Offset production standardization (2)

Third, printing standardized content

Printing standardization includes two aspects of material standardization and method standardization.

1. Material standardization.

1 paper classification. A certain kind of paper is a paper that belongs to a standard specification. Which field density is chosen for this type of paper? Because there are different types of paper and different types of ink, in order to facilitate the adjustment of the machine, each situation needs to indicate a generally applicable field density.

It is impossible to sort according to the absorption of the paper because it is necessary to establish a new hierarchical relationship for each ink.

As the thickness of the ink layer increases, the gray scale of the process color gradually increases, and the density of the process color rises, as if a certain percentage of black ink has been removed in the process color. For example, the blue ink on the printing paper is blue-blue, while the ink in the ink fountain is black-blue.

When the printing conditions (paper and ink, etc.) are different, the ink layer distribution is different, as shown in Figure 5-23. In both cases, the amount of ink per unit area is the same, but Ds1>Ds2, the color on the right appears more dirty than the left one. According to Lambert Beer's law, the density should be additive, and the distribution of the ink should not have worked, but it actually worked (Figure 5-24). As we all know, strong absorbing paper needs to print more ink than weak absorbing paper, but the absorption strength is only a linguistic simplification. The paper absorption properties are a combination of paper and ink properties, and the ink absorption of paper is not only Depending on the ink, not only depends on the paper itself.

Printing on the same paper with the same amount of ink (ie, the thickness of the ink layer on the blanket) can produce the most approximate color reproduction. This conclusion is summed up from the printing practice for two reasons:

When the same ink supply is used to print on different papers*, the ink layer thickness between the plate and the blanket is also the same in both cases, and the increase in the adjustment of the various papers is also the same. The dot coverage of each color is the most important quantity for the color of the dot image, and printing with the same ink supply amount can make the color contrast of the image and rich secondary color reproduction (such as red, green, orange, purple) In a compromise, one might want to increase the color print contrast of rough paper by increasing the amount of ink, but this will give a significant value to color prints. In the case of a brown hue (in this case, the three colors are arranged in a certain proportion), the gray value generated on the rough paper can be compensated by the mask but cannot be compensated to become a bright orange (for example: C=0%, M=50%, Y=100%).

Although the thickness of the ink-absorbing layer on the highly absorbent paper is relatively large, the density on the ground is relatively small (as shown in Figure 5-25). In both cases, the visual impression is very similar, because the rough paper has a relatively high gray content. Although the color contrast is small, both show the same darkness. The degree of vividness is the same.

The division of paper grades. First use a standard ink to print a face on standard paper, then use the same amount of ink to print and produce the actual paper. According to Table 5-8, the paper can be sorted.

Table 5-8

Group two kinds of proofs dry density difference by paper name rough classification
1 0～0.15 Coated paper
2 0.16 to 0.30 matte coated paper
3 0.31～0.45 non-coated paper

If you think that the classification in the above table is too thick, then you can subdivide the 1st and 2nd groups into two categories, for a total of 5 categories.

How to achieve the same amount of ink printing?

In any case, the thickness of the ink layer on the blanket is undetectable. For two papers with different absorptivity, visual comparison can be used to determine whether or not printing conditions are equal. For non-coated paper and coated paper, for example, there are generally the rules shown in Table 5-9.

Table 5-9 Comparison of printing effect between coated and uncoated paper

Print Condition Density Ink Thickness Adjustment Increased Visual Comparison Ink Thickness Same DN ≤ DK dN = dK TZN ≤ TZK Color of non-coated paper Too weak Color Intensity Same DN<DK dN>dK TZN=TZK VN≈VK
The same density in the field DN = DK dN> dK TZN> TZK Uncoated paper is relatively dark

The subscript N in the table indicates non-coated paper and K indicates coated paper.

It can be seen from the table that the equal ink supply printing of the printing color is between the ink layer thickness printing and the solid density printing.

As the thickness of the ink layer increases, the gray scale increases. This is because when the light passes through the transparent ink layer with different spectral ranges, it does not pass through the ink layer without hindrance, so the density increases, but the main density instead enters the saturated region, and thus increases slowly. Table 5-10 is the result of measuring the actual print.

Table 5-10 Blue ink printing results

Master Density Density Filter Adjust MCY
1.701 0.176 (10%) 0.701 (41%)
2.870 0.365 (13%) 1.781 (62%)

The percentages of the densities in the Tables 5-11 are calculated based on the main density.

Table 5-11 Magenta Ink Printing Measurement Results

Main density density filter adjustment Magenta 1.701 0.176 (10%) 0.701 (41%)
2.870 0.365 (13%) 1.781 (62%)