JPH0589448A - Video tape - Google Patents

Abstract

PURPOSE:To obtain the video tape which is excellent in both electromagnetic conversion characteristics and traveling durability by eliminating the degradation in the electromagnetic conversion characteristics based on an increase in the spacing between a head gap and a magnetic layer surface occurring in the deformation in the transverse direction of the tape by the reduction in the thickness of the high-performance magnetic video tape for recording signals of <=1mum in the shortest recording wavelength at which acicular magnetic particles are oriented at a high degree in the longitudinal direction of the tape. CONSTITUTION:The fine granular particle filler having sizes of >=1/4 times the average minor axis diameter of the acicular magnetic particles having 1/4 to 1/15 average acicular ratio (average major axis diameter/average minor axis diameter) and <=0.2mum average major axis diameter and >=2 times the average major axis diameter. With the average value being in the section in the longitudinal direction of the tape. These particles are incorporated into a magnetic layer at 1 to 10 piece ratio per 20 pieces of such magnetic particles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high performance video tape which is excellent in electromagnetic conversion characteristics and running durability.

[0002]

2. Description of the Related Art In recent years, with the trend toward higher recording densities and higher image quality of video tapes, shorter wavelengths of recording wavelengths, thinner tapes, wider recording bands, and digitization are in progress. .. Under such circumstances, in order to obtain excellent electromagnetic conversion characteristics, high-performance video tapes in which needle-like magnetic particles are highly oriented in the tape longitudinal direction have been developed.

In this high-performance video tape, in order to fully exhibit the recording / reproducing capability, the recording / reproducing magnetic head contacts the magnetic tape without causing spacing in the vicinity of the gear tape. There is a need. On the other hand, conventionally, an attempt has been made to reduce the spacing between the headgear and the surface of the magnetic layer by making the surface of the magnetic layer as smooth as possible.

[0004]

However, in a system which is thinned for high recording density and has a recording band of 10 MHz or more for high image quality, a magnetic head and a video tape at the time of recording / reproducing are used. Since the relative speed between the magnetic head and the
The amount of air entrained on the contact surface with the tape is large, and as a result, the video tape slightly rises and the tape in the width direction is
The deformed shape of the magnetic head has a smaller radius of curvature than that of the curved shape of the magnetic head, and the video tape near the gear head in the center of the magnetic head is further lifted, which causes spacing and electromagnetic conversion characteristics. There was a problem that it decreased.

This problem is recognized as a very prominent tendency, particularly when the recording wavelength is shortened, when it is used for the purpose of recording a signal having a shortest recording wavelength of 1 μm or less, and in the case of digital recording, an error occurs. -It will be a serious problem that will lead to the occurrence.

In order to overcome such a problem, it has been attempted to select and use a non-magnetic support whose strength in the width direction is increased. In this case, a non-magnetic support made of polyester film or the like is used. By nature, the strength in the longitudinal direction tends to decrease, so the video tape
Deformation in the longitudinal direction of the cup causes another problem that running durability is significantly reduced.

In view of the above-mentioned conventional circumstances, the present invention provides a high-performance video tape in which acicular magnetic particles are highly oriented in the tape longitudinal direction, and has a shorter recording wavelength and a thinner tape. In order to achieve the above, the spacing between the headgear tape and the magnetic layer surface is not increased, and the strength in the tape longitudinal direction is also satisfied. Therefore, the video tape has excellent electromagnetic conversion characteristics and running durability. The purpose is to get.

[0008]

In the process of earnestly studying the above-mentioned object, the inventors of the present invention firstly, in the conventional high-performance video tape, due to its thinness, the width direction when the magnetic head is in contact with the magnetic head. The reason why the deformation is marked is that when the acicular magnetic particles are highly oriented in the tape longitudinal direction, the strength in the width direction is greatly reduced compared to the longitudinal direction. It has been found that the decrease in strength in the tape width direction basically becomes larger as the specific surface area of the magnetic particles becomes larger, that is, as the acicular ratio becomes constant, the particle diameter becomes smaller. ..

