CN117242123A - Polyketone powder for laser sintering - Google Patents

Abstract

The present invention provides a semi-crystalline polyketone powder useful for additive manufacturing, which can be prepared by the following method: dissolving a polyketone having a single melting peak by Differential Scanning Calorimetry (DSC) at a temperature of 50 ℃ or more and lower than the melting temperature of the polyketone; the dissolved polyketone is precipitated by cooling, adding a non-solvent, or a combination thereof. The method can be used to form polyketones having DSC melting peaks with enthalpies greater than the initial polyketones.

Description

Polyketone powder for laser sintering

Technical Field

The present invention relates to powders for preparing additive manufactured articles. In particular, the present invention relates to aliphatic semi-crystalline polyketone powders.

Background

The powder-based additive manufacturing method includes the following: selective Laser Sintering (SLS) is a 3D printing technique that uses a laser to fuse a powder material in a continuous layer (see, e.g., U.S. patent No. 5,597,589). High Speed Sintering (HSS) and multi-jet fusion (MJF) 3D printing employ multiple jets that deposit successive layers of infrared (IR-absorbing) ink onto a powder material in a similar manner, and then are exposed to IR energy to selectively melt the powder layer. Electrophotographic 3D printing employs a rotating photoconductor that builds objects layer by layer from a substrate.

Selective Laser Sintering (SLS), multi-jet fusion (MJF), and high-speed sintering (HSS) 3D printing methods use the same type of free-floating, non-fixed powder bed. Since additively built objects are subjected to similar stresses, they typically have the same material requirements for compatibility with the printing process, except that different heating mechanisms are used to obtain the melt phase. In general, a free body map of a 3D printed object may be used to determine the residual stress expected in the printed object. This is necessary for the successful construction of the object. If the residual stress is too high, the object will deform or deform beyond acceptable tolerances.

The residual stress of these powder bed based 3D printers has typically been minimized by using crystalline or semi-crystalline thermoplastic polymers with a sufficiently large window between their melting temperature and their recrystallization temperature. Unfortunately, this limits the polymers (e.g., polyamides) that have been successfully used to print large or complex parts using SLS and MJF methods, thereby limiting the usefulness of these additive manufacturing methods.

Aliphatic polyketones are promising polymers, in part, because of their physical properties and chemical resistance as low cost engineering plastics. Polyketones are generally copolymers prepared by copolymerizing ethylene (and/or other alkenes or olefins) and carbon monoxide in the presence of a palladium (or other) catalyst, such as described in US4,835,250 and US 20080058494. The aliphatic polyketone is then typically separated from the other components present in the polymerization reactor. These other components may include unreacted olefin, 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 a "reactor flake". Reactor sheets, because of their fine particle size, cause handling and transportation difficulties, are typically heated and extruded to form pellets for commercial sale, resulting in undesirable characteristics such as low melting peak enthalpy and possible cross-linking of polyketones due to exposure to temperatures above the melting temperature when forming pellets.

It is therefore desirable to provide a thermoplastic polymer that avoids one or more of the problems of preparing an additive manufactured article by a method such as described above, such as SLS, HSS, MJF. In particular, it is desirable to provide a thermoplastic polymer that can provide articles that are high strength, tough, high temperature resistant, flame retardant, and in some cases optically transparent.

Disclosure of Invention

Applicants have discovered a method of treating aliphatic polyketones to achieve specific powder morphology and thermal characteristics, allowing improved additive manufacturing of these materials by a floating powder bed process. Surprisingly, in one example, the polyketone powder exhibits a DSC melting peak, which exhibits a high enthalpy peak (at least 75J/g). The enthalpy of the melting peak can be significantly increased, which can be useful when 3D printing (e.g., the enthalpy can be greater than 30, 40, 50, 60, 75, 100, 125, 150, or even 175 joules/gram polyketone), while avoiding cross-linking of the polyketone.

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

A third aspect is a method of forming an improved semicrystalline polyketone comprising:

(i) Dissolving an initial polyketone in a solvent at a temperature above 50 ℃ to below the initial melting temperature of the polyketone to form a solution consisting of the 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 modified semi-crystalline polyketone; and

(iii) Separating the modified polyketone semi-crystalline polyketone from the solvent.

The modified polyketone powder may be further processed by milling to achieve the desired particle size and further processed to alter crystallinity and alter DSC melt characteristics required for additive manufacturing (e.g. to achieve the first aspect of the invention). The isolated polyketone may be further treated to remove unwanted solvents, such as by further washing in a non-solvent.

