具体实施方式：
[0011]The present disclosure relates to a method of three-dimensional (3D) printing a 3D printed object. The method comprises:
[0012]selectively jetting a marking agent onto a first region of build material, wherein the build material comprises at least one metal and/or ceramic;
[0013]selectively jetting a binding agent onto at least a portion of the build material; and
[0014]binding the build material to form a layer; such that the marking agent is incorporated in the metal part in a predetermined arrangement that forms a detectable marker in the 3D printed object.
[0015]The method may further comprise sintering the build material e.g. after binding.
[0016]The marking agent may be selectively jetted onto a first region of the build material based on a 2D or 3D object model of the detectable marker. The model may comprise or be derived from a set of programming instructions defining how to print or form the detectable marker within the 3D printed object. Similarly, the binding agent may be selectively jetted onto at least a portion of the build material based on a model of the 3D object to be printed. The model may comprise or may be derived from a set of programming instructions defining how to print the 3D object.
[0017]In some circumstances, it may be useful for manufacturers to be able to track and trace metal 3D printed objects that are produced. For example, 3D printed parts may be assigned a unique identification number that designates information regarding e.g. the identity, origin or other characterising information on the part. This unique identification number may be imprinted into the parts produced.
[0018]In the 3D printing method of the present disclosure, a marking agent is jetted onto a first region of build material. A binding agent is jetted onto at least a portion of the first region, and the build material in contact with the binding agent is bound to form a layer, such that the marking agent is incorporated in the 3D printed object in a predetermined arrangement that forms a detectable marker in the 3D printed object. The predetermined arrangement of the marking agent may act itself as the detectable marker. Alternatively, the predetermined arrangement of the marking agent may react e.g. upon exposure to elevated temperatures (e.g. during binding and/or sintering) to form the detectable marker.
[0019]By incorporating the marking agent into a 3D printed object during the course of printing, the marking agent can be incorporated within the 3D printed object and/or on at least a part of an outer surface of the 3D printed object. In one example, the detectable marker encodes data. The marker may enable the part to be identified, located and/or tracked. The marker may encode data in machine-readable form.
[0020]In some examples, the marker may provide encode information relating to subsequent processing steps. For instance, the marker may inform the user where to perform e.g. a milling or plating operation.
[0021]The marker may be located at at least one designated location in the 3D printed object (e.g. metal part). In this example, the 3D printed object may be analyzed at the designated location for the presence of the marker.
[0022]In one example, the metal-containing marking agent is incorporated in the 3D printed object in a predetermined arrangement that forms a marker that is not detectable by visual inspection of the 3D printed object. For example, the marker itself may be invisible. Alternatively or additionally, the marker may not be located on an outside surface of the 3D printed object.
[0023]The detectable marker may have characteristic magnetic properties. For example, the marking agent may be a metal-containing marking agent that may itself have magnetic properties. Alternatively, the metal-containing marking agent may react, for example, upon exposure to elevated temperatures and/or to a reducing atmosphere (e.g. encountered during sintering), to provide characteristic magnetic properties. When such marking agents are incorporated into the 3D printed object (e.g. metal part) in a predetermined arrangement, the predetermined arrangement may form a detectable marker characterised by magnetic properties that differ from the magnetic properties of adjacent regions of the 3D printed object. This marker may be revealed when the magnetic properties of the 3D printed object (e.g. metal part) are analyzed. Where the marker is incorporated in a predetermined location in the 3D printed object, it may be possible to detect for magnetism at that predetermined location. The predetermined arrangement of the metal-containing marking agent may provide a magnetic signature, which may encode information relating to the 3D printed object, for example, information regarding the object's identity and/or purpose. In some examples, the magnetic signature may also encode information relating to subsequent processing operations relating to the 3D printed object.
[0024]In some examples, the detectable marker has characteristic mechanical properties (e.g. hardness). For instance, the marking agent may itself have mechanical properties (e.g. hardness). Alternatively, the marking agent may react, for example, upon exposure to elevated temperatures upon exposure to elevated temperatures and/or to a reducing atmosphere (e.g. encountered during sintering), to provide characteristic mechanical properties (e.g. hardness). When such marking agents are incorporated into the 3D printed object in a predetermined arrangement, the predetermined arrangement may form a detectable marker that is characterised by mechanical properties (e.g. hardness) that differ from the mechanical properties (e.g. hardness) of adjacent regions of the 3D printed object. This marker may be revealed when the mechanical properties (e.g. hardness) of the metal part are tested. Where the marker is incorporated in a predetermined location in the 3D printed object, it may be possible to detect for mechanical properties (hardness) at that predetermined location. The predetermined arrangement of the marking agent may provide a signature defined by e.g. regions or pattern within the part having characteristic mechanical properties (hardness, for example, higher or lower hardness), which may encode information relating to the 3D printed object, for example, information regarding the part's identity and/or purpose. In some examples, the encoded information may relate to subsequent processing operations relating to the 3D printed object.
