Corrugated board adhesive strength depends mainly on the quality of the adhesive and corrugated board production line sizing quality.
Adhesive quality
The quality of the adhesive depends mainly on the strength of the adhesive manufacturing process and the quality of the raw materials used. The main raw material used for the binder is starch, which generally uses cornstarch above industrial grade one. If starches with lower grades are used, due to poor processing precision, impurities such as proteins and fats will be consumed, more caustic soda will be consumed, the binder will be unstable, the bonded corrugated cardboard will absorb moisture easily, and the adhesive It is easy to produce gels with larger starch granules and impurities as the core, which deteriorates the fluidity.
Solid content, initial viscosity, viscosity, gelatinization temperature, etc., are important indicators for measuring adhesive quality:
1. Solid content
The solid content of the adhesive should be determined according to the equipment accuracy, operating speed, and the actual condition of the base paper. Once the high-speed wide corrugated board production line reaches a speed of 200 m/min or more, the solid content of the adhesive must be high. Water and starch are required. The ratio is usually between 2.5:1-3:1. The high solid content of the binder, the relative reduction of moisture, the smaller amount of glue can ensure the adhesion of corrugated board; and the change of moisture during the processing of corrugated board is small, which can reduce the warpage of corrugated board. If the precision of the enterprise equipment is low, the speed is slow, and the base paper is permeable, the solid content of the adhesive will be lower, otherwise it will cause quality problems such as degumming of corrugated cardboard, crystallization of paste lines, and popping.
2. Early tack
The initial tack is the key to ensure the adhesion of corrugated cardboard and increase the speed. In the production of corrugated board, the preheating area of ​​the base paper is increased, or the cross-linking agent is added during the production of the adhesive, and borax is added to the main body and the carrier tank to increase the solid content of the binder, and the adhesive can be coated. After a short period of time began to produce adhesion, and its viscosity can damage the paper fiber.
3. Viscosity
The lower the adhesive viscosity, the better the flowability. The fluidity of the adhesive determines the permeability of the adhesive, the uniformity of the sizing, and the amount of glue, directly affecting the speed of the vehicle, the bonding of the paperboard, the flatness and strength of the paperboard. In addition, the higher the proportion of starch in the binder, the lower the flowability; the high solid content binder can also maintain a very low viscosity by adjusting the formulation process. Under normal circumstances, when the adhesive is recycled, its viscosity will decrease once it passes through the circulation pump. At this point, it should be blended with the newly produced adhesive.
4. Gelatinization temperature
The gelatinization temperature refers to the initial temperature required to convert the starch binder into a paste. The gelatinization temperature of the binder is a problem in solving the gelatinization temperature of the binder, which is a key factor in maintaining high-speed production, except that the caustic soda is adjusted. Dosage and heating methods, the appropriate addition of some additives can also have the same effect. The gelatinization temperature should not be too low, otherwise it will cause the adhesive to gelatinize during the cycle and affect the adhesive's fluidity. The gelatinization temperature of the adhesive should be adjusted according to seasonal changes. In the winter, the gelatinization temperature can be adjusted to 55-60°C, and in the summer, the gelatinization temperature can be increased to 61°C-66.
Corrugated board production line sizing quality
In Europe and America, the most important one for checking the quality of corrugated cartons is the inspection of the width of the viscose glue line of corrugated cardboard. The standard sizing is precisely positioned, the adhesive is applied evenly and smoothly throughout the peak, the paste lines are clearly outlined, and no adhesive is ejected laterally from the corrugations, leaving no trailing glue marks.