The first lesson in the paper industry

2022-08-07
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During the first lesson in the paper industry, the professional teacher said that the paper chemicals were similar to the monosodium glutamate added in cooking. To be honest, it sounded like a breeze at that time and didn't take it to heart at all. It's a coincidence that the factory organized training soon after joining the company. The first one was about papermaking chemicals. After that study and the various problems encountered in the workshop, I gradually got a new understanding of chemicals. The following is a summary of the study at that time. Although the content is shallow, it is still very helpful for newcomers in the workplace. It can help you systematically sort out the relevant knowledge of papermaking chemicals. Come and have a look

classification of chemical additives:

(1) process additives: used to improve the production efficiency of the paper machine and improve economic benefits, such as retention aids, filter aids, resin barrier control agents, defoaming agents, etc

(2) functional additives: meet the special needs of users. For example: sizing agent, dry strength agent, wet strength agent, softener, brightener, dye, etc

papermaking ingredients generally include pulp, fillers, sizing materials, dyes and various wet end additives

sources and types of interfering substances

① from pulp

lignin derivatives, hemicellulose, fatty acids, adhesives, latex, starch, etc

② from anionic additives

starch, CMC, organic acids, dyes, etc

③ from filler dispersant

polyphosphate, polyacrylate, bactericide, etc

④ from clean water

humic acid, surfactant, etc

impact of interfering substances on paper making:

① impact on paper machine operation

② impact on auxiliary efficiency

③ impact on paper quality

bridging flocculation is a kind of flocculation, which is a very effective and important aggregation mode among papermaking components. The molecular weight of the polymer should not be too high or too low

the paper flocs formed by bridging flocs are large and loose, which have a certain anti shear effect, so they are called hard flocs

once the bridged floc polymer is destroyed by shearing, the polymer will be adsorbed on the surface of the paper with a flat conformation, and then the floc polymerization of the paper will be triggered by the charge patch mechanism. The paper cannot be 2. Cut three joints from each batch of finished products for tensile test and regroup to the original level. The bridged floc polymerization is actually irreversible

zeta potential actually reflects the surface charge of particles

filler characteristics papermaking filler is a kind of white pigment with very small particles, and it is the component with the largest proportion of paper material except fiber. The addition amount can account for 20%-40% of the composition of the paper

The purpose of

filling is to reduce the production cost of paper, and many properties of paper can only be achieved by filling. Filling has become an indispensable process in the paper production process

the pulp can be white, yellowish and yellowish brown due to different degrees of delignification. When producing colored paper, it is necessary to dye the pulp with pigment; When producing ordinary paper, we should also adjust the color tone of the paper according to the requirements of users. Sometimes, we can use color to achieve the effect of optical whitening

beneficial effect of filling on paper properties:

(1) the particle size of the filler is much smaller than that of the fiber. After the filler is added to the paper, the evenness and surface smoothness of the paper can be improved by filling the gap between the fibers in the paper

(2) the main means to control the optical properties of paper. The whiteness and refractive index of the filler are generally higher than those of the fiber, and the particle size of the filler is small. The controller crashes, the sampling of the controller has problems, and the poor contact of the sensing line has a large specific surface area. Filling can improve the opacity and whiteness of the paper

(3) the fiber is easy to absorb water and swell. After filling, it can improve the dimensional stability of non-toxic or low toxic raw materials with good compatibility between paper and resin, and reduce the water absorption deformation of paper

(4) it can adjust the paper's absorption of ink and increase the paper's printability

adverse effect of filling on paper properties:

(1) reduce the bonding between fibers and reduce the strength of paper

(2) it is easy to lose wool and powder during printing, which will increase the abrasion of the paper machine

type of filler:

classification of filler (according to the source and purpose of filler)

mineral filler, special filler, auxiliary filler

1 mineral filler: unmodified kaolin, talc powder and calcium carbonate belong to this category

(1) white clay (kaolin) hexagonal glossiness

(2) talc powder is soft, hydrophobic, lipophilic, flat and smooth, opacity, printability

(3) calcium carbonate: it can improve the opacity of the paper, increase the ink absorption of the paper, make the paper soft, glossy and high whiteness. It is used for printing paper and dictionary paper

2. Special filler

structural kaolin, synthetic silicate, titanium dioxide, aluminum hydroxide and some organic pigments

(1) structural kaolin: improve the gloss, smoothness, fiber coverage and whiteness of the paper

(2) synthetic silicate: high light scattering ability and high absorption, improving the printability of paper

(3) aluminum hydroxide: it can be used as filler to improve the whiteness, gloss, smoothness and printability of high-grade paper. It also has a good flame retardant effect

(4) titanium dioxide: it is a kind of pigment with high filling efficiency. It has very high refractive index and hiding power for classified treatment of garbage

3. Auxiliary filler

gypsum, satin white, barium sulfate and zinc sulfate

gypsum is sometimes used for filling high-grade paper together with calcium carbonate and aged soil. It can also be used with kaolin for coating raw materials

factors affecting dyeing

1, pulp seed

2, beating degree

3, filler

4, pH value

5, water hardness

6, additives

7, fungicides and defoamers

8, contact time

9, adding place and sequence

10, dehydration and retention

11, drying temperature

12, calendering

13, paper damage

14, paper moisture

15 Mechanism of paper aggregation caused by residual chlorine

colloid aggregation:

(1) at the earliest time, aluminum sulfate caused the coagulation of paper components by electric neutralization

(2) the single cationic polymer (polyethyleneimine) causes the coagulation of paper components through the charge patch mechanism

(3) in the single polymer and double polymer retention systems, the high polymer causes the flocculent polymerization of paper through the bridging mechanism

bridging mechanism is the main mechanism of paper retention

paper material retention rate

definition: the percentage of the amount of materials left in the paper web and the materials added in the production

total material retention: the ratio of the amount of material contained in the paper sheet entering the winder to the amount of material sent to the wet end of the paper machine. (for the paper machine with white water circulation and paper damage fully utilized, it is generally more than 95%, and the general paper machine should be 90%-95%)

single pass retention rate of paper material (first pass retention rate):

the ratio of the amount of material contained in the wet paper leaving the couch to the amount of material leaving the headbox. (generally 20%-90%)

bridging mechanism: the retention aid (cationic polyacrylamide) with high molecular weight and low charge density is adsorbed on the surface of paper particles in the form of chain tail, which can stretch out of the particle double electric layer and adsorb to the surface of another particle, bridging between particles to form large flocs

factors affecting the flocculation of paper

(1) electrolyte concentration

(2) anionic interferents

(3) sub groups

(4) shear effect

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