WO2011092269A2

WO2011092269A2 - Continuous extrusion of thermoplastics

Info

Publication number: WO2011092269A2
Application number: PCT/EP2011/051181
Authority: WO
Inventors: Kim Ragaert; Ludwig Cardon; Marcel Moerman
Original assignee: Universiteit Gent; Hogeschool Gent
Priority date: 2010-01-29
Filing date: 2011-01-28
Publication date: 2011-08-04
Also published as: WO2011092269A3; GB201001502D0

Abstract

The present invention provides a dispense head system (10) and method for continuous extrusion of thermoplastic materials, e.g. into filaments or fibres. The dispense head system (10) comprises - an input section (40) for receiving the thermoplastic material in granular or powder form, - a feed pipe (50) for transporting the thermoplastic material received in the input section towards an output port (300) of the feed pipe (50), - a heatable barrel (13) for receiving transported thermoplastic material from the feed pipe (50) and rendering it viscous, and - an output (EP) to the heatable barrel for extrusion of the viscous thermoplastic material. In embodiments of the present invention, the dispense head system (10) furthermore comprises a transfer zone (TZ) located at the output port (300) of the feed pipe (50) and adapted for controlled preheating of the thermoplastic material.

Description

Continuous extrusion of thermoplastics

Field of the invention

The present invention relates to extrusion of thermoplastic materials, more particularly to a dispense head system for continuous extrusion of thermoplastic materials, to an extrusion device for extruding thermoplastic material, to a method for continuous extrusion of thermoplastic materials into extruded thermoplastic material, such as e.g. filaments or fibres, and to use of the method and devices according to embodiments of the present invention.

The extruded thermoplastics may be used for example in 3D plotting Background of the invention

The family of FDA-approved biodegradable poly(a-hydroxy-esters) which includes poly-(lactic acid) (PLA), poly-(glycolic acid) (PGA) and poly-(e-caprolacton) (PCL) and their copolymers, finds wide application as scaffold material tissue engineering (TE). Susceptible to chain scission by hydrolysis, they degrade in the human body into non-toxic waste products in a period of a month to several years. Copolymerization and variations in chain length allow for a broad range of mechanical properties and in vitro/in vivo degradation characteristics.

Being semi-crystalline or amorphous thermoplastic polymers, this class of materials can be processed in their pure form by heating into melt and subsequent shaping, after or during which the polymer will solidify again. This is the case for extrusion, injection moulding and solid freeform (SFF) techniques like fused deposition modelling (FDM). Most other processing techniques (solvent casting, phase separation, electrospinning, gel formation,...) involve the use of a solvent of some sort.

Of interest is the layer wise technique of 3D plotting by micro-extrusion. The two main components to micro-extrusion are the spatial control (xyz ) unit and the dispense head. The spatial control unit is typically very precise and operates under software. The dispense head is connected to the positioning unit. The dispense head is where the actual processing of the polymer takes place. Raw material is inserted into a hopper as granulate or powder. It is heated into melt and pushed along a feeding channel by pressurized air. The feeding channel leads the material to an auger-type screw, which transports the melt forward. Eventually it is extruded as a thin length of extruded thermoplastic material, e.g. a filament or a fibre, the size of which depends on the mounted needle. This extruded thermoplastic material is deposited on the plotting table according to the pattern described by the spatial control unit, thus forming a single layer of the scaffold. This is repeated for all the subsequent layers of the product, until the 3D geometry is completed. Typical values of diameter size of extruded thermoplastic material are 100 to 500 μιτι, classifying this technique in the micro- range, whereas electrospinning would feature on the nano-scale. Although methods and devices for 3D plotting exist, there is room for improved methods and devices.

Summary of the invention

It is an object of embodiments of the present invention to provide a good dispense head system for continuous extrusion of thermoplastic materials. It is another object of embodiments of the present invention to provide a good method for continuous extrusion of thermoplastic materials into extruded thermoplastic material, such as e.g. filaments or fibres. Filaments are defined as filled cylindrical pieces of material. Fibres may be continuous lengths of material or discrete elongated pieces of material. They may be hollow or filled. They may have any suitable shape in cross-section, such as for example circular.

The above objectives are accomplished by a method and device according to embodiments of the present invention.

Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims.

In a first aspect, the present invention provides a dispense head system for continuous extrusion of thermoplastic materials, such as e.g. biodegradable, biocompatible or bioinert materials, such as for example PLA. The extrusion of the thermoplastic material is into continuous or discrete lengths of thermoplastic material, such as e.g. into filaments or fibres. The dispense head system comprises

- an input section for receiving the thermoplastic material in granular or powder form,

- a feed pipe for transporting the thermoplastic material received in the input section towards an output port of the feed pipe,

- a heatable barrel for receiving transported thermoplastic material from the feed pipe and rendering it viscous, and

- an output to the heatable barrel for extrusion of the viscous thermoplastic material.

In embodiments of the present invention, the dispense head system furthermore comprises a transfer zone located at the output port of the feed pipe and adapted for controlled preheating of the thermoplastic material.

It is an advantage of embodiments of the present invention that the transfer zone located at the output port of the feed pipe provides a controlled preheating of the thermoplastic material. On the one hand, this pre-heating allows thermoplastic material in granular of powder form larger than relevant dimensions of the heatable barrel to pass therein anyway, because due to the pre-heating the thermoplastic material may be deformed and hence pushed into the heatable barrel in a deformed state. On the other hand, the pre-heating, due to it being controlled, is limited to the transfer zone, so that material not yet to be used is not heated yet, and the degradation of the material under heat effects is thus reduced. Material to be processed is heated only just prior to its processing.

It is an advantage of the transfer zone that it provides improved heat control. It provides an increased heat transport, so that material fed by the feed pipe and kept there in cold state, is preheated to some extent, hence made somewhat supple. In preferred embodiments such transfer zone applies heat only to material being transported to the heatable barrel, hence to material already dedicated for being processed. In a dispense head system according to embodiments of the present invention, the feed pipe may be made from any of a titanium alloy, steel, stainless steel, low-carbon stainless steel, or any other suitable material which is easy to clean. In alternative embodiments, the feed pipe may be an internal channel, for example a bore, for example a cylindrical bore, in a central assembly block of the dispense head system.

In a dispense head system according to embodiments of the present invention, the barrel is made from a material which is inert with respect to biomedical materials. This prevents contamination of material, especially when used to extrude materials for use in biomedical applications. The barrel may for example be made from any of stainless steel or Ti.

A dispense head system according to embodiments of the present invention may furthermore comprise a needle coupled to the output of the heatable barrel, for extrusion of continuous or discrete lengths of thermoplastic material, such as e.g. filaments or fibres of thermoplastic material. A dispense head system according to embodiments of the present invention may furthermore comprise a heat conductive coating around the needle. This provides heat control: heat from the barrel may be fed to the needle so that the needle is at an elevated temperature. This is different from prior art systems where the needle is at a lower temperature than the barrel, the needle being cooled by surrounding air. Heating the needle with heat of the barrel avoids a temperature overshoot needing to be applied to the material in the barrel just before the needle. The heat conductive coating around the needle may be made of any of copper, a copper alloy, aluminum, an aluminum alloy, or any other suitable heat conductive material.

In a dispense head system according to embodiments of the present invention, the transfer zone may comprise first heating elements for controlled pre-heating of the thermoplastic material.

As an example, the first heating elements may comprise at least one, for example a plurality of heating spokes, for example at least three heating spokes, arranged in a cross-sectional plane of the transfer zone. The spokes may be provided with or connected to a controller for controlling the heating of the spokes.

Alternatively, the first heating elements may comprise a feed cap covering the output port of the feed pipe and having a surface in thermal contact with the heatable barrel. The feed cap may be a cap of heat conductive material. Hence, the transfer zone may be surrounded by a layer of heat conductive material.

In yet alternative embodiments, the first heating elements may be provided around the transfer zone, e.g. at the outer side thereof.

In embodiments of the present invention, the first heating elements may comprise at least one internal channel for funnelling the thermoplastic material towards an input port of the heatable barrel.

A dispense head system according to embodiments of the present invention may furthermore comprise an interruption device for interrupting a continuous flow of thermoplastic material towards heated zones, e.g. in particular the transfer zone, of the dispense head system. It is an advantage of embodiments of the present invention that the thermoplastic material flow is interrupted before the material reaches a heated zone. This implies that material not yet to be used is not heated yet, and degradation of the material under heat effects is thus reduced. Material to be processed is heated only just prior to its processing.

In a dispense head system according to embodiments of the present invention, wherein the feed pipe is a horizontal pipe adapted for receiving a predetermined amount of thermoplastic material in granular or powder form from the input section, the means for interrupting a continuous flow of thermoplastic material may comprise a plunger adapted for pushing the predetermined amount of thermoplastic material towards the output port of the feed pipe. The plunger may have a pushing side for pushing against the thermoplastic material, wherein the pushing side is profiled, e.g. conically shaped. Profiling the plunger may provide the advantage of avoiding blockage of the thermoplastic material in the feed pipe while pushing it forward.

In a dispense head system according to alternative embodiments of the present invention, the feed pipe may comprise a receptacle adapted for receiving a predetermined amount of thermoplastic material in granular or powder form from the input section, and the means for interrupting a continuous flow of thermoplastic material may comprise a driving means for moving the receptacle towards the output port of the feed pipe and for emptying the receptacle at the output port.

In a dispense head system according to yet alternative embodiments of the present invention, the feed pipe may be placed under an angle such that thermoplastic materials received from the input section can move under gravity, and the means for interrupting a continuous flow of thermoplastic material may then comprise a valve for interrupting the continuous flow. The valve may be located in the feed pipe. Alternatively, the valve may be located between the input section and the feed pipe.

