WO2022266331A1

WO2022266331A1 - Methods for surface coating additively manufactured objects

Info

Publication number: WO2022266331A1
Application number: PCT/US2022/033806
Authority: WO
Inventors: Andrew Gordon WRIGHT; Alexander DENMARK; Bob E. FELLER; Jason P. Rolland
Original assignee: Carbon, Inc.
Priority date: 2021-06-16
Filing date: 2022-06-16
Publication date: 2022-12-22

Abstract

Provided are methods of making an additively manufactured object having an outer surface coating thereon. Also provided are additively manufactured objects having an outer surface coating thereon.

Description

METHODS FOR SURFACE COATING ADDITIVELY MANUFACTURED OBJECTS

Related Applications

This application claims the benefit of and priority to U.S. Provisional Application Serial No. 63/211,035, filed on June 16, 2021, the disclosure of which is hereby incorporated by reference herein it its entirety.

Field of the Invention

Methods of surface coating additively manufactured objects are described, along with coating resins for such methods and the coated objects so made.

Background

A group of additive manufacturing techniques sometimes referred to as "stereolithography" creates a three-dimensional object by the sequential polymerization of a light polymerizable resin. Such techniques may be "bottom-up" techniques, where light is projected into the resin on the bottom of the growing object through a light transmissive window, or "top down" techniques, where light is projected onto the resin on top of the growing object, which is then immersed downward into the pool of resin.

The recent introduction of a more rapid stereolithography technique known as continuous liquid interface production (CLIP), coupled with the introduction of "dual cure" resins for additive manufacturing, has expanded the usefulness of stereolithography from prototyping to actual manufacturing of products for everyday use (see, e.g., U.S. Patent Nos. 9,211,678; 9,205,601; and 9,216,546 to DeSimone et al.; and also in J. Tumbleston, D. Shirvanyants, N. Ermoshkin et al., Continuous Liquid Interface Production of 3D Objects, Science 347, 1349-1352 (2015); see also Rolland et al., U.S. Patent Nos. 9,676,963, 9,453,142 and 9,598,606).

These developments have in turn created a need for ways to impart aesthetically attractive and/or functionally enhanced surfaces to such objects. However, techniques such as spray coating are wasteful of materials and can create suspended particles or volatilized propellants that are potentially noxious or toxic. Creating a sufficient bond between a surface coating and an underlying object can be difficult and simply creating a uniform coating on an irregularly shaped or contoured object — particularly objects that include three-dimensional lattices — can be a challenge. Accordingly, there is a need for new approaches to surface coating additively manufactured objects. Summary

Provided herein is a method of making an additively manufactured object having an outer surface coating thereon, which may comprise some or all of the steps of: (a) additively manufacturing an intermediate object from a dual cure build resin with the intermediate object having residual build resin on the surface thereof, the build resin comprising a mixture of (i) a light polymerizable first component, and (ii) a heat polymerizable second component; (b) centrifugally separating a portion of said residual build resin from said intermediate object to leave a thin film of residual build resin on the surface of said intermediate object; (c) dipping said intermediate object in a bath of heat polymerizable coating resin to produce an outer coating on top of said thin film of residual dual cure resin; (d) centrifugally separating a portion of said outer coating from said intermediate object to leave an outer film of coating resin directly contacting said thin film of residual build resin; and then (e) baking said intermediate object to: (i) further cure said intermediate object, (ii) cure said thin film of residual build resin, and (Hi) cure said outer film of coating resin, to thereby produce an additively manufactured object having an outer surface coating thereon.

In some embodiments, the intermediate object is adhered to a carrier platform upon completion of step (a), and some or all of steps (b), (c), and (d) are carried out with said intermediate object adhered to said carrier platform.

In some embodiments, the intermediate object and the additively manufactured object comprise a lattice structure (e.g., a three-dimensional lattice comprised of interconnecting struts, a three-dimensional lattice comprised of a surface lattice such as a triply periodic surface lattice, a three-dimensional lattice comprised of repeating units of walled structures, two- dimensional lattices such as a mesh or graticulate structure, combinations thereof, etc.).

In some embodiments, the object comprises a midsole, innersole, orthotic insert, body pad, or cushion.

In some embodiments, the coating resin comprises from 1 or 2 percent by weight to 20, 50 or 80 percent by weight, or more, of pigment particles, matting agent, or a combination thereof.

In some embodiments, the pigment particles comprise color pigment particles, effect pigment particles (e.g., metallic or pearlescent particles), or a combination thereof.

In some embodiments, the pigment particles have an average diameter of from 10 or 20 nanometers, up to 0.1, 0.5, 1 or 2 micrometers, or more.

In some embodiments, the coating resin further comprises at least one additional additive selected from matting agents (or gloss control agents), UV blockers, IR blockers, optical brighteners, antioxidants, flow control agents, dispersants, thixotropic agents, dilatants, adhesion promoters, slip additives, anti-slip additives, texturing additives, oil resistant additives, water resistant additives, chemical resistant additives, antimicrobial agents (including antibacterial agents), antiviral agents, nylon fillers, wax additives, and combinations thereof.

In some embodiments, the centrifugally separating step (b) is carried out in an atmosphere comprising a volatile organic solvent vapor ( e.g ., in an amount sufficient to reduce the viscosity of said residual resin).

