DE2120601B2 - METHOD AND DEVICE FOR PROCESSING AND DEGASSING THERMALLY SENSITIVE POWDERED THERMOPLASTICS - Google Patents

Description

Air, moisture and other volatile components can be withdrawn. Furthermore, an unfavorable bulk density and a poor one are disadvantageous Moving-in behavior to the next level. The products show the typical characteristics of insufficient degassing Error on.

An improvement is to be made with the “VDI paperback T14, Domininghaus, progressive Extn "5ertechnik", S. 88/89 known processes with a throttling and degassing phase may be possible. No vacuum chamber is provided here. The feed material is plasticized in the first zone, then throttled and degassed and plasticized in a further zone. The disadvantage here are the device comprising two twin screws with regard to the expenditure on apparatus and the low throughput that can be achieved

The object of the invention is to provide thermally sensitive, powdery thermoplastic plastics in to treat several zones in such a way that they are thermally gently processed, intensively degassed and after the Degassing can be drawn into the subsequent zone cheaply and evenly, with the Throughput / volume per unit of time is to be improved with a favorable drive power.

This goal is achieved according to the invention in that the feed material in the first zone at a between The softening point and melting point are agglomerated and broken up in this state and as particles with an approximately uniform, porous, granular, crumbly or flaky shape in the second Zone is transferred.

The agglomeration process step continuously produces an intermediate product that is inexpensive and is degassed with a relatively long residence time, whereby all degassed components, such as air, moisture and other volatile components are completely removed. The agglomeration takes place under favorable operating conditions, what speed, shear force, heat and itself Pressure build-up concerns. The intermediate product also has a shape and surface texture, through which it can be drawn into the third zone, loosely layered. Furthermore, through the degassed, divided agglomerate a feed material for the third zone. through which one is a relative receives a small temperature-time product in the third zone. Because of this temperature-time product, the melt is damaged as little as possible, which significantly improves the product quality will. It is essential here that the product does not have any defects due to deficiencies in degassing. The method according to the invention is also advantageous this is because the material state of the agglomerate can be varied.

The powdered plastic feed material is preferred according to a further feature of the invention at a temperature between 30 and 80 ° C, preferably 40 and 60 ° C, below the melting temperature agglomerated temperature. The procedure is advantageous to be used if PVC-Dry-blend is available as the feed item.

The method according to the invention is advantageously carried out according to a further feature so that the agglomerate for a residence time of 15 to 60 seconds, preferably 20 to 30 seconds, in the second zone, which is under negative pressure, is degassed.

The shape of the agglomerate grains - crumbs or flakes - is achieved in that one or more Agglomerate strands at the end of the first zone be mechanically divided.

To carry out the method according to the invention, a device is provided which consists of two single-shaft screw presses in a cascade arrangement and one between the two screw presses, there is a vacuum chamber connectable to an evacuation device.

The device is characterized in that an effective screw length of 6 to 12 D (D = screw diameter) having screw press of the first cascade stage at its outlet has a dividing device consisting of two systems of projections which can be rotated relative to one another and the effective screw length of the screw 10 to 14 D forming the second cascade stage (D - screw diameter). Screws with the specified L / D- (length / Diameter) ratios are known per se. The device is only used in connection with the procedure Patent protection sought after the invention.

The system of projections can be part of the screw, in particular the screw, in a known manner Screw tip, and the further system of projections can be arranged fixed to the housing. The protrusions can be used as cams. Pins, bars or comparable means are available.

One system has the task of forming passages for the agglomerate and the other system has the task of breaking up this agglomerate. These two systems make one structural and functional simple and effective device made. whereby through the interaction of the systems on easy way cheap one or more agglomerate strands produced and these in the desired Parted shape. The system of projections also gives a relatively small one and constant pumping resistance.

The combination of the above-mentioned construction features of the cascade screw press results in a proportionate short dwell times, and there are relatively high speeds with low drive power possible. The degassing of the divided material takes place without difficulty and inexpensively, because no dead spaces are formed.

The invention is explained in more detail by means of an exemplary embodiment with reference to the drawing. It shows 1 shows a cascade screw press with a vacuum chamber in longitudinal section.

F i g. 2 and 3 details of a dividing device at the outlet of the first cascade stage Screw press and screw tip of this screw in longitudinal section and in front view,

F i g. 4 and 5 details of a modified embodiment of a dividing device and Snail tip in longitudinal section and in front view.

The cascade screw press according to FIG. 1 consists essentially of a first heated Screw press 1, a vacuum chamber 2 and a second heated screw press 3. The feed hopper 4 is charged with powdered thermoplastic material or a powder mixture. The screw 5 is of conventional design and has (not designated in more detail) a Feeding, converting and discharging zones. At

the essentially open outlet 1 'of the screw press 1 is connected to a relatively long, preferably vertically arranged vacuum chamber 2. The evacuation line is denoted by 8 a and a vacuum pump is denoted by 8 b.

The shaft-like vacuum chamber 2 is at a shaft-like inlet 10 of the screw press 3 connected. The screw 11 of this screw press is also in Conventional design and has (unspecified) a feed, melting and ejection zone on. The drives of the two screw presses are labeled 12 and 13 in outlet 1 ' the screw press 1 is provided with two systems of protrusions. The free spaces between the projections 7 of the one system form passages for producing agglomerate strands. The projections 9 of the further system form a dividing device for the agglomerate strands. the Axial arrangement and the relative rotational movement of the two systems cause the agglomerate in more uniform or approximately uniform shape as crumbs, flakes od. Ä. Is present that immediately enters the vacuum chamber after the cutting process.

Here it is intensively degassed and then drawn in cheaply by the screw press of the second cascade stage.