In a dispense head system according to yet alternative embodiments of the present invention, the interruption device for interrupting a continuous flow of thermoplastic material may comprise a slide coupled to a plunger.

A dispense head system according to embodiments of the present invention may furthermore comprise a controller for controlling the means for interrupting the continuous flow of thermoplastic material. The controller may be adapted such that thermoplastic material is transported to the barrel only at a moment when fresh material is needed. This controller may physically be one and the same controller as a controller for controlling the pre-heating of the transfer zone, for example for controlling heating of the first heating elements, or both controllers may be physically separate controllers.

A dispense head system according to embodiments of the present invention may furthermore comprise an insulating coat around the feed pipe so as to prevent the input section to be heated under influence of the transfer zone. The insulating coat may for example be made from any of ceramic material or PEEK material, or any other suitable material which provides a good thermal separation. Such insulating coat provides heat control in the feed pipe. It disconnects, in terms of heat transfer, the transfer zone from the feed pipe. This allows thermoplastic material in the input section to remain in a cold state, so that it is not heated yet before actually being processed. Hence degradation of the material caused by thermal stress is alleviated or at least reduced compared to prior art systems where complete batches of material are heated while waiting to be processed.

A dispense head system according to embodiments of the present invention may furthermore comprise cooling means for actively cooling the feed pipe. Such cooling means also allows thermoplastic material in the input section to remain in a cold state, so that it is not heated yet before actually being processed, hence reducing material degradation.

A dispense head system according to embodiments of the present invention may furthermore comprise second heating elements for providing a gradual heat slope on the barrel, such as for example a plurality of heater bands which may be actuated differently, e.g. at different temperatures.

A dispense head system according to embodiments of the present invention may have a modular build-up that allows for easy disassembling. This is advantageous e.g. for cleaning, as it allows for a reduced downtime of the system. A material changeover is less of a problem and less time consuming with a dispense head system according to embodiments of the present invention than with prior art dispense head systems.

A dispense head system according to any of the embodiments of the present invention may be for use in layerwise deposition of extruded thermoplastic material, such as e.g. filaments or fibres.

In a second aspect, the present invention provides an extrusion device for extruding thermoplastic material, the extrusion device comprising a dispense head system according to any of the embodiments of the first aspect of the present invention. The extrusion device according to embodiments of the present invention may be adapted for layerwise deposition of extruded thermoplastic material.

In a third aspect, the present invention provides a controller for controlling heating of thermoplastic material in a transfer zone of a dispense head system which comprises

- a transfer zone located at the output port of the feed pipe, adapted for controlled pre-heating of the thermoplastic material,

- an output to the heatable barrel, such as e.g. a needle, for extrusion of the viscous thermoplastic material.

The controller is adapted for controlling pre-heating of thermoplastic material based on dimensions of the thermoplastic material compared to dimensions of the heatable barrel.

In a fourth aspect, the present invention provides the use of a dispense head system according to embodiments of the present invention for layerwise deposition of extruded thermoplastic material, such as e.g. thermoplastic filaments or fibres.

In a fifth aspect, the present invention provides a method for continuous extrusion of thermoplastic materials into continuous or discrete lengths of thermoplastic material, e.g. filaments or fibres. The method comprises

receiving the thermoplastic material in granular or powder form,

transporting the thermoplastic material in granular or powder form towards a heated processing zone, and

in the heated processing zone, heating the thermoplastic material and extruding it into continuous or discrete lengths of thermoplastic material, such as e.g. filaments or fibres. The method furthermore comprises pre-processing the thermoplastic material in a transfer zone before the heated processing zone so as to change the dimensions of the received thermoplastic material such that it can be pushed into the heated processing zone.

Transporting the material towards the heated processing zone may comprise discontinuously transporting the thermoplastic material. Discontinuously transporting the thermoplastic material may comprise substantially only transporting material when it is needed in the heated processing zone. Suitable control means to obtain this may be provided.

In embodiments of the present invention, discontinuously transporting the thermoplastic material may comprise actively controlling the transport of the thermoplastic material.

In a sixth aspect, the present invention provides a computer program product enabling a processor to carry out a method as described in any of the embodiments of the fifth aspect of the present invention when executed on a computing device associated with a dispense head system for continuous extrusion of thermoplastic materials. The computer program product provides the functionality of any of the methods according to the present invention when executed on a computing device. Such computer program product can be tangibly embodied in a carrier medium carrying machine-readable code for execution by a programmable processor. The present invention thus relates to a carrier medium carrying a computer program product that, when executed on computing means, provides instructions for executing any of the methods as described above. The term "carrier medium" refers to any medium that participates in providing instructions to a processor for execution. Such a medium may take many forms, including but not limited to, non-volatile media, and transmission media. Non volatile media includes, for example, optical or magnetic disks, such as a storage device which is part of mass storage. Common forms of computer readable media include, a CD-ROM, a DVD, a flexible disk or floppy disk, a memory key, a tape, a memory chip or cartridge or any other medium from which a computer can read. Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to a processor for execution. The computer program product can also be transmitted via a carrier wave in a network, such as a LAN, a WAN or the Internet. Transmission media can take the form of acoustic or light waves, such as those generated during radio wave and infrared data communications. Transmission media include coaxial cables, copper wire and fibre optics, including the wires that comprise a bus within a computer.

For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

Brief description of the drawings

FIG. 1 is a schematic 3D view of a dispense head system according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of the dispense head system illustrated in FIG. 1.

FIG. 3 is a schematic 3D view of a core block of a dispense head system according to the first embodiment of the present invention as illustrated in FIG. 1.

FIG. 4 is a cross-sectional view of the core block illustrated in FIG. 3.

FIG. 5 is a schematic 3D view of a feed pipe according to embodiments of the present invention, which may for example be introduced into the core block illustrated in FIG. 3.

FIG. 6 is a schematic 3D view of a feed cap part of a dispense head according to embodiments of the present invention.

FIG. 7 is a schematic 3D view of a barrel part of a dispense head according to embodiments of the present invention.

FIG. 8 is a cross-sectional view of the barrel illustrated in FIG. 7.

FIG. 9 is a schematic 3D view of an assembly of a feed tube, a feed cap and a barrel in accordance with embodiments of the present invention.

FIG. 10 is a cross-sectional view of the assembly illustrated in FIG. 9.

FIG. 11 is a schematic 3D view of a clamping block according to embodiments of the present invention, for clamping a barrel against a core block in accordance with embodiments of the present invention.

FIG. 12 is a rotated, semi-transparent view of the clamping block illustrated in FIG. 11.

FIG. 13 and FIG. 14 are a front view and a 3D perspective view of an embodiment of the present invention where the barrel is attached to the core block by means of belts.

FIG. 15 and FIG. 16 are a front view and a 3D perspective view of an embodiment of the present invention where the barrel is adapted for being directly attached to the core block by means of screws.

FIG. 17 and FIG. 18 are a front view and a 3D perspective view of an embodiment of the present invention where the barrel is adapted for being slid into a corresponding slot in the core block.

FIG. 19 illustrates different plunger tip profiles. FIG. 20 illustrates a dispense head system according to an embodiment of the present invention integrally mounted onto a base plate.

FIG. 21 schematically illustrates a dispense head system according to an embodiment of the present invention provided with an encapsulated needle.

FIG. 22 schematically illustrates a dispense head system according to an embodiment of the present invention provided with a channel piece for extrusion of material.

FIG. 23 illustrates a dispense head according to an embodiment of the present invention, where heater bands are provided around the barrel.

FIG. 24 and FIG. 25 illustrate a dispense head system according to an alternative embodiment of the present invention.

FIG. 26 illustrates an alternative embodiment of a dispense head system according to the present invention, where the hopper tube is placed under an angle different from 90° with respect to the feed pipe.

FIG. 27 illustrates a further embodiment of a dispense head system according to the present invention, where a tilted hopper tube is provided with means for interrupting and restarting the flow of material.

FIG. 28 illustrates an embodiment of the present invention in which a slide allows to open and close the hopper.

FIG. 29 illustrates a counter gas pressure embodiment for interrupting and restarting the flow of material in a dispense head system as illustrated in FIG. 27.

FIG. 30 illustrates an embodiment of the present invention in which a heatable barrel is positioned such that its screw is in a horizontal position.

FIG. 31 illustrates an embodiment of the present invention in which a heatable barrel is provided with a sectioned screw.

FIG. 32 illustrates one embodiment of a tube profile at the inlet of the closed section of the feed pipe tube.

FIG. 33 illustrates alternative embodiments of tube profiles at the inlet of the closed section of the feed pipe tube.

FIG. 34 illustrates a sensing device integrated in a dispense head system according to embodiments of the present invention.

FIG. 35 is a cross-sectional view of a dispense head system according to a further embodiment of the present invention, wherein the first heating elements comprises a leading torpedo, a trailing torpedo and a torpedo cap. FIG. 36 is a schematic 3D view of a core block of a dispense head system according to a further embodiment of the present invention as illustrated in FIG. 35.

FIG. 37 is a cross-sectional view of the core block illustrated in FIG. 36.

FIG. 38 is a schematic 3D view of a leading torpedo of a dispense head system according to a further embodiment of the present invention as illustrated in FIG. 35.

FIG. 39 is a projection of the leading torpedo illustrated in FIG. 38 on a plane perpendicular to a longitudinal axis of dispense head system as illustrated in FIG. 35.

FIG. 40 is a cross-sectional view of the leading torpedo illustrated in FIG. 38 taken along a line A-A as indicated in FIG. 39.

FIG. 41 is a cross-sectional projection of the leading torpedo illustrated in FIG. 38 taken along a line B-B as indicated in FIG. 39.