In some embodiments, the additively manufactured object comprises a polymer blend, interpenetrating polymer network, semi-interpenetrating polymer network, or sequential interpenetrating polymer network formed from said light polymerizable first component and said heat polymerizable second component of said build resin.

In some embodiments, the intermediate object comprises a solid polymer scaffold formed by the light polymerization of said light polymerizable first component of said build resin, and the solid polymer scaffold degrades during said baking step and forms a constituent that polymerizes with said second component of said build resin.

In some embodiments, the heat polymerizable coating resin comprises a mixture of (i) alight polymerizable first component of said coating resin, and (ii) a heat polymerizable second component of said coating resin; and the outer surface coating of said additively manufactured object comprises a polymer blend, interpenetrating polymer network, semi-interpenetrating polymer network, or sequential interpenetrating polymer network formed from said light polymerizable first component of said coating resin and said heat polymerizable second component of said coating resin.

In some embodiments, the light polymerizable component of said coating resin degrades during said baking step and optionally forms a constituent that polymerizes with said second component of said coating resin, and optionally also polymerizes with said second component of said build resin.

In some embodiments, the coating resin comprises a monomer or prepolymer having a reactive group that covalently couples to free reactive groups in said intermediate object and/or residual build resin during said baking step (for example, amine reactive groups and free reactive epoxide groups; amine reactive groups and blocked (or free) isocyanate groups; etc.).

In some embodiments, both said light polymerizable component of said dual cure build resin, and of said coating resin, comprise a blocked (e.g., a reactive blocked) poly isocyanate, so that during said baking step (e) said intermediate object (and optionally said residual build resin) and said coating resin cure and form a welded connection between said object and said outer surface coating.

In some embodiments, the method further includes: (i) initially curing said thin film of residual build resin with light (e.g., ultraviolet light) between said centrifugally separating step (b) and said dipping step (c); (ii) initially curing said outer film of coating resin with light (e.g., ultraviolet light) between said centrifugally separating step (d) and said baking step (e); or (Hi) both (i) and (ii) above.

In some embodiments, the outer surface coating has an average thickness of from 10 to 50 micrometers.

Also provided is an additively manufactured object having an outer surface coating thereon produced by a method as taught herein.

Surface coating of additively manufactured objects is described in Rolland et ak, PCT Patent App. Pub. No. W02019/204095 (24 Oct 2019). However, neither a centrifugal separation step as a pre-treatment before dip coating nor a centrifugal separation step as a posttreatment after dip coating is suggested or described.

Centrifugal separation of residual resin from additively manufactured objects is described in Murillo et ak, PCT Patent Application Pub. No. WO2019/209732 (31 Oct 2019); Day et ak, PCT Patent Application Pub. No. W02020/069152 (2 April 20200); and Converse et ak, PCT Patent App. Pub. No. W02020/146000 (16 July 2020). Again, use of centrifugal separation as a pre-treatment before dip coating is neither suggested nor described, and use of centrifugal separation as a post-treatment following dip coating is neither suggested nor described.

The foregoing and other objects and aspects of the present invention are explained in greater detail in the drawings herein and the specification set forth below. The disclosures of all United States patent references cited herein are to be incorporated herein by reference.

Brief Description of the Drawings

Figure 1 is a flow chart illustrating a first embodiment of a coating process as described herein.

Figure 2 is a flow chart illustrating a second embodiment of a coating process as descrbed herein.

Figure 3 is a photograph of a first example of an additively manufactured, dip coated, object. Figure 4 is a photograph of a second example of an additively manufactured, dip coated, object

Figure 5 schematically illustrates polymer chains of a surface coating bonded to an underlying object.

Figure 6 schematically illustrates polymer chains of a surface coating welded to an underlying object.

Figure 7 is a photograph of a third example of an additively manufactured, dip coated, object.

Figure 8 is a photograph of a fourth example of an additively manufactured, dip coated, object.

Detailed Description of Illustrative Embodiments

The present invention is now described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art.

"Volatile blocking groups" as used herein are known and examples include but are not limited to those set forth in U.S. PatentNo. 11,226,559 to Chen etal. “Volatile blocking group” refers to a substituent produced by the covalent coupling of a volatile blocking agent as described above to the reactive group (particularly an isocyanate group) of a reactive compound (such as a diisocyanate monomer or prepolymer). Examples of volatile blocking agents that may be used to carry out the present invention are likewise set forth in U.S. Patent No. 11,226,559 and include but are not limited to ketoximes, amides, imides, imidazoles, oximes, pyrazoles, alcohols, phenols, sterically-hindered amines, lactams, succinimides, triazoles, and phthalimides, such as 2-butanone oxime (also called methyl ethyl ketoxime or "MEKO"), dimethylpyrazole (“DMP”), cardanol (3-pentadecenyl-phenol), acetone oxime, cyclopentanone oxime, cyclohexanone oxime, epsilon-caprolactam, V-methylacetamide. imidazole, succinimide, benzotriazole, /V-hydroxyphthalimide, 1,2,4-triazole, 2-ethyl- 1- hexanol, phenol, 3, 5 -dimethylpyrazole, 2,2,6,6-tetramethylpiperidine, diisopropylamine, and combinations thereof. As used herein, the term "and/or" includes any and all possible combinations of one or more of the associated listed items, as well as the lack of combinations when interpreted in the alternative ("or").

