Jinling Paper Machinery-Paper dyeing, do you think it is simple?

　　Application of dyes and influencing factors

　　1) Dyeing method

　　There are four main dyeing methods for paper, namely in-pulp dyeing, sizing press dyeing, calender dyeing and coating coloring. In-pulp dyeing and sizing press dyeing are more commonly used.

　　Intraplasmic dyeing

　　The dyeing of paper is mostly in-pulp dyeing, that is, the dissolved or diluted dye is added to the headbox, pulping tank or other appropriate positions.

　　For solid dyes, the dissolution and dilution of the dye is very important. Generally, the dye is first adjusted into a paste with a small amount of water, diluted with hot water under sufficient stirring or indirect heating is used to accelerate the dissolution of the dye, and used after filtration. Do not heat the dye directly with steam, which will cause local high temperature, cause the dye to decompose, generate insoluble lakes, and produce stains on the paper.

　　Generally speaking, similar dyes can be mixed and used. Acid dyes and direct dyes have similar chemical structures, so they can be mixed.

　　In actual production, when acid dyes or direct dyes are used, a small amount of basic dyes are often added to enhance the hue. The method of dyeing in the pulp is simple, easy to operate, and even dyeing, but the disadvantage is that some of the dye is lost with the white water in the mesh, resulting in unstable chroma and poor dyeing on both sides.

　　Sizing press dyeing

　　This method is to dye one or both sides of the paper at the sizing press of the paper machine. The dyeing solution can be mixed with the surface sizing agent. The advantage is that the loss of dyeing agent is less, and it can be very easy to change the type of dyeing agent. Easily change the color of the paper. But the uniformity of dyeing is poor.

　　2) Factors affecting dyeing

　　There are many factors that affect dyeing. Different dyes have different properties and methods of use. Each component in the dye affects the color tone, and the fiber properties of the slurry, fillers and sizing materials have an impact on the dyeing effect, so attention should be paid to selecting the appropriate conditions during dyeing.

　　Pulp properties:

　　Different pulps have different affinities for dyes, which are related to fiber properties and lignin content. Basic dyes have a great affinity for lignin, so they are suitable for dyeing pulp with high lignin content; while direct dyes have a great affinity for cellulose, so they are mainly suitable for pulp with low lignin content; straw pulp is generally better than Wood pulp is easy to stain. Therefore, it is easy to produce stains or streaks when dyeing mixed slurry or mixing raw slurry with uneven cooking. Different dyeing conditions should be adopted according to different slurry composition;

　　Beating degree:

　　Fine fibers have more adsorption of dyes than long fibers, so the high-beating pulp is beneficial to dyeing, which is related to the larger surface area of ??fine fibers;

　　Rubber and bauxite:

　　Rosin gum has an obstructive effect on the dyeing of sizing materials, while alumina has a mordant effect on dyes, but it has different effects on different dyes. Because of its lack of affinity for cellulose fibers, acid dyes need to be added with alumina to promote the dyeing of pulp, and because acid dyes are negatively charged, they can only be adsorbed on negatively charged fibers by changing their charge with alumina. For direct dyes and basic dyes, a small amount of alumina can also promote the coloring, and too much use will darken the hue and weaken the ability to resist sunlight;

　　filler:

　　Many fillers have affinity for dyes and so on. When dyeing pulp containing fillers, because part of the dye can be absorbed by the fillers, the paper will have a lighter color and uneven color;

　　temperature:

　　Temperature has a great influence on the dyeing effect. Generally, increasing the temperature can improve the dyeing effect, especially for direct dyes. However, the heating of the dryer part of the paper machine often causes discoloration. For example, after some acid dyes are heated, they tend to produce lumpy stains on the paper surface, and some direct dyes tend to fade at high temperatures. For this reason, when producing colored paper, pay attention to controlling the temperature of the dryer;

　　pH value:

　　Various dyes have their most suitable pH range, therefore, the pH value should be strictly controlled during dyeing, which is an important factor for obtaining the best dyeing effect;

　　Other chemicals:

　　If oxidizing or reducing compounds remain in the pulp, it is not conducive to the dyeing of the paper. Therefore, there should be no residual chlorine in the bleached pulp. Calcium salt has an adverse effect on most dyes. Dyes are generally charged. The charge interaction between dyes and other chemicals will affect the retention and dyeing effect of dyes on fibers. Therefore, when dyeing pulp, attention should be paid to the effect of the charge of the dye and other drugs and the order of addition.

　　3) The duality of dyeing