There are three application methods:
Pulp whitening:
(The dosage is generally about 0.05%~0.2% of the dry pulp weight, pH value 7~8)
Disulfonic acid varieties are suitable for neutral or alkaline papermaking, such as C.I., 85, 113, 134, etc.;
Acidic papermaking requires Optical brighteners to be stable to acid and aluminum sulfate, and tetrasulfonic acid varieties are suitable, such as C.I.24, 220, etc.;
Since hexasulfonic acid varieties have too little affinity for pulp fibers, such as C.I. fluorescent brightener 264, etc., are not suitable for pulp whitening.
Surface Coating whitening:
(The dosage is generally 0.01%~0.2% of the coating dosage, pH value 7~8.5)
Di-, tetra- or hexa-sulfonic acid varieties can be selected, among which tetra- and hexa-sulfonic acid varieties have better effects, such as C.I. 220, 264, 357, etc.
Surface Sizing whitening:
(The dosage is generally 0.2%~1.0% of the coating dosage glue solution, pH value 8~9)
Because cationic water-soluble polymers are often contained in surface sizing, di-sulfonic acid varieties are sensitive to cationic compounds and are not suitable for use in surface sizing. It is recommended to use tetra- or hexa-sulfonic acid varieties, such as C.I. fluorescent brightener 24, 220, 264, 336, 353, 357.
In addition, when adjusting the color of whitening paper, dyes are usually added after Optical brighteners.
