Acrylic composition for three-dimensional (3D) printing

Abstract

To provide an acrylic copolymer composition useful for 3D printing that can be formed into a uniform filament and three-dimensionally printed using material extrusion additive manufacturing into an article having low warpage, low shrinkage, good internal optical properties, and good mechanical properties.SOLUTION: The acrylic copolymer has a low Tg, providing the proper stiffness for good 3D printing. The present invention also relates to the printing and process of an acrylic composition where internally transparent 3D printed thermoplastic parts can be produced at a reasonable rate (>0.05 mm per layer) with good / great layer adhesion, and almost isotropic properties.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an acrylic copolymer composition useful for 3D printing. It can be formed into a uniform filament, material extrusion printed, and 3D printed using material extrusion additive manufacturing into articles with low warpage, low shrinkage, good internal optical properties, and good mechanical properties. The acrylic copolymer composition can also be used for other 3D printing techniques, such as pellet extrusion. The acrylic copolymer has specific rheological properties for good 3D printing.

[0002] A second aspect of the invention relates to the printing and processing of acrylic compositions that can produce internally transparent 3D printed thermoplastic parts with good / excellent layer adhesion and near isotropic properties at reasonable layer heights (>0.01 mm per layer). Even at 0.4 mm per layer, internal haze ratings of less than 10% have been achieved. [Background technology]

[0003] 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.

[0004] 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.

[0005] Polylactic acid (PLA) is widely used in desktop home printers because it has high printability and very little warping. Unfortunately, its low use temperature, low chemical stability, and if not colored with dyes or pigments, will yellow (degrade) during printing. Acrylonitrile butadiene styrene (ABS) is commonly used in 3D printing as a more stable "engineering" thermoplastic, it has a higher use temperature but has a higher warping 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 because, like ABS, it has a higher use temperature and stability and improved printability, but it has a higher processing temperature, is softer, and has some discoloration in the resin.

[0006] 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.

[0007] There is a desire for a material extrusion additive print that has the physical weatherability, clarity, and appearance of an acrylic polymer, but with the reduced warping, no adhesives or heated chambers of PLA, and the mechanical and chemical properties of ABS, plus the excellent impact resistance and excellent optical clarity. Summary of the Invention [Problem to be solved by the invention]

[0008] WO2017 / 210,286 discloses dimensionally stable acrylic alloys for 3D printing, the alloys including a low melt viscosity polymer compatible with the acrylic polymer. The acrylic polymer can have a wide range of compositions, but the reference does not disclose the Tg of the acrylic polymer. [Means for solving the problem]

[0009] Surprisingly, it has been found that compositions comprising a low Tg composition below 160°C, preferably below 150°C, preferably below 140°C, preferably below 130°C, preferably below 120°C, preferably below 114°C, preferably below 100°C, preferably below 90°C, preferably below 85°C, preferably below 80°C, more preferably below 75°C provide acrylic 3D printable filaments that are dimensionally stable and have the flexibility and flow properties to print while maintaining the transparency and strength of PMMA. The low Tg acrylic composition can be an acrylic copolymer, a blend of an acrylic polymer with a non-polymeric Tg lowering additive such as a plasticizer, or a blend of a low viscosity polymer compatible with the acrylic polymer. The low Tg acrylic polymer has similar physical and printing properties as the acrylic alloys described in the prior art, but with improved transparency due to the absence of a low viscosity polymer.

[0010] 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 action of material extrusion-type 3D printing typically adds numerous layer and line 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.

[0011] 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.

[0012] Surprisingly, it has been found that by proper selection of material composition (acrylic and acrylic blends at specific Tg, viscosity, rheological conditions) as well as proper printing process conditions (adjusting minimum fan, build plate, build chamber temperatures to match material transition temperature and setting layer height), internal clear acrylic 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 normal layer height without reducing print speed.

[0013] Additionally, correlations between material and printing parameters have been established such that higher Tg acrylics can be used to produce reasonably low haze parts when printed with an appropriately heated chamber and a hotter heated build plate.

[0014] The present invention relates to an acrylic copolymer composition for use in 3D printing, the acrylic composition comprising a single matrix acrylic copolymer, optionally alloyed with less than 5% of other compatible, miscible or semi-miscible polymers, and optionally one or more additives dispersed within said matrix.

[0015] The matrix acrylic copolymer comprises methyl methacrylate monomer units and 0.1 to 60% by weight, preferably 0.5 to 40, preferably 4 to 35, more preferably 9 to 30% by weight of one or more other monomers copolymerizable with the methyl methacrylate monomer units.

[0016] The matrix acrylic copolymer contains at least 90% by weight, more preferably at least 95% by weight, and most preferably 100% by weight of (meth)acrylic monomer units, based on the total monomer units in the copolymer, and has a weight average molecular weight of 50,000 to 500,000, preferably 55,000 to 300,000, and preferably 65,000 to 200,000 g / mol.

[0017] The matrix acrylic composition has a viscosity of 230°C for 1 second when measured using a rotational viscometer according to ASTM C965.-1 and a temperature of 230° C. for 100 seconds. -1 The viscosity of the polymer composition is 20 to 2000 Pa·s, preferably 25 to 1,000 Pa·s, and more preferably 30 to 500 Pa·s at a shear rate of 100 / min. Here, the viscosity measurement is performed on a polymer composition that does not contain an impact modifier.

[0018] The acrylic polymer composition may also include one or more impact modifiers that are core-shell impact modifiers, block copolymers, or mixtures thereof. The impact modifiers are preferably refractive index matched to the acrylic polymer matrix.

[0019] The acrylic composition may further include one or more typical additives.

[0020] The acrylic copolymer composition of the present invention may also be characterized in terms of its Tg, which is less than 160° C., preferably less than 130° C., preferably less than 120° C., preferably less than 110° C., preferably less than 100° C., preferably less than 90° C., preferably less than 85° C., preferably less than 80° C., more preferably less than 75° C. The composition also comprises: a) a continuous matrix phase consisting essentially of one or more acrylic polymers; b) optionally 0 to 60 wt. %, preferably 9 to 40 wt. %, of an impact modifier; c) optionally, 0 to 50 volume %, preferably 0.01 to 40 volume %, more preferably 0.05 to 25 volume %, based on the total volume of the acrylic composition, of one or more other additives.

[0021] The acrylic polymer composition comprises an acrylic copolymer matrix phase comprising one or more acrylic copolymers having a Tg of from 70°C to 160°C, and further comprises an effective amount of at least one non-polymeric additive (preferably 2 to 40 wt % of a plasticizer) to reduce the polymer composition Tg to less than 105°C, preferably less than 100°C, preferably less than 95°C, preferably less than 85°C, preferably less than 80°C, more preferably less than 75°C.

[0022] The present invention also relates to an acrylic article, said article being transparent and capable of obtaining a 3D printed part having 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 said composition being transparent, and the internal haze of the 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%.

[0023] The acrylic polymer composition may be in the form of a powder, pellets, or filaments.

[0024] The present invention also relates to an acrylic article produced by a material extrusion additive manufacturing process using the above acrylic alloy composition, the article having one or more of the following characteristics: a) a tensile elongation measured by ASTM D638 of greater than 10%, preferably greater than 20%; b) a packing density of greater than 85%, preferably greater than 90%, and most preferably greater than 95%; c) Yield stress greater than 35 MPa as measured by ASTM D638.

