In gravure printing, the transfer rate of ink from the cell on the printing plate to the surface of the substrate is usually about 50% to 70%. About 30% to 50% of the ink always remains in the cell. The residual rate of the ink will not cause any problem if it is always maintained at a certain value. However, in the printing process, the residual rate of the ink in the cell site is often increased due to some reasons, resulting in blockage. After the blockage occurs, the printed pattern and text will be blurred, the color of the printed product will change, and serious printing cannot be continued. The shallow version is the most prone to blockage.
Blocking is mainly caused by the infiltration of the cells with insoluble substances such as cured substances, high-viscosity substances, or foreign substances in the ink.
First, cause blocking the reasons
1. Ink dried on the layout
The ink remaining in the cell is affected by certain factors (such as increased viscosity of the ink). Some of the ink will be dried and solidified. When the plate cylinder enters the ink tank again, the cured ink in the cell can hardly dissolve completely, and the ink is transferred. The rate will also decrease. Over time, the nets were blocked more and more shallowly, the ink transfer rate was getting lower and lower, and finally the blocking failure was caused. This type of blocking failure is related to the type of ink, viscosity, solvent, drying speed, printing speed and Other factors, but also has a great relationship with the structure of the printing press.
(1) The solvent is drying too fast
In order to meet the needs of the printing process, it is often necessary to adjust the drying speed of the ink during printing. When the ink dries too quickly. Before the ink has been transferred to the printed substrate, a portion of the ink will have a film. The poor re-dissolvability of the ink film will inevitably result in poor ink transfer, and accumulation of the printing plate will occur after a period of accumulation.
When the ink circulation is poor, the ink in the ink fountain is easy to crust, and it also causes blocking failure.
Of course, the above-mentioned troubles can easily be caused by the high temperature in the printing shop and the low humidity.
(2) Hot air blown out from drying oven
Some problems with the construction of the gravure printer (such as the position of the doctor blade far from the plate cylinder, the large cylinder diameter, the shallow immersion of the plate cylinder in the ink tank, etc.) can cause the hot air leaking from the drying chamber to directly blow the plate layout. This causes the ink to dry in the cells. Printing speed is too low, it is easy to make the ink dry in the cell and block the plate. When problems with the structure of the gravure printer are difficult to improve, it is necessary to increase the printing speed as much as possible, shorten the distance between the doctor blade and the nip, or use a drying agent.
2. Ink mixed with ink
Gravure printing speed is relatively fast, and the printed substrate (film) often generates static electricity during high-speed operation. Due to the electrostatic adsorption, impurities such as debris coming off the printing material in the surrounding environment will be carried into the ink. These mechanical impurities are the direct cause of clogging of the printing plate. To prevent this accident, an 80- to 120-mesh metal screen can be installed in front of the suction nozzle of the circulation pump to filter the ink to remove insoluble impurities.
(1) The gravure printing plate of 175 L/in, which is often used in gravure printing, has a maximum cell length of 130 μm and a depth of about 35 μm in the longitudinal and transverse directions. The coarse particles, insoluble substances, precipitates, or the printing process are mixed in the ink. The dust can clog it.
(2) When the ink itself undergoes separation, precipitation, and re-agglomeration of the pigment, blockage due to low re-solubility can also occur. Therefore, inks with significant differences in specific gravity should be avoided in combination with each other.
3. Low quality plate making
The gravure plate must go through many processes such as surface etching or engraving, aluminum plating, and grinding. In these processes, the unevenness of the inner wall of the cell due to corrosion or engraving, the burrs generated during grinding, and the Ω-type network cell all have a certain influence on the transfer rate of the ink. When the inert condition is severe, it often occurs. As a result, the ink transfer rate is reduced, resulting in blockage.
According to the relevant information, when using the etching process, the regular quadrilateral cell site is changed to a concave arc-shaped cell site, which can greatly reduce the phenomenon of lost dots and help to reduce the blocking failure in plastic gravure printing.
4. Poor ink dissolution (deterioration)
Due to poor ink flow, turbidity deposits, mixed inks due to incomplete cleaning after parking, misuse of other poor solvents, etc. resulting in poor ink dissolution, the transfer rate is reduced, and blocking is also caused.
(1) The deterioration of the ink and the change in the solvent balance will result in a decrease in the solvency of the ink, causing changes in the separation, precipitation, and re-agglomeration of the ink itself.
(2) In the printing process, if water is mixed in the ink, it will affect the fluidity of the ink and cause re-agglomeration of the pigment.
