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Vurdering af UV-hærdende trykfarver og -lakker i et samlet miljøperspektiv

English summary

Ultraviolet (UV) -curing printing inks and lacquers can improve the environmental conditions in the printing industry significantly. Many printing inks, especially for printing on plastic packaging, contain organic solvents, which can contaminate the environment and incriminate the occupational safety and health. UV-curing inks and lacquers are free from solvents.

Background and purpose

UV-curing products have been in use for the last 30 years, e.g. for lacquers in the furniture industry and as "plastic-fillings" in teeth. In the printing industry UV-curing inks and lacquers have been introduced for a number of purposes, where it has been important to secure fast drying and high gloss.

When introducing UV-curing products a major environmental problem is solved - the emission of vapours of organic solvents, but at the same time new problems possibly are created, such as risk of skin damage, radiation damage, the generation of ozone and contamination of food products trough the packaging. A further propagation of UV-inks might be delayed because of technical problems, and there are fields where it will be rather expensive to introduce UV-inks. The Graphic Arts Institute of Denmark has examined these issues for the Danish Environmental Protection Agency, and the results are presented in the report "UV-curing printing inks and lacquers in a total environmental perspective".

There is an interesting background for this report in the form of an agreement between the printing industry and the Minister of the Environment and Energy to reduce the emission of volatile organic compounds (VOC) by 58% before the year 2000 compared with the emission in 1988. A very large percentage of this emission comes from printing and finishing of thin plastic film packaging (flexible packaging). The introduction of UV-curing inks and adhesives is an obvious possibility to reduce the emission from this branch, and the major part of the report deals with this issue.

Research

A survey of the use of UV-curing products in the printing industry in Denmark has been carried out. A number of graphic arts companies already using UV-curing products have been visited and their experiences registered. Furthermore suppliers of UV-inks and raw materials for these, as well as suppliers of UV-lamps have been interviewed, and Danish and foreign technical literature has been examined. As UV-flexo attracts much interest in the neighbouring countries, the consultants have gathered important information by attending a couple of seminars abroad.

In connection with the project the consultants have taken part in test runs in Germany in full production scale and have had access to results from earlier test runs.

At the end of the report an attempt is made to give a total picture of the consequences to the environment, to the safety and health and to the financial consequences when introducing UV-technology.

Main conclusions

Technical aspects

A number of technical advantages can be obtained by introducing UV-technology, including a more rational production, very fast drying and improved print quality. On smaller printing machines it is no major problem to keep a constant temperature, but the temperature control will be critical on large flexographic printing machines. Here the main part of the energy supplied to the UV-lamps will heat the printing cylinder and the material to be printed, which is not acceptable. New "cold" UV-lamps, new types of ink and lacquers and the introduction of a nitrogen atmosphere in the curing zone will lead to lesser energy consumption and consequently a lesser demand for cooling and a more safe through-curing of the inks.

Economic aspects

It is assumed that there is economic balance in the graphic arts fields, where UV-curing is in current use. But it will demand substantial investments and result in increased costs to introduce the UV-technology in new areas, especialle for the production of flexible packaging.

Environmental aspects

The emission of volatile organic compounds (VOC) might be reduced with about 1,100 tons per year, if the substitution within the graphic arts industry is carried out to full extend. This reduction is mainly to be found within the production of flexible plastic packaging, where inks and laminating adhesives containing large amounts of solvents are presently used. It is within this branch as well that the energy consumption will grow when using UV-inks compared with the use of the traditional solvent based inks. But the comparison will depend upon the conditions. If the air from solvent drying is cleaned by after-burning, the energy consumption will be almost unchanged.

