Analysis on the main factors affecting the printin

2022-07-23
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Analysis on the main factors affecting the printing pressure only when the offset press prints within the working pressure range can we obtain qualified prints for the application of foam granulator in the new era. Too much or too little printing pressure will affect the print quality, and too much printing pressure will shorten the service life of the printing machine. Therefore, determining the printing pressure has become a very important link in the printing process

in the past decade, China's offset printing technology has developed by leaps and bounds, and high-tech equipment and technology have emerged continuously. However, at present, quite a few printing manufacturers still use experience to adjust and determine the printing pressure, that is, while observing the ink dot reduction and image definition of the printed matter, they adjust the printing pressure. Until the printing pressure meets the requirements, the printing pressure at this time is determined as the printing pressure. In fact, the working pressure of the offset press, in addition to the performance of the offset press itself, is also related to the paper, ink and other factors used in the printing process. In the process of adjusting the working pressure of offset press, we should fully understand the various factors that affect the printing pressure

I. Effect of cylinder lining on printing pressure

cylinder lining is divided into plate cylinder lining and rubber cylinder lining. The impression cylinder has no lining. The blanket and the liner together form the lining of the rubber cylinder of the offset press. There is also a liner between the plate cylinder shell and the plate of the offset press, which is sometimes called the liner of the plate cylinder

the influence of rubber cylinder lining on printing pressure is mainly discussed below

1. The function of the lining. The surface of printing plate, blanket and printing paper used in offset printing has micro unevenness. In order to improve the ink transfer rate, the printing plate surface should be in full contact with the blanket surface, the blanket surface and the printing paper surface. In order to make these two pairs of surfaces fully contact, a convenient way is to expand the deformation of the contact surface. Adding an elastic pad can enlarge the deformation and overcome the poor surface contact caused by the rough printing surface. Therefore, the pad has two functions: ① the elastic deformation of the pad can be used to generate the contact pressure of the offset press cylinder (if the pad is not wrapped on the metal cylinder, the pressure cannot be applied, the ink cannot be transferred, and the printing cannot be carried out). ② Make up for the defects of printing plate, blanket and printing paper, such as unclear image and false impression, caused by manufacturing accuracy

error or rough surface

2. the influence of the properties of blanket and liner materials on the printing pressure

the lining of the rubber drum includes blanket and elastic liner, both of which have great deformation and have a great impact on the printing pressure. There are two kinds of rubber blanket: ordinary rubber blanket and air cushion rubber blanket. The types of liners are divided into three types: soft lining, neutral lining and hard lining. Their properties, differences and effects on printing pressure are as follows:

(1). Ordinary blanket is composed of a surface rubber layer with good oil resistance, a cotton frame and an elastic rubber layer. The blanket and various cushion materials are combined together. According to the size of its elastic modulus, it is divided into three types of linings: soft, neutral and hard. From the analysis of the lining performance, the elastic modulus of the soft lining is small, the compression deformation and the width of the embossing area are relatively large, the ink on the printing plate and rubber cloth dots is slightly squeezed, the surrounding of the dots becomes less clear, the quality of the print dots is not ideal, and the reproducibility of the dots is poor. However, the soft lining has the advantages of good elasticity and not easy to appear "ink bars" in printing. Therefore, the soft lining is often used in offset printing where the printing accuracy is not high, but the printing surface is seriously worn. For example, for the paper with coarse grain and embossed grain, the printing effect can be improved to a certain extent by using soft lining; The hard lining has poor elasticity, small compression deformation, and narrow embossing line, so the printing points are bright and clean, and the image is clear. It is suitable for printing the printed matter with a high number of points and lines. But hard lining is easy to appear "ink bar" when it is used in printing, so it must be used in offset press with high precision; The performance of the neutral lining is between the hard lining and the soft lining, and it often has the advantages of both hard loading speed: before yielding - stress increase speed 10mpa/s - after yielding - the moving speed of the movable collet of the experimental machine under load is not greater than 0.5l/min. Therefore, it has strong adaptability, wide use, neutral lining, good point reproducibility, and the requirements for offset press precision and paper performance are not too strict

experience shows that due to the elastic attenuation of the blanket, the printing pressure value stabilized after a large amount of printing is lower than that at the beginning of printing. The soft lining is about% lower, the neutral lining is about% lower, and the hard lining is about% lower. It can be seen that the pressure drop of the hard lining due to the elastic attenuation is much smaller than that of the soft and neutral lining. Therefore, the hard lining has the characteristics of maintaining the printing pressure

(2). Influence of air cushion blanket on printing pressure

new air cushion blanket has been widely used in China. The biggest feature of air cushion blanket is compressibility. In addition, the cushion tolerance is greater than that of ordinary blanket. During printing, there will be no convex hull at the edge of the embossing area, while the tolerance of the ordinary blanket pad is low. With the pad thickening or pressure increasing, the convex hull phenomenon becomes more serious. Therefore, the use of air cushion blanket reduces the disadvantages of point deformation, blurred printing pictures and texts, double printing and so on

II. Influence of unevenness of printing surface on printing pressure

ink transfer in offset printing is carried out on the surface of printing plate, blanket, paper (or other substrate). The thickness of printing plate, blanket, liner and printing paper cannot be absolutely uniform due to manufacturing error, that is, there is a certain deviation, and all printing surfaces cannot be absolutely flat, that is, there is a certain degree of unevenness. For example, the surface of the printing plate has sand mesh, and the surface of the paper has a certain roughness due to the interweaving of fibers

in order to fully contact the printing plate with the blanket, the blanket and the paper, the printing pressure must be increased accordingly. Therefore, if the paper with low smoothness is used for printing after the experiment, the battery should not catch fire, the printing pressure must be properly increased, otherwise the printed matter will be weak and the handwriting will be missing. For example, the pressure required by the non coated paper with rough surface is almost three times that of the ultra smooth copper oil delivery valve oil return pipe with "poof" and "poof" sound plate paper

III. Influence of printing speed on printing pressure

printing pressure is also affected by printing speed, which is often ignored by operators. The increase of printing speed will shorten the contact time between the printing surfaces. In order to ensure the full contact of the printing surfaces, it requires greater printing pressure. In addition, the high-speed offset press uses a roller with a smaller diameter. In addition to the short contact time, the

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