[0025] The present invention also relates to a process for forming an extrusion additive (3D) acrylic article of the above composition, wherein the acrylic composition as a whole has a Tg of 70°C to 160°C, preferably 80°C to 150°C, preferably 90°C to 150°C, preferably 110°C to 150°C, preferably greater than 115°C, preferably greater than 120°C, preferably greater than 125°C, and wherein the build plate temperature during the printing process is maintained at least 1%, preferably 3%, preferably 5%, preferably 10%, more preferably 15%, more preferably 20% above the Tg of the acrylic composition measured in degrees Celsius. [Brief description of the drawings]

[0026] [Figure 1] FIG. 1 is a diagram of a sample for warpage testing. [Diagram 2] FIG. 2 shows the warpage results for Example 2. [Diagram 3] FIG. 3 shows the individual data points used to generate the aggregate completion rate for Example 3. [Figure 4] FIG. 4 shows the individual data points used to generate the aggregate completion rate for Example 3. [Diagram 5] FIG. 5 shows the individual data points used to generate the aggregate completion rates for Example 4. [Figure 6] FIG. 6 shows the individual data points used to generate the aggregate completion rate for Example 4. [Figure 7] FIG. 7 is a schematic diagram of the internal clear plaque measurement test. [Figure 8] FIG. 8 is a thermal image of the printed part from Example 6 as it was printed. [Figure 9] FIG. 9 is a thermal image of the printed part from Example 6 as it was printed. [Figure 10] FIG. 10 shows the optical clarity of the printed part of Example 7. [Figure 11] FIG. 11 shows the optical clarity of the printed parts of Example 7. [Figure 12] FIG. 12 shows the rheology of the parts of Example 5. [Figure 13]FIG. 13 shows the rheology of the parts of Example 5. [Figure 14] FIG. 14 shows the rheology of the parts of Example 5. [Figure 15] FIG. 15 shows the rheology of the parts of Example 5. [Figure 16] FIG. 16 shows the rheology of the parts of Example 5. [Figure 17] FIG. 17 shows the rheology of the parts of Example 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] The present invention relates to acrylic compositions that can be formed by material extrusion additive manufacturing processes (also referred to in this application as 3D printing), acrylic filaments useful in the process that have a very uniform diameter, acrylic articles made from the acrylic compositions of the present invention, and processes for making acrylic extrusion additive articles. The present invention also relates to process improvements that can be used to improve clarity. The acrylic compositions useful in the present invention have an overall 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 105°C, preferably less than 95°C, preferably less than 90°C, preferably less than 85°C, preferably less than 80°C, more preferably less than 75°C. This low Tg acrylic can be obtained in several ways. These include, but are not limited to: a) acrylic homopolymers or copolymers having the required Tg; b) blends of acrylic polymers with at least one low melt viscosity polymer; c) blends of high Tg acrylic polymers with non-polymeric components (such as plasticizers) that lower the Tg of the overall composition; and combinations thereof.

[0028] The present invention also relates to a method for producing an internally transparent part, where an acrylic composition is selected based on its chemical structure, Tg or transition temperature, viscosity, and flow characteristics. The composition is then extrusion 3D printed in a specified manner using little overflow, minimal fans, a heated build plate, and chamber temperature required to reach the appropriate internal temperature so that the internal layer lines integrate and the part becomes internally transparent. With such a composition selected under such printing conditions, the part will adhere very well to the build plate, will not warp, will print very well, will have nearly 100% internal density, and will have very good mechanical properties.

[0029] 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.

[0030] "Copolymer" is used to mean a polymer having two or more different monomers. "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.

[0031] (Meth)acrylic or (meth)acrylate means both methacrylic and acrylic, or methacrylic and acrylate. The term "acrylic" is used to mean both acrylic and methacrylic.

[0032] Tg is used as a surrogate measurement of the transition temperature, which is 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, it is desirable to have a transition temperature 10°C lower, preferably 20°C lower, even more preferably 25°C lower, 30°C lower than the internal temperature of the part during printing (approximately 130°C for current technology when printing on a heated build plate at 115°C with no heated chamber and minimal fans). The Tg of acrylic is approximately 25°C lower than the transition temperature. Depending on the temperature of the heated build plate, Tg's below 160°C, 150°C, 140°C, 130°C, 120°C, 114°C, 105°C, 100°C, 95°C, 85°C, 80°C, 75°C, and above 60°C are preferred for materials printed at room temperature on a heated build plate. When using a heated chamber, materials with higher Tg can be used due to the higher internal temperature of the part. Similarly, when using a hotter heated build plate, materials with higher Tg can be used. The glass transition temperature of polymers is measured by DSC according to the standard ASTM E1356.

[0033] The first G' / G" crossover temperature refers to the first temperature at which G' is greater than G", measured at low shear in the material by parallel plate rheology. 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 (the storage modulus G', i.e., the elastic response, and the loss modulus G", i.e., the viscous response of the polymer). At the crossover temperature (G'=G"), the elastic modulus at low temperatures dominates the viscous response and can therefore be considered the onset of curing. 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.

[0034] The clearing window is defined as the temperature difference between the first G' / G" crossover temperature and the LS transition temperature.

[0035] Transmittance and haze are measured according to ASTM D1003 using a BYK-Gardner Haze-Gard machine.

[0036] Acrylic Polymer As used herein, "acrylic polymer" is meant to include polymers 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.

[0037] 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. 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.

[0038] 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.

[0039] In another embodiment, the acrylic polymer comprises a blend of two or more of the polymers described in the above two embodiments.

[0040] The acrylic polymers can be formed by any known means, including, but not limited to, bulk polymerization, emulsion polymerization, solution polymerization, and suspension polymerization.

[0041] 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 105° C., preferably less than 95° C., preferably less than 90° C., preferably less than 85° C., preferably less than 80° C., more preferably less than 75° C. The acrylic copolymers of the present invention have a Tg of greater than 50° C., preferably greater than 55° C., more preferably greater than 60° C.

[0042] 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.

[0043] In one preferred embodiment, the acrylic copolymer is composed of greater than 90%, greater than 95%, 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.

[0044] These monomers are added at a level high enough to reduce the Tg to 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 105°C, preferably less than 95°C, preferably less than 90°C, preferably less than 85°C, preferably less than 80°C, more preferably less than 75°C. Tg is readily calculated using the Fox equation and can be 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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 160°C, and less than 90°C being preferred for increased flexibility.

[0049] 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, cellulose-based esters, polyethylene oxides, polypropylene glycols, polyethylene glycols, polypropylene glycols, styrene-acrylonitrile copolymers, polyvinyl chloride, polyvinyl acetate, polyvinyl alcohol, polyhydroxyalkanoates, ethylene-vinyl acetate copolymers, vinyl fluoride and its copolymers, olefin-acrylate copolymers, olefin-acrylate-maleic anhydride copolymers, acrylate-maleic anhydride copolymers, styrene-acrylate copolymers, styrenic polymers, maleic anhydride-styrene-vinyl acetate copolymers, other vinyl monomers commonly used in free radical polymerization, and mixtures thereof.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] The low melt viscosity polymer comprises 5 to 60% by weight, preferably 9 to 40% by weight, of the total alloy composition.

[0054] Acrylic Blends with Non-Polymers A third method to provide an overall acrylic composition with a low Tg (<160°C<150°C<140°C<130°C<120°C<114°C<105°C<100°C, <95°C, <90°C, <85°C, <80°C, preferably <75°C) 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 0.2-40% by weight, preferably 2-20% by weight, based on the weight of the acrylic polymer.

[0055] 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.

[0056] In another embodiment, phthalate esters such as di(2-ethylhexyl) phthalate, diisononyl phthalate, diisodecyl phthalate, and diisooctyl phthalate can be used.

[0057] In another embodiment, adipate salts (such as, but not limited to, di(2-ethylhexyl) adipate) can be used.

[0058] Impact Modifier 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 15-35% 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 acrylic shell.

