JPS6173235A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To make possible higher density recording and to improve wear resistance by providing a magnetic layer on at least one surface of a base, forming a non-magnetic primer coating layer between the magnetic layer and the base and incorporating a specific amt. of a lubricating agent into both layers. CONSTITUTION:The coated film of the double-layered structure consisting of the non-magnetic primer coating layer and magnetic layer is formed on one or both surfaces of the flexible base. The thickness of the magnetic layer is made up to 2mum and <=0.5mum to meet the higher-density recording. On the other hand, the primer coating layer is made thick so as to contain the more lubricating agent therein and is made at least >=0.1 times the thickness of the magnetic layer. The total thickness of the primer coating layer and the magnetic is about 1.3-3.0mum. The lubricating agent is preliminarily incorporated into the paint for primer coating and magnetic paint and the primer coating layer and magnetic layer are formed by using such paints to incorporate the lubricating agent into both layers. The amt. of the lubricating agent to be incorporated into both layers is made >=220mg for each 1m<2> unit surface area of the magnetic layer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a magnetic disk or other magnetic recording medium having a base with a magnetic layer on at least one surface.

[Prior Art] In this type of magnetic recording medium, since the magnetic layer comes into sliding contact with the magnetic head at high speed, a lubricant such as a higher fatty acid or a higher fatty acid ester is contained in the magnetic layer, thereby improving the sliding contact between the magnetic layer and the magnetic head. This prevents wear caused by contact (unspecified literature). However, in recent years, with the demand for high-density recording, thinning of the magnetic layer has been considered, and in this case, the absolute amount of lubricant contained in the magnetic layer is reduced, which improves the wear resistance of the magnetic layer. There was a problem that sufficient effects could not be obtained.

In other words, if too much lubricant is not added to the magnetic layer, the cohesive force of the magnetic layer may decrease due to plasticization of the binder, which may actually reduce the wear resistance. As a result, the spacing between the magnetic head and the magnetic layer increases, resulting in a decrease in output or a phenomenon in which the magnetic head and the magnetic layer stick together.

As described above, there is a natural limit to the amount of lubricant that can be included in the magnetic layer, so the thinner the magnetic layer is, the smaller the absolute amount must be. In general, it has been difficult to contain 200 In9 or more per unit surface area (IR) of the magnetic layer.

[Problems to be Solved by the Invention] From the above viewpoint, the present invention solves the problem of decreasing the lubricant content when reducing the thickness of the magnetic layer to 2 or less, which is compatible with high-density recording. The object of the present invention is to solve the problem and obtain a magnetic recording medium that can achieve high-density recording and simultaneously improve the wear resistance of the magnetic layer.

[Means for Solving the Problems 1] As a result of intensive studies to solve the above problems, the inventors formed a non-magnetic undercoat layer between the base and the magnetic layer, and If a lubricant is contained in both the magnetic layer or only the undercoat layer, and the lubricant contained in the undercoat layer oozes and migrates to the surface of the magnetic layer through the gaps in the magnetic layer, the warpage of the magnetic layer can be increased. Even when the magnetic layer is made thinner to accommodate density recording, the lubricant content per unit surface area (lrrf) of the magnetic layer can be increased compared to conventional methods, and the lubricant effect can be sustained over a long period of time. This invention was completed based on the knowledge that the above-mentioned problems caused by too much lubricant do not occur at all.

That is, the present invention provides a magnetic layer having a thickness of 2p or less on at least one surface of the base, and a non-magnetic undercoat layer having a thickness of 01 times or more the thickness of the magnetic layer between this magnetic layer and the base. The present invention relates to a magnetic recording medium in which a lubricant is contained in both the undercoat layer and the magnetic layer at a ratio of 220 μm or more per unit surface area (1 m') of the magnetic layer.

[Structure and operation of the invention] In this invention, a two-layered coating film consisting of a non-magnetic undercoat layer and a magnetic layer is formed on one or both sides of a polyester film or other preferably flexible base. The thickness of the magnetic layer is preferably two tones or less, usually up to 0.5 μm, and particularly preferably about one tone, in order to meet the demands for high-density recording.

