JP2688296B2 - Magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having good adhesion to a non-magnetic support, running durability and electromagnetic conversion characteristics. In particular, it has excellent surface properties of the semi-finished web in the manufacturing process and adhesion of the magnetic material to the non-magnetic support, and less migration of the lubricant component in the magnetic layer to the conductive undercoat layer even after a long time. As a product, the present invention relates to a magnetic recording medium having stable quality.

[0002]

2. Description of the Related Art Recently, magnetic recording media have come to be used as recording media for recording a large amount of information in a wide range of fields such as audio, video and computers. Along with this, there is a demand for higher density magnetic recording media. As one of means for increasing the density of a magnetic recording medium, a method of increasing the packing density of ferromagnetic magnetic powder has been studied.

[0003]

However, when an attempt is made to increase the loading of the ferromagnetic magnetic powder, the adhesiveness and adhesion of the magnetic powder to the non-magnetic support are deteriorated, and the charging property of the magnetic powder is reduced. As a result, the running property of the magnetic recording medium deteriorates, and noises due to discharge occur. As a countermeasure, but be provided with a conductive subbing layer between the magnetic layer and the nonmagnetic support is proposed, in conventional conductive undercoat layer, in the manufacturing process of the magnetic recording medium, a homogeneous It is difficult to form the surface, the adhesion to the non-magnetic support is low, and as a result, the surface property of the magnetic layer becomes poor,
Streaks and the like tend to appear in the coating direction, and electromagnetic conversion characteristics are poor. In addition, there is a problem that the liquid lubricant component contained in the magnetic layer easily migrates to the conductive undercoat layer and the running durability deteriorates with time.

The present invention has been achieved as a result of studies to solve the conventional problems, and provides a magnetic recording medium having good running durability, adhesion to a non-magnetic support, and electromagnetic conversion characteristics. Is intended.

[0005]

That is, the magnetic recording medium of the present invention comprises a non-magnetic support, a magnetic layer containing ferromagnetic magnetic powder, and a space between the support and the magnetic layer. A magnetic recording medium provided with a conductive undercoat layer, wherein the undercoat layer is
Selected from the group of cuprous iodide, silver iodide and cupric sulfide
A conductive filler of at least one metal compound,
Machine binder and, if necessary, low molecular weight isocyanate compound
It is characterized by including .

In the prior art, carbon-based fillers such as carbon black and graphite are generally used as the conductive fillers, but in order for the carbon-based fillers to exhibit a sufficient conductive function. It was necessary to select carbon particles having a large specific surface area of 100 m ² / g or more by the BET method and a large oil absorption by the DBP method (100 g / 100 g or more carbon). Such carbon particles having a large specific surface area and a large oil absorption amount are not only difficult to uniformly disperse, but also increase the surface roughness of the conductive undercoat layer, reducing the surface area of the magnetic surface and adversely affecting the electromagnetic conversion characteristics. To give.

Further, when such particles having a large oil absorption amount are present in the conductive undercoat layer, the low molecular weight (Mn <2000) lubricant component additionally contained in the magnetic layer is transferred to the conductive undercoat layer, The running durability of the surface magnetic layer tended to deteriorate with time.

Further, in order to prevent the migration of the lubricant component to the conductive undercoat layer, if a large amount of the lubricant component is present in the conductive undercoat layer in advance, the adhesion of the undercoat layer to the non-magnetic support is improved. Another problem occurs that is decreased.

On the other hand, the conductive filler used in the present invention has a much smaller oil absorption amount than the above-mentioned carbon, so that the above-mentioned problem does not occur.

However, as a matter of course, the surface roughness of the conductive undercoat layer is kept at a certain level (for example, the center line average roughness is 0.03 μm or less, preferably 0.02 μm or less, more preferably 0.015 μm or less). The average particle system (aμm) is C> a + 0.02, preferably C> 1.1a + 0.02, more preferably C> 1.5a + 0.03, with the thickness (cμm) of the undercoat layer as a parameter. Should be a range.

The binder and the above-mentioned filler are appropriately used in an amount of 5 to 100 parts by weight per 100 parts by weight of the conductive filler, and other components such as lubricant are 1 to 20 parts by weight per 100 parts by weight of the binder. It is recommended to add parts by weight.

The ratio of the conductive filler used is such that when the undercoat layer is formed to a desired thickness, the surface resistance value is 500 M.
It is advisable to control the value to a desired value of Ω / cm ² or less.

Here, as the binder resin used in the undercoat layer, vinyl chloride-vinyl acetate copolymer, polyvinyl butyral resin, fibrin resin, polyurethane resin, polyester resin, epoxy resin, Any conventionally used binder resin such as a polyether resin, an isocyanate compound, or a radiation curable resin is preferably used.

