具体实施方式：
[0032]The filamentary structure disclosed herein is manufactured during 3D printing by fused filament fabrication. Fused filament fabrication is a method of additive manufacturing or 3D printing for which a solid filament is used which is melted and extruded through a nozzle and deposited on a substrate, thereby producing a filamentary structure comprising a continuous strand of deposited material. The continuous strand comprises a thermoplastically workable material and filler particles.
[0033]As used herein, “a continuous strand” means that either one continuous strand is deposited, or a plurality of continuous strands is deposited.
[0034]The ratio of the width of the continuous strand to the height of the continuous strand is either more than 2 or less than 1.
[0035]The filler particles comprise hexagonal boron nitride (hBN) particles. The hexagonal boron nitride particles comprise hexagonal boron nitride platelets. As used herein, “platelets” means platelet-shaped particles.
[0036]The boron nitride platelets typically have a mean aspect ratio of more than 7. The aspect ratio is the ratio of the diameter to the thickness of the boron nitride platelets. More specifically, the mean aspect ratio of the boron nitride platelets may be at least 10, or at least 15, or at least 20. The mean aspect ratio of the boron nitride platelets may also be up to 40, or up to 100. The mean aspect ratio of the boron nitride platelets may be from 7 to 20, or from 20 to 40, or from 7 to 40, or from 10 to 40, or from 50 to 100. Typically, the mean aspect ratio of the boron nitride platelets is at most 500. The mean aspect ratio can be measured by scanning electron microscopy (SEM), by determining the aspect ratio of 20 particles, and calculating the mean value of the 20 individual values determined for the aspect ratio. The aspect ratio of an individual boron nitride platelet is determined by measuring the diameter and the thickness of the boron nitride platelet and calculating the ratio of the diameter to the thickness. Required magnification of the SEM images used to measure diameter and thickness of boron nitride platelets depends on the size of the platelets. Magnification should be at least 1000×, preferably at least 2000×. Where appropriate, i.e. for smaller platelets with a mean particle size (d50) of 5 to 10 μm, a magnification of 5000× should be used.
[0037]Typically, the mean particle size (d50) of the boron nitride platelets and of the boron nitride particles is at least 5 μm. The mean particle size (d50) of the boron nitride platelets and of the boron nitride particles may be at least 7 μm, or at least 10 μm, or at least 12 μm, or at least 15 μm, or at least 20 μm, or at least 30 μm. Typically, the mean particle size (d50) of the boron nitride platelets is at most 100 μm, and the mean particle size (d50) of the boron nitride particles is at most 250 μm. The mean particle size (d50) of the boron nitride platelets and of the boron nitride particles may be at most 80 μm, or at most 60 μm, or at most 50 μm, or at most 30 μm. The mean particle size (d50) of the boron nitride platelets and of the boron nitride particles may be from 5 to 100 μm. More specifically, the mean particle size (d50) of the boron nitride platelets and of the boron nitride particles may be from 5 to 50 μm, or from 5 to 30 μm, or from 10 to 30 μm, or from 15 to 35 μm, or from 15 to 50 μM or from 30 to 50 μm. The mean particle size (d50) can be measured by laser diffraction.
[0038]A portion of the hexagonal boron nitride platelets may be agglomerated to form boron nitride agglomerates. The mean particle size (d50) of the boron nitride agglomerates may be at most 250 μm and more specifically at most 200 μm, at most 150 μm or at most 100 μm. The mean particle size (d50) of the boron nitride agglomerates may be at least 50 μm or at least 70 μm. The mean particle size (d50) can be measured by laser diffraction. Typically, less than 50% of the hexagonal boron nitride platelets are agglomerated, and at least 50% of the hexagonal boron nitride platelets are used as non-agglomerated particles, that means as primary particles. Also mixtures of agglomerates and non-agglomerated primary particles may be used. The boron nitride agglomerates may be spherical, irregularly shaped or flake-shaped, the flake-shaped agglomerates having an aspect ratio of from 1 to 20.
