JPH0618070B2 - Magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium capable of high-density long-time recording, particularly a magnetic recording medium for VTR.

[Prior Art] Conventionally, as a magnetic recording medium, a magnetic recording medium in which a biaxially oriented polyethylene terephthalate film is used as a substrate and a magnetic layer mainly composed of γ-iron oxide and a polymer binder is formed on at least one surface thereof has been used. There is. Further, in recent years, a magnetic recording medium in which a magnetic layer made of a ferromagnetic metal such as cobalt or nickel is formed on at least one surface of the substrate has attracted attention and has been partially used.

Regarding these magnetic recording media, in recent years, high density recording,
There is an increasing demand for recording for a long time, and in particular with the miniaturization of household VTRs, the tape width has become narrower from 12.7 mm to 8 mm, and the cassettes have also become smaller. To impart these characteristics, thin the base film,
Further, it is necessary to make the magnetic layer thin, but the conventional base film causes various problems when the thickness is made thin, and there is a limit in imparting these characteristics. For example, if the base film is thin, (1) the stability of the film in the coating of magnetic paint or the physical vapor deposition process of ferromagnetic metal is reduced, and as a result it is difficult to form a thin and uniform magnetic layer, Also (2)
The runnability and durability of the magnetic recording medium become poor.

[Object of the Invention] An object of the present invention is to solve the above problems, to have good electromagnetic conversion characteristics, and to have excellent tape running property and durability, and a good magnetic recording medium, particularly high density recording for a long time. It is to provide a magnetic recording medium for a VTR.

According to the present invention, in the magnetic recording medium having a magnetic layer provided on at least one surface of the base film, the base film has a stress at 5% elongation in the longitudinal direction. But
15kg / mm ² or more, Young's modulus in the longitudinal direction is 650kg / mm ²
Or more and the width direction of the Young's modulus 500 kg / mm ² or more by the sum of these Young's modulus is in the range of 1400~2100kg / mm ^2, 150 ℃
In the longitudinal direction, the biaxially oriented polyethylene-2,6-naphthalene dicarboxylate film has a heat shrinkage in the longitudinal direction of 4% or more, a heat shrinkage in the width direction of 0 to 8%, and a crystallinity of 50% or less. It is achieved by a magnetic recording medium characterized by

The polymer constituting the base film in the present invention is
Polyethylene-2,6-naphthalene dicarboxylate. The polyethylene-2,6-naphthalene dicarboxylate 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.

In the present invention, the base film is required to have a 5% elongation stress (hereinafter referred to as F-5 value) in the longitudinal direction (length direction) of 15 kg / 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. Further, the base film has a Young's modulus in the longitudinal direction of 650 kg / mm ² or more, preferably 650 to 1500 kg / mm ^2.
In the width direction Young's modulus (horizontal direction) is 500 kg / mm ² or more, preferably at 500~1200kg / mm ^2, and (the sum of the longitudinal Young's modulus and the Young's modulus in the transverse direction) sum of Young's modulus 1400
Must be in the range of ~ 2100kg / mm 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 If the Young's modulus in the longitudinal direction is less than 650 kg / mm ² , the electromagnetic conversion characteristics are not sufficient, and if the Young's modulus in the longitudinal direction is too high, tearing of the tape occurs, which is not preferable. When the Young's modulus in the width direction is less than 500 kg / mm ^{2, the} electromagnetic conversion characteristics are not sufficient even if the Young's modulus in the longitudinal direction is high, and when the Young's modulus in the width direction is too high, the tape tears. It is not preferable because it will occur. Furthermore, the sum of these Young's moduli is 1500 kg / mm ²
When it is less than 1, the electromagnetic conversion characteristics are not sufficient, and when the sum of the Young's moduli exceeds 2100 kg / mm ² , it becomes difficult to obtain a biaxially oriented film without breaking.

The base film further has a heat shrinkage ratio of 4% or more in the longitudinal direction at 150 ° C. and a heat shrinkage ratio of 0 to 8 in the width direction.
Must be%. If the heat shrinkage ratio at 150 ° C in the longitudinal direction is less than 4%, the film cannot be applied with tension corresponding to the shrinkage in the width direction, and wrinkles are caused by uneven tension on the film, which may cause coating unevenness or vapor deposition. Cause spots. If the heat shrinkage ratio at 150 ° C in the width direction is negative, it is not possible to apply appropriate tension to the film during the coating or vapor deposition process of the magnetic layer, resulting in coating spots and vapor deposition spots, resulting in uniform coating. It becomes difficult to form the magnetic layer. On the other hand, if it exceeds 8%, excessive tension is applied, which makes coating and vapor deposition difficult.

