JPH10289439A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the yield and the durability of a product by synthesizing a ferromagnetic powder from a hydrothermal reaction, having a specified specific surface area by means of BET method and SiO2 adsorbed on the surface in the ratio of 0.5-2.0 to the ferromagnetic powder by wt.% to improve the dispersibility of the ferromagnetic powder. SOLUTION: The ferromagnetic powder having >=30 m<3> /g specific surface area by means of BET method and SiO2 adsorbed on the surface in the ratio of 0.5-2.0 to the ferromagnetic powder by wt.% is used. As the ferromagnetic powder, preferably a Co sticking iron oxide powder and further preferably a γ-Fe2 O3 synthesized from Fe(OH)3 by the hydrothermal reaction without passing through geothite as an intermediate material is applied. A magnetic coating film forming a magnetic layer is formed, for example, by adding the Co-sticking iron oxide, a binder (e.g. a vinyl chloride resin having a polar group), further preferably carbon black, alumina and a dispersant, mixed with an organic solvent such as methylethyl ketone, adjusted and applied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a high-density magnetic recording medium having particularly excellent electromagnetic conversion characteristics, product yield and durability.

[0002]

2. Description of the Related Art In recent years, in magnetic recording media, in particular, video tapes and floppy disks, magnetic powder having a small particle diameter and an increased coercive force has been used in order to increase the recording density. However, these magnetic powders are extremely difficult to disperse and are unstable even once dispersed, so that due to agglomeration and generation of agglomerated particles, insufficiently filled magnetic coatings, inhomogeneous It tends to develop a coating surface. For this reason, the S / N ratio is reduced due to the deterioration of the electromagnetic conversion characteristics, the track quality is deteriorated due to an increase in erasure failures (product yield is deteriorated due to an increase in extra pulse errors), and the durability is further likely to be reduced. Has disadvantages.

[0003] In response to such technical problems, extensive studies have been made on resins used as binders from the viewpoint of improving affinity for magnetic powder. For example, a resin in which a polar group such as a sulfonic acid group or a phosphoric acid group, an epoxy group, or a hydroxy group is introduced into a molecular structure has been practically used as a binder, but the dispersibility and dispersion stability of a ferromagnetic powder alone are not sufficient. Still not enough. Regarding the removal of agglomerated particles, it is necessary to remove even small agglomerated particles in order to achieve a high recording density, so the filter pore size is reduced. As a result, the solvent concentration after filtration becomes easier to increase than before filtration, and the occurrence of poor dispersion due to reagglomeration of ferromagnetic powder and solid powder due to solvent shock increases, and the frequency of filter clogging increases. As a result, the coating process becomes unstable, which is rather undesirable in terms of dispersibility and dispersion stability, and is still insufficient.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above situation, and improves the dispersibility and dispersion stability of ferromagnetic powder to maintain a uniform filling state of a magnetic coating film. It is another object of the present invention to provide a magnetic recording medium for high recording density, which has a good production yield (good track quality and low extra pulse level) and durability in a well-balanced manner.

[0005]

The present invention has the following arrangement to attain the above object. That is, in a magnetic recording medium having a magnetic layer formed by applying a magnetic coating liquid containing a ferromagnetic powder and a binder on a non-magnetic substrate, the ferromagnetic powder is synthesized from a hydrothermal reaction, and the BET method is used. When the specific surface area is 30 m ² / g or more, SiO ₂ is adsorbed on the surface and Si
The adsorption amount of O ₂ is 0.5% by weight based on the ferromagnetic powder.
The magnetic recording medium is a ferromagnetic powder of 2.0.

In the present invention, among the ferromagnetic powders, C
o Adhered iron oxide powder is preferred and applied. Further, γ-Fe ₂ O ₃ synthesized as an intermediate from Fe (OH) ₃ without passing through goethite by a hydrothermal reaction is preferably applied to the ferromagnetic powder.