[0059] Without being bound to a particular theory, it is believed that the impact modifiers provide elongation, flexibility, and toughness.

[0060] 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.

[0061] The hard core layer (Tg>0°C, preferably Tg>20°C) is typically a single composition polymer, but can also contain a small amount of low Tg seed combination on which the hard core layer is formed. For example, a small 5% rubber core seed that becomes dispersed in the hard core layer is included in the present invention as the hard core layer as long as the combination functions as the hard core layer. The hard core layer can be selected from any thermoplastic that meets the Tg requirement. Preferably, the hard core layer is mainly composed of methacrylate ester units, acrylate ester units, styrenic units, or a mixture thereof. Methacrylate ester units include, but are not limited to, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, pentadecyl methacrylate, dodecyl methacrylate, isobornyl methacrylate, phenyl methacrylate, benzyl methacrylate, phenoxyethyl methacrylate, 2-hydroxyethyl methacrylate, and 2-methoxyethyl methacrylate. The acrylate ester units include, but are not limited to, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, amyl acrylate, isoamyl acrylate, n-hexyl acrylate, cyclohyl acrylate, 2-ethylhexyl acrylate, pentadecyl acrylate, dodecyl acrylate, isobornyl acrylate, phenyl acrylate, benzyl acrylate, phenoxyethyl acrylate, 2-hydroxyethyl acrylate, and 2-methoxyethyl acrylate. Preferably, the acrylate ester units are selected from methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, and octyl acrylate.Styrene units include styrene and its derivatives, such as, but not limited to, alpha-methylstyrene, para-methylstyrene, etc. In one embodiment, the hard core layer is all acrylic.

[0062] 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. Acrylate ester units useful for forming the soft block include, but are not limited to, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, amyl acrylate, n-hexyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, pentadecyl acrylate, dodecyl acrylate, isobornyl acrylate, phenyl acrylate, benzyl acrylate, phenoxyethyl acrylate, 2-hydroxyethyl acrylate and 2-methoxyethyl acrylate. Preferably, the acrylate ester units are selected from methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, and octyl acrylate. Useful dienes include, but are not limited to, isoprene and butadiene. Useful styrenics include, but are not limited to, alpha methyl styrene and para methyl styrene.

[0063] The shell layer may be made up of one or more shell layers having a Tg>0° C., more preferably a Tg>20° C. The shell layer may be of the same or different composition as the hard core layer.

[0064] Preferably, the multi-stage polymer is a three stage composition, the stages being present in the range of 10-40% by weight of the first stage (a), preferably 10-20%, a second intermediate stage (b) of 40-70%, preferably 50-60, and a final stage (c) of 10-50%, preferably 20-40. All percentages are based on the total weight of the polymer particles of the three stages.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] In one embodiment, the acrylic polymer composition of the present invention can contain reactive functional groups by using functional monomers or by post-treatment. Once the functional polymer is processed into a useful article, it can be reacted or crosslinked, such as by UV radiation or electron beam, to enhance its integrity. Crosslinking is known in the art to generally increase the tensile and flexural modulus and reduce the solubility and permeability of the crosslinked material, all of which can be advantageous physical property improvements depending on the end use of the material.

[0069] 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.

[0070] Acrylic matrices containing high levels of comonomers such as ethyl acrylate require specially designed impact modifiers to take advantage of the increased ductility of the matrix.

[0071] In one embodiment, the multi-stage continuously produced polymer is a specially engineered impact modifier, characterized by the following: (a) an optional, but preferably non-elastomeric, relatively hard first stage having a glass transition temperature above 25° C. The first stage is polymerized from a monomer mixture of the above-mentioned monomers to obtain a rigid thermoplastic copolymer, 0-10% by weight of a copolymerizable multifunctional crosslinking monomer, and 0-10% by weight of a copolymerizable graft linking monomer having two or more addition polymerizable unsaturated reactive groups that participate in the polymerization reaction at substantially different rates (such as allyl, methallyl or crotyl esters of a,b-unsaturated carboxylic or diacids); (b) as an intermediate elastomeric stage, polymerized in the presence of a product comprising the first stage from a monomer mixture comprising 50-99.9% by weight of an alkyl acrylate and / or alkyl methacrylate mixture, the alkyl group containing from 1 to 8 carbon atoms, 0-49.9% by weight of a copolymerizable monoethylenically unsaturated monomer, 0-5.0% by weight of a copolymerizable multifunctional crosslinking monomer, and 0.05-5.0% by weight of said copolymerizable graft linking monomer, said elastomeric stage being further characterized in that it exhibits a glass transition temperature of 25°C or less when the monomers are polymerized in the absence of the product comprising the first stage; (c) one or more final stages which are relatively hard and polymerized in the presence of a product comprising the first and intermediate stages from a monomer mixture of the above monomers to obtain a rigid thermoplastic polymer, the final stages being further characterized in that they exhibit a glass transition temperature greater than 50° C. when the monomers are polymerized in the absence of a product comprising the first and intermediate stages, the graft linking monomers having two or more addition polymerizable unsaturated reactive groups which participate in the polymerization reaction at substantially different rates, and the crosslinking monomers having multiple addition polymerizable unsaturated groups which all participate in the polymerization reaction at approximately the same rate as one another.

[0072] Preferably the multi-stage polymer is a three stage composition, the stages being present in the range of 10-40% by weight of the first stage (a), preferably 10-20%, a second intermediate stage (b) of 45-70%, preferably 50-60, and a final stage (c) of 10-50%, preferably 20-40. All percentages are based on the total weight of the polymer particles of the three stages.

[0073] Multi-stage polymers can be produced by any known technique for preparing polymers produced continuously in multiple stages, for example, by emulsion polymerizing the mixture of the next stage of monomers in the presence of a preformed polymer product. As used herein, the term "sequential emulsion polymerization" or "sequential emulsion production" refers to polymers (including copolymers and homopolymers) prepared in an aqueous dispersion or emulsion, in which successive monomer charges are 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. Thus, the continuously prepared polymers of the present invention are made by a process in which the total particle content is substantially constant upon completion of the polymerization of the first stage, i.e., new additional separate particles are avoided after the formation of the particles of the first stage.

[0074] The polymerization is carried out in the presence of an initiator and may include a polymerization regulator that functions as a chain transfer agent. The final particle size of the continuously produced polymer may vary from 100 to 350 nm, with a preferred range being 200 to 300 nm.

[0075] The type and level of emulsifier used controls the particle size of the intermediate stage latex particles. In most cases, the soaps normally used in emulsion polymerization can be used satisfactorily, provided care is taken to utilize the minimum amount necessary to give the desired result and the polymer is isolated by coagulation. If the latex is isolated by spray drying, the emulsifier remains with the polymer, so the choice of emulsifier becomes more important.

[0076] The level of emulsifier is preferably less than 1% by weight, preferably 0.1-0.6%, based on the total weight of polymerizable monomers charged in all stages. Useful emulsifiers include common soaps, alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate, alkylphenoxypolyethylene sulfonates, sodium lauryl sulfate, salts of long chain amines, salts of long chain carboxylic and sulfonic acids, and the like. In general, the emulsifier should be a compound containing a hydrocarbon group of 8-22 carbon atoms bonded to a highly polar solubilizing group such as an alkali metal and ammonium carboxylate group, a sulfate half ester group, a sulfonate group, or a phosphoric acid partial ester group.

