Method of manufacturing 3D articles by FDM printing

Abstract

The invention provides a method of manufacturing a 3D article (1) by FDM printing, the method comprising depositing a 3D printable material (201) at a flow rate through a nozzle (502) having a nozzle temperature, thereby providing a stacked 3D article (1) comprising layers (322) of 3D printed material (202). The 3D printable material (201) is a thermoplastic polymer having a weight average molecular weight higher than twice the entanglement molecular weight. The method further comprises transitioning between a first printing stage and a second printing stage, where the first printing stage comprises depositing the 3D printable material (201) to form a first 3D printed material (210), where the 3D printable material is printed at a first nozzle temperature TN1 and a first flow rate FR1, thereby printing the 3D printable material below a critical shear rate, and where the second printing stage comprises depositing the 3D printable material (201) at a second nozzle temperature TN1 and a second flow rate FR1. And wherein the second printing stage comprises depositing the 3D printable material to form a second 3D printed material (220) wherein the 3D printable material is printed at a second nozzle temperature TN2 and a second flow rate FR2, thereby printing the 3D printable material above the critical shear rate.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an object by 3D printing, in particular by fused deposition modeling. The present invention also relates to an object obtainable using such a manufacturing method, and a lighting device comprising such an object. The present invention also relates to a computer program product comprising instructions which, when executed by a 3D printer, cause the 3D printer to carry out the manufacturing method described above. Background Art

[0002] Digital manufacturing is expected to increasingly transform the nature of global manufacturing. One of the primary processes used in digital manufacturing is 3D printing. The term "3D printing" refers to methods in which materials are joined or solidified under computer control to form three-dimensional objects of virtually any shape or geometry. These three-dimensional objects are typically produced using data from a three-dimensional model and are typically produced by the continuous addition of material layer by layer.

[0003] Many different 3D printing techniques are known in the art.

[0004] US5121329 discloses a device incorporating a movable dispensing head and a base member, wherein the movable dispensing head is provided with a supply of material that solidifies at a predetermined temperature, and the movable dispensing head and the base member are moved relative to each other along the "X" axis, the "Y" axis, and the "Z" axis in a predetermined pattern, thereby accumulating material discharged from the dispensing head at a controlled rate on the base member to form a three-dimensional object. This 3D printing technology is known as fused deposition modeling (FDM).

[0005] FDM, also known as fused filament fabrication (FFF) or filament 3D printing (FDP), is one of the most commonly used forms of 3D printing. In the FDM process, a 3D printer creates an object layer by layer by extruding a printable material (usually a thermoplastic filament) along a tool path generated from a digital representation of the object. The printable material is heated to above the melting temperature for semi-crystalline polymers and above the glass transition temperature for amorphous polymers and extruded through the nozzle of the 3D printer's print head. The extruded printable material fuses to the previously deposited material and solidifies when the temperature is lowered. In a typical 3D printer, the printable material is deposited as a sequence of planar layers on a substrate that defines a build plane. The position of the print head relative to the substrate is then incremented along the print axis (perpendicular to the build plane), and the process is repeated until the object is completed.

[0006] FDM printers are relatively fast, low-cost, and can be used to print complex three-dimensional objects. These printers are used to create a wide variety of shapes using a variety of 3D printable materials. The technology is also being further developed in the production of LED lamps and lighting solutions.

[0007] Especially when using 3D printed objects in lighting solutions, it is also desirable to create areas with different optical properties.

[0008] WO2021175780.A1 discloses a method in which a single wall is composed of two or more strands. The side surfaces of these strands are varied to control color, reflectivity, transmittance, or other optical properties. Summary of the Invention

[0009] It is an object of the present invention to at least partially overcome one or more of the above-mentioned disadvantages of the prior art, or to provide a useful alternative.

[0010] In a first aspect, the present invention provides a method for fabricating an object by FDM printing, wherein the method comprises depositing a 3D printable material at a flow rate through a nozzle having a nozzle temperature, thereby providing a 3D object comprising a stack of layers of the 3D printable material. The 3D printable material is a thermoplastic polymer having a weight average molecular weight greater than twice the entanglement molecular weight.

[0011] The method further includes transitioning between a first printing phase and a second printing phase, wherein the first printing phase includes depositing a 3D printable material to form a first 3D printing material, wherein the 3D printable material is printed at a first nozzle temperature TN1 and a first flow rate FR1, thereby printing the 3D printable material below a critical shear rate. The second printing phase includes depositing a 3D printable material to form a second 3D printing material, wherein the 3D printable material is printed at a second nozzle temperature TN2 and a second flow rate FR2, thereby printing the 3D printable material above the critical shear rate.

[0012] Using the method according to the first aspect of the present invention, a 3D object can be manufactured having different parts printed during two different printing phases, wherein the first and second 3D printed materials have different surface properties. The first 3D printed material printed during the first printing phase has a smooth surface, in other words, a very low surface roughness amplitude. The second 3D printed material printed during the second printing phase has a less smooth surface, with a higher surface roughness amplitude. Depending on the 3D printable material used, different aesthetic or optical effects can be achieved. Moreover, according to embodiments of the method, this can be achieved using only a single nozzle and a single 3D printable material. This has the advantage that there is no need to switch the printer nozzle and material when printing the 3D object, thereby eliminating the risk of defects arising from changing the nozzle position.

