JPH04182923A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve durability and electromagnetic transducing characteristics by forming a magnetic layer contg. magnetic metal powder having <=46m<2>/g BET surface area as a ferromagnetic body and regulating the square average surface roughness of the magnetic layer to <=6nm in the case of sampling with average height per 2mum<2>. CONSTITUTION:A magnetic layer contg. magnetic metal powder having <=46m<2>/g BET surface area is formed and the square average surface roughness of the magnetic layer is regulated to <=6nm in the case of sampling with average height per 2mum<2> and to <=8nm in the case of sampling with average height per 0.2mum<2>. Since the amt. of a resin binder required to envelop the magnetic powder is reduced by reducing the surface area of the magnetic powder, durability under various environmental conditions and electromagnetic transducing characteristics such as the output of a head are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic recording medium in which a magnetic layer is formed by applying a magnetic paint containing metal magnetic powder as a ferromagnetic material onto a substrate such as a polyester film.

2. Description of the Related Art In recent years, floppy disks, magnetic tapes, and the like have been widely used as external recording media for computers and the like. Recently, video floppy disks have also been used as image recording media. This video floppy disk is made by coating a base material such as polyester with magnetic paint, subjecting it to surface treatment, hardening it, punching it out into a disk shape, polishing the surface, and storing it in a predetermined case.

In order to achieve high recording density, magnetic recording media contain metal magnetic powder as a ferromagnetic material. Conventional video tapes using iron oxide magnetic powder have a BET surface area of approximately 45n? /g of magnetic powder is used, and BE
Attempts have been made to increase the BET surface area.Furthermore, metal magnetic powder used to aim for even higher recording densities has a BET surface area of about 48nf/g, and here too even higher BET surface area is increased. Floppy disks using such fine metal magnetic powder can easily obtain surface smoothness and improve head output, and also reduce noise from the medium and have high S. /
'N is easy to obtain. Furthermore, the frequency characteristics are improved, making it suitable for high-density recording.

Problems to be Solved by the Invention However, in the above-mentioned conventional magnetic recording media, it is difficult to improve the strength of the magnetic powder by turning the magnetic powder with a large surface area into fine particles, making it difficult to improve the durability under various environments. However, there are problems in that it is difficult to maintain high durability in all environments. For this reason, attempts have been made to intentionally form minute protrusions on the surface to lower the friction coefficient of the coating film and improve its durability.If magnetic powder with a low BET surface area is used, noise increases and the S/N decreases. A new problem arises, which is to bring about deterioration.

The present invention is intended to solve the above problems, and aims to provide a magnetic recording medium that has high durability under various environments and has excellent electromagnetic conversion characteristics.

Means for Solving the Problems In order to achieve the above objects, the present invention uses metal magnetic powder with a BET surface area of 46 nF and 2 g or less to improve the strength of the coating film, and further increases the root mean square coating surface roughness to 2μ.
When sampled at an average height of m squares, the coating film surface smoothness is 6 nm or less, and when sampled at an average height of 0.2 μm squares, it has a coating surface smoothness of 8 nm Jl)J.

Therefore, according to the invention, the BET surface area is 46Wi/
The strength of the coating film is improved by using magnetic powder with a particle size of 2 μm or less, and the root mean square surface roughness of the coating film is reduced to 6 nm or less when sampling the average height of 2 μm square.
When sampling the average height of 2μm square, it is 8μm
By doing the following, it is possible to obtain a magnetic recording medium that has improved durability under various environmental conditions and has excellent electromagnetic conversion characteristics such as head output.

In addition, since the surface area of the magnetic powder is reduced, the amount of binder resin required to enclose the magnetic powder is reduced, which improves the packing ratio of the magnetic powder in the coating film and further improves the electromagnetic conversion characteristics. . The S/N is improved by increasing the number of magnetic powders per unit volume of the coating film, and this can compensate for the decrease in S/N caused by increasing the particle size of the magnetic powder. As a result of the above, it is possible to improve the strength of the coating film without deteriorating the electromagnetic conversion characteristics, and to obtain a magnetic recording medium that has excellent durability under various environments.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

In the explanation of this example, below, the root mean square coating surface roughness when sampling the average height of 2 μm square is Rrm.
s(R), the root mean square coating surface roughness when sampling the average height of 0.2 μm square shall be expressed as Rrms(F).

The key point in the construction of a magnetic recording medium is to provide a magnetic layer on a substrate such as polyester by coating magnetic paint, and in this example, the packing ratio of magnetic powder in this magnetic layer is slightly higher than that of the conventional one. The content was set at 70.4 wt%.

As an example, after activating the surface of a polyester film with a thickness of 33 μm by corona discharge etc., the BET surface area was 4.
A magnetic paint having a composition shown in Table 1 below using metal magnetic powder of 2 to 46+J/g was applied and dried, and further calendered at 90° C. and 50 m/min. The final thickness of the magnetic layer here was set to be approximately 3.5 μm.

After that, after hardening the magnetic coating, it is punched out into a disk shape.
After polishing the surface, a center hub was attached and the medium was housed in a predetermined case to produce magnetic recording media of Examples 1 to 3, and the electromagnetic conversion characteristics and durability were measured.