FIG. 42 is a cross-sectional view of the first heating elements of a dispense head system according to a further embodiment of the present invention as illustrated in FIG. 35.

FIG. 43 is a cross-sectional view of a trailing torpedo of a dispense head system according to a further embodiment of the present invention as illustrated in FIG. 35.

FIG. 44 is a projection of the trailing torpedo illustrated in FIG. 43 on a plane perpendicular to a longitudinal axis of dispense head system as illustrated in FIG. 35.

FIG. 45 is a cross-sectional projection of the trailing torpedo illustrated in FIG. 44 taken along a line B-B.

FIG. 46 is a schematic 3D view of a torpedo cap of a dispense head system according to a further embodiment of the present invention as illustrated in FIG. 35.

FIG. 47 is a cross-sectional view of the torpedo cap illustrated in FIG. 46.

FIG. 48 is a projection of the torpedo cap illustrated in FIG. 46 on a plane perpendicular to a longitudinal axis of dispense head system as illustrated in FIG. 35.

FIG. 49 is a schematic 3D view of a first clamping block of a dispense head system according to a further embodiment of the present invention as illustrated in FIG. 35.

FIG. 50 is a cross-sectional view of a dispense head system according to a further embodiment of the present invention, wherein a slide is coupled to the plunger.

FIG. 51 is a schematic 3D view of the dispense head system as illustrated in FIG. 50.

FIG. 52 is a cross-sectional view of a core block of a dispense head system according to a further embodiment of the present invention as illustrated in FIG. 50.

FIG. 53 is a schematic 3D view of a transfer block of a dispense head system according to a further embodiment of the present invention as illustrated in FIG. 50.

FIG. 54 is a cross-sectional view of the transfer block illustrated in FIG. 53. FIG. 55 is a schematic 3D view of a slide of a dispense head system according to a further embodiment of the present invention as illustrated in FIG. 50.

The drawings are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes.

Any reference signs in the claims shall not be construed as limiting the scope.

In the different drawings, the same reference signs refer to the same or analogous elements.

Detailed description of illustrative embodiments

It would seem that using 3D plotting for the processing of polymers like biodegradable, biocompatible or bio-inert polyesters would be an ideal combination. And indeed, several groups have successfully reported the application of this technique for the creation of scaffolds in (copolymers of) PLA, PGA, PCL It has been found by the inventors of embodiments of the present invention that a serious limitation to this unison of material and processing technique is the thermal vulnerability of some of the polymers at hand. When heated for an extended time above their melting temperature, chain scission may occur, effectively degrading the material. Especially the homopolymer PLA is sensitive to this development.

In embodiments, the present invention provides a dispense head system for continuous extrusion of thermoplastic material into continuous or discrete lengths of thermoplastic material, such as e.g. filaments or fibres. With thermoplastic material in embodiments of the present invention is meant fully thermoplastic material, as well as filled thermoplastics such as composite materials, nano fillers etc.

The dispense head system according to embodiments of the present invention comprises an input section for receiving the thermoplastic material in granular or in powder form, a feed pipe for transporting the thermoplastic material received in the input section towards an output port of the feed pipe, a heatable barrel for receiving transported thermoplastic material from the feed pipe and rendering it viscous, and an output to the heatable barrel for extrusion of the viscous thermoplastic material. In accordance with embodiments of the present invention, the dispense head system furthermore comprises a transfer zone located at the output port of the feed pipe and adapted for controlled preheating of the thermoplastic material. As and example, the adaptation may comprise provision of first heating elements for controllably pre-heating thermoplastic material at the transfer zone.

A dispense head system 10 according to a first embodiment of the present invention is schematically illustrated in 3D in FIG. 1, and in cross-section in FIG. 2. The dispense head system 10 comprises a core block 11. The core block 11 is illustrated in 3D view in FIG. 3 an in a cross-sectional view in FIG. 4. The core block 11 is the central assembly part around which all other parts are mounted. In assembly, it may be provided with several other parts, like for example a feed pipe 20 and a plunger 24. In accordance with embodiments of the present invention, in order to thermally separate material supply from material processing, the core block 11 may be made out of an isolator material such as for example PEEK of thermally insulating ceramic.

The core block 11 is provided with an input port 30 for receiving thermoplastic material in granular or powder form. In the embodiment illustrated in FIG. 1 and FIG. 2, a hopper 12 connects to the input port 30.

In the core block 11, a feed pipe 20 is provided. The feed pipe 20 may be a bore in the core block 11. The bore 20 may have any suitable shape in cross-section perpendicular to the longitudinal axis of the bore, for example it may be circular in cross-section, oval, square, rectangular, polygonal. It may have a regular or irregular shape in cross-section.

In alternative embodiments, however, as illustrated In FIG. 2, the feed pipe 20 may be the interior of a tube 50 which is introduced into a bore in the core block 11. The tube and the bore preferably have matching geometries, e.g. they are both circular in cross-section, oval, square, rectangular, polygonal. Such tube 50 is illustrated in 3D view in FIG. 5. In the embodiment illustrated, the bore and the tube are circular in cross-section. The outer diameter of the tube 50 provides a fit within the bore of the core block 11. The inner diameter of the tube 50 may be dependent on the size of the granulate or powder used. The material of the tube 50 may be dependent on the application. For (bio)medical applications, where product contamination is not allowed at all, this tube 50 must be made from inert or (bio)compatible material, such as for example stainless steel or titanium. It is an advantage of embodiments of the present invention that such tube 50 can easily be taken out from the core block 11, and replaced by another tube 50, e.g. with different diameter so as to accommodate a different material without extensive cleaning of the dispense head 10, in particular of its feed pipe 20, being necessary.

Towards one of its extremities, for example towards its outlet side 51, the tube 50 is provided with an output port 300. The output port 300 may comprise positioning features for correctly positioning the tube 50 with respect to the bore in the core block 11. As an example of a positioning feature, the output port 300 of the tube 50 may be provided with a profiled section 52, e.g. a sleeve, which may be used for positioning of the tube 50 with relation to the core block 11. Therefore, the bore in the core block 11 may have a correspondingly profiled shape 41. Furthermore, the profiled section 52 may be provided with an alignment feature such a notch 53 and the profiled shape 41 of the bore in the core block 11 may be provided with a corresponding alignment features such as a corresponding protrusion 42 for alignment of the tube 50 with respect to the core block 11. In alternative embodiments, rather than the notch and the protrusion, other co-operating parts may be provided as alignment features.

At the inlet side 54 the tube 50 has an open section 55 for being positioned under the input port 30 of the core block 11 to take in material in granular or powder form. At the transition between the open section 55 and the closed tube section 56, the inlet is profiled in order to facilitate granulate intake into the closed tube section 56. This profile can be a chamfer, a radius or a complex combination of both, as illustrated in FIG. 32 and 33. FIG. 32 illustrates a feed pipe tube 50, where the transition between the open section 55 and the closed tube section 56 is profiled in the form of a chamfer. Alternative profile embodiments are illustrated in FIG. 33 as follows: (a) output radius, (b) inward radius, (c) combined chamfer and radius.

According to embodiments of the present invention, the dispense head system 10 furthermore comprises a transfer zone TZ located at the output port 300 of the feed pipe 20, as illustrated in FIG. 2. In accordance with embodiments of the present invention, the transfer zone TZ may comprise first heating elements for controlled preheating of the thermoplastic material. In the embodiment illustrated, the first heating elements comprise a feed cap 21 which covers the outside of the feed pipe tube 50 over a predetermined length. One embodiment of a feed cap 21 according to the present invention is illustrated in more detail in FIG. 6.

The feed cap 21 has a heat transfer function, thus providing a transfer zone where material is pre-heated. The feed cap 21 may be profiled such that the contact surface with the heated barrel is enlarged or made smaller in function of the required heat transfer to the material in the feed pipe 20. The feed cap 21 actually covers the outside of the feed pipe 20 over a predetermined length which is limited with respect to the length of the feed pipe, for example less than 20% of the length of the feed pipe, so that heat is transferred to the outlet side 51 of the feed pipe 20, enabling the plasticizing of the material before it enters the heated barrel. The material in which the feed cap 21 is made may also be determined according to the required heat transfer. Suitable materials could for example be copper or aluminum.

Furthermore, the feed cap 21 may have a positioning function. Therefore, it may be provided with a first protrusion 60 for fitting into a corresponding groove into the feed pipe tube 50. It may be provided with a second protrusion 61 for fitting into a corresponding groove into the core block 11. The feed cap 21 may fit against the barrel in a unique way, assuring correct positioning.

Feed cap 21 may serve as a sleeve over feed pipe 20. Since preferred materials for feed cap 21 would contain copper or aluminum, in particular embodiments of the present invention contact with the material to be extruded must be avoided to prevent contamination or corrosion reactions. Hence in embodiments of the present invention the processed material (material to be extruded) travels only though the feed pipe 20, straight into the barrel 13.

The barrel 13 is illustrated in FIG. 1 and FIG. 2, and in more detail in schematic 3D view in FIG. 7 and in cross-section in FIG. 8. The barrel 13 may fit against the core block 11. The barrel 13 has an input port 80 for receiving material from the feed pipe 20. In the barrel 13 a driving mechanism such as a screw 22 (not illustrated in FIG. 7 and FIG. 8) is provided for moving material through the barrel 13. The barrel 13 may be provided with second heating elements for heating the barrel, thus providing sufficient heat for melting the material to be processed which is present in the barrel 13, and rendering it viscous for extrusion. An example of a barrel with two heater bands 230 mounted thereon is illustrated in FIG. 23. In embodiments of the present invention, the heater band(s) 230 may encircle the barrel 13. In embodiments of the present invention, heat sensors, such as for example thermocouples, for temperature control may be mounted separately along the barrel 13 or they may be incorporated in the heater band(s). The use of multiple heater elements, e.g. multiple heater bands, along the longitudinal direction of the barrel 13, if suitably controlled, may allow for a graded heating profile towards the outlet of the barrel 13, which is the point of extrusion of material. In alternative embodiments, the heater element may for example be a heater mantle around the barrel 13, which provides a uniform heating of the barrel over its longitudinal length. Such heater mantle may be provided by means of a double wall filled with heated liquid such as oil.

