Summary of Corrugated Cardboard Adhesion Problems-Solving Poor Adhesion

As we all know, to solve the problem of poor adhesion of corrugated cardboard, it is not only necessary to have a deeper understanding of the bonding and forming principles of cardboard, but also do not have a deeper study on the operating characteristics of cardboard production equipment in order to achieve the best with the best process plan. The ideal product quality makes the cardboard production line operate at high speed, high efficiency and high quality.

In this issue, we will gather the bonding links of corrugated cardboard production to open the channel for producing high-quality cardboard.

One solution to "bad adhesion" to improve the quality of cardboard

In the production practice of corrugated boxes, the bonding between various papers is a very important link, and to a considerable extent determines the quality level of the product. Whether the adhesion between the various paper sheets is tight and firm, directly affects the quality of corrugated cardboard. The surface of corrugated cardboard with good adhesion is smooth, no foam, no wrinkle and no warpage. After processing into a corrugated box, there will be no separation between the sheets, the appearance is stiff, and it has good compression and cushioning properties, which can effectively Protect the internal goods from damage caused by external factors. However, poor corrugated board adhesion (foaming, degumming, false particles) occurs on the corrugated board production line from time to time. It is understood that nearly 70% of the waste products produced by the corrugated cardboard production line are caused by adhesion problems. Therefore, in order to truly achieve the purpose of reducing costs and increasing efficiency, the rate of waste products due to adhesion problems must be controlled within an appropriate range. Next, we will find out the cause of the "bad adhesion" of the cardboard and provide a series of solutions for you when you encounter problems in actual production.

Whether the corrugated cardboard is well bonded is an important indicator for the physical property inspection of corrugated cardboard. The reasons that affect the bonding strength of corrugated cardboard are more complicated. In a nutshell, base paper, adhesives, corrugated cardboard machinery, production planning and staff operation levels, etc., all have an impact on it. And the above factors will affect each other.

(1) Original paper

Mainly manifested in several aspects:

The moisture content of the base paper: too dry (less than 6%) or too much moisture (more than 12%) of the cardboard or corrugated base paper will cause poor adhesion of the corrugated board. When it is too dry, the moisture necessary for swelling and bonding of the adhesive is absorbed by the base paper, resulting in the phenomenon that the glue is not gelatinized. When the moisture is too large, the excess moisture absorbs heat, resulting in insufficient heat and poor adhesion. The solution is to strictly control the moisture of the base paper. When it is too dry, it must be sprayed. When the moisture is too large, the moisture and preheating area of ​​the base paper must be increased appropriately. If the effect is still not good, the paper must be replaced.

The quality of the base paper's water absorption or water permeability: the material, tightness and sizing degree of the base paper determine its water absorption or water permeability. The base paper with poor water absorption or permeability will inhibit the penetration of the adhesive. The base paper with strong water absorption or permeability will cause the glue not to gelatinize, and the glue penetration will occur. The former solution is to use additives in the adhesive, and use the additives to improve the hydrophobic properties of the base paper surface, so that the adhesive can penetrate. In addition, it is necessary to appropriately increase the amount of adhesive applied. We know that the bonding of corrugated cardboard is first corrugated corrugated peak glue, and then combined with the paper or sandwich core, the transfer of the adhesive between any layers is hindered, which will affect the bonding effect. For example, a company's grade A straw pulp corrugated paper, after heavy sizing treatment, has poor water absorption, and good adhesion cannot be obtained without the use of water-resistant adhesives. The latter solution is to appropriately increase the viscosity of the adhesive.

The length of the original paper is broken: it is the ratio of the strength of the original paper to a certain amount, which means the length of a certain width of the paper strip when it is pulled by its own weight. If the base paper has a low breaking length, when the line speed of the tile reaches a certain level, it will inevitably cause frequent paper breaks and shutdowns. At this time, the corrugated cardboard staying in the drying tunnel absorbs too much heat, and no matter how good the adhesive is, it can not get good adhesion. In this case, the solution is to reduce the speed of the machine, or to improve the quality of the base paper, and include the length of the broken paper into the base paper inspection project.

The original paper is loose on one side: if the corrugated paper is loose on one side, it will cause uneven corrugation and affect the fit with the cardboard; if the cardboard is loose on one side, it will form a wrinkle on the surface of the cardboard. In severe cases, poor adhesion is formed. The only solution is to replace the original paper.

(2) Quality of adhesive

It mainly reflects two aspects: one is the quality of starch, and the other is the quality of the adhesive production process.

