JPS6118258B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic medium, and particularly to a magnetic recording medium having a high coercive force suitable for use in magnetic cards and the like.

Magnetic recording materials are tape-shaped and used for a variety of purposes, such as analog recording (audio, image recording, etc.) and digital recording (electronic measuring instruments), but recently, disk-shaped (disc-shaped) Alternatively, in the form of cards or sheets, they are beginning to be widely used for financial labor-saving, administrative labor-saving, transportation labor-saving, etc. Card-shaped magnetic media used for labor-saving purposes are used under harsh conditions both indoors and outdoors in all-weather environments, and cannot be directly handled by human hands or by devices other than recording and reproducing devices. Often comes into contact with various objects. Magnetic cards for cash dispensers or magnetic transportation tickets (commuter passes,
Since short-distance tickets are carried around on a daily basis for the purpose of depositing and withdrawing money, they may be placed near or touched by handbag caps that use permanent magnets or office supplies that use permanent magnets, and important records may be lost. may be demagnetized or attenuated. Furthermore, in recent years, there has been a trend toward magnetization of expressway tickets, which has increased the possibility of causing the above-mentioned problems. In addition, as mentioned above, these magnetic cards are used in all weather conditions, especially in winter and in cold regions, where they are used in reading (abbreviated as card readers) and writing machines in a dry atmosphere with a relative humidity of 10% or less. As a result, contact and friction between the magnetic medium and card feeding parts such as the card reader's guide roll, pinch roller, and capstan frequently occur, causing so-called frictional electrification. The generation of this charging and static electricity is then accompanied by a discharge phenomenon, which generates noise in the card reader and peripheral circuits, which often leads to reading errors and troubles.

As mentioned above, in addition to the requirement of mechanical durability, these magnetic media are required to have anti-demagnetization properties and anti-static properties as important properties.

The present invention aims to provide a magnetic medium that satisfies these required characteristics, and will be described in detail below.

The magnetic material used in conventional magnetic cards has a coercive force (Hc) of 250 to 360 Oe, γ Fe ₂ O ₃ or
Hc: Fine powder of γ.Fe ₂ O ₃ (or magnetite Fe ₃ O ₄ ) doped or coated with cobalt (Co) of 600 to 700 Oe is widely used. Hc: 600~
The magnetic material of 700 Oe is adopted as the magnetic card specification of Nihon Den Corporation or the specification of the Japan Bankers Association unified card, because Hc: 250 to 360 Oe γ・Fe ₂ O ₃
This is because it is less likely to be demagnetized than one using . Generally, permanent magnets for clasps used in handbags, etc., are cobalt-based ferrite (Co ferrite) or barium-based ferrite (Ba ferrite) with an Hc of about 800 to 1000 Oe, and the magnetic field strength at the end face is about 200 to 600 Oe. be. If the distance is about 3 mm from this end face, the magnetic field strength will drop to 300 Oe or less. Hc in this magnetic field: 250~360Oe
In a magnetic film using γ Fe ₂ O ₃ , the prerecorded signal is reduced to about 60% of the initial output of 100. Hc: 600~
For those using a 700Oe magnetic material, the magnetic field described above is a few percent.
There is no problem in practical use as it only causes a reduction in . However, even if a magnetic material with Hc of 600 to 700 Oe is used, if it comes into direct contact with a magnet, most of it will be demagnetized or a large amount of noise will be applied.

On the other hand, in order to reduce the chargeability of conventional magnetic media such as magnetic cards, carbon powder with high conductivity is mixed with magnetic powder at a weight ratio of 10 to 30% to increase the resistivity on the order of 10 ⁸ (Ω cm). The following steps were taken to suppress the generation of static electricity to a level that does not cause any practical problems. However, mixing a large amount of carbon powder reduces the amount of magnetic powder per unit volume of the magnetic film, which is disadvantageous in terms of output.

In view of these points, the present invention provides a magnetic medium that has a high coercive force, is extremely difficult to be demagnetized by an external magnetic field, and generates little static electricity.

