Common knowledge and skills of ink

Ink is a colorant for printing. It is a kind of fluid substance which has pigment particles dispersed uniformly in the binder and has a certain viscosity.

1. Composition of ink

The ink is composed of pigments, connecting materials, fillers, additional materials, etc.

(1) Pigment

Pigments play a role in color development in the ink, and it has a direct impact on some characteristics of the ink.

Pigments are colored, black, or white powders with high dispersibility that are insoluble in water and organic solvents. According to their sources and chemical composition, they are divided into two categories: organic pigments and inorganic pigments.

â‘ Inorganic pigments are oxides of non-ferrous metals, or some metal-insoluble metal salts. Inorganic pigments are divided into natural inorganic pigments and artificial inorganic pigments. Natural inorganic pigments are mineral pigments.

â‘¡Organic pigments are colored organic compounds, which are also divided into two categories: natural and synthetic. Synthetic organic pigments are now commonly used. There are many types of organic pigments, with a relatively complete range of colors and better performance than inorganic pigments.

Dyes are organic compounds, which are soluble in water and sometimes in organic solvents. Insoluble color precipitates, called lake pigments, can be prepared from certain dyes and used in the manufacture of printing inks.

The pigments used in printing inks are quite demanding, especially the color, dispersion, light fastness, transparency, etc. The color hue of the color pigments is required to be close to the spectral color, and the saturation should be as large as possible. The transparency of the pigment must be high. All 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. The pigment should preferably have alkali resistance, acid resistance, alcohol resistance and resistance.

(2) Connection material

The binder is the main component of the ink, which plays a role in dispersing the pigment, giving the ink proper adhesion, fluidity and transfer performance, and fixing the pigment on the surface of the printed product through film formation after printing. The connecting material is commonly known as ink-adjusting oil.

The connection material can be made of various materials, such as various dry vegetable oils, most of which can be used to make ink connection materials, mineral oil can also be made of connection materials, solvents and water, and various synthetic resins can be used to make Connection material.

The rheology, viscosity, neutrality, acid value, color, water resistance and printing performance of the ink mainly depend on the connecting material. The same pigment and different connecting materials can be used to make different types of ink; and the same connecting material , Use different pigments. The ink made is still the same type of ink, because it can not change the fundamental performance of the ink, so the quality of the ink, except for the pigment, mainly depends on the connecting material.

(3) Filler

The filler is a white, transparent, translucent or unclear powdery substance. It mainly plays a role of filling, filling the pigment part, and using some fillers appropriately, which can not only reduce the amount of pigment and cost, but also adjust the properties of the ink, such as thinness, fluidity, etc., and also increase the flexibility of formula design.

(4) Additional materials

Additional materials are some materials added to improve the performance of the ink itself in the manufacture of ink and in printing. When the ink formulated according to the basic composition still cannot meet the requirements in some characteristics, or due to changes in conditions, it can not meet the requirements for printing and use, a small amount of auxiliary materials must be added to solve.

There are many additional materials, such as: desiccant, anti-drying agent, diluent, debonding agent, plasticizer and so on.

2. Types of ink

There are many types of inks, which can be classified according to various methods:

(1) According to the printing method

â‘ According to the format, there are: ink for letterpress, lithography, gravure, photogravure, screen printing, etc .;

â‘¡According to the printing method: offset printing, direct printing and other inks.

(2) By printing material

According to the printing material, there are: ink for paper, metal, plastic, cloth, etc.

(3) According to dry form

â‘  According to the drying mechanism, there are: inks of permeation drying type, oxidative polymerization type, volatile drying type, light curing type, thermal curing type, cooling curing type, etc .;

â‘¡Drying methods include: natural drying type, hot air drying type, infrared drying type, ultraviolet drying type, cooling drying type and so on.

(4) According to the characteristics of ink

â‘ According to color: yellow, red, blue, white, black, gold, silver, gold powder, fluorescent color, pearlescent color, etc .;

â‘¡According to functions: magnetic ink, anti-counterfeiting ink, edible ink, foaming ink, aromatic ink, recording ink, etc .;

â‘¢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

â‘ According to raw materials: dry oil type, resin oil type, organic solvent type, water type, paraffin type, ethylene glycol type ink;

â‘¡According to the form, there are: colloid, liquid, powder ink.

(6) According to usage

According to usage: news ink, book ink, packaging ink, building material ink, trademark ink, etc.

3. Ink characteristics

Ink is a colored paste with a certain degree of fluidity, which can be printed and dried on the substrate. Therefore, color, rheological properties and drying properties are the three most important characteristics of ink.

(1) Viscosity

Viscosity is a property that prevents the flow of fluids. It is a measure of the fluid's molecular interaction that hinders the relative movement between molecules, that is, the resistance to fluid flow.

The viscosity of the ink is related to the transfer of the ink during the printing process, and is related to the nature and structure of the paper. The ink sticks too much, the ink transfer is not easy to be uniform during the printing process, and the paper is squeezed, which causes the layout to bloom; the viscosity is too small Easily emulsified, dirty, and affect product quality.

