Method for Rapid Curing and Coating Parts Produced by Additive Manufacturing

Abstract

Describes a method for curing and / or modifying the surface of a three-dimensional (3D) printed part, the method comprising the steps of: immersing a three-dimensional (3D) printed part comprising a reactive portion in a liquid bath at a high temperature to effect polymerization of the reactive portion of the 3D printed part to provide a cured 3D printed part. The liquid bath may further comprise reactive molecules that can react with the surface of the 3D printed part to provide a coating that alters the surface properties of the 3D printed part.

Description

[0001] Cross - Reference to Related Applications

[0002] This PCT application claims priority to U.S. Provisional Patent Application No. 62 / 831,537, filed on April 9, 2019, entitled "METHODOLOGIES TO RAPIDLY CURE AND COAT PARTS PRODUCED BY ADDITIVE MANUFACTURING", the content of which is incorporated herein by reference in its entirety, including but not limited to those aspects related to three - dimensional printing and additive manufacturing. Technical Field

[0003] The present disclosure generally relates to curing and / or modifying the surface of three - dimensional (3D) printed parts. Background Art

[0004] Conventionally, stereolithography (SLA) for additive manufacturing has unique capabilities and technological opportunities compared to competing technologies. This is because SLA can deliver high printing speeds while generating objects from a robust material library.

[0005] However, rapidly building three - dimensional (3D) parts using such methods has certain drawbacks. One drawback of SLA is that the part is not fully cured when the printing process is complete. That is, the chemical reaction responsible for curing the liquid resin used as the raw material input has not reacted to 100% conversion. This can lead to the 3D part being "sticky" and possible deformation of the 3D part because "curing" is incomplete during the initial formation process. In this state, the part is commonly referred to as "green" - similar to pottery where there are "green" un - fired parts and the fired parts have very different properties.

[0006] In addition, after the 3D part is formed by the SLA process, the 3D part must be washed multiple times with various solvents to remove any uncured material, degradation products, and / or process by - products remaining on the 3D part. Washing results in high costs, increased production time, and the inconvenient necessity of proper disposal of the washing solution.

[0007] Several SLA printer manufacturers have tried to address these processing challenges using post - wash stations (such as Carbon’s Smart Part Washer, FormLab’s Form Wash station), which are designed to automate and reduce the labor for this method. After post - washing, the part must be "cured" in a light box (FormLab’s Form Cure station) or a convection oven (Carbon currently does not have an independent production line and refers customers to third - party light box and oven manufacturers).

[0008] Accordingly, there is a need to overcome one or more of the current drawbacks described above. SUMMARY OF THE INVENTION

[0009] The present disclosure surprisingly provides a method for fabricating three-dimensional printed (“3D”) parts that reduces the need for washing the parts and provides cured and / or 3D parts having surfaces that have been treated to provide surface modification of the 3D parts.

[0010] For example, in one embodiment, a method of curing and / or modifying the surface of a three-dimensional (3D) printed part includes the steps of immersing a “green” three-dimensional (3D) printed part comprising reactive moieties in a liquid bath at an elevated temperature to effect a degree of polymerization of the reactive moieties within the 3D printed part to provide a cured 3D printed part. In another embodiment, the liquid bath can comprise molecules having reactive moieties that can react with the surface of the 3D printed part. For example, free radical initiated polymerization can 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 on the surface of the 3D printed part that are responsible for additional curing processes and reactivity with the reactive molecules dispersed on the part surface. The initiator can be a photoinitiator or a thermal initiator. Initiation can be from a thermally activated catalyst. Initiation can be from a thermally cleavable group or the product of a decomposition mechanism. In some aspects, the remaining initiator in the part body and / or on the part surface can be referred to as residual initiator.

[0011] Accordingly, by way of example, the present disclosure describes the rapid curing of parts produced by 3D printing techniques by utilizing photoinitiated or thermally initiated polymerization reactions. The methods described herein help to reduce the surface tackiness (number of dangling bonds) of the resulting 3D parts and can be used to add additional chemical coatings to modify the feel and / or sensation of the final part.

[0012] Currently, most 3D printing techniques utilize extensive solvent washing to help minimize the surface tackiness of 3D printed parts, followed by curing in a high-intensity light box or long baking in a hot oven. This embodiment reduces the need for so much solvent washing and enables higher throughput in processing “green” (not fully cured / polymerized) 3D printed parts, while also enabling new coating applications (i.e., non-stick, paint adhesion promoter, electrocoating promoter, etc.).

[0013] Although multiple embodiments have been disclosed, other embodiments of the present disclosure will become apparent to those skilled in the art from the following detailed description. It is apparent that the present disclosure can be modified in various obvious aspects without departing from the spirit and scope of the present disclosure. Therefore, the detailed description is to be regarded as illustrative in nature and not restrictive. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Examples of traditional SLA post - processing are described.

[0015] Figure 2 Examples of the novel SLA post - processing method disclosed herein are described. DETAILED DESCRIPTION

[0016] In the specification and claims, the terms "including" and "comprising" are open - ended terms and should be interpreted as "including but not limited to...". These terms encompass the more restrictive terms "consisting essentially of" and "consisting of".

[0017] It must be noted that, unless the context clearly dictates otherwise, the singular forms "a", "an", and "the" as used herein and in the appended claims include plural forms. 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 be used interchangeably.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. For all purposes, all publications and patents specifically mentioned herein are incorporated by reference in their entirety, including the chemicals, instruments, statistical analyses, and methods reported in the described and published publications that may be used in conjunction with this disclosure. All references cited in this specification are considered as indicative of the level of skill in the art. Nothing in this disclosure shall be construed as an admission that the present disclosure is not entitled to antedate such disclosure by virtue of prior disclosure.

[0019] The phrases "reactive moiety" and / or "reactive moieties" refer to a polymer resin that retains some unreacted portions of the monomers used to prepare the polymer resin or the residual monomers themselves. That is, the polymer resin forming the 3D printed part is not fully cured to 100% of all potential reactive sites, such as acrylate, methacrylate, vinyl groups, olefin groups, etc. Thus, a proportion of reactive sites remain within and / or on the surface of the polymer resin forming the 3D printed part. These "reactive moieties" (one or more potentially curable functional groups within the polymer resin) can react further with reactive moieties within the polymer resin or with another reactive molecule having reactive sites in the presence of an initiator within or on the surface of the 3D printed part under suitable conditions (e.g., heat and / or UV light).

[0020] The phrases "reactive molecule" or "reactive small molecule" or "small molecule" are intended to refer to monomeric or oligomeric materials that can react with the surface of a partially or fully cured 3D printed part. As an example, a remaining initiator found within or on the surface of a 3D printed part can create a reaction between the surface of the 3D printed part and / or the residual reactive moieties present on the surface of the 3D printed part. There are other chemical mechanisms by which such reactions can occur - but the key aspect is that there are portions within or on the surface of the main 3D printed part where, in the absence of "reactive small molecules", no reaction would occur. This reaction results in a coating on the surface of the 3D printed part and can impart unique physical properties to the surface, such as smoothness, 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 for preparing the 3D printed parts described herein. Free radical initiators include photoinitiators and thermal initiators. The term is used broadly to include other initiating steps and initiators, such as cationic initiators, photoacid generators, thermally activated catalysts, or any other species attributable to initiating further polymerization within the body of the 3D printed object or attaching small molecules to the surface of the printed object. An initiator retained within the polymer part body and / or on the part surface can be referred to as a "residual initiator".