Further, the base film needs to have a crystallinity of 50% or less. The term "crystallinity" as used herein means the weight distribution crystal calculated from the film density with the crystal density of polyethylene-2,6-naphthalene dicarboxylate being 1.407 g / cm ³ and the amorphous density being 1.328 g / cm ^3. It is expressed by the degree of chemical conversion. This crystallinity is 50% from the viewpoint of adhesion to the magnetic layer.
When the crystallinity exceeds 50%, the adhesive force with the polymer binder and the vapor deposition force of the metal element decrease, and it becomes difficult to form a uniform and strong magnetic layer.

In the present invention, the base film preferably has a heat shrinkage in the longitudinal direction at 70 ° C. of 0.1% or less. If the heat shrinkage ratio is too large, the dimensional change of the magnetic recording medium will occur due to the temperature change of the use environment, and a signal shift will occur during magnetic recording and reproduction, which is not preferable.

The biaxially oriented polyethylene-2,6-naphthalene dicarboxylate film (base film) in the present invention is
The surface roughness (Ra) is 0.010μm or less, and further 0.007μ
It is preferably m or less. If the surface roughness (Ra) is too large, the magnetic layer cannot maintain the electromagnetic conversion characteristics required for a high-quality magnetic recording tape, which is not preferable.

The above surface roughness is in polyethylene-2,6-naphthalene dicarboxylate (hereinafter sometimes abbreviated as PEN).
It can be formed by incorporating inert solid fine particles into the film 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, aluminosilicates (including fired products and hydrates), 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 benzoates; C
terephthalates of a, Ba, Zn, and Mn; Mg,
Ca, Ba, Zn, Cd, Pb, Sr, Mn, Fe, C
e and Ni titanates; Ba and Pb chromates; carbon (eg carbon black, graphite etc.); glass (eg glass powder, glass beads etc.);
Examples include Ca and Mg carbonates; fluorspar and ZnS. More preferably, silicic acid anhydride, hydrous silicic acid, aluminum oxide, aluminum silicate (calcined product,
(Including hydrates), 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, etc. are exemplified. Particularly preferred are silicon dioxide, titanium oxide, and calcium carbonate. The average particle size of these inert solid fine particles is 0.05-0.6 μm,
0.08 to 0.4 μm is preferable, and the addition amount is 0.01 to 1.5
% By weight (vs. PEN), further 0.03 to 1.0% by weight (same),
It is particularly preferably 0.05 to 0.6% by weight (the same).

In the present invention, the biaxially oriented film needs to have the above-mentioned properties, but as a method of biaxial orientation, 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 respectively. Yes, but at least 2 vertically
It is preferable to stretch more than one step. The stretching conditions are, for example, the stretching temperature is the first stage stretching temperature (for example, the longitudinal stretching temperature:
T ₁ is in the range of (Tg-10) to (Tg + 45) ° C (however,
From Tg: glass transition temperature of polyester), the second stretching temperature (for example, transverse stretching temperature: T ₂ ) is (T ₁ +15)
It is good to select from the range of (T ₁ +40) ° C. The stretching ratio may be selected from a range in which the stretching ratio in the uniaxial direction is 2.5 or more, particularly 3 or more, and the area ratio is 8 or more, particularly 10 or more. Furthermore, the heat setting temperature is 180-250
C., and more preferably from 200 to 230.degree.

The thickness of the biaxially oriented film is preferably 15 to 4 μm, and the base film of the coating type magnetic layer is 9 to 4 μm.
Is preferable, and as the base film of the vapor-deposited magnetic layer,
It is preferably 14 to 6 μm.

The magnetic recording medium in the present invention is one in which a magnetic layer is provided on at least one surface of the above-mentioned base film, that is, on one side or both sides. The magnetic layer is composed of a polymer binder containing a ferromagnetic powder. , What is called a coating type magnetic layer, or a physical vapor deposition of a ferromagnetic metal,
A so-called vapor deposition type magnetic layer may be used.

