How to improve the quality of printing
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In the printing process, printing is an important part of the link, what problems appear in the previous process, some can be compensated in the printing process, and some special requirements of the printing process can be adjusted in the printing process. Therefore, the quality of the print has a direct impact on the quality of the final print. So how to improve the quality of printing, I believe that the following aspects should be noted.
(1) Correctly distinguish between proof and version
In fact, for proofing and printing, you should print two different versions. For proofing, from the structure of the proofing machine itself, it is generally platform type, the pressure of proofing is smaller than the printing pressure, and the speed is slower than the printing speed. At the same time, because the dot size caused by proofing is small, when the printing is required, the dot between 2% and 3% is retained, and 98% of the dots cannot be pasted. For printing, because the printing pressure is large and the speed is fast, the printing ink has less viscosity than the proofing ink, and it is easy to cause the dot to increase, and can be increased to 30% to 40% at most, so the same plate is used for proofing and printing. The effect is different. Therefore, when printing the printing plate, it is required to retain 4% to 5% of the dots, and 96% of the dots are not pasted, leaving room for the dot enlargement caused by printing, and the printed matter is easy to approach the proof.
(2) The printing plate is dirty
1.The printing plate is dirty due to improper printing. There are dirty spots on the glass of the printer; there are dust or scratches on the original; the transparency of the film is not good or the fog of the film is too large, and the dirt caused by insufficient exposure.
Remedy: For the cause of the problem, "the right medicine." Wipe the glass of the platen cleaner; remove the dust from the original, repair the missing marks on the original; return the unqualified original and reproduce. If the plate is dirty due to insufficient exposure, if the stain is not too serious, the diffuser can be used for supplementary exposure, and the position of the light source should be moved during exposure; the concentration of the developer can be increased and development can be performed once.
2.The printing plate is dirty due to improper development processing. During the development process, since the developer temperature is too low, the development time is too short, the proportion of each component in the developer is not suitable, and the developer is fatigued or even ineffective; the developer is wiped with a poor quality sponge or the wipe of the plate is not clean enough, and the water is not rinsed. Thorough; automatic developing machine misalignment such as poor developer circulation, unstable temperature, etc.
Remedy: Check the temperature and development time of the developer and adjust to the corresponding standard; adjust the developer according to the formula given by the manufacturer, and update the developer in time; the plate in the development should be washed thoroughly with water, wipe the plate with high-quality sponge; Machine and so on.
3.Dirty plates caused by improper handling of dirt. In the process of removing the dirt, the operation is not careful, and the dirt to be removed is omitted. In addition to the insufficient amount of dirty liquid, the short use time, and the fatigue removal of the dirty liquid for a long time, the dirtyness is not completely eliminated; On the layout, etc., it may cause the plate to be dirty.
Remedy: In addition to the dirty operation should be careful, apply the brush to remove the dirty liquid to remove dirt; the dirty time should be kept at 20 to 30 seconds; in addition to the use of dirty liquid should be tightly closed; the layout should be washed thoroughly with water after the dirty treatment.
4.The layout is dirty due to improper gluing operation. In the gluing operation, a low-concentration glue is used, and the non-image portion is oxidized. The glue coating is uneven, too thick or streaked, and printing with a dry plate causes the printing plate to be dirty. Sewage.
Remedy: increase the concentration of the glue; fully spread the glue; the plate after the glue, the plate is completely dry and then printed on the machine.
5.The printing plate caused by the tape on the original is dirty. First of all, it should be prevented. In the imposition, thin and clean transparent tape should be used as much as possible. If the tape adhesive sticks to the printing plate, it should be wiped off and developed. When printing on the plate, fully pump the air to minimize the air layer around the imprinted tape and the original film, minimizing the possibility of light interference. If there is a tape mark on the plate after exposure, it is necessary to manually remove the dirt with a dirt remover or perform a double exposure to remove dirt.
(3) The dot reproducibility is not good
The reproducibility of the dot is not good, and there is a "dark" in the outlet.
Phenomenon (ie, the periphery of the dot is not smooth, the outline is not clear), the dot is reduced or lost, and the dot is enlarged. Poor reproducibility of the dot may result in a decrease in image sharpness and a change in tone.
