Quality Control of Every Step in the Developing Process of Positive Graph PS Plate

At present, after the normal exposure of the iodine lamp, the PS plate that is commonly used in printing is required to be developed before it can be printed on the machine. The development process of the positive PS plate has both chemical and physical changes. The chemical change is represented by the tannic acid which is decomposed after the exposure of the sensitizer and the rearrangement of the molecular structure, and then reacts with the base to form a water-soluble salt; the physical change shows that the exposed photosensitive layer is peeled off from the plate base. Therefore, there are both chemical and physical factors that affect the performance of the developer. These many factors constitute a complicated and influential process. In order to achieve the desired development effect, scientific analysis should be carried out on the influencing factors in the development process and strictly controlled to ensure the development quality.

First, the preparation stage

There are roughly two types of developer materials used with the PS plate: solid state developer and liquid developer concentrate. Regardless of which type of developer material is used, the developer must first be adjusted to a suitable concentration before being used for development. This section should pay attention to the following points:

1. The material should be mixed thoroughly before use

The solid state developing material is a mixture prepared from various components such as a developer, an inhibitor, a wetting agent and the like. For the directly compounded developing powder, the specific gravity, particle shape, and size of each component are different during transportation. Bumps, so that the small-size, high-specific components concentrated distribution in the bottom of the container. Under this circumstance, the developing powders in the upper and lower parts of the container are respectively formulated into a developing solution, and the same PS plate is developed under the same developing conditions, and the developing effect thereof is obviously different; for the developed powder produced by the powder spraying process Due to the different particle sizes, the above problems also exist. Therefore, when the developing powder developer is directly taken, the developer powder should be fully mixed.

When diluting the formulated developer with the developer concentrate, attention should also be paid to the mixing problem. After the concentrate was left standing, some of the poorly soluble components settled to the bottom of the container due to the effect of gravity, and the components in the solution were not evenly distributed. Experiments have shown that only the top solution is formulated as a proportioning developer and its development effect is not good. Therefore, when taking the concentrate to prepare the developer, the mixing problem cannot be ignored.

2. Deionized water was selected as the dosing water

Under normal circumstances, there is no special requirement on the water used for disposing the developer. The user is basically using tap water or deep well water. The clear water on the surface substantially contains a lot of impurities that are invisible to the naked eye and can be roughly divided into electrolytes. , organic matter, particles, microorganisms, dissolved gases, etc. The presence of these impurities will have a negative effect on the development of the PS plate. The most obvious of these is the scaling of the developer. The developer is a basic solution with a pH of about 13. The theory of scale formation tells us that sodium silicate, which is one of the constituents of the developer, is itself a substance that is easy to form scale. Together with the combined action of calcium, magnesium, and iron ions introduced by water, it is more likely to cause alkalinity. Developer fouling. The direct effect is to cause the developer nozzles to clog, causing the developer to spray unevenly, thereby affecting the development quality. Therefore, it is best to use deionized water as the dosing water to slow down the fouling process of the developer.

3. The exact concentration of the developer

Different types of positive-acting PS plates have their associated developing materials, and the manufacturer will also provide the corresponding proportion of developer solution. For example, some grades of developer powder in the instructions for use recommend that "a bottle of developing powder is dissolved with 5:1 warm water to form a concentrated solution, and then the diluted solution is diluted 1:6 at the time of development." Here, the ratio is 1:6. The dilution ratio is the widely applicable dilution ratio that the manufacturer has obtained through extensive experiments. For a user, test development should also be performed prior to formalizing a new batch of positive-acting PS plates to determine the optimal concentration of developer for the plate. The following describes a simple and practical method: the drying plate with a print version of the PS plate for 30 60 seconds of development, observation with a high magnification magnifying glass, if the drying 98% 99% hollow spots do not stick, 1% 2% of black If the dots are not lost, the concentration of developer is appropriate.

Second, the development stage

After the preparation is ready, the positive PS plate can be developed, and the photosensitive layer decomposed on the plate surface must be completely removed, and the photosensitive layer should not be dissolved. To achieve this goal, it is necessary to start from aspects such as developer temperature, development time and developer concentration that affect the development quality, and control the development conditions within an optimal range to ensure the development quality.

1. Control the appropriate development temperature

Heat is required for hydrolysis, salt formation, and salt dissolution in the developing process. If the temperature of the developer is too low, the heat required for the development process cannot be provided, which will prevent the development from proceeding smoothly; if the temperature of the developer is too high, the unexposed image portion will be dissolved. Theory and practice show that when the temperature exceeds 30C, the binding force between the photosensitive resin and the film-forming resin in the photosensitive layer is weakened, and the resistance to alkalinity decreases. Therefore, an appropriate development temperature is one of the prerequisites for ensuring good development quality. In general, it is appropriate to control the development temperature at 25±2.

2. Control the appropriate development time

The proper development time directly affects the development quality of the PS plate. If the development time is too long, the fine dots on the layout will be easily lost. If the development time is too short, the photosensitive layer of the non-image portion cannot be completely dissolved, causing the layout to be dirty. In order to avoid the appearance of the above phenomenon, the development time should be controlled within 30 120 seconds. For a qualified PS plate, the development latitude should reach 120 seconds.

3. Maintain a suitable developer concentration

After many times of development of the developer, the active ingredients in the developer are continuously consumed. Together with the effect of the photosensitive layer that is continuously dissolved in the developer, the developing ability of the developer becomes weaker and weaker, so that the developing requirement cannot be satisfied. Aging has occurred. At this point, the developer should be treated as necessary according to the actual situation. When the aging phenomenon is not serious, it is generally taken to supplement the appropriate amount of concentrated solution to maintain the developing solution. This method is simple and easy, but it should be added at any time. When the developer is used for a certain period of time, serious aging occurs and the new fluid should be replaced promptly.

In short, the quality control of the developer is a problem that cannot be ignored. Although the development is only a part of the PS plate making process, it will play a very important role in improving the quality of the entire positive chart PS plate making process if the quality of this link can be properly controlled.

Reprinted from: Printed Materials in China