JPH06342514A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve durability over the wide range from low temp. to high temp. by specifying the storage modulus and loss modulus in the case of expressing the complex elasticity modulus of the magnetic layer of the magnetic recording medium so as to satisfy a prescribed condition. CONSTITUTION:When the complex elasticity modulus E* of the magnetic layer of the magnetic recording medium is expressed so as to satisfy the condition of the formula E*=E1+iE2 (E1 is storage modulus and E2 is loss modulus), the elastic modulus E1 at 20 deg.C is (10X10<9>)-(30X10<9>)N/m<2>. And the max. value of the temperature curve of the elasticity modulus E2 is selected in (4X10<8>)-(15X10<8>)N/m<2>, and the modulus E2 at 0 deg.C is selected in 50-100% of the max. value. Because the modulus E2 at low temp. is large, the powder from the magnetic layer of the magnetic recording medium at low temp. is low, and durability is enhanced over the wide range from low temp. to high temp., and the magnetic recording medium having a long service life is obtained.

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 used in audio equipment, video equipment, computers and the like.

[0002]

2. Description of the Related Art In recent years, with the development of camera-integrated video tape recorders and portable equipment, the operating environment of the equipment has greatly expanded from low temperature to high temperature, and the strength of magnetic tape under high temperature environment has increased. It's a problem. If the strength of the magnetic tape in a high temperature environment is insufficient, the end of the tape will be broken or deformed into a seaweed shape during repeated running, making normal recording / reproduction impossible. Further, the tape thickness has been reduced with the downsizing of equipment and recording for a long time, so that the strength of the magnetic tape has been reduced.

Such a decrease in strength of the magnetic tape is caused by the deformation of the magnetic tape under the high temperature environment as described above.
Even during normal recording / reproduction, there is a problem that the head touch is deteriorated due to the decrease in the stiffness of the magnetic tape, and the characteristics during recording / reproduction are deteriorated.

In order to deal with this problem, it is effective to improve the strength of the magnetic layer formed by coating on the main surface of the non-magnetic base film. For this purpose, the elastic modulus (Young's modulus) of the magnetic layer is used. Will need to be increased.

The magnetic layer is generally a fine powder having a ferromagnetism (magnetic powder), a fine powder having a polishing property for improving the head cleaning property and scratch resistance of the magnetic recording medium,
Consists of carbon black for antistatic, binder resin (binder resin) that binds these, a lubricant for reducing the friction coefficient of the magnetic layer surface, and a plasticizer for giving flexibility to the magnetic layer Has been done. The elastic modulus (Young's modulus) of the magnetic layer is affected by the magnetic powder, binder resin, lubricant, and plasticizer, but the magnetic powder is determined by the target magnetic recording medium, and the lubricant is indispensable for the magnetic recording medium. Therefore, the elastic modulus is generally adjusted by the binder resin and the plasticizer.

The binder resin is generally a mixture of nitrification cotton, polyvinyl chloride resin, phenoxy resin, epoxy resin and polyurethane resin.

As the plasticizer, dibutyl phthalate, trimethyl phosphate, and higher fatty acid esters are used. Among them, higher fatty acid esters are often used because they have lubricity.

[0008]

If the binder resin used in the magnetic layer has an appropriate elastic modulus in order to secure the strength of the magnetic tape at room temperature / high temperature environment, brittleness becomes large in a low temperature environment. The magnetic layer becomes brittle, and powder sliding or the like occurs due to sliding with the magnetic head. Further, due to this, durability such as still life in a low temperature environment deteriorates.

Therefore, it is necessary to add the above-mentioned plasticizer in order to improve the brittleness in a low temperature environment. However, when the plasticizer is added, the elastic modulus at the room temperature / high temperature environment side is lowered and the strength of the magnetic tape or the like is decreased. Therefore, there is a problem in the above-mentioned deformation of the magnetic tape, the characteristics at the time of recording and reproducing, and the like.

