FAQsthe Use of Fluorescent Whitening Agent OB: Let’s Clarify These Issues
Time：2025-09-20Views：
In the practical application of Fluorescent Whitening Agent OB, many users may encounter problems such as "no desired effect after addition" or "abnormalities during use"—for example, insufficient whiteness, uneven brightness, or even yellowing. Below are targeted explanations for these common issues, clarifying the causes and key precautions to help you avoid usage misunderstandings.
Why isn’t the product white enough even after adding OB?
- Mismatched OB specification: Although OB is applicable to plastics like PE, PP, and PVC, it is not universally compatible. For instance, when producing high-transparency food packaging films, OB with a purity of over 99.5% and no impurities is required. If low-cost OB mixed with fillers is used, the effective content will be insufficient, and the desired whiteness will definitely not be achieved. Additionally, for modified plastics (e.g., PVC with added tougheners), the dosage of OB must be adjusted according to the additive combination; using the conventional dosage directly will reduce the whitening effect.
- Improper dosage: Both too much and too little are problematic: OB has a "critical dosage"—more is not better. In conventional plastics, the dosage of OB is usually 0.01%–0.05% (i.e., 10g–50g per 100kg of material). If it exceeds 0.08%, the excess OB cannot absorb ultraviolet rays and will instead make the product gray and less white. If it is less than 0.01%, it will be insufficient to offset the yellow tint of the product’s base color, resulting in a weak whitening effect.
- Interference from other additives: If ultraviolet absorbers are used during production, they will "compete for" the ultraviolet rays needed by OB, preventing OB from converting them into blue-violet light for whitening. Moreover, excessive addition of white pigments (such as titanium dioxide) will also absorb part of the ultraviolet rays, impairing OB’s performance. It is recommended to test the dosage of these two additives together to find the appropriate ratio.
Why does the product have uneven and dull brightness after whitening with OB?
- Inadequate dispersion leads to "local failure": Uneven dispersion of OB in the material will cause spots or streaks where some areas are bright and others are dull. For example, in plastic processing, if OB is directly fed into the machine without pre-mixing with a small amount of resin powder, or if the stirring time is insufficient or the screw speed is too low, OB particles will not dissolve and disperse fully, resulting in uneven brightness. It is recommended to first make OB into a pre-dispersed masterbatch and then mix it with the main material—this will significantly improve brightness uniformity.
- Poor base color of the substrate limits OB’s effect: OB works by "optical color compensation" to whiten, not by bleaching dark materials. If the substrate itself has a dark base color (e.g., impurities in recycled materials or yellowing of resin due to thermal degradation during high-temperature processing), OB alone cannot cover the base color, leading to dull brightness. In such cases, the substrate must be treated first (e.g., adding a yellow-removing agent to improve the base color), and then OB can be used to enhance overall brightness.
Why does the product turn yellow gradually after using OB?
- Excessive dosage causes yellowing: Beyond OB’s critical dosage, the excess OB may precipitate on the product surface or undergo slight carbonization during processing, resulting in a pale yellow tint—this is especially noticeable in transparent or light-colored products. It is essential to conduct trial production within the range of 0.01%–0.05% to find the optimal dosage.
- Excessively high processing temperature damages OB: OB can withstand temperatures of 280°C–300°C, but if the processing temperature (e.g., during PE film blowing or PVC extrusion) exceeds 300°C for a long time, or if local overheating occurs (e.g., dead corners in the machine), OB will decompose and lose effectiveness. Not only will it fail to whiten, but it will also produce yellow decomposition products, causing the product to turn yellow. The temperature curve must be monitored to avoid exceeding the upper limit.
- Insufficient weather resistance for outdoor products: OB has average sun resistance. If the product is used outdoors (e.g., agricultural films, outdoor guardrails), prolonged exposure to sunlight and rain will damage OB molecules, preventing them from continuing color compensation, and the product will gradually turn yellow. In such scenarios, it is necessary to use OB in combination with antioxidants and light stabilizers, or mix OB with weather-resistant whitening agents to extend the retention time of whiteness.
