A few days ago, the number of domestic corrugated board manufacturers continued to increase, and corrugated board production technology also continued to improve, but how to ensure that corrugated board (box) is protected from the environment (moisture) is still facing many problems.
We know that the moisture content of corrugated cardboard is one of the important indicators of corrugated cardboard, which directly determines the quality of corrugated cardboard produced. Corrugated cardboard is made of fiber base paper and is greatly affected by environmental factors. Therefore, the biggest technical problem of corrugated cardboard packaging is that it is difficult to resist moisture and moisture. In transportation and storage, the environment with high humidity will absorb moisture and reduce the strength, which will cause the loss of the function of the corrugated box and cause damage to the product. In a high-temperature and dry environment, the corrugated cardboard will be dry and dry after the moisture drops to a certain level. Folding resistance is reduced, and finally the carton flap is broken. Therefore, the biggest defect of corrugated cardboard material is brittleness when drying, and the strength is reduced when high humidity. Therefore, how to control the moisture content of corrugated board and reduce the degree of interference of corrugated board by the environment is a very complicated and very important task.
1. Corrugated cardboard failure caused by water content
Failure caused by high water content:
Corrugated, unglued paper edges on the double-sided machine, excessive cracks on the slitting edge, corrugated damage, obvious unbonded stripes (dry stripes) on corrugated cardboard, longitudinal warpage of corrugated cardboard, uneven corrugated forming, etc.
Failure caused by too low water content: excessive slits on the slitting edge, corrugated cracks, running corrugations, uneven corrugated forming, etc.
Failure caused by uneven moisture distribution: corrugated cardboard surface and corrugated top, corrugated wrinkles, horizontal warpage of corrugated cardboard, longitudinal warpage of corrugated cardboard, S-shaped (composite) warpage of corrugated cardboard, uneven flute, uneven corrugated forming .
Second, the main factors affecting the moisture content of corrugated cardboard (box)
The production process of corrugated cardboard is relatively complicated, and its moisture content is affected by many factors, which can be summarized as the following:
(1) The moisture content of the base paper used in the production of paperboard. According to the national standard, the moisture content of the base paper in the delivery state is generally 9% to 12%. Whether the moisture content of the base paper meets the standard will directly affect the production process of corrugated cardboard and whether its moisture content meets the production requirements.
(2) Drying at the preheating drum. The function of the preheating roller is to evaporate the moisture of the base paper that is put into production and make its moisture uniform. It plays a role in adjusting the moisture of the base paper.
(3) Characteristics of paper raw 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 cardboard is high.
(4) The influence of the drying and cooling process after the cardboard is bonded. When drying, the temperature of the oven is low, the production speed is fast, the heat absorbed by the corrugated cardboard is insufficient, the drying is slow, and the moisture content is high, which makes the adhesive of the cardboard paste and curing incomplete, reducing the strength, otherwise, the moisture content is low.
(5) The impact of the production environment. Mainly include the temperature, humidity and ventilation effect of the production workshop.
(6) The influence of the circulation environment. Corrugated boxes are very easily affected by 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 in turn will affect the performance and service life of the corrugated boxes.
3. The main ways of moisture control of corrugated board
The national standard for the moisture content of corrugated cardboard is 11 ± 3%. In order to ensure carton production, good printing, firm adhesion, smooth trimming, strong resistance to pressure, reduce waste, improve labor productivity, and increase the economic benefits of enterprises, it is necessary to start from raw materials, The production process, equipment environment and other aspects have taken effective measures to control the moisture content of the corrugated board, keep it within the standard range, and ensure the production quality of the corrugated board. Therefore, the main methods of corrugated board moisture control are:
(1) Strictly control the moisture content of raw paper entering the factory. According to the provisions of national standards, the moisture content of the base paper in the delivery state is generally 9% to 12%. First of all, in the purchase of base paper, the quality should be well controlled, and the moisture content of the base paper entering the factory should be strictly checked, and the supplier should be required to supply qualified base paper. In addition, the original paper storage must set up a separate warehouse, the temperature is generally 15 ℃ ~ 20 ℃, the relative humidity is generally 30% to 40%. Do not put it in the open air, as this will easily cause changes in the moisture content of the base paper, and cause inconsistencies in the moisture content at both ends and in the middle, which will cause greater troubles for future processing.
(2) Temperature is one of the decisive factors affecting the quality of corrugated cardboard. Reasonable temperature control should be carried out during the production of corrugated cardboard. The temperature 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, many preheaters and drying boards are installed on the corrugated cardboard production line to adjust the moisture content of the base paper and single-sided cardboard, and to solidify the paste, and to adhere the corrugated cardboard layers. Normally, when the vehicle speed is above 100m / min, the curing temperature of the paste is 160 ℃ ～ 180 ℃, that is to say, the pressure of the saturated steam of the boiler should reach 0.9Mpa ～ 1.4Mpa. The temperature control mainly includes the temperature control of the preheating drum, the temperature control of the dryer, and the temperature control of the hydrophobic device.
