Carrier ink for three-dimensional (3D) printing

Description

TECHNICAL FIELD

[0001] The present invention relates to 3D (three dimensional) printing inks.BACKGROUND OF THE INVENTION

[0002] The 3D (three dimensional) printing market is maturing rapidly. 3D printing or additive manufacturing (AM) is any of various processes for making a 3D object of almost any shape from a 3D computer model or other electronic data source primarily through additive processes in which successive layers of material are laid down under computer control. A 3D printer is a type of industrial robot, which utilizes printing technologies for fabricating the required object.

[0003] Conventional 3D processes include stereo lithography employing UV lasers to cure photopolymers, inkjet printers utilizing UV radiation to polymerize photo-monomers and oligomers, metal sintering (such as selective laser sintering and direct metal laser sintering), fused deposition modeling (FDM), based on extrusion technology, and deposition of liquid binders onto powders.

[0004] Some 3D printing processes require supporting materials for supporting the printed object during its printing. These support materials are temporary, and removed once the object has been printed.

[0005] Another approach in 3D inkjet printing is the use of UV-curable polymers, similar to those of the printed object, but modified to be water soluble. Complete removal of the support is difficult in these systems and the interfaces formed are not sharp. Moreover, it is difficult for the formed water soluble support polymer to maintain its dimensions and 3D structure at high temperatures, such as the temperatures used for sintering.SUMMARY

[0006] The scope of the invention is defined by the appended claims. The present invention is directed to an ink composition as defined in claim 1, which is typically used as a support ink at certain times during printing, but may be used through the entire 3D printing process. The support inks are used, for example, for printing structures to support "negative" tilted walls of the object, which is being printed by 3D printing processes. The support inks are also used to print structures analogous to molds.

[0007] Throughout this document, the term "dispersion" generally refers to particles homogeneously distributed and suspended in a liquid.

[0008] The ink composition comprises: a dispersion of solid particles in a liquid carrier, compatible with an inkjet print head, wherein after removing the liquid carrier, the solid particles serve as support material for a three dimensional (3D) printed object, wherein the support material is separable from the 3D printed object, wherein the solid particles are sodium carbonate or calcium carbonate; and wherein the solid particles are dispersed in the liquid carrier by a polymeric dispersing agent capable of covering the solid particles via chemical or physical interactions, and wherein during printing after the liquid carrier evaporates, the dispersant remains on the particles and serves as a binder that prevents the support material from collapsing; and wherein the liquid carrier is selected from glycol ethers, and water soluble liquids such as propylene glycol.

[0009] Optionally, the solid particles have diameters of between approximately 10 nanometers to approximately 1000 nanometers.

[0010] Optionally, the solid particles are between approximately 15 to approximately 60 weight percent of the ink composition.

[0011] Optionally, the solid particles are miscible or at least partially soluble in water or aqueous acidic solution.

[0012] Optionally, the solid particles are miscible or at least partially soluble in water after heating the solid particles to above 800°C.

[0013] Optionally, the liquid carrier includes a carrier vehicle of between approximately 40 to approximately 85 weight percent of the ink composition.

[0014] Optionally, the carrier vehicle includes one or more of: solvents, water, and mixtures thereof.

[0015] Also described herein but not claimed is a method for manufacturing a three dimensional (3D) printed object. The method comprises, printing at least a portion of a 3D object with an object ink; printing at least a support associated with the 3D object with a support ink, the support ink comprising: (a) a dispersion of solid particles, the solid particles being between about 15 to about 40 weight percent of the dispersion; and a carrier vehicle for the dispersion; and, removing the support from the at least a portion of the 3D object.

[0016] Optionally, the solid particles are one or more of: inorganic salts, metal carbides, metal oxides and polymers.

[0017] Optionally, the removing the support is by at least one of: mechanical assistance degradation, evaporation, melting, dissolution, firing off.

[0018] Unless otherwise defined, all technical and / or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the invention, exemplary methods and / or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Some embodiments of the invention are herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the invention. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the invention may be practiced.

