JPH02123518A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To realize high-density recording by forming a magnetic layer containing Co-contg. magnetic iron oxides and a binder on a nonmagnetic supporting body and using a specific amount of the binder having a specific compsn. CONSTITUTION:The magnetic recording medium consists of a nonmagnetic supporting body and a magnetic layer containing Co-contg. iron oxides and a binder formed on the substrate. It is specified that the binder contains polycarbonate urethane and that the magnetic layer is 0.4 - 1.0mum thick with the residual magnetic flux density >=800 Gauss and the coersive force of 800 - 1,100 Oe. By this method, recording can be performed with shorter wavelength than in a conventional recording medium, which realizes high-density recording and large recording capacity. Moreover, the obtained medium has excellent durability for continuous reproduction and traveling stability.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a magnetic recording medium comprising a magnetic layer containing cobalt-containing magnetic iron oxide and a binder on a non-magnetic support, and particularly relates to a magnetic recording medium with a higher density. Magnetic recording media that can record data and have excellent running stability and continuous playback durability were developed.

[Conventional technology]

In recent years, as the capabilities of small computers have improved, programs and data files that are used on a daily basis require extremely large-capacity recording, and magnetic recording media such as magnetic disks are also required to have large-capacity recording media.

Further, there is a demand for smaller recording media in terms of ease of handling and space for installation or storage.

Therefore, in order to meet these demands, it became necessary to record more information on a recording medium of the same size, and for this reason, research began on recording media with so-called high recording density, in which the wavelength of the signal recorded on the recording medium was shortened. has been done.

[Problem to be solved by the invention]

However, for example, in the case of flexible disks, 1 megabyte of information can be recorded on a disk with a diameter of 90 mm (coercive force: 500 to 7,000 e%, coating thickness: 1
．． 2 to 2.0 μm) is widely used, but the shortest recording wavelength in this case is 2.9 μm (8.7 kbpi), and if recording is performed at an even shorter wavelength to increase the recording capacity, , the problem arises that the output decreases and the S/N ratio deteriorates.

In addition, in the case of digital recording, if there is a large difference between the output for long wavelengths and the output for short wavelengths, the output waveform will be distorted and the peak will be distorted when long wavelength records and short wavelength records are adjacent. A problem arises in that it deviates significantly from its original position.

[Means to solve the problem]

The inventors of the present invention have made intensive studies in view of the above circumstances, and have found that by using a specific binder, selecting a specific magnetic layer thickness, residual magnetic flux density, and coercive force, it is possible to achieve high-speed recording and It has been discovered that a magnetic recording medium with excellent stability and continuous reproduction durability can be obtained, and the present invention has been achieved.

That is, the gist of the present invention is a magnetic recording medium in which a magnetic layer containing cobalt-containing magnetic iron oxide and a binder is provided on a non-magnetic support, the binder containing polycarbonate polyurethane, The magnetic recording medium has a thickness of 0.4 to 1.0 μm, a residual magnetic flux density of the magnetic layer of 800 Gauss or more, and a coercive force of the magnetic layer of 800 to 1100 Oe.

The present invention will be explained in detail below.

In the present invention, acicular cobalt-containing magnetic iron oxide is used as the magnetic material. In particular, the long axis diameter of the magnetic material is 0.1~
A thickness in the range of 1.0 μm, preferably 0.2 to 0.6 μm is suitable. When the long axis diameter of the magnetic material is smaller than 0.1 μm, it is difficult to uniformly disperse the magnetic material in the binder, the strength of the magnetic layer becomes insufficient, and the continuous reproduction durability tends to deteriorate. If the thickness is larger than 1.0 μm, the magnetization distribution in the magnetic layer tends to become non-uniform, and noise tends to increase, resulting in a poor signal-to-noise ratio.

Furthermore, the cobalt-containing magnetic iron oxide used in the present invention has a coercive force in the range of 900 to 1000 Oe and a maximum magnetization of 70 Oe.
Emu/g or more and a specific surface area measured by the BET method in the range of 30 to 4o=/g are particularly preferably used.

