As mentioned in the introduction to this section, fount filtration plays an important part in successfully changing to printing without alcohol.

The IPA in the fount not only changes the way the fount solution and ink react to each other, but also masks the effect of dirt in the fount. Adding extra filtering prevents many of these problems from arising in the first place, so you don't need the effect of the alcohol.

The following article, kindly provided by Technotrans, explains this in detail.

Why reducing IPA doesn't have to mean increased work and costs

How fine filtration can achieve the same effects

Printers are well aware of the need to reduce IPA use, as it is a major source of VOC emissions in the print industry and therefore a contributor to air pollution. However, if the concentration of IPA in offset printing is to be lowered, then the positive chemical effects created by the alcohol in the dampening solution need to be gained in another way.

One of the advantages of IPA is to slow down the surface tension of the dampening solution on the printing plate. Water, as the ground substance of dampening solution, has a surface tension of 70 mN/m (measured in milli Newtons per meter), based upon a temperature of around 24°C.  IPA, with its surface tension of 20 mN/m, is added to the dampening solution to result in approx. 50 mN/m surface tension for the dampening solution on the printing plate. But, reducing IPA in the fount solution increases surface tension disproportionately. This can mean that as soon as IPA is lowered, the important effect of emulsification between dampening solution and ink is destabilised. This in turn causes ink build-up in the printing unit and dampening circuit, often followed by a build-up of germs, and growth of algae and bacteria. The dampening solution is contaminated quickly and when the concentration of dirt becomes too high, the dampening solution exceeds its operational range and becomes useless for the process. Further more, ink pollution in the whole dampening system speeds up.

Of course, reducing the level of IPA also reduces the efficacy of other positive effects. Dirt on the printing plate as a result of a higher surface tension in the dampening solution  cannot be compensated by conventional filtration with filter mats or filter bags in the dampening solution preparation unit because of the increased amount of smaller particles, such as ink pigments and paper components.

For the printer wishing to reduce IPA use, other solutions need to be found, such as a dampening solution fine filtration - state of the art materials can be specified, such as filters with high Zeta Plus (see note 1) Potential and increased throughput with better turbidimetric (see note 2) efficiency. Good filtration systems will offer advanced dual zone depth filters, designed to provide optimal clarification of bioprocess, biological and pharmaceutical fluids. Dampening solutions fine filtration should provide two distinct layers or zones of filter media with the upstream zone more open than the downstream zone. This structure enhances the contaminant holding capacity of the filter media, since larger particles are trapped in the upper zone of the filter media and smaller particles are trapped in the lower zone, reducing premature plugging and extending service life.

Filtration systems should be retrofitted to the dampening solution circuit in bypass to ensure they do not affect circuit parameters other than the cleaning process. This type of highly efficient cleaning has the secondary effect of removing the culture medium for germs.

Fine filtration does not just compensate for reduction of IPA in the printing process, it also offers further positive effects, such as a continuously clean dampening solution circuit, considerably reduced exchange intervals for the dampening solution and very long filter endurance. This means: greatly reduced additives to purchase, less used dampening solution to dispose of and drastically reduced cleaning and maintenance effort.

Dr Dietger Hesekamp is head of research and development at technotrans AG.
This e-mail address is being protected from spambots. You need JavaScript enabled to view it or call +49 2583 301-1000

For further information on filtration in the UK and Ireland, please contact Peter Benton, Managing Director at technotrans graphics limited.
This e-mail address is being protected from spambots. You need JavaScript enabled to view it or call 01206 224200

www.technotrans.co.uk

1  Zeta Plus is a family of patented filtration products, that result in high-efficiency sub-micron filtration.
2 Turbidity is the cloudiness or haziness of a fluid caused by individual particles (suspended solids) that are generally invisible to the naked eye.

technotrans offers fine filtration in different performance sizes: the basic.fc and alpha.f for small to mid-size sheet offset, the beta.f for mid-size to large sheet offset printing and the spinclean.d and delta.f solutions for web offset and newspaper printing.