BACKGROUND

Field

[0001] Provided herein are methods for making three dimensional printed parts by additive manufacturing using cyanoacrylates in post processing.

Brief Description of Related Technology

[0002] Additive manufacturing is fast becoming a viable alternative to traditional manufacturing techniques and in some cases the only practical alternative for making complex parts.

[0003] One draw back to additive manufacturing is with the use of photocurable resins. There the end user runs the risk of incomplete cure and thus part formation. Sometimes with incomplete cure residual photocuable resin can remain on the surface of the printed part. When that happens and the surface contains residual resin, surface imperfections may be observed, surface tackiness may be created and/or the quality of the surface finish in the intended function of the part may be compromised. Attempts have been made in the past to address the issue.

[0004] For instance, US Patent Application Publication No. US 2017/0173872 provides a method of forming a 3D object, comprising: (a) providing a carrier and a fill level, and optionally an optically transparent member having a build surface defining the fill level, the carrier and the fill level having a build region therebetween; (b) filling the build region with a polymerizable liquid, the polymerizable liquid comprising a mixture of (i) a light polymerizable liquid first component, and (ii) a second solidifiable component that is different from the first component; (c) irradiating the build region with light (through the optically transparent member when present), to form a solid polymer scaffold from the first component and also advancing the carrier away from the build surface to form a 3D intermediate having the same shape as, or a shape to be imparted to, the 3D object and containing the second solidifiable component carried in the scaffold in unsolidified and/or uncured form; (d) washing the 3D intermediate; and (e) concurrently with or subsequent to the irradiating step and/or the washing step, solidifying and/or curing the second solidifiable component in the 3D intermediate to form the 3D object. In one of the more focused and relevant sections of the ‘872 publication, the washing step according to the ‘872 publication uses “[a]ny suitable wash liquid" and lists BIO-SOLV™ solvent replacement; PURPLE POWER™ degreaser/cleaner; SIMPLE GREEN® all purpose cleaner; a 50:50 volume:volume mixture of water and isopropanol as possible choices.

[0005] To date none are believed to be without their own draw backs. For instance, many known wash liquids or cleaners are believed to comprise isopropanol and other solvents with low flash points and high volatile organic compounds.

[0006] Thus, notwithstanding the state of the art it would be desirable to facilitate the facile post processing of the three dimensional printed part.

SUMMARY

[0007] These desires are satisfied by the present invention.

[0008] Accordingly, through the use of the inventive method, three dimensional printed parts may be produced more efficiently with a cleaner surface finish, substantially free of deleterious matter and/or with little to no unwanted resin left on the surface. This is no small matter because in the past either the end user was left with a compromised surface finish on the three dimensional printed part or had to take extra measures to prepare manually the surface finish (assuming that the entirety of the surface was accessible to the end user). Thus, it is seen that the inventive method significantly contributes to the advancement of three dimensional printing into more prevalent use.

[0009] In one aspect, provided herein is a method of preparing a three- dimensional printed part made by additive manufacturing, comprising the steps of:

A. Performing additive manufacturing using a curable (meth)acrylate composition to form a three-dimensional part on a build substrate, where the three- dimensional printed part made according to data indicating a pre-determined pattern; and

B. Optionally, removing the so-formed part from the build substrate; and C. Optionally, contacting at least some of the part with an activator; and

D. Contacting the part with a cyanoacrylate composition.

DETAILED DESCRIPTION

[0010] As noted above, a method of preparing a three dimension printed part made by additive manufacturing is provided herein.

[0011] The method includes the steps of:

A. Performing additive manufacturing using a curable (meth)acrylate composition to form a three-dimensional part on a build substrate; and

B. Optionally, removing the so-formed part from the build substrate; and

C. Optionally, contacting at least some of the part with an activator; and

D. Contacting the part with a cyanoacrylate composition.

[0012] Additive manufacturing is performed to form the three dimensional printed part according to data indicating a pre-determined pattern.

[0013] The photocurable resin used to form the three dimensional printed part from an additive manufacturing technique should cure through exposure to radiation in the electromagnetic spectrum, such as IR, VIS, UV and UV/VIS.

[0014] Indeed, radiation at one portion of the electromagnetic spectrum may be used initially, oftentimes followed by radiation in another portion of the electromagnetic spectrum. Or, radiation in the electromagnetic spectrum may be used together with exposure to elevated temperature conditions. The elevated temperature should be chosen with an eye toward the cure temperature of the resin used and its cure profile with the cure package selected. The elevated temperature condition is chosen to either (1) drive further the reaction initiated by exposure to radiation in the electromagnetic spectrum toward completion or (2) in some cases, initiate a secondary cure reaction in the three dimensional print resin. Where an elevated temperature condition is chosen to advance cure of the resin, the temperature chosen should be greater than room temperature plus about 70°C, though desirably less than about 180°C.

