Mechanically stable core-shell FDM prints containing porous core
The invention provides a method for producing a 3D item by means of fused deposition modelling, the method comprising: (a) a 3D printing stage comprising: layer-wise depositing 3D printable material, wherein the 3D printable material comprises 3D printable core material and 3D printable shell material, to provide the 3D item comprising a core-shell layer of 3D printed material, wherein the 3D printed material comprises a core comprising 3D printed core material and a shell comprising 3D printed shell material, wherein the shell at least partly encloses the core, wherein the 3D printable core material comprises a pore forming material with a first concentration c 1 , wherein the 3D printable shell material comprises the pore forming material with a second concentration c 2 , wherein c 2 /c 1 ≤0.9; and (b) a pore forming stage comprising: heating one or more of (i) the printable material and (ii) the 3D printed material.
1 . A method for producing a 3D item by means of fused deposition modelling, the method comprising:
a 3D printing stage comprising: layer-wise depositing 3D printable material, wherein the 3D printable material comprises 3D printable core material and 3D printable shell material, to provide the 3D item comprising a core-shell layer of 3D printed material, wherein the 3D printed material comprises a core comprising 3D printed core material and a shell comprising 3D printed shell material, wherein the shell at least partly encloses the core, wherein the 3D printable core material comprises a pore forming material with a first concentration c 1 , wherein the 3D printable shell material comprises the pore forming material with a second concentration c 2 , wherein c 2 >0 and c 2 /c 1 ≤0.9; and
a pore forming stage comprising: heating one or more of (i) the printable material and (ii) the 3D printed material.
2 . The method according to claim 1 , wherein c 2 /c 1 ≤0.01, and wherein c 2 ≤0.04 wt %, and wherein c 1 ≥0.04 wt %.
3 . The method according to claim 1 , wherein the shell of the core-shell layer of the 3D printed item has a shell width (W 2 ), wherein the core-shell layer has a layer width (W); wherein 0.01≤W 2 /W<0.3, and wherein a first porosity p 1 of the core of the core-shell layer is in the range 5-40 vol. %.
4 . The method according to claim 1 , wherein the pore forming material has a boiling temperature, and wherein the method comprises 3D printing the 3D printable material with a nozzle temperature higher than the boiling temperature.
5 . The method according to claim 1 , selecting the pore forming material, the first concentration c 1 , the second concentration c 2 , and 3D printing conditions such that a density reduction of the core-shell layer of more than 10% is obtained, compared to the theoretical maximum density that is obtained when no pore forming material was incorporated in the 3D printable material.
6 . The method according to claim 1 , wherein the core and shell are the same thermoplastic material.
7 . The method according to claim 1 , wherein the pore forming material comprises water and wherein the pore forming stage comprises applying one or more of (i) microwave radiation and (ii) ultrasound.
8 . The method according to claim 1 , wherein the pore forming material in the core printable material and the pore forming material in the shell printable material are one of (i) the same pore forming material or the same pore forming materials at the same ratios, (ii) the same pore forming materials at different ratios, or (iii) different pore forming materials; wherein the pore forming material in the core printable material has a boiling point above room temperature.