Therefore, based on the knowledge that the tape strength depends on the shape and orientation of the magnetic particles, it is necessary to compensate for the decrease in the strength in the width direction when the needle-shaped magnetic particles are oriented in the longitudinal direction. As a result of further investigation, when a granular fine particle filler having no shape anisotropy was contained in the magnetic layer of this kind in a specific size and in a specific ratio with respect to the acicular magnetic particles, It is possible to greatly suppress the decrease in the strength in the width direction with respect to the width of the tape, and in this case, the strength in the longitudinal direction is not insufficient. Therefore, even when the recording wavelength is shortened and the tape is thinned, It was clarified that a video tape with excellent electromagnetic conversion characteristics and running durability can be obtained without increasing the spacing between the headgear tape and the magnetic layer surface due to deformation in the tape width direction. Make an invention ItaruTsuta.

That is, the present invention is a thin video tape.
Needles having an average acicular ratio (average major axis diameter / average minor axis diameter) of 1/4 to 1/15 and an average major axis diameter of 0.2 µm or less on a non-magnetic support having a thickness of 10 µm or less. A magnetic layer containing magnetic particles and a binder therefor, and the orientation ratio (residual saturation magnetization amount / maximum saturation magnetization amount) of the magnetic particles in the tape longitudinal direction is 0.78 or more, The shortest recording wavelength is preferably 1 μm or less, preferably 0.6, under the condition that the relative speed between the magnetic head and the video tape is 10 m / sec or more.
In a video tape for recording a signal of less than μm, the average minor axis diameter of the magnetic particles is 1 in the magnetic layer.
/ 4 times or more and 2 times or less of the average major axis diameter of granular fine particle fillers as an average value in the cross section in the tape longitudinal direction, at a ratio of 1 to 10 particles per 20 magnetic particles. It is related to a video tape characterized by including.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The needle magnetic particles used in the present invention include metallic magnetic particles made of Fe, Co, Ni, alloys thereof, alloys containing these and small amounts of other metals or non-metal elements, and the like. γ-Fe ₂ O ₃ , Co-containing γ-Fe
Any of needle-shaped magnetic particles conventionally known as a recording element of a magnetic recording medium, such as iron oxide magnetic particles made of ₂ O ₃ , Fe ₃ O _4, etc., can be used.

The average acicular ratio of such acicular magnetic particles is
Range of 1/4 to 1/15, particularly preferably 1/6 to 1 /
It should be in the range of 12, and the average major axis diameter is
It is preferably 0.2 μm or less and usually up to about 0.1 μm. When the average acicular ratio and the average particle size are out of the above ranges, problems such as dispersibility in the magnetic layer, orientation, filling property, and durability of the magnetic layer are likely to occur, and the resulting video tape is obtained. The electromagnetic conversion characteristics of will be impaired and running durability will deteriorate.

As the binder for dispersing and binding the acicular magnetic particles, vinyl chloride resin, vinyl chloride-vinyl acetate copolymer, fibrin resin, polyurethane resin, polyvinyl butyral resin, From polyester resins, polyisocyanate compounds as cross-linking agents, radiation curable resins that cure by irradiation with electron beams or ultraviolet rays, etc., one type is selected from those conventionally known for magnetic layers of magnetic recording media. They can be used alone or in combination of two or more.

In the present invention, when a magnetic layer containing the above-mentioned acicular magnetic particles and a binder is provided on a non-magnetic support such as a polyester film in a thickness of usually 1 to 4 μm, The orientation ratio (residual saturation magnetization amount / maximum saturation magnetization amount) in the tape longitudinal direction is set to 0.78 or more, preferably 0.80 or more, and is usually set between the magnetic head and the video tape. A video tape for recording a signal having a shortest recording wavelength of 1.0 μm or less, particularly 0.6 μm or less under a high speed condition of a relative velocity of 10 m / sec or more. Here, the above-mentioned orientation ratio of the acicular magnetic particles can be easily set by performing a magnetic field orientation treatment by a conventional method when forming the magnetic layer.