The screw tip 6 according to FIG. 2 and 3 is due to the web-like projections 7 as a groove head Outer diameter 1 D formed.

The passages for the agglomerate are in the form of longitudinal grooves 14 distributed over the circumference. Immediately in front of the head face of the screw tip 6 is a dividing device in the form a system of projections 9, which consists of a number of distributed on the periphery of the housing-fixed knife or There are pins 15 which are arranged radially.

The screw tip according to FIG. 4 and 5 is present as a pin 16, which is a number of circumferentially distributed and radially arranged knife or pins 7 carries. Between these dividing means and the screw 5 is A perforated plate 18 with passages 19 is fixed to the housing. Instead of the perforated plate, a ίο Row of circumferentially distributed, fixed cams, pins Od. The like. Be provided, the free spaces between which form passages for the agglomerate.

example

A PVC dry blend mixture or another powdery thermoplastic material as the feed material is agglomerated in the first heated cascade stage. At the outlet of this stage, the agglomerate strands formed are divided into crumbs or flakes. The material temperature in the area of the dividing point is 14O ⁰ C. The flaky or crumbly material produced is then degassed with a residence time of about 30 seconds in the vacuum chamber present low material temperature of 140 ° C and the intended vacuum of about 50 Torr. The degassed material is then conveniently drawn in, plasticized and pressed by the screw press of the second cascade stage. The diameter of the screws of the two cascade stages is 60 mm, the effective screw length of the first stage is 10 D and that of the second 12 D. The output is 85 kg / H.

1 sheet of drawings

Claims (4)

1 2 pressurized zone degassed. In the following claims: third zone, the degassed, essentially still powdery material is melted, 1. Process for processing and degassing plasticized, mixed and pressed out as a melt,
of thermally sensitive, powdery 5 This process is carried out in a box thermoplastic plastics, in particular by ksdschneckenpresse with between the cascade polyvinyl chloride, in which the powdery step arranged vacuum chamber. Plastic one after the other in a first zone. The first cascade stage of the known screw wännt and compacted, in a second, under kenpresse is relatively short dimensioned and the Underpressure standing zone degassed and in an io function after a pure conveying device, which is not third zone is plasticized, mixed, homogenized and heated. and is pressed out as melt, as a result of which only the heat is effective, characterized in that the feed material in the due to the friction between the screw and first zone is generated in one between the softening and screw housing. Yet it is not Melting point lying temperature agglomerated, 15 to avoid that the powdery material as a result iu this state divided and as particles with the compression process, in which an additional approximately uniform, porous, granular, curvilinear warming can be effective, partly in small Liger or flaky form in the second zone excessively large quantities of lumps are formed. These in turn disturb them will lead. proper functioning of the intended valve, the 2. The method as claimed in claim 1, characterized in that it is used as a resilient conveying resistor. Marked as result, that the aurgabegui lie in the first nis then differences in terms of material zone at a temperature between 30 and 80 C, preferred quantity and pressure. This becomes the instructor 40 and 60 C. below the melt temperature lying temperature is agglomerated. small particle sizes lead to uneven input 3. The method according to claim 1 or 2, characterized as tension and pressure fluctuations in the screw that the degassing in the press below the second cascade stage. Also can The second zone is under pressure while powder residues and dust settle on the valve a dwell time of 15 to 60 seconds, in front of you under the influence of the temperature on the press from 20 to 30 seconds. outlet and the steam temperature decompose. Around 4. Device for carrying out the method 30 to eliminate these disadvantages is in many cases a rens according to claims 1 to 3, consisting of two single-shaft screw presses in cascade pressure-dependent valve control device, complicated in structure and mode of operation, and an arrangement between Since the degassed material is also essentially pulverized, with an evacuation, the second cascade stage is a vacuum chamber that can be connected to the device, so that the purpose of drawing in, conveying and also opening is characterized by the effective melting of the material preferably designed as a double screw length of 6 to 12 D having a screw press. In particular, the single screw press (1) of the first cascade stage to feed and draw in powdered plastics in its outlet (1 ') one of two screw presses of any type relative to one another is associated with considerable difficulties in the rotatable systems of protrusions (7 or 9) 40 m,
Has existing dividing device and the twin screw press types are known per se for the effective screw length of the screw (11) 10 to 14 D forming the second cascade of processing powdery thermoplastics, with or without a degassing device. tion. These twin screw presses are disadvantageous 45 in terms of operational safety and investment costs, although the products obtained are not in terms of quality satisfy, because air and moist components on Due to the process technology chosen, they can only be removed from the melt inadequately.
50 In the further known methods according to the German The invention relates to a method of processing laid-open document 604 330 and the USA and degassing of thermally sensitive patent specification 3 067 462 is powdery Aufgabelichen, powdery thermoplastic material in the first zone up to the melt state fen, especially of polyvinyl chloride, in which the plasticized. powdery plastic successively in a first 55 The melt is then divided into particles and Zone heated and compressed, in a second, under in this state form in the second, under negative pressure degassed standing zone and degassed in a zone standing under pressure. After a short stay Zone plasticized, mixed, homogenized and as a time the melt particles are in the third zone Melt is squeezed out and transferred to a device and plasticized and homogenized here to carry out the procedure. 60 and pressed out as a melt. Disadvantage of this In such a method, from the United States patent specification, there is a melt without heat dissipation 470 584 or which has to be divided up to this analog German and then degassed. the Laid-Open Specification 1 554 920 known methods of divided mass particles partly stick to each other and In the first, the powdery feed material is partly attached to the dividing elements. Also results from Zone against a resilient resistance promoted 65 the dividing does not have a uniform shape. The development and condensed. As an essentially still pulverizing effect is insufficient because the enamel parver form Material will be part of the second zone due to its state and upper, out and in this state in the under surface condition not the desired amount