Acrylic support structure for 3D printed fluoropolymer products

Abstract

The present invention relates to the use of compatible, semi-miscible, or miscible polymer compositions as support structures for 3D printing of objects, including those made from polyether block amide copolymers such as Arkema's PEBAX® block copolymers, polyamides such as Arkema's RILSAN®, polyether ketone ketones such as Arkema's KEPSTAN® PEKK, and fluoropolymers such as Arkema's KYNAR® PVDF, particularly polyvinylidene fluoride and its copolymers. One particularly useful miscible polymer is an acrylic polymer that is miscible with the fluoropolymer in the melt. The support structure composition provides the necessary adhesion to the build plate and printed object and support strength during the 3D printing process, yet is removable after the fluoropolymer object has cooled. The support polymer composition is selected to be rigid and low-warp, yet flexible enough to be formed into a filament.

Description

[Technical Field]

[0001] This invention relates to the use of miscible, semi-miscible, or miscible polymer compositions as support structures for 3D printing of polyether block amides, polyamides, polyether ether ketones, polyether ketone ketones, and fluoropolymer objects, particularly polyvinylidene fluoride (PVDF) and its copolymers. One particularly useful miscible polymer is acrylic polymer, which is miscible with fluoropolymers in the molten material. The support structure composition provides the necessary adhesion to the build plate and the print and support strength during the 3D printing process, but is removable after the fluoropolymer object has cooled. The support polymer composition is selected to be rigid and have little warping, but flexible enough to form into a filament. [Background technology]

[0002] 3D printing is an additive manufacturing process that prints or produces objects by adding material layer by layer. Each layer is added on top of a previously printed layer. When printing a simple object with upright and vertical walls, the printing process is relatively straightforward. However, most objects have structures that are not so simple and include curved surfaces or surfaces that may protrude outside the body of the object. Surfaces can be sloped, oriented at various angles, and have varying thicknesses or sizes.

[0003] The printing or fabrication of such protruding or overhanging surfaces during material extrusion additive manufacturing is typically achieved by introducing support structures similar to scaffolding used in building construction. Furthermore, a sacrificial substrate printed with the secondary material is often called a raft and is frequently placed before printing with the main material. This support base provides further adhesion to the build plate and resistance to warping and delamination of the build plate. After the printing process is complete, the support is removed.

[0004] When determining the scaffolding material or support structure to be used for printing, several important factors are desirable, including a) the printability of the support material, b) high adhesion of the support material to the build plate, c) a low tendency to warp, and d) the ability of the support material and build material to bond to each other in the molten material during the printing process. Other desirable factors include e) having support material and build material with similar viscosity at the printing temperature, f) requiring support with high melt strength to support the build material, and g) preferring support with a high modulus of elasticity when supporting build material that tends to shrink or warp.

[0005] In many cases, support structures are made from the same material from which the 3D object is fabricated. By programming a small gap between the support material and the build material into the structure, the support can be easily separated from the 3D object made of build material after the 3D manufacturing process.

[0006] For example, U.S. Patent No. 8,974,213 allows the use of different materials for support and build materials. Water-soluble or solvent-soluble support structures have been used for printing acrylonitrile butadiene styrene (ABS), polystyrene (PS), polypropylene (PP), polyethylene (PE), and nylon, as seen in U.S. Patent Application Publication No. 2019 / 0202134. U.S. Patent Application Publication No. 2019 / 0001569 describes the use of cyclic olefin copolymers (COCs) and cyclic olefin polymers (COPs) as support materials for 3D printing of high-temperature polymers such as polyimides. While COC and COP polymer supports have sufficient melt strength to support the build material, they also break at room temperature due to a lack of adhesion and / or differences in thermal expansion between the support material and the build material. Key properties of polymer supports include appropriate viscosity and shear rate at the process temperature.

[0007] To date, no support materials have been developed to support fluoropolymers, particularly 3D printable polyvinylidene fluoride (PVDF) as described in U.S. Patent Application Publication No. 2019 / 0127500. Common soluble support materials such as polyvinyl alcohol (PVA) are too soft to withstand the warping of PVDF and do not adhere well to it. On the other hand, for hard materials such as ABS and other plastic breakaways, PVDF does not adhere well to them, and they do not adhere well to PVDF. PMMA has been described as being alloyed with PVDF at low PMMA levels, but it is not described solely as a separate support mechanism. International Publication No. 2017 / 210285 to Arkema (US Application No. 16 / 305,123) describes dimensionally stable acrylic polymer compositions useful for 3D printing. International Publication No. 2019 / 067857 to Arkema states that polymethyl methacrylate (PMMA) films can be used to improve the base adhesion of PVDF printing. PMMA is not used as a printable filament, and no specific types of acrylic copolymers or alloys are described. [Overview of the project] [Problems that the invention aims to solve]

[0008] The problem to be solved by this invention is to develop a useful support material for 3D printing of fluoropolymers and other polymers, particularly PVDF polymer compositions. The support material must be removable from the 3D printed object after it has been formed. The support material must be easy to print (easy to 3D print and easy to attach to the build plate), have sufficient rigidity to function as a support, and withstand warping and shrinkage caused by the cooling of the (semi-crystalline) build material. In addition, the support material must be compatible with the polymer (especially fluoropolymer) build material when melted.

[0009] Certain polymers, including polyether block amides, polyamides, polyether ether ketones, polyether ketone ketones, fluoropolymers, and especially PVDF polymers, are particularly sought after for 3D printed parts due to their extremely high chemical resistance, durability, flame retardancy, and mechanical properties. However, these polymers, especially PVDF, have a high crystalline content, resulting in high shrinkage and consequently warping, while also exhibiting poor adhesion to glass and other materials, making 3D printing extremely difficult.

[0010] New, more printable PVDF compositions have been developed by Arkema (U.S. Patent Application Publication No. 2019 / 0127500), which include blends of fluorocopolymers and fluorohomopolymers, and blends with compatible or miscible polymers. These copolymers and blends are soft and have good adhesion to glass, resulting in less warping from the bed, but due to their elastomeric and viscous properties, they tend to shrink significantly, have poor bulge resolution, and do not adhere to glass as well as other elastomer materials. [Means for solving the problem]

[0011] Surprisingly, it has now been discovered that specially selected compatible or miscible polymer compositions can be used as support materials for 3D printing of polyether block amides, polyamides, polyether ether ketones, polyether ketone ketones, and fluoropolymers. Acrylic compositions, including polymethyl methacrylate, its copolymers, blends, and alloys, can be used as effective supports for these 3D printed polymers, particularly PVDF. Specially formulated printable acrylic compositions enable the printing of parts that are much larger and more complex than previously printable. Furthermore, as supports, the support structures of the present invention enable the printing of parts and features that were previously unprintable, including parts with protruding portions, as well as parts that were previously manufactured only by conventional processes such as injection molding, thereby increasing the design freedom available to humans in 3D printing of fluoropolymers. Some of the printed parts of the present invention could not even be produced by injection molding processes.

[0012] The acrylic support composition provides excellent printability, high build plate adhesion, high rigidity (modulus of elasticity), and low warping. While impact modifiers allow for some reduction in modulus of elasticity, the resulting composition has sufficient rigidity to resist the warping of PVDF.

[0013] Compared to ABS and PETG, which have low elastic modulus and poor compatibility with PVDF, the acrylic support composition of the present invention has sufficient rigidity to resist the warping of PVDF and sufficient compatibility to adhere to the surface of PVDF and for PVDF to adhere to the surface of the acrylic support during printing.

[0014] Importantly, the acrylic support composition of the present invention can be easily removed following 3D printing of the fluoropolymer object by either physical removal or, preferably, dissolution.

[0015] In this specification, embodiments have been described in a way that enables writing clear and concise specifications, but it will be appreciated that the embodiments can be variously combined or separated without departing from the invention. For example, it will be understood that all the preferred features described herein are applicable to all aspects of the invention described herein.

[0016] Aspects of the present invention include the following: A first aspect is a support material composition for 3D printing of polyamide (PA), polyether block polyamide (PEBA), polyether ketone ketone (PEKK), and fluoropolymer compositions, wherein the support material composition comprises one or more polymer compositions that are compatible, miscible, or semi-miscible with the PA, PEBA, PEEK, PEKK, or fluoropolymer composition.

[0017] In a second aspect, the support material composition comprises an acrylic, polyester of a polycarbonate composition, preferably acrylic, and most preferably a PMMA polymer or a PMMA copolymer having more than 51 percent methyl methacrylate monomer units.

[0018] In a third aspect, the acrylic support composition is selected from an acrylic copolymer, an acrylic alloy, and an acrylic polymer blended with a non-polymer additive.

