The unevenness of the bonding strength of corrugated boxes mainly depends on the quality of the adhesive and the sizing quality of the corrugated board production line.
The quality of the adhesive mainly depends on the quality of the adhesive manufacturing process and the quality of the materials used. The main raw material used in the adhesive is starch, and corn starch above the industrial grade is generally used. If starch of lower grade is used, due to its poor processing fineness and more impurities such as protein and fat, more caustic soda will be consumed, which will make the adhesive unstable, the bonded corrugated cardboard is easy to absorb moisture, and the adhesive It is easy to gel with larger starch granules and impurities as the core, which makes the fluidity worse.
Solid content, initial tack, viscosity, gelatinization temperature, etc. are important targets to measure the quality of adhesives:
1. solid content
The solid content of the adhesive should be determined according to the accuracy of the equipment, the running speed and the actual situation of the base paper. Once the speed of the high-speed wide-width corrugated board production line reaches 200 m/min or more, the solid content of the adhesive must be high, and the water and the The ratio of starch is usually between 2.5:1-3:1. When the solid content of the adhesive is high, the moisture is relatively reduced, and a small amount of glue can ensure the bonding of the corrugated board; and the moisture change is small during the processing of the corrugated board, which can reduce the warping of the corrugated board. If the equipment accuracy of the enterprise is low, the speed of the vehicle is slow, and the base paper is easy to penetrate, the solid content of the adhesive should be lower, otherwise it will cause quality problems such as degumming of corrugated cardboard, crystallization of paste lines and burst lines.
2. Initial viscosity
Preliminary tack is the key to ensuring corrugated board bonding and increasing vehicle speed. In the production of corrugated cardboard, increasing the preheating area of the base paper, or adding a cross-linking agent when manufacturing the adhesive, adding borax to the main body and the carrier tank respectively, and increasing the solid content of the adhesive can make the adhesive coating After a short period of time, the adhesive force begins to occur, and its adhesive force can destroy the paper fibers.
The lower the viscosity of the adhesive, the better the flow. The fluidity of the adhesive determines the permeability of the adhesive, the uniformity of gluing and the amount of glue, and directly affects the speed of the vehicle, the adhesion of the cardboard, the flatness and strength of the cardboard. In addition, it is not that the higher the proportion of starch in the adhesive, the poorer the fluidity; the adhesive with high solid content can maintain a very low viscosity after adjusting the manufacturing process. Under normal circumstances, the viscosity of the adhesive will decrease every time it passes through the circulating pump during the circulating use. At this point, it should be mixed with the newly manufactured adhesive.
4. gelatinization temperature
The gelatinization temperature refers to the initial temperature required to turn the starch binder into a paste. The gelatinization temperature of the binder is a key factor in maintaining high-speed production. In addition to the dosage and heating method, appropriate addition of some additives can also have the same effect. The gelatinization temperature should not be too low, otherwise the adhesive will be gelatinized during the cycle and affect the fluidity of the adhesive. The gelatinization temperature of the adhesive should be adjusted according to the change of season. In winter, the gelatinization temperature can be lowered to 55-60℃, and in summer, the gelatinization temperature can be increased to 61-66℃.