Hot dieless foiling

Details Hot dieless foiling Hot dieless foiling

1999-03-23

2002-05-28

Crispino, Richard (Department: 1734)

Adhesive bonding and miscellaneous chemical manufacture

Methods

Surface bonding and/or assembly therefor

C156S233000, C156S234000, C156S238000, C156S241000, C156S247000, C156S277000, C156S287000, C427S146000, C427S147000, C427S148000, C428S209000, C428S914000, C428S915000

Reexamination Certificate

active

06395120

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for the application of a metallic (or pigmented) layer from a foil to a substrate, and an adhesive that is suitable for use in this technique.
In the printing industry, foils are used to enable the application of a metallic (or pigmented) layer to a substrate (i.e. a surface to be printed).
A foil is a laminated product of comprising a metallic layer or a pigmented layer and an adhesive layer on the underside of the metallic or pigmented layer, which is carried on a plastics carrier layer, for example of polyester. Usually, a thin film of release agent is interposed between the plastics carrier layer and the metallic or pigmented layer to thereby facilitate separation of the metallic or pigmented layer from the carrier layer after adhesion of the metallic or pigmented layer to the substrate has taken place.
Several techniques for the application of the metallic or pigmented layer to the substrate exist. One of the most common techniques for the application of the metallic or pigmented layer to the substrate is known as hot-stamping. According to this technique, the foil is applied to the substrate to be printed and is subjected to the simultaneous application of heat and pressure by a heated, engraved die. This causes activation of the adhesive layer and the release layer of the foil and results in firm adhesion of the metallic layer to the substrate being printed. The carrier layer can then readily be removed from the printed surface, leaving the metallic or pigmented layer firmly adhered to the printed surface.
The metallic or pigmented design applied to the substrate is dictated by the design engraved into the metallic die. It takes approximately ten days to engrave a die with the design, and to mount the die onto the printing press ready for application of the metallic or pigmented image to the substrate. The amount of time it takes to engrave the die results in increased operating costs. In addition, this method is disadvantageous in that the speed at which the printing press may be operated is fairly low, since it takes time to raise the temperature of the foil by the application of heat and pressure from the engraved metallic die to be sufficiently high to effect adhesion and separation of the metallic layer from the carrier layer to the substrate to be printed.
In order to overcome the disadvantages of this process, an alternative transfer technique known as “dieless foiling” has been developed. Two typical arrangements for dieless foiling are illustrated in FIG.
1
. According to this technique, adhesive is applied to the substrate using flexographic, lithographic or letter press techniques, so that the coverage of adhesive on the substrate corresponds to the metallic image desired to be transferred. This adhesive is applied as a wet formulation to the substrate, and is subsequently activated (rendered tacky) by one of several physical or chemical changes to the adhesive. The most common technique used to activate the adhesive involves irradiation with ultra-violet light which results in polymerisation of the adhesive components. An alternative method involves combinations of evaporation or oxidation of the applied adhesive. In the case of ultra-violet activation, the ultra-violet light initiates polymerisation of the monomer components in the adhesive.
In the time it takes the adhesive to pass through a tacky state and to cure, the substrate is passed through a foiling station in which a roll of foil is applied to the surface of the substrate and pressed against the adhesive. The distance between the UV drying station and the foiling station is critical in achieving adequate transfer and adhesion of the metallic or pigmented layer from the foil to the substrate. If the distance is too small, the adhesive will not be sufficiently tacky to adhere to the metallic layer of the foil. If the distance is too great, the adhesive will have completely cured and cannot be “reactivated”.
In addition, according to this technique it is not possible for components of the printing apparatus to impinge on the side of the substrate to which the adhesive has been applied between the UV drying station and the foiling station, since this would result in the adhesive being transferred to this component. For instance, it is not permissible for the path of the substrate to pass around a turning or rotating roller to redirect the pathway of the substrate towards the foiling station after the UV drying station. Various printing presses in existence prior to the development of dieless foiling did not contain turner bars or rotating rollers in the pathway between a UV drying station and a foiling station, and therefore could be simply modified to be operated in accordance with the dieless foiling technique. For these printing presses, this has not accordingly been a problem.
There are a number of advantages associated with dieless foiling techniques. Much finer resolution of the metallic image on the substrate can be obtained compared to the hot-foiling technique. Standard techniques for the application of inks to the substrate are used for the application of the adhesive to the substrate and consequently a metallic or pigmented image of finer resolution is available. In addition, since the foil and substrate are pressed together through pinch rollers having a smooth, cool surface in contrast to the hot-stamping technique, there is no physical bending of the substrate as it passes through the rollers.
However, not all printing presses that are currently set up for hot-stamping of a metallic or pigmented image to a substrate can be modified simply by the known methods to be usable in a cold dieless foiling method. The known dieless foiling techniques of the prior art are dependent on there being no physical obstruction to the pathway of the substrate between the UV drying station and the foiling station. However, in many existing hot-stamping foiling printing presses, a turner roller or the like is located between the UV drying station which effects drying of the ink supplied to the substrate, and the foiling station. If an adhesive is applied in an adhesive printing station and is activated by initiating cure at the UV station, the tacky adhesive will pass over the turner roller and will be removed from the substrate, thereby making it impossible to apply a metallic image to the substrate by the dieless foiling technique.
The replacement of a printing apparatus with one that does not have a turner roller is a very expensive option, and when compared to the relatively smaller cost savings of conducting the foiling operation using the dieless foiling technique, it is often not an economically viable option. Accordingly, there is a need for a dieless foiling technique that overcomes these problems.
SUMMARY OF THE INVENTION
According to the present invention there is provided a process for the application of a pigmented or metallic layer from a foil to a substrate comprising:
(i) applying an adhesive to the substrate;
(ii) curing the adhesive;
(iii) heating the substrate bearing the cured adhesive to render the adhesive tacky; and
(iv) transferring the pigmented or metallic layer from the foil to the adhesive-bearing areas of the substrate.
By using an adhesive that can be cured to an extent that it is not tacky such that the surface of the substrate bearing the adhesive can be passed over components of the printing apparatus, but that can be softened and rendered tacky by the application of heat, it is possible for existing printing processes having turner bars or the like between curing stations and foiling stations to be used in a dieless foiling technique.
Preferably, in step (ii), the adhesive is cured to the extent that the cured adhesive is not transferred to any components of the apparatus upon which the process is conducted that impinge on the pathway of the substrate between the curing step and the heating step.
Whilst any means of curing the adhesive can be used, depending on the adhesive composition inc

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