Patent Publication Number: US-6209456-B1

Title: Web- and sheet-fed printing unit using various ink types, particularly water-based inks

Description:
This application is a continuation-in-part of U.S. Pat. application Ser. No. 08/614,591, entitled “PRINTING UNIT USING VARIOUS INK TYPES,” filed Mar. 13, 1996, and now U.S. Pat. No. 5,758,580, and also a continuation-in-part of U.S. Pat. application Ser. No. 08/615,351, and now U.S. Pat. No. 5,694,848, entitled “PRINTING UNIT FOR WATER-BASED INKS,” filed Mar. 13, 1996. 
    
    
     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&#39;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 outlet, each connected to the hollow interior of the walls of the housing. A cooling agent, e.g. cold water or air, is circulated through the hollow interior of the housing, entering via the cooling inlet and exiting through the cooling outlet. The cooling agent lowers the temperature of the housing, which, in turn, lowers the temperature within the semi-enclosed space. In addition, the outer surface of the housing is insulated so that the air within the semi-enclosed space surrounded by the inner surface of the housing remains cold. A cooling valve, which is coupled either to the cooling inlet or the cooling outlet, is selectively actuated by the control unit as a function of one or more of the sensor outputs to control the cooling of the semi-enclosed space. 
     In accordance with a third embodiment of the present invention, the chemical supply includes a reservoir, a liquid solution containing the chemical agent (e.g., ethanol amine, another organic amine compound, or ammonia, in solution) and a heating element. In accordance with this embodiment, the control unit can increase the chemical agent content of the atmosphere by activating the heating element, thereby causing more of the chemical agent in the solution to evaporate. Preferably, the heating element is located relatively close to the reservoir. 
     In accordance with a fourth embodiment of the present invention, the chemical supply includes a gas intake connected to a supply mechanism for supplying the chemical agent in gaseous form. A valve is mounted between the gas intake and the supply mechanism, and controlled by the control unit. 
     The present invention can be used with a variety of ink types, including, for example, water based inks, oleoresinous inks (containing hydrocarbons in the 270° F. boiling range, e.g. Magee oils), aclylate inks cured by radiation, and high viscosity inks known as paste inks. Preferably, the present invention uses a water based paste ink which does not contain any volatile organic components (VOCs) so that the enclosed atmosphere is not subject to explosion. In accordance with the present invention, the chemical used as a pH increaser or drying prevention agent in the ink is prevented from evaporation by applying a chemical to the atmosphere in the semi-enclosed area within the housing. Preferably, the chemical applied to the atmosphere is the same chemical which serves as the pH increaser or drying prevention agent in the ink. For example, in a water based ink which uses ethanol amine as a pH increaser, ethanol amine can be added to the atmosphere in the semi-enclosed area to prevent ink dry-up. If the amount of ethanol amine in the atmosphere causes the partial pressure of the ethanol amine in the atmosphere to be equal to the vapor pressure of the ethanol amine in the ink, then the ethanol amine will not evaporate from the ink into the atmosphere. 
     If the chemical agent is the same chemical as the substance in the ink, the chemical agent can not only be used to prevent drying or precipitation of resin from the ink as described above, but also may serve as a pH increaser by increasing the amount of the substance in the ink. For example, if the substance in the ink is ethanol amine, an increase in the amount of ethanol amine in the ink will increase the pH of the ink, thereby reducing drying or precipitation of resins and solvents in the ink. If the amount of ethanol amine in the atmosphere causes the partial pressure of the ethanol amine in the atmosphere to be greater than the vapor pressure of the ethanol amine in the ink, then the ethanol amine will flow from the atmosphere into the ink, thereby increasing the amount of the ethanol amine in the ink, and the pH of the ink. 
     In accordance with a preferred embodiment of the present invention, a printing unit is provided for printing with water-based inks. Such water-based inks provide many advantages over conventional inks, but have proven difficult to use in an offset printing unit. Preferably, the present invention uses a water-based ink which is free of volatile organic components (VOCs). VOCs, such as hydrocarbons, are conventionally evaporated from inks in long driers. As a result, VOC-free water-based inks dry cleaner, with little or no air pollution. Moreover, since these water-based inks have no VOCs to evaporate, they require less temperature to dry. This, in turn, allows a reduction in the length of the driers. Finally, with the use of water-based inks with no VOCs, alternative drying mechanisms such as infra red or micro-wave drying are possible in offset presses. However, it has been found that water-based inks are difficult to use in offset printing because the ink is highly sensitive to temperature and humidity variations, and tends to dry prematurely. 
     In accordance with a preferred embodiment of the present invention, a printing unit for printing with water based inks includes a blanket cylinder for supporting a printing blanket, a print cylinder for supporting a print form, and an inking unit for applying a water-based ink over the print form. The printing blanket, print form, and inking unit each have respective ink carrying surfaces for transferring the water-based ink. A cooling unit is mounted within the printing unit for maintaining the outer ink carrying surface of one or more of the print form, printing blanket, and inking unit at a predetermined level. Since heating and cooling above the dew point will not result in condensation, the predetermined temperature level is preferably set above the dew point of the atmosphere surrounding the ink carrying surfaces to prevent condensation of the water in the atmosphere onto the ink carrying surfaces. Moreover, in accordance with a preferred embodiment of the invention, the predetermined temperature level is set just slightly above the dew point so that evaporation of water from the ink is minimized while still preventing condensation. 
     In accordance with another embodiment of the present invention, the cooling unit includes a blanket cylinder cooling unit coupled to the blanket cylinder for circulating a first cooling agent through the blanket cylinder. In addition, a blanket temperature sensor is mounted within the printing unit for monitoring the temperature at the outer ink carrying surface of the printing blanket, and a control unit is provided which has an input connected to the blanket temperature sensor, and an output connected to the blanket cylinder cooling unit. The control unit monitors the temperature at the outer ink carrying surface of the printing blanket via the blanket temperature sensors, and controls the temperature at the outer ink carrying surface of the printing blanket by controlling the temperature of the first cooling agent. 
