Patent Description:
The manufacturing of polymeric three-dimensional bodies based on a layer by layer built up of a radiation curable liquid material has become of increasing interest, especially in view of the enhancement in production speed if a bottom-up technique is employed. One disadvantage of three-dimensional printing is the limited spectrum of curable resins that can be used and the limited material type of formed polymeric bodies. It is desirable to expand the scope of polymer materials that may be formed during 3D printing to a broader spectrum of polymers, such as particularly fluoropolymers, for example, polytetrafluoroethylene (PTFE). <CIT>, a document relevant under Article <NUM> (<NUM>) EPC, describes methods for making a shaped fluoropolymer by additive processing using a polymerizable binder. Also 3D printable compositions for making shaped fluoropolymer articles, and articles comprising a shaped fluoropolymer are disclosed. From <CIT> a method for continuously forming a three-dimensional body from a mixture is known, the mixture comprising at least <NUM> vol % solid partulces and a radiation curable material. The method allows the continuous production of three-dimensional bodies comprising a high content of ceramic particles at a forming speed of at least <NUM>/hour. <CIT> discloses a three-dimensional printing build material composition including a polymer particle, and a radiation absorbing additive mixed with the polymer particle. The radiation absorbing additive has a particle size ranging from about <NUM> to about <NUM>, and the radiation absorbing additive is to absorb incident radiation having wavelengths ranging from <NUM> to <NUM>.

According to independent claim <NUM>, a method for forming a three-dimensional body is described, the method comprising providing a liquid mixture comprising a curable binder, a dye and dispersed solid fluoropolymeric particles; and forming a three-dimensional body from the liquid mixture by curing the binder to form a cured binder, wherein forming includes translation and growth of the three-dimensional body from an interface of an inhibition zone of the liquid mixture, wherein the inhibition zone is a zone of the liquid mixture comprising an inhibitor which can limit or prevent curing of the mixture by electromagnetic radiation; and wherein forming the 3D-body from the liquid mixture includes selecting an amount of the dye of at least <NUM> wt% and not greater than <NUM> wt%, based on the total weight of the mixture, to control a size resolution of the formed three-dimensional body.

For example, a process, method, article, or apparatus that comprises a list of features is not necessarily limited only to those features but may include other features not expressly listed or inherent to such process, method, article, or apparatus.

As used herein, and unless expressly stated to the contrary, "or" refers to an inclusive- or and not to an exclusive-or.

Also, the use of "a" or "an" are employed to describe elements and components described herein. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.

As used herein, the term mixture refers to a fluid of a certain viscosity, including a liquid component and solid particles. The liquid component may include a curable binder and a solvent.

As used herein, the term solid polymeric particles refers to polymeric particles that remain solid in the mixture and do not dissolve in the liquid component of the mixture during forming of the three-dimensional body. The solid polymeric particles include a fluoropolymer.

Various embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings.

The present disclosure relates to a method of forming a three-dimensional body from an interface of a mixture including dispersed solid fluoropolymeric particles, a dye, and a curable binder. The method can include removal of at least a portion of the cured binder from the formed body wherein the shape of the body can be maintained.

According to one embodiment, the method may include the following steps: <NUM>) providing a mixture comprising dispersed solid polymeric particles, a dye, and a curable binder; <NUM>) forming a three-dimensional body from an interface of the mixture; <NUM>) drying the formed three-dimensional body at elevated temperatures to remove solvent present in the formed body; <NUM>) removing at least a portion of the cured binder by heating the three-dimensional body to a decomposition temperature of the binder; and <NUM>) sintering the three-dimensional body close to a thermal transition temperature of the solid fluoropolymeric particles to form a sintered three-dimensional body. A simplified scheme of the process is illustrated in <FIG>.

In one embodiment, the mixture can be prepared by using a dispersion of solid fluoropolymeric particles in a solvent, and mixing the dispersion together with the curable binder and the dye. In one aspect, the binder may be at least partially soluble in the solvent. The forming of the three-dimensional body can be conducted in an assembly (<NUM>), as illustrated in <FIG>. The assembly can have a computer controlled electromagnetic radiation unit (<NUM>), a chamber (<NUM>), and a construction unit. The electromagnetic radiation unit (<NUM>) can be configured to deliver electromagnetic radiation to a portion of the mixture, wherein the electromagnetic radiation can have a particular wavelength, including for example an ultraviolet radiation (UV) or visible light. The assembly can include a radiation source (<NUM>), for example, a laser or a light emitting diode (LED), which can be configured to project a varying computer-aided design / computer-aided manufacturing (CAD/CAM) created two-dimensional image onto a transparent window (<NUM>) at the bottom of the chamber (<NUM>). The chamber (<NUM>) can include a mixture (<NUM>) that can include a radiation curable material and solid particles. The transparent window (<NUM>) of the chamber (<NUM>) can be semipermeable for a particular inhibitor, which may be a gaseous material. In such instances, the semipermeable layer is selectively permeable, such that it is configured to allow for the transfer of the inhibitor into the mixture, but may not allow transfer of other materials (e.g., water) through the transparent window (<NUM>). The transparent window (<NUM>) may include an additional semipermeable layer (not shown) for the penetration of an inhibitor, for example air or oxygen, into the mixture (<NUM>) of the chamber (<NUM>). During the forming process, the inhibitor may enter the chamber (<NUM>) by permeating the transparent window (<NUM>) and form an inhibition zone (<NUM>) at a bottom region of the mixture (<NUM>). In the inhibition zone (<NUM>) the inhibitor limits or prevents curing of the mixture (<NUM>) by the electromagnetic radiation.

According to one embodiment, a carrier plate (<NUM>) can be positioned above the chamber (<NUM>). The position between the carrier plate (<NUM>) and the mixture in the chamber (<NUM>) can be changed during the forming process to facilitate formation of the three-dimensional body. When the formation of the three-dimensional body is started, the carrier plate (<NUM>) can be emerged into the mixture (<NUM>) up to a pre-calculated distance from the interface of the inhibition zone (<NUM>). According to one embodiment, the pre-calculated distance corresponds to a portion of the mixture that can be radiation cured (translated from liquid to solid state) if subjected to electromagnetic radiation from the radiation unit (<NUM>) underneath the chamber (<NUM>), and is further on called "translating portion" (<NUM>). The radiation cured translating portion (<NUM>) can be adhered to the carrier plate (<NUM>) and can be vertically moved away from the interface of the inhibition zone (<NUM>). Concurrently with the upwards movements of the carrier plate (<NUM>) and the attached solidified translating portion (<NUM>), mixture (<NUM>) from the sides of the polymerization chamber or from a reservoir (<NUM>) can fill the released space. The construction is designed to move the carrier plate (<NUM>) continuously upwards in vertical direction (i.e., Z-direction) at a speed that corresponds to the time needed for radiation curing mixture (<NUM>) that replaces the upwards moved solidified translating portion.

