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Analysis of the Whitening Phenomenon in UV Optical Adhesives

Release time:

2025-08-06 10:49

Analysis of the Whitening Phenomenon in UV Optical Adhesives
Analysis of the Whitening Phenomenon in UV Optical Adhesives

In modern manufacturing, UV optical adhesives have found widespread application across numerous fields—including optical components, electronic devices, and medical equipment—thanks to their distinctive performance advantages, such as rapid curing, high transparency, and excellent bonding strength. However, the whitening phenomenon that occurs during the curing process has emerged as a critical issue affecting product quality and performance, warranting thorough investigation and resolution.

I. Causes of Shrinkage Phenomena

The shrinkage phenomenon during the curing of UV‑curable optical adhesives constitutes the physical basis for whitening. When the adhesive layer is exposed to ultraviolet light and undergoes a curing reaction, its molecular structure gradually transitions from a disordered state to an ordered crosslinked network; this transformation results in volumetric contraction of the adhesive layer. Moreover, the adhesive bond between the adhesive layer and the substrates constrains the layer as it shrinks, thereby generating internal stresses within the adhesive itself.

If the colloid itself exhibits poor flexibility and lacks sufficient deformability, these internal stresses cannot be effectively relieved through deformation. Under the sustained action of these internal stresses, numerous micron‑scale bubbles gradually form within the adhesive layer. The presence of these bubbles disrupts the optical uniformity of the layer; as light passes through, it undergoes reflection, refraction, and scattering at the bubble interfaces. Light that would otherwise propagate in a straight line is scattered in multiple directions, reducing the transmittance of the adhesive layer and giving it a whitish, hazy appearance—commonly referred to as “whitening.”

II. Differences in Bonding Scenarios Across Various Materials

Whitening phenomena exhibit distinct differences across bonding scenarios involving various materials, with glass–metal adhesion being one of the most pronounced cases. Glass possesses a smooth, hard, and chemically stable surface, while metals are similarly dense and have flat, even surfaces. At the interface between these two materials and UV‑curable optical adhesives, the bonding is relatively uniform, lacking sufficient surface roughness and porous structures to provide effective pathways for dissipating internal stresses.

During the curing process, the internal stresses generated by shrinkage of the adhesive layer are difficult to transfer across the bonding interface into the adherends and instead accumulate within the adhesive itself. As these internal stresses continue to increase, voids are more likely to form inside the adhesive layer, leading to severe whitening. In contrast, materials with rough or porous surfaces—such as plastics and wood—exhibit more complex bonding interfaces with the adhesive, providing additional pathways for stress relief and thereby mitigating the extent of whitening to some degree.

III. Long-term Effects of Whitening on Product Performance

In the short term, whitening appears to have only a minor impact on the initial adhesive strength of the bond, and the adhesive layer can still maintain a certain level of bonding performance. However, from a long-term perspective, whitening is a potential issue that cannot be overlooked and may significantly compromise the product’s long-term reliability.

The presence of bubbles compromises the internal structural integrity of the adhesive layer, giving rise to numerous microscopic defects. These defects serve as stress concentration points, making the adhesive layer susceptible to crack initiation and propagation under external loads, temperature fluctuations, or changes in ambient humidity. Over time, the progressive growth of these cracks leads to a gradual reduction in the adhesive’s bonding strength, potentially resulting in delamination, cracking, and other failure modes.

Furthermore, bubbles can accelerate the aging of the adhesive layer. The interior of these bubbles may contain air, moisture, or other impurities, which can react chemically with the adhesive, altering its chemical properties and further degrading the performance of the adhesive layer. Over prolonged use, the combined effects of these factors significantly compromise product quality and service life, increasing maintenance costs and replacement frequency, thereby inflicting financial losses and reputational damage on the enterprise.

IV. Summary

The whitening phenomenon observed after the curing of UV‑curable optical adhesives is a complex issue that spans multiple disciplines, including materials science, mechanics, and optics. A thorough understanding of its underlying mechanisms and its impact on product performance enables more accurate quality assessments in practical applications, provides a theoretical foundation for further optimizing adhesive formulations and refining manufacturing processes, and ultimately promotes the high‑quality deployment of UV‑curable optical adhesives across an expanding range of fields.

Disclaimer: The above content has been compiled from publicly available sources and is provided for reference only. If any infringement occurs, please contact us, and we will address it promptly.

Bossin Recommended Products – Liquid Optical Adhesive
Product Model/English Abbreviation Product Name/Product Type Product Features
B-2111D Aliphatic polyurethane acrylate Excellent adhesion, high elongation, and resistance to thermal shock.
B-2116 Aliphatic polyurethane acrylate Excellent adhesion, good flexibility, acid and alkali resistance, and excellent tensile strength.
B-215 Aliphatic polyurethane acrylate Good adhesion, excellent flexibility, water resistance, and acid resistance.
B-2621 Aliphatic polyurethane acrylate Excellent adhesion, resistant to strong acids and strong alkalis, and low curing shrinkage.
Monomer Recommendation
Product Model/English Abbreviation Product Name/Product Type Product Features
BM1105 (OPPEA) 邻-Phenylphenoxyethyl acrylate Low shrinkage, excellent adhesion, low volatility, high refractive index
BM1210 (PHEA) 2-Phenoxyethyl acrylate Low shrinkage, heat resistance, excellent adhesion, high refractive index
BM1211 (HPMA) Hydroxypropyl methacrylate HEMA-free, high strength, low irritation, and excellent adhesion
BM2101M (10EO-BPADMA) Bisphenol A dimethacrylate ethoxylate Low irritation, flexibility, excellent strength, and heat resistance
BM2224 (EO-HDDA) Ethoxylation of 1,6-hexanediol diacrylate It exhibits excellent adhesion to plastics, good dilutability, and low volatility.

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