CN115151598A

CN115151598A - Production of semi-crystalline powdered polycarbonate and its use in additive manufacturing

Info

Publication number: CN115151598A
Application number: CN202080096805.4A
Authority: CN
Inventors: 托马斯·加德纳; 特拉维斯·希斯洛普
Original assignee: Jabil Circuit Inc
Current assignee: Jabil Inc
Priority date: 2020-03-03
Filing date: 2020-03-03
Publication date: 2022-10-04

Abstract

A method of preparing a partially crystalline polycarbonate powder is provided that includes dissolving amorphous polycarbonate in a polar aprotic solvent at a first temperature to form a first solution of dissolved polycarbonate. The first solution is then cooled to a second temperature, the second temperature being lower than the first temperature, wherein a portion of the dissolved polycarbonate precipitates from the first solution to form a second solution comprising a partially crystallized polycarbonate powder. Certain partially crystalline polycarbonate powders produced by such methods are particularly useful in additive manufacturing processes, including powder bed melt processes.

Description

Production of semi-crystalline powdered polycarbonate and its use in additive manufacturing

Technical Field

The present technology relates to the precipitation of starch-like polycarbonate in a solvent, the formation of crystallites of the powdered polycarbonate, and the use of the precipitated powdered polycarbonate in powder-based additive manufacturing processes.

Background

This section provides background information related to the present disclosure that is not necessarily prior art.

Various additive manufacturing processes, also known as three-dimensional (3D) printing processes, may be used to form three-dimensional objects by melting certain materials at specific locations and/or in layers. The materials may be joined or cured under computer control, for example working from a Computer Aided Design (CAD) model, to create a three-dimensional object in which the materials are added together, such as liquid molecules or powder particles that are typically fused together layer by layer. Various types of additive manufacturing include adhesive jetting, directed energy deposition, material extrusion, material jetting, powder bed melting, sheet lamination, and vat photopolymerization curing.

Certain additive manufacturing processes may be performed using thermoplastic polymers (e.g., polycarbonate), which include material extrusion, fused deposition modeling, and powder bed melting. Generally, powder bed melting involves selective melting of materials in the powder bed. The method may melt a portion of a layer of powder material, move upward in the working area, add another layer of powder material, and repeat the process until an object is built therefrom. The powder bed fusion process may use unmelted media to support overhangs (overhangings) and thin walls in the object being produced, which may reduce the need for temporary secondary supports when forming the object. In selective heat sintering, a thermal print head may apply heat to a powdered thermoplastic layer; when one layer is completed, the powder bed moves downwards and the automatic roller adds a new layer of material, which is sintered to form the next cross section of the object. Selective laser sintering is another powder bed melting process that can use one or more lasers to fuse powdered thermoplastic polymers into a desired three-dimensional object.

The materials used in the powder bed fusion process preferably have a uniform shape, size and composition. It is not simple to prepare such powders from thermoplastic polymers economically and on a large scale. Furthermore, it may be difficult to use amorphous polycarbonate, particularly in powder bed melting processes such as selective laser sintering, because such polycarbonate may not exhibit a well-defined melting point. Such characteristics can result in dissipation of the applied thermal energy source (e.g., laser beam) into the surrounding area where the energy source contacts or impacts the powder bed. This undesirable dissipation of thermal energy can lead to unstable processing and poor resolution of features in the desired three-dimensional object being produced.

Certain formulations of polycarbonate powder for powder bed melting are known. For example, U.S. publication No. 2017/9567443B2, japanese patent No. 2017/095650A, and U.S. publication No. 2018/0244863A1 each discuss a method comprising dissolving a polycarbonate in a suitable organic solvent, adding a dispersion polymer to promote and maintain emulsion formation, and adding a solvent (miscible with the organic solvent but not for the polycarbonate) to cause emulsion formation and subsequent precipitation of a polycarbonate powder. Further, WO2018/071578A1 and U.S. publication No. 2018/0178413A1 describe the use of solvents to induce domain formation in preformed powder particles produced by milling methods.

Preparation of crystalline polycarbonate for powder bed melt process several technical problems still exist with this type of process of powders. In particular, existing methods of processing polycarbonate powders into a form suitable for certain processes, such as Selective Laser Sintering (SLS), multi-jet Melting (MJF), high Speed Sintering (HSS), and electrophotographic 3D printing applications, may require the use of mixed solvents and dispersants. Accordingly, there is a need to provide a single solvent process that facilitates solvent recovery and reuse that can form polycarbonate powders with optimal crystallinity and optimal particle size distribution from amorphous polymers, wherein crystallizing the polycarbonate powder results in improved powder bed melting properties.

Disclosure of Invention

The present technology includes methods, compositions, and articles related to the preparation of partially crystalline polycarbonate powders and their use in additive manufacturing processes, including powder bed melting processes.

A method of preparing a partially crystalline polycarbonate powder is provided, the method comprising dissolving an amorphous polycarbonate in a polar aprotic solvent at a first temperature to form a first solution of dissolved polycarbonate. The first solution is then cooled to a second temperature, wherein the second temperature is lower than the first temperature. A portion of the dissolved polycarbonate precipitates from the first solution to form a second solution comprising partially crystallized polycarbonate powder. Powder compositions for powder bed melting processes are provided that include partially crystalline polycarbonate powders prepared by such methods. Objects can be prepared by using such partially crystallized polycarbonate powder in a powder bed melting process to form an object.

The disclosed exemplary devices, systems, and methods provide powder polycarbonate with suitable operating windows for SLS, MJF, HSS, and electrophotographic 3D printing applications. One embodiment of the present invention may provide a precipitated powdered polycarbonate formed by precipitating a polycarbonate in a solvent to form a polymer into crystallites, and then using the precipitated powdered polycarbonate in a powder-based 3D printing process.

Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

Drawings

The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

FIG. 1: low Vacuum Secondary Electron Detector (LVSED) Scanning Electron Micrograph (SEM) of powdered polycarbonate produced as in example 1, 50 times magnification.

FIG. 2: low Vacuum Secondary Electron Detector (LVSED) Scanning Electron Micrograph (SEM) of powdered polycarbonate produced as in example 1, 500 times magnification.

FIG. 3: differential Scanning Calorimetry (DSC) of the powdered polycarbonate produced as in example 1.

FIG. 4: a Selective Laser Sintering (SLS) process to produce samples from powdered polycarbonate as described in example 1.

FIG. 5: a Selective Laser Sintering (SLS) process was used to produce a sample tensile bar from powdered polycarbonate as described in example 3.

FIG. 6: selective Laser Sintering (SLS) 1 inch cubes printed from powdered polycarbonate as described in example 3. The sides are polished to remove the outer powder coating and expose the interior of the part.

Detailed Description

The following description of technology is merely exemplary in nature of the subject matter, manufacture, and use of one or more inventions and is not intended to limit the scope, application, or uses of any particular invention claimed in this application or in any other application that may require priority to be filed or that may arise from a patent. With respect to the disclosed methods, the order of the steps presented is exemplary in nature, and thus, the order of the steps may differ in various embodiments. "a" and "an" as used herein mean that there is "at least one" item; when possible, there may be a plurality of such items. Unless otherwise expressly stated, all numerical quantities in this description should be understood as modified by the word "about", and all geometric and spatial descriptors should be understood as modified by the word "substantially" in describing the broadest scope of the technology. "about" when applied to a numerical value means that the calculation or measurement allows some slight imprecision in the value (with near-exactness in the value; approximately or reasonably near the value; nearly). As used herein, "about" and/or "substantially" means at least possible variations resulting from ordinary methods of measuring or using such parameters, provided that, for some reason, the imprecision provided by "about" and/or "substantially" is not otherwise understood in the art with such ordinary meaning.

All documents cited in this detailed description, including patents, patent applications, and scientific literature, are incorporated herein by reference, unless explicitly stated otherwise. In the event that there may be any conflict or ambiguity between the document incorporated by reference and the present detailed description, the present detailed description controls.

Although the open-ended term "comprising" is used herein to describe and claim embodiments of the present technology as a synonym for non-limiting terms such as comprising, containing, or having, the embodiments may alternatively be described using a limiting term such as "consisting of 8230 \8230; \8230compositional" or "consisting essentially of 8230; \8230;". Thus, for any given embodiment that recites a material, component, or process step, the present technology also specifically includes embodiments that consist of, or consist essentially of, such material, component, or process step, but does not include additional materials, components, or processes (for consisting of, or for consisting essentially of, or for affecting a significant property of the embodiment), even if such additional materials, components, or processes are not explicitly recited herein. For example, recitation of a composition or method listing elements a, B, and C specifically contemplates embodiments consisting of and consisting essentially of a, B, and C, and does not include element D that may be recited in the art, even if element D is not explicitly recited as excluded herein.

