The most popular problems caused by printing plate

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Faults caused by printing plates and solutions

the most common faults caused by lithographic printing plates are: paste plate and non inking (blind plate). When the non graphic area starts printing ink, there will be a paste phenomenon; When the image and text area cannot be attached with ink, white spots will appear. Paste plate when some parts of the non graphic area in the printing plate begin to be inked, a paste plate phenomenon will occur. "Non graphic" refers not only to a large area of blank area without graphics and text on the printing plate, but also to the blank area between halftone dots. Therefore, when the halftone dots begin to become full of ink, we call it paste. The mechanism of the problem is as follows: in the process of making a printing plate, the non graphic areas should be made where the ink is not sensitive, that is to say, they should be made hydrophilic and ink repellent. This is usually achieved by applying a layer of hydrophilic gum grease, such as Arabic gum. When the printing plate is cleaned, the hydrophilic adhesive layer may gradually fall off, but it will be replaced by the glue grease in the fountain solution. When the replacement cannot be carried out normally due to some reasons, the ink may infiltrate into the non graphic area of the printing plate. As a result, the printing plate is blurred. The composition of ink and paper may also be the cause of the blurring of the printing plate. Prevention of plate pasting: aluminum is a very hydrophilic metal, so in the past, plate making often faced with such problems. But now people use anodized aluminum plates to prepare printing plates. Printing plate blurring is not the main problem, but plate pasting is still one of the problems people encounter. To prevent the generation of plate paste, the printing plate must be properly hydrophilic and lipophilic treated during the process of making the printing plate, and 28 (5) 050063012180 d=6a. At the beginning of printing, it must first contact with water for wetting. If the printing plate is not used for more than one hour, its non graphic area should be protected with hydrophilic coating. If the above treatment is adopted, the printing plate shall also be moistened during printing unless an especially oily ink is used. If the printing plate begins to appear blurred, remedial measures shall be taken immediately. Once the ink is firmly adhered to the non graphic area of the printing plate, it will be very difficult to restore this part to its original state and become hydrophilic and ink repellent. Special hydrophilic dirt remover or retouching agent should be used to treat the printing plate. For the non graphic areas that have been pasted with ink, it needs a large pressure to remove the ink and replace it with hydrophilic glue. The retouching agent should eventually remain on the plate after drying, because the effect of any retouching agent can be better after drying. Such a treatment method is best to be carried out at least twice, and then consider adding a retouching agent to the fountain solution to treat the printing plate. Ink dot paste on aluminum plate: sometimes aluminum plate will produce a special paste phenomenon in lithography, which is called "ink dot paste". This paste consists of thousands of tiny dots. The area between ink dots still has good hydrophilicity. The cause of "ink dot paste plate" is that there are small corroded pits on the aluminum plate. When the product versions of the aluminum printing Jinan assaying mainly include electronic universal testing machine, hydraulic universal testing machine, spring testing machine, pressure testing machine and so on are corroded, many small spots will be generated, and these small spots will eventually become many small pits. When the hydrophilic adhesive layer on the pit is corroded, they will burn the ink and cause a paste. The reason for this phenomenon usually occurs when the printing plate surface is covered with water and the water on it evaporates slowly. On the printing plate facing the water roller, the pasted plate is often distributed in strips. If the "ink dot paste" is not too serious, it can be treated with a solution containing phosphoric acid and Arabic gum grease. White spot (printing plate without inking): if the printing plate cannot print pictures and texts, we call it a blind version. This may be caused by the corrosion of the image and text area of the printing plate, or by the fact that the image and text area is covered with a layer of hydrophilic glue or other hydrophilic substances. If the image and text area is worn away from the printing plate, we can simply call it as the printing plate is worn, and the blind plate is caused by the image and text area wear. Blind plate usually refers to the phenomenon that ink cannot be attached to the graphic area of a printing plate. When the image and text area cannot be attached with ink through the ink roller as before, then the blind version occurs. With the improvement of plate making technology, the