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Whitening of UV Adhesive During Curing: Cause Analysis

Many users encounter the issue of whitening during UV adhesive curing. Products exhibiting this whitening phenomenon often show significantly reduced bonding strength, ultimately leading to the bonded substrates detaching directly. Therefore, whitening in UV adhesive curing has a substantial negative impact on application performance. Below, we will discuss several reasons for the occurrence of whitening in UV adhesives.

I. Light Curing Conditions

Key factors to consider for UV adhesive curing include the power of the UV lamp, the exposure time, and the irradiation distance. A high-power UV lamp, a long exposure time, or a short irradiation distance can all lead to excessively fast curing. The adhesive undergoes a vigorous reaction, and curing under a high-power UV lamp can even cause smoking. In such cases, the internal stress within the adhesive layer increases, making it prone to whitening.

II. Adhesive Layer Thickness

If the bonded layer is relatively thick and cannot be cured promptly within the specified time, or if a low-power UV lamp is used resulting in insufficient UV penetration, the bottom layer of the adhesive may not cure completely. This incomplete curing can also lead to the whitening phenomenon. Therefore, when applying the adhesive, the amount used should be selected appropriately based on the power of the UV lamp.

III. Bubble Issues

Tiny bubbles can originate within the adhesive layer itself. As the adhesive shrinks during the curing process, if the layer thickness is uneven or the hardness is too high, the internal stress generated by the shrinkage cannot be released. Over time, this can cause the accumulation of micro-bubbles, which manifests as the observed whitening. For whitening caused by this reason, one can use a low-power UV lamp for the initial fixation stage. This slows down the curing speed of the adhesive. After positioning, a high-power UV lamp can then be used for deep curing. This approach helps because excessively fast curing increases the shrinkage rate of the adhesive.

The occurrence of whitening during the application of UV adhesive adversely affects the product both aesthetically and in terms of performance. In fact, as long as users understand the precautions for using UV adhesive and the principles of material selection and application, they can largely avoid improper operation and incorrect material choices. This, in turn, helps prevent various application problems.