In the magnetic layer having such an orientation ratio, when the thickness of the non-magnetic support is generally 10 μm or less to reduce the thickness of the entire tape, the width of the tape is usually smaller than that in the tape longitudinal direction. Although the strength in the direction tends to be greatly reduced, the problem is that in the present invention, a granular fine particle filler having no shape anisotropy in the magnetic layer has a specific size and is specified with respect to the acicular magnetic particles. It is solved by adding in the ratio of.

Granular fine particle filler used for this purpose
May be granular (including spherical) that does not have shape anisotropy such as needle-shaped or plate-shaped, and various conventionally known abrasives,
Inorganic or organic non-magnetic fillers such as fillers and antistatic agents can be used. Specifically, in addition to alumina particles, α-iron oxide particles, chromium oxide particles, titanium oxide particles, calcium carbonate particles, barium carbonate particles, carbon black, polyvinyl chloride, polystyrene, polyurethane are crosslinked and cured to form an organic solvent. Examples thereof include fine particles insoluble in water, fine particles of polyethylene, polyamide, fluorine resin and silicone resin.

The size of such a particulate fine particle filter is not less than 1/4 times the average minor axis diameter of the acicular magnetic particles,
The size is preferably ⅓ times or more and less than or equal to twice the average major axis diameter, preferably 1.5 times or less. Only when the particle size of the acicular magnetic particles was in such a specific range, the effect of reinforcing the coating film based on the fine particle filler was maximized, and the total thickness was reduced to 13 μm or less. It is possible to greatly suppress the decrease in strength in the width direction of the tape.

In addition to the above-mentioned particle size setting, the effect of reinforcing the coating film is obtained as an average value of the fine particle filler in the magnetic layer in the cross section along the tape longitudinal direction, that is, the tape. This is achieved for the first time by including a specific ratio of 1 to 10 per 20 acicular magnetic particles as an average value when observed in a cross-sectional photograph in the longitudinal direction.

Although the reason for this is not clear, mainly in the gaps between the acicular magnetic particles which are oriented in the longitudinal direction of the tape,
It is necessary to fill the non-magnetic fine particle filler of a suitable particle size so that it becomes dense in the width direction and eventually to reinforce the Young's modulus in the longitudinal direction and the width direction of the coating film to be isotropic. It is estimated that there is no. In fact, in the coating film filled with the above particulate fine particle filler in the above proportion,
It has been confirmed that the ratio of the Young's modulus in the width direction / Young's modulus in the longitudinal direction of this coating film is 0.6 or more, or in some cases, 0.7 or more.

The video tape of the present invention comprises the above-mentioned acicular magnetic particles, a binder and the above-mentioned particulate granular fine particle filler.
Is mixed in a specific ratio to prepare a magnetic coating material to which various known additives such as a dispersant and a coloring agent are added, if necessary, and the coating material is applied onto a non-magnetic support such as polyethylene sulphate film. Then, a magnetic field orientation treatment and a drying treatment are carried out by an ordinary method, and after calendering, it is cut into a predetermined tape width, whereby it can be manufactured. If desired, various layers such as a back coat layer and a top coat layer may be formed on this video tape by a known method.

The thus obtained video tape of the present invention has a non-magnetic support having a thickness of 10 μm or less and a magnetic layer having a thickness of 1 to 4 μm. Young's modulus is the same as the Young's modulus in the same longitudinal direction (usually 800 kg /
(mm ² or more), which is not inferior to that of ordinary steel, usually has a large value of 600 kg / mm ² or more, and sufficiently satisfies the strength in the width direction.

