JP3521002B2 - Magnetic recording medium and method for manufacturing the same - Google Patents

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 such as a magnetic tape and a method for manufacturing the same, and in particular, it is formed by applying a magnetic coating material mainly containing a ferromagnetic powder and a binder onto a non-magnetic support. The present invention relates to a coating type magnetic recording medium having a magnetic layer and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, in a coating type magnetic recording medium, a magnetic paint prepared by dispersing and kneading a ferromagnetic powder, a binder, a dispersant, a lubricant and the like in an organic solvent is used as a non-magnetic support such as a polyester film. The magnetic layer is formed by applying the composition onto the magnetic layer.

In such a coating type magnetic recording medium, in order to achieve high performance corresponding to high density recording, the ferromagnetic powder is being miniaturized and a ferromagnetic powder having a large specific surface area is used. Is starting to appear. In addition, ultrafine particles of metals having excellent magnetic properties (for example, Fe, Ni, Co, etc.) and their alloys have come to be used as ferromagnetic powders.

By the way, in a coating type magnetic recording medium, a ferromagnetic powder having an extremely fine particle diameter is highly dispersed in a binder resin to improve the surface property of the magnetic layer to improve electromagnetic conversion characteristics. At the same time, it is required to improve the durability of the magnetic coating film.

That is, in the coating type magnetic recording medium, how well the ferromagnetic powder contained in the magnetic layer is dispersed and how well it is combined with the binder are very important problems. Moreover, the durability of the magnetic coating film is impaired unless the binder itself is sufficiently crosslinked and cured.

Therefore, conventionally, in order to meet such demands, addition of a dispersant such as lecithin into a magnetic coating material, introduction of a polar group into a binder, and selection of a curing agent have been carried out.

However, when an attempt is made to disperse a fine ferromagnetic powder having a specific surface area of 45 m ² / g or more in a magnetic coating material, such a fine ferromagnetic powder has a large cohesive force, so that the above-mentioned dispersant is used. In reality, it is difficult to secure sufficient dispersibility only by adding the above or introducing a polar group into the binder.

When a dispersant such as lecithin is used, since the affinity between the dispersant and the binder is poor, the reinforcing effect at the interface is insufficient and the coating strength (durability) is reduced. It tends to deteriorate. The coating strength may also not be sufficient depending on the hardener that crosslinks the binder.

[0009]

The object of the present invention is to improve the dispersibility even when using a large ferromagnetic powder having a specific surface area of 45 m ² / g or more, excellent magnetic conversion characteristics of the magnetic coating film, and A magnetic recording medium having sufficient durability and a method for manufacturing the same.

[0010]

Means for Solving the Problems That is, the present invention provides a magnetic powder having a specific surface area of 45 m ² / g or more, and 1 to 10 parts by weight of 100 parts by weight of the magnetic powder, and a plurality of carboxyl groups. 1 to 10 parts by weight of the compound having 100 parts by weight of the magnetic powder as a binder curing agent and having an isocyanurate ring represented by the following general formula I (hereinafter referred to as compound A). The present invention relates to a magnetic recording medium having a magnetic layer formed by applying a magnetic paint containing

[Chemical 2]

[0011]

The compound A used in the present invention is a TDI such as Coronate L which has been conventionally used as a curing agent.
(Tolylene diisocyanate) It has a higher reactivity with a hydroxyl group than the adduct type. Therefore, when a magnetic powder having a specific surface area of less than 45 m ² / g is used, it exhibits good durability, but a fine magnetic powder having a specific surface area of 45 m ² / g or more in order to obtain good electromagnetic conversion characteristics. When used, the adsorption to the magnetic powder will proceed rapidly. As a result, a sufficient amount cannot be present to crosslink the binder during the curing process, which results in insufficient curing of the binder and insufficient durability. Therefore, it may be difficult to obtain a magnetic recording medium having good electromagnetic conversion characteristics and sufficient durability.

Therefore, according to the present invention, in order to exert the excellent curing action of the compound A well and to satisfy the electromagnetic conversion characteristics, its addition amount (to the magnetic coating material) is 100 parts by weight of the magnetic powder. A compound having a plurality of carboxyl groups (hereinafter referred to as compound B) is added as a dispersant for the purpose of specifying 1 to 10 parts by weight and dispersibility of the magnetic powder.

That is, by specifying the addition amount of the compound A to be 1 to 10 parts by weight (preferably 3 to 7 parts by weight),
It is possible to obtain sufficient durability and electromagnetic conversion characteristics of the magnetic coating film. On the contrary, if the addition amount is less than 1 part by weight, sufficient durability cannot be obtained, and if it is more than 10 parts by weight, electromagnetic conversion characteristics deteriorate. In addition, when a conventional curing agent (Coronate L) is used, sufficient durability cannot be obtained.

