JPS61202332A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the stability of a magnetic paint and the orientation stability of ferromagnetic powder by compounding the needle-like ferromagnetic powder having <=0.25mum long axial length and the hydrophobic inorg. pulverous powder having 5-50mmu average grain size of the primary particles and the BET specific surface area ranging 50-200m<2>/g with a magnetic layer. CONSTITUTION:The magnetic layer contains the needle-like ferromagnetic powder having <=0.25mum long axial length, the hydrophobic inorg. pulverous powder having 5-50mmu average particle size of the primary particles and the BET specific surface area ranging 50-200m<2>/g, polishing material and lubricating agent. The thixotropy of the magnetic paint is thereby improved and the setting of the magnetic paint components is prevented, by which the magnetic paint is stabilized and the decrease in the orientation of the ferromagnetic material powder during the time since the needle-like ferromagnetic material powder is oriented by subjecting the magnetic paint coated on a non-magnetic substrate to a magnetic field orientation treatment until the magnetic layer dries is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention particularly relates to magnetic recording media with improved electromagnetic conversion characteristics.

[Background of the Invention] Typical examples of magnetic recording media include audio tapes, video tapes, and floppy disks.

Magnetic recording media generally consist of a nonmagnetic support made of a high-strength resin film such as polyethylene terephthalate resin, and ferromagnetic powder dispersed in a binder provided on the nonmagnetic support. It has a basic structure consisting of a magnetic layer.

Such magnetic recording media are generally produced by applying a magnetic paint containing dispersed ferromagnetic powder onto a non-magnetic support, and then magnetically orienting the ferromagnetic powder while the coated layer is still wet. Manufactured by subjecting it to a treatment.

In magnetic recording media, for example, in video cassette tapes, methods such as shortening the recording wavelength and narrowing the track width are used to increase the recording density. is required. Furthermore, in the case of audio tapes as well, there is basically a demand for tapes that have good frequency characteristics and exhibit excellent electromagnetic conversion characteristics.

[Prior art and its problems] A common method for improving the electromagnetic conversion characteristics of a magnetic recording medium is to reduce the particle size of the ferromagnetic powder used.

However, when using a ferromagnetic powder with a small particle size, there is a problem in that it is very difficult to disperse the ferromagnetic powder in a magnetic paint. Furthermore, after applying magnetic paint on a non-magnetic support and subjecting it to magnetic field orientation treatment, a phenomenon was observed in which the orientation of the ferromagnetic powder deteriorated until the magnetic layer was completely cured. There is a problem that the electromagnetic conversion characteristics of the obtained magnetic recording medium are not sufficiently improved.

On the other hand, the applicant of the present invention has proposed a magnetic layer containing magnetic powder, an abrasive with a Mohs hardness of 6 or more, nyloidal silica, and fatty acids and fatty acid esters, mainly for the purpose of improving the durability of the magnetic layer of a magnetic recording medium. An invention relating to a recording medium has already been filed (see Japanese Patent Application Laid-Open No. 162128/1982). The magnetic recording medium obtained by this invention has good durability of the magnetic layer, and for example, the still life of a video tape is improved. It is an excellent all-in-one recording medium in that it is long and there is little wear on the magnetic head. However, there is still room for improvement regarding electromagnetic conversion characteristics.

[Object of the Invention] An object of the present invention is to provide a magnetic recording medium with particularly improved electromagnetic conversion characteristics.

More specifically, the present invention provides a magnetic recording medium that exhibits good electromagnetic conversion characteristics by improving the stability of a magnetic paint and further improving the orientation stability of ferromagnetic powder subjected to magnetic field orientation treatment. The purpose is to

A further object of the present invention is to provide a magnetic recording medium with improved electromagnetic conversion characteristics and improved durability.

[Summary of the Invention] The present invention provides a magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic powder dispersed in a binder on the support, wherein the magnetic layer has a major axis length. Acicular ferromagnetic powder with a diameter of 0.25 μm or less, an average particle diameter of primary particles of 5 to 50 m
The magnetic recording medium contains a hydrophobic inorganic fine powder having a BET specific surface area of 50 to 200 rn'/g, an abrasive, and a lubricant.

The cutoff value of the magnetic layer surface of the magnetic recording medium of the present invention is 0.
Center line average layer thickness at 0.08 mm is 0.015-010
It is preferable to set it as the range of 23 m.