[0022]

As described above, according to the present invention, a magnetic layer in which needle-like magnetic particles having a specific particle size are highly oriented in the tape longitudinal direction is formed in response to a shorter recording wavelength. In this regard, since the magnetic layer contains a particulate fine particle filter of a specific size to the magnetic particles in a specific ratio, the strength in the width direction is insufficient when the tape is thinned. It is also possible to satisfy the strength in the longitudinal direction without causing damage. Therefore, there is no increase in spacing between the headgear tape and the magnetic layer surface due to deformation in the tape width direction, providing a video tape with excellent electromagnetic conversion characteristics and running durability. be able to.

[0023]

EXAMPLES Next, examples of the present invention will be specifically described in comparison with comparative examples. In the following, "parts" means "parts by weight".

Example 1 Fe-based metal magnetic particles 100 parts (average acicular ratio 1/10, average major axis diameter 0.2 μm) Vinyl chloride-based resin 12 parts (Nippon Zeon's trade name MR110) Polyurethane resin 8 parts (Nippon Polyurethane Company trade name N-2301) Alumina particles (average particle size 0.25 μm) 6 parts Carbon black (average particle size 0.024 μm) 1 part n-butyl stearate 2 parts Toluene 65 parts Methyl ethyl ketone 65 parts Cyclohexanone 65 parts

2 of the above composition in a sand grind mill
After kneading and dispersing for 8 hours, 8 parts of a trifunctional isocyanate compound (trade name: Coronet L manufactured by Nippon Polyurethane Co.) as a curing agent and a solvent [toluene / methyl ethyl ketone / cyclohexanone = 1/1/1 (weight ratio )] 300 parts and well mixed with stirring to prepare a magnetic paint.

This magnetic coating is applied on a non-magnetic support made of polyethylene terephthalate film having a thickness of 9.8 μm, a Young's modulus in the longitudinal direction of 760 kg / mm ² , and a Young's modulus in the width direction of 440 kg / mm ^2. The coated tape was applied so that the thickness after calendering would be 2.2 μm, the magnetic particles were oriented in a facing magnetic field of 3 kilo-elstered, and then dried to obtain a raw video tape.

After the surface of the magnetic layer of the original video tape was calendered, the back surface of the tape was coated with a coating composition for a back coat layer having a thickness of 0.8 μm. After coating and drying so that
A video tape was produced by cutting into a mm width.

<Backcoat layer paint> Carbon black 70 parts (trade name MOGUL-L manufactured by KYABOT CORPORATION) Calcium carbonate particles (average particle diameter 0.1 μm) 30 parts Nitrocellulose resin 33 parts (Asahi Kasei Corp. Trade name HIG1 / 2) Polyurethane resin 36 parts (Nippon Polyurethane Company trade name N-2301) Trifunctional isocyanate compound 12 parts (Nippon Polyurethane Company trade name Coronate L) Toluene 250 parts Methyl ethyl ketone 250 Part cyclohexanone 250 parts

Example 2 100 parts of Fe-based metal magnetic particles having an average acicular ratio of 1/8 and an average major axis diameter of 0.15 μm were used, and the amount of alumina particles used was changed to 8 parts. A video tape was produced in the same manner as in Example 1.

Comparative Example 1 A video tape was produced in the same manner as in Example 1 except that the carbon black was not mixed in the magnetic paint.

Each video table of the above-mentioned embodiment and comparative example
For each type, the Young's modulus in the tape longitudinal direction and width direction, the ratio of granular fine particle filler to the acicular magnetic particles in the magnetic layer, the orientation of acicular magnetic particles, and the output (electromagnetic conversion characteristics) ), Running durability was investigated. These results
The results are shown in Table 1 below.

<Young's modulus in longitudinal and width directions of tape> A test piece of about 2 mm x 8 mm is cut out from the video tape along the direction of Young's modulus to be measured, and one end of the test piece is placed in a vibrating device. The resonance frequency (first-order natural frequency) of the test piece was determined by mounting and vibrating while changing the frequency, and the Young's modulus in the longitudinal direction and the width direction was determined according to the following equation (I).

