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Have you ever known about paper brighteners?

Pulp fiber is always yellow to gray, even after bleaching treatment, still can not eliminate this yellowish hue.
After adding fluorescent brightener to the pulp, the whitening agent absorbs ultraviolet light and emits blue fluorescence. According to the principle of optical complementarity, the pulp becomes pure white, while the pulp produces a brighter and more vivid effect.
Fluorescent Brightener, also known as Optical brightener, is a fluorescent dye, also known as white dye, is a kind of organic compounds that can absorb ultraviolet light (wavelength 300~400nm) and emit visible blue, blue-violet and other fluorescence (wavelength 400~500nm).
1. Action mechanism of fluorescent whitening agent
Fluorescent brightener molecule contains hair chromophores Regiment, Hair Chromophores Regiment has the л electron system which can happen jump, these л electronic system most common have vinyl, benzene ring, naphthalene ring, Triazine Loop, five yuan miscellaneous ring and so on. A single л electronic system generally absorbs only very short wavelengths of light, and these л electronic systems are connected to form a long conjugate double-bond system that absorbs longer wavelength light, so that the long conjugate double-bond system is the basic structure of the fluorescent whitening agent called the Hair Color system, which produces visible fluorescence from these hair color systems.
Fluorescent Brightener is absorbed by the fiber and fixed on the paper, in the light, the whitening agent can not only reflect the visible light, but also absorb the invisible ultraviolet light in daylight and turn it into visible light. Emit fluorescence of different intensities and differences from the paper. When ultraviolet light stops shining on paper, the fluorescence emitted from the paper quickly disappears.
Because of the different molecular structure of fluorescent brightener, the maximum fluorescence wavelength of the radiation is also different, so the fluorescent hue is also difference. Fluorescence wavelength in the 415~420nm interval purple hue, 430~440nm wavelength fluorescence blue tone, 440~466nm wavelength fluorescence green blue.
The micro-blue fluorescence of the whitening agent can be white with the original yellowish hue of the paper, making the paper whitening. At the same time, due to the radiation of strong visible fluorescence, so that the total visible light reflectivity of the paper increased, thereby increasing the brightness of the paper, so that white paper more white, so that light-colored paper more pleasing, bright.
Visible, fluorescent whitening agent can not only make the paper whitening, can also be bright, so the role of fluorescent whitening agent is optically brightening complementary.
2, the type and structure of fluorescent brightener according to the chemical structure classification:
(1), two stupid vinyl
This type of whitening agent includes bis-triazine amino-vinyl, mono-triazole ethylene, bis-triazole ethylene, two-goofy ethylene-benzene-type, two-stupid vinyl benzene and two-dumb ethylene biphenyl, etc.
(2), pyrazole type
(3), Coumarin class
(4), Miscellaneous ring type
(5), naphthalene imide type
Paper industry as long as the use of double-triazine amino-type Brightener, known as VBL-type whitening agent, it has a high whitening strength, good application performance and appropriate light fastness. Its structural formula is as follows:
It is an organic compound with a conjugated double bond, which has the following four types of groups:
A, fluorescent group: two amino-dimethyl vinyl. This is a large conjugate group with л electrons that can be stimulated by ultraviolet light. When the molecule absorbs ultraviolet rays, it can change from the ground state to the excited states, the unstable excited states radiate fluorescence, and then return to the ground.
b, the conversion wavelength group: such as the structure of the substituents. Substituents have the effect of converting radiant light to different wavelengths of visible light (e.g. violet, blue). Different whitening agents have different substituent bases, and the color of the present is also difference.
C, active groups: that is, the active base of triazine with a fluorescent group coupled with the conversion wavelength group, but also with cellulose affinity, is an indispensable active part of many fluorescent brightener;
D, hydrophilic groups: such as sulfonic acid base. The effect is to increase the water solubility of the whitening agent is easy to disperse and has a higher affinity with cellulose.
3. Application of fluorescent whitening agent in papermaking
The fluorescent brightener used in papermaking industry is mainly powdered and liquid fluorescent brightener. Liquid whitening agent is easy to use, more popular with papermaking enterprises. The addition of the method can be added in the slurry to increase the whiteness of the pulp and paper.
4, the main factors affecting the application of fluorescent Brightener
(1) Metal ions
The production of water in the metal ions will affect the whitening effect of fluorescent whitening agent, wherein the ca2+, mg2+, fe3+ have adverse effects on the whitening effect, especially with the greatest influence of fe3+, the production of bauxite fe3+ content to control, the fe3+ content is too high will make the tone of the pulp dark. When the water hardness is too high, the solubility of whitening agent in water can be reduced, and the whitening efficiency will be reduced.
(2), additives
Many additives in slurry have an effect on the whitening effect of fluorescent brightener. Some of the retention agents with better retention effect have a great effect on the effect of fluorescent whitening agent, such as polyethylene imide can make the whitening effect significantly reduced. Filler on the effect of different fluorescent brightener, TiO2 can absorb ultraviolet light, will reduce the fluorescence whitening effect, most of the clay can also play a role in counteracting fluorescence, reduce the whitening effect, but CaCO3 and Al (OH) 3 can reflect ultraviolet light, can enhance the whitening effect. Cationic starch and some wet-strength agents can also weaken the fluorescence effect.
(3), slurry properties
The higher the lignin content in pulp, the smaller the fluorescence whitening effect, because lignin has the characteristics of absorbing ultraviolet light. Therefore, fluorescent brightener is not suitable for processing the color of the non-bleaching slurry, but only for bleaching pulp. Paste Baidu, Whitening effect is more significant.
(4), the amount of fluorescent brightener
The amount of fluorescent brightener in papermaking production is generally less. Fluorescent whitening agent added less, with the increase in the amount of whiteness gradually increased, reached a maximum value, then increase the dosage, the whiteness will decrease, so the amount of whitening agent should not be excessive. General 0. 2~1. Between 0%.
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