A barrel 13 connected to a feed pipe tube 50 over a feed cap 21 is illustrated in 3D view in FIG. 9 and in cross-section in FIG. 10. In the embodiment illustrated in FIG. 9 and FIG. 10, the feed cap 21 has two main geometries: a contact surface 62, e.g. a flat rectangle, and the geometry of the embossment 63, e.g. cylindrical with first and second protrusions 60, 61. The inner geometry of the embossment 63 fits over the outer diameter of the feed pipe tube 50 and into the profiled section 52, e.g. sleeve, that is fashioned into its retaining collar at the outlet side. Heat from the heatable barrel 13 is transferred via feed cap 21 to the output port 300 of the feed pipe tube 50. The amount of heat transferred to the feed pipe 20 can be controlled by changing the material of the feed cap 21 and the feed pipe tube 50, by varying the length over which the feed pipe tube 50 is covered by the feed cap 21, or by enlarging or reducing the contact surface of the feed cap 21 with the heatable barrel 13. In alternative embodiments or on top of this embodiment, heater elements may be provided for heating the feed cap 21, thus providing controlled heating to the thermoplastic material fed by the feed pipe. A temperature sensor may be provided at the feed cap 21, for sensing the temperature of the feed cap, and taking into account parameters such as for example geometry of the thermoplastic material, material parameters of the thermoplastic material and/or dimensions of the input of the heatable barrel, the output of the temperature sensor may be used for driving the heater elements. Moreover, due to the specific shape of the feed cap 21 and the output port 300 of the feed pipe tube 50, a radial alignment is provided between the feed cap 21 and the feed pipe tube 20. The matching geometries of the feed cap 21 and the feed pipe tube 50 by means of the profiled section 52 with notch 53 and the protrusions 60 are only one example of matching geometries. Other shapes are possible as well.

The feed cap 21 is pushed over the feed pipe tube 50 until the end of the feed pipe tube 50 touches the back side 64 of the contact surface 62. This way, an axial positioning of the feed cap 21 with respect to the feed pipe tube 50 is provided. The outer geometry of the embossment 63 fits into the matching inner geometry of the core block 11, thus providing radial alignment of the feed cap 21 with respect to the core block 11. The circular embossment 63 with protrusion 61 which fit in a recess in the core block 11 is only one example of a matching geometry. Other matching geometries of feed cap 21 and core block 11 may be used as well, for example an embossment with circular inner shape and rectangular outer shape. In yet alternative embodiments, rather than using matching geometries, other positioning systems may be used, such as for example wedges, pins or screws.

The feed pipe tube 50, with the feed cap 21 mounted over it, is inserted into the core block

11 from the side where the barrel 13 will be mounted. The retaining collar 63 touches against the matching support in the core block 11, thus providing axial positioning of the feed pipe tube 50 with respect to the core block 11. The geometry of the contact surface 62 of the feed cap 21 fits into a matching countersinking 81 in a side of the barrel 13, thus providing axial positioning of the barrel 13 onto feed cap 21 and optimal heat transfer from the heatable barrel 13 to the feed cap 21. In the embodiment illustrated, the contact surface 62 and the matching countersinking 81 have flat surfaces. In alternative embodiments, however, these matching geometries could have other shapes.

The feed pipe 50 protrudes a small distance, for example 0.01 to 0.1 mm from the contact surface 62, and fits into its matching counterbore 82 in the barrel 13, which is deeper than the contact surface's countersink 81, thus providing alignment of the centerline 43 of feed pipe 50 to the centerline 83 of the inlet hole 80 of the barrel 13.

One side of the barrel 13 is profiled with a profiled, e.g. flat, section 84, illustrated in FIG. 8 and FIG. 9, in which profiled, e.g. flat, section 84 the countersink 81 and the counterbore 82 are made for fitting onto feed cap 21 and feed pipe tube 50. The profiled, e.g. flat, section 84 fits against a matching profiled, e.g. flat, section 31 in the core block 11, thus providing radial positioning of the barrel 13 onto the core block 11.

The barrel 13 may be secured in place by a clamping block 15, as illustrated in FIG. 1 and FIG. 2, or in more detail in FIG. 11 and FIG. 12. The clamping block 15 may be provided around the barrel 13, at a side of the barrel 13 opposite to the profiled, e.g. flat, section 84. The clamping block 15 may be attached to the core block 11, thus clamping the barrel 13 against the core block 11. The clamping block 15 and the barrel 13 preferably have matching geometries where they touch. The exact shape of the geometry is not relevant, as long as the geometries of both parts match to each other. In alternative embodiments, other positioning systems may be used, such as for example wedges or pins. The attaching of the clamping block 15 to the core block 11 may be performed by any suitable means, for example by screwing it in place into the core block 11, e.g. via screw holes 110.

In alternative embodiments, rather than using a clamping block 15, the barrel 13 may be secured in place onto the core block 11 by a direct connection of the barrel 13 and the core block 11 to one another. A first embodiment is by using belts 130 or other means of fastening barrel 13 to the core block 11. This embodiment is illustrated in FIG. 13 and FIG. 14. In alternative embodiments of the present invention the barrel 13 and the core block 11 may be adapted for direct attachment to one another by use of screws, as illustrated in FIG. 15 and FIG. 16. In this case, the barrel 13 is provided with wings 150 provided with holes 151 through which screws or other fastening means may be provided for connection to the core block 11. In yet alternative embodiments, as illustrated in FIG. 17 and FIG. 18, the barrel 13 may be provided with a sliding element 170 for sliding the barrel 13 into position in a corresponding slit the core block 11.

Since the feed pipe tube 50 is actually a fraction too long, the connection from the outlet 51 to the interior of the barrel 13 is sealed by the pressure of the clamping block 15. There is no need for extra sealing rings. In alternative embodiments, however, extra sealing rings may be provided.

In use, material enters the dispense head system 10 at a supply point SP in granulated or powder form from hopper 12, which in the embodiment illustrated in FIG. 1 and FIG. 2 is a tube tightly fitted into core block 11. In alternative embodiments, the hopper 12 may be fixed into the core block 11 by screwing, or by a clicking system. The material to be processed falls down the hopper 12 under influence of gravity of its own weight (and possibly under influence of the weight and/or movement of a hopper plunger 23). The granulate or powder falls into feed pipe 20, which in the embodiment illustrated is the interior of the feed pipe tube 50. A plunger 24 moves the granulate or powder from the supply point SP towards the output port 300 of the feed pipe 20. The granulate or powder is pushed towards the output port 300 of the feed pipe tube 50, or in general towards the output port 300 of the feed pipe 20, by means of the plunger 24. The plunger 24 may have any suitable shape in cross-section; for example it may be circular in cross-section, oval, square, rectangular, l-profile-shaped or T-shaped. The shape in cross-section of the plunger 24 preferably corresponds to the shape in cross-section of the feed pipe 20. The plunger 24 may be operated pneumatically, electrically or in any other suitable way. Control over the movement of the plunger 24 is realized by means of a control unit 14, connected to a sensing device for indicating that a certain amount of granulate or powder has traveled completely into the closed section 56 of feed pipe tube 50, for example a positioning sensor such as e.g. a reed contact or optical eye, a pressure sensor, capacitive sensor or any other suitable device. An embodiment of a sensing device 330 is illustrated in FIG. 34. The sensing device 33 comprises a first position sensor 331 and a second position sensor 332. The first position sensor 331 determines that the plunger 24 has reached a forward position, and the second position sensor 332 determines that the plunger 24 has reached a backward position. The sensing signals from the first and second position sensors 331, 332 are applied to the control unit 14 for driving the movement of the plunger 24. Alternatively, there is a sensor which does not monitor the positioning of the plunger 24, but the presence (or lack thereof) of material in the transfer zone.

The pusher end 25 of plunger 24 can be profiled to facilitate movement of the granulate or powder into the closed tube section 56. In order to facilitate material transition from the open section 55 of the feed pipe tube 50 into its closed section 56 and avoid jamming of the granulate or powder, the plunger tip 25 may be profiled. Possible (non restrictive) geometries for this tip profile are rounded, chamfered, hollowed or a complex combination of these. Examples of different types of profiles are illustrated in FIG. 19. FIG. 19(a) shows a rounded profile tip, FIG. 19(b) shows a chamfer on the profile tip, FIG. 19(c) shows a hollowed profile tip, FIG. 19(d) shows a chamfer on a rounded profile tip, FIG. 19(e) shows a hollow profile tip which is chamfered, FIG. 19(f) shows a profile tip which is rounded and hollowed, and FIG. 19(g) shows a profile tip which is rounded twice and chamfered. Some pusher ends 25 may be more suitable than others for use with particular types of granulates or powder, for example to prevent blocking of the plungers 24 pushing granulate of powder into the feed pipe 20. The plunger 24 may be interchangeable. In order to avoid jamming of the granulate or powder in the feed pipe 20, also the inlet section of the tube 50 may be profiled.

As the granulate or powder is moved closer towards the output port 300 of feed pipe tube 50, i.e. towards the transfer zone TZ of the dispense head system 10, temperatures will rise, causing the material to be processed to soften enough so that it can be pushed into the heated barrel 13. The material here crosses the transfer point TP, which is the point where the material to be processed enters the heated barrel 13 and is drawn into the extrusion screw 22.

