3D printing of internally transparent article

Abstract

To provide a material extrusion additive manufacturing method for producing a clear, internally transparent component composed of amorphous thermoplastic polymer layers with at least 0.1 mm thickness, and also an internally clear component made by the method, having an internal haze of less than 25%, less than 15%, less than 10% and even less than 5%.SOLUTION: A method creates a printed dot or line of amorphous thermoplastic polymer that remains at a high internal temperature for a long enough period of time to allow polymer chains in each layer to have mobility and fluidity, permitting sufficient inter-layer chain entanglements to reduce and eliminate layer lines. With a nearly 100% dense final component, voids are eliminated. The resultant printed article has a very high internal clarity, and can have a haze of less than 5%.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a material extrusion additive manufacturing method for producing clear, internally transparent parts composed of amorphous thermoplastic polymer layers at least 0.1 mm thick. The present invention also relates to internally transparent parts made by this method, with an internal haze of less than 25%, less than 15%, less than 10%, or even less than 5%. The method creates printed dots or lines of amorphous thermoplastic polymer that remain at a high internal temperature long enough to allow the polymer chains of each layer to be mobile and flowable, reducing sufficient interlayer chain entanglement and eliminating layer lines. A final part with nearly 100% density eliminates voids. The resulting printed article can have a very high internal transparency and a haze of less than 5%. [Background technology]

[0002] Advances in equipment and falling prices have led to widespread adoption of 3D printing in homes, schools, and industries as a fast, simple, and often inexpensive way to prototype and produce custom end-use parts. Specifically, material extrusion additive manufacturing 3D printing (also known as fused filament manufacturing or fused deposition modeling) has emerged as the tool of choice for direct-to-consumer, large-scale production, and rapid thermoplastic prototyping because it is the easiest to operate, produces the least waste, and has the shortest turnaround time of any 3D printing technique.

[0003] Many materials have been used to produce 3D printed products for a variety of end uses, from chocolate to collagen. Thermoplastic materials are particularly well suited for use in additive extrusion printers. Unfortunately, there have been few available thermoplastics that offer good mechanical properties, transparency, and ease of printing.

[0004] Polylactic acid (PLA) is widely used in desktop home printers due to its high printability and very low warpage. Unfortunately, its low service temperature, poor chemical stability, and yellowing (deterioration) during printing if not colored with dyes or pigments. Acrylonitrile butadiene styrene (ABS) is commonly used in 3D printing as a more stable "engineering" thermoplastic, which has a higher service temperature but has a higher warpage during printing, is not transparent, and has an elongation at break of less than 6% after printing. Polyethylene terephthalate glycol (PETG) and other copolyesters are very popular in the 3D printing industry due to its high service temperature and stability and improved printability like ABS, but has lower hardness and scratch resistance.

[0005] Acrylic polymers are well known for their clarity, brilliant colors, surface gloss, image depth, and weatherability. They have similar service temperatures to ABS. Unfortunately, the brittleness associated with acrylic polymers makes them impractical for creating filaments for use in extrusion additive 3D printing. Summary of the Invention [Problem to be solved by the invention]

[0006] The ability to 3D print transparent parts using thermoplastics has long been a goal of the 3D printing industry. However, despite the use of transparent materials, the act of material extrusion type 3D printing typically adds numerous polymer layer-air and / or polymer line-air interfaces that make the printed part hazy and not transparent. While exterior layer / line interfaces can be reduced by surface polishing or coating, interior layer / line interfaces cannot be easily removed.

[0007] Recently, it has been reported that "transparent" parts have been 3D printed with ABS, copolyester, and PETG filaments. The parts are usually very small and exhibit yellowing, bubbles, or cloudiness. Also, the parts are usually printed at very low layer heights (0.05 mm) and slow speeds, which results in a very long time to produce the parts. At higher layer heights or faster speeds, the resulting parts no longer appear transparent. Also, there has been no demonstration of using acrylic filaments to date. This is likely due to the difficulty of processing traditional acrylic filaments in material extrusion type 3D printers. [Means for solving the problem]

[0008] It is necessary to 3D print transparent articles with a practical layer height of at least 0.1 mm while maintaining an extrusion speed of at least 15 mm / s. Since extrusion speeds above 50 mm / s tend to cause very inaccurate printing, it is preferable to increase the layer height to reduce printing time. Surprisingly, it has been found that by properly selecting the composition, Tg, additives, and optimizing the printing process conditions (minimum fan / active cooling, build plate temperature, build chamber adjusted to the transition temperature of the material, and setting the layer height), internal transparent polymer parts can be produced with haze less than 20%, preferably less than 15%, preferably less than 10%, and as low as less than 5% of the normal layer height without reducing the printing speed. Materials and printing conditions are selected such that each printed polymer dot is maintained at a temperature of at least 25°C, more preferably 45°C, 55°C above the material Tg for at least 10, 15 or even 20 minutes, which provides mobility and flow to the polymer, layer entanglement of the polymer chains, reduction and elimination of layer lines and bubbles, and provides very high internal transparency with haze of less than 10% and 5%.

[0009] In addition to the high transparency of 3D printed parts due to the fusion of the different layers, the same fusion increases the strength of the 3D printed article in the Z direction and produces parts with minimized internal stresses. It also produces parts without internal layer lines or defects, making it suitable for opaque applications such as light diffusers and mechanically demanding parts. In such parts, color transmission is also improved.

[0010] The present invention relates to an additive manufacturing material extrusion printing process having the following steps: a) selecting an amorphous thermoplastic polymer matrix composition having a particular overall Tg; b) selecting conditions sufficient to provide an internal temperature of the composition, wherein the Tg of the entire composition is at least 20° C., more preferably at least 30° C., more preferably at least 40° C., or even at least 50° C., or even 60° C., lower than the internal temperature; c) 3D printing the amorphous thermoplastic polymer to form an article; wherein the temperature difference between the Tg of the amorphous thermoplastic polymer and the internal temperature is maintained for at least 5 minutes, preferably at least 10 minutes, more preferably at least 15 minutes, and most preferably at least 20 minutes after printing.

[0011] In a second aspect of the invention, a material extrusion process includes selecting conditions to provide a desired internal temperature selected from one or more of the following: a) selecting a build plate temperature higher than the Tg of said amorphous thermoplastic polymer composition, more preferably at least 10° C. higher than the Tg of said amorphous thermoplastic polymer composition, most preferably at least 20° C. higher; in another embodiment, the build plate temperature can also be provided as a percentage higher than the Tg of said amorphous thermoplastic polymer composition, which is at least 10% higher than the Tg of said amorphous thermoplastic polymer composition, preferably 10-50% higher, more preferably at least 20% higher, more preferably at least 30% higher, or even 40% or more higher than the Tg of said amorphous thermoplastic polymer composition; b) selecting a heated chamber temperature at least 20° C., preferably at least 30° C., preferably at least 40° C., and most preferably at least 50° C. above the Tg of said composition; c) the use of radiant heating sources to supplement heat during printing; d) Little or no fans or active cooling; e) Printing speed of 25mm / s; f) the use of selected additives in the composition to lower the Tg of the composition or to help maintain the temperature of the composition over an extended period of time;

[0012] In a third aspect of the invention, in the additive manufacturing process of any of the previous aspects, the amorphous thermoplastic polymer composition comprises a polymer selected from the group including, but not limited to, (meth)acrylic polymers, copolyesters, polycarbonates, polyamides, polyhydroxyalkanoates, amorphous polyamides, and poly(styrene-co-maleic anhydride).

[0013] In a fourth aspect of the invention, the additive manufacturing process of any of the previous aspects comprises an amorphous thermoplastic polymer composition having a Tg of less than 160°C, preferably less than 150°C, preferably less than 140°C, preferably less than 130°C, preferably less than 120°C, preferably less than 114°C, preferably less than 104°C, preferably less than 94°C, more preferably less than 80°C, and most preferably less than 75°C.

[0014] A fifth aspect of the invention is the additive manufacturing process of any of the previous aspects, wherein the amorphous thermoplastic polymer composition is selected from the group consisting of: a) a copolymer having the required Tg; b) a blend of a polymer having a Tg greater than 140° C. and a low viscosity polymer; c) A blend of a polymer having a Tg greater than 140° C. with an additive capable of lowering the Tg or increasing the open time of the polymer composition, where the open time is the time allowed for continuous molten polymer lines to fuse and / or intertwine.

