Since traditional offset printing relies on the principle of ink repellency, the use and control of fountain solution in offset printing is a key part of printing. Although waterless offset printing has been developed to a large extent, it is still not widely used in waterless printing today. How to control various indicators of fountain solution in offset printing and how to use fountain solution more rationally? It is still an important topic that we need to discuss.
Let's take a look at what wetting fluid does in offset printing:
First, the wetting liquid forms a uniform water film on the blank portion of the printing plate to resist the infiltration of the ink on the graphic portion to the blank portion.
Secondly, due to the contact and friction between the blanket cylinder, the water roller and the printing plate, and the deinking and fluffing of inks and printing materials, the friction on the surface of the printing plate causes the wear of the hydrophilic salt layer on the printing plate surface. The electrolyte in the fountain solution repairs the damaged hydrophilic layer and re-forms a new hydrophilic salt layer.
In addition, the fountain solution can also control the layout temperature during printing, taking away the heat generated by the friction between machine parts and the shearing of materials such as ink.
Fountain solution in the printing process of the ink emulsification also has a certain role in promoting (to ensure a certain degree of ink emulsification, good transfer of ink in the printing has a very important role), and quickly realize the ink balance.
Below we discuss further the control of fountain solution in production.
First, the fountain solution PH value
During the offset printing process, the hydrophilic oxide layer on the surface of the PS plate is easily destroyed due to the printing pressure during the printing process and some other causes of wear. This requires the fountain solution to ensure a certain degree of acidity in order to form a new hydrophilic salt. Layer, prompt repair of the damaged hydrophilic layer. In addition, certain weak acidity of the fountain solution is ensured in the printing process, and it can also play the role of removing oil from the blank part of the layout. Practice has proved that for the PS version, the pH value range of the fountain solution that best meets the printing technical requirements is 5-6.
When the PH value of the solution is too small, not only does it not function to repair the printing plate, but it will malignantly corrode the plate, and it will not be able to form a stable hydrophilic salt layer. The graphic part of the plate is combined with the metal plate base. It may also be destroyed, which will reduce the printing rate of the printing plate. In addition, the fountain solution reacts with the driers in the ink, thereby delaying the drying of the ink during the printing process, causing the back of the printed product to become dirty, and affecting the overprinting rate of the ink.
If the PH value of the solution is too large, the ink-receptive layer of the graphic part will be dissolved first, resulting in a decrease in the printing durability of the printing plate; in addition, the basic groups in the solution will react with the fatty acids present in the ink and the activity will be very high. Strong hydrophilic groups, a large increase in this hydrophilic group, can lead to ink emulsification during printing.
The range of pH values ​​given above is not an absolute range. The conditions encountered in actual production are various, and the pH of fountain solution is not constant. In other words, during the printing process, some appropriate adjustments to the pH of the fountain solution should be made according to the actual situation.
1. The effect of paper acidity and alkalinity on fountain solution. The pH of the paper is neutral, but in fact, because of the different papermaking processes, the pH of the paper is different. In general, non-coated paper such as offset paper has a PH value of 4.5 to 7.0 and is slightly acidic; the pH value of coated paper is 7.0 to 9.0, which is weakly alkaline. The printing worker can use the paper according to the nature of the paper. The fluid is adjusted accordingly. When the paper is acidic, the pH of the fountain solution can be larger (in the case of printing offset paper, the pH can be controlled between 5.5 and 6.5 depending on the situation). When the paper is alkaline, the pH of the fountain solution can be smaller ( When printing coated paper, the pH of fountain solution can be controlled at 4.8 to 5.0, and it can be appropriately reduced depending on the situation.
2. When the thickness of the ink layer increases, the ink in the graphic part must spread to the blank part, and it easily appears as a “dirty plateâ€. When the amount of the desiccant in the ink increases, the viscosity of the ink increases and the particles become thick, and the blank part of the printing plate The adhesiveness increases, and dirty plates are liable to occur. When the printed surface is not strong, the hydrophilic salt layer of the plate is easily worn out due to the serious phenomenon of powder off and hair loss; when the ambient temperature is high, In the ink, more free fatty acids will be separated and react with the OH hydrazine in the fountain solution, resulting in serious ink emulsification. The above situations should pay attention to properly reduce the pH of the fountain solution to increase the acidity of the solution.
Second, the amount of fountain solution
The amount of fountain solution used in the printing process also needs to be well controlled. The principle of controlling the amount of fountain solution is to reduce the amount as much as possible, on the premise that the blank part is not dirty and the ink is not emulsified.
If the amount of fountain solution is too small, it is obvious that it will not protect the blank part of the printing plate, blurring the dots, and causing stencils, dirty plates, etc.
If the amount of fountain solution is too large? Excessive water content in the layout will reduce the density of the printed product on the spot, and it will cause false printing on the screen. It will affect the dryness of the printed product and cause the back of the printed product to become dirty. The paper absorbs too much water and the fiber is overprinted.
