Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Layered – stratified traversely of length – or multiphase...
Patent
1998-02-13
2000-07-04
Silbaugh, Jan H.
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Layered, stratified traversely of length, or multiphase...
26417312, 26417318, 26417319, 26421112, 2642902, 2642101, 2642107, B29C 5518, B29C 4778
Patent
active
060834439
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for direct production of a printable, biaxially oriented polymer film containing filler and/or pigment and having one or more layers, in particular a film based on polypropylene, with a thickness of up to 250 .mu.m.
Films which, due to high proportions of fillers and/or pigments and also due to controlled creation of microscopic vacuoles in the film, are opaque and in addition are inscribable and printable are also known as "synthetic papers". The term "synthetic paper" is also used as a technical term for papers produced by the traditional processes of papermaking using fibers from synthetic materials, but the present application does not concern such papers. For the purposes of the present invention and with regard to the end application, "synthetic paper" of film type is needed as relatively thick films, the usual current production qualities having thicknesses in the range from 60 to 250 .mu.m. "Synthetic paper" of film type is generally based on polypropylene as film-forming polymer, and the explanations below therefore refer in particular to polypropylene films. For the purposes of the present patent application, "polypropylene" here is a crystallizable tactic polypropylene, in particular an isotactic, homopolymeric polypropylene, but the term also includes a use or inclusion of syndiotactic polypropylene and of copolymers which are composed predominantly of propylene units and, if desired, may contain up to 15% by weight of other olefins, such as ethylene and .alpha.-olefins having from 4 to 8 carbon atoms, in particular for top layers which are formed by coextrusion. Insofar as the teaching of the present invention can be extended to other polymers, a matter which in any particular case can be judged by the person skilled in the art using his technical knowledge, other polymers than polypropylene are also encompassed in the more general aspects of the teaching of the present invention.
Currently, polypropylene-based "synthetic paper" is fundamentally produced by processes, and using plants, which are usual for producing polypropylene films for other applications, e.g. for producing transparent polypropylene films. However, since biaxially orientated polypropylene films for other applications are usually needed and produced at lower thicknesses than that of "synthetic paper", the production of "synthetic paper" of greater thickness requires, following the usual production of polypropylene films, the creation of the final film thickness by means of downstream lamination steps, i.e. the combination of more than one film layer. This consumes effort and cost, but hitherto has been regarded as unavoidable.
The process for producing polypropylene films also used for producing highly filled and highly pigmented polypropylene films forming the basis of prior art "synthetic papers" of film type includes the following fundamental steps:
A melt of the film-forming polymer, to which are added, if desired, additives for improving processing or handling of the finished film, is produced and, in the case of production of a single-layer film, extruded through a single slot die. In the case of production of a film having more than one layer, coextrusion takes place through two or more slot dies. If a filled and pigmented film is desired, the fillers and/or pigments are incorporated in a known manner into the melt, the starting material frequently being a premix of pigmented and/or filled granules (termed masterbatches) with pure polymer granules.
In an alternative procedure, termed "direct addition", as described in German Patent Application 196 04 637.8, the use of masterbatches is dispensed with. Instead, the pigments, in particular the surface-treated fillers and/or pigments described below, are added to the melt in a twin-screw extruder and devolatilized and homogenized during extrusion.
The fillers and/or pigments used are finely divided powders of inorganic materials, such as SiO.sub.2, calcium carbonate, dolomite, titanium dioxide, kaolin, talc, barium sulphate, zinc sulphid
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Eckart Ludwig
Sahr Ulrich
Schwuchow Rainer
Stopperka Klaus
Bruckner Mashcinenbau GmbH
Eashoo Mark
Silbaugh Jan H.
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