[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 (commercially available from BASF Corp. (Florham Park, N.J., USA) under the trade name IRGACURE 651 or from Sartomer (Exton, Pa., USA) under the trade name ESACURE KB - 1). Still other exemplary photoinitiators are substituted α - keto alcohols 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) phenyl phosphine oxide (commercially available under the trade name IRGACURE 819), ethyl 2,4,6 - trimethylbenzoyl phenylphosphinate (commercially available under the trade name IRGACURE TPO - L), 1 - [4 - (2 - hydroxyethoxy)phenyl] - 2 - hydroxy - 2 - methyl - 1 - propanone (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 from Ciba Specialty Chemicals Corp. (Tarrytown, N.Y., USA) under the trade name DAROCUR 1173). Other suitable photoinitiators (Type I and Type II) include those listed in the following table.

[0023]

[0024]

[0025]

[0026]

[0027]

[0028] Chemical initiators include, for example, those indicated in the following table.

[0029] Chemical initiator

[0030]

[0031]

[0032]

[0033] The catalyst mentioned in this article is used at a concentration in the range of 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).

[0034] 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, for example, benzoyl peroxide, methyl ethyl ketone peroxide, 1-butyl hydroperoxide and their derivatives and combinations. Peroxide catalysts are generally used at a concentration in the range of about 0.1 to about 5% or more of the total weight of the composition. More particularly, peroxide catalysts are used at a concentration in the range of 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% toluene solution) can be used.

[0035] Suitable thermal initiators also include various azo compounds, such as those commercially available under the trade name VAZO from E.I.DuPont de Nemours Co. (Wilmington, Del., USA), including VAZO 67, which is 2,2'-azobis(2-methylbutyronitrile), VAZO 64, which is 2,2'-azobis(isobutyronitrile), VAZO 52, which is (2,2'-azobis(2,4-dimethylvaleronitrile)) and VAZO88, which is 1,1'-azobis(cyclohexanecarbonitrile); various peroxides, such as benzoyl peroxide (BPO, CAS No. 94-36-0), cyclohexanone peroxide, lauroyl peroxide, di-tert-amyl peroxide, tert-butyl peroxybenzoate, dicumyl peroxide and peroxides commercially available under the trade name LUPEROX from Atofina Chemicals, Inc. (Philadelphia, Pa.) (e.g., LUPEROX 101, which is 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane (CAS No. 78-63-7), LUPEROX 130, which is 2,5-dimethyl-2,5-di-(tert-butylperoxy)-3-hexyne) and LUPEROX 531, which is 1,1-di-(tert-amylperoxy)cyclohexane (CAS No. 15677-10-4)); various hydroperoxides, such as tert-amyl hydroperoxide and tert-butyl hydroperoxide; and mixtures thereof.

[0036] 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 alkylamine zinc carboxylate (K-Kat 670).

[0037] Another example of a peroxide is urea peroxide, which is typically provided at 1% by weight in solution.

[0038] Amine synergists / catalysts can also be used. The following table provides suitable examples of amine synergists / catalysts.

[0039]

[0040]

[0041] Cationic photoinitiators can also be used in the methods described herein. The following table lists suitable examples.

[0042]

[0043]

[0044] In another embodiment, a photoacid generator can be used as an initiator. Suitable examples are shown in the table below.

[0045] Omnirad 1173 2-Hydroxy-2-methyl-1-phenylpropanone 7473-98-5

[0046] Omnirad ITX 2-Isopropylthioxanthone 5495-84-1

[0047] Omnirad CPTX 1-Chloro-4-propoxythioxanthone 142770-42-1

[0048] A surface adhesion promoter can also be used in the methods described herein. Suitable examples of surface adhesion promoters include those in the table below.

[0049]

[0050] The present disclosure provides embodiments for preparing three-dimensional printed (“3D”) parts that have reduced washing requirements for the parts and provide cured 3D parts and / or 3D parts having surfaces that have been treated to provide surface modification of the 3D parts.

[0051] For example, in one embodiment, a method of curing and / or modifying the surface of a three-dimensional (3D) printed part includes the steps of: at a high temperature, immersing a three-dimensional (3D) printed part comprising a reactive moiety in a liquid bath in the presence of a residual initiator to effect polymerization of the reactive moiety of the 3D printed part to provide a cured 3D printed part. In another embodiment, the liquid bath can comprise reactive molecules. The reactive molecules include functionality that can react with the body and / or surface of the 3D printed part comprising the reactive moiety. For example, free radical initiated polymerization can occur between the reactive moiety of the 3D printed part and the reactive molecules. Generally, an initiator, e.g., a residual initiator, is present in the body and / or on the surface of the 3D printed part. The initiator can be a photoinitiator or a thermal initiator.

[0052] This example cures “green” parts (parts that are not fully cured / polymerized, i.e., parts where the chemical reaction is pushed to 100% completion after printing) without using a light box or convection oven, but instead uses a hot liquid bath to cure the 3D printed parts. This bath has advantages over traditional light boxes or hot ovens.

[0053] Without being limited by theory, one advantage provided by the present embodiment is the result of immiscibility of the liquid and the polymeric resin (low surface energy and high contact angle of the liquid on the part surface). The dangling oligomer chains on the surface of the solidified 3D part collapse and are driven back to the part surface rather than extending into the liquid. In other words, the dangling polymer chains are in a theta-solvent state (above the theta point and in the form of a poor solvent), in which they are insoluble and contract / wrap towards the part surface rather than extending into the liquid. For such a liquid, as the temperature increases, the dangling oligomers continue to react and attach back to the bulk surface of the part, preventing the extension of the dangling oligomers when the poor solvent / oil is removed. Through the final reaction with the polymer strands in the collapsed configuration, the surface tackiness of the part is significantly reduced for end-use applications.

[0054] For example, a liquid that solvates the dangling polymer chains from the bulk surface and does not promote the collapse of the dangling polymer chains towards itself is considered a good solvent. A liquid that causes the dangling polymer chains on the bulk surface to collapse towards itself is considered a poor solvent (i.e., non-solvent). A combination of solvent / poor solvent can be used to vary the percentage of polymer chains that will collapse and remain on the bulk surface of the part.

[0055] To further elaborate on the method described herein, Figure 1 An example of traditional SLA post-processing is depicted. First, most of the residual photoactive resin (red turbidity) is removed by solvent washing. Multiple washing stations are used sequentially to remove all traces of unreacted reactive oligomers (red lines). Then, the object is cured using light or heat to convert the reactive groups to a non-reactive state (black lines). These lines are not necessarily bound to the surface of the bulk part, leaving residual tackiness.

[0056] The phrases "solvent wash", "solvent washing", or "washed with a solvent" refer to a solvent used to clean / remove one or more unreacted polymeric resins, degradation products, and / or by-products remaining 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.

[0057] Typically, current methods for producing 3D printed images require 3 washes or 2 to about 5 washes to remove residual one or more polymeric resins or by-products or degradation products from the 3D printing process.