[0039]The hexagonal boron nitride particles may also comprise particles which have a low aspect ratio. A “low aspect ratio” means that the hexagonal boron nitride particles have an aspect ratio of at most 7. Typically, the proportion of hexagonal boron nitride particles with a low aspect ratio is at most 50% and more specifically at most 35% or at most 20%, based on the total amount of hexagonal boron nitride particles. The hexagonal boron nitride particles with a low aspect ratio may be agglomerated to form boron nitride agglomerates. The mean particle size (d50) of the boron nitride agglomerates formed from boron nitride particles with a low aspect ratio may be at most 250 μm and more specifically at most 200 μm, at most 150 μm or at most 100 μm. The mean particle size (d50) of the boron nitride agglomerates formed from boron nitride particles with a low aspect ratio may be at least 20 μm or at least 50 μm. The mean particle size (d50) can be measured by laser diffraction. The boron nitride agglomerates formed from boron nitride particles with a low aspect ratio may be spherical, irregularly shaped or flake-shaped, the flake-shaped agglomerates having an aspect ratio of from 1 to 20. The hexagonal boron nitride particles with a low aspect ratio may also be used as non-agglomerated particles, that means as primary particles. Also mixtures of agglomerates and non-agglomerated primary particles with a low aspect ratio may be used. The hexagonal boron nitride particles may also comprise boron nitride agglomerates that comprise boron nitride platelets and boron nitride particles with a low aspect ratio.
[0040]The hexagonal boron nitride particles and the hexagonal boron nitride platelets typically have a content of water-soluble boron compounds such as boron oxide of at most 0.2 percent by weight, based on the total amount of hexagonal boron nitride particles or hexagonal boron nitride platelets, respectively.
[0041]The filler particles may further comprise secondary fillers with a high aspect ratio, different from hexagonal boron nitride particles. The secondary fillers may be thermally conductive. The use of high aspect ratio secondary fillers enhances the predetermined orientation of boron nitride platelets in the continuous strand and enhances the directed thermal conductivity by the intrinsic thermal conductivity of the secondary filler. The aspect ratio of the high aspect ratio secondary fillers may be at least 5, or at least 10. The aspect ratio of the high aspect ratio secondary fillers may be up to 50, or up to 100. The secondary fillers having a high aspect ratio may be platelet shaped particles, or needle or fiber shaped particles. Examples for platelet shaped particles are platelet shaped ceramic platelets such as alpha alumina platelets, and platelet shaped mineral particles such as layered silicates and talcum powder comprising talcum platelets. Examples for needle or fiber shaped particles are chopped fibers made of alumina or silica, and needle shaped mineral fillers such as wollastonite. The mean particle size (d50) of the platelet shaped, high aspect ratio secondary fillers may be from 5 to 100 μm. The diameter of the needle or fiber shaped high aspect ratio secondary fillers may be from 1 to 25 μm.
[0042]The filler particles may further comprise secondary fillers having a low aspect ratio of less than 5, different from hexagonal boron nitride. The mean particle size (d50) of the low aspect ratio secondary fillers is less than 2 μm.
[0043]In some embodiments of the present disclosure, the filler particles consist of hexagonal boron nitride particles comprising hexagonal boron nitride platelets, of secondary fillers with a high aspect ratio of at least 5 or at least 10, and of secondary fillers with a low aspect ratio of less than 5 and a mean particle size (d50) of less than 2 μm. In some embodiments of the present disclosure, the filler particles consist of hexagonal boron nitride particles comprising hexagonal boron nitride platelets, and of secondary fillers with a high aspect ratio of at least 5 or at least 10, and the filler particles do not comprise low aspect ratio secondary fillers. In some embodiments, the average value of the aspect ratio of the filler particles used is at least 10. In some embodiments, the filler particles consist of hexagonal boron nitride particles comprising hexagonal boron nitride platelets.
