Cartons are widely used, and their moisture-proof operation is very important. For a long time in our country, the carton has been coated with a layer of waterproof agent, which is bright, strong, and has excellent water resistance, and will not collapse after painting. This kind of waterproof agent is often solvent based (perhaps called oil-based), which is harmful to the operator's body, the environment, and the recovery of cartons. In recent years, it has been rarely used, instead of water-based or emulsion waterproof coating. The water emulsion waterproof coating can meet the requirement of being almost impermeable when it is touched with water for a long time. However, if the coating contains more water and is naturally dry for a long time, it is easy to cause collapse or separation of face paper and corrugated.
To deal with these problems, we must start from three aspects:
The nonvolatile content of paint shall be high;
A little non-toxic volatile solvent soluble in water can be appropriately added to speed up the evaporation of water;
Change the operation method of craft painting, and produce by machine painting and drying. The first two items of the existing waterproof coatings have actually been selected, while the third item is difficult to use the existing coatings. Therefore, the dry forming temperature of corrugated paperboard is generally about 150 º C, and some of it is as high as 180 º C. The general thermoplastic polymer coating has become sticky at this temperature. When the paperboard coated with this coating passes through the hot plate, the paper is often roughened and even the surface can be torn. However, a new waterproof coating for corrugated board can overcome this defect. This coating is a combination of polymer emulsion and wax emulsion. This polymer emulsion has good film-forming property and water resistance. The particle size of the emulsion is smaller than that of the wax emulsion. After coating, the permeability of the emulsion to paper is stronger than that of the wax emulsion, because it has poor compatibility with wax. After film-forming, wax is separated from the polymer membrane. In addition, most wax particles blocked by the paper fiber float on the paper surface fiber.
When the corrugated box passes through the forming heating plate, because of the wax effect, the paper surface is less sticky, and the paper surface will not be roughened. Together, the polymer film will not be scratched under the wax maintenance effect, so that the paper board can have a lasting waterproof effect. This kind of paint also solves the problem of low painting power. Together, because of the existence of wax, it acts as a matting agent and keeps the nature of cardboard. This kind of coating is emulsion type, and printing with water-based ink will not show the phenomenon of non ink. Finally, it must be pointed out that the main resin in this polymer emulsion is easy to be dissolved by alkali water, which is also convenient for the recovery of paper. The new moisture-proof scheme, the single waterproof treatment of paperboard, is only one aspect of expanding the use of cartons. If it is considered together with water resistant adhesive, such cartons can be directly used to hold fresh fruits and vegetables. If waterproof coating has a certain strengthening effect, plus the use of reinforced adhesive, there should be advantages for those cardboard boxes made of recycled cardboard boxes and short fibers.