[0033] E: Young's modulus of video tape (Kg / mm ² ) ρ: Density of video tape (Kg / mm ³ ) L: Length of vibrating part of video tape (mm) t: Thickness of video tape ( mm) f ₀ : Primary natural frequency (Hz) of video tape

<Ratio of granular fine particle filler to acicular magnetic particles in the magnetic layer> After the entire video tape is hardened with a thermosetting resin (epoxy resin), the cross section in the longitudinal direction can be observed. Thinly cut with a microtome, and observe it with a transmission microscope. The average number was calculated. Further, from these numbers, the number of granular fine particle fillers per 20 needle-shaped magnetic particles was obtained as an average value in the cross section in the longitudinal direction.

<Orientation of Needle-like Magnetic Particles> From the video tape, a sample having a size of 6 mm × 10 mm was cut out so that its longitudinal direction coincided with the longitudinal direction of the tape, and this was cut into 4 pieces.
VSM device (VS manufactured by Toei Industry Co., Ltd.
In MP-17), the longitudinal direction is set to the magnetic field application direction under the condition of the maximum applied magnetic field of 10 kOelst, and a hysteresis curve is drawn, and the residual saturation magnetization amount (Br) is set to the maximum saturation magnetization amount (Bm). The value Br / Bm divided by was obtained as an index of orientation.

<Output (Electromagnetic conversion characteristics)> By using D-2VTR (DVTR-10) manufactured by Sony Corporation, a single frequency signal of 32 MHz is recorded / reproduced on a video tape at an optimum recording current value (recording wavelength). 0.8 μm), and the output voltage was measured. Output voltage of the video tape of Comparative Example 1 (Vo; mV)
And the output voltage (V; m) of each video tape of Examples 1 and 2.
V) and the output (dB) = 20 × log (V / Vo)
As evaluated.

<Durability> D-2VT made by Sony
Using the R (DVTR-10), a certain section corresponding to a video tape reproduction time of 5 minutes was repeatedly reproduced, rewound, and reproduced 1,000 times, and then taken out to determine the degree of damage to the tape edge. I observed. The evaluation is that there is almost no damage ○, a little damage is recognized but there is no problem in practical use △, it is greatly damaged and the edge is deformed into a wakame shape, and there is a considerable risk of increasing error and running abnormalities The case was designated as x.

[0038]

[Table 1]

From the results shown in Table 1 above, the video tapes of Examples 1 and 2 of the present invention are superior to the video tape of Comparative Example 1 in electromagnetic conversion characteristics and running durability. Is clear.

Next, an example in which the recording wavelength is shortened and the relative speed between the magnetic head and the video tape is increased in order to further improve the recording density and the high image quality is compared. A concrete description will be given in comparison with an example.

Example 3 A video tape was produced in the same manner as in Example 1 except that the tape width was cut to 12.7 mm.

Example 4 A video tape was produced in the same manner as in Example 2 except that the tape width was cut to 12.7 mm.

Example 5 As a non-magnetic support, the thickness was 11.8 μm, the Young's modulus in the longitudinal direction was 730 kg / mm ² , and the Young's modulus in the width direction was 460.
A video tape was produced in the same manner as in Example 3 except that a polyethylene terephthalate film having a weight of Kg / mm ² was used.

Example 6 As a non-magnetic support, the thickness was 11.8 μm, the Young's modulus in the longitudinal direction was 730 kg / mm ² , and the Young's modulus in the width direction was 460.
A video tape was produced in the same manner as in Example 4 except that a polyethylene terephthalate film having a weight of Kg / mm ² was used.

Comparative Example 2 A video tape was produced in the same manner as in Comparative Example 1 except that the tape width was cut to 12.7 mm.

