Positive Pattern PS Platemaking Process (6)

2. Roasted version of the PS version of the print resistance is generally in the 5 to 100,000 prints, if you need to print more than 100,000 prints, you must improve the printing plate resistance to force, one of the ways is to develop, in addition to dirty, after repair The PS plate is baked.

The method of baking plate treatment is to apply a protective liquid on the surface of the printing plate after development, removal of dirt, and repair, and then put it into a baking plate machine, and bake at a constant temperature of 23°C to 250°C for 5 to 8 mini to take out the printing plate. After being completely cooled, the developer is used again for development; finally, the protective liquid remaining on the plate is removed and dried with hot air.

During the baking process, the resin in the photosensitive layer of the PS plate is thermally cross-linked into a network of macromolecules, the photosensitive group disappears, the photosensitive layer changes from green to reddish-brown, and the photosensitive layer of the image part is sensitive to light. Sex becomes non-photosensitive, so the wear resistance, corrosion resistance, and solvent resistance of the printing plate are improved. Experiments show that after the PS plate processed by the baking plate, after printing 200,000 to 300,000 printing times, the dots on the plate surface were observed with a magnifying glass, and no obvious change was observed. The baking plate was soaked with a 30% hydrochloric acid (or sulfuric acid) solution. After the PS plate was processed, the photosensitive layer of the plate was still intact after 24 hours; it was soaked in an organic solvent such as ethanol, butanol, cyclohexanone, monomethyl ether glycol, ethyl acetate, kerosene, and gasoline. PS version, after 24 hours, no significant changes in the printing plate outlets.

However, in the baking process of the PS plate, part of the oxide film formed on the surface of the aluminum plate base by anodization loses water, and some of the pores that have been pore-treated are reopened and the strong adsorption of the plate surface is restored. Dirty faults will appear. Before baking, the plate surface is coated with a protective liquid to protect the pores that have been treated with the plugging hole. This is to prevent the dehydration of the oxide film during the baking process. Commonly used substances for the preparation of protective liquids include Pingping plus -20, Pingping plus -OP-10, Pingping plus -0, borate compounds, sodium dodecylbenzene phosphate, detergents, and the like.

Pingpingjia is a non-ionic surfactant whose main ingredient is polyoxyalkylene fatty alcohol ether, and its molecular formula is: RO-(CH2CH2O)n-CH2CH2OH. In the formula, R represents C12H25 or C13H27. Pingping has good film-forming properties and good hydrophilic oleophobicity, is easy to disperse, and is very stable to alkalis, acids and alcohols.

Potassium tetraborate, sodium tetraborate, and ammonium tetraborate are commonly used borate compounds for preparation of protective solutions. After these compounds are used together with the protective solution prepared in parallel and dried to form a film and adhered to the plate surface, cracks and crystalline structures do not appear, and coverage is good and stable.

Sodium dodecylbenzene sulphonate has good wettability and dispersibility. It will not decompose and degrade under 250°C. It will be added to the protective solution to improve the spreadability of the protective solution, making it easy to apply on the surface of the plate. Uniform. Instead of sodium dodecyl benzene sulphonate, it is possible to use other cationic, nonionic surfactants with good wettability and good dispersibility.

There are many formulas for the protective liquids, one of which is listed below for reference.

Pingping plus one OP-10 40～60 g
Ammonium tetraborate 10 g
Sodium dodecylbenzenesulfonate 10 ml
Water 1000 ~ 1500ml.

Since the substances in the protection solution are all soluble in water, the preparation method of the protection solution is very simple. Simply put the substances in water according to the above formula, stir or appropriately heat them, and dissolve them before use. When applying protection liquid to the layout, use a cotton wool to gently wipe the coating to avoid fiber shedding and affect the baking version. The amount of the protection liquid is not too much, otherwise there will be traces of water flow, resulting in difficulties in inking. The baking plate is a processing method that causes the photosensitive layer to be baked on the surface of the printing plate base under the action of heat, thereby improving the mechanical properties and physical and chemical properties of the image. After the baking treatment, the photosensitive layer is firmly attached to the plate, and dirt on the plate can no longer be removed with dirty liquid. Therefore, the plate must be completely removed before baking.

The roasting plate should be carried out in a special closed roasting plate, and the temperature should be within 2°C. The temperature of the roasting plate should be uniform.

The temperature and time of the baking plate are related to the aluminum plate base used, the photosensitive material, and the structure of the baking machine used. It is generally determined based on the change of the curing point and the color of the photosensitive layer. For example, m-cresol-formaldehyde resin is a hot-melt resin at room temperature, and when it is heated to 180°C, it starts to be cured, and when it is baked at 230°C for 5 minutes, all the resins are cured to a good degree, and the color is also improved. The green color changes to reddish brown. If the baking temperature increases or the baking time increases, the color of the resin will change from reddish brown to dark brown, indicating that the photosensitive layer is carbonized and deteriorated and cannot be reused. Therefore, for the use of m-cresol formaldehyde As a PS plate of a photosensitive material, baking at a temperature of 230°C for 5 minutes is suitable. If the baking temperature is too high and the baking time is too long, the mechanical properties of the aluminum plate base will be deteriorated and the texture will be deteriorated. In order to ensure the quality of the baking plate, the standard baking temperature and time must be determined according to the type of PS plate and baking conditions.

Plates taken from the roasting machine must be naturally cooled and must not be cooled by cold water spray. Forced cooling of the plate can cause large deformation due to rapid temperature changes. After the cooling plate, the protective liquid on the plate surface must be removed with a developer. If the protective liquid remains on the plate, the ink will be emulsified during printing. In severe cases, the graphic part may not even be adsorbed on the ink.

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