Polyketone powder for laser sintering

Abstract

Semi-crystalline polyketone powders useful for layer-by-layer manufacturing can be produced by melting a polyketone having a unimodal differential scanning calorimetry (DSC) melting peak at a temperature above 50° C., below the melting temperature of the polyketone, and precipitating the molten polyketone by cooling, addition of a non-solvent, or a combination thereof. Using this method, polyketones having DSC melting peaks with greater enthalpy than the starting polyketone can be formed.

Description

[Technical field]

[0001] The present invention relates to powders useful for producing laminated manufacturing articles. In particular, the present invention relates to aliphatic semi-crystalline polyketone powders. [Background technology]

[0002] Powder-based methods of additive manufacturing include: Selective laser sintering (SLS) is a 3D printing technique that uses a laser to fuse powdered material in successive layers (see, for example, U.S. Patent No. 5,333,933). Rapid sintering (HSS) and multi-jet fusion (MJF) 3D printing utilize multiple jets that similarly deposit successive layers of infrared absorbing (IR absorbing) ink onto a powdered material, which is then exposed to IR energy for selective melting. Electrophotographic 3D printing utilizes a rotating photoconductor that builds an object layer-by-layer from a base.

[0003] Selective laser sintering (SLS), multi-jet fusion (MJF), and high speed sintering (HSS) 3D printing methods use the same type of floating, unfixed powder bed. They generally have the same material requirements to be compatible with the printing process, since the additively built object experiences similar stresses, just with different heating mechanisms to obtain the molten phase. Typically, a free-body diagram of the 3D printed object can be used to determine the expected residual stresses in the printed object. This is necessary to successfully build the object. If the residual stresses are too high, the object will deform or bend beyond tolerances.

[0004] Residual stresses have typically been minimized for these powder-bed based 3D printers by using crystalline or semi-crystalline thermoplastic polymers with a sufficiently large window between their melting and recrystallization temperatures. Unfortunately, this has been limited to polymers (e.g., polyamides) that have been successfully used to print large or complex parts using SLS and MJF methods, thus limiting the use of these additive manufacturing methods.

[0005] Aliphatic polyketones have become promising polymers due in part to their physical properties and chemical resistance as low-cost engineering plastics. Polyketones are copolymers of ethylene (and / or other olefins or alkenes) and carbon monoxide, typically produced by copolymerization in the presence of a palladium (or other) catalyst, as described in U.S. Pat. Nos. 5,993,333 and 5,949,623. In turn, the aliphatic polyketones are typically separated from the other components present in the polymerization reactor. These other components may include unreacted alkenes, unreacted carbon monoxide, methanol (or other) reaction medium, and catalyst. The polyketone product separated from the other components (e.g., by separation and drying) is referred to as "reactor flake." Due to its fine particle size that makes it difficult to handle and ship, this reactor flake is typically heated and extruded to form pellets for commercial sale, resulting in undesirable properties such as possible crosslinking of the polyketone due to exposure to temperatures higher than the melting temperature when forming the pellets, and low peak melting enthalpy. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Pat. No. 5,597,589 [Patent Document 2] U.S. Pat. No. 4,835,250 [Patent Document 3] US Patent Application Publication No. 2008 / 0058494 Summary of the Invention [Problem to be solved by the invention]

[0007] It would therefore be desirable to provide a thermoplastic polymer that avoids one or more of the problems for producing additively manufactured articles by methods such as SLS, HSS, MJF, and others mentioned above. In particular, it would be desirable to provide a thermoplastic polymer that can provide articles with high strength, toughness, high temperature resistance, flame retardancy, and in some cases, optical clarity. [Means for solving the problem]

[0008] The applicant has discovered a method for processing aliphatic polyketones to achieve specific powder morphology and thermal properties that allow for improved additive manufacturing of these materials by floating powder bed methods. Surprisingly, in one example, polyketone powders exhibit DSC melting peaks that exhibit high enthalpy peaks (at least 75 J / g). The enthalpy of the melting peak can be increased considerably while avoiding crosslinking of the polyketone, which may be useful for 3D printing (e.g., the enthalpy can be greater than 30, 40, 50, 60, 75, 100, 125, 150, or even 175 Joules / gram of polyketones).

[0009] A first aspect of the present invention is a composition comprising a semi-crystalline polyketone powder, the semi-crystalline polyketone powder having a melting peak with a melting enthalpy of at least about 50 Joules / gram.

[0010] A third aspect is a method of forming an improved semi-crystalline polyketone, comprising the steps of: (i) dissolving an initial polyketone in a solvent at a temperature greater than 50° C. and less than the onset of melting of the polyketone to form a solution comprising dissolved polyketone; (ii) precipitating the dissolved polyketone by cooling the solution, adding a non-solvent to the solution, or a combination thereof to form the improved semi-crystalline polyketone; and (iii) separating the improved semi-crystalline polyketone from the solvent; The improved polyketone powder may be further processed by milling to achieve the desired particle size and may be subjected to further processing to alter the crystallinity and alter the DSC melting characteristics (e.g., to achieve the first aspect of the invention) as desired for additive manufacturing. The isolated polyketone may be subjected to further processing to remove undesired solvents, such as further washing in a non-solvent.

