Method and apparatus for the heat treatment of polymer powders

Abstract

A method and apparatus for heat treating a powder of a semi-crystalline or crystallizable polymer, the apparatus including a heating device for heating the powder to a temperature below the melting temperature of the highest melting crystalline form of the powder, a container for containing the powder that is exposed to heat generated by the heating device, and a movement mechanism for moving the powder in the container relative to the container.

Description

[Technical field]

[0001] The present invention relates to a method and apparatus for the thermal treatment of powders of semi-crystalline or crystallizable polymers, such as polyaryletherketone (PAEK) polymers. [Background technology]

[0002] As described in U.S. Pat. No. 9,587,107 to Arkema, the entire disclosure of which is incorporated herein by reference for all purposes, in the selective laser sintering (SLS) process, a bed of polymer powder is preheated in a preheat chamber and then distributed in a sintering chamber as a thin layer, where a laser is used to heat certain parts of the bed to selectively sinter some of the polymer powder in a predetermined pattern. This is followed by forming a second layer in the bed, and the material in the second layer is again heated and selectively sintered in a pattern. At the same time, the second layer is also fused to the sintered parts of the first layer. Such successive layering and sintering can form a three-dimensional part, which is then removed from the unsintered powder bed. Aspects of such a method are also described, for example, in U.S. Pat. No. 7,847,057, the entire disclosure of which is incorporated herein by reference for all purposes.

[0003] A preliminary heat treatment step prior to the SLS process has been shown to result in more uniform melting of the powder, improve powder flowability, and reduce wear rates in applications requiring powder handling at high temperatures. Heat treatment processes are described, for example, in U.S. Patent Application Publication Nos. 20160108229A1 and 20160122527A1, and U.S. Patent Application No. 15 / 830,100, the disclosures of which are incorporated herein by reference in their entirety for all purposes. U.S. Patent No. 9,580,551, the disclosures of which are incorporated herein by reference in their entirety for all purposes, describes a heat treatment method for improving the effectiveness of the SLS process and the quality of the product.

[0004] Although heat treatment processes are sometimes disclosed in the prior art, there are relatively few disclosures of equipment capable of performing heat treatment in large scale manufacturing quantities. For example, methods and apparatus for a preliminary heat treatment step of polymer powders to be heat treated for use in SLS processes, such as those described in U.S. Pat. No. 9,587,107, are described below.

[0005] Carrying out heat treatment in a static oven presents problems and drawbacks, since heat must be transferred by conduction, and both the polymer and air have low thermal conductivity. This heat transfer becomes even more difficult with increasing batch size, since the outer layer acts as an insulating layer. Above a certain thickness, heating of all the powder may not be possible. Summary of the Invention [Means for solving the problem]

[0006] In general, the present invention is a method and apparatus for heat treatment process of semi-crystalline or crystallizable polymer (e.g., PAEK) powder at a specific temperature (or a series of specific temperatures or temperature gradients) inside a container. The container is moved (e.g., by rotation, circulation, partial rotation, partial circulation, vibration, etc.) so that the powder is moved or moved, preferably substantially continuously, more preferably continuously, over the hot inner surface of the container, thereby providing uniform or more uniform heating of the powder and also avoiding clumping, agglomeration, and / or sticking on the container surface. This results in a higher percentage or even a higher amount of heat treated powder that can be further processed and used, for example, in an SLS process.

[0007] Compared to static ovens, rotating ovens ensure more efficient and uniform heat transfer due to the repeated contact of the powder on the hot surface of the oven. As a result, the heat treatment time of the powder can be substantially reduced and the batch size can be increased. Both of these factors improve productivity. Furthermore, the risk of overheating and agglomerate formation is reduced.

[0008] In one embodiment, the invention provides an apparatus for heat treating a semi-crystalline or crystallizable polymer, which may be in powder form and polymorphic, comprising: a heating device for heating the powder to a temperature below the melting temperature of the highest melting crystalline form of the powder; a vessel exposed to heat generated by the heating device, the vessel defining an interior region for containing the powder; and vessel movement means for moving the powder within the vessel relative to the vessel.

[0009] Another embodiment of the invention provides a method for heat treating a semi-crystalline or crystallizable polymer (including polymorphic polymer) in powder form, comprising the steps of heating a monomorphic or polymorphic semi-crystalline or crystallizable polymer powder contained within an interior region of a container to a temperature below the melting temperature of the powder's highest melting crystalline form; and moving the container to move the heated semi-crystalline or crystallizable polymer powder within the container relative to the container.

[0010] For PAEK, the heat treatment is preferably carried out at a temperature of from about 230° C. to about Tm-10° C., where Tm is the melting point of the highest melting polymorph or crystalline phase. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 shows an isometric view of a schematic representation of an apparatus for heat-treating semi-crystalline or crystallizable polymer powder according to a first exemplary embodiment of the present invention. [Figure 2A] FIG. 2 shows a cross-sectional side view of another apparatus for heat-treating semi-crystalline or crystallizable polymer powder, shown diagrammatically, in accordance with a second exemplary embodiment of the present invention. [Figure 2B] FIG. 2B is a cross-sectional side view of the device of FIG. 2A taken along line 2B-2B. [Diagram 3] 1 shows a typical temperature profile for the heat treatment of semi-crystalline or crystallizable polymer powders using a rotational molding apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] 1 shows an isometric view of an apparatus 10 for heat-treating semi-crystalline or crystallizable polymer powder, shown diagrammatically, according to a first exemplary embodiment of the present invention. The apparatus 10 generally includes a heating device 12, a container 14 for containing the powder to be heated by the heating device 12, a mixing element such as a grid or sieve 16 disposed inside the container 14 and at least partially submerged in the powder (not shown), and a means of movement 18 for the container 14.

