Detecting the dryness of gravure printing ink is essentially detecting the speed at which the solvent in the ink evaporates from the ink, or detecting the speed at which the ink becomes solid. The evaporation rate of the solvent in the ink is not only different with all the solvent types used, but also determined by the solvent release of the resin and pigment costs. Does the pure solvent volatilize quickly, the resin liquid will be slower, and the pigment will be slower after adding the pigment. Controlling the volatilization speed of the ink and formulating different drying speed indicators for different pigments are important conditions to ensure the smooth progress of printing.
According to the characteristics of gravure printing, it is necessary to control the dryness (called initial dryness) within a very short period of time (such as 15 seconds, 30 seconds) after printing, and also to control the dryness after printing to before winding and stacking (called It is thorough).
Generally, the initial dryness is 10~60mm/25°C, below 150 seconds can meet the printing dryness requirements, and if it is slower, it will cause staining or rough storage. The determination method is as follows:
(1) Initial dryness Put a little ink at 100 microns of the scraper gauge groove, scrape it off quickly, turn on the stopwatch immediately, use one piece after 30 seconds, align the lower end with the zero scale, stick it flat on the groove, and use it Press the palm quickly, peel off the paper, measure the length of the unstick ink, expressed in millimeters, that is the initial dryness (mm/25°C, relative humidity 65±5°C).
(2) Thorough dryness Place the ink at 100 microns on the scraper (the amount of ink is based on the fullness of the slot) and scrape it off quickly. Immediately cover it with a piece of scraping paper or plastic film, and press it with the palm of your hand. Peel it off immediately; at the same time, use a blank paper to stick the blot until the ink is completely dry at 100 microns and does not stick to the paper. All the time, it is completely dry (seconds/100 microns 25°C, relative humidity 65±5%) .
Precautions:
(1) Timing and operation should be synchronized.
(2) Thoroughly dry ink should be carefully observed from wet to dry.
(3) The two items need to be done three times, and the average value is taken. The error, the initial dryness does not exceed 0.5 mm, and the thorough dryness does not exceed 0.5 seconds.
