The phenomenon of fast drying of flexo printing ink and analysis of its causes

phenomenon:
(1) The ink on the plate and the anilox roller is dry. Can not be successfully transferred to the printed material.
(2) The highlights are not easily printed and the shadows are easily printed (same version).

Cause 1: The solvent in the ink is used improperly. The ink drying speed is too fast and exceeds the normal use conditions.
Solution:
(1) Correct use of printing inks. The use of solvent plus slow-drying agent adjustment, the general new ink drying speed is relatively fast, after using for a period of time, the drying speed will gradually reduce.
(2) Select the appropriate ink for the printed material to reduce the viscosity of the ink or increase the printing speed. Viscosity is the most important control index in the application of ink, it directly affects the ink transfer transfer performance and flexographic printing product quality. Viscosity is the degree to which a fluid resists flow, ie, the internal resistance to fluid flow. The viscosity of the ink is related to the viscosity of the binder, the amount of pigment added, the particle size, the solvent and compatibility, and the degree of dispersion of the pigment and the auxiliary.
(3)

Cause 2: Hot air flows around the plate and the impression cylinder, and the drying temperature is too high.
Solution:
(1) Take care not to pass hot air through the plate and impression cylinder.
(2) Attention should be paid to the heat and heat balance in the drying unit of each printing unit. The oven temperature should be determined according to the speed of the machine and the layout and graphics. When the large area is printed, the temperature is high; the mesh can be adjusted to print, the temperature is low, and even the heating is not performed. system.


Reason 3: From the beginning of the printing, there is a previously dried ink (dry ink) on the printing plate.
Solution: Wash the plate carefully before or after printing at full speed and wait until the plate is dry before printing.
Dryness of ink is a very important technical indicator. In addition to the ink's own performance, the drying speed of the ink is related to the printing speed, the drying ability of the equipment, and the printing materials.

Cause 4: After checking the pH, the ink is still dry on the plate.
Solution: Add 2% propylene glycol.

Cause 5: The ink Fountain is not covered for too long. The active ingredient may evaporate too quickly or PH<8 is not suitable.
Solution: Add stabilizer to prevent evaporation and adjust with stabilizer. After opening the bucket, do not bring in foreign matter, so that it can be used with the opening, to prevent the ammonia in the ink from evaporating and make the ink in an unstable state. Because the water-based ink has a best match point of PH value and viscosity. The normal range of PH value is 8.5~9.5. At this time, the printing performance of water-based ink is the best, and the quality of printed matter is the most stable. As ammonia is constantly evaporating during the printing process, operators will occasionally add new inks and various additives to the fountain, so the pH of the ink may change at any time. When the PH value is higher than 9.5, the alkalinity is too strong, the viscosity of the water-based ink decreases, the drying speed becomes slower, and the durable water property deteriorates; and when the PH value is lower than 8.5, that is, when the alkalinity is too weak, the viscosity of the aqueous ink is too low. It will rise, and the ink will easily dry up and get stuck on the plate and the anilox roller, causing the plate to be dirty and air bubbles to form. In a sense, the control of the pH value is even more important than the viscosity control. Producers associate the PH value with the viscosity for monitoring.

Reason 6: The temperature of the printing shop is high, the water evaporates quickly, and it loses control.
Solution: Changes in the temperature of the shop have a great influence on the drying of the printed matter and must be controlled. The workshop temperature is controlled at about 25°C, and the humidity is controlled within about 60%. It is ideal for printing because the higher humidity and the short-circuit temperature ensure the oxygen in the air and accelerate the movement of the molecules in the ink. It is beneficial for the ink in the ink to contact with the oxygen in the air to form an ink film, thereby accelerating the curing and drying of the ink on the substrate. The humidity of the environment also affects 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 easily generated, causing a series of printing failures.

Cause 7: The number of anilox roller lines was incorrectly selected, and the BCM value was incorrect (too high).
Solution: Exchange.

Source: China Tobacco Packaging Ink Information Network