At the same time, in order to improve the dispersibility, the compound B, which has a good affinity with the magnetic powder and also has an action of controlling the adsorption of the compound A to the magnetic powder, is contained in an amount of 1 to 10 parts by weight per 100 parts by weight of the magnetic powder.
Add by weight (to magnetic paint). However, this addition amount
When it is more than 10 parts by weight, electromagnetic conversion characteristics are deteriorated and durability is also deteriorated. When this compound is less than 1 part by weight or absent, electromagnetic conversion characteristics are deteriorated and sufficient durability is also obtained. I can't get it.

Examples of the compound B include dicarboxylic acid having two carboxyl groups in the molecule, tricarboxylic acid having three carboxyl groups in the molecule, and 4 in the molecule.
Tetracarboxylic acid having one carboxyl group can be used.

Specific examples of compound B include dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid. And unsaturated aliphatic dicarboxylic acids such as maleic acid and fumaric acid, and aromatic dicarboxylic acids such as phthalic acid, isophthalic acid and terephthalic acid. Examples of tricarboxylic acids include citric acid, nitrilotriacetic acid, and benzenetricarboxylic acid, and examples of tetracarboxylic acids include benzenetetracarboxylic acid.

These compound B have a weight average molecular weight of 10
It is desirable to be 00 or less. When the molecular weight exceeds 1,000, it is necessary to add a large amount in terms of quantity, which may adversely affect the physical properties of the coating film.

According to the present invention, since the above-mentioned compounds A and B are combined and added in a specific addition amount range, even if a fine magnetic powder having a specific surface area of 45 m ² / g or more is used, The dispersibility and the durability of the coating film can be realized. Therefore, it is possible to provide a magnetic recording medium having an electromagnetic conversion characteristic suitable for high recording density. Contrary to this, the specific surface area is 45 m ^2.
When a magnetic powder of less than / g was used, good durability was obtained, but the electromagnetic conversion characteristics deteriorated regardless of the presence or absence of the compound having a plurality of carboxyl groups (Compound B).

As the magnetic powder used in the present invention, any conventionally known magnetic powder can be used.
It may be an oxide magnetic powder or a metal magnetic powder.

As the magnetic oxide powder, for example, γ-Fe
₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ , Co-deposited γ-Fe ₂ O ₃ , Co-deposited Fe ₃ O ₄ , CrO _{2 and the} like can be mentioned.

Examples of magnetic metal powders include Fe, Co,
Ni, Fe-Co, Fe-Ni, Fe-Co-Ni, Co-Ni, Fe-Co-
B, Fe-Co-Cr-B, Mn-Bi, Mn-Al, Fe-Co-V, and the like, and further for the purpose of improving various characteristics of these.
A metal component such as Al, Si, Ti, Cr, Mn, Cu, or Zn may be added.

Hexagonal ferrite such as barium ferrite, iron carbide such as Fe ₅ C ₂ and iron nitride can also be used.

The magnetic layer is prepared by dispersing the above magnetic powder in a binder. As the usable binder, any resin material usually used in this type of medium can be used. However, the type is not particularly limited. Typical binder resins are, for example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer. Polymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-
Acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, thermoplastic polyurethane resin, polyvinyl fluoride,
Vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, polyvinyl acetal, cellulose derivative, styrene-butadiene copolymer, polyester resin, phenol resin, phenoxy resin, Examples thereof include epoxy resin, thermosetting polyurethane resin, urea resin, melamine resin, alkyd resin, and urea-formaldehyde resin.

Such a binder has, at least in part, a sulfonic acid metal base (-SO ₃ M; M is an alkali metal such as Na and K) or a sulfate metal base (-OSO ₃ M; M is Na, K and the like). At least one of an alkali metal and an alkyl group) is introduced in order to improve the dispersibility of the magnetic powder. The amount of these metal bases is preferably 0.2 to 0.8 μmol per 1 m ² of the surface area of the magnetic powder.

In the magnetic recording medium of the present invention,
Furthermore, if necessary, a dispersant such as lecithin, a lubricant such as stearic acid ester, an antistatic agent such as carbon black, an abrasive such as alumina, and a rust preventive may be added. As the dispersant, the lubricant, the antistatic agent, the abrasive and the rust preventive, any conventionally known materials can be used, and there is no limitation.

Examples of the nonmagnetic support usable in the present invention include polyesters such as polyethylene terephthalate film and polyethylene-2,6-naphthalate film, and aramid film. An intermediate layer or an undercoat layer may be provided on the surface of the non-magnetic support in order to improve the adhesiveness of the magnetic layer.