     In accordance with another embodiment of the present invention, the cooling unit may include a print cylinder cooling unit alone or in combination with the blanket cylinder cooling unit described above. The print cylinder cooling unit is coupled to the print cylinder for circulating a second cooling agent through the print cylinder. A print form temperature sensor is mounted within the printing unit for monitoring the temperature at the outer ink carrying surface of the print form, and the control unit has an input connected to the print form temperature sensor, and an output connected to the print cylinder cooling unit. The control unit monitors the temperature at the outer ink carrying surface of the print form via the print form temperature sensor, and controls the temperature at the outer ink carrying surface of the print form by controlling the temperature of the second cooling agent. 
     In addition, the cooling unit may also include an inker cooling unit alone or in combination with the print cylinder and blanket cylinder cooling units described above. The inker cooling unit is coupled to one or more of a plurality of rollers within the inking unit (e.g., vibrator rollers) and circulates a third cooling agent through these rollers. A inking unit temperature sensor is mounted within the printing unit for monitoring the temperature at the outer ink carrying surface of the rollers, and the control unit has an input connected to the inking unit temperature sensor, and an output connected to the inker cooling unit. The control unit monitors the temperature at the outer ink carrying surface of the rollers via the inking unit temperature sensor, and controls the temperature at the outer ink carrying surface of the rollers by controlling the temperature of the third cooling agent. 
     In accordance with a further embodiment of the present invention, an air blower is mounted within the printing unit for circulating and conditioning the atmosphere surrounding the blanket cylinder, print cylinder, and/or inking unit. While the air blower may be used independently from the cooling unit, in accordance with a preferred embodiment of the present invention, the air blower is used in combination with the cooling unit described above. 
     In accordance with a further embodiment of the present invention, the features of the invention may be incorporated into a printing unit which allows sheet-feeding of material into the press. A feed table may be used to feed a stack of sheets to a suction head, which feeds individual sheets to the printing unit, which may include the features described above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a printing unit according to the present invention. 
     FIGS. 2 a-e  show flow charts for a control unit of the printing press of FIG.  1 . 
     FIG. 3 shows an alternate embodiment of a chemical agent supply according to the present invention. 
     FIG. 4 shows an alternate embodiment of a cooling mechanism according to the present invention. 
     FIG. 5 shows a further embodiment of the present invention. 
     FIG. 6 shows a printing unit in accordance with a second embodiment of the present invention. 
     FIG.  7 ( a-c ) show illustrative flow charts for the control unit of FIG.  6 . 
     FIG. 8 shows a further embodiment of the printing unit of FIG.  6 . 
     FIG.  8 ( a ) shows an illustrative flow chart for the control unit of FIG.  8 . 
     FIG. 9,  9 ( a ) show devices for controlling a temperature of the side walls of a printing unit. 
     FIG. 10 shows the blanket cylinder of FIG. 6 in more detail. 
     FIG. 11 shows a third, sheet-fed, embodiment of the present invention. 
     FIG. 12 shows a fourth, sheet-fed, embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a printing unit  1  according to the present invention for preventing premature dry-up of ink. The printing unit  1  of a rotary printing press includes an upper inking unit  45 , an upper print cylinder  3  and an upper blanket cylinder  2 , which cooperate to print ink onto an upper side of a web of material  4 . A cylinder  13  is shown below the web  4 . A print form suitable for printing with inks (for example, water based inks) is mounted on the print cylinder  3 . If the printing unit  1  is configured as a non-perfecting press, the cylinder  13  is an impression cylinder. If the printing unit  1  is configured as a perfecting press, the cylinder  13  is a blanket cylinder and the printing unit  1  includes a corresponding lower inking unit and lower print cylinder (not shown). 
     The inking unit  45  includes an ink fountain roller  12  supplying the ink (e.g., water based ink) to rollers  5 - 11 ,  46 - 47  of the inking unit  45 . By splitting the ink film on each surface of each of the respective rollers  8 - 11 ,  46 , a thin film of ink is supplied to the surface of form rollers  5 ,  6 ,  7 . A first form roller  5 , a second form roller  6  and a third form roller  7  apply the thin film of ink onto the surface of the print form(s) which are mounted on the surface of the print cylinder  3 . Along the path the film of ink takes through the respective roller surfaces of the inking unit of the printing unit  1 , there is arranged a metering roller  47 , a plurality of distribution rollers  8 ,  9 ,  11 , and a plurality of vibrator rollers  46 . Naturally, the number, type, and arrangement of rollers in the inking unit  45  can be different from the arrangement of FIG.  1 . 
     The print form may be configured as a flat printing plate mounted on the surface of the print cylinder  3  by its leading and trailing edges, or as a sleeve shaped print form mounted axially over the print cylinder. Over the circumference of the blanket cylinder  2  there can either be arranged a conventional flat rubber blanket or a sleeve-shaped printing blanket. The blankets and print forms can be installed and removed in any conventional manner. 
     The inking unit  45  of the printing unit  1  and the printing unit cylinders  2 ,  3  are encapsulated within a housing  14 . The inking unit  45  (including rollers  5 - 12 ,  46 - 47 ), the cylinders  2 , 3 , and the housing  14  are supported by sidewalls (not shown). The housing  14  forms a semi-enclosed area  100  around the ink unit  45  and the cylinders  2 , 3 . Preferably, the housing  14  forms a semi-enclosed area around the inking unit  45 , and print  2  and blanket  3  cylinders, as shown. However, it is also possible to configure the housing to form a semi-enclosed area only around the inking mechanism  45  and print cylinder  2 ; only around the inking mechanism  45 ; or only around the print cylinder  2 . In a perfecting press, the housing  14  could also be constructed around the lower inking unit, plate and blanket cylinders. 
     The housing  14  is hollow and has an outer wall  14   a  and an inner wall  14   b . An insulating material  15  surrounds the outer wall  14   a . An air intake  16  extends from the outside the housing  14  through the inner wall  14   b . In order to provide fresh air to the semi-enclosed area  100  of the housing  14  and to the rollers  5 - 11 ,  46 - 47  and cylinders  2 , 3 , air passes through an air filter  19  mounted within the air intake  16  and into the semi-enclosed area  100 . A humidifier  18  is mounted below the air filter  19  for controlling the humidity within the semi-enclosed area. The humidifier  18  is coupled to, and controlled by, a control unit  37 . An air exhaust  53  also extends from outside the housing  14  through the inner wall  14   b . The air exhaust  53  includes an air blower  29  for exhausting air from the semi-enclosed area  100 . The air blower  29  is also connected to, and controlled by, the control unit  37 . 
     The air intake  16  further includes a reservoir  20  which is connected to a supply hose  22  and is grounded. The supply hose  22  includes a supply valve  33 . Alternatively, the reservoir  20  could be located within the semi-enclosed area  100 , or connected to the semi-enclosed area via a separate intake. The reservoir  20  contains an amount of a chemical agent, e.g,. ethanol amine, another organic amine compound, or ammonia, in a dilute solution. A sensor  21  is mounted within the reservoir for monitoring the level of the reservoir  20 . Preferably, the level of the reservoir is periodically checked by the sensor  21  to provide a precise reading of the solution level. 