The low level of starch means poor processing precision, and there are many impurities such as protein, fat and ash. The use of such starch will consume more sodium hydroxide and make the adhesive unstable and the corrugated adhesive. Cardboard is easy to absorb moisture. When placed in a humid environment for a short period of time, the corrugated cardboard will be degummed. Second, the adhesive will easily produce gel with large starch particles and impurities as the core, making the adhesive fluidity worse and uneven coating , Make the corrugated cardboard partially glueless, less glue, resulting in poor adhesion. The solution is to use high-quality starch. If it is corn starch, industrial grade one or more should be used. The quality of the adhesive production process is even more important. Corrugated cardboard adhesives have appropriate solids content, viscosity and necessary gelatinization temperature. When the general adhesive is used in circulation, its viscosity will tend to decrease every time it passes through the circulation pump. At this time, the newly prepared adhesive should be added for mixing.

In addition, during the holiday shutdown, the excess binder is stored in the storage tank, especially in the hot summer, bacteria will decompose starch, spoilage occurs and the viscosity drops sharply, resulting in starch precipitation, resulting in poor adhesion. The solution is to add preservatives, such as formaldehyde, 0.35 kg per 200 kg of starch, or 0.32 kg per 200 kg of starch during the preparation of the adhesive.

When making water-resistant paperboard, high-grade paperboard and corrugated paper are often used, together with water-resistant adhesive. The polymerization and condensation of thermoplastic resin generally added to this adhesive can still proceed, and sometimes the viscosity rises sharply, which is no longer suitable for the use conditions of corrugated board machine. The solution is to readjust the amount of glue to make the viscosity meet the requirements for use.

When the quantitative tightness of the face paper and even the sandwich paper is high (quantity 180g / m2 or more, tightness 0,70g / m3 or more), sometimes poor adhesion due to insufficient heat. Due to the higher thickness of the facial paper with a higher thickness and the denser paper with a higher density, the heat transfer is affected, and the A corrugated heat transfer requires more time, resulting in a single-sided A corrugated paper and sandwich paper Poor adhesion. The solution to this situation is to reduce the machine speed while increasing the angle between the thick paper and the preheater.

If the absolute heat of the corrugated board machine is insufficient, it is also a good way to use a binder with a low gelatinization temperature. When the tissue weight is low (below 180g / m2), it is easy to produce blisters on the surface of the tissue, called "blisters", which is a local degumming phenomenon. After a short period of time on the double-sided corrugated cardboard machine or loading the cardboard on the trolley, this phenomenon will occur on one side of the cardboard. The situation is mainly caused by the high moisture content of the lined cardboard or the excessive drying of the corrugated cardboard. Due to the imbalance of heat and moisture, the over-dried corrugated cardboard absorbs moisture at the exit of the double-sided corrugated cardboard machine. Because the longitudinal direction has been fixed, it is elongated in the lateral direction and the surface forms a small bubble. The solution is to reduce the amount of adhesive as much as possible, cut off part of the heat of the hot plate or increase the speed of the machine, making a high-solid low-viscosity adhesive is also a way, but you must master the gelatinization temperature.

(3) Mechanical factors of corrugated board machine

The factors of corrugated board machinery are mainly: the accuracy, hardness and wear degree of the core component corrugated roller: the advanced nature of the corrugated cardboard bonding device; the structure of the hot part; whether to use a fully automatic paper receiving device, etc.,

Corrugated rolls: Corrugated rolls are often compared to the heart of corrugated board machines, and their position is important.

1) Corrugated paperboard produced with new corrugated rollers has poor local adhesion. One of the important reasons is that the accuracy of corrugated rollers is not high. The solution is to use high-precision corrugated rollers. The corrugation of the finished corrugation has a small height difference on a banner, and the ideal adhesive effect can be achieved by coating less adhesive.