[0013] The heating device 12 is a mechanism for generating heat and exposing the container 14 and its contents to that heat. The heating device 12 may be an oven in which the container 14 is placed. Alternatively, the heating device 12 may be a heating element that is connected to or is part of the container 14. As another alternative, the container 14 may be heated using circulating hot oil (or other fluid). The heating device 12 may be any conventional heating mechanism known to those skilled in the art and is not limited to what is shown and described. For example, the heating device may include a heating element that converts electricity to heat in a process of resistive heating, or it may include hot oil that may be circulated.

[0014] The container 14 is a container having any shape, such as a hollow tube or cylinder, in which the powder is contained. It should be understood that the size and shape of the container 14 may vary. The container 14 is configured to rotate about its longitudinal axis A (also referred to herein as the axis of rotation). The container 14 may be constructed of a thermally conductive material, particularly a metal or metal alloy, such as stainless steel, for example grades 316L or 904. The ends of the container 14 may be either open (as shown) or closed. A removable lid closure (not shown) may be removably attached over one open end of the container 14. The container 14 may be a closed system to prevent contamination or release of powder during operation. According to another embodiment, the container 14 may be configured to allow gas (e.g., an inert gas such as nitrogen) to flow through the container 14. The container 14 may be mounted within the device 10 either removably or permanently.

[0015] The mixing element may include a sieve 16, which is a perforated plate having holes, pores, or openings through which the powder can pass. Alternatively, the sieve 16 may be provided in the form of a rack with transversely divided members, i.e., a conventional oven rack, or the like. According to an embodiment, multiple sieves may be placed inside the vessel. The size and shape of the openings of the sieve 16 may vary. The sieve 16 may be constructed of a thermally conductive material, such as, for example, stainless steel (such as grades 316L or 904) or another metal or metal alloy. Alternatively, the sieve 16 may be replaced by multiple mixing elements, for example, having a compact shape (such as a sphere, cube, cylinder, etc.), capable of independent movement within the vessel, and constructed of either metal or ceramic. As another alternative, the sieve 16 may be omitted altogether.

[0016] According to one aspect of the invention, sieve 16 is coupled to vessel 14 such that sieve 16 rotates with vessel 14. According to another aspect of the invention, sieve 16 is coupled to a fixed location (e.g., on heating device 12) such that vessel 14 rotates relative to stationary sieve 16. In yet another aspect of the invention, sieve 16 can move or rotate in the opposite direction to vessel 14.

[0017] According to one embodiment of the invention, the container 14 includes a means 17 for removing agglomerates or clumps of powder from the container surface. The means 17 may be, for example, a scraper, a brush, a wire brush, a knife, or a paddle. The means 17 may be connected to a fixed location (e.g., on the heating device 12) such that the container 14 rotates relative to the stationary means 17.

[0018] One means 18 for moving, or for example rotating, the container 14 is provided in the form of rollers as shown. The rollers engage the outer periphery of the container 14 to rotate it (see arrow indicating one of the directions of rotation). The rollers 18 can be configured to rotate the container 14 in both directions of rotation. The rollers 18 can be connected to a gear or output shaft of a motor (or other power device) to rotate the rollers 18. Alternatively, the container 14 can be directly connected to the motor and the rollers 18 can be a passive device that allows the container 14 to rotate. Passive rollers 20 also engage the outer periphery of the container 14 at a location remote from the rollers 18 that allow the container 14 to rotate.

[0019] A temperature sensor 19 may be disposed within the container 14 (or heating device 12 ) to either directly or indirectly detect the temperature of the powder within the container 14 .

[0020] The heating device 12, the movement means 18, and the temperature sensor 19 are directly or indirectly connected to a controller / processor 20. The controller / processor 20 is configured to control the operation of the heating device 12 and the movement means 18. The controller / processor 20 is configured to receive a signal from the temperature sensor 19. A user interface 21, such as a display or a keypad, is directly or indirectly connected to the controller / processor 20 for sending operating instructions to the controller / processor 20.

[0021] According to one exemplary method of operation of the apparatus 10 for heat treating a semi-crystalline or crystallizable polymer powder, the container 14 is first charged with a powder of a semi-crystalline or crystallizable polymer, such as a PAEK powder. The container 14 may then be closed by a cover (not shown). Preferably, the powder may occupy between about 10-70 percent of the volume of the container 14. More preferably, the powder may occupy between about 20-60 percent of the volume of the container 14. More preferably, the powder may occupy between about 30-50 percent of the volume of the container 14. Alternatively, the powder may occupy less than about 50% of the volume of the container 14.

[0022] The controller / processor 20 then activates the heating device 12 and the movement means 18. Upon activation, the heating device 12 heats the powder in the container 14 to a predetermined temperature that depends on the composition of the powder. This may be referred to as the heating step. As described in U.S. Pat. No. 9,587,107, the predetermined heating temperature may be a temperature value that is 20 degrees lower, preferably 10 degrees lower, more preferably 5 degrees lower than the melting temperature of the highest melting crystalline form of the polymer, or a temperature value between the two melting points of the two crystalline phases of the polymer. For example, the predetermined heating temperature may be 250° C., or 260° C., or 270° C., or 275° C., or 280° C., or preferably 285° C.