Polyketones formed by those methods in the first and second aspects are particularly useful for forming articles by additive manufacturing methods such as floating powder bed methods (e.g., SLS, HHS and MJF methods). Such polyketone powders desirably have a D of up to 300 microns ₉₀ Particle size and average particle size of 1 micron to 150 micron equivalent spherical diameter. These polyketones may be printed by floating powder bed additive manufacturing techniques such as SLS, HSS and MJF. With the properties of such engineering plastics (e.g., heat and chemical resistance and low coefficient of friction with many other materials), the composition can be made into additive manufactured articles. Examples of such applications include biocompatible (medical), electrical, transportation (e.g., automotive, rail, trucking), plumbing, aerospace, food contact, industrial (e.g., mechanical), and consumer (e.g., household) applications.

Drawings

FIG. 1 is a chart of Differential Scanning Calorimetry (DSC) of a polyketone not of the invention.

FIG. 2 is a DSC chart of polyketone powder of the composition of the invention.

FIG. 3 is a DSC chart of polyketone powder of the composition of the invention.

FIG. 4 is an optical micrograph of a polyketone powder of the present invention.

FIG. 5 is a graph of dynamic mechanical analysis of polyketones subjected to different heat treatments.

Detailed Description

The illustrations and descriptions set forth herein are intended to familiarize others skilled in the art with the present invention, its principles, and its practical applications. The specific embodiments of the disclosure as set forth are not intended to be exhaustive or to limit the scope of the disclosure.

As used herein, "one or more" means that at least one or more of the components can be used as disclosed. It should be understood that the functionality of any ingredient or component may be the average functionality due to imperfections in the starting materials, incomplete conversion of reactants, and formation of byproducts.

The method comprises dissolving an initial polyketone in a solvent at a temperature above 50 ℃ to below the initial melting temperature of the polyketone to form a solution consisting of the dissolved polyketone. Typically, the solvent is heated to a temperature above 100 ℃ to below the onset melting temperature of the particular polyketone, as determined by Differential Scanning Calorimetry (DSC) as described herein. Illustratively, the solvent is heated to above 75 ℃ or 100 ℃ and is 5%, 10% or 20% lower than the initial melting temperature of the polyketone, e.g., up to about 200 ℃, 180 ℃, 170 ℃, or 160 ℃.

The initial polyketone may be any polyketone composed of a repeating unit represented by the following formula:

where A is the residue of an olefin monomer converted to a saturated hydrocarbyl group, m is from about 1 to 6, and n is at least about 2 to any feasible amount that achieves the desired number average molecular weight useful in the present invention. Exemplary useful number average molecular weights may be those that provide a melting temperature of from about 175 ℃ or 210 ℃ to about 270 ℃ or 300 ℃ and may be from about 1000 to 250,000 or about 10,000 to 200,000.

The initial polyketone of the composition is desirably a terpolymer of carbon monoxide, ethylene and another olefin monomer (e.g., an alkene of 3 to 12, 8 or 6 carbons, particularly propylene). Such polyketones may be represented by random repeating units:

wherein G is a saturated residue of an alkene having 3 to 12, 8 or 6 carbon atoms polymerized by a double bond, and x/y is at least 2 to 100 or 50 or 20. Desirably, G is propylene. The polyketone may be capped with any useful group such as an alkyl group, a hydroxyl group, an ester, a carboxylic acid, an ether, or a combination thereof. Specific end-capping groups may be generated by using solvents such as low molecular alcohols (such as methanol) or water or combinations thereof.

The initial polyketone typically exhibits a single-peak melting peak separated from the crystallization peak, possibly due to melt extrusion of the polyketone to form the polyketone into pellets. Commercially available polyketones may be used as the initial polyketones, such as those known in the art (e.g., those purchased under the trade name POKETON, hyosung, KR).

The time at maximum heating temperature (dissolution temperature) is any time (typically 3 or 4 minutes to 3 or 4 hours) required to achieve dissolution of the polyketone. The temperature increase may be used (maintained) more than once during the process. For example, a higher temperature may be used to dissolve the polyketone (dissolution temperature) and a lower temperature may be used when precipitating the polyketone (precipitation temperature). The precipitation temperature is the temperature at which the polyketone starts to precipitate upon cooling or the temperature at which precipitation is caused by the addition of a non-solvent. The precipitation temperature may be any temperature from ambient temperature and above-20 ℃ to dissolution temperature (when precipitation is performed by addition of a non-solvent) to below dissolution temperature (e.g., to 130 ℃, 125 ℃, 100 ℃, 75 ℃, or 50 ℃). The precipitation temperature is desirably below the temperature at which the non-solvent begins to boil (the onset boiling temperature as determined by DSC in a manner similar to the melting peak as determined herein). Agitation may be used during any part or all of the process.