[0013] The method includes the steps of depositing (during the printing phase) a 3D printable material layer by layer. As used herein, the term "3D printable material" refers to the material to be deposited or printed, and the term "3D printed material" refers to the material obtained after deposition. These materials can be substantially the same, as 3D printable material can specifically refer to the material in the printer head or extruder at an elevated temperature, while 3D printed material refers to the same material at a later stage after deposition. The 3D printable material is printed and deposited as a filament. The 3D printable material can be provided as a filament or formed into a filament. Thus, regardless of the starting material applied, the filament comprising the 3D printable material is provided by the printer head and 3D printed. As used herein, the term "3D printable material" may also be referred to as "printable material." The term "thermoplastic polymer" may, in embodiments, refer to a blend of different polymers, but may also, in embodiments, refer to a substantially single polymer type having different polymer chain lengths. Thus, the terms "polymer material" or "polymer" may refer to a single type of polymer or to a plurality of different polymers. The term "printable material" may refer to a single type of printable material or to a plurality of different printable materials. The term "printing material" may refer to a single type of printing material or to a plurality of different printing materials.

[0014] Therefore, the term "3D printable material" may also refer to a combination of two or more materials. Generally, these (polymer) materials have a glass transition temperature T g and / or melting temperature T m Before exiting the nozzle, the 3D printable material will be heated by the 3D printer to a temperature of at least the glass transition temperature, and generally to at least the melting temperature. Thus, in certain embodiments, the 3D printable material comprises a 3D printable material having a glass transition temperature (T g ) and / or melting point (T m ) of a thermoplastic polymer, and the printer head action includes heating the 3D printable material above the glass transition, and if it is a semi-crystalline polymer, above the melting temperature. In yet another embodiment, the 3D printable material includes a thermoplastic polymer having a melting point (T m) of a (thermoplastic) polymer, and the printer head action includes heating the 3D printable material to be deposited on the receiving article to a temperature of at least the melting point. The glass transition temperature is generally different from the melting temperature. Melting is a transition that occurs in crystalline polymers. Melting occurs when the polymer chains fall out of their crystal structure and become a disordered liquid. The glass transition is a transition of amorphous polymers; that is, a polymer in which the polymer chains are not arranged in an ordered crystal, but are dispersed in any way, even in the solid state. The polymer can be amorphous, essentially having a glass transition temperature but no melting temperature, or can be (semi-)crystalline, generally having both a glass transition temperature and a melting temperature, the melting temperature generally being higher than the glass transition temperature.

[0015] Thus, as described above, the present invention provides a method comprising providing a filament of a 3D printable material, and printing (in a printing phase) the 3D printable material on a substrate to provide a 3D object.

[0016] The phrase "printing on a received item" and similar phrases include printing directly on the received item, or printing on a coating on the received item, or printing on 3D printing material previously printed on the received item, etc. The term "receiving item" may refer to a printing platform, a print bed, a substrate, a support, a building panel or a building platform, etc. Instead of the term "receiving item", the term "substrate" may also be used. The phrase "printing on a received item" and similar phrases include printing on the printing platform or on a separate substrate contained in the printing platform, printing on the print bed, printing on a support, printing on a building panel or on a building platform, etc. Therefore, the phrase "printing on a substrate" and similar phrases include printing directly on the substrate, or printing on a coating on the substrate, or printing on 3D printing material previously printed on the substrate, etc. In the following, further use of the term substrate may refer to a printing platform, a print bed, a substrate, a support, a building panel or a building platform, etc., or a separate substrate on or contained in these items.

[0017] The printable material is deposited layer by layer, thereby generating a 3D printed object (in the printing phase). The 3D printed object may show a characteristic ribbed structure (derived from the deposited filaments). However, after the printing phase is completed, further phases may be performed, such as a finishing phase. This phase may include removing the printed object from the receiving object and / or one or more post-processing actions. One or more post-processing actions may be performed before the printed object is removed from the receiving object, and / or one or more post-processing actions may be performed after the printed object is removed from the receiving object. Post-processing may include, for example, one or more of polishing, coating, adding functional components, etc. Post-processing may include leveling the ribbed structure, thereby producing a substantially smooth surface.

[0018] The material that can be used as a 3D printable material in the method of the present invention is a thermoplastic polymer material having a weight average molecular weight greater than twice the entanglement molecular weight.

[0019] The weight average molecular weight is the sum of the weights of all chains in a polymer divided by the total number of chains. The entanglement molecular weight is a material property of every thermoplastic polymer that characterizes the size of the entanglements in the polymer material.

[0020] In one example, the thermoplastic polymer may have a weight average molecular weight greater than 10,000 g / mol.

[0021] The material that can be used as a 3D printable material can be selected from the group consisting of (thermoplastic) polymers and silicones. In particular, the 3D printable material can include a (thermoplastic) polymer selected from the group consisting of polystyrene, polyacrylonitrile, acrylonitrile butadiene styrene (ABS), polyamides (such as nylon), polyacetate, polyesters (such as polylactic acid (PLA) and polyethylene terephthalate (PET)), polyacrylates (such as polymethyl methacrylate (PMMA)), polyalkanes (such as low-density polyethylene (LDPE) and high-density polyethylene (HDPE), polypropylene), polyvinyl chloride (PVC), polycarbonate (PC), fluorinated polymers (such as polymers containing polyvinyl fluoride (PVDF) sulfide (such as polysulfone), and polyurethane and its copolymers).

[0022] The 3D printable material is printed at a flow rate, also known as the material deposition rate. Flow rate is measured in units of weight or volume per second.

[0023] In the method of the present invention, 3D printables are printed above or below a critical shear rate. Critical shear rate is a term known in polymer processing. It is the shear rate in a printer nozzle at a specific temperature and flow rate when a thermoplastic polymer exceeds a critical value.

[0024] The printable material is printed onto a receiving object. Specifically, the receiving object can be a printing platform, or a portion of the printing platform. During 3D printing, the receiving object can also be heated. However, it is also possible to cool the receiving object during 3D printing.

[0025] In another example, during the manufacture of a 3D object, the transition between the first printing stage and the second printing stage can be performed multiple times. More than one transition between the two printing stages creates an opportunity to form optical or decorative patterns on the surface of the 3D object.

