20 common questions in papermaking(1)

 

1. What is the function of the filler?

Answer: The filler is to make the paper obtain specific properties, such as whiteness, opacity, smoothness, etc. At the same time, the addition of the filler makes the inner space of the paper smaller and thinner, thereby increasing the ink absorption of the paper and making the ink absorption change. uniform. Usually, the water-insoluble or slightly water-soluble minerals added to the slurry are about 10%-25% in the printing paper.

 

2. What are the effects of fillers on the properties of printed paper?

Answer: The printing paper adds fillers to improve the printing suitability of the paper, such as increasing the whiteness, smoothness, opacity and stiffness of the paper. Improves paper’s affinity for ink, softness and stability, thereby contributing to improved print quality.

 

Of course, too high amount of filler added to the paper also brings some adverse effects, mainly manifested in the reduction of paper strength and the reduction of sizing effect, and the phenomenon of powder and lint easily occurs during printing, and the filler particles are transferred to the printing plate and the rubber. There will be smearing and other phenomena on the cloth; due to the friction effect of the filler, the printing plate will also be worn, but filling with precipitated calcium carbonate (PCC) can minimize the wear of the printing plate.

 

3. How do fillers affect the opacity of the paper?

A: Unfilled paper is composed of fibers and air. Air exists in the pores between fibers. Due to the difference in refractive index between fibers and air, when the light beam hits the surface of the paper, part of the light is scattered at the fiber-air interface, giving the paper a certain (lower) opacity. , reflected in the printing, the main performance is that it is easy to print through. After adding a filler with a refractive index greater than cellulose into the paper, the number of light scattering interfaces inside the paper is increased, that is, there are three different types of interfaces between fibers and air, between fillers and fibers, and between fillers and air. , the difference in refractive index between filler and air is larger. The light is thus maximally scattered at the filler-air interface, resulting in increased opacity.

 

4. What is the role of pigments in paper?

Answer: Even the bleached pulp fibers are slightly yellow or gray, which is because the lignin contained in the pulp fibers tends to absorb purple and blue light with a wavelength of 400-500nm, and the more lignin content in the pulp , the darker the color. Therefore, in order to make the paper have a higher whiteness, blue-violet or red-blue dyes are often added to the bleached pulp. The production of colored paper must also be dyed.

 

5. Other chemical additives and their functions in paper accessories?

Answer: In order to meet the needs of some special purposes of paper, various types of non-fibrous additives are often mixed in pulp or paper. According to their use, they can be roughly divided into the following categories:

Wet strength agent. Wet strength agents are additives added to increase the wet strength of paper sheets, such as urea-formaldehyde resins and phenolic resins.

Dry strength agent. Such as cationic starch, polyacrylamide, etc.

Retention aid. Auxiliaries added to reduce the loss of fillers and fine fibers in the papermaking process, such as polyacrylamine, polyethylene oxide and polyethyleneimine, etc.

Defoamer. Used to eliminate foam in the papermaking process. Such as silicone oil, turpentine, tridecanol, tributyl phosphate, amyl alcohol and octanol.

Water repellent. Mainly used in paper with high requirements on water resistance. Such as paraffin, metal soap, glyoxal, melamine formaldehyde resin and dimethylaminoethyl acrylate, etc.


Post time: Jul-19-2022