Polymer filaments containing metal precursors for additive manufacturing and related methods

Abstract

The present invention is entitled "Polymer filaments containing metal precursors for additive manufacturing and related methods thereof". Additive manufacturing processes, such as fused filament fabrication, can be used to form printed objects of a range of shapes. Sometimes it is desirable to form conductive traces on the surface of the printed object. Conductive traces and similar features can be introduced in conjunction with the fused filament fabrication process by: incorporating a metal precursor into a polymer filament having a filament body comprising a thermoplastic polymer; and forming a printed object from the polymer filament by layer-by-layer deposition, wherein the metal precursor remains substantially unconverted to metal when the printed object is formed. Suitable polymer filaments compatible with fused filament fabrication may include a thermoplastic polymer defining a filament body and a metal precursor contacting the filament body, wherein the metal precursor can be activated upon laser irradiation to form metal islands.

Description

Technical Field

[0001] The present disclosure relates generally to additive manufacturing, and more particularly to methods of additive manufacturing by fused filament fabrication, wherein metal precursors capable of being activated by laser irradiation are incorporated during the printing process. Background Art

[0002] Additive manufacturing, also known as three-dimensional (3D) printing, is a rapidly growing field of technology. Although additive manufacturing has traditionally been used for rapid prototyping activities, the technology is increasingly being used to produce commercial and industrial parts (objects) with any number of complex shapes. The additive manufacturing method operates by depositing layer by layer either of the following substances: 1) a stream of molten printing material obtained from a continuous filament, or 2) powder particles of printing material. The layer-by-layer deposition is usually carried out under the control of a computer to deposit the printing material in precise locations based on a digital three-dimensional "blueprint" (computer-aided design model) of the part to be manufactured, wherein consolidation of the printing material is carried out in conjunction with the deposition to form the printed part. The printing material that forms the body of the printed part may be referred to as the "build material" herein.

[0003] Additive manufacturing methods that use a stream of molten printing material to form parts typically use thermoplastic polymer filaments as a source of molten printing material. Such additive manufacturing methods are sometimes referred to as "fused deposition modeling" or "fused filament manufacturing" methods. The latter term is used in this article.

[0004] Additive manufacturing methods using powder particles of printing material generally perform direct heating at selected locations of the particle bed after the deposition of the printing material to promote localized agglomeration of the powder particles into a consolidated part. Techniques suitable for promoting the consolidation of powder particles to form a consolidated part include, for example, powder bed fusion (PBF), selective laser sintering (SLS), electron beam melting (EBM), binder jetting, and multi-jet fusion (MJF).

[0005] Both types of additive manufacturing methods can be used to manufacture a variety of parts with a variety of shapes. One feature associated with both types of additive manufacturing methods is that in order to manufacture parts "in an additive manner", there must be an infrastructure on which the printing material is deposited to achieve the layer-by-layer accumulation of the part. The initial layer of the printed part can be deposited on the print bed (bed plate) of the 3D printer, and then subsequent layers can be deposited on the initial deposited layer. In terms of the powder deposition process, the subsequent layer can be supported by the underlying layer of the powder bed, which can be consolidated to form a part of the part or remain unconsolidated. In contrast, parts made by depositing molten printing materials such as by fused filament manufacturing lack corresponding support structures formed by unconsolidated printing materials. Because the printed parts grow from the print bed in the fused filament manufacturing method, overhangs and similar structures may exist because the shape of the part is no longer in direct contact with the print bed or the previously deposited unconsolidated printing material layer. Since the printing material cannot be deposited in free space without the presence of an underlying support, parts with overhangs and similar structures cannot be directly printed by fused filament manufacturing. As a solution to the problem of overhangs and similar structures in fused filament fabrication methods, a common strategy is to deposit build material and sacrificial printing material concurrently (e.g., from a dual extruder print head), where the sacrificial printing material can be formed into removable supports for depositing and solidifying the build material thereon at selected locations. After printing is complete, the removable supports can be eliminated using a suitable technique (such as by degradation or dissolution) to produce an unsupported (free) part.

[0006] Parts made using fused filament fabrication and by particle consolidation may look quite similar to each other on a macroscale, but they may differ on a microscale. A printed part made by particle consolidation may show traces of grain boundaries throughout substantially the entire part. Depending on the extent of particle consolidation that occurs, grain boundaries may be more prominent in some cases than in others. In contrast, a printed part made using fused filament fabrication does not have unevenly distributed grain boundaries. In fused filament fabrication, there are essentially no grain boundaries along the print lines formed by the molten polymer, but there may be traces of incomplete consolidation between adjacent print lines or layers. Therefore, in a fused filament fabrication polymer matrix, boundaries indicating incomplete print line consolidation will not show traces of residual grain structure, which may be a characteristic of the particle consolidation method.

[0007] In some cases, it may be desirable to have additional functional features on the surface of an additively manufactured part. In one particular example, conductive traces may be introduced into the surface of an additively manufactured part by a separate inkjet printing, aerosol jet or direct writing method to deposit ink infused with a conductive material (such as graphite or metal) on the surface of the part, and then solidify or sinter to facilitate the formation of conductive pathways (conductive traces). The deposition of such conductive inks occurs under conditions that are completely different from the additive manufacturing process, requiring the printed parts to be transferred between production lines. In many cases, the process may be cumbersome and time-consuming, especially when extreme accuracy is required to place the conductive traces. When conductive traces are formed in this manner, accurate placement of the conductive traces on the non-flat surface of the printed part may be particularly problematic. Additional difficulties may arise due to the poor adhesion between specific thermoplastic polymers and the conductive inks used in conjunction with the inkjet printing process and the aerosol jet printing process. Summary of the invention

[0008] The present disclosure provides a polymer filament compatible with fused filament fabrication. The polymer filament comprises: a thermoplastic polymer defining a filament body; and a metal precursor contacting the filament body, the metal precursor being activated to form metal islands when irradiated by a laser.

[0009] The present disclosure also provides a printed object, which includes a fused filament fabrication polymer matrix, the fused filament fabrication polymer matrix including a metal precursor in at least a portion thereof, the metal precursor being capable of being activated upon laser irradiation to form metal islands.

[0010] The present disclosure also provides a method for forming a printed object, the method comprising: providing a polymer filament, the polymer filament comprising a thermoplastic polymer defining a filament body and a metal precursor contacting the filament body, the metal precursor being capable of being activated upon laser irradiation to form metal islands; and forming the printed object from the polymer filament by layer-by-layer deposition; wherein when forming the printed object, the metal precursor remains substantially unconverted into metal. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The following drawings are included to illustrate certain aspects of the disclosure and should not be construed as exclusive embodiments. The disclosed subject matter is capable of considerable modification, alteration, combination, and equivalents in form and function, as will occur to those of ordinary skill in the art having the benefit of this disclosure.

