Patent Application
20070137790
The invention relates to a process for manufacturing a laminate comprising two film-shaped substrates as outer layers joined to at least one functional intermediate layer by means of adhesive layers.
The present day lamination methods used to manufacture packaging are based on individual layers that are deposited by roll-coating. The production of laminates with barrier layers is such that three or more layers are bonded together, for which a corresponding number of adhesive coating stations is required. Optimised adhesive layers require compositions that are often expensive and, if necessary, additional primers have to be employed to obtain optimum bonding. The application of these primers requires either separate passes through the coating units or additional coating stations.
To manufacture multi-layer photographic films and papers, for many years now use has been made of a liquid film coating method known as “curtain coating”. In that process several layers are deposited in free-fall simultaneously from a slit-shaped nozzle onto a moving strip of material.
Proposals have already been made to apply curtain coating technology to the coating of papers and to the production of plastic composite materials.
Described in WO-A-0154828 is a method for manufacturing a multi-layer packaging laminate with at least two superimposed layers, in which process two or more layers are deposited in the liquid state by curtain coating onto a substrate of a—possibly pre-coated—paper, cardboard or plastic film and subsequently dried. The liquid film coatings comprise barrier layers, intermediate layers acting as spacers, oxygen scavenger layers and hot-sealing layers.
Known from U.S. Pat. No. 6,845,599 is a liquid-film coating method which is an alternative to curtain viz., “slide coating”. In this alternative coating method several layers are simultaneously deposited coming from a slit-shaped nozzle and a nozzle slide face directly onto a substrate passing the run-out edge of the nozzle slide face.
The object of the present invention is to provide a process of the kind mentioned at the start in which laminates with functional intermediate layers such as e.g. barrier layers can be manufactured in a simple and cost-favourable manner.
That objective is achieved by way of the invention in that a first substrate is coated by liquid-film coating using curtain-coating or slide-coating with a multi-layer liquid film comprising at least two outer lying adhesive layers and at least one functional intermediate layer and, subsequently bonded to the second substrate.
Functional intermediate layers preferably feature at least one barrier function involving preventing the penetration of oxygen, carbon dioxide, aromas and/or water vapour by diffusion, or inhibiting the transmission of ultraviolet radiation and the scavenger function in which oxygen, water vapour and aromas are absorbed.
Functional intermediate layers with barrier properties against penetration of oxygen, carbon dioxide, aromas and/or water vapour are based e.g. on polyvinyl alcohol (PVOH), ethylene-vinyl-alcohol (EVOH), cross-linking acrylates, polyamides, PVDC (polyvinylidenchloride), epoxy-amine, fluor-polymer nanocomposites and/or layer silicates.
Functional intermediate layers with barrier properties against the penetration of ultraviolet radiation contain e.g. organic absorbers or inorganic particles.
Functional intermediate layers with a scavenger function contain e.g. inorganic or organic filler materials or molecular sieves as absorber material. Inorganic fillers are e.g. particles of oxides belonging to the alkali and alakali-earth metals such as e.g. calcium oxide (CaO).
Each of the adhesive layers is preferably functionally optimised with respect to the surface of its neighbouring substrate.
By “functionally optimised” is to be understood that the composition of adhesive used for the adhesive layers is made to suit the chemical and/or physical properties of the substrate neighbouring on the adhesive layers such that optimum adhesion is achieved between each pair viz,. substrate/adjacent adhesive layer.
This way and in a simple manner two substrates with different surface properties can be coated with an adhesive which is optimised in each case with respect to the bonding required for each substrate.
The compositions of adhesive that are optimised specifically for a given substrate are often expensive products. For that reason in some cases it may be necessary to provide a liquid film which, apart from the adhesive layers, exhibits at least one intermediate layer as additional volume, whereby the thickness of the adhesive layer is less than the thickness of the intermediate layer. The thickness of the adhesive layers usefully amounts to about 1 to 30%, preferably 1 to 10% of the thickness of the intermediate layers.
The intermediate layers are preferably of a cost favourable material such as e.g. a urethane-based adhesive, in particular a standard urethane adhesive such as e.g. aromatic or aliphatic isocyanates.
The adhesives may e.g. be made up of polyether, polyester or polybutadienepolyols, may be acrylic or epoxy based, or made up of a combination of the mentioned adhesives.
The layers of liquid films may be solvent-based, solvent-free or water-based. Solvent-free coating fluids are preferred as they do not require the normal drying step.
Substrates which may be employed are plastic films e.g. of polyethylenetherephthalate (PET). Polyethylene (PE), polypropylene (PP), polyamide (PA), paper or a combination of at least two of the materials mentioned.
Further advantages, features and details of the invention are revealed by way of the invention by way of the following description of preferred exemplified embodiments and by way of the drawing; these are shown schematically in
A nozzle arrangement 10, shown in
The superimposed coating fluids 34, 36, 38 emerging from the distribution chambers 20, 22, 24 via exit slits 28, 30, 32 onto the nozzle slide face 26 run as a three layer liquid film 42 over a run-off edge 40 on module 12 and form a free-falling curtain.
The three-layer film 42 made up of the coating fluids 34, 36, 38 impinges essentially vertically with the first strip-shaped substrate 44 moving in direction x.
The liquid film 42 in
As shown in
Using the process shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 05 405 715.3 | Dec 2005 | EP | regional |