Preferred examples of the ferromagnetic powder used in the coating type magnetic layer include γ-iron oxide, Co-containing iron oxide, iron powder, iron powder containing Co, and a combination of these with barium ferrite. These are preferably as uniform as possible.
Further, 80% by weight or more of the ferromagnetic metal powder is 0.1 to 0.3 μm.
It is preferable that the length is fine acicular iron powder. Also, as the polymer binder, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, polyvinyl butyral, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butyl acrylate-2-hydroxythiol Preferable examples include vinyl resins such as methacrylate copolymers, rubber resins such as acrylonitrile-butadiene copolymers, fiber resins such as nitrocellulose and acetylcellose, and crosslinkable resins such as epoxies, phenoxys and urethanes. These may be used alone or in combination. or,
For rust prevention, fine acicular iron powder surface-treated may be used, or a rust preventive agent may be contained in the binder.

If desired, the coating type magnetic layer may be added with other agents such as an anti-friction agent (eg alumina), a light-shielding agent (eg carbon black), a lubricant, a dispersant, an antistatic agent and the like.

The coating type magnetic layer can be formed by a conventionally known method. For coating the magnetic paint, for example, a roll coating method, a gravure coating method, a roll brushing method, a spray coating method, an air knife coating method or the like can be used. The thickness of this magnetic layer is preferably 3 to 2 μm.

Further, examples of the ferromagnetic metal used for the vapor deposition type magnetic layer include cobalt, nickel, alloys of these and chromium, and the like. This vapor deposition type magnetic layer can be formed by a conventionally known method, for example, a vacuum vapor deposition method, a sputtering method or the like. The thickness of this magnetic layer is preferably about 1 μm.

The magnetic recording medium of the present invention is improved in troubles during its production, has good running properties and durability, and has a magnetic layer that is uniformly and firmly adhered to the base film. It has excellent conversion characteristics and is useful as a medium capable of high-density, long-time magnetic recording.

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

(1) Young's modulus The film is cut into a sample width of 10 mm and a length of 15 cm.
The Young's modulus is calculated from the tangent line of the rising portion of the obtained load-elongation curve by setting it to 0 mm and pulling at a tensile speed of 10 mm / min and a chart speed of 100 mm / min with an Instron type universal tensile tester.

(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) Heat shrinkage rate at 150 ° C. The film is cut out in a 35 cm square, marked points at 30 cm intervals are provided in the longitudinal direction and the width direction, heat treatment is performed at 150 ° C. for 30 minutes, and the shrinkage rate is obtained from the dimensional change before and after the heat treatment.

(4) Heat shrinkage rate at 70 ℃ The film was cut out in the lengthwise direction of the film with a width of 6.35 mm and a length of 55 cm, and marked with a gauge length of about 30 cm, 15 g
It is read to 1/1000 mm using a digital precision length measuring machine (made by Free Co.) with a load of, and this film sample piece is heat treated at 70 ° C for 1 hour, then again after heat treatment with a digital precision length measuring machine. Read the distance between gauge points to 1/1000 mm and obtain the shrinkage ratio by the dimensional change before and after heat treatment.

(5) Film surface roughness (Ra) Center line average roughness: Ra (unit: μm) JIS-B06
This is the value defined by 01.

In the present invention, a stylus type surface roughness meter (S
URFCORDER SE-30C) is used to draw a film surface roughness curve under the conditions of a stylus radius: 2 μm, a measurement pressure: 0.03 g, and a cutoff value: 0.25 mm. A portion of the measurement length L is extracted in the direction of the line, the center line of the extracted portion is the X axis, the direction of longitudinal magnification is the Y axis, and the roughness curve is Y = f.
When expressed by (x), the value given by the following equation (Ra: μ
m) is defined as the film surface roughness.

^{_{Ra = 1 / L∫ O L |}} f (x) | In the dx present invention, the reference length was five measured as 2.5 mm, represents the Ra as four average person one to except the larger value.

(6) Electromagnetic conversion characteristics of magnetic coating film The video characteristics are VH with the recording / playback head modified to Sendust alloy.
S system VTR (manufactured by Victor Company of Japan, 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 a C / N ratio when a carrier signal of 4 MNz is recorded and the level of the reproduced amplitude modulated signal at 30 MHz is used as a noise level.

When the reproduction output and C / N are 7 dB or more, it is excellent. When it is 3 dB or more and less than 7 dB, it is good.

(7) Durability of magnetic tape Cassettes for home video tape recorders (helical scans), while running and repeating running, are fed for 100 hours to check the running state and measure the output.
When all of the following items are satisfied in this run, the runnability is judged to be good, and otherwise the runnability is judged to be poor.

