid used in the liquid bath induces dangling strands of polymer in the 3D printed part that do not return to the bulk surface of the plastic body and fully harden, thereby reducing sticking.

[0097] Reactive additives, reactive molecules, can be used in the liquid phase of the liquid bath and can be introduced to the 3D printed part and chemically link / bond to the surface of the part to impart additional properties.

[0098] The liquid bath is a faster conductor of heat, allowing the temperature of 3D printed parts to be raised and fully cured much more quickly than using a traditional oven.

[0099] When a 3D printed part is submerged in liquid, its effective mass is lower, thereby reducing the chance of deformation when heated to higher temperatures.

[0100] A liquid bath can be used in conjunction with UV light to induce further reaction / polymerization (i.e., light causes decomposition and heat accelerates reaction propagation).

[0101] The following paragraphs, listed consecutively from 1 to 23, provide various aspects of the present disclosure. In one embodiment, in the first paragraph (1), the present disclosure provides a method for hardening and / or modifying a surface of a three-dimensional (3D) printed part, comprising immersing the 3D printed part containing reactive moieties and / or residual initiator and / or residual monomer into a liquid bath to effect polymerization of the reactive moieties and increase the degree of polymerization of the 3D printed part.

[0102] 2. The method of paragraph 1, wherein the 3D printed part is washed with a solvent before being submerged in the liquid bath.

[0103] 3. The method of paragraph 1 or 2, wherein the liquid bath is at an elevated temperature that is less than the load deflection temperature of the 3D printed part.

[0104] 4. The method of paragraph 3, wherein the liquid bath is heated to about 30°C to about 300°C.

[0105] 5. Any of the methods of paragraphs 1 through 4, wherein the 3D printed part is exposed to the liquid bath for a time period between about 1 minute and about 24 hours.

[0106] 6. Any of the methods of paragraphs 1 through 5, wherein the liquid bath is a silicone oil bath, an aqueous glycol bath, a fluorinated polyether bath, an aqueous DMSO bath, or a DMSO bath.

[0107] 7. The method of paragraph 6, wherein the silicone oil has a viscosity of about 0.6 cSt to about 20,000 cSt.

[0108] 8. The method of any of paragraphs 1 through 7, further comprising increasing the temperature of the liquid bath from the starting temperature to a final temperature.

[0109] 9. The method of paragraph 8, wherein the starting temperature is about room temperature or corresponds to the initial temperature of the 3D printed part.

[0110] 10. The method of paragraph 8, wherein the maximum temperature of the liquid bath reached is less than the load deflection temperature of the 3D printed part.

[0111] 11. Any of the methods of paragraphs 8 through 10, wherein the temperature of the liquid bath is increased linearly.

[0112] 12. Any of the methods of paragraphs 8 through 10, wherein the temperature of the liquid bath is increased with a nonlinear ramp.

[0113] 13. Any of the methods of paragraphs 8 to 12, in which the increase in temperature of the liquid bath is carried out over incremental lengths of time with no increase in temperature.

[0114] 14. Any of the methods of paragraphs 1 through 13, wherein the 3D printed part having a reactive portion is formed from a thermoset or photocurable resin, including an acrylic resin, a methacrylic resin, a silicone resin, a fluororesin, a styrene resin, a polyolefin resin, a thermoplastic elastomer, a polyoxyalkylene resin, a polyester resin, a polyvinyl chloride resin, a polycarbonate resin, a polyphenylene sulfide resin, a cellulose resin, a polyacetal resin, a melamine resin, a polyurethane resin, or a polyamide resin.

[0115] 15. The method of paragraph 14, further comprising a crosslinking agent.

[0116] 16. The method of paragraph 15, wherein the crosslinker is a polyacrylate or polymethacrylate, an olefin, a dithiol, a diol, a methoxysilane, an ethoxysilane, or a polysulfide.

[0117] 17. Any of the methods of paragraphs 1 to 16, wherein the reactive moiety is within the bulk of the 3D printed part.

[0118] 18. Any of the methods of paragraphs 1 to 16, wherein the reactive moiety is present on a surface of the 3D printed part.