(3) When replacing the ink, if the printer is not thoroughly cleaned, the new ink is mixed with different types of ink, or misuse and mixing with inappropriate solvents, etc., will directly cause poor ink dissolution, resulting in blockage.
(4) When adding a solvent (especially a large amount of solvent) to the ink tank and ink tank during printing, if the addition speed is too high, the solubility may be deteriorated due to the impact of the solvent. Therefore, slowly add the solvent.
5. Chemical changes in ink
With the continuation of the printing process, two-component inks or reactive inks will gradually undergo cross-linking and other chemical reactions, resulting in poor ink flowability, increased viscosity, and reduced transfer rate, which may be the cause of blockage. Therefore, when using two-component inks or reactive inks, wipe the plates in time after shutting down, and use expired ink and remaining ink with caution. In addition, the mixing of different types of inks may cause chemical reactions that can cause blockages. Therefore, experiments should be conducted to confirm whether different types of ink can be mixed.
Second, blocking version of the failure to solve countermeasures
Based on the above analysis, we can summarize the solution to the problem of plastic gravure plate blocking.
1. When a gravitational plate jam occurs, use a solvent or a special cleaning agent to clean it, and resolve the cause of the blockage.
2. The temperature and humidity of the printing shop should be appropriate. The drying speed of the solvent must be compatible with the printing speed and the printing environment.
3. The distance between the doctor blade and the impression cylinder should be as short as possible to prevent the hot air leaking from the drying cabinet from directly blowing the layout.
4. Use a slow-drying solvent and increase the printing speed.
5. In case of blockage failure due to ink performance defects, replace the ink in time (or contact the ink supplier for resolution) and try to avoid the combination of inks with significant differences in specific gravity.
6. The ink in the ink tank should be stirred frequently so that the ink in each part is in a flowing state. New inks should also be added in a timely manner or replaced with new inks to avoid ink filming.
7. When there is a blockage caused by the quality of the inner wall of the printing plate, replate or replate.
8. Before starting or just turning on the machine, wipe the plate cylinder with solvent. During the printing process, midway parking should be avoided as much as possible. For long-term parking, the plates must be cleaned first, or the plate cylinder should be immersed in the ink tank for continuous idling.
9. In fresh ink, additives, waxes, etc. in the ink will crystallize out due to temperature differences. At this time, try to warm the ink (40-50°C) before use to dissolve it.
10. Misuse of solvents, deterioration of inks, and incorporation of dissimilar inks will significantly affect the re-solubility of the ink. Therefore, you should use a regular special dilution solvent. When replacing the ink, wash the ink tank and circulation pump thoroughly, and then pour in new ink.
Blocking is mainly caused by the infiltration of the cells with insoluble substances such as cured substances, high-viscosity substances, or foreign substances in the ink.
First, cause blocking the reasons
1. Ink dried on the layout
The ink remaining in the cell is affected by certain factors (such as increased viscosity of the ink). Some of the ink will be dried and solidified. When the plate cylinder enters the ink tank again, the cured ink in the cell can hardly dissolve completely, and the ink is transferred. The rate will also decrease. Over time, the nets were blocked more and more shallowly, the ink transfer rate was getting lower and lower, and finally the blocking failure was caused. This type of blocking failure is related to the type of ink, viscosity, solvent, drying speed, printing speed and Other factors, but also has a great relationship with the structure of the printing press.
(1) The solvent is drying too fast
In order to meet the needs of the printing process, it is often necessary to adjust the drying speed of the ink during printing. When the ink dries too quickly. Before the ink has been transferred to the printed substrate, a portion of the ink will have a film. The poor re-dissolvability of the ink film will inevitably result in poor ink transfer, and accumulation of the printing plate will occur after a period of accumulation.
When the ink circulation is poor, the ink in the ink fountain is easy to crust, and it also causes blocking failure.
Of course, the above-mentioned troubles can easily be caused by the high temperature in the printing shop and the low humidity.
(2) Hot air blown out from drying oven
Some problems with the construction of the gravure printer (such as the position of the doctor blade far from the plate cylinder, the large cylinder diameter, the shallow immersion of the plate cylinder in the ink tank, etc.) can cause the hot air leaking from the drying chamber to directly blow the plate layout. This causes the ink to dry in the cells. Printing speed is too low, it is easy to make the ink dry in the cell and block the plate. When problems with the structure of the gravure printer are difficult to improve, it is necessary to increase the printing speed as much as possible, shorten the distance between the doctor blade and the nip, or use a drying agent.
