What is the printing plate making process?

Printing plate making is one of the pre-press processes, the traditional plate making process compared with other processes, the degree of automation is relatively low, more manual processes, mainly dependent on the experience of the operator. With the popularization of CTP and digital printing plate making technology, the traditional plate making process will gradually withdraw from the market.

Printing plate process

Shear

Film (also known as film) by the phototypesetting workshop sent to the plate shop, the first thing to do is to cut off the blank part of the film, that is, shear. The correct method of operation is to place the film face up on the plate, the first to see the edition number of the odd and even, if it is odd code version, then cut off the left side of the blank part of the film; such as the middle seam, cut as far as possible to the inside, so as to avoid the collation of personnel to process again; if the even code version, then cut off the right side of the film. The above is the black and white version of the film cutting method, if the color version of the film, generally need to stay in the top and bottom of each alignment mark.

Plating

Plating is divided into two types of splicing: book and newspaper. 8-volume newspaper is usually spliced by book, and the common number of plates are 4, 8, 16, 24 and 32, and occasionally 48 or 64. Usually in the spelling, is first divided into a large number of parts of the sign, such as A. B. C. D several versions, such as 64 pages of the newspaper can be divided into A32, B32 or A, B, C, D each 16 versions. (1) the newspaper version of the regular collocation follow the following rules: ① left up and down the two sides of the plate number and the right up and down the two sides of the plate number of the sum is equal, and equal to the maximum number of plate number plus 1. such as the 32 version of the case, left and right up and down the plate number and should be 33. ② odd number of plates and even number of plates in a fixed position, and left and right side of the small plate and the large plate is also a fixed position, such as, in the collocation of the 32 edition, 32. 25, 1, 8 four plates and the large plates, and the large plate is also fixed, such as, in 32 edition collocation process, 25, 1, 8 four plates and 24, 17, 9, 16 four plates were spliced on two large plates, of which 32 and 24, 25 and 17, 1 and 9, 8 and 16 plate position is the same. (2) 4 open newspaper edition of the collocation generally follow the following rules: ① the number of editions of 20 or less, including 20, collocation is carried out in a group of four plates, and two of the four plates at the ends of the two plates and the middle of an edition respectively, that is: 1, 4 and 2, 3, 5, 8 and 6, 7, 9, 12 and 10, 11, 13, 16 and 14, 15, 17, 20, and 18, 19. ② the number of editions greater than In the case of 20, the number of plates can be subtracted from the number of integer multiples of 20 and then handled in the same way as in the first case. Such as 48 can be put together with 45, because 48 and 45 were subtracted from 2 20 obtained after the 8 and 5 are put together. (iii) Odd-numbered and even-numbered plates are fixed. I.e.: 1, 3, 5, 7, 9... and 2, 4, 6, 8, 10... plates are the same.

Folding hand

The collotype layout is obtained by folding the sample sheet, the process of folding the sample sheet is known as doing folding hand. According to the printing equipment and folding machine folding method is different, the folding method is not the same. Such as 8 open version of the head to head and foot to foot points, 4 open version of the newspaper head up and head down points. In general, for the 2 triangular plate or the use of folding machine printing equipment, the folding hand are two hands, that is, for the 16 version of the case is the first 8 large and 8 small sets together; for the 24 version of the case is the first 16 large sets together and then with the last 8 small sets together; for the 32 version of the case is the first 16 and the last 16 respectively, after the large sets and then small sets together.

Panning

Because of the newspaper printing time-sensitive, so the newspaper printing presses generally advocate a "weak exposure" of the panning method, in order to save time in the process of making the plate, the panning time is set to be shorter, and will be adjusted accordingly to the conditions of the punch plate, in order to make the plate to meet the requirements of the printing requirements. In addition, the sun plate also need to pay attention to the sun plate machine glass cleanliness and vacuum pump suction situation.

