JPH02278511A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve surface smoothness without deteriorating electromagnetic conversion characteristics by using carboxyl group-contg. polyurethane resin, isocyanate crosslinking agent and epoxy crosslinking agent as the binder components for a conductive basecoat layer. CONSTITUTION:The basecoat layer comprising carbon black, goethite, carboxyl group-contg. polyurethane resin, vinyl chloride copolymer epoxy crosslinking agent and isocyanate crosslinking agent is formed between a nonmagnetic supporting body and a magnetic layer. By this constitution, the surface electric resistance of the medium can be reduced without deteriorating electromagnetic conversion characteristics of the magnetic layer and the obtd. medium is free from contamination of dust caused by electric charging. The carboxyl group contained in the polyurethane resin reacts with the epoxy crosslinking agent to produce hydroxyl group, which reacts with the isocyanate crosslinking agent to increase the density of crosslinks of the binder resin. Thereby, solvent resistance of the binder in the basecoat layer is improved, and the basecoat does not swell nor the surface thereof is roughened when the basecoat layer is coated with a magnetic coating material. Thus, surface smoothness of the magnetic layer is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magnetic recording media, and more particularly to improvements in undercoat layer phase binders.

[Conventional technology]

Recently, magnetic recording devices have become increasingly compact, and there is a demand for high-density recording in their compact magnetic recording media.

As one of these efforts, there is an urgent need to develop a magnetic recording medium using plate-like hexagonal heptagonal hepteryte powder as magnetic particles, which can be perpendicularly magnetized and which can be applied with conventional magnetic layer coating techniques.

Plate-shaped hexagonal ferrite powder has high electrical resistance.

The magnetic layer using this magnetic powder has a very high surface electrical resistance and is easily charged by the original vibration during use.

Dropouts are likely to occur due to dust etc.

One way to reduce the surface electrical resistance is to add conductive fillers such as carbon black to the magnetic layer.
In order to reduce the surface electrical resistance to a predetermined value in a magnetic layer using plate-shaped hexagonal ferrite powder, the amount of conductive agent added is large, the content of magnetic powder is reduced, and the electromagnetic conversion characteristics are deteriorated.

Another method for reducing surface electrical resistance is to provide a conductive undercoat layer between the magnetic layer and the nonmagnetic support. This method can reduce the electrical resistance to a predetermined value ll'c, but when applying the magnetic layer on top of the nine undercoat layers,
The organic solvent in the a-based paint swells the binder in the undercoat layer, making its surface rough, which affects the smoothness of the magnetic layer surface and causes an increase in modulation noise of the magnetic recording medium.

[Problem that the invention seeks to solve]

This invention solves the problem of reducing the surface smoothness of the magnetic layer when a conductive undercoat layer is provided in order to reduce the surface electrical resistance of a magnetic recording medium by using a 5-plate-shaped hexagonal crystal ferrite magnetic powder. Therefore, it is an object of the present invention to provide a magnetic recording medium with low surface electrical resistance and excellent electromagnetic conversion characteristics.

[Means to solve the problem]

The inventors of the present invention conducted extensive research to solve the above drawbacks, and as a result, developed carbon black and goethite.

By providing an undercoat layer consisting of a carboxyl group-containing polyurethane resin, a hinyl chloride-based Kyodo Gogo 7 Evoquin crosslinking agent 2, and an Insiaite crosslinking agent between the nonmagnetic support and the magnetic layer! 77 It has been discovered that a magnetic recording medium can be obtained which reduces the electrical resistance in one direction without impairing the electromagnetic conversion characteristics of the magnetic layer, and which is free from dust resistance f (D) due to charging, and has thus arrived at the present invention.

Contained in polyurethane resin 1. The carboxyl group is

Reacts with epoxy crosslinking agent to generate hydroxyl groups. This hydroxyl group reacts with the isodino'nate crosslinking agent to improve the crosslinking density of the binder resin. This improves the bath agent properties of the binder in the undercoat layer, and even if a magnetic paint is applied on this undercoat layer, the organic bath agent in the magnetic paint prevents the undercoat from being wetted, dissolved, etc. Therefore, the layer surface will not become rough. I hesitated.

The flatness of the layer surface of the magnetic layer formed on that layer also improves, and an increase in modulation noise can be prevented.

The amount of carboxyl groups included in the polyurethane resin is 0.
0 t) l-5n11'T1o g/,! The amount of the polyurethane resin having a carboxyl group is set to 0.1 to 0.4 in terms of Kt ratio to the total amount of the binder, and the amount of the epoxy crosslinking agent is set to 1 to 1% of the total amount of the binder. The weight ratio is 0.001 to 0.1. Furthermore, the amount of carboxyl group-containing polyurethane resin to the weight of the epoxy crosslinking agent is 2
The range is preferably 200 to 200.