[Effects of the Invention] The magnetic recording medium of the present invention exhibits excellent electromagnetic conversion characteristics due to the high orientation stability of the ferromagnetic powder in the magnetic layer. This is thought to be because the magnetic paint used has favorable thixotropy, and the orientation of the ferromagnetic powder is likely to be maintained even after the applied magnetic layer is subjected to magnetic field orientation treatment.

Furthermore, since the magnetic layer of the magnetic recording medium of the present invention contains an abrasive and a lubricant, its durability is also good.

[Detailed description of the invention]

As mentioned above, the known magnetic recording medium basically consists of a non-magnetic support and a magnetic layer provided on the surface thereof, and the magnetic recording medium of the present invention also basically has the same structure. It is something to take.

Furthermore, while known magnetic recording media are generally manufactured by forming a magnetic layer on one surface of a sheet or film-like support by a coating method, the magnetic recording medium of the present invention can also be manufactured by a similar method. be able to.

As the material forming the non-magnetic support of the magnetic recording medium of the present invention, those normally used as materials for the support of magnetic recording media can be used.

Examples of the material include films or sheets made of synthetic resins such as polyethylene terephthalate, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamideimide, and polyimide, and metal foils such as aluminum foil and stainless steel foil.

The non-magnetic support generally has a length of 3 to 504 m, preferably 5 m.
The thickness is ~30 Bm.

For example, for audio tapes, those having a thickness of 3 to 1108 Lm are used, and for video tapes, those having a thickness of 5 to 50 JLm are used.

A back coat layer (barking layer) may be provided on the side of the nonmagnetic support on which the magnetic layer is not provided.

The magnetic layer is a layer formed on the surface of the non-magnetic support, and the magnetic layer is basically a layer made of ferromagnetic powder dispersed in a binder.

The main feature of the present invention is that the magnetic layer contains both an acicular ferromagnetic fine powder having a specific major axis length and a specific hydrophobic inorganic fine powder, and further contains an abrasive and a lubricant. That is.

That is, although the durability of the magnetic layer is improved by the invention described in JP-A-57-162128, there is still room for improvement in the electromagnetic conversion characteristics as described above.

As a result of further studies aimed at improving the electromagnetic conversion characteristics of the magnetic recording medium having the above-mentioned configuration, the present inventor discovered that acicular ferromagnetic powder with a specific major axis length or less and a specific hydrophobic inorganic powder By using it in combination with powder, it is possible to improve the stability of magnetic paint containing acicular ferromagnetic powder, and also to prevent agglomeration of acicular ferromagnetic powder in the magnetic paint. I found out. In addition, the combination described above makes it easier to orient the acicular ferromagnetic powder during magnetic field orientation treatment, and furthermore, by improving the thixotropic properties of the magnetic paint based on the combination of hydrophobic inorganic powder, magnetic field orientation treatment can be performed. It has been found that the deterioration of the orientation of the acicular ferromagnetic powder during the period from when the magnetic layer is dried can be prevented, and the electromagnetic conversion characteristics of the magnetic recording medium are ultimately improved.

Therefore, the shape of the ferromagnetic powder used in the magnetic recording medium of the present invention needs to be acicular, and the long axis length of the acicular ferromagnetic powder is 0.25 μm or less (preferably 0.25 μm or less).
．． 0.05 to 0.25 μm) 0 If a commonly used ferromagnetic powder with a long axis length larger than 0.25 μm is used, even if M aqueous inorganic fine powder is used in combination, For example, high playback output cannot be obtained with video tapes.

Further, in the present invention, it is preferable to use acicular ferromagnetic powder having an average acicular ratio generally in the range of 2 to 20, particularly in the range of 3 to 15. Even if a ferromagnetic powder with an average acicular ratio of less than 2 is subjected to magnetic field orientation treatment, the electromagnetic conversion characteristics will hardly improve. The ferromagnetic powder may not be dispersed smoothly.

An example of acicular ferromagnetic powder is Fe*Oa.

γ-Fe, 03. It is particularly preferred to use acicular ferromagnetic alloy fine powder, which may include cobalt-containing γ-iron oxide, ferromagnetic alloy fine powder, modified barium ferrite and modified strontium ferrite.

An example of an acicular ferromagnetic alloy powder is one in which the metal content in the ferromagnetic alloy powder is 75% by weight or more, and 80% by weight or more of the metal content is at least one ferromagnetic metal or alloy (e.g., Fe). , Co, Ni.

Fe-Co, Fe-Ni, Co-Ni, Co-Ni-
Fe), and other components (e.g., AJI, Si, S, Sc, Ti, V, C) within a range of 20% by weight or less of this metal content.
r, Mn, Cu, Zn, Y, Mo, Rh, Pd, Aμ,
Sn, Sb, Te.

