HEAT CONDUCTING COMPOSITE PRINTED BY FDM AND STRATEGIES FOR EFFECTIVE HEAT SINKING

Abstract

The invention provides a method for 3D printing a heat sink (100) by means of fused deposition modelling, the method comprising layer-wise depositing a 3D printable material to provide a plurality of layers (322) of a 3D printed material (202) whereby a heat receiving face (101) of the heat sink (100) is created, the plurality of layers (322) of 3D printed material (202) being configured parallel to planes (325) perpendicular to the heat receiving face (101), wherein the 3D printable material comprises particles embedded in the 3D printable material, wherein the particles have an anisotropic thermal conductivity, wherein the particles are available in the 3D printable material in an amount selected from the range of 5-40 vol. % relative to the total volume of the 3D printable material, and wherein the layers (322) of 3D printed material (202) have layer heights (H) selected from the range of at maximum 800 μm.

Claims

1. A method for 3D printing a heat sink by means of fused deposition modelling, the method comprising layer-wise depositing a 3D printable material to provide a plurality of layers of a 3D printed material whereby a heat receiving face of the heat sink is created, the plurality of layers of 3D printed material being configured parallel to planes perpendicular to the heat receiving face, wherein the 3D printable material comprises particles embedded in the 3D printable material, wherein the particles have an anisotropic thermal conductivity, wherein the particles have a longest dimension selected from the range of 10-200 μm, wherein the particles are available in the 3D printable material in an amount selected from the range of 5-40 vol. % relative to the total volume of the 3D printable material, and wherein the layers of 3D printed material have layer heights selected from the range of at maximum 800 μm.

2. The method according to claim 1, wherein the particles comprise one or more of flake-shaped particles and needle-shape particles, and wherein the particles are available in the 3D printable material in an amount selected from the range of 10-40 vol. % relative to the total volume of the 3D printable material.

3. The method according to claim 1, comprising controlling the layer height and a layer width by one or more of a speed of movement a of a printer head, a rate of 3D printable material extrusion through a nozzle of the printer head, and a distance between the nozzle and a receiver item on which the 3D printable material is printed, wherein the layer width is maintained at at least 1 mm, and wherein the method comprises printing the 3D printable material such that a ratio AR3 of the longest dimension of the particles and the layer height of the layers AR3=L1/H is selected from the range of 0.01≤AR3≤2.

4. The method according to claim 1, comprising using a fused deposition modeling 3D printer for layer-wise depositing the 3D printable material, wherein the fused deposition modeling 3D printer comprises a printer head with a nozzle, wherein the nozzle has an equivalent circular diameter of at least 1 mm.

5. The method according to claim 1, wherein the particles comprise one or more of graphite and boron nitride, and wherein the 3D printable material comprises one or more of polycarbonate, polyethylene, polypropylene, and polyester based thermoplastic elastomer.

6. The method according to claim 1, wherein the 3D printable material comprises a thermoplastic material having a weight averaged molecular weight of at maximum 1*10.sup.5 Dalton, wherein at least 40 vol. % of the 3D printable material consists of the thermoplastic material.

7. The method according to claim 1, wherein the 3D printable comprises at maximum 30 vol. % of a further additive, wherein the further additive is selected from the group of a polymeric additive and an inorganic additive, other than the particles having an anisotropic thermal conductivity.

8. A heat sink comprising 3D printed material, wherein the heat sink comprises a plurality of layers of 3D printed material defining a heat receiving face, wherein the plurality of layers of 3D printed material are configured parallel to planes perpendicular to the heat receiving face, wherein the 3D printed material comprises a thermoplastic material having a weight averaged molecular weight of at maximum 1*10.sup.5 Dalton, wherein at least 40 vol. % of the 3D printed material consists of the thermoplastic material, wherein the 3D printed material further comprises particles embedded in the 3D printed material, wherein the particles have an anisotropic thermal conductivity, wherein the particles have a longest dimension selected from the range of 10-200 μm, wherein the particles are available in the 3D printed material in an amount selected from the range of 5-40 vol. % relative to the total volume of the 3D printed material, and wherein the layers of 3D printed material have layer heights selected from the range of at maximum 800 μm.