[0019] In a fourth aspect, the acrylic composition of the above aspect has a Tg of less than 165°C, less than 135°C, less than 125°C, preferably less than 115°C, less than 110°C, preferably less than 95°C, preferably less than 90°C, and preferably less than 80°C. Preferably, the Tg is higher than room temperature, preferably more than 30°C, more preferably more than 40°C, more preferably more than 50°C, and even more preferably more than 60°C.

[0020] In a fifth aspect, the acrylic composition of the above aspect has a viscosity of 4 sec-1 The low shear rate viscosity measured at -1 is less than 100,000 Pa·s, preferably less than 10,000 Pa·s, more preferably less than 5,000 Pa·s at a temperature of 230°C, and the low shear rate viscosity is preferably more than 50 Pa·s, more preferably more than 100 Pa·s.

[0021] In a sixth aspect, the support material composition of the above aspect contains at least 20% by weight, preferably at least 30% by weight, more preferably at least 40% by weight, more preferably at least 51% by weight, more preferably at least 60% by weight, more preferably at least 70% by weight of one or more acrylic polymers, and the acrylic polymer includes a polymethyl methacrylate homopolymer or a polymethyl methacrylate copolymer containing at least 51% by weight and more than 70% by weight, preferably more than 75% by weight of methyl methacrylate monomer units.

[0022] In a seventh aspect, the support material composition of the above contains a copolymer containing 70 - 80 weight percent of methyl methacrylate monomer units and 20 - 30 weight percent of C 1~4 acrylate units as the acrylic polymer matrix. The support material composition can alternatively be a blend of a methacrylate copolymer, a polylactic acid polymer, and other acrylic polymers.

[0023] In an eighth aspect, the support material of the above aspect contains an acrylic composition having 5 - 60 weight percent of an impact modifier and being impact - modified.

[0024] In a ninth aspect, the support material composition of the above aspect further contains an additive selected from the group consisting of a fluorescent whitening agent, an impact modifier, a processing aid, a rheology modifier, a heat and UV stabilizer, fluorescent and non - fluorescent dyes and pigments, a radiopaque tracer, a filler, a conductive additive, a solubility enhancer, a mechanical removal promoter, a lubricant, a plasticizer, and mixtures thereof.

[0025] In the tenth embodiment, the support material composition according to any of the above embodiments is soluble in a solvent selected from the group consisting of water, hot water, alkaline aqueous solution, and ethanol.

[0026] In the eleventh embodiment, the support material composition of the above embodiment comprises the filler, which is a polymer; a salt; and other compounds that are soluble in a mild solvent such as cold water, hot water, an alkaline aqueous solution or an acidic aqueous solution, or ethanol, or in a harsher solvent such as acetone, tetrahydrofuran, toluene, dichloromethane, chloroform, xylene, and toluene.

[0027] In the twelfth embodiment, the fluoropolymer supported by the support material of the above embodiment is measured by capillary rheometry at 232°C for 4 seconds. -1 Its low shear rate viscosity is less than 13,000 Pa·s, and it was measured by capillary rheometry at a given temperature of 232°C and 100 sec in the ASTM melt flow test for its fluoropolymer. -1 The high shear rate viscosity is 30-2000 Pa·s.

[0028] In a thirteenth aspect, an acrylic support composition for 3D printing of an object is presented, the object composition comprising one or more polymers that are compatible, miscible, or semi-miscible with the acrylic compatible composition.

[0029] In the 15th embodiment, the acrylic compatible polymer is a polyvinylidene fluoropolymer or copolymer, and may be an alloy blend with an acrylic polymer or copolymer, or a PVDF copolymer such as PVDF / HFP.

[0030] In a sixteenth aspect, a method for printing a 3D object is presented, comprising the steps of printing both a 3D build material and a support material using a support material composition and a build material, wherein the support material is compatible, miscible or semi-miscible with the fluoropolymer build material, and removing the support material composition after the formation of the 3D printed object.

[0031] In the seventeenth aspect, the process of the sixteenth aspect comprises the removal of the support material by physical destruction or dissolution of the support material, wherein the dissolution includes solubility in xylene, toluene, acetone, tetrahydrofuran, toluene, dichloromethane, chloroform, cold water, hot water, ethanol, alkaline aqueous solutions, and acidic aqueous solutions, as well as mixtures thereof, and other known solvents for the support material. [Brief explanation of the drawing]

[0032] [Figure 1] Figure 1 shows the test specimens used to quantify the warpage of different polymers. Small surface area in contact with the build plate and sharp corners tend to exacerbate warpage. [Figure 2] Figure 2 shows the cross-sectional area of ​​the warpage test specimen used in the warpage test. As the specimen increases in the vertical Z direction, printing becomes more difficult as printing continues. [Figure 3] Figure 3 shows a specimen from Example 2, where the printing time was reduced by 50% to improve the stability of the part during printing. Two specimens are printed and joined simultaneously to create a specimen that does not tip over during printing. The material type is switched within the instrument to create a zone sequence for testing the bonding strength of the material interface. The specimen has both PVDF to the support interface and support to the PVDF interface. [Figure 4] Figure 4: Object printed in Example 4 with the support structure left intact. [Figure 5]Figure 5: An example component featuring a pipe fitting printed with Arkema Kynar® 826-3D resin and PLEXIGLAS® 3DS support material. [Modes for carrying out the invention]

[0033] As used herein, copolymers refer to any polymer having two or more distinct monomer units, and will include terpolymers and those having three or more distinct monomer units. Copolymers may be random or blocky, heterogeneous or homogeneous, and may be synthesized by batch, semi-batch, or continuous processes.

[0034] Molecular weight is given as the weight-average molecular weight measured by GPC. Unless otherwise specified, percentages are given as weight percentages. References cited in this application are incorporated herein by reference.

[0035] As used herein, “build material” means the material used to form the final 3D object or article.

[0036] As used herein, “support material” means material that forms a scaffold, which supports the build material, particularly protrusions of the build material, and is removed when the final item is 3D printed. Supported protrusions may be on the outside of the printed object or on the inside of a hollow object. Support material may also be used as a base or raft on which the build material and / or support material is printed. Support material may also be used to print marking labels or identification labels on the build material, which may or may not be removed.

[0037] As used herein, "low shear viscosity" refers to the measurement of melt viscosity (ASTM D3835-0) at relatively low shear rates. This relates to the viscosity of the molten material after printing. For the purposes of this invention, the low shear rate at which viscosity is measured is 4 sec, when measured by capillary rheometry. -1 Therefore, the actual shear rate of the polymer alloy after printing is virtually zero.

[0038] As used herein, "high shear viscosity" refers to the measurement of melt viscosity at relatively high shear rates. This relates to the viscosity of the molten material as it passes through the nozzle of a 3D printer. High shear rate viscosity is measured herein by capillary rheometry at 100 sec. -1 It is measured as the melt viscosity under shear. The viscosity of a melt under high shear is generally lower than that of a polymer melt under low shear due to shear fluidization.

[0039] As used herein, "miscible polymers" refer to polymers that are immiscible to each other but exhibit macroscopically uniform physical properties as a blend. Macroscopically uniform properties are generally caused by sufficiently strong interactions between the constituent polymers.

[0040] As used herein, “miscible polymer” refers to two or more polymers that form a homogeneous polymer blend having a single glass transition temperature and a single-phase structure.

[0041] As used herein to describe a support polymer composition that can be removed by dissolution, “solubility” means that at least 10% of the support polymer composition dissolves and is removed by exposure to a suitable solvent for 1 hour, or, in the case of a swelling polymer, that the mass increase of the polymer after exposure to a suitable solvent for 4 hours is at least 10 percent.

[0042] Support for compatible polymers This invention utilizes special, miscible, miscible, or semi-miscible polymer compositions as support materials for 3D printing with fluoropolymers and other polymers such as polyether block amides, polyamides, polyether ether ketones, and polyether ketone ketones. Key properties for good support are miscibility / compatibility with the build polymer, printable viscosity at printing temperature, high rigidity for providing support, low warping, sufficient flexibility to allow the support material to form on the filament and be wound onto the spool, good adhesion to the build plate during printing, and good adhesion to the build material for providing sufficient support. The miscible, miscible, or semi-miscible polymer is used as the matrix of the support composition.

[0043] Some useful miscible, miscible, or semi-miscible polymers that can serve as support matrix polymers include, but are not limited to, acrylics, PLAs, and copolyesters, as well as blends thereof. Polycarbonates may be useful when a less warped version is used.

[0044] In one embodiment, a compatible, miscible, or semi-miscible polymer support composition is specially formulated for good printability.

