JPH01134718A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To prevent degradation in the surface smoothness of a magnetic layer and to improve electromagnetic conversion characteristics by providing an intermediate layer formed by binding a specific acidic carbon black by a binder consisting of a water soluble resin between a nonmagnetic base and magnetic layer. CONSTITUTION:The water soluble resin is used as the binder of the intermediate layer. Dissolution or swelling of the underlying intermediate layer is, therefore, prevented from arising even if a magnetic coating compd. of an org. solvent system is applied thereon for the purpose of forming the magnetic layer. The acidic carbon black having >=2.0wt.% volatile component, 10-30millimum average particle size and <=4.0pH is used as the carbon black to be compounded into the intermediate layer. The surface smoothness of the intermediate layer itself is extremely good. The surface smoothness of the magnetic layer is thereby improved and the high electromagnetic conversion characteristics based thereon are obtd. In addition, the improvement in the adhesiveness, electrical conductivity and light shieldability of the magnetic layer by the intermediate layer is attained as well.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magnetic recording media such as magnetic tapes and magnetic disks.

[Conventional technology]

In magnetic recording media in which a magnetic layer is formed by bonding magnetic powder with a binder on a non-magnetic support such as a polyester film, in order to improve the adhesion of the magnetic layer, it is possible to combine this with the support. By interposing an intermediate layer in between and adding carbon black to this intermediate layer to give it conductivity and light-shielding properties, dropouts and electrostatic noise caused by adhesion of dust and abrasion powder due to charging can be prevented. It has also been known to detect the end of a magnetic tape or the index hole in a magnetic disk (for example, Japanese Patent Laid-Open No. 104003/1983).

However, since a resin that is soluble in organic solvents is used as the binder for the intermediate layer due to the dispersibility of carbon black in the paint for forming the intermediate layer, it is difficult to form a magnetic layer on this intermediate layer. When an organic solvent-based magnetic paint is applied to achieve this, the organic solvent causes partial dissolution or swelling of the intermediate layer, making the interface between the intermediate layer and the magnetic layer uneven. There was a problem in that the surface smoothness of the magnetic layer was impaired, leading to a decrease in electromagnetic conversion characteristics.

Therefore, as a means to deal with the above-mentioned difficulties, a water-soluble resin with excellent solvent resistance is used as a binder for the intermediate layer, and a specific dispersion medium for the paint for forming the intermediate layer is used to improve the dispersibility of carbon black. It has been proposed to use a mixed system of organic solvent and water (Japanese Patent Laid-Open No. 61-1826).
Publication No. 28).

[Problem that the invention seeks to solve]

However, even with the above-mentioned proposed means, it is difficult to sufficiently smooth the surface of the intermediate layer itself, and the surface smoothness of the magnetic layer is affected by the surface condition of the intermediate layer, resulting in a satisfactory electromagnetic conversion. There was a problem that the characteristics could not be obtained.

This invention was made to solve the above problems,
The object of the present invention is to prevent deterioration of the surface smoothness of the magnetic layer by smoothing the interface between the intermediate layer and the magnetic layer, thereby providing a magnetic recording medium with excellent electromagnetic conversion characteristics.

[Means for solving problems]

As a result of intensive studies to achieve the above object, the inventors discovered that a water-soluble resin is used as a binder for the intermediate layer, and that the carbon black blended into the intermediate layer has specific properties and particle sizes. When a magnetic layer is used, an intermediate layer with excellent surface smoothness can be formed, and since the intermediate layer does not dissolve or swell during the formation of the magnetic layer, the surface smoothness of the magnetic layer is extremely good. Electromagnetic conversion characteristics can be obtained, and the adhesion of the magnetic layer by the above-mentioned intermediate layer can be improved.
It was discovered that the conductivity and light-shielding properties are also sufficient, and this invention has been completed.