Comparative Example 3 As a non-magnetic support, the thickness was 11.8 μm, the Young's modulus in the longitudinal direction was 730 kg / mm ² , and the Young's modulus in the width direction was 460.
A video tape was produced in the same manner as in Comparative Example 2 except that a polyethylene terephthalate film of Kg / mm ² was used.

Using each of the video tapes of Examples 3 to 6 and Comparative Examples 2 and 3, the output characteristics (electromagnetic conversion characteristics) were evaluated by the following method. The results are shown in Tables 2 and 3 below.

<Output (Electromagnetic conversion characteristics)> MII manufactured by Matsushita
The VTR (U-650) was modified to change the rotational speed of the rotating drum equipped with a magnetic head, and the magnetic head and video tape were changed.
A single frequency signal of 10 MHz at a relative speed of 8 m / sec was recorded / reproduced at the optimum recording current value on the video tape (recording wavelength 0.8 μm) by using a device capable of changing the relative speed between Then, the output voltage was measured. Similarly, a single frequency signal of 30 MHz at a relative speed of 15 m / sec (recording wavelength 0.5 μm) and a single frequency signal of 6.7 MHz at a relative speed of 8 m / sec (recording wavelength 1.2 μm) are also output signals. Was measured.

From these measured values, first, in Examples 3 and 4
As for the video tape of Comparative Example 2, the output voltage (Vo; mV) of the video tape of Comparative Example 2 and Examples 3 and 4 were used.
From the output voltage (V; mV) of each video tape, the output (dB) = 20 × log (V / Vo) was evaluated. In addition, regarding the video tapes of Examples 5 and 6 and Comparative Example 3, the output voltage (V
o; mV) and the output voltage (V; mV) of each video tape of Examples 5 and 6, the output (dB) = 20 × log (V
/ Vo).

[0050]

[Table 2]

[0051]

[Table 3]

From the results of Tables 2 and 3 above, the thickness of the non-magnetic support is set to 10 μm in order to improve the recording density and image quality.
It is apparent that the effect of the present invention is particularly remarkable when the recording wavelength is 0.6 μm or less and the relative speed between the magnetic head and the video tape is 10 m / sec or more. On the other hand, even when the thickness of the non-magnetic support exceeds 10 μm, the recording wavelength is 1.0 μm or less, particularly 0.6 μm.
It is also clear that the effects of the present invention are exhibited when the thickness is m or less.

As described above, according to the present invention, when a magnetic signal having a short recording wavelength is recorded / reproduced, the electromagnetic conversion characteristic is less deteriorated due to the spacing, and this effect is
It can be seen that it is particularly remarkable when recording and reproducing at high speed using a thin non-magnetic support.

Claims (4)

[Claims] 1. Needle-like magnetic particles having an average acicular ratio (average major axis diameter / average minor axis diameter) of 1/4 to 1/15 and an average major axis diameter of 0.2 μm or less on a non-magnetic support. A magnetic layer containing the binder is provided, and the orientation ratio (residual saturation magnetization amount / maximum saturation magnetization amount) of the magnetic particles in the tape longitudinal direction is 0.7.
In a video tape for recording a signal of 8 or more and a shortest recording wavelength of 1 μm or less, in the magnetic layer, the average minor axis diameter of the magnetic particles is 1/4 times or more and the average major axis of the magnetic particles. Granular particulate filter with a size less than twice the diameter
Is contained in a ratio of 1 to 10 per 20 magnetic particles as an average value in the cross section in the tape longitudinal direction. 2. The non-magnetic support has a thickness of 10 μm or less, and the relative speed between the magnetic head and the video tape is recorded / reproduced at a high speed of 10 m / sec or more.
Video tape described in. 3. The video tape according to claim 1, wherein the shortest recording wavelength is 0.6 μm or less. 4. The Young's modulus of the entire tape in the width direction is 600.
The video tape according to any one of claims 1 to 3, which has a Kg / mm ² or more.