[0025]In some examples, the detectable marker may have a characteristic response to treatment with a chemical agent, for instance, an etching agent (e.g. an acid). For example, the marking agent may form an alloy or composite with the at least one metal of the build material upon sintering. Such an alloy or composite may have a chemical resistance that is different from the chemical resistance of adjacent regions of the printed part. In some examples, such an alloy or composite may have a chemical resistance e.g. to etching that is greater than the chemical resistance of adjacent regions of the printed part. This marker may be revealed when the metal part is treated with a chemical agent, for example, an etching agent. The predetermined arrangement of the marking agent may provide a signature defined by e.g. regions or pattern within the part that erode to a different (e.g. greater or lesser) extent than the remainder of the part when the part is treated with a chemical agent e.g. an etching agent. As a result, a pattern may be revealed when the part is treated with a chemical agent, e.g. an etching agent. This pattern, once revealed, may be visible to the naked eye. This pattern may encode information on the part, for example, information regarding the part's identity and/or purpose. In some examples, the encoded information may relate to subsequent processing operations relating to the 3D printed object.
[0026]In some examples, the chemical agent may be an oxidizing agent. For instance, the oxidizing agent may be air or oxygen. Where the marking agent forms an alloy or composite with the at least one metal of the build material upon sintering, such an alloy or composite may have a resistance to oxidation that is different from the resistance to oxidation of adjacent regions of the printed part. Accordingly, the marker may be revealed when the metal part is oxidized, for example, on exposure to air over time or on exposure to oxygen at an elevated temperature. The predetermined arrangement of the marking agent may provide a signature defined by e.g. regions or pattern within the part that oxidize to a different (e.g. greater or lesser) extent than the remainder of the part when the part is oxidized. As a result, a pattern may be revealed when the part is oxidized. This pattern, once revealed, may be visible to the naked eye. This pattern may encode information on the part, for example, information regarding the part's identity and/or purpose. In some examples, the encoded information may relate to subsequent processing operations relating to the 3D printed object.
[0027]The present disclosure may also relate to a multi-fluid inkjet kit for 3D printing. The kit comprises a marking agent or inkjet ink composition comprising a marking component dispersed in a liquid carrier. The marking component comprises a first metal, carbon and/or a ceramic. The kit also comprises a binding agent or inkjet ink composition comprising a binder dispersed in a liquid carrier. The binder comprises a second metal or ceramic. Where the marking component comprises a first metal and the build material comprises a second metal, the second metal is different from the first metal.
[0028]In some examples, where the marking component comprises a first metal, the first metal is ferromagnetic. The ferromagnetic metal may be selected from at least one of: iron, cobalt and nickel.
[0029]In some examples, the kit further comprises a build material comprising at least one metal.
[0030]The first metal of the marking component may be alloyable with the second metal of the build material. In other words, the first metal may be capable of forming an alloy with the metal of the build material. An alloy may be formed, for example, on exposure to heat. In some examples, an alloy may be formed, for example, during sintering.
[0031]The alloy may have different mechanical properties from e.g. the metal of the build material. For example, the alloy may have a different hardness or response to a chemical agent (e.g. an etching agent). In some examples, the build material comprises copper. The first metal may be silver. The copper may form an alloy with the silver and the resulting silver-copper alloy may have different mechanical properties from copper. For example, the alloy may have a different hardness or response to a chemical agent (e.g. an etching agent).
[0032]In some examples, the at least one metal of the build material is the same as the metal of the binder (i.e. the second metal). For example, where the build material comprises copper, the binder may also comprise copper.
[0033]In some examples, the binder comprises a salt of the second metal.
Build Material
[0034]The build material employed in the present disclosure may comprise at least one metal or ceramic. In some examples, the build material employed in the present disclosure comprises at least one metal (i.e. metallic build material). The build material may comprise particles of build material. For example, the build material may comprise a build material powder.
[0035]In an example, the build material is a single phase metallic material composed of one element.