[0045] In one embodiment, good printability can be obtained by using a low Tg composition. Tg is related to the printing conditions, and the printability is possible with a support composition Tg considerably lower than the printing parameters. In the case of a build plate, the build plate is preferably heated to a Tg higher than that of the support in order to improve the adhesion of the support material or raft to the build plate. Lower Tg of the acrylic composition can be achieved by several different means, which include forming an alloy composition having one or more acrylic polymers having one or more low viscosity polymers, a low Tg acrylic copolymer, one or more acrylic polymers blended with one or more non-polymeric additives, or a combination of these techniques.

[0046] There are several advantages to low Tg compositions: a) the acrylic composition can be formed by a material extrusion additive manufacturing process (also referred to as 3D printing in this application) at relatively low temperatures; b) the acrylic composition is flexible enough to be formed into a filament and wound up; c) the acrylic composition needs to adhere firmly to glass and not warp; and d) acrylic compositions with low Tg and low viscosity provide appropriate fluidity under printing conditions for good 3D printing. Furthermore, even if PVDF has a Tc greater than the Tg of the acrylic copolymer, no adverse effects of low Tg acrylic compositions are observed when used in combination with PVDF.

[0047] Acrylic compositions useful in the present invention have an overall Tg of less than 165°C, less than 135°C, less than 125°C, less than 105°C, less than 95°C, less than 85°C, preferably less than 80°C. Low-Tg acrylics can be obtained in several ways. These include, but are not limited to, a) acrylic homopolymers or copolymers having the desired Tg, b) blends of an acrylic polymer with at least one low-melt-viscosity polymer (which may be an acrylic copolymer), and c) blends of a high-Tg acrylic polymer with a non-polymeric component that lowers the overall composition Tg, such as a plasticizer, as well as combinations of the above.

[0048] Tg is used as a surrogate measure of transition temperature, which, as seen in rheology, is the temperature at which a material changes from a liquid state to a solid state. The transition temperature is the point at which the logarithm of viscosity versus temperature changes its slope from liquid behavior to solid behavior according to the Arrhenius equation. This transition point can be obtained by measuring the viscosity versus temperature of the material at low shear from the molten phase to room temperature. A transition temperature less than 10°C higher than the build plate temperature during printing (typically heated to 80°C to 120°C) is desirable, preferably 10°C lower, 20°C lower, even 25°C lower, and 30°C lower. The Tg of acrylic is about 25°C lower than its transition temperature. In other words, for materials printed at room temperature on a 125°C heated bed, Tg values ​​of less than 100°C, less than 85°C, less than 80°C, less than 75°C, and more than 60°C are preferred. When using a heated chamber, higher Tg materials, such as 135°C or lower, can also be used because the internal temperature of the part will be higher. The glass transition temperature of the polymer is measured by DSC according to the standard ASTM E1356. By adjusting various parameters of the process and support material, it may be possible to successfully print acrylic compositions as support materials with a Tg of 135°C or less.

[0049] In the present invention, useful acrylic polymers include polymers, copolymers, and terpolymers formed from alkyl methacrylates and alkyl acrylate monomers, as well as mixtures thereof. The alkyl methacrylate monomer is preferably methyl methacrylate, which may constitute 50 to 100 percent of the monomer mixture. 0 to 50 percent of other acrylate and methacrylate monomers or other ethylenically unsaturated monomers, as well as low concentrations of crosslinking agents, may also be present in the monomer mixture. Such ethylenically unsaturated monomers include, but are not limited to, styrene, alpha-methylstyrene, and acrylonitrile. Other methacrylate and acrylate monomers useful in monomer mixtures include, but are not limited to, methyl acrylate, ethyl acrylate and ethyl methacrylate, butyl acrylate and butyl methacrylate, isooctyl methacrylate and acrylate, lauryl acrylate and lauryl methacrylate, stearyl acrylate and stearyl methacrylate, isobornyl acrylate and methacrylate, methoxyethyl acrylate and methacrylate, 2-ethoxyethyl acrylate and methacrylate, dimethylaminoethyl acrylate and methacrylate monomers. Alkyl (meth)acrylic acids such as methacrylic acid and acrylic acid may be useful in monomer mixtures. Most preferably, the acrylic polymer contains 70 to 99.5 weight percent methyl methacrylate units and 0.5 to 30 weight percent of 1 or more C 1~8 It is a copolymer having linear or branched alkyl acrylate units.

[0050] Acrylic polymers have 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, and preferably 5,000 to 200,000 g / mol. The use of acrylics with lower weight-average molecular weights within this range has been found to improve the printability of the material, as seen in higher fluidity of the material during printing, faster printing speeds, increased transparency, and reduced warping.

[0051] Preferably, the acrylic polymer contains little to no very high molecular weight fraction polymers, and less than 5% by weight of the acrylic polymer, preferably less than 2% by weight of the acrylic polymer, has a molecular weight exceeding 500,000 g / mol.

[0052] In another embodiment, the acrylic polymer composition comprises a blend of two or more of the above-mentioned polymers.

[0053] Acrylic polymers can be formed by any known means, including, but not limited to, bulk polymerization, emulsion polymerization, solution polymerization, and suspension polymerization.

[0054] Acrylic copolymer: The acrylic copolymers of the present invention generally have a Tg of less than 165°C, less than 135°C, less than 125°C, less than 105°C, preferably less than 95°C, preferably less than 85°C, preferably less than 80°C, and more preferably less than 75°C. The acrylic copolymers of the present invention have a Tg of more than 50°C, preferably more than 55°C, and more preferably more than 60°C.

[0055] In one preferred embodiment, at least 40 weight percent, preferably at least 50 weight percent, and most preferably at least 60 weight percent of the monomer units in the acrylic copolymer are methyl methacrylate monomer units. The comonomers selected for the acrylic copolymer may be (meth)acrylic monomers, non-(meth)acrylic monomers, or mixtures thereof.

[0056] In one preferred embodiment, the acrylic copolymer is composed of more than 90% by weight, more than 95% by weight, and most preferably 100% by weight of acrylic monomer units. Low-Tg acrylic monomers that can be copolymerized to lower the copolymer Tg to a predetermined 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, lauryl methacrylate, and butyl methacrylate. These monomers are added at concentrations high enough to lower the Tg to below 85°C, preferably below 80°C, and more preferably below 75°C, and the Tg is readily calculated using the Fox equation, as is well known in the art and can be measured by DSC.

[0057] Low-Tg copolymers tend to have lower viscosity than high-Tg copolymers, but other factors such as molecular weight and branching also affect viscosity. Impact modifiers can and preferably be added to compositions to improve impact strength and increase melt flow viscosity.

[0058] Acrylic alloy An alternative means for providing an acrylic composition with an overall low Tg includes an alloy blend of an acrylic polymer with a higher Tg of 1 or more and a polymer with a lower Tg (lower melt flow) of 1 or more. This method is described in International Publication No. 2017 / 210,286.

[0059] 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 blended in such a ratio that a single, close mixture is produced without separation into separate bulk phases. As used herein, “low melt viscosity polymer” means a polymer having a melt flow rate greater than 10 g / 10 min, preferably greater than 25 g / 10 min, as measured by ASTM D1238 at a force of 230°C / 10.4 kg.

[0060] In one embodiment, the low melt viscosity polymer is a low molecular weight acrylic polymer or copolymer that meets a high melt flow rate criterion. 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, and even less than 30,000 g / mol. Acrylic copolymers are preferred, and copolymers with a Tg of less than 100°C and less than 90°C are preferred to enhance flexibility.

[0061] In preferred embodiments, the low-melting-point viscosity polymer of the present invention is a polymer other than an acrylic polymer. The non-acrylic low-melting-point viscosity polymers of the present invention include, but are not limited to, polyesters, cellulose esters, polyethylene oxide, polypropylene glycol, polyethylene glycol, polypropylene glycol, styrene-acrylonitrile copolymer, polyvinyl chloride, polyvinyl acetate, polyvinyl alcohol, ethylene-vinyl acetate copolymer, polyvinylidene fluoride and its copolymers, olefin-acrylate copolymer, olefin-acrylate-maleic anhydride copolymer, maleic anhydride-styrene-vinyl acetate copolymer, and mixtures thereof.

[0062] 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. A useful alloy blend of polylactic acid and an acrylic copolymer is the PLEXIGLAS® RNEW® resin blend from Arkema. In another embodiment, a PLA and acrylic copolymer blend can be used, and the acrylic copolymer has an acrylic comonomer of C 1~6 acrylate and / or an acidic monomer such as (meth)acrylic acid, which improves water solubility and provides easy removal of the support.

[0063] Useful cellulose esters include, but are not limited to, cellulose acetate, cellulose triacetate, cellulose propionate, cellulose acetate propionate, cellulose acetate butyrate, and cellulose acetate phthalate.

