UV Varnish Adhesion Causes and Solutions

Symptom: The coating does not adhere to the substrate.

Cause 1: The surface of the printed ink is "crystallized".
The solution: The printing process must first consider satisfying the conditions of the glazing, change the process or formulate the special varnishes.

Cause 2: The auxiliary material in the printing ink is not suitable.
Solution: ink suppliers to solve.

Cause 3: The surface tension of the UV varnish and printing material does not match and the adhesion is insufficient.
Solution: pre-print material surface before printing.

Cause 4: The light curing conditions are not suitable.
Solution: Check the cause and completely cure it.
Select UV curing should consider the following factors:
(1) The absorption spectrum of the photoinitiator should be matched with the output spectrum of the light source as much as possible so as to make maximum use of the radiant energy of the light source.
(2) The strength should be appropriate, the light is too strong, the free radicals are generated too fast, the reaction rate is increased due to the high concentration, and the cross-linking reaction is adversely affected; if the intensity is too low, the free radicals are generated too slowly.
(3) There should be a good lampshade condenser.
(4) Because the ozone is generated in the air under the irradiation of ultraviolet light, the location should have ventilation equipment. Accurately measuring UV energy metabolism can provide the necessary information to determine and maintain the most suitable conditions for effective curing. The commonly used measurement food is a radiometer. Because the radiometer provides data, it can get a real control process. After starting up every day, the operator first exposes the radiometer to the UV system and records the data to see if it is within the required normal range.
(5) Carefully check the UV light shielding device to ensure that there is no leakage of excess UV light while air is allowed to flow into the UV light curing system. The air intake filter should be kept clean with no dust and debris remaining on its surface. If a quartz plate is used during UV light curing, the quartz plate should be periodically cleaned to ensure that the nature of the transmitted UV light is still valid.

Reason 5: UV printing and UV ink layer or coating can not be too thick, or UV ink and UV not only can not be cured on the substrate.
Solution: According to the actual situation, the technologist, quality control personnel and operators decide the coating thickness.

Reason 6: The temperature of the printing material is low and curing is slow.
Solution: When the UV varnish passes through the UV lamp irradiation zone, the temperature should be 50 to 60, because the UV varnish cures quickly at this temperature and has strong adhesion after curing.

Cause 7: The degree of corona treatment on the non-absorbing material surface is not enough.
Solution: The general surface tension should reach 3.8x10N or more to get good adhesion of the ink.
Care should be taken when using corona treatment:
(1) A good corona treatment effect can be obtained when the electrode gap is approximately 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) To increase the treatment temperature, the chemical reaction rate is accelerated, the reaction degree is increased, and the treatment effect is enhanced, but the temperature should not be too high, otherwise a new weak interface layer will be formed, and the strength will be decreased. ,
(4) The humidity of the air is high, and the treatment effect will be poor. This is due to the absorption of water molecules in the air8:
Solution:

Source: China Tobacco Packaging Ink Information Network