To form a magnetic layer on a non-magnetic support, the above-mentioned components of the magnetic layer are dispersed in a binder, and ethers, esters, ketones, aromatics are added depending on the kind of the binder. A magnetic paint is prepared by dispersing it with an organic solvent selected from hydrocarbons, aliphatic hydrocarbons, organic chlorine compound-based solvents and the like, and the paint is applied to the surface of a non-magnetic support, dried and calendered.

When applying the magnetic paint, if the time until the application is 30 minutes (particularly 1 to 10 minutes) after adding the compound A to the magnetic paint, the effect as a curing agent is effectively exhibited. Further, good electromagnetic conversion characteristics and durability can be obtained.

A back coat layer is provided on the surface (rear surface) of the non-magnetic support on which the magnetic layer is not provided for the purpose of improving the running property of the magnetic recording medium, preventing charging and preventing transfer. You can The back coat layer can also contain a binder (basically the same kind of binder as that used in the magnetic layer), various conventionally known additive components for the back coat layer, and the like.

FIG. 1 shows an example of the magnetic recording medium of the present invention. That is, the non-magnetic support 1 has a magnetic layer 2 containing magnetic powder, a binder, and the above-mentioned compound A, compound B and the like. Further, the other surface may have a back coat layer 3 mainly composed of a non-magnetic powder and a binder as indicated by a chain line.

[0032]

EXAMPLES The present invention will be described below with reference to specific examples, but the present invention is not limited to these examples.

Example 1 A magnetic paint having the following composition was prepared.

<Magnetic coating composition> Magnetic powder: 100 parts by weight of Fe-based metal magnetic powder (specific surface area BET value: see Table 1 below) Binder: 10 parts by weight of polyester-based polyurethane resin (see Table 2 below) Vinyl chloride-vinyl acetate copolymer 10 parts by weight (see Table 2 below) Abrasive: Alumina (Al ₂ O ₃ ) (AKP50) 8 parts by weight Compound B (compound having a plurality of carboxyl groups: 3 parts by weight Refer to Table-3) Lubricant: 2 parts by weight of stearic acid 2 parts by weight of butyl stearate Solvent: 100/100/50 parts by weight of methyl ethyl ketone / toluene / cyclohexanone

After the above materials were dispersed in a sand mill, 5 parts by weight of compound A ₁ having the following structural formula was added as a curing agent, and within 10 minutes after stirring, this was coated on a 7.5 μm thick base film. Then, a magnetic field orientation treatment was performed, dried and wound. Furthermore, after calendering and curing treatment, after adding 20 parts by weight of a curing agent (Coronate L) to the back coat layer coating composition having the following composition, it is coated on the film surface opposite to the magnetic layer to give a thickness of 0.6 μm. The back coat layer was formed to have a large thickness.

[0036]   <Backcoat layer coating composition>   100 parts by weight of carbon black (Asahi Carbon 50 "Asahi Carbon 50")   Binder: Polyester polyurethane resin 100 parts by weight               ("Nipporan N2304" manufactured by Nippon Polyurethane Co., Ltd.)   Solvent: 500 parts by weight of methyl ethyl ketone         500 parts by weight of toluene

The total thickness obtained in this way is 10.5-10.7 μ
A wide tape of m was slit into a width of 8 mm and incorporated in an 8 mm cassette as a sample.

Examples 2 to 11 Samples were prepared in the same manner as in Example 1 except for the addition amount of Compound A, the time until the coating after addition of Compound A, and the addition amount of Compound B having a plurality of carboxyl groups. A tape was made.

Examples 12 to 16 Sample tapes were prepared in the same manner as in Example 1 except for the type of compound B having a plurality of carboxyl groups and the specific surface area of magnetic powder.

Examples 17 to 20 Sample tapes were prepared in the same manner as in Example 1 except that the type of compound A was changed to A ₂ , A ₃ , A ₄ and A ₅ .

Comparative Example 1 A sample tape was prepared in the same manner as in Example 1 except that the amount of compound A added was 0.5 part by weight.

Comparative Example 2 A sample tape was prepared in the same manner as in Example 1 except that the amount of compound A added was 15 parts by weight.

Comparative Example 3 A sample tape was produced in the same manner as in Example 1 except that the amount of the compound B having a plurality of carboxyl groups added was 15 parts by weight.

Comparative Examples 4 to 5 Sample tapes were prepared in the same manner as in Example 1 except that the addition amount of the compound B having a plurality of carboxyl groups was 0 or 0.5 parts by weight.

Comparative Example 6 The same as Example 1 except that 5 parts by weight of Coronate L (TDI adduct type curing agent manufactured by Nippon Polyurethane Industry Co., Ltd .: abbreviation in table) was added in place of Compound A. Then, a sample tape was prepared.

