Offset Ink
Main Category
Offset printing ink is also called offset printing ink.
Its varieties include offset resin ink, offset glossy ink, offset four-color printing ink, offset fast-fixing ink, offset bright quick-drying ink, offset sheet-fed ink, offset rotary press ink, offset rotary thermosetting ink, offset printing iron ink, offset Iron printing retort-resistant ink, offset plastic ink, offset photocurable ink, etc.
Three Principles
1. Water and oil are incompatible
The so-called similar compatibility principle in chemistry determines that the molecular polarity between the slightly polar water molecule and the non-polar oil molecule is different, so that water and oil cannot attract and dissolve. The existence of this rule makes the flat printing plate The idea of using water to distinguish text and blank parts is possible.
2. Choose surface adsorption
Depending on the surface tension, it can absorb different substances, which also provides the possibility for the separation of graphics and text in lithographic offset printing.
3. Dot conformation
Since the printing plate of offset printing is flat, it is impossible to rely on the thickness of the ink to express the level of the graphic on the printed matter, but it can be effectively expressed by splitting different levels into very small dot units that are imperceptible to the naked eye. Come out with rich image layers
Craft common sense
Register
That is, the accuracy of overprinting. This is a commonly used term in printing, and it is one of the important signs used to measure the printing quality of offset presses.
The term registration is only applicable to two-color and multi-color printing. It means that when printing a color print, the graphics and texts of various colors on the printing plate are accurately superimposed on the same print. Moreover, the dots of various colors are not deformed, the graphics and texts are not out of shape, and the color is gorgeous and full of three-dimensional effect.
Without accurate registration, there is no print quality. It is the minimum and most basic condition to require accurate overprinting of color prints. However, there is never absolute alignment. According to the size of the paper, the number of screen lines, and the quality requirements for printed products, etc., when printing color screen line prints, the accuracy of paper overprinting should meet the following requirements: the error of the position of the paper when it is printed should be less than two Half the distance between adjacent dots. Generally speaking, it is within the range of about 0.05-0.10 mm. For some prints that do not require high overprint quality, it can be relaxed to 0.15-0.25 mm.
In order to check the registration situation during printing, you can use the registration situation of the gauge line as a reference, and then carefully observe the graphics and text registration situation. In order to see whether it is registered, it is often observed with a magnifying glass of 3 to 6 times.
ink balance
Water-ink balance is one of the basic principles of offset printing, which is based on the immiscibility mechanism of oil and water. The immiscibility of ink and water is the basic principle of lithographic printing. However, during offset printing, ink and water must be on the same printing plate at the same time and keep a balance. In this way, the graphic part of the printing plate is required to maintain a sufficient amount of ink , At the same time, it is necessary to ensure that the blank part of the printing plate is not dirty. This balance between water and ink is called the balance of water and ink. Mastering the balance of ink and ink is a prerequisite for ensuring the quality of offset printing.
Precautions
a. The overprinting color of the color block should try to avoid using dots with too small percentage, such as flat screen dots below 20%. Because the color blocks composed of small dots are prone to local sun exposure due to insufficient air suction or small particles adhered to the negative film and the glass of the plate printing machine during printing; Dirty or worn plates cause plate drop. The above two reasons will cause the ink color of the color block to be uneven. As for the dots below 5%, ordinary offset printing process is difficult to restore, and should be avoided.
b. At the same time, try to avoid using dots with too large a percentage for overprinting colors of color blocks, such as flat screen dots with more than 80%. Because the color block composed of large dots is easy to paste if the water supply is slightly insufficient during printing or the blanket is dirty. As for more than 95% of the outlets, it should be avoided.
c. To avoid overprinting color blocks with too many solid or high-resolution dots, it is easy to cause the back to be dirty due to too thick ink layer.
d. When using the spot color printing process, try not to choose color blocks that need to be blended with too many basic color inks. Mixing too many kinds of inks will greatly increase the difficulty of mixing inks, which not only increases the time for ink mixing, but also makes it difficult to mix colors with similar hues.
e. When using a spot color to print a large area of a certain color, try to avoid using this color to print small reversed text and lines at the same time. Because the printing of large areas tends to increase the thickness of the ink layer, the ink layer is thick and easy to spread, but it will lead to small reversed text and line paste.
f. As for the text, if you print reversed small characters in the middle of the field, you should try to advise customers to use bold fonts.
g. When printing a full plate on the spot, you can use the printing plate left after the last printing, stop the water supply, and do not need to make a special plate. However, since the photosensitive adhesive in the graphic part of the PS plate and the alumina in the blank part have slightly different ink adsorption capabilities, when printing a color with strong color rendering (such as dark blue), it is best to use a completely blank one. printing plate.
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