RESINS AND METHODS FOR ADDITIVE MANUFACTURING OF ENERGY ABSORBING THREE-DIMENSIONAL OBJECTS
BACKGROUND
Some additive manufacturing techniques, particularly bottom-up and top-down stereolithography, make a three-dimensional object by light polymerization of a resin (see, e.g., US Patent No. 5,236,637 to Hull). Unfortunately, such techniques have generally been considered slow, and have typically been limited to resins that produce brittle or fragile objects suitable only as prototypes.
A more recent technique known as continuous liquid interface production (CLIP) allows both more rapid production of objects by stereolithography (see, e.g, J. Tumbleston et ah, Continuous liquid interface production of 3D Objects, Science 347, 1349-1352 (2015) and US Patent Nos. 9,205,601; 9,211,678; 9,216,546; 9,360,757; and 9,498,920 to DeSimone et ah), and the production of parts with isotropic mechanical properties (see R. Janusziewcz et ah, Layerless fabrication with continuous liquid interface production, Proc. Natl. Acad. Sci. USA 113, 11703-11708 (2016)).
Still further, the recent introduction of dual cure additive manufacturing resins by Rolland et al. (see, e.g, US Patent Nos. 9,676,963; 9,598,606; and 9,453,142), has additionally made possible the production of a much greater variety of functional and useful objects suitable for real world use.
Together, these developments have created an increased demand for additive manufacturing resins and systems that allow for the production of objects with diverse or finely-tuned mechanical properties.
SUMMARY
Provided herein according to embodiments is a polymerizable liquid useful for the production of an energy absorbing three-dimensional object comprising polyurethane, polyurea, or a copolymer thereof by additive manufacturing, said polymerizable liquid comprising a mixture of: (a) a light reactive blocked prepolymer (e.g., a (meth)acrylate blocked polyurethane ("ABPU")) having a soft segment formed from a polyol/polyamine (i.e., midblock) and having a soft segment number average molecular weight of from 200 or 250 to 700 or 800 Da; (b) a first polyol and/or polyamine chain extender having a soft segment number average molecular weight of from 1000, 1500 or 2000 to 5,000 or 10,000 Da; (c) a second polyol and/or polyamine chain extender that is a rigid chain extender (e.g., MACM) and/or a trifunctional chain extender (e.g., a trifunctional polyether amine); (d) optionally, a blocked or reactive blocked diisocyanate, or a blocked or reactive blocked diisocyanate chain extender; (e) optionally, a reactive diluent; (f) optionally, a pigment or dye; and (g) a photoinitiator.
In some embodiments, the light reactive blocked prepolymer comprises a (meth)acrylate blocked polyurethane ("ABPU").
In some embodiments, the polymerizable liquid further comprises an additional light reactive prepolymer that is not blocked and/or different from the ABPU (e.g., a methacrylate capped prepolymer such as a urethane methacrylate prepolymer) (e.g., present in an amount of from 2, 3, or 5 to 7, 8, or 10 percent by weight).
In some embodiments, the first or second chain extender is a polyether di- or triamine, and/or wherein the soft segment of the prepolymer is formed with a polyether di- or triamine.
In some embodiments, the first polyol and/or polyamine chain extender comprises a mixture of two or more polyol and/or poly amine chain extenders, each independently having a soft segment number average molecular weight of from 1000, 1500 or 2000 to 5,000 or 10,000 Da.
In some embodiments, the soft segments of the prepolymer and/or first chain extender comprise polyethers, for example, poly(tetramethylene oxide), polypropylene glycol), poly(ethylene glycol), poly(trimethylene oxide), or a copolymer of two or more thereof.
In some embodiments, the light reactive blocked prepolymer is present in an amount of 30 or 40 to 50 or 60% by weight.
In some embodiments, the reactive diluent is present in an amount of from 10 or 15 to 25 or 30% by weight.
In some embodiments, the first chain extender is present in an amount of from 15, 20 or 25 to 35 or 40% by weight; and/or wherein the second chain extender is present in an amount of from 1 or 3 to 10 or 15 percent by weight.
In some embodiments, the second chain extender comprises 4,4'-methylenebis(2- methylcyclohexyl-amine) (MACM) or a trifunctional polyether amine; and/or wherein the light reactive blocked prepolymer midblock is formed from isophorone diisocyanate (IPDI) or 4,4'-dicyclohexylmethane-diisocyanate (HMDI). Also provided is a polymerizable liquid useful for the production of an energy absorbing three-dimensional object comprising polyurethane, polyurea, or a copolymer thereof by additive manufacturing, said polymerizable liquid comprising a mixture of: (a) a light reactive blocked prepolymer (e.g., ABPU) having a soft segment formed from a polyol/polyamine (i.e., midblock); (b) a first polyol and/or polyamine chain extender having a soft segment; (c) optionally, a second polyol and/or polyamine chain extender that is a rigid chain extender (e.g., MACM) and/or a trifunctional chain extender; (d) a non-bonding filler (e.g., in an amount of from 1 or 2 to 8 or 10% by weight); (e) optionally, a blocked or reactive blocked diisocyanate, or a blocked or reactive blocked diisocyanate chain extender; (f) optionally, a reactive diluent; (g) optionally, a pigment or dye; and (h) a photoinitiator, wherein one of the blocked or reactive blocked prepolymer and first polyol and/or polyamine chain extender has a soft segment number average molecular weight of from 200 or 250 to 700 or 800 Da, and the other has a soft segment number average molecular weight of from 1000, 1500 or 2000 to 5,000 or 10,000 Da.
In some embodiments, the blocked or reactive blocked prepolymer has a soft segment number average molecular weight of from 200 or 250 to 700 or 800 Da, and the first polyol and/or polyamine chain extender has a soft segment number average molecular weight of from 1000, 1500 or 2000 to 5,000 or 10,000 Da.
In some embodiments, the blocked or reactive blocked prepolymer has a soft segment number average molecular weight of from 1500 or 2000 to 5,000 or 10,000 Da, and the first polyol and/or polyamine chain extender has a soft segment number average molecular weight of from 200 or 250 to 700 or 800 Da;
In some embodiments, the first or second chain extender (when present) is a polyether di- or triamine, and/or wherein the soft segment of the prepolymer is formed with a polyether di- or triamine.
In some embodiments, the light reactive blocked prepolymer is present in an amount of 30 or 40 to 50 or 60% by weight.
In some embodiments, the reactive diluent is present in an amount of from 10 or 15 to 25 or 30% by weight.
In some embodiments, the first chain extender is present in an amount of from 15 or 20 to 30 or to 35 or 40% by weight.
In some embodiments, the second chain extender is present in an amount of from 1 or 3 to 10 or 15% by weight. In some embodiments, the light reactive blocked prepolymer midblock is formed from isophorone diisocyanate (IPDI) or 4,4'-dicyclohexylmethane-diisocyanate (HMDI).
Further provided is a polymerizable liquid useful for the production of an energy absorbing three-dimensional object comprising polyurethane, polyurea, or a copolymer thereof by additive manufacturing, said polymerizable liquid comprising a mixture of: (a) a first light reactive blocked prepolymer (e.g., ABPU) having a soft segment formed from a polyol/polyamine (i.e., midblock) and having a soft segment number average molecular weight of from 1000, 1500 or 2000 to 5,000 or 10,000 Da; (b) a second light reactive blocked prepolymer (e.g., ABPU) having a soft segment formed from a polyol/polyamine (i.e., midblock) and having a soft segment number average molecular weight of from 200 or 250 to 700 or 800 Da; (c) a first polyol and/or polyamine chain extender having a soft segment number average molecular weight of from 200 or 250 to 700 or 800 Da; (d) a second polyol and/or polyamine chain extender that is a rigid chain extender (e.g., MACM) and/or a trifunctional chain extender (e.g., a trifunctional polyether amine); (e) optionally, a blocked or reactive blocked diisocyanate, or a blocked or reactive blocked diisocyanate chain extender; (f) optionally, a reactive diluent; (g) optionally, a pigment or dye; and (h) a photoinitiator, wherein a weight ratio of the first blocked or reactive blocked prepolymer to the second blocked or reactive blocked prepolymer is from 1:5 or 1:3 to 5:1 or 3:1.
In some embodiments, one of the first or second light reactive blocked prepolymer midblocks is formed from isophorone diisocyanate (IPDI), and the other is formed from 4,4'- dicyclohexylmethane-diisocyanate (HMDI).
In some embodiments of any of the polymerizable liquids or methods taught herein, the three-dimensional object produced has a glass transition temperature in a range of from 0 to 40 degrees Celsius.
