1,000 Offset Printing (285-299)

285. What are the processes involved in the printing process of the positive-picture PS version?
Answer: The printing process flow of the positive PS version is as follows: loading, exposure, development, revision, baking, ink extraction, and wiping.

286. What is the work point of the plate?
Answer: According to the technical requirements of the printing plate, the PS plate and the original plate are placed in the drying frame of the printing plate and positioned and fixed. The plate loading generally includes several steps such as determining the orientation of the plate, positioning the original plate, determining the set of drying modes, and evacuating the seal.

287. What is the exposure principle?
Answer: The light shines on the photosensitive layer of the positive PS plate through the blank part of the positive plate, and the blank part is changed from alkali insoluble to alkali-soluble, and the graphic part is not transparent and the solubility is not changed. Photochemical reaction occurs in the sensitized plate by exposure, and the original picture and text information is recorded, and the plated image is formed after the development.

288. What are the main factors that affect exposure?
A: The main factors affecting the exposure are the original version, photographic version, exposure, and exposure light source.

289. What is the exposure?
A: The exposure value refers to the light energy value obtained by the photosensitive material during the exposure process. It is represented by the symbol H and the unit is lx·s. Its calculation formula is H = E·t, where E - illuminance (lx), t - exposure time (s).

290. What are the main points of work for the exposure?
A: The exposure process of the printing process is the most important. Before the sun exposure, the lamp distance, lamp position and exposure time should be determined. Under the special requirements for auditing the original film and proofing, the continuous ash adjuster should be used as a reference and the third level should be used for sun exposure. For normal exposure standards.
Example: If using the Fuji Star PS plate, under the conditions of using 3000W iodine lamp and 100cm lamp distance, the printing time is suitable for 80 ~ 100s. Of course, the density of the printing plate film and the fog of the film base should also be tested. The maximum density of the graphic part of the normal, printing plate film should be more than 2.5, the film base fog should be 0.05 or less.

291. What is the principle of development?
A: The positive principle of the positive version of the PS version is to use an alkaline developer to remove the exposed part of the photosensitive layer to expose the hydrophilic metal oxide film to obtain a layout that satisfies the printing requirements.

292. What are the components of the developer?
A: PS version of the developer is a strong alkaline solvent, generally by the developer, protective agent, wetting agent and solvent and other components.
In the developing process, the control of the developer is extremely important. The developer provided by each PS plate manufacturer is corresponding to the PS plate. The components, the ratio of the developer, the use time and the temperature should be strictly controlled according to the requirements.

293. What factors affect the development quality?
A: The factors affecting the development quality include the concentration of the developer, the development time, the development temperature, the circulation and agitation of the developer, and the fatigue deterioration and replenishment of the developer.

294. What are the effects of developer concentration on printing plates?
A: The developer concentration refers to the relative content of the developer, and the development speed is proportional to the developer concentration. When the concentration of the developer is too high, on the one hand, the developing operation is not easy to control because the developing speed is too fast, and on the other hand, the corrosiveness of the graphic and textual basis is enhanced, and the network dots are easily reduced and damaged, and the bright spot of small dots is lost and the printing is resistant to printing. Reduced strengths and other defects, and corrosion and destruction of the oxide film and the sealing layer of the blank area, making the hydrophilicity and abrasion resistance of the printing plate worse. When the concentration of the developer is too small, its basicity is weak, the development speed is slow, and development is difficult, the layout becomes dirty, and the shadow darkens.
295. What are the effects of the development time on the printing plate?
A: The development time is mainly related to the type of plate, the exposure level, and the development conditions. When these conditions are constant, the development degree is proportional to the development time, but the phenomenon of dot reduction tends to occur, especially when the plate gamma is small. When the original small outlets are more imaginary and the light penetration phenomenon is more serious, the dot reduction phenomenon is more significant.

296. What is the effect of the development temperature on the printing plate?
A: The development temperature is proportional to the development speed, that is, the higher the development temperature, the faster the development speed. In general, the development speed is approximately doubled for every 12°C increase in the development temperature. If the development temperature is too high, the stability of the developing solution and the developing state will be reduced, and the expansion and dissolution of the graphic and textual basis will be aggravated. Even if the development temperature is too low, the development speed will be very slow. Fully developed. Generally, the temperature of manual development is controlled at (20±2)°C, and the temperature of machine development is controlled at (24±1)°C.

297. What is the effect of circulation and stirring of developer?
A: The development is accomplished by impregnation and dissolution between the developer and the photosensitive layer. Therefore, the dynamic development method is used. For example, shaking the developing plate during manual development, the machine can speed up the development through circulation pumps and brush rollers and other devices. Liquid flow and circulation increase the development speed and uniformity. If the developer cannot be effectively flowed or circulated, a malfunction such as a decrease in the developing speed and deterioration in uniformity tends to occur.

298. How to avoid developer fatigue deterioration?
A: During the development process, the developing solution will gradually wear out and decay due to the absorption of carbon dioxide in the air or react with the calcium and magnesium ions in the water as the development progresses. The developing performance will be deteriorated and the developing ability will be weakened. Under normal circumstances, about 2.5 m2 of PS plate per liter of developer can be used, when the pH of the developer is reduced to 11 or less (the pH of the newly formulated developer is about 13) or the development time is extended to the original development time. When doubled, it indicates that the developer has failed and must be replaced. During the development process, sealing measures can be adopted to reduce the contact between the developer and the air to reduce the speed of recession, and it is also possible to compensate for the effects of developer recession by periodically or quantitatively adding new developer.

299.PS version of the development of several ways?
A: The PS version of the development of manual development and machine development two.

---From "Printing Technology"