Surface sizing is a process in the course of paper or cardboard processing, usually at the end of the drying section of the machine, so that the sheet is sprayed with a layer of glue when it is not completely dry but with a certain strength, Cardboard surface to form a layer of film, Surface Sizing Enhanced Agent so as to achieve the purpose of changing the performance of paper or cardboard.
By surface sizing can be added to improve the performance of paper or increase the paper or cardboard water resistance of the surface additives. Originally, due to the technical level and paper requirements of the restrictions, surface sizing agent can only be used in special paper, Surface Sizing Enhanced Agent such as: banknote paper, bond paper, sea paper and so on. With the improvement of the technical level of the paper industry, the surface sizing of paper has become a conventional paper processing process, especially in recent years due to the printing, copying, fax popularization of cultural paper, wrapping paper and corrugated surface performance, strength and Water resistance made a higher demand, so the paper industry in the continuous exploration of the new surface sizing technology.
Starch is a natural macromolecule compound, which is an important surface sizing agent and paper enhancer. Corn starch is widely used, potato starch use effect is better. Surface Sizing Enhanced Agent Natural raw starch high viscosity, poor mobility, easy to gather, diluted with water easy to precipitate, in the cohesive, film-forming aspects of the existence of great limitations, so in the sizing system is the use of modified starch.
The use of starch modified as the surface sizing agent is the biggest advantage of raw materials rich, cheap, very suitable for China's national conditions, the other surface enhancement effect is obvious, can improve the printing effect. But the starch is a polymer water-soluble material, Surface Sizing Enhanced Agent the structure contains hydrophilic base, after the film is difficult to resist the penetration of liquid. This requires the use of modified starch and other surface sizing agent used to meet the requirements of paper. The most commonly used surface sizing is oxidized starch.
PAM as a surface sizing agent, and glyoxal should be mixed, both in the process of drying can form a cross-linked network. Due to the presence of trivalent aluminum ions and calcium ions in the paper sheet, some of the -CONH: groups in the PAM molecule are hydrolyzed to -COOH, Surface Sizing Enhanced Agent which produce ion-crosslinking bonds with -COOH in PAM, Paper and produce water resistance. PAM price is high, good quality, suitable for use with cheap starch.
Polyvinyl alcohol according to the degree of polymerization and degree of hydrolysis is different, divided into many grades. Generally used as a surface sizing PVA polymerization degree of l000 ~ 2000, alcoholysis degree of 98% to 99%. China's production of PVA, for the surface sizing is mainly 1798, that is, polymerization degree of l700, alcoholic degree of 98%. The PVA surface sizing paper, dry fiber has a good adhesion, Surface Sizing Enhanced Agent the surface strength is good, PVA formed by the film has a good resistance to grease, but the drawback is high viscosity, poor coating, easy to penetrate into the paper Layer (only to enhance the role of the surface strength), usually in order to achieve the desired surface sizing effect, can not help but increase the amount. Surface Sizing Enhanced Agent In order to solve this problem, boric acid pretreatment technology can be used. The principle is that the boric acid-treated paper in the coating of PVA, boric acid and PVA can be cross-linked reaction to form a gel, Surface Sizing Enhanced Agent inhibit the PVA to the paper layer Excessive penetration. To achieve the same surface strength, if only PVA may use 3% solution, but using l% ~ l.5% boric acid solution, the concentration as long as l% is enough. Surface Sizing Enhanced Agent Now the use of starch polyvinyl alcohol as a surface application of paper and paper mills continue to decrease.