[0077] The polymerization medium for each stage contains an effective amount of a suitable free radical generating polymerization initiator, which is activated either thermally or by oxidation-reduction (or redox) reactions. Preferred initiators are thermally activated initiators such as persulfates. However, redox initiators can also be used. Examples of suitable oil-soluble, water-insoluble initiators are combinations of cumene hydroperoxide-sodium metabisulfite, diisopropylbenzene hydroperoxide-sodium formaldehyde sulfoxylate, tertiary butyl peracetate-sodium hydrosulfite, cumene hydroperoxide-sodium formaldehyde sulfoxylate, and the like. Water-soluble redox initiators can also be used. Initiator combinations are sodium persulfate-sodium hydrosulfite, potassium persulfate-sodium formaldehyde sulfoxylate, and the like.

[0078] The multi-stage sequential emulsion polymerization can be carried out at temperatures ranging from about 0°C to 125°C, with 30°C to 95°C being preferred. The polymerization medium may contain chain transfer agents such as tertiary dodecyl mercaptan, secondary butyl mercaptan, normal dodecyl mercaptan, etc., in accordance with known practice, particularly if desired, to limit the molecular weight of the stage containing the lower alkyl methacrylate. The free radical initiator is used in an effective amount which varies depending on the monomer, temperature and method of addition, but generally the amount of initiator will vary from about 0.001 to 2% by weight in each polymerization stage based on the weight of the monomer charge, but should not exceed about 5% by weight based on the total weight of monomers charged in all stages.

[0079] The rigid thermoplastic copolymers consist of the monomer methyl methacrylate at a level of 50-85% copolymerized with another alkyl acrylate or alkyl methacrylate, the alkyl group consisting of 1-4 carbon atoms, and present at a level of 15-50% by weight. The molecular weight of the copolymers ranges from 50,000 to about 400,000 daltons. The preferred monomers are ethyl acrylate and methyl acrylate at a level of about 25% by weight, having molecular weights of 200,000-350,000 daltons. The rigid thermoplastics can be prepared by any standard method of preparing polymers of methacrylates and acrylates, including bulk, solvent, and emulsion polymerization.

[0080] Additives The acrylic polymer composition may further contain other additives typically present in acrylic formulations, including, but not limited to: stabilizers, plasticizers, fillers, colorants, pigments, antioxidants, antistatic agents, surfactants, toners, fragrances, deodorants, refractive index matching additives, additives with specific light diffractive or light reflective properties, and dispersing aids. When fillers are added, they represent 0.01 to 50% by volume, preferably 0.01 to 40% by volume, and most preferably 0.05 to 25% by volume of the total volume of the acrylic composition.

[0081] Fillers can be in the form of powders, platelets, beads, and particles. Smaller materials with low aspect ratios are preferred to avoid potential nozzle clogging, although this is less important when the acrylic composition is used with larger nozzle sizes. Useful fillers include, but are not limited to: carbon fiber, crushed carbon fiber, carbon powder, carbon nanotubes, boron nitride, diamond, glass beads, glass fibers, titanium dioxide, zinc oxide, PdS, barium sulfate (BaSO 4 ), silicon dioxide, nanosilica (SiO 2 ), calcium carbonate (CaCO 3 ), CaCO 4 , natural and synthetic clay based, aluminosilicates, montmorillonite, aramid fibers, polyaryletherketone fibers, graphite, graphite nanoplatelets, graphite oxide, graphene, crushed carbon fibers, nanofibers (typically with an average fiber length of 100-150 nm) and hollow glass or ceramic spheres, dyes, colorants, pigments, metal particles, metal flakes, milky dyes, fluorescent dyes, polymer particles that can be crosslinked and comprise a polymer selected from acrylic polymers, crosslinked acrylic beads (average particle size of 20-500 micrometers), styrene based particles, copolymers containing more than 50% by weight of styrene monomer units, silicones, polyamides, nanosilica, fluoropolymers, poly(tetrafluoroethylene), poly(vinylidene fluoride), and vinylidene fluoride / hexafluoropropylene copolymers, deodorants, fragrances, internal release agents, luminescent agents, diffusing particles, reflective particles, optical brighteners, flame retardants, UV stabilizers, antimicrobial additives, cellulose, antioxidants, and mixtures thereof.

[0082] In one embodiment, fillers are added to create special visual effects. Useful fillers include colorants, dyes, and inorganic particles including fluorescent dyes, metal filings, flakes, and crosslinked acrylic beads (average particle size 20 μm to 500 μm). Natural looking variegated materials with metallic or opalescent appearances can be created to simulate natural materials such as granite, minerals, stones, and metal ores. The metallic or pearlescent material is present in the acrylic composition at 0.01 to 10 wt. %, preferably 3.5 to 6.5 wt. %, based on the weight of the acrylic composition. In one embodiment, the acrylic composition includes a pearlescent compound and does not include a metal compound. In another embodiment, the thermoplastic composite includes a pearlescent compound and a metal compound. In a preferred embodiment, the thermoplastic composite includes a metal compound and does not include a pearlescent compound.

[0083] Metal compounds useful in the present invention include, but are not limited to, metal flakes, chips, and filings. Useful metal compounds include metals, metal-containing molecules and complexes of transition metals, or lanthanide metals, and combinations thereof. Examples include aluminum, copper, silver, gold, platinum, palladium, nickel, cobalt, tin, niobium, chromium, stainless steel, and combinations or alloys thereof, including, for example, brass and bronze. Metal compounds can also be metal carbides, metal oxides, metal nitrides, metal sulfides, and combinations thereof. Metal compounds can have a particle size of 1 micron to 25 microns, preferably 2 microns to 20 microns, on average in the largest direction. Metal compounds can be flat flakes or particles of various shapes. Metal flake pigments generally have a thickness in the range of 40 to 150 nm.

[0084] Pearlescent compounds useful in the present invention are known in the art and include, but are not limited to, platelets of mineral mica, which is muscovite or potassium aluminum fluoride hydroxide, and titanium dioxide-based platelets. The platelets are coated with a thin layer of a metal oxide selected from the group consisting of rutile titanium dioxide, ferric oxide, tin oxide, and mixtures thereof. The platelets of pearlescent compounds generally have a particle size of about 2 to about 130 microns, more preferably about 10 to about 50 microns. The pearlescent pigments may be colored or uncolored.

[0085] In one embodiment, diffusing, refractive, or other optical modifiers can be added to the compositions of the present invention to provide 3D printable diffusing / refractive materials.

[0086] In one embodiment, the use of deodorants and fragrances can be added to the compositions of the present invention to mask the acrylic odor. These can be in liquid or solid form and consist of detergents, gels, plastics, soaps, bleaches, etc. Additionally, the use of internal release agents / luminescent agents (waxes) - the use of release agents to release, prevent O2 inhibition, and inhibit odor - stearic acid, paraffin, stearyl alcohol, ethylene bis stearamide, AOT, lecithin.

[0087] In one embodiment, additives that provide useful optical effects such as light scattering, light reflection, and / or surface matte (such as diffusing and / or reflective materials) can be added to the compositions of the present invention to provide 3D printable materials with optical functionality. The diffusing additives can be organic or inorganic particles, or a combination of organic and inorganic diffusing particles, as in, for example, US 9,547,108 B2.

[0088] Useful organic diffusing particles having a refractive index mismatch of + / -0.01 to 0.25 with the polymer matrix, as measured according to ASTM D542, can be composed of polymers selected from acrylic polymers and copolymers, styrene-based particles and copolymers (containing more than 50% by weight of styrene monomer units), silicones, and fluoropolymers (including, but not limited to, PTFE, PVDF, and polyvinylidene fluoride / hexafluoropropylene copolymers). The organic diffusing particles can be crosslinked or uncrosslinked. The organic diffusing particles can be present at 0 to 20% by weight, preferably 0.5 to 10% by weight.

