In recent years, it has become a trend to use multiple chemical additives on the same paper grade.
The neutral sizing technology itself is a synergistic application technology of a series of chemical additives.
In order to truly understand the cooperative application mechanism of chemical additives, researchers have conducted a series of studies on the chemical system of the wet end of papermaking.
The retention rate of neutral sizing agent AKD itself is very low, and other retention aids must be used to increase its retention rate. Generally, a binary retention system composed of quaternary ammonium cationic starch and anionic PAM or cationic PAM is often used to help AKD stay on the fiber.
Among them, the cationic auxiliary partially neutralizes the anionic impurity in the papermaking system, while protecting the anionic components.
From the flocculation mechanism of retention and filtration assistance, we know that it is necessary to maintain proper flocculation to improve the retention and filtration assistance effects, but also to avoid excessive flocculation to maintain the strength and uniformity of the paper.
This is the key to the application technology of retention and filtration systems. …
Selection of cationic starch
It is best to choose cationic starch with a high degree of substitution. The higher the degree of substitution (DS), the stronger the flocculation of the slurry. In the neutral sizing system, it is advisable to select a substitution degree of 0.03～0.04;
Amount of addition.
According to the actual conditions of the paper machine, product, raw material, etc., tests should be performed before the formal application to find the best amount of addition. With this addition amount, it can significantly improve the retention and filtration effects without affecting the physical strength and uniformity of the paper.
The addition amount of cationic starch with high degree of substitution is generally 0.25~1.0%
Generally ≤1%, thin paper is about 0.5%. If> 1%, it will easily cause excessive flocculation, which will affect the evenness and strength of the paper;
Add point settings
Generally choose the position close to the flow box. The high-level box is the ideal adding point, followed by the inlet and outlet of the rotary wing screen. The specific location depends on the actual situation of the machine.
In short, the closer to the mesh, the better the retention and filtration effects, but the greater the impact on the evenness and strength of the paper.
While increasing retention and filtration effects, it is generally desirable to increase the strength of the paper sheet.
However, enhancement and retention are a pair of contradictions. Generally, retention and filtration have obvious effects, while enhancement effects are reduced; the reverse is also true.
If you want to improve the strength index while satisfying retention and filtration, you can move the adding position to the beating direction to appropriately reduce flocculation and increase the contact uniformity of starch and fiber; increase the amount of addition; add in two places, etc. .