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Talk about the performance and use of web paper

Web paper is a special paper for newspaper printing, commonly known as white paper. It is mainly used for newspapers, periodicals in letterpress printing and general printing with short service life. Because it is rewound into a cylinder after being copied, it is mostly used in rotary offset press, which greatly improves the printing efficiency

the composition of web paper is mainly mechanical wood pulp, which is about 90% of the same kind of testing instrument. In addition, about 10% of bleached chemical wood pulp is added. However, in the case of insufficient wood pulp raw materials, 3billion cubic meters of wood is replaced, supplemented by a certain proportion of mechanical straw pulp, chemical straw pulp, chemical reed pulp, etc. to replace the use of mechanical wood pulp. Due to the large amount of mechanical wood pulp used in the paper, the impurity content is large, the pulp contains a lot of short fibers, and many other non fibrous impurity points are combined to the fibers, making the paper look pure and low whiteness. With the improvement of modern papermaking technology, waste paper deinking branch technology is adopted to recycle waste printed matter. Chemicals such as ink in paper printed matter are decomposed and eliminated by high-tech technology to restore secondary paper pulp. These pulp can be added to the papermaking of paper again, which can not only reduce the cost of raw materials, but also reuse paper raw materials. The paper is made by using multi-channel pressing and multi dryer, and pressing with ordinary calender. Due to the manufacturing process of web paper and the characteristics of raw and auxiliary materials, there are unique requirements for its finished products and use

I. structure and composition of paper

paper is a mixture of plant fibers, fillers, adhesives and pigments. Plant fiber is composed of cellulose, hemifiber and lignin, and the paper structure is a porous porous structure. Pore structure is the basis of paper. Adding a filler between the paper fibers can change the physical properties of the paper

cellulose is a polysaccharide natural polymer compound composed of carbon, hydrogen and oxygen. Cellulose is a typical hydrophilic substance with relatively stable chemical properties. It is insoluble in water and neutral inorganic solvents

hemicellulose is a carbohydrate composed of some monosaccharides, which exists in the plant cell wall with cellulose. It has a branched chain structure, with a small degree of polymerization, good hydrophilicity and adsorption. It is insoluble in water, but it is very easy to absorb water and expand

lignin is a compound composed of phenylpropane monomer, which has aromatic properties. Its chemical property is very unstable. Under the action of sunlight and air, it will make the paper brittle, reduce the mechanical strength, darken the color of the paper, show the yellowish brown of lignin, and affect the whiteness of the paper

in the paper fiber structure, due to the role of hydroxyl groups and the overlapping between fibers, interwoven into shaped pores, making the paper become a strong hydrophilic material, which only adsorbs water but does not dissolve in water, and generates hydrogen bond association through the knocking action of fibers, thus enhancing the physical strength between papers

adding filler to paper refers to adding a certain amount of fine dispersed minerals to the paper, thereby changing the opacity, whiteness and smoothness of the paper surface

sizing material refers to adding a certain amount of sizing material to the paper, so that the paper has a certain water resistance and waterproof ability, hinders the penetration of water, and improves the surface strength of the paper. There are two kinds of sizing: internal sizing and paper sizing

pigment refers to the material added to bleach the pulp. Blue purple material is often added to the bleached pulp in paper benzene

II. Characteristics of web paper

paper is also printing paper, so it first has the commonness of paper. At the same time, because it is rewound into a web shape, it is mainly used for printing crystals with short service life such as newspapers, so it also has its own personality

1. strong ink absorption. Because the web paper continuously prints ink under the high-speed operation of the rotary machine, and the ink adhesion effect is good in a very short time, its ink absorption is very strong. Generally, the best ink absorption effect of web paper is 1/3 of the thickness of the paper. In addition, when copying the vertical brake pad shear tester and horizontal brake pad shear tester produced by Shandong Sida high tech machinery equipment Co., Ltd., the control of raw wood, chemical wood pulp and auxiliary materials is very particular, and the proportion of raw materials directly affects the ink absorption of paper

2. The paper is soft, with high porosity and good compressibility and elasticity. Because a large number of mechanical wood pulp and straw pulp are used in paper making, and the content of impurities is large, therefore, the paper fibers are soft, and the fibers are full of fillers. When printing, there are often a lot of paper gray. Its water resistance is poor. The filler is pressed by an ordinary calender in the fiber gap, and its surface gap is relatively large. At the same time, in order to meet its better ink absorption, paper has compressibility and elasticity. Under the high-speed operation of paper, after the paper is pressed by blanket, its better compressibility and elasticity can solve the rapid absorption of ink and realize the good copy and transfer of pictures and texts

3. the paper has low whiteness, high opacity, low fiber interweaving adhesion, and low mechanical strength. "Paper" Ma Zhanfeng said that it contains a lot of wood pulp fiber, and wood pulp contains a lot of lignin, which is very easy to oxidize and change color in the air. Generally, the whiteness of better paper is about 60 degrees. Opacity depends on the light scattering ability of the paper, the number of light scattering interfaces inside the paper and the difference in refractive index of the scattering interface. The more the scattering interface, the greater the refractive index of the scattering interface, the higher the opacity. In the process of paper making, because fillers are added, the gap between fibers is filled with fillers, which increases the light scattering interface. The scattering rate between fillers and air is large, so the opacity of paper is increased. Wood pulp is widely used in paper. In the pulping process, the fiber of wood pulp is short and thick, and the content of impurities is large. The interweaving adhesion between the fibers will inevitably be reduced, and its mechanical strength will decline$ Page break $

