External environmental factors affecting pigment paste coloring in paper pulp

The major difference between paper pigment pastes and dyes is that the pigment particles are insoluble in water or solvents and do not bind chemically with the paper fibers as the dyes do. Instead, they must rely on fixing agents to fix the pigments on the paper fibers. The low pigment retention in paper pulp coloring has been a problem that has plagued it in paper applications. We can discuss this issue from the two aspects of the pigment paste itself and the external environment of the pigment paste. This paper explores the factors affecting the pigment particle retention in terms of the external environment used in the pigment paste for papermaking.

Type of paper machine:

The paper machine net department: At present the paper machine net department has the circular net, the long net, the clip net three types, the dehydration way mainly through the vacuum suction, the gravity effect, the mechanical force these forces. Since the net department bears 70-80% of the water removal, the loss of pigment particles basically occurs. It can be said that the paper machine's network part has a crucial influence on the retention of pigment. The rotary screen machine has a small dewatering area and slow dewatering speed. The long dewatering area of ​​the long wire paper machine is dehydrated. The dewatering is decelerated because both sides are dehydrated. (The faster the dewatering is, the less favorable is the retention of pigments. ).

Speed: The speed of the paper machine is fast. On the one hand, the net department must increase the vacuum suction intensity and strengthen the dehydration intensity, which is not conducive to the retention of pigment particles; on the other hand, the speed will increase the velocity and shear force of the slurry, and also Not conducive to the retention of pigment particles.

Paper types:

Quantitative paper: Under the same conditions, the higher the paper's quantification, the thicker the fiber's thickness, the more difficult it is for the pigment to pass through the fiber layer, ie, the more difficult the “filtering” of the pigment, and the higher its retention rate. high.

Pulp types: According to the different types of paper, use different pulp raw materials for papermaking, newsprint paper generally uses deinked waste paper pulp, culture papers, specialty papers are mainly bleached chemical pulps, and waste papers such as cardboards. Mainly, different surface strength and purity of pulp raw materials are different, leading to a large difference in the retention rate of pigments. In general, the order of the retention rate of pigments is: bleached chemical pulp> deinked waste pulp> waste pulp .

Fillers in paper: general titanium dioxide, kaolin, calcium carbonate and other inorganic pigments have a certain negative charge on the surface. They are easy to compete with pigments for fixing agents, resulting in low retention of pigments. Generally, pigments are not greatly reduced. Preserve the pigment by first adding the fixing agent and finally adding the filler.

Wet chemical properties:

Fine fiber: The higher the degree of saponification of the fiber, the higher the content of fine fiber, the better the retention of the pigment. Because the fine fiber has a larger specific surface area, its surface charge is significantly higher than that of the long fiber, and its adsorption ability to chemicals is enhanced.

pH of Pulp: The negative charge of fibers is mainly due to the ionization of carboxyl groups on the surface of the fibers. The pH value increases, the degree of ionization of the carboxyl groups increases, the electronegativity of the fibers increases, and the pH value changes the reactivity and electrical properties of the wet end chemicals. Of course, these will also affect the retention of pigments.

Interfering substances: The so-called "interfering substances" here refer to substances that adversely affect the fixation of pigments. These substances are generally negatively charged, and mainly interfere with or even destroy ion adsorption or hydrogen bonding of pigments and fibers. Commonly used are dry strength agents and fillers. Rosin gum and so on.

Where to add pigments:

Pulp addition: The pigment can be mixed with the fiber better. At this time, the cleanliness of the pulp is high, the influence of the interfered substance is small, and the retention of the pigment is better. The main disadvantage is that the slurry pool is difficult to clean, and the production and replacement of paper are inconvenient. .

Adding online: It is mainly to facilitate the hue and control of hue, and the process must grasp the order and position of pigments, fixing agents, and interfering substances. (actual production will also be combined in two ways)