[0011] Polyketones formed by methods such as those in embodiments 1 and 2 are particularly useful for forming articles by additive manufacturing methods such as floating powder bed processes (e.g., SLS, HHS and MJF processes). Such polyketone powders have a D of up to 300 micrometers. 90 It is desirable to have a particle size and an average particle size of equivalent spherical diameter of 1 micrometer to 150 micrometers. These polyketones can be printed by floating powder bed additive manufacturing techniques such as SLS, HSS and MJF. The compositions can be made into additive manufactured articles taking advantage of the properties of this engineering plastic (e.g., heat and chemical resistance and low coefficient of friction with respect to many other materials). Examples of such applications include biocompatible (medical), electrical, transportation (e.g., automotive, rail, trucking), plumbing, aerospace, food contact, industrial (e.g., machinery) and consumer (e.g., appliance) applications. [Brief description of the drawings]

[0012] [Figure 1] Differential Scanning Calorimetry (DSC) Plots of Polyketones Not of the Invention [Diagram 2] DCS plot of polyketone powder of the composition of the present invention [Diagram 3] DCS plot of polyketone powder of the composition of the present invention [Figure 4] Optical microscope photograph of the polyketone powder of the present invention [Diagram 5] Dynamic mechanical analysis plots of polyketones subjected to different heat treatments DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The explanations and examples presented herein are intended to acquaint those skilled in the art with the invention, its principles, and its practical application. The particular embodiments of the present disclosure described are not intended to be exhaustive or to limit the scope of the invention.

[0014] As used herein, "one or more" means that at least one, or more, of the listed components may be used as disclosed. It will be understood that the functionality of any ingredient or component may be an average functionality due to imperfections in raw materials, incomplete conversion of reactants, and the formation of by-products.

[0015] The method involves dissolving an initial polyketone in a solvent at a temperature greater than 50° C. and less than the onset melting temperature of the polyketone to form a solution containing dissolved polyketone. Typically, the solvent is heated from greater than 100° C. to a temperature less than the onset melting temperature of the particular polyketone, which onset melting temperature is determined by differential scanning calorimetry (DSC) as described herein. Illustratively, the solvent is heated to a temperature greater than 75° C. or 100° C. and less than 5%, 10%, or 20% below the onset melting temperature of the polyketone, examples of which are up to about 200° C., 180° C., 170° C., or 160° C.

[0016] The initial polyketones were

[0017] [ka]

[0018] where A is the residue of an alkene monomer which is converted to a saturated hydrocarbon group, m is from about 1 to 6, and n is from at least about 2 to any practical amount to achieve the desired number average molecular weight useful in the present invention. Exemplary useful number average molecular weights can be those which provide a melting temperature of from about 175° C. or 210° C. to about 270° C. or 300° C., and can be from about 1000 to 250,000 or from about 10,000 to 200,000.

[0019] It is preferred that the initial polyketone of the composition is a terpolymer of carbon monoxide, ethylene and another alkene monomer, such as an olefin of 3 to 12, 8 or 6 carbons, especially propylene. Such polyketones have random repeating units:

[0020] [ka]

[0021] where G is a saturated residue of an olefin of 3 to 12, 8 or 6 carbons polymerized with a double bond, and x / y is at least 2 to 100 or 50 or 20. Desirably, G is propylene. The polyketone may be terminated with any useful group, such as alkyl groups, hydroxyls, esters, carboxylic acids, ethers or combinations thereof. Particular end groups may be generated by using solvents such as low molecular weight alcohols, such as methanol, or water or combinations thereof.

[0022] The initial polyketone typically exhibits a unimodal melting peak separated from the crystallization peak, which may be due to melt extrusion of the polyketone to form it into pellets. Commercially available polyketones, such as those known in the art (e.g., those commercially available under the trade name POKETON™ from Hyosung, Korea), may be useful as the initial polyketone.

[0023] The time at the maximum heating temperature (melting temperature) is any time that achieves the desired dissolution of the polyketone (typically 3 or 4 minutes to 3 or 4 hours). Multiple elevated temperatures may be used (held at) during this process. For example, a higher temperature (melting temperature) may be used to melt the polyketone, and a lower temperature (precipitation temperature) may be used when precipitating the polyketone. The precipitation temperature is the temperature at which the polyketone begins to precipitate upon cooling or at which precipitation is induced by the addition of a non-solvent. The precipitation temperature may be any useful temperature from ambient temperature or above, about 20°C, up to the melting temperature (if precipitated by the addition of a non-solvent) to a temperature below the melting temperature (e.g., 130°C, 125°C, 100°C, 75°C, or 50°C). It is desirable for the precipitation temperature to be below the temperature at which the non-solvent begins to boil (the onset of boiling temperature as determined by DSC in the same manner in which the melting peak is determined). Agitation may be used during any part or all of the process.

[0024] Mixing is generally understood to mean stirring ingredients in a liquid or suspension mixture under conditions that generate shear forces to create flow and turbulence patterns using impellers rotating within a stator. The mixing may be any useful shear rate that results in the desired particle size and shape. Once the impeller has drawn the mixture in, the mixture is subjected to abrupt changes in direction and acceleration such that the mixture contacts the walls of the stator with centrifugal force or is forced through the pores of the stator under pressure and velocity with eventual collapse of the change in direction and acceleration. In an exemplary embodiment of high shear mixing conditions, mixing includes operating at speeds of 50 revolutions per minute (rpm) to 500 rpm.

[0025] It is desirable for the atmosphere to be one in which the solvent and other chemicals do not adversely react with it. Typically, dissolution is carried out in a closed vessel at or near ambient pressure (e.g., ±10%, ±1%, or ±0.1% of atmospheric pressure) to minimize volatilization losses. High pressure may be used, but is not required. Exemplary atmospheres would include nitrogen or a noble gas (e.g., argon) or a combination thereof, or air (e.g., dry air), depending on the solvent.

