权利要求：
CLAIMS:
1. A method for producing a 3D item (1) by means of fused deposition modelling, the method comprising a 3D printing stage using a fused deposition modeling 3D printer (500) for layer-wise depositing 3D printable material (201) to provide the 3D item (1) comprising a layer (322) of 3D printed material (202); wherein: the 3D printer (500) comprises an extruder section (510), a nozzle section (520) configured downstream of the extruder section (510), a first feeder (530), and a second feeder (540); wherein: the nozzle section (520) comprises a core-shell nozzle (502) comprising (i) a nozzle core (521), configured downstream of the extruder section (510), and (ii) a nozzle shell (522); the first feeder (530) is configured to feed particulate material (531) comprising a first 3D printable material (1201), to the extruder section (510), wherein the first 3D printable material (1201) comprises a first material (1211); the second feeder (540) is configured to feed a filament (320) comprising second 3D printable material (2201) to the nozzle shell (522), wherein the second 3D printable material (2201) comprises a second material (2211), different from the first material (1211); the 3D printing stage comprises: feeding the particulate material (531) to the extruder section (510) and feeding the filament (320) to the nozzle shell (522); generating a core-shell extrudate (321) via the core-shell nozzle (502) and; depositing the core-shell extrudate (321) to provide the 3D printed material (202) comprising a core (330) and a shell (340), at least partly enclosing the core (330), wherein the core (330) comprises the first material (1211), and wherein the shell (340) comprises the second material (2211).
2. The method according to claim 1, wherein the first material (1211) comprises a first thermoplastic material (351) and wherein the second material (2211) comprises a
second thermoplastic material (352) different from the first thermoplastic material (351); wherein the first material (1211) and wherein the second material (2211) differ in one or more of molecular weight of the thermoplastic material, viscosity, chemical composition, filler material, filler material concentration.
3. The method according to claim 2, wherein the first thermoplastic material (351) has a first average molecular weight Mn,i, and wherein the second thermoplastic material (352) has a second average molecular weight Mn,2, wherein the first average molecular weight Mn,i is selected from the range of 60000-500000 g/mol, and wherein the second average molecular weight Mn,2, is selected from the range of 10000-100000 g/mol; wherein l<Mn,i/Mn,2<50.
4. The method according to any one of the preceding claims 2-3, wherein the first thermoplastic material (351) has a first transition temperature Tt,i selected from a first glass transition temperature Tg,i and a first melting temperature Tm,i, wherein the second thermoplastic material (352) has a second transition temperature Tt,2 selected from a second glass transition temperature Tg,2 and a second melting temperature Tm,2, wherein the method comprises controlling a nozzle temperature Tn, wherein during at least part of the 3D printing stage Tn> Tt,i and Tn> Tt,2 applies.
5. The method according to any one of the preceding claims, wherein the first material (1211) comprises a first filler material (361) at a first volume percentage VI relative to the first material (1211), and wherein the second material (2211) optionally comprises a second filler material (362) at a second volume percentage V2 relative to the second material (2211), wherein the first volume percentage VI is selected from the range of 5-50 vol.%, wherein the second volume percentage V2 is selected from the range of 0-15 vol.%, and wherein 0<V2/Vl<0.5.
6. The method according to any one of the preceding claims, wherein the first material (1211) comprises a first filler material (361) at a first volume percentage VI relative to the first material (1211), and wherein the second material (2211) comprises a second filler material (362) at a second volume percentage V2 relative to the second material (2211), wherein the first filler material (361) and the second filler material (362) are different filler materials.
7. The method according to any one of the preceding claims, further comprising a control system (300), wherein the control system (300) is configured to control 3D printing conditions; wherein the 3D printing conditions are selected from the group of: (i) a first volumetric flow rate of the particulate material (531), (ii) a second volumetric flow rate of the filament (320), and (iii) a nozzle temperature Tnas defined in claim 4.
8. A 3D item (1) comprising 3D printed material (202), wherein the 3D item (1) comprises a layer (322) of 3D printed material (202), wherein the layer (322) comprises a core-shell cross-section, comprising a core (330) and a shell (340), at least partly enclosing the core (330), wherein the core (330) comprises a first material (1211), and wherein the shell (340) comprises a second material (2211), different from the first material (1211), wherein the core (330) has a first perimeter (pl) with first deviations (Rl) therefrom defining a first root mean square roughness RMS1, wherein the shell (340) has a second perimeter (p2) with second deviations (R2) therefrom defining a second root mean square roughness RMS2, wherein RMSl/RMS2<0.5.
9. The 3D item (1) according to claim 8, wherein the first material (1211) comprises a first thermoplastic material (351) and wherein the second material (2211) comprises a second thermoplastic material (352) different from the first thermoplastic material (351); wherein the first thermoplastic material (351) and wherein the second thermoplastic material (352) differ in one or more of molecular weight of the thermoplastic material, viscosity, chemical composition, filler material, filler material concentration.
10. The 3D item (1) according to any one of claims 8 and 9, wherein the first thermoplastic material (351) has a first transition temperature Tt,i selected from a first glass transition temperature Tg,i and a first melting temperature Tm,i, wherein the second thermoplastic material (352) has a second transition temperature Tt,2 selected from a second glass transition temperature Tg,2 and a second melting temperature Tm,2.
11. The 3D item (1) according to any one of claims 8 and 10, wherein the first material (1211) comprises a first filler material (361) at a first volume percentage VI relative to the first material (1211), and wherein the second material (2211) optionally comprises a second filler material (362) at a second volume percentage V2 relative to the second material
(2211), wherein the first volume percentage VI is selected from the range of 5-50 vol.%, wherein the second volume percentage V2 is selected from the range of 0-15 vol.%, and wherein 0<V2/Vl<0.5.
12. The 3D item (1) according to claim 9, wherein the first thermoplastic material (351) has a first average molecular weight Mn,i, and wherein the second thermoplastic material (352) has a second average molecular weight Mn,2, Mn,i Mn,2<50, wherein at least one of the first material (1211) and the second filler material (362) are selected from the group of glass and fibers.
13. A lighting device (1000) comprising the 3D item (1) according to any one of the preceding claims 8-12, wherein the 3D item (1) is configured as one or more of (i) at least part of a lighting device housing, (ii) at least part of a wall of a lighting chamber, and (iii) an optical element.
14. A fused deposition modeling 3D printer (500), comprising an extruder section (510), a nozzle section (520) configured downstream of the extruder section (510), a first feeder (530), a second feeder (540), and a control system (300); wherein the fused deposition modeling 3D printer (500) is configured to provide 3D printable material (201) to a substrate (1550), thereby providing a 3D item (1) comprising 3D printed material (202), wherein: the nozzle section (520) comprises a core-shell nozzle (502) comprising (i) a nozzle core (521), configured downstream of the extruder section (510), and (ii) a nozzle shell (522); the first feeder (530) is configured to feed particulate material (531) comprising a first 3D printable material (1201), to the extruder section (510); the second feeder (540) is configured to feed a filament (320) comprising second 3D printable material (2201) to the nozzle shell (522),; and the control system (300), wherein the control system (300) is configured to execute the method according to any one of the preceding claims 1-7.
15. The fused deposition modeling 3D printer (500) according to claim 14, wherein the control system (300) is configured to control 3D printing conditions; wherein the 3D printing conditions are selected from the group of: (i) a first volumetric flow rate of the
particulate material (531), (ii) a second volumetric flow rate of the filament (320), and (iii) a nozzle temperature Tn.