Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1997-03-17
1999-10-19
Michl, Paul R.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
524445, C08K 334
Patent
active
059690070
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a masterbatch for the production of biaxially oriented polyalkylene films, a process for producing said masterbatch, the use of the masterbatch, and to biaxially oriented, co-extruded multilayer polyalkylene films containing said masterbatch.
In recent years, biaxially oriented polyalkylene films have gained more and more importance. They are mainly used as packing material for transparent packaging, and they are high in gloss, scratch-proof and durably transparent. Therefore, they represent a good alternative for cellophane as packing material.
These films may also be produced as co-extruded multilayer films consisting of a core layer and an exterior layer. However, the production of these multilayer films, in particular, frequently causes problems. Thus, in films used for printing or laminating, the exterior layer generally consists of a polyalkylene homopolymer, or of a polyalkylene random copolymer for hot-sealable films which are metallized, for example.
Such films have high film-to-film and film-to-metal friction coefficients, causing the films to adhere to each other and to develop a tendency of becoming sticky when surface pressure is applied, thereby making it difficult to use them in automated packaging machinery.
It is known from prior art to avoid these drawbacks by adding specific additives to the polymer to be processed, which prevent these effects. These additives include compounds such as natural and/or synthetic silica, talc, calcium carbonate and silicates, which are employed as hollow particles or as powders.
However, adding these additives is disadvantageous in that the optical properties of films produced from such a polymer are deteriorated. In particular, these additives frequently give rise to a decrease in gloss and an increase in haziness of the films. Another drawback is that when slitting the film, poor dispersion of fillers within the polyalkylene matrix and insufficient binding of the fillers to the polyalkylene matrix will cause powdery deposits on the film and the slitting machine, thereby substantially deteriorating the properties of the film on the one hand, and making the film more difficult to process on the other hand.
Therefore, it is the technical object of the invention to provide more suitable fillers and an appropriate additive that does not have the disadvantages described above and, in particular, provides improved dispersion and binding of the fillers within the polyalkylene matrix.
Said object is attained by using a masterbatch in the production of biaxially oriented polyalkylene films which, based on the total amount of masterbatch, contains in a matrix of polyalkylene homopolymer or copolymer from 1 to 50% by weight, preferably from 1 to 10% by weight of spherical solid silicate particles and optionally, from 0.1 to 15% by weight, preferably 10% by weight of a surface-modifying reagent which reacts with the surface of the silicate, thus improving the adherence between the silicate and the polyalkylene. In a preferred embodiment, the matrix for the masterbatch is a polypropylene homopolymer or a polypropylene random copolymer.
Within the scope of the present invention, masterbatch is understood to be a base mixture, particularly a granulate, dust-free composition of the components described above, namely polyalkylene as the matrix, spherical solid silicate particles and optionally, a surface-modifying reagent. Such a masterbatch is used in the production of said biaxially oriented films or other films together with the plastic raw material and is extruded with same to yield the product.
In principle, those surface-modifying reagents are possible which react with the surface of the silicate, thus improving the adherence between the silicate and the polyalkylene. Particularly suitable are polypropylene or polyethylene of low or high density having from 0.5 to 2% by weight of grafted maleic anhydride, or an ethylene-acrylic acid copolymer. "Grafting" is understood as opening the polymeric chain and subsequent binding of the chain ends to
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A. Schulman Plastics N.V.
Michl Paul R.
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