Failure and moisture caused by improper water cont

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Faults caused by improper control of water content in corrugated boxes and ways to control water content

recently, the number of domestic corrugated board manufacturers is increasing, and corrugated board production technology is also improving, but there are still many problems in how to ensure that corrugated board (boxes) are free from the impact of environment (water)

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 board is made of fiber base paper, which is greatly affected by environmental factors. Therefore, the biggest technical problem of corrugated board packaging is that it is difficult to resist water and moisturize. During transportation and storage, in case of high humidity environment, it will absorb moisture and reduce the strength, so that the function of corrugated box will be lost and the product will be damaged. In high temperature and dry environment, when the moisture of corrugated board is reduced to a certain extent, it will produce crispness, the folding resistance of corrugated board will be reduced, and finally the carton flap will be broken. Therefore, the biggest defect of corrugated board material is brittle when dry, and the strength decreases when high humidity. Therefore, how to control the water content of corrugated board and reduce the interference of corrugated board by the environment is a very complex and important work

I. corrugated board failure caused by water content

failure caused by too high water content:

reverse corrugation, glue opening on the edge of the face paper on the double-sided machine, excessive cracks on the longitudinal cutting edge, corrugation damage, obvious unbonded stripes (dry stripes) on the corrugated board, longitudinal warpage of the corrugated board, uneven corrugation forming, etc

faults caused by low water content: excessive cracks, corrugation cracks, runout, uneven corrugation forming, etc. on the longitudinal cutting edge

faults caused by uneven water distribution: wrinkling on the surface and top of the corrugated board, corrugation, transverse warping of the corrugated board, longitudinal warping of the corrugated board, S-shaped (composite) warping of the corrugated board, uneven corrugation, uneven corrugation forming, etc

second, the main factors affecting the water content of corrugated board (box)

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

(I) the water content of the base paper used in the production of corrugated board. According to the national standard, the water content of the base paper in the delivery state is generally 9% - 12%. Because of its biodegradable characteristics, whether the water content of the base paper meets the standard will directly affect the production process of corrugated board and whether its water content meets the production requirements

(II) preheat the drying at the drum. The function of preheating roller is mainly to evaporate the moisture of the base paper put into production and make its moisture uniform. It plays a role in regulating the moisture of the base paper

(III) characteristics of paper raw materials and glues. If the fiber structure of some core paper or corrugated paper is loose, or the viscosity of glue is poor, the moisture content of paperboard is high

(IV) the influence of drying and cooling process after paperboard bonding. When drying, the oven temperature is low, the production speed is fast, the heat absorbed by the corrugated board is insufficient, the drying is slow, and the moisture content is high, which makes the gelatinization and curing of the paperboard adhesive incomplete and reduces the strength. On the contrary, the moisture content is low

(V) impact of production environment. It mainly includes the temperature, humidity and ventilation effect of the production workshop

(VI) impact of circulation environment. Corrugated boxes are easily affected by the circulation environment in the process of use. The moisture and temperature of the circulation environment will have a direct impact on the moisture content of corrugated boxes, and then affect the performance and service life of corrugated boxes

III. The main way to control the moisture content of corrugated paperboard

the national standard for the moisture content of corrugated paperboard is 11 ± 3%. In order to ensure the production of cartons, good printing, firm bonding, smooth trimming, strong pressure resistance, reduce waste, improve labor productivity and increase economic benefits of enterprises, effective measures must be taken to control the moisture content of corrugated paperboard from the aspects of raw materials, production process, equipment environment and so on, Keep it within the standard range and ensure the production quality of corrugated board. Therefore, the main methods of corrugated board moisture control are:

(I) the moisture content of the base paper entering the factory should be strictly controlled. According to the national standard, the moisture content of base paper in delivery state is generally 9% - 12%. First of all, in the purchase of base paper, we should control the quality, strictly inspect the moisture content of the base paper entering the factory, and require suppliers to supply qualified base paper. In addition, a separate warehouse must be set up for the storage of base paper. The temperature is generally 15 ℃ ~ 20 ℃, and the relative humidity is generally 30% - 40%. Do not put it in the open air, which is easy to cause changes in the water content of the base paper, and cause inconsistencies in the water content at both ends and in the middle, which will bring greater trouble to future processing

(II) temperature is one of the decisive factors affecting the quality of corrugated board. Reasonable temperature control should be carried out in the production process of corrugated board. The temperature can not only adjust the water content of the base paper, but also affect the temperature of the base paper, so that the paste liquid solidifies in a reasonable time. Therefore, there are many preheaters and drying boards in the corrugated board production line, which are used to adjust the water content of base paper and single-sided board, solidify the paste liquid, and bond each layer of corrugated board. Generally, when the vehicle speed is above 100m/min, the curing temperature of the paste is 160 ℃ ~ 180 ℃, that is, the pressure of saturated steam in the boiler should reach 0.9mpa ~ 1.4mpa. The temperature control mainly includes temperature control of preheating drum, temperature control of dryer, temperature control of drainage device, etc