As referred to herein, unless otherwise indicated, the disclosure of ranges includes the endpoints and includes all the different values and further divided ranges within the entire range. Thus, for example, a range of "from a to B" or "from about a to about B" includes a and B. Disclosure of values and value ranges for particular parameters (e.g., amounts, weight percentages, etc.) does not exclude other values and value ranges useful herein. It is contemplated that two or more specific example values for a given parameter may define the endpoints of a range of values that may be claimed for the parameter. For example, if parameter X is illustrated herein as having a value a and is also illustrated as having a value Z, it is contemplated that parameter X may have a range of values from about a to about Z. Similarly, disclosure of two or more ranges of values for a parameter (whether these ranges are nested, overlapping, or distinct) is contemplated to encompass all possible combinations of the ranges of values that may be claimed using the endpoints of the disclosed ranges. For example, if parameter X is exemplified herein as having a value in the range of 1-10, or 2-9, or 3-8, it is also contemplated that parameter X may have other ranges of values, including 1-9, 1-8, 1-3, 1-2, 2-10, 2-8, 2-3, 3-10, 3-9, and so forth.

When an element or layer is referred to as being "on," "engaged with," "connected to" or "coupled to" another element or layer, it may be directly "on," "engaged with," "connected to," or "coupled with" another element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on," "directly engaged with," "directly connected with," or "directly coupled with" another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a similar manner (e.g., "between" and "directly between," "adjacent" and "directly adjacent," etc.). As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Terms such as "first," "second," and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

Spatially relative terms such as "inner," "outer," "below," "at \8230; below," "lower," "at \8230; above," "upper," etc., may be used herein to facilitate description of the relationship of one element or feature to another element or feature as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, exemplary terms "at 8230; \8230;" below "may include orientations" at 8230; \8230; "above" and "at 8230; \8230;" below ". The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

The present technology provides methods of making and using partially crystalline polycarbonate powders, including partially crystalline polycarbonate powders having characteristics suitable for Selective Laser Sintering (SLS), multi-jet Melting (MJF), high Speed Sintering (HSS), and electrophotographic 3D printing. Embodiments provide an amyloidogenic polycarbonate formed by precipitating polycarbonate in a solvent, forming the polymer into crystallites, and then using the precipitated powdered polycarbonate in a powder-based 3D printing process. The partially crystalline polycarbonate powder of the invention exhibits optimized characteristics for powder bed melt processes, including optimized particle size, shape, distribution and crystallinity, while using a dispersant-free single solvent process in its manufacture.

A method of preparing a partially crystalline polycarbonate powder may include dissolving amorphous polycarbonate in a Dimethylsulfoxide (DMSO) solvent to form a solution at an elevated temperature; cooling the solution to room temperature to form a powdered, partially crystalline polycarbonate precipitate having a D90 particle size of less than 150 μ ι η, an average particle size of less than or equal to 100 μ ι η, or an average particle size of 0-100 μ ι η; and a crystallinity of at least 20%, or a crystallinity of at least 25%, or a crystallinity of 25 to 35%. Existing methods of processing polycarbonate powders into a form suitable for additive manufacturing processes, such as Selective Laser Sintering (SLS), multiple jet Melting (MJF), high Speed Sintering (HSS), and electrophotographic 3D printing applications, require the use of mixed solvents and dispersants; however, the methods described herein may employ a single solvent approach, thereby facilitating solvent recovery and reuse. These methods also produce a product in which the particles may exhibit a size (average diameter of about 30 microns to about 40 microns), low dispersibility, spherical shape, and crystalline characteristics suitable for use in the printing process described above, as compared to the results of the process described above.

In certain embodiments, methods of making partially crystalline polycarbonate powders are provided. Such methods may include dissolving an amorphous polycarbonate in a polar aprotic solvent at a first temperature to form a first solution of dissolved polycarbonate. The first solution is then cooled to a second temperature, the second temperature being lower than the first temperature, wherein a portion of the dissolved polycarbonate precipitates from the first solution to form a second solution comprising a partially crystalline polycarbonate powder. The precipitated partially crystallized polycarbonate powder may be separated from the remainder of the second solution. The isolated partially crystalline polycarbonate powder may also be dried. The dissolving step may be repeated using the remaining portion of the second solution as a polar aprotic solvent, and further repeating the cooling step to form a second solution comprising another portion of the crystallized polycarbonate powder. In certain embodiments, the polar aprotic solvent can include dimethyl sulfoxide. In other embodiments, the polar aprotic solvent can consist essentially of dimethyl sulfoxide. And in still further embodiments, the polar aprotic solvent can consist of dimethyl sulfoxide.

Various temperatures may be employed in the process for preparing the partially crystalline polycarbonate powder. The dissolving step may include heating the amorphous polycarbonate in a polar aprotic solvent at a first temperature to form a first solution of dissolved polycarbonate, wherein the first temperature is greater than room temperature. The cooling step may include cooling the first solution to a second temperature, wherein the second temperature is room temperature. In certain embodiments, the first solution may be supersaturated with amorphous polycarbonate at the first temperature. For example, the first solution may be supersaturated with amorphous polycarbonate at the first temperature compared to the solubility limit of amorphous polycarbonate in the first solution at the second temperature.

Partially crystalline polycarbonate powder prepared according to the process may exhibit the following physical characteristics. The partially crystalline polycarbonate powder may have a D90 particle size of less than about 150 microns; that is, 90 volume% of the particles in the total distribution of the partially crystalline polycarbonate powder have a particle size of 150 μm or less. In certain embodiments, the partially crystalline polycarbonate powder may have an average particle size of less than about 100 microns. The partially crystalline polycarbonate powder may also have an average particle size of from about 1 micron to about 100 microns. Particular embodiments include those wherein the partially crystalline polycarbonate powder has an average particle size of from about 30 microns to about 40 microns. The partially crystalline polycarbonate powder may be in the form of spherical particles. Various crystallinity values are possible, wherein the partially crystalline polycarbonate powder may have a crystallinity of at least about 20%, a crystallinity of at least about 25%, and in certain embodiments, the partially crystalline polycarbonate powder may have a crystallinity of from about 25% to about 35%.

In certain embodiments, powder compositions for powder bed melt processes are provided, wherein such powder compositions comprise partially crystalline polycarbonate powder prepared according to the methods provided herein. For example, a powder composition for a powder bed melting process may include a partially crystalline polycarbonate powder having a D90 particle size of less than about 150 microns, an average particle size of about 30 microns to about 40 microns, and a crystallinity of about 25% to about 35%. Such powder compositions may include partially crystalline polycarbonate powders having different physical properties as well as mixtures of additives and other components as described herein.

In certain embodiments, methods of making an object are provided. Such methods may include preparing a partially crystalline polycarbonate powder by a method including dissolving amorphous polycarbonate in a polar aprotic solvent at a first temperature to form a first solution of dissolved polycarbonate. The first solution may then be cooled to a second temperature, the second temperature being lower than the first temperature, wherein a portion of the dissolved polycarbonate precipitates from the first solution to form a second solution comprising a partially crystalline polycarbonate powder. The partially crystalline polycarbonate powder is then used in a powder bed melting process to form an object. Certain methods of making an object include providing a partially crystalline polycarbonate powder having a D90 particle size of less than about 150 microns, an average particle size of about 30 microns to about 40 microns, and a crystallinity of about 25% to about 35%. The partially crystalline polycarbonate powder is then used in a powder bed melting process to form an object.

In certain embodiments, one or more objects made by an additive manufacturing process are provided. Such methods may include providing a partially crystalline polycarbonate powder prepared according to one or more methods described herein. The partially crystalline polycarbonate powder is then used in a powder bed melting process to form one or more objects.

