Insufficient adhesion of UV varnish and its solution
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Phenomenon: the coating does not stick to the substrate
Reason 1: The surface of the printed ink is "crystallized".
Solution: The printing process must first consider meeting the glazing conditions, changing the process or formulating special varnishes.
Cause 2: The auxiliary material in the printing ink is not suitable.
Solution: The ink supplier solves it.
Reason 3: The UV varnish does not match the surface tension of the printed material, and the adhesion is insufficient.
Solution: pre-treat the surface of the material.
Cause 4: The photocuring conditions are not suitable.
Solution: Check the cause and cure completely.
The following factors should be considered when choosing UV curing:
(1) The absorption spectrum of the photoinitiator is matched as much as possible with the output spectrum of the light source, so that the radiant energy of the light source can be utilized to the utmost.
(2) The intensity should be appropriate, the light is too strong, the free radicals are generated too fast, and the excessively high concentration leads to an increase in the reaction rate, which has an adverse effect on the crosslinking reaction; if the strength is too low, the radicals are generated too slowly.
(3) There should be a good lampshade to collect light.
(4) Since ozone is generated in the air under the irradiation of ultraviolet light, ventilation equipment should be provided at the location. Accurate measurement of UV energy metabolism can provide the necessary information to determine and maintain optimal conditions for effective cure. A commonly used measuring food is a radiometer. Since the radiometer provides data, a real control process can be obtained. After starting up every day, the operator first exposes to the UV system with a radiometer and records the data to see if it is within the normal range required.
(5) Carefully inspect the UV light shielding device to ensure that no excess UV light leaks while ensuring that air can flow into the UV curing system. The air intake filter should be kept clean and free of dust and debris on its surface. If a quartz plate is used in the UV curing process, the quartz plate should be periodically cleaned to ensure that the transmission of UV light is still effective.
Reason 5: UV printing and UV not only ink layers or coatings should not be too thick, otherwise UV inks and UV varnishes will not cure well on the substrate.
Solution: According to the actual situation, the craftsman, quality control and operator determine the coating thickness.
Cause 6: The temperature of the substrate is low and the curing is slow.
Solution: UV varnish should be 50~60 when passing through the UV lamp irradiation area, because UV varnish cures quickly at this temperature and has strong adhesion after curing.
Reason 7: The surface of the non-absorbent material is not corrugated enough.
Solution: Generally, the surface tension should be 3.8x10N or more in order to obtain good adhesion of the ink.
Note when using corona treatment:
(1) A good corona treatment effect can be obtained when the electrode gap is about 1 mm.
(2) The magnitude of the output current has a great influence on the corona treatment effect. The output current is too low, and the corona treatment effect is poor; the output current is increased, and the corona treatment effect is enhanced.
(3) Increasing the treatment temperature, the chemical reaction speed is increased, the reaction degree is increased, the treatment effect is enhanced, but the temperature is not too high, otherwise a new weak interface layer will be formed, and the strength will be decreased. ,
(4) The humidity of the air is large, and the treatment effect is deteriorated, which is due to the absorption of water molecules in the air.