Quality is the lifeblood of an enterprise's survival and development. In the actual operation process, a little carelessness will cause the printed product to become dirty, which directly affects the quality of the printed product. The following I will summarize in a long-term practice that these problems can be eliminated in time and accurately.
1. Water spot. According to the principle of oil-water incompatibility, if there are 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, and the offset press is placed in the air conditioning workshop, the moisture in the humid air is blown into the cool environment by the air pump and it will condense the salt water droplets, through the presser foot, and the paper blowing nozzle Blow onto the paper.
(2) The water bucket of many offset presses is made of iron sheet or copper-plated iron sheet. Due to the corrosiveness of the acidic wetting fluid, the water bucket will be gradually corroded to form trachoma, and some of the sand holes are very small. Only one or two drops of water can be dripped in one minute. In this way, water spots sometimes appear on printed products. Therefore, the operator is required to carefully inspect the water bucket against the light and find that the sand holes are soldered with tin.
(3) Some offset presses are not well maintained. The operator never cleans the water hopper. When the ink roller is cleaned, the ink on the ink roller splashes with the cleaning agent, and the ink roller is thrown into the water hopper. The fluff together forms scale, which accumulates between the bucket roller and the bucket wall as the bucket roller rotates, and over time, forms hard slag. When the bucket roller rotates, the hard slag will carry the water on the bucket roller and drip down the bucket wall from time to time, forming water spots on the printed product.
(4) When the printing plate needs to be watered urgently due to the small water paste version, the water bucket roller will transfer a large amount of water to the water transfer roller. During the transfer and extrusion process of the water transfer roller, the water transfer roller has excess water It will drip down. 1. A water baffle is installed under the water hopper of the J2108 machine, which works well, but it should avoid dripping due to too much water. And J4104 and other models do not have a water baffle, so it is necessary to stop when emergency watering.
2. Oil spots. Because the viscosity of the engine oil is much lower than the viscosity of the ink, the oil droplets will spread on the surface of the blanket after being pressed, and make the ink produce a reverse impression, forming a circular oil spot on the printed crystal. Cause analysis:
(1) The lubrication of the paper feed head is important and necessary. When refueling, you need to wipe less frequently. After refueling, start the machine and the paper conveyor to let the oil drip during the movement. Wipe it again to ensure that no extra oil will drip on the paper during normal printing.
(2) Focus on checking the air pump. If the air pump sprays oil, the presser foot and the separation nozzle will blow a lot of oil mist-like oil beads splashed on the trailing edge of the paper. Touch the refueling cap (there is a small hole) on the air pump oil chamber with your hand to check whether there is The gas spewed out. If not, the oil return effect of the air pump is not good.
(3) The transmission rod and bevel gear at the lower part of the pull gauge also need to be lubricated with oil. Of course, only a little less or a little butter should be added on it. If too much oil is added, the pull gauge will stick to the paper during the pulling process.
(4) The gripper shaft and the support spring rod on the delivery tooth move frequently. If the lubrication effect is not good, it is easy to cause abrasion, resulting in poor gripper and overprinting. Therefore, be very careful when adding lubricating oil. Wipe while lubricating, transport, and wipe with a rag after a while. However, many operators often do not add oil because they are afraid of contaminating the paper, causing the spring stays and pins to wear out.
(5) During the refueling process, the paper transfer roller and the delivery guide are easy to get oily, so pay special attention when refueling, and check and clean frequently when necessary.
3. Phoenix-like spots, stains or white spots. If there is a spot-like stain on the printing plate, it will leave an eye-like spot on the printed crystal. If there is a spot-like stain on the blanket, it will leave a spot-like stain or white spot on the printed crystal. Cause analysis:
(1) When the paper with poor surface strength is in contact with water and ink, it is easy to produce powder. Roughing phenomenon, adhere to the blanket or printing plate.
(2) When taking ink from the ink tank, the dried ink skin and ink residue should be removed because of the ink skin. Once the ink residue falls into the ink fountain, it will be transferred to the printing plate when transferring ink.
(3) There are many fluffs on the water roller velvet. When printing a solid plate, it is easy to leave burr-like and silk-like marks on the printed product. Now there is a nylon water gel fleece that is not easy to shed. If it is wrapped on the water roller, the effect will be very good. Sometimes, a water roller velvet is used in several colors, and the ink residue is stuck on it, and the ink residue will be transferred to the printing plate during the water transfer process.
(4) The cleaning and maintenance of rubber rollers are very important, but some operators do not pay attention to this work and do not take them off one by one for cleaning. The rubber roller is subject to high temperature friction and ink. The corrosion of the solvent forms cracks, especially at both ends of the rubber roller. The ink residue from the rubber roller that is cracked during printing sticks to the printing plate and is difficult to clean.
(5) For anti-sticking, the printed products are sprayed with powder. Considering that some paper has more paper powder, the powder on the paper is printed during printing. The paper powder will adhere to the blanket as the paper is imprinted, and then transferred to the printing plate. Therefore, the powder should be arranged in the last color as much as possible. If powder must be sprayed, pay attention to the size of the powder. The smaller the better, the better if it is not sticky. You can print it if necessary.