[0036]In another example, the build material is composed of two or more elements, which may be in the form of a single phase metallic alloy or a multiple phase metallic alloy. For some single phase metallic alloys, melting begins just above the solidus temperature (where melting is initiated) and is not complete until the liquidus temperature (temperature at which all the solid has melted) is exceeded. For other single phase metallic alloys, melting begins just above the peritectic temperature. The peritectic temperature is defined by the point where a single phase solid transforms into a two phase solid plus liquid mixture, where the solid above the peritectic temperature is of a different phase than the solid below the peritectic temperature. When the metallic build material is composed of two or more phases (e.g., a multiphase alloy made of two or more elements), melting generally begins when the eutectic or peritectic temperature is exceeded. The eutectic temperature is defined by the temperature at which a single phase liquid completely solidifies into a two phase solid. Generally, melting of the single phase metallic alloy or the multiple phase metallic alloy begins just above the solidus, eutectic, or peritectic temperature and is not complete until the liquidus temperature is exceeded. In some examples, sintering can occur below the solidus temperature, the peritectic temperature, or the eutectic temperature. In other examples, sintering occurs above the solidus temperature, the peritectic temperature, or the eutectic temperature. Sintering above the solidus temperature is known as super solidus sintering, and this technique may be useful when utilizing larger build material particles and/or to achieve high density. It is to be understood that the sintering temperature may be high enough to offer sufficient energy to allow atom mobility between adjacent particles.
[0037]Single elements or alloys may be used as the metallic build material. Some examples of the metallic build material include steels, stainless steel, bronzes, brasses, titanium (Ti) and alloys thereof, aluminum (Al) and alloys thereof, nickel (Ni) and alloys thereof, cobalt (Co) and alloys thereof, iron (Fe) and alloys thereof, gold (Au) and alloys thereof, silver (Ag) and alloys thereof, platinum (Pt) and alloys thereof, and copper (Cu) and alloys thereof. Some specific examples include AISM OMg, 2xxx series aluminum, 4xxx series aluminum, CoCr MPI, CoCr SP2, MaragingSteel MS1, Hastelloy C, Hastelloy X, NickelAlloy HX, Inconel IN625, Inconel IN718, SS GP1, SS 17-4PH, SS 316L, Ti6Al4V, and Ti-6Al-4V EL7. While several example alloys have been described, it is to be understood that other alloy build materials may be used, such as refractory metals.
[0038]Where the build material is ceramic, the ceramic may be nonmetallic, inorganic compounds, such as metal oxides, inorganic glasses, carbides, nitrides, and borides. Some specific examples include alumina (Al2O3), Na2O/CaO/SiO2glass (soda-lime glass), silicon carbide (SiC), silicon nitride (Si3N4), silicon dioxide (SiO2), zirconia (ZrO2), yttrium oxide-stabilized zirconia (YTZ), titanium dioxide (TiO2), or combinations thereof. In an example, the build material powder may be a cermet (a metal-ceramic composite).
[0039]The build material may be made up of similarly sized particles or differently sized particles. In some examples, the build material has an average particle size of from about 5 to about 20 microns.
[0040]The term “size”, as used herein with regard to the metallic build material 16, refers to the diameter of a particle, for example, a substantially spherical particle (i.e., a spherical or near-spherical particle having a sphericity of >0.84), or the average diameter of a non-spherical particle (i.e., the average of multiple diameters across the particle).
[0041]In some examples, particles of a particle size of from about 5 microns to about 20 microns have good flowability and can be spread relatively easily. As an example, the average particle size of the particles of the metallic build material may range from about 1 microns to about 200 microns. As another example, the average size of the particles of the metallic build material ranges from about 10 microns to about 100 microns. As still another example, the average size of the particles of the metallic build material ranges from 15 microns to about 50 microns.
Marking Agent
[0042]The marking agent may comprise a marking component in a liquid carrier. The marking component may be present in amounts of about 0.2 to about volume % of the marking agent (inkjet ink composition). In some examples, the marking component may be present in amounts of about 2 to about 8 volume %, for instance, about 4 to about 5 volume % of the marking agent. The marking agent is an inkjet ink composition.
[0043]The marking component may comprise carbon, ceramic or metal. The marking component may comprise marker nanoparticles dispersed in a liquid carrier. Alternatively, the marking component may be dissolved in a liquid carrier. For instance, the marking component may comprise a metal salt dissolved in a liquid carrier.