[0015] In a sixth aspect of the invention, the additive manufacturing process of any of the previous aspects employs an amorphous thermoplastic polymer composition further comprising an impact modifier at a level of 5 to 60 wt%, based on the weight of the total composition.

[0016] In a seventh aspect of the invention, in the additive manufacturing process of any of the previous aspects, the amorphous thermoplastic polymer composition temperature is provided and / or maintained by one or more means selected from the group consisting of: a) low or no fans or active cooling; b) a heated build plate; c) a heated chamber; and d) a radiative heat source.

[0017] In an eighth aspect of the invention, the additive manufacturing process of any of the previous aspects produces a 3D printed article having a packing density of 99% or greater.

[0018] In a ninth aspect of the invention, the additive manufacturing process of any of the previous aspects includes an amorphous thermoplastic polymer composition that is an acrylic polymer.

[0019] In a tenth aspect of the invention, in the additive manufacturing process of any of the previous aspects, the amorphous thermoplastic polymer composition is printed with a layer height of 0.05 mm or more, 0.1 mm or more, 0.2 mm or more, 0.3 mm or more, 0.4 mm or more.

[0020] In another aspect of the invention, internally transparent 3D printed articles are formed, said articles being printed with a deposition layer thickness of 0.1 mm or more, preferably 0.2 mm or more, preferably 0.3 mm or more, preferably 0.4 mm or more, and having an internal haze of less than 25%, preferably less than 20%, preferably less than 10%, preferably less than 5%.

[0021] In another aspect of the invention, the 3D printed article comprises an acrylic composition, a copolyester, an amorphous polyamide, or a polycarbonate. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 shows a schematic diagram of the test used in Example 1. [Diagram 2] FIG. 2 is an IR image of Example 3. [Diagram 3] FIG. 3 is an IR image of Example 3. [Figure 4] FIG. 4 shows the biextruded block of Example 4. [Diagram 5] FIG. 5 shows the biextruded block of Example 4. [Figure 6] FIG. 6 shows the rheological curve of the sample of Example 1. [Figure 7] FIG. 7 shows the rheological curve of the sample of Example 1. [Figure 8] FIG. 8 shows the rheological curve of the sample of Example 1. [Figure 9] FIG. 9 shows the rheological curve of the sample of Example 1. [Figure 10] FIG. 10 shows the rheological curve of the sample of Example 1. [Figure 11] FIG. 11 shows the rheological curve of the sample of Example 1. [Figure 12] FIG. 12 is a thermal image of the part of Example 6. [Figure 13] FIG. 13 is a thermal image of the part of Example 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The present invention relates to a method for producing clear, internally transparent parts from amorphous thermoplastic polymers composed of layers at least 0.1 mm thick. The present invention also relates to internally transparent parts made by this method having an internal haze of less than 25%, less than 15%, less than 10% or even less than 5%.

[0024] All cited references are incorporated herein by reference. As used herein, percentages shall mean weight % unless otherwise stated. Molecular weight is weight average molecular weight measured by GPC. When the polymer contains some crosslinking and GPC is not applicable due to insoluble polymer fraction, the molecular weight of soluble fraction / gel fraction or soluble fraction after extraction from gel is used.

[0025] "Copolymer" is used to mean a polymer having two or more different monomeric units. "Polymer" is used to mean both homopolymers and copolymers. Polymers can be linear, branched, star, comb, block, or other structures. Polymers can be homogeneous, heterogeneous, and can have a gradient distribution of comonomer units.

[0026] (Meth)acrylic or (meth)acrylate means both methacrylic and acrylic, or methacrylate and acrylate.

[0027] Tg is used as a surrogate measurement of the transition temperature, the temperature at which a material changes from liquid to solid, as seen in rheology. The transition temperature is the point at which the logarithmic slope of the viscosity versus temperature change changes from liquid-like behavior to solid-like behavior according to the Arrhenius equation. This transition point is obtained by measuring the viscosity versus temperature of the material at low shear from the molten phase to room temperature. For example, a transition temperature of 10°C lower, preferably 20°C lower, even more preferably 25°C lower, 30°C lower than the internal temperature of the part being printed (approximately 135°C for current technology when printed on a heated build plate at 120°C without a heated chamber and with minimal fans) is desired. The Tg of many acrylic materials is approximately 25°C lower than the transition temperature. In other words, Tgs below 104°C, 94°C, 84°C, and 75°C, but above 60°C, are preferred for materials printed at room temperature on a build plate heated to 120°C. When using a heated chamber, materials with higher Tg can be used due to the higher internal temperature of the part. Similarly, if a hotter heated build plate is used, a material with a higher Tg can be used. The glass transition temperature of a polymer is measured by DSC according to the standard ASTM E1356.

[0028] The first G' / G" crossover temperature refers to the first temperature, measured at low shear by parallel plate rheology, at which G' is greater than G". This is where the storage modulus G', i.e., elastic response, becomes greater than the loss modulus G", i.e., viscous response, as the material transitions from the molten state to room temperature. Generally speaking, the dynamic modulus is a measure of the viscoelastic properties of a material (storage modulus G', i.e., elastic response, and loss modulus G", i.e., viscous response). At the crossover temperature (G'=G"), the elastic modulus at lower temperatures dominates the viscous response and can therefore be considered the onset of hardening. Without being bound by theory, it is believed that the higher the first G' / G" crossover temperature, the better the material will be able to hold its shape when immersed in heat.

[0029] The transparency processing window is defined as the temperature difference between the first G' / G" crossover temperature and the LS transition temperature. Characterizing this window as a reference for transparent printing is particularly useful when the Tg of the printing material does not serve as a direct proxy for the transition temperature and / or cannot be constructively manipulated to serve as a surrogate.

[0030] Additive manufacturing or additive manufacturing process as used herein refers to melt extrusion printing or deposition of molten thermoplastics, also known as 3D printing.

[0031] Transmittance and haze are measured according to ASTM D1003 using a BYK-Gardner Haze-Gard machine.

[0032] There are several factors that can be selected to provide material properties, open times, and internal environmental conditions to allow the polymer chains of each printed layer dot / line to interact and intertwine with the polymer chains of adjacent printed dots, which are discussed below.

[0033] material composition To obtain a lower Tg overall composition, one can a) select a polymer or copolymer with the desired Tg, b) blend a high Tg polymer with a compatible low Tg, low viscosity, or c) blend a high Tg polymer with additives such as plasticizers.

[0034] Polymer Matrix The polymer matrix of the present invention is an amorphous polymer. Semi-crystalline and crystalline polymers contain crystalline regions that are known to diffract light and increase haze. Useful polymers of the present invention include, but are not limited to, (meth)acrylics, copolyesters, polycarbonates, and amorphous polyamides. The present invention is illustrated using (meth)acrylic polymers and amorphous polyamides, but one skilled in the art can apply the present invention to other amorphous polymers using the explanations and examples provided herein. The matrix polymer is preferably a single polymer with a single Tg, but it is also possible to use polymer blends or block copolymers with two or more Tgs. In the case of a matrix with two or more polymers or blocks with two or more Tgs, the lower Tg is referred to herein as the Tg of the matrix polymer. Note that this refers to the polymer matrix and does not refer to other polymer additives that may also be present in the composition, such as impact modifiers. The matrix polymer is the continuous phase of the composition.

