Ink common sense and skills
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The ink is a colorant for printing. It is a fluid substance which is uniformly dispersed in a binder by pigment particles and has a certain viscosity.
1. Ink composition
The ink is composed of a pigment, a binder, a filler, an additive, and the like.
(1) Pigments
The pigment plays a role in color development in the ink, which in turn has a direct effect on some properties of the ink.
Pigments are color, black or white, highly dispersible powders that are insoluble in water and organic solvents. They are classified into organic pigments and inorganic pigments depending on their source and chemical composition.
1 Inorganic pigments are oxides of non-ferrous metals, or some metal-insoluble metal salts. Inorganic pigments are further classified into natural inorganic pigments and artificial inorganic pigments, and natural inorganic pigments are mineral pigments.
2 organic pigments are colored organic compounds, which are also divided into two major categories, natural and synthetic. Nowadays, synthetic organic pigments are commonly used, and there are many varieties of organic pigments, and the colors are relatively complete, and the performance is superior to inorganic pigments.
Dyes are organic compounds which are soluble in water and sometimes dissolved in organic solvents. Insoluble dyes can be prepared from certain dyes, called lake pigments, for the manufacture of printing inks.
The pigments used in printing inks are quite demanding, especially the color, dispersion, light resistance, transparency, etc., and the color pigments are required to be close to the spectral color, the saturation should be as large as possible, and the magenta, cyan, and yellow used in the three primary inks. The transparency of the pigment must be high. All the pigments must not only be water-resistant, but also be quickly and evenly combined with the binder. The oil absorption capacity of the pigment should not be too large, and the pigment preferably has properties such as alkali resistance, acid resistance, alcohol resistance and resistance.
(2) Connecting material
The binder is a main component of the ink, functions as a dispersing pigment, imparts appropriate adhesion, fluidity, and transfer properties to the ink, and acts to fix the pigment to the surface of the print by film formation after printing. The connecting material is commonly known as varnish.
The binder can be made of various materials, such as various dry vegetable oils, most of which can be used to make ink binders, mineral oils can also be used as binders, solvents and water, and various synthetic resins can be used to make the binder. Connection material.
The rheology, viscosity, neutrality, acid value, color, water resistance and printing performance of the ink mainly depend on the binder, the same pigment, different binders can be used to make different types of ink; and the same binder Use different pigments. The ink is still made of the same type, because it can not change the basic performance of the ink, so the quality of the ink is good, except for the pigment, mainly depends on the binder.
(3) Filler
The filler is a white, transparent, translucent or unsuitable powdered material. Mainly filling, filling the pigment part, appropriate use of some fillers, can reduce the amount of pigment, reduce the cost, but also adjust the properties of the ink, such as thick, fluid, etc., but also improve the flexibility of formula design.
(4) Additives
Additives are materials that are added in the manufacture of inks and in the use of printing to improve the performance of the ink itself. Ink formulated according to the basic composition, in some characteristics still can not meet the requirements, or due to changes in conditions, but can not meet the requirements of printing use, must be added with a small amount of auxiliary materials.
There are many additives, such as: desiccant, anti-drying agent, thinner, detackifier, plasticizer and so on.
2. Types of ink
There are many types of inks that can be classified in various ways:
(1) According to the printing method
1 According to the layout: ink for letterpress, lithographic, gravure, photogravure, screen printing, etc.;
2 According to the printing method: offset printing, direct printing and other inks.
(2) According to the substrate
According to the substrate, there are inks for paper, metal, plastic, cloth, etc.
(3) in dry form
1 according to the drying mechanism: osmosis drying type, oxidative polymerization type, volatile drying type, light curing type, heat curing type, cooling and curing type ink;
2 According to the drying method, there are: natural drying type, hot air drying type, infrared drying type, ultraviolet drying type, cooling drying type and the like.