9. The heat sink according to claim 8, wherein the heat sink comprises a plurality of fins for dissipating heat.

10. The heat sink according to claim 8, wherein the particles are available in the 3D printed material in an amount selected from the range of 10-40 vol. % relative to the total volume of the 3D printed material, wherein the particles comprise one or more of flake-shaped particles and needle-shape particles, wherein the particles comprise one or more of graphite and boron nitride, and wherein the 3D printed material comprises one or more of polycarbonate, polyethylene, polypropylene, and polyester based thermoplastic elastomer.

11. The heat sink according to claim 8, wherein the 3D printed material comprises at maximum 30 vol. % of a further additive, wherein the further additive is selected from the group of a polymeric additive and an inorganic additive, other than the particles having an anisotropic thermal conductivity.

12. A system comprising a functional component generating heat during use, and the heat sink according to claim 8, wherein the heat receiving face of the heat sink is in thermal contact with the functional component.

13. The system according to claim 12, wherein the system comprises a lighting system comprising a light source, wherein the functional component comprises the light source.

14. A computer program product, when running on a computer which is functionally coupled to or comprised by a fused deposition modeling 3D printer, is capable of bringing about the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0084] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0085] FIGS. 1a-1c schematically depict some general aspects of the 3D printer and of an embodiment of 3D printed material;

[0086] FIG. 2a-2e schematically depict some aspects of embodiments of particles, with some of the shapes being depicted for reference purposes;

[0087] FIGS. 3a-3b schematically depict some further aspects of the invention;

[0088] FIGS. 4a-4d show some thermoconductive results; and

[0089] FIGS. 5a-5e schematically show some embodiments and aspects.

[0090] The schematic drawings are not necessarily to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0091] FIG. 1a schematically depicts some aspects of the 3D printer. Reference 500 indicates a 3D printer. Reference 530 indicates the functional unit configured to 3D print, especially FDM 3D printing; this reference may also indicate the 3D printing stage unit. Here, only the printer head for providing 3D printed material, such as a FDM 3D printer head is schematically depicted. Reference 501 indicates the printer head. The 3D printer of the present invention may especially include a plurality of printer heads, though other embodiments are also possible. Reference 502 indicates a printer nozzle. The 3D printer of the present invention may especially include a plurality of printer nozzles, though other embodiments are also possible. Reference 321 indicates a filament of printable 3D printable material (such as indicated above). For the sake of clarity, not all features of the 3D printer have been depicted, only those that are of especial relevance for the present invention (see further also below).

[0092] The 3D printer 500 is configured to generate a 3D item 1 by layer-wise depositing on a receiver item 550, which may in embodiments at least temporarily be cooled, a plurality of filaments 321 wherein each filament 310 comprises 3D printable material 201, such as having a melting point T.sub.m. The 3D printable material 201 may be deposited on a substrate 1550 (during the printing stage).

[0093] The 3D printer 500 is configured to heat the filament material upstream of the printer nozzle 502. This may e.g. be done with a device comprising one or more of an extrusion and/or heating function. Such device is indicated with reference 573, and is arranged upstream from the printer nozzle 502 (i.e. in time before the filament material leaves the printer nozzle 502). The printer head 501 may (thus) include a liquefier or heater. Reference 201 indicates printable material. When deposited, this material is indicated as (3D) printed material, which is indicated with reference 202.

