Analysis of the quality problem of the PS version of the baked version
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Under the condition of high temperature and heat, the photosensitive film of the positive-working PS plate is thermally modified to cross-link the cresol resin between the film-forming agents, and the linear shape is changed into a body-shaped structure, which enhances the photosensitive film or the printing plate. The stability, corrosion resistance and mechanical strength of the text. The baking plate can increase the printing durability of the PS plate by 3-5 times and reach 300,000-500,000 impressions, thereby achieving the purpose of reducing production cost and improving economic efficiency. However, if the operation is not carried out properly in the actual production work, there will be quality problems in the baked version.
Let's take a look at the quality of the baked version that we often encounter in production so that we can better analyze and judge when there is a problem in production.
First, the printing plate should be processed first before baking, for example, to make the surface of the printing plate clean, correct development, etc. The following are some of the problems of the printing plate quality caused by the unsatisfactory printing of the printing plate before baking.
(1) Light red after baking
This light red color is caused by a small amount of photosensitive layer in the blank portion of the printing plate, which is baked. If it is treated with developer, it will not be dirty; if the red color remains on the plate after treatment, it will be dirty. This kind of situation can be treated by removing the dirt, and then the ink inspection can generally be solved.
(2) Underexposure or incomplete development
Insufficient exposure or incomplete development may result in insufficient decomposition of the non-image portion of the photosensitive resin, and residue in the blank portion. The residual portion is strongly adsorbed with the plate during the baking process, and is difficult to remove, so that ink is absorbed during printing. Dirty. Generally, when this happens, it can only be reprinted.
(3) Before the baking, the layout is dirty and the plate is dirty.
Before the baking version, the PS version must be cleaned, and the dust, impurities, and traces of dirt should be thoroughly cleaned in time. These dirt will be firmly adsorbed on the plate after baking, causing the plate to become dirty.
(4) Dirty dirt
It is often seen in actual production. The reason is also very simple. The dirty marks that have been corroded by the dirty agent are not rinsed out in time, and the dirty marks that are exactly the same as the dirt are reflected during printing. In order to prevent the appearance of such dirty marks, after cleaning, be sure to thoroughly clean the decontaminant with a sponge or a wet towel and then rinse with water, then wipe the protective liquid to start the baking, to avoid the dirt.
Second, we found that there are many problems in the baking plate on the baking protectant, or because the protective agent is not used properly or because the formulation of the protective agent itself is not suitable.
Let us first understand the effect of applying a protective agent on the surface of the printing plate before baking. The main function 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 which have been sealed by the sealing process under the high temperature condition of the baking plate are not re-opened, and are activated again to generate ink absorption. The phenomenon of dirty.
Let's take a look at the following situations:
(1) Dirty on the plate after baking
The dirty version of the PS version is a common fault in production and is often difficult to solve. In the face of this kind of dirty problem, we should first find out the cause and then take the corresponding method. If the dirty version is washed with gasoline and the red and brown baking layer is on the bottom, the development is not complete, and the residual sensitizer is hardened by baking, and the ink is dirty, and the dirt has a solid foundation. Generally, you can't get rid of it. If you forcibly remove it, the surrounding netting will suffer. This dirty version can only prevent recurrence if it increases the time of printing or the development intensity. If there is no reddish brown baking layer under the dirty plate, it means that the concentration of the protective liquid is low, the coating is too thin, and the protective plate is not protected from contamination. At the high temperature, the microporous oxide film of the aluminum plate is re-applied. Open and contaminated with dirt. This kind of dirty version will not be displayed after ink-drawing or printing, and it will not be observed.
(2) Light streaks appear in the layout part of the layout, and the ink-receiving ability of the layout part decreases.
The printing plate cannot faithfully reproduce the tone of the original when printing, and light streaks appear. This is often caused by improper wipe protection. Due to the streaks left by the concentration of the protective agent or the unevenness of the rubbing, the hardened fixing after baking is hardly soluble in the printing plate, and the ink is not absorbed. In this case, it can be re-displayed with an alkaline solution slightly thicker than the normal developer, and then neutralized with a 3% concentration of phosphoric acid.