1.The dot appears dizzy. The main reason is that the printing machine has failed. For example, the printing machine has insufficient air pumping, low vacuum, or the glass plate and the printing plate surface are not well adhered when the printing plate is installed. Since the drying process has the scattering effect of air on the light, a dot is generated. The halo phenomenon.
Remedy: timely repair the printing machine to ensure that the vacuum pump works well and has sufficient air pumping. The rubber seal of the printing plate is good and closed. When the plate is printed, the light source can be turned on after confirming that the plate is closely attached to the original plate. Exposure; when splicing the original, you need to repair the burrs on the edge of the original, the adhesive tape should be attached as far as possible from the image, or the original original and the plate should be closely attached.
2. The dot is reduced or lost. The main reason is that the original density is too low, the thinning is excessive, the exposure time is too long, the concentration of the developer, the temperature is too high, and the development time is too long.
Remedy: If the dot is lost, you should first check the degree of dot reduction of the film itself. For example, if 50% of the dots on the film are square, 4% to 5% of the dots are complete, etc. In short, check the quality of the film, and then judge Whether the dot is lost in the process of printing. Excessive exposure and excessive developer concentration can cause the dots that should be retained on the layout to be lost or the text strokes to become thinner. The original, which has an image density of less than 1.5, must be re-formed; the optimum exposure time is obtained by test exposure and used to guide the exposure operation; the concentration and temperature of the developer are adjusted, and development is carried out according to standard development conditions.
3. The outlets are expanding. The main reason for the expansion of the dot is that the concentration and temperature of the developer are too low, the development time is too short, and the developer is aged.
Remedy: Adjust the concentration and temperature of the developer, and develop according to the standard exposure conditions according to the specifications according to the optimal exposure time.
(4) The color of the baking plate is abnormal.
The baking color is abnormal. The normal color is reddish brown. If the layout is tea green or dark green, it indicates that the baking temperature is too low or the baking time is too short. If the layout is brown, the baking temperature is too high or the baking time is too long. When the resin is partially carbonized, the printing durability of the printing plate is also reduced accordingly; if the blank portion of the layout after baking is light red, the photosensitive layer is left in a small amount due to insufficient development of the printing plate.
Remedy: If the layout is green or dark green, increase the baking temperature or extend the baking time until the color of the layout reaches reddish brown; if the layout is brown, shorten the baking time; if the blank part appears light red, you can Gently wipe with pumice powder, but it cannot be remedied when the area is large.
(5) Bad printing in the layout
The page is poorly inked. Mostly caused by improper operation in the process of printing, developing, removing dirt and sizing.
1. Improper printing. There are scratches, dust, and foreign matter on the glass of the plate, and the density of the original image is insufficiently overexposed.
Remedy: Remove the dust and foreign matter on the glass of the printing frame, reproduce the original to increase the density of the original plate; print the plate according to the optimal exposure time, check whether the shading is strict and improve the shading method.
2.Developed, dirty and improper. The development temperature is too high, the development time is too long, the washing is not thorough, the developer remains on the image, and the dirty liquid is splashed from the brush when it is dirty, and the image portion is touched when the dirty liquid is wiped off, because the layout is too wet and the dirty liquid is diffused to The image is not thoroughly cleaned except dirty.
Remedy: Check the temperature and development time of the developer, and adjust to the standard; re-dispense the developer, and carry out the test development; carefully remove the dirty operation, such as the brush to remove the dirty liquid can not be too much, the layout can not be touched by hand, After the moisture on the plate is dry, remove the dirty liquid, and then thoroughly clean the plate with water.
3. Improper gluing. The sizing method is not correct, the coating of the glue layer is uneven or too thick, the temperature at which the glue layer is dried is too high, and the glue liquid is too thick, etc., which may cause poor ink on the plate.
Remedy: Use the correct gluing method, evenly apply the glue and do not make the glue layer too thick, dry the glue layer at the appropriate temperature (generally should be around 60 °C), reduce the glue content in the glue.