[0064] The acrylic alloy composition of the present invention can be defined by its low-shear and high-shear viscosities. Preferably, the acrylic alloy composition of the present invention has a low-shear rate viscosity at a temperature of 230 °C measured by a rotational viscometer in accordance with ASTM C965 at 1 sec -1 less than 100,000 Pa·s, preferably less than 10,000 Pa·s, preferably less than 4,000 Pa·s, more preferably less than 1,000 Pa·s. Preferably, the low-shear viscosity is greater than 50 Pa·s, more preferably greater than 100 Pa·s. If the low-shear viscosity is lower than this, there may not be sufficient melt strength to produce filaments. Without being bound by a particular theory, this low-shear viscosity range allows the printed polymer to stay in place where it is placed, still having sufficient fluidity to enable good interlayer adhesion and fusion. The low-shear viscosity range and the high-shear viscosity range are those of the alloy composition before the addition of additives. Some additives can significantly increase the viscosity.

[0065] Preferably, the high shear viscosity of the acrylic alloy composition is determined by the deposition temperature and 100 seconds. -1 The viscosity is 20 to 2,000 Pa·s, preferably 25 to 1,000 Pa·s, and preferably 30 to 500 Pa·s. The important viscosity behavior is a combination of both the viscosity of the material coming out of the nozzle and how the material maintains its fluidity as the thermoplastic solidifies. A common nozzle temperature used for measuring high and low shear viscosity is 230°C.

[0066] In one embodiment, the low melt viscosity polymer has a weight-average molecular weight that is higher than the entanglement molecular weight of the polymer when measured by gel permeation chromatography.

[0067] The low melt viscosity polymer constitutes 5 to 60 percent by weight, preferably 9 to 40 percent by weight, of the total alloy composition.

[0068] In one embodiment, the support material composition may include a blend with a material that is less miscible or mismatched, in order to provide sufficiently high adhesion to the build material during printing, but also sufficiently low adhesion to improve mechanical or solvent removal after printing.

[0069] In one embodiment, the support material is formulated to improve the removal of the support material after printing. For example, a highly printable acrylic copolymer may be blended with one or more components that enhance the ability to remove the support composition. The added materials may be, for example, alkali-soluble acrylic or non-acrylic polymers such as polyvinyl alcohol (PVA) or polylactic acid (PLA). These materials are not necessarily compatible with PVDF, but when blended with the acrylic copolymer of the present invention, the composition as a whole is compatible. Examples of such blends include PMMA+PLA and PLA only.

[0070] Several non-MMA acrylic support materials exist in the art, including several alkali-soluble acrylic resins used as soluble supports in 3D printing. These are not MMA-based and are not compatible with PVDF on their own. However, when blended with the acrylic composition of the present invention, the blend will be compatible with PVDF. Such a blend would require at least 20% MMA-containing acrylic copolymer, preferably more than 30%, more than 40%, more than 50%, more than 60%, more than 70%, preferably more than 80%, and even more than 90% PMMA polymer or acrylic copolymer.

[0071] Acrylic blend with non-polymers A third method for providing an overall acrylic composition with a low Tg is to blend a higher Tg acrylic polymer with one or more compounds known to lower Tg, including but not limited to plasticizers and fillers. However, simply lowering Tg is not always sufficient to provide good printability, which is an important criterion in conjunction with low warp. Lowering Tg can, on its own, make the material too soft for good printability and result in excessive warp. The balance provided by the present invention is desirable.

[0072] The additive compound must be compatible, miscible, or semi-miscible with the acrylic polymer used as the matrix. The Tg-reducing additive is typically added at a concentration of 2–40 weight percent, preferably 4–20 weight percent, based on the weight of the acrylic polymer.

[0073] In one embodiment, a useful class of plasticizers is a specialty epoxide such as a 1,2-dihydroxyalkane with a molecular weight of more than 200 grams per mole or a vegetable oil polyol with a molecular weight of more than 200 grams per mole, as described in PCT / US2019 / 012241.

[0074] In another embodiment, phthalate esters such as di(2-ethylhexyl) phthalate, diisononyl phthalate, diisodecyl phthalate, and diisooctyl phthalate can be used.

[0075] In another embodiment, but not limited to, adipic acid esters such as di(2-ethylhexyl) adipate may be used.

[0076] In another embodiment, water-soluble or alcohol-soluble materials are added. These fillers can lower the effective Tg, but primarily serve to facilitate the removal of the acrylic support composition following 3D printing of the fluoropolymer product.

[0077] Impact modifier The acrylic composition of the present invention does not necessarily have to contain an impact modifier, but in preferred embodiments, to prevent it from becoming too brittle, the acrylic composition of the present invention contains one or more impact modifiers. Preferably, the acrylic composition contains an impact modifier at a concentration of 5 to 60 weight percent, preferably 9 to 50 weight percent, and more preferably 20 to 45 weight percent, based on the overall composition. The impact modifier can be any impact modifier that is compatible, miscible, or semi-miscible with the acrylic composition, as is known in the art. Useful impact modifiers include, but are not limited to, linear block copolymers and core-shell impact modifiers for both soft-core and hard-core polymers. In preferred embodiments, the impact modifier has an acrylic block or acrylic shell rich in MMA and improves compatibility with fluoropolymers.

[0078] While not bound by any particular theory, impact modifiers are thought to impart stretch, flexibility, and toughness.

[0079] In a preferred embodiment, the impact modifier of the present invention is a multi-stage continuous production polymer having a core / shell particle structure of at least three layers, comprising a hard core layer, one or more intermediate elastomer layers, and a hard shell layer. The presence of the hard core layer provides a desirable balance of good impact strength, high modulus of elasticity, and excellent UV resistance, which cannot be achieved with core / shell modifiers having a soft core layer.

[0080] Preferably, the multi-stage polymer is a three-stage composition, each stage comprising a first stage (a) in the range of 10-40% by weight, preferably 10-20%, a second intermediate stage (b) in the range of 40-70%, preferably 50-60%, and a final stage (c) in the range of 10-50%, preferably 20-40%. All percentages are based on the total weight of the polymer particles in the three stages.

[0081] 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.

[0082] Multistage polymers can be produced by any known technique for preparing multistage continuous production polymers, for example, by emulsion polymerization of a mixture of monomers in the presence of a previously formed polymer product. In this specification, the terms “sequentially emulsion polymerized” or “sequentially emulsion produced” refer to polymers prepared in aqueous dispersions or emulsions in which successive monomer loads are polymerized on or in the presence of a pre-formed latex prepared by the polymerization of previous monomer loads and stages. In this type of polymerization, subsequent stages are connected to and closely related to preceding stages.

[0083] A useful alternative impact modifier in this invention is a block copolymer such as NANOSTRENGTH® resin from Arkema. Smaller amounts, for example, 10-15% of NANOSTRENGTH block copolymer, can function to provide effective impact strength.

[0084] In one preferred embodiment, the acrylic copolymer comprises 70-80 weight percent of methyl methacrylate monomer units and 20-30 weight percent of methyl acrylate, ethyl acrylate units, or a mixture thereof.

[0085] In preferred embodiments, an MMA-containing impact modifier (Coreshell or Nanostrength®) is used for both flexibility and PVDF compatibility. The addition of the MMA-containing impact modifier facilitates the improvement of compatibility and adhesion of poorly compatible soluble acrylics to PVDF. Preferably, the impact modifier itself contains more than 10% by weight, more than 20% by weight, more than 30% by weight, more than 40% by weight, and even more than 50% MMA monomer units.

[0086] additives The acrylic composition may further contain, but is not limited to, other additives typically present in acrylic formulations, including stabilizers, plasticizers, fillers, colorants, pigments, antioxidants, antistatic agents, surfactants, toners, refractive index matching additives, additives with specific light diffraction or light reflection properties, lubricants, solubility enhancers, mechanical removal accelerators, and dispersion aids. If fillers are added, they represent 0.01 to 50 volume percent, preferably 0.01 to 40 volume percent, and most preferably 0.05 to 25 volume percent of the total volume of the acrylic alloy composition.

[0087] Fillers can be in the form of powders, platelets, beads, fibers, and particles. Smaller materials with a lower aspect ratio are preferred to avoid the possibility of nozzle contamination, although this is less important when acrylic alloys are used with larger nozzle sizes. Useful fillers include, but are not limited to, carbon fibers, carbon powder, pulverized carbon fibers, carbon nanotubes, glass beads, glass fibers, nanosilica, aramid fibers, polyaryletherketone fibers, BaSO4, talc, CaCO4, graphene, nanofibers (generally with an average fiber length of 100-150 nm), and hollow glass or hollow ceramic spheres. Polar, hydrophilic, or water-soluble fillers such as NaCl or other salts can be added to facilitate the removal of supports after printing. Furthermore, inert fillers such as talc, CaCO4, glass beads, and other minerals and salts can be added to facilitate the physical removal of supports from the model material, as the model material does not adhere to them sufficiently.