[0012] Figure 1 Diagram of an illustrative fused filament fabrication method for producing a printed object using a build material and a removable support material.

[0013] Figure 2 is a diagram of an exemplary printed object with an overhang.

[0014] Figure 3 is a diagram of an exemplary polymer filament having metal precursor particles homogeneously blended within the thermoplastic polymer within the body of the filament.

[0015] Figure 4 is a diagram of an exemplary polymer filament having metal precursor particles disposed on an outer surface of a filament body comprising a thermoplastic polymer.

[0016] Figure 5 is a diagram of an exemplary polymer filament having metal precursor particles disposed within an inner core surrounded by an outer shell of a filament body comprising a thermoplastic polymer.

[0017] Figure 6 is an illustrative process flow diagram showing the formation of a printed object by fuse fabrication, followed by activation of a metal precursor and electroless plating to form conductive traces. DETAILED DESCRIPTION

[0018] The present disclosure relates generally to additive manufacturing, and more specifically to an additive manufacturing method by fused filament fabrication, wherein a metal precursor capable of being activated by laser irradiation is incorporated during the printing process. According to the disclosure herein, the metal precursor may remain unactivated during the deposition of the printed material. The metal precursor may then be activated to form metal islands, which may then be interconnected to form conductive traces having a desired pattern.

[0019] As described above, additive manufacturing methods such as fused filament manufacturing are powerful tools for generating printed parts (objects) of a wide range of complex shapes. Currently, it is not feasible to introduce conductive traces on the surface of printed parts as an integrated part of the additive manufacturing process. Alternatively, a separate aerosol, inkjet or direct printing technology is used to deposit conductive ink on the surface of the printed part, followed by curing or sintering to promote conductivity. Separate printing techniques for depositing conductive inks may limit processing throughput and sometimes result in inaccurate placement of conductive traces. In some cases, there may also be poor adhesion between the thermoplastic polymer that constitutes the printed object and the conductive ink used to deposit the conductive traces.

[0020] Advantageously, the present disclosure provides a way by which metal islands can be introduced during an additive manufacturing process (performed by fused filament manufacturing) without having to transfer the parts to a separate printing line after part manufacturing. In particular, the present disclosure employs a polymer filament comprising a thermoplastic polymer defining a filament body and a metal precursor in contact with the filament body, and the metal precursor can be activated by laser irradiation (especially with a pulsed laser) to facilitate the formation of discontinuous metal islands on the surface of a printed object formed by additive manufacturing (specifically fused filament manufacturing). Suitable metal precursors are non-conductive before activation and comprise metals in a coordinated state and / or salt form. After activation, the metal precursor can be converted into a metal conductor in the form of discontinuous metal islands, which can be accurately placed by carefully positioning the laser. The discontinuous metal islands can then be interconnected to form one or more conductive traces on the surface of the printed object. The patterning of the conductive traces can determine the shape of the conductive traces formed therefrom. Advantageously, a laser for promoting the formation of metal islands can be incorporated into the printing process by fused filament fabrication, thereby allowing accurate introduction of metal islands during and / or after the formation of the printed object. Alternatively, once the printing process is complete, a laser separate from the printing process can be used to activate a metal precursor to form metal islands. In either case, metal islands are formed at specific locations of the printed object, which are appropriately activated by directed laser irradiation.

[0021] Various metal precursors can be used in the disclosure of this article and are discussed in further detail below. Advantageously, such metal precursors can be easily incorporated into polymer filaments, which are suitable for fused filament manufacturing and similar additive manufacturing methods. Such polymer filaments can be formed by thermoplastic polymers blended with metal precursors, such as produced by extruding a molten blend. The metal precursor does not interfere with the filament extrusion process, nor does it interfere with the consolidation process subsequently used to form a printed object. Alternatively, the metal precursor can be located on the outer surface of the polymer filament and / or in the inner core of the polymer filament suitable for the disclosure of this article.

[0022] As another advantage, the metal precursors are also compatible with use in conjunction with sacrificial printing materials, which can be used together to form overhangs and similar structures in printed objects. The conditions used to remove the support structure formed by the sacrificial printing material may not substantially activate the metal precursor to form a metal. Depending on the location, activation of the metal precursor may be performed before and / or after removal of the support structure formed by the sacrificial printing material.

[0023] The terms used in this specification and claims have their plain and ordinary meanings except as modified in the following paragraphs.

[0024] As used herein, the term "thermoplastic polymer" refers to a polymer material that can reversibly soften and harden when heated and cooled. Thermoplastic polymers encompass thermoplastic elastomers.

[0025] As used herein, the term "oxide" refers to both metal oxides and non-metal oxides. For the purposes of this disclosure, silicon is considered a metal.

[0026] Unless otherwise indicated, the melting point of thermoplastic polymers was determined by ASTM E794-06 (2018) with a 10°C / min ramp rate and cooling rate.

[0027] Unless otherwise indicated, the softening temperature or softening point of thermoplastic polymers is determined by ASTM D6090-17.The softening temperature can be measured by using a cup and ball apparatus from Mettler-Toledo using a 0.50 gram sample at a heating rate of 1°C / min.

[0028] As used herein, the term "near infrared" region refers to the wavelength range of about 700 nm to about 1400 nm, which region is sometimes referred to as the IR-A region (as defined by the International Commission on Illumination).

[0029] As used herein, the term "blended" refers to a state of being substantially uniformly mixed.

[0030] As used herein, the term "locally" refers to a state of being unmixed or not uniformly mixed.

[0031] Before discussing various aspects of the present disclosure in further detail, a brief discussion of additive manufacturing methods (parts) for making printed objects (parts), particularly fused filament manufacturing methods, will first be described so that certain features of the present disclosure can be better understood. Figure 1 Schematic diagram of an exemplary fused filament fabrication method for producing a printed object using a build material and a removable support material. Figure 1 As shown, the print head 100 includes a first extruder 102a and a second extruder 102b, each of which is configured to receive a filamentary printing material. Specifically, the first extruder 102a is configured to receive a first filament 104a from a first wire-releasing reel 106a and provide a molten stream 108a of the first printing material, and the second extruder 102b is configured to receive a second filament 104b from a second wire-releasing reel 106b and provide a molten stream 108b of the second printing material. The two molten streams are initially deposited on the print bed ( Figure 1114) to promote the layer-by-layer growth of the supported object 120. The first printing material (building material) supplied by the first extruder 102a may include a thermoplastic polymer for making the printed object 110, and also include a metal precursor, and the second printing material (removable support material) supplied by the second extruder 102b may be a soluble or degradable polymer, which is used to make the removable support 112 under the overhang 114. The overhang 114 is not in direct contact with the print bed or the lower print layer formed by the building material. Figure 1 In the illustrated print object arrangement, the removable support 112 is interposed between the overhang 114 and the print bed (not shown), but it should be understood that in alternatively constructed print objects, the removable support 114 may be interposed between two or more portions of the print object 110. For example, Figure 2 A diagram of an exemplary printed object 200 is shown, wherein a removable support 202 is interposed between an overhang defined between the printed object 200 and a print bed 204 , and a removable support 206 is interposed between two portions of the printed object 200 .