In certain embodiments, the present technology includes a method of converting amorphous polycarbonate to partially crystalline polycarbonate powder. Such methods may include dissolving amorphous polycarbonate in a polar aprotic solvent such as dimethyl sulfoxide (DMSO) at an elevated temperature above room temperature to form a solution, subsequently cooling the solution to room temperature to form a partially crystalline polycarbonate precipitate, and recovering the partially crystalline polycarbonate precipitate from the solvent as a substantially homogeneous polycarbonate powder. The resulting partially crystalline polycarbonate powder may have good crystallinity, particle size distribution and flowability. In particular, the partially crystalline polycarbonate powder may comprise: a D90 particle size of less than 150 μm; an average particle size of less than or equal to 100 μm or an average particle size between 0 and 100 μm; a crystallinity of at least 20%, a crystallinity of at least 25%, or a crystallinity of 25-35%. Since most of the particles of the partially crystalline polycarbonate powder may have a size of less than 150 micrometers (μm), the partially crystalline polycarbonate powder may be effectively used in a powder bed melting process, for example, a selective laser sintering process, to produce a layer having a thickness of 100 μm to 150 μm.

In certain embodiments, the present technology includes a method for a powder bed to melt a powder composition comprising a partially crystalline polycarbonate powder to form a three-dimensional object. Due to the good flowability of the partially crystalline polycarbonate powder, a smooth and dense powder bed can be formed, thus achieving the best accuracy and density of the sintered object. The partially crystalline nature of polycarbonate materials further facilitates processing, wherein the use of crystalline polycarbonate allows for the use of reduced melting energy relative to the melting of the corresponding amorphous polymeric material.

The terms "amorphous" and "crystalline" as used herein refer to their usual meaning in the polymer art with respect to the arrangement of polymer molecular chains. For example, in amorphous polymers (e.g., polycarbonate), the molecules may be randomly oriented and may intertwine with one another, like cooked spaghetti, and the polymer may have a glassy transparent appearance. In crystalline polymers, the polymer molecules may align together in ordered regions, like uncooked spaghetti. In the polymer art, some types of crystalline polymers are sometimes referred to as "semi-crystalline polymers". As used herein, the term "crystalline" refers to both crystalline and semi-crystalline polymers. As used herein, the term "partially crystalline polycarbonate" refers to a portion of a polycarbonate polymer that is in a crystalline form. As used herein, the term "percent crystallinity" or "percent crystallinity" refers to the portion of an amorphous polymer that has been converted to a partially crystalline form. The percentages being based on the total weight of the partially crystalline polymer.

The particle size of the partially crystalline polymer may affect its use in the additive manufacturing process. As used herein, D50 (referred to as "average particle size") refers to a powder particle size where 50 volume percent of the particles in the total distribution of the sample in question have the noted particle size or less. Similarly, D10 refers to a powder wherein 10 volume percent of the particles in the total distribution of the sample in question have the noted particle size or less; d90 refers to a powder particle size where 90% by volume of the particles in the overall distribution of the sample in question have the noted particle size or less; and D95 refers to a powder particle size where 95% by volume of the particles in the overall distribution of the sample referred to have the noted particle size or less. Particle size may be measured by any suitable method known in the art to measure particle size by diameter. In some embodiments, the particle size is determined by laser diffraction as known in the art. For example, a laser diffractometer such as Microtrac S3500 may be used to determine the particle size. The partially crystalline polycarbonate powders provided herein can have a D90 particle size of less than 150 μm.

The term "high shear mixing conditions" refers to a process of agitating components in a mixture (e.g., a liquid mixture) under conditions that produce high shear forces. As is known in the art, high shear mixers typically use impellers rotating within stators to create flow and turbulence patterns. Once the impeller sucks in the mixture, it causes abrupt changes in the direction and acceleration of the mixture, typically close to 90 degrees, so that the mixture is brought into contact with the stator walls under centrifugal force, or forced through holes in the stator at great pressure and speed, resulting in eventual disintegration changes in direction and acceleration. In certain embodiments of the high shear mixing conditions, the high shear mixing comprises mixing at a speed of 2,000 revolutions per minute (rpm) to 20,000rpm, specifically, 3,000rpm to 15,000rpm, more specifically, 4,000rpm to 10,000rpm. Any commercially available high shear mixer may be used to achieve high shear mixing. For example, a high shear mixer such as a Silverson L5M homogenizer may be used.

The term "powder bed fusing" or "powder bed fusing" is used herein to refer to a process in which polycarbonate is selectively sintered or melted and fused layer by layer to provide a 3-D object. Sintering may produce objects having a density of less than about 90% of the density of the solid powder composition, while melting may provide objects having a density of 90% to 100% of the density of the solid powder composition. The use of crystalline polycarbonate as provided herein may facilitate melting such that the resulting density may approach that obtained by injection molding processes.

Powder bed melting or powder bed fusing further includes all laser sintering and all selective laser sintering processes as well as other powder bed melting techniques defined by ASTM F2792-12 a. For example, sintering of the powder composition may be achieved by applying electromagnetic radiation other than that generated by a laser, with selectivity of the sintering being achieved, for example, by selectively applying inhibitors, absorbers, susceptors, or electromagnetic radiation (e.g., by using a mask or a directed laser beam). Any other suitable source of electromagnetic radiation may be used including, for example, an infrared radiation source, a microwave generator, a laser, a radiant heater, a lamp, or combinations thereof. In certain embodiments, selective mask sintering ("SMS") techniques may be used to create three-dimensional objects. For further discussion of the SMS process, see, for example, U.S. patent No. 6,531,086, which describes an SMS machine in which infrared radiation is selectively blocked using a shadow mask, resulting in selective illumination of a portion of a powder layer. If the SMS process is used to produce an object from the powder composition of the present technology, it may be desirable to include one or more materials in the powder composition that enhance the infrared absorption properties of the powder composition. For example, the powder composition may include one or more endothermic agents or a dark colored material (e.g., carbon black, carbon nanotubes, or carbon fibers).

Also included herein are all three-dimensional objects made from powder bed molten compositions comprising the partially crystalline polycarbonate powders described herein. The object may exhibit excellent resolution, durability, and strength after layer-by-layer fabrication of the object. Such objects may include a variety of articles of manufacture having a wide variety of uses, including use as prototypes, use as end products, and molds for end products.

In particular, powder bed fused (e.g., laser sintered) objects may be produced from compositions comprising partially crystalline polycarbonate powder using any suitable powder bed fusing process, including laser sintering processes. The objects may include a plurality of overlying and adhered sintered layers that include a polymer matrix that, in some embodiments, may have reinforcing particles dispersed throughout the polymer matrix. Laser sintering processes are known and are based on the selective sintering of polymer particles, wherein layers of polymer particles are briefly exposed to laser light and the polymer particles exposed to the laser light are thus bonded to one another. Successive sintering of layers of polymer particles produces a three-dimensional object. Details regarding the selective laser sintering process are found, for example, in U.S. Pat. No. 6,136,948 and in the specification of WO 96/06881. However, the partially crystalline polycarbonate powders described herein can also be used in other rapid prototyping or rapid manufacturing processes of the prior art, particularly those described above. For example, partially crystalline polycarbonate powders are particularly useful for forming polycarbonate by the SLS (selective laser sintering) process as described in U.S. patent No. 6,136,948 or WO 96/06881; molded articles are produced from the powder by the SIB process (selective inhibition of the cohesion of the powder) as described in WO01/38061, by 3D printing as described in EP 0 431924, or by the microwave process as described in DE 103 11 438.

In certain embodiments, the present techniques include forming a plurality of layers in a predetermined pattern by an additive manufacturing process. "plurality" as used in the context of additive manufacturing may comprise 5 or more layers, or 20 or more layers. The maximum number of layers may vary widely, for example, depending on factors such as the size of the object being manufactured, the technology used, the capacity and capabilities of the equipment used, and the degree of detail required of the final object. For example, 5 to 100,000 layers may be formed, or 20 to 50,000 layers may be formed, or 50 to 50,000 layers may be formed.

As used herein, "layer" is a convenient term and includes any shape, regular or irregular, having at least a predetermined thickness. In certain embodiments, the size and configuration of the two dimensions are predetermined, and in certain embodiments, the size and shape of all three dimensions of the layer are predetermined. The thickness of each layer may vary widely, depending on the additive manufacturing process. In certain embodiments, each layer may be formed to a thickness different from the previous or subsequent layer. In certain embodiments, the thickness of each layer may be the same. In certain embodiments, each layer formed may have a thickness of 0.5 millimeters (mm) to 5mm.

The object may be formed by a preset pattern, which may be determined from a three-dimensional digital representation of the desired object as known in the art and as described herein. The materials may be joined or cured under computer control, e.g., working from a Computer Aided Design (CAD) model, to create a 3D object.

