The flatness of corrugated board is one of the important indicators in carton production technology, and it is directly related to the quality of product printing, die cutting or slotting.
The corrugated board is bent and warped, and the corrugated board will have a multi-arch shape.
Mechanized adsorption printing is easy to jam and cause the cardboard to be scrapped and forced to stop for cleaning; in two-color printing or multi-color printing, it is easy to produce uneven ink, inaccurate color registration, and gaps in color overlap; open on the slotting machine If the slot is moving, the top and bottom flaps of the carton are overlapped or separated from the seam; die-cutting feeding will also produce jams and die-cutting positions, etc., which may cause the cardboard to be scrapped or equipment damage, and be forced to shut down for sorting.
In short, poor cardboard flatness will cause inconvenience in feeding, resulting in an increase in waste products in the production process.
In order to improve the flatness of corrugated board, ensure the product quality pass rate and normal production efficiency, we continuously test and analyze in the carton production practice, and find some improvement methods.
No.1 The appearance and shape of corrugated board with poor flatness
The appearance and shape of corrugated cardboard with poor flatness can be roughly divided into three types: horizontal arch, longitudinal arch and arbitrary arch.
Lateral arch, refers to the arch along the corrugated direction;
Longitudinal arches refer to the arches produced by the cardboard along the speed of the production line.
Arbitrary arch refers to an arch that undulates in any direction. The arched surface of the facial paper is called positive arch, the arched surface of the inner paper is called negative arch, and the undulating surface of the face and inner paper is called positive and negative arch.
No.2 The main reason that affects the flatness of cardboard
1. Different types and grades of lining paper. There are imported, domestic kraft paper, imitation kraft paper, corrugated paper, teaboard paper, high-strength corrugated paper, etc., and are divided into A, B, C, D, E, and grades. According to the poor quality of the paper, the surface paper is generally better than the lining paper.
2. The main technical parameters of lining paper are different. From the carton performance requirements or from the user’s consideration of reducing costs, the surface and the paper of the carton are required to be different, usually:
(1) The basis weight of the paper in the dough is different. There are some paper with a larger basis weight than the inner paper, and some with a smaller weight.
(2) The moisture content of the paper in the tissue is different. Depending on the environmental humidity of the supplier, transportation inventory, etc., some tissues have a higher moisture content than a lining paper, and some have a lower moisture content.
(3) The basis weight and moisture content of the dough and paper are different. One is that the basis weight of the tissue paper is greater than that of the lining paper, and the moisture content is greater than or less than that of the lining paper. The second is that the basis weight of the top paper is smaller than that of the lining paper, and the moisture content is greater than or less than that of the lining paper.
3. The moisture content of the same batch of paper is different. The moisture content of one part of the paper is greater than that of the other part of the paper or roll paper, the outer edge side and the inner side; the core side has a different moisture content.
4. Improper selection and adjustment of the length of the heated surface of the (wrap angle) of the paper preheater or the length of the (wrap angle) cannot be arbitrarily heated, which affects the preheating 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 increased arbitrarily.
6. After the paper has been preheated, the time for dissipating moisture is insufficient or the environmental humidity is high, the ventilation is poor, and the production line speed is improper.
7. The improper and uneven glue application of the single-sided corrugator and gluing machine leads to uneven shrinkage of the imported cardboard.
8. Insufficient and unstable steam pressure, damage to accessories such as traps, or drainage of water in the pipeline causes the preheater to fail to work normally and stably.
No.3 Related factors, parameter testing and qualitative analysis
Aiming at the problem of how to improve the flatness of cardboard, we tested and briefly qualitatively analyzed the physical properties, process equipment and other related factors and parameters of commonly used/1 paper.
1. The quantitative increase of the same kind of paper and the slight decrease in shrinkage. The relationship between the basis weight, moisture content and shrinkage of some imported kraft paper, domestic cattle (imitation) leather paper, tea board paper, and high-strength corrugated paper.
2. The steam pressure supplied by the corrugated board production line is 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. The paper with different basis weight and moisture content should be preheated and dried for the required time on the air pressure 1.0Mpa/cm2 (172℃) preheater.
