Self-adhesive labels, food labels, daily chemical labels and anti-counterfeit labels are mostly printed with flexographic LED-UV inks. Featuring fast curing, vivid color, excellent scratch resistance and great compatibility with film substrates, these inks are widely used on coated paper, synthetic paper, PP, PE, PET and other common label materials.

This article mainly analyzes typical printing defects caused by ink formula, anilox roller, UV curing energy, substrate surface tension and workshop environment, and provides targeted solutions.
star color uv label ink

1. Insufficient Curing, Stickiness and Blocking

Phenomenon

The printed ink surface remains sticky, resulting in smudging and offset after stacking. Ink peels off easily when scratched lightly, and inner labels stick together after rewinding.

Causes

  1. Insufficient power of UV lamps or aging LED beads lead to inadequate curing energy.
  2. Excess printing speed and overly thick ink layer cause surface curing while inner layer remains uncured.
  3. High workshop humidity inhibits photochemical curing reaction.

Solutions

  1. Control standard curing energy at 800-1200mJ/cm² and replace aged light sources timely.
  2. Reduce printing speed and adopt higher mesh anilox roller to form thinner ink film.
  3. Keep workshop humidity between 40% and 60%, and turn on dehumidifier in humid weather.

2. Printing Color Difference and Unstable Shade

Phenomenon

Obvious color deviation exists between different label rolls, failing to match standard color samples.

Causes

  1. Uneven wear of anilox roller leads to unstable ink transfer volume.
  2. Inadequate ink stirring causes pigment sedimentation and separation.
  3. Fluctuating UV curing temperature results in slight pigment discoloration.
  4. Mixed use of inks from different batches brings inconsistent hue.

Solutions

  1. Clean and inspect anilox roller regularly, replace severely worn ones to ensure stable ink delivery.
  2. Fully stir new ink for 8-15 minutes before use, and re-stir after long-time shutdown.
  3. Stabilize LED curing temperature within 30-50℃ to avoid color fading under high heat.
  4. Use ink from the same batch for one single order and confirm color matching before refilling ink.

3. Poor Ink Adhesion

Phenomenon

Ink falls off easily after tape peeling or nail scratching, and delamination occurs after lamination.

Causes

  1. Surface tension of film labels is lower than 38 dyn.
  2. Mismatched ink type; general UV ink cannot fit PE and PET films well.
  3. Static electricity, oil stains and dust remain on substrate surface.
  4. Low content of film-forming resin in ink formula.

Solutions

  1. Carry out corona treatment on film substrates to raise surface tension to 40-44 dyn.
  2. Select matched ink: general UV ink for paper labels, special film-type flexo UV ink for plastic films.
  3. Remove oil, dust and static electricity on substrate before printing.
  4. Adopt high-adhesion professional label UV ink with optimized resin system.

4. Plate Clogging, Spots and Fine Screen Blockage

Phenomenon

  • Fine dots get blocked after long-time printing, accompanied with dirt spots and ink flying.

Causes

  1. Excessive coarse fillers and insufficient fineness of ink.
  2. Much floating dust in printing workshop falls onto printing plate.
  3. Residual ink on plate pre-cures and crusts during downtime.

Solutions

  1. Use high-fineness dedicated label UV ink with fewer coarse particles.
  2. Keep workshop clean and reduce dust pollution.
  3. Clean anilox roller and ink supply system regularly to avoid impurity accumulation.

5. Pinholes and Cratering on Printed Surface

Phenomenon

Tiny holes and round craters appear on ink layer, failing to fully cover the substrate.

Causes

  1. Silicone oil, release agent and oil contamination remain on label surface.
  2. Mismatched surface tension between ink and substrate.
  3. Dust and oil mist mix into ink during production.

Solutions

  1. Thoroughly remove release agent and oil stains on label surface.
  2. Add appropriate UV leveling agent to improve ink wettability and spreadability.
  3. Store ink in sealed container to prevent external dust and oil mist pollution.

 

FAQ

1. What is the optimal curing energy for flexo UV label printing?
For ordinary paper labels: 800-1000mJ/cm²; for film labels: 1000-1200mJ/cm², balancing curing effect and adhesion performance.

2. How to solve ink peeling problem on PE synthetic paper labels quickly?
Strengthen corona treatment to improve surface tension, replace with special film flexo UV ink, and properly lower curing strength to prevent brittle ink film.

3. How to improve plate clogging in high-speed label printing?
Choose low-viscosity high-fluidity label UV ink, match with suitable mesh anilox roller, clean printing plate regularly and control workshop dust strictly.

4. How to solve color overlapping and bleeding in UV label printing?
Ensure full curing of the first color before overprinting, reduce bottom ink layer thickness and adopt anti-migration type label UV ink.

5. How to improve ink stickiness in low-temperature workshop in winter?
Raise workshop temperature above 20℃, properly increase curing energy and reduce the addition of slow-drying additives.