DE2941645B1

DE2941645B1 - Process and device for hot granulation of low-viscosity polymer melts with a narrow melt range

Info

Publication number: DE2941645B1
Application number: DE19792941645
Authority: DE
Inventors: Dipl.-Ing. Dr. Wolfgang 6900 Heidelberg Bauer; Dipl.-Chem. Dr. Josef Georg 6730 Neustadt Floss; Rudolf 6712 Bobenheim Plagge
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1979-10-15
Filing date: 1979-10-15
Publication date: 1981-03-19
Also published as: BE885708A

Description

Die Kühlung des austretenden Stranges mit dem Kühlmedium, z. B. Wasser, muß so bemessen werden, daß die Strömung im Düsenmundstück nicht nennens- wert gestört wird. Im Falle, daß die Kühlung durch einen rotierenden Messerkopf, beispielsweise nach DE-OS 2638 126 erfolgt, muß die Kühlwasserzufuhrgeschwindigkeit auf die Rotationsgeschwindigkeit desselben abgestimmt werden. Dies geschieht über den Kühlfak tor. Der Kühlfaktor ist der Quotient aus der Kühlwassermenge je Kühldüse dividiert mit dem Produkt Anzahl der Schneidmesser mal Messergeschwindigkeit. Dieser Quotient muß noch mit einem Geometriefaktor multipliziert werden. Der Geometriefaktor berücksichtigt die Abmessungen der Düsen und des Messerkopfes und die Anzahl der Schneidmesser. The cooling of the exiting strand with the cooling medium, e.g. B. water, must be dimensioned in such a way that the flow in the nozzle mouthpiece does not value is disturbed. In the event that the cooling by a rotating cutter head, for example according to DE-OS 2638 126 takes place, the cooling water supply speed must be adjusted to the speed of rotation of the same to be voted on. This is done via the cooling factor. The cooling factor is the quotient of the amount of cooling water per cooling nozzle divided by the product number the cutting knife times the knife speed. This quotient has to be combined with a Geometry factor must be multiplied. The geometry factor takes the dimensions into account the nozzles and the cutter head and the number of cutting knives.

Der Kühlfaktor liegt im Bereich von 0,4 bis 1,4, vornehmlich 0,6 bis 0,9. Der Geometriefaktor ist definiert als das Produkt aus 7r mit dem mittleren Durchmesser des Messerkopfes und dem Cosinus des Anstellwinkels des Sprühstrahls gegen die Messerkopfachse dividiert durch das Produkt aus der Breite des Schneidmessers, dem Sinus des Anstellwinkels des Schneidmessers gegen die Düsenfläche, der Dichte des Kühlmediums und der Austrittsfläche der Sprühdüse.The cooling factor is in the range from 0.4 to 1.4, mainly 0.6 to 0.9. The geometry factor is defined as the product of 7r with the mean Diameter of the cutter head and the cosine of the angle of attack of the spray jet against the knife head axis divided by the product of the width of the cutting knife, the sine of the angle of incidence of the cutting knife against the nozzle surface, the density of the cooling medium and the exit surface of the spray nozzle.

Unter niedrigviskosen Polymerschmelzen mit engem sChmelzbereich im Sinne der Erfindung werden insbesondere Polyamide, Mischpolyamide und teilkristalline niedermolekulare Polyester, wie Polybutylenterephthalat und Polyethylenterephthalat aber auch Polyethylenwachse verstanden. Dabei ist mit dynamischen Viskositäten von 2 bis 40 Pa ~ s zu rechnen. Among low-viscosity polymer melts with a narrow melting range in the For the purposes of the invention, polyamides, mixed polyamides and partially crystalline are in particular low molecular weight polyesters such as polybutylene terephthalate and polyethylene terephthalate but also understood polyethylene waxes. It is with dynamic viscosities of 2 to 40 Pa ~ s to be expected.

Die Schmelze wird über wenigstens einen Verteilerkanal in einem Verteilerkopf einer mit einer Vielzahl von Düsenkanälen ausgestatteten und am Verteilerkopf befestigten Düsenplatte zugeführt. Beim Übergang von den Verteilerkanälen in die Düsenkanäle erfolgt mittels einer die Gesamtheit der Öffnungen der Düsenkanäle umfassenden Drossel eine Entspannung der Polymerschmelze. Dabei hat es sich insgesamt als zweckmäßig erwiesen, wenn das Verhältnis des Drucks in den Verteilerkanälen zum Druck in den Düsenkanälen 3 bis 20, vorzugsweise 4 bis 12 beträgt. Dabei soll der spezifische Volumenstrom am Düsenmund zwischen 0,4 und 5, vornehmlich 0,7 und 4 m3 pro sec pro m2 liegen. The melt is at least one distributor channel in a distributor head one equipped with a large number of nozzle channels and attached to the distributor head Nozzle plate fed. At the transition from the distribution channels to the nozzle channels takes place by means of a throttle encompassing all of the openings in the nozzle channels relaxation of the polymer melt. It has proven to be useful overall proven when the ratio of the pressure in the distribution channels to the pressure in the Nozzle channels 3 to 20, preferably 4 to 12 is. The specific Volume flow at the nozzle mouth between 0.4 and 5, primarily 0.7 and 4 m3 per sec per m2.