[0020] In the drawings: FIG. 1 is a photograph of a printed object with its printed support, as detailed in Example 1 below.DETAILED DESCRIPTION

[0021] The present invention is directed to an ink composition as defined in claim 1, typically used in 3D (three dimensional) printing operations, which serves as a support material or support ink. This support ink is designed to fill spaces in the printed object, shielding these spaces from particles which may drift into such regions during post printing processing. The support ink is also used, for example, in a manner analogous to a mold. The support ink provides a ground for printing of a model ink layer on regions which at the end should remain empty, e.g. the space under a free standing arc.

[0022] For example, for printing an object, for example, of Tungsten Carbide / Cobalt (WC / Co), the support material has to be either removed once the object has been printed, and typically prior to any post printing processes, including heat treatments such as sintering. Alternately, the support structure printed with the support ink may remain with the printed object during post printing processes. In these cases, the support structure of the support ink must remain sufficiently soft and / or brittle to be removable after the sintering process. The metal composition of the final object is similar or close to that of the initial ink, but in some embodiments it can be different than the starting composition, due to the loss of some of the material during the printing process.

[0023] The invention is directed to ink compositions as defined in claim 1, known herein as "support inks", comprising a dispersion of solid particles, dispersed in a liquid carrier, which is selected from glycol ethers and water soluble liquids such as propylene glycol, and which is used to build a support structure adjacent to an object upon being printed. The liquid carrier is selected so as to evaporate at a predetermined temperature, wherein the dry support material is separable from the object material. The ink compositions are of viscosities between approximately 10 cPs (centipoise) to approximately 30 cPs, and typically 15±5 cPs, at jetting temperature, so as to be suitable for use as ink jet printing inks.

[0024] Initially, an inkjet printing device is used to form the 3D structure (or object), and the object is printed in successive layers. Each layer is hardened before dispensing the next or subsequent layer. When an additional shape is desired, a second or support ink is applied to the object, typically by a second ink jet printing head. The support ink is needed to provide a support for printing of an object ink layer on regions which at the end should remain empty, e.g., the space under a free standing arc. As used in this document, "negative object walls" are always supported by the support structure. For printing an object that further goes through sintering, the support material has to be either removed prior to sintering, or it has to remain sufficiently soft and / or brittle to be removable after the sintering process. Described herein are stable liquid formulations useful as support inks for 3D Printing machines. Processes of printing using the aforementioned inks are described but not claimed. Ink compositions according to the invention are as defined in the claims.Solid narticles

[0025] Particles are such that one or more types of particles may be mixed together. Particle sizes are indicated by diameters, where not specifically indicated.

[0026] The particles range in diameter from nanometer scale, e.g., (approximately 10 nm to approximately 300 nm), to submicron (approximately 0.4 µm to approximately I µm), and provide the general features of the support. Solid particles in an ink composition of the invention are calcium carbonate, and sodium carbonate.

[0027] In exemplary ink compositions, the solid particles themselves are typically between approximately 15 to approximately 60 weight percent of the ink composition.Carrier Vehicles

[0028] Carrier vehicles, such as liquid carrier vehicles, support the dispersions of the above-mentioned particles. The ink composition of the invention comprises a liquid carrier selected from glycol ethers, and water soluble liquids such as propylene glycol. Glycol ethers examples: all propylene glycol or ethylene glycol series from Dow Chemical (Midland, Michigan USA), such as Dipropylene Glycol methyl ether (DPM) or diethylene glycol butyl ether (DEGBE), Dimethoxyethane, also known as glyme, monoglyme, dimethyl glycol, ethylene glycol dimethyl ether, dimethyl cellosolve) series from Clariant and their mixtures.

[0029] The liquid carrier may be from approximately 40 to 85 weight percent of the support ink, depending on the resulting ink properties, such as viscosity as well as the thickness of formed printed layer.Dispersing Agents

[0030] Dispersing agents, such as a surfactants and polymers, may be used as stabilizers to stabilize the support ink. The dispersing agent should be of a composition, which has affinity to the surfaces of the above-detailed particles, and prevents the aggregation of the dispersed particles, by a steric, electrostatic or electrosteric stabilization mechanism.