[0094] Reference 572 indicates a spool or roller with material, especially in the form of a wire, which may be indicated as filament 320. The 3D printer 500 transforms this in a filament 321 downstream of the printer nozzle which becomes a layer 322 on the receiver item or on already deposited printed material. In general, the diameter of the filament 321 downstream of the nozzle is reduced relative to the diameter of the filament 322 upstream of the printer head. Hence, the printer nozzle is sometimes (also) indicated as extruder nozzle. Arranging layer 322 by layer 322 and/or layer 322t on layer 322, a 3D item 1 may be formed. Reference 575 indicates the filament providing device, which here amongst others include the spool or roller and the driver wheels, indicated with reference 576.

[0095] Reference A indicates a longitudinal axis or filament axis.

[0096] Reference C schematically depicts a control system, such as especially a temperature control system configured to control the temperature of the receiver item 550. The control system C may include a heater which is able to heat the receiver item 550 to at least a temperature of 50° C., but especially up to a range of about 350° C., such as at least 200° C.

[0097] Alternatively or additionally, in embodiments the receiver plate may also be moveable in one or two directions in the x-y plane (horizontal plane). Further, alternatively or additionally, in embodiments the receiver plate may also be rotatable about z axis (vertical). Hence, the control system may move the receiver plate in one or more of the x-direction, y-direction, and z-direction.

[0098] Alternatively, the printer can have a head can also rotate during printing. Such a printer has an advantage that the printed material cannot rotate during printing.

[0099] Layers are indicated with reference 322, and have a layer height H and a layer width W.

[0100] Note that the 3D printable material is not necessarily provided as filament 320 to the printer head. Further, the filament 320 may also be produced in the 3D printer 500 from pieces of 3D printable material.

[0101] Reference D indicates the diameter of the nozzle (through which the 3D printable material 201 is forced).

[0102] FIG. 1b schematically depicts in 3D in more detail the printing of the 3D item 1 under construction. Here, in this schematic drawing the ends of the filaments 321 in a single plane are not interconnected, though in reality this may in embodiments be the case. Reference H indicates the height of a layer. Layers are indicated with reference 203. Here, the layers have an essentially circular cross-section. Often, however, they may be flattened, such as having an outer shape resembling a flat oval tube or flat oval duct (i.e. a circular shaped bar having a diameter that is compressed to have a smaller height than width, wherein the sides (defining the width) are (still) rounded).

[0103] Hence, FIGS. 1a-1b schematically depict some aspects of a fused deposition modeling 3D printer 500, comprising (a) a first printer head 501 comprising a printer nozzle 502, (b) a filament providing device 575 configured to provide a filament 321 comprising 3D printable material 201 to the first printer head 501, and optionally (c) a receiver item 550. In FIGS. 1a-1b, the first or second printable material or the first or second printed material are indicated with the general indications printable material 201 and printed material 202. Directly downstream of the nozzle 502, the filament 321 with 3D printable material becomes, when deposited, layer 322 with 3D printed material 202.

[0104] FIG. 1c schematically depicts a stack of 3D printed layers 322, each having a layer height H and a layer width W. Note that in embodiments the layer width and/or layer height may differ for two or more layers 322.

[0105] Referring to FIGS. 1a-1c, the filament of 3D printable material that is deposited leads to a layer having a height H (and width W). Depositing layer 322 after layer 322, the 3D item 1 is generated.

[0106] FIG. 2a schematically depicts for the sake of understanding particles and some aspects thereof. Note that the particles used in the present invention are especially relative flat, see e.g. FIG. 2d.

[0107] The particles comprise a material 411, or may essentially consist of such material 411. The particles 410 have a first dimension or length L1. In the left example, L1 is essentially the diameter of the essentially spherical particle. On the right side a particle is depicted which has non spherical shape, such as an elongated particle 410. Here, by way of example L1 is the particle length. L2 and L3 can be seen as width and height. Of course, the particles may comprise a combination of differently shaped particles.

