How to avoid dirty problems in gravure, these problems must be noted!
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In the process of film gravure, a dirty failure occurs. For irregular dirty faults, there are many reasons for this. This article provides a detailed analysis of irregular dirty faults in terms of gravure cylinder fabrication, blade selection and installation, ink and dilution solvents, shop floor environment and production operations.
First, the production of gravure cylinder
1, the cause analysis
(1) If the hardness of the chrome-plated layer on the surface of the gravure cylinder is not up to the minimum requirement, the non-image area of the surface of the gravure cylinder is liable to cause excessive friction between the squeegee and wear, and the worn area is immersed in the ink during use. , thereby transferring to the film to create a dirty fault.
(2) If the gravure cylinder is chrome-plated and the polishing treatment is insufficient, the surface of the chrome plating layer will be rough, and a dirty fault will occur when the machine is used.
(3) There is a plate making defect in the gravure cylinder, which may cause residual ink marks to cause a dirty failure.
2, countermeasures
(1) Ensure that the surface of the gravure cylinder is smooth, high in hardness, good in wear resistance and long in service life.
(2) Determine the maximum printing capacity of each gravure cylinder by factors such as the hardness of the gravure cylinder, the depth of the cell, and the distribution of the cells. Once this value is exceeded, the surface of the gravure cylinder needs to be rechromed.
(3) Before the official printing, 800#～1000# sandpaper shall be used to grind the surface of the gravure cylinder in all directions.
Second, the blade selection and installation
1, the cause analysis
(1) The hardness of the blade is not suitable.
(2) The blade is installed incorrectly, the blade pressure is insufficient, the angle between the blade and the gravure cylinder is not suitable, the blade is not sufficiently ground, or the distance between the blade scraping point and the ink transfer point is improper.
2, countermeasures
(1) Select a self-grinding scraper with a tight material and moderate hardness.
(2) Ensure that the scraper is installed correctly and the force is even. The lining knife (also called “sub-knife”) generally selects a corrosion-resistant flat steel plate with a thickness of 0.5mm. The installation position should exceed 15-20mm of the tool holder, and the position of the scraper should be Exceeding the top of the liner is 3 to 5 mm. The angle between the blade and the gravure cylinder should be 55° to 60° and tilted upward.
(3) During the operation of the equipment, the swing amplitude of the scraper should be 5~10mm, and the swing period should be 2~5s.
(4) Before the official printing, the scraper should be fully ground with 1000# sandpaper.
(5) According to the drying speed of the ink, set a reasonable distance between the doctor blade point and the ink transfer point.
(6) For inks that are not scraped off in the non-image area, by appropriately reducing the running speed of the equipment, adding a blow pipe in the non-image area of the gravure cylinder, adding anti-cavitation aid in the ink proportionally, or not causing the net In the case of failure, appropriate measures such as quick-drying solvent are added to dry the ink in time to avoid the occurrence of dirty failure on the surface of the film.
Third, the ink and dilution solvent
1, the cause analysis
(1) The particles of the resin binder and the pigment in the ink are too large, so that they cannot be sufficiently dissolved by the dilution solvent, so that a large amount of particles are collected at the edge of the blade, although the blade of the blade can grind and disperse the particles, but still in the non-gravity roller The image area leaves ink marks, which in turn causes a dirty fault.
(2) The ink viscosity is too high, resulting in a deeper degree of wear between the gravure cylinder and the blade, which in turn causes a dirty failure.
(3) The dilute solvent of the gravure ink is mostly a mixed solvent. During the high-speed operation of the device, the fast-drying solvent will be volatilized in a large amount, and the slow-drying solvent will gradually accumulate in the ink tank, even if a new dilution solvent is continuously added for adjustment. The equilibrium ratio of the mixed solvent is also changed, resulting in slow drying of the ink, weakening of the solubility, and deterioration of the squeegee effect, so that residual ink marks are transferred to the surface of the film to cause a clogging failure.
2, countermeasures
(1) Using a dilution solvent with strong dissolving ability, a magnetic dispersing rod is placed in the ink tank, an antistatic agent may be added if necessary, and the ink manufacturer is required to finely process the ink, and the inks of different manufacturers cannot be mixed.
(2) For different color inks, filter the filter with the corresponding mesh number. In addition, a filter of 80 to 100 mesh is installed in the circulating inking unit, and the ink reflowed from the ink tank is filtered through the filter before printing.
(3) Use ink with a shorter storage time to reduce the residence time of the ink in the ink tray and the circulating inking unit. For inks with a residence time of more than two hours, the filter should be re-filtered with 150 mesh or more and adjusted to normal. The viscosity is used while stirring well to give the ink good solubility.
(4) The viscosity of the spot color and the single color ink should be moderate, and ensure the stability of the ink viscosity during the gravure printing process. The commonly used benzene-free ketone-free ink has higher viscosity requirements. In order to stabilize the viscosity of the ink, the ink viscosity should be tested every half hour and the dilution solvent should be replenished in time.
(5) Reusing the remaining ink by adding new ink, and determining the mixing ratio of the new and old ink according to the ink storage time, which is determined by the ink being sufficiently dissolved.
Fourth, the workshop environment
1, the cause analysis
Improper temperature and humidity in the production workshop and poor air cleanliness may cause dirty problems.
(1) If the temperature in the production workshop is too high, the volatilization speed of the dilution solvent and the drying speed of the ink will be accelerated. If the adjustment is not timely, the viscosity of the ink will increase, which may cause difficulty in scraping the ink, and it is not only easy to damage the gravure cylinder and the scraper. There will also be a dirty fault.
(2) If the humidity in the production workshop is too large, the solubility of the ink will be deteriorated, causing the ink particles to aggregate and cause a dirty failure.
(3) There is more dust in the air in the production workshop. If the equipment is not regularly cleaned, under the action of static electricity, the dust is easily adsorbed on the surface of the film and transferred to the surface of the gravure cylinder during the printing process, or accumulated in the ink. This causes a dirty fault.
2, countermeasures
The temperature of the production workshop should be controlled at 18~28°C as much as possible, and the humidity should be controlled at 45%~75%. At the same time, the sealing of the gravure production environment should be maintained, and the air filtration system should be installed to maintain a certain positive pressure environment in the production workshop. At the same time, pay attention to the regular cleaning of the equipment, especially around the ink tank, it is best to clean it once a day.
Failure Analysis and Corresponding Strategy of Film Gravure
Fifth, production operations
1, the cause analysis
Improper production operations can also cause dirty problems, such as pre-press preparation work is not in place, equipment debugging is not appropriate.
2, countermeasures
(1) The film gravure printing enterprise should do a good job of pre-press preparation, including the requirements for equipment cleaning, gravure cylinder and scraper installation and debugging requirements, ink blending, etc., in daily operation procedures, and the operator should strictly implement it.
(2) When the non-image area of the gravure cylinder is immersed in the ink due to improper operation, the running speed of the equipment is raised to about 150m/min, the blade pressure is adjusted to the normal state, and then the two are kept in the running-in operation for about 5 minutes. Make sure that it does not cause a dirty failure before the official printing.
(3) When the downtime exceeds 20 minutes, the blade should be kept away from the surface of the gravure cylinder to reduce the degree of wear of the blade and the gravure cylinder. When the machine is turned on again, the two should be fully ground and cleaned.