Thermoplastic microparticles comprising a carboxylic acid-based sintering aid and additive manufacturing thereof

Abstract

The invention is entitled "Thermoplastic Microparticles Including Carboxylic Acid-Based Sintering Aid and Additive Manufacturing Thereof." Additive manufacturing processes featuring consolidation of thermoplastic microparticles can form printed objects in a range of shapes. Nanoparticles disposed on the outer surface of the thermoplastic microparticles can improve flow properties of the thermoplastic microparticles during additive manufacturing, but can result in excessive porosity after consolidation. Excessive porosity can be detrimental for performance applications requiring high mechanical strength. Carboxylic acid-based sintering aids, particularly metal carboxylates, can reduce porosity of consolidated parts after sintering, and substantially not increase sticking in the powder bed. A microparticle composition suitable for additive manufacturing can include: a plurality of thermoplastic microparticles including a carboxylic acid-based sintering aid admixed with a thermoplastic polymer; and a plurality of nanoparticles disposed on the outer surface of the thermoplastic microparticles.

Description

[0001] Cross-references to related applications

[0002] not applicable. Technical Field

[0003] This disclosure relates generally to additive manufacturing, and more specifically to an additive manufacturing process characterized by the consolidation of powder particles with enhanced sintering properties. Background Technology

[0004] Additive manufacturing, also known as 3D printing, is a rapidly growing technology field. While additive manufacturing has traditionally been used for rapid prototyping activities, the technology is increasingly being used to produce commercial and industrial parts (printed objects) with any number of complex shapes. Additive manufacturing processes operate by depositing layer-by-layer materials of either: 1) a molten stream of printing material or a liquid precursor of printing material, or 2) powdered microparticles of printing material. Layer-by-layer deposition is typically performed under computer control to deposit and consolidate printing material at precise locations based on a digital 3D computer-aided design model (“blueprint”) of the part to be manufactured. Powder bed fusion (PBF) of powdered microparticles is a particularly advantageous additive manufacturing method. In a specific example, the consolidation of powdered microparticles can be performed in a powder bed deposited layer-by-layer using a 3D printing system that employs a laser or electron beam to heat precise locations in the powder bed, thereby consolidating specific powdered microparticles to form a part with a predetermined shape. Selective laser sintering (SLS) represents a specific example of a process suitable for promoting localized consolidation of powdered microparticles during powder bed fusion to form a part of the desired shape. Other similar particulate bonding techniques include, for example, electron beam melting (EBM), binder spraying, and multi-jet melting (MJF).

[0005] Among these powder particles, those containing thermoplastic polymers are suitable for 3D printing. While a wide range of thermoplastic polymers are known, relatively few possess properties compatible with current 3D printing techniques employing particle consolidation. Suitable thermoplastic polymers for particle consolidation to form parts include those exhibiting a significant difference between melt initiation and crystallization initiation, which promotes good structural and mechanical integrity, followed by directional heating to further facilitate particle consolidation. The ready-to-use formation of the deposited particles is another important consideration.

[0006] To achieve satisfactory printing performance, thermoplastic microparticles need to maintain good flow properties in the solid state. Flow properties can be assessed, for example, by measuring the fraction of thermoplastic microparticles in a sample that can pass through a standard sieve of a specified size and / or by measuring the angle of repose. A high fraction of sieveable thermoplastic microparticles indicates that the microparticles exist as essentially single, non-agglomerated particles, which is characteristic of ready-to-use powder flow. In contrast, a lower angle of repose is characteristic of ready-to-use powder flow. A relatively narrow particle size distribution and regularity of particle shape in the sample also contribute to good powder flow properties. To further promote good powder flow properties, it may also be desirable to have virtually no fine microparticles.

[0007] Thermoplastic microparticles are typically obtained commercially through cryogenic milling or precipitation processes, which can result in irregular particle shapes and wide particle size distributions. During the 3D printing process, these irregular particle shapes and wide particle size distributions can lead to poor powder flow properties and the formation of numerous voids. Poor powder flow properties can be addressed to some extent by dry mixing with fillers and flow aids, but these additives may have limited effectiveness for softer polymer materials such as elastomers due to particle aggregation.

[0008] Void formation can be more difficult to address. The significant void formation during particle consolidation can substantially reduce the final material strength of the printed object compared to the material strength achievable otherwise through casting or machining of the same thermoplastic polymer. Therefore, it may be desirable to achieve good flow properties once the thermoplastic particles have liquefied to facilitate good particle consolidation. Powder bed fusion and similar particle consolidation processes performed without external pressure, without theoretical constraints, may restrict the flow of liquefied thermoplastic polymers and lead to void formation, especially when consolidating powder particles with suboptimal dimensions and / or shape profiles.

[0009] Thermoplastic microparticles can also be formed via melt emulsification processes, such as those described in U.S. Patent 4,863,646, the entire contents of which are incorporated herein by reference. In a melt emulsification process, a thermoplastic polymer is dispersed in a carrier fluid as liquefied droplets in which the polymer has no solubility or only minimal solubility above its melting point or softening temperature. By cooling the liquefied droplets below their melting point or softening temperature, thermoplastic microparticles with a substantially spherical shape but a wide particle size distribution can be formed. Therefore, thermoplastic microparticles remain unsuitable for 3D printing processes.

[0010] The particle size distribution of thermoplastic microparticles formed during melt emulsification can be significantly reduced by incorporating multiple nanoparticles into a carrier fluid, as described in U.S. Patent Application 16 / 946,622, filed June 30, 2020, which is incorporated herein by reference. Thermoplastic microparticles formed in this manner are characterized by at least partially coating the surface of the microparticles with nanoparticles, wherein the nanoparticles are robustly adhered to and / or embedded in the microparticle surface. Adhered / embedded nanoparticles promote significantly better powder flow properties compared to those obtained when a flow aid is dry-mixed with uncoated thermoplastic microparticles. The narrow particle size distribution of thermoplastic microparticles with a nanoparticle coating allows for ready-to-use sintering, which in many cases achieves manageable amounts of void formation. While satisfactory in many cases, the nanoparticle coating may restrict robust aggregation between thermoplastic microparticles and result in porosity values ​​that may be higher than desired. Without being theoretically constrained, these problems may arise from increased surface viscosity and reduced polymer-polymer cohesion due to the presence of nanoparticles. While the mechanical strength of printed objects formed by microparticle consolidation of nanoparticle-coated thermoplastic microparticles may be sufficient in many cases, and when consolidating uncoated thermoplastic microparticles, this limited mechanical strength may not meet the performance requirements of some applications that demand particularly high structural integrity. Summary of the Invention

[0011] This disclosure provides a particulate composition suitable for additive manufacturing. The particulate composition comprises: a plurality of thermoplastic microparticles, the plurality of thermoplastic microparticles comprising a carboxylic acid-based sintering aid incorporated with a thermoplastic polymer; and a plurality of nanoparticles disposed on the outer surface of the thermoplastic microparticles.

[0012] This disclosure also provides a method for forming a solidified part using a particulate composition. The method includes: providing the particulate composition of this disclosure; depositing the particulate composition layer by layer in a powder bed; and heating a portion of the powder bed to solidify a portion of the thermoplastic particulates into a solidified part having a specific shape.

[0013] The solidified component of this disclosure formed according to the above may include a thermoplastic matrix formed by the solidification of thermoplastic microparticles, and nanoparticles and a carboxylic acid-based sintering aid incorporated with the thermoplastic matrix.

[0014] This disclosure also provides a method for forming a particulate composition suitable for additive manufacturing. The method includes: combining a thermoplastic polymer, nanoparticles, and a carboxylic acid-based sintering aid with a carrier fluid at a heating temperature at or above the melting point or softening temperature of the thermoplastic polymer; wherein the thermoplastic polymer and the carrier fluid are substantially immiscible at the heating temperature; applying sufficient shear at the heating temperature in the presence of the nanoparticles and the carboxylic acid-based sintering aid to disperse the thermoplastic polymer in the carrier fluid into liquefied droplets; after the formation of the liquefied droplets, cooling the carrier fluid to a temperature at which at least a solidified thermoplastic microparticles are formed, these thermoplastic microparticles comprising at least a portion of the thermoplastic polymer, at least a portion of the nanoparticles, and at least a portion of the sintering aid; wherein at least a majority of the nanoparticles are disposed on the outer surface of the thermoplastic microparticles; and separating the thermoplastic microparticles from the carrier fluid. Attached Figure Description

[0015] The accompanying drawings are included to illustrate certain aspects of this disclosure and should not be considered as exclusive embodiments. As will be apparent to those skilled in the art who benefit from this disclosure, the disclosed subject matter is capable of considerable modifications, alterations, combinations, and equivalents in form and function.

[0016] Figure 1 This is a flowchart of a non-limiting example method for producing thermoplastic microparticles according to this disclosure.

[0017] Figure 2A and Figure 2B Optical images of the polyurethane microparticles of Comparative Example 2 after laser sintering at 30% and 45% laser power, a scan rate of 40,000, and a temperature of 108°C are shown. Figure 3A and Figure 3B An optical image of the polyurethane microparticles of Example 4 after laser sintering under the same conditions as Comparative Example 2 is shown.

[0018] Figure 4 This is a graph showing the softening temperature of thermoplastic polyurethane microparticles containing various loadings of zinc stearate sintering aid.

[0019] Figure 5A and Figure 5B Optical images of the polyester microparticles of Comparative Example 1 after laser sintering at 30% and 45% laser power, a scan rate of 40,000, and a temperature of 115°C are shown. Figure 6A and Figure 6B An optical image of the polyester microparticles of Example 1 after laser sintering under the same conditions as Comparative Example 1 is shown. Figure 7A and Figure 7B An optical image of the polyester microparticles of Example 2 after laser sintering under the same conditions as Comparative Example 1 is shown. Figure 8A and Figure 8BOptical images of the polyester microparticles of Example 3 after laser sintering are shown, under the same conditions as Comparative Example 1 (except at 25% and 35% laser power, respectively).

[0020] Figures 9A to 9C Hot stage micrographs of the polyester microparticles of Comparative Example 1 at various temperatures are shown.

[0021] Figures 10A to 10C The following are hot-stage micrographs of the polyester microparticles of Example 2 at various temperatures. Detailed Implementation

[0022] This disclosure relates generally to additive manufacturing, and more specifically to an additive manufacturing process characterized by the consolidation of powder particles with enhanced sintering properties.

[0023] As mentioned above, thermoplastic microparticles containing thermoplastic polymers are suitable for 3D printing processes, particularly those employing selective laser sintering to consolidate a powder bed at specific locations to form parts with predetermined shapes. Currently, commercially available thermoplastic microparticles with irregular shapes and / or wide particle size distributions are available, which can lead to poor flow properties and / or incomplete particle consolidation during printing. A melt emulsification process using nanoparticles during thermoplastic microparticle formation yields thermoplastic microparticles with high sphericity and narrow particle size distribution. Nanoparticle-coated thermoplastic microparticles can undergo ready-to-use sintering to form consolidated parts with manageable porosity formation, providing sufficient mechanical strength for many applications.

[0024] For performance applications requiring exceptionally high structural integrity, it may be desirable to increase the degree of microparticle consolidation. In the case of nanoparticle-coated thermoplastic microparticles, improved microparticle consolidation and reduced void formation can be achieved to some extent by reducing the nanoparticle loading. However, the optimization window for achieving improved microparticle consolidation in this way can be quite limited, because if the nanoparticle loading becomes too low, poor powder flow properties may result, and high void volume and part defects may recur after microparticle consolidation. Therefore, when consolidating thermoplastic powder microparticles, it can be difficult to strike a balance between sufficient powder flow properties and good liquid flow properties.

