Analyze why the printed product is dirty

Quality is the lifeblood of a company's survival and development. In the actual operation process, a slight carelessness will cause the printed product to be dirty, which will directly affect the quality of the printed product. Below, I will sum up the long-term practice in the timely and accurate exclusion in the face of these failures.

1. Water spot. According to the principle of oil and water incompatibility, if there is water 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, the offset printing press is placed in the air-conditioning workshop. The moisture in the moist air will be blown into the cool environment through the air pump to condense the salt water, through the presser foot and the paper dispenser. Blow on the paper.

(2) Many water fountains for offset presses are made of sheet iron or copper-plated sheet metal. Since acidic wetting fluid is corrosive, over time, the bucket will be gradually corroded to form trachoma, and some sand holes are small. Only two or three drops of water can be dispensed in one minute. In this way, there will be water spots that are sometimes absent from the prints. Therefore, the operator needs to carefully inspect the water bucket against the light and find that the trachoma is firmly soldered.

(3) The maintenance of some offset presses is not perfect. The operator never cleans the fountain. When the ink roller is cleaned, the ink on the ink roller splashes with the cleaning agent and is thrown into the water bucket. The villi form scale together, and as the roller rotates, it accumulates between the roller and the wall of the bucket, and as time passes, a dross is formed. When the fountain roller rotates, the slag will drip with the water on the fountain roller down the wall of the fountain to form a water spot on the print.

(4) When the printing plate needs to be put into operation due to water shortage, the fountain roller will transfer a large amount of water to the transfer roller. The transfer roller will transfer the excess water during the transfer of the roller. It will trickle down. The J2108 machine is equipped with a baffle below the bucket, which works well, but to avoid too much water and drip down. The J4104 and other models do not have a baffle plate, so it is advisable to stop when there is an emergency.

2. Oil spots. Because 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 produce an inverse impression, which is a round oil spot on the printed crystal. Cause analysis:

(1) The lubrication of the paper conveying head is important and necessary. When refueling, it is necessary to reduce the amount of ground rubs. After the fuel is turned on, the machine and the paper feeder are started to allow the oil to drip in motion, and then wipe it again to ensure that there will not be any extra oil 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-dispensing blower will blow out many oil-like oil droplets and splash on the tip of the paper. Touch the filler cap on the oil pump chamber with a small hole to check if there is any. Gas spouted. If not, it means that the air pump does not return oil well.

(3) The transmission lever and the parachute gear in the lower part of the pull gauge also need to be lubricated. Of course, only a little or a little bit of butter can be added on the top. If you add too much oil, the gauge will stick to the paper during drawing.

(4) The garniture shaft and the bungee rod on the paper transfer teeth frequently move. If the lubricating effect is not good, it will easily cause wear, resulting in poor paper creping and overprinting. Therefore, be very cautious when adding lubricating oil, wipe with oil, transport, transfer and wipe with a rag after a period of time. Many operators often wear scarves and pins due to fear of oil contaminating the paper.

(5) In the refueling process, the transfer roller and the delivery guide are very easy to stick with oil, so pay special attention when refueling, if necessary, always check the cleaning.

3. Hyacinth-like spots, spots or white spots. If the plate has a bit of a stain, it will leave a wind-like spot on the crystal. If the blanket has a bit of a stain, it will leave spot-like stains or white spots on the crystal. Cause analysis:

(1) Paper with poor surface strength tends to lose powder when it comes into contact with water and ink. Pulling phenomenon, adhesion to the blanket or plate.

(2) When taking ink from the ink tank, the dried ink and ink residue should be removed because of the ink skin. Once the ink residue falls into the ink fountain, it will be transmitted to the printing plate when the ink is transferred.

(3) There are many fluff on the fleece of the water roll. When printing the solid version, it is easy to leave burr-like and filiform traces on the print. There is now a kind of non-linting nylon hydrogel, 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 is already stuck on it. During the process of transferring water, the ink residue will be transferred to the printing plate.

(4) The cleaning and maintenance of the rubber roller is very important, but some operators do not pay attention to this work and do not pick it up and clean it. As a result, the rubber roller is subjected to high temperature friction and ink. Corrosion of the solvent forms cracks, especially at both ends of the roller. The ink residue left by the cracked rubber roller during printing is stuck on the plate and is difficult to clean.

(5) Dusting the prints for preventing stickiness, taking into account the fact that some papers have more paper powder, and dusting on the paper during printing. Paper dust adheres to the blanket as the paper is imprinted, and is then transferred to the plate. Therefore, dusting should be arranged as far as possible in the last color. If it is necessary to spray the powder, it is necessary to pay attention to the size of the dusting amount. The smaller the better, the better if it is not dirty, and if necessary, it can be printed again.