(3) Wiper protector is not dirty
The PS version of the baking protectant is easy to precipitate, and after standing, the solute precipitates to the bottom of the bottle, and the protective agent poured out is thin. Wiping with such a protective agent may cause the layout protective film to be too thin or leaky, causing the PS plate to become dirty. Therefore, it must be shaken evenly before use to pour out. Also, wipe the protective agent and wipe it evenly.
(4) The performance of the protective agent is not good and the baked version is dirty.
The performance of the protective agent used in the PS version of the baking plate directly affects the quality of the baking sheet. Many manufacturers make their own preparations, pay attention to whether the formula is proper, whether the performance of the drugs used is standard, and whether the preparation method is suitable. No matter which link is faulty, it will affect the performance of the protective agent, and the protective agent will not be protected. In particular, when certain drugs are not available, it is necessary to pay special attention to the quality of the protective agent when it is replaced by an uncommon agent. In order to prevent loss of the plate material, you can try it first, and you can put it into formal production without being dirty or problematic.
(Baked plate solution: water 1000ml; ammonium tetraborate (or ammonium hexaborate) 50g; flat plus 20 (or OP-10) 10g; sodium dodecylbenzenesulfonate 10ml.)
Note that in general, the amount of baking solution should be 20-30ml / (block open version).
Third, there are problems in the operation of the baking machine.
(1) Surface scratches
The high temperature in the baking machine causes the PS plate to be deformed and bent, often scratched when scraping, and dirty when printed. Minor scratches can be removed by using a surface cleaner or decontaminant when the image is not damaged. If there is a serious slash, the photosensitive film will not be recovered.
(2) Light brown or dark brown after baking
Under normal conditions, the photosensitive layer is reddish brown after baking. If the color is dark brown, the baking temperature is too high or the baking time is too long. This type of plate belongs to excessive baking, which makes the photosensitive layer resin have different degrees of carbonization, darkening and brittleness, and the result will reduce the printing durability and ink affinity of the ps plate.
(3) Dark green after baking
This type of color 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 are not maximized, and it can be re-baked once to achieve the best effect. .
(The curing point of the general phenolic resin is 200-300 ° C, and the recrystallization temperature of the aluminum plate is 250 ° C. Therefore, the temperature of the baking sheet should generally be controlled at 200-230 ° C, and the time is preferably 5 minutes)
Fourth, there are many other factors that affect the quality of the baking sheet:
(1) The cloth of the wipe protection agent is not clean. The fibers of the cloth or cloth are peeled off on the plate, and the upper plate is caused by baking. In this case, pay attention to replacing the cloth. Wipe cloth should pay attention to the choice of long cotton fabric or special cloth.
(2) There is no timely rubbing during the middle of printing. After the boot, there is no water roller first, but the first roller roller or the oil roller with oil on the surface is put down without running the water, causing 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 cleaning solution or a retouching paste (the graphic base on the printing plate is too tight, so it will not be removed by the finishing paste), and the ink will be completely dissolved. Then, with the dampening solution washed in time, you can completely remove the dirt.
Fifth, pay attention to:
(1) The baked plate should be thoroughly cleaned before printing on the machine to avoid the phenomenon that the graphic part is not inked. Because the baking solution contains emulsifier and has strong hydrophilic and oil-repellent properties, it cannot be cleaned in time after baking, and it is easy to accelerate the emulsification of the ink, and also reduce the lipophilicity of the graphic base.
(2) In general, the regenerated PS version is not suitable for baking, and it is prone to serious deformation of the printing plate, which cannot be printed on the machine, resulting in a fee version.
Some of the above given about the temperature, time, dosage, etc. of the baking plate are not absolute. The different brands of baking protection liquids generally use different production processes, and will also be slightly different in use. In the first step, we must do the preliminary experimental work, obtain more accurate data, and then start the formal production and use, to avoid the waste of the plate and production time.