Control the process of two production stages to completely solve the unevenness of cardboard

The flatness of corrugated cardboard is directly related to the quality of printing, die-cutting, or slotting and corner cutting. Corrugated cardboard has poor flatness and is prone to getting stuck during adsorption printing, causing the cardboard to be scrapped and forced to be shut down for cleaning; In printing, it is easy to produce uneven ink application, inaccurate color matching, and gaps in color overlapping edges; It will cause displacement of the slotting size, and the top and bottom shaking covers of the cardboard box will not fit properly; Die cutting feeding can also cause problems such as jamming and size displacement, which can lead to an increase in secondary waste during the production process.

1. Summary: The main reasons affecting the flatness of cardboard

1. The types and grades of paper inside the noodles are different. There are imported and domestic kraft paper, imitation kraft paper, corrugated paper, tea board paper, high-strength corrugated paper, etc., which are also divided into A, B, C, D, E, and grades. According to the difference in paper materials, the surface paper is generally better than the inner paper.

2. The main technical parameters of the surface paper are different. From the perspective of cardboard box performance requirements or user cost reduction considerations, the requirements for the paper inside the cardboard box are usually:

(1) The quantity of paper inside the surface varies. Some have a larger quantity than the inner paper, while others have a smaller quantity.

(2) The moisture content of the tissue paper varies. Due to differences in environmental humidity, such as the supplier and transportation inventory, some types of paper have a higher moisture content than the inner paper, while others have a lower moisture content.

(3) The quantity and moisture content of the surface paper are different. One is that the quantity of the surface paper is greater than that of the inner paper, and the moisture content is greater than or less than that of the inner paper. The second is that the quantity of the surface paper is smaller than that of the inner paper, and the moisture content is greater than or less than that of the inner paper.

3. The moisture content of the same batch of paper is different. Part of the paper has a higher moisture content than the other part, or the moisture content between the two ends of the tube paper, the outer edge side, and the inner core side is different.

4. Improper selection and adjustment of the heating surface length of the paper preheater, or the heating surface length of the paper preheater cannot be adjusted arbitrarily. The former is affected by improper operation, while the latter is limited by equipment, which affects the preheating and drying effect.

5. The steam spray device cannot be used correctly or there is no spray device on the device, so the paper humidity cannot be added arbitrarily.

6. Insufficient time for paper to dissipate moisture after preheating, high environmental humidity, poor ventilation, and improper production line speed.

7. Improper and uneven gluing of single-sided corrugated machines and gluing machines can lead to uneven shrinkage of cardboard.

8. Insufficient and unstable steam pressure, damage to drain valves and other accessories, or incomplete drainage of accumulated water in pipelines, resulting in the inability of the preheater to operate normally and stably.

2. In the two stages that affect the shrinkage rate of the original paper, the key is to improve the process control

To achieve good flatness of cardboard, the shrinkage rate of each layer of paper must be basically the same, with the most important being the surface paper. The shrinkage rate of the surface paper is smaller than that of the inner paper, and the cardboard shows a positive arch shape, while the opposite shows a negative arch shape; If the shrinkage rate of the paper inside the surface is locally uneven, it will form a positive or negative arch shape. From the analysis of the process of forming cardboard on the production line, controlling the shrinkage rate can be divided into two stages.

(1) The stage of corrugated formation. The various processes from raw paper feeding to secondary gluing are crucial stages for controlling shrinkage rate. According to the actual situation of each layer of paper, steam pressure, ambient temperature and humidity of the tile in the surface, the preheating temperature, the length of the heating surface (wrap angle), the method of ventilation and moisture distribution, steam spray, glue amount, production line speed and other technical parameters should be selected and adjusted respectively, so that each layer of paper can shrink freely through appropriate and effective process control, and the final shrinkage rate is basically the same.

(2) The cardboard forming stage. It refers to the bonding, drying, and ironing from the second coating to the subsequent process. At this point, each layer of paper can no longer shrink freely, and after being glued into cardboard, the shrinkage of each layer of paper is mutually constrained. The bonding point can be said to be the starting point for the cardboard to form an arch. To select and adjust technical parameters such as glue amount, baking temperature, and production line speed, the difference in shrinkage rate should be controlled to the minimum, and the arches produced by hot stamping the cardboard should be smoothed out as much as possible.

3. Improving the flatness of corrugated paper boards requires grasping and solving the main contradiction

Firstly, it is required that the raw paper provided by the supplier has a qualified and stable quantity and moisture content, avoiding rainwater during transportation and loading and unloading, and maintaining a basically constant environmental humidity during storage in the factory.

The second is to use the same type of paper or paper with similar quantity, moisture content, and grade as much as possible for the selection of materials for the surface paper.

The third is to increase the length of the heating surface (wrapping angle) of paper with high moisture content through the preheater, which increases the ventilation and water release time, and slows down the production line speed; The length of the (wrap angle) heating surface of the preheater for the paper with small moisture content is reduced, and natural ventilation and steam spray speed up the production line.

The fourth is to maintain a consistent amount of adhesive on each layer of paper, with a uniform and moderate amount of adhesive applied along the full width of the corrugated direction.

The fifth is to maintain stable air pressure and the normal function of pipeline accessories such as drain valves.

In short, there are many factors that affect the flatness of corrugated paper boards, and the flatness changes due to the variations among various factors. Improvement needs to be tailored to local conditions, targeted, and focus on solving the main contradictions.