In-depth FAQsFluorescent Whitening Agent OB: Tackling Application Challenges
Time：2025-09-20Views：
In industrial production, Fluorescent Whitening Agent OB serves as a key additive for enhancing the whiteness and brightness of products, and is widely used in plastics, coatings, inks, and other fields. However, during practical application, many users encounter various tricky issues. Below is an in-depth analysis and solution provision for you.
I. Why Can’t Whiteness Be Improved Ultimately?
1. Mismatched Specification Selection: While OB has broad applicability, different industries and materials have distinct requirements for it. In the manufacturing of high-end optical plastic lenses, OB with high purity and low impurities is mandatory—even trace impurities can impair the lens’ optical performance, resulting in substandard whiteness and transparency. For special modified plastics (e.g., plastics containing special flame retardants), OB may interact with flame retardants; thus, adjusting OB’s molecular structure or selecting specially compounded products is necessary, otherwise, whiteness cannot be enhanced.
2. Incorrect Dosage Control: The dosage of OB follows a typical "bell-curve" relationship and is not simply "the more, the better". In conventional plastic products, the dosage of OB is generally controlled between 0.01% and 0.05%. Exceeding 0.08% leads to "supersaturation"—excess OB cannot normally absorb ultraviolet rays and convert them into blue-violet light; instead, it exhibits self-coloration, causing the product to turn gray and reducing whiteness. If the dosage is below 0.01%, OB fails to fully neutralize the yellow tint in the product’s base color, resulting in a weak whitening effect.
3. Synergistic Interference from Additives: When ultraviolet absorbers, light stabilizers, and other additives are used simultaneously in production, they compete with OB for ultraviolet absorption. Ultraviolet absorbers prioritize absorbing ultraviolet rays, depriving OB of the necessary energy to exert optical whitening effects. Certain metal ion-based additives may chemically react with OB, destroying its molecular structure and rendering it ineffective. For example, in polyolefin plastic processing, improper matching between metal salt additives (e.g., calcium stearate) and OB can compromise whiteness.
II. What Causes Uneven Brightness?
1. Defects in Dispersion Process: Uneven dispersion of OB in materials is the core cause of uneven brightness. In plastic processing, process parameters such as screw speed, screw groove depth, and mixing time all affect dispersion efficiency. Low screw speed prevents sufficient shear dispersion of OB particles; unreasonable screw groove depth shortens the material’s residence time in the screw, limiting full mixing between OB and the material. Ultimately, the product develops "speckles" or "streaks" with uneven brightness.
2. Impact of Substrate Characteristics: If the substrate itself has issues like density variation or uneven crystallinity, the distribution and efficacy of OB within it will also differ. For crystalline plastics (e.g., polypropylene), the adsorption and dispersion capacities of crystalline and amorphous regions for OB vary, leading to inconsistent OB concentration across different areas. This results in uneven whitening and brightness enhancement effects, undermining overall brightness uniformity.
III. In-depth Analysis of Product Yellowing Causes
1. Yellowing Due to Excessive Dosage: Beyond OB’s optimal dosage, excess OB may precipitate on the product surface during processing or storage, or undergo slight carbonization due to local high concentration, presenting a pale yellow hue. This is particularly noticeable in transparent or light-colored products. For instance, in transparent PVC films, excessive OB addition causes gradual yellowing at the edges.
2. Yellowing Caused by Overheating During Processing: Although OB has a certain heat resistance, prolonged exposure to temperatures exceeding its tolerance limit (generally 280°C–300°C) during processing, or local overheating (e.g., at the screw head or narrow mold runner), leads to OB decomposition and failure. This produces yellow decomposition by-products, causing the product to turn yellow and become dull, seriously affecting its appearance and performance.
3. Yellowing Due to Insufficient Weather Resistance: OB has poor weather resistance. When products are used outdoors or in high-humidity, high-corrosivity environments, ultraviolet rays, moisture, and chemicals gradually damage OB’s molecular structure, depriving it of whitening capabilities. As a result, the product gradually reverts to its base yellow tint. A typical example is plastic trash bins used outdoors—after a period of use with OB-containing raw materials, their surfaces turn yellow.