The fused layer of the powder bed melt object may have any thickness suitable for the selective laser sintering process. The individual layers may each be on average preferably at least 50 micrometers (μm) thick, more preferably at least 80 μm thick, even more preferably at least 100 μm thick. In a preferred embodiment, the plurality of sintered layers are each on average preferably less than 500 μm thick, more preferably less than 300 μm thick, even more preferably less than 200 μm thick. Thus, individual layers of some embodiments may be 50 to 500 μm, 80 to 300 μm, or 100 to 200 μm thick. Three-dimensional objects produced from the powder compositions of the present technology using a layer-by-layer powder bed melting process other than selective laser sintering may have the same or different layer thicknesses than those described above.

As used herein, "polycarbonate" refers to a polymer or copolymer having repeating structural carbonate units of formula (1):

wherein R is ¹ At least 60% of the total number of radicals being aromatic radicals, or each R ¹ Containing at least one C _6-30 An aromatic group. Specifically, each R ¹ May be derived from a dihydroxy compound such as an aromatic dihydroxy compound of formula (2) or a bisphenol of formula (3) as follows:

in the formula (2), each R ^h Independently of one another, a halogen atom, e.g. bromine, C _1-10 Hydrocarbyl radicals, such as C _1-10 Alkyl, halogen substituted C _1-10 Alkyl radical, C _6-10 Aryl or halogen substituted C _6-10 Aryl, n is 0 to 4.

In the formula (3), R ^a And R ^b Each independently is halogen, C _1-12 Alkoxy or C _1-12 And p and q are each independently an integer of 0 to 4, such that when p or q is less than 4, the valences of each carbon of the ring are filled with hydrogen. In certain embodiments, p and q are each 0, or p and q are each 1, and R is ^a And R ^b Each is C _1-3 Alkyl groups, particularly methyl groups, are meta to the hydroxyl group on each arylene group. X ^a Is a bridging group linking two hydroxy-substituted aromatic groups, wherein each C ₆ The bridging group and the hydroxy substituent of the arylene group being in C ₆ The arylene groups being in ortho-or meta-position relative to each otherOr para (especially para), for example, a single bond, -O-, -S-, -S (O) ₂ - (e.g. bisphenol-S polycarbonate, polysulfone), -C (O) - (e.g. polyketone) or C _1-18 An organic group, which may be cyclic or acyclic, aromatic or non-aromatic, and may further comprise heteroatoms such as halogens, oxygen, nitrogen, sulfur, silicon, or phosphorus. For example, X ^a C which may be substituted or unsubstituted _3-18 A cycloalkylene group; formula-C (R) ^c )(R ^d ) C of (A-C) _1-25 Alkylene, wherein R ^c And R ^d Each independently is hydrogen, C _1-12 Alkyl radical, C _1-12 Cycloalkyl radical, C _7-12 Arylalkyl radical, C _1-12 Heteroalkyl or cyclic C _7-12 A heteroarylalkyl group; or formula-C (= R) ^e ) A group of (a) wherein R ^e Is divalent C _1-12 A hydrocarbyl group. Certain illustrative examples of dihydroxy compounds that can be used are described in, for example, WO 2013/175448 A1, US 2014/0295363, and WO 2014/072923.

Specific dihydroxy compounds include resorcinol, 2-bis (4-hydroxyphenyl) propane ("bisphenol A" or "BPA"), 3-bis (4-hydroxyphenyl) phthalimidine, 2-phenyl-3, 3' -bis (4-hydroxyphenyl) phthalimidine (also known as N-phenylphenolphthalein bisphenol, "PPPBP" or 3, 3-bis (4-hydroxyphenyl) -2-phenylisoindolin-1-one), 1-bis (4-hydroxy-3-methylphenyl) cyclohexane, and 1, 1-bis (4-hydroxy-3-methylphenyl) -3, 5-trimethylcyclohexane (isophorone bisphenol).

As used herein, "polycarbonate" also includes copolymers comprising carbonate units and ester units ("poly (ester-carbonates)", also referred to as polyester-polycarbonates). In addition to the repeating carbonate chain units of formula (1), the poly (ester-carbonate) comprises repeating ester units of formula (4):

wherein J is a divalent radical derived from a dihydroxy compound (including reactive derivatives thereof) and may be, for example, C _2-10 Alkylene radical, C _6-20 A cycloalkylene group,C _6-20 An arylene or polyoxyalkylene group in which the alkylene contains 2 to 6 carbon atoms, specifically 2, 3 or 4 carbon atoms; t is a divalent radical derived from a dicarboxylic acid (including reactive derivatives thereof) and may be, for example, C _2-20 Alkylene radical, C _6-20 Cycloalkylene or C _6-20 An arylene group. Copolyesters containing a combination of different T or J groups may be used. The polyester units may be branched or linear.

Specific dihydroxy compounds include aromatic dihydroxy compounds of formula (2) (e.g., resorcinol), bisphenols of formula (3) (e.g., bisphenol A), C _1-8 Aliphatic diols such as ethylene glycol, n-propylene glycol, isopropylene glycol, 1, 4-butanediol, 1, 6-cyclohexanediol, 1, 6-hydroxymethylcyclohexane, or a combination comprising at least one of the foregoing dihydroxy compounds. Aliphatic dicarboxylic acids which may be used include C _6-20 Aliphatic dicarboxylic acids (which include terminal carboxyl groups), especially linear C _8-12 Aliphatic dicarboxylic acids such as sebacic acid (sebacylic acid); and alpha, omega-C _u Dicarboxylic acids such as dodecanedioic acid (DDDA). Aromatic dicarboxylic acids that may be used include terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, 1, 6-cyclohexane dicarboxylic acid, or a combination comprising at least one of the foregoing acids. A combination of isophthalic acid and terephthalic acid can be used wherein the weight ratio of isophthalic acid to terephthalic acid is 91.

Specific ester units include ethylene terephthalate units, n-propylene terephthalate units, n-butylene terephthalate units, ester units derived from isophthalic acid, terephthalic acid, and resorcinol (ITR ester units), and ester units derived from sebacic acid and bisphenol a. The molar ratio of ester units to carbonate units in the poly (ester-carbonate) can vary widely, for example, from 1.

The polycarbonate can have an intrinsic viscosity of 0.3 to 1.5 deciliters per gram (dl/gm), specifically 0.45 to 1.0dl/gm as determined in chloroform at 25 ℃. The polycarbonate can have a weight average molecular weight of 5,000 to 200,000 daltons, specifically 15,000 to 100,000 daltons, as measured by Gel Permeation Chromatography (GPC) using a crosslinked styrene-divinylbenzene column and calibrated to polycarbonate references. GPC samples were prepared at a concentration of 1 milligram per milliliter (mg/ml) and eluted at a flow rate of 1.5 milliliters per minute.

In certain embodiments, a method of preparing a partially crystalline polycarbonate powder comprises dissolving amorphous polycarbonate in a polar aprotic solvent, such as dimethyl sulfoxide (DMSO), at a temperature above room temperature. Room temperature is understood to be about 20 ℃ (68 ° F); thus, amorphous polycarbonate may be dissolved in DMSO at temperatures above about 20 ℃. Amorphous polycarbonate is soluble in DMSO solvent and thus forms a polycarbonate solution. Generally, the solution may be prepared at a temperature above room temperature such that the amount of amorphous polycarbonate dissolved may be considered supersaturated at room temperature. Amorphous polycarbonate may be mixed into DMSO solvent on-line or in batches. This process can be easily performed on a manufacturing scale. Upon cooling to room temperature (e.g., about 20 ℃), the dissolved amorphous polycarbonate begins to crystallize and precipitate out of the DMSO solvent, resulting in precipitation of a partially crystalline polycarbonate precipitate. It is further possible that an increased percentage of crystalline polycarbonate particles are formed while preventing the formation of firmly agglomerated polycarbonate particles when precipitation occurs under high shear mixing conditions. For example, it has been found that agglomerates can be readily broken up by crushing, high speed mixing or other low or moderate force shearing processes.

After precipitation, the DMSO solvent is removed and the partially crystalline polymer powder can be dried by heating under vacuum or non-vacuum. The resulting crystalline polycarbonate powder may have a high percentage of particles having a particle size of less than 150 microns, and a relatively narrow particle size distribution. The recovered DMSO solvent may be reused by dissolving additional amorphous polycarbonate to restart the process. This is in contrast to other methods that use one or more solvents mixed with a non-solvent to precipitate crystalline polycarbonate powder. Such mixtures of solvents and non-solvents cannot be easily reused.