The viscosity of the ink is related to the viscosity of the connecting material, the amount of pigment and additional material, the particle size of the pigment and additional material, and the dispersion of the pigment and additional material in the connecting material.

The requirements for the viscosity of the ink during the printing process are related to the printing speed of the printing press, the degree of softness of the paper structure, and the changes in the ambient temperature.

(2) Yield value

The minimum shear stress required to start the flow of liquid is called the yield value.

Ink with too large a yield value has poor flow properties and is not easy to open. For ink with a too low yield value, printed dots are prone to halo and unclear.

The yield value is related to the structure of the ink, and the size of the yield value has a direct impact on the fluidity of the ink. It is an important test indicator for the quality of offset and gravure printing inks.

(3) Thixotropy

The ink is stirred by external force, it will change from thick to thin with the action of stirring, and after rest, the ink will return to the original consistency, called thixotropy.

Due to the thixotropy of the ink, 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 after printing, the effect of external force is lost, and the ink changes from thin to thick without overflowing to the surrounding, forming a good imprint. However, if the thixotropy of the ink is too large, the ink in the ink fountain is difficult to rotate, affecting the ink transfer of the ink roller.

(4) Liquidity

The performance of ink flowing like liquid under its own gravity is called the fluidity of ink.

The fluidity of the ink is related to whether the ink can be poured from the container, transported from the storage tank to the ink fountain of the printing machine, smoothly transferred from the ink fountain, well distributed on the printing machine, transferred to the layout, and transferred to the printing Physically, it also affects the printing effect.

The fluidity of the ink is determined by the viscosity, yield value and thixotropy of the ink, and is also closely related to the temperature.

(5) Ink filament length

The procedure that the ink is stretched into a filament without breaking, is called the length of the filament.

Ink with short ink filaments is an ink with good printing performance in offset printing and letterpress printing, because it will cause flying ink phenomenon. At the same time, the ink layer on the printed product is uniform and thick. Bad.

The filament length is related to the thixotropy, yield value and plastic viscosity of the ink.

(6) Drying of ink

After the ink adheres to the printed matter to form a print, it must change from a liquid or paste to a solid film. This change process is usually called the drying of the ink.

The drying of the ink is accomplished by the binder in the ink changing from liquid or paste to solid. The connecting materials used in various inks and their proportions are different. Therefore, the drying process of forming the ink by different connecting materials is also different. After the ink is transferred from the printing plate to the surface of the printed product, part of the connecting material in the ink is penetrated. The ink layer gradually increases its viscosity and hardness, eventually forming a solid film.

Generally, relief printing inks are mainly based on permeation drying, lithographic offset printing inks are mainly based on oxidative conjunctival drying, and gravure printing inks use strong solvents as binders.

Characteristics of various inks

(1) Letterpress ink

Relief inks include: printed books and periodicals inks, letterpress rotary books and periodicals inks, printed color inks, printed plastic inks, rubber letterpress plastic inks (that is, flexographic plastic inks), letterpress water-based inks, letterpress wheel transfer newspaper inks, etc.

Printed book inks are mainly used to print books and periodicals, but also plate inks. When printing books and periodicals on a platform machine, the ink is a penetrating dry ink with a certain degree of blackness, the viscosity is lower, and the yield value is lower, to adapt to the ink roller Printing machine. The paper structure of books and periodicals is rough, but they have good oil absorption performance, so they use permeable dry ink.

Printed color inks are often used for copperplate color printing, some are called copperplate inks. The printing is carried out by a small flat press, so the pressure is relatively large and flat, and it is mainly based on printing dots, so the transfer performance of the ink is required to be good, the ink film layer in the dots should be uniform, and the fixation of the ink should be Fast, the ink film layer is not spread after imprinting, so that the dots on the printed matter have good contrast contrast, and the imprint is consistent and full.

This type of ink should have a relatively low yield value, have a certain fluidity and viscoelasticity. Once the ink is stamped on the paper, it should be able to fix and dry immediately. Therefore, the connection material of the ink is mainly based on the permeation and drying of the oxidized conjunctiva and the solvent, which not only dries quickly, but also has good ink transferability.

Relief printing ink is also called news web printing ink. It needs to adapt to high-speed printing, so news web printing ink should have good flow performance and low viscosity. Generally speaking, the faster the printing speed, the better the fluidity and viscosity of the ink. Also lower.

News rotary ink is a typical penetration drying ink, which is almost completely dependent on the absorption and drying material of paper fiber to dry.

Topographic Rotating Book Ink is suitable for books and periodicals with printing speed between platform machine and news rotating machine.

In order to adapt to the printing of high-quality paper at high speeds, the permeation drying type or the oxidized conjunctiva drying type can no longer meet the requirements, and it is easy to produce poor dryness, poor adhesion, powdering, smudging, etc. To overcome these shortcomings, thermosetting inks are used. That is, during printing, after baking at a high temperature of 200 to 250 ° C, the solution in the ink escapes, so that the ink is fixed on the printed matter.

