JPH08129743A - Magnetic recording medium - Google Patents

Abstract

PURPOSE: To obtain a magnetic recording medium having satisfactory running stability and running durability while avoiding the thermal deformation of the nonmagnetic substrate due to a curing process. CONSTITUTION: When a metallic magnetic thin film type magnetic recording medium with a back coating layer 3 is produced, an isocyanurate compd. is used as a crosslinking agent for the back coating layer 3. Polyurethane resin having >=30 deg.C glass transition temp. is suitable for use as the binder of the layer 3. A back coating layer excellent in durability can be formed without carrying out a curing process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal magnetic thin film type magnetic recording medium having a back coat layer, and more particularly to improving the durability of the back coat layer.

[0002]

2. Description of the Related Art In a so-called metal magnetic thin film type magnetic recording medium in which a magnetic layer is formed by directly depositing a ferromagnetic metal material on a non-magnetic support by a thin film forming technique such as vapor deposition, A back coat layer is usually provided on the surface of the non-magnetic support opposite to the side on which the magnetic layer is formed for the purpose of running stability, reduction of frictional resistance between tapes, and improvement of charging property. is there.

The back coat layer is formed by mainly dispersing solid particles such as an inorganic powder pigment and a binder in an organic solvent and kneading to form a coating, which is coated on a non-magnetic support and dried. .

Among these, as the binder, vinyl chloride resin such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinylidene chloride copolymer, nitrocellulose, Epoxy resin, acrylic resin, and polyurethane resin are widely used.

Further, a crosslinking agent is used in combination with these resins to form a crosslinked structure. The cross-linking agent is required to be capable of undergoing a cross-linking reaction with the binder at room temperature, obtaining high cross-linking efficiency in the reaction with the binder, and imparting durability and heat resistance to the back coat layer. Due to their relatively excellent properties, polyisocyanate compounds have been widely used as crosslinking agents. The polyisocyanate compound has a structure containing a plurality of isocyanate groups in the molecule, and the isocyanate group reacts with the hydroxyl group in the binder to form a urethane bond to form a crosslinked structure.

A typical example of this polyisocyanate compound is an adduct of a diisocyanate compound. An adduct of a diisocyanate compound has three isocyanate groups in one molecule by adding a diisocyanate compound such as tolylene diisocyanate, diphenylmethane diisocyanate, or hexamethylene diisocyanate to a trifunctional hydroxyl group-containing compound such as trimethylolpropane. It is the compound contained. The adduct of this diisocyanate compound has an appropriate reaction rate with the hydroxyl group in the binder and does not cause a crosslinking reaction at this point even if it is compounded at the time of forming a coating material, and thus it can be formed on a non-magnetic support. The cross-linking reaction gradually occurs after applying the paint.

[0007]

By the way, in the above-mentioned metal magnetic thin film type magnetic recording medium, in recent years, an increase in the signal recording amount has been increasingly demanded, and the signal line density is improved, the track pitch is narrowed, and Thinning is progressing. Following this, demands for running stability and running durability are becoming strict.

In order to improve the running stability and running durability of the medium, the characteristics of the back coat layer become a problem.
However, it is difficult to provide the backcoat layer with running stability and running durability that meet the above requirements, by using the combination of the binder and the crosslinking agent described above.

For this reason, in such a medium, measures are taken to introduce a curing step into the manufacturing step, in which the coating material is applied on the non-magnetic support and then heat-treated to accelerate the crosslinking reaction. However, when such a curing step is introduced, although the crosslinking property is certainly increased, the heat treatment causes the non-magnetic support to be deformed, resulting in deterioration of electromagnetic conversion characteristics and running stability. In particular, such thermal deformation of the non-magnetic support is a serious problem in the case of a thin film type medium.

Besides, in order to improve the durability of the back coat layer, the glass transition temperature of the binder is 30 ° C.
It is also practiced to select a resin which is relatively high as above.

For example, a nitrocellulose or vinyl chloride resin is used as such a resin. However, nitrocellulose and vinyl chloride resins are
It has a drawback that it desorbs corrosive gases such as nitric acid gas or hydrogen chloride gas, which causes rusting of the metal magnetic thin film.In addition, it is possible to raise the glass transition temperature and the rigidity is high, so it is an attempt to use polyurethane resin. Has also been done. This polyurethane resin is synthesized by combining a polyol component having an appropriate molecular weight and a glycol with a bifunctional isocyanate to give a high molecular weight,
In addition to high rigidity, it has many advantages such as excellent flexibility and dispersibility, and low possibility of generating desorbed gas.

