The Experience of Traditional Platemaking Processes (Part Two)

5. Crash

In the case of stencil printing, the proportion of the developer is generally higher than the specification concentration in the specification in order to be suitable for a weak exposure. 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 printing plate is rinsed out, it is often dirty, and there are usually two kinds of processing methods. First, the printing plate is flushed again, but it is a waste of time: the other method, and the better method is to add some to the developer. The amount of detergent is increased by increasing the activity of the printing solution.

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 to avoid dirtiness during printing. 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 the layout text and whether there are broken pens, less paintings or hair voicing, the layout of the inspection should be examined in detail. If it is even a printing plate, it is still necessary to check the deviation of the four printing plates of YMCK: one sun and two suns. Most of the copy-printing workshops rely on visual inspection to check the quality of printing plates. However, due to the small contrast between the printing plate and the blank, long-term detection will produce 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 the 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 a set of red sets, 4 sets of 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 to make one set 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. When calculating, n must be calculated as an integer multiple of 8, 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 successive editions. The ungrouped layout is generally the last 4 editions: one set of color editions is counted as 2 sets, a must be an even number, and if it is an odd number, it is incremented by 1. 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 one 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.

Source: Printing Technology