Fused liquid beads and reducers for forming 3D parts

Abstract

The present subject matter relates to a method of creating layers of interconnected or contiguous material using a heated powdered composition comprising base particles and a barrier material, and applying a reducing agent to the powdered composition. The heated powdered composition can be maintained at a temperature above its melting or softening point, and the barrier material prevents coalescence between the particles until the reducing agent is applied.

Description

[0001] Priority requirements

[0002] This application claims priority to U.S. Patent Application Serial No. 62 / 706,467, filed August 19, 2020, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The topics disclosed herein generally relate to methods, systems, and materials for forming three-dimensional structures using additive manufacturing principles. More specifically, the topics disclosed herein relate to methods, systems, and materials for powder bed melting technology. Background Technology

[0004] With the invention of new additive manufacturing (AM) or three-dimensional (3D) printing methods, the technology for processing and shaping materials into desired shapes and parts has been significantly improved. Printing technologies for polymer materials can be categorized into thermal extrusion, photopolymerization, powder bed melting, material jetting, binder jetting, and lamination. Each of these categories has its advantages and controversial disadvantages, and numerous patents have been published in an attempt to address some of these weaknesses.

[0005] Powder bed fusion technology is more widely used in industrial environments for producing final products. Compared to FDM, selective laser sintering (SLS) is faster, achieves better resolution, and produces more consistent parts; however, SLS requires the powdered starting material to be semi-crystalline, thus having material limitations that FDM does not have. Material jetting technologies, such as Polyjet, use inkjet printing on UV-curable resins. Parts manufactured using this method tend to have relatively poor strength, and large parts can develop internal stresses due to thermal gradients. Powder bed technology is more advantageous for longer build times and larger builds in reducing part warpage and internal stress.

[0006] Ideally, the best AM technology would be fast, accurate, and with good resolution, allowing for the creation of large, warp-free parts and accepting a wide variety of printable materials. AM technology would combine the material selection of thermal extrusion methods with the added advantages of powder bed-based methods without relying on grating lasers to fuse polymer particles together. Hewlett Packard (HP) U.S. Patent Application Publications 10,301,490 and 10,647,053 describe a powder bed-based AM method that uses an inkjet printhead to selectively add fusing and refining agents to help and prevent particle agglomeration under infrared heating lamps, avoiding the use of lasers; however, this method still lacks a wide selection of available printable materials. HP's U.S. Patent Application Publications 2020 / 0199383 and 2019 / 0047216 highlight a fusing and refining agent that relies on electromagnetic radiation-absorbing materials (such as carbon black) to help form 3D printing material layers. Neil Hopkinson et al. (US Patent Application Publications 7,879,282 and 8,535,036) also developed a method for printing radiation-absorbing materials to help selectively heat powdered particles to cause them to aggregate. Using pigments or dyes as radiation-absorbing materials limits the color of the printed particles and proves problematic when printing multiple different colors simultaneously, as each color absorbs a different amount of this radiation and therefore occurs at different temperatures.

[0007] When using semi-crystalline materials in current powder bed-based AM technology, precise temperature control is crucial. For this reason, many patents are based on controlling and monitoring temperature during the build-up process (US Patent Application Publications 7,515,986; 2017 / 0246810 and 10,434,573). It would be beneficial to have a powder-based AM method that eliminates some of the importance of requiring precise temperature control. Publication 2020 / 0199383 also mentions the possibility of using amorphous polymers in their printers, but this has not yet been sufficiently successful.

[0008] HP's U.S. Patent Application Publication No. 10,392,512 describes a refining agent for preventing radiation adsorption and helping to keep specific portions of powdered particles cooled to prevent their agglomeration. This is why semi-crystalline particles are easier to process, as both molten and non-molten particles can be adjacent to each other without significant agglomeration. One limitation of using amorphous polymers is that they do not have a sharp melting point or a point where viscosity drops sharply. Higher temperatures and / or chemical modifiers such as plasticizers are required to make amorphous polymers flow and coalesce into layers with higher strength and less porosity. A powder-based AM method that allows for a large temperature difference between agglomerated and non-agglomerated polymer particles and has the ability to prevent softened or sticky polymer particles from agglomerating would help address this problem.

[0009] To improve powder bed-based atomization (AM) processes, Evans, Pulsipher, and Stockton discuss a particle coating method for 3D printing in U.S. Patent Application Publication No. 9,617,394. The particles are coated with plasma, enabling them to withstand temperatures above their melting points without significant particle adhesion until the coating is thermally or mechanically destroyed. Most materials of interest in AM have low coefficients of thermal expansion. This limits the ability of the particles to expand under thermal stimulation, causing the coating to crack or break. A different method is needed that does not involve chemically attached coatings or simply chemically altering the surface of the particles to be coalesced. A method is also needed to more effectively destroy the coating and release the molten polymer without mechanical intervention.

