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Manuel Böhm

Manuel Böhm

Department
ID-cards & Print finishing

E-mail
boehm
transparent 11x15@fogra.org

Telephone
+49 89. 431 82 - 473


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Fogra test device for determining the adhesion of varnish layer LHT

The Fogra LHT enables the converter to check in advance, whether varnish layers have a sufficient adhesion on the print. With the results of this test in mind it is possible to take appropriate measures to avoid costly complaints.

LHTInsufficient adhesion of varnish layers is frequently observed in print finishing. In extreme cases, the varnish can be scratched away or detached from the surface with the thumbnail.

Varnish adhesion is in practice usually assessed by a test where an adhesive tape is applied on to the surface and then pulled off manually. This is an extremely subjective method of assessing the adhesion. Each person carrying out this test applies the adhesive film in a different way, presses the film down with differing degrees of pressure, and starts pulling it off either suddenly or slowly. Results which can be reproduced are unobtainable by these means. The information yielded by such experiments is only superficial.

In order to make it possible to determine the adhesion in an exact, objective and reproducible way, an attempt was made to retain the main features of the adhesive-tape test while at the same time mechanising the test sequence and measuring the adhesion value automatically and without any influence on the part of the tester.

 

The Fogra LHT uses a simple principle:

A piece of a customary adhesive tape is pressed onto an area covered with varnish by a mechanical press. On one end a small metal plate is fixed on the adhesive tape and inserted into the tape removal apparatus. The removing force is adjustable by varying the length of the removal spring. The manual removal is imitated by a rotating removal disc.

In principle the device can be used for all flat coatings on thin substrates.

Please click on the picture to enlarge it.



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