JPH0690784B2 - Magnetic recording tape - Google Patents

Description

The present invention relates to a magnetic recording tape, and more particularly to a VTR.
The present invention relates to a magnetic recording tape capable of long-term recording as a magnetic tape.

[Prior Art] As a conventional magnetic recording tape, a magnetic recording tape having a biaxially oriented polyethylene terephthalate film as a support and a magnetic layer mainly composed of γ-iron oxide and a polymer binder is formed on at least one surface of the support. Is used. However, these conventional magnetic recording tapes have the following drawbacks. That is, (1) electromagnetic conversion characteristics are low.

(2) If the tape thickness is made thin, the running property and durability of the tape will be poor, so there is a limit to the thickness, and as a result, there is a limit to the amount of tape that can be wound in a cassette of a predetermined size, resulting in a long recording time. Can not.

By the way, in particular, with the recent miniaturization of household VTRs, the tape width has been reduced from 12.7 mm to 8 mm and the cassette has also been miniaturized. Due to the above-mentioned drawbacks, a magnetic recording tape with a thin tape thickness can be dealt with. There was nothing satisfying.

[Object of the Invention] An object of the present invention is to solve the above-mentioned drawbacks, to provide a magnetic recording tape having excellent electromagnetic conversion characteristics and excellent running property and durability even when it is thin.

[Structure of the Invention] The present invention has a stress of 20 kg at 5% elongation in the length direction of the film.
Young's modulus is 800 Kg / mm ² or more at / mm ² or more, Young's modulus in the width direction is 600 Kg / mm ² , and the sum of these Young's moduli is 150.
0 Kg / mm ² or more and less than 2100 Kg / mm ² and a surface roughness of 0.0
A biaxially oriented polyethylene-2,6-naphthalene dicarboxylate film having a size of 04 to 0.01 μm is used as a support, and at least one surface of the support contains fine acicular ferromagnetic metal powder having a length of 0.1 to 0.3 μm. A magnetic recording tape having a tape thickness of 6 to 10 μm, which is formed by forming a magnetic layer.

The support in the present invention is a biaxially oriented polyethylene-2,6-
It consists of naphthalene dicarboxylate film. This polyethylene-2,6-naphthalene dicarboxylate (P
EN) may be copolymerized with a small proportion of a third component, or may be mixed with a small proportion of another polymer. Such polyethylene-2,6-naphthalene dicarboxylate can be produced by a known method.

The film support in the present invention has a length of 5%.
The stress during elongation (hereinafter referred to as F-5 value) must be 20 g / mm ² or more. If this F-5 value is low, a trouble will occur in the tape running system and it will not be able to withstand repeated running. This F-
The larger the 5 value, the more preferable, but this upper limit is about 40 kg / mm ^{2 because} it is limited by the upper limit of Young's modulus in the longitudinal direction described later.

Furthermore, this support has a Young's modulus in the width direction of 600 kg / mm ² or more, a Young's modulus in the length direction of 800 Kg / mm ² or more, and the sum of the Young's modulus in the width direction and the Young's modulus in the longitudinal direction. Is 15
Needs to be less than 00Kg / mm ² or more 2100 kg / mm ^2. The upper limit of the Young's modulus in the length direction and the Young's modulus in the width direction is naturally limited because the sum of these is 1500 Kg / mm ² or more and less than 2100 Kg / mm ² , and the Young's modulus in the length direction is 1500 Kg / mm2. mm ²
And the Young's modulus in the width direction is 1300 Kg / m
It does not exceed m ² . The reason why such a high Young's modulus is required is that as the film becomes thinner, the stiffness (stiffness of the waist) decreases. This is because the 600K as Young's modulus in the width direction
g / mm ^{2 to} 1200 kg / mm ² are preferred. If the Young's modulus in the width direction is less than 600 kg / mm ^{2, the} electromagnetic conversion characteristics are not sufficient even if the Young's modulus in the length direction is high, and if the Young's modulus in the width direction is too high, tearing of the tape may occur. It is not preferable because In addition, the Young's modulus in the vertical direction is 900 Kg / mm ^{2 to} 1500 K
g / mm ² is preferred. If the Young's modulus in the machine direction is less than 800 kg / mm ² , the electromagnetic conversion characteristics are not sufficient, and if the Young's modulus in the machine direction is too high, tearing of the tape occurs, which is not preferable. When the sum of this Young's modulus is less than 1500 Kg / mm ² ,
The electromagnetic conversion characteristics are not sufficient, and the sum of this Young's modulus is 21.
If it exceeds 00 kg / mm ² , it becomes difficult to obtain a biaxially oriented film without breaking.

