Printability of the hottest paper

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Printability of paper

printability of paper is a comprehensive reaction of various physical and chemical properties that should be possessed by producing good quality printed matter according to specific printing methods and necessary conditions. The specific printing method refers to offset printing, relief printing or other printing. Under the best conditions of printing plate ink and other conditions, the paper can make the printing plate ink transfer smoothly on the surface during the printing process, and obtain a complete, full and clear impression. After the ink film is solidified, it shows the best color effect and printing quality. The printability of paper is not a definite paper attribute, but a display of whether the inherent characteristics of paper are suitable for the printing conditions under different printing conditions. In other words, the printability of the same paper is significantly different under different printing methods. (these properties include smoothness, absorbability, whiteness, surface strength, pH, elasticity, gloss, sizing degree, opacity, tensile strength, compressibility, uniformity, hue, etc.)

The theory of paper printability is a complex problem, which widely involves many basic theories. Generally speaking, there are two basic theoretical problems

the concept of paper morphology. In the process of printing before printing or processing and finishing after printing and its subsequent use, the paper is required to maintain a stable and normal paper phase. The so-called paper phase refers to the shape of paper with a certain water content at a certain temperature and humidity. When the paper phase is normal, its basic feature is good flatness. If its sheets are stacked into stacks, it can maintain a stable flat phase. On the contrary, when the paper phase is abnormal, its flat phase naturally disappears, and presents various shapes such as curly concave convex. When a single sheet of paper is piled up to a height of about, it can be clearly detected whether its paper phase is normal

the so-called paper morphology, in short, is a discipline that studies the causes of abnormal paper morphology caused by paper deformation and its relationship with various factors. At present, it is still in its infancy and is a new discipline. The practical manual of the latest printing technology uses the knowledge of paper morphology, which can explore the technical methods to restore its printability from different paper phases. One of the specific applications of papholography theory in practice is to adjust the humidity of paper in production

rheological concept of paper. There are various flow and deformation phenomena in the process of paper stacking (or rolling) on the paper feeding device and becoming printed matter on the printing machine. The so-called paper rheology, in short, is a science that studies various phenomena of paper flow and deformation in the printing process, especially on the printing press, and the relationship between various factors that cause rheology. Paper rheology has become one of the theoretical bases to explore and guide the research of paper printability, which focuses on the mechanical behavior of paper. 7. Maximum change angle: 99999 ° when the paper is deformed due to stress, its elastic plastic viscoelastic creep permanent deformation contact deformation and other rheological phenomena can be seen. Paper has different suitability meanings and contents in different uses (such as writing, painting, printing, packaging, etc.)

the so-called printability of paper usually refers to that the paper used for a certain printing method should have various properties that adapt to its process and technical conditions (such as machine type working speed, printing pressure, environmental temperature and humidity, etc.), and these properties must make the printed matter produced meet certain quality requirements and effects. These properties of paper are collectively referred to as the printability of paper

the printability of paper mainly includes: the compressibility of paper, the smoothness, absorption, dimensional stability, ink absorption, surface strength, etc

the thickness of a paper in the thickness direction is a basic property of paper, which has a considerable impact on the opacity and compressibility of paper When printing, the center distance between the plate cylinder or rubber cylinder and the impression cylinder is relatively fixed to a certain extent. If the thickness of the paper is different, it will cause the change of printing pressure, so that the transfer of ink fluctuates, and the depth of the imprint is uneven, affecting the quality of the printed matter

238 gravure printing technology volume when the paper is thin, the opacity of the paper may decrease. Therefore, the possibility of through printing should be considered when printing. In order to overcome the disadvantages of through printing when printing on thinner paper, it is necessary to use thicker ink to print with less printing pressure and thinner ink layer

the compressibility of paper is particularly important for printing paper, because paper has to bear certain pressure during printing, so that ink can be transferred from the printing plate to the paper. If the paper does not have certain compressibility, the graphic part on the printing plate cannot completely contact the surface of the paper, and the ink cannot be transferred to the paper well, resulting in blurred impression and reduced printing effect. The paper with good elasticity and plasticity can appropriately reduce the smoothness of the paper and the requirements of the uneven surface of the printed text, and the clarity of the printed text is also improved

if the paper is pressed instantaneously, the paper is compressed. When the pressure is removed, the paper can return to its original state, which is called the sensitive elasticity of the paper; If the paper is pressed for a long time, in addition to the deformation of the paper at the moment of pressing, the deformation of the paper also increases slowly with the increase of the time of pressing. When the pressure is removed from the surface of the paper, the slowly deformed part of the paper reduces the working intensity of teachers and gradually recovers. This part of the recoverable slow deformation is called the anelasticity of the paper, That is to say, the elasticity of paper is composed of anelasticity and sensitive elasticity. Of course, this kind of recoverable deformation only occurs when the pressure is within a certain cycle (that is, when the elastic limit of the paper is not exceeded). If the pressure exceeds the elastic limit of the paper, there will be unrecoverable deformation, which is the plasticity of the paper

if the elastoplasticity of the paper is good, under the normal printing pressure, the surface of the paper will clearly transfer the ink of the printing part, and the elastoplasticity of the paper plays a buffer and adjustment role to the pressure. Even if the paper with low smoothness is used, good printing effect can be achieved due to the good contact between the printing plate surface and the paper surface. The elastoplasticity of paper is particularly important for gravure and letterpress printing, but the humidification system does not work

iron is more sensitive; High carbon steel and non iron are less sensitive. The compression deformation rate of paper is related to the degree of polymerization of cellulose, the binding force between fibers, the hydrogen bonding between fibers and the number of voids between fibers. The more voids, the better the elastoplasticity, and vice versa

for printing paper, uniformity is also an important property. Printers can adjust ink and printing conditions to adapt to different properties of paper, but the only condition is that the paper must have good uniformity. If the uniformity of each batch of paper, each ream of paper or each sheet of paper is different, it is difficult to print. Sometimes, in extreme cases, it causes stoppage or failure to use. Uneven thickness of paper will cause changes in printing pressure, resulting in uneven ink color and depth, which will seriously affect the printing quality

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