Next, the present invention will be explained in detail using a highway ticket using paper as a carrier as an example. Expressway tickets are made of approximately 54 x 120 mm general statistics card paper with a magnetic stripe on a portion of the paper, and the necessary coded signals are magnetically recorded. Necessary information includes issue date and time, interchange number, vehicle type, collector number, lane number, etc., and the recording density is 100 BPI. This ticket is collected by the driver at the interchange and handed to the collector at the interchange at the destination, and its usage is almost the same as that of a general expressway ticket. The coercive force Hc of the magnetic material is increased so that information will not be erased even if the permanent magnet attached to the car accessories is touched when stored in the car.
1500Oe or more is used. At present, this magnetic material is based on barium ferrite (Ba
Powder of ferrite) is used. The component of Ba-ferrite is BaO.6Fe ₂ O ₃ , and there are derivatives in which small amounts of different metal ions are added to improve temperature characteristics and other characteristics. for example,
Magnetic properties can be improved by adding 1 to 5% mole of Bi ₂ O ₃ :NaBiO ₃ to Ba ferrite, and addition of Al ₂ O ₃ can also promote an increase in Hc. Hc can be freely selected from about 1000 to 4000 Oe depending on the manufacturing method. According to an embodiment of the present invention, magnetite is added to the fine powder of barium-based ferrite or its derivative.
By adding an appropriate amount of Fe ₃ O ₄ fine powder, a magnetic medium with high coercive force and less generation of static electricity can be provided.

The magnetite used in the present invention can be written as FeO.Fe ₂ O ₃ and is a typical ferrite, which has a significantly high electrical conductivity among ferrites.
The present invention combines the magnetite's good magnetism and good electrical conductivity with the high coercive force characteristics of magnetic powder of high coercive force ferrite such as barium ferrite. It is intended to be a magnetic medium with good characteristics (low generation of static electricity).

The Ba ferrite powder has an average particle size of about 0.8μ, Hc: 2650Oe, and an acicular shape with an average axial length of 0.7μ.
The relationship between the mixing ratio and the apparent coercive force Hc when magnetite Fe ₃ O ₄ powder with Hc: 360 Oe is mixed is shown in Figure 1 of the attached drawings. In other words, the curve showing the coercive force Hc is nearly linear and is proportional to the mixing ratio.

Next, FIG. 2 shows the change in resistivity of the powder when the above magnetic powder is mixed. This resistivity is
Pack 1 g of sample uniformly into a glass cylinder with an inner diameter of 4 mm and a length of 60 mm, store it in a desiccator for 24 hours,
This is the value measured with a high resistance measuring device by placing an electrode in close contact with the end face. The Ba ferrite and magnetite used as samples are also the same as above, and when it is 100% Ba ferrite, it shows a resistivity close to about 10 ¹⁰ .
When magnetite is 100%, it shows a resistivity in the 10 ⁵ range. When these are mixed, a curve as shown in FIG. 2 is obtained depending on the mixing ratio, and it is clear that the resistivity is approximately proportional to the mixing ratio.

Generally, when magnetic cards are subjected to a magnetic card sorter or the like, it is necessary to process them in as short a time as possible to save time. For this reason, a high reading speed with a magnetic card reader is required. In other words, magnetic cards move at high speeds, and the card's travel speed can exceed 1.5 m/sec.
At this time, frictional charging as described above is likely to occur.

In general, we conducted an experiment on magnetic tapes (the carrier is a polyester film with a thickness of about 25 μm), took the resistivity of the tape as a parameter, and investigated the running speed of the tape and the ratio of static electricity generation (charged potential). become that way. Note that the tape was run with a taper handler, and the charging voltage was a value measured with a current collector potential measuring device. As is clear from this graph, the lower the resistivity, the less static electricity is generated. Magnetic films for ordinary magnetic cards are formulated with magnetic paint and processed in such a way that they exhibit a resistivity of 10 ⁸ Ω·cm or less. For example, as shown in Figure 3, if the resistivity of the magnetic film for cards exceeds the order of 10 ¹⁰ Ωcm, an electrostatic voltage of 0.5 KV or more will be generated when the relative speed between the card and the reader is high. There is a risk that this will discharge and generate noise, causing trouble in reading the card.

To form a magnetic film, magnetic powder is usually mixed with a polymeric binder, solvent, etc. to form a paint, which is then processed by the doctor method, gravure method, reverse method, offset method, dry offset method, and screen method. This is done by forming a film of uniform thickness using a printing method, etc., and drying and solidifying it. Since a magnetic film is made up of magnetic powder dispersed in a polymer, its resistivity usually takes a much larger value than when the magnetic powder itself is used alone. be. To prevent this, carbon powder is generally mixed in to lower the resistivity as described above. To reiterate, when carbon powder is mixed, the content of magnetic powder (in the magnetic film) decreases accordingly, which is disadvantageous in terms of sensitivity and in terms of magnetic properties. The present invention has succeeded in reducing resistivity without deteriorating magnetic properties by mixing magnetite Fe ₃ O ₄ powder, which has good conductivity and good magnetism, in place of such carbon powder. .

Next, an example in which a magnetic medium was prepared according to the present invention will be described.