For example, in JP-B-58-41565, a polyurethane resin in which a predetermined functional group is introduced in an appropriate ratio in order to improve the adsorptivity to an inorganic pigment powder and the dispersibility of a coating is proposed as a binder. Has been done.

However, when the polyurethane resin has a structure in which the glass transition temperature is higher than room temperature, the concentration of hydroxyl groups becomes significantly smaller than that of nitrocellulose or vinyl chloride resin. In addition, the degree of freedom of the molecular chain is low at room temperature, and the crosslinking reaction that should occur after coating the coating is difficult to proceed. For this reason, the polyurethane resin has excellent properties as described above, but the crosslink density becomes low in combination with the crosslinking agent used so far,
Sufficient durability cannot be imparted to the back coat layer.

Therefore, the present invention has been proposed in view of the above-mentioned conventional circumstances, and has a back coat layer having excellent durability, and magnetic recording that exhibits good running durability and running stability. The purpose is to provide a medium.

[0015]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors in order to achieve the above-mentioned object, the use of an isocyanurate compound as a cross-linking agent gives a back coat layer excellent in durability. As a result, it has been found that the running durability and running stability of the medium are significantly improved.

The magnetic recording medium of the present invention has been completed on the basis of such findings, and a metal magnetic thin film is formed on one surface of a non-magnetic support, and an inorganic powder pigment is bonded to the other surface. In a magnetic recording medium having a back coat layer mainly containing an agent, the above back coat layer contains an isocyanurate compound as a crosslinking agent.

The binder of the back coat layer is a resin having a glass transition temperature of 30 ° C. or higher.

Further, the binder of the back coat layer is a polyurethane resin having a glass transition temperature of 30 ° C. or higher.

In the present invention, as shown in FIG. 1, a metal magnetic thin film 2 is formed on one surface of a non-magnetic support 1, and a back coat layer 3 mainly composed of solid powder and a binder is formed on the other surface. The present invention is applied to a metal magnetic thin film type magnetic recording medium formed by forming.

In the magnetic recording medium having such a structure,
The back coat layer is provided for the purpose of improving the running property of the medium, preventing electrification and preventing transfer. In the present invention,
This backcoat layer contains an isocyanurate compound as a crosslinking agent.

The isocyanurate compound is represented by Chemical formula 1. However, in Chemical formula 1, R is an atomic group represented by Chemical formula 2, and as the isocyanurate compound, it is preferable that R is a structure represented by Chemical formula 3 or Chemical formula 4.

[0022]

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[0023]

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[0024]

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[0025]

[Chemical 4]

These isocyanurate compounds are synthesized by using polyisocyanate compounds such as tolylene diisocyanate, diphenylmethane diisocyanate and hexamethylene diisocyanate as raw materials, and adding appropriate reaction conditions, reaction temperatures and appropriate catalysts.

The reactivity of the isocyanate group in such an isocyanurate compound is much higher than that of, for example, a polyisocyanate compound. Therefore, when this isocyanurate compound is contained in the back coat layer, a back coat layer having excellent durability can be formed without a curing step in which a crosslinking reaction proceeds by heat treatment, and the medium can be formed while suppressing thermal deformation of the non-magnetic support. The running durability and running stability of will be improved.

On the other hand, the binder contained in the back coat layer preferably has a glass transition temperature of 30 ° C. or higher from the viewpoint of increasing the rigidity of the back coat layer and improving the running durability of the medium. Here, a resin having a glass transition temperature higher than room temperature has excellent rigidity, but on the other hand, at room temperature, the degree of freedom of a molecular chain is impaired, and a cross-linking agent tends to be difficult to form a cross-linked structure. However, since the isocyanurate compound used as the crosslinking agent in the present invention has high reactivity as described above, a crosslinked structure having a high density can be formed even with such a resin.

A polyurethane resin is suitable as the resin having such a glass transition temperature. The polyurethane resin has properties suitable for a binder of the back coat layer, such as high rigidity, excellent flexibility and dispersibility, and low possibility of generating desorbed gas.

