JPH0736213B2 - Magnetic recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium, and more particularly to a metal thin film type magnetic recording medium.

[Conventional technology and problems]

The conventional magnetic recording medium has been mainly of a so-called coating type in which a magnetic coating is applied to a non-magnetic support, but in recent years, as the demand for high-density recording has increased, a metal thin film formed by forming a magnetic metal thin film on the non-magnetic support. Mold media is attracting attention. This is for recording on a magnetic metal thin film having a thickness of 1 micron or less, and enables extremely high density recording as compared with the coating type.

As a method of manufacturing a thin film type medium, a vapor deposition method, a sputtering method,
Wet plating method and the like are known. Among them, the vapor deposition method, the sputtering method and the like have problems that they are not mass-produced and cost is high because they are formed in vacuum. On the other hand, the wet plating method has been extensively studied because it can be mass-produced with simple equipment.

The wet plating method is roughly classified into an electrolytic plating method and an electroless plating method. Although the electrolytic plating method has a high film deposition rate,
A non-conductive substrate such as a plastic film cannot be meshed, and in general, an electroless plating method is used for directly plating a non-conductive substrate.

An important step for plating an electrically non-conductive substrate such as a plastic film by the electroless plating method is an etching step performed prior to the electroless plating. This step has been particularly indispensable for improving the adhesion of the plated film to the substrate. Normally, the substrate is soaked in a solution of chromic acid, a mixture of chromic acid, sodium hydroxide or the like to physically surface the surface. , Is chemically roughened to obtain an anchoring effect on the plated film to obtain an adhesive force. However, in order to obtain a sufficient adhesion force by this etching process, it is necessary to perform a physical roughening, so that the surface property of the finished plating film is extremely deteriorated. For ordinary purposes such as decoration, it is sufficient if it has a beautiful gloss, but the deterioration of surface properties is fatal for a medium for high-density recording for short wavelength recording. Therefore, the development of a better method was needed. As one of the solutions, there has been proposed a method of undercoating vinylidene chloride or the like on a substrate and omitting the etching step (Japanese Patent Publication No. 58-6781). However, this method cannot obtain sufficient adhesion.

The present inventors formed a subbing layer containing a compound containing a sulfonate group or a sulfonate group, thereby eliminating the conventional etching to obtain a plating film having improved plating deposition ability and good adhesion. (Japanese Patent Application No. 60-14370). The inventors proceeded with further research,
As a result of searching for a magnetic layer having good adhesion, the present invention has been accomplished.

[Object of the Invention]

An object of the present invention is to provide a high density magnetic recording medium in which an electroless plated magnetic layer is formed on a hydrophobic non-conductive support with high adhesion strength. It is an object of the present invention to provide a magnetic recording medium having an excellent undercoat layer which enhances the adhesion of the magnetic layer to the support.

[Outline of Invention]

The present invention provides a subbing layer on at least one side of a hydrophobic non-conductive support (for example, plastic base), and mixing fine particles of 50 to 500 angstrom in the subbing layer,
A magnetic recording medium characterized by activating the undercoat layer by activation treatment and causing some fine particles to fall off, and forming an electroless plating magnetic layer (for example, a cobalt alloy film) on the surface thereof. is there.

The adhesiveness of the magnetic layer of the magnetic recording medium of the present invention is not only due to activation of the undercoat layer, but also a part of particles are missing during the activation treatment to locally roughen the surface of the undercoat layer. Is greatly improved due to the occurrence of. On the other hand, however, the surface property can be kept much smoother than in the case of ordinary surface roughening, and the surface smoothness of the magnetic layer can be increased.

[Specific Description of the Invention]

Conventionally, it is known to provide an undercoat layer for depositing electroless plating (Japanese Patent Publication No. 39-15251 and Japanese Patent Publication No. 39-1).
6467, Japanese Patent Publication Sho 58-6781 etc.). Also in the present invention, an appropriate selection is made from these known undercoat layer compositions. Such a subbing layer generally has a partially hydrolyzed compound or an active functional group,
It has a property that the surface is activated by partially hydrolyzing it by the action of the activator in the activation step.

Fine particles having a diameter of 50 to 500 angstrom are dispersed in the undercoat layer. That is, fine particles are mixed and dispersed in the undercoat layer composition in advance, and then this is dispersed in polyester,
An undercoat substrate is obtained by coating the surface of a hydrophobic non-conductive substrate such as a polyimide film and drying it.