<FIG> includes an illustration of a partially formed three-dimensional body according to an embodiment. The partially formed body includes three solidified and unified translating portions (<NUM>) and one translating portion (<NUM>) which is subjected to radiation curing.

The increase in distance between the carrier plate (<NUM>) and the mixture (<NUM>) when forming the three-dimensional body can be caused by moving either the carrier plate (<NUM>) or the chamber (<NUM>) or both carrier plate (<NUM>) and chamber (<NUM>) in relation to each other.

The carrier plate (<NUM>) of the assembly may be configured for continuous movement to facilitate formation of the three-dimensional body as the carrier plate (<NUM>) is moved.

The inhibition zone (<NUM>) is a zone of the mixture, which is only distinguished from the other part of the mixture by the presence of an inhibitor in a concentration that the mixture may not cure if exposed to electromagnetic radiation. Actual solidification and forming of the three-dimensional body starts at the interface of the inhibition zone (<NUM>). The interface of the inhibition zone (<NUM>) can also be considered as an interface of the mixture from where the forming of the three-dimensional body starts.

In order to assure curing of the mixture throughout a thickness of the translating portion (<NUM>), the cure depth (<NUM>) can be controlled that it reaches a larger distance through the mixture in Z-direction from the transparent window (<NUM>) than the thickness of the translating portion (<NUM>). In one embodiment, the cure depth (<NUM>) may reach at least <NUM>% further than the thickness of the translating portion (<NUM>), such as at least <NUM>%, at least <NUM>%, or at least <NUM>%.

In one embodiment, the thickness of the translating portion (<NUM>) can be at least <NUM>, such as at least <NUM>, at least <NUM>, such as at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, or at least <NUM>. In another embodiment, the thickness of the translating portion may be not greater than <NUM>, such as not greater than <NUM>, not greater than <NUM>, not greater than <NUM>, or not greater than <NUM>. Thickness of the translating portion can be a value between any of the maximum and minimum values note above, such as from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>.

The formation of the three-dimensional body may not necessarily be considered a layer-by-layer forming process. Instead, the forming process (e.g., curing) may be in the form of a gradient of solidification (e.g., polymerization).

As used in the context of the present disclosure, continuous translation and growth of the three-dimensional body means that the carrier plate (<NUM>) can be moved in a continuous manner or in discrete steps with short stops between each step. In certain instances, the continuous translation and growth will be characterized by a gradient of solidification that is maintained while forming the three-dimensional body. A gradient of solidification means that a continuous polymerization reaction is maintained across the thickness of the translating portion (<NUM>), with the lowest degree of solidification next to the interface of the inhibition zone (<NUM>) and the greatest degree of solidification at the opposite end across the thickness of the translating portion (<NUM>). The three-dimensional body formed by the process of continuous translation can thereby possess a non-layered internal structure, such that in a crosscut along the z-axis, changes in the morphology of the three-dimensional body are not visible to the naked eye.

In those embodiments utilizing short stops in the movement of the carrier plate (<NUM>), such stops are generally brief and suitable for maintaining the above-described gradient of solidification. According to one embodiment, the stops can be for a duration of at least <NUM> microsecond, such as at least <NUM> microseconds, at least <NUM> microseconds, at least <NUM> microseconds or even at least <NUM> microseconds. In other embodiments, the stops may be for a duration of not longer that <NUM> second, such as not longer than <NUM> seconds, not longer than <NUM> seconds or not longer than <NUM> seconds or even not longer than <NUM> seconds. It will be appreciated that the stops can have a duration within a range including any of the minimum and maximum values note above, such as from <NUM> microsecond to <NUM> second or from <NUM> microseconds to <NUM> seconds or from <NUM> microseconds to <NUM> seconds.

In further embodiments, the method of the present disclosure can also include longer stops during the forming of the three-dimensional body, such that the gradient of solidification may be interrupted and the translation is not continuous as defined above. Such longer stops may be desired for the making of a body having defined regions which are cleavable.

The inhibition zone (<NUM>) can be a part of the mixture and located next to the transparent window (<NUM>) of the chamber, where the mixture does not cure or only to a very limited extend under electromagnetic radiation. Accordingly, the inhibition zone (<NUM>) may facilitate limited or no adhesion of the radiation cured material to the bottom of the chamber (<NUM>), which may facilitate simpler release of the body from the chamber after forming is completed.

The inhibition zone (<NUM>) can be formed when the inhibitor enters the chamber (<NUM>) through the transparent and semipermeable window (<NUM>), and may be regulated in its thickness by the concentration of the inhibitor.

In one embodiment, the thickness of the inhibition zone (<NUM>) can be varied by varying the intensity of the applied electromagnetic radiation.

In another embodiment, the thickness of the inhibition zone (<NUM>) can be varied by varying the pressure of a gaseous inhibitor for forming the inhibition zone.

In one embodiment, the thickness of the inhibition zone may be at least <NUM>, such as at least <NUM>, at least <NUM>, or at least <NUM>. In another embodiment, the inhibition zone may not be greater than <NUM>, such as not greater than <NUM>, not greater than <NUM>, or not greater than <NUM>. It will be appreciated that the thickness of the inhibition zone can be a value between any of the maximum and minimum values noted above, such as from <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>.

The inhibitor may preferably be an oxygen containing gas, such as air, mixtures of an inert gas and oxygen, or pure oxygen. In another aspect, when oxygen cannot inhibit the activity of the photoinitiator (for example, when a cationic photoinitiator is used) the inhibitor can be an amine, e.g., ammonia, ethyl amine, di and trialkyl amines, carbon dioxide, or combinations thereof.

In one embodiment, the inhibitor can be pure oxygen, and the oxygen may penetrate the semipermeable layer in an amount of at least <NUM> Barrer, such as at least <NUM> Barrer, at least <NUM> Barrer, at least <NUM> Barrer, or at least <NUM> Barrer.

Although the term "inhibition zone" appears to indicate that no polymerization reaction may take place in that area of the mixture, it will be appreciated that polymerization reactions can also occur to a limited extent in the inhibition zone (<NUM>). The inhibition zone (<NUM>) may be also described as a gradient of polymerization, where with increasing distance from the bottom surface of the chamber larger amounts of polymerization reactions can happen, but these polymerization reactions may not completely cure the mixture, and the mixture is still maintained in a liquid stage. The interface of the inhibition zone (<NUM>) may be understood as the area of the inhibition zone (<NUM>) where the polymerization reactions start to form a solid material.