Also provided is a method of forming an energy absorbing three-dimensional object comprising polyurethane, polyurea, or a copolymer thereof, comprising: (a) providing a polymerizable liquid as taught herein, said liquid comprising: (i) a light polymerizable first component, and (ii) a second solidifiable component that is different from said first component; (b) producing a three-dimensional intermediate from said polymerizable liquid by an additive manufacturing process including irradiating said polymerizable liquid with light to form a solid polymer scaffold from said first component and containing said second solidifiable component carried in said scaffold in unsolidified and/or uncured form, said intermediate having the same shape as, or a shape to be imparted to, said three-dimensional object; (c) optionally cleaning said intermediate (e.g., by washing, wiping (with a blade, absorbent, compressed gas, etc.), gravity draining, centrifugal separation of residual resin therefrom, etc., including combinations thereof); and (d) concurrently with or subsequent to said producing step (b), heating, microwave irradiating, or both, said second solidifiable component in said three-dimensional intermediate, to form said energy absorbing three- dimensional object comprising polyurethane, polyurea, or a copolymer thereof.
In some embodiments, the producing step (b) is carried out by stereolithography (e.g, bottom-up stereolithography such as continuous liquid interface production).
In some embodiments, the producing step (b) is carried out by: (i) providing a carrier and an optically transparent member having a build surface, said carrier and said build surface defining a build region therebetween; (ii) filling said build region with said polymerizable liquid, and (in) irradiating said build region with light through said optically transparent member to form said solid polymer scaffold from said first component and also advancing said carrier and said build surface away from one another to form said three- dimensional intermediate.
In some embodiments, step (d) is carried out subsequent to said producing step (b), and optionally but preferably subsequent to said cleaning step (c).
In some embodiments of any of the polymerizable liquids or methods taught herein, the three-dimensional object produced has a Tan Delta (tanD) maximum occurring at a temperature of from 0°C to 40°C, and wherein the tanD maximum is greater than 0.3, when measured on a sample nominally 1 mm thick, 10 mm wide, and 10-15 mm long using a Dynamic Mechanical Analyzer with a Tension Clamp at a strain of 0.1% and at a frequency of lHz and a temperature ramp rate of 2°C/min.
In some embodiments of any of the polymerizable liquids or methods taught herein, the three-dimensional object produced comprises a UV-polymerized component and a polyurethane/polyurea component, which are interpenetrating networks or semi- interpenetrating networks, wherein the polyurethane/polyurea component comprises soft segments of low number average molecular weight (e.g., from 200 or 250 to 700 or 800 Da ) and high number average molecular weight (e.g., from 1000, 1500 or 2000 to 5,000 or 10,000 Da). In some embodiments, the UV-polymerized component and a soft segment of the polyurethane/polyurea component are phase-mixed or partially phase-mixed, and wherein the polyurethane/polyurea component comprises soft segments and hard segments that are phase- mixed or partially phase-mixed. In some embodiments of any of the polymerizable liquids or methods taught herein, the three-dimensional object produced comprises a part of automotive damping and insulation, helmet energy absorption layer, bicycle seat, or a cushioning.
Further provided is a three-dimensional object produced by a method or with a polymerizable liquid as taught herein.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1. Measuring dynamic stiffness. By matching the dynamic stiffness with a given impact velocity, the impactor will decelerate as much as possible until the densification region and peak forces will remain low. The soft material shown in the graph does not slow the impactor effectively, so at maximum displacement the resulting force is great, whereas the stiff material of Comparative Example 2 gradually slows the impactor and the peak forces remain low. The static stiffness of the two materials are comparable; however, the strain rate sensitivity of Comparative Example 2 is much greater.
FIG. 2. Measuring the dynamic properties of stiffer elastomers. Example 2 formulation results in similar dynamic stiffness although mass is reduced by 30%, as compared to Comparative Example 2.
FIG. 3. Non-bonding fillers can increase stiffness without addition of hard segment or crosslinking while maintaining high strain-rate sensitivity. This leads to higher dynamic stiffness when compared to an unfilled sample. As seen in the graph, although these materials show similar stiffness when measured at low strain rates, the dynamic stiffness is improved in Example 4 as compared with Example 3.
FIG. 4. Phase mixing from a trifunctional amine (JEFF AMINE® T403) used in Example 6 provides good dynamic performance and greatly improves compression set.
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.
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").
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly-used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and claims and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Well- known functions or constructions may not be described in detail for brevity and/or clarity.
"Shape to be imparted to" refers to the case where the shape of the intermediate object slightly changes between formation thereof and forming the subsequent three-dimensional product, typically by shrinkage ( e.g ., up to 1, 2 or 4 percent by volume), expansion (e.g, up to 1, 2 or 4 percent by volume), removal of support structures, or by intervening forming steps (e.g, intentional bending, stretching, drilling, grinding, cutting, polishing, or other intentional forming after formation of the intermediate product, but before formation of the subsequent three-dimensional product). The three-dimensional intermediate may also be washed, if desired, before further curing, and/or before, during, or after any intervening forming steps.
1. POLYMERIZABLE LIQUIDS (RESINS).
Polymerizable liquid compositions curable by actinic radiation (typically light, and in some embodiments ultraviolet (UV) light) are provided to enable the present invention. The liquid (sometimes referred to as "liquid resin," "ink," or simply "resin" herein) may include a polymerizable monomer, particularly photopolymerizable and/or free radical polymerizable monomers (e.g., reactive diluents) and/or prepolymers (i.e., reacted or larger monomers capable of further polymerization), and a suitable initiator such as a free radical initiator.
Polyurethane dual cure resins for forming a three-dimensional object comprising polyurethane, polyurea, or a copolymer thereof are described in, for example, Rolland et ah, US Patent Nos. 9,676,963, 9,598,606, and 9,453,142, the disclosures of which are incorporated herein by reference. In general, such resins can comprise: (a) light- polymerizable monomers and/or prepolymers that can form an intermediate object (typically in the presence of a photoinitiator); and (b) heat-polymerizable (or otherwise further polymerizable) monomers and/or prepolymers.
Photoinitiators useful in the present invention include, but are not limited to, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), phenylbis(2,4,6- trimethylbenzoyl)phosphine oxide (PPO), 2-isopropylthioxanthone and/or 4- isopropylthioxanthone (ITX), etc.
Light-polymerizable monomers and/or prepolymers. Sometimes also referred to as "Part A" of the resin, these are monomers and/or prepolymers that can be polymerized by exposure to actinic radiation or light. This resin can have a functionality of two or higher (though a resin with a functionality of one can also be used when the polymer does not dissolve in its monomer). A purpose of Part A is to "lock" the shape of the object being formed or create a scaffold for the one or more additional components ( e.g Part B). Importantly, Part A is present at or above the minimum quantity needed to maintain the shape of the object being formed after the initial solidification during photolithography. In some embodiments, this amount corresponds to less than ten, twenty, or thirty percent by weight of the total resin (polymerizable liquid) composition.
Examples of suitable reactive end groups suitable for Part A constituents, monomers, or prepolymers include, but are not limited to: acrylates, methacrylates, a-olefms, N-vinyls, acrylamides, methacrylamides, styrenics, epoxides, thiols, 1,3 -dienes, vinyl halides, acrylonitriles, vinyl esters, maleimides, and vinyl ethers.
In some embodiments, the light-polymerizable monomers and/or prepolymers comprises a light reactive blocked prepolymer such as ABPU. "ABPU" or "reactive blocked polyurethane" as used herein refers to UV-curable, (meth)acrylate blocked, polyurethane/polyurea (i.e., reactive blocked polyurethane) such as described in US Patent Nos. 9,453,142 and 9,598,606 to Rolland et al. A particular example of a suitable reactive (or UV-curable) blocking agent for blocking the isocyanates of the ABPU is a tertiary amine- containing (meth)acrylate (e.g., t-butylaminoethyl methacrylate, TBAEMA, tertiary pentylaminoethyl methacrylate (TPAEMA), tertiary hexylaminoethyl methacrylate (THAEMA), tertiary-butylaminopropyl methacrylate (TBAPMA), acrylate analogs thereof, and mixtures thereof).
In some embodiments, the light-polymerizable monomers and/or prepolymers may further include a prepolymer that is different from ABPU. For example, a non-blocked reactive prepolymer may be included, examples of which include, but are not limited to, an acrylate or methacrylate capped prepolymer. The prepolymer is preferably an oligomeric prepolymer having hydrogen-bonding donors and/or acceptors, such as a urethane and/or urea prepolymer. Non-limiting examples of such a non-blocked reactive prepolymer are EXOTHANE™ elastomers such as Exothane 10 (Esstech, Inc., Essington, Pennsylvania), which is a difunctional methacrylate-capped polyurethane prepolymer.