Health and safety

UV-curing products vary in their skin irritating and allergy promoting effects, and it is recommended that the most irritating components are avoided, which can be difficult. If a number of necessary precautions are taken when working with UV-curing products, the risk is considered to be small. There is a risk that non-reacted monomers still present in the ink layer can migrate through thin plastic packaging and contaminate food products. Test methods and limits are missing. It is considered that other problems concerning UV-curing products, such as annoying odour, the generation of ozone from the UV-lamps, the risk of skin and eye damage due to UV-radiation, ink misting and problems in connection with the de-inking of printed matter can be solved by taking simple precautions.

Project results

UV-products

UV-curing inks and lacquers contain reactive, high viscosity binders, so called pre-polymer acrylates, which by the curing process are transformed into a solid and strong layer of ink or lacquer. Ink or lacquer contains photoinitiators, i.e. light sensitive compounds, which by radiation become active and initiate the curing process. Low viscosity reactive monomer acrylates are used as thinners. Furthermore the inks contain pigments and small amounts of additives. The skin irritation and allergy promoting effects, which is due to some of these components have been examined, and a list of the most irritating compounds is presented together with a list of the necessary precautions to be taken.

UV-lamps

The radiation is carried out by using special UV-lamps, emitting ultraviolet radiation in the UV-A, UV-B and UV-C fields. There are several different lamp types available with different effects. Often very strong lamps are needed, and the energy consumption can be very high (as high as 240 kW for a single large printing machine in flexography).

Known areas

Persons have been interviewed within the following printing areas, where UV-curing inks and lacquers are currently in use.

The printing of self-adhesive labels by flexography and letterpress.
The screen printing of posters etc. on paper and board.
The lacquering of printed matter, normally printed by offset.
The printing of plastic buckets, plastic cups and lids by letterset.
The printing of metal boxes by tin-printing.
Offset printing of cartons for beverages.
Offset printing of Bank notes.

Great satisfaction with the UV-technology has been experienced within these fields and it is expected, that the use of the technology will grow.

New applications

New areas for the UV-technology within the printing industry can be:

The printing of flexible packaging (thin plastic films) by flexography.
The laminating of plastic films with UV-curing adhesive.
External and internal lacquering of tin plate packaging.

There is a great interest for the UV-technology especially within these fields, as it is here the largest emission of VOC from the printing industry can be found.

Furthermore there are quite new possibilities in using UV-curing inks within packaging gravure and the printing of flexible packaging etc. by web offset.

Technical aspects

The report describes the technical advantages and disadvantages, including the problems combined with the cooling of the printing machine in flexography, and the possible solutions to these problems by the use of "cold" lamps, oxygen-free atmosphere, cationic inks, etc.

The investigation includes the preparation of a financial model for UV-technology compared with traditional technology within the printing of flexible packaging. The available data do not give a precise picture of the situation, but still they give a clear indication that the UV-technology at the present stage is more expensive than the traditional technology.

Environmental assessment

A flexible packaging printed in flexography has been used as a representative example for comparing the environmental impacts concerning resources, production, usage and disposure. The most important advantages are the reduction of the VOC-emission and the reduction of the exposure to solvent vapours during printing. The most important drawbacks are the risk of skin sensibilisation and migration of uncured momomer acrylics through food packaging.

Questionaire

A questionnaire investigation has been carried out amongst persons with experience within UV-technology. In general, the results of the investigation confirm the conclusions mentioned above.

More to read

Georg Bolte & Manfried Hornschuh: UV-Flexo, G & K TechMedia 1995. (In German)

Øyvind Omland & Kristian Libak Pedersen: Hudproblemer ved anvendelse af (meth)acrylatbaserede UV-hærdende trykfarver og -lakker i Danmark. (Skin problems when using (meth)acrylate based UV-curing inks and lacquers in Denmark). Arbejdsmiljøfondet 1992-21. (In Danish)

Engel Hansen, L. et. al.: Inventering af miljøparametre ved flexografisk trykning. Delrapport: Miljøvurderinger af udvalgte produkter. (The use of environmental parameters in flexographic printing. Environmental assessment of selected products). Miljøstyrelsen. (In Danish)