[0088] The acrylic composition of the present invention is compatible with model materials, prints with minimal warping, is rigid with a tensile mode preferably greater than 1.5 GPa, >1.7 GPa, >1.9 GPa, and >2 GPa, and is flexible enough to be filamentized. When the acrylic composition of the present invention is used as a support and raft, it is possible to print much larger, less warped PVDF parts and to print specific part features (protrusions) that cannot be printed by other methods.

[0089] Based on the information in this application to those skilled in the art, modifications can be made to the acrylic polymer to make it soluble in water, ethanol, or other common solvents while simultaneously providing compatibility with PVDF. This can facilitate the removal of the support acrylic material from the final formed object. In one embodiment, NANOSTRENGTH® acrylic block copolymer from Arkema is more hydrophilic and can be easily removed after printing. If acrylic that dissolves in a completely modified alkali, or in water, ethanol, or other common solvents, becomes less compatible with fluoropolymer build materials, or no longer compatible at all and can no longer be used as a compatible support, a more soluble support can be blended with a more compatible acrylic, such as an MMA-containing acrylic(co)polymer, to improve compatibility with fluoropolymer build materials.

[0090] Fluoropolymers and other build polymers The build polymer may be a fluoropolymer or other polymer such as polyether block amide, polyamide, polyether ether ketone, or polyether ketone ketone. The present invention is described using fluoropolymers, particularly polyvinylidene fluoride. However, those skilled in the art will recognize that other polymers similar to PVDF can be substituted as the build material on the support material of the present invention.

[0091] The acrylic support composition of the present invention is used to support fluoropolymer build materials. A major advantage of the acrylic composition when supporting fluoropolymers is that the acrylic is melt-miscible with the fluoropolymer, and therefore allows for the necessary adhesion between the support material and the build material. While the present invention intends for acrylic supports for fluoropolymers, those skilled in the art will recognize from the description herein that the acrylic support can be used in combination with other 3D printed objects having compositions that are compatible, miscible, or semi-miscible with the acrylic support.

[0092] Fluoropolymers useful for 3D printing have low shear-melt viscosity, providing printability and minimal warping during cooling. Examples of such fluoropolymers are provided to Arkema in U.S. Patent Application Publication No. 2019 / 0127500. Useful fluoropolymer compositions include fluoropolymer blends and the use of specific fillers. Process conditions can be adjusted to further reduce the adverse effects of fluoropolymer crystallinity on printability.

[0093] Fluoropolymers useful in this invention include homopolymers or copolymers containing fluorinated monomers. It is known that the presence of fluorine in a polymer improves chemical resistance, reduces the coefficient of friction, increases thermal stability, and improves the material's triboelectric properties. The term "fluoromonomer" or expression "fluorinated monomer" refers to a polymerizable alkene containing at least one fluorine atom, fluoroalkyl group, or fluoroalkoxy group in its structure, thereby bonding these groups to the double bond of the alkene being polymerized. The term "fluoropolymer" refers to a polymer formed by the polymerization of at least one fluoromonomer, and includes both homopolymers and copolymers, as well as both thermoplastic and thermosetting polymers. Thermoplastic polymers can be molded into useful parts by applying heat and pressure, as is done in 3D printing. Thermosetting fluoropolymers are generally not processed in 3D printing, but their precursors and oligomers can be printed, assuming the viscosity is adjusted to a 3D printable viscosity. As is known in the art, the viscosity of the prepolymer can be increased using thickeners as needed. Conversely, the viscosity of the prepolymer can be decreased by adding plasticizers or diluents. When prepolymers are 3D printed together, they can be cured using a suitable energy source such as heat, UV radiation, electron beams, or gamma rays (reacting and crosslinking functionalities). Non-limiting examples of thermosetting fluoropolymers include the use of vinylidene fluoride monomers and hexafluoropropene monomers, and fluoropolymers having bromide functionality. Brominated fluoropolymers can be 3D printed and then radically crosslinked via bromine functionality using a pre-added thermal radical source or a source that generates radicals upon application of light, UV, electron beams, or gamma rays.

[0094] Fluoropolymers can be synthesized by known means, but are not limited to bulk, solution, suspension, emulsion, and reverse emulsion processes. As is known in the art, free radical polymerization is commonly used for the polymerization of fluoromonomers.

[0095] Fluoromers useful for carrying out the present invention include, for example, vinylidene fluoride (VDF), tetrafluoroethylene (TFE), trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), dichlorodifluoroethylene, hexafluoropropene (HFP), vinyl fluoride (VF), hexafluoroisobutylene (HFIB), perfluorobutylethylene (PFBE), 1,2,3,3,3-pentafluoropropene, 3,3,3-trifluoro-1-propene, and 2-trifluoromethyl-3,3,3-trifluoropropene. These include penes, 2,3,3,3-tetrafluoropropene, 1-chloro-3,3,3-trifluoropropene, perfluoromethyl ether (PMVE), perfluoroethyl vinyl ether (PEVE), perfluoropropyl vinyl ether (PPVE), perfluorobutyl vinyl ether (PBVE), fluorinated vinyl ethers including long-chain perfluorovinyl ethers, fluorinated dioxole, partially or fully fluorinated alphaolefins of C4 or higher, partially or fully fluorinated cyclic alkenes of C3 or higher, and combinations thereof. Fluoropolymers useful for carrying out the present invention include polymerization products of the above fluoromonomers, such as homopolymers produced by polymerizing vinylidene fluoride (VDF) itself, or copolymers of VDF and HFP.

[0096] In one embodiment, it is preferable that all monomer units are fluoromonomers, but copolymers of fluoromonomers and non-fluoromonomers are also intended by the present invention. In the case of copolymers containing non-fluoromonomers, at least 60 weight percent of the monomer units are fluoromonomers, preferably at least 70 weight percent, more preferably at least 80 weight percent, and most preferably at least 90 weight percent are fluoromonomers. Useful comonomers include, but are not limited to, ethylene, propylene, styrene, acrylates, methacrylates, (meth)acrylic acids and salts therefrom, C4 to C16 alpha-olefins, butadiene, isoprene, vinyl esters, vinyl ethers, fluorine-free halogenated ethylenes, vinylpyridines, and N-vinyl linear and cyclic amides. In one embodiment, the fluoropolymer does not contain ethylene monomer units.

[0097] In preferred embodiments, the fluoropolymer comprises vinylidene fluoride (VDF) monomer units by most weight, preferably at least 65 weight percent of VDF monomer units, more preferably at least 75 weight percent of VDF monomer units. A copolymer of VDF is preferred, preferably a copolymer of VDF and HFP. Comonomers that reduce the level of crystallinity of the copolymer.

[0098] Other useful fluoropolymers include, but are not limited to, polychlorotrifluoroethylene (CTFE), fluorinated ethylene vinyl ether (FEVE), and (per)fluorinated ethylene-propylene (FEP).

[0099] Fluoropolymers and copolymers can be obtained using known methods of solution, emulsion, and suspension polymerization. In preferred embodiments, fluoropolymers are synthesized using emulsion polymerization in which the emulsifier ("surfactant") is either fully fluorinated, fluorinated, or non-fluorinated. In one embodiment, fluorocopolymers are formed using an emulsion process that does not contain a fluorosurfactant. Examples of non-fluorinated surfactants (non-fluorinated surfactants) are described in U.S. Patents 8080621, 8124699, 8158734, and 8338518, all incorporated herein by reference. In emulsion polymerization utilizing fluorinated or totally fluorinated surfactants, some specific examples include, but are not limited to, salts of acids described in U.S. Patent No. 2,559,752. U.S. Patent No. 2,559,752 describes formula X(CF2) n -A salt of the acid COOM, where X is hydrogen or fluorine, M is an alkali metal, ammonium, substituted ammonium (e.g., an alkylamine with 1 to 4 carbon atoms), or a quaternary ammonium ion, and n is an integer from 6 to 20; a sulfate ester of the polyfluoroalkanol of formula X(CF-)2-CH2-OSO3-M, where X and M are as above; formula CF3(CF2) n -(CX2) m -A salt of an acid of SO3M, where X and M are as described above, n is an integer from 3 to 7, and m is an integer from 0 to 2, such as a salt of an acid like potassium perfluorooctyl sulfonate; The use of microemulsions of perfluoropolyether carboxylates in combination with neutral perfluoropolyethers in vinylidene fluoride polymerization is described in European Patent Application Publication No. 0816397. The amount of surfactant charged is 0.05% to 2% by weight relative to the total weight of the monomers used, most preferably 0.1% to 0.2% by weight.

