UV coating is also called UV coating or light curing coating. The main component of UV coating is composed of photosensitive resin, reactive diluent, photoinitiator and auxiliary agent. The principle is that under certain wavelength of ultraviolet irradiation, the system initiates light. The free radical of the reagent initiates the unsaturated double bond in the resin, and the key-locking polymerization reaction occurs rapidly, so that the crosslinked conjunctiva cures.
Its advantages are: high speed of coating, high film brightness, firm film surface after drying, high production efficiency, small occupied space, good mechanical and heat resistance, cold resistance, water resistance, abrasion resistance, etc. After the application of the coating, the surface of the printing can be very bright and smooth. The refraction effect produces a strong sense of the image and the color is more vivid, and the printing product has a high-grade sense. It has a wide range of uses, such as paper, wood, metal, ceramics and other materials with good surface finish and oil-impervious materials.
The disadvantage is that the UV oil itself has a high degree of polymerization and forms a poor polarity of the surface molecules, and has no pores, so the affinity of the UV film is poor. Such as UV film and some inks, plastics, metals and other surfaces do not affinity, commonly known as non-sticky, with a needle stroke will appear to pull off a small piece, to overcome the method is to be coated surface with a layer of adhesive with the underlying or electricity Halo treatment.
Common problems include the following:
1. "Matting" phenomenon causes: a. The ink has crystallized.
b. The surface tension value is large and the wetting effect on the ink layer is not good.
Solve: a. Add 5% lactic acid to the UV oil, destroy the crystallized film, remove the oil, or roughen it.
b. Lower the surface tension value and add surfactants or solvents with lower surface tension values.
2. Scratches and wrinkles Phenomenon: UV oil is too thick and the amount of coating is too large, mainly in roller coating.
Solution: Reduce the viscosity of UV oil and add appropriate amount of alcohol solvent to dilute.
3. Cause of bubble phenomenon: The quality of UV oil used is not high, UV oil itself contains bubbles, mostly occurs in the use of silk screen.
Solution: Use a high-quality UV oil or leave it for a while.
4. Orange peel phenomenon causes: a. UV oil has high viscosity and poor leveling.
b. The applicator roll is too rough and the amount of coating is too large.
c. Uneven pressure.
Solve: a. Reduce viscosity, add leveling agent and appropriate solvent.
b. Use a fine coating roller and reduce the amount of coating.
c. Adjust pressure.
5. Sticky phenomenon reasons: a. Insufficient UV light intensity or too fast.
b. UV light oil storage time is too long.
c. Excessive diluent added to the reaction.
Solve: a. When the curing speed is less than 0.5 seconds machine speed, the UV power should not be less than 120w/cm.
b. Add a certain amount of UV varnish curing accelerator or change the varnish.
c. Pay attention to the rational use of thinner.
6. Adhesion is poor, not painted or flowering.
Reasons: a. Printed ink surface produces crystallized oil, dusting and so on.
b. Ink and ink blending too much dry oil.
c. UV varnish viscosity is too low or thin coating.
d. Rubber coating roller size.
e. Irradiation conditions are not suitable.
f. The UV varnish itself has poor adhesion and poor print material adhesion.
Solve: a. Eliminates the crystallized layer, roughens, removes grease or adds 5% lactic acid.
b. Select ink components that match the UV oil process parameters, or wipe with a cloth.
c. Use a high viscosity UV light oil to increase the amount of coating.
d. Use an anilox roller that matches the UV varnish.
e. Check if the UV lamp is aging, or the speed is inconsistent. Select the appropriate drying conditions.
f. Apply primer or replace special UV varnish or choose a material with good surface properties.
7. Gloss is not good, not enough brightness reasons: a. UV light oil viscosity, thin coating, uneven coating.
b. The printed material is rough and the absorption is too strong.
c. The anilox roller is too thin and the oil supply is too small.
d. Non-participation of dry reaction solvent dilution is excessive.
Solve: a. Appropriately increase the viscosity and coating amount of UV varnish and adjust the coating mechanism to make the coating uniform.
b. Choose a weak absorbent material or apply a primer first.
c. Increase the anilox roller and increase the oil supply.
d. Reduce the addition of non-reactive diluents such as ethanol.
8. White point and pinhole phenomenon: a. The coating is too thin or the anilox roller is too thin.
b. Improper use of thinner.
c. The surface dust is more or the dusting particles are too thick.
Solve: a. Use a suitable anilox roller to increase the coating thickness.
b. A small amount of a smoothing aid is added and the reactive diluent involved in the reaction is used.
c. Keep the surface clean and the environment clean, do not dust or powder, or choose a good quality dusting.
9. Residual odor reasons: a. Incomplete drying, such as insufficient light intensity or too much non-reactive diluent.
b. Poor anti-interference ability.
Solve: a. Curing and drying should be thorough, select the appropriate light source power and speed, reduce the use of non-reactive diluents.
b. Strengthen ventilation exhaust system.
10. UV Varnish thickens or gel phenomenon reasons: a. Storage time is too long.
b. Failure to completely avoid storage c. High storage temperature Solution: a. Use according to the specified time, generally 6 months.
b. Strictly dark storage.
c. Storage temperature must be controlled at about 5 °C ~ 25 °C.
11. Causes of auto-drying after UV curing: After the temperature of the irradiated surface is too high, the polymerization reaction continues.
Solution: Increase the distance between the lamp and the surface of the object to be illuminated, cold air or cold rolling.