1. ADDITIVE MANUFACTURING METHODS, RESINS, AND OBJECTS.

Methods. With reference to Figure 1, a method of making an additively manufactured object having an outer surface coating thereon may comprise the steps of: (a) additively manufacturing an intermediate object from a dual cure build resin (12) with the object having residual build resin on the surface thereof, the build resin comprising a mixture of (i) a light polymerizable first component, and (ii) a heat polymerizable second component; (b) centrifugally ("spin") separating a portion of said residual build resin from said intermediate object (13) to leave a thin film of residual build resin on the surface of said intermediate object; (c) dip coating the object with coating resin (14) by dipping said intermediate object in a bath of heat polymerizable coating resin to produce an outer coating on top of said thin film of residual dual cure resin; (d) centrifugally ("spin") separating a portion of said outer coating from said intermediate object (15) to leave an outer film of coating resin directly contacting said thin film of residual build resin; and then (e) baking said coated intermediate object (16) to: (i) further cure said intermediate object, (ii) cure said thin film of residual build resin, and (Hi) cure said outer film of coating resin, to thereby produce an additively manufactured object having an outer surface coating thereon.

In some embodiments, such as by bottom-up and top-down stereolithography, a build platform is first installed on the apparatus (Figure 2 step 21). In this case, the centrifugal separation steps, dip coating step, and possibly even the baking steps (all discussed further below), can all conveniently be carried out with the additively manufactured object retained on the build platform. This facilitates handling of the object during manufacturing, particularly by robotic handling.

Thus, and with reference to Figure 2, a method of making an additively manufactured object having an outer surface coating thereon may comprise installing the build platform (21) prior to the steps of: (a) additively manufacturing an intermediate object from a dual cure build resin (22) with the object having residual build resin on the surface thereof, the build resin comprising a mixture of (i) a light polymerizable first component, and (ii) a heat polymerizable second component; (b) centrifugally ("spin") separating a portion of said residual build resin from said intermediate object (23) to leave a thin film of residual build resin on the surface of said intermediate object; (c) dip coating the object with coating resin (24) by dipping said intermediate object in a bath of heat polymerizable coating resin to produce an outer coating on top of said thin film of residual dual cure resin; (d) centrifugally ("spin") separating a portion of said outer coating from said intermediate object (25) to leave an outer film of coating resin directly contacting said thin film of residual build resin; and then (e) baking said coated intermediate object (26) to: (i) further cure said intermediate object, (ii) cure said thin film of residual build resin, and (Hi) cure said outer film of coating resin, to thereby produce an additively manufactured object having an outer surface coating thereon, with the intermediate object adhered to the carrier platform upon completion of step (a), and with some or all of steps (h). (c), and (d) being carried out with said intermediate object adhered to said carrier platform.

Suitable additive manufacturing methods and apparatus (Figure 1 step 12; Figure 2 step 22), including bottom-up and top-down additive versions thereof (generally known as stereolithography), are known and described in, for example, U.S. Patent No. 5,236,637 to Hull, U.S. Patent Nos. 5,391,072 and 5,529,473 to Lawton et al. U.S. Patent No. 7,438,846 to John, U.S. Patent No. 7,892,474 to Shkolnik et ak, U.S. Patent No. 8,110,135 to El-Siblani, U.S. Patent Application Publication No. 2013/0292862 to Joyce, and U.S. Patent Application Publication No. 2013/0295212 to Chen et al The disclosures of these patents and applications are incorporated by reference herein in their entirety.

In some embodiments, the additive manufacturing step is carried out by one of the family of methods sometimes referred to as continuous liquid interface production (CLIP). CLIP is known and described in, for example, U.S. Patent Nos. 9,211,678; 9,205,601; and 9,216,546; in J. Tumbleston et ak, Continuous liquid interface production of 3D Objects, Science 347, 1349-1352 (2015); and in R. Janusziewcz et ak, Layerless fabrication with continuous liquid interface production, Proc. Natl. Acad. Sci. USA 113, 11703-11708 (2016). Other examples of methods and apparatus for carrying out particular embodiments of CLIP include but are not limited to: U.S. Patent Application Publication No. 2017/0129169 to Batchelder et ak; U.S. Patent Application Publication No. US 2016/0288376 to Sun et ak; U.S. Patent Application Pub. No. 2015/0360419 to Willis et ak; U.S. Patent Application Publication No. 2015/0331402 to Anatole et ak; U.S. Patent Application Publication No. 2017/0129167 tp Castanon; U.S. Patent Application Publication No. 2018/0243976 to Feller; U.S. Patent Application Publication No. 2018/0126630 to Panzer et ak; U.S. Patent Application Publication No. 2018/0290374 to Willis et ak; PCT Application Publication No. WO 2015/164234 to Robeson et al (see also U.S. Patent Nos. 10,259,171 and 10,434,706); and PCT Application Publication No. WO 2017/210298 to Mirkin et al (see also U.S. Patent Application Publication No. 2019/0160733). In some embodiments, the light polymerizable component of said coating resin degrades during said baking step and optionally forms a constituent that polymerizes with said second component of said coating resin, and optionally also polymerizes with said second component of said build resin.

In some embodiments, the coating resin comprises a monomer or prepolymer having a reactive group that covalently couples to free reactive groups in said intermediate object during said baking step (for example, amine reactive groups and free reactive epoxide groups; amine reactive groups and blocked (or free) isocyanate groups; etc.).