[0025] This disclosure confirms that sintering aids, particularly carboxylic acid-based sintering aids with sufficiently low melting points, can be effectively incorporated into and integrated into the thermoplastic matrix defining the thermoplastic microparticles formed therefrom during melt emulsification. Surprisingly, the effect of carboxylic acid-based sintering aids on the particle size and particle size distribution of the thermoplastic microparticles formed by melt emulsification is negligible in the presence of nanoparticles. Suitable carboxylic acid-based sintering aids may include various low-melting-point metal carboxylates formed from fatty acids or dicarboxylic acids, as discussed in further detail below. In some cases, the corresponding free carboxylic acid may also constitute a suitable carboxylic acid-based sintering aid, and the corresponding free carboxylic acid may be appropriately used if a particular metal carboxylate is unavailable or has an excessively high melting point. Suitable carboxylic acid-based sintering aids, including metal carboxylates formed from free carboxylic acids, can be selected such that the melting point is high enough to avoid particle aggregation during sintering, but low enough to be below the sintering temperature used. The melting point of the carboxylic acid-based sintering aid may also be higher than the temperature at which the melt emulsification of thermoplastic microparticles occurs. Carboxylic acid-based sintering aids allow the sintering of thermoplastic microparticles to occur at lower temperatures and with lower laser powers than would otherwise be possible. Suitable carboxylic acid-based sintering aids can also reduce the porosity of solidified parts formed from thermoplastic microparticles, such as by reducing surface viscosity and promoting polymer-polymer cohesion, thus providing a pathway to obtaining performance parts with high structural integrity requirements. Under certain conditions, carboxylic acid-based sintering aids can allow the thermoplastic microparticles to undergo substantially complete fusion (rather than leaving a discernible microparticle structure after solidification), thus providing a pathway to obtaining parts with minimal porosity and / or a glossy surface. Therefore, this disclosure significantly broadens the scope of applications for nanoparticle-coated thermoplastic microparticles to be effectively used to form a wide variety of types of solidified parts. Suitable nanoparticles that can be used with metal carboxylate sintering aids are discussed in further detail below. The solidification of thermoplastic microparticles without nanoparticle coatings can be similarly enhanced by implementing the methods disclosed herein.

[0026] Agglomeration refers to the tendency of powder particles in a heated powder bed to stick together, even in locations where no additional energy input is provided to promote the consolidation of specific powder particles. Agglomeration can be a problem and limit the ability to form solidified parts of a specific shape using thermoplastic microparticles. Surprisingly, the carboxylic acid-based sintering aids disclosed herein promote little or no agglomeration when the thermoplastic microparticles of this disclosure are deposited in a heated powder bed.

[0027] In another surprising result, nanoparticles can be pre-coated with carboxylic acid-based sintering aids, particularly metal carboxylates formed from fatty acids, to achieve additional advantages during the melt emulsion formation of thermoplastic microparticles. For example, metal carboxylate sintering aids (e.g., zinc stearate) can be pre-coated onto silica nanoparticles via roller milling and then used to form thermoplastic microparticles with a narrower particle size distribution than that obtained when nanoparticles and metal carboxylates are combined alone in a melt emulsion medium (carrier fluid).

[0028] Except as modified in the following paragraphs, the terms used in this specification and claims have their ordinary and common meanings.

[0029] As used herein, the term "thermoplastic polymer" refers to a polymeric material that reversibly softens and hardens when heated and cooled above a specified temperature (e.g., melting point, softening point, glass transition temperature, etc.). Thermoplastic polymers encompass both elastomeric thermoplastic polymers and nonelastomeric thermoplastic polymers.

[0030] As used in this article, the term "nanoparticle" refers to particulate materials with a particle size ranging from about 1 nm to about 500 nm.

[0031] As used herein, the term "oxide" refers to both metal oxides and non-metal oxides. For the purposes of this disclosure, silicon is considered a metal.

[0032] As used herein, the term “oxide nanoparticles” refers to particulate materials with a particle size in the range of about 1 nm to about 500 nm and containing metal oxides or non-metal oxides.

[0033] As used herein, the term “association” refers to chemical bonding, physical blending with a matrix, or physical adhesion to a surface.

[0034] As used herein, related terms such as “admixture” and “admixture” refer to the dissolution of a first substance in a second substance or the dispersion of a first substance as a solid in a second substance, wherein the dispersion may be homogeneous or non-homogeneous. An admixture encompasses the blending of two substances in such a way that the first substance is at least partially located within the interior of the second substance. Therefore, blending methods for obtaining an admixture can be distinguished from methods that merely place the first substance on the surface of the second substance, such as those that may occur during dry mixing.

[0035] As used in this article, the term "D" 10 "D" refers to a diameter in which 10% of the sample (unless otherwise specified, on a volume basis) consists of particles with a diameter smaller than said diameter value. As used herein, the term "D" is... 50"" refers to a diameter in which 50% of the sample (unless otherwise specified, on a volume basis) consists of particles with a diameter smaller than the stated diameter value. 50 It can also be called "average particle size". As used in this article, the term "D" 90 "" refers to a diameter in which 90% of the sample (unless otherwise specified, on a volume basis) consists of particles with a diameter smaller than the stated diameter value.

[0036] As used herein, the terms “diameter span” and “span” and “span size” provide an indication of the width of the grain size distribution and are expressed in terms of (D... 90 -D 10 ) / D 50 Calculations (unless otherwise specified, each D value is based on volume).

[0037] As used in this article, the term "shear" refers to stirring or a similar process that causes mechanical agitation in a fluid.

[0038] As used herein, the term “embedded” in relation to nanoparticles and thermoplastic microparticle surfaces means that the nanoparticles extend at least partially into the surface such that the polymer contacts the nanoparticles to a greater extent than would occur if the nanoparticles were simply laid on the surface, thus making tangential contact with the surface.

[0039] As used herein, the terms "roundness" and "sphericity" refer to the degree to which a particle or particles approximate a perfect sphere. To determine roundness, an optical microscopic image of the particle is taken. The perimeter (P) and area (A) of the particle in the plane of the microscopic image are calculated (e.g., using a SYSMEX FPIA 3000 particle shape and size analyzer, available from Malvern Instruments). The roundness of the particle is C. EA / P, where C EA It is the circumference of a circle whose area is equal to the area (A) of the actual particle.

[0040] As used herein, unless otherwise specified, the viscosity of the fluid is the kinematic viscosity at 25°C, and unless otherwise specified, it is measured according to ASTM D445-19.

[0041] As used herein, the term "carboxylic acid-based" refers to both free carboxylic acid and metal carboxylates. For the purposes of this disclosure, ammonia-based cations are considered metals.

[0042] Unless otherwise specified, the melting points of the thermoplastic polymers described herein are determined by ASTM E794-06 (2018) at a ramp rate and cooling rate of 10 °C / min.

[0043] Unless otherwise specified, the softening temperature or softening point of the thermoplastic polymers described herein shall be determined according to ASTM D6090-17. The softening temperature may be measured using a cup-ball apparatus, available from Mettler-Toledo, with a 0.50 g sample and a heating rate of 1 °C / min.

[0044] The particulate composition disclosed herein may comprise: a plurality of thermoplastic microparticles comprising a carboxylic acid-based sintering aid incorporated with a thermoplastic polymer; and a plurality of nanoparticles disposed on the outer surface of the thermoplastic microparticles. The carboxylic acid-based sintering aid may be blended with the thermoplastic polymer in such a way that the thermoplastic matrix defining the thermoplastic microparticles comprises the carboxylic acid-based sintering aid, and optionally, the carboxylic acid-based sintering aid is located on the exterior of the thermoplastic microparticles. Therefore, a carboxylic acid-based sintering aid dry-mixed with pre-formed thermoplastic microparticles is not considered to be incorporated with the thermoplastic microparticles disclosed herein, because the carboxylic acid-based sintering aid does not penetrate the interior portion of the thermoplastic microparticles during dry mixing.

[0045] Multiple nanoparticles may include oxide nanoparticles, carbon black, or any combination thereof. Oxide nanoparticles suitable for this disclosure may include, for example, silica nanoparticles, titanium dioxide nanoparticles, zirconium oxide nanoparticles, alumina nanoparticles, iron oxide nanoparticles, copper oxide nanoparticles, tin oxide nanoparticles, boron oxide nanoparticles, cerium oxide nanoparticles, thallium oxide nanoparticles, tungsten oxide nanoparticles, or any combination thereof. Mixed oxides formed as nanoparticles (such as aluminosilicates, borosilicates, and aluminoborosilicates) are also covered by the term "oxide" and may be applicable to the disclosure herein. The oxide nanoparticles may be hydrophilic or hydrophobic, which may be natural to the nanoparticles or produced by surface treatments of the nanoparticles. For example, silica nanoparticles with hydrophobic surface treatments (such as dimethylsilyl, trimethylsilyl, etc.) can be formed by reacting hydrophilic surface hydroxyl groups with suitable functionalizing agents. Hydrophobic functionalized oxide nanoparticles may be particularly desirable in the methods and compositions of this disclosure, but non-functionalized oxide nanoparticles or hydrophilically modified oxide nanoparticles may also be applicable. For example, hydrophobic functionalized oxide nanoparticles are particularly compatible with hydrophobic fluids used in melt emulsification processes.

[0046] Silica nanoparticles (particularly pyrolytic silica nanoparticles with hydrophobic functionalization) may be particularly suitable for the disclosure herein, as a variety of functionalized silicas are available, with varying types and sizes of hydrophobic functionalization. Silazane and silane hydrophobic functionalization are convenient hydrophobic functionalizations that can be used in this disclosure. Therefore, the nanoparticles used in the disclosure herein may include or consist substantially of silica nanoparticles (particularly hydrophobically functionalized silica nanoparticles). Silica nanoparticles may be used in combination with another type of oxide or non-oxide nanoparticles, wherein the other type of oxide or non-oxide nanoparticles can deliver specific properties to thermoplastic microparticles or solidified bodies formed from thermoplastic microparticles that are not obtainable when silica nanoparticles are used alone.

[0047] Compared to unfunctionalized silica nanoparticles, hydrophobic functionalization makes silica nanoparticles less compatible with water. Desiredly, hydrophobic functionalization can improve the dispersion of silica nanoparticles in highly hydrophobic carrier fluids used in melt emulsions. Suitable hydrophobic functionalization can be non-covalently or covalently attached to the surface of silica nanoparticles. Covalent attachment can be achieved, for example, through the functionalization of surface hydroxyl groups on the surface of silica nanoparticles. In a non-limiting example, hexamethyldisilazane can be used to treat silica nanoparticles to provide hydrophobically modified covalent attachments. Commercially available hydrophobically functionalized silica nanoparticles include, for example, Aerosil RX50 (Evonik, average particle size = 40 nm) and Aerosil R812S (Evonik, average particle size = 7 nm).

[0048] Carbon black is another type of nanoparticle that can be present on thermoplastic microparticles as disclosed herein. Various grades of carbon black are familiar to those skilled in the art, and any of these grades is applicable to the disclosure herein. In some cases, carbon black, silica, and other types of oxide nanoparticles may be present in combination with each other.

[0049] Polymer nanoparticles are another type of nanoparticle that may be present on the thermoplastic microparticles disclosed herein. Suitable polymer nanoparticles may comprise one or more thermosetting and / or crosslinked polymers such that they do not melt when processed according to the disclosure herein by melt emulsification or similar microparticle forming techniques. Nanoparticles comprising high molecular weight thermoplastic polymers having appropriately high melting or decomposition points can similarly be used to facilitate microparticle formation as disclosed herein.

