1. What are the raw materials for modern papermaking?
The raw materials of modern papermaking are plant fibers (wood, bamboo, grass, etc.), mineral fibers (asbestos, glass filaments, etc.), other fibers (nylon, metal wire, etc.), and polymer materials obtained by cracking petroleum. At present, the paper used for writing, printing and packaging is still mainly made of plant fiber as the main raw material.
2. What are the types of raw materials for papermaking plant fibers?
At present, the raw materials for plant fibers used in the paper industry can be mainly divided into two categories: wood fiber raw materials: plant fibers obtained directly from trees. Non-wood fiber raw materials: it is also divided into grass fiber raw materials, phloem fiber materials and seed hair fiber materials.
3. What is the composition and function of commonly used auxiliary materials for paper?
Excipients refer to various additives added to paper to meet the different performance of paper. Excipients are composed of fillers, compounds, pigments and other chemical additives. Filler can improve the smoothness and opacity of the paper; the rubber compound can make the paper have water resistance;
Pigments can increase the whiteness of the paper, etc.; dyes can color the paper; and other chemical additives can change the properties of the paper to provide some special uses for the paper.
4. What is the role of the compound?
Paper produced with plant fibers can absorb water or other liquids because there are a large number of pores between the fibers themselves and the fibers, and the cellulose and hemicellulose that make up the fibers contain a large number of hydrophilic hydroxyl groups. In order to prevent the paper from being infiltrated by water or other liquids,
It is necessary to add a colloidal substance or film-forming substance with anti-liquid resistance to the paper, that is, the rubber material, to give the paper the performance of resistance to liquid penetration and diffusion. The process of applying compound in the paper industry is called sizing.
5. What are the methods of sizing?
According to the different sizing effects, the sizing method is divided into internal sizing and surface sizing. Internal sizing is the addition of the compound to the pulp and then copied into a liquid-repellent paper and cardboard. Commonly used rubber materials are rosin glue and synthetic rubber. Surface sizing is the application of a thin layer of glue to the surface of the paper, so that the paper has a hydrophobic property. Commonly used rubber materials are starch, animal glue, and synthetic rubber materials. Surface sizing is mainly used for offset paper, writing paper and wrapping paper and cardboard with hydrophobic requirements.
6. What are the effects of surface sizing on the properties of printing paper?
(1) Increase the water resistance and surface strength of the paper, which can reduce the hair loss of the paper in offset printing; (2) improve the printing adaptability, if the surface rubber material is too small, the paper in printing will absorb too much linking material in the ink, resulting in dull printing. On the contrary, if the surface rubber material is too much, it will slow down the drying rate of the ink, resulting in dirty and bright stains; (3) increase the erasability of the paper, surface sizing can reduce the penetration of the ink, so it is easy to erase the ink, increasing the anti-friction ability of the paper surface; (4) increase the strength of the paper, such as break resistance, bending resistance and tensile strength; (5) reduce the difference between the two sides of the paper and deformation.
7. What is the role of fillers?
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 internal gap of the paper smaller and thinner, thereby increasing the ink absorption of the paper, and making the ink absorption even. Usually added insoluble in water or slightly soluble in water minerals in the slurry, the content in the printing paper is about 10%-25%, different paper added to different amounts, and may vary greatly
8. What characteristics should the paper filler for printing have?
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, the best resources are abundant and the price is low.
9. What are the commonly used fillers for printing paper?
The most commonly used inorganic fillers are talc, white earth, titanium dioxide and calcium carbonate. Among them, titanium dioxide is an expensive and high-quality filler; organic synthetic filler is some polymer substances.
11. What is the opacity of paper?
Opacity refers to the nature of the paper's opacity, and the opacity of the paper depends on the paper's ability to scatter light, the number of light scattering interfaces inside the paper (i.e., the number of independent particles inside) and the size of the refractive index difference at the scattering interface. The more light scattering interfaces, the greater the difference in refractive index between scattering interfaces, the greater the light scattering ability of the paper, and the higher the opacity.
12. How does filler affect the opacity of the paper?
Paper without filler is composed of fiber and air. Air exists in the pores between fibers, because the refractive index of fibers and air is different, so when the beam of light shines on the surface of the paper, that is, some of the light scatters at the interface between fiber and air, giving the paper a certain (low) opacity, reflected in the printing, mainly manifested as extremely easy to print. After adding a filler with a refractive index greater than cellulose to the paper, the number of light scattering interfaces inside the paper is increased, that is, there are three different interfaces between fiber and air, filler and fiber, and between filler and air, in these three interfaces, the difference in refractive index between filler and air is larger. As a result, light is scattered at the interface between the filler and the air, resulting in an increase in opacity.