In view of the above, the present invention aims to improve the durability of the magnetic layer in a wide temperature range from a low temperature to a high temperature by examining changes in the physical properties of the magnetic layer without using a plasticizer.

[0011]

In the dynamic viscoelasticity measurement of a magnetic layer, viscoelasticity is expressed as a complex elastic modulus E * by the following equation.

E * = E ₁ + iE ₂ Here, E ₁ is called a storage elastic modulus, which is a dynamic Young's modulus. Further, E ₂ is called a loss elastic modulus and represents a dynamic viscosity, and is an index of the brittleness of a substance.

When the dynamic viscoelasticity-temperature curve of the magnetic layer of the magnetic recording medium was measured, it was divided into three regions, and the heat distortion temperature (glass transition point:
A temperature region below the glass transition point is called a glass region, a temperature region above the glass transition point is called a rubber region, and a region between the two is called a transition region.

In the glass region, the molecular motion of the binder resin is frozen, the storage elastic modulus E ₁ is high, and the viscosity term
The loss elastic modulus E ₂ representing the damping term is low. The transition region is where molecular motion begins, the storage elastic modulus E ₁ decreases, and the loss elastic modulus E ₂ peaks. The temperature of this peak is considered the glass transition temperature. Above the glass transition temperature is a rubbery region and the binder resin begins to soften. The storage elastic modulus E ₁ in the rubber region is very small because of the entanglement and cross-linking of the binder resin. In the rubber-like region, the molecules can move freely and do not dissipate energy as heat like a weak spring does, so there is little damping and the loss elastic modulus E ₂ is also small.

Generally, the binder resin used in the magnetic layer has a glass transition point: Tg of 40 ° C. or higher, and a storage elastic modulus E ₁ of the magnetic layer in a glass region of the glass transition point: Tg or lower.
Is in the range of 10 × 10 ⁹ N / m ² or more and 30 × 10 ⁹ N / m ² or less. The storage modulus E ₁ of the magnetic layer in the rubbery region having a glass transition point: Tg or higher is 15 × 10 ⁹ N / m ² or lower.

On the other hand, the maximum value of the loss elastic modulus E ₂ near the glass transition point: Tg is generally 3 × 10 ⁸ N / m ² or more 15
× 10 ⁸ N / m ² or less, glass region (around 0 ° C.)
The loss elastic modulus E ₂ is 5 × 10 ⁸ N / m ² or less.

For these reasons, the magnetic layer becomes brittle in the glass region (under a low temperature environment), and the durability such as powder drop due to sliding with the magnetic head and still life deteriorates.

In the present invention, the loss elastic modulus E ₂ has a profound effect on the improvement of brittleness (powder dropping, still life, etc.) in a low temperature environment where the physical properties of the magnetic layer are in the glass region.
It was found based on this finding that the brittleness decreases as the loss elastic modulus E _{2 in the} glass region (under a low temperature environment) increases.

Specifically, the solution provided by the present invention is directed to a magnetic recording medium in which a magnetic layer is formed on at least one main surface of a non-magnetic base film, and the complex elastic modulus E * of the magnetic layer is used. Is expressed as E * = E ₁ + iE ₂ (where E _{1 is the} storage elastic modulus and E _{2 is the} loss elastic modulus), the storage elastic modulus E ₁ at 20 ° C. is 10 × 10 ⁹ N / m ² or more. 30 x 10
⁹ N / m ² or less, the maximum value of the temperature curve of loss elastic modulus E ₂ is 4 × 10 ⁸ N / m ² or more and 15 × 10 ⁸ N / m ² or less, and the loss elastic modulus E at 0 ° C. ₂ is the maximum of 50
% And 100% or less.

[0020]

As described above, the maximum value of the temperature curve of the loss elastic modulus E ₂ is 4 × 10 ⁸ N / m ² or more and 15 × 10 ⁸ N / m ² or less, and the loss elastic modulus E ₂ at 0 ° C. Is the maximum of 50
% Or more and 100% or less, and the loss elastic modulus E ₂ in the glass region is large, so brittleness is eliminated, so that powder falling under a low temperature environment is reduced and the still life is extended.