[0050] The loading amount and particle size of silica nanoparticles or other types of nanoparticles on thermoplastic microparticles can vary within a wide range as disclosed herein. The loading amount of silica nanoparticles or similar types of nanoparticles can depend on the concentration of nanoparticles in the carrier fluid used to promote the formation of the thermoplastic microparticles, as further described below. In a non-limiting example, the concentration of nanoparticles in the carrier fluid can range from about 0.01 wt% to about 10 wt%, or about 0.05 wt% to about 10 wt%, or about 0.05 wt% to about 5 wt%, or about 0.1 wt% to about 2 wt%, or about 0.25 wt% to about 1.5 wt%, or about 0.2 wt% to about 1.0 wt%, or about 0.25 wt% to about 1 wt%, or about 0.25 wt% to about 0.5 wt%. The particle size of the nanoparticles can range from about 1 nm to about 100 nm, but particle sizes up to about 500 nm are also acceptable. In non-limiting examples, the particle size of the silica nanoparticles can be in the range of about 5 nm to about 75 nm, or about 5 nm to about 50 nm, or about 5 nm to about 10 nm, or about 10 nm to about 20 nm, or about 20 nm to about 30 nm, or about 30 nm to about 40 nm, or about 40 nm to about 50 nm, or about 50 nm to about 60 nm. The nanoparticles, particularly silica nanoparticles and similar oxide nanoparticles, can have a particle size of about 10 nm. 2 / g to approximately 500m 2 / g, or approximately 10m 2 / g to approximately 150m 2 / g, or approximately 25m 2 / g to approximately 100m 2 / g, or approximately 100m 2 / g to approximately 250m 2 / g, or approximately 250m 2 / g to approximately 500m 2 / g of BET surface area.

[0051] Specific examples of oxide nanoparticles suitable for use in the disclosure herein include those treated, for example, with alkylsilanes (such as hexamethyldisilazane (HMDS), dimethyldichlorosilane) or other long-chain alkylsilanes (such as decyltriethoxysilane or octyltriethoxysilane). Suitable oxide nanoparticles can vary in size from about 7 nm to about 130 nm. Specific commercial examples of hydrophobically treated silica, their particle sizes, and their hydrophobic treatment include Wacker. H13TD (16nm, PDMS) H13TM (16nm, HMDS) H13TX (16nm, HMDS / PDMS) H20TD (12nm, PDMS) H2O™ (12nm, HMDS) H20TX (12nm, HMDS / PDMS), H30TD (8nm, PDMS) H30™ (8nm, HMDS) H30TX (8nm, HMDS / PDMS) H3004 (12nm, HMDS) HO5TD (40nm, PDMS), HO5TM (40nm, HMDS), HO5TX (40nm, HMDS / PDMS); Evonik R972 (16nm, DDS), RY200S (16nm, PDMS, BET surface area = 200m²) 2 / g), R202 (16nm, PDMS), R974 (12nm, DDS), RY200 (12nm, PDMS), RX200 (12nm, HMDS), R8200 (12nm, HMDS), R805 (12nm, alkylsilane), R104 (12nm, alkylsilane), RX300 (7nm, HMDS), R812 (7nm, HMDS), R812S (7nm, HMDS, BET surface area = 300m²) 2 g), R106 (7nm, alkylsilane), NY50 (30nm, PDMS), NAX50 (30nm, HMDS), RY50 (40nm, PDMS) and RX50 (40nm, HMDS); Cabot TS530 (8nm, HMDS); and Shin-Etsu sol-gel silica X24-9163A (110nm, HMDS, BET surface area = 25m²). 2 / g) and X24-9600A-80 (80nm, HMDS, BET=40m) 2 / g).

[0052] Suitable oxide nanoparticles may also contain processing agents, including bases or alkali salts. Specific commercial examples of such processed oxide nanoparticles, their particle sizes, and their processing methods include the following: Wacker processed silica. H13TA (16nm, PDMS-NR2 / NR3) + ), H30TA (8nm, PDMS-NR2 / NR3) + ), H2015EP (12nm, PDMS-NR2 / NR3) + ), H2050EP (10nm, PDMS-NR2 / NR3) + ), H2150VP (10nm, PDMS-NR2 / NR3) + )and H3050VP (8nm, PDMS-NR2 / NR3) + ).

[0053] Other suitable oxide nanoparticles (including both their treated and untreated variants) include titanates. Suitable titanates may include, for example, CaTiO3, BaTiO3, MgTiO3, MnTiO3, SrTiO3, and Al2TiO5.

[0054] Other suitable options are treated or untreated alumina. Specific commercial examples of alumina, their particle sizes, and their treatments include, for example, Evonik C805 (13 nm, octylsilane), alumina C (13 nm, untreated), Aeroxide Alu C 100 (10 nm, untreated), Aeroxide Alu C 130 (13 nm, untreated); Cabot SpectrAL 81 (21 nm, untreated) and Cabot SpectrAl 100 (18 nm, untreated).

[0055] Other suitable oxides include treated or untreated titanium dioxide. Examples of suitable commercial titanium dioxide include: JMT-150IB with a volume average particle size of 15 nm from Tayca Corp.; JMT2000 with a particle size of 15 × 15 × 40 nm from Tayca Corp.; T805 with a volume average particle size of approximately 21 nm from Evonik; SMT5103 with a particle size of approximately 40 nm from Tayca Corp.; and STT-100H with an average particle size of approximately 40 nm from Inabata America Corporation.

[0056] Based on turbidity measurements, approximately 80% to 90% of the available nanoparticles, such as silica nanoparticles, can be associated with thermoplastic microparticles formed through melt emulsification according to the disclosure herein. Since the nanoparticle loading is measured relative to the thermoplastic polymer, the amount of nanoparticles associated with the thermoplastic microparticles can be approximately 80% to 90% of the nanoparticle loading used when forming the elastomeric microparticles. For higher or lower nanoparticle loadings in the carrier fluid, more or less nanoparticles can be associated with the thermoplastic microparticles.

[0057] The thermoplastic microparticles of this disclosure may have nanoparticles at least partially embedded in the outer surface of the thermoplastic microparticles. When embedding occurs, a portion of the nanoparticle structure may be located in pits or depressions in the outer surface, making it more difficult to remove the nanoparticles from the surface. It should be understood that even when no substantial embedding occurs, appropriately functionalized nanoparticles (such as hydrophobically functionalized silica nanoparticles) may non-covalently associate (e.g., using van der Waals interactions) to promote retention of the nanoparticles on the outer surface.

[0058] Examples of thermoplastic polymers suitable for use in the disclosure herein include, but are not limited to: polyamides (e.g., nylon-6, nylon-12, etc.), polyurethanes, polyethylene, polypropylene, polyacetals, polycarbonates, polyethylene terephthalate or polybutylene terephthalate, glycol-modified polyethylene terephthalate or polybutylene terephthalate, polystyrene, polyvinyl chloride, polytetrafluoroethylene, polylactic acid and other polyesters, polyethers, polyethersulfones, polyetheretherketones, polyacrylates, polymethacrylates, polyimides, acrylonitrile butadiene styrene (ABS), polyphenylene sulfide, vinyl polymers, polyaryl ethers, polyaryl sulfides, polyetherketones, polyaryl etherketones (PAEK), polyamide-imides, polyetherimides, polyether esters, copolymers comprising polyether blocks and polyamide blocks (PEBA or polyether block amides), grafted or ungrafted thermoplastics This disclosure includes polyolefins, functionalized or unfunctionalized ethylene / vinyl monomer polymers, functionalized or unfunctionalized ethylene / (meth)acrylate alkyl esters, functionalized or unfunctionalized (meth)acrylate polymers, functionalized or unfunctionalized ethylene / vinyl monomer / (meth)acrylate alkyl ester terpolymers, ethylene / vinyl monomer / carbonyl terpolymers, ethylene / (meth)acrylate alkyl ester / carbonyl terpolymers, methyl methacrylate-butadiene-styrene (MBS) type core-shell polymers, polystyrene-block-polybutadiene-block-poly(methyl methacrylate) (SBM) block terpolymers, chlorinated or chlorosulfonated polyethylene, polyvinylidene fluoride (PVDF), phenolic resins, poly(ethylene / vinyl acetate), polybutadiene, polyisoprene, styrene-based block copolymers, polyacrylonitrile, organosilicon, etc., and any combination thereof. Copolymers containing one or more of the foregoing substances may also be used in this disclosure. Any of the aforementioned polymers may be thermoplastic elastomers and contain crystalline "hard" segments and amorphous "soft" segments.

[0059] Particularly suitable examples of thermoplastic polymers used in the disclosure herein may include polyamides such as nylon 6 or nylon 12; acrylonitrile butadiene styrene; polylactic acid; polyurethane; poly(arylene ether); polyarylene ether ketone; polycarbonate; polyimide; polyphenylene sulfide; poly(arylene sulfone); polyesters such as polyethylene terephthalate or polybutylene terephthalate or their diol-modified variants; and any combination thereof.

[0060] More specific examples of suitable polyamides include, but are not limited to: polycaprolactam (nylon 6, polyamide 6, or PA6), poly(hexamethylene succinyl diamine) (nylon 46, polyamide 46, or PA46), polyhexamethylene adipamide (nylon 66, polyamide 66, or PA66), polypentyl hexamethylene adipamide (nylon 56, polyamide 56, or PA56), polyhexamethylene sebacate (nylon 610, polyamide 610, or PA610), polyundecanoamide (nylon 11, polyamide 11, or PA11), polydodecanoamide (nylon 12, polyamide 12, or PA12), and poly(hexamethylene terephthalamide) (nylon 6T, polyamide 6T, or PA6). Nylon 10.10 (polyamide 10.10 or PA 10.10), Nylon 10.12 (polyamide 10.12 or PA 10.12), Nylon 10.14 (polyamide 10.14 or PA 10.14), Nylon 10.18 (polyamide 10.18 or PA 10.18), Nylon 6.10 (polyamide 6.10 or PA 6.10), Nylon 6.18 (polyamide 6.18 or PA 6.18), Nylon 6.12 (polyamide 6.12 or PA 6.12), Nylon 6.14 (polyamide 6.14 or PA 6.14), semi-aromatic polyamides, and any combination thereof. Copolyamides may also be used. Examples of suitable copolyamides include, but are not limited to, PA11 / 10.10, PA 6 / 11, PA 6.6 / 6, PA 11 / 12, PA 10.10 / 10.12, PA 10.10 / 10.14, PA 11 / 10.36, PA 11 / 6.36, PA 10.10 / 10.36, and any combination thereof. Polyesteramides, polyether esteramides, polycarbonate-esteramides, and polyether-block amides may also be used in this disclosure, any of which may be elastomers.

[0061] Examples of suitable polyurethanes include, but are not limited to, polyether polyurethanes, polyester polyurethanes, blends of polyether and polyester polyurethanes, and any combination thereof. Suitable polyurethanes may include elastomeric polyurethanes prepared by the condensation of isocyanates, polyols, and chain extenders, wherein the polyol imparts flexibility to the polymer chain and typically constitutes the soft segment. Examples of suitable polyurethanes used in this disclosure include, but are not limited to: poly[4,4'-methylenebis(phenyl isocyanate)-alternating-1,4-butanediol / di(propylene glycol) / polycaprolactone], 1190A (polyether polyurethane elastomer, purchased from BASF) and any combination thereof.

[0062] Suitable polyesters are products of condensation reactions between diacids and diols, or products of self-condensation reactions of hydroxy acids such as lactic acid. Diol-modified polyesters (such as diol-modified polyethylene terephthalate or diol-modified polybutylene terephthalate) are particularly suitable for use in combination with carboxylic acid-based sintering aids as disclosed herein. Diol modification can impart desired beneficial effects, such as optical transparency and flexibility of the polymer chains.

[0063] Suitable thermoplastic polymers can be elastomers or non-elastomeric. Some of the aforementioned examples of thermoplastic polymers can be elastomers or non-elastomeric, depending on the specific composition of the polymer. For example, polyethylene, as a copolymer of ethylene and propylene, can be elastomer and is not dependent on the amount of propylene present in the polymer. HYTREL HTR 6108 is a suitable example of glycol-modified polyethylene terephthalate.

