Some common faults and solutions of UV varnish

In recent years, UV varnish has been used more and more after the UV printer prints the pattern. In addition to making the pattern bright and shiny, this post-processing process can also have the characteristics of friction resistance and weather resistance. However, many faults may occur during use.

1. Poor gloss and insufficient brightness

Main reasons:

1) The viscosity of UV varnish is too small and the coating is too thin;

2) Excessive dilution of non-reactive solvents such as ethanol;

3) Uneven application of UV varnish.

Solution: 

Appropriately increase the viscosity and application amount of UV varnish according to the different conditions of the material.

2. Poor drying, incomplete light curing, and sticky surface

Main reasons:

1) Insufficient UV light intensity;

2) Aging and weakening of UV lamp tubes;

3) UV varnish storage time is too long;

4) Too much diluent that does not participate in the reaction is added;

5) The machine speed is too fast.

Solution: 

When the curing speed is required to be less than 0.5s, the power of the LED curing lamp must be guaranteed to be generally not less than 120w/cm, and the lamp tube (bead) must be updated in time, and not wait until it breaks before replacing.

3. The UV varnish on the surface of the printed matter cannot be applied and is flowery

Main reasons:

1) The viscosity of the UV varnish is low and the coating is too thin;

2) The ink contains too much varnish or drying oil;

3) The surface of the ink has crystallized.

Solution: 

When printing products that require UV varnishing, apply UV varnish thicker. If necessary, the problem can be solved by replacing special varnish.

4. There are white spots and pinholes in the UV varnish

Main reasons:

1) The coating is too thin;

2) Excessive addition of non-reactive diluent (such as ethanol);

3) There is a lot of dust on the surface of the printed matter.

Solution: 

The production environment and the surface of the printed matter should be kept clean and the coating thickness should be increased.

5. Uneven surface coating and streaking

Main reasons:

1) UV varnish viscosity is too high;

2) The coating is too rough and not smooth;

3) Excessive coating amount;

4) Poor leveling of UV varnish.

Solution: 

Reduce the viscosity of UV varnish and reduce the amount of coating.

6. Poor adhesion of UV varnish

Main reasons:

1) Crystallization of printed ink surface;

2) Inappropriate auxiliary materials in printing ink;

3) Insufficient adhesion of UV varnish itself;

4) Improper light curing conditions.

Solution: 

The printing process should consider the varnishing conditions in advance.

7. UV varnish becomes thicker and has gelation

Main reasons:

1) UV varnish is stored for too long;

2) The varnish is not completely stored away from light;

3) The storage temperature is too high;

Solution: 

Pay attention to the effective use period of UV varnish and store it in strict light-proof conditions. The storage temperature should be 5℃~25℃.

8. Strong residual odor

Main reasons:

1) Incomplete drying and curing;

2) Insufficient UV light source or aging of lamp tube;

3) Poor anti-oxidation interference ability of UV varnish.

Solution: 

UV varnish must be dried and cured thoroughly, and ventilation must be strengthened.