The factors affecting the quality of the printing plate in the platemaking are the most, mainly including the developer concentration, the developing temperature and the developing time, the circulation stirring of the developer, and the degree of fatigue deterioration of the developer.
1. Developer concentration
The developer concentration refers to the relative content of the developer, ie, the total NaOH, Na2SiO3 content. Most of the developer liquids sold on the market are concentrated liquids, which need to be diluted in proportion. The concentration of the developer liquid is often expressed as the dilution ratio of the developer liquid. Under the premise that other conditions remain unchanged, the developing speed is in direct proportion to the developer concentration, that is, the greater the developer concentration, the faster the developing speed.
When the temperature is 22°C and the developing time is 60 seconds, the influence of the PD type developer concentration on the performance of the PS plate is shown in Table 1. From the data in the table, it can be seen that the exposure level of the level 3 cleanliness is the best for the PD type developer concentration of 1:6.
When the developer concentration is too large, the developing operation is often not easy to control due to the development speed is too fast; in particular, it has an increased corrosiveness to the graphic and textural base, which easily causes dots to be reduced, damaged, brightly tuned, small dot missing, and thinning coating. , resulting in reduced resistance and other ills; at the same time the blank part of the oxide film and the sealing layer will be subject to corrosion and damage, the layout appears whitening phenomenon, so that the hydrophilicity and wear resistance of the printing plate becomes worse. The developer has a high concentration and is also susceptible to crystal precipitation.
When the concentration of the developer is low, the alkalinity is weak, the development speed is slow, and the phenomenon of undeveloped development, stencil of the layout, dark-spotting of the white dots, and the like easily occur.
The normal concentration of the developer can be measured by a dot ladder; under the normal exposure conditions for 30 to 100 seconds, if there is a large loss of black dots, the concentration of the developer is too large; if there is a large amount of white dots, the developer will show development. The liquid concentration is low. Therefore, it is best to use the developer within the manufacturer's specified concentration range.
2. Development temperature
When the developing temperature is high, the molecular heat in the developing solution moves violently, and the dissolving power of the resin in the coating is large; the temperature is low, the molecular heat movement is weakened, and the dissolving power to the resin is poor; therefore, under the same exposure conditions, The development time required for different temperatures is also different.
The negative influence of the low development temperature on the quality of the plate is usually larger than when the temperature is high, so the user must adjust the temperature of the developer within the specified range in the winter so that the plate making can obtain satisfactory results.
Under the same conditions, the development speed of the PS plate is directly proportional to the development temperature. That is, the higher the development temperature, the faster the development speed.
The effect of development temperature on platemaking quality is obvious. After the PD-type developer stock was diluted 1:6 with water, the effect of the development temperature on the quality of the printing plate under the conditions of 1 minute development was shown in Table 2.
From this set of data, it can be seen that, for a development of 1 minute, the development temperature is preferably controlled at 20 to 24°C. The low development temperature is not easy to clean; when the development temperature is high, the binding force between the photosensitive material of the photosensitive layer and the molecules of the film-forming resin is weakened, the alkali resistance is reduced, and the photosensitive portion of the image portion not having light is also dissolved. When the development temperature is high, the percentage of the area of ​​the layout area will be reduced, and the reproducibility of the printing plate will be damaged to some extent. Under normal circumstances, the temperature rises by 12°C, and the development speed is approximately doubled. If the development temperature is too low, the development speed is slow, so that it is difficult to complete the development. Therefore, if developing for 1 minute, the developing temperature should be controlled at 22±2°C on hand and 24±2°C on machine.
3. Development time
The development time of the PS plate is mainly determined by the type of the PS plate, the exposure time, the concentration of the developer, and the development temperature. When the above conditions are determined, the degree of development of the PS plate is proportional to the development time, that is, the longer the development time, the more thorough the development. However, if the development time is too long, dots will be reduced.
The effect of the development time on the quality of platemaking is obvious. The PD type developer solution is diluted with the water in a ratio of 1:6. When the development temperature is 22°C, the effect of the development time on the quality of the plate is shown in Table 3.
