JPS62154225A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To decrease surface electric resistance and to improve durability by providing a primer layer which contains conductive powder and has the thickness larger than the thickness of a magnetic layer between a substrate and the magnetic layer formed on the substrate. CONSTITUTION:The magnetic layer of a magnetic recording medium provided with the magnetic layer contg. magnetic powder and binder component on the substrate is formed to <=0.5m thickness and the primer layer which contains the conductive powder and has the thickness larger than the thickness of the magnetic layer is provided between the magnetic layer and the substrate. A demagnetization loss increases and high-density recording is not satisfactorily executed when the magnetic layer is formed thicker than 0.5mum. The incorporation of a substantial amt. of the conductive powder and lubricating agent into the primer layer is not possible if the primer layer is thinner than the magnetic layer which is <=0.5mum and therefore, said layer is made preferably thicker than the magnetic layer having >=0.5mum thickness. Carbon black or metallic powder such as copper powder having good conductivity is adequately used as the conductive powder to be incorporated into the primer layer.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic recording medium with a magnetic layer having a thickness of 0.5 μm or less and subjected to high-density recording, and more specifically, it relates to a magnetic recording medium that has a low surface electrical resistance and is durable. The present invention relates to the magnetic recording medium having excellent properties.

[Conventional technology]

The magnetic layer of a magnetic recording medium is usually made by applying a magnetic paint consisting of magnetic powder, a binder component, an organic solvent, and other necessary components onto a substrate such as a polyester film, and drying the coating. In recent years, in order to improve the recording density of magnetic recording media produced in this way, efforts have been made to reduce the thickness of the magnetic layer as much as possible to reduce demagnetization loss. In order to improve wear resistance and reduce surface electrical resistance, lubricants and conductive powders are included in the magnetic layer. (Japanese Patent Publication No. 44-15741, Japanese Patent Publication No. 58-6209) [Problems to be Solved by the Invention] However, while reducing the thickness of the magnetic layer increases the recording density, Since the required amount of conductive powder and lubricant cannot be contained, the surface electrical resistance of the magnetic layer increases and durability deteriorates.

[Means for solving problems]

This invention was made as a result of various studies in view of the current situation, and includes a base body and a thickness of 0.
．． By providing an undercoat layer containing conductive powder and having a thickness greater than the thickness of the magnetic layer between the magnetic layer and the magnetic layer having a thickness of 5 μm or less,
The surface electrical resistance of the extremely thin magnetic layer is sufficiently reduced, and the durability is sufficiently improved to enable high-density recording to be performed satisfactorily. Furthermore, by further containing a lubricant in the undercoat layer, the magnetic layer is sufficiently supplied with the lubricant, the coefficient of friction of the magnetic layer is reduced, and the durability is further improved.

In this invention, the magnetic layer formed on the substrate via the undercoat layer is preferably 0.5 μm or less in order to enable good high-density recording; if it is thicker than this, demagnetization loss increases. high-density recording cannot be performed satisfactorily.

In addition, in the present invention, if the undercoat layer provided between the substrate and the magnetic layer is thinner than the magnetic layer with a thickness of 0.5 μm or less, it cannot contain a sufficient amount of conductive powder or lubricant. It is preferable to make the magnetic layer thicker than 5 μm or less, and if the undercoat layer is made sufficiently thick in this way,
It is possible to contain a sufficient amount of conductive powder and lubricant, and it is possible to sufficiently reduce the surface electrical resistance of the magnetic layer. The coefficient of friction can be made sufficiently small, and the wear resistance can be sufficiently improved.

As the conductive powder contained in such an undercoat layer, a carbon blank or a metal powder with good conductivity such as copper powder is suitably used. The content is preferably within the range of 85:15 to 10:90 in terms of weight ratio (conductive powder to binder component) to the binder component in the undercoat layer, and there is too little conductive powder. If the amount is too large, the surface electrical resistance of the magnetic layer cannot be made sufficiently small, and if the amount is too large, the adhesion of the undercoat layer to the substrate decreases.

In addition, the lubricants to be contained in this undercoat layer include fatty acid esters, fatty acids, metal salts of fatty acids, fatty acid amides, aliphatic/I2I lubricants such as fatty bottom alcohols, fluorine-based lubricants, silicone-based lubricants, and carbonized lubricants. Any hydrogen-based lubricant or the like is preferably used, and fatty acid esters are particularly preferred.

