How to correctly evaluate and select inks in offset printing
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People's aesthetics are improving, and the requirements for printed matter are also increasing. To get a beautiful print, hardware pen cutting has the following requirements (also called the seven elements of lithography): 1. High-quality printing press. 2. Excellent paper; 3. High quality ink; 4. Exquisite manuscript; 5. Fine plate; 6. Environmental conditions that meet the requirements; 7. Suitable dampening solution. The first impression of printed matter is color, which is expressed by ink, so we should understand the classification, composition, technical indicators and printing relationship of ink, which is crucial for how to correctly select ink in lithography.
First, the classification of ink
Printing is a professional technology with a high level of technology and extensive artistic expression. Modern printing theory has formed an independent science. This process of printing is mainly a technical process of transferring 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 paper or other objects. The inks used are classified into four types according to the printing type: 1. lithographic printing ink; 2. relief printing ink: 3, gravure printing ink; 4. filtered printing ink. Among them, lithography accounts for about 50% of the total printing, and the selection of inks should be given more attention.
Second, the classification of lithographic inks
There are many varieties of lithographic inks.
Third, the basic composition of lithographic ink
The ink is a uniform composition composed of a color pigment (dye, etc.), a binder, a filler, and an additive. It can be printed, dried on a printed object, and has a color and a certain fluidity. Slurry adhesive.
A pigment is a solid powdery substance that does not dissolve in dry water, is insoluble in oil or a binder, and has a certain color. It is not only the main solid component of the ink, but also the visible body part printed on the object. To a large extent, it determines the color, thickness, light resistance and other properties of the ink.
Link material: The binder is a kind of adhesive fluid. As the name suggests, it acts as a link. In the ink, a substance such as a powdery pigment is mixed and kneaded, and after being ground and dispersed, a paste-like adherend having a certain fluidity and viscosity is formed. The binder is the main fluid component of the ink, which determines the fluidity, viscosity, dryness, and printability of the ink. The binder is the heart of the ink.
The filler is a white, transparent, translucent or opaque powdery substance that is also a solid component of the ink. It mainly uses filling materials to properly fill the filler. In addition to reducing the amount of pigment and reducing the cost, it can also adjust the properties of the ink, such as thick, fluidity and the like.
Additives: Additives are additional parts of the ink other than the main components. It can also be used as an additive for the finished ink product, as a printing aid to change or improve certain properties of the ink such as dryness, abrasion resistance and the like.
Fourth, the technical indicators of ink
At present, the inspection methods of ink finished products are still not perfect, and there are still many unscientific and impractical. The so-called unscientific, that is to say, there are many things to be judged and evaluated by experience and by senses. The so-called impracticality means that the result of the measurement does not fully represent the needs of the actual application. In addition, some projects have a large error in the measurement results. Therefore, there are many inspection methods and data that can only be used as relative comparisons, that is, the inspection of inks is relative. Nevertheless, the technical indicators of ink are instructive for printing. Here are a few technical indicators that are closely related to printing.
1. The concentration of the ink. 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 the amount of ink is also used, and 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 of the ink, the influence of the ink concentration on the printing quality is particularly remarkable, because printing is performed when printing with a high concentration ink. The ink layer is thin and fast, which can reduce the stickiness of the printed products, and the color balance of each color can be easily adjusted. There is a small experience in the printing industry. In printing, the ink is too big and the worse the ink is printed. The ink is small and the better the printing. This experience is actually based on the concept of concentration. The ink industry judges the ink concentration by detecting the tinting strength. the size of. The method comprises the following steps: diluting the standard ink with white ink, and diluting the sample ink with white ink to change the amount of white ink of the sample so that the color of the two scraped on the scraping paper is uniform. The ratio of the amount of white ink in the sample to the amount of white ink used in the standard is expressed as a percentage.
Where: S = percentage of tinting strength (100% with standard ink) A = ink amount of white ink used for standard dilution B = ink amount of white ink used for sample dilution
2. The viscosity of the ink. The ink viscous meter is manufactured following the principle of a printing press. The viscosity of the ink is tested by an ink viscous meter. The magnitude of the viscosity of the ink refers to the amount of force separating the ink film between the two rollers of the viscous meter. The viscosity of the ink has a large 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 the printing, which affects the transferability of the ink in the printing, the thickness of the ink layer of the printed product, and the penetration. The amount and the size of the gloss. Too much or too little viscosity of the ink can affect the quality of the print. When the viscosity of the ink is too large, it is likely to cause malfunctions such as poor ink transfer, poor transferability, poor paper pull, and poor overprintability. If the viscosity is too small, it is easy to cause excessive ink transfer, flying ink, dot enlargement, emulsification and floating of the ink. At a certain temperature, the viscosity of the ink should not be too large when the printing speed is fast, and vice versa. In addition, the relative viscosity of each color ink is selected according to the printing order. Under normal conditions, there is no need to adjust the viscosity of the ink. If it needs to be adjusted, it can be adjusted according to its viscosity. Additives for consistency. Generally, when the viscosity is large and the consistency is suitable, the viscosity-reducing and non-throwning additives can be used for adjustment. Generally, when the viscosity is large and the consistency is large, an auxiliary agent which reduces viscosity and thickens can be used.