[0058] Some 3D printing companies "soak" 3D printed parts in solvents for 15 to 30 minutes. This can be a drawback as the part swells and weakens due to the solvent.

[0059] In contrast, the present embodiment only requires one or two washes, thus saving the use of one or more solvents and the time required to prepare the surface of the 3D printed part for one or more additional modifications. The method described herein does not require "soaking" the 3D printed part for a period of time (15 - 30 minutes). This eliminates the possibility of the 3D printed part swelling and reduces the manufacturing time.

[0060] A second advantage presented by the current embodiment is that the part can be coated or derivatized with a layer of reactive small molecules bound to the surface. One or more reactive molecules can be added to the liquid bath and driven to the part - liquid interface by surface energy (i.e., they act as surfactants). The reactive groups on these small molecules, such as vinyl groups, acrylate or methacrylate groups, olefin groups or thiols, can then react with the surface of the 3D printed part and chemically link to the surface. These small molecules can be used to alter important properties such as chemical resistance, hydrophobicity, hydrophilicity, biocompatibility or surface feel. In addition, chemical promoters can be attached to the part to assist in the attachment of secondary coating materials (e.g., promoters for automotive paint attachment, promoters for metal deposition by electroless plating). Importantly, the initiation of chemical reactions only occurs within or on the surface of the 3D printed part, such that these reactive small molecules do not react and polymerize with each other when dispersed in the bulk liquid phase. They can only react when in proximity to the 3D printed part including the necessary initiator.

[0061] Figure 2 Examples of the present SLA post - processing method disclosed herein are described. First, most of the residual photoactive resin (red turbidity) is removed by solvent washing. Limiting the washing step to a single bath results in the retention of residual chains. Any residual reactive oligomers (red lines) not removed during these washing steps collapse onto the surface of the part by immersion in an immiscible liquid. Then, the object is cured using light or heat, binding these oligomers to the bulk surface while transitioning from the collapsed state to the non - reactive state (black lines). Alternatively, reactive small molecules can be added to the liquid (blue - red lines) to coat the surface of the object. When heated, these molecules react with the oligomers still reactive on the part surface and form a coating (blue dangling chains). Residual initiator molecules remaining on the bulk and / or surface of the cured object can assist in the reaction.

[0062] An example of a class of reactive hydrophobic molecules (reactive small molecules) is a (meth)acrylate-containing siloxane monomer. The (meth)acrylate-containing siloxane monomer can be monofunctional, difunctional, or a combination including monofunctional and difunctional acrylate-containing siloxane monomers. In instances where the acrylate-containing siloxane monomer consists of one or more monofunctional acrylate-containing siloxane monomers (i.e., it does not contain any polyfunctional acrylate-containing siloxane monomers), the polymerizable composition will typically further include an acrylate-containing crosslinker, which is further described below. In certain instances, 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(trimethylsilyloxy)silyl]propyl methacrylate (“TRIS”), (3-methacryloyloxy-2-hydroxypropoxy)propylbis(trimethylsilyloxy)methylsilane (“SiGMA”), methyl 2-[bis(trimethylsilyloxy)silyl]propylglycerol methacrylate (“SiGEMA”), and monomethacryloyloxypropyl-functionalized polydimethylsiloxanes such as MCR-M07 and MCS-M11, which are available from Gelest (Morrisville, NC, USA).

[0063] 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.

[0064] Examples of monomers containing hydrophobic (meth)acrylate (reactive small molecules) include, but are not limited to, fluorinated (meth)acrylate alkyl esters and fluorinated (meth)acrylate siloxanes, such as monomethacryloyloxypropyl-capped poly(dimethylsiloxane).

[0065] Examples of hydrophilic vinyl-containing monomers include hydrophilic monomers having a single polymerizable vinyl ether, or vinyl ester, or allyl ester, or vinyl amide 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.

[0066] Examples of hydrophilic (meth)acrylate monomers include, for example, (meth)acrylic acid, (meth)acrylic acid hydroxyethyl ester, methyl (meth)acrylic acid hydroxypropyl ester, and mixtures thereof.

[0067] The third advantage is that the polymerization reaction occurring within the "green" printed part can be driven to completion. As described above, a light box or convection oven is typically used to increase the temperature of the part. This can be the slowest part of the production process and limits production capacity. By using a liquid bath as described herein, heat energy is transferred into the part much more quickly to increase the internal temperature. This enables the curing of 3D printed parts to be much faster than with traditional techniques.

[0068] The liquid bath used can be any commercial solvent that can be heated within a temperature range. Organic oils, silicone oils, fluorinated oils, water-based oil baths, such as water, water / ethylene glycol, water / DMSO, DMSO, etc. can be used for the liquid bath.

[0069] The fluorinated liquid can include but is not limited to fluorinated oils. Fluorinated oils generally include liquid perfluorinated organic compounds. Examples of fluorinated oils include perfluoro-n-alkanes, perfluoropolyethers, perfluoroalkyl ethers, copolymers of substantially fluorinated molecules, and combinations of the above.

[0070] The organic liquid can include but is not limited to organic oils, organic solvents, including but not limited to chlorinated solvents (e.g., dichloromethane, dichloroethane, and chloroform), and organic liquids immiscible with aqueous systems. Organic oils include neutral, non-polar organic compounds that are viscous liquids at ambient temperature and are both hydrophobic and lipophilic. Examples of organic oils include but are not limited to higher density hydrocarbon liquids.

[0071] Silicone oil is a liquid polymeric siloxane having organic side chains. Examples of silicone oils include polydimethylsiloxane (PDMS), dimethyl silicone oil, and cyclic siloxanes. For example, silicone oil is used in oil baths. Silicone oil is typically polydimethylsiloxane (PDMS) and can have a viscosity range of from about 0.65 cSt to about 2,500,000 cSt (at ambient temperature). Suitable PDMS oils include those available from Gelest, Inc., such as 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-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).

[0072] A fourth advantage of the liquid-bath system relates to the thermal deflection of the materials used to print 3D parts. For many materials in the 3D printing space, when heated, they lose their structural strength and can bend / deflect under their own weight. The temperature at which a material significantly changes its material properties in this manner is called the "heat distortion temperature". Both the oven and liquid-bath methods described herein can be used to bring the material close to its heat distortion temperature. One difference with the liquid bath is that the buoyant force acting on the object results in the 3D printed object experiencing less gravity when immersed in the liquid. In short, when an object is placed independently in an oven, it may sag and permanently deform under its own weight. In the embodiments described herein, due to the buoyant force of the liquid, the effective weight of the object is significantly reduced, thereby limiting or eliminating the degree of deformation.

[0073] The choice of solvent in the liquid bath can be reduced such that the density of the liquid is equal to or substantially equal to the density of the object. By selecting a suitable liquid for the bath, the stresses associated with the part in a typical curing environment (e.g., gravity) are reduced or eliminated, such that the object is substantially weightless in the curing bath. This reduction limits or eliminates the degree of distortion typically associated with the curing of as-formed objects. Non-limiting examples of 3D printing resins can include densities ranging from about 0.8 to about 1.3 g / mL; suitable oils can range from about 0.7 to about 2.4 g / mL, and can include, by non-limiting example, a resin-to-oil density ratio in the range of about 0.5 to about 1.5. In an alternative embodiment, the as-formed part / object can be coated with oil, without immersion in a bath, as described herein, and subjected to conventional oven curing to reduce surface tackiness. The oil coating, followed by UV and / or thermal curing treatment, can function in a similar manner as described above, where the poor solvent layer causes the collapse of the dangling surface polymer chains.

