The hottest corrugated box knowledge collection 13

2022-07-31
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Corrugated box knowledge collection

II causes and Countermeasures of corrugated board washboard and poor adhesion

the world corrugated board market is growing at an annual rate of 2.8%. It is expected that by 2010, the market demand will reach 125 million tons. After China's entry into WTO, the packaging paperboard industry should take the initiative to meet the challenge. Most of the paperboard enterprises in China are mainly in the domestic market. From the domestic perspective, the demand for paperboard is self-sufficient. It has become a direction to expand the market from home to abroad. In this direction, quality is the primary problem that enterprises should pay attention to, and the quality of paperboard is caused by many factors. For example, the phenomenon of washboard, uneven warping of paperboard, and the anti puncture strength does not meet the requirements. Some problems are more intuitive, while others are hidden and complex. Because the influencing factors of some problems often coexist and are intertwined with each other. This requires theoretical research on some quality problems

but it has been ignored by many people. 1. research and Countermeasures on washboard phenomenon of corrugated board

corrugated board is composed of sandwich paper, core paper, face paper and bottom paper. The quality of base paper plays an important role in the forming quality of corrugated board. As a carton manufacturer, it should not only purchase qualified base paper, but also observe different production situations during production, and control and adjust them at any time, otherwise there will still be quality problems such as cardboard washboard due to improper production control

1.1 influence of base paper moisture content when the paperboard appears washboard, the first consideration is generally whether the operator adjusts the main parameters of each key point as required. For example, the tension control of paperboard and the adjustment and control of the dryness and wetness of corrugated paper by steam spray on the single-sided machine. And often overlooked a very important factor - the moisture content of the base paper. It is often thought that slightly higher or lower moisture content is not a big problem. As long as the base paper can be produced on the machine, there will be no degumming of the paperboard. In fact, it is not, because the expansion rate of the paper largely depends on the water content of the paper itself. For the qualified base paper, the corrugated paper must be strictly controlled within (8 ± 2)% range. The carton paper shall be controlled between (9 ± 2)%. Too high moisture content will make the paper fiber expand and elongate due to excessive absorption of moisture; The low moisture content is not conducive to the paper bonding and forming, which is particularly obvious in the use of low weight base paper

due to the advantages of light weight and low price, low weight corrugated board is being advocated and promoted by the majority of carton manufacturers in the face of the rising international pulp market. However, due to the low quantity of base paper and the thin paper, it is difficult to manufacture corrugated board. Due to improper production adjustment, the surface of the paperboard is washboard like or bubbling. Lead to quality problems such as uneven paperboard and affected printing effect

1.2 the amount of sizing affects the washboard phenomenon of corrugated board. The flame height of collecting firewood is the physical deformation of the lining paper on the corrugated peak, which changes the tight and flat surface of the board and forms an uneven shape along both sides of the corrugated peak. But also accompanied by the phenomenon of foaming, which often occurs in the low quantitative base paper. The main reason is the excessive amount of adhesive

as far as corrugated board production is concerned, whether it is a single-sided machine or a double-sided machine, there is a problem of sizing amount. For the single-sided machine, in the gluing mechanism, the rotation speed of the gluing roller is slightly slower than that of the corrugating roller in the mechanical design, so as to ensure that an appropriate amount of adhesive carried by the gluing roller is evenly applied to the corrugating wave crest. When the paper is bonded and pressed, the adhesive penetrates into the paper fiber, and then solidifies to achieve the bonding effect. However, when the improper amount of adhesive coating results in excessive amount of adhesive, the excess adhesive is pushed out to both sides of the corrugated wave peak, resulting in the widening and enlargement of the sizing line. When these excessive adhesives shrink after drying, the shrinking force will generate wave tension on the backing paper. When the single-sided machine uses high weight backing paper, it has enough tightness to resist the wave tension, so as not to cause the backing paper to shrink and deform; When using low weight backing paper, it is easy to cause shrinkage and deformation of backing paper because the low tightness can not resist the wave tension

similarly, for the double-sided machine, when using low weight tissue paper, the tissue paper will shrink and deform due to the inability to resist the wave tension, resulting in uneven shape and even foaming in serious cases. Therefore, the only way to solve the problem when using low weight base paper is to strengthen the control and adjustment of production process and try to overcome the quality problems caused by the defect of low weight base paper. In the case of ensuring the adhesion of the paperboard, the sizing amount shall be adjusted as much as possible and the machine speed shall be increased to avoid the influence of excessive sizing or overheated temperature on the expansion and contraction of the paper fiber. The size of the glue application amount is usually 1~2mm wide on the ridge peak. The details shall depend on the quantity of top paper and bottom paper

