Research and Countermeasures on Corrugated Board Phenomenon and Bonding Problems (2)

(II) Research and Countermeasures on Bonding Quality of Corrugated Cardboard

1, adhesive

There are many reasons for the poor bonding of corrugated cardboard (such as foaming, degumming, and false-grain) in corrugated board production lines. There are problems with the moisture content of the base paper, problems with improper control of the amount of glue applied in production, and adhesion. Agent quality problems etc. Among them, the adhesive bonding mechanism is the first problem that should be solved.

There are many types of adhesives, such as starch adhesives, polyvinyl alcohol, vinyl acetate emulsions, and water glass. At present, most manufacturers use starch-based adhesives. Compared with other adhesives, starch adhesives have the following advantages: (1) strong adhesion, easy penetration into the paper to produce adhesion; (2) good initial viscosity; (3) easy storage; (4) good adhesion The appearance of the cardboard box is firm and flat, and it is not easy to run and absorb moisture. However, in the production, starch binders also have shortcomings such as long reaction time, difficult to control oxidation depth, unstable quality, and complicated reaction process. In addition, most manufacturers in the production of starch adhesives mechanically apply the reaction conditions of industrial oxidized starch, can not effectively control and adjust the adhesive formulation, process and oxidation depth, not only wasted raw materials, extended reaction time, and sticky The quality of the mixture is not controlled, affecting the performance of the corrugated board. Therefore, the use of water and a complexing agent only when used can provide a pre-oxidized starch binder for use in the bonding of corrugated cardboard. In fact, starch glues used in single-sided machines and double-sided machines are different even on the same production line. For the bonding of corrugated cardboard, the bonding mechanism is the prerequisite for the formulation of the adhesive; and in terms of the quality of the adhesive, the viscosity and gel point are two important indicators to measure quality.

2. Adhesion mechanism between core paper and face paper

The bonding of the corrugating medium to the tissue paper is mainly a cohesive bonding of the starch adhesive, which is supplemented by osmotic adhesion and surface adhesion. The sizing penetrates the inner surface of the paper and the surface of the corrugating medium, and penetrates into the fiber gap of the paperboard to cause penetration adhesion. At the same time, the face paper and the corrugating medium and the adhesive surface are formed with an adhesive shoulder, ie a surface bond is formed. The adhesive that penetrates the paperboard forms a collection with the adhesive shoulders on the paperboard surface. This intermolecular adhesion is called cohesive bonding. Three types of adhesively bond the tissue to the core paper.

Corrugated board adhesive molding each step has a direct relationship with the adhesive bonding mechanism. The nature of starch is due to the fact that the starch molecules contain hydroxyls that are prone to chemical reactions, so the starch can react chemically with many substances. In the starch molecule, hydrogen bonds can be formed between hydroxyl groups on adjacent segments, thereby increasing the stability of the starch granules in the solution. During the use of starch, it is common to first destroy the granule structure and cause swelling of the granules, so that the starch molecules hydrate and dissolve. It is called gelatinization of starch. The whole process of bonding is done on core paper with sufficient heat and humidity. The adhesive applied to the peak gradually wets, diffuses, and penetrates into the paper fiber structure. At this point, the raw starch will rapidly gel aging and evaporate the water under high temperature and finally reach full cure. When the five bonding steps of the corrugated cardboard bonding mechanism described above are synchronized, the best bonding effect will be obtained. If the adhesive gel is too fast, it will cause the glue to spread and infiltrate insufficiently to assemble on the surface of the cardboard and condense into crystals, causing false sticking of the cardboard; if the adhesive gel is too slow, there will be a lot of glue spread and penetration On the sides of the peak application line, white lines appear, and raw starch loses its viscosity due to its inability to ripen, resulting in poor adhesion of the cardboard.

Thus, finding the gel point of the adhesive will be the key to solving the adhesive effect of the paperboard. Due to the structural differences between single-sided and double-sided machines, it was decided that the adhesive formulation should be different. Under normal circumstances, single-side machine should choose the formula with low viscosity and high gel point; while the double-sided machine should choose formula with higher viscosity and lower gel point to meet the needs of cardboard adhesive forming. The reason is: in the single-sided machine, due to its unique sizing mechanism decided that the bonding process is in the high temperature, high-speed bonding state of the formation, in a matter of time to complete the glue - penetration - phase - Bonding—Fixing and other five adhesive forming steps require that the single-sided machine adhesive should be of low viscosity and high gel point in order to facilitate penetration and adhesion of glue in a very short time. On the double-sided machine, due to a long time, and the glue application mechanism is cold sizing, the double-sided machine bonding process is completed at room temperature and the adhesive molding requires the double-sided machine adhesive to be of higher viscosity. Lower gel point for slow diffusion, gelling and bonding. Under normal circumstances, single and double-sided machine adhesive quality requirements shown in Table l.

The data in Table 1 is not static. As the steam pressure and production speed provided by the equipment and the moisture content of the base paper are constantly changing during the production process, it is necessary to adjust it in a timely manner to meet the needs of various steps in adhesive forming in order to achieve the best Adhesion effect. (Author: Zhou Xiaoyuan)