Gegenstand der Erfindung ist weiterhin eine Vorrichtung zur Durchführung des Verfahrens, mit einem wenigstens einen Verteilerkanal aufweisenden Verteilerkopf, an dem eine mit einer Vielzahl von Düsenkanälen ausgestattete Düsenplatte befestigt ist, über deren Stirnfläche unter Ausübung von Scherkräften auf die ausgepreßten Fäden oder Stränge drehbar gelagerte Schneidwerkzeuge gleiten, wobei zwischen dem Verteilerkopf und der Düsenplatte eine die Gesamtheit der Öffnungen der Düsenkanäle umfassende Drossel angeordnet ist. The invention also relates to a device for implementation of the method, with a distributor head having at least one distributor channel, to which a nozzle plate equipped with a large number of nozzle channels is attached is, on the face of the squeezed out under the exertion of shear forces Threads or strands rotatably mounted cutting tools slide, with between the Distributor head and the nozzle plate one the entirety of the openings of the nozzle channels comprehensive throttle is arranged.

Die Drossel kann als Siebpaket ausgebildet sein, das aus einer oder mehreren Gewebelagen aufgebaut ist. The throttle can be designed as a sieve package, which consists of one or several layers of fabric is built up.

Das Gewebe besteht aus Fäden z. B. mit zylindrischer Form aus geeigneten Metallen, beispielsweise aus Bronze oder Nickel. Vorteilhaft werden mehrere Gewebeschichten, die gegebenenfalls an ihren Rändern durch Löten, Kleben oder durch eine Einfassung zusammengehalten werden, verwendet. Die Zahl der Schichten ist nur begrenzt durch die durch sie bedingte Druckerhöhung in den Verteilerkanälen. Bei der Verwendung mehrerer Gewebeschichten können diese bezüglich ihrer Feinheit und Fadenbindung unter sich durchaus verschieden sein. Insgesamt haben sich Maschenweiten von 0,03 bis 0,8 mm bei Drahtstärken von 0,025 bis 0,5 mm als zweckmäßig erwiesen.The fabric consists of threads z. B. with a cylindrical shape of suitable Metals such as bronze or nickel. Several layers of tissue are advantageous, possibly at their edges by soldering, gluing or by an enclosure are held together. The number of layers is only limited by the pressure increase caused by them in the distribution channels. When using several layers of fabric can do this in terms of their fineness and thread weave be quite different among themselves. In total, mesh sizes of 0.03 up to 0.8 mm with wire thicknesses of 0.025 to 0.5 mm have proven to be useful.

Eine beispielhafte Ausführungsform der erfindungsgemäßen Vorrichtung ist in der Zeichnung schematisch dargestellt und im folgenden näher erläutert. An exemplary embodiment of the device according to the invention is shown schematically in the drawing and explained in more detail below.

Im wesentlichen besteht die Vorrichtung aus einem Verteilerkopf 1 für die Polymerschmelze, in dem sich Verteilerkanäle 2, die zu einer Düsenplatte 3 führen, befinden. In der Düsenplatte 3 sind die Düsenkanäle 4 angeordnet. Mit 8 ist das in Strömungsrichtung der Polymerschmelze nach dem Verteilerkanal 2 angeordnete Siebpaket bezeichnet. Gegebenenfalls kann das Siebpaket 8 durch eine Lochplatte 9 abgestützt sein. The device essentially consists of a distributor head 1 for the polymer melt, in which there are distribution channels 2, which lead to a nozzle plate 3 lead. The nozzle channels 4 are arranged in the nozzle plate 3. With 8 is that which is arranged after the distribution channel 2 in the flow direction of the polymer melt Sieve package called. If necessary, the sieve package 8 can pass through a perforated plate 9 be supported.

Nach der Lochplatte 9 folgen die Düsenkanäle 4, die sich zur Oberfläche 5 der Düsenplatte 3 verjüngen. Auf der Stirnfläche 5 der Düsenplatte 3 rotieren Schneidmesser 6, die an einem Messerhalter 7 befestigt sind. Nach dem Schnitt wird das Granulat zuerst einer Sprühkühlung unterworfen. Diese erfolgt über im Austrittsquerschnitt und der Sprührichtung einstellbare Düsen 10.After the perforated plate 9, the nozzle channels 4 follow, which extend to the surface 5 of the nozzle plate 3 taper. Rotate on the face 5 of the nozzle plate 3 Cutting knives 6 which are attached to a knife holder 7. After the cut will be the granulate is first subjected to spray cooling. This takes place in the exit cross-section and spray direction adjustable nozzles 10.