An aspect of the solidification of Part A is that it provides a scaffold in which a second reactive resin component, termed "Part B," can solidify during a second step, as discussed further below.
Heat-polymerizable monomers and/or prepolymers. Sometimes also referred to as "Part B," these constituents may comprise, consist of or consist essentially of a mix of monomers and/or prepolymers that possess reactive end groups that participate in a second solidification reaction during or after the Part A solidification reaction. In general, for dual cure resins, examples of methods used to solidify Part B include, but are not limited to, contacting the object or scaffold to heat, water or water vapor, light at a different wavelength than that at which Part A is cured, catalysts, (with or without additional heat), evaporation of a solvent from the polymerizable liquid ( e.g ., using heat, vacuum, or a combination thereof), microwave irradiation, etc., including combinations thereof. In some embodiments, heat curing of the "Part B" resins is preferred.
In some embodiments, the second component of the dual cure resin comprises precursors to a polyurethane, polyurea, or copolymer thereof (e.g., poly(urethane-urea)), and may also comprise a silicone resin, an epoxy resin, a cyanate ester resin, or a natural rubber.
Resins may be in any suitable form, including "one pot" resins and "dual precursor" resins (where cross-reactive constituents are packaged separately, and which may be identified, for example, as an "A" precursor resin and a "B" precursor resin). Note that, in some embodiments employing "dual cure" polymerizable resins, the part, following manufacturing, may be contacted with a penetrant liquid, with the penetrant liquid carrying a further constituent of the dual cure system, such as a reactive monomer, into the part for participation in a subsequent cure. Such "partial" resins are intended to be included herein. See, e.g., WO 2018/094131 (Carbon, Inc.), the disclosures of which are incorporated herein by reference.
Examples of dual cure photopolymerizable reactive prepolymers include isocyanate or blocked isocyanate-containing prepolymers. A blocked isocyanate is a group that can be deblocked or is otherwise available for reaction as an isocyanate upon heating, such as by a urethane reaction of an isocyanate with alcohol. See, e.g, U.S. Patent No. 3,442,974 to Bremmer; U.S. Patent No. 3,454,621 to Engel; Lee et ah, "Thermal Decomposition Behaviour of Blocked Diisocyanates Derived from Mixture of Blocking Agents," Macromolecular Research, 13(5):427-434 (2005). "Isocyanate" as used herein includes diisocyanate, polyisocyanate, and branched isocyanate.
"Diisocyanate" and "polyisocyanate" are used interchangeably herein and refer to aliphatic, cycloaliphatic, and aromatic isocyanates that have at least two, or in some embodiments more than two, isocyanate (NCO) groups per molecule, on average. In some embodiments, the isocyanates have, on average, 2.1, 2.3, 2.5, 2.8, or 3 isocyanate groups per molecule, up to 6, 8 or 10 or more isocyanate groups per molecule, on average. In some embodiments, the isocyanates may be a hyperbranched or dendrimeric isocyanate (e.g., containing more than 10 isocyanate groups per molecule, on average, up to 100 or 200 or more isocyanate groups per molecule, on average). Common examples of suitable isocyanates include, but are not limited to, methylene diphenyl diisocyanate (MDI), toluene diisocyanate (TDI)), para-phenyl diisocyanate (PPDI), 4,4'-dicyclohexylmethane- diisocyanate (HMDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), triphenylmethane-4, 4’ 4 "-triisocyanate, tolune-2,4,6- triyl triisocyanate, 1, 3, 5-triazine-2, 4,6- triisocyanate, ethyl ester L-lysine triisocyanate, etc., including combinations thereof. Numerous additional examples are known and are described in, for example, US Patent Nos. 9,200,108, 8,378,053, 7,144,955, 4,075,151, 3,932,342, and in US Patent Application Publication Nos. US 20040067318 and US 20140371406, the disclosures of all of which are incorporated by reference herein in their entirety.
"Branched isocyanate" as used herein refers to diisocyanates or polyisocyanates as described above that have three or more isocyanate groups per molecule, or (with respect to mixtures of different isocyanates) more than two isocyanate groups per molecule, on average. In some embodiments, the branched isocyanates have, on average, 2.1, 2.3, 2.5, 2.8, or 3 isocyanate groups per molecule, up to 6, 8 or 10 or more isocyanate groups per molecule, on average. In some embodiments, the isocyanates may be hyperbranched or dendrimeric isocyanates as discussed above (e.g, containing more than 10 isocyanate groups per molecule, on average, up to 100 or 200 or more isocyanate groups per molecule, on average).
The blocking group may optionally have a reactive terminal group (e.g., a polymerizable end group such as an epoxy, alkene, alkyne, or thiol end group, for example an ethylenically unsaturated end group such as a vinyl ether).
In some embodiments, the dual cure resin includes a UV-curable (meth)acrylate blocked polyurethane/polyurea (ABPU). Such resins are described in, for example, Rolland et ah, US Patent Nos. 9,676,963, 9,598,606, and 9,453,142, the disclosures of which are incorporated herein by reference. An ABPU "midblock" is that section of the prepolymer or ABPU where a polyol or polyamine was reacted with isocyanate and a reactive blocking group (such as TBAEMA) to make an ABPU, including but not limited to poly(tetramethylene oxide), polypropylene glycol), poly(ethylene glycol), poly(trimethylene oxide) and copolymers thereof. See US Patent No. 9,598,606 to Rolland et al.
In some embodiments, the isocyanate may be blocked with an amine methacrylate blocking agent ( e.g ., tertiary -butylaminoethyl methacrylate (TBAEMA), tertiary pentylaminoethyl methacrylate (TPAEMA), tertiary hexylaminoethyl methacrylate (THAEMA), tertiary-butylaminopropyl methacrylate (TBAPMA), maleimide, and mixtures thereof (see, e.g., US Patent Application Publication No. 20130202392)). Note that these could be used as diluents, as well.
Chain extenders. Chain extenders are generally linear compounds having di- or poly functional ends that can react with a monomer/prepolymer or crosslinked photopolymerized polymer intermediate as taught herein. Examples include, but are not limited to, diol or amine chain extenders, which can react with isocyanates of a de-blocked diisocyanate-containing polymer.
Examples of diol or polyol chain extenders include, but are not limited to, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3 -propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, hydroquinone bis(2- hydroxy ethyl) ether (HQEE), glycerol, trimethylolpropane, 1,2,6-hexanetriol, and pentaerythritol. Natural oil polyols (biopolyols) may also be used. Such polyols may be derived, e.g, from vegetable oils (triglycerides), such as soybean oil, by known techniques. See, e.g, U.S. Patent No. 6,433,121 to Petrovic et al.
Examples of diamine or polyamine chain extenders include, but are not limited to, aliphatic, aromatic, and mixed aliphatic and aromatic, polyamines, such as diamines (for example, 4,4'-methylenedicyclohexanamine (PACM), 4,4'-methylenebis(2-methylcyclohexyl- amine) (MACM), ethylene diamine, isophorone diamine, diethyltoluenediamine), and polyetheramines (for example JEFF AMINE® from Huntsman Corporation).
Diluents. Diluents as known in the art are compounds used to reduce viscosity in a resin composition. Reactive diluents undergo reaction to become part of the polymeric network. In some embodiments, the reactive diluent may react at approximately the same rate as other reactive monomers and/or prepolymers in the composition. Reactive diluents may include aliphatic reactive diluents, aromatic reactive diluents, and cycloaliphatic reactive diluents. Examples include, but are not limited to, isobomyl acrylate, isobornyl methacrylate (IBOMA), lauryl acrylate, lauryl methacrylate (LMA), 2-ethyl hexyl methacrylate, 2-ethyl hexyl acrylate, di(ethylene glycol) methyl ether methacrylate (DEGMA), phenoxyethyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, dimethyl(aminoethyl) methacrylate, butyl acrylate, butyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, ethylene glycol dimethacrylate (EGDMA), polyethylene glycol dimethacrylate, hexanediol dimethacrylate, trimethylolpropane trimethacrylate (TMPTMA), and tert- butylaminoethyl methacrylate (TBAEMA).
Oxidizable tin salts. Oxidizable tin salts useful for carrying out the present invention include, but are not limited to, stannous butanoate, stannous octoate, stannous hexanoate, stannous heptanoate, stannous linoleate, stannous phenyl butanoate, stannous phenyl stearate, stannous phenyl oleate, stannous nonanoate, stannous decanoate, stannous undecanoate, stannous dodecanoate, stannous stearate, stannous oleate, stannous undecenoate, stannous 2- ethylhexoate, dibutyl tin dilaurate, dibutyl tin dioleate, dibutyl tin distearate, dipropyl tin dilaurate, dipropyl tin dioleate, dipropyl tin distearate, dibutyl tin dihexanoate, and combinations thereof. See also US Patent Nos. 5,298,532, 4,421,822, and 4,389,514, the disclosures of which are incorporated herein by reference. In addition to the foregoing oxidizable tin salts, Lewis acids such as those described in Chu et al. in Macromolecular Symposia, Volume 95, Issue 1, pages 233-242, June 1995 are known to enhance the polymerization rates of free-radical polymerizations and are included herein by reference.