[0023] The moving means 18 rotates the container 14 about the axis A either (i) continuously in one rotational direction, or (ii) in a reciprocating or oscillating manner (e.g., periodically reversing less than one revolution in one rotational direction and less than one revolution in the opposite rotational direction, or one or more revolutions). As another example of a reciprocating motion, the container 14 can be rotated two or three revolutions in one rotational direction and then two or three revolutions in the opposite rotational direction. This may be referred to as a rotation or moving step. The rotation of the container 14 causes movement and circulation of the powder in the container 14, which promotes substantially uniform or homogeneous heating of the powder, heats the powder more quickly, and prevents or limits hot spots in the powder. The sieve 16 (or mixing element) can separate any agglomerates that have formed and mixes the powder, thereby improving the uniformity and properties of the powder. Due to the movement of the container 14 and gravity, the powder moves against the heated inner surface of the container 14. Thus, as container 14 rotates about axis A, the particles of the powder move and do not remain in the same place on the heated interior surface of container 14. As the powder passes through sieve 16, sieve 16 either limits or substantially prevents the formation of agglomerates in the powder and / or separates any agglomerates that may have formed.

[0024] The heating and rotating steps are typically performed simultaneously for a first time during which the powder is heated from a starting temperature (e.g., room temperature) to a predetermined temperature. This first time may be more than 15 minutes and less than 10 hours, preferably less than 6 hours, more preferably 5 hours or less, more preferably 3 hours or less, and even more preferably more than 30 minutes and less than 2 hours. After the predetermined temperature is reached, the heating and rotating steps can be continued for a second time while maintaining the target temperature within ±5°C (i.e., within ±5°C of the target temperature), or preferably ±3°C. This second time may be at least at least 1 minute to 7 hours, preferably 1 minute to about 6 hours, more preferably at least 1 hour to about 5 hours, and even more preferably at least about 1 hour to about 4 hours. In another embodiment, the second time may be at least 120 minutes or more. After the powder has been sufficiently heated to the predetermined temperature for the predetermined time, the heat-treated powder is optionally cooled and removed from the container 14. The resulting polymer powder is ready for selective laser sintering, for example as described in US Pat. No. 9,587,107.

[0025] In a preferred embodiment, the vessel and / or product may be cooled, and the cooling time and rate may be controlled, for example, using forced air, water spray, or a jacket through which a fluid such as oil, water, or air is circulated. Rotation is preferably maintained as the product is cooled and during the cooling step. The cooling time, which is one of the control parameters, is generally kept as short as possible, for example less than 40 minutes, preferably less than 30 minutes, more preferably less than 20 minutes, and even more preferably less than 10 minutes.

[0026] 2A and 2B show another apparatus 110 for heat treating a semi-crystalline or crystallizable polymer powder 113, shown generally in a schematic manner, according to a second exemplary embodiment of the present invention. The apparatus 110 generally includes a heating device 112, a container 114 for containing the powder heated by the heating device 112, a grid or sieve 116 disposed within the container 114 and at least partially embedded in the powder, a means 118 for moving (e.g., rotating) the container 114 about an axis B, and a means 119 for moving (e.g., rotating) the container 114 about an axis C. The container 114, the heating device 112, and the means 118 and 119 may be conventional rotational molding apparatus. A suitable rotational molding machine is supplied by Ferry Industries, Inc. A rotational molding apparatus is described in U.S. Pat. No. 3,474,165 to ConocoPhillips, the entire disclosure of which is incorporated herein by reference for all purposes.

[0027] The heating device 112 is a mechanism for generating heat and exposing the container 114 to the heat. The heating device 112 may be an oven in which the container 114 is placed. Alternatively, the heating device 112 may be a heating element that is connected to or is part of the container 114. The heating device 112 may be any conventional heating mechanism known to those of skill in the art and is not limited to what is shown and described.

[0028] Container 114 is a hollow box-shaped container in which the powder is contained. Container 114 has a removable lid 114'. As described in more detail below, container 114 is configured to rotate about axes B and C. Container 114 is constructed from thermally conductive stainless steel, such as grades 316L or 904. Container 114 is a closed system to prevent contamination or release of powder during operation.

[0029] The sieve 116 may be a perforated plate having holes, pores, or openings through which the powder can pass. Alternatively, the sieve 116 may be provided in the form of a rack with transversely divided members, i.e., a conventional oven rack, or the like. The size, shape, and number of openings in the sieve 116 may vary. The sieve 116 may be constructed of a thermally conductive stainless steel, such as grades 316L or 904. The sieve 116 may extend between two opposing interior corners of the container 114 and is substantially fixed relative to the container 114. The sieve 116 may be movable a small amount relative to the container 114 or may be fixed in the same place within the container 114. Alternatively, as previously described, the sieve 116 may be replaced by metal balls or similar objects. As another alternative, the sieve 116 may be absent altogether.

[0030] The means 118 for moving the container 114 about axis B is (optionally) a motor having a shaft connected (either directly or indirectly) to the bottom of the container 114 as shown. The means 118 can be configured to rotate the container 114 in both directions of rotation about axis B.

[0031] The means 119 for moving the container 114 about axis C is (optionally) a motor having a shaft connected (either directly or indirectly) to the side of the container 114 as shown. The means 119 can be configured to rotate the container 114 in both rotational senses about axis C. As the means 118 rotates the container 114, the means 119 also rotates the means 118 (or vice versa), such that the means 118 and 119 can be simultaneously operated to rotate the container 114 about both axes B and C at the same time.

[0032] The means 118 and 119 may differ from those shown and described. As an alternative, one of the means 118 and 119 may be omitted. As another alternative, a third means of movement of the container may be provided for rotating the container about a third axis perpendicular to the axes B and C. As yet another alternative, the means 118 and / or 119 may shake (or vibrate) the container 114 in a reciprocating manner along the axes B and C, respectively, instead of rotating. Another means may shake (or vibrate) the container 114 in a reciprocating manner along a third axis perpendicular to the axes B and C.