[0026] The amount of polyketone soluble in the solvent may be any useful amount that may then precipitate from solution upon cooling, introduction of a non-solvent, or a combination thereof. Illustratively, the amount of polyketone soluble may be from 1%, 5%, 10% by weight, to any practical amount (without gelling), 50%, 40%, 30% or 25% by weight.

[0027] Polyketones include polymers made by polymerizing carbon monoxide and alkene monomers in the presence of Group 8 to Group 10 transition metal catalysts. Specifically, the polyketones may be made by any one of the processes described in U.S. Patent Nos. 5,138,032, 5,894,435, 5,138,032, and 5,138,032, each of which is incorporated herein by reference in its entirety. Specifically, the processes, reaction conditions, and monomers are those described in U.S. Patent No. 5,138,032, from column 2, line 52 to column 5, line 17, each of which is incorporated herein by reference in its entirety.

[0028] Desirably, the alkene monomer comprises an olefin having from 2 to 12, 8 or 6 carbons. Illustratively, the alkene monomer is ethylene, or the alkene monomer comprises ethylene and at least one other olefin monomer, such as propylene. When the polyketone is a copolymer of ethylene and another olefin monomer, such as propylene, the amount of ethylene and the other olefin is as described in U.S. Pat. No. 5,138,032, column 2, line 17 to column 3, line 14.

[0029] The solvent may be any useful solvent for dissolving polyketones, such as polar aprotic solvents. Typically, the solvent has a volatility or low viscosity that allows for easy removal in subsequent processing steps, such as separating the precipitated polyketone from the solvent. Typically, the solvent has a viscosity within an order of magnitude of that of water at ambient conditions (e.g., about 1 centipoise at about 20°C to 25°C and 1 atmosphere (about 101 kPa)). That is, the viscosity is typically less than 10 centipoise to 0.1 centipoise (cp). Similarly, the volatility, measured at boiling point (or boiling range) at 1 atmosphere (about 101 kPa), is typically from about 30°C, 50°C, or 75°C to 150°C, 200°C, or 250°C. The solvent typically has a molecular weight (weight average Mw) of up to about 500 g / mol, 200 g / mol, or even 150 g / mol, to at least about 30 g / mol, Mw. In some cases, the solvent may be a solid at ambient conditions, but is understood to have a useful viscosity (e.g., less than about 100 cp or less than 10 cp) at the boiling point and elevated temperatures at which dissolution occurs, as described above.

[0030] The solvent may be a mixture of solvents. Illustratively, the solvent may be a mixture of a solvent that is liquid at room temperature and another solvent that is solid at room temperature that dissolves in the liquid solvent, the dissolved solvent imparting one or more desired properties (e.g., improved solubility of the polyketone or the formation of particles when a non-solvent is used to precipitate the polyketone from solution).

[0031] The solvent may contain some water and still be useful for dissolution and precipitation. Generally, the amount of water in the solvent is up to about 1%, 0.5%, 0.2%, 0.1%, 0.05%, 0.01% or 10 parts per million (ppm) by weight. The water concentration may be determined by any suitable method, such as Karl Fischer titration. Any suitable method of drying the solvent, such as those known in the art, may be utilized to achieve the desired water concentration. For example, the solvent may be dried by distillation or contacted with molecular sieves to remove water. The dried solvent may be further modified as described and prescribed in 27 CFR, 21, 151. The desired water concentration may be achieved by known methods, such as distillation and adsorption.

[0032] The solvent has one or more groups that create a sufficient dipole to achieve a dielectric constant of at least 10 and typically less than about 100. Examples of such groups include ethers, carbonyls, esters, alcohols, amines, amides, imides, halogens, or any combination thereof. It is desirable for the solvent to have a dielectric constant of at least about 15 to about 90, 80, or 50, 40, or 30. The dielectric constant may be calculated from the dipoles present in the solvent molecules or may be determined experimentally, as described in J.Phys.Chem. (2017), 121, 2, 1025-1031.

[0033] The solvent may be linear, branched, aromatic or cyclic, with one or more heteroatoms (e.g., O, N, S, Si or halogens) to about 10, 8, 6, 4 or 3 heteroatoms, with an Mw as described above, so long as the solvent has a dielectric constant of at least about 10. Typically, the amount of carbon is from 1 to 24, 18, 16, 12 or 6. Examples of polar aprotic solvents that may be useful include ketones (e.g., acetone, diisopropyl ketone, and methyl butyl ketone), aliphatic or aromatic halogenated hydrocarbon solvents (e.g., chloromethane, dichloromethane, trichloromethane, 1,2-dichloroethane, or 1,1,1-trichloroethane, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, and 1,2,3-trichlorobenzene), carbonates (e.g., propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), chloroethylene carbonate, fluorocarbonate solvents (e.g., fluoroethylene carbonate and trifluoromethylpropylene carbonate), and dialkyl carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

[0034] Some examples of sulfone solvents include methyl sulfone, ethyl methyl sulfone, methyl phenyl sulfone, methyl isopropyl sulfone (MIPS), propyl sulfone, butyl sulfone, tetramethylene sulfone (sulfolane), phenyl vinyl sulfone, allyl methyl sulfone, methyl vinyl sulfone, divinyl sulfone (vinyl sulfone), diphenyl sulfone (phenyl sulfone), dibenzyl sulfone (benzyl sulfone), vinylene sulfone, butadiene sulfone, 4-methoxyphenyl methyl sulfone, 4-chlorophenyl methyl sulfone, 2 ... Examples of sulfone solvents that contain ether groups include chlorophenyl methyl sulfone, 3,4-dichlorophenyl methyl sulfone, 4-(methylsulfonyl)toluene, 2-(methylsulfonyl)ethanol, 4-bromophenyl methyl sulfone, 2-bromophenyl methyl sulfone, 4-fluorophenyl methyl sulfone, 2-fluorophenyl methyl sulfone, 4-aminophenyl methyl sulfone, sultones (e.g., 1,3-propane sultone), and sulfone solvents containing ether groups (e.g., 2-methoxyethyl(methyl)sulfone and 2-methoxyethoxyethyl(ethyl)sulfone).