[0031] The dispersing agent is molecularly compatible with the carrier vehicle, for stability purposes. In water based inks, the stabilization can be achieved by proper control of the surface properties, such as by changing the pH of the dispersion. It should be noted that the stabilizer may be bound to the particles' surface by covalent bonds or by physical adsorption. The dispersing agent should also be such that it may be removed from the printed object prior to any desired post processing stage, and specifically before heat treatments to the printer object, such as sintering.

[0032] The dispersing agents used in an ink composition of the invention are polymeric dispersing agents capable of covering the solid particles via chemical or physical interactions, such as Disperbyk 180, Disperbyk 190, Disperbyk 2013, Disperbyk 163 from Byk Chemie of Germany. Solsperse 39000, Solsperse 33000, Solsperse 35000 from Lubrizol of the UK. Rheosperse 3020, 3450, 3620 from Coatex (Arkema of France), Efka 7701, Efka 7731, Efka 7732 from BASF of Germany.

[0033] The dispersing agents may be from approximately 1 to approximately 10 weight percent of the support ink, depending on the resulting ink properties, such as viscosity.Surface Modifiers

[0034] Surface modifiers add properties such as scratch resistance and controlling the interface with the printed object. Exemplary surface modifiers include cellulosic polymers such as ethyl cellulose, carboxymethyl cellulose, hydroxypropyl methyl cellulose, cellulose acetate. Other surface modifiers may include polybutyrals (from Butvar).

[0035] When present in the support ink, the surface modifiers may be from approximately 0.1 to approximately 5 weight percent of the support ink, depending on the resulting ink properties, such as viscosity.PRINTING PROCESS

[0036] Unlike common 3D printing of plastic objects, printing of metallic objects involves elevated temperatures during the printing process as well as in post printing processes. The properties of the support (supporting) material are dictated by the printing and post-printing conditions by means of thermal stability.

[0037] By definition, the support material must be removed from the printed object in an efficient manner during the printing process, post printing process, or after the object is completed. The latest requirement has an important role in choosing the support material. Removing of the support material and separating it from the printed object can be performed by several ways which can be mechanical, chemical or thermal.

[0038] Soft material, such as fused silica particles, can be removed by applying mechanical scratching and wiping. Brittle materials, such as partially sintered titania, can be removed by mechanical breaking, while the metal object is significantly harder and resistant to mechanical forces. Inorganic salts such as Calcium Sulfate are partially soluble in water as well as aqueous acidic solution and the lattice formed in the printed object is being disintegrated by immersing the object in water or other aqueous solution. Some Calcium salts, e.g., calcium sulfate, are thermally stable and remain unchanged after heating at sintering conditions of less than 800°C. The support can be removed using a water stream after the complete sintering of the printed object. In another aspect the sintering temperature is above 800°C where after the calcium sulfate support material remains slightly soluble such that it can be removed by a stream of water. Another means of separating the support from the printed object is thermal decomposition of polymeric materials that take place during the sintering process of the object, in a situation in which the object itself is hard enough to support its own structure.

[0039] Metal carbides tend to sinter at high temperatures, higher than those cemented carbides. Based on the sintering temperature, there is an optional differentiation ability of a cemented carbide model versus non-cemented carbide that remains as a fine powder during the sintering of the printed object. The powder can then be removed by mild physical means.

[0040] A dispersion of a polymeric material in a liquid carrier can be used as support material. Upon evaporation of the liquid carrier, a matrix of plastic particles is formed. The particular polymer is a high melting point plastic, in particular polyolefin that remains solid at printing temperature in order to be able to physically support the printed object.

[0041] Upon sintering conditions, the polymer undergoes decomposition and evaporation leaving the clean printed object.

[0042] Support inks, according to the embodiments disclosed herein, comprise dispersed particles of solid materials in a carrier liquid as defined in the appended claims. The dispersions are formulated to be printable by inkjet heads, i.e. having the viscosity, surface tension and particle size meeting inkjet requirements. Regarding particle size, it should be equal or smaller than 1 / 20 of a nozzle diameter, so as to prevent clogging and improper jetting. Given for example a head having nozzles of diameter of 30 micron, particle size should be 1.5 microns or smaller. Such a head is, for example, Diamatics Sapphire QS-256 from Konica Minolta. When jetted from the ink jet head, on a heated tray, the liquid carrier evaporates, and the remaining particles form a solid layer. Applying a layer by layer methodology forms a 3D object of the solid material supported by the invented support material. The solid particles which form the supporting materials are dispersed in the liquid carrier by suitable dispersing agents (dispersants). A dispersing agent is capable of covering the solid particles via chemical or physical interactions. The interface of the covered particle is changed in such a way that the covered particles can remain in solution rather than precipitate.