[0033] A temperature sensor 123 may be disposed within the container 114 (or heating device 112 ) to either directly or indirectly detect the temperature of the powder 113 within the container 114 .

[0034] The heating device 112, the means 118 and 119, and the temperature sensor 123 are directly or indirectly connected to a controller / processor 120. The controller / processor 120 is configured to control the operation of the heating device 112 and the means 118 and 119. The controller / processor 120 is configured to receive a signal from the temperature sensor 123. A user interface 121, such as a display or a keypad, is directly or indirectly connected to the controller / processor 120 for sending operating instructions to the controller / processor 120.

[0035] According to one exemplary method of operation of the apparatus 110 for heat treating semi-crystalline or crystallizable polymer powder, the container 114 is first charged with polymer powder 113. As previously discussed, the powder can occupy less than the entire volume of the container 114. The controller / processor 120 then activates the heating device 112 and the means 118 and 119. Upon activation, the heating device 112 heats the powder in the container 114 to a predetermined temperature that depends on the composition of the powder, as previously described with respect to the apparatus 10. The temperature is controlled to avoid or minimize melting, agglomeration, or fusion of the powder.

[0036] During the heating process, the means 118 rotates the container 114 around the axis B either (i) continuously in one rotational direction, or (ii) in a reciprocating or oscillating manner (e.g., less than one revolution in one rotational direction and less than one revolution in the opposite rotational direction). Similarly, the means 119 rotates the container 114 around the axis C either (i) continuously in one rotational direction, or (ii) in a reciprocating or oscillating manner (e.g., less than one revolution in one rotational direction and less than one revolution in the opposite rotational direction). The means 118 and 119 may or may not be operated simultaneously. This may be referred to as a rotation or movement step.

[0037] As the container 114 rotates, the powder in the container 114 creates movement and circulation of the powder particles, which promotes substantially uniform or homogeneous heating of the powder and prevents or substantially limits hot spots in the powder. The sieve 116 (or mixing element) allows for separation of agglomerates that have formed and mixes the powder, thereby improving the uniformity and properties of the powder. The powder moves against the heated inner surface of the container 114. Thus, as the container 114 rotates about axes B and C, the particles of the powder move and do not stay in the same place on the heated inner surface of the container 114. As the powder passes through the sieve 116, the sieve 116 limits or substantially prevents the formation of agglomerates in the powder or separates agglomerates that may have formed.

[0038] The heating and rotating steps are typically performed as described above with respect to apparatus 10.

[0039] The vessel and / or product may be cooled, and the cooling time and rate may be controlled, for example, using forced air, water spray, or a jacket through which a fluid such as oil, water, or air is circulated. Rotation is preferably maintained as the product is cooled and during the cooling step. The cooling time, which is one of the control parameters, is generally kept as short as possible, for example less than 40 minutes, preferably less than 30 minutes, more preferably less than 20 minutes, and even more preferably less than 10 minutes.

[0040] During testing of the apparatus 110, it was found that the powder reached a predetermined temperature (e.g., about 285°C) in about 90 minutes, and that the temperature of the powder was substantially uniform due to the continuous movement of the powder on the heated surface of the container 114. Without intending to be bound by any theory, it is believed that the rotation of the container 114 constantly creates a fresh layer of powder in contact with the heated inner surface of the container 114, so that a new layer of powder constantly replaces an old layer of powder on the heated surface of the container 114. The temperature range of the heat treatment is preferably limited, maintained, and controlled, so that uniformity of the powder temperature is important. In particular, above the maximum temperature of the temperature range of the heat treatment, melting and agglomeration of the powder occurred. In contrast, effective heat treatment according to the teachings of the present invention achieved the desired modified crystal structure.

[0041] A typical temperature profile for the heat treatment of a polymer powder using a rotational molding apparatus is shown in Figure 3. The figure shows that it takes about 100 minutes for the powder to reach the target temperature of about 275 °C.

[0042] In practicing the present invention, it has been discovered that apparatus 10 and 110 are commercially viable apparatus for heat treating semi-crystalline or crystallizable polymer powders, as compared to other known apparatus described below in the Comparative Examples section.

[0043] Apparatus and methods of the type described herein are useful for use in conjunction with powders of semicrystalline or crystallizable polymers, such as polymorphic semicrystalline or crystallizable polymers. The present invention is not limited to the specific preferred embodiments described herein, and further includes any container having a means for moving the powder therein relative to the container.

[0044] Polymers that can be used in connection with the present invention include polymorphic semicrystalline polymers and / or polymers that can become semicrystalline upon exposure to temperatures above the glass transition temperature of the polymer. As used herein, the term "polymorphic semicrystalline or crystallizable polymer" means that the polymer can exist in one or more crystalline forms and that the polymer has one or more regions that are crystalline and / or capable of forming one or more crystalline regions upon heat treatment.

[0045] According to various aspects of the invention, powders of polyaryletherketone (PAEK) polymers may be used. For example, such PAEK polymer powders may be powders of polymers selected from the group consisting of polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyetherketone (PEK), polyetheretherketoneketone (PEEKK), polyetherbiphenyletherketone (PEDEK), and polyetherketoneetherketoneketone (PEKEKK). Blends or mixtures or copolymers of polyaryletherketones such as PEEK-PEDEK as disclosed in WO 2015 / 124903 may also be used within the scope of the invention. Other polymorphic polymers that may benefit from heat treatment using the device according to the invention or the method according to the invention include, but are not limited to, homopolymers and copolymers of polyamide 11 (PA11), polyamide 12 (PA12), and polyvinylidene fluoride (PVDF).

