WO2018050674A1

WO2018050674A1 - Method and device for extruding plastics

Info

Publication number: WO2018050674A1
Application number: PCT/EP2017/072976
Authority: WO
Inventors: Erich Stockmann; Ulrich Kreuz
Original assignee: Maag Automatik Gmbh
Priority date: 2016-09-13
Filing date: 2017-09-13
Publication date: 2018-03-22
Also published as: DE102016117213A1; DE102016117213B4

Abstract

A method and device for extruding plastics, preferably in conjunction with plastic strand granulation, wherein the plastic, which is heated to an extrusion temperature and extruded through one or more dies (7) of a die head (1), is irradiated with electromagnetic radiation immediately at the die outlet in such a way that plastic remaining in the region of the die outlet is heated to a higher temperature, which is higher than the extrusion temperature, preferably higher than the decomposition temperature and and optionally even higher than the combustion temperature of the plastic. At the same time, the die head (1) can be irradiated with the electromagnetic radiation in such a way that the surface of the inner wall of the dies (7) from the die outlet to at least 5 mm into the die head (1) is heated to a temperature that is higher than the extrusion temperature and is preferably below the decomposition temperature of the plastic, to avoid deposits of plastic on the die outlet.

Description

Method and apparatus for extruding plastics

The invention relates to a method and a device for extruding plastics, preferably in the form of

thermoplastic plastic strands for the production of

Plastic granules. The method and the device are particularly associated with

Kunststoffstranggranulieranlagen advantageously used.

Plastic extrusion granulation becomes more thermoplastic

Plastic extruded in the form of strands and over a

Cooling section transported to a granulator, in which the cooled strands are then pelletized into granules. The Abkühlstrecke usually includes cooling the strands by means of water either in a water bath or a

water-washed gutter.

Deposits in the form of a so-called "beard", which forms on the nozzle outlet of the individual nozzles of the nozzle head next to the actual plastic strand, prove to be problematic If the beard is torn off, there is a risk that it will go to the granulator with the plastic strand and get into the granules.

To avoid this, such plastic deposits are burned at the nozzle exits usually by means of gas flames, for example, twice per minute for 10 seconds on the off The nozzle escaping plastic can be directed directly to the nozzle exit. For this purpose, by means of appropriate gas nozzles a common flame over the entire width of

usually generated in a row arranged nozzles.

An alternative is described in DE 10 2011 106 709 AI. Accordingly, the strands are at the exit from the perforated plate by a Anstromfluid flows, which has a temperature of preferably 50 ° C to 80 ° C above the melting temperature of the plastic material. By heating the

Nozzle outlet, the plastic is prevented from attaching to the nozzle head. The exit velocity of the Anströmfluids is relatively high, preferably at 150 m / s to 200 m / s, to any

Remove deposits.

The energy input associated with the flow is high, in particular due to the need to heat the flow fluid to the required high temperatures.

Object of the present invention is an alternative to avoid and / or removal of the nozzle exit of a

To propose resulting plastic deposits extrusion nozzle head.

This object is achieved by a method and an apparatus having the features of the appended independent claims. In dependent claims are advantageous

Developments and embodiments of the invention indicated.

Accordingly, a process according to the invention provides for heating to an extrusion temperature and through or To irradiate a plurality of nozzles of a nozzle head through extruded plastic immediately at the nozzle exit with electromagnetic radiation so that in the region of the nozzle outlet lingering plastic is heated to an elevated temperature, which is above the extrusion temperature. Accordingly, a device according to the invention comprises at least one source of electromagnetic radiation, which is set up to appropriately heat the plastic staying in the region of the nozzle outlet by means of electromagnetic radiation.

The heating of the accumulating at the nozzle exit plastic over the extrusion temperature is more energy efficient than first to heat a stream of air and with the heated

Air flow to overheat the extruded plastic. However, the invention does not exclude that plastic remnants are blown off from time to time by means of an air flow, which may also be hot, whereby this blow-off is preferably carried out in a pulse-like manner.

As electromagnetic radiation comes in particular

Thermal radiation for use, preferably IR radiation. The IR radiation can advantageously be generated by means of one or more IR heating rods, which are arranged close to the nozzle outlet of the nozzle of the nozzle head. The distance is

preferably 50 mm or less, more preferably 15 mm or less, and in any case is in the preferred range between 10 mm and 50 mm.

Alternatively, other electromagnetic radiation may also be used, for example laser radiation, since laser radiation can be used in a very targeted manner and with a high energy density. Especially Laser radiation with long wavelengths is suitable, for example the radiation of a C0 ₂ laser, since thermoplastics usually absorb long-wave radiation well without any additives.

