Talking about the performance and use of web newsprint

Reel newsprint is newspaper printing paper, commonly known as white paper. It is mainly used for newspapers and periodicals in letterpress printing, as well as general printed matter with a large number of prints and shorter service life. Because it is recoiled into a cylindrical shape after copying, it is mostly used for rotary offset presses, which greatly improves the printing efficiency.

The composition of reel newsprint is mainly based on mechanical pulp, which is about 90%. In addition, about 10% of bleached chemical pulp is added, but in the case of insufficient raw materials for pulp, a certain proportion of mechanical pulp is added. Chemical pulp, chemical pulp, etc. are used instead of mechanical pulp. Due to the large amount of mechanical wood pulp used in newsprint, the content of impurities is large. Pulp contains a lot of short fibers, and many other unfiberized impurities are bound to the fibers, making the newsprint appear pure white. With the improvement of modern papermaking technology, waste paper is used for deinking, scrapped prints are recycled, and ink and other chemicals in paper prints are decomposed and eliminated using high-tech technology to restore the newsprint pulp. These pulps can be added again. The paper-making of newsprint can not only reduce the cost of raw materials, but also make paper materials reuse. Newsprint is made using multi-squeeze and multi-drying cylinders, compressed by ordinary calenders. Due to the papermaking process of reel newsprint and the characteristics of the raw and auxiliary materials, it is determined that the finished product and its use have more unique requirements.

one. Newsprint structure and composition

Newsprint is a mixture of plant fibers, fillers, compounds, and colorants. Plant fibers consist of cellulose, hemicellulose and lignin. The paper structure is a porous pore structure. The pore structure forms the basis of the paper. Adding fillers 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 material and its chemical properties are relatively stable. It is insoluble in water and neutral inorganic solvents.

Hemicellulose is a carbohydrate composed of several monosaccharides that accompany cellulose in the cell walls of plants. It has a branched-chain structure, its degree of polymerization is small, it has 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 monomers and it has aromatic properties. Its chemical properties are very unstable. Under the action of sunlight and air, the texture of the paper will be brittle, the mechanical strength will be reduced, the paper color will be darker, and the yellowish-brown color of the lignin will be affected, which will affect the whiteness of the paper.

In the paper fiber structure, due to the role of hydroxyl groups and the overlap between fibers, they are interwoven into a network of pores, making the paper a strong hydrophilic material. This material absorbs moisture but does not dissolve in water and passes through the fiber. The hydration reaction produces hydrogen bonding, which enhances the physical strength of the paper.

Adding fillers to paper means adding a certain amount of finely-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 rubber material in the paper, so that the paper has a certain degree of water resistance and water resistance, impede the penetration of water, improve the paper surface strength. Sizing is divided into two kinds of sizing and sizing.

Pigment refers to the material added to the bleaching of pulp. In benzene made from newsprint, blue-purple material is often added to bleached pulp.

two. Web features

Newsprint is also a printing paper. Therefore, it first possesses the common characteristics of paper. At the same time, it is mainly used for newsprint newspapers and other printed crystals with a short lifespan due to its rewinding into a roll shape. Therefore, it also has its own personality.

1. Strong ink absorption. Since the web newsprint paper is continuously printed under the high-speed rotation of the web, and the ink adhesion effect is good in a very short time, the ink absorption is very strong. In general reel newsprint, the best ink-absorbing effect is 1/3 of the paper thickness. In addition, during the papermaking process, the control of raw wood, chemical wood pulp and auxiliary materials is very particular. The proportion of raw materials directly affects the ink absorption of newsprint.

2. The paper is soft, has a high voidage, and is rich in good compressibility and elasticity. Due to the large amount of mechanical wood pulp and straw pulp used in newsprint papermaking, the content of impurities is large. Therefore, the paper fibers are soft, and the fibers are filled with fillers. When the paper is printed, many paper dusts often appear. Its poor water resistance, filler in the fiber gap after the ordinary calender press, the surface of the gap is relatively more, at the same time to meet its good ink absorption, newsprint paper with compressibility and elasticity, under high-speed paper running After the paper is pressed by the blanket, its good compressibility and elasticity can solve the fast absorption of the ink and realize good copy and transfer of the graphic and text.

3. The paper has low whiteness, high opacity, low fiber interweaving binding force, and low mechanical strength of the paper. Newsprint contains a large amount of wood pulp fibers, wood pulp contains a lot of lignin, lignin in the air easily oxidized discoloration, generally better newsprint, its whiteness at 60 degrees. The opacity depends on the light scattering ability of the paper, the number of light scattering interfaces inside the paper, and the difference in the refractive index of the scattering interface. The more scattering interfaces, the greater the refractive index of the scattering interface, the higher the opacity. Newsprint paper in the process of copying, because the filler was added, so that the gap between the fibers filled with filler and increase the light scattering interface, the scattering rate between the filler and air is large, it increased the newsprint opacity. Newsprint uses a large amount of wood pulp. In the process of pulping, wood pulp has short fibers and large impurities. The interwoven binding force between fibers will inevitably decrease and its mechanical strength will decrease. $Page break $

Third, the nature of reel newsprint

The nature of reel newsprint generally refers to its suitability for printing, including its performance characteristics during transportation and storage. The printing suitability refers to the comprehensive reflection of the physical and chemical properties that a certain quality of the printed matter should have in the necessary conditions. The nature of web newsprint must reflect the best print quality and color effects. During the operation of the roller, the ink on the printing plate can be smoothly transferred to the surface of the printing plate to obtain a full, full, clear and rich graphic print.