[0119] 19. The method of any of paragraphs 1 through 18, further comprising the step of adding a reactive molecule to the liquid bath.

[0120] 20. The method of paragraph 19, wherein the reactive molecule reacts with a three-dimensional (3D) printed part.

[0121] 21. The method of paragraphs 19 or 20, wherein the reactant molecule is an acrylate, a methacrylate, a vinyl-containing group, an olefin, or a thiol-containing group.

[0122] 22. The method of paragraphs 19 or 20, wherein the reactive molecule comprises a siloxane group, a fluorinated group, or a hydroxy group.

[0123] 23. Any of the methods of paragraphs 1 to 20, wherein the cured 3D printed part is washed with a solvent to remove oils and / or unreacted reactive molecules from a surface of the cured 3D printed part.

[0124] Section 1 According to the present disclosure, a method for curing and / or modifying a three-dimensional (3D) printed part can include providing a three-dimensionally (3D) printed part containing a reactive moiety, and immersing the three-dimensionally (3D) printed part containing the reactive moiety in a liquid bath to effect polymerization of the reactive moiety and change the degree of polymerization of the 3D printed part.

[0125] Item 2. The method of any preceding item, wherein providing the 3D printed part includes washing the 3D printed part with a solvent.

[0126] Item 3. The method of any preceding item, wherein the liquid bath has a temperature in the range of about 30° C. to about 300° C., and the immersing step includes exposing the 3D printed part to the liquid bath for a time in the range of about 1 minute to about 24 hours.

[0127] Item 4. The method of any preceding item, wherein the liquid bath is a poor solvent past the polymer / solvent theta point, causing polymer collapse.

[0128] Clause 5. The method of any preceding clause, wherein the immersing step includes varying the temperature of the liquid bath between a first temperature and a second temperature.

[0129] Item 6. The method of any preceding item, wherein the second temperature of the liquid bath is greater than the first temperature and less than the load deflection temperature of the 3D printed part.

[0130] Clause 7. The method of any preceding clause, wherein the 3D printed part is in the liquid bath during the step of varying the temperature of the liquid bath between the first temperature and the second temperature.

[0131] Clause 8. The method of any preceding clause, wherein varying the temperature of the liquid bath between a first temperature and a second temperature comprises at least one period of linear variation.

[0132] Clause 9. The method of any preceding clause, wherein varying the temperature of the liquid bath between a first temperature and a second temperature includes at least one period of non-linear variation.

[0133] Clause 10. The method of any preceding clause, wherein the step of varying the temperature of the liquid bath between the first temperature and the second temperature includes at least one incremental period during which no change in temperature occurs.

[0134] Clause 11. The method of any preceding clause, wherein the 3D printed part having reactive moieties is formed from a thermosetting or photocurable resin, including an acrylic resin, a methacrylic resin, a silicone resin, a fluororesin, a styrene resin, a polyolefin resin, a thermoplastic elastomer, a polyoxyalkylene resin, a polyester resin, a polyvinyl chloride resin, a polycarbonate resin, a polyphenylene sulfide resin, a cellulose resin, a polyacetal resin, a melamine resin, a polyurethane resin, or a polyamide resin.

[0135] Clause 12. The method of any preceding clause, wherein the reactive moieties include one or more crosslinking reactive moieties selected from acrylate, methacrylate, olefin, dithiol, diol, methoxysilane, ethoxysilane, and sulfide groups.

[0136] Clause 13. The method of any preceding clause, wherein the liquid bath is a silicone oil bath, an aqueous glycol bath, a fluorinated polyether bath, an aqueous DMSO bath, or a DMSO bath.

[0137] Item 14. The method of any preceding item, wherein the 3D printed part includes at least one of a UV stabilizer and a UV blocker.

[0138] Clause 15. The method of any preceding clause, wherein a thermal initiator is present in and / or on the three dimensional printed part that contains reactive moieties.

[0139] Item 16. The method of any preceding item, wherein the thermal initiator has an activation temperature in the range of about 50 to about 140° C.

