JPS621115A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To considerably decrease surface electric resistance, to prevent the output decrease which may arise from the pulverization of ferromagnetic metallic powder having <=0.45mum average major axis diameter and to conversely improve the output by forming a conductive layer on a non-magnetic substrate and forming a magnetic layer contg. said ferromagnetic metallic powder as the magnetic powder on the conductive layer. CONSTITUTION:The conductive layer is formed on the non-magnetic substrate and the magnetic layer contg. the ferromagnetic metallic powder having <=0.45mum average major axis diameter as the magnetic powder is formed on the conductive layer. The conductive coated film formed by coating a conductive paint contg. conductive material particles and binder on the non-magnetic substrate and drying the coating is usually adequate but said layer may be the conductive metallic film deposited by a means such as vacuum deposition on the substrate surface. The ferromagnetic metallic powder having <=0.45mum, more preferably <=0.35mum average major axis diameter is used for the magnetic powder to be incorporated into the magnetic layer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magnetic recording media such as magnetic tapes and magnetic disks that use ferromagnetic metal magnetic powder as a magnetic recording element.

[Prior Art] The magnetic layer of a magnetic recording medium, which is mainly composed of magnetic powder and its binder, generally has a relatively high surface electrical resistance, so it is easily charged, and the attached dust can increase dropouts and cause sliding. In addition, the above-mentioned dust may adhere to the tape running guide portion and cause wrinkles in the tape, which are fatal to magnetic recording media.

Therefore, as a countermeasure to this problem, it has been conventionally carried out to reduce the surface electrical resistance by incorporating a conductive powder such as carbon black into the magnetic layer (unspecified literature).

[Problem that the invention seeks to solve]

However, according to the studies of the inventors, the means for containing conductive powder in the magnetic layer as described above uses oxide-based magnetic powder such as ferromagnetic iron oxide or ferromagnetic chromium dioxide. However, it has been found that when ultrafine ferromagnetic metal powder is used as the magnetic powder, the surface electrical resistance of the magnetic layer cannot be sufficiently lowered.

In other words, in recent years, magnetic powders such as Fe, Co, and
The use of ferromagnetic metal magnetic powders made of Ni, alloys thereof, etc. is gradually increasing, and there is also a tendency for these ferromagnetic metal magnetic powders to be made into ultrafine particles for the purpose of improving short-wavelength high-density recording characteristics. However, according to the findings of the inventors, when the particle size of the ferromagnetic metal magnetic powder is relatively large, the surface electrical resistance can be sufficiently reduced by incorporating a conductive substance into the magnetic layer containing the ferromagnetic metal powder. However, it is possible to reduce dropouts and prevent tape wrinkles by reducing the particle size, but if the particle size is small, especially if the average major axis diameter is 0.45/
If the ultrafine particles are as follows, the surface electrical resistance cannot be lowered by the above-mentioned means, and as a result, problems such as increased dropout due to the adhesion of dust, generation of noise, and generation of tape wrinkles occur.

[Means for solving problems]

In view of this situation, the inventors have conducted extensive studies on means to reduce the surface electrical resistance of the magnetic layer containing ultrafine ferromagnetic metal magnetic powder, and have found that the relationship between the magnetic layer and the non-magnetic support The inventors discovered that if a conductive layer is formed on the surface of the magnet, the surface electrical resistance increases (decreases), and the output does not decrease due to the finer particles of the magnetic powder, but on the contrary, the output increases.This led to the creation of this invention.

That is, in this invention, a conductive layer is formed on a non-magnetic support, and magnetic powder having an average major axis diameter of 0.4 is deposited on this conductive layer.
The present invention relates to a magnetic recording medium in which a magnetic layer containing ferromagnetic metal magnetic powder of 5/'' or less is formed.

[Structure and operation of the invention]

In the magnetic recording medium of the present invention, the conductive layer interposed between the magnetic layer and the non-magnetic support is as described above, although the magnetic powder contained in the magnetic layer is ultrafine ferromagnetic metal magnetic powder. By incorporating a conductive substance into the magnetic layer, the surface electrical resistance, which has been difficult to lower, can be significantly lowered, and the output can be improved by preventing the decrease in output caused by the finer particles of magnetic powder. It has a function.

