Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-09-06
2003-03-25
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C281S020000, C281S029000, C428S172000, C428S511000
Reexamination Certificate
active
06537407
ABSTRACT:
PROCESS FOR THE MANUFACTURE OF AN IMPROVED LAMINATED MATERIAL
The present invention relates to a process for the production of an improved laminated material. The invention relates in particular to a process for the production of a laminated material in which a film of cellulose acetate, in particular cellulose diacetate, is laminated to a printed substrate.
It is known to laminate clear glossy, matt or semi-matt films of materials such as cellulose acetate or diacetate to printed material, for use for example for book covers and in packaging material.
A range of cellulose diacetate films has recently been developed, which films have a matt or semi-matt finish which is particularly distinctive and attractive and which also has other desirable properties, which are unique to these materials. These films are plastics films, in particular cellulose diacetate films, which are marketed under the Trade Mark Semitone by Acordis Acetate Products Ltd (Clarifoil). Semi-matt or matt plastics films of this type, and a process for their manufacture, are described in European Patent Application No. 0 802 069 A1, the contents of which are incorporated herein by reference, and the films described in that patent application are particularly suitable for use in the material and process of the present invention. These matt or semi-matt films are characterised by a regular embossed pattern of depth 0.5 to 10 microns and repeat distance 20 to 400 microns and it is taught in the specification that these films can be laminated over printed paperboard. The characteristic properties of these films include the ability to emit a characteristic noise of reproducible pitch when two films are rubbed together and also a high resistance to finger marking. These properties are due to the embossed surface of the film and it has therefore up until now been the practice to use a wet, cold lamination process to laminate these films to a substrate using a lamination technique which does not involve heating the film, so that no deformation of the embossed surface of the film, and hence impairment of these characteristic properties, would occur in the lamination process.
Thermal lamination is a very popular process for book cover lamination, especially for paperback books. In a thermal lamination process, a melt coating is extruded onto the film, the coated film is chilled and then wound up as a roll of film with dry adhesive already applied. The laminator then needs to run this film over a simple hot roller, melting the adhesive, and pressure nip it onto the substrate, suitably a printed board, by running the film and substrate between nip rollers. The process is more expensive than wet lamination, but requires less skill, and therefore has been taken up by printers, who can therefore shorten their turn round times by not needing out-of-house contract lamination.
In an alternative form of thermal lamination, which is also referred to as encapsulation, a printed substrate such as a restaurant menu or a poster, is laminated between two sheets of film to encapsulate the paper. Encapsulation is generally carried out with thicker films and thicker coatings than are used for thermal lamination on one side of a substrate.
Matt finishes feature prominently for book cover lamination. Matt oriented polypropylene film is widely used, but is prone to scuffing and marking. In the United States, in particular, higher levels of humidity, in particular in southern states, mean that curl of book covers can be a severe problem. So called “layflat” nylon films have been introduced which give improved curl correction, but at the expense of even worse scratch and scuff resistance.
It is an object of the present invention to provide a process for the manufacture of an improved laminate. It is a further object of the present invention to provide a process for the manufacture of an improved laminate in which the disadvantages of known laminates are reduced or substantially obviated.
The present invention provides a process for the manufacture of a laminate which comprises a thermoplastic plastics film having, on at least one side, an embossed pattern of protrusions having a height in the range of 0.5 to 10 microns and a separation in the range 20 to 400 microns, laminated to a substrate in which the improvement comprises the use of a thermal lamination process, which process includes the steps of applying a melt coating between the film and the substrate and running the film and substrate, whilst the adhesive is in a heated condition, between nip rollers to apply pressure thereto, so as to effect lamination of the film to the substrate. In a preferred embodiment of the process according to the present invention, the thermoplastic plastics film is a matt or semi-matt plastics film and is preferably a cellulose acetate film, more preferably a cellulose diacetate film.
The melt coating is preferably applied to the film, more preferably by an extrusion process. In a particularly preferred embodiment of the process according to the invention, the coated film is chilled after the adhesive has been applied and the coated film is subsequently run over a heated roller to melt the adhesive.
In a preferred embodiment of the process according to the invention, the process further includes the step of winding up the roll of film with dry adhesive applied, between the chilling step and the heating step. In a particularly preferred embodiment of the process according to the invention, the dry melt adhesive is a polyethylene homopolymer or an ethylene vinyl acetate copolymer which has a melting point between 140 and 180° C. and is preferably applied by extrusion coating at a temperature close to the melting point, at which temperature the polyethylene homopolymer or ethylene vinyl acetate copolymer is molten.
The matt or semi-matt thermoplastic plastics film for use in the process according to the invention preferably has a thickness of approximately 15&mgr; and the adhesive coating is preferably applied at a thickness of 17 to 18&mgr;, at a temperature significantly higher than the softening point of the film.
The coated film is run over a heated roller at a temperature of about 115° C., with the side of the film with the protrusions in contact with the roller, and the adhesive is heated to a temperature of about 100° C. or above, at which temperature the adhesive is softened.
The acetate film is preferably treated prior to application of the adhesive, in a manner known per se for conventional lamination films, including acetate films, with a primer and/or by a corona discharge treatment, in order to improve the adhesion between the acetate and the adhesive and between the film and the substrate.
Where the acetate film is treated with a primer prior to the application of adhesive, the primer is preferably one conventionally used for coating, such as a polyurethane or isocyanate based primer in either aqueous solution or in an organic solvent system. Typical coating thicknesses are less than one micron.
Where the acetate film is treated by a corona discharge treatment prior to application of the adhesive, the corona is generated by applying a high voltage signal to an electrode. The substrate to be treated is passed below the electrode; beneath the substrate is a dielectric layer, with an earthed plane below the dielectric layer. When a sufficiently high voltage is applied, electrical breakdown occurs in the air gap between the electrode and the substrate, so that the substrate (film) surface is bombarded with high energy electrons. The net effect is to raise the surface energy of the film substrate. The peak voltage applied is preferably up to 30 kV, preferably at an ac frequency of between 9 to 50 kHz.
It has surprisingly been found that when a matt or semi-matt thermoplastic plastics film having an embossed pattern of protrusions having a height in the range of 0.5 to 10 microns and a separation in the range 20 to 400 microns is laminated to a substrate by means of a thermal lamination process, the resultant laminated material retains the characteris
Law Paul William
Longdon Tony
Taylor Donald
Willins Gordon
Acordis Acetate Chemicals Limited
Ball Michael W.
Howson and Howson
Musser Barbara J.
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