Analysis of common problems in the drying process

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Analysis of common problems in the drying process and printing process of PS plate (Part 2)

I. common problems and treatment methods in printing plate

1. Image dizziness and unclean blank part. To solve this problem, the glass of the printer must first be kept clean. Wipe it with alcohol, both sides. If the transparency is not enough after work, the light penetration will be affected, and the exposed version will be blurred. If the film plate and the glass plate are not closely attached, it will also cause drying and filtering

sometimes, when a film base is used for a long time, there are many residual adhesives left by adhesive tape on it, and the transmittance will be affected, and the film and the film base will not be pasted so closely. Therefore, the film base needs to be replaced if it is used for a long time. When making up, if two images overlap, the image is also not real. If the blanket is used for a long time, it will age, and there will be a small amount of air leakage at some edges. The PS version and the film will not stick tightly, and the pictures and texts exposed will also be false. If the machine is used for a long time, check whether the vacuum degree of the air pump is enough

if the lamp is used too long, the cutting rate will decrease and the exposure will be insufficient. When inhaling, if you can't walk around gradually from the middle, it will cause local bubbles, and the PS version will be partially blurred. This is to check the base plate at the bottom

2. The PS version is inaccurate. To solve this problem, we should check from the film. The spots on the film used for printing should have enough blackness. The spot structure on the printing plate should be transferred to the printing plate. Never let the covered part (spot) pass through the amount of light, causing the photosensitive layer of the printing plate to become photosensitive. Otherwise, the dots on the printing plate will not be solid, and the dots will fall off when printing. Point halo, we know that the absolutely clear point, between the light transmission plane and the coverage with high blackness (7) when the experimental force is greater than the upper limit of 1, the transition is very steep, which is sudden, and the edge of the point is actually vertically rising. On the contrary, the blackness increases slowly from the edge. So the point produces an edge with a large or small inclination

the faint spots on the printing plate cause color deviation due to their unstable performance, and the phenomenon of "dot loss" can often be seen on the printing plate. To solve this problem, the film before printing should be strictly checked, and the dots should have enough blackness and clear edges

3. It cannot reflect the subtle parts of the work. Like a hair, it is on the photo, but the printing plate becomes blurred. This is mainly because the exposure is not enough or the concentration of the potion is too high when developing the version, which washes out the details

II. Common problems in printing

printing should be carried out after printing. If the temperature of the developer in the plate processor is too low, and the washing speed of the plate processor is too fast, the development time will be shortened, the development will be insufficient, and the printing plate will not be washed clean. If the developer concentration is not enough, and the time for replenishing the developer is adjusted too long, the printing plate will not be fully developed

the way to eliminate the above faults is to check the temperature and development time of the developer and adjust them to reasonable data. When using developer, the manufacturer will provide the proportion of the formula, which should be done according to the proportion. But sometimes it can be thickened. The plate punching machine should be repaired in time, the rubber rollers should be replaced, and the crystals in the tank and on the pipe wall should be cleaned regularly. The specific method is: use oxalic acid to circulate water in the plate washing machine and effectively remove dirt. At the same time, the brush roller on the machine should also be cleaned and replaced if necessary. In addition, in the process of dirt removal, careless operation, insufficient amount of dirt removal liquid, short time of using liquid, failure of dirt removal injection, and drying of dirt removal liquid on the plate after use may cause printing plate dirt

in the process of gluing, the use of low concentration glue and the oxidation of non graphic parts will cause the printing plate to get dirty. The solution to this kind of problem is: after the dirt removal injection is used up, it should be covered tightly; The layout should be fully washed after dirt removal. When gluing, the glue concentration should be increased and the glue injection should be uniform; For the printing plate after gluing, the length of the plate shall be dry before printing

III. common problems in baking version

the film-forming agent of the photosensitive layer of positive pattern PS version is made of cresol formaldehyde resin after baking, which changes from linear to body structure, enhancing the wear resistance of the graphic part, so baking version can improve the printing resistance. But in practice, there are often some problems in baking

when printing, the printing plate does not faithfully reflect the tone level of the original, but the glue channel. The glue track is often caused by improper wiping of the protective agent. The glue track left by the high concentration of the protective agent or uneven wiping is hardened and fixed on the printing plate after baking, which is difficult to dissolve in the developer, resulting in non ink absorption. In this case, it can be displayed again with alkaline injection slightly thicker than normal developer

during baking, the high temperature causes the PS plate to deform and bend, and often scratches when sending the plate, causing scratches during printing. When the slight scratches do not damage the image and text points, the dirt remover can be used to remove them. Light red after baking. This kind of light red is changed after baking because there is a small amount of photosensitive layer in the blank part of the layout. If you dispose of it with developer, it won't get dirty. If the light red is still left on the page after treatment, it must get dirty. This situation can be treated with dirt remover. Dark brown or dark brown after baking. Normally, the photosensitive layer is reddish brown after baking. If the color is dark brown or dark brown, it means that the baking temperature is too high or the finishing time is too long. This type of plate belongs to the excessive baking, and the resin of the photosensitive layer is carbonized to varying degrees, darkened and brittle, which will reduce the printing resistance of the PS version instead

dark green after baking. This kind of plate color shows that the baking temperature is low or the time is short, the photosensitive resin is not fully polymerized, and its wear resistance, corrosion resistance, solubility and inkiness have not been maximized. At this time, the second baking can be carried out to achieve the best effect

