Coatings – increasingly necessary

Coatings for plastic films have become indispensable in the card and security printing industry. They are required for the following applications:

• as composite assistance in printed areas

• as a support layer for various personalisation methods such as thermal sublimation printing and thermal transfer printing

• as an adhesion layer (undercoat, primer) for digital printing with liquid toner

• as the protective layer to increase the scratch resistance

• as a compensation layer in order to protect embedded RFID elements in the hot-cold-laminating cycle and to prevent flow marks (one-shot lamination)

 

Materials technology has made great progress in recent years particularly in adhesives. An important progression is the increase of resistance to hydrolysis which leads to a prolonged ageing resistance of the cards. In multi-layer card structure the use of these adhesives as a composite aid leads to an improved dynamic bending stress.

Cast technologies and coextrusion

Most flat films are produced on an extrusion system with a flat die and a roll calender. In a single layer monofoil only a plasticising unit (main extruder) is required. In multilayer films with different materials a side extruder (co-extruder) is also required. After melting in the extruders the various melt flows are led inseparably over each other in the feedblock or multilayer die (see illustration) while still fluid.

Illustration source: with the term "Multilayer+Manifold+Dies" via Google. Latest accessed 19 January 2016.

A good knowledge of materials is required for the production of co-extruded films, also knowledge and experience in processing and application. The best results can only be achieved when the plastic layers are optimally used in a co-extruded multilayer film.

Typical applications for co-extrusion

• Incorporating a thin layer in a card body structure which can be personalised by laser. Here a co-extruded film is required for the processing.

• Dyed middle layer as a security element for an identification application.

• Coloured core film with opaque white topcoat for bank cards.

• To combine the advantages of different polymers, PETG and polycarbonate can be co-extruded to PEC for example

Plastics for the card market

Plastics or polymers are macromolecular, organic compounds that are formed from basic substances (monomers). The macromolecules form either linear or branched chains (thermoplastics) but can also be cross-linked (thermosets or elastomers).

In the card industry, mostly thermoplastics are processed, meaning non-crosslinked plastics which either soften upon heating (at the glass transition temperature of amorphous thermoplastics) or melt (in the case of semi-crystalline thermoplastics). Thermoplastics are fused (laminated) to form a composite and solidify again (crystallize) during the cooling phase.

Properties of amorphous thermoplastics

• Molecule chains are disorderly entangled in one another

• Not mechanically durable after the glass transition point

• Good optical properties such as high transparency

• Good for printing and laminating

• Brittle

• Moderate temperature and chemical resistance

Properties of semi-crystalline thermoplastics

• Form a crystalline structure in some areas

• Translucent or opaque because the crystalline areas scatter light

• Resistant

• Mechanically durable even above the glass transition temperature

• Good temperature and chemical resistance.

When processing in the card industry, additional measures are needed for the printability (primer) and the composite adhesion (adhesives).

Advantages of co-polymerisation

Various monomers connect in co-polymerisation. Through the co-polymerisation of plastics polymer materials can be prepared with tailored properties such as the high-performance material Tritan™ which outperforms other thermoplastics in almost all material properties.

Benefits for card manufacturers

Lützelschwab Consulting AG cooperates with producers of raw materials and has wide material technical knowledge and many years of experience. Card manufacturers can benefit from this. As we offer tailor-made and future-oriented solutions for applications in the card market which meet the highest of standards.