[0043] During printing, after the liquid carrier evaporates, the dispersant remains on the particles and serves as a binder that prevent the solid matrix form from collapsing. The dispersing agent is, thus, being debinded during the thermal process of sintering.

[0044] The printed object with the support is such that the support is removable by processes including at least one of: mechanical assisted degradation, decomposition (followed by evaporation of the decomposition products) evaporation, melting, dissolution, firing off.ExamplesExample I -Titania Support (Comparative Example)

[0045] An ink formulation comprised of Titania (TiO 2 ). particles was prepared by mixing a dispersion of titania nanosize particles (approximately 20 nm to approximately 250 in liquid carrier, with surface modifying agents in the following amounts: Weight (gr)Weight %100.0026.66Rutile titania (Kronos)7.52.05Disperbyk 190 (Dispersing Agent)2.50.68Butvar B-90 (Surface Modifier)265.070.66DPM (dipropylene glycol methyl ether) (Carrier Vehicle)375.0Total Formulation Ink property15.0 ± 5.0Viscosity (cPs), 25°C29.0 ± 2.0Surface tension, 25°C

[0046] A Titania (TiO 2 ) dispersion was prepared by dispersing 50±2 wt% rutile Titania powder (Kronos 2064, a nanopowder) in glycol ethers and stabilized with a polymeric dispersant (3 wt% of the solid particles). All components were mixed in a vertical agitator (vertical agitator mill) filled with 0.8 mm ZrO 2 beads and a volume ratio of 67 / 33 (beads / product; vol / vol) for 6 hours at 15 °C. Titania ink was prepared by diluting the preformed, high loading dispersion and mixing it with a solution of the surface modifier in glycol ether, to produce the ink according to the tables above..

[0047] An object was printed in accordance with commonly owned Patent Application entitled: 3D Particle Printing (Docket No. 4619 / 20) using the ink of the ink composition disclosed in commonly owned Patent Application entitled: Printing Ink (Docket No. 4619 / 21), with the aforementioned support ink acting as a mold. The object and support ink mold are shown in FIG. 1, with the object being black and the mold of the support ink being white. When the dispersion dried, the remaining particles were only loosely attached to each other. After warming to 1000°C, the support ink particles remaining became brittle and were removable from the printed object.EXAMPLE 2 - Calcium Sulfate Support Ink

[0048] Calcium Sulfate ink was prepared by the following steps: a. Solid Anhydrous Calcium sulfate (CaSO 4 ) was ground in an agitator mill in Glycol Ether (e.g., DPM) solvent mixture with a combination of ionic (e.g., SLS) (approximately 7.5 wt%) and polymeric (e.g., Disperbyk 190) (approximately 6 wt%) dispersants to form a stable dispersion that passed a 3µm mesh filtration). b. Polymeric additives (polybutyral, e.g., Butver B-90, approximately <2 wt%) were added for scratch resistance of the printed layers.

[0049] CaSO 4 of the Calcium Sulfate Support Ink is water soluble, after printing by the techniques of Example 1, and heating the object under vacuum in an oven, the oven heated to approximately 1000°C. The resultant object with support ink was washed with water in order to separate (by partially dissolving) the support ink from the object. Weight (gr)Weight%100.0032.73Calcium sulfate7.02.3Disperbyk 190 (Dispersing Agent)8.672.83SDS (Dispersing Agent)5.781.9Butver B-90 (Surface Modifier)184.070.66DPM (Carrier Vehicle)305.560.23Total Formulation Ink property15.0 ± 5.0Viscosity (cPs), 25°C29.0 ± 2.0Surface tension, 25°C Example 3 - Tungsten Carbide Support Ink (Comparative Example)

