Intro to UV-Curing System

Outline

  • What’s UV curing technology?
  • Types of UV curing
  • Understanding of UV-curing resins
  • Applications
  • Safety Consideration

What’s UV curing technology?

UV Curing Technology is a technology of instant curing or drying in seconds in which ultraviolet is applied to resins such as coatings, adhesives, marking ink and photo-resists, etc., to cause photopolymerization.

During the process, UV energy is absorbed by a sensitizer (photopolymerization initiator), causing a reaction in the monomer which makes it hard and dry.

The key factors affecting the curing rate:

  • Chemical compounds
  • Thickness of coating
    * The amount of UV energy inside a layer of coating decreases exponentially with depth.
  • Amount of UV per Surface

Types of UV curing

  • Mercury vapor lamps
    (Most traditional, having a broader spectral distribution)
  • UV LED curing
    (emit a narrow spectrum of radiation and can be can be cycled
    on and off)
  • Fluorescent lamps
    (used where the excessive heat of mercury vapor is undesirable, or when an item needs more than a single source of light and instead the item needs to be surrounded by light)

Understanding of UV-curing resin

UV Curable Resin is a compound that consists of: monomer, oligomer, photopolymerization initiator and various additives (stabilizers, fillers, pigments, etc.).

Resin types
Acrylic radical polymerization
Epoxy cationic polymerization

Comparison

Feature Radical Cationic
Major Components Acrylic Epoxy
Curing Contraction 5-10% 2-4%
Curing inhibition by oxygen Inhibited Not inhibited
After curing irradiation Curing stops Curing continues
Curing acceleration by heat Scarced Accelerated
Heat resistance Fair Good
Chemical resistance Fair Good
Flexibility in resin designing High Low

Available curing thickness
The thinner, the better (2-3mm)
Not able to cure over 15mm

Shrinkage rate
Generally, UV-curing resins commonly shrink by 3% to 8% when they change in form from liquid to solid.

Application

Extensively used in inks for UV flexo, screen, and lithographic printing, in over print varnishes as well as in products for potting and encapsulation of sensitive electronic elements. Other important applications include scratch resistant wood, concrete and plastic coatings and UV curable acrylic adhesives.

Safety Consideration

Health Hazards
Acute (4-24 hr after explosure): Redness of the skin called erythema (similar to sunburn).
Chronic: Accelerated skin aging and skin cancer.
Safety Tips

  1. Do not look directly into the UV lamp. ALWAYS use appropriate PPE for the hazard: UV face shield, goggles, gloves, buttoned-up lab coat.
  2. NEVER temper or bypass the enclosure interlocks.
  3. Avoid touching or scratching the glass section of the UV lamp. Fingerprints weaken the lamp envelope, and this may lead to lamp explosion.
  4. Do not touch the lamp while working. Let the lamp cool at least 15 minutes before opening the lamp compartment door. The arc lamp envelope reaches very high temperatures during normal operation and can cause severe burns if touched.
  5. To avoid inhaling mercury vapor if a mercury bulb breaks, ventilate the room for at least 30 minutes.
  6. Use proper ventilation with lamps that are not ozone free.

Prepared by : Uri ZHANG
08/16/2018