As provided herein, the amorphous polycarbonate is dissolved in DMSO solvent. For example, amorphous polycarbonate may be dissolved in DMSO under conditions that result in a supersaturated solution of polycarbonate, wherein changing the conditions (e.g., changing the temperature of the solution) results in partially crystalline polycarbonate powder precipitating therefrom. In certain embodiments, the solvent may include DMSO and one or more other polar aprotic solvents. In certain embodiments, the solvent may consist essentially of DMSO in the absence of other components that substantially affect crystallization of the polycarbonate; for example, no non-solvent is present, as described in U.S. publication No. 2018/0244863. In certain embodiments, the solvent may consist of DMSO, with substantially no other solvents present, based on the purity levels achievable in the art with respect to DMSO. That is, the solvent may be substantially 100% DMSO. It should also be noted that when partially crystalline polycarbonate powder is precipitated from a solution of amorphous polycarbonate and DMSO, a portion of the dissolved amorphous polycarbonate may remain in solution. Thus, separating the precipitated partially crystalline polycarbonate powder from the remainder of the solution leaves a DMSO solution with a portion of dissolved amorphous polycarbonate, which can be reused to redissolve more amorphous polycarbonate. In the case of repeated use of DMSO (including portions of dissolved amorphous polycarbonate), it may be desirable to add less amorphous polycarbonate to achieve supersaturation, for example, where a change from a first temperature to a second, lower temperature results in another precipitation of partially crystalline polycarbonate powder.

In certain embodiments, the partially crystalline polycarbonate powder has a D85 particle size of less than 150 microns, particularly a D90 particle size of less than 150 microns. In certain embodiments, the partially crystalline polycarbonate powder has a D93 particle size of less than 150 microns, wherein 93% of the partially crystalline polycarbonate powder has a particle size of less than 150 μm. Certain embodiments include the case where the partially crystalline polycarbonate powder has a D90 particle size of less than 150 μm. Partially crystalline polycarbonate powder in which 100% of the particles have a size of less than 150 microns can also be produced by this method.

The partially crystalline polycarbonate powder may also have an average particle size of less than or equal to 100 μm. Specifically, the partially crystalline polycarbonate powder may have an average particle diameter of 10 μm to 100 μm. The average particle size of the partially crystalline polycarbonate powder may also be less than or equal to 100 μm, or include average particle sizes from 0 to 100 μm.

In certain embodiments, the partially crystalline polycarbonate powder has a percent crystallinity of at least 20%, such as 20% to 80%, specifically, at least 25%, such as 25% to 60%, more specifically, at least 27%, such as 27% to 40%. The partially crystalline polycarbonate powder may also have a crystallinity of 25% to 30%. Embodiments also include a crystallinity of 25% to 35%.

In certain embodiments, a method of making an article comprises providing a powder composition comprising a partially crystalline polycarbonate powder, and forming a three-dimensional object with the powder composition using a powder bed melting process. The at least one partially crystalline polycarbonate powder may have a D50 particle size of less than 150 microns in diameter and be prepared by the above-described method. Embodiments include those wherein the partially crystalline polycarbonate powder has a D90 particle size of less than 150 μm, an average particle size of less than or equal to 100 μm, or an average particle size between 0 and 100 μm and a crystallinity of at least 20%, or a crystallinity of at least 25%, or a crystallinity of 25 to 35%. Partially crystalline polycarbonate powders may be prepared by converting amorphous polycarbonate to crystalline polycarbonate powders as described herein. The conversion of amorphous polycarbonate comprises dissolving amorphous polycarbonate in DMSO solvent above room temperature to form a solution, cooling the solution to room temperature to form a precipitate comprising partially crystalline polycarbonate powder, removing the solvent from the precipitate, drying the precipitate, and recovering the crystalline polycarbonate powder.

The partially crystalline polycarbonate powder may be used as the sole component in the powder composition and applied directly to the powder bed melting step. Alternatively, the partially crystalline polycarbonate powder may first be mixed with other polymer powders, such as another crystalline polymer or an amorphous polymer, or a combination of partially crystalline and amorphous polymers. The powder composition for powder bed melting can include 50wt% to 100wt% of the partially crystalline polycarbonate powder, based on the total weight of all polymeric materials in the powder composition.

The partially crystalline polycarbonate powder may also be combined with one or more additives/components to produce a powder that can be used in a powder bed melting process. Such optional components may be present in sufficient amounts to perform a particular function without adversely affecting the properties of the powder composition in the powder bed melt or the objects made therefrom. The optional component may have an average particle size falling within the average particle size range of the partially crystalline polycarbonate powder or the optional flow aid. If desired, each optional component may be ground to a desired particle size and/or particle size distribution, which may be substantially similar to the partially crystalline polycarbonate powder. Optional components may be particulate materials and include organic and inorganic materials such as fillers, flow aids, and colorants. Other additional optional components may also include, for example, toners, fillers, colorants (e.g., pigments and dyes), lubricants, corrosion inhibitors, thixotropic agents, dispersants, antioxidants, adhesion promoters, light stabilizers, organic solvents, surfactants, flame retardants, antistatic agents, plasticizers, or a combination comprising at least one of the foregoing. Yet another optional component may also be a second polymer that alters the properties of the partially crystalline polycarbonate. In certain embodiments, each optional component (if present at all) may be present in the powder composition in an amount of from 0.01 wt% to 30 wt%, based on the total weight of the powder composition. The total amount of all optional components in the powder composition may be in the range of 0 to 30 wt. -%, based on the total weight of the powder composition.

In a powder bed melting process (e.g., a laser sintering process), each optional component does not necessarily have to be melted. However, each optional component may be selected to be compatible with the partially crystalline polycarbonate polymer to form a strong and durable object. For example, the optional component may be a reinforcing agent that imparts additional strength to the shaped object. Examples of reinforcing agents include one or more types of glass fibers, carbon fibers, talc, clay, wollastonite, glass beads, and combinations thereof.

The powder composition may optionally comprise a glidant. In particular, the powder composition may comprise the particulate glidant in an amount of 0.01 to 5 wt. -%, in particular 0.05 to 1 wt. -%, based on the total weight of the powder composition. In certain embodiments, the powder composition comprises the particulate glidant in an amount of 0.1 to 0.25 percent by weight, based on the total weight of the powder composition. The flow aid included in the powder composition may be a particulate inorganic material having a median particle size of 10 μm or less, and may be selected from the group consisting of: hydrated silica, amorphous alumina, vitreous silica, vitreous phosphate, vitreous borate, vitreous oxide, titanium dioxide, talc, mica, fumed silica, kaolin, attapulgite, calcium silicate, alumina, magnesium silicate and combinations thereof. The flow aid may be present in an amount sufficient to allow the partially crystallized polycarbonate polymer to flow and level on the build surface of the powder bed melting apparatus (e.g., laser sintering device). In certain embodiments, the glidant comprises fumed silica.

Another optional component is a colorant, such as a pigment or dye, e.g., carbon black, to impart a desired color to the object. The colorant is not limited so long as the colorant does not adversely affect the composition or the object made therefrom, and the colorant is sufficiently stable to retain its color under the conditions of the powder bed melting process and exposure to heat and/or electromagnetic radiation (e.g., laser light for the sintering process).

Still further additives include, for example, toners, fillers, colorants (e.g., pigments and dyes), lubricants, corrosion inhibitors, thixotropic agents, dispersants, antioxidants, adhesion promoters, light stabilizers, organic solvents, surfactants, flame retardants, antistatic agents, plasticizers, and combinations of these.

Yet another optional component may also be a second polymer that alters the properties of the partially crystalline polycarbonate powder.

The powder composition is a fusible powder composition and may be used in powder bed melting processes, such as selective laser sintering. Examples of selective laser sintering systems for making parts from fusible powder compositions, particularly for making parts from the fusible crystalline polycarbonate powders disclosed herein, can be described as follows. A thin layer of a powder composition comprising partially crystalline polycarbonate powder is distributed over the sintering chamber. The laser beam traces a computer-controlled pattern corresponding to a cross-sectional slice of the CAD model to selectively melt the powder that has been preheated to slightly below its melting temperature. After sintering of one layer of powder, the powder bed piston is lowered in predetermined increments (typically 100 μm) and another layer of powder is distributed over the previous sintered layer by the rollers. The process is then repeated as the laser melts and fuses each successive layer with the previous layer until the entire object is completed. The partially crystalline polycarbonate powders described herein can thus be used to fabricate three-dimensional objects comprising multiple fused layers.

