Adhering to correct process operation and measures to strengthen quality management are important factors to ensure printing quality. The standard operation method in the lithographic offset printing process is as follows: first, calibrate "three levels", the so-called "three levels" refer to blanket leveling, roller leveling, ink roller, and water roller leveling; secondly, adjust the "two small", the so-called "two leveling" "Small" refers to the small amount of water and low pressure; the third is to achieve "three diligence". The so-called "three diligence" refers to diligently checking printed sheets, diligently stirring ink fountains, diligently checking the water content of the layout.
1. Calibration "Sanping"
1. Blanket flat
Flat blanket means that the surface of the blanket roller should be flat. Lithographic offset printing is transferred with 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 whether it can be used correctly are directly related to the printing quality of the offset printing product, and the flat surface of the blanket is the surface characteristic of the blanket used correctly. Specifically, the flat performance of the blanket is the overall blanket Process performance. The flatness of the blanket surface is a necessary condition to achieve complete contact of the printed surface and ensure the uniform transfer of dot ink.
Today's printing materials have developed rapidly. The errors in the flatness of the blanket due to manufacturing errors have been greatly reduced. The main influence on the flatness of the blanket is the padding under the blanket. The liner must be flat. When installing the blanket, it is necessary to prevent foreign objects from being caught in the liner, and pay attention to prevent the liner from wrinkling.
Use the "Draw Map" method to fill in the low recesses of the blanket. The specific method is as follows: smear the ink on the ink roller evenly, generally use yellow ink, and press the ink roller against the plate, so that the printing plate is coated with uniform ink and then pressed. If the ink on the blanket is even, it means 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 uneven; use a pencil to draw it on the backing paper or blanket fabric, and then Use different thicknesses of paper to directly patch the fabric base fabric to make it smooth.
2. Roller flat
Roller flat means that the axes between the roller bodies must be parallel to each other, and the pressure between the roller bodies must be balanced. Cylinder pressure is the first condition to complete offset printing. If the axes between the cylinder bodies are not parallel, it will directly cause the cylinder contact pressure to be inconsistent, the ink transfer effect is not ideal, and the ink color of the printed product will be uneven. Therefore, adjusting the center distance of the rollers so that the axes of the two adjacent rollers are parallel is a crucial task and must be done carefully. It is worthwhile to spend more time on this.
Checking whether the axes between the rollers are parallel to each other is generally to measure whether the roller pillow gap is equal. The most common method for detecting the roller pillow gap is to wash the surface of the roller pillow, press the roller, and roll a soft lead wire with a diameter of about 0.5mm between the roller pillows. It is adjusted by the pressure adjustment mechanism. The thickness of the soft lead wire finally measured is the clearance of the roller pillow; it can also be measured with a micrometer feeler gauge (or thickness gauge), and a straight iron ruler is balanced with the axis of the roller Mount on the roller pillow at both ends, then gradually increase the thickness with a micrometer feeler gauge, try to insert between the drum shell surface and the iron ruler, until the thickness of the feeler gauge and the iron ruler are filled and equal, the total thickness of the feeler gauge is calculated , Is the clearance of the rolling pillow. In order to be as accurate as possible, you can measure more times and more parts. The gap between the two ends of the measuring roller must be consistent, so as to ensure that the axis between the rollers is parallel. The measurement is generally based on the impression cylinder.
It is often impossible to ensure that the axes are parallel only by measuring the gaps of the rollers to be equal. It is also necessary to measure the equidistance at the two ends and the middle of each roller shell surface to achieve the axis parallel.
3. Ink roller and water roller flat
â‘ The ink roller is flat. Ink roller flatness mainly means that the cylindricity of the ink roller body should be uniform, the axis of the plate cylinder, the axis of the inking roller (also called the plate roller) and the axis of the cross-ink 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 the flatness of the ink roller can guarantee the contact relationship between the printing plate and the inking roller, the inking roller and the inking roller. Therefore, the inking roller level 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 the flatness of the inking roller. 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, which first contact the printing plate in front and are close to the water delivery mechanism, are called inking rollers. The main function is to supply ink, and the pressure is slightly heavier to supply sufficient ink to the printing plate. The two inking rollers of the version are called inking rollers, which mainly play the role of inking ink. The pressure is slightly lighter, so that the inking ink is clean, which is conducive to the smooth and clear dot. 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 ink and the linear speed of the ink roller is equal to the linear speed of the printing plate.