[0026] Alternatively or additionally, the transition between the first printing phase and the second printing phase can be performed as a gradual transition, so that the nozzle temperature and / or the flow rate can be adjusted between TN1 and TN2 and / or between FR1 and FR2 in a plurality of steps. A gradual transition between the two printing phases provides an additional possibility of varying the decorative and optical effects that can be generated using the method of the present invention.

[0027] The first and second 3D printing materials can be printed using the same thermoplastic polymer. Using the same thermoplastic polymer for both the first and second 3D printing materials has the advantage that the 3D printable materials deposited during the first and second printing stages can be deposited from the same nozzle. Printing the entire 3D object from the same nozzle eliminates defects in the 3D object that require changing nozzle positions when printing with multiple nozzles.

[0028] Even though the first and second 3D printing materials can be printed using the same material, they can be deposited from both printer nozzles. This can save time during the printing process because printer settings (such as the first and second nozzle temperatures and the first and second flow rates) can be kept constant and there is no need to wait for, for example, the nozzles to heat up or cool down.

[0029] Alternatively, the first and second 3D printing materials can be printed using different thermoplastic polymers. Using two different thermoplastic polymers can also offer time-saving advantages, similar to printing the same thermoplastic polymer from two nozzles. Furthermore, it offers the possibility of printing with two different materials that have additional distinguishing properties, such as differences in color, transparency, light transmittance, or light reflectivity.

[0030] The transition between the first and second printing stages can be performed after depositing the first layer of the stack of 3D printed material and before depositing the adjacent second layer. In other words, the transition can be performed after one or more complete layers of the stack of 3D printed material have been deposited during the first printing stage. Thus, the interface between the first and second 3D printed materials lies between the two layers of 3D printed material. This allows for the creation of 3D objects with, for example, upper and lower portions having different optical properties or a striped appearance.

[0031] Alternatively, the transition between the first and second printing stages can be performed within a stack of layers of 3D printed material. In other words, the interface between the first and second 3D printed materials lies within a single 3D printed material layer. This allows, for example, a 3D object to be created with one optical property on the front side and a second optical property on the back side. More complex patterns, such as a checkerboard pattern, can also be achieved.

[0032] In another example, the second nozzle temperature TN2 may be lower than the first nozzle temperature TN1 , and the second flow rate FR2 may be the same as the first flow rate FR1 .

[0033] Alternatively, the first nozzle temperature TN1 and the second nozzle temperature TN2 may be the same temperature, while the second flow rate FR2 is higher than the first flow rate FR1.

[0034] The critical shear rate depends on, among other parameters, the nozzle temperature and the flow rate. During the 3D printing process, both the nozzle temperature and the flow rate can be varied to transition from a first printing phase to a second printing phase. Thus, the first nozzle temperature TN1 differs from the second nozzle temperature TN2, and the first flow rate FR1 differs from the second flow rate FR2. However, it may be most practical to keep one of the two factors constant while varying the other, to first print the 3D printable material below the critical shear rate and then print it above it.

[0035] In another example, a first 3D printing material deposited during a first printing phase can be transparent, and a second 3D printing material deposited during a second printing phase can be light-diffusing. This makes it possible to create a 3D printed object with two or more portions that differ in light transmission, such that one portion is transparent and another portion is light-diffusing.

[0036] Alternatively, the first 3D printing material deposited during the first printing phase can be specularly reflective, and the second 3D printing material deposited during the second printing phase can be diffusely reflective. This makes it possible to create two or more 3D-printed objects that exhibit different types of light reflectance. The first 3D printing material exhibits specular reflectance, meaning that the surface of the first 3D printing material can be described as shiny, glossy, polished, or smooth. The second 3D printing material exhibits diffuse reflectance, meaning that the surface of the second 3D printing material can be described as matte, dull, flat, or matte.

[0037] In a second aspect, the present invention provides a computer program product comprising instructions which, when executed by a computer functionally coupled to or comprised in a 3D printer, cause the 3D printer to perform the method according to the first aspect.

[0038] Such a computer program product can be loaded onto a computer contained in a 3D printer. The computer program product may include a computer-readable medium. The computer-readable medium and / or memory may be any recordable medium (e.g., RAM, ROM, removable memory, CD-ROM, hard drive, DVD, floppy disk, or memory card), or may be a transmission medium (e.g., a network including optical fibers, the World Wide Web, cables, and / or wireless channels using, for example, time division multiple access, code division multiple access, or other wireless communication systems). Any known or developed medium capable of storing information suitable for use with a computer system may be used as the computer-readable medium and / or memory. Additional memory may also be used. The computer-readable medium and memory may be long-term memory, short-term memory, or a combination of long-term and short-term memory. The term "memory" may also refer to multiple memories. The memory may configure the processor / controller to implement the methods, operations, and functions disclosed herein. The memory may be distributed or local, and where an additional processor may be provided, the processor may be distributed or single. The memory may be implemented as electrical, magnetic, or optical memory, or any combination of these or other types of storage devices. Furthermore, the term "memory" should be understood broadly to encompass any information that can be read from or written to an address in the addressable space accessible to the processor. According to this definition, for example, since the processor can retrieve information from the network, information on a network such as the Internet remains in memory. The controller / processor and memory can be of any type. The processor is capable of performing the various described operations and executing instructions stored in the memory. The processor can be a dedicated or general-purpose integrated circuit. Furthermore, the processor can be a dedicated processor for performing in accordance with the disclosed system, or it can be a general-purpose processor in which only one of many functions is operated in accordance with the system. The processor can operate using a program portion, multiple program segments, or can be a hardware device using a dedicated or multi-purpose integrated circuit.

[0039] In a third aspect, the present invention provides an object obtainable by the method according to the first aspect.

