Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Patent
1989-06-01
1991-07-02
Van Balen, William J.
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
428213, 4283148, 4283155, 4283159, 4283179, 428516, 428910, B32B 326
Patent
active
050284800
DESCRIPTION:
BRIEF SUMMARY
This invention concerns polymeric films, and in particular polypropylene films.
It is known to form films from polypropylene which consist of a layer of polypropylene homopolymer on a layer of voided polypropylene. Such films can be produced by coextruding a layer of polypropylene homopolymer with a layer of polypropylene homopolymer containing a voiding agent, for example particulate chalk, and thereafter biaxially orienting the coextruded structure, for example using rolls rotating at different speeds in the direction of extrusion and using a stenter in the direction perpendicular thereto. The resultant films have a surface gloss when viewed from the side of the unvoided homopolymer layer, particularly when the homopolymer layer is relatively thick. However, homopolymer layers have poor ink receptivity and this makes them unsuitable for use as packaging materials which require printed indicia.
Printable polymer layers with good gloss can be provided by a relatively thick layer of a copolymer on a voided polypropylene layer, but such copolymer layers are expensive.
According to the present invention there is provided a polymeric film comprising a layer of propylene homopolymer having a layer of voided polypropylene on one side and a layer of a printable polymer on the other side.
The layer of propylene homopolymer is preferably from 2.5 to 25 microns thick, more preferably from 10 to 25 microns thick, and advantageously about 22 microns thick.
The voided polypropylene layer is preferably from 5 to 25 microns thick, more preferably from 10 to 25 microns thick, and advantageously about 22 microns thick.
The printable polymer layer will in general be considerably thinner than either the layer of hompolymer or the layer of voided polypropylene. The printable polymer layer will, however, usually be at least 0.1, more particularly at least 0.4 microns thick. Preferably such layers are up to 5 microns thick.
The polymer used to form the printable layer can be selected from those known in the art. Acrylic polymers can be used, for example random terpolymers of methyl acrylate, methyl methacrylate and methacrylic acid, or random interpolymers of styrene, butyl acrylate, methyl methacrylate and methacrylic acid. Alternatively, co- and ter-polymers containing units derived from two or more of ethylene, propylene, but-1-ene, acrylic esters, maleic anhydride and acrylic acid can be used, if desired in admixture, and/or a linear low density polyethylene.
If desired, the voided polypropylene layer can have one or more further polymeric layers thereon to provide four or five layer structures. A further polymeric layer can be provided, for example to give heat sealability and/or printability to the surface of the film opposite the layer of printable polymer on the homopolymer layer. Suitable polymers for providing heat sealability include co- or ter-polymers containing units derived from at least two of ethylene, propylene and but-1-ene and/or a linear low polyethylene. A further polymeric layer can additionally or alternatively be provided which contains a pigment, for example to increase the opacity of the film. The pigment can, for example, be titanium dioxide. The pigmented polymer can, for example, be a propylene copolymer layer. While further printable and/or heat sealable layers will be provided as an outer layer, pigmented layers can be provided on either side of the voided layer, that is between the homopolymer and voided layers or on the voided layer opposite the homopolymer layer. If desired, a layer of a soft polymer can be provided beneath an outer heat sealable layer for improving the heat seal characteristics of the heat sealable layer. Suitable soft polymers are known in the art.
The further polymeric layer or layers are preferably from 0.5 to 5 microns thick, more preferably from 1 to 2.5 microns thick.
Films of the present invention can be produced by known methods. For example, a layer of a printable polymer, a layer of a propylene homopolymer, and a layer of polypropylene containing a voiding agent can
REFERENCES:
patent: Re30805 (1981-11-01), Rhoades
patent: 4377616 (1983-03-01), Ashcraft et al.
patent: 4438175 (1987-03-01), Ashcraft et al.
patent: 4578297 (1986-03-01), Duncan
patent: 4632869 (1986-12-01), Park et al.
patent: 4734324 (1988-03-01), Hill
patent: 4741950 (1988-05-01), Liu
Courtaulds Films & Packaging (Holdings) Ltd.
Van Balen William J.
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