Magnetic ink printing, digital watermark (on)

Magnetic ink printing, referred to as magnetic printing, is an anti-counterfeit printing technology for special inks. The method of adding magnetic materials to ink is used for printing. Magnetic printing belongs to the category of magnetic recording technology, and the magnetic recording body is manufactured by magnetic printing so that it has the required special properties. Magnetic print is a unique media produced by the combination of recording technology and printing technology. Its characteristic is that data can be written and read on magnetic cards, and words, patterns and photos can be visually seen.
Magnetic printing basic technology

The magnetic prints are formed by applying a magnetic layer on a paper or plastic substrate, printing characters or patterns on other portions, and a printed layer for displaying visual information corresponding to the use conditions. The base of magnetic prints requires moderate toughness, uniform thickness, smooth surface, no stretching or curling when the temperature and humidity changes, good water and corrosion resistance, good printing and processing adaptability, and low price. Commonly used materials include offset paper, coated paper, resin-impregnated paper, polyvinyl chloride (PVC), polyethylene terephthalate (PET), and other plastic film bases and composite materials, with a thickness of 150-800 μm. The requirements for magnetic powders are high magnetic saturation, uniform particle size, good dispersion, stability, and long aging. Commonly used magnetic hematite, iron oxide attached to iron. Magnetic ink is composed of magnetic powder pigments, binders, desiccants, antioxidants, wetting agents and other additives. Carbon black is added to the black ink, and other color pigments are added to the color ink to obtain color.

Magnetic printing adopts screen printing or offset printing to obtain ribbon or pattern magnetic layer, which can form magnetic tape where necessary for the card, thereby reducing the cost. The content of magnetic pigment in magnetic ink, the magnetic property of color and the thickness of ink layer after printing Etc. will affect magnetic properties. After the magnetic prints are printed, transparent PVC films are laminated on both sides, pressed with a hot press, and cut to size according to the specified dimensions. In order to prevent counterfeiting and tampering, magnetic printing has become increasingly more secure and confidential. Therefore, special materials or technologies are used in magnetic materials, printing, and processing methods. Such as the use of special plate-making techniques and inks in printing, including printing with fluorescent inks, thermochromic inks, absorbing infrared inks, and also using ground grain printing, micro-printing, rainbow holography and other measures to prevent counterfeiting.

Magnetic ink development

Around the 1960s, with the development of electronic technology, magnetic inks were first used in banking and postal services. The use of magnetic ink was not used for anti-counterfeiting. It was mainly used for automatic processing of bank bills and automatic sorting of postal letters. Therefore, magnetic inks were only used to print letters and numbers to enable automatic identification and processing of printed parts. , namely Magnetic Ink Character Recognition (MICR). Since the 1980s, magnetic inks are no longer limited to black or limited color ranges, but have been extended to four-color magnetic inks.

At present, the annual consumption of magnetic oil black in the world has reached as many as several thousand tons. It is mainly used for the printing of symbols and letters on cheques. The printing method is generally used for plain printing and embossing; there is also printing on credit cards. Tapes.

Another category that is basically similar to the MICR technology is Optical Character Recognition (OCR). This technique was invented around 1952. The device is simply called a reader. Also known as an optical scanner, it is a device that uses optical principles to recognize alphabetic characters. Its output system can generate magnetism or be directly input into a computer for data processing.

The ink used on this device is called OCR ink (also called optical ink). There are generally two types: non-readable and readable, the latter mainly referring to black inks, and the former to various colored inks. OCR ink can be designed according to the general type of ink, such as plain printing, embossing, gravure printing and silk printing. The content of pigments in non-readable inks is generally between 1% and 5%, and some can be used around 20%. At present, MICR has quickly been replaced by OCR in terms of document classification, because OCR information is entered into the computer faster. MICR is mainly used in printing anti-counterfeiting and information records.

Substrate substrates used for magnetic printing include two major classes of polymer materials and paper. Polymer materials are mainly made of polyester, rigid PVC, nylon, etc., while paper is selected from some finest papers. After printing, coating or film processing is performed. This has both good printing adaptability and improved paper resistance. Grinding and other mechanical properties.

The basic structure of magnetic ink

The basic composition of the magnetic ink is the same as the general ink, that is, it is composed of a pigment, a binder, a filler and an auxiliary material.

Pigments The pigments used in magnetic inks are not ordinary pigments, but ferromagnetic materials, which have the ability to retain magnetic properties after magnetic treatment. The main components in the magnetic ink are magnetic pigments, and the best magnetic pigments are iron oxide black (Fe3O4) and iron oxide brown (Fe2O3). Most of these pigments are needle-shaped crystals smaller than 1 μm, and the size and shape of these particles make them extremely easy to align in the magnetic field, resulting in relatively high residual magnetism.

