Pulp and papermaking process in the production of paper and board (3)

〖1. Papermaking process〗

1, the preparation of paper

After the screening and purification of the pulp, it is not suitable for direct use in papermaking, and it must be prepared in stages such as beating and seasoning.

(1) Beating. The use of physical methods to treat fibers suspended in water has the property of adapting to the production requirements of a paper machine and enables the produced paper to achieve the desired quality. This operation is called beating. Beating This process is a key step in papermaking and it determines the final nature of the paper. Although paper can be made without this step, because the pulp still contains a large amount of undissociated fiber bundles, there is only a small binding force between the fibers. The copied paper is not only low in strength but also appears porous and has a rough surface and cannot be satisfied. Claim. Beating is the process of defiberizing the fiber bundles into individual fibers, cutting the fibers into appropriate lengths, frictionally splitting them in the direction of the fibers, and twisting the hairs at both ends, thereby increasing the contact surface area of ​​the fibers and increasing the interweaving ability of the fibers. After pulping and squeezing, the inside of the fiber is infiltrated with water and swelled and hydrated to become soft and plastic. Such a pulp can be used for papermaking.

(2) Seasoning. The term “seasoning” is a general term for several processes such as sizing, filling, dyeing, and adding other auxiliaries, but this does not mean that all paper must go through all these processes. The purpose of the seasoning is mainly to improve certain properties of the paper from different angles and degrees, or to increase the utilization efficiency of various additives. The main functions of filling are strengthening, filtering aid, retention and defoaming, etc. The reinforcing agents are various types of starch, polyacrylamide and the like. Filling can also increase the paper's opacity and brightness, improve paper smoothness and uniformity, and improve the paper's adaptability.

2. Papermaking

After selecting and seasoning the pulp, it is necessary to prepare a paper stock solution with a concentration between 0.5% and 1%; to ensure that the fiber is suspended in water and then sent to the paper making machine to make it in the papermaking net (copper mesh or The plastic net) is interlaced with each other by dehydration, and then pressed, dried and finished to form a certain size of paper sheet.

Papermaking machines are key equipment in papermaking. The formation of paper sheets is closely related to their quality. Papermaking machines can be divided into three types according to the different shapers: long wire paper machine, rotary screen paper machine and folder paper machine. Regardless of the type of papermaking machine, they are composed of a wire section, a press section, a drying section, and a calendering section.

(1) Paper Making Machine

(2) Press section.

Although the wet paper sheet has a certain amount of strength in the net part although it has already taken off a large amount of water, the paper drawn from the vacuum roll still generally contains about 80% of water. If such a wet paper sheet is directly sent to the dryer section for drying, on the one hand, the strength of the wet paper sheet is low, and it is easy to break the head. On the other hand, such a large amount of moisture in the wet paper sheet is completely evaporated by the drying cylinder. Not only does it consume a large amount of heat energy, but the paper thus dried has a loose structure, a rough surface, and low strength. Therefore, the wet paper sheet coming out of the wire part needs to be dewatered in the press section by a mechanical pressing action to increase the degree of dehydration. At the same time, increase the tightness of the paper, increase the strength of the paper, improve the surface properties of the paper (such as smoothness), and then send it to the dryer section for drying (except for the production of napkins and the like with the exception of crepe paper). The press section of the ordinary fourdrinier paper machine is composed of more than one set of press rolls, usually two to four sets, and the last set is mostly a glossy press on ordinary fourdrinier paper machines.

(3) Drying section.

When the wet paper sheet passes through the last press of the press section, the normal dryness is only 30% to 40%. Even in a paper machine with advanced composite press rolls, the dryness can only reach 40% to 50%. Therefore, it must be With the aid of water evaporation from the dryer, the dryness of the paper is increased to 92% to 95%. The drying section not only removes the moisture in the wet paper sheet, but also has the following three functions: increasing the paper strength, increasing the paper smoothness, and completing the paper sizing.

(4) Calendering section.

A typical Fourdrinier paper machine is equipped with a calender behind the dryer section to increase the smoothness, gloss, and thickness uniformity of the paper. However, the production of thin paper (such as capacitor paper, cigarette paper, etc.), absorbent paper (such as filter paper, blotting paper, etc.) and single-sided glossy paper, do not use more calender.

(Author/Wei Fengjun Institute of Packaging Engineering, Henan University of Science and Technology)

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