use of the extrusion die

The present invention relates to an extrusion die according to the preamble of the first claim and to a process for making such a die.

The present invention also relates to a process for making the die as well as the use of the extrusion die.

Extrusion is a frequently used forming technique wherein deformable material is pressed through a die with one or more openings. These openings in the die may have complex shapes so to give the final extruded rod material or extrusion profile a specific defined shape.

Pressing the material through the die can be done under high or low pressure, but is often done with very high friction, because the extruding materials are mostly viscous or even solid substances. For certain solid substances the basic material or granules that need to be extruded may be molded and subjected to such high pressures, that the temperature hereof highly increases due to the high friction that the granules experience in such circumstances. This can cause the granules to melt or the become unstable.

In most cases, extrusion is a continuous process in which the material to be extruded is fed to the die by means of for example one or 2 screws, such as an archimedes screw, that is enclosed in a tight fitting tube. When more than one screw is used, the screws can be mounted in rotating or counter rotating way.

The material to be extruded or the granules are supplied to the screw in the beginning of the tube through a feed hopper. With a continuous supply of the granules through the rotating screw, a continuous extrusion process can be obtained.

In some industries, such as the metal industry, non- continuous extrusion processes are used as well. In this case a screw is not used, but a press which can move between two positions, will squeeze a quantity of material through the die during several multiple consecutive moving cycles.

Extrusion applications are used in various industries for extrusion of a wide range of products. This application is for example used in the plastic industry for extruding plastic profiles, but also in the food industry, for example to extrude pasta. Also in the metal industry extrusion applications are used.

In most of the above described extrusion applications, the shaping techniques are used to create elongated profiles with a defined shape and diameter. This is not always the case.

In the pharmaceutical industry for example the extrusion technique is mostly combined with a spheronization technique, the so called extrusion-spheronization process. This process is used for the production of pellets and is one of the known formulation techniques in the pharmaceutical industry. Pellets are little balls composed of pharmaceutical components and/or active products, which can have different diameter depending on the intended application. Similar pellets can also be used in the agro and plastic industry.

In a extrusion-spheronization process the pharmaceutical components are first mixed or kneaded in a separate mixer. This mixer could be a part of the extruder equipment. The end product of this sub process is a rough wet paste which is the pretreated product for the extrusion process. The extrusion process is a wet extrusion in which the granules are pushed through the die consisting of different holes or channels. Because the wet pasta is pressed through the small channels under high pressure, a high friction is obtained, which can lead to a significant increase in temperature. As an end product of this extrusion process, elongated short strings are obtained, which once they reach a certain length, break off and fall in a collector. These strings can also be cut off mechanically.

These short strings or extrudates are the base product for the spheronization process, which is the third stage in the complete process. During the spheronization the extrudates are rotated on a friction plate and become pellets. This friction plate can for example consist of a checkered pattern to optimize friction and collision of the particles. It's due to this friction that the pellets can be formed.

Spheronization of a product usually takes 2-10 minutes and with a rotating speed of 100-3000rpm, nice round pellets are obtained. The rotation speed depends on the size of the pellet and the spheronizer. Above absolute speed, it is mainly the speed in combination with the diameter of the friction plate and the depth of the chosen pattern on the friction plate that is of most importance.

After this spheronization process, the obtained pellets are dried, so they are suitable for example to be packed in gelatin capsules or to be processed further into tablets or to be coated, etc. These pellets can also form a basis for further formulation. In this case the active ingredients will be coated on the pellets or mixed with the pellets, after which they can be further processed. Since these pellets can contain a polymer, they can be extruded again together with an active ingredient.

The above described extrusion step is a very important part of the extrusion-spheronization process. A problem that may occur during the extrusion step is that the granules can be strongly heated in the extruder due to the high friction and the high pressure. More specific the granules are strongly heated just before the extrusion die and in the openings and channels of the extrusion die. For most industrial processes, such a temperature raise is not a problem, and in the plastic industry for example it is even desirable. In the pharmaceutical industry however, where very sensitive pharmaceutical and biological active substances are used, such a temperature raise can be very disastrous for the ingredient and final product. The temperature increase in the existing extrusion dies can causes a big problem in these industries.

As a consequence there is a need for an extrusion die where the temperature of the material to be extruder can be better controlled than in the existing extrusion dies.

This is achieved with an extrusion die according to the technical features of the characterizing part of the first claim.

Thereto, the extrusion die has a substantially hollow structure, in which a cavity extends inside the extrusion die in such that the cavity surrounds at least part of the channels and is separated from the channels and/or openings by means of the first side, second side and channel walls, so that the cavity itself is not in direct contact with the channels or first or second openings, and the cavity further being connected to an outer surface of the extrusion die through one or more inlet openings and one or more outlet openings, such that a heat transferable fluid can flow through the cavity of the extrusion die, the fluid entering the cavity through the cited inlet openings and exiting the cavity through the cited outlet openings.

