JPS61151834A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the titled magnetic recording medium having excellent antistatic and traveling properties by electrifying positively the surface of the magnetic layer in the magnetic recording medium wherein hexagonal-system ferromagnetic powder is incorporated as the magnetic powder. CONSTITUTION:The following methods are exemplified to electrify the surface of a magnetic layer. Firstly, magnetic powder which is easy to be positively electrified is selected from hexagonal-system magnetic powder, and used as the magnetic powder. Secondly, inorg. powder having a positively electrifiable property, a surfactant capable of providing a positively electrifiable property, and an electrification controlling agent are added into a magnetic paint or dispersed in the magnetic paint. Thirdly, a magnetic paint is coated on a positively electrified base body. Fourthly, the pH of a magnetic paint is regulated and made higher than the isoelectric point to electrify positively the surface of the magnetic layer. The methods are applied separately, or a combination of the methods is applied.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a magnetic recording medium using hexagonal ferromagnetic powder as the magnetic powder, and more specifically, to a magnetic recording medium that uses hexagonal ferromagnetic powder as the magnetic powder, and more specifically, a magnetic recording medium that uses hexagonal ferromagnetic powder as the magnetic powder. Regarding recording media.

[Technical Background of the Invention and Its Points J] Conventional magnetic recording media are made of y-Fe203, CrO2°Co-coated -FE! 1) It is constructed by coating a substrate such as a polyester film or disk with a magnetic paint containing a binder resin and a magnetic powder made of ferromagnetic powder-type needle crystals such as OQ.

These magnetic tapes and magnetic disks become charged with friction while running, which can impede stable running in magnetic recording devices, and dirt and dust can adhere to the media, increasing dropouts and deteriorating the media. In order to prevent such a situation, antistatic agents such as conductive carbon are added to the recording medium to make the coating film, that is, the surface of the magnetic layer conductive, thereby preventing static electricity.

By the way, recently, for the purpose of high-density magnetic recording, particle size 0.
．． Hexagonal ferromagnetic powders such as ultrafine barium ferrite powders of 2 μm or less have been developed.

Even in magnetic recording media using orthogonal ferromagnetic powder,
As in the prior art, it is necessary to prevent the surface of the magnetic layer from being charged in order to prevent the above-mentioned problems.

However, in the case of conventional magnetic recording media using acicular magnetic powder, the volume resistivity of the acicular magnetic powder is significantly lower than that of the macrogonal ferromagnetic powder.

The antistatic effect could be obtained simply by adding a small amount of antistatic agent to the medium. However, in the case of hexagonal magnetic powder, a satisfactory antistatic effect cannot be obtained by adding the same amount of antistatic agent as in the past.

In other words, in a magnetic recording medium using an orthogonal ferromagnetic powder, a satisfactory antistatic effect cannot be obtained simply by adding a large amount of conductivity imparting agent or antistatic agent to the binder resin. Not only is there a large amount of paint, but other inconveniences also occur, such as additives and their impurities bleeding onto the surface or inhibiting the dispersion of the magnetic paint.

[Object of the Invention] An object of the present invention is to solve the above-mentioned problems and provide a magnetic recording medium using hexagonal magnetic powder that has excellent antistatic properties and excellent running properties.

[Summary of the Invention] As a result of extensive research to achieve the above object, the present inventors have found that the antistatic effect and running properties of magnetic recording media using hexagonal ferromagnetic powder such as barium ferrite are The fact that this is affected not only by the type and amount of antistatic agent added to the medium but also by the surface charge state of the magnetic layer of the medium; The present invention was completed based on the discovery that since the surface charge generated by the polarization of the magnetic layer attenuates in a short period of time, the surface of the magnetic layer is not significantly charged to the point of inconvenience and does not adversely affect running performance.

The magnetic recording medium of the present invention is characterized in that the magnetic layer contains an orthogonal ferromagnetic powder as magnetic powder, and the surface of the magnetic layer is positively charged.

Here, positively chargeable as used in the present invention refers to a case where the surface of the magnetic layer is positively charged, or a state where there is a positive charge on the surface that decays in a short time.

The magnetic recording medium of the present invention usually consists of a substrate and a magnetic layer on which a magnetic paint made of magnetic powder, binder resin, various additives, etc. is coated.

In the above-mentioned magnetic recording medium, the method of making the surface of the magnetic layer positively chargeable is as follows: (1) Select a magnetic powder that is easily positively charged from among the hexagonal magnetic powders described below as the magnetic powder described in 1. (2) A method of adding or dispersing positively chargeable inorganic powder such as carbon, a surfactant capable of imparting positive chargeability, a charge control agent, etc. into a magnetic paint; How to apply magnetic paint on a charged substrate (4) Make the pH of the magnetic paint higher than the equipotential point!
Examples include a method of making the surface of the magnetic layer positively chargeable.

Furthermore, even if the types and amounts of compounded substances are the same and the types and particle sizes of the magnetic powders are also the same when manufacturing the media, the method used to prepare the magnetic powders cannot be determined. Therefore, the sign of the charge on the surface of the manufactured medium differs. However, even if the method for preparing the magnetic powder is determined, the sign of the surface charge is not determined accordingly.

The methods for positively charging the surface of the magnetic layer described above may be applied alone, or may be applied in an appropriate combination.

That is, it is only necessary that the surface of the finally produced medium be positively charged.

The magnetic powder used in the present invention has a particle size of 0-01 to 0.
．． It is a 34rs hexagonal ferromagnetic powder. Particularly effective is hexagonal barium ferrite or a substitute thereof.