[0064] The thermoplastic elastomers applicable to the disclosure herein generally fall into one of six categories: styrene-based block copolymers, thermoplastic polyolefin elastomers, thermoplastic vulcanizates (also known as elastomer alloys), thermoplastic polyurethanes, thermoplastic copolyesters, and thermoplastic polyamides (typically block copolymers containing polyamides). Specific examples of thermoplastic elastomers can be found in the following literature: Handbook of Thermoplastic Elastomers, 2nd edition, edited by BMWalker and C.P. Rader, Van Nostrand Reinhold, New York, 1988. Examples of suitable elastomeric thermoplastic polymers include, but are not limited to: elastomeric polyamides, polyurethanes, copolymers containing polyether blocks and polyamide blocks (PEBA or polyether block amides), methyl methacrylate-butadiene-styrene (MBS) type core-shell polymers, polystyrene-block-polybutadiene-block-poly(methyl methacrylate) (SBM) block terpolymers, polybutadiene, polyisoprene, styrene-based block copolymers, and polyacrylonitrile, silicone, etc. Elastomeric styrene-based block copolymers may contain at least one block selected from: isoprene, isobutylene, butene, ethylene / butene, ethylene-propylene, and ethylene-ethylene / propylene. More specific examples of styrene-based elastomeric block copolymers include, but are not limited to, poly(styrene-ethylene / butene), poly(styrene-ethylene / butene-styrene), poly(styrene-ethylene / propylene), poly(styrene-ethylene / propylene-styrene), poly(styrene-ethylene / propylene-styrene-ethylene-propylene), poly(styrene-butadiene-styrene), poly(styrene-butene-butadiene-styrene), and any combination thereof.

[0065] Any carboxylic acid or its salt that facilitates the sintering of thermoplastic particles by reducing post-sintering porosity, increasing particle fusion, and / or by lowering the sintering temperature can be effectively used as a carboxylic acid-based sintering aid as disclosed herein. Suitable carboxylic acid-based sintering aids can achieve the above objectives while producing little or no agglomeration in the heated powder bed. In some cases, ammonium salts (including tetraalkylammonium compounds) can be used as alternative sintering aids.

[0066] Particularly suitable carboxylic acid-based sintering aids (such as metal carboxylates) may have melting points of about 60°C or higher, or about 90°C or higher, such as about 60°C to about 300°C, or about 90°C to about 300°C, or about 150°C to about 300°C, or about 200°C to about 300°C, making them compatible with the particle deposition and consolidation conditions used to form consolidated parts during 3D printing. The carboxylic acid-based sintering aids may be selected such that they have a lower melting point than the thermoplastic polymer constituting the thermoplastic particles. Alternatively, the carboxylic acid-based sintering aids may have a melting point lower than the sintering temperature used to promote the consolidation of the thermoplastic particles, particularly when the sintering temperature is below the melting point of the thermoplastic polymer. If the melting point of the carboxylic acid-based sintering aid is too low, adhesion may occur during particle consolidation, especially for carboxylic acid-based sintering aids deposited on the surface of the thermoplastic particles. More preferably, suitable carboxylic acid-based sintering aids, such as metal carboxylates, can melt under melt emulsification conditions used to form thermoplastic microparticles, such as in a temperature range of about 200°C to about 300°C or about 200°C to about 250°C. Therefore, particularly suitable carboxylic acid-based sintering aids, such as metal carboxylates, may have melting points in the range of about 60°C to about 300°C, or about 90°C to about 300°C, or about 90°C to about 250°C, or about 90°C to about 200°C.

[0067] Suitable carboxylic acids or their metal carboxylates used in the disclosure herein may be aliphatic or aromatic, straight-chain or branched, cyclic or acyclic, saturated or unsaturated, or any combination thereof. Suitable metal carboxylates may include at least one salt selected from metal monocarboxylates, metal dicarboxylates, and any combination thereof. Metal monocarboxylates or metal dicarboxylates may contain monovalent metal cations, divalent metal cations, trivalent metal cations, or mixed metal salts containing any of the monovalent, divalent, or trivalent metal cations. Particularly suitable examples of metal carboxylate sintering aids may contain divalent or trivalent metal cations. More specific examples of suitable metal carboxylates are as follows.

[0068] Metal carboxylates comprise a metal cation component and an anionic component, the anionic component comprising a carboxylate group attached to a hydrocarbon moiety. Metal carboxylates can be formed by a reaction between a base and a carboxylic acid, wherein the metal cation component is derived from the base and the anionic component is derived from the carboxylic acid. Cation exchange can be performed to introduce a metal cation component that is not readily introduced with a base. Suitable metal cation components may include alkali metal cations, alkaline earth metal cations, transition metal cations, main group metal cations, lanthanide metal cations, or any combination thereof. The selection of a specific metal cation component for a particular carboxylate group can be chosen to provide a melting point within a suitable range for the metal carboxylate, as specified above. For example, if an alkali metal salt of a particular carboxylate group produces an excessively high melting point, a lower melting point can be achieved by using a different salt form of the carboxylate, such as an alkaline earth metal cation form or a transition metal cation form. While the melting points of many metal carboxylates are known, many are unknown or have not yet been reported in the literature. However, it should be understood that melting points can be readily determined, and those skilled in the art will be able to select a suitable metal carboxylate for a given application that benefits from this disclosure. Both the metal cation component and the carboxylate moiety can be varied to achieve suitability for a given application.

[0069] Alkali metal cations may include Li, Na, K, Rb, and Cs cations. Alkali metal cations may be selected as the metal cation component of any metal carboxylate disclosed herein, provided that the melting point of the metal carboxylate falls within a suitable range.

[0070] Alkaline earth metal cations may include Be, Mg, Ca, Sr, and Ba cations. Alkaline earth metal cations may be selected as the metal cation component of any metal carboxylate disclosed herein, provided that the melting point of the metal carboxylate falls within a suitable range.

[0071] Main group metal cations may include Al, Ga, In, Tl, Sn, Pb, and Bi cations. A main group metal cation may be selected as the metal cation component of any metal carboxylate disclosed herein, provided that the melting point of the metal carboxylate falls within a suitable range.

[0072] Transition metal cations may include Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, and Hg cations, which may exist in any available oxidation state. Main group metal cations may be selected as the metal cation component of any metal carboxylate disclosed herein, provided that the melting point of the metal carboxylate falls within a suitable range.

[0073] Lanthanide metal cations may include La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu cations, which may reside in the +2 or +3 oxidation state, typically +3. Lanthanide metal cations may be selected as the metal cation component of any metal carboxylate disclosed herein, provided that the melting point of the metal carboxylate falls within a suitable range.

[0074] In some embodiments, the carboxylic acid-based sintering aid may comprise a dicarboxylic acid or a metal carboxylate formed therefrom. Suitable metal carboxylates formed from dicarboxylic acids may comprise a monovalent metal cation, a divalent metal cation, a trivalent metal cation, or any combination thereof, particularly a divalent or trivalent metal cation. Such metal dicarboxylates may comprise an acid component derived from a saturated or unsaturated dicarboxylic acid containing about 2 to about 100 carbon atoms, or about 2 to about 20 carbon atoms, or about 4 to about 16 carbon atoms, or about 2 to about 10 carbon atoms. Specific examples of suitable dicarboxylic acids may include, but are not limited to: terephthalic acid, phthalic acid, isophthalic acid, fumaric acid, maleic acid, itaconic acid, succinic acid, dodecyl succinic acid, dodecenyl succinic acid, oxalic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, dodecanoic acid, malic acid, sebacic acid, etc., and any combination thereof. Other suitable dicarboxylic acids that can be used to form metal carboxylates include those containing C3 to C6 alicyclic rings, such as cyclohexanedicarboxylic acid, cyclopentanedicarboxylic acid, cyclobutanedicarboxylic acid, or cyclopropanedicarboxylic acid. The hydrophobic tail may extend from the dicarboxylic acid at a position between the carboxylic acid groups.

[0075] In some embodiments, the carboxylic acid-based sintering aid may comprise a monocarboxylic acid or a metal carboxylate formed therefrom. Suitable metal carboxylates formed from monocarboxylic acids may include at least one metal monocarboxylate comprising a monovalent metal cation, a divalent metal cation, a trivalent metal cation, or any combination thereof, particularly a divalent or trivalent metal cation. The metal monocarboxylate may comprise an acid component derived from a saturated or unsaturated carboxylic acid containing about 6 or more carbon atoms, or about 8 or more carbon atoms, or about 10 or more carbon atoms, or about 12 or more carbon atoms, or about 14 or more carbon atoms, or about 16 or more carbon atoms, or about 18 or more carbon atoms, or about 20 or more carbon atoms, or about 22 or more carbon atoms, or about 24 or more carbon atoms. In more specific embodiments, the metal carboxylates may comprise an acid component derived from a monocarboxylic acid containing 2 to about 30 carbon atoms, or 3 to about 26 carbon atoms, or 4 to about 24 carbon atoms, or 6 to about 20 carbon atoms, or 8 to about 18 carbon atoms. Metal carboxylates formed from monocarboxylic acids having about 12 or fewer carbon atoms may be used in combination with more hydrophobic saturated or unsaturated carboxylic acids, such as those containing about 6 or more carbon atoms, or about 10 or more carbon atoms, or about 12 or more carbon atoms, or about 14 or more carbon atoms, or about 16 or more carbon atoms, or about 18 or more carbon atoms, or about 20 or more carbon atoms, or about 22 or more carbon atoms, or about 24 or more carbon atoms. Some metal carboxylates also possess sufficient thermal stability and may be used alone or in combination with more hydrophobic saturated or unsaturated carboxylic acids. Suitable examples of monocarboxylic acids may include, but are not limited to: acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, hexanoic acid, octanoic acid, decanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, nonadecanoic acid, arachidic acid, icosanoic ... and icosanoic acid. The aforementioned acids are saturated monocarboxylic acids. Unsaturated monocarboxylic acids may also be used to form metal monocarboxylate salts suitable for the disclosure herein. Suitable unsaturated monocarboxylic acids may include, for example, crotonic acid, docosahexaenoic acid, linoleic acid, trans-linolenic acid, linolenic acid, arachidonic acid, docosahexaenoic acid, myristone acid, palmitoleic acid, sappenic acid, isoleic acid, eicosenoic acid, oleic acid, pinolenic acid, octadecanoic acid, tung oil acid, trans oleic acid, squalene acid, erucic acid, erucic acid, eicosenoic acid, eicosadienoic acid, eicostrienoic acid, eicosadienoic acid, docosahexaenoic acid, nervonic acid, medelic acid, adrenaline, etc.Suitable aromatic carboxylic acids may include benzoic acid, naphthoic acid, or substituted variants thereof. Substituted variants of benzoic acid and naphthoic acid may have C1 to C relative to the carboxylic acid group at any open valence position on the aromatic ring. 40 Saturated or unsaturated hydrocarbon groups, C1 to C 10 Saturated or unsaturated hydrocarbon groups, or C 11 To C 30 Saturated or unsaturated hydrocarbon groups, and / or heteroatom functional groups relative to carboxylic acid groups at any open valence position on the aromatic ring. Hydrocarbon groups that may be present in suitable aromatic carboxylic acids include, for example, straight-chain or branched alkyl or alkenyl groups. Specific examples of aromatic acids that may constitute the acid component of the metal monocarboxylate disclosed herein include, for example, benzoic acid, naphthoic acid, benzoic acid (including salicylic acid), hydroxynaphthoic acid, etc. Other suitable monocarboxylic acids that may suitably constitute the acid component in the metal monocarboxylate include those comprising C3 to C6 alicyclic rings, such as cyclohexanecarboxylic acid, cyclopentanecarboxylic acid, cyclobutanecarboxylic acid, or cyclopropanecarboxylic acid. Any free carboxylic acid from the foregoing may also be used as a sintering aid based on carboxylic acids in the present disclosure, provided that the melting point is within a satisfactory range (e.g., from about 60°C to about 300°C).

[0076] In specific examples, carboxylic acid-based sintering aids may include stearates, such as zinc stearate, calcium stearate, or similar stearates containing divalent metal cations. Stearates containing trivalent metal cations, such as aluminum stearate, may also be used in this disclosure. Stearates containing monovalent metal cations, such as alkali metal stearates, may also be used in this disclosure.