Varying the thickness of the translating portion (<NUM>) can include adjusting the position of the carrier plate (<NUM>) onto which the three-dimensional body is attached relative to the interface of the inhibition zone (<NUM>).

The binder of the mixture is a curable binder, particularly a radiation curable binder. During forming of the body, the mixture can be subjected to electromagnetic radiation having a wavelength in a range from <NUM> to <NUM> and thereby curing the radiated binder. In a preferred aspect, the range of the electromagnetic radiation may be from <NUM> to <NUM>, or from <NUM> to <NUM>. In embodiments, the electromagnetic radiation can be created by a laser, a light emitting diode (led), or by electron beam radiation.

In one embodiment, the electromagnetic radiation applied for curing the binder can have an energy of at least <NUM> mJ/cm<NUM>, such as at least <NUM> mJ/cm<NUM>, at least <NUM> mJ/cm<NUM>, at least <NUM> mJ/cm<NUM>, at least <NUM> mJ/cm<NUM>, at least <NUM> mJ/cm<NUM> or at least <NUM> mJ/cm<NUM>. In another embodiment, the electromagnetic radiation can have an energy not greater than <NUM> mJ/cm<NUM>, such as not greater than <NUM> mJ/cm<NUM>, not greater than <NUM> mJ/cm<NUM>, not greater than <NUM> mJ/cm<NUM>, not greater than <NUM> mJ/cm<NUM>, not greater than <NUM> mJ/cm<NUM>, or not greater than <NUM> mJ/cm<NUM>. It will be appreciated that the electromagnetic radiation energy can be a value between any of the maximum and minimum values noted above, such as from <NUM> mJ/cm<NUM> to <NUM> mJ/cm<NUM>, from <NUM> mJ/cm<NUM> to <NUM> mJ/cm<NUM>, from <NUM> mJ/cm<NUM> to <NUM> mJ/cm<NUM>, or from <NUM>/cm<NUM> to <NUM> mJ/cm<NUM>.

In a particular embodiment, the method of the present disclosure may cure the binder in the translating portion (<NUM>) during continuous forming of the three dimensional body at a UV power of at least <NUM> mW/cm<NUM>, such as at least <NUM> mW/cm<NUM>, at least <NUM> mW/cm<NUM>, or at least <NUM> mW/cm<NUM>. In another particular embodiment, the applied UV power during forming may be not greater than <NUM> mW/cm<NUM>, such as not greater than <NUM> mW/cm<NUM>, not greater than <NUM> mW/cm<NUM>, not greater than <NUM> mW/cm<NUM>, not greater than <NUM> mW/cm<NUM>, not greater than <NUM> mW/cm<NUM>, not greater than <NUM> mW/cm<NUM>, not greater than <NUM> mW/cm<NUM>, or not greater than <NUM> mW/cm<NUM>. It will be appreciated that the applied UV power can be a value between any of the maximum and minimum values noted above, such as from <NUM> mW/cm<NUM> to <NUM> mW/cm<NUM>, from <NUM> mW/cm<NUM> to <NUM> mW/cm<NUM> or from <NUM> mW/cm<NUM> to <NUM> mW/cm<NUM>.

The electromagnetic radiation (<NUM>) can cure the binder in the mixture (<NUM>) up to a certain distance throughout the mixture, hereinafter called the cure depth (<NUM>). The cure depth (<NUM>) may be affected by the size, type, and concentration of the solid polymeric particles and the refractive index of the particle slurry.

The method of the present disclosure can continuously manufacture a three-dimensional body at a high production speed. In one aspect, the creating of the three-dimensional body can be completed at a speed rate of at least <NUM>/hour, such as at least <NUM>/hour, at least <NUM>/hour, at least <NUM>/hour, at least <NUM>/hour, at least <NUM>/hour, at least <NUM>/hour, or at least <NUM>/hour. In another aspect, the forming speed may be not greater than <NUM>/hour, such as not greater than <NUM>/hour, not greater than <NUM>/hour, not greater than <NUM>/hour, or not greater than <NUM>/hour. The forming speed can be a value between any of the maximum and minimum values noted above, such as from <NUM>/hour to <NUM>/hour, from <NUM>/hour to <NUM>/hour, or from <NUM>/hour to <NUM>/hour.

The solid particles can be fluoropolymeric solid particles having a thermal transition temperature which is higher than the decomposition temperature of the cured binder. This can allow at least a partial removal of the cured polymeric binder by maintaining the shape of the three-dimensional body, wherein the solid fluoropolymeric particles form a percolated network. As used herein, the thermal transition temperature of the solid fluoropolymeric particles relates to the temperature at which the fluoropolymeric particles start melting or start to undergo a glass transition like stage. The thermal transition temperature can be determined by Differential Scanning Calorimetry (DSC) or Differential Thermal Analysis (DTA). <FIG> illustrates an example of a DSC measurement for solid PTFE particles, showing an onset ( i.e., start) of the melting point of the PTFE particles at <NUM>. Furthermore, as used herein, the decomposition temperature of the binder relates to the temperature at which 5wt% of the binder based on the total weight of the binder is decomposed into volatile compounds and removed from the body. The decomposition temperature of a binder can be determined, for example, from a Thermal Graphimetric Analysis (TGA) graph, as illustrated in <FIG>, and further explained in the examples.

The solid polymeric particles are fluoropolymers. Non-limiting examples of fluoropolymers can be polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene (FEP), perfluoroalkoxyethylene (PFA), ethylene-tetrafluoroethylene (ETFE), polyvinylidone fluoride (PVDF), ethylene-chlorotrifluoroethylene (ECTFE), perfluoromethyl vinyl ether (MFA), or any combination thereof. In a particular embodiment, the material of the solid particles can be PTFE. In another particular embodiment, the material of the solid particles can be PFA. In yet a further particular embodiment, the material of the solid particles can be FEP.

In embodiments, the fluoropolymeric solid particles can have a thermal transition temperature of at least <NUM>, such as at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, or at least <NUM>. In other embodiments, the thermal transition temperature of the solid particles may be not greater than <NUM>, such as not greater than <NUM>, not greater than <NUM>, or not greater than <NUM>. The thermal transition temperature of the solid particles can be a value between any of the maximum and minimum values noted above, such as from <NUM> to <NUM>, from <NUM>° to <NUM>, or from <NUM> to <NUM>.

