The flatness of corrugated board is one of the important indicators in the carton production technology. It is directly related to the quality of product printing, die cutting or notching. The poor smoothness of corrugated paperboard will result in a variety of arched shapes of corrugated paperboard, and it will be easy to get stuck and cause the paperboard to be scrapped and be forced to shut down and clean up when it is mechanized and adsorbed. It is easy to produce ink unevenness and color misregistration in double-color printing or multi-color printing. There are gaps in the color overlapping edge, etc.; groove size displacement on the boot press, overlapping or non-seamable flaps on the carton; die-cutting feeds also have the disadvantages of jamming and dimensional displacement, etc., all of which may lead to positive waste paperboard waste, or equipment. Damage was forced to shut down the finishing. In short, the poor flatness of the paperboard will cause inconvenience in feeding and increase the number of waste products in the production process.
In order to improve the flatness of corrugated products, ensure the qualified rate of product quality and normal production efficiency, we constantly tested and analyzed the practice of carton production and found some improvement methods. The rough outline is as follows, for reference only.
Corrugated paper sheet poor appearance appearance shape
Corrugated cardboard poor appearance of the shape of the general can be divided into three types: horizontal arch, longitudinal arch and arbitrary arch.
Lateral arching refers to the arching that occurs along the corrugated direction. Longitudinal arching refers to the arched shape of the board along the line speed of the production line. Arbitrary arches mean undulating arches in any direction. The surface of the dough paper is arched in the form of a positive arch, the arched surface of the paper is called a negative arch, and the surface of the paper has undulations called positive and negative arches.
The main reasons affecting the flatness of the board
1, the surface of paper types, different levels. There are imported, domestic kraft paper, imitation kraft paper, corrugated paper, tea board paper, high-strength corrugated paper, etc., and points A, B, C, D, E, grade. According to the paper quality material, the general paper is better than the paper.
2. The main technical parameters of the paper in the surface are different. Considering the performance requirements of the carton or the user to reduce the cost, the paper inside the carton is required to be different, usually:
(1) The amount of paper in the dough is different. There is a large amount of face paper than the paper, and there are also small ones.
(2) The moisture content of the paper in the facial tissue is different. Due to the different environmental humidity of suppliers, transportation stocks, and the fact that there is a large moisture content in the facial tissue, it is also small.
(3) The amount of paper and moisture content in the surface are all different. One is that the dough paper is greater than the paper, and the water content is greater than the paper or less than the paper. The second is that the surface paper is less than the paper, the moisture content is greater than the paper or less than the paper.
3, the same batch of paper moisture content is different. Part of the paper moisture content is greater than the other part of the paper or paper between the ends, the outer edge side and the inner core side of the water content is different.
4. The length of the heating surface of the paper (wrapping angle) is improperly selected and adjusted, or the length of the heating surface (wrapping angle) cannot be arbitrarily adjusted. The former due to improper operation, the latter due to equipment limitations, affecting the preheating drying effect.
5. The steam spray device cannot be used correctly or there is no spray device on the device, so the humidity of the paper cannot be arbitrarily increased.
6. After the paper is warmed up, the water is not distributed in sufficient time or the ambient humidity is high, the ventilation is poor, and the speed of the production line is improper.
7. Unilateral corrugating machines, gluing machines have improper sizing, uneven feeding, and uneven cardboard shrinkage.
8, steam pressure is not enough, instability, steam traps and other accessories damaged or drained water does not lead to the preheater can not work properly.
Related factors, parametric testing and qualitative analysis
For the problem of how to improve the flatness of the paperboard, we tested and analyzed the physical properties, process equipment, and other related factors and parameters of several commonly used papers.
(1) The quantitative increase of the same type of paper, the shrinkage rate is slightly reduced. The relationship among the imported kraft paper, domestic beef (imitation) leather paper, tea board paper, high-strength corrugated paper, the quantitative, moisture content, shrinkage ratio.
(2) The steam pressure supplied by the corrugated board production line is directly proportional to the surface temperature of the preheater. The higher the pressure. The higher the surface temperature of the preheater.
(3) The paper with high moisture content is quantified, preheated and dried slowly, and vice versa. Papers with different basis weight and moisture content are preheated and dried on a preheater with air pressure of 1.0Mpa/cm2 (172°C).
