The Effect of Fumed Silica on the Thickening and Thixotropic Properties of UV Light-Cured Paint

Figure 1

According to the experimental data in Figure 1, as the amount of HL-200 fumed silica added increases (0%, 0.5%, 1%, 1.5%, 2%), the coating viscosity exhibits significant and systematic changes.

At a low shear rate (6 rpm), the viscosity rises sharply from a baseline of 460 cP to 12,600 cP, representing an increase of nearly 80-fold. In contrast, at a high shear rate (60 rpm), the viscosity grows from 451.3 cP to 2,780 cP, an increase of approximately 5.2-fold. The thixotropic value rises significantly from 1.02 to 4.53, indicating a marked enhancement in thixotropy.

This data variation is not a simple linear growth but reveals the ability of fumed silica to construct a network structure within the coating system.

In a static or low-shear state, fumed silica particles form a hydrogen bond network via surface silanol groups, “locking” the coating system into a high-viscosity state, effectively preventing pigment settling and sagging during application.

HIFULL® HL-200 (BET=200㎡/g)

Under high shear (such as stirring or spraying), the hydrogen bond network is disrupted, viscosity drops rapidly, endowing the coating with good application leveling properties. Once the shear force is removed, the hydrogen bond network reforms, viscosity recovers, creating a rheological cycle of “shear thinning-structure recovery.”

In practical applications, UV light-cured paint often faces multiple requirements, including sagging on vertical surfaces during application, pigment suspension stability, and printing adaptability. By precisely controlling the addition amount, the coating’s rheological curve can be flexibly adjusted to meet the needs of diverse scenarios:

Addition amount of 0.5%-1%: Suitable for general-purpose coatings requiring moderate thixotropy, balancing leveling and anti-settling properties; Addition amount of 1.5%-2%: Suitable for high-solid-content, high-pigment systems, or vertical and uneven surface coating that demand strong anti-sagging performance.

The role of fumed silica in the UV light-cured system goes far beyond “thickening”; it endows the coating with the ability to intelligently respond to environmental stress, allowing the liquid material to switch effortlessly between flowing and setting. From 460 cP to 12,600 cP, this is not merely a jump in numbers, but a vivid embodiment of material science in microstructure design and macro-performance regulation.

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