Fault caused by improper control of water content in corrugated box and its moisture control method

A few days ago, the number of domestic corrugated board manufacturers continued to increase, and corrugated board production technology was continuously improving. However, there were still many difficulties in how to ensure that the corrugated board (box) was not affected by the environment (moisture).

We know that the moisture content of corrugated board is one of the important indicators of corrugated board, which directly determines the quality of corrugated board produced. Corrugated cardboard is made from fiber base paper and is very much affected by environmental factors. Therefore, the biggest technical problem with corrugated paperboard packaging is that it is difficult to resist moisture. During transport and storage, the environment with high humidity will absorb moisture and reduce the strength, causing the loss of the function of the corrugated carton to cause the product to be damaged. In the high-temperature and dry environment, the corrugated board will have a certain degree of moisture and produce a crisp, cardboard. The folding resistance is reduced and finally the carton flap is broken. Therefore, the biggest drawback of corrugated paperboard materials is brittle cracking during drying and lower strength at high humidity. Therefore, how to control the water content of the corrugated board and reduce the degree of disturbance of the corrugated board due to the environment is a very complicated and very important task.

First, due to the water content caused by corrugated cardboard failure

Failure caused by excessive water content:

The smashing, double-sided machine's upper edge of the paper was opened, the slits of the slits were heavy, the smashed, the corrugated board had obvious unbonded stripes (dry stripes), the corrugated board was warped longitudinally, and the corrugation was not evenly formed.

Failure caused by too low water content: excessive knife-edge cracks, cracks in the corrugation, running defects, uneven forming of corrugations, etc.

Failure due to uneven moisture distribution: corrugation on the surface of cardboard and corrugated top, corrugation, corrugation, lateral warp of corrugated board, longitudinal warp of corrugated board, warp of S-shaped (composite) corrugated board, unevenness of corrugation, uneven forming of corrugated board, etc. .

Second, the main factors affecting the corrugated board (box) moisture content

Corrugated board production process is relatively complex, and its water content is affected by many factors, can be summarized as the following:

(a) The moisture content of the base paper used to produce paperboard. According to the provisions of national standards, the moisture content of the original paper delivery state is generally 9% to 12%. Whether the moisture content of the base paper is up to the standard will directly affect the production process of the corrugated cardboard and whether its moisture content meets the production requirements.

(b) Drying at the preheating drum. The function of the preheating drum is mainly to evaporate the water of the raw paper that is put into production and make the water even. It plays the role of regulating the moisture of the paper.

(c) The characteristics of paper raw materials and glue. If some core paper or corrugated fiber has a loose fibrous structure or the glue has poor adhesiveness, the moisture content of the cardboard is high.

(d) The effects of drying and cooling processes after the cardboard is bonded. During drying, the temperature of the oven is low, the production speed is fast, the amount of heat absorbed by the corrugated cardboard is insufficient, the drying is slow, and the moisture content is high, so that the gelatinization and curing of the paperboard adhesive are incomplete, and the strength is reduced. On the contrary, the moisture content is low.

(e) Impact of the production environment. It mainly includes the temperature, humidity and ventilation effects of the production workshop.

(6) The influence of the circulation environment. Corrugated cartons are very susceptible to the circulation environment during use. The moisture and temperature of the circulating environment will have a direct impact on the water content of the corrugated boxes, which will affect the performance and service life of the corrugated boxes.

Third, the main way to control the moisture of corrugated board

The national standard for the moisture content of corrugated cardboard is 11±3%. To ensure the production of cartons, good printing, firm bonding, smooth cut edges, strong pressure resistance, reduced waste, higher labor productivity, and increased economic efficiency of enterprises, raw materials, The production process, equipment environment and many other aspects to take effective measures to control the moisture content of corrugated board to keep it within the standard range, to ensure the quality of corrugated board production. Therefore, the main methods for controlling the moisture in corrugated board are:

(a) The water content of the raw paper to be imported must be strictly controlled. According to the provisions of national standards, the water content of the original paper delivery state is generally 9% to 12%. First of all, in the procurement of base paper, it is necessary to make a good quality inspection and strictly inspect the water content of the raw paper coming into the factory, and require the supplier to supply qualified raw paper. In addition, the base paper storage must set up a separate warehouse, the temperature is generally 15 °C ~ 20 °C, relative humidity is generally 30% ~ 40%. Do not put it in the open air, it will easily cause the change of the moisture content of the raw paper, and cause the water content at both ends and in the middle to be inconsistent, which will cause greater troubles for the subsequent processing.