[0010] In AM applications, or more specifically in powder bed fusion technology, it is ideal to use barriers to prevent particle agglomeration if obstacles can be quickly and easily removed in precise areas to allow particle agglomeration. The residue from the removed barriers will be minimal and / or well incorporated into the polymer matrix, thus not significantly adversely affecting the mechanical properties of the final material. Furthermore, it is beneficial if the barriers are thermally insulating to create some thermal insulation between adjacent blocked particles and particles that have already fused or agglomerated and are at higher temperatures. This additional thermal insulation will allow for a greater temperature difference between the non-molten and molten portions of the powder bed. Such an approach also opens up possibilities for a wider range of materials, including amorphous polymers, composite polymers, or combinations of materials that can be processed in powder bed-based AM technology. Summary of the Invention

[0011] To address the shortcomings of existing technologies, this invention describes a method for creating interconnected or continuous material layers by using a heated powdered composition and applying a shrinkage agent to the powdered composition. The powdered composition comprises powdered base particles and a barrier material surrounding and / or between the base particles. When the powdered composition is heated to or maintained at a temperature close to or above a first melting or softening point of the base particles in the powdered composition, the barrier material prevents the base particles in the powdered composition from spontaneously agglomerating. The barrier material at least partially impedes the obvious binding or agglomeration of the base particles with adjacent base particles to prevent the formation of significantly larger particles or the formation of interconnected or continuous material layers. The shrinkage agent comprises a chemical that increases the flowability of the base particles by acting as a temporary plasticizer, facilitating at least partial agglomeration of the base particles with adjacent similar base particles; or the shrinkage agent helps to at least partially reduce, disperse, and / or allow thermal bridging of the barrier material contained in the powdered composition at the location where the shrinkage agent is applied. Figure 1 The diagram illustrates an instance of this method.

[0012] In some embodiments, the barrier material has surface functional groups attached that prevent significant binding to the molten base material. These surface functional groups can be hydrophobic or fully hydrophobic. The reducing agent may also contain one or more dispersants to better introduce residues of the removed material into the resulting polymer matrix.

[0013] In other embodiments, the barrier has the added benefit of providing insulation to the particles to allow for a greater temperature difference between the insulating particles and the coalesced particles. Insulating materials with a thermal conductivity below 0.09 W / m·K can provide adequate insulation between the base particles, while materials with a thermal conductivity below 0.03 W / m·K, such as aerogels, are particularly effective in this regard. The size of the barrier material can be on the same order of magnitude as or smaller than the base particles, with the aim of using as little barrier material as possible to prevent significant circumvention of the barrier material by the base particles, without significantly adversely affecting the mechanical properties of the resulting coalesced continuous portion. Here, a significant adverse effect on elongation at break can be as small as 5% in, for example, Nylon 12, or as high as a reduction of 20% in other materials. The barrier material can be particles with a diameter of 0.005-50 μm. They can also be as small or as thin as the surface functional groups directly attached to the surface of the base particles.

[0014] In some embodiments, the base particles that form part of the powdered composition are semi-crystalline materials having a melting point; however, the base particles can also be more amorphous materials having a glass transition temperature. For the purposes of this invention, more amorphous materials are possible because the powdered composition can be maintained at 5-150°C or higher, exceeding the melting point, glass transition temperature, or softening point of the base particles.

[0015] In some embodiments, the reducing agent comprises a chemical that acts as a temporary plasticizer or helps to partially reduce or disperse the barrier material in one or more of the following ways: 1) as a surfactant or solvent to break down, disrupt, dissolve, or mask the hydrophobic properties of the barrier material and help it mix into the coalescing matrix; 2) to create thermally conductive bridges between particles isolated by the use of the barrier material; and 3) by acting as a plasticizer to increase the fluidity of the softened or molten polymer chains constituting the isolated particles. The reducing agent does not need to remain in the coalesced material. The controlled evaporation of most reducing agents can help remove the barrier material without significantly adversely affecting the mechanical properties of the continuous portion of the coalescing.

[0016] In some implementations, the shrinkage agent is applied in liquid form. This liquid can be applied as droplets with a diameter less than 10 times the average diameter of the base particles used. The liquid can be applied via inkjet printing or drop-on-demand (DOD) methods.

[0017] In other embodiments, the shrinkage agent may also be solidified when applied to a hot powder composition. When the shrinkage agent reaches the temperature of the powder composition, it melts and helps to partially reduce or disperse the blocking material. The temperature of the powder composition can be varied to help melt or evaporate the shrinkage agent, and to help better aggregate the polymer particles.

[0018] In some implementations, the material group consisting of base particles, blocking material, and shrinkage agent is specific to the material to be printed. Only certain shrinkage agents can be used with certain base particles.

[0019] In some implementations, this method of forming interconnected or continuous material layers can be applied multiple times to create 3D parts from composite layers. Multiple base materials with different melting or softening points can be printed simultaneously into a single part. Furthermore, multiple shrinkage agents that react better with certain base materials can be applied simultaneously.

