JPH076351A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having satisfactory toughness even in the case of a thinned film by forming a nonmagnetic substrate with a polyester film having a prescribed compsn. CONSTITUTION:When the number average mol. wt. of polyester in a polyethylene 2,6-naphthalate film is moderately reduced, the cuttability of the film is improved while maintaining the modulus of elasticity and a nonmagnetic substrate suitable for use as the substrate of a cassette tape for long-time recording is obtd. At the time of producing a magnetic recording medium, the nonmagnetic substrate is made of a polyester film based on polyethylene 2,6-naphthalate and the number average mol. wt. of polyester, that is, the polyethylene 2,6- naphthalate forming the nonmagnetic substrate is regulated between 8,000-16,000. The objective magnetic recording medium capable of ensuring satisfactory toughness even in the case of a thinned film, excellent in cuttability and not forming a high edge at a cut section on cutting is obtd. and a cassette take for lone-time recording excellent in durability and tape characteristics is obtd.

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 suitable for application to a long-time recording tape cassette.

[0002]

2. Description of the Related Art In a tape cassette used in a video tape recorder or the like, the length of a magnetic tape is being increased in order to extend the recording time. Magnetic tapes tend to become thinner and thinner to fit inside.

When thinning the magnetic tape, first, the thickness of the non-magnetic support, which occupies most of the thickness of the magnetic tape, is adjusted without affecting the recording / reproducing characteristics, but this is a problem. Is the toughness of the tape. A polyethylene terephthalate film, which has been widely used as a non-magnetic support, has a low elastic modulus, and when it is made thin, sufficient toughness cannot be imparted to the magnetic tape, resulting in a problem in durability.

Therefore, in a magnetic tape used for a long-time recording tape cassette, a polyethylene 2,6-naphthalate film having a molecular weight of about 20,000 is generally used as a non-magnetic support instead of the polyethylene terephthalate film. Has become. This is because the polyethylene 2,6-naphthalate film has a high elastic modulus and can give the magnetic tape sufficient toughness even when it is made thin.

[0005]

However, since the toughness of polyethylene 2,6-naphthalate film currently used is conversely too high, the cut edge rises (becomes a high edge) when cut. , There is a problem in cutting workability. For example, when a magnetic recording medium in an original state is cut into a tape width and the cut edge becomes a high edge, this causes a poor contact state between the head and the magnetic tape. For example, when applied to a VTR, an audio signal Output decay occurs.

Therefore, the present invention has been proposed in view of such conventional circumstances, and is intended as a long-time recording cassette tape which is excellent in cutting workability and can obtain sufficient toughness even when it is thinned. It is an object to provide a suitable magnetic recording medium.

[0007]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the inventors of the present invention have conducted extensive studies, and as a result, by appropriately reducing the polyester number average molecular weight of a polyethylene 2,6-naphthalate film, It has been found that cutting processability is improved while maintaining the elastic modulus, and that a suitable non-magnetic support can be obtained by using it for a long-time recording cassette tape.

The magnetic recording medium of the present invention has been completed based on such findings, and in the magnetic recording medium having at least a magnetic layer on a non-magnetic support, the non-magnetic support is polyethylene 2 , 6-naphthalate as a main component and polyethylene 2,6-naphthalate constituting this non-magnetic support has a polyester number average molecular weight of 8000 to 16000.
It is characterized by being.

Further, the present invention is characterized in that the content of polyethylene 2,6-naphthalate in the polyester film is 70 mol% or more.

The magnetic recording medium to which the present invention is applied comprises a magnetic layer formed on a non-magnetic support made of a flexible polymer film.

According to the present invention, in such a magnetic recording medium, sufficient toughness can be ensured even when the film is thinned, and the cutting workability is excellent in that the cutting edge does not become a high edge. In addition, a polyester film containing polyethylene 2,6-naphthalate having a polyester number average molecular weight of 8000 to 16000 as a main component is used as the non-magnetic support.

Polyethylene 2,6-naphthalate, which is the main component of the polyester film, is a polymer having a high elastic modulus and is excellent in the effect of imparting toughness. However, in order to obtain good cutting processability, it is important that the polyester number average molecular weight is 8000 to 16000.

