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Waterless Offset Printing

Offset printing is planographic printing. That means that printed and non-printed elements are  almost on the same level. This process is based upon the opposing chemical and physical reactions of ink-accepting and ink-repellent substances. In offset printing, thin printing plates made of aluminium or polyester are used. On the surface, there are image areas (lipophilic) and non-image areas (hydrophilic). The non-image areas are being turned ink-repellent with the help of damping solution used by wetting. Offset printing as well as collotype and lithography make use of the different wetting reactions of water and ink meaning that the image and non-image areas of the printing forme are almost on the same level. The damping solution therefore repels the ink and opposite.

 

That’s why the offset process (lithography and collotype as well) needs a wetting of the non-image areas of the plate before the inking-up of the image areas starts.

The damping solution consists of water, alcohol and an additive. The wetting is done by complex dampening units with different construction and systematic.

The printer faces the problem of not being able to control the dose and distribution of damping solution as it is possible with ink.

Planographic printing is therefore dominated by the missing capability of controlling the damping solution and unsolved chemical and physical reactions appearing at border areas

In specialists’ colloquial language it is called a not perfect set up ink-water-balance.

Beside the difficulties in printing technology, wet offset also faces environmental problems which occur by the necessary use of chemical additives and alcohol/isopropanol.

 

The problems of wet offset printing technology are as follows:

  • Especially on bad absorbent and acid papers and cartons, drying difficulties of the ink appear.
  • delay in oxidation
  • Colour variations because of emulsion of the ink in rotary offset
  • Accumulation of the ink on the fountain roller of the dampening unit in rotary offset
  • Register difficulties because of distortion of the paper web in multi-colour rotary offset

 

Ecological Problems

  • Environmental pollution caused by volatile organic compounds (VOC-emissions) which are contained in damping solution will perhaps be banned in the near future. Paying charges as in Switzerland would be the alternative.
  • Observance of sewage prescription if chemical fountain additives (also alcoholic substitutes) are being used.

 

Necessary investments in wet-offset printing

  • Offset printing presses with integrated dampening units.
  • If requested, installation of damping solution rotating machines with metering facilities for additives and alcohol in order to keep the alcohol constant as well as a measuring device for permanent control of the alcoholic concentration.
  • Machines for replenishment and re-preparation of the damping solution.
  • In connection with the problems listed above, additional investments and environmental expenses, the focus is more and more put on offset printing which goes without damping solution.

 

History of waterless printing

In 1932, the famous offset-co-inventor and pioneer Caspar Herrmann (1871-1934) tried to print without damping solution by using ink additives. Sample prints of his first trials with positive results still exist.

In the following please find some examples of patents without great success:

  • Patent no. 32509 of the Royal Patent Office dated 25 December 1884
  • Patent no. 102747 of the Royal Patent Office dated 21 November 1897
  • Patent no. 425615 of the German Reich Patent Office dated 3 March 1925

In 1967, the former 3M company presented the first printing plate for waterless offset on DRUPA. Their slogan was “Dry Printing”. This gave waterless offset one of the first stimulus after WW II. This plate did not gain acceptance because of its sensitivity against scratches.

 

Today’s Waterless Offset Printing

In 1977, one of the biggest manufacturers of plastics, film and chemicals, the Japanese company named Toray, started producing waterless printing plates. Marks-3zet GmbH & Co. KG in Mülheim an der Ruhr, Germany, became distributor in Germany. Since that, waterless offset printing has been grown continuously. To meet the increasing demands of their customers for waterless printing plates, Toray has just tripled the capacity of their coating machine. So far, technical problems have been solved. Other manufacturers, e.g. Presstek also offer waterless printing plates. Also machine manufacturers have discovered the positive developments and  advantages of waterless printing by now. That’s why machines for waterless printing are offered both in sheet-fed and rotary offset. The plates for waterless offset can be imaged by CtP or DI. Almost every ink manufacturer offers appropriate inks.

Technical problems are solved and the economical advantages of printing without water, gumming and chemicals are proved in practice. At present, the EWPA is running tests on this matter.

 

Advantages in quality such as dot structure and brilliance according to printing results are acknowledged by experts. With the help of waterless printing it is possible to print on more printing materials than paper and carton, for example:

 

  • Plastic packages
  • Overhead foils
  • Credit cards
  • Plastic index
  • Dials and armatures
  • Gummed Paper

 

Ecological aspects

Nowadays, the ecological importance increases rapidly. By using liquid damping solutions contained by isopropanol (VOC emissions) and acid chemicals, ecologically undesirable sewages occur. One has to choose between paying taxes or a lavish disposal. Further laws and prescriptions coming from the EU can be expected in the near future in order to protect the environment (air, water and soil). This means that the future goes waterless.

 

Last but not least the U.V. Drying Printing

U.V. (ultraviolet) drying printing inks and varnishes consist of liquid components which interlink to a solid and dry film under the influence of high-energy U.V. radiation. The hardening occurs immediate but the length of this process depends on the press speed and the number and intensity of U.V. lamps as well as the printing material used.

Almost all U.V. inks are based upon products where polyfunctional Epoxy, polyester or polyurethane vinyl have been added together with colorants, additives and photo-initiators which trigger a polymerisation and formation of a solid film.

U.V. drying inks can be described as solvent-free. Solvents are still used for washing and cleaning the press.

U.V. drying is especially used in fields of printing and packaging industry where fast drying and high gloss enable to an immediate finishing. Most of the conventional presses and separate varnishing machines can be converted into a U.V. drying system for inks and varnishes.

U.V. drying is used in printing on cardboard and carton including medicine and food packages, labelling, plastic material and metal decorating.

 

Wolfgang Walenski - Public Relations - EWPA -

 

EWPA - European Waterless Printing Association e. V.