Miljøparametre ved flexografisk trykning

Summary

Environmental improvements in flexography

Flexographic printing is used when manufacturing wrappings and labels of plastic and paper/cardboard. A change from solvent-based to water-borne inks when printing on paper has already happened. If solvent-based inks are used the emission of volatile organic compounds should be reduced/collected and their energy should be used in production. When cleaning the printing unit used for water-borne inks there is a need for minimising the waste water and handle it properly because of the presence of environmental hazardous compounds. The components in radiation curing (ultraviolet curing) inks are all more or less hypersensitising, which means that skin contact should be avoided. The use of raw materials can in general be reduced by avoiding waste of paper/plastic and inks.

Background and aims

Environmental description of flexographic printing

An environmental project called: "Flexographic Printing and Environmental Parameters (Miljøparametre ved flexografisk trykning)" has been performed as a co-operation between EnPro ApS and dk-TEKNIK. The aims of the project are:

• To generate a general description of flexographic printing-houses, where the existing printing technique is described.

• To perform a systematic investigation of existing environmental hazards within the flexographic area.

• To describe new technologies, for instance the use of water-borne inks and UV-inks and furthermore to describe the limiting factors effecting the introduction of these new technologies.

• To perform an environmental assessment with starting point in the primary life cycle of the inks from production to waste.

• To show the possibilities for reduction or elimination of environmental hazards from the flexographic area by the use of cleaner technology.

The project is reported in two separate parts:"Technical description (Teknisk beskrivelse) " and "Environmental evaluation of chosen products (Miljøvurdering af udvalgte produkttyper)".

Performed investigations

General line of business description

The number of printing-houses using the flexopraphic technique has been found to be 76. The real number is probably higher because several of the companies that use flexographic printing have other printing techniques as their main activity and are therefore registered under these.

To describe consumption (of material and energy) and exposures, when printing different types of products nine companies have been visited.

Environmental assessment

The planned starting point for the environmental assessment of the flexographic area was to perform life cycles analysis for the three different types of inks (solvent-based, water-borne and UV-curing), that can be used in flexographic printing. Data for emission and resources have been collected from the investigated companies and have been combined with data from literature and personal communication with experts in the flexographic area (including the project group). The data have been evaluated using a screening method.

The result of the assessment led to pointing out several "red signals" within the use of each of the three different types of inks. Suggestions to improvement have been given as well. On the other hand it is not possible to use the assessment for pin pointing one of the three types as being the best environmentally speaking.

The suggestion for improvement is mainly focused towards the condition which the printing-houses them selves have influence on, i.e. adjusting the process and choosing specific inks.

Main conclusions

Size of market

The market share of flexography in Denmark based on the total turnover in the graphic industry is estimated to be 30 %. No data have been available for the determination of whether the market share is rising or decreasing. The turnover for the flexographic area is estimated to be approximately 2.5 Mia DKK.

Environmental overview

The companies are aware of the environmental demands made for the handling and printing in flexography. Several of the companies have within the last couple of years changed from solvent-based printing to water-borne printing on cellulose products (paper, corrugated cardboard etc.).

Printing with UV-inks is mainly developed in the big companies. The technique is not widespread. Some label printing-houses have use UV-lacquering and/or UV-letterpress.

The available knowledge about the environmental effects of UV-curing inks is so restricted that it is pt. not possible to ensure an optimal process from an environmental viewpoint.

The air is usually not treated before emission to the atmosphere. A few companies’ uses charcoal filters or thermal catalysis to purify the air.

Wastewater from flexographic printing-houses mainly comes from cleaning the printing press with water after printing with waterborne inks. The wastewater is usually sent to "Kommunekemi", but ultra-filtration or/and precipitation of the wastewater before disposal to the sewer is used as well.

Companies that print on several different types of substrates produce a relatively large amount of print waste of printed paper. Reuse of printed paper/substrate is only performed for pure cellulose products. Print waste from the label industry and the flexible films/laminate industry is incinerated.

