Printing – Antismut device – Drying with fluid or by heating
Reexamination Certificate
1993-10-06
2001-09-25
Hilten, John S. (Department: 2854)
Printing
Antismut device
Drying with fluid or by heating
C101S416100, C101S483000
Reexamination Certificate
active
06293196
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to accessories for sheet-fed, rotary offset and flexographic printing presses, and in particular to a dryer for printed materials which utilizes high velocity, hot air flow and extraction.
BACKGROUND OF THE INVENTION
In the operation of a rotary offset press, an image is reproduced on a sheet of paper or some other printable stock by a plate cylinder which carries the image, a blanket cylinder which has an ink transfer surface for receiving the inked image, and an impression cylinder which presses the paper against the blanket cylinder so that the inked image is transferred to the paper. In some applications, a protective and/or decorative coating is applied to the surface of the freshly printed sheets. The freshly printed sheets are then transported to a sheet delivery stacker in which the printed sheets are collected and stacked.
In each press unit, a thin printing plate is mounted on a plate cylinder. The printing plate has image areas which are oleophilic and hydrophobic, and background areas which are oleophobic and hydrophilic. The plate surface is continuously wetted with aqueous damping solution, which adheres only to the background areas. The plate is inked with oleoresinous ink composition which adheres only to the image areas of the plate as wet ink. The ink is offset-transferred to the rubber surface of a contacting blanket cylinder, and is then retransferred to the receptive surface of a web or a succession of sheets, where the ink gradually hardens or cures by oxidation after passing through a final drying station downstream of the last press unit where the volatile solvent is evaporated from the inked image.
The relatively wet condition of the printing ink composition and its solvent and/or diluent components, and the presence of a layer of moisture laden air which clings to the surface of the web or sheet to the next printing unit may interfere with the quality of the images as they are printed at each succeeding printing unit. For example, the quality of colored images, half-tone illustrations and the like undergo degradation in the uniformity of their appearance and color because of the presence of the wet ink, volatiles, and moisture within the printed substrate. Moreover, protective coatings will undergo dilution and surface degradation causing a dull finish if the underlying substrate is not dried sufficiently before the coating is applied.
Such defects, including uneven surface appearance of protective/decorative coatings, detract from the appearance of the underlying images or photographs, particularly in the case of multi-colored images or photographs. The defects are caused by residual, volatile solvents, diluents, water and the like within the oleoresinous inks of the images, and the presence of moisture in the printed material, at the time that the next successive image is printed or the protective/decorative coating is applied. Because the defects are compounded as the printed material moves through successive printing units, it is desirable that curing and drying be initiated and volatiles and moisture laden air be extracted at each interstation position, as well as at the delivery position.
DESCRIPTION OF THE PRIOR ART
Since setting and curing of the inked image is gradual, it is desirable to accelerate the drying process. It is known to provide one or more interstation dryers in multiple-unit presses for the purpose of initiating the setting of the wet ink and extracting the volatiles and moisture laden air from each printing unit.
Hot air dryers and radiant heaters have been used as delivery dryers and as interstation dryers. Interstation dryers employing radiant heat lamps are best suited for slow to moderate press speeds in which the exposure time of each printed sheet to the radiant heat is long enough to initiate ink setting. For high speed press operation, for example, at 5,000 sheets per hour or more, there is not enough available space at the interstation position to install a radiant heater having sufficient number of heat lamps for adequate drying purposes.
As press speed is increased, the exposure time (the length of time that a printed sheet is exposed to the radiant heat) is reduced. Since the number of lamps is limited by the available interstation space, the output power of the radiant lamps has been increased to deliver more radiant energy at higher temperatures to the printed sheets in an effort to compensate for the reduction in exposure time. The increased operating temperatures of the high-powered radiant heat lamps cause significant heat transfer to the associated printing unit and other equipment mounted on the press frame, accelerated wear of bearings and alterations in the viscosities of the ink and coating, as well as upsetting the balance between dampening solution and ink. The heat build-up may also cause operator discomfort and injury.
To handle high speed press operations, an off-press heater has been utilized in which high velocity, heated air is conveyed through a thermally insulated supply duct to a discharge plenum which directs high velocity, heated air onto the printed stock as it travels by the interstation dryer position. Such off-press heaters have proven to be relatively inefficient because of excessive heat loss and pressure drop along the supply duct. Attempts to overcome the heat loss and pressure drop have resulted in substantially increased physical size of the heater equipment (blower fan and supply duct) along with a substantial increase in the electrical power dissipated by the off-press heater.
OBJECTS OF THE INVENTION
The principal object of the present invention is to increase the operating efficiency of a printing press dryer of the type which utilizes high velocity hot air flow to accelerate the drying of inks on freshly printed sheets.
A related object of the present invention is to provide a high efficiency, high velocity hot air dryer which includes improved means for extracting volatiles and moisture laden air from each printing unit, thereby accelerating the drying process.
Another object of the present invention is to provide a high velocity hot air dryer of the character described which is compact and capable of being operated effectively at high press speeds in the interstation position.
Yet another object of the present invention is to provide an improved high velocity hot air dryer of the character described in which the electrical power operating requirements are reduced as compared with comparable radiant dryers and offpress hot air heaters.
Still another object of the present invention is to provide an improved high velocity hot air dryer having a heater element, high velocity air plenum and extractor, with all components being mountable and operable on-press in the interstation position.
Another object of the present invention is to provide a high efficiency, high velocity hot air dryer which includes improved extractor for eliminating the transfer of heat to nearby press parts and equipment.
SUMMARY OF THE INVENTION
The foregoing objects are achieved according to the present invention by a high velocity hot air dryer in which high velocity air from an off-press supply is heated by an internal resistance heating element. Heated air at high pressure is discharged uniformly through precision holes located in an air distribution manifold onto a freshly printed sheet as it moves along a sheet transfer path from one printing unit to the next printing unit.
According to one aspect of the present invention, the moist air layer is displaced from the surface of the printed sheet by high-velocity hot air jets which scrub and break-up the moisture-laden air layer that adheres to the printed surface of the sheet. The high-velocity hot air jets create turbulence which overcomes the surface tension of the moisture and separates the moisture laden air from the surface of the printed material. The moisture laden air becomes entrained in the forced air flow and is removed from the printing unit by a high volume extractor.
The scrubbing action
DeMoore Howard Warren
Secor Howard Curtis
DeMoore Howard W.
Hilten John S.
Locke Liddell & Sapp LLP
Nguyen Anthony H.
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