Further, the support in the present invention has a surface roughness of 0.004 to 0.010.
Must be μm. The surface roughness (Ra) of the film is 0.
If it is larger than 010 μm, the surface of the magnetic surface cannot maintain the electromagnetic conversion characteristics required for a high-quality magnetic recording tape, which is not preferable. The preferable surface roughness (Ra) is 0.007 μm or less. On the other hand, when the surface roughness (Ra) of the film is smaller than 0.004 μm, the film surface becomes too flat and the coefficient of friction increases, so the film is easy to handle during film formation of the base film and during the processing of magnetic recording materials. Is bad and causes troubles such as wrinkles, which is not preferable.

The surface roughness can be formed by incorporating inert solid fine particles into polyethylene-2,6-naphthalene dicarboxylate or by surface-treating the film surface. Of these, the method using inert solid fine particles is preferable.

In the present invention, the inert solid fine particles are preferably silicon dioxide (including hydrates, diatomaceous earth, silica sand, quartz, etc.); alumina; silicates containing 30% by weight or more of SiO ₂ (for example, Amorphous or crystalline clay minerals,
Aluminosilicate (including calcined products and hydrates), warm asbestos, zircon, fly ash, etc.); Mg, Zn, Zr and Ti
Oxides; Ca and Ba sulfates; Li, Na, and Ca phosphates (including monohydrogen and dihydrogen salts); Li, Na, and K
Benzoate of Ca; Ba, Zn, and Mn terephthalate;
Mg, Ca, Ba, Zn, Cd, Pb, Sr, Mn, Fe, Co and Ni titanates; Ba and Pb chromates; Carbon (eg carbon black, graphite etc.); Glass (eg glass powder) , Glass beads, etc.); Ca, and Mg carbonates; fluorspar and ZnS. More preferably, silicic acid anhydride, hydrous silicic acid, aluminum oxide, aluminum silicate (including calcined products, hydrates, etc.), 1 lithium phosphate,
3 lithium phosphate, sodium phosphate, calcium phosphate, barium sulfate, titanium oxide, lithium benzoate, double salts of these compounds (including hydrates), glass powder, clay (including kaolin, bentonite, clay etc.), talc , Diatomaceous earth, calcium carbonate and the like. Particularly preferably,
Examples include silicon dioxide, titanium oxide, and calcium carbonate. The average particle size of these inert solid fine particles is 0.05-
0.6μm, more preferably 0.08-0.4μm, and its addition amount is 0.01-1.5% by weight (vs PEN), further 0.03-1.0% by weight (same), especially 0.05-0.6% by weight (same) Is preferred.

In the present invention, the biaxially oriented film is required to have the above-mentioned characteristics, but as a method of biaxially oriented, it may be stretched in the longitudinal and transverse directions at the same time by using a general roll or a stenter, or in the longitudinal and transverse directions. However, it is preferable to stretch at least two stages in the longitudinal direction. More specifically, for example, PEN is melt extruded and rapidly cooled to obtain an unstretched film, and the unstretched film has a longitudinal direction of 2.0 to 100
Stretching 4.0 times, then stretching 2.5-4.5 times in the transverse direction at 120-150 ° C, stretching 1.1-2.5 times in the longitudinal direction again at 150-180 ° C, and again 1.05 in the transverse direction at 180-210 ° C. It is preferably produced by a method of stretching to 3.0 times. At that time, the area draw ratio is preferably 20 to 30 times, more preferably 22 to 28 times. After the stretching treatment, it is preferable to finally heat-set at a temperature of 200 to 250 ° C for 1 to 30 seconds.

The magnetic layer in the present invention contains fine acicular magnetic metal powder having a length of 0.1 to 0.3 μm. If the length is less than 0.1 μm, it becomes difficult to disperse the particles uniformly in the binder, and the magnetic recording characteristics deteriorate, which is not preferable. on the other hand,
If it exceeds 0.3 μm, high magnetic property is deteriorated, which is not preferable. As the metal powder, fine acicular iron powder, iron powder containing cobalt atoms, or a combination of these with a small proportion of barium ferrite powder can be preferably used. These are preferably as uniform as possible. Further, 80% by weight or more of the ferromagnetic metal powder is preferably fine acicular iron powder having a length of 0.1 to 0.3 μm.

The ferromagnetic metal powder is usually hardened using a polymer binder. As the polymer binder used for forming the magnetic layer,
Vinyl-based vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, polyvinyl butyral, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butyl acrylate-2-hydroxyethyl methacrylate copolymer, etc. Resins, rubber-based resins such as acrylonitrile-butadiene copolymer, fibrin-based resins such as nitrocellulose and acetylcellulose, crosslinkable resins such as epoxy, phenoxy and urethane may be used, or these may be used in combination. For rust prevention, fine acicular iron powder surface-treated may be used, or a binder may contain a rust preventive agent.

