1. What are the raw materials of modern papermaking?
A: the raw materials of modern papermaking include plant fibers (wood, bamboo, grass, etc.), mineral fibers (asbestos, glass fiber, etc.), other fibers (nylon, metal wire, etc.), and polymer materials obtained by pyrolysis of petroleum. At present, the paper used for writing, printing, and packaging is mainly made of plant fiber.
2. What are the types of plant fiber raw materials for papermaking?
A: at present, plant fiber raw materials used in the paper industry can be divided into two categories
Wood fiber material: plant fiber obtained directly from trees.
Fiber materials are divided into wood fiber materials and nonbast fiber materials.
3. What is the composition and function of the common auxiliary materials of paper?
A: Accessories refer to various additives added to the paper to meet the different performance of the paper. The auxiliary material is composed of filler, rubber, pigment, and other chemical additives.
Fillers can improve the smoothness and opacity of the paper; binders can make the paper have water resistance; pigments can increase the whiteness of the paper; dyes can color the paper; other chemical additives can change the properties of the paper to provide some special uses of the paper.
4. What is the function of rubber?
A: the paper produced with plant fiber can absorb water or other liquids because there are a lot of pores between the fiber itself and the fiber, and the cellulose and hemicellulose that constitute the fiber contain a lot of hydrophilic hydroxyl groups. In order to prevent the paper from being infiltrated by water or other liquids, it is necessary to add anti-liquid colloidal substances or film-forming substances into the paper to give the paper anti-liquid permeability and diffusion performance. In the paper industry, the process of sizing is called sizing.
5. What are the sizing methods?
Answer: according to the different sizing effects, the sizing method is divided into internal sizing and surface sizing. Internal sizing is to add the size to the pulp, and then make paper and paperboard with hydrophobicity. Commonly used compounds are rosin compound and synthetic compound. Surface sizing is to apply a thin layer of sizing material on the surface of the paper so that the paper has hydrophobic properties. Commonly used rubber materials are starch, animal glue, and synthetic rubber. Surface sizing is mainly used for offset paper, writing paper and packaging paper, and paperboard with hydrophobicity requirements.
6. What are the effects of surface sizing on the properties of printing paper?
A: ① increase the water resistance and surface strength of the paper, can reduce the phenomenon of paper in offset printing; ② improve the printability, if the surface glue is too little, the paper will absorb too much binder in the printing ink, resulting in matte imprinting. On the contrary, if there are too many surface sizing materials, it will slow down the drying rate of the ink, resulting in rubbing and bright stains; ③ increase the paper's abradability, surface sizing can reduce the penetration of the ink, so it is easy to wipe off the ink, increasing the anti-wear ability of the paper surface; ④ increase the paper's strength, such as bursting strength, folding strength and tensile strength; ⑤ reduce the two side difference and deformation of the paper.
7. What is the function of filler?
A: filler is to make the paper obtain specific properties, such as whiteness, opacity, smoothness, etc. at the same time, the addition of filler makes the gap inside the paper smaller and thinner, so as to increase the ink absorption of the paper and make the ink absorption more uniform. The content of insoluble or slightly soluble minerals in the pulp is about 10% - 25% in the printing paper. The amount of minerals added to different papers is different and may vary greatly
8. What are the characteristics of printing paper filler?
A: the filler of printing paper should have high whiteness, high refractive index, fine particles, low water solubility, low density, and good chemical stability. In addition, it is better to have rich resources and low prices.
9. What are the common fillers for printing paper?
A: the most commonly used inorganic fillers are talc, clay, titanium dioxide, and calcium carbonate. Among them, titanium dioxide is an expensive and high-quality filler, and organic synthetic filler is some high molecular material.
10. What are the effects of fillers on paper properties?
A: adding fillers to the printing paper can improve the printability of the paper, such as increasing the whiteness, smoothness, opacity, and stiffness of the paper. Improve the affinity, softness, and stability of paper to ink, which is helpful to improve the quality of printed matter. Of course, too much filler in the paper also brings some adverse effects, mainly for the reduction of paper strength and sizing effect. In printing, it is easy to drop powder and hair, and the filler particles will be transferred to the printing plate and blanket, resulting in paste plate and other phenomena. Due to the friction effect of filler, the printing plate will be worn, but the addition of precipitated calcium carbonate (PCC) can make the printing plate smooth Wear plates to a minimum (currently used by Jindong).