phenomenon of blind plate has been greatly reduced, and the service life of printing plate has been correspondingly extended. Abrasion of graphic area: if some parts of the graphic area are worn out, the area will no longer be inkable. The blind plate caused by plate wear is the worst case, because there is little room for remedy. It is usually caused by friction with hard, incorrectly installed rollers; It may also be caused by excessive pressure between the plate cylinder and the rubber cylinder; It may also be caused by frictional particles in ink or paper. Sometimes, the pigment particles on the paper surface are very hard and abrasive. Paper fibers also have a certain degree of abrasiveness. When paper is used for lithography, a large amount of fiber often accumulates on the rubber cylinder. This fiber accumulation (also known as paper fuzzing) causes plate wear, which often leads to the failure of inking in the graphic area. Another cause of wear is the anti rubbing and dirty spraying treatment of paper. Sometimes the substrate will be sprayed with one color first, and then the second color will be printed by the printing machine. At this time, the dry particles of the first color will wear the plates of the second printing press. The expansion of the blanket will cause its thickness to increase, which will cause the pressure between the printing plate and the rubber cylinder to increase. It will eventually lead to plate wear and blind plate phenomenon. Poor adhesion between the graphic area and the metal substrate: sometimes a printing plate starts printing well, but there is no inking during the printing process. One of the reasons for this is that the image and text area is not firmly bonded to the metal substrate. The coating layer hardened by light irradiation must be firmly bonded with the metal substrate; If painting is used, the painted base course must be firmly combined with the coating layer; Ink must be combined with painting. If the physical and chemical properties of viscose are not good, it will also cause the graphic area to be partially unable to ink. Sometimes the printer must make a new plate and make some changes in the production process or the use of raw materials to prevent the same problem from happening again. The literal part of the image and text area is hydrophilic: during the development process of the printing plate, the offset printing plate shall be treated with a water-soluble glue. In this water-soluble solution, Arabic gum or other hydrophilic gum lipids are often used. Hydrophilic glue sometimes attaches to the image and text area of the printing plate. In this case, this part of the graphic area will be attached with water instead of ink. As a result, the graphic part of the printing plate cannot be inked, that is, the image of this part cannot be printed. In the printing process, there are many situations that will cause hydrophilic glue to adhere to the graphic part and cause the printing plate to be unable to ink. These situations include: · the ink layer is too thin when printing. If the ink layer is too thin, the hydrophilic glue will easily penetrate the ink layer and combine with the following substances. If you want to lighten the printing color, you'd better add a transparent thickened layer on the ink layer, so that the ink layer can be thickened during printing· There is too much moisture in the ink. If the ink contains too much water, the ink in the graphic area of the printing plate is easily replaced by hydrophilic glue· The fountain solution contains too much hydrophilic glue. The more hydrophilic glue in the wetting solution, the easier it is to emulsify in the ink. This makes it easier for hydrophilic glue to stick to the image and text area of the printing plate· The fountain solution contains too many acids. Acid makes the hydrophilic glue more hydrophilic, so it is easier to adhere to the printing plate once the opportunity arises. There is another reason that the image and text area of the printing plate can not be inked, that is the drying problem of the printing plate ink. If the ink dries on the printing plate, this part of the printing plate is usually not easy to re ink when printing again. Therefore, when the printing plate needs to be stored overnight or temporarily, it is best to wipe it with a treatment agent before turning off the printing machine. Ink solvent and plate cleaner: the coating layer and coating layer on most printing plates that harden when exposed to light are highly resistant to printing ink or plate cleaner. Never use a plate cleaner on a positive precoated photosensitive plate that has not been treated with a baking plate. If these plates have been exposed to alkaline plate cleaner, it may attack the graphic part of the plate, causing a blind version. The photosensitive substances in UV ink have polarity and are most likely to erode the coating layer of some printing plates. Therefore, UV ink cannot be used in diazo precoated plates and instant coated photosensitive plates, while UV ink is better for many photosensitive resin plates

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