[0108] FIGS. 2b-2e schematically depict some aspects of the particles 410. Some particles 410 have a longest dimension A1 having a longest dimension length L1 and a shortest dimension A2 having a shortest dimension length L2. As can be seen from the drawings, the longest dimension length L1 and the shortest dimension length L2 have a first aspect ratio larger than 1. FIG. 2b schematically depicts a particle 410 in 3D, with the particle 410 having a length, height and width, with the particle (or flake) essentially having an elongated shape. Hence, the particle may have a further (minor or main) axis, herein indicated as further dimension A3. Essentially, the particles 410 are thin particles, i.e. L2<L1, especially L2<<L1, and L2<<L3. L1 may e.g. be selected from the range of 5-200 μm; likewise L3 may be. L2 may e.g. be selected from the range of 0.1-20 μm.

[0109] FIG. 2c schematically depicts a particle that has a less regular shape such as pieces of broken glass, with a virtual smallest rectangular parallelepiped enclosing the particle.

[0110] Note that the notations L1, L2, and L3, and A1, A2 and A3 are only used to indicate the axes and their lengths, and that the numbers are only used to distinguish the axis. Further, note that the particles are not essentially oval or rectangular parallelepiped. The particles may have any shape with at least a longest dimension substantially longer than a shortest dimension or minor axes, and which may essentially be flat. Especially, particles are used that are relatively regularly formed, i.e. the remaining volume of the fictive smallest rectangular parallelepiped enclosing the particle is small, such as less than 50%, like less than 25%, of the total volume.

[0111] FIG. 2d schematically depicts a relatively irregularly shaped particle. Hence, the particulate material that is embedded in the 3D printable material or is embedded in the 3D printed material may include a broad distribution of particles sizes. A rectangular parallelepiped can be used to define the (orthogonal) dimensions with lengths L1, L2 and L3.

[0112] FIG. 2e schematically depicts cylindrical, spherical, and irregularly shaped particles, which will herein in general not be used (see also above).

[0113] As shown in FIGS. 2b-2e the terms “first dimension” or “longest dimension” especially refer to the length L1 of the smallest rectangular cuboid (rectangular parallelepiped) enclosing the irregular shaped particle. When the particle is essentially spherical the longest dimension L1, the shortest dimension L2, and the diameter are essentially the same.

[0114] FIG. 3a schematically depicts a filament 321, such as when escaping from a printer nozzle (not depicted), which comprises 3D printable material 201. The 3D printable material comprise thermoplastic material 401 with particles 410 embedded therein.

[0115] FIG. 3b schematically depicts a 3D item 1, showing the ribbed structures (originating from the deposited filaments), having heights H. This height may also be indicated as width. Here, layers 322 with printed material 202, with heights H and widths W are schematically depicted. FIG. 3b can be seen as a stack of layers 322 of which a plurality adjacent stacks are shown in FIG. 1b.

[0116] FDM printers use a thermoplastic filament, which is heated to its melting point and then extruded, layer by layer, to create a three dimensional object.

[0117] In e.g. lighting applications for optimum functioning of LEDs efficient heat sinking is necessary.

[0118] Amongst others, herein graphite filled polymers were used to produce heat sinks It was found that printed structures show anisotropic thermal conductivity and with decreasing layer thickness the conductivity become increasingly more anisotropic. The thermal conductivity found to be highest in the plane perpendicular to the nozzle head. At layer thicknesses in the range 100-800 μm found to be optimal for realizing the desired anisotropic effect such as obtaining higher conductivity in the direction parallel to the plane while not reducing the conductivity in the direction perpendicular to the printing plane. It appeared useful that the diameter of the nozzle is above about 1 mm for facilitating printing. Hence, it is herein suggest using heat sink configurations produced by FDM printing with effective heat sinking using anisotropic thermal conductivity. In these strategies, the orientation of the heat sink design on the print platform (or the direction of the nozzle with respect to the heat sink design) is selected so that that, there is a continuous high thermal conductive path from the point of heat production to the points where heat dissipation takes place.

[0119] Polymers such as PC and Nylons filled with graphite could be used to manufacture heat sinks using injection molding. In order to obtain relatively high thermal conductivity >4 one needs to use highly graphite filled polymers.