[0035] As used herein, "acrylic polymer" is meant to include polymers, copolymers, and terpolymers formed from alkyl methacrylate and alkyl acrylate monomers, as well as mixtures thereof. The alkyl methacrylate monomer is preferably methyl methacrylate, which may comprise 50-100% of the monomer mixture. Other acrylate and methacrylate monomers, or 0-50% of other ethylenically unsaturated monomers, including but not limited to styrene, alpha methyl styrene, acrylonitrile, and low levels of crosslinkers, may also be present in the monomer mixture. Other methacrylate and acrylate monomers useful in the monomer mixture include, but are not limited to, methyl acrylate, ethyl acrylate and ethyl methacrylate, butyl acrylate and butyl methacrylate, isooctyl methacrylate and acrylate, n-octyl acrylate, lauryl acrylate and methacrylate, stearyl acrylate and stearyl methacrylate, isobornyl acrylate and methacrylate, methoxyethyl acrylate and methacrylate, 2-ethoxyethyl acrylate and methacrylate, isodecyl acrylate and methacrylate, tertiobutylcyclohexyl acrylate and methacrylate. , tertiobutylcyclohexanol methacrylate, trimethylcyclohexyl acrylate and methacrylate, methoxypolyethylene glycol methacrylate and acrylate having 2-11 ethylene glycol units, pentoxyethyl acrylate and methacrylate, alkoxylated phenol acrylate, ethoxylated phenyl acrylate and methacrylate, epoxypropyl methacrylate, tetrahydrofurfuryl acrylate and methacrylate, alkoxylated tetrahydrofurfuryl acrylate, cyclic trimethylolpropane formal acrylate, carprolactone acrylate, dimethylaminoethyl acrylate, and methacrylate monomers. Alkyl (meth)acrylic acids or their C1-C8 esters, such as methacrylic acid and acrylic acid, may be useful in the monomer mixture.Most preferably, the acrylic polymer is a copolymer having 70-99.5% by weight of methyl methacrylate units and 0.5-30% by weight of one or more Cl-8 linear or branched alkyl acrylate units.

[0036] The acrylic polymer has a weight average molecular weight of 50,000 g / mol to 500,000 g / mol, preferably 55,000 g / mol to 300,000 g / mol, preferably 75,000 g / mol to 200,000 g / mol. Use of acrylics having lower weight average molecular weights within this range has been found to result in increased density, increased clarity and reduced warping of the material extruded additive printed article.

[0037] Preferably, the acrylic polymer contains little or no very high molecular weight fraction of polymer, with less than 5% by weight, preferably less than 2% by weight, of the acrylic polymer having a molecular weight greater than 500,000 g / mol.

[0038] In another embodiment, the acrylic polymer comprises a blend of two or more of the polymers described in the above two embodiments.

[0039] The acrylic polymers can be formed by any known means, including, but not limited to, bulk polymerization, emulsion polymerization, solution polymerization, and suspension polymerization.

[0040] Acrylic Copolymer: The acrylic copolymers of the present invention have a Tg of less than 160°C, preferably less than 150°C, preferably less than 140°C, preferably less than 130°C, preferably less than 120°C, preferably less than 114°C, preferably less than 104°C, preferably less than 95°C, preferably less than 85°C, more preferably less than 75°C, and greater than 50°C, preferably greater than 55°C, more preferably greater than 60°C.

[0041] In one preferred embodiment, at least 40% by weight, preferably at least 50% by weight, and most preferably at least 60% by weight of the monomer units in the acrylic copolymer are methyl methacrylate monomer units. The comonomers selected for the acrylic copolymer can be (meth)acrylic monomers, non-(meth)acrylic monomers, or mixtures thereof.

[0042] In one preferred embodiment, the acrylic copolymer is composed of more than 90% by weight, more than 95% by weight, and most preferably 100% by weight of acrylic monomer units. Low Tg acrylic monomers that can be copolymerized to reduce the Tg of the copolymer to a specified level include, but are not limited to, methyl acrylate, ethyl acrylate, butyl acrylate, ethylhexyl acrylate, hydroxyl ethyl acrylate, hydroxyl propyl acrylate, hydroxyl butyl acrylate, hexyl methacrylate, n-octyl acrylate, lauryl methacrylate, and butyl methacrylate. These monomers are added at a high enough level to reduce the Tg to less than 95°C, 85°C, preferably less than 80°C, and more preferably less than 75°C. Tg can be easily calculated using the Fox equation and measured by DSC, as is well known in the art. For example, a 70% by weight methyl methacrylate (MMA) / 30% by weight ethyl acrylate composition has a Tg of about 75°C.

[0043] Low Tg copolymers tend to have lower viscosities than high Tg polymers, although other factors such as molecular weight and branching also affect viscosity. Impact modifiers can be, and preferably are, added to the composition to improve impact strength and also increase melt flow viscosity.

[0044] Although the acrylic composition of the present invention may be free of impact modifiers, in a preferred embodiment, in order to avoid becoming too brittle, the acrylic composition of the present invention includes one or more types of impact modifiers. Preferably, the acrylic composition includes impact modifiers at a level of 5-60% by weight, preferably 9-40% by weight, more preferably 20-35% by weight, based on the total composition. The impact modifier can be any impact modifier that is compatible, miscible, or semi-miscible with the acrylic composition, as known in the art. Useful impact modifiers include, but are not limited to, linear block copolymers, and both soft-core and hard-core core-shell impact modifiers. In a preferred embodiment, the impact modifier has an acrylic block or an acrylic shell.

[0045] Without being bound to a particular theory, it is believed that the impact modifiers provide elongation, flexibility, and toughness.

[0046] In a preferred embodiment, the impact modifiers of the present invention are multi-stage, continuously manufactured polymers having at least a three-layer core / shell particle structure consisting of a hard core layer, one or more intermediate elastomeric layers, and a hard shell layer. The presence of the hard core layer provides a desirable balance of good impact strength, high modulus, and excellent UV resistance not achieved with core / shell modifiers having a soft core layer.

[0047] The hard core layer (Tg>0°C, preferably Tg>20°C) is typically a single composition polymer, but may also contain a small amount of a combination of low Tg seeds on which the hard core layer is formed. The hard core layer may be selected from any thermoplastic that meets the Tg requirements. Preferably, the hard core layer is composed primarily of methacrylate ester units, acrylate ester units, styrenic units, or mixtures thereof. Preferably, the acrylate ester units are selected from methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, and octyl acrylate. The styrenic units include styrene and its derivatives, such as, but not limited to, alpha methyl styrene, para methyl styrene, and the like. In one embodiment, the hard core layer is all acrylic.

[0048] The intermediate layer or layers are elastomeric and have a Tg below 0°C, preferably below -20°C. Preferred elastomers include polymers and copolymers of alkyl acrylates, dienes, styrenics and mixtures thereof. Preferably, the soft intermediate layer is composed primarily of acrylate ester units. The shell layer can be made of one or more shell layers having a Tg>0°C, more preferably a Tg>20°C. The shell layer can be of the same or different composition as the hard core layer.

[0049] Preferably, the multi-stage polymer is a three-stage composition, the stages being present in the range of 10-40% by weight, preferably 10-20%, of a first stage (a), 40-70%, preferably 50-60%, of a second intermediate stage (b), and 10-50%, preferably 20-40%, of a final stage (c), all percentages being based on the total weight of the polymer particles of the three stages.

[0050] In one embodiment, the core layer is a crosslinked polymethyl methacrylate-ethyl acrylate copolymer, the intermediate layer is a crosslinked polybutyl acrylate-styrene copolymer, and the outer shell is a polymethyl methacrylate-ethyl acrylate copolymer.

[0051] Multi-stage polymers can be made by any known technique for preparing polymers produced sequentially in multiple stages, for example, by emulsion polymerizing the next stage mixture of monomers in the presence of a preformed polymer product. As used herein, the term "sequential emulsion polymerization" or "sequential emulsion production" refers to a polymer prepared in an aqueous dispersion or emulsion, in which a subsequent monomer charge is polymerized on or in the presence of a preformed latex prepared by polymerization of the previous monomer charge and stage. In this type of polymerization, the subsequent stage is connected to and closely related to the preceding stage.

[0052] In a preferred embodiment, the refractive index of the core / shell particles is matched to the overall refractive index of the matrix made of the acrylic polymer composition, meaning that the refractive index of the core / shell particles should be within 0.03 units, preferably within 0.02 units, of the matrix polymer.

[0053] In one preferred embodiment, the impact modifier is selected to have minimal impact on increasing the viscosity of the low Tg acrylic composition. Highly efficient impact modifiers with high rubber content allow lower loading and therefore have less impact on increasing the viscosity of the composition. Arkema's self-assembling Nanostrength® block copolymers also have less adverse effect on the viscosity of the composition.

[0054] Acrylic Alloy An alternative approach to providing an overall low Tg acrylic composition involves alloy blending one or more higher Tg acrylic polymers with one or more lower Tg (lower melt flow) polymers, as described in WO2017 / 210,286.