The printability of web newsprint includes the pore structure and ink absorption of the paper, the smoothness and compressibility of the paper, the surface strength of the paper, the acidity and alkalinity of the paper, and the water content and elasticity of the paper.

1. Paper pore structure and ink absorption. Paper is a kind of network structure formed by the interweaving of different kinds of plant fibers. In this network structure, the pores between fibers are filled with some fillers, rubber compounds and color materials to meet the paper itself. Has the characteristics. The filler is added to improve the whiteness, smoothness and opacity of the paper; the addition of the sizing agent makes the paper have a certain water resistance and is not easily infiltrated by water or other liquids; adding a coloring material makes the paper have higher whiteness. The paper's "L" structure is the basis for the paper's ability to absorb ink and is one of the key factors in the printing and drying of printing press crystals. Therefore, to understand the ink absorption of paper, it is necessary to first understand the paper's pore structure. Because the pore structure of the paper is closely related to the penetration of the ink, the speed of penetration, the smoothness of the printing, the osmotic solidification and drying of the ink, and the quality of the printed matter.

The pore structure of paper mainly includes the porosity of paper. The paper's porosity indicates the ratio of the volume of air in the paper to the volume of the paper. The porosity of the paper can be obtained by calculations and experimental measurements.

Paper void rate = volume of paper air (unit area)/paper volume (unit area) x 100%

From the equation above, we can see that the larger the volume of air in the paper, the higher the porosity of the paper, which also verifies the situation in the paper's pore structure. The less the paper fiber, the more interlaced and the more interspace between fibers. Larger, the poorer the pore structure of the paper. On the contrary, the more paper fibers, the denser the interweaving, the smaller the gap between the fibers, and the better the paper pore structure.

The solidification and drying of ink on paper is accelerated with the increase of voidage, and its ink absorption also increases, but the ink gloss on the paper surface decreases with the increase of voidage.

Paper has a porous structure, and the porous structure of the paper determines the breathability, hygroscopicity, absorbency and compressibility of the paper. This is the basis for the paper to absorb water, ink and other substances. In order to ensure better printing quality and printing effect, printing paper is required to have better ink absorption. The ink absorbency of paper refers to the nature of the ink penetrating into the paper and being absorbed after the paper comes into contact with the ink and transfers the ink onto the paper surface. The greater the porosity of the paper, the looser the structure, the more ink it absorbs, and vice versa, which is why we often refer to paper as poor ink absorption.

2. The smoothness and compressibility of the paper. The smoothness of paper refers to the degree to which the paper surface is even, smooth and smooth. Paper smoothness depends on the processing method used in the processing of the paper, the distribution of fibers in the paper, and the application of fillers.

Paper smoothness includes paper smoothness and print smoothness. Paper smoothness refers to the time required for a certain volume of air to pass through the gap between the paper and the glass under a certain pressure under a certain degree of vacuum, expressed in seconds. Paper smoothness is generally concentrated between 50 and 100 seconds, and as the smoothness increases, the density of the printed field increases significantly. Print smoothness refers to the ratio of the surface of the paper in contact with the surface of the smooth roll under the conditions corresponding to the printing pressure and the printing speed. The measurement of print smoothness requires special advanced equipment, and the actual operability is not strong. At present, paper smoothness is generally used to represent paper smoothness.

Reproduction of printed matter is through the network to express its color and gradation. The carrier of the graphic is the blanket. The contact between the blanket and the paper directly affects the transfer of the image point. Under the same pressure and blanket conditions, the paper smoothness It is the precondition for the transfer of images and texts. The smoother the paper is, the more the paper and paper points are attached to the paper surface, the closer the ink speeds on the paper surface are, the closer the ink speed is, the closer the image point size and the ink absorption are, the more the image and text are restored. More realistic. On the contrary, the graphic reproduction is even worse.

The effect of the compressibility of the paper on printing is that the paper is deformed in thickness during imprinting, and the surface of the paper is flattened, thereby facilitating the contact between the surface of the paper and the surface of the blanket and providing better conditions for ink transfer. . Because newsprint is flexible, it is easily compressed under the pressure of printing, so the perfect contact between the paper surface and the surface of the blanket can be guaranteed. If printing on a strong paper surface, because the paper itself has a certain thickness and uneven surface, when the blanket is in contact with the paper surface, the force on each part of the paper surface is uneven, and the blanket is transferred to the surface of the paper. There are distortions in the text such as blurring or dot distortion and loss.

3. The surface strength of the paper. The surface strength of paper is a property of the binding force between fibers, fillers, and glue on the surface of the paper. This property has a direct effect on the physical properties of the paper surface. News paper's fiber pore structure is relatively weak, especially some short wood pulp fibers and impurities affect the fiber's pore structure, in the papermaking, in order to increase the newsprint whiteness, opacity, smoothness, increase the paper's water resistance , More or less a certain amount of fillers and compounds are added. How much filler and compound is added directly affects the surface strength of the paper. In addition, the calendering of the calender directly affects the surface strength of the paper. In the actual printing process, the paper's ability to resist powder removal and pull resistance is collectively referred to as the surface strength of the paper.

At present, the measurement of paper surface strength has been represented by the value of the pulling speed. The so-called "pile speed" of paper refers to the fact that during printing, as the printing speed increases, the outward tension of the ink acting on the paper surface is greater than the binding force of the paper, causing the paper surface to start decoloring, and the speed of printing at that point when the yarn is pulled. It is the speed of pulling the paper. From this pull speed value, the correlation of paper surface strength can be known. Under the conditions of printing pressure and constant ink, the faster the printing speed is, the greater the reverse sticking force of the ink to the paper, and the greater the speed of pulling the paper. To increase the surface strength of the paper, in addition to increasing the surface bond of the paper