The amount of fountain solution used at work is not static, and some appropriate adjustments must be made according to specific circumstances:
1. Temperature: The higher the ambient temperature and the machine temperature, the greater the consumption of fountain solution. The heat source of the ink part of the printer is mainly the axial turbulent friction between the string water roller and the ink roller. The higher the temperature, the faster the fountain solution on the printing plate, the water roller, and the ink roller evaporates, and more ink will flow into the fountain solution. Therefore, when the temperature is high, it is necessary to increase the amount of fountain solution.
2. Ink: Ink emulsification is the main factor affecting the amount of fountain solution. The critical value of the ink receiving water is between 20% and 25%. When the critical value is exceeded, the pigment particles are in a free state. The viscosity of the ink is poor, the drawing property is poor, and the transfer performance is poor. The oil-in-water emulsification is presented. The ink with small viscosity and good transfer performance has a relatively small amount of fountain solution, and vice versa. In addition, if the amount of ink is large, the amount of fountain solution should also be increased accordingly.
3. Printing plate graphic area: In general, the field version is relative to the line version, the fountain solution consumption is slightly larger; the text version relative to the dot version, the amount of fountain solution is slightly larger.
4. Printing speed: When the printing speed is increased, the amount of fountain solution should also increase.
Third, regarding the alcohol fountain solution Now due to many advantages of alcohol fountain solution, its use has been quite popularized and promoted.
The main components of the alcohol fountain solution are water, a suitable amount of alcohol (or isopropyl alcohol), and a fountain solution stock solution. The concentration of alcohol has a great influence on the use of fountain solution.
First of all, let's take a look at the role of alcohol in printing:
1. Decrease the surface tension of fountain solution to make it more wettable to the plate surface.
2. Increase the viscosity of the fountain solution, making it easy to pass through the gap between the rollers.
3. Speed ​​up the emulsification speed of the ink and fountain solution, and at the same time prevent over-emulsification of the ink.
4. At the same time when volatilizing, take away heat and have cooling effect.
Here we talk about the control of alcohol fountain solution from several aspects such as alcohol concentration and temperature.
In the use of the fountain solution, the concentration of alcohol first affects the surface tension of the fountain solution. The greater the concentration, the lower the surface tension of the fountain solution. Experience has shown that controlling the concentration of alcohol at 10% to 15% is a more appropriate concentration. If the concentration of the fountain solution is less than 10%, the effect is not obvious; if it exceeds 30%, the jelly in the fountain solution will flocculate, destroying the fountain solution.
In the production process, generally set the minimum concentration of alcohol, whether it is automatic or manual measurement, all need to perform good control, especially manual measurement control, pay attention to ground measurement
Let's take a look at what wetting fluid does in offset printing:
First, the wetting liquid forms a uniform water film on the blank portion of the printing plate to resist the infiltration of the ink on the graphic portion to the blank portion.
Secondly, due to the contact and friction between the blanket cylinder, the water roller and the printing plate, and the deinking and fluffing of inks and printing materials, the friction on the surface of the printing plate causes the wear of the hydrophilic salt layer on the printing plate surface. The electrolyte in the fountain solution repairs the damaged hydrophilic layer and re-forms a new hydrophilic salt layer.
In addition, the fountain solution can also control the layout temperature during printing, taking away the heat generated by the friction between machine parts and the shearing of materials such as ink.
Fountain solution in the printing process of the ink emulsification also has a certain role in promoting (to ensure a certain degree of ink emulsification, good transfer of ink in the printing has a very important role), and quickly realize the ink balance.
Below we discuss further the control of fountain solution in production.
First, the fountain solution PH value
During the offset printing process, the hydrophilic oxide layer on the surface of the PS plate is easily destroyed due to the printing pressure during the printing process and some other causes of wear. This requires the fountain solution to ensure a certain degree of acidity in order to form a new hydrophilic salt. Layer, prompt repair of the damaged hydrophilic layer. In addition, certain weak acidity of the fountain solution is ensured in the printing process, and it can also play the role of removing oil from the blank part of the layout. Practice has proved that for the PS version, the pH value range of the fountain solution that best meets the printing technical requirements is 5-6.
When the PH value of the solution is too small, not only does it not function to repair the printing plate, but it will malignantly corrode the plate, and it will not be able to form a stable hydrophilic salt layer. The graphic part of the plate is combined with the metal plate base. It may also be destroyed, which will reduce the printing rate of the printing plate. In addition, the fountain solution reacts with the driers in the ink, thereby delaying the drying of the ink during the printing process, causing the back of the printed product to become dirty, and affecting the overprinting rate of the ink.
If the PH value of the solution is too large, the ink-receptive layer of the graphic part will be dissolved first, resulting in a decrease in the printing durability of the printing plate; in addition, the basic groups in the solution will react with the fatty acids present in the ink and the activity will be very high. Strong hydrophilic groups, a large increase in this hydrophilic group, can lead to ink emulsification during printing.