Ba, Ta, W, Re, Au, Hμ, Pb, Bi, La
, Ce, Pr, Nd, B, P). Furthermore, the ferromagnetic metal or alloy may contain a small amount of water, hydroxide, or oxide, and methods for producing these acicular ferromagnetic alloy powders are already known.

The magnetic layer of the magnetic recording medium of the present invention needs to contain a hydrophobic inorganic fine powder having a roughly specific average particle diameter of primary particles and a specific specific surface property. By blending a specific hydrophobic inorganic fine powder into the magnetic layer of the medium, the thixotropy of the magnetic paint is improved and precipitation of magnetic paint components is prevented, thereby stabilizing the magnetic paint. After the applied magnetic paint is subjected to a magnetic field orientation treatment to orient the acicular ferromagnetic powder, deterioration in the orientation of the ferromagnetic powder can be prevented while the magnetic layer dries.

The hydrophobic inorganic fine powder contained in the magnetic layer has an average primary particle diameter of 1 to 50 mg (preferably 5 to 4 mg).
0 muL) and the BET specific surface area is 50
~200rn'/g (preferably 70~170rn'/g
'/g) is used. This hydrophobic non-molecular fine powder can be produced using a known method such as bonding a methyl group to the surface of a powder particle. Note that it is also possible to use a mixture of hydrophobic Ja fine powder and steamer fine powder that has not been subjected to hydrophobic treatment.

Examples of such hydrophobic inorganic fine powders include particles of finely powdered silica, usually referred to as colloidal silica, which are produced by combustion hydrolysis of silicon tetrachloride in the gas phase. Examples include those that have been subjected to hydrophobic treatment by introducing a methyl group or the like to the surface, and those that have been subjected to hydrophobic treatment of fine powder of an oxide such as alumina. In particular, it is preferable to use finely powdered hydrophobic silica.

The blending ratio of the above hydrophobic inorganic fine powder is 1 to ferromagnetic powder.
The amount is generally 0.5 to 10 parts by weight, preferably 1 to 8 parts by weight, particularly preferably 1 to 5 parts by weight. If it is less than 0.5 parts by weight, it may not be sufficiently effective. On the other hand, if it exceeds 10 parts by weight, the viscosity of the magnetic paint may increase and it may not be possible to apply it well, but it may be relatively The blending ratio of other components such as ferromagnetic powder may become low, and the electromagnetic conversion characteristics may not be sufficiently improved.

Furthermore, the magnetic recording medium of the present invention contains an abrasive and a lubricant in the magnetic layer. Abrasives and lubricants are
Those commonly used can be used.

Examples of abrasive materials are α-Au20, 5iC1Cr20
3 and α-Fe20. These can be used alone or in combination. In particular, it is preferable to use an abrasive material with a Mohs hardness of 6 or more.

The abrasive is generally added in an amount of 0.2 to 10 parts by weight per 100 parts by weight of the ferromagnetic powder.

Examples of lubricants include fatty acids, higher alcohols, fatty acid esters, mineral oils, animal and vegetable oils, olefin low polymers, and fine powder lubricants (especially those with an average particle size of 10 to 300 m).
JL carbon black), and these can be used alone or in combination. In particular, it is preferable to use a combination of a fatty acid (eg, oleic acid, stearic acid) and a fatty acid ester (eg, butyl stearate). It is added in an amount of 2 to 10 parts by weight.

The above-mentioned acicular ferromagnetic powder, hydrophobic inorganic fine powder, abrasive material, and lubricant form a magnetic layer while being dispersed in a binder.

Examples of binder components used include cellulose derivatives (e.g., nitrocellulose, cellulose acetate, cellulose acetate), vinyl chloride/vinyl acetate copolymer resins (
Examples, vinyl chloride/vinyl acetate copolymer, vinyl chloride/vinyl acetate/vinyl alcohol copolymer, vinyl chloride/vinyl acetate/maleic anhydride copolymer), vinylidene chloride resin (e.g., vinylidene chloride/vinyl chloride copolymer) polymer, vinylidene chloride/acrylonitrile copolymer), polyester resin (e.g., alkyd resin, linear polyester),
Acrylic resin (e.g., acrylic acid/acrylonitrile copolymer, methyl acrylate/acrylonitrile copolymer)
, polyvinyl acetal resin, polyvinyl butyral resin, phenoxy resin, epoxy resin, butadiene/acrylonitrile copolymer resin, polyurethane resin, and urethane epoxy resin, which may be used alone or in combination. can.