[0046] The device or method according to the invention may also be applicable to polymeric materials with one crystalline form such as PEEK (polyetheretherketone) and PEK (polyetherketone), where treatment at high temperature increases the linear crystallinity of the crystalline lamellae, influencing in a direct manner the melting temperature and / or the shape of the melting peak of the final product as observed by DSC (during the first heating as described in ISO 11357).

[0047] The present invention is particularly useful in the case of polyetherketoneketones (PEKK). Polyetherketoneketones are well known in the art and can be prepared using any suitable polymerization technique, such as the methods described in the following patents, the entire disclosures of each of which are incorporated herein by reference for all purposes: U.S. Pat. No. 3,065,205; U.S. Pat. No. 3,441,538; U.S. Pat. No. 3,442,857; U.S. Pat. No. 3,516,966; U.S. Pat. No. 4,704,448; U.S. Pat. No. 4,816,556; and U.S. Pat. No. 6,177,518. PEKK polymers differ from the general class of PAEK polymers in that they often contain two different isomeric repeat units. These repeat units are represented by the following formulae and II: -AC(=O)-BC(=O)- I -AC(=O)-DC(=O)-II where A is a p,p'-Ph-O-Ph- group, Ph is a phenylene group, B is p-phenylene, and D is m-phenylene. The ratio of isomers of formula I to formula II, commonly referred to as the T:I ratio in the polyetherketoneketone, is selected to vary the overall crystallinity of the polymer. The T:I ratio generally varies from 50:50 to 100:0, and in some embodiments from 60:40 to 80:20, or from 55:45 to 90:10. A higher T:I ratio, such as 80:20, results in a higher degree of crystallinity compared to a lower T:I ratio, such as 60:40. According to an embodiment, the powder processed according to the present invention is a PEKK powder having a T:I ratio of about 60:40, or about 70:30, or about 80:20, or about 50:50.

[0048] Suitable polyetherketoneketones are available from several commercial sources under various brand names. For example, polyetherketoneketones are sold by Arkema under the brand name KEPSTAN® polymers. In addition to using polymers with specific T:I ratios, mixtures of polyetherketoneketones can be used.

[0049] The powders used in the present invention can be produced directly by synthesis or by various methods such as grinding, air milling, spray drying, freeze drying, or direct melt processing to fine powder. Preferably, the powder is produced first and then heat treated. The heat treatment method and the powder produced thereby are not limited to any particular particle size. The particle size of the powder can be adjusted before or after the heat treatment method based on the needs of the individual application. Generally, the powders useful in the present invention can have a median volume average particle size / diameter between 0.002 microns and 0.1 meters, more preferably between 0.01 microns and 1.0 mm. For use in selective laser sintering (SLS), a median volume average particle size / diameter of 15 to 150 microns may be preferred, more preferably 30 to 75 microns. "Median volume average particle size" and "median volume average particle size" are used interchangeably herein.

[0050] According to one non-limiting embodiment of the present invention, milling the PEKK flakes produces a PEKK powder having a median volume average particle size between about 10 microns and about 150 microns as measured using dry powders using laser light scattering methods well known in the art, such as ISO 13320:2009. As used herein, "powder" can refer to a material composed of small particles of PEKK. The PEKK powder can have a median volume average particle size of about 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, or about 150 microns. In a preferred embodiment, the PEKK powder has a median volume average particle size of about 30 microns to about 100 microns. In another preferred embodiment, the PEKK powder has a median volume average particle size of about 50 microns.

[0051] According to one non-limiting aspect of the present invention, polymorphous semi-crystalline or crystallizable polymers of various structures can be heat treated to increase, decrease or adjust the crystalline melting point or melting peak shape for better powder handling and durability in applications requiring powder flow at high temperatures. Polymorphous semi-crystalline or crystallizable polymers can be heat treated to induce crystallization and / or convert the crystalline polymer to another, more thermodynamically stable crystalline form.

[0052] In one non-limiting embodiment, the polymer comprises polyetherketoneketone (PEKK), which can have at least two crystalline forms. In this embodiment, the PEKK is initially amorphous, but upon heat treatment, it is possible that at least some of the PEKK is converted to at least one crystalline form, which can be converted at least partially to a higher melting crystalline form. The content of the higher melting crystalline form can then be increased in a heat treatment step by exposing the polymer composition to a temperature below the melting point of the highest melting crystalline form and within or above the melting range of another crystalline form for a time period that increases the content of the highest melting crystalline form relative to another crystalline form in the polymer composition.

[0053] In yet another embodiment, a method for increasing the content of one crystalline form of polyetherketoneketone is provided, comprising at least the step of heat treating a polymer composition comprising another crystalline form of polyetherketoneketone at or above the melting range of the lower melting crystalline form of polyetherketoneketone and below the melting point of the higher melting crystalline form of polyetherketoneketone. In this embodiment, the starting polyetherketoneketone is initially amorphous, but the heat treatment can convert at least a portion of the polyetherketoneketone to one or both of the other crystalline forms.

[0054] Powders heat treated using the apparatus according to the invention or the method according to the invention can be converted into useful articles or coatings on articles using any suitable or known method for converting polymer powders, such as, but not limited to, selective laser sintering, rotational molding, and powder coating.

[0055] Example 1: A rotatable container placed in an oven as shown in FIG. Material: Kepstan® 6002 PL PEKK powder (a product of Arkema, Inc.) having a median volume average particle size of about 50 microns. Filling: Approximately 30% of the container's volume.