Adjustment sequence: first inside and then outside. Load the ink roller group first, then the ink roller group. Ink roller and string roller first, then inking roller and plate.
Adjustment process: After installing the second ink roller (one inside) of the ink roller group, jog the machine until the blank part at the end of the printing plate drops the ink roller. Use a micrometer gauge (thickness 0.15mm ~ 0.25mm) to measure the pressure of the inking roller and the inking roller (lift the ink landing gear), select both ends and the middle as the test point, and use three fingers to hold the thousand The tail end of the gauge is inserted and pulled, and it is slightly slower when it is pulled out. It feels the resistance when it is pulled out. Adjusting to the feel has both frictional resistance and smooth pulling of the steel sheet. This feel is more suitable. Check the pressure with the embossing method, make the ink roller infuse, rotate or jog the machine at a low speed to stop it for a few seconds, then reverse it a little, and the contact stripes can be seen on the surface of the ink roller. Generally, the contact stripes obtained are uniform and have a width of about 6 mm to 8 mm. Measure the pressure of the inking roller and the printing plate (drop the ink landing gear), and use the feeler gauge to measure and adjust the operation as above. Check the pressure with the embossing method to make the ink roller evenly inked so that it is coated with a certain thickness of the ink layer, and then "jog" the machine to turn the plate image part to the position corresponding to the inking roller and pull Ink the roller control handle to make it rise and fall several times, which can leave ink stripes on the printing plate. Generally, the contact stripes obtained are uniform and the width is about 8 mm to 10 mm. The adjustment methods of other inking rollers are analogous. In addition, it can also be measured by the paper strip tensile method.
â‘¡The water roller is flat. Water roller flat mainly means that the axis of the plate cylinder, the axis of the water roller and the axis of the water roller are parallel lines. The function of the water delivery mechanism is to supply water evenly, stably and continuously to the surface of the printing plate. Similar to the ink roller, the water roller level is a necessary condition for the water delivery mechanism to function normally. It is also possible to indicate the flatness of the water roller by the uniformity of the pressure of the printing plate and the water roller, the water roller and the water roller.
The adjustment of the water roller is basically the same as the adjustment of the ink roller, but it should be noted that the interaction between the upper and lower water rollers. It is necessary to control the pressure of adjusting the upper water roller and the water roller not to be too large. If the pressure is too large, the water will be squeezed on the upper water roller. [next]
Second, adjust the "two small"
â’ˆSmall amount of water
The role of the PS version of the wetting fluid is to achieve dampening, cleaning, and purifying the plate surface. The small amount of water means that the water supply amount is controlled to the smallest possible range without affecting the stability of the blank part of the printing plate (that is, the blank part is not sticky), and the water supply amount and the ink amount are in a relatively stable state.
The amount of water (ie, wetting fluid) directly affects the ink, printing plate and paper, and the ink, printing plate and paper directly affect the printing quality. The small amount of water can ensure the consistency of the ink color before and after the color and the stability of the printing operation, which can print a more ideal product.
If the amount of dampening fluid is too large, the biggest impact is on ink and paper, followed by the printing plate. If the amount of wetting fluid is too large, it will destroy the water-ink balance state, accelerate ink emulsification, and the ink cannot be transferred normally, or even cause the "pattern" of the layout and the color of the printed ink to become lighter. Too much water on the printing plate surface will cause the inking performance of the graphics and text to be abnormal, the printed image will lose its luster, the color will not be bright, the gradation will be poor, and the product performance will be flat. Excessive amount of wetting liquid will affect the printing performance of the paper, causing the paper to fluff and de-powder; excessive moisture content of the paper will cause the paper to expand and contract, affecting the quality of the overprint; in addition, excessive moisture content of the paper will cause the paper to change Soft, resulting in uneven paper collection, slow drying of the blotting ink layer, and the back side of the paper is sticky.
It is more important to estimate the water consumption of the layout in advance than to adjust it afterwards. It is an important prerequisite for adjusting the water-ink balance of the layout. Therefore, the main factors affecting the amount of wetting fluid should have a more important understanding before determining the amount of water on the plate. In actual production, the amount of wetting fluid depends on: the graphic area distribution of the layout; paper properties; ink properties; machine speed; ambient temperature and humidity and air circulation.