Cobalt-containing magnetic iron oxides include α-Fe, Fe-Co alloys, and Fe-Co-Ni, which are known as magnetic materials that can produce magnetic recording media with large coercive force and residual magnetization.
Compared to metal magnetic powders such as alloys, it is less susceptible to oxidative deterioration and has good environmental resistance.The magnetic material itself has high hardness, so the strength of the magnetic layer is high, and the resulting magnetic recording medium has excellent durability. ing.

The binder used in the present invention is characterized by containing polycarbonate polyurethane. Here, polycarbonate polyurethane refers to polycarbonate polyol (
It is a polyurethane obtained by reacting A) with an organic diisocyanate (B) and, if necessary, reacting the remaining isocyanate groups in the reaction product with a low molecular weight diol (C).

The polycarbonate polyol (A) is, for example, a known polyhydric alcohol, such as 1,5-bentanediol, 1
．． It is a polyol having a carbonate bond obtained by dehydrochloric acid condensation of 6-hexanediol, 1,8-octanediol, etc., and phosgene, etc.

Examples of the organic diisocyanate (B) include hexamethylene diisocyanate (HMDI), xylylene diisocyanate (XDI), and lylene diisocyanate (TD).
I), known organic diisocyanate monomers such as 4,4'-diphenylmethane diisocyanate (MDI), and mixtures thereof, but especially when TDI and/or MDI is used, durability and running stability can be improved. The effect is remarkable.

Examples of the low molecular weight diol (C) to be reacted with the isocyanate group remaining after the polycarbonate polyol (A) and organic diisocyanate (B) are reacted include diethylene glycol, triethylene glycol, propylene glycol, 1.4-7'tanediol, etc. used.

The molecular weight of the polycarbonate polyurethane of the present invention is preferably 50,000 or more in weight average molecular weight in terms of polystyrene. If the molecular weight is less than 50,000, the strength of the magnetic layer will be insufficient and the continuous reproduction durability will deteriorate.

In addition to the above-mentioned polycarbonate polyurethane, the binder used in the present invention may be a mixture of those commonly used as binders for magnetic materials, and specifically, polyester polyurethane, polyether polyurethane, Examples include vinyl chloride-vinyl acetate copolymers, epoxy resins, cellulose resins, polyester resins, acrylic resins, rubber resins, and polyisocyanate compounds.

The binder is usually used in an amount of 10 to 50 parts by weight per 100 parts by weight of the magnetic material.
Use parts by weight.

In addition to the magnetic material and binder, the magnetic layer may contain abrasives such as aluminum oxide fine particles and chromium oxide fine particles, lubricants such as various fatty acids and fatty acid esters, and conductive carbon black, etc., as necessary. A conductivity imparting agent and the like can be contained.

It is desirable to use the abrasive in an amount of 1 to 20 parts by weight, preferably 1 to 10 parts by weight, based on 100 parts by weight of the magnetic material, from the viewpoint of improving continuous reproduction durability.

The lubricant is preferably contained in 1 to 10 parts by weight per 100 parts by weight of the magnetic material. If it is less than 1 part by weight, the effect as a lubricant will not be sufficiently exhibited, and if it is more than 10 parts by weight, the lubricant is likely to bleed out.

The conductivity imparting agent is used in an amount of 1 to 10 parts by weight per 100 parts by weight of the magnetic material.
It is preferable to contain it in parts by weight. If it is less than 1 part by weight, the surface electrical resistance of the magnetic recording medium tends to increase, and if it is more than 10 parts by weight, continuous reproduction durability tends to be poor.