[0044]In some examples, the marking component comprises marker nanoparticles dispersed in a liquid carrier. The marker nanoparticles may be formed of carbon, ceramic and/or metal.
[0045]The marking component (e.g. marker nanoparticles) may be employed to impart distinctive properties to selected regions of the 3D printed object. These distinctive properties allow a detectable marker to be incorporated in the 3D printed object. For example, the marking component (e.g. marker nanoparticles) may comprise a metal that alloys with the metal of the build material. The alloy may have properties that are distinguishable from the properties of the build material. Alternatively, the marking component comprises marker nanoparticles that comprise carbon, which can be used to alter the carbon content of build material comprising iron (e.g. steel). In some examples, the marking component comprises marker nanoparticles that comprise ceramic fillers that can be used to form a reinforced composite material from the build material.
[0046]Where the marking component (e.g. marker nanoparticles) comprise metal, the metal may be a metal alloy and/or metal compound. When a metal is present in the marking agent, the metal in the marking agent may be different from a metal in the build material. In one example, the marking agent may include a metal that is different from the metal in the build material and any metal in the binder. In other words, the binder may include a second metal that is different from the first metal of the marking agent. As described below, the metal in the binder (where present) may be the same as the metal of the build material at least in the locality of the detectable marker.
[0047]The marking agent may include marker nanoparticles with dimensions that are in the nanometer size range, that is, from about 1 nanometer to about 1,000 nanometers. In an example, the nanoparticles may be in a size range of about 1 nanometers to about 100 nanometers, and for example within a range of about 1 to about 50 nanometers. The nanoparticles may have any shape.
[0048]Suitable marker nanoparticles for the marking agent include nanoparticles formed from: AlN, SiC, Si3N4, WC, Al2O3, Al(OH)3, Fe2O3, Fe3O4, MgO, SiO2, TiO2, Y2O3, ZnO, ZrO2, BaCO3, In2O3, SnO2, nickel oxide (e.g. NiO), cobalt oxide (e.g. CoO, Co3O4), carbon, magnesium, manganese, aluminum, iron, titanium, niobium, tungsten, chromium, tantalum, cobalt, nickel, vanadium, zirconium, molybdenum, palladium, platinum, copper, silver, gold, cadmium, zinc, tin, silicon, lead, boron, and combinations of these with each other and/or with a non-metallic element or elements.
[0049]Where the marking component comprises a metal salt, suitable metal salts include salts of copper, silver iron, nickel, manganese or cobalt. In some examples, the metal salt may be a salt of copper. Examples of salts include nitrates, sulfates, formates, and acetates. Suitable salts may be selected from the group consisting of copper nitrate, iron nitrate, nickel nitrate, manganese nitrate, cobalt nitrate, iron acetate, and combinations thereof. In one example, the metal salt is copper nitrate. The metal salt may be hydrated.
[0050]The marking agent employed in the present disclosure is a marking agent that can be incorporated into the 3D printed object (also referred to as a “printed part”) in a predetermined arrangement. As discussed above, the predetermined arrangement forms a detectable marker. In some examples, the detectable marker may not be detectable by visual inspection. This can allow covert marking of the printed substrate.
[0051]In some examples, the detectable marker is invisible. For example, the detectable marker may have characteristic magnetic properties. In some examples, the marking component (e.g. marker nanoparticles) may comprise a first metal that is magnetic. The metal may be present in any form, for example, as a pure metal, an alloy and/or a metal compound (e.g. metal oxide). Examples of such magnetic metals include ferromagnetic metals, for instance, iron, nickel and cobalt. In one example, the marking component (e.g. marker nanoparticles) comprises iron. The iron can be incorporated into the printed part in a predetermined arrangement to provide a characteristic magnetic arrangement (e.g. magnetic signature) within the part. This magnetic arrangement (e.g. magnetic signature) can encode information regarding e.g. the identity and/or purpose of the part, allowing the part to be tracked and traced. Since the magnetic arrangement (e.g. magnetic signature) is invisible, it may be possible to track and trace the part covertly. For example, if the signature is applied at a predetermined location within the part, the magnetism of the part can be tested at least at the predetermined location to e.g. identify or obtain information on the part. The magnetic arrangement (e.g. magnetic signature) may be located at a predetermined location in the part e.g. within the body of the part or at least partly on the surface of the part. The magnetic materials may be incorporated into predetermined locations of the part as an alloy or composite with the build material.