(3) Reasonably adjust the quality of the paste, the amount of paste, the size, thinness, and thickness of the amount of water. If the amount of paste water is large, the paste is thin and penetrates quickly, the moisture content of the cardboard is high, otherwise the moisture content is small. When the amount of paste is large, the moisture content of the cardboard is large; the amount of paste is small, the moisture content is small. Therefore, the paste should be prepared strictly in accordance with the amount of water and the ratio of the paste and the stirring time, and the viscosity of the paste should be mastered.
(4) Carry out anti-water and moisturizing treatment on corrugated cardboard. First, prepare a water-resistant humectant emulsion, use the principle of energy balance to penetrate into the paper fiber material, and form a protective film on its surface, using the spray system to achieve its surface tension, surface free energy and solid-liquid attachment work , And then achieve the balance between emulsion penetration and film formation. The corrugated packaging board with water resistance and moisturizing properties is produced without affecting printing.
(5) By coating paraffin, silicone, varnish and other hydrophobic agents on the surface of corrugated cardboard, the corrugated cardboard has a hydrophobic function. Water-repellent corrugated paperboard is also called water-repellent corrugated paperboard. When it is exposed to water for a short time, the processed surface of the paperboard makes the water splash into water droplets and prevents water from seeping into the interior of the paperboard. The hydrophobic corrugated cardboard is suitable for packaging dry powdery articles, especially powders that are easy to agglomerate after absorbing water, and is also suitable for packaging commodities that often enter and exit the cold storage. It is easy to dew on the wall of the box after being taken out of the cold storage, and ordinary corrugated cardboard will quickly absorb The reduction of the compressive strength causes the carton to be crushed by the stacking pressure. The cardboard after the hydrophobic processing will not significantly reduce the compressive strength before the dewdrop evaporates, which can effectively protect the goods.
(6) The molten synthetic resin or paraffin mixture flows down from the hopper mouth into a film and is coated on corrugated cardboard running horizontally. A resin film or wax film is formed on the surface of the cardboard, which has good water-blocking performance. If necessary, circulate the film once on the other side in order to obtain double-sided waterproof performance, so that the corrugated cardboard has water resistance. Waterproof (water-retaining) corrugated cardboard is also called water-shielding corrugated cardboard. Its surface is almost impermeable to water for a long time, but it cannot be immersed in water, otherwise it will lose its waterproof performance.
(7) Using special technology to make corrugated cardboard with strong water resistance. Corrugated paperboard is soaked in water for a long time after processing, and the strength is not greatly reduced is called strong water-resistant corrugated paperboard. There are two commonly used manufacturing methods. One is the primary processing method: that is, the base paper is endowed with water resistance during the papermaking stage; and the secondary processing method: the processing method that is endowed with water resistance in the corrugated board manufacturing stage.
The one-time processing method is a method of combining water-resistant linerboard and water-resistant corrugated base paper and then using water-resistant adhesives to make corrugated board after processing. Since the water resistance of the base paper with water resistance is divided into medium water resistance and high water resistance, the corrugated cardboard produced also has two kinds of medium water resistance and high water resistance.
There are two secondary processing methods: coating method and dipping method:
The coating method refers to installing a roll coating machine on the corrugated board machine, applying paraffin to the liner board and the corrugated board, and then bonding. After applying the adhesive on one side of the corrugated base paper before it enters the hot plate, spray the waterproof coating on the corrugated base paper; sometimes in order to improve the water resistance of the corrugated board end surface, the corrugated board machine must be Spray water-proof paint on the incisions at both ends.
The dipping method is to make the paperboard pass through the dipping tank of molten waterproof paint, so that the waterproof paint soaks the surface of the paper, and then send the paperboard to the drying section, which is heated by hot air above 105 ° C to allow the paperboard surface to absorb the waterproof paint. It will be fixed on the surface of the cardboard to make the cardboard have good waterproofness. Using the impregnation method When the additional amount of impregnation of the waterproof coating reaches 40% to 50% of the weight of the base paper used, the strength of the paperboard can be greatly improved, but when it is used for general linerboard, the color of the paperboard will become black.
4. Conclusion
The performance of corrugated cardboard is closely related to its moisture content. To this end, we must understand the influencing factors of the moisture content of corrugated cardboard, and from these influencing factors, combine the actual production and processing activities to reasonably control the moisture content of corrugated cardboard to ensure the quality of corrugated cardboard .
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