Composite sheet having improved adhesive properties and methods

Details Composite sheet having improved adhesive properties and methods Composite sheet having improved adhesive properties and methods

1995-09-25

1997-09-16

Nakarani, D. S.

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Including a second component containing structurally defined...

427384, 427387, 4273884, 4273977, 4274071, 4274121, 4274125, 428323, 428341, 428446, 428451, 428483, 428517, 428519, C08J 704, C08J 706

Patent

active

056678860

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a composite sheet, and in particular to a composite sheet suitable for use as a packaging material.


BACKGROUND OF THE INVENTION

There is a commercial requirement for packaging materials, especially films for packaging edible products, which exhibit barrier properties, particularly oxygen and water barrier. Existing commercially available packaging films consist of a multiplicity of layers, generally comprising a metallic or polyvinylidene chloride layer to provide the required barrier, particularly oxygen barrier, properties. However, there is presently a perceived requirement for more environmentally acceptable materials than polyvinylidene chloride resins. In addition, coating materials which are less energy intensive than metal, such as aluminium, are required.
Coated materials comprising layer minerals are known. The layer minerals have been used to impart a variety of properties to film substrate materials, such as flame retardancy, antistatic property and gas, particularly oxygen, barrier, as disclosed, for example in Japanese Unexamined Patent Application No 62-181144, EP-A-235926 and U.S. Pat. No. 3,499,820.
Japanese Unexamined Patent Application No 63-233836 discloses a polymeric film having steam and gas barrier properties comprising a coating layer of a laminar silicate and a vinylidene chloride resin.
One particular type of commercially available packaging material, is a film laminate or composite sheet comprising, in order, substrate layer (e.g. polyester film)/polyvinylidene chloride (or metal) coating layer/thermoset polyurethane adherent layer/heat-sealable (e.g. polyethylene) layer.
Unfortunately, when the polyvinylidene chloride (or metal) coating layer, in the aforementioned laminate structure is replaced by a layer mineral coating layer, poor adhesion is observed between the layer mineral layer and the heat-sealable layer, even when the intermediate thermoset polyurethane adherent layer is employed.


SUMMARY OF THE INVENTION

We have now devised a composite sheet comprising a layer mineral coating layer which can exhibit barrier, particularly to oxygen, properties and improved adhesion to a subsequently applied heat-sealable layer.
Accordingly, the present invention provides a composite sheet comprising a substrate layer having on at least one surface thereof a coating layer comprising a layer mineral, the remote surface of said coating layer having thereon a flexible adherent layer having a percentage elongation to break of greater than 150%.
The invention also provides a method of producing a composite sheet by forming a substrate layer, applying to at least one surface thereof a coating layer comprising a layer mineral, and applying to the remote surface of said coating layer a flexible adherent layer having a percentage elongation to break of greater than 150%.


DETAILED DESCRIPTION OF THE INVENTION

A substrate layer for use in the production of a composite sheet according to the invention suitably comprises any film or web material, such as paper, paperboard, or synthetic paper. In a preferred embodiment of the invention the substrate is formed from polymeric material, which is preferably capable of forming a self-supporting opaque, or preferably transparent, film or sheet.
By a "self-supporting film or sheet" is meant a film or sheet capable of independent existence in the absence of a supporting base.
The substrate layer of a composite sheet according to the invention may be formed from any film-forming, polymeric material. Suitable thermoplastics, synthetic, materials include a homopolymer or a copolymer of a 1-olefine, such as ethylene, propylene or butene-1, especially polypropylene, a polyamide, a polycarbonate, and particularly a synthetic linear polyester which may be obtained by condensing one or more dicarboxylic acids or their lower alkyl (up to 6 carbon atoms) diesters, e.g. terephthalic acid, isophthalic acid, phthalic acid, 2,5-, 2,6- or 2,7-naphthalenedicarboxylic acid, succinic acid, sebacic acid, adipic acid,

REFERENCES:
patent: 5232755 (1993-08-01), Komiya et al.

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