JPH0626016B2 - Magnetic tape - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic tape, and more particularly to a magnetic tape in which tape damage is remarkably improved, and the tape has excellent slittability and video sensitivity.

[Prior art]

Since the magnetic tape, particularly the magnetic tape for VTR, generally has a certain limit on the winding diameter, it is desirable to make the magnetic tape as thin as possible in order to increase the amount of recordable information.

However, if the tape is made thin in this way, the mechanical strength becomes insufficient, the so-called waist strength of the tape becomes weak, and the tape easily becomes stretched, and the tape is easily damaged during running. Here, tape damage means V for magnetic tape.
This refers to the stretching deformation of the tape that occurs when recording / reproducing over TR and the bending of both ends in the tape width direction. Tape damage occurs even during normal running, but is particularly likely to occur during loading and unloading. This is because the tension applied to the tape is larger during loading and unloading than during normal running. There are β type and VHS type VTRs, but tape damage is more remarkable in the VHS type.

Therefore, there has been proposed a magnetic tape or the like in which the mechanical strength in the longitudinal direction is enhanced by using a film having a higher Young's modulus in the longitudinal direction, that is, a polyester film stretched more in the longitudinal direction than the width direction as a substrate. But,
With this magnetic tape, the mechanical strength in the width direction has not been improved, so that breakage or the like of the tape edge portion cannot be effectively prevented.

Therefore, it has been proposed to further increase the Young's modulus in the width direction of the magnetic layer by magnetically orienting the magnetic powder in the magnetic layer in the width direction. This method improves the tape damage, but conversely It has the drawback of poor video sensitivity.

On the other hand, a magnetic tape using a film having a higher Young's modulus in the transverse direction, that is, a polyester film stretched more in the transverse direction than in the longitudinal direction as a substrate has been proposed, but this magnetic tape has a drawback that the slitting property is deteriorated. .

[Object of the Invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems, to provide a magnetic tape which is remarkably improved in tape damage and has excellent tape slitting property and video sensitivity.

[Constitution / Effect of Invention]

An object of the present invention is, according to the present invention, a magnetic tape comprising a polyester base film provided with a magnetic layer, the film having a transverse Young's modulus (Y _T ) of 550 (kg / mm ² ) or more. , Young's modulus (Y _M ) in the vertical direction is 500 (kg / m
m ² ) or more and the difference between the Young's moduli of both is in the range of | Y _T −Y _M | <200 (kg / mm ² ), and the Young's modulus (M _This is achieved by a magnetic tape characterized in that the ratio of M 2) to Young's modulus (M _T ) in the lateral direction is in a range satisfying M _M / M _T = 1.0 to 2.0.

In the present invention, the term "polyester" refers to an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid or naphthalene-2,6-dicarboxylic acid as a main acid component, and a glycol such as ethylene glycol, diethylene glycol, tetramethylene glycol or neopentylene glycol. It is a linear thermoplastic polyester containing the main glycol component. Representative polyesters include polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate, and the like. The linear polyesters include not only homopolymers but also copolymers modified by copolymerizing a small proportion of other acid components and glycol components. The polyester may contain, for example, stabilizers such as phosphoric acid, phosphorous acid and esters thereof, titanium dioxide, fine particle silica, and matting agent lubricants such as kaolin.

The polyester film is not particularly limited according to its manufacturing method, but the Young's modulus in the transverse direction (Y _T ) is 550 kg / mm ² or more, the Young's modulus in the longitudinal direction (Y _M ) is 500 kg / mm ² or more, and both Young's modulus difference is | Y _T −Y _M | <200 kg / mm ²
Must be in the range. Young's modulus (Y _M ) in the vertical direction is 5
00kg / mm ² smaller than and transverse direction Young's modulus (Y _T) is not preferable because the tape damage 500 kg / mm ² smaller than the tape becomes poor. The difference between both Young's moduli is | Y _T −
If Y _M |> 200 kg / mm ² and the Young's modulus (Y _M ) in the longitudinal direction is 500 kg / mm ² or more, the Young's modulus in the lateral direction (Y _T ) becomes low and the tape damage becomes bad, which is not preferable.

Furthermore, if | Y _T −Y _M |> 200 kg / mm ² and the Young's modulus in the transverse direction is 550 kg / mm ² or more, the Young's modulus in the machine direction becomes low, resulting in strong stretching in the cross direction. It is not preferable because it causes the state and the slitting property deteriorates.

The polyester base film is more preferably transverse direction Young's modulus (Y _T) and the longitudinal direction of the Young's modulus (Y _M) is O
<(Y _T −Y _M ) <200 kg / mm ² . The film thickness is preferably 15 μm or less, more preferably several μm to 15 μm.