[0040] In an example according to the third aspect, a first 3D-printed material may have a first surface, and a second 3D-printed material may have a second surface. The surface roughness amplitude of the first surface may be less than 1 micron, such that the first surface may not exhibit a shark skin effect or a melt fracture effect. The surface roughness amplitude of the second surface may be greater than 1 micron, such that the second surface may exhibit a shark skin effect or a melt fracture effect.

[0041] During the second printing phase, the 3D printable material is printed at a shear rate above a critical rate. The second 3D printed material can have a larger surface roughness amplitude greater than 1 micron. Printing thermoplastic polymers at shear rates above a critical rate can lead to the occurrence of so-called sharkskin effects and / or melt fracture effects, also known as elastic turbulence or bamboo. These effects can cause distortion in the flow of 3D printable material, resulting in surface defects with periodic surface roughness amplitude and frequency.

[0042] In another example, a first 3D printing material deposited during a first printing phase can be transparent, and a second 3D printing material deposited during a second printing phase can be light-diffusing. This makes it possible to create a 3D printed object with two or more portions that differ in light transmission, such that one portion is transparent and another portion is light-diffusing.

[0043] Alternatively, the first 3D printing material deposited during the first printing phase can be specularly reflective, and the second 3D printing material deposited during the second printing phase can be diffusely reflective. This makes it possible to create two or more 3D-printed objects that exhibit different types of light reflectance. The first 3D printing material exhibits specular reflectance, meaning that the surface of the first 3D printing material can be described as shiny, glossy, polished, or smooth. The second 3D printing material exhibits diffuse reflectance, meaning that the surface of the second 3D printing material can be described as matte, dull, flat, or matte.

[0044] As described above, 3D printed objects can be used for different purposes. 3D printed objects can be used for lighting, etc. Therefore, in another aspect, the present invention also provides a lighting device comprising a 3D object as defined herein. In a specific aspect, the present invention provides a lighting system comprising (a) a light source configured to provide (visible) light source light, and (b) a 3D object as defined herein, wherein the 3D object can be configured as one or more of the following: (i) at least a portion of a housing, (ii) at least a portion of a wall of a lighting chamber, and (iii) a functional component, wherein the functional component can be selected from the group consisting of: an optical component, a support, an electrically insulating component, a conductive component, a thermally insulating component, and a thermally conductive component. Therefore, in a specific example, the 3D object can be configured as one or more of the following: (i) at least a portion of a lighting device housing, (ii) at least a portion of a wall of a lighting chamber, and (iii) an optical element. Since a relatively smooth surface can be provided, the 3D printed object can be used as a mirror or lens, etc. In an example, the 3D object can be configured as a cover. The device or system can include multiple different 3D printed objects with different functions.

[0045] Instead of the term "fused deposition modeling (FDM) 3D printer", the shortened term "3D printer", "FDM printer" or "printer" may be used. The printer nozzle may also be referred to as a "nozzle", or sometimes as an "extruder nozzle". BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which like reference numerals indicate like parts, and in which:

[0047] Figures 1a to 1c schematically depict some general aspects of a 3D printer and 3D printing materials;

[0048] Figure 2 shows a schematic diagram depicting the behavior of a typical thermoplastic polymer when processed by a 3D printer;

[0049] Figure 3 a to Figure 3 b Schematically depicts some aspects related to 3D printing materials;

[0050] Figure 4 Some other aspects related to 3D printing materials are schematically depicted;

[0051] Figure 5 shows a schematic diagram of the transition between the first printing stage and the second printing stage;

[0052] Figures 6a to 6b Schematically depicts some other aspects related to 3D printing materials and 3D objects;

[0053] Figure 7 An experimental flow chart is shown; and

[0054] Figure 8 The application is schematically depicted.

[0055] The schematic diagrams are not necessarily drawn to scale. DETAILED DESCRIPTION

[0056] Figure 1a schematically depicts some aspects of a 3D printer 500. Reference numeral 530 denotes a functional unit configured for 3D printing, in particular FDM 3D printing; this reference numeral may also denote a 3D printing stage unit. Here, only a printer head 501 for providing 3D printing material, such as an FDM 3D printer head, is schematically depicted. The 3D printer 500 may include multiple printer heads. Reference numeral 502 denotes a printer nozzle. The 3D printer of the present invention may include multiple printer nozzles. Reference numeral 320 denotes a filament (such as indicated above) that can print the 3D printable material 201. For the sake of clarity, not all features of the 3D printer are depicted, but only those features that are particularly relevant to the present invention (see also further below). Reference numeral 321 denotes an extrudate (of the 3D printable material 201).

[0057] The 3D printer 500 is configured to generate a 3D object 1 by depositing a plurality of layers 322 layer by layer on a receiving object 550 that can be at least temporarily cooled, wherein each layer 322 comprises a material such as a material having a melting point T m 3D printable material 201. 3D printable material 201 can be deposited on substrate 1550 (during the printing phase). Through deposition, 3D printable material 201 has become 3D printing material 202. 3D printable material 201 exiting nozzle 502 can also be represented as extrudate 321. Reference numeral 401 denotes a thermoplastic material.

[0058] The 3D printer 500 can be configured to heat the filament 320 material upstream of the printer nozzle 502. This can be accomplished, for example, using a device having one or more of an extrusion and / or heating function. Such a device is indicated by reference numeral 573 and is arranged upstream of the printer nozzle 502 (i.e., before the filament material leaves the printer nozzle 502 in time). The printer head 501 can (thus) include a liquefier or a heater. Reference numeral 201 represents a printable material. After deposition, the material is referred to as (3D) printing material, indicated by reference numeral 202.