As the fatty acid ester, for example, oleyl oleate, 2-ethylhexyl oleate, butyl stearate, octyl myristate, stearic acid monoglyceride, palmitic acid monoglyceride, oleic acid monoglyceride, pentaerythritol tetrastearate, etc. are preferably used, and as the fatty acid, For example, lauric acid, myristic acid, parimitic acid, oleic acid, stearic acid, behenic acid, etc. are preferably used. Preferred examples of these metal salts include lithium salts, sodium salts, calcium salts, magnesium salts, aluminum salts, iron salts, cobalt salts, zinc salts, barium salts, and lead salts. . Examples of fatty acid amides include caproic acid amide, capric acid amide, lauric acid amide, palmitic acid amide,
Behenic acid amide, oleic acid amide, linoleic acid amide, methylene bisstearic acid amide, etc. are preferably used, and as the aliphatic alcohol, for example, stearyl alcohol, myristyl alcohol, etc. are preferably used.

In addition, as the fluorine-based lubricant, for example, trichlorofluoroethylene, perfluoropolyether, perfluoroalkyl polyether, perfluoroalkyl carboxylic acid, etc. are preferably used, and specific examples of commercially available products include:
Examples include Guiflon #20 manufactured by Daikin, Talite Sox M manufactured by DuPont, Talite Sox H1 Vida Sox AR, and Fomblin Z manufactured by Montegisson. Further, as the silicone/rJfk agent, silicone oil, modified silicone oil, etc. are preferably used, and as the hydrocarbon-based lubricant, for example, liquid paraffin, squalane, synthetic squalane, etc. are preferably used. .

The amount of these lubricants used is preferably within the range of 0.1 to 40% by weight based on the total amount of all solid components of the undercoat layer, and if it is less than 0.1% by weight, It is not possible to sufficiently improve the wear resistance of the magnetic layer by replenishing a sufficient amount of lubricant, and if the amount exceeds 40ffi1%, 0.
The adhesive force with the magnetic layer of 5 μm or less becomes low, and sufficient durability cannot be ensured.

An undercoat layer containing such conductive powder and a lubricant is usually prepared by mixing and dispersing the conductive powder and a lubricant together with a binder resin and an organic solvent to prepare an undercoat paint, which is then coated with polyester. It is formed by applying it onto a substrate such as a film and drying it.

Here, the binder resin used for the undercoat layer includes vinyl chloride-vinyl acetate copolymer, polyvinyl butyral resin, cellulose resin, polyurethane resin, polyester resin, epoxy resin, and polyether resin. , isocyanate compounds, radiation-curable resins, and other binder resins that have been widely used in the past are all suitably used.

In addition, as the organic solvent, conventionally commonly used organic solvents such as acetone, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, toluene, ethyl acetate, tetrahydroyalan, and dimethyl formamide can be used alone or in a mixture of two or more. Ru.

The magnetic layer on the undercoat layer is formed using r-Fe2Q3 powder, F
e3O4 powder, Co-containing r-Fe203 powder, Co-containing Fe3O4 powder, Fe powder, C.

A magnetic paint was prepared by mixing and dispersing various conventionally known magnetic powders such as powder, Fe-Ni powder, barium ferrite, and strontium ferrite together with a binder resin and an organic solvent, and this magnetic paint was formed on a substrate. It is formed by coating and drying on the undercoat layer.

At this time, the binder resin and organic solvent used are preferably the same as those used in forming the undercoat layer.

In addition, various commonly used additives such as lubricants, dispersants, abrasives, antistatic agents, etc. may be appropriately added to the magnetic paint.

〔Example〕

Next, embodiments of the invention will be described.

Examples 1 to 4 Carbon black (specific surface area 25 resistance/g based on 70 parts by weight according to BET method, average particle size 75 μm) Vinyl chloride-vinyl acetate-vinyl alcohol copolymer polyurethane resin 15...Isocyanate compound 10 〃Oleyl oleate
12〃Cyclohexanone
A composition of 200% toluene and 200% was mixed and dispersed in a ball mill for 72 hours to prepare an undercoat wear paint, and this was coated on both sides of a 75 μm thick polyethylene terephthalate film with the thickness as shown in Table 1 below. A different coating was applied, dried, and calendered to form an undercoat layer.

Next, on the undercoat layer on both sides of this polyethylene terephthalate film, a magnetic paint with the following composition was applied and dried.
Calendering was performed to form magnetic layers having different thicknesses as shown in Table 1 below. After that, it was punched into a disk shape to create a magnetic disk.