That is, the present invention provides an acidic carbon having a volatile content of 2.0% by weight or more and an average particle size of 10 to 30 mm and a pH of 4.0 or less between a nonmagnetic support and a magnetic layer containing magnetic powder. The present invention relates to a magnetic recording medium provided with an intermediate layer formed by binding black with a binder made of a water-soluble resin.

[Structure and operation of the invention]

In this invention, since a water-soluble resin is used as a binder for the intermediate layer interposed between the non-magnetic support and the magnetic layer, an organic solvent-based magnetic paint is applied to form the magnetic layer. In addition to not causing dissolution or swelling of the underlying intermediate layer, as mentioned above, the carbon black blended into the intermediate layer has a volatile content of 2.0% by weight or more and an average particle size of 10 to 3.
Since an acidic material with a P H4,Q of 0 mm μm or less is used, the surface smoothness of the intermediate layer itself is very good, resulting in a smooth interface between the intermediate layer and the magnetic layer, making it possible to In addition, the above-mentioned interface does not adversely affect the surface properties of the magnetic layer, and the magnetic layer has extremely good surface smoothness.

The reason why the use of a specific carbon black improves the surface smoothness of the intermediate layer containing it as described above is not clear, but since this carbon black is acidic and contains a large amount of volatile matter, Coupled with the high hydrophilicity of its particle surface and its relatively small particle size, its dispersibility in an aqueous intermediate layer forming coating containing a water-soluble resin is better than that of other common carbon blacks. It is thought that this is due to the formation of an intermediate layer in which carbon black is extremely uniformly dispersed.

The above acidic carbon black is as described above (PH is 4
．． If the pH is higher than 4.0, good dispersibility cannot be obtained. Further, as mentioned above, the volatile content must be 2.0% by weight or more, and if it is less than 2.0% by weight, the dispersibility in the aqueous medium will be insufficient. Furthermore, the average particle diameter is 10 to 3 as described above.
It should be in the range of 0 mm μm; if it is smaller than 10 mm μm, it is due to poor dispersion, and if it is larger than 30 mm μm, the surface smoothness of the intermediate layer decreases due to its own particle size. This will adversely affect the surface properties of the magnetic layer.

Such acidic carbon black can be produced by various methods, but typical methods include continuous partial combustion of natural gas, oil, or a mixture thereof in a high-temperature furnace, or periodic thermal decomposition. In particular, the so-called furnace black obtained by mixing natural gas heated to a temperature slightly lower than the decomposition temperature and air preheated to a higher temperature in the above-mentioned furnace in a ratio insufficient for complete combustion. There is a method of acidifying the material by applying an appropriate acid treatment, for example, a post-treatment as described in "Carbon Black Handbook" (edited by Carbon Black Association), page 137.

Incidentally, as a commercially available acidic carbon black that can be suitably used in this invention, the product name RA manufactured by Colombian Co., Ltd.
VEN5000, RAVEN3500, RAVENI
255, RAVEN1 035, and trade name MOGUL-L manufactured by Cabot Corporation.

Various types of water-soluble resins can be used as the binder for the intermediate layer, but those mainly composed of water-soluble polyester resins are particularly preferred. In other words, since polyester films such as polyethylene terephthalate films are generally used as non-magnetic supports for magnetic recording media such as magnetic tapes and magnetic disks, they have good affinity for the water-soluble polyester resins mentioned above. The adhesion between the intermediate layer containing the polyester resin and the support is improved.

Any of the existing water-soluble polyester resins can be used, including polybasic acids such as adipic acid and phthalic acid, 1,3-butylene glycol, and 1,3-butylene glycol.
A polymer synthesized by reaction with a polyhydric alcohol such as 4-butanediol is made into a water-soluble salt by the action of an alkali such as caustic alkali, and the acid value is usually 5.0 mg.
KOH/g or less, average molecular weight 6.000
~20,000 polymers, etc. are used. In addition, commercially available products of such water-soluble polyester resin include Nippon Gosei Co., Ltd.'s product names WR-901, WR-900,
WR-930, WR-950, product name M manufactured by Toyobo Co., Ltd.
D-1200, MD-1400, MD-1530, MD
-1900 etc.