[0089] Useful organic diffusing particles having a refractive index mismatch of + / - 0.01 to 0.5 with the polymer matrix as measured according to ASTM D542 can be selected from titanium dioxide, zinc oxide, PdS, barium sulfate, silicon dioxide, calcium carbonate, natural and synthetic clay systems (aluminosilicates, e.g., montmorillonite). Inorganic diffusing particles can be present at 0-20% by weight. Some inorganic diffusing particles may also help reflect light.

[0090] Optical brighteners can also be added to the compositions of the present invention to provide 3D printable materials with improved optical effects in the printed parts. Optical brighteners can be white pigments with particle sizes in the nanoscale range, preferably with an average particle size of 10-300 nm. Examples include, but are not limited to, nano titanium dioxide, nano zinc compounds (including but not limited to nano zinc borate). Brighteners can be present at 0.00001-1 wt%, 0.0001-0.5, 0.001-0.1 wt%.

[0091] characteristics The primary performance characteristics of the compositions of the present invention include: 1) Excellent optical clarity. 3D printed parts are more difficult to provide optical clarity than injection or compression molded parts because of the many interlayer interfaces. For a 3.2 mm thick 3D printed part, a total white light transmittance of greater than 80%, preferably greater than 84%, more preferably greater than 86%, and most preferably greater than 88% can be obtained. A haze of less than 80%, preferably less than 70%, and more preferably less than 60% can be obtained. Haze and total white light transmittance are obtained according to ASTM D1003. Surface treatments such as polishing can improve the haze of the article.

[0092] In one embodiment, 3D printed internal transparent parts can be printed with a layer height of 0.05 mm, or even 0.1 mm, to produce excellent transparency and very low haze (less than 50%, preferably less than 40%, or even less than 25% haze based on ASTM D1003 for a 2 mm thick part). As known in the art, layer height is the Z-direction thickness of the constituent layers as they are deposited in the XY direction by an extruder. The best transparency is obtained with printing temperatures above 60° C., build plate temperatures above the Tg of the acrylic composition, and without a fan. Post-treatments such as coating, sanding, finishing, tumbling, and steam polishing can further improve the transparency of the print.

[0093] Without being bound to a particular theory, it is believed that the high transparency is due to the internal temperature of the print during printing, which in one embodiment is about 130°C. This temperature is significantly above the Tg, fusing the layer lines and releasing internal stresses, completely densifying the part and making it internally transparent. This Tg difference is maintained for at least 5 minutes, preferably 10 minutes, and more preferably 20 minutes or more after printing. This allows the polymer chains to become mobile and fluid, entangling with those of the material added above, below, and to the side, thereby reducing or eliminating the interfaces between the layers, leading to both internal transparency and superior Z-direction mechanical properties, and typically more robust, stronger, and closer to isotropic parts.

[0094] 2) Tensile Elongation at Break: The compositions of the present invention have a tensile elongation of greater than 10%, preferably greater than 20%, when printed and tested in the XY direction according to ASTM D638.

[0095] 3) Little to no warping over a wide temperature range of 220° C. to 260° C. allows the acrylic compositions of the present invention to be used in a wide range of commercial and specialty printers that may have parts as large as 12 inches. Warping is measured using the following warping test (see details in Example 2).

[0096] Test specimens are printed to evaluate the warp tendency of various acrylic compositions. The geometry is specifically designed to exacerbate the fundamental warp properties of the polymer when printed. The part thickness increases with height, making the part more difficult as printing progresses. The higher the percentage of the test specimen that can be printed without warping or delaminating from the build plate, the better the print performance. If the entire part can be printed and remains flat, the material has optimal warp properties and large parts (>10 inches) can be printed without warping.

[0097] Warpage is related to the ability of the part to adhere to the base plate of the melt extrusion printer, which is necessary for successful printing.

[0098] 4) Yield Stress: The stress at yield is greater than 30, more preferably greater than 35 MPa, as measured by ASTM D638.

[0099] 5) Packing density: Extrusion printed articles additively manufactured with the acrylic composition of the present invention have a packing density of more than 95%, preferably more than 98%, preferably more than 99%, calculated by dividing the density of the printed part by the bulk density of the material. High packing density can be promoted by slight overflow of material at each specific spot.

[0100] 6) Transparency of the printed article: Extruded additively manufactured articles using the acrylic composition of the present invention have a light transmission of greater than 50%, preferably greater than 60%, and more preferably greater than 65%, when measured on a 2.1 mm thick sample using ASTM D1003, assuming the printed article has 10 layers and each layer has a line width of 0.4 mm.

[0101] The low Tg acrylic copolymers of the present invention provide greater transparency than acrylic alloys. Without being bound by any theory, it is believed that the lower transparency of the alloys is due to a lack of compatibility between the alloy components.

[0102] 7) "Ideal" Articles: The compositions of the present invention produce transparent articles that do not yellow over time. Other techniques, such as UV-cured SLA-type printing, produce yellow, brittle parts. Other non-acrylic thermoplastics produce either yellow parts (ABS, copolyester) or hazy parts (PC, PetG). With other acrylic materials outside of the present invention, layers and lines within the part and poor Z-build direction properties would be observed (as with all other 3D material extrusion printing materials). However, with the present set of materials and printing windows, it is possible to obtain internally transparent materials, relative internal densities of 99% or more, and nearly isotropic parts.

[0103] filament In one embodiment, the acrylic composition is extruded into a filament for use in a material extrusion additive process. The filament may be a single strand of the acrylic composition or may be in the form of a co-extruded multiphase filament. In one embodiment, the filament has an intermediate layer composition of the acrylic composition surrounded by a sheath comprising a different acrylic composition, for example, including a special effect additive, or vice versa.

[0104] Filaments formed from the acrylic composition of the present invention form filaments with very little shrinkage or warping and with a very uniform diameter. Filaments with the acrylic composition of the present invention vary in diameter by less than + / - 5% over a 10 foot length, preferably less than 3% over a 10 foot length. Low filament diameter variation is essential for use in material extrusion additive manufacturing processes, since feed rate calculations and the resulting density of the printed article are based on calculations that assume the filament diameter is constant.

[0105] 3D Printing Process: The acrylic 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.

[0106] The acrylic 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 the acrylic composition), at any speed. Such machines can be any machine that falls within the definition of material extrusion or hybrid systems that include one or more material extrusion heads according to ISO / ASTM52900. 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 potentially be sprayed with a spray nozzle (sprayed molten plastic) onto the surface to be printed, such as by the Arburg Freeformer technique.

[0107] A general description of the printing process includes the following steps: A filament, pellets, or powder of the acrylic composition is fed into a 3D 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 acrylic composition to a heated nozzle at a set rate, and the printer moves the nozzle to the appropriate position to deposit the set amount of the acrylic composition.

[0108] In a preferred embodiment, the polymer has a low shear melt viscosity as described above.

[0109] In a preferred embodiment, the material extrusion additive manufacturing printer has a heated build plate, generally between 50 and 150° C. (preferably greater than 60° C., more preferably greater than 75° C.). In another embodiment, the build plate temperature during the printing process is maintained at least 1%, preferably 3%, preferably 5%, preferably 10%, more preferably 15%, more preferably 20% above the Tg of the acrylic composition, measured in degrees Celsius.

[0110] The printer includes one or more heated nozzles through which the material is extruded. These nozzles can reach 200° C. (preferably 250° C., more preferably greater than 300° C.). The printer includes a build environment that is open to ambient conditions or enclosed. In another embodiment, the printer can include additional controls, such as an actively heated or cooled build environment. An actively heated build environment can be used to reduce warping of the acrylic composition during printing. In another embodiment, the printer can include radiant heating elements within an open or enclosed build volume.