4. Dough. The powder sprayed on the printed product, because the ink was not completely dried and the printed product appeared a mass of powder. Cause analysis:
(1) If the machine that needs to be sprayed cannot be cleaned and maintained for a long time, the paper suction bracket and chain. The platen fan will be covered with powder. When printing, due to machine shake or the rotation of the paper pressure fan, the powder will fall on the printed product.
(2) When spraying powder, if the heating switch is not turned on, the dry powder will be condensed into lumps in a humid environment. The powder injection valve of some machines is installed in the hood (such as J4104 machine). When the oil is automatically filled in the hood, the oil will drip on the powder injection valve and form a sludge with the powder in the valve. These powder blocks and oil sludge are blown down by the air blowing pipe, leaving powder dust on the printed product, so the channel of powder spraying must be kept in a clean and dry environment.
5. The prints are dirty due to human reasons such as improper operation. Cause analysis:
(1) In order to improve the print quality, the paper must be smooth, straight and easy to separate. Therefore, the operator needs to beat the paper. After printing some large-area full-page dark solid areas (such as red and purple), the paper tends to curl downward, and these curled papers cannot be transported normally, so special care should be taken when handling these papers. If you beat it too hard, it will inevitably cause creases in the paper, and white streaks will appear in the creases. The correct method is to simply press up slightly to make the paper gripper and trailing tip smooth.
(2) Operators often need to take a pile of printed products to the sample stand to check the color registration. For some full-page and large-area prints, take them lightly, otherwise they will easily cause the prints to become dirty. Because of the large amount of ink in these printed products, they will curl down on the delivery table. It is not easy to sample sheets from the machine table, and the speed of the machine is fast, so be careful not to scratch the printed products.
(3) After the product is printed, wait for a while before picking or unloading to prevent the printed product from sticking and staining.
6. Rubbing dirty. In the process of paper feeding, stamping and receiving, scratches and scratches on printed products may occur. Sprained. Cause analysis:
(1) The paper pick-up roller on the paper pick-up roller presses down the paper after the paper suction nozzle blows. If the ink is not over 1,000, 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 and heavy, there will be two spots on the paper.
(2) When the paper passes through the paper feeding table, the paper receiving roller and the paper pressing roller. The brush wheel and the paperweight ball will drag the ink out of two or three ink traces, especially when the paper feeding tooth accelerates the paper, the brush wheel and the paperweight ball are easy to drag out the trace.
(3) The pull gauge of J2108 and J4104 machines has a roller which is a twist roller. When printing both sides of the front and back, especially when printing dark ink on the back, there will be a few "dental marks". Therefore, you should try to leave a little white edge for the pull gauge and pull the paper, and pay attention to the direction of the mouth when printing, and place the light color (such as light yellow, light cyan, etc.) ink on the pull gauge. Therefore, it is necessary to fully consider the shortcomings in this aspect of domestic pull regulations.
(4) When handing over paper, because of the printing of relatively straight paper with a basis weight of 350g / m2 or more, it is easy to scratch the paper during the return of the top swing type front gauge, such as J2108 and J4104. When the paper is delivered by the paper delivery roller, because the front swing angle of the hem is not large, it is easy to scratch scratches on the back of the printed product, causing the back side to be dirty, such as the PZ2660 machine.
(5) The printing surface of the multi-color machine's paper transfer cylinder is wrapped on the cylinder during the paper transfer process. Due to insufficient cleaning and maintenance of the machine, the residual ink on the roller will leave silky traces on the printed product, so it is best to print the large-area imprint on the last color to avoid getting dirty on the transfer roller.
(6) After being imprinted by the imprinting cylinder, the printed product is gripped by the paper-receiving teeth, and then conveyed to the paper-receiving table by the conveying wheel. Since there is no anti-rubbing cloth on the domestic paper turning wheel, it will drag out traces on the printed product, which are mainly on the trailing part 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 trademark splicing place; if you print the instructions, adjust the flip wheel at the spine; if you print a picture, do not place the flip wheel on the same color block, but Place it in brightly colored areas, even if there is a scratch.
(7) J2104, PZ2660, etc. have a small cylinder diameter. When printing paper with a basis weight of 200g / m2 or more (WH47-NP printing paper with a basis weight of 105g / m2 or more), because the paper has a certain degree of stiffness, it is not It will be wrapped on the surface of the roller in a flat uniform. During the movement, the centrifugal force will be affected by the n-direction, and it will be wrapped on the bar and the imprinting shaft. According to the specific situation, the paper guide bar will be reasonably distributed and installed, or on the bar or the imprinting shaft Put sponges and other wrappers on the paper to prevent the paper from being thrown out and scratched.
(8) Printing large areas of dark colors. When spot color ink is used, if the slow paper absorbs too much air. If the teeth are opened too early, the paper will fall prematurely, and a printed product will rub, causing scratches. In addition, due to the various stains caused by the quality of the PS version, many articles have been introduced and will not be analyzed here.
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