[0059] Reference numeral 572 denotes a spool or roller with material, particularly in the form of a wire, which may be represented as filament 320. The 3D printer 500 converts this into an extrudate 321 downstream of the printer nozzle 502, and then into a layer 322 on the receiving article or on the deposited printing material. Generally, the diameter of the extrudate 321 downstream of the nozzle 502 is reduced relative to the diameter of the filament 320 upstream of the printer head 501. Therefore, the printer nozzle is sometimes (also) referred to as an extruder nozzle. By arranging the layers 322 layer by layer, a 3D object 1 can be formed. Reference numeral 575 denotes a filament providing device, including a spool or roller and a drive wheel, etc., which are represented by reference numeral 576.

[0060] Reference symbol A denotes the longitudinal axis or filament axis.

[0061] Reference C schematically depicts a control system, such as in particular a temperature control system configured to control the temperature of the received item 550. The control system C may comprise a heater capable of heating the received item 550 to a temperature of at least 50°C, but in particular to a range up to about 350°C, such as at least 200°C.

[0062] Alternatively or additionally, the receiving plate can be movable in one or both directions within the xy plane (horizontally). Furthermore, alternatively or additionally, the receiving plate can be rotatable about the z axis (vertically). Thus, the control system can move the receiving plate in one or more of the x, y, and z directions.

[0063] Alternatively, the printer 500 may have a head 501 that can also rotate during printing. The advantage of such a printer is that the printed material cannot rotate during printing.

[0064] The layer is denoted by reference numeral 322 and has a layer height H and a layer width W.

[0065] Note that the 3D printable material 201 is not necessarily provided to the printer head as a filament 320. Furthermore, the filament 320 can also be produced in the 3D printer 500 from a block of 3D printable material.

[0066] Reference symbol D represents the diameter of the nozzle (through which the 3D printable material 201 is pushed).

[0067] Figure 1 b schematically depicts in more detail the printing of the 3D object 1 under construction in a 3D diagram. Here, in this schematic diagram, the ends of the filaments 321 lying in a single plane are not interconnected, although this could be the case in practice.

[0068] Reference numeral H denotes the height of the layer. The layer is denoted by reference numeral 322. Here, the layer has a substantially circular cross-section. However, the cross-section may be generally flat, such as having an outer shape similar to a flattened oval tube or a flattened oval pipe (i.e., a round rod with a compressed diameter and a height less than the width, wherein the sides (defining the width) are (still) round).

[0069] Thus, Figures 1a-1b schematically depict aspects of a fused deposition modeling 3D printer 500, which includes (a) a first printer head 501 including a printer nozzle 502, (b) a filament supply device 575 configured to supply filament 321 comprising 3D printable material 201 to the first printer head 501, and optionally, (c) a receiving article 550. In Figures 1a-1b, the first or second printable material, or the first or second printing material, are collectively referred to as printable material 201 and printing material 202, respectively. Immediately downstream of the nozzle 502, the filament 321 comprising the 3D printable material becomes a layer 322 comprising the 3D printing material 202 after deposition.

[0070] FIG1c schematically depicts a stack of 3D printed layers 322, each layer having a layer height H and a layer width W. Note that in certain examples, the layer widths and / or layer heights of two or more layers 322 can be different. Reference numeral 252 in FIG1c denotes an object surface of the 3D object (schematically shown in FIG1c).

[0071] 1a to 1c , filaments of deposited 3D printable material 321 form a layer having a height H (and width W). Layers 322 are deposited one after another, generating a 3D object 1 . A single-walled 3D object 1 is depicted very schematically in FIG1c .

[0072] In a conventional 3D printing process, 3D printable materials are printed below a critical shear rate. Generally, it is often desirable to process polymers below a critical shear rate to obtain a stable melt flow and a surface free of any surface defects (such as shark skin effect or melt fracture effect).

[0073] The subject of critical shear rate, shark skin effect and melt fracture in polymer extrusion processes has been extensively studied. These effects are known to those skilled in the art and their definitions can be found, for example, in "Polymer Technology Dictionary" by Tony Whelan (1994, Chapman & Hall, ISBN 0 412 58180 0, pp. 243, 389).

[0074] Research attempts to understand these effects and the factors that influence them during polymer extrusion. Consequently, most research efforts aim to prevent or delay the onset of sharkskin and melt fracture effects, for example by adding additives to the polymer material or by manipulating the extrusion die and print head.

[0075] Figure 2A schematic diagram depicting the behavior of a typical thermoplastic polymer when processed by a 3D printer 500 is shown. Shear rate is plotted on a logarithmic axis on the abscissa, and shear stress is plotted on a logarithmic axis on the ordinate. At low shear rates, shear stress increases proportionally to the shear rate. Once a critical shear rate is reached, the behavior and properties of the polymer melt during 3D printing change. This is indicated by a sharp bend in the line for the polymer in the diagram, after which the slope of the line changes. Printing thermoplastic polymers at shear rates above the critical shear rate results in the occurrence of sharkskin and / or melt fracture effects.

[0076] Measurements showing this typical behavior of thermoplastic polymers have been described, for example, in "Control of the shark skin instability in the extrusion of polymer melts using induced temperature gradients" (Erik Miller et al., Rheola Acta (2004) 44: 160-173, Figure 7 ) is disclosed in the .

[0077] The main factors affecting the occurrence of shark skin effect and melt fracture effect are: nozzle temperature (critical shear rate increases with increasing temperature), flow rate or deposition rate, average molecular weight and average molecular weight distribution (the larger the weight, the lower the critical shear rate), entanglement molecular weight and the geometry of the printer nozzle, especially the nozzle diameter and length.

[0078] The method of the present invention utilizes critical shear rate, shark skin effect and melt fracture phenomenon to create 3D printed objects with different parts, and these different parts have different optical properties and / or surface structures.