The solid particles contained in the mixture can have an average primary particle size of at least <NUM>, such as at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, or at least <NUM>. In another aspect, the solid particles can have an average primary particle size of not greater than <NUM>, such as not greater than <NUM>, not greater than <NUM>, or not greater than <NUM>. The average primary size of the solid particles can be a value between any of the minimum and maximum values noted above, such as from <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>. As used herein, the average primary particle size of the solid polymeric particles relates to the average particles size in single form, not including particle agglomerates.

In a certain embodiment, the solid polymeric particles dispersed in the mixture can form solid polymeric particle aggregates. In one aspect, the solid particles aggregates can have an average particle size of not greater than <NUM>, such as not greater than <NUM>, not greater than <NUM>, or not greater than <NUM>.

In a further embodiment, the solid fluoropolymeric particles can have a molecular weight of at least <NUM>×<NUM><NUM> g/mol, such as at least <NUM>×<NUM><NUM> g/mol, at least <NUM>×<NUM><NUM> g/mol, at least <NUM>×<NUM><NUM> g/mol, or at least <NUM>×<NUM><NUM> g/mol. In another embodiment, the molecular weight of the solid fluoropolymeric particles may be not greater than <NUM>×<NUM><NUM> g/mol, such as not greater than <NUM>×<NUM><NUM> g/mol, or not greater than <NUM>×<NUM><NUM> g/mol. The molecular weight of the solid fluoropolymeric particles can be a value between any of the maximum and minimum values noted above, such as from <NUM>×<NUM><NUM> g/mol to than <NUM>×<NUM><NUM> g/mol, from <NUM>×<NUM><NUM> g/mol to <NUM>×<NUM><NUM> g/mol, or from <NUM>×<NUM><NUM> g/mol to <NUM>×<NUM><NUM> g/mol.

In yet a further embodiment, the solid fluoropolymeric particles in the mixture, before forming of a three-dimensional body and sintering of the body, can have a crystallinity of at least <NUM>%, such as at least <NUM>%, at least <NUM>%, or at least <NUM>%.

A solid fluoropolymeric particle, as used herein, remains solid in the mixture during preparing of the mixture and forming of the three-dimensional body and can include at least <NUM> wt% of polymers based on the total weight of the particle, such as at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, or at least <NUM> wt% polymer based on the total weight of the solid particle. Other components in the solid fluoropolymeric particle may be inorganic or organic compounds. In a particular embodiment, the solid fluoropolymeric particles of the present disclosure may consist essentially of a fluoropolymer including only unavoidable impurities.

The amount of the solid particles contained in the mixture can be in a range that a percolated network be formed, and that the created three-dimensional body can be densified without falling apart upon burnout of the binder. In one embodiment, the amount of the solid particles can be at least <NUM> vol%, such as at least <NUM> vol%, at least <NUM> vol%, at least <NUM> vol%, or at least <NUM> vol% based on the total volume of the mixture. In another embodiment, the particle content can be not greater than <NUM> vol%, such as not greater than <NUM> vol%, not greater than <NUM> vol%, not greater than <NUM> vol%, or not greater than <NUM> vol%. It will be appreciated that the amount of solid particles can be a value between any of the maximum and minimum values noted above, such as from <NUM> vol% to <NUM> vol %, from <NUM> vol% to <NUM> vol%, or from <NUM> vol% to <NUM> vol% based on the total volume of the mixture.

In a certain embodiment, the mixture can be prepared by using as starting material a dispersion of the solid particles. In one aspect, the dispersion may include solid fluoropolymeric particles, a solvent, and a surfactant. The solid polymeric particles may not dissolve in the solvent of the dispersion and remain solid. Suitable solvents of the dispersion can be water, ethanol, acetone, dimethyl sulphoxide (DMSO), dimethylformamide (DMF), tetrahydrofuran (THF), methyl-ethylketone, ethyl acetate, methylene chloride, N-methyl-<NUM>-pyrrolidone (NMP), a fluor-solvent, or any combination thereof.

In one embodiment, the solvent can be a component of the mixture exceeding the amount of the binder and/or the solid particles. In aspects, an amount of the solvent can be at least <NUM> wt% based on a total weight of the mixture, such as at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, or at least <NUM> wt%. In another aspect, the amount of the solvent can be not greater than <NUM> wt% based on a total weight of the mixture, such as not greater than <NUM> wt%, not greater than <NUM> wt%, not greater than <NUM> wt%, not greater than <NUM> wt%, or not greater than <NUM> wt%. The amount of solvent in the mixture can be a value between any of the maximum and minimum numbers noted above, such as from <NUM> wt% to <NUM> wt%, from <NUM> wt% to <NUM> wt%, or from <NUM> wt% to <NUM> wt%.

In a certain embodiment, it is desirable that the curable binder is at least partially soluble in the solvent contained in the mixture. The curable binder of the mixture of the present disclosure can comprise polymerizable monomers and/or polymerizable oligomers. Non-limiting examples of polymerizable monomers and oligomers can be: an acrylate, an acrylamide, an urethane, a diene, a sorbate, a sorbide, a carboxylic acid ester, or any combination thereof. In a particular embodiment, the curable binder can include a water-soluble difunctional acrylic monomer. In another particular embodiment, the curable binder can be a combination of a water-soluble difunctional acrylic monomer and a water-insoluble polyester acrylate oligomer. Further examples of acrylate binder can be <NUM>,<NUM>,-butanediol diacrylate or <NUM>,<NUM>-hexanediol diacrylate.

In an embodiment, an amount of the curable binder can be at least <NUM> wt% based on a total weight of the mixture, such as at least <NUM> wt%, at least <NUM> wt%, or at least <NUM> wt%. In other embodiments, the binder may be present in an amount not greater than <NUM> wt% based on a total weight of the mixture, such as not greater than <NUM> wt%, not greater than <NUM> wt%, not greater than than15 wt%, not greater than <NUM> wt%, or not greater than <NUM> wt%. The amount of the curable binder in the mixture can be a value between any of the maximum and minimum values noted above, such as from <NUM> wt% to <NUM> wt%, from <NUM> wt% to <NUM> wt%, or from <NUM> wt% to <NUM> wt% based on a total weight of the mixture.

In order to keep the solid particles well dispersed in the mixture, one or more surfactants can be added to the mixture. If a dispersion of solid particles is used as starting material, the surfactant contained in the dispersion may be sufficient to keep the solid particles dispersed in the final mixture. The surfactant can be a non-ionic surfactant, an anionic surfactant, a cationic surfactant, or any combination thereof. In certain embodiments, the surfactant can be a fatty acid ester, a fluorosurfactant, or a combination thereof.