[0035] Said polar aprotic solvent may be silicon-containing, for example, siloxane or silane.Some examples of siloxane solvents include hexamethyldisiloxane (HMDS), 1,3-divinyltetramethyldisiloxane, polysiloxane, and polysiloxane-polyoxyalkylene derivatives.Some examples of silane solvents include methoxytrimethylsilane, ethoxytrimethylsilane, dimethoxydimethylsilane, methyltrimethoxysilane, and 2-(ethoxy)ethoxytrimethylsilane.

[0036] Other examples of polar aprotic solvents include diethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, diglyme, triglyme, 1,3-dioxolane, and fluorinated ethers (e.g., mono-, di-, tri-, tetra-, penta-, hexa-, and per-fluoro derivatives of any of the above-mentioned ethers) and 1,4-butyrolactone, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, formic acid (e.g., methyl formate, ethyl formate, or propyl formate), and fluorinated esters (e.g., mono-, di-, tri-, tetra-, penta-, hexa-, and per-fluoro derivatives of any of the above-mentioned esters). Some examples of nitrile solvents include acetonitrile, benzonitrile, propionitrile, and butyronitrile. Some examples of sulfoxide solvents include dimethyl sulfoxide, ethyl methyl sulfoxide, diethyl sulfoxide, methyl propyl sulfoxide, and ethyl propyl sulfoxide. Some examples of amide solvents include formamide, N,N-dimethylformamide, N,N-diethylformamide, acetamide, dimethylacetamide, diethylacetamide, gamma-butyrolactam, and N-methylpyrrolidone.

[0037] Polar aprotic solvents include diethyl ether, tetrahydrofuran, and dioxane, hexamethylphosphoramide (HMPA), N-methylpyrrolidinone (NMP), 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU), and propylene glycol monomethyl ether acetate (PGMEA).

[0038] The non-solvent used to induce precipitation at the precipitation temperature may be any suitable one. Illustratively, the solvent may be NMP, DMPU, PGMEA or HMPA, and the non-solvent may be a protic solvent such as water, a low molecular weight alcohol (e.g., C1 to C4 alcohols) or a mixture thereof. The amount of non-solvent may be any amount necessary to effect precipitation at a given precipitation temperature, and the amount is any useful to achieve the desired precipitated polyketone particle size, particle size distribution and morphology. Typically, the concentration of non-solvent added may be from 0.1%, 1%, 5% or 10% by volume of the solvent and non-solvent, typically 75%, 50% or 25% by volume.

[0039] Typically, a mixture (slurry) of the initial polyketone powder and solvent is prepared at ambient conditions while stirring the slurry. Typically, the temperature is raised to a dissolution temperature at which the polyketone dissolves. It is desirable for the dissolution temperature to be at least 10° C. below the boiling point of the solvent. The solution is cooled to promote precipitation and formation of the desired particles, and the precipitation temperature causes the polyketone to precipitate from the solution, preferably in powder form. The polyketone powder may then be separated by any suitable method, such as filtration, centrifugation, buoyancy or other known methods or combinations thereof. Separation may be promoted by one or more additives, such as low molecular weight solvents, surfactants, buoyancy enhancers, etc. Separation may be performed by filtration (e.g., vacuum filtration).

[0040] Additives may be added during the process to impart one or more desired properties to the polyketone powder useful in floating bed lamination manufacturing techniques. For example, one or more of UV stabilizers, fillers, lubricants, plasticizers, pigments, flow aids, or flame retardants may be added. If the additive remains solid in the solvent when the process is carried out, it may act as a nucleating agent and be surrounded by the precipitating polyketone. The amount of any particular additive may be any useful amount to achieve a particular property in terms of printing or properties of the article formed therefrom. In general, the amount of additive(s), if present, is up to about 50%, 25%, 10% or 5% by volume of the composition. The flow aid may be any known compound for improving the flowability of powders, examples of which include fumed silica (e.g., Aerosil 200).

[0041] The filler may be any useful filler, such as those known in the art. Examples of fillers include ceramic, metal, carbon (e.g., graphite, carbon black, graphene), polymeric particulates that do not melt or decompose at printing temperatures (e.g., crosslinked polymeric particulates, vulcanized rubber particulates, etc.), plant-based fillers (e.g., wood, nut shell, grain and rice husk powder or particles). Exemplary fillers include calcium carbonate, talc, silica, wollastonite, clay, calcium sulfate, mica, inorganic glass (e.g., silica, aluminosilicate, borosilicate, alkali aluminosilicate, etc.), oxides (e.g., alumina, zirconia, magnesia, silica "quartz", and calcia), carbides (e.g., boron carbide and silicon carbide), nitrides (e.g., silicon nitride, aluminum nitride), oxynitrides, combinations of oxycarbides, or combinations thereof.