13. How does filler improve paper surface smoothness?
The network formed by the interweaving of fibers always has a large number of pores and uneven surfaces, and the addition of fine particles can improve the softness and plasticity of the paper, and can be better calendered, which can improve the smoothness of the paper after calendering.
14. How does filler affect paper strength?
The combination between fibers is the basis of paper strength, and the addition of fillers reduces the combination between fibers, so adding a large amount of fillers will significantly reduce the strength of the paper. Among them, the tensile strength, bending resistance and break resistance decrease greatly, the tearing degree decreases less, and the amount of filler used has certain limitations.
15. How does the filler affect the bulk of the paper?
The density of paper fibers is about 1g/cm3, while the density of fillers is mostly 2.5-3.0g/cm3. Therefore, the addition of filler will reduce the bulk of the paper. However, when the amount of filler added is small, the bulk thickness increases with the increase of filler volume, especially for short-fiber paper.
16. How does the filler affect the stiffness of the paper?
The stiffness of the paper is a function of the thickness and elastic modulus of the paper. The influence of filler on stiffness should be considered in conjunction with the effect of filler on bulk thickness and tensile strength. When the amount of filler is added, the addition of filler basically does not affect the stiffness of the paper, and when the amount of filler is increased, the stiffness decreases significantly with the increase of filler.
17. What is the role of pigments in paper?
Even the bleached pulp fibers are slightly yellow or grayish white, which is due to the fact that the lignin contained in the pulp fiber tends to absorb purple and blue light with a wavelength of 400-500 nm, and the more lignin content in the pulp, the darker the color. Therefore, to make the paper have a higher whiteness, a blue-purple or red-blue dye is often added to the bleaching paste. The production of colored paper must also be dyed.
18. What are the components of the pigment?
Pigments are pigments and dyes used for paper dyeing and color grading. Pigments are mostly inorganic, most of them are insoluble in water; dyes have natural dyes and synthetic dyes, and synthetic dyes have completely replaced natural dyes, most of the dyes are soluble in water, or soluble in water after chemical treatment.
19. Other chemical additives and their roles in paper excipients?
In order to meet the needs of some special uses of paper, various types of non-fibrous additives are often mixed in pulp or paper. According to its use, it can be roughly divided into the following categories: (1) wet strength agents. Wet strength agent is an additive added to increase the wet strength of the paper, such as urea-formaldehyde resin and phenolic resin. (2) Dry strength agent. Such as cationic starch, polyacrylamide and so on. (3) Retention aid. Additives added to reduce the loss of fillers and fine fibers during the papermaking process, such as polyacrylamine, polyethylene oxide and polyethyleneimide. (4) Defoamer. Used to eliminate foam in the papermaking process. Such as silicone oil, turpentine, tridecanol, tributyl phosphate, pentanol and octanol and the like. (5) Water resistance. It is mainly used in paper with high requirements for water resistance. Such as paraffin, metal soap, glyadaldehyde, melamine methyl awakening resin and dimethylaminoacetamide acrylate.
20. How can I classify paper simply?
Paper can usually be divided into cultural paper, industrial paper, household paper and special paper according to the use, and its Chinese paper can be simply divided into non-coated paper and coated paper. Uncoated paper is called non-coated paper, such as newsprint, offset paper, electrostatic copy paper and writing paper, etc.; coated processed paper is called coated paper, such as coated paper, wall calendar paper, matte paper, cellophane and the like.
21.What is the process flow of papermaking?
The process flow of papermaking is composed of the following main links: pulping section: raw material selection→ cooking and separating fiber→s→ washing→ washing→ and screening → concentrating or copying into pulp sheets→ storing spare paper reading sections: slurry → removing impurities→ refining → beating → mixing of various additives → paper materials→ the flow of paper materials→ → the mesh → pressing part→ the drying part→ surface sizing → drying → calendering → rolled into paper
Coating section: coated base paper→ coater coating → drying → coiling → rewinding → super calendering processing section: rewinding → cutting flat plate (or reel) → sorting packaging → into storage
22. What is pulping?
Pulping refers to the production process of using chemical or mechanical methods or a combination of both to dissolve plant fibers into a colorant or bleached pulp.