[0055] The low melt viscosity polymer in the acrylic alloy composition must be compatible, semi-miscible, or miscible with the acrylic polymer. The low melt viscosity polymer and the acrylic polymer must be blendable in a ratio such that a single intimate mixture is produced without separation into separate bulk phases. As used herein, "low melt viscosity polymer" refers to a polymer that has a melt flow rate of greater than 10 g / 10 min, preferably greater than 25 g / 10 min, as measured by ASTM D1238 at 230°C / 10.4 kg force.

[0056] In one embodiment, the low melt viscosity polymer is a low molecular weight acrylic polymer or copolymer, which meets the high melt flow criteria. The low molecular weight acrylic polymer has a weight average molecular weight of less than 70,000, preferably less than 50,000, more preferably less than 45,000, or even less than 30,000 g / mol. Acrylic copolymers are preferred, with copolymers having a Tg of less than 100°C, and less than 90°C being preferred for increased flexibility.

[0057] In a preferred embodiment, the low melting polymer of the present invention is a polymer other than an acrylic polymer. Non-acrylic low melting polymers of the present invention include, but are not limited to, polyesters, cellulosic esters, polyethylene oxides, polypropylene glycols, polyethylene glycols, polypropylene glycols, polyhydroxyalkanoates, styrene-acrylonitrile copolymers, polyvinyl chloride, polyvinyl acetate, polyvinyl alcohol, ethylene-vinyl acetate copolymers, polyvinylidene fluoride and its copolymers, olefin-acrylate copolymers, olefin-acrylate-maleic anhydride copolymers, maleic anhydride-styrene-vinyl acetate copolymers, and mixtures thereof.

[0058] Useful polyesters include, but are not limited to, poly(butylene terephthalate), poly(ethylene terephthalate), polyethylene terephthalate glycol, and polylactic acid. A preferred polyester is polylactic acid.

[0059] Useful cellulosic esters include, but are not limited to, cellulose acetate, cellulose triacetate, cellulose propionate, cellulose acetate propionate, cellulose acetate butyrate, and cellulose acetate phthalate.

[0060] In one embodiment, the low melt viscosity polymer has a weight average molecular weight higher than the entanglement molecular weight of the polymer, as measured by gel permeation chromatography.

[0061] The low melt viscosity polymer comprises 5 to 60% by weight, preferably 9 to 40% by weight, of the total alloy composition.

[0062] Acrylic Blends with Non-Polymers A third method to provide an overall acrylic composition with a low Tg is to blend a higher Tg acrylic polymer with one or more compounds known to lower the Tg, such as, but not limited to, plasticizers. The additive compound must be compatible, miscible, or semi-miscible with the acrylic polymer. Tg lowering additives are typically added at 2-40% by weight, preferably 4-20% by weight, based on the weight of the acrylic polymer.

[0063] In one embodiment, a useful class of plasticizers are specialty epoxides such as 1,2 dihydroxyalkanes having a molecular weight greater than 200 g / mole or vegetable oil polyols having a molecular weight greater than 200 g / mole, as described in PCT / US2019 / 012241.

[0064] In another embodiment, phthalate esters such as di(2-ethylhexyl) phthalate, diisononyl phthalate, diisodecyl phthalate, and diisooctyl phthalate can be used.

[0065] In another embodiment, adipate salts (such as, but not limited to, di(2-ethylhexyl) adipate) can be used.

[0066] viscosity The polymer composition of the present invention has a viscosity of 230° C. for 1 second when measured using a rotational viscometer according to ASTM C965. -1 and a viscosity of less than 100,000 Pa·s, preferably less than 20,000 Pa·s, preferably less than 10,000 Pa·s, at a shear of 100 s. -1 The polymer has a viscosity of 20-2000 Pa·s, preferably 25-1,000 Pa·s, and more preferably 30-500 Pa·s at a shear rate of 100° C. This viscosity is useful for 3D printing the composition and also provides the composition with a sufficient flowability at internal temperatures to allow fusion of polymer chains in adjacent layers.

[0067] Once the composition is printed, the viscosity of the printed dot / line of the amorphous thermoplastic polymer composition remains constant for at least 5, preferably 10, preferably 15, preferably 20, preferably 25 minutes after printing, at least 1 second. -1 The viscosity is maintained at less than 200,000 Pa·s, preferably less than 100,000 Pa·s, and more preferably less than 50,000 Pa·s, at a shear of 100,000 Pa·s.

[0068] Printed Part Density To most effectively eliminate small gaps that scatter light, the density of the final part should be at least 95%, preferably 98%, and preferably 99% of the bulk density of the polymer as measured by ASTM D792. High density is achieved by overfilling the print by 1-10%, combined with temperature conditioning to allow the composition to flow. This provides time and a low enough viscosity to allow air pockets to be eliminated.

[0069] An added benefit of using internally dense parts and fusing the internal layer lines is improved mechanical performance in the Z direction. The process of printing internally transparent parts also produces parts that are near isotropic.

[0070] Layer Height As known in the art, layer height is the thickness of a component layer in the Z direction as it is deposited in the XY direction by an extruder. Due to the viscosity of the polymer, the traces deposited within the layer have a geometric stadium cross section (also known as mismatch angles). The rounded edges of the polymer traces create inter-raster and inter-layer voids that scatter light as it passes through the printed object. In addition, the rounded outer layers act as tiny lenses, further scattering the light. This light scattering causes a moderate decrease in transmission and a significant increase in the haze of the print (both measured according to ASTM D1003).

[0071] At very low layer heights (0.05mm), it has been shown that FFF printing can produce somewhat transparent parts. By printing at these very low layer heights, the nozzle is able to reheat the material and remove any internal voids that would otherwise be present. To appear transparent, the outer part surface must be ground and polished. Unfortunately, thinner layers significantly increase print times, a simple 10cm tall object would require 2,000 individual layers. If this object were a simple 1000cm cube, the individual layers would each take about 20 minutes to print at a print speed of 25mm / s, resulting in a final print time of about 27 days. Thin layer heights result in unacceptably long print times, since it is not possible to increase the rate at which the layers are deposited without significantly sacrificing accuracy. As layer heights increase, the transparency of the part decreases significantly. Through manipulation of process parameters and modification of the rheological properties of the resin, it was possible to overcome these limitations and print transparent parts with layer heights down to 0.4mm.

[0072] printing speed The main parameter used to control the speed of movement of the print head is usually called the printing speed. In the preferred embodiment, the printing speed is greater than 10 mm / s, preferably greater than 15 mm / s, and most preferably greater than 20 mm / s. However, it is preferably less than 55 mm / s. Improvements beyond this point do not result in significant reductions in printing time, since the printing speed only controls the maximum speed of the nozzle in the XY plane, and both the nozzle acceleration and jerk are limited. These limitations vary depending on the printer and its configuration. Furthermore, extrusion speeds above 75 mm / s tend to be very inaccurate due to the inertia of the fluid polymer during deposition.

[0073] Printer design For material extrusion additive manufacturing 3D printing, the printer typically has a heated build plate, between 50-150°C (preferably 60°C or higher, more preferably 75°C or higher). The printer includes one or more heated nozzles through which material is extruded. These nozzles can generally reach 200°C (preferably 250°C, more preferably 300°C or higher). The printer includes a build environment that is open to ambient conditions or enclosed. The printer may include additional controls, such as an actively heated or cooled build environment. The printer may include radiant or forced convection heating elements within the open or enclosed build space to raise or maintain the temperature of internal components.

[0074] The printer may be equipped with a mixing head that combines multiple ingredients, such as a Diamond Hotend, where any of the ingredient compositions, or the final composition after mixing, meets the specifications described herein. In another embodiment, the printer is fed multiple compositions that are combined directly in the print head of a pellet extruder, where either the compositions or the final mixed composition meets the specifications described herein.

[0075] Printing temperature, internal temperature Printing temperature, or internal temperature, as used herein, is meant to define the temperature of the printed material composition after it passes through the printer nozzle and is deposited on the build plate. This is also called internal temperature and should not be confused with nozzle temperature. The printed material constitutes the dots of the printed layer, and the associated printing temperature decreases as the material cools. The internal temperature must be at least 20°C, more preferably at least 30°C, more preferably at least 40°C, or even at least 50°C, or even 60°C, higher than the Tg of the printed composition for a specified time after the material is deposited. The internal temperature can be influenced by several factors, including but not limited to: the printer nozzle temperature, the temperature of the build plate, the ambient temperature in the surrounding or heated chamber, the fan or active cooling rate, and added radiant or convective energy.

