1 Preface
In an effort to improve the quality of offset printing, special attention should be paid to the temperature condition of the offset press because the temperature is a particularly important operating parameter for offset printing. The reason for this is the relationship between the main material and process performance and temperature described below:
The viscosity and viscosity of printing inks decrease with increasing temperature. When the machine is cold, the paper will be pulled and the temperature will be too high will make the tone full. This is particularly evident on waterless offset printing because it lacks the cooling effect of evaporation of the fountain solution. In the rapid operation of the machine, evaporation of the dampening solution evaporation can reach the order of 800 W per meter of machine width.
The fountain solution absorbed by the ink increases with increasing temperature because the viscosity and viscosity of the ink are reduced. As a result, the enlargement of the tone value will increase. In addition, there is less room for adjustment of the dampening moisture, and the humidity of the printing plate becomes critical as the temperature increases.
The elastic roller pressure in the inking unit has a great relationship with the temperature because the elastic ink roller surface layer is much more thermally expanded than the metal end surfaces of the ink roller. If the temperature difference is 30~C, the ink roller pressure increases by about 0.1mm. This hinders the transfer of ink on the ink roller. Increase the wear of the ink roller, and then increase the heat.
Recent papers published by Traber on the thermal balance of web offset ink inking devices discuss the various processes of heat generation and heat dissipation. After the normal operating temperature is reached, the ink runs through the nip on the inking device to produce a temperature of about 1300 W of thermal power per meter (inker width). The back and forth movement of the ink stringer and the rolling work of the rest of the elastic roller resulted in about 20% of the heat generated. When the heat is dissipated, the fountain solution evaporates and plays a major role. It can dissipate about two-thirds of the heat. The rest of the heat dissipates the same share through the convection and radiation of the flowing air; the insignificant amount is carried away by the ink. The inking device cooling system can dissipate one-third of the heat generated, so air convection and radiation are not important. This single item of thermal balance is largely related to the inking device temperature, printing speed, ink viscosity, and ink stick positioning. The effects of the ink received by the printing plate, the cooling of the fountain solution, and the alcohol concentration in the fountain solution are not significant.
The temperature relationship between the "internal friction of the ink" and the "rolling work of the surface of the ink roller" is opposite to each other; the viscosity and viscosity of the ink decrease as the temperature rises, instead the roller compaction Work increases with temperature because the thermal expansion of the roller surface increases the line pressure between the nips. Therefore, it is important to adjust the ink roller to be correct according to the operating temperature of the machine, and it is not possible to consider the cold machine. In this respect, the temperature of the inking device can also keep the temperature unchanged. The Traber's research results confirm that the use of a constant-temperature tandem roller for heat dissipation is very effective. In this regard, the thin layer of nylon (type II polyamide fiber) coating on the screed roller has unexpectedly hindered the heat conduction. . In theory, the constant temperature of the ink stringer can serve as a transpiration cooling for the fountain solution, but it does not have any effect on the cooling of the printing plate and the blanket. As indicated by waterless offset printing, evaporation of fountain solution as a temperature regulator is not an alternative.
As has been confirmed herein, the cooling of fountain solution is difficult to effect the thermal balance of the inking device. However, the significance of dampening of the fountain solution is that, on the one hand, the isopropanol in the container and the water delivery device are reduced; on the other hand, the viscosity of the fountain solution is increased. This can promote the formation of a uniform film of dampening liquid on the alcohol moistening device.
Up to now, there are three solutions that can be achieved by adjusting the temperature of the inking device via a thermostatic device. The first adjustment scheme is to keep the surface temperature of one of the ink fountain rollers of the inking unit constant (adjustment method 1). The second solution is to adjust the temperature of the water while flowing a constant temperature roller (Regulation Method 2). The third method of adjustment is to maintain the temperature in the central tank of the thermostat.
The goal of this research work was to compare local and short-term temperature changes and their effect on print quality in the three mentioned adjustment methods. For each comparison, the temperature of the surface of the ink roller and the blanket is measured. When the adjustment method 1 is performed, the signal is adjusted according to the infrared ray sensor on the ink stick and the ink flows into each ink when the methods 2 and 3 are adjusted. The constant temperature water of the device or the contact thermometer of the central regenerative water tank indicates adjustment. The distribution of the temperature on both sides must be especially concerned with the cooling of the oil circulating in the side shields of the printing press. This oil cooling exists on every machine that performs the experiment.
