Under the condition of high temperature heating, the photosensitive film of the positive PS type plate is heat-modified to make the cross-linking effect of a cresol-formaldehyde resin between the film formers, from linear to body-shaped structure, and the photosensitive film is printed. The stability, corrosion resistance, and mechanical strength of the text section. The roasting plate can increase the printing rate of the PS plate by 3-5 times and reach 30-50 thousand lines, thus reducing the production cost and improving the economic benefits. However, if it is not properly handled in the actual production work, the baking version will have quality problems.
In the following, we will analyze the quality of the roasting plates that we can often meet in production so that we can better analyze and judge when problems occur in production.
First, the plate should be processed first before baking. For example, the surface of the plate is cleaned, the development is correct, and so on. Here are some problems with plate quality due to unsatisfactory plate processing before baking.
(1) Light red after baking The light red color is due to a trace amount of photosensitive layer in the blank part of the printing plate, which becomes after baking. If it is treated with a developer, it will not get dirty; if the light red remains on the plate after being processed, it must be dirty. This situation can be used in addition to dirty agent treatment, and then ink inspection, generally can be resolved.
(2) Underexposure or insufficient development Insufficient underexposure or underdeveloped development may result in insufficient decomposition of the photosensitive resin in the non-graphic part and residual in the blank part, and the residual part is strongly adsorbed on the plate base in the baking process and is difficult to remove. , so that when printing, it will attract the dirt on the ink. In general, this situation can only be reprinted.
(3) Before grilling, the layout contamination causes the front plate of the plate on the plate to be dirty and the PS plate must be handled cleanly, and the traces of dirt, impurities, traces of dirt, etc. must be thoroughly and thoroughly cleaned. These stains will be firm after baking. Adsorption onto the plate, causing the plate to be dirty.
(4) Dirty dirt is often seen in the actual production, and the reason is very simple, that is, the dirty marks that are corroded by the dirt removing agent are not rinsed completely in time, and the same dirty marks as the dirt removing agent are reflected in printing. In order to prevent such dirty marks from appearing, be sure to thoroughly clean the dirt remover with a sponge or a wet towel after washing and then rinse with water, and then wipe the protective solution to start baking. Avoid dirtiness.
Second, we found that there are many problems in the baking plate on the baking plate protection agent, either due to improper use of the protective agent or due to improper formulation of the protective agent itself.
We first understand the role of the protective agent on the surface of the printing plate before baking. The most important role of the protective agent is to protect the blank part of the printing plate during the baking process, so that the pores of the oxide film that has been subjected to the sealing treatment at the high temperature of the baking plate do not reopen and are activated again to generate ink absorption. Dirty phenomenon.
Let's take a look at the following situations:
(1) Dirty plates after roasting plates Dirty plates on the PS plates are common failures in production and are often difficult to solve. We should first find out the cause of this kind of filthy problem, and then take a corresponding approach. If the dirty version uses gasoline to wash off the ink, there is a reddish-brown baking layer on the bottom, which means that the development is not complete, there is residual sensitizer baking hardening, the ink is dirty, this dirty has a solid foundation, Generally can not afford to go, if forced to remove, the surrounding reticulation will suffer. This dirty version can prevent recurrence only by increasing the time or intensity of the printing. If there is no red-brown baking layer beneath the dirty plate, it may be that the concentration of the protective liquid is low, the coating is too thin, and there is no effect of protecting the plate from contamination, and the micropores of the aluminum plate oxide film at high temperature are renewed. Open and contaminated. This dirty version will show up after the ink is drawn or printed, but it will not be observed at ordinary times.
(2) Shallow streaks appear on the layout text part, and the ink-receptive ability of the layout part decreases. The printing plate cannot faithfully reproduce the gradation of the original, and light-colored stripes appear. This is often caused by improper protection of the eraser. As the concentration of the protective agent is too high or the streak left by the rubbing is not uniform, it hardly dissolves in water after being baked and hardened on the plate, resulting in no ink absorption. In this case, the alkaline solution slightly thicker than the normal developer can be re-exposed and then neutralized with 3% phosphoric acid.
