Overprint Errors in Printed Materials (3)

Third, the overlay error of the printing press

The overlay error of the printing press is mainly caused by the overprinting error and the overprinting error. After a long-term production practice, people believe that the overlay error of the continuous paper is 0.03 to 0.05 mm, and the paper transfer error is 0.02 to 0.03 mm. It was also suggested that 98% of the printed sheets can be printed with high quality fine web self-printing when the overprinting error is 0.02 mm and the overprinting error is 0.01 mm. However, to increase the accuracy of the press by 1%, the cost will increase a lot. Therefore, the general overprint accuracy does not have to exceed the level required by the process. Different types of printing presses have different print overlay tolerances.

When using a monochrome printer for four-color printing, four consecutive passes and four passes are required. If the error in the continuous sheet is 0.05 mm, the overprint error between any two inks on the print is 0. 05mm. Since the same sheet of paper is to be reprinted on the printing press four times, the same process must occur four times successively. That is, when the second color is printed to the fourth color, it should be the same as the first color printing process. The quasi-error is the same. In this case, the overprint error will not be more than 0.05mm. This shows that when monochrome printing is performed, the overprint error on the printed matter is the same as the overprinting error of the monochrome printing machine. Thus, when printing on a monochrome printing machine, the overprinting error is 0.05 mm, which can satisfy the requirement. Process requirements. If the microscopic ability of the human eye is considered to be 0.1mm, since the maximum error of the printed matter will not exceed 0.05mm, the overprint error left for the prepress processing and plate making process cannot exceed 0.05mm, otherwise, the quality of the printed matter It will fall.

When using a four-color offset press for color printing, it only takes a single pass. After the image has been placed on the paper for the first time, the colors are the same. However, the sum of overprint errors that occur during the transfer of paper between printing units constitutes the actual overprint error between the individual colors on the printed sheet. If the paper transfer error value is set to 0.03 mm, and the normal distribution addition rule is used, the actual print error between the first color and the fourth color on the printed sheet can be obtained.

S1,4=(0.032+0.032+0.032)1/2=0.00271/2=0.052mm

The overlay error between other colors will be smaller. Calculations show that the 0.03mm transfer error can meet the registration accuracy required by the printing press, and the remaining 0.048mm registration error, used in the production of negatives and plate making The overprint can not appear in the problem.

[Example 8-1] Four-color printing is performed on a two-color offset press on a tandem printing machine. There are two continuous feeds and two passes. If the overlay error is 0.05 mm, the pass-through overlay error is 0.03 mm. Is the overprint error between colors the largest?

Solution: S1, 2 between the first color and the second color is 0.03mm;

The S2,3 between the first color and the third color is 0.05mm (equivalent to a monochrome printer);

Between the first color and the fourth color, S1, 4 is:

S1,4=(0.05/2+0.032)1/2=0.058mm;

S2,3 between the second color and the third color are:

S2,3=(0.032+0.052)1/2=0.058mm;

Between the second color and the fourth color, S2, 4 is:

S2,4=(0.032+0.052+0.032)1/2=0.066mm;

The Sz3,4 between the third color and the fourth color is 0.03 mm.

From the calculations, it is known that the unit type two-color printing press has the largest overlay error in the second color and the fourth color, which is 0.066 mm. If the maximum allowable overlay error is 0.1 mm, then it is left as The error of overprinting for making negatives and plates is only 0.034mm.

The overprint error of a printed matter is the sum of the overprint error accumulated in each process in the printing copy. Because ink transfer is an extremely complicated process, the overprinting errors in the production of negatives and plate making processes should be reduced as much as possible, leaving a large overprinting error for printing presses in order to improve the printing quality. In the actual production, in order to improve the printing quality, people often reduce the printing speed, which can reduce errors caused by paper or machine. In addition, for fine mesh high-quality prints, the error of paper transfer is often increased to 0.02 mm, and the error of continuous paper is increased to 0.03 mm.