The Generation and Solution of Improper Post-baking of PS Plate

With the advancement of PS plate processing technology, the printability of the PS plate is getting better and better, and the printing rate is getting higher and higher. However, the same plate has different printing rates on different models. For example, on the BB machine, the PS plate has a lower printing rate. In order to improve the printability of the printing plate, it is necessary to carry out baking processing on the PS plate. After baking the PS plate, the printing rate of the PS plate can be increased by 3 to 4 times. However, in the baking process, if the operation is improper, it will cause some defects. , not only can not save the plate but cause waste. The following describes the causes of the layout and the solutions to the problem by changing the color of the layout after baking and the inking situation during printing.

1. Anomaly of color change after baking of PS plate

After the PS plate is baked, the color of the layout photosensitive layer will change. Under normal circumstances, after the plate is baked at a constant temperature of 230~250°C for 5~8min, the photosensitive layer turns from the original green to reddish brown, but if any of the printing, development, baking temperature and baking time etc. Improper control will have an impact on the quality of the roasting plate, causing anomalies in the layout color.

1) baking plate blank part of the light red

After the PS plate is baked, the normal color of the film surface is reddish-brown, and the blank part of the plate is the basic color of the plate. If the blank part of the plate surface appears light red, there is still a trace amount of photosensitive layer, which is caused by baking. If the bakeplate is developed a second time, its light red color disappears, and it will not cause smudging during printing. If the blank part of the plate is still light red after the second development, it may cause squalor during printing. In this case, gently wipe with pumice powder to reduce or eliminate the dirtiness. If it is severe, it is very difficult. Save, this version will be scrapped. The former micro-photosensitive layer is caused by the long time of the PS plate or excessive temperature during coating, which results in the oxidation of the photosensitive layer and Al2O3 of the aluminum plate base. This trace substance does not generally cause scumming. Bake will not cause viscera, and most of the latter will be caused by underexposure or insufficient development, and it will also cause viscera. Therefore, the plate to be baked should pay more attention to the time of the printing and the control of the development.

2) baking plate after the photosensitive layer was dark brown or dark brown

The appearance of such a color indicates that the baking temperature is too high or the baking time is too long, and the resin in the photosensitive layer is partially carbonized. At the same time, the plate base will be deformed, softened, and the mechanical strength will be weakened, which will affect the printing plate. The printing rate, the darker the color, the lower the printing rate, the solution is to reduce the baking temperature or reduce baking time.

3) baking plate after the photosensitive layer was dark green

The color of the photosensitive layer after roasting is such that the baking temperature is too low or the baking time is too short, the resin in the photosensitive layer is not completely cured, the purpose of baking is not achieved, and the printing rate is also low. In this case, you can immediately re-insert into the baking machine, extend the time or increase the temperature for a second baking, so that the color of the baking plate reaches a reddish brown color.

2. Anomalous situation of printing ink on the plate after printing on the plate

Although it can be seen from the layout color whether the baked printing plate is qualified, sometimes the layout color is normal. When printing on the machine, there are problems such as dingy and ink incomplete.

1)When printing on the machine, the phenomenon of "doctor" inking appears incomplete

Before the baking version, it is necessary to apply a protective agent to the PS plate. The main component of the protective agent is an emulsifier, which has a hydrophilic and oleophobic property. When the protective agent coating is too thick, it is hardly soluble in a developer with a low concentration. (After baking, PS protector must be washed off the developer, ie secondary development). Therefore, some protective agents remain on the surface of the plate and cause no inking. This “bead-like” phenomenon is due to the excessively high concentration of the protective agent that has been rubbed and marks that are not uniform. In this case, use a developer that is slightly thicker than the usual PS plate developer to scrub once. After brushing, neutralize the plate with 3% phosphoric acid. Rinse the plate with PS plate developer, or directly wipe it with gasoline. Plates can also be used to extract ink, which can eliminate the "doctor" shape without ink.

2) When the machine is printing on the local dirty or full version dirty

There are two general conditions for this phenomenon. First, if the bottom layer has a reddish-brown baking layer after washing with sloppy gasoline, the development is insufficient. This type of dirty is generally not easy to remove. Second, if there is no red-brown baking layer, it means that the concentration of the protection liquid is too low, and the overcoating layer is too thin to protect the layout from contamination. This contamination can not be found immediately. Only when the printing plate is inked or printed can it be discovered. Although this dirty condition is more difficult to solve, it is possible to use the PS version of the revised paste to wipe the plate (the revised paste is baked. Membrane does not work), can eliminate dirt. If the solution used for the baking plate is left standing for a long period of time, the solute will precipitate, and the solution that is poured out first will have a low concentration, and the protective layer that is rubbed will be too thin. In severe cases, it will cause viscera. Therefore, before each use, it should be shaken or stirred to make it evenly mixed, so that the above disadvantages can be avoided.

3) After the printing on the machine, the surface of the plate gradually appears as a film or tape

After the plate has been baked, dirt spots on the plate, film blots, etc. can not be repaired with repair paste, so before the baking plate operators generally have to carefully check the plate, revision, but sometimes the film blots and The tape is very lightly imprinted and cannot easily be found during the revision process. After baking, a very light red-brown imprint can be found after careful inspection. After the printing on the machine, the imprinting of the film becomes more and more obvious. In this case, use a pumice stick to wipe the imprint on the plate, wipe the place where the pumice stick has been wiped with the repair paste, and wipe the plate with water cloth to remove the above imprint.

3. Problems that should be noticed when applying protective agent and baking plate

Some of the oxide pores of the original closed oxide layer reopened if not protected before baking, and the baking changes as follows:

These micropores are highly adsorptive, so the blanks are very easily contaminated, and if they are improperly protected, they will be smeared.

1) How to apply protective agent

Dirty the developed printing plate, rinse with water, scrape off the water on the plate, pour the protective agent on the plate, use about 20~30ml for each block, and wipe the entire plate with degreasing gauze. Uniform (Note must be uniform, can not have traces of water flow), can be placed in the baking plate baking version. Baking time is 5~8min. After taking out the cooling plate, the developer is used for secondary development to remove the protective agent on the plate surface. After air drying, the gum arabic can be used for standby printing.

2) Note

After baking, the photosensitive film is strongly adsorbed on the plate surface, and it is difficult to remove it from the plate with a revised paste, so the plate must be repaired before baking.

After repair, be sure to use water to rinse off the repair paste, otherwise, the remaining repair paste and the dirt that has been removed will contaminate the plate and cause dirt on the plate.

The amount of protective agent should not be too much, too many will appear water-like traces, serious phenomenon of the above-mentioned "Daozi" inked incomplete phenomenon, but the amount can not be too little, otherwise it will lose its protective effect and the occurrence of Shangdang phenomenon. The dosage is generally controlled so that there is no trace of water flow after rubbing.

Grease protector should be used when the degreasing gauze, so as to avoid the loss of fiber in the baking version of the layout. Do not apply too much force when rubbing, so as to avoid gauze fiber off and affect the quality of baking.

The baking temperature and baking time should be determined according to the level of the curing point of the photosensitive layer: baking temperature is too high or too long will cause the carbonization of the photosensitive layer, the deformation of the plate base, softening, affecting printing plate printing rate; temperature Too little or too little time will not cure enough to achieve a baked version.

After baking, you must naturally cool, do not force cooling, so as not to deform the aluminum plate base. After the plate is naturally cooled, the plate developer is used for secondary development.