     A cooling inlet  23  and cooling outlet  24  each extend from outside the housing  14  through the outer wall  14   a . A cooling agent, e.g. cold water or cold air, enters the hollow interior of the housing via the cooling inlet  23  and exits via the cooling outlet  24  to allow for temperature control over the housing  14  and consequently over the atmosphere which surrounds the rollers  4 - 11 ,  46 - 47  and cylinders  2 , 3 . The flow of the cooling agent through the inlet  23  and outlet  24  can be adjusted by controlling valve  35  which can be mounted at the outlet  24 , at the inlet  23 , or at both the outlet and inlet. Preferably, the valve  35  is mounted at the outlet  24  as shown. The valve  35  is connected to, and controlled by, the control unit  37  for controlling the flow of the cooling agent through the hollow interior of the housing  14 . 
     A first sensor set  30 , including first sensors  30 . 1 ,  30 . 2 , and  30 . 3 , and a second sensor set  31 , including second sensors  31 . 1 ,  31 . 2 ,  31 . 3 , are arranged within the semi-enclosed area  100  of the housing  14 . The first sensor set  30  is arranged adjacent to the inking unit  45  to monitor the atmosphere surrounding the inking unit  45 . The second sensor set  31  is arranged adjacent to the cylinders  2 ,  3  to monitor the atmosphere surrounding the cylinders  2 ,  3 . The first and second sensor sets  30 ,  31  are connected to the control unit  37 . Each sensor set  30 ,  31  includes a respective temperature sensor  30 . 1 ,  31 . 1 , a relative humidity sensor  30 . 2 ,  31 . 2 , and a chemical agent (e.g., ethanol amine, other organic amine, or ammonia) sensor  30 . 3  and  31 . 3 . It is understood that additional sensor sets can be mounted in key locations as necessary. Each of the sensors  30 . 1 ,  30 . 2 ,  30 . 3 ,  31 . 1 ,  31 . 2 ,  31 . 3  have respective output(s) which are individually connected to the control unit  37 . 
     A central control system  50  includes the control unit  37 . The control unit  37  includes an input  38  for receiving input from the sensors  30 ,  31  and an output  39  for controlling the air blower  29 , the humidifier  18 , the supply valve  33 , and the cooling outlet valve  35 . A display  40  and keyboard  41  are connected to the control unit  37  to allow a press operator to monitor the status of the sensors and to control the state of the valves and the air blower. 
     In order to provide optimum printing conditions, and to prevent premature ink dry-up, the control unit maintains the temperature, relative humidity, and chemical agent content of the atmosphere within the semi-enclosed area within desired ranges. The precise temperature and humidity levels, and the type and amount of chemical agent may vary depending on the type of ink and the location within the housing. The present invention can be used with a variety of ink types, including, for example, water based inks, oleoresinous inks (containing hydrocarbons in the 240-320° F. boiling range, e.g., Magee oils), acrylate inks cured by radiation, and high viscosity inks known as paste inks. Preferably, the present invention uses a water based ink, which does not contain any volatile organic components (VOCs). In general, the temperature should be kept within a temperature range which is high enough to promote good ink transfer, and low enough to prevent toning. The relative humidity, in turn, should be low enough to prevent condensation, but high enough to minimize evaporation of water from the ink. In order to prevent premature ink dry-up, the amount of chemical agent in the atmosphere should be sufficient to reduce the evaporation of the chemical substance acting as a pH increaser or drying prevention agent in the ink. The amount of chemical agent needed, in turn, is a function of the nature of the chemical agent, the nature of the chemical substance in the ink, the relative humidity, and the temperature of the atmosphere within the semi-enclosed area  100  adjacent to the ink transferring surfaces. The desired levels for the temperature, humidity, and chemical agent can be empirically determined through testing various temperature, humidity, and chemical agent levels with the desired ink. 
     In accordance with the illustrative embodiment of the present invention shown in FIG. 1, a press operator inputs a desired temperature level, relative humidity level, and chemical agent level for the printing unit  1  to the control unit  37  via the keyboard  41 . The control unit  37  monitors the outputs of the temperature sensors  30 . 1 ,  31 . 1 , the relative humidity sensors  30 . 2 ,  31 . 2 , and the chemical agent sensors  30 . 3 ,  31 . 3 . If the control unit determines that the temperature is above the desired level, it will open the cooling outlet valve  35  and circulate the cooling agent through the hollow interior of the housing  14 , thereby cooling the atmosphere within the semi-enclosed area  100 , e.g., by conduction, convection, and radiation. Once the temperature drops below the desired temperature level, the valve  35  will be closed. As a result, the temperature in the semi-enclosed area  100  will continually oscillate about the desired temperature level. Similarly, if the control unit determines that the humidity is below the desired level, it will activate the humidifier thereby adding moisture to the air traveling through the air intake  16  into the semi-enclosed area  100 , and increasing the humidity of the atmosphere within the semi-enclosed area  100 . Once the humidity rises above the desired humidity level, the humidifier will be turned off As a result, the humidity in the semi-enclosed area  100  will continually oscillate about the desired humidity level. Finally, if the control unit determines that the chemical agent level is below the desired level, it will activate a heater  48  thereby causing the chemical agent in the reservoir to evaporate from the solution more quickly into the air passing through the air intake  16  to the semi-enclosed area and increasing the chemical agent content of the atmosphere within the semi-enclosed area  100 . Once the chemical agent level rises above the desired level, the heater  48  is turned off. As a result the chemical agent content in the semi-enclosed area will continually oscillate about the desired level. 
     The present invention will now be described in more detail with regard to water based inks. The print form is suitable for receiving and transferring an image using water based inks. It has been found that “waterless” type printing plates, such as those manufactured by Toray Industries, or those described in U.S. Pat. No. 5,370,906 to Danker are also suitable for printing with water based inks. As an example, a Toray Industries printing plate having an aluminum oxide substrate with an image area coated with a photopolymer whose surface is hydrophilic in nature and a non-image area coated with a silicone polymer may be used. 
     An illustrative water-based ink for use with the present invention may include the components set forth below. The water phase of the ink is supplied by the water present in the acrylic resin latex, hydroxypropyl cellulose, hydroxyethyl ethylene urea, and the maleated rosin ester. The pH increaser in the ink is supplied by the ethanol amine: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Component 
                 Amount, wt. % 
               