The present invention has been made as follows. In a magnetic recording medium in which a magnetic layer is formed by applying a magnetic coating solution containing a ferromagnetic powder and a binder on a non-magnetic substrate, the ferromagnetic powder is synthesized by a hydrothermal reaction, and SiO ₂ is formed. By using the adsorbed ferromagnetic powder, carbon black to be added as necessary,
By adding a known binder such as a vinyl chloride resin or a urethane resin and a known dispersant to a vehicle containing all solid powders contained in a magnetic coating solution such as an abrasive in the same manner as in the related art, The dispersibility and dispersion stability of all the solid powders to be dispersed contained in the liquid in the liquid vehicle are improved, and the desired product yield (extra pulse ella level) and durability are improved. The headline was made. Hereinafter, the present invention will be described in detail including embodiments.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The ferromagnetic powder used in the present invention is:
It is synthesized from a hydrothermal reaction and has a specific surface area of 30 according to the BET method.
It is a ferromagnetic powder having m ² / g or more and adsorbed on the surface of SiO ₂ in an amount of 0.5 to 2.0 wt% with respect to the ferromagnetic powder. Examples of the ferromagnetic powder include conventionally known iron oxide-based magnetic powders such as Co-containing γ-Fe ₂ O ₃ and Co-containing γ-Fe ₃ O ₄ .

The ferromagnetic powder synthesized by the hydrothermal reaction is
Like γ-Fe ₂ O ₃ below, it becomes a dense crystal without vacancies, easily dispersed, and is effective in reducing the extra pulse level. That is, γ-F synthesized by a hydrothermal reaction
Since e ₂ O ₃ is synthesized from Fe (OH) ₃ as an intermediate without going through goethite, dehydration and sealing of goethite is not required in the synthesis process, so that branching of individual magnetic particles is small. Since it is a dense crystal having no voids due to dehydration, it is easier to disperse than γ-Fe ₂ O ₃ synthesized by a general camras method using goethite as an intermediate, and the extra pulse level is reduced. It is considered to be effective.

Further, adsorbing SiO ₂ to the ferromagnetic powder not only facilitates the dispersion of the magnetic paint, but also has the effect of improving the durability. It is thought that it is raising the nature.
In addition, the magnetic powder having a specific surface area of less than 30 m ² / g cannot achieve the purpose of increasing the recording density because it is difficult to reduce the extra pulse level.

As the binder of the present invention, known binders such as thermoplastic resins, thermosetting resins, and reactive resins are applied. Specific examples include vinyl chloride resin and urethane resin.

Among them, a vinyl chloride resin having a polar group,
Specifically, sulfonic acid group, phosphate group, carboxyl group,
A vinyl chloride resin containing an epoxy group or a hydroxy group is preferably applied. The applied vinyl chloride resin has a degree of polymerization of 100 to 500 and an average molecular weight of 1000 to 1000.
It is preferably in the range of 0, for example, copolymerizing a vinyl chloride monomer, a copolymer monomer containing an alkali salt of sulfonic acid or phosphoric acid, an epoxy group-containing monomer, a hydroxyl group-containing monomer and, if necessary, other copolymer monomers. Can be obtained by This copolymerization method is already known, and is disclosed in JP-A-60-235814 and JP-A-60-358814.
No. 238306, No. 60-238309, No. 60-2
No. 38309, No. 1-262626, No. 1-2
No. 6627 and the like. However, the above hydroxyl group may be supplied as a monomer, or may be generated by partial hydrolysis of a copolymer using a fatty acid vinyl such as vinyl acetate as another copolymer component monomer.
The amount of the vinyl chloride resin to be added is 1 to 20 parts by weight per 100 parts by weight of the ferromagnetic powder.

Various known solid powders are added to the magnetic recording medium of the present invention, if necessary, in addition to the above ferromagnetic powder.