[0044]The thermoplastically workable material is selected from the group consisting of thermoplastic materials, thermoplastically workable duroplastic materials, and mixtures thereof. In particular the thermoplastic materials polyamide (PA), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyethylene terephthalate glycol-modified (PETG), polyphenylene sulfide (PPS), polycarbonate (PC), polyethylene (PE), polypropylene (PP), thermoplastic elastomers (TPE), thermoplastic polyurethane elastomers (TPU), polyether ether ketones (PEEK), liquid crystal polymers (LCP), polyoxymethylene (POM), polylactic acid (PLA), acrylonitrile butadiene styrene copolymer (ABS), high impact polystyrene (HIPS), acrylic ester-styrene-acrylonitrile copolymer (ASA), polymethyl methacrylate (PMMA), and elastomers may be used. Examples for elastomers that may be used are liquid silicon rubber (LSR), ethylene propylene diene rubber (EPDM), nitrile rubber (NBR), hydrated nitrile rubber (HNBR), fluorocarbon rubber (FKM), acrylate rubber (ADM), and ethylene acrylate rubber (AEM).
[0045]Particularly advantageously, thermoplastic elastomers (TPE) may be used. Examples for thermoplastic elastomers are thermoplastic copolyamides (TPA), thermoplastic polyester elastomers (TPC), olefin based thermoplastic elastomers (TPO), styrene block copolymers (TPS) and urethane based thermoplastic elastomers (TPU).
[0046]Examples for thermoplastically workable duroplastic materials that can be used are phenolformaldehyde materials, epoxide materials, melamine formaldehyde materials and urea formaldehyde materials.
[0047]The continuous strand may comprise 5 to 60 percent by volume of hexagonal boron nitride particles, based on the total amount of the continuous strand. More specifically, the continuous strand may comprise 10 to 55, or 5 to 25, or 10 to 30, or 40 to 60 percent by volume of hexagonal boron nitride particles, based on the total amount of the continuous strand. The continuous strand may comprise 5 to 80 percent by volume of filler particles, based on the total amount of the continuous strand. The continuous strand may comprise up to 72 percent by volume, or up to 64 percent by volume, of secondary fillers, based on the total amount of the continuous strand. The secondary fillers may be high aspect ratio secondary fillers or low aspect ratio secondary fillers or both.
[0048]The continuous strand may comprise 20 to 95 percent by volume of thermoplastically workable material, based on the total amount of the continuous strand. If the continuous strand does not comprise secondary fillers, the continuous strand may comprise 40 to 95 percent by volume of thermoplastically workable material, based on the total amount of the continuous strand.
[0049]In some embodiments of the filamentary structure disclosed herein, the ratio of the width of the continuous strand to the height of the continuous strand is more than 2. More specifically, the ratio of the width of the continuous strand to the height of the continuous strand may be at least 3, or at least 4, or at least 5, or at least 10, or at least 20. The ratio of the width of the continuous strand to the height of the continuous strand may be at most 100. As used herein, the ratio of the width of the continuous strand to the height of the continuous strand may also be referred to as the aspect ratio of the continuous strand. The aspect ratio of the continuous strand may be from more than 2 to 50, or from 3 to 50, or from 5 to 50, or from 10 to 50, or from 5 to 40, or from 10 to 40, or from 15 to 50, or from 5 to 100.
[0050]If the ratio of the width of the continuous strand to the height of the continuous strand is more than 2, the height of the continuous strand may be 500 μm or less. More specifically, the height of the continuous strand may be at most 200 μm, or at most 100 μm. The height of the continuous strand may also be at most 50 μm, or even at most 20 μm. The height of the continuous strand may be selected depending on the specific application.
[0051]If the ratio of the width of the continuous strand to the height of the continuous strand is more than 2, high in-plane thermal conductivities can be obtained.