Fillers. Any suitable filler may be used in connection with the present invention, depending on the properties desired in the part or object to be made. Thus, fillers may be solid or liquid, organic or inorganic, and may include reactive and non-reactive rubbers: siloxanes, acrylonitrile-butadiene rubbers; reactive and non-reactive thermoplastics (including but not limited to: poly(ether imides), maleimide-styrene terpolymers, polyarylates, polysulfones and polyethersulfones, etc.) inorganic fillers such as silicates (such as talc, clays, silica, mica), glass, carbon nanotubes, graphene, cellulose nanocrystals, etc., including combinations of two or more of the foregoing. Suitable fillers include tougheners, such as core-shell rubbers, as discussed below.
In some embodiments, the fillers are non-bonding fillers. Suitable examples include, but are not limited to, nylon particles, fused silicas, calcium carbonates, and core-shell rubbers. The fillers may provide improved energy dissipation from heat generation during chain slippage or separation of the filler from the matrix. In the case of nylon fillers, some amount of secondary, non-covalent interactions between the matrix and the filler may exist. This could be hydrogen bonding, which may provide additional stiffness at high strain rates.
Tougheners. One or more polymeric and/or inorganic tougheners can be used as a filler in the present invention. The toughener may be uniformly distributed in the form of particles in the cured product. The particles could be less than 5 microns (pm) in diameter. Such tougheners include, but are not limited to, those formed from elastomers, branched polymers, hyperbranched polymers, dendrimers, rubbery polymers, rubbery copolymers, block copolymers, core-shell particles, oxides or inorganic materials such as clay, polyhedral oligomeric silsesquioxanes (POSS), carbonaceous materials ( e.g ., carbon black, carbon nanotubes, carbon nanofibers, fullerenes), ceramics and silicon carbides, with or without surface modification or functionalization. Examples of block copolymers include the copolymers whose composition is described in U.S. Pat. No. 6,894,113 (Court et ah, Atofina, 2005) and include "NANOSTRENTH®" SBM (polystyrene-polybutadiene- polymethacrylate), and AMA (polymethacrylate-polybutylacrylate-polymethacrylate), both produced by Arkema (King of Prussia, Pennsylvania). Other suitable block copolymers include FORTEGRA® and the amphiphilic block copolymers described in U.S. Pat. No. 7,820,760B2, assigned to Dow Chemical. Examples of known core-shell particles include the core-shell (dendrimer) particles whose compositions are described in US20100280151A1 (Nguyen et ah, Toray Industries, Inc., 2010) for an amine branched polymer as a shell grafted to a core polymer polymerized from polymerizable monomers containing unsaturated carbon- carbon bonds, core-shell rubber particles whose compositions are described in EP 1632533A1 and EP 2123711A1 by Kaneka Corporation, and the "KaneAce MX" product line of such particle/epoxy blends whose particles have a polymeric core polymerized from polymerizable monomers such as butadiene, styrene, other unsaturated carbon-carbon bond monomer, or their combinations, and a polymeric shell compatible with the epoxy, typically polymethylmethacrylate, polyglycidylmethacrylate, polyacrylonitrile or similar polymers, as discussed further below. Also suitable as block copolymers in the present invention are the "JSR SX" series of carboxylated polystyrene/polydivinylbenzenes produced by JSR Corporation; "Kureha Paraloid" EXL-2655 (produced by Kureha Chemical Industry Co., Ltd.), which is a butadiene alkyl methacrylate styrene copolymer; "Stafiloid" AC-3355 and TR-2122 (both produced by Takeda Chemical Industries, Ltd.), each of which are acrylate methacrylate copolymers; and "PARALOID" EXL-2611 and EXL-3387 (both produced by Rohm & Haas), each of which are butyl acrylate methyl methacrylate copolymers. Examples of suitable oxide particles include NANOPOX® produced by nanoresins AG. This is a master blend of functionalized nanosilica particles and an epoxy.
Core-shell rubbers. Core-shell rubbers are particulate materials (particles) having a rubbery core. Such materials are known and described in, for example, US Patent Application Publication No. 20150184039, as well as US Patent Application Publication No. 20150240113, and US Patent Nos. 6,861,475, 7,625,977, 7,642,316, 8,088,245, and elsewhere.
In some embodiments, the core-shell rubber particles are nanoparticles (i.e., having an average particle size of less than 1000 nanometers (nm)). Generally, the average particle size of the core-shell rubber nanoparticles is less than 500 nm, e.g., less than 300 nm, less than 200 nm, less than 100 nm, or even less than 50 nm. Typically, such particles are spherical, so the particle size is the diameter; however, if the particles are not spherical, the particle size is defined as the longest dimension of the particle.
In some embodiments, the rubbery core can have a glass transition temperature (Tg) of less than -25 °C, more preferably less than -50 °C, and even more preferably less than -70 °C. The Tg of the rubbery core may be well below -100 °C. The core-shell rubber also has at least one shell portion that preferably has a Tg of at least 50 °C. By "core," it is meant an internal portion of the core-shell rubber. The core may form the center of the core-shell particle, or an internal shell or domain of the core-shell rubber. A shell is a portion of the core-shell rubber that is exterior to the rubbery core. The shell portion (or portions) typically forms the outermost portion of the core-shell rubber particle. The shell material can be grafted onto the core or is cross-linked. The rubbery core may constitute from 50 to 95%, or from 60 to 90%, of the weight of the core-shell rubber particle.
The core of the core-shell rubber may be a polymer or copolymer of a conjugated diene such as butadiene, or a lower alkyl acrylate such as n-butyl-, ethyl-, isobutyl- or 2- ethylhexylacrylate. The core polymer may in addition contain up to 20% by weight of other copolymerized mono-unsaturated monomers such as styrene, vinyl acetate, vinyl chloride, methyl methacrylate, and the like. The core polymer is optionally cross-linked. The core polymer optionally contains up to 5% of a copolymerized graft-linking monomer having two or more sites of unsaturation of unequal reactivity, such as diallyl maleate, monoallyl fumarate, allyl methacrylate, and the like, at least one of the reactive sites being non- conjugated.
The core polymer may also be a silicone rubber. These materials often have glass transition temperatures below -100 °C. Core-shell rubbers having a silicone rubber core include those commercially available from Wacker Chemie, Munich, Germany, under the trade name GENIOPERL®.
The shell polymer, which is optionally chemically grafted or cross-linked to the rubber core, can be polymerized from at least one lower alkyl methacrylate such as methyl methacrylate, ethyl methacrylate or t-butyl methacrylate. Homopolymers of such methacrylate monomers can be used. Further, up to 40% by weight of the shell polymer can be formed from other monovinylidene monomers such as styrene, vinyl acetate, vinyl chloride, methyl acrylate, ethyl acrylate, butyl acrylate, and the like. The molecular weight of the grafted shell polymer can be between 20,000 and 500,000.
One suitable type of core-shell rubber has reactive groups in the shell polymer which can react with an epoxy resin or an epoxy resin hardener. Glycidyl groups are suitable. These can be provided by monomers such as glycidyl methacrylate.
One example of a suitable core-shell rubber is of the type described in EiS Patent Application Publication No. 2007/0027233 (EP 1 632 533 Al). Core-shell rubber particles as described therein include a cross-linked rubber core, in most cases being a cross-linked copolymer of butadiene, and a shell which is preferably a copolymer of styrene, methyl methacrylate, glycidyl methacrylate and optionally acrylonitrile. The core-shell rubber is preferably dispersed in a polymer or an epoxy resin, also as described in the document.
Suitable core-shell rubbers include, but are not limited to, those sold by Kaneka Corporation under the designation Kaneka Kane Ace, including the Kaneka Kane Ace 15 and 120 series of products, including Kaneka Kane Ace MX 120, Kaneka Kane Ace MX 153, Kaneka Kane Ace MX 154, Kaneka Kane Ace MX 156, Kaneka Kane Ace MX170, Kaneka Kane Ace MX 257 and Kaneka Kane Ace MX 120 core-shell rubber dispersions, and mixtures thereof.
