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Application of optical brightener agent in Papermaking
Apr 24, 2018

Fluorescent brighteners are fluorescent white dyes that use fluorescence to give our visual organs a sense of whiteness, which, like dyes used in various fibers, can dye a variety of fibers. On cellulosic fibers, it seems that direct dyes can dye paper, cotton, linen, viscose fibers, etc. Fluorescent whitening agent was discovered in 1920s, and formally supplied shopping malls in 1939. It has been over 80 years ago. There are many kinds of fluorescent whitening agents, and they are widely used in all walks of life.

1 principle of fluorescent whitening

The fluorescent brightener is a colorless dyestuff that is rich in conjugated double bonds and has extraordinarily slippery properties. Under sunlight, it absorbs ultraviolet light (wavelength 300~400nm) in sunlight to activate molecules and then revert to the ground state. The ultraviolet energy is not part of the energy, and it is converted into lower energy visible light. In addition, the blue violet light, which reflects the wavelength of 420~500nm, increases the total reflected light on the paper, and the blue purple light reflection on the paper, and then counteracts the Yellow sense of the paper fiber caused by too much reflection of the yellow light, which makes the whiteness of the paper increased, and the white and bright effect can occur.

When the incident light is changed, the effect of the fluorescent brightener is changed. Assuming that the outside content of the incident light is high, the effect is particularly obvious, and the whitening effect is very small or no effect in the light with low ultraviolet light or no ultraviolet light.

The fluorescent brighteners of different types of fluorescent brighteners are different, depending on the wavelength of absorption of ultraviolet light, the absorption of 335nm below, the redness of the fluorescence, the absorption of more than 365nm, and the greenness of the fluorescence, which is decided by the properties of the substitute group in the molecular structure. (1)

2 types of paper industry

Pulp fibers are usually yellow or gray, because lignin absorbs wavelengths of 400~500nm light. Using the method of adding dyes or chemical bleaching, the brightness of pulp is limited. The whiteness of bleached pulp is usually at 85%ISO. It is assumed that severe bleaching will greatly damage the strength of paper fibers in order to find whiteness. By adding fluorescent brighteners in paper making, it can produce high whiteness paper. The paper has been increased after fluorescent whitening agent, and the whiteness can be more than 10%.

(2) there are three ways to use the fluorescent brighteners in the paper industry to make use of the dye manufacturers: the whitening of the pulp - the whitening of the pulp directly to the pulp; the appearance of the glue is added to the glue liquid on the surface of the glue; the surface coating is added to the guessing of the coating process of the paper.

The manufacturers of fluorescent brighteners for paper industry need to satisfy the following requirements:

(1) excellent compatibility with all kinds of paper filler, paper chemicals and adhesives.

(2) a certain degree of acidity and alkalinity can be used to the demand of the technological process of papermaking.

(3) it has affinity for paper fiber and high whiteness.

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