[0076] Nozzle Temperature The nozzle temperature is easily adjustable. Because the polymer composition is in contact with the nozzle for a short period of time, the nozzle temperature has only a small effect on the internal temperature, especially over time. The nozzle temperature serves to add heat to each layer with the build-up of each additional layer. The nozzle is typically heated to 170°C to 300°C, preferably 210°C to 240°C. Preferably, the nozzle is set near the upper processing temperature limit of the material.

[0077] Build Plate Temperature The build plate helps to keep the internal temperature of the print higher. The effect of a heated build plate on the temperature of the part can be observed 10, 20, 30, or even 40 layers above the plate. This is because it provides a continuous supply of heat to the interior of the printed article. A heated build plate also helps to reduce warping.

[0078] The build plate should be set above the Tg of the polymer composition, preferably up to 10° C., even 20° C., 25° C., and 30° C. above the polymer composition Tg. Alternatively, the build plate can be set as a percentage above the Tg of the composition, preferably 10%, 20%, 30%, 40% above the Tg, as measured in degrees Celsius.

[0079] High build plate temperatures surprisingly had the unexpected effect of allowing transparent parts to be printed while still printing thicker individual layers. At thicker layer heights, all previous methods showed a dramatic increase in optical haze. By setting the heated build plate at temperatures well above the material's Tg, we were able to print 3.2mm thick plaques with less than 10% internal haze at layer heights of 0.2mm, 0.3mm, and even 0.4mm (see examples 1 and 2).

[0080] Due to the high build plate temperature and lack of cooling fans / active cooling, the most recently printed layers can maintain their temperature and mobility of about 6 mm on the top layer of the printed surface. At a given print speed, this means about 20 minutes before a given layer cools below a temperature that significantly reduces flowability. The part becomes internally transparent due to the increased flowability caused by the higher internal temperature, but the initial G' / G" crossover temperature is high (190°C) so that the material solidifies sufficiently to achieve more complex shapes. In essence, the material composition selected in accordance with the present invention can be maintained for a sufficient time in the transparent processing temperature range to provide a transparent part while maintaining good part geometry definition.

[0081] Heated chamber The use of a heated chamber allows the part to cool slower and have a higher internal temperature, allowing the use of higher Tg materials. The chamber temperature should be selected to be higher than ambient temperature and lower than the Tg of the polymer composition. Chamber temperatures above 30°C, 40°C, 50°C, and preferably above 60°C can be useful. However, parts with good internal transparency can be 3D printed at ambient temperatures with careful selection of the composition's Tg and build plate temperature.

[0082] Radiant Energy In one embodiment, the heat at the printing point can be supplemented by a radiant energy source, such as an infrared heater.

[0083] Parts Cooling Fan To increase the internal temperature of the print, the active part cooling system (usually a fan) is turned off or disabled during printing. In a preferred embodiment, this system consists of one or more radial or axial fans with variable speed control. In another embodiment, a system that directs the airflow using a series of valves or ducts can be set up so that the airflow is directed away from the print. In another embodiment, the airflow is preheated, so that the airflow interacting with the printed part does not cause significant cooling and can potentially actively heat the part. Other forms of forced convection heating instead of cooling may also be considered.

[0084] Layer Height It is known that lowering the layer printing height to 0.05mm or less improves the transparency of the printed part. This is mainly due to the increased amount of heat added to each printed layer as the heat from the nozzle is constantly renewed. Unfortunately, the increased printing and heat can also lead to polymer degradation and yellow or brown coloration. In the present invention, parts can be printed using layer heights of 0.1mm, 0.2mm, 0.3mm, and even 0.4mm while achieving internal haze of less than 15%, less than 10%, and even less than 5%.

[0085] time A key parameter for achieving good clarity in the print is that a high positive differential T (the temperature of the printed material minus the Tg of the material) is maintained for more than 5 minutes, preferably at least 10 minutes, at least 15 minutes, and more preferably at least 20 minutes. This longer time frame at elevated temperatures above the material Tg provides time and fluidity for polymer chains to fuse with adjacent polymer chains, thus reducing or eliminating print lines in the article.

[0086] The long temperature differential time is provided by a large positive initial differential T, near 100% packing density, and build plate and chamber temperatures to reduce heat dissipation from the article.

[0087] In one embodiment, low levels of a phase change material, such as a phase change polymer, can be added to help maintain the temperature of the print.

[0088] Material Extrusion Additive Process The amorphous thermoplastic polymer compositions of the present invention are used as powders or pellets and, in a preferred embodiment, are formed into filaments, typically by an extrusion process.

[0089] The compositions are 3D printed with a material extrusion (fused deposition modeling, fused filament manufacturing) type 3D printer, with or without filaments (diameter of any size, including 1.75 mm, 2.85 mm or other sizes), with any size nozzle (one that can use filaments, pellets, powders or other forms of acrylic composition), at any speed. The 3D printing of the present invention is not a laser sintering process. The compositions can be made into filaments for such purposes. They can also be sprayed with a spray nozzle (sprayed molten plastic) onto the surface to be printed, such as by the Arburg Freeformer technique.

[0090] A general description of the printing process includes the following steps: Feed filaments, pellets, or powder of the polymer composition into a material extrusion printer. The printer's computer controls are set to provide a set amount of material flow and place printed lines at specific intervals. The machine feeds the polymer composition into a heated nozzle at a set rate, and the printer moves the nozzle to the appropriate position to deposit the set amount of polymer composition.

[0091] In a preferred embodiment, the polymer has a low shear melt viscosity as described above. The printer has a heated build plate, generally between 50-150°C (preferably above 60°C, more preferably above 75°C). The printer has one or more heated nozzles through which the material is extruded. The printer has a build environment that is open to ambient conditions or enclosed.

[0092] In one preferred embodiment, the 3D printer is programmed to operate with a slight overflow (also known as overfill) of 1% to 10% overflow. This means that the amount of polymer composition dispensed by the printer is greater than the calculated amount needed for the 3D article being formed. The overflow packs the acrylic composition more tightly, increasing part density while enhancing the strength, mechanical, and optical properties of the printed article. The overflow can be set in two different ways. In the first method, the software is set to dispense a higher percentage of material to the nozzle than would normally be needed. In the second method, the software is set to narrow the spacing between the rows, creating overlaps in the rows, resulting in excess material being printed on the article.

[0093] The process parameters of the 3D printer can be adjusted to produce 3D printed parts with optimal strength and elongation with minimal shrinkage and warpage. The use of the selected process parameters applies to any extrusion / fusion 3D printer, preferably filament printing.

[0094] Other process conditions improve the open time of the printed article and provide excellent clarity and Z-physical properties. These include increasing the temperature of the printer's build plate and / or build chamber. For best results, it is believed that the internal temperature of the print should be at least 25° C. higher than the Tg of the material, more preferably at least 35° C., more preferably at least 45° C., more preferably at least 55° C., or even 65° C. or 75° C. higher than the Tg of the polymer composition. In a preferred embodiment, the external shell of the printed article needs to be sufficiently hard and cool fast enough for some part resolution, while the internal temperature is as high as possible.

[0095] Transparent Material Extrusion Additive Process : In one embodiment, the 3D printer is programmed to turn off the part cooling fan and run the extrusion nozzle at a slightly slower speed than the normal printing speed (25 mm / sec) to allow the part to retain more heat. The 3D printer is set to extrude very thin layers with a layer height of 0.05 mm. The 3D printer is operated with a slight overflow of 1% to 10% to fill the voids between layers. The build plate is set near or slightly above the Tg of the material and the nozzle is set near the upper processing temperature limit of the material. Using this method (with a build plate heated only to 85°C), it was demonstrated that internal transparency can be achieved with low Tg acrylics. Surprisingly, when the transparency and haze were measured according to ASTM D1003 on 3.2 mm thick plaques using BYK-Gardner Haze-Gard, the acrylic material was the only material that could achieve haze less than 20%, preferably 15%, 10%, and most preferably 5%, and transmittance greater than 84%, 86%, 88%, and 89%. This was also the case for a layer height of 0.1 mm.