That is, the polyethylene 2,6-naphthalate film has a polyester number average molecular weight of 8000.
If it is less than the above range, the tape strength is rapidly deteriorated, so that, for example, film breakage occurs in the stretching step during film formation, and production itself is difficult. Therefore, the number average molecular weight of polyester must be 8,000 or more to form a non-magnetic support.

On the other hand, the polyester has a number average molecular weight of 160.
A polyethylene 2,6-naphthalate film having a thickness of more than 00 has a high edge at the cut end when cut into a tape width, and has a problem in cut workability.

The above polyester film is made of polyethylene 2,6 having a polyester number average molecular weight of 8000 to 16000, which provides good tape strength and cutting processability.
-Mainly naphthalate. Therefore, by using such a polyester film as a non-magnetic support, sufficient toughness can be secured even when the film is thinned, and magnetic recording excellent in cutting workability does not occur at the cutting edge of cutting work being a high edge. The medium is won. If such a magnetic recording medium is set to have a small film thickness and cut into a tape width, a long-time recording magnetic tape excellent in durability and tape characteristics can be obtained.

Incidentally, the polyester film mainly composed of polyethylene 2,6-naphthalate mentioned here means that polyethylene 2,6-naphthalate is at least 70 mo.
It is a film containing 1% or more. 70 mol%
By using the above polyethylene 2,6-naphthalate, a non-magnetic support having the above effects can be realized.

Further, polyethylene 2, which is regulated by the present invention,
The polyester number average molecular weight of the 6-naphthalate film is calculated from the intrinsic viscosity of polyethylene 2,6-naphthalate. The polyester number average molecular weight of the polyethylene 2,6-naphthalate film is, for example, the reaction time at the time of polymerizing the raw material monomer, the reaction temperature, the pressure,
It can be adjusted by controlling the raw material monomer concentration and the catalyst.

The recording magnetic layer provided on the non-magnetic support as described above is a magnetic coating film formed by applying a magnetic coating material such as magnetic powder or resin binder to the surface of the non-magnetic support, or It is a ferromagnetic metal thin film deposited on a non-magnetic support.

In the case where the recording magnetic layer is a magnetic coating film, any conventionally known magnetic powder, resin binder, etc. can be used without any limitation. As magnetic powder,
γ-Fe ₂ O ₃ , ferromagnetic iron oxide particles such as γ-Fe ₂ O ₃ coated with cobalt, ferromagnetic chromium dioxide particles, Fe, C
Examples thereof include ferromagnetic metal-based particles made of metals such as o and Ni and alloys containing these, and hexagonal plate-shaped hexagonal ferrite fine particles.

Examples of the resin binder include polymers such as vinyl chloride, vinyl acetate, vinyl alcohol, vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, butadiene and acrylonitrile, or a copolymer of two or more of them. Examples include coalesce, polyurethane resin, polyester resin, and epoxy resin. A hydrophilic group such as a sulfonic acid group, a carboxyl group, or a phosphoric acid group may be introduced into these binders in order to improve the dispersibility of the magnetic powder.

In addition to the above magnetic powder and resin binder, a dispersant, an abrasive, an antistatic agent, a rust preventive, etc. may be added to the magnetic coating film.

On the other hand, when the recording magnetic layer is a ferromagnetic metal thin film, the ferromagnetic metal thin film is formed as a continuous film by a vacuum thin film forming technique such as a vacuum deposition method, an ion plating method and a sputtering method.

The vacuum vapor deposition method is 10 ^-4 to 10 ^-8 Tor.
resistance heating, high frequency heating of ferromagnetic metal materials under vacuum of r
The evaporation metal (ferromagnetic metal material) is deposited on the disk substrate by evaporating it by electron beam heating or the like. Generally, in order to obtain a high coercive force, the ferromagnetic metal material is obliquely deposited on the substrate. The vapor deposition method is adopted.
Alternatively, the above vapor deposition is also included in order to obtain a higher coercive force.