To form the intermediate layer, prepare a water-based intermediate layer paint containing a binder made of the above-mentioned acidic carbon black and water-soluble resin, and optionally additives such as a dispersant, and apply this paint to a polyester film. It may be applied to the surface of a non-magnetic support such as and dried. In addition, in order to make the coating film uniform during drying, the dispersion medium of this intermediate layer paint contains water and a water-soluble alcohol such as isopropyl alcohol, butyl alcohol, and ethyl alcohol in an amount of 5 to 2% of the total dispersion medium.
It is recommended that it be used in a proportion that accounts for about 0% by weight.

The above acidic carbon black/binder weight ratio is 45
A range of about 155 to 65/35 is preferable. If the amount of carbon black is too small, the conductivity of the intermediate layer will be insufficient, and the electrical resistance of the magnetic layer will not be sufficiently lowered, for example, below the preferred electrical resistance value of 107 Ω/d, and the electrical resistance will not be charged. This increases the occurrence of dropouts and electrostatic noise, and also results in insufficient light-shielding properties. On the other hand, if the amount of carbon black is too large, the binding force of the binder will be insufficient, and problems will arise in the adhesion of the intermediate layer to the non-magnetic support.

In addition, the thickness of the intermediate layer is preferably about 0.2 to 1.5 μm; if it is too thin, the magnetic layer may be adversely affected by minute irregularities or scratches on the surface of the non-magnetic support, and the conductive effect may be reduced. If it is insufficient, or if it is too thick, it will take a long time to dry, reducing workability.

The magnetic layer provided on the intermediate layer may be formed according to a conventional method, and is formed by preparing an organic solvent-based magnetic paint containing magnetic powder and a binder, coating it on the surface of the intermediate layer, and drying it. be done.

The above magnetic powder includes γ-FezO=, Fe3O4
, co-containing 7-Fe, 03, acicular iron oxide powder such as CO-containing Fe3O4, hexagonal ferrite powder such as barium ferrite, strontium ferrite, Fe
, Co, and Ni%.Any of those conventionally known as recording elements for magnetic recording media can be used, such as metal powders such as alloys of these.

Binders for the magnetic layer include vinyl chloride resin, vinyl acetate resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, and vinyl chloride-vinyl acetate-vinyl alcohol-maleic acid copolymer. Conventional magnetic recording materials include polymers, polyurethane resins, cellulose resins, polyester resins and their sulfonated versions, vinylidene chloride-acrylonitrile copolymers, isoprene rubber, butadiene rubber, and radiation-curable resins with double bonds. Known binders for the magnetic layer of the medium can be used alone or in combination of two or more, and a crosslinking agent such as an isocyanate compound may also be used together with these, if necessary.

Note that the above magnetic paint contains a dispersant and a lubricant.

Various conventionally commonly used additives such as abrasives and antistatic agents may be appropriately blended.

〔Effect of the invention〕

The magnetic recording medium according to the present invention is provided with an intermediate layer formed by binding specific acidic carbon black with a binder made of a water-soluble resin between the non-magnetic support and the magnetic layer, This intermediate layer has excellent surface smoothness and does not dissolve or swell during the formation of the magnetic layer.
There is no adverse effect on the surface properties of the magnetic layer due to the interface between the intermediate layer and the magnetic layer as in the past, the surface smoothness of the magnetic layer is extremely good, and excellent electromagnetic conversion characteristics can be obtained based on this. The conductivity of the intermediate layer reduces the surface electrical resistance of the magnetic layer and makes it difficult to charge, suppressing dropouts and electrostatic noise caused by this charging.Furthermore, the intermediate layer provides light-shielding properties and improves the relationship between the magnetic layer and the non-magnetic support. Adhesion is also good.

〔Example〕

Hereinafter, this invention will be specifically explained based on Examples.

In addition, in the following, parts mean parts by weight.