               
                   
                   
               
             
            
               
                   
                 Styrene/maleic anhydride resin 
                  12 
               
               
                   
                 Phthalocyanine Blue pigment 
                  12 
               
               
                   
                 Acrylic resin latex (50% wt. % solids) 
                  5 
               
               
                   
                 Hydroxypropylcellulose (3% wt. % solids) 
                  10 
               
               
                   
                 Hydroxyethylethylene urea (70% wt % solids) 
                  8 
               
               
                   
                 Monoethanol amine 
                  2 
               
               
                   
                 Polyethylene Wax 
                  2 
               
               
                   
                 Ethoxylated acetylenic diol surfactant 
                  2 
               
               
                   
                 Maleated rosin ester (50% wt. % solids) 
                  47 
               
               
                   
                 Total 
                 100 
               
               
                   
                   
               
            
           
         
       
     
     In order to provide optimum conditions for the printing with water based inks, and to prevent the ink from drying prematurely in the inking unit or cylinders, the relative humidity, temperature, and ethanol amine level within the semi-enclosed area  100  in the housing  14  are maintained at certain predetermined levels. For example, in a water based ink containing 2% ethanol amine, it has been found that by providing an atmosphere containing 300 to 20,000 parts per million of ethanol amine at a temperature of 93-95° F. and a relative humidity between 75% and 95%, high print quality can be maintained. Naturally, these levels are merely illustrative, and may vary in accordance with a number of factors including the particular construction of the printing unit, the particular composition of the water based ink, print form and paper being used. The temperature, relative humidity, and ethanol amine levels are monitored by the control unit, and the atmosphere within the semi-enclosed area  100  is maintained within the desired temperature, relative humidity, and ethanol amine level ranges by selectively activating the cooling outlet valve  35 , the heater  48 , and the humidifier  18  as described above. 
     When a printing press is first started, the printing unit components  2 , 3 ,  5 - 12 ,  14 - 15 ,  46 - 47  will be relatively cold. Therefore, the control unit  37 , by monitoring the temperature sensors  30 . 1 ,  31 . 1 , will determine that the temperature within the semi-enclosed area  100  is below the desired temperature level for the water based ink, print form, and paper being used. The control unit  37  will then display a message on the display  40  advising the press operator to pre-heat the printing unit  1  prior to printing. Such a preheating could be accomplished by running the press while off impression until the temperature within the semi-enclosed area  100  has reached the desired level. Alternatively, a heating element (not shown) could be arranged within the semi-enclosed area to pre-heat the atmosphere, and controlled via the control unit  37  . 
     In contrast, after the printing press has been printing for a period of time, the temperature within the printing unit  1  may rise above the desired temperature level. The control unit  37 , by monitoring the temperature sensors  30 . 1 ,  31 . 1 , will determine that the temperature within the housing  14  is above the desired temperature level for the water based ink, print form, and paper being used, and will then lower the temperature within the semi-enclosed are by opening the cooling outlet valve  35  as described above. 
     The rise in temperature caused by operation of the press may also affect the relative humidity within semi-enclosed area  100  of the housing  14 . For example, an increase in temperature results in a decrease in relative humidity, thereby causing the atmosphere surrounding the surface of the rollers carrying the ink film to become too dry. This, in turn, causes evaporation of ethanol amine and water from the ink. The control unit  37 , by monitoring the humidity sensors  30 . 2 ,  31 . 2 , or additional sensors placed in critical areas, will determine that the humidity within the housing  14  is below the desired level for the water based ink being used. Upon determining that the humidity is below the desired level, the control unit will increase the humidity by controlling the humidifier  18  as described above. 
     As discussed above, the percentage of ethanol amine in the air within the semi-enclosed area  100  of the housing  14  will also affect ink dry-up. The control unit  37 , by monitoring the sensors  30 . 3 ,  31 . 3 , will determine that the ethanol amine level within the housing  14  is below the desired level for the water based ink being used. The control unit  37  can then increase the ethanol amine level in the atmosphere by activating the heater  48 . If the ethanol amine level rises above acceptable levels, the amount of ethanol amine in the semi-enclosed area within the housing  14  can be decreased by activating the air blower  29  to remove the excess ethanol amine from the semi-enclosed area. 
     FIGS. 2 a-e  show illustrative flow charts for the control unit  37  of FIG.  1 . The control unit  37  monitors the output of the sensors and compares them to various set point values and alarm values as set forth below. Based upon these comparisons, the control unit  37  controls the valves  33 ,  35 , the humidifier  18 , the air blower  29 , and the heater  48 . The above referenced flow charts, however, are merely illustrative, and could be replaced with any suitable algorithm known in the art for matching a measured value to a desired value. For example, while the flow charts of FIGS. 2 a-e  may result in measured values which oscillate about the desired value, it is contemplated that other known closed loop control algorithms can be used which would reduce or eliminate these oscillations. It is further understood that additional sensors and control devices can be added to control the temperature, humidity, and chemical agent concentration more locally to provide for control over local variation in the humidity, temperature, chemical substance levels. For example, since the gear side of a printing press generally gets hotter than the work side of the printing press, it may be desirable to separately monitor the gear and work sides of the press, and to control them accordingly. 
     Referring to FIGS.  2 ( a, e ), the control unit  37  maintains a set point R  and alarm R  level which establish a minimum and maximum relative humidity value for the atmosphere within the semi-enclosed area  100 ; a set point T  and alarm T  level which establish a minimum and maximum temperature value for the atmosphere within the semi-enclosed area  100 ; and a set point A  and alarm A  level which establish a minimum and maximum ethanol amine level for the atmosphere within the semi-enclosed area  100 . These alarm and set point levels are selected as a function of the particular ink being used. For example, for a water based ink containing 2% ethanol amine, the following set points and alarms have been found to be effective for controlling the atmosphere within the semi-enclosed area: 
     set point T =93 degrees Fahrenheit 
     alarm T =98 degrees Fahrenheit 
     set point R =75% 
     alarm R =95% 
     set point A =300 parts per million 
     alarm A =20,000 parts per million 
     Moreover, additional alarm values may also be useful. For example, extremely low relative humidity, e.g., below 35%, may increase the likelihood of a web break due to the high tack of the ink at low humidity. Therefore, an additional relative humidity alarm could be triggered by the relative humidity dropping below 35%. 
     As shown in FIG. 2 e , if the average of any one of the humidity levels (R 1 +R 2 )/2, the temperature levels (T 1 +T 2 )/2 or ethanol amine levels (A 1 +A 2 )/2 exceed their respective alarm levels (alarm R , alarm T , alarm A ), then the air blower  29  is activated to expel the atmosphere from the semi-enclosed area  100  of the housing  14 , and all other valves  32 - 35  are closed, and the heater  48  is turned off. 
     Referring to FIG. 2 a , if the average of the relative humidity signals (R 1 +R 2 )/2 are below the set point R  and there is no alarm R, T, or A , the humidifier  18  will be turned on until the set point R  is reached. Similarly, the cooling outlet valve  35  will be opened if there is no alarm R, T, or A  and the average of the temperature signals (T 1 +T 2 )/2 are above the set point T . If the average of the ethanol amine percentage signals (A 1 +A 2 )/2 is below the set point A  and there is no alarm R, T, or A , the heater is turned on until the set point A  is reached. 
     In addition, the ethanol amine solution level (L) in the reservoir  20  can be checked via a level sensor  21 . If the Level (L) is below a set point L , and there is no alarm R, T, or A , or A the supply valve  33  is turned on until the set point L  is reached. 