In the embodiment illustrated above, three zones are provided. A first zone, supply zone SZ, starts at the supply point SP and runs over the closed section 56 of the feed pipe tube 50, i.e. over the portion of the feed pipe tube 50 being uncovered by the feed cap 21. A second zone, transfer zone TZ, is provided between the end of the feed pipe section 56 and between the transfer point TP. The transfer zone TZ thus comprises the output port 300 of the feed pipe tube 50, i.e. the portion of the feed pipe tube 50 covered by feed cap 21. A third zone, processing zone PZ, is then provided between the transfer point TP and the extrusion point EP. In particular embodiments of the present invention, the supply zone SZ is a "cold" zone, i.e. a zone at a temperature much cooler than the transfer zone and the processing zone, hence at a temperature below the melting temperature of the material to be processed. When leaving the supply zone SZ, the material enters the transfer zone TZ, in the embodiment illustrated comprising feed cap 21, and is rendered partially viscous by means of the heat transfer between the heatable barrel 13 and the feed pipe tube 50. The preheating process may be controlled amongst others by the properties of the feed cap 21, for example the shape of the feed cap 21 and the material from which the feed cap 21 is fabricated. It is an advantage of a dispense head system 10 according to embodiments of the present invention that the controlled pre-heating and softening allows the otherwise rigid and large granulates to be pushed from the transfer zone TZ into the heated barrel 13 of the processing zone PZ. Once inside the heatable barrel 13, the temperature is high enough to completely melt the material into a viscous compound, which is transported by screw 12 towards the extrusion point EP, where the material leaves the dispense head 10 as extruded material. In particular embodiments, the barrel is provided with a needle at its output port, and the extruded material leaves the barrel 13 as an extruded continuous or discrete length of thermoplastic material, such as e.g. a filament or fibre.

In a particular embodiment of a dispense head system 10 according to the present invention, the sidewalls of the feed pipe tube 50 being uncovered by the feed cap 21 may be covered by an insulating coat, for example a ceramic coat or a PEEK coat, so that the supply SZ is not heated under influence of transfer zone TZ and the processing zone PZ, and hence material present in the feed pipe is not subject to thermal stress and thus does not degrade. In alternative embodiments, cooling means, for example a cooling band surrounding the portion of the feed pipe tube 50 being uncovered by the feed cap 21, may be provided for actively cooling the feed pipe tube 50.

It is an advantage of a dispense head system according to the first embodiment of the present invention, as illustrated in particular in FIG. 1 and FIG. 2, that the movement of the plunger 24 may be so as to interrupt a continuous flow of the material to be processed towards the heated zones TZ and PZ of the dispense head 10, in particular towards the output port 300 of the feed pipe tube 50 and towards the heated barrel 13. The control unit 14 may be adapted, e.g. programmed, specifically for obtaining this. For example, the plunger 24 may be actuated only when the stock of material to be processed, which previously was provided to the barrel 13, is substantially completely molten and extruded e.g. as filaments or fibres. This way, fresh material to be processed is not kept in a heated state for a long time, and hence is not degraded. The thermoplastic material is under thermal stress only in the transfer zone TZ and in the processing zone PZ, not in the supply zone SZ. In accordance with embodiments of the present invention, the thermoplastic material only enters the transfer zone TZ and the processing zone PZ just prior to its being processed, so as to minimize thermal stress (and related degradation) on the material.

According to an embodiment of the present invention, a dispense head system 10 according to embodiments of the present invention may be mounted on a base plate 200, as illustrated in FIG. 20. Such base plate can be made interchangeable and compatible with any clamping system or XYZ guidance system.

The barrel 13 in embodiments of the present invention is designed so that it can be fitted with an extrusion needle for extruding the thermoplastic material into continuous or discrete lengths of thermoplastic material, such as filaments or fibres, e.g. into filaments or fibres of 100 a 500 μιτι diameter. In embodiments of the present invention, as illustrated in FIG. 21, an encapsulated needle 210 is provided that is positioned onto the barrel 13 by means of a needle cap 211. In this needle cap 211, a needle sleeve 212 may be inserted to optimize heat transfer from the barrel 13 to the thin needle section. The needle sleeve 212 is made of a material with good heat transfer, e.g. copper- based or aluminum-based material. By actively providing heat transfer towards the thinnest section of material passage, the barrel 13 must not be overheated in order to prevent freeze-off of the material. Hence a reduced thermal stress is implied on the material. A needle ring 213 can be placed on top of the needle 210 in the needle cap 211 to ensure a good fit between the outlet of the barrel 13 and an inlet of the encapsulated needle 210.

By adding a needle 210, the extrusion point of the dispense head system 215 is moved to the tip of the needle 210.

In yet an alternative embodiment, as illustrated in FIG. 22, no encapsulated needle is provided as in the embodiment illustrated in FIG. 21, but a piece 220 is attached to the outlet of the barrel 13 where an internal channel 221 functions as a needle canal.

It is an advantage of embodiments of the present invention that they are easily assembled and disassembled. With each material changeover, the thermoplastic used may have different geometry (shape and size of the granulate or powder) and thermal properties (melting temperature, sensitivity to thermal stress). The embodiments of the present invention where a feed pipe tube 50 is provided are adaptable to each new granulate by their extremely modular design.

To accommodate different shapes and sizes of granulates, the supply zone SZ needs adaptation. This may be achieved by adapting the feed pipe tube 50 and the profiled plunger 24, both of which can be easily removed from and replaced within the core block 11. In essence, a simple set of feed pipe tube 50 and plunger 24 can exist per material type used, thus reducing costs as it implies only providing two extra components per granulate type, rather than a completely new dispense head system, and reducing required time for performing a material changeover. Depending on melting temperature and thermal sensitivity (degradation by thermal stress), the new material will require not only a different heating regime, which is easily achieved by changing input on the heater elements, e.g. heater bands, but also a different heat transfer in the transfer zone TZ. This may be achieved by using different feed caps 21 for different materials to be processed, e.g. by changing the material of the feed cap 21, by changing the length over which the feed cap 21 covers the feed pipe tube 50, or by changing the size of the contact surface with the heated barrel 13.

With a material changeover, the entire pathway needs to be rigorously cleaned to avoid contamination of one thermoplastic to the next. This means that even if components need not be replaced (e.g. different grade of same material), the dispense head must be disassembled and cleaned. In a dispense head system 10 according to embodiments of the present invention, the number of components that contact the semi-molten material is limited to a few: feed pipe tube 50, barrel 13, screw 22, needle 210 and needle ring 213, as opposed to other systems where the material runs through the core block 11 unshielded. Hence, instead of having to disassemble and clean the entire dispense head, only these few components need to be removed, cleaned and replaced. This implies a reduction in changeover time, a reduction in material loss (the material in the supply zone that has not been heated yet can be recovered) and a reduction of wear on mechanical fittings in the system by repeated (dis)assembly.

In embodiments of the present invention, the material supply system is the (set of) component(s) responsible for interrupting and restarting the material flow in the supply zone, and hence the material supply system forms the means for interrupting a continuous flow of thermoplastic material towards heated zones of the dispense head.

One example is illustrated in FIG. 24 and FIG. 25. In the embodiment illustrated, the material supply system comprises the hopper 240, the horizontal feed pipe 241 and the plunger 242. The plunger 242 may be moved forward by a pneumatic valve, an electrical valve or a mechanical valve actuated by a control unit 243 controlled by the output of sensors, e.g. two Reed contacts, which tell whether the plunger 242 is in its forward or backward position. In alternative embodiments, the control unit 243 may be controlled by a mechanical input, such as for example a switch pin which is pushed and which connects to the control unit.

Components of the head dispense system illustrated in FIG. 24 and FIG. 25 which are not described here in detail are similar to corresponding components in other embodiments of dispense heads according to the present invention, and are explained hereinabove in more detail.

In this embodiment, material is transported towards the transfer zone TZ by means of the plunger 242, which is a slide adapted to catch a small batch of material as illustrated in FIG. 24 and move it towards the transfer zone as illustrated in FIG. 25. A valve like for example a closing slide may be provided between the hopper 240 and the feed pipe 241 to interrupt the flow of material while material is transported from the hopper towards the barrel 13.

A supplementary feed pipe 245 is provided under the feed pipe 241 for catching the small batch of material transported by means of the plunger 242. The supplementary feed pipe 245 comprises an output port 246 and first heating elements located at the output port 246 for a controlled preheating of the thermoplastic material. The first heating elements may for example be a feed cap 247 allowing for heat transfer between the heatable barrel 13 and the output port 246 of the supplementary feed pipe 245, or controllable heater elements for heating the output port 246 of the supplementary feed pipe 245.

In case of a feed cap 247, the sidewalls of the feed pipe 241 and the sidewalls of the portion of the supplementary feed pipe 245 being uncovered by the feed cap 247 may be covered by an insulating coat, so that the supply SZ is not heated under influence of the processing zone PZ and the transfer zone TZ, and hence material present in the feed pipe is not subject to thermal stress and thus does not degrade. Also in case of controllable heater elements being provided, and for the same reason, sidewalls of the supplementary feed pipe 245 may be covered by an insulating coat.

Another example of embodiments where the material supply system is responsible for interrupting and restarting the material flow in the supply zone is illustrated in FIG. 26. In this embodiment, the hopper 260 is placed under an angle to feed material into the supply zone, where it is taken up by a plunger as in FIG. 3 or by a slide as in FIG. 24.

An alternative example is illustrated in FIG. 27, where a hopper 270 is placed under an angle.