[0052]In some embodiments of the filamentary structure disclosed herein, the ratio of the width of the continuous strand to the height of the continuous strand is less than 1. More specifically, the ratio of the width of the continuous strand to the height of the continuous strand may be at most 0.9, or at most 0.7, or at most 0.5. The ratio of the width of the continuous strand to the height of the continuous strand may also be at most 0.3, or at most 0.1. The aspect ratio of the continuous strand may be less than 1 and at least 0.05, or at least 0.01. The aspect ratio of the continuous strand may be from 0.1 to less than 1, or from 0.1 to 0.9, or from 0.1 to 0.7, or from 0.1 to 0.5, or from 0.5 to less than 1, or from 0.5 to 0.9, or from 0.5 to 0.7, or from 0.01 to 0.5.
[0053]If the ratio of the width of the continuous strand to the height of the continuous strand is less than 1, the height of the continuous strand may be up to 2 mm. More specifically, the height of the continuous strand may be up to 1 mm, or up to 500 μm, or up to 200 μm. The height of the continuous strand may be selected depending on the specific application.
[0054]If the ratio of the width of the continuous strand to the height of the continuous strand is less than 1, high through-plane thermal conductivities can be obtained.
[0055]In some embodiments of the filamentary structure disclosed herein, the continuous strand comprises portions being oriented parallelly to one another. Preferably, a large proportion of the continuous strand comprises portions being oriented parallelly to one another. For example, at least 10% of the continuous strand may comprise portions being oriented parallel to one another, or at least 25%, or at least 50%, or at least 70%, or at least 90% of the continuous strand may comprise portions being oriented parallelly to one another.
[0056]The continuous strand may comprise portions having close contact to one another, or may comprise portions that overlap each other. The overlap may be to an extent of 10 to 50%. The continuous strand may also comprise portions which are crossing each other.
[0057]Further disclosed herein is a 3D printable filament for manufacturing the filamentary structure disclosed herein during 3D printing. The filament comprises a thermoplastically workable material and filler particles. The filler particles comprise hexagonal boron nitride particles comprising hexagonal boron nitride platelets. The filament comprising a thermoplastically workable material and filler particles is used as manufacturing material in a 3D printing process for extruding the filamentary structure.
[0058]The 3D printable filament may comprise 5 to 60 percent by volume of hexagonal boron nitride particles, based on the total amount of the 3D printable filament. More specifically, the 3D printable filament may comprise 10 to 55, or 5 to 25, or 10 to 30, or 40 to 60 percent by volume of hexagonal boron nitride particles, based on the total amount of the 3D printable filament. The 3D printable filament may comprise 5 to 80 percent by volume of filler particles, based on the total amount of the 3D printable filament. The 3D printable filament may comprise up to 72 percent by volume, or up to 64 percent by volume, of secondary fillers, based on the total amount of the 3D printable filament. The secondary fillers may be high aspect ratio secondary fillers or low aspect ratio secondary fillers or both.
[0059]The 3D printable filament may comprise 20 to 95 percent by volume of thermoplastically workable material, based on the total amount of the 3D printable filament. If the 3D printable filament does not comprise secondary fillers, the 3D printable filament may comprise 40 to 95 percent by volume of thermoplastically workable material, based on the total amount of the 3D printable filament.
[0060]The hexagonal boron nitride particles comprising hexagonal boron nitride platelets and the thermoplastically workable material that are used for the 3D printable filament have been described above in more detail.
[0061]The 3D printable filament can be made by extruding the thermoplastically workable material and the filler particles which comprise hexagonal boron nitride particles comprising hexagonal boron nitride platelets. For extruding, various extruders such as a twin screw extruder, a single screw extruder, or a planetary extruder can be used. By gravimetric dosing, granulates of the basic polymer are fed into the extruder and are melted subsequently. By a side feeder, fillers can be introduced in the polymer melt. Mixing and shear elements disperse the filler in the polymer melt to form a compound. The compound is forced through nozzles, cools down and solidifies in the shape of filaments. To improve the homogeneity of the filament, the extruded filament can be extruded again through an extruder to form a homogenous filament.
[0062]Further disclosed herein is a 3D printed component part comprising at least one portion formed from the filamentary structure disclosed herein.