2) The surface of the ordinary corrugated roll is chrome plated to increase the hardness. Since the middle and low grade corrugated paper has a certain sand content, the main component of the sand is silica, and its hardness is second only to diamond, so the surface of the ordinary corrugated roll is chrome plated. severe. There are many types of corrugated cardboard produced by general carton companies. For example, the width of 2200mm is used. The specifications may range from 1200mm to 2200mm. There are high, medium and low grades, plus long-term paper feeding in the middle, just a few months. The mid-height of the corrugated roller may be lost. This kind of corrugated board produced under the green condition has poor adhesion even in the middle. In order to get the ideal adhesion in the middle, the pressure roller pressure has to be increased, but this is only an expedient measure, and the time is not long. This situation is more serious. The pressure roller pressure is increased until the two ends of the cardboard are bitten by the corrugated roller. Unable to obtain adhesion. The solution to this situation, in addition to avoiding the use of corrugated base paper with high sand content, integrate small specifications into large specifications (use uniform technology if necessary, rationally match production), replace new corrugated rollers, especially use sprayed tungsten carbide instead of chrome-plated corrugated roller It is the most effective (but the cost is higher, it must be considered in conjunction with the business situation). The service life of chrome-plated corrugated rolls is 20 million meters, the number of repairs is up to 3 times and the outer diameter decreases gradually. The service life of the sprayed tungsten carbide corrugated roller is doubled, and the corrugated shape and the body are not damaged, and the outer diameter is not reduced. Paper saving and high strength are also its advantages.

Corrugated cardboard sticking device: The glued single-sided corrugated cardboard and board paper are usually bonded by pressure roller (also called riding wheel). Long-term friction with paper will also cause wear and tear, resulting in inconsistent bonding of the entire banner, which in turn leads to poor local adhesion of corrugated cardboard, which is more common at both ends. Solution: Increase the pressure to improve the bonding at both ends, but the middle corrugation may be deformed by pressing; sticking tape on the roller surface at both ends of the pressure roller can also improve the bonding, but it is difficult to control and may deform the corrugations at both ends ; It is the best choice to use pressure bar instead of pressure roller. The touch pressure bar is composed of a set of spring-loaded compression plates with a length and width of about 12.2cmX 8.8cm. No additional power is required during work. Parallel and appropriate gaps are reserved. On the contact surface of the cardboard, the pressure bar pressure plate is specially designed to have the same curvature as the paste wheel to stabilize the pressure and apply the adhesive evenly. There is an independently controlled spring on each touch pressure piece, which can automatically adjust irregular runout to prevent flattening. The hot plate part replaces the gravity roller with hot pressing sheet, so that each layer of corrugated cardboard is fully bonded, and the quality of bonding can be greatly improved.

The structure of the hot part: the ordinary tile line, the heating and pressing mechanism of the hot part is composed of a fixed hot plate and a gravity pressure device, so its heat transfer is a fixed value. In production, the hot plate temperature is generally controlled by adjusting the steam pressure according to the grade, basis weight and thickness of the base paper. In the production process, when there is insufficient tension of the base paper (mainly manifested in insufficient cracking length, as mentioned above), lack of material (which will cause stress concentration), joints, broken heads, etc., paper breakage often occurs, resulting in deceleration continued ( Unless there is a fully automatic paper pick-up device) or even a shutdown, the change in machine speed breaks the balance of heat transfer, and the fixed hot plate cannot adjust the heat. As a result, the corrugated paper in the drying tunnel is overheated, causing degumming and warping. The solution at this time can only make the corrugated paper separate from the hot plate by lifting the canvas belt device (the canvas belt device must be lifted when the machine is stopped for more than 40 seconds). Although the phenomenon of degumming and warping is greatly improved, local degumming phenomenon cannot be avoided, and it is accompanied by Creases appear on the surface of the cardboard, which affects the appearance and causes certain difficulties in the printing process. If the hot plate is designed as a heating system with a hydraulic machine to promote variable heat, by adjusting the inclination of the hot plate during production, a certain gap is generated between the hot plate and the corrugated paper, and part of the heat is dissipated from the gap, thereby reducing the transfer of the hot plate to the corrugated cardboard The heat reaches the balance of heat transfer. Or design and install a narrow nozzle at the gap of the hot plate, and use a group of air-conditioning valves to open the adjustment valve when the speed is reduced, so that the air blown between the hot plate and the corrugated cardboard diffuses to form a corrugated paper. The thin air film lifted from the hot plate by the canvas belt device achieves the purpose of reducing excessive heat transfer from the hot plate to the corrugated cardboard.

Automatic paper pick-up device: the use of automatic paper pick-up device avoids deceleration and stoppage, thus ensuring the stable transfer of heat from the end to the end. Production planning and staff operation level

For general carton companies, due to the variety of corrugated cardboard specifications and materials used, this involves production planning arrangements.