[0074] As used herein, "polymerizable liquid" includes any small building blocks that combine to form a larger structure, e.g., monomers / oligomers crosslinked by conventional polymer chemistry, small particle / colloidal materials bound together, metal ions deposited to form a bulk metal, or any other number of chemical to micro building blocks. It should be understood that the polymerizable liquids described herein can include various additives, and once polymerized, the polymerizable liquid provides an as-formed object / composition that can be further cured as detailed herein.

[0075] In the embodiments described herein, the polymerizable liquid can include monomers or oligomers, particularly photopolymerizable and / or free-radical polymerizable monomers and oligomers, and suitable initiators such as free-radical initiators. Examples include, but are not limited to, acrylates, methacrylates, acrylamides, styrenes, olefins, halogenated olefins, cycloolefins, maleic anhydride, olefins, alkynes, carbon monoxide, functionalized oligomers, multi-functional curing site monomers, functionalized PEGs, etc., including combinations thereof. Examples of liquid resins, monomers, and initiators include, but are not limited to, those set forth in U.S. Patent Nos. 8,232,043; 8,119,214; 7,935,476; 7,767,728; 7,649,029; WO 2012129968; CN 102715751; JP 2012210408.

[0076] In the embodiments described herein, the polymerizable liquid includes monomers or oligomers selected from the group consisting of: acrylates, methacrylates, urethanes, acrylates, polyesters, cyanoesters, acrylamides, maleic anhydride, functionalized PEG, dimethacrylate oligomers, or combinations thereof.

[0077] In other embodiments described herein, the polymerizable liquid includes monomers or oligomers selected from the group consisting of: olefins, halogenated olefins, cycloolefins, olefins, alkynes, and combinations thereof. In an embodiment, 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), 2 - hydroxyethyl methacrylate (HEMA), and combinations thereof.

[0078] Acid - catalyzed polymerizable liquid. As described above, various embodiments provide a polymerizable liquid including a free - radical polymerizable liquid. In other embodiments, the polymerizable liquid includes an acid - catalyzed or cationic - polymerizable liquid. In such embodiments, the polymerizable liquid includes monomers containing groups suitable for acid catalysis, such as epoxy groups, vinyl ether groups, etc. Thus, suitable monomers include olefins such as methoxyethylene, 4 - methoxystyrene, styrene, 2 - methyl - 1 - propene, 1,3 - butadiene, etc.; heterocyclic monomers (including lactones, lactams, and cyclic amines) such as ethylene oxide, thiirane, tetrahydrofuran, oxazoline, 1,3 - dioxepane, 2 - oxetanone, etc., and combinations thereof. Suitable (usually ionic or non - ionic) photoacid generators (PAGs) are included in the acid - catalyzed polymerizable liquid. Examples thereof include, but are not limited to, onium salts, sulfonium, and iodonium salts, such as diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroarsenate, diphenyliodonium hexafluoroantimonate, dipheny(p - methoxyphenyl) trifluoromethanesulfonate, dipheny(p - tolyl) trifluoromethanesulfonate, dipheny(p - isobutylphenyl) trifluoromethanesulfonate, dipheny(p - tert - butylphenyl) trifluoromethanesulfonate, triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroarsenate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium trifluoromethanesulfonate, dibutylnaphthalenesulfonium trifluoromethanesulfonate, etc., including mixtures thereof. See, for example, U.S. Patent Nos. 7,824,839; 7,550,246; 7,534,844; 6,692,891; 5,374,500; and 5,017,461; also see Photoacid Generator Selection Guide for the electronics industry and energy curable coatings (BASF 2010).

[0079] Base - catalyzed polymerizable liquid. In some embodiments, the polymerizable liquid includes a base - catalyzed polymerizable liquid. Suitable base - catalyzed polymerizable liquids include, but are not limited to, malachite green methanol base, which generates hydroxide upon irradiation with green light.

[0080] Hydrogels. In some embodiments, suitable polymerizable liquids include photocurable hydrogels such as poly(ethylene glycol) (PEG) and gelatin. PEG hydrogels have been used for delivering a variety of biologics, including growth factors; however, a significant challenge with PEG hydrogels crosslinked by chain-growth polymerization is the potential for irreversible protein damage. Conditions for maximizing the release of biologics from photocured PEG diacrylate hydrogels can be enhanced by including an affinity-binding peptide sequence in the monomer resin solution prior to photopolymerization allowing for sustained release. Gelatin is a biopolymer commonly used in the food, cosmetic, pharmaceutical, and photographic industries. It is obtained by thermal denaturation or chemical and physical degradation of collagen. Gelatin is classified into three types, including those found in animals, fish, and humans. Gelatin from cold-water fish skin is considered safe for pharmaceutical applications. UV or visible light can be used to crosslink appropriately modified gelatin. Methods for crosslinking gelatin include curing derivatives from dyes such as rose bengal.

[0081] Silicone resins. Suitable polymerizable liquids include silicones. Silicones can be photocured or can be cured by a Michael reaction between thiol and vinyl residues using a free radical photoinitiator. Suitable photoinitiators include, but are not limited to, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, vinylmethoxysiloxane homopolymer, and (mercapto propyl)methylsiloxane homopolymer.

[0082] Biodegradable resins. Biodegradable polymerizable liquids are particularly important for implantable devices for delivering drugs or for temporary performance applications such as biodegradable screws and stents (U.S. Pat. Nos. 7,919,162; 6,932,930). Biodegradable copolymers of lactic and glycolic acid (PLGA) can be dissolved in PEG dimethacrylate to produce a transparent resin suitable for use. Polycaprolactone and PLGA oligomers can be functionalized with acrylic or methacrylic groups to make them effective resins for use.

[0083] Photocurable polyurethanes. Particularly useful polymerizable liquids are photocurable polyurethanes. A photopolymerizable polyurethane composition comprising (1) a polyurethane based on aliphatic diisocyanate, poly(hexamethylene isophthalate) and optionally 1,4-butanediol; (2) a polyfunctional acrylate; (3) a photoinitiator; and (4) an antioxidant can be formulated into a hard, wear-resistant, and stain-resistant material (U.S. Pat. No. 4,337,130). Photocurable thermoplastic polyurethane elastomers contain a photoreactive diacetylene diol as a chain extender.

[0084] High-performance resins. In some embodiments, the polymerizable liquid includes a high-performance resin. Such high-performance resins may sometimes require heating to melt and / or reduce their viscosity, as described above and further discussed below. Examples of such resins include, but are not limited to, resins for materials used in liquid crystal polymers sometimes referred to as esters, ester-imides, and ester-amide oligomers, as described in U.S. Patent Nos. 7,507,784; 6,939,940. Since such resins are sometimes used as high-temperature thermosetting resins, in the present disclosure, they further include suitable photoinitiators, such as benzophenone, anthraquinone, and fluoroenone initiators (including their derivatives), to initiate crosslinking upon irradiation, as further discussed below.