In one embodiment, the surfactant contained in the mixture can be present in an amount of at least <NUM> wt%, such as at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt% or at least <NUM> wt% based on the total weight of the of the mixture. In another embodiment, the amount of surfactant may be not greater than <NUM> wt%, such as not greater than <NUM> wt%, not greater than <NUM> wt%, or not greater than <NUM> wt% based on a total weight of the mixture. The amount of surfactant can be a value between any of the maximum and minimum values noted above, such as from <NUM> wt% to <NUM> wt%, from <NUM> wt% to <NUM> wt% or from, or from <NUM> wt% to <NUM> wt%.

The mixture can further include a photoinitiator. The photoinitiator can be a free-radical photoinitiator. In a particular aspect, a free-radical photoinitiator can be employed, which can be inhibited by the presence of oxygen. Non-limiting examples of free-radical photoinitiators can include ketones or phosphine oxides, such as IRGACURE™ <NUM> (bis(<NUM>,<NUM>,<NUM>-trimethylbenzoyl)-phenylphosphineoxide), ESSTECH TPO (<NUM>,<NUM>,<NUM>-trimethylbenzoyl)-phenylphosphineoxide) or a combination thereof.

In an embodiment where a cationic photoinitiator is used, the photopolymerization generally tends to be slower and cannot be inhibited by oxygen. In this aspect, instead of oxygen as inhibitor, a Bronsted acid or Lewis acid, such as metal halides and their organometallic derivatives can be employed and released from the bottom window of the polymerization chamber to form an inhibition zone. The mixture further includes a dye. The dye can function as an additional inhibitor by absorbing excess radiation energy and may improve the resolution of the formed three-dimensional body. In one embodiment, the dye can be a fluorescent dye. The fluorescent dye can be selected from the classes of rhodamine dyes, fluorone dyes, acridine dyes, cyanine dyes, phenanthrine dyes, or acridine dyes. In one aspect, the dye can be a rhodamine, for example, Rhodamine B, Rhodamine <NUM>, Rhodamine <NUM>, or a rhodamine derivative, e.g., Rhodamine B isothiocyanate. In a particular aspect, the dye may be Rhodamine B. In another aspect, the dye can be a fluorone dye, for example Fluorescein. Other suitable examples of dyes, but not limited thereto, can be IR-<NUM> perchlorate (<NUM>,<NUM>',<NUM>,<NUM>,<NUM>',<NUM>'-<NUM>,<NUM>',<NUM>,<NUM>'-di-benzo-<NUM>,<NUM>'-indotricarbocyanine perchlorate), Crystal Violet, or a combination thereof.

The suitability of a dye with regard to the resolution and the strength of the formed body can vary largely. For example, it has been observed that Rhodamine B can be advantageous for improving the resolution of a printed body with no detrimental influence on the strength of the body, while Fluorescin may improve the resolution of a formed body under certain conditions but can be of disadvantage regarding a desired strength of the body.

The amount of dye in the mixture for forming a three dimensional body having an improved resolution of the formed body in comparison to not using a dye can depend on several factors, for example, the amount of solid polymeric particles in the mixture, the thickness of the inhibition zone, the radiation intensity during forming, the forming speed, the amount of photoinitiator, or a combination thereof. The dye is present in an amount of at least <NUM> wt% based on the total weight of the mixture, such as at least <NUM> wt%, or at least <NUM> wt%, or at least <NUM> wt%, or at least <NUM> wt% based on the total weight of the mixture. In another embodiment, the amount of dye in the mixture may be not greater than <NUM> wt%, such as not greater than <NUM> wt%, or not greater than <NUM> wt%, or not greater than <NUM>. The amount of dye in the mixture is a value between any of the maximum and minimum values noted above, namely from <NUM> wt% to <NUM> wt%, from <NUM> wt% to <NUM> wt%, or from <NUM> wt% to <NUM> wt% based on the total weight of the mixture. In a particular embodiment, the dye can be Rhodamine B in an amount of at least <NUM> wt% to not greater than <NUM> wt%.

The mixture of the present disclosure can further include one or more additives. Non-limiting examples of additives can be plasticizers, dispersing agents, debinding accelerators, cross-linking monomers, pH regulators, a pharmaceutically active ingredient, a defoamer, a processing aid, or any combination thereof.

The rheological properties of the mixture containing solid particles and a radiation curable material may be controlled to facilitate suitable formation of a stable and suitably formed three-dimensional body, including for example, a polymeric three-dimensional body having sufficient strength to be self-supporting and capable of handling without detrimental deformation. Also, the force required to continuously pull-up the carrier the force utilized to pull the carrier plate away from the chamber may be adjusted based on various parameters, including but not limited to the rheology of the mixture.

In a further aspect, the mixture may have a low shear viscosity to prevent particle settling over the duration of the forming of the three-dimensional body. Furthermore, the solid polymeric particles contained in the slurry may be uniformly dispersed throughout the radiation curable material when electromagnetic radiation is conducted such that that the three-dimensional body can shrink uniformly during sintering. Non-uniform distribution of the solid polymeric particles may result in forming of undesirable macro-structural or microstructural features, including for example, undesirable porosity.

Under low shear rate may be understood a range of not greater about <NUM> and at least about <NUM>, with corresponding viscosities from at least <NUM> mPa·s (<NUM> cP) to not greater than <NUM> mPa·s (<NUM> cP).

In one embodiment, the mixture may be formed such that the content of agglomerates of the solid particles is limited. In a certain embodiment, the mixture can be essentially free of agglomerates of solid polymeric particles.

In one aspect, the yield point of the mixture may be less than <NUM> Pa, such as less than <NUM> Pa, less than <NUM> Pa, or less than <NUM> Pa at room temperature.

After forming of the three-dimensional body, the body can be subjected to drying for removing the solvent from the formed body. Drying can be conducted at an elevated temperature and/or under applied vacuum. In one embodiment, the drying temperature can be close to the boiling temperature of the solvent being removed from the body, but should not exceed the boiling point of the solvent by more than <NUM>. In a certain aspect, the solvent contained in the three-dimensional body can be water, and the body can be dried at a temperature not greater than <NUM>, such as not greater than <NUM>, not greater than <NUM>, or not greater than <NUM>.