     Moreover, a pH sensor  49  may be mounted within an ink pan  49  of the printing unit and connected to the control unit  37 . It has been found that the tendency for an ink to dry prematurely is related to the pH level of the ink. Specifically, the lower the pH level of the ink, the lower the ethanol amine content of the ink, and the faster the ink will dry. The desired pH level can be set as a set point. If the pH reading is below the set point pH , and there is no alarm T R, T, or A , then the heater  48  will be turned on. The heat from the heater  48  will cause additional ethanol amine to evaporate from the reservoir  20  into the semi-enclosed space  100 . Once the ethanol amine content of the atmosphere begins to exceeds its saturation point, some ethanol amine will flow out of the atmosphere into the ink on the rollers  5 - 12 ,  46 ,  47 , and in the ink pan  49  thereby increasing the ethanol amine content of the ink and the pH of the ink. The pH sensor  49  may be used as a substitute for the ethanol amine sensor  30 . 3 , or in addition to the ethanol amine sensor  30 . 3 . 
     In accordance with another embodiment of the present invention, the humidifier and humidity sensor can be eliminated, and the humidity in the semi-enclosed space  100  can be controlled by adding an appropriate amount of water to the ethanol amine solution in the reservoir  20 . Since the water in the ethanol amine solution will, like the ethanol amine, evaporate as a function of the temperature and relative humidity of the atmosphere in the semi-enclosed space, by selecting the proper ratio of water to ethanol amine in the ethanol amine solution, the humidity in the semi-enclosed space will be maintained within the desired range. While this approach provides the advantage of eliminating the humidifier and humidity sensor, it requires that more attention be paid to the composition of the ethanol amine solution. 
     In accordance with an alternative embodiment of the present invention, and referring to FIG. 3, the reservoir  20  and heater  48  can be replaced with an ethanol amine gas inlet pipe  52  connected to a source of gaseous ethanol amine  53  through a valve  52   a . In this embodiment, the ethanol amine content of the atmosphere can be increased by controlling the supply of ethanol amine gas into the semi-enclosed area  100 . 
     FIG. 4 shows another embodiment of the present invention. Similar components bear the identical reference numbers as FIG.  1 . In accordance with this embodiment, a closed loop is formed between the air intake  16  and the air blower  29  and a cooling unit  60  is arranged in the closed loop between the air intake  16  and the air exhaust  53 . The air blower  29  continuously circulates air out of the semi-enclosed area  100 , through the cooling unit  60 , the air filter  19 , the humidifier  18 , over the reservoir  20 , and back into the semi-enclosed area  100 . The humidifier  18  and heater  48  are activated as a function of the sensor outputs in the same manner as described above with regard to FIGS. 1-3. The cooling unit  60  replaces the cooling inlet  23  and cooling outlet  24  of FIG.  1  and is activated if the temperature in the semi-enclosed space  100  rises above the set point T . If the average of any one of the humidity levels (R 1 +R 2 )/2, the temperature levels (T 1 +T 2 )/2 or ethanol amine levels (A 1 +A 2 )/2 exceed their respective alarm levels (alarm R , alarm T  alarm A ), then an exhaust valve  59  is opened to expel the atmosphere from the semi-enclosed area  100  of the housing  14 , and the valves  32 ,  33 , the heater  48 , and the cooler  60  are disabled until all the levels have fallen below their alarm levels. 
     FIG. 5 shows an alternative embodiment of the present invention, with similar components bearing similar reference numerals to FIG. 1. A first sub-housing  14 . 1  having insulation  15 . 1  surrounds a fountain roller  12 , a metering roller  47 , and a distribution roller  8 . A second sub-housing  14 . 2  having insulation  15 . 2  surrounds form rollers  5 ,  6 ,  7 , vibrator rollers  46 , and a back side of the print cylinder  3  and blanket cylinder  2 . A third sub-housing  14 . 3  having insulation  15 . 3  surrounds a front side of the print cylinder  3  and blanket cylinder  2 . Each sub-housing includes respective temperature ( 30 . 1 ,  30 ′. 1 ,  30 ″. 1 ), humidity ( 30 . 2 ,  30 ′. 2 ,  30 ″. 2 ), and chemical agent ( 30 . 3 ,  30 ′. 3 ,  30 ″. 3 ) sensors for monitoring the atmosphere within the respective semi-enclosed areas  100 . 1 ,  100 . 2 ,  100 . 2 . In addition, each housing includes respective cooling inlets  23 . 1 ,  23 . 2 ,  23 . 3  and cooling outlets  24 . 1 ,  24 . 2 ,  24 . 3  for circulating cooling agent through the housing  14 . 1 ,  14 . 2 ,  14 . 3 . In addition, each sub-housing includes a respective air intake  16 . 1 ,  16 . 2 ,  16 . 3  including air filters  19 . 1 ,  19 . 2 ,  19 . 3 , humidifiers  18 . 1 ,  18 . 2 ,  18 . 3 , reservoirs  20 . 1 ,  20 . 2 ,  20 . 3 , and heaters  48 . 1 ,  48 . 2 ,  48 . 3  for controlling the humidity and chemical agent levels in the atmosphere in the semi-enclosed areas  100 . 1 ,  100 . 2 ,  100 . 3 . Finally, each sub-housing includes blowing devices  29 . 1 ,  29 . 2 ,  29 . 3  and air exhausts  53 . 1 ,  53 . 2 ,  53 . 3  for exhausting the atmosphere from the semi-enclosed areas  100 . 1 ,  100 . 2 ,  100 . 3 . The control unit  37  includes respective inputs connected to the sensors ( 30 . 1 ,  30 . 2 ,  30 . 3 ,  30 ′. 1 ,  30 ′. 2 ,  30 ′. 3 ,  30 ″. 1 .  30 ″. 2 ,  30 ″. 3 ) and respective outputs connected to the cooling inlet ( 23 . 1 ,  23 . 2 ,  23 . 3 ), the humidifiers ( 18 . 1 ,  18 . 2 ,  18 . 3 ), the air blowers ( 29 . 1 ,  29 . 2 ,  29 . 3 ), the heaters ( 48 . 1 ,  48 . 2 ,  48 . 3 ). In accordance with this embodiment, the atmosphere within each semi-enclosed area ( 100 . 1 ,  100 . 2 ,  100 . 3 ) can be independently controlled. It should be noted that the subdivisions shown in FIG. 5 are merely illustrative. For example, in certain applications, it may be advantageous to provide separate sub-housings for the print cylinder and blanket cylinder, or to enclose the entire inking unit in a single sub-housing. It may be desirable to subdivide the enclosed space across the printing rolls so that side to side or middle variations inherent in the printing unit may be adequately compensated. 
     Independent control of several semi-enclosed areas provides several advantages. For example, since the semi-enclosed areas are smaller, there will be less variation in temperature, humidity, and ethanol amine levels across each semi-enclosed space. Moreover, since certain components of the printing unit may become hotter than others during press operation, it may be advantageous to control the atmosphere surrounding different components in separate control systems. In addition, it may be advantageous to provide different set point and alarm levels for different sub-housings. For example, since the ink film on the ink carrying surfaces of the fountain roller  12 , metering roller  47 , and distribution roller  8  is thicker than the ink film on the distribution rollers  5 , 6 , 7 , and print cylinder  3 , evaporation of ethanol amine and water may be of less concern in sub-housing  14 . 1  than in sub-housings  14 . 2  and  14 . 3 . Therefore, a press operator might wish to set the humidity and ethanol amine set points for sub-housing  14 . 1  lower than in sub-housings  14 . 2  and  14 . 3 . In this manner, a different set point and alarm can be set for the front side of the print and blanket cylinders than for the fountain roller  12 , metering roller  47  and distribution roller  8 . 
     In accordance with further embodiments of the present invention, cooling units can be provided for circulating a cooling agent through one or more of the print cylinders, blanket cylinders, vibrator rollers, and fountain rollers of the printing unit. By controlling the circulation of cooling agent through one or more of the cylinders and rollers, additional control over the temperature of the ink carrying surfaces of the cylinders and rollers can be obtained. 
     FIG. 6 shows a printing unit  101  in accordance with the present invention. The printing unit  101  includes side walls  102  supporting upper and lower inking units  155 . 1 ,  155 . 2 , blanket cylinders  104 ,  106  and print cylinders  103 ,  105 . The upper inking unit  155 . 1  includes a fountain roller  150 . 1  and metering roller  151  which apply an ink film to distributor rollers  152 , and to vibrator rollers  109 ,  110  and  111  for splitting the ink film and providing an even ink profile over the width of the printing unit. The vibrator rollers  110 ,  111  distribute the ink film to a group of upper form rollers  116 . The upper form rollers  116 , in turn, apply the ink film to a print form  170 . 1  mounted on the upper print cylinder  103 . Similarly, the vibrator rollers  113 ,  114  distribute the ink film to a group of lower form rollers  117 , and the lower form rollers  117  apply the ink film to a print form  170 . 2  mounted on the lower print cylinder  105 . 
     The print form  170  may be constructed as a flat plate mounted by its respective ends to the print cylinder, as a sleeve-shaped print form mounted axially over the print cylinder, or in any other known manner. In any case, the print form  170  is suitable for receiving and transferring an image using water based inks, as described above with regard to the embodiment of FIG.  1 . 