[0079] Figure 3 Figure a schematically depicts a first 3D printed material 210 deposited during a first printing phase. During the first printing phase, 3D printable material 201 is deposited to form first 3D printed material 210. 3D printable material 201 is printed at a first nozzle temperature TN1 and a first flow rate FR1, thereby printing 3D printable material 201 below a critical shear rate. Printing a thermoplastic polymer below a critical shear rate produces first 3D printed material 210 having a smooth first surface 211. First surface 211 has substantially no surface roughness or very low surface roughness, with a surface roughness amplitude of less than 1 micron. The term "surface roughness amplitude" refers to the surface roughness within a layer 322 of first 3D printed material 210. It does not refer to surface roughness formed by depositing layers 322 of 3D printable material 201 upon layers 322, thereby creating interlayer roughness that is typically inherent and characteristic of 3D printed objects.

[0080] Because the first 3D printing material 210 is printed below the critical shear rate, there is no shark skin effect and / or melt fracture effect on the first surface. Depending on the type of thermoplastic polymer used as the 3D printable material 201, the first 3D printing material 210 can be transparent, which is achieved by its low surface roughness. In other examples of other 3D printable materials 201, the surface can appear specular, glossy, shiny, or smooth.

[0081] Figure 3 Figure b schematically depicts second 3D printed material 220 deposited during a second printing phase. During the second printing phase, 3D printable material 201 is deposited to form second 3D printed material 220. During this second printing phase, 3D printable material 201 is printed at a second nozzle temperature TN2 and a second flow rate FR2, thereby printing 3D printable material 201 above a critical shear rate. Printing thermoplastic polymers above a critical shear rate typically produces second 3D printed material 220 having a non-smooth second surface 221. The second surface 221 has a higher surface roughness magnitude than the first surface 211. Again, herein, the term "surface roughness magnitude" refers to the surface roughness within a layer 322 of the second 3D printed material 210. The surface roughness magnitude of the second surface can be greater than 1 micron, or greater than 10 microns, or greater than 100 microns, or can be between 1 micron and 300 microns.

[0082] Because the second 3D printing material 220 is printed above a critical shear rate, the second surface 221 exhibits a sharkskin effect and / or a melt fracture effect, also known as elastic turbulence or bamboo. Depending on the type of thermoplastic polymer used as 3D printable material 201, the second 3D printing material 211 may be light-diffusing due to its high surface roughness. In other examples of other 3D printable materials 201, the surface may be diffuse, matte, dull, or flat.

[0083] Figure 4A magnified view of second surface 221 of second 3D-printed material 220 is schematically depicted. As described above, second 3D-printed material 220 is printed above a critical shear rate, resulting in second surface 221 exhibiting a sharkskin effect or melt fracture effect. The specific form of this effect may vary depending on the polymer, but it generally repeats periodically with a certain frequency f and surface roughness amplitude A. This effect can manifest as transverse ridges, but second surface 211 may also exhibit ripples, helical twists, or kinks. Regardless of the specific form of the effect, the surface roughness amplitude A of second surface 211 is measured from the lowest point on second surface 211 to the highest point on second surface 211 within one cycle of the effect.

[0084] Materials suitable for the methods of the present invention are thermoplastic polymers that exhibit a critical shear rate and can be printed above the critical shear rate within the parameters of the 3D printer 500 used to produce the 3D object 1. Parameters that influence the critical shear rate of a particular material in the 3D printer 500 are the size and material of the nozzle 502, the nozzle temperature, and the flow rate. Different nozzles can be used to print the 3D object 1, and for each nozzle 502, the nozzle temperature and flow rate can vary within specific ranges. If the critical shear rate of the 3D printable material 201 is within these parameter ranges, the material is suitable for the methods of the present invention.

[0085] Thermoplastic polymers with high weight average molecular weights may be particularly suitable because shark skin and melt fracture effects occur at low shear rates for these materials. Of particular importance is the relationship between the weight average molecular weight and the entanglement molecular weight. The weight average molecular weight can be greater than twice the entanglement molecular weight of the thermoplastic polymer.

[0086] The weight average molecular weight of the 3D printable material 201 of the present invention can be higher than 10,000 g / mol, but can also be higher than 20,000 g / mol, higher than 25,000 g / mol, or higher than 35,000 g / mol. The 3D printable material 201 should not contain any additives that prevent the sharkskin effect or melt fracture effect.

[0087] Another different way to characterize materials suitable for the present invention can be by their viscosity. Thermoplastic polymers that can be used as 3D printing materials in the present invention have a weight average molecular weight above a critical weight average molecular weight (Mc), above which the viscosity increases rapidly.

[0088] Therefore, the viscosity of the polymer also plays an important role. The viscosity of the polymer is a temperature-dependent variable. Therefore, in the example, the 3D printable material was printed above and below the critical temperature at a given shear rate.

[0089] During the first printing phase, the 3D printable material has a low viscosity, resulting in a stable melt flow during the deposition of the 3D printable material. The viscosity of the 3D printable material changes significantly during the second printing phase. The 3D printable material now exhibits a high viscosity that causes the sharkskin effect or melt fracture effect.

[0090] In one example, the viscosity of the 3D printable material changes from a first viscosity in a first printing phase with a first nozzle temperature TN1 to a second viscosity in a second printing phase with a second nozzle temperature within 50s. -1 The viscosity changes measured at shear rates range from 3000 to 300 Pa·s.

[0091] In the finished 3D object 1, the stack of layers 322 can take on various shapes and sizes. The stack of layers 322 can have at least 10 layers, at least 50 layers, or at least 100 layers. Which portion of the stack of layers 322 is printed using the first printing stage and which portion is printed using the second printing stage can also vary significantly depending on the implementation of the method. Some examples are described below, but it should be noted that those skilled in the art will be able to devise many more alternatives for printing a 3D object 1 using the method of the present invention.