III. nature of web paper

the nature of web paper generally refers to its printability suitable for printing, including some performance characteristics in the process of transportation and storage. Its printability refers to the comprehensive reflection of physical and chemical properties that reproduction of a certain quality of printed matter should have under necessary conditions. The nature of web paper must reflect the best printing quality and color effect. During the operation of the drum, the ink adsorbed on the printing plate can be smoothly transferred to its surface, and a complete, full, clear and rich graphic imprint can be obtained

the printability of web paper includes the pore structure and ink absorption of paper, the smoothness and compressibility of paper; Surface strength of paper; The acidity and alkalinity of paper and the water content and flexibility of paper

1. pore structure and ink absorption of paper. Paper is a kind of shape structure made of various plant fibers interwoven with each other. In this shape structure, the pores between the fibers are filled with some fillers, glues and colorants to meet the characteristics of the paper itself. Adding filler is to improve the whiteness, smoothness and opacity of the paper; Adding rubber is to make the paper have certain water resistance, and it is not easy to be soaked by water or other liquids; Add pigments to make the paper have higher whiteness. Paper? L-gap structure is the basis for paper to absorb ink, and it is one of the key factors for newspaper printing crystal penetration drying. Therefore, to understand the ink absorption of paper, we must first understand the pore structure of paper. Because the pore structure of paper is closely related to the penetration amount, penetration speed, printing smoothness, penetration solidification and drying of ink, and the quality of printed matter

the pore structure of paper mainly includes the porosity of paper. The voidage of paper represents the ratio of the air volume in the paper to the paper volume. The voidage of paper can be obtained by calculation and experimental measurement

porosity of paper = volume of air in paper (unit area)/volume of paper (unit area) X100%

from the above equation, the larger the volume of air in paper, the higher the porosity of paper, which also verifies the situation in the pore structure of paper. The less paper fibers, the less interwoven, the larger the gap between fibers, and the worse the pore structure of paper. On the contrary, the more paper fibers, the denser the interweaving, the smaller the gap between the fibers, and the better the pore structure of the paper

the solidification and drying of ink on paper are accelerated with the increase of porosity, and its ink absorption is also increased, but the gloss of ink on paper is reduced with the increase of porosity

paper has pore structure, which determines that paper has air permeability, moisture absorption, absorption and compressibility, which is the basis for paper to absorb water, ink and other substances. In order to ensure better printing quality and printing effect, printing paper needs to have good ink absorption. The ink absorption of paper refers to the nature that the ink penetrates into the paper and is absorbed after the paper contacts with the ink and transfers the ink to the surface of the paper. The larger the porosity of the paper, the looser the structure, the more ink it absorbs, and vice versa. This is the reason why we often say that the ink absorption of the paper is good or bad

2. Smoothness and compressibility of paper. The smoothness of paper refers to the degree that the surface of paper is uniform, flat and smooth. The smoothness of paper depends on the processing method adopted in the processing process, the fiber distribution in the paper, and the application of fillers

paper smoothness includes paper smoothness and printing smoothness. Paper smoothness refers to the time required for a certain volume of air on the paper surface to pass through the gap between the paper and the glass under a certain vacuum and pressure, expressed in seconds. The smoothness of paper is generally concentrated between 50 ~ 100 seconds, and with the increase of smoothness, the printing field density increases significantly. Printing smoothness refers to the ratio of the surface of the paper to the surface of the smooth roller under the condition equivalent to the printing pressure and printing speed. The measurement of printing smoothness requires special advanced instruments, and the actual operability is not strong. At present, the paper smoothness is generally used to express the paper smoothness

the image and text reproduction of printed matter is to express its tone and level through points. The carrier of image and text is blanket. The contact between blanket and paper directly affects the transfer of image and text points. Under the same pressure and blanket conditions, the smoothness of paper is the prerequisite for image and text transfer. The smoother the paper is, the image and text points are attached to the paper, the closer the ink speed of the paper absorption point is, the closer the size of image and text points and the amount of ink absorption are, The overall restoration of graphics and texts is more realistic. On the contrary, the picture and text restoration is even worse

the influence of the compressibility of paper on printing is that the paper deforms in thickness during stamping, and the paper surface flattens, which is conducive to the good contact between the paper surface and the blanket surface, and provides better conditions for the transfer of ink. Because the paper has softness, it is easy to be compressed under the action of printing pressure, so the more it can ensure the full contact between the paper and the surface of the blanket. If you print on a strong paper, because the paper itself has a certain thickness and uneven surface, when the blanket is in contact with the paper, the force borne by all parts of the paper will be uneven, and the pictures and texts transferred by the blanket to the paper surface will be distorted, such as virtualization, point deformation, loss and so on

3. surface strength of paper. The surface strength of paper is the paper table

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