[0100] The fluoropolymers of the present invention can be defined by the low shear viscosity and high shear viscosity of the fluoropolymer at temperatures defined for each fluoropolymer by the ASTM melt flow rate test method. Preferably, the low shear rate viscosity of the fluoropolymer of the present invention is determined by capillary rheometry in accordance with ASTM D3835 at the melt deposition temperature, 4 seconds. -1 When measured, the low shear viscosity is less than 13,000 Pa·s, more preferably less than 6,000 Pa·s. Preferably, the low shear viscosity is greater than 250 Pa·s, more preferably greater than 600 Pa·s, and more preferably greater than 1,000 Pa·s. If the low shear viscosity is lower than this, there may not be enough melt strength to manufacture the filament. Although not bound by any particular theory, this low shear viscosity range will allow the printed polymer to stay in place and still be fluid enough for good interlayer adhesion and fusion. The higher the low shear viscosity of the PVDF, the higher the level of warping and shrinkage. Preferably, the high shear viscosity of the thermoplastic material is suitable for melt deposition at the temperature and 100 sec -1 The viscosity is 30 to 2000 Pa·s, preferably 100 to 1700 Pa·s, and more preferably 300 to 1200 Pa·s. The important viscosity behavior is a combination of both the viscosity of the material coming out of the nozzle and the degree to which the material retains fluidity as the thermoplastic resin solidifies and crystallizes. In the case of polyvinylidene fluoride polymers or copolymers, the above melt viscosity range is satisfied when measured at 232°C.

[0101] Preferably, the fluoropolymer or copolymer of the present invention is semi-crystalline. Amorphous polymers function under the above conditions and are not bound by any particular theory, but a certain degree of crystallinity is useful for 3D printing because it improves interlayer adhesion, and it is thought that there is a certain period during the crystallization phase transition when chain entanglement between adjacent layers increases.

[0102] In one embodiment, the fluoropolymer of the present invention may contain reactive functional groups by using functional monomers or by post-treatment. Once the functional polymer is processed into a useful article, it may be reacted or crosslinked by UV radiation or electron beams, etc., to enhance its integrity. Crosslinking is generally known in the art to increase the tensile and flexural moduli and to decrease the solubility and permeability of the crosslinked material, all of which can result in improvements to advantageous physical properties depending on the end use of the material.

[0103] The present invention aims to provide blends of two or more different fluoropolymers, as well as blends of two or more fluoropolymers having the same or similar monomer / comonomer composition but different molecular weights. In one embodiment, a softer elastomer PVDF / hexafluoropropene (HFP) copolymer can be blended with a harder PVDF homopolymer.

[0104] Blends between fluoropolymers and compatible or miscible nonfluoropolymers are also considered. In one embodiment, this is at least 50 wt percent, more preferably at least 60 wt percent, more preferably at least 70 wt percent of PVDF containing polymethyl methacrylate (PMMA) homopolymer or acrylic copolymer. The acrylic copolymer of the alloy contains at least 50 wt percent, more preferably at least 75 wt percent of methyl methacrylate monomer units. Melt-miscible blends of PVDF and PMMA offer a surprising number of advantages, including reduced and controlled warping, improved optical clarity where desired, reduced shrinkage, improved base adhesion, improved interlayer adhesion, and improved z-axis mechanical properties. Furthermore, overall print quality is dramatically improved. Compatible or miscible nonfluoropolymers of low viscosity and very low viscosity can also be used to improve printability.

[0105] A miscible nonfluoropolymer may be a block copolymer containing at least one miscible block. The miscible block may provide other properties such as enhanced impact, ductility, optical properties, and adhesive properties. Functional groups can be included in either block. In one embodiment, blocks of poly(meth)acrylate homopolymers and copolymers can be used as miscible blocks of the block copolymer.

[0106] Blends of fluoropolymers with other fluoropolymers or non-fluoropolymers can be achieved by any practical means, including physically blending different polymers as dry components in latex form or in molten form. In one embodiment, filaments of two or more polymers are co-extruded into a core-sheath, an island in the sea, or other physical structure.

[0107] 100s -1 Furthermore, blends of very low viscosity PVDF, homopolymers, or copolymers with a viscosity of 30-1000 Pa·s at 232°C can be blended with high viscosity PVDF to improve interlayer fusion / adhesion. The overall blend will have an average melt viscosity within the range of the present invention.

[0108] For example, blending low-viscosity PMMA polymers with homopolymer PVDF was found to improve base adhesion, base warpage, shrinkage, and overall printability. Surprisingly, adding small amounts of PMMA polymer or copolymer (~5%) to the PVDF composition significantly improved base warpage and reduced shrinkage by 28%, while adding ~10% PMMA further improved base warpage and reduced shrinkage by 37%.

[0109] Similarly, the addition of a small amount (~10%) of very low-viscosity PVDF copolymer made the parts more rubbery, improved base adhesion, and reduced shrinkage by 16%.

[0110] Throughout this application, PVDF and its blends and copolymers are used as exemplary fluoropolymers. Those skilled in the art will understand that other fluoropolymers can be processed in a similar manner and offer similar advantages in 3D printing.

[0111] filler A second method found to provide good fluoropolymer filaments for the manufacture of 3D printed articles involves the use of fillers blended with fluoropolymers. While not bound by any specific theory, fillers are thought to facilitate the modification of the crystallinity of the polymer matrix. Lower crystallinity of the filled fluoropolymer blend composition results in lower shrinkage. The use of fillers also reduces the volume change from molten to solid, further reducing shrinkage. Furthermore, fillers can improve the tensile modulus, further reducing warping and shrinkage.

[0112] Fillers can be added to fluoropolymers by any practical method. Twin-screw melt compounding is one common method that allows for the uniform dispersion of fillers in fluoropolymers and the pelletization of the filled composition. Fillers can also be dispersed in a fluoropolymer emulsion, and the blend can be simultaneously spray-dried to create a more closely blended material.

[0113] In one embodiment, the filler may be compounded with a PVDF-miscible polymer (such as PMMA), and the filled miscible polymer is then added to the PVDF.

[0114] Surprisingly, when the low-shear-melt viscosity PVDF homopolymer described above was blended with approximately 20 weight percent carbon powder based on the volume of the PVDF / carbon blend, the resulting 3D printed parts exhibited less warping and shrinkage, and the print quality was significantly better compared to commercially available 3D printing filaments. This filled sample showed superior 3D print quality, including higher resolution, than the unfilled homopolymer.

[0115] Surprisingly, the mechanical performance of 3D printed parts made from both the filled and unfilled fluoropolymers of the present invention was sufficient integrity to produce strong snap-fit ​​components, while parts made from commercially available polyamide filaments cracked when manufactured into similar snap-fit ​​products. For example, in the case of vertically printed ball joint snap-fit ​​parts, parts printed from commercially available polyamide filaments broke along the x and y directions (breakage in the z direction), while parts printed from carbon-filled PVDF homopolymer filaments did not break. It was expected that the filled material would show reduced adhesion between layers, but this reduction in layer adhesion was not observed with carbon powder-filled PVDF.

[0116] Fillers can be added to the fluoropolymer at an effective concentration of 0.01 to 50 weight percent, preferably 0.1 to 40, more preferably 1 to 30 volume percent, based on the total volume of the fluoropolymer and filler. Fillers can take the form of powders, platelets, beads, and particles. Smaller materials with a lower aspect ratio are preferred to avoid the possibility of nozzle contamination. Fillers useful in the present invention include, but are not limited to, carbon fibers, carbon powder, pulverized carbon fibers, carbon nanotubes, glass beads, glass fibers, nanosilica, aramid fibers, PVDF fibers, polyaryletherketone fibers, BaSO4, talc, CaCO3, graphene, nanofibers (typically with an average fiber length of 100 to 150 nanometers), and hollow glass or hollow ceramic spheres.

[0117] Another alternative to the particulate fillers tested so far could be the use of particles with aspect ratios designed to improve mechanical strength.

[0118] It was found that the melt viscosity of PVDF increased with the addition of fillers, but the PVDF composition remained printable as long as the overall melt viscosity parameter was within the specified range. Adding fillers improved print quality and reduced warping.

[0119] Fillers, particularly fibers, are expected to offer excellent shrinkage reduction. One problem with fibers is that they tend to increase the viscosity of the molten material and can clog nozzles. This effect can be minimized by using fluoropolymers with lower melt viscosity, fibers with shorter aspect ratios, or larger nozzle sizes. Additionally, filled materials can warp away from the build plate, and supports can be used to reduce this tendency and allow for the printing of protrusions and other features that are difficult to print.

[0120] Other common additives, not limited to adhesion promoters and plasticizers, may be added to the fluoropolymer composition in effective amounts.