Printing on flexible films/laminate (non-absorbent substrate) is mainly performed with solvent-based flexo inks.

On the other hand it can be concluded that the use of solvent-based inks can be attractive as printing with water-borne inks as long as known methods for reduction of emissions are used.

Results

Description of existing technology

The trends within development of flexo printing machines are:

• More inking units in the same printing unit. That makes it possible to obtain better colour separation both in solid print as well as halftone print.

• Higher printing speed, quicker change of printing jobs.

• More precision in register.

• More precise ink transfer. Therefore an increase in use of closed doctor blade inking units and anilox rollers with fine screens is observed.

• Reduction of noise.

• Easier operations by further automisation and computerising of the processes.

• Reduction in the use of energy (lower costs).

Supplementary equipment is developed as well:

• Cleaning processes becomes more efficient and less hazardous for the environment. New methods are developed.

• New photopolymer plates are developed, for instance plates, which can be washed out with water, laser engraving of rubber as well as photopolymers. The use of micromarks for mounting the plate on the printing machine.

Environmentally "red signals"

On basis of the collected data from the companies it has, with precaution, been possible to pin point several trends concerning the resources and waste. The trends are as follows:

• The used amount of energy when printing with water-borne inks is in the upper end of the observed use of energy.

• The used amount of energy does not depend on whether the substrate is paper or plastics.

• The amount of wasted substrate varieties a lot (between 4 % to 40 %). The largest observed amount of waste is when printing on labels.

It is not possible to differentiate the waste of inks for the different types of ink, but it is expected that the waste is higher for water-borne ink than for solvent-based.

Concerning the exterior environment following areas seem to be the most problematic:

• Emission of volatile organic compounds (VOC).

• Discharging of (environmental) hazardous compounds to the water environment.

• Lack of knowledge about chemical and environmental characteristics of the components in UV-curing inks.

In the health and safety area the assessment led to pin pointing the following areas as the most problematic:

• Emission of organic solvent to the working environment.

• The use of plasticisers in solvent-based inks.

• The use of several components in water-borne inks that are irritating and /or can lead to hypersensitivity.

• The use of monomers and photo initiators in UV-curing inks that are strongly irritating and/or can led to hypersensitivity.

• Lack of knowledge about chemical and health and safety characteristics of the components in UV-curing inks.

Suggestions for improvements

Due to lack of quantitative data the suggestions can only be made in general terms. The suggestions are:

• Improvement of the drying capacity by suitable elaboration of drying units and by recirculating the hot air.

• Investigation of the possibility for reduction in the used amount of energy for UV-lamps by substitution with so called "cold" lamps.

• Minimisation of energy loss from emission of organic solvent by emission reduction facilities plus catching the emitted volatile compounds and the use the energy potential of these.

• Reduction in the amount of used raw materials. Partly by controlling the printing process to reduce the waste of substrate and partly by minimising the use of inks. The latter can be obtained by closing and emptying the ink containers thoroughly, by reusing the remainders etc.

• More detailed assessments of environmental and health aspects of components used in water-borne ink.

• A more thorough knowledge of the characteristics of components used in UV-curing inks.

• Increased use of already known methods for reduction of emissions of organic solvents in the working environment as well as the exterior environment.

• Organising the work with water-borne inks in such a manner that the risk for irritations and allergy is eliminated or at least reduced.

• Handling all UV-curing inks as the risk for hypersensitivity exists.

• Reduce or totally avoid the use of UV-curing inks containing monomers that are listed by SBPIM as being potentially the most irritant and hypersensitising.

Other information

References

A Project called "Environmental optimisation using water-borne flexographic inks" ("Miljøoptimering ved anvendelse af vandfortyndbare flexofarver") has been initiated as a follow up on the here described project. The new project is coordinated by The Institute for Water Environment (VKI).