In the present invention, the thickness of the magnetic layer is 0.4 to 1.0 μm.
It is necessary to do so. If the magnetic layer is thinner than 0.4 μm, the strength of the magnetic layer is insufficient and the continuous running durability deteriorates. If it is thicker than 1.0 μm, the difference between the two becomes large because the output voltage does not increase for short wavelength recording while the output voltage increases for long wavelength recording, and in the case of digital recording, the output voltage increases for long wavelength recording. When the output waveform and short wavelength recording are adjacent to each other, the output waveform is distorted and the peak deviates significantly from its original position, making it unsuitable for use as a large-capacity, high-density medium.

Further, the residual magnetic flux density of the magnetic layer needs to be 800 Gauss or more. If it is less than 800 Gauss, the output voltage will be small and accurate reading of records will not be possible.

Furthermore, the coercive force of the magnetic layer needs to be in the range of 800 to 1100 Oe. The coercive force of the magnetic layer is 800 O
If it is smaller than 1100 Oe, the output voltage when recording a short wavelength signal will be small, and if it is larger than 1100 Oe, the erasing characteristics will be poor, and if overwriting is performed, the already recorded signal will remain and it will be difficult to record the signal again. When reading, a problem arises in that signals recorded later cannot be read correctly.

In the present invention, as the non-magnetic support, polyesters such as polyethylene terephthalate, polyethylene,
Plastics such as polyolefins such as polypropylene, polycarbonate, polyphenylene sulfide, and polyimide are usually used, but non-magnetic metals, ceramics, paper, etc. may also be used depending on the purpose.

The magnetic recording medium of the present invention can be produced by, for example, combining the binder, the magnetic material, and, if necessary, an abrasive, a lubricant, a conductivity imparting agent, etc., together with an organic solvent such as methyl ethyl ketone, isobutyl ketone, cyclohexanone, or toluene, by ball milling. After mixing and dispersing using a mixing and dispersing machine such as a sand mill or two rolls to obtain a paint-like 6N composition, the paint-like composition is applied onto a non-magnetic support, dried, and heat-cured. It can be manufactured by

〔Example〕

Hereinafter, the present invention will be described in detail using Examples, but the present invention is not limited by the Examples unless the gist thereof is exceeded.

Example 1 Magnetic powder 100 parts by weight acicular co-
rFetox Coercive force 960 Oe Major axis diameter 0.5 μm Polycarbonate polyurethane elastomer 12.9 parts by weight A polycarbonate polyol obtained by dehydrochloric acid condensation of 1.6-hexanediol and phosgene is reacted with MDI to form a reaction product. 1. to the remaining isocyanate groups in the
Polyurethane elastomer obtained by reacting 4-butanediol, diethylene glycol, and triethylene glycol; weight average molecule it (polystyrene equivalent)
110,000 parts by weight Vinyl chloride-vinyl acetate copolymer 15.7 parts by weight Polyisocyanate compound 5.9 parts by weight Phosphoric ester dispersant 4 parts by weight Abrasive (aluminum oxide powder) 1.5 parts by weight Stearate ester
8 parts by weight Conductive carbon black 10 parts by weight A mixture of organic solvents such as methyl ethyl chloride and cyclohexanone 390 parts The above composition was mixed and dispersed using a sand mill, uniformly coated on a 75 μm square polyethylene terephthalate film, and dried. Thereafter, it was calendered and punched into a donut shape with a diameter of 3.5 inches to obtain a magnetic disk. The thickness of the magnetic layer was 0.64 μm.

The coercive force and residual magnetic flux density of the obtained magnetic disk were measured using a vibrating sample type magnetometer, and the thickness of the magnetic layer was measured using a stylus type surface roughness meter.

Table 1 also shows the D50 and short wavelength recording output voltage when recording and reproducing were performed at a position with a radius of 24.7 fins using a ferrite head with a head gap of 0.9 μm, rotating at 300 rpm. .

Note that D50 represents the recording density at which the output becomes 50% of the reproduced output when recording a long wavelength signal, and is a measure of the maximum recording density that can be realized as an apparatus. D50
If it is 25 kbpi or more, it can be said that it is suitable for recording at a higher density than before. Further, the output voltage must be sufficiently large compared to the amplifier noise, and is preferably 2 .mu. or more.