Stirring is generally understood to mean stirring components in a liquid or pasty mixture under the generation of shear forces, generally using impellers rotating within a stator to create flow and turbulent flow patterns. The agitation may be any agitation useful for achieving a shear rate that achieves the desired particle size and shape. Once the impeller has sucked in the mixture, it undergoes a sudden change in direction and acceleration of the mixture, causing the mixture to contact the wall of the stator under the influence of centrifugal force, or to be forced through the holes in the stator under the influence of pressure and speed, thus eventually changing direction and acceleration. In an exemplary embodiment of the high shear mixing conditions, mixing includes operating at a speed of 50 revolutions per minute (rpm) to 500 rpm.

Desirably, the atmosphere is any atmosphere with which solvents and other chemicals do not react deleteriously. Typically, dissolution is performed in a closed vessel at or near ambient pressure (e.g., ±10%, ±1% or ±0.1%) applied pressure to minimize volatilization losses. Boost may be used, but is not required. Depending on the solvent, an exemplary atmosphere may include nitrogen or a noble gas (e.g., argon) or a combination thereof or air (e.g., dry air).

The amount of polyketone dissolved in the solvent may be any useful amount that can be subsequently precipitated from solution upon cooling, introduction of a non-solvent, or a combination thereof. For example, the amount of dissolved polyketone may be from 1%, 5%, 10% to any practical amount (ungelatinized), 50%, 40%, 30% or 25% by weight.

Polyketones herein include polymers polymerized from carbon monoxide and olefin monomers in the presence of a group 8 to 10 transition metal catalyst. In particular, the polyketone may be any of those prepared by any of the methods described in, for example, U.S. patent nos. 4,835,250, 4,894,435, 5,138,032 and 2008/0058494, each of which is incorporated by reference in its entirety. In particular, the methods, reaction conditions, and monomers are those described in U.S. patent No. 5,138,032, column 2, line 52 to column 5, line 17, the details of which are incorporated herein by reference.

Desirably, the olefin monomer consists of an olefin having 2 to 12, 8 or 6 carbons. Illustratively, the olefin monomer is ethylene or the olefin monomer includes ethylene and at least one other olefin monomer such as propylene. When the polyketone is a copolymer of ethylene and another alkene monomer (e.g., propylene), the amounts of ethylene and other alkene are as described in U.S. patent No. 5,138,032, column 2, line 17 to column 3, line 14.

The solvent may be any useful solvent for dissolving polyketones, such as a polar aprotic solvent. Typically, the solvent has a volatile or low viscosity, which makes it easy to remove in a subsequent processing step, e.g. separating the precipitated polyketone from the solvent. Typically, the viscosity of the solvent falls within the order of magnitude of the viscosity of water at ambient conditions (e.g., about 20 ℃ to 25 ℃ and 1 centipoise at 1 atmosphere). That is, the viscosity is typically less than 10 centipoise to 0.1 centipoise (cp). The volatility, also measured by boiling point (or boiling point range) at 1 atmosphere pressure, is typically about 30 ℃,50 ℃ or 75 ℃ to 150 ℃, 200 ℃ or 250 ℃. The molecular weight (weight average Mw) Mw of the solvent is typically up to about 500 g/mol, 200 g/mol, or even 150 g/mol to at least about 30 g/mol. It should be appreciated that in some cases, the solvent may be a solid at ambient conditions, but have the boiling point temperatures described above and a useful viscosity at elevated temperatures (e.g., less than about 100cp or 10 cp), at which time dissolution occurs.

The solvent may be a mixture of solvents. As an example, the solvent may be a mixture of a liquid solvent at room temperature and another solvent that is a solid that will dissolve in the liquid solvent at room temperature, wherein the dissolved solvent imparts one or more desired properties (e.g., solubility or particle formation of the polyketone improves when precipitating the polyketone from solution using a non-solvent).

The solvent may contain some water and still be available for dissolution and precipitation. Typically, 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 fischer titration. To achieve the desired water concentration, any suitable method of drying the solvent may be used, such as those known in the art. For example, the solvent may be dried by distillation or contacted with a molecular sieve to remove water. The dried solvent may be further modified as described and specified in U.S. federal regulation chapter 27, section 21.151. The desired water concentration can be achieved by known methods (e.g., distillation and adsorption).

The solvent has one or more groups that create sufficient dipoles 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. Desirably, the dielectric constant of the solvent is at least about 15 to about 90, 80 or 50, 40 or 30. The dielectric constant may be calculated from dipoles present in the solvent molecule or determined experimentally, such as described in j.Phys.chem. (2017), 121,2,1025-1031.

