Analysis of Causes of Poor Saturation of Spot Color Inks
During the printing process, the saturation of the spot color ink has an important influence on the effect of the printed matter. So today we will explain in detail the reasons for the poor saturation of spot color inks during the printing process.
The concept of ink saturation: mainly refers to the fact that the ink cannot show a smooth and full printing effect on the substrate during normal printing.
State of performance: From the appearance of the printed matter, it is observed with the naked eye that it is densely granular and the ink particles are coarse. Observed by a microscope, the ink dispersibility is poor, the resin and the pigment are separated, and the ink dots appear to be severe.
There is a problem of poor saturation. According to what we have encountered, such problems generally appear in green, pink, purple, etc. We need to analyze why this type of problem occurs, and we need to analyze it from the source. The following is the author's analysis and summary.
The main factors that affect the saturation of ink printing are as follows:
1. Viscosity value. The viscosity of the ink should be controlled within a proper range, which means that the viscosity must be proportional to your vehicle speed and solvent drying speed. The printing machine we are currently using is a high-speed printing machine. In the process of high-speed operation, the solvent volatilization speed is relatively fast, and the viscosity of the ink is required to be relatively low. The higher the viscosity, the lower the ink transfer rate. For example, when the speed of our production machine is 150 m/min, the viscosity of the spot color should be 16-18 seconds. If this viscosity is well controlled, it will have a very important effect on the ink bloom. In the case of faster speed, the viscosity can also be reduced to 15S for production.
2. Embossing roller. It is more important to choose the right pressure roller. The spot color layout is large, and the transfer rate of the ink on the plate roller is relatively high. If the printing roller with higher hardness is selected for production, the ink cannot be well leveled and wetted on the entire plate surface during transfer, which will reduce the ink content. Transfer rate to the printing substrate. When the soft press roller is selected for production, when the press roller and the plate roller are in high-speed printing, the flexible space between the ink and the press roller allows the ink to be effectively transferred to the printing material. But the premise is: the pressure value of the soft pressing roller must be within the range of 0.18-0.2MPA, and the pressing roller must be kept clean, and there must be no foreign matter that affects the entire ink transfer. The pressing roller can choose a soft pressing roller of 60-65 degrees for printing.
3. Ink. Similar problems are prone to occur when all the old inks are used for production. Old ink is mainly stored for a long time. If you do not pay attention to sealing, ink oxidation may occur, the solvent in the ink evaporates, and the water in the air is absorbed. The resin and pigment in the ink are relatively reduced, and the gloss of the ink decreases. Therefore, it is not possible to use all the old inks for production. The old and new inks must be used together, and the ratio should be around 7:3. Before using the old ink on the machine, be sure to stir it thoroughly and filter it on the machine. Secondly, the fineness and type of ink will also affect the ink bloom problem! Using a better stirring roller to keep good rotation can effectively improve the ink guiding effect of the stirring roller and improve the leveling of the ink, which has a certain effect on the ink bloom. If necessary, polyurethane ink can be used for production. It can be adjusted by adding a small amount of white ink. The premise is that the color must be darker to avoid large fluctuations in the color. A small amount of white ink can be added to have a certain effect.
4. Solvent. The solvent ratio is the key. In high-speed printing, the drying speed of the solvent should not be too fast, and slow-drying solvents should be used for production! Now we are using fat-soluble benzene-free ketone-free chlorinated polypropylene ink, n-propyl is the main solvent, butyl ester, and isopropanol are the co-solvents. When the main solvent volatilizes quickly during the production process, it will cause the solvent system to be unbalanced, and other printing problems such as knife lines and plate blocking will occur. Note: The principle of adding the solvent frequently, adding less frequently, add it from the ink filter socks and stir while not adding it from the ink basin, and the force should not be too strong, otherwise it will affect the hue of the ink.
5. Scraper angle. The squeegee for the spot color edition should not be too hard. It can be relatively soft. The distance between the squeegee and the impression roller can be relatively far. The angle of the squeegee should be produced at an angle of 45-50 degrees, and it should not be too flat or too steep! In this way, the problem of ink bloom and dry plate can be considered.
6. Production Environment. When we shut down in the early stage, a layer of water mist will appear on the surface of the plate roller. The current relative humidity in our workshop is measured to be 80%. A normal relative humidity in the printing workshop is 50%. When printing in a humid environment, moisture will penetrate into the ink and solvent through the air, causing the solubility and leveling transfer of the ink to deteriorate, and the water content of the solvent exceeds the standard, resulting in ink blooming. In addition, dust and foreign matter brought in from the raw materials will be electrostatically attracted to the pressure roller, resulting in a thick layer, which will have a certain impact on the transfer of the pressure roller.
7. Plate roller. If the mesh of the plate roller is relatively deep and the grooves of the plate roller are not well done, the ink cannot be leveled normally, and the ink transfer rate will be effectively reduced. In addition, if the mesh of the plate roller is clogged, the transfer rate of the ink will decrease, which will also have a certain impact on the ink bloom. In particular, the plate roller must be cleaned after the machine is off, so as not to block the plate and cause the ink to be unable to transfer normally and the hue will also change. Be sure to wash it with solvent before loading and pre-polishing with 600# water sandpaper. If the plate roller is lighter, the amount of ink on the ink will be reduced, and the inability to fill in the ink will also have an impact. It is recommended to produce with a mesh angle of 40-45 degrees.
8. Raw materials. The corona intensity value of the raw material film must be tested before printing. If it is low, the ink cannot be transferred sufficiently, especially in the shallow screen printing, there will be poor transfer and quality problems like blockage. This problem is mainly caused by the surface of the film. The corona impact strength is not good, the film does not form a rough surface, the surface tension of the material is greater than the surface tension of the ink, the ink cannot form effective adhesion on the film, and the ink cannot be transferred sufficiently, so that the ink cannot appear Out effect.
summarized some key words, please keep in mind. The pressure roller is selected for cleaning, viscosity control, solvent ratio, and doctor blade angle. Production Environment. Use ink correctly.