(4) According to ink characteristics
1 by color: yellow, red, blue, white, black, gold, silver, gold powder, fluorescent color, pearlescent color, etc.;
2 according to the function: magnetic ink, anti-counterfeiting ink, edible ink, foaming ink, aromatic ink, recording ink, etc.;
3 According to the resistance, there are inks such as light resistance, heat resistance, solvent resistance, abrasion resistance, alcohol resistance, and chemical resistance.
(5) According to ink composition
1 according to the raw materials are: dry oil type, resin oil type, organic solvent type, water-based type, paraffin type, ethylene glycol type and other inks;
2 according to the form: gelatinous, liquid, powdered ink.
(6) by purpose
According to the purpose: news ink, book ink, packaging ink, building materials ink, trademark ink and so on.
3. Ink characteristics
The ink is a paste with a color and a certain degree of fluidity that can be printed and dried on the substrate. Therefore, color, rheological properties and drying properties are the three most important features of the ink.
(1) Viscosity
Viscosity is a property that prevents fluid flow and is a measure of the interaction of fluid molecules to produce the ability to block relative movement between molecules, ie, the resistance of fluid flow.
The viscosity of the ink and the transfer of the ink during the printing process are related to 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 be uniform, and the phenomenon of pulling the paper occurs, causing the surface to smear; the viscosity is too small, the ink Easy to emulsify, dirty, affecting product quality.
The viscosity of the ink is related to the viscosity of the binder, the amount of pigment and additives, the particle size of the pigment and the additive, and the dispersion of the pigment and the additive in the binder.
The requirement for the viscosity of the ink during the printing process is related to the printing speed of the printing press, the softness of the paper structure, and the change in the ambient temperature.
(2) Yield value
The minimum shear stress required to initiate the flow of liquid is called the yield value.
Ink with excessive yield value, poor flowability, not easy to open, ink with too small yield value, printed dots are easy to faint, not clear.
The yield value is related to the structure of the ink, and the magnitude of the yield has a direct influence on the fluidity of the ink. It is an important indicator for the quality of offset and gravure inks.
(3) Thixotropy
The ink is stirred by external force, and it will become thicker and thicker with the effect of stirring. After the stillness, the ink returns to the original consistency, which is called thixotropy.
Since the ink is thixotropic, when the ink is mechanically rotated on the ink roller, its fluidity increases, and its ductility increases, making the ink easy to transfer. When the ink is transferred to the paper by printing, the external force is lost, and the ink is thickened and thickened without overflowing to the surroundings, forming a good imprint. However, if the thixotropy of the ink is too large, the ink in the ink fountain is not easily rotated, which affects the ink transfer of the ink roller.
(4) Liquidity
The performance of the ink flowing like a liquid under its own gravity is called the fluidity of the ink.
The fluidity of the ink is related to whether the ink can be poured out of the container, transported from the storage tank to the ink fountain of the printing machine, smoothly transferred from the ink fountain, distributed well on the printing machine, transferred to the layout, and transferred to the printing substrate. On the object, it also affects the effect of printing.
The fluidity of the ink is determined by the viscosity, yield and thixotropy of the ink and is also closely related to temperature.
(5) Ink length
The procedure in which the ink is stretched into a filament without breaking is called the length of the ink.
The short ink of ink is good printing ink in offset printing and letterpress printing net, because it will cause flying ink phenomenon. At the same time, the ink layer of the printing product is even and thick, and the length of ink is often used to measure the performance of ink. Bad.
The length of the ink is related to the thixotropy, yield value and plastic viscosity of the ink.
(6) Drying of the ink
After the ink adheres to the print to form a print, it must be changed from a liquid or paste to a solid film. This change process is usually called drying of the ink.
Drying of the ink is accomplished by changing the binder in the ink from liquid or paste to solid. The binders used in various inks and their ratios are different. Therefore, the drying process for forming the ink from the difference in the binder is also different. After the ink is transferred from the printing plate to the surface of the printing product, a part of the connecting material in the ink is infiltrated, and at the same time, the solvent in the connecting material starts to volatilize, and some of the connecting materials generate a chemical reaction and a physical reaction, thereby causing the printing of the surface of the printing substrate. The ink layer gradually increases its viscosity and hardness, eventually forming a solid film layer.
