Printing – Inkers – Roller
Patent
1984-01-10
1985-09-24
Fisher, J. Reed
Printing
Inkers
Roller
101365, B41F 3104, B41F 3106, B41L 2708
Patent
active
045426937
DESCRIPTION:
BRIEF SUMMARY
The invention relates to inking of printing machines with greasy ink.
The principal problem posed by the inking of an offset or letterpress press consists of depositing in a regular manner, from a body of greasy ink, a layer of a few microns thickness uniformly spread on the printing parts of a plate impression cylinder. The ink so deposited on the cylinder is then transferred on to the paper, either directly in the case of letterpress printing, or indirectly, by the intermediary of a cylinder covered with a layer of rubber called a blanket in the case of offset printing.
The main inking arrangements have numerous inconveniences, notably a complex mechanism which is comprised essentially of a very hard steel roller scraped by a steel blade called a scraper, the greasy ink being included between this roller and its scraper. A large number of adjusting screws spread along the length of this scraper permit adjustment with the best possible precision of the space between the roller and the edge of the scraper, thus allowing passage of more or less ink according to the degree of tightening of each screw. This assembly called "an inker" distributes the ink in the direction transverse to the paper.
The quantity of ink freed by each screw ought to correspond to the consumption of ink taken by each transverse zone of the paper. For example, if the printing has many printed bands in the longitudinal direction and separated transversely by spaces remaining blank, the adjusting screws of the inker ought to be adjusted tight in the blank zones and more or less open in the printed zones, according to the intensity of colour of these bands.
From this inking roller and scraper are arranged in contact with each other a battery of rollers covered with rubber or plastic of which certain have a transverse oscillating movement for helping the distribution of the ink. This battery is provided with two to four rubberised rollers called "inking rollers" which are in contact directly with the printing cylinder.
In fact, in the case of letterpress one has a printing cylinder in direct contact with the paper, held by a free cylinder called an "impression cylinder", and in the case of offset printing one has two cylinders of which a plate cylinder and a transfer cylinder in contact with the paper, always held under pressure by an impression cylinder. In the case of "wet offset" these two cylinders are completed by a more or less complex damping arrangement.
The quantity of ink to be deposited on each printed zone must be extremely precise if one wishes to preserve uniform colouring. On the contrary, in the transverse direction, the screws of the inker permit an approached adjustment, obtained by successive approximations, which causes significant losses of paper. Certain manufacturers have gone to the extent of motorising each screw by means of small motors controlled step by step from a console, either manually or from measurements of the density of colour made continuously on the sheet produced by means of complex electronic systems.
In the longitudinal direction no adjustment is possible. Thus a zone inked with a strong consumption of ink preceded by a blank zone will appear more pronounced than a continuously inked zone juxtaposed to the former. This is a frequent example in the case of printing of a frame. In effect, during the production of a blank zone there will be an accummulation of ink in the roller. When the inked zone which follows comes in contact with the over-inked inking rollers, it receives more ink than the neighbouring zone and appears darker. This phenomenon is well known to offset printers and is called a "set-off".
Only the provision of the inking battery, by multiplication of the number of rollers and by certain arrangements, permits reduction of this phenomenon.
It results from the above that the complexity of the mechanism and the electronic circuits result in significant investments which can only be amortised over long runs. In effect, the times for adjustment are raised, from 2 to 8 hours for 4 colours an
REFERENCES:
patent: 3026795 (1962-03-01), Dietrich
patent: 3566787 (1971-03-01), Moos
patent: 3585932 (1971-06-01), Granger
patent: 3978788 (1976-09-01), Cappel et al.
patent: 4041864 (1977-08-01), Dahlgren et al.
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