Discussion on the application of magnetic ink (on)
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First, Introduction
The principle of magnetic ink (Magnetic Ink) is derived from the magnetic recording technology. Since magnetic printing is a special ink anti-counterfeiting printing technology in which a magnetic substance (iron oxide powder) is added to the ink for printing, and the magnetic recording body is completed, It has the special properties required. Therefore, the magnetic ink can be said to be the protagonist in magnetic printing. This article is to explore the principle characteristics, printability and application of magnetic ink.
Second, the principle and characteristics of magnetic ink
Since magnetic inks rely on magnetic recording technology, it is necessary to understand what magnetics are before discussing magnetic inks. How do we apply its characteristics to the printing field and become the "magnetic printing" we know.
(1) Basic concepts of magnetism
According to the theory of electromagnetism, we can assume that the magnetic body is composed of many very small magnetic domains. Each magnetic domain contains 1012~1015 molecules, and has south and north poles, which is equivalent to a small permanent. magnet.
Generally speaking, when the magnetic body is not magnetized, the arrangement of the magnetic domains is disordered, and the magnetic properties of each other cancel each other out, so that the magnetic field is not magnetic, as shown in Fig. 1(a). If a current is applied to the coil outside the magnetic body, and the magnetic body is in the magnetic field, the magnetic domain is affected by the magnetizing force, and a tendency tends to be uniformly arranged, as shown in Fig. 1(b). If the magnetization of the magnetic body is increased again, the arrangement of the magnetic domains is more uniform, and finally the magnetic properties of the magnetic body will reach a maximum value, as shown in Fig. 1(c). In other words, the magnetic field at this time has reached saturation level. When the external magnetic field disappears, the arrangement of the magnetic domains of the magnetic body remains in a neat state, becoming a permanent magnet.
The above is the basic concept of magnetism.
(a) The current is zero
(b) Small current
(c) High current
(2) Principles and characteristics of magnetic records
The principle of magnetism is used for recording as "magnetic recording", and the earliest application of magnetic recording technology was exhibited in the Paris International Exhibition in 1898. The principle of magnetic recording is as follows:
The principle of magnetic recording of the anti-counterfeit magnetic ink is basically the same as that of the magnetic tape. The magnetic head used for recording is composed of a toroidal core with a gap inside and a line pattern wound around the core.
The magnetic card is made of a base of a certain material and a granular magnetic material uniformly coated on the base. The principle of the recording operation is that the magnetic surface of the magnetic card (or the recording head) moves at a certain speed, respectively. Record the gap of the head(or magnetic side) contact. Once the current is applied to the coil of the head, a magnetic field proportional to the current is generated at the gap between the two, and the magnetic body in contact with the gap between the magnetic card and the gap is magnetized to generate a magnetic force.
Sometimes, the recording signal current changes with time, and the magnetic card (head) is in a moving state, so when the magnetic body on the magnetic card passes through the gap, it is magnetized to varying degrees with the magnitude of the current. After the magnetic card is magnetized, the magnetic layer of the magnetic card leaving the gap leaves "remanence" corresponding to the change in current.
In magnetic recording, it must be noted that in order to make the magnetic card move smoothly, the shape of the surface of the magnetic head must be such that the magnetic card can smoothly move over the magnetic head, and the magnetic card and the magnetic head surface are kept in contact by pressure. In this process, except for some leakage flux generated through the slit and through the non-ferromagnetic substrate, most of the magnetic flux passes through the oxide magnetic layer on the magnetic card, and the maximum magnetic flux density is between the two poles. .
The characteristics of the magnetic recording body are as follows:
1. The machine used for recording is small in size and convenient to carry;
2. The materials used for recording are stable in physical and chemical properties;
3. When recording, the fixing does not use chemicals;
4. Stability under normal climatic conditions, easy to keep records;
5. It can be eliminated and reused, which is quite economical.
Since the magnetic recording body has the above characteristics, most of it is applied to security printing, such as magnetic cards, tickets, passbooks, etc., to avoid counterfeiting.