     The printing unit  101  is designed to maintain acceptable printing conditions for printing with water based inks through the use of one or more cooling units. Referring to FIG. 6, a print cylinder cooling unit  107  is assigned to the upper and lower print cylinders  103 ,  105 . The print cylinder cooling unit  107  includes a print cylinder inlet pipe  107 . 1  and a print cylinder outlet pipe  107 . 2  for each of the print cylinders  103 ,  105 . A lower print cylinder sensor  119 . 2  is arranged near the lower print cylinder  105 , and an upper print cylinder sensor  119 . 1  is arranged near the upper print cylinder  103 . A pair of relative humidity sensors  160 . 1 ,  160 . 2  are mounted within the printing unit  101  to measure the relative humidity of the atmosphere in the upper print unit section  101 . 1  and lower printing unit section  101 . 2 , and a pair of temperature sensors  160 . 3 ,  160 . 4  are mounted within the printing unit  101  to measure the temperature of the atmosphere in the upper print unit section  101 . 1  and lower printing unit section  101 . 2 . A control unit  118  has respective inputs connected to the print cylinder sensors  119 . 1 ,  119 . 2 , the relative humidity and temperature sensors  160 . 1 ,  160 . 2 ,  160 . 3 ,  160 . 4  and an output connected to the cooling unit  107 . The control unit  118  periodically monitors the temperature of the print cylinders  103 ,  105  via the sensors  119 . 1 ,  119 . 2 , and of the atmosphere with the relative humidity sensors  160 . 1 ,  160 . 2  and temperature sensors  160 . 3 ,  160 . 4 , and then controls the print cylinder cooling unit  107  as a function of the monitored temperature values. 
     The print cylinder sensors  119 . 1 ,  119 . 2  can be constructed, for example, as infrared sensors mounted adjacent to the print cylinders  103 ,  105  to monitor the surface temperature of the print cylinders. The cooling unit  107  continuously circulates a cooling agent (e.g. water or air) through the print cylinders  103 ,  105  via the print cylinder inlet and outlet pipes  107 . 1 ,  107 . 2 . By controlling the temperature of the cooling agent via the controlling device  118 , the temperature of the cylinders  103 ,  105  can be maintained at a predetermined level (e.g., at a setpoint or within a predetermined range). The predetermined level is preferably set slightly above the dew point of the atmosphere surrounding the ink carrying surfaces of the print cylinders in order to prevent condensation of water from the atmosphere onto the ink carrying surfaces, and to minimize evaporation of water from the water-based inks into the atmosphere. 
     The predetermined level can be set as follows based upon the sensor readings. Relative humidity (RH) is a function of the amount of water per volume of air which is actually present in the atmosphere (VA) and the amount of water per volume of air which is necessary to saturate the air (VS): VA/VS×100=RH. VS, in turn, is a function of the temperature of the atmosphere: VS=f(t). Since the temperature of the atmosphere is known from sensors  160 . 3 ,  160 . 4 , and the relative humidity of the atmosphere is known from sensors  160 . 1 , and  160 . 2 , VA and VS for the temperature of the atmosphere surrounding the ink carrying surfaces are readily determined by the control unit  118 . Therefore, in order to maintain the temperature of the ink carrying surfaces above the dew point, the control unit can assume VA to remain constant, and choose a predetermined temperature level for the cylinders  103 ,  105  which has a corresponding VS which is slightly greater than VA. 
     The upper and lower blanket cylinders  104 ,  106  have printing blankets  171 . 1 ,  171 . 2  mounted thereon for transferring an inked image from the print forms  170 . 1 ,  170 . 2  to a web of material  122  as shown in FIG.  8 . The printing blanket  171  may be constructed as a flat blanket mounted by its respective ends to the blanket cylinder, as a gapless tubular printing blanket mounted axially over the blanket cylinder, or in any other known manner. 
     A blanket cylinder cooling unit  108  is assigned to the upper and lower blanket cylinders  104 ,  106 . The blanket cylinder cooling unit  108  includes a blanket cylinder inlet  108 . 1  and a blanket cylinder outlet  108 . 2  for each blanket cylinder. A lower blanket cylinder sensor  120 . 2  is arranged near the lower blanket cylinder  106 , and an upper blanket cylinder sensor  120 . 1  is arranged near the upper blanket cylinder  104 . The control unit  118  has respective inputs connected to the blanket cylinder sensors  120 . 1 ,  120 . 2  and an output connected to the cooling unit  108 . The control unit  118  periodically monitors the temperature of the blanket cylinders  104 ,  106  via the sensors  120 . 1 ,  120 . 2 , and then controls the blanket cylinder cooling unit  108  as a function of the monitored temperature values as described above with regard to the print cylinders. The sensors  120  and cooling unit  108  can be constructed and controlled in the same manner as the sensors  119  and cooling unit  107 . 
     An inker cooling unit  115  is assigned to the upper vibrator rollers  109 ,  110 ,  111 , the lower vibrator rollers  112 ,  113  and  114 , and the upper and lower fountain rollers  150 . 1 ,  150 . 2  respectively. The cooling unit  115  includes an upper section  115 . 1  assigned to the upper inker  155 . 1  and a lower section  115 . 2  assigned to the lower inker  155 . 2 . An inker inlet pipe  115 . 3  and outlet pipe  115 . 4  is connected to each roller  109 - 114 ,  150 . 1 ,  150 . 2 . A respective inker sensor  121 . 1 ,  121 . 2  is assigned to each inking unit  155 . 1 ,  155 . 2 . In the configuration of FIG. 6, sensor  121 . 1  senses the temperature at an outer ink carrying surface of roller  111 , and sensor  121 . 2  senses the temperature at an outer ink carrying surface of roller  114 . The control unit  118  has respective inputs connected to the inker sensors  121 . 1 ,  121 . 2  and an output connected to the inker cooling unit  115 . The control unit  118  periodically monitors the temperature of the vibrator rollers  111 ,  114  via the sensors  120 . 1 ,  120 . 2 , and then controls the inker cooling unit  115  as a function of the monitored temperature values as described above with regard to the print cylinders. The sensors  121  and cooling unit  115  can be constructed and controlled in the same manner as the sensors  119  and cooling unit  107 . 
     FIGS.  7 ( a-c ) show an illustrative flow chart for the control unit  118 . Referring to FIG. 7 a , the control unit monitors the surface temperature of the upper blanket (Tb 1 ) and of the lower blanket (Tb 2 ) via the sensors  120 . 1 ,  120 . 2  (steps  200 ,  210 ). If an average of these sensor readings is above a set point (step  220 ), then the control unit  118  lowers the temperature of the cooling agent in the blanket cooling unit  108  by an amount X (step  225 ), waits a time period T (step  230 ), and then monitors the outputs of the sensors  120 . 1 ,  120 . 2  again. These steps are repeated until the average of the sensor readings is equal to the set point. Similarly, if the average of these sensor readings is below the set point (step  230 ), then the control unit  118  raises the temperature of the cooling agent in the blanket cooling unit  108  by an amount X (step  235 ), waits a time period T (step  245 ), monitors the outputs of the sensors  120 . 1 ,  120 . 2  again, and repeats these steps until the average of the sensor readings is equal to the set point As illustrated in FIGS. 7 b  and  7   c , the control unit monitors and controls the temperature of the print cylinders  103 ,  105  (steps  300 ,  310 ,  320 ,  330 ,  325 ,  335 ,  340 ) and inker rollers  109 - 114 ,  150 . 1 ,  150 . 2  (steps  400 ,  410 ,  420 ,  430 ,  425 ,  435 ,  440 ) in the same manner. Preferably, the setpoint is set slightly above the dew point of the atmosphere surrounding the print cylinders, blanket cylinders, and inking unit. In this manner, the relative humidity of the atmosphere surrounding the ink carrying surfaces of the inking unit, blanket cylinders, and print cylinders will be high enough to prevent any significant evaporation of water from the ink, but low enough to prevent condensation of water from the atmosphere onto the ink carrying surfaces. The set point can be obtained based upon the monitored values of the sensors  160 . 1  through  160 . 4  as described above. 
     It should be noted that since the temperature of the cylinders and rollers in the printing unit  101  tend to rise naturally due to the heat generated from the operation of the press, it is possible to eliminate steps  330  and  335  in the flow charts of FIGS. 7 a  through  7   c , and to rely instead on the natural tendency of the temperature of the cylinders and rollers to rise over time. In such an embodiment, the cooling units  107 ,  108 , and  115  need not include a device for heating the cooling agent. Moreover, the above referenced flow charts are merely illustrative, and could be replaced with any suitable algorithm known in the art for matching a measured value to a desired value. 