Generally, the letterpress printing ink is mainly osmotic drying, the lithographic offset printing ink is mainly dried by oxidized conjunctiva, and the gravure printing ink is a binder with a strong solvent, so it is mainly volatile and dry.
Various ink characteristics
(1) Letterpress ink
The letterpress inks include: printed printing ink, letterpress rotary book ink, printed color ink, printed plastic ink, rubber relief plastic ink (ie, flexographic plastic ink), letterpress water ink, letterpress wheel transfer ink.
The printed inks are mainly used for printing books and magazines, and the book printing inks. When printing books on the platform machine, the ink is a permeable dry ink with a certain degree of blackness. The viscosity is smaller and the yield value is lower to accommodate the uniform roller. Printing press. Book papers have a rougher structure, but they have better oil absorption properties, so they use osmotic drying inks.
Printed color inks are often used for copperplate color printing, and some are copperplate inks. When printing, it is carried out with a flat flat type smaller printing machine, so the pressure is relatively large and flat, and the printing dot is mainly used. Therefore, the transfer performance of the ink is required to be good, the ink film layer in the dot should be uniform and uniform, and the fixing of the ink should be Fast, the ink film layer is not spread after imprinting, so that the dots on the printed product have a good contrast contrast, and the imprint is uniform and full.
Such inks should have a relatively low yield value, have a certain fluidity and stick to the ink, and once the ink is embossed onto the paper, it should be able to dry and dry immediately. Therefore, the binder of the ink is mainly etched and dried by the oxidized conjunct film and the solvent portion, so that not only the drying is fast, but also the transfer property of the ink is good.
The letterpress wheel transfer newspaper ink is also called news rotary ink. It should adapt to high speed printing. Therefore, the news rotary ink should have good flow performance and low viscosity. Generally speaking, the faster the printing speed, the better the fluidity of the ink is required. The lower it is.
News Rotary Ink is a typical permeation-drying ink that is almost completely dry depending on the absorbent binder of the paper fibers.
The letterpress rotary book ink is suitable for use in book rotation machines between the platform machine and the news machine.
In order to adapt to printing high-quality paper at high speed, the permeation-drying type or the oxidized conjunctiva drying type can not meet the requirements, and it is easy to produce poor dryness, poor adhesion, chalking, smudging, etc. To overcome these drawbacks, a thermosetting ink is used. That is, in printing, after baking at a high temperature of 200 to 250 ° C, the solution in the ink is allowed to escape, so that the ink is fixed on the printed matter.
(2) lithographic ink
The lithographic inks include various offset inks, lithographic iron inks, lithographic photosensitive iron inks, stencil inks, offset thermosetting inks, and the like.
One of the characteristics of offset printing ink is that the coloring power of the ink is high. Because the offset printing is indirect printing, the ink footprint printed on the printed matter is very thin, and only a strong coloring power can meet the requirements, because the printing speed is getting faster and faster. The ink should have good flow properties as well as good drying properties. According to the characteristics of offset printing, the ink should have good water resistance, so the water resistance of the pigment in the ink is very high. Most of the lake pigments are soluble in water and can cause turbidity. If the binder is hydrophilically emulsified, the ink will be poorly transferred and the dryness will be lowered. The resin type binder is more resistant to water than the oil type binder.
(3) Gravure ink
Gravure inks include various photogravure inks, engraved gravure inks, gravure plastic film inks, and the like.
Photogravure ink is a typical volatile dry ink. Its viscosity is the lowest of all kinds of inks. It has good fluidity and low surface tension. It is easy to fill into the concave hole of the printing plate. The ink adhesion is strong and the paper pressure is guaranteed. After printing, the ink can be transferred from the recessed hole to the surface of the printing brush to the utmost extent, and the ink is dried very quickly on the printed matter, and thoroughly.
The characteristics of the engraved gravure ink are thick and non-sticky, loose and short, and have appropriate thixotropic properties. The ink should be easy to fill the inking hole of the intaglio plate, and it is easy to wipe off the ink on the blank part of the plane when printing. Part of the ink should also be easily transferred to the printed matter. After the ink is printed on the printed product, the dotted lines of the graphic should not be spread out and should be dried quickly.