23. What is chemical pulping?
Chemical pulping is the use of aqueous solutions of chemicals to treat plant fiber raw materials at a certain temperature and pressure, the raw materials in the lignin and non-fiber carbohydrates and oils, resins, etc. are dissolved, and as far as possible to retain cellulose and different degrees of retention of hemicellulose, so that the raw material fibers are separated from each other into a pulp. The most representative pulping methods in the chemical method are sulfate method and sulfite method.
24. What is mechanical pulping?
Mechanical pulping is the use of mechanical methods to process the fiber raw materials to dissociate the fibers. Wood is called mechanical wood pulp. The main application of the paper industry is mechanical wood pulp, also known as milled wood pulp. Mechanical pulp retains a large amount of lignin in the raw material, and the pulp yield is higher than that of chemical pulp.
25. What is the purpose of bleaching pulp?
Pulp prepared by chemical and mechanical methods is called natural color pulp, and natural color pulp has a certain color (generally yellow or brown). In order to meet the requirements of paper use, the pulp must be bleached to make the paper have a high whiteness. Bleaching is the use of appropriate bleaching agents through oxidation, reduction or decomposition and other reactions, so that the residual lignin in the pulp is dissolved, or the colored substances fade while retaining lignin.
26. What are the common methods of bleaching pulp?
There are two commonly used bleaching pulp methods: one is the oxidation bleaching method, which uses oxidized bleaching agents to destroy the structure of lignin and dissolve it to achieve the purpose of improving the purity and whiteness of pulp. Such bleaching agents include Cl2, Clo2 and hypochlorite. Oxidative bleaching is still the main bleaching method. Oxidizing bleach, because it is chlorine-containing bleaching, is seriously polluted and will gradually be replaced by oxygenated bleaching methods. The other is the reductive bleaching method, which uses a reductive bleach to change the structure of the hair chromatin group and decolorize it. Since it does not cause the loss of fiber components and can maintain the characteristics of the raw slurry, it is particularly suitable for bleaching of pulps with high pulp yields such as ground wood pulp and chemical mechanical pulp. Such bleaching agents include zinc disulfite, sodium trisulfite, hydrogen peroxide and sodium peroxide. The whiteness stability of the pulp bleached by the reduced bleach is poor, and the original color will be restored after a long period of illumination in the air. Of course, in the practice of bleaching, a method can not be used to bleach the slurry to a higher whiteness, often a variety of bleaching methods are used together, that is, the so-called multi-stage bleaching, such as three-stage bleaching, five-stage bleaching, etc., in order to make the slurry bleach to meet the whiteness of the use requirements.
27. Why beat?
Pulp that has undergone cooking or mechanical grinding, washing, screening and bleaching cannot be used directly to copy paper. Because the fibers in the pulp lack the necessary flexibility, the connection between the fibers and the fibers is not good, if you use it to copy paper, the paper will be loose, porous,
The surface is rough and the strength is low, which cannot meet the requirements of use. Pulping is the use of mechanical methods to process the fibers in the pulp, so that it broom and moderately cut, more importantly, the fibers absorb water and expand during the pulping, so that it has high elasticity and plasticity, to meet the requirements of paper machine production, so that the paper produced can meet the expected quality indicators.
28. What are the methods of copying paper?
The method of paper sheet copying can be divided into two categories: dry and wet, the main difference is: dry papermaking with air as the medium, mainly used for synthetic fiber copying non-woven fabrics, diapers, etc.; wet papermaking with water as the medium, suitable for plant fiber paper copying. At present, the vast majority of paper is copied by wet method.
29.What are the wet paper machines?
According to the structure of the paper forming part, the wet paper machine is divided into three categories: long net paper machine, round mesh paper machine and interlayer paper machine. Long mesh and circular mesh paper machines in the forming of paper pages are single-sided dehydration, resulting in two sides of the paper page difference; while the mesh paper machine uses spraying double-sided dehydration, effectively reducing or eliminating the two sides of the paper page difference, can improve the uniformity of the paper.
