3D PRINTING SYSTEM FOR PREPARING A THREE-DIMENSIONAL OBJECT

Abstract

A three-dimensional printing system for preparing a three-dimensional object made at least partially of an expanded polymer includes a printing device configured to prepare an expandable polymer melt and deposit a strand of expandable, expanding or expanded polymer onto a surface and a three-dimensional movement device for 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 at an upstream end of the printing device, a heating section, a pressurizing section, a blowing agent supply line, a mixing section, a cooling section and a terminal printing head section at a downstream end of the printing device including a die configured to deposit the strand of the expandable, expanding or expanded polymer 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: a printing device configured to prepare an expandable polymer melt and deposit a strand of 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 precise position within the three-dimensional matrix, the printing device comprising a feed section at an upstream end of the printing device, a heating section, a pressurizing section, a blowing agent supply line, a mixing section, a cooling section and a terminal printing head section at a downstream end of the printing device including a die configured to deposit the strand of the expandable, expanding or expanded polymer onto the surface, the mixing section and the cooling section arranged downstream of the feed section, of the heating section and of the pressurizing section, the blowing agent supply line having one or more discharge end connected with one or more of the pressurizing section, the mixing section or the cooling section, the cooling section being a tubular section, which comprises a tube, and a Peltier element, a resistance heater, a heat exchanger or cooling fins disposed on an outer wall of the tube, and the pressurizing section comprising a piston compressor, a screw compressor or a gear compressor.

2. The three-dimensional printing system in accordance with claim 1, wherein at least the sections are tubular sections having the same inner diameter, which is between 1 and 10 mm.

3. The three-dimensional printing system in accordance with claim 1, wherein the feed section, the heating section, the pressurizing section, the mixing section, cooling section and the printing head are arranged in this order from the upstream end to the downstream end of the printing device, or the feed section, the heating section, the pressurizing section, the mixing section, cooling section and the printing head are arranged from the upstream end to the downstream end of the printing device in the following order: feed section followed by the pressurizing section followed by the heating section followed by the mixing section followed by the cooling section followed by the printing head section, or the feed, heating and pressurizing sections are combined into one section, which is followed by the mixing section which is followed by the cooling section which is followed by the printing head section.

4. The three-dimensional printing system in accordance with claim 1, wherein the heating section is a tubular section comprising a tube, and cooling fins are disposed on the outer wall of the tube.

5. The three-dimensional printing system in accordance with claim 1, wherein a wall of the pressurizing section comprises a heating element, which is a Peltier element, a resistance heater or a heat exchanger.

6. The three-dimensional printing system in accordance with claim 1, wherein the cooling section is arranged downstream of the mixing section, and the blowing agent supply line has one discharge end, which is connected with the mixing section.

7. The three-dimensional printing system in accordance with claim 1, wherein the cooling section is arranged upstream of the mixing section, and the blowing agent supply line has one discharge end, which is connected with the cooling section or with the mixing section.

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

9. A method for preparing a three-dimensional object made at least partially of an expanded polymer, the method comprising: preparing the object in the three-dimensional printing system in accordance with claim 1.

10. The method in accordance with claim 9, wherein the method comprises: melting the polymer so as to obtain the polymer melt, pressurizing the polymer melt so as to obtain a pressurized polymer melt, dosing at least one blowing agent into the pressurized polymer melt so as to obtain an expandable pressurized polymer melt, homogenizing the expandable pressurized polymer melt by passing the polymer melt through at least one mixer and by passing the polymer melt through at least one static mixer so as to obtain a homogenized expandable pressurized polymer melt, cooling the homogenized, expandable pressurized polymer melt so as to obtain a cooled homogenized expandable pressurized polymer mixture, and f) shaping, depositing and foaming the cooled homogenized expandable pressurized polymer mixture by extruding the cooled homogenized expandable pressurized polymer mixture through the die of the printing device.

11. The method in accordance with claim 9, wherein at least one nucleating agent is added to the polymer, and the at least one nucleating agent is added before the melting the polymer or after the melting the polymer, but before the homogenizing the expandable pressurized polymer melt, or before the melting the polymer and after the melting the polymer, but before the homogenizing the expandable pressurized polymer melt.

12. The method in accordance with claim 9, 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.

13. The method in accordance with claim 9, wherein the blowing agent is a physical blowing agent.

14. The method in accordance with claim 9, wherein the expandable pressurized polymer melt has a temperature of 60 to 270° C. and is pressurized to 2 to 50 MPa.

15. (canceled)

Description

BRIEF DESCRIPTION OF DRAWINGS

[0067] The invention will be explained in more detail hereinafter with reference to the drawings.

[0068] 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.

[0069] FIG. 2 shows a square monolayer of PET obtained in example 1.

[0070] FIG. 3 shows the two PET cubes obtained in example 2.

[0071] FIG. 4 shows magnified pictures of the strand which was extruded through the printing nozzle in example 2.

