JPH0349029A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve squareness ratio of a magnetic recording medium by constituting a magnetic layer of plural coating films containing a same kind of magnetic powder with controlled orientation. CONSTITUTION:The magnetic layer is formed on at least one side of a nonmagnetic supporting body, and this magnetic layer consists of plural coating films containing same magnetic powder with controlled orientation. Each coating film is preferably made about <=4 mum thick. By orienting the major axis of magnetic powder particles to a specified direction, high squareness ratio of the magnetic layer can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a so-called coated magnetic recording medium in which a magnetic layer is formed by coating a magnetic paint, and particularly relates to an improvement in squareness ratio.

(Summary of the Invention) The present invention relates to at least one surface of a non-magnetic support (prior art). Conventionally, in the field of magnetic recording, on a non-magnetic support made of polyester, polyethylene terephthalate (PET), A magnetic layer is formed by applying a magnetic paint in which powders such as magnetic oxides such as ferrite and chromium oxide or magnetic alloys containing Fe, Co, Ni, etc. as main components are dispersed in a binder made of an organic polymer material. So-called coated magnetic recording media are widely used.

Magnetic recording media are required to have various properties in order to obtain good recording/reproducing properties, and one of them is the squareness ratio (y!! Ratio of residual magnetic flux density B to total magnetic flux density B). (expressed as a percentage) is the bias characteristic, sensitivity 1
It is deeply involved in frequency characteristics, distortion factor 1, maximum output level, etc., and is a characteristic that is required to be as close to 100% as possible. In order to increase the squareness ratio, conventional methods have been to improve the dispersibility of tiling particles by optimizing the specific surface area of magnetic powder, the composition of the binder, etc., or by using a dispersant together, or by improving the dispersibility of tiling powder, After coating, a magnetic field orientation treatment is performed under a high orientation magnetic field.

[Problem to be solved by the invention]

However, there is a limit to the improvement of the squareness ratio simply by increasing the dispersibility and orientation of the 4fi material by the above-mentioned means, and it is no longer possible to meet the recent demands for high-speed recording and high-density recording. It is.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a magnetic recording medium that can easily achieve a high squareness ratio.

[Means to solve the problem]

A magnetic recording medium according to the present invention is proposed to achieve the above-mentioned object, and is a magnetic recording medium in which an IF property is formed on at least one surface of a non-magnetic support, and the magnetic recording medium It is characterized in that the layer is composed of a plurality of coating films containing the same type of magnetic film whose orientation is controlled.

The above n-type layer is formed by applying a magnetic paint containing the same magnetic powder multiple times. Here, the composition of the magnetic paint used each time does not need to be particularly limited other than choosing the same magnetic paint, and it may contain an appropriate combination of conventionally known binders and various additives. Best, and most simply, the magnetic layer can be formed by applying the same paint two or more times.

However, as long as it does not deteriorate the mechanical properties such as adhesion at the laminated interface of each coating film or the magnetic properties of the magnetic layer as a whole, for example, changing the type of binder for each coating film, or changing the work during the coating process can be done. In order to improve the properties, it is necessary to add a large amount of curing agent to the lower N layer (the layer closer to the non-R support), and to add a large amount of abrasive or lubricant to the top layer (the layer that makes sliding contact with the magnetic head). Even if you try these methods, it won't go sideways.

Here, the thickness of each coating film is preferably about 4 μm or less; if the thickness is greater than this, it becomes difficult to obtain a high squareness ratio. The lower limit of the coating film thickness is not particularly limited, but is subject to manufacturing equipment and technical constraints! The thickness at which the FF paint can be applied uniformly is about 2 μm. The magnetic paint can be applied by conventionally known methods such as gravure coating, reverse roll coating, doctor blade coating, and spin coating.

When forming the magnetic layer, it is desirable to perform a magnetic field orientation treatment every time the magnetic paint is applied, and to eliminate the fluidity of the paint film through curing and drying. In addition to making the work easier, the orientation of the magnetic powder is highly controlled at any location inside the formed magnetic layer.

[Effect]

In the present invention, the reason why the squareness ratio is improved when the magnetic layer is composed of a plurality of coating films containing the same magnetic powder is considered to be due to the following reason.

In the first place, magnetic powders such as iron oxide magnetic powder, chromium dioxide magnetic powder, and metal magnetic powder used in coated magnetic recording media are fine needle-like crystals with a length of about 1 μm or less, and the shape Due to its magnetic anisotropy, it has an axis of easy magnetization in the long sleeve direction. Therefore, the long sleeves of these magnetic powders move in a certain direction within the coating (in the case of magnetic tape, the long direction).
If they are aligned, a high squareness ratio will be obtained. In the manufacturing process of magnetic recording media, when the IF paint is prepared, the magnetic powder crystals are dispersed with their long sleeves oriented in random directions, but the magnetic paint is coated sufficiently thinly on the non-magnetic support. As a result, the degree of freedom of movement of the magnetic powder in the film thickness direction within the coating film is reduced, and the long axes of the magnetic powder are aligned in the in-plane direction to some extent even without magnetic field orientation treatment or the like. Furthermore, when magnetic field orientation treatment is performed in this state, the magnetic powder becomes highly oriented in the in-plane direction, and is further hardened.

