Paper Dyeing

At present, the main dyestuffs used in the paper dyeing Market are liquid dyestuffs, which are generally used in the dyeing of cardboard and kraft linerboard, and some with bright colors are used in colored paper, with small single amount and high price. Most color paper generally use powder dyes, low cost is its biggest advantage. The following is an analysis of the dyeing characteristics of powdery dyes for papermaking

I.Pigments
Pigment is insoluble in water. It is actually a kind of colored filler and has no affinity with fiber. The quality of dyeing mainly depends on the strength of pigment and its dispersion on paper. The main advantages of pigment are: strong light resistance, acid and alkali resistance, chlorine resistance, among which the chlorine resistance depends on the variety. Its dyeing performance is generally not as good as dyes, and it is easy to produce two sides of dyeing. Carbon black, iron oxide red and iron oxide yellow are widely used in the market

II.Dyes
Dyestuffs are generally soluble in water, with strong coloring power and simple dyeing operation. Basic dyes, acid dyes and direct dyes are widely used.

• Basic Dyes
Basic dyes are the most commonly used dyes in the production of common color paper, such as basic rhodamine B, basic chrysoidine, basic auramine O, etc. Features: easy to color fiber, bright color, light resistance, heat resistance is not strong, easy to fade. It is not suitable to use hard water and alkaline water to dissolve, otherwise it is easy to produce color spots. Bleached pulp does not color well.

• Acid Dyes
t has no affinity with fiber and needs sizing agent aluminum sulfate to remain on fiber, so it is usually used on sizing paper. The coloring rate and brightness of acid dyes are not as good as those of basic dyes, but they have better light resistance and heat resistance. When the pH value is 4.5-4.7, the coloring is the best. Non sizing paper generally can not use acid dyes, mixed pulp dyeing generally use acid dyes, because uniform coloring will not produce color spots. Common products are acid red 3R, acid red GR,acid golden yellow G, etc.

• Direct Dyes
Direct dyes have strong affinity with the fibers and can be dyed directly. Direct dyes are especially suitable for non sizing paper, with a wide range of pH values between 4.5-8 and the best dyeing effect at 50 ℃. If it is used for sizing paper seed dyeing, it will agglomerate under the influence of aluminum ion and sulfate ion and reduce the dyeing strength. Therefore, it is generally necessary to add dyes first, and then add aluminum sulfate for dyeing after a period of time. The dyeing ability and brightness of direct dyes are far less than that of basic dyes, but the heat resistance and light resistance of direct dyes are far better than that of basic and acid dyes. The most widely used dyes are direct scarlet 4BS, yellow R, orange S, red brown RN, copper blue 2R, lake blue 5B, fast black G, etc.