Analysis of the Causes of Full Plate Failure of Plastic Film in Gravure Printing

When using plastic film for gravure printing, products often appear to be printed in full or on a large area. This situation often leads to full version failures due to improper process control or other reasons, and the manifestations of failures in actual products are also different. So it is necessary to conduct a detailed analysis and find the best solution from it. In summary, there are several main types of full plate malfunctions, including full plate white ink, full plate color ink, large area white ink, and large area color ink.
The cause of full version failure
1. When the gravure printing is full of white ink, it is easy to cause quality issues with the full plate. The main manifestation is that the ink scraper on the printing plate cannot scrape clean, causing excess ink that is not in the mesh hole to be printed on the film with the operation of the plate roller. Usually, this situation is not easy to occur in the new version, but the premise is that the pressure and angle of the printing scraper should be moderate. Under normal circumstances, the pressure of the scraper cannot exceed 3kg, and the optimal angle is 35 degrees. We know that excessive pressure will severely wear out the printing plate and shorten its service life. A large angle of the printing scraper can also affect the service life of the printing plate, while a small angle can lead to full plate failure. In addition, the balance of the scraper is also important, and it is generally required that the scraper be parallel. Mainly refers to the elongation distance between the blade and the scraper holder, as well as the tangent distance between the scraper edge and the printing plate. If the left side of the tool holder is higher than the right side or the right side is higher than the left side, full plate quality accidents often occur. The elongation of the blade generally does not exceed the distance of the blade holder by 2.5cm, and the optimal state is that the blade's toughness is generally at 45 degrees from the printing plate tangent.
The optimal printing angle and pressure position are prerequisites for ensuring uniform ink application, and a large amount of ink application can also cause quality accidents in the full plate. Excessive consideration of ink cost by manufacturers may also lead to full plate accidents, as some products require composite aluminum coatings to be free from white spots or rough white ink particles. Some manufacturers will use low-priced white ink to compensate. If the quality of cheap white ink is poor and the particles are rough, it may cause the full plate fault mentioned above. Poor quality white ink particles not only have poor covering power, but are also more prone to compound white spot faults; At the same time, it will lead to the lifespan of the scraper and the plate drum.
In the process of gravure printing, the production of white ink is relatively simple and the price is much lower than other color inks. Poor quality white ink has a yellowish hue, and the most common issue is that the fineness of titanium dioxide powder does not meet the requirements, resulting in poor dispersion in the resin and poor printing suitability of the ink. The titanium dioxide in white ink belongs to inorganic substances, and it cannot fuse well with various types of resins belonging to organic polymers due to different polarity. In addition, some manufacturers add titanium dioxide powder as a filler to the resin when processing white ink. This is the direct reason for the reduced lifespan of the scraper and printing plate drum, as well as the unstable periodicity of printed product quality. During the printing process, due to the high hardness of titanium dioxide, rough particles, static electricity, and the continuous reduction of resin, it is often found that there is a thick layer of white material at the bottom of the ink plate when cleaning, which is the reason for the excessive amount of titanium dioxide used. Therefore, flexible packaging printing factories should conduct strict testing on the products provided by ink suppliers, generally with a diameter of ≥ 12 microns for white ink. Testing the fineness of ink is called a fineness meter, and scraping a sample under a certain pressure is called reading a numerical value, which is the fineness value.
2. Different and immiscible inks were used during printing, which means mixing inks from different resin systems. Incompatible printing will cause many printing failures, but in reality, it is impossible for any manufacturer to use the same resin system ink for printing, which is mainly determined by the requirements of graphics and text. In the actual printing process, it should be avoided to mix ink from different resin systems as much as possible to ensure product quality. Mixing inks with different resin systems often leads to quality accidents such as water marks, graphic and text leaks, and obvious defects can occur when composite aluminum coatings are used.
3. The production of full plate is also closely related to the control of ink viscosity. The so-called viscosity refers to the difficulty of liquid or semi flow. Viscosity is crucial at every stage of ink use and is an important indicator for evaluating ink properties. The viscosity of the white film of printing ink is often tested using a 2 # viscosity cup, and it is most suitable for printing between 17 seconds and 19 seconds. The depth of the general printing white plate roller ranges from 35 microns to 40 microns.
The viscosity of ink is often suitable between 14 seconds and 16 seconds. High viscosity and poor mesh hole transfer also result in quality accidents of full plate. If the viscosity of the ink is too high, the following problems can occur: (1) The fluidity decreases correspondingly, making it difficult to fill or unable to fill each mesh hole, making it impossible for the dots to be completely transferred to the substrate, leading to printing faults such as white spots. (2) The impact on the ink scraper increases, making it difficult to scrape the ink and prone to printing faults such as blade lines. (3) It is not conducive to the transfer of ink and is prone to printing faults such as plate blockage.
Ink viscosity is too low and its fluidity is too good, which can cause problems such as water marks and reduced clarity. At the same time, it is also prone to static electricity, which is not conducive to controlling ink color.
Reasons for the phenomenon of full color ink on the plate
Color ink mainly refers to the three primary colors of blue, red, and yellow ink, as well as corresponding spot colors. Such as deep blue, medium red, orange, etc. The first printing problem that is prone to occur with full color ink is twill. There are also many reasons for this phenomenon:
Firstly, there is a quality issue with the printing roller itself. Mainly reflected in poor concentricity or uneven surface, low hardness, etc. In addition, due to pressure issues, there is an imbalance between the left and right sides due to excessive pressure, errors in the fit between the guide pillar and guide sleeve, and overall looseness of the guide pillar. The detection method is to adjust the imprinting drum and carefully observe whether the state of the twill has changed, so as to find the cause based on the results.
Secondly, the reason for the ink. Uneven mixing of ink can also cause the above situation. If the ink is used for a long time, it is recommended to filter to eliminate foreign objects and reduce the generation of twill quality. Water marks, nail marks, and circle marks often occur in spot colored ink with a large amount of white ink added, such as light blue, light yellow, etc. If the above situation also occurs in the primary color ink of printing, it is mostly due to the quality of the ink itself.
Thirdly, the generation of static electricity can also easily cause water marks and nail marks.
Fourthly, the printing speed is closely related, and it should reach a speed of over 100 meters/min.
Fifth, the square roll tension of printing. If the printing tension is too loose and the material cannot be printed evenly and smoothly, it will also produce a twill pattern. The solution is to adjust the tension appropriately according to the requirements of the printed product.
Full version fault - "pitting"
When using intaglio printing for plastic film printing, it is easy to produce pits. Irregular shaped pits are mainly caused by high ink viscosity, and the increase in viscosity is mainly due to rapid solvent evaporation or differences in operating environment temperature and humidity. The solution is to reduce the viscosity of the ink. Generally, the temperature of the printing operating environment should be 21 ℃, and the relative humidity should be controlled at 60%. In addition, the occurrence of irregular spots may also be caused by static electricity, and the solution is to install an electrostatic eliminator. The circular pockmarks are mainly caused by foreign objects on the pressure roller, such as the accumulation of dirt. It is also possible that the printing scraper is damaged, and it should be carefully observed and resolved in conjunction with the actual situation. Regular line pitting is caused by two reasons: there are defects on the pressure roller, which usually appear in one cycle of thickness; Or if there is damage to the printing plate roller, such as leaks, the solution is to repair the plate roller.