[0077] The loading amount of the carboxylic acid-based sintering aid in the thermoplastic matrix defining the thermoplastic microparticles disclosed herein can range from about 0.05 wt% to about 5 wt%, or from about 0.05 wt% to about 2 wt%, relative to the thermoplastic polymer. The loading amount of the carboxylic acid-based sintering aid can represent the amount that effectively promotes sintering and reduces void formation while not promoting adhesion when placed in a heated powder bed.

[0078] In a non-limiting example, the thermoplastic microparticles disclosed herein can be formed by melt emulsification. Such methods for producing thermoplastic microparticles may include: combining a thermoplastic polymer, nanoparticles, and a carboxylic acid-based sintering aid (such as a metal carboxylate) with a carrier fluid at a heating temperature at or above the melting or softening temperature of the thermoplastic polymer; wherein the thermoplastic polymer and the carrier fluid are substantially immiscible at the heating temperature; applying sufficient shear at the heating temperature to disperse the thermoplastic polymer into liquefied droplets in the presence of the nanoparticles and the carboxylic acid-based sintering aid; after the formation of the liquefied droplets, cooling the carrier fluid to a temperature at which at least a solidified form of thermoplastic microparticles comprising the thermoplastic polymer, at least a portion of the nanoparticles disposed on the outer surface of the thermoplastic microparticles, and at least a portion of the carboxylic acid-based sintering aid; and separating the thermoplastic microparticles from the carrier fluid. In the nanoparticles associated with the thermoplastic microparticles, at least a majority of the nanoparticles are disposed on the outer surface of the thermoplastic microparticles.

[0079] Figure 1 This is a flowchart of a non-limiting example method 100 for preparing thermoplastic microparticles according to the present disclosure. As shown, at 108, a thermoplastic polymer 105, a carrier fluid 104, nanoparticles 106, and a carboxylic acid-based sintering aid 107 are combined to produce a mixture 110. The thermoplastic polymer 105, carrier fluid 104, nanoparticles 106, and carboxylic acid-based sintering aid 107 may be combined at 108 in any order and mixed and / or heated. Optionally, the carboxylic acid-based sintering aid 107 may be pre-coated onto the nanoparticles 106, such as by roller milling. In a particular example, the carrier fluid 104 may be heated to a temperature above the melting point or softening temperature of the thermoplastic polymer 105 before combining other components with it. Alternatively, all components may be mixed together in the carrier fluid 104 and then heated to a temperature above the melting point or softening temperature. The carboxylic acid-based sintering aid 107 may also be melted at a heating temperature used to promote melting or softening of the thermoplastic polymer 105. Nanoparticles 106 can remain solid at heating temperatures, allowing them to be disposed on the outer surface of the resulting thermoplastic microparticles.

[0080] Heating to a temperature above the melting point or softening temperature of thermoplastic polymer 105 can be carried out at any temperature below the decomposition temperature or boiling point of any component in the melt emulsion. In non-limiting examples, heating can be carried out at temperatures approximately 1°C to approximately 50°C, or approximately 1°C to approximately 25°C, or approximately 5°C to approximately 30°C, or approximately 20°C to approximately 50°C, higher than the melting point or softening temperature of thermoplastic polymer 105. The carboxylic acid-based sintering aid 107 may have a melting point higher or lower than the melting point of thermoplastic polymer 105. In this disclosure, the melting point can be determined using a ramp rate of 10°C / min and a cooling rate according to ASTM E794-06 (2018). Unless otherwise specified, the softening temperature or softening point of the thermoplastic polymer can be determined using ASTM D6090-17. The softening temperature can be measured using a cup-ball apparatus purchased from Mettler-Toledo, with a 0.50 g sample and a heating rate of 1°C / min. The melting point or softening temperature of the thermoplastic polymer 105 in this disclosure can be in the range of about 50°C to about 400°C. In a more specific example, the heating temperature can be in the range of about 100°C to about 300°C or about 200°C to about 250°C, provided that the thermoplastic polymer 105 melts or softens within this range.

[0081] The mixture 110 is then processed at 112 by applying sufficient shear at a temperature above the melting or softening temperature of the thermoplastic polymer 105 to produce liquefied droplets of the thermoplastic polymer 105, thereby forming a melt emulsion 114. Without being theoretically limited, it is believed that, all other things being equal, increasing shear can reduce the size of the liquefied droplets in the carrier fluid 104. It should be understood that at some point increasing shear and consequently reducing droplet size may have a diminishing return, and / or may cause damage to the droplet contents at higher shear rates. Examples of suitable mixing apparatus for producing the melt emulsion 114 include, but are not limited to, extruders (e.g., continuous extruders, batch extruders, etc.), stirred reactors, mixers, reactors with in-line homogenizer systems, and devices derived therefrom.

[0082] In non-limiting examples, the size of the liquefied droplets can be from about 1 μm to about 1,000 μm, or from about 1 μm to about 500 μm, or from about 1 μm to about 200 μm, or from about 1 μm to about 150 μm, or from about 1 μm to about 130 μm, or from about 1 μm to about 100 μm, or from about 10 μm to about 150 μm, or from about 10 μm to about 100 μm, or from about 20 μm to about 80 μm, or from about 20 μm to about 50 μm, or from about 50 μm to about 90 μm. The resulting thermoplastic microparticles formed after curing can reside within a similar size range. In other words, the size of the thermoplastic microparticles in the microparticle compositions and methods of this disclosure can be from about 1 μm to about 1,000 μm, or from about 1 μm to about 500 μm, or from about 1 μm to about 200 μm, or from about 1 μm to about 150 μm, or from about 1 μm to about 130 μm, or from about 1 μm to about 100 μm, or from about 1 μm to about 200 μm, or from about 10 μm to about 100 μm, or from about 20 μm to about 80 μm, or from about 20 μm to about 50 μm, or from about 50 μm to about 90 μm. Particle size measurement can be performed by analyzing optical images or using the onboard software of a Malvern Mastersizer 3000Aero S instrument, which uses light scattering technology for particle size measurement.

[0083] For light scattering technology, the product name Quality Audit Standards QAS4002 can be used. TM A control sample of glass microspheres with diameters ranging from 15 μm to 150 μm was purchased from Malvem Analytical Ltd. The sample could be analyzed as a dry powder dispersed in air using the dry powder dispersion module of the Mastersizer 3000 Aero S. Particle size could be determined using the instrument software based on a graph of bulk density versus size.

[0084] The molten emulsion 114 is then cooled 116 to solidify the liquefied droplets into solidified thermoplastic microparticles. The cooling rate may be in the range of about 100 °C / s to about 10 °C / h or about 10 °C / s to about 10 °C / h, including any cooling rate in between. Shearing may be interrupted during cooling or may be maintained at the same or different rates during cooling. The cooled mixture 118 may then be treated at 120 to separate the thermoplastic microparticles 122 from other components 124 (e.g., carrier fluid 104, excess nanoparticles 106, excess carboxylic acid-based sintering aid 107, etc.). Washing, filtration, and / or similar operations may be performed at this stage to further purify the thermoplastic microparticles 122, wherein the thermoplastic microparticles 122 comprise at least a portion of the thermoplastic polymer 105, at least a portion of the nanoparticles 106 coating the outer surface of the thermoplastic microparticles 122, and at least a portion of the carboxylic acid-based sintering aid 107 incorporated with the thermoplastic matrix comprising the thermoplastic microparticles 122. Depending on non-limiting factors such as temperature (including cooling rate), type of thermoplastic polymer 105, and type and size of nanoparticles 106, nanoparticles 106 may become at least partially embedded in the outer surface of thermoplastic microparticles 122 during the process of becoming disposed on the outer surface of thermoplastic microparticles 122. Even if embedding does not occur, nanoparticles 106 may maintain robust association with thermoplastic microparticles 122 to facilitate their further use.

[0085] In the foregoing, thermoplastic polymer 105 and carrier fluid 104 are selected such that these components are immiscible or substantially immiscible (<1% wt% solubility) at a variety of processing temperatures (e.g., from room temperature to the temperature at which liquefied droplets form and remain as two or more phases).

[0086] After the thermoplastic microparticles 122 are separated from the other components 124, further processing 126 of the thermoplastic microparticles 122 may be performed. In a non-limiting example, further processing 126 may include, for example, sieving the thermoplastic microparticles 122 and / or blending the thermoplastic microparticles 122 with other substances to form processed thermoplastic microparticles 128. The processed thermoplastic microparticles 128 may be formulated for desired applications, such as additive manufacturing in the non-limiting example.

[0087] Thermoplastic microparticles can have a density of approximately 0.3 g / cm³. 3 Approximately 0.8 g / cm³ 3 or approximately 0.3 g / cm³ 3 Approximately 0.6 g / cm³ 3 or approximately 0.4 g / cm³ 3 Approximately 0.7 g / cm³ 3 or approximately 0.5 g / cm 3 Approximately 0.6 g / cm³ 3 or approximately 0.5 g / cm 3 Approximately 0.8 g / cm³3 The packing density.

[0088] In specific examples of this disclosure, shear sufficient to form liquefied droplets can be applied by stirring the carrier fluid. In non-limiting examples, the stirring rate can be in the range of about 50 revolutions per minute (RPM) to about 1500 RPM, or about 250 RPM to about 1000 RPM, or about 225 RPM to about 500 RPM, or about 1000 RPM to about 2000 RPM. The stirring rate during melting of the thermoplastic polymer can be the same as or different from the stirring rate used after liquefied droplets have formed. The liquefied droplets can be stirred for a stirring time of about 30 seconds to about 18 hours or longer, or about 1 minute to about 180 minutes, or about 1 minute to about 60 minutes, or about 5 minutes to about 6 minutes, or about 5 minutes to about 30 minutes, or about 10 minutes to about 30 minutes, or about 30 minutes to about 60 minutes.

[0089] The loading (concentration) of the thermoplastic polymer in the carrier fluid can vary over a wide range. In a non-limiting example, the loading of the thermoplastic polymer in the carrier fluid can range from about 1 wt% to about 99 wt% relative to the weight of the carrier fluid. In a more specific example, the loading of the thermoplastic polymer relative to the weight of the carrier fluid can range from about 5 wt% to about 75 wt%, or about 10 wt% to about 60 wt%, or about 20 wt% to about 50 wt%, or about 20 wt% to about 30 wt%, or about 30 wt% to about 40 wt%, or about 40 wt% to about 50 wt%, or about 50 wt% to about 60 wt%. The thermoplastic polymer may be present in an amount ranging from about 5% to about 60% by weight, or from about 5% to about 25% by weight, or from about 10% to about 30% by weight, or from about 20% to about 45% by weight, or from about 25% to about 50% by weight, or from about 40% to about 60% by weight, relative to the combined amount of the thermoplastic polymer and the fluid carrier.

[0090] After thermoplastic microparticles are formed in the presence of nanoparticles according to the disclosure herein, at least a portion of the nanoparticles (such as silica nanoparticles or other oxide nanoparticles) may be disposed as a coating or a localized coating on the outer surface of the thermoplastic microparticles. In some cases, the coating may be disposed substantially uniformly on the outer surface. As used herein with respect to coating, the term "substantially uniform" refers to a uniform coating thickness across the surface area covered by the nanoparticles (particularly the entire outer surface). The coating coverage on the thermoplastic microparticles may range from about 5% to about 100% of the microparticle surface area, or about 5% to about 25%, or about 20% to about 50%, or about 40% to about 70%, or about 50% to about 80%, or about 60% to about 90%, or about 70% to about 100%. The coverage can be determined by image analysis of SEM micrographs.

