Third, post-processing
After the positive PS version is exposed and developed, it is also subjected to processing such as removing dirt, repairing, baking, developing black ink, and gluing, collectively referred to as the Ps version of post-processing.
1. Dirty and repair
1) In addition to dirty. In addition to the dirty, it uses the dirty liquid to remove the excess lines, adhesive paper, marks left on the original edge, dust and dirt, etc. on the plate.
In addition to dirty liquid, also known as trimming fluid, should have the following properties: on the plate surface stains, dirty marks have a strong solubility; have a certain degree of emulsification, so that the dissolved lipophilic substances are no longer dirty plates; The plate can be wetted relatively quickly and it cannot be spread freely on the plate to prevent dirt from spreading to parts of the text that do not need to be removed. In order to make dirty liquids have these properties, the components of the dirty liquid should include ink solvents, photosensitive layer solvents, wetting agents, thickeners, pigments, and the like.
The ink solvent is used to dissolve the developed black ink and ink attached to the surface of the image to be removed, exposing the underlying photosensitive layer. Commonly used ink solvents are benzene, toluene, xylene and so on.
The photosensitive layer solvent is used to dissolve the photosensitive layer, and a solvent having a small volatility and a fast dissolving speed is selected so that the dissolved photosensitive layer can be quickly detached from the surface of the plate, and the resolubilized surface will not be regenerated. Commonly used photosensitive layer solvents include methyl ethyl ketone, butanone, cyclohexanone, butyronitrile, valerolactone, diethylene glycol, dimethylformamide, ethylene glycol monomethyl ether, and ethylene glycol ether alone.
The wetting agent is used to reduce the surface tension of the dirty liquid, so that it can be rapidly dispersed to various parts of the plate surface that need to be removed, and the dirt removal efficiency is improved. If a wetting agent with both emulsifying and emulsifying capabilities is used, it can also prevent the photosensitive layer from dissolving after it has been dissolved and the effect is better. Commonly used wetting agents include Tween-60, sodium dodecylbenzenesulfonate, and the like.
The thickening agent is used to increase the viscosity of the dirty liquid and make it a thick fluid. When it is used, it will not flow freely, and damage the graphic part of the printing plate. The commonly used thickener is a particle diameter of 2 ~ 4μm Nmousewheel="return bbimg(this)" alt="" src="" class="lazy" original="" onload="" border="undefined" /> (silica fume).
Nmousewheel="return bbimg(this)" alt="" src="" class="lazy" original="" onload="" border="undefined" /> is a porous, granular substance that has a strong Adsorption capacity, the smaller the particles, the stronger the adsorption capacity, the greater the thickening effect.
The function of the pigment added to the dirty liquid is to observe the effect of removing the dirty, and the color is obviously different from the color of the photosensitive layer to facilitate the identification. Commonly used pigments are alcohol-soluble red and blue pigments.
Different PS plates, the sensitivity of the solvent solubility is not the same, the preparation of dirty liquid (or choose to remove the dirty fluid), must be based on the PS version of the photosensitive layer to select the various components of the dirty fluid (or choose to remove dirty Liquid type).
Here are two recipes for removing dirty fluids for reference.
Formula 1:
Xylene 70 g
Valerolactone 10 g
Tween-60 0.3 g
Silica powder 0.5 g
Basic brilliant blue BO trace
Formula 2:
Methyl ethyl ketone 1～1.5 g
Diethylene glycol 2~6 g
Silica powder 1～3 g
In addition to the long-term contact with the air, the dirty liquid will degenerate. In addition to the reduced dirt capacity, deteriorating dirt can not be used. In addition to the dirty liquid contains more volatile substances, should be stored in a closed container.
When using dirty liquid in addition to dirty, the operation must be careful, in addition to the dirty droplets in the graphics, the graphic immediately dissolved, you need to re-print. Care should be taken when removing the small stains on the adjacent parts of the picture and text. You can use the grindstone bar, pumice bar or scraper to remove the photosensitive layer at the stain and then apply the dirty liquid to the stain to wipe off dirt.
2) Repair. The developed PS plate sometimes requires additional graphics, and sometimes it is found that the image is missing due to various reasons and can be repaired. There are two commonly used patching methods. One method is to supplement the text, that is, to apply a photo-sensitive liquid on the surface of the board again, supplementing the photo with the supplementary text, and using the repair liquid to fill the pen.
The formulation of a repair solution is listed below for reference.
M-cresol formaldehyde resin (viscosity greater than 0.4 Pa·S) 7g
Ethylene glycol monoacetic acid 15ml
Basic grid blue BO trace
To repair the pen, first use a developer (dilute alkali solution) to scrub the parts that need to be repaired, then wipe off the developer with a wet towel, and use 2% of the remaining developer waves. Nmousewheel="return bbimg(this)" alt="" src="" class="lazy" original="" onload="" border="undefined" /> neutralization solution, then rinse with water After the stencil is completely dried, the pen is repaired with a brush pen repair fluid; finally, the plate is again blown with hot air so that the solvent (ethylene glycol diacetate) in the repair solution volatilizes rapidly, m-cresol formaldehyde The resin dries into a film and firmly adheres to the plate. Sometimes the repair liquid can be replaced with wax, but the wax has a dissolving effect on the photosensitive layer of the PS plate. When the pen is filled, the adhesive tape for plate making needs to be affixed around the graphic to protect the graphic.
When the mending liquid or wax is used to fill up the pens on the printing plates, the details of the graphic parts are very difficult to fix, and even if they are reluctant to fill in the pens, they are also difficult to be the same as the original ones, or they can be added. The graphic text achieves the same resistance as the original graphic text. In this case, the method of applying sunburn is more appropriate.
After all, repair is a remedial measure to ensure the quality of the printing plate. It is impossible to obtain perfect results. The fundamental method for improving the quality of the printing plate is to increase the quality of the original plate as much as possible, and to reduce or even eliminate the defects of the printing plate.
2. Bakeware
The PS version of the print resistance is generally between 5 and 100,000 prints, if you need to print more than 100,000 prints, you must improve the print plate's resistance to printing force, one way is to develop, remove dirt, repair the PS plate after baking Edition processing.
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 component is polyoxyalkylene fatty alcohol ether. Its molecular formula is: Nmousewheel="return bbimg(this)" alt="" src="" class="lazy" original="" onload="" border="undefined" />, where R stands for
Nmousewheel="return bbimg(this)" alt="" src="" class="lazy" original="" onload="" border="undefined" /> or
Nmousewheel="return bbimg(this)" alt="" src="" class="lazy" original="" onload="" border="undefined" /> . Pingping has good film-forming properties and good hydrophilic oleophobicity, is easy to disperse, and is very stable to alkalis, acids and alcohols.