(3) Improper protection of smear protector PS version of the roasting protector is easy to precipitate, and the solute is deposited on the bottom of the bottle and the protective agent poured out is thin. The use of such a protective agent to wipe the plate will cause the plate surface protection film to be too thin or have a leaky area, causing the PS plate to become dirty. So be sure to shake it evenly before using it. Also wipe the protective agent must be rubbed evenly.
(4) Poor performance of the protective agent, and the baking plate is dirty.
The performance of the protective agent used in the PS plate baking directly affects the quality of the baking plate. Many manufacturers are self-made, should pay attention to whether the formula is appropriate, whether the performance of the drug used is standard, the preparation method is not appropriate. No matter which part of the link goes wrong, the performance of the protective agent will be affected and the protective agent will not be protected. In particular, when certain medicines are not available and they are replaced with infrequent pharmaceuticals, special attention must be paid to the quality of the protective agent. In order to prevent the loss of media, it is possible to try it out first, and you can put it into formal production only if there is no problem with it.
(Baking solution formula: water 1000ml; ammonium tetraborate (or ammonium hexaborate) 50g; flat plus 20 (or OP-10) 10g; sodium dodecylbenzenesulfonate 10ml.)
Note that under normal circumstances the amount of baking liquid to 20-30ml / (block split version) is appropriate.
Third, there will be such problems in the operation of the baking machine.
(1) Surface Scratches The high temperature in the roasting press causes the PS plate to deform and bend, often scratching the plate at the time of delivery, and causing scratches during printing. Slight scratches can be removed by using a plate cleaner or a dirt remover without damaging the image. If there is a serious scratch, destroying the photosensitive film cannot be recovered.
(2) Light brown or dark brown after baking The photosensitive layer is red-brown after baking. If the color is dark brown, the baking temperature is too high or the baking time is too long. This version is over-baked, so that the photosensitive layer of the resin has a different degree of carbonization, darkening and brittle, the result will reduce the print version of the printing capacity and ink affinity.
(3) After the baking plate is dark green, this indicates that the baking temperature is low or the time is short, the photosensitive resin is not completely polymerized, and its stability, corrosion resistance, and mechanical strength have not been maximized and can be supplemented. Bake it once to get the best results.
(Usually the curing point of the phenolic resin is 200-300Â°C, and the recrystallization temperature of the aluminum plate is 250Â°C. Therefore, the temperature of the baking plate should generally be controlled at 200-230Â°C for a time of five minutes.)
Fourth, there are many other aspects that affect the quality of baking plates:
(1) The fabric of the wipe protector is not clean. The fabric on the layout or the cloth is peeled off on the surface of the plate. If this happens, be careful to change the cloth. Wiping cloths should pay attention to the selection of long fiber cotton fabrics, or special cloth.
(2) The printer did not wipe the glue in time during the stoppage of the printing. After turning on the machine, it did not discharge the water roller first, but the ink roller or the roller with oil on the surface was put down without running water, resulting in a large number of layouts. Some ink. If the ink is washed with gasoline, the surface is clean, and it will be dirty when it is turned on. In this case, you can use a clean cloth, a cleaning solution, or a correction paste (the graphic base on the plate is already tight and tight, so it will not be removed by the correction paste). Scrub slowly until all the ink is dissolved. , And then wash with the fountain solution in time, you can completely remove the stains.
Fifth, pay attention to:
(1) The printed plate must be thoroughly cleaned before it is printed on the machine to avoid the phenomenon that the graphic part is not inked. Because the baking solution contains emulsifiers, and has a strong hydrophilic and oil-resistant, if you can not timely clean the baking version, it will easily accelerate the emulsification of the ink, and will also reduce the graphic basis of the lipophilicity.
(2) In normal circumstances, the recycled PS plate is not suitable for baking, and it is prone to severe deformation of the printing plate and printing on the machine, resulting in a fee.
The temperature, time, amount, etc., given above for baking are not absolute. Different brands of baking solutions generally use different production processes and will use slightly different in the production process. We must first do a good job of the preliminary experimental work, get more accurate data, and then start the formal production and use, to avoid the waste of media and production time.
Reprinted from: E Road Network
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