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Several tricks for producing high quality kraft paper

1. Strictly control the bleaching process to avoid excessive bleaching and reduce strength

The hardness of the slurry directly determines the amount of bleaching liquid. In determining the amount of bleaching liquid, the hardness of each pot will always be different, and the pulp temperature will be different in different seasons, especially in the north, and the temperature difference between winter and summer can reach above 15 °C. Therefore, the bleaching time of each pulp material is also different, up to 0.5 h or more, so the bleaching time must be strictly controlled. Otherwise, due to the extension of the bleaching time, although the whiteness of the pulp can be increased to a certain extent, the paper is reduced. The mechanical strength, and the timing of the yellowing of the paper is increased, and the quality is not stable.

By controlling the bleaching temperature between 30 and 40 ° C, excellent bleaching is achieved and excellent mechanical strength is achieved.

2. Strictly control the cleanliness of the pulp to avoid calcium accumulation in pipelines and equipment

The production requirements for refined kraft paper are sized, and the bleach remaining in the pulp generally does not affect the sizing. However, in the practice of production operations, in order to ensure the whiteness requirements of the semi-bleaching slurry, some factories add a small amount of bleaching liquid to the pulp pool after bleaching to ensure the whiteness of the slurry, perhaps because the bleaching slurry is not completely washed, resulting in drifting. The post-mortem still contains a large amount of calcium base, which is subjected to the sizing station, and the free rosin acid anion causes the accumulation of calcium rosinate, and the sulfate ion in the alum causes CaSO4 accumulation. This kind of deposit combines with rubber and resin and has a certain viscosity. It is very simple to deposit on the transportation pipelines and equipment.

When there are many deposits, it can directly affect the paper making, and together reduce the sizing effect and affect the quality of the paper. This phenomenon becomes very obvious in the high temperature climate in summer, and high-calcium content in some areas will cause similar problems.

The deposits on the pipeline and equipment will be thickened in a concentric manner. When the pipeline or equipment is violently sensation, random drops will occur, which will be broken into 1~2mm after being removed by the sand remover and the rotor screen. Light yellow particles (up to 3mm or more) can enter the headbox through the rotor screen due to their low density. After the particles are connected to the net with the slurry, the paper sheet is crushed by the calender, causing holes of 1 to 2 cm2, causing severe paper disease.

Therefore, in the production, the cleaning degree of the semi-bleaching pulp should be strictly controlled, and the operation of adding the bleaching liquid to the bleaching pulp pool should be completely eliminated to ensure the normal application of the glue and avoid the occurrence of paper diseases such as holes in the paper sheet.

3. Strengthen the purification screening system to remove particulate impurities

Most of the particulate impurities can be removed after passing through the 600 cone desander and the rotor screen. Once a large number of pale yellow particles of calcium precipitate are present, it is clear that the accumulation of the system has reached the limit. This phenomenon will continue for a period of time, ranging from 3 to 5 days, up to more than 1 month, severely affecting normal production.

After presenting the above problems, the first two stages of the 606 tapered slag removal system are activated and can be processed.

4. Correct understanding of the difference between pulp whiteness and paper whiteness, suitable for reducing the whiteness of the slurry

Strictly control the whiteness of refined kraft paper semi-bleaching pulp. On the one hand, it is the requirement of paper color, on the other hand, it is the requirement of paper strength, the whiteness is improved, the mechanical strength of paper forming is reduced, so it should be reasonably controlled in production. The semi-bleaching whiteness is intended to achieve the maximum paper strength when the whiteness reaches the required together.

The same pot slurry, as seen from the whiteness of the paper, the whiteness of the slurry and the whiteness of the paper are not consistent. The whiteness of the pulp is generally 2% to 3% lower than the whiteness of the paper, especially the pressure. The refined kraft paper after the light is more obvious. The reason for this phenomenon is that the surface slip is improved after the paper is passed through the calendering, and the same pulp, because of the rough surface, the reflection can be lower, and the whiteness of the paper formation is higher than the whiteness of the pulp.

The production experience shows that the whiteness of the pulping can be properly lower than the whiteness requirement of the paper by 1%~2%. When the whiteness is guaranteed, the paper breaking length can be increased by 2%~3%. Together, it can also shorten the bleaching time and reduce the production cost.

5. Moderate calendering to improve paper gloss and whiteness

In order to improve the gloss of the paper, the groove is pressed and pressed, and finally can be calendered by a 4~6 roller calender to improve the gloss of the paper, reduce the double-sided difference of the paper, and properly improve the whiteness of the paper together. degree. In the production, it is found that the gloss of the paper processed by calendering is improved, the double-sided difference is reduced, and the whiteness of the paper is increased by 1 to 2 percentage points, and the effect is very obvious. The calender of 6 rolls or more, even with the 8-roll supercalender, is not very effective in improving the glossiness of the sheet, the double-sided difference, and the whiteness of the paper.

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