Explaining the mentioned issues is important for the printing company, because a printing device is thermostatted, especially with infrared sensors, and it costs a lot to invest and maintain. This high expenditure must be achieved with the best results for good reason.
Therefore, the professional printing department recommended that this research work be supported by the German Printing Association and the Bavarian State Government and be implemented by the German Printing Institute (FOGRA).
Measurements were carried out at a packaging printing plant in Bavaria, where local temperature distributions and their short-term changes were measured on a large sheet-fed offset press. In addition, the effect of temperature changes on print quality is checked by regular sampling. Chapter 3 of this article describes the details of the experiment.
2. Adjustment technology concept
In terms of regulation technology, people adjust the approximate rating that can be achieved, that is, the measured value of a given parameter can be expressed as an adjustment amount. The adjustments and given parameters in this paper mainly relate to temperature. For example, the temperature at the measurement point predetermined at the inlet of the printing device is the adjustment amount; the rated temperature specified for this is the given parameter.
When the adjustment is unattended and reached or maintained close to a given parameter by adjusting the loop, people call it adjustment. When in control, the amount of adjustment approaches the given parameter by the direct influence of the controller (Figure 1). For example, the control is through the printer to set the moisturizing water. Adjustment is the constant temperature of the inking device. For example when adjusting mode 1, the control loop is such that the surface temperature of the ink fountain roller (: adjustment amount) is compared with the infrared sensor measurement value and the electronic adjustment device measurement value with the set value (: given parameter). If the temperature of the tandem roller is hot, then the mixing valve attached to the printing unit will have more cold water flowing through the tandem roller. Therefore, the temperature of the tandem roller decreases and approaches the given parameter value. When comparing again, the difference between the adjustment and the given parameter is not so great, and the incoming cold water is reduced.
3. experimental method
The experiment was conducted on two VI-size offset presses at a packaging printing plant. It was first performed on a 6-color Mann Rolland 806 offset press, which was supplemented with infrared and hot air drying and equipped with an oil cooling and inking unit thermostat. The constant temperature device is not adjusted according to the surface temperature of the tandem roller (measured in the middle of the ink roller) or according to the inlet temperature of the printing unit. The 6th printing unit is used for polishing. Figure 2 shows the constant temperature water flow chart of the printing unit. The constant temperature water circulates through the two tandem rollers and the ink fountain roller. The mixing valve MV is adjusted according to the actual conditions of the actual temperature (adjustment amount) and the rated temperature (reference parameter). If the actual temperature is too high, then more cold water flows from the central cooler and mixes in. If the actual temperature is too low, the incoming cold water is throttled. If the temperature is still not reached, the heat will be switched on. The remaining inking units are also adjusted, but the control loops are independent of each other.
The second machine that performed the experiment was the 5-color offset press of the Mann Rollin 805+L/Z type coating machine. The machine has no oil cooling device. The inking units of the five units are all cooled, that is, all the inking units are injected with circulating water at the same temperature. This water temperature is measured and adjusted in a central cooling tank. The incubator temperature on these two machines includes two tandem rollers and ink fountain rollers.
The preliminary test results showed that if the oil cooling of the Model 806 Offset Press is turned off and the constant temperature is set uniformly to 29°C, then the situation of the 2nd Model 805 Offset Press can be accurately adjusted according to the 1st 806 Machine. Just need to wait about 2 hours. The advantage of this experimental method is that all other effects can be ruled out when comparing adjustment methods.
On the press, four infrared temperature sensors are mounted on the printer. The sensor continuously detects the surface temperature of the roller through the opening of the screen. The temperature of the blanket should be measured using an infrared sensor that reacts particularly quickly. In FIG. 3, the measurement points of the infrared sensor are indicated by arrows. In addition, four contact-type temperature sensors are also installed to measure the temperature of the two water delivery devices and the temperatures on the sides and the top of the machine.