     In the embodiment shown in FIGS. 6 and 7 a-c , separate sensors  1   19 . 1 ,  119 . 2  are provided for the upper and lower print cylinders  103 ,  105 , and the temperature of the cooling agent applied to both cylinders is a function of the average of the two sensor readings. However, it is also possible to control the temperature of the cooling agent as a function of the temperature measured at only one of the cylinders ( 103  or  105 ) by one sensor ( 119 . 1  or  119 . 2 ). Similarly, a single temperature sensor ( 160 . 3  or  160 . 4 ) and humidity sensor ( 160 . 1  or  160 . 2 ) could be used. In such an embodiment, the temperature of the cooling agent circulated within both print cylinders will be a function of the temperature measured at the ink carrying surface of only one of the cylinders ( 103  or  105 ). The sensor pairs  120 . 1 ,  120 . 2  and  121 . 1 ,  121 . 2  could likewise be replaced with single sensors measuring the temperature at one of the blanket cylinders ( 104  or  106 ) and at one of the inking units ( 155 . 1  or  155 . 2 ). 
     Moreover, it is also possible to provide separate cooling units for some or all of the cylinders  103 , 104 , 105 ,  106  and rollers  109 ,  110 ,  111 ,  112 ,  113 ,  114 ,  150 . 1 ,  150 . 2  and to control the temperature of the cooling agent applied to these cylinders and rollers individually via the control unit as a function of separate sensors. 
     In order to provide acceptable conditions for printing with water based inks, the temperature of the ink and of the surfaces the ink is applied to should be maintained at certain predetermined levels. For example, in a water based ink containing 2% ethanol amine or ammonia, if the temperature of the print cylinders is maintained between 93-95 degrees, and 75-95% humidity, high print quality can be maintained. Naturally, these levels are merely illustrative, and may vary in accordance with a number of factors including the particular construction of the printing unit, the particular composition of the water based ink, and the paper being used. In accordance with the present invention, the temperature of the cylinders  103 - 106  and rollers  109 - 114  are monitored by the control unit, and is maintained within the desired temperature range (or at a desired set point) by selectively controlling the temperature of the cooling agent flowing through these cylinders and rollers. This control may be similar to the control described above with reference to the embodiment of FIG.  1 . 
     For example, when a printing press is first started, the printing unit components  103 - 106 ,  109 - 114 ,  150 . 1 ,  150 . 2  will be relatively cold. Therefore, the control unit  118 , by monitoring the temperature sensors  119 - 121 , will determine that the temperature on the ink carrying surfaces of the blanket cylinders  104 ,  106 , print cylinders  103 ,  105 , and vibrator rollers  111 ,  114  is below the desired temperature level for the water based ink and paper being used. The control unit  118  will then advise the press operator to pre-heat the printing unit  101  prior to printing. Such a preheating could be accomplished by running the press while off impression until the temperature of the blanket cylinders  104 ,  106 , print cylinders  103 ,  105 , and vibrator rollers  111 ,  114  has reached the desired level. Alternatively, the control unit  118  could raise the temperature of the cooling agent in the blanket cylinder cooling unit  108 , the print cylinder cooling unit  107 , and the inker cooling unit  115  until the temperature of the blanket cylinders  104 ,  106 , print cylinders  103 ,  105 , and vibrator rollers  111 ,  114  has reached the desired level. 
     In contrast, after the printing press has been printing for a period of time, the temperature on the ink carrying surfaces of one or more of the blankets, print forms or rollers ( 170 ,  171 ,  109 - 114 ,  150 . 1 ,  150 . 2 ) within the printing unit  101  may rise above the desired temperature level. The control unit  118 , by monitoring the temperature sensors  119 - 121 , will detect that the temperature on the ink carrying surfaces of the blankets, print forms, and/or vibrator rollers ( 171 . 1 ,  171 . 2 ,  170 . 1 ,  170 . 2 ,  111 , and/or  114 ) is above the desired temperature level for the water based ink and paper being used, and will then lower the temperature of the cooling agent in the respective cooling units ( 107 ,  108 , and/or  115 ) as necessary until the temperature of the blankets, print forms, and/or vibrator rollers has reached the desired level. 
     FIG. 8 shows a further embodiment of the printing unit of FIG.  6 . The pipes  107 . 1 ,  107 . 2 ,  108 . 1 ,  108 . 2 ,  115 . 3 ,  115 . 4  and sensors  119 - 121  have been omitted for ease of illustration. In accordance with this embodiment, blowing sections  123 . 1 ,  123 . 2  are mounted within the printing unit  101 , and connected to a blowing unit  123  via an air inlet pipe  124 . 1  and an air exhaust pipe  124 . 2 . The blowing unit  123  includes an air cooling mechanism and an air heating mechanism, and is coupled to and controlled by the control unit  118  to maintain the temperature of the water based ink carrying surfaces of the blanket cylinders  104 ,  106  at the set point. The blowing devices  123 . 1  and  123 . 2  each include outputs  180  to blow air onto the surfaces of the blanket cylinder  104 ,  106  carrying the water based ink films. The blowing devices  123 . 1  and  123 . 2  also include suction inputs  181  for sucking the atmosphere surrounding the water based ink carrying surfaces out through the air exhaust pipe  124 . 2 . In this manner, the water based ink carrying surfaces of the blanket are cooled or heated from the outside via the blowing unit  123 , and from the inside via the cooling units  108 . 
     Referring to FIG. 8 a , the control unit  118  monitors the surface temperature of the upper blanket cylinder (Tb 1 ) and of the lower blanket cylinder (Tb 2 ) via the sensors  120 . 1 ,  120 . 2  (steps  500 ,  510 ). If an average of these sensor readings is above the set point (step  520 ), then the control unit  118  lowers the temperature of the air output from the air inlet  124 . 1  by an amount X (step  525 ), waits a time period T (step  540 ), and then monitors the outputs of the sensors  120 . 1 ,  120 . 2  again. These steps are repeated until the average of the sensor readings is equal to the set point. Similarly, if the average of these sensor readings is below the set point (step  530 ), then the control unit  118  raises the temperature of the air output from the air inlet  124 . 1  by an amount X (step  535 ), waits a time period T (step  540 ), monitors the outputs of the sensors  120 . 1 ,  120 . 2  again, and repeats these steps until the average of the sensor readings is equal to the set point The heating and/or cooling of the air by the blowing device  123  can be accomplished inside or outside the blowing devices  123 . 1 ,  123 . 2 . Moreover, in accordance with a further embodiment of the present invention, the blowing devices  123 . 1 ,  123 . 2  could be arranged within the printing unit  101  to blow air on both the print cylinders  103 ,  105  and the blanket cylinders  104 ,  106 . 
     As discussed above with regard to FIGS.  7 ( a-c ), since the temperature of the cylinders and rollers in the printing unit  101  tends to rise naturally due to the heat generated from the operation of the press, it is possible to eliminate steps  530  and  535  in the flow charts of FIG. 8 a , and to rely instead on the natural tendency of the temperature of the cylinders and rollers to rise over time. In such an embodiment, the air heating mechanism can be omitted from the blowing device  123 . In addition, the above referenced flow chart is merely illustrative, and could be replaced with any suitable algorithm known in the art for matching a measured value to a desired value. 
     In accordance with another embodiment of the present invention, the blowing unit  123  includes a humidifier  255  which is controlled by the control unit  118  and supplied by water supply lines  250 . 1 ,  250 . 2 . The humidifier  255  may be arranged within the blowing unit  123 , within the blowing devices  123 . 1 ,  123 . 2 , in between the blowing unit  123  and blowing devices  123 . 1 ,  123 . 2 , or in any other suitable location. If the control unit  118  determines that the monitored relative humidity is below a humidity set point, it will activate the humidifier until the monitored humidity is equal to the humidity set point. By maintaining the humidity of the atmosphere surrounding the ink carrying surfaces at the humidity setpoint (e.g. between 75% and 95% relative humidity), evaporation of water from the water-based ink can be minimized while still preventing condensation of water into the ink. Moreover, by controlling the humidity within the atmosphere surrounding the print and/or blanket cylinders, the temperature set point can be set at a static value (e.g., 93-95 degrees Fahrenheit). 
     FIG. 9 shows a temperature controlling device in accordance with the present invention for maintaining an even temperature profile across the printing unit  101 . The sidewalls  102  include a gear-side wall  102 . 1  and a work-side wall  102 . 2 . During press operation, the gear-side wall  102 . 1 , which houses the gears which drive the cylinders and/or rollers in the printing unit  101 , tends to become significantly hotter than the work-side wall  102 . 2 . Consequently, it is advantageous to cool the gear-side wall  102 . 1  to provide an even temperature profile over the width of said printing unit  101 . 