The above-mentioned ion plating method is also a kind of vacuum vapor deposition method, and DC glow discharge and RF glow discharge are generated in an inert gas atmosphere of 10 ^-4 to 10 ^-3 Torr,
That is, the ferromagnetic metal material is vaporized during discharge.

The above-mentioned sputtering method is 10 ^-3 to 10 ^-1
A glow discharge is caused in an atmosphere containing Torr's argon gas as a main component, and the atoms on the target surface are knocked out by the generated argon gas ions. The glow discharge method is a direct current 2-pole or 3-pole sputtering method or a high frequency wave. There are a sputtering method, a magnetron sputtering method using magnetron discharge, and the like. When this sputtering method is used, a base film of Cr, W, V or the like may be formed.

In any of the above methods,
Bi, Sb, Pb, Sn, Ga, on the non-magnetic support in advance
A base film of a nonmagnetic metal such as In, Cd, Ge, Si, Tl is formed in advance, and the above ferromagnetic metal material is vapor-deposited or sputtered from the vertical direction to diffuse these nonmagnetic metals in the ferromagnetic metal thin film. The orientation may be eliminated and the coercive force may be secured.

When forming a metal magnetic thin film by such a vacuum thin film forming technique, as a ferromagnetic metal material to be used, in addition to metals such as Fe, Co and Ni, Co-Ni alloy and Co-Pt are used. Alloy, Co-Ni-Pt alloy, Fe-C
o alloy, Fe-Ni alloy, Fe-Co-Ni alloy, Fe
-Co-B alloy, Co-Ni-Fe-B alloy, Co-C
Examples include r alloys and alloys containing metals such as Cr and Al. In particular, when a Co—Cr alloy is used, a perpendicular magnetization film is formed.

In the magnetic recording medium of the present invention, the surface on which a top coat layer made of a rust preventive agent or a lubricant is provided on the recording magnetic layer or the magnetic layer on the non-magnetic support is not formed. The back coat layer may be provided on the back surface.

[0029]

Function: Polyester number average molecular weight is 8000 to 160
The polyethylene 2,6-naphthalate, which has a moderately low value of 00, has a high elastic modulus and is excellent in cutting workability without forming a high edge in the cutting work. Therefore, such polyester number average molecular weight is 8000-
A magnetic recording medium having a polyester film mainly composed of polyethylene 2,6-naphthalate of 16000 as a non-magnetic support has sufficient toughness even when it is thinned when used as a cassette tape,
In addition, the cut end cut into the tape width has a good shape, and the cassette tape has excellent durability and tape characteristics.

[0030]

EXAMPLES Preferred examples of the present invention will be described based on experimental results.

[0031]Example 1 First, the number of polyesters from the raw material monomer through the polymerization reaction
Polyethylene 2,6-naphtha with an average molecular weight of 16000
The rate was synthesized and film-formed. This film molding
The body is biaxially stretched to prepare a 12 μm thick non-magnetic support.
It was The elastic modulus of the non-magnetic support is 700 in the longitudinal direction.
kg / mm², 740 kg / mm in width direction ²Is.

On the other hand, various magnetic coating compositions were weighed out and mixed according to the following composition. Composition of magnetic paint Magnetic powder Co-γ iron oxide: 100 parts by weight (specific surface area 40 m ² / g) Binder vinyl chloride copolymer: 10 parts by weight (Sekisui Chemical Co., Ltd., trade name S-REC A) Polyester polyurethane: 5 Parts by weight (Nippon Polyurethane Industry Co., Ltd., trade name N-2304) Polyester Polyurethane: 5 parts by weight (Nippon Polyurethane Industry Co., Ltd., trade name N-3109) Additive Alumina: 7 parts by weight (Abrasive: Sumitomo Chemical Co., Ltd. , Trade name AkP-30) Furnace carbon: 2 parts by weight (Colombian Carbon Co., trade name SC carbon) Myristylamine (dispersant): 1.5 parts by weight Butyl stearate (lubricant): 2 parts by weight Solvent methyl ethyl ketone: 180 parts by weight Toluene: 60 parts by weight

Then, this magnetic paint mixture was dispersed in a sand glider mill for 6 hours to prepare a magnetic paint.
Then, after the magnetic coating material is subjected to a filter treatment, 4 parts by weight of a curing agent Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) is added, and the above non-magnetic support is coated with a thickness of 2.5 μm and calendered. By doing so, a magnetic layer was formed and a tape raw material was produced.