[0092] In the most basic embodiment, the 3D object 1 consists of a stack of layers 322, wherein a first portion of the stack of layers 322 has been printed by depositing one or more layers of 3D printable material 201 during a first printing phase, and a second portion of the stack of layers 322 has been printed by depositing one or more layers of 3D printable material 201 during a second printing phase. Thus, a 3D object 1 is formed having one transition from the first printing phase to the second printing phase, thereby forming a 3D object 1 having, for example, a transparent lower portion and a diffuse upper portion.

[0093] The transition between the first printing phase and the second printing phase can also take place multiple times during the formation of the 3D object 1. In this way, for example, a striped appearance with glossy and matte areas can be obtained.

[0094] The transition between the first printing stage and the second printing stage can occur in a single step, directly from TN1 to TN2 and / or directly from FR1 to FR2. This forms a hard change in the optical properties from the first 3D printed material 210 to the second 3D printed material 220.

[0095] Figure 5A schematic diagram of an alternative embodiment is schematically shown. Here, the transition between the first printing phase and the second printing phase occurs gradually in multiple steps while depositing one or more layers. In this particular example, the nozzle temperature is reduced in four steps, starting from TN1 and ending at TN2. In other examples, the flow rate can be increased in several steps instead or in addition. The number of steps can be greater than 3, greater than 10, or greater than 100. In fact, the number of steps can be selected to provide essentially step-free adjustment between the first and second printing phases. The advantage of a gradual transition between printing phases is that the optical properties also gradually change while depositing one or more layers 322 in the stack of layers 322. Thus, for example, a 3D object 1 can be formed with a gradual transition from transparent to diffuse.

[0096] Figure 6a The schematic diagram illustrates an example in which the transition between the first printing phase and the second printing phase can be performed after depositing one or more complete layers 322 in a stack of layers 322 of 3D printed material 202. First, one or more layers 322 in the stack of layers 322 can be printed in the first printing phase. Subsequently, one or more layers 322 in the stack of layers 322 can be printed in the second printing phase. Thus, the transition between the first printing phase and the second printing phase occurs after depositing the first layer 322 and before depositing the adjacent second layer 322. Consequently, the interface between the first 3D printed material 210 and the second 3D printed material 220 is located between the two layers 322. This transition can be repeated multiple times to achieve the complete stack of layers 322 required to complete the 3D object 1. This transition can occur, for example, at every layer, every other layer, or every fifth layer. The number of layers 322 deposited before transitioning from one printing phase to another can be variable, thereby changing the number of layers at each transition.

[0097] Figure 6b The schematic diagram illustrates an example in which the transition between the first printing stage and the second printing stage is performed within a layer 322 in a stack of layers 322 of 3D printed material 202. Thus, the interface between the first 3D printed material 210 and the second 3D printed material 220 is located within layer 322. Each layer 322 has a portion printed in the first printing stage and a portion printed in the second printing stage. The transition between the first printing stage and the second printing stage can occur once within a single layer 322 in the stack of layers 322, or multiple times within a single layer 322 in the stack of layers 322. Adjacent layers 322 can have the same portion, or different portions. This allows for the formation of, for example, a 3D object 1 that is transparent on one side and diffuse on the other. More complex patterns, such as a checkerboard design or simple logos or pictograms embedded in the stack of layers 322, can also be achieved.

[0098] As described above, the critical shear rate depends on several factors. Therefore, for each configuration of the 3D printer 500 and each 3D printable material 201, the critical shear rate needs to be identified experimentally.

[0099] Figure 7 A basic flow chart depicts an example method for easily determining the critical shear rate in practice. Initially, 3D printable material 201 needs to be deposited at a nozzle temperature and flow rate. This first set of settings can be freely selected, but an example of a suitable first setting uses a first nozzle temperature and a first flow rate. These are typically standard printing conditions, perhaps even recommended by the manufacturer of the 3D printable material 201. The 3D printable material is deposited and observed to see if it prints above the critical shear rate. This can be easily assessed by observing sharkskin or melt fracture effects on the surface of the 3D printable material 201. If the 3D printable material 201 is not printing above the critical shear rate, the flow rate and / or nozzle temperature should be increased by a certain amount, which can also be freely selected. The 3D printable material 201 is deposited again under these new printing conditions and the sharkskin or melt fracture effects on the surface of the 3D printable material 202 are again examined. This process is repeated until the critical shear rate is reached. At this point, the current nozzle temperature is suitable as the second nozzle temperature for the second printing stage, and the current flow rate is suitable as the second flow rate.

[0100] Experiments with the method of the present invention were conducted in-house using several different thermoplastic polymers such as polycarbonate, polypropylene, and PHA.

[0101] Experiments were conducted using standard polycarbonate as the 3D printable material 201. The printer nozzle 502 had a nozzle diameter of 1.8 mm and a nozzle length of 2 mm. During the first printing phase, the first nozzle temperature was 290°C and the first flow rate was 4 g / s. During the second printing phase, the second nozzle temperature was selected to be 250°C, and the second flow rate was higher than 4 g / s.

[0102] By using these parameters and using transparent polycarbonate, it is possible to obtain a 3D object 1 having transparent and diffuse areas. Similarly, using white polycarbonate, it is possible to obtain a 3D object 1 having glossy and matte areas.

[0103] Experiments were also conducted using polypropylene. The printer nozzle 502 had a nozzle diameter of 1.8 mm and a nozzle length of 2 mm. During the first printing phase, the first nozzle temperature was 310° C., and the first flow rate was 1.3 g / s. During the second printing phase, the second nozzle temperature was selected to be 250° C., and the second flow rate was 2.4 g / s.

