company news about Deep curing vs. surface drying: How to ensure complete curing of UV adhesive by adjusting the UV lamp power?

The curing process of UV adhesives is essentially a process in which photoinitiators absorb ultraviolet light energy, initiating monomer polymerization.

Surface Drying (Surface Dry): Ultraviolet light irradiates the adhesive surface. Because oxygen inhibits curing (oxygen inhibition), the surface typically requires a high light power density (intensity) to instantly activate enough initiators to counteract the effects of oxygen and achieve a dry feel.

Deep Curing (Inner Dry): Ultraviolet light must penetrate the adhesive layer to reach the bottom. However, pigments, fillers, and even the photoinitiators themselves in the adhesive absorb or scatter ultraviolet light. If the surface absorbs too much energy, the light energy reaching the bottom will be drastically reduced.

Many operators believe that "incomplete drying means insufficient power," so they blindly increase the UV lamp output. However, this often backfires:

• Surface Over-curing: Excessive power causes an instantaneous film to form on the surface, creating a "shielding effect" that hinders further penetration of ultraviolet rays.
• Heat Damage: Excessive power generates a large amount of infrared heat, causing deformation of substrates such as acrylic and plastic, or excessive internal stress in the adhesive.
• False Drying: The surface appears perfect, but the internal adhesive remains in a "jelly-like" state due to insufficient energy, causing the product to peel off after a period of use.

To achieve comprehensive curing from the inside out, it is recommended to adjust the power in the following three dimensions:

1. Finding the Balance Point of "Low Intensity, Long Duration"
   For thicker adhesive layers (e.g., 3mm or more), high-intensity instantaneous irradiation is often less effective than medium-low intensity irradiation with appropriately extended irradiation time. Allow sufficient time for the ultraviolet light to penetrate the underlying layer, ensuring that the accumulated radiant energy (joules/cm²) reaches the adhesive's curing threshold.
2. Matching the Wavelength Characteristics of the Adhesive
   
   • 365nm Wavelength: Strong penetration, suitable for deep curing.
   • 395nm/405nm Wavelength: Concentrated energy, suitable for overcoming oxygen inhibition and improving surface drying. Adjustment Recommendation: If deep curing is inadequate, check if the UV lamp's spectrum includes a sufficiently long wavelength of ultraviolet light and ensure the lamp head height is at the optimal focal length.
3. Staged Curing Strategy
   For precision assembly, a "pre-curing + main curing" model can be adopted:
   • Step 1: Use low power for a short time to irradiate the adhesive, allowing it to initially position and begin reacting from the inside out.
   • Step 2: Use standard power for the main irradiation to complete the final sealing. This method effectively reduces internal stress and ensures consistent curing levels inside and out.