[0063]In some embodiments, at least 30% of the 3D printed component part is formed from the filamentary structure disclosed herein. In other embodiments, at least 50% or at least 80% of the 3D printed component part is formed from the filamentary structure disclosed herein. In some embodiments, 100% of the 3D printed part is formed from the filamentary structure disclosed herein. For example, if the 3D printed component part is a thin sheet or pad with a thickness of, for example, up to 1 mm, 100% of the 3D printed component part may be formed from the filamentary structure disclosed herein. Another example of a 3D printed component part of the present disclosure is a heatsink of which only one portion is formed from the filamentary structure disclosed herein and having a high through-plane thermal conductivity, e.g. in the region of contact to a CPU, and a high in-plane thermal conductivity, e.g. in the region of the cooling fins, whereas other portions of the 3D printed component such as the mounting segment may be printed with a different 3D printable filament which may have good mechanical properties and which may comprise glass fibers and no hexagonal boron nitride particles. It is also possible that one portion of the 3D printed component part is formed from the filamentary structure disclosed herein and having a ratio of the width of the continuous strand to the height of the continuous strand of more than 2, and having a high in-plane thermal conductivity, and another portion of the 3D printed component part is formed from the filamentary structure disclosed herein and having a ratio of the width of the continuous strand to the height of the continuous strand of less than 1, and having a high through-plane thermal conductivity. The texture index can be measured separately on the two portions of the 3D printed component.
[0064]In some embodiments of the 3D printed component part of the present disclosure, the at least one portion of the component part formed from the filamentary structure disclosed herein has a texture index of at least 8, and the ratio of the width of the continuous strand to the height of the continuous strand in the filamentary structure is more than 2. More specifically, the texture index may be at least 10, or at least 12, or at least 15, or at least 20, or at least 30, or at least 50, or at least 100, and the ratio of the width of the continuous strand to the height of the continuous strand in the filamentary structure is more than 2. The texture index may be from 8 to 400, or from 10 to 400, or from 15 to 400, or from 8 to 300, or from 10 to 300, or from 15 to 300, and the ratio of the width of the continuous strand to the height of the continuous strand in the filamentary structure is more than 2.
[0065]If the ratio of the width of the continuous strand to the height of the continuous strand in the filamentary structure is more than 2, a high in-plane thermal conductivity can be obtained. With increasing aspect ratio of the continuous strand, the texture index and the in-plane thermal conductivity increase, and the through-plane thermal conductivity decreases. In-plane thermal conductivity is measured in a direction parallel to the substrate on which the continuous strand is deposited, through-plane thermal conductivity is measured in a direction perpendicular to the substrate on which the continuous strand is deposited.
[0066]By the texture index, the degree of orientation of the hexagonal boron nitride platelets can be measured. The texture index can be measured on the 3D component part formed from the filamentary structure disclosed herein.
[0067]The texture index is determined by an X-ray method. For this, the ratio of the intensities of the (002) and of the (100) reflection measured on X-ray diffraction diagrams is determined and is divided by the corresponding ratio for an ideal, untextured hBN sample. This ideal ratio can be determined from the JCPDS data and is 7.29. The intensity of the (002) reflection is measured within a 20 range from 25.8 to 27.6 degrees and that of the (100) reflection within a 20 range from 41.0 to 42.2 degrees. The texture index (TI) can be determined from the formula:
TI<mspace width="0.3em" height="0.3ex"/>=<mspace width="0.3em" height="0.3ex"/>I(002),<mspace width="0.3em" height="0.3ex"/>sample/I(100),<mspace width="0.3em" height="0.3ex"/>sampleI(002),<mspace width="0.3em" height="0.3ex"/>theoretical/I(100),<mspace width="0.3em" height="0.3ex"/>theoretical=I(002),<mspace width="0.3em" height="0.3ex"/>sample/I(100),<mspace width="0.3em" height="0.3ex"/>sample7.29
[0068]The intensity of the (100) reflection should be at least 1.0. If the intensity of the (100) reflection is below 1.0, the measurement speed in the 20 ranges from 25.8 to 27.6 degrees and from 41.0 to 42.2 degrees can be decreased to obtain a sufficient intensity of the (100) reflection.