The pigment expression of engraved gravure inks is mainly ink, and transparent pigments cannot be used. Engraved intaglios are mostly used for the printing of valuable securities, so the various properties of the pigments are required to be high, such as light resistance, water resistance, heat resistance and oil resistance. In order to prevent counterfeiting, some special additives are often added to the ink.
(4) stencil ink
The stencil ink includes screen printing ink, screen plastic ink, oil type writing ink, water type writing ink and the like.
Because the imprint of the silk screen is thicker by the ink applied by the squeegee and the pressure is applied, the flow characteristics of the screen printing ink should be thick, loose, and non-sticky, and the pigment content in the ink can be correspondingly less, so that the ink can be smoothly. Through the wire mesh.
The oxidative drying ink in the screen printing ink is printed on the printed matter, the faster the drying, the better, and the volatile drying ink is heated to facilitate the evaporation of the solvent.
The printing ink is generally not too fluid, and the viscosity is relatively small, mainly relying on osmosis drying.
(5) Special function ink
The microcapsule ink, which has a special function, is sealed in a capsule, and is made into an ink by using a suitable connecting material, and is printed by a method that does not damage the capsule, so that the printed matter has special properties. For example, liquid crystal ink, the color of the liquid crystal is changed by the difference of temperature and pressure, and is used to represent the number of the thermometer and the calculator; the fragrance ink is made into a capsule by using a fragrance, the capsule is destroyed to emit a fragrance; and the foaming ink is used as a foaming agent, After printing, it is heated and foamed for printing printed matter such as Braille.
Gold and silver ink, using metal powder instead of pigment. In the past, gold powder and silver powder were attached to the sheet metal and silver ink. Gold and silver printing is carried out, and the varnish is mixed with gold powder or silver powder before printing, and there are also mixed inks. The brass powder for the gold powder and the aluminum powder for the silver powder are all pulverized in a sheet form to give a metallic luster.
Fluorescent inks are inks that use fluorescent pigments, which bring vivid and intense color effects. They are often used in eye-catching prints such as advertising, packaging materials, advertisements, and exhibits. Fluorescent pigments dissolve fluorescent dyes in synthesis. In the resin, the particles are coarse and the light resistance is also weak, and after being irradiated by the ultraviolet lamp, a more brilliant effect can be obtained.
Magnetic ink, an ink made of magnetic iron oxide powder, used for magnetic ink text reading, controlling the magnetic properties of magnetic powder, reading from magnetic beams emitted by special literature and fonts printed, mainly used for printing credit cards Tape on the film.
Safety ink (anti-counterfeiting ink) is an ink for printing various securities. It must have various excellent light, heat, water and oil resistance properties. Gravure ink is one. In order to prevent counterfeiting and tampering, it is necessary to use a compound which can see a special reaction, and a safety ink which is used as an ink to disappear, discolor, discolor, fade or color.
The conductive ink is an ink made of gold, silver, copper or conductive carbon black, and the dried ink layer has electrical conductivity and is used for printing on printed circuits, electrodes, and the like. Gold powder, silver powder and copper powder produce their own electrical conductivity, but the price of gold and silver is too high, and copper is easily oxidized. Carbon black is prone to difference due to different properties of raw materials. Graphite crystals have the best conductivity and are currently used. One.
The ink is duplicated, the ink is overwritten by the voucher, and the ink is printed by hot melt melting. Carbonless copying is colorless due to colorless coloring. It is not necessary to use a desensitizing ink in the rewriting portion, and the contact between the rewriting is reduced to lose the rewriting effect, and a chemical functional material that prevents color formation is used.
There are many other functional inks, such as monitoring inks that change color under the action of gas, temperature indicating inks that change color due to temperature changes, and color-developing inks that change from colorless to colored under the action of light. Edible ink printed on food, fired ink printed on the friction part of the matchbox, and the like.