The ends of the tape do not break or become wakame-like. No squeaking of the tape occurs during running. The tape does not tear or break Example 1 Pellets of polyethylene-2,6-naphthalene dicarboxylate (PEN) with an intrinsic viscosity of 0.60 After pre-drying at 110 ° C for 3 hours and further drying at 180 ° C for 4 hours, supply to the extruder hopper and melt at a melting temperature of 295 to 305 ° C. Finish the surface of this molten polymer through a slit die with an opening of 1.0 mm.
It was molded and extruded on a rotary cooling drum having a surface temperature of 60 ° C. and a surface temperature of about 0.3 S to obtain an unstretched film of 140 μm in thickness.

The unstretched film thus obtained is preheated to 120 ° C. by a known roll stretching method and then stretched 5.0 times in the machine direction while being heated to 150 ° C. with an infrared heater (first stage stretching). , Further, by the known stenter method, 130
Stretching 4.0 times in the transverse direction while heating to ℃ (second stage stretching), heat setting at 200 ℃, and then continuing at 180 ℃ in the transverse direction 1.
The film was stretched 05 times (third stage stretching) to obtain a biaxially oriented PEN film having a thickness of 7.0 μm.

On the other hand, needle-like α-FeOOH containing 5% cobalt
Α-Fe ₂ O ₃ obtained by heating and decomposing the above was reduced with hydrogen to obtain a 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 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 After the above dispersion treatment, further Was added and kneading was continued 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 obtained coating liquid was applied onto the PEN film having a thickness of 7.0 μm to give a dry film thickness of 3.0 μm.

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 1/2 inch width to obtain a magnetic tape for video having a thickness of 10 μm.

The evaluation results of the magnetic tape thus obtained are as shown in Table 1, the electromagnetic conversion characteristics were excellent, and the tape durability was also good.

Examples 2 to 3 In Example 1, the thickness of the unstretched film, the stretching ratio and the heat treatment conditions were adjusted to obtain magnetic tapes each having a thickness of 10 μm.

The evaluation results of this magnetic tape are shown in Table 1.
Like the above, the electromagnetic conversion characteristics and the durability of the tape were good.

Comparative Example 1 A magnetic tape having a thickness of 10 μm was obtained in the same manner as in Example 1 except that the heat setting temperature was changed to 250 ° C. The evaluation results of this tape are shown in Table 1. The electromagnetic conversion characteristics of C / N were poor and the tape was unsatisfactory as a magnetic recording medium.

Example 4 In Example 3, the third stage stretched film was aged at 80 ° C. for 24 hours. The 70 ° C. heat shrinkage of the film of Example 3 is
0.08%, but the film after aging is 0.03%
Is. A magnetic layer was formed on this film in the same manner as in Example 3.

The tape thus obtained had good running properties, durability, and electric conversion characteristics, like the tape which was not subjected to the temperature change even after 100 cycles in the atmosphere of temperatures 0 ° C. and 50 ° C.

Comparative Examples 2 and 3 In Example 1, the thickness of the unstretched film, the stretching ratio and the heat treatment conditions were adjusted to obtain magnetic tapes each having a thickness of 10 μm.

The evaluation results of this magnetic tape are shown in Table 1. Comparative Example 2
The film of Comparative Example 3 has a low F-5 value and Young's modulus in the longitudinal direction, and the film of Comparative Example 3 has a low Young's modulus in the width direction and has poor reproduction output and C / N as electromagnetic conversion characteristics, which is unsatisfactory as a magnetic recording medium. It was a thing.

 ─────────────────────────────────────────────────── ─── 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-47-38006 (JP, A) JP Sho 49-114916 (JP, A) JP 62-28918 (JP, A)

Claims (2)

[Claims] 1. A magnetic recording medium having a magnetic layer provided on at least one surface of a base film, wherein the base film has a stress at 5% elongation in the longitudinal direction of 15 kg / mm ² or more,
Young's modulus in the longitudinal direction is 650 kg / mm ² or more, Young's modulus in the width direction is 500 kg / mm ² or more, and the sum of these Young's moduli is 1400 to 2
Within the range of 100 kg / mm ² , the heat shrinkage in the longitudinal direction at 150 ° C is 4% or more, and the heat shrinkage in the width direction is 0 to 8%.
And a biaxially oriented polyethylene with a crystallinity of 50% or less
A magnetic recording medium comprising a 2,6-naphthalene dicarboxylate film. 2. A magnetic recording medium according to claim 1, wherein the thermal shrinkage of the film at 70 ° C. in the longitudinal direction is 0.1% or less.