Additional resin ingredients. The liquid resin or polymerizable material can have solid particles suspended or dispersed therein. Any suitable solid particle can be used, depending upon the end product being fabricated. The particles can be metallic, organic/polymeric, inorganic, or composites or mixtures thereof. The particles can be nonconductive, semi-conductive, or conductive (including metallic and non-metallic or polymer conductors); and the particles can be magnetic, ferromagnetic, paramagnetic, or nonmagnetic. The particles can be of any suitable shape, including spherical, elliptical, cylindrical, etc. The particles can be of any suitable size (for example, ranging from 1 nm to 20 pm average diameter). The particles can comprise an active agent or detectable compound as described below, though these may also be provided dissolved solubilized in the liquid resin as also discussed below. For example, magnetic or paramagnetic particles or nanoparticles can be employed.
The liquid resin can have additional ingredients solubilized therein, including pigments, dyes, active compounds or pharmaceutical compounds, detectable compounds (e.g, fluorescent, phosphorescent, radioactive), etc., again depending upon the particular purpose of the product being fabricated. Examples of such additional ingredients 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.
Non-reactive light absorbers. In some embodiments, polymerizable liquids for carrying out the present invention include a non-reactive pigment or dye that absorbs light, particularly UV light. Suitable examples of such light absorbers include, but are not limited to: (i) titanium dioxide (e.g, included in an amount of from 0.05 or 0.1 to 1 or 5 percent by weight), (ii) carbon black (e.g, included in an amount of from 0.05 or 0.1 to 1 or 5 percent by weight), and/or (Hi) an organic ultraviolet light absorber such as a hydroxybenzophenone, hydroxyphenylbenzotriazole, oxanilide, benzophenone, thioxanthone, hydroxyphenyltriazine, and/or benzotriazole ultraviolet light absorber (e.g, Mayzo BLS1326) (e.g, included in an amount of 0.001 or 0.005 to 1, 2 or 4 percent by weight). Examples of suitable organic ultraviolet light absorbers include, but are not limited to, those described in US Patent Nos. 3,213,058; 6,916,867; 7,157,586; and 7,695,643, the disclosures of which are incorporated herein by reference.
Inhibitors of polymerization. Inhibitors or polymerization inhibitors for use in the present invention may be in the form of a liquid or a gas. In some embodiments, gas inhibitors are preferred. In some embodiments, liquid inhibitors such as oils or lubricants (e.g, fluorinated oils such as perfluoropolyethers) may be employed, as inhibitors (or as release layers that maintain a liquid interface). The specific inhibitor will depend upon the monomer being polymerized and the polymerization reaction. For free radical polymerization monomers, the inhibitor can conveniently be oxygen, which can be provided in the form of a gas such as air, a gas enriched in oxygen (optionally but in some embodiments preferably containing additional inert gases to reduce combustibility thereof), or in some embodiments pure oxygen gas. In alternate embodiments, such as where the monomer is polymerized by a photoacid generator initiator, the inhibitor can be a base such as ammonia, trace amines (e.g, methyl amine, ethyl amine, di and trialkyl amines such as dimethyl amine, diethyl amine, trimethyl amine, triethyl amine, etc.), or carbon dioxide, including mixtures or combinations thereof.
Polyurethane segments. In some embodiments, resin compositions of the present invention useful to form an energy absorbing three-dimensional object include components having soft segments of different number average molecular weights. For example, the resin may include components (e.g., prepolymers and/or chain extenders) having a lower average molecular weight soft segment of 200-900 Da, such as 250-700 Da; and components having a higher average molecular weight of 1000-10,000 Da, such as 1500-5000 Da.
"Soft segment" and "hard segment" as used herein have their usual meaning in the polymer chemistry field and refer to sections of a polymer or prepolymer.
"Soft segment" refers to a typically oligomeric (or repeating low molecular weight) segment of the polyurethane chain that has a glass transition temperature less than room temperature, is generally amorphous or partially crystalline, provides flexibility to the copolymer, and generally has a large number of degrees of freedom. Examples of soft segments include, but are not limited to, polyethers, such as poly(tetramethylene oxide), polypropylene glycol), poly(ethylene glycol), poly(trimethylene oxide) and copolymers thereof.
"Hard segment" as used herein refers to a higher glass transition temperature, generally crystalline, rigid, segment that can provide mechanical integrity or strength to the segmented copolymer. Examples of hard segments include, but are not limited to, those formed from the reaction of isocyanates (such as IPDI, HMDI, HDI) and isocyanate-reactive amines and polyols (such as MACM).
In some preferred embodiments, there is phase mixing of different formulation components in the final article with different glass transition temperatures, such that the glass transition temperature (Tg) of the combined article is in the desired temperature of interest, preferably 0-40°C.
Stoichiometry of Part B components. In some embodiments, resin compositions of the present invention useful to form an energy absorbing three-dimensional object include Part B components present in molar deficiency or excess to the molar amount of blocked reactive groups. For example, the resin composition may include polyol and/or polyamine chain extenders that are present in an amount such that the moles of reactive groups (e.g., active hydrogen of amines or alcohols) are unequal to the moles of blocked functional groups (e.g., diisocyanates). As an example, the molar ratio of blocked isocyanates to polyol/polyamine in the resin may be 0.75-1.25, preferably 0.8-0.95 or 1.05-1.2.
2. ADDITIVE MANUFACTURING METHODS AND APPARATUS.
The polymerizable resins may be used for additive manufacturing, typically bottom- up or top-down additive manufacturing, generally known as stereolithography. Such methods are known and described in, for example, US Patent No. 5,236,637 to Hull, US Patent Nos. 5,391,072 and 5,529,473 to Lawton, US Patent No. 7,438,846 to John, US Patent No. 7,892,474 to Shkolnik, US Patent No. 8,110,135 to El-Siblani, US Patent Application Publication No. 2013/0292862 to Joyce, US Patent Application Publication No. 2013/0295212 to Chen et ah, and US Patent Application Publication No. 2018/0290374 to Willis et al. The disclosures of these patents and applications are incorporated by reference herein in their entireties.
In general, top-down three-dimensional fabrication with a dual cure resin is carried out by:
(a) providing a polymerizable liquid reservoir having a polymerizable liquid fill level and a carrier positioned in the reservoir, the carrier and the fill level defining a build region therebetween;
(b) filling the build region with a polymerizable liquid (i.e., the resin), said polymerizable liquid comprising a mixture of (i) a light (typically ultraviolet light) polymerizable liquid first component, and (ii) a second solidifiable component of the dual cure system; and then
(c) irradiating the build region with light to form a solid polymer scaffold from the first component and also advancing (typically lowering) the carrier away from the build surface to form a three-dimensional intermediate having the same shape as, or a shape to be imparted to, the three-dimensional object and containing said second solidifiable component (e.g., a second reactive component) carried in the scaffold in unsolidified and/or uncured form.
A wiper blade, doctor blade, or optically transparent (rigid or flexible) window, may optionally be provided at the fill level to facilitate leveling of the polymerizable liquid, in accordance with known techniques. In the case of an optically transparent window, the window provides a build surface against which the three-dimensional intermediate is formed, analogous to the build surface in bottom-up three-dimensional fabrication as discussed below. In general, bottom-up three-dimensional fabrication with a dual cure resin is carried out by:
(a) providing a carrier and an optically transparent member having a build surface, the carrier and the build surface defining a build region therebetween;
(b) filling the build region with a polymerizable liquid (i.e., the resin), said polymerizable liquid comprising a mixture of (i) a light (typically ultraviolet light) polymerizable liquid first component, and (ii) a second solidifiable component of the dual cure system; and then
(c) irradiating the build region with light through said optically transparent member to form a solid polymer scaffold from the first component and also advancing (typically raising) the carrier away from the build surface to form a three-dimensional intermediate having the same shape as, or a shape to be imparted to, the three-dimensional object and containing said second solidifiable component ( e.g ., a second reactive component) carried in the scaffold in unsolidified and/or uncured form.
In some embodiments of bottom-up or top-down three-dimensional fabrication as implemented in the context of the present invention, the build surface is stationary during the formation of the three-dimensional intermediate; in other embodiments of bottom-up three- dimensional fabrication as implemented in the context of the present invention, the build surface is tilted, slid, flexed and/or peeled, and/or otherwise translocated or released from the growing three-dimensional intermediate, usually repeatedly, during formation of the three- dimensional intermediate.
In some embodiments of bottom-up or top-down three-dimensional fabrication as carried out in the context of the present invention, the polymerizable liquid (or resin) is maintained in liquid contact with both the growing three-dimensional intermediate and the build surface during both the filling and irradiating steps, during fabrication of some of, a major portion of, or all of the three-dimensional intermediate.