In some embodiments, both of said light polymerizable component of said dual cure build resin and said light polymerizable component of said coating resin comprise a blocked ( e.g ., a reactive blocked) polyisocyanate, so that during said baking step (e) said intermediate object and said coating resin cure and form a welded connection between said object and said outer surface coating.

In particular embodiments of the foregoing, the light polymerizable component of the dual cure resin comprises a reactive blocked polyisocyanate, and the coating resin comprises a polyisocyanate blocked with a non-reactive blocking group such as a volatile blocking group (see, e.g., U.S. PatentNo. 11,226,559), so that during the baking step (e) the intermediate object and the coating resin cure and form a welded connection between the object and the outer surface coating.

In some embodiments, the method further includes: (i) initially curing said thin film of residual build resin with light (e.g., ultraviolet light) between said centrifugally separating step (b) and said dipping step (c) (which may improve the appearance of the surface coating, particularly for objects with complex geometries); (ii) initially curing said outer film of coating resin with light (e.g., ultraviolet light) between said centrifugally separating step (d) and said baking step (e); or (Hi) both (i) and (ii) above.

Resins. Dual cure resins are currently preferred as build resins for carrying out the present invention. Such resins are known and described in, for example, U.S. Patent Nos. 9,676,963, 9,453,142 and 9,598,606 to Rolland et al. In some embodiments, the dual cure resin comprises a mixture of (i) a light polymerizable first component, and (ii) a heat polymerizable second component. Particular examples of suitable dual cure resins include but are not limited to Carbon Inc. resins including medical polyurethane, elastomeric polyurethane, rigid polyurethane, flexible polyurethane, cyanate ester, epoxy, and silicone dual cure resins, all available from Carbon, Inc., 1089 Mills Way, Redwood City, California 94063 USA. The dual cure build resin used to form an intermediate object by light polymerization will contain a photoinitiator as necessary for the additive manufacturing step (not necessary in the coating resin discussed below), but need not, and preferably does not, contain ingredients included in the coating resin (as also discussed below). The build resin and the coating resin do, however, in some preferred embodiments, contain substantially the same polymerizable constituents (though in some embodiments it is also found that the polyisocyanate prepolymer in the coating resin can be blocked with a non-reactive blocking group (i.e., a blocking group that does not participate in a light polymerization, such as a volatile blocking group), as noted above and also discussed further in Example 5 below).

Objects. Any of a variety of objects can be made. In some embodiments, the objects comprise a rigid, flexible, or elastic lattice. Lattices may be two-dimensional or three- dimensional, with three-dimensional lattices preferred for cushioning and impact absorption purposes. A three-dimensional lattice, for example, may be comprised of interconnecting struts, a surface lattice such as a triply periodic surface lattice, repeating units of walled structures, etc., including combinations thereof. Two-dimensional lattices may include, for example, a mesh or graticulate structure, combinations thereof, etc. Examples of such objects include footware midsoles, inner soles, and orthotics for shoes; body cushion pads such as helmet liner cushions, lumbar supports, knee and shoulder pads, and the like; compression garments such as sports bras, compression sleeves ( e.g for arms and legs, such as for treatment of medical conditions such as lymphadema), and brassieres (which may utilize a two-dimensional rather than a three-dimensional lattice such as a mesh or graticulate structure), etc.

In some embodiments, the intermediate object comprises a solid polymer scaffold formed by the light polymerization of said light polymerizable first component of said build resin, and the solid polymer scaffold degrades during said baking step and optionally forms a constituent that polymerizes with said second component of said build resin.

2. FIRST CENTRIFUGAL SEPARATION.

The first centrifugal separation step (Figure 1 step 13; Figure 2 step 23) can be carried out in accordance with known techniques, such as discussed in U.S. Patent Application Publication No. 2021/0237358 to Price et al; PCT Patent Application Publication No. WO2019/209732 to Murillo et al.; U.S. Patent No. 11,084,216 to Murillo et al.; PCT Patent Application Publication No. W02020/069152 to Day et al.; and PCT Patent Application Publication No. W02020/146000 and U.S. Patent No. 11,247,389 to Converse et al. Optionally, but preferably, the objects remain on the build platform for this step, as illustrated in Figure 2 Step 23).

While centrifugal separation can be carried out in an ambient atmosphere at ambient temperature, in some embodiments, the centrifugal separation step can be carried out in an atmosphere including a volatilized organic solvent vapor. In some embodiments, the atmosphere includes a volatile organic solvent vapor in an amount sufficient to reduce the viscosity of said residual resin.

Suitable solvents for volatilization include, but are not limited to, alcohol, ester, dibasic ester, ketone, acid, aromatic, hydrocarbon, ether, dipolar aprotic, halogenated, base organic solvents, and combinations thereof. In some embodiments, the solvent comprises a hydrofluorocarbon, a hydrofluoroether, or a combination thereof. In some embodiments, the solvent is or includes an azeotropic mixture comprised of at least a first organic solvent and a second organic solvent. Solvents can be heated to aid in their volatilization as necessary, and the inner chamber of the separator can be heated to maintain the solvent in a volatile state as necessary. Particular examples of solvents include, but are not limited to, methanol, acetone, isopropanol, and non-flammable organic solvents (e.g., trichlorethylene, methylene chloride, NOVEC™ solvent, VERTREL™ solvent, etc.).

