Corrugated board (box) water content control
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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. Corrugated cardboard is made of fiber base paper and is greatly affected by environmental factors. Therefore, the biggest technical problem in corrugated cardboard packaging is that it is difficult to resist moisture. In transportation and storage, the environment with high humidity will absorb moisture and reduce the strength, which will cause the corrugated box to lose its function and cause damage to the product. In the high-temperature and dry environment, the moisture of the corrugated cardboard will be dry after a certain degree of moisture reduction, and the folding resistance of the cardboard will be reduced, and finally the carton flap will be broken. Therefore, the biggest drawback of corrugated board is that it is brittle when dry and the strength is lowered when it is wet. Therefore, how to control the water content of corrugated board and reduce the environmental interference of corrugated board is a very complicated and very important work.
The fault is closely related to the water content
It has been found through statistics that the moisture content of corrugated cardboard is too high, too low, and uneven water distribution can cause corrugated cardboard to malfunction. Details are as follows.
The faults caused by excessive water content are: smashing, opening of the edge of the paper on the double-sided machine, excessive cracking of the slitting edge, smashing damage, corrugated pressing, obvious unbonded stripes on the corrugated cardboard (dry stripes), The corrugated cardboard is warped longitudinally, and the corrugated sheet is unevenly formed.
The faults caused by the low water content are: heavy cracks in the longitudinal cutting edge, corrugated cracks, running shovel, uneven corrugation and the like.
The faults caused by uneven water distribution are: wrinkling of corrugated surface and corrugated top, corrugated wrinkles, transverse warping of corrugated cardboard, longitudinal warping of corrugated cardboard, S-shaped (composite) warping of corrugated cardboard, unevenness of niobium, uneven formation of corrugated Wait.
Main factors affecting water content
Corrugated board production process is relatively complicated, and its water content is affected by many factors, which can be summarized as follows.
(1) The moisture content of the base paper used for the production of paperboard.
According to the national standard, the water content of the raw paper is generally 9% to 12%. Whether the moisture content of the base paper meets the standard will directly affect the production process of the corrugated board and whether the water content meets the production requirements.
(2) Drying at the preheating drum.
The function of the preheating roller is mainly to evaporate the water in the raw paper put into production and to make the water uniform, which plays a role in regulating the moisture of the base paper.
(3) Characteristics of paper materials and glue.
If the fiber structure of some core paper or corrugated paper is loose, or the viscosity of the glue is poor, the moisture content of the paperboard is high.
(4) The influence of the drying and cooling process after the cardboard is bonded.
When drying, the oven temperature is low, the production speed is fast, the heat absorbed by the corrugated cardboard is insufficient, the drying is slow, and the water content is high, so that the paperboard adhesive is incompletely gelatinized and solidified, and the strength is lowered; on the contrary, the water content is low.
(5) The impact of the production environment.
It mainly includes the temperature, humidity and ventilation effect of the production workshop.
(6) The impact of the circulation environment.
Corrugated boxes are very susceptible to the circulation environment during use. The moisture and temperature of the circulation environment will have a direct impact on the moisture content of the corrugated boxes, which will affect the performance and service life of the corrugated boxes.
Main ways of moisture control
The national standard for moisture content of corrugated board is (11±3)%. In order to ensure the production of carton, good printing, strong bonding, smooth trimming, strong pressure resistance, reduced waste, improved labor productivity and increased economic benefits, it is necessary to , production process, equipment environment and other aspects to take effective measures to control the moisture content of corrugated board, so that it is maintained within the standard range to ensure the production quality of corrugated board.
The main methods for moisture control of corrugated board are as follows.
(1) The water content of the raw paper entering the factory should be strictly controlled.
According to the national standard, the water content of the raw paper in the delivery state is generally 9% to 12%. First of all, in the procurement of the base paper, the quality should be checked, and the moisture content of the raw paper entering the factory should be strictly checked, and the supplier should be required to supply the qualified base paper.
In addition, the original paper storage must set up a separate warehouse, the temperature is generally 15 ~ 20 ° C, the relative humidity is generally 30% ~ 40%.
Do not put it in the open air, which will easily cause the change of water content of the base paper, and cause the water content of the two ends and the middle part to be inconsistent, which will bring more trouble to the processing in the future.
(2) Perform reasonable temperature control.
Temperature is one of the determining factors affecting the quality of corrugated board. Reasonable temperature control is required during corrugated board production. The temperature can adjust the water content of the base paper and affect the temperature of the base paper, so that the paste can be solidified in a reasonable time.
