company news about Why is your UV adhesive not drying? You may have selected the wrong UVA lamp wavelength

In the process of precision assembly or DIY crafts, one of the most frustrating moments is when the glue is still sticky to the touch, or even still liquid inside, after being exposed to a UV lamp for a long time. Many people's first reaction is that "the glue is of poor quality" or "the lamp's power is insufficient." But in reality, "wavelength mismatch" is the number one hidden killer that causes UV glue to fail to cure.

To understand why wavelength is important, we must first understand the curing principle of UV adhesive. UV adhesive contains a key component called a photoinitiator.

The photoinitiator is like a lock; it can only be activated and induce monomer polymerization, causing the adhesive to cure, after absorbing energy of a specific wavelength.

The wavelength of the UVA lamp is like the key. If the key's teeth (wavelength) don't match the lock cylinder, no matter how strong the light or how long the exposure time, the adhesive won't budge.

Industrial-grade UVA LED lights typically focus on three main bands: 365nm, 385nm, and 395nm (and 405nm). Choosing the wrong band will drastically affect the results.

This is currently the most widely used standard band. Most high-quality industrial UV adhesives (such as lens bonding and glass bonding) are developed around 365nm.

Advantages: Concentrated energy, can excite most photoinitiators, and the cured surface has good dryness (not sticky to the touch).

Misconception: If the adhesive packaging says "requires 365nm," using a 395nm light may reduce efficiency by more than 80%.

These two bands are closer to visible light.

Applications: Commonly used in UV inkjet printing, nail art, or certain thick coatings.

Drawbacks: They have low energy density, and if used in demanding precision optical adhesives, they are prone to causing a "sticky surface" phenomenon.

If you are bonding two pieces of plastic (such as PC or UV-resistant glass), these materials automatically filter out ultraviolet light below 365nm. In this case, if you use a 365nm lamp, the energy will not reach the adhesive layer.

Solution: In this situation, you need to use a longer wavelength like 395nm, taking advantage of its stronger penetrating power to pass through the plastic layer.

Short wavelengths (e.g., 365nm): Excellent at surface curing, allowing the surface to harden quickly.

Long wavelengths (e.g., 395nm): Excellent at deep penetration.

If your adhesive layer is thick but you only use 365nm, you may experience a phenomenon of "surface skinning but internal fluidity."

Some adhesives are very sensitive to oxygen at 395nm. Oxygen in the air will hinder surface curing.

Problem: Even after prolonged exposure, the surface still feels greasy to the touch.

Solution: Switch to a high-intensity 365nm lamp, or cure under nitrogen atmosphere.

If you are experiencing glue not drying properly, please follow these steps to check:

1. Read the instruction manual: Confirm the peak absorption wavelength of the glue. Is it 365nm or 395nm?
2. Test the LED: Many cheap "UV lamps" have severely offset wavelengths; a nominal 365nm LED may actually be a low-quality 400nm LED. It is recommended to use a professional UV energy meter for measurement.
3. Consider transparency: Observe whether the ultraviolet light needs to penetrate obstacles. If it needs to penetrate thick glass or plastic, try increasing the wavelength or the irradiation energy.

UV curing isn't simply a matter of "shining a lamp on it"; it's a precise photochemical match. Choosing the right wavelength means curing takes only seconds; choosing the wrong wavelength means you'll be shining the lamp until dark and still not getting any results.

Next time the adhesive doesn't dry, don't rush to change it. Check if your lamp and its wavelength are truly "compatible."

For any inquiries regarding selecting the correct wavelength for UV lamps.

please contact: Shenzhen Super-curing Opto-Electronic CO., Ltd.