DE1804553A1 - Process for the production of polyethylene terephthalate granules suitable for injection molding after thermal treatment in the solid phase - Google Patents

Description

Process for the production of polyethyltorephthalate granules suitable for injection molding after thermal treatment in the solid phase.

It is known that polyethylene terephthalate assumes excellent mechanical properties through thermal treatment in the solid phase at temperatures of more than 200 ° C. as a result of the condensation which occurs to higher molecular weights and that this plastic can be processed in the highly condensed form by the injection molding process. Spray !, ^c; ußmaschinen but make the outer shape of the unprocessed plastic certain rights. It must ζ.Β, be perfectly free-flowing »must not stick and should not tend to form bridges, since otherwise it cannot be evenly drawn into the injection molding machine. The granulation processes previously used for polyethylene terephthalate now usually produce granulate forms, so-called chips, which are unsuitable for processing in injection molding machines. Particularly noteworthy here is the band granulation leading to chips, which is currently the commonly used type of packaging for polyethylene terephthalate. Polyesters of this molecular weight range with a specific viscosity of approx. 800, which are used as the starting material for the thermal condensation in the solid phase, can only be converted into strand pellets with great difficulty using conventional extruders, for example. Much cheaper behaves in this one

009822/1654

8AD GRlGJNAL

Ge. ΗλΖ

1804563

Regarding a thermally treated polyester with a specific viscosity of e.g. IhQO or 15ΟΟ. It can readily be processed into strand pellets, so that it is easily possible in terms of apparatus to produce the desired pellet shape after the thermal treatment has taken place. However, this method requires the additional costly process steps of remelting and extruding and also has a partial process. Degradation of the polyethylene terephthalate result, which partially reverses the result of the thermal treatment. Therefore, it was desirable, the appropriate form of granules already immediately after the Schmelzkondexisatioji _t at which a viscosity of about 800 is achieved, to obtain and then supply it to granulate the solid thermal condensation.

It has now been found ₉ that poly-ethylene terephthalate granules, which are to be used for injection molding after thermal treatment in the solid phase, can advantageously be produced if the poly-ethylene terephthalate melt obtained in the melt condensation carried out in a known manner can be produced by means of a Underwater pelletizer converted into strand pellets.

The starting material to be brought into granulated form, wolchos * is produced by the usual melt condensation and generally has a specific viscosity between about ¹ JQQ and 1000, preferably 800 to 850, is processed directly from the melt. For this purpose, the polyester melt, which has a temperature of around 280 C, is fed to an underwater granulator, which is built, for example, in such a way that the hot plastic strand pushed out of the nozzle is captured by a water jet coming from a nozzle, cooled and fed through an underwater cooling section to a cutting device. The length and cross-section of the resulting cylindrical granulate have been influenced by the speed of the cutting device and the withdrawal speed of the water. The granules

J09822 / ¹ 654. 3 -

8AD ORiGiNAL

-3- 1 8 O 4 5 b

Ge. h 12

then runs over to separate from the flowing water Siob and then will

The strand pellets obtained according to the invention have, for example, the shape of cylinders or slightly flattened cylinders of 3 - h mm in length and a diameter of 2.5 - 3 camouflaged. A particular advantage of the process is that granules of very uniform shape are obtained without the addition of dust and chips, which is useful for subsequent processing, especially when this is in a thermal post-condensation in a solid state to give higher molecular weight polyesters suitable for injection molding exists, is extremely cheap.

The procedure is explained below using an example:

From an agitation vessel in which 1.6 tons of polyethylene terephthalate have been condensed under vacuum to a specific viscosity of approx. 800, the 280 hot melt is attached to the bottom of the vessel with the aid of a nitrogen pressure of 10 atmospheres in the course of approx. 5 minutes , consisting of 36 nozzles and an equal number of extraction devices underwater granulator. Each nozzle has a circular opening with a diameter of 6 mm, the total water throughput for drawing off and for cooling the strand is 150 m / h. The emerging strands are chopped up after passing through an approx. 4 m long cooling section by a cutting device, the speed of which is set so that the granulate has a length of 3 mm. The diameter of the cylindrical granules is 2.5-3 mm. Following the cutting device, the granulate runs over a sieve, which separates the solid from the water. The latter is circulated via a cooler. After drying, the wet granulate can be used for thermal post-condensation.

009822/1654

BATHROOM OBiQIHAl.

Claims (2)

Ge. h12 claims: 1. Process for the production of after thermal treatment Polyethylene terephthalate granules to be used in the solid phase for injection molding, characterized in that the Scluuelz condensation carried out in a known manner The resulting polyethylene terephthalate melt is converted into strand pellets by means of an underwater pelletizer . W. 2. Use of underwater granulatoron for manufacture of suitable for injection molding after thermal aftertreatment Polyethylene terephthalate strand pellets. BAD OBiGiNAL