[0042] It has been found that the method can produce aliphatic polyketones with DSC melting peaks having higher enthalpy, which may also have a bimodal shape (bimodal peak). The enthalpy of the melting peak may be 10%, 20% or 30% or more higher than the starting melting peak enthalpy of the starting polyketone. Typically, after carrying out the method, the melting peak onset temperature does not overlap with the onset of crystallization temperature. It has also been found that when a polyketone with a high melting enthalpy is heated to within 5%, 10% or 20% of the melting onset temperature of the polyketone, a polyketone may be formed that still has a melting peak that does not overlap with the crystallization peak and may have a reduced enthalpy, but the process can provide tuning of the separation of the melting peak onset temperature and the crystallization onset temperature.

[0043] Illustratively, the polyketone after precipitation by the method of the present invention may be heated in any suitable atmosphere, such as air, an inert atmosphere, or nitrogen. The heating rate may be any useful rate and may depend on the peak temperature (annealing temperature) used. For example, a faster heating rate may be desirable when the annealing temperature is higher, such as 1° C. or higher, 5° C. or higher, 10° C. or higher, 20° C. or higher, than the melting onset temperature of the polyketone. Similarly, the annealing temperature may be held for any useful time, which, like the heating rate, may depend on the annealing temperature used. Illustratively, when the annealing temperature is at or above the melting onset temperature, the annealing time is typically less than 2 hours, less than 1 hour, or less than 0.5 hours.

[0044] It has also been found that the method avoids problems with crosslinking, or in the case of partial crosslinking, of polyketones, which can render them unusable for laminate manufacturing, for example by interfering with fusion and adhesion within and between layers. The degree of crosslinking can be indicated by dynamic mechanical analysis, where increasing crosslinking is indicated by increasing temperature at which the storage modulus decreases until melting behavior is eliminated (no decrease in storage modulus is observed). A typical heating rate of 3°C / min and a frequency of 1 Hz, as described in ASTM D4065, can be used. That is, the method can be used to prepare polyketone powders that do not have any crosslinking or a greater amount of crosslinking than the as-formed polyketone has. It would be preferable to utilize a heating and slow cooling method that minimizes the problems of heating and cooling large masses, such as those known in the art, including, for example, fluidized beds, rotary kilns, or vertical tube furnaces.

[0045] Depending on the agitation and the particular method used for precipitation, the polyketone formed may be further classified, ground, etc., by any suitable method, such as those known in the art. Exemplary classification methods would include centrifugation, settling, and air cyclones. Size reduction (comminution) may be performed by any suitable method, such as those known in the art. By way of illustration, milling at a temperature at which the semi-crystalline polyketone becomes brittle may be used, and is commonly referred to as freeze milling. In general, freeze milling temperatures may range anywhere from about below 0° C., below −25° C., below −50° C., to about −75° C., −100° C., −150° C., or −190° C. In one embodiment, cooling is achieved by dry ice or liquid nitrogen. After freeze milling, the milled polyketone powder may be further classified, where any particles larger than the desired size are separated and subjected to further milling, and particles that are too small may be fused, classified, or milled in any suitable manner to achieve the desired size.

[0046] The crystallization or recrystallization peak (used interchangeably herein) can overlap with the melting peak in the initial DCS scan of a polyketone powder and still produce a powder with good properties, no warping or distortion, and capable of additive manufacturing, but typically the melting and crystallization onset temperatures do not overlap.

[0047] The crystallization temperature (Tc) of polyketone powders is lower than the melting temperature (Tm) of semicrystalline polymers, which is determined by the melting peak and the crystallization peak, and in the case of a bimodal peak, by the lower temperature peak. Generally, the Tc of polyketones is about 5° C. to 40 or 50° C. lower than the Tm. Tm and Tc are determined from the DSC melting peak as described in ASTM D3418, using the midpoint of the melting peak. The onset of the Tm and Tc peaks are determined as per ASTM D3418 (i.e., deviation of the scan from linearity).

[0048] Directly produced polyketone powders may have a morphology that allows for layer-by-layer manufacturing without the need for flow aids. Desirably, polyketones with such desirable flow properties have particle shape, particularly particle roundness, which aids in flowability and may be expressed in terms of circularity, or circularity, derived from microscopic images of individual particles, where the circularity of an individual particle is determined by the formula: 4πA / P 2where A is the area of ​​the particle and P is the perimeter of the particle, both viewed from a random perspective. A related parameter, sphericity, is derived as the square root of the circularity. Circularity is a number greater than zero and less than or equal to 1. A perfectly circular particle is said to have a circularity of 1.00. Tables of population circularity data are presented in such a way that various levels of circularity (e.g., 0.65, 0.75, 0.85, 0.90, and 0.95) are accompanied by the percentage of the particle sample population that has a circularity greater than the tabulated value. Circularity is determined at a solidity filter level of 0.9 or 0.95. Solidity filters are filters used to remove overlapping particles in two-dimensional micrographs that are available in commercially available image analysis software. Solidity is essentially the area of ​​the particle (particle area) that lies on the area of ​​the region defined by the major and minor axes of the particle area in a two-dimensional micrograph. The size and shape of the particles can be measured by any suitable method known in the art for measuring particle size by diameter. In some embodiments, the size and shape of the particles are determined by laser diffraction as known in the art. For example, the particle size can be determined using a laser diffractometer such as a Microtrac S3500 equipped with a static image analysis accessory using PartAnSI software to analyze captured images of the particles. It is desirable that at least about 65%, 70%, 80%, 95% or 99% (by number) of the particles have a circularity of at least about 0.8, 0.85, 0.9 or 0.95 for the powder separated from the reactor and classified without further processing other than purification.

[0049] Similarly, polyketone powders that do not have any added flow aids will generally have a flowability of at least about 0.5 g / sec, 1 g / sec, or 2 g / sec, or any practically achievable rate (e.g., 50 g / sec) using a 15 mm nozzle as determined by Method A of ASTM D1895.