The solvent may be a linear, branched, aromatic, or cyclic solvent having one or more heteroatoms (e.g., O, N, S, si or halogen) to about 10, 8, 6, 4, or 3 heteroatoms having a Mw as described above, so long as the solvent has a dielectric constant of at least about 10. Typically, the amount of carbon is 1 to 24, 18, 16, 12 or 6. Polar aprotic solvents that may be used include ketones (e.g., acetone, diisopropyl ketone, and methyl butyl ketone), aliphatic or aromatic halogenated hydrocarbon solvents (e.g., methyl chloride, methylene chloride, chloroform, 1, 2-dichloroethane, or 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 trifluoromethylpropene carbonate), and dialkyl carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylethyl carbonate (EMC), methylpropyl carbonate (MPC), and ethylene carbonate (EPC).

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), vinylidene sulfone, butadiene sulfone, 4-methoxyphenyl methyl sulfone, 4-chlorophenyl methyl sulfone, 2-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).

The polar aprotic solvent may also be silicon-containing, such as a siloxane or silane. Some examples of siloxane solvents include Hexamethyldisiloxane (HMDS), 1, 3-divinyl tetramethyl disiloxane, polysiloxanes, and polysiloxane-polyoxyalkylene derivatives. Some examples of silane solvents include methoxytrimethylsilane, ethoxytrimethylsilane, dimethoxydimethylsilane, methyltrimethoxysilane, and 2- (ethoxy) ethoxytrimethylsilane.

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., monofluoro, difluoro, trifluoro, tetrafluoro, pentafluoro, hexafluoro, and perfluoro derivatives of any of the foregoing ethers and 1, 4-butyrolactone, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, or ethyl butyrate), formates (e.g., methyl formate, ethyl formate, or propyl formate) and fluorinated esters (e.g., monofluoro, difluoro, trifluoro, tetrafluoro, pentafluoro, hexafluoro, and perfluoro derivatives of any of the foregoing 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-dimethylformamide, N-diethylformamide, acetamide, dimethylacetamide, diethylacetamide, γ -butyrolactam, and N-methylpyrrolidone.

Polar aprotic solvents may also be diethyl ether, tetrahydrofuran and dioxane, hexamethylphosphoramide (HMPA), N-methylpyrrolidone (NMP), 1, 3-dimethyl-3, 4,5, 6-tetrahydro-2 (1H) -pyrimidinone (DMPU) and Propylene Glycol Methyl Ether Acetate (PGMEA).

The non-solvent used to induce precipitation at the precipitation temperature may be any suitable non-solvent. Illustratively, the solvent may be NMP (N-methylpyrrolidone), DMPU (N, N-dimethylpropenyl urea), PGMEA (propylene glycol methyl ether acetate), or HMPA (hexamethylphosphoric triamide), and the non-solvent may be a protic solvent such as water, a low molecular weight alcohol (e.g., C1 to C4 alcohol), or a mixture thereof. The amount of non-solvent may be any amount necessary to cause precipitation at a given precipitation temperature that is useful for achieving the desired polyketone particle size, particle size distribution, and morphology of precipitation. Typical concentrations of added non-solvent may be 0.1%, 1%, 5% or 10% to typically 75%, 50% or 25% of the volume of solvent and non-solvent.

Typically, a mixture (slurry) of the starting polyketone powder and the solvent is prepared under ambient conditions while the slurry is stirred. Typically, the temperature is raised to promote the dissolution temperature, thereby dissolving the polyketone. Desirably, the dissolution temperature is at least 10 ℃ below the boiling point of the solvent. To facilitate the precipitation and formation of the desired particles, the solution is cooled to a temperature at which precipitation occurs to precipitate the polyketone, preferably in powder form, from the solution. The polyketone powder may then be separated by any suitable method, such as filtration, centrifugation, flotation, or other known methods, or combinations thereof. Separation may be facilitated by one or more additives such as low molecular weight solvents, surfactants, flotation enhancers, and the like. Separation may be performed by filtration (e.g., vacuum filtration).

Additives may be added during the process to impart one or more desired characteristics to the polyketone powder for use in the floating bed additive manufacturing technique. For example, one or more of a UV stabilizer, filler, lubricant, plasticizer, pigment, glidant, or flame retardant may be added. When the process is carried out, if the additive remains solid in the solvent, it may act as a nucleating agent and be surrounded by the precipitated polyketone. The amount of any particular additive may be any useful amount to achieve the particular properties for printing or characteristics of the article formed therefrom. Typically, the amount of one or more additives, when present, is up to about 50%, 25%, 10% or 5% by volume of the composition. The glidant may be any known compound for improving powder flow, for example fumed silica (e.g., aerosil 200).

