Common Issues and Solutions in UV Coating Process

Common Issues and Solutions in UV Coating Process

During the coating process,there are often many issues with the UV coating process.Below is a list of these issues along with discussions on how to resolve them:

Pitting Phenomenon

Causes:

a.Ink has undergone crystallization.

b.High surface tension,poor wetting of the ink layer.

Solutions:

a.Add 5%lactic acid to the UV varnish to break the crystallized film or remove the oil quality or perform a roughening treatment.

b.Reduce surface tension by adding surfactants or solvents with lower surface tension.

Streaking and Wrinkling Phenomenon

Causes:

a.UV varnish is too thick,excessive application,mainly occurring in roller coating.

Solutions:

a.Reduce the viscosity of the UV varnish by adding an appropriate amount of alcohol solvent to dilute it.

Bubbling Phenomenon

Causes:

a.Poor quality of the UV varnish,which contains bubbles,often occurring in screen coating.

Solutions:

a.Switch to high-quality UV varnish or let it stand for a while before use.

Orange Peel Phenomenon

Causes:

a.High viscosity of UV varnish,poor leveling.

b.Coating roller is too coarse and not smooth,with excessive application.

c.Uneven pressure.

Solutions:

a.Reduce viscosity by adding leveling agents and appropriate solvents.

b.Select a finer coating roller and reduce the application amount.

c.Adjust the pressure.

Sticky Phenomenon

Causes:

a.Insufficient ultraviolet light intensity or too fast machine speed.

b.UV varnish has been stored for too long.

c.Excessive addition of non-reactive diluents.

Solutions:

a.When the curing speed is less than 0.5 seconds,the ultraviolet light power should be no less than 120w/cm.

b.Add a certain amount of UV varnish curing accelerator or replace the varnish.

c.Pay attention to the reasonable use of diluents.

Poor Adhesion,Inability to Coat or Mottling Phenomenon

Causes:

a.Crystallized oil or spray powder on the surface of the printed material,

b.excessive ink and drying oil in the water-based ink.

c.Too low viscosity of UV varnish or too thin coating.

d.Too fine an anilox roller.

e.Inappropriate UV curing conditions.

f.Poor adhesion of the UV varnish itself and poor adhesion of the printed material.

Solutions:

a.Eliminate the crystallized layer,perform roughening treatment or add 5%lactic acid.

b.Choose ink auxiliaries that match the UV oil process parameters,or wipe with a cloth.

c.Use high-viscosity UV varnish and increase the application amount.

d.Replace the anilox roller that matches the UV varnish.

e.Check if the ultraviolet mercury lamp tube is aged,or if the machine speed is not suitable,and choose appropriate drying conditions.

f.Apply a primer or replace with special UV varnish or choose materials with good surface properties.

Lack of Gloss and Brightness

Causes:

a.Too low viscosity of UV varnish,too thin coating,uneven application.

b.Rough printing material with strong absorption.

c.Too fine an anilox roller,too little oil supply.

d.Excessive dilution with non-reactive solvents.

Solutions:

a.Appropriately increase the viscosity and application amount of UV varnish,adjust the application mechanism to ensure even application.

b.Choose materials with weak absorption,or apply a primer first.

c.Increase the anilox roller to improve oil supply.

d.Reduce the addition of non-reactive diluents such as ethanol.

White Spot and Pinhole Phenomenon

Causes:

a.Too thin application or too fine an anilox roller.

b.Inappropriate selection of diluents.

c.Excessive surface dust or coarse spray powder particles.

Solutions:

a.Select appropriate anilox rollers and increase the coating thickness.

b.Add a small amount of smoothing agent and use reactive diluents that participate in the reaction.

c.Maintain surface cleanliness and environmental cleanliness,do not spray powder or spray less powder or choose high-quality spray powder.

Strong Residual Odor

Causes:

a.Incomplete drying,such as insufficient light intensity or excessive non-reactive diluents.

b.Poor antioxidant interference capability.

Solutions:

a.Ensure thorough curing and drying,choose appropriate light source power and machine speed,reduce or avoid the use of non-reactive diluents.

b.Strengthen the ventilation and exhaust system.

UV Varnish Thickening or Gelation Phenomenon

Causes:

a.Excessive storage time.

b.Incomplete light avoidance during storage.

c.Storage temperature is too high.

Solutions:

a.Use within the specified time,generally 6 months.

b.Strictly store in a light-avoiding manner.

c.The storage temperature must be controlled around 5℃25℃.

UV Curing and Automatic Bursting

Causes:

a.After the surface temperature is too high,the polymerization reaction continues.

Solutions:

a.If the surface temperature is too high,increase the distance between the lamp tube and the surface of the object being illuminated,and use cold air or a cold roller press.