Brief analysis of the working principle and process flow of mechanical proofing
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Mechanical proofing is the method of using a proofing machine to transfer the graphic ink on the printing plate to the substrate under the same conditions as the printing conditions, and to print small batch samples. The method of proofing completely simulates the printing method, and realizes the transfer of graphic ink by the pressure principle, which can accurately reflect the performance characteristics of the printing plate and the printing process, and the proof is consistent with the printed matter.
How mechanical proofing works
It consists of two processes: work and auxiliary.
The working stroke refers to the movement process of the drum from left to right. First, the ink stick transfers ink to the layout. The blanket roller rolls over the layout, transfers the graphic ink of the layout to the blanket, and then supplies the water to the water surface. To prevent the printing plate from being dirty, transfer the ink transferred from the blanket to the paper when the roller frame continues to run to the right through the paper table. When the drum frame returns to the right end point, it is completed a work cycle process, in which the water stick and the inking roller are always raised when passing through the paper table.
The auxiliary stroke refers to the movement process of the roller frame from right to left (as viewed from the operating side). Before the operation, the roller frame is at the right end of the frame, and the water stick keeps enough moisture, and the ink supply roller replenishes the ink to the ink roller and then runs to the left. When passing the plate, the water stick and the inking roller sequentially deliver water to the printing plate on the plate, and finally reach the left end point, and the water roller sticks the dampening solution to the water stick, and the rubber roller is always raised during the stroke. Until the left endpoint, it falls.
The lithographic proofing process is: upper plate → damp inking → paper overprinting → color washing and post-processing.
First, the previous version
The upper version refers to the operation process of clamping the printing plate onto the printing plate platform of the proofing machine, and generally includes the following three steps:
1, plate inspection
In order to avoid unnecessary proof of rework and waste materials on the printing plate, the quality of the printing plate must be carefully checked according to the production process sheet and proofing requirements. The contents mainly include: checking the printing plate. Whether the name, quantity and color are consistent with the process list, whether the color number is complete; check whether the plate quality, the bite size and the graphic direction meet the proofing requirements; determine the plate color; measure the plate thickness.
2, loading positioning
The basic method of positioning the plate during proofing is to first lift the clip handle, open the clip cover, and then insert the plate face up, insert the bite into the bite, and center the pendulum in the direction of the coming and going. Positive, finally put down the folder handle to make the jaws close the plate.
The proofing machine with positioning holes and pins can be positioned in the positioning holes of the printing plate and the plate in the loading plate to improve the positioning speed and accuracy of the plate loading. When the proofing machine without the positioning pin is installed, the position of the printing plate can be measured and marked according to the edge of the plate or the frame as the positioning reference, and this can be used as a reference for positioning the multi-color version.
The two-color version of the two-color version of the clamping position is based on the one-color version, by positioning the eyepiece of the eyepiece to adjust the two-color version of the registration, the two-color version of the method has the manual direct movement of the plate and the use of a special wrench to change the folder Position moving plates are two.
Plate sleeve positioning points and precautions:
(1) The orientation of the plate bite is recognized and the device is correct.
(2) The printing plate is flat and the four corners are not lifted to prevent the rubber blanket from being crushed.
(3) After the plate is clamped, a little water can be wiped on the plate to remove the air layer between the plate and the plate, so that the plate and the plate are closely adsorbed and bonded together to enhance the stability. .
(4) One-color version Under normal circumstances, do not rely on the close-up clip, so as to leave some adjustment room for the post-color version of the clamping and paper positioning overprint.
3, layout cleaning
The layout cleaning refers to the process of scrubbing the layout after the positioning and positioning, and is also referred to as the opening. Its purpose is mainly to improve the activity of the layout, enhance the water absorption of the blank part and the ink in the graphic part. The method of scrubbing is to first wipe the protective film on the plate with a damp cloth, and then use the gasoline to absorb the graphic ink on the plate. If the plate remains and can not be washed away, the dirt can be dissolved and removed.
Second, damp infusion
1, damp
In lithographic proofing, the plate must be dampened before the plate is inked, so that the blank part of the plate is evenly adsorbed with a dampening solution, and the plate is always kept moist during the proofing process to prevent the ink from getting dirty. phenomenon.
(1) dampening mode
There are three types of proofing and dampening methods: automatic dampening of the water delivery device, manual wiping and dampening, and low temperature plate condensing and dampening. The proofing can be flexibly applied according to the specific conditions. Under normal circumstances, the watering device of the proofing technology is mainly used for automatic dampening, and the hand rubbing water dampening plate is supplemented, and the low temperature plate condensing dampening plate stabilizes the dampening state, reducing the volatilization of the dampening solution.
