Section 1 Functional Ink --1

The so-called functional ink, as the name implies, has a function of ink. Although the function is added as a means of imparting information such as transmitted color or the like, this function is divided into two types, the ink itself having and the ink having been printed so that the printed matter has.

First, the magnetic ink (a) magnetic ink printing applications Magnetic ink printing (Magnetic Ink Printing) as a special ink printing technology, refers to the use of magnetic ink mixed with iron oxide printing.
Magnetic ink 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. At present, magnetic printing has been applied in many fields. For example, tickets, monthly passes, printing, bank passbooks, ID cards, etc. can all use magnetic cards. The price list indicates that the magnetic film is used on the card; the data registration form and check can also be printed with magnetic ink. Amount and other items. In short, the use of magnetic printing is increasingly widespread.
(B) The magnetic principle 1. The basic concept of magnetism According to the concept of electromagnetism, it can be assumed that magnetic relaxation consists of many very small magnetic domains. The volume of the magnetic domain is very small, the larger magnetic domain is only 10-7-10-3cm. Each magnetic domain contains 1012 to 1015 molecules. It has its own south pole and north pole, which is equivalent to a small permanent magnet. In the case of a magnetic body that is not magnetized, the arrangement of these magnetic domains is sloppy. At this time, the magnetic properties of each other cancel each other out, and as a whole, they do not appear magnetic. This situation can be represented by Figure 2-1(a). If we pass a current to the coil outside the magnetic body, the magnetic body is affected by the magnetizing force due to the presence of the magnetic field, and there is a tendency toward uniform alignment, as shown in Figure 2-1 (b). If the external magnetic force is not strong enough, the directions of the magnetic domains cannot be completely aligned, and the phenomenon of mutually canceling the magnetic forces cannot be completely eliminated, and the magnetic properties of the magnetic body cannot be maximized. If the magnetization of the magnetic material is further increased, the alignment of the magnetic domains becomes more and more uniform so as to finally reach the degree of the complete agent shown in FIG. 2-1(c), and the magnetic properties of the magnetic material reach a maximum value. Afterwards, even though the current of the coil is increased, the magnetic body will not have more magnetism. In other words, the magnetic lines of force of the magnetic body at this time have reached saturation. When the external magnetic field disappears, the arrangement of the magnetic domains remains in a neat state. This is the permanent magnet.
(1) Magnetic field, magnetic force line, magnetic flux, and magnetic induction In the vicinity of the bar magnet, the compass is deflected, and the iron chips are arranged in a certain direction. These phenomena result from the interaction between magnetic poles. The magnetic pole and the current-carrying body and the space around them generate a field, a magnetic field, and one of the basic properties of the magnetic field is that it exerts a force on the magnetic pole and the electric current-carrying body placed therein.
The situation of the magnetic field can be described visually with an imaginary magnetic line of force. The magnetic line of the bar magnet is shown in Figure 2-2.
The direction of the magnetic lines of force is the same as that of the compass N pole. The total number of lines of magnetic force passing through a certain cross-sectional area within a magnetic field is called magnetic flux, expressed as φ, and the unit is wei (wb). The number of lines of magnetic force per unit area perpendicular to the lines of magnetic force is called the density of lines of magnetic force, also called magnetic flux density or magnetic induction, denoted by B, and the unit is special (T).
(2) Magnetic field strength and magnetic permeability The magnetic flux and magnetic induction intensity vary depending on the medium. In order to define a medium-independent quantity, magnetic induction in a vacuum is called a magnetizing force or a magnetic field strength and is expressed in H in units of amperes per meter (A/m). The ratio of B to H is called permeability and expressed as μ, ie: μ=B/H.
Experiments have shown that the air μ=1; the ferromagnetic material (iron, permalloy, etc.) μ can reach thousands or tens of thousands.
(3) Hysteresis Loop Among various magnetic media, the most important one is iron, which is a kind of very strong magnetic material. They are called ferromagnetics. In ferromagnetic materials, the permeability μ is not constant, it changes with H and also varies with the original magnetization.
The BH relationship of the ferromagnetic material in the magnetization process is the magnetization curve, as shown in Figure 2-3.
It can be seen from the magnetized common bristles that BH has a nonlinear relationship. In the initial magnetization section oa of the curve, the magnetizing force does not exceed the instep of the magnetization curve. Due to magnetic domain inertia, when H increases, B cannot immediately rise quickly, the curve is more balanced, and the function of the weak magnetization force is reversible. The magnetization force is removed and the magnetism disappears automatically; in the ab section, the magnetization force is on the instep of the magnetization curve. Between the knees. Since most of the magnetic domains are under the action of external magnetic fields, they all tend to H direction, and B increases rapidly. The curve is steeper and is called straight line segment. In the bc segment, since most of the magnetic domain directions have been turned to the H direction, H increases. Only a few magnetic domains continue to turn, B increases slowly, and the curve slows down, forming a knee; after point c, because the magnetic domain almost all tends to the H direction, and with the increase of H, B hardly increases, which is called the saturation stage.