The range of pH values ​​given above is not an absolute range. The conditions encountered in actual production are various, and the pH of fountain solution is not constant. In other words, during the printing process, some appropriate adjustments to the pH of the fountain solution should be made according to the actual situation.
1. The effect of paper acidity and alkalinity on fountain solution. The pH of the paper is neutral, but in fact, because of the different papermaking processes, the pH of the paper is different. In general, non-coated paper such as offset paper has a PH value of 4.5 to 7.0 and is slightly acidic; the pH value of coated paper is 7.0 to 9.0, which is weakly alkaline. The printing worker can use the paper according to the nature of the paper. The fluid is adjusted accordingly. When the paper is acidic, the pH of the fountain solution can be larger (in the case of printing offset paper, the pH can be controlled between 5.5 and 6.5 depending on the situation). When the paper is alkaline, the pH of the fountain solution can be smaller ( When printing coated paper, the pH of fountain solution can be controlled at 4.8 to 5.0, and it can be appropriately reduced depending on the situation.
2. When the thickness of the ink layer increases, the ink in the graphic part must spread to the blank part, and it easily appears as a “dirty plateâ€. When the amount of the desiccant in the ink increases, the viscosity of the ink increases and the particles become thick, and the blank part of the printing plate The adhesiveness increases, and dirty plates are liable to occur. When the printed surface is not strong, the hydrophilic salt layer of the plate is easily worn out due to the serious phenomenon of powder off and hair loss; when the ambient temperature is high, In the ink, more free fatty acids will be separated and react with the OH hydrazine in the fountain solution, resulting in serious ink emulsification. The above situations should pay attention to properly reduce the pH of the fountain solution to increase the acidity of the solution.
Second, the amount of fountain solution
The amount of fountain solution used in the printing process also needs to be well controlled. The principle of controlling the amount of fountain solution is to reduce the amount as much as possible, on the premise that the blank part is not dirty and the ink is not emulsified.
If the amount of fountain solution is too small, it is obvious that it will not protect the blank part of the printing plate, blurring the dots, and causing stencils, dirty plates, etc.
If the amount of fountain solution is too large? Excessive water content in the layout will reduce the density of the printed product on the spot, and it will cause false printing on the screen. It will affect the dryness of the printed product and cause the back of the printed product to become dirty. The paper absorbs too much water and the fiber is overprinted.
The amount of fountain solution used at work is not static, and some appropriate adjustments must be made according to specific circumstances:
1. Temperature: The higher the ambient temperature and the machine temperature, the greater the consumption of fountain solution. The heat source of the ink part of the printer is mainly the axial turbulent friction between the string water roller and the ink roller. The higher the temperature, the faster the fountain solution on the printing plate, the water roller, and the ink roller evaporates, and more ink will flow into the fountain solution. Therefore, when the temperature is high, it is necessary to increase the amount of fountain solution.
2. Ink: Ink emulsification is the main factor affecting the amount of fountain solution. The critical value of the ink receiving water is between 20% and 25%. When the critical value is exceeded, the pigment particles are in a free state. The viscosity of the ink is poor, the drawing property is poor, and the transfer performance is poor. The oil-in-water emulsification is presented. The ink with small viscosity and good transfer performance has a relatively small amount of fountain solution, and vice versa. In addition, if the amount of ink is large, the amount of fountain solution should also be increased accordingly.
3. Printing plate graphic area: In general, the field version is relative to the line version, the fountain solution consumption is slightly larger; the text version relative to the dot version, the amount of fountain solution is slightly larger.
4. Printing speed: When the printing speed is increased, the amount of fountain solution should also increase.
Third, regarding the alcohol fountain solution Now due to many advantages of alcohol fountain solution, its use has been quite popularized and promoted.
The main components of the alcohol fountain solution are water, a suitable amount of alcohol (or isopropyl alcohol), and a fountain solution stock solution. The concentration of alcohol has a great influence on the use of fountain solution.
First of all, let's take a look at the role of alcohol in printing:
1. Decrease the surface tension of fountain solution to make it more wettable to the plate surface.
2. Increase the viscosity of the fountain solution, making it easy to pass through the gap between the rollers.
3. Speed ​​up the emulsification speed of the ink and fountain solution, and at the same time prevent over-emulsification of the ink.
4. At the same time when volatilizing, take away heat and have cooling effect.
Here we talk about the control of alcohol fountain solution from several aspects such as alcohol concentration and temperature.
In the use of the fountain solution, the concentration of alcohol first affects the surface tension of the fountain solution. The greater the concentration, the lower the surface tension of the fountain solution. Experience has shown that controlling the concentration of alcohol at 10% to 15% is a more appropriate concentration. If the concentration of the fountain solution is less than 10%, the effect is not obvious; if it exceeds 30%, the jelly in the fountain solution will flocculate, destroying the fountain solution.
In the production process, generally set the minimum concentration of alcohol, whether it is automatic or manual measurement, all need to perform good control, especially manual measurement control, pay attention to ground measurement
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