When the dampening is started, the watering device can be used for multiple times of water rolling and manual ring rubbing to speed up the dampening speed and improve the uniformity of the wetting of the plate.
(2) Inspection of the amount of dampening water
The methods for checking the amount of water in the layout mainly include visual observation method and instrument detection method. The visual observation method is to judge the amount of water in the layout by observing the intensity of the reflection light on the layout. The reflected light of the layout is stronger and the gloss is larger, indicating that the water volume of the layout is larger; on the opposite side, the reflected light is weaker and the gloss is higher. Small, when the layout is dark, it indicates that the water volume is small. The observation method is simple and easy, but the accuracy is poor. It is greatly affected by factors such as the angle of observation, the thickness of the layout sand and the size of the layout image. The experience and technical requirements of the inspectors are relatively high.
Under normal circumstances, the surface is darkened, there is no obvious reflected light and watermark, and the water quantity is controlled by the standard.
The instrument detection method detects the amount of reflected light on the plate surface and converts the amount of reflected light into a water film thickness value. This type of detection is more accurate, but the monitoring instrument is more expensive and is rarely used at present.
(3) Factors affecting the amount of dampening water
The factors that affect the amount of water in the layout are as follows:
1 proofing temperature, when the proofing temperature is high, the water consumption is large.
2 layout sand fineness. The water content of the plate is large when it is coarse.
3 ink layer thickness. When the ink layer is thick, the amount of water should be increased.
4 ink properties. When the ink is easily emulsified, it is necessary to reduce the amount of water.
5 dampening fluid performance. When the surface tension of the fountain solution is small, the amount of water should be reduced.
2, inking
(1) Ink process
The inking operation consists of three steps: ink refilling, ink leveling and inking. The ink is added to the ink stick of the ink supply device by using the ink knife. To ensure uniform and rapid ink distribution, an ink can be added to the ink stick to turn an angle and add a line. Ink, then turn the ink filling method at an angle. After the ink is added, the ink supply device is started to rotate and evenly disperse, and the ink mixing process is generally 3 min to 4 min. The high speed can be adopted at the beginning stage, and the ink is evenly spread on the ink stick and then changed to a low speed to avoid the ink drying on the ink stick. Fixed. After the ink is evenly distributed, the roller frame can be opened, and the ink is rolled onto the plate by the ink stick while the plate is evenly watered. At the beginning, the ink absorption of the layout is poor, and it can be repeatedly rolled 4 to 5 times until the layout is evenly inked. In the process of inking, the wet cloth can be used to wipe the layout evenly, and the ink and dirt in the blank portion are cleaned by the wetting and rubbing action, and the image portion is quickly and evenly inked.
(2) Ink control
Ink control mainly refers to two aspects of the ink infusion area and the amount of ink infusion control. When the proof is small, when the size of the graphic is small, if the normal whole printing method is used, one will cause ink waste, and the other is easy to produce ink emulsification and dirty surface. Therefore, it is required to adopt an appropriate method for the control of the inking area. In the direction of the direction, the length of the ink on the ink stick is generally controlled according to the width of the image, and the position of the movable guide rail is adjusted according to the height of the image in the front and rear direction, so that the ink stick is only in the figure. The text part is pressed and rolled.
There are two ways to control the amount of ink infusion. One is to change the amount of ink added to the ink supply stick; the other is to change the number of inks. There are two kinds of ink inking methods: single ink and double ink. The double ink and ink stick are in contact with the plate during the round trip, which can improve the uniformity of the ink and increase the thickness of the ink.
The standard for controlling the amount of ink infusion is: the sample ink color is uniform, the solid density and the dot gain value are within the allowable range, and there is no ink drawing on the ink stick, and the ink reaches equilibrium.
Third, the paper is overprinted
The paper is overprinted, that is, the paper is conveyed to the paper table, and the printing ink on the printing plate is transferred to the paper by the embossing of the blanket cylinder.
1, paper feeding positioning
The platform currently used is a lithographic proofing machine which is mostly a semi-automatic proofing machine. Most of the proofing methods are manual paper feeding, paper feeding, and paper feeding methods.
2, pressure transfer transfer
The pressure transfer printing is a process of transferring the graphic ink on the printing plate to the paper by the pressure contact between the blanket cylinder and the proofing platform, which generally includes two steps of trial printing and positive printing.
Fourth, color change ink washing and post-processing
In the process of color proofing, after each color is printed, it is necessary to carry out color changing and washing. First, the printed plate is removed, the color plate is replaced, and then the ink roller, blanket and imprinting platform are sequentially cleaned. Prepare for post-color proofing.
1. Cleaning and protection of the printing plate.
2. Clean the ink roller.
3. Clean the blanket.
4. Clean the imprinting platform.