(4) The greater the length of the heating surface (wrapping angle) when the paper is dried on the preheater, the lower the water content. The relationship between the length of the heating surface and the moisture content after baking was determined at a preheater temperature of 172°C and a line speed of 0.83 m/s for papers of different basis weights with a moisture content of 10%.
(5) After the single-faced corrugated paper is warmed up, it naturally emits water slowly, and the fans are ventilated back to powder quickly. Quantitatively, the moisture content of 220g/m2 and 150g/m2 single-faced corrugated paper after preheating at 172°C is 13%, and the natural distribution of moisture in the greenhouse at 20°C and humidity 65% ​​is compared with the speed of fan ventilation.
Qualitative analysis
The above test results show that the paper, the quantitative, and the moisture content are different, and its shrinkage is also different. This is an important physical property of the paper. With the same paper material in the surface, the cardboard can easily achieve a good flatness. On the contrary, it is difficult. To comprehensively consider the changes of the above five major factors, make appropriate adjustments. The goodness of flatness depends on the shrinkage of each layer of the paper. To make the paperboard have a better flatness, the shrinkage of the paper must be basically the same, and the most important one is the paper in the surface. The shrinkage of the tissue paper is smaller than that of the paper and it is a negative arch. On the other hand, the local unevenness of the paper shrinkage becomes positive and negative arch. From the analysis of the process of board formation in the production line, the control shrinkage rate can be divided into two stages.
(1) The formation of corrugations. This is the key step for controlling the shrinkage rate, which is the various processes before feeding the raw paper to the secondary coating. According to the actual conditions of the paper, steam pressure, ambient temperature and humidity in each layer of the tile, adjust the preheating temperature, the length of the heated surface (wrapping angle), the method of ventilating water distribution, the steam spray, and the amount of glue respectively. The technical parameters of the speed lamp of the production line are such that each layer of paper is controlled by suitable and effective processes, each of which is free to shrink, and the final shrinkage rate is basically the same.
(2) The cardboard forming stage. It is the bonding, drying and ironing of the secondary coating to the subsequent process. At this point, each layer of paper has not been able to shrink freely. After being glued into cardboard, the shrinkage of each layer of paper is restricted by each other. The bonding point can be said to be the starting point of cardboard arching. To select and adjust the technical parameters such as the amount of glue, the temperature of the baking board, and the speed of the production line, control the difference in shrinkage ratio to the minimum, and iron the arches generated by the cardboard as much as possible.
In order to improve the flatness of corrugated products, ensure the qualified rate of product quality and normal production efficiency, we constantly tested and analyzed the practice of carton production and found some improvement methods. The rough outline is as follows, for reference only.
Corrugated paper sheet poor appearance appearance shape
Corrugated cardboard poor appearance of the shape of the general can be divided into three types: horizontal arch, longitudinal arch and arbitrary arch.
Lateral arching refers to the arching that occurs along the corrugated direction. Longitudinal arching refers to the arched shape of the board along the line speed of the production line. Arbitrary arches mean undulating arches in any direction. The surface of the dough paper is arched in the form of a positive arch, the arched surface of the paper is called a negative arch, and the surface of the paper has undulations called positive and negative arches.
The main reasons affecting the flatness of the board
1, the surface of paper types, different levels. There are imported, domestic kraft paper, imitation kraft paper, corrugated paper, tea board paper, high-strength corrugated paper, etc., and points A, B, C, D, E, grade. According to the paper quality material, the general paper is better than the paper.
2. The main technical parameters of the paper in the surface are different. Considering the performance requirements of the carton or the user to reduce the cost, the paper inside the carton is required to be different, usually:
(1) The amount of paper in the dough is different. There is a large amount of face paper than the paper, and there are also small ones.
(2) The moisture content of the paper in the facial tissue is different. Due to the different environmental humidity of suppliers, transportation stocks, and the fact that there is a large moisture content in the facial tissue, it is also small.
(3) The amount of paper and moisture content in the surface are all different. One is that the dough paper is greater than the paper, and the water content is greater than the paper or less than the paper. The second is that the surface paper is less than the paper, the moisture content is greater than the paper or less than the paper.