[0052]In some examples, the marker nanoparticles may contain metal (e.g. magnetic metal), but may not themselves be magnetic. For example, the marker nanoparticles may contain the metal in the form of a metal compound (e.g. a metal oxide). However, upon exposure to elevated temperatures and/or to a reducing atmosphere, magnetic materials may be formed. Examples of such magnetic materials include ferromagnetic metals, for instance, iron, nickel and cobalt. In one example, the magnetic material is iron. The magnetic materials formed may be incorporated into predetermined locations of the part as an alloy or composite with the build material e.g. during the sintering process.
[0053]In one example, marker nanoparticles comprising iron oxide may be used in the marking agent. When such particles are incorporated into the printed part and the part is exposed to elevated temperatures and/or a reducing atmosphere (e.g. sintering), the iron oxide may be reduced to iron. This can leave a magnetic arrangement (e.g. magnetic signature) within the 3D printed object. This magnetic arrangement (e.g. magnetic signature) can encode information regarding e.g. the identity and/or purpose of the part, allowing the 3D printed object to be tracked and traced. Since the magnetic arrangement (e.g. magnetic signature) is invisible, it may be possible to track and trace the 3D printed object covertly, for example, if the signature is applied at a predetermined location within the 3D printed object.
[0054]Inks that are suitable for incorporating magnetic arrangements (e.g. magnetic signatures) into the part include magnetic ink character recognition (MICR) inks, i.e. inks used for printing magnetic ink character recognition (MICR) codes. Such magnetic ink character recognition (MICR) inks may include iron oxide (e.g. Fe3O4) nanoparticles.
[0055]The detectable marker may have characteristic mechanical properties. properties. For example, the detectable marker may have characteristic hardness properties. Such hardness properties may be determined using a hardness tester (e.g. Rockwell hardness, ASTM E-18-19).
[0056]In some examples, the marker nanoparticles may have characteristic mechanical properties that are readily distinguishable from those of the build material (e.g. when the build material is sintered under the same conditions). In other examples, on exposure to elevated temperatures and/or a reducing atmosphere (e.g. during sintering), materials with characteristic mechanical properties may be formed. These materials may be incorporated into predetermined locations of the part as an alloy or composite with the build material. It is this alloy or composite that may form the detectable marker e.g. with the characteristic hardness properties.
[0057]In one example, the marking agent comprises a metal compound, e.g. iron oxide nanoparticles. The metal compound, e.g. iron or other metal oxide, may be incorporated into the printed part to form a composite materials in a predetermined arrangement within the part. On exposure to elevated temperatures and/or a reducing atmosphere e.g. during sintering, at least some of the metal compound converted to metal. In the case of iron or another metal oxide, the iron or other metal may be reduced. The iron or other metal may form an alloy or composite with the metal of the build material in a predetermined arrangement within the 3D printed object. The mechanical properties where the composite or alloy is present will be different from the mechanical properties in adjacent regions of the 3D printed object, providing the object with a predetermined hardness arrangement (e.g. a hardness signature) defined by characteristic mechanical properties. This predetermined hardness arrangement (e.g. hardness signature) can encode information regarding e.g. the identity and/or purpose of the 3D printed object, allowing the 3D printed object to be tracked and traced. Where the predetermined hardness arrangement (e.g. hardness signature) is invisible from the exterior of the part, it may be possible to track and trace the 3D printed object covertly, for example, if the hardness arrangement (e.g. hardness signature) is applied at a predetermined location within the 3D printed object.
[0058]Other examples of materials that can be included in the marking agent to form an alloy or composite with the build material include carbon, nickel, copper, oxygen, chromium, boron cobalt, silicon, nitrogen, titanium, molybdenum, manganese, aluminium, cerium, niobium, tungsten, magnesium, zinc, tin, lead, zirconium and vanadium. For example, where the build material comprises steel, the marking agent may comprise carbon to produce a higher carbon steel alloy at selected, predetermined locations. This higher carbon steel alloy forms a predetermined hardness arrangement that can act as a hardness signature in the 3D printed object.
