Substrate with an undercoat for printing purposes

Details Substrate with an undercoat for printing purposes Substrate with an undercoat for printing purposes

1999-06-07

2001-03-13

Cain, Edward J. (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C524S449000, C524S451000, C523S209000, C523S216000, C523S521000

Reexamination Certificate

active

06201041

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a substrate with an undercoat as bonding layer for a printing medium to be deposited subsequently on the substrate in a laser printing process. Also within the scope of the invention is a suitable coating composition providing an undercoating on a substrate and the use of a printed substrate.
Aluminum and plastic lidding foils for blister packs are almost always provided with printed decorative patterns or images. Suitable for large series are flexo-printing and photo-gravure printing processes; for smaller series the printing may be performed in-line on the packaging equipment. Smaller elements of the image that consistently change from image to image, such as EAN and number codes, are added to these images normally by means of ink-jet printing. In order to provide smoothness, protection of the substrate and adhesion for the printing medium, by far the greater part of these images is deposited on a thin undercoat. This undercoat must be able to withstand the normal hot sealing at temperatures of up to 260° C. experienced on sealing the blister pack, and it must not adhere to the blank or coated metallic, hot sealing tools. For that reason only organic coating materials with the smallest possible thermoplasticity come into question.
Recently, in addition to the above mentioned printing methods, a new printing process has been developed which, as with flexo, printing and photo-gravure printing—for images of similar size, offers the possibility to change the image completely from print to print with practically negligible time delay. This may take place externally or in-line on the packaging equipment. The mode of operation is similar to that in laser printing on paper. A printing medium is transferred to a laser activated printing roll and fixed on the substrate by the thermal energy of a flash of light, e.g. by a xenon arc lamp.
This thermal energy is many times smaller than that provided in the thermal activation of laser printing. Under these conditions, the organic undercoats used up to now have provided only insufficient bonding of the printing medium. By adjusting the composition of the organic undercoat to the basic binding agent of the printing medium it has been possible to improve the adhesion of the printing medium to the organic undercoat, but only insignificantly.
SUMMARY OF THE INVENTION
In view of the above, the object of the present invention is to provide a substrate of the kind mentioned at the start or to provide a suitable composition of organic undercoat, by means of which the adhesion between the undercoat and the printing material is improved in a simple manner. The substrate should in particular make it possible to use laser printing processes also when applying low thermal energy to activate the medium used for printing. The aim is, thereby, to overcome the conflicting requirements of thermally activating the powdered printing medium in order to bond it to the substrate and the thermal resistance or low thermoplasticity of the organic undercoat.
That objective is achieved by way of the invention in that the organic undercoat is fine grained and contains organic and/or inorganic substances, whereby the surface of the inorganic constituents is treated or provided with a layer of organic substances.
By addition of the fine grained constituents the surface area of the undercoat layer is greatly increased.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Preferred fine grained constituents are highly dispersed silica, talcum, siliceous earth, untreated or pre-surface-treated mica, the surfaces of which are treated with organic materials such as resins or polymers, or are provided with a coating of organic materials. The organic particles may also be organic additives, resins or polymers such as e.g. polyamides and PU-resins which do not dissolve in the organic coating material and therefore increase the size of the surface in the same way as the organic fillers.
Preferred substrates include foils of metal, plastic, paper or laminates made therefrom.
The concentration of fine grained constituents in the organic undercoat or in the undercoat composition is preferably between about 0.1 and 20 wt. %, preferably between 0.3 and 10 wt. %.
It has been found that a variety of commercially available organic binders may be used for the preparation of the undercoat. Good adhesion between the undercoat and the printing medium is obtained e.g. with an undercoat based on melamine or polyesters that are cross-linkable with urea type resins or polystyrene-acrylates, non cross-linkable cellulose nitrates or multiple addition cross-linkable systems, in particular systems based on isocyanate, isocyanurate cured organic coatings based on polyester or polyacrylate basis, if desired mixed with non cureable fractions.
The surface of the inorganic constituents is preferably covered with the same substances as are employed to make up the organic undercoat. Of course other organic components may be employed for coating the inorganic constituents.
A preferred field of application for a printed substrate according to the invention in which the substrate is of aluminum, plastic or an aluminum/plastic composite is hot-sealable packaging films, in particular as film material for sealing blister packs by hot sealing, or for pouches.


REFERENCES:
patent: 4346149 (1982-08-01), Sullivan
patent: 5036118 (1991-07-01), Martinez
patent: 5049594 (1991-09-01), Jeffs
patent: 5250591 (1993-10-01), Fujii et al.
patent: 5667580 (1997-09-01), Babler
patent: 5711793 (1998-01-01), Dannhorn et al.
patent: 158619 (1975-12-01), None
patent: 8178417 (1983-11-01), None

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