4, powder group. The dust was splashed on the print, and the ink appeared a mass of powder as the ink was not completely dry. Cause analysis:

(1) Machines that need to be dusted If they are not cleaned and maintained for a long period of time, paper suction brackets and chains are used. The paper press fan is full of powder. During the printing, the powder will fall on the freshly printed product due to the machine shake or the fan pressure.

(2) When powder is sprayed, if the heating switch is not opened, the dry powder will not be condensed in a humid environment. Some machines have dusting valves installed in the hood (such as the J4104). When the hood is automatically refueled, the oil will drip on the powder valve and form sludge with the powder in the valve. These powders and sludge are blown down by blowpipes to leave powder on the prints. Therefore, the dusting path must be maintained in a clean, dry environment.

5. The printed product 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 smooth, crisp and easy to separate. So the operator needs to beat the paper. After printing some large areas full of dark colors (such as red, purple), the paper tends to curl downwards, and these curled papers cannot be transported normally. Therefore, special care must be taken when handling these papers. If you beat too hard, it will inevitably cause creases in the paper, and white streaks will appear in creases. The correct method is to lightly press up and press the paper so that the mouth and the tip of the paper can be flattened.

(2) Operators often need to take a freshly printed product to see the sample stand to detect color registration. For some full-size, large-area prints, use less light, otherwise it is easy to cause dirty prints. Because these inks have a large amount of ink, they will curl downwards on the delivery table. It is not easy to take samples from the machine table and it is fast. So be careful not to scratch the prints.

(3) After the product is printed, wait a short while to refresh or blank the material to prevent the printed product from getting dirty when the paper is moved.

6. Dirty. In the process of paper feeding, embossing, and delivery, scratches and scratches may occur on printed products. Friction. Cause analysis:

(1) The take-up roller on the take-up roller presses the take-up paper after it is blown by the delivery nozzle. If the ink is not enough, it will leave two stains on the paper. If the J2108 machine's take-up roller has a large stroke, the control cam is steep. When the take-up roller is pressed and pressed, it will leave two spots on the paper.

(2) When the paper passes through the transfer table, take the paper, pressure roller. Brush wheel, paperweight ball, etc. will drag the ink out of two or three inks, especially when the delivery tooth speeds up the delivery of paper, the brush wheel and paper ball can easily pull out traces.

(3) J2108, J4104 machine pull gauge has a roller is a twist roller, when the positive and negative sides of the printing, especially when the dark ink is printed on the opposite side, it will "click" a few "dental teeth". Therefore, when you open the material, you should try to leave a little white edge to pull the paper. Also pay attention to the direction of the rinsing when printing, and put the light color (such as light yellow, light blue, etc.) ink on the gauge. Therefore, we must fully consider the defects of domestic pull gauges.

(4) When the delivery paper is delivered, due to the stiffer paper with the printing quantity of 350g/m2 or more, it is easy to scratch the paper when the pendulum-type front gauge is returned, such as the J2108, J4104, etc. When the delivery roller handed the paper, because the hem before the sway angle is not large, it is easy to scrape scratches on the back of the print, resulting in dirty scratches, such as the PZ2660 machine.

(5) The transfer roller of the multi-color machine is wrapped in the roller during the transfer process. Due to insufficient cleaning and maintenance of the machine, the residual ink on the roller will leave traces on the printed product. Therefore, it is better to place the large-area printed layout on the last color to avoid dirt on the transfer roller.

(6) After being impressed on the impression cylinder, the print product is caught by the delivery paper and conveyed by the turning roller to arrive at the delivery table. Because there is no moth-proof cloth on the domestic turning roller, traces will be dragged on the print. This mark is mainly on the tip of the paper, so it is necessary to adjust the turning wheel according to the actual situation. If you are printing a trade mark, you must consciously leave two blank spaces at the stitching point of the trade mark; if you print the manual, adjust the turning roller at the spine; if you print a painting, do not place the turning roller at the same color block. Place it in a colorful place, even if there is a scratch.

(7) The roller diameters of the J2104 and PZ2660 machines are small. When printing paper with a basis weight of 200 g/m2 or more (WH47-NP has a printing weight of 105 g/m2 or more), the paper does not have a certain degree of stiffness. Will be wrapped flat on the surface of the drum, in the course of the movement, by the centrifugal force of the n direction, wrapped in the bar, the imprinting shaft, according to the specific circumstances, reasonable distribution and installation of paper guide bar, or on the bar or imprinting shaft Sponges and other wraps are placed on the pad to hold the paper so that it will not be thrown out and scratched.

(8) printing a large area of ​​dark colors. When 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 print will rub, causing scratches on the printed product. In addition, due to the quality of the PS plate, various articles have been introduced and are no longer analyzed.

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