[0140] Clause 17. The method of any preceding clause, wherein the immersing step includes varying the temperature of the liquid bath between a first temperature and a second temperature, the second temperature of the liquid bath being higher than the first temperature and lower than a load deflection temperature of the 3D printed part, and an activation temperature of the initiator being within the range of the first temperature and the second temperature.

[0141] Clause 18. The method of any preceding clause, further comprising adding a reactive molecule to the liquid bath to react with the three-dimensional (3D) printed part.

[0142] Clause 19. The method of any preceding clause, wherein adding reactive molecules to the liquid bath includes adding reactive molecules to react with a surface of the three-dimensional (3D) printed part.

[0143] Clause 20. The method of any preceding clause, wherein the reactant molecule is an acrylate, a methacrylate, a vinyl-containing group, an olefin, or a thiol-containing group.

[0144] Clause 21. The method of any preceding clause, wherein the reactive molecule comprises a siloxane group, a fluorinated group, or a hydroxy group.

[0145] Clause 22. The method of any preceding clause, wherein the providing step includes providing a three dimensional printed part having a cure rate within a range of about 20% to about 80%.

[0146] Clause 23. The method of any preceding clause, further comprising subjecting the three dimensional printed part to a UV light treatment during a period including at least one of before, during, and after the immersing step.

[0147] The present disclosure will be further described with reference to the following non-limiting examples. It is clear to those skilled in the art that many modifications can be made in the described embodiments without departing from the scope of the present disclosure. Therefore, the scope of the present disclosure should not be limited to the embodiments described in this application, but only by the embodiments described by the language of the claims and the equivalents of those embodiments. Unless otherwise indicated, all percentages are by weight. EXAMPLES

[0148] 3D printing resin: Example: Basic 3D printing resin formulation Photoinitiators, IGM resins Omnirad 819 (phenylbis(2,4,6-trimethylbenzyl)phosphine oxide, CAS 162881-26-7) or BASF TPO (diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, CAS 75980-60-8). Weight percentages of initiator ranging from 0.05% to 5% were used.

[0149] A reactive diluent, 1,6-hexanediol diacrylate (HDDA) monomer diluted with mass percentages ranging from 20% to 80%, was used.

[0150] BOMAR™ BR-970BT (a proprietary polyurethane difunctional acrylate available from Dymax Corporation) was used, with a weight percent of the reactive oligomer ranging from 20% to 80%.

[0151] Thermal initiators, benzyl peroxide (thermal decomposition / thermal onset 60° C.-80° C.) or N-tert-butyl-benzothiazole sulfonamide (thermal decomposition / thermal onset 120° C.), with a mass % of 0.05%-5% were used.

[0152] 3D object design, slicing, video creation and UV projection 3D STL objects were designed in Blender, an open source CAD rendering software adapted for graphic arts and video processing. These objects were then transferred to Autodesk Netfabb where support structures (if necessary) could be applied. Using Netfabb, the STL objects and associated supports were sliced ​​into 10 μm layer JPEG images with lateral resolution corresponding to the UV projection source. Once the image stack was generated, the images were loaded back into Blender and compiled into AVI video files that played at 12 frames per second (12 fps x 10 μm / frame = 120 μm / sec video). Once compiled, these videos could be played back by standard video codecs and media players, such as VLC media player. In addition, the frame rate of the videos could be sped up or slowed down within these media players (users could run the videos at speeds of 30 μm / sec, 60 μm / sec, or 240 μm / sec). The videos were projected by a series of DLP (Digital Light Processing) projectors modified to project UV light. The lamp source varied with the different presses; some projection systems used medium pressure Hg lamps, others monochromatic UV LEDs. The projectors were strung together to create a large continuous projection field (maximum projection field was 15'' x 24'' at 240 μm pixel resolution).

[0153] Printing Procedure Resin was poured into the print vat. The print stage, held by a ball screw actuator arm, was then brought into contact with the print interface. A UV exposure time of 30 seconds was used to produce an initial adhesive layer of resin on the steel build platform, and the video was started in conjunction with the retraction of the build platform at 120 μm / s. Print speeds of 240 μm / s could be achieved, but the quality of such prints and the reliability of the printing process were substantially reduced.

