Short for optical brightening agent, usually a stilbene derivative that absorbs ultraviolet around 350 nm and fluoresces in the blue at roughly 430 to 440 nm, filling in the blue reflectance lost to yellowish fiber. It is added at the wet end, in the size press or in coating colors. Response flattens at high dosage and the sheet starts to turn greenish, so every grade has a practical ceiling.
OBA is up to 12 kilos a ton and whiteness barely moved, we're at the ceiling on this furnish.
OBA is cheap whiteness up to a point; past the greening point every extra kilo costs money and makes the sheet look worse.
Also heard as
- FWA
- OWA
- fluorescent whitening agent
- optical brightener
Related terms
Fluorescence
Light a sample emits after absorbing UV, measured in paper as the gap between UV-included and UV-excluded readings.
Greening
The greenish cast a sheet takes on when optical brightener is dosed past its effective range.
Quenching
Loss of optical brightener response caused by chemicals or materials that suppress its fluorescence.
Carrier
Water-soluble polymer such as PVOH that boosts optical brightener efficiency in coatings and size-press starch.
Tetra
Shorthand for a tetrasulfonated stilbene optical brightener, the general-purpose OBA type.