Example 1 Magnetic card using magnetic paint for manufacturing magnetic film by doctor coating Ba ferrite powder with coercive force Hc 2650 Oe at wt% 43
A is a magnetic powder in which 57% wt% of Fe ₃ O ₄ powder with a coercive force of Hc360Oe is uniformly mixed.

A Magnetic powder 1200gr PVC binder (e.g. Vinylite VYHH) 55gr Plasticizer (e.g. dioctyl phthalate) 22gr Silicone oil 17gr Toluene 190gr Methyl ethyl ketone 60gr Mix in a ball mill for 30 hours. At this time, it is easier to disperse the A magnetic powder more uniformly by pre-treating it with a wetting agent such as Elkin (crude soybean lecithin). Apply this in stripes to a thickness of approximately 10 μm on the statistical card using the doctor method. The coercive force of the created magnetic film is 1570 Oe and the resistivity is 10 ⁷ Ω・cm
We obtained sufficient characteristics for practical use on the stand.

Example 2 Method of creating magnetic cards using dry offset ink using dry offset method 0.8 in a ball mill for 20 hours to form an ink.
This was printed twice on statistical paper using the dry offset method to create a magnetic film with a thickness of about 4 μm. The coercive force of the magnetic film was 1550 Oe, and the resistivity was on the order of 10 ⁷ Ωcm, which is sufficient for practical use.

In Examples 1 and 2, no carbon powder was added to improve the conductivity, but if necessary, it may be practically acceptable to add carbon powder in an amount of 10% or less of the magnetic powder by weight.

As mentioned above, the magnetic card according to the present invention uses Ba ferrite powder and Fe ₃ O ₄ powder as its magnetic powder, but for example, an external demagnetizing field of about 400 Oe, which has a coercive force higher than that of Fe ₃ O ₄ , is applied from the outside. When exposed to Fe ₃ O ₄ magnetic powder, the signal recorded on the Fe 3 O 4 magnetic powder is demagnetized and the corresponding signal output becomes less than 50% of the initial value.
The signal output recorded in the ferrite powder is hardly affected. Therefore, the signal can be read effectively.

The composition of the magnetic paint or ink described in the above examples is one example, but the electrical conductivity of the magnetic film depends not only on this composition but also on the dispersion method of the magnetic powder. The resistivity of the magnetic film is
It varies by about 10 ² Ω・cm. According to experiments conducted by the present inventors, when the mixing ratio of Ba ferrite magnetic powder and magnetite powder is 30:70 from 85:15, the resistivity of the mixed magnetic powder is on the order of 10 ⁸ Ωcm to 10 ⁶
Changes to the order of Ω・cm. Generally speaking, when magnetic powder with such a resistivity is dispersed in a polymer binder, the resulting magnetic film has a higher resistivity than the magnetic powder itself, as mentioned above, but the magnetic film with a resistivity on the order of the above If it is a powder, it is easy to make the resistivity of the magnetic film on the order of 10 ⁷ Ωcm by adding 10% or less of carbon powder, and since the amount of carbon powder added is small, the magnetic properties of the magnetic film itself and the electromagnetic properties can be improved. The conversion characteristics will not be significantly impaired.

Furthermore, although the above-mentioned high coercive force materials have been mainly explained based on Ba ferrite, the same applies to other high coercive force ferrites, such as cobalt ferrite (Co ferrite) or derivatives thereof.

[Brief explanation of the drawing]

Figure 1 of the attached drawings is a diagram illustrating the relationship between the mixing ratio of a mixture of Ba ferrite powder and magnetite powder and coercive force, and Figure 2 is a diagram illustrating the relationship between the mixing ratio and resistivity of a mixture of Ba ferrite powder and magnetite powder. FIG. 3 is a diagram illustrating the relationship between tape running speed and static electricity generation.

Claims (1)

[Claims] 1. A magnetic medium whose main magnetic material is a mixture of ferrite powder having a high coercive force and magnetite powder, which is a magnetic material with high electrical conductivity, in which the amount of the magnetite powder mixed with the ferrite powder is is characterized in that the coercive force of the magnetic medium can be maintained at a value close to the coercive force of the ferrite powder, and the electric resistivity of the magnetic medium can be maintained at a value of the order of 10 ⁸ Ω·cm or less. magnetic media. 2 The mixing ratio of the magnetic material is at least 15 in terms of weight ratio.
%, up to 70% magnetite powder. 3. The magnetic medium according to claim 1 or 2, wherein the ferrite powder is a powder of barium-based ferrite or a derivative thereof. 4. The magnetic medium according to claim 1 or 2, wherein the ferrite powder is a powder of cobalt-based ferrite or a derivative thereof.