DE4231232C1 - High efficiency degassing process for e.g. thermoplastic melts - mixes melt with injected liq. under pressure in extruder, releases pressure to form foam breaks up foam, degasses and spreads into thin film - Google Patents

Abstract

In a high efficiency degassing process for thermoplastic melts or similar liquids the melt is added to a single-screw extruder; here its pressure is increased continuously in the direction of movement, back flow is prevented, an entrainment material is injected early in the flow, the melt/entrainment material mix is mixed intensively and homogenised and is then suddenly depressurised and foamed up. The mix is next subjected to a roller effect to break up the foam and is then fed to a high efficiency thin film degassing extruder where its thin layers are spread over a larger area and subjected at the same time to a degassing vacuum. ADVANTAGE - The process is free from the problems of existing methods i.e. it does not allow deposits to form which can decompose thermally and return to the melt (e.g. as monomers)

Description

The invention relates to a high-performance degassing process and -extruder, as described in the preamble of the first claim.

DE-PS 40 01 986 from the applicant is a multi-wave thin Layer reactor known, which is also used for degassing purposes becomes. The extruder has a vertical housing. With inside a self-cleaning profile on an inner wall having thin-film waves. The waves are through a planet gear both in rotary motion about its own axis and too a circulation along the housing inner wall driven.

The thermoplastic melt is degassed when the layers spread out on the thin-film waves Melt facing the interior. The interior is over a Coaxially arranged therein, having an axial degassing hole Small diameter shaft connected to a vacuum source. Since the Surface of the thin-film waves have melt layers  overall a very large area of thin layers is formed, so that even with highly viscous and therefore difficult to degas Melt excellent degassing results can be achieved.

The thickness of the melt that forms on the thin-film waves layer is determined by the distance of the screw sealing profile a shaft to the screw sealing profile of the neighboring and thus in meshing engaging standing shaft.

Such a degassing process fails because of coaxial degassing hole in the central shaft with a Vacuum source is connected. It turns out that this hole after a certain time due to entrained residual monomer components sets, so that the degassing comes to a standstill.

From DE-PS 40 01 988 of the applicant, a Entgasungseinrich device is known which is basically the same as the device of the above DE-PS 40 01 986. In Figs. 4 and 5 a further embodiment of the degassing device is shown, which operates with a central gear shaft, and the planetary spindles.

The central shaft has a helical toothing, which with the Ver serration of the thin-layer shaft rotating and rotating around its axis len combs.

There is an annular degassing space on the outside around the thin-film waves arranged to which a vacuum or vacuum source is connected is. The ring-shaped degassing space enables the negative pressure to act on the outer circumference of the thin-film waves. It there is therefore a very large melt layer on the thin Layer waves are available for the degassing process.  

This device also shows that the degassing after one certain tent due to entrained residual monomer to a halt comes, which came on the inner wall of the annular degassing build up and remove it at this point very difficult are.

Since a return of the deposits is not possible, therefore frequent business interruptions are essential.

It is the object of the present invention, the degassing device tions of the type described above to improve without it malfunctions described comes. It must be ensured, that no deposits can form, the zer as thermal put components back in the processing process nen. In particular, however, it should be ensured that when in use of entraining agents when carrying out the degassing process good degassing results can be achieved.

The task is characterized by the features in the characterizing part of the most or second claim in connection with the features of the preamble solved.

The melt / entrainer mixture foams after the pressure relief, d. H. after injection into the planetary roller using an annular nozzle divide very strongly because this mixture has a temperature of 150- 300 ° C and the injected entrainer (e.g. water) from the liquid changes to the vaporous state and thus enormously foams.

The foaming process creates very thin layers of melt, very much large degassing surfaces and a partial pressure reduction of the degassing Honomer- or solvent content reached.  

The foam of the mixture of plastic melt, entrainer, rest becomes monomeric in the planetary roller part by the rotation of the planets with simultaneous circulation around the central spindle through the roller destroyed, causing a large part of the melt bubbles to burst and the released gas is sucked out of the bubbles by the negative pressure becomes.

The planetary roller part conveys the melt into the thin area Layer process part in which the actual degassing process takes place.