Such an extrusion die can be cooled down during the extrusion process by for example a cooling liquid, which is an important advantage. This cooling liquid will flow through the cavity via the inlet- and outlet openings and will in this manner be able to exchange heat with the channels through which the extruded material is pressed. Sensitive pharmaceutical products have therefore a significant reduced risk of damage due to the warming up under high pressure.

The extrusion die in this invention is not limited to the function of cooling down the material to be extruded, it can also be heated by hot water or another warm fluid flowing through the cavities in the die.

An additional advantage of this extrusion die is that the extrusion speed can be increased, as the heat produced during the extrusion can be controlled better.

This extrusion die in this invention is not only limited to applications for the pharmaceutical sector and can be used in all different industries where extrusion is used.

The walls of the extrusion die in this invention can be executed very thin. The wall thickness can be limited to 0.5, 1mm or to 1.5mm or even limited to 0.3mm or less. These wall thicknesses limited to 1.5mm, 1 mm, 0.5mm or even 0.3mm allow a good heat transfer through the walls. At the same moment this allows the total thickness of the die to be limited. The shape and the dimensions of the channels for extrusion do not need to be changed to allow sufficient thickness in the walls to obtain the cavity for heating or cooling.

Wall thickness in this invention means the shortest distance between the inside and the outside of the wall, for instance the shortest possible distance between the first or the second side of the extrusion die and the side of the wall dividing the wall from the cavity, or for example the outside of the channel wall at the channel and the inside of the channel wall which separates the channel wall from the cavity.

Walls in this invention means the walls which delimit the extrusion die. The wall separates the extrusion die for example from the spaces around the die, such as the channels, as well as separating the cavity within the die. The walls are for example the channel walls, but also the walls containing the first and the second side. In certain preferred embodiments of this invention, the cavity in the die is delimited by inside walls, in such a way that the cavity comprises a grid connecting the inside walls with each other.

Due to the fact that the die in this invention comprises a cavity, and in certain spaces receives a double wall structure, it is possible that the strength of the die in these locations is affected. To warrant sufficient stiffness of the die one can choose to install a grid structure in the die, that connects both inside walls of the cavity with each other, or in other words it will connect the walls of the double wall with each other.

This grid can be any kind of grid known by teh person skilled in the art, and should preferably be executed in such a way, that the flow from heat transferable fluid in the die will not be influenced, meaning that the temperature control of the material to be extruded by means of the flowing fluid will remain well controllable.

According to preferred embodiments of this invention the extrusion die will have the shape of a dome, in which the first wall is concave and the other wall is convex.

This dome can have the shape of a sphere, dome or an ellipse or others. In this embodiment the pasty mass of the material to be extruded or the granules are pushed from the inside of the dome shaped die to the outside of this die through different channels in the die. Due to the dome shape of the structure, the material to be extruded will, at the end of the feeding apparatus, for example the screw, be pushed in a radial outside direction through the channels of the dome. Hence a well balanced force distribution is obtained which results in more efficient extrusion, lowered friction and consequently a lower temperature.

According to a further preferred embodiment of this invention the attachment means are located between the first and the second side of the die.

In this way the extrusion die can be assembled to the extrusion machine or extruder in a simple and very strong way, without the attachment means disturbing the flow of the material to be extruded.

Preferentially the extrusion die is made out of metal.

Here, further preference goes to stainless steel or titanium.

The described die should be made out of strong material which can resist high pressure and high forces. Metals usually comply with the conditions that apply to materials out of which an extrusion die is made.

This invention also applies to a process for making an extrusion die in which case the extrusion die will be reproduced by a technique chosen out of the group of 3D printing, laser sintering, RM Precise Rapid Manufacturing Laser melting, Electron Beam Melting (EBM), stereolithography, or combinations hereof, by preference the extrusion die will be produced by means of RM Precise Rapid Manufacturing Laser melting.

An extrusion die with a complex structure as described above will be very difficult to be produced with traditional production techniques like for instance turning and milling. The fact that the extrusion die is preferentially made of strong material like metal, will make this process of production even more complex. The above described techniques are however able to produce such complex structures. For example by using the sintering techniques the different structures are built by laser, layer by layer, in this way constructions can be built which were impossible or nearly impossible to build with earlier techniques. The layers which are built up with these techniques have a very limited layer thickness. In this way layer thicknesses or precisions of 100 micron or even better can be reached with an important accuracy.

Moreover, at present these techniques can be used with metals, while a few years back they could only be used with plastics. In this way, for example, titanium structures can be produced.

