Analysis of the causes of dirty goods
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Quality is the lifeblood of the survival and development of an enterprise. In the actual operation process, a slight inattention will cause the printed matter to be dirty and directly affect the quality of the printed product. In the following, I will summarize in the long-term practice to eliminate these faults in a timely and accurate manner.
1. Water spots. According to the principle of oil-water incompatibility, if there is water droplets on the paper, a water spot will be left on the printed product. Cause analysis:
(1) If the air pump is in a high temperature and humidity environment, the offset printing machine is placed in the air conditioning workshop, and the moisture in the humid air is condensed into the cool environment by the air pump, and the salt water droplets are condensed through the presser foot and the paper separation nozzle. Blow on the paper.
(2) The water buckets of many offset presses are made of iron or copper-plated iron. Due to the corrosive nature of the acidic wetting fluid, the water bucket will gradually corrode to form blisters, and some sand holes are small. You can only drop two or three drops of water in one minute, so that there will be water spots that are sometimes absent on the printed product. Therefore, the operator is required to carefully check the water bucket against the light and find that the sand hole is soldered firmly.
(3) Some offset printing machines are not well maintained, the operator never cleans the water bucket, and when the ink roller is cleaned, the ink on the ink roller is splashed with the cleaning agent, and is sucked into the water bucket with the water roller. The fluff forms scale together, and accumulates between the bucket roller and the bucket wall as the bucket roller rotates, forming a hard slag over time. When the water roller rotates, the hard slag will drip down the water bucket wall with the water on the water bucket roller, forming a water spot on the printed product.
(4) When the printing plate needs emergency water supply due to the small paste of water, the water roller will transfer a large amount of water to the water transfer roller, and the excess water is transferred during the transfer and extrusion process of the water transfer roller. It will drip down. There is a water retaining plate under the water bucket of the J2108 machine. The effect is very good, but it is necessary to avoid dripping the water too much. The J4104 and other models do not have a water retaining plate, so it is necessary to stop when it is urgently launched.
2. Oil spots. Since the viscosity of the oil is much lower than the viscosity of the ink, the oil droplets will expand on the surface of the blanket after being pressed, and the ink will have a reverse impression, and a round oil spot will be formed on the crystal. Cause analysis:
(1) Lubrication of the paper feed head is important and necessary. When refueling, add less rubbing. After refueling, start the machine and the paper feeder, let the oil drip down during the movement, and then wipe it to ensure that there will be no excess oil on the paper during normal printing.
(2) Focus on checking the air pump. If the air pump is injecting oil, the presser foot and the paper-blowing nozzle will blow out a lot of oil-like oil beads splashing on the tip of the paper. Touch the fuel filler cap on the oil pump chamber (with a small hole on it) to check if there is any The gas is ejected. If not, it means that the oil pump is not good.
(3) The transmission rod and bevel gear on the lower part of the pull gauge also need to be lubricated. Of course, you can only add a little or apply a little butter on it. If there is too much oil, the pull gauge will stain the paper during the paper pulling process.
(4) The dentition shaft and the spring rod on the transfer paper frequently move. If the lubrication effect is not good, it is easy to cause abrasion, causing poor crepe paper and inaccurate overprinting. Therefore, be careful when adding lubricating oil, wipe it with oiling, transport it, and then wipe it with a rag after a while. Many operators often do not add to the paper because they are afraid that the oil will contaminate the paper, causing the spring rod and pin to wear.
(5) During the refueling process, the transfer roller and the delivery guide are easy to stick to the oil, so pay special attention when refueling, and always check the cleaning if necessary.
3. Phoenix eye spots, spots or white spots. If there is a bit of stain on the plate, it will leave a wind-eye spot on the crystal. If the blanket is a little stained, it will leave a spot or white spot on the crystal. Cause analysis:
(1) Paper with poor surface strength is prone to powder removal when it comes into contact with water and ink. Pulling, sticking to a blanket or plate.
(2) When taking ink from the ink tank, the dry ink and ink residue should be removed because of the ink. Once the ink residue falls into the ink fountain, it will pass to the printing plate when the ink is transferred.
(3) There are a lot of fluff on the water roller, and when printing the solid version, it is easy to leave burr-like and silky marks on the printed product. There is now a nylon water soft lint that is not easy to shed, and if it is wrapped on a water roller, the effect will be good. Sometimes, a water roller is used in several colors, and the top is covered with ink residue. During the water transfer process, the ink residue is transferred to the printing plate.
(4) The cleaning and maintenance of the rubber roller is very important. Some operators do not pay attention to this work, and do not pick it up one by one for cleaning. The rubber roller is subjected to high temperature friction as well as ink. Corrosion of the solvent forms cracks, especially at both ends of the rubber roller. The ink residue falling from the cracked rubber roller during printing adheres to the printing plate and is difficult to clean.
(5) To spray the printed product for anti-sticking, considering that some paper has more paper powder, the powder on the paper is printed during printing. The paper powder adheres to the blanket as the paper is embossed and then transfers to the printing plate. Therefore, the powder should be arranged in the last color as much as possible. If it is necessary to spray the powder, pay attention to the amount of powder. The smaller the better, the less the dirt should be. If necessary, you can print it again.