[0085] Additional exemplary resins. Resins particularly useful for polymerizable liquids and dental applications include EnvisionTEC's Clear Guide, EnvisionTEC's E-Denstone Material. Resins particularly useful for the hearing aid industry include EnvisionTEC's e-Shell 300 series resins. Particularly useful resins include EnvisionTEC's HTM140IV high-temperature molding material, which can be used directly with vulcanized rubber in molding / casting applications. Materials particularly useful for manufacturing rigid and non-flexible parts include EnvisionTEC's RC31 resin. Resins particularly useful for investment casting applications include EnvisionTEC's Easy Cast EC500.

[0086] Sol-gel polymerizable liquids. In some embodiments, the polymerizable liquid may include a sol solution or an acid-catalyzed sol. Such solutions typically include metal alkoxides in a suitable solvent, including silicon and titanium alkoxides, such as tetraethoxysilane (tetraethyl orthosilicate; TEOS). Products with a wide range of properties can be produced in this way, from rubbery materials (e.g., using silane-capped silicone rubber oligomers) to very hard materials (glass using only TEOS), and properties intermediate between those obtained using combinations of TEOS and various silane-capped oligomers. As is known in the art, additional components such as dyes and dopants may be included in the sol solution, and post-polymerization firing steps known in the art may be included. See, for example, U.S. Patent Nos. 4,765,818; 7,709,597; 7,108,947; 8,242,299; 8,147,918; 7,368,514.

[0087] Additional resin components. In some embodiments, the polymeric liquid includes particulate or colloidal materials that can bind together. In other embodiments, the polymeric liquid includes metal ions that can deposit to form bulk metal. The polymerizable liquid resin or material can have solid particles suspended or dispersed therein. Any suitable solid particles can be used, depending on the final product being manufactured. The particles can be metallic, organic / polymeric, inorganic, ceramic, or a composite or mixture 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, oval, cylindrical, etc. The particles can include active agents, although these can also be provided by dissolving them in the liquid resin as discussed below. For example, magnetic or paramagnetic particles or nanoparticles can be used.

[0088] The polymerizable liquid can have additional components dissolved therein, including pigments, dyes, UV blockers (also known as UV inhibitors), active compounds or pharmaceutical compounds, detectable compounds (e.g., fluorescent, phosphorescent, radioactive), etc., again depending on the specific use of the product being manufactured. Examples of such additional components include, but are not limited to, proteins, peptides, nucleic acids (DNA, RNA) such as siRNA, sugars, small organic compounds (drugs and drug-like compounds), etc., including combinations thereof.

[0089] UV blockers / inhibitors / absorbers (also known as stabilizers, UVA’s) dissipate the light energy absorbed from UV lines in the form of heat through reversible intramolecular proton transfer. Since this method does not rely solely on UV curing to cure green parts, UVA’s can be included in 3D printing resin formulations. After printing, the methods described herein can allow for complete curing of the entire part. With standard only-UV post-curing, the interior of the part may remain partially uncured and may exhibit mechanical properties different from those of the part surface.

[0090] Suitable UV blockers include, but are not limited to, benzophenone, benzotriazole, aryl esters, oxanilide, acrylates, formamidine black, hindered amines, nickel quenchers, phenolic antioxidants, metal salts, zinc compounds, hydroxybenzophenone (e.g., 2-hydroxy-4-n-octyloxybenzophenone), hydroxybenzotriazine, cyanoacrylate, benzoxazinone (e.g., 2,2'-(1,4-phenylene)bis(4H-3,1-benzoxazin-4-one), commercially available from Solvay under the trade name CYASORB UV-3638), aryl salicylates, hydroxybenzotriazole (e.g., 2-(2-hydroxy-5-methylphenyl)benzotriazole, 2-(2-hydroxy-5-tert-octylphenyl)benzotriazole, and 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)-phenol, commercially available from Solvay under the trade name CYASORB 5411), etc., or combinations including at least one of the aforementioned UV stabilizers.

[0091] Other examples of UV absorber UVA’s include, but are not limited to, benzotriazole (e.g., commercially available from BASF / Azelis under the trade names “TINUVIN P 213”, “TINUVIN P 234”, “TINUVIN P 326”, “TINUVIN P 327”, “TINUVINP 328” and “TINUVIN P 571”); hydroxyphenyltriazine, such as a mixture 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 (e.g., commercially available under the trade names “TINUVIN 400” and “TINUVIN 405”), and a mixture of bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate (CAS No. 41556-26-7) and methyl 1,2,2,6,6-pentamethyl-4-piperidyl sebacate (CAS No. 82919-37-7) (commercially available from BASF / Azelis under the trade name “TINUVIN 292”).

[0092] Other suitable UVA's include, but are not limited to, 9-anthraldehyde (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).

[0093] In use, the amount of UVA in any particular composition can be from about greater than 0 to about 1 wt%, particularly 0.05 to 0.75 wt%, and particularly 0.1 to 0.5 wt%, based on the total weight of the composition.

[0094] The polymerizable liquid can further include one or more additional components dispersed therein, including carbon nanotubes, carbon fibers, and glass filaments.

[0095] A polymerizable liquid carrying live cells. In some embodiments, the polymerizable liquid can carry live cells as "particles" therein. Such polymerizable liquids are typically aqueous and can be oxidized and can be considered "emulsions" where the live cells are the discrete phase. Suitable live cells can be plant cells (e.g., monocots, dicots), animal cells (e.g., mammalian, avian, amphibian, reptilian cells), microbial cells (e.g., prokaryotes, eukaryotes, protozoa, etc.), etc. The cells can be differentiated cells from or corresponding to any type of tissue (e.g., blood, cartilage, bone, muscle, endocrine gland, exocrine gland, epithelium, endothelium, etc.), or can be undifferentiated cells such as stem cells or progenitor cells. In such embodiments, the polymerizable liquid can be a liquid that forms a hydrogel, including but not limited to those described in U.S. Patent Nos. 7,651,683, 7,651,682, 7,556,490, 6,602,975, 5,836,313.

[0096] The polymerizable liquid that produces the polymer resin can include one or more crosslinking agents. The phrase "polyethylenically unsaturated crosslinking agent or monomer" is well recognized in the art and is intended to include those crosslinking agents having two or more reactive double bonds present in the monomer backbone. The unsaturation provides the ability to polymerize with one or more other crosslinking agents and ethylenically unsaturated monomers to form a network of polymeric material. A "polyethylenically unsaturated crosslinking agent" can have multiple unsaturations associated with the reagent, e.g., two, three, four, or five.

[0097] "Crosslinking agent" is any compound having two or more ethylenically unsaturated groups and a molecular weight of less than about 2,000. Thus, a crosslinking agent can react with functional groups on two or more polymer chains to bridge one polymer to another. "Acrylate-containing crosslinking agent" has at least two polymerizable acrylate functional groups and no other types of polymerizable functional groups. "Vinyl-containing crosslinking agent" has at least two polymerizable vinyl groups and no other types of polymerizable functional groups. Non-limiting examples of crosslinking agents include, such as trimethylolpropane trimethacrylate (TMPTMA), divinylbenzene, diepoxides, triepoxides, tetraepoxides, divinyl ethers, trivinyl ethers, tetravinyl ethers, and combinations thereof.