The polyester film can be manufactured, for example, as follows. That is, an amorphous unstretched polyethylene terephthalate film is stretched at about 80 ° C. with a longitudinal stretching ratio of 3 to 4 times, and then at 70 to 90 ° C. within a range of 1.5 times or more and 90% or less of all transverse stretching ratios. First stage transverse stretching, then 85-
Stretching was carried out at a temperature of 150 ° C. and a temperature exceeding the first-stage transverse stretching temperature so that the total transverse stretching ratio was 4.0 to 6.0 times.
It is obtained by heat setting at 0 to 230 ° C. The reason why the transverse stretching temperature is set to two stages is to prevent breakage during film formation, increase the stretching ratio, increase Young's modulus, and reduce transverse heat shrinkage.

In the above method, if necessary, the film may be further stretched in the machine direction before heat setting.

Magnetic layer provided on a polyester base film described above in the present invention is not particularly limited in One by its coating設法, longitudinal Young's modulus of the magnetic layer (M _M) and transverse Young's modulus of the (M _T) The ratio must be in the range M _M / M _T = 1.0-2.0. If this ratio is M _M / M _T <1.0, the video sensitivity is significantly lowered, and if M _M / M _T > 2.0, tape damage is unfavorable. Furthermore, the longitudinal direction of the Young's modulus of the entire magnetic tape (T _M) and transverse direction Young's modulus (T _T) is | _{T M} -T T | <is preferably in the range of 70 kg / mm ^2, which in this way As a result, the tape damage is extremely excellent, and the slitting property and video sensitivity are also excellent,
An excellent magnetic tape can be obtained overall.

To form a magnetic layer on a polyester base film, magnetic powder, a binder, an organic solvent and other additives are applied by any means such as spraying a magnetic coating material or roll coating and drying. The magnetic field orientation of the magnetic powder in the magnetic layer is often performed by passing the undried coating film through an orientation magnetic field generated by a solenoid coil, a permanent magnet or the like.

The magnetic powder is preferably needle-shaped, which is easily oriented in a magnetic field,
The filling rate in the magnetic layer is preferably in the range of 60 to 90% by weight. If this filling rate is too low, sufficient magnetic properties cannot be obtained, and if it is too high, a binder (binder)
Adhesion due to is insufficient and satisfactory mechanical strength cannot be obtained, which is not preferable. Specific examples of such magnetic powder include, for example, needle-shaped γ-Fe ₂ O ₃ powder, Fe ₃ O ₄ powder, Co-containing γ-Fe ₂ O ₃ powder, Co-containing Fe ₃ O ₄ powder, and CrO. ₂ powder, Fe and other magnetic metal powders.

As the binder, for example, vinyl chloride / vinyl acetate resin,
Any of those commonly used as a binder for magnetic powders such as a fibrous resin and a polyurethane resin isocyanate compound can be used.

The organic solvent is not particularly limited, and a solvent suitable for dissolving the above-mentioned binder, for example, methyl isobutyl ketone, cyclohexanone, ethyl acetate, tetrahydrofuran, dioxane, toluene, xylene, etc., alone or in combination of two or more. Can be used.

Furthermore, pigments and other additives may be added to the magnetic paint in order to improve the elastic modulus of the magnetic layer.

The magnetic tape of the present invention is remarkably improved in tape damage, has excellent tape slitting property and video sensitivity, and is useful as a magnetic tape having a high recording density.

〔Example〕

Hereinafter, the present invention will be further described with reference to examples. Each property in the examples was evaluated by the following methods.

(1) Young's modulus (A) Base Young's modulus, tape Young's modulus A film or magnetic tape is sample width 10 mm, length 150 mm
Cut to 100 mm between the chucks and pull speed 10 mm /
Min, a chart speed of 500 mm / min, using an Instron type universal tensile tester. Young's modulus is calculated from the tangent line of the rising portion of the obtained load-elongation curve.

(B) Young's modulus of magnetic layer From the base Young's modulus (Y _M , Y _T ) tape Young's modulus (T _M , T _T ) obtained in (A) above, the magnetic layer Young's modulus (M _M , M _T ) is Calculate from the following formula.

M _M = (T _M × t _TAPE −Y _M t _BASE ) / t _MAG M _T = (T _T × t _TAPE −Y _T t _BASE ) / t _MAG where t _TAPE : Total thickness of magnetic tape (μm) t _BASE : Base film thickness (μm) t _MAG : Magnetic layer thickness (μm) The thickness is measured with an electronic micrometer.

(2) Tape damage A magnetic tape is wound around a VHS video cassette for 345 m, loaded into a VHS video tape recorder, and then run for 300 m from the beginning of the tape. , The unloading is repeated 5 times, and the degree of damage to the tape edge portion is visually observed, and evaluated according to the following criteria (ranked).