(2) Temperature is one of the decisive factors affecting the quality of corrugated board. Reasonable temperature control is required during the production of corrugated board. The temperature level can not only adjust the moisture content of the base paper, but also affect the temperature of the base paper, so that the paste can be cured in a reasonable time. Therefore, there are many preheaters and drying boards on the corrugated cardboard production line, which are used to adjust the moisture content of the base paper and the single-sided paperboard, and to make the paste liquid to solidify and bond the various layers of corrugated cardboard. Under normal circumstances, when the vehicle speed is above 100m/min, the curing temperature of the paste liquid is 160°C-180°C, that is, the pressure of the boiler saturated water vapor should reach 0.9Mpa-1.4Mpa. The temperature control includes preheating drum temperature control, dryer temperature control, and hydrophobic device temperature control.

(3) Rational regulation of the quality of the paste, the size of the paste, the amount of water, the thinness, and the thickening. If the paste has a large amount of water, the paste will be thin and the penetration will be fast. The water content of the cardboard will be high, whereas the water content will be small. When the amount of paste is large, the water content of the board is large; the amount of paste is small and the water content is small. Therefore, we must strictly follow the paste water volume and mix ratio and mixing time to paste, master the paste viscosity.

(d) Water-repellent moisturizing treatment of corrugated board. First of all, a water-resistant moisturizer emulsion is prepared. The principle of energy balance is used to penetrate the paper fiber material, and a protective film is formed on the surface. The surface tension, surface free energy and attachment between the solid and liquid are achieved by means of a spraying system. , and then to achieve the balance of emulsion infiltration and film formation process. Finally, a corrugated packaging board that does not affect the printing but has water-resistant moisturizing properties is prepared.

(5) The corrugated paperboard is provided with a hydrophobic function by applying a hydrophobic agent such as paraffin, silicone, and varnish on the surface of the corrugated cardboard. Hydrophobic corrugated paperboard, also known as water-repellent corrugated paperboard, is exposed to water for a short time. After processing the surface of the paperboard, the water is splashed into water droplets to prevent water from penetrating into the interior of the paperboard. The hydrophobic corrugated paperboard is suitable for packaging dry powdered articles, especially powders that are easily agglomerated after absorbing water, and is also suitable for packaging goods that often enter and leave the cold storage. After being taken out of a cold storage, condensation on the wall of the box is easy, and ordinary corrugated cardboard can be quickly absorbed. The reduction of the compressive strength causes the carton to be crushed without stacking pressure, and the cardboard after hydrophobic processing will not significantly reduce the compressive strength before dew evaporation, and can effectively protect the goods.

(6) The molten synthetic resin or paraffin mixture is dropped from the hopper mouth into a film-like shape, coated on horizontally running corrugated cardboard, and a layer of resin film or wax film is formed on the surface of the paperboard, which has good water-blocking performance. If necessary, the film is circulated once again on the other side so as to obtain double-sided waterproof performance, so that the corrugated board has water resistance. Water-repellent (water-blocking) corrugated paperboard is also called water-blocking corrugated paperboard. Its surface is in contact with water for a long time and is almost impermeable to water, but it cannot be immersed in water, otherwise it will lose its waterproof performance.

(seven) using a special process to make corrugated board with strong water resistance. Corrugated board is treated with water-repellent corrugated paperboard after being processed for a long time. The strength is not greatly reduced. There are two commonly used manufacturing methods. One is a one-time processing method, that is, water resistance is imparted to the base paper at the papermaking stage, and a secondary processing method is a processing method that imparts water resistance during the manufacture of corrugated cardboard.

The primary processing method is a method of forming a corrugated paperboard by combining a water-resistant linerboard and a water-resistant corrugated base paper and then using a water-resistant adhesive. Because of its water resistance, the base paper has a medium water resistance and a high degree of water resistance. The manufactured corrugated paperboard also has medium water resistance and high water resistance.

The secondary processing method includes coating method and impregnation method:

The coating method refers to installing a roll coater on a corrugated board machine, applying paraffin wax to the linerboard and corrugated cardboard, and then bonding. After the corrugated paper is applied to the hot plate, it is coated with adhesive on one side, and then the waterproof coating is sprayed on the corrugated paper; sometimes, in order to improve the water resistance of the corrugated board, the corrugated board is also used before the paper cutting machine of the corrugated board machine. Spray on the two ends of the waterproof coating.

Impregnation method is to make the board through the molten waterproof coating impregnated tank, so that the waterproof coating soaked the surface of the paper, and then send the cardboard into the drying section, subjected to hot air heating above 105 °C, so that the cardboard surface adsorption waterproof coating, after cooling, waterproof coating It is fixed on the surface of the board, so that the board has good water resistance. When the impregnation method is used, when the impregnation amount of the waterproof coating reaches 40% to 50% of the weight of the base paper, the strength of the paperboard can be greatly improved, but when used for a general linerboard, the color of the cardboard will become black.

Fourth, the conclusion

The performance of corrugated board is closely related to its moisture content. For this reason, we need to understand the influencing factors of the water content of corrugated board, and proceed from these influencing factors, combine the actual production and processing activities to control the water content of corrugated board reasonably and ensure the quality of corrugated board. .

Reprinted from: Guangdong Packaging Magazine