(3) Magnetic ink printing and its characteristics
After understanding the basic principles of magnetism and magnetic recording, I began to enter the subject of this article—magnetic inks.
As described in the previous section - Magnetic Recording Principle, the principle of magnetic recording for anti-counterfeit magnetic inks is basically the same as that of audio tapes. The difference is that the magnetic recording of anti-counterfeit magnetic inks is relatively low and sensitive. The magnetic properties of the latter magnetic materials are also lower.
Magnetic printing is the application of magnetic ink, and the basic technology of magnetic printing is to apply a magnetic layer on a paper or plastic substrate, and then print characters or patterns on other parts to become a printing material for displaying visual information corresponding to the use condition. The layer, after being subjected to molding processing, becomes a commonly known "magnetic print", which can be said to be a unique recording medium produced by combining recording and printing techniques.
In general, in the magnetic printing technology, the screen or graphic magnetic layer is mostly obtained by screen or lithography because it can form the characteristics of the magnetic tape only where necessary for the card, thereby reducing the cost of magnetic printing. After printing, the transparent PVC sheet coated on both sides is pressed by a hot press, die-cut according to a predetermined size, and finally becomes a magnetic printed product.
In anti-counterfeiting, in order to prevent counterfeiting and tampering, magnetic ink printing is increasingly safe and confidential. Therefore, special materials or techniques are often used in magnetic materials, printing and processing methods, such as special plate making techniques and inks used in printing. Including fluorescent ink, thermochromic ink, absorbing infrared ink printing, also using shading printing, micro-printing, rainbow hologram, etc., are all materials or methods commonly used in magnetic printing to prevent counterfeiting.
For magnetic ink printing, the characteristics can be summarized as follows:
1. The data can be written and read on the magnetic card, and the text, pattern and photo can be visually seen;
2. The magnetic detector can be used to detect the magnetic signal with a pattern or logo printed by the magnetic ink;
3. Messages such as printed passwords printed with magnetic ink can be read by the decoder.
Third, the printing suitability factors related to magnetic ink printing
The so-called printability is simply the property of the substrate, ink, plate, printing process and printing room conditions suitable for printing. In the following, the magnetic ink, the magnetic film, the magnetic number, and the substrate for printing affect the factors related to the printing quality of the magnetic ink.
(1) Magnetic ink
Magnetic inks were developed around the 1960s in order to integrate with electronic technology and apply automatic processing of stamps, automatic sorting of letters, and automatic processing of form classification. Since magnetic inks were not used for anti-counterfeiting at the time, magnetic inks were mainly used for printing letters and digits to facilitate automatic recognition and processing of printed materials. Since the 1980s, magnetic inks have broken the limits of only a few colors in black or limited, and expanded them to four-color magnetic inks.
Magnetic ink is mainly made of fine powder magnetic material and synthetic resin varnish and dry oil. At present, the annual consumption of magnetic ink in the world has reached several thousand, mainly used for the symbol on the check. Printing with letters, printing methods are generally lithographic and embossed, and also used to print tape strips on credit cards.
The basic composition of the magnetic ink is the same as that of the general ink, that is, it consists of a pigment, a binder, a filler, and an auxiliary. The difference is that the pigment used in the magnetic ink is not a pigment but a ferromagnetic material. Here are the explanations as follows:
1. Pigment
The magnetic ink uses a ferromagnetic material which retains magnetic properties after magnetic field treatment. Among them, the best magnetic pigments are iron oxide black (Fe3O4) and iron oxide brown (Fe2O3), since most of these pigments are needles smaller than 1 μm. Crystallized, so they are more easily aligned in the magnetic field and have higher residual magnetic properties. Among them, 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%. The synthetic iron oxide black has excellent impermeability and chemical resistance. Light resistance, almost non-toxic, heat resistance is acceptable, because when heated to about 177 ° C, iron oxide black will oxidize to iron oxide red. The disadvantage of these pigments is that the oil absorption is relatively large and the transfer performance is not very good, so sometimes some granular or cubic iron oxides are used in combination to improve the printing performance.