(6) The printing plate's printing durability is declining
The main reason for the decrease in printing durability is the two aspects of printing operation and printing. In terms of printing: 1 before the exposure or before development occurs; 2 film density is not high; 3 due to the high temperature and concentration of the developer, long development time or excessive excess caused by over-expansion; 4 strong acid, strong alkali, organic solvent In addition to the dirty liquid and other chemicals attached to the printing plate; 5 too many times with the plate cleaning agent, etc., these will affect the printing durability of the printing plate. In terms of printing, if the printing pressure is too large or the paper powder is excessive, and a strong plate cleaning agent and a drum cleaning agent are used in the UV printing, the printing durability is inevitably lowered.
(7) Bottom blue on the dried printing plate
In production, a version of the sun is exposed, whether it is due to the problem of pre-production of the plate, or the matching conditions of the body exposure and development time are not suitable, and the dried version has a bottom blue. The "secret" of the bottom blue is: 1 when the plate is made, the sand is too thick, the current of electrolytic oxidation is not matched; 2 the exposure is insufficient or the concentration of the developer is insufficient, or the two conditions are not properly matched. The bottom blue phenomenon has caused headaches for many operators. This problem occurs, and more development is not possible, and less development is not possible. If multiple developments are made, the dots that need to be retained will be reduced or lost; if less developed, the entire layout will be affected. Under the condition of moderate exposure and development, the bottom blue will be dirty after the completion of the shadow, but once it is dirty, there will be a watermark on the plate, and the watermark plate will be printed on the machine, and the watermark will be around. If you want to get dirty, if you use the repairing liquid to fix the dirt, you will find another circle of dirt. If you are lying on the picture, text or network, the plate will not be used at all. To solve this problem, it is necessary to apply a thin layer of glue before removing the dirt, and high quality prints cannot use this version.
(8) Master the correct printing time
By properly controlling the exposure time, it is possible to ensure that the printed screens are smooth, well-defined, and the images are copied accurately. At the same time, it is also the key to avoid the problems of "hollow", "burr" and "virtual edge". In daily printing work, set different exposure times according to different situations. First, the large version of the textbook version of the sulfuric acid paper and the photo film of the photo film directly discharged by the computer, the exposure time is 120s. This exposure not only ensures that the text lines are intact, but also develops thoroughly, but the edges of the base and the traces of the tape will remain on the plate, so be sure to remove the dirt carefully. Some original text lines are not black enough, especially the horizontal strokes of the Song characters are relatively thin, and the printing time is too short to be short-lived; the pattern is not black enough, and the printing time is long. After the PS plate is developed, the gloss is lost, and the ink performance during printing is poor, which affects the printing quality. Second, the large version of the line text version photographed or copied, the exposure time is about 250 s. Because these original images have a density of 4.0. The exposure time increases, and there is no obvious influence on the line text, but the original film edge and the tape paper trace can be fully exposed. After the development, the printing plate is very clean, and basically no need to remove the dirt, which can improve the work efficiency of the printing plate. Third, the monochrome level dot version printing time is about 120 s. This type of printing can not be too much time, especially to prevent 3% of small outlets from disappearing due to excessive printing time. Fourth, the color layer version with flat screen printing, 10% flat screen version, more time for printing, there will be "bad network"; more than 30% of the flat screen version, the printing time will not be a little more There is a "bad network". 1.In the color layer version, there is a large version of the collage with 10 to 20% flat net, and the exposure time is about 120 s; 2.The color version has a collage version with more than 30% flat net, and the exposure time is about 140s. 5. In the color layered version, there is no flat net, but there is a larger title word or pattern on the ground. This type of printing is often used in printing: the ink color of the printed dots is enough, but the color of the solid parts is not enough, and the ink layer is not thick enough. If the amount of ink is increased, the color of the solid part is enough, but the color of the dot is partially Not enough. If the printing time is properly increased, the outlets will be reduced, that is, the printing plate will be lightened, and some of the gaps caused by the large amount of ink in the field will be compensated fors.
In summary, pay more attention to the above common problems in the printing plate, you can truly reproduce the original, ensure the quality of printed products, improve work efficiency and minimize the occurrence of waste products.