[0020] Although some aspects of the subject matter disclosed herein have been described above and are realized in whole or in part by the subject matter currently disclosed, other aspects will become apparent when described in conjunction with the accompanying drawings, as best described below. Attached Figure Description

[0021] The characteristics and advantages of the subject matter of this article will be more readily understood from the following detailed implementation, which should be consistent with the appendix. Figure 1 For the purposes of this study, please refer to the accompanying figures, which are given only in an illustrative and non-limiting manner, in which:

[0022] Figure 1 This is a flowchart illustrating an example of the methods disclosed in this paper.

[0023] Figures 2A, 2B, and 2C illustrate thermal test results of powdered compositions containing polymer particles and using various materials as barrier materials, according to embodiments of the subject matter herein.

[0024] Figures 3A, 3B, 3C, 3D and 3E illustrate the results of applying droplets of various examples of shrinkage agents to various powdered compositions maintained at high temperatures, according to embodiments of the subject matter herein. Detailed Implementation

[0025] This article provides methods, systems, and materials for forming three-dimensional structures using additive manufacturing principles. Interconnected or continuous layers of material are created by using a heated powdered composition and applying a shrinkage agent to it. The powdered composition comprises powdered base particles and barrier material surrounding and / or between the base particles. When the powdered composition is heated to or maintained at a temperature close to or above the melting or softening point of the base particles in the powdered composition, the barrier material prevents the base particles in the powdered composition from spontaneously agglomerating. The barrier material at least partially prevents the base particles from significantly binding or agglomerating with adjacent base particles to prevent the formation of significantly larger particles or the formation of interconnected or continuous layers of material. The shrinkage agent includes a chemical that helps the base particles at least partially agglomerate with adjacent similar base particles by acting as a temporary plasticizer; or the shrinkage agent helps to at least partially reduce, disperse, and / or allow thermal bridging of the barrier material contained in the powdered composition at the location where the shrinkage agent is applied.

[0026] In one aspect, the subject of this article provides a method for creating interconnected or continuous layers of material by using a heated powdered composition and applying a shrinkage agent to the powdered composition. Figure 1 The diagram illustrates one embodiment of the method. The powdered composition comprises a powdered base material and a barrier material surrounding and / or between the base particles. In some embodiments, the base particles are composed of a polymeric material. When the powdered composition is heated to or maintained at a temperature above the melting point of the base particles or significantly above their softening point, the base material can form liquid beads of molten material, but the barrier material at least partially prevents the base particles from significantly binding or coalescing with adjacent base particles to prevent the formation of significantly larger particles or interconnected or continuous layers of material.

[0027] To selectively agglomerate these "molten liquid marbles" into the desired arrangement, a shrinkage agent is added to substantially overcome the ability of the blocking material to keep the base particles separated at the site where the shrinkage agent is applied. The shrinkage agent comprises a chemical that increases the flowability of the base particles by acting as a temporary plasticizer, or by helping to at least partially reduce, disperse, and / or allow thermal bridging of the blocking material contained in the powdered composition, thereby facilitating the agglomeration of the base particles at least partially with adjacent similar base particles.

[0028] To prevent the base particles from significantly binding or agglomerating together, the barrier material is configured to prevent significant binding to the molten base particles and to prevent nearby base particles from binding to each other. In this regard, in some embodiments, the barrier material is coated with surface functional groups that will prevent the base particles from completely wetting the barrier material or significantly binding to the molten base material. When a drop of liquid is placed on a surface and the resulting surface contact angle is 0 degrees, the material is completely wetted by the liquid. If the surface contact angle is between 0 and 90 degrees, then the surface is wettable. In some embodiments, the barrier material comprises nanoparticles having hydrophobic or fully hydrophobic surfaces, which can prevent significant binding with adjacent particles in a manner similar to the formation of liquid marbles. Such functional groups are provided in the composition, wherein the barrier material is present in the powdered composition at a content of 0.5-30% by weight. It is preferred to have a low amount (0.5-2% by weight) of barrier material in the powdered composition to limit harmful mechanical properties in the created 3D parts; however, some base particles with low surface energy may require a higher amount of barrier material to prevent agglomeration. Because higher temperatures are required to significantly soften, for example, amorphous polymers, higher quantities of barrier materials are also needed. Hydrophobically treated nanoparticles can be any particles that do not significantly reduce the important properties of the film or the 3D component being created. Barrier materials can include organic, metallic, or ceramic particles that can withstand the high temperatures used and prevent the aggregation of the base particles.

[0029] The size of the barrier material can be on the same order of magnitude as or smaller than that of the base particles. The aim is to use as little barrier material as possible to prevent it from being significantly bypassed by the base particles, while not significantly adversely affecting the mechanical properties of the resulting aggregated continuous portion. In some embodiments, the barrier material can be, for example, particles with a diameter of 0.005-50 micrometers. They can also be as small or as thin as the surface functional groups directly attached to the surface of the base particles.

