ink
Ink is a kind of fluid substance that is uniformly dispersed in the binder by pigment particles, fillers, additives, etc., and has a certain viscosity.
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1, the composition of the ink
The pigment is a color, black or white highly disperse powder material that is insoluble in water and organic solvents and plays a role of color in the ink. According to the source and chemical composition of pigment components, organic pigments and inorganic pigments can be divided into two categories: inorganic pigments are composed of non-ferrous metal oxides or some metal-insoluble metal salts, and inorganic pigments can be further divided into natural inorganic pigments (minerals). Pigments) and artificial inorganic pigments; organic pigments refer to colored organic compounds, which can also be divided into natural and synthetic categories according to their sources. Nowadays, organic inks for printing are basically synthetic organic pigments with complete colors and superior performance to inorganic pigments.
The requirements for ink pigments during printing are high, especially the color purity, dispersion, lightfastness, transparency, and the like. Normally, the hue of the pigment of the color ink is required to be close to the spectral color, the saturation is as large as possible, and the pigment transparency of the three primary color inks (cyan, magenta, and yellow) must be high, otherwise the quality of the printed matter will be greatly affected. Regardless of the kind of pigment, it must have good water resistance, can be quickly and uniformly combined with the binder, and has good acid and alkali resistance, alcohol resistance, heat resistance and other properties.
The binder is a chemical substance that acts as a dispersing pigment, imparts proper viscosity, flowability and transferability to the ink, and fixes the pigment on the surface of the print by filming after printing, commonly known as a varnish. The binder can be made using various materials such as dried vegetable oils, mineral oils, solvents and water, and various synthetic resins. The flowability, viscosity, neutral acid value, shade of color, water resistance, and properties of printed materials during the use of the ink are all determined by the binder. The same pigment can use different binders to make different types of ink; the same kind. Because of the use of different pigments, the connecting material is still made of the same type of ink, because the connecting material does not have to change the fundamental performance of the ink, so the quality of the ink is not only related to the pigment itself, but also depends on the connection. material.
The filler is a white transparent, translucent or opaque powdery substance that acts as a filling. Appropriate use of some pigment fillers, can reduce the amount of pigment to reduce costs, but also can adjust the ink dilute, fluidity, but also can improve the flexibility of the ink formulation design.
Additives are materials that are added to improve the ink's own performance during ink manufacturing or printing. When the ink according to the basic recipe still cannot meet the requirements for use in certain characteristics, or when the requirements for printing use cannot be satisfied due to changes in conditions, a small amount of additional material must be added to solve the problem.
2, the type of ink
According to different methods, inks can also be divided into different types. Commonly used are flexographic printing inks, lithographic printing inks, gravure printing inks, screen stencil printing inks, special functional inks, and the like.
Toppan printing inks can be divided into lead-printing inks, lead-printing inks (copper inks), lead-printing plastic inks, rubber letterpress plastic inks (flexible plastic inks), letterpress inks, letterpress printing inks, etc. according to different characteristics. . This type of ink is basically a penetrating dry type ink. In the printing process, it is necessary to pay attention to the occurrence of ill-adherence such as poor adhesion, powdering, and contamination.
Lithographic printing inks include various offset inks, lithographic iron inks, lithographic photosensitive inks, offset thermosetting inks, and the like. Lithographic printing inks require high color strength and water resistance, and have good flowability and drying speed.
Intaglio printing inks include various gravure inks, engraved gravure inks, gravure plastic film inks, and the like.
Silk screen printing inks include screen printing inks, screen plastic inks, oil-type inks, water-type inks, and the like.
In addition to the above-mentioned several commonly used inks, there is also an ink that can play a special effect, such as micro-particle ink, gold and silver ink, fluorescent ink, magnetic ink, security ink, conductive ink, carbon ink, monitoring ink, Temperature indication ink, color ink, edible ink, etc.
3, the characteristics of the ink
Ink is a paste adhesive with a certain degree of fluidity. Viscosity, yield value, thixotropy, fluidity, and drying all determine the performance of the ink.
Viscosity: A property that prevents the flow of fluids. It is a measure of the ability of fluids to interact with each other and create a barrier to their relative mobility between molecules, that is, the resistance to fluid flow. The viscosity of the ink is related to the transfer of the ink in the printing process, the nature and structure of the paper, the viscosity of the ink is too large, the transfer of the ink during the printing process is not easy to uniform, and the phenomenon of pulling on the paper occurs, making the printing on the printing surface; the viscosity is too small. Ink is easy to emulsify, dirty, affect the quality of printed matter. The requirements for the viscosity of the ink in the printing process depend on factors such as the printing speed of the printing press, the degree of public software on the paper structure, and changes in temperature and humidity in the surrounding environment.
Yield value: refers to the minimum movement stress required to start fluid flow. If the ink yield value is too large, the fluidity will deteriorate and it will not be easy to open. If the yield value is too small, the dots at the time of printing will easily start to halo and cause the printed matter to be unclear. The size of the yield value is related to the structure of the ink and has a direct influence on the flow of the ink. It is an important indicator for the quality of offset and gravure inks.
Thixotropy: It refers to the phenomenon that the ink is stirred by the action of stirring when the external force is stirred, and the stirring operation stops and the complex recovers to its original consistency. Due to the thixotropy of the ink, after the ink is rotated by the printing press on the ink roller, the fluidity is increased, the ductility is increased, and the ink is easily transferred; when the ink is transferred to the paper by printing, the external force is lost. The ink thickens from the thin and does not spill around, forming a good print. If the thixotropy of the ink is too large, the ink in the ink fountain is not easily rotated, which affects the ink transfer function of the ink roller.
Fluidity: refers to the ink under its own gravity, will flow like a liquid, by the ink viscosity, yield value and thixotropy decided, but also with the temperature is also closely linked. The fluidity of the ink is related to whether the ink can be poured from the container, transferred from the ink tank to the ink fountain of the printing press, smoothly transferred from the ink fountain, well distributed on the printing press, transferred to the printing plate, and transferred. On the substrate, it also affects the printing effect.
The length of the ink: refers to the extent to which the ink is initially drawn into a filament without breaking. The length of the ink is related to the thixotropy, yield value, and plastic viscosity of the ink. The ink with short silk ink is an ink with excellent printing performance in offset printing and letterpress printing. It will not cause ink flying in the printing process. At the same time, the ink layer on the print is also uniform and thick. The length of ink is a common method when measuring ink performance.
4. Drying of ink: Drying of ink refers to the process of the ink changing from liquid or pasty to solid after the ink is attached to the printed matter on the printed matter. This process is caused by the side material in the ink from the liquid or paste. It is completed as a solid. Because the binder used in various inks and their formulation ratios are not the same, the drying process of the ink is also not the same. After the ink is transferred from the printing plate to the surface of the printing material, part of the connecting material in the ink penetrates, the solvent in the connecting material begins to volatilize, and some of the connecting materials begin to produce a chemical reaction or a physical reaction, so that the ink on the surface of the substrate is imprinted The layer gradually increases its viscosity and hardness, eventually forming a solid film layer. In general, letterpress printing inks are mainly made of permeability drying, lithographic offset printing inks are mainly dried by oxidized conjunctiva, and gravure printing inks are mainly volatile, because they use highly volatile solution as the connecting material.