JPH07235042A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve such characteristics as antistatic performance, running stability and error rate by specifying the properties and components of a nonmagnetic inorg. pigment contained in a magnetic layer formed by coating on the nonmagnetic substrate of a coating type magnetic recording medium. CONSTITUTION:A nonmagnetic inorg. pigment having <=2OMEGAcm electric resistance as powder, a Mohs hardness of 5-7 and <=0.3mum average particle diameter is used. A magnetic layer contg. the nonmagnetic inorg. pigment by 40-70 pts.wt. per 100 pts.wt. magnetic iron oxide is formed. Electrification is suppressed while ensuring durability of the magnetic coating film, running stability is improved and dropout can be reduced by preventing the sticking of dust, etc., and irregular winding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating type magnetic recording medium in which a magnetic layer is formed by coating a magnetic coating on a non-magnetic support, and more particularly to a magnetic recording medium for digital recording.

[0002]

2. Description of the Related Art In recent years, there has been a remarkable trend toward high density recording in magnetic tape with the development of equipment. Furthermore, the recording method is changing from the conventional analog recording to digital recording. Particularly in the field of audio, a digital audio tape (hereinafter abbreviated as DAT) is also developed and commercialized and put on the market for consumer use.

However, the head of the DAT is installed on a rotary cylinder similar to that of a conventional video tape recorder (hereinafter abbreviated as VTR), and the tape running mechanism has almost the same structure as that of the VTR, and only the DAT dedicated tape is recorded. Can't play. Therefore, it has been more than 5 years since it was commercialized and put on the market, but it has not yet spread enough. Based on such a background, there has been a demand for the development of a digital recording system compatible with an analog recording compact cassette (hereinafter abbreviated as CC). Although each manufacturer has been keenly developing about this, recently, due to the development of the fixed type multi-channel head by applying the semiconductor thin film forming technology, and further the development of the signal compression technology,
A digital compact cassette system was developed and proposed. And each tape maker is developing a new high-performance digital compact cassette tape (hereinafter referred to as DCC tape) compatible with the system.

Further, with the widespread use of portable magnetic recording / reproducing devices, the magnetic recording / reproducing devices have come to be used in all kinds of indoor and outdoor environments, and the use environment of the recording medium has become wider and more severe than ever. Therefore, it is extremely important to further improve the durability and running stability of the magnetic recording medium, and various efforts have been made as countermeasures. For example, there is a method of improving the strength of a coating film by containing an inorganic pigment having a high Mohs hardness such as an abrasive in the coating film (JP-A-4-79063).

[0005]

In consideration of a system capable of digital recording while maintaining upward compatibility with CC,
The relative speed of the head and tape is very slow (4.8 cm)
/ Sec) to achieve high density recording. For that purpose, it is expected that short wavelength recording with the shortest recording wavelength of 1 μm or less and narrowing of track by multi-channeling of the head. In such a system, the medium is required to have high magnetic energy and high output.

In order to design a medium of high magnetic energy, metal powder has been conventionally used as magnetic powder.
AT tapes and CC metal tapes have been commercialized. DAT laminated amorphous head or CC
In the case of the Permalloy bulkhead, the coercive force Hc, like that of a metal tape, can be obtained by improving the recording current and setting it to an appropriate value.
It is possible to record even on high tape, and DAT
In, the characteristics equivalent to those of the CD (compact disk) are obtained, and in CC, the output improvement in the high frequency band (12 kHz) is achieved. However, in the case of DCC, since a thin film multi-channel head is used, if the coercive force of the medium is set too high, the head will be magnetized and saturated, and sufficient recording will become impossible and the required electromagnetic conversion characteristics will not be obtained. . Furthermore, the overwrite characteristic is also deteriorated, and in the worst case, the error rate is deteriorated.

On the other hand, in order to achieve a good error rate as a system, it is of course important for the magnetic tape to have excellent electromagnetic conversion characteristics, but there is no foreign substance in or on the magnetic layer. It is extremely important to use a magnetic tape with little dropout. Since it is a fixed head and the relative speed with the tape is very slow,
It is impossible to self-clean by ejecting minute dust and dust adhering to the magnetic layer of the magnetic tape by high-speed rotation of the head (1800 rpm in the case of VHS) like a rotary head. Considering that short wavelength recording with a minimum recording wavelength of 1 μm or less is essential as a system, micron-order minute dust and dust adhering to the surface of the magnetic layer rather than in the magnetic layer is the main cause of dropout. Becomes

Dust and dust on the magnetic layer may intrude from the outside, but rather, it is often caused by dusting of the tape itself such as abrasion of the magnetic layer due to running, dust falling, etc., and how to suppress it. Is very important. That is, it has been indispensable to design a magnetic layer with less powder falling and shaving under various environments from extremely low temperature to high temperature and high humidity in order to achieve a good error rate. Further, it is necessary to prepare a magnetic coating film having a low electric resistance because dust, dust, and the like are easily attached to the magnetic coating film due to electrification of the magnetic coating film, which causes dropout.