One of the solid powders preferably used is carbon black. The carbon black to be applied is a so-called conductive carbon black for imparting conductivity (antistatic property) to the magnetic coating and, if necessary, a solid lubricant for reducing friction between the coating and the drive head. And carbon black for lubrication.

The conductive carbon black generally has a small particle size (30 nm or less) and a large specific surface area (100 m ² /
g or more) Those having a developed structure are preferably used. Conversely, carbon black for lubrication has a large particle size (50 nm or more) and a small specific surface area (100 m ² /
g or less) Those having little development of the structure are preferably used. The total amount of these carbon blacks is 1 to 20 parts by weight per 100 parts by weight of the ferromagnetic powder.

In the present invention, it is preferable to add an abrasive. As the abrasive, specifically, α-alumina, α-alumina
Known materials such as iron oxide can be applied, and usually 0.05 μm to 2 μm.
μm is used, particularly preferably 0.1 μm.
Those having a size of μm to 1 μm are used. The addition amount is usually 1 to 20 parts by weight per 100 parts by weight of the ferromagnetic powder.

In the magnetic recording medium of the present invention, in addition to the above, various additives such as a dispersant, a lubricant and the like are used as necessary. Specifically, a silane coupling agent, a titanium coupling agent, lecithin or the like can be added as a dispersant, and a fatty acid ester, silicone oil, modified silicone oil, paraffin, wax, or the like can be added as a lubricant regardless of solid or liquid. .

The magnetic recording medium of the present invention is manufactured as follows. The magnetic coating liquid for forming the magnetic layer is prepared by adding the above-described ferromagnetic powder such as Co-coated iron oxide, a binder such as a vinyl chloride resin having the polar group, more preferably carbon black, alumina and a dispersant to an organic solvent. For example, it is prepared by mixing with methyl ethyl ketone, methyl isobutyl ketone, toluene, cyclohexanone, tetrahydrofuran and the like. At this time, it is common to add a binder such as the aforementioned thermoplastic resin, thermosetting resin, or reactive resin, or a conventionally known additive alone or in combination, if necessary.

In kneading and dispersing the above components, the ferromagnetic powder and each component are all charged to the dispersing machine simultaneously or individually. As the disperser, for example, a ball mill, a sand grinder, a high-speed impact mill, a pressure kneader, an ultrasonic mixer, a homogenizer, a planetary mixer, a high-speed disper, or the like can be used alone or in combination.

The obtained magnetic coating liquid is applied to a non-magnetic substrate. As the nonmagnetic substrate, a plastic film is generally used in applications such as a magnetic tape and a floppy disk. Specifically, a polyethylene terephthalate polymer film, a polyethylene naphthalate polymer film, or the like is preferably used. Such a film is preferably a biaxially oriented film.

The surface (one side or both sides) of such a nonmagnetic substrate
A conventionally known coating method can be used for applying the magnetic coating liquid to the coating liquid. As an application method, for example, an air doctor coat, a blade coat, an air knife coat, a squeeze coat, an impregnation coat, a reverse roll coat, a gravure coat, a die coat and the like can be used. The coating amount is preferably in a range where the thickness of the coating film (magnetic layer) after drying and calendering treatment is 0.3 to 6 μm, and is determined depending on the use, shape, specifications and the like of the magnetic recording medium.

The post-coating treatment may be performed, if necessary, by subjecting the ferromagnetic powder to a conventionally known treatment such as an orientation treatment or a non-orientation treatment, a calendar treatment, a curing treatment, and a punching treatment.
It is a desired type of magnetic recording medium.

The magnetic recording medium of the present invention has excellent electromagnetic conversion characteristics, product yield and durability as shown in the following examples, and is useful as, for example, a magnetic tape or a floppy disk with a high recording density. .

[0024]

EXAMPLES Examples and comparative examples will be described below. Incidentally, "parts" are parts by weight in the example, the adsorption amount of SiO ₂ are percentages by weight with respect to Shigerusei powder. The characteristics of the magnetic recording medium were measured by the following method.