Comparative Examples 7 to 8 Sample tapes were prepared in the same manner as in Example 1 except that the specific surface area of the magnetic powder was reduced.

The still tape characteristics and electromagnetic conversion characteristics of each sample tape manufactured as described above were evaluated by the following methods. The results are shown in Table 4 below.

Still characteristics: Using an 8 mm VCR modified to measure still for a long time, 45 ° C, 80% RH
The time until the RF output was attenuated by 3 dB from the initial stage was obtained under the above environment.

Electromagnetic conversion characteristics: An 8 mm video deck capable of recording / reproducing in Hi8 mode was used, and a signal of 7 MHz was input to the tape for 10 minutes under the environment of 25 ° C. and 60% RH.
The difference between the output at MHz and the noise at -1 MHz was calculated from the difference and was taken as the S / N. Taking the value obtained in Example 1 as 0 dB,
The values of other sample tapes are shown relative to this.

[0050]

[0051]

[0052]

[0053]

Embedded image Structural formula of compound A:

[0054]

[Chemical 4]

[0055]

[Chemical 5]

[0056]

[Chemical 6]

[0057]

[Chemical 7]

[0058] * The unit of addition amount is parts by weight.

[0059] * The unit of addition amount is parts by weight.

As is apparent from Table 4, based on the present invention, magnetic powder having a specific surface area of 45 m ² / g or more was used, and 1 to 10 parts by weight of compound B having a plurality of carboxyl groups was added. Moreover, the magnetic paint containing 1 to 10 parts by weight of the compound A having an isocyanurate ring as a curing agent is used for 30 mi.
The magnetic recording medium obtained by coating on the substrate within n 2 can maintain the electromagnetic conversion characteristics and can obtain good still characteristics.

The amount of the compound A added is suitably 1 to 10 parts by weight. If it is less than that, sufficient durability cannot be obtained, and if it is more than that, the electromagnetic conversion characteristics deteriorate. Further, when a conventional curing agent (Coronate L) is used, sufficient durability cannot be obtained.

In the medium according to the present invention, since the resin used as the binder in the magnetic paint is a polyurethane resin and its glass transition temperature is 60 ° C. or higher, the dispersibility and rigidity of the obtained magnetic layer are not sufficient. In addition, since the magnetic layer contains the isocyanurate compound A as a crosslinking agent,
A sufficient cross-linking reaction occurs between the binders, and a magnetic layer having good running stability and running durability can be obtained.

A suitable amount of the compound B having a plurality of carboxyl groups is 1 to 10 parts by weight, and good results were obtained with other compounds having the same structure. However, if the addition amount is more than 10 parts by weight, the electromagnetic conversion characteristics deteriorate and the durability also deteriorates. Further, if the amount of this compound is too small or if it is not present, electromagnetic conversion characteristics deteriorate and sufficient durability cannot be obtained.

It is important to use a magnetic powder having a specific surface area of 45 m ² / g or more in order to obtain good electromagnetic conversion characteristics. However, when a magnetic powder having a specific surface area of less than 45 m ² / g is used, good magnetic properties are obtained. Compound B having durability but having a plurality of carboxyl groups
The electromagnetic conversion characteristics deteriorated regardless of the presence or absence of.

Further, if the time until coating after addition of the compound A is within 30 min, more excellent electromagnetic conversion characteristics and durability can be obtained.

[0066]

As described above, the present invention has a specific surface area of
Even when using a fine magnetic powder of 45 m ² / g or more, 1 to 10 parts by weight of a compound having a plurality of carboxyl groups is added,
Also, the magnetic paint containing 1 to 10 parts by weight of a compound having an isocyanurate ring as a curing agent is used for 30 min.
By coating on the substrate within the above range, it is possible to provide a magnetic recording medium having a magnetic layer having good electromagnetic characteristics and good durability.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a structural example of a magnetic recording medium to which the present invention is applied.

[Explanation of symbols]

1. Non-magnetic support 2 ... Magnetic layer 3 ... Back coat layer

Claims (3)

(57) [Claims] 1. A magnetic powder having a specific surface area of 45 m ² / g or more, a compound having 1 to 10 parts by weight with respect to 100 parts by weight of this magnetic powder and having a plurality of carboxyl groups, and a curing agent for a binder. 1 to 10 with respect to 100 parts by weight of the magnetic powder
A magnetic recording medium having a magnetic layer formed by coating a magnetic coating material, which is added in parts by weight and contains a compound having an isocyanurate ring represented by the following general formula I. [Chemical 1] 2. A method of manufacturing a magnetic recording medium, wherein a magnetic layer is formed by applying the magnetic paint according to claim 1. 3. The production method according to claim 2, wherein the time from the addition of the curing agent to the application of the magnetic coating material is within 30 minutes.