[0121] The composition of the present invention is useful as a removable support for PVDF objects. It should be noted that PVDF is a semi-crystalline polymer and will exhibit some degree of warping even after filling. Printing very large support parts can be difficult due to the chemical structure of PVDF.

[0122] The acrylic support material of the present invention is used as a support material for fluoropolymers in 3D printing processes, but the acrylic support may also be useful as a support for other build materials that are compatible, semi-miscible, or miscible. Indeed, the acrylic support material can be used to support other acrylic polymer build materials. It can also be used to support polyamide, polyether block amide, polylactic acid, polyether ketone, polyether ether ketone, and polypropylene 3D build materials.

[0123] 3D printing process 3D printing processes using support polymers involve the simultaneous printing of support material and build material, followed by the removal of the support material.

[0124] The 3D printer used must be capable of selectively depositing both support and build material compositions by either using multiple nozzles, using a single nozzle with a material multiplexer setup that allows multiple materials to be extruded using the same nozzle, or both. Such a machine may be any known machine that falls under the definition of material extrusion, or a hybrid system including one or more material extrusion heads in accordance with ASTM F2793.

[0125] As used herein, the term “support” refers to geometry intended to be removed from an object before the object is considered complete. Support structures can be procedurally generated by software or manually designed and added to a model. It is not necessary to print the entire support from a single material. In one embodiment, the initial support can be printed using three-material 3D printing from a strong, rigid material optimized for rapid printing, while the interface material of the support that comes into contact with the build material object can be optimized for its solubility and compatibility with the main build material. Any of the support materials may be the support polymer compositions described above.

[0126] Furthermore, the support material may consist of a minutely varied mixture of two or more feed materials (filaments, pellets, etc.) that are actively blended within the nozzle to produce an acrylic support composition.

[0127] The support structure of the present invention can be used for a variety of purposes. In one embodiment, the support is used when printing structures that branch and protrude from a model, or structures that bridge over long distances, by providing a support structure that allows the fluoropolymer to be printed in the desired shape without falling or sagging, and that allows for dimensional changes in the fluoropolymer. Furthermore, the support is used when printing acute angles (less than 45 degrees or less than 30 degrees from the glass surface) in the model material and it is desired to maintain the desired shape without sagging.

[0128] In another embodiment, supports are used to improve print quality by providing a structure that traps material seeping from the nozzle. In yet another embodiment, supports are used to enhance adhesion to the build surface and counteract the tendency of the build material to shrink and deform during cooling. Support structures also help protect delicate elements of the model. Supports can also be structures that assist in post-processing or function as some form of sacrificial tool during post-processing and assembly. Supports can also be used to mark or write letters, numbers, QR codes®, or other identifying symbols on the surface of the model. Furthermore, support compositions can be used in combination of one or more of the above motivations.

[0129] For a composition to function as a support, it must adhere to the main build composition. In a preferred embodiment, the support material will adhere to the build material regardless of the order in which they are printed. While not bound by any particular theory, compatible, miscible, and semi-miscible material compositions are generally considered to have better adhesion to the build material.

[0130] For example, PVDF can be printed on PVA, but PVA cannot be printed on PVDF due to low compatibility between the materials and the difference in processing temperatures between the two materials. When extruded from the nozzle, PVA does not have the thermal energy necessary to remelt the PVDF surface. Tested acrylic copolymer compositions and PMMA-PLA alloys could be printed on PVDF, and PVDF could be printed on them. The ability to switch materials allows for more complex geometries. Furthermore, it should be noted that PVDF does not adhere well to PLA, cannot be printed on PLA, and is incompatible with PLA, while PVDF adheres to PMMA-PLA alloys, can be printed on them, and is compatible with those alloys.

[0131] Generally, a raft is first printed on a glass plate using only the support polymer composition for the first few layers, and then the 3D object is printed. Once the build material is printed, support scaffolds are printed as needed to support the object.

[0132] Following the printing of the object and supports, the support material is removed.

[0133] To remove supports after printing, there are several options, though not limited to the following: a) Physical removal. A small gap can be printed between the support and the printed object, essentially adding a perforation between the support and the object. Gaps of 0.2 mm or more can be used. This gap allows the support layer to be separated, which is also called breakaway support. With this method, the warp reduction is not very effective because the support is discontinuous. Another modification is to print the final support contact layer extremely thin but continuously, similarly limiting the support of the printed object and resulting in less warp reduction. Another method of physical removal is to remove the support material using a sharp object such as a knife. b) Dissolution of support material. In this method, there is no gap or only a very thin gap between the contact layers, improving support. The support layer can then be dissolved, or softened or swollen and then decomposed using a solvent, but is not limited to xylene, ethyl acetate, and toluene. Fluoropolymer materials have higher chemical resistance than acrylic supports, making it possible to dissolve the support layer without affecting the printed object; these are known as soluble supports. This more complete contact between the support layer and the build layer leads to better adhesive support and therefore less warping.

[0134] In preferred embodiments, the support composition is selected to allow dissolution using a mild solvent such as alcohol, cold or warm water, or an alkaline or acidic aqueous solution. In one embodiment, the acrylic polymer support may be synthesized to include functional monomer units such as acidic monomers that are hydrophilic and soluble in alkaline solutions.

[0135] Once the polymer matrix of the support material is selected to be compatible, miscible, or semi-miscible with the build material, other additives can be added to the support material composition to facilitate the dissolution of the support polymer composition. These include small water-soluble polymer particles such as PVA and PVOH, soluble salts, or other soluble materials. In another embodiment, an acrylic with high compatibility and miscibility with the build material can be added to a polymer that is less compatible with the build material but soluble in a mild solvent to improve compatibility with the build material.

[0136] In one embodiment, a support material can be used that has weak bonding to the build material and is easy to remove, but also provides moderate warp reduction. An example is a PLA / PMMA blend.

[0137] In the 3D printing process for support materials, it is important that the support material has a certain degree of rigidity to support the build layer. In one preferred embodiment, a blower is used to cool the support layer for faster development of rigidity. Preferably, the support layer has a rigidity (modulus of elasticity) greater than that of the build material.

[0138] This acrylic copolymer support material has been found to be effective in both filled and unfilled PVDF resins, as well as in both homopolymer and copolymer PVDF printable resins. For best warpage reduction, the PVDF is printed on a solid layer of acrylic copolymer with no gaps in the Z direction. In gapless printing, the acrylic copolymer layer is removed by dissolution. If less warpage reduction is acceptable, a gap of about 0.2 or approximately 1 layer in height in the Z direction can be used to facilitate subsequent support release. Protrusions are still adequately supported, but the support becomes more easily released.

[0139] In one embodiment, the acrylic copolymer of the present invention was used as both a support and a base raft. It was found that the warping of the PVDF object was reduced by more than half, and parts could be printed to twice their length or twice their height before warping occurred. [Examples]

[0140] The glass transition temperature (Tg) is determined by DSC at a heating rate of 20 K / min, according to the standards ISO 11357-1:2009 and ISO 11357-2 and 3:2013.

[0141] Example 1: Warpage Test: Determination of Compatible Support Composition The following tests were used to measure the compatibility or incompatibility of support and build layers. During FFF 3D printing, each printed layer exerts shear forces on previously printed layers as it cools, causing the material to warp or curl. The semi-crystalline structure of polymers such as PVDF allows the polymer to maintain its rigidity even above its glass transition temperature. This problem is further exacerbated by the shrinkage of the polymer that occurs when it crystallizes. The main force that counteracts the warping effect of the polymer is adhesion to the build surface or support structure. PVDF and other fluoropolymers have poor adhesion to glass and PEI build surfaces, and their shrinkage due to crystallization limits the size of parts that can be printed.

[0142] As a common performance evaluation tool for comparing various polymer compositions, a test has been developed to quantify the warpage of various polymers. It features a test specimen (Figure 1) with a small surface area in contact with the build plate and sharp corners that tend to exacerbate warpage. The cross-sectional area of ​​the specimen increases in the vertical Z-direction, making it increasingly difficult to print the part as printing continues. Different polymer compositions can be compared based on the amount of model the composition was able to print before severe warpage caused the model to detach from the build plate. In terms of warpage, a material that can complete the entire test is considered superior. (Figure 2)

[0143] When printing with secondary support material, the support material can act to improve the adhesion of the main material to the build plate.

[0144] Two different PVDF compositions were tested against compositions spanning a range of commercially available PVDF filaments. Each contains some degree of alloy or copolymer to reduce warping caused by the high shrinkage of PVDF during cooling. Composition 1 has properties most similar to PVDF homopolymer but exhibits the highest warping. This warping makes it the most difficult to support, as it easily peels off the support substrate if adhesion is insufficient. Composition 2 is a PVDF / HFP copolymer.

[0145] [Table 1]

[0146] Acrylic materials have better adhesion to glass than PVDF, and due to their compatibility and miscibility with PVDF, they adhere very well to PVDF. Various support materials were tested with PVDF materials that exhibit significant warping when printed alone. These results are shown in Table 1. Filaments made with Kynar® 826-3D build material could only print 1.23 mm of a 12.2 mm test specimen without using a support interface. HIPS and ABS supports performed even worse than this baseline due to their incompatibility with PVDF material, although moderate improvements were possible with PETG, PLA, and PVA. Surprisingly, Stratasys SR-30, an alkali-soluble acrylic containing support material, did not adhere to PVDF. If this material contains more PVDF-compatible acrylic as referred to in this invention, it can support PVDF.

[0147] Only the PLEXIGLAS® 3DS acrylic copolymer composition and the PLEXIGLAS® RNEW® B514 PMMA-PLA alloy were able to significantly improve the warpage performance of the PVDF material. The 3Diakon® PMMA material itself exhibited significant warpage, causing the entire raft to detach from the bed when printed at the manufacturer's recommended build plate temperature of 100°C. If this PMMA composition can be modified to reduce warpage and print better by changing the composition or printing conditions, it could be a viable support for PVDF. All of these tests were performed using an Ultimaker S5 desktop 3D printer with a glass build surface coated with PVA adhesive. It is noteworthy that, with the exception of 3Diakon® PMMA, all tested materials exhibited excellent printability and could print fully warped specimens when printed alone.

[0148] [Table 2]

[0149] [Table 3]

[0150] Materials that provide a print height of more than 4 mm, preferably more than 6 mm, and more preferably more than 10 mm are considered compatible. Alternatively, materials that provide an increase in print height from the build material itself of 2 mm, 3 mm, 4 mm, preferably more than 5 mm are considered compatible with the build material.

[0151] Example 2: Layer adhesion strength between support material and PVDF To quantify the adhesion between dissimilar polymers, we developed test specimens with alternating material printing (Figure 1). These specimens are broadly based on standards such as AWSG1.6 and DVS2203-5, which outline methods for testing the tensile strength of thermoplastic welds using a tensile dogbone with a splice section in the center of the instrument. The developed specimen was based on the ASTM D638 Type 1 specimen, but shortened by 50% to reduce printing time and improve part stability during printing. Two specimens are printed and joined simultaneously to create a specimen that does not tip over during printing. To test the bonding strength at the material interface, the material types are switched within the instrument to create a zone sequence. The specimens feature both PVDF at the support interface and support at the PVDF interface (Figure 3).

[0152] The test results (Table 3) show significant adhesion between the acrylic composition and the PVDF alloy. The test specimens showed fracture points both from PVDF to the acrylic composition and from the acrylic composition to PVDF, suggesting relatively close bond strengths between the two different transition types. An adhesive strength of approximately 11 MPa corresponds to a load of approximately 500 N, which is strong enough to support the weight of an object with a mass of 5 kg. However, in the case of using PVA filament, it was not possible to print test specimens because the PVA material could not be printed onto the PVDF material.

[0153] [Table 4]

[0154] Example 3: Use of acrylic materials to support other compatible materials Other materials were also tested for adhesion to acrylic substrates. PEBAX®, a poly(ether block amide) with excellent printability and compatibility with other supports such as PVA, was able to complete the entire 12.2 mm warp test in Example 1 when printed on PLEXIGLAS® 3DS support material. Higher Tg acrylic copolymers (Tg 90-92°C) were tried as support material for PEKK (Tg 160°C). This also completed, but there was a 6-7 mm curl at the edges. The curl was caused by the acrylic copolymer, which was too soft because the PEKK printing conditions were at least 110-120°C at the build plate temperature. Higher Tg acrylic compositions were able to support PEKK more effectively because the materials adhered very well to each other.

[0155] Example 4 3D-supported objects are printed using PLEXIGLAS® 3DS as the support material. A PVDF copolymer blend is used as the build material. The support setup is between separable and soluble support, with a raft and a solid top, and selected to have a 0-1 layer gap between the support material and the build material. The build plate is initially heated to 70-100°C. PLEXIGLAS® 3DS is printed at 240°C, and PVDF is printed at 260°C. A heating chamber is not required. Figure 4 shows an object printed with the support structure intact.

[0156] Example 5: Use of acrylic supports with Arkema826-3D resin Figure 5 shows a part from another embodiment. This features a pipe fitting printed with ArkemaKynar® 826-3D resin and PLEXIGLAS® 3DS support material from Example 4, but with added pigment to the PLEXIGLAS® 3DS to give it a black appearance. This part demonstrates the complexity that can be achieved with appropriate support material, such as female threads on any plane of the part. The part design also requires both build material printed on the support material and support material printed on the build material. Acrylic copolymers were able to successfully handle these transitions. The support discussed here was dissolved in xylene, an excellent solvent for acrylic copolymers, but without affecting the PVDF. The xylene bath was stirred, and the support was completely dissolved over 4-8 hours. Once the support was dissolved, the 1-inch NPT female threads were able to function together with other 1-inch NPT male threaded parts.

Claims

1. A support material composition for 3D printing of polyamide (PA), polyether block polyamide (PEBA), polyether ether ketone (PEEK), polyether ketone ketone (PEKK), and fluoropolymer compositions, wherein the support material composition comprises one or more polymer compositions that are compatible, miscible, or semi-miscible with the PA, PEBA, PEEK, PEKK, or fluoropolymer composition, and the polymer composition comprises a matrix polymer selected from the group consisting of acrylic, polyester, and polycarbonate.

2. The support material composition according to claim 1, wherein the support material composition is an acrylic composition.

3. The support material composition according to claim 2, wherein the acrylic composition is selected from the group consisting of acrylic copolymers, acrylic alloys, and acrylic polymers blended with nonpolymer additives.

4. The support material composition according to claim 2, wherein the acrylic composition has a Tg of less than 165°C, and the Tg is higher than room temperature.

5. The acrylic composition was measured by capillary rheometry in accordance with ASTM C965 for 4 seconds. -1 The support material composition according to claim 2, wherein the low shear rate viscosity measured is less than 100,000 Pa·s at a temperature of 230°C.

6. The acrylic composition was measured by capillary rheometry at a given temperature in an ASTM melt flow test for its fluoropolymer at 232°C and 100 sec. -1 The support material composition according to claim 2, wherein the high shear rate viscosity is 30 to 2000 Pa·s.

7. The support material composition according to claim 2, wherein the acrylic composition contains at least 20% by weight of one or more (meth)acrylic polymers, and the (meth)acrylic polymer comprises a polymethyl methacrylate homopolymer or a polymethyl methacrylate copolymer containing at least 51% by weight of methyl methacrylate monomer units.

8. The support material composition according to claim 7, wherein the acrylic composition comprises an acrylic copolymer, and the acrylic copolymer constitutes at least 20 percent by weight of the support material composition.

9. The acrylic composition comprises 70 to 80 weight percent methyl methacrylate monomer units and 20 to 30 weight percent C 1～4 The support material composition according to claim 2, comprising a copolymer containing acrylate units.

10. The support material composition according to claim 2, wherein the acrylic composition comprises a blend of a methacrylate copolymer and a polylactic acid polymer.

11. The support material composition according to claim 2, wherein the acrylic composition is impact-modified by having 5 to 60 weight percent of an impact modifier.

12. The support material composition according to claim 2, further comprising additives selected from the group consisting of stabilizers, plasticizers, fillers, colorants, pigments, antioxidants, antistatic agents, surfactants, toners, refractive index matching additives, additives having specific light diffraction or light reflection properties, lubricants, solubility enhancers, mechanical removal accelerators, and dispersion aids, as well as mixtures thereof.

13. The support material composition according to claim 1, wherein the support material composition is soluble in a solvent selected from the group consisting of water, hot water, alkaline aqueous solution, and ethanol.

14. The support material composition according to claim 1, wherein the support material composition comprises a filler containing a polymer, a salt, and another compound soluble in a solvent selected from the group consisting of cold water, hot water, an alkaline aqueous solution or an acidic aqueous solution, ethanol, xylene, and toluene.

15. The fluoropolymer composition was measured by capillary rheometry at 232°C for 4 seconds. -1 The low shear rate viscosity is less than 13,000 Pa·s, and the viscosity was measured by capillary rheometry at a given temperature of 232°C and 100 sec in the ASTM melt flow test for the fluoropolymer. -1 The support material composition according to claim 1, wherein the high shear rate viscosity is 30 to 2000 Pa·s.

16. The support material composition according to claim 1, wherein the fluoropolymer composition comprises PVDF.

17. The support material composition according to claim 1, wherein the fluoropolymer composition comprises PVDF blended with an acrylic polymer or copolymer, or a PVDF copolymer.

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