When the offset printing plate is printed on the machine, the blank part is sometimes dirty, which is generally caused by incomplete development. The photosensitive resin in the blank part of the printing plate is not completely clear, and there is resin residue.
To make the blank part of the printing plate free of resin, on the one hand, the exposure is determined according to the sensitivity of the PS plate during the printing. If the exposure is insufficient, the development will be unclean under normal developing conditions, and a small amount of resin will remain on the plate. On the other hand, different kinds of printed products should be treated differently, such as high-end exquisite color work, copying time control in the gray ladder feet 3 clean, or even 2 clean to ensure that the small outlets do not lose the sun; and print version, the sun The version is controlled to be clean at level 5 of the gray ladder, sometimes even grades 6 and 7 are clean, and the method of strong exposure and strong display is adopted in order to shorten the time of plate making and ensure the timeliness of printing. Under certain conditions, underexposure can also improve the quality of the printing plate through enhanced development, and over-exposure can be remedied by using weaker means.
This article selects a representative sample of three brands of positive models in the current domestic PS plate to do the sample, to the positive part of the positive version of the PS version of the net (no small green dot) as a clear net standard for PS version of the development process Experiment to explore the correct development method.
In this experiment, the exposure of the PS plate was controlled at a level of 5 on the gray scale and then 18 at low temperature. C. Room temperature 23. C, high temperature 28. Under the condition of C, four different types of positive PS plates were manually developed with different concentrations of Huaguang PD type developer, and the clear development time was the best development time of the plate.
Each grade of positive PS plate, due to different photosensitive resin formulations, the structure of the film-forming resin used is different, so the development process is not the same, some suitable for strong display, and some for weak display. If the version with strong resistance to strong display is treated with weak display, it will often show no net; if the version with weak display is strong, it will often destroy the photosensitive resin layer, that is, the part that should not be dissolved is also dissolved.
(1) Developer concentration
The developer concentration is the first of the three elements of the developer and must be prepared at the manufacturer's recommended concentration. Under normal circumstances, the greater the developer concentration, the shorter the development time used, if you want to shorten the development time must increase the developer concentration. Of course, many users determine the development conditions according to the actual situation. For example, a newspaper printing factory, in order to shorten the plate making time, often adopts strong exposure and strong display platemaking conditions. The developer concentration adopts the developer stock solution: water=1: (3 to 4). Even 1:2 ratio; while high-end color printing, requires small outlets do not lose, large outlets do not shine, generally according to the normal exposure conditions exposure, gray scale control 3 clean, the developer concentration is generally 1: (5-6) dilution ratio. In addition, the developer concentration must meet the requirements of the PS version used.
At the same development temperature (23°C) and development time (about 60s), to meet the development requirements, Agfa P51 must use PD-type development stock solution; Fuji Starlight VP type and Huaguang YP-II type PS version, with 1: 2 of the PD type developer can be; and Huaguang YP-S PS version, PD type developer is a 1:4 ratio.
(2) Development temperature
The effect of the development temperature on the development effect of the PS plate is also large, and it is apparent from some data of the application that the development temperature of the PS plate is controlled at 23 to 28. C, preferably higher, to ensure the development time is not too long.
The development time of the PS plate is a decisive factor in whether or not the blank part of the PS plate can be clearly expressed. However, in the development process of the PS plate, the development time has often been set, especially the machine development, usually set within 20 ~ 40s. The development time of the machine is controlled to be about 30 seconds, not less than 20 seconds, and the developer concentration is 1:4. The development time of the manual development is preferably controlled at about 60s, and the development temperature is not to be lower than 23. C, the developer concentration is about 1:5, which is easy to control. Some factories to speed up plate making, development time is only ten seconds or even 7 ~ 8s. The development conditions often recommended by PS manufacturers are (23±2). C. Developing for 60s. For example, the use of Huaguang PD type developer at a dilution ratio of 1: (5 to 6), the actual development conditions at the factory are obviously out of line with the manufacturer's requirements.
(3) Stirring method
Whether the PS version can be significantly netted is also related to factors such as the agitation speed of the development, the fatigue of the developer, and so on. The machine display is also related to whether or not the developing machine is equipped with a brush.
The above recommended conditions are most suitable for processing of Fuji Starlight VP and Huaguang YP-S positive PS plates, and are also basically suitable for Huaguang YP-II positive plate PS plates. The Agfa P51 should also be used for enhanced development.
Of course, the actual use situation of each printing factory is not the same. The control of the printing ash level scale is inconsistent, and the processing conditions are not exactly the same. The above recommended conditions are for reference only.
This article is based on manual test data, such as machine display, especially with a developing machine equipped with a brush, at the same developer concentration, the development temperature, the development time can be significantly shortened.
Source: "Printing Technology", Issue 7, 2005