3. Dryness of the ink. The drying process of the lithographic ink on the paper is a process in which the ink changes from a relatively fluid non-polar gel to a fixed state. The lithographic ink dry ink industry is divided into two indicators; one is the fixing speed, which means that the ink changes from a natural fluid state to a semi-solid state, that is, when the printed product is superimposed to a certain height, it is not sticky, and the printing is called initial drying. The initial drying of the ink is determined by the resin structure chosen for the design. The initial drying time is short but not completely dry. The second is that the oxidized conjunctiva is dry, that is, the drying is said to be dry, the drying time is longer, and the drying time is more than 8 hours, which is completely dry. The drying of the ink is determined by the type and amount of the desiccant. It can be adjusted within a certain range. Currently, the lithographic inks are all resin-type, and the fixing speed is fast. In theory, the quicker the better, the better. However, if the initial drying is too fast, it will affect the gloss of the printed matter. The height of the gloss and the speed of the fixing are generally contradictory and should be balanced. People always hope that the ink will be printed on the paper quickly, but it will not dry in the ink fountain. About 80% of the ink conjunctiva drying time in the market is between 16-30 hours. If the conjunctiva drying time is too short, it is easy to cause in the machine. On the crust-holding roller, you can choose non-skinning ink when printing general coated paper and long version, especially the ink with longer drying time of conjunctiva, not forever peeling. Non-skinning inks are not suitable for printing short runs (bonding prints for about 12 hours) or paper jams with high-permeability coated paper, which is recommended to use faster-drying inks.
4. The gloss of the ink. The gloss of the ink is the ratio of the amount of light reflected by a particular source to a particular source of light and the amount of light reflected by the standard panel, expressed as a percentage. The brightness of the print gives a straight impression.
Generally, the higher the gloss, the better the printing effect. Although the gloss of the printed matter is related to the absorbency of the printed matter and the absorbency of the paper, it is mainly determined by the ink, and the form of the ink mainly depends on the binder and the pigment therein. The binder and pigment in the ink must have good leveling property, good printability, and high gloss of the resin itself. Such ink is printed on paper with high gloss. Glossy inks tend to be slightly slower at the beginning of the drying process. When printing on a single machine, the glossy ink must be controlled for the overprinting time, otherwise the crystallization of the printed matter may occur.
5. Fineness of the ink. The fineness of the ink indicates the pigment in the ink, the particle size of the filler, and the uniformity of distribution in the binder. Ink fineness and pigment
The nature of the (solid material) is directly related to the particle size. When the particles are soft and the wettability of the binder is good, it is easy to be finely ground, and the fineness of the ink property is more stable. When the fineness of the ink is poor, the printing plate is prone to low printing plate or pile of ink in the printing, the dot is empty, the expansion and the dot are not clean, and so on. The ink should be selected with fine fineness, and the fineness of the ink is more Fine, the net is more full and powerful, the coloring power is strong at the same color content, but the production cost is increased for the production plant.
6. The light resistance of the ink. Under the action of sunlight, the color of the ink remains unchanged. You are the lightfastness of the ink. In fact, inks that are absolutely resistant to light and invariant color are not available. Under the action of sunlight, the color of ink prints has different degrees of change, and the light resistance of ink is mainly determined by the light resistance of the pigment in the ink. If you have special requirements on the light resistance of printed matter, you should give it to the ink production unit in advance. put forward. It is printed with light-resistant ink, and its printed color is bright and can be stored for a long time. Ink prints that are resistant to light are prone to fading and discoloration.
Can not be a long-term village. Printed posters, slogans, advertisements, etc., which are exposed to sunlight for a long time, should choose inks with good light resistance.
The light resistance of the ink was determined by walking the ink on paper and drying it with a color exposure machine. Determination of light resistance according to the light fastness blue standard is eight, the first level of fading is serious, the surface light resistance is the worst, eight grades are not easy to fade, indicating the best light resistance. The blue ink of the lithographic four-color ink should reach 7-8, and the red and yellow ink should be between 3-5. Ink with low light resistance should pay more attention when color matching and dilution. In short, the variety of inks varies and their properties vary.
The easiest way to judge whether a lithographic ink is good or bad is to have three highs and one fast, high light, high concentration, high printability, fast drying speed, and generally conform to this standard ink as a good ink. Of course, some prints also require good light resistance.
Understand and master the basic knowledge and technical indicators of ink, which is of great help to the correct selection of ink during printing. When printing, the ink is selected and the quality of the printed matter can be guaranteed.