[0021]

EXAMPLES Examples of the present invention will be described below.

The composition and manufacturing method of the magnetic paint used in the examples and comparative examples are the same, and are as follows.

[Composition of magnetic paint] 100 parts by weight of magnetic powder 1 part by weight of carbon black (0.05 μm in particle size) 7 parts by weight of alumina (0.15 μm in particle size) 16 parts by weight of binder resin 2 parts by weight of myristic acid lubricant Stearic acid 1 part by weight n-Butyl stearate 1 part by weight Curing agent Polyisocyanate 4 parts by weight [Method for producing magnetic paint] Mixture of methyl ethyl ketone / toluene / cyclohexanone in a mixture obtained by removing the lubricant and the curing agent from the composition of the magnetic paint. Solvent (weight ratio 3/3 /
After 1) is added to obtain an appropriate viscosity, the magnetic powder is sufficiently kneaded and dispersed by using a biaxial extrusion kneader and a sand mill disperser. After that, when the above mixture is applied onto a non-magnetic base film for the production of a magnetic recording medium, a lubricant and a curing agent are added so as to have the above solid content composition, and a solid content ratio of 30 is obtained by a mixed solvent. Adjust the magnetic coating composition for application by weight.

Next, the prepared magnetic coating material for coating is coated on a non-magnetic base film, oriented and dried, and then calendered to prepare magnetic recording media, which are used as materials for evaluation of the respective magnetic recording media. To do.

In the case of a magnetic tape, a back coat layer may be formed on the main surface of the base film opposite to the magnetic layer, if necessary. In the case of a floppy disk, magnetic layers are formed on both main surfaces of the base film.

[Measurement of Dynamic Viscoelasticity of Magnetic Layer of Magnetic Recording Medium] The dynamic viscoelasticity of the magnetic recording medium in Examples and Comparative Examples was evaluated by the following method.

Measuring device: Toyo Baldwin RHE
OVIBRON (Dynamic Viscoelastometer) RHEO-2000 type Vibration frequency: 11 Hz Temperature rising rate: 2 ° C./min To calculate the elastic modulus of only the magnetic layer coated on the base film from the elastic modulus E of a layered sample such as a magnetic recording medium. It was calculated from the dynamic viscoelasticity of the magnetic recording medium (base film + magnetic layer) and the dynamic viscoelasticity of the base film only, assuming that the effect of the boundary layer is ignored and the following additivity is established. It was assumed that the same relationship holds for the storage elastic modulus: E ₁ and the loss elastic modulus: E ₂ .

(T1 + t2) × E = t1 × E1 + t2 × E2 E: Elastic modulus of magnetic recording medium (base film + magnetic layer) t1: Thickness of base film E1: Elastic modulus of base film t2: Thickness of magnetic layer E2: Elastic modulus of magnetic layer

(Example) Using a metal alloy powder (BET specific surface area 55 m ² / g) as the magnetic powder and changing the kind of the binder resin, the glass transition temperature (Tg) and storage elastic modulus (E ₁ ) were changed. Almost the same, four types of magnetic tapes (1/2 inch width) having different loss elastic moduli (E ₂ ) were manufactured. Fig. 1 shows the results of the dynamic viscoelasticity measurement of the magnetic layer of each of these magnetic tapes.
(Storage elastic modulus) and FIG. 2 (loss elastic modulus) are shown.

The magnetic tapes A and B are generally known conventional tapes as comparative examples, and are of a type in which the brittleness becomes large and the magnetic layer becomes brittle in a low temperature environment.

The magnetic tapes C and D, which are examples of the present invention, reduce the loss elastic modulus decrease in a temperature environment below the glass transition temperature by blending a binder resin, and reduce the loss of the magnetic layer from a low temperature to a high temperature. Changes in physical properties are less.