Punching (developer)

Punching in order to fit the weak exposure of the plate conditions, the ratio of the developer is generally higher than the instructions on the ratio of concentration. To develop the liquid, for example, the instructions require the original liquid and water ratio of 1:5 ~ 1:8, and "weak exposure" is generally to be prepared by the concentration of 1:4. Printing plate rinsed out, often with a dirty situation, there are usually two ways to deal with it, one is to rinse the plate again, but it is too much time; another method, but also a better method is to add a certain amount of detergent to the developer solution, through the enhancement of plate-flushing liquid molecules active method of getting dirty.

Trimming

The most critical point in trimming the plate is to remove the film edge marks that should not be on the plate. After repairing the dirty marks with a plate repair pen must also be used to wipe off with a damp cloth in a timely manner, so as not to print on the dirty. For the scratches on the printing plate, you can use a fine brush dipped in a little dilute sulfuric acid coated in the scratches to deal with.

Check the quality of collocation

Page check is the last process before the printing plate on the machine, if this process is not strict, will bring greater economic losses to the printing press. Inspection of the layout in addition to checking the layout of the text and pictures with or without broken pens, less painting, the situation of false, but also on the layout of the layout of the plate for detailed inspection. If the plate is even sunshine also need to test YMCK four plates a sunshine and two sunshine deviation. Tanning workshop is mostly rely on visual inspection of the quality of the printing plate, but due to the printing plate graphic and blank part of the contrast is small, a long time to detect fatigue, and some errors are not easy to detect. A better test method is to wash the plate in time after the ink, increase the contrast of the plate to adapt to the human eye's observation habits.

Calculate the number of plates

In the printing plate on the machine, be sure to point out the number of plates. Calculate the number of plates to distinguish between 8 open or 4 open newspaper plates. (1) 8 open newspaper version of the calculation formula: n/4 + a × 3 + b × 1. n for the total number of plates, the calculation, n must be 8 integer multiples, if not, to be greater than the number of the nearest 8 integer multiples of the calculation. For example, if the total number of plates is 28, the number of plates is 32. a is the number of color plates, 4 color plates that can be put together is 1 set, and less than 4 are also counted as 1 set. b is the number of red plates, 4 red plates that can be put together is 1 set, and less than 4 are also counted as 1 set. c is the number of red plates, 4 red plates that can be put together is 1 set, and less than 4 are also counted as 1 set. d is the number of red plates, and less than 1 set. For example, the total number of 28 plates (n = 32), of which the number of color plates for 16 (a = 4), 2 plate red (b = 1), then do a set of plates need to be ps plate total number of: 32/4 + 4 × 3 + 1 × 1 = 21 pieces. The above formula is suitable for narrow width single multiplier tower rotator. (2) 4 open newspaper version of the calculation formula: n/2 + a × 3 + b × 1 + c. n for the total number of plates, the calculation of n must be calculated according to the 8 integer multiples, otherwise to be greater than the value of the nearest 8 integer multiples. a for the number of sets of color plate, can be pieced together with the 2 color plate for a set of two color plates can not be pieced together with the 2 color plate counted as a set of two. The 8 consecutive plates from the 1st edition are a group, and the non-grouped pages are generally the last 4; a set of colored plates is counted as 2 sets, a must be an even number, and if it is an odd number, then 1 is added. b is the number of sets of red plates, the 2 red plates that can be put together are 1 set, and the 2 that can't be put together are counted as 2 sets, the 8 consecutive plates from the 1st edition are a group, and the non-grouped pages are generally the last 4, and 1 red plate is counted as 2 sets. b must be an even number, and if it is odd, then 1 is added. b must be an even number, and if it is odd, then 1 is added. for an even number, such as an odd number is added 1. c for the number of white plates, in a group of plates (8 consecutive plates from the beginning of the 1 edition for a group) if the color plate and set of red plate sets for 1, then you need a white plate. The color plate requires 3 pieces and the red plate requires 1 piece. For example, assuming that the total number of 20 (n = 24), 1, 4, 5 for the color version (a = 2), 9, 12, 17, 20 for the red version of the set (b = 3), the number of white version of the c = 1, then do a set of version of the total number of ps version needed for: 24/2 +2 × 3 +3 × 1 +1 = 22. The above formula is suitable for the narrow double-size "Y " type rotary offset press. In addition, in the calculation of the number of plates, should be combined with the actual structure of the printing machine, do not dead set formula.