[0030] Specifically, in some embodiments, the barrier material comprises insulating or porous particles to allow for a greater temperature difference between the insulating particles and the aggregated particles. In some embodiments, for example, the barrier material may comprise insulating materials with a thermal conductivity below 0.09 W / m·K, and materials with a thermal conductivity below 0.03 W / m·K can be particularly effective in this regard. Hollow glass microspheres and porous ceramic particles are some examples of barrier materials with thermal conductivity close to 0.09 W / m·K. Examples of materials with a thermal conductivity below 0.03 W / m·K are those classified as foams and aerogels. Aerogels have some of the lowest known thermal conductivity, reaching 0.03–0.004 W / m·K. Barrier materials with these low thermal conductivity and low density will allow molten particles to remain adjacent to non-molten particles for longer periods. Particulate ceramic aerogel materials are well-suited for this purpose. Aerogel materials are notorious for their low mechanical strength, as their structure can even be disrupted or degraded by the capillary action of water. This is one of the reasons why most silica aerogel materials have a hydrophobic treatment. However, for use in this system and method, the fragility of the low-density aerogel structure can be utilized to encourage structural degradation of the aerogel after the application of a shrinkage agent.

[0031] Regardless of the specific composition or structure of the barrier material, the type of base particles that can be used in this powder bed fusion technology can vary beyond the semi-crystalline materials limited by previous systems, by utilizing the ability to restrict the bonding of base particles when exposed to temperatures above the melting point or significantly above the softening point of the base particles. In this regard, in some embodiments, the base particles in the powdered composition are semi-crystalline or amorphous polymeric materials. As used herein, the term "polymer particles" refers to particulate semi-crystalline and amorphous polymers that become flexible or malleable above a specific temperature (glass transition temperature or melting point) and solidify upon cooling to below a specific temperature. These polymeric materials may include, but are not limited to: (PA) polyamide; polyetherimide (PEI); polycarbonate (PC); polyetheretherketone (PEEK); polyethylene (PE); polyphenylene ether (PPO); polyethylene terephthalate (PET); polyphenylene sulfide (PPS); polyethersulfone (PESU); acrylonitrile-butadiene-styrene (ABS); polyoxymethylene (POM); polylactic acid (PLA); polybenzimidazole (PBI); polypropylene (PP); polystyrene (PS); polyvinyl chloride (PVC); and fluoropolymers (e.g., polytetrafluoroethylene). As used herein, the term "semi-crystalline polymer" refers to a polymer containing a significant degree of crystallinity, or about 10% to about 80%. As used herein, the term "amorphous polymer" refers to a polymer that does not contain a significant degree of detectable crystalline structure. In some embodiments, composite polymer particles are used, and combinations of polymer particles with different melting points or softening points are used in the same process. Although various polymer particles have been discussed herein, those skilled in the art will recognize that any of a variety of other types of materials that soften or melt at high temperatures can serve as the base particles in this system and method. In other embodiments, for example, the base particles in the powdered composition are metal or alloy particles.

[0032] For any type of base particles, powdered compositions can be maintained at temperatures 5–150°C or higher than the melting point, glass transition temperature, or softening point of the base particles. Processing powder bed-based materials at higher temperatures allows amorphous polymer particles to enter a more desirable processable range, where the higher melt flow rate of the polymer becomes more liquid. These higher temperatures will result in better mechanical properties of the coalesced components because the previously separated molecular chains will have more time to fuse into an interconnected network of molecular chains before solidification. Higher melt flow and a better interconnected material network will also increase the density of the coalesced components. The higher temperatures of this process are limited by the thermal decomposition or oxidation of the base particles being processed, and by the composition of the shrinkage agent that can function at said temperatures without significant degradation. By controllably releasing molten liquid pellets with shrinkage agents, more material can be processed using powder bed-based AM technology.

[0033] In other implementations, less extreme temperatures can be used, or temperatures close to or only slightly above the material's melting or softening point. This allows for a larger processing window and thus allows for more polymeric material to be processed using powder bed-based AM technology. It also reduces the amount of barrier material needed to prevent particle agglomeration. Even with little or no barrier material, shrinkage agents can help with particle agglomeration. Using shrinkage agents alone can lower the required processing temperature because they help temporarily plasticize the particles.

[0034] Depending on the selected base particles and barrier materials, a shrinkage agent can be chosen to control the interconnection of the base particles. In some embodiments, for example, the shrinkage agent can act as a surfactant or solvent to break down, disrupt, dissolve, or mask the hydrophobic properties of the barrier materials and facilitate their incorporation into the coalescing matrix. The shrinkage agent may comprise a combination of additives and surfactants, for example, to introduce fully hydrophobic particles into the polymer matrix, suppress vigorous boiling, prevent polymer degradation, or prevent polymer oxidation.