This polyurethane resin can be synthesized by reacting a polyhydroxy compound with a polyisocyanate. As the starting polyhydroxy compound, a polyol component such as polyester polyol, polycarbonate polyol, polyether polyol, etc. Thus, glycols such as ethylene glycol and 1,4-butanediol are used as needed.

Further, as the above polyisocyanate,
Examples include tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, and the like.

The ratio of the isocyanurate compound serving as a crosslinking agent to these binders is 1 to 100 parts by weight, more preferably 5 to 30 parts by weight, based on 100 parts by weight of the binder. Appropriate.

In the present invention, the above-mentioned predetermined cross-linking agent,
The binder is used in the back coat layer, and as the solid particles, those having an antistatic effect and a lubricating effect which are usually used in the back coat layer can be used.
Examples thereof include inorganic powder pigments such as graphite, carbon black, carbon black graft polymer, tungsten disulfide, molybdenum disulfide, and titanium oxide.

In order to form a backcoat layer having such a constitution, solid particles are dispersed in a binder, and this is kneaded with an organic solvent to prepare a backcoat coating material, and a crosslinking agent is further added. Mix. Then, the backcoat layer is formed by applying this backcoating material to the surface of the nonmagnetic support opposite to the surface on which the magnetic layer is formed.

As the organic solvent used for forming the coating material, ketone-based, alcohol-based, ester-based, ether-based, hydrocarbon-based, halogenated carbon-based, etc. can be used. It may be selected in consideration of compatibility.

To disperse and knead the above back coat paint,
A roll mill, a ball mill, a sand mill, a kneader, an extruder, a homogenizer, an ultrasonic disperser or the like is used.

A gravure coater, a knife coater, a blade coater, a reverse roll coater, a die coater and the like are used for coating the coating material.

In the magnetic recording medium of the present invention, a metal magnetic thin film is formed as a magnetic layer on the surface of the non-magnetic support opposite to the side on which the back coat layer is formed.

The metal magnetic thin film is a continuous film formed by depositing a metal magnetic material on a non-magnetic support by a PVD method such as plating, sputtering or vacuum deposition. Examples of such a metal magnetic thin film include Fe,
Metal materials such as Co and Ni, Co-Ni, Co-Pt,
Co-Pt-Ni, Fe-Co, Fe-Ni, Fe-C
An example is an in-plane magnetization recording type metal magnetic thin film made of an alloy material such as o-Ni. In the case of such an in-plane magnetization recording type metal magnetic thin film, B is previously formed on the non-magnetic support.
i, Sb, Pb, Sn, Ga, In, Ge, Si, Ti
It is advisable to form an underlayer of a low-melting point non-magnetic material such as, for example, and vapor-deposit or sputter a metallic magnetic material from above on it in the vertical direction. When the metallic magnetic material is deposited on the underlayer, the low melting point nonmagnetic material of the underlayer diffuses in the metallic magnetic thin film, the orientation is eliminated, the in-plane isotropic property is secured, and the anti-magnetism is improved. improves.

The magnetic layer may be a single layer film of these metal magnetic thin films or a multilayer film in which two or more layers are laminated. In addition, these metal magnetic thin films include an underlayer between the non-magnetic support and the metal magnetic thin film, and in the case of a multi-layered film, between layers for the purpose of improving adhesion and controlling coercive force. You may make it provide an intermediate | middle layer.

The non-magnetic support includes polyesters,
Any conventionally known material such as polyolefins and celluloses can be used. The form is not limited at all, and may be any form such as tape, sheet, and drum.

Further, the non-magnetic support may be subjected to a surface treatment for forming fine irregularities in order to control its surface property.

The above is the basic structure of the magnetic recording medium of the present invention. In the present invention, however, like the normal magnetic recording medium, other elements are added to further improve the characteristics. Is also good.

For example, a lubricant, an extreme pressure agent, a rust preventive agent, etc. may be coated on the magnetic layer and the back coat layer, if necessary. Lubricants, extreme pressure agents, and rust preventives are not particularly limited as long as they are materials usually used in magnetic recording media of this type, and on the magnetic layer, as a protective film for rust prevention, etc., PVD such as carbon plating, sputtering, vacuum deposition, etc.
You may form and adhere by the method of.

[0045]

According to the present invention, a metal magnetic thin film type having a metal magnetic thin film formed on one surface of a non-magnetic support and a back coat layer mainly composed of solid powder and a binder is formed on the other surface. In the above magnetic recording medium, the above-mentioned back coat layer contains an isocyanurate compound as a crosslinking agent.

