As one of the three primary colors, yellow seems to be different from other primary colors. Because in offset printing, most of the yellow ink is printed as the first color. For this reason, the ink volume, tone and subtle reproduction of the yellow version must be mastered properly. After all, the first color version is the foundation. Therefore, the printing of yellow ink is particularly important.
Why yellow is often used as the first color
The pigment of yellow ink used in general color prints is an inorganic pigment belonging to chromium salt. It is divided into 5 types: lemon yellow, light yellow, medium yellow, deep yellow, and orange, with a specific gravity of 5.6 to 6. It has small oiliness and large specific gravity. , Coarse particles, strong covering power. Yellow ink is often used as the first color printing, mainly for the following considerations:
1. From the perspective of the relationship between ink transparency and printing color sequence, in general, inks with poor hiding power, that is, strong transparency should be placed behind the printing. Due to the strong hiding power of yellow ink, if it is overprinted on other inks, it will make the printed matter lack gloss. For example: the first color is printed with yellow ink, and the second color is printed with red ink, so the printed red effect is very good; otherwise, the red ink is printed first, and then the yellow ink is overprinted, the printed red effect is very poor.
Of course, with the continuous improvement of printing inks, the transparency of yellow inks is also increasing. Taking domestic offset printing light quick-drying inks as an example, its transparency is better. If you choose a high-quality ink with high transparency and overprinting Color order, its effect is also possible. In fact, many manufacturers have chosen this color sequence.
2. The first color printing yellow ink can play the role of filling the rough surface of a certain paper, and because of its low oil content, the next color ink is easy to overprint.
3. Judging from the depth of the ink color, the dark color is overprinted on the light color. If there is a slight amount of overprint, it is not very conspicuous. On the contrary, overprinting light colors on dark colors, if overprinting is not accurate, it will be completely exposed.
Therefore, when using the red version to stack the yellow version, there is a slight amount of inaccuracy in the overprint.
What should be paid attention to when printing yellow ink
Because the yellow color is lighter and the human eye is not sensitive to it, it is much more difficult to control the ink level of the yellow version and the fine-grained control of the dots during printing than to print the red and blue versions.
The following are some aspects that require special attention when printing yellow ink:
1. Before the official printing, the printing plate should be checked by using a magnifying glass 5 to 10 times to identify the depth of the printing plate to see if its dots are the same size as the dots of the four-color film. Under normal circumstances, the printing plate is allowed to be slightly smaller than the dots of the electronic separation film. If the printing plate has a larger dot than the color separation film, it means that the printed plate is too dark. After checking the depth of the printing plate, we also have to see if the quality of the outlet meets the requirements.
2. Yellow ink can be roughly divided into three shades, namely: light yellow ink with a little cyan, medium yellow ink, and dark yellow ink with a little red. As for the yellow ink used for offset printing, it should be determined according to the hue of the original. When printing a yellow plate, it is necessary to estimate the changes of the ink itself, the changes after drying, such as the yellow ink above the neutral color is easy to red after drying. When the offset printing is turned on, the ink color should be checked according to the monochrome sample.
3. When checking the yellow ink color during printing, pay attention to the surrounding light. For example: the incandescent lamp emits orange yellow, and the fluorescent lamp emits a little blue and purple. Observing the color under such a lamp will cause a visual deviation.
In addition, when inspecting yellow, blue glass is often used. Because the light source is not uniform, it is easy to judge clearly, and the blue (yellow complementary color) glass can avoid the error caused by the unstable light source. Or when checking yellow, wear blue sunglasses.
4. During normal printing, the printed sheet should be checked frequently, and the printed matter should be carefully compared with the sample sheet. The method of comparison is to compare the samples of the printed matter and the sample sheets at adjacent positions of the same light source. It is best to identify the depth of ink color and the color shift of overprinting under natural light in the workshop. Only in this way can the ink color of the printed matter and the proof be consistent.
5. When controlling the amount of yellow ink, ensure that the printed sample conforms to the reflection density of the monochrome sample interaction / exchange sheet. When conditions permit, a color reflection densitometer can be used to measure and calculate yellow to achieve data-based and standardized technical quality management.
If the ink color can be measured and calculated well, and the evidence can be supported, the labor productivity can be improved, the raw material can be effectively saved, and the backward quality management such as visual and empirical control of ink color size and network expansion can be fundamentally changed. method.
6. When printing in the Y, M, C, and K color sequence for a monochrome offset press, printing yellow is the key first step, and the amount of yellow ink must be controlled. The amount of yellow ink is large, and the magenta, cyan, and black inks of the post-print must increase the amount of ink, otherwise the phenomenon of color cast will occur. For example, in a character-based screen, the skin color of the person is the focus of printing and copying. If the amount of yellow ink is large and the amount of magenta ink is small, the printed person's skin color will be yellow, which will give people a feeling of unhealthy skin color. If it is a landscape painting, it mainly reflects the natural landscape, cyan is the main color, and yellow is the auxiliary color. It is very important to print landscape paintings in yellow. The blue sky and white clouds are mainly green, and the green flowers and trees are the colors of the yellow and blue dots. The yellow ink is large and the blue ink is small. , The green plants will turn yellow.
In short, when printing the yellow version, we must master the ink color size. Avoid the disadvantages of large ink color, enlarged dots, dirty version, paste version, slow drying of blots, small ink color, dull ink layer, weak dots, faint and faint, unclean and unclear dots and ground.
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