As the fine particles, for example, Al ₂ O ₃ , SiO ₂ , FeO ₃ , CaCO ₃ ,
It is appropriately selected from many known fine particles such as colloidal particles of Au, Ni or the like, or colloidal particles obtained by using these as nuclei. It is not important that the fine particles remain after the activation of the undercoat layer, and it is more important that the recesses remain after the fine particles fall off. Such recesses serve as anchors for base metals such as palladium and magnetic alloy particles. If the size of the recess is large, the surface property is deteriorated, so the size of the fine particles is set to 500 angstroms or less, preferably 100 angstroms or less.

The method of forming the undercoat layer on the hydrophobic non-conductive substrate such as a plastic film is described in detail in, for example, JP-A-58-68227. These are conventionally used for improving the runnability and dropout characteristics of the metal thin film magnetic recording medium by the vacuum method, and even if they are similar in structure, their function is extremely different from that of the undercoat layer of the present invention. Different. The present invention makes use of the partial dropout of fine particles. The undercoat layer may be formed by any coating method such as gravure coating, reverse coating, spin coating, etc. When the substrate is a biaxially stretched polyester film, it can be coated in the middle of stretching to be uniformly thinned. is there.

After drying, the undercoat layer is activated in an activation step without performing an etching step. In this step, an activator containing an acid such as hydrochloric acid is used. For example, a part of the undercoat layer is hydrolyzed by the action of hydrochloric acid so that the surface is chemically activated and adsorbs the underlying metal particles such as palladium with good adhesion.
In addition to that, in the present invention, some fine particles are missing due to the hydrolysis reaction of the surrounding binder during the activation treatment, and the surface of the undercoat layer is physically roughened locally. It will be more strongly adsorbed.

After that, a metal film is formed on the undercoat layer in an electroless plating bath. A known bath capable of precipitating magnetic grains such as cobalt or cobalt alloy may be used as the plating bath. The metal or alloy magnetic film binds to the activated surface of the undercoat layer and palladium, and furthermore, due to the very strong anchoring effect due to the fine holes lacking fine particles,
It is possible to obtain a magnetic film having good adhesiveness that cannot be obtained by the conventional method.

Comparing the method of the present invention with the plating film formed through the conventional etching process, the present invention has a better surface property. The average surface roughness required for a high-adhesion magnetic recording medium is 0.05 μm or less, preferably 0.03 μm or less, and this method enables this level. In addition, even though the surface roughness is small in this way, it becomes a deep recess after the loss of fine particles, so that a strong anchoring effect is produced and high adhesion is ensured. On the other hand, in a general etching method, if an attempt is made to obtain such a deep recess, the entire surface will be greatly roughened. In the case of a partial recess, the touch with the head is kept good, the adverse effect is relatively small, and there is an advantage that a fatal adhesion problem can be greatly improved in the case of a magnetic recording medium of the type. The above is schematically shown in FIG. 1, and the surface state of the substrate immediately before the plating is shown in FIG. 1 (a) in the ordinary etching method, in FIG. 1 (b) in the conventional undercoating method, and in the present invention. The fine particle type undercoating method is as shown in FIG.

Example 1 and Comparative Examples 1 and 2 Vinylidene chloride-vinyl chloride copolymer (vinylidene chloride / vinyl chloride = 30/70, degree of polymerization 400, softening point 130 ° C.) of 2 wt% solid content using butyl acetate as a solvent The solution
It was lipase coated on a 12 micron polyethylene terephthalate film (PET) to a thickness of 1000 angstroms. This is designated as sample a. Next, in the above binder, colloidal silica (Si
(O ₂ particles) is mixed and dispersed by 15 wt% in terms of particle solid content, and then re-perforated on PET in the same manner to obtain a sample b. Then the same P
ET is alkali-etched with a 10% NaOH solution at 60 ° C. for 20 minutes to obtain a sample c.

These samples were subjected to electroless plating by the following method and then slit to a width of 8 mm to obtain a magnetic tape. The tape from a is referred to as A (Comparative Example 1), the tape from b is referred to as B (Example 1), and the tape from c is referred to as C (Comparative Example 2).