(2) Lithographic ink

Lithographic inks include various offset printing inks, lithographic iron printing inks, lithographic photosensitive iron printing inks, colographic printing inks, offset printing thermosetting inks, etc.

One of the characteristics of offset printing ink is that the color of the ink is higher in coloring. Because offset printing is indirect printing, the ink printed on the printed matter is very thin, and only a strong coloring power can meet the requirements. As the printing speed becomes faster and faster, The ink should have good flow properties and 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 lake pigments are soluble in water and will cause scumming. If the connecting material is hydrophilic emulsified, it will cause poor ink transfer and dryness. The resin type connecting material is more resistant to water than the oil type connecting material.

(3) Gravure ink

Gravure inks include various photogravure inks, engraved gravure inks, and gravure plastic film inks.

Photographic gravure ink is a typical volatile dry ink, the viscosity is the lowest of various inks, it has good fluidity and low surface tension, which is convenient for filling into the concave holes of the printing plate, the ink adhesion is strong, and the paper pressure After printing, the ink can be transferred from the concave hole to the surface of the printed product to the maximum extent. The ink dries extremely fast on the printed product and must be thoroughly.

The characteristics of engraved gravure ink are thick and non-sticky, both loose and short, with appropriate thixotropy, the ink should be able to easily fill the ink hole of the gravure, and it is easy to wipe off the blank part of the ink on 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 matter, the dots and lines of the graphic should not be spread out and become larger, but should be dried quickly.

The pigment expressive power of engraving gravure ink is mainly ink color, and transparent pigment cannot be used. Engraved gravure is more commonly used in the printing of marketable securities, so it has higher requirements for various properties of pigments, such as light resistance, water resistance, heat resistance, oil resistance, etc. 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 transcription ink, water-type transcription ink, etc.

Because the silk screen print is thickened with a rubber squeegee and pressed, the flow characteristics of the silk screen 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 smooth Through the wire mesh.

The oxidative drying ink in the screen printing ink, after printing on the printed matter, the faster the drying, the better, and the volatile drying ink uses heating process to facilitate the solvent volatilization.

Transcription inks are generally not very fluid and have relatively low viscosity, and mainly rely on penetration drying.

(5) Special function ink

Microcapsule inks, substances with special functions are sealed in capsules, made with appropriate connecting materials, and printed in a way that does not damage the capsules, so that the printed matter has special properties. For example, the liquid crystal ink uses the difference in temperature and pressure to change the color of the liquid crystal, which is used to represent the numbers of thermometers and calculators. The perfume ink is made of spices, and the capsules are broken to give out fragrance; the foaming ink uses a foaming agent. After printing, it is heated and foamed for printing Braille and other printed materials.

Gold and silver ink, use metal powder instead of pigment. Previously, gold powder and silver powder were attached to the gold and silver inks. For gold and silver printing, mix the ink and gold powder or silver powder just before printing. There are also mixed inks. Brass powder for gold powder and aluminum powder for silver powder are made of flakes, giving metallic luster.

Fluorescent inks are inks that use fluorescent pigments, which bring bright and strong color effects, so they are often used in eye-catching prints such as posters, packaging materials, advertisements, and exhibits. Fluorescent pigments dissolve fluorescent dyes in synthetic In the resin, the particles are coarse, and the light resistance is also weak. Once irradiated by the ultraviolet lamp, a more brilliant effect can be obtained.

Magnetic ink is an ink made of magnetic iron oxide powder. It is used to read the magnetic ink characters, control the magnetic properties of the magnetic powder, read from the magnetic beam emitted from the printed special literature and fonts, and is mainly used to print credit cards. Tape strip on the tablet.

Security ink (anti-counterfeit ink) is an ink for printing various securities. It must have various excellent light resistance, heat resistance, water resistance and oil resistance properties. Gravure ink is one type. In order to prevent forgery and tampering, it must be compounded with a compound that can see a special reaction, and it is also used as a safety ink for ink disappearance, discoloration, discoloration, discoloration, or color.

Conductive ink is an ink made of gold, silver, copper or conductive carbon black. The dried ink layer has conductivity and is used for printing of printed circuits and electrodes. Gold powder, silver powder, and copper powder produce their own conductive properties, but the price of gold and silver is too high, copper is easy to oxidize, carbon black is prone to differences due to different raw material properties, and graphite type crystals have the best conductivity and are currently more commonly used. One kind.

Reprint ink, subpoena reprint ink, use hot-melt type heating and melting to print. Carbonless copying is made by colorless coloration due to pressure. Unnecessary copying parts use desensitizing ink to reduce contact during copying and lose the copying effect. Chemical functional materials that prevent color formation are used.

There are many other functional inks, there are monitoring inks that change color under the action of gas, temperature indication inks that change color due to temperature changes, color-developing inks that change from colorless to colored under the action of light, and Edible ink printed on food, pyrotechnic ink printed on the friction part of matchbox, etc.

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