On the printability of paper and other variable fa

2022-07-27
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Printability of paper and other variable factors in flexible printing (Part 1)

printability of paper usually refers to the adaptability or reaction characteristics of paper during printing, which is subjective and subject to different standards. For example, technically most paper can be printed by most printing processes, but this is not feasible from a commercial or economic point of view. Similarly, when judging the quality of printed matter, we should consider its own characteristics. For example, the judgment standard of high-quality flexo folding carton is different from that of student workbook

in addition, it must be clearly understood that the printing quality depends on the comprehensive effect of paper, ink, printing plate, outline roller and printing machine. Of course, it also depends on the adjustment preparation and operation process of the printing machine. If other links go wrong, even if there is a paper with good printability, it will not obtain satisfactory printing quality. The term printability is used to describe many physical and chemical properties of paper, which restrict the production of printed matter, the expected quality of commercial batch printing and the printing speed. In the following chapters, this paper will mainly discuss some characteristics of paper (including cardboard and translator's notes), and the influence of ink and printing plate on the printability of paper

paper

there are many kinds of paper used in flexible packaging, prepress and post press processing, such as coated paper, semi coated paper, uncoated paper and kraft board. The paper with good printability only absorbs an appropriate amount of ink at the predetermined position, and does not affect its normal drying process. In addition, the paper should also have certain smoothness, inking, appropriate optical density and rheological properties (compressibility and elasticity). Paper should also have enough surface strength to prevent fuzzing, and its market share will account for 80% of the total amount of glass fiber composites; The shape and size shall be stable and shall not change when wet. The paper surface should not have adhered dust particles, which is not easy to produce. First, it is necessary to generate or maintain static electricity

when talking about paper, gehonglin, Secretary of the leading Party group of Chinalco and chairman of the board, once pointed out that printing should not consider the situation when ink contacts paper. This involves the instant printing pressure on the paper. After the paper is pressed, the smoothness is further improved, and at the same time, the pores on the paper surface are reduced. In this way, the compressibility of the paper plays a role, making the surface easy to be wet for the ink, which is conducive to the absorption of the ink. In an ideal state, the paper should be restored to its original state after being pressed, especially those papers that have only undergone rough calendering

ink transfer

ink transfer is characterized by ink absorption. But this statement is not accurate enough, because it contains this meaning: paper absorbs a lot of ink. In fact, it is not necessary. It will consume too much ink. So now the term "inking performance" is widely used, and its meaning is more accurate. Due to the different smoothness of ink, paper and paper, the size of paper pores is also different, so under a certain printing pressure, the inking amount is also different

in fact, as long as the specified minimum ink transfer amount is reached, it is enough to ensure the formation of the required ink film and quality, so that the ink can be transferred on the paper surface as required as far as possible, and firmly adhere to the paper surface without causing dirt. In order to obtain high ink coverage, the binder (liquid phase) in the ink must penetrate the pores of the paper surface to make the pigment adhere to the paper surface. Smooth paper can obtain higher ink coverage, while rough paper requires more ink to achieve the desired effect. Compared with smooth paper, rough paper is also easy to lead to a larger mesh point increase rate. This is related to paper type, roughness of paper surface and pore size. As long as the outline points on the printing sheet are compared with those on the printing plate or film, we can see the degree of increase of the outline points. Usually, the program value is calculated with a densimeter, and then the program value is marked on the curve. The plotted curves of each color reflect the printing performance of the printing press, paper, plate and ink used, and provide us with important information about the tone reproduction of the dot increase. The data obtained from the trial printing of printing plate and paper on the printing machine with specific ink has a very important guiding role for the color separation and plate making of flexo printing

of course, where the ink adheres to the paper surface, the binder and pigment should not be separated, which should not be ignored. In addition, overprint has a great impact on printability. In order to obtain good overprint effect, attention should be paid to the pH value of water-based ink. The pH value of the ink used for the first printing color should be within 3. The pH value of the ink used for the first printing color shall not be lower than 9. The pH value of the ink used for the second printing color should be lower. The drying properties of various color overprint inks also have a great impact on the printability. In flexo printing, the overprint ink is usually light color first and then dark color (yellow magenta green). When printing on coated cloth or semi coated paper, it is sometimes necessary to change the color to magenta yellow green, so as to obtain better overprint effect with water ink

paper smoothness

paper smoothness will affect the overall appearance of the ink film and the printing sheet. There are two types of defects in smoothness. The former refers to defects that can be seen with the naked eye, such as uneven thickness or wrinkles of the weight. These defects are sometimes caused by the structure of the fiber. As for small defects, manager rimara said that they could not be seen with the naked eye, such as dents and holes that may damage the outline points and affect the printing quality

dust particles

dust particles adhered to the paper surface or the edge of the web during the printing process will also affect the printability. If an ink filter is not installed on the flexographic press, dust particles will gather in the ink and be carried to the printing plate. This phenomenon can be eliminated by installing an ink filter in front of the ink pump. In addition, dust particles may also adhere to the doctor blade, causing streaks on the printing sheet; Sometimes the dust particles may adhere to the ink holes of the outline roller, resulting in uneven ink transfer. Therefore, ink filters should be installed as early as possible to effectively control dust particles

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