The present techniques provide certain benefits and advantages. One advantage is the use of a single solvent in the preparation of the partially crystalline polycarbonate powder, which facilitates the recovery and reuse of the solvent. Another advantage is that amorphous polycarbonate can be converted into polycarbonate powder with optimized crystallinity and optimized particle size distribution. Yet another advantage is that the partially crystalline polycarbonate powder provides improved powder bed melting properties. Thus, additive manufacturing processes employing powder bed melting, including Selective Laser Sintering (SLS), multi-jet Melting (MJF), high Speed Sintering (HSS), and electrophotographic 3D printing, can benefit from the formation and use of partially crystalline polycarbonate powders produced as described herein.

The following examples further illustrate the above concepts.

Example 1

Illustrative embodiments of a method of making powdered polycarbonate suitable for additive manufacturing are as follows. To a 5-L four-necked round bottom flask equipped with an overhead stirrer, 1kg of polycarbonate (Lupoy 1303EP-22,MW = ca.38,000Da) and 3L of DMSO (99.7%, acros Organics) were added. The solvent was sprayed and the flask was flushed with a nitrogen atmosphere for 20 minutes. The mixture was heated to 160 ℃ with an electrothermal mantle under stirring at 200rpm to obtain a solution of polycarbonate in DMSO. The electric jacket was removed to allow the reactor temperature to cool at a rate of 1 deg.C/min while continuing to stir at 200 rpm. The polycarbonate precipitates between about 70 ℃ and about 80 ℃. The thick slurry was removed from the reactor and poured into a 50 μm nylon mesh bag nested within a 100 μm nylon mesh bag of equivalent size. The DMSO was isolated by squeezing the bag. The residual powder was washed 3 times with 4L water: the first wash was for 30 minutes, the second for 15 hours, and the third for 4 hours. The powder slurry was filtered and dried at 120 ℃ for 16 hours, then sieved sequentially through 250 μm and 180 μm sieves.

Density and flowability. The powdery polycarbonate prepared in this embodiment had an average bulk density of 0.42g/cm ³ . The average tap density is 0.52g/cm ³ (average Hausner ratio =1.26, karr index 0.20). The flowability was determined using a cone with a nozzle diameter of 10mm and an average value of 2.58 g/s.

Particle size, shape and distribution (PSSD). PSSD was determined in water using a Microtrac S3500 instrument. D ₉₀ ＝67.8μm；D ₅₀ ＝37.7μm；D ₁₀ =16.8 μm. The sphericity data is shown in table 1.

TABLE 1

>0.65	97.03％
		>0.75	89.64％
>0.85	64.43％
		>0.90	28.70％
>0.95	7.01％

And (3) molecular weight. GPC samples were prepared at a concentration of 2mg/mL Tetrahydrofuran (THF) and eluted at a flow rate of 1mL/min on a Waters GPC instrument equipped with a Styragel HR4 5- μm 7.8x 300mm (THF) column and a 2414 refractive index detector. Peak molecular weight (MP) =38093Da for the starting polycarbonate; m of powdery polycarbonate _P ＝29900Da。

Scanning Electron Microscopy (SEM). SEM images show spherical, partially agglomerated particles of typical size consistent with PSSD results.

Differential Scanning Calorimetry (DSC) and crystallinity. The DSC was scanned on a TA Instruments DSC 250 instrument at a rate of 20 ℃/min and is shown in figure 3. Melting began to occur at 208.88 ℃ and peaked at 236.39 ℃. On cooling, glass transition appeared at 142 ℃ and again on secondary heating at 147 ℃ after which no melting behaviour was observed.

The percentage of crystallinity of the semi-crystalline powdered polycarbonate was estimated by measuring the melting enthalpy in the melting peak (31.407J/g) and comparing it with a reference value of melting enthalpy for 100% crystalline polycarbonate (reported in the literature as 134J/g) (K.Varadarajan, et al., J.Polym.Sci.Polym.Phys.1982,20 (1), 141-154). Thus, the estimated crystallinity of the semi-crystalline polycarbonate is 23.4%.

SLS printing of powdered polycarbonate. Powdered polycarbonate was used in the laser sintering process of the Farsoon ST252P laser sintering system. Three kilograms of material was loaded into the feed piston of the machine and set down into the piston using a cement shaker to achieve the optimum tap density. The material was moved from the feed piston to the part piston in a layer-by-layer manner using counter-rotating rollers in a layer thickness of 0.080mm under an inert nitrogen atmosphere. The layers were laid down at 90 second intervals to absorb sufficient heat from the near infrared heater during which time the temperature of the feed piston rose from 60 ℃ to 180 ℃ and the part bed temperature rose from 60 ℃ to 207 ℃. Once the part bed temperature reaches the set point of 207 ℃, the part region is exposed using the scanning system parameters shown in table 2 to melt the selected region into a solid part.

TABLE 2

Laser spot size (mum)	450
		Filling scanning speed (mm/s)	10,160
Filling scanning space (mm)	0.28
		Filling laser power (W)	30

The resulting parts included thin discs, crosses, "window" test specimens, and ASTM D638 type IV tensile bars. Parts are characterized by a yellowish tint, but are mostly translucent, lacking the opaque appearance of typical laser sintered materials.

Example 2

Illustrative embodiments of a method of making powdered polycarbonate suitable for additive manufacturing are as follows. To a 20-L reactor equipped with an overhead stirrer were added 4.0kg of polycarbonate (Lexan 121R 112) and 15.73L of DMSO (99.7%, acros Organics). The solvent was sprayed and the flask was flushed with an argon atmosphere for 4 hours. The mixture was heated to 160 ℃ with an oil jacket under stirring at 180rpm to give a solution of polycarbonate in DMSO. The reactor was allowed to cool at a rate of 0.1-0.2 deg.C/min while continuing to stir at 180 rpm. The polycarbonate precipitates between about 70 ℃ and about 80 ℃. The thick slurry was removed from the reactor and poured into a 50 μm nylon mesh bag nested within a 100 μm nylon mesh bag of equivalent size. The DMSO was isolated by squeezing the bag. The remaining powder was soaked in 1x 30L of water for 3 days. This is removed by using the bag described above. The residual powder was soaked in 1x 10L of methanol for 2 hours and separated using 5 μm filter paper in a 20L vacuum filter. The powder was dried at 120 ℃ for 33 hours and then sieved sequentially through 250 μm and 180 μm sieves.

Particle Size and Distribution (PSD). PSD was determined in air using a Microtrac S3500 instrument. D ₉₀ ＝22.48μm；D ₅₀ ＝14.96μm；D ₁₀ =10.93 μm. Sphericity data is as follows:

differential Scanning Calorimetry (DSC) and crystallinity. The DSC was scanned on a TA Instruments DSC 250 instrument at a rate of 20 ℃/min and is shown in figure 3. Melting began to occur at 207.56 ℃ and peaked at 241.28 ℃.

The percentage crystallinity of semi-crystalline powdered polycarbonate is estimated by measuring the melting enthalpy in the melting peak (31.377J/g) and comparing it with a reference value of the melting enthalpy for 100% crystalline polycarbonate (reported in the literature as 134J/g) (K.Varadarajan, et al., J.Polym.Sci.Polym.Phys.1982,20 (1), 141-154). Thus, the estimated crystallinity of the semi-crystalline polycarbonate is 23.4%.

SLS printing of powdered polycarbonate. Powdered polycarbonate was used in the laser sintering process on a Farsoon ST252P laser sintering system. 2.5 kg of material was loaded into the feed piston of the machine and set down into the piston using a cement shaker to achieve the optimum tap density. The material was moved in a layer-by-layer manner from the feed piston to the part piston using counter-rotating rollers in a layer thickness of 0.061mm under an inert nitrogen atmosphere. The layers were laid down at 90 second intervals to allow sufficient heat to be absorbed from the near infrared heater during which time the temperature of the feed piston rose from 60 ℃ to 180 ℃ and the part bed temperature rose from 60 ℃ to 207 ℃. Once the part bed temperature reaches the set point, it is lowered to 205.5 ℃ as the part bed begins to crack, exposing the part region using the scanning system parameters in table 3 to melt the selected region into a solid part.

