At present, the main types of dyes used in the paper dyeing Market are liquid dyes, which are generally used in box board and kraft linerboard dyeing, as well as bright colors which are used in color paper, with small single consumption and high price. Most color papers are usually made of powdery dyes, and its most advantage is low cost. The following is an analysis of the dyeing characteristics of powdery dyes for paper making:

 

1、 Pigment

 

Pigment is not soluble in water, in fact, it is a kind of colored filler, which 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 pigments are: strong light resistance, acid and alkali resistance, chlorine resistance, which varies according to the variety. Its dyeing performance is generally inferior to that of 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

 

2、 Dye

 

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

 

1. Basic dye

 

Alkaline dyes are the most commonly used dyes in the production of common color paper, such as rose essence, alkaline orange block, alkaline light yellow o, etc. Features: easy to make fiber color, bright color, single light, 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 is not well colored.

 

2. Acid dye

 

It has no affinity with the fiber and needs the aid of sizing agent aluminum sulfate to stay on the fiber, so it is usually used on sizing paper. The coloring rate and brightness of acid dyes are lower than those of basic dyes, but they have better light and heat resistance. When pH value is 4.5-4.7, the color is the best. The paper without sizing can't use acid dyes generally, and the dyeing of mixed pulp usually uses acid dyes, because the color will not produce spots even. The common products are red 3R, red GR, golden g, etc.

 

3. Direct dye

 

Direct dyes have strong affinity with fibers and can be dyed directly. Direct dyes are especially suitable for non sizing paper, with a wide range of pH values, ranging from 4.5-8 and the best dyeing effect at 50 ℃. If it is used for sizing paper dyeing, it will agglomerate under the influence of aluminum ion and sulfate ion and reduce the dyeing strength, so it is generally added with the dye for a period of time before adding aluminum sulfate for dyeing. The dyeing ability and brightness of direct dyes are far less than that of basic dyes, but the heat and light resistance of direct dyes are far better than that of basic and acid dyes, which are the most widely used dyeing dyes in the paper market. The most widely used dyes are 4BS red, yellow R, orange s, red brown RN, copper blue 2R, lake blue 5b, black G, etc.

 

 

 

Wang Liping, application department