In one embodiment, the three-dimensional body may shrink during drying. The shrinkage of the three-dimensional body after drying, based on the size of the body before drying, can be at least <NUM>%, such as at least <NUM>%, at least <NUM>%, or at least <NUM>%. In another embodiment, the shrinkage after drying can be not greater than <NUM>%, such as not greater than <NUM>%, not greater than <NUM>%, not greater than <NUM>%, or not greater than <NUM>%, based on the total size of the body before drying. The shrinkage can be a value between any of the minimum and maximum values note above, such as from <NUM>% to <NUM>%, from <NUM>% to <NUM>%, or from <NUM>% to <NUM>%. As used herein, the shrinkage in any of the three dimensions (x, y, z) is calculated according to equation <MAT>, where l<NUM> and lf are respectively the initial and final dimensions of the object measured with a caliper.

After drying, the three-dimensional body can be subjected to further heating to remove the cured binder by decomposition to volatile compounds. In a certain embodiment, the decomposition temperature of the binder can be at least <NUM>, such as at least <NUM>, at least <NUM>, or at least <NUM>. In another embodiment, the temperature for decomposing the binder may be not greater than <NUM>, such as not greater than <NUM>, or not greater than <NUM>. The temperature for decomposing the binder can be a value between any of the minimum and maximum values noted above, such as from <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>.

In one embodiment, the cured binder can be decomposed during heat treatment such that a weight loss of the binder in the body can be at least <NUM> wt% based on the total weight of the cured binder, such as at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least 70wt%, at least 80wt%, at least 90wt%, at least 95wt%, at least 98wt%, at least 99wt%, or at least <NUM> wt%.

In one aspect, the temperature during the binder removal can be increased above a decomposition temperature of the binder, but below the thermal transition temperature of the solid polymeric particles contained in the body. In another aspect, complete binder removal may be obtained above the sintering temperature.

Following the removal or partial removal of the cured binder, the three-dimensional body can be subjected to high temperature sintering. During high temperature sintering, the solid polymeric particles of the body can coalesce to form a more densified body by lowering the surface energy.

In one embodiment, the sintering temperature may be not less than <NUM> below a thermal transition temperature of the solid particles, such as not less than <NUM>, not less than <NUM>, not less than <NUM>, not less than <NUM>, not less than <NUM>, or not less than <NUM>.

In another embodiment, the sintering temperature can be not less than <NUM> below the decomposition temperature of the solid polymeric particles, such as not less than <NUM>, not less than <NUM>, not less than <NUM>, not less than <NUM>, or not less than <NUM> below the decomposition temperature of the solid particles.

After high temperature sintering, the bulk density of the sintered three-dimensional body can be at least <NUM>/cm<NUM>, such as at least <NUM>/cm<NUM>, at least <NUM>. cm<NUM>, at least <NUM>/cm<NUM>, at least <NUM>/cm<NUM>, at least <NUM>/cm<NUM>, at least <NUM>/cm<NUM>, at least <NUM>. cm<NUM>, or at least <NUM>/cm<NUM>.

In further embodiments, the sintered three-dimensional body can have a crystallinity of at least <NUM>%, such as at least <NUM>%, at least <NUM>%, or at least <NUM>%.

The formed fluoropolymeric bodies of the present disclosure can have desired strength properties. In one embodiment, a formed fluoropolymeric body after high temperature sintering can have a tensile strength at maximum load of at least 5MPa, such as at least <NUM> MPa, at least <NUM> MPa, at least <NUM> MPa, at least <NUM> MPa, or at least <NUM> MPa, or at least <NUM> MPa. In another aspect, the tensile strength at maximum load may be not greater than not greater than <NUM> MPa, such as not greater than <NUM> MPa, not greater than <NUM> MPa, or not greater than <NUM> MPa. The tensile stress at maximum load may be a value between any of the minimum and maximum values noted above.

The sintered three-dimensional body of the method of the present disclosure can further have an elongation at break at a temperature of <NUM> of at least <NUM>%, such as at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>%, such as at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>%, or at least <NUM>%. In another embodiment, the elongation at break can be not greater than <NUM>%, such as not greater than <NUM>%, not greater than <NUM>%, not greater than <NUM>%, not greater than <NUM>%, not greater than <NUM>%, or not greater than <NUM>%. The elongation of break at a temperature of <NUM> can be a value between any of the minimum and maximum values note above.

In a further embodiment, the sintered three-dimensional body can have a relative density of at least <NUM>%, such as at least <NUM>%, at least <NUM>%, or at least <NUM>%, at least <NUM>%, at least <NUM>%, or at least <NUM>% with respect to a fluoropolymeric material having a density of <NUM>/cm<NUM>.

The process of the present invention can form sintered three-dimensional polymeric bodies from solid polymeric particles which are already fully polymerized in the uncured mixture and possess a high melting temperature, wherein the melting temperature is higher than the decomposition temperature of the cured binder. The polymeric particles are fluoropolymer particles because of their high melting temperature.

In a particular embodiment, the sintered three-dimensional body can consist essentially of PTFE particles. As used herein, consisting essentially of PTFE particles is intended to mean that the sintered body includes at least <NUM> wt% PTFE, such as at least <NUM> wt%, or at least <NUM> wt% based on the total weight of the sintered body. The process of the present disclosure allows a unique way of producing complex three-dimensional PTFE bodies which cannot be made by other known techniques or require much higher production efforts. It is known that PTFE, unlike other thermoplastics, is not melt-flow processable, which means it does not flow when heated above its melting point. Accordingly, PTFE cannot be injection molded, which makes it very difficult to produce complex conventional shapes with PTFE that can be easily produced with other polymers.

The method of the present disclosure forms three dimensional bodies comprising fluoropolymeric particles, which may have after sintering a high size resolution. In one embodiment, the size resolution of the sintered body can be not greater than <NUM> (<NUM> microns), such as not greater than <NUM> (<NUM> microns), not greater than <NUM> (<NUM> microns), not greater than <NUM> (<NUM> microns), not greater than <NUM> (<NUM> microns), not greater than <NUM> (<NUM> microns), or not greater than <NUM> (<NUM> microns). As used herein, the term size resolution means that the process is capable of forming a three-dimensional body having an isolated body feature of a height of <NUM> and a thickness of not greater than <NUM> (<NUM> microns), such as not greater than <NUM> (<NUM> microns), not greater than <NUM> (<NUM> microns), not greater than <NUM> (<NUM> microns), not greater than <NUM> (<NUM> microns), not greater than <NUM> (<NUM> microns), or at not greater than <NUM> (<NUM> microns).

As further demonstrated in the Examples below, the method of the present disclosure can produce complex three-dimensional fluoropolymeric bodies with a high resolution in a continuous and fast forming process. The solid polymeric particles can be pre-selected in form of commercially available solid particle dispersions and integrated in a mixture comprising a curable binder.

Many different aspects and embodiments are possible. Some of those aspects and embodiments are described herein.