[0056] Method: A container was filled with polymer powder at room temperature. The filled container was placed in an oven. The set point temperature of the oven was fixed at 293°C. A set point temperature of 293°C resulted in heat treatment of the polymer powder at 285°C. The set point temperature (293°C) was reached after 2 hours and was subsequently maintained for 3 hours. The container was moved at a constant rotation of 10 rpm. The container filled with powder was then removed from the oven and then cooled with pulsed air. Rotation of the container was maintained during this stage. The treated powder can be sieved before further use. The median volume average particle size of the powder thus obtained was measured to be about 50±3 microns.

[0057] Example 2: A rotatable container placed in an oven as shown in FIG. Material: Kepstan® 6002 PL PEKK powder with a median volume average particle size of about 50 microns. Filling: About 10% of container.

[0058] Method: A container was filled with polymer powder at room temperature. The filled container was placed in an oven. The set point temperature of the oven was fixed at 293°C. Heat treatment of the powder took place at 285°C with a set point temperature of 293°C. The set temperature (293°C) was reached within 2 hours and subsequently maintained for 3 hours. The container was moved at a constant rotation of 10 rpm. The container filled with powder was removed from the oven and then cooled with pulsed air. Rotation of the container was maintained during this stage. The treated powder can be sieved before further use. The median volume average particle size of the powder thus obtained was measured to be about 50±3 microns.

[0059] Example 3: A rotatable container placed in an oven as shown in FIG. Material: Kepstan® 6002 PL PEKK powder with a median volume average particle size of about 50 microns. Filling: About 50% of the container's volume.

[0060] Method: The container was filled with polymer powder at room temperature. The filled container was placed in an oven. The set point temperature of the oven was fixed at 293°C. A set point temperature of 293°C resulted in heat treatment of the polymer powder at 285°C. The set temperature (293°C) was reached within 2 hours and was subsequently maintained for 3 hours. The container was moved at a constant rotation of 10 rpm. The powder filled container was removed from the oven and then cooled with pulsed air. Rotation of the container was maintained during this stage. The treated powder can be sieved before further use. The median volume average particle size of the powder thus obtained was measured to be about 50±3 microns.

[0061] Example 4: A rotatable container placed in an oven as shown in FIG. Material: Kepstan® 6002 PL PEKK powder with a median volume average particle size of about 50 microns. Filling: Approximately 55% of container.

[0062] Method: A container was filled with polymer powder at room temperature. The filled container was placed in an oven. The set point temperature of the oven was fixed at 293°C. A set point temperature of 293°C resulted in heat treatment of the polymer powder at 285°C. The set point temperature (293°C) was reached after 2 hours and was subsequently maintained for 5 hours. The container was moved at a constant rotation of 10 rpm. The container filled with powder was then removed from the oven and then cooled with pulsed air. Rotation of the container was maintained during this stage. The treated powder can be sieved before further use. The median volume average particle size of the powder thus obtained was measured to be about 50±3 microns.

[0063] Example 5: A rotatable container placed in an oven as shown in FIG. Material: Kepstan® 6002 PL PEKK powder (a product of Arkema, Inc.) having a median volume average particle size of about 50 microns. Filling: Approximately 30% of the container's volume.

[0064] Method: A container was filled with polymer powder at room temperature. The filled container was placed in an oven. The set point temperature of the oven was fixed at 281°C. A set point temperature of 281°C resulted in heat treatment of the polymer powder at 275°C. The set point temperature (281°C) was reached after 2 hours and was subsequently maintained for 3 hours. The container was moved at a constant rotation of 10 rpm. The container filled with powder was then removed from the oven and then cooled with pulsed air. Rotation of the container was maintained during this stage. The treated powder can be sieved before further use. The median volume average particle size of the powder thus obtained was measured to be about 50±3 microns.

[0065] Example 6: A rotatable container placed in an oven as shown in FIG. Material: Kepstan® 6002 PEKK powder (a product of Arkema, Inc.) having a median volume average particle size of about 70 microns. Filling: Approximately 30% of the container's volume.

[0066] Method: A container was filled with polymer powder at room temperature. The filled container was placed in an oven. The set point temperature of the oven was fixed at 293°C. A set point temperature of 293°C resulted in heat treatment of the polymer powder at 285°C. The set point temperature (293°C) was reached after 2 hours and was subsequently maintained for 3 hours. The container was moved at a constant rotation of 10 rpm. The container filled with powder was then removed from the oven and then cooled with pulsed air. Rotation of the container was maintained during this stage. The treated powder can be sieved before further use. The median volume average particle size of the powder thus obtained was measured to be about 70±5 microns.

[0067] Example 7: A rotatable container placed in an oven as shown in FIG. 2A Material: Kepstan® 6002 PL powder having a median volume average particle size of about 50 microns.

[0068] Device: 431×431×675mm 3 The STP Lab 40 Rotomolder used a parallelepiped chamber made of 4.76 mm 304 stainless steel with dimensions of 0.01 mm.

[0069] Method: 20 kg of polymer powder was placed in the chamber with stainless steel grids placed diagonally in the chamber as shown in Figure 2B. The volume occupied by the powder was about 42% of the total volume of the chamber. The oven temperature was set at 285°C. The chamber was placed in the oven and rotated continuously around two axes as shown in Figure 2A. The temperature of the powder inside the mold was monitored and recorded with a rotolog. After about 2 hours, the powder reached the target temperature of 285±3°C as shown in Figure 3, and the powder was then maintained at this temperature for an additional 3 hours. Note that Figure 3 has been modified to smooth the curve showing the powder temperature. The chamber was then removed from the oven and cooled using forced air. Upon removal, the powder was a free-flowing powder with less than 15% agglomerates that were easily separable from the powder by sieving at 260 microns. It was found that these agglomerates could be easily broken down by applying gentle pressure, returning to a fine powder. No debris / agglomerates / melt products were observed on the walls of the chamber. The median volume average particle size of the powder thus obtained was measured to be about 50±3 microns.