[0069]In some embodiments of the 3D printed component part of the present disclosure, the at least one portion of the component part formed from the filamentary structure disclosed herein has a texture index of less than 1, and the ratio of the width of the continuous strand to the height of the continuous strand in the filamentary structure is less than 1. More specifically, the texture index may be at most 0.9, or at most 0.8, or at most 0.5, or at most 0.2, or at most 0.1, or at most 0.05, or at most 0.01, and the ratio of the width of the continuous strand to the height of the continuous strand in the filamentary structure is less than 1. The texture index may be from 0.1 to less than 1, or from 0.1 to 0.9, or from 0.1 to 0.8, or from 0.1 to 0.5, or from 0.01 to 0.5, or from 0.03 to 0.3, and the ratio of the width of the continuous strand to the height of the continuous strand in the filamentary structure is less than 1.
[0070]If the ratio of the width of the continuous strand to the height of the continuous strand in the filamentary structure is less than 1, a high through-plane thermal conductivity can be obtained. With decreasing aspect ratio of the continuous strand, the texture index decreases and the through-plane thermal conductivity increases, and the in-plane thermal conductivity decreases.
[0071]In some embodiments of the 3D printed component part of the present disclosure, the at least one portion of the component part formed from the filamentary structure disclosed herein has a relative density of at least 60% of the theoretical density of the filamentary structure. The relative density of the at least one portion of the component part may also be at least 80% or at least 90% of the theoretical density of the filamentary structure, that is of the theoretical density of the matrix material-boron nitride compound without any pores. The density can be determined by using the Archimedes method.
[0072]The 3D printed component part disclosed herein may be made by a 3D printing method comprising
[0073]providing a 3D printable filament, the 3D printable filament comprising a thermoplastically workable material and filler particles, wherein the filler particles comprise hexagonal boron nitride particles comprising hexagonal boron nitride platelets,
[0074]melting the 3D printable filament,
[0075]extruding the molten filament from a nozzle to form a continuous strand and depositing the continuous strand on a substrate in a predetermined pattern layer by layer to form a filamentary structure, and
[0076]cooling the filamentary structure to form a 3D printed component part comprising the thermoplastically workable material and filler particles dispersed therein, wherein the filler particles comprise hexagonal boron nitride particles comprising hexagonal boron nitride platelets, the hexagonal boron nitride platelets having a predetermined orientation in the cooled thermoplastically workable material.
[0077]By this method, the at least one portion of the 3D component part formed from the filamentary structure disclosed herein can be obtained.
[0078]The filament used for the method for making the 3D printed component part comprises a thermoplastically workable material and filler particles, wherein the filler particles comprise hexagonal boron nitride particles comprising hexagonal boron nitride platelets. The thermoplastically workable material and the filler particles have been described above in more detail. The filament may further comprise secondary fillers as described above.
[0079]The filament is solid and has a defined diameter so that it can be fed into the nozzle. The diameter of the filament may be from 0.5 to 3 mm, for example. For lower contents of boron nitride filler, the filament may be used as a wound coil and continuously fed into the nozzle. For higher contents of boron nitride filler, the filament may be used in discontinuous portions as round rods that are fed into the nozzle.
[0080]During 3D printing, the 3D printable filament is melted and a continuous strand is extruded from a nozzle and deposited on a substrate. For melting the 3D printable filament and for extruding the continuous strand and depositing the continuous strand on a substrate, a 3D printer or a robot may be used. The 3D printer is operating according to the principle of fused filament fabrication (FFF). By fused filament fabrication, a solid filament is melted and is deposited on a substrate in the shape of a continuous strand, thereby forming the filamentary structure.
