Cause analysis of the most popular prints with dir

Analysis on the causes of dirty prints

quality is the lifeblood of enterprise survival and development. In the actual operation process, a little attention will cause dirty prints, which will directly affect the quality of prints. Below, I will summarize from long-term practice that these faults can be eliminated in time and accurately

1. water spots. According to the principle of oil-water incompatibility, if there are water drops on the paper, a water spot will be left on the print. Cause analysis:

(1) if the air pump is in a high temperature and humidity environment, and the offset press is placed in the air conditioning workshop, the moisture in the humid air will be blown to the cool environment through the air pump, which will condense salty water droplets, which will be blown to the paper through the presser foot and the separation blowing nozzle

(2) the bucket of many offset printing machines is made of iron sheet or copper plated iron sheet. Because the acidic wetting liquid is corrosive, over time, the bucket will be gradually corroded to form sand holes. Some sand holes are very small, and only twoorthree drops of water can be dropped a minute. In this way, water spots that sometimes do not appear on the print will appear. Therefore, the operator needs to carefully check the water bucket against the light, and solder it firmly with tin if sand holes are found

(3) the maintenance of some offset printing machines is not perfect, and the operators never clean the water bucket. In addition, when cleaning the ink roller, the ink on the ink roller splashes everywhere with the cleaning agent, and the ink thrown into the water bucket forms scale together with the fluff of the water roller. With the rotation of the water bucket roller, it accumulates between the water bucket roller and the water bucket wall, and over time, it forms hard slag. When the bucket roll rotates, the hard slag will drip down the bucket wall from time to time with the water on the bucket roll, forming water spots on the print

(4) when the printing plate needs to be urgently watered due to small water paste, the water bucket roller will transfer a large amount of water to the water transfer roller, and the excess water will drip down during the transmission and extrusion process of the water transfer roller A water baffle is installed under the water bucket of J2108 machine, which has a good effect, but it is necessary to avoid dripping down due to too much water. J4104 and other models do not have water deflectors, so it is enough to fill the water in an emergency

2. Oil spots. Since the viscosity of the engine oil is much lower than that 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, forming circular oil spots on the printing crystal. Cause analysis:

(1) the lubrication of the paper feeding head is important and necessary. When refuelling, you should wipe less frequently. After refuelling, start the machine and the paper feeder to let the oil drip down during movement, and then wipe it again to ensure that there will be no excess oil dripping on the paper during normal printing

(2) focus on checking the air pump. If the air pump injects oil, the presser foot and the paper separation nozzle will blow out many oil droplets in the form of oil mist, splashing on the paper trailing tip. Touch the oil filler cap on the oil chamber of the air pump with your hand (there is a small hole on it) to check whether there is gas ejected. If not, the oil return effect of the air pump is not good

(3) the transmission rod and umbrella gear at the lower part of the pull gauge also need to be lubricated, of course, only a little less or a little butter on it. If you refuel too much, the gauge will stick to the paper during the paper pulling process

(4) the gripper shaft and spring rod on the paper delivery tooth move frequently. If the lubrication effect is not good, it is easy to cause wear and tear, resulting in poor gripper and inaccurate overprint. Therefore, be very careful when adding lubricating oil. Wipe it while adding oil, transport it, and then wipe it with a rag after running for a period of time. Many operators often do not add oil because they are afraid that oil will pollute the paper. 2. How to prevent the error of the electronic tensile testing machine, resulting in the wear of the spring rod and pin

(5) in the process of refueling, the paper transfer roller and the paper receiving guide rod are easy to stick with oil, so pay special attention to refueling, and often check and clean if necessary

3. Crested spots, color spots or white spots. If there is a dot on the printing plate, it will leave eye like spots on the printing crystal. If there is a dot on the blanket, it will leave Bian dot like color spots or white spots on the printing crystal. Cause analysis:

(1) when the paper with poor surface strength is in contact with water and ink, it is easy to produce powdering and galling, and adhere to the blanket or printing plate

(2) when taking ink from the ink tank, remove the dried ink cover and ink residue, because the ink cover. Once the ink residue falls into the ink bucket, it will be transferred to the printing plate when the ink is transferred

(3) there are many fluff on the water roller fluff. When printing the field version, it is easy to leave burr like and filiform marks on the print. Now there is a kind of nylon water glue wool that is not easy to fall off. If it is wrapped on the water roller, the effect will be very good. Sometimes, a water roller is used in several colors, and the ink residue has been stuck on it. During the water transfer process, the ink residue will be transferred to the printing plate

(4) the cleaning and maintenance of COTS is very important, but some operators do not pay attention to this work and do not take it off one by one for cleaning, resulting in high-temperature friction and ink on cots. The corrosion of the solvent causes cracking, especially at both ends of the rubber roller. When printing, the ink residue from the cracked rubber roller sticks to the printing plate, which is difficult to clean

(5) in order to prevent sticking and dirt, the printed matter is sprayed with powder. Considering that some papers have more paper powder, the paper is sprayed with powder during printing. The paper powder will adhere to the blanket as the paper is imprinted, and then transfer to the printing plate. Therefore, we should try to arrange the powder spraying in the last color. If it is necessary to spray powder, we should also pay attention to the size of the powder spraying amount. On the premise of not sticking and dirty, the smaller the better. If necessary, we can empty print it again