[0070] Comparative Examples: KEPSTAN® 6002 PL polymer powder having a median volume average particle size of about 50 microns was used during testing for each of the following comparative examples.

[0071] Comparative Example 1: Circulating Air Oven After extensive testing, it was found that circulating air ovens were less efficient and productive. Due to the low heat transfer coefficient of powder, only a thin layer of powder was processed at a time, which slowed the process too much to be acceptable. In one example, a 5 cm thick powder layer required approximately 7 hours for the powder's internal temperature to reach the oven temperature (e.g., 285°C).

[0072] Comparative Example 2: Screw / agitator / mixing device Some prior art references, such as US Patent Publication No. 20120364697 (the entire disclosure of which is incorporated herein by reference for all purposes), mention the possibility of immersing an agitation device in the powder to circulate the powder. They mention that the container in which the powder is contained remains stationary. In comparative tests, it was found that this method can result in uneven heating and hot spots of the powder, which can lead to molten polymer, deposits on the walls of the device (thus slowing down the heat transfer process), agglomerated powder, and lumps in the heat-treated powder.

[0073] Comparative Example 3: Fluidized Bed In a fluidized bed heater, the powder is contained within a vessel and the exterior walls of the vessel are heated. At the same time, a gas (such as air) is passed through the vessel at a velocity fast enough to suspend the solids in the air stream. In comparative testing, it was found that the amount of air required to fluidize the powder did not allow the powder to reach a predetermined heat treatment temperature before it left the vessel.

[0074] Comparative Example 4: Paddle Dryer A paddle dryer is an indirect heat transfer device with mechanical agitation that adds or removes heat from the processing mass. Paddle dryers can be used for indirect drying, heating, cooling, pasteurization, crystallization, and reaction of powders and granules. During operation, the container and paddles are heated and powder is dispensed into the container. In comparative testing, it was found that the powder does not reach a predetermined heat treatment temperature (e.g., 260°C instead of the target temperature of 285°C), at least in part due to an insulating layer formed by the agglomeration of the powder placed inside the paddle dryer.

[0075] Comparative Example 5: Vibration Heat Treatment Unit In a vibration heat treatment unit, an electric current both vibrates and heats a helical tube. Powder is introduced into the bottom opening of the tube, and the vibration transports the powder inside the heated helical tube, where it is heated and exits the bottom opening of the tube. In comparative tests, it was found that the powder begins to pack inside the helix and cannot exit through the top opening.

[0076] Aspects of the invention Various illustrative aspects of the present invention can be summarized as follows: Aspect 1: A method for heat treatment of a powder of a polymorphic semicrystalline or crystallizable polymer, comprising: heating the powder contained within an interior region of the container to a temperature below the melting temperature of the highest melting crystalline form of the polymer; moving the container to move powder within the container relative to the container; The method includes:

[0077]

[0023] Aspect 2: The method of aspect 1, wherein the powder comprises a polyaryletherketone (PAEK), more preferably a polyetherketoneketone (PEKK), and most preferably a polyetherketoneketone (PEKK) having a T:I ratio of about 60:40.

[0078] Aspect 3: The method of aspect 2, wherein the powder comprises polyetherketoneketone (PEKK) and the heating step comprises heating the PEEK powder to a temperature of 230°C to 295°C or 260°C to 290°C.

[0079] Aspect 4: The method of any of Aspects 1-4, further comprising the step of laser sintering the heat-treated powder.

[0080] Aspect 5: The method of any of aspects 1-4, wherein the heating step comprises heating the powder to a temperature above the glass transition temperature (Tg) of the polymer.

[0081] Aspect 6: The method of any of aspects 1-5, further comprising either moving the powder through a sieve disposed within the container or moving a mixing element having a compact shape through the powder.

[0082] Aspect 7: The method of any of aspects 1-6, further comprising the steps of moving the powder through a sieve disposed within the container and rotating the sieve with the container.

[0083] Embodiment 8: The method of any of embodiments 1-7, further comprising rotating the container in one rotational direction about a first axis of the container.

[0084] Embodiment 9: The method of any of embodiments 1-8, further comprising rotating the container in two different rotational directions about the first axis of the container.

[0085] Aspect 10: The method of any of aspects 1-9, further comprising the steps of rotating the container in a first rotational direction about a first axis of the container, and rotating the container in a second rotational direction opposite the first rotational direction before the container reaches one rotation.

[0086] Embodiment 11: The method of any of embodiments 1-10, further comprising rotating the container about a second axis of the container that is perpendicular to the first axis.

[0087] Aspect 12: The method of aspect 11, further comprising the step of simultaneously rotating the container about the first and second axes.

[0088] Embodiment 13: The method of any of embodiments 1-12, further comprising placing the container in an oven.

[0089] Embodiment 14: The method of any of embodiments 1-13, wherein the container forms part of a rotomolding unit.

[0090] Aspect 15: The method of any of aspects 1-14, further comprising the step of removing agglomerates from an interior surface of the container during movement of the container.

