3D PRINTING SYSTEM FOR PREPARING A THREE-DIMENSIONAL OBJECT WITH AN AUTOCLAVE

Abstract

A three-dimensional printing system for preparing a three-dimensional object made at least partially of an expanded polymer includes an autoclave, a printing device and a three-dimensional movement device. The printing device prepares an expandable polymer melt and deposits a strand of the expandable, expanding or expanded polymer onto a surface. The three-dimensional movement device adjusts the position of the printing device in a predefined three-dimensional matrix so as to enable depositing of the strand of expandable, expanding or expanded polymer at a predetermined time at a precise position within the three-dimensional matrix. The printing device includes a feed section, a cooling section, a backflow prevention section, a heating section and a terminal printing head section including a die for depositing the expandable, expanding or expanded polymer strand onto the surface.

Claims

1. A three-dimensional printing system for preparing a three-dimensional object made at least partially of an expanded polymer, comprising: an autoclave; a printing device configured to prepare an expandable, expanding or expanded polymer melt and deposit a strand of the expandable, expanding or expanded polymer onto a surface; and a three-dimensional movement device configured to enable depositing of the strand of expandable, expanding or expanded polymer at a predetermined time at a position within the three-dimensional matrix, the printing device comprising: a feed section, a cooling section, a backflow prevention section, a heating section, and a terminal printing head section including a die configured to deposit the expandable, expanding or expanded polymer strand onto the surface.

2. The three-dimensional printing system in accordance with claim 1, wherein the autoclave is configured to resist a pressure of up to 150 bar and a temperature of up to 300° C.

3. The three-dimensional printing system in accordance with claim 1, wherein the autoclave is connected directly or indirectly with the feed section of the printing device so that an expandable polymer mixture prepared in the autoclave is capable of being transferred from the autoclave directly or indirectly into the feed section of the printing device.

4. The three-dimensional printing system in accordance with claim 3, wherein the autoclave is connected directly with the feed section of the printing device so that an expandable polymer mixture prepared in the autoclave is capable of being transferred from the autoclave directly into the feed section of the printing device.

5. The three-dimensional printing system in accordance with claim 3, wherein a conveyor is arranged between the autoclave and the feed section of the printing device, so that the expandable polymer mixture prepared in the autoclave can be transferred from the autoclave via the conveyor into the feed section of the printing device.

6. The three-dimensional printing system in accordance with claim 1, wherein at least one of the feed section, the cooling section, the backflow prevention section and the heating section are tubular sections having a same inner diameter as at least one of an other of the feed section, the cooling section, the backflow prevention section and the heating section.

7. The three-dimensional printing system in accordance with claim 1, wherein the feed section, the cooling section, the backflow prevention section, the heating section and the printing head section are arranged in this order from an upstream end to a downstream end of the printing device.

8. The three-dimensional printing system in accordance with claim 1, wherein the cooling section or the heating section or the cooling section and the heating section are a tubular section comprising a tube, and a Peltier element, a heat exchanger or cooling fins are disposed on an outer wall of the tube.

9. The three-dimensional printing system in accordance with claim 1, wherein the backflow prevention section is a tubular section, an inner diameter of at least a part of a length of the tubular section is smaller than an inner diameter of the cooling section and the heating section.

10. The three-dimensional printing system in accordance with claim 1, wherein the printing head section is a tapered tubular section, the downstream part of the printing head section is tapered so as to form the die, and the upstream part of the printing head section has a same inner diameter as at least one of the feed section, the cooling section the backflow prevention section and the heating section.

11. A method, comprising: performing three-dimensional printing with the three-dimensional printing system in accordance with claim 1 to prepare the three-dimensional object made at least partially of an expanded polymer.

12. The method in accordance with claim 11, wherein the performing three-dimensional printing includes providing polymer in the form of beads or filaments, impregnating the polymer in the autoclave with a blowing agent at a temperature below a melting point of the polymer and at a pressure of 2 to 50 MPa for 1 minute to 48 hours so as to provide an expandable polymer mixture, transferring the expandable polymer mixture into the feed section of the printing device, cooling the expandable polymer mixture in the printing device, e) heating the expandable polymer mixture in the printing device so as to obtain the expandable, expanding or expanded polymer melt, and f) shaping, depositing and foaming the expandable, expanding or expanded polymer melt by extrusion through the die of the printing device.

13. The method in accordance with claim 11, wherein the polymer is selected from the group consisting of thermoplastic polyurethanes, polyolefins, polyesters, ethylene vinylacetate copolymers, ethylene butyl acrylate copolymers, polystyrenes, polylactic acids, thermoplastic elastomers, nitrile rubbers, copolymers of acrylonitrile and butadiene, polychloroprenes, polyimides, polyvinyl chlorides and arbitrary combinations of two or more of the aforementioned polymers.