Volatilization of the solvent can be carried out with a vapor generator operatively associated with the centrifugal separator. Such vapor generators can be configured in a variety of ways, all of which preferably avoid spraying liquid solvent on the objects from which residual resin is to be separated. For example, a solvent pool can be included in the separator chamber, and a gas line operatively associated with that pool for bubbling gas (such as ambient air) through the solvent in the pool. As the bubbles pass through the liquid solvent, they absorb volatilized solvent and carry it into the main chamber space. A heater can, if desired, be operatively associated with the gas line, the pool, or both the gas line and the pool, to aid in the volatilization of the liquid solvent. An example of a suitable bubbler is a Duran bubbler set with frit DO, available from Paul Gothe GmbH, Wittener Str. 82, D-44789, Bochum, Germany. In another alternative, an external vapor generator can be positioned outside the chamber, to generate a solvent vapor outside the chamber, which is then passed into the chamber. The ambient atmosphere within the chamber can be directed back to the vapor generator, though this is not essential.

3. DIP COATING.

Dip coating of objects (Figure 1 step 14), in some embodiments preferably while the objects remain on the build platform (Figure 2 step 24), is carried out by immersing the objects into, and withdrawing the objects out of, a vat of liquid coating resin, in accordance with known techniques.

The coating resin is preferably reactive with the light polymerized dual cure build resin (from which the intermediate object is formed) during the baking step. Any of a variety of coating resins can be used, including but not limited to those set forth in Rolland et ak, PCT Patent Application Publication No. W02019/204095.

In some embodiments, the coating resin comprises a monomer or prepolymer having a reactive group that covalently couples to free reactive groups in said intermediate object during said baking step (for example, amine reactive groups and free reactive epoxide groups; amine reactive groups and blocked (or free) isocyanate groups; etc.) (See, for example, the reactive group pairs set forth in U.S. Patent Nos. 9,676,963, 9,453,142, and 9,598,606 to Rolland et al.)

In some embodiments, the polymerizable components of the coating resin are substantially the same as those in the build resin. Thus, in some embodiments the coating resin contains a light-polymerizable component, more preferably contains a blocked light- polymerizable component such as a blocked polyisocyanate, and most preferably contains a reactive blocked light-polymerizable component (i.e., one that is terminated with light- polymerizable groups). This is the case even though the coating resin need not contain, and in some embodiments does not contain, a photoinitiator (at least not in an amount sufficient to solidify the resin when exposed to light such as ultraviolet light at an effective wavelength and intensity to solidify the build resin). In other embodiments, however, the coating resin need not contain a light polymerizable component, but may simply contain a blocked polyisocyanate that is blocked with a non-reactive blocking group such as e-caprolactam.

While the coating resin need not contain an effective amount of photoinitiator (or in some embodiments, any photoinitiator), the coating resin can contain other constituents that would be undesirable to include in the build resin. For example, the coating resin may comprise from 1 or 2 percent by weight to 20, 30, 40, 50, 60, 70 or 80 percent by weight, or more (e.g., 85 or 95 percent by weight) of pigment particles and/or additional constituents, as further discussed below. The pigment particles may comprise color pigment particles, including white pigment particles such as titanium dioxide particles, effect pigment particles (e.g., metallic or pearlescent particles), or a combination thereof. In some embodiments, the build resin comprises a white pigment (e.g., titanium dioxide; e.g., in an amount of from 0.1 to 1 or 2 percent by weight) and said coating resin comprises a white pigment (e.g., titanium dioxide). In some embodiments, the weight ratio of white pigment when present in said coating resin to white pigment when present in said build resin is at least 1.2:1 or 1.4: 1.

In some embodiments, the pigment particles have an average diameter of from 10 or 20 nanometers up to 0.1, 0.5, 1 or 2 micrometers, or more (e.g., 5 or 10 micrometers). In some embodiments, weight ratio of photoinitiator in said coating resin (when present) to photoinitiator in said build resin is not more than 1:10, 1:15, or 1:20.

Reflective, metallic, or pearlescent particles or flakes (referred to as “effect pigments” herein) can be included in the coating resin. Such effect pigments are known. See, e.g., U.S. Patent Nos. 9,914,846 and 5,997,627, the disclosures of which are incorporated herein by reference. Particular examples include, but are not limited to, metallic effect pigments such as aluminum, titanium, zirconium, copper, zinc, gold, silver, silicon, tin, steel, iron and alloys thereof or mixtures thereof, and/or pearlescent pigments, mica or mixtures thereof.

Additional constituents that can be included in the coating resin include, but are not limited to, matting agents (i.e., gloss control agents, including silica particles and/or waxes), ultraviolet light blockers (UV blockers), infra-red light blockers (IR blockers), optical brighteners, antioxidants, flow control agents, dispersants, thixotropic agents, dilatants, adhesion promoters, slip additives, anti-slip additives, texturing additives, oil resistant additives, water resistant additives, chemical resistant additives, antimicrobial agents (including antibacterial agents), antiviral agents, nylon fillers, wax additives, and combinations thereof. (See, e.g., U.S. Patents Nos. 10,948,745, 10,934,439; and 10,155,857; Micro Powders, Inc., High Performance Wax Additives (2019); Arkema, ORGASOL® and RILSAN® Coating Additives (2014)). 4. SECOND CENTRIFUGAL SEPARATION AND BAKING STEPS.