[0035] In some implementations, the shrinkage agent forms a thermal bridge on the barrier material. Most solvents have a thermal conductivity between 0.1 and 0.6 W / m·K, which is at least five times greater than that of aerogel particles. The thermal shrinkage agent can cause the polymer particles to heat up and coalesce more quickly. Once the particles coalesce, the temperature of the molten layer does not need to be as hot as the next layer that coalesces above it. Therefore, the particles may only be temporarily exposed to high temperatures.

[0036] In some implementations, shrinkage agents increase the fluidity of the softened or molten polymer chains that constitute the insulated particles by acting as plasticizers. Traditionally, plasticizers are chemicals used to increase the flexibility and ductility of polymers. The migration, fluidity, and volatility of plasticizers after introduction into the polymer are generally undesirable characteristics. Chemicals as simple as water can serve as plasticizers for many nylon materials. As used herein, the term "plasticizer" is used as a term that emphasizes the function of chemicals in adding fluidity to polymer chains to increase the melt flow rate of the polymer. This enhanced fluidity only needs to persist until the polymer is fully aggregated. Thereafter, it is preferable that the plasticizer largely evaporates and is removed from the polymer matrix.

[0037] The plasticizers used herein can constitute conventional plasticizer chemicals, including but not limited to: trimellitates (such as trimethyl trimellitate and tri-(2-ethylhexyl) trimellitate), phthalates (such as phthalic anhydride and esters of phthalic anhydride, such as diethyl phthalate), terephthalates, benzoates (e.g., chemicals derived from benzoic acid, such as methyl benzoate, ethyl benzoate, propyl benzoate, and dibenzoate), polyethers, sulfonamides, alkyl citrates, and their derivatives. Other chemicals that also temporarily increase the fluidity of polymer chains and act as temporary plasticizers may be used in this system and method, including but not limited to: propylene carbonate, naphthalene, anthracene, triphenylphosphine, benzophonone, xylene, high-temperature siloxanes (e.g., phenylmethylsiloxane), and their derivatives.

[0038] In some embodiments, the shrinkage agent is applied in liquid form. In some embodiments, the shrinkage agent can be applied as droplets of controlled size. The liquid can be applied by inkjet printing or another drop-on-demand (DOD) method. In some embodiments, for example, the inkjet head can be configured to deliver droplets of controlled volume, for example, by using a piezoelectric mechanism. The inkjet head can be heated to facilitate the delivery of the shrinkage agent and its components, which are solid at room temperature. The droplet size must be large enough to allow the shrinkage agent time to function before evaporation, but droplets that are too large will result in bubbles and voids remaining in the aggregated polymer. In some embodiments, for example, the diameter of the shrinkage agent droplets can be less than 10 times the average diameter of the base particles used. Other thermally based inkjet technologies can be used to deliver controlled shrinkage agent droplets to specific areas of a powder bed.

[0039] In other embodiments, when applied to a hot powdered composition, the shrinkage agent can be provided in a solidified form. When the temperature of the shrinkage agent reaches the temperature of the powdered composition, the shrinkage agent melts and helps to partially reduce or disperse the blocking material. Solid shrinkage agents can be particularly useful when used with metallic or alloy base particles that require higher temperatures to melt or soften. In such embodiments, the shrinkage agent can be selected to have sufficient thermal stability at high temperatures corresponding to the melting or softening points of the base particles to allow the metallic or alloy base particles to agglomerate before evaporation. The temperature of the powdered composition can be locally modified to aid in the melting or evaporation of the shrinkage agent and to help better agglomerate the base particles.

[0040] After selectively applying a shrinkage agent to achieve the desired interconnection of the basic particles, the shrinkage agent can be removed from the aggregated material. For example, in some embodiments, controlled evaporation of most of the shrinkage agent can help remove blocking material without significantly adversely affecting the mechanical properties of the continuous aggregated portion.

[0041] This system and method can be used to create 3D parts from composite layers of coalescing materials, for any selected combination of base particles, barrier materials, and shrinkage agents. In some embodiments, this method of forming interconnected or continuous material layers can be applied multiple times to create 3D parts from composite layers. Multiple base materials with different melting or softening points can be printed simultaneously into a single part. Furthermore, multiple shrinkage agents that react better with certain base materials can be applied simultaneously. While laser irradiation is not required to coalesce polymer materials, it can help produce better parts. Laser irradiation can help combine multiple materials with different melting or softening points into a single part.

[0042] In some implementations, the material group consisting of polymer particles, barrier materials, and shrinkage agents is specific to the material to be printed. Because different chemicals have varying plasticizing abilities on certain polymer materials, some shrinkage agents are better suited to certain polymer particles. For example, propylene carbonate does not plasticize or help PEEK polymer particles aggregate with their neighboring particles. It simply evaporates too quickly, leaving the particles unchanged.

[0043] In some embodiments, the powdered composition can be processed under a vacuum. To achieve the lowest possible thermal conductivity of the aerogel particles, they can be placed in a vacuum. Performing this method under even a slight vacuum also facilitates the collection of shrinkage agent vapors for safe and reusable applications. In some embodiments, the shrinkage agent vapors are collected, condensed, and recovered for processing and creating more continuous layers of material.