Further, Table 1 shows the results of continuous reproduction durability tests under similar conditions and the values of rotational torque due to friction between the magnetic layer and the head.

The continuous playback durability test was performed by holding an environment at a temperature of 45°C and a relative humidity of 80% for 7 hours, then increasing the temperature to an environment of 5°C and a relative humidity of 50% for 5 hours, maintaining this environment for 7 hours, and then holding the environment for 5 hours.
The test was carried out under periodic environmental changes, with one cycle of a total of 24 hours returning to the initial environment over time. Indicates that no scratches were observed, and × indicates that a decrease in output or the occurrence of scratches on the medium was observed before 100 hours had elapsed.

Example 2 Example 1 except that the thickness of the magnetic layer was 0.41 μm.
A magnetic disk was obtained in the same manner. The results are shown in Table 1.

Example 3 A magnetic disk was obtained in the same manner as in Example 1, except that TDI was used as the organic diisocyanate that was a component in the polyurethane elastomer, and the weight average molecular weight of the polyurethane elastomer was 80,000. The results are shown in Table 1.

Comparative Example 1 Magnetic powder was made of acicular Co-rFe20. and the thickness of the magnetic layer is 1.62μ
A magnetic disk was obtained in the same manner as in Example 1 except that m was used. The results are shown in Table 1.

Comparative Example 2 A magnetic disk was obtained in the same manner as in Example 1, except that the magnetic powder was acicular CO-γFe2O3 with a coercive cuff of 30 Oe and a major axis diameter of 0.8 μm. The results are shown in Table 1.

Comparative Example 3 Comparative Example 2 except that the thickness of the magnetic layer was 0.54 μm
A magnetic disk was obtained in the same manner. The results are shown in Table 1.

Comparative Example 4 Example 1 except that the thickness of the magnetic layer was 1.22 μm.
A magnetic disk was obtained in the same manner. The results are shown in Table 1.

Comparative Example 5 A magnetic disk was obtained in the same manner as in Example 1, except that a polyester polyol obtained by condensation of 1,4-butanediol and adipic acid was used instead of the polycarbonate polyol, which is a component in the polyurethane elastomer. Ta.

The results are shown in Table 1.

As is clear from Table 1, when the coercive force of the magnetic layer is lower than 800 Oe as in Comparative Examples 1.2.3, the output voltage is small when short wavelength signals are recorded. Further, even if the coercive force and the maximum residual magnetic flux density are the same as those of the example as in Comparative Example 4, when the thickness of the magnetic layer becomes thicker than 1.0 μm, the output voltage is sufficient but the D50 becomes worse.

In addition, when polyester polyurethane was used and polycarbonate polyurethane was not used as in Comparative Example 5, the rotational torque was high and the continuous regeneration durability was poor.
The magnetic layer peeled off during the test.

〔Effect of the invention〕

According to the present invention, a magnetic recording medium enables recording at a shorter wavelength than conventional magnetic recording media, enables high-density recording, has a large recording capacity, and has excellent continuous playback durability and running stability. can be obtained.

Procedural amendment (voluntary) Indication of the case Patent Application No. 27 61 of 1988, Reason for amending the name of the invention Mitsubishi (and 1 other person) 2-5-2 Marunouchi, Chiyoda-ku, Tokyo 10 Contents of the amendment (1) ) In the specification, page 11, line 13, "methyl ethyl kent" is corrected to "methyl ethyl ketone."

Claims (1)

[Claims] (1) A magnetic recording medium comprising a magnetic layer containing cobalt-containing magnetic iron oxide and a binder on a non-magnetic support, the binder containing polycarbonate polyurethane, and the thickness of the magnetic layer being 0.4 ~1.0μm, the residual magnetic flux density of the magnetic layer is 800 Gauss or more, and the coercive force of the magnetic layer is 80
A magnetic recording medium characterized in that it has a magnetic field strength in the range of 0 to 1100 Oe.