Table 1 below shows the carbon blacks used in the following Examples and Comparative Examples. Furthermore, among the product names in the table, RAV
ENI 4, RAVEN450 and RAVENl 2
50 is manufactured by Colombian, MONARCH800 is manufactured by Cabot, and the others are as described above.

Table 1 Example 1 <Coating composition for intermediate layer> Carbon black A1 55 parts water
280 parts Isopropyl alcohol 120 parts A paint for the intermediate layer was prepared by dispersing and mixing the above composition in a ball mill for 150 hours, and this paint was applied onto a 13 μm thick polyester film to a dry thickness of about 1 μm and dried. An intermediate layer was formed.

On the other hand, after dispersing and mixing the following composition in a ball mill for 72 hours, 3 parts of a polyisocyanate compound (product name Coronate, manufactured by Nippon Polyurethane Co., Ltd.) was added and mixed to prepare a magnetic paint, and this paint was applied on the above intermediate layer. The dry thickness is about 4μ
Apply so that it becomes m.

After drying to form a magnetic layer and applying mirror polishing treatment, 1
A magnetic tape was prepared by cutting each section into 2-inch width pieces.

<Magnetic paint composition> Myristic acid 2.4 parts Nitrocellulose 9 parts Polyurethane resin 8 parts Cyclohexanone
82 parts toluene
82 parts Examples 2 to 5 Instead of carbon black A1 in the intermediate layer coating, 55 parts of carbon black of A2 in Example 2, A3 in Example 3, A4 in Example 4, and A5 in Example 5 were used. A magnetic tape was produced in the same manner as in Example 1 except for the following.

Comparative Examples 1 to 4 In place of carbon black A1 in the intermediate layer paint, 55 parts of carbon black of Bl in Comparative Example 1, B2 in Comparative Example 2, B3 in Comparative Example 3, and B4 in Comparative Example 4 were used, respectively. A magnetic tape was produced in the same manner as in Example 1.

For each of the magnetic tapes of the above Examples and Comparative Examples, the surface electrical resistance of the magnetic layer, the surface roughness of the magnetic layer, and the C/N ratio were measured. These results are shown in Table 2. In addition,
The surface roughness is measured using a stylus type surface roughness meter with a cutoff of 0.08++.
The center line average roughness was measured at n. The C/N ratio was measured at a recording wavelength of 4.5 MHz, and is expressed as a relative value with the magnetic tape of Comparative Example 3 as a reference (OdB).

Table 2 From the results in Table 2, it can be seen that this intermediate layer containing carbon black A1 to A5 with specific properties such as a volatile content of 2.0% by weight or more, an average particle diameter of 10 to 30 mm, and a pH of 4.0 or less. The magnetic tapes of the invention (Examples 1 to 5) had the following characteristics compared to the magnetic tapes (Comparative Examples 1 to 4) including intermediate layers containing carbon blacks 81 to B4 in which at least one of the above property items was not specified. It is clear that the surface smoothness of the magnetic layer is extremely excellent, the electromagnetic conversion characteristics represented by the C/N ratio are extremely good, and the surface electrical resistance of the magnetic layer is also sufficiently low.

Claims (4)

[Claims] (1) Between the non-magnetic support and the magnetic layer containing magnetic powder,
Volatile content 2.0% by weight or more, average particle size 10-30 mmμ
A magnetic recording medium provided with an intermediate layer formed by binding acidic carbon black with a pH of 4.0 or less with a binder made of a water-soluble resin. (2) The magnetic recording medium according to claim (1), wherein the nonmagnetic support is made of a polyester film, and the water-soluble resin is mainly composed of a water-soluble polyester resin. (3) The weight ratio of carbon black/binder in the intermediate layer is 4
Claim No. 5/55 to 65/35 (
The magnetic recording medium according to item 1) or item (2). (4) The magnetic recording medium according to any one of claims (1) to (3), wherein the intermediate layer has a thickness of 0.2 to 1.5 μm.