Factors affecting the quality of the printing plate

The concentration of the developer

The most important factors affecting the quality of the printing plate in the plate making, mainly the concentration of the developer, the developer temperature and developer time, as well as the circulating and stirring of the developer, the fatigue degree of the developer's recession, and so on. The concentration of the developer refers to the relative content of the developer, that is, the total content of NaOH, Na2SiO3. Developer sold on the market is mostly a concentrated liquid, the use of which needs to be diluted proportionally, and the concentration of the developer is mostly expressed in terms of the dilution ratio of the developer. Under the premise of other conditions remain unchanged, the development speed is proportional to the concentration of developer, i.e. the greater the concentration of developer, the faster the development speed. When the temperature is 22 ℃, the development time is 60 seconds, PD-type developer concentration on the performance of the PS version of the impact of Table 1 (omitted). From the data in the table, it can be seen that the exposure amount of 3 levels of clean prevail, PD-type developer concentration of 1:6 is the best. When the concentration of developer is too large, often due to the development speed is too fast and make the development operation is not easy to control; in particular, it is on the graphic base of the corrosive enhancement, easy to cause dot shrinkage, residual damage, bright tone of the small dot loss and thinning of the coating, resulting in a decline in print resistance and other ills; at the same time, the blank parts of the oxide film and sealing layer will be corroded and damaged, the layout of the whitish phenomenon, the hydrophilicity of the printing plate and abrasion resistance deterioration. The hydrophilicity and abrasion resistance of the printing plate will deteriorate. Developer concentration is large, but also easy to have crystal precipitation. When the concentration of the developer is low, the alkaline is weak, the development speed is slow, easy to develop not clean, the layout of the dirty, the dark tone of the small white spots paste dead and other phenomena. The normal concentration of the developer can be tested through the dot ladder; in the normal exposure conditions when developing 30 to 100 seconds, if there is a small black dot loss of more than the developer concentration is too large; if there is a small white dot paste more than the death of the developer concentration is low. So it is best to use the developer within the concentration range specified by the manufacturer.

Development temperature

Development temperature is high, the molecular thermal movement of the developer is intense, the coating of the resin solvency; low temperature, the molecular thermal movement is weakened, the solvency of the resin is poorer; so the result of the same exposure conditions, the different temperatures required by the different time of the developer. Developing temperature is low when the negative impact on the quality of the plate is usually greater than the temperature is high, so the user in the winter must be the temperature of the developing solution to the specified range, so that the plate can get satisfactory results. Under the condition that other conditions remain unchanged, the development speed of PS plate is directly proportional to the development temperature, i.e. the higher the development temperature, the faster the development speed. Developing temperature on the quality of the plate is obvious. 1:6 dilution of PD-type developing solution and water, in the development of 1 minute under the condition of developing temperature on the quality of the plate is shown in Table 2 (omitted). From this set of data can be seen, such as developing 1 minute, developing temperature is best controlled at 20 ~ 24 ℃. Developing temperature is low is not easy to show clean; developing temperature is high when the light-sensitive layer of light-sensitive substances and film-forming resin molecules between the binding force weakened, alkaline resistance decreased, the light has not been seen in the graphic part of the light-sensitive layer will also be dissolved. When the development temperature is high, the percentage of dot area on the page will also be reduced, and the reproducibility of the printing plate will be damaged to a certain extent. Under normal circumstances, the temperature rises 12 ℃, the development speed is about 1 times faster. If the development temperature is too low, the development speed is slow, or even difficult to complete the development. Therefore, such as developing 1 minute, the development temperature should be controlled at 22 ± 2 ℃, 24 ± 2 ℃ machine development.

Development time

PS version of the development time is mainly by the type of PS version of the exposure time and the concentration of the development fluid, development temperature and other conditions to determine. When the above conditions are determined, the degree of PS plate development and development time is directly proportional to the relationship, that is, the longer the development time, the more complete development. However, too long development time will produce phenomena such as dot shrinkage. The effect of development time on the quality of the plate is obvious, with the PD-type developer liquid original liquid and water diluted at a ratio of 1:6, the development temperature of 22 ℃, the development time on the quality of the printing plate impact is shown in Table 3 (omitted). As can be seen from Table 3, the PS version of the development time is too long, the layout of the small dots are easily lost. But the development time is not enough to achieve the purpose of the development, that is, the non-image part of the photographic layer can not be completely dissolved and lead to printing on the machine when the layout of the dirty.