The ferromagnetic materials used for magnetic ink pigments mainly include magnetic elements such as iron (Fe), cobalt (Co), and nickel (Ni), alloys containing Fe-Mo and Fe-W ferromagnetic elements, and Mn-Al and Mn Alloys such as Ni-type crystal structures such as Bi. Most magnetic ink pigments are ferrite. Ferrite refers to an inorganic compound generally represented by XO-Fe2O3, wherein X is a divalent metal ion, and there are manganese-ferrite, iron-ferrite, copper-ferrite, etc. depending on the type of X. .

In the composition of iron oxide black, the content of ferrous oxide is generally between 18% and 26%, and the content of iron oxide is between 74% and 82%. Synthetic iron oxide black has excellent impermeability, chemical resistance (acid, antimony), anti-rotation, is almost non-toxic, and the dispersion is between good and excellent. The heat resistance is better. Only when the temperature exceeds 177°C, the iron oxide black will be oxidized to red iron oxide. The iron oxide black has better particle consistency, and after diluting it has a clean blue-gray hue. Iron oxide black is generally a reaction, and their particle shape is generally cubic or spherical.

Adhesives The fluidity, tackiness, dryness, and printability of inks are primarily dependent on the binder. The binder is part of the fluid in the ink. The magnetic ink binder is also the basis for the quality of the ink. The link material of the magnetic ink is similar to the link material of the general ink, and vegetable oil, animal oil, and mineral oil can be used, but more synthetic resin is used as the link material of the magnetic ink.

The basic chemical composition of vegetable oils is a mixture of glycerides of fatty acids, or triglycerides. All oils and fats can be regarded as the product of the reaction of various fatty acids and glycerol. If the grease is thinly spread on the glass, after a certain period of time, the thin oil film will gradually become thicker and more elastic due to the absorption of oxygen from the air, and finally form a solid state. This is the drying process of grease. The shorter this process, the better the oil's dryness. The dryness of grease depends on the number and location of unsaturated double bonds in the grease structure. The iodine value can be used to determine the degree of unsaturation of the oil. In general, the iodine value is between 140-200 dry oil, between 100-140 semi-dry oil, and less than 100 dry oil. It can be seen that the more unsaturated double bonds, the better the dryness. In other words, the more unsaturated fatty acids, the better the dryness.

The use of synthetic resins in the ink industry is becoming more and more widespread, so various types of resin-based binders have become the main research content. The properties of the resin determine the properties of the binder. The main drawback of pure linseed vegetable oil type linking material is its relatively low molecular weight, so the produced ink is liable to cause emulsification in offset printing, which brings a series of ills, so that the printing cannot be performed smoothly, and the printing effect is not good. . The resin-based binder almost completely overcomes this defect, which greatly improves the quality of printing.

When the alkyd resin is used in a paste ink, a resin plasticizer may be considered. Because of its good adhesion and flexibility, the dryness and solidification time of the ink may also be adjusted. When an alkyd resin is used in an oil type ink, its reactivity with the pigment, the reactivity with the hard resin, and its film forming property should generally be considered. The wettability of the isocyanate alkyd resin is even more pronounced. When inks are formulated with linking materials made of alkyd resins and hard resins, attention should be paid to the pigments used. If the pigments absorb excessively low-molecular-weight binders, the balance of hard resins and alkyd resins in the binder should be taken into consideration. General paste inks use mostly long oil (65%) alkyds. Oily long oils are also generally more soluble, so they are also widely used in screen (mesh) inks. This type of resin has good color retention when used in iron inks, has good light, and has excellent adhesion.

In order to achieve fast drying and bright light, the content of the resin in the magnetic ink is higher and the solid speed is faster, so that more of the binder is left on the surface, and the binder is required to have better water resistance and lubricity of the pigment. Filler can also reduce the amount of pigment in the magnetic ink, reduce the cost, but also can adjust the properties of the ink, such as thick, fluidity, etc., also improves the flexibility of formula design, and the additive in the magnetic ink can be pigment The additional part of the linking material can also be used as an additional part of the finished ink, depending on the characteristics of the product.

The application of magnetic printing At present, magnetic printing has been applied in many fields, such as ticket, monthly pass, printing, bank passbook, ID cards, etc. Magnetic card can be used; price indicates that the magnetic film is used on the card; data registration form, check also Magnetic ink can be used for printing.

Japan uses magnetic inks to print yen, but where is the ink used, and how much is used is absolutely confidential. The relevant experts examined the Japanese yen banknote with a denomination of 10,000 yuan. The magnetic ink is in the upper right corner. The ink can detect as many as 14 elements, of which the magnetic metals are iron, cobalt, and nickel.

Paper magnetic field intensity is 12 gauss, which is an order of magnitude higher than geomagnetism.

Magnetic materials are easily available, and magnetic inks printed on the products are susceptible to external friction and other effects, resulting in magnetic loss or even disappear, affecting its anti-counterfeiting effect. According to reports, anti-counterfeiting inks that have been developed after being excited by electromagnetic waves have been successfully developed in China.