The following non-limiting examples illustrate the present invention.

A mixture was prepared by combining <NUM> vol% of an aqueous PTFE dispersion (DAIKIN D-610C from Daikin) with two water soluble binders: <NUM>) <NUM> vol% of an acrylic-di-functional polyethylene glycol (SR344 from Sartomer, Arkema), and <NUM>) <NUM> vol% of a polyester acrylate oligomer (CN2302 from Sartomer, Arkema) and <NUM> vol% of photo-initiator IRGACURE <NUM> from BASF. The DAIKIN D610C PTFE dispersion contained <NUM> vol% PTFE particles having an average particle size of <NUM> and <NUM> vol% of a liquid including water and surfactant. The amount of surfactant in the DAIKIN dispersion was <NUM> wt% based on the amount of solid PTFE particles. A summary of the components of the mixture based on total weight and volume of the mixture is also shown in Table <NUM> The mixture had a viscosity at a temperature of <NUM> and at a shear rate in a range of <NUM>-<NUM> to <NUM>-<NUM> between about <NUM> to <NUM> mPa·s (about <NUM> to <NUM> cP) (see <FIG>).

The mixture prepared in Example <NUM> was placed in a chamber of an assembly having a similar design as shown in <FIG>. As electromagnetic radiation unit was an array of LEDs having a UV wavelength maximum at <NUM>.

A series of flower-bud shaped bodies were formed by varying from experiment to experiment the forming speed (between <NUM>/min and <NUM>/min) and a radiation intensity of <NUM> mW/cm<NUM>. Best results could be obtained at a forming speed of <NUM>/min and a radiation intensity of <NUM> mW/cm<NUM>.

The formed flower-bud body was dried (removing of the water) at room temperature in an open lab environment for about <NUM> hours to a stable weight. The body had a weight loss of <NUM> wt% corresponding to the water evaporation. During drying, the flower-bud body has shrinked by about <NUM>%.

After drying, the body was subjected to a further heat-treatment regime to remove the cured binder and to conduct high temperature sintering. The temperature was increased at a speed of <NUM>/min up to a maximum sintering temperature of <NUM>. The temperature was maintained for <NUM> minutes at <NUM>, followed by free cooling (uncontrolled free cooling speed of the oven, about <NUM>-<NUM>/min). After sintering, the shrinkage of the body was about <NUM>% based on the size of the formed bodies before drying and sintering, but the shape of the body was maintained, see also <FIG>. The weight loss after sintering was <NUM> wt% based on the total weight of the body after drying, which corresponds to the binder content of about <NUM> wt% and about <NUM> wt% leftover water in the dried body.

The material of the sintered PTFE bodies had a density between <NUM>/cm<NUM> and <NUM>/cm<NUM>, measured by the Archimedes method, which corresponds to a relative density of <NUM>%-<NUM>%, assuming a density of <NUM>/cm<NUM> for dense non-porous PTFE.

A mixture including solid PTFE particles was prepared similar as in Example <NUM>, except that a dye was further added (Rhodamine B) in an amount of <NUM> wt% based on the total weight of the mixture, and only one type of binder (SR <NUM>) was used in an amount of <NUM> vol% based on the total volume of the mixture. The exact composition (S2) can be seen in Tables 1A and 1B below.

Different types of three dimensional bodies were formed from the mixture S2 according to the printing conditions described in Example <NUM>.

The formed bodies showed an improved resolution compared to the three dimensional bodies of Example <NUM> (S1), and a variety of shapes after drying and before sintering can be seen in <FIG>.

The bodies were subjected to drying and sintering according to the following heat-treatment regime: <NUM>/min up to <NUM>; <NUM>/min up to <NUM>; <NUM> isothermal heating at <NUM>; and cooling to room temperature at <NUM>/min.

<FIG> shows a comparison of a PTFE comprising body printed from mixture S2. The left image shows the body directly after forming and the right image after drying and sintering. The shrinkage rate after sintering was about <NUM>% (in comparison to the size before drying); the sintered PTFE body had a density of <NUM>/cm<NUM>, and a relative density of about <NUM>%.

A mixture was prepared containing an aqueous dispersion of <NUM> sized PFA particles (Teflon PFAD 335D from Chemours) mixed with water-soluble binder (SR344), a photoinitiator (IRGACURE <NUM>), and a dye (Rhodamine B from Sigma Aldrich). A similar mixture was prepared using an aqueous dispersion of solid FEP particles with an average size of <NUM> (Teflon FEPD <NUM> from Chemours) instead of the PFA dispersion; the amount of the other ingredients of the mixture was the same. The amounts of each ingredient based on a total amount of the mixtures are shown in Tables 1A and 1B (samples S3 and S4).

From the prepared mixtures, three-dimensional bodies were formed according to the method described in Example <NUM> at a forming speed of <NUM>/min and an applied radiation intensity of <NUM> mW/cm<NUM>. It could be observed that the presence of the dye showed a large improvement of the resolution of the formed bodies. <FIG> illustrate a three-dimensional body comprising FEP formed with mixture S3 after drying. The addition of <NUM> wt% Rhodamine B could cause a remarkable improvement in the resolution of a honeycomb structured body (right image, <FIG>) in comparison to the body formed without the presence of the dye (left image, <FIG>). Bodies with very good resolution could be also obtained with other complex body structures, such as a flower-bud or a threaded screw.

The following heat-treatment regimes were applied for drying and sintering of the FEP comprising bodies:.

After high temperature sintering according to the heat treatment regime A) of up to <NUM>, the bodies partially collapsed.

At a lower maximum sintering temperature of <NUM> (heat treatment regime B), the sintered bodies maintained their shape, see <FIG>.

A thermogravimetric analysis (TGA) of a FEP comprising body after drying (i.e., Sample S3, after removal of the water) is illustrated in <FIG>. It can be seen that after drying, only a very minor amount of water (< <NUM>%) stayed in the body. A noticeable decrease in weight started at a temperature of <NUM>, which corresponds to the decomposition of the cured binder. A weight loss of about <NUM> wt% binder based on the total amount of the binder was reached at a temperature of about <NUM>, which relates to the decomposition temperature of the binder in accordance with the present disclosure. No remarkable differences in the speed of the weight decrease could be observed until the melting point of the FEP particles (<NUM>) and the maximum sintering temperature (<NUM>), which indicates that after sintering, a certain amount of binder was still present in the body. A first plateau was reached at a temperature of about <NUM>, indicating that at this point, all binder was removed. The following large drop in mass starting at about <NUM> appears to relate to the decomposition of the FEP particles. The density of the material of the FEP-based body after sintering at <NUM> was <NUM>/cm<NUM>. The density was determined by the Archimedes method.