Circulation of the developer

Development is accomplished through the contact between the developer and the photographic layer of the PS plate, and dissolution, and therefore the power development method is mostly used. Such as manual development need to shake the development plate, mechanical development of the development of the circulating pump and brush roller device to speed up the development of liquid flow and circulation, so that the development speed and uniformity of development to improve. On the contrary, the static development mode, the developer can not effectively flow circulation, the development speed will be significantly reduced, the development of uniformity is also poor.

Developer supplement

Development process, the developer will develop with the development of carbon dioxide in the air and due to the absorption of water or calcium, magnesium and other ions in the water and gradually fatigue decline, development performance deterioration, development ability to weaken. Generally speaking, when the printing plate development, and in the same exposure conditions in the sun out of the gray scale blank level to observe the development effect, such as the development effect is not good, need to replace the developer in time. With the increasing amount of plate punching and CO2 in the air constantly dissolved into the concentration of OHˉ in the developer will decline, the pH value will be lower and lower, the development time should slowly become longer and longer, to the end of the normal exposure conditions under the PS version can not develop, which is the phenomenon of fatigue decline of the developer. However, as the pH value of the developer decreases, the corrosive power of the lye on the oxide layer and coating resin decreases, and the dot reproducibility and print resistance of the plate is better than that of the newly formulated developer. But must pay attention to two points: First, the amount of punch must be controlled within the allowable range of the developer; Second, after the developer must be sealed to save the developer with air isolation, because even if it is not developed a version of the developer exposed to the air, a week after the developer performance will be significantly reduced. Machine display also pay attention to the following points: ① regular maintenance of the developer to ensure that the PS plate has been exposed to the development can be carried out normally. ② in the development must be kept before the drive roller clean, if the traction roller is not clean, the development of the printing plate is easy to stick on the dirty spots. ③ If the developer has a gluing device, be sure to pay attention to the glue roller to keep clean, otherwise it will be dirty plate. Generally speaking, the developing capacity of PS plate developing solution (original solution) is 10m2/L. ⑤ When applying the protective glue, be sure to apply the glue evenly, not too thick, so as not to cause cracking of the coating after drying and dropping of the plate.

Baking

If the number of prints is large, it is necessary to bake the plate, baking the plate should pay attention to: ① first of all, choose a good baking glue, baking glue can not be too dirty. If the preparation of solid peach glue, be sure to use hot water to dissolve the glue, the glue should be thoroughly dissolved, filtered and then used. ② the appropriate amount of baking adhesive coated on the page, with a sponge to rub the page evenly. ③ The baking adhesive should not be wiped with a dry cloth. ④Bake the plate in the oven, and the image area will change color evenly. The baking time, temperature and final color will not be the same for different PS plates, so it is necessary to determine the baking conditions by test. Baking plate should also be noted: ① baking box of infrared lamps must be arranged horizontally, such as vertical arrangement, often leading to corrugated deformation of the printing plate and affect the use. ② baking plate adhesive concentration should be appropriate, such as baking plate adhesive is too thick, baking effect and ink effect will not be satisfactory; such as baking plate adhesive is too thin, baked plate is easy to dirty. ③ baking temperature can not be too high, the temperature is too high will also lead to aluminum plate base toughening and softening, the resin layer caramelization, affecting the print resistance. Baking time is too long to lead to the printing plate on the dirty, baking time is too short to achieve the effect of baking. It seems that the plate making process is not too complicated, but to produce a qualified plate, it really needs the operator to be attentive to the plate, patient production.

Printing plate even if the future

Traditional pre-press plate making process is more complicated, at present, the vast majority of newspaper and periodical printing presses have basically realized the upgrade of digital plate making technology, the traditional plate making process has become a supporting role, it is bound to withdraw from the booklet printing process, be replaced by the CTP collocation technology.

I hope you can help!