[0096] In another embodiment, the heated build plate temperature can be increased above the material's Tg to further slow the cooling rate of the extruded plastic and allow it to remain above its liquid-solid transition point for an extended period of time. Increasing the build surface temperature much above the material's Tg would cause the material to sag and deform; however, it has surprisingly been found that the acrylic material of the present invention can retain its shape during the printing process at build plate temperatures of 40° C. or more above the material's Tg. Without being bound to a particular theory, it is believed that the large difference between the first G' / G" crossover point on the rheological curve and the LS transition (referred to herein as the transparent process range) allows the acrylic to be soft yet still hold its shape. In one embodiment, using an IR thermal camera showed that the interior of the part was 50°C above the Tg of the material, but the part held its shape because the interior temperature was still below the first crossover point. Higher build plate temperatures improve transparency. A wider transparent process range allows for higher build plate temperatures to be used without the part losing its shape, and therefore a wider transparency process range is desirable, preferably over 40°C, 50°C, 60°C, 70°C, and 80°C.

[0097] The higher build plate temperature had the unexpected effect of removing the need to print very thin layers / minimized layer heights. Surprisingly, 3.2 mm plaques printed at 25 mm / s with layer heights of 0.2 mm, 0.3 mm, and even 0.4 mm showed less than 10% haze. While 0.3 mm and 0.4 mm layer heights are often reserved for faster, less precise, or very large 3D printing, the technique produces internally clear parts with minimal layer lines. Using 0.4 mm layers, objects can be produced 8 times faster than using 0.05 mm layers.

[0098] Purpose / Use Acrylic resins are widely used in applications where beneficial properties (such as transparency, weather resistance, etc.) are required. This 3D printable acrylic material can be used in multiple markets including, but not limited to: automotive, building and construction, capstock, aviation, aerospace, solar power, medical, computer related, telecommunications, and wind energy. These applications include, but are not limited to, exterior panels, automotive body panels, vehicle body trim, recreational vehicle body panels or trim, recreational sporting goods exterior panels, marine equipment, exterior panels for outdoor lawn, garden and agricultural equipment, and exterior panels for marine, aerospace structures, aircraft, and public transportation applications, interior panel applications, automotive interior trim, vehicle headlight or taillight components, lenses, prototyping, display panels, interior panels for marine equipment, interior panels for aerospace and aircraft, interior panels for public transportation applications, and panels for appliances, furniture, cabinets, recreational vehicles, sports equipment, marine, aerospace, decks, handrails, siding, window and door profiles, dishwashers and dryers, refrigerators and freezers, appliance housings or doors, bathtubs, shower stalls, spas, counters. , and storage facilities, decorative exterior trim, molded side trim, quarter panel trim panels, fenders and fender extensions, louvers, rear end panels, caps for pickup truckbacks, rearview mirror housings, accessories for trucks, buses, campers, vans, and mass transit vehicles, b-pillar extensions, etc.; lawn and garden tools, bathroom fixtures for mobile homes, fencing, pleasure boat parts, mobile home exterior parts, lawn furniture such as chairs and table frames, pipes and pipe end caps, luggage, mobile home shower stalls, toilet seats, signs, spas, air conditioner and heat pump parts, kitchen appliances, bead molded picnic coolers, picnic trays and jugs, and trash cans; venetian blind parts; sporting equipment such as sailboats, yachts, etc.; plumbing parts such as lavatory parts;In addition to the aforementioned parts, construction parts, add-on parts include architectural moldings, door moldings, louvers, and shutters, mobile home skirting, residential or commercial doors, siding accessories, window cladding, storm window frames, skylight frames, end caps for gutters, awnings, car park roofs, lamps, lighting fixtures, sensors, custom carry caches for consumer goods, silverware, car trim, prototypes, figurines, dentures, hardware, cabinets, ball joints, hoses, glass, cages, UV protector screens, windows, signs, toys, medical devices and equipment parts such as implants, lighting appliques, luminaires, window coverings, surface modifications, and visualization-assisted 3D models based on medical images, architectural models, terrain data, mathematical analyses, or other datasets. Educational aids, Props, Costumes, Park benches, Robot parts, Electrical enclosures, 3D printer parts, Jigs, Fixtures, Manufacturing aids, Molds, Sculptures, Statues, Board games, Miniatures, Dioramas, Trophies, Drones, UAVs, Medical devices (Class I, II and III as per FDA Code of Federal Regulations Title 21), Light guides, Interior lighting, Integrated optics, Display components, Instrumentation, See-through components, Solar cells, Photovoltaic system fixtures and rigging, Artificial nails, Dosimeters, Jewelry, Footwear, Fabrics, Firearm parts, Cell phone cases, Packaging; EXAMPLES

[0099] Example 1: Internal transparency plaque measurement A variety of plastic filaments were used to 3D print 35 mm x 35 mm plaques with a thickness of 3.2 mm on an Ultimaker S5 3D printer. The transmittance and haze of each of these plaques were measured using a BYK-Gardner Haze-Gard. The rough surface of the plaques causes the ridges to scatter light, resulting in very high haze values. Rather than manually grinding and polishing the surface, a nearly refractive index-matching liquid was used to make the surface uniform. The 3D printed plaques were coated with glycerol (n ≈ 1.45) and measured by pressing them against an acrylic plate. The plaques were measured without glycerol, with glycerol on one side, and with glycerol on both sides. A schematic of the tests is shown in Figure 1. These results are shown in Table 1.

[0100] The 15-30% ethyl acrylate modified copolymer was able to obtain the highest transmittance, with the lowest measured haze of 3.5% among the materials. Without modified copolymers to lower the Tg and modify the rheology, the mid-Tg PMMA could only achieve a haze of 14% under the most ideal conditions. The printer used was limited in the build plate temperature it could achieve and did not have a heated chamber, so the internal parts could not reach the required temperatures of 10°C, 20°C, or 30°C above the LS transition point, resulting in the mobility required to completely eliminate the layer interface. Without being bound to a particular theory, it is believed that impact modified, Tg of about 105-110°C PMMA could achieve haze of less than 10% or even less than 5% if the build plate was set at a temperature high enough to reach an internal temperature of about 160°C.

[0101] [Table 1]

[0102] Example 2 Printing clear parts with thicker layer heights Optical plaques were printed at a printer speed of 25 mm / s at a variety of different layer heights using impact-modified low Tg acrylic compositions comprised of 15-30% low Tg comonomer content. These 35 mm x 35 mm x 3.2 mm plaques were tested using the same procedure outlined in Example 1. The optical haze of each of these plaques is shown in Table 2. Plaques printed using layer heights of 0.05 mm and 0.1 mm feature low haze, but when the layer height is increased to 0.2 mm, the haze increases to 37.9%. This layer height limitation is a major drawback, as 0.2 mm layers are considered standard in the art, and 0.1 mm and 0.05 mm layers double and quadruple the time it takes to print an object, respectively.

[0103] [Table 2]

[0104] To reduce printing time while keeping haze low, the build plate temperature was increased to 120 °C. Surprisingly, the specific rheological properties of the acrylic composition allowed it to maintain its shape despite being heated well above its Tg. The extra mobility of the polymer while maintaining dimensional stability allowed it to fill voids even when printing in thick layers. By increasing the build plate temperature from 75 °C to 120 °C, the haze of the finished part decreased from 37.9% to 8.6% when printed using a 0.2 mm layer height. Plaques printed using 0.3 mm and 0.4 mm layer heights performed even better than plaques printed with a 0.2 mm layer height. Using a 0.4 mm layer height at a print speed of 25 mm / s, plaques were printed in only 22 minutes, but with similar optical performance to plaques that took several hours to produce using lower layer heights at lower build plate temperatures.

[0105] [Table 3]

[0106] An impact modified PMMA with a Tg of 105-110°C was also tested (Table 4). When printed with a layer height of 0.05 mm in Example 1, a rather low haze of 14.0% was obtained, but when a thicker layer height was used, this material could not be printed transparently. The printer used was only able to reach a build plate temperature of 120°C, and after 10-15 minutes the internal temperature was 10-15°C above the Tg. Without being bound to a particular theory, this level of heat soak was not sufficient to print the material with low haze at thicker layer heights. However, if a higher internal temperature could be reached via a hotter build plate or heated chamber, it is believed that it would be possible to print this acrylic composition with a low haze of 0.2 mm or more, as seen with the lower Tg acrylic compositions.