DETAILED DESCRIPTION

[0072] 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: [0073] i) a feed section 16, [0074] ii) a cooling section 18 [0075] iii) a heating section 20, [0076] iv) a pressurizing section 22, [0077] v) a mixing section 24, [0078] vi) a cooling section 28 and [0079] vii) a terminal printing head section 30 at the downstream end of the printing device including a die 32 for depositing the strand of expandable, expanding or expanded polymer onto the surface
wherein a blowing agent supply line 26 having a discharge end is provided, which is connected with the upper part of the mixing section 24.

[0080] While the feed section 16 is the upstream tubular end section of the printing device 10, the cooling section 18 is embodied as a tubular section disposed on the outer wall thereof with cooling fins. The heating section 20 is a tubular section comprising Peltier elements on the outer tube wall, whereas the pressurizing section 22 comprises a screw compressor. The mixing section 24 is a tubular section comprising a static mixer, whereas the cooling section 28 is a tubular section, the outer wall thereof being provided with Peltier elements.

[0081] 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: [0082] i) feeding a polymer into the feed section 16, [0083] ii) cooling the polymer in the cooling section 18 so as to avoid a melting already in the feed section 16, [0084] iii) melting the polymer in the heating section 20 so as to obtain a polymer melt, [0085] iv) pressurizing the polymer melt in the pressurizing section 22 so as to obtain a pressurized polymer melt, [0086] v) dosing at least one blowing agent through the gas supply line 26 into the pressurized polymer melt in the upstream part of the mixing section 24 so as to obtain an expandable pressurized polymer melt, [0087] vi) homogenizing the expandable pressurized polymer melt by passing it through the mixer provided in the mixing section 24 so as to obtain a homogenized expandable pressurized polymer melt, [0088] vii) cooling the homogenized, expandable pressurized polymer melt in the cooling section 28 so as to obtain a cooled homogenized expandable pressurized polymer mixture and [0089] viii) shaping, depositing and foaming the cooled homogenized expandable pressurized polymer mixture by extruding it through the die 32 of the printing head section 30 of the printing device 10.

[0090] Subsequently, the present invention is further illustrated by non-limiting examples.

Example 1

[0091] The hot end (printing head) of a 3D printer was constructed in accordance with an embodiment of the present disclosure to directly solubilize blowing agent into the molten polymer. The inner diameter of the melting section was 1.7 mm. The blowing agent was pumped by means of a HPLC pump into the blowing agent supply line. The mixture of molten polymer and blowing agent passed through a static mixer (4 elements of SMX DN3), where the blowing agent was homogenized with the polymer. Finally, the impregnated melt passed through a standard 0.4 mm printing nozzle. The melting section and the blowing agent injection were heated by an electrically heated aluminum block, while the static mixer was cooled by an aluminum block without heating cartridge (heat dissipation to the environment). Both heating blocks were heated to the same temperature.

[0092] The printing conditions were as follows:

Filament: Pro Fill PET from 3D-Printerstore.ch
Printing temperature: 205° C.
Extrusion speed: 15 mm/min (times 0.6 with blowing agent)
Blowing agent: Acetone (0.005 ml/min)
Blowing agent content (17% w/w)

[0093] FIG. 2 displays a square monolayer of PET. The printing proceeded from the outside to the inside, i.e. the outer rounds of strand were laid down first. During the third round the blowing agent flow was started and the extrusion speed reduced by 40%. The strand of the first two round were transparent and clear, while the next strands clearly contain bubbles caused by the blowing agent.

[0094] In the performed test, the foaming process was stable; the polymer filament foamed constantly as function of time, without visible change in size and/or flow rate.

[0095] The dimensional precision on the final object was not visually affected by the foaming process. In order to compensate the decrease of density, the flow rate was decreased during printing the foamed object.

[0096] A good adhesion among the layers in the foamed objects was observed and could be confirmed by squeezing the foamed objects manually.

Example 2

[0097] Two PET cubes printed with the same printing nozzle movement were shown in FIG. 3. The left cube was printed without adding blowing agent while the right cone was printed with 17% blowing agent and a filament extrusion speed reduced by a factor of 0.6. The foamed cube was 35% lighter than the cube printed without blowing agent. As in the monolayer above the bubbles in the strands were visible.

[0098] FIG. 4 shows magnified pictures of the strand which was extruded through the printing nozzle. On the right PET filament was extruded without adding a blowing agent with an extrusion speed of 15 mm/min. The strand was clear and homogeneous, there were no bubbles visible. On the left the PET was extruded with 9 mm/min and acetone as blowing agent was added. Due to the blowing agent the strand was now containing bubbles, i.e. it was foamed.

[0099] In the performed test the foaming process was stable; the polymer filament foamed constantly as function of time, without visible change in size and/or flow rate.

[0100] The dimensional precision on the final object was not visually affected by the foaming process. In order to compensate the decrease of density, the flow rate was decreased during printing the foamed object.

[0101] A good adhesion among the layers in the foamed objects was observed and could be confirmed by squeezing the foamed objects manually.