[0044] Example

[0045] The following embodiments are provided to illustrate preferred embodiments of the invention. These embodiments will help those skilled in the art to recognize more advantageous details of the invention. The procedures performed in the following embodiments represent procedures and techniques discovered by the inventors to demonstrate the functionality and practice of the invention. However, given the disclosure of this invention, those skilled in the art should understand that considerable changes can be made to specific embodiments without departing from the scope and intent of the invention, while still obtaining similar results.

[0046] Example 1:

[0047] Figure 2 illustrates the use of three different barrier materials. The presence of these barrier materials in the powdered composition enables the polymer material to withstand high temperatures for extended periods. Figure 2aAerogel particles (D5) (powdered particles from JIOS aerogel) were added to used or recycled PA2200 (a PA-12 from Advanced Laser Materials) at loadings of 0, 1, 2, 3, 5, and 10%. The powdered composition was placed on a glass slide and then heated on a hot plate set to 280°C. The slide was heated for specified times of 0, 1, 5, 15, and 45 minutes, after which the timing was stopped, and the slide was removed from the heat source to cool. Then, after each time interval, a razor blade was scraped across the powder surface at room temperature; if the powder had not yet visibly fused together, the razor blade would draw a line across the powder. The timing was restarted when the slide was placed back on the hot plate. The powdered composition containing only PA2200 powder, without any obstructing particles, melted rapidly after 1 minute because the melting point of PA2200 powder is 172-180°C, while the hot plate is at least 100°C higher than that melting point. After 5 minutes, the polymer particles in the 1% and 3% powder compositions began to agglomerate, forming larger polymer flakes. After 15 minutes, the 0%, 1%, 2%, and 3% powder compositions fused together. After 45 minutes, the 5% powder composition began to agglomerate and fuse into larger flakes, but the 5% and 10% compositions remained loose and could be scraped off the substrate, as shown. Figure 2a The rightmost image is shown. This example simply illustrates the benefits of using hydrophobic aerogel particles for insulation and the insulation particles themselves.

[0048] Example 2:

[0049] Hydrophobically treated fumed silica (FS) (Cabot TS-530) particles can also be used as barrier particles in powdered compositions. These particles have a surface treatment to repel adjacent softened or melted particles, and they also possess a degree of thermal insulation due to their interconnected chain network of silica nanoparticles. Figure 2bThe table shows the percentage of loading required to prevent significant agglomeration of PA2200 polymer particles after time intervals of 1, 5, 15, and 45 minutes when maintained at a temperature 100°C above the melting point. After 1 minute of heating, only the powdered composition with 0% FS of PA2200 particles agglomerated, and the composition with 1% FS also showed significant agglomeration because the blade could not separate the powder. After 5 minutes of heating, the compositions with 0–3% FS agglomerated, and only the compositions with 5% and 10% FS remained powdery. After 15 minutes, significant powder oxidation or browning was observed, and only 10% FS could be moved or scraped off, but it had begun to peel off. At this 10% loading, the PA2200 powder did not have enough polymer material or a sufficiently high melt flow rate to form an agglomerated film, and the PA2200 powder was dispersed very thinly. After 45 minutes, no load could be easily scraped off the glass slide (scratched). Figure 2a Compared to powdered compositions using D5 as a barrier material, higher FS loading and a shorter time at T=280°C are required to keep PA2200 powder from agglomerating.

[0050] Example 3:

[0051] Polytetrafluoroethylene (PTFE) particles FLUO 400SM from Micro Powders can also act as a barrier in powdered compositions. These particles have a low surface energy and are more hydrophobic, helping to repel adjacent softened or melted particles. While these particles have a higher density than aerogel or fused silica particles, and significantly higher thermal conductivity (PTFE has a thermal conductivity of approximately 0.25 W / m K, compared to 0.02–0.03 W / m K for aerogel), they are also effective in preventing particle formation. Figure 2c This demonstrates the adverse effect of higher PTFE loading on the dry flowability of the powdered composition. Higher loading compositions are more prone to agglomeration. Figure 2b Compared to powdered compositions using FS as a barrier material, compositions with 5% PTFE agglomerated before compositions with 5% FS agglomerated, but due to differences in powder packing density, the volume of PTFE in the 5% PTFE composition was smaller than the volume of FS in the 5% FS composition. After 1 minute, compositions with 3% and 5% PTFE had fused together. After 5 minutes, compositions with 10-30% PTFE remained powdery. After 45 minutes, only compositions with 20% and 30% PTFE could still be scraped apart. The order of effectiveness of barrier materials in preventing PA-12 particle agglomeration is D5 > FS > PTFE. Among the limited materials tested so far, the best results were observed when the barrier material included D5 silica aerogel particles.