Isocyanurate compounds have markedly higher reactivity with isocyanate groups than, for example, those of polyisocyanate compounds. Therefore, even for a resin having a glass transition temperature of 30 ° C. or higher, a high-density crosslinked structure can be formed at room temperature. Therefore, when such a isocyanurate compound is contained in the backcoat layer, a backcoat layer having excellent durability can be formed without a curing step of promoting a crosslinking reaction by heat treatment, and thermal deformation of the non-magnetic support is prevented. While suppressing, the running durability and running stability of the medium are improved.

[0047]

EXAMPLES Hereinafter, specific examples of the present invention will be described, but it goes without saying that the present invention is not limited to these examples. First, on a polyethylene terephthalate film having a thickness of 10 μm, Co is vapor-deposited by the oblique vapor deposition method to obtain a film thickness of
A 0 nm metal magnetic thin film was formed. Then, a lubricant and a rust preventive agent were applied on the metal magnetic thin film.

Next, each backcoat composition was weighed according to the following composition and mixed in a ball mill for 48 hours to prepare a backcoat paint. Composition of backcoat paint 100 parts by weight carbon black (Colombian company Product name RAVEN-1255) Polyurethane resin A 100 parts by weight (glass transition temperature 30 ° C., containing SO ₃ Na 0.05% as a functional group) Methyl ethyl ketone 220 parts by weight Toluene 220 parts by weight Cyclohexanone 220 parts by weight For this prepared back coat Isocyanurate compound of tolylene diisocyanate as a cross-linking agent in paint (Nippon Polyurethane Industry Co., Ltd., trade name Coronate 2030)
Was added to the surface of the polyethylene terephthalate film having the metal magnetic thin film formed in the previous step on the side opposite to the side having the metal magnetic thin film formed thereon, and dried to form a back coat layer. The thickness of the back coat layer after drying was 0.7 μm.

Then, a magnetic tape was prepared by cutting the raw tape having the back coat layer thus formed into a width of 8 mm.

Example 2 A magnetic tape was prepared in the same manner as in Example 1 except that an isocyanurate compound of diphenylmethane diisocyanate was used as a crosslinking agent in place of the isocyanurate compound of tolylene diisocyanate in forming the back coat layer. .

Example 3 A magnetic tape was prepared in the same manner as in Example 1 except that an isocyanurate compound of hexamethylene diisocyanate was used as a crosslinking agent in place of the isocyanurate compound of tolylene diisocyanate in forming the back coat layer. did.

Example 4 In forming the back coat layer, polyurethane resin B (glass transition temperature 20
A magnetic tape was produced in the same manner as in Example 1 except that 0 ° C., containing 0.05% of SO ₃ Na as a functional group) was used as a binder.

Comparative Example 1 When forming a back coat layer, a trimethylolpropane adduct of tolylene diisocyanate (trade name: Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) was used as a cross-linking agent in place of the isocyanurate compound of tolylene diisocyanate. A magnetic tape was produced in the same manner as in Example 1 except for the above.

Comparative Example 2 When forming a back coat layer, a trimethylolpropane adduct of hexamethylene diisocyanate (trade name: Coronate HL, manufactured by Nippon Polyurethane Industry Co., Ltd.) was used as a crosslinking agent in place of the isocyanurate compound of tolylene diisocyanate. A magnetic tape was produced in the same manner as in Example 1 except for the above.

Comparative Example 3 In forming the back coat layer, polyurethane resin B (glass transition temperature 20
A magnetic tape was produced in the same manner as in Comparative Example 1 except that 0 ° C., containing 0.05% of SO ₃ Na as a functional group) was used as a binder.

With respect to the magnetic tapes produced in Examples 1 to 4 and Comparative Examples 1 to 3 as described above, the surface roughness Ra of the back coat layer, the friction coefficient, and the occurrence of scratches after the shuttle traveled. The running stability and running durability were evaluated by measuring the situation and the RF output of the magnetic layer. The measurement results are shown in Table 1. The surface roughness Ra of the back coat layer, the coefficient of friction, the occurrence of scratches after the shuttle travel, and the method for measuring the RF output of the magnetic layer are as follows.

