In the dyeing process of papermaking, the object of dye action is paper fiber. Dye and different slurry have different action mechanism. For example, basic dye has strong affinity for slurry containing more lignin, suitable for dyeing pulp with high lignin content, and acid dye with less affinity for fiber. , the deposition effect produced by the fixing agent or the fixing agent needs to be fixed on the fiber.
The requirements of the paper industry for dyes, in addition to the chemical structure of the paper dye, depend on the final use of the paper. Paper or paperboard used for packaging, its light resistance performance is not high or not required, so you can use basic dyes for dyeing, while high-grade writing paper or sanitary paper needs dyes with good light resistance, paper for special occasions, such as Decorative paper base paper can be dyed with pigment.
In the wet end of the paper, there are many factors that influence the dyeing process or the application of the dye. The following are some common influencing factors:
(1) slurry
In the paper industry, the pulp used in different paper grades is different, so the choice and application of dyes have different degrees of influence. For pulps with higher lignin content of chemical pulp and unbleached pulp, basic dyes are usually used, and direct dyes are suitable for most pulps.
Usually the same amount of dyeing, bleaching sulfite needle pulp is darker than bleached sulfite broadleaf pulp; the color paste is yellower than the bleached pulp; the dyed pulp or secondary pulp is dyed more than the bleached pulp. The dyeing effect is yellow; due to the increase of fine fiber content, the dyeing of the sulfite broadleaf pulp and the secondary pulp is more likely to remain on the carpet surface.
(2) Degree of beating
Reflecting the degree of beating is an indicator of the ease of dewatering of the slurry. It can comprehensively reflect the extent to which the fibers are cut, swelled, separated, and fibrillated.
Generally, increasing the degree of beating of the slurry can increase the dyeing yield of the dye; the sticky beating is darker than the pulp dyed by the free pulping. The reason is that the higher the degree of beating, the higher the degree of fibrillation of the fiber, the larger the specific surface area, and the better the dyeing retention rate; the density of the pulp increases, the voids between the fibers decrease, and the paper becomes The paper sheet is tight, so the exchange surface between the fiber and the air is reduced, thereby reducing the amount of reflected light, so that the amount of light transmitted is increased, which is beneficial to the dye absorbing the amount of light of a certain wavelength. Therefore, the higher the degree of beating, the dyeing of the pulp. The darker the paper color. On the contrary, the unstained slurry has poor dye-absorbing ability and large dye loss, and the paper color is light under the same amount of dye.
(3) Water hardness
The hardness of water is very different for different kinds of dyes, and has little effect on cationic direct dyes and basic dyes, but has a greater influence on anionic dyes and brighteners. For example, the electrostatic repulsion between the anionic direct dye and the cellulose fibers prevents the dye from being adsorbed on the cellulose fibers, but in addition to increasing the binding between them by adding a cationic fixing agent, it is also possible to increase the water. The hardness is used to eliminate this electrostatic repulsion and improve the bonding between them.
It is worth noting that paper mills are distributed in various regions of the world, and the water quality in each region is also very different. Generally, the water hardness in the north is relatively high, while the water hardness in the south is relatively low. The hardness of the water can be increased by adding magnesium sulfate or sodium chloride (calcium chloride, which can also be adjusted in a non-size system).
(4) Reaction time and pH
Generally, the longer the reflection time, the better the dyeing effect of the dye on the fiber. pH has varying degrees of effect on different dyes. It will cause some change in the hue of the dye.
(5) Papermaking filler
In the paper industry, the use of fillers increases the opacity and whiteness of the paper, improving printability and other paper properties. Whether it is kaolin, calcium carbonate, titanium dioxide or talc, they have an effect on the tonal depth of the paper. For a certain quality of paper, the proportion of filler remaining inside the paper should be kept at a specific level. If it needs to be changed for some reason, it will have a corresponding influence and change on the hue of the paper.
Since the mesh surface of the wet paper sheet is subjected to the suction force of the dewatering equipment of the net portion, the filler in the paper surface is easily taken away by the white water, and the specific surface area of the filler is larger than the specific surface area of the fiber, and the dye is more easily adsorbed on the filler, which easily causes paper. The two-sided problem of color. Usually reduce the two-sided difference by selecting the type of dye, or by strengthening the retention and drainage system or the adjustment of the process, such as changing the addition point.
(6) Add points and add order
1 Add point
The paper grades and conditions produced by each paper mill are different, so the dyeing methods used are different, and the dye addition points are not used. In batch dyeing, the dye is usually added to a portion of the slurry; in continuous dyeing, the dye is usually added near the headbox; in segmented dyeing, the dye can be added in two segments, usually 70% to 80%. The % dye is added to the pulping tank and the remaining dye is usually added to the suction zone of the slurry tank or to the slurry line behind the headbox.
Typically, the anionic direct dye addition point is higher, and the cationic direct dye can be added near the headbox.
2 Add order
The following rules are generally followed: Keep the anionic direct dye away from the cationic direct dye and the base dye. Keep dyes and brighteners away from other cationic additives. Try to separate the dye from the fixing agent. The requirements of the production conditions are different. The fixing agent can be added in two ways: one is added to the front of the dye to fully react with the fiber; the other is added to the dye before the other part is added to the dye. To reduce the color of the return water.
(7) Other wet papermaking aids
Conventionally, since both the whitening agent and the dye are anionic substances, they easily react with the cationic substance, causing a problem of color spots. Therefore, the two substances should be added before all chemicals are added, such as a mixed pulp tank or a paper machine pulp tank, so that they have enough time to react with the fibers to avoid interference from other cationic substances. On the other hand, certain low molecular weight, high charge cationic polymers, wet rosin and cationic starch can adsorb anionic dyes and increase dye retention.
Retention aids are the most important component of papermaking and are generally divided into two categories: low charge density, high molecular weight, and high charge density and low molecular weight. The former has a relatively small effect on the dye, and the possible negative effect is that it increases the retention of the filler and the fine fibers, resulting in a two-sided difference in paper color. The latter has a relatively large influence on the dye, which may darken the color of the paper, reduce the light fastness, and cause the dye to flocculate and other negative effects.
Therefore, in the dyeing work, the types of wet-end additives of each paper mill and their addition points should be known to avoid their negative effects on the application of dyes, so that the dyes can exert the maximum effect in papermaking.
EMPEROR company recommed paper dye as below:
Basic violet 10, Basic yellow 2, Basic red 46, Basic green 4, Basic Blue 9
Direct red 23, Direct red 31, Direct Blue 86, Direct yellow 11, Direct yellow 12, Direct Black 19
Acid yellow 36, Acid orange 7
any more information if you need, pls call 0086-15958136613 Ms Gloria Xu directly