Preferably on the top of a horizontally arranged housing a vent opening is introduced, on which a so-called Ent gassing dome with a vacuum line connected to it is arranged.

In contrast to conventional degassing extruders, this machine uses Nengattung achieved that only through a relatively small degassing The entire process interior is exposed to negative pressure becomes. The negative pressure is planted through the respective melt-free Gusset areas and in the axial direction through the open cross cuts the screw profile to the surfaces of all thin layers waves and tears off residual monomer bubbles, in which reaction gap Products and the like are contained in the melt layers on the on the thin-film waves by the mutual stripping of the Form the screw sealing profile of the thin-film shafts.

But not only plants in the axial direction to the thin-film waves the negative pressure in the housing continues. Also in the radial direction the individual thin film waves around, d. H. through the so-called "Erdmenger profile" through, the negative pressure acts on the melt  layer and leave the tiny residual mono there mer bubbles burst so that the gas thus released is drawn off becomes.

With conventional single-screw extruders, only the one below can be used area of the degassing opening and a small part of the Worm threads are exposed to negative pressure.

But also with twin-screw extruders with intermeshing screws the degassing negative pressure only plants in a smaller area in the housing because the housing is outside the degassing opening extends into the gusset area between the screws. For the self-cleaning of the snails is the extension of the casing indispensable down to the gusset areas.

In the device according to the invention, it is the first time for the maintenance of self-cleaning is no longer necessary, the Ge down to the gusset areas between the screws to lead.

According to the invention, the device is self-cleaned by the rotation of the rotating thin-film waves around the central shaft. Through this circulation, the thin-film waves graze both the casing inner wall as well as the central shaft and thus work completely self-cleaning.

Despite the fact that in the gusset areas between the thin layered shafts there is no housing as with the twin screws, will get self-cleaning.

In addition, the degassing negative pressure spreads considerably water throughout the housing because the gusset areas are free. The  free volume inside the case is because of the free gusset rich much larger, which means that the free for the Un attainable surfaces are much larger than at ago conventional twin screw extruders.

It is therefore possible for the first time to use the entire process interior the thin layers of melt on the surfaces of the thin-layer wel len from a negative pressure using only a small degassing opening add, so that outstanding degassing results even at highly viscous sen thermoplastics, such as. B. in the post-condensation or demonomerization of polyamides.

Due to the toothless design of the inner wall of the housing is achieved that the intermeshing thin-film waves on the Slip along the smooth inner wall of the housing and wipe it off nigen.

In the same way, the rotating around their axis and the same in time around the central, smooth wave rotating thin-film waves the central shaft, so that there are no deposits bil that can.

However, no shelves are built on the thin-film waves themselves efforts because there is constant combing out.

An embodiment of the invention is shown in the drawing.

Show it:

Fig. 1 shows a longitudinal section through a device with a high-performance thin-layer extrusion solution.

FIG. 2 shows a cross section along the line II-II in FIG. 1.

Fig. 3 shows a cross section along the line III-III.

Fig. 4 is a plan view of a settlement of all thin-film waves lined up next to each other.

Fig. 5 is a cross section along the line VV in FIG. 1.

The high-performance degassing device shown in FIG. 1 is composed of different sections, which are listed below.

Section 30 is a drive section with back pressure, radial bearing and mechanical seal.

Section 31 is a feed screw section with a melt feed opening.

Section 32 has a so-called "blister", which is provided for the formation of a melt seal in the direction of the melt feed opening.

Section 33 has a toothed disk region with toothed disks 26 , as is also shown in cross section in FIG. 2 and which is used to achieve a good mixing of the entrainer injected through the opening of the entrainer injector 25 with the melt.

Section 34 has an annular nozzle 20 which injects the melt / entraining agent mixture into the planetary roller part. The highest pressure after the screwing in is partially built up by the ring nozzle 20 , ie the blister section 32 and the ring nozzle are conveyed at high pressure by the single screw. The high pressure is required so that the Schleppmit tel, z. B. H ₂ O can be mixed in a liquid state without evaporation from the toothed disks 26 .