[0032] See again Figure 1 Once printing of the printed object 110 and removable supports 112 is complete, the supported object 120 may be subjected to support removal conditions 125, resulting in the elimination of the removable supports 112 (e.g., dissolution or disintegration conditions) and leaving the printed object 110 with an unsupported overhang 114 thereon. The support removal conditions 125 may include, for example, contacting the supported object 120 with a solvent or other liquid medium in which the removable supports 112 are soluble or degradable, while the printed object 110 is not. The removable supports 112 may include a different thermoplastic polymer than the printed object 110 to support selective dissolution or degradation.

[0033] The polymer filaments of the present disclosure suitable for additive manufacturing (specifically fused filament manufacturing) may include a thermoplastic polymer defining a filament body and a metal precursor contacting the filament body, wherein the metal precursor can be activated upon laser irradiation (particularly with a pulsed laser) to form metal islands.

[0034] Non-limiting configurations of polymer filaments that can be used in fused filament fabrication are referred to below. Figures 3 to 5 Be discussed. As discussed in more detail below, any of these polymer filaments may be suitable for forming metal islands in a printed object. Exemplary forms of polymer filaments may include a blend of a metal precursor and a thermoplastic polymer in a filament body, a metal precursor positioned on the outer surface of the filament body and / or a metal precursor positioned in the inner core of the polymer filament and a filament body as a shell surrounding the inner core. In any polymer filament configuration, the metal precursor may exist as a plurality of particles contacting the filament body. Figure 3 is a diagram of an exemplary polymer filament 300 in which metal precursor particles 302 are uniformly blended with a thermoplastic polymer in a filament body 304 . Figure 4 is a diagram of an exemplary polymer filament 400 in which metal precursor particles 402 are disposed on an outer surface of a filament body 404, which comprises a thermoplastic polymer. Figure 5 Figure for exemplary polymer filament 500, wherein metal precursor particles 502 are arranged in inner core 503, and this inner core is surrounded by the shell 504 of the filament body comprising thermoplastic polymer.It is also possible to have the polymer filament of metal precursor particles at multiple positions, and can be used for this paper disclosure.In non-limiting embodiments, metal precursor particles can be blended with thermoplastic polymer and be placed on the outer surface of filament body, or both are present in inner core and are placed on the outer surface of filament body.When being placed on the outer surface of filament body, metal precursor particles can be at least partially embedded in thermoplastic polymer, be bonded to thermoplastic polymer, be covalently bonded to thermoplastic polymer or their any combination with adhesive and sizing material.The manufacturing technology that is applicable to produce various types of polymer filaments is further discussed below.

[0035] The diameter of the polymer filament of the present disclosure can be in the range of from about 0.5mm to about 5mm, especially in the range of about 1.5mm to about 3.5mm.For many three-dimensional printers adopting fused filament manufacturing technology, the standard filament diameter is about 1.75mm or 3.0mm.It should be recognized that any suitable polymer filament diameter can be used according to the disclosure herein, provided that the polymer filament is compatible with the specific printing system of the user.Similarly, it is believed that the length and / or color of the polymer filament are not particularly limited in the disclosure herein.Similarly, it is believed that the polymer filament comprising removable support material is not particularly limited.Preferably, the polymer filament disclosed herein is continuous and has a length that can be wound, for example, at least about 1 foot, or at least about 5 feet, or at least about 10 feet, or at least about 25 feet, or at least about 50 feet, or at least about 100 feet, or at least about 250 feet, or at least about 500 feet, or at least about 1000 feet.

[0036] Metal precursor can be mixed in or on the filament body in the process of manufacturing polymer filament disclosed herein.The uniform mixing of metal precursor and thermoplastic polymer can be realized by melt blending / extrusion method, to provide substantially uniformly distributed metal precursor in the whole filament body of polymer fiber.The polymer filament of the inner core with metal precursor and the shell limited by the filament body can be formed by modified melt blending / extrusion method.Optionally, when forming the inner core, metal precursor can be blended with thermoplastic polymer, wherein the thermoplastic polymer in the inner core can be the same or different from the thermoplastic polymer present in the shell forming the polymer filament in the filament body.Metal precursor can be deposited on the outer surface of the filament body of polymer fiber, for example, by spraying an aerosol of metal precursor particles on polymer fiber after extrusion and before the thermoplastic polymer is fully solidified or a solution containing metal precursor is deposited, wherein the metal precursor is attached to the outer surface of polymer fiber.Alternatively, polymer filament can pass through the dispersion of metal precursor in solvent, to provide the metal precursor deposition based on dip coating on the outer surface. Thus, in at least some examples, suitable metal precursors may be thermally stable at temperatures greater than or equal to the melting point or softening temperature of the thermoplastic polymer comprising the filament body in order to be compatible with melt blending / extrusion or similar methods. Other properties of suitable metal precursors may include, for example, non-conductivity (before conversion to metal), good weatherability, easy blending of metal precursor particles with thermoplastic polymers and / or solubility of the metal precursor in thermoplastic polymers, and low toxicity.

[0037] When combined as particles with a thermoplastic polymer, the metal precursor may have a size in the range of from about 10 nm to about 100 μm, or a size in the range of from about 50 nm to about 10 μm, or a size in the range of from about 100 nm to about 1 μm. In this disclosure, particle size refers to “D 50 " value, refers to the diameter at which 50% of the sample (on a volume basis unless otherwise specified) consists of particles having a diameter less than that stated. 50 It may also be referred to as "average particle size". Such average particle size measurements can be performed by analyzing optical images or using the built-in software of a Malvern Mastersizer 3000Aero S instrument, which uses a light scattering technique to perform particle size measurements. Optionally, the particles of the metal precursor may be further treated with an organic coupling agent (e.g., a silane coupling agent, etc.) to promote compatibility, dispersion, and / or combination with the thermoplastic polymer that defines the filament body. The infrared radiation absorber particles discussed further below may be incorporated into or within the polymer filaments by a similar method and may exist in a similar range of sizes, which may be the same or different from the particles of the metal precursor.