[0050] The use of cobalt free carbide support has an advantage due to the fact that it is as similar to the object material as possible. This inhibits cross contamination between the two printed materials (3D object and support). The Tungsten Carbide (WC) dispersion was prepared by dispersing 55±2 wt% Tungsten Carbide (WC) powder (0.8 micron, as milled from WC particles available from General Carbide Corporation, Greensburg, PA, USA) in glycol ethers, e.g., DPM in the table below, and stabilized with a polymeric dispersant e.g., Disperbyk 163 (5 wt% on WC particles), listed as the "WC Dispersion" in the table below. All components were mixed in a vertical agitator (vertical agitator mill) filled with 0.5 mm WC beads and a volume ratio of 67 / 33 (beads / product; vol / vol) for 6 hours at 15°C, in accordance with the following table: Metal (gr)Weight (gr)160.0290.00WC dispersion (55% metal)30.0DPM and DEGBE mix (1:1 wt%) (Carrier Vehicle)160.0320Total Formulation Ink property15.0 ± 5.0Viscosity (cPs), 25°C29.0 ± 2.0Surface tension, 25°C

[0051] The terms "comprises", "comprising", "includes", "including", "having" and their conjugates mean "including but not limited to". This term encompasses the terms "consisting of" and "consisting essentially of".

[0052] The phrase "consisting essentially of" means that the composition or method may include additional ingredients and / or steps, but only if the additional ingredients and / or steps do not materially alter the basic and novel characteristics of the claimed composition or method.

[0053] As used herein, the singular form "a", "an" and "the" include plural references unless the context clearly dictates otherwise. For example, the term "a compound" or "at least one compound" may include a plurality of compounds, including mixtures thereof.

[0054] The word "exemplary" is used herein to mean "serving as an example, instance or illustration". Any embodiment described as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments and / or to exclude the incorporation of features from other embodiments.

[0055] The word "optionally" is used herein to mean "is provided in some embodiments and not provided in other embodiments". Any particular embodiment of the invention may include a plurality of "optional" features unless such features conflict.

[0056] Throughout this application, various embodiments of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0057] Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases "ranging / ranges between" a first indicate number and a second indicate number and "ranging / ranges from" a first indicate number "to" a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween.

[0058] When expressing amounts, ranges and sizes, dimensions and other measurable quantities the words "approximately" and "about" are used interchangeably.

[0059] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

[0060] Although the invention has been described in conjunction with specific embodiments thereof, it is evident that the scope of the invention is defined by the appended claims.

Claims

1. An ink composition comprising: a dispersion of solid particles in a liquid carrier, compatible with an inkjet print head, wherein after removing the liquid carrier, the solid particles serve as support material for a Three Dimensional (3D) printed object, wherein the support material is separable from the 3D printed object, wherein the solid particles are sodium carbonate or calcium carbonate; and wherein the solid particles are dispersed in the liquid carrier by a polymeric dispersing agent capable of covering the solid particles via chemical or physical interactions, and wherein during printing after the liquid carrier evaporates, the dispersant remains on the particles and serves as a binder that prevents the support material from collapsing; and wherein the liquid carrier is selected from glycol ethers, and water soluble liquids such as propylene glycol.

2. The ink composition of claim 1, wherein the solid particles have diameters of between approximately 10 nanometers to approximately 1000 nanometers.

3. The ink composition of claim 2, wherein the solid particles are between approximately 15 to approximately 60 weight percent of the ink composition.

4. The ink composition of claim 1, wherein the solid particles are miscible or at least partially soluble in water or aqueous acidic solution.

5. The ink composition of claim 1, wherein the solid particles are miscible or at least partially soluble in water after heating the solid particles to above 800°C.

6. The ink composition of claim 1, wherein the liquid carrier includes a carrier vehicle of between approximately 40 to approximately 85 weight percent of the ink composition.

7. The ink composition according to any of claims 1-6, wherein the liquid carrier is selected from propylene glycol, and glycol ethers such as Dipropylene Glycol methyl ether (DPM) or diethylene glycol butyl ether (DEGBE), Dimethoxyethane and mixtures thereof.