The filler may be any useful filler such as those known in the art. Examples of fillers include ceramics, metals, carbon (e.g., graphite, carbon black, graphene), polymer particles that do not melt or decompose at printing temperatures (e.g., crosslinked polymer particles, vulcanized rubber particles, etc.), plant-based fillers (e.g., wood, nut shells, grain and rice hull meal or particles). Exemplary fillers include calcium carbonate, talc, silica, wollastonite, clay, calcium sulfate, mica, inorganic glass (e.g., silica, aluminosilicates, borosilicates, alkali aluminosilicates, etc.), oxides (e.g., alumina, zirconia, magnesia, silica "quartz" and calcium oxide), carbides (e.g., boron carbide and silicon carbide), nitrides (e.g., silicon nitride, aluminum nitride), oxynitrides, combinations of oxycarbides, or combinations thereof.

It has surprisingly been found that the process is capable of preparing aliphatic polyketones having DSC melting peaks with a greater enthalpy, but also peaks of bimodal shape (bimodality). The enthalpy of the melting peak may be 10%, 20% or 30% or more higher than the enthalpy of the initial melting peak of the initial polyketone. Typically, after the process is performed, the melting peak onset temperature cannot overlap with the crystallization onset temperature. It has also been found that if a polyketone having a high melting enthalpy is heated to within 5%, 10% or 20% of the initial melting temperature of the polyketone, a polyketone having a melting peak which does not overlap with the crystallization peak can still be formed and can have a reduced enthalpy, but the process can achieve adjustability of the separation of the melting peak initial temperature and the crystallization initial temperature.

Illustratively, the polyketone precipitated in the process 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 and may depend on the peak temperature (annealing temperature) used. For example, when the annealing temperature is higher, such as above the initial melting temperature of the polyketone (e.g., greater than or equal to 1 ℃,5 ℃,10 ℃, 20 ℃), the heating rate may desirably be faster. Also, the annealing temperature may be maintained for any useful time and may depend on the annealing temperature used in the same manner as the heating rate. Illustratively, if the annealing temperature is equal to or greater than the onset melting temperature, the annealing time is typically less than 2 hours, 1 hour, or 0.5 hours.

It has also been found that this approach avoids the problem of polyketone cross-linking which may render it unusable for additive manufacturing or, if partially cross-linked, hinder for example intra-and inter-layer fusion and adhesion. The degree of crosslinking can be shown by dynamic mechanical analysis, wherein increased crosslinking is shown by increased temperature, wherein the storage modulus decreases until there is no melting behavior (storage modulus does not show a decrease). Typical heating rates, for example 3C/min and a frequency of 1Hz, such as described in ASTM D4065, may be used. That is, the method can be used to prepare polyketone powders that do not contain any crosslinks or have a crosslinking amount that is not greater than the amount of crosslinks that the polyketone formed has. Heating and annealing methods that minimize the problems of heating and cooling bulk materials, such as those known in the art, may be preferably employed, including, for example, fluidized bed, rotary kiln, or stack furnace.

The polyketone formed may be further fractionated, crushed, etc. by any suitable method such as those known in the art, depending on the agitation and the particular method used for precipitation. Exemplary classification methods may include centrifugation, sedimentation, and air-cyclone. Size reduction (comminution) may be carried out by any suitable method such as those known in the art. By way of example, milling at a temperature at which the semicrystalline polyketone becomes brittle may be used and is commonly referred to as low temperature ball milling. In general, the temperature of the low temperature ball milling may be any temperature below about 0 ℃, -25 ℃, -50 ℃ to about-75 ℃, -100 ℃, -150 ℃, or 190 ℃. In one embodiment, cooling is provided by using dry ice or liquid nitrogen. After low temperature ball milling, the milled polyketone powder may be further classified to isolate any particles larger than desired and further milled, and the undersized particles may be melted, classified or milled in any suitable manner to achieve the desired size.

In an initial DSC scan of the polyketone powder, crystallization peaks or recrystallization peaks (used interchangeably herein) can overlap with melting peaks and still result in a powder that can be additively manufactured with good properties and without warpage or deformation. But typically the melting and crystallization onset temperatures do not overlap.

The crystallization temperature (Tc) of the polyketone powder is lower than the melting temperature (Tm) of the semi-crystalline polymer, which is determined by the melting peak and the peak value of the crystallization peak, and in the case of the bimodal, by the lower temperature peak. Typically, the Tc of the polyketone is about 5 ℃ to 40 or 50 ℃ below Tm. Tm and Tc are determined from the melting peak of DSC described according to ASTM D3418, using the midpoint of the melting peak. The onset of Tm and Tc peaks is also determined according to ASTM D3418 (i.e., deviation of scan from linearity).