Furthermore, materials shaped through the sinter processes are very hard due to the fact that the material cores are heated to very high temperatures at which they nearly melt. In this way the points of contact between the cores grow, obtaining very hard materials. Sintered wolfram carbide is for example one of the hardest materials existing at the moment. Moreover it is very corrosive proof and accepted as good manufacturing practice (GMP) in the pharmaceutical industry.

As explained earlier, the process according to the current invention makes it is possible to make an extrusion die with one or more cavities, by which the extrusion die can have a double wall or even a multi wall structure. In addition to this, the process according to the current invention allows to make an extrusion die in such a way that the thickness of a single metal wall can be limited to 1.5, 1 , 0.5 or even 0.3mm or less, through which the total thickness of the extrusion die, measured from the first side to the second side can remain limited to, or in other words be maximum 5mm or by preference even maximum 0,5 to 2mm, even on places where the extrusion die has a double wall structure. Of course larger total thicknesses are possible for extrusion dies with multiple wall structures.

This makes it possible to make a double wall extrusion die, for which the temperature can optimally be regulated due to the flowing through heat transferring fluid, in which the total length of the channels, in accordance to the total thickness of the extrusion die, remains limited to, in other words, maximum 5mm, more preferably maximum 0.5 to 2mm, which is a mayor advantage. The total length of the channels will also be limited by the wall thickness and vice versa, taking in consideration the desired dimensions of the cavity between the walls of the extrusion die which contains the first and the second side.

A multi wall extrusion die with multiple cavities has the mayor advantage one can control the temperature of the die in the neighborhood of the different holes more precisely, for instance by using different fluid flows with different temperatures through the different cavities. It was found that in this way a specific temperature gradient can be obtained in the die. Through the high strength of the laser molten material in the die, the die will maintain its strength and stiffness, despite the thin execution of the die. Because of this the very thin executed double walled die with cavities inside will resist to very high pressures.

This invention also relates to a method for producing parts of an extrusion machine by which the extrusion machine parts are produced by means of a technique chosen out of the group of 3D printing, laser sintering, RM Precise Rapid Manufacturing Laser melting, Electron Beam Melting (EBM), stereolithography, or a combination hereof, by preference the part will be produced by means of RM Precise Rapid Manufacturing Laser melting.

These techniques are the same as those described above and hence have the same advantages. It's not only an advantage to produce the extrusion die by means of this technique, but also other components of this machine can be produced the same manner, given the fact that they can also have a complex structure and shape, making it difficult to produce with traditional techniques.

In this way parts of the extrusion machine can be chosen from the group of a screw, an extrusion die, a dome shaped extrusion die, a press, an extrusion tube, a feeding hopper, a hopper and extrusion shaft and different attachment means to assemble the extrusion die.

Al these parts often have a complex shape, in which way it is an advantage to produce them by the described process methods. It has to be remarked that in the above named group of parts, an extrusion die and a dome shaped extrusion die are mentioned. With this we mean extrusion dies as they generally exist and not only as the one described above and in which a cavity is built. In other words, this invention also includes to the above mentioned process for making traditional extrusion dies as for example used in the plastic industry, because these traditional dies can be produced in a very efficient way using the described process method.

The invention further includes a process for making a part of an extrusion machine for which the part of the extrusion machine essentially has a hollow structure, in in which a cavity extends inside the part of the extrusion machine is connected to an outer surface of the part of the extrusion machine through one or more inlet openings and one or more outlet openings, such that a heat transferable fluid can flow through the cavity of the part of the extrusion machine, and by which the cited fluid enters the cavity through the cited inlet openings and exits the cavity through the cited outlet openings

In this way one can not only produce the extrusion die with a cavity but one can produce every part of the extrusion machine with similar cavities.

In this respect it is for example possible to provide a screw with similar cavities, so that the screw can be heated or cooled through a heat transferable fluid, and this before, during or after the extrusion process.

In this way it is possible to design and produce from each component of the extrusion machine a variant for which the temperature of the processed extrusion materials can be controlled and regulated in a much more stable way than in the today's version of technology.

Hence, for example one can develop a device for melt extrusion in a simple way. Melt extrusion is an extrusion technique in which the material to be extruded undergoes different thermal treatments during the extrusion process. By equipping the extrusion die and other potential components from the extruding machine with cavities through which heat transferable fluids will flow, one can develop a melt extrusion process by which, the material to be extruded, will go through different heat treatments, and by which the process will be better controlled compared to existing melt extrusion techniques.

The invention further includes the use of the extrusion die according to the present invention for extruding deformable material.

The invention will further be clarified by means of the included drawings.

Figure 1 shows a cross section of an extrusion die comprising a cavity that can be produced according to the process of the present invention.

Figure 2 shows a top view in perspective of the extrusion die from figure 1 , on which also inlet and outlet tubes are visible.

