Video of sodium alginate used in flat screen printing machine

　　Sodium alginate is widely used in printing and spinning industry. For example, it has a long history as warp sizing, finishing sizing and printing sizing, but it is mainly used as printing paste in printing sizing. Sodium alginate paste has unique properties and excellent printing effect. It is not only suitable for cotton fiber printing, but also suitable for wool, silk and synthetic fiber printing. Sodium alginate has a wide viscosity range, which can meet the requirements from screen printing (such as flat screen printing and rotary screen printing) to drum printing color paste. Therefore, sodium alginate plays an important role in printing paste.

　

　

　The paste-forming rate of sodium alginate is related to its viscosity. The viscosity of the solution rises sharply with the increase of solution concentration. The high concentration sodium alginate is a typical pseudoplastic fluid, and its rheological property is close to Newtonian fluid with the decrease of solution concentration. The viscosity of sodium alginate depends on the degree of molecular polymerization. By adjusting the production process, the molecular weight can be properly controlled to produce sodium alginate with different viscosity specifications. In this way, when sodium alginate is used as printing paste, the range of paste forming rate is larger, and users can choose different specifications of sodium alginate according to their own needs.

　　Printing viscosity index (PVI value) is an index indicating the printing performance of the original paste, which is used to predict the printing performance of the original paste in the actual printing process. The range of PVI value is generally between 0.1 and 1.0, which is influenced by the molecular weight, concentration and additives of the original paste. The higher the concentration of sodium alginate, the greater the molecular weight, which is more conducive to the formation of structural viscosity, thus increasing the structural viscosity index and the lower the PVI value. In addition, if the electrolyte is added to the original paste, the PVI value will also be affected, because sodium alginate is a kind of organic salt of polymer. After the electrolyte is added, its solvation degree will be affected, and the structural viscosity index will be increased, thus the PVI value will be reduced.

　　When urea is added, the fluidity of the original paste will be improved, the structural viscosity index will be reduced, and the PVI value will be increased. The PVI value of sodium alginate varies widely, so it is suitable for rotary screen, flat screen and drum printing, and can meet the requirements of various water-absorbent fibers and hydrophobic fibers by properly adjusting the concentration of color paste.

　　Sodium alginate paste has good washability and high paste removal rate. Sodium alginate is different from most other thickeners. After printing, the film formed on the fabric has certain adhesion and flexibility, and will not fall off the fabric or form creases during the stacking of the fabric.

　　However, because sodium alginate is easily soluble in water and does not react with dyes and other auxiliaries, this film can be easily removed in the washing process even after baking or steaming at high temperature, thus making the fabric feel soft.

　　The pigment of sodium alginate itself is light, and there is no direct pigment on the fiber, so it can be washed off in the water washing process after printing, so it will not affect the bright color of printed fabric.

　　The original paste of sodium alginate has good chemical compatibility, and the general organic acids, alkaline agents, weak oxidizing agents and reducing agents have little influence on it. When the PH value is kept at 5.8-11, the chemical properties are relatively stable. Good compatibility with other pastes, and can be combined with various original pastes. Sodium alginate solution is negatively charged, so it can't be used as a paste for cationic dyes, and it can't be used together with other auxiliaries with cationic properties, because it will coagulate and precipitate out. However, anionic dyes have good chemical compatibility with sodium alginate. However, it should be noted that the fillers in the same dye may be different due to different manufacturers or different batches of the same manufacturer, and the rheological properties of sodium alginate paste may be affected, resulting in different printing effects.

　　The color paste made of sodium alginate has good permeability. At present, the sodium alginate with good quality has high purity and few insoluble colloids and impurities, so it will not block the screen in the printing process. Under the force exerted by the scraper, the paste can easily pass through the printing screen, transfer the dye to the fabric, and print a complete and uniform pattern with good levelness and uniform color.

　　Sodium alginate has strong hygroscopicity. In reactive printing, the transfer and diffusion of dye into fiber is accomplished by steaming, which is directly related to the amount of water absorbed. The higher the hygroscopicity of the paste, the greater the degree of fiber expansion, and the better the printing coloring effect. Adding urea can enhance its hygroscopicity. In addition, sodium alginate has good water holding capacity, which can effectively absorb excess water when printing steam fixation, reduce the free movement of water in the paste, prevent the infiltration of patterns, ensure the clear outline of patterns and improve the printing effect.