Printing – Processes – With heating or cooling
Reexamination Certificate
1998-01-09
2001-04-03
Eickholt, Eugene (Department: 2854)
Printing
Processes
With heating or cooling
C101S488000, C101S489000, C101S491000, C101S147000, C101S349100, C101S216000
Reexamination Certificate
active
06209456
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns a printing unit for a rotary printing press which can utilize various ink types, and which is applicable to both web-fed and sheet fed environments. In particular, the present invention concerns a printing unit which allows the use of water-based inks, for easy clean-up and ink changing.
BACKGROUND OF THE INVENTION
U.S. Pat. Nos. 5,309,838, and 5,375,518 each purport to disclose a system for keeping the printing plates of a printing press at a moderate temperature. A cooling air blower girder extends longitudinally over the printing plate surface and blows cold air onto the printing plate's surfaces in order to keep its temperature at a desired value. The blast air girder contains at least one heat exchanger and at least one blower as well as at least one air return duct, which together forms a cooling air cycle, through which the air blown onto the printing plate surface is returned to the air inlet of the heat exchanger and optionally mixed with fresh air blown by the blower once again through the heat exchanger onto the printing plate surface. The blast air girder purportedly presents an energy saving compact structural unit for keeping the printing plate surface at a moderate temperature.
U.S. Pat. No. 5,452,657 purportedly relates to a temperature control system for printing press cylinders. It contains at least one compressed air line having at least one blast air opening for blowing cold air against a cylinder which is to be cooled. At least one recirculation circuit which is separate from the cold air of the compressed air line, and by which air which has been blown by the blast air opening onto the cylinder is drawn off by a blower contained in the circulation circuit and thereafter is blown parallel to the cold air again onto the cylinder. In this way, the temperature of the cold air can be active, without prior change of temperature on the cylinder. The cold air deflected by the cylinder is returned to the cylinder for additional cooling.
U.S. Pat. No. 5,098,478 relates to water based ink compositions. The water based ink composition includes water, a pigment, a non-ionic surfactant having a solubility in water of less than about 0.5 wt % and a solubilizing agent sufficient to solubilize substantially all of the non-ionic surfactant.
U.S. Pat. No. 5,026,755 purports to disclose a water based printing ink prepared from polyamid/acrylic graft copolymers. It is prepared by reacting the polyamid with the acrylic monomer or monomers in an alcohol solution in the presence of a free radical peroxidic initiator. The graft copolymer purports to be particularly useful as the resin component of a water based printing ink.
Finally, German laid open patent application DE 41 19 348 A1 purports to disclose a method for offset printing and a printing unit for waterless offset printing. A conventional offset plate is used with a water based printing ink, containing a pigment, water, 5-50 % water soluble macromolecular binding agents, and a hygroscopic organic fluid, preferably a multivalent alcohol.
SUMMARY OF THE INVENTION
The use of prior art air blasting control devices is ineffective in preventing premature dry-up of ink in printing presses and, in fact, may contribute to premature dry-up. This is particularly problematic on those components within the printing unit which are difficult to clean or to gain access to. Moreover, in order to clean the dried ink off of these components, the press must be shut down. Since a shutdown of the press in order to clean off dried ink residue reduces the productivity of the press, there is a need to reduce the formation of dried ink buildup.
The present invention reduces the formation of dried ink build-up by taking advantage of the fact that ink dry-up is caused by the evaporation of a volatile substance, e.g., VOC (volatile organic components), ammonia, ethanol amine or other amine compounds, and/or water, from the ink. In accordance with the present invention, a printing unit is provided which prevents or reduces the evaporation of the substance from the ink, thereby preventing premature ink dry up. The printing unit according to the present invention includes an inking mechanism, a plate cylinder, and a blanket cylinder supported within a frame. During operation of the printing unit, ink is applied as an ink film through the inking mechanism and onto a print form mounted on the print cylinder. A housing is mounted within the frame which at least partially surrounds the inking mechanism and print cylinder. In this manner, a semi-enclosed space surrounds the print cylinder and inking mechanism. Alternatively, the housing may also partially surround the blanket cylinder. The printing unit further includes a chemical supply for applying a chemical agent, e.g., water, VOC, ammonia, ethanol amine (or any other organic amine), in gaseous form into an atmosphere within the semi-enclosed space. By selectively introducing the chemical agent into the atmosphere, evaporation of the substance from the ink film on the inking mechanism and print form is reduced and controlled.
In accordance with a first embodiment of the present invention, the printing unit further includes a cooling mechanism and a humidifier for controlling the atmospheric conditions within the semi-enclosed space. The cooling mechanism and humidifier improve printing conditions in a number of ways. First, the ability of the atmosphere within the semi-enclosed space to absorb the substance from the ink film is a function not only of the amount of the chemical agent in the atmosphere, but also of the temperature and humidity in the atmosphere. In addition, temperature and relative humidity affect print quality independent of ink-dry up problems. For example, if the temperature of the ink (or the surface the ink is being applied to) is too low, ink transfer will be impeded. However, if the temperature is too high, then the ink will adhere to the non-imaged area of the plate as well as the imaged area of the printing plate. This phenomena is known as “toning” of the image. Similarly, if the humidity is too high, condensation will occur, resulting once again in toning.
A control unit controls the cooling mechanism, the humidifier, and the chemical supply to provide a suitable temperature, relative humidity, and chemical agent content in the atmosphere for high quality printing without ink dry up. The control unit monitors the temperature, humidity, and chemical agent content of the atmosphere within the semi-enclosed space via respective temperature, humidity, and chemical agent sensors, and then selectively activates the cooling mechanism, the humidifier, and the chemical supply as a function of the sensor readings.
For example, if the printing unit is configured to print with a water based ink, then ink dry-up can be controlled by controlling the evaporation of ethanol amine (or, for example, another organic amine compound or ammonia) from the ink. The evaporation of ethanol amine from the ink, in turn, can be prevented by injecting a sufficient amount of ethanol amine into the atmosphere within the semi enclosed space to prevent the evaporation of the ethanol amine from the ink. As an illustration, at 85 percent relative humidity and 93 degrees Fahrenheit, a concentration of 300-20,000 parts per million of ethanol amine (or ammonia) in the atmosphere will provide acceptable printing conditions for a water based ink containing 2% ethanol amine (or ammonia).
In certain cases where the volume of the semi-enclosed space is small and relatively well sealed, and the printing unit components enclosed within the semi-enclosed space generate little heat, there will be no need for a cooling mechanism, humidifier or chemical supply. In such a case, the gases in the atmosphere will quickly come to equilibrium locally near the ink transferring parts to prevent ink dry-up.
In accordance with a second embodiment of the present invention, the walls of the housing are hollow, and the cooling mechanism includes a cooling inlet and a cooling out
Murray Robert Richard
Palmatier Roland Thomas
Eickholt Eugene
Heidelberger Druckmaschinen AG
Kenyon & Kenyon
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