14. The method in accordance with claim 12, wherein the blowing agent is a physical blowing agent.

15. A three-dimensional object being obtained by the method in accordance with claim 11.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0052] The invention will be explained in more detail hereinafter with reference to the drawings.

[0053] FIG. 1 shows a schematic cross-section of a printing device for preparing an expandable polymer melt and for depositing a strand of the expandable, expanding or expanded polymer onto a surface of a 3D printing system for preparing a three-dimensional object made at least partially of an expanded polymer in accordance with one exemplary embodiment of the present invention.

[0054] FIG. 2 shows two rectangular slabs printed from TPU as described in the examples and comparative examples.

[0055] FIG. 3 shows a scanning electron microscope (SEM) scan of a cut through the upper object of FIG. 2.

[0056] FIG. 4 shows a SEM scan of a cut through the bottom object of FIG. 2.

[0057] FIG. 5 shows two printed circles.

[0058] FIG. 6 shows a SEM scan of a cut through the left object of FIG. 5.

[0059] FIG. 7 shows a SEM scan of a cut through the right object of FIG. 5.

[0060] FIG. 8 shows two cubes printed with PLA filament.

[0061] FIG. 9 shows a SEM scan of a cut through the left object of FIG. 8.

[0062] FIG. 10 shows a SEM scan of a cut through the right object of FIG. 8.

[0063] FIG. 11 shows two squares consisting of only one layer of printed strands.

[0064] FIG. 12 shows a SEM scan of the surface of the left object of FIG. 11.

[0065] FIG. 13 shows a SEM scan of the cross-section of the left object of FIG. 11.

[0066] FIG. 14 shows a SEM scan of the surface of the right object of FIG. 11.

[0067] FIG. 15 shows a SEM scan of the cross-section of the right object of FIG. 11.

DETAILED DESCRIPTION

[0068] The printing device 10 shown in FIG. 1 comprises from its upstream end 12 to its downstream end 14 the following sections in this order: [0069] a) a feed section 16, [0070] b) a cooling section 18, [0071] c) a backflow prevention section 20, [0072] d) a heating section 22 and [0073] e) a terminal printing head section 24 including a die 26 for depositing the expandable, expanding or expanded polymer strand onto the surface.

[0074] While the feed section 16 is the upstream tubular end section of the printing device 10, the cooling section 18 is embodied as tubular section provided on the outer wall thereof with cooling fins. The heating section 22 is a tubular section comprising Peltier elements on the outer tube wall, whereas the backflow prevention section 20 comprises three O-rings 28, which are arranged, spaced from each other, over the lengths of the tube, wherein each of the O-rings 28 reduces the inner diameter of the tube compared to the areas of the tube being free from the O-rings 28ings.

[0075] During operation, a method for preparing a three-dimensional object made at least partially of an expanded polymer is performed, which comprises the following steps: [0076] a) providing beads or filaments of a polymer, [0077] b) impregnating the beads or filaments provided in step a) in an autoclave with a blowing agent at a temperature below the melting point of the polymer and at a pressure of 2 to 50 MPa for 1 minute to 48 hours and preferably for 1 to 24 hours, [0078] c) transferring the impregnated beads or filaments provided in step b) into the feed section of the printing device, [0079] d) cooling the beads or filaments in the printing device, [0080] e) heating the beads or filaments in the printing device so as to obtain an expandable polymer melt, and [0081] f) shaping, depositing and foaming the expandable polymer melt by extruding it through the die of the printing device.

[0082] Subsequently, the present invention is further illustrated by non-limiting examples and comparative examples.

Examples 1 to 4 and Comparative Examples 1 to 4

Equipment and Process Parameters

[0083] A 3D printer with an autoclave in accordance with embodiments of the present patent disclosure was used. Commercially available filament was impregnated the autoclave with the conditions given in Table 1. Then the filament containing the blowing agent was printed with the 3D printer equipped with a 0.4 mm printing nozzle.

[0084] Filament TPU: NinjaflexTPU 3DNF0817505 1.75 mm, transparent

[0085] Filament PLA: PLA Natural Transparent 2.85 mm, from Verbatim

TABLE-US-00001 TABLE 1 Processing conditions and printing results for impregnated filament Sol. Sol. Sol. Extrusion Extrusion Cell Blowing Temp Time Pressure temp speed Printed Weight size Case Polymer agent [° C.] [h] [bar] [° C.] [mm/min] shape reduction [um] Figures CE1 TPU no na na 230 15 Rectangular na FIG. 2, slab FIG. 3 Ex. 1 TPU CO.sub.2 30 1 30 230 15 * 0.6 Rectangular 30% 10 - 50 FIG. 2, slab FIG. 4 CE2 TPU No na Na na 210 - 230 15 Circle Na FIG. 5, FIG. 6 Ex. 2 TPU CO.sub.2 30 1 40 210 - 230 15 * 0.6 Circle 20% 30 - 60 FIG. 5, FIG. 7 CE3 PLA no na Na na 220 20 Cube FIG. 8, FIG. 9 Ex. 3 PLA CO.sub.2 70 2 40 220 20 * 0.6 Cube 45% 50 FIG. 8, FIG. 10 CE4 PLA No na na Na 220 20 Monolayer FIG. 11, FIG. 12, FIG. 13 Ex. 4 PLA CO.sub.2 70 2 40 220 20 * 0.6 Monolayer 50 - 100 FIG. 11, FIG. 14, FIG. 15 CE—Comparative Example Ex.—Example

