Printing plate making

Plate making process

Clip

After the film (also known as film) is sent from the phototypesetting workshop to the platemaking workshop, the first thing to do is to cut off the blank part of the film, that is, cut the film. The correct method of operation is to place the film face up on the stand, and first see the parity of the version number. If it is an odd-code version, cut off the blank part on the left side of the film; It may be on the inside to avoid reprocessing by the imposition personnel; if it is an even-code version, cut off the right side of the film. The above is the cutting method of black and white film. If it is color film, it is generally necessary to leave a registration mark on the upper and lower sides.

Imposition

The imposition is divided into two spelling methods: book version and newspaper version. The 8 opening version generally adopts the book version spelling. The common versions are 4, 8, 16, 24 and 32, and occasionally there are 48 or 64 versions. Usually in the imposition, it is first to divide the large number into several parts with signs, such as A. b. c. Several editions of D, such as the 64-page newspaper edition, can be divided into A32, B32 or 16 editions each of A, B, C, and D. (1) The regular imposition of the newspaper version follows the following rules: ①The sum of the upper and lower version numbers on the left is equal to the sum of the upper and lower version numbers on the right, and is equal to the maximum version number plus 1. For example, in the case of version 32, the sum of the upper and lower version numbers on the left and right sides should be 33. ②The position of odd-numbered layout and even-numbered layout is fixed, and the small layout and large layout on the left and right sides are also fixed. The four editions of 17, 9, and 16 are respectively spelled on two large editions, of which 32 and 24, 25 and 17, 1 and 9, and 8 and 16 are in the same position. (2) The imposition of the 4th edition generally follows the following rules: ① When the number of editions is within 20, including 20, the imposition is performed in a group of 4 editions, and the 2 editions at the two ends of the 4 editions and the middle one Versions are put together, namely: 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. ②If the number of editions is greater than 20, you can subtract the integer multiple of 20 from the number of editions, and then deal with the method in the first case. For example, 48 can be combined with 45, because 8 and 5 obtained by subtracting two 20s from 48 and 45 are combined together. ③The odd-numbered version and the even-numbered version are fixed. That is: 1, 3, 5, 7, 9... and 2, 4, 6, 8, 10... positions are the same.

origami

The imposition layout is obtained by folding the proof sheets, and the process of folding the proof sheets is called folding hands. According to the different folding methods of printing equipment and folding machines, the folding methods are also different. For example, the 8th edition has head-to-head and foot-to-foot points, and the 4th edition has the header up and the header down. Under normal circumstances, for printing equipment with 2 triangular plates or using a folding machine, the folding hands are both hands, that is, for the 16 version, the front 8 large and the rear 8 small sets are set together; for the 24 version, the front The 16 large sets are put together with the rear 8 small sets; for the 32 version, the front 16 and the rear 16 are separate large sets and then small sets are put together.

copy

Due to the strong timeliness of newspaper printing, the plate-making workshop of the newspaper printing factory generally advocates the "weak exposure" printing method, in order to save time in the plate-making process, set the printing time to be shorter, and make the printing conditions better. Adjust accordingly to produce a printing plate that meets the printing requirements. In addition, when printing, you also need to pay attention to the cleanliness of the glass of the printing machine and the suction of the vacuum pump.

printing

In order to suit the printing conditions of weak exposure during printing (development), the proportion of developer is generally higher than the proportion in the instruction manual. Taking the developer as an example, the instruction manual requires that the ratio of stock solution and water is 1:5~1:8, and "weak exposure" is generally prepared at a concentration of 1:4. After the printing plate is washed out, it is often dirty. There are usually two ways to deal with it. One is to wash the printing plate again, but it is too time-consuming; the other method is also a better method. The amount of washing powder is used to remove dirt by enhancing the molecular activity of the printing solution.

revision

The most critical point when retouching the plate is to remove the film edge marks that should not be present on the printing plate. The traces after repairing with a retouching pen must also be wiped off with a damp cloth in time to avoid getting dirty during printing. For scratches on the printing plate, you can use a fine brush dipped in a little dilute sulfuric acid to apply to the scratches.

Check imposition quality

Layout inspection is the last process before the printing plate is put on the machine. If this process is not strictly controlled, it will bring great economic losses to the printing factory. In addition to checking whether the text and pictures on the layout are broken, less drawn, and false, the layout of the layout should also be checked in detail. If it is a continuous printing plate, it is necessary to check the deviation of the first and second printing plates of the four YMCK printing plates. Most of the printing workshops rely on visual inspection to inspect the quality of the printing plates. However, due to the small contrast between the graphics and the blank parts of the printing plates, long-term inspection will cause fatigue, and some errors are not easy to detect. A better inspection method is to pick up the ink in time for the washed printing plate and increase the contrast of the printing plate to adapt to the observation habits of the human eye.

Calculate the number of editions

When the printing plate is put on the machine, be sure to check the number of printing plates. When calculating the number of editions, it is necessary to distinguish whether it is an 8-open or a 4-open edition. (1) Calculation of the 8th edition The calculation formula is: n/4+a×3+b×1. n is the total number of editions. When calculating, n must be an integer multiple of 8. If not, it should be calculated as an integer multiple of the nearest 8 that is greater than this number. If the total number of editions is 28, the number of editions should be calculated as 32. a is the number of sets of color plates, 4 color plates that can be put together are 1 set, and those less than 4 are counted as 1 set. b is the number of sets of red editions, 4 sets of red editions that can be put together are 1 set, and less than 4 sets of red editions are counted as 1 set. For example, if the total number of editions is 28 editions (n=32), of which the number of color editions is 16 (a=4) and 2 editions are in red (b=1), the total number of ps editions required to make a set of editions is: 32/ 4+4×3+1×1=21 blocks. The above formula is suitable for narrow-width single-diameter tower rotary machines. (2) Calculation of the 4th edition The calculation formula is: n/2+a×3+b×1+c. n is the total number of editions. When calculating, n must be calculated as an integer multiple of 8, otherwise, it should be calculated as an integer multiple of the nearest 8 that is greater than this value. a is the number of sets of color plates, 2 color plates that can be put together are 1 set, and 2 color plates that cannot be put together are counted as 2 sets. A group of 8 consecutive editions starting from the 1st edition is a group, and the layouts that are not grouped are generally the last 4 editions; a set of color editions counts as 2 sets, and a must be an even number, and if it is an odd number, add 1. b is the number of sets of red editions, 2 sets of red editions that can be put together are 1 set, 2 sets that cannot be joined are counted as 2 sets, 8 consecutive editions from the 1st edition are a group, and the layouts that are not grouped are generally the last 4 editions version, 1 set of red version counts as 2 sets. b must be an even number, if it is an odd number, add 1. c is the number of white editions. In a group of editions (a group of 8 consecutive editions starting from edition 1), if the number of colour editions and red editions is 1, white editions are required. The color version needs 3 pieces, and the red version needs 1 piece. For example, assuming the total number is 20 (n=24), 1, 4, and 5 are color versions (a=2), 9, 12, 17, and 20 are red versions (b=3), and the number of white versions c=1, The total number of PS versions required to make a set of versions is: 24/2+2×3+3×1+1=22. The above formula is suitable for narrow double diameter "Y" type web offset press. In addition, when calculating the number of editions, the actual structure of the printing press should be combined, and the formula must not be rigid.