Claims

Claims: 1. Process for hot granulating low viscosity Polymer melts with a narrow melting range in which the polymer melt has at least a distribution channel and conveyed through nozzle channels and in the form of threads or Strands is squeezed out, and the threads or strands with simultaneous cooling are cut transversely, characterized in that the polymer melt at the transition is relaxed from the distribution channel into the nozzle channels, the ratio of the pressure in the distribution channel for the pressure in the nozzle channels is 3 to 20 and the polymer melt depending on their viscosity at pressures from 10 to 60 bar and a specific volume flow at the nozzle mouth 0.4 to 5 m3 per second per m2 is discharged from the nozzle channels.

2. Apparatus for performing the method according to claim 1, with one having at least one distributor head, on which one with a plurality of nozzle channels equipped nozzle plate is attached over the End face under the exertion of shear forces on the extruded threads or strands rotatably mounted cutting tools slide, characterized in that between the distributor head (1) and the nozzle plate (3) one the entirety of the openings the nozzle channels (4) comprehensive throttle is arranged.

3. Apparatus according to claim 2, characterized in that between the distributor head (1) and the nozzle plate (3) a sieve package (8) is arranged.

4. Apparatus according to claim 3, characterized in that the sieve package (8) consists of a single or multilayer metal wire mesh.

The invention relates to a method for hot granulation low-viscosity polymer melts with a narrow melt range in which the polymer melt conveyed via at least one distribution channel and through nozzle channels and in shape is squeezed out of threads or strands, and the threads or strands under simultaneous Cooling are cross-cut as well as on a device for carrying out the method.

Plastics are usually obtained from synthesis in a form that before further processing, the so-called packaging, makes necessary. Powdery or flaky, as regrind or amorphous melt Incidental plastic raw materials are used - from coloring and mixing with others Apart from materials - generally pressed through nozzles by conveying and kneading machines, optionally cooled and crushed to granules. The last two steps are often applied directly to the discharge site to avoid repeated heat supply of the conveying and kneading machine, on which nozzle plates with many ejection openings are arranged, on which the emerging threads are cut into granules and only then be cooled. The latter procedure is called hot granulation or hot stamping.

From GB 1112 623 there is a hot die-cutting process for production of granules made of thermoplastic polymeric substances known in which the plastic threads pressed directly from the squeeze out in a Kühlnüs fluid and immediately at the ejection openings during immersion in the liquid before going through have cooled to the solid state, are cross-cut.

Devices for carrying out this process are designed in such a way that that the polymer melt via distributor channels in a distributor head of a nozzle plate fed and from the nozzle plate equipped with a large number of nozzle channels is squeezed. The emerging melt is propeller-like in front of the nozzle plate rotating mostly cantilever blades, which are in one with the cooling liquid The spray-humid atmosphere formed is moved, knocked off and the resultant Granulate with the liquid coolant flow up to a sieve of the appropriate mesh size carried along and then carried out. When hot granulating low-viscosity polymer melts with a narrow melting range, however, occur in the cooling of those emerging from the nozzle plate Melt strands often encounter difficulties. If the cooling is too low, the Melt either drawn into threads instead of being cut into granules or solidified if there is too much cooling in the nozzle in front of the outlet. In the case of the so-called Freezing a nozzle channel is the polymer melt due to the low flow resistance the nozzle channels are discharged through the remaining channels without reducing the pressure the polymer melt increases significantly, but this results in a reduction in the Granulation quality that can even make the granulate unusable.

The invention was therefore based on the object of a hot die-cutting process to create the production of granules from low-viscosity polymer melts allowed with a narrow melt range and in particular the production of a uniform Granules from these polymer melts made possible.

In the case of a method, this task is described at the outset Type solved according to the invention in that the polymer melt at the transition from the distribution channel is relaxed in the nozzle channels, the ratio of the pressure in the distribution channel to the pressure in the nozzle channels is 3 to 20 and the polymer melt depending on its Viscosity at pressures from 10 to 60 bar and a specific volume flow am Nozzle mouth of 0.4 to 5 m3 per sec per m2 is discharged from the nozzle channels. The relaxation is carried out in such a way that the individual nozzle channels in several Nozzles cannot influence each other.

At the same time, the process ensures that the specific volume flow the nozzle mouthpiece has reached a minimum value.

The volume flow of the polymer melt is below the specific volume flow understood in the unit of time divided by the cross section at the nozzle mouth.

The relaxation can take place via throttle elements known per se. The pressure ratio is the quotient of the measured pressure before and after Throttle element formed in the flow direction of the polymer melt.