(to be continued)
In an effort to improve the quality of offset printing, special attention should be paid to the temperature condition of the offset press because the temperature is a particularly important operating parameter for offset printing. The reason for this is the relationship between the main material and process performance and temperature described below:
The viscosity and viscosity of printing inks decrease with increasing temperature. When the machine is cold, the paper will be pulled and the temperature will be too high will make the tone full. This is particularly evident on waterless offset printing because it lacks the cooling effect of evaporation of the fountain solution. In the rapid operation of the machine, evaporation of the dampening solution evaporation can reach the order of 800 W per meter of machine width.
The fountain solution absorbed by the ink increases with increasing temperature because the viscosity and viscosity of the ink are reduced. As a result, the enlargement of the tone value will increase. In addition, there is less room for adjustment of the dampening moisture, and the humidity of the printing plate becomes critical as the temperature increases.
The elastic roller pressure in the inking unit has a great relationship with the temperature because the elastic ink roller surface layer is much more thermally expanded than the metal end surfaces of the ink roller. If the temperature difference is 30~C, the ink roller pressure increases by about 0.1mm. This hinders the transfer of ink on the ink roller. Increase the wear of the ink roller, and then increase the heat.
Recent papers published by Traber on the thermal balance of web offset ink inking devices discuss the various processes of heat generation and heat dissipation. After the normal operating temperature is reached, the ink runs through the nip on the inking device to produce a temperature of about 1300 W of thermal power per meter (inker width). The back and forth movement of the ink stringer and the rolling work of the rest of the elastic roller resulted in about 20% of the heat generated. When the heat is dissipated, the fountain solution evaporates and plays a major role. It can dissipate about two-thirds of the heat. The rest of the heat dissipates the same share through the convection and radiation of the flowing air; the insignificant amount is carried away by the ink. The inking device cooling system can dissipate one-third of the heat generated, so air convection and radiation are not important. This single item of thermal balance is largely related to the inking device temperature, printing speed, ink viscosity, and ink stick positioning. The effects of the ink received by the printing plate, the cooling of the fountain solution, and the alcohol concentration in the fountain solution are not significant.
The temperature relationship between the "internal friction of the ink" and the "rolling work of the surface of the ink roller" is opposite to each other; the viscosity and viscosity of the ink decrease as the temperature rises, instead the roller compaction Work increases with temperature because the thermal expansion of the roller surface increases the line pressure between the nips. Therefore, it is important to adjust the ink roller to be correct according to the operating temperature of the machine, and it is not possible to consider the cold machine. In this respect, the temperature of the inking device can also keep the temperature unchanged. The Traber's research results confirm that the use of a constant-temperature tandem roller for heat dissipation is very effective. In this regard, the thin layer of nylon (type II polyamide fiber) coating on the screed roller has unexpectedly hindered the heat conduction. . In theory, the constant temperature of the ink stringer can serve as a transpiration cooling for the fountain solution, but it does not have any effect on the cooling of the printing plate and the blanket. As indicated by waterless offset printing, evaporation of fountain solution as a temperature regulator is not an alternative.
As has been confirmed herein, the cooling of fountain solution is difficult to effect the thermal balance of the inking device. However, the significance of dampening of the fountain solution is that, on the one hand, the isopropanol in the container and the water delivery device are reduced; on the other hand, the viscosity of the fountain solution is increased. This can promote the formation of a uniform film of dampening liquid on the alcohol moistening device.
Up to now, there are three solutions that can be achieved by adjusting the temperature of the inking device via a thermostatic device. The first adjustment scheme is to keep the surface temperature of one of the ink fountain rollers of the inking unit constant (adjustment method 1). The second solution is to adjust the temperature of the water while flowing a constant temperature roller (Regulation Method 2). The third method of adjustment is to maintain the temperature in the central tank of the thermostat.
The goal of this research work was to compare local and short-term temperature changes and their effect on print quality in the three mentioned adjustment methods. For each comparison, the temperature of the surface of the ink roller and the blanket is measured. When the adjustment method 1 is performed, the signal is adjusted according to the infrared ray sensor on the ink stick and the ink flows into each ink when the methods 2 and 3 are adjusted. The constant temperature water of the device or the contact thermometer of the central regenerative water tank indicates adjustment. The distribution of the temperature on both sides must be especially concerned with the cooling of the oil circulating in the side shields of the printing press. This oil cooling exists on every machine that performs the experiment.
