Treatment of solutions

Details Treatment of solutions Treatment of solutions

1999-02-24

2001-12-04

Funk, Stephen R. (Department: 2854)

Printing

Planographic

Dampeners

C210S243000, C210S748080

Reexamination Certificate

active

06324974

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the treatment of solutions used in a printing process, and in particular, though not exclusively, to the treatment of dampening or fountain solutions used in lithographic printing.
2. Description of the Related Art
The fountain solution is the liquid which is applied to the printing plate of a lithographic press so as to desensitize the background or non-image areas on the latter, i.e. only those areas that are not to be receptive to ink. It commonly consists of water, to which other substances are usually added for various purposes. In this connection it is conventional to add one or more wetting agents, for example long and short chain alcohols (notably isopropyl alcohol), fatty acid esters, glycol and butanol esters, and a large variety of surfactants. Most of these agents emit volatile organic compounds, which, as has long been recognized in the printing industry, has a major disadvantage, mainly for safety and environmental reasons. Other disadvantages are also well known.
Various ways to reduce or eliminate the use of chemical additives so as to reduce these drawbacks, especially the emission of volatile organic compounds, have been proposed. One of these proposals involves the direct injection of electromagnetic radiation at a radio frequency (typically around 43 KHz) into the solution, via an injector which is coupled to an RF generator by means of a tuned cable.
In this last-mentioned proposal, the injector transmits the RF signals into the fountain solution by means of a conductor which is in direct contact with the liquid to be treated.
SUMMARY OF THE INVENTION
According to the invention in a first aspect, in a method for treating a fountain solution in a printing process by applying electromagnetic radiation to a liquid consisting of the fountain solution itself and/or water for inclusion in the solution, the radiation is applied through an antenna immersed in the liquid, contact between the liquid and electrically conductive elements of the antenna being absent.
In a second aspect, the invention provides apparatus for treating a fountain solution in a printing process, comprising electromagnetic radiation generating means and at least one antenna connected electrically to the generating means for receiving and retransmitting radiation generated by the latter, the antenna comprising a coil impedance-matched to the generating means and a layer of insulating material impervious and inert to the said liquid, the said layer sealing within it all electrically-conductive elements of the antenna.
The apparatus typically operates by broadcasting a wide band of frequencies (for example both audio and radio frequencies) into either the water that is to be used in making and/or mixing the fountain solution, or into the solution itself, or both.
The radiation is preferably applied in successive steps of different frequencies over a predetermined period of time, so that a wide frequency band (e.g. 50 Hz to 11 KHz) is covered, after which the process may be restarted.
The invention is suitable for use in any printing apparatus in which water or an aqueous solution is used for desensitizing the non-image areas. In the context of lithographic printing, it is suitable for use with dampening systems of any type that uses either water or an aqueous fountain solution. These systems include “contact” systems in which the solution is applied mechanically to the plate, e.g. through a set of rollers, either in continuous flow or with the use of a vibrating feed roller or a cloth-covered roller; and “non-contact” systems in which the solution is sprayed or atomized on to the plate.
The invention eliminates the possibility of electrochemical corrosion in the press generally, and in its fountain solution mixing, storage and circulation systems in particular, that would arise where any component of the press in contact with the solution is of a metal such that an electromotive force is set up between such components and a conductive element of the RF injector, where the latter is also in direct contact with the solution. Under such circumstances either the injector element or the other component is very likely to become a sacrificial electrode.
The invention has been shown to produce a significant reduction in the amount of wetting agents required, and also a noticeable reduction in mineral contamination. This improvement manifests itself as a reduction in the deposition of water-receptive minerals, such as the carbonates of calcium and magnesium, on the blankets and the ink and damping rollers of the press.
A further improvement afforded by the invention is that many species of micro-organism, and organisms such as algae and fungi, are rendered moribund in the treated aqueous solution. This reduces the likelihood of blockages in the circulation system, and enables downtime for cleaning to be reduced.
Moreover, under some circumstances the invention is thought to have a lethal effect on certain micro-organisms and other organisms.
Where the fountain solution is applied by a non-contact (spray) type of system, the method and apparatus of the invention inhibits blocking of the fine holes in the spray nozzles by water-hardening agents.


REFERENCES:
patent: 4238326 (1980-12-01), Wolf
patent: 4545887 (1985-10-01), Arnesen et al.
patent: 4801370 (1989-01-01), Arnesen
patent: 4808287 (1989-02-01), Hark
patent: 4865748 (1989-09-01), Morse
patent: 4886593 (1989-12-01), Gibbs
patent: 238945 (1986-09-01), None
patent: WO 93/19939 (1993-10-01), None

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