4, powder group. The powder splashed on the print, and the print appeared a mass of powder because the ink was not completely dried. Cause analysis:
(1) If the machine that needs to be dusted is not cleaned and maintained for a long time, paper suction bracket and chain. The platen fan will be covered with powder. As the machine shakes or the platen fan rotates during printing, the powder falls on the newly printed print.
(2) When the powder is sprayed, if the heating switch is not turned on, the dry powder will be condensed into a block in a humid environment. Some machines have a powder spray valve installed in the hood (such as the J4104 machine). When the hood is automatically refueled, the oil will drip on the powder spray valve to form sludge with the powder in the valve. These powder blocks and sludge are blown off by the blowing pipe to leave a powder on the printed product, so the passage of the powder must be kept in a clean and dry environment.
5. The printed matter is dirty due to human factors such as improper operation. Cause analysis:
(1) In order to improve the quality of printed products, the paper must be flat, crisp and easy to separate. So the operator needs to tap on the paper. After printing a large area full of dark solids (such as red, purple), the paper is easy to curl down, and these curled paper can not be transported properly, so be careful when handling these papers. If you hit it too hard, it will inevitably cause creases in the paper, and white streaks will appear in the creases. The correct way is to simply press up one by one to make the paper's mouth and tail flat.
(2) The operator often needs to take a printed copy of the printed product to the sample stand to detect the color registration. For some full-size, large-area prints, take less care, otherwise it will easily cause the print to be dirty. Because the amount of ink in these prints is large, it will curl down on the delivery table, it is not easy to take samples from the machine, and the speed is fast, so be careful not to scratch the prints.
(3) After the product is printed, wait a little while to wake up or unload the material to prevent the printed product from being dirty when the paper is handed.
6. Dirty. In the process of paper feeding, imprinting and delivery, scratches and scratches may occur on printed products. Bruises. Cause analysis:
(1) The paper feed roller on the paper feed roller presses the paper after the paper feed nozzle blows. If the ink is not thousands, it will leave two spots on the paper. For example, if the J2108 machine has a large take-up roller stroke and the control cam is steep, it will leave two spots on the paper because the pick-up roller is pressed and pressed.
(2) When the paper passes through the paper feeding table, the paper pick-up wheel and the paper-feeding wheel. The brush wheel, the paper ball, etc. will drag the ink out two or three inks, especially when the paper transfer paper is accelerated, the brush wheel and the paper ball are easy to drag out.
(3) The pull gauge of J2108 and J4104 machines has a roller which is a twisting roller. When printing on both sides, especially when printing dark ink on the reverse side, it will "snap" a few "dental marks". Therefore, when opening the material, try to leave a little white edge to pull the paper to the pull gauge. Also pay attention to the direction of the mouth when printing, and put the light color (such as light yellow, light cyan, etc.) on the pull gauge. Therefore, we must fully consider the shortcomings of this aspect of domestically produced pull gauges.
(4) When the paper is delivered by the transfer paper, because the printing quantity is more than 350g/m2, the paper is easy to scratch when it is returned to the front, such as J2108, J4104 machine. When the paper feed roller delivers paper, because the hem angle of the hem is not large, it is easy to scratch the back of the printed product, causing the reverse side to be dirty, such as the PZ2660 machine.
(5) The transfer roller of the multi-color machine is wrapped on the roller during the paper transfer process. Due to insufficient cleaning and maintenance of the machine, residual ink on the drum will leave traces on the print, so the large-area printed layout should be placed in the last color to avoid dirty on the transfer cylinder.
(6) After the impression is imprinted by the impression cylinder, the printed matter is caught by the delivery paper and conveyed by the paper-feeding roller to the delivery table. Since there is no anti-mite cloth on the domestic paper-turning wheel, the trace will be dragged on the printed product. This mark is mainly at the tip of the paper, so the paper-turning wheel should be adjusted reasonably according to the specific situation. If you print a trademark, you should consciously leave two blanks at the stitching of the trademark; if you print the instructions, adjust the paper-turning wheel at the spine; if you print a painting, do not put the paper-turning wheel in the same color block, but Place it in a colorful place, even if there is a scratch.
(7) The diameter of the drum of J2104, PZ2660, etc. is small. When printing paper with a basis weight of 200g/m2 or more (WH47-NP is printed with a paper weight of 105g/m2 or more), since the paper has a certain degree of stiffness, it is not Will be wrapped in the surface of the drum, in the process of movement, subject to the shadow of the centrifugal force, wrapped in the bar, the impression shaft, according to the specific circumstances, the distribution and installation of the paper guide rod, or on the bar or the impression shaft Wrap the sponge and other wraps to hold the paper and not scratch it.
(8) Printing a large area of dark color. When the spot color ink is used, if the slow paper suction is too large. If the teeth are opened too early, the paper will fall prematurely, and a printed product will rub, causing scratches on the printed matter. In addition, due to the various types of dirty caused by the quality of the PS version, there have been many articles introduced, and will not be analyzed here.