4. Dough. Spray powder splashed on the print, because the ink was not completely dry and made the print appear a lot of powder. Cause analysis:

(1) if the machine requiring powder spraying cannot be cleaned and maintained for a long time, the paper suction support, chain and paper pressing fan will be full of powder. During printing, due to the shaking of the machine or the rotation of the paper pressing fan, the powder will fall on the newly printed products

(2) when spraying powder, if the heating switch is not turned on, the powder that cannot be dried will condense into blocks in a humid environment. The powder spraying valve of some machines is installed in the hood (such as J4104 machine). When the hood is filled automatically, oil will drip on the powder spraying valve and form sludge with the powder in the valve. These powder blocks and oil sludge are blown down by the blowing pipe, leaving powder balls on the prints, so the channel of powder spraying must be kept in a clean and dry environment

5. Dirty printing caused by improper operation. Cause analysis:

(1) in order to improve the printing quality, the paper must be flat, crisp and easy to separate. Therefore, the operator needs to knock the paper. After printing some large-area full-size dark fields (such as bright red and purple), the paper is easy to curl downward, and these curled papers cannot be transported normally, so you should be particularly careful when handling these papers. If you knock too hard, the paper will inevitably have creases, and white stripes will appear where there are creases. The correct method is to gently press upward to make the mouth and trailing tip of the paper flat

(2) operators often need to take a stack of newly printed prints to the sample viewing table to detect the color registration. For some full-size, large-area prints should be handled with less care, otherwise it is easy to cause the prints to be sticky and dirty. Because these prints have a large amount of ink, they will curl down on the paper receiving table, so it is not easy to sample sheets from the machine. In addition, the machine speed is fast, so be careful not to scratch the prints

(3) after the product is printed, wait a moment before waking up or blanking, so as to prevent the printing from being sticky and dirty when moving the paper by hand

6. Rub dirty. During the process of paper feeding, stamping and receiving, the printed matter will be scratched and scratched. Throw injury. Cause analysis:

(1) the paper receiving wheel on the paper receiving roller is pressed down after the paper delivery suction nozzle blows air. It adopts the key mode to receive the paper. If the ink is not thousands, two color spots will be left on the paper. For example, the paper receiving wheel of J2108 machine has a large stroke and the control cam is steep. Because the paper receiving wheel is pressed down quickly and heavily, two spots will be left on the paper

(2) when the paper passes through the paper feeding table, the paper receiving wheel, paper pressing wheel, brush wheel, Paperweight ball, etc. will drag out twoorthree traces of ink, especially when the paper delivery teeth accelerate the delivery of paper, the brush wheel and Paperweight ball are easy to drag out traces

(3) one roller of the pull gauge of J2108 and J4104 machines is a fried dough twist roller. When printing on both sides, especially when printing dark ink on the opposite side, several "tooth marks" will be "caught". Therefore, when cutting, try to leave a little white edge for the drawing gauge to draw the paper. Also, pay attention to the direction of its mouth when printing, and put light color (such as light yellow, light cyan, etc.) ink on the drawing gauge. Therefore, we should fully consider the defects of domestic pull rules

(4) when the paper is delivered by the paper delivery teeth, due to the relatively crisp paper with a printing quantity of more than 350g/m2, the paper is easy to be scratched when the swing up front gauge returns, such as J2108, J4104 machines, etc. When the paper is delivered by the paper delivery roller, due to the small swing angle of the front rule of the hem, it is easy to scratch on the back of the print, resulting in dirty scratch on the back, such as pz2660 machine

(5) the printing surface of the drum in the paper transfer of the multi-color machine is wrapped on the drum during the paper transfer process. Due to the insufficient cleaning and maintenance of the machine, the residual ink on the drum will leave filiform traces on the prints, so the layout with large area of imprinting is best placed in the last color for printing to avoid getting dirty on the paper transfer drum

(6) after being imprinted by the imprinting cylinder, the printed matter is held by the paper receiving tooth and transported to the paper receiving table by the paper turnover wheel. Because there is no anti friction cloth on the domestic paper turnover FM - the total average friction wheel during the experiment will drag marks on the printed matter, which are mainly on the paper trailing tip, so the paper turnover wheel should be adjusted reasonably according to the specific situation. If the trademark is printed, two gaps should be consciously left at the trademark splicing; If printing instructions, adjust the paper turning wheel at the spine; If you print a picture, don't put the paper turning wheel at the same color block, but place it at the place with bright colors, even if there is a scratch, it is not obvious

(7) the roller diameter of j2104, pz2660 machines, etc. is small. When printing paper with a weight of more than 200g/m2 (wh47-np printing paper with a weight of more than 105g/m2), because the paper has a certain stiffness, it will not be smoothly wrapped on the surface of the roller. In the process of movement, the shadow n direction of centrifugal force is wrapped on the bar and embossing shaft, and the paper guide rod is reasonably distributed and installed according to the specific situation, Or pad Shanghai cotton and other packages on the bar or embossing shaft to hold the paper so that it will not be thrown out and scratched

(8) when printing large areas of dark and spot color ink, if the slow paper absorbs too much air. If the teeth are opened too early, the paper will fall too early, and a print will be rubbed, causing the print to be scratched. In addition, there are many articles about various kinds of dirt caused by the quality of PS version, which will not be analyzed here

source: Asia Pacific printing Author: zhangfangming