[0081]FIG. 11 illustrates the arrangement of a 3D printer operating according to the principle of fused filament fabrication (FFF 3D printer). The FFF 3D printer comprises drive wheels 12 shown counter-rotating in relation to each other, a heated liquefier 13, a nozzle 1 and a printing plate 14. The printing plate 14 may be heated. The heated liquefier 13 is designed to maintain a uniform temperature throughout the liquefier. In FIG. 11, a 3D printable filament 15 as disclosed herein is shown being transported by the two counter-rotating drive wheels 12 and being guided through the heated liquefier 13 and the nozzle 1. The 3D printable filament 15 is heated and melted as it passes through the heated liquefier 13 and typically will be of a reduced thickness or diameter as it is ejected from the nozzle 1.
[0082]The molten filament is extruded from the nozzle 1 to form a continuous strand 2 which is deposited on a substrate. The substrate may be the printing plate 14 or a separate substrate placed on the printing plate 14. The heated liquefier 13 and the nozzle 1 may be moved in a variety of directions indicated by “x” and “y” relative to the printing plate. The direction “y” indicates a direction into the plane of the page and is approximately at right angles to the direction indicated by “x”. Directions other than in the “x” and “y” direction are also possible.
[0083]As used herein, “melting the 3D printable filament” is to be understood that the thermoplastically workable material contained in the 3D printable filament is heated up to a temperature above the glass transition temperature Tg of the thermoplastically workable material. In the heated liquefier 13, the thermoplastically workable material is heated up to a temperature above the glass transition temperature, Tg. On leaving the liquefier, the melt is well above this temperature. Heat from the material leaving the liquefier increases the temperature of the substrate it is deposited on above Tg to enable bonding of deposited portions of the continuous strand.
[0084]As the molten filament comprises hexagonal boron nitride platelets and has a high thermal conductivity, the molten filament solidifies rapidly after leaving the heated liquefier 13 and the nozzle 1. To ensure a good bonding of deposited portions of the continuous strand, the printing plate 14 of the FFF 3D printer may be heated.
[0085]A continuous strand is extruded from the nozzle, and the continuous strand is deposited on a substrate in a predetermined pattern layer by layer to form the filamentary structure. The continuous strand being deposited layer by layer forms a stack of layers of the continuous strand. In some embodiments, only one single layer is deposited. An application example where only one single layer may be deposited are heat spreaders for LED applications, where heat is spreaded within a layer having a high in-plane thermal conductivity and a texture index of more than 8. Another application example where only one single layer may be deposited is a cooling plate or pad for a battery for automotive electrification, the cooling plate or pad having a high through-plane thermal conductivity to remove heat from the battery cells by transporting it to the cooling plate or pad.
[0086]In other embodiments, a plurality of layers of the continuous strand is deposited. As used herein, “a plurality of layers” means that at least two layers or more layers are deposited. The number of layers is not particularly limited, for example, 5, 10, 20, 30, 50, 100 or more layers may be deposited. The continuous strand may be deposited continuously on the substrate without interruptions, or may be deposited in multiple portions, each portion being deposited continuously.
[0087]The substrate may be planar. The substrate may also have a 3D contour, for example for electronic applications. The material of the substrate is not specifically limited, it may be of metal, glass, ceramics, graphite, or of a polymer material, for example. The substrate may also be, for example, a CPU or a cooling plate or pad. If the substrate has a 3D contour, the predetermined pattern for 3D printing can be adapted to the 3D contour. In some embodiments, the nozzle can be tilted to adapt the deposition of the continuous strand to an inclined area of the substrate. This is possible for a deposition for high in-plane thermal conductivity, with an aspect ratio of the continuous strand of more than 2, as well as for a deposition for high through-plane thermal conductivity, with an aspect ratio of the continuous strand of less than 1. In some embodiments with a deposition for high through-plane thermal conductivity and with an aspect ratio of the continuous strand of less than 1, the nozzle is rotated at a certain angle, as the deposition of the continuous strand is limited to one side of the nozzle (see FIGS. 9A-9D). The rotation of the nozzle is not being carried out continuously but only at a certain angle to allow the deposition of the continuous strand in a different direction.
[0088]In some applications of the 3