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People's aesthetics are improving, and the requirements for prints are also increasing. To get a beautiful print, hardware sharpening has the following requirements (there are also seven elements called lithography): 1. High-quality printing presses. 2. Excellent paper; 3. High-quality ink; 4. Exquisite manuscript; 5. Fine printing plate; 6. Meet the required environmental conditions; 7. Appropriate fountain solution. The first impression of printed matter is color, which depends on the performance of the ink, so we should understand the relationship between the classification, composition, technical indicators and printing of ink, which is very important for the correct selection of ink in lithography.
1. Classification of ink
Printing is a professional technique with high technical level and wide artistic expression. Modern printing theory has formed an independent science. The printing process is mainly a technical process that transfers the ink on the plate to the surface of paper or other objects by force (such as pressure) to reproduce the text pattern on the surface of the paper or other objects. The inks used are divided into four types according to the printing plate type: 1. Lithographic printing ink; 2. Letterpress printing ink: 3. Gravure printing ink; 4. Filtered printing ink. Lithography accounts for about 50% of the total printing volume, and the selection and use of its ink should be given more attention.
Second, the classification of lithographic ink
There are many types of lithographic ink, the main classification is shown in the figure below:
3. The basic composition of lithographic ink
Ink is a homogeneous compound composed of colored pigments (dye, etc.), binders, fillers and additional materials, which can be printed and dried on the object to be printed. Pasty adhesive body.
Pigment is a solid powdery substance that is neither soluble in dry water, nor soluble in oil or binder, and has a certain color. It is not only the main solid component of the ink, but also the colored body visible on the object. To a large extent determines the color, thinness, light resistance and other properties of the ink.
Linking material: Linking material is a kind of sticky fluid, as the name implies, it plays a role in connecting. In the ink, powdery pigments and other substances are mixed and connected, so that after grinding and dispersion, a paste-like adhesive body with a certain degree of fluidity and viscosity is formed. The binder is the main fluid component in the ink, which determines the fluidity, viscosity, dryness and printability of the ink. The binder is the heart of the ink.
Filler is a white, transparent, translucent or opaque powdery substance, which is also a solid component of ink. It mainly plays a role in filling and properly selects some fillers. In addition to reducing the amount of pigment and cost, it can also adjust the properties of the ink, such as thinness and fluidity.
Additional material: The additional material is the additional part of the ink in addition to the main components. It can also be used as an additive to finished ink products, as a printing aid to change or improve certain properties of the ink, such as drying and friction resistance.
Fourth, the technical indicators of ink
At present, the inspection method of finished ink products is still not perfect, and there are still many unscientific and impractical. The so-called unscientific means that there are many contents that must be judged and evaluated based on experience and senses. The so-called impracticality means that the measurement results cannot fully represent the needs of practical application. In addition, the measurement results of some items have large errors. Therefore, there are many inspection methods and data that can only be used as a relative comparison, that is to say, the inspection of ink is relative. Nonetheless, the technical indicators of ink are of guiding significance for printing. The following introduces several technical indicators that are closely related to printing.
1. Ink density. Ink concentration is an indicator of its pigment content. Pigments generally account for about 2% of the total ink. When printing, the ink concentration is large, and with the same amount of ink, the color of the printed matter is thick; otherwise, the color of the printed matter is light. The ink concentration is large, and the amount of ink used in printing is small, the ink layer is thin, and the drying is relatively fast, especially when printing a large area on the ground, the effect of the ink concentration on the printing quality is particularly significant, because when printing with high concentration ink The ink layer is thin and fast, it can reduce the stickiness of the printed product, and the color balance of each color is easy to adjust. The printing worker has a small experience that when printing, the greater the ink is, the worse the printing is, and the smaller the ink is, the better the printing. This experience is actually based on the concept of density. The ink industry judges the ink density by detecting the coloring power. the size of. The method is to dilute the standard sample ink with white ink, and to dilute the sample ink and white ink to change the amount of white ink in the sample so that the colors of the two scraped on the scraping paper are the same. The ratio of the amount of white ink of the sample to the amount of white ink of the standard sample expressed as a percentage is the coloring power.
In the formula: S = percentage of coloring power (standard ink is 100%) A = amount of white ink used for standard sample dilution B = amount of white ink used for sample dilution
2. The viscosity of the ink. The ink viscosity meter is manufactured following the principle of a printing machine. The viscosity of the ink is tested with an ink viscosity meter. The value of the ink viscosity refers to the force that separates the ink film between the two rollers of the viscosity meter. The viscosity of the ink has a greater relationship with the ambient temperature and the speed of the printing press. The viscosity of the ink increases with the increase of the running speed of the copper roller and decreases with the increase of the ambient temperature. The viscosity of the ink is an important indicator in printing, which affects the transferability of the ink during printing, the thickness of the ink layer of the printed product, and the penetration Volume and gloss size. The viscosity of the ink is too large or too small will affect the quality of printing. When the viscosity of the ink is too large, it is easy to cause failures such as poor ink transfer, poor transferability, paper pulling, and poor overprinting. If the viscosity is too low, it is easy to cause excessive ink transfer, flying ink, dot expansion, ink emulsification, floating dirt and other failures. At a certain temperature, the viscosity of the selected ink should not be too large when the printing speed is fast, and vice versa. In addition, the relative viscosity of each color ink should be selected according to the printing order. Under normal conditions, there is no need to adjust the viscosity of the ink. Choose additives for consistency. Generally, when the viscosity is high and the consistency is appropriate, it can be adjusted with additives that reduce viscosity but not reduce viscosity. Generally, when the viscosity is high and the consistency is large, an auxiliary agent that reduces both viscosity and viscosity can be used.