The second centrifugal separation step (Figure 1 step 15; Figure 2 step 25) can be carried out in a similar manner to the first centrifugal separation step. While the same centrifugal separator can be employed for both steps, a different centrifugal separator is preferably employed for the second step so that excess build resin, and excess coating resin, are not mixed with one another in the separator. This facilitates the separate recapture, and optional re-use, of one or both of the resins.

Baking of the coated object step (Figure 1 step 16; Figure 2 step 26) is carried out in accordance with known techniques, in ambient atmosphere or in an inert atmosphere, at times and temperatures depending on the particular build and coating resins employed. As will be seen in the examples below, uniform coating can be achieved even on lattice structures that would be difficult to coat with techniques such as spray coating.

The methods, materials and objects described herein are further illustrated in the non- limiting examples set forth below.

EXAMPLE 1

Dip Coating with Matte Black Resin

Materials used in this example, their abbreviations and their sources, are given in Table 1 below.

Note: % is weight percent.

In a 200 mL container was added 68.9 parts ABPU and 4.6 parts Aerosil R 7200. The content was then mixed (mixing profile: 2000 rpm for 4 minutes and 2200 rpm for 30 seconds via a THINKY™-mixer). The black pigment (1.8 parts) was then added and mixed followed by addition of DPMA (17.6 parts). After mixing again, MACM (7.1 parts) was added and mixed, yielding resin A. Separately, a 0.8 mm thick, 12.5 x 5.5 cm slab was printed (called object B) on a Carbon Ml printer from a formulation (called resin B) containing ABPU, D608M, SR350DD, Jayflex DINA, Irganox 245, TPO, DMM, white pigment dispersion, and MACM (as described in Wright, Chen, and Feller, Low Viscosity Dual Cure Additive Manufacturing Resins, PCT Pub. No. WO 2020/223058 (05 Nov. 2020)).

The freshly produced white slab (object B), with residual liquid resin B on surface, was then submerged into the black resin A. The coated slab was withdrawn from resin A and hung vertically in an oven. The coated part was then heated to 130°C for 4 hours under nitrogen, resulting in a flexible part with a black, matte finish on both sides.

EXAMPLE 2

Dip Coating with Glossy Black Resin

Table 1 is incorporated into this example. In a 200 mL container was added 70.7 parts ABPU. The black pigment (3.9 parts) was then added and mixed followed by addition of DPMA (18.1 parts). After mixing again, MACM (7.3 parts) was added and mixed, yielding resin C. Separately, a 0.8 mm thick, 12.5 x 5.5 cm slab was printed (called object D) on a Carbon Ml printer from a formulation (called resin D) containing ABPU, D608M, SR350DD, Jayflex DINA, Irganox 245, TPO, DMM, white pigment dispersion, stabilizers, and MACM.

One side of the freshly produced white slab (object D), with residual liquid resin D on surface, was pressed into the liquid black resin C. The coated slab was withdrawn from resin C and placed flat on a tray in the oven, with the black coated side facing up. The coated part was then heated to 130°C for 4 hours under nitrogen, resulting in a flexible part with a black, glossy finish on the top surface.

EXAMPLE 3

Dip Coating of Lattice Objects with Particulate Pigment These examples are carried out in a manner similar to Examples 1-2 above, except that lattice midsole objects are produced from an elastic polyurethane dual cure resin (such as Carbon, Inc. EPU 41 elastic polyurethane dual cure resin) by additive manufacturing, excess resin is separated from the midsoles by centrifugal separation, and then the midsoles are dip- coated in an elastic polyurethane resin loaded with pigment particles (5 to 25 micrometer average diameter colored mica powders, as typically used in cosmetics). After dip coating, excess surface coating resin is separated from the midsoles by centrifugal separation as described above, and the midsoles are then baked as described above.

After baking, the struts of the resulting midsoles are uniformly coated, and uniformly pigment, with the now-polymerized surface resin strongly adhered thereto. Illustrative results (obtained with a comparable light-polymerizable elastic polyurethane dual cure resin) are given in Figures 3-4. In Figure 3, a 20: 1 mass ratio of resin to pigment particles is employed, and in Figure 4 a 4: 1 mass ratio of resin to pigment particles is employed.

Without wishing to be bound to a particular theory, it is currently believed that, by including in the dip coating resin a light polymerizable monomer or prepolymer that, upon

5 heating, degrades and forms a heat-polymerizable constituent, the heat polymerization reactions occur in the two regions and consequently a substantially deeper co-mingling of the surface polymer components with the underlying, additively manufactured, polymer components is achieved. C. Sweeney, B. Lackey, et al. (Science Advances 3: el 700262, 14 June 2017) refer to such a result as a welding, rather than a bonding, of two regions. Such a

10 structure is schematically illustrated in Figures 5-6 herein, where di is the depth of co-mingling of polymer drains from two different sources (e.g., 3D printing, then dip coating) across a bonded interface, and di is the depth of co-mingling of polymer chains from two different sources across a welded interface.

15 EXAMPLE 4

This example is carried out in like manner to Example 3 above, except that the coating resin was comprised of a blend of:

Part A: ABPU, DPMA, and carbon black (20 percent by' weight of Clariant Hostatint™

20 Black A-N 100, pre-dispersed pigment); and

PartB: MACM.

No photoinitiator or other components are included.

