Precautions for offset yellow ink printing Yellow, as one of the three primary colors, 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 amount of ink, gradation, and the reproduction of the subtle gradations of the yellow version must be properly mastered. 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 in general color prints. The pigment of yellow ink is a kind of inorganic pigment belonging to chromium salt. It is divided into 5 types: lemon yellow, light yellow, medium yellow, dark yellow, and orange, with a specific gravity of 5.6～ 6. It has the characteristics of low oiliness, high specific gravity, coarse particles and strong hiding power. Yellow ink is often printed as the first color, mainly for the following considerations:
1. From the perspective of the relationship between ink transparency and printing color sequence, in general, the ink with poor hiding power, that is, with strong transparency, should be printed at the back. Due to the strong hiding power of yellow ink, if it is overprinted on other inks, the printed matter will lack gloss. For example, if the first color is printed with yellow ink and the second color is printed with magenta ink, the scarlet effect is very good; on the contrary, if the red ink is printed first, and then the yellow ink is overprinted, the printed scarlet effect is very poor. Of course, with the continuous improvement of printing inks, the transparency of yellow inks is also increasing day by day. Take domestic offset printing bright and quick-drying inks as an example, its transparency is better. If you choose high-quality high-transparency inks for overprinting, Color sequence, its effect is also possible. In fact, many manufacturers have already chosen this color sequence.
2. The yellow ink of the first color can fill up the rough surface of some paper, and because of its low oil content, the next color ink is easy to overprint.
3. Judging from the intensity of the ink color, overprinting a darker color on a lighter color, if there is a small amount of inaccuracy, it is not very conspicuous. Conversely, if you overprint a light color on a dark color, if the overprint is incorrect, it will be exposed. Therefore, when the red plate is used to overlap the yellow plate, it is difficult to notice the slight inaccuracies in the overprinting, and when the yellow plate is used to overlap the red plate, it is easy to observe if the overprint is inaccurate. What problems should be paid attention to when printing yellow ink Because the yellow is lighter, the human eye is not sensitive to it, so when printing, it is much more difficult to control the amount of yellow ink and the fine gradation of dots than to print red and blue plates.
The following are some aspects that need special attention when printing yellow ink:
1. Before the formal printing, the printing plate should be inspected by using a magnifying glass of 5 to 10 times to identify the depth of the printing plate to see if its dots are the same 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 electrical separation film. If the dots of the printing plate are larger than the dots of the color separation film, it indicates that the printing plate is too dark. After checking the darkness of the printing plate, we must also see if the quality of the dots meets the requirements.
2. Yellow ink can be roughly divided into three tones, namely: light yellow ink with a slight cyan color, medium yellow ink, and a dark yellow ink with a reddish color. As for the choice of yellow ink for offset printing, it depends on the hue of the original manuscript. When printing a yellow plate, it is necessary to estimate the change of the ink itself, the change after drying, such as the yellow ink above the neutral color is easy to become red after drying. When the offset printing is turned on, the ink color should be proofread according to the single-color sample.
3. When checking the yellow ink color during printing, pay attention to the surrounding light. For example: the incandescent lamp emits orange-yellow light, and the fluorescent lamp emits a little blue-violet light. Visual deviation will occur when observing the color under such a lamp. In addition, blue glass is often used when checking yellow. Because the light source is not uniform, it is easy to be unclear, and the use of blue (yellow complementary color) glass can avoid the error caused by the unstable light source. Or put on blue sunglasses when checking for yellow.
4. During normal printing, you should look at the printed sheet frequently and carefully compare the printed matter with the proof sheet. The method of comparison is to compare samples and proofs of printed matter at adjacent positions of the same light source. It is best to distinguish the shade of ink and color cast in the workshop under natural light in the workshop. Only in this way can it be ensured that the ink color of the printed matter is consistent with that of the proof sheet.
5. When controlling the amount of yellow ink, ensure that the printed sample conforms to the reflection density of the single-color sample interaction / exchange sheet. If conditions permit, a color reflection densitometer can be used to measure and calculate yellow to achieve digital and standardized technical quality management. If the ink color can be measured and calculated well, and if it is based on evidence, it can improve labor productivity, effectively save raw materials, and fundamentally change the backward quality management of visually and empirically controlling ink size and dot expansion. method.
6. When the monochrome offset printing machine prints in the color sequence of Y, M, C, K, printing yellow is the key first step, and the amount of yellow ink must be controlled. The yellow ink has a large amount of ink, and the magenta, cyan, and black inks that are printed later must be increased accordingly, otherwise the color cast will occur. For example, people's skin color is the focus of printing and copying in a picture of people. If the amount of yellow ink is large and the amount of magenta ink is small, the printed person's skin color is yellowish, which will give people a feeling of unhealthy skin color. If it is a landscape painting, it mainly reflects the natural landscape, with cyan as the main hue and yellow as the auxiliary hue. It is very important to print landscape paintings in yellow. The blue sky and white clouds are mainly blue, while the green flowers and trees are the colors of the yellow and blue dots. The yellow version has a large amount of ink and the green version has a small amount of ink. , The green vegetation will be yellowish. In short, you must master the ink size when printing yellow plates. Avoid the disadvantages of large ink color, enlarged dots, dirty plates, paste plates, slow drying of imprints, small ink colors, dull ink layers, weak dots, weak and weak dots, and unclear dots and areas.