3. Dryness of ink. The drying process of lithographic ink on paper is the process that the ink changes from a non-polar colloid with high fluidity to a fixed state. The dry ink industry for measuring lithographic inks is divided into two indicators; one is the fixing speed, which means that the ink changes from a natural flow state to a semi-solid state. The initial drying of ink is determined by the resin structure selected in the design. The initial drying time is very short, but it is not completely dry. The second is the drying of oxidized conjunctiva, which is the thorough drying mentioned in the printing. The drying time is longer, generally more than 8 hours, and it is completely dry. The thorough drying of ink is determined by the type and amount of desiccant. It can be adjusted within a certain range. The current lithographic inks are all resin-based, and the fixing speed is faster. In theory, the faster the initial drying, the better. However, if the initial drying is too fast, it will affect the gloss of the printed matter. The gloss level and the fixing speed are generally contradictory, and should be well balanced. People always hope that the ink printed on the paper will dry quickly, but it will not dry in the ink fountain. About 80% of the ink on the market has a drying time of 16-30 hours. If the drying time is too short, it is easy to cause the machine You can choose non-crusting ink when printing general coated paper and long version. It is an ink with a longer drying time of the conjunctiva. It is not forever. Non-crust ink is not suitable for printing short work with high-grade poorly coated paper (about 12 hours for bound prints) or printing with cardboard. This type of printing is recommended to use a fast drying ink.
4. The gloss of the ink. The gloss of the ink is the ratio of the amount of light reflected by the ink print under a specific light source and at a certain angle to the amount of regular reflection of the standard plate, expressed as a percentage. The lightness of the prints gives a straight sensory impression.
Generally speaking, the higher the gloss, the better the printing effect. Although the gloss of the printed matter has a certain relationship with the potions used in the printed matter and the absorbency of the paper, it is mainly determined by the ink. This form of ink is mainly determined by the binders and pigments. The binders and pigments in the ink must have good leveling and good printability. The resin itself should have a high gloss. The gloss of such ink printed on paper is high. Ink with good gloss tends to be a little slower after initial drying. When overprinting on a single machine, the ink with high gloss must control the overprint time, otherwise it will be easy to crystallize the printed matter.
5. Ink fineness. The fineness of the ink indicates the size of the pigment and filler particles in the ink and the uniformity of the distribution in the binder. Ink fineness and pigment
The properties of (solid material) have a direct relationship with the particle size. The softness of the particles and the good wettability of the binder make it easier to grind, and the better the fineness, the more stable the ink properties. When the fineness of the ink is poor, the printing rate is likely to be low during printing, such as low pattern or piled ink, empty dots, expansion and unclean dots, etc. The ink should be selected with good fineness, the finer the ink The thinner, the fuller and more powerful the dots, the stronger the tinting power at the same color content, but the production cost increases for the production plant.
6. Lightfastness of ink. Under the effect of sunlight, the color of the ink remains unchanged. You are the light resistance of the ink. In fact, there is no ink that is absolutely lightfast and does not change color. Under the influence of sunlight, the color of the ink printed matter changes to varying degrees, and the lightfastness of the ink is mainly determined by the lightfastness of the pigment in the ink. put forward. Printed with good lightfast ink, the printed product has bright color and can be stored for a long time. Prints that use poorly fastened inks tend to fade and change color.
Can't watch the village for a long time. For printing posters, slogans, advertisements and other long-term exposure to sunlight, inks with good light resistance should be selected.
The light resistance of the ink is measured by walking the ink on paper and drying it with a color exposure machine. According to the light fastness blue standard for measuring light fastness, it is eighth grade. The first grade is seriously discolored, and the surface lightfastness is the worst. Among the lithographic four-color inks, the blue ink should reach 7-8 grades, and the red and yellow inks should be between 3-5 grades. Ink with a low lightfastness level should be paid more attention to when color matching and diluting. In short, there are many varieties of inks, and their properties are also different.
The easiest way to judge the quality of lithographic ink is three high and one fast, high gloss, high density, high printability, fast drying speed, generally meet this standard ink is good ink. Of course, some prints also require good light resistance.
Knowing and mastering the basic common knowledge and technical indicators of ink is of great help to the correct selection of ink during printing. The ink must be properly selected during printing to ensure the quality of the printed matter.
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