If the amount of carboxyl groups is too large, some carboxyl groups will not participate in the crosslinking reaction, and this will give the coating film tack.

The 10,000 epoxy crosslinking agent leaves too much unreacted crosslinking agent, which bleeds out and impedes running stability during coating of the magnetic layer.

t of polyurethane resin is relative to the total amount of binder.

When the VC is less than 0.1, the crosslinking ff1lf of the binder decreases.

Organic solvent resistance deteriorates. When this value is 0.4 or more, the crosslinking density becomes too high, resulting in a disadvantage that the coating film becomes brittle.

The surface electrical resistance of the undercoat layer is preferably in the range of 10'-10' Ω/in 2 . For this reason, carbon black is added as a conductive agent, but adding carbon black alone will not add much power, and it is difficult to control because of its relationship with air resistance, which is an insulating addition! It is used as a mixture of goethite as an agent.

The blending weight ratio of carbon black and goethite in this mixture is preferably in the range of 80:20 to 50:50.

When carbon black exceeds 80, it becomes difficult to control the relationship between the amount added and the electrical resistance.
If it is less than 0, there will be a lot of violets added to lower the electrical resistance, which will cause the surface smoothness of the 9 layers of undercoat to deteriorate.

An organic bath agent for making an undercoat paint and 1~ru, toluene, methyl ethyl ketone, methyl imbutyl ketone, cyclohexanone, and tetrahydrofuran.

Conventionally used organic bath agents such as ethyl acetate can be used alone or in combination of two or more.

A coating material for an undercoat layer having the above-mentioned composition is applied onto a non-magnetic support such as a polyester film using any coating means such as a roll coater, and is cured if necessary. Furthermore, a magnetic layer containing plate-shaped hexagonal ferrite magnetic powder is coated on top of the magnetic layer by any coating means such as a roll coater to form a magnetic recording medium.

〔Example〕

The detailed VC will be explained below based on all the embodiments of the present invention.

Example 1 The following composition was dispersed in a sand grind mill for 2 hours to obtain an undercoat paint.

Carbon black (Cabot 2 Mogul L, 5R
ET, 138yr/, 9) 550 parts goenite (manufactured by Titan Kogyo Co., Ltd., Y-4V, 5BET.

71r7//g) 450 parts Vinyl chloride co-metallic polymer (manufactured by UCC, VAG) I) 40
0 parts carboxyl group-containing polyurethane resin (carboxyl group content, 0.24 mmoJ/, 9) 130 parts trifunctional incyaneto compound (manufactured by Nippon Polyurethane Co., Ltd., Coronate L) 130 parts epoxy crosslinking agent (tetraglycidyl metaxylene diamine )
1 part cyclohexanone
1800 parts toluene
1800 copies top 11c overcoat 1c! The coating was applied onto a polyester film having a thickness of 5 μm so that the thickness after drying was 0.7 μm. This coating film was cured at 60° C. for 24 hours to form an undercoat layer. On this undercoat layer, the following composition was dispersed for 2 hours using a sand grinder mill to prepare a magnetic coated disc.

Plate-like hexagonal crystal powder (plate ratio, 51 particle size, 0.
06μm, He, 5000e, am, 56 partsm
u/g) 100 parts Vinyl chloride comonomer manufactured by CUCC, VAG) I) 11
Polyurethane resin (Dainippon Ink Co., Ltd. fi, T5201)
7 parts α-k120s 8 parts Butylselon stearate 6 parts Trifunctional inanate compound (manufactured by Nippon Polyurethane Co., Ltd., Coronate L
) 4-part cyclohexanone
90 parts toluene
90 parts Example 2 A floppy disk was prepared in the same manner as in Example 1, except that 1 part of the epoxy crosslinking agent in the coating composition was changed to 40 parts.

Example 3 Example IVc below, a! It is clear that fluorocarbons can be nourished in the same manner as in Example 1, except that 11,130 parts of the carboxyl group-containing polyurethane resin in the coating composition was changed to 90 parts.

Kaken applicant Hitachi Maxell Co., Ltd. representative water well thickness

Claims (1)

[Claims] In a magnetic recording medium comprising a conductive undercoat layer on a non-magnetic support, and a magnetic layer containing plate-shaped hexagonal ferrite magnetic powder and a binder coated on the layer, the conductive undercoat layer binder is provided. A magnetic recording medium characterized in that a carboxyl group-containing polyurethane resin, an isocyanate crosslinking agent, and an epoxy crosslinking agent are used as agent components.