[0091] Embodiment 16: An apparatus for heat treating a powder of a polymorphic semicrystalline or crystallizable polymer, comprising: a heating device for heating the powder to a temperature below the melting temperature of the highest melting crystalline form of the polymer; a container exposed to heat generated by a heating device, the container defining an interior region for containing a powder; a container movement means for moving the powder in the container relative to the container; 13. An apparatus comprising:

[0092]

[0041] Aspect 17: The apparatus of aspect 16, further comprising a sieve disposed within the container to sift the powder within the container by movement of the container.

[0093] Embodiment 18: The apparatus of embodiment 17, wherein the screen is a perforated panel.

[0094]

[0041] Aspect 19: The apparatus of any of aspects 16-18, wherein the motion means is a motor shaft configured to rotate the container, and the motor shaft is attached either directly or indirectly to the container.

[0095] Embodiment 20: The apparatus of any of embodiments 16-19, wherein the motion means is a motorized roller placed in contact with the container to rotate the container.

[0096] Embodiment 21: The apparatus of any one of embodiments 16 to 20, wherein the container is a cylindrical tube.

[0097] Embodiment 22: The apparatus of any one of embodiments 16 to 20, wherein the container is box-shaped.

[0098] Embodiment 23: The apparatus of any of embodiments 16-22, wherein the heating device is an oven and the container is placed within the oven.

[0099] Embodiment 24: The apparatus of any of embodiments 16-22, wherein the heating device is a heating element, and the heating element is connected to the container.

[0100] Embodiment 25: The apparatus of any of embodiments 16-24, wherein the apparatus is a rotational molding unit.

[0101] Embodiment 26: The apparatus of any of embodiments 16-25, further comprising a means for removing agglomerates from an interior surface of the vessel.

[0102] Although the embodiments have been described herein in a manner that enables a clear and concise specification to be written, it is contemplated, and it will be recognized that the embodiments can be variously combined or separated without departing from the invention, and for example, it will be recognized that all preferred features described herein are applicable to all aspects of the invention described herein.

[0103] Although the invention has been illustrated and described herein with reference to specific embodiments, it is not intended that the invention be limited to the details shown. Rather, various modifications in the details can be made within the spirit and range of equivalents of the claims without departing from the invention.

Claims

1. A method for heat treating a powder of a semi-crystalline or crystallizable polymer, including a polyaryletherketone (PAEK), comprising: heating the powder contained within an interior region of a container to a temperature below the melting temperature of the highest melting crystalline form of the polymer; moving the container to move the heated powder within the container relative to the container; The method includes:

2. The method of claim 1 , wherein the powder comprises polyetherketoneketone (PEKK).

3. 10. The method of claim 1, wherein the powder comprises polyetherketoneketone (PEKK) and the heating step comprises heating the powder to between 230°C and 295°C.

4. The method of any one of claims 1 to 3, wherein the heating step comprises heating the powder to a temperature above the glass transition temperature (Tg) of the polymer.

5. A method according to any one of claims 1 to 4, further comprising either a step of moving the powder through a mixing element or a step of moving a mixing element having a compact shape through the powder.

6. 6. The method of claim 1, further comprising the steps of moving the powder through a sieve disposed within the container and rotating the sieve with the container.

7. The method of any one of claims 1 to 6, further comprising rotating the container in one rotational direction about a first axis of the container.

8. The method of any one of claims 1 to 7, further comprising rotating the container in two different rotational directions about the first axis of the container.

9. 9. The method of claim 1, further comprising rotating the container in a first rotational direction about the first axis of the container, and rotating the container in a second rotational direction opposite to the first rotational direction before the container reaches one rotation.

10. The method of any one of claims 1 to 9, further comprising rotating the container about a second axis of the container that is perpendicular to the first axis.

11. The method of claim 10 further comprising the step of simultaneously rotating the container about the first and second axes.

12. The method of any one of claims 1 to 11, further comprising placing the container in an oven.

13. A method according to any one of the preceding claims, wherein the container forms part of a rotational moulding unit.

14. A method according to any preceding claim, further comprising removing agglomerates from an inner surface of the container during movement of the container.

15. An apparatus for heat treating a powder of a semi-crystalline or crystallizable polymer, including polyaryletherketone (PAEK), comprising: a heating device for heating the powder to a temperature below the melting temperature of the highest melting crystalline form of the polymer; a container exposed to heat generated by the heating device, the container defining an interior region for containing the powder; a container movement means for moving the powder in the container relative to the container; 13. An apparatus comprising:

16. 16. The apparatus of claim 15, further comprising either a sieve disposed in the container for sieving the powder in the container by movement of the container, or a mixing element having a compact shape and configured to operate independently within the container, disposed in the container for contacting the powder by movement of the container.

17. 16. The apparatus of claim 15, wherein the apparatus further comprises a sieve that is a perforated panel disposed within the container to deagglomerate the powder within the container upon movement of the container.

18. Apparatus according to any one of claims 15 to 17, wherein the movement means is a motor shaft arranged to rotate the vessel, the motor shaft being either directly or indirectly attached to the vessel.

19. An apparatus according to any one of claims 15 to 18, wherein the movement means is a motorised roller arranged in contact with the container to rotate the container.

20. The apparatus according to any one of claims 15 to 19, wherein the vessel is a cylindrical tube.

21. The device according to any one of claims 15 to 19, wherein the container is box-shaped.

22. The apparatus of any one of claims 15 to 21, wherein the heating device is an oven and the container is placed in the oven.

23. Apparatus according to any one of claims 15 to 21, wherein the heating device is a heating element, the heating element being connected to or part of the vessel.

24. Apparatus according to any one of claims 15 to 23, wherein the apparatus is a rotational moulding unit.

25. An apparatus according to any one of claims 15 to 24, further comprising means for removing agglomerates from the interior surface of the vessel.

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