The directly derived polyketone powder may have a morphology that allows it to be additively manufactured without a glidant. Desirably, the polyketone having such desirable flow characteristics has sphericity in terms of particle shape and in particular particle rounding to aid flowability, and as derived from photomicrograph images of individual particles, may be represented by a rounded feature or roundness, where roundness of individual particles is defined as 4pi A/P ² Where A is the area of the particle and P is the perimeter of the particle, both from a random perspective. The sphericity of the relevant parameter is derived as the square root of the roundness. Roundness is a value greater than zero and less than or equal to one. Perfect circular particles are meant to have a roundness of 1.00. The table of overall roundness data is presented in such a way that various roundness levels (e.g., 0.65, 0.75, 0.85, 0.90, and 0.95) accompany a percentage of the population of particle samples having a roundness greater than the table value. Roundness is determined at a reliability filter (reliability filter) level of 0.9 or 0.95. Reliability ofA filter (reliability filter) is a filter for removing overlapping particles in a two-dimensional micrograph, and is available in commercial image analysis software. Reliability is essentially the area of particles (particle area) over the entire area in the region defined by the major and minor axes of the particle region of the two-dimensional micrograph. Particle size and shape can be measured by any suitable method known in the art to measure particle size by diameter. In some embodiments, particle size and shape are determined by laser diffraction as known in the art. For example, a laser diffractometer (such as Microtrac S3500) with a static image analysis accessory may be used to analyze the captured image of the particles using PartAnSI software to determine particle size. Desirably, at least about 65%, 70%, 80%, 95% or 99% of the particles (by number) have a roundness of at least about 0.8, 0.85, 0.9 or 0.95 for the powder separated and classified from the reactor without further treatment other than purification.

Likewise, polyketone powders without any glidants added typically have a flowability of at least about 0.5g/s, 1g/s or 2g/s to virtually any rate achievable using a 15mm nozzle (e.g., 50 g/s), as determined by method A of ASTM D1895.

The above semicrystalline polyketones of the present invention have a crystallinity of at least about 15% to substantial crystallization by weight, with higher crystallinity being desirable. Desirably, the crystallinity is from 20%, 25% or 30% to substantially crystalline, 90%, 80%, 75%, 60% or 55%. 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, for example, wide angle x-ray diffraction (WAXD), such as by using a Rigaku SmartLab x-ray diffractometer, or Differential Scanning Calorimetry (DSC), such as by using a differential scanning calorimeter ASTM D3418-15 with TA Instruments DSC.

The polyketone of the composition may have the enthalpy of any DSC melting peak used to prepare a powder for additive manufacturing (such as SLS). Typically, the enthalpy is at least 3 joules/gram, but desirably is at least 5 joules/gram, 10 joules/gram, 20 joules/gram, 30 joules/gram, 40 joules/gram, 50 joules/gram, 60 joules/gram, 70 joules/gram, or 75 joules/gram or more to any practical amount, such as 200 joules/gram. The enthalpy of the DSC melting peak can be determined in accordance with the manner described in ASTM D3418.

The semi-crystalline polyketones of the above particles generally have particle sizes and particle size distributions useful for making additive manufactured articles, and generally have an average or median particle size (D) of from about 1 micrometer (μm), 10 μm, 20 μm, 30 μm or 40 μm to 150 μm, 125 μm, 110 μm or 100 μm ₅₀ ) (by volume). Also, in order to be able to heat and fuse the powder uniformly, it is desirable to have a D of at most 300 μm, 200 μm or 150 μm ₉₀ . To facilitate flowability, the polyketone desirably has a D of at least 0.1 μm, 0.5 μm or 1 μm by volume ₁₀ 。“D ₉₀ "means particle size (equivalent spherical diameter) in a particle size distribution wherein 90% by volume of the particles are less than or equal to that size; similarly, D ₅₀ Refers to particle size (equivalent spherical diameter) in a particle size distribution wherein at least 50% by volume of the particles are smaller than this size, and D ₁₀ Refers to particle size (equivalent spherical diameter) in a particle size distribution wherein at least 10% by volume of the particles are smaller than this size. Particle size may be determined by any suitable method, such as those known in the art, including, for example, laser diffraction or image analysis of a photomicrograph of a sufficient number of particles (-100 to-200 particles). Representative laser diffractometers are produced by Microtrac, such as Microtrac S3500.