[0154] Traditional Light Curing: 3D printed parts are placed in a curing box lined with highly reflective material and UV curing lamps (high intensity LED or mercury lamps; wavelength 350nm-450nm) for periods of 8-48 hours. The sealed box results in both heat buildup, reaching temperatures of approximately 50°C, and high intensity UV light impinging on the part from all directions. This serves two purposes: the light initiates further decomposition of photoinitiators that are not consumed during the 3D printing process, while the heat generated from the lamp system helps to drive the resulting reaction. Thicker / larger parts tend to have challenges due to limited light penetration into the interior of the part.

[0155] Rapid curing in silicone oil: 3D printed parts were immersed in a bath of silicone oil (100 cSt oil) that was slowly heated to a cure temperature ranging from 50°C to 150°C. The 3D printed parts were incubated between 30 minutes and 1 hour before cooling and removal from the bath. The incubation temperature was selected based on the load deflection temperature of the 3D printed material and the decomposition / initiation temperature of the thermally activated radical initiator or catalyst (if present) that further induces the polymerization reaction within the solidified part. The surface tack of the parts was substantially reduced, while the "baked" (cured) mechanical properties of the parts were greatly superior to the "green" (partially cured) parts due to the complete conversion of the reactions.

[0156] In the case of the oil bath example, there were pre and post wash steps. The first wash was in methanol to remove excess resin from the printing process. After most of this resin was removed, the parts were given a liquid (oil) bath. After the parts were removed from the oil bath, the oil was removed. Removal of the silicone oil was quite simple with warm water and dish soap; this is not always the same depending on what liquid is used in the heated bath that needs to be removed.

[0157] Rapid cure in silicone oil with silicone finish: To apply a smooth, low-tack surface finish to the part, silicone acrylates were dispersed in the silicone oil phase at 1% by weight to form self-assembled monolayers (SAMs) on the 3D printed parts. Exemplary monomers included monomethacryloxypropyl-terminated poly(dimethylsiloxane) (GELEST MCR-M07) and monomethacryloxypropyl-functional tris[poly(dimethylsiloxane)] (GELEST MCT-M11). Other siloxane molecules with reactive functional groups can be used, the central principle being that there is a reactive group (acrylate, methacrylate, vinyl, olefin, thiol / mercaptan, etc.) that can be initiated by radical propagation in conjunction with a group that gives the desired surface finish. Since the silicone acrylates are dispersed in the bulk silicone phase, there are no radicals present to cause polymerization of the monomeric components. Only when these monomeric reactive molecular units come into contact with reactive radicals present on the surface of the 3D printed part will they react to form a monolayer. As a result, a silicone bath containing 1% monomer can be thermally cycled continuously (coating parts multiple times) without depleting / reacting the monomer dispersed therein.

[0158] Rapid cure in silicone oil with fluorinated finish: This procedure follows that for silicone finish described above. In this scenario, 1% by weight of monomethacryloxypropyl terminated poly(3,3,3-trifluoropropyl)methylsiloxane (GELEST MFR-M15) was dispersed in the silicone oil phase. When the molecules coated the 3D printed part, they left a thin fluorinated phase on the outer surface. This both reduces the stickiness of the part and makes it completely smooth. In addition, the fluorinated phase adds a layer of chemical protection and resistance from oxidizing chemistry. This is useful when you want to make your 3D printed parts chemically resistant to reactions (e.g., tubes carrying corrosive oxygen gas, gas masks exposed to mustard gas, parts in contact with strong acids or bases). The layer provides protection in two ways. First, it is essentially non-reactive with most agents to which it is exposed, and second, it creates a fluorinated phase through which most agents cannot pass and reach the more susceptible inner materials.

[0159] Although the present disclosure has been described in terms of preferred embodiments, those skilled in the art will recognize that changes can be made in form and in detail without departing from the spirit and scope of the present disclosure. All references cited throughout this specification, including those in the background, are incorporated herein in their entirety. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the present disclosure specifically described herein. Such equivalents are intended to be encompassed by the following claims.