The thickness of the tape composed of the support of the present invention and the magnetic layer is 6 to 10 μm. When the thickness is less than 6 μm, the running property and durability of the tape are poor, and when the thickness is more than 10 μm, the purpose of long-time recording cannot be achieved.

EFFECT OF THE INVENTION The magnetic recording tape of the present invention has a surface roughness of 0.004 to 0.010.
A biaxially oriented film of μm is used as a support, and
Since the magnetic layer made of fine acicular ferromagnetic metal powder having a length of 0.1 to 0.3 μm is formed, it has a feature that the coercive force is large. Furthermore, the support has a Young's modulus in the width direction of 600 kg / mm ²
With the above, the stress at 5% elongation in the longitudinal direction is 20 kg / mm ² or more,
It is a biaxially oriented film with a Young's modulus of 800 Kg / mm ² or more, and the sum of the Young's modulus in the width direction and the Young's modulus in the length direction is 1500 Kg / mm ² or more and less than 2100 Kg / mm ² for magnetic recording. Even if the thickness of the tape is 6 to 10 μm, the tape has good running property and durability, and the tape thickness of the magnetic recording tape can be thinned even in the case of the beta type or the 8 mm type cassette of the home VTR. Therefore, it is possible to record for a long time.

[Examples] The present invention will be further described based on Examples below. Incidentally, various physical properties and characteristics in the present invention are measured and defined as follows.

(1) Young's modulus The film is cut into a sample with a width of 10 mm and a length of 15 cm.
The tensile modulus is 10 mm / min and the chart speed is 100 mm / min, and the Young's modulus is calculated from the tangent line of the rising portion of the obtained load-elongation curve.

(2) F-5 value When the Young's modulus is measured, the tensile speed is 100 mm / min, and the chart speed is 100 mm / min.

(3) Film surface roughness (Ra) Center line average roughness: Ra (unit: μm) is a value defined by JIS-B0601.

In the present invention, the stylus type surface roughness meter (SU
RFCORDER SE-30C), stylus radius: 2 μm, measurement pressure: 0.
03g, Cut-off value: Draw a film surface roughness curve under the condition of 0.25mm, extract the measured length L part from the obtained film surface roughness curve in the direction of its center line, and extract the center line of this extracted part. Is the X-axis, the vertical magnification direction is the Y-axis, and the roughness curve is represented by Y = f (x), the value (Ra: μm) given by the following equation is defined as the film surface roughness.

In the present invention, 5 pieces are measured with a reference length of 2.5 mm, and Ra is expressed as an average value of 4 pieces, one of which is the largest value.

(4) Electromagnetic conversion characteristics of magnetic coating film The video characteristics are VHS system VTR (Nippon Victor Company Ltd.)
7300 ”) was used to measure the playback output at 4 MHz. The standard tape is a commercially available γ-Fe ₂ O ₃ layer coating type 1 / 2VHS tape.

The C / N ratio is the C / N ratio when a carrier signal of 4 MHz is recorded and the level of the reproduced amplitude-modulated signal at 30 MHz is the noise level.

(5) Durability of magnetic tape A cassette was recorded in a home video tape recorder (helical scan) and the running condition was checked for 100 hours while starting and stopping the running repeatedly. The running condition was measured and the output was measured. If you want to drive:
Good, if not so, runnability: judged as poor.

The end of the tape does not break or wakame-like tape does not squeal during running The tape does not tear or break Example 1 Polyethylene with an average particle size of 0.15 μm and 0.15% by weight of silica having an intrinsic viscosity of 0.65 After drying the pellets of -2,6-naphthalene dicarboxylate (PEN) at 180 ° C for 4 hours,
It is supplied to the extruder hopper and melted at a melting temperature of 295 to 305 ℃, and this molten polymer is molded and extruded on a rotating cooling drum with a surface finish of about 0.3 S and a surface temperature of 70 ℃ through a slit die with a 0.8 mm opening, and the An unstretched film of 113 μm was obtained.

The unstretched film thus obtained was stretched in the longitudinal direction to 3.0 times in the longitudinal direction while heating at 120 ° C. by a known roll stretching method, and further in the transverse direction while heating at 130 ° C. by a known stenter method. Stretching 3.5 times, then while stretching at 170 ℃ by roll stretching method, draws 2.0 times, then stretches 1.2 times at 190 ℃ with a stenter, then heat set at 240 ℃, biaxially oriented PEN of 4.5 μm thickness I got a film.