[0038] Particularly suitable metal precursors can be activated by lasers operating in the infrared region (including the near infrared region), the visible light region, or the ultraviolet region of the electromagnetic spectrum. Therefore, suitable laser irradiation wavelengths can be selected from those laser irradiation wavelengths residing in the range of about 200nm to about 14,000nm, especially irradiation wavelengths in the range of from about 1020nm to about 1070nm. Suitable lasers, especially pulsed laser variants thereof, may include solid-state lasers, fiber lasers, semiconductor lasers (laser diodes), CO2 lasers (with an emission wavelength of 10,600nm), and excimer lasers operating in the ultraviolet region of the electromagnetic spectrum. When used to promote metal activation, the CO2 laser can be operated at a laser intensity (laser power per unit area) that is higher than the laser intensity for promoting polymer consolidation by melting or softening thermoplastic polymers. Due to the high laser intensity, pulsed wave operation of the laser may be desirable when activating metal precursors.

[0039] In the present disclosure, a frequency doubled or tripled Nd:YAG laser or similar solid-state laser can provide visible radiation (532nm) or ultraviolet radiation (355nm), while a non-frequency doubled variant can provide near infrared radiation at 1064nm. Other frequency doubled lasers can also be used in the present disclosure.

[0040] The near-infrared region may be particularly suitable for practicing the disclosure herein due to the availability of solid-state lasers or fiber lasers that provide electromagnetic radiation in this region of the electromagnetic spectrum. For example, suitable lasers operating in the near-infrared region of the electromagnetic spectrum include, for example, Nd (neodymium) doped solid-state lasers with an emission wavelength of about 1064 nm, such as Nd:YAG (yttrium aluminum garnet), Nd:YVO4 (yttrium orthovanadate), and Nd:YLF (yttrium lithium fluoride) lasers; solid-state lasers doped with other metals with an operating wavelength of about 1020 nm to about 1050 nm; and fiber lasers with an emission wavelength of about 1030 nm to about 1070 nm, such as Yb-doped fiber lasers. Lasers suitable for activating metal precursors for the disclosure herein may be operated in a pulsed wave mode to provide high pulsed laser intensity to effectively convert metal precursors into metal islands, as well as to provide polymer surface ablation and roughening to promote strong metal adhesion after activation of the metal precursor. The specific example of suitable metal precursor can include those metal precursors that can be activated by pulsed laser beams in the range of from about 1020nm to about 1070nm, and the emission wavelength is located in the near infrared region of the electromagnetic spectrum. Such lasers can operate at a power of about 1W to about 10W, a pulse frequency of about 10kHz to about 120kHz, and a scanning speed of about 0.1m / s to about 10m / s. The specific metal precursors used can determine the type of pulsed lasers used to form metal islands and their emission wavelengths, as described below for some specific examples.

[0041] Specific examples of suitable metal precursors for use in the present disclosure that can be activated in the foregoing manner may include one or more of the following materials:

[0042] - Copper oxide, or a mixed oxide of copper and a metal selected from the group consisting of antimony, aluminum, cesium, cobalt, chromium, magnesium, manganese, nickel, tin, titanium, silver, iron, zinc and zirconium. Specific examples of mixed oxides of copper include, for example, copper oxide chromium spinel (copper chromite), copper aluminum oxide, copper iron oxide, etc. Copper chromite can be suitably activated, for example, at a pulsed laser emission wavelength of 1060 nm (such as using an Nd:YAG laser).

[0043] - Copper hydroxide, basic copper phosphate, copper phosphate, copper sulfate, copper thiocyanate, or any combination thereof. Unless otherwise specified, these copper salts contain copper in the +2 oxidation state (ortho-copper salts). Copper thiocyanate can exist in the +1 or +2 oxidation state.

[0044] -Metal organic complex (metal-ligand complex), the metal-organic complex comprising a metal selected from copper, silver, palladium or any combination thereof. Suitable metal-organic complexes may include, for example, metal monocarboxylate complexes, metal dicarboxylate complexes, metal acetylacetonate complexes, metal salicylaldimine complexes, and the like. Specific examples of suitable metal-organic complexes may include, but are not limited to, copper carboxylates and copper dicarboxylates, such as copper oxalate and copper oleate; copper acetylacetonate; salen copper (salen = N, N'-bis (salicylidene) ethylenediamine); silver carboxylates, such as silver neodecanoate; and palladium carboxylates, such as palladium acetate and palladium neodecanoate. Pulsed lasers emitting in the ultraviolet region of the electromagnetic spectrum (such as with an excimer laser) may be used to convert palladium-containing metal-organic complexes into metals. In contrast, some silver-containing metal-organic complexes may be suitably converted into metals using pulsed lasers emitting in the visible region of the electromagnetic spectrum.

[0045] Even more specific examples of metal precursors suitable for use in the present disclosure may include, for example, PK3095 black pigment (Ferro Corporation) and Black 1G Pigment Black 28 (The Shepherd Color Company), both of which contain copper chromate spinel.

[0046] In addition to the metal precursor, the polymer filaments of the present disclosure may also include an infrared radiation absorber. Exemplary materials that can absorb infrared radiation to promote the formation of metals by metal precursors are further discussed below. When present, the infrared radiation absorber may be present in the same position as the metal precursor and / or in a different position from the metal precursor. Similar to the metal precursor, the infrared radiation absorber may also be present in the polymer filaments disclosed herein as a plurality of particles.

[0047] The intensity of absorption of infrared radiation (particularly infrared radiation in the near infrared region of the electromagnetic spectrum) by the metal precursor can determine whether irradiation with a pulsed laser results in sufficient conversion of the metal precursor to the corresponding metal. In the case where the absorption is sufficiently strong, the metal precursor may only be sufficient. If the infrared radiation absorption intensity is weak, an infrared radiation absorber may also be mixed with the thermoplastic polymer to promote a more efficient conversion of the metal precursor to a metal. Suitable infrared radiation absorbers may include, but are not limited to, non-stoichiometric metal oxides containing metals (e.g., antimony, bismuth, boron, copper, indium, titanium, tin, cesium, zirconium, molybdenum, vanadium, iron, or any combination thereof). Specific examples of suitable infrared radiation absorbers may include, for example, antimony-doped tin oxide, antimony-doped indium tin oxide; reduced indium tin oxide, oxygen-deficient bismuth oxide, and any combination thereof. In some cases, carbon black may also constitute a suitable infrared radiation absorber. When present, the infrared radiation absorber may be included in the polymer filament in an amount of about 0.01% to about 10% by weight or about 0.5% to about 5% by weight relative to the thermoplastic particles.