[0107] [Table 4]

[0108] Amphora HT copolyester (Table 5) had the same properties as standard Tg PMMA: it was characterized by low haze when printed in 0.05 mm layers, but the level of heat soak achievable by the printer was insufficient to print the material transparently at thicker layer heights. Amphora HT showed a less dramatic increase in haze as layer height increased due to the lower Tg of the material compared to the mid-Tg PMMA compositions.

[0109] [Table 5]

[0110] PETG was also tested, but despite similar thermal properties to the low Tg acrylic compositions, the polymer could not be printed at higher build plate temperatures because its viscosity at low shear at high temperatures was too low; specifically, due to a clear processing window of only 35 °C (G' / G" first crossover temperature of 122 °C, LS transition temperature approximately 87 °C). While printing was occurring, the material drooped / flowed and the plaque lost its shape. The resulting haze was increased by this deformation as the fluid polymer emptied the original printed volume leaving internal voids.

[0111] Some polymers with good optical properties, such as polycarbonate, have a Tg in the range of 100-140° C. Without being bound to any particular theory, it is believed that printers that allow the build plate temperature to exceed 5%, 10%, 15%, or 20% of the Tg can print transparently at thicker layer heights, provided that these materials have the appropriate rheological properties as discussed above.

[0112] Example 3 IR thermal image of the part being printed While printing the transparent parts using the outlined method, the Flir E60IR thermal camera recorded images of the printing process of Sample 1 with a build plate at 120 °C. These images established that the internal part temperature can be kept well above the Tg of the material and the material can still maintain its shape. The thermal image shown in Figure 2 shows a 110 mm x 20 mm part with a height of 3 mm at the time the image was taken. The build plate was at 120 °C and the nozzle at 245 °C. The temperature of the measurement point at the center of the screen is 137 °C. Although the internal temperature throughout the part is over 130 °C, the part was able to maintain its shape over the 5-hour printing process, after which the final part height was 20 mm.

[0113] The second IR image shown in Figure 3 shows a part that is 20mm x 30mm and 19mm tall as printed. The final part is shown in Figures 4 and 5. The thermal images show that heat has penetrated to the top of the part. Due to the high build plate temperature and lack of a cooling fan, the most recently printed layers can only maintain their temperature and mobility of about 6mm from the top layer of the printing surface. At a given printing speed, this means about 20 minutes for a given layer to cool below 130°C. The part is transparent internally due to the increased fluidity caused by the higher internal temperature, but the high initial crossover temperature (190°C) allows the material to solidify sufficiently to achieve more complex shapes.

[0114] Example 4 The blocks shown in Figures 4 and 5 were printed with two filaments. The transparent filament was of the same composition as Sample 1 described in Examples 1 and 2. An opaque red ABS filament was used to create the internal "A" shape. These two filaments were extruded together by an Ultimaker S5. The object was printed in 0.3 mm layers. Layer ridges can be seen in the ABS letters, but in the acrylic sections, the layer interface has been removed by the process described above. The block was transparent enough to read the text through its 20 mm width. The block was finished using an Edge Finisher Model EF-200 to create a flat, transparent surface.

[0115] The dual-extrusion block demonstrates that plastic can be purposefully and precisely positioned using this method, even though the temperature of the internal components is above the material Tg. The plastic remains fluid for long periods of time, yet is thick enough to hold its position, and complex internal geometries can be achieved within the clear acrylic.

[0116] Example 5 Rheology of Materials The general description of the developed rheological method consists of melting the resin between parallel plates with a narrow gap of 1.8 mm to 0.5 mm. If fillers are present, the gap must be at least 10 times larger than the larger filler particles in the resin. It is desirable to heat the sample at least 30-50 °C above the melting temperature but significantly below the decomposition temperature. The rheometer used in this invention is an MCR502 from Anton Paar. The software is programmed to shear the sample by applying a small oscillatory force while simultaneously decreasing the temperature at a constant cooling rate (recommended between 5 °C / min and 10 °C / min). Tests should always be performed within the linear viscoelastic region, which can be determined by performing a strain amplitude sweep for each resin prior to the temperature sweep experiment.

[0117] The rheology of low and high Tg acrylics is shown in Figures 6 & 7, 8 & 9, 10 & 11. From the viscosity curves, the liquid to solid transition temperature can be obtained. From the elastic modulus, the first crossover temperature (G'>G") was obtained where the part begins to show some curing behavior.

[0118] Generally speaking, the dynamic modulus is a measure of the viscoelastic properties of a material (storage modulus G', i.e. the elastic response, and loss modulus G", i.e. the viscous response of the polymer). At the crossover temperature (G'=G"), the elastic modulus at lower temperatures dominates the viscous response and can therefore be considered as the onset of curing. Furthermore, the LS transition temperature can be obtained and the clear processing range can be calculated.

[0119] Example 6 Evaluation of transparency between one low Tg and one high Tg amorphous polyamide Measurement of internal clear plaque In this test, the transparency of parts made from two amorphous polyamides (PA) based on PA11 / aromatic PA copolymers was evaluated. The aim is to demonstrate that the ability of a material to print transparent parts is mainly related to its Tg, and more specifically, how the heating parameters of the 3D printer allow the temperature of the internal part to be higher than the Tg of the material during printing, making it less dependent on the material chemistry and its flow rate. To this end, the two selected PA materials display different Tgs, as explained in Table 6.

[0120] [Table 6]

[0121] To conduct this test, 35 mm x 35 mm plaques with a thickness of 3.2 mm were printed on an Ultimaker S5 3D printer using both PA materials. All printing conditions for solid (100% filled) plaques, as well as the resulting transmittance and haze data, are summarized in Table 7. The transmittance and haze of each of these plaques were measured as in Example 1.

[0122] [Table 7]

[0123] Under the printing conditions described, parts printed from PA1 showed high transmittance and low haze of 89.1% and 9.25%, respectively. This indicates that amorphous thermoplastics with suitable rheological properties can be printed to produce parts with high transmittance and low haze when the build plate temperature is kept high relative to the Tg of the material (120 °C and 101 °C, respectively). PA1 has an initial G' / G” crossover temperature of 175 °C and a LS transition of ~125 °C, thus resulting in a clear processing range of 50 °C. On the other hand, the high Tg PA2, despite having a higher MFR than PA1, could only achieve 18.7% under the most ideal conditions in experiment 3 (low layer height, which helps retain heat between layers during printing).

[0124] IR images of various PA materials To confirm the above statement relating the temperature of the internal part during printing to the resulting PA part transparency level, images of the printing process were recorded using a Flir E60 IR thermal camera (similar to Example 3). For this purpose, each amorphous PA filament was used to print a solid (100% filled) block of 20 × 30 mm (X × Y) with a height of 20 mm (Z) on an Ultimaker S.5 printer according to the printing conditions described in Table 8.

[0125] [Table 8]

[0126] The thermal image in Figure 12 shows a PA1 part measuring 20 mm x 30 mm with a height of 8 mm at the time the image was taken. The temperature at the measurement point in the center of the screen is 134 °C. The recorded image shows that the high build plate temperature (120 °C), high nozzle temperature (280 °C) and lack of a cooling fan allow the temperature of the internal part to be kept above the Tg of the material during printing (ΔT = 33 °C) while maintaining its shape as it is printed. These measurements of the temperature of the internal part can be directly related to the superior transparency performance of PA1. To confirm the above statement, a thermal image of a PA2 part was also recorded and is shown in Figure 13 with a height of 8 mm when the image was taken. However, even with the build plate increased to 140 °C, the internal temperature was only heated to 148 °C, not reaching the ΔT required to exceed the Tg and print a highly transparent part. Thus, even though it exhibited high flow, the PA2 material was not able to reach the same level of transparency that PA1 exhibited.

Claims

1. The material extrusion additive manufacturing process includes the following steps: a) selecting an amorphous thermoplastic polymer composition having a particular overall Tg; b) selecting conditions sufficient to provide an internal temperature of the composition upon printing, wherein the Tg of the entire composition is at least 25° C., more preferably at least 35° C., more preferably at least 45° C., more preferably at least 55° C., at least 65° C., and at least 75° C. lower than the internal temperature; c) melt extrusion printing said amorphous thermoplastic polymer to form an article; wherein the temperature difference between the Tg of said amorphous thermoplastic polymer and the internal temperature of a given printed dot or line of said thermoplastic polymer composition is maintained for at least 5 minutes, preferably at least 10 minutes, more preferably at least 15 minutes, and most preferably at least 20 minutes after printing.