Magnetic paint Co-containing rFe2O3 powder 72 parts by weight (specific surface area 25.47g by BET method, retention power 850 oersted) Nitrocellulose 14.l Polyurethane resin 8.4 = Isocyanate compound 5,6//α-A1203 powder (average particle 7 .2 = diameter 0.3μm) Carbon black 10.8"oleyl oleate 7.2〃Cyclohexanone
115〃Toluene 11
5 Example 5 An undercoat layer was formed in the same manner as in Example 1, except that the same amount of 2-ethylhexyl oleate was used in place of oleyl oleate in the composition of the paint requiring undercoat in Example 1, and a magnetic disk was coated. I made it.

Example 6 In the composition of the paint requiring undercoat in Example 1, the same amount of 2-ethylhexyl oleate was used instead of oleyl oleate, and in the composition of the magnetic paint, the same amount of 2-ethylhexyl oleate was used instead of oleyl oleate. An undercoat layer was formed in the same manner as in Example 1, except that a magnetic disk was manufactured.

Example 7 An undercoat layer was formed in the same manner as in Example 1, except that the same amount of copper powder was used instead of carbon black in the composition of the paint requiring undercoat in Example 1, and a magnetic disk was produced.

Example 8 The same amount of 2-ethylhexyl oleate was used instead of oleyl oleate in the composition of the magnetic paint in Example 1, and the same amount of copper powder was used instead of carbon black in the composition of the paint that required an undercoat. An undercoat layer was formed in the same manner as in Example 1 to produce a magnetic disk.

Example 9 An undercoat layer was formed in the same manner as in Example 5, except that the same amount of copper powder was used instead of carbon black in the composition of the paint requiring undercoat in Example 5, and a magnetic disk was produced.

Example 10 An undercoat layer was formed in the same manner as in Example 6, except that the same amount of copper powder was used in place of the carbon blank in the composition of the paint requiring undercoat in Example 6, and a magnetic disk was produced.

Comparative Examples 1 to 3 An undercoat layer was formed in the same manner as in Example 1, except that the formation of the undercoat layer was omitted and the thickness of the magnetic layer was changed as shown in Table 1 below. I made a disc.

Comparative Examples 4 to 6 An undercoat layer was formed in the same manner as in Example 1, except that the thickness of the undercoat layer and the thickness of the magnetic layer were changed as shown in Table 1 below. I made a disc.

The surface electrical resistance, durability, lubricant content, and recording density characteristics of the magnetic disks obtained in each Example and Comparative Example were investigated. Durability is measured by inserting a magnetic disk into a magnetic recording/reproducing device and measuring the amount of decrease in playback output level due to abrasion of the magnetic layer of the magnetic disk while sliding the magnetic disk against a magnetic head at 360 rpm. The running time until the output decreased to 70% of the original output was measured and investigated. The lubricant content was determined from the change in weight of the undercoat layer and magnetic layer of the obtained magnetic disk after washing with n-hexane. Furthermore, the recording density characteristic was expressed as the recording density I)so at which the output is 50% of the long wavelength recording/reproducing output. This I)so serves as a guideline for the maximum recording density that can be realized by the device.

Table 1 below shows the results.

〔Effect of the invention〕

As is clear from Table 1 above, the magnetic disks obtained according to the present invention (Examples 1 to 10) have a higher i11 lubricant content and magnetic The surface electrical resistance of the layer is sufficiently low, the durability is good, and the recording density characteristics are also good. Therefore, the magnetic recording medium obtained by this invention can be used for high-density recording, and has sufficient surface electrical resistance. It can be seen that it is small and has sufficiently improved durability.

Claims (1)

[Claims] 1. In a magnetic recording medium in which a magnetic layer containing magnetic powder and a binder component is provided on a substrate, the thickness of the magnetic layer is 0.5 μm.
A magnetic recording medium 2 characterized in that it has the following properties and an undercoat layer containing conductive powder and having a thickness greater than the thickness of the magnetic layer is provided between the magnetic layer and the substrate, the conductivity contained in the undercoat layer The magnetic recording medium 3 according to claim 1, wherein the powder is carbon black, and the magnetic recording medium 4 according to claim 1, wherein the conductive powder contained in the undercoat layer is copper powder. The magnetic recording medium 3 according to claims 1 to 3 further contains a lubricant, and the magnetic recording medium 3 according to claim 4, wherein the lubricant further contained in the undercoat layer is a fatty acid ester. magnetic recording medium