[0048] Depending on the intensity of infrared radiation absorption and the presence or absence of infrared radiation absorbers, the metal precursor can account for about 1 weight % to about 30 weight % of the polymer filaments disclosed herein, based on the total mass, or about 2 weight % to about 25 weight % of the polymer filaments, based on the total mass, or about 5 weight % to about 15 weight % of the polymer filaments, based on the total mass.

[0049] According to the disclosure herein, thermoplastic polymers suitable for forming the main body of the filament may include, but are not limited to, acrylonitrile-butadiene-styrene (ABS), high impact polystyrene (HIPS), polystyrene, polylactic acid (PLA), polyurethane (PU), polyvinyl pyrrolidone-polyvinyl acetate copolymer (PVP-co-PVA), any copolymer thereof or any combination thereof. These are the most common thermoplastic polymers used as building materials in additive manufacturing. In the disclosure herein, other suitable building materials for forming polymer filaments include, for example, polyamides, polyesters, polycarbonates, polyethylene, polypropylene, polyethylene terephthalate, polyetheretherketone and various copolymers thereof. In some cases, polymer composites may also be used as suitable building materials. In the disclosure herein, thermoplastic polymers suitable for use as building materials may exhibit a softening temperature or melting point sufficient to allow them to be extruded at a temperature ranging from about 150°C to about 300°C, or from about 175°C to about 275°C, or from about 180°C to about 250°C, as determined by the ASTM method cited above. For example, PLA has a melting point in the range of about 150°C to about 160°C.

[0050] According to the disclosure herein, some or other examples of thermoplastic polymers that may be suitable for forming polymer filaments include, but are not limited to, polyamides (e.g., nylon-6, nylon-12, etc.), polyurethanes, polyethylenes, polypropylenes, polyacetals, polycarbonates, polyethylene terephthalates, polybutylene terephthalates, polystyrenes, polyvinyl chlorides, polytetrafluoroethylenes, polyesters (e.g., polylactic acid), polyethers, polyethersulfones, polyetheretherketones, polyacrylates, polymethacrylates, polyimides, acrylonitrile butadiene styrene (ABS), polyphenylene sulfide, vinyl polymers, polyarylethers, polyarylene sulfides, polysulfones, polyetherketones, polyaryletherketones (PAEK), polyamide-imides, polyetherimides, polyetheresters, copolymers comprising polyether blocks and polyamide blocks (PEBA or polyether block amides), grafted or non-grafted thermoplastic polyolefins. , functionalized or non-functionalized ethylene / vinyl monomer polymers, functionalized or non-functionalized ethylene / (meth) acrylate alkyl esters, functionalized or non-functionalized (meth) acrylic polymers, functionalized or non-functionalized ethylene / vinyl monomer / (meth) acrylate alkyl ester terpolymers, ethylene / vinyl monomer / carbonyl terpolymers, ethylene / (meth) acrylate alkyl ester / carbonyl terpolymers, methyl methacrylate-butadiene-styrene (MBS) core-shell polymers, polystyrene-block-polybutadiene-block-poly(methyl methacrylate) (SBM) block terpolymers, chlorinated or chlorosulfonated polyethylene, polyvinylidene fluoride (PVDF), phenolic resins, poly(ethylene / vinyl acetate), polybutadiene, polyisoprene, styrenic block copolymers, polyacrylonitrile, silicones, and the like, and any combination thereof. Copolymers comprising one or more of the foregoing substances may also be used in the present disclosure.

[0051] Particularly suitable examples of thermoplastic polymers for use in the present disclosure may include polyamides, such as nylon 6 or nylon 12; acrylonitrile butadiene styrene; polylactic acid; polyurethane; poly(arylene ether); polyaryletherketone; polycarbonate; polyimide; polyphenylene sulfide; poly(arylene sulfone); polyesters, such as polyethylene terephthalate or polybutylene terephthalate; and any combination thereof.

[0052] More specific examples of suitable polyamides include, but are not limited to, polycaprolactam (nylon 6, polyamide 6, or PA6), poly(hexamethylene succinamide) (nylon 46, polyamide 46, or PA46), polyhexamethylene adipamide (nylon 66, polyamide 66, or PA66), polypentamethylene adipamide (nylon 56, polyamide 56, or PA56), polyhexamethylene sebacamide (nylon 610, polyamide 610, or PA610), polyundecanamide (nylon 11, polyamide 11, or PA11), polydodecaneamide (nylon 12, polyamide 12, or PA12), and polyhexamethylene terephthalamide (nylon 6T, polyamide 6T, or PA6 T), nylon 10.10 (polyamide 10.10 or PA10.10), nylon 10.12 (polyamide 10.12 or PA10.12), nylon 10.14 (polyamide 10.14 or PA10.14), nylon 10.18 (polyamide 10.18 or PA10.18), nylon 6.10 (polyamide 6.10 or PA6.10), nylon 6.18 (polyamide 6.18 or PA6.18), nylon 6.12 (polyamide 6.12 or PA6.12), nylon 6.14 (polyamide 6.14 or PA6.14), semi-aromatic polyamide, etc., and any combination thereof. Copolyamides can also be used. Examples of suitable copolyamides include, but are not limited to, PA11 / 10.10, PA 6 / 11, PA 6.6 / 6, PA 11 / 12, PA 10.10 / 10.12, PA 10.10 / 10.14, PA 11 / 10.36, PA 11 / 6.36, PA 10.10 / 10.36, etc. and any combination thereof. Polyesteramides, polyetheresteramides, polycarbonate-esteramides and polyether-block-amides may also be used, which may be elastomeric.

[0053] Examples of suitable polyurethanes include, but are not limited to, polyether polyurethanes, polyester polyurethanes, mixed polyether and polyester polyurethanes, and the like, and any combination thereof. Examples of suitable polyurethanes include, but are not limited to, poly[4,4'-methylenebis(phenyl isocyanate)-alternative-1,4-butanediol / di(propylene glycol) / polycaprolactone], 1190A (a polyether polyurethane elastomer available from BASF), 1190A10 (a polyether polyurethane elastomer available from BASF), etc. and any combination thereof.

[0054] Suitable thermoplastic polymers may be elastomeric or non-elastomeric. Some of the foregoing examples of thermoplastic polymers may be elastomeric or non-elastomeric, depending on the specific composition of the polymer. For example, polyethylene, which is a copolymer of ethylene and propylene, may be elastomeric and independent of the amount of propylene present in the polymer.