TABLE 3

Laser spot size (mum)	450
		Filling scanning speed (mm/s)	10,160
Filling scan interval (mm)	0.20
		Filling laser power (W)	60
Number of scans	3
		Layer spacing(s)	23

Example 3

Illustrative embodiments of a method of making powdered polycarbonate suitable for additive manufacturing are as follows. A20-L reactor equipped with an overhead stirrer was charged with 3.21kg of polycarbonate (Lupoy 1080C 70, MW = ca.30, 000Da) and 13.76L of DMSO (99.7%, acros Organics) [ a second batch consisting of 3.00kg of polycarbonate (Lupoy 1080C 70) and 12.96L of DMSO (99.7%, acros Organics) was carried out simultaneously ]. The solvent was sprayed and the reactor was flushed with an argon atmosphere for 3 hours. The mixture was heated to 160 ℃ with an oil jacket under stirring at 180rpm to give a solution of polycarbonate in DMSO. The reactor was allowed to cool at a rate of 0.1-0.2 deg.C/min while continuing to stir at 180 rpm. The polycarbonate precipitates between about 70 ℃ and about 80 ℃. The slurry was removed from the reactor, combined with the second batch, and poured into a 20L vacuum filter flask with 4 μm filter paper. 15L DMSO was recovered using this method. The residual powder was treated with 140L of deionized water and 20L of acetone as follows: soaking in 2x 15L water for 1 day; filtering and soaking in 1x 25L water for 1 day; filtering, washing with 2 × 20L water, and soaking in 25L water for 1 day; the mixture was filtered and washed with 1x 20L water and 1x 20L acetone. The powder was dried at 110 ℃ for 72 hours and then passed through a 250 μm sieve to provide 4.5kg of powder.

Density and flowability. The average bulk density of the powdery polycarbonate prepared in this embodiment was 0.42g/cm ³ . The average tap density is 0.48g/cm ³ (average Hausner ratio =1.15, karl index 0.12). The flowability was determined using a cone with a nozzle diameter of 15mm, with an average value of 8.93 g/s.

Particle Size Distribution (PSD). PSD was determined in air using a Microtrac S3500 instrument. D ₉₀ ＝101.5μm；D ₅₀ ＝69.56μm；D ₁₀ ＝45.69μm。

And (3) molecular weight. GPC samples were prepared at a concentration of 2mg/mL Tetrahydrofuran (THF) and eluted at a flow rate of 1mL/min on a Waters GPC instrument equipped with a Styragel HR4 5- μm 7.8x 300mm (THF) column and a 2414 refractive index detector. Peak molecular weight (M) of the starting polycarbonate _P )＝30318Da。

Scanning Electron Microscopy (SEM). SEM images showed spherical, partially agglomerated particles of typical size consistent with PSSD results.

Differential Scanning Calorimetry (DSC) and crystallinity. The DSC was scanned on a TA Instruments DSC 250 instrument at a rate of 20 ℃/min and is shown in figure 3. Melting began to occur at 196.67 ℃ and peaked at 233.97 ℃. After the second heating, glass transition occurred at 138.84 ℃, after which no melting behavior was observed.

The percentage of crystallinity of the semi-crystalline powdered polycarbonate was estimated by measuring the melting enthalpy in the melting peak (31.407J/g) and comparing it with a reference value of melting enthalpy for 100% crystalline polycarbonate (reported in the literature as 134J/g) (K.Varadarajan, et al., J.Polym.Sci.Polym.Phys.1982,20 (1), 141-154). Thus, the estimated crystallinity of the semi-crystalline polycarbonate is 26.9%.

SLS printing of powdered polycarbonate. Powdered polycarbonate was used in the laser sintering process on a Farsoon ST252P laser sintering system. 4.5kg of material was loaded into the feed piston of the machine and settled into the piston using a cement shaker to achieve the optimum tap density. The material was moved from the feed piston to the part piston in a layer-by-layer manner using counter-rotating rollers in a layer thickness of 0.102mm under an inert nitrogen atmosphere. The layers were laid down at 90 second intervals to absorb sufficient heat from the near infrared heater during which the temperature of the feed piston rose from 60 ℃ to 200 ℃ and the part bed temperature rose from 60 ℃ to 219 ℃. Once the part bed temperature reached the set point of 219 ℃, the part region was exposed using the scanning system parameters shown in table 4 to melt the selected region into a solid part.

TABLE 4

Laser spot size (mum)	450
		Filling scanning speed (mm/s)	10,160
Filling scan interval (mm)	0.20
		Filling laser power (W)	35
Number of scans	2
		Layer spacing(s)	30

The resulting parts included thin discs, crosses, large cubes, and ASTM D638 type IV tensile bars. Parts are characterized by a yellowish tint, but are mostly translucent, lacking the opaque appearance of typical laser sintered materials.

Example 4

30g of Lexan 121 polycarbonate was dissolved in 100ml of acetophenone. The mixture was placed in a 300ml conical flask and stirred and heated to 182 ℃ on a magnetic hot plate. At this temperature, complete dissolution of the polycarbonate was observed. The heater was turned off and the solution was allowed to cool while stirring. The solution was visually hazy when viewed at about 52 ℃. The solution was kept at ambient conditions (about 20 ℃) overnight for about 15 hours. 200ml of acetone diluted solution was added and then filtered by vacuum filtration. The solids separated from the solution were dried by placing them in a ventilated laboratory cabinet overnight.

Method

An illustrative method of manufacturing powdered polycarbonate for additive manufacturing and other applications includes: adding the polycarbonate to a reaction vessel containing a solvent, which may be selected from the group comprising: dimethylsulfoxide (DMSO); acyclic and cyclic ketones, such as cyclopentanone, cyclohexanone or acetophenone; acyclic and cyclic secondary amides (e.g., N-methylpyrrolidone (NMP) or N, N-Dimethylformamide (DMF)); acyclic and cyclic esters (gamma-butyrolactone); halogenated hydrocarbons (e.g., dichloromethane); anisole; or phenols (e.g., m-cresol); optionally mixed in additive materials (e.g., inorganic oxides, organic compounds, carbon microfibers, glass microfibers, and/or secondary polymers) for particle nucleation, particle dispersion, IR absorption, mineralization and reinforcement, flame retardancy, and/or coloration purposes; applying an inert atmosphere to the vessel and stirring the mixture; increasing the temperature within the vessel; forming a solution of polycarbonate; cooling the solution to a precipitation temperature of the polycarbonate; precipitating the polycarbonate from the solution in the form of a powder; removing the polycarbonate powder slurry from the reactor; separating the polycarbonate from the solvent by filtration; washing the polycarbonate powder with an amount of a washing solvent (e.g., water and/or a volatile organic solvent in which the polycarbonate is not significantly soluble, such as an alcohol, ketone, ether, ester, or hydrocarbon) to remove the reprecipitation solvent; and drying the polycarbonate by heating, preferably under reduced pressure, at 150 ℃ or more, preferably 175 ℃ or more, most preferably 195 ℃ or more but not more than 205 ℃.

It is believed that the presence of a polar solvent that exhibits effective intermolecular interactions with polar functional groups in the polycarbonate chains facilitates organization of the polymer chains into crystalline domains during the precipitation process.

Various methods can be used to chemically precipitate the above-mentioned polymers. One skilled in the art will appreciate that other precipitation methods may be employed in embodiments based on the illustrative methods described below, although they are not explicitly disclosed herein.

Another illustrative method for preparing powders from polycarbonate may include evaporation limited agglomeration (evaporation limited coalescence) and anti-solvent precipitation.

The term "agitating a mixture" refers to a process of agitating components in a liquid or slurry mixture under conditions that generate shear forces, typically using an impeller rotating within a stator, thereby creating flow and turbulence patterns. Once the impeller sucks in the mixture, it causes a sudden change in direction and acceleration of the mixture, causing it to contact the stator walls under the effect of centrifugal force, or to be forced through the holes in the stator under the effect of pressure and velocity, resulting in a final disintegration change in direction and acceleration. In an exemplary embodiment of high shear mixing conditions, the mixing comprises operating at a speed of 50 revolutions per minute (rpm) to 500 rpm. Any commercially available mixer can be used for stirring; for example, a mixer such as a Hei-Torque 200 reactor agitator motor may be used.

It will be appreciated that the rotational speed of the stirrer, the precipitation temperature and the time may be modified to potentially affect the particle size of the resulting polycarbonate powder. It will also be appreciated that the powder may be reprecipitated.

It is also understood that the polycarbonates may also be mixed in different ratios and particle sizes. This may have the effect of altering or controlling the properties of the resulting powdered polycarbonate. It is further contemplated that the polycarbonate may be formed in powder form by other chemical precipitation methods.

Melting points and enthalpies can be determined using Differential Scanning Calorimetry (DSC); for example, TA Instruments Discovery series DSC 250.

Powder flow can be measured using method a of ASTM D1895.