â’‰ Low pressure
Printing pressure is the first condition to complete offset printing. Whether the pressure between cylinders is ideal is the key to ensuring the printing quality. Small pressure means that the pressure can reduce the printing pressure between the cylinders as much as possible on the basis of ensuring the good transfer of the ink (that is, ensuring that the printed matter is strong in the imprint, the dots are full but not spread, and the tone level is clear and rich). Whether the pressure is low (that is, using ideal pressure) is one of the important signs to measure the level of technology, and it is also an important condition for ensuring high quality and high yield.
Excessive printing pressure has a great impact on product quality. Excessive pressure can easily cause dot deformation, paste, thick ink color, and even image distortion. Excessive pressure will also accelerate plate wear and roller wear.
The best printing pressure adjustment method is to make the gear in the standard meshing state and achieve the best printing suitability by changing the thickness of the pad.
When printing thick paper, the best method for adjusting the printing pressure is to reduce the blanket thickness of the rubber cylinder accordingly and increase the blanket thickness of the plate cylinder. Minor differences can be adjusted by changing the center distance between the cylinders and readjusting the ink roller pressure.
The most commonly used and most straightforward method of printing pressure inspection is the bar method. The specific operations are as follows: lift the water roller, drop the ink roller, run the machine at low speed and press together, and wait until the surface of the three rollers is evenly inked, and then you can stop. Each roller has an ink bar at the parking place, such as the width of the ink bar is uniform within the value range given by the machine, and the width of the ink bar of the impression cylinder and the rubber cylinder is greater than the width of the ink bar of the plate cylinder and the rubber cylinder , It means that the pressure adjustment is uniform and appropriate. If the width of the pressure bar is wide and narrow, the biggest possibility is that the center distance between the two sides of the roller is inconsistent.
3. Achieve "three diligence"
â’ˆCheck the printed sheet
Inspecting printed sheets frequently refers to constantly checking product quality during the printing process. During the offset printing process, various situations may occur that affect the quality of the product, resulting in a large number of defective products or even waste products. Therefore, in printing operations, diligent inspection of printed sheets is essential.
The diligent inspection of printed sheets includes the following: check whether the overprint is accurate, check the ink color, check the dot quality, and check for the presence of dirty spots, white spots, paste plates, and flower plates.
â’‰ Qin stirring ink fountain
Stirring the ink fountain frequently refers to stirring the ink in the ink fountain at intervals during the printing process. Stirring the ink fountain frequently can ensure continuous and continuous ink inking, which is the premise of ensuring uniform ink color before and after the printed matter.
Ink is a plastic fluid with thixotropic properties that gradually change its fluidity with external forces. That is, when the ink is kept at a certain temperature, after applying a certain external force to the still ink, the ink gradually becomes thinner and softer, and the rheology becomes better; when the external force stops stirring, the ink gradually thickens and hardens, and the fluidity becomes difference. If the ink fountain is not stirred for a long time, the ink fluidity will be poor, which will make the ink in the ink fountain inferior, resulting in the phenomenon of blocking or no ink, the ink roller is difficult to transfer ink, and the ink is uniform. The breakage in the middle of the ink causes the remaining ink layer to protect the plate surface and cause plate-off.
An ink stirrer can be installed in the ink fountain to stir the ink at a uniform speed to increase the fluidity of the ink. An ink knife can also be used to stir the ink in the ink fountain.
â’Š Qin to check the layout moisture
Checking the water content of the plate frequently refers to constantly checking the size of the water content of the plate during the printing process.
In the printing process, it is an important prerequisite to correctly grasp and control the moisture content of the layout to achieve the balance of water and ink during the printing process, and to correctly identify the moisture content of the layout. The method of discriminating the size of the water content in the production process:
â‘ Visual method. In daily production, the visual inspection is generally based on the operator's experience. The method is to obliquely illuminate the layout with the lighting lamp, and determine the size of the moisture of the layout according to the strength of the reflection of the layout; The lighter the weaker.
â‘¡ Judging by the fault phenomenon of the printed product. If there is paste or dirty version, please pay attention to whether the moisture on the layout is too small; if the printed matter is matt, patterned, curled, or unevenly received, the moisture on the layout may be too large.
In the printing process, if we can adhere to the "Sanping, Sanqin, two small" process measures, we can stabilize and improve the output and quality of offset printing products.
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