[0120] Herein, polymers are used with up to about 40 wt % (about 30 vol. %) filled with graphite. Such filaments are relatively brittle and difficult to extrude and print. Hence, for continuous printing relatively large nozzle diameters above 1 mm, or even above 2 mm to be able to print these highly filled polymers. It was also helpful to use thin filaments, such as with a thickness around 2 mm, or smaller. Filaments filled with graphite to produce cubes schematically shown in FIG. 4a by using different layer heights during printing.

[0121] The thermal conductivity of the samples was measured at different directions after printing. Thermal conductivity in the direction parallel to the plane and in the direction perpendicular to the plane for different layer thicknesses are shown in FIG. 4b for Polyamide and for Polycarbonate in FIG. 4c. On the x-axis is the height H in mm, and on the y-axis the thermal conductivity in W/mK.

[0122] It can be seen that in the range 100-800 μm the conductivity shows anisotropy. In the case of FIG. 4c at layer height of 100 μm highest thermal conductivity is obtained.

[0123] Anisotropy in thermal conductivity is related to the property of graphite. Graphite sheets show high thermal conductivity in the plane of the sheets than in direction perpendicular to the sheets. Thus the behavior observed is related to this as we induce orientation in graphite layers by controlling the layer height.

[0124] FIG. 4d shows the thermal conductivity in W/mK (y-axis) dependent upon the volume concentration vol. % (x-axis) of graphite in thermoplastic elastomer based on polyester copolymer, at a layer thickness of 200 μm parallel to the plane.

[0125] In further examples, the thermal conductivity was determined as function of volume % graphite, between about 17.5 vol. % and about 29 vol. %, with the polymeric material being elastomeric copolyester composite. The layer thickness was 400 μm. The graphite particles had a longest dimension (L1) of either 20 μm or 50 μm. the thermal conductivity for about 17.5 vol. % graphite was about 2.8 W/mK and 4.2 W/mK for the 20 μm and 50 μm graphite containing elastomeric copolyester composite 3D printed material, respectively, and for about 29 vol. % about 5.6 W/mK and about 5.9 W/mK for the 20 μm and 50 μm graphite containing elastomeric copolyester composite 3D printed material, respectively. Hence, the 50 μm graphite particles provide a relative higher thermal conductivity, especially at lower volume percentages. Further, the thermal conductivity increases with increasing volume percentage.

[0126] In order to benefit from the high thermal conductivity it is desirable that the heat sink design orientation on the print platform is selected so that that in direction of heat spreading needs to take place the printed object has the highest heat conductivity.

[0127] In the heat sink shown in FIG. 5a below, the heat sink was printed as shown above the XY plane high heat sinking is obtained while in the z direction thermal conductivity is low. When a light source 10, such as a LED, is placed on top heat is spread in the XY plane but as in the z direction heat is not high conductive path. A light source is an example of a functional component 1010. Of course, the invention may also be applied for other functional components.

[0128] It may therefore be relevant to choose the orientation of the heat sink during printing as shown in FIG. 5b. In this case the high thermal conductivity is in the x-y plane. Thus heat can be spread continuously first towards the fins along y axis and then along the fins along x axis where the heat can be removed by convection or irradiation.

[0129] Likewise, a structure as schematically shown in FIG. 5c can be 3D printed, with in the middle a hole for receiving a thermal conductive (insert) element and/or a functional element. The structure shown in FIG. 5c has a good conduction in the XY plane. The hole (in the center) can be used to insert high conductive material such as aluminum. It is also possible to print thermally conductive insert element with a good conductivity in Y direction and insert it in the hole. For instance, a system as schematically shown in FIG. 5d with a relatively highly efficient heat sinking can be obtained. When using this 3D printed heatsink, or combination of heatsink, the heat generating source, such as a LED, may be configured in thermal contact with the insert, like an aluminum insert. For instance, the solid state light source may be placed on top of the insert. In such arrangement, the (aluminum) insert has a relatively high conductivity (e.g. ≥100 W/Km) (along a z direction). The insert may transport the heat to the fins. The fins, with relatively high thermal conductivity in the XY plane, may spread the heat, by which the heat is transported away from the solid state light source.

