After the 1960s, the PS version was increasingly used in the world. At present, it has become an indispensable important material for offset printing. The application of the PS version of the new technology for offset printing to improve work efficiency, print quality, and accelerate the development of offset printing technology is extremely early conditions. The quality of the print version of the PS plate is the most direct factor that affects the quality of the printed product. Therefore, the key to selecting the scientific plate making process and the strict operation quality control of the PS plate. The following is from the development, removal of dirty, revision and other aspects of the printing process is always easy to appear and its influencing factors, and propose a reasonable solution.
First, development
In the development, the visible light decomposing part is removed together with the alkali-soluble resin under the action of the alkaline solution, and the exposed aluminum plateau sand becomes the hydrophilic non-image part on the printing plate, and the unexposed part is retained due to insolubility in the developing solution. Go down and become part of the printed image.
1. Positive PS version of the principle of development
2,1,5 photosensitizer see light decomposition, release the atmosphere, cause the opening of the ring, rearrangement of the molecular structure, the formation of fluorenone, with water to produce hydrazine carboxylic acid, insoluble in water; case of alkali will produce sodium and soluble in water . The dissolution rate of sodium salt is related to the temperature and concentration of the developer. The higher the development temperature, the faster the dissolution rate; the higher the developer concentration, the faster the development speed, and vice versa.
2. Positive Photo Plate Developer Solution Design
The positive developer for the PS version of the positive version uses sodium hydroxide, potassium hydroxide, sodium silicate, etc., and is mainly used to dissolve photosensitizers and photosensitive resins that have been decomposed by light. Since sodium hydroxide or potassium hydroxide is easy to contact with air, The reaction of carbon dioxide to produce sodium carbonate, so that the development of alkali in the north, the PH value is not stable, difficult to grasp, so to add the main amount of (3% -7%) inhibitor sodium phosphate or sodium silicate, which can be hydrolyzed The deuterium hydroxide is generated to stabilize the PG value of the developer within a certain range. If the PS plate has not been sealed, sodium silicate must be used because it can act as a post-sealing hole. The caustic soda is then used to adjust the alkali action of the developer. Alkali forces should be controlled to a minimum (to avoid 5% or so), so the design is both real and cheap. Developers can also add some surfactants, such as sodium dodecyl benzene sulphonate, detergent, so that the developer is evenly filled with layout, to achieve the purpose of uniform development, and increase the blank part of the water.
The temperature of the developer is proportional to the speed of development, especially manual development (the temperature is generally controlled at about 25 degrees Celsius), but also pay attention to the temperature change of the developer at any time.
As the positive photo-sensitive layer of the PS plate of the positive picture is decomposed by light, the alkaline action force of the developer in the developing solution is gradually weakened due to alkali dissolution, so the new solution should be added at any time in the developing process, and it should be replaced after a certain period of time. Liquid, so that the alkali effect in a stable range to ensure the quality of development.
Yang Tu PS version of the developer formula example:
Sodium hydroxide 40-60 grams Potassium chloride 20-30 grams Sodium phosphate 5-15 grams Sodium dodecylbenzenesulfonate 20-30 grams Water 10 litres
3. Negative PS plate development principle and developer design
Taking a negative PS plate made of a photosensitive resin with a diazonium salt as an example, in this PS sunlight process, a photolysis reaction occurs in the light-receiving part, the diazonium resin becomes water-insoluble, and then it is developed with water. The water-dissolved, non-visible light portion is removed leaving a water-insoluble light-emitting image portion.
An example of a negative PS version developer formulation is as follows:
Formula I Benzyl alcohol 15 g Isopropyl naphthalene sulfonate 5 g Sodium silicate (40%) Aqueous solution 5 g Water 95 g Formula Diphenylmethanol 10 g Sodium silicate (40%) Aqueous solution 20 g Isopropyl naphthalene sulfonic acid Sodium 5g Sodium nitrate 10g Water 95g
4. Developing operation
The PS plate development methods include manual development, semi-mechanical spray development and mechanical development.
Manual development is generally performed in shallow polyvinyl chloride baths. Put the sunlight PS plate into the developing tank, so that the developer is completely immersed in the plate, gently brushing with a soft brush, especially the PS plate version of the negative should be scrubbed, until the developed part is completely dissolved and detached, the plate is removed. Out, rinse the remaining developer on the plate with water, and then use it for neutralization with the aqueous solution of % acid. Due to prolonged exposure to air, the sodium hydroxide in the developer is easily neutralized by pens in the air. The developing solution in the tank undergoes several times of development and dissolves the photosensitive layer containing the dye, which has been decomposed by visible light, and changes from colorless, transparent, to green or dark green, which affects the observation of the development effect, and therefore the quality is not good enough to grasp.
Second, in addition to dirty
In addition to the dirty is mainly to rule on the layout of the many lines, negative film blots, tape strips, blots, etc. removed. The removal method of the PS plate is relatively simple. It is painted on the excess photosensitive layer with a pen or a painter. The dirt remover immediately dissolves the excess light layer, and then the residual dirt remover is removed with clean water. The dissolved substance is washed away.
Examples of decontamination formulations are as follows:
Diethylene glycol 14-18 parts Butanone 5-10 parts Dimethylformamide 5-10 parts Cyclohexanone 10-14 parts Silica powder 2-6 parts Hydrofluoric acid 0.12-0.18 parts Dyes 0.5-2 servings
Third, revision
In the PS plate making and printing process, if it is found that due to the disadvantages of the negative film, photosensitive layer of the PS plate, or other methods and people's layout graphics, lines or broken lines can be repaired.
1. When it is found in the plate making process that it needs to be repaired, after the plate is developed, the place to be repaired should be blown with hot air, covered with a brush or repaired with a repair ballpoint pen, and then dried with hot air of 60-70 degrees Celsius. You can.
2. When it is found in the printing process that it needs to be repaired, because it has been coated with hydrophilic substances such as gum liquid and water medicine, it is not firm to apply the repair liquid directly. The surface of the printing plate must be surface-treated. The spring treatment method is first to remove the cotton wool. The place where the developing solution is scrubbed is to be repaired. The developer solution is wiped off with a wet hair paste, neutralized with 3% phosphoric acid, and then washed with water and dried with hot air to perform repair. After repairing, use hot air to dry the machine.
3. The correction recipe is as follows:
M-toluene-formaldehyde resin (above 118 degrees Celsius softening point) 7 g Ethylene glycol ether 15 ml Basic brilliant blue trace
Nowadays, the PS version has achieved gratifying research results and has been widely used. This opens up broad prospects for the development of PS plate making and offset printing.
Source: Spark Design