Each of the magnetic tapes A, B, C and D is 2
Storage elastic modulus E ₁ at 0 ° C. is 10 × 10 ⁹ N / m ² or more 3
It is 0 × 10 ⁹ N / m ² , and the maximum value of the temperature curve of the loss elastic modulus E ₂ is 4 × 10 ⁸ N / m ² to 15 × 10 ⁸ N / m ^2.
Is. In this respect, there is no feature compared with the conventional magnetic tape, but the loss elastic modulus at 0 ° C. is different from the conventional one, the magnetic tape C is about 55% of the maximum value, and the magnetic tape D has the maximum value. Is about 75%. This point is a feature of the present invention.

These magnetic tapes A, B, C and D are VH
Rolled up in S cassette (tape length 246m), VHS video tape recorder manufactured by Matsushita Electric Industrial Co., Ltd. (Part number NV
-FS900), 40 ℃ ・ 80% RH and 5 ℃ ・
An endurance test was carried out 200 times in a round trip in each environment of 40% RH. Thus, the durability of the magnetic tape under each environment of high temperature and low temperature was evaluated.

The evaluation contents are the increase rate of dropout (after running / initial value) and the decrease of S / N (initial value is ± 0 dB) due to powder falling or the like. The results are shown in (Table 1).

[0035]

[Table 1]

It can be understood from Table 1 that the magnetic tapes C and D have good durability even in a low temperature environment.

Further, in order to evaluate the still durability, the above video tape recorder is used, and the temperature is 25 ° C./50%R.
The still life was evaluated under each environment of H and -10 ° C. The still life was measured at the time when the output of the recorded signal (5 MHz) decreased by -8 dB from the initial value.
The results are shown in (Table 2).

[0038]

[Table 2]

As can be seen from these evaluations, the magnetic tapes C and D show little change in the physical properties of the magnetic layer even in a low temperature environment, and show good durability even in a low temperature environment.

[0040]

As described above, according to the magnetic recording medium of the present invention, the loss at the complex elastic modulus E * = E ₁ + iE ₂ (where E _{1 is the} storage elastic modulus and E _{2 is the} loss elastic modulus). The maximum value of the temperature curve of the elastic modulus E ₂ is 4 × 10 ⁸ N / m ²
15 × 10 ⁸ N / m ² or less, the loss elastic modulus E ₂ at 0 ° C. is 50% or more and 100% or less of the maximum value, and the loss elastic modulus E ₂ in the glass region is large, Brittleness disappears, less powder falls under low temperature environment,
Still life is extended.

Therefore, according to the present invention, it is possible to realize a magnetic recording medium having excellent durability in a wide temperature range from high temperature to low temperature, and its practical value is great.

[Brief description of drawings]

FIG. 1 shows magnetic tapes A and B as comparative examples and examples.
It is a characteristic view which shows the temperature characteristic of storage elastic modulus of C and D.

FIG. 2 shows magnetic tapes A and B as comparative examples and examples.
It is a characteristic view which shows the temperature characteristic of loss elastic modulus of C and D.

Claims (1)

[Claims] 1. A magnetic recording medium having a magnetic layer formed on at least one main surface of a non-magnetic base film,
When the complex elastic modulus E * of the magnetic layer is represented by E * = E ₁ + iE ₂ (where E _{1 is the} storage elastic modulus and E _{2 is the} loss elastic modulus), the storage elastic modulus E ₁ at 20 ° C. 10 x 10 ⁹ N / m
² or more and 30 × 10 ⁹ N / m ² or less, and loss elastic modulus E
The maximum value of the temperature curve of ₂ is 4 × 10 ⁸ N / m ² or more 15 ×
A magnetic recording medium, which has a loss modulus E _{2 of} 10 ⁸ N / m ² or less and 50 ° C. or more and 100% or less of its maximum value at 0 ° C.