Section 35 In this section, the mixture foams very strongly because a large pressure drop has been created between sections 34 and 35 through the annular nozzle 20 . The foam of the mixture of polymer melt, entraining agent and residual monomers is destroyed by the rotating and rotating planet wheels 4 ( FIG. 5) by a roller effect. Residual monomer bubbles are destroyed by this process and the gas thus released from the bubbles is sucked off by the underpressure starting from the degassing opening 12 .

Section 36 In this high-performance degassing section, the melt is spread into thin layers and the high-performance degassing process takes place.

The sections 30 - 36 can be degassed material be arbitrarily often again be connected in series according to the. The screwing part in section 31 , the blister in section 32 and the toothed disk part 26 in section 33 have a common shaft 11 which is connected to the central spindle in a rotationally fixed manner.

The maximum performance degassing device shown in section 36 is described in detail below.

A central shaft 2 is arranged coaxially in a housing 1 . To the shaft 2, the thin film shafts 3 are at equal intervals arranged with each other in a meshing engagement as shown in FIG. 3 and FIG. 4 can be seen.

The drive for the rotation of the thin-film shafts 3 about their own axis and at the same time about the central shaft 2 takes place via toothed planet wheels 4 which are connected to the shaft ends in a rotationally fixed manner and which interact with a likewise driven, driven central spindle 5 .

The single-screw part shown in section 31 , the toothed disk area shown in section 33 , the shaft in the ring nozzle area 34 , the central spindle 5 , the shaft 2 , the central spider of the planetary part 5 a and a screw part 13 are connected to one another in a rotationally fixed manner.

From the cross section shown in Fig. 5, the rotational movement is evident.

By rotating the central spindle 5 having a toothing, the planet wheels 4 , which likewise have a toothing, are set in rotation about their own axis and at the same time in a movement running around the central spindle 5 , which is represented by arrows 6 , 7 and 8 .

Since the planet wheels 4 are connected in a rotationally fixed manner to the thin-film shafts 3 and the central spindle 5 is connected in a rotationally fixed manner to the shaft 2 , the parts (arrows 6 , 7 , 8 ) of the component shown in section 36 are rotated as shown in FIG. 3.

In Fig. 3, the free gusset areas 9 and 10 not filled with melt are shown by checkered hatching.

Through the only a small annular gap ring nozzle 20 ge reaches the melt in the planetary roller drive part, consisting of the planet wheels 4 and the central spindle 5 and is promoted in the direction of the egg degas device by the oblique teeth of the spindles.

The melt is taken over by the thin-film shafts 3 and evenly distributed on the surface of the thin-film shafts 3 due to the intermeshing, brushing process of the screw web 14 with the adjacent screw web 15 of the adjacent thin film shaft 3 ( FIGS. 3 and 4).

The thin layer is formed corresponding to the thickness of the Abstan of 16 of a screw flight 14, 15 to the gear base 17 of the adjacent thin shaft 3, as shown in Fig. 4. Thus, there is produced on all thin film shafts 3 a uniformly thick molten layer degas excellently by vacuum lets, ie the thin wall of the tiny residual monomer bubbles burst when the free space is exposed to a vacuum. The released gas from the bubbles (residual monomers or the like) is then sucked out through the degassing opening 12 .

The course of the negative pressure is shown starting from the degassing opening 12 in FIGS. 3 and 4.

The arrows 18 in FIGS. 3, 4 and 5 show the gas flow when a negative pressure or vacuum is applied to the degassing opening 12 .

From this schematically illustrated course it is clear that the entire inner housing and all gusset areas 9 and 10 in the housing and the adjacent planetary zen areas (arrow 18 in Fig. 5) the vacuum or vacuum sets out only through a degassing opening.

It is therefore possible for the first time to also subject the lower region of an extrusion device facing away from the degassing opening to a degassing process because the melt remains on the thin-film waves. The gusset areas 9 and 10 do not fill with melt because the thin-film shafts 3 hold the melt.

Since the thin-film shafts 3 fully rotate about their own axis, they may take melt adhering to the smooth inner wall 1 of the housing or the smooth shaft wall of the shaft 2 back into the screw flights. Since the screw webs 14 and 15 are arranged at an angle to each other, the melt is continuously conveyed through the planetary part 5 a to the single-screw part 13 and to the discharge opening 19 .