Figure 3 shows a bottom view in perspective of the extrusion die from figure 1 , on which also inlet and outlet tubes are visible.

Figure 4 shows a second embodiment of the extrusion die that can be produced according to the process of the present invention.

Figure 5 shows the cross sections of some preferred embodiments of the channels in the extrusion die according to the present invention.

Figure 6 shows the cross sections of some preferred embodiments of extrusion dies and matching screws that can be produced according to the process of the present invention.

Figure 7 shows the cross sections of some further preferred embodiments of extrusion dies that can be produced according to the process of the present invention.

Figure 8 shows some detail views of an extrusion die according to the present invention, showing the cavity.

Figure 9 shows some further detail views of an extrusion die according to the present invention, showing the cavity.

Figure 10 shows a cross section of a channel with a bleed line or water drainage channel. 1. Extrusion die

2. Channel

3. First opening

4. Second opening

5. First side

6. Second side

7. Cavity

8. JAttachment means

9. Inlet opening

10. Outlet opening

11. Feed screw

12. Bleed line / water drainage channel

The extrusion die shown in figure 1 is an example of an extrusion die that can be produced according to the process of the present invention. The extrusion die comprises of a cavity through which a heat transferable fluid can flow, attachment means to attach the extrusion die to the extrusion device, and several channels that are delimited by a channel wall, a first opening and a second opening.

The cavity through which the heat transferable fluid can flow is in this embodiment of the extrusion die circular and thus limited to surrounding the channels that are closest to the edge of the extrusion die. The invention is in no way limited hereto and in other embodiments of this invention the cavity extends further into the extrusion die, so the cavity can surround a larger amount of channels.

Such an embodiment is shown in figures 8 and 9. In these figures a preferred embodiment of an extrusion die according to the present invention can be seen. The extrusion die has a double dome shape in which a large amount of channels can be seen, each delimited by a first opening, a second opening and channel walls. This extrusion die comprises two domes because it is meant for an extruder with twin screws. In this extrusion die, the cavity extends far into the die. It is clearly shown that the cavity surrounds several channels. In doing so an excellent heat exchange is obtained with the material that is extruded through these channels.

The extrusion dies in the embodiments shown in figures 1-3 and in the embodiments shown in figures 8 and 9 have a dome shape. The invention is in no way limited to this shape and a professional can freely determine any other structure or shape.

The channels shown in figures 1-3 are mainly linear, but the invention is also not limited to this shape. For instance channels with a conical shape or channels with a contraction or expansion in the centre could be chosen. Figure 5 shows some examples of preferred embodiments of the channels. The shape of the channels is important as during the extrusion they can build in different effects such as relaxation, calibration and/or compression of the material to be extruded, which in specific circumstances can be very desirable. In traditional dies it can be difficult to obtain such steps successively within one die, as a result of which it can be necessary to extrude in multiple steps. Because the process of the current invention easily allows complex structures to be shaped, it is now possible to run through these different steps in one single die.

Figure 10 shows an example of such a channel in which first a compression and subsequently a relaxation of the extruded product is obtained. Furthermore, figure 10 also shows a bleed line or water drainage channel that is connected to the channel. According to the present invention it is possible to produce an extrusion die in which each channel has such a bleed line or water drainage channel.

Furthermore the shape of the cross section of a channel can freely be determined. Square, triangular, oval and other cross section shapes of the channels can be chosen, by which the shape of the extrusion profile can be varied.

In figure 4 a second embodiment of an extrusion die is shown. This extrusion die does not comprise of a cavity for the flow through of a heat transferable fluid en does not fall within the scope of the first conclusion, but is an example of an extrusion die that can be produced according to the process of the present invention. According to this process, in principle any part of an extrusion device can be produced though a technique chosen from the group of 3D printing, laser sintering, RM-Precise Rapid Manufacturing Lasermelting, Electron Beam Melting (EBM), stereolithography, and combinations hereof, preferably the part of an extrusion device is produced by means of RM-Precise Rapid Manufacturing Lasermelting.

The extrusion die shown in figure 4 is a good example of a part that can be produced by means of the above mentioned techniques as it has a fairly complex structure. Such a structure will be very difficult to produce using traditional production methods such as turning, milling, etc.

Further examples of complex extrusion dies that can be produced according to the process of the current invention are shown in figures 6 and 7. In figure 6, the second preferred embodiment of an extrusion die also shows a mating screw of which the shape is complementary to the shape of the extrusion die. Such complex shapes of a complementary extrusion die and screw are also difficult to obtain using the traditional production methods, but do not raise a problem for the process described in the present invention.

In the extrusion dies shown in figures 6 and 7 the direction in which the granules or the material to be extruded will be extruded is also shown. Depending on the position of the channels in the extrusion die, the direction can be adapted and varied according to wish.