Results

Rectangular Slab TPU

[0086] In FIG. 2 two rectangular slabs printed from TPU are shown. Case 1 (above) was printed with an untreated filament, while Case 2 (below) was printed with the same filament but it was impregnated in the autoclave. Both objects were printed with the same print head temperature. The difference in optical appearance was directly related to the fact that the object below was printed with a foaming filament. The solid TPU was clear and slightly yellow while the foamed TPU appears white. To print both objects shown in FIG. 2 the same movement of the printing nozzle was used. For the print with the impregnated nozzle the extrusion speed of the filament was multiplied with a factor of 0.6. Although both objects have the same geometry, using the impregnated filament resulted in a weight reduction of the object of 30%.

[0087] FIG. 3 shows a scanning electron microscope (SEM) scan of a cut through the upper object. The cut was done along the blue line in FIG. 1. An object made by a 3D printer can always contain void spaces depending on the pattern with of the filament extrusion. It is clearly visible in FIG. 3 that the rectangular slab printed with an untreated filament has such void surfaces. But it is important to note that the strand which was laid down by the printing head was indeed made of solid material. On the other hand, the strands of the filament which was impregnated with CO2 in the autoclave contain clearly bubbles as shown in FIG. 4. The SEM scan in FIG. 4 shows the cross section of the foamed rectangular slab at the bottom of FIG. 2.

[0088] FIG. 5 shows two printed circles where the left circle was printed with untreated TPU filament and the right circle was printed with TUP filament impregnated in the autoclave. Again the foamed structure of the right object is visible because the top layer appears white and not transparent as the top layer of the left object. SEM scans along the line indicated in FIG. 5 are shown in FIG. 6 (not foamed) and FIG. 7. As described earlier it is clear that the untreated filament leads to solid strands which were partially surrounded by void areas while the in the strands from the impregnated filament there were also bubbles in the middle of the strand. Again the extrusion speed of the impregnated filament was reduced by a factor of 0.6 and the same movement of the printing nozzle was used for both objects. The foamed circle weights 20% less than the solid circle.

[0089] During the printing of the foamed circle (FIG. 5 right), the temperature of the melting section and the nozzle was varied. The printing was started with 210° C. and then increased to 230° C. before it was reduced to 210° C. again. The result is visible in the SEM scan in FIG. 7. A printing temperature of 210° C. is apparently too low to achieve a good foaming of the impregnated filament. In the middle of the object there were more bubbles indicating that the foaming works better at 230° C. This example serves to illustrate that the foam structure can be influenced by adjusting the printing temperature.

[0090] Two cubes printed with PLA filament are displayed in FIG. 8. The left cube was printed with untreated filament for the right cube a filament impregnated in the autoclave as described in the patent application was used. Visible that the right cube includes foam (obaque, white) while the left cube was printed from solid polymer (glossy, transparent).

[0091] SEM cross sections of the PLA cubes are shown in FIG. 9 (not foamed) and FIG. 10 (foamed). Again the bubbles in the printed strands is clearly visible in FIG. 10, while the polymer in the strand in FIG. 9 is homogenous.

PLA Monolayer

[0092] Two squares consisting of only one layer of printed strands are displayed in FIG. 11. In the monolayer objects it is better visible that the not foamed polymer (right) was transparent, and the foamed object was opaque and white. SEM scans of the surface of the not foamed monolayer square are given in FIG. 12 and the same surface of the foamed object is shown in FIG. 14. SEM scans of the cross section as indicated by the lines in FIG. 11, are given in FIG. 13 and FIG. 15, for the not foamed and the foamed PLA, respectively.

Process Remarks

[0093] In all the performed example the foaming process was stable; the polymer filament foamed constantly as function of time, without visible change in size and/or flow rate. The cross section of the 3D printed foamed objects (i.e. FIG. 4, FIG. 7, FIG. 10, FIG. 14 and FIG. 15) show a constant diameter of the foamed filament that is a good evidence of a stable foaming process.

[0094] The dimensional precision on the final object was not, visually, affected by the foaming process. In order to compensate the decrease of density, it was decreased the flow rate during printing the foamed object.

[0095] Good adhesion among the layers in the foamed objects was confirmed by the SEM pictures.