Causes and Countermeasures of washboard phenomenon

2022-08-12
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Reasons and Countermeasures for corrugated board washboard phenomenon and poor adhesion

the world corrugated board market is growing at a rate of 2.8% per year. 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, and 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, there are problems such as washboard like phenomenon, uneven warpage of paperboard, and the 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

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 choose qualified base paper, but also observe different production situations in production. At any time, there should be gaps of different sizes between each spring plate to control and adjust, otherwise there will still be quality problems such as paperboard washboard due to improper production control

1.1 influence of base paper moisture content

when the paperboard appears washboard like phenomenon, 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 single-sided machine. And often overlooked a very important factor - the moisture content of the base paper. It is often thought that a slightly higher or lower moisture content is not a big deal, as long as the base paper can be produced on the machine without degumming of the cardboard. In fact, it is not, because the expansion rate of paper depends largely on the water content of the paper itself. In terms of qualified base paper, 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; Low moisture content is not conducive to the bonding and molding of paper, 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, since the base paper is 210f/g, the quantity is low, and the paper is thin, which brings certain difficulties to the manufacturing of corrugated board. Often due to improper production adjustment, the surface of the paperboard is washboard shaped or blistered. It leads to quality problems such as uneven paperboard and affected printing effect

1.2 effect of sizing amount

the washboard phenomenon of corrugated board 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. It is also accompanied by foaming, which often occurs in base paper with low quantity. The main reason is the excessive amount of adhesive

in terms of corrugated board production, both single-sided and double-sided machines often have the 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 is evenly applied on the corrugating crest by the gluing roller. 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 leads to 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, this shrinkage force will produce a wave tension on the backing paper. When the single-sided machine uses high quantitative 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 a low quantity of backing paper, it is easy to cause shrinkage and deformation of the backing paper because the low tightness cannot resist the wave tension, as shown in Figure 1

similarly, for the double-sided machine, when using low weight tissue paper, the tissue paper will shrink and deform because it cannot resist the wave tension, resulting in uneven shape, and even blistering in serious cases. Therefore, when using low weight base paper, the only solution 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 should be adjusted as much as possible and the machine speed should 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 should depend on the quantity of the top paper and the bottom paper

2 research and Countermeasures on the quality problems of different valid periods of corrugated board gluing 3 certificates

2.1 adhesive problem

the phenomenon of poor adhesion (blistering, degumming, false particles) of corrugated board occurs from time to time on the corrugated board production line. There are many reasons, including the high and low moisture content of base paper, the improper control of sizing amount in production, and the quality of adhesives. Among them, the bonding mechanism of adhesive is the first problem to be solved. If you know little about the bonding mechanism of adhesive, it will be difficult to deal with it calmly, or be helpless, or solve the surface problems on the surface phenomenon when there is poor bonding in production. If you don't grasp the essence of the problem, it will be difficult to completely cure it. 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 adhesives have 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 and absorb moisture. However, in the production of starch adhesives, there are also some shortcomings that cannot 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 when producing starch adhesives, which can not effectively control and will seriously affect the measurement results of equipment. Adjusting the formula, process and oxidation depth of adhesives not only wastes raw materials, The reaction time is prolonged, and the quality of the adhesive is not controlled, which affects the various properties of corrugated board. Therefore, when using, just add water and complexing agent to obtain pre oxidized starch adhesive for the bonding of corrugated board

in fact, even in the same production line, the starch glue 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 penetration bonding and surface bonding. 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 and corrugated core paper form the adhesion between the adhesive and the surface of the adhesive, 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 molecules of this kind of adhesion is called condensation adhesion. Three kinds of bonding tightly bond the face paper and the core paper

every step of corrugated board bonding molding 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 links, which increases the stability of starch pellets in solution. In the process of using starch, it usually destroys the aggregate structure first, resulting in the swelling of the aggregate. The hydration and dissolution of starch molecules is generally called the gelatinization process of starch. The whole bonding process is completed on the core paper with sufficient heat and humidity. The adhesive applied to the ridge peak gradually soaks, diffuses and penetrates into the paper fiber structure. At this time, the raw starch will quickly mature and evaporate the 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 accumulate on the surface of the paperboard due to insufficient diffusion and penetration of the glue and condense into crystals, resulting in false adhesion of the paperboard; If the adhesive gel is too slow, there will be a large number of glue diffusion and penetration to both sides of the Lengfeng sizing line, showing a white line shape. At this time, the raw starch loses its viscosity because it cannot be matured, resulting in poor paperboard adhesion

it can be seen that finding the adhesive gel point will be the key to solve the bonding effect of paperboard. Due to the 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 should 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 and molding. The reasons are as follows: on the single-sided machine, because its unique sizing mechanism determines that its bonding process is formed under the state of high temperature and high speed, it is necessary to complete 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, so the bonding process of the double-sided machine is to complete the bonding molding at room temperature. This requires that the adhesive of double-sided machine should be high viscosity and low gel point, which is conducive to slow diffusion, gel and bonding. Under normal circumstances, see Table 1 for the requirements of adhesive quality problems of single-sided and double-sided machines

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

3 conclusion

to sum up, to solve the problem of washboard shape and poor bonding of corrugated board, we need not only to have a deeper understanding of the bonding and forming principle of the board, but also to have a deeper study on the operation characteristics of the board production equipment, so as to achieve the best product quality with the best process plan, and make the board production line operate with high speed, high efficiency and high quality

reprinted from: Dazheng Packaging Machinery Co., Ltd

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