[0050] The semi-crystalline polyketones of the present invention have a crystallinity of at least about 15% by weight to substantially crystalline, with higher degrees of crystallinity being more desirable. Desirably, the crystallinity is anywhere from 20%, 25% or 30% to substantially crystalline, 90%, 80%, 75%, 60% or 55%. The crystallinity may be determined by any suitable method, such as those known in the art. Illustratively, the percent crystallinity may be determined by X-ray diffraction, including wide-angle X-ray diffraction (WAXD), for example, using a Rigaku SmartLab X-ray diffractometer, or by differential scanning calorimetry (DSC), for example, using a TA Instruments DSC250 differential scanning calorimeter ASTM D3418-15.

[0051] The polyketone of the composition may have any DSC melting peak enthalpy useful for producing powders useful in additive manufacturing, such as SLS. Typically, the enthalpy is at least 3 Joules / gram, but desirably at least 5, 10, 20, 30, 40, 50, 60, 70, or 75 Joules / gram or more, up to any practical amount, such as 200 Joules / gram. The enthalpy of the DSC melting peak may be determined according to the manner described in ASTM D3418.

[0052] The semi-crystalline polyketone particles described above generally have particle sizes and size distributions that are useful for producing laminated manufacturing articles, typically having a mean or median particle size (D) of about 1 micrometer (μm), 10 μm, 20 μm, 30 μm, or 40 μm, to 150 μm, 125 μm, 110 μm, or 100 μm, by volume. 50 Similarly, semi-crystalline polyketones have D of up to 300 μm, 200 μm or 150 μm to allow for consistent heating and melting of the powder. 90 To aid in flowability, the polyketone preferably has a D by volume of at least 0.1 μm, 0.5 μm or 1 μm. 10 It is desirable to have D 90means the particle size (equivalent spherical diameter) in the particle size distribution in which 90% by volume of the particles are equal to or smaller than that size, and similarly, D 50 means the particle size (equivalent spherical diameter) in a particle size distribution below which at least 50% by volume of the particles are smaller, and D 10 means the particle size (equivalent spherical diameter) in a particle size distribution below which at least 10% by volume of the particles are. Particle size may be determined by any suitable method, such as those known in the art, including, for example, laser diffraction of a sufficient number of particles (about 100 to about 200 particles) or image analysis of photomicrographs. Exemplary laser diffractometers are those manufactured by Microtrac, such as the Microtrac S3500.

[0053] The composition of the present invention may further include useful additives, such as those known in the art for producing articles, such as laminated manufacturing articles. For example, the composition may have one or more of UV stabilizers, fillers, lubricants, plasticizers, pigments, flow aids, flame retardants, or solvents. It is desirable for the composition to be substantially free of solvents (i.e., up to 10 parts per million (ppm) by weight of the composition, up to 1 ppm, even trace amounts). The amount of any particular additive may be any useful amount to achieve a particular property or characteristic for printing of the article formed therefrom. In general, the amount of additive, if present, is up to about 50%, 25%, 10% or 5% by volume of the composition. The flow aid may be any known compound for improving the flowability of powders, examples of which include fumed silica (e.g., Aerosil 200).

[0054] It has been found that the polyketone of the composition of the present invention can form shaped articles that do not deform or have undesirable amounts of residual stress. For example, but not limited to, the composition of the present invention can be manufactured into objects by additive manufacturing methods such as SLS, MJF, HSS or electrophotography. By way of illustration, in SLS, a layer of the composition of the present invention can be deposited on a bed at a fixed temperature below the melting temperature of the polyketone powder, and predetermined (selected) areas of the bed are sintered (fused) together using a heat source that is laser controlled and directed as described above. Multiple layers are then deposited in succession and sintered within and to previous layers to build an additively manufactured part.

[0055] Typically, the "working range" for additive manufacturing of semi-crystalline thermoplastic polymers is the temperature difference between the onset temperature at which the material melts and the onset temperature at which it recrystallizes ("Tc"), which is generally as large as possible. As mentioned above, polyketones may be tuned by heating quickly and holding at that temperature (annealing temperature) for a short period of time to tune the melt peak shape and onset melt temperature. For example, the polyketone may be further optimized such that the working range is anywhere from 5°C, 10°C, or 20°C to 60°C, 50°C, 30°C, or 25°C, or any realized temperature difference.

[0056] Since the polyketone powders of the compositions of the present invention exhibit good three-dimensional printability, they may be recycled and reused without further processing after being printed in a powder additive manufacturing process that includes heating and maintaining a bed of powder at a temperature just below the starting melting temperature of the polyketone. If desired, the recycled powder may be mixed with any of the polyketone powders described herein that have not yet been additively manufactured to achieve the desired printability or part properties. The proportion of recycled polyketone that constitutes the compositions of the present invention may be any amount, from substantially all, 90%, 75%, 50%, 40% or 30% by weight of the composition, to about 1%, 5% or 10% by weight. The thermal properties of the recycled powder are generally as described above for the granulated and ground polyketones for the polyketone powders of the present invention. The morphology and size distribution are similarly as described herein, with the morphology most similar to that of the particular initial polyketone powder used to form the additively manufactured article.