[0098] Suitable acrylate-containing crosslinking materials include, for example, 2-hydroxypropyl-1,3-diacrylate and dimethacrylate, 3-hydroxypropyl-1,2-diacrylate and dimethacrylate, pentaerythritol diacrylate and dimethacrylate, polyethylene glycol (400) diacrylate and dimethacrylate, glycerol dimethacrylate and diacrylate, and pentaerythritol trimethacrylate and triacrylate, the reaction product of pyromellitic dianhydride and glycerol dimethacrylate (PMGDM), the addition product of 2-hydroxyethyl (meth)acrylate and pyromellitic dianhydride (PMDM), 2,2'-bis[4-(3-methacryloyloxy-2-hydroxypropoxy)-phenyl]propane (bis-GMA), lower alkylene glycol dimethacrylates such as triethylene glycol dimethacrylate (TEGDMA) or ethylene glycol dimethacrylate (EDGMA), and mixtures thereof.

[0099] Additional examples of (meth)acrylate-containing crosslinking agents that can 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, methylenebis(meth)acrylamide, and 1,3-bis(3-methacryloyloxypropyl)tetramethyldisiloxane.

[0100] Examples of vinyl-containing crosslinking agents that can 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.

[0101] Additional examples of vinyl-containing crosslinkers include divinyl ethers such as triethylene glycol divinyl ether (TEGDVE) or diethylene glycol divinyl ether (DEGDVE). And acrylate-containing crosslinkers are lower alkylene glycol dimethacrylates such as triethylene glycol dimethacrylate (TEGDMA) or ethylene glycol dimethacrylate (EDGMA).

[0102] This embodiment provides one or more of the following advantages. The liquid used in the liquid bath drives the incompletely cured suspended polymer chains of the 3D printed part back to the main body surface of the plastic object, thereby reducing the viscosity.

[0103] Reactive additives, reactive molecules can be used in the liquid phase of the liquid bath and then be driven to the 3D printed part and can be chemically linked / bound to the surface of the part, imparting other properties.

[0104] The liquid bath is a faster heat conductor and can raise the temperature of the 3D printed part and cure it completely faster compared to a traditional oven.

[0105] When the 3D printed part is immersed in the liquid, its effective weight is reduced, thereby reducing the possibility of deformation when heated to a higher temperature.

[0106] The liquid bath can be used together with UV light to drive further reactions / polymerizations (i.e., light causes decomposition while heat accelerates reaction transfer).

[0107] The following items numbered continuously from 1 to 23 provide various aspects of the present disclosure. In one embodiment, in item (1), the present disclosure provides a method for curing and / or modifying the surface of a three-dimensional (3D) printed part, the method comprising the steps of: immersing a three-dimensional (3D) printed part containing a reactive moiety and / or a residual initiator and / or a residual monomer in a liquid bath to effect polymerization of the reactive moiety and increase the degree of polymerization of the 3D printed part.

[0108] 2. The method according to item 1, wherein the 3D printed part is washed with a solvent before being immersed in the liquid bath.

[0109] 3. The method according to item 1 or 2, wherein the liquid bath is at a high temperature below the heat distortion temperature of the 3D printed part.

[0110] 4. The method according to item 3, wherein the liquid bath is heated to about 30 °C to about 300 °C.

[0111] 5. The method according to any one of items 1 to 4, wherein the 3D printed part is subjected to the liquid bath for a period of about 1 minute to about 24 hours.

[0112] 6. The method according to any one of items 1 to 5, wherein the liquid bath is a silicone oil bath, an aqueous ethylene glycol bath, a fluorinated polyether bath, an aqueous DMSO bath, or a DMSO bath.

[0113] 7. The method according to item 6, wherein the silicone oil has a viscosity of from about 0.6 cSt to about 20,000 cSt.

[0114] 8. The method according to any one of items 1 to 7, further comprising the step of raising the temperature of the liquid bath from a starting temperature to a final temperature.

[0115] 9. The method according to item 8, wherein the starting temperature is about room temperature or matches the initial temperature of the 3D printed part.

[0116] 10. The method according to item 8, wherein the highest temperature reached by the liquid bath is lower than the heat distortion temperature of the 3D printed part.

[0117] 11. The method according to any one of items 8 to 10, wherein the temperature of the liquid bath is raised in a linear manner.

[0118] 12. The method according to any one of items 8 to 10, wherein the temperature of the liquid bath is raised in a non-linear ramp manner.

[0119] 13. The method according to any one of items 8 to 12, wherein the temperature increase of the liquid bath is carried out over the following time periods: no temperature increase during the time period in a stepwise manner.

[0120] 14. The method according to any one of items 1 to 13, wherein the 3D printed part having a reactive portion is formed from a thermosetting or photocurable resin comprising: an acrylic resin, a methacrylic resin, a silicone resin, a fluororesin, a styrene resin, a polyolefin resin, a thermoplastic elastomer, a polyoxyolefin 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.

[0121] 15. The method according to item 14, further comprising a crosslinking agent.

[0122] 16. The method according to item 15, wherein the crosslinking agent is a polyacrylate or polymethacrylate, an olefin, a dithiol, a diol, a methoxysilane, an ethoxysilane, or a polysulfide.

[0123] 17. The method according to any one of items 1 to 16, wherein the reactive portion is in the body of the 3D printed part.

[0124] 18. The method according to any one of items 1 to 16, wherein the reactive portion is present on the surface of the 3D printed part.

[0125] 19. The method according to any one of items 1 to 18, further comprising the step of adding a reactive molecule to the liquid bath.

[0126] 20. The method according to item 19, wherein the reactive molecule reacts with the three-dimensional (3D) printed part.

[0127] 21. The method according to any one of items 19 or 20, wherein the reactive molecule is an acrylate, methacrylate, vinyl group-containing, olefin or thiol group-containing.

[0128] 22. The method according to any one of items 19 or 20, wherein the reactive molecule comprises a siloxane group, a fluorinated group, a hydroxyl group.

[0129] 23. The method according to any one of items 1 to 20, wherein the cured 3D printed part is washed with a solvent to remove oil and / or unreacted reactive molecules from the surface of the cured 3D printed part.

[0130] Clause 1. According to the present disclosure, a method for curing and / or modifying a three-dimensional (3D) printed part may comprise the steps of: providing a three-dimensional printed part comprising a reactive portion, and immersing the three-dimensional (3D) printed part comprising the reactive portion into a liquid bath to effect polymerization of the reactive portion and change the degree of polymerization of the 3D printed part.

[0131] Clause 2. The method according to any one of the foregoing clauses, wherein providing the 3D printed part comprises washing the 3D printed part with a solvent.

[0132] Clause 3. The method according to any one of the foregoing clauses, wherein the liquid bath has a temperature in the range of about 30 °C to about 300 °C, and the immersion comprises placing the 3D printed part in the liquid bath for a period of time in the range of about 1 minute to about 24 hours.

[0133] Clause 4. The method according to any one of the foregoing clauses, wherein the liquid bath is a poor solvent that has passed through the polymer / solvent theta point to cause polymer collapse.

