Card Overlay Films, Why Different Markets Take Different Solutions

Part Two of a Two Part Series
By Mario Ognibeni, INEOS Films

In the first of this two part series, I addressed chemical and physical properties of card overlay films. In this second part of the series, I will address coating overlays.

Coated overlays - different typologies
The right coated overlay choice represents a fundamental part of each printed card project. In order to determine the correct coated overlay, typology lamination process temperatures and the printing technology adopted are the most important factors to consider. The coating behavior, in terms of adhesion performance and distortion absence, must precisely meet all the cards’ production process requirements. In the card manufacturing industry, there are water based and solvent based coatings and their use is dependent on historical reasons or local constraints. What seems to be most consistent by manufacturers is that water based coatings present a better lamination process window and are balanced by a lower adhesion level.

Standard coatings
Card producers typically prefer lamination process temperatures located within 120°C to 140°C range, as it enables standard coating a very good adhesion level on fully offset inked cards surfaces and results in no printing distortion. At this lamination temperature level it is possible to process split cores cards with white material VicatA50 between 80 °C - 81 °C. The use of higher Vicat cores, 83 °C - 84 °C or more, requires a lamination process temperature increase in order to avoid a critical adhesion value between the two card cores, additionally ABS polymer must be present in the formulations to achieve this. At this temperature level, standard coatings may experience printing distortion, therefore it is not usually recommended. A thermal glue, applied by silk screen between the two cores, may enable the use of high Vicat core materials at standard lamination process temperatures.

Anti distortion coatings
The latest coating developments have permitted cards to achieve significant improvements in terms of adhesion level on the kind of inks determined to be “critical” for the card industry, such as dark blue or some composite colors. These developments also enable a better coating thermal performance process, able to overcome printing distortion problems if the lamination process temperature increases to 145 °C to 160 °C. A simplified clear card production process is achievable with a direct high temperature lamination and the printing distortion risk is drastically reduced.

Digital printing coatings
These coatings are divided in two classes, based on the final application. In the first one, there is the coated overlay able to assure the best adhesion level on digital printing inks. This coating chemistry has been studied in order to achieve the best compatibility with the digital inks chemistry, able to overcome the adhesion critical aspect that sometimes occurs when a standard coating is used. In the second one, there is the coated overlay that can be printed with a digital printing machine, which is more common and used with the coated white cores.

Laserable overlays
This kind of overlay is widely used when a highly secure card laser personalization is required. Selecting the right technical choice, one that can guarantee the expected laser performance, is not easy. The type of laser technology, working by a continuous ray or by dots, and its power setting can completely alter the final quality. There are different kinds of laserable overlays characterized mainly by the content of the laser sensitive agent and therefore able to produce engravings with different resolution and quality. Also the type of artwork can have a big impact on the final result. Characters, for example, yield reduced burned area, if compared with bar codes or images. As a result, the best way is to proceed with a classic laserable overlay screening based on direct laserable trials. In every situation, there are some technical constraints that have to be taken into consideration in order to avoid a high rejection rate. Overlay thickness of 80 to 100 microns are generally recommended, because they have a better ability to dissipate the laser ray heat inside the overlay matrix. This thickness guarantees the laser engraving will not reach the printed core surface, which would result in the overlay detaching at the interface and the undesired burning effects that compromise the final personalization quality. This doesn’t mean that 50 and 60 micron laserable overlay can’t be used, but it requires a very good technical knowledge and an optimized laser power adjustment.

Overlay – Special technical applications
Overlays can cover some of the most technical necessities addressed in the “cards process improvements” application field. A classic example is the ability to work between two high Vicat cores, allowing a lamination process characterized by mild temperatures and pressure conditions. In this case, an uncoated 50 micron thickness overlay film acts like glue between the other two layers, melting and providing a very strong bond exactly where the most critical card process aspect are located. Obviously this additional thickness value must be properly considered during the card structure planning phase. Another interesting application is the adoption of a low thickness overlay as an external layer of high tech inlay structure. The necessity to use precise Vicat materials in order to achieve the best inlay flatness quality, dictated by some of the consolidated production technologies, could result as a critical aspect during the final contactless card lamination process. The lower the Vicat, the easier the lamination and therefore it is also clear why the overlay external presence is not only assuring the best lamination conditions but, it also offers the best flexibility in the choice of the two printed external layers in terms of Vicat point. Sometimes the laser personalization artwork requires a very high quality level in order to meet the most stringent specification requirements. It is not acceptable if roughness of the card surface can be felt by touch, normally located in the densest part of the image, which is typically the hair. Also in this case, technical support is coming from the correct overlay use. A standard thin overlay is applied over the laserable one, permitting the laser ray to go through it without detectable signs and working into the right substrate. Another kind of process improvement can be obtained in the D2T2 personalization sector of the white cards. This technology requires the best possible glossy surface finish and surface mechanical adaptability in order to provide the highest quality. Also in this case an uncoated low Vicat overlay, used as external layer, represents the best technical choice assuring an easy achieving of both the required targets. Another example of the overlay versatility its direct use in the transparent cards production and transparent high tech inlays production fields where, due to its very good flow characteristics, can assure the best lamination result at low temperature and pressures. Thus, preserving the expensive electronics from mechanical damaging.

Overlay – Future technical evolution
As technology progresses, no technical fields that can remain completely untouched. For this reason, the overlay films are now in an evolution phase. The main goal is to improve the existing card markets and consolidate card markets, finding, when possible, new fields of applications. It is clear that we are speaking about company know-how and customers collaboration and for this reason it is not possible to discuss the relevant project details but, in every case, general information can be given. The overlay production process evolution and the new technologies presented in the market would be the basis on which it will be possible to achieve new high tech overlay films performances, that today are not only unachievable due to some technical constraints, but also not considered at all. The future overlay developments will prove this assertion.

A deep overlay film sector knowledge will enable us to run card production processes with the highest degree of confidence. We must not underestimate the fundamental role of overlay performance to realize the forecasted project savings in terms of money and human resources while achieving the planned technical expectations.

Mario Ognibeni is the Technical Service Manager at INEOS Films in Castiglione Olona - Varese (Italy). He is responsible for new cards structure, development and materials optimization, in order to meet the more stringent card market requirements. Prior to this he worked in EVC Rigid Films Card Division. He has an Industrial Chemistry degree, by Padova University. Mario has spoken at several ICMA Events.