11. What is the opacity of paper?
A: opacity refers to the opacity of paper. The opacity of paper depends on the light scattering ability of paper, the number of light scattering interfaces inside the paper (i.e. the number of independent particles inside), and the refractive index difference of the scattering interface. The more light scattering interfaces, the greater the refractive index difference between scattering interfaces, the greater the light scattering ability, and the higher the opacity of the paper.
12. How does filler affect the opacity of paper?
A: paper without filler is composed of fiber and air. Air exists in the pores between the fibers. Because the refractive index of the fiber and air is different when the light beam irradiates the paper surface, part of the light scatters on the interface between the fiber and air, giving the paper a certain (lower) opacity, which is reflected in the printing, and the main performance is easy to pass through. After adding fillers with a refractive index higher than cellulose into the paper, the number of light scattering interfaces in the paper increases, that is, there are three different interfaces between fiber and air, between filler and fiber, and between filler and air. Among these three interfaces, the difference of refractive index between filler and air is larger. As a result, the light scattering at the interface between the filler and the light gets the maximum opacity.
13. How can fillers improve the smoothness of the paper surface?
A: the network formed by interweaving fibers always has a large number of pores and surface irregularities. Adding fine particle filler can improve the softness and plasticity of the paper, and can carry out better calendering treatment, so as to improve the smoothness of the paper after calendering.
14. How does filler affect paper strength?
A: the combination between fibers is the basis of paper strength. The addition of fillers reduces the combination between fibers, so adding a large number of fillers will significantly reduce the paper strength. Among them, the tensile strength, folding strength, and bursting strength decrease greatly, while the tear strength decreases slightly. The amount of filler used is limited to a certain extent.
15. How does filler affect the bulk of paper?
Answer: the density of paper fiber is about 1g / cm3, while the density of filler is mostly 2.5-3.0g/cm3. Therefore, the addition of filler will reduce the loose thickness of the paper. But when the amount of filler is small, the loose thickness increases with the increase of filler, especially for short fiber paper.
16. How does filler affect paper stiffness?
A: paper stiffness is a function of paper thickness and elastic modulus. The influence of fillers on stiffness should be considered in combination with the influence of fillers on the loose thickness and tensile strength. When the amount of fillers is small, the addition of fillers does not affect the paper stiffness. When the amount of fillers increases, the paper stiffness decreases significantly with the increase of the number of fillers.
17. What is the role of color in the paper?
A: even the bleached pulp fiber is slightly yellow or gray. This is because the lignin in the pulp fiber tends to absorb violet and blue light with a wavelength of 400-500nm. The more lignin in the pulp, the darker the color. Therefore, in order to make the paper have higher whiteness, blue-purple or red-blue dyes are often added to the bleached pulp. The production of the colored paper must also be dyed.
18. What are the ingredients of pigments?
A: pigments are pigments and dyes used for paper dyeing and color matching. Pigments are mostly inorganic, and most of them are insoluble in water. Dyes can be divided into natural dyes and synthetic dyes. At present, synthetic dyes have completely replaced natural dyes, and most of them are soluble in water, or soluble in water after chemical treatment.
19. Other chemicals in paper accessories and their functions?
A: in order to meet the needs of some special uses of paper, various types of non-fiber additives are often used in pulp or paper. According to their uses, they can be roughly divided into the following categories:
① Wet strength agent. A wet strength agent is a kind of additive added to increase the wet strength of paper, such as urea-formaldehyde resin and phenolic resin.
② Dry strength agent. Such as cationic starch, polyacrylamide, etc.
③ Retention aids. Additives such as polyacrylamide, polyethylene oxide, and polyethyleneimine are added to reduce the loss of fillers and fines in the papermaking process.
④ Defoamer. It is used to eliminate foam in the papermaking process. Such as silicone oil, turpentine, tridecanol, tributyl phosphate, pentanol, and octanol.
⑤ Water-resistant agent. It is mainly used in paper with a high requirement of water resistance. Such as paraffin, metal soap, glyoxal, melamine resin, and dimethylamino ethyl acrylate.
20. How to classify paper simply?
A: paper can be divided into cultural paper, industrial paper, household paper, and special paper according to its use. Cultural paper can be simply divided into uncoated paper and coated paper. Uncoated paper is called uncoated paper, such as newsprint, offset paper, xerographic paper, and writing paper; coated paper is called coated paper, such as coated paper, calendar paper, matte paper, glass card paper, etc.