The cause and treatment of greasy PS edition

2022-07-18
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Causes and treatment methods of greasy PS plate

according to the principle of offset printing, the graphics and text on the PS plate are lipophilic and the non graphics and text are hydrophilic. In order to obtain good printing quality, it is necessary to ensure that the graphic part is not hydrophilic, and the non graphic part is not greasy. To achieve the above purpose, we must use acids and salts to prepare the fountain solution. The acidic substances in the fountain solution react with the aluminum plate to form a hydrophilic salt layer on the surface of the plate. It has good hydrophilic and oil repellent ability to ensure the cleanness of the non graphic parts, and the greasiness on the PS plate is caused by the destruction of the inorganic salt layer of the non graphic parts of the printing plate, Or the hydrophilic colloid generated by the fountain solution itself is slow to generate, so that the non graphic part cannot supplement the inorganic salt layer in time, resulting in the lipophilic phenomenon of the non graphic part. According to the previous experience in printing practice, there are several reasons for greasiness in the non graphic part of PS version

1. The acidity of the fountain solution is too strong or too weak. Weak acidity, slow formation of hydrophilic salt layer and poor fat removal ability; Acid is too strong, the plate sand corrosion, make the plate shiny; It will cause version loss and aggravate the emulsification of ink, which will affect the service life of PS version. To control the acidity and alkalinity of the fountain solution, a pH test paper can be used for testing. Under normal circumstances, magenta ink is 4, yellow ink is 5, green and black are about 5, and the overall control is appropriate at 4 ~ 6. When printing on the spot and the ink layer is thick, the pH value of the fountain solution is smaller. On the contrary, when the ink layer of line printing is thin, the pH value of the fountain solution should be larger

2. The pressure of the landing roll is improperly adjusted. It is also an important factor for the smooth progress of the experiment and the accuracy of the experimental results. When the pressure of the water roller and the water roller is adjusted too heavily, there will be two situations. In addition, there are many equipment that we need to inspect and pay attention to. First, the water flannel on the water roller will be squeezed and lose its elasticity. Second, the water roller will be squeezed in the front part of the contact between the water roller and the water roller when rotating, In fact, the plate can not get the proper water distribution, resulting in grease sensing. Therefore, when correcting the pressure between the water roller and the water roller, it should not be too tight. If the 0.8mm steel sheet can be inserted and gently pulled out, it can be adjusted properly. The watermark can also be tested by pressing the water roller on the page. After the water roller is filled with enough water, press the watermark against the page. The width of the watermark should be about 5mm, and the pressure at both ends and the middle must be consistent

3. Aging and improper adjustment of inking roller. The inking roller with good quality should have good elasticity, oil resistance, heat resistance and acid and alkali resistance, so as to ensure the quality of printed matter. At present, most printing enterprises use a high efficiency rubber roller that can preheat the wire core and dry the cable core. When the synthetic resin and acid of the ink are immersed, the surface will be hard and shiny, affecting the elasticity and ink transfer performance. The ink on the hard and shiny inking roller is easy to produce ink emulsification. The viscosity of the emulsified ink is reduced, and the necessary adhesion between molecules is lacking. When the ink roller rolls on the printing plate surface, The ink lacking adhesive force is easy to enter the sand of the printing plate, and gradually causes the hydrophilic inorganic salt layer to be lipophilic and lipophilic, resulting in the greasy phenomenon of the printing plate. The treatment methods are generally as follows: ① grind the ink roller. The ink roller after grinding has a large amount of ink, has a good ink transfer and receiving effect, full points, clear layers, and the non graphic parts can be kept clean, which can effectively prevent greasy; ② Always keep the ink roller clean; ③ If the pressure of the inking roller and the inking roller plate is not adjusted properly, the pressure at both ends of the inking roller must be kept basically the same during adjustment, which is the key factor to prevent greasiness

4. The pressure between the plate cylinder and the rubber cylinder is too high. Under the ideal pressure state, the pressure between the printing cylinder and the rubber cylinder is about 0.1mm, but most machines can not meet this requirement, which is above the ideal pressure. At the same time, due to the paper structure, inconsistent surface roughness and uneven thickness, in order to keep the point solid and the normal transmission of point marks, pads are often added under the rubber blanket during the operation process, sometimes because the size of the print is large, The left bite is small, so it is possible to borrow the bite, which will increase the pressure between the rubber cylinder and the printing plate cylinder and damage the hydrophilic layer on the surface of the PS plate, resulting in greasy and lipophilic phenomenon. In view of this situation, it is necessary to correctly master the pressure between the printing plate cylinder and the rubber cylinder. Rough paper should be solved by adjusting the center distance between the rubber cylinder and the plate cylinder. If the bite is uneven, the rubber cylinder should be borrowed from the bite as much as possible. However, it must be noted that if the blanket and liner on the bite are pressed down, the above measures still fail to print pictures and texts. If a batch of key strategic materials such as special alloys and high-performance fibers for high-end equipment are conquered, the blanket and liner should be replaced, Or it can be solved by transferring the rubber blanket

5. The ink is too thin or oily; Sometimes in the process of operation, the surface structure of the paper is not tight, and it is easy to lose hair and powder when peeling with the rubber drum. In order to eliminate such failures, during operation, too much ink blending oil and adhesive are often added to the ink, which destroys the transfer conditions of the ink layer, greatly reduces the viscosity of the ink, increases the oiliness, reduces the ink adsorption performance of the ink roller, makes the remaining ink layer of the PS plate insufficient, and the image and text parts are dirty due to the exposed thickness and wear. Therefore, if the ink is too thin, you can replace it with a new ink, or add an appropriate amount of thick ink blending oil to increase its viscosity. At the same time, you should also increase the acidity of the fountain solution and increase the Arabic resin glue. For the old PS version, you can wipe the greasy with liquid medicine, dip a clean wiping cloth with copper sulfate, and the copper sulfate reacts with the PS version to produce a new hydrophilic layer, which has a certain effect on preventing greasy

to sum up, the reasons for greasy PS pages are nothing more than the above. Here are some experiences on how to reduce greasy PS pages

1. Pay attention to product quality ideologically. At the same time, do a good job in machine maintenance and repair, and solve problems in a timely manner. Only by ensuring the normal operation of the machine can it be of high quality, high efficiency and low loss

2. Strengthen the protection of PS plate, properly adjust the pressure between water roller and PS plate, and try to reduce axial movement. When they are not in contact with the PS plate, their circumferential rotation is flexible. At the same time, appropriate lining should be selected according to the actual situation. Frequent speed change should be avoided during printing. It is required that the surface linear speed of the embossing area should be consistent; Prevent the PS version from friction and damage the point foundation. In case of shutdown for more than 3 minutes in summer and 5 minutes in winter, PS version shall be protected with protective glue

3. Select PS version with stable performance and high quality; At the same time, the printing process should be improved. In the printing process, the effects of developer temperature, concentration and pH value should be comprehensively considered, carefully adjusted and operated

4. Control the acidity and alkalinity of the fountain solution and the balance of water and ink, watch the water frequently and master the pH value of the fountain solution

5. For the preparation and recording of ink, the auxiliary agent shall be used as little as possible, and the original records shall be made

(text/liutiefu)

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