2 research and Countermeasures on the bonding quality of corrugated paperboard

2.1 adhesive problems often occur in the corrugated paperboard production line. There are many reasons, such as the high and low moisture content of base paper, improper control of sizing amount in production, and the quality of adhesives. Among them, the adhesive mechanism is the first problem to be solved. If you know little about the bonding mechanism of the adhesive, it will be difficult to deal with it calmly or at a loss when poor bonding occurs in production, or to solve the surface problems based on the surface phenomena without grasping the essence of the problem, and it will be difficult to completely eradicate the problem. Therefore, the author focuses on the bonding mechanism of adhesives

although the proportion of adhesive in the manufacturing cost of corrugated board is very small, it plays a decisive role in the quality of corrugated board. Therefore, the formulation and quality control of adhesives have become a long-term research topic for experts at home and abroad

there are many kinds of adhesives. Such as starch series adhesives, polyvinyl alcohol, etc. At present, most manufacturers use starch series adhesives. Compared with other adhesives, starch adhesive has the following advantages: 1) strong adhesion, easy to penetrate into paper to produce adhesion; 2) Good initial viscosity; 3) Easy to store; 4) The pasted cardboard box has a firm and flat appearance, which is not easy to run off the edge and absorb moisture. However, in the production of starch adhesives, there are also some shortcomings that can not be ignored, such as long reaction time, difficult to control the oxidation depth, unstable quality, complex reaction process, etc. in addition, most manufacturers mechanically apply the reaction conditions of industrial oxidized starch in the production of starch adhesives, which can not effectively control and adjust the formula, process and oxidation depth of adhesives, which not only wastes raw materials and prolongs the reaction time, And the quality of adhesive can not be controlled, which affects the various properties of corrugated board. Therefore, when in use, just add water and complexing agent to obtain the pre oxidized starch adhesive for the bonding of corrugated board

in fact, even in the same production line, the starch adhesive used by single-sided machine and double-sided machine is different. As far as the bonding of corrugated board is concerned, the bonding mechanism is the premise to determine the adhesive formula; As for the quality of adhesives, viscosity and gel point are two important indicators to measure the quality

2.2 bonding mechanism between core paper and face paper the bonding between corrugated core paper and face paper is mainly the condensation bonding of starch adhesive, supplemented by the penetration bonding and surface bonding with low indication value. The glue penetrates the inner surface of the paper and the surface of the corrugated core paper, and enters the fiber gap of the paperboard to cause penetration bonding. At the same time, the surface paper, the corrugated core paper and the adhesive surface form the adhesion between the adhesives, that is, the surface adhesion. The adhesive penetrating into the paperboard forms a collection with the adhesive on the surface of the paperboard. The adhesion between the molecules of this kind of adhesion is called condensation adhesion. Three kinds of bonding closely bond the face paper and the core paper

every step of corrugated board bonding is directly related to the bonding mechanism of the adhesive. The property of starch is that starch molecules contain hydroxyl groups that are prone to chemical reactions, so starch can react with many substances. In starch molecules, hydrogen bonds can be formed between hydroxyl groups on adjacent chain links, which increases the stability of starch pellets in solution. In the process of using starch, the aggregate structure is usually destroyed first, resulting in the swelling of the aggregate. The hydration and dissolution of starch molecules, in general, is called the gelatinization process of starch. The whole bonding process is completed on the core paper with sufficient heat and humidity. The adhesive applied on the ridge is gradually infiltrated, diffused and penetrated into the paper fiber structure. At this time, the raw starch will quickly mature in gel and evaporate water under the action of high temperature, and finally achieve complete solidification. When the five bonding steps of corrugated board are synchronized according to the above bonding mechanism, the best bonding effect will be obtained. If the adhesive gel is too fast, it will cause the glue to accumulate on the surface of the paperboard due to insufficient diffusion and penetration and coagulate into crystals, resulting in false adhesion of the paperboard; If the adhesive gel is too slow, a large amount of glue will diffuse and penetrate into both sides of the Lengfeng sizing line, presenting a white line shape. At this time, the raw starch will lose its viscosity due to its inability to mature, resulting in poor adhesion of the paperboard

it can be seen that looking for the adhesive gel point will be the key to solve the paperboard bonding effect in terms of durability. Due to the mechanism difference between single-sided machine and double-sided machine, the adhesive formula should be different. Generally, the formula with low viscosity and high gel point shall be selected for single-sided machine; The double-sided machine should choose the formula with high viscosity and low gel point to meet the needs of paperboard bonding. The reasons are as follows: on the single-sided machine, because its unique sizing mechanism determines that its bonding process is bonded and formed under the state of high temperature and high speed, it is necessary to complete the five bonding and forming steps of gluing - penetration - connection - bonding - finalization in a moment. This requires that the adhesive of single-sided machine should be low viscosity and high gel point, so as to facilitate the penetration and bonding of glue in a very short time. On the double-sided machine, the time is long, and the gluing mechanism is cold. Therefore, the bonding process of the double-sided machine is completed at room temperature. This requires that the adhesive of the double-sided machine should be of high viscosity and low gel point, so as to facilitate slow diffusion, gel and bonding. Under normal conditions, the requirements for adhesive quality problems of single-sided and double-sided machines are shown in Table 1

Table 1 adhesive quality index of single-sided and double-sided machine gel point/℃ viscosity/s system temperature/℃

the data in the table are not unchanged. During the production process, the steam pressure, production speed and moisture content of base paper provided by the machine are constantly changing, so it is necessary to adjust them in a targeted and timely manner to meet the needs of each step of bonding forming and achieve the best bonding effect

3 conclusion

to sum up, to solve the problem of washboard shape and poor adhesion of corrugated board, it is not only necessary to have a deeper understanding of the principle of paperboard adhesion and forming, but also to have a deeper study on the operation characteristics of paperboard production equipment, so as to achieve the most ideal product quality with the best process scheme and make the paperboard production line operate with high speed, high efficiency and high quality

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