In some embodiments of bottom-up or top-down three-dimensional fabrication as carried out in the context of the present invention, the growing three-dimensional intermediate is fabricated in a layerless manner (e.g., through multiple exposures or "slices" of patterned actinic radiation or light) during at least a portion of the formation of the three- dimensional intermediate.
In some embodiments of bottom-up or top-down three-dimensional fabrication as carried out in the context of the present invention, the growing three-dimensional intermediate is fabricated in a layer-by-layer manner (e.g, through multiple exposures or "slices" of patterned actinic radiation or light), during at least a portion of the formation of the three-dimensional intermediate.
In some embodiments of bottom-up or top-down three-dimensional fabrication employing a rigid or flexible optically transparent window, a lubricant or immiscible liquid may be provided between the window and the polymerizable liquid ( e.g a fluorinated fluid or oil such as a perfluoropoly ether oil).
From the foregoing it will be appreciated that, in some embodiments of bottom-up or top-down three-dimensional fabrication as carried out in the context of the present invention, the growing three-dimensional intermediate is fabricated in a layerless manner during the formation of at least one portion thereof, and that same growing three-dimensional intermediate is fabricated in a layer-by-layer manner during the formation of at least one other portion thereof. Thus, operating mode may be changed once, or on multiple occasions, between layerless fabrication and layer-by-layer fabrication, as desired by operating conditions such as part geometry.
In some embodiments, the intermediate is formed by continuous liquid interface production (CLIP). CLIP is known and described in, for example, US Patent Nos. 9,205,601; 9,211,678; 9,216,546; 9,360,757; and 9,498,920 to DeSimone et al. In some embodiments, CLIP employs features of a bottom-up three-dimensional fabrication as described above, but the irradiating and/or advancing steps are carried out while also concurrently maintaining a stable or persistent liquid interface between the growing object and the build surface or window, such as by: (i) continuously maintaining a dead zone of polymerizable liquid in contact with the build surface, and (ii) continuously maintaining a gradient of polymerization zone (such as an active surface) between the dead zone and the solid polymer and in contact with each thereof, the gradient of polymerization zone comprising the first component in partially-cured form. In some embodiments of CLIP, the optically transparent member comprises a semipermeable member (e.g., a fluoropolymer), and the continuously maintaining a dead zone is carried out by feeding an inhibitor of polymerization through the optically transparent member, thereby creating a gradient of inhibitor in the dead zone and optionally in at least a portion of the gradient of polymerization zone. Other approaches for carrying out CLIP that can be used in the present invention and potentially obviate the need for a semipermeable "window" or window structure include utilizing a liquid interface comprising an immiscible liquid (see L. Robeson et al., WO 2015/164234), generating oxygen as an inhibitor by electrolysis (see I. Craven et al., WO 2016/133759), and incorporating magnetically positionable particles to which the photoactivator is coupled into the polymerizable liquid ( see J. Rolland, WO 2016/145182), and approaches described in US Patent Application Publication No. 2018/0126630 to Panzer et al., and US Patent Application Publication No. 2018/0243976 to Feller.
Further curing may be carried out subsequent to the producing step, such as by heating, microwave irradiating, contacting the object to water, contacting the object to a polymerization catalyst, irradiating the object with light at a different wavelength from that used in the producing step, or a combination thereof. Alternatively, further curing may be carried out concurrently with the producing step, such as by heating, e.g., when the producing step is an exothermic reaction that may generate heat sufficient to carry out a further curing.
Heating may be active heating (e.g, in an oven, such as an electric, gas, or solar oven), or passive heating (e.g, at ambient (room) temperature). Active heating will generally be more rapid than passive heating and in some embodiments is preferred, but passive heating — such as simply maintaining the intermediate at ambient temperature for a sufficient time to effect further cure — is in some embodiments preferred.
3. OBJECTS PRODUCED.
The methods of the present invention can be used to make a variety of useful articles having a variety of mechanical properties, including but not limited to those articles and those properties described in US Patent No. 9,598,606 to Rolland et al., the disclosure of which is incorporated herein by reference.
Polymeric materials designed for energy attenuation reduce energy transfer during impact through strain-rate dependent stiffening and low energy return. During a high velocity impact event, the dynamic stiffness of the material will determine how energy is transferred from the impactor to the specimen. The dynamic stiffness can be compared to the static or quasi-static stiffness to determine strain rate sensitivity or the dilatant nature of a material. If the material is too soft for a given impact velocity, then acceleration of a sensor (impactor or headform, for example) at the densification region of the material will be great, resulting in high peak forces. By matching the dynamic stiffness with a given impact velocity, the impactor will decelerate as much as possible until the densification region and peak forces will remain low. This is shown in FIG. 1. The soft material does not slow the impactor effectively, so at maximum displacement the resulting force is great.
Polymer phase transitions are frequency dependent and by designing a system with a glass transition temperature near the operating temperature of the object or device, material stiffening is expected during an impact event. For example, if a device is to be effective at 25°C the material would be designed such that the temperature of the major phase transition, often termed the glass transition temperature (Tg), is between 17°C and 23°C when measured at 1 Hz. The magnitude of this transition can be a predictor of the damping nature of the material.
Formulation components which provide increased phase mixing between hard and soft segments also increase strain-rate dependent stiffening. Secondary interactions, such as hydrogen bonding interactions, between the hard and soft segments or between soft segments, can flow or creep at low strain rates but provide rigidity when measured at high strain rates. These types of interactions can come from the ABPU or chain extender, as well as the soft segment or hard segment.
In some embodiments, the three-dimensional (3D) object comprises a polymer blend, interpenetrating polymer network, semi-interpenetrating polymer network, or sequential interpenetrating polymer network formed from said first component and said second component.
In some embodiments, the object comprises a UV-polymerized component and a polyurethane/polyurea component, which are optionally interpenetrating networks, semi- interpenetrating networks, or polymeric blends.
In some embodiments, the UV-polymerized component and polyurethane/polyurea component are phase-mixed or partially phase-mixed, where these phases consist of a single, combined tanD peak. In some embodiments, the polyurethane/polyurea component comprises soft segments and hard segments that are phase-mixed or partially phase-mixed.
In some embodiments, the polyurethane phase comprises soft segments of low number average molecular weight (e.g., from 200 or 250 to 700 or 800 Da ) and high number average molecular weight (e.g., from 1,000, 1,500 or 2,000 to 5,000 or 10,000 Da).
In some embodiments, the polyurethane phase comprises hard segments of dissimilar backbone structure, such as those formed from isocyanates having different numbers of cycloaliphatic rings. For example, IPDI has one cycloaliphatic core ring, whereas HMDI and MACM each have two cycloaliphatic core rings, and thus the hard segments formed from them have different numbers of cycloaliphatic rings in their backbone structures.
In some embodiments, the three-dimensional object is (i) rigid, (ii) semi-rigid and flexible, or (Hi) elastomeric.
The three-dimensional object can be (i) uniform or symmetric in shape, or (ii) irregular or asymmetric in shape. The object may be energy absorbing with a maximum Tan Delta occurring between 0- 50°C. and wherein the Tan Delta max is greater than 0.3, when measured on a sample nominally 1 mm thick, 10 mm wide, and 10-15 mm long using a Dynamic Mechanical Analyzer with a Tension Clamp at a strain of 0.1% and at a frequency of lHz and a temperature ramp rate of 2°C/min. See, e.g. , US Pat. No. 9,920,192 to Eastman Chemical.
In some preferred embodiments, the object is elastomeric and energy absorbing in nature, in which tanD maximum at lHz is from 0, 5, 10 or 15°C to 30, 35 or 40°C, and with a maximum magnitude greater than 0.3.
A material which shows increased stiffness in response to high strain rates, similar to a non-newtonian dilatant fluid, aids energy absorption/attenuation and provides more efficient energy dissipation across a greater range of impact velocities. Such increased stiffness may be accomplished in some embodiments by inclusion of hard segments in the prepolymer (such as ABPU) and/or imparted by the reacted chain extender (e.g., rigid chain extenders such as MACM, PACM, isophorene diamine, etc.).
Targeting a glass transition temperature (Tg) near the operating range of the material, when measured at lHz, can lead to high sensitivity to strain rate. The glass transition temperature may be adjusted, for example, with the use of mixtures in the resin components such as the reactive diluents, chain extenders, and/or prepolymers. In some embodiments, the Tg of the produced article is in a range of from 0 to 40 degrees Celsius.
Increased phase mixing and the use of higher loadings of low molecular weight soft segment (through the prepolymer(s) and/or chain extender(s)) also leads to increased stiffness change at high strain rate. Phase mixing from both the UV-polymerized component and polyurethane/polyurea component, such as in an interpenetrating network or semi- interpenetrating network, is beneficial.