2. Ink mixed with ink
Gravure printing speed is relatively fast, and the printed substrate (film) often generates static electricity during high-speed operation. Due to the electrostatic adsorption, impurities such as debris coming off the printing material in the surrounding environment will be carried into the ink. These mechanical impurities are the direct cause of clogging of the printing plate. To prevent this accident, an 80- to 120-mesh metal screen can be installed in front of the suction nozzle of the circulation pump to filter the ink to remove insoluble impurities.
(1) The gravure printing plate of 175 L/in, which is often used in gravure printing, has a maximum cell length of 130 μm and a depth of about 35 μm in the longitudinal and transverse directions. The coarse particles, insoluble substances, precipitates, or the printing process are mixed in the ink. The dust can clog it.
(2) When the ink itself undergoes separation, precipitation, and re-agglomeration of the pigment, blockage due to low re-solubility can also occur. Therefore, inks with significant differences in specific gravity should be avoided in combination with each other.
3. Low quality plate making
The gravure plate must go through many processes such as surface etching or engraving, aluminum plating, and grinding. In these processes, the unevenness of the inner wall of the cell due to corrosion or engraving, the burrs generated during grinding, and the Ω-type network cell all have a certain influence on the transfer rate of the ink. When the inert condition is severe, it often occurs. As a result, the ink transfer rate is reduced, resulting in blockage.
According to the relevant information, when using the etching process, the regular quadrilateral cell site is changed to a concave arc-shaped cell site, which can greatly reduce the phenomenon of lost dots and help to reduce the blocking failure in plastic gravure printing.
4. Poor ink dissolution (deterioration)
Due to poor ink flow, turbidity deposits, mixed inks due to incomplete cleaning after parking, misuse of other poor solvents, etc. resulting in poor ink dissolution, the transfer rate is reduced, and blocking is also caused.
(1) The deterioration of the ink and the change in the solvent balance will result in a decrease in the solvency of the ink, causing changes in the separation, precipitation, and re-agglomeration of the ink itself.
(2) In the printing process, if water is mixed in the ink, it will affect the fluidity of the ink and cause re-agglomeration of the pigment.
(3) When replacing the ink, if the printer is not thoroughly cleaned, the new ink is mixed with different types of ink, or misuse and mixing with inappropriate solvents, etc., will directly cause poor ink dissolution, resulting in blockage.
(4) When adding a solvent (especially a large amount of solvent) to the ink tank and ink tank during printing, if the addition speed is too high, the solubility may be deteriorated due to the impact of the solvent. Therefore, slowly add the solvent.
5. Chemical changes in ink
With the continuation of the printing process, two-component inks or reactive inks will gradually undergo cross-linking and other chemical reactions, resulting in poor ink flowability, increased viscosity, and reduced transfer rate, which may be the cause of blockage. Therefore, when using two-component inks or reactive inks, wipe the plates in time after shutting down, and use expired ink and remaining ink with caution. In addition, the mixing of different types of inks may cause chemical reactions that can cause blockages. Therefore, experiments should be conducted to confirm whether different types of ink can be mixed.
Second, blocking version of the failure to solve countermeasures
Based on the above analysis, we can summarize the solution to the problem of plastic gravure plate blocking.
1. When a gravitational plate jam occurs, use a solvent or a special cleaning agent to clean it, and resolve the cause of the blockage.
2. The temperature and humidity of the printing shop should be appropriate. The drying speed of the solvent must be compatible with the printing speed and the printing environment.
3. The distance between the doctor blade and the impression cylinder should be as short as possible to prevent the hot air leaking from the drying cabinet from directly blowing the layout.
4. Use a slow-drying solvent and increase the printing speed.
5. In case of blockage failure due to ink performance defects, replace the ink in time (or contact the ink supplier for resolution) and try to avoid the combination of inks with significant differences in specific gravity.
6. The ink in the ink tank should be stirred frequently so that the ink in each part is in a flowing state. New inks should also be added in a timely manner or replaced with new inks to avoid ink filming.
7. When there is a blockage caused by the quality of the inner wall of the printing plate, replate or replate.
8. Before starting or just turning on the machine, wipe the plate cylinder with solvent. During the printing process, midway parking should be avoided as much as possible. For long-term parking, the plates must be cleaned first, or the plate cylinder should be immersed in the ink tank for continuous idling.
9. In fresh ink, additives, waxes, etc. in the ink will crystallize out due to temperature differences. At this time, try to warm the ink (40-50°C) before use to dissolve it.
10. Misuse of solvents, deterioration of inks, and incorporation of dissimilar inks will significantly affect the re-solubility of the ink. Therefore, you should use a regular special dilution solvent. When replacing the ink, wash the ink tank and circulation pump thoroughly, and then pour in new ink.
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