As can be seen from Table 3, the development time of the PS plate is too long, and the fine dots on the layout are easily lost. However, when the development time is insufficient, the purpose of development cannot be achieved, that is, the photosensitive layer of the non-image portion cannot be completely dissolved, resulting in the screen being dirty when printed on the printer.
4 developer circulation stirring
The development is accomplished by contacting and dissolving the developer with the photosensitive layer of the PS plate. Therefore, the power developing method is often used. For example, when the developer is used for developing, the developing plate needs to be shaken. When the mechanical developing is performed, the circulation pump and the brush roller device are used to accelerate the flow and circulation of the developer, so that the developing speed and the development uniformity are improved. On the other hand, the static developing method is used, the developer cannot effectively flow, the developing speed is significantly reduced, and the developing uniformity is also poor.
5. Developer fatigue deterioration and supplement
In the developing process, the developing solution gradually fatigues and degrades as the development proceeds and reacts with absorption of carbon dioxide in the air or with ions of calcium, magnesium, etc. in the water, and the developing performance is deteriorated and the developing ability is weakened.
In general, when the printing plate is developed, the development effect can be observed with the blank scale of the gray scale under the same exposure conditions. If the development effect is not good, the developer needs to be replaced in time.
With the continuous increase in the amount of bluntness and the constant dissolution of CO2 in the air, the OH-concentration in the developer will decrease, the pH will become lower and lower, and the development time will gradually increase, until finally under normal exposure conditions. The PS plate cannot be developed. This is the phenomenon of developer fatigue deterioration. However, as the pH value of the developer decreases, the lye's corrosive force on the oxide layer and the coating resin decreases, and the dot reproducibility of the plate and the anti-printing force are better than those of the newly prepared developer. However, two things must be noticed. First, the amount of photographic plate must be controlled within the permissible range of the developer. Second, the used developer must be sealed and kept from the air, because even a single plate of developer is not exposed to the air. After a week, the developing performance will drop significantly.
The following points should also be noted during the display:
1 It is necessary to regularly maintain the developing machine to ensure that the exposed PS plate can be developed normally.
2 Before the development, each drive roller must be kept clean. If the traction roller is not clean, the plate is easy to get dirty.
3 If the developing machine has a gluing device, be sure to pay attention to the roller to keep it clean, otherwise it will dirty the plate.
4 Under normal circumstances, the developing capacity of the positive-acting PS plate developer (stock solution) is 10m2/L.
When applying protective glue, be sure to apply the glue evenly and not too thick so as to prevent the coating from cracking and plate-off after drying.
6. Bakeware
If you need to bake, pay attention to:
1 First, you must select the baking version, and the baking version should not be too dirty. If you use solid peach gum preparation, be sure to use hot water sol, glue to be completely dissolved, filtered and reused.
2 Apply a proper amount of roasting paste on the plate, and wipe the plate evenly with a sponge.
3 baking gum can not be wiped with a dry cloth.
Plate 4 baking in the baking box, the image area will be evenly discolored. Different PS versions, baking time, temperature and final color will be inconsistent, so the baking conditions need to be determined through experiments.
Please also pay attention to baking version:
1 The infrared lamps in the baking box must be horizontally arranged, such as the longitudinal arrangement, which often leads to the corrugated deformation of the printing plate and affects the use.
2 baking version of the glue concentration to be appropriate, such as baked version of the glue is too thick, baking effect and ink on the effect will not be satisfactory; such as baked version of the glue is too thin, baked version of the dirt easily.
3 baking temperature can not be too high, the temperature is too high can lead to aluminum base toughening and soft, resin layer coking, affecting the resistance force.
If the baking time is too long, the printing plate is dirty, and the baking time is too short to reach the baking plate effect.
It seems that the plate making process is not too complicated, but in order to produce a qualified printing plate, it is really necessary for operators to carefully print and carefully process plates.