[0134] Clause 5. The method according to any one of the foregoing clauses, wherein the immersion comprises varying the temperature of the liquid bath between a first temperature and a second temperature.

[0135] Clause 6. The method according to any one of the preceding clauses, wherein the second temperature of the liquid bath is higher than the first temperature and lower than the heat distortion temperature of the 3D printed part.

[0136] Clause 7. The method according to any one of the preceding clauses, wherein the 3D printed part is within the liquid bath while the temperature of the liquid bath varies between the first and second temperatures.

[0137] Clause 8. The method according to any one of the preceding clauses, wherein varying the temperature of the liquid bath between the first and second temperatures includes at least one linearly varying time period.

[0138] Clause 9. The method according to any one of the preceding clauses, wherein varying the temperature of the liquid bath between the first and second temperatures includes at least one non-linearly varying time period.

[0139] Clause 10. The method according to any one of the preceding clauses, wherein varying the temperature of the liquid bath between the first and second temperatures includes at least one stepped time period without temperature change.

[0140] Clause 11. The method according to any one of the preceding clauses, wherein the 3D printed part having a reactive portion is formed from a thermosetting or photocurable resin comprising: acrylic resin, methacrylic resin, silicone resin, fluororesin, styrene resin, polyolefin resin, thermoplastic elastomer, polyoxyolefin resin, polyester resin, polyvinyl chloride resin, polycarbonate resin, polyphenylene sulfide resin, cellulose resin, polyacetal resin, melamine resin, polyurethane resin or polyamide resin.

[0141] Clause 12. The method according to any one of the preceding clauses, wherein the reactive portion includes one or more crosslinking reactive portions selected from the group consisting of: acrylate, methacrylate, olefin, dithiol, diol, methoxysilane, ethoxysilane and sulfide.

[0142] Clause 13. The method according to any one of the preceding clauses, wherein the liquid bath is a silicone oil bath, an aqueous ethylene glycol bath, a fluorinated polyether bath, an aqueous DMSO bath or a DMSO bath.

[0143] Clause 14. The method according to any one of the preceding clauses, wherein the 3D printed part includes at least one of a UV stabilizer and a UV blocker.

[0144] Clause 15. The method according to any one of the preceding clauses, wherein a thermal initiator is present in and / or on the three-dimensional printed part comprising the reactive portion.

[0145] Clause 16. The method according to any one of the preceding clauses, wherein the thermal initiator has an activation temperature in the range of about 50 to about 140 °C.

[0146] Clause 17. The method according to any one of the preceding clauses, wherein the immersion comprises varying the temperature of the liquid bath between a first and a second temperature, wherein the second temperature of the liquid bath is higher than the first temperature and lower than the heat distortion temperature of the 3D printed part, and the activation temperature of the initiator is within the first and second temperatures.

[0147] Clause 18. The method according to any one of the preceding clauses, further comprising adding a reactive molecule to the liquid bath to react with the three-dimensional (3D) printed part.

[0148] Clause 19. The method according to any one of the preceding clauses, wherein adding the reactive molecule to the liquid bath comprises adding the reactive molecule to react with the surface of the three-dimensional (3D) printed part.

[0149] Clause 20. The method according to any one of the preceding clauses, wherein the reactive molecule is an acrylate, methacrylate, vinyl group-containing, olefin or thiol group-containing.

[0150] Clause 21. The method according to any one of the preceding clauses, wherein the reactive molecule comprises a siloxane group, a fluorinated group, a hydroxyl group.

[0151] Clause 22. The method according to any one of the preceding clauses, wherein providing comprises providing the three-dimensional printed part having a curing percentage in the range of about 20% to about 80%.

[0152] Clause 23. The method according to any one of the preceding clauses, further comprising subjecting the three-dimensional printed part to UV light treatment during at least one time period including before, during and after immersion.

[0153] The present disclosure will be further described with reference to the following non-limiting examples. It will be apparent to those skilled in the art that many changes can be made to the described embodiments without departing from the scope of the present disclosure. Accordingly, the scope of the present disclosure should not be limited to the embodiments described in this application, but only by the embodiments described in the language of the claims and equivalents of those embodiments. Unless otherwise indicated, all percentages are by weight.

[0154] Examples

[0155] 3D Printing Resin:

[0156] Example-based 3D Printing Resin Formulation

[0157] Photoinitiator, IGM Resin 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). An initiator in the range of 0.05% to 5% by weight is used.

[0158] A reactive diluent in the range of 20% to 80% by weight, 1,6-hexanediol diacrylate (HDDA) monomer diluent is used.

[0159] A reactive oligomer BOMAR in the range of 20% to 80% by weight is used. TM BR-970BT (a proprietary polyurethane difunctional acrylate available from Dymax Corporation).

[0160] A thermal initiator in the range of 0.05% to 5% by weight is used, benzoyl peroxide (thermal decomposition / initiation at 60°C to 80°C) or N-tert-butyl-benzothiazole sulfonamide (thermal decomposition / initiation at ~120°C).

[0161] 3D object design, slicing, video preparation and UV projection

[0162] 3D STL objects are designed in Blender, an open-source CAD rendering software for graphic arts and video processing. These objects are then transferred to Autodesk Netfabb, where support structures can be applied (as needed). Netfabb is used to slice the STL objects and the accompanying supports into JPEG images with 10-μm layers, whose lateral resolution corresponds to the UV projection source. After generating the image stack, the images are loaded back into Blender and compiled into an AVI video file, which is played at 12 frames per second (12 fps x 10 μm / frame = 120 μm / second video). After compilation, these videos can be played through a standard video decoder and media player (such as the VLC media player). Additionally, the frame rate of the said video can be increased or decreased in these media players (allowing the user to run the video at rates of 30, 60 or 240 μm / sec). These videos are projected by a series of DLP (Digital Light Processing) projectors modified to project UV light. The light sources of different printers are different; some projection systems use medium-pressure Hg lamps, while others use monochromatic UV LEDs. The projectors are tiled together to create a continuous large projection field of view (at a 240-μm pixel resolution, the maximum projection field of view is 15” x 24”).

[0163] Printing procedure

[0164] Pour the resin into the print vat. The printing table supported by the ball screw actuator arm is then brought into contact with the printing interface. Use a 30-second UV exposure time to generate an initial resin adhesion layer on the steel build platform, and then start the video while retracting the build platform at a speed of 120 μm / s. Although a printing speed of 240 μm / sec can be achieved, the quality of such prints and the reliability of the printing process are significantly reduced.

[0165] Conventional photocuring: Place the 3D printed part in a curing chamber lined with a highly reflective material and a UV curing lamp (high-intensity LED or mercury lamp; wavelength 350 nm to 450 nm) for a period ranging from 8 - 48 hours. Sealing the chamber causes heat to accumulate, reaching a temperature of approximately 50 °C, and high-intensity UV light impinging on the part from all directions. This serves two purposes - photo-initiation of the further decomposition of photo-initiators not consumed during 3D printing, while the heat generated by the lamp system helps to accelerate the resulting reaction. Thicker / larger parts tend to have problems due to limited light entering the interior of the part.

[0166] Rapid curing in silicone oil: Immerse the 3D printed part in a silicone oil (100 cSt oil) bath, which is slowly heated to a curing temperature ranging from 50 °C to 150 °C. The 3D printed part is incubated for 30 minutes to one hour and removed from the bath before cooling. The incubation temperature is selected based on the heat distortion temperature of the 3D printing material and the decomposition / initiation temperature of the thermally activated free radical initiator or catalyst (if present) to further drive the polymerization reaction within the cured part. The surface tackiness of the part is significantly reduced, while the "fired" (cured) mechanical properties of the part are much superior to those of the "green" (partially cured) part due to the complete conversion of the reaction.

[0167] In the case of the oil bath example, there are washes before and after. The first wash is in methanol to remove excess resin from the printing process. After removing most of the resin, the part is placed in a liquid (oil) bath. After removing the part from the oil bath, the oil is removed. Removing the silicone oil with warm water and dish soap is quite straightforward; this is not always the same as it depends on the liquid used in the heating bath that needs to be removed.

[0168] Rapid Curing and Silicone Finishing in Silicone Oil: To apply a smooth, low-adhesion surface finish on parts, 1% by weight of silicone acrylate is dispersed in the silicone oil phase to form a self-assembled monolayer (SAM) on 3D printed parts. Exemplary monomers include monomethacryloxypropyl-terminated poly(dimethylsiloxane) (GELEST MCR-M07) and monomethacryloxypropyl-functionalized tris[poly(dimethylsiloxane)] (GELEST MCT-M11). Other silicone-based molecules with reactive functional groups can be used - the core principle is the presence of reactive groups (acrylate, methacrylate, vinyl, olefin, thiol / mercaptan, etc.) that can be initiated by radical transfer and combined with groups that provide the desired surface finish. Since the silicone acrylate is dispersed in the bulk silicone phase, there are no free radicals that cause the polymerization of the monomer components. Only when these monomer-reactive molecular units come into contact with the reactive free 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 multiple rounds of parts) without depleting / reacting the monomers dispersed therein.

[0169] Rapid Curing and Fluorinated Finishing in Silicone Oil: This procedure follows the procedure for silicone finishing discussed above. In this case, 1% by weight of monomethacryloxypropyl-terminated poly(3,3,3-trifluoropropyl)methylsiloxane (GELEST MFR-M15) is dispersed in the silicone oil phase. When the molecule coats the 3D printed part, it leaves a thin fluorinated phase on the outer surface. This both reduces the adhesion of the part and makes it very smooth. Additionally, the fluorinated phase increases the chemical protection layer and antioxidant properties. This is very useful when one wants to fabricate 3D printed parts with resistance to chemical reactions (e.g., tubes for transporting corrosive oxygen, 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 reagents it may be exposed to; second, it forms a fluorinated phase through which most reagents will not reach the more vulnerable internal materials.

[0170] Although the present disclosure has been described with reference to preferred embodiments, those skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the disclosure. All references cited throughout the specification, including references in the background art, are incorporated herein by reference in their entirety. Those skilled in the art will recognize or be able to determine, using only routine experimentation, many equivalents to the specific embodiments of the disclosure specifically described herein. Such equivalents are intended to be encompassed within the scope of the following claims.

Claims

1. A method for curing and / or modifying a three-dimensional printed part, comprising: providing a three-dimensional printed part comprising a reactive moiety; adding a reactive molecule to a liquid bath; and immersing the three-dimensional printed part comprising the reactive moiety into the liquid bath to affect the polymerization of the reactive moiety by the reactive molecules in the liquid bath and change the degree of polymerization of the three-dimensional printed part.

2. The method according to claim 1, wherein Providing the three-dimensional printed part includes washing the three-dimensional printed part with a solvent.

3. The method according to claim 1, wherein, The liquid bath has a temperature in the range of 30 °C to 300 °C, and the immersion includes placing the three-dimensional printed part in the liquid bath for a period of time in the range of 1 minute to 24 hours.

4. The method according to claim 1, wherein The liquid bath is a poor solvent that causes polymer collapse through the polymer / solvent theta point.

5. The method according to claim 1, wherein The immersion includes varying the temperature of the liquid bath between a first temperature and a second temperature.

6. The method according to claim 5, wherein, The second temperature of the liquid bath is higher than the first temperature and lower than the heat distortion temperature of the three-dimensional printed part.

7. The method according to claim 5, wherein, During the variation of the temperature of the liquid bath between the first temperature and the second temperature, the three-dimensional printed part is within the liquid bath.

8. The method according to claim 5, wherein Varying the temperature of the liquid bath between the first temperature and the second temperature includes at least one linearly varying period.

9. The method according to claim 5, wherein Varying the temperature of the liquid bath between the first temperature and the second temperature includes at least one non-linearly varying period.

10. The method according to claim 5, wherein Varying the temperature of the liquid bath between a first temperature and a second temperature includes at least one stepwise period without temperature change.

11. The method according to claim 1, wherein, The three-dimensional printed part having a reactive moiety is formed from a thermosetting or photocurable resin including: acrylic resin, methacrylic resin, silicone resin, fluororesin, styrene resin, polyolefin resin, thermoplastic elastomer, polyoxyolefin resin, polyester resin, polyvinyl chloride resin, polycarbonate resin, polyphenylene sulfide resin, cellulose resin, polyacetal resin, melamine resin, polyurethane resin or polyamide resin.

12. The method according to claim 1, wherein, The reactive moiety includes one or more crosslinking reactive moieties selected from the group consisting of: acrylate, methacrylate, olefin, dithiol, diol, methoxysilane, ethoxysilane and sulfide.

13. The method according to claim 1, wherein, The liquid bath is a silicone oil bath, an aqueous ethylene glycol bath, a fluorinated polyether bath, an aqueous DMSO bath or a DMSO bath.

14. The method according to claim 1, wherein, The three-dimensional printed part includes at least one of a UV stabilizer and a UV blocker.

15. The method according to claim 1, wherein, A thermal initiator is present in and / or on the three-dimensional printed part comprising the reactive moiety.

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

17. The method according to claim 15, wherein, The immersion includes varying the temperature of the liquid bath between a first temperature and a second temperature, wherein the second temperature of the liquid bath is higher than the first temperature and lower than the heat distortion temperature of the three-dimensional printed part, and the activation temperature of the thermal initiator is within the first temperature and the second temperature.

18. The method according to claim 1, wherein, Adding the reactive molecule to the liquid bath includes adding the reactive molecule to react with the surface of the three-dimensional printed part.

19. The method according to claim 1, wherein The reactive molecule is acrylate, methacrylate, vinyl group-containing, olefin or thiol group-containing.

20. The method according to claim 1, wherein The reactive molecules include siloxane groups, fluorinated groups, and hydroxyl groups.

21. The method according to claim 1, wherein, Providing includes providing the three-dimensional printed part having a curing percentage in the range of 20% to 80%.

22. The method according to claim 1, further comprising subjecting the three-dimensional printed part to UV light treatment during at least one time period including before immersion, during immersion, and after immersion.

23. The method according to claim 1, wherein, The step of adding reactive molecules to the liquid bath is before the step of immersing the three-dimensional printed part comprising the reactive portion into the liquid bath.

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