1) If the small specifications are finished, the large specifications will be replaced immediately, and the two ends of the large-size corrugated cardboard will often have poor adhesion. The main reason is: after the paper is fed in the middle, after the small-sized corrugated board is made, the temperature of the middle of the hot plate is lower than that of the two ends. After the large-sized corrugated board is replaced, the adhesive at both ends may have gelatinized, while the two ends The adhesive is too gelatinized and the result is degumming at both ends. Moreover, according to the principle of thermal expansion and contraction, due to the paper in the middle, the expansion of the middle of the hot plate is not as good as the two ends of the hot plate. From the lateral view of the hot plate, it is no longer a plane, but a curved surface, between the corrugated paper and the hot plate The adhesion is not uniform in the entire transverse direction, resulting in differences in the amount of heat absorbed, and the degree of gelatinization of the adhesive is also different, resulting in poor adhesion. The solution is: in the production planning and arrangement, as far as possible, first produce large-scale corrugated paper, so that all kinds of corrugated cardboard are heated uniformly, and the paste is uniform. If the above arrangement cannot be realized due to customer's urgent order, then before switching from small size to large size corrugated board, the machine should be stopped for at least half an hour to redistribute the heat on the hot plate.

2) When changing from one type of corrugated cardboard to another type of corrugated cardboard, the requirements for adhesives are different for different types. The solution is to optimize the combination of corrugated board, compress the types of base paper from dozens to several types, and match small-sized corrugated board into large-sized corrugated board.

3) Statistics show that the main cause of waste products in corrugated board lines is caused by paper replacement, and about 70% of them are poor adhesion. The reason is that the machine speed changes or stops when changing paper. The solution is: in addition to compressing the types of base paper, appropriately increase the grade of base paper, replace low-quantitative high-strength base paper with high-quantitative low-strength base paper, appropriately increase the grade of base paper, and replace low-quantitative strength base paper with high-quantitative low-strength base paper. When the batch size is large, this method is effective. Because a roll of base paper of the same weight, the lower the basis weight, the longer the number of meters, which not only reduces inventory and transportation costs, but also reduces the number of paper changes during use.

(4) Staff operation level is also an important factor.

1) Sometimes, the produced corrugated cardboard forms regular white lines without paste at the bonding place, or the overall adhesion is poor. The reason for the former is that the corrugated paper is too strong or has too much water, or the paper guide is stuck in the glue groove, which causes no adhesive to coat the corrugated roof at the position of the paper guide. Solution: Adjust the strength and moisture of corrugated paper, increase the amount of adhesive coating properly, and adjust the paper guide.

2) The cause of poor overall adhesion: the quality of the adhesive is not high, or the adhesive in the glue tank is insufficient, and the coating amount is too small; the adhesive paste temperature is too high, or the temperature obtained is too small to make the adhesive at the bonding place It cannot be pasted or the molecular structure of the adhesive is damaged due to high temperature, and the adhesive properties are lost; or the gap between the top roller and the corrugated top surface is large and the absorption of the base paper is not good. Solution: If the quality of the adhesive is not high, the quality must be improved; if the adhesive in the glue tank is insufficient, the amount of adhesive in the tank should be increased to achieve an appropriate coating amount; if the temperature of the adhesive paste is too high: it should be adjusted For the formulation of rubber, increase the amount of sodium hydroxide to reduce the gelatinization temperature. If the single-sided corrugated cardboard is poorly bonded, it may be that the condensate is not discharged in time. The hot steam in the corrugated roller releases heat and becomes condensed water. If it is not discharged in time, it will absorb part of the heat of the steam and cause the surface temperature of the corrugated roller to be insufficient, resulting in overall poor adhesion. The solution is to pay close attention to the adhesion of single-sided corrugated cardboard and discharge condensate in a timely manner. In the same way, if the double-sided corrugated cardboard is not fully bonded, it may also be that the condensate is not discharged in time at the hot plate, and the solution is the same as above;

3) Most cases are caused by paper change or shutdown, the reason is: the paper change is too slow, the shutdown time is too long. Solution: Skilled in changing paper, it should be completed within 40 seconds; the downtime cannot exceed 1 minute, otherwise the canvas device must be lifted. If the gap of the top surface of the corrugated rubber roller is large: it must be adjusted. If the absorbency of the base paper is not good, the base paper with appropriate absorbency must be replaced.

In summary, to solve the problem of poor adhesion of corrugated cardboard, not only need to have a deeper understanding of the bonding and forming principles of cardboard, but also a deeper study of the operating characteristics of cardboard production equipment, so as to achieve the best The process plan achieves the most ideal product quality and enables the cardboard production line to operate at high speed, high efficiency and high quality.

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