Thermoplastic material is inserted at an open end 272 of the hopper 270 and falls down under influence of gravity. Alternatively, the material may be fed into the hopper by means of a plunger. In yet another alternative embodiment, pressurized gas, e.g. pressurized air, may be used to encourage the flow of thermoplastic material into hopper 270. The hopper 270 is at the same time used as hopper to provide material, and as feed pipe to transport the material towards the heated zones, in particular towards a transfer zone TZ located at an output port 273 of the tilted hopper 270. The tilted hopper 270 may furthermore comprise means for interrupting and restarting material flow, for example an open/close element such as a valve 271, for example a hinged valve, a shutter, e.g. a hinged shutter, a telescopic valve. Alternatively, as illustrated in FIG. 28, the hopper 270 may be provided with a slide 283 which can slide into hopper 270 to interrupt the flow of thermoplastic material. In yet another embodiment, as illustrated in FIG. 29, opposing gas pressure may be used to keep the thermoplastic material away from the heated transfer zone TZ. In case of opposing gas pressure, a gas inlet 280 is provided in the hopper 270, at a location downstream of where fresh material is introduced. If an opposing gas stream 281 is introduced into the hopper 270, the fresh material is pushed upstream and is prevented from flowing, hence the open/close element is closed. If, on the other hand, no opposing gas pressure is provided, the open/close element is open and material can freely flow in the hopper 270. The open/close element, be it a physical element or a provided gas pressure, may be controlled by a supply control system. When material is required at the inlet of the heatable barrel 13, the open/close element, e.g. the hinged valve 271 or the slide 283, is opened and material falls in the transfer zone TZ where, in accordance with embodiments of the present invention, it is preheated before entering the heatable barrel 13. The transfer zone TZ may comprise first heating elements for a controlled preheating of the thermoplastic material, e.g. a feed cap covering the outside of the hopper 270 over a predetermined length, or heater elements provided around or inside the transfer zone TZ. The transport of the thermoplastic material towards the heatable barrel 13 and the transfer zone TZ may be supported by means of an extra pressurized air flow, e.g. a secondary gas flow 284 which is introduced through gas inlet 280 into the hopper 270. Alternatively, a suction effect caused by the movement of the molten thermoplastic material downwards into the heatable barrel 13 by means of extrusion screw 22 may improve the flow of material towards the transfer zone TZ and the heatable barrel 13.

In all embodiments of the present invention, the sensor that gives the control unit its signal to interrupt or re-open the material supply into the supply zone may be a position sensor reading out the position of the component that moves material forward, such as a plunger or a slide. Examples are a Reed contact, a touch contact, an optical eye; however, the list is not limited thereto. In alternative embodiments, the sensor that gives the control unit its signals to interrupt or re-open the material supply into the supply zone may be a sensor which checks material level in the supply zone, such as a touch contact or an optical eye.

Yet another alternative embodiment of the present invention is illustrated in FIG. 30, where the heated barrel is placed such that its screw is in substantially horizontal position. Material from the supply zone (cold zone as in previous embodiments) can be provided to transfer zone TZ for controlled preheating of the thermoplastic material. The transfer zone comprises first heating elements, for example a feed cap 296 as described above. Alternatively, at the location of the feed cap as illustrated, heater elements may be provided. Partially melted, or at least plasticized, the thermoplastic material will be pushed into the barrel 290 where it is transported towards the outlet 291 of the barrel 290, for example under influence of rotation of a screw 292. Embodiments of the present invention are then provided with an additional heated block 293 provided with an internal channel 294 to release the extruded material in a vertical direction.

In an alternative embodiment, which can be implemented in all embodiments of dispense heads according to the present invention, comprises a sectioned extrusion screw 300, as illustrated in FIG. 31. The sectioned extrusion screw 300 has varying profiles over its different sections. Advantages of a sectioned extrusion screw 300 are that it provides a better mixing of filler components, that it provides a build-up of pressure towards the extrusion point EP, hence a better extrusion, and that it has a deeper screw section inlet at the barrel entrance for uptake of only half-molten granulate. At the outlet of the barrel with sectioned extrusion screw 300, a needle or a needle piece may be mounted (not illustrated in FIG. 31) as discussed above with reference to FIG. 21 and FIG. 22.

FIG. 35 illustrates yet another alternative embodiment of a dispense head system 10 according to present invention. Components of the head dispense system illustrated in FIG. 35 which are not described below in detail may be similar to corresponding components in embodiments of dispense head systems 10 according to the present invention, as described hereinabove in more detail.

The dispense head system 10 illustrated in FIG. 35 comprises a core block 303 which is illustrated in 3D view in FIG. 36 and in a cross-sectional view in FIG. 37. In assembly, the core block

303 may be provided with several other parts, like for example a plunger 24 and a plunger control unit 14. In the core block 303, a feed pipe 305 is provided. As illustrated in FIG. 35 and in FIG. 37, the feed pipe 305 may be an internal channel, for example a bore, for example a cylindrical bore, in the core block 303. In alternative embodiments, the feed pipe 305 may be the interior of a tube which is introduced into a bore in the core block 303. The tube and the bore preferably have matching geometries, e.g. they are both circular in cross-section, oval, square, rectangular, polygonal.

A dispense head system 10 according to embodiments of the present invention furthermore comprises a heatable barrel 13 with an input port 80 for receiving material from the feed pipe 305.

Towards one of the extremities of the feed pipe 305, i.e. towards the extremity facing the heatable barrel 13, the feed pipe 305 may be provided with an output port 300. As illustrated in FIG. 37, the output port 300 of the feed pipe 305 may be an extension of the bore in the core block 303, for example a cylindrical extension, which may for example have a diameter being slightly larger than the diameter of the central part of the feed pipe 305. The output port 300 of the feed pipe 305 may furthermore be adapted for receiving first heating elements for a controlled pre-heating of the thermoplastic material before entering the input port 80 of the heatable barrel 13. According to embodiments of the present invention, the first heating elements may for example comprise a leading torpedo 304, a trailing torpedo 306, a heater element embedding the leading torpedo 304 and the trailing torpedo 306, and a torpedo cap 310. FIG. 38 illustrates a 3D-view of a leading torpedo

304 according to embodiments of the present invention, whereas FIG. 39 shows a projection of the leading torpedo 304 of FIG. 38 on a plane perpendicular to the longitudinal axis of the feed pipe 305. As illustrated in FIG. 39, the leading torpedo 304 comprises at least one cavity, for example several cavities 312. The cavities 312 may run through the entire thickness of the leading torpedo 304, thereby forming internal channels through which the thermoplastic material can travel from the feed pipe 305 towards the heatable barrel 13 of the dispense head system 10. This is illustrated in more detail in cross-section in FIG. 40. The cavities 312 may be formed between at least one spoke, for example a plurality of spokes 314 of the leading torpedo 304. As illustrated in FIG. 39, the spokes 314 may be, but do not need to be, equidistantially arranged in a plane perpendicular to the longitudinal axis of the feed pipe 305, around a central point 316 of the leading torpedo projection. The leading torpedo 304 may be a three-spoke unit, comprising three spokes 314 with an angle of approximately 60° between the longitudinal axes of the spokes 314. Alternatively, the leading torpedo 304 may comprise less or more than three spokes, and the angles between the longitudinal axes of the spokes 314 may be different from 60°. In yet another embodiment, the cavities 312 in the leading torpedo 304 may be formed by using a perforated leading torpedo structure 304. According to a preferred embodiment of the present invention, the shape and the dimensions of the cavities 312 may be chosen such that contact between the thermoplastic material and the components of the leading torpedo 304 surrounding the cavities 312, e.g. the spokes 314 or the outer edge 322 of the leading torpedo 304, is optimized without substantially disturbing the flow of thermoplastic material through the leading torpedo 304. At its side facing away from the input port 80 of the heatable barrel 13, the leading torpedo 304 may furthermore comprise a central protrusion 318 around which the spokes 314 are arranged. The protrusion may have a sharp edge, or, as illustrated in FIG. 40, may be a blunted protrusion. Moreover, as illustrated in cross-section in FIG. 41, the spokes 314 may have a sharp edge at their side facing away from heatable barrel 13. Alternatively (not illustrated in the drawings), the spokes 314 may have a blunted or any suitable otherwise profiled edge protrusions. The central protrusion 318 and the profiled edges of the spokes 314 avoid that thermoplastic material, traveling from the feed pipe 305 towards the heatable barrel 13, remains pushed against the leading torpedo 304. The central protrusion 318 equally may have a heat transfer function, adding the heat to the material in the centre of the feed pipe channel. The leading torpedo 304 may furthermore have an outer diameter being substantially equal to the inner diameter of the output port 300 of the feed pipe 305 such that the leading torpedo 304 can be fitted into the output port 300. This is illustrated in more detail in FIG. 42.