2. 2. The additive manufacturing process of claim 1, wherein the selection of conditions to provide a desired internal temperature includes one or more of the following: a) selecting a build plate temperature higher than the Tg of said amorphous thermoplastic polymer composition, more preferably at least 10° C., 20° C., 25° C., and most preferably at least 30° C. higher than the Tg of said amorphous thermoplastic polymer composition; b) selecting a heated chamber temperature of at least 30° C., preferably at least 40° C., preferably at least 50° C., most preferably at least 60° C.; c) the use of radiative, conductive, or forced convection heating sources to supplement heat during printing; d) Little or no fans or active cooling; e) the use of selected additives in the composition to lower the Tg of the composition or to help maintain the temperature of the composition for an extended period of time; f) The use of pre-heated airflow that interacts with the printed part to reduce the cooling or cooling rate and also actively heat the printed article.

3. 2. The additive manufacturing process of claim 1 , wherein the heated chamber temperature, radiant heating and / or heating fan speed vary over time.

4. 10. The additive manufacturing process of claim 1, wherein the amorphous thermoplastic polymer composition comprises a polymer selected from the group consisting of (meth)acrylic polymers, copolyesters, and polycarbonates, amorphous polyamides.

5. 2. The additive manufacturing process of claim 1, wherein said amorphous thermoplastic polymer composition has a Tg of less than 160°C, preferably less than 150°C, preferably less than 140°C, preferably less than 130°C, preferably less than 114°C, preferably less than 105°C, 95°C, preferably less than 90°C, preferably less than 85°C, more preferably less than 80°C, and most preferably less than 75°C.

6. 2. The additive manufacturing process of claim 1, wherein the amorphous thermoplastic polymer composition is selected from the group consisting of: a) a copolymer having the required Tg; b) a blend of a polymer having a Tg greater than 160° C. and a low viscosity polymer; c) A blend of a polymer having a Tg greater than 160° C. with an additive capable of lowering the Tg or increasing the open time of the polymer composition.

7. The composition has a viscosity of 1000 s at 230° C. for 1 second when measured using a rotational viscometer according to ASTM C965. -1 and a viscosity of less than 100,000 Pa·s, preferably less than 10,000, at a shear of 100 s. -1 2. The additive manufacturing process of claim 1, wherein the polymer has a viscosity of 20 to 2000 Pa.s, preferably 25 to 1,000 Pa.s, more preferably 30 to 500 Pa.s at a shear rate of 100 .mu.m.

8. 2. The additive manufacturing process of claim 1, wherein the composition has a clear processing range, defined as the difference between the L-S transition temperature and the first crossover temperature, greater than 40°C, greater than 50°C, greater than 60°C, preferably greater than 70°C, more preferably greater than 80°C, as measured by rheology.

9. 2. The additive manufacturing process of claim 1, wherein said amorphous thermoplastic polymer composition further comprises an impact modifier at a level of 5 to 60 wt%, preferably 10 to 35 wt%, more preferably 15 to 30 wt%, based on the weight of the total composition.

10. 2. The additive manufacturing process of claim 1, wherein the amorphous thermoplastic polymer composition temperature is provided and / or maintained by one or more means selected from the group consisting of: a) low or no fans or active cooling; b) a heated build plate; c) a heated chamber; and d) a radiative heat source.

11. 2. The additive manufacturing process of claim 1, wherein said 3D printed article comprises said amorphous thermoplastic polymer composition having a density of at least 95%, 97%, preferably 98%, preferably 99% of the bulk density of the polymer when measured according to ASTM D792.

12. 10. The additive manufacturing process of claim 1 , wherein the amorphous thermoplastic polymer composition comprises an acrylic polymer.

13. 2. The additive manufacturing process of claim 1 , wherein the amorphous thermoplastic polymer composition is printed with a layer height of 0.05 mm or more, 0.1 mm or more, 0.2 mm or more, 0.3 mm or more, 0.4 mm or more.

14. 1. An internally transparent 3D printed article, said article comprising an amorphous thermoplastic polymer composition having a print layer thickness of 0.1 mm or more, preferably 0.2 mm or more, preferably 0.3 mm or more, preferably 0.4 mm or more, and having an internal haze of less than 25%, preferably less than 20%, preferably less than 10%, preferably less than 5%.

15. 15. The 3D printed article of claim 14, wherein the amorphous thermoplastic polymer composition comprises an acrylic composition, a copolyester, a polycarbonate, or an amorphous polyamide.

16. 15. The internally transparent 3D printed article of claim 14, wherein the article is transparent and has a total white light transmission of greater than 80%, preferably greater than 84%, more preferably greater than 86%, and most preferably greater than 88%, at a thickness of 2 mm, as measured according to ASTM D1003, and a haze of less than 80%, preferably less than 70%, and more preferably less than 60%, and wherein the composition is transparent and an internal haze for a 2 mm thick 3D printed part printed with a line height of 0.1 mm or more, 0.2 mm or more, 0.3 mm or more, 0.4 mm or more is less than 25%, preferably less than 20%, more preferably less than 15%, more preferably less than 10%, and most preferably less than 5%.

17. 15. The internally transparent 3D printed article of claim 14, wherein the article is selected from the group consisting of: automotive articles, building and construction articles, capstock articles, aviation articles, aerospace articles, solar power articles, medical articles, computer related articles, telecommunications articles, wind energy articles, exterior panels, automotive body panels, vehicle body trim, recreational vehicle body panels or trim, recreational sporting goods exterior panels, marine equipment, exterior panels for outdoor lawn, garden and agricultural equipment, exterior panels for marine, aerospace structures, aircraft, public transportation applications, interior panel applications, automotive interior trim, vehicle headlight, taillight components, lenses, prototyping, display panels, interior panels for marine equipment, aviation. Interior panels for space and aircraft, interior panels for public transportation applications, and panels for appliances, furniture, cabinets, recreational vehicles, sports equipment, marine, aerospace, decks, handrails, siding, window and door profiles, dishwashers and dryers, refrigerators and freezers, appliance housings or doors, bathtubs, shower stalls, spas, counters, and storage facilities, decorative exterior trim, molded side trim, quarter panel trim panels, fenders and fender extensions, louvers, rear end panels, caps for pickup truckbacks, rearview mirror housings, accessories for trucks, buses, campers, vans, and mass transit vehicles, b-pillar extensions, and the like;Lawn and garden tools, mobile home bathroom fixtures, fencing, pleasure boat parts, mobile home exterior parts, lawn furniture, chairs, table frames, pipes and pipe end caps, luggage, shower stalls, toilet seats, signs, spas, air conditioner and heat pump parts, kitchen appliances, bead molded picnic coolers, picnic trays and jugs, and trash cans, venetian blind parts, sporting goods, sailboats, yachts, plumbing parts, washroom parts, construction parts, architectural moldings, door moldings, louvers, shutters, mobile home skirting, residential or commercial doors, siding accessories, window cladding, storm window frames, skylight frames, gutter end caps, awnings, medical devices, car park roofs, lamps, lighting fixtures, sensors, consumer goods, silverware, car trim, prototypes, figurines, dentures, hardware, cabinetry , ball joints, hoses, glass, cages, UV protector screens, windows, signs, toys, medical devices and equipment such as implants and equipment parts, lighting appliques, luminare, window coverings, surface modification, visualization aids, medical image models, architectural models, topographical data models, mathematical analysis models, teaching aids, props, costumes, park benches, robot parts, electrical enclosures, 3D printer parts, jigs, fixtures, manufacturing aids, molds, sculptures, statues, board games, miniatures, dioramas, trophies, drones, medical devices (Class I, Class II, and Class III as per FDA's Code of Federal Regulations Title 21), light guides, interior lighting, integrated optics, display components, instrumentation, see-through components, solar cells, fixtures and rigging for photovoltaic systems, artificial nails, dosimeters, jewelry, footwear, textiles, firearm parts, cell phone cases, packaging.

Images