With the development of economy, the wide application of labels on commodities has led to the rapid development of the label printing industry. However, at present, people know much less about label printing inks than about the label materials, printing methods, etc. Label printing inks need to be recognized and explored as a mysterious field.
There are many types of label printing inks. According to the different solvents used, they can be divided into three categories: water-based label printing inks, solvent-based label printing inks, and UV label printing inks: (1) Water-based inks are safe, hygienic and non-polluting, and comply with environmental protection requirements. It is beneficial to human health; but there are also drawbacks, such as slow drying rate, low color saturation, poor stability, etc. It is not appropriate to print large areas on the ground, and long-term placement is prone to precipitation and delamination. (2) Solvent-type label printing inks have strong adaptability to label materials, stable performance, and high printing quality; however, there are environmental pollution problems, and some volatile solvents are harmful to the human body. (3) The UV label printing ink has excellent performance, reliable quality and wide application range; but the price is high, and it requires special drying equipment, and also has certain requirements for supporting materials.
When choosing the label printing ink, it is necessary to comprehensively consider the types of printing materials, printing methods and printing conditions, customer's special requirements, post-press processing technology, the use of the label and the conditions of use, cost and other factors. The properties of label printing inks mainly include hue, fineness, saturation, glossiness, adhesion, viscosity, and drying properties. These properties have an important influence on the printing process and print quality.
The impact of the printing shop environment on ink performance and print quality is mainly reflected in the following two aspects:
(1) The viscosity and dryness of the ink are sensitive to the ambient temperature. When the temperature rises, the ink viscosity decreases, and the drying speed becomes faster.
On the contrary, the ink viscosity increases and the drying speed becomes slower. In addition, the humidity of the environment has an influence on the dryness of the ink. Too high humidity in the workshop is not conducive to the drying of the ink; if the workshop is too dry, it is easy to cause printing failure due to static electricity.
(2) The hygienic condition of the printing shop is also very important. Therefore, the printing shop should be kept clean, dust-free and well ventilated and exhausted.
In the printing process, we often encounter problems such as poor adhesion of ink, poor drying of ink, adhesion of ink layer, bubbles, paste plate, dry plate, poor ink transfer, color deviation, etc. 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 substrate, and ink properties are poor. Solution: surface treatment of substrate materials, adding wetting agent to reduce ink tension, replace ink.
(2) Poor ink dryness. 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 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 version. 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) Bad 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, improper ink drying speed, poor ink stability, performance of printing materials, and changes in the printing process. Solution: Replace the ink, adjust the solvent ratio, and adjust the printing process parameters.
(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.