On the other hand, the undercoat layer is preferably made as thick as possible so that a large amount of lubricant can be contained in this layer, but it is at least 0.1 times the thickness of the magnetic layer, preferably 0.3 times or more, and usually up to about 5 times the thickness of the magnetic layer. It is better to

The total thickness of the undercoat layer and magnetic layer is generally 1.3~
It is desirable that it be about 30-. If the undercoat layer becomes too thick, there will be problems such as loss of flexibility when obtaining a magnetic disk or magnetic tape, which is not preferable.

The non-magnetic undercoat layer can be formed by, for example, applying and drying an undercoat paint made by dissolving a suitable binder in an organic solvent on one or both sides of the base, and the magnetic layer can be formed by applying the undercoat paint made by dissolving an appropriate binder in an organic solvent or the like to one or both sides of the base. Various conventionally known magnetic paints containing a binder and magnetic powder may be coated on the layer and dried according to a conventional method.

The binders used for the undercoat layer and the magnetic layer may be the same or different, and include vinyl chloride-vinyl acetate copolymers, polyurethane resins, polyester resins, and cellulose-based binders commonly used for magnetic layers. A wide variety of binders can be used, such as resins, polyvinyl butyral resins, polyacetal resins, and low molecular weight polyisocyanates. There are no particular restrictions on the magnetic powder contained in the magnetic layer, and T
-Fe203, Fe50. Any conventionally known magnetic powder such as powder, cobalt-containing iron oxide magnetic powder, iron powder, cobalt powder, oxide magnetic powder such as iron-cobalt alloy powder, or metal or alloy magnetic powder can be used.

A method of including a lubricant in both the undercoat layer and the magnetic layer is to mix the above lubricant into the undercoat paint and magnetic paint in advance, and apply the undercoat using these paints in the above-described method. Methods of forming the layers and magnetic layers are preferred. In this method, it is preferable to include as much lubricant as possible in the undercoating paint and to reduce the amount of lubricant added to the magnetic paint, or to add no lubricant. Even when no additive is used, the lubricant in the undercoat layer gradually oozes into the voids of the magnetic layer over time.

In addition to the above-mentioned method of mixing a lubricant into the paint, there is a method of forming an undercoat layer and a magnetic layer, and then top-coating a lubricant solution from the surface side of the magnetic layer and impregnating it into the magnetic layer and undercoat layer. May be adopted.

The amount of lubricant contained in both the undercoat layer and the magnetic layer can be 220 m9 or more, preferably 250 m'j or more, and usually up to 700 mq per unit surface area (li) of the magnetic layer. At this time, by increasing the thickness of the undercoat layer according to the above-mentioned lubricant content, the aforementioned problems caused by too much lubricant, such as the problem of a decrease in cohesive force of the magnetic layer and the problem of a decrease in output, are completely avoided. be done.

As the lubricant to be used, any conventionally known lubricant that is liquid or semi-solid at room temperature can be used, such as higher fatty acids, higher fatty acid esters, hydrocarbons, silicone oils, fluorine oils, and polyethers.

Note that the above lubricant content is for the undercoat layer and magnetic layer provided on one side of the base, so if the undercoat layer and magnetic layer are provided on both sides, the amount of lubricant on each side is The magnetic recording medium of the present invention may include a base and a non-magnetic undercoat layer and a magnetic layer provided on at least one surface of the base as essential components. If necessary, an appropriate layer such as an adhesive layer may be further interposed between the base and the undercoat layer. [Effects of the Invention] As described above, the magnetic recording medium of the present invention Since the thickness of the magnetic layer is 2p or less, it can easily meet the recent demands for high-density recording, and a lubricant is impregnated between the magnetic layer and the base to create a vine undercoat layer. Since the structure is such that the amount of lubricant per unit surface area (IH) of the magnetic layer is increased, this improves the wear resistance of the magnetic layer without causing problems such as a decrease in the cohesive force of the magnetic layer or a decrease in output. performance can be significantly improved.

[Example 1] Examples of the present invention will be described below in comparison with comparative examples. In addition, in the following, parts shall mean parts by weight.

