It is with interest and – also some astonishment – we have read the articles by Michel Caza about UV screen printing in the December 2004 and January 2005 editions of Screen Print India and would like to comment as follows:

The author of these articles gives an explicit warning to the readers about the contents of an article published by the ESMA TDS committee in the April 2004 edition of Screen Print India. In that context he also gives his own recommendation with reference to information given in that article.

We would like to comment as follows:
1. Mistakes:
Despite warnings against wrong information given in the context of our article we cannot find any reference whatsoever regarding this “wrong information”. None of our comments are questioned.

2. Post-Polymerisation:
Mr Caza has ignored the topic of post-polymerisation in our article. The amount of post-curing reaction of UV inks is quite different and depends on ink type and/or the binding agents contained. We do consider postpolymerisation as an important side aspect. However, we deliberately omitted this matter in our basic description of the main factors of UV-curing.
3. Brittleness of material caused by correct UV-curing:
In connection with correct polymerisation of UV-inks it is said that during further processing like die-cutting or grooving plastic materials will splinter due to brittleness of the material caused by correct UV-curing. We have assumed in our article that appropriate inks are used for a specific application, taking account of any post print processing that is required.
4. “Minimal” curing to prevent thermal problems with the substrate:
We would always recommend that UV inks are adequately cured to ensure full adhesion. Undercuring, as well as affecting adhesion may result in other issues such as blocking. Therefore thermal influences should be reduced using an effective cooling system in the dryer.
5. Reflector types in the UV-dryers:
In our article this topic has been described in a sufficient and much more understandable manner.
6. Measurement of UV-emission in the UV-“drier” vs. measurement of polymerisation:
Finally we reach a real topic for discussion: We do recommend measurement of UV radiation emitted by the UV-lamps. This type of equipment is not too expensive, measurement tolerances are acceptable, application is easy and measurement values are easily understood in practical use. We did describe other analytical processes to determine degree of polymerisation, however we do not consider these as suitable for screen applications. Mr. Caza, however, considers measurement of radiation as unimportant and recommends to determine degree of polymerisation of an ink instead and also mentioned a suitable measurement device and its disadvantage, a price of approx. 4,800 Euros.

Then, however in another article of published in January 05 edition of Screen Print India about “Measuring the level of curing in UV Printing” he informs the reader, that unfortunately that device is not suitable, as it does not give any data of importantance for screen printers! Therefore reference is made to a second generation of the same device, which is not available yet (!!!). Not one word is mentioned about the complex handling during the measurement and interpretation of measured values. The equipment manufacturer on the other hand honestly recommends this device as an analytical device for chemical research and development of UV inks. We would like to leave it up to the reader to form his own opinion.

ESMA considers itself as a partner in the screen printing sector working closely with screen printers. Our work in the ESMA committees is done to facilitate better and more reproducible screen printing to ensure that it remains a competitive printing process for the future. We are always ready to discuss the quality of that work, however this should be done in an informed, fair, sound and competent manner.

Best regards
Johann Bauer,
on behalf of ESMA TDS-Committee

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