FIG. 43 is a cross-sectional view of a trailing torpedo 306 according to embodiments of the present invention. The trailing torpedo 306 has a trailing torpedo surface 324 facing away from the heatable barrel 13 which may contact a leading torpedo surface 326 of the leading torpedo 304, thereby forming a leading torpedo 304/trailing torpedo 306 assembly as illustrated in FIG. 42. Similar as the leading torpedo 304, the trailing torpedo 306 may comprise cavities 328 through which the thermoplastic material can travel from the feed pipe 305 towards the heatable barrel 13 of the dispense head system 10. The cavities 328 may for example be formed between spokes 330 of the trailing torpedo 306. This is illustrated in more detail in FIG. 44. At the trailing torpedo surface 324, the cavities 328 may have a matching position and shape with the cavities 312 in the leading torpedo 304. As such, internal channels 332 are created in the first heating elements through which the thermoplastic material can travel from the feed pipe 305 towards the input port 80 of the heatable barrel 13, as illustrated in FIG. 42. The cavities 328 in the trailing torpedo 306, i.e. the inner channels in the trailing torpedo 306, may have a slope with respect to a central axis 336 of the trailing torpedo 306 in such way that the thermoplastic material is funneled towards the central axis 336 of the trailing torpedo 306. This is illustrated in cross-section in FIG. 43. The slope of the cavities 328 may be a continuous slope. Alternatively, the slope of the cavities 328 may for example be a stepwise slope, or a combined stepwise/continuous slope. Similar as the leading torpedo 304, the trailing torpedo 306 may have a central protrusion 338, which may for example be centered around the central axis 336 of the trailing torpedo 306 and which may face the heatable barrel 13. The central protrusion 338 equally may have a heat transfer function, adding the heat to the material in the centre of the feed pipe channel. As illustrated in cross-section in FIG. 45, the leading torpedo spokes 330 may have a sharp edge, which may also face the heatable barrel 13. Alternatively, the leading torpedo spokes 330 may have a blunted or otherwise profiled edge. Likewise, the central protrusion 338 of the trailing torpedo 306 may have a sharp edge or, as illustrated in FIG. 43 and in FIG. 45, may be a blunted protrusion.

The leading torpedo 304 and the trailing torpedo 306 may be embedded by a heater element, for example by a heater band or by a resistive element or a mantle with heated fluid, which supplies heat to the leading torpedo 304/trailing torpedo 306 assembly. Leading torpedo 304 and trailing torpedo 306 may be made from a thermally conductive material, for example from copper, a copper alloy, aluminum, an aluminum alloy, or any other suitable heat conductive material. In a particular embodiment, the leading torpedo 304 and the trailing torpedo 306 may be coated with an inert layer, for example with a stainless steel or Ti layer in order to avoid contamination between the thermoplastic material to be processed and the possibly reactive materials of the leading torpedo 304 and the trailing torpedo 306.

The first heating elements of the dispense head system 10 may furthermore comprise a torpedo cap 310. The torpedo cap 310 is illustrated in 3D in FIG. 46, in cross-section in FIG. 47 and as a projection on a plane perpendicular to the longitudinal axis of the feed pipe 305 in FIG. 48. The torpedo cap 310 may be a cylindrical torpedo cap comprising a first cap edge 342 with an outer diameter substantially equal to the outer diameter of the leading torpedo surface 326. The first cap edge 342 may face away from the heatable barrel 13, thereby contacting the leading torpedo surface 326 of the leading torpedo 304 as illustrated in FIG. 40. The torpedo cap 310 may furthermore comprise a second cap edge 343. The geometry of the second cap edge 343 may be chosen such that the torpedo cap 310 fits into a matching countersinking 81 in a side of the heatable barrel 13, thus providing axial positioning of the barrel 13 onto torpedo cap 310 and optimal heat transfer from the heatable barrel 13 to the torpedo cap 310. The torpedo cap 310 may furthermore comprise a first cavity 344 and a second cavity 346, the first cavity 344 facing away from the heatable barrel 13 and the second cavity 346 facing towards the heatable barrel 13. The shape of the first cavity 344, e.g. its length and its diameter, may be chosen such that the trailing torpedo 306 can be fit into the first cavity 344 with a first torpedo cap surface 347 contacting a second trailing torpedo surface 334 of the trailing torpedo 306. The second cavity 346, i.e. the cavity facing the heatable barrel 13, may be a cylindrical cavity, which may funnel towards the centerline 83 of the inlet hole 80 of the heatable barrel 13. The shape of the second cavity 346 may be chosen such that the central protrusion 338 of the trailing torpedo 306 fits into the second cavity 346, in such way that the longitudinal axis of the second cavity 346 coincidences with the longitudinal axis of the central protrusion 338. The second cavity 346 may furthermore have a diameter slightly larger than the outer diameter of the central protrusion 338 such that a spacing 349 is provided between the side walls of the second cavity 346 and the central protrusion 338 of the trailing torpedo 306. This is illustrated in FIG. 42. As such, the internal channel 332 created in the leading torpedo 304 and the trailing torpedo 306 will extend through the torpedo cap 310, funneling the thermoplastic material towards the inlet hole 80 of the heatable barrel 13.

In the embodiment illustrated above, three zones are provided: a supply zone SZ between the supply point SP and the output port 300 of the feed pipe 305, a transfer zone TZ which begins at the output port 300 of the feed pipe 305 and ends at the inlet hole 80 of the heatable barrel 13, and a processing zone PZ between the inlet hole 80 of the heatable barrel 13 and the extrusion point EP. In particular embodiments of the present invention, the supply zone SZ is a "cold" zone, i.e. a zone at a temperature much cooler than the processing zone, hence at a temperature below the melting temperature of the material to be processed. When leaving the supply zone SZ, the material is pushed against the leading torpedo 304, e.g. against the spokes 314 or against the outer edge 322 of the leading torpedo 304, and is rendered partially viscous by means of the heat transferred from the heat member surrounding the leading torpedo 304/trailing torpedo 306 assembly. It is an advantage of a dispense head system 10 according to embodiments of the present invention that the controlled preheating and softening allows the otherwise rigid and large granulates to be pushed from the transfer zone TZ into the heated barrel 13 of the processing zone PZ. Once inside the heatable barrel 13, the temperature is high enough to completely melt the material into a viscous compound, which is transported by screw 12 towards the extrusion point EP, where the material leaves the dispense head 10 as extruded material.

In a particular embodiment of a dispense head system 10 according to the present invention, the torpedo cap 310 of the first heating elements may have a heat control function. Depending on the requirements of the thermoplastic material to be processed, the torpedo cap 310 may be made from a thermally conductive material, for example copper, a copper alloy, aluminum, an aluminum alloy, or any other suitable heat conductive material, such that additional heat can be transferred from the heatable barrel 13 to the first heating elements. Alternatively, the torpedo cap 310 may be fabricated from a thermally isolating material, for example from ceramic material or PEEK material, or any other suitable material which provides a good thermal separation, such that heat transfer between the heatbale barrel 13 and the first heating elements is avoided.

It is an advantage of the embodiment illustrated in FIG. 35 that the components of the heatable barrel 10 can be easily assembled and disassembled, thereby facilitating the cleaning process and allowing using different components for different thermoplastic materials to be processed. When assembled, the plunger 24 is inserted in the core block 303 from the side facing the heatable barrel 13 and is fixed to the plunger control unit 14. Next, the leading torpedo 304 and the trailing torpedo 306 are assembled together. Contact between the trailing torpedo surface 324 of the trailing torpedo 306 and the leading torpedo surface 326 of the leading torpedo 304 may be realized by using fixing means, for example position pins or screws. The leading torpedo 304 and the trailing torpedo 306 are surrounded by a heater element, for example a heater band and the leading torpedo 304 of the leading torpedo 304/trailing torpedo 306 assembly is inserted in the output port 300 of the feed pipe 305. A torpedo cap 310 may furthermore be fixed around the trailing torpedo 306, with a first clamping block 350 arranged over the trailing torpedo 306/torpedo cap 310 assembly. A schematic 3D view of a first clamping block 350 according to embodiments of the present invention is illustrated in FIG. 49. Next, the heatable barrel 13 is fitted against the torpedo cap 310 and the first clamping block 310. Alignment of the heatable barrel 13 with the trailing torpedo 306/torpedo cap 310 assembly may for example be achieved by the matching profile of the second cap edge 343 of the torpedo cap 310 with the countersinking 81 in a side of the barrel 13. Alternatively, profiled pins may for example be used to assemble the barrel 13 with the trailing torpedo 306/torpedo cap 310 assembly. A second clamping block 380, having a matching profile with the side of the barrel 13 facing away from the core block 303, may be fitted around the heatable barrel 13. The core block 303 and the second clamping block 380 may be clamped together, for example by using bolts, thereby sealing the barrel 13 and the torpedo cap 310 against one another. Torpedo cap 310 may furthermore serve as a sleeve over the trailing torpedo 306, thus avoiding contact between the thermoplastic material on the one hand and the first clamping block 350 on the other hand. Hence in embodiments of the present invention the processed material (material to be extruded) travels only though the feed pipe 20 and the internal channels 332, straight into the barrel 13.

FIG. 50 (cross-sectional view) and FIG. 51 (3D view) show yet another alternative embodiment of a dispense head 10 according to the present invention. Components of the head dispense system 10 illustrated in FIG. 50 and FIG. 51 which are not described below in detail are similar to corresponding components in embodiments of dispense head systems 10 according to the present invention, as described hereinabove in more detail. The dispense head system 10 illustrated in FIG. 50 and in FIG. 51 comprises a feed pipe 353 and a transfer zone TZ located at an output port of the feed pipe 353 for a controlled preheating of the thermoplastic material. As illustrated in FIG. 52, the feed pipe 353 may for example be an internal channel, i.e. a bore, in a core block 355. Alternatively, the feed pipe 353 may be the interior of a tube which is introduced into a bore in the core block 355. The feed pipe 353 comprises a first opening 352 for receiving the thermoplastics material, a second opening 354 facing away from the heatable barrel 13 for receiving the plunger 24, and a third opening 356 facing towards the heatable barrel 13. The third opening 356 may serve as an output port of the feed pipe 353 and may be adapted for receiving first heating elements of the dispense head system 10. The first heating elements may be a leading torpedo 304/trailing torpedo 306 assembly as described above. Alternatively, the first heating elements may for example comprise a transfer block 358, for example a thermally conductive transfer block 358, which may be heated by an external heating element, for example by means of a heating band. FIG. 53 (3D) and FIG. 54 (cross-section) illustrate a transfer block 358 according to embodiments of the present invention. The transfer block 358 may be a cylindrical transfer block, which may have an outer diameter being substantially equal to the diameter of the third opening 356 in the feed pipe 353. The transfer block 358 may furthermore comprise an internal channel 360 through which thermoplastic material can travel from the feed pipe 353 towards the heated barrel 13. The internal channel 360 may be a cylindrical channel, which may for example have a diameter which gradually decreases towards an end profile 362 of the transfer block 358. The decrease of the diameter may for example be a continuous decreasing, a stepwise decreasing, or a combined continuous/stepwise decreasing. As illustrated in FIG. 49, the end profile 362 of the transfer block 358 may have a matching profile with a countersinking 81 in a side of the heatable barrel 13, such that a unique alignment of the transfer block 358 with the heatable barrel 13 is achieved. In a preferred embodiment of a dispense head system 10 according to the present invention, a longitudinal axis 357 of the internal channel 360 of the transfer block 358 may coincidence with the centerline 83 of the inlet hole 80 of the heatable barrel 13. As such, thermoplastic material which is preheated in the transfer block 358 will be funneled towards the inlet hole 80 of the heatable barrel 13. A clamp block 359, having a matching profile with the side of the barrel 13 facing away from the core block 355, may be fitted around the barrel 13. The core block 355 and the clamp block 359 may be clamped together, for example by using bolts, thereby sealing the barrel 13 and the transfer block 358 against one another.