A number of preheaters and drying plates are provided on the corrugated board production line to adjust the water content of the base paper and the single-sided paperboard, and to solidify the paste and bond the corrugated board of each layer. Under normal circumstances, when the vehicle speed is above 100m/min, the curing temperature of the paste liquid is 160-180 °C, that is, the pressure of the saturated steam of the boiler should reach 0.9-1.4Mpa. The temperature control mainly includes temperature control of the preheating drum, temperature control of the dryer, temperature control of the draining device, and the like.
(3) Reasonable regulation of the quality of the paste, the size of the paste, the size of the water content, and the thickening.
If the water content of the paste liquid is large, the paste is thin and the penetration is fast, the water content of the paperboard is high, and the water content is small. When the amount of paste is large, the water content of the paperboard is large; the amount of paste is small, and the water content is small. Therefore, it is necessary to strictly follow the water content and ratio of the paste and the mixing time to make the paste, and master the viscosity of the paste.
(4) Anti-moisturizing treatment of corrugated cardboard.
The anti-moisturizing agent emulsion is prepared, and the principle of energy balance is used to penetrate into the paper fiber material, and a protective film is formed on the surface thereof, and the surface tension, the surface free energy and the solid-liquid intercalation work are realized by means of a spraying system. The balance between the emulsion penetration and the film formation process is finally achieved, and finally the corrugated packaging board which does not affect the printing and has the moisture resistance property is obtained.
(5) The corrugated board has a hydrophobic function by coating a surface of the corrugated board with a hydrophobic agent such as paraffin, silicone or varnish.
Hydrophobic corrugated board is also called water-repellent corrugated board. When it is exposed to water for a short time, the surface of the processed cardboard makes the water splash and prevents water from penetrating into the inside of the cardboard.
The hydrophobic corrugated board is suitable for packaging dry powdery articles, especially the powder which is easy to agglomerate after water absorption. It is also suitable for packaging goods that often enter and leave the cold storage. It is easy to dew on the wall after being taken out of the cold storage, and the ordinary corrugated cardboard will be quickly absorbed. The compressive strength is reduced, and the carton cannot be crushed by the stacking pressure. The hydrophobically processed paperboard does not significantly reduce the compressive strength before the dewdrop evaporates, and can effectively protect the commodity.
(6) Coating the resin on corrugated board.
The molten synthetic resin or paraffin mixture is formed into a film form from the mouth of the hopper, and coated on a horizontally running corrugated cardboard, and a resin film or a wax film is formed on the surface of the paperboard to have good water retaining performance. If necessary, the film is circulated once on the other side to obtain double-sided waterproofing properties, so that the corrugated board has water resistance.
Waterproof (water retaining) corrugated cardboard, also known as water-repellent corrugated cardboard, has a surface that is almost impervious to water for a long time, but cannot be immersed in water, otherwise it will lose its waterproof performance. The result is similar to ordinary corrugated cardboard. Water-resistant corrugated boxes are used to transport a class of commodities with extremely high water content such as live fish and seafood.
(7) Using a special process to make corrugated board have strong water resistance.
Corrugated cardboard is soaked in water for a long time after processing, and the strength is not greatly reduced. It is called strong water-resistant corrugated cardboard. There are two commonly used manufacturing methods, one is a one-time processing method: that is, the base paper is rendered water-resistant at the papermaking stage; and the secondary processing method is to impart water resistance at the manufacturing stage of the corrugated board.
The one-time processing method is a method in which a water-resistant linerboard, a water-resistant corrugated base paper is used together, and a water-resistant adhesive is used, and the corrugated cardboard is processed. Because of the water resistance of the base paper with water resistance, it is moderately water-resistant and highly water-resistant. The corrugated board produced is also moderately water-resistant and highly water-resistant.
The secondary processing method has two methods of coating and dipping.
The coating method refers to installing a roll coater on a corrugated board machine, applying paraffin wax to the liner board and corrugated board, and then bonding. After the corrugated base paper is applied to the hot plate and coated with a binder on one side, the waterproof coating is sprayed on the corrugated base paper. In order to improve the water resistance of the corrugated board end face, it is also necessary to spray the waterproof coating on both ends of the corrugated board before the paper cutting machine of the corrugated board machine.
The dipping method is to make the cardboard through the molten waterproof coating dipping tank, so that the waterproof coating penetrates the surface of the paper, and then the cardboard is sent to the drying section, and is subjected to hot air heating above 105 ° C, so that the surface of the cardboard is adsorbed with the waterproof coating, and after cooling, the waterproof coating It is fixed on the surface of the cardboard to make the cardboard waterproof. 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 general linerboard, the color of the cardboard becomes black.