Young's modulus of elasticity and tensile strength may be determined according to ASTM D790.

Scanning electron microscopy was performed using a JEOL instrument operating in Low Vacuum Secondary Electron Detection (LVSED) mode.

A method of modifying the resulting powdered polycarbonate material for additive manufacturing may comprise: adding at least one compatible filler to the polycarbonate, wherein the filler is organic or inorganic; at least one filler is selected from the group consisting of glass, metal or ceramic particles, pigments, titanium dioxide particles, and carbon black particles; the particle size of the at least one filler is about equal to or less than the particle size of the polycarbonate; the particle size of the at least one filler does not vary by more than about 15-20% of the average particle size of the polycarbonate; at least one filler is less than about 3% by weight of the polycarbonate; adding a flow aid into the powdered polycarbonate; the flow aid is selected from at least one of fumed silica, calcium silicate, alumina, amorphous alumina, magnesium silicate, vitreous silica, hydrated silica, kaolin, attapulgite, vitreous phosphate, vitreous borate, vitreous oxide, titanium dioxide, talc and mica; the glidant has a particle size of about 10 microns or less; the flow aid does not significantly alter the glass transition temperature of the polycarbonate; the flow aid is present in an amount less than about 5% by weight of the polycarbonate.

Also disclosed herein are methods for powder bed melting of a powder composition comprising a partially crystallized polycarbonate powder to form a three-dimensional article. The spherical shape of the polymer powder particles results in a partially crystalline polycarbonate powder with good flowability and therefore a smooth and dense powder bed can be formed allowing for optimal precision and density of the sintered part. Furthermore, the partially crystalline nature of the polymeric material allows for easy processing.

"powder bed melting" or "powder bed fusing" includes all laser sintering and all selective laser sintering processes as well as other powder bed melting techniques defined by ASTM F2792-12 a. For example, sintering of the powder composition may be achieved by applying electromagnetic radiation other than that generated by a laser, the selectivity of sintering being achieved, for example, by selectively applying inhibitors, absorbers, susceptors, or electromagnetic radiation (e.g., by using a mask or a directed laser beam). Any other suitable source of electromagnetic radiation may be used including, for example, an infrared radiation source, a microwave generator, a laser, a radiant heater, a lamp, or combinations thereof.

All three-dimensional products made by melting these powder compositions through a powder bed are also included herein. After layer-by-layer fabrication of the article, the article may exhibit excellent resolution, durability, and strength. These articles can have a wide range of uses, including as prototypes and as end products and molds for end products.

In some embodiments of the method, the plurality of layers are formed in a predetermined pattern by an additive manufacturing process. "multilayer" as used in the context of additive manufacturing includes five or more layers, or twenty or more layers. The maximum number of layers may vary widely, for example, as determined by factors such as the size of the article being manufactured, the technique used, the capabilities of the equipment used, and the degree of detail desired in the final article.

As used herein, "layer" is a convenient term that includes any regular or irregular shape having at least a predetermined thickness. In some embodiments, the size and configuration of the two dimensions are predetermined, and in some embodiments, the size and shape of all three dimensions of the layer are predetermined. The thickness of each layer may vary widely, depending on the additive manufacturing process. In some embodiments, each layer is formed to a different thickness than the previous or subsequent layer. In some embodiments, the thickness of each layer is the same. In some embodiments, each layer is formed to a thickness of 0.05 millimeters (mm) to 5mm.

The preset pattern may be determined from a 3D digital representation of the desired article, as is known in the art and described in more detail below.

The fused layer of the powder bed fused article may have any thickness suitable for selective laser sintering processing. The individual layers may each on average preferably be at least 100 μm thick, more preferably at least 80 μm thick, and even more preferably at least 50 μm thick. In a preferred embodiment, the plurality of sintered layers are each, on average, preferably less than 500 μm thick, more preferably less than 300 μm thick, and even more preferably less than 200 μm thick. Thus, the layer of some embodiments may be 50 to 500 μm, 80 to 300 μm, or 100 to 200 μm thick. Three-dimensional articles produced from the powder compositions of the invention using a layer-by-layer powder bed melting process other than selective laser sintering may have layer thicknesses the same as or different from those described above.

Powder-based 3D printing includes a part bed and a feed mechanism. The component bed is typically at a stable temperature prior to being subjected to the energy source. The energy source is raised until the fusion temperature is reached. The powdered polycarbonate may be placed in a feeder at an initial temperature. During operation, additional polycarbonate is placed on top of the original polycarbonate which is cooled and needs to be warmed again. It is believed that only the portion of the polycarbonate directly subjected to the energy will melt, rather than the surrounding polycarbonate.

For the purposes of this disclosure, an "operating window" is defined by the typical range between melting and recrystallization (or glass transition) temperatures. Semi-crystalline polycarbonates have a defined melting point, allowing operating temperatures close to the melting point of the polycarbonate to be established in SLS, MJF, HSS and possibly electrophotographic 3D printing applications. This well-defined melting behavior allows an operating window that keeps the remaining material from melting, even if a laser or IR heater is used during 3D printing of solid forms. The unmelted solid material may then be used as a support structure for the molten polycarbonate.

The exemplary embodiments are provided so that this disclosure will be thorough and will fully convey the scope to those skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. Equivalent changes, modifications and variations of some embodiments, materials, compositions and methods may be made within the scope of the present technology with substantially similar results.

Claims

1. A method of making a partially crystalline polycarbonate powder, the method comprising:

dissolving amorphous polycarbonate in a polar aprotic solvent at a first temperature to form a first solution of dissolved polycarbonate; and

cooling the first solution to a second temperature, the second temperature being lower than the first temperature, wherein a portion of the dissolved polycarbonate precipitates from the first solution to form a second solution comprising the partially crystalline polycarbonate powder.

2. The method of claim 1, further comprising separating the precipitated partially crystalline polycarbonate powder from a remainder of the second solution.

3. The method of claim 2, further comprising drying the isolated partially crystalline polycarbonate powder.

4. The method of claim 2, further comprising repeating the dissolving step using the remaining portion of the second solution as the polar aprotic solvent and repeating the cooling step to form a second solution comprising additional partially crystallized polycarbonate powder.

5. The method of claim 1, wherein the polar aprotic solvent comprises dimethyl sulfoxide.

6. The method of claim 1, wherein the polar aprotic solvent consists essentially of dimethyl sulfoxide.

7. The method of claim 1, wherein the step of dissolving includes heating the amorphous polycarbonate in the polar aprotic solvent at the first temperature to form the first solution of dissolved polycarbonate, the first temperature being greater than room temperature.

8. The method of claim 7, wherein the step of cooling comprises cooling the first solution to the second temperature, the second temperature being room temperature.

9. The method of claim 1, wherein the first solution is supersaturated with amorphous polycarbonate at the first temperature.

10. The method of claim 1, wherein the partially crystalline polycarbonate powder has a D90 particle size of less than about 150 microns.

11. The method of claim 1, wherein the partially crystalline polycarbonate powder has an average particle size of from about 1 micron to about 100 microns.

12. The method of claim 1, wherein the partially crystalline polycarbonate powder has an average particle size of from about 30 microns to about 40 microns.

13. The method of claim 1, wherein the partially crystalline polycarbonate powder is in the form of spherical particles.

14. The method of claim 1, wherein the partially crystalline polycarbonate powder has a crystallinity of at least about 20%.

15. The method of claim 1, wherein the partially crystalline polycarbonate powder has a crystallinity of from about 25% to about 35%.

16. A powder composition for use in a powder bed melt process, the powder composition comprising a partially crystalline polycarbonate powder prepared according to the method of claim 1.

17. A powder composition for a powder bed melting process, the powder composition comprising a partially crystalline polycarbonate powder having a D90 particle size of less than about 150 microns, an average particle size of about 30 microns to about 40 microns, and a crystallinity of between about 25% and about 35%.

18. A method of making an object comprising:

preparing a partially crystalline polycarbonate powder according to the method of claim 1; and

using the partially crystalline polycarbonate powder in a powder bed melting process to form the object.

19. A method of making an object comprising:

providing a partially crystalline polycarbonate powder having a D90 particle size of less than about 150 microns, an average particle size of from about 30 microns to about 40 microns, and a crystallinity of between about 25% to about 35%; and

using the partially crystallized polycarbonate powder in a powder bed melting process to form the object.

20. An object prepared by an additive manufacturing process, the process comprising:

providing a partially crystalline polycarbonate powder prepared according to the method of claim 1; and