Plastic and nonmetallic article shaping or treating: processes – Vacuum treatment of work – To degas or prevent gas entrapment
Patent
1997-03-05
1999-06-15
Tentoni, Leo B.
Plastic and nonmetallic article shaping or treating: processes
Vacuum treatment of work
To degas or prevent gas entrapment
264211, 26421112, 366 75, 366 85, 425203, 425204, B29C 4700, B29C 4776
Patent
active
059119292
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of producing web-shaped plastic foil in which granular or pulverulent polymer and particulate filler are intermingled and extruded through a flat gap die aperture. The present invention also relates to an apparatus for producing web-shaped plastic foil employing the method according to the present invention.
BACKGROUND ART
Web-shaped plastic foils of the type described above are previously known, for example, from EP-A-O 353 496 and EP-A-O 353 991. The prior art web-shaped plastic foils are produced from a particulate starting material of propylene homopolymer or ethylene-propylene copolymer and between 50 and 80 weight per cent filler, and are intended to be used as packaging materials for configurationally stable, liquid-tight food packages. Similar web-shaped plastic foils are also known from GB-A-1 554 143.
According to the above-described prior art technology, see for example GB-A-1 554 143, the web-shaped plastic foil is produced from particulate starting materials of polymer and filler, by an extrusion process comprising three mutually discrete process steps which each requires its own individual process equipment and which it has not hitherto been possible to integrate into a single continuous process cycle.
In the prior art extrusion process, a pulverulent polymer is fed, in a first process stage, together with such components as stabilisers, into a first extrusion plant which produces stabilised polymer granules by extrusion in a known manner. In a second process stage, the stabilised polymer granules are fed from the first process stage together with particulate filler into a second extrusion plant which produces stabilised polymer granules including filler, by extrusion in a known manner. The stabilised polymer granules containing filler from the second process stage are finally fed, in a third process stage, into a third extrusion plant which produces web-shaped plastic foil by extrusion of the polymer material through a flat gap die aperture. The extruded plastic foil is then calendered to the desired foil thickness with the aid of calender rollers disposed in association with the discharge end of the third extrusion plant.
OBJECTS OF THE INVENTION
It is obvious that the above-described prior art extrusion process for producing web-shaped plastic foil suffers from serious drawbacks, including high capital and investment costs for the process equipment, and one object of the present invention is therefore to propose an improved process by which these drawbacks may be obviated. One particular object of the present invention is to realise a method according to which web-shaped plastic foil may be produced from particulate starting materials of polymer and filler, in a process stage using a single extruder apparatus, as opposed to the process according to the above-described prior art technology which requires no less than three mutually discrete process stages with each respective extrusion plant. Yet a further object of the present invention is to realise an apparatus for producing web-shaped plastic foil employing the method of the present invention.
SUMMARY OF THE INVENTION
Particulate polymer which is employed as one of the starting materials in the method according to the present invention, together with other particulate starting materials including filler, contains relatively large volumes of air and other process gases which unavoidably accompany the starting material into the extruder apparatus and which, through the mechanical processing by the apparatus, or compression of the infed starting materials, tend to be released from the compressed material while excess pressure is built up, which counteracts continued mechanical processing of the plasticized polymer mass. This undesirable, but inevitable air volume increases and expands the smaller the particle size of the infed starting material particles. If extremely fine-particulate starting materials are employed, for example pulverulent polymer together with filler par
REFERENCES:
patent: 3985348 (1976-10-01), Skidmore
patent: 4110844 (1978-08-01), Nakamura
patent: 4663103 (1987-05-01), McCullough et al.
Tentoni Leo B.
Tetra Laval Holdings & Finance S.A.
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