CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national phase entry under 35 U.S.C. § 371 of PCT/EP2017/084200 filed Dec. 21, 2017, which claims priority to Swiss Patent Application No. 00002/17 filed Jan. 3, 2017, the entirety of each of which is incorporated by this reference.

FIELD OF THE INVENTION

The invention relates to PET regranulate having high intrinsic viscosity and and method for the production thereof.

BACKGROUND ART

The production of plastic containers, in particular plastic bottles, for example of polyethylene or polypropylene, usually takes place in an extrusion blow molding method. Thereby, a plastic tube is extruded from a tube head, which is introduced into a blow-molding tool with a cavity, inflated via a blow mandrel by overpressure and thereby pressed against the inside of the cavity and cured by cooling. Due to the curing on the inside of the cavity, the blow-molded article assumes the contour of the inside of the cavity on its outside. After curing, the blow-molded article is removed from the blow-molding tool. The extrusion blow molding machines used for this purpose generally have at least one extruder for feeding and melting the plastic material. The outlet of the extruder is connected to the tube head, at the outlet nozzle of which, preferably adjustable in the opening width, the extruded tube emerges. When closing the blow-molding tool for squeezing the plastic tube introduced between its tool halves, parts of the plastic tube project on the top and the bottom, so-called slugs, which are separated in a separate work step and can be fed to the recycling stream. The plastic tube can be single-layered or multi-layered, it can be extruded as a plastic tube with viewing strips, decorative strips or related to the circumference, with several, for example, different colored segments.

The blowing station with the blow mandrel is usually arranged laterally of the tube head, wherein the blow-molding tool supplied with the extruded plastic tube must be moved into the blow station, where the blow mandrel is then usually driven into the blow mold cavity from above.

In most cases, the plastic tube is extruded vertically. Due to gravity, the plastic tube exiting at the blow nozzle is pulled downwards. However, if the material of the plastic tube is too thin, i.e. has no sufficient melt strength, it is changed in its length due to the own weight of the plastic tube such that the subsequent blowing process is no longer possible.

For the production of PET containers on extrusion blow molding machines, extrusion blow molding can only be used if the PET molding compound has the necessary melt strength, i.e. the plastic tube has a shape and consistency when the blow mold halves are closed, which leads to a hollow body during subsequent inflation and curing that meets the specified specifications. The melt strength of the PET material used in the stretch blow molding process in which the containers are formed from a preform made by injection molding, a so-called preform, does not meet the requirements for extrusion blow molding, as its intrinsic viscosity is too low and leads to the mentioned impermissible lengths of the plastic tube when used in extrusion blow molding. For extrusion blowing, the PET material must be modified accordingly.

According to the prior art, PET molding compounds are used for extrusion blow molding, which are known by short designations such as PET X (extrudable), PET G (glycol modified) and PET B (branched). In the USA, terms such as EPET, PETE or even EBM PET are common. These are PET materials specially developed for extrusion blow molding, produced quantity of which is low and therefore has a correspondingly high price. However, the PET hollow bodies produced with these PET molding compounds with the EBM method can partially not be supplied to the PET recycling stream, as they cannot be processed like standard PET during recycling.

Standard PET types are understood to be linear PET types (not branched) with a low copolymer fraction of less than 5% by weight and an intrinsic viscosity (IV) of between 0.74 and 0.86 dl/g (according to ASTM D 4603).

In US 2013/0029068 A1, a PET molding composition is proposed, which is suitable for the EBM process and is said to behave without problems in the PET recycling stream. The PET molding compound is made of PET virgin material, that is, so-called “virgin PET” or short v-PET. By definition, PET virgin material has not been extruded from fossil raw materials or renewable raw materials after its production.

Due to the low melt strength, post-consumer PET, so-called r-PET, is not suitable for use in an EBM machine. The reason for the too low melt stability of r-PET is probably due to the fact that the plastic mass is degraded again during extrusion by the repeated heat exposure and the impact of shear forces and thus the molecular weight is reduced again.

Standard PET (polyethylene terephthalate) is not suitable for extrusion blow molding due to its low melt strength. Therefore, modified PET molding compounds have been developed which have an improved melt strength. The improved melt strength can be affected among others by an extension or crosslinking of the molecular chains by adding chain extension or crosslinking additives to the PET. However, such PET molding compounds cannot be supplied to the PET recycling stream from the containers produced from a preform, as the extension and crosslinking additives are regarded as contamination of the PET recycling stream.

Post-use PET, so-called PET recyclate (r-PET), as available on the market, has an intrinsic viscosity of at most 0.88 dl/g according to ASTM D 4603 and is unsuitable for use in the extrusion blow method.

Advantages of the Invention

From the disadvantages of the described prior art, the present invention results in a PET molding compound which contains at least a certain proportion of PET recyclate and is suitable for extrusion blow molding.