On the other hand, α-Fe ₂ O ₃ obtained by thermally decomposing needle-shaped α-FeOOH containing 5% of cobalt was hydrogen-reduced to obtain ferromagnetic iron powder having an average needle-shaped length of 0.2 μm.

100 parts by weight of the above ferromagnetic iron powder (hereinafter simply referred to as "part") and the following composition were kneaded and dispersed in a ball mill for 12 hours.

Polyester polyurethane 12 parts Vinyl chloride-vinyl acetate-maleic anhydride copolymer 10 parts α-alumina 5 parts Carbon black 1 part Butyl acetate 70 parts Methyl ethyl ketone 35 parts Cyclohexanone 100 parts Further after dispersion Add 1 part of fatty acid ester (amyl stearate) and knead for 15 to 30 minutes. Further, 7 parts of a 25% ethyl acetate solution of a triisocyanate compound was added, and the mixture was subjected to high-speed shear dispersion for 1 hour to prepare a magnetic coating solution. The coating solution thus obtained was dried on a PEN film having a thickness of 4.5 μm to give a dry film thickness of 2.5 μm.
Was applied so that

Then, after orientation treatment in a direct current magnetic field, it was dried at 100 ° C. After drying, it was calendered and slit into a width of 1/2 inch and a width of 8 mm to obtain a magnetic tape for video having a thickness of 7 μm.

The evaluation results of the magnetic tape thus obtained are as shown in Table 1, and the electromagnetic conversion characteristics were sufficiently high with a C / N ratio of + 7.0αB and the durability of the tape was good.

Furthermore, the maximum tape length that can be stored in a commercially available 8 mm video cassette was 158 m.

Examples 2 to 3 In Example 1, the dry film thickness and the draw ratio of the magnetic layer of the unstretched film were adjusted to obtain magnetic tapes having a thickness of 9 μm and 10 μm, respectively. The evaluation results of this tape are shown in Table 1. Similar to Example 1, the electromagnetic conversion characteristics and the durability of the tape were good, and the maximum tape lengths that could be stored in the 8 mm video cassette were 123 m and 111 m, respectively.

Comparative Example-1 In Example 1, γ-Fe ₂ O ₃ was used instead of the ferromagnetic iron powder having an average acicular length of 0.2 μm.

The characteristics of this tape are shown in Table 1. As the electromagnetic conversion characteristics, the reproduction output was small and it was not preferable as a magnetic recording tape.

Comparative Example-2 A magnetic recording tape having a tape thickness of 11 μm was obtained by increasing the unstretched thickness in Example-2, but the electromagnetic conversion characteristics and durability are good, but the tape length that can be stored in an 8 mm video cassette is long. Was only 101m.

Comparative Example-3 In Example-2, the average particle size is 0.6 instead of silica.
μm kaolin was used.

The magnetic recording characteristics are shown in Table 1. As the electromagnetic conversion characteristics, the video output was insufficient and the magnetic recording tape was unsatisfactory.

Comparative Example-4 Polyethylene terephthalate (PET) having an intrinsic viscosity of 0.67 was used in place of PEN in Example-2. However, the melting temperature was 275 to 295 ° C., the cooling drum temperature was 40 ° C., and the stretching ratio and stretching temperature in the first and second stages in the longitudinal and transverse directions were appropriately lowered. Table 1 shows the characteristics of the obtained tape.
There was nothing that could withstand the running and durability of the tape, and the electromagnetic conversion characteristics were insufficient.

Comparative Examples-5 and 6 Tapes with different F-5 Young's moduli were obtained by changing the stretching conditions in Example-1, but none of these had satisfactory durability. The results are shown in Table 1.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Yamamoto 3-37-19 Oyama, Sagamihara City, Kanagawa Prefecture, Teijin Ltd. Plastics Laboratory (56) Reference JP-A-50-54306 (JP, A) JP 62-135339 (JP, A) JP-A-55-125588 (JP, A)

Claims (2)

[Claims] 1. The stress at 5% elongation in the length direction of the film is 20.
Young's modulus kg / mm ² or more and is 800 Kg / mm ² or more and the Young's modulus in the transverse direction is 600 Kg / mm ² or more, the sum of these Young's modulus be less than 1500 Kg / mm ² or more 2100 kg / mm ² And biaxially oriented polyethylene having a surface roughness of 0.004 to 0.01 μm
Tape thickness obtained by using 2,6-naphthalene dicarboxylate film as a support and forming a magnetic layer containing fine acicular ferromagnetic metal powder having a length of 0.1 to 0.3 μm on at least one surface of the support. 6-10 μm magnetic recording tape. 2. 80% by weight or more of the ferromagnetic metal powder is 0.1 to 0.3.
The magnetic recording tape according to claim 1, which is fine needle-shaped iron powder having a length of μm.