The use of electromagnetic radiation can

According to the invention advantageously used in two ways, namely on the one hand to unwanted

To remove plastic deposits and on the other hand to avoid that such plastic deposits ever form, both goals can also be combined.

According to the first approach, the plastic remaining in the region of the nozzle outlet is heated by means of the electromagnetic radiation to a temperature which is not only above that

Extrusion temperature but above the decomposition temperature of the plastic in question. This will be

Plastic deposits dissolved and do not get into the granules. If decomposition residues adhere to the plastic strands and thus get into the granules, these residues are so small and so small in dimension that they for the quality of

Granules are meaningless.

If - preferably - it should be avoided that it is to

Flammbildung comes, the elevated temperature is preferably on the one hand above the decomposition temperature but on the other hand below the combustion temperature of the plastic in question. The combustion or ignition temperature is at the

vast majority of plastics about 50 ° C to 100 ° C above the respective decomposition temperature. Aiternativ the elevated temperature but also over the

Combustion temperature are, so it wanted to

Flame formation occurs, as occurs in the prior art in the case of burning by means of gas flames. The risk that combustion residues in relevant quantities with the

Plastic strands could get into the granules, is not critical.

The extruded plastic strands themselves have the

electromagnetic radiation has no effect because of the

Residence time of the plastic strands in the radiation

exposed area is too short, that the strand material could be heated significantly by the radiation. However, in order to prevent the nozzle head from overheating itself, in particular in the first approach pursued here, in which the elevated temperature is above the decomposition temperature or optionally even above the combustion temperature of the plastic, it may be advantageous to use the irradiation only temporarily, in particular periodically.

According to the second approach, the addition or formation of a beard of the plastic in the nozzle exit area should not occur at all but should be suffocated as far as possible in the bud. This approach is based on the assumption that the beard already arises within the nozzle and is slowly pushed out of the nozzle. To counteract this, the nozzle head is irradiated immediately adjacent to the nozzle exit of the nozzles with the electronic radiation, in such a way that the

Inner wall surface of the nozzle from the nozzle outlet to at least 5 mm, preferably 10 mm, heated into the nozzle head to a temperature above the extrusion temperature and below the decomposition temperature of each extruded Plastic lies. Preferably, the inner wall temperature is between 5 ° C and 20 ° C, more preferably between 10 ° C and 15 ° C above the extrusion temperature. When starting the system, the inside wall temperature can also be set to a temperature of approx. 25 ° C above the melt temperature (extrusion temperature) and shortly afterwards reduced to the abovementioned values. Although the nozzles are normally heated anyway, but with significantly lower temperatures for the particular purpose, when starting the extruder in the nozzles "frozen"

Plastic, so plastic that has solidified by cooling, melt. This melting temperature is slightly above the melting temperature of the material, but well below the extrusion temperature. The extrusion temperature is the temperature that the plastic melt actually has, in other words the melt temperature. In the case of carbonate, for example, the melting temperature is 220 to 230 ° C, the

Melting temperature for melting frozen

Plastic in the nozzle of the nozzle head at about 250 ° C and the actual melt or extrusion temperature of the

Plastic material regularly well over 250 ° C.

Now, according to the second approach, the

Inner wall surface of the nozzle at a temperature above the extrusion temperature and preferably below the

Decomposition temperature is maintained, the formation of a bar at the nozzle exit counteracted from the outset.

By means of radiant heaters, especially IR heating rods, it is now very possible to use thermal radiation targeted. IR heating elements can be easily adapted to shape and, for example, as a heating coil, which the individual nozzles at least partially, along the row of nozzles and / or around individual nozzles.

Preferably, a device is provided, with which the

Radiation source can be moved away from the nozzles and towards the nozzles to avoid a collision with a scraper, which is moved via the outlet nozzles to strip after the startup process of the extruder initially emerging from the nozzle plastic before the subsequent plastic the Granulator is fed for pelleting. In that regard, it may be advantageous to the radiation source from the

Movement path of the scraper temporarily move out. Also, for cleaning purposes and / or for adjusting the temperatures generated at the nozzle, it may be advantageous to

Radiation source away from the nozzles or closer to the nozzles to move.

Alternatively or additionally, a collision of the scraper with the radiation source can be prevented if the trajectory of the scraper between the radiation source and the nozzle head extends, so if there is a distance between the radiation source and the nozzle head, in which moves the scraper. According to another alternative, the scraper may advantageously be arranged to be movable between opposing radiation sources along a surface of the nozzle head (for example when the nozzles are arranged in series and one or more on each side of the nozzle row)

Radiation sources are arranged).