As illustrated in FIG. 50 and FIG. 51, the dispense head system 10 may furthermore comprises a connector pin 364 and a slide 366, which allow to interrupt the continuous flow of thermoplastic material travelling towards the heated transfer zone TZ and the heated processing zone PZ of the dispense head system 10. A slide 366 according to embodiments of the present invention is illustrated in more detail in 3D in FIG. 55. The slide 366 comprises a first opening 368 adapted to receive the connector pin 364 and a second opening 370 with a diameter being substantially equal to the inner diameter of the hopper 12. The slide 366 is connected via connector pin 364 to the plunger 24, and lies in a cavity 372 formed between the upper surface of the core block 355 and the lower surface of a base plate 374. The slide mechanism regulates the access of cold material to the feed pipe 353 and to the preheated transfer block 358. In the backward position of the plunger 24 with respect to the barrel 13, the hopper 12 is closed by the slide 366 and the unprocessed material is cut off from the preheated transfer zone TZ. As material is required for extrusion, the control unit 14 will drive the plunger 24 forward, thereby equally opening the hopper 12 by a forward movement of the second opening 370 of the slide 366. In one embodiment, the second opening 370 of the slide 366 may be placed exactly above the end portion of the plunger 24 facing the heatable barrel 13. In an alternative embodiment, the second opening 370 of the slide 366 may be positioned relatively forward with respect to the end portion of the plunger 24 facing the heatable barrel 13. As such, thermoplastic material will fall in front of the plunger 24 before the plunger 24 reaches the channel inlet.

As the plunger 24 moves backward, the hopper 12 is closed again. In order to prevent thermoplastic material being caught between the slide 366 and the cavity 372, the walls of the second opening 370 of the slide 366 may be profiled, for example by having a sharp edge. As such, when the plunger 24 moves backward, the thermoplastic material is either pushed upwards back into the hopper 12, or downwards into the feed pipe 353 of the core block 355.

In an alternative embodiment, rather than coupling the movement of slide 366 to the movement of plunger 24, the slide 366 and the plunger 24 may be controlled by two separate controllers.

It is an advantage of a dispense head system according to the embodiment illustrated in FIG. 50 and FIG. 51, that the movement of the plunger 24 may be so as to interrupt a continuous flow of the material to be processed towards the heated zones TZ and PZ of the dispense head 10, in particular towards the output port 356 of the feed pipe 353 and towards the barrel 13. This way, fresh material to be processed is not kept in a heated state for a long time, and hence is not degraded.

The foregoing description details certain embodiments of the invention. It will be appreciated, however, that no matter how detailed the foregoing appears in text, the invention may be practiced in many ways. It should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being re-defined herein to be restricted to include any specific characteristics of the features or aspects of the invention with which that terminology associated.

Claims

1. - A dispense head system for continuous extrusion of thermoplastic materials, comprising

- an output to the heatable barrel for extrusion of the viscous thermoplastic material, wherein the dispense head system furthermore comprises a transfer zone located at the output port of the feed pipe and adapted for controlled preheating of the thermoplastic material.

2. - A dispense head system according to claim 1, wherein the feed pipe is made from any of a titanium alloy, steel, stainless steel, low-carbon stainless steel.

3. - A dispense head system according to claim 1, wherein the feed pipe is an internal channel formed in a block member.

4. - A dispense head system according to any of the previous claims, wherein the barrel is made from a material which is inert with respect to biomedical materials.

5. - A dispense head system according to any of the previous claims, furthermore comprising a needle coupled to the output of the heatable barrel, for extrusion of continuous or discrete lengths of thermoplastic material.

6. - A dispense head system according to claim 5, furthermore comprising a heat conductive coating around the needle.

7. - A dispense head system according to any of the previous claims, wherein the transfer zone comprises first heating elements for controlled preheating of the thermoplastic material.

8. - A dispense head system according to claim 7, wherein the first heating elements comprise a central protrusion and/or heating spokes arranged in a cross-sectional plane of the transfer zone.

9. - A dispense head system according to claim 7, wherein the first heating elements comprise a feed cap covering the output port of the feed pipe and having a surface in thermal contact with the heatable barrel.

10. - A dispense head system according to any of claims 7 to 9, wherein the first heating elements comprise at least one internal channel for funneling the thermoplastic material towards an input port of the heatable barrel. A dispense had system according to any of the previous claims, furthermore comprising an interruption device for interrupting a continuous flow of thermoplastic material towards heated zones of the dispense head system.

A dispense head system according to claim 10, the feed pipe being a horizontal pipe adapted for receiving a predetermined amount of thermoplastic material in granular or powder form from the input section, wherein the interruption device for interrupting a continuous flow of thermoplastic material comprises a plunger adapted for pushing the predetermined amount of thermoplastic material towards the output port of the feed pipe.

A dispense head system according to claim 12, the plunger having a pushing side for pushing against the thermoplastic material, wherein the pushing side is profiled.

A dispense head system according to claim 11, the feed pipe comprising a receptacle adapted for receiving a predetermined amount of thermoplastic material in granular or powder form from the input section, wherein the interruption device for interrupting a continuous flow of thermoplastic material comprises a driving means for moving the receptacle towards the output port of the feed pipe and for emptying the receptacle at the output port.

A dispense head system according to claim 11, the feed pipe being placed under an angle such that thermoplastic materials received from the input section can move under gravity, wherein the interruption device for interrupting a continuous flow of thermoplastic material comprises a valve for interrupting the continuous flow.

A dispense head system according to claim 15, wherein the valve is located in the feed pipe. A dispense head system according to claim 15, wherein the valve is located between the input section and the feed pipe.

A dispense head system according to claim 12, wherein the interruption device for interrupting a continuous flow of thermoplastic material comprises a slide coupled to the plunger.

A dispense head system according to any of claims 11 to 18, furthermore comprising a controller for controlling the interruption device for interrupting a continuous flow of thermoplastic material, the controller being adapted such that thermoplastic material is transported to the barrel only when fresh material is needed.

A dispense head system according to any of the previous claims, furthermore comprising a thermally insulating coat around the feed pipe so as to prevent the input section to be heated under influence of the transfer zone.

A dispense head system according to claim 20, wherein the insulating coat is made from any of ceramic material or PEEK material. A dispense head system according to any of the previous claims, furthermore comprising cooling means for actively cooling the feed pipe.

A dispense head system according to any of the previous claims, furthermore comprising second heating elements for providing a gradual heat slope on the barrel.

A dispense head system according to any of the previous claims, wherein the dispense head system has a modular build-up that allows for easy disassembling.

A dispense head system according to any of the previous claims for use in layerwise deposition of extruded thermoplastic material.

An extrusion device for extruding thermoplastic material, the extrusion device comprising a dispense head system according to any of claims 1 to 25.

An extrusion device according to claim 26, adapted for layerwise deposition of extruded thermoplastic material.

A controller for controlling heating of thermoplastic material in a transfer zone of a dispense head system comprising

- a transfer zone located at the output port of the feed pipe adapted for controlled preheating of the thermoplastic material,

- an output to the heatable barrel for extrusion of the viscous thermoplastic material, wherein the controller is adapted for controlling preheating of the thermoplastic material based on dimensions of the thermoplastic material compared to dimensions of the heatable barrel.

Use of a dispense head system according to any of claims 1 to 25 for layerwise deposition of extruded thermoplastic material.

Method for continuous extrusion of thermoplastic materials into extruded thermoplastic material, comprising

receiving the thermoplastic material in granular or powder form,

in the heated processing zone, heating the thermoplastic material and extruding it into continuous or discrete lengths, wherein the method further comprises pre-processing the thermoplastic material in a transfer zone before the heated processing zone so as to change the dimensions of the received thermoplastic material such that it can be pushed into the heated processing zone.

A method according to claim 30, wherein transporting the material towards the heated processing zone comprises discontinuously transporting the thermoplastic material.

A method according to claim 31, wherein discontinuously transporting the thermoplastic material comprises substantially only transporting material when it is needed in the heated processing zone.

A method according to any of claims 31 or 32, wherein discontinuously transporting the thermoplastic material comprises actively controlling the transport of the thermoplastic material.

A computer program product enabling a processor to carry out a method as described in any of claims 30 to 33 when executed on a computing device associated with a dispense head system for continuous extrusion of thermoplastic materials.

A machine readable data storage storing the computer program product of claim 34.