[0091] The carrier fluid applicable to the disclosure herein includes those carrier fluids in which the thermoplastic polymer and the carrier fluid are substantially immiscible, the carrier fluid having a boiling point above the melting point or softening temperature of the thermoplastic polymer, and the carrier fluid having sufficient viscosity to form substantially spherical liquefied droplets after the thermoplastic polymer has melted therein. Examples of suitable carrier fluids include, but are not limited to: silicone oil, fluorinated silicone oil, perfluorinated silicone oil, polyethylene glycol, alkanes, liquid petrolatum, mink oil (vison oil), turtle oil, soybean oil, perhydrosqualene, sweet almond oil, calophyllum oil, palm oil, parleam oil, grapeseed oil, sesame oil, corn oil, rapeseed oil, sunflower oil, cottonseed oil, almond oil, castor oil, avocado oil, jojoba oil, olive oil, cereal germ oil, esters of lanolic acid, esters of oleic acid, esters of lauric acid, esters of stearic acid, fatty acid esters, higher fatty acids, fatty alcohols, polysiloxanes modified with fatty acids, polysiloxanes modified with fatty alcohols, polysiloxanes modified with polyoxyethylene, and any combination thereof.

[0092] A suitable carrier fluid can have a concentration of approximately 0.6 g / cm³. 3 Approximately 1.5 g / cm³ 3 The density, and thermoplastic polymers can have a density of approximately 0.7 g / cm³. 3 Approximately 1.7 g / cm³ 3 The density of thermoplastic polymers is similar to, lower than or higher than that of the fluid carrier.

[0093] Particularly suitable silicone oils are polysiloxanes. Exemplary silicone oils suitable for the purposes of this disclosure include, for example, polydimethylsiloxane (PDMS), methylphenyl polysiloxane, alkyl-modified polydimethylsiloxane, alkyl-modified methylphenyl polysiloxane, amino-modified polydimethylsiloxane, amino-modified methylphenyl polysiloxane, fluorinated polydimethylsiloxane, fluorinated methylphenyl polysiloxane, polyether-modified polydimethylsiloxane, polyether-modified methylphenyl polysiloxane, and any combination thereof.

[0094] In a non-limiting example, the carrier fluid and thermoplastic polymer can be heated at a temperature of about 200°C or higher. A suitable heating temperature can be selected based on the melting point or softening temperature of the thermoplastic polymer and the boiling point of the carrier fluid. The cooling rate after the liquefied polymer droplets form can be varied as needed. In some cases, cooling can be achieved by dissipating heat to the surrounding environment at an inherent (uncontrolled) rate after heating is interrupted. In other cases, cooling at a controlled rate can be employed (e.g., by gradually decreasing the heating temperature and / or using jacket temperature control to increase or decrease the cooling rate).

[0095] Suitable carrier fluids (such as polysiloxanes, including PDMS) may have viscosities of about 1,000 cSt to about 150,000 cSt, or about 1,000 cSt to about 60,000 cSt, or about 40,000 cSt to about 100,000 cSt, or about 75,000 cSt to about 150,000 cSt at 25°C. The viscosity of the carrier fluid may be obtained from commercial suppliers or, if desired, may be measured using techniques known to those skilled in the art.

[0096] Thermoplastic microparticles can be separated from the carrier fluid using any of a variety of known separation techniques. Gravity sedimentation and filtration, decanting, centrifugation, etc., can all be used to separate thermoplastic microparticles from the carrier fluid. The thermoplastic microparticles can be washed during the separation process using a solvent that is soluble in the carrier fluid and insoluble in the thermoplastic microparticles. Alternatively, before initially separating the elastomer microparticles from the carrier fluid, a solvent that is soluble in the carrier fluid and insoluble in the thermoplastic microparticles can be mixed with both the carrier fluid and the thermoplastic microparticles.

[0097] Suitable solvents for washing thermoplastic microparticles or mixing with a carrier fluid may include, but are not limited to, aromatic hydrocarbons (e.g., toluene and / or xylene), aliphatic hydrocarbons (e.g., heptane, n-hexane and / or n-octane), cyclic hydrocarbons (e.g., cyclopentane, cyclohexane and / or cyclooctane), ethers (e.g., diethyl ether, tetrahydrofuran, diisopropyl ether and / or dioxane), halogenated hydrocarbons (e.g., dichloroethane, trichloroethane, dichloromethane, chloroform and / or carbon tetrachloride), alcohols (e.g., methanol, ethanol, isopropanol and / or n-propanol), ketones (e.g., methyl ethyl ketone and / or acetone); esters (e.g., ethyl acetate, etc.), water, etc., and any combination thereof. After washing the thermoplastic microparticles, heating, vacuum drying, air drying, or any combination thereof may be performed.

[0098] At least a majority of the thermoplastic microparticles obtained according to the disclosure herein may be substantially spherical in shape. More typically, about 90% or more, or about 95% or more, or about 99% or more of the thermoplastic microparticles prepared by melt emulsification according to the disclosure may be substantially spherical in shape. In other non-limiting examples, the thermoplastic microparticles of the disclosure may have a sphericity (roundness) of about 0.9 or greater, including about 0.90 to about 1.0, or about 0.93 to about 0.99, or about 0.95 to about 0.99, or about 0.97 to about 0.99, or about 0.98 to 1.0. Sphericity (roundness) can be measured using a Sysmex FPIA-2100 flow cytometer. To determine roundness, optical microscopic images of the microparticles are taken. Calculate the perimeter (P) and area (A) of the particles in the plane of the microscopic image (e.g., using a SYSMEX FPIA 3000 particle shape and size analyzer, available from Malvern Instruments). The roundness of the particles is C. EA / P, where C EA It is the circumference of a circle whose area is equal to the area (A) of the actual particle.

[0099] The thermoplastic microparticles of this disclosure may have an angle of repose of about 25° to about 45°, or about 25° to about 35°, or about 30° to about 40°, or about 35° to about 45°. The angle of repose can be determined using the Hosokawa Micron Powder Characterization Tester PT-R, based on ASTM D6393-14, "Standard Test Method for Bulk Solids Characterization by CarrIndices".

[0100] The thermoplastic microparticles separated from the carrier fluid according to the disclosure above can be further processed to suit the intended application. In one example, the thermoplastic microparticles may pass through a sieve or similar structure with an effective screening size larger than the average particle size of the thermoplastic microparticles. For example, an exemplary screening size for processing thermoplastic microparticles suitable for 3D printing may have an effective screening size of about 150 μm. When referring to sieving, the aperture / sieve size is described according to the American Standard Sieve (ASTM E11-17). Other screening sizes (larger or smaller) may be more suitable for thermoplastic microparticles specified for other applications. Sieving can remove larger particles that may have formed during melt emulsification and / or remove agglomerated particles that may have poor flow properties. Generally, sieves with effective screening sizes ranging from about 10 μm to about 250 μm can be used.

[0101] Additionally, thermoplastic microparticles, including sieved thermoplastic microparticles, can be mixed with one or more additional components, such as flow aids, fillers, or other substances designed to tailor the properties of the thermoplastic microparticles for an intended application. The mixing of the additional components with the thermoplastic microparticles can be performed using dry mixing techniques. Suitable examples of flow aids (e.g., carbon black, graphite, silica, etc.) and similar substances are well known to those skilled in the art. Such flow aids differ from nanoparticles contained in melt emulsions because, when dry-mixed, the flow aid does not robustly adhere to the surface of the thermoplastic microparticles.

[0102] In specific applications, the compositions disclosed herein can be used in additive manufacturing processes, particularly those employing selective laser sintering or other powder bed melting processes to promote microparticle consolidation. The additive manufacturing method disclosed herein may include: providing the microparticle composition of this disclosure (a microparticle composition comprising a plurality of thermoplastic microparticles including a thermoplastic polymer, nanoparticles disposed on the outer surface of the thermoplastic microparticles, and a carboxylic acid-based sintering aid incorporated with the thermoplastic matrix of the thermoplastic microparticles); depositing the microparticle composition layer by layer in a powder bed; and heating a portion of the powder bed to consolidate a portion of the thermoplastic microparticles into a consolidated part having a specific shape. The carboxylic acid-based sintering aid and nanoparticles may remain associated with the consolidated part.

[0103] In specific process configurations, selective laser sintering (SLS) can be used to consolidate thermoplastic microparticles. It is believed that suitable conditions for performing SLS or other powder bed microparticle consolidation processes to form consolidated parts are not particularly limited. Lasers suitable for performing SLS can include both continuous-wave and pulsed-wave lasers to provide the energy required to facilitate the consolidation of thermoplastic microparticles into consolidated parts. Due to the high absorption rate of polymers to the emission wavelength of CO2 lasers, CO2 lasers are commonly used to promote the consolidation of thermoplastic microparticles during additive manufacturing. Operating conditions of the CO2 laser or a similar laser selected to promote microparticle consolidation can be chosen such that microparticle consolidation occurs to the desired degree. Standard laser settings (e.g., power, scan rate, bed temperature, etc.) for promoting microparticle consolidation can be selected based on the knowledge of those skilled in the art. The selection of specific conditions for selective laser sintering or similar microparticle consolidation techniques can be influenced by non-limiting factors such as the type of thermoplastic polymer used, the size and composition of the thermoplastic microparticles, the type of printed object produced, the type and amount of the carboxylic acid-based sintering aid present, and the intended use conditions of the printed object. In a non-limiting example, the selection of sintering conditions can affect the porosity obtained after microparticle consolidation. When using a carboxylic acid-based sintering aid, as in this disclosure, the consolidated part may comprise a thermoplastic matrix having a porosity of about 10% or less, or about 5% or less, or about 2% or less, or about 1% or less.

[0104] Examples of printed objects formed using the particulate compositions disclosed herein are considered to be without particular limitation and may include, for example, containers (e.g., for food, beverages, cosmetics, personal care compositions, pharmaceuticals, etc.), shoe soles, toys, furniture parts, decorative home furnishings, plastic gears, screws, nuts, bolts, cable ties, medical supplies, prostheses, orthopedic implants, the preparation of artifacts for assisting learning in education, 3D anatomical models for assisting surgery, robots, biomedical devices (orthotics), household appliances, dental devices, automotive and aircraft / aviation components, electronic devices, sporting goods, etc. Many of these printed objects may benefit from the introduction of one or more conductive traces thereon, as described below.

[0105] The implementation plan disclosed in this article includes:

[0106] A. A composition comprising powdered microparticles. The composition comprises: a plurality of thermoplastic microparticles, the plurality of thermoplastic microparticles comprising a carboxylic acid-based sintering aid incorporated with a thermoplastic polymer; and a plurality of nanoparticles disposed on the outer surface of the thermoplastic microparticles.

[0107] B. A method for forming a printed object by microparticle consolidation. The method includes: providing a microparticle composition according to embodiment A; depositing the microparticle composition layer by layer in a powder bed; and heating a portion of the powder bed to consolidate a portion of the thermoplastic microparticles into a consolidated part having a specific shape.

[0108] C. Consolidated component. The consolidated component comprises: a thermoplastic matrix formed by the consolidation of thermoplastic microparticles, and nanoparticles and a carboxylic acid-based sintering aid incorporated with the thermoplastic matrix.

[0109] D. A method for forming powder particles. The method comprises: combining a thermoplastic polymer, nanoparticles, and a carboxylic acid-based sintering aid with a carrier fluid at a heating temperature at or above the melting point or softening temperature of the thermoplastic polymer; wherein the thermoplastic polymer and the carrier fluid are substantially immiscible at the heating temperature; applying sufficient shear at the heating temperature in the presence of the nanoparticles and the carboxylic acid-based sintering aid to disperse the thermoplastic polymer in the carrier fluid into liquefied droplets; after the formation of the liquefied droplets, cooling the carrier fluid to a temperature at which at least a solidified thermoplastic particle is formed, the thermoplastic particle comprising at least a portion of the thermoplastic polymer, at least a portion of the nanoparticles, and at least a portion of the carboxylic acid-based sintering aid; wherein at least a majority of the nanoparticles are disposed on the outer surface of the thermoplastic particle; and separating the thermoplastic particle from the carrier fluid.