Example 1 The following undercoating paint was applied to both sides of a polyester film with a thickness of 75 μm, and the dry thickness was 2.5 μm on each side. A pair of undercoat layers serving as OP were formed.

Undercoat paint> The following magnetic paint was applied onto both of the above undercoat layers using 210 parts of Ncrohexanone and 210 parts of methyl ethyl ketone to form a pair of magnetic layers having a dry thickness of 10 - on each side. Thereafter, it was subjected to calendering treatment and punched out into a disk shape to produce a magnetic disk. The amount of lubricant per unit surface area (1 m') of the magnetic layer in this disk was measured at a distance of 300 m on both the front and back surfaces.

<Magnetic paint> CO-containing T-Fe2Q3 powder 270 parts VA
GH (mentioned above) 40 parts Bandex T-5250 (mentioned above) 40 parts Coronate L (mentioned above) 20 parts H5-500 (trade name manufactured by Asahi Carbon Co., Ltd.; 34 parts carbon black) α-Fe203 powder 10 parts Methyl Isobutyl ketone 500 parts Torr
En 5
00 parts Example 2 Except that 5 parts of fatty acid ester (same as described in Example 1) was added as a lubricant to the magnetic paint,
A magnetic disk was produced in the same manner as in Example 1. The amount of lubricant per unit surface i (I n? ) of the magnetic layer in this disk was 350 mq on both the front and back surfaces.

Example 3 A magnetic disk was produced in the same manner as in Example 1, except that the amount of fatty acid ester used in the undercoating paint was changed from 10 parts to 20 parts. The amount of lubricant per unit surface area (1 m2) of the magnetic layer in this disk was 600 mq on both the front and back surfaces.

Example 4 A magnetic disk was produced in the same manner as in Example 1, except that 10 parts of liquid paraffin was used instead of 10 parts of fatty acid ester in the undercoating paint. The amount of lubricant per unit surface area (1 m') of the magnetic layer in this disk was the same as in Example 1 on both the front and back surfaces.

Comparative Example 1 The same procedure as Example 1 was carried out, except that the formation of the undercoat layer was omitted and 5 parts of fatty acid ester (same as that described in Example 1) was added as a lubricant to the magnetic paint. A magnetic disk was created. The amount of lubricant per unit surface area (one door) of the magnetic layer in this disk was 50 mg on both the front and back surfaces.

Comparative Example 2 A magnetic disk was produced in the same manner as Comparative Example 1 except that the amount of fatty acid ester added was 20 parts.The amount of lubricant per unit surface (1rrf) of the magnetic layer in this disk was Same as Example 1.

Each of the magnetic disks obtained in the above examples and comparative examples was subjected to the following durability test using a magnetic disk durability tester manufactured by Hitachi Maxell, and the results were as shown in the table below. .

Durability Test> Recording was performed under the conditions of a disc rotation speed of 300 rpm, a relative speed of 1 yn/sec, and a writing frequency of 125 KHz, and the running time until the playback output reached 70% of the initial output was defined as the durability time.

As is clear from the above results, the magnetic disk of the present invention has a magnetic layer as thin as one layer, and can easily meet the demands for high-density recording.
It can be seen that the Ti abrasion resistance is good and the durability is low. The magnetic disk of Comparative Example 2, in which a large amount of lubricant is contained in a thin magnetic layer without providing an undercoat layer, has a high degree of durability improvement like the magnetic disk of the present invention due to the reduction in the cohesive force of the magnetic layer. Not only was it not effective, but it was also found that excessive leaching of lubricant onto the surface of the magnetic layer caused problems such as a decrease in output and sticking to the magnetic head.

Claims (1)

[Claims] (1) A magnetic layer with a thickness of 2 μm or less is provided on at least one surface of the base, and a non-magnetic undercoat layer with a thickness of 0.1 times or more the thickness of the magnetic layer is formed between this magnetic layer and the base. The lubricant is added to both the undercoat layer and the magnetic layer at a rate of 220 m2 per unit surface area (1 m^2) of the magnetic layer.
A magnetic recording medium in which the magnetic recording medium is contained in a proportion of 1.5 g or more.