(1) Activator Concentrated hydrochloric acid 30 parts PN-PS (World Metal Co.) 15 parts Distilled water 55 parts 40 ° C, 1 minute (2) Accelerator concentrated sulfuric acid 20 parts Distilled water 80 parts Room temperature, 1 minute (3) Electroless Plating bath Cobalt sulfate 0.06 mol / Nickel sulfate 0.04 mol / Natonium hypophosphite 0.2 mol / Potassium sodium tartrate 0.5 mol / Ammonium sulfate 0.5 mol / NaOH alkalized pH9.5 70 ° C for 2 minutes After thoroughly washing with distilled water Dried.

Example 2 and Comparative Example 3 Epoxidized polydimethylcycloxane emulsion, magnesium chloride emulsion, and water-soluble emulsion containing titanium oxide colloid were applied to a 50 μm thick polyimide film and dried. When this sample was measured by a scanning electron microscope, a transmission electron microscope using an ultrathin film section, etc., the thickness of the undercoat layer was 800 Å,
Fine particles of 0 angstrom diameter were uniformly dispersed at about 20 million pieces / mm ² . Let this sample be d. Next, the composition obtained by removing the fine particle component from the emulsion is applied in the same manner to obtain a sample e. This sample was subjected to electroless plating by the following method to obtain a magnetic disk having a diameter of 5 inches. The disk from d is D (Example 2), and the disk from e is E (Comparative Example 3).

(1) Activator Same as in Example 1 (2) Accelerator Same as in Example 2 (3) Electroless nickel plating bath for base Blue Sumer (Kanigen Co., Japan) 70 ° C, 1 minute (4) Magnetic electroless plating bath for sulfuric acid Cobalt 1.00 mol / sodium hypophosphite 0.2 mol / sodium citrate 0.3 mol / ammonium sulfate 0.8 mol / NaOH alkalized pH 10.0 65 ° C. for 3 minutes Next, the results of Examples and Comparative Examples are shown.

Regarding the evaluation method of Table 1, the coercive force is VSM (manufactured by Toei Industry Co., Ltd.), the adhesion is a rubbing test with a finger, and the output stability is 8 mm video deck (Kodakku), respectively.
And a 5-inch Floppy disc unit. The surface roughness was measured with a stylus type roughness measuring instrument (Talister, Taylor-Hobson).

The adhesiveness and output stability are represented by the following ranks.

Comparative Examples 4 and 5 A gold thin film having a thickness of 50 angstrom was formed by sputtering on one surface of the PET film before activation and plating of sample b (having an undercoat layer containing fine particles) described in the examples. Since gold has catalytic activity, activation treatment (activator, accelerator) was not performed, and gold was immersed in an electroless plating bath similar to samples a and c to form a magnetic layer. This tape sample was designated as Tape F (Comparative Example 4).

Next, alumina particles having a diameter of 600 angstroms (0.06 μm) were mixed in the same binder as the sample a in an amount of 10 wt% in terms of particle solid content, and coated on the tape in the same manner as a sample g. After the activation treatment as in Samples a, b, and c, electroless plating was performed, and the tape from Sample g was used as Tape G (Comparative Example 5). When the properties of these samples were measured, the results shown in Table 3 were obtained.

From the above results, it is clear that by mixing the fine particles in the undercoat layer, a strong adhesion can be obtained, and as a result, a stable output can be obtained.

[Brief description of drawings]

FIG. 1 shows how the surface is roughened before the plating bath (after the activation treatment) in a visually easy-to-understand manner.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Hisae Shimizu Hisae Shimizu 1-13-1 Nihonbashi, Chuo-ku, Tokyo, TDK Corporation (56) References JP-A-52-56509 (JP, A) JP-A-58 -68227 (JP, A)

Claims (4)

[Claims] 1. An electroless plating magnetic layer provided on at least one side of a hydrophobic non-conductive support, which is a subbing layer containing fine particles having a diameter of 500 angstroms or less, in which fine recesses are formed. A magnetic recording medium characterized by the above. 2. The magnetic recording medium according to claim 1, wherein the fine recesses are recesses in which the fine particles are partially removed from the surface layer of the magnetic layer. 3. The magnetic recording medium according to claim 1, wherein the magnetic layer is a cobalt alloy and the surface roughness is 0.05 μm or less. 4. The magnetic recording medium according to claim 1, wherein the particle size of the fine particles is less than 100 angstroms.