◎: No damage to the tape edge portion ○: There is slight damage to the tape edge portion, but there is no problem in practical use △: Damage to the tape edge portion is a little problem in practical use ×: Damage to the tape edge portion is severely impractical (3) Slit A tape is wound around the cassette under the specified conditions of a video device and left in a constant temperature and humidity room at 20 ° C and 60% RH for 1 week. Then, the tape is pulled out from the reel and placed on a flat surface. The tape is not completely flat. Shia evaluates whether the edge of the tape is wavy according to the following criteria (with rank).

◎: No wavy ○: Slight wavy but practically problem X: Wavy, practically problem (4) Video sensitivity Wrap a magnetic tape in a VHS video cassette and record / play it back with a VHS video tape recorder. Then
The relative value with the reference tape is taken and evaluated by ranking as follows.

◎: +2 dB or more ○: 0 to +2 dB △: -2 to 0 dB ×: -2 dB or less (5) Comprehensive evaluation Comprehensive evaluation is the worst (defect) of tape damage, slitting property, and video sensitivity. And rank as follows:

⊚: Good ∘: No problem in practical use Δ: Some problem in practical use ×: Not practically applicable Examples 1 to 4 and Comparative Examples 1 to 7 Kaolin having an average particle size of 0.8 μ was added at the time of polymerization in a content ratio of 0.2% by weight. The above-mentioned kaolin-containing polyethylene terephthalate was melt-extruded according to a conventional method, cooled to form an amorphous unstretched film, and then this film was roll-stretched at a longitudinal stretching ratio shown in Table 1 at 80 ° C. and rapidly cooled, Subsequently, the film was stretched in the transverse direction at 90 ° C. by 2.5 times and further at 105 ° C. at all transverse magnifications shown in Table 1, and heat-set at a heat-setting temperature of 210 ° C. for 10 seconds to obtain a biaxially oriented film.

In Comparative Example 3, three-stage stretching (longitudinal stretching-horizontal stretching-
Re-longitudinal stretching) was performed. This three-stage stretching was performed in the same manner as above except that the stretching ratio shown in Table 1 was adopted to obtain an unheated solid biaxially stretched film, and this film was further longitudinally stretched at the ratio shown in Table 1 and then A biaxially oriented film was obtained by heat setting at a heat setting temperature of 210 ° C. for 10 seconds.

On the other hand, the magnetic paint was prepared as follows.

Co-coated needle-like γ-Fe ₂ O ₃ 100 parts by weight Granular α-Fe ₂ O ₃ (average particle size 1.0 μ) 4〃 carbon black 4〃 zinc stearate 0.5〃 nitrocellulose IIIG 1 10〃 (manufactured by Asahi Kasei Nitrocellulose) Estan 5702 (Urban elastomer manufactured by Good Rituchichem 9 KK, urethane elastomer) -n-butyl stearate 1 〃 Myristic acid 0.5 〃 Cyclohexanone 95 〃 Toluene 95 〃 After mixing and dispersing this composition for 40 hours in a ball mill, Nippon Polyurethane Co., Ltd. Coronate L (isocyanate compound) 3 parts by weight, cyclohexanone 2 parts by weight, toluene 2
What was melt | dissolved in the mixed solvent of 1 part by weight was added, and the mixture was further dispersed for 1 hour to prepare a magnetic coating material. This magnetic coating is applied on a biaxially oriented film (thickness 11 μm) so that the dry thickness is 4 μm, dried while applying an orienting magnetic field in the width direction of the tape or the longitudinal direction of the tape, and calendered to make a magnetic film. A web was prepared and slit to a width of 1/2 inch with a slitter to obtain a magnetic tape.

The characteristics of this magnetic tape are shown in Table 1.

Claims (3)

[Claims] 1. A magnetic tape comprising a polyester base film provided with a magnetic layer, wherein the film has a lateral Young's modulus (Y _T ) of 550 (kg / mm ² ) or more and a longitudinal Young's modulus (Y _T ). Y _M ) is 500 (kg / mm ² ) or more, and the difference between the Young's moduli is in the range of | Y _T −Y _M | <200 (kg / mm ² ), and the magnetic layer magnetic tape ratio of the longitudinal Young's modulus (M _M) and transverse direction Young's modulus (M _T) is equal to or in the range satisfying _M M / M _T = 1.0~2.0 of. 2. Young's modulus (Y _T ) in the lateral direction of the base film
The difference between the longitudinal direction of the Young's modulus _{(Y M) (Y T -Y} M) is _{O <(Y T -Y M)} <200 (kg / mm 2) claims in the range of the first claim of Magnetic tape. Difference 3. A magnetic tape longitudinal Young's modulus of (T _M) and transverse direction Young's modulus (T _T) is | _{T M} -T T | <a range satisfying the 70 (kg / mm ²⁾ The magnetic tape according to claim 1 or 2.