Although it is not clear why the presence of this conductive layer actually improves the output as described above, it is presumed as follows. In other words, in general, the finer the magnetic powder becomes, the more it loses its aggregate-like action and the strength of the magnetic layer decreases.
During recording and reproducing, the contact stability with the magnetic head deteriorates, which tends to cause a decrease in output. However, the presence of the conductive layer increases the strength of the entire magnetic recording medium, compensating for the decrease in strength due to the finer grain size. Since the effect is so large, it is presumed that the output will actually improve.

As such a conductive layer, a conductive coating film formed by coating and drying a conductive paint containing conductive substance particles and a binder on a non-magnetic support is usually suitable, but it is preferable to use a conductive coating film formed by coating and drying a conductive paint containing conductive material particles and a binder, but It may also be a conductive metal film deposited on the surface of the support by means of other means. In addition, the thickness of the conductive layer is preferably about 0.2 to 1.5 p for the former conductive coating film, and about 0.1 to 0.5 p for the latter conductive metal film; if it is too thick, the flexibility of the tape will decrease. On the other hand, if the tape is too thin, its ability to lower the surface electrical resistance and the effect of improving the overall strength of the tape will be insufficient.

Examples of conductive material particles used to form a conductive layer consisting of a conductive coating include carbon black, graphite, etc., and the average particle size of these particles is 0.02
A value of approximately ˜o, ioμ is suitable. In addition, the amount of such conductive substance used is preferably in the range of about 30 to 70% by weight of the entire conductive layer; if it is too small, the aforementioned conductive function will not be fully exhibited, and if it is too large, the conductive layer will deteriorate. The surface smoothness of the magnetic layer deteriorates, and the adhesion with the magnetic layer formed thereon as well as the surface smoothness of the magnetic layer are impaired, and the binding force of the conductive material particles is insufficient due to a relative decrease in the binder ratio. This causes a decrease in the strength of the conductive layer itself and causes powder to fall off.

The binder used for the conductive layer is vinyl chloride.
Vinyl chloride resins such as vinyl acetate copolymers, vinyl chloride-vinyl acetate copolymers containing hydroxyl or carboxyl groups, butyral resins, cellulose resins, urethane resins, acrylic resins, and other thermoplastic resins However, thermosetting resins or radiation curable resins such as electron beams may be used together with these thermoplastic resins. This radiation-curable resin can be used alone, and the use of such a radiation-curable resin has the advantage of increasing the strength of the conductive layer. These binders may also contain crosslinking agents such as polyisocyanate compounds.

In addition, the conductive paint used for forming the conductive layer may contain barium sulfate, Bengara, calcium carbonate, zinc oxide,
α-AI! Various additives may be blended, such as non-magnetic inorganic fine powder such as chromium oxide, which improves the strength of the coating film, and known dispersants such as fatty acids and lecithin, which improve the dispersibility of conductive material particles.

In this invention, the magnetic powder contained in the magnetic layer is as follows:
As mentioned above, ferromagnetic metal magnetic powder having an average major axis diameter of 0.45/a or less, particularly preferably 0.35 μ or less, is used. In other words, the use of such ultrafine ferromagnetic metal magnetic powder can improve the short wavelength characteristics of magnetic recording media and achieve high recording density, as described above, but it is It is difficult to reduce the surface electrical resistance of the magnetic layer by adding a conductive substance to the magnetic layer.

As the ferromagnetic metal magnetic powder, any of those conventionally known as recording elements of magnetic recording media can be used, such as Fe, Co, Ni, alloys of these metals, these metals and other metals, or a small amount of non-metal. Examples include powders such as alloys containing elements.

In addition, conventional binders for binding the magnetic powder include vinyl chloride-vinyl acetate copolymers, butyral resins, cellulose resins, urethane resins, acrylic resins, and polyisocyanate compounds as crosslinking agents. Any known magnetic powder binder can be used. By making at least a part of the binder of this magnetic layer and the conductive layer the same or similar components, the affinity of both layers is improved, and the adhesion and adhesion strength of the interface of both layers is increased, which improves magnetic recording. The strength of the entire medium is improved,
It has the advantage of higher output.