1) Extra pulse (EP) level The evaluation of the electromagnetic conversion characteristics was performed for each sample using a 3.5-inch floppy disk drive (FDDMPF-
73W), the extra pulse level was measured, and the measurement was performed at this extra pulse level. The extra pulse level mentioned here is a value obtained by recording a 2f signal on 10 tracks 70 to 79 by a predetermined drive, performing DC erasure, and dividing the peak value of the reproduced signal by the average signal amplitude of the same track. (Extra pulse) was obtained, and the values from the worse of the extra pulse to the tenth value from each track were totaled and averaged and defined.

2) Accelerated durability The drive was operated under a room temperature environment (temperature: 20 to 25 ° C., humidity: 50) under the condition of high speed rotation (1500 rpm) and high load (80 g weight).
(Up to 65% RH), and the media surface (sliding trace, peeling) after driving for 2 hours was visually observed and ranked on a scale of 5 out of 5 points. Judgment is 5 points when there is no change in the media, 4 points when only weak sliding marks are observed, 3 points when strong sliding marks are observed, and when weak peeling is also observed, 2 points and 1 point respectively when strong peeling was observed
This was done by scoring as points.

3) Cycle Durability The temperature and humidity conditions of the following four cases are switched every six hours in the following order, and a floppy disk drive is installed in a constant temperature layer operated one cycle a day, and a continuous rotation test is performed. went. [25 ° C, 50% RH] → [52 ° C, 80% RH] →
[25 ° C., 20% RH] → [5 ° C., humidity free] The continuous rotation test uses a 3.5-inch FDD FD1337C made by NEC for a floppy disk drive, and has a normal rotation speed (360 rpm) and a normal tension. , The head was loaded on the outer circumference (track 00) of the sample magnetic disk and continuously rotated and run on the same track. The evaluation was performed by visually observing the coating film surface every 12 hours and evaluating the durability by the total number of rotations (the number of passes) until peeling occurred on any one surface of the coating film. It should be noted that the time for checking and the like was subtracted, and converted into one day = 500,000 passes. The result was represented by the average of n = 3 passes (10,000 passes).

Example 1 The following components were charged into a sand grinder together with glass beads in the following composition, and kneaded and dispersed for 2 hours. The Co-containing iron oxide powder is the above-mentioned γ-Fe ₂ O ₃ powder synthesized as an intermediate from Fe (OH) ₃ by a hydrothermal method without passing through goethite. The unit of the coercive force is Oersted (oe). (Components and Composition) Co-containing iron oxide powder (specific surface area 30 m ² / g, hydrothermal synthesis, 100 parts SiO ₂ adsorption 2.0 wt%, coercive force 720 oe) Carbon black (Ketjen Black EC manufactured by Lion Akzo) 8 parts Abrasive (HIT50 manufactured by Sumitomo Chemical Co., Ltd.) 15 parts Dispersant (lecithin) 2 parts PVC resin containing sulfonic acid group (MR-110 manufactured by Zeon Corporation) 10 parts Solvent (mixed solvent of toluene and cyclohexanone) 200 parts

Next, while being separated from the glass beads and stirred with a high-speed disper, the following composition prepared in advance was added as a diluent to prepare a magnetic paint. (Components and Composition) Polyurethane (Sten 5701F manufactured by Kyowa Hakko Co., Ltd.) 8 parts Polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) 5 parts Lubricant (mixture of butyl stearate and oleyl oleate) 3 parts Solvent (mixed solvent of toluene and cyclohexanone) 100 parts) The obtained nourishing paint was applied to a 75 μm polyethylene terephthalate film after drying and calendering to a coating thickness of 1.0.
It was applied on both sides to a thickness of μm. Next, drying was performed, the surface of the magnetic layer was smoothed by calendering treatment, and heating and curing were performed to prepare a magnetic recording medium.