     In accordance with the present invention, a gear-side temperature sensor  126  is mounted on the gear-side wall  102 . 1  and a work-side temperature sensor  128  is mounted on the work-side wall  102 . 2 . Each of the temperature sensors  126 ,  128  is connected to the control unit  118 . A friction reducing fluid such as mineral oil or synthetic oil is conventionally provided within a gear box  132  of the gear-side wall  102 . 1  to lubricate the moving parts within the gear-side wall  102 . 1 . A fluid distribution  182  is provided for circulating the friction reducing fluid to and from a heat exchanger  129 . The heat exchanger  129  may be of conventional construction, and operates to cool the fluid in the fluid distribution  182  by, for example, inter-twining the fluid distribution  182  with a fluid pipe  162  containing a cooling fluid such as water. The control unit  118  monitors the temperature of the work-side and gear-side walls  102 . 2 ,  102 . 1  via the sensors and controls a fluid cooling unit  161  as a function of the monitored temperatures. The control unit  118 , via the fluid cooling unit  161 , adjusts the temperature of the cooling fluid within the fluid pipe  162  in order to maintain a temperature differential between the values measured at sensors  126  and  128  within a certain setpoint range (e.g. |T 26 −T 28 |≦7 degrees Fahrenheit). 
     In the above embodiment, it is anticipated that the design of the work-side frame components is such that the temperature of the work-side frame at  127  does remains within approximately 10 degrees Fahrenheit of the ambient temperature of the surrounding atmosphere. If, however, the work-side frame exceeds the ambient temperature by more than 10 degrees Fahrenheit, it may be necessary to provide a work-side cooling mechanism for the work side frame  102 . 2 . Referring to FIG.  9 ( a ), the cooling mechanism, could, for example, include a cooling unit  199  which circulates a cooling agent through pipes  198  which are mounted to the work-side frame  102 . 2 . The cooling unit  199  could monitor the ambient temperature of the air surrounding the work-side frame  102 . 2  via a temperature sensor  127 , monitor the temperature of the work-side frame  102 . 2  via the sensor  128 , and lower the temperature of the cooling agent if the difference between the monitored values exceed 10 degrees Fahrenheit. 
     FIG. 10 shows a longitudinal section of one of the blanket cylinders  104 ,  106 . The blanket cylinder  104 ,  106  includes the blanket cylinder inlet  108 . 1  and a blanket cylinder outlet  108 . 2  for circulating the cooling agent through the blanket cylinder. In addition, the blanket cylinder includes a compressed air inlet  136  which transmits compressed air across the length of the cylinder and out a plurality of apertures  138  along the surface of the blanket cylinder in order to axially install and remove a printing blanket. In accordance with a preferred embodiment of the present invention, the air inlet  136  is isolated from the cooling agent circulating within the cylinder in the manner described in U.S. Pat. No. 5,535,674, issued Jul. 16, 1996, the specification of which is hereby incorporated by reference. The cooling agent can be circulated through the print cylinder  103 ,  105 , and rollers  109 - 114  in a similar manner. 
     FIG. 11 shows an embodiment of the present invention in a sheet-fed printing unit. From a stacked sheet feed pile  601 , sheets are delivered to a feed table  603 . The feed pile may be mounted on a feed table which moves upwardly to ensure that the top sheet of the feed pile  601  is adjacent a gripping head  602 . The gripping head  602 , including suction grippers  602   a , reciprocates back and forth under the action of a suitable actuator  602   b . The suction grippers  602   a  separate a top sheet from the feed pile  601  and feeds it onto the feed table  603 , either separately or in shingled form. The feed table  603  is preferably in the form of a conveying belt  603   a . An aligning device  604  at the end of feed table  603  aligns the sheets in preparation for receipt by a pregripper  605 . The pregripper  605  includes a gripper at one end, which grasps an end of an aligned sheet, and accelerates and feeds that sheet into a gripping drum  606  in a first printing unit  617 . Gripper drum  606  includes a gripper which grips a sheet fed from pregripper  605  and rotates that sheet and feeds it to an impression cylinder  607 . The impression cylinder  607  feeds a sheet against a blanket cylinder  608 , which blanket cylinder  608  prints an image upon the sheet carried upon the impression cylinder  607 . The blanket cylinder may carry either a conventional gapped blanket or a gapless blanket. The surfaces of the impression cylinder  607  and the blanket cylinder  608  may be cleaned by a pivotable washing device  609 . Mounted above the blanket cylinder  608  is a plate cylinder  610  carrying a conventional print form or print plate, and which transfers an image to blanket cylinder  608 . The plate cylinder may be inked by a conventional inking form rollers  611  and wetted or dampened by conventional damping cylinders  612 . An inker  613  transfers printing ink from an ink fountain  614  to the form rollers  611 . 
     After the sheet on impression cylinder  607  has been printed upon by blanket cylinder  608 , a second gripper drum  615  grips the sheet and transfers it to a conventional perfecting device  616  which transfers the sheet to its opposite side. The sheet, having been reversed to its other side by perfecting device  616  is then transferred to a third gripper drum  706  in a second printing unit  717 . The second printing unit  717  has similar structure to that of the first printing unit  617 , including gripper drum  706 , an impression cylinder  707 , blanket cylinder  708 , plate cylinder  710 , form rollers  711 , damping cylinders  712 , inker  713  and ink fountain  717 . Each of these elements operate in the same manner as the similar elements in first printing unit  617 . After a sheet has had both sides printed upon by first and second printing units  617 ,  717 , the sheet is fed to a delivery stack  726  by a transport chain  720  in a delivery device  722 , which grips the sheets and delivers them to a position above delivery stack  726 . A guiding device  719  may guide sheets to the transport chain  720 , and an optional numbering cylinder  728  may be used to imprint numbering information on sheets leaving the impression cylinder  707 . Transport chain  720  includes a series of gripper elements  721  for gripping and transporting sheets to the delivery stack  726 . The numbering cylinder  728  may be colored by a removably mountable color head  729 . A series of blowers  724  may be mounted above transport chain  720  to blow sheets onto the delivery stack  726 . An operating console  727  may be used to input information to control the overall printing process. 
     Hoods or housings  618 ,  718  preferably cover the first and second printing units  617 ,  717 , respectively. Alternatively, a single hood could cover both printing units  617 ,  717 , or multiple hoods (like those shown in the embodiment of FIG. 5) could be used with each printing unit  617 ,  717 . As shown in FIG. 11, inlets  800  and outlets  801  can be used to provide heated or cooled air, humidity, and/or chemicals in the manner described above with reference to the embodiments of FIGS. 1-11. It is to be understood that although FIG. 11 shows a single inlet  800  and a single outlet  801 , multiple inlets and outlets could be provided in the manner, e.g., shown in FIGS. 5,  6 ,  8 . Additionally, the hoods  618  or  718  can include insulation and heating in the manner shown in, e.g., FIGS. 1,  4 ,  5  or  8 , and cylinders  608 ,  610 ,  708 ,  710 , inking form rollers  611 ,  711 , damping cylinders  612 ,  712  and inkers  613 ,  713  can include cooling of the type shown in FIG.  6 . 
     FIG. 12 shows an alternative embodiment to the embodiment of FIG.  11 . Like elements to those in FIG. 11 are labeled with like reference numerals in FIG.  12 . In the embodiment of FIG. 12, a longer transport chain  720  is used, which has a larger number of gripper elements  721 . A series of infrared or ultraviolet drying elements  723  may be used to dry sheets transported on transport chain  720 . In the area between the impression cylinder  707  and the delivery stack  726  can be a series of air cushion devices  725  which deliver pressurized air. The pressurized air cushion created by air cushion devices  725  can transport sheets, without physical contact with the sheets, to the delivery stack  726 . This contactless transport prevents smearing of the printed image. In all other respects, the embodiment of FIG. 12 is similar to the embodiment of FIG. 11 described above. 
     It is to be understood that the above description is of preferred embodiments, and that other embodiments are contemplated to fall within the scope of the invention. It will be understood by those skilled in the art that other embodiments or configurations fall within the scope of the claims below.