How to solve the curved edge of corrugated cardboard
The flatness of corrugated paperboard is one of the important indexes in the production technology of carton, which is directly related to the quality of product printing, die cutting or slotting,using a good corrugator conveyor belt is also a right way.
Corrugated cardboard is warped, resulting in a corrugated cardboard multi-arch shape.
It is easy to get stuck during mechanized adsorption printing and cause the cardboard to be scrapped and forced to stop cleaning. In two-color printing or multi-color printing, it is easy to produce uneven ink, misregistration of colors, and gaps in color stacking. The slot moves, the upper and lower flaps of the carton overlap or leave the seam; die-cutting feeding also has the disadvantages of jamming and die-cutting, etc., which may lead to scrapped cardboard or equipment damage, and will be forced to shut down and arrange.
In short, the poor flatness of the cardboard will cause inconvenient feeding, resulting in an increase in secondary waste during the production process.
In order to improve the flatness of corrugated cardboard, to ensure the product quality qualification rate and normal production efficiency, we have continuously tested and analyzed in the carton production practice, and worked out some improvement methods.
No.1 appearance of corrugated cardboard with poor flatness
The appearance of corrugated cardboard with poor flatness is roughly divided into three types: horizontal arch, vertical arch, and arbitrary arch.
Horizontal arch refers to the arch formed along the corrugated direction;
Longitudinal arch refers to the arch formed by the cardboard along the speed direction of the production line.
Arbitrary arch refers to an arch that produces undulations along any direction. The surface arched on the surface of the paper is called a positive arch, the surface arched on the inside of the paper is called a negative arch, and the surface and the surface on the inside of the paper are called a positive and negative arch.
No.2 Main factors affecting flatness of cardboard
1. There are different types and grades of paper. There are imported, domestic kraft paper, imitation kraft paper, corrugated paper, teaboard paper, high-strength corrugated paper, etc., which are divided into A, B, C, D, E, and grade. According to the poor quality of the paper, the normal paper is better than the inner paper.
2. The main technical parameters of the paper are different. From the performance requirements of the carton or the user to reduce costs, the paper inside the carton is required to be different, usually:
(1) The basis weight is different. Some papers have a larger basis weight than lining papers, and some are smaller.
(2) The moisture content of the paper in the tissue is different. Due to the different environmental humidity of the supplier, transport inventory, etc., some papers have a higher moisture content than lining paper, and some have a smaller moisture content.
(3) The basis weight and moisture content of the paper are different. One is that the basis weight of the face paper is greater than that of the inside paper, and the moisture content is greater than or less than that of the inside paper. use a high moisture corrugator belt.The second is that the weight of the face paper is smaller than that of the lining paper, and the moisture content is greater than the lining paper or less than the lining paper.
3． The moisture content of the same batch of paper is different. Part of the paper has a higher water content than the other part of the paper or tube, between the two ends, the outer edge side and the inside; the core side has a different water content.
4． The length of the heating surface of the paper passing through the preheater is incorrectly selected and adjusted, or the length of the heating surface of the paper cannot be arbitrarily affected, which affects the preheating and drying effect.
5. The steam spray device cannot be used correctly or there is no spray device on the equipment, so the humidity of the paper cannot be arbitrarily increased.
6. After the paper has been preheated, the time to distribute moisture is insufficient or the ambient humidity is large, the ventilation is poor, and the production line speed is improper.
7. Single-sided corrugating machines and glue coating machines introduce improper and uneven gluing and introduce uneven shrinkage of cardboard.
8. Insufficient and unstable steam pressure, damaged steam traps and other parts, or stagnant water in the pipes, lead to the preheater not working normally and stably.
No.3 related factors, parameter testing and qualitative analysis
Aiming at the problem of how to improve the flatness of paperboard, we tested and briefly analyzed the physical properties, process equipment, and other related factors and parameters of a commonly used paper.
1. The same kind of paper has a quantitative increase, and the shrinkage rate slightly decreases. The relationship between the quantitative, moisture content, and shrinkage of some imported kraft paper, domestic bovine (imitation) paper, teaboard paper, and high-strength corrugated paper.
2. The steam pressure supplied by the corrugated cardboard production line is directly proportional to the surface temperature of the preheater. The higher the air pressure, the higher the surface temperature of the preheater.
3. For paper with large basis weight and high moisture content, preheating and drying are slow, and vice versa. Papers of different basis weights and moisture contents are preheated and dried on a preheater with a pressure of 1.0Mpa / cm2 (172 ° C).
