It is well known that to solve the problem of poor adhesion of corrugated board, it is necessary not only to have a deeper understanding of the bonding and forming principles of the board, but also to have a deeper understanding of the operating characteristics of the board production equipment in order to realize the best process solutions. The ideal product quality enables the cardboard production line to operate with high speed, high efficiency and high quality.

In this issue, we will open up the production of high-quality cardboard channels for the bonding of aggregated corrugated board production.

A solution to "poor bonding" improves board quality

In the production practice of corrugated boxes, the bonding between various papers is a very important link, and to a certain extent determines the quality level of the products. Whether the adhesion between the layers of paper sheets is tight and firmly affects the quality of the corrugated cardboard. The well-bonded corrugated cardboard has a smooth surface without blistering, wrinkles, or warping. After processing into a corrugated box, no separation occurs between the sheets, and the appearance is firm, and the compression and cushioning properties are good and can be effective. Protecting interior contents from being damaged by external factors. However, corrugated paperboards have poor adhesion (bubbling, degumming, and spurious) on corrugated paperboard production lines. It is understood that nearly 70% of the waste defectives produced by corrugated board production lines are due to adhesion problems. Therefore, in order to achieve the objective of cost reduction and efficiency improvement, it is necessary to control the scrap rate due to the adhesion problem within a suitable range. Next, we will find out the cause of the poor adhesion of cardboard, and provide a series of solutions for your problems in the actual production.

Whether or not the corrugated board is well bonded is an important indicator of the physical properties of the corrugated board. The reasons that affect the adhesive strength of corrugated board are relatively complex. In general, the base paper, adhesives, corrugated board machinery, production planning arrangements, and staff operating levels all exerted influence on it. And the above factors will also affect each other.

(a) The base paper

Mainly in several aspects:

The moisture content of the base paper: Containerboard or corrugated base paper is too dry (less than 6%) or excessive moisture (greater than 12%), resulting in poor adhesion of corrugated cardboard. When it is too dry, the moisture necessary for the swelling and adhesion of the adhesive is absorbed by the base paper, resulting in a phenomenon that the adhesive is not gelatinized. When moisture is too large, the excess moisture absorbs heat, resulting in insufficient heat and poor adhesion. The solution is to strictly control the moisture of the base paper. When it is too dry, it must be wetted. When the moisture is too large, the base paper must be properly increased in moisture and warm-up area. If the effect is still not good, the paper must be changed.

Whether the water absorption or water permeability of the base paper is good or bad: The material, tightness and sizing degree of the base paper determine its water absorption or water permeability. Raw papers with poor water absorbability or water permeability will inhibit the penetration of the adhesive and the base paper with high water permeability or water permeability will cause the glue to become ungelatinized, and secondly, it will produce the phenomenon of glue penetration. The former solution is to use additives in the adhesive, and use additives to improve the hydrophobic properties of the surface of the paper to allow the adhesive to penetrate. In addition, it is also necessary to appropriately increase the amount of adhesive applied. We know that the adhesiveness of corrugated board is first of all, paper-bonding, and then combined with the paper or sandwich in the surface, the transfer of adhesive between any layers is hindered, and it will affect the adhesive effect. For example, a company's grade A straw pulp and corrugated paper, after heavy sizing treatment, has poor water absorption and cannot be bonded well without the use of water-resistant adhesives. The latter solution is to appropriately increase the viscosity of the adhesive.

Base paper split length: it is the ratio of the original paper strength to the basis weight, which indicates the length required when a certain width of the paper strip is broken by its own weight. If the base paper has a low split length, frequent breaks and shutdowns will occur if the wire speed reaches a certain level. The corrugated board that stays in the drying tunnel at this time absorbs too much heat, and no matter how good the adhesive can not be bonded well. In this case, the solution is to reduce the speed, or improve the quality of the base paper, and include the crack length in the inspection of the base paper.

Looseness of the base paper: If it is loose on one side of the corrugated paper, it will cause unevenness and corrugation, affecting the fit of the paperboard; if the paperboard is loose on one side, it will form wrinkles on the surface of the paperboard. Poor adhesion is formed when severe. The only solution is to replace the base paper.

(B) The quality of adhesives

Mainly reflect two aspects: First, the quality of starch is good or bad, the second is the merits of adhesive production process.

The lower starch grade means that the fineness of the processing is poor, and impurities such as protein, fat, and ash are more. Using such a starch, it will consume more sodium hydroxide, making the binder unstable, and bonding the corrugated Paperboard is easy to absorb moisture, and placed in a humid environment for a short period of time will debond the corrugated cardboard. Second, the adhesive will tend to produce gels with larger starch particles and impurities as the core, resulting in poor fluidity of the adhesive and uneven coating. Therefore, the corrugated paperboard has no local glue and little glue, resulting in poor adhesion. The solution is to use high-quality starch. If it is corn starch, industrial grade one or more should be used. Advantages and disadvantages of adhesive preparation process are even more important. Corrugated board adhesives, with proper solids content, viscosity, and necessary gelatinization temperature. In general, the viscosity of a conventional adhesive has a decreasing tendency every time it passes through the circulation pump. At this point, new binders should be added for mixing.

In addition, when the holiday is shut down, excess binder is stored in the tank, especially in hot summer season, the bacteria decompose the starch, cause corruption and cause a sharp drop in viscosity, resulting in starch precipitation, resulting in poor adhesion. The solution is to add a preservative such as formaldehyde, 0.35 kg per 200 kg starch, or sodium pentachlorophenol, with 0.32 kg per 200 kg starch.

When making water-resistant paperboard, advanced board paper and corrugated paper are often used, and water-resistant adhesives are used in combination. Polymerization and condensation of thermoplastic resins commonly used in such adhesives can still be carried out, and sometimes the viscosity rises sharply, which is not suitable for the use conditions of corrugated board machines. The solution is to readjust the amount of glue so that the viscosity meets the requirements for use.

When the surface paper or even the core paper has a high specific tightening degree (above 180 g/m2 basis weight and a tightness of 0,70 g/m3 or more), poor adhesion may be caused by insufficient heat. Due to the higher basis weight and the higher tightness of the tissue, the tightness of the tissue is affected and the heat transfer is affected. However, the heat transfer of the A-Watt requires more time, resulting in the occurrence of single-faced A-wax and sandwiched paper. Poor adhesion. The solution to this situation is to reduce the speed and increase the wrap angle between the thick paper and the preheater.

If the absolute heat of the corrugated board machine is insufficient, it is also a good idea to use a binder with a low gelatinization temperature. When the dough paper has a low basis weight (less than 180g/m2), it tends to produce a bubble-like phenomenon on the surface of the dough paper, which is called "bubble", which is a partial degumming phenomenon. After a short period of time on a double-sided corrugated board machine or after the board is mounted on a cart, this phenomenon occurs on one side of the board, which is mainly caused by the large moisture of the board or the dryness of the corrugated board. Due to the imbalance of heat and moisture, the excessively dry corrugated board absorbs moisture at the exit of the double-faced corrugated board machine. Since the longitudinal direction has been fixed, it stretches laterally and the surface forms a small bubble. Solution In addition to minimizing the amount of adhesive, cutting off part of the heat of the hot plate or increasing the speed, making a high-solids, low-viscosity adhesive is also a solution, but be sure to have a good gelatinization temperature.

(to be continued)