The compositions of the present invention may also contain useful additives such as those known in the art for use in the manufacture of articles such as additive manufactured articles. For example, the composition may have one or more of a UV stabilizer, filler, lubricant, plasticizer, pigment, glidant, flame retardant, or solvent. Desirably, the composition is substantially free of solvent (i.e., up to trace amounts, which may be up to 10 parts per million (ppm), 1ppm, by weight of the composition). The amount of any particular additive may be any useful amount to achieve the particular properties for printing or characteristics of the article formed therefrom. Typically, the amount of one or more additives, when present, is up to about 50%, 25%, 10% or 5% by volume of the composition. The glidant may be any known compound for improving powder flow, for example fumed silica (e.g., aerosil 200).

It has been found that the polyketones of the compositions of the invention allow the formation of shaped articles which are not deformed or which do not have an undesirable amount of residual stress. For example, but not limited to, the compositions of the present invention may be fabricated into bodies by additive manufacturing methods such as SLS, MJF, HSS or electrophotography. Illustratively, in SLS, a layer of the composition of the present invention may be deposited on a bed at a fixed temperature below the melting temperature of the polyketone powder and the predetermined (selected) regions of the bed sintered (fused) together using a laser controlled and directed heat source as described above. The layers are then successively deposited and sintered onto the previous layer and build up the additive manufactured part within the layer.

In general, the "operating window" for additive manufacturing of semi-crystalline thermoplastic polymers is the temperature difference between the onset of melting of the material and the onset of recrystallization thereof ("Tc"), which should generally be as large as possible. As described above, polyketone can be adjusted by rapid heating and holding at that temperature (annealing temperature) for a short period of time to adjust the melting peak shape and the starting temperature. For example, polyketones may be further optimized, wherein the operating window may be a temperature difference from 5 ℃,10 ℃ or 20 ℃ to any realization, such as 60 ℃,50 ℃, 30 ℃ or 25 ℃.

Because the polyketone powders of the compositions of the invention exhibit good 3d printability, they can be recovered and reused without further processing after printing by a powder additive manufacturing process that includes heating and maintaining the powder bed just below the initial melting temperature of the polyketone. The reclaimed powder can be mixed with any of the polyketone powders described herein that have not been additively manufactured, if desired, to achieve the desired printability characteristics or part properties. The proportion of recovered polyketone constituting the composition of the invention may be any amount from substantially all of the composition, 90%, 75%, 50%, 40% or 30% to about 1%, 5% or 10% by weight of the polyketone powder of the composition. The thermal properties of the reclaimed powder are generally the same as those of the reduced size particulate polyketone described above for use in the polyketone powder of the invention. Morphology and size distribution as also described herein, the morphology is most similar to that of the particular initial polyketone powder used to form the additive manufactured article.

The compositions of the present invention are useful in the manufacture of additive manufactured articles composed of the various molten polyketones of the present invention. In particular, the composition may be used to manufacture an additive manufactured article made by sequentially selectively heating powder layers to fuse particles between and within layers such as SLS, HSS, and MJF.

Examples

Example 1:

polyketone powder was prepared by a method in the manner described in U.S. patent No. 5,138,032, column 2, line 52 to column 5, line 17, and melt-extruded (-240 ℃) polyketone powder to form pellets of polyketone (particulate polyketone). The thermal behavior of the granular polyketone was shown in the DSC curve of FIG. 1, the enthalpy of the melting peak was 40J/g, the initial melting peak temperature was 180℃and the initial crystallization temperature was 175 ℃.

10 g of the particulate polyketone are dissolved in 100mL of N-methylpyrrolidone (NMP) at 130℃to 150℃with stirring. After complete dissolution in NMP, the temperature was reduced to just about 130 ℃. The viscosity increases significantly and the solution can be further cooled to form a gel if desired. When the solution temperature reached about 130 ℃, room temperature DI (deionized) water was added to the solution to precipitate the polyketone from the solution, forming a viscous slurry. Water was added until no further precipitation was observed. The precipitated powder was vacuum filtered from the solvent and further washed with water to remove any residual NMP. The dried precipitated powder was dried in air at 110 ℃. The thermal behavior of the resulting powder is shown in figure 2. As is evident from fig. 2, the precipitated powder has a higher melting peak enthalpy than the starting polyketone, and the onset temperatures of the enthalpy peak and the crystallization peak do not overlap. Also shown in fig. 2, the polyketone had a significantly reduced melting peak enthalpy upon a second heating at a heating rate of 10 ℃/min and a holding at a temperature of 250 ℃ for about 2 minutes.

Example 2:

example 1 was repeated except that non-solvent water was introduced at a temperature of about 95 ℃ until precipitation ceased. FIG. 3 is a DSC of the polyketone of this example showing a melting peak enthalpy of greater than 175J/g, and the onset temperatures of the melting and crystallization peaks do not overlap. On the second heating, the melting peak decreased by more than an order of magnitude. Fig. 4 is an optical micrograph of porous polyketone particles formed by the described method, which may then be milled as needed to produce a powder useful in additive manufacturing.