In the present invention, the magnetic layer can be formed according to a conventional method, by preparing a magnetic paint containing the above-mentioned magnetic powder and a binder, and coating and drying the magnetic paint on the conductive layer previously provided on the support. Bye.

In addition, various additives such as a dispersant, an abrasive, a lubricant, etc. can be appropriately added to the above-mentioned magnetic coating material as necessary.

〔Effect of the invention〕

The magnetic recording medium according to the present invention has an average long sleeve diameter of 0.45.
Since a conductive layer is interposed between the magnetic layer containing ferromagnetic metal magnetic powder of μ or less and the non-magnetic support, the surface is difficult to reduce by conventional means of containing a conductive substance in the magnetic layer. Electrical resistance decreases significantly, resulting in increased dropouts due to dust adhesion, noise generation during sliding,
It has excellent features such as preventing the occurrence of tape wrinkles, and not only compensating for the decrease in output due to the atomization of the magnetic powder, but also improving the output.

[Example] Hereinafter, this invention will be specifically explained based on examples.

In addition, all parts below mean parts by weight.

Example 1 α-AI! 203 (abrasive) 6 parts stearic acid (lubricant) 25 parts n-butyl stearate (lubricant) 1 part hydroxyl group-containing vinyl chloride-vinyl acetate copolymer 9.2 parts (Meiko Slets, a product manufactured by Tsukisui Kagaku Co., Ltd.) A) Cyclohexanone
Part 96
After mixing and dispersing 96 parts of the above composition in a sand mill for 4 hours, 3.1 parts of a trifunctional polyisocyanate compound (trade name: Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) was added and mixed for an additional 0.5 hours to obtain a magnetic paint. was prepared.

On the other hand, the following composition was mixed and dispersed in a sand mill for 6 hours.

Cyclohexanone 400 parts
Le en 40
0 part Subsequently, 50 parts of an electron beam curable resin (trade name DPHA, manufactured by Nihon Kagaku Co., Ltd.) was added to the above mixture, and further 0.
A conductive paint was prepared by mixing for 5 hours.

This conductive paint was applied onto a support made of a polyester film with a thickness of 13 μm so that the thickness after drying was approximately 1.0 μm. After drying, the surface of the formed conductive layer was mirror-finished, and then It was cured by irradiation with an electron beam of 6 Mrad. Next, the magnetic paint was applied onto this conductive layer to a dry thickness of about 2.8 px and dried to form a magnetic layer.The surface was mirror-finished and cut into % inch width. A videotape was made.

Example 2 As magnetic powder, average long axis diameter 0.35/'', average axial ratio 1:9
A videotape was produced in the same manner as in Example 1, except that 100 parts of ferromagnetic Fe--Ni alloy powder was used.

Example 3 A videotape was produced in the same manner as in Example 1, except that 100 parts of ferromagnetic Fe--Ni alloy powder with an average major axis diameter of 0.4 μm and an average axial ratio of 1:8 was used as the magnetic powder.

Example 4 Hydroxyl group-containing urethane resin (same as above) was used in place of the electron beam curing resin used in the conductive paint in Example 1.
A videotape was prepared in the same manner as in Example 1, except that 35 parts of the trifunctional polyisocyanate compound (same as above) were used.

Comparative Example 1 A videotape was produced in the same manner as in Example 1, except that a magnetic layer was formed directly on the support without forming a conductive layer.

Comparative Example 2 A videotape was produced in the same manner as Comparative Example 1, except that 10 parts of carbon black (same as above) was added as a conductive substance to the magnetic paint.

Comparative Example 3 A videotape was produced in the same manner as Comparative Example 2 except that 100 parts of ferromagnetic Fe--Ni alloy powder having an average particle size of 0.6 μm and an average axial ratio of 1 nia was used as the magnetic powder.

Regarding the magnetic tapes obtained in the above Examples and Comparative Examples, the surface electrical resistance of the magnetic layer, tape strength, dropout, various video characteristics, RF output reduction, and tape running properties were measured by the following methods. The results are shown in the table below.