Further advantageously, the device further comprises a

Guide on which serves the extruded plastic during the start of the extruder from the subsequent transport path lead away ("dissipative plate"), so that the extruded plastic during the start-up phase for

Granulator arrives, or after the start of the

subsequent transport route ("feeding plate"), so that the plastic only during the actual

Production phase reaches the granulator. For this purpose, the guide between a first position in which the extruded from the nozzle plastic gravity on the

Guide device falls and in which the guide device is preferably rinsed with water, and a second position in which the plastic extruded from the nozzles past the guide device, displaced. The scraper for stripping the emerging from the nozzle plastic is advantageously coupled to the guide, so that with the stripping of the plastic at the end of the starting process, the guide device moves in or out of the transport path of the extruded plastic, depending on whether it is an zuleitende or dissipative conducting device.

Further features and advantages of the invention will become apparent from the following description of embodiments according to the invention and further alternative embodiments in conjunction with the appended drawings, which show schematically:

1 shows a device for the extrusion of plastics with feeding guide device,

2 shows a device for the extrusion of plastics with dissipative guide device, FIG. 3 shows a nozzle head in a bottom view for use with a device according to FIG. 1 or FIG. 2,

Fig. 4, the nozzle head of Fig. 3 in the longitudinal side

Cross-sectional view

Fig. 5 shows the nozzle head of Fig. 3 in transverse side

Cross-sectional view and

Fig. 6 shows a variant of the nozzle head of Figs. 3 to 5 in cross-sectional view.

Figure 1 shows a Kunststoffstranggranulieranlage with a

Nozzle head 1 of an extruder C, from which plastic strands KS emerge molten and meet a guide device 2, with which the plastic strands KS are fed to a subsequent transport chute 3 (feeding guide device). The

Kunststoffstranggranulieranlage in Figure 1 is shown in its operating phase, that is, the zuleitende guide 2 detects the plastic strands KS and directs them designed as an inclined, rigid groove transport device 3. The guide device 2 is connected in the usual way to a water connection, and water (H ₂ 0) flows over the surface of a plate 2 b (see Fig. 4) further down the gutter 3 to a circulating

Conveyor belt 4, wherein the water entrains the plastic strands KS. The cooling water is withdrawn at the lower end of the gutter 3 substantially completely via a dewatering device 5. The conveyor belt 4 serves as

Temperature compensation path, so that the temperature profile homogenized over the cross section of the plastic strands before the Plastic strands are fed to a granulator 50 for granulation there.

Instead of the circulating belt 4, others can

Assemblies for the treatment of the plastic strands may be provided. If necessary, the circulating belt 4 can also be completely eliminated or equipped with additional elements, such as blowing nozzles or water spray nozzles.

The guide device 2 can be made of the one shown in FIG

Operating position in a start-up position, not shown

preferably be displaced in the direction perpendicular to the plane of the drawing. For each displacement from one position to the other position, the plastic strands are separated with a separating element 9 shown in more detail in the following figures 3 to 6. If now in the case of the illustrated in Figure 1

Kunststoffstranggranulieranlage with zuleitender guide 2 the guide 2 is displaced perpendicular to the image plane, meet the ends of the following plastic strands automatically on the second, leading to a waste granulator 60 transport device 10, which is also designed as an inclined, rigid, wasserbespülte gutter. In the then occupied, designated as the start position position of the guide 2, the

Plastic strands KS thus granulated directly in the waste granulator 60.

In Figure 2, a corresponding Kunststoffstranggranulieranlage is shown, in which the guide device 2, however, is designed as a discharge guide. Shown is the

Kunststoffstranggranulieranlage in this case in their

Start-up phase, that is, from the extruder 1 molten exiting plastic strands KS strike the surface of the guide 2 and are from the cooling water H ₂ O.

entrained and fed to the transport device 10, which directs the plastic strands in the illustrated example case directly to the waste granulator 60.

As soon as the plastic strands KS have the desired consistency, the guide device 2 becomes of its in FIG. 2

shown start-up position, preferably in a direction perpendicular to the image plane, wherein the plastic strands KS at the same time by means of a in this figure again not

severed severing knife are severed. The ends of the following plastic strands then fall vertically down directly on the water-washed drainage channel 3 and, as explained above in connection with Figure 1, the

Production Granulator 50 fed.

Both Kunststoffstranggranulieranlagen is furthermore

in common that they have a source 6 for electromagnetic

Radiation comprising one or more IR heating elements in these embodiments.

