â– Reporter: What are the major performance requirements for label printing inks? How do they affect label printing?
Guests: The performance indicators of label printing inks mainly include hue, fineness, saturation, gloss, adhesion, viscosity, and drying properties. These properties have a very important influence on the printing process and print quality. Here are some of the performance indicators highlighted.
(1) The stability of the ink viscosity is one of the prerequisites for ensuring the consistency of the quality of the printed matter. The high or low viscosity of the ink is not conducive to printing. Therefore, the control of the viscosity of the ink is very important. Generally speaking, in the printing process, as the moisture and solvent in the ink continuously evaporate, the ink viscosity will gradually increase, so the viscosity of the ink should be measured frequently, and the viscosity change record should be made and adjusted in time.
(2) The dryness of the ink also has a great influence on the label printing. Drying too quickly may cause the pattern to become lighter or even dry. If the drying is too slow, it may cause the ink to stick or the print to become dirty. In general, the drying speed of the ink should be compatible with the printing speed, the drying ability of the printing apparatus, and the area of ​​the printed pattern.
(3) pH value control is very important for water-based label printing inks, usually between 8 and 9. Changes in the pH of water-based inks can also cause changes in viscosity. Therefore, an appropriate amount of pH stabilizer is added to the ink at regular intervals during the printing process.
â– Reporter: What impact does the printing room environment have on the performance of label printing inks and print quality?
Guests: The printing shop environment has a great influence on ink performance and printing quality, which is mainly reflected in the following two aspects.
(1) The effect of the temperature and humidity of the printing shop on the performance of the ink. The viscosity and dryness of the ink are sensitive to the ambient temperature. When the temperature rises, the viscosity of the ink decreases and the drying speed becomes relatively faster. On the contrary, the ink viscosity increases and the drying speed becomes slower. In addition, the humidity of the environment has an effect on the dryness of the ink. Too high humidity in the workshop is not conducive to the drying of the ink. On the contrary, if the workshop is too dry, static electricity is likely to occur, causing a series of printing failures. Therefore, if conditions permit, it is best to install air conditioning and humidity control equipment in the printing shop so that the temperature and humidity in the workshop can be kept constant to facilitate the stability of the printing process. In general, the temperature of the printing shop is controlled at 18-25°C and the humidity is controlled at 55%-65%.
(2) The hygienic condition of the printing shop is also very important. If the hygienic conditions in the workshop are relatively poor, a large amount of dust particles or various foreign particles may fall into the ink tank or adsorb on the surface of the label material, thereby affecting the printing quality. Therefore, the printing shop should be kept clean, dust-free and well ventilated and exhausted.
â– Reporter: What problems have you encountered in using label printing inks? How to solve?
Guests: In the printing process, we often encounter problems such as poor adhesion of ink, poor drying of ink, adhesion of ink layers, bubbles, paste plate, dry plate, poor ink transfer, and color shift. These failures are analyzed as follows.
(1) Poor adhesion of ink. Reason: The surface tension of the substrate is too low, the type of ink does not match the type of substrate, and the performance of the ink is poor. Solution: surface treatment of substrate materials, adding wetting agent to reduce ink tension, replace ink.
(2) Poor ink drying. Reasons: Improper ink solvent ratio, too fast printing speed, and high ambient humidity. Solution: Adjust the solvent ratio, reduce the printing speed, increase the drying temperature, and reduce the ambient humidity.
(3) Ink adhesion. Reasons: poor ink drying, ink is too soft, printing pressure is too large, the environment humidity is too high. Solution: Adjust ink solvent ratio, add appropriate amount of anti-adhesive agent, increase drying temperature, reduce printing pressure, and reduce environmental humidity.
(4) Bubbles. Cause: The ink contains air, the surface tension of the ink is too large, the ink viscosity is too low, and the printing speed is too fast. Solution: Add an appropriate amount of defoamer, adjust the ink viscosity, and appropriately reduce the printing speed.
(5) Paste. Cause: The ink pigment particles are too thick, the ink viscosity is too high, the amount of ink is too large, the printing pressure is too high. Solution: Replace the ink, reduce the viscosity of the ink, reduce the amount of ink, and reduce the printing pressure.
(6) Dry version. Reason: The ink is drying too fast, the drying temperature is too high, the printing speed is too slow. Solution: Adjust the ink solvent ratio, reduce the drying temperature properly, and increase the printing speed.
(7) Poor ink transfer. Cause: The type of ink and printing materials do not match, ink viscosity is too high, static electricity and so on. Solution: Replace ink, adjust ink viscosity, add antistatic agent.
(8) Color cast. Reasons: Inaccurate hue of ink, inappropriate ink drying speed, poor ink stability, changes in the properties of the substrate, and changes in the printing process. Solution: Replace ink, adjust solvent ratio, adjust printing process parameters, etc.
(9) Static electricity. Cause: The ink is too thin, the printing speed is too fast, and the environment is too dry. Solution: Add antistatic agent, increase ink viscosity, reduce printing speed, adjust humidity, etc.
â– Reporter: What issues should be noted during the use of label printing inks?
Guests: In the printing process, we should also pay attention to the following issues.
(1) Try to use the same brand of ink produced by the same ink manufacturer to avoid mixing different manufacturers and different types of ink to prevent printing failures.
(2) Before the ink is used, it must be fully stirred, and it must be stirred frequently during the printing process to ensure that the ink system is dispersed evenly.
(3) Each time the formulated ink should not be too much, the principle of “adding less, adding more†should be followed, which is not only beneficial to the stability of ink performance, but also can effectively avoid waste. In addition, for spot color inks, you should also make a deployment record.
(4) In the printing process, in order to ensure the quality of label prints and smooth production, some auxiliaries may be added to the ink, such as antistatic agents, defoamers, and rewinders, etc. Control within the specified range, otherwise it may cause quality accidents.
â– Reporter: What are the shortcomings of label printing inks currently on the market?
Guests: The most prominent issue is the ink hue deviation problem. On the one hand, the hue of the same ink produced by different ink manufacturers is different, such as the same color red ink, some manufacturers' hue is red, and some manufacturers' hue is yellow, and the degree of color shift is also different. On the other hand, even if the same type of ink produced by the same manufacturer has a different batch, the hue may be deviated and sometimes there may even be a large deviation. For this reason, label printing plants often have to stop for adjustments, which is very detrimental to the stability of the printing quality, and it also brings great inconvenience to production and seriously hinders the improvement of the quality of printed matter.
In addition, there is still a certain gap between domestic ink and imported ink, especially in the high-end product market. Therefore, domestic ink manufacturers should improve their technical level and production capacity as soon as possible, and drive the overall level of the entire ink manufacturing industry. The improvement.
(to be continued)