4. The greater the length of the heating surface (wrap angle) of the paper on the preheater, the lower the water content. The relationship between the length of the heated surface and the moisture content after baking at a preheater temperature of 172 ° C and a production line speed of 0.83 m / s for paper with a different moisture content of 10%.
5. After preheating the single-sided corrugated paper, it will naturally emit water slowly, and the fan fan will emit water quickly. After preheating 172g / m2 of 220g / m2 and 150g / m2, the moisture content is 13%. The natural emission of water in a greenhouse at 20 ° C and 65% humidity is compared with the speed of fan ventilation.
No.4 Qualitative analysis
The above test results show that the shrinkage of the paper is different depending on the paper quality, basis weight and moisture content, which is an important physical property of the paper. The same materials are used in the face paper, and it is easy for the cardboard to achieve a good flatness, otherwise it is difficult. It is necessary to comprehensively consider the changes of the above five main factors and make appropriate adjustments.
The degree of flatness depends on the shrinkage of each layer of paper. To make the board have a good flatness, the shrinkage of each layer of paper must be basically the same, the most important of which is the liner. The shrinkage rate of the face paper is smaller than that of the inner paper, which is a positive arch, otherwise it is a negative arch, and the local unevenness of the shrinkage of the paper is positive and negative arch. From the analysis of the process of forming cardboard on the production line, controlling the shrinkage can be divided into two stages.
(1) Corrugation formation stage. That is, the various processes before the base paper is fed to the second coating, which is the key stage to control the shrinkage rate. According to the actual conditions of the paper, steam pressure, ambient temperature and humidity of the various layers of the tile, adjust the preheating temperature, the length of the heated surface (angle), the method of venting moisture, steam spray, the amount of glue, The production line speed technical parameters enable each layer of paper to be controlled through appropriate and effective processes, and each of them can shrink freely, and the final shrinkage rate is basically the same.
(2) The cardboard forming stage. It is the bonding, drying and ironing from the second glue application to the subsequent process. At this time, each layer of paper can no longer shrink freely, and the shrinkage of each layer of paper after being bonded into cardboard is restricted by each other. The bonding point can be said to be the starting point of the arch of the cardboard. It is necessary to select and adjust the technical parameters such as the amount of glue, the temperature of the baking plate, and the speed of the production line, control the difference in shrinkage to a minimum, and flatten the arches produced by the cardboard as much as possible.
No.5 Thoughts on Improving the Flatness of Corrugated Board
First, the base paper provided by the supplier is required to have a qualified and stable basis weight and moisture content, avoid rainwater during transportation and loading and unloading, and maintain a basically constant environmental humidity during storage in the factory.
Second, as far as possible, use the same kind of paper or paper with the same basis weight, moisture content and grade.
3. The length of the heated surface (cover angle) of the paper with a large water content is increased, and the fan is used to ventilate, increase the time to dissipate moisture, and slow down the production line speed; the paper with a small moisture content passes through the preheater (angle) The length of the heating surface is reduced, natural ventilation and steam spray are used to speed up the production line.
Fourth, the sizing amount of each layer of paper is consistent, and the sizing amount is uniform and moderate along the entire width of the corrugated direction.
Fifth, the air pressure is stable, and the pipe fittings such as traps maintain normal functions.
There are many factors that affect the flatness of corrugated cardboard. With the changes between the factors of flatness, the improvement needs to be tailored to local conditions, targeted, and the major contradictions should be seized and resolved. The following are examples of common problems in the production of single and double corrugated cardboard.
No.6 cardboard arched horizontally
Known: The face paper is 250g / m2A grade kraft paper with a moisture content of 7.7%; (clip) tile paper is 150g / m2 domestic high-strength corrugated paper with a moisture content of 10%; the inner paper is 250g / m29B grade kraft paper with a moisture content of 14%; 1.1Mpa / cm2 production line speed is 60m / min.
ways to improve:
(1) The length of the heated surface of the lining (pile) tile paper through the preheater (cover angle) is increased by 1 to 1.6 times and 0.5 to 1.1 times respectively.
(2) The ri (clamp) tile line is moved on the production line bridge with 0.9KW electric speed ventilation, and the windows of the workshop are naturally ventilated.
(3) Even a small amount of steam spray on the tissue.
(4) The production line speed is reduced to about 50m / min.
Properly adjusted according to the above selection parameters, the original transverse positive arch can disappear.