[0055] Elastomeric thermoplastic polymers generally belong to one of six categories: styrenic block copolymers, thermoplastic polyolefin elastomers, thermoplastic vulcanizates (also known as elastomeric alloys), thermoplastic polyurethanes, thermoplastic copolyesters, and thermoplastic polyamides (generally block copolymers containing polyamides), any of which may be used in the disclosure herein. Examples of elastomeric thermoplastic polymers may be found in the following document: Handbook of Thermoplastic Elastomers, 2nd edition, edited by BMW Walker and CP Rader, Van Nostrand Reinhold, New York, 1988. Examples of elastomeric thermoplastic polymers include, but are not limited to, elastic polyamides, polyurethanes, copolymers comprising polyether blocks and polyamide blocks (PEBA or polyether block amides), methyl methacrylate-butadiene-styrene (MBS) core-shell polymers, polystyrene-block-polybutadiene-block-poly(methyl methacrylate) (SBM) block terpolymers, polybutadiene, polyisoprene, styrenic block copolymers and polyacrylonitrile, silicones, and the like. Elastic styrenic block copolymers may include at least one block selected from the following: isoprene, isobutylene, butene, ethylene / butene, ethylene-propylene, and ethylene-ethylene / propylene. More specific examples of elastic styrenic block copolymers include, but are not limited to, poly(styrene-ethylene / butylene), poly(styrene-ethylene / butylene-styrene), poly(styrene-ethylene / propylene), poly(styrene-ethylene / propylene-styrene), poly(styrene-ethylene / propylene-styrene), poly(styrene-ethylene / propylene-styrene-ethylene-propylene), poly(styrene-butadiene-styrene), poly(styrene-butylene-butadiene-styrene), and the like, and any combination thereof.

[0056] In certain applications, the polymer filaments disclosed herein can be used in an additive manufacturing method performed by fused filament manufacturing. The printed object initially obtained by the additive manufacturing method may have a fused filament manufacturing polymer matrix (i.e., formed by layer-by-layer consolidation of polymer filaments containing thermoplastic polymers), the polymer matrix containing a metal precursor in at least a portion thereof, wherein the metal precursor can be activated to form metal islands when irradiated by a laser. The printed objects formed by layer-by-layer consolidation of polymer filaments and those prepared by consolidation of polymer particles (e.g., in a powder bed fusion method) can be distinguished by the absence of grain boundary characteristics of incomplete particle fusion. That is, in the printed objects formed by powder bed fusion and other particle consolidation methods, there may be residual grain boundaries between incompletely fused polymer particles, while those printed objects formed by fused filament manufacturing are characterized by boundary traces between adjacent printed lines and layers. However, when properly implemented, the printed objects formed by these two technologies may be largely indistinguishable from each other on a macroscopic scale. From a cost perspective, fused filament manufacturing may be advantageous because less printing material may be wasted during layer-by-layer deposition. For example, a printed object formed from the polymer filaments of the present disclosure may contain similar amounts of metal precursors within the polymer matrix, such as from about 1% to about 30% by weight of the printed object.

[0057] Subsequently, laser irradiation (such as that provided by a pulsed laser and described in more detail above) can be used to convert the metal precursor in the printed object into metal in a desired pattern (e.g., a plurality of discontinuous metal islands). Once formed, the metal islands can then be interconnected by chemical plating to form one or more conductive traces on the surface of the printed object.

[0058] Therefore, the additive manufacturing method of the present disclosure may include: providing a polymer filament, the polymer filament comprising a thermoplastic polymer defining a filament body and a metal precursor contacting the filament body, wherein the metal precursor can be activated to form a metal island when irradiated with a laser (such as with a pulsed laser); and forming a printed object from the polymer filament by layer-by-layer deposition, so that when the printed object is formed, the metal precursor remains substantially unconverted to metal. Such a printed object may include a polymer matrix formed by layer-by-layer consolidation of the polymer filament, so that the metal precursor is present in at least a portion of the printed object. When present, an infrared radiation absorber may also be present in at least a portion of the printed object. The metal precursor and the infrared radiation absorber may be present in the same position or different positions within the printed object.

[0059] It is believed that the conditions suitable for layer-by-layer deposition and consolidation of polymer filaments by fused filament fabrication are not particularly limited and can be performed under conventional deposition conditions familiar to those of ordinary skill in the art. Generally speaking, fused filament fabrication conditions occur above the melting point or softening temperature of the thermoplastic polymer and occur under computer control.

[0060] According to the disclosure herein, after forming a printed object comprising a metal precursor, a portion of the metal precursor may be converted into metal islands, which may then be converted into one or more conductive traces comprising metal. More specifically, the method of the present disclosure may include activating a portion of the metal precursor within the printed object using laser irradiation (particularly a pulsed laser) to form a plurality of discontinuous metal islands in a predetermined pattern on the surface of the printed object. Suitable pulsed lasers may include, but are not limited to, Nd:YAG lasers, vanadate lasers, and fiber lasers. Other suitable lasers and conditions for promoting metal formation are specified above.

[0061] After forming the discontinuous metal islands, the metal islands can be interconnected to form one or more conductive traces by performing chemical plating. The one or more conductive traces are conductive and metallic, and can be formed by a variety of suitable metals (such as copper, silver, gold or nickel). In a non-limiting example of the present disclosure, the multiple conductive traces can be separated from each other by about 150 μm or less. Suitable chemical plating conditions will be familiar to those of ordinary skill in the art and can be used in the disclosure of this article. For example, copper can be plated under electroless conditions using copper diamine tetraacetic acid complex (Cu-EDTA) / formaldehyde. In another specific example, copper-nickel alloys can be plated under electroless conditions using copper hypophosphite in the presence of nickel ions as a mediator. Nickel can be plated under electroless conditions using nickel salts (e.g., nickel sulfate) and reducing agents (such as hypophosphites or borohydrides).

[0062] Figure 6 6 is an exemplary process flow diagram showing the formation of a printed object by filament fabrication, followed by activation of a metal precursor and electroless plating to form conductive traces, as viewed from the top of the printed object. In method 600, a printed object 602 is first formed in a manner similar to that described in more detail above, particularly with reference to Figure 1 The details of the print are as follows ( Figure 6 It should be understood that the metal precursor may be present in the entirety or in part of the polymer matrix within the printed object 602. Figure 6, the metal precursor is located in the metallizable region 604. The non-metallizable region 606 can be deposited concurrently with the metallizable region 604 by concurrently depositing (printing) a polymer filament lacking a metal precursor. In addition and / or alternatively, one or more overhangs within the printed object 602 can be formed by depositing a removable support formed by a degradable and / or soluble material provided by a separate polymer filament. Thus, the fused filament fabrication method of the present disclosure can utilize at least one polymer filament containing a metal precursor, and optionally can utilize one or more additional polymer filaments that lack a metal precursor for forming a printed object 602 of a desired shape having metallization capability thereon.