After a disk having a diameter of 90 mm was punched out of the obtained magnetic recording medium and polished, a floppy disk sample was prepared by a known method.

[Example 2] A floppy disk sample having the same structure as in Example 1 except that the amount of adsorbed SiO ₂ of the Co-containing iron oxide powder was changed to 0.5 wt% in Example 1 was used. Created in the same way.

Comparative Example 1 In Example 1, the Co-containing iron oxide powder was replaced with the Co-containing iron oxide powder (specific surface area: 22 m ² /
g, a hydrothermal synthesis method, a floppy disk sample having the same configuration as in Example 1 was prepared in the same manner as in Example 1, except that the amount of SiO ₂ adsorption was 1.0 wt% and the coercive force was changed to 720 oe.

Comparative Example 2 In Example 1, the Co-containing iron oxide powder was replaced with the Co-containing iron oxide powder (specific surface area: 30 m ² /
g, a hydrothermal synthesis method, no addition of SiO ₂ , and a coercive force of 720 oe) were used, and a floppy disk sample having the same configuration as in Example 1 was prepared in the same manner as in Example 1.

Comparative Example 3 In Example 1, the Co-containing iron oxide powder was replaced with a Co-containing iron oxide powder (specific surface area: 30 m ² /
g, Kamurasu synthesis method, SiO ₂ is not added, the coercive force 720o
A floppy disk sample having the same configuration as in Example 1 was prepared in the same manner as in Example 1 except for changing to e).

[Comparative Example 4] Except that the Co-containing iron oxide powder was changed to a Co-containing iron oxide powder (specific surface area: 30 m ² / g, Camras synthesis method, SiO ₂ adsorption amount: 1.0%, coercive force: 720 oe) A sample of a floppy disk having the same configuration as in Example 1 was prepared in the same manner as in Example 1. Table 1 shows the evaluation results of the floppy disks obtained in Example 1 to Comparative Example 4 described above.

[0036]

[Table 1]

From Table 1, it can be seen that the catalyst was synthesized from the hydrothermal reaction of the present invention.
And the specific surface area by the BET method is 30 m ^Two/ G or more
0.5 to 2.0 wt% SiO based on ferromagnetic powder
_TwoThe use of ferromagnetic powder with adsorbed
Exchanging characteristics, and both operating environment and sliding durability are sufficient.
To be able to obtain a magnetic recording medium with satisfactory product yield
You can check.

[0038]

As described above, according to the present invention, the conventional ferromagnetic powder is synthesized by a hydrothermal reaction and has a specific surface area of 3
0 m ² / g or more, 0.5 to 0.5
Only by using ferromagnetic powder to which 2.0 wt% of SiO ₂ is adsorbed, the dispersibility of the ferromagnetic powder of the magnetic paint is improved, the inside of the coating film and the surface are made uniform, and excellent electromagnetic conversion characteristics and tracks are achieved. This realizes a high-density magnetic recording medium having high quality and durability, and is very advantageous in that it can be directly used in a conventional manufacturing process.

Claims (3)

[Claims] 1. A magnetic recording medium comprising a magnetic layer formed by applying a magnetic coating solution containing a ferromagnetic powder and a binder on a non-magnetic substrate, wherein the ferromagnetic powder is synthesized from a hydrothermal reaction, BE
When the specific surface area by T method is 30 m ² / g or more,
A magnetic recording medium, wherein the magnetic recording medium is a ferromagnetic powder in which O ₂ is adsorbed and the amount of adsorbed SiO ₂ is 0.5 to 2.0 by weight% based on the ferromagnetic powder. 2. The magnetic recording medium according to claim 1, wherein the ferromagnetic powder is a Co-coated iron oxide powder. 3. The ferromagnetic powder reacts with Fe (O) by a hydrothermal reaction.
_3. The magnetic recording medium according to claim 1, wherein H) is γ-Fe ₂ O ₃ synthesized without passing through goethite as an intermediate from ₃ ).