[0104] With these parameters, a 3D object 1 with shiny and matte areas can be obtained.

[0105] Figure 8 An example of a lamp or luminaire 2 is schematically depicted, comprising a light source 10 for generating light 11. The lamp 2 may comprise a housing or cover or other element, which may comprise or may be a 3D printed object 1. Here, a hemisphere (in the cross-sectional view) schematically indicates the housing or cover. The lamp or luminaire 2 may be or may comprise a lighting device 1000 (comprising the light source 10). Thus, the lighting device 1000 comprises a 3D object 1. The 3D object 1 may be configured as one or more of: (i) at least a portion of a lighting device housing, (ii) at least a portion of a lighting chamber wall, and (iii) an optical element. Thus, the 3D object 1 may reflect the light source light 11 and / or transmit the light source light 11. Here, the 3D object 1 may be, for example, a housing or cover.

[0106] It should be noted that the purpose of the above-described embodiments is to describe rather than limit the present invention, and that a person skilled in the art may design multiple alternative embodiments without departing from the scope of the appended claims. In the claims, any figure signs in brackets shall not be interpreted as limiting the claims. The use of the verb "comprise" and its variations does not exclude the presence of other elements or steps than those stated in the claim. The article "a" or "an" preceding an element does not exclude the presence of multiple such elements. The present invention can be implemented by means of hardware comprising several different elements and a suitably programmed computer. In a device claim that lists a plurality of means, a plurality of these means may be embodied by one and the same item of hardware. The fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to obtain an advantage.

[0107] The various aspects discussed in this patent can be combined to provide additional advantages. In addition, it should be understood by those skilled in the art that the embodiments can be combined, and more than two embodiments can also be combined.

Claims

1. A method for manufacturing a 3D object (1) by FDM printing, the method comprising: Deposit a 3D printable material (201) through a nozzle (502) having a nozzle temperature at a first flow rate to provide the 3D article (1), the 3D article including a stack of layers (322) of 3D printing material (202); wherein the 3D printable material (201) is a thermoplastic polymer having a weight average molecular weight greater than twice the entanglement molecular weight of the thermoplastic polymer; wherein the method further includes transitioning between a first printing stage and a second printing stage; wherein the first printing stage includes depositing the 3D printable material (201) to form a first 3D printing material (210), wherein the 3D printable material (201) is printed at a first nozzle temperature TN1 and a first flow rate FR1, thereby printing the 3D printable material (201) at a shear rate below a critical shear rate; and wherein the second printing stage includes depositing the 3D printable material (201) to form a second 3D printing material (220), wherein the 3D printable material (201) is printed at a second nozzle temperature TN2 and a second flow rate FR2, thereby printing the 3D printable material (201) at a shear rate above the critical shear rate.

2. The method according to claim 1, wherein The weight average molecular weight of the thermoplastic polymer is greater than 10,000 g / mol.

3. A method according to any one of the preceding claims, wherein The 3D printable material is selected from the group consisting of: polystyrene, polyacrylonitrile, acrylonitrile butadiene styrene (ABS), polyamide, polyacetate, polyester, polyacrylate, polyalkane, polycarbonate (PC), fluorinated polymers such as polyvinylidene fluoride (PVDF), polyurethane, and copolymers thereof.

4. A method according to any one of the preceding claims, wherein During the manufacture of the 3D article (1), the transition between the first printing stage and the second printing stage is performed multiple times.

5. A method according to any one of the preceding claims, wherein The transition between the first printing stage and the second printing stage is performed in a gradually transitioning manner such that the nozzle temperature and / or the flow rate is adjusted in multiple steps between TN1 and TN2 and / or between FR1 and FR2.

6. A method according to any one of the preceding claims, wherein The first 3D printing material (210) and the second 3D printing material (220) are printed using the same thermoplastic polymer.

7. The method according to any one of claims 1 to 6, wherein The transition between the first printing stage and the second printing stage is performed after depositing the first layer (322) in the stack of layers (322) of 3D printing material (202) and before depositing an adjacent second layer (322).

8. The method according to any one of claims 1 to 6, wherein The transition between the first printing stage and the second printing stage is performed within a layer (322) in the stack of layers (322) of 3D printing material (202).

9. A method according to any one of the preceding claims, wherein (i) TN2 < TN1 and FR2 = FR1, or (ii) TN2 = TN1 and FR2 > FR1.

10. A computer program product comprising instructions that, when executed by a computer functionally coupled to or included in a FDM printer (500), cause the FDM printer (500) to perform the method according to any one of claims 1 to 9.

11. A 3D object (1) obtainable by a method according to any one of claims 1 to 9.

12. The 3D article (1) according to claim 11, wherein The first 3D printing material (210) has a first surface (211), and the second 3D printing material (220) has a second surface (221), wherein the surface roughness amplitude of the first surface (211) is less than 1 micron, so that the first surface (211) has no shark skin effect or melt fracture effect, and wherein the surface roughness amplitude of the second surface (221) is greater than 1 micron, so that the second surface (221) exhibits a shark skin effect or melt fracture effect.

13. The 3D article (1) according to any one of claims 11 to 12, wherein The first 3D printing material (210) deposited during the first printing phase is transparent, and wherein the second 3D printing material (220) deposited during the second printing phase is light diffusing.

14. The 3D article (1) according to any one of claims 11 to 12, wherein The first 3D printing material (210) deposited during the first printing phase is specularly reflective, and wherein the second 3D printing material (220) deposited during the second printing phase is diffusely reflective.

15. A lighting device (1000) comprising a light source (10) and a 3D object (1) according to any one of claims 11 to 14, wherein: The 3D object (1) is configured as one or more of: (i) at least a portion of a lighting device housing, (ii) at least a portion of a wall of a lighting chamber, and (iii) an optical element.

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