The process of partially dissolving the photosensitive layer (positive PS plate) that has been exposed and decomposed with the developer to form the two portions of the plate, the image and the non-image, is referred to as development.
Development principle: After the exposure of the PS plate, the photosensitive resin decomposes, releases nitrogen gas, causes cracking of the ring, rearranges the molecular structure, forms an anthraquinone compound, and forms a tannic acid compound in water. This compound meets alkali to form a sodium salt and dissolves in water. Exposed aluminum plate base, forming a blank area without images, these areas naturally form a hydrophilic layer, and the non-photosensitive part retains the oleophilic properties of the original photosensitive resin, naturally forming the image part of the printing plate, when printing Acceptable ink.
The developer is an alkaline aqueous solution that consists of a developer, a protective agent, a wetting agent, and water.
It is used to dissolve the light-sensitive part of the photosensitive layer, mainly alkaline substances, commonly used drugs are sodium hydroxide, potassium hydroxide, sodium silicate, sodium phosphate and so on.
a. Sodium hydroxide
It belongs to strong alkali, has the characteristics of strong developing ability, fast developing speed, and low price, but it also has a certain erosion effect on the unsensitized coating, so that the film retention rate on the layout is reduced, and the blank aluminum plate base after development can also be made. The oxide film is infringed. Therefore, when using sodium hydroxide as a developer, pay attention to the following principles:
It is commonly used in PS plates with thick oxide film and hole sealing.
Commonly used in photosensitive layer anti-alkali type PS plate.
The developing solution of sodium hydroxide easily absorbs carbon dioxide in the air to form sodium carbonate, which results in poor stability.
At present, the use of sodium hydroxide alone is not much, often used in conjunction with other materials, the amount of which will vary according to different requirements, in general, the weight percentage of O. 1% O. 5%
Potassium hydroxide and sodium hydroxide have similar properties, and their aggressiveness is slightly weaker than that of sodium hydroxide. Therefore, the use amount of potassium hydroxide as a developer can be more than that of sodium hydroxide. 4 times.
b. Sodium silicate
It is a strong base and weak acid salt, with the characteristics of fast development, stable performance and long service life. Sodium silicate is easily hydrolyzed to generate hydroxide ions, which can compensate for the loss of hydroxide ions during the development process and stabilize the pH of the developer.
The acid sodium silicate formed after hydrolysis can be dehydrated, and the resultant product is adsorbed into the pores of the oxide film of the printing plate to protect the oxide film and increase the hydrophilicity of the printing plate. This phenomenon can be referred to as the printing plate. After sealing hole. Therefore, unsealed PS plates are often used as sodium silicate.
2 protective agent
The main role is to stabilize the developer, reduce the corrosion of the developer during the development process on the printing plate, and protect the photosensitive layer of the graphic part from the erosion of the developer. Therefore, the protective agent is also called an inhibitor. Common inhibitors are sodium phosphate or potassium chloride.
The buffering principle of sodium phosphate (Na3 P03): It regulates the pH of the developer when it is hydrolyzed in water.
Phosphoric acid produced by the hydrolysis reaction also has the effect of removing dirt from the plate, which is beneficial to the removal of residual alkali liquor after development.
Sodium chloride can also be used as a protective agent. The chloride ions formed during the development of sodium chloride have the effect of inhibiting the swelling of the photosensitive layer and the effect of building-up.
3 wetting agent '
The main purpose is to reduce the surface tension of the developer, so that the developer has better wettability and dispersion uniformity, and improves the uniformity of the development. The main material is a surfactant, such as sodium dodecylbenzene sulfonate.
It is mainly water, but the requirements for water are relatively high. Normal tap water, due to the presence of large amounts of calcium and magnesium salts, is liable to produce precipitates or flocs, so it is better to use deionized or demineralized water.
Developer Formula Example
Sodium hydroxide and sodium silicate mixed formula:
Add water to
Use developer note:
1 In actual use, the developer is often formulated as a solution with a relatively high concentration called a concentrate, which is mixed with a certain proportion of water during development.
2 Due to the difference in manufacturing technology of manufacturers of PS plates, there is a big difference in the alkali resistance of the development. Manufacturers generally recommend their own developer to be compatible with their plates. Manufacturers should recommend the use of developers.
3 From the perspective of environmental protection, the developer concentration tends to develop in the direction of weaker alkalis, which not only reduces the corrosion performance but also reduces the discharge of waste liquid.
Hand rub type: It is rarely used again. Pay attention to the evenness and safety of the operation. Due to the manual operation, the development is not uniform, and some versions are not suitable for this type of development.
Groove display: The development temperature is the same as the room temperature, and the environment has a great influence on the development effect, especially in the winter season. Pay attention to the effect of sink volume on water flow and water pressure, and develop a reasonable developer ratio. For the PS version, this is a relatively good development method. Both the development and the washing are sufficient. The development is relatively simple and will not be affected by other factors.
Machine display: mainstream development method, automatic control of the development process, the development machine is the key. Most of the contents of this chapter are also suitable for CTP developing machine
Lighting: different types of plates have different lighting requirements, with the printing requirements
Relative humidity: about 60%
Air cleanliness: smooth ventilation is conducive to the discharge of exhaust gas, maintain positive air pressure, no dust, to ensure the cleanliness of the version of the room
According to different brands of media, developer and actual development results and follow the supplier recommended settings
Development temperature: generally 23--28Â°C
Development density: 1:4--1:
Development time: 18--28s (the time the plate stays in the developer)
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