Illustrative results (obtained with a comparable light-polymerizable elastic polyurethane dual cure resin) are given in Figures 7-8. Again, after baking, the struts of the

25 resulting midsoles are uniformly coated and uniformly pigment, with the now-polymerized surface resin strongly adhered thereto.

EXAMPLE S

Coating White Lattice Objects with White Pigmented Resin

30 A problem with additively manufactured objects produced from a white pigmented resin may be instability of the white color. This instability may be manifested by some or all of unfavorable ultraviolet aging, poor hydrolysis performance, excess fading under ambient light, and/or the white color simply being insufficiently bright. The methods described herein advantageously permit the significant reduction or elimination of photoinitiator in the coating resin as compared to, and necessarily required in, the build resin. Presence of photoinitiator in the build resin is believed to be a significant contributor to color instability in white colored additive manufacturing resins.

5 In addition, the methods described herein advantageously permit an increase in the amount of white pigment in the coating resin as compared to, and at levels unfavorable for use in, the build resin. Greater levels of white pigment in the coating resin can substantially improve white color brightness.

This example was carried out in similar manner to Examples 3-4 above, except that the

10 coating resin was comprised of the ingredients set forth in Table 2 below. Note particularly that a commercially available, e-caprolactam blocked isocyanate prepolymer, DESMODUR® BL 1100/1 (available from Covestro) is used in this formulation, rather than the light-reactive, tert-butylaminoethyl methacrylate (TBAEMA) blocked isocyanate prepolymers described in the previous examples.

15

TABLE 2

PART A

Component Component weight percent (grams)

DESMODUR® BL 1100/1 blocked

41.29% 206.45 isocyanate (available from Covestro)

HOSTATINT™ SI Titanium White tint

45.9% 229.5

(available from Clariant)

TINUVIN® 400 stabilizer (available from

1.39% 6.95 BASF Corporation)

TINUVIN® 765 stabilizer (available from

.92% 4.6 BASF)

AEROSIL® R202 firmed silica (available

2.5% 12.5 from Evonik Corporation)

The coating resin may be prepared from the above ingredients as follows:

1. In a Flacktek Speedmixer container, mix white dispersion and prepolymer and mix on a Flacktek Speedmixer for 20 minutes at 2000 rpm.

2. Add DPMA solvent and TINUVIN stabilizers and mix for an additional 4 minutes at 2000 rpm

3. Add Aerosil R202 with a paper funnel and mix for an additional 10 minutes at 2000 rpm.

4. Add MACM and mix for an additional 4 minutes at 2000 rpm.

The coating process may be carried out with the above coating resin as follows:

1. Produce lattice midsoles on an LI printer available from Carbon, Inc. (Redwood City California USA) from an elastic polyurethane dual cure resin as described in US Patent No. 9,453,142 to Rolland et ak, containing from 0.1 to 1 or 2 percent by weight of titanium dioxide particles ( e.g 0.24 percent by weight of titanium dioxide particles). Remove the build platform from the printer with the lattice midsoles thereon and centrifugally separate excess resin from the midsoles by spinning at 625 rpm for 3 minutes.

2. With the midsoles still attached to their build platforms, remove excess resin from around the midsoles by wiping, scraping, or blotting. Leave the midsoles attached to their build platform.

3. Flood cure the midsoles on their build platform with ultraviolet light in a Dreve PCU 90 chamber for 2.5 minutes. 4. Remove midsoles on their build platforms platform from the chamber. Leave midsoles attached to their build platform.

5. Pour coating resin over midsoles until full coverage, or dip midsoles in a bath of coating resin, again while leaving the midsoles attached to their build platforms.

6. Spin the coated midsoles on their build platform in the centrifugal separator at 400 rpm for 3 minutes.

7. Remove the build platforms from the centrifugal separator and remove the midsoles from their build platforms, being careful not to disrupt the coating.

8. Bake the coated midsoles at an appropriate temperature in accordance with known techniques to produce the finished, coated, lattice midsoles. For example, the parts can be baked in a Blue M oven (available from Thermal Products Solutions (TPS) under a nitrogen atmosphere, with a bake schedule of 130 degrees C for 2 hours followed by 150 degrees C for 1.5 hours.

Results: Lattice products coated as described above have a noticeably brighter white appearance as compared to lattice products produced from the same white tinted build resinin the same manner described above but without the additional resin coating step. The coated products also have satisfactory wash durability in a horizontal drum, front-loading Wascator test, in spite of the use of the commercial blocked (but not light-reactive blocked) polyisocyanate prepolymers in the coating resin.

The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. The invention is defined by the following claims, with equivalents of the claims to be included therein.

Claims

What Is Claimed Is:

1. A method of making an additively manufactured object having an outer surface coating thereon, comprising the steps of:

(a) additively manufacturing an intermediate object from a dual cure build resin with the intermediate object having residual build resin on the surface thereof, the build resin comprising a mixture of (i) a light polymerizable first component, and (ii) a heat polymerizable second component;

(b) centrifugally separating a portion of said residual build resin from said intermediate object to leave a thin film of residual build resin on the surface of said intermediate object;

(c) dipping said intermediate object in a bath of heat polymerizable coating resin to produce an outer coating on top of said thin film of residual dual cure resin;

(d) centrifugally separating a portion of said outer coating from said intermediate object to leave an outer film of coating resin directly contacting said thin film of residual build resin; and then

(e) baking said intermediate object to: (i) further cure said intermediate object, (ii) cure said thin film of residual build resin, and (Hi) cure said outer film of coating resin, to thereby produce an additively manufactured object having an outer surface coating thereon.

