Platemaking experience

In the printing industry, compared with other work, the traditional platemaking process has a low degree of automation and manual participation, so the operating experience is particularly important. The author has been engaged in plate-making for many years and now summarizes some of his work experiences and shares them with readers.

1. Clip

After the film is sent from the photocopying workshop to the platemaking workshop, the first thing to do is to cut out 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 viewing table, first look at the parity of the clear version, if it is a strange code version, cut off the left part of the film; if there is a seam, cut it It is possible to rely on the inside to prevent the imposition staff from reprocessing; if the code is even, cut off the right side of the film. The above is the cutting method for black-and-white film. If it is a color film, it is generally required to leave one alignment mark above and below.

2. Imposition

Two spellings, split edition and newspaper edition. 8 Open editions generally use the book edition spelling. Common editions are 4, 8, 16, 24, and 32 editions. Occasionally, there are 4th editions or 64th editions. Usually in the imposition, it is first divided into a large number of signs with a few parts, such as A. B. C. Several editions of D, such as 64 pages, can be divided into A32, B32 or 16 editions of A, B, C, and D.

(1) Regular edition of newsprint follows the following rules:

1 The sum of the upper and lower left and right side edition numbers is equal to the sum of the upper and lower right side edition numbers, and is equal to the maximum edition number plus 1. As in the case of 32 editions, the sum of upper and lower edition numbers on the left and right sides should be 33.

2The odd and even edition positions are fixed, and the small and large editions of the left and right sides are also fixed. For example, in 32 editions, 32, 25, 1, and 4 editions and 24, The four editions of 17, 9, and 16 were spelled in two large editions, of which 32 and 24, 25 and 17, 1 and 9, 8 and 16 were the same.

(2) 4 imposition version of the opening version generally follows the following rules:

1 edition is 20 or less. Including 20 hours, 4 editions are used to make a group, and the 2 editions at the two ends of the 4 editions are combined together with the middle one, 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.

If the number of editions is greater than 20, you can reduce the number of editions by an integer multiple of 20, and deal with the first case. For example, 48 can be combined with 45 because 48 and 45 are subtracted from 2 and 20 are 8 and 5 are put together.

3 Odd and even editions are fixed. That is: 1,3,5,7,9... is the same as the 2,4,6,8,10... slot.

3. Fold

The imposition layout is obtained by folding proofs. The folding process is called folding. According to the difference between the printing equipment and the folding machine, the folding method is not the same. If the 8th edition has the head-to-head and the foot-to-foot distinction, the 4th edition has the head of the head up and the head of the head down. Under normal circumstances, for a printing device with two triangles or using a depositing machine, its folding hands are both hands, that is, for the 16th edition, the former 8 and the latter 8 are combined together; for the 24 edition, the situation is the former. 16 sets together and then together with the rear 8 small sets; for the 32 version, is the first 16 and the rear 16 respectively after a large set of small sets together.

4. Printing

Due to the timeliness of newspaper printing, newspaper printing platemaking workshops generally advocate the “weak exposure” of printing, in order to save time in the process of plate making, set the printing time to be shorter, and the Chinese version conditions; Make appropriate adjustments to produce printing plates that meet the printing requirements. In addition, when printing, you also need to pay attention to the cleanliness of the platen glass and the suction of the vacuum pump.

5. Crash

In the case of stencil printing, the ratio of the developer is generally higher than the specification concentration in the specification in order to be suitable for the weak exposure printing conditions. Taking the developer as an example, the specification requires that the ratio of the stock solution to the water is 1:5 to 1:8, and the “weak exposure” is generally formulated at a concentration of 1:4. After the plate is washed out, it is often dirty, and there are usually two methods of treatment. One is to reprint the plate; the second is to wash it, but it is a waste of time; the other method, and the better method is to develop. A certain amount of detergent powder is added to the liquid, and the dirt is increased by enhancing the molecular activity of the liquid.

6. Revision

The most critical point in revising is to remove unexistent film marks on the plate. After repairing the dirty marks with the revised pen, be sure to wipe it with a damp cloth in time so that it will not be dirty when printed. For the scratches on the plate, you can use a thin brush to dip a little dilute sulfuric acid on the scratches.

7. Check the quality of the imposition

The layout inspection is the last process before the printing plate is put on the machine. If this process is not strictly followed, it will bring greater economic losses to the printing house. In addition to checking whether the layout text and pictures have broken pens, less paintings, and false appearances, the inspection layout must be checked in detail. If it is even a printing plate, it is necessary to check the deviation of the four printing plates of YMCK from the sun and the sun. Most of the copy-printing workshops rely on visual inspection to check the quality of the printing plate. However, due to the small contrast between the printing plate and the blank, long-term detection can cause fatigue, and some errors are not easy to detect. A better test method is to rinse the printed plates in a timely manner and increase the contrast of the plates to suit the viewing habits of human eyes.

8. Calculation version

When printing on the plate, certain points must be printed. When calculating the edition, it is necessary to distinguish whether it is 8 open or 4 open edition.

(1) Calculation of the 8th edition

The formula is: n/4+a×3+b×1.

n is the total version number. 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 is 28, then it should be calculated as 32. a is the number of color versions, and 4 color versions that can be put together are 1 set, and less than 4 are also counted as 1 set. b is the number of red sets, 4 red sets that can be put together are 1 set, and less than 4 are also counted as 1 set.

For example, the total number of editions is 28 editions (n=32), in which the number of colorful editions is 16 (a=4), and 2 editions are red (b=1), then the total number of PS editions required for making one edition is: 32/ 4+4×3+1×1=21 blocks. The above formula is suitable for narrow single-radius tower type rotary machines.

(2) Calculation of the 4th edition

The formula is: n/2+a×3+b×1+c.

n is the total version number, and n must be calculated as an integer multiple of 8 when calculating, otherwise it is calculated as an integer multiple of the nearest 8 that is greater than this value. A is the number of color versions, 2 color versions that can be put together are 1 set, and 2 color versions that cannot be spelled are 2 sets. From the 1st edition, there are 8 consecutive editions, and the ungrouped editions are generally the last 4 editions. A set of color editions is counted as 2 sets. A must be an even number, and if it is an odd number, 1 is added. b is the number of sets of red sets, 2 sets of red sets that can be put together are 1 sets, 2 sets of 2 sets that cannot be spelled, and 8 sets of consecutive versions are set from 1 set, and the ungrouped layout is generally the last 4 sets. Edition, 1 set of red edition counts as 2 sets. b must be even, plus 1 if odd. c is the number of white editions. In the case of a set of editions (a group of eight consecutive editions starting from the first edition), if the number of copies of the red edition and the red edition is 1, the white edition is required. Color version requires 3 pieces, and red version requires 1 piece.

For example, assuming that the total number is 20 (n=24), 1, 4, and 5 are color versions (a=2), 9, 12, 17, and 20 are red editions (b=3), and the white version number is c=1. The total number of PS versions needed to do a set is:

24/2+2×3+3×1+1 = 22.

The above formula is suitable for a narrow double-diameter "Y" type web offset press.

In addition, in the calculation of the number of editions, the actual structure of the printing press should be combined, and die-cutting formulas must not be avoided.

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