Figure 3 shows a nozzle head 1, as it can be used in connection with the embodiments of Figure 1 and Figure 2, in a view from below. In this particular embodiment, the source 6 for electromagnetic radiation is formed by a single IR heating element, which is heated by means of a current or voltage source 8 and

electromagnetic radiation in the form of heat radiation, in particular IR radiation releases. The IR heating element 6 extends on both sides of a row of nozzles 7 of the nozzle head 1, from which heated to extrusion temperature plastic in the form of plastic strands KS exudes molten. The IR heating element 6 is arranged near the nozzle exit of the nozzles 7, so that the thermal radiation reaches at least the plastic emerging from the nozzles 7 directly at the nozzle exit. The distance of the IR heating element 6 from the nozzle outlets of the nozzles 7 and the

Temperature of the heating element 6 are chosen so that in the region of the nozzle outlet lingering plastic is heated to an elevated temperature, which is above the extrusion temperature. The

Extrusion temperature is the average over the strand cross-section temperature of the extruded plastic at the nozzle outlet of the nozzle 7, also referred to as the melt temperature. Instead of a heating element 6, it is also possible to use a plurality of heating rods 6, for example one heating element in each case on each side of the row of nozzles 7 or one heating element per nozzle. In particular, the heating element (s) may completely or at least partly surround the individual nozzles, as shown in FIG. 3, where the heating element 6 is guided along the row of nozzles 7 as a heating coil.

As mentioned above, the electromagnetic radiation source 6 or the IR heating rod is used, if necessary, in the region of

To heat nozzle outlet lingering plastic to a temperature above the extrusion temperature, wherein this temperature is preferably above the decomposition temperature of the plastic. The decomposition residues of the plastic are so small compared to the total plastic throughput that they

Quality of the produced plastic granulate not

impair, as far as they get into the granulator 50 at all. Alternatively, the temperature of lingering in the region of the nozzle outlet plastic by means of the electromagnetic

Radiation source even be heated above the combustion temperature of the plastic, which is less preferred. The plastic burns then similar to the prior art when burning by means of a gas flame.

For energetic reasons, the electromagnetic

Radiation source 6 operated only temporarily, especially when the device is operated in the mode that lingers in the region of the nozzle exit plastic on one above the

Combustion temperature of the plastic lying increased

Temperature is heated, so that in this case only from time to time any plastic residues are burned at the nozzle outlet. Optionally, the decomposition or combustion residues may be blown away by a blowing device which may be cyclically operated (not shown in the figures).

By means of the electromagnetic radiation source 6, in particular also by means of the heating rod specifically used here, the radiant energy can be localized very locally. According to a preferred variant, not only is possible in the area of

Nozzle exit lingering plastic on one over the

Extrusion temperature lying elevated temperature heated, but also the nozzle head 1 itself is irradiated immediately adjacent to the nozzle exit of the nozzle 7 with the electromagnetic radiation. The radiant energy is chosen so that the inner wall surface of the nozzles 7 of the respective

Nozzle outlet to at least 5 mm, preferably at least 10 mm, heated into the nozzle head 1 into a temperature, the above the extrusion temperature and below the

Decomposition temperature of the plastic is. As a result, the formation of a plastic bar at the outlet of the nozzle. 7

counteracted.

As mentioned above in connection with the description of Figures 1 and 2, is used in the start-up phase of

Kunststoffstranggranuliervorrichtung a scraper 9 to the strands generated in the start-up plastic strands separate from the nozzle head 1, before the subsequent plastic strands are fed to the granulator 50 for granulation. In order to avoid a collision of the scraper 9 with the electromagnetic radiation source 6, a, not shown in the figures,

Means be provided, with which the radiation source 6 can be moved away from the nozzles 7 and after the stripping again close to the nozzles.

On the other hand, FIGS. 3 to 5, on the one hand, and FIG. 6, on the other hand, show two preferred exemplary embodiments, which show such a device for displacing the radiation source 6

can make dispensable. In the embodiment according to Figures 3 to 5, a scraper 9, which may be formed for example as a separating knife, strands for stripping the emerging from the nozzle 7 plastic strands provided between the radiation source 6 and the nozzle head 1 along a

Surface of the nozzle head 1 is movable. The direction of movement is indicated in Figure 3 by two arrows. The scraper 9 is in turn fixedly coupled via a holder 10 with the guide device 2, as in Figures 4 and 5 in two orthogonal

Cross sections is shown schematically. Also in Figure 4, the direction of movement of the scraper 9 and the guide device is the second indicated by two arrows. When the scraper 9 is moved together with the guide device 2 from its position shown in Figure 4 to the left in a position in which the

Guide device 2 is located below the nozzle head 1, so are from the nozzles 7 of the. During this sequence of movements

Nozzle head 1 leaking plastic strands by means of

Scraper 9 is severed and the following plastic strands fall on a water-rinsed plate 2b and are taken with the water from the water supply line 2a (H ₂ 0). The coupling of the scraper 9 with the guide device 2 via the holder 10 is clearly shown schematically in FIG.