3, the same batch of paper moisture content is different. Part of the paper moisture content is greater than the other part of the paper or paper between the ends, the outer edge side and the inner core side of the water content is different.
4. The length of the heating surface of the paper (wrapping angle) is improperly selected and adjusted, or the length of the heating surface (wrapping angle) cannot be arbitrarily adjusted. The former due to improper operation, the latter due to equipment limitations, affecting the preheating drying effect.
5. The steam spray device cannot be used correctly or there is no spray device on the device, so the humidity of the paper cannot be arbitrarily increased.
6. After the paper is warmed up, the water is not distributed in sufficient time or the ambient humidity is high, the ventilation is poor, and the speed of the production line is improper.
7. Unilateral corrugating machines, gluing machines have improper sizing, uneven feeding, and uneven cardboard shrinkage.
8, steam pressure is not enough, instability, steam traps and other accessories damaged or drained water does not lead to the preheater can not work properly.
Related factors, parametric testing and qualitative analysis
For the problem of how to improve the flatness of the paperboard, we tested and analyzed the physical properties, process equipment, and other related factors and parameters of several commonly used papers.
(1) The quantitative increase of the same type of paper, the shrinkage rate is slightly reduced. The relationship among the imported kraft paper, domestic beef (imitation) leather paper, tea board paper, high-strength corrugated paper, the quantitative, moisture content, shrinkage ratio.
(2) The steam pressure supplied by the corrugated board production line is directly proportional to the surface temperature of the preheater. The higher the pressure. The higher the surface temperature of the preheater.
(3) The paper with high moisture content is quantified, preheated and dried slowly, and vice versa. Papers with different basis weight and moisture content are preheated and dried on a preheater with air pressure of 1.0Mpa/cm2 (172°C).
(4) The greater the length of the heating surface (wrapping angle) when the paper is dried on the preheater, the lower the water content. The relationship between the length of the heating surface and the moisture content after baking was determined at a preheater temperature of 172°C and a line speed of 0.83 m/s for papers of different basis weights with a moisture content of 10%.
(5) After the single-faced corrugated paper is warmed up, it naturally emits water slowly, and the fans are ventilated back to powder quickly. Quantitatively, the moisture content of 220g/m2 and 150g/m2 single-faced corrugated paper after preheating at 172°C is 13%, and the natural distribution of moisture in the greenhouse at 20°C and humidity 65% ​​is compared with the speed of fan ventilation.
Qualitative analysis
The above test results show that the paper, the quantitative, and the moisture content are different, and its shrinkage is also different. This is an important physical property of the paper. With the same paper material in the surface, the cardboard can easily achieve a good flatness. On the contrary, it is difficult. To comprehensively consider the changes of the above five major factors, make appropriate adjustments. The goodness of flatness depends on the shrinkage of each layer of the paper. To make the paperboard have a better flatness, the shrinkage of the paper must be basically the same, and the most important one is the paper in the surface. The shrinkage of the tissue paper is smaller than that of the paper and it is a negative arch. On the other hand, the local unevenness of the paper shrinkage becomes positive and negative arch. From the analysis of the process of board formation in the production line, the control shrinkage rate can be divided into two stages.
(1) The formation of corrugations. This is the key step for controlling the shrinkage rate, which is the various processes before feeding the raw paper to the secondary coating. According to the actual conditions of the paper, steam pressure, ambient temperature and humidity in each layer of the tile, adjust the preheating temperature, the length of the heated surface (wrapping angle), the method of ventilating water distribution, the steam spray, and the amount of glue respectively. The technical parameters of the speed lamp of the production line are such that each layer of paper is controlled by suitable and effective processes, each of which is free to shrink, and the final shrinkage rate is basically the same.
(2) The cardboard forming stage. It is the bonding, drying and ironing of the secondary coating to the subsequent process. At this point, each layer of paper has not been able to shrink freely. After being glued into cardboard, the shrinkage of each layer of paper is restricted by each other. The bonding point can be said to be the starting point of cardboard arching. To select and adjust the technical parameters such as the amount of glue, the temperature of the baking board, and the speed of the production line, control the difference in shrinkage ratio to the minimum, and iron the arches generated by the cardboard as much as possible.
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