Surface roughness Ra: manufactured by Kosaka Laboratory, trade name S
It measured using the surface roughness meter of E-30H. The measurement conditions are magnification 50000 times, measurement length 2 mm, cutoff 0.08.
mm.

The surface roughness Ra serves as an index of running stability. In order to obtain sufficient running stability, it is desirable that the surface roughness Ra be 20 μm or less.

Friction coefficient: The back coat layer was brought into contact with the stainless steel guide pins to run the shuttle, and the friction coefficient was measured when the number of shuttles was 10 and 200.

The friction coefficient serves as an index of running durability. In order to obtain good running durability, it is desirable that this friction coefficient be 0.18 or less. Scratch occurrence situation: 200 pass shuttle travel while the back coat layer is in contact with the stainless guide pin, back coat after shuttle travel The degree of scratches on the layer was visually observed. The evaluation criteria are the following three levels A, B, and C.

A: In the case of almost no scratches B: In case of slight scratches (unusable) C: In case of large scratches (unusable) RF output: Sony 8mm video The signal frequency was measured at 7 MHz using a deck. However, the dB value in the table is
It is a relative output when the output of the magnetic tape of Example 1 is set to 0 dB. This RF output comprehensively evaluates running stability and running durability.

[0062]

[Table 1]

As is clear from Table 1, the magnetic tapes of Examples 1 to 4 using the isocyanurate compound as the cross-linking agent for the back coat layer are the comparative examples 1 to 1 using the trimethylolpropane adduct of diisocyanate. Compared with the magnetic tape of Comparative Example 3, the surface roughness Ra is small and the friction coefficient is 0.18 or less, which is a low value. Further, the increase in the friction coefficient due to repeated shuttle travel is small, and a good surface state is maintained after 200 shuttle travels. Moreover, the RF output of the magnetic layer is also high.
That is, it exhibits excellent running durability and running stability.

In the magnetic tapes of Examples 1 to 4, such good measurement results were obtained because the isocyanurate compound used as the cross-linking agent worked effectively in the cross-linking reaction with the polyurethane resin and was high. This is because the crosslinked structure was formed at the density.

On the other hand, in the magnetic tapes of Comparative Examples 1 to 3, since the dimethylolpropane adduct of diisocyanate used as the crosslinking agent has low reactivity, a sufficiently crosslinked structure is formed between the polyurethane resins. Not done. Therefore, it is considered that the durability of the back coat layer was impaired and sufficient running stability and running durability could not be obtained.

From the above results, the isocyanurate compound is far superior to the trimethylolpropane adduct of diisocyanate as the cross-linking agent for the back coat layer, and the back coat layer is formed by using this compound. It was found that a magnetic recording medium having excellent running durability and running stability can be obtained.

When the friction coefficients of the magnetic tapes of Examples 1 and 4 having the same kind of the crosslinking agent but different kinds of the polyurethane resin were compared, it was found that the polyurethane resin having the glass transition temperature of 30 ° C. was used. The magnetic tape of Example 1 has a lower friction coefficient than the magnetic tape of Example 4 using a polyurethane resin having a glass transition temperature of 20 ° C. Therefore, it is desirable to select a polyurethane resin having a glass transition temperature of 30 ° C. or higher as a binder of the back coat layer for a medium used in a system in which running durability is particularly required.

[0068]

As is apparent from the above description, in the present invention, in a metal magnetic thin film type magnetic recording medium having a backcoat layer, an isocyanurate compound is used as a crosslinking agent for the backcoat layer, so that the manufacturing process is improved. A backcoat layer having excellent durability can be formed without introducing a curing step. Therefore, it is possible to obtain a magnetic recording medium that exhibits good running stability and running durability while avoiding thermal deformation of the non-magnetic support due to the curing step.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an essential part 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)

[Claims] 1. A magnetic recording medium comprising a nonmagnetic support on one surface of which a metal magnetic thin film is formed, and on the other surface of which a backcoat layer mainly composed of solid powder and a binder is formed. A magnetic recording medium, wherein the layer contains an isocyanurate compound as a crosslinking agent. 2. The magnetic recording medium according to claim 1, wherein the binder of the back coat layer is a resin having a glass transition temperature of 30 ° C. or higher. 3. The magnetic recording medium according to claim 2, wherein the binder of the back coat layer is a polyurethane resin having a glass transition temperature of 30 ° C. or higher.