[0052] Example 4:

[0053] Preventing polymer particle agglomeration or maintaining their separation at temperatures above the melting or softening point of the polymer particles is only part of the answer. A shrinkage agent is used to agglomerate the particles. Figure 3 shows some possible components of shrinkage agents used for various powdered compositions. The shrinkage agent used corresponds to the chemical composition of the system and the temperature range used. Clean glass slides were prepared, on which five different powdered compositions were placed. The powdered compositions contained a barrier material in the range of 0-10% by weight. The slides were then placed on a heated plate set to a specified temperature above the melting or softening point of the polymer particles contained in the powdered compositions. The slides were held at the specified temperature for 5 minutes, and then a shrinkage agent was dropped onto the powder using a pipette. After 9 minutes, the slides were removed from the heated plate and cooled to room temperature. Excess powder was then removed from the slide by shaking the powder on it. Excess powder was not scraped off the slide.

[0054] Methyl benzoate (MBz) of 99.9% purity from Southern Tier Scientific is an example of a shrinkage agent used with PA2200 polymer particles, such as... Figure 3a As shown. MBz evaporates within minutes, leaving behind agglomerated material. A shrinkage agent composed of pure MBz helps agglomerate powdered compositions in the 2-10% D5 range. As the percentage of barrier material in the powdered composition increases, the agglomerated polymer film becomes more easily torn upon cooling. Ideally, a minimum amount of barrier material should be used to create stronger parts. Figure 3a As shown, without the application of a shrinkage agent, the powdered composition remains a free-flowing powder that easily falls off the slide. With an increasing percentage of blocking material in the powdered composition, less powder remains in the area where the shrinkage agent was not applied.

[0055] Figure 3b The possibility of using propylene carbonate (ProCarb) of 99.9% purity from Southern Tier Scientific as a shrinkage agent component was demonstrated. Compared to compositions with 5% and 10%, compositions with 2% and 3% showed fewer cracks and smaller bubbles in the coalescing zone where the shrinkage agent was applied. Specific shrinkage agents are more effective for specific polymers and powdered compositions. It is also noteworthy that if the shrinkage agent is applied before the particles reach a temperature close to their melting or softening point, and the temperature is raised to that point, the shrinkage agent simply evaporates, without sufficient time to facilitate coalescence between particles.

[0056] Example 5:

[0057] Figure 3cThe possibility of using xylene (Klean-Strip GXY24 Xylol) as a shrinkage agent component is shown. More importantly, it demonstrates the possibility of using the amorphous material of the present invention. Polyvinyl chloride (PVC) powder from Vinnolit GmbH & Co. SA1062 / 7 is used as the polymer component of the powdered composition, wherein 0%, 0.5%, 1%, 2%, and 5% of the composition are due to a barrier material, in this case, D5 particles. It is important to note that a smaller amount of barrier material is required to prevent particle agglomeration. The 0.5% powdered composition did not leave any significant amount of powder after shaking the slide. The 0% powdered composition fused together after 9 minutes, although its surface was not as smooth or translucent as the other 0% powdered compositions in Figure 3.

[0058] Another amorphous polymeric polycarbonate (PC) powder from Lexan 40 is used with a ProCarb-based shrinkage agent, such as... Figure 3d As shown. A powdered composition containing 2% or more of a barrier material including D5 is sufficient to create a significant agglomeration region at the site where the shrinkage agent is applied. Other more important amorphous powders can also be used in this invention in a similar manner.

[0059] To further demonstrate the significance of this invention, re-ground PEEK material PEEK 450G Mp140 was obtained from Polyclean Technologies as a polymer component of the powdered composition, wherein 0%, 1%, 2%, 3%, and 5% of the composition are due to a barrier material, in this case, said barrier material is D5 particles of silica aerogel, such as... Figure 3e As shown. In this case, a shrinkage agent component with a higher temperature is used. Some key components of shrinkage agents that can be used at the high temperatures required for materials similar to PEEK can be: phenylmethylsiloxane oligomer (PDM-7040), triphenylphosphine, anthracene, phthalic anhydride, benzophenone, and other available high-temperature chemicals, most of which evaporate at the temperature of the polymerized film. Bezophone from Southern Tier Scientific was used as... Figure 3e The main components of the shrinkage agent. This embodiment illustrates how high-temperature polymer materials and shrinkage agents are used in this invention; it is conceivable that this invention can also be applied to high-temperature amorphous polymers.

[0060] Due to the coarse nature of large droplets applied to the powder using a pipette, these large droplets result in a significant excess of shrinkage agent being applied to the heated powdered composition. Consequently, more shrinkage agent will evaporate, leading to bubbles visible in images of coalesced films. Several methods can be used to prevent these bubbles in the coalesced film and are considered within the scope of this invention. These methods may include, but are not limited to: using less shrinkage agent; using various additives or mixtures in the shrinkage agent or powder to slow or reduce the evaporation rate; maintaining a higher temperature at the top of the heated powdered composition than at the bottom; applying a small amount of shrinkage agent a second time to maintain greater fluidity at the top surface; increasing the application temperature over time; using a thinner layer of powder for coalescence; and other such methods. Insufficient shrinkage agent will cause evaporation to occur too rapidly before the film can benefit from the increased melt flow resulting from the plasticizing effect of the shrinkage agent. Insufficient shrinkage agent will also not allow sufficient time for thermal bridging to occur.