What is the particle size of hexagonal ferromagnetic powder?

It represents the maximum distance between corner vertices on the hexagonal surface of a hexagonal columnar body or a hexagonal plate-like body, and the thickness represents the height or thickness of the columnar body or plate-like body.

If the particle size is less than 0.01 pm, the saturation magnetization (σS: e
mu/g) is not sufficiently large, and conversely exceeds 0.3 JLm, not only will high-density recording not be achieved, but the noise generated during recording and reproduction will increase, making it unsuitable. Those with crystal system-axial magnetic anisotropy, such as iron nitride and CO or Fe, Ni
Ca alloy containing; MnB1 alloy; MnAfL alloy: RCo5, which is an alloy of various rare earths (R) and CO;
R2Ca17: 82, Sr, Pb,
Hexagonal ferrite containing Ca or the like; or a part of the Fe of the hexagonal ferrite containing Go, Ti, Ni,
MTI, Cu, Zn, In, Ga.

Examples include substituted hexagonal ferrite substituted with at least one element selected from the group of Nb, Zr, V, and AfL. Among these magnetic powders, substituted anhombic ferrite is suitable for use in the present invention.

Among the above-mentioned macrogonal magnetic powders, the following magnetic powders are particularly easily charged positively.

For example, Go, Ti-substituted barium ferrite powder produced by glass crystallization method, Go, T produced by coprecipitation method
These include il-substituted barium ferrite powder, Go and Ti-substituted barium ferrite powder produced by an autoclave method, and the like.

The magnetic powder according to the present invention is disclosed in, for example, Japanese Patent Application Laid-open No. 56-6790.
Glass crystallization method disclosed in No. 4 or JP-A-58-
It can be prepared using techniques such as the coprecipitation method, flux method, and autoclave method disclosed in No. 180328.

In the present invention, examples of the /-inder resin that constitutes the magnetic layer together with the magnetic powder include vinyl chloride-vinyl acetate copolymer, vinylidene chloride copolymer, acrylic ester copolymer, polyvinyl butyral resin, and polyurethane resin. Resins, polyester resins, stellate resins, cellulose derivatives, epoxy resins, or mixtures of two or more of these resins are used.

In addition to the above-mentioned magnetic powder and binder resin, various additives such as ordinary dispersants, lubricants, and abrasives may be used as components of the magnetic paint, especially on the surface of the magnetic layer. Positively charged inorganic powder and surfactant to make it positively chargeable.

A charge control agent or the like may be added to the magnetic paint.

Examples of such positively charged inorganic powder include carbon, Au2o3, and the like.

Examples of the surfactant that imparts positive chargeability include cationic surfactants and anionic surfactants.

Examples include ionic surfactants such as amphoteric surfactants.

. Examples of charge control agents that impart positive chargeability include various amine compounds such as benzyldimethylamine, aluminum chelate compounds or coupling agents, and aluminum nitrate. It is used by attaching it to a medium or adding it to a medium.

Examples of the substrate to which the magnetic coating material containing the above-mentioned components is applied include polyethylene terephthalate film, polyimide film, polyamide film, aromatic polyester film, and polyamideimide film.

To manufacture a magnetic recording medium, a magnetic paint is prepared by blending the above-mentioned magnetic powder, a binder resin, and various additives, and after this magnetic paint is applied to a substrate, it is subjected to orientation, drying, and smoothing treatments.

During production, the surface of the magnetic layer is positively charged by adding positively charged magnetic powder and various additives, adjusting the p) of the magnetic paint, or using a positively chargeable substrate. Make it sexual.

Methods for determining whether the surface charge of the magnetic layer of a manufactured magnetic recording medium is positive include, for example, a blow-off charge measuring device (for example, manufactured by Toshiba Chemical Co., Ltd.) or a surface resistance meter (for example, manufactured by Takeda Riken Co., Ltd.). This can be done using a product such as the following:

In the case of a blow-off charge amount measuring device, the sign of the charge can be determined by making the magnetic recording medium into a powder form and comparing the voltage of this powder with the reference voltage of FeO. Furthermore, in the case of a surface resistance meter, the sign of the surface charge can be determined by checking the polarity when a voltage as low as tOV is applied to the medium.

The surface of the medium in the present invention determined by the method described above only needs to be positively chargeable, and the amount of charge or surface resistance does not matter.

[Embodiments of the invention] Various magnetic powders listed in Table 1 were prepared.

Table 1 A magnetic paint was prepared using the magnetic powder shown in Table 1 and various additives in the proportions shown in Table 2, and after filtering with a TG intestinal filter,
PE paint? applied to film.

Table 2 Next, the surface of the film was calendered to smooth the surface of the magnetic layer, and then the film was cut into a ζ inch width to obtain a test piece tape.

For each film using magnetic powders 1 to 6, determination of the sign of surface charge, tape adhesion, coefficient of friction and number of dropouts before and after the runnability test were measured, and the results are summarized in Table 3. Ta.

Table 3 [Effects of the Invention] As is clear from the Examples above, the magnetic recording medium of the present invention has excellent runnability and reliability without any adverse effects due to frictional electrification, and is industrially useful as a high-density magnetic recording medium. It is.

Claims (1)

[Claims] 1. A magnetic recording medium containing hexagonal ferromagnetic powder as magnetic powder in a magnetic layer, characterized in that the surface of the magnetic layer is positively charged. . 2. The particle size of the hexagonal ferromagnetic powder is 0.01 to 0.3μ
The magnetic recording medium according to claim 1, wherein the magnetic recording medium is m.