Excellent results were also obtained when using the inventive Equipment for post-condensation and simultaneous degassing of highly viscous polyamide melts achieved with conventional degassing solution extruders are very poor in their residual monomer content can be freed.

Reference list

1 housing
2 wave
3 thin film waves
4 planet wheels
5 central spindle
5 a planets
6 arrow
7 arrow
8 arrow
9 gusset area
10 gusset area
11 common wave
12 vent opening
13 single-screw part
14 screw flight
15 screw flight
16 distance
17 gangway
18 arrows
19 discharge opening
20 ring nozzle
25 entrainer injector
26 tooth lock washers
30 section
31 section
32 section
33 section
34 section
35 section
36 section

Claims (8)

1. High-performance degassing process for thermoplastic plastic melts, high-molecular polymers or similar liquid to viscous substances to be degassed, in which the melt is poured into a single-screw extruder part, a melt pressure is continuously built up in the extruder in the working direction, against the direction of conveyance by the melt, a melt seal is created in the single-screw part, upstream of the melt seal, an entrainer is injected into the melt, the melt / entrainer mixture is subjected to an intensive mixing and homogenization, the melt / entrainer mixture is subjected to an abrupt pressure relief and then foamed, characterized in that
that the foamed melt / entrainer mixture is subjected to a mechanical, foam destroying roller effect and fed to a high performance thin film degassing extruder, and
that the melt is coated over a large area into thin layers and is simultaneously subjected to a degassing vacuum in the entire thin-film process space. 2. Device for carrying out the degassing process according to claim 1, characterized in that
that a melt section and a melt sealing blister section ( 32 ) is arranged following a melt pressure building up a screw section ( 31 ),
that the blister section ( 32 ) has a mixing and ho mogenizing effect ensuring toothed disk section ( 33 ) is arranged downstream,
that an entraining agent injection nozzle ( 25 ) is associated with the toothed disk section ( 33 ),
that an annular nozzle section ( 34 ) is arranged after the toothed disk section ( 33 ),
that the ring nozzle section ( 34 ) a rolling effect exerting planet roller section ( 35 ) closes, and
that the planetary roller section ( 35 ) is followed by a high-performance thin-film degassing extruder ( 36 ). 3. Apparatus according to claim 2, characterized in that the single-screw section ( 31 ) has a length of 3- 5 D (D = screw diameter). 4. The device according to claim 2, characterized in that the toothed disc section ( 33 ) has a length of 1-3 D. 5. The device according to claim 2, characterized in
that the planetary roller section ( 35 ) has planet wheels ( 4 ) and a central spindle ( 5 ) and
that the planet wheels (4) surrounding a cooperating housing with the planet wheels (4) internal toothing has. 6. The device according to claim 2, characterized in that
that the high-performance thin-film degassing extruder ( 36 ) has a housing ( 1 ) with a non-toothed inner wall,
that a central, smooth, drivable, cylindrical shaft ( 2 ) is arranged coaxially in the housing ( 1 ),
that around the smooth shaft ( 2 ) arranged at regular intervals from each other, a wiping, self-cleaning screw sealing profile, rotating around its own axis and rotating around the shaft ( 2 ) are arranged thin film shafts ( 3 ),
that the thin-film shafts ( 3 ) on the smooth inner wall of the housing ( 1 ) and on the smooth cylindrical wall of the central shaft ( 2 ) are designed to roll and graze,
that the housing ( 1 ) has a degassing opening ( 12 ). 7. The device according to claim 2, characterized in that
that the worm of the single-screw section ( 31 ), the blister of the blister section ( 32 ), the toothed disks ( 26 ) of the toothed disk section ( 33 ) are arranged on a common shaft ( 11 ), and
that the common shaft ( 11 ) are rotatably connected to the central spindle ( 5 ) and the smooth shaft ( 2 ). 8. Apparatus for carrying out the method according to claim 2, characterized in that the first high-performance thin-film degassing extruder ( 36 ) is followed by a second and between each of which a single-screw section ( 31 ), a blister section ( 32 ), a toothed-disk section ( 33 ) and a Ring nozzle section ( 34 ) are arranged.