In particular, it is preferable to use a combination of a polyurethane resin and a vinyl chloride Φ vinyl acetate copolymer.

When a polyurethane resin and a vinyl chloride/vinyl acetate copolymer are used in combination as a binder, the durability of the magnetic layer is further improved by using a polyisocyanate compound as a hardening agent.

The magnetic layer of the magnetic recording medium of the present invention has a center line average roughness (Ra value) of 0.08 mm at a cutoff value of 0.08 mm.
It is preferably in the range of 0.015 to 0.023 μm,
When a magnetic paint containing 11iIi aqueous inorganic fine powder is applied onto a non-magnetic support by a normal method, the dispersibility of the acicular ferromagnetic powder in the magnetic paint is good, so the Ra value is lower than that of a normal magnetic layer. However, by further smoothing using a super calender roll, the Ra value can be set to a value smaller than 0.015 to 0.02.
It can be in the range of 3 parts m.

By setting the Ra value within the above range, the electromagnetic conversion characteristics are further improved.

The magnetic layer of the present invention includes ferromagnetic powder, aqueous inorganic fine powder,
In addition to the abrasive, lubricant, and binder, carbon, various dispersants, antistatic agents, and the like may of course be included.

The above magnetic layer components are kneaded together with an organic solvent to form a magnetic paint. Kneading can be carried out by a conventional method.

The magnetic paint prepared in this way is applied to the surface of the support to form a coating layer, and then, before the coating layer is dried and solidified, a magnetic field is applied to it to orient it, and then it is dried. It can be obtained by subjecting the coating layer to surface smoothing treatment such as calendering, if desired.

Next, Examples and Comparative Examples of the present invention will be shown.

Note that the expression "1 part" shown below means "part by weight" unless otherwise specified.

[Example 1] 100 parts of acicular ferromagnetic alloy powder (Fe-
Ni alloy, Ni content = 5% by weight, average long axis length: 0.2I
Lm, average acicular ratio: lO/l) Vinyl chloride-vinyl acetate/vinyl alcohol copolymer 11 parts (manufactured by Nippon Zeon ■, 40OXll0A) Polyurethane resin
11 parts (manufactured by Nippon Polyurethane, N-2
301) Hydrophobic silica 2 parts (manufactured by Nippon Aerosil, product name: Aerosil R-972 Average particle size: 16 parts BET specific surface [120±30m''/g) Carbon black 1 part (average particle size 401Lm)
) α-A 20 pieces (Mohs hardness = 9) 1 part stearin # 1 part olein m
1 part butyl stearate 1 part methyl ethyl ketone
After cross-dispersing 500 parts of each of the above components in a batch type sand grinder for 6 hours, polyisocyanate (
A magnetic paint was prepared by dissolving 8 parts of Coronate L (trade name, manufactured by Nippon Polyurethane Co., Ltd.) in 100 parts of methyl ethyl ketone, followed by cross-dispersion for 30 minutes, and filtration with a filter having an average pore size of Iμ, m.

Apply the above coating solution to 14μ, m polyethylene terephthalate)
(PET) film is coated to a dry film thickness of 51, m, and while the film is not dry, it is oriented using an electromagnetic field, and then dried, with a cut-off value of 0.08 m.
Calendar processing was performed so that the center line average roughness (Ra value) of m was 0.017 parts m. This was slit into 1/2 inch width to produce a VH5 videotape.

Note that the center line average roughness (Ra value) is the value at a cutoff value of 0.08 mm measured using a stylus type surface roughness meter (manufactured by Tokyo Seimitsu ■, Surfcom 800A type).

The following characteristics of the videotape obtained by the above method were measured and the results are shown in Table 1.

(a) Hm5 ko using a square specific vibration sample type magnetometer (manufactured by Toei Kogyo)
The Br/Bm value at e was measured.

(b) Recording wavelength 1 when the output level of the playback output reference tape is OdB
The reproduction output level in μm was measured. Each measured value was shown as a relative value when the cassette tape manufactured in Comparative Example 1 was used as a reference tape, and the measured value of this tape was defined as Od'B.

The reproduction output was measured by attaching a ferrite head to a VTR (V-500D) manufactured by Toshiba ■ and running the tape at half the normal tape running speed.

[Comparative Example 1] A VHS videotape was produced in the same manner as in Example 1 except that hydrophobic silica was not used.