[0110] Each of implementation schemes A, B, C, and D may have one or more of the following additional elements in any combination:

[0111] Element 1: The multiple nanoparticles include oxide nanoparticles, carbon black, or any combination thereof.

[0112] Element 2: Among them, oxide nanoparticles include silicon dioxide nanoparticles;

[0113] Element 3: Among them, sintering aids based on carboxylic acids include metal carboxylates.

[0114] Element 4: The metal carboxylate has a melting point of about 90°C to about 300°C or about 60°C to about 300°C.

[0115] Element 5: wherein the metal carboxylate includes at least one salt selected from metal monocarboxylates, metal dicarboxylates, and any combination thereof.

[0116] Element 6: The metal carboxylate includes at least one metal monocarboxylate, which contains a monovalent metal cation, a divalent metal cation, or a trivalent metal cation.

[0117] Element 7: wherein the metal carboxylate includes at least one metal monocarboxylate having about 6 or more carbon atoms.

[0118] Element 8: Wherein the metal carboxylate includes at least one metal monocarboxylate having about 10 or more carbon atoms.

[0119] Element 9: wherein the metal carboxylate includes at least one metal monocarboxylate having about 16 or more carbon atoms.

[0120] Element 10: Among which carboxylic acid-based sintering aids include stearates.

[0121] Element 11: wherein the thermoplastic microparticles have a D in the range of about 1 μm to about 1,000 μm. 50 .

[0122] Element 12: wherein the thermoplastic microparticles contain about 0.05% by weight to about 2% by weight of a carboxylic acid-based sintering aid, as measured relative to the thermoplastic polymer.

[0123] Element 13: wherein the thermoplastic microparticles comprise about 0.05% by weight to about 5% by weight of nanoparticles, as measured relative to the thermoplastic polymer.

[0124] Element 14: Heating is performed via selective laser sintering.

[0125] Element 15: Wherein, sintering aids based on carboxylic acids and nanoparticles remain associated with the solidified components.

[0126] Element 16: Among them, metal carboxylates have melting points higher than the heating temperature.

[0127] Element 17: The carrier fluid includes silicone oil.

[0128] Element 18: Wherein the carboxylic acid-based sintering aid is pre-coated onto the nanoparticles before being combined with the carrier fluid.

[0129] As a non-limiting example, exemplary combinations applicable to A, B, C, and D include, but are not limited to: 1 or 2, and 3; 1 or 2, and 4; 1 or 2, and 5; 1 or 2, and 6; 1 or 2, and 7, 8, 9, or 10; 1 or 2, and 11; 1 or 2, and 12; 1 or 2, and 13; 3 and 4; 3 and 5; 3 and 6; 3, and 7, 8, 9, or 10; 3 and 11; 3 and 12; 3 and 13; 4 and 5; 4 and 6; 4, and 7, 8, 9, or 10; 4 and 11; 4 and 12; 4 and 13; 5, and 7, 8, 9, or 10; 5 and 11; 5 and 12; 5 and 13; 6, and 7, 8, 9, or 10; 6 and 11; 6 and 12; 6 and 13; 7, 8, 9, or 10, and 11; 7, 8, 9, or 10, and 12; 7, 8, 9, or 10, and 13; 11 and 12; 11 and 13; and 12 and 13. For B through D, any of the foregoing can be further combined with one or more of 14, 15, 16, 17, or 18.

[0130] To facilitate a better understanding of this disclosure, the following embodiments, which are preferred or representative, are provided. These embodiments should not be construed as limiting or restricting the scope of the invention.

[0131] Example

[0132] In the following examples, the powder flow of thermoplastic microparticles was characterized by sieving and angle of repose measurement. Sieving was performed using a 150 μm American standard sieve (ASTM E11) without specific force conditions or duration. Angle of repose measurements were performed using a Hosokawa Micron Powder Properties Tester PT-R, according to ASTM D6393-14, "Standard Test Method for Characterizing Bulk Solids by Karl Index".

[0133] The average particle size and particle size distribution were determined by light scattering using a Malvern Mastersizer 3000 Aero S particle size analyzer. For light scattering techniques, the Quality Audit Standards QAS4002 (trade name) can be used. TM A control sample of glass microspheres with diameters ranging from 15 μm to 150 μm was purchased from Malvern Analytical Systems. The sample could be analyzed as a dry powder dispersed in air using the dry powder dispersion module of the Mastersizer 3000 Aero S. Particle size could be determined using the instrument software based on a graph of bulk density versus size.

[0134] In the following embodiments, the weight percentage is measured relative to the polymer.

[0135] Example 1: Polyester microparticles formed in the presence of zinc stearate. 280 g of poly(dimethylsiloxane) (PDMS) (PSF-30000, Clearco), 0.25 g (0.20 wt%) of AEROSIL RX50 silica nanoparticles (average particle size = 40 nm, Evonik), 1.2 g (1.0 wt%) of zinc stearate (ZnFP, NOF) with a particle size of 4 to 6 μm, and 120 g of... were added to a 500 mL glass reactor equipped with a heating mantle. HTR6108 granules (a polyester block copolymer containing polybutylene terephthalate and long-chain glycol monomer units, DuPont). The reactor was set to a stirring rate of 300 RPM, and the temperature was raised to 240°C over 30 minutes under flowing argon purging. Once the temperature reached 240°C, the stirring rate was increased to 500 RPM. After 60 minutes, heating and stirring were stopped, and the slurry was allowed to cool to room temperature. The slurry was then diluted with heptane and filtered, followed by washing the particles three times with heptane. After vacuum drying overnight, the particles were then sieved through a 150 μm filter.

[0136] Example 2: Polyester microparticles formed in the presence of zinc stearate. Example 2 was carried out in the same manner as Example 1, except that 0.5% by weight of AEROSIL RX50 silica nanoparticles were used.

[0137] Example 3: Polyester microparticles formed in the presence of zinc stearate. Example 3 was carried out in the same manner as Example 1, except that 0.5 wt% AEROSIL RX50 and 0.5 wt% zinc stearate were used.

[0138] Example 3A: Polyester microparticles formed in the presence of sodium decanoate. Example 3A was carried out in the same manner as Example 3, except that sodium decanoate was used instead of zinc stearate.

[0139] Example 3B: Polyester microparticles formed in the presence of stearic acid. Example 3B was carried out in the same manner as Example 3, except that zinc stearate was replaced with stearic acid.

[0140] Example 4: Polyurethane microparticles formed in the presence of zinc stearate. Example 4 was carried out in the same manner as Example 1, except that ELASTOLLAN 1190A10 (a polyether polyurethane elastomer with a Shore hardness of A 90) was used instead of HTR 6108. In addition, 0.5% by weight of AEROSIL RX50 and 0.5% by weight of zinc stearate were used.

[0141] Example 4A: Polyurethane microparticles formed in the presence of zinc stearate pre-coated on silica nanoparticles. Example 4A was carried out in the same manner as Example 4, except that the silica nanoparticles and zinc stearate were mixed and milled for 3 hours, then added to PDMS and melt-emulsified.

[0142] Example 5: Polyurethane microparticles formed in the presence of zinc stearate. Example 5 was carried out in the same manner as Example 4, except that 1.0 wt% AEROSIL RX50 and 0.2 wt% zinc stearate were used.

[0143] Example 6: Polyurethane microparticles formed in the presence of zinc stearate. Example 6 was carried out in the same manner as Example 4, except that 1.0 wt% AEROSIL RX50 and 0.5 wt% zinc stearate were used.

[0144] Example 7: Polyurethane microparticles formed in the presence of zinc stearate. Example 6 was carried out in the same manner as Example 4, except that 0.5% by weight of AEROSIL RX50 and 1.0% by weight of zinc stearate were used.

[0145] Example 8: Polyurethane microparticles formed in the presence of zinc stearate. Example 6 was carried out in the same manner as Example 4, except that 0.5% by weight of AEROSIL RX50 and 0.1% by weight of zinc stearate were used.

[0146] Comparative Example 1: Polyester microparticles formed in the absence of zinc stearate. 140 g of PDMS (PSF-10000), 0.6 g (1.0 wt%) of AEROSIL RX50 silica nanoparticles, and 60 g of [unspecified ingredient] were added to a 500 mL glass reactor equipped with a heating mantle. HTR 6108 granules. The reactor was set to a stirring rate of 200 RPM, and the temperature was raised to 200 °C over 30 minutes under flowing argon purging. Once the temperature reached 200 °C, the stirring rate was increased to 1000 RPM. After 60 minutes, heating and stirring were stopped, and the slurry was allowed to cool to room temperature. The slurry was then diluted with heptane and filtered, followed by washing the particles three times with heptane. After vacuum drying overnight, the particles were then sieved through a 150 μm filter.

[0147] Comparative Example 2: Polyurethane microparticles formed in the absence of zinc stearate. 871 g of PDMS (PSF-10000), 50 g of PDMS / AEROSIL RX50 slurry containing 2.9 g (0.5 wt%) of AEROSIL RX50, and 580 g of ELASTOLLAN 1190A10 polyurethane were added to a 2 L Buchi reactor. The reactor was purged with nitrogen and stirred at 200 RPM. The jacket temperature was raised to 240 °C over 60 minutes. Once the reactor temperature reached 200 °C, the stirring rate was increased to 500 RPM and the nitrogen flow was shut off. The slurry was stirred at 240 °C for 30 minutes and then discharged hot. After cooling, the slurry was washed twice with hexane and the microparticles were separated by vacuum filtration. After vacuum drying overnight, the microparticles were then sieved through a 150 μm filter.

[0148] Tables 1 and 2 below summarize some of the formation conditions and characteristics of the thermoplastic microparticles formed as described above.

[0149] Table 1: Polyester Microparticles

[0150]

[0151] Table 2: Polyurethane microparticles

[0152]

[0153]

[0154] As shown in Tables 1 and 2, various concentrations of zinc stearate did not significantly alter the average particle size or angle of repose of the thermoplastic microparticles produced during melt emulsification. While the diameter span sometimes increased in the presence of zinc stearate, the span values ​​remained within acceptable levels for use in 3D printing. Pre-coating silica nanoparticles with zinc stearate resulted in a narrower span and a reduced angle of repose compared to values ​​obtained when these components were added alone during the melt emulsification production of polyurethane microparticles. Spherical polyester microparticles were also obtained in the presence of sodium decanoate, although the particle size was slightly larger than that of polyester microparticles prepared under the same conditions in the presence of zinc stearate. In contrast, stearic acid provided spherical polyester microparticles with properties more similar to those produced in the presence of an equal amount of zinc stearate.

[0155] Microparticle consolidation – The presence of zinc stearate in polyurethane microparticles during melt emulsification has a significant impact on the ease of sintering. Figure 2A and Figure 2B Optical images of the polyurethane microparticles of Comparative Example 2 after laser sintering at 30% and 45% laser power, a scan rate of 40,000, and a temperature of 108°C are shown. Figure 3A and Figure 3B Optical images of the polyurethane microparticles of Example 4 after laser sintering under the same conditions as the Comparative Example are shown. The comparison of the optical images clearly shows that the microparticles are consolidated much more completely in the presence of the zinc stearate sintering aid than in the absence of it. Some adhesion was observed during the consolidation of the polyurethane samples, even with a loading of 0.1% to 0.2% by weight of the zinc stearate sintering aid. In the presence of silica nanoparticles and zinc stearate, Example 4 initiated sintering at approximately 35% laser power, while Comparative Example 2 initiated sintering at approximately 25% laser power. Pre-coating the silica nanoparticles in Example 4A with zinc stearate reduced the laser power at the start of sintering to approximately 30%.

[0156] Figure 4 This is a graph showing the softening temperatures of thermoplastic polyurethane microparticles containing various loadings of zinc stearate as a sintering aid. As shown, the thermoplastic polyurethane microparticles containing only silica nanoparticles exhibit significantly higher sintering temperatures. As shown, increasing the amount of zinc stearate steadily decreases the softening temperature.