ps version dirty after baking is a common fault. There are several reasons for this. The dust, impurities and dirt removal scratches on the plate before baking were not thoroughly cleaned in time. After baking, these dirt will be firmly adsorbed on the plate, causing dirt on the printing plate; Insufficient exposure or incomplete development will cause insufficient decomposition of photosensitive resin in non graphic parts, and ink absorption and dirt during printing; Wipe the protective agent improperly and get dirty. PS plate baking protector is easy to precipitate. After placing, the solute precipitates to the bottom of the bottle, and the protective solution poured out on the back is thin. Wiping the plate with this protector will cause the plate protection to be too thin or have glue leakage, resulting in dirt on the PS plate. Therefore, it must be shaken evenly before use, and poured out for use, and it must be wiped evenly and leveled when wiping the protective agent; The printing machine stopped halfway and did not wipe the glue in time. After starting up, it did not discharge the water roller first, but first drop the ink roller, resulting in a large number of ink tracks on the layout. If the ink duct is washed with gasoline, the surface will be clean and dirty as soon as it is turned on. In this case, wipe it slowly with a clean cloth and a little pine oil. After all the ink ducts are dissolved, wash it in time with clean water, that is, restore it as before, and there is no dirt; The performance of protective agent is poor, and the baking version is dirty. The performance of the protective agent used in the baking plate of PS plate directly affects the quality of the baking plate @5. Press reset and then press the peak key. Many manufacturers prepare it by themselves. Pay attention to whether the formula is appropriate, whether the performance of the drugs used is standard, and whether the preparation method is appropriate. No matter which bad book goes wrong, it will lead to the performance problems of the protective agent, resulting in the unprotected effect of the protective agent. In particular, when some drugs are not available and are replaced by drugs that are not commonly used, special attention should be paid to whether the quality of protective agents is reliable. In order to prevent the loss of plates, you can try them first, not dirty, and put them into normal production after there is no problem. In order to obtain better printing quality, while belonging to the above always, pay special attention to the control of the pH value of the fountain solution during the printing process, and master the balance of water and ink

IV. problems prone to occur in the printing process of PS version

the task of PS version is to make the graphic part as accurately as possible transmitted to the blanket. The graphic part is hydrophilic, and the non graphic part is ink friendly. But in fact, without this personal ideal, there will be all kinds of problems related to PS version. Here are some examples and discussions

1. The non graphic part of the layout is dirty, that is, the non graphic part is ink friendly The reasons are as follows

a. the chemical composition of the fountain solution is improperly configured, eroding the hydrophilic layer of the blank part. The treatment method is to replace the fountain solution and use the fountain solution correctly configured according to the manufacturer's instructions. B. The roll sleeve of the water roller against the plate is too dirty or worn, damaging the blank surface. Treatment method: clean or replace the water roller sleeve against the plate. Wet washing can protect the printing plate. C. In halftone printing, too much ink will cause ink expansion, which will eventually increase the sense of non graphic areas. Treatment: printing with ink film with thin pigment. D. There are sand particles of sandpaper on the rubber cloth, which wears the printing plate. Ball filling measures: clean the rubber cloth and change the paper; Add anti accumulation agent to the fountain solution; Adjust the amount of water to the minimum, and add more carrier, gum arabic and/or alcohol or alcohol substitutes as needed to keep the non graphic part of the printing plate clean on the basis of reducing the amount of water; In B-B printing, reduce the pressure between the plate and the rubber. If there is an impression cylinder, check the pressure between the impression cylinder and the paper; If the accumulation mainly occurs in the first printing unit, increase the amount of water to help clear the debris on the paper. E. Oxidation of aluminum substrate. Oxidation dirty looks like a lot of clear dots or doughnut shaped spots on the canal. It often appears in the area in contact with the wet version water roller for a long time. If the printing plate dries too slowly, or is stored in a wet place before development or during two printing production, oxidation is easy to occur. If the printing machine stops printing when the printing plate is not dry, the printing plate will also be oxidized. Action: follow the recommended plate handling procedures. The printing plates should be stored in a dry place. In the process of plate making, coarse cotton cloth is used to dry the printing plate quickly. In the process of printing, if you stop, you should leave the plate roller and drive the car empty until the plate is dry. F. The water roller and/or ink roller in the ink system work incorrectly, which may cause circumferential or axial dirty bars in printing. Measures: check the pressure, cleanliness, geometric accuracy and overall state of each roller in the ink system. G. The printing plate is pre exposed (grayed out) in the prepress stage. Measures: keep the printing plate in a box away from light; Install appropriate safety lighting at the plate making site. H. The ink is too soft or oily. At this time, contact the ink manufacturer. 1. Too much fountain solution causes the imprint to be snow flake; The ink color is gray on the ground, and the color is dimmed on the ground; When you zoom in, you will find that the field is uneven and full of tiny white spots. Too much fountain solution is emulsified in the ink. When the ink film splits, water droplets are exposed, which hinder the transmission of the ink to the paper. At this time, reduce the water supply

2. Some pictures and texts of PS version are worn. There are two reasons: first, there is too much resin in the fountain solution; Second, there is too much acid in the fountain solution. The solution is to re allocate the fountain solution and check the pH value

3. There are white fibers on the printing plate. This is mainly caused by too much paper wool or the fabric falling off by the water roller. The treatment method is to clean the printing plate

4. The graphic part of the plate cannot be inked properly. There are two reasons: first, there is a cured product of resin or revision solution in the graphic area of the printing plate, so it is only hydrophilic rather than ink friendly; The second is in cots, plates and rubber

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