4. The greater the length of the heated surface (wrap angle) of the paper drying on the preheater, the lower the moisture content. The relationship between the length of the heated surface and the moisture content after drying when the preheater temperature is 172°C and the production line speed is 0.83m/s for paper with different basis weights with a moisture content of 10%.
5. After the single-sided corrugated paper is preheated, it will naturally emit moisture slowly, and the fan will emit moisture quickly. Quantitative 220g/m2 and 150g/m2 single-faced corrugated paper has a moisture content of 13% after preheating at 172g/m2. The natural emission of water in a greenhouse at 20°C and a humidity of 65% is compared with the speed of fan ventilation.
No. 4 Qualitative Analysis
The above test results show that the paper quality, basis weight, and moisture content are different, and its shrinkage rate is also different, which is an important physical property of paper. With the same material used in the paper and paper, it is easy for the cardboard to achieve better flatness, and vice versa. It is necessary to comprehensively consider the changes in 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 cardboard have better flatness, the shrinkage of each layer of paper must be basically the same, and the most important one is the surface paper. The shrinkage rate of the tissue paper is smaller than that of the inner paper, and it is a positive arch, otherwise it is negative. From the analysis of the production line cardboard forming process, controlling the shrinkage rate can be divided into two stages.
(1) Corrugated formation stage. That is, the various processes from the feeding of the base paper to the second gluing are the key stages to control the shrinkage rate. According to the actual conditions of the paper, steam pressure, ambient temperature and humidity of each layer of the tile in the surface, select and adjust the preheating temperature, the length of the heated surface (wrap angle), the way of ventilating moisture, steam spray, the amount of glue, The technical parameters of the production line speed enable each layer of paper to pass through appropriate and effective process control, and each layer of paper 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 glued into a cardboard is mutually restricted. The bonding point can be said to be the starting point for the cardboard to produce an arch. It is necessary to select and adjust the technical parameters such as the amount of glue, the temperature of the baking sheet, the speed of the production line, etc., to control the difference in shrinkage to a minimum, and to flatten the arches produced by the cardboard as much as possible.
No.5 Improvement Ideas for Corrugated Board Flatness
1. The raw paper provided by the supplier is required to have a qualified and stable basis weight and moisture content, avoid rain during transportation and loading and unloading, and maintain a basically constant environmental humidity during storage in the factory.
2. The selection of flour and lining paper should use the same paper quality or paper with the same basis weight, moisture content and grade as much as possible.
3. The length of the heating surface (wrap angle) of the paper with high moisture content is increased by the preheater, and the fan is used for ventilation, which increases the time of moisture dissipating, and slows down the production line; the paper with low moisture content is passed through the preheater (wrap angle) The length of the heating surface is reduced, natural ventilation, and steam spray are used to speed up the production line.
4. The amount of glue on each layer of paper is kept consistent, and the amount of glue on the full width along the corrugated direction is even and moderate.
5. 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 board. With the changes between the various factors of flatness, improvement needs to be tailored to local conditions, with a target, and grasp the main contradictions to solve them. The following examples illustrate common problems in the production of single and double corrugated cardboard.
No.6 The cardboard is arched horizontally
Known: The facial paper is 250g/m2A grade kraft paper with a moisture content of 7.7%; (clip) corrugated paper is 150g/m2 domestic high-strength corrugated paper with a moisture content of 10%; the inner paper is 250g/m2B 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 heating surface of the inner (clamped) tile paper is increased by 1 to 1.6 times and 0.5 to 1.1 times respectively through the preheater (wrap angle).
(2) The li (clamp) tile line adopts 0.9KW electric medium-speed ventilation at the moving position on the production line bridge, and the workshop opens windows for natural ventilation.
(3) A small amount of steam spray evenly on the tissue.
(4) The production line speed is reduced to about 50m/min.
Properly adjust according to the above selection parameters, and the original horizontal arch can disappear.
The improvement method for the cardboard to be negatively arched from the longitudinal direction:
(1) The movement resistance of the tissue paper is increased in front of the three-layer preheater, and the rotation braking force of the roll paper is increased.
(2) The guide wheel and tension wheel of the Liwa paper in front of the three-layer preheater reduce the movement resistance.
