JPH02267720A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording medium with high S/N and excellent durability by forming an emulsion coating film essentially comprising acrylate and including a specified amt. of monomers which make crosslinkages on a nonmagnetic supporting body and then forming a ferromagnetic metal thin film thereon by vapor deposition, etc. CONSTITUTION:The magnetic recording medium consists of a ferromagnetic thin film formed on a nonmagnetic supporting body. The emulsion essentially comprises acrylate and includes monomers which make crosslinkages by 0.1 - 15pts.wt. to 100pts.wt. of the acrylate, and is applied on the nonmagnetic supporting body to form the coating film. The ferromagnetic metal thin film is formed thereon. By this method, adhesion property and cohesion property can be properly controlled to give such a magnetic recording medium with high S/N and excellent durability.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a so-called thin-film type magnetic recording medium in which a ferromagnetic metal thin film is formed on a non-magnetic support by techniques such as thin deposition and sputtering. .

[1 Summary of the Invention] The present invention provides a coating film by applying an emulsion containing an acrylic acid ester as a main ingredient and a predetermined amount of a crosslinking monomer onto a nonmagnetic support, and then forming a ferromagnetic metal thin film layer. Excellent S/N by forming by means such as vapor deposition
The objective is to provide a magnetic recording medium that has high performance ratio and runnability.

[Conventional technology]

As a magnetic recording medium, ferromagnetic ferric oxide (ferric oxide) is conventionally used on a non-magnetic support such as a polyester film.
So-called coated type 6F recording media, which are formed by coating a paint containing a magnetic material such as Oz)ilA powder, are widely used. A ferromagnetic metal thin film was formed by the method of Metsuki et al. So-called thin film magnetic recording media have also been proposed.

This thin-film magnetic recording medium has large coercive force Hc and residual magnetic flux density Br, and the thickness of the magnetic layer can be made extremely thin, so recording i<t and thickness loss can be significantly reduced. In addition, since the magnetic layer does not contain organic binder material, which is a non-magnetic substance, it has the advantage of increasing the packing density of magnetic material. This trend is becoming more and more important, especially as this trend is rapidly intensifying.

However, because the thickness of the magnetic layer in this thin film type medium can be significantly reduced as described above, new problems have arisen.

In general, the signal-to-noise ratio of a magnetic recording medium, the so-called S/N ratio, is closely related to the minute irregularities on its surface, that is, the surface roughness, and in order to obtain a medium with a good S/N ratio, it is necessary to improve the surface smoothness. This has become an important issue. In this type of thin film type media, the thickness of the magnetic layer is small (for example, about 200 nm) as described above, so the surface roughness is mostly determined by the surface condition of the nonmagnetic support. Therefore, in order to improve the S/N ratio, a film or the like with extremely excellent surface smoothness may be used as the nonmagnetic support.

However, although this alone improves the S/N ratio, the running performance of the tape deteriorates significantly. Therefore, a proposal has been made to improve running stability by forming fine irregularities on the surface of the non-magnetic support.

A technique of applying emulsilon to form these fine irregularities is conventionally known. Japanese Patent Publication No. 60214423
, Japanese Patent Publication No. 61-9822. The description can be found in JP-A-61-13427, JP-A-61-13428', JP-A-61-13437, etc., and the optimum conditions such as emulsion particle size and emulsion coating density are disclosed. By forming these fine irregularities, the contact area with rolls, guides, etc. is reduced, and the stability of the running of the medium is improved.

[Problems to be Solved by the Invention] By the way, in order for the applied emulsion to fulfill its intended purpose, it is necessary to ensure that the emulsion adheres reliably to the surface of the non-magnetic support during production and use of the medium. Two points are particularly required: (1) that the emulsion does not peel off during storage, and (2) that the emulsion does not easily stick to adjacent layers when storing the medium in a rolled state. However, in the above-mentioned technology, there is a lack of consideration regarding these points.For example, the adhesiveness of Emulsilon is insufficient and the still durability deteriorates when used as a magnetic recording medium, and the adhesiveness is too strong and it may become difficult to use during use. It has become clear that problems such as media sticking together occur.

Therefore, the present invention solves these problems and provides excellent S/
The purpose of the present invention is to provide a magnetic recording medium with good N ratio, running stability, and durability.

[Problem to be solved by the invention]

The present inventors carried out studies to achieve the above object, and found that by using an acrylic ester emulsion to which a crosslinking monomer was added, a film with a good balance in both adhesion and tackiness was created. Based on this knowledge, we have completed the present invention.

That is, the magnetic recording medium according to the present invention is a magnetic recording medium in which a ferromagnetic metal thin film is provided on a non-magnetic support, and in which a ferromagnetic metal thin film is provided on the non-magnetic support, the acrylic ester is mainly composed of 100% by weight of the acrylic ester. 0 for part
．． It is characterized in that an emulsion coating containing 1 to 15 parts by weight of a crosslinking monomer is formed, and the ferromagnetic metal thin film is provided thereon.

According to the knowledge obtained by the present inventors, tackiness can be improved by adding a crosslinking monomer to an emulsion mainly composed of acrylic ester. However, if this is made too large, the adhesiveness will be reduced. In other words, the amount of crosslinking monomer added, whether too large or too small, is inappropriate for the purpose of the present invention. Regarding this point, the present inventors have made various studies and determined the range of the optimum amount of the crosslinking monomer that can obtain good characteristics.