(III) reasonably regulate the quality of paste solution, the size of paste amount, and the size, thinness and thickening of water doubling. 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 will be high, otherwise the water content will be small. When the amount of paste is large, the moisture content of the paperboard is large; Less paste, less water content. Therefore, the paste should be made in strict accordance with the times the amount of water, the proportion and the mixing time, and the viscosity of the paste liquid should be well controlled

(IV) carry out water-resistant and moisturizing treatment on corrugated board. First, the emulsion of water-resistant humectant is prepared, and the principle of energy balance is used to make it penetrate into the paper fiber materials, and form 6. Graphics on its surface: appropriate graphics and tables are equipped with user-defined graphics, labels and automatic adjustment proportion protective film. With the help of the spraying system, its surface tension, surface free energy and the attached work between solid and liquid are realized, and then the balance in the process of emulsion penetration and film formation is realized. Finally, the corrugated packaging board with water-resistant and moisturizing properties that does not affect printing is prepared

(V) by coating paraffin, silicone, varnish and other hydrophobic agents on the surface of corrugated board, the corrugated board has the function of hydrophobicity. Hydrophobic corrugated board is also known as water repellent corrugated board. When it is drenched by water for a short time, the processed surface of the board will splash water into droplets to prevent water from penetrating into the inside of the board. Hydrophobic corrugated board is suitable for packaging dry powdery goods, especially the powder that is easy to agglomerate after absorbing water. It is also suitable for packaging goods that often go in and out of the cold storage. After being taken out of the cold storage, it is easy to condense on the box wall. Ordinary corrugated board will quickly absorb and reduce the compressive strength, causing the paper box to collapse due to the stacking pressure. The hydrophobic processed paperboard will not significantly reduce the compressive strength before the dew evaporates, which can effectively protect the goods

(VI) melt the synthetic resin or paraffin mixture into a film from the hopper mouth and coat it on the corrugated board running horizontally. A layer of resin film or wax film is formed on the surface of the board, which has good water retaining performance. If necessary, cycle the film on the other side once to obtain double-sided waterproof performance and make the corrugated board water-resistant. Waterproof (water retaining) corrugated board is also known as water blocking corrugated board. Its surface is almost impervious to water for a long time, but it cannot be immersed in water, otherwise it will lose its waterproof performance

(VII) special technology is adopted to make corrugated board have strong water resistance. The corrugated board that is soaked in water for a long time after processing and has little reduction in strength is called strong water-resistant corrugated board. There are two commonly used manufacturing methods: one is the one-time processing method: that is, giving the base paper water resistance at the papermaking stage; There is also the secondary processing method: that is, the processing method of giving water resistance in the corrugated board manufacturing stage

the one-time processing method is to combine the water-resistant vermicelli board and water-resistant corrugated base paper, and then use the water-resistant adhesive to make corrugated board after processing. Because the base paper with water resistance can be divided into medium water resistance and high water resistance, the corrugated board produced also has medium water resistance and high water resistance

there are two kinds of secondary processing methods: coating method and impregnation method:

coating method refers to installing a roller coater on the corrugated board machine, coating paraffin on the surface board and corrugated board, and then bonding. Before the corrugated base paper enters the hot plate, apply adhesive on one side, and then spray waterproof paint on the corrugated base paper; Sometimes, in order to improve the water resistance of the end face of the corrugated board, waterproof paint is sprayed on the cuts at both ends of the corrugated board in front of the paper cutter of the corrugated board machine

impregnation method is to make the paperboard pass through the molten waterproof coating impregnation tank, so that the waterproof coating saturates the surface of the paper, and then send the paperboard to the drying section, which is heated by hot air above 105 ℃, so that the waterproof coating is adsorbed on the surface of the paperboard. After cooling, the waterproof coating is fixed on the surface of the paperboard, so that the paperboard has good waterproof property. Using the impregnation method, when the additional amount of waterproof coating impregnation reaches 40% - 50% of the weight of the base paper, the strength of the paperboard can be greatly improved, but when it is used for general vermicelli paperboard, the paperboard will turn black with high color accuracy

IV. conclusion

the performance of corrugated board is closely related to its water content. Therefore, we should understand the influencing factors of corrugated board water content, and starting from these factors and the improvement of fuel efficiency, we should reasonably control the water content of corrugated board in combination with actual production and processing activities to ensure the quality of corrugated board

reprinted from: Guangdong packaging magazine

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