[0009]

In order to solve the above-mentioned problems, the present invention provides a magnetic layer comprising a magnetic iron oxide, an organic binder and a non-magnetic inorganic pigment as main components on a non-magnetic support. In this magnetic recording medium, a non-magnetic inorganic pigment having a powder electric resistance of 2 Ωcm or less, particularly a Mohs hardness of 5 is added to the magnetic layer.
˜7, 40 to 70 parts by weight of a non-magnetic inorganic pigment having a particle diameter of 0.3 μm or less is included with respect to 100 parts by weight of magnetic iron oxide.

[0010]

With the above-described structure, the present invention makes it possible to manufacture a tape adapted to a DCC system capable of digital recording while maintaining the upward compatibility of CC.

That is, in a magnetic recording medium in which a magnetic layer containing a magnetic iron oxide, an organic binder and a non-magnetic inorganic pigment as main components is coated on a non-magnetic support, fine particles are used as powder in terms of coating strength. A magnetic layer that has a specific hardness with low electrical resistance added to magnetic iron oxide in a specific amount has excellent antistatic properties, and is free from abrasion and powder loss during durable running in all environments from low to high temperatures. It becomes possible to According to the examination of the present invention, the hardness of the abrasive used is preferably 5 or more in Mohs' hardness. If the Mohs hardness is less than 5, the effect of reinforcing the coating film is small. If the powder electric resistance is larger than 2 Ωcm, the antistatic effect of the coating film is small and the particle size is 0.3 μm.
If it is larger than the above range, the surface property of the magnetic layer is deteriorated and the output is decreased.

Further, the amount of addition to the magnetic layer is magnetic iron oxide 10.
It is preferably 40 to 70 parts by weight with respect to 0 parts by weight. If it is less than 40 parts by weight, the effect of reinforcing the coating film is small,
If the amount is more than 70 parts by weight, the effect of reinforcing the coating film is great, but head wear occurs and the filling property of the magnetic particles decreases.

The conductive inorganic pigments used in the present invention include inorganic pigments such as α-iron oxide and titanium oxide, and metal oxides having excellent conductivity such as tin oxide, indium oxide, zinc oxide and magnesium oxide. The deposited powder can be used.

By making the magnetic layer have the above-mentioned basic constitution, the durability of the magnetic coating film is ensured, the charging is reduced, the running stability is improved, and the adhesion of dust or the disturbance of the winding. By preventing, dropouts can be reduced. In addition, by reducing substances such as carbon and abrasives that do not directly participate in recording in the magnetic coating film, it is possible to improve the packing property of magnetic particles, and it is possible to create a higher density magnetic recording medium. Become.

[0015]

The present invention will be specifically described below.

The magnetic iron oxide for the magnetic layer used in the present invention is not particularly limited, and acicular fine γ-Fe ₂ O ₃ and Co particles are used.
There are deposited γ-Fe ₂ O ₃ and Co deposited Fe ₃ O ₄ . These magnetic iron oxides may be used alone or in combination of two or more.

The organic binder used in the present invention includes vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinylidene chloride polymer, polyurethane resin, polyester resin. Acrylonitrile-butadiene copolymer, cellulose-acetate-butyrate, epoxy resin, acrylic resin, polyvinyl acetal resin, polyvinyl butyral resin and the like are preferably used.
These resins may be used alone, but are usually used as a mixture of two or more kinds.

If necessary, higher fatty acid as a lubricant,
It is also possible to add a fatty acid ester and carbon black or the like as an antistatic agent.

Further, a magnetic coating material is prepared by dispersing the constituent materials of the magnetic layer in an organic solvent, and the magnetic coating material is applied onto a non-magnetic base. In this case, the solvent of the magnetic coating material is a ketone (eg acetone, methyl ethyl ketone). , Methyl isobutyl ketone, cyclohexanone, etc.), alcohols (eg methanol, ethanol, propanol,
Butanol), esters (eg methyl acetate, ethyl acetate, ethyl lactate, glycol acetate, monoethyl ether etc.), glycol ethers (eg ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, dioxane etc.), aromatic hydrocarbons ( Examples thereof include benzene, toluene, xylene, etc.), aliphatic hydrocarbons (eg, hexane, heptane, etc.), nitropropane and the like.

The non-magnetic support to which the magnetic paint is applied includes polyester (eg polyethylene terephthalate, polyethylene naphthalate etc.), polyolefin (eg polypropylene, polyethylene etc.), cellulose derivative (eg cellulose triacetate, cellulose diacetate etc.), Preferable examples include polyvinyl chloride, polyimide and polyamide.

