Apparatus for producing injection-molded parts

Abstract

Apparatus for producing injection-molded parts, particularly PET preforms, includes a twin-screw extruder or multi-screw extruder for preparing and/or plasticizing material, preferably in granular form, which is transferred to a transfer reservoir. A piston unit further processes the material. The extruder has a plurality of processing zones, whereby at least two process zones are configured as degassing zones.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS [0001] This application is a continuation of prior filed copending PCT International application no. PCT / EP2005 / 052870, filed Jun. 21, 2005, which designated the United States and has been published but not in English as International Publication No. WO 2006 / 024553 A1 and on which priority is claimed under 35 U.S.C. §120, and which claims the priority of German Patent Application, Serial No. 10 2004 041 689.3, filed Aug. 27, 2004, pursuant to 35 U.S.C. 119(a)-(d), the contents of which are incorporated herein by reference in its entirety as if fully set forth herein.BACKGROUND OF THE INVENTION [0002] The invention relates, in general, to an apparatus for producing injection-molded parts, in particular PET preforms. [0003] Nothing in the following discussion of the state of the art is to be construed as an admission of prior art. [0004] An apparatus for producing injection-molded parts, in particular PET preforms, typically includes an extrude...

AI Technical Summary

Benefits of technology

[0024] This extruder may also be constructed as twin-screw extruder. However, advantages are achieved by equipping such injection compounder with multiple, continuously operating screws. For example, there would be no problem with incorporating the additives in the material, for example also in powder form. As additional advantages, it becomes possible to also pre-dry PET or another material instead of PET, for example PP—polypropylene—which is ductile, PEN—polyethylene aphthalate which has excellent barrier characteristics, or combinations—PET / PEN—polyethylene terephthalate / polyethylene aphthalate—or PET / PA—polyethylene terephthalate / polyamide—or PET / EVOH blends—polyethylene terephthalate / ethylene / vinyl alcohol blends—with again good barrier characteristics, as well as also amorphous / partially crystalline recycled substances and flakes, and also PLA—polylactic. The materials can also be employed in an apparatus according to the invention which includes degassing, preferably vacuum degassing. As already described above, such pre-drying can be eliminated by providing adequate vacuum degassing. This would result in significant energy savings compared to conventional processing, because the pre-drying step can be eliminated. This is even more significant when processing recycled materials, because a suitable dryer would necessitate approximately 3 times the size as a consequence of the low apparent density of the flakes. These dryers must also be stirred because the flakes have the tendency to stick together during pre-crystallization. As an additional advantage, a plasticizing step may be eliminated entirely.

[0025] The apparatus according to the invention has the additional advantage that additives, such as fillers, can be metered for processing, if desired, for example in powder form. The fillers can be, e.g., TiO2—titanium dioxide, talcum, nano-composites or similar materials which can be added for protection against different destructive properties, for example photo oxidation. Also conceivable are additives operating as UV stabilizer, as brightener or for increasing the viscosity or for changing other properties. Another possible additive involves oxygen scavengers, e.g., Amasorb from the company ColorMatrix. Also feasible would be the addition of PA—polyamide—or partially aromatized PA as an aroma barrier. Color additives, in liquid form or as master batch, may therefore be metered in a simple manner as an additive. The plasticizing capability of such a machine system is practically unlimited, since it depends only on the rating of the installed motor or on the employed extruder.

[0026] More particularly, such apparatus advantageously employs a single-stage fabrication process and is capable to process, for example, powders, but also other components or undried materials, thereby reducing the energy consumption and also costs. Moreover, the polymer is subjected to only a single plasticizing process which in turn exposes the product to little stress. The concept of the invention can be applied, as mentioned above, to other packaging articles and other packaging materials and is therefore not limited to PET preforms.

[0027] For a particularly effective pre-drying and / or degassing, one of the processing zones may be configured as degassing zones. In a particularly advantageous manner, at least two processing zones may be constructed as degassing zones, thereby realizing a particularly effective pre-drying. It is of particular advantage, when the admixture of additives provides barrier properties of the processed material.

Problems solved by technology

Because PET is hygroscopic and because moisture causes a hydrolytic decomposition of polymer chains, the material is pre-dried in a most complex process, in particular when material in granular form is involved.

In this single-screw plasticization with pre-drying, energy consumption is significantly increased in relation to the temperature increase of the material, typically to 0.55 kWh / kg.

In addition, drying plants require significant installation space, which considerably increases the vertical dimensions of the apparatus for producing injection-molded parts.

This plasticizing approach without pre-drying, is not applicable however in certain fields, like for example PET preforms, because there are concerns with respect to hydrolytic decomposition and a possible increase of the acetaldehyde content—M content—in the melt.

A high M content hereby adversely affects the taste of the beverages.

Using a twin-screw extruder for producing PET preforms also poses problems with the synchronization of the cyclic operation of an injection molding machine and the continuously operating twin-screw extruder.

Processing such additives with a single screw extruder is presently not possible at all or only with insufficient quality.

Even incorporating 50% titanium dioxide—TiO2-PET master batches—for achieving a 10% TiO2 fraction in a milk bottle, as required for adequate O2 barrier characteristics, is not possible because of the insufficient mixing effect of a single-screw extruder.

Powdered TiO2 cannot be processed with a single-screw extruder, at least not in the required quantity.

However, this requires additional facilities which is time consuming and therefore expensive.

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