Formation and treatment of color spots on the hott

2022-09-22
  • Detail

Formation and treatment of color spots on box board paper

in recent years, the newly designed paper machine adopts K-type vacuum pressing, which has many advantages, which can greatly improve the dryness of wet paper sheets, reduce the possibility of wet paper sheets being crushed, allow wet paper sheets to have higher moisture before pressing, and adopt higher line pressing, prolong the service life of blankets, reduce wet paper sheet breakage, etc

in Guangdong, many manufacturers use waste pulp as raw material to produce carton board. After K-type vacuum pressing and dehydration, regular hole color spots sometimes appear on the paper surface, which affects the appearance of the paper. K-type press is generally composed of three press rollers (as shown in Figure 1), in which the vacuum press roller and blind hole roller form a press zone, and the vacuum press roller and stone roller form a two press zone, which is generally called three roll two press zone. In the process of use, the vacuum press roller is covered with an upper blanket, and the blind hole roller is covered with a lower blanket. The paper with high moisture content first enters the first pressing area of the double blanket. In the first pressing area, the pressure of the part corresponding to the paper sheet and the blind hole pressing hole is low, while the pressure of the part corresponding to the hole is high. Driven by this pressure gradient, the paper sheet deforms from the periphery of the hole to the hole. In addition, the water flow carries micro components to the hole, and these micro components accumulate on the paper sheet corresponding to the hole, so that the density here is high and the water content is large, forming a "shadow mark" corresponding to the pressed hole, which is called box board paper stain

Figure 1 K-type press layout is not intended

because there is a distance from the first press zone to the second press zone, generally, the upper blanket is thinner than the lower blanket, and the paper sheet is transferred from the lower blanket in the first press zone to the upper blanket. The paper leaves a pressing area and changes from two blankets to one blanket. Under the suction action of the second vacuum chamber of the vacuum roller pin disc collet (10) and the pin disc friction pair (11), (12), due to the effect of air flow, it absorbs water on the paper sheet corresponding to the eyelet, and the water flow carries micro components (including dyes) through the paper sheet and the upper blanket and is sucked away, while the corresponding parts between the holes remain unchanged. According to the above analysis, after the paper is pressed and pumped in the first press zone, it passes through the strong suction from the first press zone to the second press zone, and the air flow is sucked away with water and fine components. Therefore, at this stage, the following three situations may occur on the paper: 1. The dark spots forming holes in a pressing area are significantly reduced; 2. The color spots formed in the first pressure zone remain unchanged; 3. The color spots with light hole color and dark hole color are re formed

the following factors have a certain impact on the color spots of box board paper

various systems and working principles of digital universal material testing machine: 1. Dye

due to the use of dyes, the micro components in the paper are increased, and the dyes are colored. If the dyes deposit in a part of the paper, the density here will increase and obvious color spots will be formed. Therefore, in general, it is best not to use dyes in papermaking. If dyes must be used, it is best to choose dyes with good affinity for papermaking fibers, or change the dyeing in pulp to surface sizing dyeing, or choose other dyeing methods

2. the beating degree of the paper is high, and it is difficult to filter water, so that the paper before being pressed has high moisture content, which is easy to cause color spots

3. at this time, the machine automatically prints out the sample number and the value of f1p1 and f2p2, and the -flill of the experimental stiffness p12 value is large, which is conducive to dehydration, but should not be too large. The larger the aperture is, the larger the stain is, the more obvious it is

4. The thickness of the upper blanket should be moderate. Too thin will aggravate the stain, and too thick and poor air permeability will hinder dehydration

5. Dirty blankets and poor water filtration will aggravate stains

6。 The water content of the paper at the inlet of the press is high, and the paper is easy to deform under pressure. At the same time, the water flow concentrates a large number of micro components (including dyes) to the hole. After passing through a pressing area, the water fork carries the micro components with low affinity for fiber and is pumped away, which may form obvious color spots

7。 If the vehicle speed is too slow, the color spots may increase. Because the color spots are mainly caused by pressing and vacuum suction, the speed is slow and the suction time is long, so the micro components have more opportunities to be sucked away, and the formation of color spots is significant

8。 Line pressure and vacuum degree of the first pressure zone: the line pressure of the first pressure zone should not be too high, which is easy to produce a lot of water pressure. The vacuum effect of vacuum pressing is only to extract the air in the eyelet in the first pressure zone to facilitate the drainage of the pressure zone, while between the first pressure zone and the second pressure zone, a large amount of air is discharged with water and fine components under the suction of the second vacuum chamber. Therefore, the vacuum degree should not be too large, and the relationship between vacuum degree and pressure should be reasonably adjusted during operation

9. the quantity of paper is low, and the finished paper is easy to form color spots. Therefore, the pressure and vacuum of thick paper and thin paper are different. In general, the vacuum of tissue paper should not be too high

1O。 The thicker the face paper is, the more serious the stain is. Proper use of the k-press two press zone, one positive press and two positive press, is conducive to reducing the color spots (shadow marks) formed on the paper before the k-press two press zone to the minimum. Before the paper enters the k-press zone, due to the deformation of the paper and the obvious difference in water content between the holes, if it is not treated, the color spots will be quite obvious. However, the moisture content of the paper is generally about 70% - 75% before it enters the second pressure zone of K pressure. If you want to reduce the moisture content of the paper to about 50% ~ 55%, there is still a large amount of moisture. Yu Wei, deputy director of the raw materials department of the Ministry of industry and information technology, needs to take off in the k-pressure second pressure zone, the first positive pressure and the second positive pressure. Therefore, make reasonable use of the k-press two press zone, the first positive press and the second positive press, so that the paper can be leveled and the water content of the whole paper can be even while a large amount of paper moisture is removed under the promotion of the press pressure gradient. The effect on reducing color spots (shadow marks) is quite significant

in the k-press-2 press zone, because the pressure of the press line is greater than that of the k-press-1 press zone, and the paper sheet has only a thin upper blanket cushion, and the vacuum chambers of the two press zones are connected, and the vacuum suction force is the same, which is the same as that of the k-press-1 press zone. Driven by this pressure gradient, the paper sheet deforms more from the periphery of the hole to the hole, and the water flow again carries fine components (including dyes) to the hole

come out of the k-press two press area, and the paper enters the first positive press and the second positive press. Due to the large line pressure of the first and second positive pressures, the deformation of the paper can be basically eliminated while removing a large amount of moisture, and the moisture of the whole paper (mainly the uneven moisture between the holes formed by K pressure) will also be evenly distributed

in this way, after the dehydration and finishing of the press, the color spots on the paper will be reduced to the lightest degree

the effective methods to solve the stain of box board paper are as follows:

① change the dyeing method of the pulp or choose a dye with good affinity for fiber

② use thick upper blankets to strengthen the cleaning of each blanket and improve the dryness before k-pressing

③ try to increase the press line pressure of the first positive pressure and the second positive pressure, reduce the water content of the paper entering the drying part, and make the water content of the whole paper uniform

④ if the color of the hole is light and the color of the hole is dark, increase the pressure of the K press line and reduce the vacuum degree of the second vacuum chamber of the vacuum roller

⑤ if the color of the hole is darker and the color of the hole is lighter, reduce the pressure of the K press line and improve the vacuum degree of the second vacuum chamber of the vacuum roller

source: Panyu Tanzhou Huayue resin factory

Copyright © 2011 JIN SHI