[0059]The detectable marker may have a characteristic response to a chemical agent. In some examples, the detectable marker may have a lesser resistance to a chemical agent. In other examples, the detectable marker may have a greater resistance to a chemical agent. The chemical agent may be an etching agent, for example, an acid. In one example, the detectable marker may have a characteristic response to an etching agent, such that the detectable marker is more resistant to etching than areas of the 3D printed object where the detectable marker is absent. Accordingly, when the part is treated with a chemical (e.g. etching) agent at least at a relevant location, the detectable marker may be revealed as areas surrounding the marker may be etched away. In another example, the chemical agent may be an oxidizing agent, for instance, air. In one example, the detectable marker may have a characteristic response to exposure to air or other oxidizing environment (e.g. at an elevated temperature), such that the detectable marker is more resistant to such exposure than areas of the 3D printed object where the detectable marker is absent. Accordingly, when the part is exposed to air or other oxidizing environment (e.g. at elevated temperatures) at least at a relevant location, the detectable marker may be revealed as areas surrounding the marker may be more readily oxidized.
[0060]In some examples, the marker nanoparticles may have characteristic response to a chemical agent that is readily distinguishable from that of the build material. In other examples, on exposure to elevated temperatures and/or a reducing atmosphere e.g. during sintering, a material with a characteristic response to the chemical agent may be formed. Examples of materials include silver, copper, chromium, manganese, nickel, molybdenum, vanadium, silicon, boron, aluminium, cobalt, cerium, niobium, tungsten, tin, zinc, lead and zirconium. These materials may be incorporated into predetermined locations of the part as an alloy or composite with the build material e.g. during the sintering process.
[0061]In one example, where the marking agent comprises silver nanoparticles, the silver nanoparticles may be incorporated into the printed part to form a composite materials in a predetermined arrangement within the part. On exposure to elevated temperatures e.g. during sintering, the silver forms an alloy with the metal (e.g. copper) of the build material in a predetermined arrangement within the part. The chemical resistance (e.g. to etching) where the composite or alloy is present will be different from the mechanical properties in adjacent regions of the part. This may provide the 3D printed object with a distinctive arrangement (e.g. signature) that can be revealed by treatment with a chemical agent (e.g. etching agent) in a relevant location on the part. This signature can encode information regarding e.g. the identity and/or purpose of 3D printed object part, allowing the 3D printed object to be tracked and traced. The signature can also encode data relating to subsequent processing steps, e.g. by delineating sections of the part to which other portions are to be attached.
[0062]In some examples, the marking agent comprises a metal. In some examples, the metal may be magnetic, or may be a metal that is alloyable with a metal present in the build material.
[0063]The marking agent may be a liquid composition comprising nanoparticles and a liquid carrier. The marking agent may be a jettable composition, i.e. an inkjet ink composition. Suitable liquid carriers include water or a non-aqueous solvent (e.g. ethanol, acetone, n-methyl pyrrolidone, aliphatic hydrocarbons or combinations thereof).
[0064]In some examples, the marking agent may further comprise at least one of: a co-solvent, a surfactant, a dispersant, a biocide, an anti-kogation agent, viscosity modifiers, buffers, stabilizers, and combinations thereof. The presence of a co-solvent, a surfactant, and/or a dispersant in the agent may assist in obtaining a particular wetting behaviour when the marking agent is applied to the build material.
[0065]Examples of co-solvents that may be used include aliphatic alcohols, aromatic alcohols, diols, glycol ethers, polyglycol ethers, 2-pyrrolidones, caprolactams, formamides, acetamides, glycols, and long chain alcohols.
[0066]Examples of these co-solvents include primary aliphatic alcohols, secondary aliphatic alcohols, 1,2-alcohols, 1,3-alcohols, 1,5-alcohols, ethylene glycol alkyl ethers, propylene glycol alkyl ethers, higher homologs (C6-C12) of polyethylene glycol alkyl ethers, N-alkyl caprolactams, unsubstituted caprolactams, both substituted and unsubstituted formamides, both substituted and unsubstituted acetamides, and the like. Other examples of some suitable co-solvents include water-soluble high-boiling point solvents (i.e., humectants), which have a boiling point of at least about 120° C., or higher. Some examples of high-boiling point solvents include 2-pyrrolidone (boiling point of about 245° C.), 2-methyl-1,3-propanediol (boiling point of about 212° C.), and combinations thereof.
[0067]The co-solvent(s) may be present in the marking agent in a total amount ranging from about 1 wt % to about 70 wt % based upon the total weight of the marking agent, depending upon the jetting architecture of the applicator.
[0068]Surfactant(s) may be used to improve the wetting properties and the jettability of the marking agent. In some examples, the surfactant can be Dowfax™ 2A1. Examples of suitable surfactants include a self-emulsifiable, nonionic wetting agent based on acetylenic diol chemistry (e.g., SURFYNOL® SEF from Air Products and Chemicals, Inc.), a nonionic fluorosurfac