[0063] In metal conversion 610, metallized regions 604 are selectively illuminated with a pulsed laser beam 616 from a pulsed laser 614 to define metal islands 622 in a desired pattern on the surface of printed object 602. In a particular process configuration, laser 614 may be a near infrared pulsed laser.

[0064] After forming the metal islands 622, electroless plating 630 may then be performed to define conductive traces 632 in a desired pattern on the surface of the printed object 602. The conductive traces 632 interconnect the metal islands 622 to each other. Figure 6 In the depicted configuration, the conductive traces 632 remain confined within the metallized regions 604 , but in alternative configurations may extend across the entire surface of the printed object 602 .

[0065] Examples of printed objects that may be formed using the polymer filaments disclosed herein are considered to be not particularly limited, and may include, for example, containers (e.g., for food, beverages, cosmetics, personal care compositions, pharmaceuticals, etc.), shoe soles, toys, furniture parts, decorative homewares, plastic gears, screws, nuts, bolts, cable ties, medical supplies, prostheses, orthopedic implants, learning aids, 3D anatomical models, robotic parts, biomedical devices (orthotics), household appliances, dental implants, automotive and aircraft / aerospace parts, electronic devices, sporting goods, etc. Many of these printed objects may benefit from the introduction of one or more conductive traces thereon, as described herein.

[0066] Embodiments disclosed herein include:

[0067] A. A polymer filament compatible with fused filament fabrication. The polymer filament comprises: a thermoplastic polymer defining a filament body; and a metal precursor contacting the filament body, the metal precursor being capable of being activated upon laser irradiation to form metal islands.

[0068] B. Printed object. The printed object comprises: a fused filament fabrication polymer matrix comprising a metal precursor in at least a portion thereof, the metal precursor being capable of being activated upon laser irradiation to form metal islands.

[0069] C. A method for forming a printed object by fused filament fabrication. The method comprises: providing a polymer filament comprising a thermoplastic polymer defining a filament body and a metal precursor contacting the filament body, the metal precursor being capable of being activated upon laser irradiation to form metal islands; and forming a printed object from the polymer filament by layer-by-layer deposition; wherein the metal precursor remains substantially unconverted to metal when forming the printed object.

[0070] Each of embodiments A to C may have one or more of the following additional elements in any combination:

[0071] Element 1: The metal precursor can be activated by an infrared or near-infrared pulsed laser.

[0072] Element 2: wherein the metal precursor is capable of being activated at a wavelength ranging from about 1020 nm to about 1070 nm.

[0073] Element 3: wherein the metal precursor is blended with the thermoplastic polymer, located on the outer surface of the filament body, or any combination thereof.

[0074] Element 4: wherein the metal precursor is located in the inner core of the polymer filament, and the filament body serves as an outer shell surrounding the inner core.

[0075] Element 5: The metal precursor comprises at least one material selected from the group consisting of: copper oxide; mixed oxides of copper and a metal selected from the group consisting of: antimony, aluminum, cesium, cobalt, chromium, magnesium, manganese, nickel, tin, titanium, silver, iron, zinc and zirconium; copper chromium oxide spinel; copper aluminum oxide; copper hydroxide; basic copper phosphate; copper phosphate; copper sulfate; copper thiocyanate; a metal-organic complex comprising a metal selected from the group consisting of: copper, silver, palladium and any combination thereof; and any combination thereof.

[0076] Element 6: wherein the metal precursor comprises from about 1% to about 30% by weight of the polymer filament.

[0077] Element 6A: wherein the metal precursor comprises from about 1% to about 30% by weight of the printed object.

[0078] Element 7: wherein the polymer filament further comprises an infrared radiation absorber in contact with the body of the filament.

[0079] Element 7A: wherein the polymeric filaments further comprise an infrared radiation absorber within the polymer matrix.

[0080] Element 8: wherein the infrared radiation absorber comprises a non-stoichiometric metal oxide.

[0081] Element 9: wherein the metal precursor comprises a plurality of particles.

[0082] Element 10: wherein the metal precursor is thermally stable at a temperature greater than or equal to the melting point or softening temperature of the thermoplastic polymer.

[0083] Element 11: The method further comprises activating a portion of a metal precursor within the printed object using a pulsed laser to form a plurality of discontinuous metal islands in a predetermined pattern on a surface of the printed object.

[0084] Element 12: wherein the method further comprises performing electroless plating to form one or more conductive traces interconnecting the plurality of discontinuous metal islands.

[0085] As a non-limiting example, exemplary combinations suitable for A, B, and C include, but are not limited to: 1 and 2; 1, and 3 or 4; 1 and 5; 1, and 6 or 6A; 1, and 7 or 7A; 1, 7 or 7A, and 8; 1 and 9; 1 and 10; 2, and 3 or 4; 2 and 5; 2, and 6 or 6A; 2, and 7 or 7A; 2, 7 or 7A, and 8; 2 and 9; 2 and 10; 3 or 4, and 5; 3 or 4, and 6 or 6A; 3 or 4, and 7 or 7A; 3 or 4, 7 or 7A, and 8; 3 or 4, and 9; 3 or 4, and 10; 5, and 6 or 6A; 5, and 7 or 7A; 5, 7 or 7A, and 8; 5 and 9; 5 and 10; 6 or 6A, and 7 or 7A; 6 or 6A, 7 or 7A, and 8; 6 or 6A, and 9; 6 or 6A, and 10; 7 or 7A, and 8; 7 or 7A, and 9; 7 or 7A, and 10; and 9 and 10. Embodiment C can have any of the above elements, and also includes further combinations of 11 and / or 12 with any of the above elements.

[0086] In order to facilitate a better understanding of the present disclosure, the following examples of preferred or representative embodiments are given. The following examples should in no way be construed as limiting or defining the scope of the present invention.

[0087] Example

[0088] The filaments were prepared using a Filabot EX6 filament extruder. The extruder consisted of an extruder, an air path, and a filament winder. The extruder had four heating zones: i) a feed inlet nozzle, ii) a rear zone, iii) a middle zone, and iv) a front zone. The extrusion speed was controlled by adjusting the voltage. The nozzle was interchangeable with nozzles having different diameters. The air path for the air flow was adjustable. The position of the air path could be adjusted relative to the distance from the nozzle or the air path could be lifted on a jack to maintain a constant filament diameter. The filament diameter was measured using an online thickness gauge.