Examples of the magnetic tape of the present invention will be described below. It was made into a paint using the following materials.

(Example 1-1) Preparation of coating material for magnetic layer 100 parts by weight of cobalt-γ-iron oxide (BET 5 × 10 ⁴ m ² / kg) (σ _s 1 × 10 ^-4 Wbm / kg) (Hc 6.2 × 10 ⁴ A / m) 50 parts by weight of conductive titanium oxide (average particle diameter 0.2 μm) (electric resistance of powder 1 Ωcm) (Mohs hardness 7) 10.4 parts by weight of polyvinyl chloride resin (Tg = 75) C.) Methyl isobutyl ketone (MIBK) 16 parts by weight Toluene 16 parts by weight Cyclohexanone 5 parts by weight The above materials were kneaded for a certain period of time using a biaxial continuous kneader. Materials having the following composition were further added to the obtained kneaded product, diluted with a dissolver, and then dispersed with a sand mill to obtain a magnetic coating material.

Kneaded material 177.4 parts by weight α-alumina 3 parts by weight Polyurethane resin 5.6 parts by weight (Tg = −23 ° C.) MIBK 63 parts by weight Toluene 63 parts by weight Cyclohexanone 21 parts by weight Based on the entire magnetic paint obtained. Then, a material having the following composition was added, and the mixture was stirred with a dissolver. Further, materials having the following compositions were added to obtain a magnetic layer coating material.

Stearic acid 1.5 parts by weight Myristic acid 2 parts by weight Olive oil 0.5 parts by weight Polyisocyanate 6 parts by weight A magnetic coating material for each magnetic layer is applied to one surface of a polyethylene terephthalate film having a thickness of 9 μm as a non-magnetic support. ,
In the undried state, a solenoid magnetic field treatment was performed, an orientation treatment was performed so as to have an easy axis of magnetization in the film running direction, and then a calendar treatment and a heat curing treatment were performed. 3.78 after curing
The magnetic tape of Example 1 was produced by cutting into a width of mm.

Example 1-2 Except that the conductive titanium oxide in the magnetic paint was replaced with conductive α iron oxide (average particle size: 0.2 μm, powder electric resistance: 1 Ωcm, Mohs hardness: 5). A magnetic tape was prepared in the same manner as in Example 1-1.

(Example 2-1) Example 1-in a magnetic coating material
A magnetic tape was prepared in the same manner as in Example 1-1, except that 40 parts by weight of the conductive titanium oxide used in Example 1 was added.

(Example 2-2) Magnetic properties were the same as in Example 1-1, except that the conductive titanium oxide of Example 2-1 was replaced with conductive α-iron oxide (same as Example 1-2). I made a tape.

(Example 3-1) Example 1-in a magnetic coating material
A magnetic tape was prepared in the same manner as in Example 1-1, except that the conductive titanium oxide used in Example 1 was added in an amount of 70 parts by weight.

(Example 3-2) Magnetic properties were the same as in Example 1-1, except that the conductive titanium oxide of Example 3-1 was replaced with conductive α-iron oxide (same as Example 1-2). I made a tape.

Comparative Example 1 A magnetic tape was prepared in the same manner as in Example 1-1, except that 20 parts by weight of the conductive titanium oxide used in Example 1-1 was added to the magnetic coating material.

Comparative Example 2 A magnetic tape was prepared in the same manner as in Example 1-1, except that 80 parts by weight of the conductive titanium oxide used in Example 1-1 was added to the magnetic coating material.

Comparative Example 3 Titanium oxide (average particle size: 0.2 μm, powder electric resistance: 1000 Ωcm, Mohs hardness: 7) was used in the magnetic paint instead of the conductive titanium oxide used in Example 1-1. A magnetic tape was prepared in the same manner as in Example 1-1 except that 50 parts by weight of was added.

Comparative Example 4 7 parts by weight of carbon black (average particle size: 0.2 μm) was used in Comparative Example 3 instead of the conductive titanium oxide used in Example 1-1 in the magnetic paint. A magnetic tape was prepared in the same manner as in Example 1-1, except that 50 parts by weight of titanium was added.

(Comparative Example 5) All except that 7 parts by weight of carbon black (average particle size: 0.2 μm) was added to the magnetic paint instead of 50 parts by weight of the conductive titanium oxide used in Example 1-1. A magnetic tape was prepared in the same manner as in Example 1-1.

Comparative Example 6 A magnetic tape was prepared in the same manner as in Example 1-1, except that 50 parts by weight of conductive titanium oxide (average particle size: 0.5 μm) was added to the magnetic coating material.

The various magnetic tape samples obtained in the above Examples and Comparative Examples were subjected to the following evaluation tests, and the results are shown in (Table 1), (Table 2) and (Table 3). .