Ferromagnetic materials of various steps have different BH magnetization curves. See Figure 2-4. If the ferromagnetic material is originally in the neutral state, H gradually increases from zero until the saturated H value, B follows the oa line; after reaching a point, if H is gradually reduced until H=0, then B Follow the ab line to change; if H is increased in reverse from point b, until B = 0, then B follows the bc line; if it continues from the point C, it increases the value of H, until the saturation value, B The cd line changes; after that, the value of H is reduced from point d to H=0, and B follows the de line; if the value of H increases again from point e, until the saturation value, B follows the ea. Line change, apparently abcdefa is a closed curve, it is called "loop." Since B lags behind H (for example, at point b, H=0, wjg B>0; at point c, Hm means that the oc value is called “coercive force”, which is expressed by Hc. The value of ga is called saturation induction, which is represented by Bs.
Let's take a look at the situation of B changing with the probation situation. In Figure 2-4, 0, b, and e are all H=0, but the magnetization is different, so the B value is also different. The concept of residual magnetic induction (abbreviated as residual induction) is often encountered in magnetic recording. Then look at Figure 2-4. If B moves from the ac segment to the m point (H=H2), then gradually decreases the H value in the opposite direction until H=0, then the residual magnetic induction B1 is obtained; if B follows the ac After the segment is changed to n point (H=H1), the H value is gradually decreased until H=0, then the residual magnetic induction B2 is obtained.
Each type of ferromagnetic material has different hysteresis loops. Hysteresis loops are the basis for studying the magnetic properties of ferromagnetic materials.
(4) Remanent magnetic induction curve If the residual magnetic induction corresponding to each point on the initial magnetization curve (Fig. 2-5) is drawn, the residual magnetic induction curve shown in Fig. 2-6 is obtained.
2. Magnetic recording principle The principle of magnetic recording for magnetic printing is basically the same as the magnetic recording principle of audio tapes, except that the magnetic recording magnetic recording requirements are relatively low, and the magnetic quality of the magnetic material after magnetic induction is also lower.
The recording head is shown in Fig. 2-7 and consists of a toroidal core with a gap and a coil wound around the core. For example, a magnetic card is made of a base material of a certain material and a particulate magnetic material uniformly coated on the base. During recording, the magnetic surface of the magnetic card moves at a certain speed, or the recording head moves at a certain speed, and comes into contact with the gap of the recording head or the magnetic surface of the magnetic card, respectively. Once the coil of the magnetic head is applied with a current, a magnetic field proportional to the current is generated at the gap, so that the magnetic body of the magnetic card in contact with the gap is magnetized. If the recording signal current changes with time, when the magnetic body on the magnetic card passes through the gap (because the magnetic card or the magnetic head is moving), it is magnetized to varying degrees with the change of the current. After the magnetic card is magnetized, the magnetic card magnetic layer leaving the gap leaves a residual magnetization corresponding to the change in current.
Of course, the surface of the magnetic head is shaped so that the magnetic card moves smoothly over the magnetic head, and the magnetic card is held in contact with the surface of the magnetic head by pressure. The distribution of the magnetic field through the magnetic card is shown in Figure 2-8. Here, in addition to generating some leakage flux through gaps and through non-ferromagnetic substrates, most of the magnetic flux passes through the oxide magnetic layer on the magnetic card, and the maximum magnetic flux density is in the space between the two pole shoes.
If the current signal (or magnetic field strength) changes in a sinusoidal manner, then the residual magnetic flux on the magnetic card also changes in a sinusoidal manner. When the current is positive, it causes a magnetic polarity from left to right (from N to S); when the current is reversed, the magnetic polarity also reverses. The final result can be seen as a wavelength on the magnetic card from N to S and then back to N. It can also be regarded as two magnetic bars connected to the same polarity. This is a somewhat simplistic result, however, it must be remembered that the remanence Br is sinusoidal. When the signal current is maximum, the longitudinal flux density also reaches its maximum. The recorded signal is recorded in a sinusoidally remanent form shown in Figs. 2-9 and stored on the magnetic card.
The signal wavelength recorded by the magnetic card is the length of one revolution of the recording current. It is proportional to the moving speed of the magnetic card and inversely proportional to the frequency of the recording current, as shown in Fig. 2-10. which is:
λ=v/f where λ—the wavelength of the signal recorded on the magnetic card, cm
v——Magnetic card movement speed, cm/s
f - the frequency of the recorded signal, Hz
The magnetic flux density on the magnetic card surface is inversely proportional to the wavelength. That is, when the recording signal current is constant, the magnetic flux density on the magnetic card surface increases at the same time as the proportional relationship and the frequency.
3. The working principle of the magnetic card The residual magnetic flux density Br on the magnetic card plays a decisive role in the working process of the magnetic card. The magnetic card passes through a working magnetic head equipped with a coil at a certain speed, and an external magnetic line of the magnetic card cuts the coil to generate an induced electromotive force in the coil, thereby transmitting the recorded signal. Of course, it is also required that a wide frequency response, a small distortion, and a high output level be recorded in the magnetic card operation.
A very thin metal line can be used as a simple playback device. The metal straight line is in close contact with the magnetic card and the direction is perpendicular to the running direction of the magnetic card, as shown in Figure 2-11. When the magnetic card is running, the metal linearly cuts the magnetic force line to generate an induced electromotive force, and the magnitude of the electromotive force is proportional to the magnetic force line that is cut. When the running speed of the magnetic card remains unchanged, the induced electromotive force of the metal line is directly proportional to the residual magnetic induction on the magnetic card surface, and the induced electromotive heat in the conductor can be expressed by the following equation:
e=BrWv where Br—surface residual magnetic induction;
W - record the track width;
v - The speed of the magnetic card during playback.
In the case of Br=(2πf/v)·ψrmcos2πft