[0089] The polymer composite for filament preparation was first prepared by melt mixing 100 parts by weight of polymer resin with 10 parts by weight of copper chromium oxide spinel in a 600P Haake batch mixer. The resulting polymer blend was then crushed into small pieces and fed to a filament extruder.

[0090] Composite filaments were prepared using polyamide-12 (PA-12), acrylonitrile-butadiene-styrene (ABS) or polycaprolactone (PCL). These samples are referred to as Samples 1 to 3 in Table 1 below.

[0091] Table 1

[0092] Example 1 Example 2 Example 3 Polymer resin PA 12 ABS PCL Feed temperature 45℃ 45℃ 40℃ Rear zone temperature 175℃ 170℃ 80℃ Middle zone temperature 175℃ 170℃ 80℃ Front zone temperature 175℃ 170℃ 70℃ Nozzle size 3.0mm 3.0mm 3.0mm airflow 100％ 100％ 100％ Winding speed 1.0rpm 1.0rpm 0.6-0.8rpm Average filament diameter 1.6mm 1.7mm 1.6mm

[0093] Additional samples were obtained under similar conditions by mixing 5 wt% copper (II) acetylacetonate and 1 wt% antimony tin oxide (average particle size = 15 nm) in ABS and forming composite continuous filaments under similar conditions.

[0094] All documents described herein are incorporated herein by reference for the purpose of all jurisdictions allowing such practice, including any priority documents and / or testing procedures, as long as they do not conflict with this article. As is apparent from the foregoing general description and specific embodiments, although the form of the present disclosure has been shown and described, various modifications may be made without departing from the spirit and scope of the present disclosure. Therefore, the present disclosure is not intended to be limited thereby. For example, the composition described herein may not contain any component or composition that is not explicitly described or disclosed herein. Any method may lack any step that is not described or disclosed herein. Similarly, the term "comprising" is considered to be synonymous with the term "including". Whenever there is a transition phrase "comprising" before a method, composition, element or element group, it should be understood that we also envision that there is a transition phrase "substantially consisting of...", "consisting of...", "selected from..." or "is" before the narration of the composition, element, multiple elements, or the same composition or element group, and vice versa.

[0095] Unless otherwise indicated, all numbers used in this specification and the related claims expressing the number of components, characteristics (such as molecular weight), reaction conditions, etc. should be understood to be modified by the term "about" in all cases. Therefore, unless otherwise indicated, the numerical parameters listed in the following specification and the attached claims are approximate values, which may vary according to the desired characteristics sought to be obtained by the embodiments of the present invention. At a minimum, and without attempting to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be interpreted according to the reported significant digits and by applying conventional rounding methods.

[0096] Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range are specifically disclosed. Specifically, each value range disclosed herein (in the form of "about a to about b", or equivalently, "about a to b", or equivalently, "about ab") should be understood to set forth each value and range covered within the wider value range. In addition, the terms in the claims have their ordinary, common meanings unless otherwise explicitly and clearly defined by the patentee. In addition, the indefinite articles "a" or "an" used in the claims are defined herein to mean that there is one or more than one of the elements introduced therein.

[0097] One or more exemplary embodiments are presented herein. For the sake of clarity, all features of physical implementation are not described or shown in this application. It should be understood that in the development of the physical implementation of the present disclosure, many specific decisions must be made to achieve the goal of the developer, such as meeting system-related constraints, business-related constraints, government-related constraints and other constraints, which vary and change over time due to implementation. Although the efforts made by the developer may be time-consuming, such efforts will be a routine task for those of ordinary skill in the art who benefit from the present disclosure.

[0098] Therefore, the present disclosure is well suited to achieve the goals and advantages mentioned, as well as those inherent therein. The specific embodiments disclosed above are merely exemplary, as the present disclosure may be modified and implemented in different but equivalent ways apparent to one of ordinary skill in the art having the benefit of the teachings herein. In addition, no limitations are contemplated on the details of construction or design shown herein, except as described in the following claims. Therefore, it is apparent that the specific exemplary embodiments disclosed above may be altered, combined or modified, and all such variations are considered to be within the scope and spirit of the present disclosure. The embodiments exemplarily disclosed herein may be appropriately implemented in the absence of any element not specifically disclosed herein and / or any optional element disclosed herein.

Claims

1. A polymer filament compatible with fused filament fabrication, the polymer filament comprising: a thermoplastic polymer defining a filament body; and A metal precursor contacts the filament body, the metal precursor being capable of being activated upon laser irradiation to form metal islands, wherein the metal precursor comprises copper chromite.

2. The polymer filament of claim 1, wherein the metal precursor is capable of being activated by an infrared or near infrared pulsed laser.

3. The polymer filament of claim 1, wherein the metal precursor is capable of being activated at a wavelength ranging from 1020 nm to 1070 nm.

4. The polymer filament of claim 1, wherein the metal precursor is blended with the thermoplastic polymer, located on an outer surface of the filament body, or any combination thereof.

5. The polymer filament of claim 1, wherein the metal precursor is located in an inner core of the polymer filament, and the filament body surrounds the inner core as an outer shell.

6. The polymer filament of claim 1, wherein the metal precursor comprises 1% to 30% by weight of the polymer filament.

7. The polymer filament of claim 1, further comprising: An infrared radiation absorber is in contact with the filament body.

8. The polymer filament of claim 7, wherein the infrared radiation absorber comprises a non-stoichiometric metal oxide.

9. The polymer filament of claim 1, wherein the metal precursor comprises a plurality of particles.

10. The polymer filament of claim 1, wherein the metal precursor is thermally stable at a temperature greater than or equal to the melting point or softening temperature of the thermoplastic polymer.

11. A method for forming a printed object, the method comprising: providing a polymer filament comprising a thermoplastic polymer defining a filament body and a metal precursor contacting the filament body, the metal precursor being capable of being activated upon laser irradiation to form metal islands; as well as forming a printed object from the polymer filament by layer-by-layer deposition; Wherein upon forming the printed object, the metal precursor remains substantially unconverted to a metal, wherein the metal precursor comprises copper chromite.

12. The method according to claim 11, further comprising: A pulsed laser is used to activate a portion of the metal precursor within the printed object to form a plurality of discontinuous metal islands in a predetermined pattern on a surface of the printed object.

13. The method according to claim 12, further comprising: Electroless plating is performed to form one or more conductive traces interconnecting the plurality of discontinuous metal islands.

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