[0037]

[Table 1]

(1) Error rate A commercially available DCC deck (RS-DC1 manufactured by Matsushita Electric Industrial Co., Ltd.)
0) and error rate measuring device (Japan Phillips
The error rate after initial running and after endurance running was measured using DEMS2000 manufactured by Co., Ltd. The environment for durable running is as follows.

3 ° C 80% RH 100 pass 40 ° C 80% RH 100 pass

[0040]

[Table 2]

(2) Electromagnetic conversion characteristics A commercially available DCC deck (RS-DC1 manufactured by Matsushita Electric Co., Ltd.)
0) was used to measure outputs at 9.6 kHz and 48 kHz. The measured values are shown in Example 1 as 0 dB. (3) Drop Out (D.O.) Change Rate D. O. (15μs per minute,
The number of occurrences of output reduction of 16 dB or more) was measured under the following environment, and then reproduction and rewinding were repeated 100 times. After that, D. O. Was measured, and D.I. O. The rate of change was calculated. D. after running test O. If the rate of change was less than twice the initial value, it was rated as O.

3 ° C 80% RH 100 pass 40 ° C 80% RH 100 pass

[0043]

[Table 3]

(4) Head wear Commercially available DCC deck (RS-DC1 manufactured by Matsushita Electric Co., Ltd.)
0) was used to visually determine the wear state of the head surface after running for 500 hours.

◯: No head wear is observed Δ: Head surface is partially peeled off.

X: The head surface is completely peeled off. (5) Magnetic measurement Using a vibrating sample magnetometer, the saturation magnetization (Bm) of the tape
And the squareness ratio (sq) was calculated. (6) Scratch property This shows the number of passes until the magnetic layer is completely peeled off from the base film when a 3φ hard ball is slid on the tape magnetic layer at a load of 40 g at 4 cm / sec. (7) Electric resistance The produced magnetic tape was cut into a length of 7 cm, and 500
After charging under V, 1 minute, electrical resistance measuring device (YO
The resistance value was measured by KOGAWA HEWLETT PACKARD, 4329A).

As shown in (Table 1), Examples 1-1 to 1-1
By using 40 to 70 parts by weight of the inorganic pigment as in Example 3-2 and Comparative Examples 2, 3, 5, and 6, the strength of the coating film is improved and the error rate after endurance is hardly deteriorated. On the other hand, when the amount of the inorganic pigment is less than 40 parts by weight (Comparative Examples 1 and 4), the coating film strength cannot be ensured and the error rate after endurance is significantly deteriorated.

In addition, from (Table 2), D. O. It can be seen that the rate of change also hardly changes in the tape in which the conductive inorganic pigment or the inorganic pigment is added by 40 parts by weight or more, and the output does not decrease in the addition range of 40 parts by weight to 70 parts by weight. On the other hand, when the conductive inorganic pigment and the inorganic pigment are added in an amount of more than 70 parts by weight as in Comparative Example 2, the packing rate of the magnetic particles decreases and the output deteriorates. When conductive titanium oxide having an average particle size larger than 0.3 μm is used as in Comparative Example 5, the surface property of the coating film is deteriorated and the output is reduced.

As shown in (Table 3), when titanium oxide is added in an amount of 80 parts by weight or more as in Comparative Example 2, head wear occurs and the filling rate of magnetic particles decreases, so that Bm and sq decrease. In addition, in scratch, Example 1-1
As shown in Examples 3-2 and Comparative Examples 1, 2, 3, 4, and 6, the amount is increased by adding a conductive inorganic pigment or an inorganic pigment, and particularly, it reaches a practical level at 40 parts by weight or more. Further, by using 40 to 70 parts by weight of the conductive inorganic pigment, the electric resistance is lowered and the coating film can be prevented from being charged.

[0050]

As described above, according to the present invention, it is possible to reduce the electric resistance by forming a magnetic layer having a strong coating film strength and free from head abrasion while maintaining the required output.
As a result, it is possible to provide an excellent digital audio tape having a good error rate after the initial running and after the running.

Continuation of the front page (72) Inventor ▲ Yoriko Takai 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A magnetic recording medium in which a magnetic layer containing magnetic iron oxide and an organic binder is formed on a non-magnetic support, and a non-magnetic inorganic pigment having a powder electric resistance of 2 Ωcm or less is contained in the magnetic layer. 40 parts by weight based on 100 parts by weight of the magnetic iron oxide
A magnetic recording medium characterized by containing up to 70 parts by weight. 2. A magnetic recording medium in which a magnetic layer containing magnetic iron oxide and an organic binder is formed on a non-magnetic support, and the powder has an electric resistance of 2 Ωcm or less and a Mohs hardness of 5 in the magnetic layer. ˜7, a non-magnetic inorganic pigment having an average particle size of 0.3 μm or less is added to 4 parts by weight based on 100 parts by weight of the magnetic iron oxide.
A magnetic recording medium containing 0 to 70 parts by weight.