30. What is the process of copying the pages?
The following takes the most advanced mesh papermaking as an example to introduce the copying process of the paper page: the paper machine is composed of two parts: the wet part and the cadre, the wet part includes the pulp box, the net part and the pressing department; the cadres include the drying department, the calendering department and the paper rolling machine. The paper suspension sent by the purification system is sprayed to the middle of the two nets at a uniform and stable pulping speed through the pulp box (generally sprayed at a 45 degree angle or 90 degree angle), and after most of the water is removed from the double side of the two nets, it is sent to the advanced shoe press for press dehydration, and improves the paper page performance, increasing the tightness and surface smoothness of the paper sheet. After the paper is dehydrated by pressing machinery, it is sent to the drying section to further dehydrate using thermal energy to meet the requirements of the water content of the paper. Offset paper should also be subjected to surface sizing treatment in the drying part to improve the surface strength of the paper and other properties to adapt to the requirements of high-speed printing. The surface of the paper that comes out of the dry part is still very rough and cannot adapt to the requirements of printing and writing. In order to improve the smoothness of the paper and adjust the thickness of the paper, the paper page must also be calendered by one or several metal pressure rollers (usually two calenders). The calendered paper can be cut into flat paper or rolled into webs with a rewinder.
31. Why should paper coating processing be carried out?
After calendering, the paper fibers are no longer loosely arranged, but have a certain tightness, but the smoothness of the surface still cannot meet the requirements of high-grade fine printing. The surface uniformity of non-coated paper is poor, the ink color after printing is uneven, the gloss is low, the fine dots cannot be restored, resulting in the loss of layers, and the uniformity of the field part of the image is reduced, affecting the printing reproduction effect, so the fine printing paper must be processed with paper surface coating to further improve the surface performance of the paper.
32. What is the purpose of paper coating processing?
The purpose of the paper coating process is to cover the surface of ordinary paper with large pores formed by fibers, covered with a layer of fine particles that has good absorption of ink, so as to obtain a paper surface with good uniformity and smoothness.
By coating, you can also improve the gloss of the paper, improve the stability and opacity of the paper, these characteristics increase with the increase of the amount of coating.
33. What are the types of printing coated paper?
Printing coatings can generally be divided into two categories: ordinary coated paper and special coated paper. Ordinary coated paper is the use of ordinary coating method to coat the paint on the surface of the base paper, after drying and then calendering treatment, and finally cut or rewind into flat paper or web paper, such as coated paper, matte paper, lightweight coated paper, etc.; special coated paper refers to the use of special coating or special processing methods made of printing coated paper, such as cast coated paper (cellophane), embossed paper and matte coated paper.
34. What is the production process of printing coated paper?
The production process of printing coated paper is as follows: the selection of base paper → the preparation of coatings→ the coating machine coating → drying→ calendering or surface finishing→ slitting or rewinding.
35. How is the coating process classified?
Coating operation according to the relationship between the coater and the paper machine is divided into in-machine and out-of-machine type, according to the number of coatings divided into single-layer coating and double-layer coating, in-machine coating is installed on the paper machine, so that papermaking and coating continuously, double-layer coated paper than single-layer coated paper has better printing adaptability, can improve the quality of coated paper. There are three main types of coating machines for coating operations: roller coater, air knife coater and scraper coater.
36. What are the drying methods of coated paper?
After the paint is coated on the surface of the base paper, it cannot be dried directly with the drying cylinder like non-coated paper, because the coating is still in a wet state, and direct contact with drying will make the paint stick to the surface of the drying cylinder. Generally, infrared drying or hot air drying should be used, or these drying methods should be used to dry to a certain degree of dryness, and then contact drying should be carried out with an oven.
37. What is the calendering effect on the surface of coated paper?
There are still a large number of subtle bumps on the surface of the coated and processed base paper, which cannot meet the smoothness required by printing, and at the same time does not have gloss. Surface calendering is therefore mandatory, with the most commonly used method of calendering being super calendering. The super calender consists of multiple metal rollers and paper meal rollers, and the paper is subjected to pressure and friction force as it passes between the rollers and produces a gloss. Matte coated paper does not require super calendering, or only slight calendering.
38. What are the requirements for base paper for coated paper?
The quality of the base paper has a very important impact on the coated paper, and poor control will affect the performance of the coated paper. From the base paper pulp, copper plate base paper mostly uses sulfate wood pulp, of which 70% is hardwood pulp, and the rest is softwood pulp. For low-quantity, high-quality coated base paper, the amount of coniferous paddles should be correspondingly higher. In terms of strength, copper plate base paper should have high tensile strength and surface strength, in addition to changing the composition of the pulp, it should also be used to improve the beating degree and surface sizing and other measures to improve the strength of the base paper. In terms of surface properties, the base paper should not be too rough or too smooth. In addition, the absorbency of base paper should be moderate.