Claims

1. (i) providing a three-dimensional printed part containing a reactive moiety; (ii) adding reactive molecules to the liquid bath for reaction with the three dimensional printed part; and (iii) immersing the three-dimensional (3D) printed part containing a reactive moiety in the liquid bath to polymerize the reactive moiety with reactive molecules in the liquid bath and change the degree of polymerization of the 3D printed part. A method for curing and / or modifying a three-dimensional (3D) printed part, comprising:

2. The method of claim 1 , wherein providing the 3D printed part comprises cleaning the 3D printed part with a solvent.

3. 10. The method of claim 1, wherein the liquid bath has a temperature in a range of 30° C. to 300° C., and immersing comprises exposing the 3D printed part to the liquid bath for a time in a range of 1 minute to 24 hours.

4. The method of claim 1 , wherein the liquid bath is a poor solvent past the polymer / solvent theta point, causing polymer collapse.

5. The method of claim 1 , wherein the immersing step comprises varying the temperature of the liquid bath between a first temperature and a second temperature.

6. 6. The method of claim 5, wherein the second temperature of the liquid bath is greater than the first temperature and less than a deflection temperature under load of the 3D printed part.

7. 6. The method of claim 5, wherein the 3D printed part is in the liquid bath during the step of varying the temperature of the liquid bath between the first temperature and the second temperature.

8. 6. The method of claim 5, wherein varying the temperature of the liquid bath between the first temperature and the second temperature comprises a linear change for at least one period.

9. 6. The method of claim 5, wherein varying the temperature of the liquid bath between the first temperature and the second temperature comprises at least one period of non-linear variation.

10. 6. The method of claim 5, wherein the step of varying the temperature of the liquid bath between a first temperature and a second temperature includes at least one step period during which no change in temperature occurs.

11. 10. The method of claim 1, wherein the 3D printed part having reactive moieties is formed from a thermosetting or photocurable resin, including an acrylic resin, a methacrylic resin, a silicone resin, a fluororesin, a styrene resin, a polyolefin resin, a thermoplastic elastomer, a polyoxyalkylene resin, a polyester resin, a polyvinyl chloride resin, a polycarbonate resin, a polyphenylene sulfide resin, a cellulose resin, a polyacetal resin, a melamine resin, a polyurethane resin, or a polyamide resin.

12. 2. The method of claim 1, wherein the reactive moieties comprise one or more crosslinking reactive moieties selected from acrylate, methacrylate, olefin, dithiol, diol, methoxysilane, ethoxysilane, and sulfide groups.

13. 10. The method of claim 1, wherein the liquid bath is a silicone oil bath, an aqueous glycol bath, a fluorinated polyether bath, an aqueous DMSO bath, or a DMSO bath.

14. The method of claim 1 , wherein the 3D printed part includes at least one of a UV stabilizer and a UV blocker.

15. 10. The method of claim 1 , wherein a thermal initiator is present in and / or on the three dimensional printed part containing reactive moieties.

16. The method of claim 15, wherein the thermal initiator has an activation temperature in the range of 50 to 140° C.

17. 16. The method of claim 15, wherein the immersing step includes varying a temperature of the liquid bath between a first temperature and a second temperature, the second temperature of the liquid bath being higher than the first temperature and lower than a deflection temperature under load of the 3D printed part, and an activation temperature of an initiator being within the range of the first temperature and the second temperature.

18. The method of claim 1, comprising a step of adding the reactive molecule to react with the surface of the three-dimensional (3D) printed part.

19. The method of claim 1 , wherein the reactive molecule is an acrylate, a methacrylate, a vinyl-containing group, an olefin, or a thiol-containing group.

20. The method of claim 1 , wherein the reactive molecule comprises a siloxane group, a fluorinated group, or a hydroxy group.

21. The method of claim 1, wherein step (i) includes preparing the 3D printed part having a cure rate in the range of 20% to 80%.

22. The method of claim 1, further comprising a step of subjecting the three-dimensional printed part containing a reactive moiety to a UV light treatment during a period including at least one of before, during, and after the step of immersing the three-dimensional printed part into the liquid bath.

23. 2. The method of claim 1, wherein step (ii) of adding reactive molecules to a liquid bath precedes step (iii) of immersing the three-dimensional (3D) printed part containing a reactive moiety into the liquid bath.

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