Waterless Offset Printing
Explanation and history
Offset printing is a planographic printing process. Here are printing and non-printing drawing elements virtually almost in one plane. The method is based on the opposite physico-chemical behavior of certain substances that are ink-accepting and color-repellent.
In offset printing, these are usually thin printing plates such as aluminum or polyester, on the surface of which ink-accepting (lipophilic) image areas and non-image (hydrophilic) areas are made by wetting with a dampening solution or fountain solution must be made ink repellent. The offset printing and also the other planographic printing methods, such as e.g. The lithographic impression and also the historical light pressure, are therefore based on the very different wetting behavior of printing ink and water or the almost in a plane lying printing and non-printing image areas of the printing form. The ink film is thus repelled by the dampening solution and vice versa.
For this reason, during the printing process in offset printing, and also in the two mentioned other planographic printing process before inking or rolling of the image locations with ink always first a moistening the non-image areas of the printing plate with a dampening solution consisting of water and a usually acid dampening solution additive and often alcohol, necessary.
This moistening takes place in offset printing with elaborate dampening systems of very different construction and systematics. Although it would be very important to worry about both the amount of dampening solution required and the even distribution across the entire width of the machine or print format, the printer, unlike the ink, does not have the ability of the dampening solution to accurately control dosage. The planographic printing processes are thus particularly clearly determined by various, not always completely controllable and sometimes not completely clarified, chemical-physical interfacial processes in connection with missing, accurate and objective control and control options of the dampening solution in the production.
In this context, the technical vernacular is also spoken of a not always correctly adjusted color-water balance.
In addition to the immediate printing technical difficulties in the so-called wet offset printing resulting from the necessary use of chemical additives and also by the addition of alcohol / isopropanol not inconsiderable environmental problems.
The printing problems in the wet offset are primarily:
- Drying difficulties or more or less severe drying problems (oxidation retardation) of the ink, especially on poorly absorbent substrates and acidic papers and cardboard boxes
- Color variations due to water absorption (emulsification) of the printing ink
- Wiping out the printing ink in web offset printing
- Emergence of the ink on the fountain roller of the dampening unit in web offset printing
- Passer difficulty by a delay of the web in web-fed printing in multi-color printing
The ecological problems:
- Pollution-causing emissions through the use of volatile organic compounds (VOC emissions) in dampening solution, which will soon be either completely prohibited or, as in Switzerland, associated with not inconsiderable steering charges.
- Compliance with the new TA Luft for very large plants (eg web offset plants)
- In connection with the use of chemical fountain additives (also alcohol substitutes) compliance with and compliance with the regulation on requirements for the discharge of waste water (wastewater ordinance)
Necessary investments for wet offset printing:
- Offset machines with integrated dampening units
- Depending on the desired equipment, installation of dampening solution circulation systems with metering device for additives and alcohol as well as with constant alcohol control and device for continuous measurement of alcohol concentration
- Systems for the regeneration and reprocessing of the dampening solution
In connection with the problems just listed here, the additional investments and the increasing importance of the environmental regulations, attention now focuses much more than previously on an offset printing that can be practiced without a dampening solution.
Historical data for waterless offset printing
Already the co-inventor of offset printing, namely the large offset pioneer Caspar Herrmann (1871 - 1934) already tried about 1932 to get along by certain color additives without a dampening solution. There is even a print sample that proves the positive results of his experiments. Other old patents that had not been beating were:
- Patent specification of the Imperial Patent Office No. 32509 of 25 December 1884
- Patent specification of the Imperial Patent Office No. 102747 of 21 November 1897
- Patent specification of the Reich Patent Office No. 425615 dated 3 March 1925
Only at the DRUPA in 1967 did the then 3Mcompany introduce a printing plate for the waterless offset and advertise it with the slogan "pressure dry". This again gave the first impulses for the revival of the waterless offsetting technique after the Second World War. However, this plate could not prevail because the surface was very scratch sensitive.
Waterless Offset Printing today
In 1977, one of the largest plastics, film and chemical manufacturers, the Japanese company Toray, decided to produce printing plates for waterless offset printing. As a distribution partner could win in Germany marks-3zet GmbH & Co. KG, Mülheim an der Ruhr. Since that time, waterless offset printing has experienced a steady upward and upward development. To meet the increasing demand for printing plates for waterless offset printing, Toray has recently increased the capacity of its coating line three-fold. The technical problems are solved and also other manufacturers, such. Presstek today offer plates for waterless offset printing. The machine industry has also recognized the advantages and the further positive development of waterless technology. Today, machines for sheetfed printing and web offset printing are specially designed for waterless technology. The plates for the waterless offset printing can be exposed both externally CtP or with the DI technology within the machine. The corresponding inks are also available from almost every ink manufacturer. The technical problems are thus solved and the economic benefits of the absence of water, gumming and any chemistry have been proven in many cases. Further investigations are currently being carried out in a complex EWPA project.
Also, the qualitative aspects of the waterless offset technique in terms of dot structure, strength and brilliance of the printing results are recognized by experts. In addition, substrates printed without water can be printed, which are predestined for waterless offset printing. In addition to all paper and board grades, here are some examples to mention that can be printed particularly well in waterless offset printing:
- Plastic packaging
- Overhead transparencies
- Check and credit cards
- Dials fittings
- unbreakable children's books
- Gummed papers
Of increasing importance are ecological aspects. They are pushing more and more into the foreground. By using an aqueous dampening solution which must be enriched with isopropanol (VOC emissions!) And also with acidic chemicals that are not always acceptable, polluting effluents result which, on the basis of existing regulations, are subject to a levy or must be subjected to costly disposal. It has to comply with other EU directives and regulations, which should further contribute to achieving a high level of protection for air, water and soil. For this reason too, waterless offset printing will be given constantly growing opportunities for the future.
Text from Wolfgang Walenski (†2013)