What should be considered when coloring and whitening white irregular profiles?

What should be considered when coloring and whitening white irregular profiles?

Rutile-type (R-type) titanium dioxide is the optimal pigment for white profile products. As shown in the figure below, it also serves as an excellent light barrier agent, enhancing the weather resistance of profiles and inhibiting the release of hydrogen chloride from PVC, thereby delaying PVC degradation. However, only about 5 parts are generally required; when the titanium dioxide content reaches around 8% in the product, its hiding power tends to level off. Adding more beyond this point offers no additional benefit and may instead increase material viscosity, reduce flowability, raise torque, and make processing more difficult. 
Insufficient whiteness of profiles can generally be improved by adding a small amount of optical brightener, which enhances surface brightness and makes colors clearer and more vivid, achieving a "radiant" whitening effect. Common domestic brighteners such as type PF have low decomposition temperatures (initial decomposition at 178°C), peak absorption wavelength at 363 nm, and exhibit sublimation, resulting in poor performance despite their low cost. In contrast, type OB has a melting point of 196–203°C and a decomposition temperature above 220°C, with a maximum absorption wavelength of 375 nm; "OB-1" has a melting point of 353–359°C, a maximum absorption wavelength of 374 nm, and a maximum fluorescent emission wavelength of 434 nm. Among these, "127" is particularly suitable for PVC products. 
A small amount of blue pigment can be added to white profiles to "mask yellow" and achieve a whiter appearance. However, when selecting blue pigments, it should be noted that ultramarine has poor acid resistance and generally cannot be mixed with lead-, tin-, or cadmium-based heat stabilizers; whereas phthalocyanine blue has strong coloring power, which may easily result in uneven color distribution.
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