FIG. 5 shows the results of dynamic mechanical analysis of polyketones at different heating temperatures. It is thus evident that the polyketone will crosslink even below its melting temperature and that the method allows the production of polyketone for additive manufacturing without causing crosslinking and without the influence of heating the polyketone. The observed temperature indicates that the polymer is flowing or melting, whereas the absence of such temperature indicates that the polymer is crosslinked. An increase in temperature indicates an increase in crosslinking.

Claims (28)

1. A composition comprising a semi-crystalline polyketone powder having a melting peak with a melting peak enthalpy of 50 joules/gram less, said melting peak enthalpy determined by Differential Scanning Calorimetry (DSC) using a heating rate of 10 ℃/min.

2. The composition of claim 1, wherein the composition has a D of up to 300 microns ₉₀ Particle size and average particle size of 1 micron to 150 micron equivalent spherical diameter.

3. The composition of claim 1 or 2, wherein at least 80% of the particle number of the semi-crystalline polyketone powder has a roundness of at least about 0.8.

4. A composition according to any one of claims 1 to 3, wherein the polyketone consists of a repeating unit represented by the formula:

wherein A is the residue of an olefin monomer converted to a saturated hydrocarbyl group, m is from about 1 to 6, and n is at least about 2 to 10,000.

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

6. The composition of claim 5, wherein the other olefin monomer is propylene.

7. The composition of claim 1, wherein the melting peak and recrystallization peak do not overlap.

8. The composition of claim 7, wherein the melting peaks have an onset melting peak temperature and a recrystallization peak onset temperature that are at least 10 ℃ apart.

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

10. The composition of any of claims 7-9, wherein the semi-crystalline polyketone powder has: (i) D of less than about 150 μm ₉₀ Particle size, (ii) D of at least 10 μm ₁₀ And (iii) an average particle size of about 20 μm to about 150 μm.

11. The composition of any of claims 7 to 10, wherein the melting peak has a melting enthalpy of at least 75 joules/gram.

12. The composition of any of claims 1-6 and 11, wherein the melting enthalpy is at least 100 joules/gram.

13. A method of forming a polyketone powder for use in preparing an additive manufactured article, comprising:

(i) Dissolving an initial polyketone having an initial melting temperature in a solvent having a temperature of 50 ℃ or higher and lower than the initial melting temperature of the initial polyketone to form a solution composed of the 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.

14. The method of claim 13, further comprising pulverizing the polyketone powder to form a pulverized polyketone powder.

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 initial melting temperature of the semi-crystalline polyketone to form a heat treated polyketone.

16. The method of claim 15, wherein the semi-crystalline polyketone has a melting peak enthalpy of at least 75 joules/gram.

17. The method of claim 16, wherein the melting peak enthalpy is at least 100 joules/gram.

18. The method of claim 14, wherein the crushed polyketone powder has (i) a D of less than about 150 μιη ₉₀ Particle size, (ii) D of at least 10 μm ₁₀ (iii) an average particle size of about 20 μm to about 150 μm, and (iv) at least 80% of the number of crushed polyketone powders has a roundness of at least about 0.8.

19. The method of claim 16, wherein the conditions to increase crystallinity comprise heat treating any of the polyketone powders at a temperature from 50 ℃ to below a melting peak temperature determined by DSC for a time to increase the crystallinity to form a polyketone having increased crystallinity.

20. The method of any one of claims 13 to 19, wherein the dissolving is performed at a temperature from 100 ℃ to 150 ℃.

21. The method according to any one of claims 13 to 20, wherein the precipitation is performed by adding a non-solvent comprising water.

22. The method of claim 21, wherein the precipitation is performed at a temperature from 75 ℃ to 130 ℃.

23. The method of claim 22, wherein the precipitation is performed at a temperature of 80 ℃ to less than 100 ℃.

24. The method of any of claims 13 to 22, wherein the initial polyketone has a unimodal melting peak and a crystallization peak, each having a non-overlapping onset temperature.

25. The method of any one of claims 21 to 24, wherein the non-solvent is water.

26. The method of any one of claims 21 to 25, wherein the solvent is a polar aprotic solvent.

27. The method of claim 26, wherein the solvent has a dielectric constant of 15 to 50.

28. The method of claim 25, wherein the solvent is selected from the group consisting of N-methylpyrrolidone, tetrahydrofuran and dioxane, hexamethylphosphoramide (HMPA), 1, 3-dimethyl-3, 4,5, 6-tetrahydro-2 (1H) -pyrimidinone (DMPU) and Propylene Glycol Methyl Ether Acetate (PGMEA), dimethylformamide.