Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Composite article making
Patent
1999-05-06
2000-12-19
Kuhns, Allan R.
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Composite article making
264 54, 264540, B29C 4904, B29C 4402
Patent
active
061623806
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a method of producing a hollow foamed plastic body made of polyethylene or polypropylene in an extrusion, blow-molding process with a single-screw extruder and with a blow-molding tool, in which the plastic material is foamed by means of a chemical blowing agent and a pre-molded tube blank formed from the foamed plastic material is blow-molded in the blow-molding tool.
In the course of attempts to reduce material outlay for hollow plastic bodies, in particular in packaging, it is known to produce packaging containers (bottles) from foamed plastic material. Packaging containers of this type are frequently used in areas of application in which a smooth exterior surface is an essential functional feature, so as to present an attractive appearance of the product. However, the foamed hollow bodies produced in extrusion blow-molding have an irregular bulging of the exterior surface caused by gas bubbles in the foam. The distribution of the gas bubbles in the wall of the foamed hollow bodies is also frequently not sufficiently homogeneous, which results in irregular gas cavities and which affects in turn the exterior surface as well as the mechanical properties of the wall. These effects are particularly serious where the wall thicknesses of the hollow bodies are in the range of less than 1.5 mm. In order to avoid this drawback in the case of extrusion blow-molded foamed hollow bodies, a compact, smooth outer skin for example is extruded on in the coextrusion process. Other methods, such as for example in accordance with DE 1504359-A, suggest producing a compact outer skin by rapid cooling of the extruded tube on the outside thereof before the blow-molding process. In this case, an attempt is made at the same time to regulate an uncontrolled foam expansion on the tube.
In a further publication PCT/EP96/05485 it is proposed to produce a smooth outer skin by encasing a container with a smooth container decoration.
All the steps and methods described have the drawback that special applications have to be performed with respect to the smooth outer skin, which increase costs in such a way that a substantial proportion of the cost advantage is offset by the foamed hollow body.
In a further publication DE 19525198-A a method is described which is intended to allow an extrusion blow-molded foamed hollow body to be produced whilst maintaining specific parameters. For this purpose, a foaming agent is admixed with a commercially available PE granulate. This usually takes place as a batch granulate on the basis of PE with a grain size of from 3 to 5 mm or as a powder which is admixed with the PE granulate. In addition, the plastics-material melt is heated to from 20 to 30.degree. above the melting temperature of the compact plastics material and a pressure of the blowing air of from 0.5 to 2.5 bar is applied. In this case, the blow-molding tool is cooled to a temperature of from 7 to 15.degree. C. When setting these parameters, which only represent the prior art, although a foamed hollow body can be produced, it does not meet the requirements with respect to the desired properties, in particular the smooth outer surface and the fine distribution of the gas bubbles in the plastics-material matrix.
SUMMARY OF THE INVENTION
The object of the invention is to provide a method of making a hollow foamed plastic body of the above-described kind from polyethylene or polypropylene by an extrusion blow-molding process with a single-screw extruder and a blow-molding tool respectively by which a smooth exterior surface and a fine distribution of the gas bubbles is achieved by method steps which require practically no costly additional outlay.
This object, and others which will be made more apparent hereinafter, is attained in a method of producing a hollow foamed plastic body made of polyethylene or polypropylene in an extrusion, blow-molding process with a single-screw extruder and with a blow-molding tool, in which the plastic material is foamed
REFERENCES:
patent: 3225127 (1965-12-01), Scott, Jr.
patent: 3502753 (1970-03-01), Rhoads
patent: 4546899 (1985-10-01), Williams
patent: 4668567 (1987-05-01), Williams
patent: 4874649 (1989-10-01), Daubenbuchel et al.
patent: 5328651 (1994-07-01), Gallagher et al.
patent: 5819991 (1998-10-01), Kohn et al.
Kohn Udo
Steigerwald Franz
Kuhns Allan R.
Striker Michael J.
Wella Aktiengesellschaft
LandOfFree
Method for producing foamed plastic hollow bodies does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for producing foamed plastic hollow bodies, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for producing foamed plastic hollow bodies will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-268530