[0111] In another embodiment, the printer is equipped with a mixing head that combines multiple raw materials, such as a Diamond Hotend, where any raw material composition, or the final composition after mixing, meets the specifications described herein. In another embodiment, the printer is fed with multiple compositions that are combined in a direct pellet extruder print head, where either the compositions or the final mixed composition meets the specifications described herein. In one preferred embodiment, the 3D printer is programmed to operate with a slight overflow of 1% to 10% overflow. This means that the amount of acrylic composition dispensed by the printer is greater than the calculated amount required for the 3D article being formed. The overflow packs the acrylic composition more tightly, increasing part density while increasing 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 feed 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.

[0112] 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.

[0113] Other process conditions improve the open time of the printed article and provide excellent clarity and Z-direction physical properties. These include, for example, increasing the temperature of the printer's build plate and / or build chamber. Without being bound to a particular theory, it is believed that for best results, the internal temperature of the print should be at least 25° C., preferably at least 30° C., preferably at least 40° C., and most preferably 50° C. higher than the Tg of the acrylic 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.

[0114] 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 print speed (25 mm / sec) to allow the part to retain more heat. The 3D printer will extrude very thin layers of 0.05 mm. The 3D printer can operate with a slight overflow of 1% to 10% to fill in 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 at 85°C), 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.

[0115] 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 been surprisingly found that the acrylic material of the present invention can retain its shape during the printing process at build plate temperatures that are 40°C or more above the material's Tg. The acrylic polymer is believed to be soft and able to retain its shape due to the large distance between the LS transition point and the first G' / G" crossover point on the rheology curves described above / below. Using an IR thermal camera, it was shown that the interior of the part was 50°C above the material's Tg, yet the part retained its shape because the interior temperature was still below the first crossover point. The higher build plate temperature improves clarity.

[0116] 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 can be used to produce internally clear parts without layer lines. Using 0.4 mm layers, objects can be produced 8 times faster than using 0.05 mm layers.

[0117] 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

[0118] Example 1 Filaments were extruded having the compositions listed below. The filaments were 3D printed and tested for XY tensile strength, XY tensile modulus, XY elongation at break, Z tensile strength, and Z elongation at break. The data is shown in the table below. Sample 1 = Acrylic copolymer with 22-28% EA and high impact modifier content Sample 2 = Acrylic copolymer with 22-28% EA and low impact modifier content

[0119] [Table 1]

[0120] Example 2 Warpage of various PMMA compositions To evaluate the warpage tendencies of various acrylic compositions, test specimens in Figure 1 were printed. The geometry was specifically designed to exacerbate the fundamental warpage properties of the polymer when printed. The part thickness increases with height, making the part more difficult as the print progresses. The higher the percentage of the specimen that can be printed without warping or delaminating from the build plate, the better the print performance. If the entire part can be printed and remains flat, the material has optimal warpage properties and large parts (>10 inches) can be printed without warping.

[0121] Warping is highly dependent on the temperature of the build plate relative to the Tg of the material. The curling effect, known in the art as warping, is caused by the shrinkage of the material as it cools after being deposited by the nozzle. This shrinkage creates shear forces between the layers, which results in the part bending. By heating the build plate close to the Tg of the polymer, the polymer remains in the mobile phase longer, reducing the effect of these shear forces.

[0122] Various build plate temperatures were used, ranging from 70% of the polymer's Tg to 110% of the polymer's Tg, and the percent complete of the specimens was recorded at these various temperatures. Percent complete was defined as the minimum printed height measured perpendicular to the xy printing plane divided by the theoretical maximum height of the specimen. When the specimen is printed, any warping will cause the final dimensions of a particular section to be smaller than the nominal dimensions of the model. Measuring the minimum thickness captures the section of the part most affected by warping. The minimum thickness can also be thought of as the section of the specimen that is lifted from the build plate the fastest.

[0123] Summing the percent completion across the Tg range of 70% to 110% gives an aggregate percent completion that can be used to compare the relative performance of different polymers. 100% is the theoretical maximum for material that completed all prints across the full range. Results for a range of compositions are shown in Table 2 and Figure 2.

[0124] [Table 2]

[0125] Using the described experimental procedure, a variety of compositions were tested. Samples 3-10, shown in Table 2 and Figure 2, contained various amounts of ethyl acrylate comonomer to reduce the Tg of the material. Comonomer loading varied from 0.3% to 28%. Each sample contained 15-35% core-shell impact modifier. The molecular weight of the samples varied from 50,000 g / mol to 300,000 g / mol. As shown in Figure 1, the ability of a composition to print parts without warping is highly dependent on the Tg of the composition. Surprisingly, the amount of warping did not seem to correlate with molecular weight, as sample 10, which had one of the highest molecular weights, performed the best overall. Sample 3 had a similar molecular weight to sample 8, but the sample with the lower Tg (sample 8) had a much better completion rate.

[0126] Because percent completion uses percent Tg as input for build plate temperature, percent completion is the sum of specimen completions as the build plate temperature varies from 70% to 110% of the material's Tg, already taking into account the material's Tg. Surprisingly, despite being normalized by Tg, the percent completion results show a strong dependence on the material's Tg. In other words, samples with lower Tg not only print better at lower build plate temperatures overall, but also print better after accounting for the lower Tg, allowing for a broader range of build plate temperatures that can be printed. Other classes of amorphous materials have not shown this strong dependence on Tg for warpage. This unexpected trend may explain the lack of commercial success of traditional high Tg acrylics in the filament market.

[0127] The composition listed as Sample 11 featured the addition of 10% plasticizer to the composition of Sample 5 to reduce the Tg without the addition of copolymer. This sample also performed well in percent completion tests, matching the results of samples whose Tg was altered by the addition of copolymer.

[0128] Example 3 The aggregate completion rate feature in Example 2 evaluates the warpage characteristics of a material across its processing window. In current desktop 3D printers, the build plate temperature can fluctuate due to changing ambient conditions, and unexpected cooling can occur due to drafts or other unexpected air currents. As such, materials that dominate the market today, such as PLA and PETG, have wide processing windows and can be printed at a range of build plate temperatures without warping.

[0129] If current technology continues to advance, these limitations may no longer be relevant for material selection in FFF 3D printing. Current printers are in fact limited to a maximum build plate temperature of approximately 120 °C, a limitation common to all but the most expensive 3D printers. Similarly, current printers do not feature a heated chamber or enclosure, so the air temperature around the part is always the same as the room temperature.

[0130] Figures 3 and 4 show the individual data points used to generate the aggregate completion percentage. The aggregate completion percentage shown in Example 2 is the area under the curve shown in Figure 3, evaluated by the trapezoidal rule from a ratio of 0.7 to a ratio of 1.1. Thus, the lower the temperature relative to the Tg at which the material can reach the full 12 mm specimen height, the greater the area under the curve and the higher the aggregate completion percentage. It is noteworthy that while the high performing materials all have curves that shift to the lower temperature end of the spectrum, all materials maintain a positive correlation between build plate temperature and completed height. Given this positive correlation, it can be proposed that higher Tg acrylic compositions will show better completion percentages when printed at build plate temperatures above 110% of the material's glass transition temperature. Additional printer features such as heated chambers and additional radiant heating elements also allow for heat immersion of the part, allowing for full completion of warped specimens.

[0131] Example 4 Another variation made in the composition characteristics in Table 2 was the impact modifier composition. Samples 6 and 7 have the same acrylic copolymer matrix and both use 20-30% impact modifier, but use different compositions of core-shell impact modifier.