<Surface electrical resistance> Two rod-shaped metal electrodes with a radius of 1 cIn are placed at the same distance as the width of the video tape, and the video tape is placed on top of these electrodes so that their lengths are perpendicular to each other. A load of 5 oNyJ was applied to each end of this tape, a voltage of 500 V was applied to both electrodes, and the surface electrical resistance of the magnetic layer was measured.

Tape strength> As the elastic modulus of the videotape in the longitudinal direction, the tensile strength value at room temperature with a tensile elongation of 1% was measured.

Adopted.

<Dropouts> When a VH5 type VTR modified for high Hc was loaded and recorded and reproduced, the number of dropouts of 5 μsec or more per minute was investigated.

Video characteristics> VHS system VTR modified for %RF output high Hc
A 50% white video signal was recorded and reproduced on a videotape using a 50% white video signal, and the level of the FM modulated reproduced signal was measured using an oscilloscope and expressed as a relative value with respect to the reference tape (Comparative Example 1).

VH5 type VTR modified for 5 chroma output crab high Hc
Record and play back the one-color chroma signal on videotape using
The reproduced signal level of the low frequency converted color signal was measured using an oscilloscope, and is expressed as a relative value with respect to the reference tape (Comparative Example 1).

Video S/N ratio: VH5 system V modified for high Hc
A 50% white video signal was recorded and played back on a videotape using a TR, and the noise of the playback signal was measured using a color video noise measuring device to calculate the S/N ratio, and compared with the reference tape (Comparative Example 1). expressed as a relative value.

Color S/N ratio: VH5 system V modified for high He
A one-color chroma signal is recorded and played back on a videotape using a TR, and the A of the playback signal is measured using a color video noise measuring device.
The S/N ratio was calculated by measuring M noise, and the reference tape (
It is shown as a relative value with Comparative Example 1).

(RF Output Decrease) It is shown in the degree of decrease (dB) from the initial value of low RF output after 20 hours of tape running.

Tape running properties> Indicated by the presence or absence of stick-slip. Note that stick-slip is a phenomenon in which when running on a video cassette deck, the tape does not stick to the tape and the tape does not run at a constant speed.

As is clear from the results in the table above, when the magnetic powder contained in the magnetic layer is a ferromagnetic metal magnetic powder with an average major axis diameter of more than 0.45μ, as in Comparative Example 3 (conductive material powder in the magnetic layer) The surface electrical resistance can be sufficiently lowered by means of containing , and although the S/N ratio is lowered, it is possible to reduce dropouts and improve tape runnability.

However, when the magnetic powder becomes ultrafine particles with an average major axis diameter of 0.45/==1 or less, as shown in the comparison between Comparative Example 1 and Comparative Example 2, the above means cannot reduce the surface electrical resistance. It can be seen that this method has almost no effect in terms of dropout reduction or tape runnability, and that the S/N ratio also decreases.

On the other hand, in the video tapes of Examples 1 to 4 according to the present invention in which a conductive layer was interposed between the magnetic layer and the support,
Although the magnetic powder is ultrafine particles with an average major axis diameter of 0.45μ or less, the surface electrical resistance is greatly reduced, reducing dropouts and improving tape runnability.
In addition, the S/N ratio is improved, and the tape strength is thicker (improved) than those without a conductive layer (Comparative Examples 1 and 2).In addition, unlike conventional magnetic layers, conductive material powder is not provided in the magnetic layer. (Comparative Examples 2 and 3), a decrease in output due to the presence of non-magnetic powder is unavoidable, and the output decreases after running for a long time, resulting in inferior durability.However, according to the present invention, the output is It can be seen that the performance is improved, and there is almost no decrease in output after running for a long time, indicating excellent durability.

Claims (1)

[Claims] (1) A magnetic recording medium in which a conductive layer is formed on a nonmagnetic support, and a magnetic layer containing ferromagnetic metal magnetic powder with an average major axis diameter of 0.45 μm or less as magnetic powder is formed on this conductive layer. .