[0061] The present invention may be implemented in other forms without departing from the spirit and essential characteristics of the subject matter. Therefore, the described embodiments should be considered illustrative rather than restrictive in all respects. Although certain preferred embodiments have been described, other embodiments that will be apparent to those skilled in the art are also within the scope of the present invention.

Claims

1. A method for creating interconnected or continuous layers of material, the method comprising: Heating a layer of a powdered composition comprising base particles and a powdered barrier material located around or between the base particles, wherein the barrier material at least partially prevents the base particles from binding or agglomerating together; and When the layer of the powder composition is raised to or maintained at a high temperature at or above the melting or softening point of the base particles, a shrinkage agent is selectively applied to the powder composition. The melting point or softening point of the barrier material is higher than that of the base particles; and The shrinkage agent includes a chemical that increases the flowability of the base particles by acting as a temporary plasticizer, or helps the base particles to at least partially agglomerate at the location where the shrinkage agent is applied by helping to at least partially reduce, disperse, and / or allow the blocking material contained in the powdered composition to form thermal bridges.

2. The method of claim 1, wherein the barrier material has chemical functional groups on its surface that prevent the molten base particles from completely wetting the barrier material.

3. The method of claim 1, wherein the percentage of the blocking material present in the powdered composition is selected to block the base particles from binding or agglomerating together without significantly adversely affecting the mechanical properties of the continuous portion of the agglomeration formed by the base particles after the application of the shrinkage agent.

4. The method of claim 1, wherein the barrier material comprises a thermally insulating material selected to have a sufficiently low thermal conductivity to substantially prevent the base particles from agglomerating at locations where no shrinkage agent has been applied.

5. The method of claim 1, wherein the blocking material comprises particles whose diameter is selected to block the basic particles from agglomerating or coalescing together without significantly adversely affecting the mechanical properties of the continuous portion of the coalescing formed by the basic particles after the application of the shrinkage agent.

6. The method of claim 1, wherein the barrier material comprises a coating or surface functional groups deposited directly on the base particles.

7. The method of claim 1, wherein the base particles comprise a semi-crystalline polymer.

8. The method of claim 1, wherein the base particles comprise an amorphous polymer.

9. The method of claim 1, wherein heating the layer of the powdered composition comprises maintaining the powdered composition at a sufficiently high temperature to generate an interconnected network of molecular chains before solidification, said temperature exceeding the melting point, glass transition temperature, or softening point of the base particles.

10. The method of claim 1, wherein the shrinkage agent comprises a plasticizer, surfactant, or solvent that does not decompose at the high temperature.

11. The method of claim 1, comprising evaporating excess shrinkage agent at the said high temperature.

12. The method of claim 11, further comprising collecting the vapor of the reducing agent for safe and repeated use.

13. The method of claim 1, wherein selective application of the shrinkage agent comprises applying the shrinkage agent by printing, inkjet printing or by on-demand dripping technology.

14. A three-dimensional object comprising multiple interconnected or continuous layers of material formed using the method of claim 1.

15. A material composition for additive manufacturing, the material composition comprising: A powder composition comprising: Basic particles having a first melting point, glass transition temperature, or softening point; and A powdered barrier material located around or between base particles, the barrier material being configured to at least partially prevent the base particles from binding or agglomerating together at or above a first melting point or softening point. and The shrinkage agent is configured to, when the layer of the powdered composition is raised to or maintained at the said high temperature, increase the flowability of the base particles by acting as a temporary plasticizer, or selectively help the base particles to at least partially agglomerate at the location where the shrinkage agent is applied by helping to at least partially reduce, disperse, and / or allow the blocking material contained in the powdered composition to form thermal bridges.

16. The material composition of claim 15, wherein the barrier material comprises a thermally insulating material selected to have a sufficiently low thermal conductivity to substantially prevent the base particles from agglomerating at locations where no shrinkage agent has been applied; Furthermore, the barrier material has chemical functional groups on its surface to prevent the molten base particles from completely wetting the barrier material.

17. The material composition of claim 15, wherein the percentage of the blocking material present in the powder composition is selected to block the basic particles from binding or agglomerating together without significantly adversely affecting the mechanical properties of the continuous portion of the agglomeration formed after the application of the shrinkage agent.

18. The material composition of claim 15, wherein the base particles comprise a semi-crystalline polymer.

19. The material composition of claim 15, wherein the base particles comprise an amorphous polymer.

20. The material composition of claim 15, wherein the powdered composition is configured to be held at a sufficiently high temperature to generate an interconnected network of molecular chains before solidification, said temperature exceeding the melting point, glass transition temperature, or softening point of the base particles.

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