Inclusion of a mixture of the different soft segment molecular weights allows for control between damping and resilient behavior. For instance, increasing the amount of low molecular weight soft segment can promote more phase mixing between the hard and soft segments, which leads to greater energy dissipation and damping during an impact event. The amount of energy return and resiliency in the object can be improved by increasing the amount of the higher molecular weight soft segments.
Embodiments of the present invention are explained in greater detail in the following non-limiting examples. EXAMPLES
Definitions:
ABPU: reactive blocked (e.g, (meth)acrylate blocked) polyurethane prepolymer
DEGMA: (diethylene glycol)methyl ether methacrylate
DUDMA: diurethane dimethacrylate
EGDMA: ethylene glycol dimethacrylate
HMDI: 4,4'-dicyclohexylmethane-diisocyanate
IPDE isophorone diisocyanate (Covestro Desmodur I)
IBOMA: isobornyl methacrylate
JEFF AMINE® D230: polyoxypropylene diamine, MW approx. 230 JEFF AMINE® D2000: polyoxypropylene diamine, MW approx. 2000 JEFF AMINE® T403: trifunctional polyetheramine, MW approx. 440 JEFF AMINE® THF100: poly ether diamine, MW approx. 1000 LMA: lauryl methacrylate
MACM: 4,4’ -methylenebis(2-methy cyclohexyl-amine) (a chain extender) ORGASOL® 2001 EXD NAT 1 (nylon filler)
PEG600DMA: polyethylene glycol dimethacrylate with PEG unit MW approx. 600 SpecraRay IJ UVD-J207 (ETV absorbing pigment)
TMPTMA: trimethylolpropane trimethacrylate
TPO: diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (a photoinitiator)
CLIP: continuous liquid interface production
Exothane 10: difunctional methacrylate capped polyurethane prepolymer
Comparative Example 1
Dual Cure Resin Formulation and Use in Additive Manufacturing
The components as shown in Table 1, except Chain Extenders, were added to a container and thoroughly mixed (either by an overhead stirrer or a centrifugation mixer such as THINKY™ mixer) to obtain a homogeneous resin. Then Chain Extenders were added to the resin and mixed for another 2-30 min depending on the volume and viscosity of the resin. The resin was formed by CLIP into D638 Type IV dog-bone-shaped specimens and 35 mm x 10 mm x 1 mm specimen for dynamic mechanical analysis followed by thermal curing at 120 °C for 8h. The cured elastomer specimens were tested following ASTM D412 on an Instron apparatus and with dynamic mechanical analysis at 1 Hz and at a heating rate of 2 °C/min. Dynamic performance of elastomers was evaluated through high strain-rate tensile testing or by forming a latticed geometry by CLIP and measuring dynamic stiffness with a drop tower at a range of impact energies or velocities. The latticed geometry would be 75x75x30 mm.
Table 1
Component Parts by weight
ABPU ABPU-2k-IPDI 57.08
APBU ABPU-650g/mol-HMDI 9.41
Reactive Diluent LMA 15.04 Reactive Diluent DEGMA 5.01 Reactive Diluent IBOMA 4.04 Reactive Diluent TMPTMA 1.23 Chain Extender MACM 4.64 Chain Extender JEFF AMINE® D230 2.56 Pigment SpecraRay IJ UVD-J207 0.18 Initiator TPO 0.80
Chord Modulus (MPa) 21
Tensile Strength (MPa) 16
% Elongation at Break 263 Tan Delta (°C) 24
Tan Delta Magnitude 0.50
Comparative Example 2 Dual Cure Resin Formulation and Use in Additive Manufacturing
The components as shown in Table 2, except Chain Extenders, were added to a container and thoroughly mixed (either by an overhead stirrer or a centrifugation mixer such as THINKY™ mixer) to obtain a homogeneous resin. Then Chain Extenders were added to the resin and mixed for another 2-30 min depending on the volume and viscosity of the resin. The resin was formed by CLIP into D638 Type IV dog-bone-shaped specimens and 35 mm x 10 mm x 1 mm specimen for dynamic mechanical analysis followed by thermal curing at 120 °C for 8h. The cured elastomer specimens were tested following ASTM D412 on an Instron apparatus and with dynamic mechanical analysis at 1 Hz and at a heating rate 2 °C/min. Dynamic performance of elastomers was evaluated through high strain-rate tensile testing or by forming a latticed geometry by CLIP and measuring dynamic stiffness with a drop tower at a range of impact energies or velocities. The latticed geometry would be 75x75x30 mm. Table 2
Component Parts by weight
ABPU ABPU-2k-IPDI 51.62
APBU ABPU-650g/mol-HMDI 6.15
Reactive Diluent LMA 13.59 Reactive Diluent DEGMA 6.61 Reactive Diluent IBOMA 9.42 Reactive Diluent PEG600DMA 1.01 Reactive Diluent DUDMA 1.29 Chain Extender MACM 6.24 Chain Extender JEFF AMINE® D2000 1.49 Chain Extender JEFF AMINE® T403 1.36 Pigment SpecraRay IJ UVD-J207 0.18 Initiator TPO 1.00
Chord Modulus (MPa) 20 Tensile Strength (MPa) 9 % Elongation at Break 210
Tan Delta (°C) 24 Tan Delta Magnitude 0.48
Example 1 Dual Cure Resin Formulation and Use in Additive Manufacturing
The components as shown in Table 3, except Chain Extenders, were added to a container and thoroughly mixed (either by an overhead stirrer or a centrifugation mixer such as THINKY™ mixer) to obtain a homogeneous resin. Then Chain Extenders were added to the resin and mixed for another 2-30 min depending on the volume and viscosity of the resin. The resin was formed by CLIP into D638 Type IV dog-bone-shaped specimens and 35 mm x 10 mm x 1 mm specimen for dynamic mechanical analysis followed by thermal curing at 120 °C for 8h. The cured elastomer specimens were tested following ASTM D412 on an Instron apparatus and with dynamic mechanical analysis at 1 Hz and at a heating rate of 2 °C/min. Dynamic performance of elastomers was evaluated through high strain-rate tensile testing or by forming a latticed geometry by CLIP and measuring dynamic stiffness with a drop tower at a range of impact energies or velocities. The latticed geometry would be 75x75x30 mm. Table 3
Component Parts by weight
APBU ABPU-650g/mol-IPDI 40.29
Reactive Diluent DEGMA 19.5
Chain Extender MACM 8.36
Chain Extender JEFF AMINE® D2000 30.22
Pigment SpecraRay IJ UVD-J207 0.12
Initiator TPO 1.01
Chord Modulus (MPa) 26
Tensile Strength (MPa) 12
% Elongation at Break 437
Tan Delta (°C) 22
Example 2
Dual Cure Resin Formulation and Use in Additive Manufacturing
The components as shown in Table 4, except Chain Extenders, were added to a container and thoroughly mixed (either by an overhead stirrer or a centrifugation mixer such as THINKY™ mixer) to obtain a homogeneous resin. Then Chain Extenders were added to the resin and mixed for another 2-30 min depending on the volume and viscosity of the resin. The resin was formed by CLIP into D638 Type IV dog-bone-shaped specimens and 35 mm x 10 mm x 1 mm specimen for dynamic mechanical analysis followed by thermal curing at 120 °C for 8h. The cured elastomer specimens were tested following ASTM D412 on an Instron apparatus and with dynamic mechanical analysis at 1 Hz and at a heating rate of 2 °C/min. Dynamic performance of elastomers was evaluated through high strain-rate tensile testing or by forming a latticed geometry by CLIP and measuring dynamic stiffness with a drop tower at a range of impact energies or velocities. The latticed geometry would be 75x75x30 mm. FIG. 2 shows that the dynamic stiffness of example 2 allows for similar plateau stiffness with reduced mass. Comparative example 2 was printed in a lattice geometry which resulted in a mass of 38g. Example 2 was printed in a similar lattice geometry but with less mass, resulting in a mass of 26g - a 30% reduction in weight. When impacted with the same mass and velocity, the plateau stiffness of the two latticed materials were similar. Table 4
Component Parts by weight
ABPU ABPU-2k-IPDI 50.57
APBU ABPU-650g/mol-HMDI 18.03
Reactive Diluent DEGMA 19.8 Chain Extender MACM 6.27 Chain Extender JEFF AMINE® D230 4.19 Pigment SpecraRay IJ UVD-J207 0.12 Initiator TPO 1.03
Chord Modulus (MPa) 32 Tensile Strength (MPa) 14 % Elongation at Break 384 Tan Delta (°C) 22
Example 3 Dual Cure Resin Formulation and Use in Additive Manufacturing
The components as shown in Table 5, except Chain Extenders, were added to a container and thoroughly mixed (either by an overhead stirrer or a centrifugation mixer such as THINKY™ mixer) to obtain a homogeneous resin. Then Chain Extenders were added to the resin and mixed for another 2-30 min depending on the volume and viscosity of the resin. The resin was formed by CLIP into D638 Type IV dog-bone-shaped specimens and 35 mm x 10 mm x 1 mm specimen for dynamic mechanical analysis followed by thermal curing at 120 °C for 8h. The cured elastomer specimens were tested following ASTM D412 on an Instron apparatus and with dynamic mechanical analysis at 1 Hz and at a heating rate of 2 °C/min. Dynamic performance of elastomers was evaluated through high strain-rate tensile testing or by forming a latticed geometry by CLIP and measuring dynamic stiffness with a drop tower at a range of impact energies or velocities. The latticed geometry would be 75x75x30 mm.