Table 1 shows the squareness ratio and reproduction output of the obtained videotape.

L Comparative Example 2 A VH3 type video was produced in the same manner as in Example 1 except that acicular ferromagnetic alloy powder with a major axis length of 0.3 JLm was used instead of the acicular ferromagnetic alloy powder with a major axis length of 0.2 μm. manufactured the tape.

Table 1 shows the squareness ratio and reproduction output of the obtained videotape.

(Example 2J A VH3 type videotape was manufactured in the same manner as in Example 1 except that the amount of hydrophobic silica was changed to 4 parts. The squareness ratio and reproduction output of the obtained videotape are shown in Table 1. Describe it.

[Example 3] A VH3 type videotape was produced in the same manner as in Example 1 except that the amount of hydrophobic silica was changed to 8 parts. Table 1 shows the squareness ratio and reproduction output of the obtained videotape.

[Example 4] VH5 was prepared in the same manner as in Example 1 except that calender treatment was performed so that the Ra value was 0.025 μm.
A model videotape was manufactured. Table 1 shows the squareness ratio and reproduction output of the obtained videotape.

Table 1 Square shape ratio Reproduction output (dB) Example 1 0.82 +4 Comparative example 1
0.77 0 same 2 0.79
-1 Example 2 0.82
+2 same 3 0.82
+1 same 4 0.82
+0.5 From the results shown in Table 1, it is clear that the videotape of the present invention has a high squareness ratio and good orientation of the acicular ferromagnetic alloy powder. It is also clear that the reproduction output is high and the electromagnetic conversion characteristics are good.

On the other hand, the videotape obtained in Comparative Example 1 did not contain hydrophobic silica, so the squareness ratio was low, the orientation of the acicular ferromagnetic alloy powder was poor, and the electromagnetic conversion characteristics were poor. It is understood that the improvement is also insufficient. Furthermore, Comparative Example 2 using acicular ferromagnetic alloy powder with a long major axis length
It can be seen that the videotape obtained had a low squareness ratio and a low playback output, the orientation of the acicular ferromagnetic alloy powder was not good, and the electromagnetic conversion characteristics were not sufficiently improved.

Patent applicant: Fuji Photo Film Co., Ltd. Agent
Patent Attorney Yasushi Yanagawa Procedural Amendment May 2, 1985 1985 Patent Application No. 42417 2 Name of the invention Magnetic recording medium 3 Relationship with the person making the amendment Patent applicant name (520) Fuji Photo Film Co., Ltd. 4, agent address: 8 Mitsuya Yotsuya Building, 2-14 Yotsuya, Shinjuku-ku, Tokyo
Floor 6: Number of inventions increased by amendment None 7: Subject of amendment: Column 8 of “Detailed Description of the Invention” in the description, Contents of amendment We will correct it as follows.

Record that's all

Claims (1)

[Claims] 1. A magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic powder dispersed in a binder on the support, wherein the magnetic layer has a major axis length. Acicular ferromagnetic powder of 0.25 μm or less, average particle diameter of primary particles of 5 to 50 mμ, B
A magnetic recording medium comprising a hydrophobic inorganic fine powder having an ET specific surface area in the range of 50 to 200 m^2/g, an abrasive, and a lubricant. 2. The magnetic recording medium according to claim 1, wherein the center line average roughness of the surface of the magnetic layer at a cutoff value of 0.08 mm is in the range of 0.015 to 0.023 μm. 3. The magnetic recording medium according to claim 1 or 2, wherein the hydrophobic inorganic fine powder is hydrophobic silica. 4. The method according to claim 1 or 2, wherein the hydrophobic inorganic fine powder is contained in an amount of 0.5 to 10 parts by weight per 100 parts by weight of the acicular ferromagnetic powder. magnetic recording medium. 5. The long axis length of the acicular ferromagnetic powder is 0.05 to 0.25μ
3. The magnetic recording medium according to claim 1 or 2, wherein the magnetic recording medium is in the range of m. 6. The magnetic recording medium according to claim 5, wherein the acicular ferromagnetic powder has an acicular ratio in the range of 2 to 20. 7. The magnetic recording medium according to claim 1 or 2, wherein the acicular ferromagnetic powder is an acicular ferromagnetic alloy powder. 8. The magnetic recording medium according to claim 1 or 2, wherein the abrasive has a Mohs hardness of 6 or more. 9. The magnetic recording medium according to claim 1 or 2, wherein the lubricant contains a fatty acid and/or a fatty acid ester.