Improved method of negative arch of cardboard from longitudinal:
(1) The tissue paper increases the motion resistance in front of the three-layer preheater and increases the rotation braking force of the tube paper.
(2) The guide rollers and tension rollers of Liwa paper in front of the three-layer preheater reduce the movement resistance.
After proper adjustment, the original longitudinal positive arch can disappear.
No.7 Cardboard is negatively arched
It is known that the face paper is 200g / nfB grade imitation kraft paper with a water content of 8%; the air pressure is 1.0Mpa / cnf; the production line speed is 50m / min.
ways to improve:
(1) The length of the heated surface of the tile (clip) tile paper increased by 0.9 to 1.4, 0.6 to 1.12 times through the preheater.
(2) Liner paper reduces the length of the heating surface of the preheater or sprays it with a small amount of steam.
(3) The production line speed is increased to about 60m / rain. Cardboard longitudinal negative arch
ways to improve:
(1) The tissue paper is in front of the three-layer preheater to reduce the movement resistance and the rotation braking force of the tube paper.
(2) The guide rollers and tensioning wheels of the paper in front of the three-layer preheater increase movement resistance. After proper adjustment, the original longitudinal positive arch can disappear.
No.8 Cardboard is negatively arched longitudinally
It is known that the face paper is 200g / m2B grade kraft paper with a moisture content of 13%; (clip) tile paper is 150g / m2 high-strength corrugated paper with a moisture content of 10%; the inner paper is 200g / m2B grade kraft paper with a moisture content of 8%; Air pressure 1.0Mpa / cm2; production line speed 50m / rain.
ways to improve:
(1) The length of the heated surface of the surface (clamp) tile paper increased by 0.9 to 1.4 and 0.6 to 1.1 times through the preheater.
(2) Liner paper reduces the length of the heating surface of the preheater or sprays it with a small amount of steam.
(3) The production line speed is increased to about 60m / min. Cardboard longitudinal negative arch
ways to improve:
(1) Facial paper reduces motion resistance in front of three-layer preheater
Less web rotation braking force.
(2) The guide tension of the Riva wire in front of the three-layer preheater increases the movement resistance.
No.9 cardboard is arched
Because there are generally two types of positive and negative arches, the different methods of improvement only explain the common lateral positive and negative arches.
Known: face paper is 180g / m2 kraft paper, moisture content 8 value 14%; air pressure is 1.1Mpa / cm2; production line speed 70m / min improved method
(1) Partially apply steam to the inside of the laterally arched area
(2) Local steam spray of paper in the area of transverse negative arch.
(3) The production line speed is reduced to about 60m / min.
(4) Adjust the direction of 180 ° for Liwa paper.
In addition, there is a way to make up for the partially arched cardboard that has just been made from the production line. About 10 sheets are stacked in front and back, and the top pressure plate is stacked, so that the cardboard is subjected to the front and back during the storage of semi-finished products. The flattened external force can achieve a good flatness after a few hours (according to the ventilation and heat dissipation conditions of the plant).
Ideas and suggestions
At present, with the improvement of the level of production automation in the packaging industry, multi-functional machine operations such as cardboard printing, die cutting, slotting and cutting, gluing, binding, and strapping, and machine packaging production lines for carton users are widely used. The higher and higher, the non-compliant cardboard will be automatically stopped or withdrawn by the packaging production line.
Therefore, there should be a standard for the flatness of corrugated cardboard, which is convenient for operators and quality inspectors to follow the job inspection and is conducive to controlling process quality.
The flatness of corrugated cardboard shall be measured after it is placed horizontally without any external force, and the chord height shall be taken as the value. Flatness is divided into 3 levels:
The first-level accuracy is suitable for the production of multi-functional machines such as printing die cutting, slotting, and cutting angles, and is used for high-precision machine packaging cartons;
The second-level accuracy is suitable for the production of printing and die-cutting machines, and is used for high-precision packaging cartons;
The three-level accuracy is suitable for single-machine production such as printing, slitting and creasing, and slotting machines, and is used for general-precision packaging cartons.
Improve and improve corrugated cardboard production line equipment
(1) The preheater required for each layer of paper, especially the preheater required for the inner paper, should be able to make the length of the heated surface of the paper (the wrap angle) arbitrarily adjustable;
(2) There should be enough space for the paper to emit moisture after passing through the preheater, especially the space for the paper to emit moisture;
(3) Fans shall be installed in the area where the paper emits moisture after preheating.
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