Explaining the mentioned issues is important for the printing company, because a printing device is thermostatted, especially with infrared sensors, and it costs a lot to invest and maintain. This high expenditure must be achieved with the best results for good reason.
Therefore, the professional printing department recommended that this research work be supported by the German Printing Association and the Bavarian State Government and be implemented by the German Printing Institute (FOGRA).
Measurements were carried out at a packaging printing plant in Bavaria, where local temperature distributions and their short-term changes were measured on a large sheet-fed offset press. In addition, the effect of temperature changes on print quality is checked by regular sampling. Chapter 3 of this article describes the details of the experiment.
2. Adjustment technology concept
In terms of regulation technology, people adjust the approximate rating that can be achieved, that is, the measured value of a given parameter can be expressed as an adjustment amount. The adjustments and given parameters in this paper mainly relate to temperature. For example, the temperature at the measurement point predetermined at the inlet of the printing device is the adjustment amount; the rated temperature specified for this is the given parameter.
When the adjustment is unattended and reached or maintained close to a given parameter by adjusting the loop, people call it adjustment. When in control, the amount of adjustment approaches the given parameter by the direct influence of the controller (Figure 1). For example, the control is through the printer to set the moisturizing water. Adjustment is the constant temperature of the inking device. For example when adjusting mode 1, the control loop is such that the surface temperature of the ink fountain roller (: adjustment amount) is compared with the infrared sensor measurement value and the electronic adjustment device measurement value with the set value (: given parameter). If the temperature of the tandem roller is hot, then the mixing valve attached to the printing unit will have more cold water flowing through the tandem roller. Therefore, the temperature of the tandem roller decreases and approaches the given parameter value. When comparing again, the difference between the adjustment and the given parameter is not so great, and the incoming cold water is reduced.
3. experimental method
The experiment was conducted on two VI-size offset presses at a packaging printing plant. It was first performed on a 6-color Mann Rolland 806 offset press, which was supplemented with infrared and hot air drying and equipped with an oil cooling and inking unit thermostat. The constant temperature device is not adjusted according to the surface temperature of the tandem roller (measured in the middle of the ink roller) or according to the inlet temperature of the printing unit. The 6th printing unit is used for polishing. Figure 2 shows the constant temperature water flow chart of the printing unit. The constant temperature water circulates through the two tandem rollers and the ink fountain roller. The mixing valve MV is adjusted according to the actual conditions of the actual temperature (adjustment amount) and the rated temperature (reference parameter). If the actual temperature is too high, then more cold water flows from the central cooler and mixes in. If the actual temperature is too low, the incoming cold water is throttled. If the temperature is still not reached, the heat will be switched on. The remaining inking units are also adjusted, but the control loops are independent of each other.
The second machine that performed the experiment was the 5-color offset press of the Mann Rollin 805+L/Z type coating machine. The machine has no oil cooling device. The inking units of the five units are all cooled, that is, all the inking units are injected with circulating water at the same temperature. This water temperature is measured and adjusted in a central cooling tank. The incubator temperature on these two machines includes two tandem rollers and ink fountain rollers.
The preliminary test results showed that if the oil cooling of the Model 806 Offset Press is turned off and the constant temperature is set uniformly to 29°C, then the situation of the 2nd Model 805 Offset Press can be accurately adjusted according to the 1st 806 Machine. Just need to wait about 2 hours. The advantage of this experimental method is that all other effects can be ruled out when comparing adjustment methods.
On the press, four infrared temperature sensors are mounted on the printer. The sensor continuously detects the surface temperature of the roller through the opening of the screen. The temperature of the blanket should be measured using an infrared sensor that reacts particularly quickly. In FIG. 3, the measurement points of the infrared sensor are indicated by arrows. In addition, four contact-type temperature sensors are also installed to measure the temperature of the two water delivery devices and the temperatures on the sides and the top of the machine.
(to be continued)
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