When the fluidity of the coating film disappears due to drying or the like, the above-mentioned orientation state is fixed. By repeating such operations, a plurality of sufficiently thin coating films each having controlled orientation are stacked to form a Cn layer. Compared to the case where it is formed by multiple coatings, the n-type layer exhibits excellent orientation everywhere inside the 6fi-type layer.

[Example] Hereinafter, preferred examples of the present invention will be described based on experimental results.

Example! In this example, Co-coated 1-Fe was used as the magnetic powder.

Apply the magnetic paint of the same & [1 composition containing 04 twice,
This is an example of a magnetic tape in which a magnetic layer consisting of two layers, an upper layer and a lower layer, is formed.

First, a magnetic layer li composition was prepared according to the following composition.

Co coated a r Fe yon CN magnetic powder
600 parts by weight Vinyl chloride-vinyl acetate copolymer [Binder] (U, C, C, 1 product name V A G H)
50 overlapping parts Polyurethane resin [Binder] (Japan (manufactured by 'I?Shin Kogyo Co., Ltd., product Meimon-5033)
50 stacked parts liter/inch [dispersant]
9 weight 815 alumina [abrasive]
12 parts by weight Stearic acid [Lubricant 31.8 parts by weight Butyl stearate [Lubricant] 1.8 parts by weight The above magnetic coating composition was dispersed in a mixed solvent of methyl ethyl ketone and methyl isobutyl ketone (bl), and then milled in a ball mill. The mixture was mixed for 24 hours, filtered through a 3 μm filter, and 15 parts by weight of an isocyanic non-1-based curing agent (manufactured by Nippon Polyurethane Kogyo Co., Ltd., trade name: Coronet H) was added.
Stir for a minute.

This magnetic paint was applied onto a PET film of 14 μmj9- to form a lower layer so that the coating thickness after drying would be 4 ttm, followed by magnetic field orientation treatment and drying.

Furthermore, the same magnetic paint was applied to form an upper layer with a dry coating thickness of 2 μm, and after being subjected to magnetic field bidirectional treatment, drying, and calendering, it was cut into 1/2 inch pieces. A sample tape was created. The total thickness of the magnetic layer of this sample tape was 6 μm.

Example 2 This example is an example of a magnetic tape in which the magnetic layer t4 described in Example 1 was applied three times to form a magnetic layer consisting of three layers: an upper layer, a middle layer, and a lower layer.

The thickness of each coating is 2 μm, so the total layer thickness of the magnetic layer is 6 μm.

Squareness ratio R1 and coercive force Ht were measured. The results are shown in Table 1. In the table, for Examples, the individual measured values of each layer constituting the magnetic layer are also listed.

Table 1 Comparative Examples For comparison, sample tapes were prepared in the same manner, except that the above magnetic paint was applied once so that the thickness of the coated film after drying was 6 μm.

As described above, the residual magnetic flux density Br was determined for each sample tape created in the Examples and Comparative Examples.

The above-mentioned layers are all formed by applying the same magnetic paint, but there is a tendency for the thinner the coating film to have a higher squareness ratio.

(If the thickness of the entire magnetic layer is the same, the difference between Example 1 (whole) and Comparative Example 1, or the difference between Example 2 (whole) and Comparative Example 1, It is clear that it is more advantageous to construct it from paint.

In addition, when the maximum output level at the reference frequency 31511z was measured for each sample tape obtained in Example 1 and Comparative Example, the former was 0.5 d lower than the latter.
B It was expensive.

〔Effect of the invention〕

In the magnetic recording medium according to the present invention, since the magnetic powder is extremely well oriented inside the magnetic layer, the squareness ratio is improved, and as a result, bias characteristics, sensitivity two-frequency characteristics, distortion rate, maximum output level, etc. Improves core characteristics. The above-mentioned magnetic recording medium can be manufactured by a method in which a magnetic coating material containing the same magnetic powder is applied in multiple steps. Therefore, it is more economical than, for example, a so-called two-layer coating medium in which magnetic layers containing different types of magnetic powder are laminated to achieve flat frequency characteristics.

Productivity is extremely high.Furthermore, since the type of magnetic powder is the same throughout the magnetic layer, there are no distortions caused by differences in the characteristics of the magnetic powder, or a decrease in output in the midrange.
No problems arise with the coating medium.

Claims (1)

[Claims] A magnetic recording medium comprising a magnetic layer formed on at least one surface of a non-magnetic support, wherein the magnetic layer is composed of a plurality of coating films containing the same type of magnetic powder with controlled orientation. A magnetic recording medium characterized by: