"Sanping, Sanqin, two small" operation method in offset printing process
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Adhering to the correct process operation and strengthening quality management measures are important factors to ensure print quality. The standardized operation method in the lithographic offset printing process is as follows: Firstly, the calibration of "Sanping" means that the blanket is flat, the roller is flat, the ink roller and the water roller are flat; the second is to adjust the "two small", the so-called " "Two small" means: the amount of water is small, the pressure is small; the other is to achieve "three diligence", the so-called "three diligence" means: diligently check the printed sheets, diligently stir the ink fountain, and diligently check the moisture of the layout.
First, calibration "three flats"
1. Rubber blanket
The blanket flat means that the surface of the blanket cylinder should be flat. The lithographic offset printing is transferred by a blanket, mainly because the blanket not only has good elasticity, but also has good ink transfer performance. Therefore, the quality of the blanket and its correct use are directly related to the printing quality of the offset product, and the flat surface of the blanket is the surface feature of the blanket that is correctly used. Specifically, the flatness of the blanket is the overall of the blanket. Process performance. The flatness of the surface of the blanket is a necessary condition for achieving complete contact of the printing surface and ensuring uniform transfer of ink at the dot.
Nowadays, the printing materials have been rapidly developed. The error in the flatness of the blanket has been greatly reduced due to the manufacturing processing error. The flatness of the blanket is mainly the underlay under the blanket. To make the blanket flat, The padding must be flat. When installing the blanket, prevent foreign matter from being caught in the pad and take care to prevent the pad from wrinkling.
Use the "paint map" method to fill the depression of the blanket. The specific method is as follows: the ink on the ink roller is evenly mixed, generally yellow ink is used, and the ink roller is pressed against the plate to make the ink uniformly coated on the printing plate. If the ink on the blanket is uniform, it means that the surface of the blanket is flat; if the surface of the blanket is uneven like a map, it means that the surface of the blanket is not flat; you can use a pencil to draw it on the liner or blanket fabric, and then Apply paper of different thickness directly to the fabric base fabric to make it flat.
2. Roller flat
The flattening of the drum means that the axes between the drum bodies are parallel to each other, and the pressure between the drum bodies is balanced. Roller pressure is the primary condition for complete offset printing. If the axes between the drum bodies are not parallel, the roller contact pressure will be directly inconsistent, the ink transfer effect is not satisfactory, and the ink color of the printed product will be uneven. Therefore, adjusting the center distance of the rollers to make the axes of the adjacent two rollers parallel, this is a crucial task, must be done carefully, it is worthwhile to spend more time in this area.
It is generally measured whether the axis between the rollers is parallel to each other. The most common method for detecting the gap between the rollers is to clean the surface of the roller and then press the roller to roll a soft lead wire with a diameter of about 0.5 mm between the rollers. And through the pressure adjustment mechanism to adjust, the final measured soft lead wire thickness is the gap of the roller; can also be measured with a thousand gauge feeler (or thick gauge), with a straight iron ruler, balanced with the drum axis Place the roller on both ends, then gradually increase the thickness with a thousand-point gauge, and try to insert between the roller shell surface and the iron ruler. When the thickness of the feeler gauge and the gap between the iron feet are filled and equal, calculate the total thickness of the feeler gauge. Is the gap of the roller. In order to be as accurate as possible, you can measure several times and measure several parts. The gap between the ends of the measuring roller must be the same, so that the axes between the rollers are parallel. The measurement is generally based on an impression cylinder.
Only by measuring the equal gap of the measuring drum, it is often impossible to ensure that the axes are parallel, and it is also necessary to measure the equidistance at three points in the middle and the middle of each drum shell surface in order to realize the parallelism of the axes.
3. Ink roller, water roller flat
3.1 ink roller is flat. The ink roller flat mainly means that the knurling roller body has a uniform cylindricity, the axis of the plate cylinder, the axis of the inking roller (also referred to as the plate roller), and the axis of the squeezing roller are parallel lines. The function of the inking mechanism is to supply ink uniformly, stably and continuously to the surface of the printing plate. Only when the ink roller is flat can the contact relationship between the printing plate and the inking roller, the inking roller and the inking roller be ensured. Therefore, the ink roller flat is a necessary condition for the inking mechanism to function normally.
In production practice, we often simply use the uniformity of the pressure between the printing plate and the inking roller, the inking roller and the inking roller to indicate that the ink roller is flat. The adjustment method is as follows:
Adjustment principle: ● The pressure of the four inking rollers should be 1>2>3>4, that is, the pressure of the first inking roller is the largest and the fourth is the smallest. There are usually four inking rollers. The two inking rollers that contact the printing plate and are close to the water delivery mechanism are called the inking roller. The main function is to supply ink. The pressure is slightly heavy to supply the ink to the printing plate. The two inking rollers of the edition are called ink-receiving rollers, which mainly serve to absorb ink, and the pressure is slightly light, so that the ink is cleaned, which is beneficial to the smoothness of the dots. ● The pressure of the inking roller and the inking roller is slightly lighter or equivalent to the pressure of the inking roller and the printing plate. This is to ensure the normal transfer of the ink and the line speed of the ink roller is equal to the line speed of the printing plate.
Adjustment order: first inside and outside. First, the ink roller group and the rear ink roller group. First the ink roller and the ink roller, then the ink roller and the printing plate.
Adjustment process: ● After loading the second ink roller (one inside) of the inking roller group, jog the machine to the blank portion of the printing plate to drop the ink roller. ●Measure the pressure of the ink roller and the ink roller by using a thousand-foot gauge (thickness 0.15-0.25mm) (lift the ink landing gear), select the test points at the ends and the middle, and pinch the thousand fingers with three fingers. The end of the splitter is inserted at the end of the tap, which is slightly slower when pulled out. It feels the resistance when it is pulled out. It adjusts to the hand and has frictional resistance, and it can make the steel sheet smoothly pull, which is more suitable. Check the pressure by embossing, inflate the ink roller, rotate or jog the machine at a low speed, stop it for a few seconds, then reverse it a little, and the contact streaks are visible on the surface of the squeezing roller. Generally, the contact stripes obtained are uniform and the width is about 6 to 8 mm. ● Measure the inking roller and plate pressure (drop the ink landing gear), and measure and adjust with the feeler gauge as described above. Check the pressure by embossing method, make the ink roller uniformly ink, apply a certain thickness of the ink layer, and then “click” the machine to rotate the graphic part of the printing plate to the position corresponding to the inking roller. The ink roller handles, causing it to rise and fall several times, can leave ink streaks on the plate. Generally, the contact stripes are uniform and the width is about 8 to 10 mm. ●The adjustment method of other inking rollers is analogous.
In addition, it can also be measured by the paper strip pull method.
3.2 water roller flat. The water roller flat mainly refers to the axis of the plate cylinder, the axis of the watering roller, and the axis of the water roller are parallel lines. The function of the water delivery mechanism is to supply water uniformly, stably and continuously to the surface of the printing plate. Similar to the ink roller, the water roller flat is a necessary condition for the water delivery mechanism to function normally. It is also possible to indicate that the water roller is flat with the pressure uniformity of the printing plate and the water roller, the water roller and the water roller pressure.
The adjustment of the water roller and the adjustment of the ink roller are basically the same, but it is necessary to pay attention to the mutual influence between the upper and lower water rollers. It is necessary to grasp that the pressure of the upper water roller and the water roller should not be too large, and the excessive pressure water will be squeezed on the upper water roller, and the water cannot be normally supplied to the plate, and the water cannot be transferred to the water roller.
Second, adjust the "two small"
1. Small amount of water
The role of the PS version of the wetting fluid is to achieve dampening, cleaning and purifying the layout. The small amount of water means that the water supply amount is controlled to be as small as possible without affecting the stability of the blank portion of the printing plate (that is, the blank portion is not sticky), and the water supply amount and the ink amount are relatively stable.
The amount of water (ie, wetting fluid) directly affects inks, plates, and paper, while inks, plates, and paper directly affect print quality. The small amount of water ensures that the ink color is consistent before and after the printing and the printing operation is stable, and the ideal product can be printed.
The amount of dampening fluid is too large, the most influential is ink and paper, followed by the printing plate. If the amount of dampening solution is too large, it will destroy the balance state of the ink and ink, accelerate the emulsification of the ink, the ink can not be transported normally, and even lead to the "flower plate" of the layout, and the ink color of the print becomes lighter. Too much water in the plate layout will cause the ink in the graphic part to be abnormal. The printed image will lose its luster, the color will not be bright, the tone level will be poor, and the product performance will be dull. If the amount of dampening solution is too large, it will affect the printing performance of the paper, causing the paper to fluff and powder. The excessive moisture content of the paper will cause the paper to stretch and affect the quality of overprinting. In addition, if the water content of the paper is too high, the paper will become Soft, causing misfeeds, drying speed of the imprinted ink layer is slow, and the back side of the paper is dirty.