In addition, a floppy disk was prepared as a comparative example under the same conditions as in the above example except that magnetic powder having a different BET surface area was used, and its durability was measured in the same manner as in the example. At that time, Rr m s (R) was all 4.3 nm to 5. O
nm, and Rrms (F) is also 6.0 to 8.
It was in the range of 0 nm. The device used to measure the surface roughness was TOPO-3D manufactured by WYKO, and the Rrms
To measure (R), use a 20x objective lens, Rr m s
A 200x objective lens was used to measure (F).

The results of the durability tests for Examples and Comparative Examples are shown in Table 2 below.

Table 2 The durability under the environmental conditions of 3° C. and 80% RH is also shown in FIG. In the measurements, the end of the durability test was defined as the time when the output decreased to 70% of the initial output. In this durability test, the still durability was measured at 25 tracks. Second
As is clear from the table and Figure 1, when the BET surface area of magnetic powder exceeds 48 d/''g, the durability decreases rapidly.The reason why the durability is good when the BET surface area is 45+j/g or less is that This is thought to be because the smaller the BET surface area of the powder, the larger the particle size of the magnetic powder and the improved magnetic coating strength.
If it exceeds i/g, not only can no improvement in coating film strength be expected, but also the binder resin tends to stick to the magnetic surface.
Its role as a binder is rapidly reduced.

From these results, BE of magnetic powder is required to achieve high durability.
It can be seen that it is necessary to make the T surface area 46i/g or less.

Next, the BET surface area of magnetic powder is 46 nt/g and 42 ra.
/g of magnetic powder, and by changing the calendering conditions of the magnetic coating film when forming the magnetic coating film having the composition shown in Table 1, magnetic coating films with different surface roughness were formed. That is, the surface roughness of the magnetic coating was changed by changing the calender temperature in the range of 90° C. to 50° C. and decreasing the number of stages of the calender.

The surface roughness of the magnetic coating films of Examples 1 and 3 thus produced was measured using a TOPO-3D using a 200x objective lens. The relationship between surface roughness and S/N at this time is
As shown in the figure. Here, S/H was evaluated as an example of electromagnetic conversion characteristics. Further, the S/N here is based on recording a 9 MHz signal on 25 tracks, and is expressed as a reference ratio. The reference medium is a magnetic recording medium having characteristics approved by the Electronic Still Camera Conference of the Japan Electronics Industry Association. BET surface area of magnetic powder 46j/
The magnetic recording medium of Example 3 having Rr m s (
Example 1 with F) of 9.2 nm or less, S/N higher than the reference media, and BET surface area of 42j/g
Even in the magnetic recording medium, Rr m s (F) is 8
The S/N exceeded that of the reference media below nm. The video floppy recorder used here is an R5000H manufactured by Fuji Photo Film Co., Ltd., which has been modified to record and reproduce a single signal.

Next, the BET surface area of magnetic powder is 46 j / g and 42 i
For magnetic recording media whose Rrms (F) /g is 8 nm or less, the objective lens of TOPO-3D was changed to 20 times, and the surface roughness of the magnetic coating film was measured. The relationship between the surface roughness Rrms (R) and S/N at that time is shown in FIG. In this case, the difference between the two was not as large as Rrms (F) shown in Figure 2, but when Rrms (R) is 6 nm or less, the difference is that of a magnetic recording medium using magnetic powder with a BET surface area of 42j/g. The S/N exceeds that of the reference media.From this, the surface roughness of the magnetic coating film is Rrms (R).
It can be seen that by setting both of and Rrms(F) to be 6 nm or less and 8 nm or less at the same time, the electromagnetic conversion characteristics exhibit a value greater than that of the reference medium. In Rrms (F), the precise roughness of the coating surface can be seen, but large irregularities cannot be seen. On the other hand, in Rrms (R), only large irregularities can be seen, so excellent electromagnetic conversion characteristics can be obtained by reducing both of these to a predetermined value or less.

Thus, according to the above embodiment, the BET surface area of the magnetic powder is 46 ni,'g or less, and the surface roughness of the magnetic coating is R,
r m s (R) or less than 6 nm, Rrms (F) or less
By making the thickness less than nm, high durability and excellent electromagnetic conversion characteristics can be obtained.

Effects of the Invention As is clear from the above examples, the present invention provides BE
Contains metal magnetic powder with a surface area of 46i,・'g or less, and has an average surface roughness of 2 μm square of the magnetic layer of 5 nm or less, 0
．． Because it forms a magnetic layer with an average surface roughness of 8 nm or less per 2 μm square, it has excellent durability under various environments and has an extremely large effect on improving electromagnetic conversion characteristics such as S7・'N. That's what you get.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram showing the relationship between the BET surface area value of metal magnetic powder and the durability at 3°C and 80% RH in the example of the present invention and the conventional example, and Figure 2 is the magnetic recording of the example of the present invention. R r m 5(F) and S,' in the medium
FIG. 3 is a characteristic diagram showing the relationship between Rrms(R) and SN in the same magnetic recording medium. Name of agent Patent attorney Haruaki Koyaku et al. 28 No. 1 BEr&i-zuke of Fusuma Kensho (M force) Fig. 2 Rrms (F) (77rn) Fig. 3

Claims (1)

[Claims] In a magnetic recording medium in which a magnetic layer is provided by coating a magnetic paint on a substrate such as a polyester film, the magnetic layer is a ferromagnetic material and has a BET surface area of 46 m^2/
Contains metal magnetic powder of less than
1. A magnetic recording medium characterized in that the mean square surface roughness is 8 nm or less when sampled at an average height of 0.2 μm square.