[0157] Microparticle consolidation – As observed with polyurethane microparticles, the presence of zinc stearate during melt emulsification also has a significant impact on the ease of sintering polyester microparticles. Figure 5A and Figure 5B Optical images of the polyester microparticles of Comparative Example 1 after laser sintering at 30% and 45% laser power, a rate of 40,000, and a temperature of 115°C are shown. Figure 6A and Figure 6B An optical image of the polyester microparticles of Example 1 after laser sintering is shown, and Figure 7A and Figure 7B Optical images of the polyester microparticles of Example 2 after laser sintering are shown, each under the same conditions as the comparative example. Figure 5A and Figure 5B As shown, after sintering the polyester microparticles of Comparative Example 1 without zinc stearate as a sintering aid, a considerable amount of microparticle structure remained. In contrast, the sintered sample containing zinc stearate showed significantly less microparticle structure, indicating more complete fusion. Figure 6A , Figure 6B , Figure 7A and Figure 7B In the previous example, the polyester microparticles appeared completely melted, likely due to the tendency of the zinc stearate sintering aid to lower the melting point. Complete melting could be used to impart a glossy surface during printing if desired, but this could lead to deformation of the printed object. In contrast, the polyester microparticles of Example 3, sintered at 25% and 35% laser power, a scan rate of 40,000, and a temperature of 115°C, showed increased microparticle structure retention, such as... Figure 8A and Figure 8B As shown separately. The retention of the microparticle structure is evident, but not to the extent observed in Comparative Example 1. At laser power above 35%, a greater quantity of Example 3B polyester microparticles melted.

[0158] The particles of Example 3A (containing sodium decanoate instead of zinc stearate) underwent sintering at 25% laser power, but the sintering was not as complete as that that occurred in the presence of zinc stearate (Example 3). The incomplete sintering of the particles from Example 3A can be attributed to their relatively large particle size. Furthermore, compared to the smaller particles completely free of metal carboxylates (Comparative Example 1), the particles of Example 3A underwent sintering at a lower laser power.

[0159] The microparticles of Example 3B (containing stearic acid but not zinc stearate) underwent sintering at laser power between 25% and 35%, similar to the polyester microparticles of Example 3.

[0160] Figures 9A to 9C Hot-stage micrographs of the polyester microparticles of Comparative Example 1 at various temperatures are shown. As shown, the sample began to sinter at approximately 160°C and began to flow at approximately 180°C. Full flow was observed at approximately 185°C. Figures 10A to 10C Hot-stage micrographs of the polyester microparticles of Example 2 at various temperatures are shown. As shown, the sample began to sinter at approximately 165°C and started to flow at approximately 172°C. Full flow was observed at approximately 175°C. Therefore, the zinc stearate sintering aid lowered the melting point of the sample by approximately 10°C, indicating that solidified components can be formed at lower bed temperatures and / or lower laser powers in the presence of the zinc stearate sintering aid.

[0161] In the consolidated sample made from the polyester microparticles of Comparative Example 1, the sintered layer was too brittle to operate at laser power below 30% in the absence of zinc stearate sintering aid. Moderate adhesion occurred in the polyester sample containing 1.0 wt% zinc stearate sintering aid, but adhesion was significantly reduced or absent at lower zinc stearate loadings. Table 3 shows a comparison of the sintered samples made from the polyester microparticles of Comparative Example 1 with those made from the polyester microparticles of Examples 2, 3A, and 3B at various laser powers. Selective laser sintering (SLS) was performed using a Snow White SLS printer system (Sharebot). Each type of polyester microparticle was deposited in 30 mm × 30 mm squares using the SLS printer system and then sintered under the various laser power conditions specified in Table 3. The percentage of voids after sintering was calculated using digital microscopy software.

[0162] Table 3

[0163]

[0164]

[0165] 1 Multiplying the reported scan rate by 0.04 gives the scan rate in mm / s.

[0166] As shown in the figure, sintering is achieved at a lower laser power in the presence of zinc stearate sintering aid, resulting in fewer voids.

[0167] All documents described herein are incorporated herein by reference for purposes permissible in all jurisdictions for such practices, including any priority documents and / or test procedures, provided they do not conflict with this document. As will be apparent from the foregoing general description and specific embodiments, while the form of this disclosure has been shown and described, various modifications may be made without departing from the spirit and scope of this disclosure. Therefore, this disclosure is not intended to be limiting. For example, a composition described herein may not contain any component or composition not expressly stated or disclosed herein. Any method may omit any step not stated or disclosed herein. Similarly, the term “comprising” is considered synonymous with the term “including.” Whenever a method, composition, element, or group of elements is preceded by the transitional phrase “comprising,” it should be understood that we also contemplate the same composition or group of elements preceding the description of the composition, element, or plurality of elements with the transitional phrases “consistently composed of,” “composed of,” “selected from,” or “is,” and vice versa.

[0168] Unless otherwise specified, all figures regarding the quantity of expressed components, properties (such as molecular weight), reaction conditions, etc., used in this specification and related claims should be understood to be modified by the term "about" in all cases. Therefore, unless stated to the contrary, the numerical parameters listed in the following specification and appended claims are approximations, which may vary depending on the desired properties sought to be obtained according to embodiments of the invention. To a minimum and without attempting to limit the application of the doctrine of equivalence to the scope of the claims, each numerical parameter should be interpreted at least according to the number of significant figures reported and by applying customary rounding.

[0169] Whenever a numerical range with a lower and upper limit is disclosed, any quantity falling within that range and any included range are specifically disclosed. Specifically, each range of values ​​disclosed herein (in the form of “about a to about b,” or equivalently, “approximately a to b,” or equivalently, “approximately ab”) should be understood to describe every numerical value and range encompassed within a wider range of values. Furthermore, the terms in the claims have their ordinary, common meaning unless otherwise explicitly and clearly defined by the patentee. Additionally, the indefinite articles “an” or “a” used in the claims are defined herein as meaning that the element described has one or more elements.

[0170] This document presents one or more exemplary embodiments. For clarity, not all features of the physical implementation are described or illustrated in this application. It should be understood that in the development of the physical implementations of this disclosure, many implementation-specific decisions must be made to achieve the developer's goals, such as compliance with system-related constraints, business-related constraints, governmental constraints, and other constraints that vary from implementation to implementation and change over time. While the efforts made by the developer may be time-consuming, such efforts will be a routine task for those skilled in the art who will benefit from this disclosure.

[0171] Therefore, this disclosure is well-suited to achieving the stated objectives and advantages, as well as those inherent therein. The specific embodiments disclosed above are merely exemplary, as different but equivalent ways may be modified and implemented in a manner obvious to those skilled in the art who benefit from the teachings herein. Furthermore, no limitation is contemplated on the details of the constructions or designs shown herein, except as set forth in the following claims. Therefore, it is apparent that the specific exemplary embodiments of the above disclosure may be altered, combined, or modified, and all such changes are considered to be within the scope and spirit of this disclosure. The embodiments disclosed herein by way of example may be suitably implemented in the absence of any elements not specifically disclosed herein and / or any optional elements disclosed herein.

Claims

1. A particulate composition, said particulate composition comprising: A plurality of thermoplastic microparticles comprising a thermoplastic polymer; 0.05 wt% to 2 wt% of a carboxylic acid-based sintering aid blended with the thermoplastic polymer, measured relative to the thermoplastic polymer; and 0.2 wt% to 2 wt% of a plurality of nanoparticles, measured relative to the thermoplastic polymer. The carboxylic acid-based sintering aids mentioned therein include free carboxylic acids or metal carboxylates; Furthermore, the carboxylic acid-based sintering aid is not pre-coated on the nanoparticles and is at least partially located within the thermoplastic microparticles, and at least a majority of the plurality of nanoparticles are disposed on the outer surface of the thermoplastic microparticles, wherein the nanoparticles refer to particulate materials with a particle size in the range of 1 nm to 500 nm.

2. The particulate composition according to claim 1, wherein the plurality of nanoparticles comprises oxide nanoparticles, carbon black, or any combination thereof.

3. The particulate composition according to claim 2, wherein the oxide nanoparticles comprise silicon dioxide nanoparticles.

4. The particulate composition according to claim 1, wherein the carboxylic acid-based sintering aid comprises a metal carboxylate, and the metal carboxylate has a melting point of 60°C to 300°C.

5. The particulate composition of claim 1, wherein the carboxylic acid-based sintering aid comprises a metal carboxylate, and the metal carboxylate comprises at least one salt selected from metal monocarboxylates, metal dicarboxylates, and any combination thereof.

6. The particulate composition of claim 1, wherein the carboxylic acid-based sintering aid comprises a metal carboxylate, and the metal carboxylate comprises at least one metal monocarboxylate, the metal monocarboxylate comprising a monovalent metal cation, a divalent metal cation, or a trivalent metal cation.

7. A method, the method comprising: - The thermoplastic polymer, nanoparticles, and carboxylic acid-based sintering aid are combined with a carrier fluid at a heating temperature at or above the melting point or softening temperature of the thermoplastic polymer. The thermoplastic polymer and the carrier fluid are substantially immiscible at the heating temperature; - In the presence of the nanoparticles and the carboxylic acid-based sintering aid, sufficient shear is applied at the heating temperature to disperse the thermoplastic polymer into liquefied droplets in the carrier fluid; - After the liquefied droplets are formed, the carrier fluid is cooled to a temperature at which at least a solidified thermoplastic microparticles are formed, the thermoplastic microparticles comprising the thermoplastic polymer, at least a portion of the nanoparticles, and at least a portion of the carboxylic acid-based sintering aid; The carboxylic acid-based sintering aid is present in an amount of 0.05% to 2% by weight, as measured relative to the thermoplastic polymer, and the nanoparticles are present in an amount of 0.2% to 2% by weight, as measured relative to the thermoplastic polymer. The carboxylic acid-based sintering aids mentioned above include free carboxylic acids or metal carboxylates; and The carboxylic acid-based sintering aid is not pre-coated onto the nanoparticles, and at least a majority of the nanoparticles are disposed on the outer surface of the thermoplastic microparticles. as well as - Separate the thermoplastic microparticles from the carrier fluid.

8. The method of claim 7, wherein the nanoparticles comprise oxide nanoparticles, carbon black, or any combination thereof.

9. The method according to claim 8, wherein the oxide nanoparticles comprise silicon dioxide nanoparticles.

10. The method of claim 7, wherein the carboxylic acid-based sintering aid comprises a metal carboxylate, and the metal carboxylate has a melting point of 60°C to 300°C.

11. The method of claim 7, wherein the carboxylic acid-based sintering aid comprises a metal carboxylate, and the metal carboxylate comprises at least one salt selected from metal monocarboxylates, metal dicarboxylates, and any combination thereof.

12. The method of claim 7, wherein the carboxylic acid-based sintering aid comprises a metal carboxylate, and the metal carboxylate comprises at least one metal monocarboxylate, the metal monocarboxylate comprising a monovalent metal cation, a divalent metal cation, or a trivalent metal cation.

13. The particulate composition of claim 1, wherein the plurality of nanoparticles are present in an amount of 0.25% to 1% by weight, measured relative to the thermoplastic polymer.

14. The particulate composition of claim 13, wherein the carboxylic acid-based sintering aid is present in an amount of 0.2% to 1% by weight, measured relative to the thermoplastic polymer.

15. The particulate composition of claim 1, wherein the plurality of nanoparticles are present in an amount of 0.25% to 0.5% by weight, measured relative to the thermoplastic polymer.

16. The particulate composition of claim 15, wherein the carboxylic acid-based sintering aid is present in an amount of 0.2% to 1% by weight, measured relative to the thermoplastic polymer.

17. The particulate composition of claim 1, wherein the carboxylic acid-based sintering aid is present in an amount of 0.2% to 1% by weight, measured relative to the thermoplastic polymer.

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