[0015] Here, depending on the physical properties desired from the three dimension printed part, the subsequent energy exposure step may be avoided in lieu of the provision of the cyanoacrylate coating formed through the inventive methods. [0016] Depending on the chemistry of the three dimensional print resin, the cure package may vary widely in both nature and amount. For instance, the cure package may be chosen to be one triggered by exposure to radiation in the electromagnetic spectrum or elevated temperature conditions, or both.

[0017] After conducting the inventive method, the part should possess at least one of improved surface finish, improved transparancy and reduced tackiness. In addition, the part should emit little to no odor.

[0018] When used in the inventive method, the activator is a species capable of initiating anionic polymerization. Broad examples of the activator thus include nitrogen- containing components and transition metal compounds.

[0019] Where the activator is a nitrogen-containing compound, that compound may be in a solution. The activator should be applied to the part before the cyanacrylate composition. But in some instances it may be applied after the cyanoacrylate composition instead.

[0020] The activator may be a nitrogen-containing compound, such as an alkyl or aryl amine, like a tertiary amine for instance a trialkyl amine. Other examples include 1 ,2-di-(4-pyridyl-ethane), 4,4'-dipyridyl disulfide, 3-(3-hydroxypropyl)pyridine, 1 ,2- bis(diphenylphosphino)-ethane, pyridazine, methylpyridazine or 4,4'-dipyridyl.

[0021] When used in a solution, the activator, which is optionally an amine, should be used in an amount of about 0.5 to about 5 percent by weight in an organic solvent. The organic solvent should have a boiling point between about 30 ^° C and 100 ^° C, such as about 45 ^° C to 75 ^° C, desirably about 50 ^° C to about 65 ^° C. The organic solvent may be selected from acetonitrile, alkyl alcohols (such as methanol and isopropanol), alkyl esters (such as ethyl acetate), alkanes (such as pentane and cyclopentane, hexane, and heptane), halogenated alkanes (such as dichloromethane and chloroform), and combinations thereof.

[0022] Useful transition metal compounds include ones based on copper, vanadium, cobalt and iron.

[0023] For instance, as regards copper compounds, copper compounds where copper enjoys a 1 + or 2+ valence state are desirable. For instance, copper carboxylates, copper naphthenates, copper acetates, copper octoates, copper laurates, copper benzoates, fatty acid salts of copper, copper formates, copper metal, copper acetyl acetonates, 2,4-pentanedione copper complex, any other analogous copper compounds, alloys, amalgams, and copper derivatives known to those skilled in the art may be used. A non-exhaustive list of examples of such copper (I) and (II) compounds include copper (II) 3,5-diisopropylsalicylate hydrate, copper bis(2,2,6,6-tetramethyl-3,5- heptanedionate), copper (II) hydroxide phosphate, copper (II) chloride, copper (II) acetate monohydrate, tetrakis(acetonitrile)copper (I) hexafluorophosphate, copper (II) formate hydrate, tetrakisacetonitrile copper (I) triflate, copper(ll)tetrafluoroborate, copper (II) perchlorate, tetrakis(acetonitrile)copper (I) tetrafluoroborate, copper (II) hydroxide, copper (II) hexafluoroacetylacetonate hydrate and copper (II) carbonate. These copper (I) and (II) compounds should be used in an amount of about 100 ppm to about 5,000 ppm, such as about 500 ppm to about 2,500 ppm, for instance about 1 ,000 ppm.

[0024] As regards vanadium compounds, vanadium compounds where vanadium enjoys a 2+ and 3+ valence state are desirable. Examples of such vanadium (III) compounds include vanadyl naphthanate and vanadyl acetylacetonate. These vanadium (III) compounds should be used in an amount of 50 ppm to about 5,000 ppm, such as about 500 ppm to about 2,500 ppm, for instance about 1 ,000 ppm.

[0025] As regards cobalt compounds, cobalt compounds where cobalt enjoys a 2+ valence state are desirable. Examples of such cobalt (II) compounds include cobalt naphthenate, cobalt tetrafluoroborate and cobalt acetylacetonate. These cobalt (II) compounds should be used in an amount of about 100 ppm to about 1000 ppm.

[0026] As regards iron compounds, iron compounds where iron enjoys a 3+ valence state are desirable. Examples of such iron (III) compounds include iron acetate, iron acetylacetonate, iron tetrafluoroborate, iron perchlorate, and iron chloride. These iron compounds should be used in an amount of about 100 ppm to about 1000 ppm. [0027] The cyanoacrylate composition comprises a cyanoacrylate monomer within the following structure: H ₂ C=C(CN)-COOR, where R is selected from alkyl, alkoxyalkyl, cycloalkyl, alkenyl, aralkyl, aryl, allyl and haloalkyl groups.

[0028] More specifically, the cyanoacrylate composition comprises a cyanoacrylate monomer selected from methyl cyanoacrylate, ethyl-2 -cyanoacrylate, propyl cyanoacrylates, butyl cyanoacrylates, octyl cyanoacrylates, allyl cyanoacrylate, b- methoxyethyl cyanoacrylate and combinations thereof.

[0029] The cyanoacrylate composition may be used in a solution. In such case, the cyanoacrylate composition is used in an amount of about 0.5 to about 10 percent by weight. As above, the organic solvent should have a boiling point between about 30 ^° C and 100 ^° C, such as about 45 ^° C to 75 ^° C, desirably about 50 ^° C to about 65 ^° C. The organic solvent may be selected from acetonitrile, alkyl alcohols (such as methanol and isopropanol), alkyl esters (such as ethyl acetate), alkanes (such as pentane and cyclopentane, hexane, and heptane), halogenated alkanes (such as dichloromethane and chloroform), and combinations thereof.

[0030] Significantly though the chosen organic solvent should not readily solubilize poly cyanoacryalte at room temperature.

[0031] The organic solvent used with the activator and the organic solvent used with the cyanoacrylate may be the same or different.

[0032] The activator and/or cyanoacrylate composition may be applied to the three dimesional printed part by spraying, dipping, rolling, immersing, or vapor exposure, among other techniques.

[0033] It may be desirable in some instances to provide onto at least a portion of a surface of a build substrate of the printer a release coating material to facilitate removal of the three dimensional printed part once formed from the build substrate. [0034] The release coating material may be present at a concentration in the liquid carrier in an amount of about 0.05 to about 10 percent by weight, such as about 2.5 to about 5 percent by weight.

[0035] The chosen release coating material should have a contact angle measurement of greater than about 75° but less than about 108°.

[0036] Alternatively, the inventive method of post processing a three dimensional printed part made by additive manufacturing, comprise the steps of:

A. Providing an additive manufacturing-made three dimensional printed part having at least one surface, said three dimensional printed part made from a photocurable resin composition; and B. Contacting said surface of said additive manufacturing-made three dimensional printed part with (I) optionally, an activator and (ii) a cyanoacrylate composition to form a coating over said surface.

[0037] The time during which the various steps occur may range from about 2 minutes to about 60 minutes, such as about 2 minutes to about 10 minutes, desirably about 5 minutes to about 10 minutes.

[0038] The temperature at which the various steps occur may range from about 15°C to about 60°C, such as about 20°C to about 55°C, desirably about 25°C to about 45°C.

[0039] The following example is illustrative.

EXAMPLE

[0040] Here, a LOCTITE ^® PR-10 Printer was used with LOCTITE ^® 3D 3870 Black resin to print the specimens for evaluation. The LOCTITE ^® PR-10 Printer was set at a print resolution of 0.1 mm, which is the thickness of each layer of the print. The print takes about 2-4 hours to complete at this setting. The printed part in each case is a three dimensional rectangle that is 1” x 2” x 0.125” (2.54 x 5.08 x 0.318 cm) in size. [0041] As noted, LOCTITE ^® 3D 3870 Black resin was used to make three dimensional printed parts in the LOCTITE ^® PR-10 Printer. LOCTITE ^® 3D 3870 Black resin is promoted as a black, opaque, light cure, low viscosity, acrylic resin that may be used for prototyping via stereolithography. It cures with very short exposure to monochromatic light sources such as LED or laser. Printed articles exhibit good print resolution and high flexibility. It is printable at room temperature across various laser SLA and DLP platforms. The manufacturer reports that LOCTITE ^® 3D 3870 Black resin contains 2-[[(Butylamino)carbonyl]oxy]ethyl acrylate, 20 - 30 percent by weight; 2- Hydroxyethyl acrylate, polymer with aEpichlorohydrin, phthalic anhydride, 4,4'- Bisphenol A and e-Caprolactone, 20 - 30 percent by weight; Isobornyl acrylate, 20 - 30 percent by weight; 2-Propenoic acid, 2-hydroxyethyl ester, polymer with 1 ,1'- methylenebis[4- isocyanatocyclohexane] and a,a',a"-1 ,2,3- propanetriyltris[, 10 - 20 percent by weight; Diacrylate ester, 1 - 5 percent by weight; and 2-Hydroxyethyl acrylate, 0.1 - 1 percent by weight. [0042] Three dimensional printed parts in the shape of dog bones were made with LOCTITE ^® 3D 3870 Black resin using the LOCTITE ^® PR-10 Printer with the printing parameters set forth below in Table A.

Table A

[0043] To the so made parts, an activator (5 percent by weight of triethyl amine in hexane) was applied over the surface and once the hexane evaporated a cyanoacrylate composition (5 percent by weight of ethyl cyanoacrylate in acetonitrile) was applied thereover. When the acetonitrile evaporated, the parts had a tack free surface which was more optically clear than prior to post processing.