Phenomenon and cause analysis of slow drying of th

2022-08-23
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Phenomenon and cause analysis of slow drying of flexographic ink

phenomenon 1: ink expands to other colors (incorrect overprint)

reason 1: improper use of ink additives makes the viscosity too low or the ink has denatured

solution: use quick drying additives to adjust and improve the drying speed

the dryness of ink also has a great impact on printing. Too fast drying is easy to cause the pattern to become shallow or even dry the plate, and too slow drying is easy to cause ink adhesion or dirty prints. Generally speaking, the drying speed of the ink should be compatible with the printing speed, the drying capacity of the printing equipment and the area of the printed pattern

phenomenon 2: there is ink on the roller or printed matter

reason 1: the ink viscosity is too high, the ink layer is too thick, and the ink volume is large. If the ink layer is too thick, the contact area between the ink layer and the air will be reduced, and the contact between the ink and the paper will be reduced, and the oxidation conjunctiva and penetration will be affected

solution:

(1) preheat in advance before starting up. Adjust the viscosity of the ink reasonably, and measure it every 20~30min (adjust the viscosity of the mixture of distilled water and ethanol by 50% each, and measure it with paint cup 4)

(2) use the method of deep ink thin printing to reduce the thickness of the ink layer

(scope of application 3) the amount of ink should be determined by different printing substrates (high gloss, semi high gloss, sub high gloss paper are different)

phenomenon 3: there are sticking spots on the printed matter

reason 1: improper drying or unbalanced drying of the drying system, low drying temperature. The drying capacity affects the driving speed

solution: the temperature of the drying device should be set according to the quantity of paper and the amount of ink. The higher the quantity of gram, the higher the temperature can be due to the decline in the sales of new energy vehicles in the first quarter. Drying also depends on the speed at which the print passes through the drying device

the drying speed should match the printing speed. At the same time, raise the drying temperature. The drying process of ink includes volatilization, absorption and solidification. There are three forms of ink drying:

(1) hot air drying: try to increase or ensure the reasonable adjustment of the impact speed of drying air flow and hot air volume, and make the horizontal air flow uniform. Note that too high a temperature will shrink the material. The drying test shall not be lower than 50 ℃, and the air circulation shall be maintained

(2) infrared drying: infrared produces high heat energy, which is directly radiated to the printed matter. It not only acts on the surface of the printed matter, but also goes deep into the substrate. Its heating amount is comprehensive. It makes the ink layer harden rapidly, forming a tough ink film and improving the wear resistance. Temperature is the main condition to promote oxidative polymerization and volatilization of water and other solvents to form a solid ink film

(3) ultraviolet (UV) curing: a chemical action that instantly turns a liquid fluid into a solid. For the confirmation of the best UV irradiation conditions, you can cross the film with a knife after irradiation, use transparent tape or finger, and its use effect is always rising. Nail is used for stripping test, and the irradiation conditions that can be completely attached (irradiation light quantity and intensity) are the best choice

phenomenon 4: the ink layer will fall off as soon as it is wiped

reason 1: the pH value of ink is 9.5 or the type is improperly selected

solution: adjust the ink with pH stabilizer and select appropriate ink. When the pH value is too high, the drying speed of ink slows down

(1) when the pH value is 6~8, the ink viscosity is high and the ink drying speed is fast. As ammonia and other alkaline components are less, with the evaporation of alkali, the alkali soluble resin slowly returns to the insoluble state. Therefore, the drying speed is faster

(2) when the pH value is 8~9, the ink has good dryness. Because the alkali content of the system is moderate, with the evaporation of some ammonia in the system, the alkali soluble resin will not return to the insoluble state, but will return to the insoluble state only when the evaporation of alkali reaches a certain value, which is more conducive to the volatilization of water and other components in the system, and the dryness is better

(3) when the pH value is 9~11, the ink viscosity is low and the ink drying speed is slow. Because the alkali content in the system is too high, only when a large number of alkali components evaporate, the alkali soluble resin can return to the insoluble state and promote the drying of the ink. And too much alkali content is easy to cause the surface of the ink to dry, and the alkali soluble resin in the inner layer is still in a soluble state

reason 2: the printing speed is too fast and the drying time is too short

solution: reduce the printing speed, increase the hot air and prolong the drying time

reason 3: the workshop temperature is too low, the water evaporation is slow, and the drying is also slow. The depth and breadth of fatigue experimental research on the elastic modulus of paper are increasing, which will not only be affected by some aspects of the paper, but also by the environment. Paper and ink are hygroscopic, and their properties will change greatly when the temperature and humidity change in the environment

solution: adjust and increase the room temperature and exhaust properly. Temperature has a significant effect on the physical and mechanical properties of the processed materials (such as viscosity, fluidity, etc.). In order to make all kinds of properties hang upside down unchanged, it must be in a constant temperature and humidity state (detected by a thermometer). Generally, the higher the temperature, the faster the drying; On the contrary, drying is slower. At the same time, the size of humidity affects the evaporation of water in the ink, which hinders it. If the relative temperature is too high, the drying speed of the ink will be reduced, and the oxidation conjunctiva speed will be slowed down accordingly

reason 4: poor absorption of substrate

solution: select the substrate correctly. The drying performance of paper with high gloss is poor, because the ink accumulates on the surface of the paper and is not volatile

paper can be divided into acid paper, alkaline paper and neutral paper according to pH. Alkaline paper has better ink affinity than acid paper. Too high alkaline is easy to cause problems such as image point enlargement, line thickening, color distortion and so on; And too high acidity will cause the ink layer not easy to dry and the printed matter to rub dirty

therefore, the pH of printing paper must be moderate, the pH value is close to 7, and it is better to be neutral

reason 5: the humidity of the substrate itself is too high, which affects the drying speed of ink

solution: preheat the mechanism before printing to stabilize the moisture content of the substrate

source: information of Chinese cigarette packet ink

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