An ex ante estimate of the amount of water used in the layout is more important than an after-the-fact adjustment. It is an important prerequisite for adjusting the balance of the ink on the layout. Therefore, the main factors affecting the amount of dampening fluid should have a more important understanding before determining the amount of water in the plate. In actual production, the amount of dampening fluid depends on: the layout of the layout image; the nature of the paper; the nature of the ink; the speed of the machine; the ambient temperature and humidity and the air circulation.
2. Low pressure
Printing pressure is the primary condition for lithographic offset printing. The ideal pressure between the rollers is the key to ensuring print quality. The pressure small finger is based on the pressure to ensure good ink transfer (that is, to ensure that the print is strong in the print, the dot is full but not spread, the tone level is clear and rich), to minimize the printing pressure between the rollers. The ability to achieve low pressure (ie, the use of ideal pressure) is one of the important indicators to measure the level of technology, but also an important condition to ensure high quality and high yield.
Excessive printing pressure has a great impact on product quality. Excessive pressure can easily cause dot deformation, paste, product darkness, and even image distortion; excessive pressure will accelerate plate wear and roller wear.
The optimum printing pressure is adjusted by placing the gears in a standard engagement state and by changing the thickness of the liner to achieve optimum printability.
When printing thick paper, the optimal printing pressure is adjusted by reducing the thickness of the blanket of the blanket cylinder and increasing the thickness of the liner of the plate cylinder. The slight difference can be adjusted by changing the center distance between the rollers, and the ink roller is readjusted. pressure.
The most common and most straightforward method of printing pressure testing is the bar pressing method. The specific operation is as follows: lift the water roller, drop the ink roller, run the machine at low speed and press it together, and wait until the surface of the three rollers is evenly inked, then stop. Each roller has a ink bar at the parking place, such as the width of the ink bar is uniform and uniform within the numerical value given by the machine, and the ink bar width of the impression cylinder and the blanket cylinder is larger than the ink bar width of the plate cylinder and the blanket cylinder. , indicating that the pressure adjustment is even and appropriate. If the width of the pressure bar is narrow at one end and the width is narrow, the maximum distance between the two sides of the roller may be inconsistent.
Third, to achieve "three diligence"
1. Check the printed sheets
Diligent inspection of the printed sheets means that the quality of the products is constantly checked during the printing process. During the lithographic offset printing process, various conditions may occur, which may affect the quality of the product, resulting in a large number of defective products or even waste products. Therefore, in the printing operation, it is indispensable to check the printed sheets.
Checking the printed sheets includes the following: check the overprinting accuracy, check the ink color, check the quality of the dots, check for dirty spots, white spots, pastes, and patterns.
2. Mix the ink fountain
Diligent mixing of the ink fountain means that the ink in the ink fountain is stirred at intervals during the printing process. Stirring the ink fountains in a timely manner ensures the continuous underground ink, which is the prerequisite for ensuring uniform ink color before and after the print.
The ink is a plastic fluid having a thixotropic property in which the fluidity gradually changes with the action of an external force. That is, when the temperature is kept constant, the ink is gradually weakened and softened by applying a certain external force to the stationary ink, and the rheology becomes good. When the external force stops stirring, the ink gradually becomes thick and hard, and the fluidity changes. difference. If the ink fountain is not stirred for a long time, the ink fluidity is deteriorated, the ink in the ink fountain is poor, and the ink is blocked or not inked. The ink roller is difficult to disperse ink and the ink is difficult to be inked. The intermediate breakage of the ink causes the remaining ink layer to protect the layout and cause the release.
An ink agitator can be installed in the ink fountain to stir the ink at a constant speed to increase the fluidity of the ink. The ink in the fountain can also be agitated with an ink knife.
3. Check the layout moisture regularly
Diligently viewing the moisture in the layout means constantly checking the moisture content of the printing plate during the printing process.
In the process of printing operation, correctly grasping and controlling the moisture of the layout to achieve the balance of ink and water in the printing process, and correctly identifying the moisture of the layout is an important prerequisite. Identification method of the moisture content of the layout during production:
3.1 visual method. In daily production, visual inspection is usually carried out based on the operator's experience. The method is to use the illumination lamp to slant the layout, and judge the size of the moisture according to the intensity of the reflection of the layout; the thicker the water film, the stronger the reflection, the thinner the water film is. The light is weaker.
3.2 According to the phenomenon of print defects. If there is a paste plate or dirty plate, please pay attention to whether the moisture of the plate is too small; if the print is dull, stenciled, curled, and the paper is not properly received, the moisture of the plate may be too large.
In the printing process, if you can adhere to the "three flat, three diligent, two small" process measures, you can stabilize and improve the output and quality of offset printing products.