Different PS plates have different compositions of photo-resist, and the main components that make up the photo-sensitive layer and the polymer compounds used in the film-forming resin are also different. Although the photosensitizers used in the positive-acting PS plates are all o-diazoin-type compounds, the positions of the photosensitized groups are also different, some being 2.1.5 and some being 2.1.4. In addition, the development adaptability of each brand, each type of PS version is not the same, so when the new PS version of each plant is launched, it also provides a dedicated PS version of the developer.
In recent years, many users have noticed problems such as black spots, blue spots, etc. after the PS version is intolerant of printing, off-printing, dirtiness, and then on-street printing. We have found that a considerable number of problems in the technical service are caused by improper use. To process the PS plate into qualified plates that are resistant to high force, not dirty, and do not touch the plate, the plate must be properly used, and the printing and developing processes should be standardized.
(A) PS version of knowledge
PS version is based on aluminum plate as a support, after the surface of the aluminum plate is roughened, coated with a diazo photosensitive layer.
Aluminum plate base is the support of the photosensitive layer, usually with 0.25 ~ 0.30mm high quality aluminum plate, light printing PS plate generally use 0.15mm aluminum plate.
The sand layer is a layer of solid oxide film formed by roughening the surface of the aluminum plate and then anodizing it. It has good hydrophilicity and is the hydrophilic area of ​​the plate.
The photosensitive layer is composed of a photosensitive compound, a film-forming resin, and the like. The positive photo-sensitive PS version uses a photolytically decomposable photosensitive resin, which is decomposed after light exposure (blank portion), and is exposed by the developer to expose the sand mesh layer and has hydrophilicity; the photosensitive layer (image portion) having no light portion has Lipophilicity.
The matte layer is coated on the surface of the photosensitive layer with a layer of bead-like particles with a certain elasticity. The size of the particles is generally 10-20 μm, and has a good air conduction effect when evacuated.
In order to produce a qualified plate, the quality of the PS plate is on the one hand, and the use of the PS plate is often more important.
(II) Specification printing plate making work
To produce a qualified plate, first of all, there must be standard platemaking conditions: 1 The production room should be fully enclosed to prevent dust; 2 the best use of yellow safety lights lamp; 3 indoor temperature should be controlled at 23 ± 3 °C; relative The humidity should be controlled at 60% ± 5%; the sun surface of the 4 rooms is best not to leave windows, if the windows are covered with yellow curtains; 5 At the time of revision, the lights must not be too bright and not too close to the layout.
To produce a qualified plate, the printing conditions of the PS plate are also important. First, the film used in the printing shall be of a standard and the density shall be the same; the printing standard shall stipulate that the fog of the plate-making film shall have D0 ≤ 0.15; the density in the field shall be ≥ 3.50; and the layout shall be clean, free of scratches and crease-free.
The working status of the printing machine should be kept the best: 1 The layout must be clean. Clean; 2 vacuum effect is better, the vacuum is better to maintain at 20kPa or more; 3 lamp light source lamp to be standard, that is, the spectral range in the blue-violet light (320 ~ 450nm), to iodine lamp (metal halogen lamp) The most suitable; 4 voltage should be stable; 5 exposure time to be accurate.
If the PS version is too long, it will damage the graphics and text, and the light will affect the printing effect. In severe cases, it will result in the waste version. The printing time is too short, the non-image part is not exposed, and the resin film still remains after the development process, which will cause the upper printing machine to be dirty, and it will also affect the printing resistance indirectly.
It is best to control the printing conditions using a test strip and a 21-step grayscale ruler. When the printing plate is evacuated, the film and the PS plate must be tangled and there must be no residual air in the middle. The density of the negative film used in the make-up must be the same. Do not mix the sulfuric acid paper with the density inconsistently with the film.