Abstract: The sizing mechanism of AKD and its application in special packaging papers were studied.
With the rapid development and progress of the social economy, people have higher and higher requirements for the quality of special packaging papers, and their use has become increasingly widespread. The traditional packaging paper for rosin sizing has been difficult to meet the requirements of users. One of the main trends in the chemistry of papermaking wet end during the past 10 years has been the conversion from acidic sizing to neutral sizing. The paper is manufactured at high pH under neutral sizing conditions. The advantage is that the corrosiveness of the equipment is reduced, the fiber can be well swelled, the strength is greatly increased, the filler content is increased, the paper web is easy to dry, the vehicle speed is increased, and the output is increased. Energy consumption is reduced, pollution is reduced, and aluminum sulfate is not used to avoid yellowing and brittleness of paper, facilitating long-distance transportation and long-term storage of paper. AKD neutral sizing is one of its typical representatives. According to reports, as far back as 1997, global cultural paper production used neutral sizing, with 95% in Europe, 72% to 75% in North America, and 35% in Japan. In 1986, China began to use the imported AKD to make medium-to-high-grade paper and succeeded.
Although Minfeng Paper Company has a history of more than 70 years, it still uses traditional acid sizing technology in the production of special packaging paper. Special packaging paper is one of the leading products of the series of packaging paper used by Minfeng Special Paper. Its final products are mainly exported to South Korea, Japan, the United States and other countries and Taiwan. Recently, users have repeatedly reported that special packaging paper has the problems of easy yellowing and brittleness, and the appearance quality after printing and storage is poor, which affects the normal use of customers. The application research of AKD neutral sizing technology in special packaging paper not only solves the problems reflected by users, but also expands the product raw material selectivity, so that the inherent quality, appearance and feel of special packaging paper are very good. Great change, at the same time, lower production costs, waste water pollution load.
1 AKD sizing mechanism
AKD is an abbreviation of alkyl ketene dimer and is a fiber-reactive synthetic sizing agent. Under alkaline conditions, its reactive functional group can react with the hydroxyl group on cellulose to form a covalent bond and fixate on the fiber. In the above, a stable film is formed on the surface of the fiber, and the fiber is changed from hydrophilic to hydrophobic, so that the paper obtains water resistance.
Although AKD has a functional group capable of reacting directly with a cellulose hydroxyl group, it does not substantially react at the wet end of the paper machine. After the AKD emulsion is added to the slurry, the sizing agent particles are only dispersed in the slurry system, and multiple sizing agent particles can form relatively large agglomerates. These agglomerates and individual sizing agent particles are adsorbed on the fine fibers. , filler and fiber surface, after the Internet with fine material retention and retained in the wet paper sheets, when AKD is only in electrostatic adsorption and free form, its covalent bond with cellulose has not yet formed. In the drying section, as the moisture in the sheet decreases, the AKD particles melt and expand on the surface of the fiber due to the influence of the drying temperature. The reactive functional groups of the molecules face the fibers, and the hydrophobic groups partially face outward, towards the reactive functional groups of the fibers. The hydroxyl group of cellulose reacts to form a covalent bond, thereby fixing it on the surface of the fiber and completing the sizing process.
2 Production and Application of AKD Neutral Adhesive
2.1 Introduction to Special Packaging Paper Special packaging paper is a kind of high-grade packaging paper. Its main features are high whiteness, smooth surface, high smoothness, non-destructive packaging, good single-sided printing performance, high strength, and paper quality. yellow. The main technical indicators are shown in Table 1.
2.2 Production process conditions
Raw material ratio: w=60% bleached wood pulp, w=40% bleached straw pulp.
Beating, mixing process conditions:
(1) Crusher: 1.5 packs of Russian bleached softwood pulp and 0.5 packs of domestic bleached straw pulp per row. Control the pulp concentration 14 ~ 18g, special packaging paper back to the paper with a uniform trial. Add 1200mL of SS-02 imported dye per row. SS-02 imported dye added method: Take SS-02 imported dye 1kg, add 10kg water to dilute to the desired dye. When the material is crushed to half, 1kg of the dye is taken into the pulp after filtered through a 100 mesh screen. It is strictly forbidden to add it prematurely or too late to avoid chromatic aberration.
(2) Slurry: Wood pulp slurry is controlled at 26 to 30° SR and wet weight is 4.5 to 5.5 g. The pulp slurry was controlled at 22-26 SR and wet weight 2.0-3.0 g. (3) Slurry: After the pulp slurry is filled with the pulp tank, add SN-01 cationic starch w = 1 % (for desiccated pulp), (SN-01 cationic starch dissolution method: take a packet of 25 kg of starch in the rosin The water in the tank is dissolved into half a barrel, heated and stirred until it becomes transparent. The pump is pumped into the sump until ready for use), and then N-03 calcium carbonate 50kg is added. [N-03 Calcium Carbonate Dissolving Method: Dissolving in Paper Machine Filler Add 2 bags of N-03 calcium carbonate (50kg) into the barrel, mix with water and dissolve it evenly. Add it to the sump through the filter screen]. Controlled paper ash content ≤ 6%; domestic AKD neutral collagen solution was added in the high tank, the flow rate was 120 mL/min (liquid glue, solids content 15%), and the control pulp consistency was 12.0 to 15.0 g.
The production process flow chart is shown in Figure 1.