After proper adjustment, the original longitudinal arch can disappear.
No.7 The cardboard is negatively arched horizontally
Known: The facial paper is 200g/nfB grade imitation kraft paper, with 8% moisture content; air pressure 1.0Mpa/cnf; production line speed 50m/min.
ways to improve:
(1) The length of the heating surface of the surface (clip) tile paper through the preheater is increased by 0.9 to 1.4 and 0.6 to 1.12 times respectively.
(2) The inner paper reduces the length of the heating surface of the preheater or sprays with a small amount of steam.
(3) The production line speed is increased to about 60m/rain. The cardboard is longitudinally negatively arched
ways to improve:
(1) The tissue paper reduces the movement resistance before the three-layer preheater and reduces the roll paper rotation braking force.
(2) The guide wheels and tension wheels of the Liwa paper in front of the three-layer preheater increase the movement resistance. After proper adjustment, the original longitudinal arch can disappear.
No.8 The cardboard is longitudinally negatively arched
Known: Facial paper is 200g/m2B grade kraft paper with a moisture content of 13%; (clip) corrugated paper is 150g/m2 high-strength corrugated paper with a moisture content of 10%; lining paper is 200g/m2B grade imitation 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 (clip) tile paper through the preheater is increased by 0.9 to 1.4 and 0.6 to 1.1 times respectively.
(2) The inner paper reduces the length of the heating surface of the preheater or sprays with a small amount of steam.
(3) The production line speed is increased to about 60m/min. The cardboard is longitudinally negatively arched
ways to improve:
(1) The tissue paper reduces the movement resistance in front of the three-layer preheater
Rotational braking force for small rolls of paper.
(2) The guiding tension of the Riva line in front of the three-layer preheater increases the movement resistance.
No.9 The cardboard is in a positive and negative arch shape
Because there are generally two types of positive and negative arches, the improvement methods are different. This only explains the common lateral positive and negative arches.
Known: The facial paper is 180g/m2 kraft paper, the moisture content is 8 value is 14%; the air pressure is 1.1Mpa/cm2; the production line speed is 70m/min. Improved method
(1) Use steam spray on the facial tissue in the horizontal arch area.
(2) In the horizontal negative arch area, the paper is partially steam sprayed.
(3) The production line speed is reduced to about 60m/min.
(4) Adjust the 180° direction of the Liwa paper.
In addition, there is a way to make up for the partially arched cardboard just made from the production line, stacking the front and back in a stack of about 10 sheets, and then the upper pressure plate, so that the cardboard will be exposed to the front and back during the storage of the semi-finished products. The external force of flattening can achieve a better flatness after a few hours (according to the ventilation and heat dissipation conditions of the workshop).
Ideas and suggestions
At present, with the improvement of the production automation level of the packaging industry, multi-function machine operations such as cardboard printing, die cutting, slotting, gluing, binding, and strapping, and machine packaging production lines for carton users have been widely used, and the flatness requirements are more and more The higher the coming, the cardboard that does not meet the requirements will be automatically shut down or exited by the packaging production line.
Therefore, there should be a standard for the flatness of corrugated board, which is convenient for operators and quality inspectors to follow the operation inspection and is beneficial to control the quality of the process.
The flatness of corrugated cardboard must be measured after being placed horizontally without any external force, with the chord height as the measurement value. The flatness is divided into 3 levels:
The first-level precision is suitable for the production of multi-function machines such as printing, die-cutting, slotting and corner cutting, and is used for machine-packing cartons with high precision;
The secondary precision is suitable for printing and die-cutting machine production, and is used for packaging cartons with higher precision;
The three-level precision is suitable for single-machine production such as printing, slitting, creasing, and slotting machines, and is used for packaging cartons with general precision.
Improve and perfect the equipment of corrugated board production line
(1) The preheater required for each layer of paper, especially the preheater required for the face and inner paper, should enable the length of the heated surface (wrap angle) of the paper to be adjusted arbitrarily;
(2) There must be enough space for each paper to emit moisture after passing through the preheater, especially to ensure the space for the facial paper to emit moisture;
(3) The area where each paper emits moisture after preheating needs to be equipped with electric fan ventilation device.