In addition, although there is a description of an emulsion with a glass transition point Tg of 30°C or less in the above-mentioned Japanese Patent Application Laid-Open No. 61-13437, this is the result of consideration in relation to the amount of crosslinking monomer added as in the present application. are completely different.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described based on experimental results.

Examples 1 to 3 and the present examples and comparative examples are examples in which an acrylic acid ester emulsion to which divinylbenzene was added as a crosslinking monomer was applied to a magnetic recording medium.

First, an acrylic ester emulsion containing butyl acrylate, methyl meccrylate, and acrylic acid as component monomers and divinylbenzene as a crosslinking monomer was prepared according to the following procedure.

First, 0.2 parts of sodium lauryl sulfate, 0.5 parts of potassium persulfate, and 100 parts of ion-exchanged water are charged into a polymerization tank, and the inside of the polymerization tank is maintained at a predetermined temperature (for example, 70°C). While stirring, an emulsion consisting of 100 parts of a seven-mer mixture having the composition shown in Table 1 below, divinylbenzene (the amount added is as shown in Table 1), 0.3 parts of sodium lauryl sulfate, and 80 parts of ion-exchanged water was added dropwise. Emulsions a to e shown in Table 1 were obtained by polymerizing for 4 hours while maintaining the polymerization temperature at 70°C.

Table 1 Next, the above emulsions a to e were actually applied to an optical recording medium.

First, the adhesion and tackiness when the above-mentioned emulsions a''-e were coated on a non-magnetic support were investigated.

Adhesiveness was evaluated as follows. That is, emulsions a to e were diluted with ethanol and water overnight, coated on a polyester film with a thickness of 1011 m and a surface roughness of 5 nm, and dried at 70°C for 10 minutes to form a film with a thickness of about 0.1 m.
A coating was formed on the 05 shell. Cover the surface of this film with gauze.
The adhesion was determined by the amount of polymer rubbed off from the film during 0 reciprocal rubbing.

The basis for judgment is as follows.

O: No or almost no polymer is rubbed off.

Δ: The polymer is slightly rubbed.

×: A considerable amount of polymer is scraped off.

Next, the adhesiveness was evaluated by coating emulsions a to C on a polyester film at a coating density of 200,000 pieces/mm2.
The test was carried out by applying the film over a length of 0.00 m and examining the presence or absence of adhesion between the films at the winding core.

The basis for judgment is as follows.

○: No adhesive.

△: Slightly sticky.

×: Adhesion is quite strong.

(The emulsion will stick to the back side when it is rolled up after application.
A condition in which it peels off from the coated surface. ) Furthermore, the still characteristics of a videotape with an &f layer were measured. That is, each emulsion has a thickness of 10 μm2 and a surface roughness of Ra
The emulsion density was applied to a 5 nm polyester film at an emulsion density of 200,000/ml112, and a ferromagnetic alloy thin film having a composition of C0qsNis (however, the numbers represent atomic %) was deposited on the film by oblique vapor deposition.
The characteristics of stills are formed to a thickness of 100 nm, cut to 8 mm width after going through the usual process, and assembled into an 8 mm video cassette. Evaluation was made by measuring the time required for the drop to decrease by 3 dB.

Table 2 shows the results of the evaluation of adhesion, tackiness, and still characteristics.

There are changes in both Table 2, and good results cannot be obtained if the amount added is too large or too small.

Disaster difference mt example J = Next, the type of crosslinking monomer was changed and the adhesiveness, tackiness, and still characteristics were evaluated.

That is, various copolymers as shown in Table 3 were prepared,
An emulsion film was formed on each of them in the same manner as in Examples 1 to 3, and the films were evaluated. The results are shown in Table 4.

Table 3 Examples 1 to 3 and Comparative Example 1. As shown in Comparative Example 2, when divinylbenzene is used as a crosslinking monomer in an acrylic acid ester emulsion, adhesion and tackiness are optimally controlled depending on the amount added, resulting in a high S/N ratio. It becomes possible to provide a magnetic recording medium that achieves this and has excellent durability.

Examples 4 to 6 show that if the range of addition of the crosslinking monomer is appropriate, good results can be obtained regardless of the type of the crosslinking monomer.

Claims (5)

[Claims] (1) In a magnetic recording medium in which a ferromagnetic metal thin film is provided on a non-magnetic support, the non-magnetic support has an acrylic ester as a main component, and 0.1 to 0.1 to 100 parts by weight per 100 parts by weight of the acrylic ester. 1
1. A magnetic recording medium comprising an emulsion coating containing 5 parts by weight of a crosslinking monomer, on which the ferromagnetic metal thin film is provided. (2) The magnetic recording medium according to claim (1), wherein the crosslinking monomer is divinylbenzene. (3) The magnetic recording medium according to claim (1), wherein the crosslinking monomer is N-methylolacrylamide. (4) The magnetic recording medium according to claim (1), wherein the crosslinking monomer is ethylene methacrylate. (5) The magnetic recording medium according to claim 1, wherein the crosslinkable monomer is glycidyl methacrylate.