[0057] The compositions of the present invention may be used to produce layered manufactured articles comprised of a plurality of fused polyketones of the present invention. In particular, the compositions may be used to produce layered manufactured articles produced by sequential selective heating of powder layers to fuse particles within and between layers, such as SLS, HSS and MJF. EXAMPLES

[0058] Example 1: Polyketone powder is produced in the course of the procedure described in U.S. Pat. No. 5,138,032, column 2, line 52 to column 5, line 17, and melt extruded (about 240° C.) to form pellets of polyketone (pelletized polyketone). The thermal behavior of the pelletized polyketone is shown in the DSC curve of FIG. 1. The melting peak enthalpy is 40 J / g, the melting peak onset temperature is 180° C., and the crystallization onset temperature is 175° C.

[0059] 10 grams of pelletized polyketone is dissolved in 100 mL of N-methylpyrrolidone (NMP) at 130° C. to 150° C. with stirring. Upon complete dissolution in NMP, the temperature is reduced to approximately 130° C. The viscosity increases considerably, and the solution may be further cooled to form a gel, if desired. When the temperature of the solution reaches approximately 130° C., room temperature DI (deionized) water is added to the solution to precipitate the polyketone from the solution to form a thick slurry. Water is added until no further precipitation is observed. The precipitated powder is vacuum filtered from the solvent and further washed with water to remove residual NMP. The dried precipitated powder is dried in air at 110° C. The thermal behavior of the resulting powder is shown in FIG. 2. From FIG. 2, it is clear that the precipitated powder has a higher enthalpy melting peak than the starting polyketone, and the onset temperatures of the enthalpy peak and the crystallization peak do not overlap. Also from FIG. 2 it is shown that when heated a second time at a heating rate of 10° C. / min and held at a temperature of 250° C. for about 2 minutes, the polyketone has a substantially reduced peak enthalpy of melting.

[0060] Example 2: Example 1 is repeated, except that the non-solvent water is introduced at a temperature of about 95° C. until precipitation is complete. FIG. 3 is a DSC of the polyketone of this example, which shows a melting peak enthalpy of greater than 175 Joules / gram, and shows that the melting peak and crystallization peak onset temperatures do not overlap. Upon heating a second time, the melting peak drops by more than an order of magnitude. FIG. 4 is an optical micrograph of porous polyketone particles formed by this method, which can then be subsequently ground as needed to produce powders useful for additive manufacturing.

[0061] Figure 5 shows the results of dynamic mechanical analysis of polyketones exposed to different heating temperatures. It is readily apparent from this figure that polyketones crosslink even below their melting temperature, and that this method can produce polyketones useful for additive manufacturing without introducing crosslinks and without the effects of heat on the polyketone. The temperatures listed represent flow or melting of the polymer, while the absence of such temperatures represents a crosslinked polymer. Increasing temperatures represent increasing crosslinking.

[0062] Preferred embodiments of the present invention will be described below in detail.

[0063] EMBODIMENT 1 A composition comprising a semi-crystalline polyketone powder having a melting peak with a melting peak enthalpy of at least 50 Joules / gram as determined by differential scanning calorimetry (DSC) using a heating rate of 10° C. / min.

[0064] EMBODIMENT 2 The composition has a D of up to 300 micrometers. 90 2. The composition of embodiment 1, having a particle size and an average particle size equivalent spherical diameter of 1 micrometer to 150 micrometers.

[0065] EMBODIMENT 3 3. The composition of claim 1 or 2, wherein at least 80% by number of the particles of the semi-crystalline polyketone powder have a circularity of at least about 0.8.

[0066] EMBODIMENT 4 The polyketone is:

[0067] [ka]

[0068] wherein A is the residue of an alkene monomer which is converted to a saturated hydrocarbon group, m is from about 1 to 6, and n is at least about 2 to 10,000.

[0069] EMBODIMENT 5 The composition of embodiment 4, wherein the semicrystalline polyketone powder is a copolymer of ethylene, carbon monoxide, and at least one other alkene monomer.

[0070] EMBODIMENT 6 The composition of embodiment 5, wherein the other alkene monomer is propylene.

[0071] EMBODIMENT 7 2. The composition of embodiment 1, wherein the melting peak and recrystallization peak do not overlap.

[0072] EMBODIMENT 8 8. The composition of embodiment 7, wherein the melting peak has a melting peak onset temperature and a recrystallization peak onset temperature that are separated by at least 10° C.

[0073] EMBODIMENT 9 9. The composition of embodiment 7 or 8, wherein the semi-crystalline polyketone powder has a crystallinity of at least about 15% by volume.

[0074] EMBODIMENT 10 The semi-crystalline polyketone powder has (i) a D 90 (ii) a particle size D of at least 10 μm 10 and (iii) an average particle size of about 20 μm to about 150 μm.

[0075] EMBODIMENT 11 The composition of any one of embodiments 7 to 10, wherein the melting peak has a melting enthalpy of at least 75 Joules / gram.

[0076] EMBODIMENT 12 12. The composition of any one of embodiments 1 to 6 and 11, wherein the enthalpy of melting is at least 100 Joules / gram.

[0077] EMBODIMENT 13 1. A method of forming a polyketone powder useful for producing a laminated manufactured article, comprising: (i) dissolving an initial polyketone having an onset melting temperature in a solvent at a temperature greater than 50° C. and less than the onset melting temperature of the initial polyketone to form a solution comprising dissolved polyketone; (ii) precipitating the dissolved polyketone by cooling the solution, adding a non-solvent to the solution, or a combination thereof to form a semi-crystalline polyketone powder; and (iii) separating the semi-crystalline polyketone powder from the solvent; The method includes:

[0078] EMBODIMENT 14 14. The method of embodiment 13, further comprising grinding the polyketone powder to form a ground polyketone powder.

[0079] EMBODIMENT 15 15. The method of claim 13 or 14, further comprising heating the semi-crystalline polyketone powder of step (iii) to a temperature within 20% of the onset of melting temperature of the semi-crystalline polyketone to form a heat-treated polyketone.