Table 5
Component Parts by weight
APBU ABPU-650g/mol-IPDI 47.53
Reactive Diluent DEGMA 20.54 Chain Extender MACM 4.80 Chain Extender JEFF AMINE® THF100 25.99 Pigment SpecraRay IJ UVD-J207 0.12 Initiator TPO 1.01
Chord Modulus (MPa) 10 Tensile Strength (MPa) 11 % Elongation at Break 356 Tan Delta (°C) 22
Example 4
Dual Cure Resin Formulation and Use in Additive Manufacturing The components as shown in Table 6, except Chain Extenders, were added to a container and thoroughly mixed (either by an overhead stirrer or a centrifugation mixer such as THINKY™ mixer) to obtain a homogeneous resin. Then Chain Extenders were added to the resin and mixed for another 2-30 min depending on the volume and viscosity of the resin. The resin was formed by CLIP into D638 Type IV dog-bone-shaped specimens and 35 mm x 10 mm x 1 mm specimen for dynamic mechanical analysis followed by thermal curing at 120
°C for 8h. The cured elastomer specimens were tested following ASTM D412 on an Instron apparatus and with dynamic mechanical analysis at 1 Hz and at a heating rate of 2 °C/min. Dynamic performance of elastomers was evaluated through high strain-rate tensile testing or by forming a latticed geometry by CLIP and measuring dynamic stiffness with a drop tower at a range of impact energies or velocities. The latticed geometry would be 75x75x30 mm.
Table 6
Component Parts by weight
Filler ORGASOL® 2001 EXD NAT 1 5
APBU ABPU-650g/mol-IPDI 45.54
Reactive Diluent DEGMA 18.84 Chain Extender MACM 4.60 Chain Extender JEFF AMINE® THF100 24.91 Pigment SpecraRay IJ UVD-J207 0.12 Initiator TPO 1.01
Chord Modulus (MPa) 11 Tensile Strength (MPa) 9 % Elongation at Break 376 Tan Delta (°C) 22
Fillers can increase stiffness without addition of hard segment or crosslinking while maintaining high strain-rate sensitivity. This leads to higher dynamic stiffness when compared to an unfilled sample. As shown in FIG. 3, though the materials of Example 4 and Example 3 show similar stiffness when measured at low strain rates, the dynamic stiffness is improved.
Example 5 Dual Cure Resin Formulation and Use in Additive Manufacturing
The components as shown in Table 7, except Chain Extenders, were added to a container and thoroughly mixed (either by an overhead stirrer or a centrifugation mixer such as THINKY™ mixer) to obtain a homogeneous resin. Then Chain Extenders were added to the resin and mixed for another 2-30 min depending on the volume and viscosity of the resin. The resin was formed by CLIP into D638 Type IV dog-bone-shaped specimens and 35 mm x 10 mm x 1 mm specimen for dynamic mechanical analysis followed by thermal curing at 120 °C for 8h. The cured elastomer specimens were tested following ASTM D412 on an Instron apparatus and with dynamic mechanical analysis at 1 Hz and at a heating rate of 2 °C/min. Dynamic performance of elastomers was evaluated through high strain-rate tensile testing or by forming a latticed geometry by CLIP and measuring dynamic stiffness with a drop tower at a range of impact energies or velocities. The latticed geometry would be 75x75x30 mm. Compression set testing was conducted by compressing a latticed specimen to 50% displacement and holding for 24 hours at 120°F. The sample was then removed from heat and from the fixture to let rest for 24 hours before measuring the height. Percent compression set = [(t0-tf)/t0] x 100, where tO is the height before compression and tf is the height after compression.
Table 7
Component Parts by weight
ABPU ABPU-650g/mol-IPDI 49.07
Reactive Diluent PEG600DMA 16 Reactive Diluent EGDMA 2 Chain Extender MACM 4.96 Chain Extender JEFF AMINE® THF100 26.84 Pigment SpecraRay IJ UVD-J207 0.12 Initiator TPO 1.01
Chord Modulus (MPa) 10 Tensile Strength (MPa) 11 Tan Delta (°C) 20 Compression Set 35% Example 6
Dual Cure Resin Formulation and Use in Additive Manufacturing
The components as shown in Table 8, except Chain Extenders, were added to a container and thoroughly mixed (either by an overhead stirrer or a centrifugation mixer such as THINKY™ mixer) to obtain a homogeneous resin. Then Chain Extenders were added to the resin and mixed for another 2-30 min depending on the volume and viscosity of the resin. The resin was formed by CLIP into D638 Type IV dog-bone-shaped specimens and 35 mm x 10 mm x 1 mm specimen for dynamic mechanical analysis followed by thermal curing at 120 °C for 8h. The cured elastomer specimens were tested following ASTM D412 on an Instron apparatus and with dynamic mechanical analysis at 1 Hz and at a heating rate of 2 °C/min. Dynamic performance of elastomers was evaluated through high strain-rate tensile testing or by forming a latticed geometry by CLIP and measuring dynamic stiffness with a drop tower at a range of impact energies or velocities. The latticed geometry would be 75x75x30 mm. Compression set testing was conducted by compressing a latticed specimen to 50% displacement and holding for 24 hours at 120°F. The sample was then removed from heat and from the fixture to let rest for 24 hours before measuring the height. Percent compression set = [(t0-tf)/t0] x 100, where tO is the height before compression and tf is the height after compression.
Table 8
Component Parts by weight
ABPU ABPU-650g/mol-IPDI 52.25
Reactive Diluent PEG600DMA 16
Reactive Diluent EGDMA 2
Chain Extender JEFF AMINE® T403 11.41
Chain Extender JEFF AMINE® THF 100 16.61
Pigment SpecraRay IJ UVD-J207 0.12
Initiator TPO 1.01
Chord Modulus (MPa) 12
Tensile Strength (MPa) 15
Tan Delta (°C) 22
Compression Set 5% Phase mixing from a trifunctional amine (JEFFAMINE® T403) provides good dynamic performance and greatly improves compression set, as shown in the data presented in FIG. 4 Example 7
Dual Cure Resin Formulation and Use in Additive Manufacturing
The components as shown in Table 9, except Chain Extenders, were added to a container and thoroughly mixed (either by an overhead stirrer or a centrifugation mixer such as THINKY™ mixer) to obtain a homogeneous resin. Then Chain Extenders were added to the resin and mixed for another 2-30 min depending on the volume and viscosity of the resin. The resin was formed by CLIP into D638 Type IV dog-bone-shaped specimens and 35 mm x 10 mm x 1 mm specimen for dynamic mechanical analysis followed by thermal curing at 120 °C for 8h. The cured elastomer specimens were tested following ASTM D412 on an Instron apparatus and with dynamic mechanical analysis at 1 Hz and at a heating rate of 2 °C/min. Dynamic performance of elastomers was evaluated through high strain-rate tensile testing or by forming a latticed geometry by CLIP and measuring dynamic stiffness with a drop tower at a range of impact energies or velocities. The latticed geometry would be 75x75x30 mm.
Table 9
Component Parts by weight
APBU ABPU-650g/mol-IPDI 5L7
Reactive Diluent DEGMA 10
Reactive Diluent PEG600DMA 3
Prepolymer Exothane 10 7
Chain Extender MACM 2.4
Chain Extender JEFF AMINE® T403 8.1
Chain Extender JEFF AMINE® THF-100 16.65
Pigment SpecraRay IJ UVD-J207 0.12
Initiator TPO 1.01
Chord Modulus (MPa) 12
Tensile Strength (MPa) 23
% Elongation at Break 260
Tan Delta (°C) 25
The non-blocked reactive prepolymer Exothane 10 (Esstech, Inc., Essington, Pennsylvania) provides a good balance of toughness and tensile strength. Secondary interactions and increased phase mixing between the non-blocked prepolymer and cured urethane/urea also provide high strain rate sensitivity, high dynamic stiffness, and low energy return. 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.