[0132] The following chemicals were used in all improver emulsions: MMA = methyl methacrylate EA = Ethyl acrylate BA = butyl acrylate Sty = styrene ALMA = Allyl methacrylate

[0133] Sample 6 utilized the impact modifier composition described below. A three-stage polymer prepared by the method of Owens (US3793402) initiated with potassium persulfate and stabilized with potassium dodecylbenzenesulfonate. The ratio of the three stages was 35 / / 45 / / 20. Stage 1: MMA / EA / ALMA (95.8 / 4 / 0.2) Stage 2: BA / Styrene / ALMA (80.2 / 17.8 / 2) Stage 3: MMA / EA (4 / 96)

[0134] Sample 7 utilized an impact modifier as described below. 1. Polymers of multi-stage continuously produced composition. 2. The ratio of the three stages was 12 / / 55 / / 33. 3. The composition of the three stages is Stage 1: 74.8 / 25 / 0.2 MMA / EA / ALMA Stage 2: 83.5 / 15.5 / 1.0 BA / Sty / ALMA Stage 3: 95 / 5 MMA / EA

[0135] The monomer charge, consisting of 34% of stage 1, was emulsified in water using potassium dodecylbenzenesulfonate as an emulsifier and polymerized using potassium persulfate at an elevated temperature, using potassium carbonate to control the pH. The remainder of stage 1 was then added to the preformed polymer emulsion and polymerized at an elevated temperature using potassium persulfate, controlling the amount of soap added to prevent the formation of a significant number of new particles. Stage 2 monomer was then added and polymerized at an elevated temperature using potassium persulfate, controlling the amount of soap added to prevent the formation of a significant number of new particles. Stage 3 monomer was then polymerized at an elevated temperature using potassium persulfate, again controlling the amount of soap added to prevent the formation of a significant number of new particles. The polymer was isolated by coagulation, freeze drying, or spray drying.

[0136] The impact modifiers incorporated into the acrylic copolymer by melt processing did not affect print performance as much as the Tg, but certain chemistries performed better than others, with Sample 7 performing better than Sample 6. Figures 5 and 6 show the individual data points used to generate the aggregate completion percentage.

[0137] Example 5 Internal transparency plaque measurement A variety of plastic filaments were used to 3D print 35mm x 35mm plaques with a thickness of 3.2mm 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 below in Figure 7. These results are shown in Table 3.

[0138] The 15-30% ethyl acrylate modified copolymers were 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, standard 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, so the internal parts could not reach the required temperature differential 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 PMMA can achieve hazes of less than 10% or even less than 5% if the build plate is set at a temperature sufficient to reach an internal temperature of approximately 160°C.

[0139] [Table 3]

[0140] Example 6 IR thermal image of the part being printed While printing a transparent part using the outlined method, a Flir E60IR thermal camera recorded images of the printing process. These images established that the temperature of the internal parts can be kept well above the Tg of the material and the material can still maintain its shape. The thermal image shown in Figure 8 shows a 110mm x 20mm part with a height of 3mm at the time the image was taken. The build plate was at 120°C and the nozzle was 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 is able to maintain its shape over the 5-hour printing process, after which the final part will have a height of 20mm.

[0141] The second IR image shown in Figure 9 shows a part that is 20mm x 30mm and 19mm high as printed. The final part is shown in Figures 10 and 11. 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 approximately 6mm of mobility on the printing surface. At a given printing speed, this means approximately 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.

[0142] The above block was printed with two filaments. The transparent filament was of the same composition as 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 0.3mm 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 20mm width. The block was finished using an Edge Finisher's Model EF-200 to create a flat, transparent surface for a post-print surface finishing step.

[0143] The dual-extruded block demonstrates that plastic can be purposefully and precisely positioned using this method, even though the temperature of the interior parts 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.

[0144] Example 8 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.

[0145] The rheology of a high EA content, low Tg acrylic and a low EA, high Tg acrylic are shown below. From the viscosity curve, 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.

[0146] 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 the onset of curing. The results for Samples A, B, and C from Example 5 are shown in Figures 12-17.

Claims

1. 1. An acrylic polymer composition for use in 3D printing, comprising a single matrix acrylic copolymer, optionally alloyed with less than 5% of other compatible, miscible or semi-miscible polymers, and optionally one or more additives dispersed within said matrix.

2. 2. The acrylic polymer composition of claim 1, wherein the matrix acrylic copolymer comprises methyl methacrylate monomer units and 0.1 to 60%, preferably 0.5 to 40, preferably 4 to 35, more preferably 9 to 30% by weight of one or more other monomers copolymerizable with the methyl methacrylate monomer units.

3. 2. The acrylic polymer composition of claim 1, wherein the matrix acrylic copolymer comprises at least 90% by weight, more preferably at least 95% by weight, and most preferably 100% by weight, of (meth)acrylic monomer units, based on the total monomer units in the copolymer.

4. The acrylic polymer composition of claim 1, wherein the matrix acrylic copolymer has a weight average molecular weight of 50,000 to 500,000, preferably 55,000 to 300,000, preferably 65,000 to 200,000 g / mol.

5. The matrix acrylic copolymer has a viscosity of 230° C. for 1 second when measured using a rotational viscometer according to ASTM C965, the viscosity being measured on a polymer composition that does not contain an impact modifier. -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 acrylic polymer composition of claim 1, having a viscosity of 20 to 2,000 Pa·s, preferably 25 to 1,000 Pa·s, more preferably 30 to 500 Pa·s at a shear rate of 1000.

6. The acrylic polymer composition of claim 2, wherein the matrix acrylic copolymer comprises at least one other acrylic monomer unit selected from the group consisting of methyl acrylate, ethyl acrylate and ethyl methacrylate, butyl acrylate and butyl methacrylate, isooctyl methacrylate and acrylate, n-octyl acrylate, lauryl acrylate and lauryl methacrylate, stearyl acrylate and stearyl methacrylate, isobornyl acrylate and methacrylate, methoxyethyl acrylate and methacrylate, 2-ethoxyethyl acrylate and methacrylate, isodecyl acrylate and methacrylate, tert-butyl cyclohexyl acrylate and tert-butyl cyclohexyl acrylate. and methacrylates, tertiobutylcyclohexanol methacrylate, trimethylcyclohexyl acrylate and methacrylate, methoxypolyethylene glycol methacrylate and acrylates having 2 to 11 ethylene glycol units, pentoxyethyl acrylate and methacrylate, alkoxylated phenol acrylates, ethoxylated phenyl acrylate and methacrylate, epoxypropyl methacrylate, tetrahydrofurfuryl acrylate and methacrylate, alkoxylated tetrahydrofurfuryl acrylate, cyclic trimethylolpropane formal acrylate, carprolactone acrylate, dimethylaminoethyl acrylate, methacrylate monomers, and mixtures thereof.

7. 10. The acrylic polymer composition of claim 1, wherein the acrylic polymer composition further comprises an impact modifier which is a core-shell impact modifier or a block copolymer.

8. 10. The acrylic composition of claim 1, wherein said impact modifier is refractive index matched to said acrylic polymer matrix.