In contrast, FIG. 6 shows a second exemplary embodiment.

Instead of moving the scraper 9 between the radiation source 6 and the nozzle head 1, the scraper 9 is here between radiation sources 6, with respect to the nozzles 7 each other

opposite, along the surface of the nozzle head 1 movable. This arrangement makes it possible to arrange the radiation source 6 even closer to the surface of the nozzle head 1.

The following table shows typical extrusion temperatures and decomposition temperatures of common plastics. The combustion or ignition temperature is in most plastics about 50-100 ° C above the above

Decomposition temperature. It should be noted that the decomposition is not exclusively temperature dependent. Even at lower temperatures and correspondingly long time can

Decompose plastics. Some plastics (eg PET, PA) are hygroscopic, and in the presence of H ₂ O (steam) at elevated temperature, a reversal of the condensation reaction, ie

Molecular chain degradation, a. Plastic extrusion temperature [° C] decomposition temperature [° C]

LDPE 180-200> 340

HPPE 210-240> 340

LLDPE 190-230> 340

PP 190-240> 330

PC 260-290> 350

PET 260-280> 300

PA6 240-260> 300

PS 180-220> 300

PMMA 180-240> 280

Claims

Patent claims

1. A process for extruding plastics, preferably in the form of plastic strands (KS) for the production of granules, comprising the following steps:

- Extruding the heated to an extrusion temperature

Plastic by one or more nozzles (7) of a

Nozzle head (1) through and

- Irradiation of the out of the nozzles (7) exiting plastic directly at the nozzle exit with electromagnetic radiation such that in the region of the nozzle outlet lingering plastic is heated to an elevated temperature, which is above the extrusion temperature.

2. The method of claim 1, wherein the elevated temperature is above the decomposition temperature of the plastic, preferably below the combustion temperature of the plastic.

3. The method according to claim 1 or 2, wherein the

electromagnetic radiation is heat radiation, preferably IR radiation, particularly preferably IR radiation generated by means of one or more IR heating rods (6).

4. The method according to any one of claims 1 to 3, wherein the irradiation takes place only temporarily.

5. The method according to any one of claims 1 to 4, wherein also the nozzle head (1) immediately adjacent to the nozzle outlet of the nozzle (7) is irradiated with the electromagnetic radiation.

6. The method according to claim 5, wherein the irradiation of the

Düsenkopfs takes place such that the inner wall surface of the nozzle (7) from the nozzle outlet to at least 5 mm,

preferably at least 10 mm, heated in the nozzle head (1) into a temperature which is above the extrusion temperature and preferably below the decomposition temperature of the plastic.

7. Device for the extrusion of plastics, preferably in the form of plastic strands (KS) for the production of granules, comprising:

- A nozzle head (1) with one or more nozzles (7) for the extrusion of molten plastic and

- At least one source (6) for electromagnetic radiation, which is adapted to, in the region of the nozzle outlet lingering plastic by means of electromagnetic

To heat radiation.

8. Apparatus according to claim 7, wherein the radiation source (6) comprises one or more IR heating elements.

9. Apparatus according to claim 7 or 8, wherein the nozzles (7) of the nozzle head (1) in at least one row and the radiation source (6) on both sides of the row of nozzles (7) are arranged.

10. Device according to one of claims 7 to 9, wherein the radiation source (6) surrounds the individual nozzles (7) at least partially.

A device according to any one of claims 1 to 10, comprising means for displacing the radiation source away from the nozzles (7) and towards the nozzles (7).

12. Device according to one of claims 7 to 11, wherein a scraper (9) for stripping of the nozzles (7) exiting plastic is provided between the radiation source (6) and the nozzle head (1) along a surface of the nozzle head ( 1) is movable.

13. Device according to one of claims 7 to 11, wherein a scraper (9) for stripping of the nozzles (7) exiting plastic is provided, between radiation sources (6), with respect to the nozzles (7) facing each other, along a Surface of the nozzle head (1) is movable.

14. Device according to one of claims 7 to 13, comprising a guide device (2) which falls between a first position in which the extruded from the nozzles (7) plastic gravitationally on the guide device (2) and in which the guide device (2 ) is preferably rinsed with liquid (H ₂ O), and a second position in which the plastic extruded from the nozzles (7) on the guide device (2) falls past, is displaced.

15. The apparatus of claim 14, comprising a with the guide device (2) coupled scraper (9) for stripping of the nozzles (7) exiting plastic.