As the organic solvent, acetone, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, toluene, ethyl acetate, tetrahydrofuran,
Any of the conventionally commonly used organic solvents such as dimethylformamide may be used alone or in admixture of two or more.

The low molecular weight isocyanate compound used in the present invention includes 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate and 4,4'-
There are diisocyanates such as diphenylmethane diisocyanate, hexamethylene diisocyanate, and xylene diisocyanate, and trifunctional low-molecular isocyanate compounds obtained by reacting 3 mol of these diisocyanates with 1 mol of triol, and many commercially available products can be used. Possible (for example, Coronate 2036 manufactured by Nippon Polyurethane Company, Death Module L manufactured by Sumitomo Bayer, Death Module 14, Sumidule T-80, Takenate D102, Takenate M40 manufactured by Takeda Pharmaceutical Co., Ltd.)
There are 3 mag. ).

[0016]

Since the present invention uses a non-carbon black type undercoating agent, the electric conductivity does not vary depending on the particle size of the undercoating agent and has a stable electromagnetic conversion characteristic. And, it has a close adhesiveness with a magnetic layer such as barium ferrite.

[0017]

The present invention will be described below with reference to examples.

[0018]

Example 1 (Preparation of Undercoat Layer Coating Material) Cuprous iodide 75 parts by weight Sodium sulfonate-containing 25 parts by weight Polyester urethane ^{(Toyobo Byron)} Low molecular weight polyurethane 2 parts by weight ^{(Nippon Polyurethane Coronate L)} Cyclohexanone 200 parts by weight Parts The above composition was put into a ball mill, mixed and dispersed for 72 hours,
The undercoat paint was adjusted. This undercoat paint is 75 μm thick
Of polyethylene terephthalate film on both sides to a dry thickness of 1.0 μm, dried and 10 MΩ / cm ²
An undercoat layer having a surface resistance of 1 was formed and then calendered. Next, a magnetic coating composition having the following composition was applied to both surfaces of this polyethylene terephthalate film so that the dry thickness was 0.7 μm, and the coating was dried and calendered. Then 3.5 "(inch) the web
After punching into a disc shape and polishing treatment, a magnetic disk was prepared according to a known method.

Magnetic paint Ba-Ferrite powder 80 parts by weight BET specific surface area 50 m ² / g ^{Plate ratio 4.2} Alumina (average particle size 0.3 μm) 7 parts by weight Sulfonate-containing vinyl chloride / vinyl acetate resin 10 parts by weight ^{( Nippon Zeon MR110)} Polyurethane resin 10 parts by weight Low molecular weight polyurethane 10 parts by weight ^{(Nippon Polyurethane Company Coronate L)} oleyl oleate 7 parts by weight Cyclohexanone 300 parts by weight Toluene 100 parts by weight

[0020]

[Comparative Example 1] An undercoat layer of a carbon-containing composition having the following composition was produced (applied) in the same manner as in Example 1, and then the magnetic coating material of Example 1 was applied, followed by the same procedure as in Example 1. Was manufactured. Carbon black 30 parts by weight ^{(Lion Akzo Ketjen black)} Sodium sulfonate 70 parts by weight Polyester urethane ^{(Toyobo Byron)} Low molecular weight polyurethane 2 parts by weight ^{(Nippon Polyurethane Coronate)} Cyclohexanone 200 parts by weight

[0021]

Example 2 and Example 3 A magnetic disk was manufactured in the same manner as in Example 1 except that copper iodide in Example 1 was replaced with cupric sulfide and silver iodide. The results are referred to as Examples 2 and 3.
The results are shown in Table 1 together with Example 1 and Comparative Example 1.

[0022]

[Table 1] *) The peeling strength of the coating film is obtained by cutting the magnetic coating film to a width of 1 cm, attaching an adhesive tape to the tape-shaped magnetic surface, and the tape-shaped magnetic film and the base when the adhesive tape is pulled in the 180 ° direction at 10 cm / sec. The force of peeling the film and the magnetic layer **) The disk was heat-treated at 80 ° C. for 100 hours, and a lubricant transfer acceleration test was performed.

Then 3.5 ″ floppy disk drive (NEC1135c) (head tension 80g,
The time to scratch the coating film was measured at a rotation speed of 1200 rpm.

Continuation of front page (56) Reference JP 62-89219 (JP, A) JP 63-140420 (JP, A) JP 59-165239 (JP, A) JP 4-195819 (JP , A) JP-A-4-192111 (JP, A)

Claims (1)

(57) [Claims] 1. A magnetic recording medium comprising a non-magnetic support, a magnetic layer containing ferromagnetic magnetic powder, and a conductive undercoat layer provided between the support and the magnetic layer. Te, and a conductive filler of at least one metal compound undercoat layer is selected from the group consisting of cuprous iodide Gin及 beauty sulfide cupric iodide,
And an organic binder, the magnetic recording medium you; and a low-molecular isocyanate compound optionally.