2. The method of claim 1, wherein said intermediate object is adhered to a carrier platform upon completion of step (a), and steps (b), (c), and (d) are all carried out with said object adhered to said carrier platform.

3. The method of any preceding claim, wherein said additively manufactured object comprises a lattice structure ( e.g a three-dimensional lattice comprised of interconnecting struts, a three-dimensional lattice comprised of a surface lattice such as a triply periodic surface lattice, a three-dimensional lattice comprised of repeating units of walled structures, two- dimensional lattices such as a mesh or graticulate structure, combinations thereof, etc.).

4. The method of any preceding claim, wherein said object comprises a midsole, innersole, orthotic insert, body pad, or cushion.

5. The method of any preceding claim, wherein said coating resin comprises from 1 or 2 percent by weight to 20, 50 or 80 percent by weight, or more, of pigment particles, a matting agent, or a combination thereof.

6. The method of claim 5, wherein said pigment particles comprise color pigment particles, effect pigment particles (e.g., metallic or pearlescent particles), or a combination thereof.

7. The method of any preceding claim, wherein said pigment particles have an average diameter of from 10 or 20 nanometers to 0.1, 0.5, 1 or 2 micrometers or more.

8. The method of any preceding claim, wherein said coating resin further comprises at least one additional additive selected from matting agents (or gloss control agents), UV blockers, IR blockers, optical brighteners, antioxidants, flow control agents, dispersants, thixotropic agents, dilatants, adhesion promoters, slip additives, anti-slip additives, texturing additives, oil resistant additives, water resistant additives, chemical resistant additives, antimicrobial agents (including antibacterial agents), antiviral agents, nylon fillers, wax additives, and combinations thereof.

9. The method of any preceding claim, wherein said centrifugally separating step (b) is carried out in an atmosphere comprising a volatile organic solvent vapor ( e.g ., in an amount sufficient to reduce the viscosity of said residual resin).

10. The method of any preceding claim, wherein said additively manufactured object comprises a polymer blend, interpenetrating polymer network, semi-interpenetrating polymer network, or sequential interpenetrating polymer network formed from said light polymerizable first component and said heat polymerizable second component of said build resin.

11. The method of any preceding claim, wherein: said intermediate object comprises a solid polymer scaffold formed by light polymerization of said light polymerizable first component of said build resin, and said solid polymer scaffold degrades during said baking step and forms a constituent that polymerizes with said second component of said build resin.

12. The method of any preceding claim, wherein: said heat polymerizable coating resin comprises a mixture of (i) a light polymerizable first component of said coating resin, and (ii) a heat polymerizable second component of said coating resin; and wherein: said outer surface coating of said additively manufactured object comprises a polymer blend, interpenetrating polymer network, semi-interpenetrating polymer network, or sequential interpenetrating polymer network formed from said light polymerizable first component of said coating resin and said heat polymerizable second component of said coating resin.

13. The method of claim 12, wherein said light polymerizable component of said coating resin degrades during said baking step and forms a constituent that polymerizes with said second component of said coating resin, and optionally also polymerizes with said second component of said build resin.

14. The method of any preceding claim, wherein said coating resin comprises a monomer or prepolymer having a reactive group (e.g., an amine reactive group) that covalently couples to free reactive groups in said intermediate object (e.g., free reactive epoxide groups or blocked or free isocyanate groups) during said baking step.

15. The method of any preceding claim, wherein both said dual cure build resin and said coating resin comprise a blocked polyisocyanate, so that during said baking step (e) said intermediate object and said coating resin form a welded connection between said object and said outer surface coating.

16. The method of claims 1 to 15, wherein said light polymerizable component of said dual cure build resin comprises a reactive blocked polyisocyanate and said coating resin comprises anon-reactive blocked polyisocyanate (e.g., a polyisocyanate blocked with a volatile blocking group) so that during said baking step (e) said intermediate object and said coating resin form a welded connection between said object and said outer surface coating.

17. The method of any preceding claim, further comprising initially curing said thin film of residual build resin with light (e.g., ultraviolet light) between said centrifugally separating step (b) and said dipping step (c).

18. The method of any preceding claim, further comprising initially curing said outer film of coating resin with light (e.g., ultraviolet light) between said centrifugally separating step (d) and said baking step (e).

19. The method of any preceding claim, wherein said outer surface coating has an average thickness of from 10 to 50 micrometers.

20. The method of any preceding claim, wherein said build resin comprises a photoinitiator, said coating resin optionally comprises a photoinitiator, and the weight ratio of photoinitiator in said coating resin when present to photoinitiator in said build resin is not more than 1:10, 1:15, or 1:20.

21. The method of any preceding claim, wherein said build resin comprises a white pigment (e.g., titanium dioxide; e.g., in an amount of from 0.1 to 1 or 2 percent by weight) and said coating resin comprises a white pigment (e.g., titanium dioxide).

22. The method of any preceding claim, wherein the weight ratio of white pigment when present in said coating resin to white pigment when present in said build resin is at least 1.2:1 or 1.4:1.

23. An additively manufactured object having an outer surface coating thereon produced by a method of any preceding claim.