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In order to improve the flatness of corrugated board, ensure the qualified rate of product quality and normal production efficiency, we constantly test and analyze in the practice of carton production, and have found some improvement methods. The rough outline is as follows, for reference only.
Corrugated paperboard poor appearance of the shape of flat Corrugated paperboard poor appearance of the shape is roughly 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 paperboard are: 1. There are different paper types and grades in the paper. 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 poor quality paper, the general paper is better than the paper.
2. The main technical parameters of the surface paper 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 moisture 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 moisture content of the same batch of paper 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 heating surface of the paper (wrapping angle) of the preheater 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 preheated, the water is not distributed in sufficient time or the environment has high humidity, ventilation is poor, and the speed of the production line is improper.
7. Unfavorable sizing and uneven gluing of single-faced corrugating machines and gluing machines cause uneven shrinkage into the cardboard.
8. The steam pressure is insufficient, unstable, and parts such as steam traps are damaged or the water in the pipes is not drained. As a result, the preheater cannot work normally.
Relevant factors, parameter testing and qualitative analysis For the problem of how to improve the flatness of the paperboard, we tested and analyzed the physical factors, process equipment, and other related factors and parameters of several commonly used papers.
The formula for the shrinkage (ε) is:
ε = length of sample paper at a certain moisture content - length of sample paper when moisture content is zero/length of sample paper when a moisture content is × 100%
Test results of related factors and parameters (1) The quantitative increase of the same type of paper resulted in a slight decrease in shrinkage. The relationship between the quantification, moisture content and shrinkage of some imported kraft paper, domestic beef (imitation) paper, tea board paper and high-strength corrugated paper is shown in Figure 2.
(2) The steam pressure supplied by the corrugated board 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, see Table 1.
Table 1
MPa/cm3 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3
Temperature 151 157 163 168 172 177 181 185
(3) The paper with high moisture content is quantified, preheated and dried slowly, and vice versa. For papers with different basis weights and moisture content, the time required for preheating and drying on a preheater with air pressure of 1.0Mpa/cm2 (172°C) is shown in Figure 3.
(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 heated surface and the moisture content after baking was shown in Figure 4 for the different quantitative papers with a water content of 10% at a preheater temperature of 172°C and a line speed of 0.83 m/s.
(5) After single-sided corrugated paper is warmed up, it will naturally emit water slowly, and the fans will be ventilated to distribute water quickly. The moisture content of rations of 220g/m2 and 150g/m2 single-faced corrugated paper after preheating at 172°C is 13%, and the natural distribution of moisture in greenhouses at 20°C and humidity 65% ​​is compared with the speed of fan ventilation.
Qualitative analysis The above test results show that the paper, quantitative, and 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. It is negative arching and vice versa. The local unevenness of paper shrinkage is 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. Technical parameters such as the speed of the production line, so that each layer of paper is controlled through appropriate and effective processes, each of which is freely contracted, 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.
Cardboard flatness improvement method The improvement idea of ​​flatness of corrugated paperboard: First, the base paper provided by the supplier is required to have a qualified and stable basis weight and moisture content, to prevent rainwater from getting wet during transportation and handling, and to maintain a substantially constant ambient humidity when stored in the factory. The second is that the surface of the paper choice of materials as much as possible using the same type of paper or quantitative, moisture content, the same grade of paper. Thirdly, the paper with high water content is heated by the heating surface (wrapping angle) of the preheater, and is ventilated by the electric fan to increase the time for distributing water and slow down the speed of the production line. Paper with a small moisture content passes through the preheater ) The length of the heating surface is reduced, natural ventilation and steam spray are used to speed up the production line. Fourth, the amount of glue on each layer of paper remains the same, and the amount of glue on the entire width of the paper along the direction of the corrugation is even and moderate. Fifth, pressure stability, traps and other pipe fittings to maintain normal function.
There are many factors that affect the flatness of corrugated board, and the changes between the various factors of flatness will change. Improvements must be made according to local conditions and targeted, and the main contradiction must be resolved. The following is an example of the common problems in producing single and double corrugated cardboard.
It is known that the paperboard is horizontally arched: the face paper is imported into grade A kraft paper of 250g/m2 with a moisture content of 7.7%; (clamps) 150g/m2 domestic high-strength corrugated paper with moisture content of 10%; the paper is 250g/m2B class Kraft paper moisture content 14%; air pressure 1.1Mpa/cm2 production line speed 60m/min. ways to improve:
(1) The length of the heated surface of the (jaw) tile through the preheater (wrap angle) is increased by 1 to 1.6 times and 0.5 to 1.1 times, respectively.
(2) The medium-speed ventilation of the 0.9KW electric fan is adopted for the inner (clamp) tile line moving on the bridge of the production line, and the workshop is opened for natural ventilation.
(3) The face paper is evenly sprayed with a small amount of steam.
(4) The production line speed is reduced to about 50m/min. Adjusted according to the above-mentioned selection parameters, the original transverse arch can disappear.
Cardboard is negatively arched longitudinally. Improved method:
(1) Face paper increases the movement resistance in front of the three-layer preheater and increases the rotational force of the tube paper.
(2) The guide wheels and tensioning wheels of the Liwa paper in front of the three-layer preheater reduce movement resistance. Appropriate adjustment of the original longitudinal arch can disappear.
It is known that the paperboard is negatively arched horizontally: the face paper is 200g/m2B imitation kraft paper, the moisture content is 13%; the (clamp) corrugated paper is 150g/m2 high-strength corrugated paper moisture content 10%; the paper uses 200g/m2B grade imitation kraft paper Rate 8%; air pressure 1.0Mpa/cm2; production line speed 50m/min. ways to improve:
(1) The length of the heating surface of the surface (jaw) tiles through the preheater increases by 0.9 to 1.4 times and 0.6 to 1.12 times, respectively.
(2) The paper reduces the length of the preheater heating surface or sprays it with steam.
(3) The production line speed increased to about 60m/min.
Cardboard is negatively arched longitudinally. Improved method:
(1) Face paper reduces movement resistance in front of the three-layer preheater, reducing the rotational force of the web.
(2) Liva paper increases the resistance of the guide wheel and the tensioning wheel in front of the three-layer preheater. Appropriate adjustment of the original longitudinal arch can disappear.
There are two types of positive and negative arches. There are two types of positive and negative arches. The methods of improvement are different. Here, only the common transverse positive and negative arches are described. Known: face paper is 180g/m2A kraft paper, moisture content of 7 to 12.6%; (clamp) tile 125g/m2 high-strength corrugated paper, moisture content of 12%; paper for 180g/m2C grade kraft moisture content of 8 values ​​14%; The pressure is 1.1Mpa/cm2; the line speed is 70m/min. ways to improve:
(1) The paper is partially sprayed with steam in the transversely arched area.
(2) Local steam spray in the transversely negatively arched area.
(3) The production line speed is reduced to about 60m/min.
(4) Adjust the 180o direction of the liner paper.
In addition, there is a way to make up for the partial arch that has just been made from the production line.
Talking about the Improvement of Flatness of Corrugated Board
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.; the slot size displacement of the printing boot, the overlapping of the carton flap cover or not; the die-cutting feeding will also have the disadvantages of jamming and dimensional displacement, etc., all of which may lead to the waste or equipment of the whole board. 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.