A magnetic tape was produced by cutting this raw tape material into a length of 20000 m and a width of 1/2 inch using a shear cutter. The shear cutter used was one just after polishing.

Examples 2 and 3 A magnetic tape was prepared in the same manner as in Example 1 except that a polyethylene 2,6-naphthalate film having a polyester number average molecular weight shown in Table 1 was used as the non-magnetic support. Was produced. The elastic modulus of the non-magnetic support is also shown in Table 1.

Comparative Example 1 and Comparative Example 2 As shown in Table 1, the same as Example 1 except that a polyethylene 2,6-naphthalate film having a polyester number average molecular weight outside the predetermined range was used as the non-magnetic support. Then, a magnetic tape was produced. The elastic modulus of the non-magnetic support is also shown in Table 1.

Comparative Example 3 A magnetic tape was produced in the same manner as in Example 1 except that a polyethylene terephthalate film was used as the non-magnetic support.

[0038]

[Table 1]

With respect to the magnetic tape thus produced, the high edge level of the cut end, the audio output characteristic, and the durability were examined. The results are shown in Table 2. The high edge level was evaluated by observing both ends of the tape with an optical microscope (× 1000).

The audio output fluctuation was evaluated by incorporating a magnetic tape into a cassette and examining the output fluctuation level when reproducing with an audio fixed head. For durability, magnetic tape is installed in the cassette for 10 minutes,
After repeating a recording / reproducing cycle of recording, rewinding, reproducing, and rewinding 50 times, the deterioration state of the tape edge was visually observed and evaluated.

[0041]

[Table 2]

As shown in Table 2, each of the magnetic tapes of Examples 1 to 3 using a polyethylene 2,6-naphthalate film having a polyester number average molecular weight in a predetermined range as a non-magnetic support is running durability. It has excellent properties.
Further, the high edge level is small, and therefore the contact state with the magnetic head is good and the audio output attenuation is small. On the other hand, the magnetic tape of Comparative Example 3, which uses polyethylene terephthalate as the non-magnetic support, has insufficient elasticity and therefore has insufficient running durability.

On the other hand, even when the polyethylene 2,6-naphthalate film was used as the non-magnetic support, the high-edge level was large in the magnetic tape of Comparative Example 2 in which the polyester number average molecular weight thereof exceeded 16000, which resulted in audio loss. Output decay has been triggered. On the other hand, when polyethylene 2,6-naphthalate having a polyester number average molecular weight of less than 8000 is used (Comparative Example 1), film breakage occurs during biaxial stretching of the film molded body, and at that time, production of the magnetic tape is stopped. I have no choice.

From the above, a polyester having a number average molecular weight of 8 is used as a non-magnetic support for a thin film type magnetic tape.
It has been found that polyethylene 2,000 to 16,000 polyethylene 2,6-naphthalate film is suitable.

[0045]

As is apparent from the above description, in the magnetic recording medium of the present invention, polyethylene 2,6-naphthalate, which has a reasonably low polyester number average molecular weight of 8000 to 16000, is mainly used as the non-magnetic support. Since a polyester film is used, it is possible to obtain a magnetic recording medium excellent in cutting workability, in which sufficient toughness can be secured even when the film is thinned and the cut edge does not become a high edge when cut. . Therefore, for such a magnetic recording medium, it is possible to obtain a long-time recording cassette tape having excellent durability and tape characteristics by setting the film thickness to be thin and cutting the tape width.

Claims (2)

[Claims] 1. A magnetic recording medium having at least a magnetic layer on a non-magnetic support, wherein the non-magnetic support is a polyester film containing polyethylene 2,6-naphthalate as a main component, and the polyethylene 2,6. A magnetic recording medium characterized in that the naphthalate has a polyester number average molecular weight of 8000 to 16000. 2. The magnetic recording medium according to claim 1, wherein the content of polyethylene 2,6-naphthalate in the polyester film is 70 mol% or more.