9. 8. The acrylic composition of claim 7, wherein the core-shell impact modifier comprises: a) as a first stage, an optionally non-elastomeric, relatively hard polymer having a glass transition temperature above 25° C., which is polymerized from a monomer mixture of 100-80% by weight of the monomers described above to obtain a rigid thermoplastic polymer, 0-10% by weight of a copolymerizable multifunctional crosslinking monomer, and 0-10% by weight of a copolymerizable graft linking monomer having two or more addition polymerizable unsaturated reactive groups that participate in the polymerization reaction at substantially different rates; b) as intermediate stage, which is elastomeric and is polymerized in the presence of the first stage from a monomer mixture comprising 50-99.9% by weight of an alkyl acrylate and / or alkyl methacrylate mixture, the alkyl group of which contains 1-8 carbon atoms, 0-49.9% by weight of a copolymerizable monoethylenically unsaturated monomer, 0-5.0% by weight of a copolymerizable multifunctional crosslinking monomer, and 0.05-5.0% by weight of said copolymerizable graft linking monomer, said intermediate stage being further characterized in that it exhibits a glass transition temperature of 25° C. or less when the monomers are polymerized in the absence of the first stage; and at least one final stage, which is relatively hard and is polymerized in the presence of the first and intermediate stages from a monomer mixture of said monomers to obtain a rigid thermoplastic polymer. The final stage is further characterized in that it exhibits a glass transition temperature greater than 50° C. when the monomers are polymerized in the absence of the first and intermediate stages, the graft linking monomer has two or more addition polymerizable unsaturated reactive groups that participate in the polymerization reaction at substantially different rates, and the crosslinking monomer has a plurality of addition polymerizable unsaturated groups, all of which participate in the polymerization reaction at approximately the same rate as one another.

10. 10. The acrylic composition of claim 1, further comprising one or more additives selected from the group consisting of fillers, carbon fibers, ground carbon fibers, carbon powder, carbon nanotubes, boron nitride, diamond, glass beads, glass fibers, titanium dioxide, zinc oxide, PdS, barium sulfate (BaSO 4 ), silicon dioxide, nanosilica (SiO 2 ), calcium carbonate (CaCO 3 ), natural and synthetic clay systems, aluminosilicates, montmorillonite, aramid fibers, polyaryletherketone fibers, graphite, graphite nanoplatelets, graphite oxide, graphene, crushed carbon fibers, nanofibers, hollow spheres, dyes, colorants, pigments, metal particles, metal flakes, milky dyes, fluorescent dyes, polymer particles that can be crosslinked and comprise a polymer selected from acrylic polymers and copolymers, crosslinked acrylic beads having an average particle size of 20 to 500 micrometers, styrene-based particles, copolymers containing more than 50% by weight of styrene monomer units, silicones, polyamides, fluoropolymers, poly(tetrafluoroethylene), poly(vinylidene fluoride), and vinylidene fluoride / hexafluoropropylene copolymers, deodorants, fragrances, internal release agents, luminescent agents, diffusing particles, reflective particles, optical brighteners, flame retardants, UV stabilizers, antimicrobial additives, cellulose, antioxidants, and mixtures thereof.

11. 1. An acrylic polymer composition for use in 3D printing, said acrylic composition having a Tg of less than 160°C, preferably less than 130°C, preferably less than 120°C, preferably less than 110°C, preferably less than 100°C, preferably less than 90°C, preferably less than 85°C, preferably less than 80°C, more preferably less than 75°C, comprising: a) a continuous matrix phase consisting essentially of one or more acrylic polymers; b) optionally 0 to 60 wt. %, preferably 9 to 40 wt. %, more preferably 15 to 30 wt. % of an impact modifier; c) optionally, 0 to 50 vol. %, preferably 0.01 to 40 vol. %, more preferably 0.05 to 25 vol. %, based on the total volume of the acrylic composition, of one or more other additives.

12. 12. The acrylic polymer composition of claim 11, wherein the polymer composition comprises an acrylic copolymer matrix phase comprising one or more acrylic copolymers having a Tg from 70°C to 160°C, and further comprises an effective amount of at least one non-polymeric additive to reduce the polymer composition Tg to less than 105°C, preferably less than 100°C, preferably less than 95°C, preferably less than 85°C, preferably less than 80°C, more preferably less than 75°C.

13. The acrylic polymer composition of claim 12, wherein the additive comprises 2 to 40 wt%, more preferably 4 to 20 wt%, of a plasticizer, based on the total weight of the acrylic polymer matrix.

14. 14. The acrylic polymer composition of claim 13, wherein the plasticizer is selected from the group consisting of phthalates, epoxides, and adipates.

15. 1. An acrylic article, wherein the article is transparent and capable of obtaining 3D printed parts at a thickness of 2 mm having a total white light transmission of greater than 80%, preferably greater than 84%, more preferably greater than 86%, and most preferably greater than 88%, 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 the 2 mm thick 3D printed parts printed with line heights of 0.1 mm or more, 0.2 mm or more, 0.3 mm or more, 0.4 mm or more have an internal haze of less than 25%, preferably less than 20%, more preferably less than 15%, more preferably less than 10%, and most preferably less than 5%.

16. 16. The acrylic article of claim 15, wherein the article comprises the acrylic polymer composition of claim 1 or 12.

17. 12. The acrylic polymer composition of claim 1 or claim 11, wherein the composition is in the form of a powder, pellets, or filaments.

18. 12. An acrylic article produced by a material extrusion additive manufacturing process using the acrylic alloy composition of claim 1 or claim 11.

19. 20. The article of claim 18, wherein the article has one or more of the following characteristics: a) a tensile elongation of greater than 10%, preferably greater than 20%, as measured by ASTM D638; b) an internal packing density of greater than 90%, preferably greater than 95%, and most preferably greater than 97%; c) A yield stress greater than 35 MPa as measured by ASTM D638.

20. A process for forming an extrusion additive (3D) acrylic article, comprising the steps of: - presetting the 3D printer software to a volume flow and line spacing set for printing said article; - Optionally, using a heated build plate; - supplying the acrylic composition of any of claims 1 or 12 in the form of a filament, pellet or powder to said 3D printer, - delivering a melt of the acrylic composition to a heated nozzle by the printer; - Depositing the acrylic composition melt at set locations, line spacing, and flow rates set by the software to form an article.

21. 21. The process of claim 20, wherein the acrylic composition overall has a Tg of from 70°C to 160°C, preferably from 80°C to 150°C, preferably from 90°C to 150°C, preferably from 110°C to 150°C, preferably greater than 115°C, preferably greater than 120°C, preferably greater than 125°C, and wherein the build plate temperature during the printing process is maintained at least 1%, preferably 3%, preferably 5%, preferably 10%, more preferably 15%, more preferably 20% above the Tg of the acrylic composition, measured in degrees Celsius.

22. 21. The process of claim 20, wherein the flow rate and / or line spacing represents an overflow of 1 to 10%.

23. 3D printed articles comprising an acrylic composition having a Tg of less than 110°C, 100°C, preferably less than 95°C, preferably less than 90°C, 85°C, preferably less than 80°C, more preferably less than 75°C.

24. 24. The article of claim 23, wherein the article and article or part is selected from the group consisting of transportation articles, lighting articles, building and construction articles, medical articles, sanitary articles, designer kitchenware, medical, and electronic articles. 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, countertops, and storage. pipework, decorative exterior trim, molded side trim, quarter panel trim panels, fenders and fender extensions, louvers, rear end panels, pickup truck back caps, rearview mirror housings, truck, bus, camper, van, and mass transit vehicle accessories, b-pillar extensions, and the like; lawn and garden tools, mobile home bathroom fixtures, 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; sailboats, yachts, and other sporting equipment; 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, gutter end caps, 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 device parts such as implants, lighting appliques, luminaires, window coverings, surface modifications, and visualization-assisted 3D models based on medical images, architectural models, topographical data, mathematical analysis, or other data sets; 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's Code of Federal Regulations Title 21), light guides, interior lighting, integrated optics, display components, instrumentation, see-through components, solar cells, solar power system fixtures and rigging, artificial nails, dosimeters, jewelry, footwear, fabrics, firearm parts, cell phone cases, packaging.

Images