[0080] EMBODIMENT 16 16. The method of embodiment 15, wherein the semi-crystalline polyketone has a peak enthalpy of melting of at least 75 Joules / gram.

[0081] EMBODIMENT 17 17. The method of embodiment 16, wherein the peak melting enthalpy is at least 100 Joules / gram.

[0082] EMBODIMENT 18 The ground polyketone powder has (i) a D 90 (ii) a particle size D of at least 10 μm10 (iii) has an average particle size of about 20 μm to about 150 μm; and (iv) at least 80% by number of the ground polyketone powders have a circularity of at least about 0.8.

[0083] EMBODIMENT 19 17. The method of embodiment 16, wherein the conditions for increasing crystallinity comprise heat treating any one of the polyketone powders at a temperature from 50° C. to below the peak melting onset temperature as determined by DSC for a period of time that increases the crystallinity to form a polyketone having increased crystallinity.

[0084] EMBODIMENT 20 20. The method of any one of claims 13 to 19, wherein the melting step is carried out at a temperature of 100°C to 150°C.

[0085] EMBODIMENT 21 21. The method of any one of embodiments 13 to 20, wherein the precipitating step is carried out by adding a non-solvent consisting of water.

[0086] EMBODIMENT 22 22. The method of embodiment 21, wherein the precipitating step is carried out at a temperature of from 75° C. to 130° C.

[0087] EMBODIMENT 23 23. The method of embodiment 22, wherein the precipitating step is carried out at a temperature of from 80° C. to less than 100° C.

[0088] EMBODIMENT 24 23. The method of any one of embodiments 13 to 22, wherein the initial polyketone has unimodal melting and crystallization peaks, each having a non-overlapping onset temperature.

[0089] EMBODIMENT 25 25. The method of any one of embodiments 21 to 24, wherein the non-solvent is water.

[0090] EMBODIMENT 26 The method of any one of embodiments 21 to 25, wherein the solvent is a polar aprotic solvent.

[0091] EMBODIMENT 27 27. The method of embodiment 26, wherein the solvent has a dielectric constant of 15 to 50.

[0092] EMBODIMENT 28 26. The method of embodiment 25, wherein the solvent is selected from the group consisting of N-methylpyrrolidone, tetrahydrofuran, dioxane, hexamethylphosphoramide (HMPA), 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU), propylene glycol monomethylethyl acetate (PGMEA), and dimethylformamide.

Claims

1. A composition comprising a semi-crystalline aliphatic polyketone powder having a melting peak with a melting peak enthalpy of at least 50 Joules / gram as determined by differential scanning calorimetry (DSC) using a heating rate of 10° C. / min.

2. The composition has a D of up to 300 micrometers. ９０ 10. The composition of claim 1 having a particle size and an average particle size equivalent spherical diameter of 1 micrometer to 150 micrometers.

3. The semi-crystalline aliphatic polyketone comprises: 【Chemistry 1】 2. The composition of claim 1, comprising repeating units represented by the formula:

4. 4. The composition of claim 3, wherein the semi-crystalline aliphatic polyketone powder is a copolymer of ethylene, carbon monoxide, and at least one other alkene monomer.

5. The composition of claim 4 wherein said other alkene monomer is propylene.

6. The composition of claim 1, wherein the melting peak has a melting peak onset temperature and a recrystallization peak onset temperature that are separated by at least 10°C.

7. 2. The composition of claim 1, wherein the semi-crystalline aliphatic polyketone powder has a crystallinity of at least 15% by volume.

8. 8. The composition of claim 1, wherein the melting peak has a melting enthalpy of at least 75 Joules / gram.

9. 1. A method of forming an aliphatic polyketone powder useful for producing a laminated manufactured article, comprising: (i) dissolving an initial aliphatic polyketone having an onset melting temperature in a solvent at a temperature greater than 50° C. and less than the onset melting temperature of the initial aliphatic polyketone to form a solution comprising dissolved aliphatic polyketone; (ii) precipitating the dissolved aliphatic polyketone by cooling the solution, adding a non-solvent to the solution, or a combination thereof to form a semi-crystalline aliphatic polyketone powder; and (iii) separating the semi-crystalline aliphatic polyketone powder from the solvent; Including, The aliphatic polyketone powder has a melting peak having a melting peak enthalpy of at least 50 Joules / gram as determined by differential scanning calorimetry (DSC) using a heating rate of 10° C. / min.

10. 10. The method of claim 9, further comprising heating the semi-crystalline aliphatic polyketone powder of step (iii) to a temperature within 20% of the onset of melting temperature of the semi-crystalline aliphatic polyketone to form a heat-treated semi-crystalline aliphatic polyketone.

11. 10. The method of claim 9, wherein the dissolving step is carried out at a temperature of from 100°C to 150°C and the precipitating step is carried out at a temperature of from 75°C to 130°C.

12. 10. The method of claim 9, wherein the precipitating step is performed by adding a non-solvent consisting of water, said solvent being a polar aprotic solvent having a dielectric constant of 15 to 50.

13. 13. The method of any one of claims 9 to 12, wherein the initial aliphatic polyketone has unimodal melting and crystallization peaks, each having a non-overlapping onset temperature.

14. 13. The method of claim 12, wherein the solvent is selected from the group consisting of N-methylpyrrolidone, tetrahydrofuran, dioxane, hexamethylphosphoramide (HMPA), 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU), propylene glycol monomethyl ethyl acetate (PGMEA), and dimethylformamide.

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