The basic principle of the lithographic process is to use the law of the mutual dissolution of oil and water. Therefore, the layout of the graphic and text are almost on the same plane. To achieve normal printing, the balance control of water and ink is an important cup. Due to operational technology, equipment and other reasons, print quality failures caused by poor dampening have occurred. This article analyzes and discusses some fault phenomena in the daily production process.
1. Water bar marks and their causes
The so-called water streak refers to the one or several strips printed in the horizontal direction when printing a textured or solid version product, the position of which is uncertain or fixed, and the white marks are equal or unequal in pitch. . The main causes are:
1. When there is wear on the shaft head or bearing of the water roller, the water roller will inevitably jump or slide during the rolling process and cause the water bar failure. This should be repaired to the worn shaft head or damaged bearing, so that The shaft head or damaged bearing of the water roller is repaired so that the water roller keeps rolling evenly and contacts the printing plate evenly.
2. Water bar caused by uncomfortable pressure between water roller and printing plate. When the contact pressure between the water roller and the printing plate is too light, and the water roller and the printing plate have poor contact, it is not only easy to make the plate surface dirty, but also easy to cause water bar phenomenon, so the water roller and the printing plate should be adjusted Pressure to keep them in even contact.
3. When the contact pressure between the water roll and the water roll is too large, the water transfer or uneven rolling of the water roll will inevitably occur due to the squeeze, and the water bar phenomenon is also easy to occur. Contact pressure.
4. When the surface ink of the water roller is strong, it will also affect the normal and uniform transmission of the fountain solution, and it is easy to introduce the water bar phenomenon, so the water roller should be cleaned to maintain the uniform water transmission and prevent the water bar The phenomenon occurs.
5. If the PH value of the fountain solution is too large, water bars are likely to be generated. The PH value should be adjusted to reduce the acidity.
2. Dirty version, paste version, flower version phenomenon and its causes
1. Dirty version. The contact pressure between the inking roller and the printing plate is too low, which makes the water transfer unsmooth and uneven. The large water on the plate surface causes the dirty plate. The contact pressure between them should be adjusted; the pressure between the inking roller and the water roller is too tight. The fountain solution will be squeezed and stay on the water roller and the water roller, so that the water supply is abnormal and causes the dirty version. The pressure between them should be adjusted; when the water jacket is installed, there is no uniformity at both ends and in the middle Stitching after flattening and tightening, resulting in uneven thickness affects the normal dampening; the water fleece cover is very frayed, the water absorption and water transfer performance are poor, and the abnormal water supply is also the source of the dirty version. The thickness is uniform, and the worn fleece cover should be replaced in time; the proper contact pressure between the water transfer roller, the water bucket roller and the water string roller to ensure the normal water supply to prevent the dirty version. [next]
2. Paste. The pressure between the water roller and the printing plate is too small or too large; the pressure between the water roller and the water roller is uncomfortable, which will cause paste plates due to insufficient water delivery and unevenness. The appropriate pressure between them should be adjusted; the water bucket roller Oil stain on the surface affects normal water transfer and pastes. Scrub the water bucket roller; the pressure between the water transfer roller and the water bucket roller and the water cross roller is too small, so that the fountain solution cannot be transmitted, and the paste version should be adjusted. Good pressure between them. In addition, the fleece sleeve of the water roller is worn badly and the angle of the water bucket roller is small or the rotation speed is too slow, etc., and it will also cause lay-up due to insufficient water supply.
3. Flower version. The pressure between the water roller and the printing plate is too large, which aggravates the friction damage to the mask layer of the plate and causes the flower plate. For this, the pressure should be adjusted; the supply of the plate fountain solution is too large, which causes the flower plate. Angle or reduce the rotation speed of the water bucket roller to prevent the pattern; the acidity of the fountain solution will damage the surface of the printing plate and cause the failure of the pattern. The concentration of fresh water should be washed to reduce its PH value. The PH value of the general PS version is preferably between 5 and 5.5.
3. Failure phenomenon of water roller and its treatment
1. The water roller cannot be closed.
The position of the screw on the clutch swing frame is not suitable, and the screw position should be adjusted; the lack of oil and expansion of the rotating shaft and the abnormal working state of the spring make the water roller unable to press, and check the part that has a problem and deal with it accordingly; The sliding key in the shaft is stuck, the manual closing cannot be pressed, and the lock lever cannot be pushed in. The position of the sliding key should be checked and adjusted; the damage of the connecting rod component causes the water roller to press on the water, and the damaged part should be repaired.
2. The water roller does not fill the water. The position of the water roller is not suitable, and the contact position between the water roller and the printing plate should be adjusted; the bearings at both ends of the water roller head are damaged, and new bearings should be replaced; the aging of the water roller fleece and the adhesion of ink dye affect water absorption, For water transmission performance, a new water wool cover should be replaced or the dirty water roller should be cleaned.
3. The water transfer of the water transfer roller is uneven. If the roller bearing is damaged and the rotation is uneven or stuck, a new bearing should be replaced; the contact position of the water transfer shaft with the bucket roller and the water string roller is unsuitable, and the contact position between them should be adjusted; Adjust the amount of string movement; when the fleece cover is dirty or worn and aging exists, it should be cleaned or replaced to avoid the phenomenon of water transmission.
In summary, there are many kinds of quality failures caused by poor dampening system. As long as you are good at analyzing and researching carefully and carefully observing the characteristics of the failure phenomenon, you can quickly and accurately eliminate the failure phenomenon caused by various reasons. Ensure product printing quality.
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