Mixtures were prepared including solid PTFE particles with varying concentration of Rhodamine B. The mixtures contained <NUM> vol% of an aqueous PTFE dispersion (DAIKIN D-610C from Daikin) having an average particle size of <NUM>, <NUM> vol% of an acrylic difunctional polyethylene glycol (SR344 from Sartomer, Arkema), <NUM> vol% of a photoinitiator (IRGACURE <NUM> from BASF) and about <NUM> vol. % of a defoamer. The Rhodamine B concentration was varied at concentrations of <NUM> wt%, <NUM> wt%, <NUM> wt%, and <NUM> wt% based on the total weight of the mixture.

A summary of the tested compositions is shown in Tables 2A and 2B. All concentrations are shown in vol% and wt% based on the total volume or weight of the mixtures.

From the mixtures listed in Table 2A/2B, defined three dimensional bodies were continuously formed according to the method described in Example <NUM> at a forming speed of <NUM>/min and an applied radiation intensity of <NUM> mW/cm<NUM>. Three-dimensional bodies were formed from mixtures S5-S7 (mixture S8 was not printable under the defined conditions). The form of the printed bodies was based on a specifically designed 3D model to investigate the minimum printable feature size in dependency to the amount of Rhodamine B in the mixture. The 3D model contained six parallel arranged walls of <NUM> height, with varying wall thickness: <NUM> (<NUM> microns), <NUM> (<NUM> microns), <NUM> (<NUM> microns), <NUM> (<NUM> microns), <NUM> (<NUM> microns), and <NUM> (<NUM> microns). A magnified drawing of the 3D model is shown in <FIG>.

The difference in the obtained resolution of the formed bodies after drying is illustrated in the comparison of <FIG>, which show images of formed three dimensional dried bodies printed from mixtures including <NUM> wt%, <NUM> wt%, and <NUM> wt% Rhodamine B respectively. Drying was conducted at <NUM> until a stable weight was obtained. It can be seen that at <NUM> wt% (<FIG>) and at <NUM> wt% (<FIG>) Rhodamine B, the resolution of the formed bodies was not sharp and each wall showed large irregularities and no clear gap between the walls could be formed. At <NUM> wt% Rhodamine B concentration (<FIG>), the printed three dimensional body included three of the six walls of the 3D model, missing only the thinnest walls with a thickness of <NUM> (<NUM> microns), <NUM> (<NUM> microns) and <NUM> (<NUM> microns).

<FIG> show top view images of the PTFE body shown as side view in <FIG>, formed with <NUM> wt% Rhodamine B. It can be seen that the walls do not connect with each other. In <FIG>, the thickness of each of the formed walls was measured at five different locations and compared with the wall thickness of the corresponding model. In <FIG>, the gap size between two adjacently formed walls at five different positions was measured and an average value calculated. A summary of the measured data is shown in Tables <NUM> and <NUM>. The thinnest isolated wall structure which could be formed had a thickness of <NUM> ± <NUM> (<NUM> microns ± <NUM> microns). The resolution data indicate that by carefully selecting the concentration of Rhodamine B in the printing mixture, fine structure units having a size resolution of not greater than <NUM> (<NUM> microns) can be formed in a dried body. As used herein, the term size resolution of not greater than <NUM> (<NUM> microns) relates to the printing of an isolated structure unit having a height of at least <NUM> and a thickness of not greater than <NUM> (<NUM> microns) after drying.

The average gap size (average value of measured gap size at five different positions and standard deviation) was <NUM> ± <NUM> (<NUM> microns ± <NUM> microns) between the largest and medium thick walls, while the gap between the medium and smallest formed wall was <NUM> ±<NUM> (<NUM> microns ±<NUM> microns). While the distance (gap) between the walls is in good agreement with the predicted drying shrinkage of <NUM>%, the formed wall thicknesses were lower than what is estimated from a <NUM>% shrinkage. This can be related to the fact fine features (like a thin wall) may require more UV exposure during printing than larger features to be fully formed. This effect can be corrected by either adding more radiation intensity when forming fine features or by over scaling in order to compensate and achieve a desired feature size.

The three dimensional body formed with a concentration of <NUM>. 075wt% Rhodamine B was further subjected to high temperature sintering of the following heat treatment regime: <NUM>/min up to <NUM>; <NUM>/min up to <NUM>; <NUM> isothermal heating at <NUM>; and cooling to room temperature at <NUM>/min.

Images of the three dimensional body after sintering are shown in <FIG>. It can be seen that the three walls of the body (resolution lines) survived the sintering process. <FIG> illustrates the positions of measuring the wall thickness after sintering. <FIG> shows the positions of measuring the distance between the walls, which are called herein also gaps.

The data demonstrate that it is possible by carefully selecting the concentration of Rhodamine B in the printing mixture to form fine thin structure units at a size resolution of not greater than <NUM> microns in the sintered PTFE bodies.

Rectangular PTFE rods were continuously formed from mixtures as described in Example <NUM>, using <NUM> wt% Rhodamine B and as PTFE dispersion Daikin 210C, containing PTFE particles with an average particle size of <NUM>-<NUM>. After continuous forming and drying the PTFE comprising bodies, the dried bodies were high temperature sintered according to the temperature regime described in Example <NUM>. The rectangular rods were tested in x-y direction for tensile strength at maximal load and elongation at break according to modified ASTM <NUM>. As used herein, modified ASTM <NUM> means that the shape of the tested body was different. The rectangular shape of the sintered PTFE body to be tested had a length of <NUM>, a width of <NUM>, and a thickness of <NUM>. Each test was repeated six times and an average value calculated with error estimated as three times the standard deviation divided by the square root of the numbers of tests. A summary of the test results is shown in Table <NUM>. An illustration of a tested PTFE body before and after strain break is shown in <FIG>.

Claim 1:
A method of forming a three-dimensional body, comprising:
providing a liquid mixture comprising a curable binder, a dye and dispersed solid fluoropolymeric particles; and
forming a three-dimensional body from the liquid mixture by curing the binder to form a cured binder, wherein forming includes translation and growth of the three-dimensional body from an interface of an inhibition zone of the liquid mixture,
wherein the inhibition zone is a zone of the liquid mixture comprising an inhibitor which can limit or prevent curing of the mixture by electromagnetic radiation;
and wherein forming the 3D-body from the liquid mixture includes selecting an amount of the dye of at least <NUM> wt% and not greater than <NUM> wt%, based on the total weight of the mixture, to control a size resolution of the formed three-dimensional body.