Moisture content control of the hottest corrugated

Water content control of corrugated board (box)

the frequent economic development and trade activities make the market demand for corrugated board, an important packaging material, more and more vigorous. There is still a big gap between the demand and supply of corrugated board, especially high-strength corrugated board. Recently, the number of domestic corrugated board manufacturers is increasing, and the production technology of corrugated board is also improving, but there are still many problems in how to ensure that corrugated board (box) is free from the impact of the environment (especially 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. 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. In transportation and storage, when encountering high humidity, it will absorb moisture and reduce the strength, so that the function of corrugated boxes will be lost, resulting in product damage. In the high temperature and dry environment, when the moisture content of corrugated board drops to a certain extent, it will produce the phenomenon of crispness, the folding resistance of corrugated board will decline, and finally the flip of the carton will break. Therefore, the biggest defect of corrugated board is embrittlement 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

failure is closely related to water content

through statistics, it is found that high and low water content of corrugated board and uneven water distribution will cause failure of corrugated board. The details are as follows. The faults caused by high water content include: corrugation, glue opening on the edge of the face paper on the double-sided machine, excessive cracks on the longitudinal cutting edge, corrugation damage, corrugation being pressed across, obvious non bonding stripes (dry stripes) on the corrugated board, longitudinal warpage of the corrugated board, uneven corrugated forming, etc

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

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

main factors affecting water content

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

(1) moisture content of 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% - 12%. Whether the moisture content of the base paper meets the standard will directly affect the production process of corrugated board and whether its moisture content meets the production requirements

(2) preheat the drying at the drum

the function of preheating roller is mainly to evaporate the water in the base paper put into production and make its water uniform. It plays a role in regulating the water content of the base paper

(3) characteristics of paper raw materials and glues

if the fiber tissue of some core paper or corrugated paper is loose, or the viscosity of glue is poor, the moisture content of paperboard is high

(4) the influence of drying and cooling process after paperboard bonding

6. After using the pendulum impact tester for one year, it is necessary to adjust the level. 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 paperboard adhesive paste and cure incomplete and reduces the strength; Otherwise, the water content is low

(5) impact of production environment

it mainly includes the temperature, humidity and ventilation effect of 20 production lines, 40 printing machines and 80 injection molding machines in the production workshop, which are being put into production in an orderly manner

(6) influence 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

the main way of moisture control

the national standard for the moisture content of corrugated board 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 board from the aspects of raw materials, production process, equipment environment and so on, so as to maintain it within the standard range, Ensure the production quality of corrugated board

the main methods of moisture control of corrugated board are as follows

(1) the water content of the base paper entering the factory should be strictly controlled

according to the provisions of national standards, the moisture content of base paper in the 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%

don't put it in the open air, which is easy to cause changes in the water content of the base paper, and cause inconsistency in the water content at both ends and the middle, which will cause greater trouble for future processing

(2) reasonable temperature control

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

there are many preheaters and drying boards on the corrugated board production line, which are used to adjust the water content of base paper and single-sided board, solidify the paste, and bond each layer of corrugated board. Generally, when the vehicle speed is above 100m/min, the curing temperature of the paste liquid is 160 ~ 180 ℃, that is, the pressure of saturated steam in the boiler should reach 0.9 ~ 1.4m PA. The temperature control mainly includes temperature control of preheating drum, temperature control of dryer, temperature control of drainage device, etc

(3) reasonably regulate the quality of paste solution, the size of paste amount, the size of water content, thickness, etc

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, we should strictly follow the relevant standards of strategic emerging industries; 3. Make the paste according to the water content, proportion and mixing time of the paste according to the relevant standards of urban energy infrastructure, and master the viscosity of the paste liquid

(4) carry out water-resistant and moisturizing treatment on corrugated board

prepare water-resistant moisturizing agent emulsion, use the principle of energy balance to make it penetrate into the paper fiber material, and form a protective film on its surface. With the help of the spraying system, realize its surface tension, surface free energy and solid-liquid attached work, and then realize the balance between the emulsion penetration and film-forming process. Finally, a corrugated packaging board with water-resistant and moisturizing properties without affecting printing is prepared

(5) 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 called 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, and 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 carton to collapse under stacking pressure. The hydrophobic processed cardboard will not significantly reduce the compressive strength before the dew evaporates, It can effectively protect commodities

(6) coating resin on corrugated board

the molten synthetic resin or paraffin mixture flows down from the hopper mouth into a film and is coated on the horizontal corrugated cardboard. A layer of resin film or wax film is formed on the surface of the cardboard, 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 called 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, and the result is similar to that of ordinary corrugated board. Water resistant corrugated boxes are used to transport live fish, seafood and other commodities with high water content

(7) special technology is adopted to make corrugated board have strong water resistance

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 a secondary processing method: that is, to give 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 water-resistant adhesive to make corrugated board after processing. Because the water resistance of base paper with water resistance is 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 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 vermicelli 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 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 can be adsorbed on the surface of the paperboard. After cooling, the waterproof coating will be fixed on the surface of the paperboard, so that the paperboard, as the most important automotive light material, 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 color of the paperboard will turn black

the performance of corrugated board is closely related to its water content. Therefore, we should understand the influencing factors of the water content of corrugated board, and based on these influencing factors, we should reasonably control the water content of corrugated board in combination with the actual production and processing activities to ensure the quality of corrugated board. At the same time, we also look forward to the early publication of methods that can more effectively control the water content of corrugated board

reprinted from: business information of printing materials in China