[0130] FIGS. 5b-5d schematically depict embodiments of a 3D item 1 comprising 3D printed material 202 wherein the 3D item 1 comprises a heat sink 100 comprising a plurality of layers 322 of 3D printed material 202 defining a heat receiving face 101. The plurality of layers 322 of 3D printed material 202 are configured parallel to planes 325 perpendicular to the heat receiving face 101, wherein the 3D printed material 202 further comprises particles (not shown) embedded in the 3D printed material 202, wherein the particles have an anisotropic thermal conductivity. The particles are available in the 3D printed material 202 in an amount of at maximum 30 vol. % relative to the total volume of the 3D printed material 202 (of the respective layers 322), and wherein the (respective) layers 322 of 3D printed material 202 have layer heights H selected from the range of at maximum 800 μm.

[0131] FIGS. 5b-5d also schematically depict embodiments of a system 1000 comprising a functional component 1010 generating heat during use, and the 3D item 1, wherein the heat receiving face 101 of the heat sink 100 is in thermal contact with the functional component.

[0132] Especially, the system 1000 comprises a lighting system comprising a light source 10, wherein the functional component 1010 comprises the light source 10.

[0133] Hence, in embodiments the 3D printed item may include fins extending in different directions. Further, the fins may extend essentially perpendicular to a heat receiving face. The 3D printed item may include a rotational symmetric shape. In embodiments, the heat receiving surface may be circular, such as cylindrical. The heat receiving face may be configured such that it may host a thermally conductive medium, such as a solid body of (aluminum) metal.

[0134] FIG. 5e schematically depicts in more detail an embodiment of a 3D item 1, here with—by way of example—three layers 322 with layer heights H, wherein it is shown that the particles 410 are aligned with the layers with an average orientation of the long axis of the graphite of particles being parallel to the plane of the layers. For instance, in the orientation distribution function full width at half maximum corresponds may be about 100° or smaller; the half maxima may especially be at about −50° and 50°, and the maximum at about 0° to relative to a plane through the layer 322 (parallel to a layer axis).For instance, the full width half maximum may be at maximum about 80°, like at maximum 60°. Further, the maximum is especially at about 0°±5°.

[0135] The term “substantially” herein, such as “substantially consists”, will be understood by the person skilled in the art. The term “substantially” may also include embodiments with “entirely”, “completely”, “all”, etc. Hence, in embodiments the adjective substantially may also be removed. Where applicable, the term “substantially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term “comprise” includes also embodiments wherein the term “comprises” means “consists of”. The term “and/or” especially relates to one or more of the items mentioned before and after “and/or”. For instance, a phrase “item 1 and/or item 2” and similar phrases may relate to one or more of item 1 and item 2. The term “comprising” may in an embodiment refer to “consisting of” but may in another embodiment also refer to “containing at least the defined species and optionally one or more other species”.

[0136] Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

[0137] The devices herein are amongst others described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation or devices in operation.

[0138] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb “to comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0139] The invention also provides a control system that may control the apparatus or device or system, or that may execute the herein described method or process. Yet further, the invention also provides a computer program product, when running on a computer which is functionally coupled to or comprised by the apparatus or device or system, controls one or more controllable elements of such apparatus or device or system.

[0140] The invention further applies to a device comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterizing features described in the description and/or shown in the attached drawings.

[0141] The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some of the features can form the basis for one or more divisional applications.

[0142] It goes without saying that one or more of the first (printable or printed) material and second (printable or printed) material may contain fillers such as glass and fibers which do not have (to have) influence on the on T.sub.g or T.sub.m of the material(s).